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- Front Matter: Volume 6519
- Invited Session
- Materials and Processes for Immersion Lithography I
- Materials and Processes for Immersion Lithography II
- Resist Materials
- ARC/Multilayer Process
- Resist Processing
- Resist Processes and Simulation
- Resist Fundamentals
- LER
- NGL
- Novel Processes/Applications
- Joint Session with Conference 6517 on EUV Resists
- Poster Session: Materials and Processes for Immersion Lithography
- Poster Session: Resist Materials
- Poster Session: ARC/Multilayer Processes
- Poster Session: Resist Processing Technology
- Poster Session: Resist Fundamentals and Simulation
- Poster Session: NGL
- Poster Session: Novel Processes and Applications
Front Matter: Volume 6519
Front Matter: Volume 6519
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This PDF file contains the front matter associated with SPIE
Proceedings Volume 6519, including the Title Page, Copyright
information, Table of Contents, Introduction, and the
Conference Committee listing.
Invited Session
Identifying materials limits of chemically amplified photoresists
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Chemically amplified photoresists are likely to remain the primary imaging materials for the
semiconductor industry. As feature sizes decrease to dimensions comparable to the characteristic size of
the molecules in the photoresist, a significant challenge lies in identifying the ultimate resolution limit of
these materials. To address this challenge, we investigated model photoresist materials with high
resolution measurements to examine the effect of individual factors among interdependent process steps on
line-edge roughness (LER). Using a bilayer film sample geometry, we measured the internal deprotection
interface with nanometer resolution as a function of photoacid size, initial resist copolymer composition,
and amine base quencher by neutron reflectivity and infrared spectroscopy. After development, we found
that the resist chemistry and additives can play an important role in LER through its influence on acid
diffusion. However, these model experiments suggest that there is a limit in LER even with an idealized
exposure image contrast and decreases in the width of the reaction-diffusion front. However, there may be
opportunities to further decrease LER during development by tuning the response of the photoresist to the
developer solution.
Emerging patterning materials: trends, challenges, and opportunities in patterning and materials by design
Show abstract
Patterning technology is entering the nanomaterials era. Breakthrough advances in the
basic sciences over the last twenty years are catalyzing novel material and assembly
options. In the near future, these options may warrant consideration for fabricating
advanced information processing technologies. However, material technology advances
alone are not sufficient to induce changes and chemical substitution in manufacturing. In
fact, manufacturing technology will change only when no other option exists. Therefore,
the concurrent trend in lithographic challenges is noteworthy. Recent revisions of the
International Technology Roadmap for Semiconductors (ITRS) indicate that it is
becoming increasingly difficult for mainstream lithographic technologies to satisfy
projected ITRS dimensional scaling requirements, shown in Table 1.
Materials and Processes for Immersion Lithography I
Fluoro-alcohol materials with tailored interfacial properties for immersion lithography
Show abstract
Immersion lithography has placed a number of additional performance criteria on already stressed resist materials.
Much work over the past few years has shown that controlling the water-resist interface is critical to enabling high scan
rates (i.e. throughput) while minimizing film pulling and PAG extraction (i.e. defectivity). Protective topcoat polymers
were developed to control the aforementioned interfacial properties and emerged as key enablers of 193 nm immersion
lithography. Achieving the delicate balance between the low surface energies required for high water contact angles
(generally achieved via the incorporation of fluorinated groups) and the base solubility required for topcoat removal is
challenging. More recently, additional strategies using fluoropolymer materials to control the water-resist interface have
been developed to afford topcoat-free resist systems. In our explorations of fluoroalcohol-based topcoat materials, we
have discovered a number of structure-property relationships of which advantage can be taken to tailor the interfacial
properties of these fluorinated materials. This paper will address the effect of structure on immersion specific properties
such as water contact angle, aqueous base contact angle, and dissolution rate.
Development of non-topcoat resist polymers for 193-nm immersion lithography
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Recently it is known well that blending hydrophobic additives into conventional resist polymer drastically improve its
film surface hydrophobicity. So we thought that this approach was one of candidates and most promising to
achieve a non-topcoat resist process for immersion lithography. And it would be able to maintain original resist
performance because only a small amount of additives were added into conventional resist. Then we have investigated
hydrophobic polymers for use as additives of non-topcoat resists.
We have newly successfully synthesized various new highly fluorinated monomers by our peculiar fluorination
process. We found that some specific methacrylate ,which have perfluorinated cyclic structure, showed excellent
hydrophobicity. The other hydrophobic candidates is our fluoropolymer, FUGU, which had already developed, having
partially fluorinated monocyclic structure. However its hydrophobicity is insufficient due to presence of acidic
hydroxyl group which act as dissolution unit into the developer. To improve the its hydrophobicity, we protected all or a
part of its hydroxyl group. The protected FUGU polymer provide good hydrophobicity whose sliding angle (S.A.) and
receding angle (R.A.) were 7 degree and 90 degree respectively , compared to original polymer, FUGU.
In this paper, we describe a characteristics and evaluation of these our hydrophobic polymers to apply to additives for
non-topcoat resists.
We have optimized these polymers to apply to additive for conventional resist. As a result, various kinds of additives
were obtained. For example, some of them dissolve in developer due to the presence of alkali soluble group in the
polymer, the others are soluble in developer after deprotection reaction by post exposure bake. We call the former one is
'top-coat type', the latter is 'resist type'. Two type additives were investigated to give the hydrophobicity and to depress
the leaching amount to conventional resist.
Building an immersion topcoat from the ground up: materials perspective
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Over a period of last several years 193 nm immersion lithography from a remote and unlikely possibility
gradually became a reality in many fabrication facilities across the globe and solid candidate for high volume
manufacturing for the next generation technology node. It is being widely understood in the industry that top-coatless
resist approach is a desirable final stage of the immersion process development. However creating low-defect high
performance top-coatless resist materials requires understanding of the fundamental material properties of the top layer,
responsible for leaching suppression, immersion fluid meniscus stability, and in this way enabling high speed low-defect
scanning.
While a lot of progress has been made in implementing specific top coat materials into the process flow, clear
understanding effects of the top coat properties on the lithographic conditions and printing capability is still lacking. This
paper will discuss top coat materials design, properties and functional characteristics in application to novel
fluoroalcohol polymer-based immersion top coat.
We have used our fluoroalcohol based-series designs (titled MVP top coat materials further on in the paper) as a
test vehicle for establishing correlations between top coat performance and its physical and chemical properties including
hydrophobicity, molecular weight/dispersity etc. Effects of polymer-solvent interactions on the contact angle and
characteristics of the top coat material are explored, providing valuable understanding transferable to design of new
generation top coats and top-coatless materials. Our resultant new designs demonstrated excellent lithographic
performance, profiles and low leaching levels with commercially available resist and high receding contact angles,
comparable to the commercial top coat materials.
Novel materials design for immersion lithography
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The technology of 193nm immersion lithography has been progressing rapidly toward half-pitch 45 nm generation
device manufacturing. However, some intrinsic issues, the photoacid leaching and the watermark defect have remained
in the immersion process. Most of approaches to overcome them were the introduction of cover coating materials (top
coat) onto the resist film. Recently, we have established the non-top coat resist using novel two kinds of materials, a low
leaching PAG (PhotoAcid Generator) and a surface modifier. The hydrophobic photoacid generated from the low
leaching PAG decomposes by heating, and the acid migration changes to reduce the line-width roughness (LWR). The
surface modifier behaves as builded-topcoat by the distribution around resist surface and enhances the surface
hydrophobicity. Herein we propose the concept of novel PAG and surface modifier for immersion lithography.
Materials and Processes for Immersion Lithography II
Novel high-index resists for 193-nm immersion lithography and beyond
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A preliminary Quantitative Structure Property Relationship (QSPR) model for predicting the refractive index of small
molecules and polymers at 193 nm is presented. Although at this stage the model is only semiquantitative we have found
it useful for screening databases of commercially-available compounds for high refractive index targets to include in our
program of synthesis of high refractive index resist polymers. These resists are targeted for use in 2nd and 3rd generation
193 nm immersion lithography. Using this methodology a range of targets were identified and synthesized via free
radical polymerization. Novel resist polymers were also synthesized via Michael addition polymerization. Preliminary
dose to clear experiments identified a number of promising candidates for incorporation into high refractive index resist
materials. Furthermore, we have demonstrated imaging of a high index resist using water-based 193 nm immersion
lithography.
Screening of second-generation high-index liquids
Show abstract
A series of experiments were designed to probe the interaction between second generation High Index Liquids (HIL,
n=1.65) and the resist stack. Three different second-generation high index liquids were tested in five experiments:
measurement of the contact angle of the liquid with the resist surface; leaching of Photo-Acid Generator (PAG) into the
liquid; residue analysis of droplets evaporated from the resist surface; impact of liquid soaking on resist profiles; and
imaging through high-index liquids at 72nm pitch. The selected liquids were the main candidates from two potential
vendors. In parallel, tests have also been done for water. The tests show that one of the main differences between highindex
liquids and water is their much smaller contact angles on the organic photoresist films. This contact angle can be
influenced by a topcoat, but currently seen contact angles may force a new immersion hood concept. Imaging was not
affected strongly by the high-index liquids. For some liquids, low evaporation rates and a tendency to leave residue on
resist were observed, which may require a dedicated liquid removal strategy to reduce defectivity.
High-refractive index material design for ArF immersion lithography
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High-refractive-index fluids (HIFs) are being considered to replace water as the immersion fluid
in next generation 193nm immersion scanner. At SPIE 2006, we have demonstrated the attractive optical
properties and good imaging performance for our HIF candidates, HIL-001 and HIL-002. In this paper, we
will describe our latest results on the remaining issues for the practical application of HIF candidates, as
well as introduce 3rd generation fluids for the further extension of ArF immersion lithography. In order to
improve the fluid transparency, we have tried two approaches. One is the improvement of transparency for
HIL-001 based on a refining technology and the other is to develop a novel HIF candidate by using
computational chemistry, which is named HIL-203. By passing through a suitable refining unit, HIL-001
can reach a transmittance of >99%/mm, which is as high as water. This new purification method can be
applied to an on-site reuse system. It was also found that the refining unit was very effective to eliminate
the impurities coming from the photo-degradation of HIL, chemical substances contamination under the air
exposure, and leaching of resist components such as photo-acid generator or quencher. We have developed
a new fluid for 3rd generation immersion fluids. It had a higher refractive index than that of HIL-001 or
HIL-203; however, it still falls short of our target value. Additionally, by using a novel design concept, we
have developed a top-coat with high refractive index for HIL immersion lithography, which gave an
appropriate contact angle for scanning exposure.
Adapting immersion exposure to mass production by adopting a cluster of novel resist-coating/developing and immersion-exposure equipment
Show abstract
The demand for even denser semiconductor devices is driving efforts to reduce pattern dimensions in semiconductor
lithography. It has been found that 193-nm immersion lithography technology can achieve smaller patterns without
having to modify the infrastructure technology of existing state-of-the-art 193-nm dry lithography. This has made
193-nm immersion lithography a promising technology for next-generation mass production processes. It is now under
full-scale development and is about to enter a commercial stage applicable to mass production.
In 193-nm immersion lithography, the space between the optical projection system and silicon wafer is filled with
liquid thereby immersing the resist film in de-ionized water during exposure. This generates a number of concerns, such
as the penetration of moisture into the resist, the leaching of resist components into deionized water, and the presence of
residual moisture, all of which can lead to defects that can affect post-processing. It has been reported; however, that
rinse processing before and after exposure can be effective in reducing such defects [1]. Also, the trend toward finer
patterns has resulted in large aspect ratios that can lead to pattern collapse, but the application of a surfactant has been
found to ease this problem. Controlling the drying process after rinsing has also been found to reduce residue adhering to
the resist.
The stability of process data is considered to be a crucial factor in the adapting of 193-nm immersion lithography to
mass production. In this report, we obtain long-term data on defects and critical dimension (CD), examine this data for
process stability, and discuss the applicability of 193-nm immersion lithography to mass production.
Immersion defectivity control by optimizing immersion materials and processes
Show abstract
Volume production of 55nm node device using Nikon immersion lithography tool, S609B, has started. One very
important issue for volume production immersion lithography is defectivity control. The mainstream resist process for
the initial stage of immersion is to use a topcoat, because chip manufacturers can continue to use conventional resist
whose lithographic properties are well characterized. On the other hand, because of its simplicity and cost effectiveness,
a topcoat-less resist process is an attractive candidate for the second stage of immersion lithography. Intensive study and
development of topcoat-less resist is being done by resist vendors. One unexpected benefit of topcoat-less resist is it is
much easier to increase hydrophobicity than developer soluble topcoat. For defectivity analysis of both topcoat and
topcoat-less process, a dedicated immersion cluster comprised of a volume production immersion exposure tool, S609B,
with NA of 1.07 and a resist coater-developer LITHIUS i+ (TEL) is used. Excellent defectivity data obtained using
various materials and processes are shown in this paper.
Understanding the root cause of defects is very important to control them. Defect source analysis (DSA) revealed
particles cause many types of defects. Interesting correlations between particles and other topcoat defects and resultant
pattern defects are shown in this paper. In the immersion resist process, wafer edge condition is one key issue. Using
topcoat-less resist, wafer edge condition and its defectivity dependency is discussed and analyzed.
Measurement and evaluation of water uptake by resists, top coats, stacks, and correlation with watermark defects
Show abstract
With immersion lithography approaching the insertion in production, watermarks remain as one of the main concerns for
immersion specific defects. They require special attention because of their size and associated high kill-ratio, and their
increasing occurrence at higher scan speeds. IMEC has been working to understand the underlying mechanism of why
remaining water droplets cause these defects.
This work focuses on water uptake measurements and how this parameter correlates to watermark defectivity.
Ellipsometric Porosimetry (EP) is used to measure the water uptake tendencies of resist and top coat materials and stacks
thereof, and investigate what parameters are affecting it. The influence of material and process parameters and the
presence of a top coat on water uptake by the resist are evaluated. In parallel, the quartz crystal microbalance (QCM)
technique has been used as an alternative option to measure the water uptake. Though a one-to-one comparison between
the results is not straightforward, the main trends are identical for both techniques.
No perfect correlation of watermark defectivity with water uptake has been found in this study. Nevertheless, the results
show a tendency towards higher watermark sensitivity with higher water uptake by the film. It is recognized that the total
watermark defectivity is most probably a complex interplay of different parameters with water uptake being only one of
them.
Resist Materials
High-performance 193-nm photoresists based on fluorosulfonamide
Show abstract
The combination of immersion lithography and reticle enhancement techniques (RETs) has extended 193nm
lithography into the 45nm node and possibly beyond. In order to fulfill the tight pitch and small critical dimension
requirements of these future technology nodes, the performance of 193nm resist materials needs to further improve. In
this paper, a high performance 193nm photoresist system based on fluorosulfonamide (FSM) is designed and
developed. The FSM group has good transparency at 193nm. Compared to the commonly used hexafluoroalcohol
(HFA) group, the trifluoromethyl sulfonamide (TFSM) functionality has a lower pKa value and contains less fluorine
atoms. Polymers containing the TFSM functionality have exhibited improved dissolution properties and better etch
resistance than their HFA counterparts. Resists based on the FSM-containing polymers have shown superior
lithographic performance for line, trench and contact hole levels under the 45nm node exposure conditions. In
addition, FSM resists have also demonstrated excellent bright field and dark field compatibility and thereby make it
possible to use one resist for both bright field and dark field level applications. The structure, property and lithographic
performance of the FSM resist system are reported.
Novel diamantane polymer platform for enhanced etch resistance
Show abstract
The dominant current 193 nm photoresist platform is based on adamantane derivatives. This paper reports on the use of
derivatives of diamantane, the next higher homolog of adamantane, in the diamondoid series, as monomers in
photoresists. Due to their low Ohnishi number and incremental structural parameter (ISP), such molecules are expected
to enhance dry etch stability when incorporated into polymers for resist applications. Starting from the diamantane
parent, cleavable and non-cleavable acrylate/methacrylate derivatives of diamantane were obtained using similar
chemical steps as for adamantane derivatization. This paper reports on the lithographic and etch performance obtained
with a number of diamantane-containing monomers, such as 9-hydroxy-4-diamantyl methacrylate (HDiMA), 2-ethyl-2-
diamantyl methacrylate (EDiMA), and 2-methyl-2-diamantyl methacrylate (MDiMA). The etch advantage, dry and wet
lithographic performance of some of the polymers obtained from these diamantane-containing polymers are discussed.
Hybrid optical: electron-beam resists
Show abstract
Combining optical and electron beam exposures on the same wafer level is an attractive approach for extending
the usefulness of current generation optical tools. This technique requires high-performance hybrid resists that perform
equally well with optical and e-beam tools. In this paper Rohm and Haas EPICTM 2340, a 193-nm chemically amplified
photoresist, is used in a hybrid exposure role. The e-beam tool was used to pattern 45 nm half-pitch features and a 193-
nm immersion stepper was used to pattern 60-nm half-pitch features in the same resist layer. The effects of processing
parameters and delay times were investigated.
Evaluation of immersion lithography processes for 55-nm node logic devices
Show abstract
We have investigated relationship between immersion topcoats and water, and between topcoats and ArF resist films for
the use in ArF immersion lithography from the stand point of the work of adhesion characteristics. We evaluated surface
free energy of topcoat films and resist films each from the contact angle measurement. From values of measured free
energy, we obtained work of adhesion between topcoats and water, and between topcoats and resist films. In addition,
we calculated an interfacial free energy between topcoats and resist films, which is related to the interface stability. As a
result of evaluation of the interfacial free energy of four different kinds of topcoats, the topcoat which has lower surface
free energy was found to have lower work of adhesion between topcoat and water, and lower interfacial free energy
between a topcoat and a resist. These results indicate that the topcoat which has lower surface free energy has more less
interaction between water and topcoat and stabile interface between a topcoat and a resist film.
Photo-deprotection resist based on photolysis of o-nitrobenzyl phenol ether; challenge to half-pitch 22 nm using near-field lithography
Show abstract
We propose a non chemically-amplified positive-tone photoresist based on photolysis of o-nitrobenzyl phenol ether
(NBP). The increase in the amount of the phenolic hydroxyl group just after the exposure to the i-line propagation light
is observed via IR spectroscopy. Using near-field lithography (NFL) combined with the NBP, we form half-pitch (hp) 32
nm line and space (L/S) patterns with lower line edge roughness (LER) than those of a chemically amplified resist
(CAR). The high-resolution feature of the NBP is attributed to the photoreaction system without the acid diffusion,
which is inherently involved in CARs, although the NBP requires six times as much exposure dose as the CAR does. A
Hp 32 nm L/S patterns with 10 nm depths are successfully transferred to the 100 nm thick bottom-layer resist through the
tri-layer resist process. Hp 22 nm L/S patterns with 10 nm depths are also fabricated on the top portion of a single-layer
of NBP.
ARC/Multilayer Process
Enhancing photoresist performance with an adhesion promoting photo-acid generator
Show abstract
Concentration gradients of photoacid generator through the thickness of the photoresist film can profoundly affect the
material's performance. To engineer the acid concentration through resist thickness, we have developed a new type of
resist adhesion promoting layer that incorporates photo acid generator chemistry. These adhesion promoting photo acid
generators, called as a class "APPAG" enhance acid concentration at interface between the resist and the substrate. We
will provide an overview on the preparation and characterization of two siloxane based APPAG materials along with a
performance comparison of commercial DUV, EUV and E-beam photoresists on APPAG.
Nonaflate analog (APPAG 6) with shorter acid diffusion length was found to have a mild impact on 250nm node DUV
lithography. However the triflate analog (APPAG 9), owing to the larger acid diffusion length, was shown to provide a
greater influence. APPAG 9 was found to give nearly a 50% improvement in depth of focus.
For EUV lithography, both APPAG 6 and APPAG 9 will be shown to substantially improve performance envelope for
100nm dense lines and spaces and at reduced post exposure bake (PEB) temperatures. This indicates that this approach
can be used to gain margin at reduced PEB which is desirable to minimize thermally driven diffusion effects. Thus the
materials represent an important new approach to extending photoresist performance margins.
Second-generation radiation sensitive developable bottom anti-reflective coatings (DBARC) and implant resists approaches for 193-nm lithography
Show abstract
We will discuss our approach towards a second generation radiation sensitive developable bottom antireflective
coating (DBARC's) for 193 nm. We will show imaging results (1:1 L/S features down to 140 nm) for some first
generation implant resist material based upon a fluorinated resins and also show relative implant resistance of these first
generation fluorinated resists towards As implantation (15 KeV at 5x1015 dose with 20 x 10-4 amp). Also, discussed
will be a second generation of implant resists based on a non-fluorinated resins. Surprisingly, we found that the nonfluorinated
materials gave better implant resistance (~2-3 X1011 atoms/cm2) despite the higher atomic number of
fluorine compared to hydrogen in the fluorinated implant materials (~2-5X1012 atoms/cm2). Finally, we will give an
update on the lithographic performance of this second generation of implant resists.
Spin-on trilayer approaches to high NA 193nm lithography
Show abstract
New challenges face ArF bottom antireflection coatings (BARCs) with the implementation
of high NA lithography and the concurrent increase use of spin-on hard masks. To achieve superior
reflectivity control with high NA at least two semi-transparent ARC layers, with distinct optical
indices, are necessary to effectively lower substrate reflectivity through a full range of incident
angles. To achieve successful pattern transfer, these layers in conjunction with the organic resist,
should be stacked with an alternating elemental composition to amplify vertical resolution during
etch. This will circumvent the inherent low etch resistance of ArF resist and the decreasing film
thicknesses that accompanies increasing NA. Thus, incorporating hard mask properties and
antireflection properties in the same two layer system facilitates pattern transfer as a whole rather
than just enhancing lithography. As with any material expected to exhibit multiple roles there is a
delicate balance between optimizing materials with respect to one of its roles while not impairing its
other roles. We will discuss some of these conflicts and present Si-BARCs and carbon rich
underlayers which aim to balance these conflicts. In this paper we will explore simulations aimed at
finding the best film thicknesses and optical indices, etch rate selectivity, and lithographic
performance of high silicon content and high carbon content BARC materials designed to meet the
demands of both high NA lithography and trilayer processing.
Progress of hard mask material for multi-layer stack application
Show abstract
Multi-layer stack application will be established at manufacturing process beyond 65nm node. Multi-layer stack
application means laminated layer like a Photoresist, Si contained hard mask, and Carbon hard mask on substrate. Multilayer
stack application can be solved anti-reflection at hyper NA (that means more than 1 numerical aperture) and less
etching resistance in thinner film resist, so Multi-layer stack application is required for 193nm immersion lithography
process. And criteria of our material in Multi-stack application are spin-on and drain compatible type. In this report, we
will discuss about Spin-on Si-contained hard mask and spin-on carbon hard mask criteria, our experiment and results to
solve issue.
Spin-on Si-contained hard mask is required 3-factors that is unti-reflection from substrate at hyper NA conditions, resist
matching, and higher etching resistance. It is general that higher Si-content ratio in based polymer can't be matched with
current 193nm photoresist. But Lower Si-contained Hard Mask can't be resisted by dry etching. In this report, we will
discuss about our material approach for good resist matching (no footing issue) without reduction of Si-content ratio,
pattern transfer ability by dry etching, and reflectivity simulation results at Hyper-NA condition.
LWR issue after dry etching is key factor of Multi-layer stack application. We estimate that composition of based
polymer in carbon hard mask material and film density in carbon Hard Mask is relative to LWR issue after dry etching.
In this report, we will discus about our material approach for less LWR issue after dry etching.
Silicon-based anti-reflective spin-on hardmask materials with improved storage stability for 193-nm lithography
Show abstract
As the feature sizes of integrated circuits shrink, thinner photoresist coating should be used in order to avoid
high aspect ratio which can cause pattern collapse. Especially for 193 nm lithography, photoresist coating is too thin to
subsequent etching step. One of the solutions to this problem is using hardmasks which have good etch selectivity to
adjacent layers. In this paper, silicon-based anti-reflective spin-on hardmasks (Si-SOH) are described. One of the
major problems of silicon based polymers in the hardmask compositions is poor storage stability because silanol group is
reactive enough to condense each other, which can instigate molecular weight increase to yield gel-type particles. The
storage stability of our hardmask materials have been improved by thermodynamically controlled synthesis and reactive
mask strategy. Especially the reactive masked silanol groups can take part in crosslinking reaction under the process
conditions without additional deprotection step. Although this strategy could encounter intermixing problems with
other layers, we can produce silicon-based hardmasks without any deleterious effects. These hardmasks show antireflective
properties and great etch selectivity to both photoresists and organic hardmasks (C-SOH).
Novel developers for positive tone EUV photoresists
Show abstract
While much work has been done in the design of photo resist for EUV lithography, these materials have typically been
optimized for so called "standard developer" i.e., 2.38% tetra methyl ammonium hydroxide. However we felt that it
would be reasonable to consider specifically the developer as opposed to the resist design. Indeed it has been suggested
that the polarity and cation size in developer are important positive tone resist performance. It is our hypothesis that a
base that could wet and penetrate faster into partially deprotected resist could result in a faster photo speed, and thus
make more process margin available for resist design; for example a slower system incorporating higher quencher
loadings. Additionally, we sought to probe the effects of solvent polarity with varying amounts of non-aqueous solvent
additive. By reorganization of the nascent solvent shell with the non aqueous additives, we sought to perturb the
development kinetics and thus change the resist's performance envelope by accelerating photo speed and potentially
increasing contrast. This approach has been applied to non chemically amplified resist to good effect. In the three
positive tones EUV and a 193nm photo resist was evaluated with the prototype developers we found that the
performance was profoundly impacted by these two probes (i.e. solvent polarity and cation hydrophobicity).
Resist Processing
The application of high-refractive index photoresist for 32-nm device level imaging
Show abstract
The lithography prognosticator of the early 1980's declared the end of optics for sub-
0.5&mgr;m imaging. However, significant improvements in optics, photoresist and mask
technology continued through the mercury lamp lines (436, 405 & 365nm) and into laser
bands of 248nm and to 193nm. As each wavelength matured, innovative optical
solutions and further improvements in photoresist technology have demonstrated that
extending imaging resolution is possible thus further reducing k1. Several author have
recently discussed manufacturing imaging solutions for sub-0.3k1
and the integration
challenges.
Our industry will continue to focus on the most cost effective solution. What
continues to motivate lithographers to discover new and innovative lithography
solutions? The answer is cost. Recent publications have demonstrated sub 0.30 k1
imaging. The development of new tooling, masks and even photoresist platforms impacts
cost. The switch from KrF to ArF imaging materials has a significant impact on process
integration.
This paper will focus on the need to increase the refractive index of ArF photoresist
systems to enhance process capability for ultra-high NA's that are near the limitation of
the immersion fluid. Data will be presented demonstrating the impact of higher refractive
index photoresist systems have on the further extension of ArF Immersion. Advanced
RET's will be incorporated to further explore improvements in critical imaging levels
along with dominant mask effects.
Performance of chemically amplified resists at half-pitch of 45 nm and below
Show abstract
The chemically-amplified resists have been exposed by hyper-NA 193nm immersion and EUV lithography. Patterns
with 45nm half-pitch and below are investigated for process windows and line-edge roughness. Although the 193nm
immersion and EUV lithography have totally different optics, an overlap of the resolution capability is clearly observed
around 45nm half-pitches. Both lithographic processes show comparable process windows for 45nm dense lines. The
193i resist better responds to its aerial image than that of the EUV resist. Although the EUV tool has the resolution
capability down to 20nm half-pitch, immature resist process limits the current resolution to 35nm half-pitch.
Evaluation of ArF lithography for 45-nm node implant layers
Show abstract
Scaling of designs to the 45nm or future nodes presents challenges for KrF lithography. The purpose of this work was to
explore several aspects of ArF lithography for implant layers. A comparison of dark loss seen in a KrF resist and TARC
system to that seen in an ArF system showed significant differences. While the KrF resist yielded dark loss that varied
with CD and pitch, the ArF resist showed very little dark loss and no significant variation through the design space. ArF
resist were observed to have marginal adhesion to various substrates. Improvements in adhesion performance were
shown by pre-treating the substrate with various processes, of which an ozone clean provided the best results.
Optimization of the HMDS priming conditions also improved adhesion, and it was observed that the HMDS reaction
proceeds at different rates on different subsatrates, which is particularly important for implant layers where the resist
must adhere to both Si and SiO2. The effect of ArF resist profile with varying reflectivity swing position is shown, and
some investigation into reflectivity optimization techniques was performed. Low-index ArF TARC was shown to
reduce the CD variation over polysilicon topography, and wet developable BARC was demonstrated to provide
consistent profiles on both Si and SiO2 substrates. Finally, a comparison of ArF and KrF resists after As implant
indicates that the ArF resist showed similar shrinkage performance to the KrF resist.
Characterization of photo-acid redeposition in 193-nm photoresists
Show abstract
Time-of-flight secondary-ion mass spectrometry (TOF-SIMS) imaging is demonstrated as a sensitive qualitative method
for characterizing surface acid concentrations and accompanying chemical changes at resist surfaces. We show its utility
in analyzing the 'chemical flare' phenomenon associated with some chemically amplified photoresists. Two commercial
193 nm photoresists were studied: 'photoresist A' displays lithographic defects linked to chemical flare at die edges;
'photoresist B' does not. TOF-SIMS imaging of the surface of 'photoresist A' following exposure and post-exposure
bake (PEB) reveals that die edge defects are well correlated with pronounced emanation of surface acid concentrations
from, and blocking group depletion beyond, the die edge. Both photoresists also exhibit longer-range surface
acidification that is not well correlated with lithographic effects. A plurality of evidence leads us to infer that photoacid
migration from exposed to unexposed regions underlies the lithographic defects observed in 'photoresist A.'
A novel plasma-assisted shrink process to enlarge process windows of narrow trenches and contacts for 45-nm node applications and beyond
Show abstract
Limits to the lithography process window restrict the scaling of critical IC features such as holes (contact, via) and
trenches (required for interconnects and double patterning applications). To overcome this problem, contacts or trenches
can be oversized during the exposure, followed by the application of a shrink technique. In this work, a novel shrink
process utilizing plasma-assisted polymer deposition is demonstrated: a polymer is deposited on the top and sidewalls of
photoresist by alternating deposition and etch steps, reducing the dimension of the lithography pattern in a controlled
way. Hence very small patterns can be defined with wide process latitudes. This approach is generic and has been
applied to both contacts and trenches. The feasibility of the plasma-assisted shrink technique was evaluated through
extensive SEM inspections after lithography, after shrink, and after etch, as well as through electrical evaluations.
Resist Processes and Simulation
A novel method for characterizing resist performance
Show abstract
In this paper, the use of a single Figure-of-Merit to judge resist performance with respect to line width roughness, resolution and sizing dose is proposed and evaluated. Chemically amplified photoresists used in advanced lithography nodes need to fulfill stringent requirements for a considerable number of resist and process characteristics. Along with resolution, line width roughness and resist sensitivity are important examples where the specifications have become very tight. Previously, it has been shown that resolution, line width roughness and resist sensitivity are fundamentally interdependent. Hence, when evaluating or optimizing resist performance it is very important to take these three characteristics into consideration simultaneously. We propose to combine these characteristics in a single photoresist Figure of Merit KLUP. This Figure of Merit, which is determined from sizing dose, imaging wavelength, exposure latitude, acid diffusion length, line width roughness and pitch allows for a direct comparison of very different resist formulations independent of the exposure tool used. Thus, KLUP has great potential to assist in evaluating resist performance for the next lithography nodes, for both ArF and for EUV wavelengths.
The tri-lateral challenge of resolution, photospeed, and LER: scaling below 50nm?
Show abstract
A simple analytical model for line-edge roughness in chemically amplified resists is derived from an
accounting of stochastic fluctuations of photon ("shot noise") and acid number densities. Statistics
from this counting exercise are applied to a region defined by the effective acid diffusion length;
these statistics are then modulated by the slope of the image intensity to produce a value for LER.
The model produces the familiar dependence of LER on aerial image (more specifically on latent
image) and dose also seen in many other models and data. The model is then applied to the special
case of interference imaging, for which the aerial image is a simple, known analytic function. The
resulting expression is compared to experimental data at both relatively large half-pitches, shot with
257nm, and sub-50nm half-pitches shot with 13.5nm and hyper-NA 193nm. The model captures the
primary scaling trends seen at the larger length scales, however at the sub-50nm problems arise. It
appears that additional effects not covered by counting photons and acids are becoming increasingly
important as length scales drop below about 50nm. These additional effects will require increased
attention in order to improve LER in lockstep with diminishing CD and pitch.
PAG segregation during exposure affecting innate material roughness
Show abstract
We have developed an improved AFM-based technique to measure intrinsic material roughness (IMR) after
base development. We have found that similar results can be obtained by measuring the film roughness with a fixed
develop time and variable dose to that of the previously reported interrupted development method, and thus a simple
contrast curve can yield information on the innate material roughness of the exposed resists. It was found that the IMR
is dependent on the PAG and the polymer employed in the resist. The IMR of the resist is also strongly dependent on
the bake conditions, with increasing IMR at higher bake temperatures. Several PAGs have been identified that result in
significantly lower material roughness and thus the potential for significantly reduced line width roughness in resist
imaging. Evidence is presented that PAG segregation during the bake steps is responsible for increased IMR in exposed
resists, presumably by increasing the dissolution rate inhomogeneity on a nano-scale level. It is also shown that the
effects of PAG segregation can be mitigated by the choice of PAG and polymer for the resist.
Mechanistic simulation of line-edge roughness
Show abstract
Physically-based photoresist models, such as those in PROLITH, have been very successful
in describing photolithography from a continuum standpoint. These models allow engineers to
accurately predict the final resist CD on the wafer and to analyze process robustness. However,
as the critical dimension continues to shrink, yield-limiting phenomena are observed that are
related to the molecular nature and reaction kinetics of photoresist materials.
An example of these phenomena is line-edge roughness (LER). In this paper, the origin of
LER is hypothesized to be caused by fluctuations occurring in the initial position of the reactants,
fluctuations during the exposure process (shot noise) and fluctuations occurring during
thermally-induced reaction-diffusion (post-exposure bake). We have developed a lattice-based
mechanistic simulator to better understand the stochastic nature of reactant initial position, the
exposure step, the importance of the discrete nature of the reactants, the coupling to the
deprotection kinetics and the deep complexity evident in the diffusion-limited acid-quencher
reaction.
The characterization of photoresist for accurate simulation beyond Gaussian diffusion
Show abstract
With the continued shrink of integrated circuit fabrication groundrules, the achievement of good critical dimension
(CD) control becomes more and more dependent on optical proximity correction (OPC). Current simulation
capabilities involve a first principle aerial image simulation algorithm, such as the transmission cross coefficient
(TCC) algorithm, and a resist model, which captures the dynamics of the chemical amplification and the developing
process. In the past few years, it has been found that the key photolithographic parameters, such as, the exposure
latitude (EL) and the mask error factor (MEF) for the dense features can be very accurately simulated by the
algorithm in which the latent image are made by simple Gaussian diffusion of the aerial image. However, more
detailed comparison between the simulation and experiment in isolated features, or two-dimensional features
indicates that the current modeling algorithm is still not good enough. This may have resulted in the fact that even
advanced model based OPC may require hundreds, even more than a thousand experimental data points for model
building. In addition, the model made with such endeavor does not usually extend well beyond the minimum
groundrule, which can cause sub-groundrule test structures to fail. We have studied one process parameter of the
photoresists, the MEF, and we found that a single Gaussian can not explain well the CD behavior and it seems that
such difference varies with different resists. The effective diffusion length of some resists are found to vary with line
to space ratio within a dense pitch.
Resist Fundamentals
Direct measurement of the in-situ developed latent image: the residual swelling fraction
Show abstract
The spatial distribution of polymer photoresist and deuterium labeled developer highlights a fraction of material at a
model line edge that swells, but does not dissolve. This residual swelling fraction remains swollen during both the in
situ development and rinse steps uncovering that the final lithographic feature is resolved by a collapse mechanism
during the drying step. We demonstrate that contrast variant neutron reflectivity provides a general method to probe the
nanometer resolved in situ development and rinse process step.
Fundamental limits to EUV photoresist
Show abstract
Recent experimental results indicate that current resists lack the ability to simultaneously meet the 2005 International
Roadmap for Semiconductors (ITRS) goals for Resolution, Line Edge Roughness (LER) and Sensitivity
(RLS). This RLS tradeoff has also been demonstrated through modeling work. Here we use a model to explore
the impact on the RLS tradeoff of anisotropic acid diffusion and increased quantum yield. We show that both
these effects can significantly improve the RLS tradeoff.
Etch resistance: comparison and development of etch rate models
Show abstract
Etch resistance and post etch roughness of ArF photoresists still remain some of the critical issues during process
integration for sub-100nm technology nodes. Compared to phenyl-containing KrF polymers, methacrylate
polymers commonly used for ArF lithography show weak bulk etch resistance in addition to a highly damaged
surface after standard etch processes. Counter to the photoresist, the etch rates of BARC are required to be very
fast to prevent degradation of the photoresist before the image has been transferred to the substrate.
There are a number of etch models in the literature which attempt to describe the correlation between polymer
structure and blanket etch rates. Ohnishi Parameter and Ring Parameter are the most common etch models
correlating atomic and structural trends in the resist polymer and etch rates. These etch models have been tested
in two ways: systematically changing the composition of a terpolymer and using polymers with different
functional groups. By comparing the etch rates of this large series of polymer structures it was found that these
etch models were not sufficient in describing the relationship between the atomic or structural trends in polymer
with etch rates. New etch models that describe the structure property relationship and etch rate trends have been
developed. These new models show a better correlation with the observed experimental results. Finally, new
polymers have been developed, for both ArF and BARC applications. These materials show a significant
improvement in term of etch properties.
Dissolution behavior of resist polymers studied by Quartz-Crystal-Microbalance method II
Show abstract
Characteristic matrix method was applied to study the anomalous Quartz-Crystal-Microbalance (QCM) data such as
sequential peaks of resonance frequency and impedance. The formation of swelling layer was found to cause the broad
peak of resonance frequency at the beginning of development. An impedance peak followed the frequency peak when
the rigidity of the swelling layer decreased to ca. 105 Pa due to absorption of the developer. Constant thickness of a
swelling layer makes double sets of sequential peaks in frequency and impedance. Continuous changes in swelling layer
thickness caused a single set of peaks during development. A fast data-acquisition system for QCM was set up and
showed the sampling time of 1 kHz with the accuracy of 0.5 nm. It gives good and precise information for resist of large
dissolution rate and interface region between resist and substrate.
LER
Component segregation in model chemically amplified resists
Show abstract
We have applied chemical force microscopy (CFM) to probe the surface roughness of partially developed model resist
materials in order to understand the fundamental materials properties of the resists leading to line edge roughness
(LER). CFM is capable of providing simultaneous information about surface topography and chemical heterogeneity of
partially developed resist films. We have used CFM to study ESCAP type resists that are used in 248 nm and extreme
ultraviolet (EUV) lithography. We observe changes in both the innate material roughness and chemical heterogeneity
of the resist with the introduction of photoacid generator (PAG) and with exposure and post exposure bake (PEB). We
find several mechanisms by which chemical heterogeneity can contribute to increasing the innate material roughness of
the resist.
FTIR measurements of compositional heterogeneities
Show abstract
A general approach to characterize compositional heterogeneity in polymer thin films using Fourier transform
infrared (FTIR) spectroscopy has been demonstrated Polymer films with varying degrees of heterogeneity were
prepared using a model chemically amplified photoresist where a photoacid catalyzed reaction-diffusion process results
in the formation of methacrylic acid (MAA)-rich domains. Within these domains, the carboxylic acid groups dimerize
through hydrogen bonding. FTIR measurements of the relative fraction of hydrogen-bonded versus free carboxylic
groups are used to quantify the degree of compositional heterogeneity. It was shown that the degree of the spatial
heterogeneity varies with changes in the deprotection level and initial copolymer composition. The degree of
heterogeneity is small at very low and very high deprotection level and maximize when the deprotection level is around
0.25. Increased non-reactive comonomer content decreases the degree of heterogeneity by reducing the hydrogen
bonding efficiency.
Changes in resist glass transition temperatures due to exposure
Show abstract
We have developed an AFM-based technique to measure intrinsic material roughness (IMR) after base
development. Employing this technique we have deconstructed the resist into component parts and have shown that
PAG is a major contributor to intrinsic material roughness. When PAG is exposed and thermal polymer deprotection is
allowed to occur increased levels of IMR are present. The IMR of the resist is strongly dependent on the bake
conditions, with increasing IMR at higher bake temperatures. This leads to the suspicion that the resist glass transition
temperature (Tg) may be responsible for the changes in the level of IMR observed with both different PAGs, polymers
and bake temperatures. We have measured the Tg in a series of model resists, both exposed and unexposed, and show
the effect of changes in resist glass transition as a function of exposure dose and not the level of polymer deprotection.
The Tg of the resists does not decrease with exposure or bake as may be expected, but instead is either unchanged or
slightly increases. The change in Tg occurs due to exposure only with subsequent bake steps not affecting the resist Tg.
A study on the material design for the reduction of LWR
Show abstract
It is generally believed that the chemically amplified reaction between photo-generated acid catalyst and acid labile
group of polymer during post-exposure bake (PEB) process plays a critical role for the reduction of line width roughness
(LWR) in ArF lithography. In this work, we revealed experimentally how large the chemically amplified reaction affects
LWR, and developed a new resist system with low LWR. Aerial image contrast dependence on LWR revealed that the
innate LWR in a conventional ArF photoresist, which is independent of the aerial image contrast, was 5 nm. Surface
roughness of a non-patterned resist film at half-exposed area, which was well correlated with LWR, was measured by
AFM. The surface roughness increased from 1.7 nm to 10.8 nm during PEB process. The half-exposed area was baked
and again dissolved into organic solution, and spin-coated on Si wafer, and then developed with 2.38 % TMAH solution.
The recoated half-exposed resist film caused a 60 % reduction on the surface roughness. It revealed that uniform
distribution of deblocked polymer was important factor for roughness reduction. HPLC analysis indicated that
distribution of acidic group formulation in the polymer was gradually extended with increasing exposure dose. A Resist
system that suppresses the chemically amplified reaction successfully reduced LWR from 6.5 nm to 4.8 nm.
Line-edge roughness in 193-nm resists: lithographic aspects and etch transfer
Show abstract
We describe methods to determine transfer functions for line edge roughness (LER) from the photoresist pattern through
the etch process into the underlying substrate. Both image fading techniques and more conventional focus-exposure
matrix methods may be employed to determine the dependence of photoresist LER on the image-log-slope (ILS) or
resist-edge-log-slope (RELS) of the aerial image. Post-etch LER measurements in polysilicon are similarly correlated to
the ILS used to pattern the resist. From these two relationships, a transfer function may be derived to quantify the
magnitude of LER that transfers into the polysilicon underlayer from the photoresist.1
A second transfer function may be derived from power spectral density (PSD) analysis of LER. This approach is
desirable based on observations of pronounced etch smoothing of roughness in specific spatial frequency ranges.
Smoothing functions and signal averaging of large numbers of line edges are required to partially compensate for large
uncertainties in fast-Fourier transform derived PSDs of single line edges. An alternative and promising approach is to
derive transfer functions from PSDs estimated using autoregressive algorithms.
Impact of line-width roughness on Intel’s 65-nm process devices
Show abstract
Line Width Roughness (LWR) is the random variation of MOS gate length along the gate width. LWR is undesirable
because it degrades drive current (Ion), increases off-current (Ioff), and causes a random variation of device parameters
across a die. Previously, it was determined that LWR did not impact Intel's 130 nm process devices. As device sizes
shrink, the sensitivity to LWR increases, so the amount of LWR that can be tolerated in future generations needs to be
re-assessed. In this paper we will present the experimental results of the effects of LWR on Intel's 65 nm process.
It was found that both nominal drive current and its variation degrade with increased LWR. Additionally, Ioff increased
exponentially with increased LWR. In order to maintain less than 2% degradation in Ion from LWR, the 3-Sigma %
LWR should be less than 10% of the nominal final check critical dimension (FCCD). Thus, for future generations,
LWR needs to scale as gate lengths decrease or else any potential benefits in increased drive current would be offset by
large amounts of leakage.
NGL
Impact of curing kinetics and materials properties on imprint characteristics of resists for UV nano-imprint lithography
Show abstract
UV curable resist formulations for nanoimprint must satisfy criteria for cure rate, volatility, viscosity, cohesion of the
cured material and release from the template in addition to being successfully imprintable. We describe an investigation
of the properties of a series of formulations comprising polyhedral oligomeric silsesquioxane and selected diluents as
candidates for imprintable dielectrics. Although all have low viscosity and volatility and are successfully imprinted,
significant variations in cure rate, mechanical and adhesion properties with resist composition are found. The trends
observed are not all predictable from the literature, indicating that formulation optimization for this application requires a
focus on the fundamentals of both materials and processes.
Material design of negative-tone polyphenol resist for EUV and EB lithography
Show abstract
In order to enable design of a negative-tone polyphenol resist using polarity-change reaction, five resist
compounds (3M6C-MBSA-BLs) with different number of functional group of &ggr;-hydroxycarboxyl acid were prepared
and evaluated by EB lithography. The resist using mono-protected compound (3M6C-MBSA-BL1a) showed 40-nm hp
resolution at an improved dose of 52 &mgr;C/cm2 probably due to removal of a non-protected polyphenol while the
sensitivity of the resist using a compound of protected ratio of 1.1 on average with distribution of different protected
ratio was 72 &mgr;C/cm2. For evaluation of the di-protected compound based resist, a di-protected polyphenol was
synthesized by a newly developed synthetic route of 3-steps reaction, which is well-suited for mass production. The
resist using di-protected compound (3M6C-MBSA-BL2b) also showed 40-nm hp resolution at a dose of 40 &mgr;C/cm2,
which was faster than that of mono-protected resist. Fundamental EUV lithographic evaluation of the resist using
3M6C-MBSA-BL2b by an EUV open frame exposure tool (EUVES-7000) gave its estimated optimum sensitivity of 7
mJ/cm2 and a proof of fine development behavior without any swelling.
Photosensitivity and line-edge roughness of novel polymer-bound PAG photoresists
Show abstract
Substantially improved photoresist material designs, which can provide higher photosensitivity and precise critical
dimension and edge roughness control, will be required to enable the application of next generation lithography
technology to the production of future sub-65 nm node IC device generations. The development and characterization of
novel material platforms that solve the aforementioned basic problems with chemically amplified resists (CARs) is
essential and is already one of the major subjects of modern lithography research. In that regard, we have pursued
development of a variety of 193 nm and EUV CARs that contain photoacid generator (PAG) units covalently bonded
directly to the resin polymer backbone. However, the detailed structure-property relationships that result from this
direct attachment of the PAG functional group to the polymer have previously not yet been rigorously characterized. In
this work, the lithographic properties of a polymer-bound PAG CAR (GBLMA-co-EAMA-co-F4-MBS.TPS) and its
blended-PAG analog resist (GBLMA-co-EAMA blend F4-IBBS.TPS) were studied and compared. The direct
incorporation of PAG functionality into the resist polymer, where the resulting photoacid remains bound to the polymer,
showed improved photosensitivity, resolution, and lower LER as compared with the analogous blended-PAG resist.
The improved resolution and LER were expected due to the restricted photoacid diffusion and uniform PAG distribution
provided by direct incorporation of the PAG into the polymer backbone to make a single-component resist material.
The ability to load higher levels of PAG into the resist provided by this PAG incorporation into the polymer, as compared
to the low PAG concentrations attainable by traditional blending approaches, overcomes the sensitivity loss that should
result from reduction in photoacid diffusivity and concomitant smaller acid-catalytic chain lengths. In fact, the
polymer-bound PAG resist achieves a faster photospeed than the blended-PAG analog material under DUV radiation in
the case of the materials reported here while still providing all of the aforementioned improvements such as the improved
line edge roughness.
Novel anionic photoacid generator (PAGs) and photoresist for sub-50-nm patterning by EUVL and EBL
Show abstract
A new series of anionic photoacid generators (PAGs), and corresponding polymers were prepared. The thermostability
of PAG bound polymers was superior to PAG blend polymers. PAG incorporated into the polymer main chain showed
improved resolution when compared with the PAG blend polymers. This was demonstrated by Extreme Ultraviolet
lithography (EUVL) results: the fluorine PAG bound polymer resist gave 45 nm (1:1), 35 nm (1:2), 30 nm (1:3) and 20
nm (1:4) Line/Space as well as the 50 nm (1:1),30 nm (1:2) elbow patterns.
Novel Processes/Applications
Self-aligned, self-assembled organosilicate line patterns of ~20nm half-pitch from block-copolymer mediated self assembly
Show abstract
We report the formation of robust organosilicate line patterns of ~20nm half-pitch on surfaces from the self-assembled
lamellar phase of a diblock copolymer of polystyrene and poly(ethylene oxide), PS-b-PEO, and an oligomeric
organosilicate precursor mixtures. We could control the orientation and alignment of microdomains of this hybrid to the
same degree of the thin films of organic block copolymers. By controlling the surface energy of substrates using dense
organosilicate, the perpendicular orientation of lamellae to the surface was achieved. Topographic prepatterns were
generated by E-beam lithography and used for alignment of the line patterns from lamellar phase. Upon removing the
organic component (i.e. PS-b-PEO) by thermal treatment, the organosilicate microdomains remain as periodic line
patterns with global alignment on surfaces. This method gives well-aligned silicon-containing line patterns with sublithographic
length scales on surface. The self-assembled organosilicate line patterns were successfully transferred into
underlying silicon substrate using anisotropic plasma etching.
Gray-scale lithography of photosensitive polyimide and its graphitization
Show abstract
Gray scale lithography GSL was implemented using an aqueous developing photosensitive polyimide, HD8820.
Silicon carbide high kilo-volt power diodes and transistors fabrication required a tapered barrier for dopant ion
implantation and annealing at elevated temperatures for formation of junction edge terminations. The GSL
photomask was made by electron beam lithography 32-bit gray scale intensity profile exposure of a silver doped
HEBS glass that is sensitive to electron beams but not to ultra-violet UV radiation. When the photosensitive
polyimide HD8820 was exposed through the gray scale photomask in a UV lithography system, the desired
polyimide tapered profile was obtained. The polyimide patterns were subsequently converted to amorphous graphite
at 650°C in a nitrogen furnace. Boron and aluminum high temperature ion implantations at several energies and
doses were performed and the resulting dopant profiles, characterized using secondary ion mass spectroscopy SIMS,
were found to correlate well with computer simulations. The GSL tapered photosensitive polyimide can therefore
serve as an effective ion implantation barrier to obtain precisely graded dopant profiles. Micro-optics components
such as gratings and Fresnel micro-lenses were also successfully fabricated using gray scale lithography of the
photosensitive polyimide.
A novel top surface imaging approach utilizing direct-area selective atomic layer deposition of hardmasks
Show abstract
A novel method for performing top surface imaging (TSI) on a single polymeric photoresist film using area selective
atomic layer deposition (ALD) is presented. In this method, exposure of the polymer thin film creates reactive hydroxyl
sites on the film surface in the exposed areas that subsequently act as nucleation and growth sites for deposition of metal
oxide features using a chemically selective ALD process. It is demonstrated that titanium isopropoxide and water can be
used as ALD precursors in conjunction with a chemically amplified photoresist film, formulated using a protected
polymer (poly-tertbutylmethacrylate (PtBMA)) and a photoacid generator (triphenylsulfonium tris(perfluoromethanesulfonyl)
methide), to successfully perform such an area selective ALD TSI process. Using this material set and
methodology, micron scale photoresist features are defined, metal oxide patterns are produced, and these patterns have
been transferred through the polymer film via plasma etching. A comparison is also made between the silylation
chemical contrast obtained from earlier TSI methods and the metal oxide deposition contrast obtained using the ALD
TSI method. It is shown that the ALD TSI chemical contrast for metal oxide deposition can be much higher than the
corresponding silylation-based silicon incorporation contrast This result translates into a unique feature of the ALD TSI
process which is it can be achieved without requiring the descum etch that is commonly needed with other TSI methods
based on silylation.
Novel photodefinable low-k dielectric polymers based on polybenzoxazines
Show abstract
The development of spin-on photodefinable dielectrics for use in microelectronic device fabrication and
packaging has traditionally focused mainly on the use of soluble polymer precursors because the desired final dielectric
polymer structure is generally insoluble in any appropriate casting solvent. One major drawback to this approach
however is that high temperature processes (often >300 °C) after imaging and development are generally required to
convert the imaged precursor polymer into the desired low dielectric constant material. These high processing
temperatures make such materials impractical for a variety of applications. The goal of the work reported in this paper
was to overcome this problem by developing new low dielectric constant polymers that can be formulated into photodefinable
materials and processed at lower temperatures. In this work the use of a novel hexafluoroisopropanol
(HFA)-substituted diamine to synthesize novel polybenzoxazines is reported. Whereas polybenzoxazoles form a five
membered ring by situating an alcohol ortho to an amide, the benzoxazine rings in the polymer backbone described in
this work are formed by the dehydration of a hexafluoroalcohol (HFA) group situated ortho to the amide to form a six
membered ring. Of this general class of new polybenzoxazine amide alcohol precursor polymers, it will be shown that
selected polymers exhibit good solubility in developer solutions and can be formulated into photosensitive compositions
by addition of a DNQ inhibitor. Polybenzoxazine film properties including dielectric constant, thermal expansion
coefficient, glass transition temperature, water absorption and dissolution rate have been measured. In particular, the
dielectric constant for polybenzoxazine is reported to be as low as 2.2. In contrast to polybenzoxazoles which are
known to cyclize at temperatures well above 280 °C, the new polymers reported here can be cyclized at temperatures as
low as 210 °C. This significantly lower thermal cyclization temperature greatly alleviates many problems with other
photodefinable dielectric polymers such as thermal stress build-up during curing and also allows these materials to be
integrated with a wider variety of materials that would not survive the significantly higher processing temperature
required with most current polyimides and polybenzoxazoles.
Patterning of biomolecules on a biocompatible nonchemically amplified resist
Show abstract
A simple lithographic process in conjunction with a novel biocompatible nonchemically amplified photoresist material
was successfully used for the patterning of biomolecules such as cells and proteins. UV light irradiation on selected
regions of the nonchemically amplified resist film renders the exposed regions hydrophilic by the formation of
carboxylic groups. Mouse fibroblast cells were found to be preferentially aligned and proliferated on the UV light
exposed regions of the nonchemically amplified resist film, where carboxylic groups were present. For streptavidin
patterning, amine-terminated biotin was linked to the carboxylic groups of the UV light exposed regions, which was
further used to bind streptavidin to the UV light exposed regions.
Joint Session with Conference 6517 on EUV Resists
Resist evaluation for EUV application at ASET
Show abstract
Although EUV lithography has been prepared for next generation litho-technique for several years, there are still lots of
obstacles on its way. Especially, phase defect from the mask, and immaturity in the resist should be solved as soon as
possible because they are directly related to realizing patterns on the wafer. ASET has been focusing on these two
problems, that is, the mask-related defect control and the resist screening for EUV application. In this study, we
concentrate on the resist evaluation for the EUV lithography application, mainly commercial CAR (Chemically-
Amplified Resist) type resist, for example, ArF resist based on polymethacrylate and KrF resist based on poly(4-
hydroxystyrene) (PHS). We screened tens of resists in viewpoint of resolution, photo-speed, and LWR (Line Width
Roughness). We used two METs (Micro-Exposure Tools). The one is HiNA in ASET and the other is MET in Lawrence
Berkeley National Lab. (LBNL) to evaluate resist. And we used EUV masks fabricated by DNP and ASET. Some resist
showed modulation on the wafer for 28nm-hp line and space pattern and some resist showed very high photo-speed
about 5mJ/cm2. Photo-speed could be improved about 25% by controlling the amount of additives, PAG and quencher.
However, improvement in photo-speed caused degradation in resolution. This means there are trade-off relation
between resolution and photo-speed. And we also evaluated polymer-bound PAG resist, which showed new possibility
for EUV resist. And we encountered unexpected problem, pattern lifting, which was solved by using bufferlayer to
increase attachment force between resist and wafer surface. We conclude that polymer bound PAG resist is a good
approach to lower LWR of resist for EUVL application and bufferlayer tuning and matching with resist is also needed
for low LWR. The EUVL masks were fabricated by Dai Nippon Printing Co., Ltd. The HiNA set-3 projection optics
were developed and provided by Nikon Corporation. This work was supported by NEDO.
Molecular glass photoresists containing photoacid generator functionality: a route to a single-molecule photoresist
Show abstract
A single molecule photoresist composed of tris(4-(tert-butoxycarbonyloxy)-3,5-dimethylphenyl) sulfonium
hexafluoroantimonate (TAS-tBoc) was successfully synthesized and characterized. The synthesized triarylsulfonium was
found to perform comparably to a commercial triphenylsulfonium triflate photoacid generator (PAG) when used purely
as a PAG in blended molecular glass resist. TAS-tBoc formed excellent amorphous films when spin-coated out of
solution. When exposed to 248 nm UV radiation, TAS-tBoc showed a sensitivity of 4 mJ/cm2 and a contrast ratio
between 6 and 15, depending on development conditions. Its etch rate under standard silicon dioxide etch conditions was
0.87 as standardized to that of tBoc-PHOST in the same RIE plasma conditions. The outgassing level of the resist under
EUV exposure was determined to be 1.08 x 1013 molecules/cm2, well below the maximum outgassing cutoff that is
considered acceptable for EUV imaging. When imaged by e-beam, TAS-tBoc showed a relatively high dose-to-clear of
150 &mgr;C/cm2 as compared to conventional chemically amplified photoresists. Lines down to 50 nm wide with aspect
ratios of 2.5:1 were imaged using e-beam. These lines exhibited an LER of only 3.96 nm, significantly better than the
typical LER for polymeric chemically amplified resist, even when imaged using e-beam, and also one of the lowest
values reported for molecular glass materials in general.
The resist materials study for the outgassing reduction and LWR improvement in EUV lithography
Show abstract
The continuous studies for both the outgassing reduction and the sensitivity improvement by applying low outgassing
photo acid generator with a various kinds of polymer protection group were discussed in this paper. Further reduction of
the outgassing segments from the resist was demonstrated to achieve the total outgassing amount below the detection
limit of GC-MS (ca. less than 1E+10 molecules / cm2). Loading a large sized acetal group could be successfully reduced
the amount of the outgassing segments from polymer below the tool detection limit, which would be acceptable for a
high volume manufacturing tool usage. The development properties of PHS based bulky acetal polymers were measured
by changing molecular weight. The high dissolution rate contrast was obtained with the bulky acetel protected low
molecular weight polymer. A resolution capability study was carried out with micro exposure tool (MET) at LBNL and
Albany. The correlation between LWR through CD and DOF was measured by loading various amounts of quencher.
The resolution capability of newly developed EUV resist had been successfully improved by modifying both resist
polymer matrix and quencher amount optimization. It was possible to obtain 27.7nm lines with MET tool, where LWR
value at 35 nm L/S was 3.9 nm with reasonable sensitivity range.
An analysis of EUV-resist outgassing measurements
Show abstract
Optics contamination is a concern for extreme ultraviolet (EUV) lithography. To protect EUV optics, all materials used
in EUV vacuum exposure chambers must be screened prior to use. Photoresists are a concern since a freshly coated
wafer will be introduced into the chamber approximately every minute in a high volume production tool. SEMATECH
and the International EUV Initiative (IEUVI) have begun a resist outgassing benchmarking experiment to compare
different outgassing methodologies. Samples of the same batch of resist were sent to eight researchers. The results show
a large variation of four orders of magnitude in the amount of measured outgassing products. The next steps are to
correlate outgassing measurements to witness plate experiments.
Poster Session: Materials and Processes for Immersion Lithography
Contact angles and structure/surface property relationships of immersion materials
Show abstract
Surface properties of materials are an important, even vital, consideration in immersion lithography. Many
investigations have shown that sessile drop static contact angles are not entirely useful in the design of high performance
immersion lithography surfaces. We have synthesized and characterized a broad family of "hydrophobic" materials and
this paper will share information on the role of molecular structure on contact angles and hysteresis of these immersion
materials. Insight into the relationship between structure and contact angles for future immersion materials will be
presented.
Mechanism of immersion specific defects with high receding-angle topcoat
Show abstract
A dynamic receding contact angle (RCA) is a well-known guideline to estimate the degree of watermark (WM)
defects, which shapes circle and bridges inside of the defect and reduces with enlarging the RCA of topcoat (TC).
However, our recent investigation revealed the occurrence of the circular shape defects in spite of using the TC with a
large RCA, bringing about a change of line and space pattern pitch. In this paper, we clarify the origin of these defects
and propose a new key factor of the dynamic surface properties of immersion-specific defects. It was found that the
pitch-change defect is caused by the lens effect of the air bubbles embedded between advancing water meniscus and the
TC. To well understand generation of the bubble defects, we defined the "effective" hysteresis (EH) as the hysteresis of
dynamic contact angle taken the effects of water-absorption into account. An analysis with the EH indicates that the
bubble defect arises from not only to the large ACA but also small amount of water uptake and the amount of
water-absorption could be substituted by the dissolution rate of TC. It was demonstrated that the EH proposed is a new
key factor for estimating the number of bubble defects. The EH is very useful for analyzing the bubble defects in
immersion lithography. The characteristics of the bubble defect are also discussed with a focus on the structure of the
polymer attached to water.
Defectivity reduction studies for ArF immersion lithography
Show abstract
Immersion lithography is widely expected to meet the manufacturing requirements of future device nodes. A critical
development in immersion lithography has been the construction of a defect-free process. Two years ago, the authors
evaluated the impact of water droplets made experimentally on exposed resist films and /or topcoat. (1) The results
showed that the marks of drying water droplet called watermarks became pattern defects with T-top profile.
In the case that water droplets were removed by drying them, formation of the defects was prevented. Post-exposure
rinse process to remove water droplets also prevented formation of the defects.
In the present work, the authors evaluated the effect of pre- and post-exposure rinse processes on hp 55nm line and
space pattern with Spin Rinse Process Station (SRS) and Post Immersion Rinse Process Station (PIR) modules on an inline
lithography cluster with the Tokyo Electron Ltd. CLEAN TRACKTM LITHIUS TM i+ and ASML TWINSCAN
XT:1700Fi , 193nm immersion scanner.
It was found that total defectivity is decreased by pre- and post-exposure rinse. In particular, bridge defects and large
bridge defects were decreased by pre- and post-exposure rinse.
Pre- and post-exposure rinse processes are very effective to reduce the bridge and large bridge defects of immersion
lithography.
Study on the reduction of defects in immersion lithography
Show abstract
ArF Immersion lithography is expected to be a production-worthy technology for sub-60nm DRAM. It gives wider
process window and better CD uniformity at the cost of defects and overlay accuracy. It is generally mentioned that
immersion defects are generated during exposure and removed through pre-soak and post-soak process. A lot of efforts
are being made towards less defect generation during exposure and more defect removal through pre-soak and postsoak
process.
We have experienced a variety of immersion defects and classified them into four types: bubble defect, water mark
defect (T-top & Stain), swelling defect and bridge defect (Macro & Micro). We have worked very hard to reduce each
immersion defects with immersion exposure and system. In this paper, we investigate method to reduce each
immersion defects: bubble, water mark, swelling and bridge through our experiment.
Modified polymer architecture for immersion lithography
Show abstract
In the past several years, ArF immersion lithography has been developed rapidly for practical applications. ArF
immersion lithography is now researched actively and developed for the purpose of implementing the 45-nm technology
node. For the device designs involved immersion lithography, line width roughness (LWR) and film wettability are very
important criteria to control in the point of high resolution and defectivity.
Free radical polymerization in the presence of thiocarbonylthio compounds of general structure Z-C(=S)S-R provides
living polymers of predetermined molecular weight and narrow molecular weight distribution by a process of reversible
addition-fragmentation chain transfer (RAFT). A rationale for selecting the most appropriate thiocarbonylthio
compounds for a particular monomer type is presented with reference to the polymerization of methacrylates, styrenes,
acrylates, acrylamides, and vinyl acetate.
In this study, resist polymers with narrow polydispersity (PD) and controlled molecular structure were prepared using
controlled radical polymerization techniques, such as RAFT polymerization. PD index of polymers showed between
about 1.2 to 1.4 and in some instances, between about 1.1 to 1.2 or less. Additionally, each polymer chain has a RAFT
end group. That is the resulting polymer contains a chain transfer agent (CTA) moiety at each terminal end of polymer
backbone. It is possible that hydrophobic CTAs can be used to decrease the hydrophilicity of resist film.
Tailoring surface properties of ArF resists thin films with functionally graded materials (FGM)
Show abstract
Our recent research effort has been focused on new top coating-free 193nm immersion resists with regard to leaching of
the resist components and lithographic performance. We have examined methacrylate-based resins that control the
surface properties of ArF resists thin films by surface segregation behavior. For a better understanding of the surface
properties of thin films, we prepared the six resins (Resin 1-6) that have three types fluorine containing monomers, a new
monomer (Monomer A), Monomer B and Monomer C, respectively. We blended the base polymer (Resin 0) with Resin
(1-6), respectively. We evaluated contact angles, surface properties and lithographic performances of the polymer blend
resists. The static and receding contact angles of the resist that contains Resin (1-6) are greater than that of the base
polymer (Resin 0) resist. The chemical composition of the surface of blend polymers was investigated with X-ray
photoelectron spectroscopy (XPS). It was shown that there was significant segregation of the fluorine containing resins
to the surface of the blend films. We analyzed Quantitative Structure-Property Relationships (QSPR) between the surface
properties and the chemical composition of the surface of polymer blend resists. The addition of 10 wt% of the polymer
(Resin 1-6) to the base polymer (Resin 0) did not influence the lithographic performance. Consequently, the surface
properties of resist thin films can be tailored by the appropriate choice of fluorine containing polymer blends.
Development of top coat materials for ArF immersion lithography
Show abstract
We have investigated higher hydrophobic developer-soluble topcoat by combination of developer-soluble unit with
higher hydrophobic unit. We have already reported a series of fluoropolymers, FUGU having a partially fluorinated
monocyclic structure and having acidic hydroxyl group which act as dissolution unit into alkaline solution. In
addition, recently we have developed new series of highly fluorinated monomers which was expected to act as
hydrophobic unit. In this paper, we describe results of co-polymersization of FUGU with these hydrophobic monomers
and evaluation of them. Some of them showed good hydrophobicity keeping moderate developer solubility.
Furthermore, we found that higher hydrophobic developer-soluble materials were achieved by adding small amount
of highly hydrophobic polymer to developer-soluble polymer, for example FUGU, and in fact this type of blending
polymer showed high hydrophobicity keeping high dissolution. We have obtained various kind of new type of topcoat
materials whose receding angle varied from 70-90 degree and patterning profile without dissolution residue could be
obtained by using two beam interference.
Transfer mechanism of defects on topcoat to resist pattern in immersion lithography process and effects on etching process
Show abstract
For the scaling down of the semiconductor design rule, 193-nm lithography technology is entering the 65-nm-node
generation. In 65-nm and finer processes, the practical application of 193-nm immersion lithography is progressing due
to its high numerical aperture (NA), which is achieved by using de-ionized water (DIW) as the medium between the lens
and wafer in the exposure system. Immersion lithography, however, generates two main concerns: the penetration of
moisture into resist film and the leaching of resist components into DIW as a result of immersing the resist film in DIW.
To prevent these effects, the use of a topcoat process has been adopted, but there have been reports that defects caused
by remaining droplets on the topcoat or particles can be transferred to the resist pattern and degrade resolution. Research
to date has clarified the generation mechanism of defects due to water droplets, and the importance of preventing
droplets from remaining is now understood. However, there are few research reports on the generation of particles, and
to reduce defects caused by the immersion process. It is essential that the generation mechanism of particle-related
defects on the resist pattern be clarified and that a suitable approach to reducing particles is needed. It is also known that
particles on the resist pattern that acts as a mask in the dry etching process can be associated with defects in etching,
which makes particle control in the process steps between lithography and dry etching all the more important.
In this paper, we clarify the defect-generation mechanism on resist pattern due to particles put on
topcoat and investigate the effects of such particles on the dry etching process.
Models for predicting the index of refraction of compounds at 193 and 589 nm
Show abstract
A simple empirical model is presented that predicts the index of refraction at 589 nm (D-line) and 193 nm for molecules based solely on chemical structure. The model was built by comparing literature values of refractive indices (sodium D-line 589 nm) of compounds with representative functionalities and has 18 adjustable parameters. Published values for nD and n193 were used to extrapolate the predictions from values of nD to values of n193. These simple, accessible models can be run using only Excel software on a laptop computer.
Outlook for potential third-generation immersion fluids
Show abstract
In a search for alkane candidates for 193 nm immersion fluids, several alkanes and cycloalkanes were synthesized,
purified and screened to ascertain their absorption at 193 nm, refractive index and temperature dispersion coefficient in
the context of the actual application. In general, cycloalkanes, and more specifically polycycloalkanes, possess a higher
refractive index than do linear alkanes. Decalin, cyclodecane, perhydrophenanthreme (PHP), perhydrofluorene (PHF)
and perhydropyrene (PHPY) are examined as potential second and third generation immersion fluids. The use of
perhydropyrene, which possesses a high refractive index of 1.7014 at 193 nm, may be limited as an immersion fluid
because of high absorption at 193 nm. Mixtures of cycloalkanes can lead to a higher enhancement of the refractive index
together with a decrease on the viscosity. Exhaustive purification of the fluids is a critical step in determining the real
absorption of the different fluids at 193 nm. Two simple purification processes of these cycloalkanes were developed
that led to low absorption fluids in the VUV region. The possibility of forming the oxygen complex in aerated fluids was
reduced by purging samples with argon or nitrogen. This easy elimination of the oxygen complex shows the weak
bonding nature of this complex.
Behavior and effects of water penetration in 193-nm immersion lithography process materials
Show abstract
The development of next-generation exposure equipment in the field of lithography is now underway as the demand
increases for faster and more highly integrated semiconductor devices. At the same time, proposals are being made for
lithography processes that can achieve finer pattern dimensions while using existing state-of-the-art ArF exposure
equipment.
Immersion exposure technology can use a high-refraction lens by filling the space between the exposed substrate and the
projection lens of the exposure equipment with a liquid having a high refractive index. At present, the development of
193-nm immersion exposure technology is proceeding at a rapid pace and approaching the realm of mass production.
However, the immersion of resist film in de-ionized water in 193-nm immersion exposure technology raises several
concerns, the most worrisome being the penetration of moisture into the resist film, the leaching of resist components
into the water, and the formation of residual moisture affecting post-processing. To mitigate the effects of directly
immersing resist in de-ionized water, the adoption of a top coat is considered to be beneficial, but the possibility is high
that the same concerns will rise even with a top coat.
It has been reported that immersion-specific defects in 193-nm immersion exposure lithography include "slimming,"
"large bridge," "swell," "micro-bridge," and "line pitch expansion," while defects generated by dry lithography can be
summarized as "residue," "substrate induced," "discoloration," and "pattern collapse." Nevertheless, there are still many
unexplained areas on the adverse effects of water seeping into a top coat or resist. It is vitally important that the
mechanisms behind this water penetration be understood to reduce the occurrence of these immersion-induced defects.
In this paper, we use top coats and resist materials used in immersion lithography to analyze the penetration and
diffusion of water. It is found that the water-blocking performance of protective-film materials used in immersion
lithography may not be sufficient at the molecular level. We discuss the diffusion of water in a top coat and its effects.
Process optimization for developer soluble immersion topcoat material
Show abstract
The 193 nm immersion lithography has been increasingly applied to the semiconductor device mass production. Topcoat
material would be used in many such cases. Topcoat film can maximize the scan speed during immersion exposure step
and also prevent small molecules from leaching out of resist film. However, the use of the topcoat material in the mass
production affects productivity including throughput and chemical cost. To manage this problem, we attempted to
improve topcoat coating process to reduce the topcoat material consumption. Using JSR NFC TCX041, the developersoluble
type topcoat material, as a model material, we examined a new coating process which introduces a pre-wet
treatment using a solvent which was chosen to be appropriate for this purpose. With this new coating process, we
achieved 65 percent (or more) reduction of the topcoat material consumption compared with the current standard coating
process (dynamic coating). From the result of film surface observations and leaching tests, it was learned that the topcoat
film properties by the new coating process are equivalent to those by the standard coating process. The process
performance after development also indicated good results.
Defect transfer from immersion exposure process to post processing and defect reduction using novel immersion track system
Show abstract
As a promising way to scale down semiconductor devices, 193-nm immersion exposure lithography is being developed
at a rapid pace and is nearing application to mass production. This technology allows the design of projection lens with
higher numerical aperture (NA) by filling the space between the projection lens and the silicon wafer with a liquid
(de-ionized water). However, direct contact between the resist film and water during exposure creates a number of
process risks. There are still many unresolved issues and many problems to be solved concerning defects that arise in
193-nm immersion lithography.
The use of de-ionized water during the exposure process in 193-nm immersion lithography can lead to a variety of
problems. For example, the trapping of microscopic air bubbles can degrade resolution, and residual water droplets left
on the wafer surface after immersion exposure can affect resolution in the regions under those droplets. It has also been
reported that the immersion of resist film in de-ionized water during exposure can cause moisture to penetrate the resist
film and dissolve resist components, and that immersion can affect critical dimensions as well as generate defects.
The use of a top coat is viewed as one possible way to prevent adverse effects from the immersion of resist in water, but
it has been reported that the same problems may occur even with a top coat and that additional problems may be
generated, such as the creation of development residues due to the mixing of top coat and resist. To make 193-nm
immersion lithography technology practical for mass production, it is essential that the above defect problems be solved.
Importance must be attached to understanding the conditions that give rise to residual defects and their transference in
the steps between lithography and the etching/cleaning processes.
In this paper, we use 193-nm immersion lithography equipment to examine the transference (traceability) of defects that
appear in actual device manufacturing. It will be shown that defect transfer to the etching process can be significantly
reduced by the appropriate use of defect-reduction techniques.
Polymer structure modifications for immersion leaching control
Show abstract
ArF Immersion lithography is the most promising technology for 45nm node and possibly beyond. However, serious
issues in ArF immersion lithography for semiconductor mass production still exist. One of the issues is immersion
specific defects, which are caused by photoresist component leaching and residual water droplets. In order to minimize
immersion specific defects, preventing water penetration into the resist film is regarded as an important factor. Several
research groups have reported that higher receding contact angle reduced defectivity. High receding contact angle of
film surface prevent water penetration into the resist film due to the hydrophobic nature. Resist component leaching
phenomenon also can be caused by the water penetration into the film, so hydrophobic resist can reduce leaching
quantity.
In this paper, to investigate chemical leaching from resist surface, we evaluated the leaching value of PAG anion and
contact angles of various polymers according to their hydrophobicity. Hydrophilicity of a polymer was changed by the
degree of hydrophobic group substitution to polymer chain. We measured receding contact angle with four different
resists composed of water-repellent functiona group. Receding contact angle of resist surface increased as the portion of
water-repellent functional group increased. Also, the leaching amount of PAG anion decreased as the receding contact
angle of film surface increased. We expect that higher receding contact angle prevents chemical leaching from resist film
by repelling water at the surface. We will report detailed results in this paper.
A multi-tiered approach to 193nm immersion defect reduction through track process adjustments
Show abstract
This paper discusses the optimization of process conditions on a 193 nm immersion lithography cluster tool to minimize
defects. A 45 nm gate process was selected for optimization but a 65nm reticle was used for defect testing so that a nonimmersion
baseline could be collected for comparison. Previous testing has shown defect counts and density are
sensitive to rinsing of wafers before and after exposure. This sensitivity was dependent on the topcoat contact angle
and resist-plus-topcoat porosity. This paper expands on that study in several ways. (1) The immersion process was
simulated by scanning a develop rinse nozzle to observe, with a microscope, any peeling that could cause contamination
in the exposure tool. (2) Different EBR strategies were compared to reduce defects causing by edge residue while
maximizing the productive area of the wafer. (3) The appearance of some defect types was found to be related to the
delay between exposure and post rinse. (4) Bake time and temperature were also added to the testing to determine if the
impact to the film composition would influence the number of defects. (5) The addition of HMDS before BARC was
tested as a way to control defects caused by delaminating at the edge of the wafer. The paper distinguishes between
defects which are specific to the immersion process and those that would still be expected to occur in dry processing.
Formulated surface conditioners in 50-nm immersion lithography: simultaneously reducing pattern collapse and line-width roughness
Show abstract
With the introduction of immersion lithography into IC manufacturing for the 45nm node, pattern collapse and line
width roughness (LWR) remain critical challenges that can be addressed by implementing formulated surface
conditioners. Surface conditioners are capable of solving multiple issues simultaneously and are easily integrated into
the post-develop photolithography process.
In this paper, we assessed the impact and reported our findings using a formulated surface conditioning solution in an
immersion lithography process to improve the non-pattern collapse and LWR process windows on 300mm Si wafers
having 50 nm L/S features. The non-pattern collapse and LWR process window results were then compared to wafers
processed using traditional developer processing methods, a DI Water (DIW) rinse.
We report our findings using Focus Exposure Matrix (FEM) wafers having 50nm dense lines/spaces (L/S) and a 2.4:1
aspect ratio to determine the non-collapse and LWR process windows. An ASML TWINSCAN XT:1700TM Scanner
and a 6%attPSM mask were used to pattern the FEM and LWR wafers. The wafers were then developed using an
optimized developer recipe on an RF3iTM coater-developer track. Each wafer was analyzed and evaluated to determine
the impact to CD and LWR with respect to the non-pattern collapse process window
Formulated surface conditioners having dual capabilities, reduced pattern collapse and LWR, have demonstrated that
multiple ITRS Roadmap goals can be achieved and easily implemented into standard IC processing in order to meet
these challenges.
BARC (bottom anti-reflective coating) for immersion process
Show abstract
193nm immersion Lithography will be installed at 45nm and beyond. For severe CD control, BARC (Bottom Antireflective
Coating) has been used and this material must be used for immersion lithography.
So far, we have developed several BARCs with various advantages (fast etch rate, broad resist compatibility, high
adhesion, conformal...etc). Especially in an immersion process, development of BARC has to satisfy for the optical
control and defectivity.
The reflectivity control at Hyper NA is not same as the lower NA, because optical pass length in the BARC is not the
same between low NA and High NA. In order to achieve enough etch selectivity to the substrate, hard mask materials are
necessary. These under layers have absorption at 193nm. As a result of simulation, target optical parameters of next
BARC should be low k value (k = ~0.25) for multi BARC stack.
On the other hand, the defect issue must be decreased in the immersion process. However, the generation of many
kinds of defects is suspected in the immersion process (water mark, blob defect, sublimation defect...etc). Regarding the
BARC, there are also several specific defects in this process. Especially, after edge bead rinse, film peeling at edge area
is one of the concerns. We researched the root cause of edge peeling and a solution for this defect.
In this paper, we will discuss the detail of our BARC approach for litho performance, optical parameter, leaching,
sublimation, edge peel defects and etch selectivity, and introduce new BARC for 193nm immersion lithography.
Organic ArF bottom anti-reflective coatings for immersion lithography
Show abstract
Substrate reflectivity control plays an important role in immersion lithography. Multilayer
bottom anti-reflective coatings (B.A.R.C.s) become necessary. This paper will focus on the
recent development in organic ArF B.A.R.C. for immersion lithography. Single layer low k ArF
B.A.R.C.s in conjunction with multilayer CVD hard mask and dual layer organic ArF B.A.R.C.
application will be discussed. High NA dry and wet lithography data will be presented. We will
also present the etch rate data, defect data and out-gassing property of these new B.A.R.C.
materials.
Multilayer BARCs for hyper-NA immersion lithography process
Show abstract
Organic Bottom Anti-Reflective Coatings (BARCs) has been used in the lithography process. BARCs may play an important
role to control reflections and improve swing ratios, CD variations, reflective notching, and standing waves.
In 32-45nm node, application of the immersion lithography technique is not avoided to obtain the high resolution. To obtain
the high resolution, numerical aperture (NA) of the optical system needs the Hyper-NA lens of 1.0 or more but come up to the
problem of affections the polarized light in the Hyper-NA lens. The substrate of reflection control also will become more
difficult by using single BARCs system and the thin film resist becomes the necessity and indispensable at Hyper-NA
lithography. To achieve an appropriate reflection control, to suppress the CD difference to the minimum, and to prevent the
pattern collapse, hard mask with the spin coating film and antireflection characteristic is needed. In order to solve these issues,
we designed and developed new materials with the suitable optical parameter, square resist shape and large dry etching
selectivity. These Multi-layer materials of each process are spin-coated by using the current system and conventional ArF
photo resist or immersion resist is available in this process. This paper presents the detail of our newest materials for Hyper NA
lithography.
Initial process evaluation for next generation immersion technology node
Show abstract
In order to prepare for the next generation technology manufacturing, ASML and TEL are working together to
investigate the process performance of the LITHIUSi+/ TWINSCAN XT:1700i lithocluster through decreasing critical
dimension patterning. In this evaluation, process performance with regards to critical dimension uniformity and
defectivity are compared at different critical dimensions in order to determine areas of concentration for equipment and
process development. Specifically, design of experiments were run using immersion rinse processing at 60nm hp and
45nm hp. Defects were classified to generate a pareto for each technology node to see if there is any change in the defect
types as critical dimensions are shrinking. Similarly, critical dimension uniformity was compared through technology
nodes to see if any budget contributions have increased sensitivities to the smaller patterning features. Preliminary gauge
studies were performed for the 45nm hp evaluation, as metrology at this design rule is not yet fully proven. More work
is necessary to obtain complete understanding of metrology capabilities as this is crucial to discern precise knowledge of
processing results. While preliminary results show no adverse impact moving forward, this work is a first screening of
45nm immersion processing and more work is needed to fully characterize and optimize the process to enable robust
manufacturing at 45nm hp.
Poster Session: Resist Materials
Novel polymeric anionic photo-acid generators (PAGs) and photoresists for sub-100-nm patterning by 193-nm lithography
Show abstract
A series of new anionic PAGs, as well as PAG bound polymers designed for use in 193 nm photoresist materials have
been synthesized and characterized. These novel materials provide optical transparency at 193 nm and also etch
resistance. The fluorine substituted PAG bound polymer and PAG blend resist provided 110 nm (220 nm pitch)
line/space at 11.5, 13.0 mJ/cm2, and 80 nm isolated features at 3, 1 mJ/cm2, respectively. The LER (3&sgr;) results showed
the fluorinated PAG bound polymer have LER values 6.7 nm and 6.8 nm for isolated 80 nm and dense 110 nm lines
respectively, which were lower than the PAG Blend polymers
Development of nanocomposite resists with high plasma etch resistance
Show abstract
We report about the development of novel nanocomposite resists that incorporate colloidal silica nanoparticles into
conventional resist materials to yield thick coatings with both excellent lithographic properties and significantly
increased plasma etch resistance. 10-50 wt% silica nanoparticles of 10-15 nm in size were dispersed homogeneously in a
variety of standard resist resins by a simple process. The nanocomposite resists have similar lithographic performances
to conventional resists without silica nanoparticles. The nanocomposite resists also show excellent process window
capability and stability. Oxygen plasma etch and deep reactive ion etching (DRIE) processes were used to evaluate the
etch resistance of the nanocomposite resists. Compared with standard photoresists, the oxygen plasma etch rate is
reduced by 38-80% when the silica content increases from 20 to 50 wt%. The etch selectivity of nanocomposite resists
with 40 wt% silica is increased by 70% in DRIE test.
Chemical composition distribution analysis of photoresist copolymers and influence on ArF lithographic performance
Show abstract
For getting information about the distribution of chemical composition, several model polymers were prepared under
different polymerization conditions and were measured by critical adsorption point-liquid chromatography (CAP-LC).
In the copolymer system of 8- and 9- (4-oxatricyclo[5.2.1.02,6]decane-3-one) acrylate (OTDA) and 2-ethyl-2-adamantyl
methacrylate (EAdMA), the peak shapes of the CAP-LC chromatogram varied according to the polymerization condition
although they indicated same molecular weight and averaged chemical composition. The difference of the CAP-LC
elution curves was related to the chemical composition distribution of copolymers for CAP-LC measurement combined
with proton nuclear magnetic resonance (1H-NMR). The terpolymers consisted of α-hydroxy-γ-butyrolactone
methacrylate (GBLMA), 2-methyl-2-adamantyl methacrylate (MAdMA) and 1-hydroxy-3-adamantyl methacrylate
(HAdMA) were prepared under various polymerization conditions. In the terpolymer system that had same molecular
weight and average chemical composition, the solubility parameter (&dgr;) and the dissolution rate were measured. The &dgr;
value and the dissolution rate curve were different among these terpolymers. It was suggested that the &dgr; value and the
chemical composition distribution of these terpolymers have a significant influence on the lithographic performance.
Single component chemically-amplified resist based on dehalogenation of polymer
Show abstract
For chemically amplified resists which generally consists of a polymer and an acid generator, the homogeneity of resist
materials is a serious issue. The incorporation of acid generators into polymers via covalent bonds has attracted much
attention because it removes the compatibility problem of acid generators with polymers. In this study, we designed a
single-component chemically amplified resist, taking advantage of the difference of reaction mechanisms between
electron beam and photoresists. The designed resist has a hydroxyl group as a proton source and halogen atoms as an
anion source for acid generation. The developed resist showed an excellent performance.
Novel 193-nm positive photoresist composed of ester acetal polymer without phenyl group
Show abstract
1,3-adamantanedicarboxylic acid and acrylpimaric acid were reacted with an aliphatic divinyl ether,
1,4-cyclohexanedimethanol divinyl ether, to give novel ester acetal polymers without phenyl group. These polymers can
be dissolved in common solvents and possess high thermal stability. The ester acetal polymer can be quickly
decomposed at the presence of strong acid generated by PAG above 100°C and become easily soluble in dilute aqueous
base. Two-component photopolymer consisting of the ester acetal polymer and PAG can be used as positive photoresists.
The polymer derived from 1,3-adamantanedicarboxylic acid displayed higher transparency at 193 nm and can be used
for 193 nm photoresist.
Two-component photoresists based on acidolytic cleavage of novel ester acetal polymer
Show abstract
The reaction of acrylpimaric acid and several divinyl ether compounds, including 1,3-Bis(2-(vinyloxy)ethoxy)benzene,
2,2-bis(4-[2-(vinyloxy)ethoxy]phenyl)propane, and 1,4-Bis(2-(vinyloxy)ethoxy)benzene, can take place in the presence
of organic solvents to form novel ester acetal polymer with the average molecular weight of 4000-6000(Mn) measured
by GPC. These polymers can be easily dissolved in common solvents and show high thermal stability. The ester acetal
polymers can be quickly acidolyzed at the presence of strong acid generated by PAG above 100oC and become easily
soluble in dilute aqueous base. Two-component positive photoresists can be formed by the ester acetal polymer and PAG.
The lithographic performance of the resist material composed of the ester acetal polymer and a sulfonium triflate PAG
was studied on i-line exposure instrument. Clear pattern with 2 &mgr;m resolution was obtained and the photosensitivity was
below 20mj/cm2.
Nonchemically amplified resists for deep-UV lithography
Show abstract
A novel monomer containing a diazoketo functional group was designed and synthesized. Polymers were synthesized
using the diazoketo-functionalized monomer and their physical properties were evaluated. The polymers were
synthesized by radical copolymerization of cholic acid 3-diazo-3-ethoxycarbonyl-2-oxo-propyl ester methacrylate,
methyl methacrylate, and γ-butyrolacton-2-yl methacrylate. These polymers showed 0.7 &mgr;m line and space patterns using
a mercury-xenon lamp in a contact printing mode.
Non-ionic photoacid generators for chemically amplified resists: evaluation results on the application-relevant properties
Show abstract
Recently we have developed and reported some novel non-ionic photoacid generators (PAGs) which generate a
strong acid (perfluorobutanesulfonic acid) by light irradiation and is applicable to chemically amplified ArF
photoresist, such as 2-[2,2,3,3,4,4,5,5-octafluoro-1-(nonafluorobutylsulfonyloxyimino)-pentyl]-fluorene (ONPF), 2-
[2,2,3,3,4,4,4-heptafluoro-1-(nonafluorobutylsulfonyloxyimino)-butyl]-fluorene (HNBF) and so on. Here the
lithographic property of ONPF in some ArF model formulations was evaluated under 193 nm dry and immersion
exposure comparing one of the most typical ionic PAGs, triphenylsulfonium perfluorobutanesulfonate (TPSPB), on
lithographic application-relevant properties, e.g. exposure latitude, line edge roughness (LER) and so on, by top-down
view SEM observation. 80 nm line and space (L/S) patterning was successfully conducted. Additionally we
investigated the striation issue with ONPF when the matrix polymer of resist was changed. It was revealed that ONPF
showed better coating property in a copolymer of &ggr;-butyrolactone methacrylate, 2-ethyladamantyl methacrylate and
hydroxyladamantyl methacrylate than in a copolymer of &dgr;-methacryloyloxynorbornane butyrolactone in lactone unit.
PAG distribution and acid thermal diffusion study in ultra-thick chemically amplified resist films
Show abstract
The introduction of chemically amplified (CA) resist technology to thick films, 10 to 100 um in thickness introduced a
number of behavior differences not experienced in thinner films to the same magnitudes. Resist image profile
deformation, insensitivity to standing waves and the reduction in polymer deblocking temperatures are significantly
affected in thick films to a larger extend than in thinner films. The major contributing factors to these differences are
discussed in this paper: 1) the influence of photo-acid generator (PAG) structure on its distribution in resist depth on
Cu substrates and 2) thermal acid diffusion, influenced by greater amounts of retained solvents in thick films than in
thinner films.
Poster Session: ARC/Multilayer Processes
Study of 193nm resist degradation under various etch chemistries
Show abstract
The effectivity of 193nm photoresists as dry etch masks is becoming more and more critical as the size of integrated
devices shrinks. 193nm resists are known to be much less resistant to dry etching than 248nm resists based on a
poly(hydroxystyrene) polymer backbone. The decrease in the resist film budget implies a better etch resistance to use
single layer 193nm photoresists for the 65nm node and beyond. In spite of significant improvements made in the past
decade regarding the etch resistance of photoresists, much of the fundamental chemistry and physics that could
explain the behaviour of these materials has to be better understood. Such knowledge is necessary in order to propose
materials and etch processes for the next technology nodes (45nm and below).
In this paper, we report our studies on the etch behaviour of different 193nm resist materials as a function of etch
chemistry. In a first step, we focus our attention on the interactions between photoresists and the reactive species of a
plasma during a dry etch step. Etch experiments were carried out in a DPS (Decoupled Plasma Source) high density
chamber. The gas chemistry in particular was changed to check the role of the plasma reactive species on the resist. O2,
Cl2, CF4, HBr and Ar gas were used.
Etch rates and chemical modifications of different materials were quantified by ellipsometry, Fourier Transformed
Infrared Spectroscopy (FTIR), and X-Ray Photoelectrons Spectroscopy (XPS). We evaluated different materials
including 248nm model polymer backbones (pure PHS or functionalized PHS), and 193nm model polymers (PMMA
and acrylate polymers) or resist formulations. Besides the influence of resist chemistry, the impact of plasma parameters
was addressed.
Development of high-performance multi-layer resist process with hardening treatment
Show abstract
In the manufacture of devices beyond the 45 nm node, it is important to employ a high-performance multi-layer resist (MLR) process that uses silicon containing ARC (Si-ARC) and spin on carbon (SOC). We examined an additional hardening process of SOC by H2 plasma treatment in order to improve the etching durability of the MLR. The dry etching durability of H2-plasma-hardened SOC film showed a drastic improvement, while the wiggling features of the MLR without H2 treatment observed after SiO2 etching disappeared completely. The hardening mechanism of SOC was analyzed by Fourier transform infrared spectroscopy (FTIR) with gradient shaving preparation (GSP) and Raman spectrometry. The formation of diamond-like amorphous carbon at a depth of approximately 50 nm was observed and was attributed to the improvement in the dry etching durability. In addition, the MLR stack with hardening has good reflectivity characteristics. The simulated reflectivity at the interface between the bottom of the resist and top surface of the MLR stack with hardening below 0.6% was attained over a wide range of Si-ARC thicknesses and hyper NA (~1.3) regions. The measured refractive indices of the hardened SOC film at 193 nm had a high value at the surface; however, they gradually decreased toward the inner region and finally became the same as those of untreated SOC. This might be the origin of the estimated excellent reflectivity characteristics.
Correlation between etching and optical properties of organic films for multilayer resist
Show abstract
The correlation between the amount and rate of etching and various properties of organic film for multi-layer resist
(MLR) was investigated. The etching critical dimension (CD) of 140-nm pitch interconnects is controlled by the etching
conditions as well as by the properties of the organic film used as the bottom layer resist. Six organic films were tested
that had different densities, hardness values, refractive indexes, and FT-IR peaks. Patterned samples of these films were
exposed using electron projection lithography. The results showed amount of side etching, which effects the etching CD
of interconnects, of the bottom layer depended on the etching rate of the film. In turn, the etching rate depended on a
film's hardness and refractive index, but not on its density. The etching rate decreased with increasing hardness and with
increasing refractive index in the visible wavelength spectrum. Consequently, the etching CD of interconnects can be
better controlled by using an organic film as the bottom layer resist when the film has appropriate properties.
Rework/stripping of multilayer materials for FEOL and BEOL integration using single wafer tool techniques
Show abstract
As feature sizes continue to the 45nm and 32nm nodes, significant challenges will continue to arise in both
front-end-of-line (FEOL) and back-end-of-line (BEOL) applications. The reduced thickness, as well as the
reduced etch resistance, of the photoresist (PR) makes it nearly impossible to use the PR as both an imaging
and a pattern transfer layer. This etch challenge has led device manufacturers and vendors to explore the
use of multi-layer (trilayer) stacks. Multilayer stacks are typically comprised of a thick via-filling organic
layer that will provide adequate etch resistance while etching into low-k and ultra-low-k dielectrics. A
silicon-containing layer is then applied on top of the via-filling layer, which will provide improved
imaging, as well as etch resistance for the organic layer. The PR is then applied on top to complete the
multilayer stack. While many challenges have presented themselves in multilayer stacks, new challenges
such as rework and cleaning have arisen. As low-k and ultra-low-k dielectrics become more prevalent,
traditional oxygen ashing processes for the removal of PR and anti-reflective coatings can cause damage to
the dielectric layer due to the chemical and physical structures of the materials involved. While some
processes have been developed to replace damaged dielectric material during ashing and etching through
silyation, alternate processes are being developed where entirely wet stripping processes can remove
multilayer stacks. One advantage of an entirely wet removal process is that it can prevent damage caused
by ashing or etching, and the wet stripper is developed so it does not attack the dielectric films. While an
entirely wet removal process has potential advantages, it still must be proven that these processes can
remove residues that are left after etch processes, sufficient removal of particles are obtained, and any
material loss of the dielectric layer meets the requirements of the customer and the International
Technology Roadmap for Semiconductors (ITRS). Other challenges are presenting themselves, as many
customers would like to move from batch-type wet rework or cleaning processes to single wafer tool
processes.
It is the intent of this paper to not only identify new wet cleaning materials that can be used to remove
multilayer materials by means of an entirely wet process, but also to find single wafer tool processes that
produce fewer particles (defects) and cause no dielectric material loss.
Spin-on Organic Hardmask Materials in 70nm Devices
Show abstract
In ArF lithography for < 90nm L/S, amorphous carbon layer (ACL) deposition becomes inevitable process because thin
ArF resist itself can not provide suitable etch selectivity to sub-layers. One of the problems of ACL hardmask is surface
particles which are more problematic in mass production. Limited capacity, high cost-of-ownership, and low process
efficiency also make ACL hardmask a dilemma which can not be ignored by device makers. One of the answers to these
problems is using a spin-on organic hardmask material instead of ACL hardmask. Therefore, several processes including
bi-layer resist process (BLR), tri-layer resist process (TLR), and multi-layer resist process (MLR) have been investigated.
In this paper, we have described spin-on organic hardmask materials applicable to 70nm memory devices. Applications
to tri-layer resist process (TLR) were investigated in terms of photo property, etch property and process compatibility.
Based on the test results described in this paper, our spin-on hardmask materials are expected to be used in mass
production.
Materials for and performance of multilayer lithography schemes
Show abstract
The 45-nm node will require the use of thinner photoresists, which necessitates the use of multilayer pattern transfer
schemes. One common multilayer approach is the use of a silicon-rich anti-reflective hardmask (Si BARC) with a
carbon-rich pattern transfer underlayer (spin-on carbon, or SOC). The combination of the two layers provides a highly
planar platform for a thin resist, and provides a route to etch substrates due to the alternating plasma etch selectivities of
the organic resist, inorganic Si BARC, and organic SOC. Yet such schemes will need to be optimized both for pattern
transfer and optics. Optimizing optics under hyper-NA immersion conditions is more complicated than with standard
(that is, NA<1) lithography. A rigorous calculation technique is used to evaluate and compare standard lithography to a
hyper-NA case using a multilayer stack. An example of such a stack is shown to have reasonable lithographic
performance.
Advanced developer-soluble gap-fill materials and applications
Show abstract
For the via-first dual damascene process, a planarizing anti-reflective material and gap-fill material are typically used to
ensure a lithography process produces the best profiles and critical dimension (CD) control and integrates structures
having small feature sizes. Traditionally a gap-fill material is usually coated in a thick layer, and then plasma etching is
used to remove the extra gap-fill material above the substrate surface. We have developed a unique developer-soluble
gap-fill material, BSI.G05013, which can be etched back in standard photoresist developer, instead of by plasma beam
irradiation. By careful design of both the polymer and the formulation, our developer-soluble gap-fill materials fill vias
and trenches on different substrates without void formation. Also, these gap-fill materials do not exhibit swelling or
peeling problems during the developer etch-back process. Dissolution rate is adjustable by customizing the material with
regard to the chemical structure of the polymer and the formulation composition. This new generation of developersoluble
gap-fill material has broad process windows for bake temperature and develop time. The local bias between
dense and isolated via areas and the global bias from wafer center to wafer edge are significantly reduced after develop
back due to the dissolution rate difference between the bulk material and the material inside of the vias. Material is spin
bowl compatible and does not precipitate in rinsing solvents. It is stable in storage conditions for a long period. Both dry
plasma cleaning and wet developer cleaning can be used to remove the residual gap-fill material after processing. This
new generation of develop-soluble gap-fill material, BSI.G05013 is robust and the process is economically favorable,
which makes this solution convenient for planarizing surfaces.
Novel low-reflective index fluoropolymers-based top anti-reflective coatings (TARC) for 193-nm lithography
Show abstract
Implant lithography, which has up to now utilized 365-nm (i-line) and 248-nm (KrF) light sources, must now turn to
193-nm (ArF) sources. In implant lithography, an anti-reflective material is often used to coat the resist-film. The top
anti-reflective coating (abbreviated to TARC) is most often used to reduce CD swing. TARC materials must have low
refractive index and water solubility. The TARC materials for used 193-nm use must have very low reflective index
and alternatives to perfluorooctylsulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) must be found. We
synthesized some novel fluorinated amorphous polymers as 193-nm TARC candidates. Their fundamental properties
were characterized, such as transparency and reflective index at 193-nm (wavelength) along with their solubility in
water and a standard alkaline developer. High transparency, i.e., k value less than 0.01, and very low reflective index,
i.e., lower than n=1.4 at 193-nm wavelength are confirmed. Their dissolution behaviors are studied using the Quartz
Crystal Microbalance (QCM) method. In surprise finding, we find that several of the polymers examined, those that
have high fluorine content, dissolved in water. Test results show that the proposed polymers can be applied as top anti
reflective coatings .
Effect of solvents and cross-link reaction group concentration on via filling performance in gap fill materials
Show abstract
This study relates to characterization of gap fill materials for advanced ArF lithography process that allows the
formation of the gap fill materials having an excellent planarization property on a substrate having irregularities such as
nanometer scale pattering holes and trenches to increase the depth of focus and resolutions, and large CF4 gas etching
rate as compared with that of a resist while providing an excellent resist pattern without causing an intermixing with a
resist layer, and that it can be specifically used in a damascene process for the introduction of a wiring material Cu
(copper) used for reducing a wiring delay of a semiconductor device in recent years.
In the characterization of gap fill materials for an excellent planarization property of lithography, it was obtained two
key factors such as a specific relationship between the cross-link reaction group concentration of the polymers contained
in the gap fill materials and the via filling performance, and a specific relationship between a solvent used in the polymer
solution and the via filling performance. The application of gap fill materials based on this characterization is one of the
most promising processes ready to be investigated into mass production of the present 65-90 nm node dual damascene
lithography.
Optimization of hardmask for dual anti-reflection layers
Show abstract
The continuous shrinkage of critical dimensions has driven ArF lithography to resolve very small features and ever
thinner resist films to prevent pattern collapse. Also importance of hardmask technology is becoming increasingly
evident as the demand for both the critical dimension control and sufficient thickness of etch mask.
We have developed a silicon based hardmask prepared by plasma-enhanced chemical vapor deposition (PECVD) to
match organic anti-reflective coating (ARC). The ordinary single dielectric ARC or organic ARC is very sensitivity to the
substrate topology. Dual ARC (dielectric ARC + organic ARC) perform a less CD variation than single ARC. In addition,
this material can serve as an effective hardmask etch barrier during the plasma etch.
The most advantage of Dual ARC is that we have good critical dimension uniformity (CDU) regardless of substrate
thickness variation.
A novel approach to developer-soluble anti-reflective coatings for 248-nm lithography
Show abstract
A novel approach to developer-soluble bottom anti-reflective coatings (BARCs) for 248-nm lithography
was demonstrated. The BARC formulations are photosensitive, dye-filled systems incorporated with a
polymer binder. The films are generated by thermally crosslinking the polymer matrix, and are then
photochemically decrosslinked in order to render them soluble in developer solutions. The BARCs are
compatible with solvents commonly used in the industry. Easy modification of the films with regard to
optical properties for potential use with various substrates was also demonstrated. The BARCs exhibit
anisotropic development in aqueous tetramethylammonium hydroxide (TMAH) solutions subsequent to
simulated photoresist application, exposure, and post-exposure bake.
Optimization of material and process parameter for minimizing defect in implementation of MFHM process
Show abstract
Silicon-containing material has recently attracted attention as new hard mask material. We have studied the applicability
of MFHM (Multi-Functional Hard Mask)/SOC (Spin on Carbon) materials as an alternative to the BARC/SiON/
amorphous carbon (a-C) process. This process is very useful in terms of cost reduction and process simplicity compared
to a-C process. Evaluation results have showed good lithographic and etch performances. However, this MFHM process
has showed specific defects related to material. This paper will focus on defect type and suggest its solution.
A novel 248-nm wet-developable BARC for trench applications
Show abstract
A novel polyamic acid-based, 248-nm wet-developable BARC has been prepared to improve structure clear-out
and lessen post-development residue. This material showed an excellent process window and controllable
development rates that can be achieved by simply changing the formulation. It is a highly absorbing BARC
with n and k values equal to 1.73 and 0.49, respectively. Lithography with this material has shown 180-nm
dense profiles with P338 and M230Y. These profiles exhibited minimal undercutting with good clearing
between the lines. Clear-out has been demonstrated for 120-nm trenches. Post-development residue of the
material was tested at various temperatures and was determined to be 6 Å or less. In addition, sublimation
was evaluated.
Wet-recess gap-fill materials for an advanced dual damascene process
Show abstract
This paper describes the new developer-soluble gap fill materials, which are called wet gap fill materials, with wide process
window. In order to reduce isolated/dense fill bias that comes from substrate topography, dry gap fill materials are used in
combination with a plasma dry etch-back process. At the same time, the wet gap fill materials are coated thick enough to
planarize all the topography and is then recessed using a standard 0.26N tetramethylammonium hydroxide (TMAH)
developer. The material recess process takes place in the same track where it is coated and therefore simplifies the process
and increases wafer throughput. We developed easy-to-use wet gap fill materials recently. Performances and properties of
three types of wet gap fill materials (NCA2546, NCA2549, and NCA2550) based on the same polymer platforms will be
discussed.
Novel approach of UV cross- link process for advanced planarization technology in 32-45 nm lithography
Show abstract
Conventional method of patterning trenches in a via first trench last Dual Damascene process involves filling the thickness bias with thermal cross-link gap fill material and then applying the photoresist followed by trench lithography. The major problem of this process is the large thickness bias (step height) observed as the via pattern pitch and density changes across the wafer.
Now, the new approach of UV cross-link system instead of thermal cross-link gap fill material is proposed. The material is referred to as UV cross-link film (XUVTM).
The main properties of UV cross-link film are small thickness bias of blanket field and dense-via pattern, high planarization, and void free by using the newest UV cross link process that we studied in UV-photo irradiation system. The process for UV cross-link film is very simple, just UV ray irradiate the film for about 10 s in the same coater-developer tool.
In this paper, we study the novel approach, UV cross-link process for reducing the thickness bias. The planarization of XUVTM was very high as compared with that of the film obtained from thermal cross-link gap fill material as the reference. The application of UV cross- link process using XUVTM is one of the most promising processes ready to be investigated into mass production to leave out the dry etch back process before patterning trench in via first trench last Dual Damascene lithography.
Overcome the challenge of CD-bias with organic bottom anti-reflective coating removal process
Show abstract
This paper presents a review of two bottom anti-reflective coating (BARC) removal processes incorporated into subhalfmicron
contact etching. They are believed to represent different etching mechanisms. Accuracy of size feature transfer
was taken as a primary criterion for comparison of different BARC removal processes. These processes are based on
application of glow discharge in the following basic gas mixtures: CF4+O2 and CO+O2. The first process based on
CF4+O2 gas mixture shows a behavior of neutral etching species model that cause a footing developing during BARC
removal. Roughly this may be explained by the continuous direction spectrum of neutral active species movement. The
access of active neutral species to the BARC layer is dependant upon the window mask size, resist profile and the
thickness of resist layer. The second process based on CO+O2 gas mixture represents another etching mechanism − ion bombardment induced etching. On contrary to the previous partially isotropic process this one provides anisotropic
etching. This is due to stimulating and activating the etching reaction by ion bombardment. Anisotropic features are
achieved because of directional ion flux normally to wafer surface. This process is proved to be independent of profile
and mask opening size features. Data presented show that process based on CO+O2 gas mixture provides consistent close
to zero CD bias at BARC removal step while CF4+O2 gas mixture based process causes negative CD bias with apparent
dependence upon the window mask size. Robust results of CO+O2 process allow one to consider it and its basic etching
mechanism to be a mainstream of process development for different applications.
Thin bilayer resists for 193-nm and future photolithography II
Show abstract
Bilayer, Si-containing resists are a technique of interest and a strong candidate to replace chemical vapor deposition
(CVD) hardmask processes for small critical dimensions (CDs). Previously, we proposed a very thin film approach using
bilayer resists for future lithography, defined the requirements for the resists, and demonstrated 55nm transferred
patterns with high aspect ratios using 2-beam interferometer exposure. In this paper, we have demonstrated smaller-than-
60nm transferred patterns with a high numerical aperture (NA) scanner, as well as 45nm and 40nm transferred patterns
with a 2-beam system using a 20% Si-containing thin bilayer resist. Immersion scanner exposure and a 35nm CD with 2-
beam system were also studied.
Radiation sensitive developable bottom anti-reflective coating (DBARC) for 193nm lithography: first generation
Show abstract
A first generation DBARC applicable for 1st minimum 193nm lithography is described in this paper. The polymer used in
this DBARC is insoluble in the casting solvent of the resist, which is propyleneglycolmonomethyletheracetate (PGMEA).
Photo acid generator (PAG) and base extractions from the DBARC coating by the resist casting solvent were examined
by the DBARC dissolution rates in the developer, before and after solvent treatments. Although the resist and the
DBARC do not appear to intermix, strong interaction between the two is evident by their lithographic performance and
dissolution rate study.
Poster Session: Resist Processing Technology
Post exposure bake unit equipped with wafer-shape compensation technology
Shigehiro Goto,
Akihiko Morita,
Kenichi Oyama,
et al.
Show abstract
In 193nm lithography, it is well known that Critical Dimension Uniformity (CDU) within wafer is especially influenced
by temperature variation during Post Exposure Bake (PEB) process. This temperature variation has been considered to
be caused by the hot plate unit, and improvement of temperature uniformity within hot plate itself has been focused to
achieve higher CDU. However, we have found that the impact of the wafer shape on temperature uniformity within
wafer can not be ignored when the conventional PEB processing system is applied to an advanced resist technology.
There are two factors concerned with the wafer shape. First, gravity force of the wafer itself generates wafer shape
bending because wafer is simply supported by a few proximity gaps on the conventional hot plate. Next, through the
semiconductor manufacturing process, wafer is gradually warped due to the difference of the surface stress between
silicon and deposited film layers (Ex. Si-Oxide, Si-Nitride). Therefore, the variation of the clearance between wafer
backside and hot plate surface leads to non-uniform thermal conductivity within wafer during PEB processing, and
eventually impacts on the CDU within wafer. To overcome this problem concerned with wafer shape during PEB
processing, we have developed the new hot plate equipped with the wafer shape compensation technology. As a result
of evaluation, we have confirmed that this new PEB system has an advantage not only for warped wafer but also for flat
(bare) wafer.
Reducing bubbles and particles associated with photoresist packaging materials and dispense systems
Show abstract
A review of bubble energetics is presented to provide background into gas saturation and bubble formation in
semiconductor resists. Nitrogen was used as a drive gas to push liquid out of several package materials versus a
mechanical pump. The incorporation of dissolved gas was measured and a barrier liner was found to be superior
versus a bottle with no liner. We have demonstrated that a pressure dispense package with an appropriate barrier
liner provides a means to deliver lithographic chemicals and resist without the use of a mechanical pump.
Resist evaluation for contact hole patterning with thermal flow process
Show abstract
In this paper, we investigate the capabilities to form small contact holes with various 193nm
resists applying a thermal flow process. We first compare the material properties (glass
transition temperature Tg and thermal deprotection TD) of different 193nm resists to our
reference process for thermal reflow, namely the 248nm reference resist (RoR). The main
difficulty related to 193nm acrylate backbone is the high Tg value, which implies some flow
bake temperature closed to or superior to the deprotection temperature. Depending on the
resist chemistry, different behaviours have been observed such as acceleration of the flow
rate, formation of bubble defects linked to gaseous by-products or even contact hole diameter
increase. These results are strongly dependent on the chemical reactions occurring in the resist
film at the same time as the film softening. In order to better select the most promising 193nm
resist candidates for contact hole reflow technique, we also develop a polymer flow
measurement with Dynamic Mechanical Analysis (DMA). By measuring the creep
compliance of the resist film spin-coated onto a silicon wafer under various bake
temperatures, we are able to define the optimal temperature range for resist flow.
Effect of novel rinsing material and surfactant treatment on the resist pattern performance
Show abstract
Surfactant treatments, with SCR101 and EX01, were applied to both line-space and hole
patterns in this report. 10% Reduction of line-width roughness and the raise of normalized
aspect ratio were observed in line-space patterns after surfactant treatments, compared with
those only treated with DI water. From top-view and cross-section images of hole patterns, it
was found that bottom scum was eliminated and the contact-edge roughness (CER) was also
improved after surfactant treatments. Although 1 to 5% shrinkage of patterns appeared, the
depth of focus (DOF) of hole patterns was still increased due to removal of bottom scum. By
applying the surfactant treatment, we were able to improve not only line width roughness and
collapse margin of line-space patterns, but also CER and DOF of hole patterns.
Impact of airborne NH3 and humidity against wafer-to-wafer CD variation in ArF lithography through 45-nm technology node
Show abstract
An impact of air-borne NH3 and humidity against a wafer-to-wafer (WTW) CD variation is investigated. An
environmental stability of ArF resist materials is also investigated through the design of experiment (DOE) analysis,
where the different resist formulations are chosen as variation factors. Assuming the most environmentally sensitive ArF
resist material used in the 45nm 1:1 LS pattern imaging (worst case scenario), the WTW CD variations caused by
air-borne NH3 and humidity fluctuations are estimated to be 0.10nm and 0.29nm, respectively.
Proximity effect correction for the chemical shrink process of different type contact holes
Show abstract
Small contact hole patterning had become the most difficult task in optical lithography as design rule of semiconductor
continuously shrinks below 65nm. Conventional contact hole scheme need to avoid side-lobe and conduct complicated
dense-isolated bias for resolution enhancement and depth of focus (DOF) improvement. To overcome this issue, some
RETs (Resolution Enhancement Techniques) by process had been investigated, like RELACS (resolution enhancement
lithography assisted by chemical shrink). RELACS is one of feasible procedures which could provide enough
improvement in resolution, photo-resist profile, DOF, and CD uniformity (CDU). Proximity effect is one of significant
topics to evaluate chemical shrink bias of different type contacts. Research of shrink bias of different size and pitch
contacts had been investigated broadly in the past. In general, the constant bias of shrinkage for difference pattern sizes
was an assumption. However, according to our evaluative results, we had characterized the correlation about the shrink
bias versus pattern size. In this paper, we not only show DOF, CDU, shrink bias of RELACS, but also present chemical
shrink bias of different size and different pitch contact holes and then we could follow this correlation rule to define
general rule for proximity effect correction.
Mechanism of post develop stain defect and resist surface condition
Show abstract
In regards to stains appearing on the resist pattern after developing, this study succeeded in the reduction of these stain
defects by improving the develop process. Furthermore the mechanism of this stain defect was considered by analyzing
components of the defect.
Since the stain defects of former generation such as i-line or KrF resist defect are known well, even now this defect is
seen on the ArF resist. The appearance of this stain defect was caused by a kind of resist or pattern. Until now this defect
has been resolved by improving the resist.
In this study however, we tried to resolve the stain defect by the improvement of the developing process. As this
improvement was able to greatly reduce this defect with no change to the resist or pattern, it was understood this defect
is much influenced by the developing process. Thus it is projected the resist surface condition during the develop process
was the important key to decreasing this defect. It should be understood the number of defects was changed by the kind
of resist or pattern. First we analyzed the components of the stain defect itself. Next we analyzed the change in resist
surface condition by the new develop process.
As a result, it was realized this stain defect was from the developer chemical, it was considered that the developer
remaining on the resist film caused the stain defect. As the resist surface condition was changed by the improved
develop process, resulting in a sharp decrease in the stain defect.
New ArF resist introduction for process through-put enhancement
Show abstract
In this study, the four ArF resists having methacrylate structure have been evaluated to check the reliability of
process through-put enhancement in track by applying the different baking time. The dense L/S and isolated
patterns of T80nm and T66nm node device are investigated for these models. The chemical properties of
applied resists are slightly different for each other in the respect of protecting ratio and molecular weight. The
applied resist thickness are 2,000Å and 1,700Å for the patterning of T80nm and T66nm node device,
respectively. The process margins of evaluated patterns for T80nm node device show the almost similar
results for DOF and E/L for 90s, 60s and 45s baking time conditions. And the LER of these patterns also is not
much changed by the different baking time conditions. Form the experimental results, it is confirmed that the
less baking time below 60s for T80nm node pattern is available to apply for enhancing the through-put in litho
process. The process margins and LER of evaluated patterns for T66nm node device are slightly affected by
their chemical properties like molecular weight and protecting ratio of resin for the different baking time
conditions. However, the more improved pattern profile and process margin can be obtained by optimizing the
chemical properties in the certain experimental range. And also, it is found that the less baking time below 45s
can be applied for the reliable patterning process of T80nm and T66nm node device through the crosssectional
SEM views with the more optimizing the material compositions.
A heater plate assisted integrated bake/chill system for photoresist processing
Show abstract
A thermal processing module, which consists of a dense distribution of multivariate controlled heat/chill elements,
is developed to achieve temperature uniformity of a silicon wafer throughout the processing temperature
cycle of ramp, hold and quench in microlithography. In the proposed unit, the bake and chill steps are conducted
sequentially within the same module without any substrate movement. The unit includes two heating
sources. The first is a mica heater which serves as the dominant means for heat transfer. The second is a set
of thermoelectric devices (TEDs) which are used to provide a distributed amount of heat to the substrate for
uniformity and transient temperature control. The TEDs also provide active cooling for chilling the substrate
to a temperature suitable for subsequent processing steps. The feasibility of a practical system is demonstrated
via detailed modeling and simulations based on first principle heat transfer analysis.
Molecular contamination control technologies for high-volume production phase in high-NA 193-nm lithography
Show abstract
The current semiconductor lithography process is in the high volume production phase of 193nm high NA (Numerical
Aperture) exposure, and further reaching the high volume production phase with 193nm immersion exposure
lithography. As a result of miniaturization of the devices, it has becomes necessary to reduce the concentration of basic
compounds (such as ammonia, amines, and N-methyl-2-pyrrolidone (NMP), which are used to insolubilize the chemical
amplified resist in developing process, in the environment surrounding the wafer. For this purpose, chemical filters are
used. In the clean room, in addition to these basic gases, there exist various organic compounds and the effects of organic
compounds on the chemical filter cannot be ignored. This paper reports the results of basic research on the adsorption
behavior of physical adsorption under the presence of the above-mentioned basic compounds and ion exchange reaction.
Then the adsorption behavior of activated carbon chemical filter impregnated with acidic chemicals and strongly acidic
cation exchange chemical filter for basic compounds was studied in the coexistence of organic components. The
performance of impregnated activated carbon chemical filter deteriorates due to the coexisting organic compounds
because removal of NMP is based on the physical adsorption mechanism. On the other hand, the performance to remove
ammonia and NMP of strongly acidic cation exchange chemical filter is not affected by organic compounds because the
filter exchanges ions with weakly basic compounds. The strongly acidic cation exchange chemical filter can provide
desired performance for basic compounds under an actual clean room environment.
Printing of structures less than 0,3 µm by i-line exposure using resists TDMR-AR80 and TDMR–AR95
A. Behrendt,
T. Dow,
K. Stoeflin
Show abstract
There is increasing interest in high resolution i-line resists which allow the printing of structures smaller than
0.3&mgr;m.
We have evaluated the resists TDMR-AR80 und TDMR-AR95 from TOK Company in order to check their
potential concerning minimum line sizes with sufficient process window in regard to focus/exposure process
latitude, with our main focus on trench structures. The Bossung Plots of dense lines and semi-dense lines
were determined. The resist and etch profiles were characterised both by inline-SEM measurements and
cross-sections. The influence of several stepper illumination modes and Off Axis Illumination (OAI) on the
focus/exposure process window was investigated.
The resists TDMR-AR80 and TDMR-AR95 enable printing of trench structures less than 0.3&mgr;m. For 0.3&mgr;m
lines, our specification limit of 0.3&mgr;m +/- 10% was reached within a focus range from - 0.1 to 1.0 microns.
OAI illumination mode enlarged the focus window by 20% in comparison to the standard illumination mode.
Structures of 0.28&mgr;m and 0.26&mgr;m were printed with a focus window of 0.7&mgr;m which shows the high potential
of this resist generation.
The implementation of the resist in production provides large amounts of data which enable the calculation of
parameters related to process stability (wafer to wafer and lot to lot CD-standard deviation, Cp-, Cpk-values
etc.).
Various factors of the image blur in chemically amplified resist
Show abstract
In the current optical lithography, the resolution is being pushed for 45 nm half-pitch, and the chemically amplified
resist will be used for wide variety of applications including immersion lithography. So far the chemical amplification
has brought high performance for lithography. In the future, for the ArF lithography beyond 45nm half-pith, it will be
important to control pattern size. On the other hand, chemically amplified resist which utilized acid catalyzed deprotecting
reaction is sensitive to physical and chemical factor. Thus, there are various factors in the each process
(Resist coating, Pre bake, Exposure, Post exposure bake, Development and Rinse) to cause the resist blur. For example,
it's acid diffusion on PEB. The influence of these factors for the resist blur is a significant issue for lithography beyond
45 nm half-pitch. Therefore the need to reduce these factors on the resist blur becomes higher in order to extend the ArF
lithography beyond 45 nm half-pith.
In this paper, acid diffusion coefficient (D) and resist blur with changing anion size of PAG, size of protecting group
in typical ArF resist was reported. The relationship between acid diffusion coefficient and resist blur was discussed on
the basis of their difference in structure and characteristics.
Image tone optimization in advanced mask making for DUV lithography
Show abstract
Deep-UV (DUV) lithography has been developed to define minimum feature sizes of sub-100 nm dimensions of devices
semiconductor. In response to this trend, DUV mask technology has been proposed as an effective technique for
considering the reduction of mask making cost, especially, in low volume designs. However, the requirement of tight CD
control of the mask features in advanced devices is resulted in increasing of mask cost. In this research, we discussed
two different typed image tones comparison, positive and negative tone, in DUV lithography. The choice of final mask
tone needs to be selected as function of pattern density and shape. The evaluation items to judge if the mask is good are
the OPC model accuracy, resolution and mask throughput. Both mask process and manufacturing throughput are affected
by image tone type of positive and negative. This paper will show the procedures and results of experiment.
Automatic viscosity controlled production of photoresist
Show abstract
Viscosity of photoresist is an important product parameter because it determines film thickness during spin coating.
Producers of photoresist, therefore, have established manufacturing procedures which require that fluid viscosity be
measured several times during production to ensure product quality. Periodic samples are taken off-line to an analytical
laboratory where viscosity is measured under controlled conditions. However, off-line measurements, interrupt
production, engage valuable human resources, and fail to provide adequate process feedback. This paper describes the
implementation of an automatic viscosity-controlled production process of photoresist using a unique in-line viscometer.
The automated photoresist production process increases throughput and improves product quality. With sufficient
accuracy and repeatability of the measurements, it is now possible to correlate and predict film thickness with viscosity
values taken during photoresist production.
Photoresist adhesion effect of resist reflow process
Show abstract
Making a sub-100 nm contact hole pattern is one of the difficult issues in semiconductor process. Compared with
another fabrication process, resist reflow process is a good method to obtain very high resolution contact hole. However
it is not easy to predict the actual reflow result by simulation because very complex physics and/or chemistry are
involved in resist reflow process. We must know accurate physical and chemical constant values and many fabrication
variables for better prediction. We made resist reflow simulation tool to predict approximate resist reflow as functions of
pitch, temperature, time, array, and so on. We were able to see the simulated top view, side view and the changed hole
size. We used Navier-Stokes equation for resist reflow. We had varied the reflow time, temperature, surface tension, and
3-dimensional volume effect for old model. However the photoresist adhesion is another very important factor that was
not included in the old model. So the adhesion effect was added on Navier-Stokes equation and found that there was a
distinctive difference in reflowed resist profile and the contact hole width compared to the case of no adhesion effect.
Poster Session: Resist Fundamentals and Simulation
Simulation of the combined effects of polymer size, acid diffusion length, and EUV secondary electron blur on resist line-edge roughness
Show abstract
Device shrinking combined with material manipulation under various process conditions becomes a
difficult task if specific optimization conditions should be met. Nanolithography is limited by effects
as line-edge and line-width roughness (LER and LWR respectively) and secondary electron blur
(SEB). Simulation studies could show the direction of solving design for manufacturing problems. In
the current article a simulation methodology is presented, based on the concept of stochastic modeling
of exposure, material, and process aspects of lithography and pattern transfer with plasma etching in
order to get information about the evolution of critical dimensions (CD), LER and LWR in the layout.
The study reveals that under certain process conditions, the effect of acid diffusion on LER is more
important than the one of SEB, although both deal with blurring, because acid diffusion is supposed
to extend in longer radius. However, when resists of low degree of polymerization are used, SEB
should also be considered explicitly since the deteriorations from blurring on both LER and CD are
enhanced due to the graining nature of the material. In any case, etching smoothing effects of high
frequency LER components should be considered in terms of CD loss.
Distribution control of protecting groups and its effect on LER for EUV molecular resist
Show abstract
We have designed and synthesized a molecular resist material, which has no distribution of the protecting
groups and have evaluated its performance as a molecular resist with EB and EUV exposure tool. The molecular resist
attained a resolution of sub-45 nm patterning at an exposure dose of 12 mJ/cm2. It was found that controlling the
distribution of the protecting groups in a molecular resist material has a great impact on improving Line Edge
Roughness (LER). Low LER values of 3.1 nm (inspection length: L = 620 nm) and 3.6 nm (L = 2000 nm) were
achieved with this molecular resist using Extreme UltraViolet (EUV) lithography tool.
Evaluation of the 3D compositional heterogeneity effect on line-edge-roughness
Show abstract
The controlling factors in the formation of the compositional heterogeneity at the deprotection front were
investigated using 3D computer simulation. The results illustrate that the chemical composition fluctuation (CCF)
formed by the photoresist deprotection reaction is an important factor contributing to the line-edge-roughness (LER) in
addition to the deprotection gradient (DG) of the reaction front. The magnitude of the chemical composition fluctuation
and the deprotection gradient are found to depend on the ratio of the deprotection reaction rate constant to diffusion
coefficient (kP/D) and the number of hoping step (n) With this new finding, the influence on LER from various
process/material parameters such as dose/contrast, diffusivity, and reactivity can all be understood through their effects
on kP/D and n.
Observing morphology on surface of poly(methacrylate) in ArF lithography using AFM phase image
Show abstract
In recent years, ArF lithography has required a half-pitch size (DRAM) of 45 nm or less. To achieve the
requirement, line edge roughness (LER) is recognized as one of the most serious problems in lithography today,
because LER directly degrades device characteristics and affects system performances. Although the uniformity of
polymer film is important for reducing LER, little is known about polymer morphology after coating. In this study, we
observed the surface of poly(methacrylate) samples after coating with AFM tapping mode and found specific
morphology in the phase images for the first time (the height image was flat).
A study of process extension technologies
Show abstract
Current 193 nm optical lithography and commercially available 193 nm resists are pushed far beyond previously
expected critical dimension by using the process extension technology for the resolution enhancements technology. This
paper deals with three kinds of process extension technologies such as thermal treatment, polarization, and double
patterning. Those technologies are tried to model and analyze. Supposed the 50% pattern shrinkage due to thermal
treatment, 25% resolution enhancement due to polarization, and the 50% pattern shrinkage due to double patterning, an
effective combination can generate a sub-50 nm pattern. When pattern size is smaller, optical proximity effects are more
severe. After describing optical proximity effects for each of technologies, optical proximity correction methods are
discussed.
32-nm pattern collapse modeling with radial distance and rinse speed
Show abstract
Chemically amplified resist materials are now available to reach critical dimensions of the pattern close to 32 nm values.
Pattern collapse is a very serious problem in fine patterning less than 32 nm critical dimension, because it decreases the
yield. The pattern collapse is the pattern response to unbalanced capillary forces acting on the pattern walls during the
spinning drying step after development process. Centrifugal force has not considered for pattern collapse modeling up to
now, so that pattern collapse due to spinning is studied. In this study we investigate the 32 nm node pattern collapse
mechanism with radial distance and rinse speed of dense patterns. In the process of creating the simulation tool, the
rotating model is used. As rinse speed and radial distance are increased, critical aspect ratio is decreased. As a result,
pattern collapse is increased.
The rational design of polymeric EUV resist materials by QSPR modelling
Show abstract
We present the initial results of the development of a qualitative structure property relationship (QSPR) model to guide
in the design and synthesis of high-sensitivity, non-CAR materials for EUV lithography. The model was developed
using the fragmentation data of low molecular weight species at 70 eV using a mass spectrometer (MS) with an electron
ionization source as the input parameter. The preliminary model has highlighted a number of structural elements which
will be important in the future design of resists, however, limitations with the current set of input data for molecules
which fragment readily have been identified and these are currently being addressed. Additionally, a correlation
between &ggr; (1 MeV) and EUV (92 eV) radiolysis of selected polymers has been established and it is proposed that the
higher energy (1 MeV) irradiation source is a suitable model process for EUV and can, therefore, be used in the future
screening of polymeric materials.
Some non-resist component contributions to LER and LWR in 193-nm lithography
Show abstract
Improvement of line edge roughness (LER) and line width roughness (LWR) is required for integration of semiconductor
devices. This paper describes various process factors affecting LER/LWR of 193 nm resists such as mask layout (bright
field/dark field), pitches, optical settings, substrates, film thickness, baking temperature and development condition. The
origins of line roughness are discussed in view of aerial image contrast, transmittance of resists and pattern profiles.
Bright field mask exhibited lower LER/LWR values than dark field mask, LER/LWR deteriorated as larger pitches and
illumination condition affected roughness and these results are explained using normalized image log-slope (NILS).
BARC dependence of line roughness is explained by pattern profile difference due to interactions between resist and
BARC and in some cases BARC reflectivity. Contributions of film thickness, SB & PEB temperature and development
condition to line roughness are also reported.
Depth-of-focus (DOF) and line-width roughness (LWR) performance of novel surface conditioner solutions for immersion lithography
Show abstract
As lithographic technology goes beyond the 45nm node, depth of focus (DOF) and
line width roughness (LWR) for poly gates have become critical parameters. There is a
growing interest in applying surface conditioner solutions during the post-develop
process to increase DOF and reduce LWR. Surface conditioners interact with resist
sidewall selectively, causing surface plasticization effect and smoothing the sidewall
profile. As a result, the LWR can be reduced and the poor pattern profile located in the
focus marginal area due to poor image contrast will be improved so that the depth of
focus (DOF) can be increased significantly. In this paper, the features of lines/spaces
patterned for the 45nm node by immersion lithography were used to evaluate surface
conditioner performance with regards to DOF increase and LWR reduction. The results
demonstrate there is about 1.5 nm LWR reduction, as well as a significant improvement
on the process window for DOF, for which there is 37.5% increase for ISO poly gates
and 36% increase for DENSE poly gates. No negative impact on the effect of optical
proximity correction (OPC) and resist profile were observed with the new process.
In addition, etch testing was conducted to determine how much post-develop LER
reduction has been retained through etch by comparing post-etch and post-develop LER
for both baseline and surface conditioner processes.
Poster Session: NGL
Effect of photo-acid generator concentration and developer strength on the patterning capabilities of a model EUV photoresist
Show abstract
Current extreme ultraviolet (EUV) photoresist materials do not yet meet requirements on exposure-dose sensitivity,
line-width roughness (LWR), and resolution. Fundamental studies are required to quantify the trade-offs in materials
properties and processing steps for EUV photoresist specific problems such as high photoacid generator (PAG) loadings
and the use of very thin films. Furthermore, new processing strategies such as changes in the developer strength and
composition may enable increased resolution. In this work, model photoresists are used to investigate the influence of
photoacid generator loading and developer strength on EUV lithographically printed images. Measurements of line
width roughness and developed line-space patterns were performed and highlight a combined PAG loading and
developer strength dependence that reduce LWR in a non-optimized photoresist.
A study of EUV resist outgassing characteristics using a novel outgas analysis system
Show abstract
We have designed a novel outgas analysis system to help gain a better understanding of EUV resist outgassing characteristics.
In this paper, we will discuss the performance results of this outgas analysis system which incorporates a stand-alone
discharge produced plasma extreme ultra violet (EUV) source of comparatively high power output and various outgas
evaluation methods such as quadropole mass spectrometry (QMS), gas chromatography - mass spectrometry (GC-MS),
quartz crystal microbalance (QCM) and 'witness mirror'.
In this analysis system, the GC-MS evaluation set-up is quite unique from the commonly available outgassing systems with
the utilization of the 'cold-trap sampling technique'. In this sampling technique; a 'trap box' is used with an cryostat-based
internal cooling system used to lower the trap-box temperature to increase the efficiency of the trapping of outgas elements
released from the resist wafer fragment during exposure. After exposure, the trap-box is then transferred to a heating
chamber where the outgas elements that have adhered is heated and released to a thermal desorption tube for GC-MS
analysis.
After successive experiments using a polymer resist, we have succeeded in proving the improved efficiency of outgas
trapping through the cold-trap method. Compared to the amount of trapped outgas at room temperature, a considerable
amount of resist outgas was measured with the trap-box cooled at very low temperatures. With the QMS analysis results, it
was also observed that the low molecular-type resist released lesser outgassing elements compared to the polymer resist.
This work is partially supported by the New Energy and Industrial Technology Development Organization (NEDO).
Sub 10-nm contact holes with aspect ratio over sixty formed by e-beam resist shrinkage techniques
Show abstract
E-beam chain scission resist ZEP520A with 400 nm thickness was studied for sub-10 nm contact holes with high
aspect ratio formed by CD shrinkage techniques of thermal reflow and SAFIER. CD shrinkage temperatures and
repeating times were process parameters to be studied. Design parameters of initial CD of 40-100 nm and
line/space ratio of contact hole with 1/3 and >1/20 before shrinkage were also studied. Process window of
thermal reflow for the aforementioned initial CDs is 155-165 °C while that of SAFIER is 150-165 °C. There is
no shrinkage for both methods for temperatures below 140 °C. CD shrinkage rates of both methods decrease for
more than one time of heating. Thermal reflow has a larger CD shrinkage rate than SAFIER. The dependence of
shrinkage rate on initial CD size and spatial frequency is not apparent. CD nearly ceases shrinking for further
heatings as the CD reaches an ultimate CD size. The ultimate CD for a larger initial CD is also larger. The
smallest shrunk CD is found to be 5.8 nm with aspect ratio over sixty for 50 nm initial designed CD. CD
uniformity also studied for both processes with 3-sigma smaller than +/-10%. The contact holes shrunk by
thermal reflow process generally show funnel-shape profiles while those shrunk by SAFIER process show
similar profiles with wider undercut. In summary, the thermal reflow process results in better profile while the
SAFIER with slower CD shrinkage rate has a better control on CD and uniformity.
Study on photochemical analysis system for EUV lithography
Show abstract
A system for photo-chemical analysis of EUV lithography processes has been
developed. This system has consists of 3 units: (1) an exposure that uses the Z-Pinch
(Energetiq Tech.) EUV Light source (DPP) to carry out a flood exposure, (2) a
measurement system RDA (Litho Tech Japan) for the development rate of photo-resists,
and (3) a simulation unit that utilizes PROLITH (KLA-Tencor) to calculate the resist
profiles and process latitude using the measured development rate data. With this
system, preliminary evaluation of the performance of EUV lithography can be
performed without any lithography tool (Stepper and Scanner system) that is capable of
imaging and alignment. Profiles for 32 nm line and space pattern are simulated for the
EUV resist (Posi-2 resist by TOK) by using VLES that hat has sensitivity at the 13.5nm
wavelength. The simulation successfully predicts the resist behavior. Thus it is
confirmed that the system enables efficient evaluation of the performance of EUV
lithography processes.
Effect of deprotection activation energy on lithographic performance of EUVL resist
Show abstract
As the feature size becomes smaller, it is difficult for the lithography progress to
keep pace with the acceleration of design rule shrinkage and high integration of memory device.
Extreme Ultra Violet Lithography (EUVL) is a preferred solution for the 32nm node. In this
paper, we have synthesized two types of polymers. One is based on hydroxy phenol, the other
is based on hydrocarbon acrylate type polymer. We have diversified each polymer type
according to different activation energies for deprotection reaction. In this experiment, we have
observed on the resist lithographic performance such as resolution, LER (Line Edge
Roughness), photo-sensitivity, and out-gassing during exposure. Different properties according
to activation energy were well explained by acid diffusion and polymer free-volume.
Photoresist dissolution into a CO2 compatible salt and CO2 solution: Investigation of Processing Conditions
Show abstract
New lithographic techniques are being implemented to help further reduce feature sizes in microelectronics. A
technique for the development of standard extreme ultraviolet (EUV) photoresists in a carbon dioxide compatible salt
(CCS) and supercritical carbon dioxide (scCO2) solution is being investigated to reduce line edge roughness and image
collapse of high aspect ratio features.1,2 To understand the kinetics and overall mechanism of photoresist dissolution
into the high pressure CCS/scCO2 solution, a quartz crystal microbalance (QCM) was previously used to measure the
effects of temperature, pressure, and density on the photoresist removal rate.3,4 In this paper, the effects of a CO2 drying
step before development and an adhesive coating on the photoresist removal rate and the formation of residual
photoresist droplets were studied at 50°C and 5000 psi. The results implied that neither the CO2 drying step nor the
HMDS coating had an effect on the bulk photoresist removal rate. It was also found that using an HMDS adhesive
coating reduces residual photoresist droplet size on the substrate due to the lower substrate / photoresist surface energy.
Exposure of molecular glass resist by e-beam and EUVIL
Show abstract
Molecular resist have potential interest for low CDs and LERs required in future lithography
technology. The lithographic ability of one of them is exposed in this study, by e-beam and by EUV-IL. Work
on process condition is described and leads to dense-lines resolution down to 32.5nm for.
Sub-10-nm structures written in ultra-thin HSQ resist layers using electron-beam lithography
Show abstract
Isolated dots and lines with 6 nm width were written in 20 nm thick Hydrogen silsesquioxane (HSQ) layers on silicon
substrates, using 100 keV electron beam lithography. The main factors that might limit the resolution, i.e. beam size,
writing strategy, resist material, electron dose, development process, are discussed. We demonstrate that, by adjusting
the development process, a very high resolution can be obtained. We report the achievement of 7 nm lines at a 20 nm
pitch written in a 10 nm thick HSQ layer, using a KOH-based developer instead of a classical TMAH developer. This is
the smallest pitch achieved to date using HSQ resist. We think that the resolution can be improved further, and is
presently limited by either the beam diameter (which was not measured separately) or by the not fully optimized
development process.
Phenolic molecular glasses as resists for next-generation lithography
Show abstract
In this contribution, we describe our efforts to develop novel chemically amplified molecular glass (MG) photoresists
based on bulky phenol structures. In contrast to conventional polymeric materials, MG resists possess distinct
advantages, such as smaller molecular size and uniformity in composition. A number of compounds which possess rigid
aromatic backbones were synthesized in our laboratories and evaluated for electron beam lithography. Herein, two new
MG photoresists are discussed in terms of their physical and lithographic properties. In the first section, we introduce
tert-butoxycarbonyl (t-Boc) protected 'Noria-Boc' photoresists as a promising candidate for next generation
lithographic technique. Noria-Boc was synthesized through a condensation reaction between resorcinol and 1,5-
pentanedial. After protection with di-tert-butyl dicarbonate [(t-Boc)2O], the cyclic, bulky and amorphous material was
characterized by a high glass transition temperature (Tg > 120 °C) and excellent film-forming properties. Post-exposure
bake at 140 °C was necessary to ensure complete development of the exposed area and produced sub-100 nm lines. In
the second part, we describe the synthesis and lithographic evaluation of partially t-Boc-protected bulky phenol 'CR1'.
CR1 is also characterized by high glass transition temperature (Tg ≈ 130 °C) and good film-forming properties. Postapply
bake at 130 °C and post-exposure bake above 130 °C were necessary to ensure good contrast under deep UV
(DUV) exposure conditions.
Poster Session: Novel Processes and Applications
Study on diazonaphthoquinone positive photoresist composition for LCD
Show abstract
We report on a study of the diazonaphthoquinone (DNQ) positive photoresist composition for LCD. Photoresist is
the important material used for the electrode of LCD. LCD photoresist consists of photoactive compounds, binder
resin and organic solvent. We first study the esterification of 3,4,5-trihydroxybenzophenone, 2,2',4,4'-tetrahydroxybenzophenone and 1,2-DNQ-4-or-5-sulfonylchloride, then the conventional photoactive compounds were
synthesized. The properties of the conventional photoresist composition were also studied. Our work focuses on
exploring new type of photoactive compounds. We prepared the new phenol compounds:
7,8-dihydroxy-4-methylcoumarin, 6,7-dihydroxy-3,3-diphenyl-3H-benzenefuran-2- ketone, and then reacted with 1,2-DNQ-4-or-5-sulfonyl chloride. The new photoactive compounds were used with PGMEA as organic solvent and the
novolac resin as binder resin, then the photoresist composition was prepared. The photoresist composition was
coated on the pretreated ITO films and ITO glasses. After the prebake, exposure, developing, hard bake, a desired
pattern was produced . The properties of photoresist composition, for example: photosensitivity, resolution and
developing performance were good, and the photosensitivity can reach to 40.5mJ.cm-2, the resolution can be 1&mgr;m.
The use of a black pigment polyimide, DARC300, as a light absorber on an optical sensor
Show abstract
In the design and fabrication of arrayed opto-electronic detection devices, it is critical to provide optical
isolation between the individual array cells to prevent optical crosstalk between channels and contribution
from stray light that would otherwise result in degraded signal-to-noise performance. To accomplish this,
the light incident between the cells' optical apertures and around the periphery of the array must be blocked
from entering the active semiconductor layers. One approach has been to use an opaque layer of metal, but
this can lead to reflections and light trapping and ultimate absorption of this stray light in device active
regions. Another approach is to use an absorbing material to block stray light. DARC300, a registered
trademark of Brewer Science, is an optically absorbing, photo-definable polyimide designed for exactly this
purpose. Presented here are the results of the DARC300 blocking layers, including a review of the process
development and issues addressed along the way. The most prevalent issues with the DARC300 were the
remnants of black pigments after develop, and the insufficiently developed features. A normalized spectral
response of a 4-channel, fixed cavity, Fabry-Perot micro spectrometers, with and without the optical
blocking layer between cells and around the periphery of the array are shown to greatly enhance device performance with the use of the DARC300 layer.