Proceedings Volume 1925

Advances in Resist Technology and Processing X

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Proceedings Volume 1925

Advances in Resist Technology and Processing X

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Volume Details

Date Published: 15 September 1993
Contents: 5 Sessions, 70 Papers, 0 Presentations
Conference: SPIE'S 1993 Symposium on Microlithography 1993
Volume Number: 1925

Table of Contents

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Table of Contents

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  • Mechanistic and Materials Aspects of Chemically Amplified Resists
  • New Lithographic Materials and Methods
  • Dissolution Inhibition Systems: Mechanistic/Chemical Aspects
  • Top-Surface Imaging Systems
  • Poster Presentations
Mechanistic and Materials Aspects of Chemically Amplified Resists
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Relationship between resist performance and diffusion in chemically amplified resist systems
Theodore H. Fedynyshyn, Charles R. Szmanda, Robert F. Blacksmith, et al.
This paper describes a method to measure acid diffusion in different negative I-line resist systems. Diffusion of this acid plays a critical part in the image formation process. While some diffusion is necessary to achieve high resist sensitivity, excessive acid diffusion can cause an unacceptable loss of resolution. For this reason, diffusion must be controlled within certain limits during standard resist processing. The threshold crosslink theory of image formation, which states that a minimum concentration of acid is required to render the resist insoluble for a given development condition can be used in conjunction with a reaction- diffusion model to determine the magnitude of acid diffusion in the resist. This relatively straightforward method of measuring acid diffusion is then applied to determining an optimum resist process. Several different negative I-line acid catalyzed resists are investigated and the differences in the magnitude of acid diffusion are determined.
Delay-time effects between exposure and post-exposure bake in acetal-based deep-UV photoresists
Horst Roeschert, Charlotte Eckes, Hajime Endo, et al.
This paper presents some methods for the investigation of delay time I3 induced effects typical of an advanced acetal-based photoresist, and strategies to improve the latent image stability. Dissolution rate monitoring was used to investigate the increasing formation of a surface inhibition layer with extended intervals I3. The impact of certain additives, the application of a protective coating (AZR Aquatar), and modified process conditions on the inhibition layer were studied in detail. The photoacid induced acetal cleavage was monitored by UV-spectroscopy (248 nm). Upon KrF excimer laser irradiation the resist absorbance increases, due to the progressing formation of a strongly absorbing aldehyde fragment. SEM pictures confirm a linear relationship between the efficiency of the acetal cleavage and acid diffusion into unexposed resist areas. Acid evaporation during PEB was determined by a novel method, the so-called Sandwich `Blue' Test. Interpretations of the experimental results and some optimization strategies are given.
Study on the over-top-coating suppressing surface insoluble layer generation for chemical amplification resist
Teruhiko Kumada, Youko Tanaka, Akemi Ueyama, et al.
Most positive chemical amplification resists do not have enough stability to process delay. It has been claimed that airborne contaminants neutralize acids from photo-acid generators. It has been found by means of x-ray photoelectron spectroscopy that an onium salt used as a photo-acid generator is deficient at the surface of the prebaked resist film. The over-top coating using water-soluble polymers with organic acids has been investigated in order to not only separate the resist surface from airborne contaminants but also supply acids to the resist surface. We have succeeded in the suppression of the surface insoluble layer generation and of the pattern size change for more than 8 hours.
Influence of polymer properties on airborne chemical contamination of chemically amplified resists
William D. Hinsberg, Scott A. MacDonald, Nicholas J. Clecak, et al.
We describe here an extensive study of the relation between polymer structure and rates of NMP uptake for a set of polymer films with a very broad range of properties. NMP labeled using radioactive 14C was introduced at a concentration of 12 ppb into a stream of purified air. The film of interest was then immersed in the airstream for a predetermined time under controlled conditions. The radionuclide serves as a tag which allows precise quantitation of NMP absorbed by the polymer film. NMP uptake rates measured using this method are shown to correlate with polymer physical properties in a straightforward manner. The observed trends are in accord with those expected on the basis of the solution diffusion model of polymer permeation. These data provide a basis for the rational design of polymers for chemically amplified resists which are insensitive to airborne contaminants.
JESSI Project E 162: status of the deep-UV resist
Dirk J. H. Funhoff, H. Binder, Han J. Dijkstra, et al.
Within the joint European project `JESSI E 162' we pursue deep UV image processing for 0.35 micrometers lithography in chip production. To reach this goal, major advancements have to be made in three areas: stepper, resist, and track. In this paper, the status of the JESSI positive deep UV resist is presented. Based on the SUCCESS resist concept a stable resist process was developed. The major achievements are: linewidth stability for 0.35 micrometers lines and larger ones during delay times up to 120 min between exposure and PEB, 0.24 micrometers lines stable for 30 min, linearity down to 0.35 micrometers (NA 0.42), resolution of 0.22 micrometers with phase-shift mask (NA 0.42), and dry etch resistance better than conventional novolac resists.
Molecular design for stabilization of chemical amplification resist toward airborne contamination
Hiroshi Ito, William Preston England, Nicholas J. Clecak, et al.
This paper describes the first logical approach to the design of chemical amplification resists that are stable toward airborne contamination. This molecular design is based on the observation that uptake of N-methylpyrrolidone (NMP) by thin polymer films is primarily governed by glass transition temperatures (Tg) of the polymers. This concept has led to the design of environmentally very robust chemical amplification resists that provide positive images upon development with aqueous base.
Delay-time stable chemically amplified deep-UV resist
Klaus Juergen Przybilla, Yoshiaki Kinoshita, Takanori Kudo, et al.
This paper describes a newly developed acetal-based positive tone deep UV photoresist called DX 46. The material consists of a 4-hydroxystyrene/4-hydroxy-3-methylstyrene copolymer, a polymeric dissolution inhibitor, and a bleachable diazo-photoactive compound. Each of the three compounds is specially designed to fit to each other for high performance sub-halfmicron resolution. The main idea is the use of a poly-N,O-acetal for dissolution inhibition which undergoes efficient acid catalyzed bond cleavage that produces strong dissolution promoting fragments in the exposed area. We determined the activation energy for hydrolysis reaction of our polyacetal to be 10 Kcal/mol. The radiation induced acid catalyzed hydrolysis reaction starts right after exposure and is accomplished by a mild post exposure bake at low temperature. This resist system is not sensitive to airborne contamination and no charcoal filtered air or diffusion barrier top coats are necessary for T-top free performance.
Effect of using a resin coating on KrF chemically amplified positive resists
Akira Oikawa, Nobuaki Santoh, Shuichi Miyata, et al.
We tried several resins to protect chemically amplified positive resists from contaminants such as ammonia and amines. Polymethyl silsesquioxane (PMSS), a hydrophobic resin, significantly reduced the severity of T-tops and improved delay-time stability. Polyolefinic resin (POR) was the most effective hydrophobic resin and improved the performance of all chemically amplified resists we tried. The pattern profiles were not significantly affected by the protective resin thickness; resin films from 400 angstroms to 9500 angstroms were equally effective. We also used resin coatings to identify when resists are contaminated. We found that contamination begins just after exposure and continues to the end of postexposure bake (PEB).
New Lithographic Materials and Methods
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New three-component aqueous base developable negative-resist systems incorporating chemical amplification and tunable sensitivities
Jean M. J. Frechet, S. Ming Lee
A series of new polyfunctional latent electrophiles capable of acting as crosslinkers in the photoimaging of aromatic polymers has been prepared and tested in chemically amplified photoresist formulations. Extremely high sensitivities have been achieved with a variety of modes of irradiations: deep-UV (DUV) (ca. 0.1 - 0.3 mJ/cm2), E-beam (< 1 (mu) C/cm2) and x ray (ca. 15 mJ/cm2). In some cases, the sensitivities of these materials are so high that they have surpassed the capabilities of many existing exposure tools, making it desirable to lower them. This can be achieved through the addition of an electron rich species to the resist formulations to partially capture the photogenerated acid. It was shown that there is a linear correlation between the amount of additive and the sensitivities of the resulting resists.
1,3-dioxolyl acetals as powerful crosslinkers of phenolic resin
Ulrich P. Schaedeli, Norbert Muenzel, Heinz E. Holzwarth
The principle of chemical amplification has proven to be successful for the design of highly sensitive, high resolution resist materials of both positive and negative tone, respectively. This paper discusses our new approach to a high resolution, aqueous base developable deep-UV negative tone resist. It is based on the acid catalyzed cleavage of acetal blocked aromatic aldehydes, which, if treated with strong Broensted acid, react with the surrounding phenolic resin in a Friedel-Crafts type reaction, thereby leading to matrix crosslinking. Resists based on this type of crosslinking chemistry show good deep-UV transparency, have high sensitivity, and can be developed with an aqueous base.
Negative DUV photoresist for 16Mb-DRAM production and future generations
Will Conley, William R. Brunsvold, Richard A. Ferguson, et al.
This paper discusses a new negative tone aqueous base developable photoresist that has demonstrated excellent sub-half micron resolution with commercially available DUV (deep ultraviolet) exposure systems. This system which consists of a phenolic resin (pHOST), a glycoluril crosslinker (TMMGU), and a triflic acid generating material is currently in use for the manufacturing of 16 M b-DRAM and related CMOS logic technology. We provide supporting manufacturing data relating to our experiences with this program, along with the benefits realized by the implementation of a negative tone photoresist system.
Novel negative resists using thermally stable crosslinkers based on phenolic compounds
Toru Kajita, Eiichi Kobayashi, Toshiyuki Ota, et al.
This is a preliminary report on a family of crosslinkers based on phenolic compounds for negative-working photoresists which are suitable for KrF excimer laser exposure using poly(hydroxystyrene) (PHS) as a base resin. The crosslinkers are benzylic derivatives having etherificated or esterificated phenolic hydroxyl group. Several effects upon the resist performances of chemically amplified (CA) resist systems comprising onium salt, PHS, and the crosslinkers are mainly discussed: i.e., sort of substituent, sort of mother molecular structure, sort of crosslinkable group, baking conditions, PHS's molecular weight, additives, and so on. The CA resist gives quarter-micron line and space pairs without swelling using a KrF excimer laser exposure. Moreover, in this report another effective method for inhibiting the swelling is proposed. Finally, a unique negative resist, which is not a CA resist, is also presented. It gives negative-tone images by thermal crosslinking reaction following photo- induced dissociation of the protective group of crosslinker.
Plasma deposition, characterization, and photochemistry of organosilicon hydride network polymers: versatile resists for all-dry mid-deep UV photolithography
Timothy W. Weidman, Ajey M. Joshi
Plasma polymerization of various mono- and di-substituted organosilanes (R1R2SiH2; R1 equals alkyl, aryl and R2 equals H or alkyl) provides an effective approach to a new class of organosilicon resists useful in all dry photolithographic processing. For example, parallel plate rf plasma deposition systems may be used to deposit photosensitive films from low power discharges in methylsilane (MeSiH3) gas between 200 and 500 mTorr. Characterization by FTIR, UV-Visible, and NMR spectroscopy suggests that methylsilane undergoes predominantly dehydrogenative coupling reactions, giving Si-Si bonded network materials of general composition [(MexSiHy)n], with x and y between 0.5 and 1.0. Such films exhibit intense, near-UV absorption band edges characteristic of materials with Si-Si backbones, and undergo photo-oxidative crosslinking with bleaching when irradiated with mid-deep UV light ((lambda) < 365 nm) in the presence of oxygen.
Chemical amplification positive deep-UV resist using partially tetrahydropyranyl-protected polyvinylphenol
Takashi Hattori, Leo Schlegel, Akira Imai, et al.
Chemical amplification positive resists using tetrahydropyranyl-protected polyvinylphenol (THP-M) were investigated for deep UV lithography. Infrared spectroscopy measurements showed that THP-M in the resist film cannot be completely deprotected by photo-generated acid. This causes a poor developability of the resist containing highly tetrahydropyranyl (THP)-protected polyvinylphenol in an aqueous base developer. In order to improve the developability in the pure aqueous base developer, we utilized partially THP-protected polyvinylphenol. To determine the optimum protection degree, we examined the relation between the dissolution rate of THP-M films and THP-protection degree in developers. A resist formulated from 20% THP-protected polyvinylphenol and bis(tert-butylphenyl)iodonium triflate resolved 0.30 micrometers line-and-space patterns with the aqueous base development using a KrF excimer laser stepper with a dose of 46 mJ/cm2.
Positive chemically amplified resist for deep-UV lithography
Omkaram Nalamasu, Allen G. Timko, May Cheng, et al.
A novel approach to chemically amplified resists based on the `base cleavage' mechanism where t-boc groups serve as the imaging units and acetoxy functionalities provide solubility differential between the exposed and unexposed resist areas was realized with poly(4- acetoxystyrene-4-t-butoxycarbonyloxystyrene sulfone, PASTBSS) terpolymer based resist formulations. The acidolytic cleavage of t-boc groups occurs in both the poly(4- acetoxystyrene-4-t-butoxycarbonyloxystyrene, PASTBS) copolymer and poly(4- acetoxystyrene-4-t-butoxycarbonyloxystyrene sulfone, PASTBSS) terpolymer resist formulations but the base induced acetyl removal occurs in the solid state (in the film) only in the PASTBSS resists, indicating the need for sulfur dioxide in the polymer backbone. Not surprisingly, acetoxy groups can be removed in solution from both PASTBS and PASTBSS polymers or their t-boc deprotected analogs.
Acid-catalyzed single-layer resists for ArF lithography
A positive-tone single-layer resist for use with 193 nm radiation has been developed. The system contains a terpolymer of methyl methacrylate, methacrylic acid, and (tau) -butyl methacrylate, along with a photoacid generator. The chemically amplified deprotection of the (tau) -butyl methacrylate into methacrylic acid increases the polarity of the resist and allows selective dissolution in metal-ion-free aqueous base solutions. The resist sensitivity is less than 10 mJ/cm2, and its inherent resolution is better than 0.1 micrometers . These acrylate-based systems have potential for both lower cost and better environmental stability compared with the deep ultraviolet chemically amplified resists which use phenolic resins.
Dissolution Inhibition Systems: Mechanistic/Chemical Aspects
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Simulation of spray/puddle resist development
Stewart A. Robertson, J. Tom M. Stevenson, Robert J. Holwill, et al.
This work describes how spray/puddle development can be simulated using two separate sets of dissolution rate parameters. The first set of values is derived under continuous spray conditions and represents the wetting, or `spray,' period of the process; the second set, derived during stationary puddle development, deals with the remaining process period. The validity of decoupling the two development stages is supported by the good agreement between SAMPLE simulations and experimental results. Process windows and clearing doses are calculated and measured for a fixed time development process, as the spray to puddle time ratio is reduced from one to zero.
Characterization and simulation of acid-catalyzed DUV positive photoresist
Nicholas K. Eib, Eytan Barouch, Uwe Hollerbach, et al.
An investigation of the dissolution behavior of an acid catalyzed deep ultraviolet (DUV) positive resist has been completed. The immersion develop dissolution rate as a function of dose and post exposure bake temperature was measured by Perkin Elmer Dissolution Rate Monitor (DRM) for single layer resist on a silicon substrate. A reaction-diffusion model has been built to describe the dependence of development rate on exposure dose and post exposure bake (PEB) time/temperature. A mixed diffusion model has been built to account for catalyst diffusion and quenching. Developed images have been compared with simulated image quality, line width, and process window.
Physical and chemical factors governing dissolution of novolak resin films
Kenji Honda, Andrew J. Blakeney, Rodney J. Hurditch, et al.
The authors have investigated the dissolution of a series of novolac resins with different structures and properties with various quaternary ammonium hydroxides using a new technique called Spectroscopic Dissolution Rate Monitoring (SDRM). This technique allows direct spectral measurement of an absorption band attributed to cation complex formation. The rate of formation of this complex is used as an approximation or surrogate for cation diffusion. The rate of formation of the complex is approximately the same as the rate of dissolution when using a rinse. This evidence supports cation diffusion as the rate determining step even in TMAH development of high ortho, ortho bonded systems. Our studies also suggest that polymer flexibility and microstructure exert a strong influence on the cation diffusion rate.
Host-guest effects in the interaction of developers with phenolic resins
Ralph R. Dammel, Mohammad A. Khadim
NMR-spectroscopic evidence is presented for a strong interaction between polyphenolates and various onium ion species (i.e., tetramethylammonium, tetramethylphosphonium and trimethylsulfonium salts). In model compounds, a large decrease in solubility leading to precipitation is observed for a mixed Na/TMA+ complex. The formation of onium/phenolate complexes explains such diverse phenomena as the mutual poisoning of metal-ion free and metal ion containing developers, the behavior of developers containing quaternary ammonium surfactants, the anomalous temperature effects observed for tetramethylammonium hydroxide (TMAH) developers, or the dissolution inhibition effect of triarylsulfonium photoacid generators.
Dissolution rate modeling of a chemically amplified positive resist
Takeshi Ohfuji, Allen G. Timko, Omkaram Nalamasu, et al.
The reactions of a chemically amplified positive resist, CAMP6, which is composed of poly tert-butoxycarbonyl(t-BOC)-styrene copolymer as a base resin and 2,6-dinitrobenzyl tosylate as a photoacid generator, were analyzed. The resist system generates acid upon exposure, undergoes acid catalyzed t-BOC deprotection during post-exposure bake and selectively dissolves in an aqueous base developer to give positive tone images. The acid generation and t-BOC deprotection reactions were analyzed by FTIR spectrometer and modeled successfully. The dissolution rates were measured by a Perkin Elmer development rate monitor (DRM). A new and simple dissolution rate model is presented since the dissolution rate behavior of chemically amplified positive resists can not be explained by the conventional models that are designed primarily for novolac/dissolution inhibition systems. The new dissolution rate model expresses the resist dissolution as a product of inhibition effect by the t-BOC groups and dissolution enhancement effect by the acid. Furthermore this new model can also explain surface inhibition effect by considering acid loss (deactivation) due to airborne contaminant diffusion from the resist surface. Prolith/2 was modified to incorporate the model and profile simulations were carried out successfully.
Design of PACs for high-performance photoresists (II): effect of number and orientation of DNQs and -OH of PACs on lithographic performances
Ryotaro Hanawa, Yasunori Uetani, Makoto Hanabata
PACs which have a defined number of DNQs and -OH groups were synthesized with high yield by the selective esterification method, and the relationship between number and orientation of DNQs, and lithographic performances and dissolution properties, were examined and measured by puddle development. From our present and previous examinations, it is concluded that existence of one -OH group and two DNQs, which are separated from each other on a ballast molecule, is the most preferable structure of PAC, which provides a photoresist not only a high (gamma) -value and resolution capability but also suitable sensitivity and a scum-free pattern. According to concept of polyphotolysis results are discussed quantitatively by dissolution inhibition effect and the number of DNQs of the PAC.
Novel novolac resins produced from 2,6-bishydroxymethyl-p-cresol, p-cresol, and m-cresol: a method to more evenly distribute p-cresol units throughout a novolac resin
Alfred T. Jeffries III, David J. Brzozowy, Nancy N. Greene, et al.
In an effort to improve the performance of positive resists by increasing the amounts of o,o- bonding, some m-/p-cresol novolacs were prepared in which a portion of the p-cresol was replaced by 2,6-bishydroxymethyl-p-cresol (BHMPC). This work distinguishes itself from earlier work in which BHMPC was the sole source of p-cresol. Fractionated BHMPC polymers were shown to incorporate more p-cresol into their higher molecular weight portions of the molecules. The parent novolacs possessed lower molecular weights and polydispersivities than conventional m-/p-cresol novolacs of the same composition. The lithographically acceptable polymers were evaluated on an 0.52 NA i-line stepper. The resists made from the fractionated BHMPC polymers exhibited a direct relationship between the amount of p-cresol in the higher molecular weight fractions and resolution. The reasons for the difference in performance are discussed in terms of the m-/p-cresol contents of the fractionated and unfractionated polymers as determined by carbon-13 nmr.
New chemistry in the design of chemically amplified positive resists
Robert D. Allen, Quan P. Ly, Gregory M. Wallraff, et al.
The quest for high performance positive deep-UV resist is a significant challenge. In this paper we discuss a new approach to chemically amplified positive resists involving the use of a new and versatile class of polymeric dissolution inhibitors. Methacrylate terpolymers originally designed as chemically amplified positive resists for printed circuit board technology have been found to form stable, one-phase mixtures with a variety of phenolic resins. These new dissolution inhibitors based on MMA-TBMA-MAA terpolymers have unusual and useful properties, including excellent optical transmission at 248 nm, high glass transition temperatures, and dissolution inhibition/promotion power which can be tailored to accommodate the dissolution properties of the particular phenolic resin being used.
Top-Surface Imaging Systems
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Role of surface tension in silylation processes
Andre P. Weill, Patrick Jean Paniez, Olivier P. Joubert, et al.
The DESIRER process has been proposed as an attractive solution to lithographic problems, combining the performance of multilayer systems to the simplicity of monolayer processes. Despite the large number of studies devoted to this type of process, the various mechanisms involved during the silylation and dry development steps are not yet totally understood. The first part of the paper deals with the changes in solubility of the resist layer before and after silylation and suggests that the polarity of the resist is modified during the process. Surface tension measurements are then reported in order to quantitatively evaluate the changes in polarity of the silylated resist. Finally it is shown that the work of adhesion between silylated and non-silylated material can easily explain both the stability of the silylated islands during the HMDS process and the motion of these silylated areas during the dry development step.
Processing techniques for improving performance of positive-tone silylation
Edward K. Pavelchek, Gary S. Calabrese, Bruce W. Dudley, et al.
Many approaches to surface imaging rely upon selective incorporation of silicon into an already imaged resist layer. SAHRTM (silylated acid hardened resist) obtains its selectivity by a lower rate of silicon incorporation into exposed and crosslinked areas, providing a positive tone image after RIE development. Two difficulties with the practical implementation of this approach have been the overflow of silylated material onto crosslinked areas, and reduced silicon incorporation in small openings. We have found that surface treatment with a bifunctional silylation agent (the `two gas process') can prevent overflow, and that removing part of the resist layer with dilute tetramethyl ammonium hydroxide (TMAH) (the `presilylation develop process') minimizes overflow and improves silicon incorporation in small features. With a predevelop step, feature size linearity is obtained below k1 equals 0.7, with uniformity and repeatability consistent with VLSI manufacturing practices.
Comparison of liquid- and vapor-phase silylation processes for 193-nm positive-tone lithography
Mark A. Hartney, Roderick R. Kunz, Lynn M. Eriksen, et al.
Liquid- and vapor-phase silylation processes are compared for a 193 nm positive-tone lithographic process using polyvinylphenol as a resist. The liquid-phase process, using a mixture of xylene, hexamethylcyclotrisilazane, and propylene glycol methyl ether acetate, was found to have higher silylation contrast, better sensitivity, and a smaller proximity effect (a decrease in silylation depth for smaller feature sizes). These factors result in a larger exposure latitude, particularly at feature sizes below 0.5 micrometers . These advantages are greatly offset, however, by the increased chemical costs, which are estimated to be more than 100 times greater than for the vapor-phase process.
Positive-tone dry-develop resist based on crosslinking a phenolic resin
Scott A. MacDonald, Carl E. Larson, Hubert Schlosser, et al.
We have previously shown that a copolymer of p-hydroxstyrene and p-acetoxymethylstyrene can be used as a sensitive deep UV resist. In that study we demonstrated that a formulation of this copolymer and an onium salt could be exposed, baked and developed in aqueous base to yield a high resolution negative tone relief image. In this paper we discuss a gas phase silylation process that converts this negative tone solvent-developable resist system into a positive tone dry-developable resist system. We have used an FT-IR microscope, coupled to a motorized X-Y stage, to study the silylation process as a function of UV exposure dose and silylation processing parameters. By altering the copolymer ratio, we found that resist contrast increased when the amount of acetoxymethylstyrene increased. This resist system and dry develop process were used to print 0.35 micrometers images at a DUV dose of approximately 25 mJ/cm2.
Deep-UV positive-tone dry-development process using chemically amplified resist and its application to 256 Mbit DRAM
Woo-Sung Han, Joong-Hyun Lee, Jung-Chul Park, et al.
Top surface imaging and subsequent dry development were known to improve lithographic performance. Since negative working DESIRE process was introduced, several alternative methods have also been proposed. We propose a new resist system (SS-201), which is positive working in DUV lithography. We characterized this resist in view of top surface imaging (TSI) process and applied it to our 256 mega bit DRAM test device. Since conventional TSI process has a swelling problem by nature, WEBS (wet development before silylation) technique is proposed to minimize swelling. Special attention was focused on contact holes since our TSI process enables positive tone mask, which has a definite advantage in reducing potential defects in mask making.
New simplified positive-tone DESIRE process using liquid phase silylation in DUV lithography
Ki-Ho Baik, Kurt G. Ronse, Luc Van den Hove, et al.
A simplified positive tone process using liquid phase silylation in DUV lithography is presented in this paper. The diffusion enhanced silylated resist (DESIRE) process has been demonstrated as an attractive solution not only to improve resolution and process latitudes but also to cope with linewidth variations over highly reflective topography. Traditionally the silylation process has been carried out using hexamethlydisilazane (HMDS) although more lately alternative gaseous agents such as tetramethyldisilazane (TMDS) have begun to exhibit certain advantages. This technique requires stringent control of silylation track and dry development equipment. Several new resists (which consist of a novolac based resin with a photo-crosslinker) have been formulated for deep-UV, allowing silylation at room temperature. By using this photo-crosslinker, the PSB (pre-silylation bake) step can be removed. In this way the process can be even more simplified. Characterization of the silylation reaction and mechanism have been performed using thickness measurements, CO emission spectroscopy, Fourier transform infrared absorption (FTIR), and Rutherford backscattering spectroscopy (RBS). In order to explore the limits, this process has also been evaluated using phase shifting masks. The influence of partial coherence on the resolution and process latitudes has also been studied.
Poster Presentations
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Advances in deep-UV processing using cluster tools
Gary C. Escher, Gary Tepolt, Robert D. Mohondro
Deep-UV laser lithography has shown the capability of supporting the manufacture of multiple generations of integrated circuits (ICs) due to its wide process latitude and depth of focus (DOF) for 0.2 micrometers to 0.5 micrometers feature sizes. This capability has been attained through improvements in deep-UV wide field lens technology, excimer lasers, steppers and chemically amplified, positive deep-UV resists. Chemically amplified deep-UV resists are required for 248 nm lithography due to the poor absorption and sensitivity of conventional novolac resists. The acid catalyzation processes of the new resists requires control of the thermal history and environmental conditions of the lithographic process. Work is currently underway at several resist vendors to reduce the need for these controls, but practical manufacturing solutions exist today. One of these solutions is the integration of steppers and resist tracks into a `cluster tool' or `Lithocell' to insure a consistent thermal profile for the resist process and reduce the time the resist is exposed to atmospheric contamination. The work here reports processing and system integration results with a Machine Technology, Inc (MTI) post-exposure bake (PEB) track interfaced with an advanced GCA XLS 7800 deep-UV stepper [31 mm diameter, variable NA (0.35 - 0.53) and variable sigma (0.3 - 0.74)].
Prebake and post-exposure bake effects on the dissolution of AZ-PF
We have performed experiments to study the kinetics of dissolution of the positive chemically amplified resist AZ-PF (Hoechst AG). The resist dissolution in exposed regions was shown to have non-linear time dependence, with a delay time strongly dependent on prebake and post- exposure bake conditions. Effect of the presence of a low-solubility surface layer on patterning of submicron features as well as on roughness of the developed film has been demonstrated.
Track oriented chemically-amplified resist processes for quarter-micron lithography
The establishment of standard resist processes are a primary requirement for the X-ray Lithography National Test Bed at the Center for X-ray Lithography. For this, experimental design is a necessary component of the methodology given the large parameter space associated with chemically amplified resists (CARs). The process development is carried out in three phases. DOX is applied to several steps in the development. The vacuum hot plate pre-bake, post-bake time, temperature and the exposure dose have the greatest effect on controlling the performance of the resist. Constraints are placed on the contrast, develop time and unexposed resist loss. The exposure dose needed to meet these requirements is obtained from the modified response surface of the bulk behavior. The final optimization is based on the CD control and side wall angle for quarter-micron features in resist. The process is run on a sampled basis in order to determine the control issues. Control limits are set from these data, and the process performance is determined.
Alpha-hydroxymethlbenzoin sulfonic acid esters--a versatile class of photoacid generating compounds for chemically amplified deep-UV photoresists
Horst Roeschert, Charlotte Eckes, Georg Pawlowski
This paper describes some physico-chemical properties and early lithographic results of deep- UV resist systems containing (alpha) -hydroxymethylbenzoin sulfonic acid esters as photoacid generating compounds. (alpha) -Hydroxymethylbenzoin sulfonic acid esters have been prepared in a three-step synthesis in good yields. The favorable thermal and optical properties of selected compounds are discussed in more detail. Uniform optical parameters at 248 nm and nearly identical photoacid generating efficiencies guarantee the formation of different sulfonic acids in comparable concentrations. Therefore (alpha) -hydroxymethylbenzoin sulfonic acid esters can serve as model compounds for systematic studies, i.e., determination of the inhibitor cleavage efficiency or diffusion characteristics of their acids. The influence of acid size and acid strength on the photosensitivity of resist formulations is discussed. The lithographic performance of an acetal-based deep-UV photoresist in terms of resolution, depth of focus, and exposure latitude demonstrates the suitability of (alpha) -hydroxymethylbenzoin sulfonic acid esters as an attractive class of photoacid generating compounds in chemically amplified UV 2-photoresists.
Resist materials design: base-catalyzed chemical amplification
C. Grant Willson, James F. Cameron, Scott A. MacDonald, et al.
Many chemically amplified resists that function on the basis of acid catalysis of thermolytic reactions have been described as well as systems that function on the basis of free radical chain reactions. But there have been very few reports on the use of base catalysis of chemical transformations in resist materials. We describe here our initial results on base catalyzed chemically amplified deep-UV photoresists. Photogenerated amines were used as catalysts for the decarboxylation of carboxylic acids. Two approaches to building resists around this chemistry were investigated. (1) Decarboxylation of a low molecular weight carboxylic acid led to base induced dissolution inhibition of a phenolic polymer giving negative tone images. (2) A carboxylic acid polymer was synthesized which also is susceptible towards base catalyzed decarboxylation. Wet development of this resist material gives negative tone images. Site specific gas-phase silylation of the carboxylic acid allows the use of this material in a positive tone dry develop process. A 0.5 micrometers line-space pattern obtained by this dry develop process illustrates the potential of base-catalyzed chemical amplification.
Advanced i-line lithography: evaluation of a new chemical amplification negative resist
Gilles R. Amblard, Andre P. Weill, Christophe M. Brault
A new chemical amplification negative resist for i-line lithography (XP 2068 F1 from Shipley) is evaluated. First, a process for 0.5 micrometers features is developed and optimized, using a Tagushi matrix: the compatibility of the resist absorption with the polysilicon and aluminum reflectivities is then tested, and the high thermal stability demonstrated. Second, the process latitude is evaluated in terms of dose-focus latitude, CD linearity, and PEB temperature latitude. Finally, the suitability of the resist for gate fabrication is studied: 0.5 micrometers features are transferred into polysilicon using two different plasma chemistries.
Evaluation of a deep-UV bilayer resist for sub-half micron lithography
William R. Brunsvold, Kevin J. Stewart, Premlatha Jagannathan, et al.
A chemically amplified silicon-containing resist has been formulated and evaluated as a thin imaging layer in a positive tone deep UV (DUV) bilayer scheme. The key component is a silicon-containing polymer which has been characterized by GPC, UV, and dissolution rate studies. Dose and focus latitudes were determined for 0.4 and 0.5 micrometers patterns exposed on a SVGL Micrascan I step and scan system and on KrF excimer laser steppers. The dose latitude on a GCA (0.35 NA) excimer was found to be 20% for 0.4 micrometers features and about 30% for 0.5 micrometers features (+/- 10% CD variation). Focus latitude was at least 2 micrometers for 0.5 micrometers patterns. Wafer to wafer LW uniformity as well as within water uniformity is shown. Typical processing involves 5 - 10 mJ/cm2 exposure doses, employing a 90 degree(s)C post-expose bake (PEB) and a 60 sec 0.21 N TMAH develop. The dependence of linewidth upon PEB was found to be about 13 nm per degree C for 0.5 micrometers features. Pattern transfer into the hardbaked i-line resist underlayer was done in an MLR chamber on an AME 5000. A low pressure etch is preferred to eliminate residue but this can lead to a higher non-uniformity across the wafer. Sidewall roughness was prevalent and this could be partially attributed to `feet' on the silicon-containing imaging layer.
Dissolution kinetics of chemically amplified resists
Toshiro Itani, Katsuyuki Itoh, Kunihiko Kasama
The dissolution rate characteristics of two typical DUV chemically amplified resists (negative resist A and positive resist B) were investigated, by comparing with an i-line novolac resist (resist C). The negative resist A here was based on crosslinking between phenolic resin and melamine derivatives, and the positive resist B was composed of tert-BOC protected phenolic resin.
Evaluation of a new zirconium-containing, negative-working, single-layer resist with enhanced oxygen and fluorocarbon reactive-ion etch resistance
Ashwin S. Ramachandran, Treva Long, Ferdinand Rodriguez
Resists for use in electron beam lithography usually have been made using polymers alone, or polymers with monomeric additives. The monomer may perform the role of a plasticizer or a sensitizer to radiation or enhance the reactive-ion resistance of the imaged resist. In the present work, a new approach was used. A negative working resist system containing two monomers, zirconyl dimethacrylate (ZrDMA) and dipentaerythritol pentaacrylate (DPEPA), was lithographically evaluated. The DPEPA acts as a sensitizer to electron beam radiation by enhancing exposure-induced crosslinking, while the presence of zirconium in the form of an organometallic results in the formation of an oxide based barrier to etch in oxygen and CF4/O2 plasmas. This results in a drop in the etch rate with time in situ.
Evaluation of a 193-nm resist and imaging system
This paper describes the use of a 193 nm surface imaging resist in a new small-field, deep-UV projection exposure system. The 193 nm surface imaging technology utilizes commercial photoresists, in conjunction with a small field step-and-repeat exposure system. Typical processing characteristics of the imaging chemistry are presented, along with a detailed description of the projection exposure system. The resist uses vapor phase silylation with oxygen RIE developing and has been shown to provide wide focus latitude and better than 0.2 micrometers resolution. The imaging system uses a catadioptric lens with 0.5 NA for 0.20 images.
Evaluation of liquid silylated resists for 213-nm exposure
John M. Hutchinson, K. Kalpakjian, Robert Schenker, et al.
We explore the bulk and imaging properties of two commercially available resists, Shipley SAL-601 and AZ 5214, to 213 nm radiation operating in a liquid silylation mode. We use FTIR and thickness measurements to characterize the silicon uptake process, and explore the use of high frequency RIE etching of silylated resists to increase selectivity and reduce post- etch residues. We demonstrate sub quarter micron lithography using 213 nm exposure of a liquid silylation resist process etched in a 60 MHz O2 plasma.
Electron beam hardening of photo resist
William R. Livesay, Anthony L. Rubiales, Matthew F. Ross, et al.
Electron beam hardening is investigated and compared with conventional thermal hardening on a diazoquinone novolac (DQN) photoresist. The electron beam hardening is accomplished without significant heating of the resist thereby eliminating resist flow or melting. The electron beam cured polymer is fully cross-linked throughout its entire thickness (full matrix cure). Thermal stability of the resist versus electron beam dose is examined. The results of varying amounts of electron beam dose show that the shrinkage of the photoresist can be reduced almost to zero by sufficient curing. The elimination of shrinkage of the resist also greatly reduces the amount of stress in the cured film. After this electron beam cure, no resist stress or shrinkage is experienced even when the resist is subjected to thermal bakes in excess of 200 degree(s)C. In fact, thermal stability of better than 400 degree(s)C has been demonstrated. The resist shrinkage is eliminated due to the resist being fully cross-linked well below its glass transition temperature. These fully cross-linked resists exhibit superior performance in plasma processing and yet remain strippable by conventional plasma ashing processes.
Study of trimethylsilyldiethylmine (TMSDEA) as a vapor priming agent
Myron R. Cagan, James Bradford Gushaw, Joseph Wiseman, et al.
TMSDEA gives consistently higher contact angles than HMDS on substrates typically encountered in IC processing. The effect of water drop contact angle on resist adhesion is demonstrated. A solution of 0.5% vol TMSDEA in HMDS, used at a 50 degree(s)C hotplate temperature, was found to be optimum for a Tokyo Electron Laboratory Mk-V track vapor prime process. Observations made with three reticle levels on bare silicon do not show any exposure dose or resist profile differences between TMSDEA and HMDS vapor primed wafers.
Effect of ultraviolet curing temperature on the state of stress and mechanical properties of photoresists
Jeffrey F. Taylor, Quinn K. Tong, Richard J. Farris
Ultraviolet curing, typical during processing of photoresist coatings, often results in residual stress. This stress is critical since it is the driving force for failure in a coating. Increasing the stress usually corresponds to a decrease in the mechanical performance. The source of residual stress was illustrated to be a result of thermal expansion mismatch between the substrate and the coating during the cooling stage following UV cure. The objective of this investigation was to reduce the residual stress by decreasing the ultraviolet curing temperature. A photoresist coating was UV cured at 3 different temperatures and the state of stress and mechanical properties were evaluated. A reduction in the state of stress of the photoresist coating was observed. Using incremental elasticity, this reduction in stress was determined to be primarily a result of decreasing the thermal stresses associated with cooling. When the cure temperature was close to the glass transition temperature, a decrease in the ultimate strength and modulus were observed, which was attributed to a decrease in the efficiency of the crosslinking reaction present during UV cure.
Comparison between equilibrium cooling and thermal shock
Jeffrey F. Taylor, Quinn K. Tong, Richard J. Farris
One of the harsh environments that a photoresist experiences is that of cold temperature. Cooling a photoresist coating constrained on a substrate often results in a sizable stress. This stress is important to understand since it is the driving force for coating failure. A membrane deflection technique was used to measure the stress of a photoresist coating as a function of temperature. The resulting stress was compared to the ultimate properties as a function of sub- ambient temperature. It is shown that failure occurred when the cooling stress exceeded the ultimate strength. Cooling over a temperature range of 30 to 65 degree(s)C was performed slowly (over a period of 6 hours) as well as suddenly (simulating a thermal shock). Using an incremental elastic approach a relationship between equilibrium cooling and thermal shock is presented. This relationship between stresses associated with equilibrium cooling and thermal shock is used to describe the typical decrease in mechanical performance of coatings in a thermal shock environment.
Experimental investigation of high-focus latitude concepts
Medhat A. Toukhy, Sydney G. Slater, John E. Ferri
The purpose of this paper is to investigate experimentally the important concepts affecting resist focus latitude. Exposure margin (EM), contrast, inhibition, and the newly introduced parameter (RD/EM) were investigated for a variety of resist systems. The quantity (RD), is the removal dose for some fractional film thickness near mask edge. The resist examples employed in this study included positive and negative, chemically amplified resists and novolac/DNQ systems. It is concluded in this work that the focus tolerance of the resist is influenced largely by (EM) in one direction and by resist inhibition and contrast in the other.
Effects of fluorescence on the spatial resolution of photoresist materials
J. J. M. Vleggaar, A. H. Huizer, Cyril A.G.O. Varma
Five-substituted diazo-naphthoquinones (DNQs) are photolyzed in novolac and in various solvents in the presence of H2O. HPLC analysis reveals that, depending on the matrix or the solvent, a large fraction of the DNQ is converted into products other than indene carboxylic acid (ICA). These include products from fragmentation, dimerization, and azo- coupling as well as products from the reaction of the solvent with intermediates in the main photoreaction. A larger amount of fragmentation products is found by excimer laser exposure at 308 nm or 248 nm. The side products mentioned above are fluorescent and their fluorescence band overlaps with the first UV-absorption band of the DNQ. Photolysis of the photosensitizer by this fluorescence may affect the spatial resolution of a photoresist. Numerical simulation of the magnitude of this effect shows that, in practice, the conversion of photosensitizer due to fluorescence is in the order of a few percent at most.
Hydrosiloxane-modified styrene-diene block copolymer resists
Allen H. Gabor, Eric A. Lehner, Guoping Mao, et al.
Block copolymers are a class of polymers deserving of more investigation by the resist community. We are investigating styrene-hydrosiloxane modified diene block copolymers which have good properties for use as negative tone, electron sensitive resists. Resolution better than 0.1 micrometers , sensitivity of 30 (mu) C/cm2 and contrast of 2.8 have been demonstrated using a poly(styrene)-pentamethyldisiloxane modified poly(isoprene) block copolymer (PS-b-PDPI). Used in a bilayer resist scheme, PS-b-PDPI has an oxygen RIE selectivity ratio of 42 with respect to poly(imide). A poly(styrene)-heptamethyltrisiloxane modified poly(butadiene) block copolymer (PS-b-HTPB) has an oxygen RIE selectivity ratio of 54 with respect to poly(imide). In a bilayer resist system, using PS-b-PDPI as the imageable layer, patterns of 0.3 micrometers wide lines and 1.5 micrometers wide spaces have been transferred through a 1.2 micrometers thick poly(imide) planarizing layer.
Model of the process of dissolution and swelling of thin polymethylmethacrylate films
Vladimir N. Genkin, M. Yu. Myl'nikov
In the fabrication of integrated circuits (IC) the solubility dependence of a polymer on its macromolecular length is used. The development process is multistage and involves series thicknesses just as in photo and plasma etching. In lithography this process is considered surface and its rate depends on average molecular mass. We expect that the dissolution rate is a time function and that it depends not only on M, but also on the mass-molecular distribution. We propose that the swelling factor is important too. The aim of this work is to construct a model of swelling and dissolution processes and to estimate the positive resists contrast dependence on the polymerization degree and solvent thermodynamic quality.
Composition of inorganic photoresists and its EBE experiment
Changtai Yu, Hua Yu, Fengzhen Guo, et al.
We report the composition of inorganic photoresist, film making way and its EBE experiment. With the composed inorganic photoresist, the graph of 0.6 micrometers line width is gained in our experiment.
Effect of surface inhibition on process latitudes
Casper A. H. Juffermans, Han J. Dijkstra, Yvonne Verhulst-van Hout
In extending the latitudes of high-contrast positive i-line resists both bulk development contrast and surface inhibition are important. Measurements of these parameters with a DRM show large variations when the resist thickness and baking conditions are varied. The relative importance of both contributions on especially the focus latitude are studied. Using the measurements of bulk contrast and surface inhibition time our i-line resist processing is optimized.
Influence of residual casting solvent on the dissolution behavior of diazonaphthoquinone resists
Veena Rao, William D. Hinsberg, Curtis W. Frank, et al.
Residual casting solvent present in resist films can have a profound effect on their dissolution behavior. We have used a radiolabeling technique to make quantitative measurements of solvent remaining in spin cast films after they have undergone different baking protocols. Films of poly (3-methyl-4-hydroxystyrene) were found to contain a significant fraction of propylene glycol methyl ether acetate (as much as 50% by weight) depending on the baking conditions. Films that were 1000 angstroms thick contained a higher percentage of residual solvent than films that were 1 micrometers . The solvent concentration in films containing a mixture of polymer and photoactive compound was a maximum for films containing 5 wt% PAC.
Effects of absorptive dye loading and substrate reflectivity on a 0.5-micron i-line photoresists process
Jeffrey R. Johnson, Gregory J. Stagaman, John C. Sardella, et al.
The effects of an increasing amount of absorptive dye contained in a positive i-line photoresist were studied for a 0.5 micrometers process on two substrates with substantially different reflectivities. Parameters such as dissolution rates, focus latitudes, and resistance to reflective notching were simulated and compared to experimental results. Reductions in resist profile and focus latitude were observed as the photoresist non-bleachable absorbance was increased, and as the substrate reflectivity was decreased. It was also found that a reduction in substrate reflectivity was more effective than increasing the resist dye loading in suppressing reflective notching of the photoresist.
Understanding the novolak synthesis reaction
Leonard E. Bogan Jr.
We describe new tools for the characterization of novolac resins, for the understanding of the novolac synthesis reaction, and for the prediction of resin structures. These tools have been used to optimize the performance of photoresists for microlithography. The current state-of- the-art describes novolac copolymer compositions as the ratio of monomers charged in the reaction, even though it is well known that the actual product composition is quite different. Quantitative 13C NMR spectroscopy provides a direct method for accurately determining copolymer composition by integrating methyl carbon resonances. By using this method to analyze the results of competition reactions, relative monomer and site reactivities for phenol and the cresols with formaldehyde have been determined. These observed reactivities have been used in a simple, kinetic model to accurately predict copolymer composition, branch density, and molecular weight.
Scaling law for the dissolution of phenolic resins in aqueous base
Tung-Feng Yeh, Arnost Reiser, Ralph R. Dammel, et al.
A scaling law derived from percolation theory for the dissolution of phenolic resins in aqueous base is tested and confirmed on seven groups of amphiphilic resins. The scaling law can be presented in the dimensionless form: log(R/R1) equals 2 log[(p - pc)/(1 - pc)]. Here R and R1 are the dissolution rates of the resin and of a standard resin for which p equals 1, the percolation parameter, p, linked to the concentration of hydrophilic sites (OH-groups) in the material, and pc is the percolation threshold below which dissolution no longer occurs. In the group of resins of this study Pc equals 0.20. In its dimensionless form the scaling law provides a single function which applies to all resins of this study and, we believe, to amphiphilic resins in general. This allows the prediction of dissolution rates and the selection of polymer structures which are likely to have specified dissolution kinetics.
Solvents in novolak synthesis
Chet J. Sobodacha, Thomas J. Lynch, Dana L. Durham, et al.
Novolac resins may be prepared with or without a solvent present. We have found that solvent power greatly affects the properties of the finished resin and thus gives the resist chemist another variable with which to `fine-tune' resist properties. Using designed experiments, we investigated the effect of solvent power, as measured by Hansen's Solubility Parameters, of a number of solvents and solvent mixtures on the final properties of the novolac resin. We found that the relative molecular weight (RMW) and dissolution rate of a novolac resin can be varied by selection of a solvent or solvent mixture with the appropriate polarity and hydrogen- bonding characteristics. The solvent polarity and hydrogen-bonding characteristics may affect the stability of the cresol/formaldehyde transition state, thus causing the observed changes in RMW and dissolution rate.
Blended novolac resins with improved lithographic performance
Thomas J. Lynch, Chet J. Sobodacha, Valerie R. Paradis, et al.
Statistically designed experiments were performed to optimize novolac blending techniques which would yield superior photoresists. The best lithographic performance was obtained when two novolacs to be blended had dissimilar relative molecular weights (RMW) while also having matched dissolution rates (DR), (lithographic performance equals (RMWA - RMWB)/(DRA - DRB). A calculated plot of (RMWA - RMWB)/(DRA - DRB) matched the experimental plot of lithographic performance well.
High-resolution pattern formation featuring excellent dimension correlation by enhanced wettability development technology
Shigeki Shimomura, Hisayuki Shimada, Rita Au, et al.
We have demonstrated that the addition of surfactant to developer results in (1) the resolution of the contact holes as small as 0.30 micrometers with good dimension correlation, (2) an increase in the depth of focus at the minimum feature size, and (3) a reduction in the exposure energy needed to form fine patterns. The surfactant enhances the wettability of the developer to the photoresist, thus promoting dissolution of the photoresist, especially in narrow spaces such as contact holes. The optimal surfactant concentration in the developer performs superior development characteristics. In addition, we also demonstrate the effect of the molecular structure of surfactant on development performance.
Thermal properties of state of the art novolak-diazonaphtoquinone systems: differences between bulk and film properties
Patrick Jean Paniez, Jean-Paul E. Chollet, Michel J. Pons
As demonstrated by both thermal analysis (DSC) and thermal flow experiments, the latest resists for advanced i-line lithography exhibit improved thermal properties. Emphasis is placed upon experimental details to obtain reliable and meaningful data. In addition to the results of these experiments, the high glass transition temperatures (Tg) measured, equal or superior to the recommended soft-bake conditions, raise new questions concerning the formation and properties of the resist film. The Tg of the film is shown to be different from that of the bulk material and to depend on the bake conditions. The DSC results are confirmed by thermal flow experiments and a good correlation is obtained between the two methods. The consequences induced by the use of high Tg materials on other steps in the lithographic process, namely standing wave reduction and plasma durability, are also discussed.
Photoresist surface induction and its effect on swing behavior
Steven G. Hansen, Rodney J. Hurditch, David J. Brzozowy, et al.
Thin film optical interference causes a sinusoidal variation in lithographic properties with film thickness known as the swing effect. The most well known manifestations are the threshold clearing energy (E0) and critical dimension (CD) swings which arise due to variations in the in-coupling efficiency of light. The E0 swing is conceptually simple, requiring only that the amount of photo-active compound (PAC) conversion is constant within a swing film thickness cycle. The present work verifies that E0 swing is a purely optical effect and is independent of bulk dissolution curve details. For resists of identical optical properties, the faster one will have the lower E0 swing. `Secondary' swing effects, defined here as lithographic changes arising due to remnant standing wave phase at the film surface, include variations in gamma, resolution, focus latitude, and profile. Some i-line photoresists, particularly those which give significant surface induction in development, show large oscillations in these performance measures depending on swing phase.
Statistical experimental design on the optimization of high-performance photoresist
Stanley A. Ficner, Ping-Hung Lu, Thomas Kloffenstein, et al.
The ultimate photolithographic performance of a photoresist is essentially determined by the nature and relative concentration of the chemical components in the formulation and the process conditions selected. To meet the stringent performance requirements demanded by the advanced microlithography technology, each individual constituent of the photoresist process described must be optimized simultaneously. This study presents an effective and time saving approach using experimental design techniques to address the complicated multi-variable of resist formulation and process condition optimization. The responses for the design experiment in terms of lithographic performance were: exposure and focus latitude, photosensitivity and resist pattern thermal flow temperature are correlated with the resin dissolution characteristics, relative photosensitizer concentration, pre- and postexposure bake temperatures and development time.
193 nm lithography with ultrathin surface imaging resist systems
Charles S. Dulcey, Tim S. Koloski, Walter J. Dressick, et al.
Deep UV photochemical patterning of chemisorbed metal-binding (ligating) organosilane films has been previously used to demonstrate sub-0.5 micrometers patterned additive metallization by electroless deposition. Significant photospeed advantages have now been obtained using a two step process in which an organosilane film is first patterned and then functionalized to impart the ability to metallize. This is achieved by photochemical patterning of a film which lacks a ligating group, but which is optimized for photospeed. The pattern of chemical functions so created is then reacted with an organic ligand which selectively places the ligand functionalities on the surface. Treatment with an aqueous Pd catalyst followed by electroless plating deposits metal in patterns defined by the irradiation step. Using several chemical approaches based upon this concept, metal patterns have been fabricated to 0.5 micrometers feature width at doses of 50 mJ/cm2 at 193 nm.
Modeling of silylated resist profile in DESIRE process
Bhvanesh P. Mathur, Khalil I. Arshak, Jules Braddell, et al.
In DESIRE process, silylation is probably the most critical step since the final resist profiles are mainly determined by the Si distribution between the exposed and unexposed areas of the upper part of the resist. In the past, the silylation contrast was used to predict the silylation profile for a given silylation condition. In this paper, a new method to calculate the silylation profile is presented. A new module is added in ANKAN simulator to predict the silylated profile using this method. Extensive simulation was carried out for a one dimensional line space object under various process conditions. Change in silylation depth at the center and corner of the line has been computed to study the effect of aerial image on silylation profile for both PLASMASK 200G and 301U photoresists.
New silicon-containing negative resist for bilayer lithography
Premlatha Jagannathan, Ratnam Sooriyakumaran, Harbans S. Sachdev
The increasing use of high density integrated circuits has created a need for development of new resist materials and lithographic schemes involving process simplification in semiconductor device fabrication to lower defect levels and improve product reliability. Towards that goal, we have developed a new negative working photoresist applicable to a bilayer resist scheme using optical and E-beam exposures. In this paper, we discuss the synthesis and lithographic applications of the silicon containing resist PHBS-AZIDE. The resist comprises a single component in which the photoactive group, an azide moiety, is chemically bonded to the base polymer, poly(4-hydroxybenzylsilsesquioxane) via an esterification reaction. The new polymer is easily synthesized and has the advantageous properties of aqueous base developability, excellent oxygen RIE resistance and high sensitivity to DUV, i-line and E-beam exposures. Sub-half micron images have been demonstrated using PHBS-AZIDE as a thin top imaging layer in a bilayer mode.
Influence of process parameters on the lithographic performance characterization in the top imaging process by silylation
Tai-Kyung Won, Seung-Chan Moon, Hyeong-Soo Kim, et al.
Single level dry developable resist process based on gas phase silylation has great promise for sub-halfmicron pattern imaging due to shallow exposure, which leads to a thin silicon incorporation layer during silylation process in the top exposed region. In this paper the influence of process key parameters on the lithographic performance characterization has been investigated. For this experiment, two kinds of commercial i-line photoresists based upon novolac-diazoquinone and tetramethyldisilazane as a silylation agent were used for analyzing the process properties. As a result, it was observed that the ultimate resolution of 0.30 micrometers with vertical profiles, projected with an i-line of 0.54 NA lens, was obtained. However, it was found that CD linearity characteristics strongly depend on the compositions and the structure of photoresist, independent of other process parameters. Selectivity of dry development with a range of 13 - 15 was achieved using the oxygen/argon mixtures at 5 mTorr with MERIE. Major factors affect on the resist pattern profile were proven to be dry development parameters as well as the latent image formation of silylation. In particular, lower power and higher magnetic field conditions at low pressure allowed a good resist pattern profile without sidewall roughness and residues. And effects of silylation parameters on process latitudes has also been studied by comparing resolution capability, DOF, and exposure latitude, respectively.
Simulation of self-diffusion effects of silylated polymers during dry development
Ulrich A. Jagdhold, Hartmut H. Erzgraeber
A model is presented to study self diffusion effects of silylated polymers during dry development. The effect is discussed in connection with mechanisms of the formation of the oxide mask during different O2-RIE conditions. Furthermore, the influence on the CD control is outlined.
Plasma-deposited organosilicon hydride network polymers as versatile resists for entirely dry mid-deep-UV photolithography
Ajey M. Joshi, Timothy W. Weidman, Andrew D. Johnson, et al.
Plasma polymerized organosilicon films were used as negative tone deep-UV resists in a new all­ dry bilayer process. Quarter micron thick organosilane films were photo-oxidatively patterned using a GCA deep-UV stepper (248 nm, NA = 0.35 or 0.48) at exposures between 50-200 mJ cm-2. Patterns were dry developed with up to 15:1 selectivity by low energy chlorine plasma etching employing conditions similar to those used for the selective etching of polysilicon over Si02. Pattern transfer into underlying organic layers was achieved with greater than 50: 1 selectivity in a bilayer processing sequence by switching the etching gas to oxygen. The oxide-like etch resistance of the exposed resist to subsequent processing allowed direct, high resolution (0.25-0.35 µm US) patterning of polysilicon and aluminum using appropriate dry etch chemistries. This provides an attractive, step-saving alternative to current bi- and trilevel schemes involving deposition and multistep patterning of hard etch masks such as Si02. Photo-oxidative patterning of plasma deposited organosilane resist films and subsequent RIE development comprise a new, versatile, entirely dry photolithographic process that is compatible with commercially available deposition, exposure and plasma processing tools, and is well-suited for integration into cluster tool technology.
Mechanism of dissolution inhibition in phenolic resins
Chen-Chy Lin, Tung-Feng Yeh, Arnost Reiser, et al.
It was suggested in an earlier communication that dissolution inhibition in phenolic resins comes about through the blocking of some of the hydrophilic OH-groups by a hydrophobic effect of the inhibitors. Honda et al. have shown that the hydrophobicity of the additive is not a sufficient condition, and that the polar groups of the inhibitor, such as the diazoquinone function, play an important role in the inhibition effect. They found that additives with very similar skeletal structures, but differing in the polar anchor group, have very different inhibition efficiencies in a common novolac resin. In this study we investigate the interaction between phenols and the anchor groups of the inhibitors by determining the equilibrium constants of their association reaction. From this, the fraction of bound acceptor groups (inhibitors) can be estimated for the casting solution of the films at the point of solidification. It can be shown that this fraction correlates quite satisfactorily with the inhibition effect of the additives used in Honda's study.
Base-catalyzed photosensitive polyimide
Dennis R. McKean, Gregory M. Wallraff, Willi Volksen, et al.
A scheme for imaging of polyimide films is described which is based on the amine-catalyzed imidization of poly(amic alkyl ester) precursor polymers. Films containing amine photogenerators along with poly(amic alkyl esters) are patterned by exposure followed by heating to partially imidize the exposed portion of the film. Negative images are developed by taking advantage of the greater solubility of the precursor polymer which is dissolved in an appropriate solvent mixture. A final cure is carried out to complete the imidization of the patterned film.
Process optimization of positive novolac resists for electron-beam lithography resist characterization using single or multiple development steps with either a sodium-hydroxide or metal ion-free dev
Robert L. Dean, Gary E. Flores
OCG895i and Tokyo Ohka OEBR2000 (both commercially available) and two experimental resists were evaluated by experimental design. The design factors investigated included developer normality, softbake temperature, and develop time with a sodium hydroxide-based developer. The design responses included optimum dose, remaining film thickness, and dose latitude (change in critical dimension per unit dose). The best results were given by AZ141C, an experimental resist from Hoechst. At 90 degree(s)C prebaking temperature, AZ141C could be imaged at 4.0 (mu) C/cm2 with good film thickness retention and dose latitude. A second set of optimization experiments was done evaluating metal ion-free developer. Finally, multiple develop processing was evaluated for improving process latitude and film thickness loss and for minimizing the dose required. A two-step process shows promise: it consists of a high initial normality develop for a short time to accomplish breakthrough of the resist surface inhibition layer, followed by a second low normality develop. Another sequence of statistically designed experiments performed to optimize this scheme and results of the optimizations are presented.