Proceedings Volume 0771

Advances in Resist Technology and Processing IV

Murrae J. Bowden
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Proceedings Volume 0771

Advances in Resist Technology and Processing IV

Murrae J. Bowden
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 25 August 1987
Contents: 1 Sessions, 44 Papers, 0 Presentations
Conference: Microlithography Conferences 1987
Volume Number: 0771

Table of Contents

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Table of Contents

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New Diazoketone Dissolution Inhibitors For Deep U.V. Photolithography
C.Grant Willson, Robert D. Miller, Dennis R. McKean, et al.
The results of studies directed toward the design of diazoketone dissolution inhibitors for deep U.V. photolithography are described. This work has identified a useful chromophore, the 1,3-diacy1-2-diazo linkage which has the requisite spectral characteristics for use in the deep UV. Incorporation of appropriate hetero-atomes into the structure has allowed synthesis of analogs that survive common processing sequences. A detailed study of the photochemistry of these analogs led to an understanding of the importance of the stability of the ketene photoproduct on resist contrast. Imaging results are presented for a trilayer application and for excimer laser projection printing.
A Novel, Diazonium-Phenolic Resin Two-Layer Resist System Utilizing Photoinduced Interfacial Insolubilization
Shou-ichi Uchino, Takao Iwayanagi, Takumi Ueno, et al.
This paper deals with a negative two-layer photoresist system utilizing a photoinduced insolubilization process at the interface. The bottom layer is a phenolic resin either with or without aromatic azide and the top layer is a photosensitive layer comprised of an aromatic diazonium compound and a water soluble polymer. Upon exposure to light, the diazo compound decomposes to cause insolubilization at the interface between the two layers. The system exhibits high contrast due to the combination of interfacial insolubilization and contrast enhancement by photobleaching of the diazonium compound. Patterns of 0.5 um lines and spaces are obtained using an i-line stepper and a resist system containing 4-diazo-N,N-dimethylaniline chloride zinc chloride in the top layer and 3-(4-azidostyry1)- 5,5-dimethyl- 2-cyclohexen-1-one in the bottom layer. Resists with varying spectral responses from mid-UV to g-line can be designed by selecting the kind of diazo compound used in the top layer.
Brominated Poly(1-Trimethylsilylpropyne): A Sensitive Deep-Uv Resist For Two-Layer Lithography
Antoni S. Gozdz, Gregory L. Baker, Cynthia Klausner, et al.
Brominated poly(1-trimethylsilylpropyne) (PTMSP-Br) is a sensitive, positive DUV resist suitable for application in a two-layer lithographic process. It is readily degraded in the presence of oxygen by DUV radiation (λ<280 nm), has excellent film formingproperties and is stable in air up to ~200°C. The sensitivity of PTMSP-Br is dependent on the degree of bromination and time and temperature of post-exposure baking. Samples having xB, from 0.1 to 0.2 per monomer unit and post-exposure baked for 1 h at 140°C exhibit sensitivities (Dr) of 20 to 25 mJ/cm2 with a contrast (γ) of 3.5-4.0. Half-µm lines and spaces have been generated by contact printing at 260 nm using 1-butanol as a developer and transferred into 1.5-2.5 µm-thick planarizing layers by anisotropic reactive ion etching. The etching rate ratio of PTMSP-Br vs. a hard-baked Novolac-type photoresist is better than 1:25.
Positive/Negative Mid Uv Resists With High Thermal Stability
Hiroshi Ito, C. Grant Wilson, Jean M.J. Frechet
New mid UV resist systems based on poly(p-vinylbenzoates) sensitized with diphenyl-4-thiophenoxyphenylsulfonium hexafluoroantimonate are described. t-Butyl, cyclohexenyl, a-methylbenzyl, and a-methylallyl esters are converted upon postbake to poly(p-vinylbenzoic acid) through thermolysis reaction catalyzed by the photochemically generated Bronsted acid, inducing a large change in the polarity of the repeating units. Thus, development in aqueous base such as MF312/water or alcohol provides a positive tone image of the mask, while the use of a nonpolar organic developer allows a negative tone imaging. Because the glass transition temperature of poly(p-vinylbenzoic acid) is ca. 250° C, the negative image is devoid of thermal flow to this temperature even without any hardening processes. Another interesting feature of the benzoate resists is their high opacity in the deep UV region. The optical density of a 1μ thick film of poly(p-vinylbenzoic acid) is 3.5 at 254 nm and the benzoate polymers are as absorbing as the acid polymer. This high deep UV absorption of the resin necessitates the imaging above 300 nm for good light penetration (or by e-beam or X-ray) and makes the use of this resist as an imaging layer in the PCM scheme very attractive. This imaging layer is especially useful when employed in conjunction with a planarizing layer absorbing above 240 nm (for example, PMGI) as addition of a dye is not required.
Characteri Zation Cf A New Organ 3 Silicon Phcficiresist
Wells C. Cunningham Jr.
For a number of years, there has lo'ep. great interest in organometallic based photoresists for use as the top layer in multilevel resist schemes.-' In general, bilevel approaches to lithography are forced upon the industry as a means of planarizing topography for a subsequent patterning step. This pattern is initially defined by exposure and development of a thin top layer (0.3 to 0.5μm) over the thicker bottom layer (1.0 to 2.0μm). (See Figure 1). In a conventional bilevel approach, the chosen bottom layer is photoactive at a wavelength for which the top is relatively opaque. The top level acts as a portable conformable mask (PCM) for image transfer through the bottom layer after its exposure and wet development. By using a silicon containing photoresist on the top image transfer may be accomplished using an oxygen plasma instead of a second exposure and development. The PCM in this case acts as an etch mask by forming a silicon dioxide crust in the plasma which slows the etch rate of the top versus the bottom layer. A generic curve of etch rate of a photoresist versus percent silicon by weight is shown in Figure 2. The shape is similar over a wide range of organosilicon polymers.5,6
Langmuir-Blodgett Films For Half Micron Lithography Using Krf Excimer Laser And X-Ray
K. Ogawa, H. Tamura, M. Sasago, et al.
For photo-resist in the semiconductor photo-lithography, the study was extended to five LB-Films for KrF Excimer (EX) Laser, i.e. three fatty acids of Diacetylene derivatives (Diynoic acids), w-Tricocynoic acid, and Octadecylacrylic acid, and other three LB-Films for X-ray, i.e. Arachidic acid, w-Tricosenoic acid, and w-Tricocynoic acid. In terms of the pattern shape and photo sensitivity, Pentscosa-diynoic acid for EX Laser and w-Tricocynoic acid for X-ray were better than others. Using Pentacosa-diynoic acid LB-Films, 0.3 pm pattern could be fabricated by the EX stepper, the size of which is the theoretical resolution limit of our lens. On the other hand, using w-Tricocynoic acid, 0.4 pm pattern could be fabricated by the X-ray stepper, of which size is at the limitation of X-ray mask which could be fabricated at present. But, if the smaller patterns of X-ray mask could be fabricated, it will be possible to make them below 0.1 μm. So these technology will become useful surely for the fabrication of 64Mbit D-RAMs.
High Temperature Photonegative Resists Based On Styrylpyridinium Units
MinYu Li, Eli M. Pearce, S. Narang
Four types of condensation linear polymers containing styrylpyridine units were prepared as high temperature stable photoresists: polyester and polyurethane derived from 2,6-bis(p-hydroxystyryl) pyridine, and polyamide and polyimide derived from 2,6-bis(paminostyryl)py-ridine or 2,6-bis(p-carboxystyryl)pyridine. The polymers are thermally stable in the temperature range between 360 to 500°C except for the polyurethane. The decomposition temperature is higher for the aromatic polymers, lower for their aliphatic analogs. The polymers are photoreactive and crosslink based on the 2+2 cycloaddition mechanism under UV irradiation. The highest photosensitivity of these polymers, as measured by gel dose, is in the region of 10-40 mJ/cm2. The quantum yield of the photoreaction and the relationship of the photosensitivity with the morphology in the polymer systems were studied.
Chemical Factors Affecting Npr Performance
R. G. Tarascon, J. Frackoviak, E. Reichmanis, et al.
NPR, a material consisting of a novolac resin blended with poly(2-methyl-l-pentene sulfone) (PMPS), is an attractive positive electron beam resist. However, it exhibited a number of problems during processing. For example after the development step, NPR patterns were surrounded by a halo due to resist thickness differences in the region next to the exposed areas. Also, a thin residual film appeared in the developed regions. A study of these problems showed that immiscibility between the two NPR components was responsible for many of the results. Also, Fourier Transform Infra Red Spectroscopy showed that a low molecular weight PMPS, [n] - 20 cm3/g, considerably improved compatibility and reduced the defects mentioned above. For this reason a study of PMPS molecular parameters by Gel Permeation Chromatography (GPC), light scattering and intrinsic viscosity was undertaken. This study related the molecular variables to synthetic conditions and a reproducible synthesis was established. A new NPR system was prepared with 9% low molecular weight sulfone polymer. This resist exhibits good film quality after development and displays a sensitivity of 8pC/cm2 with excellent (0.25μm) resolution.
A New Process For Contrast Enhancement Of Photoresist Patterns
Yoshimitsu Okuda, Tohru Ohkuma, Yukio Takashima, et al.
A new simple photoresist process for contrast enhancement of submicron pattern plofiles is proposed. This process consists of the conventional positive photoresist process steps and a deep UV flood exposure step after the image exposure . In the printing experiments novolac resists and g-line steppers with N.A. value of 0.42 and 0.35 are used. Using the new process 0.6 μm line and space are distinctly resolved for S-1400 (Shipley). The resolution is improved by 0.2 μm and the edge acuity of 80-90° is obtained compared with 60-65° by the conventional process for OFPR-500053 (Tokyo Ohka dyed photoresist). The effect of contrast enhancement is verified by the meausrements of photoresist dissolution rate in the developer. Dissolution rate in the new process is suppressed by 60% of that in the conventional process at the surface of resists. The contrast enhancement with the use of the new process is confirmed by the simultation based on the program SAMPLE in which the results of the dissolution rate measurements are used.
The Mechanism Of The Desire Process
B. Roland, R. Lombaerts, C. Jakus, et al.
Multilayer resist techniques have been studied for several years already. Especially with the trilayer systems very good results can be obtained, but only at the expense of added complexity. Their complexity has caused some reluctance to implement these techniques into IC manufacturing lines. Using the PLASMASK resist in the so called DESIRE process, even better performance can be obtained, without any of the disadvantages of multilayer techniques. The process is based on a silylation which results from the selective diffusion of a silylating agent into the resist matrix. The basic chemistry that enables this differentiation in diffusion is discussed, as well as the principle advantages of the diffusion-controlled process.
Highly Sensitized Electron-Beam Resist By Means Of A Quenching Process
F. Shigemitsu, K. Usuda, T . Tsuchiya, et al.
It was found that the sensitivity of poly(2,2,2-trifluoroethyl-a-chloroacrylate) (EBR-9) is greatly enhanced to around 0.1μC/ci when EBR-9 is quenched at 160°C/sec after baking. This sensitivity is about 27 times higher than that obtained by cooling at 65t/min in an atmosphere of still air. This result indicates that the sensitivity of an electron-beam resist depends on the cooling rate. In particular, a change in the cooling rate within the glass-transition region of EBR-9 leads to a drastic change in sensitivity. One method of thermal analysis, differential scanning calorimetry(DSC), made it clear that the slower the resist is cooled through the glass-transition region, the more enthalpy relaxation is produced. Furthermore, it was proved that a resist with much reduced enthalpy indicates a lower solubility rate, and that the annealing method was valid to estimate the reduced enthalpy using DSC. It is concluded that the quenched resist becomes more sensitive as a result of the enhanced solubility because of little enthalpy relaxation.
Novolak Design For High Resolution Positive Photoresists
M. Hanabata, A. Furuta, Y. Uemura
The mechanism of resolution improvement in novolak-based positive photoresists was investigated from the stand-point of the image formation process. The image formation process in the novolak-quinonediazide system involves the dissolution inhibition in unexposed parts and the dissolution promotion in exposed parts. The 4-(gamma)-value, which is one of the indexes of resolution capabilities, depends greatly on the difference between the solubility of unexposed parts and that of exposed parts, i.e.-the lower dissolution rate in unexposed parts(Ro) and the higher one in exposed parts(Rp) are desirable to obtain high γvalues.
Dissolution And Swelling Studies Of Poly(Methyl Methacrylate) Resist Films
J. S. Papanu, J. Manjkow, D. W. Hess, et al.
The swelling and dissolution of thin film poly(methyl methacrylate), PMMA, in methyl isobutyl ketone (MIBK), and in solvent/nonsolvent mixtures of MIBK/methanol and methyl ethyl ketone/isopropanol have been investigated. Films were monitored using in situ ellipsometry. Parametric studies of the effects of molecular weight, molecular weight distribution, softbaking quench rate, solvent size, and temperature were performed with MIBK. These parameters were shown to have a significant effect on dissolution. The effects of solvent composition and temperature on swelling and dissolution were investigated with the binary solvents. Ternary diagrams based on Flory-Huggins interaction parameters were used to interpret the thermodynamics of swelling and dissolution. A narrow transition region (NTR) where the developer changed from a swelling to dissolving agent with a small change in composition or temperature was observed.
Mechanistic Study Of A Selective Gas-Phase Reactive Microlithographic System
T. B. Brust, S. R. Turner
The gas-phase functionalization of poly(p-hydroxystyrene) (PPHS), prepared imagewise by the acid-catalyzed deprotection of poly(t-butoxycarbonyloxystyrene) (PBOCST) was investigated using a piezoelectric quartz crystal microbalance fitted inside a temperature- and pressure-controlled chamber. This apparatus allowed the real-time monitoring of the mass changes in the resist film during acid-catalyzed thermolysis of the t-butoxycarbonyl groups and subsequent vapor treatment with hexamethyldisilazane (HMDS). Effects of optical exposure, presilylation baking, vapor treatment conditions, and copolymerization with Tn-lowering acrylate esters were investigated and suggest the following: (1) Gas-phase fanctionalization rates are dependent on vapor treatment temperature and pressure, as well as other process variables that alter polymer chain mobility. (2) Rapid diffusion of HMDS takes place in the exposed areas due to the plasticization and increases in void space caused by the evolution of isobutylene and carbon dioxide during photoacid-catalyzed thermolysis of the pendant t-butoxycarbonyl groups. (3) Silicon incorporation appears to be initially reaction-rate limited due to the void space enhanced diffusion.
Mechanism And Kinetics Of Silylation Of Resist Layers From The Gas Phase
Robert-Jan Visser, Jack P.W. Schellekens, Marian E. Reuhman-Huisken, et al.
The silylation from the gas phase of photoresists based on diazoquinone and novolac or polyvinylphenol, which can be used in dry developable systems has been investigated. It is shown that the phenolic hydroxyl groups are almost completely silylated. The kinetics of the reaction have been followed by gravimetry, IR spectroscopy and Rutherford backscattering spectrometry. During the reaction a completely silylated, swollen layer is formed with a sharp front separating it from the unreacted resin. The rate controlling processes are the relaxation of the polymer and the diffusion of the reagent. When the relaxation is slow with respect to diffusion, linear reaction kinetics as in Case II diffusion are observed. When the relaxation is fast the reaction proceeds with the square root of time. The increase of the reaction rate with UV exposure of the resist is attributed to an increase in the relaxation rate of the resist. A model explains the higher photoselectivity of the reaction at elevated temperatures. Results with a number of model resists indicate that some diazoquinones can act as physical crosslinks between polymer chains via the formation of hydrogen bonds whereas the corresponding indenecarboxylic acids cannot. Due to the high content of silicon after the treatment these resists become highly etch-resistant towards oxygen plasmas.
Process Parameters For Submicron Electron Beam Lithography Of NPR
J. Frackoviak, R. G. Tarascon, S. Vaidya, et al.
NPR (Novolac Positive Resist), a high resolution (0.25 pm) positive electron beam resist, is a blend of a cresol novolac and a polymeric dissolution inhibitor, poly(2- methyl-l-pentene sulfone) (PMPS) which undergoes spontaneous depolymerization during electron irradiation. Stringent control of processing parameters is necessary to obtain optimum resist sensitivity and contrast. The study of the chemistry of NPR has been discussed previously. In this paper we report on the role of processing variables on pattern quality and identify some of the conditions necessary for submicron resolution. The effect of NPR prebake temperature on resist pattern quality was studied and thermal analysis data compiled. The contrast of NPR as a function of the developing mode (dip, pubble, spray) was examined. The influence of electron beam parameters such as beam size and beam defocus on resist line edge quality was looked at extensively. The results and conclusions of these studies are reported in this paper. The application of NPR in trilevel resist systems was carefully evaluated. Excellent submicron resolution capabilities of the resist will be illustrated with scanning electron micrographs. Proximity effects were reduced through the use of "ghosting" techniques and examples of improved linewidth control will be shown.
A Comparison Of The Dissolution Behavior Of Poly(P-Hydroxystyrene) With Novolac
Michael J. Hanrahan, Kathleen S. Hollis
An examination of the literature revealed that aqueous-processable positive-working photoresists based on novolac resins have been frequently reported, while analogous resists employing poly(p-hydroxystyrene) as the binder have not. In a functional resist formulation, poly(p-hydroxystyrene) would be expected to be similar to novolac in its development characteristics; however, this is not true. The dissolution properties of these two types of binders have been examined in order to identify the crucial differences. This paper presents the determination of the dissolution kinetic expression for both polymers. Additionally, the dissolution behavior of these materials in a resist-like environment is also discussed. From the results of our study, it can be concluded that poly(p-hydroxystyrene) does not exhibit as high a discrimination between exposed and unex-posed dissolution rates as does novolac.
On The Dissolution Kinetics Of Positive Photoresists: The Secondary Structure Model
Michael K. Templeton, Charles R. Szmanda, Anthony Zampini
Dissolution kinetics of several model resins with well defined molecular structures were studied extensively. These include a pure m-cresol formaldehyde novolac resin and an alternating m,R-cresol novolac. Other phenolic materials, such as poly(4-hydroxy-styrene), were also examined. Secondary structures of these materials were predicted by molecular mechanics energy minimization techniques and corroborated by comparison with existing experimentally determined X-ray crystallographic data, where available. The excellent agreement between theory and experiment for simple systems lends credence to structural predictions for our model systems. The salient conformational features of these molecules are manifested in the variety of inter- and intramolecular hydrogen bonding interactions which influence strongly the dissolution properties of a given resin. Dissolution kinetics were studied as a function of cation type, developer ionic strength, normality and temperature. The results are explained in terms of the inter- and intramolecular interactions predicted for these resins. Finally we show results which indicate the utility of our model to the design of resist/developer systems.
A Study Of The Dissolution Kinetics Of A Positive Photoresist Using Organic Acids To Simulate Exposed Photoactive Compounds
Lauren Blum, Mariorie E. Perkins, Andrew W. McCullough
The dissolution kinetics of a positive photoresist have been simulated using mixtures of an organic carboxylic acid and a photoactive compound (PAC) to mimic the partially exposed PAC in the photoresist. The dissolution rate of the novolac resin film was 200 A/s. When acid was added to the resin at a resin/acid ratio of 6/1, the dissolution rate of the film increased as much as four-fold depending on the acid used. The dissolution rate of a resist containing the PAC, a 2,1,4-diazonaphthoquinone monoester, was obtained as a function of inhibitor concentration M. The M values were then simulated by replacing the amount of exposed PAC in the resist with an acid (i.e. for M= 0.6, the "PAC" would consist of 40% acid + 60% PAC). The dissolution rates of the films containing 2-naphthoic and 4-t-butylbenzoic acid matched those of the exposed resist quite closely. The dissolution rates of the films containing the acid of the photolyzed PAC were much higher than those of the exposed resist.
Effect Of Diffuse Reflectivity On Photoresist Linewidth Control
Stephen A. Casalnuovo, Clifford L. Renschler, Robyn E. Stiefeld, et al.
Recent studies in our laboratory have shown that the diffuse reflectivity of sputtered A1/1% Si films plays a significant role in the lot to lot control of photoresist linewidth for 2.0 m features on our 16K SRAM device. The exposure energy required to produce 2.0 m resist lines on product wafers at this level was monitored and correlated with both the total and diffuse reflectivity as measured on control wafers included with the product wafers during Al/Si deposition. Fourteen product lots were monitored over a period of several months. The results show a strong correlation between changes in the diffuse reflectivity and the exposure energy. An increase of 64% in the diffuse reflectivity of the Al/Si film is accompanied by an increase of 80% in the exposure energy required to produce 2.0 m lines in positive resist. For these same lots, the total reflectivity varies by less than ±3%, usually taken as an indication of good process control at metal deposition, with no apparent correlation to the exposure energy. Several different resist processes were investigated to control the effects of changes in the diffuse reflectivity. The most promising of these has been a new dyed photoresist developed at Sandia. The unbleachable dye has been selected for optimal performance at the exposure and alignment wavelengths used in the Ultratech stepper. The diffuse reflectivity of Al/Si films coated with dyed resist is diminished by a factor of eight over the reflectivity of films coated with our standard resist. The total reflectivity is diminished by a factor of five.
Processing Photostructural Materials
David J. Rosenblatt, Jay N. Zemel, Wayne E . Feely
Results are presented on a resin system that can be crosslinked to yield 3D negative images that are thermally stable to temperatures greater than 300°C. The conditions needed to process films up to 1511m thick were studied. To produce microstructures in these thick films the exposure intensity must be controlled to allow adequate time for nitrogen gas, released by the diazoquinone sensitizer, to diffuse from the image region before super-saturation levels nucleate bubble defects.
Computer Simulation Of The Percolational Development And Pattern Formation In Pulsed Laser Exposed Positive Photoresists
A. L. Bogdanov, A. A. Polyakov, K. A. Valiev, et al.
The exposure of positive photoresists like AZ-2400 and AZ-2415 with pulsed excimer XeCl laser (λ= 308 nm) results in a thresholdlike growth of sensitivity and contrast of the resists [1]. The effect appears when pulse energy density W is in interval 3.106 - 5.106W/cm2, which is little lower than the ablation threshold of the resists - W = 5.10 W/cm2. We called exposure in this interval of W as preablation mode of exposure.
Enhancement Of Rie Resistance Of Conventional Resist Materials
H. Hiraoka
With the increasing use of dry processes for etching silicon, silicon dioxide, aluminum, and other materials, the enhancement of etch resistance of resist images in such severe dry processing conditions becomes an important issue. This is particularly so in cases where both high resist sensitivity and high reactive ion etch (RIE) resistance are required. This paper describes the enhancement of RIE resistance of conventional resists by incorporating aluminum, magnesium or silicon into resist images. The process has been carried out in vapor phase and/or in liquid phase. In some cases, resist solutions were mixed with certain organometallic materials to give wet developable resist films which exhibit enhanced resistance without any further processing.
Applications Of The Mold Controlled Profile (MCP) Technique For Resist Processing
Burn J. Lin
The Mold Controlled Profile (MCP) technique consists of coating a layer of immiscible polymer over a prepatterned resist image. This structure can be heated to an extremely high temperature without lateral distortion of the original resist profile, while the patterned resist undergoes significant chemical changes. After removal of the mold, the resultant image can be used in many areas of application. Here, the hardening aspect and the compensation of interfacial layer in the capped deep-uv Portable Conformable Masking (PCM) system are given to demonstrate the advantages of the MCP technique and to stimulate other new applications.
Spin Coating And Planarization
Larry E. Stillwagon, Ronald G. Larson, Gary N. Taylor
This paper reports the results of a study of topographic substrate planarization with films applied by a spin-coating process. We show that spin coating produces conformal film profiles over gaps on the substrate with widths greater than about 50 pm and that filling of these gaps can only occur after spinning has ceased provided the film is able to flow over large distances. A comparison of the major forces acting on the film leads to the conclusion that the flow is driven primarily by capillary forces when the width of the gap is less than 5000 μm. A theory is developed that relates the time required to fill the gaps to their width and to the thickness and viscosity of the film. The results of experiments performed to test the theory are presented and discussed.
New Principle For Image Enhancement In Single Layer Positive Photoresists
P. Trefonas III, B. K. Daniels
Positive photoresists containing a dissolution inhibitor as the photoactive compound (PAC) are potentially high resolution materials. For the case of PAC materials with two or more diazonaphthoquinone (DAQ) groups attached to the same ballast molecule (a poly-DAQ PAC), the DAQ groups can photolyze essentially independently in a sequential manner to form a distribution of photoproducts containing both DAQ groups and indene-carboxylic acid groups (ICA) bonded to the ballast molecule, and ultimately, a poly-ICA photoproduct. Equations are deduced for the concentrations of these photoproducts with dose. Dissolution rate is taken to be a function of the relative contributions of each photoproduct to the dissolution rate. These equations show that poly-DAQ PACs can enhance resolution, with maximum resolution occurring in the specific case of ideal selectivity: when the poly-ICA photoproduct has a large contribution to the dissolution rate and the intermediate photoproducts have a negligible contribution to the dissolution rate. This process we call "Polyphotolysis"*. The difficulty in approaching ideal selectivity is discussed in terms of dissolution rates required to maintain photospeed. Polyphotolysis is experimentally demonstrated for a resist with ideal selectivity. Analytical expressions for approximate treatment of gamma, E0 and absorption are,given as a function of PAC functionality. SAMPLE has been modified to include these basic equations and model profiles are generated. These profiles are compared with experimental patterned resists in which the number of DAQ groups per ballast molecule have been varied between 1 and 6.
Sub-Halfmicron Negative Resist Systems By Image Reversal
K. Chiong, H. Hiraoka
There has been a rising interest in image reversal of positive working resists. For optical and X-Ray applications, one practical advantage of image reversal is the elimination of the need of two sets of complementary masks to do positive and negative imaging. For direct write serial lithography such as electron beam and ion beam lithography, there is a great saving on writing time if the unexposed areas are much larger than the exposed areas. In this paper, we report the conversion of an e-beam generated positive pattern to a negative pattern by an image reversal technique which employs the filling of the positive trenches with silicon containing materials. The surface of the planarized positive images is etched back in CF, RIE to reveal the resist surface. A subsequent 02 RIE image transfer step completes the reversal process. The vertical sidewall angles of the positive images have a strong influence over the resulting linewidths of the reversed images. Negative images of excellent linewidth control are obtained using this technique unlike most negative resists which swell during development. This technique allows one to achieve a negative resist pattern which keeps the resolution and the linewidth control of the original positive resist system. The effects of the sidewall slopes of the positive images on linewidth variation of the resulting negative images are discussed. The choice of the planarizing materials to provide good planarization over various sizes of topography and the RIE etchback uniformity will also be described.
A Practical Approach To Submicron Lithography
Vic Marriott, Cesar M. Garza, Mark Spak
This paper will describe the characterization and optimization of a high resolution image reversal process using dissolution rate data and the development simulation computer program, PROSIM, and compare the results with experimental data. AZ®5214 E photoresist was chosen for its simplicity of processing in negative tone and the potential to print submicron lines and spaces with good latitude using a 0.35 NA I-line stepper. This resist is unique in the sense that the image reversal process is thermally induced after exposure and requires no pre- or post-exposure chemical treatment. Without the post-exposure bake this resist is positive working, and in either tone is developed with standard aqueous alkali developers. The key variables in the optimization are the temperature of post-exposure bake, the concentration of developer, type of developer, and the time of development. The driving force in the optimization was to achieve a high resolution process with good contrast and process latitude. Development rate data and the development simulation computer program, PROSIM, were used to assist in determining the process conditions with the best contrast and broadest process latitude. Using a process which included a flood exposure after the post-exposure bake it is possible to use a 110°C to 120°C post-exposure bake and developer concentration of 0.21N TMAH. Such a process produced the best resolution with excellent side wall profiles and wider process latitude, but with some sacrifice of photospeed. Also the effect of defocus was examined near the limits of resolution and superior latitude to a comparable positive tone system was found. Thin film interference effects were examined for their impact on linewidth control and process consistency and image reversal was found to suppress linewidth variation as compared to conventional positive tone resists. The AZ 5214 E in image reversal is sensitive over a broad spectrum of exposure energy. Data for image reversed patterns produced from g-line steppers and from a 248 nm excimer laser will be presented.
A Practical Approach To Lift-Off
Susan K. Jones, Richard C. Chapman, Edward K. Pavelchek
Lift-off technology provides an alternate metal patterning technology to that of subtractive etching. In this raper, we describe an image reversal process which provides a practical means for reliably producing resist stencils which are required for successful lift-off in a 2.0 μm metal pitch CMOS process, as well as for experimental submicron processing. Experimental data and PROSIM simulations are presented to show the effects of patterning exposure dose, flood exposure dose, develop time, and focus parameters on resist linewidths as well as for control of resist retrograde (undercut) sidewall angles. Deposition and subsequent lift-off of Al/Cu alloys and sandwich metallizations is demonstrated. Because the image reversal process enables pattern definition at the top of the resist film, it is demonstrated that thicker resist films can be used to produce finer resolution of lift-off stencils over topography than would have been expected without resorting to multilayer resist structures.
Application Of Halogenated Polymethylstyrenes To X-Ray Resists
Tsuguo Yamaoka, Mitsunobu Koshiba, Yoichi Kamoshida, et al.
A series of chlorinated polymethylstyrenes (CPMSs) and brominated polymethylstyrenes (BPMSs) were synthesized by anionic polymerization of methylstyrene followed by radical halogenation. Radiation chemistry of CPMSs and BPMSs were investigated using RhLa X-rays as a radiation source. Resist sensitivity of CPMSs and BPMSs increases with increases in molecular weight and halogen content up to 90 unit% of halogenation. In addition, CPMSs have higher sensitivity than BPMSs toward RhLa X-rays. Infrared spectroscopic studies of radiation induced chemical reactions of the polymers showed that X-ray radiation caused the dissociation of C-X (Cl or Br) bonds and that the dissociation was much faster for CPMSs than BPMSs in spite of lower mass absorption coefficients of CPMSs. CPMS-5 (Mw=49x104, Cl cont.=92 unit%) exhibits the highest sensitivity of 15 mJ/cm2 (Dg) while maintaining high contrast value of 1.3. The patterning tests of CPMS-5 were done with a MICRONIX MX-15 which had a palladium source. As a result, 0.6 μm resist patterns were obtained despite its penumbral blurring being 0.35 μm. It is confirmed that CPMS-5 is one of the best X-ray resists from a practical point of view.
Lithographic Evaluation Of Copolymers With Enhanced Dry Etch Resistance
Y. M.N. Namaste, S. K. Obendorf, J. M. Rosenblum, et al.
Alternating copolymers of alphamethylstyrene (AMS) with maleic anhydride (MA) and methyl maleate (MeM) are evaluated as positive electron resists. The chain scission efficiency (Gs) of P(AMS-MA), determined by exposure to 50 keV electrons, is 0.90 scissions/100 eV. When the maleic anhydride in the copolymer is reacted with sodium methoxide to form its methyl ester, P(AMS-MeM), the Gs increases to 2.9 for electrons and to 3.5 for gamma radiation. Based on these G-scission values, this copolymer is expected to exhibit enhanced sensitivity, while having good dry etch resistance due to the aromatic nature of alphamethylstyrene. Lithographically, P(AMS-MeM) is more sensitive than P(AMS-MA), as expected from G-scission data. Film properties such as adhesion are also superior for P(AMS-MeM). Using a one hour prebake at 140°C, 10% thinning of unexposed P(AMS-MeM) occurs upon development of pads exposed to an incident electron dose of 8 jC/cm2 (accelerating voltage = 20 kV). The contrast (1) is 2.0 for development of 12 iiC/cm exposur2es. In comparison, P(AMS-MA) exhibited 10% thinning for an incident dose of 40 pC/cm, which is similar to observations with PMMA. The copolymers are developed with mixtures of ethyl 3-ethoxypropionate and 1-methoxy-2-propanol acetate. The dry etch rate of P(AMS-MA) in CFI.' plasma with 8% 02 varies from 45 to 53% of the etch rate of a PMMA standard. The etch rate of P(AMS-MeM) after a 140°C prebake is about 65% that of PMMA. Thus, much of the etch resistance of alphamethylstyrene is maintained in copolymers with maleic anhydride or methyl maleate, while the copolymer with methyl maleate also exhibits significantly enhanced sensitivity.
High Resolution Positive E-Beam Resist With Dry Etch Durability
Akira Akimoto, Toru Seita, Yoshitaka Tsutsumi
Electron beam exposure characteristics,such as sensitivity and contrast,and durability against oxygen plasma were measured with poly(1-pheny1-2.2.2-trifluoroethyl-α-chloro-acrylate) PCLTF prepared by solution free radical polymerization. New developers were examined for this type of polymer. Using mixtures of diisobutyl ketone DIBK and isopropyl alcohol IPA (35:65),PCLTF was preciously imaged at 25pc/cm2(0.5μm lines and spaces). Moreover with use of suitable mixture of diisopropyl ketone DIPK and isopropyl alcohol (35:65),the image at 8pc/cm2(1μm lines & spaces) is also possible. PCLTF was 1.5 times the high dry etching durability of PMMA against oxygen plasma,and showed considerably high contrast and fine gaps as narrow as 0.2μm.
Development Induction Mechanism In Novolak Based Resist Systems For Submicron Optical Lithography
Medhat A. Toukhy
Novolaks are phenolic polymers prepared by the condensation of phenols or substituted phenols with aldehydes in acidic reaction medium. Because of their many favorable characteristics, novolaks are the polymer most widely used in commercial positive photoresists. The non-swelling aqueous alkali solubility behavior of novolaks is a key property required to produce high resolution resist images. Novolak dissolution rates and development induction can be altered by changes made in their chemical composition, structure and molecular weight. The relationship of some novolak chemical compositions and their aqueous alkali solubility behavior is discussed in this paper. Positive photoresist solutions formulated with relatively high dissolution rate novolaks resolved submicron images with unique profiles, provided higher photosensitivities and plasma etch resistance than lower dissolution rate systems. Although this conclusion was confined to specific cresol novolaks investigated in this work, it is believed that many other novolak compositions show similar correlations. This behavior was attributed to the presence of a protective surface layer or "skin" on top of the resist film. This "skin" was formed during the softbaking of the resist coating and has a sufficiently different dissolution rate than the resist bulk. Detailed DRM studies provided evidence of development induction on the resist surface caused by the "skin". This effect may also be viewed as a surface contrast enhancement effect during the development. Resist systems requiring more aggressive developers due to their lower dissolution rates exhibited total or partial removal of the "skin" or micro peeling in some cases as observed by scanning electron microscopy. The resist thickness and softbaking conditions were found to affect the thickness of the "skin". On the other hand, the removal or preservation of that layer depended largely on the resist composition and the developing process. The exact chemical composition of the "skin" is not known, however, the literature suggests several possibilities. Novolak sensitizer reactions in absence of trace water, novolak oxidation and the changes in resist surface morphology as the solvent is removed are all different mechanisms that can occur during the softbaking of the resist, particu-larly on the surface.
New Pcm (HR-PCM) Technique Using Novolak-Diazide Type Photoresist As A Bottom Layer
Yoshio Yamashita, Hideyuki Jinbo, Ryuji Kawazu, et al.
A new High dry etching Resistivity Portable Conformable Masking, HR-PCM, has been developed. HR-PCM consists of a negative working resist and an image reversal resist as upper and bottom layers, respectivery. LMR-UV (Low Molecular weight Resist for UV lithography) is used as an upper layer and AZ-5214 or MP-2400A (added amine to MP-2400) as a bottom layer. As these resists are of novolak based resin, the dry etching resistivity of HR-PCM is much higher than that of conventional PCM whose bottom layer is PMMA. LMR-UV is a negative working resist and can be coated on the bottom layer and developed without damaging it because both a coating solvent and a developer are of organic solvent having small polarity such as monochlorobenzene. The latent image of the bottom layer formed by the penetrated light through the upper layer is reversed by the post exposure baking. The bottom layer under the exposed upper layer is more resistive to an alkaline. developer than the unexposed one. Therefore, HR-PCM can reliably forms double layer resist patterns. 0.55 and 0.6 μm line and space patterns are obtained on an i- and a g-line wafer steppers, respectively.
Deep Uv And Thermal Hardening Of Novolak Resists
Kevin J. Orvek, Michael L. Dennis
The use of deep UV resist hardening for high temperature resist-masked processes is becoming more widespread throughout the semiconductor industry. In this report we present data on the wavelength and thermal dependence of the deep UV crosslinking process in novolak resin obtained through dissolution studies and SEM micrographs. An excimer laser was used to provide light of differing wavelengths. The results indicate that longer wavelengths near 308 nm promote crosslinking throughout the 1.5 micron thick resin, while shorter wavelengths induce crosslinking to limited depths. Heating of the wafer during the deep UV exposure is shown to greatly accelerate the crosslinking process, compared to a sequential expose and bake process. SEM micrographs of various stages of hardening in resist are shown. The resist hardening process employed by one commercial system is discussed in terms of the findings of this study.
Applications Of Response Surface Methodology: I. A General And Practical Approach To Process Optimization
Daniel J.C. Herr
Response surface methodology is used to model properties of positive photoresist which have been subjected to several operations in a photolithographic process. The impact of these models on process performance and latitude has been investigated and a general approach to process optimization has been proposed: m P[X(1),X(2), . . . 1 = fl F(i) i =0 where P[X(1),X(2), . . .1 represents an overall process optimization function. It measures the overall performance and stability of a process as a func-tion of process variables X(1), X(2), etc. This optimization function is defined as the product of normalized signal-to-noise ratios, F(i), for the set of responses, i, considered. The function F(i) quantifies the ability of a process to achieve the specified response and the sensitivity of the response to perturbations in the process variables. This approach is particularly useful when more than one response must be optimized with a given process. The application of this approach can result in a several-fold increase in process performance and latitude. Examples are presented and discussed.
Resist Contrast Measurements Using A Development Rate Monitor
Nigel R. Farrar
The variation of energy density with depth in electron exposed resists leads to contrast measurements which can depend on film thickness and development time. In this work, two new contrast parameters are defined. One of these is independent of resist thickness and may be used to characterize resist-developer material properties. The other is thickness and process dependent but can be related to feature profile quality. A development rate monitor was used to determine these contrast parameters by simultaneously measuring the dissolution rates from areas of resist exposed at different doses. The doses were chosen to model an isolated unexposed space in the resist, the worst contrast feature in electron beam lithography.
Linewidth Uniformity: A Critical Evaluation Of Spray Geometry And Process Interactions In Ultrasonic Nozzles
David DeBruin, M.Richard Hannifan, Marie Ha, et al.
Spatial linewidth replication is a dominant yield limiting factor for most current photolithography processes, typically consuming,/ 50% of the total linewidth variation allowance. Therefore, the reduction of across wafer variation is critical to successful process development. In this study, the primary factors affecting spatial linewidth replication were investigated. These factors include agitation uniformity, wafer rotation rate, develop temperature control, and photo-optimization. Key results are: 1. Nitrogen assisted ultrasonic spray nozzles produced a spatial linewidth standard deviation of .03 μm, compared to .05 μm for a fan spray nozzle. 2. Developer consumption for ultrasonic spray nozzles is approximately 60% less than for standard fan spray nozzles. 3. Head positioning of ultrasonic nozzles is less critical relative to fan spray nozzles for standard organic and inorganic developers. Head positioning for both ultrasonic and fan spray is critical when using high contrast MIF developers. 4. Rotation speeds of 600 - 1000 rpm were found to be optimal for both ultrasonic and fan spray. 5. Developer temperature controls parallel CD variation trends and can be minimized by use of developer temperature controllers and/or exhaust controllers. 6. Photo-optimization typically produced a 3-fold or greater improvement in linewidth uniformity across the wafer. The effect upon linewidth uniformity is demonstrated in a systematic study of the predominant variables.
Optimized Tri-Layer Resist Technique For Volume Production
E. Kawamura, J. Konno, K. Inayoshi, et al.
Tri-layer resist technique has been developed for volume production of VLIs to achieve 0.8 μm line and space pattern using an NA 0.35 stepper. The 0.8 μm feature process was done mostly by optimizing normality of developer for top-layer resist. Patterned resolution dep-ends strongly on normality of the developer. The lower normality gives much wider latitude to CD control. Possibility of application of tri-layer resist process whose structure consists of top-layer resist, middle-layer silicone resine, and underlayer resist was examined.
Negative-Acting Aqueous Base-Developable Photoresist With Submicron Resolution Capabilities Over Topography
John J. Grunwald, William F. Cordes III, Giora Ben-Shushan, et al.
A family of negative-acting "image reversal" photoresists identified as the MacDermid XNR 2000 series is characterized here in some detail. Although its photoresist chemistry is based on the conventional positive resist concept using cresol Novolak resins together with a somewhat novel 2-1-4 naphthoquinone-diazo-oxide-ester, the conversion of the resist to the negative mode is primarily based on the addition of a new generation of thermal crosslinking agents to a typical positive resist formulation. The processing cycle evolved for this series consists of: (a) spin-coat, (b) soft-bake, (c) UV expose,(d) post-exposure-bake (PEB), and then (e) develop with either metal-ion containing or metal-ion-free developer(s) in either immersion or in-line mode(s).
Dynalith ® Resists For Mid-Uv Applications: * Formulation Optimization For Gaas Related Processing
Richard M. Lazarus, Sunit S. Dixit
Recent advances in optical lithography driven by the use of mid-UV radiation (365/313 nm) require resists optimized to operate effectively at these wavelengths. New positive resist formulations have been developed to meet this need. DYNALITH resists X-1608 and X-1605 display enhanced sensitivity toward mid-UV exposure. Comparison data vs. standard and deep UV resists are presented. A variety of exposure modes, including projection and contact, have been investigated. DYNALITH Positive Resist X-1608 is based on a novolac and 2,1,4 quinone diazides which are optimized for resist performance. This new resist la.s sensitivity which is improved over standard resists in mid-UV exposures. Sensitivity of 30-70 mJ/cm is demonstrated at 313 nm and 365 nm. X-1608 mid-UV resist demonstrates submicron imaging capability with high contrast and wide process windows. DYNALITH Positive Resist X-1605 is based on a novolac and the more standard 2,1,5 quinone diazide. This resist formulation provides an overhung or reentrant sidewall profile with the use of standard processing steps. The absence of the necessity of a chlorobenzene soak coupled with the appearance of sidewall profiles as displayed indicates the X-1605 resist to have application for metal lift off processing. The suitability of consistent resist sidewall profiles for metal lift off provides an application for X-1605 resist in GaAs lithography. A control of the degree of curvature and overhang displayed by the resist profiles relative to formulation is described. Process stability of soft bake and exposure is presented for DYNALITH X-1608 on mid-UV projection aligners. Dry etch data relating resists X-1608 and X-1605 to standard resists is presented. Statistical process control (SPC) is an important control method as production requirements shrink to the one micron regime. The use of process control (X) and range charts (R) generated for coating DYNALITH X-1608 resist is presented. SEM photos characterizing the resists and certain process latitudes are presented. Analytical techniques, such as GPC and C13 NMR, assisted the characterization of structure/performance relationships.
An Improved Technique For 1/4 Micrometer Gate Length Gaas Mesfet Fabrication By Optical Lithography
Brad D. Cantos, Ronald D. Remba
This paper describes an innovative photolithographic method for the fabrication of 1/4 micrometer gates in gallium arsenide Metal-Semiconductor Field Effect Transistors (GaAs MESFETs). The method utilizes image reversal technology, in which negative polarity images are produced in positive diazide photoresists. This work describes improvements obtained using ammonia as the image reversal catalyst over work previously described which used imidazole [1]. The ammonia based image reversal process is characterized with respect to sensitivity to several process parameters and uniformity of the resultant linewidth. The linewidth uniformity attained using this process is ± 0.03 micrometer over a 50 mm diameter wafer and is currently used to fabricate 1/4 micrometer gate MESFETs on gallium arsenide.
Oxygen Reactive Ion Etching For Multilevel Lithography
Mark A. Hartney, Wayne M. Greene, Dennis W. Hess, et al.
Oxygen plasmas used for pattern transfer in multilevel lithography have been characterized over a range of plasma parameters such as power and pressure. Etch rates of silicon dioxide and representative silicon-containing and planarizing polymers are correlated with these plasma parameters. Plasma diagnostic measurements include DC self-bias voltage, ion flux and incident ion energy distributions. Measurement of ion energy distributions yields fundamental information about the etching process since Si02 sputter rates and oxygen ion implant depths are strong functions of ion energy.
High Resolution Positive Photoresist For Submicron Photolithography
Hidekatsu Kohara, Hatsuyuki Tanaka, Masanori Miyabe, et al.
Optical lithography is achieving itself into submicron region. In the limitation of resolution for stepper there is a decrease in contrast and so it requires more exposure amount than that of D. Also it is not possible to achieve faithful transcription of fine pattern dimension. The resolution of TSMR-8800 which is developed as high resolution positive photoresist is 0.6 μm. Faithful transcription of the mask pattern is possible for 0.7 μm line and space pattern. It shows good properties compared with conventional photoresist.