Masayuki Endo

Resist interaction in 193-/157-nm immersion lithography

We have investigated the interaction of resists with water and perfluoropolyether (PFPE) as immersion fluids. We found that some unique behaviors occurred in immersion lithography. An acetal protected poly(p-hydroxystyrene) type resist in water immersion showed decreased resist thickness after exposure. The deprotection reaction during exposure appeared to be accelerated by water. A COMA (cycloolefine-mareic anhydride alt-copolymer) type resist in water immersion showed an increased dissolution rate. FT-IR measurements indicated that the hydrolysis of maleic anhydride occurred during exposure and post-exposure baking. A reduction in the dissolution rate was observed in the immersion lithography of most resists. In water immersion, the formation of a surface insoluble layer and swelling was observed. We confirmed that a photochemical acid generator (PAG) or generated acid eluted into the water by TOF-SIMS. In PFPE immersion, we think that PFPE penetrating across the resist film blocks the penetration of the alkaline aqueous developer.

Dry etching resistance of methacrylate polymers for ArF excimer laser lithography

We have investigated dry-etching resistance of methacrylate polymers for use as ArF chemically amplified resists and proposed a new etching model that can predict the etching rate very accurately. The examined polymers were methacrylate polymers with alicyclic groups. The polymers were dry etched using a LAM TCP-9400 machine under the chlorine-based gas conditions used for poly-silicon etching. The obtained etching rate was explained in term of a carbon- atom-density parameter known as the ohnishi parameter. However, the fitting accuracy is not good enough especially for alicyclic polymers (R equals 0.87). And a ring parameter model also resulted in a similar fitting accuracy (R equals 0.86). Hence, we proposed a new model that introduced polymer-structure dependence into the carbon-atom-density model. The new model gives excellent agreement with measured data (R equals 0.99). And it is very useful in designing ArF resist polymers and predicting etching resistance of future ArF resists.

Half-Micron KrF Excimer Laser Stepper Lithography With New Resist And Water-Soluble Contrast Enhanced Materials

Half-micron patterns have been fabricated using a newly developed high-speed KrF excimer laser stepper system with new resist, NOEL (Novolak based resist for Excimer Laser), and water-soluble contrast enhanced material, WSP-EX.

Analysis of molecular diffusion in resist polymer films simulated by molecular dynamics

The diffusion process of acids plays important roles in chemically amplified resists. Polymer matrices from the diffusion path, and the structure significantly influences the behavior of the acid diffusion. We have simulated the diffusions of molecules in polymer matrices by molecular dynamics in order to analyze the diffusion mechanism in chemically amplified resist syste. To represent bulk state conditions of the polymer film, we prepared the molecular structures under the 3D periodic boundary conditions utilizing the molecular simulation. This amorphous cell contained three chains of methacrylate polymers such as poly(methacrylate), poly(tert-butylmethacrylate), poly(isobornylmethacrylate) and one diffusion molecule such as oxygen and methanesulfonic acid. The structure was energy-minimized and equilibrated under stable conditions. The free volumes in the system were estimated as the volumes enclosed by the iso-potential surfaces around the polymer using the Gusev-Suter method. The average size of the free volumes in the poly(methylmethacrylate) system was obtained as 3.7 angstrom3 with large standard deviation of 11.1 angstrom3, which indicates the large width of the size- distribution of free volumes scattered at random in the system. Molecular diffusion in the energy-minimized cell was simulated for 50 picoseconds by the molecular dynamics. The time dependence of the mean-square displacements of diffusing molecules was obtained from the dynamics treatments and it determined the diffusion constant in the resist systems. It is shown that the molecules do not always rapidly diffuse with larger free volumes, but the diffusions also depend upon the interaction with the polymer, and that the computer simulation tools provide the potentia for the molecular level study of resists chemistry.

Improved Bilayer Resist System Using Contrast-Enhanced Lithography With Water-Soluble Photopolymer

A new water-soluble contract enhanced material, WSP (Water-soluble Photopolymer), has been developed. The WSP is composed of a mainpolymer and a photobleachable reagents. The mainpolymer is a water-soluble polymer mixed with pullulan (refined through biotechnological process) and polyvinyl-pyrolidone (PVP). The photo-bleachable reagent is of a diazonium compound gorup. The introduction of the mainpolymer and photobleach-able reagent mixture has improved filmity, gas transparency, photobleaching characteristics and solubility in alkaline which are essential to the device fabrication. Submicron photoresist patterns are successfully fabricated by a simple sequence of photolithography process. The WSP layer has been applied to the bilayer resist system--deep-UV portable conformable masking (PCM)--that is not affected by VLSIs topography, and is able to fabricate highly accurate pattern. The aqueous developable layer, PMGI, with high organic solvent resistance is used in the bottom layer. Therefore, no interfacial mixing with conventional positive resist top layer is observed. Furthermore, deep-UV exposure method has been used for the KrF excimer laser optical system in order to increase high throughput. From the experiments, it has been confirmed that good resist transfer profile can be realized by the use of WSP, and that the submicron resist patterns with high aspect-ratio can be developed on the nonplaner wafer with steps of up to 41m by the combination of the WSP with the PCM system. By this technology, has been improved the weak point: variation in the line width due to the thickness of contrast-enhanced layer when the CEL technology is applied, and dependency of both the finished resist profile and the line-width accuracy on the thickness of the top layer resist when the PCM system is adopted.

New 157-nm resist platform based on etching model for fluoropolymers

We designed platforms for a 157-nm resist polymer that have both high transparency and high etch resistance. We measured the etching rate of various fluoropolymers under the conditions of poly etch and oxide etch processes. Most of the fluoropolymers showed good correlation with an etching rate ratio and a value of (NC-NO-NF) / NT (NT, NC, NO, and NF was the number of total atoms, carbon, oxygen, and fluorine atom in a monomer unit, respectively). This index, (NC-NO-NF) / NT was named IERF (index for etch resistance of fluoropolymers). It became easy to design a fluoropolymer that has high etch resistance using this index. Moreover, the acrylic polymer that has a particular kind of fluorinated alicyclic compound in its side chain was not in the above-mentioned correlation, however, it was found to have higher etch resistance. Base upon these results, two platforms were built, one of the copolymer type with polyacrylate (PA) and polystyrene (PS), the other of the copolymer type with PA and polycycloolefin (PC). Resists belonging to the two platforms were made and a high resolution of 85 nm or less was obtained by using the Microstepper (NA0.6, (sigma) 0.3, alternating phase shift mask). These resists showed a slightly higher etch resistance as compared with a COMA (cycloolefin-maleic anhydride) type resist with comparatively high etch resistance even during the ArF resist.

Temperature dependence of acid molecular diffusion in resist polymer films simulated by molecular dynamics

The diffusion process of acids plays important roles in chemically amplified resists. Polymer matrices form diffusion paths and the structure significantly influences the behavior of acid diffusion. We have simulated the diffusions of molecules in polymer matrices by molecular dynamics in order to analyze the diffusion mechanism in chemically amplified resist systems. To represent the bulk-state conditions of the polymer film, the molecular structures were prepared under the three-dimensional periodic boundary conditions utilizing the molecular simulation software, Insight II and Discover from Molecular Simulations, Inc. This amorphous cell contained three chains of methacrylate polymers such as poly(methylmethacrylate), PMMA, poly(tert-butylmethacrylate), PtBuMA, poly(isobornylmethacrylate), PIBMA and poly(adamantylmethacrylate), PAdMA and one diffusion molecule, methanesulfonic acid, MSA. The free volumes in the system were also estimated as the volumes enclosed by the isopotential surfaces around the polymer. Molecular diffusion in the energy-minimized cell was simulated for 50 picoseconds by the molecular dynamics to determine the diffusion coefficient in the resist systems. The temperature dependence of the diffusion coefficient was studied. The flexible polymers such as PMMA and PtBuMA showed a lower activation-energy value than the rigid polymers such as PIBMA and PAdMA. It was also shown that the molecules did not always rapidly diffuse with larger free volumes, but the diffusions also depended upon the interaction with the polymer.

Theoretical analysis of line-edge roughness using FFT techniques

Although the line-edge roughness of resist patterns is becoming a serious problem as the size of resist patterns are decreased, quantitative analysis has rarely been seen so far. We investigate the line-edge roughness of ArF resist patterns using the FFT method. We found that all the observed line-edge roughness had a specific FFT spectrum shape composed of a flat area at low frequency and a 1 (root) f component area at high frequency. The amount of line-edge roughness is independent of dose and linewidth but has a strong dependence on defocus. The patterns formed using TSI also have similar FFT spectrum shapes. Based on these findings, we proposed a line-edge roughness simulation method that achieves the observed FFT spectrum.

Process Modeling for Photoresist Development and Design of DLR/sd (Double-Layer Resist by a Single Development) Process

This paper describes a new simple process model for photoresist development. The model includes the consideration of chemical reactions between a photoresist and a developer, and takes the developer concentration dependence into account. The model is applied to the design of practical photo-lithography processes to determine development conditions. Through the introduction of the model-based lithographic simulations, the multilayer resist process has been successfully designed and has obtained satisfactory patterns.

Study of half‐micron photolithography by means of contrast enhanced lithography process

A simple, but efficient, analysis method has been developed to evaluate material properties, process conditions, and effectiveness of contrast enhanced lithography (CEL). The method, realized as a result of the systematic calculation and concept, is based on the evaluation of the energy transmittance of the contrast enhancing material (CEM). In practical applications of the new method to the design and evaluation of both CEM characteristics and half‐micron contrast enhanced photolithography, the method has been proved to be useful in the precise design as it shows good agreement with experimental results. The study has brought us pieces of important information on such design as the optimum exposure conditions, the ideal CEM characteristics, etc. Based on the information, we have developed a new CEM, water soluble photopolymer (WSP) for i and g lines. Through the simulation, it has been confirmed that the ultimate resolution can be improved by 20% to 30%.