Akiko Katsuyama

Design Concepts of Single-Layer Resists for Vacuum Ultraviolet Lithography

We investigated the possible use of single-layer resists in vacuum ultraviolet (VUV) lithography. The transmittances in the VUV region of commonly used polymers for photoresists were almost the same. These values were about 20% at 157 nm per 1000 ?-thickness at most. The transmittance at 157 nm of a poly (p-hydroxystyrene) (PHS)-type polymer was slightly increased by halogenation of the aromatic group. Negative working behavior was observed for PHS-type resists. It is thought that both crosslinking and deprotection occurred in PHS-type polymers. A methacrylate-type resist showed high contrast due to the photodecomposition of the base polymer and photo-deprotection in addition to acidic deprotection. It was estimated that the resolution capability of this resist was 80 nm lines and spaces (L/S) (?157 nm, NA 0.65) using a PROLITH/3D lithography simulator with experimental dissolution data.

Overlay Accuracy Measurement Technique Using the Latent Image on a Chemically Amplified Resist

An overlay accuracy measurement technique has been devised using the latent image on a chemically amplified resist developed in-house. A latent image with step height of over 0.1 µ m was formed after KrF excimer laser irradiation. It has been confirmed that it is possible to measure overlay accuracy using this latent image with measurement accuracy within 10 nm. This technique is very useful for overlay accuracy measurement of an exposure system using a double exposure method with a chemically amplified resist. It has been verified that heterodyne holographic wafer alignment (HHWA) has the capability to detect a latent image with shallow step height. Overlay accuracy within 60 nm was obtained using overlay error correction with this developed overlay accuracy measurement technique.

Approach for VUV positive resists using photodecomposable polymers

We investigated characteristics of resists consisting of well- known resist polymers by the F2 excimer laser exposure. Negative-resist behavior due to crosslinking or decarboxylation was observed for poly(p-hydroxystyrene) based resists, polysilsesquioxane based resists and polynorbornenecarboxylate based resists. On the other hand, polymethacrylate based resists indicated a clear positive- resist behavior with high contrast without crosslinking. Therefore we studied further details of the characteristics of resists consisting of photodecomposable polymers such as methacrylate polymers and found methacrylate polymers bearing alicyclic groups to be resist with high dissolution contrast and little outgassing. The 200 nm L/S pattern with vertical profile at 1000 angstrom thickness was obtained by F2 excimer laser contact exposure in spite of poor transmittance of 30% per 1000 angstrom thickness. It was showed that the resolution by a 157 nm scanner with the lens of NA0.7/(sigma) 0.7 was 70 nm L/S and 40 nm iso-line at 1000 angstrom thickness by PROLITH/3D lithography simulator using experimental parameters.

Application of a New Adhesion Promoter to Stable Chemically Amplified Resist Pattern Fabrication on Boron Phosphorus Silicate Glass Substrates

We have developed a new, non-ammonia generating adhesion promoter, 4-trimethylsiloxy-3-pentene-2-one. Its adhesion ability to a substrate is superior to the conventional adhesion promoter, hexamethyldisilazane, due to its high reactivity. We obtained high-aspect-ratio and precise chemically amplified resist patterns on boron phosphorus silicate glass (BPSG) substrates using this new adhesion promoter.

Stable process for chemically amplified resists using a new adhesion promotor

We have developed a stable process for chemically amplified resists against the airborne contamination using a new adhesion promoter. The new adhesion promoter does not produce ammonia when it decomposes and its trimethylsilyl group adheres to a substrate. We have applied this new adhesion promoter to KrF excimer laser lithography. The excellent 0.30 micrometer pattern profiles were achieved without skin-layer or T-top profiles after leaving the exposed wafer in the atmosphere of the new adhesion promoter for 15 minutes before PEB. We also found that the adhesion strength of the new adhesion promoter to a substrate is as good as the conventional adhesion promotor and obtained large depth of focus latitude using the new adhesion promoter.

New chemically amplified positive resist for electron beam lithography

A novel chemically amplified positive resist with high sensitivity for electron beam (EB) direct‐writing lithography has been developed for deep submicron pattern fabrication. This positive EB resist consists of a tert‐butoxycarbonyl group‐protected poly (p‐vinylphenol) type matrix polymer installing cyano group and a metal‐free photoacid generator (PAG). The matrix polymer is insoluble in aqueous alkaline solutions. The acid‐catalyzed deprotection of matrix polymer results in poly (p‐vinylphenol), which can be easily dissolved in an aqueous alkaline solution. Three types of monomers, which can generate an acid by EB irradiation, are investigated as PAG in this resist system. Resist pattern profile is dependent on PAG characteristics, and the profile could be tapered in spite of the high contrast. It is found that ketosulfone‐type PAG is one of the most effective catalysts for this resist system. High resist sensitivity below 1.5 μC/cm2 at 20 keV is obtained after postexposure bake at 90 °C. Reverse taper...

Design concepts of single-layer-resists for VUV lithography

We have studied the design of single-layer-resists for VUV lithography. From the point of view of transparency, phenol resins may be used as well as methacrylate polymers in VUV lithography. The resulting high contrast is thought due to the effect of direct photodecomposition of base polymer and photo-deprotection in addition to the deprotection by acids. We are planning to investigate the polymers with higher transparency (ex. halogen-substituted phenol resins) and the polymer structure inhibiting the crosslinking.

Advanced Thermal Improvement Method for Chemically Amplified Resists.

We have developed a new method to achieve both, thermal durability and critical dimension (CD) control using short-duration, deep UV irradiation for chemically amplified resists at moderate irradiation intensity and moderate substrate temperature. We obtained thermal durability up to 140° C and CD control within ±5% between as-developed resists and those obtained after baking at 140° C.