Process optimization of a negative-tone CVD photoresist for 193-nm lithography applications

New photoresists and processes are required for sub 0.15 micrometers design rules and currently an important effort is on- going for single layer resists optimization at 193 nm. Top surface imaging can be an interesting alternative approach. An all dry chemical vapor deposition (CVD) process based on plasma polymerized methylsilane (PPMS) or plasma polymerized dimethylsilane (PP2MS) provides a thin conformal and photosensitive layer at 193 nm. A thin amorphous film of Si- Si bonded material is deposited using plasma enhanced chemical vapor deposition with methylsilane or dimethylsilane as the gas precursor. Upon 193 nm exposure under air, photo-induced oxidation of the CVD resist occurs, generating a latent image. The image is then developed in a chlorine-based plasma, providing a negative tone process. This mask can be used to pattern a thick organic underlayer to provide a general bilevel process. Lithographic results on both a 193 microstepper as well as a full field production stepper are presented: resolution down to 0.10 micrometers equal L/S was obtained. A preliminary comparison between PPMS and PP2MS materials is presented, including FTIR results, stability of the films in air and lithographic performance including line edge roughness.