Characterization of TFE/norbornene-based fluoropolymer resist for 157-nm lithography

Fluoropolymers are key materials in the single-layer resists used in 157-nm lithography. We have been studying fluoropolymers to determine their potential use as base resins. These polymers are main-chain fluorinated polymers synthesized by co-polymerizing tetrafluoroethylene (TFE) and functional norbornene. We developed a new polymer that is highly transparent and has high dry-etching resistance by attaching a PG-F protecting group, which has high dry-etching resistance, to a TFE/norbornene-based fluorinated polymer. The dry-etching rate for the 15 % blocked polymer was 1.50 times that of a KrF resist and its absorption coefficient at a 157-nm-exposure wavelength was 1.06 /μm. We introduced various photoacid generators (PAGs) to the polymer, and compared lithographic performance. As a result, we found polymer with a triphenylsulfonium-salts-based PAG had a good pattern profile, and polymer with a high-acidity PAG resolved a fine pattern. In particular, polymer with a triphenylsulfonium perfluorooctane sulfonate PAG was able to resolve a 60-nm line and space pattern. We then added various quenchers to the polymer and the PAG, and compared pattern profiles. We found that the use of a high-basicity quencher improved the resolution of the resist and line edge roughness. Consequently, that the polymer with the triphenylsulfonium perfluorooctane sulfonate PAG and tributylamine quencher could resolve a 55-nm line and space pattern. These results provided guidelines for choosing the PAG and quencher for this polymer.