Alicyclic polymers for chemically amplified resists

Abstract

Chemically amplified resists (CARs) with KrF excimer laser lithography are the most promising technologies for sub-micron patterns because of their high transparency and sensitivity. However, while the resolution of CAR has advanced to better than 0.5㎛, there still remain some problems. One of the most serious problems is the deterioration of CAR performance due to airborne contamination. The basic contaminants such as ammonia and 1-methyl-2-pyrrolidinone in the air can neutralize the surface acid in the exposed area of the photoresist during post-exposure delay (PED) between the exposure and the post-exposure bake steps, and cause T-shaped profiles and skin insoluble layer. Another PED effect is acid diffusion into the unexposed area which can cause resist linewidth and profile changes. Special methods such as overcoats, chemical filters and stabilizing additives have been used in order to reduce the PED. However, the best way to solve the problem would be to prepare a new resist system that is resistant to those effects. In this study, chemically amplified resists containing a basic monomer, 3-(t-butoxycarbonyl)-1-vinyl-2-caprolactam, in the matrix polymer were prepared for PED stability. Poly(t-butyl methacrylate-co-3-(t-butoxycarbonyl)-1-vinyl caprolactam) and poly(isobornyl methacrylate-co-3-(t-butoxycarbonyl)-1-vinyl caprolactam) were synthesized and evaluated as matrix resins. These polymers have low absorbance in deep UV region and good thermal stability up to 200℃. The diffusion lengths of photo-generated acid in the resist films were studied for various fractions of the basic monomer in the copolymers. The results show the copolymer with a basic monomer can control the acid diffusion without a severe decrease in sensitivity. This new resist system enables us to form sub-micron patterns and attain 2 h PED stability without any additional treatment.