Relationship between Remaining Solvent and Acid Diffusion in Chemically Amplified Deep Ultraviolet Resists

Abstract

For clarification of the diffusion path of photogenerated acid in the resist film, the prebake temperature dependence and tert-butoxycarbonyl ( t-BOC) blocking level dependence on acid diffusion were investigated for chemically amplified deep ultraviolet (DUV) positive resists. The resists consisted of a t-BOC protected polystyrene base resin and a 2,4-dimethylbenzenesulfonic acid derivative as a photoacid generator (PAG). The concentration of remaining solvent in the resist film decreased as the prebake temperature or t-BOC blocking level increased. The acid diffusion coefficient was almost independent of exposure dose; however, it decreased with increasing prebake temperature or blocking level. Therefore, it was considered that the concentration of remaining solvent in the resist film corresponds to one of the acid diffusion paths. Moreover, hydrophilic OH sites, whose concentration was the reciprocal of the blocking level, were also considered to correspond to a diffusion path in the polymer matrix, based on the fact that the acid diffusion length increased gradually with decreasing t-BOC blocking level, even when the solvent concentration remained constant. Based on the experimental analysis results, the existence of two diffusion paths, as well as of explicit relationships among the remaining solvent, t-BOC blocking level and acid diffusion length was confirmed.