Modeling photoacid diffusion in chemically amplified resists via proximity effect correction in electron beam lithography

Chemically Amplified Resists (CARs) are widely used in semiconductor patterning due to their high sensitivity but controlling acid diffusion during the post-exposure bake process remains a challenge, as it can cause pattern blurring and reduced resolution. This study models and investigates acid diffusion by employing mid-range correction factors to traditional Proximity Effect Correction (PEC) in Electron-Beam Lithography (EBL). SU-8, a negative-tone photoresist with high mechanical robustness, is chosen as a model system to examine acid diffusion challenges. Traditional PEC methods incorporating long- and short-range correction factors are first applied to mitigate electron scattering effects. A systematic set of nanoscale line-space patterns with varying densities is then fabricated using EBL, wherein exposure dose and density dependency of the Critical Dimension (CD) are further analyzed to revise PEC model using empirical mid-range correction factors. The modified PEC model is adapted for accounting not only the proximity effects caused by electron exposure but also the photoacid (H⁺) diffusion within SU-8 matrix for improving the resolution and CD Uniformity (CDU) of high-resolution patterning. Comparative patterning experiments and Z-factor calculations validate this model’s effectiveness and evaluate different mid-range correction factors. Furthermore, we extend this approach to study the impact of base additives in SU-8, demonstrating its potential as a general method for understanding the effects of various additives in CARs for advanced lithographic patterning applications.