Lithographic Effects of Acid Diffusion in Chemically Amplified Resists

Abstract

Chemically amplified resists are based on the generation of acid during exposure to light, followed by an acid catalyzed reaction during a post-exposure bake which changes the solubility of the photoresist in developer. Acid generation is typically assumed to follow standard first order kinetics. However, polymer or dye absorption followed by electron transfer or fluorescent exposure of the photoacid generator (PAG) will also be examined. Amplification will be modeled as a reaction of the acid with the polymer, first order in polymer reactive sites and of arbitrary order in acid. Another important mechanism to consider is acid loss. There are four common pathways for acid loss: atmospheric base contamination, evaporation of acid from the top of the film, neutralization of the acid at the substrate, and bulk acid quenching. All four mechanisms will be treated in this work. The effects of acid diffusion will be investigated by providing a full solution to the reaction-diffusion system of equations for the kinetics of chemically amplified resists. This reaction-diffusion model will include the possibility of a reaction dependent acid diffusivity.