Molecular level simulation of the free volume effect on acid transport

Chemically amplified photoresists are highly sensitive because the product of a single photolysis can catalyze many of the deprotection reactions that change the solubility of the resist film. In deep-ultraviolet (DUV) resists, mass transport of photogenerated acid during the post exposure bake allows a single acid molecule to catalyze several deprotection reactions. However, lateral transport of acid into unexposed regions of the resist can complicate control over the critical dimension of printed features. An understanding of the factors that contribute to acid mobility would allow resist manufacturers to tailor resist transport properties to their needs: however, the exact mechanism of acid transport still remains poorly understood. In this paper the efect of the lifetime of excess free volume upon resist performance has been studied with a molecular scale model.