Delay-time effects between exposure and post-exposure bake in acetal-based deep-UV photoresists

摘要

This paper presents some methods for the investigation of delay time I$-3$/ induced effects typical of an advanced acetal-based photoresist, and strategies to improve the latent image stability. Dissolution rate monitoring was used to investigate the increasing formation of a surface inhibition layer with extended intervals I$-3$/. The impact of certain additives, the application of a protective coating (AZ$+R$/ Aquatar), and modified process conditions on the inhibition layer were studied in detail. The photoacid induced acetal cleavage was monitored by UV-spectroscopy (248 nm). Upon KrF excimer laser irradiation the resist absorbance increases, due to the progressing formation of a strongly absorbing aldehyde fragment. SEM pictures confirm a linear relationship between the efficiency of the acetal cleavage and acid diffusion into unexposed resist areas. Acid evaporation during PEB was determined by a novel method, the so-called Sandwich `Blue' Test. Interpretations of the experimental results and some optimization strategies are given.