In photolithography, air bubbles on the surface of a photoresist have been found to produce defects characterized by significant underexposure and geometry-dependent pattern distortion. The polymers with tertiary butyl groups, widely used for chemically amplified photoresists, release the volatile byproduct, isobutene, by acid-catalyzed deprotection reaction and produced air bubbles.
A novel monomer for low-outgassing resist was synthesized. Tertiary caprolactone group was synthesized from camphor by Baeyer-Villiger oxidation. Tertiary caprolactone group was cleaved and the carboxylic acid functionality was formed by acid-catalyzed ring-opening reaction in the exposure region after post-exposure bake. This group do not produce volatile byproducts during the deprotection reaction.