Preparation of acid-cleavable branched polymers for argon fluoride photoresists via reversible addition-fragmentation chain-transfer polymerization

摘要

A series of branched polymers for chemically amplified resists (CARs) were prepared through the reversible addition-fragmentation chain-transfer (RAFT) copolymerization of three monomers with lithographic functionalities and an acid-cleavable dimethacrylate monomer. The three monomers with lithographic functionalities were 2-ethyl-2-adamantyl methacrylate, α-γ- butyrolactone methacrylate, and 3-hydroxy-1-adamantyl methacrylate. The acid-cleavable monomer was 2,5-dimethyl-2,5-hexanediol dimethacrylate (DMHDMA), and 2-cyanoprop-2-yl-1-dithionaphthalate was used as a chain-transfer agent. Because DMHDMA contains two methacrylate groups, it induced the branched structures of the polymers. The degree of branching could be controlled by the molar fraction of DMHDMA in the monomer mixtures. The size and structure of the polymers obtained after hydrolysis were very close to those of linear polymers prepared by RAFT copolymerization with the same amount of reagents, only without the acid-cleavable monomer. A preliminary lithography test using an argon fluoride source demonstrated that the acid-cleavable branched polymers could be promising candidates for CAR materials.