A novel electron beam-induced reaction of a sulfonium salt for EB-resist materials

The electron beam (EB)-induced reaction of triphenylsulfonium methanesulfonate (1) in the solid state gave the benzene-substituted product, biphenyldiphenylsulfonium methanesulfonate (2), which has not been observed by either photolysis or EB-induced reaction in a solution. Biphenyl salt 2 was accumulated as an intermediate product at an early stage, and consequently decomposed to diphenylsulfide (3) and three regioisomers of phenylthiobiphenyls (4). A kinetic model of the EB-induced reactions of 1 and 2 revealed that the biphenyl salt 2 exhibited 3.7 times greater kinetic constants for consumption and 6.8 times higher efficiency for acid generation than those of 1. Furthermore, the EB-induced reaction of 1 is comprised of two disparate pathways, one pathway is an unimolecular rearrangement leading to only ortho-isomer of 4 and the other is a bimolecular displacement of phenyl radical leading to 2 and 3. (author)