Synthesis and reactivity of some diaryliodonium salts for photoresist application.

Abstract

Diaryliodonium and triarylsulfonium salts with non-nucleophilic metal halide anions are well known photoinitiators for cationic polymerization as well as photosensitive super acid generators, and play an important role in the chemical amplificated resists. Generally, photosensitizer is required to enhance the spectral response of resists or polymerization systems into the longer wavelength region, due to the low absorptivity of the simple diphenyliodonium salts at above 300nm. In order to circumvent the need for a second component, auxochromic or other groups were incorporated into the iodonium salt molecule which can increase or shift the absorptivity to longer wavelengths. Therefore, a number of new unsymmetrical iodonium salts of general structure(I) were prepared by us by modifying a method already reported. The photoactivity of these iodonium salts were investigated by gel time study. The results indicated that the iodonium salts incorporated with auxochromic groups exhibited higher photoactivity than that of diphenyliodonium salt. The 2-phenylsulfur methhyl 2′, 4′dimethyl diphenyliodonium salt showed the highest activity and an intramolecular electron transfer mechanism was proposed to explain the unexpectedly high activity.