Nonionic photoacid generator behavior under high-energy exposure sources

Abstract

A series of nonionic photoacid generators (PAGs) are synthesized and their acid generation efficiency measured under deep ultraviolet (DUV) and electron beam exposures. The acid generation efficiency is determined with an on-wafer method that uses spectroscopic ellipsometry to measure the absorbance of an acid sensitive dye (Coumarin 6). Under DUV exposures, common ionic onium salt PAGs show excellent photoacid generation efficiency, superior to most nonionic PAGs tested in this work. In contrast, when under 100-keV high energy e-beam exposures, almost all of the nonionic PAGs show significantly better acid generation performance than the ionic onium salt PAGs tested. In particular, one nonionic PAG shows almost an order of magnitude improvement in the Dill C acid generation rate constant compared to a triarylsulfonium PAG. The high energy acid generation efficiency is found to correlate well with the electron affinity of the PAGs, suggesting that improvements in PAG design can be predicted. Nonionic PAGs merit further investigation as a means for producing higher sensitivity resists under high energy exposure sources.