Resist thickness effect on acid concentration generated in poly(4-hydroxystyrene) film upon exposure to 75 keV electron beam

The thickness dependence of resist performance has been investigated. It has been reported that principal properties such as resist sensitivity show strong dependence on resist film thickness. In current standard resist called chemically amplified resist, acids play the most important role in resist pattern formation. However, the dependence of acid concentration on resist thickness has not been reported. Better understanding of acid related issues is important for the development of high performance resists and the precise simulation of resist pattern profiles. In this work, the acid density in poly(4-hydroxystyrene), which is a widely-used backbone polymer for chemically amplified resists, was measured quantitatively by spectroscopic experiments. The average acid concentration nonlinearly increased by 14% with the increase of resist thickness from 65 to 4000 nm.