Photoacid generators in chemically amplified resists

It is well known that onium salt structure has an influence on resist resolution and post exposure delay stability as well as solubility in typical resist solvents. As a result of our study, it was found that resists have higher contrast when t-butylphenyl substituents replaced phenyl or alkyl substituents in the cation segment of onium-type photoacid generators in both iodonium and sulfonium systems. Dissolution inhibition appeared to play a primary role. In this paper we also report the results of our investigation into onium-type photoacid generators possessing reduced diffusion, lower volatility and suitable acidity to cleave common protecting groups such as t-butoxycarbonyl, acetal and t-butyl. Substituted benzene sulfonic acids were very useful for cleaving common protecting groups in polyhydroxystyrene based Deep-UV resist systems. The addition of alkyl groups to the ring had only slight effect on acid diffusion. Perfluoro sulfonic acids were required to cleave adequately, the acid stable leaving groups in methacrylate resist systems.