Reaction mechanisms of Sn-based polarity-change copolymer resists with different counter anions, designed for extreme ultraviolet lithography

Abstract

The development of high-resolution resists with a highly absorptive element for extreme ultraviolet (EUV) photons has attracted much attention for next-generation lithographic applications. In this study, the radiation-induced reactions of polarity-change copolymer resists comprising tetraphenyltin (an EUV absorption unit) and phenyl dibenzothiophenium salts (polarity-change units) are investigated via electron-pulse radiolysis, electron-beam (EB) radiolysis, γ radiolysis, time-of-flight secondary-ion mass spectrometry (TOF-SIMS), quartz crystal microbalance (QCM) method, and contact angle measurement. Their lithographic performances are preliminary evaluated using a 125 keV EB writer. Trifluoromethanesulfonate, benzene sulfonate, and salicylate are used as counter anions for phenyl dibenzothiophenium cations. The effects of the counter anions on the radiation-induced reactions and yields of the main radiolytic products are small, whereas the resolution and sensitivity improve significantly with the increase in the pKa (or dipole moment) of corresponding acids for counter anions owing to the suppression of transient swelling layer formed during the development.