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 p K a (or dipole moment) of corresponding acids for counter anions owing to the suppression of transient swelling layer formed during the development.