Reactivity of model compounds of ArF immersion, ArF, and KrF resists with diphenylsulfinyl radical cation, a cage-escape product of photochemistry of triphenylsulfonium salts

Reactivity of diphenylsulfinyl radical cation (Ph 2 S . + ) with model compounds of "dry/wet" ArF resists and KrF resists was investigated by pulse radiolysis technique, in order to reveal the reaction between Ph 2 S . + and a polymer. Ph 2 S . + is an intermediate of photolysis of triphenylsulfonium salts. Some Ph 2 S . + react with other intermediate of phenyl radical, leading to the formation of (phenylthio)biphenyl products and proton (H + ). The reaction, referred to as rearrangement reaction, is mainly responsible for acid generation. However, some Ph 2 S . + react with a polymer. Acid-generation efficiency might be enhanced if H+ is also formed by this reaction. Among 25 model compounds employed, Ph 2 S . + was scavenged by phenolic compounds which have lower electrochemical half wave reduction potential (E 1/2 ) than that of Ph 2 S. However, resulting radical cations of the phenolic compounds were not observed. Ph 2 S . + was not scavenged by the other compounds with higher E 1/2 . Decay rate constant of Ph 2 S . + scavenged by additives clearly depends on the change of E 1/2 between Ph 2 S and the additives including pyrene from which charge transfer was observed to Ph 2 S . + . The reaction is therefore charge transfer between the model compounds and Ph 2 S . + . The resulting radical cations of phenolic compounds are known to decompose to phenoxy radical and proton (H + ), suggesting that the compounds contribute to the enhancement of acid-generation efficiency in a chemically amplified resist. From the viewpoint of reaction of Ph 2 S . + with resists, conventional polymer of KrF resist is therefore appropriate for H+ source. Phenolic compounds are generally not appropriate for the component of "dry/wet" ArF resists because of their strong absorption at 193 nm. However, the electron proved to be transferred from fluorinated methylphenols to Ph 2 S . + . Fluorinated methylphenols may have a potential for candidate of resist components improving acid generation in "dry/wet" ArF lithography.