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Reactivity of diphenylsulfinyl radical cation (Ph2S.+) with model compounds of "dry/wet" ArF resists and KrF
resists was investigated by pulse radiolysis technique, in order to reveal the reaction between Ph2S.+ and a
polymer. Ph2S.+ is an intermediate of photolysis of triphenylsulfonium salts. Some Ph2S.+ 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 Ph2S.+
react with a polymer. Acid-generation efficiency might be enhanced if H+ is also formed by this reaction.
Among 25 model compounds employed, Ph2S.+ was scavenged by phenolic compounds which have lower
electrochemical half wave reduction potential (E1/2) than that of Ph2S. However, resulting radical cations of the
phenolic compounds were not observed. Ph2S.+ was not scavenged by the other compounds with higher E1/2.
Decay rate constant of Ph2S.+ scavenged by additives clearly depends on the change of E1/2 between Ph2S and the
additives including pyrene from which charge transfer was observed to Ph2S.+. The reaction is therefore charge
transfer between the model compounds and Ph2S.+. 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
Ph2S. + 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 Ph2S.+.
Fluorinated methylphenols may have a potential for candidate of resist components improving acid generation in
"dry/wet" ArF lithography.
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