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.
Effect of protecting groups to outgassing characteristics of F2 resists was investigated by using in-situ quadrupole mass spectrometry. The base polymers employed were protected fluorocyclic polymers (FCPs). The protecting groups employed were methoxymethyl (MOM), t-butoxycarbonyl (t-BOC), methoxyethoxymethyl (MOEOM), n-hexanoxymethyl (HOM), and neopentanoxymethyl (NOM) groups. Mass spectra of outgassed species were measured by quadrupole mass spectrometer in the exposure of FCPs with and without photoacidgenerators (PAGs). Kinetic traces of mass spectral intensity were also measured with regard to some noteworthy outgassed species related to deblocking reactions of protecting groups. In the exposure of FCP-HOM with PAGs and FCP-NOM with PAGs, one of the outgassed species related to deblocking reactions are mainly produced only during exposure although that kind of outgassed species originate from irradiated FCP-MOM with PAGs, FCP-MOEOM with PAGs, and FCP-t-BOC with PAGs not only during exposure but also after exposure. Some outgassed species related to the deblocking reactions after exposure are depressed by selecting appropriate protecting groups.
We directly measured mass spectra and change in mass spectral intensity as a function of time for outgassed species from fluoropolymers and fluorine-containing resists during 157 nm exposure using quadrupole mass spectrometer at pressure about 4×10-7 Torr, in order to investigate dependence of outgassing characters on the structure of resist base polymers. We also investigated pressure increase resulting from outgassed species from 157-nm-irradiated fluoropolymers and their resists. The information obtained is as follows: (1) Side-chain-fluorinated polymers produce fluorine-containing outgassed species via scission of side chain. (2) Some fluoropolymers produce HF during 157 nm exposure. Fluorine is suggested to easily dissociate and react with hydrogen to form HF in the exposure of copolymer of tetrafluoroethylene and tert-butyl α-fluoroacrylate. (3) Outgassed species related to deprotection of blocking group originate from some acetal resists during and after exposure at room temperature, although the species were observed only during exposure in the exposure of corresponding base polymer. (5) Regarding base polymers and their resists employed, pressure increase in vacuum chamber becomes smaller in the next order, base polymers with ester groups in their side chains, base polymers having side chains other than ester groups, base polymers without side chains.
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