Photoacid generator protonation

Intramolecular photoinduced electron transfer (PET) may lead to the generation of acid (i.e., protons) from an anthracene-based sulphonium salt. An amphiphilic anthracene-based photoacid generator (An-PAG) has been synthesized and was reported to induce acid-catalyzed hydrolytic degradation of certain lipids upon UV exposure (Shum et al., 2001). At present, the application of this technique is limited by the short wavelength required to trigger the response. 

A new simple and reliable method for monitoring photoinduced acid generation in polymer films and in solutions of the kind used in 193 nm and deep-UV lithography was developed. By using N-(9-acridinyl)acetamide, a fluorescent acid-sensitive sensor, we have been able to study the effects of trifluoroacetic acid and photoacids generated from triphenylsulfonium hexafluoroantimonate on the spectral properties of the acid sensor in THF solution and in alicyclic polymer resist films exposed at 193 nm. In both cases a hypsochromic spectral shift and an increase in fluorescence intensity were observed upon protonation. This technique could find application in the study of diffiisional processes in thin polymer films. 

Acidic a protons on the ketone group show smooth protection and proton reproduction.33 Then a poly(OCMA-co-AdMA) resist was prepared for a superior CA resist. The structure of the copolymer is shown in Figure 2.14. The copolymer is sensitized by TPSF as PAG and dissolved in cyclohexanone as a resist solution. Protected OCMA is dissociated by acid H+ as shown in Figure 2.15. Methyl groups were introduced into poly(OCMA-co-AdMA) to obtain a more sensitive CA resist. Figure 2.16 shows copolymer-introduced methyl groups. The resist was formulated with 2 wt% TPSF as a photoacid generator. The resist exhibited L/S 200 nm. 

Removal of mask anti light source creates a patterned image due to generated photoacid protonating die fluonophorc. 

The design concept of chemical amplification is based on generation of a chemically stable catalytic species (commonly referred to as a photoacid and designated as a proton H, as illustrated in Fig. 17.22 for a resist system comprising a copolymer—poly(4-hydroxystyrene-co-4-t-butyloxycarbonyloxystrene)—in... 

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