Mechanistic studies on the poly(4-tert-butoxycarbonyloxystyrene)/triphenylsulfonium salt photoinitiation process

Abstract

Studies on the poly(4-tert-butoxycarbonyloxystyrene)/triphenylsulfonium salt (TBOC resist) photoinitiation process show strong evidence for a dual photoinitiation process. Photolysis studies on the relative quantum yields and also the ratios for in-cage versus cage-escape sulfide show that the TBOC polymer behaves differently from other polymers and likely sensitizes the decomposition of some of the triphenylsulfonium salt. Also the TBOC resist shows photoactivity at 300 nm, where the polymer absorbs but the triphenysulfonium salt has only very weak absorbance, which suggests that the sensitization process is initiated by the polymer. However the fact that substantial amounts of in-cage products are also formed from photolysis of the TBOC resist, implicates a direct photodecomposition of the triphenylsulfonium salt. Fluorescence quenching studies on TBOC resist films show that the sensitization proceeds by electron transfer from the singlet excited state of the TBOC polymer and that a mainly static quenching mechanism is involved. The photoinitiation of the TBOC cleavage reaction proceeds by a dual initiation pathway which involves both the excited state of the polymer and the excited state of the triphenysulfonium salt.