SYNTHESIS OF SOME ONIUM SALTS AND THEIR COMPARISON AS CATIONIC PHOTOINITIATORS IN AN EPOXY RESIST

Several onium salts have been synthesized and compared as cationic pho toinitiators in an epoxy resist. 1-(4-Hydroxy-3-methylphenyl)tetrahydr othiophenium hexafluoroantimonate exposed at 365 nm gave the best resu lts, due to its superior absorption at this wavelength. A series of bi s-(triphenyl phosphoranylidene) ammonium salts performed poorly with 2 54 nm, 365 nm and E-beam irradiation even with the addition of photose nsitizer. Triphenyl sulfonium hexafluoroantimonate and triphenyl sulfo nium triflate formulated the most sensitive epoxy resist materials to both 254 nm and E-beam radiation sources (0.32 mJ cm(-2) and 0.3 mu C cm(-2), 59.2 mJ cm(-2) and 8.0 mu C cm(-2) at 20 kV, respectively). (C ) 1997 Elsevier Science Ltd.