Mechanistic similarities in the photochemistry of two classes of photoacid generators: a laser flash photolytic study

An understanding of the fundamental photochemistry of photoacid generators (PAGs) is essential for the design of new PAGs for use in materials for 193 nm and DUV lithography. The photochemical behavior of some N-oxysuccinimidoarylsulfonate (1) and 1,2-di(arylsulfonyl)hydrazine (2) PAGS has been studied by means of nanosecond laser flash photolysis ((lambda) exc equals 266 nm) and steady-state photolysis ((lambda) exc equals 254 nm) in order to investigate the mechanism of reaction, particularly, that of photoacid generation. Upon photoexcitation, the formation of arylsulfonyl radicals has been detected by laser flash photolysis for both of these classes of PAGs. The arylsulfonyl radicals can undergo desulfonylation thereby generating SO 2 and aryl radicals; which in O 2 -saturated solution are converted into arylperoxy radicals. The arylsulfonyl radical generates acid via reaction with O 2 to yield a peroxysulfonyl radical which subsequently reacts with a hydrogen atom donor to yield a peroxysulfonic acid. The sulfonic acids detected in product studies are presumably the stable decomposition products of this first formed peroxysulfonic acid. Photoacid generation quantum yields upon laser excitation were found to range from 0.04 - 0.05 for 1 and 0.05 - 0.1 for 2. Photoacid generation quantum yields upon lamp irradiation were considerable higher, approximately 0.4. Based on this work, these materials may offer potential as PAGs for 193 nm and DUV lithography.