Fundamental Studies of the Effects of Photo-additive Structure on Resist Outgassing.

Abstract

The effect of different photoadditives in high and low activation energy resist resins on resist outgassing during lithographic exposure was studied by quartz microbalance and gas chromatography/mass spectroscopy techniques. The resist outgassing was analyzed both qualitatively and quantitatively and structure-property relationships were developed between resist outgassing and the molecular structure of photoacid generators (PAG) and other additives. The photoadditives examined included, aryl iodonium perfluoroalkylsulfonates, triarylsulfonium perfluoroakylsulfonates, photogenerators of sulfamic acids, 2-nitrobenzyl PAG's and doxyl derivatives. It was found that during exposure sulfonium salt formulated resists gave a lower outgassing of aromatic compounds than iodonium salt formulated resists while a formulation with a nitrobenzyl PAG did not show any aromatic materials outgassing. The use of a stable free radical additive, methyl 5-doxyl stearate, in a resist formulated with an iodonium salt was found to also dramatically reduce outgassing of aromatic compounds probably through termination of triplet state radical photoproducts. Sweet PAG resist formulations were found to have greatly decreased outgassing during exposure originating from the cleavage of low activation energy acetal protecting groups.