Acid generation and acid diffusion in photoresist films

Abstract

Triarylsulfonium salts have been widely used as acid photogenerators in chemically amplified photoresists. A technique was developed for measuring the amount of acid which is generated on irradiation of polymer films containing sulfonium salts and the results of these measurements were used to obtain an understanding of the importance of acid chemistry on the lithographic performance of acid-catalyzed resists. The results from both electron beam and ultraviolet irradiations suggest that polarity effects are very important factors in determining the efficiency of acid generation. The effect of sulfonium salt loading percentage on acid generating efficiency was also studied. Thermal analysis of polymer films containing sulfonium salts has shown greater plasticization effects for sulfonium salts in polar polymer films indicating that the interaction between sulfonium salts and polymers is better for polar polymers. ESR experiments have determined the nature of the radicals which are produced following irradiation and these results suggest a mechanistic understanding of the polymer structural effects.In the case of acid-sensitive polymers, it has been possible to determine the extent of acid-catalyzed chemistry which, in turn, provides a means of estimating the acid diffusion range in this polymer film.