Tailored Glass Transition of ArF Resists for Resolution Enhancement at sub-50 nm node

Abstract

Fundamental aspects of the thermal characteristics of ArF photoresists were investigated in terms of structure-property relationship. A series of model polymers were prepared and characterized in order to understand how changes in structure affect resin's thermal property that is of prime importance in designing resin structure for fine property tuning. Variations were given to the distance between bulky side groups and methacrylic main chain by systematically increasing the number of in-between methylene groups and the effect of side group's position on resin's glass transition behavior was monitored. It was noted that at one extreme case increase in side chain length from C0 to C4 corresponded to about 100°C glass transition temperature decrease, presumably due to a considerable free volume change. A careful study of a set of experimental results reveals that control of chain flexibility through pendent group's spatial positioning as well as one dimensional plasticizing by copolymerization of small size comonomers significantly changes the thermal property of resins and their thermo-physical response during the resist process. While it was reasonably expected that structural variation would result corresponding property change based on numerous previous study and widely accepted glass transition theory, some of the results learned from this investigation are still surprising and worth reviewing. With precise tuning ability of resin's thermal property via structural modification in addition to well-controlled synthetic methodology, glass transition behavior of current ArF resists can be better understood as technology keeps scaling down its dimension below 50 nm.