Dependence of acid yield on chemically amplified electron beam resist thickness

The feature sizes in microfabrication have decreased with the progresses in lithographic technology. With the reduction in lateral dimensions, the resist thickness has also decreased. The resist thickness is projected to decrease to, 65-110 nm at a 32 nm technology node. The thickness dependence of resist performance has been reported. As many factors are involved in resist pattern formation, it is difficult to elucidate the mechanism behind the thickness dependence. It is important to evaluate the effect of each factor quantitatively. In this work, the thickness dependence of acid yield was quantitatively measured in spectroscopic experiments. Better understanding of acid-related issues is important for the development of high-performance resists and the precise simulation of resist pattern profiles. The average acid concentration nonlinearly increased by 14% with an increase in resist thickness from 65 to 4000 nm. The dependence was analyzed from the viewpoint of forward and backward exposures.