Photoresist exposure parameter extraction from refractive index change during exposure

Abstract

The refractive indices of photoresist are usually measured by an ellipsometer or spectrophotometer, but the values are limited to pre-exposure. It is known that the real and imaginary indices are changed during the exposure. But there is little report on these variations since it is difficult to measure this refractive index change at deep ultraviolet. The Dill ABC parameters show a significant variation with the resist and substrate thickness as well as the experimental conditions. A method is suggested to extract the parameters from the refractive index changes. We can get the refractive index change and extract the Dill ABC exposure parameters from that. The multiple thin film interference calculation is used to fit the measured transmittance data. The results of our experiments and calculations for several resists including 193 nm chemically amplified resists are compared with other methods. The results are agreed well with the full multilayer thin film simulation.