Analysis and modeling of the optical endpoint signal for precision etching

Abstract

Endpoint detection is an essential methodology for process control in dry etching for modern semiconductor manufacturing technology. In this paper, an analysis has been performed on the factors, such as the local etch rate, the local film thickness differences, and the open area and the global uniformities of the etch rate and film thickness, affecting the change in the optical emission endpoint signals on a patterned device wafer. Also, a model of the endpoint signal evolution, which includes an effective open ratio, the ratio of the relative open area after considering the local difference in the etch rate and the film thickness to the total open area at the very beginning of the etch process, has been established. Compared to the conventional open ratio, which is the ratio derived from the reticle used for lithography, the effective open ratio is better in explaining and predicting the endpoint signal change. The effective open ratio can be used to design dummy patterns that are used to improve endpoint detection in critical dry etch processes such as gate cuts in logic gate formation, etc.