Run-to-run control and performance monitoring of overlay in semiconductor manufacturing

Abstract

In the manufacture of semiconductor products, overlay is one of the most critical design specifications. Overlay is the position of a pattern relative to underlying layers, and overlay control largely determines the minimum feature size that may be incorporated into semiconductor device designs. Overlay control must be performed on a run-to-run basis, i.e. at the end of a run when product characteristics are available, because they cannot be directly measured during a run. In this research a process model and a run-to-run control scheme was developed for overlay control, based on linear model predictive control, and successfully implemented in a commercial facility. Performance monitoring of the closed-loop process was also carried out.