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

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. (C) 2003 Published by Elsevier Ltd.