Methodology for feedback variable selection for control of semiconductor manufacturing processes - Part 2: Application to reactive ion etching

The PVVM methodology for feedback variable selection introduced in a companion paper (Patterson et al., 2003) is applied to a gate etch process. The primary purpose of this paper is to illustrate the practical aspects of utilizing this methodology. Particular attention is given to the challenging task of process modeling. The model-building procedure and constraint-limited exhaustive search is demonstrated to perform superior to other model-building procedures including principal component regression and partial least squares regression for use in this methodology. A second purpose is to present the results for the etch process. Advanced sensors considered for real-time process control of this process include an RF probe, mass spectroscopy and optical emission spectroscopy. Feedback variables are selected to reduce variation in etch rate, nonuniformity and lateral etch rate. The advantages of treating location on the wafer as a disturbance to the etch rate model so that both etch rate and nonuniformity may be captured in one model are presented and experimentally verified.