Adaptive variable EWMA controller for drifted processes

The double exponentially weighted moving average (dEWMA) feedback controller is a popular run-to-run (RTR) controller that is used to adjust semiconductor manufacturing processes that have a linear drift. Although this controller, with suitable fixed discount factors, can guarantee long-term stability, it usually requires a moderately large number of runs to bring the process output to its target value. To overcome this difficulty, an enhanced controller called the “adaptive variable EWMA controller,” is proposed. This controller brings the process output to a desired target much more quickly. An analytical expression of the process output of this controller and its long-term stability conditions are derived. Furthermore, examples are presented that compare the performance of the proposed controller with several competing controllers. It is demonstrated that the proposed controller has the best performance of the considered controllers in terms of the reduction of total mean square errors.[Supplementary materials are available for this article. Go to the publisher's online edition of IIE Transactions for the following supplemental resource: Appendix]