Smith–EWMA run-to-run control schemes for a process with measurement delay

Abstract

The Exponentially Weighted Moving Average (EWMA) controller is a popular run-to-run controller in the semiconductor manufacturing industry. The controller adjusts input based on measurement information from previous runs. EWMA controllers can guarantee satisfactory results in many cases; however, when there is a measurement delay in the process, the stability properties and performance of the EWMA controller cannot be guaranteed. In order to maintain the satisfactory outcomes of EWMA controllers, a Smith predictor control scheme is introduced, created particularly for time delay systems in control theory, into EWMA controllers. A modification of the EWMA controller, called the Smith–EWMA run-to-run controller, is proposed. Comparisons between the stability properties of Smith–EWMA and EWMA run-to-run controllers are studied. Moreover, a performance comparison with the EWMA and recursive-least-square controllers under disturbance conditions based on simulation is conducted. The results show that when there is a measurement delay, the proposed Smith–EWMA run-to-run controllers enlarge the stability region and also achieve better performance when there is serious metrology delay and model uncertainty under process disturbances. [Supplementary materials are available for this article. Go to the publisher's online edition of IIE Transactions for the following free supplemental resource: Appendix]