A time-varying weights tuning method of the double exponential-weighted moving average controller

In recent years, the exponential-weighted-moving-average (EWMA) statistic based controllers are popular in semiconductor manufacturing. However, the single EWMA controller is not sufficient for compensating for the wear-out process. Thus, a double EWMA controller was proposed to enhance the capability for controlling the drifting process. In the literature, in the solution of the double EWMA controller, only the “trade-off” solution weights are used to tune the controller. However, it is a fixed weight tuning method, and it is known that a time-varying weight will produce a superior performance over that of a fixed one. Therefore, this study aims to develop a heuristic time-varying weights tuning methods for the double EWMA controller. The numerical results showed that the proposed time-varying tuning method possesses an improvement of least 10% over that of the fixed weight scheme.