Improved variable EWMA controller design
The exponentially weighted moving average (EWMA) controller is a popular run-to-run (RtR) control scheme in semiconductor manufacturing because of its effectiveness and simplicity. In this paper we propose an improved variable EWMA controller design method. The optimal discount factor of the EWMA controller is determined by minimizing the mean square error (MSE) of process output at each run. The proposed method overcomes some potential problems of Tseng's method and can be applied to general autoregressive integrated moving average (ARIMA) processes. Simulation examples are given to show the effectiveness of the proposed method.