EWMA Controller with Concurrent Adjustment for a High-Mixed Production Process
The exponentially weighted moving average (EWMA) feedback controller is a very popular run-to-run (RtR) process control scheme in the semiconductor industry. Traditionally, the manufacturing environment was simplified as a single product and single tool process. In the feedback control, the adjustment of the recipe for the next run is related to the deviation of the current output against the desired target. However, in a commercial foundry, every tool always works for many products. It is called a multiple products and single tool (MPST) process. The challenge of this process is how to adjust the recipes among different products in a production row.
In this study, a modified threaded EWMA feedback controller, the EWMA with concurrent adjustment, is proposed to deal with the issue of multiple products in a tool. When the process disturbances follow an IMA(1,1) time series model, the stability of the proposed method will be proven. The optimum discount factors of the proposed EWMA controller will be investigated by several simulations in terms of the number of multiple products, their distribution and the scheduling of the process. Moreover, according to results of the performance comparisons with threaded EWMA, the proposed controller is advantage in the large number of multiple products and in low-frequency products .
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