Cycle forecasting EWMA (CF-EWMA) approach for drift and fault in mixed-product run-to-run process

In semiconductor manufacturing processes, mixed-products are usually fabricated on the same set of process tool with different recipes. Run-to-run controllers which based on the exponential weighted moving average (EWMA) statistic are probably the most frequently used in industry for the quality control of certain semiconductor manufacturing process steps. However, for mixed-product drifted process, if the break length of a product is large, then the process output at the beginning runs of each cycle will far deviate from the target value which will lead to a possible high rework rate and lots of waste wafers. Therefore, this study aims to develop a new approach named cycle forecasting EWMA (CF-EWMA) approach to deal with the problem of large deviations in the first few runs of each cycle. Furthermore, a common fault, i.e., the step fault, is also considered in this paper, and fault tolerant cycle forecasting EWMA (FTCF-EWMA) approach is proposed. Simulation study shows that the proposed approaches are effective. 2010 Elsevier Ltd. All rights reserved.