A real-time feedback control system is being developed in a wafer fabrication line at IBM's San Jose plant. The goal of the system is to minimize the alignment drifts, and hence to increase wafer yields and chip quality, by automatically adjusting the set points of the exposure machines. The major challenges of implementing the feedback control system are: (1) no modification on the existing equipment, (2) minimum interruptions to the production operation, (3) asynchronous operations and communications of multiple computers, (4) computational algorithm of new set points, (5) large volume of data, (6) data grouping, and (7) data filtering. These challenges and the methods taken to address them are discussed.
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