A hybrid look-ahead SOM-FBPN and FIR system for wafer-lot-output time prediction and achievability evaluation

A hybrid system is constructed in this study for wafer-lot-output time prediction and achievability evaluation, which are critical tasks for a wafer fab (fabrication plant). In the first part of the hybrid system, a look-ahead self-organization map fuzzy-back-propagation network (SOM-FBPN) is constructed to predict the output time of a wafer lot. Compared with traditional approaches in this field, the look-ahead SOM-FBPN has three advanced features: incorporating the future release plan, classifying wafer lots, and incorporating expert opinions. According to experimental results, the prediction accuracy and efficiency of the look-ahead SOM-FBPN were significantly better than those of many existing approaches. In the second part of the hybrid system, a set of fuzzy inference rules (FIRs) are established to evaluate the achievability of an output time forecast, which is defined as the possibility that the fabrication on the wafer lot can be finished in time before the output time forecast. Achievability is as important as accuracy and efficiency but has been ignored in traditional studies. With the proposed methodology, both output time prediction and achievability evaluation can be concurrently accomplished.

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