Dynamic average method for cycle time estimator in an IC fab

The forecast of process cycle time is difficult in an IC manufacturing system, especially in an environment with multiple products and various processes. In this paper, a simple forecast mechanism is developed to provide the forecast of a product´s cycle time and product´s remaining process cycle time, and other useful processing information. The proposed algorithm is based on a dynamic average of historical process data stored in a database to generate runtime, wait-time and hold-time information, and the results are further classified in terms of tool group (or tool), technology and stage-ID hierarchically. The product´s remaining process cycle time can be obtained by looking for the product´s state from on-line data in the database first, and then utilizing the product´s operation flow table and the average process time given above to calculate it. For calculating product´s cycle time, it works in a similar way. Since the run-time, wait-time and hold-time of each lot can be shown from the proposed algorithm, it is easy to forecast the operation bottleneck of the lot. This method is proved to be useful by testing in Fab 3 of TSMC (Taiwan Semiconductor Manufacturing Company)