Demand-driven, iterative capacity allocation and cycle time estimation for re-entrant lines

Daily production target setting for each production stage of a semiconductor wafer fabrication factory is a challenging machine capacity allocation problem due to the complex and re-entrant process flows. This paper summarizes a methodology developed by the author for the design of a daily target setting system over the past few years. The methodology realizes PULL-then-PUSH and proportional capacity allocation principles to meet production demands in a smooth way while maximizing machine utilization. As machine capacity allocation and available wafer flows are intertwined, the target setting problem can be viewed as a fixed-point iteration problem. A deterministic queueing analysis-based algorithm is designed to estimate cycle times and hence wafer flows. The methodology iterates between capacity allocation and cycle time estimation until a fixed-point capacity allocation is achieved.