Wafer Sojourn Time Fluctuation Caused by Activity Time Variation in DualArm Cluster Tools

With wafer residency time constraints, wafer sojourn time in a processing module should be carefully controlled such that it is in a permissive range. Activity time variation often results in wafer sojourn time fluctuation and makes an originally feasible schedule infeasible. Thus, it is very important to know how the wafer sojourn time changes when activity time varies. With proposed Petri net (PN) model and real-time control policy, this paper analyzes the effect of activity time variation on wafer sojourn time delay and presents its upper bounds in dual-arm cluster tools.