Optimal scheduling of dual-armed cluster tools with complex scheduling requirements by general robot task sequences

Abstract

In a dual-armed cluster tool, the swap operation method that exchange a wafer on a robot arm with another wafer at a chamber has been mostly used. It is known to minimize the tool cycle time although it restricts the robot task sequence. Recent cluster tools have new scheduling requirements such as reentrant wafer flows for atomic layer deposition processes, constraints on the wafer delay times within chambers after processing, and concurrent processing of different wafer types. The restricted swap operation method may neither minimize the tool cycle time nor satisfy the wafer delay constraints, and even cause a deadlock. We examine new robot task sequences for dual-armed cluster tools that use the two robot arms more flexibly than the conventional restricted swap operation method. In this thesis, we first examine new robot task sequences for a dual-armed cluster tool with basic scheduling requirements. We develop a systematic method of modeling the tool operational behaviors for non-swap operation sequences by using Petri nets. By examining the net model, we show that if the routing decisions on a conflict place of the model are made in cyclic order, the net is behaviorally equivalent to an event graph. We also identify conditions to prevent deadlocks to enhance computation time. From the results, we develop a mixed integer programming model for determining the optimal tool operation sequence, schedule, and cycle time. Finally, we discuss how our works can be applied to each of the additional scheduling requirements such as residency time constraints and concurrent wafer flows. Second, we address modeling and scheduling issues for dual-armed cluster tools with reentrant job flows. There have been some researches addressing the issues, however, it is not yet clearly determined or investigated how the dual-armed robot can be fully utilized with the flow. To do this, we first propose a systematic way of modeling the tool operational behaviors with ree...