A New Scheduling Approach to Wafer-Residency-Time-Constrained Dual-Arm Cluster Tools Concurrently Processing Multivariety Wafers

In the periodic scheduling problems of a dual-arm wafer-residency-time-constrained (W-R-T-C) cluster tool (CT) with multivariety wafers, it is important to balance workload at each step. This work proposes a method of processing module (PM) two-layer configuration. First, one PM configuration is made for each wafer type, i.e., the suitable number of PMs is selected for processing wafers, ensuring that the natural workload is balanced at each step for a type of wafers. Then, the other PM configuration is made, i.e., adopt a virtual module method for balancing the natural workload at bottleneck processing steps of different types of wafers. Based on two-layer PM configuration, this work derives necessary and sufficient conditions for a CT’s schedulability, which are less restrictive than the current state-of-the-art ones. It proposes a polynomial-time algorithm for computing its minimum periodic schedule when it is schedulable. Several examples are given to show our algorithm’s superiority over existing ones.