Scheduling of Close-down Process for Dual-armed Cluster Tools with Mask Change Operation

With the diversification of wafer processing size, the complexity of the processing process, the traditional batch processing technology is difficult to adapt to the new processing needs. Therefore, in order to ensure efficient and high-quality wafer production, the use of automated cluster tools for wafer processing is particularly important, and the application of its monolithic wafer processing technology effectively improves the production efficiency of wafers. In order to further improve the utilisation of the cluster tool, it was considered the feasibility of scheduling the parallel operation of wafer processing and mask change in the close-down process for a dual-armed cluster tool without violating the wafer residency constraint in this paper. First, a new scheduling strategy based on the virtual wafer method was proposed, the Petri net model of the close-down process under a new strategy was established and the transition triggering conditions to avoid deadlock and control system operation were established. Then,according to the process requirements and time characteristics, different scheduling conditions had been considered, the waiting time in the close-down process had been redistributed and the mask changing time and the sequence of manipulator activities had been output.Finally, the feasibility of the strategy was verified by two examples. The experimental results show that the proposed scheduling scheme can effectively reduce the batch switching time of single-product wafers without affecting the close-down time of the termination transient., that is the mask changeover time is minimized,compared with the original process of mask change after wafer processing.