Design of a Petri net supervisor for multi-cluster tools to improve scheduling performance

Cluster tools are widely used for semiconductor manufacturing. A multi-cluster tool consists of several single cluster tools which are interconnected with each other. The multi-cluster tool causes a deadlock due to nonexistence of intermediate buffer. Deadlock is a serious problem leading decrease of throughput and deterioration of wafers. In this paper, the optimal supervisor proposed by Chen et al. (2011) is applied to a Petri net model of the multi-cluster tools. From the comparison of performance with the conventional deadlock prevention policies, we find that the maximally permissive supervisor does not always produce a better scheduling performance. We propose a design method of a Petri net supervisor to improve the scheduling performance. Our main idea is to eliminate legal markings that may eventually cause the increase of makespan. The proposed method is applied to the two-connected multi-cluster tool. The results indicate that the scheduling performance can be improved by the proposed method without lowering maximal permissivity.