Cyclic scheduling of cluster tools with equipment front-end module and multifunctional load locks

This paper proposes a cyclic scheduling method for cluster tools in semiconductor manufacturing with equipment front-end module and multifunctional load locks. In this special configured cluster tools, the equipment front-end module consists of an aligner, a signal-arm robot, and two load locks integrated with coolers. Hence, the two load locks both have multifunction of filling, pumping, and cooling wafers. The multifunctional load locks may become scheduling bottleneck for a certain specified recipe. To solve this problem, the Petri net models of the above configured cluster tool is developed first. Then, based on the Petri net models and state equations, a mixed integer programming model is presented, which can efficiently determine the optimal scheduling sequence in steady state. Through experiments, the effectiveness of the cyclic scheduling method proposed in this paper is verified.