A Novel Approach to Scheduling of Single-Arm Cluster Tools with Wafer Revisiting

This paper conducts a study for scheduling single-arm cluster tools with typical wafer revisiting pattern (m(i), m(i+1))(k) where i means the ith-step and m(i) and m(i+1) mean the corresponding quantity of the modules in i and i+1-th steps, and k the number of visiting times. With a Petri net (PN) model, it is shown that, m(i)=m(i)+1 =1, the optimal schedule for the revisiting process is deterministic and unique, and the minimal cycle time can be calculated by an analytical expression. It is also shown that, when m(i) = 1 and m(i+1) = 2 or m(i) = 2 and m(i+1) = 1, the optimal one-wafer cyclic schedule for the revisiting process can be obtained in k deterministic schedules by comparing their cycle times. Based on the scheduling and cycle time analysis of a revisiting process, a novel method is presented to schedule the overall system by treating the revisiting process as a macro step.