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.