Mean cycle time optimization in semiconductor tool sets via pm planning with different cycles: A G/G/m queueing and nonlinear programming approach

In semiconductor manufacturing, preventive maintenance (PM) activities are typically scheduled via a two tier hierarchical decomposition approach. The first decision tier determines a PM cycle plan while the second tier schedules these planned events into the manufacturing operations. Following recent work based on the use of G/G/m queueing approximations for PM planning, we develop a method to allow for multiple PM cycles in a tool set. We formulate a nonlinear program with the PM cycle durations as continuous decision variables with the objective of minimizing the mean cycle time. We examine certain special cases and characterize the optimal solutions. Numerical studies are conducted with realistic multiple PM cycle data to assess the implications of the proposed approach. The results suggest that it may be possible to obtain significant improvements in the overall cycle time performance of tool sets in semiconductor manufacturing relative to existing PM planning procedures.