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Cyclic Scheduling Analysis of Single-arm Cluster Tools with Wafer Residency Time Constraint and Chamber Cleaning Operations

In semiconductor manufacturing, a cleaning operation that takes significant time is required for eliminating the chemical residual in a chamber after a wafer being processed and removed from it. Such a cleaning operation makes a traditional backward strategy inefficient. In the existing work, it is shown that the productivity can be improved if some of chambers at a step are kept empty. With this idea, an extended backward strategy is proposed by deciding the optimal number of empty chambers. Based on such a strategy, this work studies the challenging problem for scheduling a single-arm cluster tool with both chamber cleaning operations and wafer residency time constraint for the first time. By building timed Petri net model for the system, two linear programs are proposed to determine the minimal cycle time and test the existence of a feasible schedule. At last, an industrial example is used to demonstrate the obtained results.