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Scheduling Robotic Two-Cluster Tools in Case of a Process Module Failure*

The semiconductor manufacturing industry adopts multi-cluster tools as wafer fabrication equipment. If one of process modules fails, a multi-cluster tool cannot follow the normal schedule to complete the process recipe of work-in-process wafers and must empty these wafers by a closing down phase. It is economically paramount to shorten the close-down process with a process module failure (FCDP) and make no loss of wafers. However, due to the wafer residency time constraints, it is rather difficult to respond to a module failure and find a corresponding optimal schedule. By assuming no parallel modules at a step, this work studies this important issue for multi-cluster tools. For process-dominant multi-cluster tools whose optimal steady state schedule is known, we analyze the task sequences to avoid deadlock at the shared buffer modules. Algorithms are proposed to synthesize the proper sequences for robots in case of a process module failure, then, a nonlinear program model is derived to find an optimal schedule for the corresponding close-down process or decide no feasible solutions. An example is present to show the application of our proposed method.