How to start-up dual-arm cluster tools involving a wafer revisiting process

For some wafer fabrication processes, e.g., atomic layer deposition, wafers need to visit some process modules for a number of times instead of once, which leads to a revisiting process. It is complicated to schedule cluster tools with wafer revisiting in semiconductor fabrication. Most studies on cluster tool scheduling aim to find the optimal steady state schedule. However, the recent trend to run small batches of different wafers has raised more needs for efficient start-up and close-down processes of cluster tools with wafer revisiting. This paper introduces two scheduling strategies to schedule the start-up transient process. After the tool finishes it from the idle state, it reaches a required steady state from which an optimal one-wafer cyclic schedule can be put into use. An industrial case is given to show the applications of the obtained results.