Cooperative Scheduling of Twin-cluster Tools with Wafer Residence Time Constraints

In semiconductor wafer fabrication, adhering to residency time constraints is crucial to prevent damage to the wafers. Moreover, the use of twin-cluster tools adds complexity to the scheduling process owing to the need for resource coordination between two units. We investigate a steady-state cycle scheduling challenge of twin-cluster tools equipped with a complete concurrent processing module, particularly for wafer residence time constraints. Initially, a resource-oriented Petri net model is developed to elucidate the operation of twin-cluster tools under steady-state conditions by integrating wafer residency time constraints with a complete concurrent processing module. Afterward, a control strategy is introduced to prevent system deadlock. Subsequently, the conditions without robot task interference are determined by analyzing the workload of the processing module and robot tasks. In scenarios with robot task interference, schedulable conditions for the twin-cluster tool system are derived, and two algorithms are developed to calculate the steady state cycle time of the system and the robot schedule. Finally, these findings confirm the feasibility and effectiveness of the algorithms.