Scheduling Transient Processes for Time-Constrained Single-Arm Robotic Multi-Cluster Tools

Multi-cluster tools are highly productive yet expensive wafer fabricating facility in semiconductor industry. Current competitive business trend requires high-mix and low-volume production of wafers. The size of a wafer lot is becoming smaller and wafer lots change more frequently. This brings up with many start-up and close-down processes. It is thus more and more important to control these transient processes to ensure the highest utilization of expensive facility. Since many wafer fabrication processes have strict residency time constraints after a wafer's processing, this work aims to schedule optimally the transient processes of single-arm multi-cluster tools subject to such constraints. For such tools whose optimal steady state schedules can be found, we propose linear programs to find the optimal schedules for start-up and close-down processes for the first time. The obtained schedules make the transitions between transient and steady states seamlessly. Examples are presented to illustrate how the proposed method outperforms the existing ones by about 10% throughput.