A steady-state throughput analysis of cluster tools: dual-blade versus single-blade robots

An analysis of throughput in a cluster tool with a dual-blade robot operating in steady-state mode is presented. The analysis is based on a single-wafer serial processing cluster tool. Two types of schedules are distinguished, called transport-bound schedules and process-bound schedules. In a transport-bound schedule changes in process times do not affect the throughput of the cluster tool, and denotes the maximum throughput achievable in the cluster tool. In a process-bound schedule, the process time predominates the effect on the throughput. The analysis indicates that a dual-blade robot improves the throughput of the cluster tool over a single-blade robot under process-bound conditions. Under process-bound conditions, a cluster tool with a single-blade robot would need to double the speed of the robot, compared with a dual-blade robot of equivalent speed, to achieve similar throughput. Under transport-bound conditions, the throughput of the cluster tool is the same for both dual-blade and single-blade cluster tools.