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 op erating in steady-state mode is presented. The analysis is based on a single-wafer serial processing cluster tool. Two types of schedules ar e distinguished, called transport-bound schedules and process-bound sc hedules. In a transport-bound schedule changes in process times do not affect the throughput of the cluster tool, and denotes the maximum th roughput achievable in the cluster tool. In a process-bound schedule, the process time predominates the effect on the throughput. The analys is indicates that a dual-blade robot improves the throughput of the cl uster tool over a single-blade robot under process-bound conditions. U nder process-bound conditions, a cluster tool with a single-blade robo t would need to double the speed of the robot, compared with a dual-bl ade robot of equivalent speed, to achieve similar throughput. Under tr ansport-bound conditions, the throughput of the cluster tool is the sa me for both dual-blade and single-blade cluster tools.