Steady-state throughput and scheduling analysis of multicluster tools: A decomposition approach

Cluster tools are widely used as semiconductor manufacturing equipment. While throughput analysis and scheduling of single-cluster tools have been well-studied, research work on multicluster tools is still at an early stage. In this paper, we analyze steady-state throughput and scheduling of multicluster tools. We consider the case where all wafers follow the same visit How within a multicluster tool. We propose a decomposition method that reduces a multicluster tool problem to multiple independent single-cluster tool problems. We then apply the existing and extended results of throughput and scheduling analysis for each single-cluster tool. Computation of lower-bound cycle time (fundamental period) is presented. Optimality conditions and robot schedules that realize such lower-bound values are then provided using "pull" and "swap" strategies for single-blade and double-blade robots, respectively. For an M-cluster tool, we present O(M) lower-bound cycle time computation and robot scheduling algorithms. The impact of buffer/process modules on throughput and robot schedules is also studied. X chemical vapor deposition tool is used as an example of multicluster tools to illustrate the decomposition method and algorithms. The numerical and experimental results demonstrate that the proposed decomposition approach provides a powerful method to analyze the throughput and robot schedules of multicluster tools. Note to Practitioners-Modeling and scheduling of cluster tools are critical to improving the productivity and to enhancing the design of wafer processing flows and equipment for semiconductor manufacturing. This paper presents a decomposition method to calculate the maximum throughput and to analyze the robot action schedule for a cluster tool that contains multiple transfer robots. The proposed algorithms utilize and extend the existing results for the single-cluster tool that only has one transfer robot. Buffer modules between two interconnected clusters are treated as either fictitious cassette modules or fictitious process modules. Therefore, we can decompose the interconnected multicluster tool into multiple single-cluster tools. The outcome of this research work provides not only answers to possible maximum throughput for a given cluster tool system but also robot schedules that address how to reach such a maximum throughput. The scheduler can be implemented and run efficiently on the cluster tool computer of a general configuration cluster tool. Comparing with rule-based and simulation-based scheduling methods, the benefits of the proposed analytical approach include better throughput estimation, faster what-if analysis, and optimal scheduling solutions with varying processing times and cluster tool configurations. We have successfully tested the methodology in this paper on dozens of cluster tools at Intel Corporation.