Capacity planning of serial and batch machines with capability constraints for wafer fabrication plants

Abstract

Capacity planning is crucial to the investment and performance of wafer fabs. This research proposes a practical procedure to calculate the required number of machines with serial and batch processing characteristics, respectively. Several formulae are first presented. Five heuristic algorithms are then proposed to determine the lower bound, the upper bound, and the near-optimal of the number of machines of the type with capability constraint. Data from real foundry fabs are used in a case study to determine the required number of 64 types of equipment and to evaluate the performance of the proposed procedure. The algorithm using the best ratio of production efficiency and equipment cost to select the machine type with capability constraint results in the least required number of machines, the highest machine utilisation, and the lowest equipment investment. An AutoSched AP simulation model is used to evaluate if a wafer fab using the calculated number of machines of each type can result in a preset monthly output rate. Simulation results indicate that the proposed procedure can quickly and accurately calculate the required number of machines leading to the required monthly production target. Fab managers can use this tool to conduct what-if analysis for equipment investment alternatives.

Keywords:

• semiconductor manufacturing
• capacity planning
• wafer fabrication
• capability

Acknowledgements

This paper was supported in part by National Science Council (NSC) of Taiwan, Republic of China and Taiwan Semiconductor Manufacturing Company (TSMC) under contracts NSC 95-2221-E-033-035 and NSC 87-2622-E-002-004.