Fundamental simulation studies of CONWIP in front-end wafer fabrication

Abstract

Production planning and control in semiconductor manufacturing is complicated by high-level of re-entrant. Job batching is commonly used to reduce required setup time and maximize workstation utilization. New research promotes CONWIP in pull production systems, while limiting overall work-in-process. However, the implications of batching on CONWIP systems have not been well studied. This paper describes a series of simulation studies and adopted ANOVA and response surface methodology to investigate the effects and relationship of batching on different numbers of CONWIP cards, demand composition, re-entrant, and setup times. Simulation results show that all batching systems exhibited a high number of CONWIP cards and low job mix, total layers, and setup times when the lowest average flow time as well as the highest throughput level and workstation utilization are achieved. The overall result reveals that batching systems outperform non-batching systems in the simulation model of a CONWIP production control system in semiconductor manufacturing.

Keywords:

• CONWIP
• re-entrant process flow
• simulation
• wafer fabrication
• batching system

Acknowledgments

We wish to acknowledge APEX grant (no: 910345) and FRGS grant (no: 6071276) as the financial sponsors of this research. We also wish to express our appreciation to the editor and the anonymous reviewers for the comments and suggestions which have greatly improved the manuscript.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. In wafer fabrication, the efficiency of a process such as diffusion is optimized through lots reprioritization and regrouping to form new batches. The maximum number of lots in a batch has to be capped to match the capacity of the process, especially when a large number of WIP is present at the incoming buffer. The CONWIP maintains WIP at a relatively low level and liberating restriction on batch size would be inconsequential to the experiments.