Model to determine the backup capacity of a wafer foundry

Abstract

Foundry companies are very concerned about fully utilizing equipment and increasing productivity because of the rapid depreciation and large investments made in equipment. Factory output is limited by its bottleneck machine. If a discrepancy exists between the planned and actual product mix, a new machine will become the bottleneck and will have a strong impact on the capacity. All famous foundry companies, such as TSMC, UMC, and others, implement backup solutions to such problems. However, the level of protective capacity at the non-bottleneck workstations strongly affects production performance. Therefore, the backup quantity should be well managed. Accordingly, a backup capacity determination model is presented in two parts: the Backup Capacity Determination Model (BCDM) and the Performance Evaluation Model (PEM). The concept of protective capacity is applied to determine the backup capacity in the BCDM. The determination of protective capacity is based on the statistical fluctuation of factors that include machine downtime and unreasonable queuing time in front of the non-bottleneck workstations. The PEM applies queuing theory and Little's Law to evaluate the effects of the backup capacity exceeding the backup capacity on throughput, work in process and the cycle time of the backup factory. A backup capacity determination model provides important information, so that managers have access to a sufficient and reliable reference when confronted with a problem that involves backup capacity.

Keywords:

• Foundry
• Backup capacity
• Protective capacity
• Non-bottleneck workstation

Acknowledgement

The authors would like to thank the National Science Council of the Republic of China for financially supporting this research under contract No. NSC 90-2218-E-216-001.