Simulating AMHS performance for semiconductor wafer fabrication

This paper presents the methods and results of modeling and simulating the performance of interbay automated material-handling systems (AMHS) for semiconductor wafer fabrication. Along with a case study of a wafer fab AMHS model, this paper includes an alternate approach to modeling interbay arrivals and delays and explores periods of peak transport demands. A From:To matrix was developed from a detailed simulation model with process flows to represent the hourly demand of bay-to-bay movements. A second From:To matrix was generated to represent the mean transport time of automated material handling. We examine the effect that these matrices have on simulation output and model performance. Three distributions, Constant, Normal, and Exponential, were used with each table. The comparison between detailed and matrix input results included the mean and 95th percentile of delivery times and lot cycle time differentials, as well as car utilization and model execution time. The Exponential distribution provided results closest to those of the detailed model.