SIMULATING AMHS PERFORMANCE FOR SEMICONDUCTOR WAFER FABRICATION

摘要

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.rnA 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.rnA challenging and often overlooked characteristic of wafer fab dynamics is the rush-hour occurrence usually experienced during meal breaks and shift changes. This paper provides an analysis of rush-hour movements in a wafer fab and their effect on interbay AMHS, while providing an approach to modeling this phenomenon. We developed a scalar array to represent the deviation from the mean hourly transport demand. This extra level of detail provided only a small improvement to the output statistics. Each of the three alternate approaches discussed provided at least a 50% reduction in model execution time.