Estimating wafer processing cycle time using an improved G/G/M queue

Wafer processing cycle times have been successfully calculated using the basic G/G/m queue by relying on historical data to determine the required variability component. The basic equation was found to work well for a highly utilized factory but provided less accurate results at low factory utilization points. Implementation of an improved G/G/m queue as suggested by existing research has resulted in improved correlation with factory performance even during times of lower factory utilization. An overview of the original implementation is presented, followed by the equation for the improved G/G/m queue, its implementation, and subsequent validation results.