Which Spare Parts Service Measure to Choose for a Front-end Wafer Fab?

We are interested in the influence of spare part service measures on the performance of the front-end wafer fabrication process. This process is characterized by re-entrant flows due to the multiple layers present on chips. This exacerbates the effects of flow variability. We focus on the bottleneck resource. We consider three different service measures. The traditional aggregate fill rate and downtime waiting for parts do not take into account the number of outliers in the case of stock out. The third service measure is the number of extreme long downs, specifically designed at limiting outliers. We develop an improved method, combining optimization and simulation, to compare the performance of a front-end wafer fabrication process under these three service measures. In the studied case, the extreme long down service measure delivers superior performance and transparency. Our approach can help practitioners to choose the appropriate spare parts service measure, increasing fab performance.