Optimized inspection capacity for out of control detection in semiconductor manufacturing

In-line inspection is designated to detect out-of-control (OOC) performance in order to increase quality output, and thus profit. Since inspection capacity is costly, it raises the question of how much capacity should be acquired to minimize OOC. Clearly, lower OOC requires higher capacity. This paper suggests a model that optimizes inspection capacity and OOC tradeoff. It is based on a typical process step monitored by an inspection facility. Processed items are sampled and inspected, considering inspection rate and response time, in order to minimize OOC rate at a given capacity. The inspection operating curve is established for demonstrating the tradeoff between OOC rate and inspection capacity. It exhibits that OOC decreases at a reduced rate with increasing capacity. Fab specific financials can provide the cost ratio between capacity and OOC for determining the preferred working point on the inspection operating curve.