Setting defect charts control limits to balance cycle time and yield for a tandem production line

Abstract

Control limits in use at metrology stations are traditionally set by Yield requirements. Since deviations from these limits usually trigger a machine׳s stoppage, the inspection design has a direct impact on the station׳s availability, and thus on the product cycle time (CT). In this research we formulate a trade-off between the expected values of the CT and the die Yield. Based on the impact of the inspection׳s control limits on both performance measures, we formulate the CT to Yield Pareto-optimal set for a tandem production line.We consider a semiconductor production line in which production stations are afflicted by a defect deposition process and immediately followed by an inspection step. First we study the impact of the upper control limit on both expected values of Yield and CT on a single station. Then, we extend our result to a tandem production line and present an optimal greedy algorithm that provides the Pareto-optimal set of Upper Control Limit (UCL) values for the line. The obtained model enables decision makers to knowingly sacrifice Yield to shorten CT and vice versa.