In-line inspection impact on Cycle Time and Yield

Semiconductor industry constantly drives for high yield and low cycle time (CT), while most current manufacturing practices consider them separately. This research investigates the relationship between CT and yield as impacted by in-line metrology inspections of production lots. It reduces the CT accumulated due to inspections, while considering the impact on yield as a result. The research assumes a simple production cell model of a mini production-line segment and evaluates different inspection policies via simulation and analytical methods. The results of ten inspection policies present a typical concave curve for yield versus CT. Increased inspection increases both yield and CT until the yield reaches a maximum and starts to decline. The cause is a delay in corrective feedback of an out-of-control tool due to longer inspection waiting time. It is shown that the commonly used Fixed Measure Rate policy is inferior to some of the proposed dynamic policies. Finally, an objective function is developed to evaluate the preferred inspection policy. Future research would adapt the Production Cell model to a full production-line simulation.