Combined process window monitoring for critical features

摘要

After critical lithography steps, overlay and CD are measured to determine if the wafers need to be re-worked. Traditionally, overlay metrics are applied per X/Y-direction and, a CD metric is computed independently. From design standpoint, electrical failure is based on a complex interaction between CD deviations and overlay errors. We propose a method including design constraints, where results of different measurement steps are not judged individually, but in a combined way. We illustrate this with a critical design feature consisting of a contact requiring minimum distance to a neighboring metal line, resulting in much better correlation to yield than traditional methods.