In-depth analysis of sampling optimization methods

High order overlay and alignment models require good coverage of overlay or alignment marks on the wafer. But dense sampling plans are not possible for throughput reasons. Therefore, sampling plan optimization has become a key issue. We analyze the different methods for sampling optimization and discuss the different knobs to fine-tune the methods to constraints of high volume manufacturing. We propose a method to judge sampling plan quality with respect to overlay performance, run-to-run stability and dispositioning criteria using a number of use cases from the most advanced lithography processes.