In-depth analysis of indirect overlay method and application in production environment

摘要

Overlay measurements are done for verification of the exposure and creation of process corrections for the next lots. As throughput of the overlay measurement tools is limited, it is desirable to avoid unnecessary measurements. Another concern can be that in-transparent stacks do not allow measuring a critical overlay relation directly. We developed methods for calculation of the overlay relation between two different layers between which there is no direct overlay measurement. We qualify the impact of sampling plans and the number of dependent layers. The indirect overlay calculation is applied on a significant high volume data set.