Mix and match overlay optimization strategy for advanced lithography tools(193i and EUV)

In state of the art production, in order to obtain the best possible overlay performance between critical layers, wafers are often dedicated to one scanner and all layers processed on that scanner, and in the case of scanners with dual stages, this often extends to stage dedication as well. Meeting the overlay performance requirements becomes even more complex with the introduction of EUV lithography into production. It will not be possible to expose all critical layers on an EUV scanner, which will only be used for some of the most critical layers, the other critical layers will remain on 193nm immersion scanners. It therefore needs to be demonstrated that the same overlay performance is achievable when tool types are mixed and matched as when we run with tool dedication. To do this it is critical that we understand the overlay matching characteristics of 193nm immersion and EUV scanners and from this learn how to control them, so that the optimum strategy can be developed and overlay errors between these tool types minimized. In this work we look at the matching performance between two generations of 193nm immersion scanner and an EUV pre-production tool. We evaluate the matching in both directions, first layer on immersion, second layer on EUV and vice-versa, and demonstrate how optimum matching can be achieved, so that insertion of an EUV scanner into production for the required imaging does not result in a degraded overlay capability. We discuss the difference in grid and intrafield signatures between the tool types and how this knowledge can be used to minimize the overlay errors between them and if there are any new concerns which impact the chosen strategy when the two tool types are mixed and matched.