Resolution enhancement technique requirements drive continuously increasing mask pattern complexity which creates an increasingly serious problem of ever longer mask writing times. Shot count is highly correlated to the writing time of VSB writing tools. Therefore shot count management is one proposed direction for practical writing time reduction. Shots may be induced from small features and pattern jogs due to OPC and other factors. Optimizing shot count without compromising pattern quality is required for the optimization solution. An effective shot count management solution is tested in this paper to remove the small-sized shots produced by misaligned vertices on both pattern edges under certain conditions. We demonstrate a post-OPC small shot removal solution with vertex alignment before pattern fracture. The shot optimization induced mask pattern differences are verified in the flow to ensure that they do not violate OPC requirements. As shot counts are reduced by the solution compared with the original pattern, the efficiency of the shot count reduction and writing time savings are evaluated. Meanwhile the pattern quality is also evaluated to ensure no degradation using both a mask level and wafer level check.
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