Unfolding the curves: novel designs and metrology methods for curvilinear masks qualification

The ongoing scaling of semiconductor devices necessitates increasing development of new and disruptive technologies. Curvilinear layout design and optical proximity correction (OPC) are among the innovations facilitating these advancements in technologies. However, they face challenges in mask enablement technology, including issues with mask writing, data volume management, design complexity, mask data representation, mask qualification, and metrology. In this paper, curvilinear mask test patterns and measurement methodologies are newly proposed for mask qualification and masks specification. Using contour-based mask metrology, edge placement error (EPE), mean-to-target (MTT) and uniformity (CDU) based on target maximum curvature (TMC) are measured and used as the main qualification metrics instead of traditional metrics such as critical dimensions (CD). These novel methods will partly complement standard qualification methods used for non-curvilinear (Manhattan) masks. A set of unique mask test structures are also proposed to extract the minimum set of curvilinear mask rules which enables experimental definition and verification of the manufacturing process.