Curvature based fragmentation for curvilinear mask process correction

Photomask technology has advanced substantially with the introduction of Multi Beam Mask Writers (MBMW), which achieve acceptable mask write times even with very complex mask patterns. In addition, Inverse Lithography Technology (ILT) and similar techniques generating complex curvilinear mask shapes, have been shown to improve wafer lithography process window significantly. Both of those factors and the increasing power of computing resources increase the use of such mask shapes for DUV and EUV lithography. However, when processing complex curvilinear mask shapes in the mask data preparation flow, file size and data processing time, for example in Mask Process Correction (MPC), become a bottleneck[4]. In order to reduce the impact of curvilinear mask shapes on overall data preparation time, this work introduces a Curvature Based Fracturing (CBF) method, feasible for reducing file size and data processing time. CBF fragments curvilinear shapes based on their curvature. This method generates short segments along the shape edges where curvature is large and longer segments where curvature is small. Fragmenting curvilinear shapes this way is important for MPC to work well and achieve small Edge-Placement-Errors (EPE) even at high curvature regions. In addition, the method only generates small fragments where they are required for good MPC convergence but relaxes segment length at low curvature areas. That way, in many cases the result is a reduction in fragment count per shape and therefore a reduction in MPC runtime. The reduced fragment count also translates directly into smaller file sizes. In order to optimize the entire mask data preparation flow, CBF is applied during curvilinear OPC or ILT, so that all following data processing steps, in particular MPC, can benefit from an optimized fragmentation.