white paper

Curvature-based fragmentation for curvilinear mask process correction

Using inverse lithography technology (ILT) to generate curvilinear masks improves lithography process window significantly but at the cost of large file size and data processing time that has made steps like mask process correction (MPC) a bottleneck in the post-tapeout flow. This paper describes a method to reduce the impact of curvilinear mask shapes on overall data preparation time called curvature based fragmentation (CBF).

CBF fragments curvilinear shapes based on their curvature. This method generates shorter 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.

To optimize the entire mask data preparation flow, CBF is applied during curvilinear optical proximity correction (OPC) or inverse lithography technology (ILT), so that all following data processing steps, in particular MPC, can benefit from an optimized fragmentation.

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