An efficient shift invariant rasterization algorithm for all-angle mask patterns in ILT

Lithography simulation is an essential technique to guide the design of inverse lithography technology (ILT) masks. To reduce the complexity in modern lithography simulation, a widely used approach is to first rasterize the ILT masks before they are inputted to the simulation tools. Currently, there is no high performance technology to handle the rasterization of all-angle polygons, which are very common in modern ILT masks. Traditional rasterization technology is very expensive in term of runtime and memory usage. In this paper, we propose an efficient rasterization algorithm for all-angle polygons based on a pre-computed lookup table (LUT). We expect that the convolution for a majority of large pixels can be performed in a single lookup table query, which decreases the overall runtime dramatically. The experimental results demonstrate that our proposed algorithm can speed up rasterization process by almost 500× while maintaining small variations in CD. Meanwhile, the time for pre-computing the lookup table and the size of it can be kept within very reasonable limits.