When manufacturing an integrated circuit, we have always made masks with Manhattan and 45-deg edges. Contact holes, for example, are designed square, even though the shape that is actually printed on wafer is a circle. It turns out that the ideal mask pattern to print such a circle is in fact a circle; the ultimate process-window-maximizing curvilinear mask shape. Curvilinear masks are now possible using multi-beam mask writers and EDA tools that handle curvilinear data are coming online.
This paper discusses the benefits of curvilinear (CL) masks and how electronic design automation (EDA) tools including inverse lithography technology enable this new generation of IC manufacturing.
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