The present disclosure describes methods of forming a mask. In an example, the method includes receiving an integrated circuit (IC) design layout, modifying the IC design layout data using an optical proximity correction (OPC) process, thereby providing an OPCed IC design layout, and modifying the OPCed IC design layout data using a mask rule check (MRC) process, wherein the MRC process corrects rule violations of the OPCed IC design layout data using a mask error enhancement factor (MEEF) index, thereby providing a MRC/OPCed IC design layout.
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