The present disclosure provides for many different embodiments. An exemplary method can include providing a mask fabricated according to a design pattern; extracting a mask pattern from the mask; converting the mask pattern into a rendered mask pattern, wherein the simulated design pattern includes the design pattern and any defects in the mask; simulating a lithography process using the rendered mask pattern to create a virtual wafer pattern; and determining whether any defects in the mask are critical based on the virtual wafer pattern. The critical defects in the mask can be repaired.