1. A non-transitory tangible machine-readable medium having code stored thereon, the code comprising instructions for: applying an optical proximity correction (OPC) to a mask layout for a photolithography process to generate a post-OPC layout; determining a plurality of stochastic error mask layouts from the post OPC layout, the plurality of stochastic error mask layouts from the post OPC layout include a probability distribution of errors that are applied to the post OPC layout in order to more accurately simulate mask process variability; and analyzing the plurality of stochastic error mask layouts for critical dimension uniformity (CDU).