1. A method of refining an optical proximity correction (OPC) simulation tool for use in semiconductor fabrication, said method comprising the steps of: designing a mask having at least one feature from a predetermined layout; preparing a mask according to the mask design; creating at least one structure corresponding to the at least one mask feature on a semiconductor wafer using the mask; measuring the at least one mask feature; measuring the at least one structure to determine its fidelity to the layout; comparing the measurements of the at least one mask feature and the at least one structure to determine mask error; and revising the OPC tool based on the results of the comparison.