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; simulating a fabrication operation to generate a simulated mask image according to the mask design; comparing the predetermined layout to the simulated mask image to determine at least one simulated mask error (ERR s ); 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 at least one actual mask error (ERR m ); comparing the simulated mask error (ERR s ) to the actual mask error (ERR m ) to determine at least one fitness value; determining, based at least in part on the at least one fitness value, whether to modify the mask design; and revising the OPC tool based on the results of the comparison of at least one of comparing the predetermined layout step or comparing the measurement step.