A method comprises: selecting a circuit pattern or network of circuit patterns in a layout of an integrated circuit (IC) to be fabricating using double patterning technology (DPT). Circuit patterns near the selected circuit pattern or network are grouped into one or more groups. For each group, a respective expected resistance-capacitance (RC) extraction error cost is calculated, which is associated with a mask alignment error, for two different sets of mask assignments. The circuit patterns in the one or more groups are assigned to be patterned by respective photomasks, so as to minimize a total of the expected RC extraction error costs.