A method includes performing a place and route operation using an electronic design automation tool to generate a preliminary layout for a photomask to be used to form a circuit pattern of a semiconductor device. The place and route operation is constrained by a plurality of single patterning spacer technique (SPST) routing rules. Dummy conductive fill patterns are emulated within the EDA tool using an RC extraction tool to predict locations and sizes of dummy conductive fill patterns to be added to the preliminary layout of the photomask. An RC timing analysis of the circuit pattern is performed within the EDA tool, based on the preliminary layout and the emulated dummy conductive fill patterns.