A method is disclosed for controlling the sheet resistance of copper trenches formed on semiconductor wafers. The method includes forming a plurality of copper-filled trenches on a wafer, measuring the sheet resistance of each of the plurality of copper-filled trenches, and comparing the measured sheet resistance values to a predetermined sheet resistance value. Photolithography steps performed on subsequent wafers are adjusted according to a difference between the measured sheet resistance values and the predetermined value. In one embodiment, this adjustment takes the form of adjusting a photolithographic extension exposure energy to thereby adjust the cross-section of the resulting trenches.