Photolithography apparatus includes a radiation source, a mask to modify radiation from the radiation source so the radiation exposes photoresist layer disposed on a semiconductor substrate in patternwise manner, a wafer stage, and a controller. The wafer stage supports the semiconductor substrate. The controller determines target total exposure dose for the photoresist layer and target focus position for the photoresist layer; and controls exposure of first portion of the photoresist layer to first exposure dose of radiation at first focus position using first portion of the mask, moving the semiconductor substrate relative to the mask; and exposure of the first portion of the photoresist layer to second exposure dose of radiation using second portion of the mask at second focus position, and exposure of second portion of the photoresist layer to the second exposure dose at the second focus position using the first portion of the mask.