Fabrication of an integrated circuit includes forming a photoresist layer over a substrate. Target regions defined on the substrate are exposed using a reticle that defines a first exposure window for a first doped structure of a first type; the first exposure window has a first plurality of openings and a first plurality of dopant blocking regions. A respective exposure dose for each of the target regions is determined by an exposure map and provides controlled variations in the size of the first plurality of openings across the plurality of target regions. Subsequent to the exposure and to developing the photoresist, a dopant is implanted into the substrate through the first plurality of openings.