A method for fabricating a semiconductor device includes forming a plurality of isolation structures in a semiconductor substrate and forming a plurality of blocking structures over the isolation structures. The blocking structures have a lower reflectivity than the isolation structures. The method further includes forming a photoresist layer on the semiconductor substrate, exposing the photoresist layer to a light source through a mask, and developing the photoresist layer to create a patterned photoresist feature that covers a first region of a portion of the semiconductor substrate between two of the isolation structures. The portion of the semiconductor substrate having a second region that is exposed.