A method includes forming a first inter-layer dielectric (ILD) layer over source and drain regions of a semiconductor structure; forming a first mask material over the first ILD layer; etching first openings in the first mask material; filling the first openings with a fill material; etching second openings in the fill material; filling the second openings with a second mask material; removing the fill material; and etching the first ILD layer using the first mask material and the second mask material as an etching mask to form openings in the first ILD layer that expose portions of the source and drain regions of the semiconductor structure.