1. A method of making a mask layout for forming contact holes on a semiconductor device, the method comprising: patterning a first feature along a first axis; determining a first set of areas adjacent to the first feature, wherein each of the areas in the first set of areas is within a first angle away from the first axis, and wherein each of the areas in the first set of areas is within a first distance away from the first feature; and patterning a second feature in at least one of the first set of areas so as to form a mask layout, wherein each of the first feature and the second feature are one of a virtual feature and a real feature.