1. A method of making a semiconductor device, the method comprising: forming a layer over a substrate; forming a plurality of spaced apart features of imagable material over the layer; forming sidewall spacers on the plurality of features; filling a space between a first sidewall spacer on a first feature and a second sidewall spacer on a second feature with a filler feature; removing the sidewall spacers to leave the first feature, the filler feature and the second feature spaced apart from each other; and etching the layer using the first feature, the filler feature and the second feature as a mask.