A method of forming a device includes depositing a first etch mask layer over a mandrel formed using a lithography process. The method includes depositing a second etch mask layer over the first etch mask layer. The method includes, using a first anisotropic etching process, etching the first etch mask layer and the second etch mask layer to form an etch mask including the first etch mask layer and the second etch mask layer. The method includes removing the mandrel to expose an underlying surface of the layer to be patterned. The method includes, using the etch mask, forming a feature by performing a second anisotropic etching process to pattern the layer to be patterned, where during the first anisotropic etching process, the first etch mask layer etches at a first rate and the second etch mask layer etches at a second rate, and where the first rate is different from the second rate.