Multiple spacer patterning schemes

The present disclosure provides forming nanostructures utilizing multiple patterning process with good profile control and feature transfer integrity. In one embodiment, a method for forming features on a substrate includes forming a mandrel layer on a substrate, conformally forming a spacer layer on the mandrel layer, wherein the spacer layer is a doped silicon material, and patterning the spacer layer. In another embodiment, a method for forming features on a substrate includes conformally forming a spacer layer on a mandrel layer on a substrate, wherein the spacer layer is a doped silicon material, selectively removing a portion of the spacer layer using a first gas mixture, and selectively removing the mandrel layer using a second gas mixture different from the first gas mixture.