Embodiments of the invention describe a method for controlling etching in pitch doubling. According to one embodiment, the method includes receiving a substrate having a pattern thereon defined by spacers formed on sidewalls of a plurality mandrels, and transferring the pattern defined by the spacers into the substrate using a plasma etch process that etches the mandrels and the substrate, the transferring forming first recessed features in the substrate below the mandrels and second recessed features in the substrate between the mandrels, where the plasma etch process utilizes an etching gas containing O2 gas, and the relative amount of O2 gas in the etching gas is selected to control the depth of the first recessed features relative to the depth of second recessed features. According to another embodiment, the substrate contains a mask layer thereon and a pattern on the mask layer.