Methods for forming silicon nitride hard masks are provided. The silicon nitride hard masks include carbon-doped silicon nitride layers and undoped silicon nitride layers. Carbon-doped silicon nitride layers that are deposited from a mixture comprising a carbon source compound, a silicon source compound, and a nitrogen source in the presence of RF power are provided. Also provided are methods of UV post-treating silicon nitride layers to provide silicon nitride hard masks. The carbon-doped silicon nitride layers and UV post-treated silicon nitride layers have desirable wet etch rates and dry etch rates for hard mask layers.