A method of forming a sidewall spacer on a gate electrode is described. The method includes generating a first plasma from a silicon containing precursor and oxide precursor, and forming a silicon oxy-nitride layer on the sidewall of the gate electrode. The method also includes generating a second plasma from the silicon containing precursor and a nitrogen precursor, and forming a nitride layer on the silicon oxy-nitride layer. The silicon containing precursor can flow continuously between the generation of the first and the second plasmas. Also, a method of forming a sidewall spacer on the side of a gate electrode on a substrate. The method includes forming an oxy-nitride layer on the sidewall, and forming a nitride layer on the oxy-nitride layer, where the substrate wafer is not exposed to air between the formation of the layers.