A method of forming a sidewall spacer on a gate electrode of a metal oxide semiconductor device that includes striking a first plasma to form an oxide layer on a side of the gate electrode, where the first plasma is generated from a oxide gas that includes O₃ and bis-(tertiarybutylamine)silane, and striking a second plasma to form a carbon-doped nitride layer on the oxide layer, where the second plasma may be generated from a nitride gas that includes NH₃ and the bis-(tertiarybutylamine)silane. The first and second plasmas may be formed using plasma CVD and the bis-(tertiarybutylamine)silane flows uninterrupted between the striking of the first plasma and the striking of the second plasma.