A method and apparatus for depositing a low dielectric constant film includes depositing a silicon oxide based film, preferably by reaction of an organosilicon compound and an oxidizing gas at a low RF power level from about 10W to about 500W, exposing the silicon oxide based film to water or a hydrophobic-imparting surfactant such as hexamethyldisilazane, and curing the silicon oxide based film at an elevated temperature. Dissociation of the oxidizing gas can be increased in a separate microwave chamber to assist in controlling the carbon content of the deposited film. The moisture resistance of the silicon oxide based films is enhanced.