A method and apparatus for depositing a low dielectric constant film by reaction of an organosilane or organosiloxane compound and an oxidizing gas at a low RF power level from 10 250 W. The oxidized organosilane or organosiloxane film has good barrier properties for use as a liner or cap layer adjacent other dielectric layers. The oxidized organosilane or organosiloxane film may also be used as an etch stop or an intermetal dielectric layer for fabricating dual damascene structures. The oxidized organosilane or organosiloxane films also provide excellent adhesion between different dielectric layers. A preferred oxidized organosilane film is produced by reaction of methylsilane, CH.sub.3SiH.sub.3, or dimethylsilane, (CH.sub.3).sub.2SiH.sub.2, and nitrous oxide, N.sub.2O, at an RF power level from about 10 to 200 W or a pulsed RF power level from about 20 to 250 W during 10 30% of the duty cycle.