Methods and apparatus are provided for processing a substrate with a hermetic dielectric layer. In one aspect, the invention provides a method for processing a substrate including providing the substrate to a processing chamber, introducing a processing gas comprising a reducing agent, an oxygen containing compound, and an organosilicon compound, into the processing chamber, generating a plasma from a dual frequency RF power source, and depositing a dielectric material comprising silicon, carbon, and oxygen. The dielectric material may be used as an etch stop, an anti-reflective coating, or a passivation layer.