Methods and apparatus of the present invention deposit fluorinated silicate glass (FSG) in such a manner that it strongly adheres to an overlying or underlying barrier layer or etch stop layer, and has a lower dielectric constant, among other benefits. In one embodiment, silicon tetrafluoride (SiF4), oxygen (O2), and argon (Ar) are used as the reactant gases, with the ratio of oxygen to silicon controlled to be at between about 2:1 to 6:1. Such O2 levels help reduce the amount of degradation of ceramic chamber components otherwise caused by the elimination of silane from the process recipe.