An improved deposition chamber (2) includes a housing (4) defining a chamber (18) which houses a substrate support (14). A mixture of oxygen and SiF.sub.4 is delivered through a set of first nozzles (34) and silane is delivered through a set of second nozzles (34a) into the chamber around the periphery (40) of the substrate support. Silane (or a mixture of silane and SiF.sub.4) and oxygen are separately injected into the chamber generally centrally above the substrate from orifices (64, 76). The uniform dispersal of the gases coupled with the use of optimal flow rates for each gas results in uniformly low (under 3.4) dielectric constant across the film.