A method of depositing a dielectric film, such as tantalum oxide, on a substrate is described. In one example, a substrate is placed in a process zone to face a metal target and a pulsed DC voltage is applied to the target. A sputtering gas comprising a non-reactive component and an oxygen-containing component is introduced to the process zone in a volumetric flow ratio selected to achieve the desired x and y values in the deposited dielectric film, for example, in the deposition of a non-stoichiometric Ta_xO_y film or in the deposition of a tantalum oxide film in which the oxidation state of tantalum is less than +5. The sputtering gas is removed from the process zone by condensing at least some of the non-reactive component on a cooled surface external to the process zone, and exhausting at least some of the oxygen-containing component from the process zone with moving rotors. A multiple layer dielectric film having different stoichiometric ratios in the layers can also be deposited by the instant method.