Abstract: Using a sputter deposition system to reactively deposit a material such as an oxide, it is relatively easy to achieve either an oxygen-doped film with appreciable metallic content or an oxide film. However it is difficult with known systems to obtain an intermediate film having an accurately controlled resistivity, transparency, and composition, such films being of much use in semiconductor applications, in displays and in photovoltaic cells. It is now proposed that an apertured barrier be used to accurately fix the flow rate of target material to the substrate and in addition, that reactive gas flow be regulated and directed only to the immediate vicinity of the substrate. In this way the composition of the film can be accurately fixed. By establishing an r.f. field at the substrate, increased dissociation of the reactive gas can be achieved to render the gas more reactive and so enhance certain film properties such as transparency.