Structural and electrical properties of films sputtered from a Pt cathode in argon−oxygen mixtures

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Abstract
Films have been deposited on glass and polycrystalline alumina substrates by reactive dc sputtering of platinum in oxygen−argon mixtures. The films properties depend on the oxygen/argon ratio and on the discharge parameters. Whereas the resistivity was 25 μΩ cm in an argon discharge at 5 kV, it was higher than 1.5 Ω cm in an oxygen discharge at 2 kV. Corresponding changes were obtained in the temperature coefficient of resistance; values from +2000 to −25000 ppm/°C were measured. As the resistivity increased, the film density decreased from 21.5 to 15.5 g/cm3. These results are interpreted in terms of a cermetlike film structure consisting of mixtures of Pt and oxides of platinum. X−ray and electron diffraction analysis confirms the presence of a phase isostructural with PdO which is considered to be PtO. This phase decomposes to Pt on heating in air at temperatures above 600 °C and thermogravimetric analysis showed that the film composition changed from Pt to PtO1.3 as the temperature coefficient of resistance changed from +2000 to −11000 ppm/°C. It is porposed that an amorphous PtO2 phase is also present in these films and ESCA spectra have confirmed the presence of Pt, PtO, and PtO2. Analysis of the sputtering discharge characteristics and changes in the gas composition during sputtering are consistent with gettering of oxygen by the sputtered Pt.