Pulsed DC magnetron sputtered Al2O3 films and their hardness

Al2O3 films were deposited by reactive ionized magnetron sputtering and their hardness was measured by nanoindentation. The magnetron was powered with a pulsed DC power supply, and the substrate was negatively biased with a pulsed DC voltage supply. An RF powered coil was located above the substrate to vary the ion flux hitting the substrate. As measured with transmission electron microscopy and X-ray diffraction, the films were amorphous in the temperature range 200 to 600 °C, when only a low flux of ions hit the film during growth. At 200 °C, with increasing ion bombardment, 100 nm large clusters of small crystalline grains of γ-Al2O3 with sizes of the order of 5 nm were embedded in the amorphous phase. Increasing the flux of ions and/or the temperature further enabled us to make films consisting only of crystalline γ-Al2O3. A systematic study was carried out of the dependence of the nanostructure on a) the RF power of the coil creating the ions bombarding the growing film, on b) the bias voltage, and on c) the substrate temperature. The hardness values of the films were measured and correlated to the film nanostructure.