Influence of substrate bias voltage on structure and properties of hard Si–B–C–N films prepared by reactive magnetron sputtering

We systematically investigated the effect of the rf induced negative substrate bias voltage, Ub, on characteristics of novel quaternary Si–B–C–N films. The films were deposited on Si(100) or glass substrates by reactive dc magnetron co-sputtering of silicon, boron and carbon from a single C–Si–B or B4C–Si target in nitrogen–argon gas mixtures at substrate temperatures of 180–350 °C. Elemental compositions of the films, their surface bonding structure, and mechanical and electrical properties were primarily controlled by the Ub values, varied from a floating potential (being between − 30 and − 40 V) to Ub = − 700 V. The energy and flux of ions bombarding the target and the growing films were evaluated on the basis of the measured discharge characteristics. The films were found to be amorphous with thickness up to 5 μm and density around 2.4 g/cm3. They exhibited hardness up to 44 GPa, modified Young's modulus between 170 and 280 GPa, elastic recovery up to 82% and good adhesion to substrates at a low compressive stress (0.6–1.8 GPa). The results of stress measurements were compared with predictions of the model developed by Davis and a beneficial role of silicon in reducing the compressive stress in the films was proved. Electrical conductivity of the semiconductive Si–B–C–N films with a high (approximately 40 at.%) carbon content was controlled by the nitrogen–argon gas mixture composition and the Ub values.