Magnetron sputtered Hf–B–Si–C–N films with controlled electrical conductivity and optical transparency, and with ultrahigh oxidation resistance

The paper deals with Hf–B–Si–C–N films deposited onto Si and SiC substrates using pulsed magnetron co-sputtering of a single B4C–Hf–Si target (at fixed 15% Hf and 20% Si fractions in the target erosion area) in argon–nitrogen gas mixtures. We focus on the effect of the nitrogen fraction in the gas mixture (in the range from 0% to 50%) and of the voltage pulse length (50 μs and 85 μs with the corresponding duty cycle of 50% and 85%, respectively) on the structure and properties of the films. We show that an increasing nitrogen fraction in the gas mixture and consequently in the films (up to 52 at.%) results in a strong amorphization of the film structure, decrease in the film hardness, and rapid rise in the electrical resistivity and the optical transparency of the films. Very high oxidation resistance in air even up to 1500 °C is demonstrated for two sufficiently hard (20–22 GPa) Hf–B–Si–C–N films: the electrically conductive Hf7B23Si22C6N40 film and the optically transparent Hf6B21Si19C4N47 film, both with a contamination level < 3 at.%. The results are important for designing high-temperature protective coatings of electronic and optical elements, and sensors for severe oxidation environments.