Reactive magnetron sputtering of Si–C–N films with controlled mechanical and optical properties

Abstract

Si–C–N films were deposited on p-type Si(1 0 0) substrates by dc magnetron co-sputtering of silicon and carbon using a single sputter target with variable Si/C area ratios in nitrogen–argon mixtures. The film characteristics were controlled by the silicon fraction (5–80%) in the erosion target area for a 50% N 2+50% Ar gas mixture and by the argon concentration (0–75%) in the gas mixture at a fixed 40% silicon fraction in the erosion target area. The total pressure and the discharge current on the magnetron target were held constant at p=0.5 Pa and I m=1 A, the substrate temperature was adjusted at T s=600 °C by an ohmic heater and the r.f. induced negative substrate bias voltage, U b, was −500 V. The films, typically 1.0–1.5 μm thick, were found to be amorphous with a very smooth surface ( R a≤0.8 nm) and good adhesion to substrates. It was shown that not only the composition of the C–Si target but also the nitrogen–argon gas mixture composition makes it possible to control surface bonding structure of the formed films and their mechanical and optical properties over a wide range. Increasing the silicon fraction in the erosion target area from 5 to 80% resulted in a rapid rise in optical transparency of the films and in their friction coefficient (from 0.24 to 0.53) at an almost constant film hardness close to 30 GPa. Increasing the argon concentration in the gas mixture from 0 to 75% led to a progressive increase in film hardness (up to 40 GPa) and to a higher optical transparency of the films at almost constant values (0.40–0.46) of their friction coefficient.