Microstructure, mechanical properties, and wetting behavior of Si–C–N thin films grown by reactive magnetron sputtering

Silicon–carbon–nitride (Si–C–N) thin films were deposited by reactive magnetron co-sputtering of C and Si targets in a mixed Ar/N2 discharge. Films were grown to a thickness of more than 0.5 μm on graphite and Si(001) substrates held at a negative floating potential of ∼−35 V, and substrate temperature between 100 and 700°C. The total pressure was constant at 0.4 Pa (3 mtorr), and the nitrogen fraction in the gas mixture was varied between 0 and 100%. As-deposited films were analyzed with respect to composition, state of chemical bonding, microstructure, mechanical properties, and wetting behavior by Rutherford backscattering spectroscopy (RBS), energy dispersive spectroscopy (EDS), X-ray photoelectron spectrometry (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), nanoindentation and contact angle measurements, respectively. Depending on the deposition condition, ternary SixCyNz films within the composition range 1≤x≤34 at.%, 34≤y≤81 at.%, and 16.5≤z≤42 at.% were prepared with a textured, amorphous-to-graphite-like microstructure. For Si–C–N films with low Si content, CC, CN and SiC bonds were present. At higher Si content, N preferentially bonds to Si, while less CN bonds were observed. Films containing more than ∼12 at.% of Si contained widely dispersed crystallites, 2–20 nm in diameter. Incorporation of a few at.% Si resulted in a dramatic reduction of the film surface energy compared to pure CN films. The measured contact angles using distilled water and glycerol liquids were for some films comparable with those on a polytetrafluoroethylene (PTFE), Teflon® surface. The hardness of Si–C–N films could be varied over the range 9–28 GPa.