Growth of CN_xH_y films by reactive magnetron sputtering of carbon in Ar/NH₃ discharges

Abstract

Results on hydrogenated carbon nitride (CN_xH_y) thin films grown by reactive magnetron sputtering in a mixed Ar/NH₃ discharge are reported. Depending on the growth temperature (T_s) and negative substrate bias voltage (V_s), both the composition and the microstructure were altered. Using nuclear reaction analysis and resonant backscattering spectroscopy, the maximum N and H content were both 15 at. %. Both the hydrogen and nitrogen content of the films was found to decrease with increasing growth temperature. The results also show pronounced chemical resputtering effects, resulting in no net film growth for V_s > 75–100 V. X-ray photoelectron spectroscopy showed no signs of N bound to sp³ hybridized C. Also, the microstructure of the films was found to change with T_s. For T_s < 150 °C, a structure with crystalline clusters embedded in an “fullerene-like” matrix was observed by high-resolution transmission electron microscopy. Power-spectra obtained from the clusters could be identified with the cubic diamond structure. For T_s ⩾ 300 °C, no crystalline clusters were found and the films had a homogeneous “fullerene-like” microstructure with strongly bent planes and closed shell-like features resembling bucky-onions. Evaluation of nanoindentation results from the homogeneous “fullerene-like” films gave hardness values between 7 and 11 GPa and elastic recoveries of 55–60%. This should be compared with hardness and elastic recoveries of 40–60 GPa and 85–90%, respectively, previously reported for on nonhydrogenated carbon nitride CN_x films grown under the same conditions, but in pure N₂ discharges.