Effects of nitrogen gas ratio on composition and microstructure of BCN films prepared by RF magnetron sputtering

BCN films are prepared by a radio frequency (RF) magnetron sputtering in a mixture of Ar and N2 gases using a combination of half-moon shaped B4C (BC) and graphite (G) targets where the substrates are faced to each target side (BC-side and G-side) which allows us to obtain the BCN films with a different composition at the same time. The compositional and structural changes are examined under the different conditions of the ratio of N2 to Ar gases and the sample-set-positions by field emission-scanning electron microscopy/energy dispersive X-ray spectroscopy (FE-SEM/EDX), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), visible– and ultraviolet (UV)–Raman measurements. Nanoindentation test is also carried out to evaluate the mechanical properties. It is found that all films exhibit amorphous structure. With increasing N2 ratio, the B concentration in the films is decreased, while the amount of C–N bonds is increased. For the G-side films, C concentration and the amount of B–C bonds are increased as compared with the BC-side films. The results suggest that the increase of N2 ratio causes the decrease of sputtered B and the enhancement of C–N bond formation. In the case of the G-side films, BC1.4N0.4 films are obtained at N2 ratio of 100%. The relation between the results of Raman spectroscopy and hardness of the films and possible scheme of the microstructure are discussed.