Nano-structured CrN/CN_x multilayer films

CrN/CN_x nano-scale multilayered films were deposited on Si (100) substrate by closed-field unbalanced magnetron sputtering. Designed experimental parameters enabled an evaluation of the effects of negative substrate bias voltage (V_b), and bi-layer thickness λ (by changing substrate rotation rate) during deposition on the structural and mechanical properties of multilayer films. These multilayers were characterized and analyzed by transmission electron microscope (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), and nanoindentation measurements. In all cases, the CN_x layers were amorphous and independent of V_b, while the microstructures of the CrN layers were dependent primarily on V _b. The CrN layers showed a mixed structure phase consisting of CrN, Cr₂N, and Cr at V_b = -(40-120) V. At higher V_b values (-140 V or above), the Cr₂N phase was dominant along with low CrN phase content. AFM measurements revealed that the root-mean-square (rms) surface roughness of the CrN/CN_x film was 2 nm at V_b= -200 V whereas the rms values were about 9.5-3.3 nm for lower V_b values of-(40-180 V). By nanoindentation measurements, a maximum hardness of about 36 GPa was observed at V_b= -140 V. The improved mechanical properties of the films are correlated to the phase formation during deposition.