Characterization of sputter-deposited chromium nitride thin films for hard coatings

CrN and Cr2N thin films were deposited on silicon, quartz, HSS-steel and carbon substrates by rf reactive magnetron sputtering. The phase and texture were determined by X-ray diffraction analysis. The chemical composition was measured by electron probe microanalysis. Atomic force microscopy revealed a finely grained morphology. The nitrogen content in the sputtering gas influences the film composition and morphology. At N-2 partial pressure below 20% (0.08 Pa) of the total pressure (0.67 Pa) the hexagonal Cr2N phase is present, while above 40%, the cubic CrN phase only is observed. Thin films grown at high substrate temperatures (T-s greater than or equal to 400 K) exhibit larger grain sizes of up to 20 nm. The real and imaginary parts of the dielectric function were determined by spectroscopic ellipsometry in the photon energy range of 1.5 to 5.0 eV. The core levels and the valence band were analyzed using X-ray photoelectron spectroscopy. The degree of ionicity of the Cr-N bonding increases continuously with the N-2 partial pressure promoting the CrN phase. Hardness values of 2950 HV for Cr2N films and 1800 HV for CrN films were obtained by microindentation. (C) 1997 Elsevier Science S.A.