Investigation of substoichiometric titanium nitride grown by unbalanced magnetron sputtering

TiNx (stoichiometric factor, x=0.1–0.4) films were deposited at a substrate temperature typically of 480°C using an industrial-sized multi-target PVD coating machine. The stoichiometric factor, x, depended on the manner of substrate rotation as well as the reactive gas flow during depositing. In parallel, multiphase compositions of αTi(N), εTi2N and δTiN were found with hardness values varying from 1500 to 2300 Hk, and 2100 Hk for ε phase Ti2N. The XRD spectral showed Bragg reflections associated with mixed phase compositions. The almost pure εTi2N phase was found in the film with x close to 0.34 and the XRD diffraction pattern of this film perfectly matched the ε phase documented as referred to in the JCPDS file 17-386. SEM and TEM cross-sections exhibited a very fine grain structure for films containing dominant εTi2N phase. The microstructure of εTi2N film was extremely homogeneous throughout the complete film growth. The surface of εTi2N film was surprisingly smooth.