Structural and chemical properties of sputter-deposited Ti–Ge–N thin films

Ti–Ge–N single-layer and TiN/GeN-multilayer thin films were deposited by reactive magnetron sputtering on Si and WC–Co substrates at constant temperature Ts = 240 °C, from confocal Ti and Ge targets in a mixed Ar/N2 atmosphere. The nitrogen partial pressure, the TiN deposition time tTi and the power on the Ti and Ge targets were kept constant. In order to obtain various GeN layer thicknesses in the films, the deposition time ratio tGe/tTi was varied. TiN/GeN multilayer films with TiN thickness ∼ 5 nm and various GeN thicknesses between 0.5 and 5 nm were deposited. A nanocrystalline multilayer film is formed, where the suppression of crystal growth is controlled by the successive deposition of two phases. TEM investigations revealed important changes induced by GeNx thickness variation: the columnar single-layer morphology switches into a multilayer morphology. The critical GeN thickness for changing the type of morphology is controlled by the diffusion of Ge atoms at the TiN crystallite boundaries. The morphology modification from single-layer to multilayer type determines the film hardening. Electron probe microanalyses (EPMA), scanning tunneling microscopy (STM), transmission electron microscopy (TEM), nanoindentation and X-ray diffraction (XRD) techniques were employed to characterize single- and multilayer films. The properties of alternate-deposited films are compared to those of co-deposited ones and interpreted.