Structural transitions in hard Si-based TiN coatings: the effect of bias voltage and temperature

(Ti,Si)N films were grown by reactive magnetron sputtering. X-Ray diffraction experiments (XRD) showed the development of a mixture of two crystalline phases with lattice parameters higher (a=0.429 nm: phase 1 — indexed with TiN) and lower (a=0.418 nm: phase 2 — indexed to a Ti–Si–N phase) than that of bulk TiN (a=0.424 nm). Transmission electron microscopy revealed nanocrystalline grains of an fcc structure in both crystalline phases. X-Ray absorption spectroscopy results indicated that in these films there are Si atoms bonded to Ti. This means that in phase 2 there must be some Si atoms occupying Ti positions within the TiN lattice, which explains the lower lattice parameter for that phase. Phase 2 was the only phase observed for low surface mobility conditions of the deposited material (low temperature =300°C and absence of ion bombardment of the growing film). This low surface mobility conditions of the deposited material might explain the claimed substitution of Ti with Si in TiN. When present, the lattice parameter of phase 2 is approximately the same for all Si contents, which ranged from 2.5 up to nearly 20 at.%. The enhancement of the surface mobility, either by a temperature increase or by ion bombardment during film growth, induces higher phase segregation, and therefore the XRD diffraction peaks from phase 2 disappear. For deposition temperatures near ∼ 500°C, and/or biased substrates, the complete segregation of phases was observed (no traces of phase 2), thus forming a nanocomposite structure composed of nanocrystalline grains of TiN embedded in an amorphous silicon nitride phase-nc-TiN/a-Si3N4.