On the growth, orientation and hardness of chemical vapor deposited Ti(C,N)

Highlights: • Chemical vapor deposited Ti(C,N) films with improved hardness were grown. • Epitaxial ⟨111⟩ films had the highest hardness, 37 GPa. • TiCl₃ and HCN were identified as the major growth species for Ti(C,N) deposition. - Abstract: Chemical vapor deposition (CVD) of Ti(C,N) from a reaction gas mixture of TiCl₄, CH₃CN, H₂ and N₂ was investigated with respect to gas phase composition and kinetics. The gas phase composition was modelled by thermodynamic calculations and the growth rate of the CVD process was measured when replacing H₂ for N₂ while the sum of partial pressures H₂ + N₂ was kept constant. The N₂/H₂ molar ratio was varied from 0 to 19. Single crystal c-sapphire was used as substrates. It was found that low molar ratios (N₂/H₂ molar ratio below 0.6) lead to an increased Ti(C,N) growth rate with up to 22%, compared to deposition without added N₂. The mechanism responsible for the increased growth rate was attributed to the formation and increased gas phase concentration of one major growth species, HCN, in the gas phase. The texture of the Ti(C,N) films were also studied. ⟨211⟩ textured layers were deposited at N₂/H₂ molar ratios below 9. At higher molar ratios, ⟨111⟩ oriented Ti(C,N) layers were deposited and the grain size increased considerably. The films deposited at a N₂/H₂ ratio above 9 exhibited superior hardness, reaching 37 GPa. The increased hardness is attributed to an almost epitaxial orientation between the layer and the substrate. The Ti(C,N) layers were characterized by elastic recoil detection analysis, X-ray photo electron spectroscopy, scanning electron microscopy, X-ray diffraction and nanoindentation.