Evolution of chemical, structural, and mechanical properties of titanium nitride thin films deposited under different nitrogen partial pressure

•N-doped Ti thin films with varying nitrogen partial pressure are fabricated.•Ti transforms from the hcp α-Ti phase to the fcc δ-TiN phase after the addition of nitrogen.•N atoms produce expansions causing compressive stress in the Ti lattice.•Surface roughness constantly decreases with an increase in the nitrogen ratio from 0% to 20%. In this study, to explore the impact of nitrogen on chemical composition, morphology, microstructure, as well as intrinsic stress of titanium films, nitrogen-doped titanium thin films prepared by direct current reactive magnetron sputtering, with different ratio of nitrogen doping into the Argon gas, have been characterized. After the check of grazing incidence X-ray reflectometry (GIXR), thickness of all samples were ensured to be approximately 40 nm. Using the X-ray photoelectron spectroscopy (XPS) combined with X-ray diffraction (XRD), nitrogen atoms were found to transform Ti crystals from the hexagonal close-packed (hcp) α-Ti phase with Ti(100) and Ti(002) orientation to the face-centered cubic (fcc) δ-TiN phase with TiN(111) and TiN(200) orientations, accompanied by the formation of TiO and TiON. XRD diffraction patterns further revealed the expansion of the TiN lattice and the intensity transform of TiN(111) and TiN(200). Atomic force microscopy (AFM) results indicated that the surface roughness declined continuously. A compressive stress was found to increase gradually with increasing nitrogen content. Variations in stress are caused by the expansion of the crystal lattice. It is obvious that the incorporation of nitrogen into titanium films can effectively reduce the roughness, but it will result in an increase in the compressive stress. Therefore, an appropriate nitrogen partial pressure should be chosen to control the intrinsic stress while reducing the roughness effectively.