Surface/interface analysis and optical properties of RF sputter-deposited nanocrystalline titanium nitride thin films

Abstract

Titanium nitride (TiNx) thin films were grown by radio-frequency (RF) magnetron sputter deposition by varying the nitrogen content in the reactive gas mixture over a wide range. The effect of nitrogen gas flow rate on the surface and interface morphology, chemical composition and optical properties of TiN thin films was studied employing atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). Analysis of the optical properties probed with SE has shown that films deposited at low (0–5sccm) nitrogen flow rates have the highest absorption at energies <2eV. It was also shown that Lorentz oscillators with energy positions lower than 2eV can be distinguished from the Drude oscillator function during parameter fitting. AFM imaging analysis indicates that the roughness decreases and plateaus at approximately 1.5nm with the introduction of a small N2 flow rate, remaining consistent thereafter. SEM cross-sectional imaging analysis indicates the dense, columnar structure for the films grown at lower nitrogen flow rates. XPS analysis of atomic composition and the chemical states indicate that the atomic composition remained nearly constant while the chemical states varied significantly among the samples as a function of N2 flow rate. XPS analyses confirm the presence of TiNx, TiO2 and TiOxNy. These process–property relationships derived could be useful for defining and expanding the range of optical and electronic applications of titanium nitrides and (oxy)nitrides.