Effect of nitrogen doping on surface morphology, microstructure, chemical composition and intrinsic stress of nickel thin films deposited by reactive sputtering

Abstract

N-doped nickel thin films were fabricated by direct current reactive magnetron sputtering, with varying nitrogen contents (0%–20%) added to the sputtering gas (Ar). To investigate the effect of nitrogen contents on morphology, microstructure, chemical composition and intrinsic stress of nickel thin films, characterizations were carried out using grazing incidence X-ray reflectivity (GIXRR), X-ray scattering (XRS), atomic force microscopy (AFM), X-ray diffraction (XRD), cross-sectional transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS) and intrinsic stress measurements. GIXRR and AFM results showed that the roughness achieves minimum with 8% nitrogen, corresponding to minimum average grain size obtained by XRS and XRD measurements. XRD patterns simultaneously indicated that the position and intensity of the Ni(111) and Ni(200) peaks shifted. This is because Ni lattice structure changed after the introduction of N atoms at interstitial sites, which were octahedrally surrounded by Ni atoms. Cross-sectional TEM images confirmed that Ar + 8%N2 as sputtering gas can suppress the crystallization and effectively smoothen the surface of Ni film. Moreover, no nickel nitride was found in the N-doped Ni films by XPS analysis and the intrinsic stress remained unchanged after the addition of 8% nitrogen.