Reactive Sputtering Process Study for Vanadium Oxynitride Films

In this study, vanadium oxynitride thin films were deposited by reactive magnetron sputtering using pure vanadium targets, Ar as a plasma carrier, and a mix of N₂ and O₂ as reactive gases. Various ratios of mass flow rates between two reactive gases were maintained as a constant during the process. To obtain crystalline phases of oxynitrides, rapid thermal annealing in Ar atmosphere at 600 °C and 700 °C for 5 min was conducted after the deposition. This study aims to define the range of the process parameters of magnetron sputtering to deposit vanadium oxynitride thin films. The assessment for the characterization of films utilizes the surface profiler, scanning electron microscope, X-ray diffraction, X-ray photoelectron spectroscopy, four-point probe, Hall analyzer, and UV-visible-NIR spectrometer. Experimental results reveal that the annealed films can be oxynitrides when the oxygen flow rate is below 0.25 sccm, and the ratio of oxygen/nitrogen is no more than ~1/10. The annealed vanadium oxynitride films, in terms of their properties, are closer to vanadium nitrides than to oxides, due to the intended low supply of oxygen during deposition. For instance, the film is more metallic than semi-conductive with dark appurtenance and high optical absorbance across the spectrum between 200 and 900 nm. For practical purposes, the deposition conditions of O₂:N₂ = 1/20, O₂ < 0.25 sccm, and 600 °C annealing are recommended to obtain vanadium oxynitride films with relatively lower resistivity (10⁻² Ω cm) and optical transmittance (<15%) through films.