(530c) Effect of Process Variables On Microestructure and Composition of HWCVD Tungsten Oxides Thin Films

This research work is focused on obtaining process maps to elaborate tungsten and tungsten oxides thin films, which allows relating structural and composition characteristics with the operating conditions of the HWCVD reactor. In the experimental set-up a 0.5 mm diameter filament was placed at a distance of 10 mm from substrate surface and was employed both as precursor source and as species decomposition mechanism. The filament temperature was regulated by applying different voltage to current ratios, and determined by optical pyrometry. An independent heating system was used to set substrate temperature. Films were deposited over silicon (100) and glass substrates at reduced pressure. The substrate temperature was modified in the range of 400°C to 600°C and the oxygen partial pressure was varied from 1x10^-1 to 1X10^-2 mbar, by using a rotary vane pump and controlled air input. Homogeneous and well adhered deposits with high growth rates were obtained and investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic force microscopy (AFM). Significant structure and composition differences were found as a function of PO₂ and substrate and filament temperature. Nanostructured films comprising needles, rods and/or agglomerated sphere-like geometries were found. The resulting composition ranges from highly metallic deposits to W_xO_y oxides with diverse stoichiometries. While rich-tungsten films were obtained at deposition rates of 0.05 μm/min, oxides growth rate were about 1μm/min. Finally, this study proposes possible formation mechanisms and discusses the influence of process parameters and substrate nature on growth and nucleation phenomena.