The electron scattering at grain boundaries in tungsten films

Abstract

The impact of electron scattering at grain boundaries in polycrystalline tungsten (W) thin films is studied with a unique approach. Two nominally 300nm-thick films, a (110)-oriented epitaxial and a (110)-textured polycrystalline W film, were prepared in identical fabrication conditions except for the substrates, i.e., Al2O3 substrate for the epitaxial film and thermally oxidized Si substrate for the polycrystalline film. The significantly larger dimension of the film thickness than the electron mean free path in W allows the contribution of surface scattering to be negligible, and the additional resistivity for the polycrystalline W film relative to the epitaxial film is attributed to grain boundary scattering. The Mayadas–Shatzkes (MS) grain boundary scattering model is employed for quantitative analyses, with the grain boundary reflection coefficient determined to be 0.42±0.02 and 0.40±0.02 at 293K and 4.2K, respectively, using the measured lateral grain size of 119±7nm. Based on the grain boundary reflection coefficient determined in this study and the surface scattering coefficient (p=0.11) of the Fuchs–Sondheimer model given elsewhere, the resistivity of W lines having line-widths less than 10nm is predicted to be lower than that of Cu lines.