Classical size effect in nanometric Cu films: the dominant role of grain boundary scattering

Surface and grain boundary electron scattering contribute significantly to resistivity as the dimensions of polycrystalline metallic conductors are reduced to, and below, the electron mean free path. In this work, a methodology is reported to independently evaluate surface and grain boundary scattering in encapsulated polycrystalline Cu thin films, with thicknesses of 28-158 nm, grain sizes of 35-466 nm, and interface roughnesses of 0.2-2 nm. The film resistivity, measured at both room temperature and at 4.2 K, is compared for samples having different grain sizes and film thicknesses. The resistivity contribution from grain boundary scattering is found to be dominant in SiO$_{2}$/Cu/SiO$_{2}$ and Ta/ SiO$_{2}$/Cu/Ta/SiO$_{2}$ films. Resistivity data for a third set of samples, namely SiO$_{2}$/TaSiN$_{x}$/Cu/TaSiN$_{x}$/SiO$_{2}$, will also be presented.