The maximum electrical conductivities in polycrystalline Cu interconnects with sub-100 nm linewidth were extrapolated from the measured resistivities of the Cu interconnects with various linewidths (100-1000 nm) using a Mayadas-Shatzkes (MS) model. These polycrystalline Cu interconnects with TiN cap layers were fabricated by the focused ion beam technique. The scattering parameters by the surface and grain boundary, which were needed to extrapolate the resistivities of the sub-100 nm Cu interconnects (using the MS model), were determined to be zero and 0.5, respectively. The result suggested that the grain boundary scattering primarily increased the resistivity of the polycrystalline Cu interconnects. We concluded that large grained Cu interconnects and ultrathin barrier layers were essential to realize low resistance nano-scale Cu interconnects in the future ultralarge scale integration devices. (c) 2006 American Vacuum Society.