Quantitative analysis of the impact of surface and grain boundary scattering on the resistivity of nanometric Cu films

摘要

We report a quantitative analysis of surface and grain boundary scattering in encapsulated Cu thin films where film thickness (27 nm to 158 nm) and grain size (35 nm to 425 nm) were varied so that a series of grain sizes at given film thicknesses were obtained. Two types of samples, namely, SiO_2/Cu/SiO_2 and SiO_2/Ta/Cu/Ta/SiO_2 were prepared by sub-ambient temperature deposition followed by annealing. Average grain size values were determined from populations of 400 to 1,500 grains per sample using hollow cone dark field transmission electron microscopy imaging. Film thickness and roughnesses of the upper and lower Cu surfaces were determined by specular X-ray scattering. Film resistivities were measured at room temperature and at 4.2 K and were compared with several scattering models in order to quantify the contributions of surface and grain boundary scattering. Grain boundary scattering is found to provide the most significant contribution. However, a comparison of the high and low temperature data indicates that a weak surface scattering contribution to the size effect is likely present. The implications of our results to the future scaling of Cu interconnect resistivity will be discussed.