Resistivity of thin Cu films coated with Ta, Ti, Ru, Al, and Pd barrier layers from first principles

We present an atomistic first-principles calculation for the resistivity of rough Cu thin films coated with barrier layers of Ta, Ti, Ru, Al, and Pd. A significant difference in resistivity due to different barrier metals is found. Ti, Ta, and Ru barriers increase the resistivity whereas Al and Pd lower the resistivity, in comparison with that of bare Cu films having the same degree of roughness disorder. It is found that Al/Pd barrier atoms produce density of states (DOS) that match rather well with the DOS of Cu atoms on a Cu film with a perfectly flat surface while the DOS of Ti, Ta, and Ru do not match. Our results suggest that the geometrical roughness on the Cu film that causes diffuse scattering, can be smoothed out electronically by certain barriers such that the surface scattering becomes more specular.