Co films were selectively deposited as Cu capping layers by chemical-vapor-deposition technique. X-ray fluorescence spectroscopy determined the Co deposition selectivity as a function of the deposition temperature and substrate materials. The Co/Cu interfacial property was characterized and revealed no detectable oxygen at the interface. The selectivity of the Co deposition process and the property of the resulted Co/Cu interface were further confirmed with time-dependent-dielectric-breakdown and electromigration tests. © 2010 IEEE.