Nucleation-controlled growth of Cu thin films electrodeposited directly on ALD Ru diffusion barrier in additive-free electrolyte for Cu interconnect

Abstract

Direct Cu electrodeposition on a 3-nm-thick atomic-layer-deposited (ALD) Ru diffusion barrier layer was investigated for Cu interconnect in Si-based microelectronic devices. A Cu-ammonia-citrate (Cu-NH3-Cit) electrolyte was employed with no additives. The nucleation behavior of Cu on Ru was dependent on the cathodic potential applied to ALD Ru/SiO2/Si wafer specimen whether it is instantaneous or progressive. Preferable instantaneous nucleation with a high area density of Cu nuclei on Ru contributed to the formation of uniform Cu thin films. Lastly, direct Cu electrodeposition onto Ru at a constant cathodic potential of −1.0 V filled 30-nm-wide and 120-nm-deep trenches with void-free Cu.