Potentiostatic electrodeposition of Cu thin films directly on ALD Ru diffusion barrier and trench-filling for Cu interconnect

Abstract

Potentiostatic electrodeposition of Cu directly on 3-nm-thick atomic-layer-deposited (ALD) Ru diffusion barrier layer was investigated without the use of a Cu seed layer for the Cu interconnect fabrication in Si-based microelectronic devices. Polyethylene glycol (PEG) was added as a suppressor to a neutral Cu-ammonia-citrate (CuNH3-Cit) electrolyte. Constant reduction potentials in the range of -0.8 to -1.1 V versus SCE were applied to blanket and patterned wafer specimens, which acted as rotating disk electrodes. The diffusion-controlled reduction of Cu2(Cit)2OH3- ions to Cu metal atoms at a more negative potential of -1.1 V was efficient in improving the thickness uniformity and surface morphology of electrodeposited Cu thin films. Lastly, the potentiostatic Cu electrodeposition at -1.1 V was performed to fill 30-nm-wide and 90-nm-deep trenches with Cu for the patterned wafer specimens. The instantaneous nucleation tendency and high area density of Cu nuclei were important for generating thin, uniform Cu films directly on the ALD Ru, and filling the trenches while reducing the probability of defect creation within Cu deposits.