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Cu was electrodeposited directly on a 3-nm-thick atomic-layer-deposited (ALD) Ru diffusion barrier layer in Cu-citrate-based electrolytes for Cu interconnect. The nucleation and growth behavior of Cu thin films on the ALD Ru was compared between an additive-free electrolyte and a polyethylene glycol (PEG)/janus green B (JGB)-added electrolyte. The suppression effect of additives in the PEG/JGB-added electrolyte led to lower Cu deposition rate. It was accordingly responsible for the growth of thin and uniform Cu films from smaller Cu nuclei of higher area density. In consequence, Cu filling of 30-nm-wide and 120-nm-deep trenches coated by the 3-nm-thick ALD Ru layer was much improved in the PEG/JGB-added electrolyte compared with the additive-free electrolyte.

N-incorporated Ru films were deposited by atomic layer deposition (ALD) at a deposition temperature of 270 °C using 1-isopropyl-4-methylbenzene-cyclohexa-1,3-dienyl ruthenium and N 2 /H 2 mixture plasma as the precursor and reactant, respectively. The N content in the ALD-Ru films was controlled by changing the gas ratio [N 2 versus the total gas (N 2 + H 2 ) flow rates] in the reactant from 0.82 to 1. Secondary ion mass spectrometry depth profiling revealed an increase in N content in the film with increasing gas ratio. The amount of N in the ALD-Ru films had a considerable effect on the film properties, such as resistivity, crystallinity and microstructure. Although the resistivity of the pure ALD-Ru film was ~ 19 μΩ cm, the N-incorporated ALD-Ru films deposited with a gas ratio of 0.86 (N/Ru: ~ 0.38) showed a resistivity of ~ 340 μΩ cm, which increased continuously with increasing gas ratio. X-ray and electron diffraction revealed degradation in film crystallinity and decrease in grain size with increasing N incorporation into ALD-Ru films. Transmission electron microscopy showed that N-incorporated ALD-Ru films formed nanocrystalline and non-columnar grain structures. This is in contrast to that observed in the pure ALD-Ru film, which had a polycrystalline columnar grain structure. The growth rate of a representative N-incorporated Ru film deposited with a gas ratio of 0.86 showed a linear dependency on the number of ALD cycles; growth rate of 0.051 nm/cycle at short incubation cycles of ~ 3. The step coverage was approximately 98% over the trench structure (aspect ratio: 4.5) with a top opening width of 25 nm. The direct plating of Cu on an optimized N-incorporated ALD-Ru film (5 nm in thickness) was possible. The structure of Cu (80 nm)/N-incorporated ALD-Ru (8 nm)/Si was found to be stable without the formation of copper silicide after annealing at 600 °C for 30 min.

Polyethylene glycol (PEG) and Janus Green B (JGB) have been widely used as suppressor and leveler, respectively, for copper electrodeposition to fill damascene structures of highly integrated silicon devices. In this study, we investigated fundamental nucleation behavior of copper electrochemically deposited on tungsten diffusion barrier without using a copper seed layer in a citrate-based, neutral electrolyte. Concentrations of PEG and JGB were varied to optimize the nucleation and growth of a thin and uniform copper film on tungsten, ultimately considering the application of this copper electrodeposition method to copper fill of sub-45 nm damascene structures. Important fundamental properties of copper nucleation directly on tungsten such as the nuclei density, size distribution, 3D nucleation mode, and surface roughness were investigated when forming a uniform copper film thinner than 30 nm on tungsten by manipulating additive composition in electrolyte. In consequence, a thin and smooth copper film was electrodeposited resulting from instantaneous nucleation and high area density of copper clusters in the electrolyte including 10 μM PEG and 10 μM JGB.

Ruthenium (Ru) thin films were grown on thermally-grown SiO 2 substrates using atomic layer deposition (ALD) by a sequential supply of (ethylbenzene)(1,3-cyclohexadiene)Ru(0) (EBCHDRu, C 14 H 18 Ru), and molecular oxygen (O 2 ) at deposition temperatures ranging from 140 to 350 °C. A self-limiting film growth was confirmed at the deposition temperature of 225 °C and the growth rate was 0.1 nm/cycle on the SiO 2 substrate with a negligible number of incubation cycles (approximately 2 cycles). Plan-view transmission electron microscopy analysis showed that nucleation was started after only 3 ALD cycles and the maximum nuclei density of 1.43 × 10 12 /cm 2 was obtained after 5 ALD cycles. A continuous Ru film with a thickness of ~ 4 nm was formed after 40 ALD cycles. The film resistivity was decreased with increasing deposition temperature, which was closely related to its crystallinity, microstructure, and density, and the minimum resistivity of ~ 14 μΩ-cm was obtained at the deposition temperature of 310 °C. The step coverage was approximately 100% at trench (aspect ratio: 4.5) with the top opening size of ~ 25 nm. Finally, the ALD-Ru film was evaluated in terms of its performance as a seed layer for Cu electroplating.