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In situ transport measurements on 7 nm thick epitaxial Ru(0001)/Al2O3(0001) films with and without Ti cap layers during low-pressure 0.05 mTorr O2 exposure are employed to examine the impact of surface chemistry on electron scattering at Ru(0001) surfaces. The sheet resistance Rs of Ru(0001) films increases by 1.0% during oxygen exposure and by 1.0%–2.6% during deposition of 0.1–0.5 nm thick Ti cap layers. These increases are attributed to a perturbation of the surface potential which causes diffuse electron surface scattering corresponding to a 0.08–0.20 decrease in the scattering specularity. In contrast, Ti oxidation reduces the resistance due to a decreasing density of localized surface states which facilitates specular scattering at Ru–TiOx interfaces. These results show that the interface scattering specularity and the overall Ru conductivity are maximized if the Ru conductor remains metallic but the Ti cap layer oxidizes. They demonstrate the potential of surface-state engineering to increase the conductivity of narrow interconnects. Overall, the electron scattering at Ru(0001) surfaces is only weakly affected by the chemistry of add-layers, with a measured decrease in scattering specularity of only −0.20 and −0.08 when coated with a Ti cap and exposed to oxygen, respectively. These values are 1.5–6 and 6–10 times smaller than those observed for competing metals including Cu, Co, and Rh. This superior stability and reduced sensitivity to surface state-induced scattering is a promising feature for future Ru metallization.
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This content will become publicly available on July 7, 2027
Effect of atomic-scale surface roughness on the electrical resistivity of epitaxial Ru(0001) thin films
The effect of atomic-scale surface roughness on electron transport is investigated using 6.5 nm-thick epitaxial Ru(0001) films, a promising metal for next-generation interconnects. Sputter deposition at 350 °C followed by stepwise vacuum annealing to 950 °C yields atomically smooth Ru(0001)/Al2O3(0001) films which are subsequently roughened by depositing ΘRu = 0.5, 1.0, and 2.0 monolayers (MLs) of additional Ru at room temperature. In situ four-point probe measurements show a resistivity ρ = 9.08–9.44 μΩ cm for 6.5 nm-thick films and a 4%–6% increase in sheet resistance upon roughening, attributed to electron scattering at atomic-height surface steps. The measured resistivity penalty Δρr = 0.41 μΩ cm caused by a ΘRu = 0.5 ML coverage suggests formation of 2D islands with an average step-edge separation ls = 2.7 nm, as quantified by a step-edge scattering model. This is in good agreement with ls = 3.6 ± 0.3 nm estimated from atomic force micrographs. Increasing ΘRu further to 1.0 ML causes a slight decrease in roughness and Δρr, indicating coalescence of 2D islands which increases ls to 3.0 nm. However, a ΘRu = 2.0 ML coverage causes 3D mound formation, an increased resistivity penalty Δρr = 0.49 μΩ cm, and a reduced ls = 2.3 nm, consistent with a significant damping of Kiessig fringes measured by x-ray reflectivity. These results demonstrate that atomic-scale topographical variations impose significant resistivity penalties for deeply scaled metallic interconnects.
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- Award ID(s):
- 2328906
- PAR ID:
- 10698657
- Publisher / Repository:
- aip
- Date Published:
- Journal Name:
- Journal of Applied Physics
- Volume:
- 140
- Issue:
- 1
- ISSN:
- 0021-8979
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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