In a previous study, we developed an abrasive-free polishing method called catalyst-referred etching (CARE). By using water and Pt as an etchant and a catalyst, respectively, atomically smooth surfaces were realized on Si, SiO₂, and SiC substrates. OH generated on the Pt catalyst surface via water molecule dissociative adsorption attaches to a step edge atom, forming a hypervalent state. This hypervalent state reduced the activation energy, leading to cleavage of the back bond of the step edge atom. According to this mechanism, provided surface oxidation, metal materials with chemical stability and high hardness can be etched efficiently using the CARE method. In this study, we demonstrated Ru etching using the CARE method with oxidation. Anode oxidation was employed as surface oxidation. When 0.4 V was applied to the Ru, an atomically smooth surface without an oxidation layer was obtained. Ru is a promising next-generation wiring material. However, in the conventional polishing technique, because of chemicals added to the etchant, Ru wiring on the patterning substrate is over-polished. This phenomenon, which is called erosion and dishing, degrades the device performance. In contrast, CARE preferentially etches the topmost site of the sample surface. Therefore, the pattered substrate with Ru wiring can be planarized without erosion and dishing. The proposed method can produce a high-performance electric device with Ru wiring.

1. [1] J. Li, Y. H. Liu, Y. Pan, and X. C. Lu, “Chemical roles on Cu-slurry interface during copper chemical mechanical planarization,” Appl. Surf. Sci., Vol.293, pp. 287-292, 2014. https://doi.org/10.1016/j.asusc.2013.12.150
2. [2] E. S. Jung, J. H. Choe. C. Y. Lee, J. U. Yoom T. M. Choi, H. R. Lee, D. H. Kim, and S. G. Pyo, “Investigation of persulfate oxidizers in Co CMP slurry through Co surface adsorption and oxidation behaviors,” Appl. Surf. Sci., Vol.687, Article No.162287, 2025. https://doi.org/10.1016/j.apsusc.2024.162287
3. [3] X. Chen, R. Wang, Z. Du, Y. Zhu, Z. Liang, Y. Dong, and T. Zheng, “Effect of 2-Mercapto-1-methylimidazole on the Dual Action of Chemical Mechanical Polishing of Cu and Ta,” Langumuir, Vol.40, No.52, pp. 27430-27444, 2024. https://doi.org/10.1021/acs.langmuir.4c03686
4. [4] T. Nakano, Q. T. Le, H. Kawarazaki, T. Tanaka, and E. A. Sanchez, “A cleaning method for post-etch ruthenium residue removal using UV and liquid chemical,” Solid State Phenom., Vol.346, pp. 335-340, 2023. https://doi.org/10.4028/p-82Lqsf
5. [5] D. Gall, “The search for the most conductive metal for narrow interconnect lines,” J. Appl. Phys., Vol.125, No.5, Article No.050901, 2020. https://doi.org/10.1063/1.5133671
6. [6] D. Gall, “Electron mean free path in elemental metals,” J. Appl. Phys., Vol.119, No.8, Article No.085101, 2016. https://doi.org/10.1063/1.4942216
7. [7] A. Isohashi, P. V. Bui, D. Toh, S. Matsuyama, Y. Sano, K. Inagaki, Y. Morikawa, and K. Yamauchi, “Chemical etching of silicon carbide in pure water by using platinum catalyst,” Appl. Phys. Lett., Vol.110, Article No.201601, 2017. http://doi.org/10.1063/1.4983206
8. [8] D. Toh, P. V. Bui, K. Yamauchi, and Y. Sano, “Photoelectrochemical oxidation assisted catalyst-referred etching for SiC (0001) surface,” Int. J. Automation Technol., Vol.15, No.1, pp. 74-79, 2021. https://doi.org/10.20965/ijat.2021.p0074
9. [9] P. V. Bui, Y. Sano, Y. Morikawa, and K. Yamauchi, “Characteristics and mechanism of catalyst-referred etching method: Application to 4H-SiC,” Int. J. Automation Technol., Vol.12, No.2, pp. 154-159, 2018. https://doi.org/10.20965/ijat.2018.p0154
10. [10] D. Toh, P. V. Bui, A. Isohashi, N. Kidani, S. Matsuyama, Y. Sano, Y. Morikawa, and K. Yamauchi, “Catalyzed chemical polishing of SiO₂ glasses in pure water,” Rev. Sci. Instrum., Vol.90, Article No.045115, 2019. https://doi.org/10.1063/1.5090320
11. [11] D. Toh, K. Kayao, K. Yamauchi, and Y. Sano, “Fabrication of YAG ceramics surface without damage and grain boundary steps using catalyzed chemical wet etching,” CIRP J. Manuf. Sci. Technol., Vol.47, pp. 1-6, 2023. https://doi.org/10.1016/j.cirpj.2023.09.001
12. [12] P. V. Bui, D. Toh, A. Isohashi, S. Matsuyama, K. Inagaki, Y. Sano, K. Yamauchi, and Y. Morikawa, “Platinum-catalyzed hydrolysis etching of SiC in water: A density functional theory study,” Jpn. J. Appl. Phys., Vol.57, Article No.055703, 2018. https://doi.org/10.7567/JJAP.57.055703
13. [13] H. Ma, J. Zhou, C. Wang, Y. Zhang, Z. Li, X. Zhang, and G. Liu, “Role of diethylene triaminepentaacetic acid pentapotassium salt on ruthenium CMP in H₂O₂-based slurries,” ECS J. Solid State Sci. Technol., Vol.11, Article No.124002, 2022. https://doi.org/10.1149/2162-8777/aca790
14. [14] H. Gui, J. H. Park, and J. G. Park, “Effect of oxidizers on chemical mechanical planarization of ruthenium with colloidal silica based slurry,” ECS J. Solid State Sci. Technol., Vol.2, No.1, pp. 26-30, 2013. https://doi.org/10.1149/2.030301jss
15. [15] T. P. Luxton, M. J. Eick, and K. G. Scheckel, “Characterization and dissolution properties of ruthenium oxides,” J. Colloid Interface Sci., Vol.359, No.1, pp. 30-39, 2011. https://doi.org/10.1016/j.jcis.2011.03.075
16. [16] M. Pourbaix, “Atlas of electrochemical equilibria in aqueous solutions,” Natl. Assn. of Corrosion Engineers, pp. 343-349, 1979.
17. [17] R. Kötz, H. J. Lewerenz, and S. Stucik, “XPS studies of oxygen evolution on Ru and RuO₂ anodes,” J. Electrochem. Soc., Vol.130, No.4, pp. 825-829, 1983. https://doi.org/10.1149/1.2119829