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Electroless Plating of Ru Using Hydrazine Hydrate as a Reducing Agent

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Abstract

Ruthenium (Ru)—a high-melting-point precious metal—has attracted attention for use as ultrafine interconnections in large-scale integrations. This is because the resistivity of Ru interconnects is not expected to increase with a reduction in the interconnect width owing to their short mean free path for electrons. In this study, we investigated electroless plating of Ru using hydrazine hydrate as a reducing agent to obtain low-resistivity Ru films. We obtained polycrystalline Ru films on a thin (10-nm) catalytic chemical-vapor-deposited Ru underlayer. The electroless Ru films exhibited significant grain growth upon annealing at 600°C in a forming gas (N2:H2 = 9:1). The Ru (101) and (100) crystalline orientations were strengthened by annealing, and the resistivity decreased from 160 µΩ cm to 22 µΩ cm concomitantly. Thermal desorption spectroscopy showed that the electroless Ru films contained impurities, such as CO, CO2, NH3, O, C, and H2. Desorption of C, CO, CO2, and NH3 showed peak maxima at approximately 450–500 K. These impurity molecules likely came from the inclusion of the complexing agents (tartaric acid: C4(OH)4O2, and ammonium chloride: NH4Cl) and reducing agent (hydrazine: N2H2) into the Ru film. Desorption of these molecules during annealing may improve the grain growth of polycrystalline Ru and reduce its resistivity.

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Acknowledgments

The authors are grateful to Mr Y. Morita for his great contribution in the early stage of this study, and to the High Voltage TEM Research Center of Osaka University. We thank Adam Brotchie, PhD, from Edanz (https://jp.edanz.com/ac) for editing a draft of this manuscript.

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Authors and Affiliations

  1. Faculty of System Engineering, Kansai University, 3-3-35 Yamate-cho, Suita, Osaka, 564-8680, Japan

    Ryota Saida, Tomohiro Shimizu, Takeshi Ito & Shoso Shingubara

  2. Nano ICT Laboratory, National Institute of Information Technology, 588 Iwaoka, Nishi-ku, Kobe, Hyogo, Japan

    Yukihiro Tominari & Shukichi Tanaka

  3. Graduate School of Engineering, University of Hyogo, Shosha, Himeji, Hyogo, 2167, Japan

    Naoki Fukumuro & Shinji Yae

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  1. Ryota Saida
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Saida, R., Shimizu, T., Ito, T. et al. Electroless Plating of Ru Using Hydrazine Hydrate as a Reducing Agent. J. Electron. Mater. 52, 6690–6698 (2023). https://doi.org/10.1007/s11664-023-10605-5

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