Electroless Plating of Ru Using Hydrazine Hydrate as a Reducing Agent

• Published in: Journal of electronic materials 2023-10, Vol.52 (10), p.6690-6698
• Main Authors: Saida, Ryota, Shimizu, Tomohiro, Ito, Takeshi, Tominari, Yukihiro, Tanaka, Shukichi, Fukumuro, Naoki, Yae, Shinji, Shingubara, Shoso
• Format: Article
• Language: English
• Subjects: Ammonia; Ammonium chloride; Annealing; Carbon dioxide; Characterization and Evaluation of Materials; Chemical vapor deposition; Chemistry and Materials Science; Desorption; Electrical resistivity; Electroless plating; Electronics and Microelectronics; Grain growth; Hydrazines; Impurities; Instrumentation; Materials Science; Melting points; Optical and Electronic Materials; Original Research Article; Polycrystals; Reducing agents; Ruthenium; Solid State Physics; Tartaric acid; Thermal desorption spectroscopy; Thin films; Ultrafines
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-023-10605-5

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 (N 2 :H 2  = 9:1). The Ru (101) and (100) crystalline orientations were strengthened by annealing, and the resistivity decreased from 160  µ Ω cm to 22 µ Ω cm concomitantly. Thermal desorption spectroscopy showed that the electroless Ru films contained impurities, such as CO, CO 2 , NH 3 , O, C, and H 2 . Desorption of C, CO, CO 2 , and NH 3 showed peak maxima at approximately 450–500 K. These impurity molecules likely came from the inclusion of the complexing agents (tartaric acid: C 4 (OH) 4 O 2 , and ammonium chloride: NH 4 Cl) and reducing agent (hydrazine: N 2 H 2 ) into the Ru film. Desorption of these molecules during annealing may improve the grain growth of polycrystalline Ru and reduce its resistivity.