Electrodeposition and Evaluation of Ruthenium Film from Divalent Ruthenium Electrolyte

Introduction

Ruthenium is a platinum-group element with properties similar to those of rhodium, which also is a platinum-group element. Compared to rhodium, ruthenium is considerably cheaper and its industrial applications have gradually been increasing. Ruthenium plating films are expected to be used for electrical contact parts due to their low contact resistance, abrasion resistance, and corrosion resistance. However, very few studies on ruthenium plating have been reported thus far. As ruthenium has a small hydrogen overpotential, the generation of hydrogen gas during electrodeposition should occur easily. Therefore, electrodeposition of ruthenium from ionic liquids instead of aqueous solutions has been investigated.^1,2) In addition, ruthenium plating baths containing trivalent ruthenium ions are often used for electrodeposition. We have examined the electrodeposition of ruthenium films from a bath containing divalent ruthenium ions.³⁾

In the present study, the electrodeposition behavior and microstructure of these films were studied.

Experimental

An electroplating bath containing 0.1 M RuCl₃•nH₂O and 0.5 M L (+)-ascorbic acid was prepared. Trivalent ruthenium ions were changed to divalent ions by the addition of ascorbic acid. Copper plates were used as substrates. Plating was performed at 80°C with aeration under galvanostatic conditions (current density; 5 A dm^-2, electrical charge; 50 C cm^-1). A phase structure analysis of the deposits was performed using X-ray diffraction (XRD). The surface morphology and cross-sectional texture were observed using field–emission scanning electron microscopy (FE-SEM). Elemental mapping was carried out using electron probe X-ray micro-analysis (EPMA). Wear testing was performed using a scratch tester. The surface hardness was measured using a micro-Vickers hardness tester.

Results and Discussion

 Figure 1 shows an SEM image of the ruthenium plating film surface. Some cracks are seen on the surface of the film. Figure 2 shows a cross-sectional SEM image of the film, which has a thickness of about 2 µm. Although a crack is seen, there are no voids in the film. It was found that the film had a low degree of crystallinity and contained a certain amount of chlorine, by XRD analysis and EPMA analysis, respectively.

Properties of the ruthenium film will be discussed at the meeting.

References

1) O. Mann, W. Freyland, O. Raz, Y. Ein-Eli, Chem. Phys. Lett., 460, 178 (2008).

2) O. Raz, G. Cohn, W. Freyland, O. Mann, Y. Ein-Eli, Electrochim. Acta, 54, 6042 (2009).

3) Y. Miyagawa, S. Arai, M. Endo, Abstract of the Electrochemical Society Japan Fall Meeting 2006, p.271 (2006).

4)  S. Chiba, S, Arai, T, Fujinami, Abstract of The Surface Finishing Society of Japan 128th Meeting, p.27 (2013).