Conformal Deposition of RuO₂ on Cu via a Galvanic Cementation Reaction

Abstract

We develop a seedless wet chemical process to deposit uniform RuO 2 on a Cu substrate. Our approach entails the synthesis of volatile RuO 4 colloids in a pH 9 aqueous solution from the oxidation of RuCl 5 2− by ClO − , followed by a galvanic cementation reaction in which the Cu undergoes a mild oxidation in conjunction with the reduction of RuO 4 to produce a dense and conformal RuO 2 thin film on the Cu surface. The nature for the chemical reactions and constituents involved are investigated by UV-Vis, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Both as-deposited and annealed RuO 2 films are characterized by scanning electron microscope and X-ray diffractometer. The as-deposited RuO 2 film, with a thickness of 199 nm, reveals an amorphous structure and after an Ar annealing, becomes crystalline in rutile phase. In between the RuO 2 and Cu, there are presence of CuO from the displacement cementation reaction, and Cu 2 O from the parasitic Cu corrosion as expected from the Pourbaix diagram. These Cu oxides, with a thickness of 330 nm, provide sufficient adhesive bonding between RuO 2 and Cu.