Electroless Deposition of Ru Films Via an Oxidative-Reductive Mechanism

Abstract

An electroless Ru plating bath is prepared by mixing Ru precursor (K(2)RuCl(5).xH(2)O), oxidizer (NaClO), stabilizer (NaOH), and reducing agent (NaNO(2)) simultaneously in deionized water at a molar ratio of 1:1:20:10. Instead of conventional direct reduction route, the RuCl(5)(2-) experiences an oxidative-reductive sequence to form metallic Ru on an activated Si substrate. Spectra from ultraviolet-visible and X-ray absorption spectroscopy indicate that the RuCl(5)(2-) is oxidized to form RuO(4) initially, followed by a slight reduction becoming RuO(4)(2-). The RuO(4)(2-) solution is relatively stable and is able to undergo further reduction to render metallic Ru via heterogeneous nucleation and growth. Images from scanning electron microscope demonstrate a solid film of 100 nm with scattered protrusions and cavities after 120 min plating time. Analysis from atomic force microscope determines its surface roughness of 7.8 nm. From X-ray diffraction patterns, the as-deposited film reveals an amorphous structure but turns crystalline after Ar annealing at 400 degrees C for 2 h. Curve-fitting of Ru 3p(3/2) signal from X-ray photoelectron spectroscopy suggests a film composition of 92.49 atom % Ru and 7.51 atom % RuO(2). The electroless Ru plating bath exhibits impressive life time (137 h) and negligible homogeneous precipitation without involving surfactants and unnecessary chemical additives. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3592996] All rights reserved.