Bottom-up Filling of Damascene Trenches with Gold in a Sulfite Electrolyte

Superconformal Au deposition is demonstrated in a Na₃Au(SO₃)_{2 +} Na₂SO₃ electrolyte using Bi species to catalyze the reduction of Au(SO₃)₂ ^3-. Micromolar additions of Bi³⁺ to the sulfite-based electrolyte accelerate the reduction of Au(SO₃)₂ ^3- as shown by hysteretic voltammetry and rising chronoamperometric transients. Superconformal feature filling is observed over a defined range of Bi³⁺ concentration, potential and hydrodynamics. Over a more limited parameter range, approximately -0.9 V to -0.95 V, void-free, bottom-up filling of Damascene trenches is achieved. Furthermore, in the presence of significant convection the bottom-up filling is accompanied by passivation of the free surface. Bottom-up feature filling is characterized by a counterintuitive dependence of the free surface reactivity on the available flux of the Bi³⁺ accelerator species suggestive of an unusual coupling between hydrodynamic transport, shear and interfacial chemistry.