Two-additive electropolishing (EP) electrolytes exhibit an extremely high planarization-efficiency in Cu damascene schemes, independent of pattern sizes (1-50 μm). This electrolyte is demonstrated by adding alcohols and organic acids to the H3PO4 electrolyte. The high wetting ability of alcohols allows such additives to easily access the damascene bottom. This mechanism, assisted by the reduced polishing rate associated with the high surface viscosity caused by alcohol additives, greatly passivates the damascene bottom from elecropolishing. Accordingly, the superpolishing functionality reported by Chang et al. [Electrochem. Solid-State Lett., 6, G72 (2003)] in the two-additive electrolyte outperforms in the one-additive electrolyte.