In this work, microvia filling was performed by copper electroplating using two plating formulas with and without a leveler at a low concentration of chloride. The base plating solution contained CuSO4, H2SO4, polyethylene glycol (PEG), his (3-sulfopropyl) disulfide (SPS) and Cl-. When the Cl- concentration was lower than 30 ppm, the plating formula without a leveler became dead for bottom-up filling, resulting in conformal deposition. The addition of I ppm Alcian Blue, used as a leveler, could effectively recover the filling performance of the plating formula with low chloride concentration. Electrochemical analyses revealed possible mechanisms. The results demonstrate that the usage of Alcian Blue can widen the operation window of chloride concentration, since it can assist PEG in competing with SPS in adsorption at low chloride concentration. (c) 2008 Elsevier Ltd. All rights reserved.