The electrodeposition of copper from a citrate solution has been investigated as a function of pH of the plating bath, and applied to the filling of 500 nm trenches. Speciation diagrams of copper in aqueous citrate solution were used to select four deposition baths with different dominant copper-citrate complexes, which was corroborated using UV-vis spectrophotometry. The electrochemical properties of the plating baths were determined in order to relate the deposition kinetics to the morphology of deposits in trenches. SEM images illustrate that the plating bath at pH 3.1, where only mild inhibition of the deposition kinetics is observed, is capable of adequately filling the trenches. (C) 2011 Elsevier Ltd. All rights reserved.