The properties of electroplated Cu films prepared using copper-hexafluoro-silicate (CuSiF6), copper sulfate (CuSO4), and their mixtures in different mixing ratios as electrolytes were investigated. We compared the stress, resistivity, self-annealing effect, microstructure, growth rate, impurity, and reliability of the as-deposited electroplated Cu films. We found that electroplated Cu films using a higher fraction of CuSiF6 in the electrolyte exhibited lower resistivity, a denser structure, lower stress, and a less-apparent self-annealing effect. A reliability comparison between the CuSO4 and the CuSiF6 electroplated Cu films was also conducted. A fixed current was applied through a simple metal line structure at an elevated temperature of 225 degrees C. The CuSiF6 electroplated films had a longer time-to-failure than the CuSO4 electroplated Cu films. (c) 2005 The Electrochemical Society. All rights reserved.