The nucleation and growth of copper directly electroplated on Ta is studied in this paper using electrochemical methods. It is shown that little Cu deposition on Ta occurs from an acid sulfate copper plating electrolyte, while a deposited nuclei density of similar to 10(9) cm(-2) is possible using a basic citrate electrolyte. Experimental results indicate that when plating directly onto Ta, besides a high current efficiency, the nucleation characteristics of an electrolyte are important. Using a basic citrate chemistry, deposition currents were found to be higher on Cu than on Ta, suggesting that when both are present, deposition occurs preferentially on Cu. Because the relative deposition rates are a function of applied potential, deposition on Ta instead of Cu may be encouraged by the judicious control of this deposition parameter. (c) 2007 The Electrochemical Society.