Continuous Cu films are deposited on Ta by a two-step process; galvanic displacement of Ta by Cu from ammonium fluoride solutions and subsequent electroless Cu deposition from a formaldehyde-containing bath. The conditions necessary for good adhesion are discussed. The extent of oxide film removal in the HF pretreatment solution is studied by electrochemical impedance spectroscopy. The charge-transfer resistance of about 57 Omega-cm(2) is several orders of magnitude lower than that measured for the Ta native oxide. These results are consistent with the removal of the Ta2O5 portion of the native oxide. (C) 2004 The Electrochemical Society.