Electrical properties of sputtered Cu/Ta interfaces under electric current stressing were measured using four-terminal Kelvin structures. It has been found that the Cu/Ta interfacial resistivity was effectively reduced by applying hydrogen plasma treatment on Ta surface prior to deposition of Cu thin film. Besides, a marked and irreversible reduction of contact resistance was observed when applying an electric current through the Cu/Ta interface above some threshold levels. A thermally assisted junction breakdown process is believed to be responsible for the huge contact resistance drop. The conduction mechanism through the Cu/Ta interfaces is also briefly discussed. © 2005 American Vacuum Society.