The degradation of the copper oxide passivated copper line prepared from a room temperature plasma-based etch process under the electromigration condition has been studied. The copper line surface was oxidized into the copper oxide layer in a parallel-plate plasma reactor operated under the plasma etching or reactive ion etching mode. The surface roughness of the oxide is contributed by the high ion bombardment energy. The lifetime of the sample was shortened by the addition of the oxide passivation layer. It was also decreased with the increase of the stress current density. The sample with the thin bulk copper layer is more resistant to the thermal stress than that with the thick bulk copper layer, which delayed the voids formation in the line breakage process.