We investigated the properties of the interface between Cu and TaN, Cu resistivity, and Ti diffusion in Cu/Cu(Ti)/TaN/Ta systems with Cu (0.5-7.7 wt % Ti) alloy films as the seed layer of electrochemical deposited (ECD) Cu film. The Cu(Ti) alloy films' interfaces to the TaN/Ta underlayer were improved compared with the Cu film interface. The use of Cu(Ti) films as a seed layer in the Cu/Cu(Ti)/TaN/Ta structure led to excellent thermal stability of Cu filling. The Cu(Ti) seed layers with Ti content above 0.5 wt % prevented voids from forming in Cu in a trench even after annealing at 450 degrees C for 3 h, whereas a Cu seed layer caused voids. The Cu(Ti) layer affected not only the interfacial properties but also the resistivity of the ECD Cu film. The resistivity of ECD Cu films with Cu(Ti) alloys depended on the annealing temperature and Ti content. The resistivities of ECD Cu with Cu (7.7 wt % Ti) increased with annealing temperature. However, the ECD Cu with less than 1 wt % Ti had low resistivity (2.1 mu Omega cm) even after 450 degrees C annealing. The resistivity increase in each sample after annealing corresponded to the amount of Ti diffused from Cu(Ti) alloys to ECD Cu. These results clearly indicate that Cu(Ti) seed layers with less than 1 wt % Ti are potentially good for advanced Cu interconnects where both superior interfacial stability and low resistivity are required. (C) 2007 The Electrochemical Society.