The synergistic effect of polymer additives such as gelatin, polyethylene glycol (PEG) and Cl- on Cu electrodeposition behavior have been investigated by measuring the polarization curves for Cu deposition, by rotating ring-disk electrode technique and by AC impedance measurement. In the polymer additive-free solution containing Cl-, the cathode potential shifted to less noble direction with increased concentration of Cl- in solution, resulting in a decrease in grain size of deposited Cu. The rotating ring-disk electrode technique revealed that Cu deposition in the solution containing slight amount of Cl- proceeded with preceding formation of adsorbed intermediate CuClad. The reduction of intermediate CuClad to Cu seems to polarize the cathode potential for Cu deposition. In the solutions containing both polymer additives and Cl-, the cathode potential for Cu deposition was more greatly polarized and deposited Cu was consisted of smaller grains, showing evident synergistic effect of polymer additives and Cl- on Cu deposition. The Nyquist plots obtained by AC impedance techniques suggest that the reduction of CuClad to Cu is suppressed by polymer additives.
