Electrochemical examination of surface films formed during chemical mechanical planarization of copper in acetic acid and dodecyl sulfate solutions

Electrochemical impedance spectroscopy (EIS) is employed to study the competitive reactions of surface corrosion and passivating film formation on a Cu-rotating disc electrode (RDE) in pH-adjusted solutions of H2O2, acetic acid (HAc) and ammonium dodecyl sulfate (ADS). The surface reactions that occur at the open circuit potential of this system are relevant for chemical mechanical planarization (CMP) of Cu-interconnect structures. The results show how the discontinuous film of Cu-oxides formed by H2O2 acts both to dissolve (via reactions with HAc) and to passivate the Cu surface. The relatively more continuous ADS film serves as a dissolution suppressor and regulates the removal of Cu/Cu-oxide surface layers. The results presented here also demonstrate the utility of EIS involving RDEs to design slurry chemistries for Cu-CMP.