Tribo-electrochemical characterization of copper thin films

The frictional behavior of a patterned wafer during polishing depends on the applied potential. This relationship was investigated by using a tribo-electrochemical approach. Under a sweeping potential ranging from −0.5 V to 1.0 V, increase in potential caused decrease in friction coefficient. The surface roughness and porosity of the copper oxide film were analyzed as factors that affect friction coefficients by using an electrochemical impedance spectroscopy (EIS). EIS results, combined with an equivalent circuit model, showed that the resistance of copper oxide films decreased and their capacitance increased with increasing DC potential. These results indicate that the higher the DC potential, the thicker and more porous the copper oxide layer. This resulted in less contact area with the pad and less chance for abrasive particles to participate in mechanical removal, causing the decrease in friction coefficients. The in situ evaluation of the changes in copper oxide can provide helpful information for CMP or ECMP processes.