Chemical mechanical planarization of copper using abrasive-free solutions of oxalic acid and hydrogen peroxide

In this work we study aqueous solutions of oxalic acid and hydrogen peroxide as possible abrasive-free slurries for chemical mechanical planarization (CMP) of Cu. We show that the addition of (3 wt%) colloidal silica abrasive particles has no measurable effects on the already relatively high polish rates of Cu. These results suggest that chemical rather than mechanical effects dominate removal of Cu surface layers in this system. The Cu removal efficiency of this slurry can be controlled by adjusting its acidity and H2O2 content. By combining measurements of Cu polish and dissolution rates with electrochemical experiments, we propose a reaction scheme that describes the mechanism of Cu removal in abrasive-free solutions of H2O2 and oxalic acid as a function of pH and H2O2 concentrations.