Electrochemical investigation of surface reactions for chemically promoted chemical mechanical polishing of TaN in tartaric acid solutions

In this work we use cyclic voltammetry, linear polarization resistance (LPR) measurements and Fourier transform electrochemical impedance spectroscopy (FT-EIS) to study the chemical mechanisms of chemical mechanical polishing (CMP) of TaN wafers in pH-controlled solutions of Tartaric acid (C4H6O6) and H2O2. These solutions can support CMP of TaN diffusion-barriers in the fabrication of interconnect structures, and can be particularly useful for chemically dominant low-pressure CMP in a non- or weakly alkaline environment to avoid OH− induced damages to Si-based low-k dielectrics. Electrochemical results presented here demonstrate how the individual and synergistic chemistries of C4H6O6 and H2O2 control the removal of TaN surface layers. LPRs measured in tartaric acid solutions at pH 3–8 exhibit strong correlations with TaN wafer polish rates obtained in these solutions. A.C. impedance measurements help to clarify the underlying chemical mechanisms of material removal. These findings indicate that the Ta sites of TaN are oxidized to Ta2O5 by O2 and H2O2 in the solution, followed by structural weakening of the oxide film due to the formation of Ta(OH)5 and mechanically fragile Ta-tartarate surface complexes.