Chemical effects in chemical mechanical planarization of TaN: investigation of surface reactions in a peroxide-based alkaline slurry using Fourier transform impedance spectroscopy

TaN and Ta are used as diffusion-barriers for Cu interconnects in semiconductor microchips, and both these materials are patterned using the technique of chemical mechanical planarization (CMP). In the present work, we find satisfactory polish rates (∼120 nm/min) for both Ta and TaN by employing an alkaline slurry containing H2O2 and mixed abrasive particles. By combining potentiodynamic measurements with Fourier transform electrochemical impedance spectroscopy (FT-EIS), we show that the chemical mechanism for CMP of TaN is essentially identical to that we recently reported for Ta. This mechanism is governed by catalytic decomposition of H2O2 at the TaN-slurry interface, which leads to a local increase in the interfacial pH, and consequently, leads to conversion of Ta-oxide surface sites into soluble hexatantalate anions.