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

Abstract

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 H 2O 2 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 H 2O 2 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.