Electrochemical investigation of the roles of oxyanions in chemical-mechanical planarization of tantalum and tantalum nitride

Nitrate, sulfate, and phosphate oxyanions are shown to serve as effective surface-modifying agents for low-pressure chemical-mechanical planarization (CMP) of Ta and TaN barrier layers of interconnect structures. The surface reactions that form the basis of this CMP strategy are investigated using cyclic voltammetry, open circuit potential and polarization resistance measurements, and impedance spectroscopy. The results suggest that forming structurally weak layers of surface oxides is crucial to chemically controlling the CMP of Ta/TaN at low polish-pressures. It is shown that in oxyanion-based slurries, this can be accomplished by modifying the sample surfaces with anion-incorporated oxide films of Ta or TaN, which, in turn, can readily be removed with moderate abrasion. Electrochemical results elaborate the reaction mechanisms that lead to anion-modified oxides, such as Ta2O5(1-x)(NO3)(10x) , Ta2O5(1-x)(SO4)(5x) , and Ta2O5(1-x)(PO4)(10x/3) on both Ta and TaN surfaces in pH-controlled solutions of KNO3, K2SO4, and KH2PO4 solutions, respectively.