Role of iodate ions in chemical mechanical and electrochemical mechanical planarization of Ta investigated using time-resolved impedance spectroscopy

Chemical mechanical planarization (CMP) is currently used in the processing of Cu/Ta interconnect structures. Electrochemical mechanical planarization (ECMP) is an emerging extension of CMP that can potentially allow low down-pressure planarization of newer interconnect structures containing easily breakable porous dielectrics. In both CMP and ECMP of Ta, it is necessary to chemically (or electrochemically) form a “soft” surface film that can be easily removed by minimum mechanical abrasion. Alkaline KIO3 solutions appear to serve this purpose in CMP of Ta and, as we show in this work, may also be utilized in ECMP of Ta. Using time-resolved impedance spectroscopy we study here the relevant surface reactions of IO3− that lead to a structurally weak surface film of soluble hextantalate [(Ta6O19)8−] embedded in (native or electro-generated) Ta2O5 on Ta. Catalytic reduction of IO3− on Ta2O5 enhances the local pH at the oxidized surface and promotes the conversion of Ta2O5 to (Ta6O19)8−. The chemical role of iodate ions in material removal through these reactions is similar to that of hydrogen peroxide in CMP of Ta in alkaline media.