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

摘要

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 KIO_3 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 IO_3~- that lead to a structurally weak surface film of soluble hextantalate [(Ta_6O_(19))~(8-)] embedded in (native or electro-generated) Ta_2O_5 on Ta. Catalytic reduction of IO_3~- on Ta_2O_5 enhances the local pH at the oxidized surface and promotes the conversion of Ta_2O_5 to (Ta_6O_(19))~(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.