Polish rates of copper and tantalum were measured using potassium iodate-based slurries containing silica abrasives for several concentrations of potassium iodate and pH. The tantalum polish rate increases rapidly with pH beyond pH 10.0 and with 3% silica reaches a value of about 215 nm/min while copper polish rate under the same conditions is only about 45 nm/min. Also, the dissolution/passivation behaviors of copper as well as tantalum were investigated by electrochemical measurements.