Ruthenium (Ru) chemical mechanical planarization (CMP) with a slurry using sodium periodate (NaIO4) as an oxidizer was carried out as a function of pH. The Ru polishing rate was highest at pH 7 and decreased as the pH decreased or increased. In addition, a similar trend in the corrosion current density as a function of pH was found. Two equivalent circuit models were proposed to explain the electrochemical impedance spectroscopy (EIS) results of Ru in NaIO4 solution as a function of pH. From results of EIS, we found that the Ru film had a lowest charge transfer resistance in a neutral region than that in an acidic or alkaline region. This different charge transfer resistance of the Ru film as a function of pH resulted from the different surface composition of Ru oxide species, which was analyzed with X-ray photoelectron spectroscopy. Finally, we briefly derived a series of reaction equations between Ru and NaIO4 on the basis of the above results and discussion. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.103203jes] All rights reserved.