Oxalic acid is a complexing agent used in both chemical mechanical planarization (CMP) of copper and post-CMP cleaning. Aqueous solubility diagrams and potential-pH diagrams at different total dissolved copper and oxalic acid activities were derived to examine the electrochemistry of copper in aqueous oxalic acid solutions. The predictions of the diagrams are discussed in terms of the experimental data available in the electrochemistry and Cu CMP literature. Good correlations were found. (c) 2005 The Electrochemical Society. All rights reserved.