Electrochemical planarization (ECP) of copper surfaces in a phosphoric acid-based electrolyte solution is discussed. A first-principles, quantum chemistry modeling work is presented that further validates the water-facilitated (and water rate limited) chemistry model for copper oxidation at the anode. This model has been previously deduced by other researchers [R. Vidal and A. West, J. Electrochem. Soc. 142, 2689 (1995); B. Du and I. I. Suni, J. Appl. Electrochem. 34, 1215 (2004); R. Vidal and A. West J. Electrochem. Soc. 142, 2682 (1995)] based on electrochemical experiments. Resulting water-limited model is validated against experimental data and applied to study the planarization behavior of a set of surface features. Aspect ratios and dimensions of these features were chosen to represent realistic (nonidealized, low aspect ratio structures) post-Damascene electroplate surface topography. Results are presented in a form of remaining feature amplitude versus mean copper thickness removed [A. C. West et al., J. Electrochem. Soc. 152, C652 (2005)]-allowing at-a-glance evaluation of the process against desired targets. The dominant effects of the mass transport boundary layer (BL) thickness on this planarization efficiency are discussed as are the challenges seen at typical flow conditions in ECP systems. Impact of changing the BL thickness and the requisite modulation of flow conditions analysis is included. Insights into practical challenges associated with BL buildup transient and associated surface roughening are summarized [D. Padhi et al., J. Electrochem. Soc. 150, 610 (2003)]. Challenges of applying ECP as a straightforward substitute to the robust chemical mechanical polish (CMP) process are significant. Practical modifications to upstream process flow to enable ECP would include optimized electroplating process or a CMP preprocessing step. (c) 2007 American Vacuum Society.