Electrochemical mechanical deposition (ECMD) is a new technique that has the ability to deposit planar copper films on nonplanar substrate surfaces. This technique involves electrochemical deposition and simultaneous sweeping of the substrate surface with a planarization pad. In this study we show that planarization of low-aspect-ratio features on a wafer surface by ECMD is due to a newly identified "mechanically induced superfilling'' phenomenon. Sweeping of the top surface of the wafer at preset intervals establishes a transient differential in the surface coverage of organic additives at the top surface and the cavity regions, preferentially increasing the current flow into the cavities. Planarization decreases as the time interval between sweeps increases. Increase in the deposition rate of copper into the low-aspect-ratio features results in an associated decrease of deposition onto the top surface under galvanostatic conditions. A model that invokes surface coverage transients of accelerator species is offered to explain the experimental results. (C) 2004 The Electrochemical Society.