Electrochemical mechanical deposition of copper on a patterned wafer surface involves sweeping the surface with a pad during deposition and yields a planarized copper layer. In this work, the mechanism of this planarization phenomenon was studied by electroplating copper films on blanket wafer surfaces while sweeping a portion of the wafer surface with a small pad. Suppression of current density within the swept region was observed in the case when both organic suppressor and accelerator additives were present in the plating electrolyte. The degree of suppression in the deposition current density was found to be a strong function of the wafer rotation speed. Experimental and modeling results agreed well with the mechanically induced super filling mechanism which suggests that the difference between the current densities at the swept and unswept regions on the wafer surface is due to an additive surface coverage differential created by the sweeping action of the pad. (c) 2006 The Electrochemical Society.