The effect of an accelerator on the morphological evolution during copper electrodeposition was investigated with the designed one-directional (1-D) pattern which has a seed layer only at the bottom of the pattern. Field-emission scanning electron microscope images showed that there was no superfilling found in the pattern with 0.2 mu m width trench and no reduction in the surface area during electroplating. This indicates that superfilling in a damascene pattern results from the accumulation of the accelerator. It was found that copper damascene electroplating for ultralarge-scale integration is a simple electroplating system that is controlled by the activation overpotential of adhered organic additives, not by the concentration overpotential of copper ions. (c) 2006 The Electrochemical Society.