This article aims to provide practical information on the performance of a hot-filament radical source, with which it becomes feasible for metallization in ultralarge-scale integrated circuits, which has not been studied in detail thus far. A very simple arrangement using this technique allows the highly efficient generation of hydrogen radicals and a quick recovery of oxidized Cu surfaces to their original metallic state. The amount of CuO reduction was evaluated by measuring sheet resistance and also by transmission microscopy. The reduction started when the specimen temperature exceeded 100 degrees C, and several tens of nanometers Cu of film was formed without resulting in a serious increase in the specimen temperature. The amount of reduction was found to increase almost proportionately to the hydrogen radical flux. The Cu layer had a very flat surface topography showing no trace of self-agglomeration of Cu. The reduction of a thermally oxidized Cu specimen was also demonstrated. (C) 2007 American Vacuum Society.