Formation of copper interconnects by the reflow of sputtered copper films

The formation of Cu interconnects using conventional sputtering and reflow processes has been studied. The use of W, Mo, and TiN underlayers makes it possible to fill grooves with Cu at reflow temperatures as low as 450 degrees C. There is a close relationship between filling characteristics and agglomeration. Cu films agglomerate more easily on W, Mo, and TiN underlayers than on TiW and Ta underlayers because of their low Cu wettability. It was found also that Cu agglomeration was affected drastically by underlayer surface roughness. By adding the CMP process to the conventional sputtering and reflow processes, Cu interconnects down to 0.6 mu m in width have been fabricated successfully. The resistivity of the interconnects is about 1.9 mu Omega . cm.