We have investigated the Cu texture in damascene interconnect structures formed by the reflow method of sputtered Cu film and electromigration (EM) performance in Cu damascene interconnects. The texture of reflowed Cu film depends on Cu deposition temperature and line width. Improved <111> texture in blanket films is obtained when Cu is deposited at temperatures over 200degreesC. However, Cu films form voids in the trench patterns at deposition temperatures of 350degreesC or more, and the voids cannot be filled even after the reflow process. Thus, it is necessary to choose the optimum deposition temperature to fabricate void-free Cu damascene interconnects. it was found that the Cu (111) peak intensity in reflowed Cu lines measured by using x-ray diffraction decreases as trench width decreases. This can be explained by aspect ratio changes of Cu lines in trenches, which affect the dominating Cu texture components originating from sidewall or bottom nucleations. Underlayer metals at sidewalls affect the Cu texture. In damascene interconnects, Cu <111> orientation normal to the substrate surface degrades in the edge regions near the sidewalls more than it does in the center region of the trenches. Even in these damascene structures, highly reliable Cu interconnects can be obtained by using an rapid-thermal-nitrided TiN (RTN-TiN) underlayer with a strong <111> orientation in both wide polycrystalline Cu lines and narrow bamboo-like Cu lines. An RTN-TiN underlayer decreases the void growth rate in Cu interconnects during EM testing. The improved EM lifetime can be explained mainly by the reduced Cu migration along the Cu interface and the underlayer metal. The Cu migration along the RTN-TiN underlayer progresses more slowly than it does along a reactively sputtered TiN underlayer, because the strong crystallographic bonding between Cu and the RTN-TiN underlayer decreases Cu migration. In wide polycrystalline lines, the difference in Cu migration at grain boundaries also affects the EM lifetime. In this case, the use of an RTN-TiN underlayer also leads to a strong Cu <111> texture with low-angle grain boundaries and reduces Cu migration along grain boundaries. C 2004 American Vacuum Society.