Electromigration resistance-related microstructural change with rapid thermal annealing of electroplated copper films

Abstract

Electromigration is now a primary concern regarding reliability of ultralarge scale integrated circuits (ULSI) because of increasing current density in miniatured devices. Effects of rapid thermal annealing (RTA) treatment on the microstructural parameters on the electromigration resistance of electroplated Cu films were determined using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) analysis techniques. Also electron backscattered diffraction (EBSD) patterns were used to characterize the texture of the Cu thin films.It has been found that the electromigration resistance of the electroplated Cu film is enhanced with increasing the annealing temperature in the temperature range from 200 to 500 °C. Nitrogen is more favorable than vacuum as RTA atmosphere since nitrogen atmosphere offers lower resistivity and smoother film surface. Also the dependence of the bamboo structure on the annealing temperature and the line width of the Cu interconnect is discussed. If the line width is a quarter micron, a bamboo structure will be obtained by the RTA treatment at temperatures higher than 500 °C. On the other hand, if it is less than 0.1 μm, RTA at any temperature above 200 °C will result in the bamboo structure.