Texture analysis of damascene-fabricated Cu lines by x-ray diffraction and electron backscatter diffraction and its impact on electromigration performance

The texture of electroplated Cu lines of 0.375, 0.5 and 1.5 mu m widths with Ta and TiN barrier layers was analyzed using x-ray pole figure and electron backscatter diffraction (EBSD) techniques. Both techniques indicate a strong (111) fiber texture relative to the bottom surface of the trench for samples with a Ta barrier layer and a 400 degrees C, 30 min, postelectroplating anneal. Samples with a TiN barrier and no anneal exhibit a weak (111) texture. For both barrier layers the quality of the texture, as measured by (111) peak intensity, fraction of randomly oriented grains and (111) peak width, degrades with decreasing linewidth. EBSD data also indicate (111) texture relative to the sidewalls of the trench in samples with a Ta barrier and postelectroplating anneal. Electromigration tests at 300 degrees C of 0.36 mu m damascene Cu lines with the same process conditions show that samples with very weak (111) texture have median time to failures that exceed those of the strongly textured Cu lines. These results indicate that diffusion at interfaces, such as the Cu/barrier and Cu/overlayer interfaces, along with diffusion along an electroplating seam play more dominant roles in electromigration failure in damascene-fabricated lines than diffusion along grain boundaries within the interconnect. (C) 1999 American Institute of Physics. [S0021-8979(99)02905-9].