The texture of electroplated Cu lines with Ta and TiN barrier layers and widths of 0.375, 0.5 or 1.5µ, was analyzed by using X-ray pole figure and electron back-scattering diffraction techniques. Both techniques indicated the existence of a strong (111) fibre texture, relative to the bottom surface of the trench, for samples with a Ta barrier layer after post-electroplating annealing (400C, 0.5h). Samples with a TiN barrier, and no annealing, exhibited a weak (111) texture. For both barrier layers, the quality of the texture - as deduced from the (111) peak intensity, fraction of randomly oriented grains and (111) peak width - decreased with decreasing line-width. The electron back-scattering diffraction data also revealed a (111) texture relative to the side-walls of the trench, in samples with a Ta barrier, after post-electroplating annealing. Electromigration tests at 300C, of 0.36µ damascene lines after the same processing, showed that samples with a very weak (111) texture had median times to failure that exceeded those of the strongly textured Cu lines. The results indicated that diffusion at interfaces, such as the Cu/barrier and Cu/overlayer interfaces - together with diffusion along an electroplating seam - played more dominant roles during electromigration failure in damascene-fabricated lines than did diffusion along grain boundaries within the interconnect.

Texture Analysis of Damascene-Fabricated Cu Lines by X-Ray Diffraction and Electron Back-Scatter Diffraction and its Impact on Electromigration Performance. L.Vanasupa, Y.C.Joo, P.R.Besser, S.Pramanick: Journal of Applied Physics, 1999, 85[5], 2583-90