The crystallinity of the fine interconnections was evaluated quantitatively by using electron back-scatter diffraction (EBSD) analysis The image quality (IQ) value, the average sharpness of Kikuchi pattern obtained from the analysis was applied to the quantitative evaluation of the quality of grains and grain boundaries in polycrystalline metalic thin-film interconnections. It was found that the main degradation path under high current density was along porous grain bundaries in the polycrystalline materials, and therefore, the effective lifetime due to electromigration varied drastivally depending on the volume ratio of the grain boundaries with low crystallinity in the interconnections. The crystallinity of fine interconnections varied depending on their fabrication process and their thermal hystory after the fabrication. In the case of electroplating, it was found to be important to control the lattice mismatch between the electroplated thin film and the substrate material used for the electroplating. The effective lifetime of copper interconnection varied about 100 times as a strong function of the crystallinity.