Grain-Scale Strain and Orientation Measurements during Electromigration in Al Conductor Lines by Synchrotron X-Ray Microbeam Diffraction

Al conductor lines, with Ti-Al top and bottom layers and SiO2 passivation, were stressed with current density 1.5 × 106 A/cm2at 190°C, and the strains developed during electromigration were measured in-situ by white and monochromatic beam synchrotron x-ray microdiffraction. Grain-scale deviatoric strain measurements with 0.4µm beam size and perpendicular full strain measurements with 1.0µm beam size were made repeatedly during electromigration. A strong strain gradient developed along the upstream half of the conductor lines during electromigration, although no resistance changes, voids or extrusions were seen. Orientation maps showed near-bamboo grain structure. Results from an approximate analytic model, using the Eshelby inclusion theory, are consistent with the measurement results for late-stage electromigration-induced strains.