Topographic measurement of electromigration-induced stress gradients in aluminum conductor lines

We report a set of data on the evolution of stress in thin-film metallization wires during the transient region of electromigration. The excellent strain sensitivity of the x-ray microbeam topography technique allows real-time, spatially resolved measurements at the lowest currents reported to date (1.0×104–1.4×105 A/cm2). While the steady-state results agree qualitatively with the Blech’s stress gradient model [I. A. Blech, J. Appl. Phys. 47, 1203 (1976)], the threshold-length product calculated from our data is about 2–3 times smaller than previously reported values. Stress evolution during the transient state displays local fluctuations which cannot be attributed to experimental errors, indicating possible microstructural effects on local flux divergence even in the case of wide, nonbamboo wires.