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 metallizati on wires during the transient region of electromigration. The excellent str ain sensitivity of the x-ray microbeam topography technique allows real-tim e, spatially resolved measurements at the lowest currents reported to date (1.0 x 10(4) - 1.4 x 10(5) A/cm(2)). While the steady-state results agree q ualitatively with the Blech's stress gradient model [I. A. Blech, J. Appl. Phys. 47, 1203 (1976)], the threshold-length product calculated from our da ta is about 2-3 times smaller than previously reported values. Stress evolu tion during the transient state displays local fluctuations which cannot be attributed to experimental errors, indicating possible microstructural eff ects on local flux divergence even in the case of wide, nonbamboo wires. (C ) 2000 American Institute of Physics. [S0003-6951(00)03525-7].