Thermal and electromigration strain distributions in 10 mu m-wide aluminum conductor lines measured by X-ray microdiffraction

X-ray microdiffraction was applied to study the thermal and electromigration strains in 10 mu m-wide Al conductor lines with 10 mu m spatial resolution. X-rays were collimated either by pinholes or by tapered glass capillaries to form x-ray microbeams. Measurements were made in a symmetric-reflection geometry so that the strains normal to the sample surface could be examined at different positions along the conductor lines. Results of thermal strain measurements show that the SiO2 passivation plays an important role in limiting relaxation of in-plane compressive thermal stresses in the Al lines, but that the passivation is not effective in confining the overall thermal expansion of the Al line along the film normal. Electromigration strain measurements show that a linear stress gradient developed within the first hour of electromigration. The magnitude of the stress gradient changed little until fast stress relaxations occurred near the anode end of the Line. Possible mechanisms are discussed in light of these observations.