Real-time observation of electromigration-induced stress changes with imaging x-ray topography

Abstract

We have observed the evolution of stress in Al interconnect lines during the electromigration process using x-ray topography in a new imaging configuration. Monochromatic x rays from a synchrotron source were reflected in a symmetric geometry by the Si substrate of the interconnect structure. We used a Fresnel zone plate in an off-axis imaging geometry to obtain magnified images of the sample. The results show the establishment of a constant stress gradient in the steady state where the electromigration damage is halted as well as time-dependent behavior of stress leading to that state. The imaging x-ray topography technique offers a number of advantages including better spatial resolution potential by eliminating the blur that occurs in conventional topography due to the finite distance between the sample and the detector.