Development of x-ray topographic microscopy for the study of electromigration in interconnects

We have performed x-ray topography experiments in a new configuration using a Fresnel zone plate to form a magnified image of the sample intensity distribution on the detector plane. The main difference from the x-ray topography techniques where no optics is used between the sample and the detector, is the absence of free space propagation effects in the image and the possibility to form a magnified image. Other advantages include large working distance around the sample and low background radiation on the detector. As a first application, we recorded x-ray topographs of an Al interconnect structure as a function of time in an in situ electromigration experiment. The contrast in the images is explained in terms of lattice deformations caused by the stress in the metal films. The results show the evolution of stress due to the electromigration process. The technique should make it possible to obtain best possible spatial resolution allowed by the sample in x-ray topography