Tomography of Integrated Circuit Interconnect With an Electromigration Void
Zachary H. Levine, A R. Kalukin, M Kuhn, S P. Frigo, I McNulty, C C. Retsch, Y Wang, Uwe Arp, Thomas B. Lucatorto, Bruce D. Ravel, Charles S. Tarrio
An integrated circuit interconnect was subject to accelerated-life conditions to induce an electromigration void. The silicon substrate was removed, leaving only the interconnect encased test structure encased in silica. We imaged the sample with 1750 eV photons using the 2-ID-B scanning transmission x-ray microscope at the Advanced Photon Source, a third-generation synchrotron facility. Fourteen views through the sample were obtained over a 170 range of angles (with a 40 gap) about a single rotation axis. Two sampled regions were selected for three-dimensional reconstruction: one of the ragged end of a wire depleted by the void, the other of the adjacent interlevel connection (or via). We applied two reconstruction techniques: the simultaneous iIterative reconstruction technique and a Bayesian reconstruction technique, the generalized Gaussian Markov random field method. The stated uncertainties are total, with one standard deviation, which resolved the sample to 200 70 and 140 30 nm, respectively. The tungsten via is distinguished from the aluminum wire by higher absorption. Within the void, the aluminum is entirely depleted from under the tungsten via. The reconstructed data show the applicability of this technique to three-dimensional imaging of buried defects in submicrometer structures relevant to the microelectronics industry.