Dynamical x-ray microscopy investigation of electromigration in passivated inlaid Cu interconnect structures Page: 4 of 17
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nm thick passivation layers.6 However, because SEM images do not provide a linear
relationship between mass loss and image intensity, bulk voids cannot be detected.
Tomographic imaging based on transmission electron microscopy (TEM) images
provides high resolution 3D information; however this technique requires electron
energies of 300 keV or greater and needs samples significantly less than 1 pm in
thickness to avoid multiple-scattering of the electrons. The high-voltage TEM, with
about 1 MeV electron energy, permits imaging of thicker samples. However, the high
momentum transfer of the electrons to the atoms in the sample can lead to severe
radiation damage, especially if multiple images have to be recorded over hours, as in the
case of our EM studies. In addition, real time quantitative mass transport measurements
are not possible in either SEM or TEM studies.
In this Letter, we study void development and dynamics in passivated Cu line / via
structures using x-ray microscopy. X-rays can penetrate samples that are many
micrometers thick. Additionally, due to their unique interaction with matter, x-rays
provide a natural image contrast between different elements, which we exploit to image
Cu interconnect lines embedded within SiO2.
The test structures used for the EM experiments were located within the scribelines of
production wafers. Fig. lA shows a schematic cross-section of the EM test structures
used in the experiments with a two-level Cu interconnect. The samples were fabricated
using dual-inlaid Cu technology, with a PVD-Tantalum barrier layer and a PECVD-
Si3N4 (PEN) caplayer for the metal lines (see Fig. IA). The structure consists of an array
of metal lines. Depending on which level of metallization is tested, this array of lines is
referred to as either Metal 1 or Metal 2 of a two-level structure. In this study, Metal 2 was
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Schneider, G.; Denbeaux, G.; Anderson, E.H.; Bates, B.; Pearson, A.L.; Meyer, M.A. et al. Dynamical x-ray microscopy investigation of electromigration in passivated inlaid Cu interconnect structures, article, April 26, 2002; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc740985/m1/4/: accessed July 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.