X-Ray Microbeam Studies of Electromigration

9708003 Cargill This study of electromigration using X-ray microdiffraction and electron microscopy builds on the experience and confidence gained during work supported by a one-year SGER NSF award. This work has shown that thermal and electromigration induced strains can be successfully measured with 10 micron spatial resolution and with strain sensitivities on the order of 0.0002 by X-ray microdiffraction. The past work has confirmed that linear strain gradients develop during electromigration in conductor lines with no reservoirs and that abrupt strain relaxation occurs during the later stages of electromigration under the conditions used in the studies. The new project extends the work on a limited number of 10 micron-wide, 200 micron-long pure Al conductor lines to narrower line widths with bamboo and near-bamboo microstructures, to shorter lines which should be able to sustain larger strain gradients, to A1(Cu) lines where electromigration of Cu and of A1 can be separately followed by X-ray microfluorescence, and finally to Cu and Cu(Sn) lines, which should be more resistant to electromigration than A1(Cu). The work utilizes higher spatial resolution X- ray instrumentation to extend composition, microstructure and strain mapping to the submicron scale and to permit measurements on single grains within polycrystalline conductor lines. The study includes transmission electron microscopy, scanning electron microscopy (SEM), and SEM- based grain orientation mapping observations as complements to the X-ray microbeam microstructure, composition, and strain mapping. Finite element modeling is employed with realistic microstructures and misorientation dependent grain- boundary diffusivities. The study will be extended to short range, microstructure related strain gradients, and to effects of pulsed and reversal current on electromigration strains. %%% The expected significance of the research is that it provides a better experimental base for underst anding electromigration. Successful direct measurements of strain distributions during electromigration will provide tests and focus for further theoretical work in this area. ***