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Nanotomography

contact person: Alan Kubis (ajk7s@virginia.edu)

Visualization of the three-dimensional relationship of structures in materials has become an important tool in the materials science community. As structures have become smaller in the semiconductor industry, and the field of nanotechnology has emerged it is increasingly important to be able to reconstruct features at the sum-micron level. Our group uses the FIB to obtain serial sections of materials with tens of nanometer resolution allowing the visualization and interrogation of nanoscale structures. By using the in situ milling capability of the FIB and its high resolution imaging power three-dimensional reconstructions can be produced using various computer algorithms and visualization packages.  

Several systems have been investigated using this technique. Using the imaging and ion mapping capabilities of the FIB in our facility electronic via structures were looked at to show the techniques ability to correlate structural features with their elemental constituents. Below the Secondary electron reconstruction can be compared with the Aluminum, Titanium and Oxygen reconstructions clearly delineating the Al fill, TiN diffusion layer and SiO₂ dielectric layer.

Comparison of Secondary Electron reconstructions with three different elemental reconstructions

D.N. Dunn, R. Hull, Appl. Phys. Lett. Reconstruction of three-dimensional chemistry and geometry using focused ion beam microscopy, 75(21) 3414-3416 (1999).

An aluminum grain structure was also reconstructed to show the applicability to metallurgical systems. In both cases, a fairly simple reconstruction was used to create these structures. A more complex algorithm was written, based on techniques used in the Medical imaging field, using a shape based interpolation (SBI) method. This method allows much more complex morphologies to be studied and more accurately reconstructs features at the nanoscale level. In conjunction with Gary Shiflet’s group (UVa, Dept. of Materials Science) a Cu-15In colony was reconstructed using the SBI method. The highly complex morphology of these colonies can be clearly observed and in the case of c) the elemental distribution of Indium in the colony can be easily reproduced.

D.N. Dunn, G.J. Shiflet, R. Hull, Quantitative three-dimensional reconstruction of geometrically complex structures with nanoscale resolution, Rev. Sci. Instru. 73(2) 330-334 (2002).

To more clearly observe the morphology in these complex structures cross sections of the volumes can be put into animations so that the full structure can be observed. Below is a three-dimensional reconstruction of a Nickel-Based Superalloy used in jet aircraft engines. The gamma prime phase is shown with the gamma phase removed. By clicking on the image below layers will be removed allowing the whole structure to be observed. 

Nickel-Based Superalloy provided by D. Backman, GE Aircraft Engines

We are currently working to increase the resolution of this technique to study Self-assembled quantum dot structures in support of the MRSEC Center for Nanoscopic Research. Other materials, such as devitrified aluminum glasses, are being investigated in conjunction with Gary Shiflet’s research group.