Developments in limited data image reconstruction techniques for ultrahigh-resolution x-ray tomographic imaging of microchips

The use of soft x-ray (about 1.8 KeV) nanotomography techniques for the evaluation and failure mode analysis of microchips was investigated. Realistic numerical simulations of the imaging process were performed and a specialized approach to image reconstruction from limited projection data was devised. Prior knowledge of the structure and its component materials was used to eliminate artifacts in the reconstructed images so that defects and deviations from the original design could be visualized. Simulated data sets were generated with a total of 21 projections over three different angular ranges: -50 to +50, - 80 to +80 and -90 to +90 degrees. In addition, a low level of illumination was assumed. It was shown that sub-micron defects within one cell of a microchip (< 10 pm3) could be imaged in 3-D using such an approach.