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Researchers from IBM and electron-optical instrumentation firm Nion Co. have created the most precise electron microscope to date, and it should help develop a greater understanding of the materials used in building future semiconductors with smaller features.

The new technique, which is reported in the Aug. 8 issue of Nature, significantly extends the capabilities of the electron microscope. Electron microscopes use magnetic lenses to focus electrons into very small beams to look at small, atomic-scale details in thin slices of materials. For the past 50 years, electron optics engineers have sought to improve the precision of electron microscopes by counteracting the image-blurring effects of lens imperfections, called aberrations.

The largest imperfection is called spherical aberration, and it cannot be fixed in a single lens. To fix the problem, scientists from IBM and Kirkland, Wash.-based Nion combined seven new sets of magnetic lenses with modern computers to actively correct the aberration in real-time. Once this was done, the microscope could produce an electron beam only three billionths of an inch wide, smaller than a single hydrogen atom

By fixing such imperfections, scientists will be able to learn more about the atomic structure of important defects in semiconductor materials, such as missing or extra atoms. For example, by examining the interaction of silicon (a semiconductor) with silicon oxide (an insulator), scientists can look at how the silicon and oxygen atoms bond to each other and determine the quality of the insulator. If the insulator has any defects, scientists can suggest ways to fix them, such as setting the right conditions to optimize the growth of silicon and silicon oxide materials.

"We can't fix what we can't see," said Dr. Philip Batson of IBM's T.J. Watson Research Laboratory in Yorktown Heights, N.Y. "As the dimensions of computer chips shrink, scientists need new tools to explore the structures and properties of materials used in these chips. This breakthrough improves our ability to see and thoroughly explore properties of electronic materials."

The breakthrough could also help scientists improve the properties of silicon by allowing them to better understand how the atoms inside materials interact in certain environmental conditions. Watching how atoms assemble, move around and interact with other atoms is fundamental to understanding the properties of materials and may lead to a better understanding of how to control environmental conditions so future computer chips could self-assemble.

Comparison with previous performance for Ge30Si70

This panel compares the performance of the electron microscope with and without the spherical aberration correction developed by IBM and Nion. The top panels show a "shadow map" pattern that tells us about the quality of the optical system. The featureless patch in the middle is an area that transmits electrons faithfully to make the very small electron beam. The bigger the patch, the better. The middle shows the image results. The image on the left cannot resolve the pairs atom columns in Si that are separated by 0.135 nm. On the right, the pairs are easily resolved. The patterns at the bottom, again, indicate the faithfulness of the structure's image. The greater number of spots on the right indicate that smaller spatial distances are being reproduced on the right. Source: IBM