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Magic butterfly cleans up chip.

Magic butterfly cleans up chips

Osamu Ueda is a renowned collector ofreal-life butterflies. But among those likely to gain him the most fame is this microscopic one, discovered while he was visiting the Massachusetts Institute of Technology. The expert electron microscopist, who works for Fujitsu Laboratories in Kawasaki, Japan, found the butterfly and others like it in the silicon wafers used to make integrated-circuit chips while he was working with MIT's Kris Nauka and Mark Goorski.

The "butterfly' is actually a beneficialdefect that Ueda found had formed during the high-temperature annealing of crystalline silicon in the processing of wafers to make chips. What makes it so special is that it removes metal impurities from the top 100 microns of a wafer--where they could alter the performance of any integrated circuits or devices eventually placed there-- and locks them deep within the silicon.

Many techniques have been engineeredto gather up and channel detrimental impurities, introduced during chip making, away from the regions where chip devices will operate. But such "gettering' processes can take 16 or more hours--far too long to be useful with the rapid thermal annealing techniques being developed for the processing of much smaller, very-large-scale-integration chips, according to MIT materials scientist Jacek Lagowski. Since the discovery, the researchers have developed a way to produce the butterfly intentionally. "We believe this butterfly is the only gettering process which can work in times on the order of seconds,' says Lagowski.

As the inset diagram shows, the roughly1-micron defect results from a three-dimensional deformation of the lattice structure of crystalline silicon. The butterfly pattern emerges only when the deformation is viewed at one of several select angles.
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Title Annotation:butterfly-shaped defect found to remove metal impurities from semiconductor chips
Author:Raloff, Janet
Publication:Science News
Date:Jul 25, 1987
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