Bell Labs scientists image single impurity atoms in silicon

April 25, 2002 – Murray Hill, NJ – Scientists at Bell Labs, the research and development arm of Lucent Technologies, have found a way to peer deep inside a semiconductor and create an image of a single impurity atom in silicon. The feat – claimed by Bell Labs to be the first time that an individual impurity has been pictured in its undisturbed state within a crystal — was achieved using a special electron microscope, and is as difficult as seeing a footprint on the moon from the Earth.

This breakthrough will allow scientists to gain an understanding of
how exactly impurities influence the properties of semiconductors, which is needed to shrink the size of future generations of high-speed electronic equipment.

The breakthrough is described in an article published in the journal

In an accompanying commentary in Nature, Professor Paul Peercy, dean of
engineering of the University of Wisconsin at Madison and a former president of International SEMATECH, writes that the Bell Labs results “are important in understanding the distribution of impurities in silicon at an atomic level; they will also be important in increasing our understanding of a wide range of complex materials.”

Impurities – or “dopants”, as they are known in the electronics industry — are introduced into semiconductors like silicon to provide charge carriers that control the semiconductor’s electrical properties. As chip components continue to shrink in accordance with Moore’s Law, which maintains that the processing power of electronic components such as transistors doubles every 18 months as their size shrinks by half, the industry is approaching a point where just a few atoms of impurities could determine the function of a particular device.

“It has become critically important to both image and understand the
chemical and physical environment within devices, because these properties will ultimately determine the extent to which we can continue to shrink silicon dimensions,” said Elsa Reichmanis, director of the materials research department at Bell Labs. “This work builds a solid foundation for our ongoing research in this important area of technology.”

By using a scanning transmission electron microscope, a team led by physicist David Muller of Bell Labs succeeded in directly imaging individual antimony dopant atoms within crystalline silicon. Previous techniques had not been able to look inside crystals; when dopants were imaged, they were only imaged on the surface. Yet, scientists knew that atoms inside a crystal behave very differently to those on a surface.

“Now we can look at things hidden inside a solid, in their natural environment, ” said Muller. “It’s as qualitatively different as seeing how an animal behaves in a zoo and how it behaves in its natural habitat.”

The Bell Labs technique is extremely sensitive and can be applied to almost any material, not just semiconductors. It has already proved useful in troubleshooting and characterizing optoelectronics components.

“If you think of an 8-inch silicon wafer on which we grow our chips as the size of the United States, a single transistor is the size of a car, and a single atom is the size of a pin. We are able to locate the equivalent of a few pins, hidden in a few cars, somewhere in the United States,” Muller said.

Other members of the research team were Paul Voyles, John Grazul and Paul Citrin of Bell Labs and Hans Gossmann of Agere Systems.

“This work opens up a new chapter in materials science and technology:
microscopy with spatial and chemical resolution at an atomic scale in the bulk,” said Federico Capasso, physical research vice president at Bell Labs.


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