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Light lens precisely guides atom beams.

Today's semiconductor manufacturers use photolithography to etch microscopic circuits onto computer chips: They shine light through a mask onto a photosensitive surface to create the circuit's pattern. But to make nanometer-size circuits--about 1,000 times finer than current ones--these companies may one day use light in a very different way.

To work, photolithography depends on atoms in a mask to block light from parts of its target surface. But in a new process developed by AT&T Bell Laboratories in Holmdel, N.J., light does the blocking for atoms. "Instead of using matter to control light, we're using light to control matter," says Bell Labs physicist Gregory Timp. "We built a light pattern and transferred [the pattern] onto the surface."

For this technique, the researchers use a beam of atoms to deposit a thin film on a surface. To place the atoms, they tune a laser to a wavelength close to that which causes a particular atom to resonate. Because of light's wave-like nature, its intensity periodically increases, then decreases, creating peaks and valleys of high and low energy along its path, Timp says.

As an atom approaches this wave, it senses these energy differences because of its dipole moment (the internal polarization that causes the atom to prefer a specific position), Timp explains. The atom shifts to where the light's energy is most compatible with this dipole moment. If the laser's frequency is slightly lower than the one that causes the atom to resonate, then the atom heads to the brightest spots, Timp says. The light acts as a lens.

First, the scientists demonstrated how light affected the deposition of incoming atoms. Mara Prentiss, now at Harvard University, and her Bell lab colleagues describe these results in the Feb. 24 Applied Physics Letters. In another report, submitted to Physical Review Letters, they show how energy peaks in a standing wave of light focus sodium atoms into parallel lines.

The researchers say they can create interference patterns by using two standing waves at an angle to each other and can focus incoming atoms on a single, movable point. "You can distort the wave any way you want," Timp adds.

Timp sees great potential for light optics with neutral-atom lithography, as the team calls this technique. Because different atoms respond to specific wavelengths, one could theoretically guide the deposition of several kinds of atoms simultaneously by using light of different colors: for example, blue for indium, yellow for sodium. Moreover, engineers can refigure the circuit just by adjusting the angle of phasing of the lasers, a much simpler process than that used today. "The utility of light is that allegedly you can be very fast and also very precise," Timp adds. "It could represent a big savings."

Of course, such fine control means little if atoms still shift positions once they have landed, Timp says. And quantum mechanics may also limit the precision.
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Author:Pennisi, Elizabeth
Publication:Science News
Date:Mar 14, 1992
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