Quantum effect for chipmaking confirmed

By Eric Smalley, Technology Research News

A physics experiment has confirmed the mind-bending bit of quantum theory that says two photons linked in the quantum state of entanglement will expose only half the area that a single photon would when they shine through an opening onto an underlying surface.

This phenomenon could effectively give computer chip manufacturers smaller chip building tools. If light consisting of entangled photons can be used in photolithography, manufacturers could use it to etch computer chips with smaller circuits than those made using ordinary light. What's more, the effect increases with the number of entangled photons.

Chip manufacturers need to produce smaller features to continue making faster computer chips, and in order to produce smaller features they need to use shorter wavelengths of light. One problem with simply using shorter wavelengths than today's methods is very short wavelengths behave differently. Below about 100 nanometers, in the extreme ultraviolet and x-ray range, light is unaffected by ordinary lenses and mirrors, which are used in today's chipmaking processes to reduce the size of the circuit patterns that are chemically etched into silicon chips.

Researchers from the University of Maryland at Baltimore County have demonstrated that a pair of entangled photons beats the diffraction limit, which is the law of physics that determines the smallest area that ordinary light can expose.

The diffraction limit is half the light's wavelength. For example, if red light, which has a wavelength of around 700 nanometers, shines through a tiny slit or pinhole, it can expose an area no smaller than 350 nanometers.

"We have demonstrated the working principle of... two-photon lithography, which has beaten the classical diffraction limit by a factor of two," said Yanhua Shih, a professor of physics at the University of Maryland.

To confirm the entanglement diffraction theory, the researchers directed a beam of ordinary light through a pair of slits and found that it exposed an area 916 nanometers wide. They then entangled pairs of photons of the same light and found that the exposed area was 458 nanometers wide.

In theory, increasing the number of entangled photons will increase the effect. For example, entangling three photons would beat the diffraction limit by a factor of three, yielding an exposure one-third the width of the area exposed by ordinary light of the same wavelength.

Some chipmakers are building manufacturing facilities that use special materials to control extreme ultraviolet light. These facilities are expensive but could produce chips with lines as small as 10 nanometers in the next five to ten years. Quantum lithography is a potentially less expensive alternative because the light needed to produce such small lines could be controlled by the equipment in existing facilities.

Two challenges have to be met before quantum lithography can be used in practical applications, said Shih. First, researchers need to be able to reliably entangle larger numbers of photons, and second, they must find a material that efficiently absorbs entangled photons, he said.

"As predicted, diffraction with what are called maximally [entangled] states involving two photons is reduced," said Christopher Gerry, an assistant professor of physics at Lehman College. "However, there are a number of problems that need to be overcome if lithographic procedures are going to benefit."

One problem is finding a material that absorbs two-photon light more readily than the usual single-photon light, he said. The higher the number of entangled photons, the more difficult it is to find a suitable material, he added.

Another challenge is being able to reliably produce entangled-photon light at sufficient intensities for commercial photolithography, said Gerry.

Shih's team is working on the problem of entangling larger numbers of photons and could have positive results in a couple of years, he said. Other research teams are working on the material challenge, he said.

Shih's research colleagues were Milena D'Angelo and Maria V. Chekhova of the University of Maryland, Baltimore County. They published the research in the July 2, 2001 issue of the journal Physical Review Letters. The research was funded by the National Security Agency (NSA), the Office of Naval Research and the National Science Foundation (NSF).

Timeline:   20 years
Funding:   Government
TRN Categories:   Integrated Circuits; Quantum Computing
Story Type:   News
Related Elements:  Technical paper, "Two-Photon Diffraction and Quantum Lithography," Physical Review Letters, July 2, 2001


August 15, 2001

Page One

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Quantum effect for chipmaking confirmed


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