Interference scheme sharpens focus

If computers are to continue getting faster, researchers must find ways to make smaller logic circuits. Today's lithographic processes are only precise enough to continue to make smaller devices for the next five or ten years.

The challenge in continuing to use today's manufacturing processes beyond the next decade is finding a way to get around the diffraction limit, which keeps lightwaves from being focused more narrowly than half the light's wavelength.

Researchers from the University of Rochester have found a way to improve the resolution of lithographic systems that could extend the lifetime of the manufacturing technique. The researchers' proof-of-principal experiments show that the technique improves resolution by three times. In theory further improvements are possible, according to the researchers.

The method is a form of multi-photon absorption lithography, which uses materials that can absorb two or more photons at a time in the same spot and the interference patterns that cancel out the outer portion of a spot while reinforcing the center of the spot.

In many multi-photon absorption lithography schemes the interference patterns are caused by entangled, or linked photons, but it is difficult to produce bright sources of entangled photons.

The University of Rochester scheme simplifies a method of using a pair of ordinary ordinary laser beams rather than an entangled photon source first developed at the University of California at Los Angeles. The Rochester approach involves firing multiple pulses and shifting the phase of successive pulses by a fixed amount.

The technique could be used practically in two to five years, according to the researchers. The work appeared in the November 15, 2004 issue of Optics Express.