Compiled by Photonics Spectra staff
COLLEGE PARK, Md. – At the University of Maryland, scientists have achieved a breakthrough
in using visible light to make tiny integrated circuits. Although the technology
may not become commercially available for more than a decade, it may eventually
make it possible to produce computer chips that are smaller, faster and cheaper.
A new lithography process could take today's computer chips such as the one pictured here
into the realm of smaller, faster and cheaper.
Called RAPID lithography, the technique uses visible light to
attain lithographic resolution comparable to, and maybe even better than, the resolution
attainable with shorter-wavelength radiation. Essential to the process is a special
photoinitiator that may be excited by one laser beam and deactivated by another.
The advance could one day replace photolithography in the manufacture of integrated
In photolithography, each computer chip is built up in layers,
with conductive materials piled on a chip and coated with chemicals that harden
when exposed to light. The light shined through a mask, or stencil, projects a detailed
pattern onto the photoresist, which hardens where it is exposed. The unhardened
areas and underlying metals are then etched away with a chemical. The remaining
photoresist is etched away using different chemicals, leaving an underlying layer
of metal with the same shape as the mask.
Building multiple circuits on a chip has meant forming ever-smaller
circuits with shorter and shorter wavelengths of light, or even charged particles.
The new technique, however, uses visible light, which is far less expensive to generate,
propagate and manipulate and does not require high-vacuum conditions.
In their work, the researchers used a beam of ultrafast pulses
for the excitation step and a continuous laser for deactivation. They found recently
that with materials deactivation, however, they could use ultrafast pulses for both
the excitation and deactivation of the molecules. The discovery resulted in findings
that higher exposures can lead to smaller features, leading to what they call proportional
velocity (PROVE) dependence.
“PROVE behavior is a simple way to identify photoinitiators
that can be deactivated efficiently, which is an important step toward being able
to use RAPID in an industrial setting,” said John Fourkas, chemistry professor
at the university.
They found that they were able to demonstrate a photoresist for
which the resolution was independent of the exposure over a range of exposure times
when combining a PROVE photoinitiator with one that had a conventional exposure
Their work appeared in Nature Chemistry, March 2011 (doi: 10.1038/nchem.965).