STED-like lithographic process could lead to cheaper high-resolution microchips

Trisha Andrew (Photo: M. Scott Brauer)

Salt Lake City, UT and Cambridge, MA--A type of optical lithography based on a photochromic transition creates a super-resolution effect similar to that in stimulated emission depletion imaging (STED) microscopy. Researchers at the University of Utah and Massachusetts Institute of Technology (MIT) have used this effect and a two-beam interferometer to create isolated lines in photoresist as narrow as one-eighth wave (78 nm) at the exposure wavelength.¹ This could allow inexpensive chips to be made with features smaller than the diffraction limit.

While large chipmakers such as Intel, who use exposure tricks to push 193 nm lithography to its limits, are already making one-eighth-wave features (22 nm) on silicon wafers, the required equipment costs tens of millions of dollars. A much less-expensive approach, even if its not developed to the same degree as leading-edge conventional lithography, could serve many purposes of scientists and engineers.

Trisha Andrew, one of the MIT researchers and a co-author of the work as well as a 2009 paper that described a way of creating finer lines on chips, says this work builds on that earlier method. But unlike the earlier technique, called absorbance modulation, this one allows the production of complex shapes rather than just lines, and can be carried out using less expensive light sources and conventional chip-manufacturing equipment. "The whole optical setup is on a par with what's out there" in chip-making plants, she says. "We've demonstrated a way to make everything cheaper."

As in the earlier work, this new system relies on a combination of approaches: namely, interference patterns between two light sources and a photochromic material that changes color when illuminated by a beam of light. But, Andrew says, a new step is the addition of photoresist. In addition to one-eight-wave isolated lines, the technique allows spacing between features to be as narrow as one-quarter wave (153 nm).

In addition to enabling the manufacture of chips with finer features, the technique could also be used in other advanced technologies, such as the production of photonic devices. "It can be used for any process that uses optical lithography," Andrew says.

Source: http://web.mit.edu/newsoffice/2011/update-optical-nanopatterns-1214.html


REFERENCE:

1. Nicole Brimhali et al., Physical Review Letters, 107, p. 205501 (2011).