MIT patterning method could aid scaling
Most techniques reliant on light for patterning cannot produce patterns much smaller than the wavelengths of light themselves. According to MIT, its method makes it possible to create lines that are only about one-tenth as wide as the wavelength of light used to create them.
By Suzanne Deffree, Managing Editor, News -- EDN, April 13, 2009
Researchers at MIT are claiming a method for patterning extremely narrow lines on a microchip, one that has produced lines just 36-nm wide.
The method uses a material that can be switched from transparent to opaque, and vice versa, by exposing it to certain wavelengths of light. MIT admitted that such materials are not new, but claimed that its researchers found a way of harnessing that property to create a mask with exceptionally fine lines of transparency and that that mask can then be used to create a correspondingly fine line on the underlying material.
As described by MIT, the key to the method is using interference patterns, in which different wavelengths of light sometimes reinforce each other and in other places cancel each other out. The researchers exposed the photochromic material -- one that changes its color, and therefore its transparency, in response to light -- to a pair of such patterns, each of a different wavelength, simultaneously, according to MIT.
"When the bright lines at one wavelength coincide with the dark lines at the other wavelength, extremely narrow lines of clear material are formed interspersed with the opaque material. This banded layer then serves as a mask through which the first wavelength illuminates a layer of material underneath, similarly to the way a photographic negative is used to make a print by shining light through it onto a sheet of photo paper underneath," MIT described in a statement.
The researchers call the method "absorbance modulation" and claim it makes it possible to create lines that are only about one-tenth as wide as the wavelength of light used to create them. The researchers also claimed they could place many such lines spaced a similar distance apart.
The research was carried out by MIT Research Engineer Rajesh Menon of the Research Laboratory of Electronics and graduate students Trisha Andrew in the Department of Chemistry and Hsin-Yu Tsai in the Department of Electrical Engineering and Computer Science, and was reported in a paper published in the April 10 issue of Science.
Such a technique "could have a significant impact on chip making," Menon said in a statement, and could also help to enable new work in a variety of emerging fields that rely on nano-scale patterning, including nanophotonics, nanofluidics, nanoelectronics, and nano-biological systems.
Menon said he expects the work to lead to commercial production within five years.
The MIT team is also pursuing possible use of the research for imaging systems, with possible applications in biology and in materials science.
MIT further said its researchers are looking for ways of using the technique to create even smaller patterns, down to the scale of individual molecules.
The work was partly funded by grants from LumArray Inc, where Menon is co-founder, the MIT Deshpande Center for Technological Innovation, and DARPA.
