Evanescent wave litho to surface at SPIE
SAN JOSE, Calif. Is a technology called evanescent wave lithography (EWL) the next big thing in semiconductor manufacturing?
For years, researchers at the California Institute of Technology, the University of California at Berkeley and other universities have been exploring EWL. Some know this near-field technology as "contact lithography."
In this approach, which is still in the R&D stage but talked about for some time, an evanescent optical field is set up directly below a contact mask, enabling sub-micron resolutions, according to researchers.
At the upcoming SPIE Microlithography conference here, which is slated from Feb. 19-24, the Rochester Institute of Technology (RIT) is expected to present a paper that claims it has produced a 26-nm image based on EWL. This, in turn, opens EWL as an extension to conventional projection lithography as a means for sub-32-nm chip production, according to RIT.
“This is very different from the evanescent wave imaging, also called near-field or contact imaging, at Berkeley and others,” said Bruce Smith, RIT’s professor of microelectronic engineering and director of the Center for Nanolithography Research in the Kate Gleason College of Engineering.
“We do not place a mask in contact with an image plane, which would be difficult to implement into manufacturing. Our evanescent wave lithography (EWL vs. evanescent wave imaging) is a more logical extension to optical lithography," Smith said.
"We are using projection imaging to direct images
from the bottom element of the optical system through media with refractive indices lower than the numerical aperture of the imaging system,” he said. “We have been able to achieve numerical apertures up to 1.85 NA,
well beyond the refractive index of any immersion fluid or photoresist currently available for 193-nm exposure."
The technology has potential in the future . "Immersion lithography has pushed the limits of optical imaging," he added. "Evanescent wave lithography continues to extend this reach well into the future.”
Immersion lithography is limited by Snell's Law to numerical apertures (NA) less than the lowest refractive index material in a lithography imaging system. Currently, with fused silica optics, high-index immersion fluids, and ArF photoresists, the largest theorectical numerical aperture is about 1.65.