Many believe that 193-nm immersion could hit the wall at 45-nm, due in part to limitations with the refractive index of water or related fluids. But RIT claims to have devised 31-nm images with 193-nm immersion, thereby demonstrating that conventional optical technologies can be extended for several generations. It also implies that the technology could push out the need for extreme ultraviolet (EUV) lithography, which is targeted for the 32-nm node in 2009, according to analysts.

In immersion lithography, the space between the projection lens and the wafer is filled with a liquid. Immersion technology could offer better resolution enhancement and higher numerical apertures (NA) over conventional projection lithography.

"We will be presenting what we believe will be the smallest imaging resolution using immersion lithography at 193-nm at the SPIE conference," said Bruce Smith, associate dean of the College of Engineering and the Intel Professor of Microelectronic Engineering at RIT (Rochester, N.Y.).

"We have imaged 31-nm lines/spaces in photoresists using a hydrogen phosphate immersion fluid and a numerical aperture (NA) of 1.54," Smith said. "This is truly at the limits of optical lithography using fused silica (quartz) optics. The refractive index of quartz is 1.56 and we are at the most extreme imaging angle possible."

RIT's efforts represent another big step for the technology. Last year, it showed patterns with 38-nm lines and spaces via 193-nm immersion (see Jan. 23, 2004 story).

Fabian Pease, a professor at Stanford University, will present RIT's new images at his keynote address on Monday (Feb. 28). In addition, ASML Holding NV and Nikon Corp. will present their respective findings for 193-nm immersion (see Feb. 27 story).

Meanwhile, RIT is attempting push the technology down even further. "We are now working toward 28-nm imaging using sapphire optics, which has a refractive index near 1.93," Smith said. "Though we have achieved modulation at this dimension, we are still looking for a photoresist to allow us to capture these images. Using a combination of high index immersion fluids and sapphire optics, we feel that 25-nm resolution can be achieved at a 193-nm ArF excimer laser wavelength."

During the SPIE Microlithography conference, RIT is also expected to present a paper on solid immersion lithography for 25-nm designs and beyond (see Feb. 27 story).