RIT to describe solid immersion for 25-nm lithography

SAN JOSE, Calif. — During the SPIE Microlithography conference here this week, the Rochester Institute of Technology (RIT) is expected to present a paper on solid immersion lithography for 25-nm designs and beyond.

Unlike "wet" immersion, solid immersion does not use water as a means to boost the resolution in a lithography tool. Instead, the technology, which is still in the R&D stage, appears to be more related to novel and exotic approaches like atomic force microscopy (AFM) and dip-pen lithography.

Researchers from the University of Arizona last year described this "maskless lithography" concept, which employs an array of solid immersion lens nano-probes (see Sept. 14, 2004 story).

RIT (Rochester, N.Y.) takes another approach to push the limits of immersion. For 193-nm "wet" immersion, the fluid is the limiting factor with a refractive index of 1.45, according to RIT. With solid immersion, RIT believes that 28-nm circuits can be patterned for a resist index of 1.75 and 25-nm designs with an index of 1.95.

By using a cylindrical aluminum oxide or sapphire element, RIT claims it can increase the refractive index to 2.1. The solid immersion lithography "system is based on two-beam Talbot interference of a phase grating mask, illuminated with highly polarized 193-nm ArF radiation," according to RIT.

"The two diffracted beams are directed toward an Al203 cylindrical lens and stepped along the length of the lens to produce periodic features with k₁ values ranging between 1.0 and 0.25."