Litho for 32-nm remains a question mark

SAN JOSE, Calif. — Despite the breakthroughs in semiconductor manufacturing, lithography still remains a huge question mark for chip production at the 32-nm node in 2009, warned an expert at Belgian research organization IMEC.

Speaking at the SPIE Microlithography conference here on Monday (Feb. 20), Kurt Ronse, director of the lithography department at IMEC, indicated that there is still little or no industry consensus about which lithography technology will work for the 32-nm node.

At present, there are several viable lithography candidates for the 32-nm node: extreme ultraviolet (EUV), 193-nm immersion and double-exposure techniques, Ronse said.

The technologist surprised the audience at SPIE when he noted that 193-nm immersion with double-exposure techniques represents the “lowest risk to the 32-nm half-pitch node.”

IMEC believes the industry could move towards low k₁ imaging with a 193-nm immersion tool with a numerical aperture (NA) of 1.35-to-1.40. In the lab, IMEC claims to have printed 40-nm lines and spaces with a 193-nm immersion tool with a low k₁ factor of 0.19.

The problem with double-exposure is cost. In double-exposure, chip makers must use two masks, make two exposures, among other steps, thereby reducing cycle times and increasing costs, he said.

Another possibility is 193-nm immersion without double-exposure techniques. At present, 193-nm immersion, with water at a refractive index of 1.35, could enable half-pitch images from 38-to-40 nm.

The industry is exploring second- and third-generation liquids with refractive indices of 1.65 and 1.8, which, in theory, could enable 32-nm half-pitch images, according to IMEC.

However, these liquids remain in the experimental stage. “A lot of work needs to be done,” according to the Ronse.

EUV’s problems are well documented. The biggest problem with EUV is resist resolution, sensitivity and line-edge roughness, he said.

At present, there are no adequate power sources for EUV. The shelve life of a condenser for an EUV tool is about a month right now. Many had hoped to see shelf lives of about four years by now.

Even the biggest proponent of EUV is having some issues with the technology. Unable to obtain the tools and materials in time, Intel Corp. has apparently pushed out its efforts to bring EUV lithography into “high-volume production” for the 32-nm node by 2009. Instead, the company said that it plans to extend 193-nm lithography for mass production at 32-nm.