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193 nm Immersion Lithography Rated Suitable for Fab Evaluation, Participants at International SEMATECH Conference Told

Los Angeles, CA (27 January 2004) – Immersion lithography appears to have resolved the original technical issues identified just over a year ago, and looks ready to be evaluated for volume manufacturing, industry professionals learned here today during the Third Immersion Workshop sponsored by International SEMATECH (ISMT).

With fresh results on resists, materials, and fluids on hand and additional data still coming in as the conference began, more than 250 semiconductor industry professionals appeared to have many of their concerns addressed on whether immersion can be adapted effectively to existing 193 nm lithography.

“We have seen a tremendous amount of progress here today,” said Walt Trybula, ISMT Senior Fellow and workshop organizer as the meeting wrapped up. “We have gone from the science phase to the engineering and testing phase. And although we now have a lot of knowns, we still have to migrate them into manufacturing.”

Tuesday’s workshop (at the Hyatt Regency at Macy’s Plaza) was the third in a pioneering series of meetings that ISMT sponsored at the industry’s request, beginning in December 2002 and continuing last July. This most recent session included multiple presentations from academic and industry researchers who described the previous six months of advances in fluids, materials and resists. Additionally, key suppliers revealed their progress in developing 193 nm immersion tools, and provided their plans for delivering production tools.

During their presentations, the industry’s top three litho tool suppliers – ASML, Canon, and Nikon – all said they are designing and planning to ship commercial lithography tools between late 2004 and 2006. ASML and Nikon both said they will develop 193 nm immersion systems at 0.85 numerical aperture (NA) by the third quarter of this year, while Canon said it plans to build a 193 nm tool with NA greater than 1.0 by early 2006.

In immersion lithography, a liquid is interposed between an exposure tool’s projection lens and the wafer. Immersion technology offers the opportunity for better resolution over conventional projection lithography because the lens can be designed with NAs greater than one, thus creating the ability to produce smaller features.

As in last July’s workshop, groups of researchers focusing on resists, fluids, and materials provided detailed presentations on their most recent findings. Speaking for the resist scientists on Tuesday, Will Conley of ISMT said his group had come from a point where “we didn’t know anything” to being able to rule out the effects of water on resist as a serious barrier to immersion.

Several speakers declared that test resists supplied by Japanese manufacturer TOK were almost unaffected by exposure to water for short times. University of Texas researcher Robert J. LeSuer reported that the TOK resists showed “very small amounts of leaching” in 30 seconds or less, and almost no leaching at all after a half-minute. (Clariant and Shipley resists also showed good performance.)

Similarly, Alex Raub of the University of New Mexico found that immersing resists for as long as 10 minutes did not degrade their ability to produce sharp, production-worthy images. “Even after soaking a wafer for 10 minutes, I can still measure images at 65 nm half-pitch lines,” he said. Raub said his work with high-performance liquid chromatography (HPLC) showed “no problem imaging into resist on immersion.”

Meanwhile, Bruce Smith of the Rochester Institute of Technology (RIT) elaborated on his organization’s recently announced development of a 193 nm immersion microstepper. With the new system able to etch 100 nm linewidths, Smith said he is confident of reaching even smaller dimensions, especially if the liquid can be successfully doped to increase its refractive index from approximately 1.45.

Experiments with cesium sulfate, which mixes readily with water, can produce a liquid with a refraction index of 1.6, according to Smith. Combined with a high NA of 1.05, such a property could allow an immersion-based linewidth as small as 30 nm, Smith noted.

Other observations emerging from the workshop included:

  • Ultrapure water (UPW) for immersion cannot be stored for long periods, or it will leach chemicals from its container and become unusable. “You really want to make your water at the point of use,” said Mike Switkes of the MIT Lincoln Laboratories.
  • Degassing water appears to be a solid solution to the formerly worrisome issue of nanobubbles. “If you degas the water, you get a very smooth surface,” said Switkes. “I think that for lithography, the problem is solved.”
  • The next optical wavelength, 157 nm, could be made extensible to 32 nm linewidths by applying to it the lessons gained from 193 nm immersion, asserted Mordy Rothschild of MIT Lincoln Labs. Development of a new immersion liquid with a refractive index greater than water could drive these features even lower, he added.
  • ISMT is planning a 157 nm and Immersion Symposium in August that will cover remaining immersion issues and options for 157 technology, Trybula said.

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