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IMEC favors EUV litho for 22nm node

Posted: 23 Oct 2008 ?? ?Print Version ?Bookmark and Share

Keywords:EUV lithography? 22nm? wafer?

Kurt Ronse, director of the advanced lithography program, IMEC, has favored extreme UV lithography (EUVL) as most likely how the semiconductor industry will make ICs with minimum geometries of 22nm and finer.

This is despite that wafers' throughput on prototype machines is still running at about 2.5 wafers per hour and needs to be up close to or beyond 100 wafers per hour to be comparable with optical lithography.

Speaking to the press before the IMEC Annual Research Review Meeting held at Leuven, Beglium, Ronse said neither of the two options to extend immersion optical lithography seemed likely to make good progress.

"The first option to raise the refractive index of the immersion medium beyond that of water was unlikely to happen because the development of glass material and third-generation liquid could not be done in time to stay with the International Technology Roadmap for Semiconductors timeline," Ronse said. The second option to increase the k1 factor also looked technically difficult. "To get to 22nm half-pitch with 1.35 NA double patterning needs an extremely aggressive k1 (k1=0.15) and will be very expensive," he added. "Wavelength scaling is the most likely." he noted, indicating the move to EUV.

As a result, even though IMEC has been a pioneer of immersion lithography using the XT:1900i stepper from ASML Holdings NV, much of the effort is now going into EUVL. IMEC expects to receive a pre-production EUVL tool early in 2010. The institute got its EUVL alpha tool from ASML in August 2006 and has been working on the tool development. "First light" was achieved in April 2007 and first images in September 2007 before the machine finally reached site acceptance in June 2008.

Since then a great deal of work has been made on the machine by IMEC and its core partners such as Intel Corp. and Samsung. The production of 32nm SRAM circuits represented the highest achievement so far.

Ronse said the major challenges facing EUVL have changed in recent months. The problems remain in source, masks, optics and resist, but he added that there has been clear progress in resist performance over the last six months using the alpha development tool. Several resists can be used down to 32nm half-pitch and an ultimate resolution of 28nm half-pitch has been taken.

However, the first issue remains on the need to have a reliable high-power source. With the progress in resists, they have slid to the third-ranked challenges and have been eclipsed by defect-free masks. "The optics, which must now be all reflective and their degradation, is the fourth-ranked concern," Ronse said.

- Peter Clarke
EE Times Europe

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