Aachen EUV winner
The crux of EUV lithography is to have an efficient and economic EUV source available, says Klaus Bergmann of the Fraunhofer Institute for Laser Technology (ILT). EUV radiation can be produced in extremely hot plasma in two different ways: by gas discharge or by laser induction. The researchers at the Aachen-based institute proposed a hollow-cathode gas discharge method.
The foundations for the patented concept were laid at the ILT and the department of laser technology in the period from 1997 to 2000. An international comparison revealed that the Aachen lamp was superior to the solutions proposed in the US. However, it needed strong partners in industry to enable it to compete effectively.
In 2000, Rainer Lebert, who at that time was employed by Fraunhofer ILT, span off a new company, AIXUV. The company manufactures and sells compact, reliable EUV sources for basic investigations in laboratories, and follow-up systems for EUV measurement engineering and quality assurance.
"We supplied Infineon with an EUV photoresist exposure device capable of producing structures at 50nm. And then for Schott, we developed an reflectometer for mask qualification," reports Lebert.
The researchers took a further important step towards industrial-scale production in 2001 with the foundation of Philips Extreme UV, a joint venture of the Fraunhofer-Gesellschaft and Philips. The companyÕs mission is to develop EUV sources for series production of semiconductors. Its first step was to sign a contract with ASML, the leading manufacturer of lithographic equipment in the Netherlands, for the delivery of four prototypes.
Joseph Pankert, CEO of Philips Extreme UV, comments: "The great advantage of our concept is that it is the cheapest, the simplest and the most compact. We plan to deliver the next prototype of a high performance EUV source to ASML next year."
The EUV source must produce EUV light with a power output of at least 100W. Researchers working for Philips Extreme UV have meanwhile succeeded in improving the world record to about 30W. Cost-effective chip production calls for the exposure of about 120 wafers per hour. The plasma must not exceed 1mm in size, and must reach a temperature of 220,000degreesC. Such extreme temperatures can only be controlled in short high-energy pulses so as not to destroy the materials the light source is made from.
Intel plans to use EUV in mass-producing chips from 2009 onwards. EUV lithography uses radiation with a wavelength of only 13.5nm. However, EUV radiation is strongly absorbed by all materials including air, meaning that the entire lithography process has to be performed in a vacuum. Conventional optical systems cannot focus light of such short wavelengths, so multi-layer mirrors have to be used instead. Semiconductor manufacturers thus face a multitude of unsolved technical problems and a gigantic investment risk.
