Tokyo A consortium of nine Japanese companies working on extreme-ultraviolet (EUV) lithography says it is making steady progress toward a spring 2006 target for fielding an alpha tool that would provide 10 watts of EUV output power. The effort seeks to bring Japan's effort in line with EUV progress made abroad.
The Extreme Ultraviolet Lithography System Development Association (EUVA) is supporting two parallel movements to develop a source of 13.5-nm wavelength EUV radiation. Commercial EUV scanners will require 110 W or more of EUV power for high-throughput systems. The current EUVA source generates only 0.6 W, although it has a frequency of 10 kHz, the highest reported to date.
Based on EUVA's work, commercial vendors expect to develop beta tools in 2007 and production systems by the end of 2009, according to the EUVA road map.
Established in June 2002, the EUVA ( www.euva.or.jp) was set up under the auspices of Japan's Ministry of Economy, Trade and Industry (METI). The association includes lithography manufacturers Canon Inc. and Nikon Corp.; light source manufacturers Komatsu Ltd., Ushio Inc. and Gigaphoton Inc.; and device manufacturers Fujitsu Ltd., NEC Electronics Corp., Renesas Technology Corp. and Toshiba Corp. (Hitachi Ltd. and Mitsubishi Electric Corp. were each EUVA members before they founded Renesas in April 2003.)
Challenges at the source
EUV lithography requires reflective optics, employing a series of mirrors with some 40 precisely deposited layers of silicon and molybdenum, rather than the refractive lenses used in today's scanners. Developing a source of EUV radiation is particularly challenging, with the associated task of ensuring that debris from the source does not contaminate the optics.
Japan has capabilities in "all segments of semiconductor production," from materials and equipment to light sources and device fabrication, said Masashi Ogawa, EUVA's executive director. "Taking advantage of those resources, we believe that our EUV R&D work will catch up and take the lead in overall performance and cost, though we came late."
EUVA began source development work last year at corporate labs operated by Ushio and Komatsu. The association set up work on exposure tools and metrology at Canon and Nikon in April 2003.
EUVA is pursuing parallel development efforts for the EUV radiation source: a laser-produced plasma (LPP) method, which is being pursued at Komatsu's Hiratsuka R&D center, and a discharge-produced plasma (DPP) method, which is being worked on at Ushio's Gotenba lab.
The LPP method uses lasers to bombard a target, while the DPP approach employs a cathode-anode system.
The two groups are competing to reach a goal of 4 W of output power at the intermediate focus of the reflective optical system by March 2004. The Hiratsuka lab recently reported that it has generated plasma using xenon gas and a pulsed laser at a 10-kHz repetition rate with a pulse width of 30 nm. The lab is now changing to a laser with a pulse width of 7 nm. The engineers are predicting that the reduction in pulse width will raise the EUV power fourfold. To achieve the targeted 4 W at the intermediate focus, the engineers are working to achieve 13.8-W EUV power at emission.
Meanwhile, the Gotenba team working on the DPP method reported 6.3 W of EUV output power at a 2-kHz frequency. The engineers working on the DPP source estimate that 28 W is necessary at EUV emission to achieve 4 W of EUV output power at the intermediate focus. "It is not necessarily true that a higher repetition rate [with the DPP method] is better. We think 5 to 6 kHz is optimum," said Hiroto Sato, lead researcher of the EUVA Gotenba branch.
By improving the EUV conversion efficiency, which is now a scant 0.1 percent, to a more respectable 0.5 percent, and by increasing the repetition rate to 6 kHz, the team expects to achieve 28 W at emission and 4 W at the intermediate focus by next spring.
"We are at the level of just having succeeded in generating EUV light. But our final target is 100 W, the level required for production systems. We think we'll be able to catch up to competitors that are now ahead of us," said Sato.
Other companies and research organizations have reported better performance of their prototype light sources. Cymer Inc. (San Diego) has reported an efficiency of 0.5 percent and a repetition frequency of 4 kHz to get nearly 60 W of usable power. Xtreme Technologies GmbH (Gottingen, Germany) achieved about 0.55 percent efficiency and a repetition rate of 6 kHz, but with usable power of roughly 45 W.
EUVA intends to review progress by its two teams next March and may select one method to boost the source of EUV radiation to 10 W.
The National Institute of Advanced Industrial Science and Technology (AIST), a public research organization operating under METI, is also working on the source challenge apart from the EUVA effort. AIST is experimenting with tin (Sn) as the target material, and the researchers claim to have developed a method for controlling the debris generated when tin is used.
Controlling debris is essential to keeping the cost of ownership for EUV systems within the budgets of semiconductor makers. The collector is particularly vulnerable to debris, and the set of mirrors in the collector must be kept free from carbon and other contaminants in order to reflect EUV radiation precisely.
The peak wavelength of Sn plasma is near the 13.5 nm required for EUV lithography, and AIST researchers believe that Sn-based plasma has a much better spectral efficiency than xenon gas-based plasma, which has a peak wavelength of approximately 11 nm. The AIST team hopes to realize 5 percent efficiency this year using tin as the target material.
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