Highest conversion efficiency demonstrated for EUV energy
Oyama, Japan -- Gigaphoton Inc., a major lithography light source manufacturer, says its latest results for extreme ultraviolet (EUV) lithography show a maximum of 5.2% conversion efficiency (CE), with an average of 4.7%. The industry target is 5.0% CE required for the first-generation production EUV scanner.
"This confirms our R&D path to manufacture a mass-production LPP source that ensures stable operation at higher output and lower running cost," stated Hitoshi Tomaru, president of Gigaphoton. "I believe this will further increase momentum for device manufacturers to introduce EUV lithography tools as the next-generation lithography technology."
The company's laser-produced plasma (LPP) EUV light source utilizes a tin (Sn) plasma material as the source with a proprietary pre-pulse laser technique. The LPP light source releases optimum EUV energy from the plasma by first irradiating a droplet of Sn with a short-wavelength, solid state laser as a pre-pulse, then irradiating the enlarged droplet with the main-pulse CO2 laser. This maximum CE of 5.2% was achieved with 150 mJ CO2 laser energy, equivalent to 175 W EUV output at 100 kHz CO2 laser frequency.
The anticipated production ramp-up for EUV lithography among semiconductor manufacturers is around 2014-2015, but its adoption has been delayed several times already. Gigaphoton has been working on the development of laser-produced plasma (LPP) light sources for EUV lithography since 2002. (Originally a JV between Komatsu and Ushio, Gigaphoton was handed off to Komatsu in April 2011 while Ushio pursues its own discharge-produced plasma [DPP] light source technology.) Among its contributions are on-demand supply of Sn target droplets of <20 μm diameter, an optimum combination of the short-wavelength solid state laser pre-pulse and the main CO2 laser pulse, as well as debris mitigation and removal using magnetic fields to protect the collector mirror.
One of the persistent problems with EUV lithography has been creating and maintaining sufficient source power to support the semiconductor manufacturing industry's needs for volume production: roughly >200 W of source power, translating to throughput of ~100 wafers/hour. Earlier this year Gigaphoton topped 7 W of EUV power with its LPP technology; competitor Cymer has its own EUV source technology touting 20 W output qualified in the field now, anticipating 50 W later this year and 100 W in early 2013.
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