We report the development progress of key technologies for the Sn-LPP (Laser-produced-plasma) EUV light source system at Gigaphoton Inc. EUV light source systems have come to be used for a wide range of applications such as lithography exposure tools and inspection tools. In both applications, high power and high radiance together with high operation availability are required. To meet these requirements, we developed and optimized a long lifetime droplet generator, a pre-pulse irradiation scheme, laser-droplet shooting control and debris mitigation with hydrogen gas for lifetime extension of the EUV collector mirror. To achieve high operation availability, the collector mirror and the Sn droplet generator lifetime are the most important contributions. The collector mirror lifetime is mainly determined by the reflectivity degradation due to sputtering, implantation, and deposition by Sn ions, Sn atoms, Sn fragments, and hydrogen-induced blisters. The developed droplet generator with in-line Sn fuel feed system has demonstrated stable droplet generation for more than 1,300 hours in our EUV light source. An advanced pre-pulse technology achieved higher CE without increasing the energy of the Sn plasma. Our Sn mitigation scheme works efficiently for lower energy ions and lower fragment deposition rates. Our optimized in-situ shooting control system improved the EUV energy and dose error. With these technologies, we have demonstrated no reflectivity degradation (i.e. no fragment deposition) on EUV sample mirrors after 25 Billion pulse irradiation tests. The advanced capping layer has demonstrated to suppress blister formation.
The extreme ultraviolet (EUV) light source has been developed together with the lithography EUV scanner. As tool with a 10 W EUV light source, ASML shipped the “a-demo tool” in 20071) and Nikon shipped EUV-1 in 20082). Then ASML developed the b-tool, NXE-3100, at the beginning of 2011 with a 100 W EUV light source.3)4) Requirement of the EUV exposure tool is now covered by the g-tool; NXE3300 (for high volume manufacturing (HVM))5). The required EUV power is 250 W clean power (after purifying infrared (IR) and deep ultra violet (DUV) spectra) at intermediate focus (IF). However, the demonstrated power level was around 80 W6)7) in 2013.
Gigaphoton develops CO2-Sn-LPP EUV light source which is the most promising solution as the 13.5nm high power light source for HVM EUVL. Unique and original technologies including; combination of pulsed CO2 laser and Sn droplets, dual wavelength laser pulses for shooting and debris mitigation by magnetic field have been applied. We have developed first practical source for HVM; “GL200E” 1) in 2014. Then it is demonstrated which high average power CO2 laser more than 20kW at output power in cooperation with Mitsubishi Electric2). Pilot#1 is up running and it demonstrates HVM capability; EUV power recorded at 111W on average (117W in burst stabilized, 95% duty) with 5% conversion efficiency for 22 hour operation in October 20163). Availability is achievable at 89% (2 weeks average), also superior magnetic mitigation has demonstrated promising mirror degradation rate (= 0.5%/Gp) at 100W or higher power operation with dummy mirror test. We have demonstrated >300W operation data (short-term) and actual collector mirror reflectivity degradation rate is less than 0.15%/Gp by using real collector mirror around 125W (at I/F clean) in burst power > 10 Billion pulses operation4). Also we will update latest challenges for >250W average long-term operation with collector mirror at the conference.
REFERENCE
1) Hakaru Mizoguchi, et. al.: “Sub-hundred Watt operation demonstration of HVM LPP-EUV source”, Proc. SPIE 9048, (2014)
2) Yoichi Tanino et.al.:” A Driver CO2 Laser Using Transverse-flow CO2 Laser Amplifiers”, EUV Symposium 2013, ( Oct.6-10.2013, Toyama)
3) Hakaru Mizoguchi, et al: ” High Power HVM LPP-EUV Source with Long Collector Mirror Lifetime”, EUVL Workshop 2017, (Berkley, 12-15, June, 2017)
4) Hakaru Mizoguchi et al.:” Challenge of >300W high power LPP-EUV source with long collector mirror lifetime for semiconductor HVM”, Proc. SPIE 11323, Extreme Ultraviolet (EUV) Lithography XI (2019) [11323-28]
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