EUVL workshop touts progress in scanners, sources, mask defects

June 29, 2010 – Touting extreme ultraviolet (EUV) lithography as the industry’s best bet to extend Moore’s Law below the 2Xnm generation, experts gathered at the 2010 International Workshop on EUV Lithography (June 21-25 in Hawaii) described "steady progress" in source power, resist performance, mask defect reduction, and other major EUVL challenges.

"Although scanner throughput needs improvement, the remaining specs for beta scanners are expected to be met," said Vivek Bakshi, organizing chair of the workshop and president of EUV Litho Inc. 40W sources are expected this year, and 60W next year, offering enough throughput in beta scanners to support development of processes for high-volume manufacturing (but far short of the ≥200W expected for actual HVM).

Jos Benschop, VP of research at ASML, noted the company is exploring the possibility of multiple suppliers, and both laser-produced plasma (LPP) and discharge-produced plasma (DPP) technologies, for EUV sources to go into beta tools. He cited EUV’s advantages over competing litho technologies — lower manufacturing costs, increased fab capacity, and extensibility to <5nm resolutions — as "the best balance between cost, shrink and absence of design restrictions [...] It is the only cost-effective way to extend Moore’s Law." Areas targeted for further work include source power, mask improvements (pellicles, defect mitigation, flatness), and more precise targets for line-edge roughness (LER).

Source development dominated the meetings. Gigaphoton expanded on its recent announcement of 104W source power (at intermediate focus). Komatsu described methods of improving a CO2 laser system, where tests have verified a 21.2kW beam (M2 of 1.5) from simulation, which can also achieve 20kW operation at a 100% duty cycle.

Other papers talked about sub-13.5nm source wavelengths. EUV sources using LPP-produced terbium and gadolinium plasmas can get down to 6.5-6.7nm wavelengths, reported Padraig Dunne of University College Dublin, but low multilayer reflectivity and higher power density requirements could make 8.8nm a better choice.

Another big area of discussion was EUV mask defects and metrology for measuring them. Invited speaker Kenneth A. Goldberg of Lawrence Berkeley National Labs noted that because EUV penetrates deeply into ML pairs, it is important to mitigate buried defects in ML-based EUV masks. Current defect detection capability (30nm) needs to improve by 13×, he said. Still, solutions for ≤22nm mask defect inspection can be found with 13.5nm-wavelength actinic inspection technology, the same as is used in printing circuits.

Other presentations at the event:

  • Toshiyuki Uno, Asahi Glass, reported 0.05cm2 mask blank defect density at sphere equivalent volume diameter of 54nm, and 0.12cm2 at 34nm SEVD. Flatness of 38nm (frontside)/48nm (backside) has been achieved, with a new Ru-based film as the capping layer offering better chemical and thermal durability than current Ru films.
  • Selete’s Iwao Nishiyama described Japan’s contributions to EUV development, and current status of domestic work in source, mask, resist, and optics.
  • Chris Mack, longtime litho consultant (and "gentleman scientist") Chris Mack pointed at reducing LER as "the ultimate limiter" for not only EUV but also 193nm immersion lithography. Current LER models lack several key elements, he said, including EUV resist exposure mechanism, base quencher, and development rate uncertainty.
  • Experimental results on defect printability show critical dimension of a phase defect is <100nm2, reported Hiroo Kinoshita, University of Hyogo (Japan).
  • Sergey Zakharov of NANO-UV and Debbie Gustafson of Energetiq described development of high-brightness EUV light sources for actinic mask defect metrology.

Also at the EUV workshop, Obert Wood of GlobalFoundries was honored with a Lifetime Achievement Award for his work in pioneering EUVL research, including a 33-year career at Bell Labs. And ASML was recognized with an Outstanding Contribution Award for significant technical achievements in developing EUV scanners.

A related meeting of the EUV Source Technical Working Group (TWG) is planned for mid-November in Ireland, focusing on ≤13.5nm wavelengths for next-generation EUV sources, as well as technology for high-brightness metrology sources at 13.5nm. Contact Vivek Bakshi or Padraig Dunne for information about submitting paper abstracts.

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