LONDON — Sources for extreme ultraviolet lithography are not yet sufficiently
bright to allow commercial wafer throughputs, but they are improving
sufficiently for beta tools shipping in 2011, according to participants at a
workshop held in Maui, Hawaii.
"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. (Austin, Texas). "Based on the present
data, it appears that 40-watt sources will be available this year and 60-watt
next year for integration in the beta scanners. These sources should provide
sufficient throughput for beta scanners to allow chip-makers to develop
processes for high volume manufacturing.
During the workshop ASML (Veldhoven, The Netherlands) announced it has
received six orders for its NXE:3100 beta scanner, and plans to ship the first
tool this year and the others in 2011. The first tool is expected to go to the
IMEC research institute (see EUV litho keeps progressing, keeps slipping).
Jos Benschop, vice president of research at ASML, said his company is looking
at multiple suppliers of both laser produced plasma (LPP) and discharge produced
plasma (DPP) technologies for EUV sources for beta scanners. "EUV offers the
best balance between cost, shrink and absence of design restrictions," said
Benschop, in a statement issued by EUV Litho.
The attendees at the workshop also looked at other technical areas that
require effort to prepare EUVL for high volume manufacturing. Obert Wood of
GlobalFoundries Inc. (Sunnyvale, Calif.) listed these as mask pellicles, mask
defect mitigation, mask flatness, and more precise targets for acceptable
However, discussion on EUVL sources dominated the meeting including details from
supplier Gigaphoton of a source offering 104-watt power at intermediate focus.
The company said it expects to increase source lifetime through improved
thermal-load handling. The source currently offers 2.5 percent conversion
efficiency, 7.9-kW CO2 laser operation, 20 percent duty cycle, 1.04 millijoules
pulse energy at IF with a 100-kHz operation frequency.
Next-generation EUV sources are expected to have wavelengths shorter than the
current 13.5-nm, according to several papers presented at the workshop.
Padraig Dunne of University College Dublin (UCD) spoke of LPP-produced
terbium and gadolinium plasmas as EUVL sources with wavelengths of between
6.5-nm and 6.7-nm. If multilayer reflectivity at these wavelengths is low and
higher power density is needed to produce the plasma at these wavelengths,
another wavelength such as 8.8-nm may be a better choice, Dunne noted.
Invited speaker Kenneth A. Goldberg of Lawrence Berkeley National Laboratory
(LBNL) reviewed research work on the mask defect inspection at various labs
around the world.
Goldberg said the EUV wavelength penetrates deep into mask layers and for
that reason is important to mitigate buried defects in multilayer EUV masks. He
also noted that the current defect density at 30-nm needs to improve by a factor
of 13. Longtime lithography consultant Chris Mack described the challenges of
reducing LER, which he called "the ultimate limiter for EUV and 193i based