26-05-2012, 01:37 PM
Extreme Ultraviolet Lithography Imaging the Future
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Creating a Virtual Laboratory
Two years ago, three Department
of Energy national laboratoriesÑ
Lawrence Livermore, Lawrence
Berkeley, and Sandia/CaliforniaÑ
formed the Virtual National Laboratory
(VNL) to research and develop extreme
ultraviolet lithography (EUVL)
technology. The VNL is funded by the
Extreme Ultraviolet Limited Liability
CompanyÑa consortium of Intel
Corporation, Motorola Corporation,
Advanced Micro Devices Corporation,
and Micron Technology, IncorporatedÑ
in one of the largest cooperative research
and development agreements within
the Department of Energy. The threeyear,
$250-million venture is dedicated
to developing the EUVL technology
for commercial manufacturing of
computer chips and to move this
technology into production facilities
in the first decade of the 21st century.
Brighter Light Is Key
The ETS (see the box on p. 7)
includes a condenser optics box and
a projection optics box. Both boxes
house complex optical trains of
precision concave and convex
aspherical mirrors.
The main role of the condenser
optics box is to bring light to the
reflective pattern on the mask. ÒWe
want to bring as much light to the mask
and, ultimately, the wafer, as possible,Ó
explains Sweeney. ÒThe more light we
deliver, the shorter the exposure time.
ItÕs like taking a picture with a camera.
A picture taken in bright noonday sun
requires a shorter exposure time than
does a picture of the same scene taken
at twilight.
Applying Uniform Thin Films
Part of the success of the EUVL
technology is due to the immense strides
Lawrence Livermore has made in
producing the highly reflective
multilayers that are used on the ETSÕs
optical mirrors as well as on the mask.
The projection and condenser
optical systems require mirrors that
reflect as much EUV light as possible.
Manufacturing these mirrors has been
a challenge because, in addition to
being highly reflective, they must have
surface coatings that are essentially
perfectly uniform.
Measuring at the Atomic Level
Until recently, it was impossible to
accurately measure a mirror surface
for high and low spots of a few atoms.
An R&D 100 AwardÐwinning
interferometer developed at the
Laboratory two years agoÑcalled the
phase-shifting diffraction interferometer
(PSDI)Ñchanged all that. (See S&TR,
October 1997, p. 6.)
Like all interferometers, the PSDI
uses the interference pattern of two
waves of light to measure objects or
phenomena.