NY (14 February 2006) -SEMATECH North researchers
working on extreme ultraviolet lithography (EUVL)
have achieved an important breakthrough in the complex
process of cleaning mask blanks, the base material
for the stencil-like photomasks that are used to
describe patterns on semiconductor wafers.
Engineers using a proprietary cleaning regimen
on quartz substrates were able to remove
all particles as small as 43 nm, a dimension
so small that 18 billion such particles could
fit on the head of a pin. For EUV masks to
be used in microchip production, none can
have a substrate defect larger than 40 nm
for pilot lines and 25 nm for volume manufacturing.
"This achievement is a critical and necessary step in generating a zero-defect
mask blank," said David Krick, program manager for SEMATECH North's Mask
Blank Development Center (MBDC). "It demonstrates that the MBDC now has
world-class cleaning capability in addition to our world-class deposition expertise."
SEMATECH North, an external program of
Austin-based SEMATECH, is located at
Albany NanoTech, a global center for nanoelectronics research and development
and home to the College of Nanoscale Science and Engineering at the University
at Albany. SEMATECH North focuses primarily on developing EUVL infrastructure
for its member companies and the semiconductor industry.
"The successful demonstration of SEMATECH's mask blank cleaning process
at the College of Nanoscale Science and Engineering's Albany NanoTech complex
will pave the way for future development of cutting-edge nanoelectronics technologies," said
Robert Brainard, associate professor of nanoscience at CNSE. "At the same
time, it shows both the power of CNSE's collaborative model for research partnerships,
as embodied by SEMATECH North, and the strategic vision that is enabling New
York State to be a world leader in the innovation-driven economy of the 21st
An advanced form of lithography, EUVL uses extremely
short wavelength (13.5 nm) light and reflective
photomasks to image circuit patterns onto the
surface of semiconductor wafers. The microchips
that will be produced with EUV technology will
contain features 32 nm wide or smaller, and are
projected to be as much as 100 times faster,
with 1,000 times the memory capacity of today's
most powerful computer chips.
The significance of the MBDC's cleaning milestone
lies in the intricate and demanding science of
producing usable masks for EUV manufacturing,
Krick explained. First, the basic mask material,
called a substrate, must be made almost perfectly
free of nonremovable defects, such as pits or
scratches. Second, the mask substrate must be
cleaned of removable defects, such as airborne
particles, down to 25 nm. This cleaning process
paves the way to the final step of depositing
a multi-layered reflective coating on the substrate,
allowing the resulting photomask to effectively
reflect EUV energy.
"Cleaning of defects is a critical and necessary step in generating a zero-defect
mask blank, because defects in the substrate become defects in the multilayer,
which ruins the mask blank," Krick noted. A related challenge involves
working with suppliers to produce mask substrates with no nonremovable defects
larger than 25 nm, he added.
Krick said the MBDC's cleaning project was challenged
by the limitations of metrology, since even the
most powerful commercial mask inspection microscopes
cannot reliably detect particles smaller than 50
nm. The SEMATECH team, using an upgraded confocal
microscope from Lasertec, compensated with a repetitive cleaning and overlay
methodology that effectively "enlarged" the sub-50 nm particles so
that they could be detected.
"A great deal of work still remains for getting EUV mask blanks ready for
manufacturing, but our cleaning methodology has removed another barrier," Krick
said. "We are well positioned for the tasks ahead."
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delivers significant leverage to our semiconductor and emerging technology
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