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Posted: Apr 24, 2006
Researchers develop detailed design rules for nanoimprint lithography processing
(Nanowerk News) Using a combination of experimental data and simulations, researchers have identified key parameters that predict the outcome of nanoimprint lithography, a fabrication technique that offers an alternative to traditional lithography in patterning integrated circuits and other small-scale structures into polymers.
Results of the three-year study, conducted by researchers at the Georgia
Institute of Technology and Sandia National
Laboratories, provide a “road map” to guide development
of next-generation micron- and nanometer-scale high-resolution imprint
manufacturing. By reducing cost and time, the design rules could help
make high-volume production of nanotechnology-based products more economically
“This work provides a rational link between what engineers want
to make using nanoimprint lithography and the path for creating them,”
said William King, an assistant professor in Georgia Tech’s School of Mechanical Engineering. “We have developed manufacturing
design rules that will give future users of this technology a predictive
tool kit so they’ll know what to expect over a broad range of parameters.”
The research results have been published in the Journal of Vacuum
Science Technology B and the Journal of Micromechanics and Microengineering.
The research was supported by awards for King through the National Science
Foundation’s CAREER program and the PECASE award program of the
U.S. Department of Energy.
Nanoimprint lithography is the ultra-miniaturized version of the decades-old
embossing process in which a master tool – or a mold – is
pressed into a soft material to create detailed patterns. Using a broad
range of polymer materials, nanoimprint lithography produces structures
on the micron or nanometer size scales, offering the potential for lowering
However, quality issues caused by unpredictable polymer flow into the
non-uniform features of embossing tools pose a major stumbling block.
Earlier research into this complex process has produced often conflicting
recommendations, forcing manufacturers to pursue costly trial and error.
Using the results of experimental work and a simulation program adapted
in collaboration with researchers at Sandia National Laboratories, King’s
research team examined every variable involved in the nanoimprinting process,
recording the outcome of each incremental change through the design space.
They studied such variables as shear deformation of the polymer, elastic
stress release, capillary flow and viscous flow during the filling of
imprinting tool cavities that had varying sizes and shapes.
“This helped us to resolve the phenomenological events that occur
during the manufacturing process and to link them to the observed experimental
outcomes,” King explained. “Because we have blanketed the
entire design space, we have a firm understanding on the linkage between
process parameters and outcomes.”
At the micron- and nanometer-size scales studied by the researchers,
the fundamental laws of physics remain the same as at larger scales, but
manifest themselves in different ways.
“At the small scale with embossing and nano-imprinting, different
issues are important,” King said. “For instance, we can have
gradients in surface tension that are very important to how polymer nanostructures
are formed. We can also have high pressure gradients inside our embossing
tools that are almost ridiculously high compared to what you would expect
at the macro scale.”
The research examined, for example, how large differences in cavity
sizes on the imprinting tool lead to non-uniform filling and non-local
polymer flow. It also provided recommendations on how to minimize such
The research ultimately pointed to specific parameters that determine
the outcome of the process. These include key geometric parameters that
predict the polymer deformation mechanism. The research also developed
a new non-dimensional measure, the “Nanoimprint Capillary Number,”
which predicts the flow driving mechanism that ultimately governs all
of the polymer flow details.
By reducing the complex set of variables to key parameters, King –
along with Georgia Tech graduate student Harry D. Rowland and collaborators
Amy C. Sun and P. Randall Schunk of Sandia National Laboratories –
have been able to account for the varying process outcomes reported by
other researchers in dozens of papers, King said.
The results apply to any polymeric material that follows standard viscous
flow rules and produces feature sizes larger than 50 nanometers. The next
step in the research would be to modify the simulation software to account
for physics changes that occur on smaller size scales.
The results could have applications in semiconductor manufacturing,
where nanoimprinting offers a potential alternative to increasingly expensive
lithography processes to produce circuitry. It could also help make high-volume
production of nanoscale structures for optoelectronic, biomedical and
other applications more economically feasible.
“Nanoscale products are too expensive to manufacture, and they
will continue to be too expensive until something fundamentally changes
in the process,” King added. “Nanotechnology will not be successful
until you can go into a grocery store or discount store and routinely
purchase products based on nanotechnology. That’s what we want to