Graduate
student Andrew Cannon shows a plastic sheet containing
micro-mechanical features. (Georgia Tech Photo: Gary
Meek)
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
feasible.
“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 production costs.
Researcher
William King (l) and Graduate student Andrew Cannon
show a plastic sheet containing micro-mechanical
features. (Georgia Tech Photo: Gary Meek)
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 issues.
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 accomplish.”
Research News & Publications Office
Georgia Institute of Technology
75 Fifth Street, N.W., Suite 100
Atlanta, Georgia 30308 USA
Media Relations Contacts : John Toon (404-894-6986); E-mail: (jtoon@gatech.edu)
or Jane Sanders (404-894-2214); E-mail: (jane.sanders@edi.gatech.edu).
Technical Contact : Bill King (404-385-4224); E-mail: (bill.king@me.gatech.edu).
