Deep canyons can be etched into materials at the nanoscale with a new SIS-based lithography technique by Argonne National Laboratory scientists. Image: Argonne National Laboratory |
Imagine
yourself nano-sized, standing on the edge of a soon-to-be computer chip. Down
shoots a beam of electrons, carving precise topography that is then etched the
depth of the Grand Canyon into the chip.
From the
perspective of scientists at the U.S. Department of Energy’s Argonne National
Laboratory, this improved form of etchingcould open the door to new technologies.
Argonne
nanoscientist Seth Darling and colleagues at Argonne’s
Center for Nanoscale Materials and Energy Systems Division say it has the
potential to revolutionize how patterns are transferred onto different
materials, paving a new approach for the next generation of energy, electronics,
and memory technologies.
The
innovation combines new tricks with an old technology.
One of the
biggest recent questions facing materials science has involved the development
of better techniques for high-resolution lithographies such as electron-beam,
or e-beam, lithography. E-beam lithography is used to manufacture the tiniest
of structures, including microelectronics and advanced sensors; beams of
electrons are part of a process that “prints” desired patterns into
the substance.
Transferring
patterns more deeply into materials would allow scientists to craft better
electronics.
To create
a pattern using e-beam lithography, researchers have conventionally traced a
pattern within a layer called a “resist,” which is then etched into the
underlying substrate.
Because
the resist is thin and fragile, an intermediate “hard mask” is generally
laid between the resist and the substrate. Ideally, the hard mask would stick to the substrate long
enough for the desired features to be etched and then be cleanly removed—though
the extra layer often results in blurriness, rough edges, and additional costs
and complications.
But over
the course of the past several years, Darling and his colleagues have developed
a technique called sequential infiltration synthesis (SIS). Another method of
building custom designs at the nanoscale level, SIS involves the controlled
growth of inorganic materials within polymer films. This means that scientists
can construct materials with unique properties and even with complex, 3D
geometries.
“With
SIS, we can take that thin, delicate resist film and make it robust by
infiltrating it with inorganic material,” Darling explains. “That
way, you don’t need an intermediate mask, so you get around all the problems
associated with that extra layer.”
Although
some resists might work better than others under certain conditions, no single
approach had yet demonstrated the ability to ingrain a pattern with the ease,
depth, and fidelity of the Argonne approach,
Darling says.
“It’s
possible we might be able to create very narrow features well over a micron
deep using only a very thin, SIS-enhanced etch mask, which from our perspective
would be a breakthrough capability,” he says.
By
combining sequential infiltration synthesis with block copolymers, molecules
that can assemble themselves into a variety of tunable nanostructures, this
technique can be extended to create even smaller features than are possible
using e-beam lithography. The key is to design a selective reaction between the
inorganic precursor molecules and one of the components in the block copolymer.
“This
opens a wide range of possibilities,” says Argonne
chemist Jeff Elam, who helped create the process. “You can imagine
applications for solar cells, electronics, filters, catalysts—all sorts of
different devices that require nanostructures, but also the functionality of
inorganic materials.”
“Hopefully,
our discovery gives scientists an extra advantage when it comes to creating
deeper patterns with higher resolution,” Darling says.
