IBM scientists have created a 3D map of the earth so small
that 1,000 of them could fit on one grain of salt.
The scientists accomplished this through a new technique
that uses a tiny, silicon tip with a sharp apex - 100,000
times smaller than a sharpened pencil - to create patterns
and structures as small as 15 nanometers at greatly reduced
cost and complexity. This patterning technique opens new
prospects for developing nanosized objects in fields such as
electronics, future chip technology, medicine, life
sciences, and optoelectronics.
To demonstrate the technique's unique capability, the team
created several 3D and 2D patterns, using different
materials for each one as reported in the scientific
journals Science and Advanced Materials:
- A 25-nanometer-high 3D replica of the Matterhorn, a
famous Alpine mountain that soars 4,478 m (14,692 ft) high,
was created in molecular glass, representing a scale of 1:5
- Complete 3D map of the world measuring only 22 by 11
micrometers was "written" on a polymer. At this size, 1,000
world maps could fit on a grain of salt. In the relief, one
thousand meters of altitude correspond to roughly eight
nanometers (nm). It is composed of 500,000 pixels, each
measuring 20 nm2, and was created in only 2 minutes and 23
- 2D nano-sized IBM logo was etched 400-nm-deep into
silicon, demonstrating the viability of the technique for
typical nanofabrication applications.
The core component of the new technique, which was developed
by a team of IBM scientists, is a tiny, very sharp silicon
tip measuring 500 nanometers in length and only a few
nanometers at its apex.
"Advances in nanotechnology are intimately linked to the
existence of high-quality methods and tools for producing
nanoscale patterns and objects on surfaces," explains
physicist Dr. Armin Knoll of IBM Research Zurich. "With
its broad functionality and unique 3D patterning capability,
this nanotip-based patterning methodology is a powerful tool
for generating very small structures."
The tip, similar to the kind used in atomic force
microscopes, is attached to a bendable cantilever that
controllably scans the surface of the substrate material
with the accuracy of one nanometer - a millionth of a
millimeter. By applying heat and force, the nano-sized tip
can remove substrate material based on predefined patterns,
thus operating like a "nanomilling" machine with ultra-high
Similar to using a milling machine, more material can be
removed to create complex 3D structures with nanometer
precision by modulating the force or by readdressing
individual spots. To create the 3D replica of the
Matterhorn, for example, 120 individual layers of material
were successively removed from the molecular glass
Comparing to e-beam lithography
The new IBM technique achieves resolutions as high as 15
nanometers, with a potential of going even smaller. Using
existing methods such as e-beam lithography, it is becoming
increasingly challenging to fabricate patterns at
resolutions below 30 nanometers, where the technical
limitations of that method are reached.
What's more, compared to expensive e-beam-lithography tools
that require several processing steps and equipment that can
easily fill a laboratory, the tool created by IBM
scientists - which can sit on a tabletop - promises improved and
extended capabilities at very high resolutions, but at
one-fifth to one tenth of the cost and with far less
Yet another advantage of the nanotip-based technique is the
ability to assess the pattern directly by using the same tip
to create an image of the written structures, as the IBM
scientists demonstrated in their experiments.
Potential applications range from the fast prototyping of
nano-sized devices for future computer chips to the
production of well defined micron-sized optical elements
like aspheric lenses and lens-arrays for optoelectronics and
on-chip optical communication.
In the two publications, the scientists describe their novel
3D-nanopatterning methodology for two very distinct and
promising types of substrate materials: a polymer called
polyphthalaldehyde and a molecular glass similar to
substrate materials used in conventional nanofabrication
techniques, so-called resists. Identifying these two
materials was a key factor for the breakthrough performance
and reliability of the technique.
In their search for suitable and efficient substrate
materials, the scientists concentrated on organic materials
that could be used as resists, thereby following the same
philosophy as used for today's semiconductor technology,
which is important for further integration.
"The material was a 'make it or break it' issue," explains
Jim Hedrick, scientist at IBM Research ? Almaden. "We had to
find and synthesize materials which form mechanically tough
glasses and yet can be easily thermally decomposed into
non-reactive volatile units."
The molecular glass that was used in the Matterhorn
experiment consists of snow-flake-like molecules, measuring
about one nanometer and having an almost spherical shape. At
a tip temperature above 330 degrees C (626 degrees F), the
hydrogen bonds that hold the molecules together break,
allowing the molecular parts to become mobile and to escape
from the surface. A particular strength of the material is
that the patterned molecular glass can be transferred by
means of conventional etching techniques to, for example,
silicon, which is common in the semiconductor industry.
Molecular glass was first proposed in the late 1990s by
Mitsuru Ueda of Yamagata University, Japan, for use as
high-resolution photoresists and was thereafter developed by
Chris Ober of Cornell University.
The nanosized 3D world map was created in a polymer called
polyphthalaldehyde, a polymer originally developed by IBM
Fellow Hiroshi Ito in the 1980s. Exposed to substantially
elevated temperatures, the components of this chain-like
organic molecule unzip and fall into volatile pieces. A
self-amplified reaction causes the molecule to decompose and
then accelerates the entire patterning process by being even
faster than the mechanical motion of the tip.