Understanding Imaging of Silicon and Germanium Nanowires Through Simulation
(1/7/2006) Future Fab Intl. Issue 20
By T. Hanrath, University of Texas at Austin
D.C. Lee, University of Texas at Austin
B.A. Korgel, University of Texas at Austin
Alexander Thesen, Carl Zeiss SMT-Nano Technology
Marco Matijevic, Carl Zeiss SMT-Nano Technology
Alain C. Diebold, College of Nanoscale Science and Engineering, University at Albany
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Research, development and manufacturing
of nanotechnology, especially
nanoelectronic technology, requires the
ability to image at near atomic dimensions.
In many circumstances, transmission
electron microscopy (TEM) can now
provide the necessary imaging. The
recent introduction of aberration-corrected
lens technology has extended
spatial resolution to less than 0.1nm.
High-resolution TEM images and electron
diffraction patterns of nanowires
show phenomena not present in images
of bulk materials. In this paper we discuss
how simulating these images provides
new insight into the interpretation
of these images. Simulated electron
diffraction patterns point toward the
possibility of determining the surface
morphology of nanowires. This understanding
will provide the methodology
necessary for imaging nanoelectronic
devices such as FINFETs. Most people believe what they see.
Humans interpret images as corresponding
directly to the size, shape, morphology
and other properties of the object in
question. Unfortunately, this is the case
with our interpretation of images from
electron microscopes. For example,
most people correlate the phase contrast
image of the silicon crystal lattice taken
by high-resolution transmission electron
microscopy (HR-TEM) as an image of
atoms. It is really an interference pattern
that represents the location of the atoms
in some circumstances. Many do not
realize that the bright and dark regions
of this image change with focus. When
the focus and other conditions are
known, the image can be interpreted in
terms of atomic locations. In some circumstances,
simulations are needed to
directly interpret the image. This is why
the atomic number contrast of scanning
TEM equipped with HA-ADF (high angle
– annular dark field) detectors has
become so popular. In many circumstances,
the HA-ADF STEM images can
be directly interpreted.
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