CARBON NANOTUBE DEVELOPMENT FOR AFM TIPS
SEMATECH PROJECT, Start Date: November 30, 2004
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Dimensional measurements are a crucial part of the patterning process
inherent in semiconductor manufacturing, both during the mask
generation/verification process and during circuit fabrication. However,
conventional methods using optical or Scanning Electron Microscope
techniques are problematic for deep sub-micron technologies. For example,
advanced reticles for current applications employing complicated phase
shift structures or OPC corrections are becoming sub-resolution for
optical inspection methods, and SEM strategies are also problematic due to
potential charging issues with isolated features, non vertical patterns,
etc. In addition, CD measurements employing low voltage SEM methods show
serious complications due to changes in secondary electron yield along
sidewalls as well as scalloped and undercut features.
Atomic Force Microscopy (AFM) offers the possibility of dimensional
measurements with sub-nm precision. One major challenge with the
application of AFM methods in CD metrology is the manufacture of
well-defined probes required for reproducible measurements across
measurement platforms. While advanced high aspect ratio Silicon probes are
available, their failure rate results in frequent probe exchange,
requiring probe qualification procedures which slow down the measurement
process.
Carbon nanotubes (CNT) have demonstrated their longevity in scanning probe
applications and have therefore been identified as a promising alternative
to Silicon probes. The main challenge to be overcome before CNT probes can
routinely be used is the mass manufacture of well-defined CNT probes.
Previous efforts have demonstrated that chemical vapor deposition (CVD) is
a viable method for this task. The scope of the present project is the
further development of this process to allow CNT probe manufacture on the
wafer scale.
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New Flexible-Tip AFM Mode for High Aspect-Ratio
Feature
Metrology, Phase I
National Science Foundation, SBIR Project, Start Date: January 1,
2006
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This Small Business Innovation Research (SBIR) project demonstrated the
feasibility of a new AFM imaging mode that exploits lateral bending and
lateral oscillation of flexible tips, including carbon nanotube tips, as
an advantage rather than trying to deal with lateral tip flexure as a
disadvantage. The flexible tip AFM mode will enable the semiconductor
industry community to access and image both sidewalls and depths of high
aspect features. Tips designed to implement the new imaging mode will
enable customers to use carbon nanotubes to image high aspect ratio
trenches, contact holes and vias without the sidewall sticking problem
that occurs when carbon nanotube tips are used with existing AFMs. Both
non contact and contact mode operation will be investigated as well as tip
characterization, needed for metrology applications and vertical
operation, needed to measure and image feature bottoms, tops and corners.
The new AFM imaging mode leverages existing, patented carbon nanotube
growth process which are now being used to fabricate carbon nanotubes
directly on the apexes of AFM tips for use by semiconductor industry
manufacturers. Commercially, introduction of a flexible tip scanning mode
innovation has the potential to expand the usefulness of carbon nanotubes
as AFM tips beyond the semiconductor industry. AFM users in biology,
medicine, materials science, forensics and other fields have increasing
needs to image three dimensional structures. The same flexible tip
technology used to image challenging semiconductor features at the nm
scale can also be used to image features of interest to this broader
community of AFM users.
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Aligned Carbon Nanotubes for Use as Atomic
Force Microscope Tips,
Phase II
National Science Foundation, SBIR Project, Start Date: September 15,
2000
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This Small Business Innovation Research (SBIR) Phase II project helped to
establish the first-ever, large-scale production capability needed to
manufacture carbon nanotube tips for scanning probe tools. To achieve
this, Xidex combined several fabrication technologies in a unique way. We
also solved challenging problems related to the design, structural form
and attachment of the tips themselves that will enable Xidex, as the
manufacturer, to guarantee that the products sold meet customers'
performance specifications. The core technology being commercialized stems
from a new approach for growing a single, aligned carbon nanotube directly
on a cantilever, originally identified by Xidex.s Principal Investigator.
This approach is suitable for fabricating both the carbon nanotube tip and
the cantilever in one continuous process, ideal for large-scale
manufacturing. Xidex will develop, manufacture and sell carbon nanotube
tips for use with critical dimension atomic force microscopes (CD-AFMs),
scanning capacitance microscopes (SCMs), regular atomic force microscopes
(AFMs) and scanning tunneling microscopes (STMs).
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Aligned Carbon Nanotubes for Use as Atomic
Force Microscope Tips,
Phase I
National Science Foundation, SBIR Project, Start Date: January 1,
1999
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This Small Business Innovation Research Phase I project demonstrated the
feasibility of a new approach for fabricating aligned carbon nanotubes for
use as Atomic Force Microscope (AFM) tips. The feasibility of
manufacturing a single aligned carbon nanotube on an AFM cantilever was
demonstrated in a process suitable for large-scale manufacturing. The
approach raised interrelated material-process compatibility challenges and
design considerations, which had not previously been considered within the
same context. The importance of this work to critical dimension metrology
for wafer fabrication and use of AFMs for mask repair led to endorsements
by Texas Instruments and SEMATECH. This work helped enable Xidex to plan,
develop, manufacture and sell integrated carbon nanotube tips for in-line
CD metrology and mask repair tools used within the semiconductor industry.
These tips can also be used for lateral force microscopy, precision
surface profiling, biological sampling and other nanoprobe research
instrumentation.
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