Manufacture of High Aspect Ratio Carbon
Nanotube Atomic Force Microscopy Probes
Y.N. Emirov1, J.D. Schumacher1, M. M. Beerbom1, B. Lagel1
B.B. Rossie2, and R. Schlaf1*
1)
University of South Florida, Dept. of Electrical Engineering
2)
USF Center for Ocean Technology
*)
email: [email protected]
Need: Atomic Force Microscopy Nanotube Cantilevers For
High Aspect Ratio Feature Critical Dimension Metrology
Image features incorrect
Image features correct
Carbon Nanotube Growth by PE-CVD
~1 mbar
Filament
Precursors in
DC Plasma
exhaust/to pump
Substrate heater
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•
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Plasma Enhanced Chemical Vapor Deposition (PECVD)
Precursors: Methane, acetylene, propane
Catalysts needed: Ni, Fe, Co (allows directed assembly)
DC Plasma helps cracking the precursor molecules
Directed Assembly of CNT Through Catalyst
Patterning
Focused Ion Beam Patterning of Catalyst
Ga-ion gun
Electron analyzer
(for imaging purposes)
• Focused Ga-ion beam
sputters sample
• Computer controlled,
complicated patterns
are possible
• 5 nm resolution
• Dual beam instrument
with integrated SEM
X-Y deflector plates
Focused Ga beam
(for cutting patterns)
Precision cut in sample
(~5nm resolution)
Process: Masking Layers with Sockets
• Cr masking layers
prevent CNT growth
in unwanted
locations (i.e. on tip
cone)
• Access to buried
catalyst through
cylindrical cavity
extending into the
catalyst.
Result: Good control over Ni patch
CNT Growth From Si-Ox Sockets
• Sockets in 130 nm Si-Ox layers
• 10nm/30nm Cr/Ni at bottom of sockets
• CNT with well defined diameter grow from each
socket, ~25% are straight.
64 nm Tubes From 130 nm Sockets
• Smaller CNT diameters possible
• However, yield appears to depend on diameter
Recent CNT Cantilevers
•
•
•
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70 nm x 400 nm CNT
Grown from cavity
Cold cathode PECVD
Acetylene/Ammonia
precursors
• Grown at 10 deg angle
suitable for Nanoscope
CNT Probe Test on Mikromasch TGZ02 Standard
Quic kT i me™ and a T IFF (Unc ompres s ed) dec ompres s or are needed t o s ee thi s pi c
Standard Si Probe
• TGZ02: 100 nm high steps
• CNT probe shows better
defined height image
• Sharper edges
CNT probe
CNT vs. Standard Si Probe Comparison
~12% FWHM difference
between CNT (
) and
standard (
) probe
100 nm
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
distance [µm]
• Traces across Mikromasch test sample
• FWHM of lines much smaller with CNT probe
• Much steeper side wall curves
7.5
8.0
8.5
Forward/Backward Scan Comparison
CNT Probe
Scan to the right
Scan to the left
Regular Si
Probe
100 nm
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
distance [µm]
• CNT probe shows much smaller difference between
opposite direction scans than standard Si probe
CNT Probe Before and After Scanning
• No apparent damage to CNT from scanning process
• CNT attached strongly enough to withstand torques
during scanning
• Socket provides stability
Latest Results:
• New, stable process
• CNT are well-defined
• Testing of these
probes is underway
• Patent pending
Dimensions: 1µm long/50 nm wide
Summary
• Goal: Well-defined CNT on standard AFM tips
suitable for critical dimension metrology
• Concept has been demonstrated
• Focused ion beam/e-beam litho patterning
used for prototyping
• Outlook: Testing on state-of-the-art industry
structures/expansion of process to wafer scale
• Thank you for your kind attention!
Contact: [email protected]