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: schlaf@eng.usf.edu

Need: Atomic Force Microscopy Nanotube Cantilevers For High Aspect Ratio Feature Critical Dimension Metrology

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Carbon Nanotube Growth by PE-CVD

• 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

exhaust/to pumpPrecursors in

Substrate heater

Filament

DC Plasma

~1 mbar

Directed Assembly of CNT Through Catalyst Patterning

Focused Ion Beam Patterning of Catalyst

• 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

Ga-ion gun

Electron analyzer(for imaging purposes)

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

• 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

• TGZ02: 100 nm high steps• CNT probe shows better defined height image• Sharper edges

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Standard Si Probe CNT probe

CNT vs. Standard Si Probe Comparison

• Traces across Mikromasch test sample• FWHM of lines much smaller with CNT probe• Much steeper side wall curves

8.58.07.57.06.56.05.55.04.54.03.53.02.5

distance [µm]

~12% FWHM differencebetween CNT ( ) andstandard ( ) probe 100 nm

Forward/Backward Scan Comparison

• CNT probe shows much smaller difference between opposite direction scans than standard Si probe

7.57.06.56.05.55.04.54.03.53.02.52.0

distance [µm]

Scan to the right → Scan to the left ←

100 nm

CNT Probe

Regular SiProbe

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: schlaf@eng.usf.edu