Manufacture of High Aspect Ratio Carbon Nanotube Atomic Force Microscopy Probes

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

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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

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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: [email protected]