Researcher: Li-Han (Leon) Chen, research Scientist, CMRR and MAE Dept.

Collaborators: Edward Choi, Postdoctoral Researcher, Justin Kim, Isaac Liu, Graduate Student, , CMRR and MAE Dept.

Advisor: Sungho Jin, Professor, CMRR and MAE Dept.

Outline

•Introduction•Control growth of carbon nanotubes•Fabrication of sharp carbon nanocones & Si Nanotips Arrays

•Potential applications

•Summary

Nanoprobe Arrays for Controlled and Massively Parallel Nanofabrication

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Introduction and Rationale• High-throughput nanofabrication --- Essential for successful

technology transfer of nano material/device innovations to viable manufacturing levels.

• Need viable solutions to two major bottleneck issues in nano manufacturing, i.e., i) precise placement of nanomaterials /devices in high enough densities, and ii) convenient high-throughput fabrications.

• E-beam lithography is too costly and not fine enough. Optical fab techniques such as EUV may be too costly and equipment intensive.

• AFM probe lithography based on many parallel-cantilevers (such as IBM’s Millipede indentation writing on polymer) --- uncertain whether such complex systems would be convenient enough for industrial nanofab applications.

• Therefore, new approaches for high-throughput nano-manufacturing using “Massively Parallel AFM probe Arrays” are being pursued, using CNT tips or Si tips.

• To develop multi-tip parallel probe writing processes to enable fabrications of predictable and periodic nano-island arrays.

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• CNTs are powerful electron field emitters.

• Vertical aligned carbon nanotubes can be produced as an array of very sharp nanocone structure by DC Plasma CVD growth. • A single CNT nanocone on AFM Si cantilever also fabricated for potential use as a new, ultra sharp AFM and MFM probes.

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Field emission I-V CurveSharp-tip Vertical CNT array

Periodic Carbon Nanocone Array

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Manipulation of CNT probe configuration during CVD growth

1 µm1 µm1 µm1 µm1 µm1 µm1 µm1 µm1 µm1 µm1 µm1 µm

Nanotubegrowth

Nanoconegrowth

Two-step growth

Sicantilever

CNT probe

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--- Very sharp and durable

--- Tip radius of curvature as small as ~ 1 nm regime

--- Electrically conductive – For bioconductance measurements of ion channels, etc.

~1 nm diameter CNT tip (by TEM)

Extremely Sharp (1 nm Tip) Carbon Nanotube AFM Probe on Si Cantilever

1 µm

(a)

(b)

10 nm

Si Cantilever

Si Cantilever

Sharp CNT

Sharp CNT

• By patterning of a single Ni island on cantilever by lithography + E-field guided chemical vapor deposition of carbon nanocone)

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500 nm

~50 nm dia. Si nano-pillar array

Deposit metal etch mask (Ni, or Au)

Balled-up etch mask

Si etch by RIE

(a) (b) (c) (d) (e)

Remove metal mask

-- Periodic Si pillar array with 50x50 nm square (or circular) top surface (100

million pillars with identical height have been fabricated by DUV etch

process on a 6 x 6 mm area (Left),

---which can be utilized as a basis for fabrication of 5~10 nm diameter Si

probe at each pillar top using balled-up metal mask and RIE as

illustrated in the schematics (Right).

-- Low- coating (e.g., TaC or LaB6) can be coated for easier field emission.

[in progress]

Ultra-Sharp, 5-10 nm Si tips formed on 50 nm dia pillar top

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Multi-tip AFM nano manufacturing of many devices simultaneously (e.g., 100 million identical devices fabricated at the same time)• e.g., nano transistor array, Qbit array, memory element array (magnetic memory, phase change memory)

Si with a resist layer

108 identical nano patterns

108 probe tips with identical height

AFM cantilever

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Massively Parallel Write Probes on a Single Cantilever (AFM or XYZ Manipulated)

Si nano-pillar + CNT on top • For combination of CNT tip good field emitter array with convenient Si base array structure (100 million fabricated on 6 x 6 mm area by DUV).• Guided growth of sharp nanotubes (~10 – 30 nm tip dia.) on each Si pyramid by planarization of Si array with polymer filler + Ni deposit + lift-off + CNT growth on Ni islands). • Field emission measurements in progress.

Vertical CNT arrays

Si nano-pillar (pedestal) array

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Uprooted CNCs

-- SEM image corresponds well to peaks in lateral force vs. displacement plot

-- Bonding energy per CNC has been calculated as 8-10 pJ.

Adhesion and stability of CNTs

-- Nanoindenter lateral scratch test through individual CNCs

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500 nm500 nm

Extremely sharp Si nanotip array (<~5 nm dia tip, 200-500 nm spaced) fabricated by DUV etch for potential use as multi-tip probe array.

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100 nm

2 mm

10 µm

10 nm island (20 nm pitch) Si island array over large- area

Blown up image

50 nm

10nm dia x 20nm height

1.6 Terabit/in2 density

(a) (b)

Nano-imprint stamp fabricated. (a) Periodic nano island array pattern with ~10 nm diameter Si islands and spacing (1.6 terabits/in2 density), (b) Long range order of uniform array over 2 mm x 2 mm area produced by large-area e-beam lithography (as compared to typical 100 µm size). This larger area master-pattern is to fabricate daughter stamps for further tip sharpening for nano-tip writer arrays.

Si-Based, 10 nm Regime Nanotip Array by Nano-Imprinting

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(a)

10 nm dia, 10 nm spaced (1.6 tera probes/in2) Si pillar array by nano-imprinting

(b)

(c)

(d)

Mask deposit on 10 nm dia pillar array top and RIE etch for tall and sharp Si pillars

Remove the mask for sharp 10 nm field emission probe array

Deposit low work function () field emitter coating (e.g., TaC, LaB6) for parallel e-beam exposure

Tip Sharpening and Low- surface Coating on Si Tips

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Photo detector

FeedbackControl

Multi-tip AFM Field Emitter Probe Array (Laterally movable emitter tips)

Laser Mirror

Amplifier

Substrate

Nano e-beam exposed dots

Probe Cantilever

Resist layer

Multi-tip AFM lithography using a single AFM cantilever containing many parallel tips with identical height.

R&D progress made so far-- Sharp carbon tips made for multi-tip AFM probes.-- Sharp Si tips also made for multi-tip AFM probes.-- AFM lithography patterning has been demonstrated. 13

• Carbon multi-probes on a Si pedestal on AFM cantilever (by EBID e-beam process)

• Carbon multi-probes on tipless AFM cantilever

Multi-tip AFM cantilever fabrication at UCSD

1 2

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Carbon tip

Si pedestal

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• Cantilever spring constant : 0.65 N/m (soft) • Ambient condition : humidity 60 %• Lithographic condition: 3 carbon tips on Si pedestal, XE-100 (Park Systems Inc.)• Contact mode, DC sample bias: 25 V, set point: 20 nN

Multi-probe AFM lithography (Repeat Scan Anodization)

Dots: 150 nm dia., ~10 nm tall

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1. To enable sub-20 nm and sub-10 nm level high resolution nanopatterning, massively parallel AFM lithography is being investigated, with some progress toward 100 million simultaneous tips fabrications and some preliminary multi-tip AFM lithography.

2. Both carbon nano-tip array and Si nano-tip array have been fabricated on Si pedestal array on a single cantilever.

3. Collective wisdom and nano-materials/nano-devices expertise can be utilized to advance such high-throughput nanofab technology to usher in a new era of nanotechnology.

Summary

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