Nanoprobe Arrays for Controlled and Massively Parallel Nanofabrication 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

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. 2

Periodic Carbon Nanocone Array 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. Field emission I-V Curve Sharp-tip Vertical CNT array 3

Extremely Sharp (1 nm Tip) Carbon Nanotube AFM Probe on Si Cantilever By patterning of a single Ni island on cantilever by lithography + E-field guided chemical vapor deposition of carbon nanocone) --- 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)

Ultra-Sharp, 5-10 nm Si tips formed on 50 nm dia pillar top -- 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] 6

Massively Parallel Write Probes on a Single Cantilever (AFM or XYZ Manipulated) 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) 7

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 8

Adhesion and stability of CNTs Uprooted CNCs -- Nanoindenter lateral scratch test through individual CNCs d -- SEM image corresponds well to peaks in lateral force vs. displacement plot -- Bonding energy per CNC has been calculated as 8- 10 pJ.

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.

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

Tip Sharpening and Low- surface Coating on Si Tips 10 nm dia, 10 nm spaced (1.6 tera probes/in2) Si pillar array by nano-imprinting (a) Mask deposit on 10 nm dia pillar array top and RIE etch for tall and sharp Si pillars (b) Remove the mask for sharp 10 nm field emission probe array (c) Deposit low work function () field emitter coating (e.g., TaC, LaB6) for parallel e-beam exposure (d)

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.

Multi-tip AFM cantilever fabrication at UCSD Carbon multi-probes on a Si pedestal on AFM cantilever (by EBID e-beam process) Carbon multi-probes on tipless AFM cantilever Carbon tip Si pedestal 14

Multi-probe AFM lithography (Repeat Scan Anodization) 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 Dots: 150 nm dia., ~10 nm tall

Summary 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. Both carbon nano-tip array and Si nano-tip array have been fabricated on Si pedestal array on a single cantilever. 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. 16