Lithography NANO 101 Introduction to Nanotechnology 1.

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NANO 101Introduction to Nanotechnology12LithographyPhotolithographyElectron beam lithographyX-ray lithographyFocused ion beam lithographyPhotoengraving Transfer pattern into reactive polymer film (resist) Use resist to replicate pattern into thin film or substrate2

3PhotolithographyPrintingTransfer of the pattern using an optical techniqueResist = photoresist; photoactive polymer, positive or negativeCoat substrate with resistMask; expose with lightDevelop (dissolve exposed OR unexposed areas with chemicals)Etch unprotected areas or deposit layer of metalStrip resist

34PhotolithographyMaximum resolution (minimum size) of individual features limited by diffractionDiffraction: bending of light around an edge through a slit past an object (edges) direction changes wavelength, frequency stay the same


Maximum resolution:

bsd5 Modes of Photolithography

7Photolithography: Shadow PrintingContact mode:s = 0Best resolution; near 100% accuracyMaximum resolution rarely achievedSubstrate and resist film rarely completely uniform

Proximity mode:Small gap between mask and substrateNeed extremely flat substrates and resist films

8Photolithography: Projection PrintingResolutionWorse resolution than shadow printingLens imperfectionsIncreased diffractiontype of resist materialoptical system (apertures)exposure wavelength ()Best resolution ~ /2

89Radiation with smaller wavelengthsDeep Ultra-Violet (DUV): < 300 nm Need to use special lasersMinimum pattern size ~ 100 nmExtreme UV (EUV): = 11-13 nmMinimum pattern size ~ 60 nmStrong absorption of light by lensesLow reflectance of light by mirrors

9Current State of EUVSustained 100W average source power1,000 wafers processed in 24 hrs10

Other Options:ArF laser (193 nm) is current state of art Immersion (change refractive index)Double Patterning 11

Diffraction limitn = index of refractionn air : 1.0n water: 1.311Double Patterning

13X-Ray LithographyX-Rays0.04 nm < < 0.4 nmSystemMaskX-ray absorbing material pattern on a thin X-ray transparent materialX-ray sourceBright enough in necessary wavelength rangeExpensiveX-ray sensitive material

LIGALithography, Electroplating, Molding14 Beam LithographyE-beam:Finely focused beam of electrons (few nm dia.)Electrons deflected accurately and precisely to write pattern without maskResolution Diffraction not an issue < 1 (0.1 nm)ScatteringForward (in resist layer)Backwards (substrate)

1516Electron Beam Lithography SystemElectron source (gun)Electron column (forms beam)Mechanical stageControl Computer

17Focused Ion Beam (FIB) LithographyIons scatter much less than electronsSources: Liquid metal ions (Ga; Au-Si-Be alloys)Long lifetime, high stabilityResolutionsub-m dimensions (~250 nm)High resist exposure sensitivityNegligible ion scattering in resistLow back scattering from substrateExtensive substrate damage

Also used for etching, deposition, and doping1718Focused Ion Beam (FIB) ApplicationsEtchingPhysical sputtering etchingBombard areas to be etched with energetic ion beamsSimple, applicable to any sample materialChemical etchingChemical reactions between substrate surface and gas molecules adsorbed onto surfaceIncreased etching rate, little residual damageDepositionDirection deposition (low energy ions)Chemical-assisted deposition18FIB etching/deposition19

Nano Factory Achieved by Focused Ion BeamToshiaki Fujii, and Takashi Kaito, Microsc Microanal 11(Suppl 2), 2005 - See more at: - DepositionDeposition of Pt on Al substrate to form micro-grating for measuring material deformation20

21Soft LithographyTechniques:Microcontact printingNanoimprintAlternative to photolithographyCheaper / more flexiblePrinting of Self-Assembled Monolayers (SAMs)Molding of liquid precursors22Microcontact PrintingStamp madePour liquid polymer into a mold to make a stampMold often made by photolithographyInk the stampDip into solution so SAM formed on surface of stampStamp the substratePlace the inked stamp on a substrateSAM transferred to substrate in specific pattern

2223Microcontact Printing

Voskuhl, J., Wendeln, C., Versluis, F., Fritz, E.-C., Roling, O., Zope, H., Schulz, C., Rinnen, S., Arlinghaus, H. F., Ravoo, B. J. and Kros, A. (2012), Immobilization of Liposomes and Vesicles on Patterned Surfaces by a Peptide Coiled-Coil Binding Motif . Angew. Chem. Int. Ed., 51:1261612620. doi:10.1002/anie.2012048362324NanoimprintMake templateCoat substrate with polymer

3. Press stamp into polymer at high temperature; polymer deforms4. Cool polymer and pull stamp away5. Polymer can be then be etched or used as isD.R. Hines et al., Appl. Phys. Lett. 86 (16), 163101 (2005).2425Nanomanipulation and NanolithographyBased on Scanning Probe Microscopy (SPM) techniques- can be used for molecular manipulation

Types of Scanning Probe Microscopy (SPM)Scanning Tunneling Microscopy (STM)Electrically conducting materialsAtomic Force Microscopy (AFM)Dielectric (insulating) materials

26NanomanipulationSTM with Tungsten tipPlaced Xenon atoms on surfaceUHV and low temperatureClean environment and surfaceAbsence of thermal diffusion on surface

D.M. Eigler and E.K. Schweizer, Nature 344, 524 (1990).The Worlds Smallest Movie2727

28Nanomanipulation with AFMPerpendicular Processes: atoms lifted, then dropped

Parallel Processes: atoms dragged along surfacePushingPullingSliding

C. Baur, et al., Nanotechnology 9, 360 (1998).2829SPM NanofabricationAdvantagesNanoscale control in three dimensions, necessary for atomic manipulationManipulation and characterization

DisadvantagesSmall scanning areaSlow scanningTips must be high quality and consistentSurface must be flat and smooth UHV and low temperatures2930Dip-Pen Nanolithography (DPN)Works under ambient conditionsScan tip across substrate, atoms or molecules move from AFM tip to substrate

C. Mirkin, Northwestern Univ.30Water-filled capillary Chemisorption: Made 15 nm dots, spaced ~5 nm apart to form an N (gold substrate)Polymer Pen LithographyDPN + CP31

Science 19 September 2008:vol. 321 no. 5896 1658-1660 million pen array32SummaryPhotolithographyReaching size limits (diffraction, etc.)Soft LithographyRelatively newFabrication of nanostructrures and nanodevicesSPM-based techniques Relatively newPromise for using atoms and molecules as building blocks32


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