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Lithography. MAIN TYPES OF LITHOGRAPHY: * Photolithography * Electron beam lithography –X-ray lithography –Focused ion beam lithography –Neutral atomic

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Text of Lithography. MAIN TYPES OF LITHOGRAPHY: * Photolithography * Electron beam lithography –X-ray...

  • Lithography

  • MAIN TYPES OF LITHOGRAPHY:* Photolithography* Electron beam lithographyX-ray lithographyFocused ion beam lithographyNeutral atomic beam lithography

    * = most common, we will talk about these!Lithography = Photoengraving

    Transfer pattern into reactive polymer film (resist) Use resist to replicate pattern into thin film or substrate

  • The invention of photolithography is arguably as important as that of the wheel, bronze, or movable type in terms of its impact on society. It is, however, a technology that is specialized for use in microelectronics.

  • PHOTOLITHOGRAPHYWhat is it? A transfer of the pattern using an optical technique. Resist = photoresist, a photoactive polymerSTEPS:Coat substrate with resistMaskExpose with lightDevelop (dissolve exposed (POSTIVE) OR unexposed areas with chemicals (NEGATIVE))Etch unprotected areas or deposit layer of metalStrip resist (take it off)

  • Fun with Playdough

  • The maximum resolution (minimum size) of individual features is limited by diffractionDiffraction: bending of light- around an edge- through a slit- past an object (edges)

  • http://www.youtube.com/watch?v=9x3Lh1ZfggM Awkward Cornell scientist showing photolithographyridiculous music. I apologize.

  • Electron Beam LithographyE-beam:Finely focused beam of electrons (few nm diameter)Electrons deflected accurately and precisely to write pattern without maskResolution Diffraction not an issue < 1 A (0.1 nm)Scattering (is an issue)Forward (in resist layer)Backwards (substrate) Its more expensive and WAY SLOWER

  • Electron Beam LithographyElectron scatteringE beam loses energy as it enters a solidElectrons have elastic and inelastic collisionsLeads to broadening of beam, exposure sites, imagesDepends on velocity of electrons, atomic number and density of substrate and resist

  • Scanning Electron Beam Lithography How it worksElectron source (gun)Thermionic Heat material until electrons emitted from surfaceField emissionUse electric field to extract electrons from the tip of a very sharp point of tungstenElectron column (forms beam)Mechanical stage (moves around under beam)Control ComputerControls subsystems and transfers pattern data

  • Scanning Electron Beam LithographyMechanical StageMoves substrate through the deflected e-beam

  • Soft Lithography2 Common Soft Lithography Techniques:Microcontact printingNanoimprintAlternative to photolithographyits not used with metals or semiconductors (hence the name soft)Printing of Self-Assembled Monolayers (SAMs)Molding of liquid precursors

  • Microcontact 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

  • Your turnPick a stampDraw out the process that would be required to make the shape of your stamp as a divot on a silicon wafer with an oxide layer.Imagine you poured the rubber material that makes up your stamp into the divot to create your stamp.Ink it and stamp it!

  • Microcontact PrintingYou can even roll out patterns since its soft!

  • SummaryPhotolithographyIs reaching size limits (diffraction, etc.)Soft LithographyIs relatively newUsed in fabrication of nanostructrures & nanodevices

    ******Elastic: electron change direction but dont lose energyInelastic: electron changes direction and loses energy

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