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