62E-beam lithography

E-BeamandConventionalLithographyEE--BeamandConventionalLithographyBeamandConventionalLithographyDSSCHeadandMediumResearchSeminarDSSCHeadandMediumResearchSeminarYiJiangYiJiangOutlineOutline9Introduction9Opticallithography¾Contactprinting¾Proximityprinting¾Projectionprinting9E-BeamLithography¾E-BeamSystem¾PMMAPhoto-resist¾ElectronScattering9ExamplesLithographyProcessLithographyProcess1.WaferCleaning2.DehydrationBaking3.WaferPriming4.Photo-resistCoating5.Soft-Baking6.Exposure7.Development8.Lift-offoretching9.After-DevelopmentLithographyTechnologiesLithographyTechnologiesƒSerialƒElectronBeamƒLaserwritersƒLaserprintersƒDigitalmicromirrorarraysƒFocusedIonBeam(FIB)ƒParallelƒOpticalƒX-rayƒIonBeamƒExtremeUltraviolet(EUV)ƒDirectTransferƒImprintƒStep&FlashPhotolithographyE-BeamLithographyOpticalLithographyOpticalLithographyƒResolutioncontrolledbyλandzƒMaskissues:1x,damageƒResolutionaffectedbyλ,NAƒMask4x,protectedGap(z)ContactObjectiveLensSourceMaskSubstrateProximityProjectionDiffractioninOpticalLithographyDiffractioninOpticalLithographyNearField(Fresnel)DiffractionFarField(Fraunhofer)DiffractionWzW2/λz1W2/λz19Ideally,Lightthatpassmaskissquare,eg.ContactPrinting9Innearfield,LightshaveFrenselDiffraction,eg.ProximityPrinting9Infarfield,lightshaveFraunhoferdiffraction,eg.ProjectionprintingContact/ProximityLithographyContact/ProximityLithography2/1min)2/(32Sbλ=2/1min)(32Sbλ=9Lightpassthemastshouldbesquarewave.9Itisneverasquarewavebecausediffraction.9Photo-resisthelptocompensatefordiffractionandgiveusauniformpattern9theResolutionlimitsnm405=λmsµ1=mµ25.0msµ5.0=nm220=λmµ68.0mµ48.0mµ50.09Stepperusedinprojectionprinting.9Thewaferstepsandrepeatlithography.9Resolution9DepthofFocusStepperinOpticalLithographyStepperinOpticalLithographyNAkRλ1=StepperOpticsmaxsinθnNA=22NAkDOFλ=E-BeamLithographyE-BeamLithographyƒWhyE-BeamNotDiffraction-limited,Resolution20nmLightDiffractionLimitsMinimumfeaturesize50nmatbestPointbyPointExposure,limitsspeedHighSpeed,ParallelExposureHighspeedforcomplexpatternsHighspeedforlargeshapesE-BeamPhoto-lithographySchematicofE-BeamLithographySchematicofE-BeamLithography10-100.22eV5nm109ColdFE10-90.9eV25nm108TFE10-82-3eV10um106LaB610-62-3eV25um105TungestonVacuumRequired(Torr)EnergySpreadSourceSizeBrightness[amp/cm2/str]SourceTypeSchematicofE-BeamLithographySchematicofE-BeamLithography9MagneticLens:focusbeam9Blanker:blankorpassbeam9BeamDeflector:DeflectbeamE-BeamScanE-BeamScanWritingMethodRastorScanVectorScan9directwritesystemsuseaelectronbeamspotthatismovedwithrespecttothewafertoexposethewaferonepixelatatime.ShapedBeamPhoto-resistforE-BeamPhoto-resistforE-BeamPMMA(polymethylmethacrylate)9PMMAisthemostcommonlyusedphoto-resistforE-Beam9PMMAisaclearplasticPMMAthicknessvs.SpinSpeedScatteringinE-BeamScatteringinE-BeamScatteringForwardScatteringBackwardScatteringMonte-carlosimulationforscattering10kv20kv50kv9Resolutiondependslessonspotsize,andmoreonscattering.ExamplesExamplesMagneticRingsfabricatedbyE-BeamLithographyL.Heyderman,“Nano-scalemagneticrings”,JAP,Vol.93,Nov12,2003ExamplesExamplesSmallGap9TwoAuelectrodsexposedintwoseparatesteps9Bychangingoffsetbetweentheelectrodes,canobtainsub-10nmgap9Investigateelectrontransportinatomic-scalediametercontactsExamplesExamplesNano-ScaleFabrication950nmstringon“nano-guitar”9Harold.G.Craighead,DustinCarr(CornellUniveristy)SummarySummary9E-BeamLithographyisamodifiedSEMsystem9E-Beamlithographyissuitableforcomplexpatternslikecircles,rings,andforsmallstructures.9Aserialprocess,exposeasinglepixelatatimeandmovetonextpixel9Resolutionisnotlimitedbydiffractionlimits,butbyscatteringofelectron,theresolutionisaround10nm-20nmE-BeamLithographyE-BeamLithographyE-BeamLithographyE-BeamLithography