8-电子束光刻Electron-beam-lithography-2

Electronbeamlithography(EBL)1.Overviewandresolutionlimit.2.Electronsource(thermionicandfieldemission).3.Electronoptics(electrostaticandmagneticlens).4.Aberrations(spherical,chromatic,diffraction,astigmation).5.EBLsystems(raster/vectorscan,round/shapedbeam)6.Interactionofelectronswithmatter(scattering,x-ray,Auger).7.Proximityeffectandhowtoreduceit.8.Resistcontrastandsensitivity.9.Severalpopularresistmaterials.10.HighresolutionEBL,resolutionlimit.11.Grey-scaleEBLfor3Dstructurefabrication.12.Anti-chargingtechniques.ECE730:Fabricationinthenanoscale:principles,technologyandapplicationsInstructor:BoCui,ECE,UniversityofWaterloo;~bcui/Textbook:Nanofabrication:principles,capabilitiesandlimits,byZhengCuiInteractionsofelectronswithmatter•UnlikeX-rays,electronsinteractverystronglywithmatter•Elasticscattering(i.e.nolossofenergy)ofelectronscanbetreatedclassicallyasaformofRutherfordbackscattering•Inelasticscatteringarisesfromnumerousinteractions:oLowenergysecondaryelectronsgeneration.oInnershellexcitations(x-rayfluorescenceandAugerelectrons)oElectron-holepaircreationandrecombinationoPhononexcitation(heat)2Informationfromelectronbeam-specimeninteractionsWhenelectronbeamstrikesthesample,bothphotonandelectronsignalsareemitted.3Interactionvolume4BestspatialresolutionforSEMBetterZcontrastforSEM(brighterforhigherZ)BestanalyticalforEDXSecondaryelectron(SE)regionforimaging(SEisactuallyproducedwhereverprimaryelectrongoes,butonlythosenearsurfacecangoouttoreachSEdetectorforimaging)Back-scatteredelectron(BSE)regionforimaging(Again,BSEisactuallyproducedwhereverprimaryelectrongoes.Ithashigherenergy,sotravellongerthanSE)X-rayregionforEDX(x-rayisactuallyproducedwhereverprimaryelectrongoes.Ittravels/penetratesevenfartherthanBSE)WhichregionisforwhichapplicationBSEhaslowerresolutionthanSEsignal,andisusedonlywhenchemical(Z)contrastiswanted.TEM(transmissionEM)givesmuchhigherresolutionthanSEMbecauseofthemuchlowerinteractionvolumeofthehighenergyelectrons(200keV!)passingthethinsamples.X-raygenerationbyelectronbombardmentEnergylevels:2256.13nZEn1isduetoscreening(=0foridealmodel).n=1(K-shell),2(L-shell),3(M-shell)….Emittedx-rayenergyEx-rayK:Ex-ray=E1-E2K:Ex-ray=E1-E3L:Ex-ray=E2-E3….6Energy-dispersivex-rayspectroscopy(EDS,EDX)•SEMisoftenequippedwithEDXthatdetectx-rayemitted(needsonlyextra$50K).•Eachelementhasitscharacteristicx-ray,soEDXisforelementalanalysis.•Sincebothprimaryelectronsandemittedx-raycanpenetratecertaindepth(uptomanym),EDXisnotfortopsurfaceanalysis(AESis,seenextslides).•Theprincipleisthesameaselectronimpactx-raysource,buthereafocusedelectronbeamisusedto“impactorbombard”thesample.•Lightelement(Z4)usuallycannotbedetected,sincetheircharacteristicenergyislowerandthuscannotgothroughthex-raydetectorwindow.(Weknowthatlongerwavelengthshorterattenuation/penetrationlength).•EDXissimilartox-rayfluorescence(XRF).Theonlydifferenceisthat,forEDXinnershellelectronsarekickedoffbyhighenergyelectrons;forXRFitisbyhighenergyx-raywithenergyemittedcharacteristicx-rayenergy,orevenby-ray.7EDXanalysisofamaterialThepeakforWcouldbeL(itsKenergyismuchhigher)AugerelectronemissionECoreState,EB,EC':corelevel(heren=1),firstoutershell(n=2),secondoutershell(n=2)electronenergies.(ECoreState−EBisthesameenergyasthecharacteristicx-rayenergy)Sinceorbitalenergiesareuniquetoanatomofaspecificelement,analysisoftheenergyofejectedelectronscanyieldinformationaboutthechemicalcompositionofasurface.:Ekin=ECoreState−EB−EC'ForEDXFluorescenceandAugerelectronyieldsasafunctionofatomicnumberforKshellvacancies.ForAESKickoffelectronAugerElectronSpectroscopy(AES)•AESisgoodforlightelement(e.g.Li)whereAugerelectrondominatex-rayemissionyield.•Itisforsurfaceanalysis,abletoanalyzeonlythetopsurface(2-5nm).•ScanningAugerMicroscope(SAM)isatypeofAES,butwithfocusedelectronbeamtogivehighresolutionspatialinformationofelementdistribution.9fromBriggsandSeah,PracticalSurfaceAnalysis2ndEditionJohnWiley&Sons,1990,p.207.Attenuationlengthasafunctionofenergy(dependsonZ)AugerelectronElectronenergy(eV)1-10monolayersamplingdepthAugerspectrumofacoppernitridefilm(weaksignal,oftenneedderivativetoshowthepeaks)Electronbeamlithography(EBL)1.Overviewandresolutionlimit.2.Electronsource(thermionicandfieldemission).3.Electronoptics(electrostaticandmagneticlens).4.Aberrations(spherical,chromatic,diffraction,astigmation).5.EBLsystems(raster/vectorscan,round/shapedbeam)6.Interactionofelectronswithmatter(scattering,x-ray,Auger).7.Proximityeffectandhowtoreduceit.8.Resistcontrastandsensitivity.9.Severalpopularresistmaterials.10.HighresolutionEBL,resolutionlimit.11.Grey-scaleEBLfor3Dstructurefabrication.12.Anti-chargingtechniques.10Forward/backscatteringeventsScattering:spreadingofthebeam,lostofresolutionProperties:VeryoftenSmallangleVeryinelastic(i.e.loseenergy)GenerationofSE(secondaryelectrons)withlowenergy.Properties:Occasionally(collisionwithnucleus)Largeangles,thusmainlyelasticHighenergy,samerangeas