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MethodsforMinimizingSlotDieCoatingEdgeEffectsandPatternedCoating

MiguelFriedrich,GregGibsonnTact(FASHoldingsGroupLLC)10480MarkisonRoad,Dallas,TX

m.friedrich@nTact.com 214.343.5387Keywords:SlotDieCoating,PatternedCoating,SelectiveCoating,PatchCoating,SelectiveRemoval,EdgeEffect,LeadingEdge,TrailingEdge,ActiveArea.Abstract:

Theslotdiecoatingmethodistypicallyusedforcoatingessentiallytheentireareaofthesubstrate.AnewmethodofslotdiecoatinghasbeendevelopedbynTactwhichallowsthe“macropatterning”ofaslotdiecoatedfilmtoproduceanarrayofrectangularshapes(activeareas)overtheareaofthesubstrate.Whencoatingonlargersubstrateswhichmaycontainvarioussmallerdevicestructures,thistechniqueisprovingtobeausefulwayofdepositingthematerialonlyintheactiveareawherethedevicesarelocated.Inaddition,withsomeofthestricteredgeexclusionrequirementsemergingfromnewdevicestructuresanddesigns,thehistorical10mmedgeexclusionusedintheLCDindustryisnolongeracceptableformanynewerapplications.Whilethelatestslotdiecoatingsoftwarecontrolsandhardwareallowforareduced5mmedgeexclusionformanymaterials,insomecasesthisisstillnotsufficient.Tomeettheseverysmalledgeexclusions,alowcost(bycomparison)thinfilmremovalmethodknownasSelectiveRemovalwasdeveloped,whichcanbeusedtoessentiallyeliminateleading(beginningofthecoating)andtrailing(endofthecoating)edgenon-uniformitiesandreducetheedgeexclusiontolessthan1mm.Background:

Historically,slotdiecoatinghasbeenregardedasaveryeffectivemethodfordepositingfilmsoverlargeareasoftheentiresubstratesurface,otherthanasmalluncoatedparameterofacoupleofmillimetersfromtheedges.Thosefamiliarwiththeartunderstandthemostchallengingaspectofsheet-to-sheet/discretepanelslotdiecoatingisminimizingtheedgeexclusion/edgeeffect,inparticularfortheleadingandtrailingedges.Theedgeexclusionreferstotheareaaroundtheedgesofacoatedsurfacethatisrequiredforthecoatingprocesstoachievesteadystatesthicknessandtargetuniformity,whichistypically±3%to±5%.Inthepast,forLCDmanufacturingprocesses,anedgeexclusionofupto10mmwasacceptable.Inotherwords,havinganon-uniformareaof10mm(orless)intheleading,trailingorsideedgesofthecoatedfilmwasacceptable.Butformanynewapplications,thisisnolongerallowable.Forexample,manynewdisplayapplicationsanddesigns(forOLEDandothers)nowhaveverythinoralmostnon-existentbezels,whichrequireamuchthinneredgeexclusionofoftenlessthan5mm.Systemdevelopersfrequentlyarethenfacedwiththedecisionwhethertouseasubsequent,oftenexpensiveremovalprocess,suchaslaserablation,ortoidentifyanalternatewaytodepositthesefilms.Thesealternativedepositionmethodsusuallyalsoinvolvemoreexpensiveprocessoptionssuchasinkjetprintingprocesses(significantlymorecomplexandexpensiveequipment,andstillatsomewhatdevelopmentalstage)orvacuumdeposition(expensiveequipmentandwithpoormaterialutilization)processes.Inaddition,inmostcases,asinglesubstrateisusedtomanufacturenumerousdevices.Sooperatorsendupprocessingseveral“activeareas”withinasinglelargerpane.Ideally,materialwouldbedepositedonlyonthoseactiveareas,butithasalwaysbeenchallengingtouseslotdiecoatingtodoanysortof

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patterneddepositiononthesubstrate,suchasacoatinganarrayofrectangularshapestocoveronlytheactiveareas.Theuseofmaskshasnotbeenaneffectivewaytodothisforsolutionbasedprocessing,andifthestarting(leadingedge)andstopping(trailingedge)controlisthemostchallengingpartoftheslotdiecoatingprocess,doingthisnumeroustimesthroughoutthecoatingprocessofasinglesubstratetodefinemultiplecoatedareasonthatsurfaceincreasesthedifficultyofachievinganacceptablecoatedfilm.Approach:

Toaddressthechallengeofcoatingonlyondesiredactiveareasofasubstrate,nTactdevelopedthetechniqueofSelectiveCoating,oftenreferredtoas“PatchCoating”,whichgivesoperatorstheabilitytocoatanarrayofrectangularshapesonadiscretesubstratesurfaceinasinglepass(seeFigure1andFigure2below).

Figure1:IllustrationofSelectiveCoatingProcess

Figure2:ExampleofSelectivelyCoatedPanel

TheSelectiveCoatingmethodusesaspeciallydesignedslotdiewithmultipleopeningstodefinecoatedanduncoatedareas(stripes)acrossthewidthofthesubstrate.Thestripesaretypicallyofuniformwidthandspacing,althoughasymmetricalarrangementsarealsopossible.Thestripearrayisgenerallydesignedtocoatthedesiredwidthonthefinaldevice,plusasmallamountofextrawidthoneachside.Thisextrawidth,or“sideedgeexclusion”,isneededtocompensateforthicknessnon-uniformitiesattheedgeofthecoatingandforpotentialoverlayinaccuracieswheremultiplelayersmustbealigned.Thestripecoatingiscombinedwithpreciseandproprietarysoftwarecontrolsgivingthesystemtheabilitytopreciselystartandstopthecoatingmultipletimesdownthelengthofthesubstrate,therebyenablingthedepositionofanarrayofrectangularshapes.Thestart/stopoperationinvolvesthecarefulcontrolofnumerouscoatingparameters,includingtheflowofmaterialthroughthedieandthepositionofthediewithrespecttothesubstrate.Thepositionofthecoatingstartandstoplocationscanbe

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preciselycontrolledandthelocationsaretypicallyprogrammedtocorrespondtothedesiredcoatedareas,alongwithasmallamountofadditionalcoatinglengthtocompensateforedgethicknessnon-uniformitiesandoverlayinaccuracies.ThecombinationofthisspecificallydesignedslotdieandnTact’soptimizedproprietarysoftwareandcontrolsschemegivestheoperatornotonlytheabilitytoselectivelycoatapatternedarrayofrectangularshapesonasubstratesurface,butalsotypicallyachieveabetterthan5mmedgeexclusionforthedepositionofmostfilms.

However,althoughachievableforsomeprocesses,limitingtheedgeeffectbelowthat5mmthresholdisstillquitechallenging.Today’ssmallbezeldisplaydesignsandotherapplicationrequirementsoftencallforanedgeexclusionoflessthan2mm,whichisquitedifficulttoattainwithmaterialsthroughtheuseofslotdiecoating.Toachievethis,theoperatoristypicallyforcedtouseasubsequentremovalstep/process.nTactdevelopedalowcost(bycomparison)materialremovalmethodcalledSelectiveRemoval,whichallowsdeveloperstolimittheedgeexclusiontolessthan1mminmostcases.TheSelectiveRemovaltechniqueimplementsaproprietarymechanismtoremoveportionsofthecoatingmaterial,suchastheleadingandtrailingedge,afterdeposition.Theremovalmechanismisajetspraynozzlethatusesasolventthatiscompatiblewiththecoatingfluidtodissolvethecoatedlayer,whilesimultaneouslyremovingthesolutionfromthesurfaceofthesubstrate.Thenozzledoesnottouchthesubstrate,thez-axiscontrollingtheheightabovethesurface,alongwiththex-axisandy-axismotionofthedevice,iscontrolledtoensureprocessreliabilityandrepeatability.Asthenozzleismovedalongaprogrammedpath,thecoatingmaterialisremoved,leavingacoatedareaofpreciseshapeanddimensions.Thenozzlemechanismisdesignedsothatthedissolvedsolutioniscompletelycontainedandremovedfromthesubstratewithnoyieldimpactonthecoatedpanel.ThroughtheuseofSelectiveRemoval,theoperatorisabletoeliminatetheunwanted,non-uniformedgeeffectattheleading,trailingand/orsideedges,leavingnearlytheentirecoatedareawithintargetuniformity.Thetechniquecouldalsobeusedtocreatecomplex,non-rectilinearshapesofcoatedmaterials.Theremovalmechanismcanbeconfiguredtoremoveanarrowbandofmaterial(lessthan1mmasshowninFigure3),oramuchwiderband(20mmormore),providingfurtherflexibilityinthewaythatthefinalcoatedpatterncanbegenerated.

Figure3:592µmlineremovedfrom9µmthickFluoropolymerfilm.Edgeeffectof235µm

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Implementation:

SelectiveCoatingandSelectiveRemovalprovideprocessflexibilitythatallowsanoptimizedapproachtocreatingthedesiredshapeandedgeprofileofacoatedarea.SelectiveCoatingaloneallowsthedepositionofadefinedarray,thoughwithsomeedgeeffectsaroundtheperimeterofeachcoatedarea.SelectiveRemovalcanbeusedwithSelectiveCoatingtomorepreciselydefineboththecoatedareaandthecoatingedgeprofile.SelectiveRemovalcanalsobeusedtocreateanarrayofshapesfromasinglecoatedarea,independentofSelectiveCoating.SelectiveCoatingcanbeimplementedasanadditionalfeatureandcapabilityoftheslotdiecoatersystem.Itisacombinationofaspecificallydesignedcoatingdieanddiecomponentswhichgiveyoutheabilitytocoatstripesinthecoatingdirection(x-axis)andsoftwarecontrolswhichprovidetheoperatortheparameterinputsandcapabilitytostartandstopthecoatingprocessinthey-axisdirection.Thecombinationofthesetwofeaturesandfunctionscangenerateafilmwithanarrayofrectangularshapes.TheimplementationofSelectiveRemovalcanbedoneeitherin-situ,directlyonthecoater,orasaseparateprocessstation.Formanyresearchanddevelopmentapplications,asinglemechanismsysteminstalledonthecoatersystemprovidesadequatethroughput.Inthiscase,theSelectiveRemovalmechanismisinstalledonthecrossbarandtakesadvantageofthealreadyexistinglinearmotorsofthecoatertomovethenozzleinthe“X”direction.AdditionalmotorsandcontrolsareaddedtogivetheSelectiveRemovalnozzletheabilitytointheY-axismovealongthecoatercrossbaraswellasZ-axismotion.Forproductionapplications,multiplemechanismsaswellastheimplementationofaseparateSelectiveRemovalstation(s)ormodule(s)canbeusedtoincreasesystemthroughput.Results:

SelectiveCoatinghasbeentestedandsuccessfullyimplementedwithavarietyofmaterialsrangingfromverylowviscositytomuchmoreviscousmaterials.Table1showsuniformitydateofaselectivelycoatedPEDOT:PSSfilm,atypicalOLEDHoleInjectionmaterial,coatedat70nm.Thematerialwasdepositedusingacoatvelocityof45mm/sectogenerate18segmentsonaGen2(370x470mm)borosilicatedisplayglasssubstrate.Anoveralluniformityofbetterthan±4%wasachieved,andtargetuniformity/steadystatewasreachedwithanedgeexclusionontheleadingandtrailingedgesoflessthan5mmandbetterthan2mmontheside

STRIPES73.48 73.74 74.19 72.56 73.04 71.8172.45 73.78 74.18 73.06 72.85 72.23

69.99 73.09 75.70 73.29 72.92 72.8472.53 73.45 72.33 73.91 72.65 72.42

72.60 73.11 74.40 73.78 72.85 73.2073.90 73.17 72.49 73.79 72.73 72.07

370mm71.50 71.19 71.33 72.97 72.11 72.7673.28 72.35 70.99 71.84 72.71 72.19

71.80 72.05 71.57 72.88 72.49 72.8971.38 72.51 72.65 71.74 72.77 73.25

72.05 72.62 73.00 72.19 72.46 71.8772.57 72.33 72.12 71.37 71.92 71.56

TrailingEdge 5mm 5mm LeadingEdge

Max Min Range Avg Unif. (+/-)75.70 69.99 5.71 72.64 3.92%

Lateralmeasurementstaken3mmfromedges

2

1

470mm

unit:nm

6

5

4

3

Table1:SelectiveCoatingofPEDOT:PSS

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edges.ThisprovedtobeadequatefortheOLEDLightingapplicationforwhichthisprocesswasoptimized.SelectiveRemovalprovidesfortheeliminationofthecoatingmaterialasthemechanismtravelsalongadefinedpath.Thedurationoftheremovalprocessdependsonthepathlengthandthevelocityofthemechanism,thelatterofwhichisheavilyinfluencedbythecoatingmaterialandremovalsolvent.Somematerialsaremucheasiertodissolvewithagivensolventandthereforequickertoremove,whileothermaterialswilldissolveataslowerpacetakinglongertoeliminate.Figure4:~46µmEdgeEffect Figure5:~108µmEdgeEffect

nTacttestedtheremovalprocessundervariousconditions,includingremovalofawetfilm(immediatelyaftercoating)asemidryfilm(aftersoftbakeorvacuumdryprocess)oradryfilmafteramorethoroughthermalcuringprocess.Resultshavevariedandbeenverymaterialspecific,withsomematerialsperformingbetterwhenremovedwetimmediatelyaftercoating,andothersbenefitingfromsomesolventevaporationprocess,suchavacuumdry,toimproveperformance.However,SelectiveRemovalonamostlydryfilmgenerallyprovedtobetheleasteffective.Whileitworkedinsomecases,theremovalprocessprovedtobesignificantlyslowerthanunderwetfilmorasemi-dryfilmconditions.

MostfilmsalsobenefittedfromasecondpassorsubsequentadditionalSelectiveRemoval,significantlyminimizingtheedgeexclusion.FollowingyouwillfindtheremovalofpositivephotoresistmaterialwithasinglepassandadoublepassofSelectiveRemoval.

CoatedArea

SubstrateAreaSubstrateArea

CoatedArea

Figure6:Removalaftersoftbake,70umEdgeExclusion Figure7:RemovalOnWetFilm,30µmEdgeExclusion

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Figure8:SinglePassRemoval Figure9:DoublePassRemoval

Withadoublepassremoval,animpressiveedgeexclusionofapproximately15µmwasachieved.However,whiledoublepassremovalimprovedtheedgeexclusionbyafactoroffive(5),a70-75µmedgeexclusionisacceptableformanyapplications,andasinglepassremovalsignificantlyimprovesthroughput.Forcertainhardtoeliminatematerials,however,morethanonepassmaybenecessarytoachievethedesiredremovalperformance.Ingeneral,manyofthesametypesofparameterswhichaffecttheoutcomeofaslotdiecoatingprocessneedtobeadjustedforSelectiveRemoval.Nozzlevelocity,removalgap(meaningthespacebetweenthenozzleandthetopsurfaceofthefilm/substrate)andsolventdispenseratecanallhaveanimpactandinfluenceSelectiveRemovalresults.Andjustaswithslotdiecoating,eachparameterneedstobeoptimizeddependingonthematerial/chemistrybeingremoved.

Figures10and11showtheresultsofSelectiveRemovalatdifferentremovalspeeds/nozzlevelocities.RemovalofaFluoropolymerfilmat10mmpersecondyieldedanedgeexclusion108µmcomparedtoathicker470µmedgeexclusionusingafasternozzlevelocityof20mmpersecond.Theslowernozzleandremovalspeedrepresentsanedgeexclusionimprovementwhichisalmostfive(5)timesthinner.However,anedgeexclusionoflessthan500µmmaystillbeadequateformanyapplications.Inthiscase,theoverallprocessmaybenefitfromasignificantlyfasternozzlespeed,resultinginanoverallimprovedthroughputorTACT.

AZ1518–singlepassremovalAcetoneat10mm/sec.~70µmedgeexclusion

Figure10:SelectiveRemovalat10mm/sec100µmgap

Figure11:SelectiveRemovalat20mm/sec

AZ1518–doublepassremovalAcetoneat10mm/sec.~15µmedgeexclusion.

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Conclusion/Summary:

Thesepatentpendingmethodspresentprocessimprovementsandpotentialsolutionstothechallengesinslotdiecoating.TheSelectiveCoatingmethodimprovesuponthewell-establishedandwidelyadopteduseofslotdiecoatingmethodtoformthinfilmlayersofpolymers,addressingahistoricallimitationoftraditionalslotdiecoatingtechniques.Mostmicroelectronicdevicesproducedtodayrequireoneormoreselectivelyformedcoatedlayersduringthemanufacturingprocess.Increasingly,thosefilmsareappliedaspatternsonlargersubstratessothatmanufacturingefficiencies,economiesofscaleandoverallcostreductionscanberealized.WithSelectiveCoatingoperatorscannowimplementbasicpatterningbydepositinganarrayofrectangularshapesinasinglepass,eachrepresentingadeviceonalargersubstrate.SelectiveRemovalcancomplementandenhanceSelectiveCoatingasitaddressesoneofslotdiecoating’sbiggestchallenges,minimizingthefilmedgeexclusion,throughthesubsequentremovalofnon-uniformitiestypicallyfoundintheleadingandtrailingedgesofaslotdiecoatedpanel.Thesetechniquescanbeappliedtoamultitudeofapplicationsincludingflatpaneldisplay,SolidStateLighting,SmartGlass,andotherorganicandprintedelectronicsapplications.

WhilethereisstillongoingresearchbynTacttocontinuetoimproveandfurtherdevelopbothofthesetechniques/methods,SelectiveAreCoatinghasalreadybeensuccessfullyimplementedonseveralpilotproductionlineswithplanstomoveintofullproductioninthenearfuture.Bothtechniquesshowrealpromiseasacosteffectivewaytoexpandthecapabilityofusingslotdiecoatingprocessfornumerousprocesses.

References:

[1] UnitedStatesPatentnumber7,169,229,“MovingHead,CoatingApparatus”

[2] G.Gibson,S.Snodgrass,“SelectiveCoatingandRemovalTechnologiestoProducePatternedFilmsforPrintedElectronics”,LOPE-CProceedings(2011)

[3] T.J.Faircloth,J.G.Innocenzo,C.Lang,“43.3:SlotDieCoatingforOLEDDisplays”,SIDSymposiumDigest39645(2008)

[4] Sonehara,etal,“48.3:ContinuousCoatingofPhoto-AlignmentLayeronaFlexibleColorFilterforLCDsUsingaRoll-to-RollManufacturingProcess”,SIDSymposiumDigest371579(2006)

[5] J.Gabel,I.deVries,R.Mandamparambil,A.Langen,R.Andriessen,“ProgressinpatterningtechnologiesforR2RslotdiecoatingforOLEDandOPVapplication”,EuropeanCoatingSymposium(2011)