旋涂技术

SpinCoatingProcessTheorySpincoatinghasbeenusedforseveraldecadesfortheappli-cationofthinlms.Atypicalprocessinvolvesdepositingasmallpuddleofauidresinontothecenterofasubstrateandthenspinningthesubstrateathighspeed(typicallyaround3000rpm).Centripetalaccelerationwillcausetheresintospreadto,andeventuallyoff,theedgeofthesubstrateleav-ingathinlmofresinonthesurface.Finallmthicknessandotherpropertieswilldependonthenatureoftheresin(viscos-ity,dryingrate,percentsolids,surfacetension,etc.)andtheparameterschosenforthespinprocess.Factorssuchasnalrotationalspeed,acceleration,andfumeexhaustcontributetohowthepropertiesofcoatedlmsaredened.Oneofthemostimportantfactorsinspincoatingisrepeatability.Subtlevariationsintheparametersthatdenethespinprocesscanresultindrasticvariationsinthecoatedlm.Thefollowingisanexplanationofsomeoftheeffectsofthesevariations.SpinCoatingProcessDescriptionAtypicalspinprocessconsistsofadispensestepinwhichtheresinuidisdepositedontothesubstratesurface,ahighspeedspinsteptothintheuid,andadryingsteptoeliminateexcesssolventsfromtheresultinglm.TwocommonmethodsofdispenseareStaticdispense,andDynamicdispense.Staticdispenseissimplydepositingasmallpuddleofuidonornearthecenterofthesubstrate.Thiscanrangefrom1to10ccdependingontheviscosityoftheuidandthesizeofthesubstratetobecoated.Higherviscosityandorlargersubstratestypicallyrequirealargerpuddletoensurefullcoverageofthesubstrateduringthehighspeedspinstep.Dynamicdispenseistheprocessofdispensingwhilethesubstrateisturningatlowspeed.Aspeedofabout500rpmiscommonlyusedduringthisstepoftheprocess.Thisservestospreadtheuidoverthesubstrateandcanresultinlesswasteofresinmaterialsinceitisusuallynotnecessarytodepositasmuchtowettheentiresurfaceofthesubstrate.Thisisaparticularlyadvantageousmethodwhentheuidorsubstrateitselfhaspoorwettingabilitiesandcaneliminatevoidsthatmayotherwiseform.Afterthedispensestepitiscommontoacceleratetoarelativelyhighspeedtothintheuidtonearitsnaldesiredthickness.Typicalspinspeedsforthissteprangefrom1500-6000rpm,againdependingonthepropertiesoftheuidaswellasthesubstrate.Thisstepcantakefrom10secondstoseveralminutes.Thecombinationofspinspeedandtimeselectedforthisstepwillgenerallydenethenallmthickness.Ingeneral,higherspinspeedsandlongerspintimescreatethinnerlms.Thespincoatingprocessinvolvesalargenumberofvariablesthattendtocancelandaverageoutduringthespinprocessanditisbesttoallowsufcienttimeforthistooccur.Aseparatedryingstepissometimesaddedafterthehighspeedspinsteptofurtherdrythelmwithoutsubstantiallythinningit.Thiscanbeadvantageousforthicklmssincelongdryingtimesmaybenecessarytoincreasethephysicalstabilityofthelmbeforehandling.Withoutthedryingstepproblemscanoccurduringhandling,suchaspouringoffthesideofthesubstratewhenremovingitfromthespinbowl.Inthiscaseamoderatespinspeedofabout25%ofthehighspeedspinwillgenerallysufcetoaidindryingthelmwithoutsignicantlychangingthelmthickness.EachprogramonaCeespincoatermaycontainuptotenseparateprocesssteps.Whilemostspinprocessesrequireonlytwoorthree,thisallowsthemaximumamountofexibilityforcomplexspincoatingrequirements.SpinSpeedSpinspeedisoneofthemostimportantfactorsinspincoating.Thespeedofthesubstrate(rpm)affectsthedegreeofradial(centrifugal)forceappliedtotheliquidresinaswellasthevelocityandcharacteristicturbulenceoftheairimmediatelyaboveit.Inparticular,thehighspeedspinstepgenerallydenesthenallmthickness.Relativelyminorvariationsof±50rpmatthisstagecancausearesultingthicknesschangeof10%.Filmthicknessislargelyabalancebetweentheforceappliedtosheartheuidresintowardstheedgeofthesubstrateandthedryingratewhichaffectstheviscosityoftheresin.Astheresindries,theviscosityincreasesuntiltheradialforceofthespinprocesscannolongerappreciablymovetheresinoverthesurface.Atthispoint,thelmthicknesswillnotdecreasesignicantlywithincreasedspintime.AllCeespincoatingsystemsarespeciedtoberepeatabletowithin±5rpmatallspeeds.Typicalperformanceis±1rpm.Also,allprogramminganddisplayofspinspeedisgivenwitharesolutionof1rpm.AccelerationTheaccelerationofthesubstratetowardsthenalspinspeedcanalsoaffectthecoatedlmproperties.Sincetheresinbeginstodryduringtherstpartofthespincycle,itisimportanttoaccuratelycontrolacceleration.Insomeprocesses,50%ofthesolventsintheresinwillbelosttoevaporationintherstfewsecondsoftheprocess.Accelerationalsoplaysalargeroleinthecoatpropertiesofpatternedsubstrates.Inmanycasesthesubstratewillretaintopographicalfeaturesfrompreviousprocesses;itisthereforeimportanttouniformlycoattheresinoverandthroughthesefeatures.Whilethespinprocessingeneralprovidesaradial(outward)forcetotheresin,itistheaccelerationthatprovidesatwistingforcetotheresin.Thistwist-ingaidsinthedispersaloftheresinaroundtopog-raphythatmightotherwiseshadowportionsofthesubstratefromtheuid.AccelerationofCeespinnersisprogrammablewitharesolutionof1rpm/second.Inoperationthespinmotoraccelerates(ordeceler-ates)inalinearramptothenalspinspeed.FumeExhaustThedryingrateoftheresinuidduringthespinprocessisdenedbythenatureoftheuiditself(volatilityofthesolventsystem