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Influence

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InfluenceInflue

    Influence

InfluenceofDepositionParametersonSurface

    ;EvolutionofSputteredTantalumThinFilms

    ;LUOXiangdong.LUOChongtai

    ;(1.LanzhouPhysicsResearchInstituteofChinaAcademyofSpaceTechnology,Lanzhou730000,CHN;

    ;2.PeiliCollegeofEngineeringTechnology,LanzhouCityUniversity,Lanzhou730070,CHN)

    ;Abstract:Tantalumthinfilmswithdifferentthicknessesvaryingfrom5Oamto600nmweredepositedonSi

    ;suhstratesbyradiofrequencymagnetronsputteringasfunctionsofdepositiontemperature(Ts)andbiasvoltage

    ;(Ub).Surfaceroughnessanditsdynamicevolutionbehaviorwerequantitativelyinvestigatedbyusingatomic

    ;forcemicroscopy(AFM).Withincreasingfrom300Kto600K,surfaceroughnessRanddynamic

    ;exponentpdecreasesgradually.WiththeincreaseofUbfrom0Vto

    150V,R.andpfirstdecreaseandthen

    ;increase.ThedependenceofTsandUbonthefilmsurfaceevolutionhasbeendiscussedintermsofsurface

    ;diffusion,moundgrowth,andionimpingingeffect.

    ;Keywords:tantalumthinfilm;surfaceevolution;sputtering;processparameters ;CLCnumber:TN30Documentcode:AArticleID:10070206(2008)030147—06’

    ;1IntrOductiOn

    ;Inthelastseveralyearstantalumthinfilmshaveattractedconsiderabletechnologicalinterestduetoits

    ;attractivepropertiessuchashighdielectricconstant,highdurability,andchemicalinertness~].

    ;In

    ;particular,therehasbeenatremendousinterestonitsapplicationasdiffusionbarrierbetweenCuandSi

    ;inelectronicsdevices[2..ThepropertiesofTadiffusionbarrierstronglydependonitsmicrostructureand

    ;surfacemorphology,w.hicharerelatedtothedepositionmethodandprocedure. ;OneofthemostpromisingtechniquesinpreparationofTathinfilmisthesputteringdeposition.in

    ;whichdepositiontemperatureandbiasvoltagearesomeofthekeyparametersthatinfluencethefilm

    ;structureProperties.Thoughmanystudieshavebeendevotedtotheeffectoftheseparametersonthe

;filmtextureandstress.

    ,sofar,littleworkhassystematicallyinvestigatedtheireffectonthefilm ;surfacemorphology.Especially,withcontinueminimizationofelectronicsdevices,Tafilmsurface

    ;morphologyplaysamoreimportantroleinthedeviceperformance.For.example,inmulti-1evel

    ;interconnectionsystem,Tafilmsurfacerriorphologycanleadtoadifferentqualityoftheadj

    acentCu

    ;film,whichiscrucialinthereliabilityofthissvstemCS~.

    ;

    ;InthispaperweinvestigatethesurfacemorphologiesofsputteredTathinfilmsasfunctionsof

    ;depositiontemperatureandbiasvoltage,withaspecialemphasisonsurfaceroughnessaswe11ason

    ;dynamicrougheningbehavior.

    ;2ExperimentalDetails

    ;2.1FilmDeposition

    ;!ilmswithdifferentthicknessesrangingfrom50nmto600nmwe’redepositedontosingle

    ;Receiveddate:20080611;reviseddate:20080721

    ;?

    ;147?

    ;

    ;SemiconductorPhotonicsandTechnologyAug.2008

    ;crystallineSi(110)substratesbyusingradio

    ;frequency(RF)magnetronsputteringfromahigh

    ;puretantalumtarget(99.99).Priorto

    ;deposition,Sisubstrateswereuhrasonicallycleaned

    ;intheacetoneandthenativeoxideonthesilicon

    ;waferswasremovedbyRFdischargeinAr

    ;atmosphere.Thedepositionparameterssuchas

    ;depositiontemperature(T)andbiasvohage(Ub)

    ;arelistedinTab.1.Thefilmthicknessd(50nm

    ;Tab.1DepositionparametersofTathinfilms

    ;ProcessvariableValues

    ;Backgroundpressure/Pa3×1O

    ;Workingpressure/PaO.4

    ;Argasflow-rate/(ml/min)20

    ;Sputteringpower/W1OO

    ;Targettosubstratedistance/ram65

    ;Rotationvelocityofsubstrateho!der/rpm40

    ;Depositiontemperature(T)/K3OO600

    ;Biasvoltage(Ub)/vO,一15O

    ;600nm)wascontrolleitbyusingaquartz-crystalmonitorcalibratedwithadiamondstylusp

rofilometer.

    ;2.2FilmSurfaceCharacterizatiOn

    ;Filmsurfacemorphologywasobtainedwithanatomicforcemicroscopy(AFM,DigitalIns

    truments

    crystalSitipwitharadius;NanoscopeIl1)operatedintappingmodeusinganetchedsingle

    of10nm.

    ;Collecteddataconsistedofheightinformationonsquare512×512arraysofpixels.

    ;Thescanareais

    ;1ffmX1Hmforeachsample.Theresuhswerecheckedforreproducibilitybyimagingsever

    alregionsof

    ;thesamesample.

    ;FromAFMimage,thefilmsurfacemorphologywasquantitativelycharacterizedbyroot

    mean-square

    ;roughnessR..Rsisdeterminedbyusingthestandarddefinitionasfollows:

    ;R=:

    ;whererepresentstheheightofthethdata.

    ;isthenumberofthedata.

    ;(1)

    ;isequaltothemeanheightofinAFMimage,andN ;Further,sui’facedynamicevolutionofthefilmwas

    ;equatton:

    ;quantitativelyanalyzedbyusingthefollo~ring ;R.cd(2)

    ;Here,isthedynamicexponentwhichdescribesthesurfacerougheningprocess

    ;,e.g.the”lmthickness

    ;dependenceofsurfaceroughness,andcallbeusedtorevealthefilmgrowthmechanism

    ;.

    ;3ResultsandDiscussion

    ;3.1FilmSurfaceMorphology

    ;Fig.1SHOWSsuFfacemorphologiesof100nm

    ;thickTafilmsandtheirheightdistribution ;diagramsFilmsurfaceiscomtSrised.fregu1ar ;mounds.AFMSCaNsizeislargerthanthe

    ;characteristicscaleofsurfacemoundsandthe ;surfaceheightfluctuationsexhibitagoodnorma1 ;distributioncharacterwhichimpliestt1atAFM ;imagecarlaccuratelyrevealthewholesurface ;morphology.

    ;ThechangeinsllrfacemorphologyofTafilmsas ;afunctionofdepositiontemperatm’egscanbeseen

    ;4.38illn

    ;0.00

    ;:

    ;0,00.

;Typical1ffmX1”mAFMimagesof100nrn—thick

    ;Tafilmsdepositedatdifferentprocess

    ;pai’ameters:(a)300K,Ub0V;(b)

    ;500K,Ub0V;(c)T.300K,Ub一一5OV;

    ;(d)300K,Ub一一150V

    ;

    ;??

    ;

    ;Vo1.14No.3LUOXD,etal.InfluenceofDepositionParametersonSurfaceEvolutionofSp

    utteredTantalumThinFilms

    ;inFig.1(a)and(b).WiththeincreaseofT,thecharacteristicscaleofsurfacemoundsincrease

    s

    ;gradually,andthemoundsurfacebecomessmoother. ;Thedependenceo{biasvoltageUbonthesurfacemorphologycanbefoundbycomparingA

    FMimages

    ;showninFig.1(a),(c).and(d).WhenUbincreasesfrom0Vto

    50V,thesurfacemound’sgrowth

    ;isnotobvious,butthemoundsurfacebecomessmoother.WithincreasingUbto100V,themound

    ;growsslightlyandawelldefinedgranularstructurecanbeobserved.Itseemsthatthefilm

    depositedat

    ;higherUbhasaroughersurface.

    ;3.2FilmSurfaceRoughness

    ;InordertoquantitativelyinvestigatetheeffectofTandUbonthesurfacemorphology,wecal

    culated

    ;thefilmsurfaceroughnessR.accordingtoEq.(1). ;Fig,2showsR…valuesof50nm—thickand600

    ;nm-thickTafilmsdepositedatTs===300K,400K, ;500K,and600K.ThebiasvoltageUhisfixedat ;0V.ItcanbeobservedthatRdecreaseswiththe ;increaseofT.R.resultsareingoodagreement ;withtheobservationinFig.1.Otherfilmsdeposited ;fordifferentvaluesofUbexhibitthesimilar ;behavior.Itisacknowledgedthatthedependanceof ;thechangeofsurfaceroughnessondeposition ;temperaturecanbeexplainedbythecompetition ;betweensurfacediffusionandsurfacemound ;growth.Inourcase,itcanbeconcludedthat ;Depositiontemperatum/K

    ;Fig.2SurfaceroughnessRvsdepositiontemperature ;for50nm-thickand600nm-thick,I’afilms

    ;surfacediffusionmechanismdominatessurfaceroughnessevolutionofTafilm.Withincre

    asing,

    ;depositionparticlescandiffuseongrowingsurface,whichleadtosurfacesmoothening.Its

houldbe

    ;notedthatthesurfacemoundsalsobecomebiggerwithincreasingT,whichmayleadtotheincreaseof

    ;R.However,withinthedepositiontemperaturerangestudiedhere.theeffectofsurfacemound

    ;growthonsurfaceroughnessisnotobvious.Botezeta1.studiedthetemperatureofsurfaceroughening

    ;ofCufilmsL.TheyfoundthatthefilmsurfaceroughnessdecreaseswiththeincreaseofTfrom16OK

    ;to370K.Liueta1.investigatedthegrowthtemperatureeffectonsurfaceroughnessofthinfilmsby

    ;usingalinearcontinuummodel[.TheydemonstratedthatTincreaseleadstosmallerR.vahles,

    ;whicharisefromtheenhancementofsurfacediffusionduringfilmgrowthprocess.Ourresultsarewell

    ;consistentwiththosestudies.However,therearesomedifferentfindingsasreportedinprevious

    ;literatures.Sittnereta1.studiedthesurfaceevolutionofpolycrystallineA1filmsdepositedatelevated

    ;temperatureandobservedthatRincreasedwiththeincreaseofTandthegraingeometrystructureof

    ;thefilmchangedwithT.intheircase[.Thechangeofgraingeometrystructuremayleadtos

    ignificant

    ;heightdifferenceofgrainsonfilmsurface,whichprovidesanadditionalrougheningmechanismfor

    ;surfaceevolutionandlargersurfaceroughness.Structurezonemodel(SZM)hasstudiedthecorrelation

    ;betweenfilmgrainstructureandnormalizedtemperatureT/Ym(Tisthemeltingpointoffilm

    ;materia1)Eg].Thismode1demonstratesthatfilmgrainstructurecanremainunchangedwittlinacertain

    ;T/

    lnrange,e.g.,Ts/Tmd0.3.Inourcase,duetothehighervalue(3269K)of1,amateriaianda ;limitedTrange(300K~600K),T/

    mvariationisonlyinthesmallrangefrom0.09to0.18.Hence,

    ;thegraingeometrystructureofTafilmsstudiedhereremainsunvaried. ;?

    ;149?

    ;Su,s8《嚼?2?Jlfn?

    ;

    ;SemiconductorPhotonicsandTechnology

    ;Aug.2008

    ;Fig.3showstypicalsurfaceroughnessofTafilms

    ;depositedatT300KasafunctionofUb.Itcan

    ;beseenthatRmevolutioniscomprisedoitwo ;differentregimes:forthefirstregime,RHns ;decreaseswithUbincreasingfrom0Vto50V;

    ;forthesecondregime,RincreasesasUblncrease ;from50Vto150V.Ingeneral,biasvoltage

    ;hasthetwofoldeffectonfilmsurfaceevolutionby ;Fig.4showsatypicalloglogplotofsurface

    ;roughnessRVS.filmthicknessdforTafilms ;depositedatT300KandUb0V…R.displaysa

    ;goodpowerlawdependenceond,implyingthatthe ;filmsurfaceexhibitsdynamicrougheningbehavior. ;AccordingtoEq.(2),thedynamicexponentJ8?

    ;0.53forthefilmcanbeobtainedbyfittingthis ;plot.Thevaluesofotherfilmsdepositedunder ;differentTand/orUbconditior~scanalsobe ;determinedbyusingthismethod.

    ;Fig.5illustratestypicalvaluesofTafilmsas ;[unctionsoftheprocessparametersT(Ub0V)

    ;Filmthickness/nm

    ;Fig.4TypicaldoubllogarithmicplotofSurface ;roughnessRVS.filmthickneSSdforTafilms ;depositedatT5=300KandUbOV

    ;andUb(T300K).WiththeincreaseofT.,

    ;decreasesfrom0.52to0.37,whichimpliesthathigherdepositiontemperatureinducesasma

    llervelocity

    ;ofsurfaceroughening.WithincreasingUb,firstslightlydecreasesfrom0.52to0.46inthere

    gimeof

    ;Ub?50vandthensteep1yincreasest.0.70inth;regime.fUb>

    5OV.Thisshowsthatthesma11er

    ;Ubcouldinduceas1owersurfacerougheningandthehigheroneleadstoquicksurfacerough

    ening?TheJ9

    ;_E11?01I_I?I120磊亭?_EIII\??0II0l0_J.I

    ;

    ;Voi.14No.3LUOXD,etai.InfluenceofDepositionParametersonSurfaceEvolutionofSp

    utteredTantalumThinFilms

    ;evolutionofotherfilmsfordifferentTandUb ;valueshasthesimilarcharacteristics.Itshouldbe ;noticedthatthedependenceofevolutiononT.and ;UbisconsistentwiththoseR.evolutionmentioned ;above.

    ;Numerousstudieshavestudiedthedynamical ;evolutionbehavioroffilmsurfacerougheningandits ;relationtothefilmgrowthmechanismsbybuilding ;theoreticalgrowthmodels.Thesetheoretical

;studiesshowthatdifferentvaluesofcorrespondto

    ;thefilmgrowthprocessesincludingdifferent

    ;microscopicmechanisms.Forexample,hasthe

    ;universalityvalueof0.5forthefilmgrowthprocess

    ;withlowadatommobility,and0.25(or0.20)for

    ;0.75

    ;0.50

    ;0.25

    ;Biasvoltage/V

    ;Depositiontemperature/K

    ;Fig.5Variationofdynamicrougheningexponent

    ;valuesofTafilmswithdifferentdeposition

    ;temperatures(Ub0V)orbiasvoltage(300K)

    ;thefilmgrowthwhichiscontrolledbysurfacediffusionmechanismL.

    .Inourcase.withtheincrease

    ;ofT.,thediffusionabilityofdepositionparticlesisenhancedgradually,leadingtothedecreaseof&

    ;Similarly,forthefilmdepositedatlowerUb,thedepositionparticlemobilityisalsoenhanced,andthus

    ;decreases.However,thefilmdepositedathigherUbhasalargervalueoffl>0.5,whichisnot

    ;consistentwiththosepredictedbyprevioustheoreticalmodels.Severalpreviousexperimentalstudies

    ;alsofoundhighervalueoffi>0.5.Itisbelievedthatlargervaluemaybeinducedbythesefactorssuch

    ;asbulkdiffusion[.thenonuniformpotentialfieldinchemicalvapordepositionc]andshadowing

    ;effect.,etc.Forourcase,thosefactorscanbeexcludedowingtoourfilmdepositiontechnologvand

    ;processparameters,e.g.,bulkdiffusionmechanismcanbeexcludedduetothefactthatourfilmswas

    ;depositedatlowerTs/Tmandthuscontrolledbylowadatommobility:shadowingeffectisalso

    ;impossibleowingtotherotationofoursubstrateholderduringthefilmdeposition.Therefore,basedon

    ;theabovediscussionaboutthefilmsurfaceroughness,itisexpectedthatthelarger8valuefortheTa

    ;filmdepositedathigherUbarisesfromtheionimpingingeffect.Becauseofthiseffect.thepreferentia1

    ;resputteringoccursandthustheheightdifferenceofgrainsongrowingsurfaceincreasessignificantly.It

    ;canprovideanadditionalrougheningmechanismforsurfaceevolution,leadingtoalarger8va1ue.

    ;4Conclusions

    ;InthispaperTathinfilmswithdifferentthicknessesweredepositedbyradiofrequencymagnetron

    ;sputteringatdifferentdepositiontemperature(T.)andbiasvoltage(Ub).Wehavestudiedthefilm

    ;surfaceroughnessanditsdynamicevolutionbehavior.TheresultsshowthatsurfaceroughnessRand

    ;dynamicexponentdecreasesgraduallywithincreasingTfrom300Kto600K. ;Thisarisesfromthe

    ;enhancementofsurfacediffusionwithincreasingT..WhenUbincreasesfrom0Vto

    50V.the

    ;enhancementinducesthedecreaseofbothR.andHowever,forthefilmsdepositedathigherUb>

    ;

    ;5OV,Rand

    steeplyincreases,especiallyp>0.5inthiscase,whicharisesfromthepreferentia1re

    ;sputteringinducedbyionimpingingeffect.’

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