MicroelectroniCEngineering88(2011)2000-2003

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MicroelectronicEngineering

FISEVIERjournaIhomepage:www・elsevier,com/Iocate/mee

Developmentofcoherentscatterometrymicroscope

HirooKinoshitaa'c'*,TetsuoHaradaa'c,MasatoNakasUjia'c,YutakaNagatab，c,TakeoWatanabea,caUnive応ityQfHyqgo,mbomtolyqfAdwmcedS℃ie"cE〔md泥cfmoIQgWbrIndusny,1-1-2KOutOKtImjgouriAko弓gun,HyOgoP7Ef678-1205,ﾉﾛPqnbRike〃2-1HimsawqWtIko,SditqmqP7Ef351-0198,J《Ipan

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ARTICLEINFO ABSTRACT

ArtidehiStD1y：

Availableonlinel2FebruaIy2011

KEywordS：EUVL

DefEctinspectionCDmeasurement

Mask

HighharmoniclasersourEe

AnewmaskinspectionsystemfbrEUVLisbeingdeveloped・Theresolutionofpreviouslydevelopedacti-nicinspectionsystems,whichemployIZPorSchwarzschildoptics,islimitedto60nm､Thispromptedustodevelopanewunorthodoxmaskinspectionsystem：alenslessmicroscopeⅧthacoherentlightsource・ThissystemcandetectdefEctsonlyafewnanometerswide,anditenablesCDmeasurementswitha3ぴaccuracyofO32nm．

◎2011ElsevierB.V・Allrightsreselved．

1.Intmduction

Acriticalissueinextremeultravioletlithography,whichisex-

pectedtobeusedfbrtheproductionofsemiconductordevicesatthe32-nmnode,isthefabricationofdefect-freemasks・AnEUVL

maskconsistsofanabsorberpattemandamultilayeronaglasssubstrateAMoSimultilayerexhibitsahighreflectivityof70％attheworkingwavelength(13.5,m)ofEUVlithography,AccordingtothelTRSI11,defEctsmustbelessthan20nmwideatthe32-nmnode・EUVLmaskshavetwotypesofdefects：amplitude

defEcts，whichareeitherparticlesononeofthelayersofthe

multilayerorflawsinthemultilayer；andphasedefEcts,whicharecreatedwhenthemultilayerisdepositedoverabumporpit

ontheglasssubstrate･

WehavedevelopedanEUVmicroscopethatemploysSchwarzs-childopticsandanX-rayzoomingtubeI2-8landhaveinstalleditattheNewSUBARUsynchrotronfacility､IthasahighNAofO､3,amagnificationof30×，andalaIgefieldwithadiameterof1．5mm・TheX-rayzoomingtubehaselectromagneticlenses・ItmagnifiesapmjectedmaskimagebylO-200×;sothetotalmagni‐ficationofthemicroscopeis300-6000×・ThissystemenablesobservationoffinishedmaskpattemslessthanlOOnminsizeandpit-typephasedefEctslessthan20nmwide・However,whenareflectiveobjectiveisused,thefigureoferrorofthemirrorsandthealignmentaccuracyoftheopticsmustbeexceptionally

＊Correspondingauthorat:UniversityofHyogo,IaboratoryofAdvancedScienceandTeChnologyfbrlndustry，1-1-2KoutoKamigouriAko-gun，HyogoPref678-1205,Japan､泥1.:＋81791582546;fax:＋81791582504．

E-mqiIqddress:kinosita@lasti・u-hyogo､acjp(H､Kinoshita)．

0167-9317/$‐seefmntmatter◎2011ElsevierB.V・AllrightsreseIved・doi:10.10161j,mee,2011.02.060

high・ThismakesitverydifYiculttodesignandfabricatereflectiveopticswithahighNAfbrEUVlight・

Thus,anewinspectionmethodthatdoesnotemployaconven-tionalobjectiveisbeingdevelopedfbrtheinspectionofEUVLmasksfbrthehp-22-nmnode・Itshouldbeabletodetectpattemdefectslessthan20nmwideandmeasuretheCDtoanaccuracy

oflessthan0．01，m・ThesystemisbasedonX-raydiffraction

microscopyandconsistsofacoherent13.5-nmsource，amaskandmaskstage,andanEUVcharge-coupled-device(CCD)camera・ItrequiresnoobjectiveandusesonlycoherentEUVlight・Thelightsourceisahigh-harmonic-generatio、(HHG)beamwithawave‐lengthof13．5nmproducedbyintensefemtosecondlaserpulsesI9,101.

2.Experiments

Thecoherentscatterometrymicroscope(CSM)wearedevelop‐

ing(Fig.1)consistsofanHHGEUVsource,amaskstage,anX-rayCCDcamera,andacomputingsystem・Thissystemprovidesaberra-tion-free,diffraction-limitedimagingwithahighNAbyusingthe

cameratorecordcoherentEUVlightdiffractedfromamaskI111･

WithanimagingsetupbasedonFraunhofErdiffraction，theobjectivecollectsbothphaseandamplitudeinfbrmationfromasample・Incontrast，theCSMrecordsonlydiffractionintensity；andthustheimagesitproducescontainonlyamplitudeinfbrma-tion・ThemissingphaseinfOrmationisretrievedbyusingahybridinput-output(HIO)algorithm[12-14],whichiterativelycalculatestheFouriertransfbrmandtheinverseFouriertransfbrm,subjectto

constraints・Thisenablesacompleteimageofasampletobereconstructed．

H・KinosI1itqetqI./MicroeIec"OnicE唾neemlg88(20刀ﾉ2000-2003 2001

蕊議慰

CSM

Coherent

Source(13.5-nmHHG）

PinhoIe

X－rayCCD

CompLIting

systenlGasceIlfbrionization

I monochromatizesthebeam・ThepinholeprovidesaspatialcoherencelargeenoughfbrobservationswiththeCSMNext，a

concavesphericalmirrorreflectsthebeam（incidentangle：3｡）

①

"

/＝雲琴雲凋 LMonochromatoI。

6025XYStage

Vacu而而1泊illber

59-orderEUVIight

Fig､1．Comgurationofcoherentscatterometrymlcroscope．

Twoorfburcopiesofthesamepattemareusuallymadeonamask､Amaskinspectionsystemcomparestwoofthemtodeter－mlnewhetherornottheycontainanydefEcts、

WithFraunhoferdiffraction,thediffractionimageofarepeatedpattemisdeterminedbythepitchofthepattem・Forthisreason，thepattemwidthisestimatedfromtheratiooftheintensitiesof

theOth-orderand±1st宮orderdiffractedlight、Thecriticaldimension(CD)requiresanaccuracyoflessthan

26nmfbrthe32-nmnode[11.Toachievethatlevelofaccuracy，itisnecessarytobeabletoprecise1ydeterminethelinewidthofamaskpattem、Thus，at-wavelengthobservationwithanEUVmicroscopeisessentialfbrestimatingtheactinicCDoftherenec-tionprofile．

図

3.Resultsanddiscussion

ToexaminethefEasibiliwofdefEctinspectionandCDmeasure-mentwiththeCSM,theCSMwasinstalledontheBL-3Cbeamline

oftheNewSUBARUsynchrotronfacility,whichhasabending-mag-netsource

Figs､2and3showaschematicandaphotograph,respectively，oftheCSMattheendstationoftheBL-3CTheopticalpathintheCSMchamberbeginswitha5-mm-diameterpinholeanda200-nm-thickZrfilter,whichreducesthebeamdiameterandpartially

Fig.3．PhotographofCSM．

hp88nm

Fig､4．DetectionimageofundersizedefEct．

CSMCCDImage

L1s1orderl．刈ぴhorderl |÷1割order｜

一汐

300hm

Back-

iIIuminated

CCDcameraPinhoIc

,/Undersizedefect

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CD－SEMimage(“↓1m）MC/Si

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Fig2･SchematicdiagramofCSMinNewSUBARU．

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AcoherentscatterometrymicroscopeisbeingdevelopedfbrthedefEctinspectionandCDmeasurementof22-nm-nodeEUVmasks、

AnundersizedefEctinaline-and‐spacepattemwasclearlyob-served；andtheCDofaperiodicL＆Spattemwasaccuratelymea-sured・The3ぴCDaccuracyisO､32，m，whichsatisfIesthelTRS

specificationsfbrthehp-22-nmnode・Furthermore，a13.5-nm

HHGsourcebasedonacommercial30-fSlasersystem（SpectraPhysics)hasalreadybeenbuilt,ExperlmentalresultsobtainedwiththissourcewillbereportedinthenearfUture

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(a）SEMimage （b）CSMimage

Fig､5．Exampleofreconstructedimageof28-nm-nodebitlinemaskpattem．

andElplanarmirrorreflectsit(incidentangle:39｡)ontoanEUV

maskThetwomirrorsarecoatedwith40pairsofMoSilayers，whichhaveElpeakreflectiviwof43％at入＝13．4，mand52％at

ﾉl＝13．5，m.TheZrfilterandthethreeMoSimultilayersofthebranchingmirrorandthetwomirrorsoftheCSMmonochromatize

thewhitelight,yieldingalargetemporalcoherence、Fig.4showsdefEctinspectionresultsfbranundersizedefect

(width:30，m)inanhp-88-nmline-and-spacepattemonamask：

(a)CSMCCDimage(diffTactionpattern)and(b)CD-SEMimage・Inthediffractionpattem,thiswpeofdefEctappearsasalmeperpen-diculartotheL8zSpattem・

Fig.5showsdefEctinspectionresultsfbranhp-112-nmbitlinemaSkpattemobtainedwith(a)anSEMand(b)theCSM､TheHIO

algorithmfaithfilllyreconstructsthepattem・Fromthisimage，thedefEctresolutionwasestimatedtobelessthan30nm・

WhentheCSMisusedtoestimatetheCD,theresultsaccuratelyrenecttheshadowmgoftheabsorberpattembecausetheangleofincidencefbranEUVmaskis6o,whichisthesameasthatfbrtwo

alphaEUVexposuretools,theADT(ASML)andtheEUV1(Nikon)．

Fig.6showsresultsfbrCDmeasurementsofamaskfbrthehp-32-nmnodethatwasfabricatedattheUniversiwofHyogo・Thewidthofspacesvariesfroml28tol80nm・Thesevaluesinclude

theeffEctsofthevariationinilluminationintensityduringthemeasurements・Aftercompensationfbrthisvariatio､,theresults

arelinear,Acomparisonofvaluesfbrthehorizontalandvertical

directionsrevealedanalmostl8-nmdiffErenceduetoShadowing・Thisagreeswellwiththetheoreticalvaluefbranabsorberthick-nessof70nm・

Fig.7showsrecentresultsobtainedwith13.5-nmHHGpro＝ducedusiI1g30-fSlaserpulsesfromacommerciall-kHzTi:sap-phirelasersystem(SpectraPhysics)withalasingwavelengthof800nmandanoutputpowerof6W・Theresultsarebetterthan

anticipated,TheaverageintensityofthesourceislOOOtimeshigh－erthanthatoftheBL-3beamline．

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160

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20000

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C医SEMSpaceWidth(nm）

Fig.6．CDmeasurementresultsfbrCSMandCD-SEM．

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HHGspectlum

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59th(13.5nm）

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Fig､7．HHGintensiwspectrum．

HKnloShimetqL/MiCmeIectmniCEnginee而ng88a011）2000-2003 2003

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