Epitaxial growth of Al–Cr–N thin films on MgO(111)

Coatings CrAlN

ThinSolidFilms517(2008)598–602

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ThinSolidFilms

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EpitaxialgrowthofAl–Cr–Nthin lmsonMgO(111)

H.Willmanna,b, ,M.Beckersb,J.Birchb,P.H.Mayrhoferc,C.Mittererc,L.Hultmanb

abc

MaterialsCenterLeoben,8700Leoben,Austria

IFMMaterialPhysics,DivisionofThinFilmPhysics,LinköpingUniversity,58183Linköping,SwedenDepartmentofPhysicalMetallurgyandMaterialsTesting,UniversityofLeoben,8700Leoben,Austria

articleinfoabstract

CubicrocksaltstructureAl0.60Cr0.40NandAl0.68Cr0.32N lmsofdifferentthicknessesweregrownepitaxiallyontoMgO(111)substratesbyreactiveunbalancedmagnetronsputteringat500°C.RutherfordbackscatteringspectroscopyrevealsstoichiometricnitrideswithAl/Crratiosclosetotheonesoftheusedcompoundtargetsof60/40and70/30.HighresolutionX-raydiffractionprovesepitaxialgrowthoverthewhole lmthicknessuptothicknessesof～1.8μm.ReciprocalspacemapsandselectedareaelectrondiffractionshowthattheAlxCr1 xN lmsgrowfullyrelaxed.Scanningandtransmissionelectronmicroscopyimagingrevealscolumnarmicrostructureswithcolumnwidthsbetween12–16nmand{001}surfacefacetingonindividualcolumns.Thefullyrelaxedgrowthandthecolumnarstructurecanbeattributedtolimitedad-atommobilityontheinitialAlxCr1 xN(111)growthsurface.

©2008ElsevierB.V.Allrightsreserved.

Articlehistory:

Received22June2007

Receivedinrevisedform27May2008Accepted6July2008

Availableonline10July2008Keywords:AlCrNCrAlN

CoherencelengthMosaicity

WurtzitestructureEpitaxy

1.Introduction

Ternarynitridesareusedinawiderangeofapplicationsfromsemiconductorstoprotectivehardcoatings.ThebinarynitridesAlNandCrNwithwurtziteandrocksaltcrystallographicstructures,respectively,exhibitverylowsolubilityforeachotherinthethermo-dynamicequilibrium,evenat1000°C[1].Thismiscibilitygapcan,however,beovercomebyphysicalvapordeposition(PVD)techniqueswiththeformationofmetastableAlxCr1 xNsolidsolutionsincrystal-lographicmodi cationsofthecorrespondingbinarysystems,whereAlandCratomsaresubstitutingeachother[2–9].Dependingonthedesiredapplication,thin lmsynthesisintheAlN–CrNsystemisapproachedfromtwosidesofthepseudobinaryphasediagram.Startingfromhexagonal(wurtzite,B4)AlN,substitutionbyCrleadstowurtziteAlxCr1 xN(w–AlxCr1 xN)whichisappliedforbandgapengineeringandtheproductionofdilutemagneticsemiconductorsinthe eldofspintronics[10–15].Viceversa,alloyingcubic(rocksalt,B1)CrNwithAlresultsinrocksaltstructureAlxCr1 xN(c–AlxCr1 xN)withimprovedmechanicalproperties[2–6].Thisopensupopportu-nitiesforcuttingapplications,inparticularforAlcontentsclosetothemaximumsupersaturationfortheB1/B4transitioninPVD lmsatx=0.7 0.75[2–5,16].

Bothbinarysystems,CrNandAlN,havebeengrownasepitaxialsinglelayersintheirnativeB1andB4structuremodi cations,respectively[17,18].However,uptodate,onlypolycrystallineternaryc–AlxCr1 xNthin lmshavebeenstudied.Herewepresentresultsonepitaxialc–AlxCr1 xN lmswithcompositionsdeepwithinthemiscibilitygap.Theyweredepositedbyreactiveunbalancedmagne-tronsputteringontosingle-crystalMgO(111)templates.MgOalsocrystallizesintherocksaltstructureandexhibitsonlyasmalllatticemismatchof+2.5%fortheinvestigatedc–AlxCr1 xN lmswith0.60bxb0.68.

2.Experimentaldetails

All lmsweregrowninahigh-vacuumdepositionsystemequippedwithtwoplanarunbalancedmagnetronstiltedby25°tothesubstratenormal.Adetaileddescriptionofthesystemisgivenelsewhere[19,20].ForthedepositionoftheAlxCr1 xN lms,onlyonemagnetronwasused,mountedwithAl/Crcompoundtargetswithatomratiosof60/40or70/30,respectively.Thesubstrateswerepositionedonarotatingmulti-specimensubstrateholder,symme-tricallyarounditsrotationaxistoachieveuniform lmproperties.ThedistancebetweenthesubstratesandtheØ75mmtargetwas92mm.Thebasepressureofthechamberwas2.67×10 4Pa(2×10 6Torr),achievedusinga510l s 1turbomolecularpump.ThereactivesputteringwascarriedoutinapureN2(99.999%)atmosphereatapressureof0.4Pa(3×10 3Torr),measuredbyacapacitancemanometer.

Correspondingauthor.MaterialCenterLeobenForschungGmbH,Roseggerstraβe12,8700Leoben,Austria.Tel.:+4338424024237;fax:+4338424024202.

E-mailaddresses:herwi@ifm.liu.se(H.Willmann),jens.birch@ifm.liu.se(J.

Birch).0040-6090/$–seefrontmatter©2008ElsevierB.V.Allrightsreserved.doi:

10.1016/j.tsf.2008.07.003

Coatings CrAlN

H.Willmannetal./ThinSolidFilms517(2008)598–602599

PolishedMgO(111)wafersof10×10×0.5mm3sizewithanaverageroughness(Ra)of0.114nmwereusedastemplatesforthe lms.Additionally,equallysizedpyrolyticgraphitesubstrateswereusedfordetailedcompositionalevaluation.Priortodeposition,theMgO(111)substratesweredegassedandcleanedbyholding～750°Cfor60min.Duringdeposition,thesubstrateswerekeptataconstanttemperatureof500°C,measuredbyacalibratedpyrometeronanAlxCr1 xNcoateddummysubstrate.Aftercoolingdowntoroomtemperaturethesampleswereremovedfromthedepositionchamberviaaloadlocksystem.

Themagnetronwasoperatedat0.75Ausingaconstantcurrentregulation,resultinginsteadydischargevoltagesof370Vand330Vforthe60/40and70/30target,respectively.Inordertoprovidelow-energyionbombardmentduringgrowth,asubstratebiasof 40Vwasapplied.Beforestartingthedeposition,thetargetwasplasmaetchedfor3minwiththesubstratesprotectedbyashutter.Thein uenceofthe lmthicknessonthedevelopedmicrostructurewasaddressedbysamplesgrownwithdifferentdepositiontimes(10,60,and180min)tocover lmthicknessesfrombelow100tomorethan1000nm.

Thechemicalcompositionofthe lmswasanalyzedbyRutherfordbackscatteringspectroscopy(RBS)withabeamof2MeV4He+ionsimpingingatanincidenceangleof7°withrespecttothesurfacenormal,andbeingdetectedatascatteringangleof167°.TherecordedspectrawereevaluatedusingtheSIMNRAcode[21].Forimprovednitrogenquanti cation,also lmsdepositedontopyrolyticgraphiteincorrespondingbatchesweremeasured,sothatthemaximumerrorfornitrogenis~2at.%,whileitis~1at.%fortheheavierAlandCr.

Structuralcharacterizationbyhigh-resolutionsymmetricX-raydiffraction(HR-XRD),rockingcurves,andreciprocalspacemaps(RSM)wasperformedusingaPhilipsX'pertMRDtripleaxisdiffractometerequippedwithaCulab-source.Theusedopticswereaparabolicgradedmultilayermirrorcollimator,followedbyachannel-cut2-bounceGe(220)monochromatorontheprimarysideandanasym-metric2-bounceGe(220)analyzercrystalonthesecondarysideresultinginCu–KαmonochromacyofΔλ/λ=4.183×10 4.SymmetricandasymmetricRSMswererecordedaroundtheMgO111andMgO113reciprocallatticepoints,respectively.In-planeandout-of-planelatticespacingswereevaluatedfrombothRSMs,withtheasymmetric113RSMbeingprojectedontothe[111]and[110]crystallographicaxes.AzimuthalXRDscansrecordedonthe lmandsubstrate002re ectionsweremeasuredwithanopendetectoratatiltof54.7°withrespecttothediffractionplane(Ψ-tilt).

AZeissEVO50scanningelectronmicroscope(SEM)equippedwithatungsten lamentwasusedtostudythedevelopingmorphologybyplan-viewandfracturecross-sectioninvestigationsindependenceofthe lmthickness.

Cross-sectionaltransmissionelectronmicroscopy(TEM)wasper-formedonaTecnaiG2TF20UTmicroscopeoperatingat200keVfordetailedstudiesofthemicrostructure.Thespecimenswerepreparedbymechanicalgrindingandpolishingbeforedimplinganda nalionmillingstepwithAr-ionsinaGatanprecisionionpolishingsystem.3.Resultsanddiscussion

TheRBSinvestigationsrevealstoichiometricnitrideswithan(Al+Cr)/Nratioof1.00forall lms.TheAl/Crratiosarehomogeneousoverthewhole lmthicknessandclosetotheonesofthecorrespondingtargets,withchemicalcompositionsofAl0.60Cr0.40NandAl0.68Cr0.32Nforthe60/40and70/30targets.AssumingbulkatomicCrNdensity,the ttedRBSspectrayielddepositionratesof9.7and4.9nm/minforthe60/40and70/30targets,respectively.Thedepositiontimesof10,60,and180minresultintotalthicknessesof100,580,and1750nmfortheAl0.60Cr0.40Nand50,300,and900nmfortheAl0.68Cr0.32N lms.Despiteidenticaldepositioncurrents,thedifferentcompositionaffectsthetargetpoisoningduringthereactivesputtering.ThemorelikelypoisoningoftheAlresultsinalowerdischargevoltage,hencea

lowertotalpowerandthereforesigni cantlyreduceddepositionrateforthe70/30setup.

OverviewconventionalXRD2θ-ωscansfrom25–85°indicatesingle-phasec–AlxCr1 xN lms,withcorrespondingMgOandc–AlxCr1 xN

peaks.Now–AlxCr1 xNphasewasobserved,despiterelationshipof(111)||(0001) thepotential

epitaxial

MgOw-AlCrNand[110]MgO||[1210]w-AlCrN.HR-XRDwasusedtoinvestigatetheregion34°≤2θ≤50°,coveringthec–AlxCr1 xNandMgO111and002peakpositions,respectively.Fig.1aandcshowthecorresponding2θ-ωscansofc–Al0.60Cr0.40Nandc–Al0.68Cr0.32N lmsfordifferentthicknesses.Sampleswith180mindepositiontimearecomparableinpeakpositionandintensitytothecorresponding60minsamplesandforreasonsofclaritynotdisplayedinFig.1.Thepeakcenterpositionslieat2θvaluesof～36.94°forMgO111,at～37.83°forc–Al0.60Cr0.40N111,andat～38.05°forc–Al0.68Cr0.32N111.Onlynegligibletracesofac–Al0.60Cr0.40N002peakat～43.5°canbeobserved.

Theout-of-planelatticeparameterscalculatedfromthevaluesaboveresultin4.211ÅforMgO,whichcorrespondswelltotheliteraturevalueof4.211Å[22].Thec–AlxCr1 xNlatticeparametersdependontheAlcontentasshownforpolycrystallinecoatings[3–6,8].Here,thecalculatedlatticeparametersare4.116ÅfortheAl0.60Cr0.40Nand4.093ÅfortheAl0.68Cr0.32N lms,whichareingoodagreementwithreportedvalues.ViatheScherrerformula(ξ⊥=λ/(2Γ2θ ωcosθ))thepeakfullwidthsathalfmaximum(FWHM)in2θ-ωscandirection(Γ2θ ω)canbeusedasameasurefortheverticalsizeofcoherentlyscatteringvolumesξ⊥[17,23–25].Smallervaluesindicatefewerdefects,and/oralargercrystalsizealongthegrowthdirection.TheΓ2θ ωvaluesforthebulkMgOsinglecrystalsubstratesarelikelytobesmallerincomparisontotheΓ2θ ωvaluesofthe lms,whosemaximumverticalsizeofcoherentlyscatteringvolumesislimitedbythe lmthickness.Disregardingthein uenceofmicrostrainthevaluesareξ⊥=120nm(Γ2θ ω=0.08°)forthe580nmand1750nmthickAl0.60Cr0.40N lmsand54nm(Γ2θ ω=0.17°)forthe100nmthickAl0.60Cr0.40N.Forthe300nmand900nmthickAl0.68Cr0.32N lmsξ⊥=85nm(Γ2θ ω=0.11°),andξ⊥=38nm(Γ2θ ω=0.24°)forthe50

nm

Fig.1.HR-XRDscansofAl0.60Cr0.40N(a)andAl0.68Cr0.32N lms(c)withthecorrespondingrockingcurves(b)and(d),respectively,recordedatthepositionofmaximum2θintensity.ThetheoreticalpositionsforMgO[22]areindicatedwithatriangle,arangeforc–AlxCr1 xNisindicatedwithboarderscorrespondingtoCrN[17]andc–AlN[22].

Coatings CrAlN

600H.Willmannetal./ThinSolidFilms517(2008)598–602

Fig.2.AzimuthalXRDscansforΨ=54.7°onthe002re ectionsofepitaxialAl0.60Cr0.40N(a)andAl0.68Cr0.32N lms(b)aswellasfromtheMgO(111)substrate

(c).

Al0.68Cr0.32Nthick lmisobtained.Thetrendofdecreasingξ⊥/thicknessratiowithincreasing lmthicknessisduetogrowingin uenceoftheinstrumentalbroadening.Theξ⊥valuesforthethicker lms(depositiontime60and180min),arewithintherangeofthecalculatedξ⊥valuesforthebulksingle-crystalMgOsubstratevalueof150nm(Γ2θ ω=0.04°).Itcanthereforebeconcludedthatthesizeofcoherentlyscatteringvolumeslieswithintherangeofthe lmthicknessandthatcontributionofstructuraldefaults,andhencemicrostrainisnegligible.Thisinturnjusti estheuseofthesimpleScherrerequationtoevaluateξ⊥.

Fig.1bandddisplayrockingcurves(ω-scans)overthe111c–AlxCr1 xN lmpeaksthatcorrespondtothe2θ-ωscansofFig.1aandc.AbsolutevaluesfortheFWHMΓωofthethickest lmsareΓω=0.87°fortheAl0.60Cr0.40N111peakandΓω=1.11°fortheAl0.68Cr0.32N111peak.TheseΓωvaluesarehighercomparedtopreviouslyreportedvaluesforepitaxiallayersofrocksaltstructurebinarynitrideswithcomparablelatticemismatch,like0.14°forTiN[23],0.15°forCrN[17],or0.6°forTaN[26].Alsomaterialsthatexhibitsigni cantlylargerlatticemismatchestoMgOlikeHfN(Δa～7.5%)andScN(Δa～7%)showsmallerΓωof0.58°[24]

and0.87°[25],respectively.Γωisamongotherfactorsin uencedbythelateralsizeofcoherentlyscatteringvolumesξ||,strainduetodislocationsandmosaicity[27].RockingcurvesontheAl1 xCrxN222peaks,notshown,revealthatinreciprocalspacetheFWHMinqxdirectionΓqxforAl1 xCrxN111issmallerthanforAl1 xCrxN222.Thisimpliesacontributionofξ||andmosaicity,sinceforpurelateralcoherencelengthin uenceΓqx111andΓqx222shouldbethesameaccordingtothemosaicblockmodelofepitaxial lms[28].

ThehigherΓωvaluesofthepresentc–AlxCr1 xN lmscanhencebeexplainedbyeitherlowerlateralcoherencelengthorincreasedstrainandmosaicity.Thelatteroneismainlylinkedtotheformationofdislocations,andhencelattice-mismatchdependent.Thereforedifferent lmmaterialscannotdirectlybecompared.Evenforthesame lmmaterialareducedlateralcoherencelengthcanbeinducedbythechoiceofthesubstrate.TheMgO(111)templatesusedforepitaxialgrowthinthisworkforexampleprovidealessstableheteropolarsurfaceresultinginhigherdefectdensitiescomparedtothelowenergyMgO(001)surfaceusedintheotherstudies[17,23–26].Also,ac–AlxCr1 xN(111)growthplaneprovidesthreebackbonds,whichdrasticallydecreasesthead-atomsurfacemobility.Thisin uenceisfurtheraggravatedbythelowersubstratetemperatureemployedinthepresentstudy.

TheepitaxialrelationsbetweentheMgOsubstrateandtheAl0.60Cr0.40NandAl0.68Cr0.32N lmswerefurtherinvestigatedby360°azimuthalscansoverthe002peaks(Fig.2).Thescanswereperformedat2θ=44.055°fortheAl0.60Cr0.40N(Fig.2a),44.287°fortheAl0.68Cr0.32Nsample(Fig.2b),and42.930°fortheMgOsubstrate(Fig.2c),andprovethecube-on-cubeepitaxialrelation(111)MgO||(111)c-AlCrNand[110]MgO||[110]c-AlCrNsincethe lmintensitymaximalieatidenticalazimuthalanglesasthe(111)substratepeaks.AdditionaltothethreefoldsubstratepeaksFig.2aandbalsodisplayasecondthreefoldsymmetrywithpeaksofminorintensitiesatanazimuthalshiftof60°.Thesecontributionsareduetotheexistenceofeitherdoublepositioningdomains[29]orstackingfaults/microtwinsonthe(111)planes.However,theirlow0.5%intensityratiotothemainepitaxialpeaksindicatesamarginalquantitythatcanonlybeseenwiththeopendetectorsetupandonthelogarithmicscale.

Fig.3showsRSMsrecordedaroundthe113MgOreciprocallatticepointsfor lmsofbothcompositions,withqzandqxaligned

along

Fig.3.AsymmetricRSMsaroundtheMgO113reciprocallatticepointforepitaxialAl0.60Cr0.40N(a)andAl0.68Cr0.32N lms(b)grownonMgO(111).Theintensitycontoursareprojectedintotheplanewiththeorthogonaldirections[001]and[110].

Coatings CrAlN

H.Willmannetal./ThinSolidFilms517(2008)598–602601

[001]and[110].Themeasuredintensitiesofthe580nmthickAl0.60Cr0.40Nandthe300nmthickAl0.68Cr0.32N lmsandthecorrespondingMgOsubstratesaredisplayedinFig.3aandb,respectively.Thearrowedlinesindicatethedirectionofthereciprocallatticevector.Both lmintensitydistributionsarecenteredonthislinesuggestingfullyrelaxedgrowthduringthedepositionprocess[30,31].Consequently,thecalculatedin-plane(a||)andout-of-plane(a⊥)latticeparametersareidenticalwithintheaccuracyofthemeasure-ment.Absolutevaluesarea||=a⊥=4.211ÅforMgO,a||=4.116anda⊥=4.117ÅforAl0.60Cr0.40N,aswellasa||=4.095anda⊥=4.096ÅforAl0.68Cr0.32N.Thesevaluescorrespondwelltotheresultsfromthe2θ-ωdiffractiondatainFig.1aandc.Differencesinmaximuminten-sitiescanbeexplainedbythelowerthicknessoftheAl0.68Cr0.32NcomparedtotheAl0.60Cr0.40N lm.Also,theintensitydistributionsofthe lmslieessentiallyperpendiculartothereciprocallatticevector,indicatingaminorin uenceofξ||,butmainlybroadeningduetomosaicity.

Inconclusion,theX-rayinvestigationssuggestfullyrelaxedgrowthoftheAl0.60Cr0.40NandAl0.68Cr0.32N lmswiththeverticalsizeofcoherentlyscatteringvolumesextendingoveralmostthefull lmthicknessesof1750nmand900nm,respectively.

Tofurtherevaluatethe lmmicrostructure,SEMimageswereobtainedofwhichFig.4exemplarydisplays(a)thefracturecross-sectionand(b)thetopviewfromthe1750nmthickAl0.60Cr0.40N lm.Thecross-sectionrevealsthefractureoftheMgOsubstratealongthe{001}cleavageplanesandalsoillustratesa brouscolumnarstructureofthe lm,whichhascrackedalongboundariesinbetweenindividualcolumns.ThecolumntipsexhibitgrowthfacetsthatareclearlyvisibleinthetopviewofFig.4b.Thesecubecornershapedsurfacefacetsformedbythree{001}planesaroundthe[111]directionhasbeenreportedinliteraturebeforeforrocksaltstructuresgrownwith(111)texture[32].SEMinvestigationsofAl0.60Cr0.40N lmswithdifferent lmthicknessesrevealedfulldevelopmentofthesefacetsalreadyafter50nm,followedbyasteady-stategrowthconditionwithlittlecompetitionforgrowthbetweenindividualcolumnsasissuggestedalsobytheiruprightboundariesinFig.4a.AreasofbiggerfacetsseeninFig.4bcanberelatedtosurfacedefectsoftheinitialMgOsubstrate[33,34].

Thecolumnarmicrostructureisalsoapparentincross-sectionalTEM(XTEM)asillustratedinFig.5awhichisanoverviewimagefromthe1750nmthickAl0.60Cr0.40N lm.Itcon rmstheHR-XRDresultsthattheverticalsizeofcoherentlyscatteringvolumes–i.e.columns–extendsoverthewhole lmthickness.Fig.5bshowstheinterfaceregionofthe900nmthickAl0.68Cr0.32Nsamplewhichalreadyfeaturesacolumnarstructure.Themagni edviewinFig.5c,however,revealsthatthecolumnswith～12nmareslightlynarrowercomparedtotheAl0.60Cr0.40N lmwith～16nm.ThesecolumnwidthsmatchtheaveragediffusionpathlengthontheAl1 xCrxN(111)surfaceofonly～12nm,calculatedbasedontheapplieddepositionparametersandtheoreticalsurfacebindingenergiesofTiN[35],isostructuraltotheCrNandAl1 xCrxN.AdifferentcolumnwidthforAl0.60Cr0.40Nand

Fig.4.SEMmicrographsoffracturecross-section(a)andtopview(b)ofa1750nmthickAl0.60Cr0.40N lmgrownonMgO(111).

Fig.5.Cross-sectionalTEMmicrographsfromAl0.60Cr0.40N(a)andAl0.68Cr0.32N(b) lmsgrownonMgO(111)withamagni edviewofthecolumnarstructurein(c)andaSAEDspotpatternoftheinterfaceareain

(d).

Al0.68Cr0.32NmaybeattributedtochangedoverallmobilitywithincreasingAlcontent.TakingintoaccounttheaveragelatticeconstantsforMgO(4.211Å)andAl1 xCrxN(4.105Å),thetheoreticaldistancebetweentwodislocationsis～39planespacings,i.e.～12nm

alongthe[11

0]direction.Hence,theaveragediffusionpathlength,parableresultshavebeenobservedfornanocolumnarGaN lmsgrowninalowsurfacemobilityregime[36].Thisagainjusti estheapplicationoftheScherrerformulatocalculateξ⊥.Theinterfaciallatticemismatchbetweenthe lmandtheMgOcanbeaccommodatedbyvoidsatthecolumnarboundaries,whichhavebeendescribedforTiNandNbNepitaxial lmsbefore[37].ThevoidsaredetectableinFig.5casregionsoflowerdensityalongthecolumnsboundaries.Theyresultfromthelimitedadatommobilitycalculatedabove,whichyieldsanon-planargrowthfrontwithsurfacefacetingaccompaniedbyself-shadowingatthe lmsurfacecusps.Fig.5calsoillustratesthateachcolumnisslightlytiltedwithrespecttotheothers.Duetotheirsmalllateralsizethesuperpositionofthesetiltedcrystallinecolumnsinreciprocalspacehasthesameappearanceasatiltofmosaicblocksseparatedbydislocations,hencethisexplainstheintensitydistributionperpendiculartothereciprocallatticevectorintheasymmetricRSMsofFig.3.ThisisalsoonereasonforthebroadeningoftherockingcurvewidthΓωinFig.1.

Fig.5dshowsaselectedareaelectrondiffraction(SAED)pattern,includingtheinterfaceregionoftheAl0.68Cr0.32NsampleandtheMgOsubstrate.Thedistinctspotpatternfurthercon rmsepitaxialcube-on-cuberelationandthefullyrelaxedgrowthmode,sincethepeaksplitsofMgOsubstrateandAl0.68Cr0.32N lm,especiallyseenforhigherorderre ectionslike(402),arealignedtowardsthedirectbeamspot.FromtheXTEManalysisalsotheobtaineddepositionratesfromRBScouldbeveri ed.4.Conclusion

EpitaxialAl0.60Cr0.40NandAl0.68Cr0.32N lmscanbegrownonMgO(111)substratesbyreactiveunbalancedmagnetronsputtering

at

Coatings CrAlN

602H.Willmannetal./ThinSolidFilms517(2008)598–602

adepositiontemperatureof500°C.The lmsgrowintherocksaltstructurewithfullyrelaxedlatticeparametersof～4.116ÅfortheAl0.60Cr0.40Nand～4.093ÅfortheAl0.68Cr0.32Ncomposition.Aself-organized3Dislandgrowthmodewithlowadatommobilityisobserved,resultingin brousepitaxialcolumns.Thecolumnsextendoverthewhole lmthicknessandexhibitthreefold{001}facetsontop.Thelowdiffusionpathlengthofonlyafewnanometerandhencehighnucleationdensityontheinitial(111)surfacede nesthe nalcolumnwidth.Theobserveddifferencesinthecolumnwidthbetween12and16nmdependingonthe lmcompositionarelikelyconnectedtodifferentAlandCradatommobilityonthegrowthsurface.

Acknowledgments

TheauthorsthankF.ErikssonandN.GhafooraswellasF.GiulianiandD.Trinh(IFM—ThinFilmPhysicsDivision,LinköpingUniversity)forsupportregardingthedepositionsystemandtheTEM,respec-tively.TheTandemAcceleratorLabatUppsalaUniversity,SwedenisacknowledgedforRBSbeamtime.TheChristianDopplerLaboratoryforAdvancedHardCoatingsattheUniversityofLeobenandthePlanseeGmbH,Lechbruck,Germany,areacknowledgedforprovidingtargetmaterials.WorkdoneinLeobenwas nancedwithintheframeworkoftheAustrianKplusCompetenceCenterProgram.TheworkdoneinLinköpingwas nancedbytheSwedishResearchCouncil(VR)andtheSwedishFoundationforStrategicResearch(SSF)withintheStrategicResearchCenterMS2EonMaterialsScienceforNanoscaleSurfaceEngineering.References

[1]C.Kunisch,R.Loos,M.Stüber,S.Ulrich,Z.Meta.kd.90(1999)847.

[2]H.Hasegawa,M.Kawate,T.Suzuki,Surf.Coat.Technol.200(2005)2409.

[3]Y.Ide,T.Nakamura,K.Kishitake,in:B.Mishra,C.Yamauchi(Eds.),Second

InternationalConferenceonProcessingMaterialsforProperties,TMS(TheMinerals,Metals&MaterialsSociety,SanFrancisco,2000,p.291.[4]M.Kawate,A.Kimura,T.Suzuki,J.Vac.Sci.Technol.A20(2002)569.

[5]M.Hirai,Y.Ueno,T.Suzuki,W.H.Jiang,C.Grigoriu,K.Yatsui,Jpn.J.Appl.Phys.Part

1—Regul.Pap.ShortNotesRev.Pap.40(2001)1056.

[6]A.E.Reiter,V.H.Der inger,B.Hanselmann,T.Bachmann,B.Sartory,Surf.Coat.

Technol.200(2005)2114.

[7]Y.Makino,Surf.Coat.Technol.193(2005)185.

[8]P.H.Mayrhofer,H.Willmann,A.Reiter,ProceedingsoftheSocietyofVacuum

Coaters49thannualTechnicalConference,Washington,D.C.,042006,p.575.

[9]H.Willmann,P.H.Mayrhofer,P.O.Å.Persson,A.E.Reiter,L.Hultman,C.Mitterer,

Scr.Mater.54(2006)1847.

[10]A.Y.Polyakov,N.B.Smirnov,A.V.Govorkov,R.M.Frazier,J.Y.Liefer,G.T.Thaler,C.R.

Abernathy,S.J.Pearton,J.M.Zavada,Appl.Phys.Lett.85(2004)4067.

[11]R.M.Frazier,G.T.Thaler,B.P.Gila,J.Stapleton,M.E.Overberg,O.R.Abernathy,S.J.

Pearton,F.Ren,J.M.Zavada,J.Electron.Mater.34(2005)365.

[12]D.Kumar,J.Antifakos,M.G.Blamire,Z.H.Barber,Appl.Phys.Lett.84(2004)5004.[13]Q.Wang,A.K.Kandalam,Q.Sun,P.Jena,Phys.Rev.B73(2006)115411.

[14]A.Y.Polyakov,N.B.Smirnov,A.V.Govorkov,R.M.Frazier,J.Y.Liefer,G.T.Thaler,C.R.

Abernathy,S.J.Pearton,J.M.Zavada,J.Vac.Sci.Technol.B22(2004)2758.

[15]S.Y.Wu,H.X.Liu,L.Gu,R.K.Singh,L.Budd,M.vanSchilfgaarde,M.R.McCartney,D.J.

Smith,N.Newman,Appl.Phys.Lett.82(2003)3047.

[16]W.Kalss,A.Reiter,V.Der inger,C.Gey,J.L.Endrino,Int.J.Refract.Met.HardMater.

24(2006)399.

[17]D.Gall,C.S.Shin,T.Spila,M.Odén,M.J.H.Senna,J.E.Greene,I.Petrov,J.Appl.Phys.

91(2002)3589.

[18]J.Birch,S.Tungasmita,V.Darakchieva,in:T.Paskova,B.Monemar(Eds.),Vacuum

ScienceandTechnology:Nitridesasseenbythetechnology,ResearchSignpost,Kerala,2002,p.421.

[19]C.Engström,T.Berlind,J.Birch,L.Hultman,I.P.Ivanov,S.R.Kirkpatrick,S.Rohde,

Vacuum56(2000)107.

[20]F.Eriksson,G.A.Johansson,H.M.Hertz,J.Birch,Opt.Eng.41(2002)2903.

[21]M.Mayer,TechnicalReport,Max-Planck-InstitutfürPlasmaphysik,Garching,

Germany,1997.

[22]PowderDiffractionFile(Card45-0946forMgO,Card46-1200forc-AlN),

InternationalCentreforDiffractionData,ICDD-JCPDS,1998.

[23]C.S.Shin,S.Rudenja,D.Gall,N.Hellgren,T.Y.Lee,I.Petrov,J.E.Greene,J.Appl.Phys.

95(2004)356.

[24]H.S.Seo,T.Y.Lee,J.G.Wen,I.Petrov,J.E.Greene,D.Gall,J.Appl.Phys.96(2004)878.[25]D.Gall,I.Petrov,N.Hellgren,L.Hultman,J.E.Sundgren,J.E.Greene,J.Appl.Phys.84

(1998)6034.

[26]C.S.Shin,D.Gall,P.Desjardins,A.Vailionis,H.Kim,I.Petrov,J.E.Greene,M.Odén,

Appl.Phys.Lett.75(1999)3808.

[27]J.E.Ayers,J.Cryst.Growth135(1994)71.

[28]R.Chierchia,T.Böttcher,H.Heinke,S.Einfeldt,S.Figge,D.Hommel,J.Appl.Phys.93

(2003)8918.

[29]Y.Xin,P.D.Brown,C.J.Humphreys,T.S.Cheng,C.T.Foxon,Appl.Phys.Lett.70(1997)

1308.

[30]P.v.d.Sluis,J.Phys.D:Appl.Phys.26(1993)A188.

[31]M.Birkholz,ThinFilmAnalysisbyX-RayScattering,Wiley-VCHVerlagGmbH&Co.

KGaA,Weinheim,2006.

[32]B.Warot,E.Snoeck,J.C.Ousset,M.J.Casanove,S.Dubourg,J.F.Bobo,Appl.Surf.Sci.

188(2002)151.

[33]P.W.Tasker,J.Phys.CSolidState12(1979)4977.

[34]L.E.Toth,TransitionMetalCarbidesandNitrides,AcademicPress,Inc.,NewYork,

1971.

[35]D.Gall,S.Kodambaka,M.A.Wall,I.Petrov,J.E.Greene,J.Appl.Phys.93(2003)

9086.

[36]K.L.Averett,J.E.VanNostrand,J.D.Albrecht,Y.S.Chen,C.C.Yang,J.Vac.Sci.Technol.

B25(2007)964.

[37]L.Hultman,L.R.Wallenberg,M.Shinn,S.A.Barnett,J.Vac.Sci.Technol.A10(1992)

1618.

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