光学薄膜的堆积密度及密度均匀性的分析与计算最全word资料.docx
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光学薄膜的堆积密度及密度均匀性的分析与计算最全word资料.docx
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光学薄膜的堆积密度及密度均匀性的分析与计算最全word资料
AnAnalysisandCalculationoftheOpticalThinFilmPackingDensityandDensityUniformity
TANGQi KIKUCHIKazuo
(ShincronCo.,Ltd,Tokyo14028540
Abstract:
Thepackingdensityofdepositedopticalthinfilmsisusuallycal2
culatedbythevariationofindexvaluesinvacuumandinatmospherichumidity.
InourIADexperiments,wefoundthatthepackingdensityofsomefilmscalcu2
latedbythismethodislargerthan1.0.Thismeansitsstructureisdenserthan
thatofamorphousnature.Thereasonforthisisithasastrongcompressive
stressinfilm.Wealsofoundthatthewavelengthshiftsofsomefilmsdeposited
byIADdon′thaveadependenceuponthepackingdensitybecausetheyhavedif2
ferentmicrostructuraluniformityunderdifferentprocessparameters
.Thepack2ingdensityanddensityuniformitycoefficientdepositedbyEBandIADwithdif2
ferentprocessparametersarecalculatedandanalyzed.Themicrostructuresof
thefilmwereinvestigatedbymeansofSEM.
KeyWords:
OpticalThinFilm,PackingDensity,DensityUniformity,Mi2
crostructure.
光学薄膜的堆积密度及密度均匀性的分析与计算
唐 骐 菊池和夫
(新科隆株式会社,东京 14028540
摘要:
光学薄膜的堆积密度通常是利用薄膜在真空及大气中折射率的变化来计算,在IAD实验中,我们发现有些薄膜的堆积密度大于110,这意味着薄膜的密度比自然界中的材料密度还要密积,原因是薄膜具有较大的内压应力,我们还发现了薄膜的波漂不依从于堆积密度。
这是因为它们在不同的蒸发条件下具有不同的密度均匀性,在用EB及不同条件的IAD的情况下,我们计算并分析了堆积密度及密度均匀系数,并用SEM观察了薄膜的微结构。
关键词:
光学薄膜,堆积密度,密度均匀性,微结构。
1 Introduction
Awatersorptionphenomenoninopticalcoatingshasbeenunderstood.Thepackingden2sityofdepositedopticalcoatingsisgreatlyaffectedbythemicrostructure.Sinceion2beamtechniqueswereappliedinopticalcoatings,adensefilmcanbeobtainedtoimprovethe
第21卷 第425期
1999年10月 光 学 仪 器OPTICALINSTRUMENTSVol.21,No.425 October,1999
environmentalstability.Todistinguishtheseproperties,thepackingdensityPisusually
adopted
[1,2]
.Thedepositedopticalthinfilmcanbedivideintotwoparts,one,theimpenetra2
bleskeleton(solidpartofthefilmconsistingofthedepositedfilmmaterial,andtheotherthepore(voidpart.Then,thepackingdensityisdefinedas:
P=(volumeofthesolidpartofthefilm(totalvolumeofthefilm1(1
Thetheoryandresultsofexperimentshowthefollowingmodel:
Inthefilmgrowthdur2ingdepositionwithouttheion2beambombardment,smallstructuralnucleisuchasthenucle2usforlatergrowingdendritesareformedatfirstandthenthevoidsappearinthefilmsa2mongthesenucleiofappropriatesize.Duringfurtherfilmthicknessgrowth,thestructuralu2
nitstendtoclusterintolargergroups
.Thevoidsinthegroupareclosed,suchthatlargervoidsappearamongthegroupsratherthanthedendrites,andthesegroupsofdendritesform
theobservedcolumns
.Inthefilmgrowthduringdepositionwiththeion2beambombardment,sincebombardmentoftheenergeticionactsasthedisplacementeffectandthepromotionef2fectofmigrationforadherentatomsormolecules,thefilmmicrostructurewillbeimproved,andthepackingdensitywillbehigher.
However,thepackingdensitycalculatedbyequation(1isdifficulttosolve.Incaseoftheopticalthinfilmsignoringtheabsorption,itisusuallycalculatedbythefilmindexinvac2uumandinatmospherichumidity.Inthisexperiment,wefoundthatsomefilmsdepositedbyIADarewithapackingdensitylargerthan1.0,andsomedonotshowadependenceofwave2lengthshiftuponpackingdensity.Thesephenomenawillbeexplained,andthenewdefini2tionsofrelativepackingdensityanddensityuniformitywillbeintroducedinthispaper.2 AnAnalysisandCalculationoftheOpticalThinFilmPackingDensity
Toobtainthevalueofthepackingdensity,twomethodshavebeenintroduced[1].Oneisbyascanningspectrometer,andtheotherbyaquartzcrystalmicrobalance.Thescanningspectrometerhasbeenextensivelyinuserecently.SomecalculationmodelsaredescribedbyKinoshitaandNishibori[3]adoptinganon2structuralmodelwherethefilmwillbecomposed
oftheskeleton,i
.e.solidpartandvoids,Chopraetal.[4],BraggandPoppard[5],andrespec2
tivelyshowingthefollowing:
P=(n-nv(nb-nv(2
P=[(nb2+2(n2-nv2][(n2+2(nb2-nv2](3
P=[(nv2+nb2(n2-nv2]
[(nb2-nv2(n2+nv2](4wherenb,nv,andnarebulk,void,andfilmrefractiveindex,respectively.Invacuum,nv=1andncanbecalculatedutilizingthedataobtainedbyaspectrometer.Forthepackingdensity,
VariouskindsofmaterialbychangingfivedifferentparameterswerecalculatedbyOgura[1].
Alltheresultsofpackingdensityarelessthanthatofunity.However,incaseofaprocesswiththepresenceofenergeticions,therearesomeunsolvedproblemsinequations(2~(41Forexample,intheIADprocesswithoxygenionbombardmentexperiments,anindexofamorphousSio2filmwithexcellentstoichiometrycanbeobtainedathighvaluesofabout
・421・ 光 学 仪 器第21卷
第425期TANGQietal:
AnAnalysisandCalculationoftheOpticalThinFilmPackingDensityandDensityUniformity 1.476at550nmthanwiththebulkindexvalueofSiO2,1.460at550nm,givenbyJ.R.
Pilipp[6].InsertingthethinfilmindexandbulkindexofSiO2intoequations(2~(4yieldsvaluesofPat1.035,1.030,and1.026,respectively.Alltheresultsofpackingdensityarelargerthanunity.ThisphenomenondoesnotonlyappearinthecaseofSiO2film,butalsoinalmostalldielectricfilms,particularlythoseobtainedbyion2beamorplasmaassisteddeposi2tion.Apossibleexplanationisthatthefilmisverydensewithalargerinternalcompressivestress.
Anotherproblemishowtodeterminethebulkindexnforanamorphousmaterialthatdoesnotexistinnatureorneverinvestigatedbefore.Forexample,inthecaseofTiO2film,itsbulkindexisverydifficulttodetermine.Ontheotherhand,TiO2filmispossibleoftheindex
valuesfrom2.18to2.65atthewavelengthof550nmdepositedbyvariousmethods
[7~9].Forcalculatingthepackingdensityinthiscase,anarbitrarybulkindexvalueissupposedandde2finedastherelatedbulkindex.IfsettingtherelatedbulkindexvalueofTiO2to2.50or2.70atawavelengthof550nm,thecorrespondingevaporatedfilmindicesaresetat2.180,2.285,
2.365,and2.650.Inthecaseoftherelatedbulkindexvalueof2.50andusingequation(4,thepackingdensitieswithrespecttotheaboveTiO2filmindicesare0.9008,0.9370,0.9621,0.9987,and1.0367,respectively.Theratiosoftheirpackingdensitiesare0.8689:
0.9038:
0.9280:
0.9633:
1.0.Inthecasethebulkindexvalueis2.70,thepackingdensitiesoftheabovefilmindicesare0.8597,0.8943,0.9182,0.9531,and0.9894,respectivelywithratiosof0.8689:
0.9038:
0.9280:
0.9633:
1.0.Thus,theyyieldthesameratiosthoughtheyhavedif2ferentpackingdensitiescalculatedbydifferentbulkindices.Thesameresultscanbeobtainedbyequations(2and(3.Therefore,thepackingdensitycanbedefinedasrelativepackingdensity.
3 AnAnalysisandCalculationoftheOpticalThinFilmDensityUniformity
InaccordancewiththeaboveresultsofTiO2film,doesthewavelengthshiftpossessasimplerelationtotherelatedpackingdensity?
Thiswillbeshownbythefollowingexperi2
ments
.Thecalculationmethodissimilartoequations(2~(4.Whenthethinfilmareexposedtoahumidatmosphere,thewavelengthshiftofthethinfilmisrelatedtoitsownmicrostruc2ture.Becausethefilmindexninequations(2~(4ismeasuredinahumidatmosphere,therefractiveindexnvisafunctionofrelativehumidity,with
1.0≤nv(r.h.≤1133(5
Intheexperiment,theamorphousTiO2thinfilms,depositedbyIADusingdifferentde2positionparameters,areinvestigated,andbothoftheirindicesare2.390measuredinvacuumatwavelengthof550nm.Ifgivingarelativebulkindexvalueof2.50andusingequation(2,therelativepackingdensitiesareall0.9267.Whenexposingthethinfilmstohumidatmo2sphere,themeasureddriftedindicesare2.390and2.399,respectively.Itisreasonabletoas2sumethevalueofnv2as1.33whenthewatermoleculepenetratesthevoidsinthefilm.If
・
521・
relativepackingdensityisstillcalculatedbyequation(2,bothoftheirrelativepackingden2sitiesare0.9060and0.9137,respectively.Thisresultshowsthattheyhaveadifferentrela2tivepackingdensityinvacuumandinhumidatmosphere.Thereasonforthisisthatallthe
voidsarenotcompletelyfilledwithwatermolecules
.Thiscanbeexplainedbyuniformityofthemicrostructure.Itisdifficulttocalculatethepackingdensitybytheaboveequationsbe2causethebulkindexvalueisassumed,andthewatermoleculescannotpenetrateintosomeofthemocro2voids.Thus,itis
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