程其进 - 太阳能 - 厦门大学能源学院|能源研究院
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个人履历Brief CV
程其进博士，厦门大学副教授。曾经在新加坡南洋理工大学、澳大利亚悉尼大学、澳大利亚联邦科学与工业研究组织从事低维半导体纳米材料及纳米器件的研究工作。现已在权威国际期刊上发表SCI论文四十多篇，包括Journal of Materials Chemistry, Applied Physics Letters, Acta Materialia等；被引用400多次，H影响因子是13；并已在Journal of Materials Chemistry和Nanoscale上发表了两张封面图片；被国外十多家学术刊物邀请为特约审稿人。
2013-至今 厦门大学能源研究院副教授
澳大利亚联邦科学与研究组织材料科学与工程所，博士后
澳大利亚悉尼大学，博士后
新加坡南洋理工大学，博士
研发方向Research Interests
1.低温等离子体的开发和诊断；
2.低维半导体纳米材料的制备和表征；
3.低维半导体纳米材料的成核和生长；
4.低维半导体纳米器件（包括太阳能电池、气体传感器、场发射器件等）。
荣誉及奖励Honors and Awards
2013年入选&福建省高等学校新世纪优秀人才支持计划&
出版物代表作Selected Publications
1. Q. J. Cheng and K. Ostrikov, Property-performance control of multidimensional hierarchical single-crystalline ZnO nanoarchitectures, ChemPhysChem 13, ).
2. Q. J. Cheng and K. Ostrikov, Temperature-dependent growth mechanisms of low-dimensional ZnO nanostructures, CrystEngComm 13, ) .
3. Q. J. Cheng, S. Xu, and K. Ostrikov, Controlled-bandgap silicon nitride nanomaterials: deterministic nitrogenation in high-density plasmas, J. Mater. Chem. 20, )。
4. Q. J. Cheng, E. Tam, S. Xu, and K. Ostrikov, Si quantum dots embedded in an amorphous SiC matrix: nanophase control by non-equilibrium plasma hydrogenation, Nanoscale 2, 594 (2010)..
5. Q. J. Cheng, S. Xu, and K. Ostrikov, Single-step, rapid low-temperature synthesis of Si quantum dots embedded in an amorphous SiC matrix in high-density reactive plasmas, Acta Mater. 58, 560 (2010) .
6. Q. J. Cheng, S. Xu, S. Y. Huang, and K. Ostrikov, Effective control of nanostructured phases in rapid, room-temperature synthesis of nanocrystalline Si in high-density plasmas, Cryst. Growth Des. 9, ).
7. Q. J. Cheng, S. Xu, and K. Ostrikov, Rapid, low-temperature synthesis of nc-Si in high-density, non-equilibrium plasmas: enabling nanocrystallinity at very low hydrogen dilution, J. Mater. Chem. 19, ).
8. Q. J. Cheng, S. Xu, and K. Ostrikov, Structural evolution of nanocrystalline silicon thin films synthesized in high-density, low-temperature reactive plasmas, Nanotechnology 20, 09).
9. Q. J. Cheng, S. Xu, J. D. Long, and K. Ostrikov, Deterministic plasma-aided synthesis of high-quality nanoislanded nc-SiC films, Appl. Phys .Lett. 90, 07).
10. Q. J. Cheng, S. Xu, J. D. Long, S. Y. Huang, and J. Guo, Homogeneous nanocrystalline cubic silicon carbide films prepared by inductively coupled plasma chemical vapor deposition, Nanotechnology 18, 07).
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12Matsuda TSF337 1999 Growth mechansim of microcrystalline silicon obtained from reactive plasmas
ThinSolidFilms337(1999)；1±6；Growthmechanismofmicrocr；plasmas；AkihisaMatsuda*；ElectrotechnicalLaborato；Abstract；Threemodelsproposedforth；Keywords:Microcrystallin；1.Introduction；Hydr
ThinSolidFilms337(1999)1±6GrowthmechanismofmicrocrystallinesiliconobtainedfromreactiveplasmasAkihisaMatsuda*ElectrotechnicalLaboratory,1-1-4Umezono,Tsukuba-shi,Ibaraki305-8568,JapanAbstractThreemodelsproposedforthegrowthmechanismofhydrogenatedmicrocrystallinesilicon?lms(mc-Si:H)fromreactive(silaneandhydrogenmixture)plasmasarereviewed.The`etchingmodel'isdiscussedusingexperimentallyobtainedrelationshipbetweenradicalgenerationrateinplasmasandgrowthrateof?lms.The`chemicalannealingmodel'isinvestigatedthroughthegrowthof?lmsusingalayer-by-layermethodwithandwithoutcathodeshutter.Substrate-temperaturedependenceofcrystallinityoftheresulting?lmsandinitialgrowthbehaviorofsilicon?lmsonatomicallyˉatGaAssubstrateclearlysupportthe`surfacediffusionmodel'.q1999ElsevierScienceS.A.Allrightsreserved.Keywords:MicReactiveplasmas1.IntroductionHydrogenatedmicrocrystallinesilicon(mc-Si:H)preparedfromsilaneandhydrogenmixtureusingplasmaenhancedchemicalvapordeposition(PECVD)atlowtemperatureisanattractivematerialforavarietyofapplica-tionssuchasthin?lmtransistorsandthin?lmsolarcells.Understandingofgrowthmechanismofmc-Si:Hisessentialtoimprovedeviceperformancesthroughmicroscopicnetworkstructurecontrolofmaterials.Atpresent,threepredominantmodelshavebeenproposed[1±3]toexplaintheformationofmc-Si:H.Inthisreport,eachmodelisreviewedcarefullythroughexperimentscarriedoutforveri-fyingthemodel.2.ThreemodelsModelsproposedtoexplainthegrowthofmc-Si:Hfromreactive(silaneandhydrogenmixture)plasmasareclassi-?edintothreecategories:`surfacediffusionmodel',`etch-ingmodel',and`chemicalannealingmodel'.2.1.SurfacediffusionmodelFig.1showsamc-Si:Hformationmaponhydrogendilu-tionratio(denotedasR??100SiH4=??SiH41H2????andr.f.*Tel.:181-298-545252;Fax:181-298-54-5425;e-mail:amatsuda@etl.go.jp.(13.56MHz)powerdensityspacereportedin1983[1].Anareaofquartercircleandadiameterofopencirclerepresentcrystallinevolumefractionandaveragecrystallitesize,respectively,inmc-Si:Hdepositedundergivenconditionsatasubstratetemperatureof3508C.Asisseeninthe?gure,goodcrystallinityisobtainedunderhighhydrogendilutionandlowpowerdensityconditionsasindicatedbyanarrow.Fig.2showstherelationshipbetweencrystallinevolumefractionintheresultingmc-Si:H?lmsandsubstratetemperatureduringgrowthofthe?lmsforthreehydrogendilutionvalues[1].Thesurfacediffusionmodelwasproposedtoexplaintheseresults[1].Namely,thesurfacediffusioncoef?cient(length)onthehydrogen-coveredsurfaceisenhancedbyelevatingthesubstratetemperature,leadingtoanenhancementofcrystallinevolumefraction.Thesurfacediffusion,however,isdisturbednotonlybyionsimpingingtothegrowthsurfacebutalsobythepresenceofsurfacedanglingbondsappearingthermallyabove4008C,givingrisetoadeteriorationofcrystallinityintheresulting?lmsasshownbyanarrowinFig.2.AdetailedsurfacediffusionmodelisschematicallydepictedinFig.3.Suf?cientˉuxdensityofatomichydro-genfromahydrogendilutedsilaneplasmarealizesafullsurfacecoveragebybondedhydrogenandalsoproduceslocalheatingthroughhydrogen-recombinationreactionsonthegrowthsurfaceofthe?lm[4].Thesetwoeventsoccurringonthesurfaceenhancethesurfacediffusionlengthof?lmprecursors(SiH3).Asaconsequence,?lmprecursorsadsorbedonthesurfacecan?ndenergetically2A.Matsuda/ThinSolidFilms337(Fig.2.Crystallinevolumefractionintheresulting?lmsplottedagainstsubstratetemperatureduringgrowth.Fig.1.Formationmapofmc-Si:Hinr.f.powerdensityandhydrogendilutionratioplane.favorable(stable)sites,leadingtoaformationofatomicallyˉatsurface.At?rst,mcnucleusisformed.Aftertheforma-tionofnucleus,epitaxiallikecrystalgrowthtakesplacewithasimilarlyenhanceddiffusionof?lmprecursors.2.2.EtchingmodelAnetchingmodelwasproposedbasedontheexperimen-talfactthat?lmgrowthrateisreducedbyanincreaseofhydrogendilution[2].AschematicconceptoftheetchingmodelisshowninFig.4.Anatomichydrogenprovidedonthe?lm-growingsurfacebreaksSiZSibonds,preferentiallytheweakbond,involvedintheamorphousnetworkstruc-ture,leadingtoaremovalofaSiatombondedmoreweakly(amorphousmode)toanotherSi.Thissiteisreplacedbyanew?lmprecursor,formingarigidandstrongSiZSibond(crystallinemode).Thisistheetchingmodelfortheforma-tionofmc-Si:H.AnimportantconceptinthemodelistheremovalprocessofSi(etching)fromthesurfacebyatomichydrogen(presumablybyformingSiH4)andthereplace-mentwithanotherSiformingrigidcrystallinestructure.2.3.ChemicalannealingmodelAmodelsimilartotheetchingmodelwasproposedforexplainingtheexperimentalfactthatcrystalformationisobservedduringhydrogenplasmatreatmentinalayer-by-A.Matsuda/ThinSolidFilms337(3Fig.4.Etchingmodelformc-Si:Hformation.layergrowthbyanalternatingsequenceofamorphous?lmgrowthandhydrogenplasmatreatment[3].Severalmono-layersofamorphoussiliconaredepositedandtheselayersareexposedtohydrogenatomsproducedinthehydrogenplasma.Theseprocessesarerepeatedalternatelyforseveraltentimestofabricatetheproperthicknessforevaluationof?lmstructure.Theabsenceofaremarkablereductionof?lmthicknessduringthehydrogenplasmatreatmentishardtoexplainbytheetchingmodelandanewmodelisproposedasshownschematicallyinFig.5.Duringthehydrogenplasmatreatment,manyhydrogenatomsarepermeatinginthesub-surfaceregion(calledagrowthzone[3]),givingrisetoacrystallizationofamorphousnetworkthroughtheformationofaˉexiblenetworkwithasuf?cientamountofatomichydrogeninthesub-surfaceregionwithoutanyremoval(etching)processofSiatoms.Thisisnamedasthechemicalannealingprocess.3.Experimentalresultsanddiscussionforstudyingeachmodel3.1.StudyoftheetchingmodelAsmentionedabove,theetchingmodelinvolvestheremovalofSiatomsaftertheformationofweakbondson4A.Matsuda/ThinSolidFilms337(Fig.density6.sionintensity.and(a)A(b)conceptionactualrelationofrelationbetweenbetween?lmdepositiongrowthraterateandandradicalSi*emis-ˉuxthelinear?lm-growinggrowingrelationshipsurface.Therefore,somedeviationfromawhenmc-Si:Hsurfaceisandbetweenformedactualas?lmˉuxsketchedgrowthdensityinratereachingthe?lm-Fig.isexpectedonlysilane-hydrogenItisreasonableˉuxplasmatouseSi*opticalemission6a.intensityfromtionofratedensityinthereachingplasma,theasameasureofSiH3?lmprecursorbeinggrowthproportionalsurface.TheSiH3genera-Si*SiHtotheˉuxdensityspaceemission3totheintensity?lm-growinginawidesurface,rangeisofproportionalplasmaparametertothepureFig.Si*6bsilanefortheshowsasgrowthofamorphoussilicon(a-Si:H)fromthewellactualashydrogen?lmdilutedsilaneplasmas[5].genopticalconditionsdilutionemissionratiosfromintensitydepositionR??for5differentrateasafunctionoftoR??silanetohydro-weresetasfollows,substrate0:05.temperatureDepositionofmTorr,andar.f.powerdensityof0.38W/cm2intiontheandrate?gure,andSi*aclearemissionproportionality.AsshownintensityfromisseenR??between5toR??deposi-0:25,belowaclearobservedR??deviation0:125.Nevertheless,fromthislineartherelationpresenceisobservedhighresultas2.5,inRamanfallingspectraclearlyforthe?lmsdepositedofatmRcasisprocessshownsaryconditionofweaklyinFig.6b,itinisconcludedthelinearregion.thattheFromremovaltheforbondedtheformationSiatomsprocess(etching)ofmisc-Si:H.notaneces-3.2.Veri?cationofthechemicalannealingmodelhydrogenTocheckwhethercrystallinemethodprocedurewasplasmatreatment,layer-by-layerformationoccursdepositionduringFig.reactor.7a,hydrogenisused.Aconventionalˉowofusinglayer-by-layerdeposition36reactionapparatusshowninpowergrowthdensityInstepof1,0.038asilaneW/cmˉowsccm2ofis4constantlysccmisfedfedintoandtheêissilaneinappliedthicknessforr.f.9030ssafterforthearegasoffeeding.a-Si:HlayerInstepof102,silaneAˉowandplasmapowerthehydrogencutandproduceddilutionwaitforcondition.90stoavoidFinally,thedepositionhydrogenunderplasmahighisforformally120sbytoapplyingperformaar.f.hydrogenpowerdensityplasmaof0.38W/cm2fortroscopy.40timesdepositedThetoevaluatea-Si:H?lmobtained?lmlayer.crystallinityThisproceduretreatmentfromaconventionalusingRamanisrepeatedoflayer-by-spec-Fig.layer7.Schematicsketchof(a)conventionalapparatususedforlayer-by-depositionmethodand(b)improvedapparatusforavoidingchemicalA.Matsuda/ThinSolidFilms337(5Fig.methods8.Ramanwithandspectrawithoutofcathode?lmsobtainedshutter.fromlayer-by-layerdepositionlayercm21methodlizationinaRamanasmentionedspectrum,aboveshowsasharppeakat520shouldtakesplaceduringtheashydrogenshowninplasmaFig.8,astreatment.ifcrystal-Itonconsiderationthebecounternoticed,electrodehowever,(cathode)thatthepresenceshouldbeofsilicontaken?lmtionundertheconventionallayer-by-layerdeposi-intodepositedconditionmoleculesonthementionedcathodemayabove.beetchedNamely,outformingsilicon?lmsSiH4hydrogenanddiffusedintohydrogenplasmaduringthemc-Si:Hunderplasmahightreatment,hydrogengivingdilutionrisecondition.tothegrowthToavoidofFig.9.ThicknessdependenceofSiandGaAESdifferentialintensitythis,surfacewetreatment(nousedSiamechanical?lmoncathodeshutterhavingacleanconventionalDepositionasshownthesurface)duringthehydrogenprocedureinFig.was7b.theaboveterexceptthatlayer-by-layersameasthatforthethecathodedepositionprocedureshowntrumonlyduringthehydrogenplasmaiscoveredtreatment.byacathodeRamanspec-shut-withpeaktheforannealingat520cathodethe?lmcm2shutterobtained1.Therefore,isshownbyourweinlayer-by-layermethodconcludeFig.8andthatshowsnouseduniversalhereanddoesthatnottheoccurchemicalunderthedepositionconditionschemicalobservedmodelfortheformationannealingprocessofconceptmc-Si:H.isnotTheahydrogenabsenceetchingandplasmamc-Si:Htreatmentofchangegrowth.isindue?lmtocoexistingthicknessduringprocesstheof3.3.modelExperimentalevidencesupportingthesurfacediffusionexplainTwopopularmodelmc-Si:Hmodelsformationdescribedprocess.aboveThearenotenoughtomodelsseemsdiffusionproposedtoupbetothenow.mostHowever,plausibletoverifyamongsurfacethethediffusionsurfacethreefortheinstance,model,furtherexperimentalevidenceisneeded,of?lmsurfaceprecursorsdiffusionanexperimentallyobservedenhancementofundercoef?cient(surfacediffusionlength)underToseeevolutionthethehydrogensurfacediffusionhydrogenbehaviordilutionofcondition.?lmprecursorsinitialsubstrategrowthofsurfacedilutionmorphologycondition,wasinvestigatedthekineticsofinthethedilutionpressureratiohavingofofRterracesSionan??2:5,asatomicallyˉatêGaAstotalbroadˉowasrate1000A.Hydrogen(001)withof50mTorr,andr.f.powerdensityofof400scam,13totalweretriodeSiusedtocon?gurationgrowthe?lms.tominimizeFig.ionbombardmentW/cm2signalandGaAugerelectronspectroscopy9shows(AES)thedifferentialfractionofêthreeunderdifferentintensitiessubstratefrom?lmstemperaturesofthicknessesof50,150,of0±50Aforexperimentalthehydrogenand?gure.8C(typicalresultdilutioncondition.Asareference,thea-Si:Hundergrowthundilutedcondition)conditions??R??100??atofThecurvesinthe?gurerepresentisthealsosimulatedshowninresultthetionsthelayer-by-layer(LBL)growthêmodel.followedwithobeySitheandLBLGamodefrac-islandbythicknessadeviationlessfromthan5theALBLmodeindicatingthicknessformation.dashedofislandSimulationcoalescence,analysiswhichalsoisgivengivesbytheonsetingislandthelineofcoalescencesubstrateinthe?guretemperature,(detailsseeRef.[7]).Whenincreas-athickisreduced.ThistheisonsetcausedthicknessbytheincreasefortheItsurfaceisnoteddiffusionthatthelengthonsetofthickness?lmprecursors.islargerinthecaseof包含各类专业文献、中学教育、高等教育、幼儿教育、小学教育、文学作品欣赏、外语学习资料、12Matsuda TSF337 1999 Growth mechansim of microcrystalline silicon obtained from reactive plasmas等内容。　Thin Solid Films 337 (Growth mechanism of microcrystalline silicon obtained from reactive plasmasAkihisa Matsuda*Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba
-shi, Ibaraki 305-8568, JapanAbstract Three models proposed for the growth mechanism of hydrogenated microcrystalline silicon ?lms (mc-Si:H) from reactive (silane and hydrogen mixture) plasmas are reviewed. The `etching model' is discussed using experimentally obtained relationship between radical generation rate in plasmas and growth rate of ?lms. The `chemical annealing model' is investigated through the growth of ?lms using a layerby-layer method with and without cathode shutter. Substrate-temperature dependence of crystallinity of the resulting ?lms and initial growth behavior of silicon ?lms on atomically ?at GaAs substrate clearly support the `surface diffusion model'. q 1999 Elsevier Science S.A. All rights reserved. Keywords: Micr Reactive plasmas1. Introduction Hydrogenated microcrystalline silicon (mc-Si:H) prepared from silane and hydrogen mixture using plasma enhanced chemical vapor deposition (PECVD) at low temperature is an attractive material for a variety of applications such as thin ?lm transistors and thin ?lm solar cells. Understanding of growth mechanism of mc-Si:H is essential to improve device performances through microscopic network structure control of materials. At present, three predominant models have been proposed [1±3] to explain the formation of mc-Si:H. In this report, each model is reviewed carefully through experiments carried out for verifying the model. 2. Three models Models proposed to explain the growth of mc-Si:H from reactive (silane and hydrogen mixture) plasmas are classi?ed into three categories: `surface diffusion model', `etching model', and `chemical annealing model'. 2.1. Surface diffusion model Fig. 1 shows a mc-Si:H formation map on hydrogen dilution ratio (denoted as R ? 100 SiH4 =?SiH4 1 H2 ?? and r.f.* Tel.: 181-298-545252; Fax: 181-298-54-5425; e-mail: amatsuda@etl.go.jp.(13.56 MHz) power density space reported in 1983 [1].An area of quarter circle and a diameter of open circle represent crystalline volume fraction and average crystallite size, respectively, in mc-Si:H deposited under given conditions at a substrate temperature of 350 8C. As is seen in the ?gure, good crystallinity is obtained under high hydrogen dilution and low power density conditions as indicated by an arrow. Fig. 2 shows the relationship between crystalline volume fraction in the resulting mc-Si:H ?lms and substrate temperature during growth of the ?lms for three hydrogen dilution values [1]. The surface diffusion model was proposed to explain these results [1]. Namely, the surface diffusion coef?cient (length) on the hydrogen-covered surface is enhanced by elevating the substrate temperature, leading to an enhancement of crystalline volume fraction. The surface diffusion, however, is disturbed not only by ions impinging to the growth surface but also by the presence of surface dangling bonds appearing thermally above 4008C, giving rise to a deterioration of crystallinity in the resulting ?lms as shown by an arrow in Fig. 2. A detailed surface diffusion model is schematically depicted in Fig. 3. Suf?cient ?ux density of atomic hydrogen from a hydrogen diluted silane plasma realizes a full surface coverage by bonded hydrogen and also produces local heating through hydrogen-recombination reactions on the growth surface of the ?lm [4]. These two events occurring on the surface enhance the surface diffusion length of ?lm precursors (SiH3). As a consequence, ?lm precursors adsorbed on the surface can ?nd energetically/$ - see front matter q 1999 Elsevier Science S.A. All rights reserved. PII S0 040- 65-12A. Matsuda / Thin Solid Films 337 (Fig. 2. Crystalline volume fraction in the resulting ?lms plotted against substrate temperature during growth.Fig. 1. Formation map of mc-Si:H in r.f. power density and hydrogen dilution ratio plane.favorable (stable) sites, leading to a formation of atomically ?at surface. At ?rst, mc nucleus is formed. After the formation of nucleus, epitaxial like crystal growth takes place with a similarly enhanced diffusion of ?lm precursors. 2.2. Etching model An etching model was proposed based on the experimental fact that ?lm growth rate is reduced by an increase of hydrogen dilution [2]. A schematic concept of the etchingmodel is shown in Fig. 4. An atomic hydrogen provided on the ?lm-growing surface breaks SiZSi bonds, preferentially the weak bond, involved in the amorphous network structure, leading to a removal of a Si atom bonded more weakly (amorphous mode) to another Si. This site is replaced by a new ?lm precursor, forming a rigid and strong SiZSi bond (crystalline mode). This is the etching model for the formation of mc-Si:H. An important concept in the model is the removal process of Si (etching) from the surface by atomic hydrogen (presumably by forming SiH4) and the replacement with another Si forming rigid crystalline structure. 2.3. Chemical annealing model A model similar to the etching model was proposed for explaining the experimental fact that crystal formation is observed during hydrogen plasma treatment in a layer-by-Fig. 3. Surface diffusion model for mc-Si:H formation.A. Matsuda / Thin Solid Films 337 (3Fig. 4. Etching model for mc-Si:H formation.layer growth by an alternating sequence of amorphous ?lm growth and hydrogen plasma treatment [3]. Several monolayers of amorphous silicon are deposited and these layers are exposed to hydrogen atoms produced in the hydrogen plasma. These processes are repeated alternately for several ten times to fabricate the proper thickness for evaluation of ?lm structure. The absence of a remarkable reduction of ?lm thickness during the hydrogen plasma treatment is hard to explain by the etching model and a new model is proposed as shown schematically in Fig. 5. During the hydrogen plasma treatment, many hydrogen atoms are permeating in the sub-surface region (called a growth zone [3]), giving rise to a crystallization of amorphous network through theformation of a ?exible network with a suf?cient amount of atomic hydrogen in the sub-surface region without any removal (etching) process of Si atoms. This is named as the chemical annealing process.3. Experimental results and discussion for studying each model 3.1. Study of the etching model As mentioned above, the etching model involves the removal of Si atoms after the formation of weak bonds onFig. 5. Chemical annealing model for mcSi:H formation.4A. Matsuda / Thin Solid Films 337 (mTorr, and a r.f. power density of 0.38 W/cm 2. As shown in the ?gure, a clear proportionality is seen between deposition rate and Si* emission intensity from R ? 5 to R ? 0:25, and a clear deviation from this linear relation is observed below R ? 0:125. Nevertheless, the presence of mc is observed in Raman spectra for the ?lms deposited at R as high as 2.5, falling clearly in the linear region. From the result shown in Fig. 6b, it is concluded that the removal process of weakly bonded Si atoms (etching) is not a necessary condition for the formation process of mc-Si:H. 3.2. Veri?cation of the chemical annealing model To check whether crystalline formation occurs during hydrogen plasma treatment, layer-by-layer deposition method was used. A conventional layer-by-layer deposition pro using reaction apparatus shown in Fig. 7a, hydrogen ?ow of 36 sccm is constantly fed into the reactor. In step 1, a silane ?ow of 4 sccm is fed and r.f. power density of 0.038 W/cm 2 is applied for 30 s for the ? growth of a-Si:H layer of 10 A in thickness 90 s after the silane gas feeding. In step 2, silane ?ow and plasma power are cut and wait for 90 s to avoid the deposition under high hydrogen dilution condition. Finally, hydrogen plasma is produced by applying a r.f. power density of 0.38 W/cm 2 for 120 s to perform a hydrogen plasma treatment of formally deposited a-Si:H layer. This procedure is repeated for 40 times to evaluate ?lm crystallinity using Raman spectroscopy. The ?lm obtained from a conventional layer-by-Fig. 6. (a) A conception of relation between growth rate and radical ?ux density and (b) actual relation between ?lm deposition rate and Si* emission intensity.the ?lm-growing surface. Therefore, some deviation from a linear relationship between ?ux density reaching the ?lmgrowing surface and actual ?lm growth rate is expected only when mc-Si:H is formed as sketched in Fig. 6a. It is reasonable to use Si* optical emission intensity from silane-hydrogen plasma as a measure of SiH3 ?lm precursor ?ux density reaching the growth surface. The SiH3 generation rate in the plasma, being proportional to the ?ux density of SiH3 to the ?lm-growing surface, is proportional to the Si* emission intensity in a wide range of plasma parameter space for the growth of amorphous silicon (a-Si:H) from pure silane as well as hydrogen diluted silane plasmas [5]. Fig. 6b shows the actual ?lm deposition rate as a function of Si* optical emission intensity for different silane to hydrogen dilution ratios from R ? 5 to R ? 0:05. Deposition conditions were set as follows, substrate temperature of 3508C, total ?ow rate of 40 sccm, total pressure of 500Fig. 7. Schematic sketch of (a) conventional apparatus used for layer-bylayer deposition method and (b) improved apparatus for avoiding chemical etching of Si from the cathode during hydrogen plasma treatment.A. Matsuda / Thin Solid Films 337 (5this, we used a mechanical cathode shutter having a clean surface (no Si ?lm on the surface) during the hydrogen treatment as shown in Fig. 7b. Deposition procedure was the same as that for the conventional layer-by-layer deposition procedure shown above except that the cathode is covered by a cathode shutter only during the hydrogen plasma treatment. Raman spectrum for the ?lm obtained by our layer-by-layer method with the cathode shutter is shown in Fig. 8 and shows no peak at 520 cm 21. Therefore, we conclude that chemical annealing does not occur under the deposition conditions used here and that the chemical annealing concept is not a universal model for the formation process of mc-Si:H. The observed absence of change in ?lm thickness during the hydrogen plasma treatment is due to coexisting process of etching and mc-Si:H growth.Fig. 8. Raman spectra of ?lms obtained from layer-by-layer deposition methods with and without cathode shutter.layer method as mentioned above shows a sharp peak at 520 cm 21 in a Raman spectrum, as shown in Fig. 8, as if crystallization takes place during the hydrogen plasma treatment. It should be noticed, however, that the presence of silicon ?lm on the counter electrode (cathode) should be taken into consideration under the conventional layer-by-layer deposition condition mentioned above. Namely, silicon ?lms deposited on the cathode may be etched out forming SiH4 molecules and diffused into hydrogen plasma during the hydrogen plasma treatment, giving rise to the growth of mc-Si:H under high hydrogen dilution condition. To avoid3.3. Experimental evidence supporting the surface diffusion model Two popular models described above are not enough to explain mc-Si:H formation process. The surface diffusion model seems to be the most plausible among the three models proposed up to now. However, to verify the surface diffusion model, further experimental evidence is needed, for instance, an experimentally observed enhancement of the surface diffusion coef?cient (surface diffusion length) of ?lm precursors under hydrogen dilution condition. To see the surface diffusion behavior of ?lm precursors under the hydrogen dilution condition, the kinetics of the evolution of surface morphology was investigated in the initial growth of Si on an atomically ?at GaAs (001) ? substrate having terraces as broad as 1000 A. Hydrogen dilution ratio of R ? 2:5, total ?ow rate of 40 scam, total pressure of 50 mTorr, and r.f. power density of 0 13 W/cm 2 with triode con?guration to minimize ion bombardment were used to grow the ?lms. Fig. 9 shows the fraction of Si and Ga Auger electron spectroscopy (AES) differential ? signal intensities from ?lms of thicknesses of 0±50 A for three different substrate temperatures of 50, 150, and 2508C under the hydrogen dilution condition. As a reference, the experimental result under undiluted conditions ?R ? 100? at 2508C (typical a-Si:H growth condition) is also shown in the ?gure. The curves in the ?gure represent the simulated result of the layer-by-layer (LBL) growth model. Si and Ga frac? tions with thickness less than 5 A obey the LBL mode followed by a deviation from the LBL mode indicating island formation. Simulation analysis also gives the onset thickness of island coalescence, which is given by a thick dashed line in the ?gure (details see Ref.[7]). When increasing the substrate temperature, the onset thickness for the island coalescence is reduced. This is caused by the increase of surface diffusion length of ?lm precursors. It is noted that the onset thickness is larger in the case of no hydrogen dilution even at 2508C. This result clearlyFig. 9. Thickness dependence of Si and Ga AES differential intensity fractions for the sample grown on GaAs.6A. Matsuda / Thin Solid Films 337 (indicates that the surface diffusion length of ?lm precursors is enhanced under the hydrogen dilution condition. Together with results shown here, a real time spectroscopic ellipsometry (RTSE) at the initial stage of ?lm growth also shows clear evidence of the enhancement of surface diffusion length under hydrogen dilution conditions and demonstrates the appearance of atomically ?at surface at the nucleation stage of mc-Si:H [6]. These results support the validity of the surface diffusion model for the growth of mc-Si:H from reactive plasmas. 4. Summary Three models proposed for explaining the formation of mc-Si:H have been reviewed. Detailed experiments were carried out to study the validity of these models. It is concluded that the etching model and the chemical annealing model are insuf?cient to explain the formation process of mc-Si:H. The surface diffusion model, on the contrary, is supported by a multiple experimental evidence.Acknowledgements Author would like to express great thanks to Drs. Michio Kondo, Kimihiko Saito, Tatsuaki Nishimiya, Makoto Fukawa, Guo Lihui and Hiroyuki Fujiwara for their experiments and fruitful discussions, and also thanks to Dr. Paul Stradins for his critical reading of the manuscript. References[1] A. Matsuda, J. Non-Cryst. Solids 59/60 (. [2] C.C. Tsai, G.B. Anderson, R. Thompson, B. Wacker, J. Non-Cryst. Solids 114 (. [3] K. Nakamura, K. Yoshida, S. Takeoka, I. Shimizu, Jpn. J. Appl. Phys. 34 (. [4] S. Veprek, Z. Iqbal, F.A. Sarott, Phil. Mag. B 45 (. [5] A. Matsuda, T. Goto, Mater. Res. Soc. Symp. Proc. 164 (1990) 3. [6] J. Koh, H. Fujiwara, R.W. Collins, Y. Lee, C.R. Wronski, Proc. Int. Conf. Amorphous and Microcrystalline Semiconductors, 1998, in press. [7] K. Saitoh, M. Kondo, M. Fukawa, T. Nishimiya, W. Futako, I. Shimizu, A. Matsuda, Mater. Res. Soc. Symp. Proc., 1998, in press.
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