DTIC ADA593440: Molecular Layer Deposition of Hybrid Organic-Inorganic Polymer Films using Diethylzinc and Ethylene Glycol

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DOI: 10.1002/cvde.200806756
Full Paper
Molecular Layer Deposition of Hybrid Organic-Inorganic
Polymer Films using Diethylzinc and Ethylene Glycol**
ByByunghoon Yoon, JenniferL.O’Patchen,Dragos Seghete, AndrewS.Cavanagh,and StevenM.George*
Themolecularlayerdeposition(MLD)ofahybridorganic-inorganicpolymerbasedonzincisdemonstratedusingsequential
exposuresofdiethylzinc(DEZ,Zn(CH CH ) )andethyleneglycol(EG,HOCH CH OH).Thispolymerisrepresentativeofa
2 3 2 2 2
classofzincalkoxidepolymerswithanapproximateformulaof((cid:1)Zn(cid:1)O(cid:1)R(cid:1)O(cid:1)) thatcanbecalled‘‘zincones’’.Thefilm
n
growthandsurfacechemistryduringzinconeMLDisstudiedusingin-situFouriertransforminfrared(FTIR)measurements.
TheabsorbanceoftheinfraredfeaturesofthezinconefilmincreaseprogressivelyversusthenumberofMLDcycles.TheFTIR
spectraaftertheDEZandEGexposuresareconsistentwiththegainandlossofabsorbancefromC(cid:1)H,O(cid:1)H,C(cid:1)O,andZn(cid:1)O
stretchingvibrations.FTIRstudiesalsoconfirmtheself-limitingnatureofthesurfacereactionsandmonitorthetemperature
dependenceofthefilmgrowth.Transmissionelectronmicroscope(TEM)imagesofZrO nanoparticlesshowveryconformal
2
zinconefilmsanddeterminethatthegrowthratevariesfrom4.0A˚ perMLDcycleat908Cto0.25A˚ perMLDcycleat1708C.
Quartzcrystalmicrobalance(QCM)andX-rayreflectivity(XRR)measurementsshowlinearzinconegrowthversusthenumber
ofMLDcycles.XRRstudiesonsiliconwafersareconsistentwithagrowthrateof0.7A˚ perMLDcycleat1308C.Thehigher
growth rate on the ZrO nanoparticles is attributed to the lower gas conductance and possible CVD reactions in the ZrO
2 2
nanoparticles. The reaction mechanism for zincone MLD is dependent on temperature. At higher temperatures, there is
evidence for ‘‘double’’ reactions of EG because no free hydroxyl groups are observed in the FTIR spectrum after the EG
exposures.ThezinconefilmcangrowintheabsenceoffreehydroxylgroupsifDEZcandiffuseintothezinconefilmandreact
duringthesubsequentEGexposure.ThezinconefilmsinitiallyadsorbH Ouponexposuretoairandthenareverystablewith
2
time.
Keywords:Hybrid organic-inorganic materials, Molecular layerdeposition,Polymer films, Surfacechemistry
1. Introduction atomic layer deposition (ALD) techniques that have been
developed for the growth of inorganic materials.[3–5] Both
Molecularlayerdeposition(MLD)isbasedonsequential MLD and ALD can be used to fabricate conformal,
and self-limiting surface reactions of reactants containing continuous, and pinhole-free films.[6–9] The self-limiting
organic constituents.[1,2] MLD methods are very similar to natureofthesurfacechemistryallowsconformalMLDand
ALD films to be grown on high aspect ratio and porous
structures.[10]
[*] Prof.S.M.George,Dr.B.Yoon,J.L.O’Patchen,D.Seghete
DepartmentofChemistryandBiochemistry,UniversityofColorado Recent work has demonstrated the MLD of organic
Boulder,CO80309-0215(USA)
polymer films using homobifunctional reactants. For
E-mail:[email protected]
example, polyamide films such as Nylon 66 have been
A.S.Cavanagh
DepartmentofPhysics,UniversityofColorado depositedusingadipoylchlorideand1,6–hexanediamineas
Boulder,CO80309-0215(USA) the reactants.[11] Poly(p–phenylene terephthalamide) films
Prof.S.M.George,A.S.Cavanagh have also been grown using terephthaloyl chloride and p–
DARPACenterforIntegratedMicro/Nano-Electromechanical
Transducers(iMINT),UniversityofColorado phenylenediamineasthereactants.[12]TheMLDoforganic
Boulder,CO80309-0215(USA) polyimidefilmshasalsobeenreportedusingdiaminesand
Prof.S.M.George carboxylic anhydrides.[13] Earlier work also demonstrated
DepartmentofChemicalandBiologicalEngineering, the MLD of polyimides,[2,14] polyamides,[15] and polyur-
UniversityofColorado
Boulder,CO80309-0215(USA) eas.[16] In some of the these earlier studies, the method of
[**] ThisworkwassupportedbytheNationalScienceFoundation(CHE- sequential, self-limiting surface reactions was known as
0715552).Someoftheequipmentusedinthisresearchwasprovidedby alternating vapordeposition polymerization.[15,17]
the Air Force Office of Scientific Research. DS was supported by
DARPA/MTO, SPAWAR (Contract No. N66001-07-1-2033). ASC InadditiontotheMLDoforganicpolymers,theMLDof
wassupportedbytheDARPACenteronNanoscaleScienceandTech- hybridorganic-inorganicpolymerfilmswasrecentlyaccom-
nology for Integrated Micro/Nano-Electromechanical Transducers
plished using trimethyl aluminum (TMA, Al(CH ) ) and
(iMINT)fundedbyDARPAN/MEMSS&TFundamentalsProgram 3 3
(HR0011-06-1-0048). EG.[6]Theseorganic-inorganiccompositefilmscombinean
112 (cid:1)2009WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim Chem.Vap.Deposition2009,15,112–121
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4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
Molecular Layer Deposition of Hybrid Organic-Inorganic Polymer Films
5b. GRANT NUMBER
using Diethylzinc and Ethylene Glycol
5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
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Biochemistry,Boulder,CO,80309
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inorganicreactant,TMA,withanorganicreactant,EG.The
general family of organic-inorganic polymers with the
approximate form of ((cid:1)Al(cid:1)O(cid:1)R(cid:1)O(cid:1)) are known as
n
‘‘alucones’’.[6,18] The reaction of TMA and EG is one of a
largenumberofreactionsbetweenmetalalkylsandorganic
diols. The metal alkyl molecule can be described by MR
x
and the diol can be described by HOR’OH. The general
MLDreactionsbetweenthemetalalkylandthediolcanbe
written asEquations 1 and2.[6]
ðAÞROH(cid:2)þMR0 !RO(cid:1)MR0(cid:2) þR0H (1)
x x(cid:1)1
ðBÞMR0(cid:2)þHOROH!M(cid:1)OROH(cid:2)þR0H (2)
The asterisks indicate the surface species. These A and B
reactions in an ABAB... sequence of metal alkyl and
organic diol can lead to the growth of the hybrid organic-
inorganicpolymeric films.
Many metal alkyls and organic reactants can be used to
define various hybrid organic-inorganic MLD polymers.[1] Fig.1.SchematicforgrowthmechanismofzinconeMLDfilmusingDEZand
Forexample,zincalkylssuchasZn(CH CH ) (diethylzinc EG.
2 3 2
(DEZ))andTiCl (titaniumtetrachloride)shouldreactwith
4
diolsinasimilarMLDprocess.Othermetalalkylsthatcan
becausethesamebondsarebrokenandformedduringthe
easily reactwithoxygen precursorsarealso candidatesfor
DEZþEG and DEZþH O reactions. There is also
hybridorganic-inorganicpolymerMLD.Examplesinclude 2
precedencefortheDEZþEGMLDreaction.Polymeriza-
metal alkyls based on magnesium (Mg) and manganese
tionreactionsusingorganicdiolsanddialkylzincprecursors
(Mn), such as Mg(C ) and Mn(C ) where C is the
p 2 p 2 p
cyclopentadienylligand,thatreactreadilywithH O.[19,20]In have been studied in organic solution under an argon
2 environment.[28]
addition, many other oxygen-containing bifunctional
This investigation of zincone MLD concentrated on in-
organic reactants are possible suchas carboxylic acids and
aldehydes.[21] Homobifunctional organic reactants such as situ FTIR spectroscopy to monitor the zincone MLD
growth, to identify the surface species following the DEZ
diaminesordithiols shouldalso bepossibleprecursors.
and EG reactions, and to verify the self-limiting nature of
In this paper, the MLD of a hybrid organic-inorganic
thesurfacereactions.XRRstudiesmeasuredthethickness
polymer based on zinc was demonstrated using DEZ and
EG as the reactants.[22,23] These zinc-containing polymer of the zincone films and the linearity of zincone MLD
growth versus number of MLD cycles. TEM was used to
films are part of a class of zinc alkoxide polymers with a
image the zincone films on ZrO nanoparticles and obtain
composition approximated by ((cid:1)Zn(cid:1)O(cid:1)R(cid:1)O(cid:1)) . This 2
n
the temperature dependence of the zincone MLD growth.
class of zinc alkoxide films can be called ‘‘zincones’’ in
analogywiththeclosely-relatedalucones.[6,18]Theproposed In-situQCMmeasurementswereusedtoverifythelinearity
ofzinconeMLD.X-rayphotoelectronspectroscopy(XPS)
surfacereactionsforzinconeMLDusingDEZandEGare
wasemployedtocharacterizetheelementalcompositionof
expected to follow the chemical reactions described by
the zincone films. These studies help to establish the
Equations1and2.AschematicdepictingthezinconeMLD
generalityandfeasibilityofMLDreactionsbasedonmetal
growth isshownin Figure1.
alkylsandorganic diols.
The overall zincone MLD reaction using DEZ and EG
can bewritten asEquation 3.
2. Results and Discussion
nZnðCH CH Þ þnHOCH CH OH
2 3 2 2 2
!ð(cid:1)Zn(cid:1)O(cid:1)CH2CH2(cid:1)O(cid:1)ÞnþnCH3CH3 (3) 2.1.Zincone MLDGrowth
ThereactionofDEZandEGisanalogoustothereactionof ZinconeMLDwasstudiedusingin-situFTIRstudiesover
DEZþH O!ZnOþ2C H for ZnO ALD.[24–26] This the temperature range 90–1708C. FTIR spectra were
2 2 6
reaction has favorable thermochemistry with an enthalpy recorded after various numbers of MLD cycles and after
ofreactionofDH¼(cid:1)70.0kcal.[27]TheDEZþEGreaction each reactant exposure. The FTIR spectra after various
is expected to have a very similar enthalpy of reaction numbersofMLDcyclesmonitortheprogressivegrowthof
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Fig.2.In-situFTIRspectraduringthegrowthofzinconeMLDfilmsafter1,5,
10,15,and20MLDcyclesat1308C.
Fig.3.FTIRdifferencespectraafterDEZandEGexposuresduringzincone
MLD film growth at 1308C. a) DEZ-EG after DEZ exposure on a film
previously reacted with EG. b) EG-DEZ after EG exposure on a film
the zincone film. Figure 2 displays the FTIR spectra previouslyreactedwithDEZ.
following the EG exposures after 1, 5, 10, 15, and
20 MLD cycles at 1308C. The infrared absorbance grows previousstudiesthatexploredDEZreactionsonZrO and
2
progressivelywith number ofMLD cycles. BaTiO surfaces.[25] A negative absorbance feature is
3
ProminentabsorbancesareobservedinFigure2at2800– observed in Figure 3a at 3100–3730cm(cid:1)1. This feature
3000cm(cid:1)1corresponding totheC(cid:1)Hstretchingvibrations isconsistentwiththeremovalofhydroxylspecies.Thereis
oftheethylenelinkagesbetweenoxygenatomsinthezinc alsoevidenceforaslightfrequencyshiftandreductionofthe
alkoxidepolymer.Atlowerfrequencies,largeabsorbanceis absorbance at 1100cm(cid:1)1 corresponding to the C(cid:1)O
also observed at 888cm(cid:1)1 and 1100cm(cid:1)1. These absor- stretching vibration.
bances are assigned to Zn(cid:1)O and C(cid:1)O stretching InthedifferencespectrumforEG-DEZinFigure3b,the
vibrations. Smaller absorbances at 1456cm(cid:1)1, 1365cm(cid:1)1, spectrumappearsastheinverseoftheDEZ-EGspectrumin
and1256cm(cid:1)1arealsomonitoredinFigure2andassigned the O(cid:1)H and C(cid:1)H stretching region. The positive
to CH scissors, wag, and twist modes, respectively. These absorbance features are observed for the O(cid:1)H, C(cid:1)O,
2
vibrational features are all consistent with the growth of a and Zn(cid:1)O stretching vibrations at 3100–3730cm(cid:1)1,
zinc alkoxide polymer that may be approximated by 1100cm(cid:1)1, and 888cm(cid:1)1, respectively. There are also
((cid:1)Zn(cid:1)O(cid:1)CH CH (cid:1)O(cid:1)) .Thereisalsoaweakandbroad positive absorbance features for the CH symmetric and
2 2 n 2
absorbanceat3100–3730cm(cid:1)1assignedtoO(cid:1)Hstretching asymmetricstretchingvibrationsat2850and2885cm(cid:1)1.The
vibrations.ThisvibrationalfeatureisobservedaftertheEG negativefeaturesaretheabsorbancesfortheCH andCH
2 3
exposures. stretchingvibrationsfortheethylgroupoftheDEZsurface
Thechangeinsurfacespeciesduringeachreactioncanbe speciesat2910and2941cm(cid:1)1.ThegainandlossofCH and
2
monitored by the FTIR difference spectra. The surface CH featuresleadstoacomplicatedspectrumintheC(cid:1)H
3
species that are added appear as positive absorbance stretching vibrationregion.
features and the surface species that are removed appear The integrated absorbance of the C(cid:1)H stretching
as negative absorbance features. The FTIR difference vibrationsat2800–3000cm(cid:1)1andtheintegratedabsorbance
spectra for the DEZ exposure referenced against the EG oftheO(cid:1)Hstretchingvibrationsat3100–3730cm(cid:1)1canbe
exposure (DEZ-EG) and the EG exposure referenced usedtomonitortheself-limitingnatureoftheDEZandEG
againsttheDEZexposure(EG-DEZ)at1308Careshown reactions.TheintegratedabsorbancefortheC(cid:1)Hstretch-
inFigures 3aand3b, respectively. ing vibrations versus DEZ exposure at 1308C is shown in
InthedifferencespectrumforDEZ-EGinFigure3a,the Figure 4a. The integrated absorbance for the O(cid:1)H
positive features are the absorbances of the CH and CH stretching vibrations versus EG exposure at 1308C is
2 3
stretchingvibrationsfortheethylgroupoftheDEZsurface showninFigure4b.Inbothcases,theexposuresaredefined
species at 2910 and 2941cm(cid:1)1. The gain of these C(cid:1)H by the number of microdoses of DEZ or EG. Figure 4a
stretchingvibrationsfromtheethylgroupisverysimilarto indicatesthattheDEZreactionisself-limitingandreaches
114 www.cvd-journal.de (cid:1)2009WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim Chem.Vap.Deposition2009,15,112–121
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viously.[29] The Zn(cid:1)O stretching vibration was assigned
totheabsorbancefeatureat888cm(cid:1)1.Incontrast,arecent
FTIRstudyofthereactionofDEZwithalcoholsobserveda
vibrationalfeatureat755cm(cid:1)1thatwastentativelyassigned
totheZn(cid:1)Ostretchingvibration.[30]OtherstudiesonZnO
nanoparticles have observed features at 400–600cm(cid:1)1 that
havebeenassociatedwithZn(cid:1)Ovibrations.[31]Additional
investigations of the metal-organic vapor pressure epitaxy
growthofZnOwithDEZandN Ohaveobservedabroad
2
infraredfeatureat760–950cm(cid:1)1.[32]Thisinfraredpeakwas
believed to correspond with various polymer fragments
resultingfromC H OZnC H ,Zn(OC H ) ,HOZnOC H ,
2 5 2 5 2 5 2 2 5
andZn(OH) reactionproductsthatoligomerizebyforming
2
Zn(cid:1)Obonds.[32]
ToconfirmthattherearenoZn(cid:1)Ostretchingvibrations
atfrequencieslowerthan888cm(cid:1)1thatmaybeobscuredby
absorption from ZrO nanoparticles, zincone MLD was
2
performedonSiO nanoparticles. Inthesestudies,nonew
2
vibrational features were observed in the EG-DEZ
difference spectrum between 600–850cm(cid:1)1. The absence
ofvibrationalfeaturesatlowerfrequencieshelpstoconfirm
thatthevibrationalfeatureat888cm(cid:1)1ischaracteristicfor
the Zn(cid:1)Ostretching vibration inthe zincone films.
Fig.4.Integratedabsorbancefora)C(cid:1)Hstretchingvibrationsversusnumber
Anothervibrationalfeaturewasobservedwithapeakat
ofDEZmicrodoses,andb)O(cid:1)HstretchingvibrationsversusnumberofEG
microdoses.BothDEZandEGexposureswereperformedat1308C. (cid:3)1590cm(cid:1)1whentheEGwasexposedinastaticmodewith
the gate valve closed to the pumps. This feature was
completionaftertenDEZmicrodoses.EachDEZdosewas accompanied by an increased absorbance in the O–H
definedbya0.3sexposureat70mTorrofpartialpressure. stretching region at (cid:3)3000–3680cm(cid:1)1. These two features
Likewise, Figure 4b indicates that the EG reaction also is areconsistentwiththeabsorptionofH Omoleculesonthe
2
self-limiting and reaches completion after 10 EG micro- surfaceofthezinconefilm.H OmaybeanimpurityinEG
2
doses. Each EG dose was defined by a 0.3s exposure at andisadecompositionproductofEG.[33]Thesefeaturesat
8–10mTorrofpartial pressure. (cid:3)1590cm(cid:1)1and(cid:3)3000–3680cm(cid:1)1observedafterstaticEG
exposures suggest that zincone MLD growth may be
strongly affected by pumping speed and purging times.
2.2.Assignmentof VibrationalFeatures Wenotethatthefeatureat(cid:3)1590cm(cid:1)1wasalsoobserved
whenthe liquidN trapwas notpumpingonthe reactor.
2
Theassignmentsofthevibrationalfrequenciesobserved
duringzinconeMLDgrowtharegiveninTable1.Mostof
these vibrational features have been identified pre- 2.3.TemperatureDependence of ZinconeMLD
The integrated absorbance of the C(cid:1)H stretching
vibrations can be used to determine the temperature
Table1.AssignmentofvibrationalpeaksobservedduringzinconeMLD.
dependence of zincone MLD. For these experiments, the
Frequency[cm(cid:1)1] Assignment absorbanceintheC(cid:1)Hstretchingregionwasmeasuredafter
tenzinconeMLDcyclesatvarioustemperaturesintherange
3730 O(cid:1)Hstretch,EG
90–1708C.TheseFTIRspectraintheC(cid:1)Hstretchingregion
2941 CH3asymmetricstretch,DEZ
2910 CH2asymmetricstretch,DEZ areshowninFigure5.AftertenMLDcycles,theabsorbance
2885 CH2asymmetricstretch,EG in the C(cid:1)H stretching region decreases progressively for
2871 CH2stretch,DEZ zinconeMLD at higher temperatures. This decrease in the
2850 CH2symmetricstretch,EG zincone MLD growth per cycle at higher temperatures is
2787 CH2stretch,DEZ consistentwithpreviousresultsforaluconeMLD.[6]
2697 EGcombination
ThetemperaturedependenceofthezinconeMLDgrowth
1456 CH2scissors
1365 CH2wag percyclewasalsomeasuredusingTEManalysisofzincone
1256 CH2twist filmsgrownonZrO2nanoparticlesatvarioustemperatures.
1100 C(cid:1)Ostretch TheTEMimageofazinconefilmafterthirtyMLDcyclesat
888 Zn(cid:1)Ostretch,EGandDEZ 1308CisshowninFigure6.ThisTEMimagerevealsthatthe
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Fig.7.ComparisonbetweentheintegratedabsorbancefortheC(cid:1)Hstretch-
ingvibrationsinFig.5after10MLDcyclesandthegrowthpercyclefor
zinconeMLDmeasuredbyTEManalysisofZrO2nanoparticlesat90,110,
130,150,and1708C.
results from the TEM and integrated absorbance analysis
are inexcellent agreement.
ThedecreaseinthezinconeMLDgrowthpercycleversus
temperaturecanbepartlyattributedtothediffusionofDEZ
Fig.5. FTIR vibrational spectra for absorbance in the C(cid:1)H stretching intothezinconefilm.SimilartoaluconeMLD,[6]thezincone
vibrationregionafter10MLDcyclesat90,110,130,150,and1708C.
film growth is believed to occur by both the surface
chemistry,describedbyEquations1and2,andthediffusion
zincone film is very conformal on the ZrO nanoparticles. of DEZ into the zincone film. The DEZ molecules that
2
The thickness of 61A˚ after thirty MLD cycles at 1308C is diffuseintotheMLDfilmareavailabletoreactduringthe
consistent with a zincone MLD growth rate of 2.0A˚ per subsequent EG exposure to form new zincone polymer
MLDcycle.ThirtycyclesofzinconeMLDwasrepeatedon chains. This additional growth mechanism is similar to a
ZrO nanoparticlesatvarioustemperaturesintherange90– CVD reaction in the near-surface region of the zincone
2
1708C. The TEM images were consistent with a zincone polymer. This diffusion mechanism can explain the
MLD growth rate that was 4.0A˚ per MLD cycle at 908C, temperature dependence of the zincone MLD growth. At
andreduced to 0.25A˚ perMLD cycle at1708C. highertemperatures,lessDEZmaydiffuseintothezincone
Figure 7 displays the zincone MLD growth per cycle film. In addition, the DEZ in the zincone film may desorb
versustemperaturedeterminedbytheTEManalysis.These
resultsarecomparedwiththeintegratedabsorbanceforthe
C(cid:1)H stretching vibrations of zincone films after ten MLD
cycles at various temperatures. The integrated absorbance
hasbeenscaledtomatchthegrowthpercycledeterminedby
the TEM measurements. The temperature-dependent
Fig.6.TEMimageofzinconeMLDfilmonZrO2nanoparticlesafter30MLD Fig.8.FTIRdifferencespectrafora)DEZ-EGat1708C,b)EG-DEZat
cyclesat1308C. 1708C,c)DEZ-EGat908C,andd)EG-DEZat908C.
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from the film at a faster rate at higher temperatures. Less vibrations suggests that much of the DEZ is diffusing into
diffusionintothefilmandmoredesorptionofDEZfromthe thezinconepolymerwithoutreactingwithhydroxylgroups
filmwouldyieldalowerzinconeMLDgrowthpercycleat at 908C. The spectrum for EG-DEZ in Figure 8d shows a
highertemperatures. loss of absorbance from C(cid:1)H stretching vibrations of the
InadditiontolowergrowthpercycleforzinconeMLDat ZnCH CH (cid:2) species, and a gain of absorbance from C(cid:1)O
2 3
highertemperatures,the mechanismof zinconeMLD also and Zn(cid:1)O stretching vibrations. These absorbance
changes with temperature. Figure 8 compares FTIR changes,togetherwiththepresenceofabsorbancechanges
difference spectra for DEZ-EG and EG-DEZ at 908C for the O(cid:1)H stretching vibrations, are consistent with the
and 1708C. For growth at 1708C, there is negligible reaction between EG and ZnCH CH (cid:2) species to form
2 3
absorbancechangeintheO(cid:1)Hstretchingvibrationregion both ZnOCH CH OH(cid:2) and (cid:1)ZnOCH CH OZn(cid:1) species
2 2 2 2
in Figure 8a for DEZ-EG or Figure 8b for EG-DEZ. The at 908C.
absence of hydroxyl groups either removed by DEZ or
producedbyEGsuggeststhatmostoftheEGreactionsare
‘‘double’’ reactions at 1708C. If EG reacts with two 2.4.LinearZincone MLDGrowth
ZnCH CH (cid:2)species,thentherearenonewO(cid:1)Hstretching
2 3
vibrationsafterthe EGexposure. The quality and thickness of zincone films grown on Si
AlthoughthereisnegligibleabsorbancechangeforO(cid:1)H wafers at 1308C was also measured using ex-situ XRR
stretchingvibrationsshowninFigure8a,thereisanincrease analysis. The XRR scans were fitted using the REFS data
in absorbance for C(cid:1)H stretching vibrations of the fittingsoftwarefromBedeScientific.ForthisXRRanalysis,
ZnCH CH (cid:2)speciesafterDEZexposures.Thisabsorbance anAl O ALDfilmwithathicknessof(cid:3)640A˚ wasinitially
2 3 2 3
increase is consistent with the diffusion of DEZ into the deposited on the silicon wafer using TMA and H O.
2
zincone film at 1708C. Figure 8aalso shows that the DEZ Subsequently,zinconefilmsweregrownontheAl O ALD
2 3
exposureproducesverylittleincreaseintheabsorbancefor layer. Figure 9a shows the XRR scan, approximately one
the C(cid:1)O and Zn(cid:1)O stretching vibrations that would be hour after deposition, of a zincone film grown using
consistent with (cid:1)ZnOCH CH OZn(cid:1) species. This obser- 500MLDcyclesat1308C.Thisscandisplaysanoscillatory
2 2
vation argues that the DEZ diffuses into the zincone film reflectedintensityversusangle.Theoscillationoccursasthe
withoutreactingwith hydroxylgroups. intensity drops over many orders of magnitude. This
Figure8bshowsthattheEGexposureat1708Cremoves behaviorisconsistentwith averysmoothandhighquality
absorbance for the C(cid:1)H stretching vibrations from film.Theoscillatoryintensityresultsfromthefilmthickness
ZnCH CH (cid:2) and adds absorbance for the C(cid:1)H stretching and the individual Al O and zincone layers. Figure 9b
2 3 2 3
vibrations from (cid:1)OCH CH O(cid:1) species. There are also displaystheXRRscanofthesamefilmafterfiveweeksin
2 2
increases in the absorbance of the C(cid:1)O and Zn(cid:1)O air.TheXRRscansinFigures9aand9barenearlyidentical,
stretching vibrations. These absorbance changes, together andindicate that the zinconefilm isverystable.
with the absence of absorbance changes for the O(cid:1)H Figure 10a shows the zincone film thicknesses measured
stretchingvibrations,areconsistentwiththereactionofEG byXRRafter80,150,and500MLD cyclesat1308C.The
withtwoZnCH CH (cid:2)speciestoform(cid:1)ZnOCH CH OZn(cid:1) film thickness versus number of MLD cycles is linear and
2 3 2 2
at 1708C. The ‘‘double’’ reactions of EG remove consistent with a growth rate of 0.7A˚ per MLD cycle at
ZnCH CH (cid:2) sites and do not generate ZnOCH CH OH(cid:2) 1308C.Thegrowthrateof0.7A˚ perMLDcycleat1308Con
2 3 2 2
hydroxyl sites for zincone film growth. However, a finite the silicon wafer is less than the growth rate of 2.0A˚ per
amountofDEZdiffusionintothezinconefilmduringDEZ
exposuremaintainsthelowzinconegrowthrateof(cid:3)0.25A˚
perMLD cycle at1708C.
Muchlargergrowthratesof(cid:3)4.0A˚ percycleareobserved
at the low temperature of 908C. Figures 8c and 8d reveal
that hydroxyl groups are active during zincone MLD at
908C.Figure8cshowsthatthereisadecreaseinabsorbance
for O(cid:1)H stretching vibrations after the DEZ exposure.
Likewise,Figure8drevealsagaininabsorbanceforO(cid:1)H
stretchingvibrationsaftertheEGexposure.Therestillmay
bedoublereactionsduringtheEGexposure.Howeverthere
arealsoEGreactionsthatproducehydroxylgroupsonthe
zincone film.
The spectrum for DEZ-EG in Figure 8c reveals that
thereisalargeabsorbanceincreaseintheC(cid:1)Hstretching
region for the ZnCH CH (cid:2) species. The correspondingly
2 3 Fig.9.XRRscansofzinconefilmgrownonSiwaferusing500MLDcyclesat
lowincreaseofabsorbanceforC(cid:1)OandZn(cid:1)Ostretching 1308Caftera)(cid:3)1hexposureinair,andb)(cid:3)5weeksexposureinair.
Chem.Vap.Deposition2009,15,112–121 (cid:1)2009WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim www.cvd-journal.de 117
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exposures. Although the zincone MLD growth was linear
versus number of MLD cycles under one set of reaction
conditions, the absolute mass gain per cycle and the mass
gainsfortheindividualDEZandEGreactionsduringone
cyclewerenotconsistentforexperimentsondifferentdays.
Thisinconsistencyisbelievedtoresultfromthevariationsin
the pumping speed during different zincone MLD growth
experiments.
2.5.Compositionand Stabilityof ZinconeFilms
The composition of the zincone films was investigated
using XPS.Figure 11showsXPS resultsfor a zinconefilm
grown using 500 MLD cycles at 1308C. The average
compositionobtainedfromseveralsuchfilmswas10%zinc,
22%carbon,and68%oxygen.Theuncertaintyontheseat.-
% values is <2%. These atomic percentages are based on
peakareasofeachcomponent.Theadventitiouscarbonat
285eV was not included in this XPS analysis. No other
elements are present in the zincone film. In contrast, a
compositioncanbepredicted(20%zinc,40%carbon,and
40% oxygen) for the zincone film based on the reaction
mechanism shown in Figure 1, and a possible polymer
formulaof((cid:1)Zn(cid:1)O(cid:1)CH CH (cid:1)O(cid:1)) .Thezinconefilmhas
2 2 n
less zinc and more oxygen than predicted by the expected
formula. The higher oxygen and lower zinc atomic
percentages are related to the adsorption of H O into the
2
zincone films uponexposure to air. As discussed earlier in
Section 2.2, the in-situ FTIR spectra during static EG
Fig.10.a)XRRmeasurementsofzinconefilmthicknessversusnumberof
exposures were consistent with H O adsorption. Features
MLDcyclesat1308C.b)QCMmeasurementsofmassgainversustimefor 2
zinconeMLDfilmgrowthat1358C. assignedtoH2Oadsorptionat(cid:3)1590cm(cid:1)1werealsopresent
whentheliquidN trapwasnotusedtopumponthereactor.
2
MLD cycle at 1308C on the ZrO nanoparticles. The
2
different growth rates on the Si wafer and the ZrO
2
nanoparticlescanbeexplainedbyeitherdifferentpumping
speedsduringthezinconeMLDgrowthexperiments,orthe
lowgasconductanceintheZrO nanoparticles.IntheZrO
2 2
nanoparticles, longer exposure times are needed for the
reactantstoreachtheentiresurfacearea.Inaddition,longer
purgetimesareneededtoremovethereactantsaftertheir
exposure.Ifthereactantisnotcompletelypurgedfromthe
bedofnanoparticles,thenthezinconeMLDgrowthratecan
increaseresultingfrom CVDgrowth.
In-situQCMmeasurementsalsorevealedthatthezincone
MLDgrowthwaslinearversusthenumberofMLDcycles.
TypicalresultsfromtheQCManalysisofzinconeMLDat
1358CareshowninFigure10b.Thereactantpulsesequence
duringoneMLDcyclewas;DEZdosefor0.75s,purgefor
120s, EG dose for 0.45s, and purge for 120s. These dose
times resulted in approximate exposures of 65mTorr s for
DEZand80mTorrsforEG.ThemassgainperMLDcycle
was 20.4ng cm(cid:1)2 for the QCM results at 1358C shown in
Figure 10b. The QCM measurements also demonstrated
thattheDEZandEGreactionswereself-limiting.Themass
Fig.11.XPSanalysisofzinconeMLDfilmcompositionafter500MLDcycles
gains reached an asymptotic limit versus DEZ and EG at1308C.
118 www.cvd-journal.de (cid:1)2009WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim Chem.Vap.Deposition2009,15,112–121
FullPaper
8.9%,respectively.TheseXPSresultsindicatethatthezinc
atomicpercentagesareveryconsistentoverthefullrangeof
temperatures. The changes in the zincone MLD growth
mechanismandtheobservationofonlydoubleEGreactions
at higher temperatures do not alter the zincone film
composition.
3. Conclusions
The MLD of a new zinc-containing organic-inorganic
polymerwasgrownusingthesequentialexposuresofDEZ
andEG.Thispolymerrepresentsanewtypeofzincalkoxide
polymersthatcanbecalledzincones.TheMLDprocedure
used to grow the zincone film is similar to the sequential
exposures of TMA and EG used for alucone MLD. This
work indicates that a variety of different hybrid organic-
Fig.12.a)Absolutein-situFTIRspectrumofzinconefilmgrownusing40 inorganicpolymerscanbegrownbyMLDusingmetalalkyl
MLDcyclesat1108C.Thisspectrumwasrecordedwiththezinconefilm precursorsand variousorganic precursors.
undervacuumintheMLDreactor.b)AbsoluteFTIRspectrumofthesame
The film growth and surface chemistry during zincone
filmafter(cid:3)1hexposureinair.
MLDwasstudiedbyin-situFTIRmeasurements.TheFTIR
spectraincreasedprogressivelyversusthenumberofMLD
There was also evidence from the FTIR spectra for H O cycles.FTIRspectraaftertheEGandDEZexposureswere
2
adsorptionintothezinconefilmsafterexposingthezincone consistent with loss and gain of the absorbance for C(cid:1)H,
filmsto air. O(cid:1)H,C(cid:1)O,andZn(cid:1)Ostretchingvibrations.FTIRstudies
Figure12ashowstheabsolutein-situFTIRspectrumofa also confirmed the self-limiting nature of the surface
zincone film deposited after 40 MLD cycles at 1108C. This reactionsandmonitored lowerzinconeMLD growthrates
spectrumwasrecordedwiththezinconefilmundervacuumin athighertemperatures.
the MLD reactor. Figure 12b displays the absolute FTIR TEMmeasurementsonZrO nanoparticlesobservedvery
2
spectrum of the same zincone film after approximatelyone conformalzinconefilms.TheTEMstudiesalsodetermined
hour of air exposure. This spectrum reveals the growth of that the zincone MLD growth rate varied from 4.0A˚ per
absorbancecorrespondingwithO(cid:1)Hstretchingvibrationsin MLDcycleat908Cto0.25A˚ perMLDcycleat1708C.XRR
the range 2700–3700cm(cid:1)1. There are also adsorbed H O measurements on silicon wafers displayed linear zincone
2
modes and broadened CH features in the range 1300– MLD growth with a lower zincone MLD growth rate of
2
1700cm(cid:1)1.[34] Very little subsequent change was observed 0.7A˚ perMLDcycleat1308C.Differentpumpingspeeds,
afterweeksofairexposure.TheseFTIRresultsindicatethat lower gas conductance, and possible CVD reactions may
thezinconefilmsadsorbH Ouponexposuretoair.However, explainthehigherzinconeMLDgrowthratesontheZrO
2 2
theFTIRandXRRresultsrevealthatthezinconefilmsare nanoparticles.QCMmeasurementsconfirmedlineargrowth
verystablefollowingthisinitialH Oadsorption. for thezincone filmsversusthe number ofMLD cycles.
2
AftertheinitialadsorptionofH Ouponexposuretoair, The FTIR difference spectra indicated that the reaction
2
the zincone MLD films are more stable than the alucone mechanism for zincone MLD was dependent on tempera-
MLDfilmsstudiedpreviously.[6]Thestabilityofthezincone ture.Athighertemperatures,nofreehydroxylgroupswere
films was confirmed bythe XRR measurements at various presentinthezinconefilmasdemonstratedbytheabsence
timesafterfilmgrowthshowninFigure9.TheseXRRscans of O(cid:1)H stretching vibrations in the FTIR spectra. The
revealed almost no change in the thickness of the zincone absence of free hydroxyl species may be explained by a
films after aging for weeks at room temperature under double reaction of EG with two ZnCH CH (cid:2) species. The
2 3
ambientairconditions.Forexample,forazinconefilmwith lackofhydroxylgroupsdoesnotstopthezinconeMLDfilm
a thickness of (cid:3)335A˚ grown using 500 MLD cycles at growthathighertemperatures.TheFTIRspectrasuggested
1308C,thethicknessdecreasedonly2.4%afteragingforfive thatDEZcandiffuseintothezinconefilmandnucleatethe
weeks. In contrast, the alucone MLD film thicknesses growth ofa new zincone polymerchain.
decreased about 22% in the first six days after growth at The zincone MLD films were observed to adsorb H O
2
roomtemperature underambient airconditions.[6] afterexposuretoair.ThisH Oadsorptionismonitoredby
2
Thezinccompositionwasalsoinvestigatedaftergrowthat theFTIRspectraandisconsistentwiththehighoxygenand
varioustemperatures.XPSmeasurementsonzinconeMLD lowzinccompositioninthezinconefilmsobtainedbyXPS
samplesgrownusing80MLDcyclesat90,110,130,150,and analysis. Following the H O adsorption, the zincone films
2
1708Cyieldedzinccompositionsof10.7,10.6,10.0.9.9,and are very stable for multiple weeks as determined by FTIR
Chem.Vap.Deposition2009,15,112–121 (cid:1)2009WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim www.cvd-journal.de 119
FullPaper
theXRRmeasurements.ThethicknessesofthezinconefilmsonSiwafers
wereextractedusingtheREFSdatafittingsoftwarefromBedeScientific.
Borondopedp-typesiliconwaferswithathinnativeoxide(SiliconValley
Microelectronics,Inc.)wereusedforthisex-situanalysis.
XPSimagesforC1s,O1s,andZn2pwereobtainedfromaPerkin-Elmer
5600photoelectronspectrometerwithmonochromaticKasource(12.5mA,
12kV) under a pressure of 2(cid:5)10(cid:1)10Torr. The binding energies were
referencedtotheadventitiousC1speakat285eV.TheTEManalysiswas
performedusingaPhilipsCM10transmissionelectronmicroscopewithan
80kVbeamenergy.ThezinconeMLDgrowthpercyclewasdeterminedby
measuring the film thickness of the zincone polymer on the ZrO2
nanoparticlesanddividingbythenumberofMLDcycles.
Received:October22,2008
Revised:March02,2009
[1] S.M.George,B.Yoon,A.A.Dameron,Acc.Chem.Res.2009,42,498.
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andXRRmeasurements.Thesenewzinconefilmsaddtothe [8] M.D.Groner,J.W.Elam,F.H.Fabreguette,S.M.George,ThinSolid
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[10] J.W.Elam,D.Routkevitch,P.P.Mardilovich,S.M.George,Chem.
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[11] Y.Du,S.M.George,J.Phys.Chem.C.2007,111,8509.
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[13] M.Putkonen,J.Harjuoja,T.Sajavaara,L.Niinisto,J.Mater.Chem.
2006,17,664.
AschematicdiagramoftheviscousflowMLDreactorequippedwithanin- [14] T. Yoshimura, S. Tatsuura, W. Sotoyama, A. Matsuura, T. Hayano,
situFTIRspectrometerisshowninFigure13.ThisviscousflowMLDreactor Appl.Phys.Lett.1992,60,268.
isverysimilartopreviousreactorsusedforMLD[6,11,12].Thereactantswere
[15] H. I. Shao, S. Umemoto, T. Kikutani, N. Okui, Polymer 1997, 38,
pumpedthroughaliquidN2trapbyamechanicalpump,whichmaintaineda 459.
pressureof0.60Torrwithacarriergasflowof100sccmintothereactor.The
carriergaswasultrahighpuritynitrogen(Airgas),whichhelpedtransport [16] A.Kim,M.A.Filler,S.Kim,S.F.Bent,J.Am.Chem.Soc.2005,127,
reactantsintothereactorandremovereactionproductsfromthereactor. 6123.
Thein-situFTIRstudieswereperformedwithaNicoletNexus870FTIR [17] A.Kubono,N.Okui,Prog.Polym.Sci.1994,19,389.
spectrometerequippedwithaliquid-N2cooledmercury-cadmium-telluride [18] C.N.McMahon,L.Alemany,R.L.Callender,S.G.Bott,A.R.Barron,
(MCT-B)infrareddetector.Spectrawerecollectedwithamirrorspeedof Chem.Mater.1999,11,3181.
1.8cm(cid:4)s(cid:1)1, andaveragedover100 scansusing4cm(cid:1)1resolution. TheIR
[19] B.B.Burton,F.H.Fabreguette,S.M.George,ThinSolidFilms2009,(In
transparent windows on the viscous flow MLD reactor were KBr disks
Press).
suppliedbyInternationalCrystalLaboratories.Thespectrometersetupwas
purgedwithdryandCO2-freeairdeliveredfromapurgegasgenerator. [20] B.B.Burton,D.N.Goldstein,S.M.George,J.Phys.Chem.C.2009,113,
ThetransmissionFTIRspectroscopymeasurementsrequiredhighsurface 1939.
area samples to obtain a sufficient signal-to-noise to monitor the surface [21] O.Nilsen,H.Fjellvag,PatentCooperationTreaty(PCT),WorldIntel-
species. The high surface area samples were approximately spherical lectual PropertyOrganization, PublicationNumberWO2006/071126
nanoparticles with average diameters of 25nm for ZrO2 and 11nm for A1,PublicationDateJuly6,2006,Title:ThinFilmsPreparedwithGas
SiO2.Thenanoparticleswerepressedintoastainlesssteelgridusingmethods PhaseDepositionTechnique.
describedearlier[7,35].ThestainlesssteelgridssupportingtheZrO2orSiO2 [22] WeinitiallyreportedourresultsonzinconeandaluconeMLDusing
nanoparticles were obtained from Tech Etch. The ZrO2 and SiO2 alkylmetalsandvariousorganicdiolsattheAVSTopicalConferenceon
nanoparticleswereobtainedfromSigma-Aldrich. Atomic Layer Deposition (ALD2008) in Bruges, Belgium, June 28–
ThezinconeMLDgrowthwasmonitoredat90,110,130,150,and1708C. July2,2008(B.Yoon,J.L.O’Patchen,S.D.Davidson,D.Segehte,A.S.
EachDEZexposureconsistedoftwo1.0sdosesofDEZ.EachDEZdose Cavanagh, S.M. George, Molecular Layer Deposition of Hybrid
producedapartialpressureof200mTorr.EachEGexposureconsistedoffive Organic-InorganicPolymersBasedonMetalAlkylandDiolReactants,
1.0sdosesofEG.EachEGdoseproducedapartialpressureof20mTorr. July2,2008).
Purgetimeof120swereusedaftereachDEZandEGdose.OnesetofDEZ [23] ZinchybridmaterialfromDEZandEGwasalsoreportedattheAVS
andEGexposuresdefinedoneMLDcycle.TheDEZandEGreactantswere TopicalConferenceonAtomicLayerDeposition(ALD2008)inBruges,
obtainedfromSigma-Aldrich. Belgium,June28–July2,2008(Q.Peng,R.M.Vangundy,G.N.Parsons,
Thein-situQCMmeasurementtechniquehasbeendescribedpreviously AtomicLayerDepositionofZincOxide/OrganicHybridMaterialfrom
[36].TheQCMmeasurementswereperformedinalargerviscousflowreactor DiethylZincandEthyleneGlycol,July2,2008).
usingaTM-400(Maxtek)thinfilmdepositionmonitor[6].Thesemeasure-
[24] J.W.Elam,Z.A.Sechrist,S.M.George,ThinSolidFilms2002,414,
mentsemployedaMaxtekBSH-150bakeablesensor,andaquartzcrystal
43.
withapolishedAufaceanda6MHzoscillationfrequency(ColoradoCrystal
Corp.). [25] J.D.Ferguson,A.W.Weimer,S.M.George,J.Vac.Sci.Technol.A
Ex-situ XRR data were acquired by a high resolution Bede D1 2005,23,118.
Diffractometer(BedeScientific).ACuKaX-raytubewithawavelength [26] B.S.Sang,A.Yamada,M.Konagai,Jpn.J.Appl.Phys.Part21998,37,
of1.54A˚,afilamentcurrentof40mA,andavoltageof40kVwereusedfor L206.
120 www.cvd-journal.de (cid:1)2009WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim Chem.Vap.Deposition2009,15,112–121