SurfaceandCoatingsTechnology,
64(1994)127-130127
Influenc梵高作品欣赏 eofdepositionparametersontherefractiveindexandgrowth
rateofdiamond-likecarbon:films
,
X.
Zheng,,
DepartmentofMaterialsScienceandEngineering,NorthwesternPolytechnicalUniversity,Xian710072(China)
(ReceivedSeptember6,1993;acceptedinfinalformNovember5,1993)
Abstract
Inordertoudiamond-likecarbon(DLC)filmsasprotectiveandantireflectioncoatingsforIRopticalmaterialxpodtohostile
environments,aninvestigationhasbeensystematicallyconductedontheinfluenceofthedepositionparametersontherefractive
indexandgrowthrateofDLCfilms,whicharetwoofthemostimportantparametersinevaluatingopticalcharacteristicsof
erimentalresultsshowthatboththerefractiveindexandgrowthrateofDLCfilmsdependstrongly
onthenegative
d.c,
ractiveindexincreaswithincreasingbiasvoltageanddecreaswithincreasingpartial
wthrateincreasgreatlywhenthebiasvoltageislarger
iousparameterswr
transformIRspectroscopyre手抄报爱祖国 sultsshowthatthestrengthofthe
C-Hstretchingabsorptionbandintherange3300-2850cm
-1
is
graduallergybombardmentofthegrowingfilm
playsanimportantroleinthestructureandhencethepropertiesofDLCfilms.
uction
Inrecentyearsdiamond-likecarbon(DLC)filmshave
beenthesubjectofextensiveinvestigationowingtotheir
unusualandhighlydesirablepropertiessuchaxtreme
hardness,resistancetochemicalattack,highthermal
conduction,highintrinsicelectricalresistivity,wideband
gapandopticaltransparencyintheIRregion,which
makethemufulforelectronicdevicesandvarious
opticalandmechanicalapplications[1,2].DLCfilms
canbedepositedatlowtemperatureandhighdeposition
rateoverlargeareasusingavarietyofplasma-enhanced
chemical
vapourdeposition(PECVD)techniques[3].
Anumberofattemptshavebe右文 enmadetodisclo
complexdeposition
parameters-structure-property
relationshipsinthefilms[4,5].Thepropertiesof
DLCfilmschangeasafunctionofdepositionparameters
suchaspowerdensity,ltage,feed
gasflowrate,
reactorpressure,ractive
indexofDLCfilmsvariesfrom1.6to2.9depending
onthedepositionmethodandconditions[2,6].
However,evenforthesamedepositionmethod,the
experimentallawsgoverningthechangeinrefractive
indexwithdepositionparametersarenotexactlyiden-
tical[7,
8].Therefore,beforedepositingantireflection
filmson
IRopticalmaterials,itisveryimportantto
understandfullytherelationshipbetweentherefractive
indexandgrowthrateofDLCfilmsandthedepositionparameters.
InthisworkDLCfilmsaredepositedbyther.f
earchemphasisisplacedon
therelationshipbetweenthepropertiesoftheDLCfilms
iationin
refractiveindex
opticalabsorptioncharacteristicsofthefilmsarealsoinvestigated.
mentaldetails
depositionsystem
ech-
nique.
Theexperimentalapparatusudinthisworkis
auimprovedGDM-300BN-typehighvacuumcoater
whichconsistsoffourctions:thevacuumsystem,the
gasinletsystem,thepowersource
andtheelectrodes.A
water-cooledcopperelectrodeactedassubstrate
holder
andwascapacitativelycoupledtothe13.56MHz
d.
r.f
powerwasmeasuredbyawattmeterandwasvaried
ltage
canbe
continuouslyadjustedinthewiderange300-1000V.
Acetyleneormethanegasdilutedwithhighpurity
argon
wrateofeachgaswas
controlledbya
D08-3/ZMtypemassflowcontroller.
Atypicalbackgroundpressurewas1.33x
10-
3
depositionparametersarelistedinTable1.
0257-8972/94/$7.00
SSDI0257-8972(93)02225.2
htsrerved
128
t01.
j
RefractiveindexandgrowthrateofDLCfilms
TABLE
1.
Plasmadepositionparameters
(W)
Biasvoltage
-Va(V)
Totalgaspressure(Pa)
Contentof
hydrocarbons
10%-100%C
2H
2
5%-100%CH4
Depositiontime(min)
Substrate
temperature
("C)<100
20-1200-10005.33-13.315-90
atematerialsandpretreatments
Monocrystallinesilicon(Si)andgermanium(Ge)
sheetswithdimensionsof10x20x0.34mm"and0
13x0.26mnr'
surfacesofGeandonesurfaceofSiwerepolishedtoa
pleswerethoroughlycleanedultra-
sonicallyinacetoneandthencleanedbyhighenergy
Ar"bombardmentfor5-15minpriortodeposition.
Thoroughsurfacecleaningwasfoundtobeanimportant
stepinimprovingtheadhesionbetweenthe
DLCfilmsandthesubstrates.
terizationofDLCfilms
TherefractiveindexandthicknessoftheDLCfilms
weremeasuredat0.6328urnusinga1T75-1-typelar
ellipsometer
andthemeasurementofthefilmthickness
IR
transmittance
intherange4000-400em
-1
wasmeasuredbyemploying
a60SXRFouriertransform
IR
(FTIR)spectrometer
(Nic1ot,USA).Thespectrawererecordedataresolution
of4em
-1andaveragedover32scans.
sanddiscussion
tiveindex
Theexperimentalresultsobtainedusingtheortho-
gonaltestmethodshowthatdepositionparameterssuch
asthepowerdensity,ltage,concen-
trationofthehydrocarbongasandflowrateofthe
mixtureareofgreatimportanceindeterminingthe
2.7
refractiveindexofDLC
paperthepower
densityisfixedat30Wem-
2
Torr
-1
andtheeffectofthe
otherparametersontherefractiveindexisinvestigated.
Figure1showsthedependenceoftherefractiveindex
oftheDLCfilmsgrownonsiliconandgermanium
ractive
indexofthe
DLCfilmsonSisubstratesincreasfrom
2.2at
Vb
=-
300Vto2.45at
Vb
=-
Vb
values
higherthan-500Vtherefractiveindexincreasslowly
toabout2.65(eFig.1(ve-mentionedexperi-
mentallawisingoodagreementwith
thatobtainedby
Koidl
etal.
[7].TherefractiveindexoftheDLCfilms
voltage
Vbintherange300-900V(eFig.l(b)).
ltagecancauahighenergy
ionbombardmentofthegrowingfilmsurface,whichwill
resultinanenhancementoftheadhesivestrength
betweenthe
bombardmentalsocausapreferentialsputteringof
weaklybondedcarbonphafromthefilmsurfaceand
henceincreastherelativeconcentrationof
Sp3bonds.
Alltheabove-mentionedfactorsleadtoanincreaintherefractiveindexoftheDLCfilms.
Figure2showstheinfluenceofthebiasvoltage
Vb
onthe
IR
transmittancespectrumoftheDLCfilmson
thepolishedSisurface(withtheothersurfaceunpol-
ished).Withincreasingbiasvoltagethetransmittance
decreasandtheintensityoftheabsorptionpeakat
2920em
-1
(or3.4urn),reprentingthestretchingvibra-
tionmodesofCHorCH
2
specieslocalizedattetrahedral
(Sp3)sites
[9],isgraduallyweakened.
Itisindicated
I
~
2.62.5
X
2.5
2.32.1
1.9
~
~
2.22.1
400
600
(a)
~
800
1000
BIASVOLTAGE(-V)
1.7300
500
(b)
700900
BIASVOLTAGE(-V)
Fig.
enceofrefractiveindexonbiasvoltagefor(a)DLCjSiand(b)DLCjGe.
et
al./Refractiveindexandgrow记叙文600字 thrateofDLCfilms
129
70
~
60~
eJ
50
j-300V
2-400Vg
~
3-SOOv
102.0
5.0
8.0
11
.0
14.0
WAVELENGTH(11m)
ittancespectraofDLC/Siundervariousbiasvoltages.
thattheionbombardmentcausaconsiderablecrack-
ingofC-Hbonds,leadingtoareducedhydrogencontentinthefilm.
Therelationshipsbetweentherefractiveindexandthe
contentofthehydrocarbongasandtotalflowrateof
refractiveindexdecreaswithincreasingflowrateratio
ofC
2H2
orCH
4
toC
llyspeaking,therefractive
2H
2
+
ArorCH
4
+
Arrespectively
indexincreaswithdecreasinghydrogenconcentration
[10].Thereforealowervalueofrefractiveindexis
caudbyahigherproportionofHatomsbondedinto
the
DLCfilmswithincreasingpartialpressureofhydro-
carbongasandtotalflowrate,whichhasbeenproved
intensityofthe
C-Habsorptionbandnear2900cm-
I
isgraduallyweakenedwithdecreasingflowrateratioof
C
2H2
toC
2H2
+
ArandtheIRabsorptionb胆红素高吃什么药 andwas
obrvedtodisappearwhentheratiowaslowerthan
25%C
near
2900
2H
2
.
Filmswithoutthe权御盛唐 C-Habsorptionband
em
-I
intheIRabsorptionspectrumwere
2.1
1.6
o
2
HYDROCARBONCONTENT(%)
Fig.
3.
DependenceofrefractiveindexofDLCfilmson
Si
substratesonhydrocarboncontent.
2.3
2.2
3.6
5.4
7.2
9.0
TOTALFLOWRATE(SCCM)
enceofrefractiveindexofDLCfilmsonSisubstrates
on
totalflowrate.
WAVENUMBER
(em-I)
Fig.
5.
InfluenceofC
2
H
2
contentonIRabsorptionspectrumofDLC
filmson
Gesubstrates.
consideredtobeunhydrogenatedamorphouscarbon
films[11,12].
It
canalsobeenfromFig.3thatthe
refractiveindexhasarelationwiththenatureofthe
ractiveindexofDLCfilms
depositedfromAr
-C
2H
2
islowerthanthatofDLC
filmsdepositedfromAr-CH
4
underidenticaldepositionconditions.
rate
Figure6showsthedependenceofthegrowthrateof
theDLCfilmsdepositedonGesubstratesonthenega-
ltage.
It
isobrvedthatthereisa
thresholdbiasvoltagevalueV
th
ofaround
-600
growthrateincreas天安门广场 withincreasingbiasvoltageand
for
Vb
higherthan
J-;h
thegrowthrateincreasrapidly.
Thethresholdvaluehasarelationwiththenatureof
thesubstratematerial,thesubstratesurfaceareawith
respecttothatofthecathodeelectrode,andthesubstrate
thicknesswithrespecttothedistancebetweenthe
llerthesurfaceareaandthethicker
thesubstrate,thelarger
J!;h
andthelowerthedeposition
7
showsthevariationinfilmthicknesswithdeposition
ltageof
-600
expected,thefilmthicknessincreaswiththedepos-itiontime.
250200
150
100"===::::::::"':"'-.-.
__
...L-...J
3
BIASVOLTAGE(-V)
enceofgrowthrateofDLCfilmsonGesubstratesonbiasvoltage.
130
tal./RefractiveindexandgrowthrateofDLCfilms
........
1.60
'-'
~
1.20
......
t3
0.80
~
~>x-c
2
DEPOSITIONTIME(min)
Fig.
7.
DependenceoffilmthicknessofDLCfilmsonGesubstratesondepositiontime.
Thenetgrowthratedependsontwocompetingpro-
cess,
depositionandetching,whichoccurduring
thewholeprocessofpreparingDLCfilmsfrombegin-
hingprocessplaysasignificantrole
intheopticalandmechanicalpropertiesoftheDLC
ltageandtheconcen-
trationofArgascanbeudtocontroltheetchingrate.
ThereforethenetgrowthratedependsonthebiasvoltageandArcontent.
Thedepositionparameterssuchaspowerdensity,
negativebiasvoltage,Arconcentration,totalflowrate,
nfluencethestructureandpropertiesofDLC
filmsareinterrelated,whichimpliesthatidenticalexperi-
mentalresultscanbeobtainedbyadjustingtheother
tance,toincreatherefrac-
tiveindexoftheDLCfilm,increasingthepowerdensity
orArconcentrationiquivalenttoincreasingthe
negativebiasvoltageundercertainconditions.
It
hasto
bedeterminedthroughacomprehensiveanalysisaccord-
ingtopracticalsituationxactlywhichdepositionpro-cessisadopted.
Accordingtotheabove-mentionedexperimentallaws,
wehavesuccessfullypreparedantireflectionandprotec-
tivefilmsonGesubstratesbyusingasuccessiveapproxi-
imumIRtransmittanceofGe
withasingle-layer
DLCfilmononesideandbothsides
hasreachedthetheoreticalvaluesof64%and99%
ransmittanceofanon-uniform
DLCfilm,whorefractiveindexchangesgradually
alongthefilmthickness,coatedonbothsidesofaGe
r85%.
sions
TherefractiveindexofDLCfilmsincreaswith
ltagebetweentheplasma
andtheelectrodeanddecreaswithincreasingcontent
ofthehydrocarbongasandtotalflowrateofthemixture.
Thegrowthrateincreaswithincreasingnegative
holdbias
voltagevalue
~h
existsinthedependenceofthegrowth
wthrateincreas
rapidlywhenthebiasvoltageislargerthanthethresh-oldvalue.
Thedepositionparameterswhichinfluencetheoptical
andmechanicalpropertiesofDLCfilmsareinterrelated.
Thehighenergybombardmentonthegrowingfilms
caudbythenegativebiasvoltageplaysaveryimpor-
tantroleinthestructureandpropertiesofDLCfilms.
Theintensityoftheabsorptionbandat
2900
em
-1
is
graduallyweakenedorevendisappearswithincreasingbiasvoltageandArconcentration.
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