2001
IEEE
7 h In e na ional Con e ence on Solid Dielec ics, June 25-29,2001, Eindho en, he Ne he lands
303
DIELECTRIC BREAKDOWN
OF
Si02
THIN
FILMS
DEPOSITED
BY
ION BEAM
INDUCED AND PLASMA ENHANCED CVD.
A. Ba anco, bA. Jimknez,
bF.
F u os,
"J.
Co ino,
'F.
Yube 0:J.P. Espinbs, aA.R. Gonzhlez-Elipe
a*
"Ins i u e
de Ciencia de Ma e iales de Se illa (CSIC-Uni e sidad de Se illa). A da. AmL ico Vespucio
s/n.
41092
Se illa, Spain.
'Dp o. de Fisica A dmica, Molecula
y
Nuclea . Facul ad de Fisica. Uni e sidad de Se illa. A da. Reina Me cedes
dn.
41012
Se illa, Spain.
bDepa amen o de Fisica Aplicada
I.
Facul ad de In om' ica. Uni e sidad de Se illa. A da. Reina Me cedes
dn.
41012
Se illa, Spain.
co esponding au ho
:
[email p o ec ed]
INTRODUCTION
Silicon dioxide in he o m o hin ilms is a e y
in e es ing ma e ial o elec onic, op ical o
passi a ion laye applica ions [l-31. Fo many o hese
pu poses, in pa icula mic oelec onics, i is c i ical
ha compac laye s o Si02 can be ob ained a low
empe a u e. Howe e , mos o he es ablished me hods
o p epa a ion a e based ei he on he mal CVD,
equi ing in his case e y high empe a u es, o on
plasma CVD. When wo king a low empe a u e, he
mic os uc u e o he
ilm
is usually no su icien ly
good and he composi ion is no well de ined. In
p ac ice, plasma-ac i a ed p ocedu es o p epa a ion
o
Si02 hin ilms wi h op ical o elec onic applica ions
yield op imal mic os uc u es a in e media e
empe a u es
o
he o de o 200-300 "C. [4-51
This pape p esen s a compa a i e s udy o Si02 hin
ilms p epa ed a oom empe a u e by ion beam
induced chemical apo deposi ion (IBICVD) and
plasma enhanced chemical apo deposi ion (PECVD)
me hods. The ilms
a e
cha ac e ized by
AFM,
TEM,RBS, ERDA,
NRA,
X-
ay e lec ome y and
spec oscopic ellipsome y. While he ilms p epa ed
by IBICVD
a e
e y compac and dense and ha e a
high e ac i e index
(n
=
1.48 a
0
=550
nm),
hose
p epa ed by PECVD exhibi a lowe e ac i e index
alue (n
=
1.45 a
0
=
550
nm)
lowe densi y and ha e
a highe su ace oughness. Films p epa ed by IBICVD
p esen s a b eakdown elec ic ield alue (49.14
MV/cm), ou imes highe han ha
o
he ilms
p epa ed by PECVD (12.11 M /cm) and o he SiOz
ma e ials epo ed in he li e a u e. This highe alue is
a consequence o he low oughness and high densi y o
he IBICVD ilms. This ype o mic os uc u e
is
p oduced by he e ec o he highly ene ge ic ion
beams (e. g. 400 eV) impinging on he su ace o he
g owing ilms du ing hei p epa a ion.
Expe imen al
Si02 hin ilms ha e been p epa ed a oom empe a u e
by wo ac i a ed CVD p ocesses: IBICVD and
PECVD. In bo h cases Si(CH3)3 C1 has been used
as
ola ile p ecu so o Si. The i s me hod consis s o he
decomposi ion o he p ecu so on he su ace o he
di e en subs a es by he ac ion o a beam o
accele a ed
02+
ions. A ull accoun
o
his
me hod has
been epo ed p e iously
[6].
PECVD deposi ion was ca ied ou by using an ex e nal
mic owa e ECR sou ce
(SLAN)
ope a ed a 400 Wa s.
A ull desc ip ion o he cha ac e is ics o
his
sou ce
can be ound in e [7].
Fou ie T ans o m In a ed (FT-IR) spec a we e
collec ed in ansmission a no mal geome y in a
Nicole
5
10 spec ome e .
T ansmission elec on mic oscopy (TEM) analysis was
pe o med wi h a Philips CM200 mic oscope wo king
a 200 kV. KB subs a es we e used o con en ional
TEM examina ion.
A omic o ce mic oscopy
(AFM)
images we e ob ained
in ai using a Topome ix Explo e mic oscope wo king
in he non-con ac mode.
Spec oscopic ellipsome y analysis we e pe o med
using a SOPRA comme cial-a ailable sys em Fo he
anspa en ilms s udied (ex inc ion coe icien
Id),
he analysis p ocedu e consis s
in
a eg ession using a
Cauchy law o simula e he e ac i e index
n(
0)
o
he
laye .
X- ay e lec ome y spec a we e collec ed wi h a
special se -up using he angle- esol ed dispe si e mode
wi h a posi ion-sensi i e p opo ional coun e . The
echnique is able o de e mine he hickness and densi y
o hin laye s.
Ru he o d Backsca e ing spec oscopy
(RBS)
and
Elas ic Recoil De ec ion Analysis (ERDA)
measu emen s o he ilms we e pe o med in he Ion
Accele a o ARAMIS (O say, F ance) using
1.5
MeV
He+ and 3 MeV He" pa icles, espec i ely. The ene gy
esolu ion
o
he
de ec o used in he
RBS
measu emen s was 15 keV and 45 keV
in
he ERDA
0-7803-6352-3/01/$10.00
0
2001 IEEE
304
measu emen s.
RBS
and ERDA spec a we e simula ed
using he RUMP code.
B eakdown ol ages ha e been ob ained h ough a
ol age amp wi h a cons an slope o 20
V/s
by using
he expe imen al a angemen shown in Fig.1. This
ol age was applied sepa a ely o Au con ac s
o
diame e lmm e apo a ed on he sample su ace.
-
Figu e
1.
Expe imen al a angemen used o measu e
b eakdown elec ic ield and cha ge o b eakdown:
unc ion gene a o ,
G,
wi h his load esis o ,
I&-,
hin
ilm
sample,
M,
and oscilloscope p obes,
SI
and
S2.
The unc ion gene a o
G
is able o gene a e ol ages
up o
400
V, wi h 100
mA
o
maximum cu en , and o
pe o m amps
o
slopes anging om 20 V/S o
lo6
V/S
wi h 2% o ou pu ipple. The sys em is based on a
swi ching DC powe supply ( lyback con e e ),
con olled by a compu e (on-boa d mic ocon olle ).
Ou pu ol age wa e o m is gene a ed by he
mic ocon olle using a s o ed da a pa e n, wi h a
sampling in e al
o
0.1
ms.
S o ed da a pa e n can be
modi ied a any ime by compu ing a new pa e n wi h
he on boa d mic ocon olle (only amps a e allowed),
o by down loading
a
new pa e n om an ex e nal hos
compu e , using he on-boa d RS232 po . In he la e
case, any ol age shape complying he es ic ions
men ioned abo e can be pe o med. As an added alue,
he sys em is able o s o e he eal ou pu ol age which
can be downloaded back o he hos compu e o
analysis (s udy
o
dielec ic b eakdown).
This
makes
unnecessa y he p esence
o
addi ional elemen s, e.g.
oscilloscopes.
S1 and S2 a e digi al oscilloscope p obes
in
single
igge mode. S2 measu es he applied ol age o he
sample,
M,
and S1 he ol age
in
a load esis ance o
1wZ
in
o de o calcula e he cu en
h ough
he
sample a any ime. Bo h signals can be s o ed by
means o a HP-VEE so wa e o hei la e s udy.
In Figu e 2, we show he cu en a ia ion as well as he
applied ol age amp a a pa icula Au con ac o a
IBICVD sample. F om bo h we can ob ain he alues o
b eakdown elec ic ield and, by nume ical in eg a ion,
o
he cha ge o b eakdown.
A pa icula sui ed dis ibu ion, namely ex eme alue
s a is ics, was used o calcula e he in insic b eakdown
and cha ge o b eakdown o he sample[8-9].
i............................
01020304050
Tim
(s)
Figu e
2.
Elec ic signals om a pa icula Au con ac
in a IBICVD sample: (1) applied ol age amp;
(2)
cu en a ia ion.
Resul s
and Discussion
The composi ion o he hin ilms p epa ed by ei he
IBICVD o PECVD was de e mined by a combined
RBS/NRA
analysis. They a e o med only by
Si
and
0
a oms. The ob ained
O/Si
s oichiome y we e 2
k
0.02
in all samples.
Si02
composi ion a he su ace was also ob ained by
XPS.
Some ca bon was
de ec ed ha was eadily emo ed by mild
A +
o
0,'
bomba dmen .
This
ca bon is he con amina ion
o
he
samples by exposu e o
ai .
The con en o
H
in he samples was de e mined by
ERDA
measu emen s. The WSi a io was less han 0.25
and
0.35
o ion and plasma ilms, espec i ely. These
alues a e simila o lowe han hose epo ed in he
li e a u e o Si02
hin
ilms
p epa ed by he md. o
plasma CVD [lo]. I is also shown below by FI'-IR
analysis ha he concen a ion o
-OH
g oups
is
highe
in
PECVD-Si02
han in IBICVD-Si02
ilms,
a
ea u e
ha can be explained by he oughe mic os uc u e o
hese
ilms.
Figu e
3
shows opog aphic AFM images o he su l'ace
o Si02 ilms app oxima ely
100
nm
hick p epa ed by
IBICVD and PECVD. The images, p esen ed wi hin
he same cu en scale, clea ly indica e ha he
IBICVD-Si02 sample has lowe su ace oughness. 'The
oo mean squa e
(RMS)
su ace oughness alues
deduced om he
AFM
images a e
0.21
and 1.5 o he
IBICVD and PECVD
ilms
hus con i ming he
p e ious assessmen o su ace oughness o he
samples.
305
Plana - iew TEM images ha e been ob ained o he
wo
ypes
o
oxide hin
ilms
s udied he e. The
IBICVD-Si02
ilm
shows an uni o m con as wi hin
he ilm (homogeneous laye ) whe e no oids a e
dis inguishable. On he o he hand, he PECVD-Si02
sample, exhibi s a con as wi h g anula s uc u e
cha ac e ized by agglome a es o -20
nm
ha
supe impose o o m he whole ilm hickness. This
g anula s uc u e is ela ed o he highe su ace
oughness (c . Figu e 3) o hese ilms.
samples he in e ace is less de ined, being appa en he
supe posi ion o he subs a e poin s wi h some
shadowed zones ha indica e he o ma ion o
Si02/Si0, (xe2) inclusions wi hin he subs a e.
The di e en mic os uc u e o he wo ypes o
samples mus yield di e en physical and chemical ilm
p ope ies. Re ac i e index
n(A),
ob ained using
spec oscopic ellipsome y in he spec al ange
0.21pm-1.2pm, a e p esen ed in Fig 4. One can clea ly
obse e ha , o he en i e spec al ange, he
n
alue
o he IBICVD- Si02 sample is highe han ha
measu ed o he PECVD-Si02 laye
(n
=
0.03). The
highe e ac i e index o he IBICVD ilms ag ees
wi h he alue o densi y ob ained o his sample by X-
ay e lec ome y. This e ac i e index is wi hin he
highes alues epo ed
in
li e a u e o Si02 hin ilms
p epa ed by di e en me hods [12].
IBICVD
The p e ious esul s ha e shown ha Si02 hin
ilms
p epa ed by IBICVD a e mo e compac and dense han
hose p epa ed by PECVD. Main ac o o
his
enhanced compac ion o he ilm is he kine ic ene gy
o he impinging ions
[
131.
Figu e 3.
AFM
images o he wo samples
In o ma ion abou densi y and su ace and in e ace
oughness o hin ilms was ob ained by X- ay
e lec ome y. The densi y
o
he
ilms
was
deduced
om
he o al e lec i i y angle
cl,,
by his p ocedu e,
he densi y o he IBICVD-Si02 and PECVD-Si02
ilms we e 2.46 and 2.08 g ~m-~, espec i ely ( he
densi y o bulk silica is 2.20
g
cm-3
).
Fo he IBICVD ilm, he absence o an in e e ence
pa e n in he e lec ome y spec a (no shown) could
be ela ed o a no well de ined in e ace be ween he
ilm and he subs a e. This may seem con adic o y
wi h he low su ace oughness de e mined by
AFM
o
his
sample. Howe e , a ough subs a ehilm in e ace
is expec ed owing o he ac ha
02'
ions o ela i ely
high ene gy (i.e. 400 eV) a e used o he deposi ion o
he
ilms.
Based on TRIM calcula ions [ll], a
pene a ion dep h o 1.5-2.0
nm
is expec ed o hese
oxygen ions. Oxygen di usion h ough he Si subs a e
could be
an
addi ional eason o he absence o
in e e ence iinges.
The hypo hesis o a poo ly de ined ilmhubs a e
in e ace was checked by high esolu ion TEM
(HRTEM) c oss-sec ion obse a ion o he in e ace.
The ilmhubs a e in e ace in he la e sample is well
de ined, ha ing a hickness smalle han 1.2
nm
o he
whole obse a ion a ea.
In
ac , he well o de ed
s uc u e o he Si single c ys al subs a e, cha ac e ized
by an o de ed a angemen
o
poin s, gi es ise ab up ly
o he homogeneous shadowed s uc u e ypical o
amo phous Si02 laye . Howe e , o he IBICVD
1.401
1.354
.
,
.
,
.
,
.
,
.
,
.
,
.
I
0.0
0.2
0.4
0.6
0.8
1.0
1.2 1.4
X
@m)
Figu e
4.
Re ac i e index s
A
o
IBICVD and PECVD samples
Fo he IBICVD sample
(70
nm
wid h o
Si02
on
Silicon) and using he ex eme alue s a is ics, a
b eakdown ol age o b=344 V was ob ained which
means a b eakdown elec ic ield o Eb=49.14 MV/cm.
Cha ge o b eakdown is
Qb=105
mC. Fo he PECVD
sample (140
nm
wid h o Si02 on Silicon) he
co esponding alues a e Vb=169.6 V, Eb=12.11
W/cm and
Qb=
73.13 mc.
CONCLUDING
REMARKS
The p e ious esul s ha e clea ly illus a ed he
impo ance o ballis ic in e ac ions
o
impinging
pa icles o an enhanced compac ness o Si02 ilms.
This enhanced compac ness leads o a modi ica ion o
hei physical p ope ies as
o
example he e ac i e
indices (c . Fig. 2), which is o g ea in e es o
mic oelec onic and op ical applica ions. I
is
also
306
wo h o men ion ha ion beams migh be also used o
a selec i e deposi ion o he
ilms
acco ding o a
li hog aphic echnique. In ac , deposi ion by IBICVD
occu s a oom empe a u e only in he zones whe e ion
beams a e impinging on he subs a e su ace. The use
o ocused beams as e ed acco ding o a gi en pa e n
o ha o a mask pu be ween a b oad beam and he
subs a e should p oduce such pa e ned ilms o a la ge
in e es o mic oelec onic applica ions. A p esen ,
esea ch is being ca ied ou in ou labo a o y o
explo e
his
possibili y
o
he IBICVD p ocedu e.
This pape has also shown ha a b oad in e ace
de elops be ween he silicon subs a e and he SiOz
laye g own by IBICVD.
A
way o minimizing such
in e laye hickness could be ob ained by deposi ing an
ini ial Si02 hin laye , ei he by PECVD o lowe ing he
ene gy o he ion beam o educe he mixing. Then, he
hin ilm could be g own on he op o his hin laye as
i is desc ibed in he pape .
BIBLIOGRAPHY
P Balk Ad . Ma e . 7 (1995) 703.
D.L. G iscom. MRS Bull. Jun-Aug. 20 (1987).
W
Ke n, R.S. Rosle . J. Vac. Sci. Technol. 14
(1977) 1082.
T. Roppel, D.K. Reinha d, J. Asmussen. J.
Vac. Sci. Technol. B 4 (1986) 295.
K. S a e . RCA Re . Dec. (1968) 61
8.
J.P. Espinbs, A. Fe nindez, V.
M.
Jimknez, J.
C. Sinchez-Mpez, L. Con e as, D. Leinen,
A.R. Gonzdez-Elipe. A d. Ma . CVD
3
(1997) 219.
F.
We ne ,
D.
Ko zec,
J.
Engemann,
Plasma
Sou ces Sci. Technol.,
3
(1994)
473.
J.F. Ve weij and J.H. Kloo wijk, “Dielec ic
b eakdown I: a e iew o oxide b eakdown”,
Mic oelec onics Jou nal, 27, pp.
61
1-622,
1996.
V.A. Rozhko e al., “Elec ical b eakdown o
a e ea h oxide insula o hin ilms in silicon
MIS s uc u es”, 1995 IEEE
5”
In .
Con .
on
Conduc ion and B eakdown in Solid
Dielec ics, Leices e (UK), July 10-13, pp.
R. E emadi, C. Gode ,
C.
Pe in, J. Bou ee, B.
D e illon,
C.
Cle c.
Su .
Coa . Technol.
80
(1996)
8
J.F Ziegle , J.P Bie sack, U. Li ma k, The
S opping and Range o Ions in Solids, Vols I-
11,
Pe gamon, New Yo k. 1986.
L. Zajicko A, J. Janca,
V.
Pe ina. Thin Solids
Films 338 (1999) 49.
0.
Auciello, R. Kelly (eds). Ion Bomba dmen
Modi ica ion o Su aces. Else ie Science
Publishe s B.V., 1986.
418-422, 1995.