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Vacuum 71 (2003) 349–359
Intermediate gas phase precursors during plasma
CVD of HMDSO
D. Theirich*, Ch. Soll, F. Leu, J. Engemann
Universit.at Wuppertal, Forschungszentrum f .ur Mikrostrukturtechnik-fmt, Campus Freudenberg, Geb. FM, Rainer-Gruenter-Strasse 21,
42119 Wuppertal, Germany
Received 28 May 2002; accepted 7 November 2002
Abstract
In plasma enhanced chemical vapor deposition (PECVD) from complex molecules like hexamethyldisiloxan
(HMDSO) often not the molecules themselves but intermediate and reactive radicals or molecules are the precursors for
film growth. Additionally, such PECVD processes are volume or mass flow limited under many process conditions. In
these cases growth rate and film homogeneity is mainly dominated by the precursor content and its spatial distribution
in the gas or plasma phase. Therefore the identification of such intermediate precursors is an important task to optimize
a PECVD process and also helps us to understand the plasma chemical reactions during PECVD. A combined mass
spectrometry and IR absorption study is used to identify intermediate gas phase precursors in HMDSO/O2 PECVD
remote plasmas. For this study a microwave plasma CVD system was used with HMDSO/O2 ratios between 0.1 and 1
at typical operating pressures between 20 and 70 Pa. Three reactive intermediate species are proposed to act as aprecursor for SiO
x film growth from HMDSO/O2 plasmas. All three having a mass of 148 amu. The related reactive
groups are the silanon (Si=O), silanol (Si–OH) and aldehyde (C=O) groups.
r 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Plasma; Polymerization; CVD; HMDSO; Infrared absorption; Mass spectrometry; Precursor
1. Introduction
In recent years plasma enhanced chemical vapor
deposition (PECVD) of silicon containing filmshas become a widely used technique for thin film
deposition especially for semiconductor, optical,
wear protection, diffusion barrier and many other
applications [1–6]. Besides silane, tetraethyloxysi-
lane (TEOS) and others hexamethyldisiloxane
(HMDSO: (CH3)3SiOSi(CH3)3) is a commonly
used precursor gas for the PECVD of SiO2 and
non-stochiometric SiOx
films, whereby the latter
may have varying hydrocarbon contents. HMDSO
is much easier to handle as for example silane andyields a high deposition rate up to more than 1 mm/
min [7]. HMDSO also represents a trend to use
more and more complex organic molecules as
precursors for PECVD and plasma polymeriza-
tion, because they often yield a very versatile
control of film properties by controlling the degree
of retention of molecular structure, functional
groups and elemental composition. For example
the control of the hydrocarbon and oxygen
content in SiOx
films deposited from HMDSO
*Corresponding author. Fax: +49-202-439-1412.
E-mail address: [email protected]
(D. Theirich).
0042-207X/03/$ - see front matter r 2003 Elsevier Science Ltd. All rights reserved.doi:10.1016/S0042-207X(02)00763-7
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also gives control over film hardness and elasticity
and its optical and diffusion properties [5,7,8].
High rate PECVD processes with complex
organic molecules such as HMDSO especially onflat substrates are mostly performed in a volume
limited process regime. This means that the film
deposition rate is limited by the content of the
precursor in the plasma phase. As a result film
deposition is usually inhomogeneous on three-
dimensional substrates and thus those processes
are used for flat or almost flat substrates. This is in
contrast to conventional thermal CVD processes as
for example the CVD of silane [9] and some earlier
work on HMDSO which was performed in a
different process regime [10,11]. In both cases the
process was surface limited. For example the silane
is adsorbed on the surface and is thermally
decomposed by the surface temperature and forms
a thin film. The volume limitation of the PECVD
of complex molecules is caused by the relative
stability of the used molecules. Only when they
undergo collision processes in the plasma they
dissociate into reactive intermediate radicals. These
reactive intermediate radicals undergo further
reactions, some of them actually resulting in film
growth, others resulting for example in powder
growth, in etching or in stable volatile products,which are pumped away from the reaction chamber
[12,13]. To control the deposition process in terms
of rate, homogeneity or resulting film properties it
is necessary to control the density and spatial
distribution not only of the precursor gas but also
of the reactive intermediate precursor radicals in
the PECVD reactor. Therefore it is necessary to
identify the reactive intermediate precursors actu-
ally forming the film. This paper presents a study
based on mass spectrometry and infrared absorp-
tion spectroscopy to identify possible intermediateprecursors in HMDSO/O2 remote plasmas for
SiOx
film deposition.
2. Experimental
2.1. Plasma system
All diagnostic experiments were performed in a
vacuum chamber with a microwave remote plasma
setup, which can also be used as a plasma CVD or
plasma polymerization system for the deposition
of scratch resistant SiOx
films from HMDSO. A
SLAN I microwave plasma source is mounted ontop of a cubic stainless steel vacuum chamber
(400 400 400 mm3). The plasma source, which
is described in detail elsewhere [14] can be
separated from the chamber by a stainless steel
grid with a transparency of 50%. The source
basically consists of a ring shaped circular wave-
guide, which couples microwaves via slot antennas
into a quartz dome with 160 mm inner diameter,
where the plasma is ignited. The non-film forming
carrier gases argon and oxygen are introduced into
this quartz dome by a gas inlet. The plasma source
is powered by a 6 kW microwave generator via a
circulator and sensor for reflected power. The
generator can be operated in cw and pulsed mode.
HMDSO is introduced directly into the vacuum
chamber by a gas shower ring downstream the
separation grid. The whole process gas is pumped
b y a 6 0 m3 h1 rotary pump with a 500 m3 h1
roots blower. Pumping speed and pressure can be
controlled by a butterfly valve. Flow rates of argon
and oxygen are controlled by mass flow control-
lers. HMDSO is vaporized in a tank at a
controlled temperature of 351C and introducedinto the chamber through a precise leakage valve.
All components connecting the monomer tank
with the vacuum chamber are heated to avoid
condensation of the monomer. Pressure measure-
ments are made with a gas independent pressure
sensor (baratron). Base pressure of the system is
3 102 Pa. Typical operating pressures were
between 20 and 70 Pa. Typical flow rates were
20–50 sccm for HMDSO and 0–300 sccm for
oxygen and argon. When the plasma is switched
on the ionized, dissociated or excited argon andoxygen flows out of the plasma source where it
mixes with the HMDSO forming a remote plasma
in the deposition chamber. For deposition pur-
poses a substrate can be placed 200 mm down-
stream the plasma source outlet in the center of
the vacuum chamber. A detailed description of the
whole setup as well as data for typical ion and
radical densities can be found elsewhere [7,15,16].
In order to identify reaction products in-
cluding possible reactive intermediate precursors
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information on the molecular weight as well as on
the molecular structure of the molecules and
radicals in the remote plasma zone is needed.
Mass spectrometry together with infrared absorp-tion spectroscopy are well suited to gain this
information. Since the HMDSO/O2 plasma is a
strongly depositing plasma several measuring
signal degradations can occur during in situ
measurements. Therefore diagnostical methods
which obtain many data in a short time are
necessary. To meet all these demands we chose
neutral particle mass spectrometry and FTIR
absorption spectroscopy for this study.
2.2. Mass spectrometry
For mass spectrometry the substrate is removed
and a mass spectrometer (Balzers PPM 421) is
flanged to a side flange of the vacuum chamber.
The neutral particles enter the spectrometer
through a 100mm aperture. In the spectrometer
the particles sequentially pass a cross beam
ionization source, an energy filter consisting of a
cylindrical mirror analyzer (which is not active
during neutral particle analysis) and a quadrupole
mass filter. Then they are detected by a secondaryelectron multiplier. Electrons of 70 eV energy were
used for post-ionization in the spectrometer for all
experiments shown in this work. The whole
spectrometer is differentially pumped. The whole
system is mounted with a bellow on a carriage and
can be separated from the chamber by a shut-off
valve. When the spectrometer is moved into the
chamber the aperture, through which the neutrals
are extracted into the spectrometer, is placed
200 mm downstream the plasma source. Due to
this construction the mass spectrometer is exposedto the depositing plasma only during the measure-
ment and therefore contamination by film deposi-
tion or powder formation inside the spectrometer
are minimized. Nevertheless the transmission of
the energy analyzer still shifts during a single
measurement due to deposition effects of the ion
optics. Therefore in all experiments at least
10sccm argon have been added and all mass
signals have been detected relative to the argon
signal at 40 amu.
2.3. FTIR
The mass spectrometer was replaced by a FTIR
spectrometer (Bruker Equinox 55) for the infraredgas phase absorption experiments. The infrared
beam is coupled through KBr windows into the
vacuum chamber. An external MCT detector is
used to detect the infrared light passing through
the gas and plasma, respectively. The whole
optical path outside the vacuum chamber is
purged by dry and CO2 free air. The beam is
positioned 200 mm downstream the plasma source.
Therefore the IR beam probes the same plasma
region as the mass spectrometer and the same
region where thin films could be deposited. At a
typical operating pressure of 60 Pa in the vacuum
chamber a single beam pass is enough to gain a
good absorption signal. Before each measurement
a reference spectrum was taken without HMDSO
and plasma. After each measurement Ar/O2plasma cleaning of the chamber and test spectra
recording was done consecutively until no change
in two consecutive test spectra could be detected.
The last test spectrum was then taken as a new
reference for the next measurement. The plasma
cleaning was done in order to remove organic
residues from adsorbed HMDSO and to yield afull oxidation of the silicon films on the walls and
especially on the KBr windows.
3. Results and discussion
Fig. 1 shows some typical results for deposition
rates and deposition characteristics in a HMDSO/
O2 microwave remote plasma. Argon was intro-
duced additionally for these experiments to keep
the total gas flow rate (600 sccm) and thus themean residence time in the reaction zone constant
while varying the oxygen/HMDSO ratio. First of
all the absolute deposition rates are quite high and
achieve values close to 800 nm/min (for cw
plasmas). The second result from Fig. 1 is that
the whole deposition process in the remote region
of an HMDSO/oxygen/argon plasma is flow rate
limited in terms of oxygen flow. This is reflected in
the increase of the deposition rate with increasing
oxygen content in the total gas flow. Plasma
D. Theirich et al. / Vacuum 71 (2003) 349–359 351
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chemical reactions with oxygen being dominant
for the film deposition process over electron
collision processes can also be assumed comparing
the relevant particle densities in the remote region(here 200 mm downstream the plasma source) and
taking into account the electron energy distribu-
tion function. In a comparable set-up electron
densities of 108 –109 electrons/cm3 and electron
temperatures of 1–3 eV have been measured whilethe oxygen radical density reach values of 1013 –
1014 radicals/cm3 [15,16]. Additional to oxygen
flow rate effects an influence of the time modula-
tion of the plasma power can be observed (cw case
and 100 Hz rectangular pulses with 50% duty
cycle).
In order to get a more inside view of the plasma
process first neutral particle mass spectrometry has
been carried out. Neutral particle mass spectro-
metry needs a postionization in the spectrometer.
As a drawback this leads to a strong additional
dissociation of the HMDSO in the mass spectro-
meter itself. Fig. 2 shows a mass spectrum of pure
HMDSO without plasma. This spectrum reflects
the dissociation in the spectrometer. As expected a
very large number of various fragments occur in
the spectrum whereas the peak at 162 amu of the
unfragmented HMDSO is very small. For mass
line identification see for example Ref. [17]. The by
far strongest peak in the spectrum appears at
147 amu. It can be attributed to Si2OðCH3Þþ5 ;
which is produced by dissociative ionization of
0
200
400
600
800
1000
0 2 4 86 10
Oxygen/HMDSO ratio
D e p o
s i t i o n r a t e ( n m / m i n )
Fig. 1. Deposition rate as a function of the oxygen/HMDSO
ratio for cw (J) and pulsed (; 100 Hz, 50% duty cycle)
plasma. Mean power: 2 kW; pressure: 40–70 Pa; 30sccm
HMDSO; 0–300sccm oxygen; 0–270 sccm argon. Concerning
the difference between the deposition rate in the pulsed and cw
plasma see Ref. [18] and the discussion of Fig. 5a.
Fig. 2. Neutral mass spectrum of HMDSO at 50 Pa chamber pressure.
D. Theirich et al. / Vacuum 71 (2003) 349–359352
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HMDSO under dissociation of a methyl group.
This leads to the result that dissociation of a single
methyl group is the most probable dissociation
appearing in the spectrometer under the appliedoperating conditions.
Adding oxygen and measuring under plasma
conditions changes the mass spectrum. Especially
the oxygen itself and the oxidation products of
HMDSO like H2O, CO and CO2 now occur in the
spectrum much above their residual gas level. In
order to investigate the role of oxygen we observed
the mass lines of these oxidation products and the
strongest lines of HMDSO fragments at 59, 66, 73,
131, 133 and 147 amu while varying the oxygen
flow. The results are shown in Fig. 3 for a pulsed
plasma at 10 Hz and 50% duty cycle and in Fig. 4.
for 200 Hz, respectively. The oxidation products in
Fig. 3(a) increase with increasing oxygen flow.
Typical oxidation chains can be observed. First the
CO line increases. Adding more oxygen to the
plasma leads to a further oxidation of CO and
consequently also the CO2 line increases. Finally,
also the O2 line increases, because more oxygen is
introduced than is needed for the oxidation of
carbon and hydrogen. But oxygen is also needed
for the oxidation of silicon in the gas phase or at
the surface. Fig. 3(b) shows a decrease of allHMDSO fragments except the fragment at
133 amu, which shows a strong increase. The
results at 200 Hz pulsing frequency are very
similar. The only differences are the increase of
the O2 line at even smaller oxygen flows (Fig. 4(a))
and the not so strongly developed increase of the
133 amu line (Fig. 4(b)). But also at 200 Hz pulsing
frequency the line at 133 amu still reveals a
different behavior than the other fragment lines.
Assuming that similar to the dissociative ioniza-
tion of the HMDSO molecule the detected ion at133 amu is most probably created by dissociative
ionization under dissociation of a methyl group in
the spectrometer, the 133 amu line originates from
a species with 148 amu. The question now is, can
the species at 148 amu be an intermediate gas
phase precursor for SiOx
film growth with x close
to 2. The Si:O ratio in the HMDSO molecule is
2:1. To grow a SiOx
film with a Si:O ratio close to
1:2 a silicon containing precursor plus additional
oxygen is needed. For a volume or flow limited
deposition process the growth rate should dependmainly on the precursor impact rate on the
surface. In this case and at constant pressure and
temperature the precursor content in the gas phase
and the growth rate of the film should be positively
correlated. Therefore above results suggest the
species at 148 amu to be the dominant silicon
containing precursor for SiOx film growth from
HMDSO. This correlation has additionally been
investigated when varying the pulse frequency and
the pressure. The results are shown in Fig. 5(a) for
0
0.8
0.6
0.4
0.2
1
0 100 200 300
Oxygen flow (sccm)
I / I m a x
1
1.2
0.8
0.6
0.4
0.2
I / I m a x
(a)
0 100 200 300
Oxygen flow (sccm)(b)
Fig. 3. Relative intensities of mass lines in a pulsed HMDSO/
O2/Ar microwave remote plasma (20 sccm HMDSO, 15 sccm
Ar, 50Pa, 2 kW mean power, 10 Hz, 50% duty cycle) as a
function of the oxygen flow rate: (a) data for oxidation
products CO (’); H2O (); CO2 (J); O2 (&), and (b) data
for monomer fragments at 59 amu (’); 66amu (&); 73amu
(); 131amu (J); 133amu (m); 147 amu (+).
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the deposition rate and in Fig. 5(b) for the gasphase content of the precursor with 148 amu. At a
pressure of 50 Pa a minimum appears for 200 Hz
pulse frequency for the growth rate as well as for
the precursor content. At a lower pressure of 20 Pa
both curves are much more flat indicating only a
small influence of the pulse frequency on film
growth rate and precursor content. Reasons for
the pulse frequency influencing the growth process
of SiOx films from HMDSO has been discussed
elsewhere [18]. Summarizing, film growth rate and
the content of the 148 amu species in the gas phase
show a strongly positive correlation when varying
oxygen flow, pulse frequency and pressure. All this
indicates the 148 amu species to be a precursor forSiO
x film growth. This is in contrast to some other
work, which proposed the Si2O(CH3)5 radical to
be one of the dominant precursors [19]. But the
same work also reports about a strong signal in the
positive ion spectra at 148 amu, which is attributed
to a HSi2OðCH3Þþ5 ion (see also Eq. (1)). But
signals at 148 amu may result from several other
molecules or radicals as will be discussed below.
First of all there is a fragment of HMDSO after
dissociation of a methyl group and attachment of
a hydrogen atom
Me32Si2O2Si2HMe2; ð1Þ
where Me means a methyl group. Another
possibility is a molecule with a silanon type of
bond (Eq. (2)).
O
Me3−Si−O−Si .
Me
ð2Þ
There are several reactions possible that canresult in such a molecule. Some of them are
described below. First there can be a reaction
scheme (Eq. (3)) starting with a dissociative
ionization by an electron and followed by a
reaction with atomic oxygen similar to the
proposed mechanism in an Argon plasma by
Wr !obel et al. [12,20].
Me32Si2O2Si2Me3þe-
Me32Si2O2Si2Me2þMe þ 2e;ð3aÞ
Me3232Si2O2Si2Meþ2 þO-
Me32Si2O2Si2O2Meþ2 ;
ð3bÞ
Me32Si2O2Si2OMeþ2-
Me32Si2O2Si2O2Me þ Meþ
:
ð3cÞ
Another possibility might be a direct reaction
with atomic oxygen und dissociation of two
0
0.2
0.4
0.6
0.8
1
0 100 200 300
Oxygen flow (sccm)
0 100 200 300
Oxygen flow (sccm)
I / I m a x
0.2
0.4
0.6
0.8
1
1.2
I / I m a x
(a)
(b)
Fig. 4. Relative intensities of mass lines in a pulsed HMDSO/
O2/Ar microwave remote plasma (20sccm HMDSO, 15 sccm
Ar, 50Pa, 2kW mean power, 200Hz, 50% duty cycle) as a
function of the oxygen flow rate: (a) data for oxidation
products CO (’); H2O (); CO2 (J); O2 (&), and (b) data
for monomer fragments at 59 amu (’); 66amu (&); 73amu
(); 131amu (J); 133amu (m); 147 amu (+).
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methyl groups
Me32Si2O2Si2Me3þO-
Me32
Si2
O2
Si2
O2
Me þ 2Me; ð4Þ
or a reaction with molecular oxygen forming a
CH2 group and methanol
Me32Si2O2Si2Me3 þ O2-
Me32Si2O2Si2O2Me þ CH3OH þ CH2:ð5Þ
Besides these also other reaction channels may
result in a molecule with a silanon group (Si=O).
Moreover this molecule can rearrange into a
molecule with a silanol group (Si–OH) and a
silene group (Si=CH2)
O OH
Me3−Si−O−Si Me3−Si−O−Si .
Me CH2
↔ ð6Þ
Both molecules in Eq. (6) might act as a
precursor for SiOx
film growth and would be
detected in the mass spectrometer after dissocia-
tion of a methyl group at 133 amu. The silanon
type of bond was found under liquid phase
chemistry conditions to oligomerize easily into
cyclic and linear polysiloxanes [21] as it is
10 100 1000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
50 Pa
20 Pa
10 100 1000
Pulse frequency (Hz)
R e l a t i v e d e p o s i t i o n r a t e
d / d c w
2 kW
40 sccm HMDSO
200 sccm O2
10 100 1000
0.6
0.8
1.0
1.2
1.4
20 Pa
10 100 1000
Pulse frequency (Hz)
R e l a t i v e I n t e n s i t y I / I c w
2 kW
40 sccm HMDSO
200 sccm O2
50 Pa
(a)
(b)
Fig. 5. Deposition rate (a) and mass line intensity of the precursor at 133 amu (b) as a function of the pulse frequency for different
pressures. Plasma parameters are: 50% duty cycle; 2 kW mean power; 40 sccm HMDSO; 200 sccm Oxygen; 15 sccm Argon at 50 Pa and
100 sccm Ar at 20 Pa, respectively. Deposition rate and mass line intensities are given relative to their cw values.
D. Theirich et al. / Vacuum 71 (2003) 349–359 355
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necessary for film formation under plasma chemi-
cal conditions. Several authors have proposed
molecules containing silanol groups to be pre-
cursors for SiOx film growth [22–24]. Two silanolgroups can react to a siloxane group and water
(Eq. (7)) and form polysiloxanes
2 R2Si2OH-R2Si2O2Si2R þ H2O: ð7Þ
Both possible precursor molecules in Eq. (6)
represent oxidized HMDSO molecules. This ex-
plains why the intensity of the 133 amu line in
Fig. 3(b) shows a variation with the oxygen flow
similar to the oxidation products in Fig. 3(a). The
less significant behavior in Fig. 4(b) might be
caused by a larger contribution of the non-
oxidized HMDSO fragment from Eq. (1) to the
signal at 133 amu in case of 200 Hz pulse
frequency. This also explains, why the oxygen
signal in Fig. 4(a) (200 Hz) increases earlier than in
Fig. 3(a) (10 Hz). Under conditions of Fig. 3(a)
more oxygen is needed to oxidize also HMDSO
molecules and therefore the oxygen signal in-
creases only at higher oxygen flows compared to
Fig. 4(a). Moreover under those conditions also a
higher growth rate can be observed (Fig. 5(a)).
To identify the molecular structure of the
plasma chemical reaction products infrared ab-sorption experiments have been performed. Fig. 6
shows an absorption spectra of HMDSO and
argon gas in the vacuum chamber at 60 Pa without
plasma. The typical absorptions of the siloxan
bond (Si–O–Si), the Si–CH3 bond and the methylgroup itself can be identified [13, 19, 25]. The
Argon does not add any signal. The spectrum in
Fig. 7 was measured with the plasma switched on
plus an additional oxygen flow of 100 sccm. The
O2:HMDSO ratio was 90:50. Several additional
absorption signals can be identified in Fig. 7.
Amongst others there are H2O, CO, CO2, OH,
SiHn
absorptions and an interesting region around
1.700 cm1 where a H2O signal overlaps with the
C=O stretch signal either from CH2O or CH2O2[19]. A detailed analysis of the infrared absorption
results will be published elsewhere. Of special
interest for this paper are the oxygen flow
dependences of the oxidation products and the
monomer fragments, which are shown in Fig. 8(a)
and (b), respectively. All intensities are evaluated
from peak areas and are normalized to their
maximum. If necessary a peak decomposition
analysis has been done.
The following signals were used to evaluate the
absorption intensities in Fig. 8: CO: area under
CO rotational spectrum between 2000 and
2250 cm1
; H2O: area of a single line at3854 cm1; CO2: area under CO2 asymmetric
Si(CH3)n bend
Si(CH3)n bend
SiOSi bend
CH3 stretch
SiOSi asym. stretch
4000 3000 2000 1000
0.0
0.2
0.4
0.6
A b s o r b a n c e
Wavenumber cm−1
Fig. 6. FTIR absorption spectrum of a HMDSO/Ar mixture at 60 Pa chamber pressure without plasma. Flow rates:
HMDSO:Ar=50:300.
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Summarizing the results from this study there
are three candidates for intermediate precursor
molecules in HMDSO/O2 plasmas presented inEqs. (6) and (8). Between these IR absorption
spectroscopy was not able to decide due to two
reasons. First data on IR absorption of the silanon
group (Si=O) are not available and second
possible absorption signals from the silanol group
(Si–OH) are almost not detectable due to the large
amount of OH and water as volatile oxidation
products of HMDSO. Therefore one, two or all
three of the precursors found may contribute to
SiOx
film growth from HMDSO.
4. Conclusion
Three reactive intermediate species have been
proposed which can act as a precursor for SiOxfilm growth in HMDSO/O2 plasmas. All three
having a mass of 148 amu. The related reactive
groups are the silanon (Si=O), silanol (Si–OH)
and aldehyde (C=O) groups. Further work is
necessary to distinguish between theses groups.
The gas phase content of these precurors can be
used to control and to optimize the deposition
process.
Acknowledgements
This work was supported by the Federal
Ministry for Education and Research under
contract no. 13N6720 and the state Ministries of
Economics and Technology and of Science and
Research of Northrhein-Westfalia. We also like to
thank Dr. Kim for intense and fruitful discussions
of our results.
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00 1 2 3 4 5 6
0.2
0.4
0.6
0.8
1.2
1
Oxygen/HMDSO flow
0 1 2 3 4 5 6
Oxygen/HMDSO flow
I / I m a x
0
0.2
0.4
0.6
0.8
1.2
1
I / I m a x
(b)
(a)
Fig. 8. Relative intensities of infrared absorption lines in a cw
HMDSO/O2/Ar microwave remote plasma (50 sccm HMDSO,
300sccm Ar+O2, 60Pa, 1.4 kW power) as a function of the
oxygen/argon flow rate ratio: (a) data for oxidation products
CO (’); H2O (); CO2 (J), and (b) data for monomer
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