Non-monotonous evolution of hybrid PVD–PECVD process
characteristics onhydrocarbon supply
T. Schmidtová, P. Souček, V. Kudrle, P. Vašina ⁎
Department of Physical Electronics, Kotlářská 2, Masaryk University, 61137 Brno, Czech Republic
a b s t r a c ta r t i c l e i n f o
Article history:
Received 25 February 2013
Accepted in revised form 13 May 2013
Available online 21 May 2013
Keywords:
Magnetron sputtering
Diagnostics of deposition process
Nanocomposites
Metal–carbon coatings
Hybrid PVD–PECVD process of titanium sputtering in argon and acetylene atmosphere combines aspects of
both conventional techniques: sputtering of titanium target (PVD) and acetylene as a source of carbon
(PECVD). This process can be used for preparation of metal carbon nanocomposites (MeC/C(:H)) or DLC
layers doped with metal (DLC:Me). The aim of this paper is to describe and understand elementary processes
inﬂuencing the hybrid PVD–PECVD process. A non-monotonous dependence of cathode voltage and current,
total pressure and spectral line intensities on acetylene supply ﬂow is reported. Explanation of nonmonotonous
evolutions through the analysis of the target state correlating the process characteristics with
properties of coatings prepared by this process is proposed.
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
Hybrid deposition systems combine more than one deposition
technique [1]. These techniques are mutually independent and they
are being used often in separate deposition chambers [1–4]. An overview
of various deposition systems can be found in [2]. The sputtering
of a metal target in a mixture of an inert gas and a hydrocarbon gas
can be classiﬁed as a hybrid process combining PVD and PECVD techniques
[5–8]. The source of carbon in the hybrid PVD–PECVD process
is dissociated hydrocarbon vapour.
Hybrid PVD–PECVD process is being used for synthesis of metal
hydrogenated carbon nanocomposite (MeC/C(:H)) [6,8–13] layers
or DLC layers doped with metal (DLC:Me) [14–17]. For example
nc-WC/a-C:H [18–21] or nc-TiC/a-C:H [9,22–24] are reported to
have good mechanical and tribological properties combining high
hardness, good toughness with low friction coefﬁcient and wear
which makes these materials industrially attractive for different
applications. For the speciﬁc case of the titanium target sputtering
in hydrocarbon containing atmosphere there exits variety of papers
that are focused on the inﬂuence of process parameters on properties
of deposited coating [8,25–29]. Process features are often omitted.
Hybrid PVD–PECVD process has been previously compared to the
conventional reactive magnetron sputtering [30]. Even though the
addition of the hydrocarbon is very similar to the adding of oxygen
or nitrogen as a reactive gas in reactive sputtering, it was found [30]
that hysteresis behaviour typical for reactive magnetron sputtering
described by Berg model [31] was completely suppressed during hybrid
PVD–PECVD process. Therefore, the hybrid PVD–PECVD depositions do
not require complex feedback control. The absence of the hysteresis
region was explained [30] by the capability of surfaces to be covered
by thick carbon rich layers. In these thick carbon rich layers the carbon
can be bound mutually in contrary to metal oxides/nitrides formation
on surfaces during classical reactive magnetron sputtering where
oxygen/nitrogen can be bound only to the metal. Nevertheless the
target covering by these carbon rich layers during the hybrid PVD–
PECVD process is still similar to the target poisoning by a reactive gas
because it prevents the sputtering of the metal. So for description of
both processes the phrases ‘target poisoning’ and ‘target cleaning’ can
be understood and used.
The aim of this paper is to describe and understand elementary
processes inﬂuencing the hybrid PVD–PECVD process governing the
properties of the deposited coatings. We report a non-monotonous
dependence of cathode voltage and current, total pressure and spectral
line intensities on acetylene supply ﬂow. We report on the dependence
of the chemical composition and mechanical properties of the
coatings on the acetylene ﬂow. We provide an explanation of nonmonotonous
dependences through the analysis of the target state.
The role of RF bias on the substrate and magnetron DC power on
the process characteristics is also discussed.
2. Experimental conﬁguration
Experimental measurements were done on semi-industrial magnetron
sputtering system Alcatel SCM 650. Experimental setup drawing
is shown in Fig. 1. A titanium target (purity 99.99%) 20 cm in
diameter was mounted on a well balanced magnetron head, sputteringup
geometry was used. The magnetron plasma was well localized near
the target, it does not extent to the substrate. The target-to-substrate distance
was 7 cm. The chamber was pumped by turbomolecular pump
Surface & Coatings Technology 232 (2013) 283–289
⁎ Corresponding author: Tel.: +420 549 496 479.
E-mail address: vasina@physics.muni.cz (P. Vašina).
0257-8972/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.surfcoat.2013.05.014
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(700 l s−1
) backed by Roots pump. The base pressure was typically
10−4
Pa. During the deposition the pump was throttled to the
pumping speed of 40 l s−1
. The argon (purity 99.999%) ﬂow was
kept constant at 20 sccm for all experiments. The typical working
pressure was around 1 Pa.
For the study of the hybrid PVD–PECVD process acetylene (purity
99.6%) was used as carbon source. The acetylene ﬂow ranged from 0 to
16 sccm. Magnetized plasma was ignited by DC power (1 kW or
2 kW) combined with or without RF substrate bias (225 W ~ –100 V).
To enable comparison of the deposition process and deposited coating
properties, the values of DC power, RF bias and supply ﬂows of Ar and
C2H2 were selected to correspond to values used in paper [23,24]
where properties of deposited n-TiC/a-C:H coatings were studied in
details. The DC generator was operated in constant power mode. Prior
to each experiment, the target was thoroughly cleaned both mechanically
and by Ar bombardment until the discharge voltage typical for
pure Ti target was reached.
Spectrometer Avantes SD2000 was used as a diagnostic tool.
Atomic spectral lines of titanium at 365 nm, argon at 420 nm and hydrogen
at 656 nm were chosen for the study. There were no lines attributed
to carbon or other fragments of acetylene in observed
spectral range of 250–670 nm. Discharge parameters used for electrical
diagnostics were the target voltage and the discharge current. The
total pressure in the vacuum chamber was also recorded using MKS
Baratron.
The depositions were carried out for 45 min at constant acetylene
ﬂow on high speed steel (HSS) and cermet tungsten carbide (WC)
substrates. The DC power to the magnetron was set at the desired
value and the substrate bias was −100 V. Chemical composition of
the coatings was determined by Rutherford backscattering (RBS)
and elastic recoil detection analysis (ERDA) methods using a Van de
Graaff generator and TANDETRON with linear electrostatic accelerators.
Fischerscope H100 depth sensing indenter equipped with a
Berkovich tip was used to study the indentation response of the coating
samples. The hardness and the indentation modulus were evaluated
using the standard procedure proposed by Oliver and Pharr
[32]. The EDX measurements were performed on JEOL JSM 6460
with Inca Energy EDX detector at 20 kV acceleration voltage.
For the study of the target state the following experimental settings
were used. The depositions for various C2H2 ﬂows were performed at
conditions described in [23,24]. Target photo-documentation was
done after each opening of the vacuum chamber. In order to quantify
the target state on the evolution on the acetylene supply the pixel
counting for target areas of interest were done for each taken photograph.
The pixel counting determined the relative amount of studied
parts. The pixel count was done at the racetrack part only, because the
racetrack, the target erosion zone, plays the key role for the magnetron
discharge. For the EDX (Energy-dispersive X-ray spectroscopy) study
of the target racetrack coverage by Ti–C phases, Ti square samples
(1 cm × 1 cm) were used and placed on the racetrack zone. One edge
of Ti sample was placed in the racetrack centre and the other at the
racetrack outer edge.
3. Results and discussion
3.1. Process characteristics
Typical overall hybrid PVD–PECVD process characteristics are
given in Fig. 2. There are shown the dependences of cathode voltage
and discharge current together with total pressure and spectral emission
line intensities on the acetylene supply ﬂow for 2 kW DC power
applied on the magnetron target with −100 V RF bias.
Before measurement of each point, the target was thoroughly
cleaned by Ar bombardment without the presence of acetylene to
ensure the same target conditions and to eliminate the inﬂuence of
previous measurements. The cleaning of the target covered by thick
carbon rich layers takes long time [30]. The steady-state conditions
of the hybrid PVD–PECVD process are reached in order of tens of
minutes after acetylene injection. In Fig. 2 the full black square points
denote the measured values with increasing acetylene ﬂows — on the
way from the clean target. When measuring with the decreasing
acetylene ﬂows, the cleaned target was exposed for 3 min to
30 sccm of C2H2 for full poisoning. The Fig. 2 the hollow red circle
points denote measured values with decreasing acetylene ﬂows —
on the way from the poisoned target.
Fig. 2 demonstrates that the hybrid PVD–PECVD process does not
exhibit hysteresis behaviour. The electrical characteristics in Fig. 2(a)
and (b) are non-monotonous; a certain local minimum in voltage
and local maximum in discharge current evolutions is observed. The
discharge voltage and current are increasing and decreasing respectively
while the DC generator was operated in constant power mode
meaning that the current and voltage dependencies are inverted.
There is also no rapid evolution of total pressure in the chamber
with acetylene ﬂow, see Fig. 2(c). The pressure is increasing with increasing
acetylene ﬂow almost linearly.
Dependence on acetylene supply ﬂow of hydrogen, titanium and
argon emission lines given by optical emission spectra are shown in
Fig. 2(d)–(f). In Fig. 2(d) the non-monotonous evolution of hydrogen
alpha line is plotted. It is increasing rapidly with increasing acetylene
ﬂow but for higher ﬂows it is sharply decreasing, a maximum of
hydrogen line intensity is observed for certain acetylene supply
ﬂow. The evolution of titanium emission line in Fig. 2(e) is different,
it is almost linear. Looking at the argon emission line, see Fig. 2(f),
its intensity is slightly decreasing, increasing and then decreasing as
acetylene ﬂow increases.
From the general overview of presented data, one can conclude
that there exist three distinctive zones in which studied parameters
evolve in a characteristic way. For 2 kW DC power applied on the
magnetron target there is zone I from 0 to approximately 6 sccm of
C2H2, zone II approximately from 6 to 12 sccm of C2H2 and zone III
for higher ﬂows than 12 sccm of C2H2.
The zone I is characterized by the increasing discharge voltage,
pressure and hydrogen emission intensity and by the increase in
discharge current, titanium emission intensity and slight decrease in
argon emission. The zone II is characterized by the increase in
discharge current, pressure, hydrogen emission intensity and slight
increase in argon emission together with decreasing discharge voltage
and titanium emission. In the zone III again the increase in the
target voltage together with the slight increase in the total pressure
can be observed, the decreasing values of the discharge current, titanium,
hydrogen and argon is characteristic. Summarizing overview of
each parameter evolutions within three deﬁned zones is given in
Table 1.
Fig. 1. Drawing of the experimental setup.
284 T. Schmidtová et al. / Surface & Coatings Technology 232 (2013) 283–289
3.2. Film properties
A set of coatings was prepared using this hybrid PVD–PECVD process
at acetylene ﬂows of 8–14 sccm (i.e. in zones II and III) and analysed
[24]. The chemical composition of the coatings behaves more monotonously
as can be seen in Fig. 3. Titanium content decreases while carbon
content increases with higher acetylene ﬂow. Hydrogen content remains
stable b10% and also the oxygen contamination remains low
for the whole deposition range. The stoichiometric composition where
a) Discharge voltage b) Discharge current
c) Total pressure d) Hydrogen emission
e) Titanium emission f) Argon emission
Fig. 2. Dependences of discharge voltage, discharge current, total pressure and spectral emission lines on acetylene ﬂow. Black full square points are values obtained with increasing
acetylene ﬂow – on the way from clean target and red hollow circular points are values obtained with decreasing acetylene ﬂow – on the way from poisoned target.
Table 1
Summarizing overview of each parameter evolutions within zones I–III.
Voltage
(current)
Spectral intensity Relative density
H Ti Ar H Ti Ar
Zone I ↗ (↘) ↗ ↘ ↘ ↗ ↗ →
Zone II ↘ (↗) ↗ ↗ ↗ ↗ ↘ →
Zone III ↗ (↘) ↘ ↘ ↘ → ↗ →
285T. Schmidtová et al. / Surface & Coatings Technology 232 (2013) 283–289
Ti/C = 1 was achieved for acetylene ﬂow of ~10.5 sccm, which belongs
to aforementioned zone II.
The mechanical properties show a distinct peak at acetylene ﬂow
of 12 sccm (see Fig. 4). At this point the hardness reaches 46 ±
2 GPa and Young's modulus 414 ± 7 GPa. The mechanical properties
decrease with both lower and higher acetylene ﬂows. The ﬂow of
12 sccm lies on the border between zones II and III.
More detailed study of the properties of the thin ﬁlms deposited
by the hybrid PVD–PECVD process including evolution of the deposition
rate, residual stress, microstructure, etc. with acetylene supply
was presented in the associated paper [24].
3.3. The state of the target
For reactive magnetron sputtering, it was reported that the
electrical characteristics are related to the state of the target; the
target poisoning by a compound of different coefﬁcient of secondary
electron emission from the original target material results in a change
in the target voltage [33]. In classical reactive magnetron sputtering
the cathode voltage decreases/increases monotonously with the
partial pressure of the reactive gas as there is a monotonous and continuous
coverage of the target surface by a compound. However the
electrical characteristics in Fig. 2(a) and (b) have distinctive evolution
on the acetylene ﬂow. A characteristic local minimum (maximum)
in voltage (current) evolution is observed. As the pressure is evolving
in Fig. 2(c) only a little its inﬂuence on the electrical characteristics
should be negligible and the presence of the local minimum (maximum)
should be related to the evolution of the state of the target in
a different way during hybrid PVD–PECVD process than during classical
reactive magnetron sputtering.
For hybrid PVD–PECVD process a target surface photography is
shown in Fig. 5. The target was covered by three differently ‘coloured’
regions. The following can be distinguished: a metallic region, a black
region, and a grey region. The metallic region is of the same colour as
the original titanium target, so it is denoted as titanium (Ti). The black
layer which was easily removable by hand or an abrasive resembles
the soots and so it is denoted as carbon (C). The grey region which
is matt, compact and very difﬁcult to remove by an abrasive is a transition
between the metallic and black regions. It is similarly coloured
to titanium carbide so this region is denoted as titanium carbide (TiC).
It was of interest to see the target surface changes after sputtering
in the same conditions for various acetylene ﬂows. In Fig. 6 are shown
photographs of three target halves for selected 3, 9 and 13 sccm of
acetylene ﬂows. For better visualization the target racetrack is
delimited by red highlights. For 3 sccm of C2H2 the target racetrack
was mostly Ti, for 9 sccm of C2H2 the target was mainly grey — mainly
TiC and for 13 sccm of C2H2 the racetrack was carbon rich with black
and grey regions. Clearly some evolution of the target state with the
acetylene ﬂow is visible.
Calculation of the relative target racetrack coverage by Ti, TiC and
C parts as was done by the pixel counts as described in the experimental
section. In Fig. 7 shown are racetrack coverage percentages
Fig. 3. Chemical composition of nc-TiC/a-C:H coatings depending on acetylene ﬂow
during deposition.
Fig. 4. Mechanical properties of nc-TiC/a-C:H coatings depending on acetylene ﬂow
during deposition.
Fig. 5. Photograph of the target after sputtering by 2 kW DC power with RF substrate
bias −100 V for 12 sccm of acetylene at steady-state conditions. Along the racetrack
region three differently ‘coloured’ regions are visible. The pure metallic region is
denoted as Ti, the grey as TiC and black as a-C.
Fig. 6. Photographs of three selected target halves for 3, 9 and 13 sccm of acetylene
after achievement of steady-state conditions during deposition. The target racetrack
region is highlighted.
286 T. Schmidtová et al. / Surface & Coatings Technology 232 (2013) 283–289
for the three studied parts and the results are also correlated with the
three zone behaviour of voltage characteristics.
In the zone I from 0 to approximately 6 sccm of C2H2 Ti regions are
diminishing on behalf of TiC regions, the racetrack is titanium rich. In
the zone II approximately from 6 to 12 sccm of C2H2 the racetrack is
composed mainly by TiC region. For higher ﬂows of C2H2 in the
zone III the TiC parts are overtaken by C, the racetrack becomes
carbon rich. Combining information from discharge voltage characteristics
with the racetrack coverage we can conclude that the voltage
increase in the zone I is connected with the creation of TiC on the
target racetrack. In the zone II, the voltage slightly decreases with
acetylene inﬂow (by about 5%) and the voltage local minimum is
observed at 11 sccm of acetylene supply. In the zone II, mainly the
presence of the grey colour TiC was detected in the racetrack region
(see Fig. 7) leading us to a conclusion that the voltage decrease should
be related with the evolution of TiC Invoking the phase diagram of
Ti–C [34,35], we suppose the voltage decrease to be caused by the
evolution of the TiC stoichiometry in the racetrack region from the
substoichiometric TiC (at 6 sccm of C2H2) to stoichiometric TiC
(around 11 sccm of C2H2). The rapid voltage increase with higher
acetylene ﬂows in the zone III is clearly related to the carbon formation
in the racetrack. Its composition is therefore carbon rich TiC/C.
Therefore increasing of the acetylene supply ﬂow results in continuous
phase change from Ti-rich Ti/TiC (zone I) to mainly single phase
TiC (zone II) and ﬁnally to carbon-rich TiC/C(zone III). The evolution
of the target state is similar to phase changes in the growing TiC/C
ﬁlms with increase carbon content as can be found for example in
[10,35].
For the better understanding of the racetrack coverage by Ti–C
phases the analysis was performed on the Ti square samples placed
on the cathode surface. The results for the three studied zones of acetylene
ﬂows are shown in Fig. 8. Note that the EDX method gathers the
information from approximately 1 C2H2 volume of the top layer of the
analysed material. As the thickness of the target layer which has been
modiﬁed by the process is unknown and probably varies with acetylene
supplies, only qualitative information of Ti and C compositions
can be derived. From Fig. 8 the racetrack homogeneity is clearly
observed. For low acetylene ﬂows in the zone I the Ti/C ratio is very
high and approaching the zone II the Ti and C abundances become
equal. In the zone III where the amorphous carbon enters the racetrack
region a clear evolution of composition is seen from racetrack
centre to its edge where Ti/C ratio is reversed.
In our case, the maximal hardness of 46 ± 2 GPa and indentation
modulus of 415 ± 7 GPa were measured for coatings with 55 at.% C
deposited at the conditions close to the frontiers between zones II
and III, where the target surface is covered by stoichiometric TiC.
According to the generic design concept [36,37], this high hardness
is based on the combination of the absence of dislocation activity in
the small TiC nanocrystals and blocking of a-C:H grain boundary
sliding by the formation of a strong interface between the two phases.
Thus, the coatings with maximal hardness should show certain excess
of carbon over titanium to form nanocomposite structure. In hybrid
PVD–PECVD process, both the target and the substrate are being
exposed to the ﬂux of carbonaceous species originating from acetylene
dissociations. Simultaneously to target poisoning, the target is
being sputter cleaned providing additional ﬂux of carbon atoms on
the substrate. Similarly to reactive magnetron sputtering [31], higher
relative amount of carbon could be expected to be found in the growing
ﬁlm than at the target surface which has been experimentally
proved for sputtering of Ti in mixture of Ar and CH4 [25]. In our experimental
conﬁguration, deposition process at conditions between
zones II and III caused the optimal conditions for the growth of the
nc-TiC/a-C:H with the maximal hardness. Depending on the experimental
conditions, such as the magnetron head design and position
of argon and acetylene gas inlet, the conditions to deposit coatings
with maximal hardness could be slightly shifted, however they should
be expected to be located always close to the frontiers between the
zones II and III, where the target is covered by TiC and coating composition
is slightly overstoichiometric with respect to carbon.
3.4. Relative evolution of concentrations of Ar, H and Ti in plasma
Assuming direct excitation of a ground state particle by an electron
impact, the intensity of a spectral line depends on the concentration
of electrons in the plasma bulk, concentration of ground state
particles and excitation rate which is a factor proportional to overlap
of excitation cross section and electron energy distribution function
(EEDF). The ﬂux of ions to the sheath edge is proportional to the ion
density (which is equal to the electron density in the plasma) times
the ion acoustic velocity, typically with a factor of 0.6 according to
Bohm presheath diffusion criterion [38]. The ions are then accelerated
by the sheath potential and bombard the cathode/target surface
causing secondary electron emission and sputtering. Thus, the evolution
of the concentration of electrons in the plasma is reﬂected by the
discharge current. Assuming that electron energy distribution function,
i.e. excitation rate and ion acoustic velocity does not depend
on C2H2 supply, ratio of the atomic line intensities and discharge
current provides the evolution of the ground state particle densities
in plasma.
Fig. 7. Racetrack coverage by Ti, TiC and C on acetylene supply. Voltage characteristics
with three zones behaviour is correlated with plotted racetrack coverage.
Fig. 8. EDX analysis of three Ti square samples (1 cm × 1 cm) placed in the target racetrack
during the deposition at different acetylene ﬂows. Position 0 marks the racetrack
centre, position 11 marks the racetrack outer edge.
287T. Schmidtová et al. / Surface & Coatings Technology 232 (2013) 283–289
The evolution of the relative concentrations of Ar, H and Ti in
plasma volume is plotted in Fig. 9 together with marked zones I, II
and III. The comparison of evolutions of the relative concentrations
with other process parameters can be found in Table 1. Despite that
the Ar line intensity evolves with C2H2 ﬂow the calculated Ar concentrations
are constant for all zones supporting the hypotheses on EEDF
and ion acoustic velocity to be independent on C2H2 supply. Decrease
of Ar line intensity in zone I, increase in zone II and decrease in
zone III that follow the evolution of the discharge current perfectly
(compare Fig. 2(b) and (f)) is caused by evolution of the plasma
density and not by the evolution of the buffer gas concentration
with the acetylene supply. The titanium concentration is decreasing
almost linearly though all zones showing that by increasing the
C2H2 ﬂow the amount of sputtering Ti is decreasing linearly without
any rapid transition.
The hydrogen concentration is increasing in zones I and II and
despite that the well pronounced maximum of hydrogen line intensity
was observed at the frontiers between the zones II and III, in the zone
III the hydrogen concentration is not increasing anymore but it stays
rather independent on C2H2 supply. The decrease of hydrogen emission
in the zone III (see Fig. 2(d)) is not caused by decrease of hydrogen
atom concentration (see Fig. 9) but should be related to the steep
decrease of discharge current (i.e. plasma density) linked with a steep
increase in the discharge voltage to maintain the discharge (see
Fig. 2(a)) while the generator was operating in the constant power
mode. For high amount of acetylene in the volume it is difﬁcult to
estimate the extent of the volume reactions of acetylene fragments.
The constant hydrogen atom density in the zone III could be caused
by two opposite effects that act simultaneously — an increase of
acetylene supply is followed by the reduced ability of the plasma to
dissociate acetylene molecules and produce hydrogen atoms due to
lower plasma density (lower discharge current, higher voltage to
sustain plasma). It is therefore possible that the production of atomic
hydrogen is constant or even decreasing with the acetylene supply
in the zone III. Other possible explanation for constant hydrogen
atom concentration with acetylene supply could be that the substrate
ﬁlm is growing with high content of carbon matrix where signiﬁcant
amount hydrogen could be stored. However the ﬁlm analysis in the
acetylene in the range between 9 and 14 sccm showed, that the
hydrogen content in the ﬁlms is constant around 5% [23,24].
3.5. Inﬂuence of magnetron power and substrate bias
The effect of DC power applied on the magnetron target on the
hybrid PVD–PECVD process evolution on acetylene supply was studied.
By lowering the applied DC power from 2 kW to 1 kW the general
trends (three zones behaviour) observed at electrical characteristics
Fig. 2(a), (b) and Fig. 7 are preserved, see Fig. 10. The three zones
are only shifted towards lower acetylene ﬂows, as applying half
power on the magnetron target shifts the boundaries of three zones
roughly to half the acetylene ﬂows.
The effect of applying RF bias to the substrate can also be seen in
Fig. 10. Substrate bias of −100 V was set by 225 W RF power which
was a quarter of the 1 kW DC power applied on the magnetron target.
Such relatively high RF power applied on the substrate could be
inﬂuencing the evolution of hybrid PVD–PECVD process on acetylene
supply. Fig. 10 demonstrates that the three zones of the target state
and entire process characteristics are not shifted with respect to
C2H2 ﬂow providing only negligible inﬂuence of RF plasma near the
substrate on the evolution of the trends of deposition process
characteristics.
4. Conclusions
The hybrid PVD–PECVD process of titanium sputtering in argon
and acetylene atmosphere does not show the hysteresis behaviour.
The absence of hysteresis region avoids process stability problems
met in conventional reactive magnetron sputtering making the
hybrid PVD–PECVD process relatively easy to control. Three distinctive
zones were identiﬁed in the process evolution with the acetylene
supply.
For the low range of acetylene ﬂows (zone I) the voltage is
increasing due to TiC formation on the surface of the target racetrack
at the expense of Ti and the relative concentration of Ti in plasma is
decreasing while the H concentration is increasing due to acetylene
fragmentation in plasma volume. For medium range of acetylene
ﬂows (zone II) the target voltage stops increasing or it is slightly
decreased. The racetrack is covered mainly by TiC. Ti concentration
in plasma phase is still decreasing and hydrogen concentration continues
to increase. Stoichiometric TiC coatings are being deposited
at this zone. For high acetylene ﬂows (zone III) the target voltage is
rapidly increasing, the carbon layers start to penetrate into the target
racetrack and the composition of the racetrack surface becomes carbon
rich. The Ti concentration in plasma phase is still decreasing but
H concentration is not evolving further, it remains more or less constant.
On the border of zones II and III the nc-TiC/a-C:H coatings
with highest hardness and Young's modulus were prepared. For the
studied range of acetylene supply the Ar concentration remains the
same.
Reduction of the power applied on the target keeps the three zone
behaviour of the process. It shifts zone boundaries towards lower
acetylene ﬂows. Halving the magnetron power shifts the boundaries
to half of the acetylene ﬂows. RF bias does not signiﬁcantly inﬂuence
Fig. 9. Dependence of the relative concentrations of Ti, Ar and H in plasma on acetylene
supply.
Fig. 10. Voltage characteristics on the acetylene supply ﬂow for 1 kW DC with and
without applied RF bias (225 W ~ –100 V).
288 T. Schmidtová et al. / Surface & Coatings Technology 232 (2013) 283–289
the hybrid PVD–PECVD process characteristics. By varying the RF bias
for constant magnetron power desired self-bias on the substrate can
be set without modifying the overall process behaviour.
Acknowledgement
This research has been supported by Czech Science Foundation
contract 104/09/H080 and 205/12/0407 and R&D centre for lowcost
plasma and nanotechnology surface modiﬁcations CZ.1.05/
2.1.00/03.0086 funded by European Regional Development Fund.
Pavel Souek acknowledges the Brno City Municipality as holder of
Brno PhD Talent Financial Aid. The authors would like to acknowledge
Dr. V. Peřina from the Nuclear Physics Institute of the ASCR for
RBS measurements and Dr. J. Buršík from the Institute of Physics of
Materials of the ASCR for EDX measurements.
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