Surface & Coatings Technology 228 (2013) S210–S213
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Surface & Coatings Technology
journal homepage: www.elsevier.com/locate/surfcoat
Synthesis and characterization of zirconium oxynitride coatings deposited by filtered
cathodic vacuum arc technology
Yi-Ming Chen, Bin Liao, Xian-Ying Wu, Hui-Xing Zhang, Xu Zhang ⁎
Key Laboratory of Beam Technology and Material Modification of Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875, PR China
a r t i c l e
i n f o
Available online 13 June 2012
Keyword:
Filtered arc
Zirconium oxynitride
Air
Mechanical property
a b s t r a c t
Thin films of zirconium oxynitride (ZrOxNy) were deposited onto glass and Si substrate at room temperature
by filtered cathodic vacuum arc (FCVA) technology using air as a reactive gas. The compositions and structures of the zirconium oxynitride films influenced by air flow rate were investigated by scan electronic spectroscopes, X-ray diffraction and X-ray photoelectron spectroscopes. The results showed that crystal structure
of the films transformed from ZrO and ZrN mixed phases to ZrN phase with the increasing air flow rate. The
hardness, elastic modulus and elastic recovery parameter (ERP) of the zirconium oxynitride films were also
determined by nano indentation tests. At the optimum deposition parameters, the hardness and elastic modulus values reached 28.94 GPa and 253.44 GPa respectively; good wear resistant properties were also
achieved due to the high H/E ratio (0.115) and good elastic recovery (86.18%). The optical band gap of the
film at the optimum deposition parameter was 1.91 eV, implying that the film had great potentials in
many photocatalytic and optoelectronic applications.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Transition metal oxynitride film, especially zirconium oxynitride
(ZrOxNy), had attracted considerable interests in the last few years
due to their remarkable properties. ZrOxNy thin films had been widely applied in gate dielectrics [1], temperature sensor element in magnetic fields up to 32 T operating at temperatures between 2 and 286 K
[2], corrosion resistance coatings [3], and decorative films such as
eyeglass frames, wristwatch casings, and wristbands [4]. The appearance of oxygen during deposition process leads to a formation of ionic
metal–oxygen bonds in a matrix of covalent metal–nitrogen bonds; it
generates a new structure (metal–oxynitride) with different properties [5]. Therefore, by variation of the oxygen/nitrogen ratio it allows
us to tailor the structural, optical, mechanical and electronic properties of the transition metal oxynitride film. Various techniques were
used to prepare zirconium oxynitride films like radiofrequency (RF)
reactive magnetron sputtering, direct current (DC) reactive magnetron sputtering, and reactive cathodic arc evaporation [6]. Traditionally, N2/O2 mixtures were employed as reactive gases during deposition;
other gases had also been used such as water vapor–nitrogen atmosphere
[7] and air [8]. It is worth mentioning that air as a reactive gas can reduce
the processing time because of the low vacuum.
Reactive cathodic arc evaporation was adopted by M. Laurikaitis et al.
to prepare ZrNxOy films, however, macroparticles were found in their
work [19]. Filtered cathodic vacuum arc (FCVA) technology, free of
⁎ Corresponding author. Tel.: + 86 10 6220 8249; fax: + 86 10 6223 1765.
E-mail address: zhangxu@bnu.edu.cn (X. Zhang).
0257-8972/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.surfcoat.2012.06.015
macroparticle contamination, had been widely confirmed as an excellent
method for deposition films with better qualities [9]. So in our present
work, ZrOxNy thin films were prepared by FCVA technology using air as
a reactive gas. Furthermore, we investigated the effect of air flow rate
on the compositional, structural, optical and mechanical characteristics
of the ZrOxNy films.
2. Experimental details
Zirconium oxynitride films were deposited onto glass and Si (100)
substrate, a 90 mm in diameter zirconium plate of 99.8% purity was
used as the cathodic arc source. The plasma was produced and then introduced into the processing chamber by 90° bent magnetic filter duct.
This procedure removed the unwanted neutral particles and the
macroparticles. The base pressure in the processing chamber was
about 3 × 10 − 2 Pa during the experiment. Before deposition the zirconium was pre-implanted to get a zirconium seed layer, which could enhance the ZrOxNy thin films' adherence force to the substrate. The
deposition parameters, such as substrate bias voltage (200 V), filter coil
current (2.0 A), and substrate temperature (room temperature) were
kept the same except for the air flow rates. The crystal structure of the
films was determined by grazing incidence X-ray diffraction (improved
D/max-RB type)(θ=1°) operated at 40 kV and 200 mA with a Cu Ka
(λ=0.154 nm) excitation source. The average grain size of film (D) was
calculated from the full width at half maximum (FWHM) using Scherrer's
formula:
D¼
kλ
:
B cosθ
Y-M. Chen et al. / Surface & Coatings Technology 228 (2013) S210–S213
S211
where constant k=0.89, B is the FWHM (degree), λ is the wavelength
(nm), and θ is the diffraction angle (degree). The thickness and curvature
of the film were measured by the surface morphology device with the
pattern of Talysurf 5P-120 from Rank Taylor Hobson. The elemental composition of the film was obtained from the energy disperse spectroscopy
(EDS) on the Hitachi S-4800 system and X-ray photoelectron spectroscopy (XPS) on VG ESCALAB MKII spectrometer. Film's hardness and Young's
modulus were determined from the loading and unloading curves on
MML NanoTest UK. The maximum load used was 2 mN, with a loading
time of 20 s, holding 5 s, and unloading in 20 s, producing an average
number of 9 indentations per sample. UV–visible spectroscopy (SPECORD
200) was employed to investigate the absorption spectra of the film over
the spectral range of 200–800 nm, the optical band gap was calculated
from obtained spectra.
3. Results and discussions
3.1. Crystal structure
Grazing incidence X-ray diffraction analysis was carried out to investigate the phase of deposited films. Fig. 1 showed the GIXRD patterns of
the ZrOxNy films prepared with air flow rate varying from 10 to 70 sccm.
At low air flow rate (10–30 sccm), the (200), (220) and (311) peaks of
ZrO [PDF#20-0684] were observed, when the air flow rate increased,
those peaks shifted slightly toward higher angles and transformed into
(200), (220) and (311) of the ZrN [PDF#65-0961]. The atomic concentrations of films varying with air flow rate were shown in Fig. 2(a). Generally speaking, the formation of zirconium oxide was more favorable than
zirconium nitride. However, in our present work, it seemed to be contrary except for the low flow rates (10–30 sccm), which was consistent
with the results reported by Mu-Hsuan Chan [8]. The atomic concentrations in Fig. 2(a) were well consistent with the above-mentioned analysis. The content of oxygen increased and that of nitrogen decreased as
the air flow rate varies from 10 to 30 sccm. On the contrary, at high air
flow rate ranging from 40 to 70 sccm, the concentration of nitrogen enlarged rapidly.
J. M. Ngaruiya et al. deduced that formation of ZrO2 reduced the
Gibbs free energy the most, it meant that formation of ZrO2 was
expected to be observed [10], however, there were no remarkable
peaks of ZrO2 that exist in all our XRD patterns. From thermodynamic
point of view, ZrO2 (ΔGf,0ZrO2: −1091.6 kJ/mol) is energetically more favorable than ZrN (ΔGf,0ZrN: −364.3 kJ/mol) [8]. While in our work, the
nitridation of Zr is easier than the oxidation especially at high air flow
rate, which may be attributed to molecule kinetics theory [8]. Oxygen
Fig. 2. (a) The atomic concentrations of films varying with air flow rate. (b) The average
grain size of deposited films varying with air flow rate.
electronegativity is 3.5 and it is larger than that of nitrogen (3.0),
which indicates that oxygen is more likely to attract electrons than nitrogen. A similar phase transition to ZrN was also found in Rizzo's work [12].
The mechanism of phase formation and transition is a complex issue, and
it needs to be further investigated.
The average grain size of deposited films was measured and also
showed in Fig. 2(b). The average grain size increased from 5 nm to
11 nm as the air flow rate increases from 20 sccm to 70 sccm. The
highest deposition rate of 160 nm·min− 1 was 10 times as fast as the
data reported in the other paper [8]; high efficiency was one of the
advantages of the FCVA technology [9].
3.2. Chemical composition
Fig. 1. The GIXRD patterns of the ZrOxNy films prepared with air flow rate varying from
10 to 70 sccm.
The XPS technique was used to identify elements and their chemical
states present in the outermost surface of zirconium oxynitride film.
The XPS spectra of Zr 3d for the air flow rate of 10, 40 and 70 sccm
were shown in Fig. 3. The Zr 3d peak had been decomposed into three
components, corresponding to the nitride, oxynitride and oxide phase
of zirconium. The oxynitride component (labled 2) was located in the
BE range of 181.1–182.1 eV [7], the doublet labled 1 was associated
with nitride phase which was positioned in BE ~178.8 eV [11], the
third doublet 3 had the Zr 3d centered at 182.2 eV, which represented
the oxide [12]. Peak positions of Zr 3d deconvoluted components and
their percentage were collected in Table 1. As shown in Table 1, the percentage of nitride increased from 4.52% to 22.37% as the air flow rate increases from 10 to 70 sccm, which was consistent with the XRD analysis
and atomic concentration results. Furthermore, a shift of about 1.0 eV of
S212
Y-M. Chen et al. / Surface & Coatings Technology 228 (2013) S210–S213
30
70sccm
Hardness
28
2
10
internal stress
3
Hardness/GPa
Intensity /arb.units
26
40sccm
2
3
1
10sccm
8
24
6
22
20
4
18
2
2
16
3
1
10
180
185
40
50
60
70
0
Fig. 4. The hardness and internal stress of ZrOxNy films as a function of the air flow rate.
Fig. 3. The Zr3d XPS spectra of the ZrOxNy films prepared with air flow rates of 10, 40
and 70 sccm, labels 1, 2 and 3 represented nitride phase, oxynitride phase and oxide
phase, respectively.
ZrN peaks to higher binding energy was observed. A similar tendency
was reported by P. Carvalho et al. [11], the reason was correlated to
the change in the ionic valences induced by the chemical environment.
3.3. Mechanical property and optical band gap
The thickness of ZrOxNy thin film prepared with air flow rate varying from 10 to 70 sccm was within the range of 0.378–1.26 μm. The
internal stress of the film (σ) can be calculated by the Stoney formula:
σ¼
30
air flow rate/sccm
190
Binding Energy /eV
1 Es t2s
1
1
;
−
6 ð1−νs Þt Rn R0
where Es (180 GPa) is Young's modulus of the silicon substrate, ts
(0.5 mm) is the thickness of silicon substrate, νs (0.26) is the Poisson's
ratio, t is the thickness of deposited film, and R0, and Rn are the radii of
curvature before and after deposition respectively, usually R0 approximately equals to infinity. Fig. 4 showed the hardness and internal stress
of ZrOxNy films as a function of the air flow rate, with the air flow rate
increased from 10 to 60 sccm; the hardness of films increased to the maximum value of 28.94 GPa, and further increase of air flow rate would decrease the hardness. The situation for internal stress was almost the same
except for the sample at air flow rate of 50 sccm.
Based on the above analysis, the content of ZrN phase enriched with
the increase of air flow rate, and covalent nitrides such as ZrN were the
more attractive candidates for achieving high hardness than ionic
compounds since electrostatic interactions were omnidirectional [13].
On the other hand, the average grain size in Fig. 2(b) showed the size
of 9 nm in the 60 sccm, grain growth was also playing an important
role in hardness [4]. The highest internal stress in 60 sccm could be associated with the incorporation of oxygen within the ZrN lattice, which
would induce lattice defects in the film structure acting as obstacles for
the dislocation motion, resulting in the enhanced hardness [14].
The hardness/elasticity (H/E) ratio was used to describe the failure
mechanism of the materials. The ratio H/E of ZrOxNy films was measured between 0.088 and 0.115. The elastic recovery parameter (ERP)
values were also determined in the nanoindentation test. Fig. 5 showed
the elastic modulus and ERP of ZrOxNy films as a function of air flow
rate. As can be seen from the figure, the elastic modulus and ERP
value reached the maximum simultaneously when the air flow rate
was 60 sccm. The large H/E ratio (0.115) and ERP value (0.8618) indicated good wear resistant properties of the ZrOxNy thin film prepared
at the air flow rate of 60 sccm [15,16].
The UV–visible absorption spectra of the film prepared with the air
flow rate of 60 sccm, filter coil current of 2.0 A and bias voltage of
200 V, were measured, as shown in Fig. 6(a). The optical band gap Eg
of the film was determined by the following formula [20],
n
αhν∝ hν−Eg
Where α is the absorption coefficient related to A = αd [A is the absorption intensity, d is the film's thickness [17], hνis the incident photon
energy, Eg is the optical band gap energy, and n, a number which characterizes the transition process, equals 2 for ZrOxNy [18]]. Plots of (αhν)1/2
versus hν for ZrOxNy film are shown in Fig. 6(b). Value of Eg is evaluated
by extrapolating the linear portion of the curve to (αhν)1/2 =0. The Eg
260
1.2
elastic modulus
1.1
250
ERP
Elastic modulus/GPa
175
20
240
1.0
230
0.9
0.8
220
ERP
1
12
internal stress/GPa
Zr-3d
0.7
210
0.6
200
Table 1
Peak positions of Zr3d deconvoluted components and their percentage.
0.5
190
Air flow rate/
sccm
1
2
3
Zr–N
%
Zr–O–N
%
Zr–O
%
10
40
70
178.31
178.85
179.59
4.52
8.46
22.37
181.51
181.18
181.77
68.73
77.09
62.88
182.18
182.11
182.22
26.75
14.45
14.75
0.4
180
10
20
30
40
50
60
70
air flow rate/sccm
Fig. 5. The elastic modulus and ERP of ZrOxNy films as a function of air flow rate.
Y-M. Chen et al. / Surface & Coatings Technology 228 (2013) S210–S213
a
3.0
ZrN phase as the air flow rate varying from 10 to 70 sccm. The XPS results were consistent with the change of the XRD patterns. Hardness
measurements showed that the optimum experiment parameters were
determined, hardness and elastic modulus of ZrOxNy films reached
28.94 GPa and 251.44 GPa respectively. The phase transition, average
grain size and internal stress were the factors to interpret the hardness
data. Good wear resistant properties were also achieved due to the
high H/E ratio (0.115) and good elastic recovery (86.18%). The optical
band gap of the film at the air flow rate of 60 sccm was 1.91 eV, implying
that the film had great potentials in many photocatalytic and optoelectronic applications.
2.5
Abs
2.0
1.5
1.0
0.5
Acknowledgment
0.0
200
300
400
500
600
700
This work was financially supported by the National Science Foundation of China under Grant no. 10975020.
800
λ/ nm
References
b
2000
1/2
(
αhν)
/[eV*cm-1]1/2
S213
1500
1000
500
0
1
2
3
4
5
6
7
hν/eV
Fig. 6. (a) The UV–visible absorption spectra of the film prepared with the air flow rate of
60 sccm; (b) Plots of (αhν)1/2 versus hν for ZrOxNy film at the air flow rate of 60 sccm.
value of the film is 1.91 eV, it is close to the value reported in the literature (Eg = 1.94 eV), which is possibly due to the high nitrogen incorporation in the film [8].
4. Conclusions
Zirconium oxynitride thin films were deposited by using filtered cathodic vacuum arc technique in the presence of air gas. The crystal
structure of the films transformed from ZrO and ZrN mixed phases to
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