Plasma diagnostics during synthesis of copper-organosilicon
composites films
Bogdana Mitu, Veronica Satulu, Gheorghe Dinescu
ational Institute for Lasers, Plasma and Radiation Physic,
409 Atomistilor Street, PO BOX MG 36, Magurele-Bucharest, 077125, Romania,
e-mail: [email protected]
Abstract: In the present work we report on the plasma characteristics during the
synthesis of organosilicon containing copper material by sequential exposure of
the substrate to a PECVD process and to an RF magnetron sputtering source. The
plasma generated by each source was investigated by mass spectrometry (MS)
and optical emission spectroscopy (OES) in order to obtain in-situ information on
the species present during synthesis process. Optical emission spectroscopy
studies revealed the atomic emission of Cu, Ar and H as well as band emission
coming from the CO, and OH radicals, while the mass spectrometry analysis
showed the presence of various neutral and ionic fragments, indicating the
HMDSO fragmentation and the effective sputtering of the copper atoms.
Keywords: copper-organosilicon composites, PECVD, magnetron sputtering,
plasma diagnostics
1. Introduction
Metal-polymer composite materials are among the
most studied systems nowadays due to their various
properties like antibacterial effect, enhanced
conductivity, protective capability, and catalytic
activity [1, 2]. These various effects can be
controlled by tuning the dimension and density of
the metallic particles embedded in the used
polymeric matrix [3]. One of the materials largely
investigated for its potential applications in
microelectronics, optical coatings and scratch
resistant coatings, as well as in anti-biofouling
applications is the silicon dioxide-like thin films
obtained
by
plasma
polymerization
of
hexamethyldisiloxane (HMDSO) precursor. On the
other side, there is a growing interest in using copper
as metallic inclusions in nanocomposites both for its
catalytic potential, as for the antimicrobial effect.
The present work focuses on the plasma diagnostics
by means of Optical Emission Spectroscopy (OES)
and Mass Spectrometry (MS) measurements during
the synthesis of organosilicon-copper composite
material by sequential exposure of the substrate to
PECVD and magnetron sputtering plasma sources.
2. Experimental
The process is conducted in a stainless steel
cylindrical reaction chamber on which two separate
plasma sources are mounted perpendicular one in
respect to the other, as can be seen in Figure 1. The
RF powered electrode of the PECVD plasma source
is constructed as a shower through which a
controlled HMDSO [(CH3)3-Si-O-Si-(CH3)3] flow
(2 sccm) is carried in vapour phase by an Ar flow
(20 sccm). Oxygen was introduced as well in the
mixture, at gas flows in the range 0 – 20 sccm. The
applied RF power during plasma polymerization of
HMDSO was set in the range 5 - 50 W. The working
pressure during the PECVD step was in the range
Copper target
Optical fiber
slot
Towards the vacuum
system
Vacuum
Visualization window
3500
a)
Specifically, mass spectrometry technique was
offered information about the ionic and neutral
species in the plasma, while the optical emission
spectroscopy was used as a complementary
technique for detecting the radiative species and
short lifetime radicals.
3. Results and discussion
The emission spectra of the plasma generated by the
magnetron sputtering plasma source with Cu target
is dominated by the Cu I lines as well as Ar I and Ar
II lines; however, small bands associated to the
Emission intensity (a.u.)
Figure 1. Schematic of the experimental set-up for the synthesis
of Cu - organosilicon composites.
8000
OH 3064 system
2 +
2
(A Σ - X Π)
3000
No oxygen
20 sccm oxygen
2500
2000
1500
1000
No oxygen
10 sccm oxygen
Hβ
b)
Ar II
7000
Emission intensity (a.u.)
Argon
inlet
3
Mass
spectrometer
head
Magnetron
sputtering
plasma source
3
Angled probe holder (450)
The emission spectra of the PECVD plasma working
in Ar/HMDSO mixture reveal the presence of
excited Ar atoms and ions as well as Hα and Hβ
lines, and also a small signal corresponding to the
OH and CO emission [4], proving the dissociation of
HMDSO in plasma. However, the formation of OH
and CO radicals in the plasma is strongly enhanced
by the addition of oxygen in the plasma, suggesting
the efficient removal of methyl radicals from the
precursor [5], as it is clearly shown in Figures 3 a)
(C Π-B Π, ∆v = +1)
Ar, O2, HDMDSO mixture
PECVD plasma
source
presence of impurities in the reaction chamber are
also visible, through the N2 emission. In Figure 2a)
is presented a typical emission spectrum of the
magnetron, evidencing the Cu I lines at 323.57 nm
and 327.39 nm, and the Ar I line at 696.54 nm; their
intensity as function of the applied RF power is
shown in Figure 2b). The maximum intensity of the
copper line is obtained around 100 W, value which
was chosen for composite synthesis.
N2 SPS system
0.14 -0.3mbar. The magnetron sputtering source has
a 2” Cu target mounted, which is sputtered by
igniting a discharge in argon (5 sccm) at RF powers
between 80 - 120 W, working pressure 0.07 mbar.
The mass spectrometer (EQP 1000, Hiden
Analytical) is mounted in front of the magnetron
head, while the optical fiber which collects the
plasma light on the entrance slit of a Horiba JobinYvone HR spectrograph (grating 2400 mm-1) is
positioned perpendicular.
6000
CO Angstrom System
Ar II
5000
4000
3000
2000
1000
500
0
0
306
308
310
312
314
478
316
480
482
484
486
488
Wavelength (nm)
Wavelength (nm)
Figure 3. The emission spectra of Ar/HMDSO (black line)
and Ar/HMDSO/O2 plasma in the regions corresponding to
a) OH 3064 system and b) CO Angstrom system.
and b). No signal coming from CH or C2 radicals
could be identified in the emission of
Ar/HMDSO/O2 plasma under the condition
investigated in the present work. The evolution of
the Ar I line at 696.54 nm and Hα line at 656.27 nm
as function of the applied RF power on the PECVD
plasma source and the injected oxygen flow in the
discharge are presented in Figure 4 a) and b). Both
600000
a)
Cu I lines
b)
Cu I
Ar I
200000
100000
80
330
335
Wavelength (nm)
690
695
700
90
100
110
30000
200000
20000
150000
10000
100000
Ar flow = 20 sccm
HMDSO flow = 2 sccm
O2 flow = 5 sccm
120
RF power (W )
Magnetron sputtering plasma source
Figure 2. a) OES spectrum of the magnetron sputtering
discharge working in Ar atmosphere at 100 W;
b) Cu and Ar emission intensities as function of the applied
RF power on the magnetron
0
Emission intensity Ar I (a.u.)
300000
10000
325
Ar I (696 nm)
Hα
Emission intensity Hα (a.u.)
20000
130000
250000
400000
Emission intensity Ar I (a.u.)
Emission Intensity (a.u.)
3
Ar I lines
3
30000
(C Π-B Π , ∆v = 0)
40000
0
320
7000
40000
N2 SPS system
Emission intensity (a.u.)
500000
50000
Ar I (696 nm)
Hα
120000
5000
110000
4000
100000
3000
2000
90000
Ar flow = 20 sccm
HMDSO flow = 2 sccm
RF power = 10 W
80000
1000
0
50000
0
10
20
30
RF power (W)
PECVD plasma source
40
50
6000
70000
0
5
10
15
20
Oxygen flow (sccm)
Figure 4. Evolution of Ar and Ha emission intensity when
a) RF power increases; b) O2 flow increases
Emission intensity Hα (a.u.)
60000
500000
800
0
0
400
80
90
100
110
40
60
120
120
RF power (W)
Magnetron sputtering source
Figure 5. Dependence of the Ar and Cu abundances in the
mass spectra as function of the applied RF power masses
the RF power show a maximum intensity of the Ar
neutrals around 100 W and of Cu neutrals around
110 W, as presented in Figure 5. The ionic mass
spectra (Figure 6a) are evidencing mostly the Cu
ions, the small intensity of the Ar ions proving their
18000
3000
+
C2H3
14000
ArH
+
ArH
Intensity (cps)
Cu
+
2000
1000
+
Si(CH3)2
+
+
6000
+
+
Si(CH3)3
0
0
4000
+
Si2O(CH3)5
Si3O(CH3)8
+
Si3OC5H16
+
Si3O2C5H16
H3
2000
20
40
Mass (amu)
60
80
0
120
140
160
180
200
220
Ar
+
Ar2
0
0
40
50
60
Mass (amu)
70
80
240
Mass (amu)
Figure 8. Mass spectra of ions in Ar/HMDSO plasma
generated at 50 W RF power.
2000
+
Intensity (cps)
+
CH3
6000
4000
2500
+
90 W
120 W
+
C3H3
+
8000
8000
+
Intensity (cps)
Cu
+
C2H5
10000
CO2H , SiOH
a)
RF power = 120 W
1250
Intensity (cps)
12000
10000
3750
160
formation of an important number of ions of small
masses, like H3+ and methyl ions, C2H3+ and C2H5+,
but also some clusters at masses above that of
HMDSO, like Si3OC5H16+ (mass 176 amu) or
Si3O(CH3)8+ (mass 220 amu), most probably by ion
– neutral reactions of the precursor fragments in the
16000
5000
140
Figure 7. Mass spectra of Ar/HMDSO mixture without
plasma (black line) and with 20 W RF plasma (red line).
500
650
645
20
Mass (amu)
655
(CH2)SiOSi(CH3)3
600
660
H2
H2O
+
Ar intensity (cps)
700
665
Cu intensity (cps)
670
O2
Ar/2
680
675
Si2O(CH3)5
(CH2)SiOSi(CH3)3
2000000
900
Ar
Cu
0W
20 W
Ar
3000000
Si(CH3)3
685
4000000
N2, C2H4, CO
The mass spectra of neutral species present in the
reactor during magnetron sputtering of Cu (not
shown) are dominated by the Ar peak (40 amu) and
the Cu peaks at 63 and 65 amu, corresponding to the
isotopes, but small traces of water, nitrogen and
oxygen were also noticed. Their dependence upon
The mass spectra of Ar/HMDSO mixture evidence
the typical cracking pattern of the precursor inside
the mass spectrometer, presenting the main peaks at
73 amu (Si(CH3)3), 132 amu (Si2OC4H11) and 147
amu (Si2O(CH3)5). When the plasma is ignited, these
peaks are diminishing due to additional dissociation
processes of HMDSO in the plasma, while the peaks
corresponding to the generated products, at mass 2
amu (H2), 28 amu (Si or CO) and 18 amu (H2O) are
increasing. The ionic mass spectra of a discharge
generated at 50 W, presented in Figure 8, show the
Intensity (cps)
lines increase with increasing the applied RF power
due to the increased energy for dissociation provided
by the plasma. Instead, their behavior when the
oxygen flow increases is in direct relation to the
plasma chemistry in the discharge, namely by
increasing the oxygen amount available in the
discharge, the dissociation of the HMDSO molecule
in small fragments as OH and CO is favored and
more atomic hydrogen is formed.
0
10
20
30
40
50
Ion energy (eV)
Figure 6. a) Typical ionic mass spectra of the magnetron
sputtering source working in Ar with Cu target; b) Energy
distribution of the Cu 63 ions for 90 W and 120 W applied
RF power.
efficient energy transfer to the magnetron Cu target.
The energy scan presented in Figure 6b) evidences
that the Cu ions are quite energetic, with a maximum
around 17 eV for the 90 W and present a shift
toward higher energy when the RF power in the
magnetron sputtering source is increased.
plasma phase [6].
The dependence of the mass signal for the main
peaks related to the HMDSO dissociation in the
plasma and the new formed products upon the
applied RF power is presented in Figure 9. The mass
corresponding to Si2O(CH3)5 and Si(CH3)3 were used
for monitoring the decomposition of HMDSO
thorugh their depletion (defined as the difference
between the signal without plasma and with plasma,
divided by the initial signal). At the same time, the
hydrogen, water and mass 28, which can be
associated to CO or Si were used as a measure of
byproducts formation upon dissociation. It seems
that the consumption of HMDSO in the plasma is
initially correlating to the formation CO, OH and H2,
species which were seen also in the emission spectra
3.5
mass 18 - H2O
100
12
mass 28 - Si, CO, N2
3.0
mass 2 - H2
10
2.5
8
2.0
6
ION/IOFF
60
40
20
4
1.5
mass 73 - Si(CH3)3
mass 147 - Si2O(CH3)5
0
2
1.0
0
10
20
30
40
50
RF power (W)
PECVD plasma source
On the other hand, it was proven that the HMDSO is
immediately dissociated in the plasma, even at RF
powers as low as 5 W, but in order to obtain
polymer-like or silica-like matrix in the
nanocomposites, the used RF power and oxygen
flow should be tuned.
ION/IOFF
Depletion (%)
80
It was shown that the copper atomic and ionic
density available at the substrate level, as well as
their energy, can be controlled by the RF power
injected in the magnetron sputtering system.
Acknowledgements
0
0
10
20
30
40
50
RF power (W)
PECVD plasma source
Figure 9. a) Depletion of mass 73 amu and 147 amu upon the
supplied RF power; b) Generation of hydrogen, water and
CO/Si as function of the applied RF power.
of the discharge, but also at higher RF powers to the
stronger dissociation with formation of carbon and
oxygen atomic species. The dissociation to small
fragments is even stronger when oxygen is also
added in the discharge. In this case, practically no
positive or negative ions could be detected,
suggesting that the entire energy provided by the
plasma is consumed for chemical reactions in
plasma phase between the HMDSO fragments and
the oxygen molecules.
4. Conclusions
In this contribution we investigated the species
present in the plasma during the synthesis of copperorganosilicon composites by a sequential deposition
method in which the substrate is alternatively
exposed to a magnetron sputtering plasma with Cu
target and to a PECVD plasma generated in
Ar/HMDSO/O2 mixture.
The financial support of the Romanian Ministry of
Education and Research through the Human
Resources project TE_229/2010 is gratefully
acknowledged.
References
[1] C. Walter, V. Bruser, A. Quade, K.D. Weltmann,
Plasma Process. Polym. 6 (2009) 803
[2] P. Navabpour, D. Teer, X. Su, C. Liu, S. Wang,
Q. Zhao, C. Donik, A. Kocijan, M. Jenko, Surf.
Coat. Technol. 204 (2010) 3188
[3] H. Wei, H. Eilers, J. Phys. Chem. Sol. 70 (2009)
459
[4] R. W. B. Pearse, A. G. Gaydon, The
identification of molecular spectra, London:
Chapman and Hall, 1976, 4th ed.
[5] A. Granier, M. Vervloet, K. Aumaille, C. Vallée,
Plasma Sources Sci. Technol. 12 (2003) 89
[6] D. Magni, Ch. Deschenaux, Ch. Hollenstein,
A. Creatore, P. Fayet, J. Phys. D: Appl. Phys. 34
(2001) 8