Simulating study of plasmachemical erosion of a-C:H films in a ECR discharge plasma
The dynamics of interference figure of the reflection spectrum for stainless steel and copper mirrors with specially deposited carbon-containing film (ɚ-C:H) were studied when the film was gradually eroded under impact of a deuterium plasma produced in conditions of electron cyclotron resonance (E...
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| Zitieren: | Simulating study of plasmachemical erosion of a-C:H films in a ECR discharge plasma / V.G. Konovalov, M.N. Makhov, I.V. Ryzhkov, A.N. Shapoval, A.F. Shtan’, O.A. Skorik, S.I. Solodovchenko, A.I. Timoshenko, V.S. Voitsenya // Вопросы атомной науки и техники. — 2011. — № 1. — С. 146-148. — Бібліогр.: 5 назв. — англ. |
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irk-123456789-909552016-01-07T03:02:45Z Simulating study of plasmachemical erosion of a-C:H films in a ECR discharge plasma Konovalov, V.G. Makhov, M.N. Ryzhkov, I.V. Shapoval, A.N. Shtan’, A.F. Skorik, O.A. Solodovchenko, S.I. Timoshenko, A.I. Voitsenya, V.S. Низкотемпературная плазма и плазменные технологии The dynamics of interference figure of the reflection spectrum for stainless steel and copper mirrors with specially deposited carbon-containing film (ɚ-C:H) were studied when the film was gradually eroded under impact of a deuterium plasma produced in conditions of electron cyclotron resonance (ECR). The refraction coefficient of the film was estimated and the rate of the film removal was obtained. Досліджувалася динаміка інтерференційної картини спектру віддзеркалення сталевих і мідних дзеркал з штучно нанесеною вуглецьвмісною плівкою (a-C:H) по мірі розпилювання в дейтерієвій плазмі ЕЦР-розряду. Проведена оцінка коефіцієнта заломлення плівки. Отримана кількісна оцінка швидкості розпилювання. Исследовалась динамика интерференционной картины спектра отражения стальных и медных зеркал с искусственно нанесенной углеродсодержащей пленкой (a-C:H) по мере распыления в дейтериевой плазме ЭЦР-разряда. Проведена оценка коэффициента преломления пленки. Получена количественная оценка скорости распыления. 2011 Article Simulating study of plasmachemical erosion of a-C:H films in a ECR discharge plasma / V.G. Konovalov, M.N. Makhov, I.V. Ryzhkov, A.N. Shapoval, A.F. Shtan’, O.A. Skorik, S.I. Solodovchenko, A.I. Timoshenko, V.S. Voitsenya // Вопросы атомной науки и техники. — 2011. — № 1. — С. 146-148. — Бібліогр.: 5 назв. — англ. 1562-6016 PACS: 52.50.Sw http://dspace.nbuv.gov.ua/handle/123456789/90955 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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English |
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Низкотемпературная плазма и плазменные технологии Низкотемпературная плазма и плазменные технологии |
| spellingShingle |
Низкотемпературная плазма и плазменные технологии Низкотемпературная плазма и плазменные технологии Konovalov, V.G. Makhov, M.N. Ryzhkov, I.V. Shapoval, A.N. Shtan’, A.F. Skorik, O.A. Solodovchenko, S.I. Timoshenko, A.I. Voitsenya, V.S. Simulating study of plasmachemical erosion of a-C:H films in a ECR discharge plasma Вопросы атомной науки и техники |
| description |
The dynamics of interference figure of the reflection spectrum for stainless steel and copper mirrors with specially
deposited carbon-containing film (ɚ-C:H) were studied when the film was gradually eroded under impact of a deuterium
plasma produced in conditions of electron cyclotron resonance (ECR). The refraction coefficient of the film was
estimated and the rate of the film removal was obtained. |
| format |
Article |
| author |
Konovalov, V.G. Makhov, M.N. Ryzhkov, I.V. Shapoval, A.N. Shtan’, A.F. Skorik, O.A. Solodovchenko, S.I. Timoshenko, A.I. Voitsenya, V.S. |
| author_facet |
Konovalov, V.G. Makhov, M.N. Ryzhkov, I.V. Shapoval, A.N. Shtan’, A.F. Skorik, O.A. Solodovchenko, S.I. Timoshenko, A.I. Voitsenya, V.S. |
| author_sort |
Konovalov, V.G. |
| title |
Simulating study of plasmachemical erosion of a-C:H films in a ECR discharge plasma |
| title_short |
Simulating study of plasmachemical erosion of a-C:H films in a ECR discharge plasma |
| title_full |
Simulating study of plasmachemical erosion of a-C:H films in a ECR discharge plasma |
| title_fullStr |
Simulating study of plasmachemical erosion of a-C:H films in a ECR discharge plasma |
| title_full_unstemmed |
Simulating study of plasmachemical erosion of a-C:H films in a ECR discharge plasma |
| title_sort |
simulating study of plasmachemical erosion of a-c:h films in a ecr discharge plasma |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2011 |
| topic_facet |
Низкотемпературная плазма и плазменные технологии |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/90955 |
| citation_txt |
Simulating study of plasmachemical erosion of a-C:H films in a ECR discharge plasma / V.G. Konovalov, M.N. Makhov, I.V. Ryzhkov, A.N. Shapoval, A.F. Shtan’, O.A. Skorik, S.I. Solodovchenko, A.I. Timoshenko, V.S. Voitsenya // Вопросы атомной науки и техники. — 2011. — № 1. — С. 146-148. — Бібліогр.: 5 назв. — англ. |
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Вопросы атомной науки и техники |
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| fulltext |
146 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2011. 1.
Series: Plasma Physics (17), p. 146-148.
SIMULATING STUDY OF PLASMACHEMICAL EROSION
OF FILMS IN A ECR DISCHARGE PLASMA
V.G. Konovalov, M.N. Makhov, I.V. Ryzhkov, A.N. Shapoval, A.F. Shtan’, O.A. Skorik,
S.I. Solodovchenko, A.I. Timoshenko, V.S. Voitsenya
Institute of Plasma Physics, NSC “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine
E-mail: konovalov@ipp.kharkov.ua
The dynamics of interference figure of the reflection spectrum for stainless steel and copper mirrors with specially
deposited carbon-containing film ( -C:H) were studied when the film was gradually eroded under impact of a deuterium
plasma produced in conditions of electron cyclotron resonance (ECR). The refraction coefficient of the film was
estimated and the rate of the film removal was obtained.
PACS: 52.50.Sw
1.INTRODUCTION
For decreasing the influx of impurities into the plasma
confinement volume, the wall conditioning procedures are
in practice at every fusion device, with the use of different
kind stationary or pulse discharges in hydrogen: glow,
Ohmic, radio frequency (RF) in conditions of electron
cyclotron resonance (ECR). The control for the state of
wall surfaces is realized by means of special collectors,
the surface of which is time to time analyzed with some
standard methods. For providing surface analyses, the
collectors are taken out from the vacuum vessel.
Recently it was suggested to control the quality of
cleaning the walls of vacuum chamber of the stellarator
type fusion device Uragan-2M by means of mirrors
installed into the vacuum chamber. The idea of this
suggestion is as follows. Before mirror installation, the
carbon-containing film (i.e., a-C:H film) is deposited on
its surface, and the in situ measurements of reflectance
(e.g., at the He-Ne laser wavelength) during the
conditioning procedure can give possibility to make
conclusion about the cleaning efficiency. Or such
measurements can be provided ex situ with taking
samples out through a lock chamber. For evaluation of the
prospect of this method, the modeling experiments with
the use of ECR discharge in deuterium were provided.
2. EXPERIMENTAL DETAILS
The main procedures, when providing simulation
experiments, were as follows:
i) deposition on metallic mirror of a carbon-containing
film thick enough for obtaining an interference figure in
reflection spectrum ( =0.3…0.6 m); ii) step-by-step
sputtering of deposited film in plasma of ECR discharge;
iii) ex situ measurements of reflectance; iv) monitoring of
dynamics of interference figure in the course of gradual
film erosion, with an aim to obtain an estimation of the
film erosion rate.
Films were deposited in the device described in [1].
The stainless steel (SS) samples (carbide-forming
material) and Cu samples (metal that does not form stable
carbides [2]) were coated with a-C:H film in a non-self-
maintained discharge in a propane-butane mixture at
pressure 3×10-3 Torr. The mirror specimens (22×22 mm2)
were immersed into a flow of ions ejected from the
hollow anode. On a check test piece the step of deposited
material was formed which was used for measuring the
deposited film thickness. The analysis showed that the
film is amorphous; its thickness was measured by means
of interference microscope (M I I-4). The error in the
range of thickness of 0.3…0.6 µm is within 10%. Besides,
the samples were weighted (with accuracy ± 50 µg)
before and after film deposition for additional control of
the film sputtering rate.
An erosion of the deposited film down to its full
disappearance was provided in the DSM-2 stand [3],
which is a simple double-mirror magnetic trap with a SS
vacuum chamber pumped by a turbomolecular pump up
to ~2x10-6 Torr. Working gas deuterium was continuously
flowing through the chamber at pressure (2…4)×10-4 Torr.
ECR plasma was produced by UHF power 200 W at
frequency 2.37 GHz. The electron temperature did not
exceed 5 eV, and the plasma density in the place of mirror
location was ~5×109 m -3. No any voltage was applied to
the mirror holder thus the ion energy was <15 eV. The
gas composition was monitored before and during
discharge. After every exposure in the stand, the sample
was drawn out for weighing and measuring the
reflectance.
For measurements of reflectance the scheme suggested
by S.Tolansky [4] was used; it includes two stabilized
light sources for UV and Visible ranges, the
monochromator DR-2 and a couple of gage units with
photomultipliers. The reflectance of mirror samples, R( ),
at normal incidence was measured in the range
220…650 nm with the step 10 nm along the wavelength
spectrum. The issued repeatability of measurements along
a uniform surface was 1…1.5 %. The size of the
irradiated spot Ø=2 mm (S=3 mm2). Because of possible
non-uniformity of the deposited film, very important is to
fix the spot, what was assured by a special pattern. The
processing of interferograms was provided with the use of
a well-known relation 2d·(n2-sin2 )0.5 – 0.5 = m , where
d is a geometrical depth, n - refractive index, - angle of
incidence, m = 0, 1, 2. During step-by-step sputtering, the
number of interference periods for a fixed wavelength
was tracked down to the full disappearance of the
interference figure.
mailto:konovalov@ipp.kharkov.ua
147
3. RESULTS
To work-out the method, the SS and Cu mirror
samples were deposited with films of
approximately equal thickness. In Fig. 1, a and Fig. 1, c
are shown the initial reflectance values and the ones just
after deposition of the film of ~0.5 m in thickness with
typical interference figures. The film density was
estimated as 2.06 g/cm3. After plasma exposing during
185 min, the interference figures disappeared (Fig. 1, b
and 1, d) and R( ) became to be similar to the initial ones
but at much lower level (open squares). With that, only
~10% of the initial film thickness remained on specimens
according to weight loss measurements. Taking into
account the accuracy of weight loss measurements, one
can say that practically the whole film was removed. The
mean removal rate was estimated to be 2.9 nm/min.
However, the optical data indicate that a quite strongly
absorbing film does still exist. For the full removal of the
rest film the ion energy has to be increased. In the case of
SS specimen the 50-minute exposure to ions with
accelerating voltage -20 eV results in practically full
restoration of reflectance (Fig. 1, b, triangles) but for the
Cu specimen the rate of reflectance restoration was much
slower, as Fig. 1, d demonstrates (triangles). Note, that Cu
mirror specimens were chosen for this experiment
because copper does not form stable carbides.
Fig. 1. ), c) - initial stage of R( ) for SS and Cu
samples; b), d) – pre-final stage (disappearance of the
interference figure with total time equals 185 min (6 time-
steps), U-biasing of mirror) and the final stage, i.e.,
return to the initial R( ) stage of the substrate
After sample experiments the optimal characteristics of
films and the time for step-by-step film erosion
were chosen. On the specimen SS #3 the film thickness
was ~0.35 m. The film density was as above, 2.06 g/cm3.
On the assumption of the full visible disappearance of
the interference figure and taking into account periodicity
for every chosen wavelength 360, 440 and 540 nm the
refraction coefficients of the deposited films were
estimated: n 1.3 (accordingly: 1.3 -1.34 -1.29).
Similar processing of the interferograms for samples
Cu #2 and SS #2 with initial film thickness 0.25 m gave
for wavelengths 340 , 420 and 550 nm, correspondingly,
n = 1.43-1.45-1.43 and n = 1.47-1.47-1.47, and the rate of
erosion 3.1-3.5 nm/min. These results were obtained by
processing all interference figures for every specimen
curves similar to those shown in Fig. 2.
According to [5], such n values indicate that the
hydrogen content in the film is 40-60 %, i.e., the film is
so called ‘soft film’.
At the same time, if additional exposure time for R( )
restoration to the initial value (SS #3, Cu #2, SS #2) is
taken into account, then applying similar procedure of
data processing, one can obtain for the same wavelengths
n 1.63-1.68. Such a rise of n can be connected with
transformation (at the latest phase of sputtering) of the
film into a ‘hard film’ with lower hydrogen
content, which has lower rate of erosion.
Fig. 2. Interchange of interference orders for = 340,
420 and 550 nm depending on the time of the film etching.
(The total exposure time for the full disappearance of the
interference figure is 70…80 min)
The rate of erosion of the film with initial thickness
0.35 and 0.25 m was found ~3.3 nm/min on average.
Taking into account the accuracy of weighing, the
accuracy of film thickness measurement, the moment of
disappearance of the interference figure, and peculiarities
of the film deposition, one can consider that the rates of
film removal, 2.9 (for 0.5 m) and 3.3 nm/min for thinner
films, are in a good agreement. Note, that during cleaning
the mirrors in ECR plasma, the traces of water vapors
(H2 , D2 , DO) are present in discharge. This can
intensify the effect of cleaning in comparison with pure
148
deuterium plasma. However, similar situation will be
probably met in the U-2M device during wall
conditioning.
4. CONCLUSIONS
The experiments were provided with SS and Cu mirror
specimens aiming a quantitative evaluation of the
efficiency for the vacuum chamber walls to be cleaned
from hydrocarbons by means of ECR discharge in
hydrogen. The films were deposited on SS mirrors,
i.e. made from a carbide-forming material and on Cu
mirrors – from material which does not form a stable
carbides.
1. The dynamics of the shift of interference picture in the
spectral reflectance was studied when the artificially
deposited hydrocarbon film was gradually eroded from
SS and Cu mirror specimens by plasmachemical
treatment in deuterium plasma.
2. The rate of film erosion was measured.
3. The refraction coefficient of the film in the range
340…550 nm was estimated.
4. It was found that after pronounced disappearance of the
interference picture the rest of film can be taken off only
with negative biasing of the specimen holder in the range
20…100 V for both SS and Cu specimens.
This fact indicates that:
(i) taking into account the behavior of R( ) for SS and Cu
samples at a completion phase of cleaning, the rest film is
probably not the result of carbides formation, (ii) for
effective cleaning of the vacuum chamber walls in U-2M
it will be necessary to combine the low-ion-energy plasma
(ECR plasma) with high-ion-energy plasma (e.g., glow or
RF discharge plasma) during wall conditioning
procedures.
REFERENCES
1. A.I. Timoshenko, et al. Plasma characteristics of two-
step vacuum-arc discharge and its application for a
coating deposition // Problems of Atomic Science and
Technology. Series “Plasma Physics” (13). 2007, N 1,
p. 179-181.
2. Physical-chemical properties of elements / Reference
book edited by G.V. Samsonov. Kiev: ”Naukova
dumka”, 1965 (in Russian).
3. A.F. Bardamid, et al. Ion energy distribution effects on
degradation of optical properties of ion-bombardet
copper mirrors // Surface & Coatings Technology.
1998, v. 103-104, p.365-369.
4. S. Tolansky. High Resolution Spectroscopy. Moscow,
1955, p. 380 (in Russian).
5. B.M. Sinel’nikov, et al. Optical properties of
amorphous hydrogenated of carbon films deposited
with HF discharge // Vestnik Sev. Kav. GTU. 2006, #2
(b) ISBN 5-9296-0329-4 (in Russian).
Article received 25.10.10
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