Сontrolling parameters determining technological properties of a helicon discharge system
In experiments on two helicon sources driven by a planar antenna, it is shown that the plasma density in the drift chamber and the energies and density of the ion flux onto the substrate holder can be effectively controlled by changing the local magnetic field and the holder potential.
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| Дата: | 2013 |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2013
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| Цитувати: | Сontrolling parameters determining technological properties of a helicon discharge system / V.F. Semenyuk, V.F. Virko, I.V. Korotash, L.S. Osipov, D.Yu. Polotsky, E.M. Rudenko,V.M. Slobodyan, K.P. Shamrai // Вопросы атомной науки и техники. — 2013. — № 4. — С. 179-182. — Бібліогр.: 10 назв. — англ. |
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irk-123456789-1121832017-01-23T22:30:51Z Сontrolling parameters determining technological properties of a helicon discharge system Semenyuk, V.F. Virko, V.F. Korotash, I.V. Osipov, L.S. Polotsky, D.Yu. Rudenko, E.M. Slobodyan, V.M. Shamrai, K.P. Плазменно-пучковый разряд, газовый разряд и плазмохимия In experiments on two helicon sources driven by a planar antenna, it is shown that the plasma density in the drift chamber and the energies and density of the ion flux onto the substrate holder can be effectively controlled by changing the local magnetic field and the holder potential. Експериментами на двох геліконних джерелах з плоскою збуджуючою антеною показано, что густиною плазми в дрейфовій камері та енергіями і густиною іонного потоку на підкладинкотримач можна ефективно керувати зміненням локального магнітного поля і потенциалу тримача. Экспериментами на двух геликонных источниках с плоской возбуждающей антенной показано, что плотностью плазмы в дрейфовой камере и энергиями и плотностью ионного потока на подложкодержатель можно эффективно управлять изменением локального магнитного поля и потенциала держателя. 2013 Article Сontrolling parameters determining technological properties of a helicon discharge system / V.F. Semenyuk, V.F. Virko, I.V. Korotash, L.S. Osipov, D.Yu. Polotsky, E.M. Rudenko,V.M. Slobodyan, K.P. Shamrai // Вопросы атомной науки и техники. — 2013. — № 4. — С. 179-182. — Бібліогр.: 10 назв. — англ. 1562-6016 PACS: 52.50.Dg; 52.50.Qt. http://dspace.nbuv.gov.ua/handle/123456789/112183 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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DSpace DC |
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English |
| topic |
Плазменно-пучковый разряд, газовый разряд и плазмохимия Плазменно-пучковый разряд, газовый разряд и плазмохимия |
| spellingShingle |
Плазменно-пучковый разряд, газовый разряд и плазмохимия Плазменно-пучковый разряд, газовый разряд и плазмохимия Semenyuk, V.F. Virko, V.F. Korotash, I.V. Osipov, L.S. Polotsky, D.Yu. Rudenko, E.M. Slobodyan, V.M. Shamrai, K.P. Сontrolling parameters determining technological properties of a helicon discharge system Вопросы атомной науки и техники |
| description |
In experiments on two helicon sources driven by a planar antenna, it is shown that the plasma density in the drift chamber and the energies and density of the ion flux onto the substrate holder can be effectively controlled by changing the local magnetic field and the holder potential. |
| format |
Article |
| author |
Semenyuk, V.F. Virko, V.F. Korotash, I.V. Osipov, L.S. Polotsky, D.Yu. Rudenko, E.M. Slobodyan, V.M. Shamrai, K.P. |
| author_facet |
Semenyuk, V.F. Virko, V.F. Korotash, I.V. Osipov, L.S. Polotsky, D.Yu. Rudenko, E.M. Slobodyan, V.M. Shamrai, K.P. |
| author_sort |
Semenyuk, V.F. |
| title |
Сontrolling parameters determining technological properties of a helicon discharge system |
| title_short |
Сontrolling parameters determining technological properties of a helicon discharge system |
| title_full |
Сontrolling parameters determining technological properties of a helicon discharge system |
| title_fullStr |
Сontrolling parameters determining technological properties of a helicon discharge system |
| title_full_unstemmed |
Сontrolling parameters determining technological properties of a helicon discharge system |
| title_sort |
сontrolling parameters determining technological properties of a helicon discharge system |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2013 |
| topic_facet |
Плазменно-пучковый разряд, газовый разряд и плазмохимия |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/112183 |
| citation_txt |
Сontrolling parameters determining technological properties of a helicon discharge system / V.F. Semenyuk, V.F. Virko, I.V. Korotash, L.S. Osipov, D.Yu. Polotsky, E.M. Rudenko,V.M. Slobodyan, K.P. Shamrai // Вопросы атомной науки и техники. — 2013. — № 4. — С. 179-182. — Бібліогр.: 10 назв. — англ. |
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Вопросы атомной науки и техники |
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ISSN 1562-6016. ВАНТ. 2013. №4(86) 179
CONTROLLING PARAMETERS DETERMINING TECHNOLOGICAL
PROPERTIES OF A HELICON DISCHARGE SYSTEM
V.F. Semenyuk1, V.F. Virko2, I.V. Korotash1, L.S. Osipov1, D.Yu. Polotsky1, E.M. Rudenko1,
V.M. Slobodyan2, K.P. Shamrai2
1G.V. Kurdyumov Institute for Metal Physics, NASU, Kiev, Ukraine;
2Institute for Nuclear Research, NASU, Kiev, Ukraine
E-mail: bees@voliacable.com
In experiments on two helicon sources driven by a planar antenna, it is shown that the plasma density in the drift
chamber and the energies and density of the ion flux onto the substrate holder can be effectively controlled by
changing the local magnetic field and the holder potential.
PACS: 52.50.Dg; 52.50.Qt.
INTRODUCTION
Helicon sources, which are based on a magnetic
field assisted rf inductive discharge, produce dense
plasmas and, for this reason, can serve as efficient
plasma tools for various technologies. Except for mate-
rials processing [1], recent helicon source applications
include space propulsion in both high and low thrust
schemes (e.g., [2 - 4]) and nanomaterials production
(e.g., [5, 6]). These sources can be used either alone, or
as units of hybrid discharge systems for performing spe-
cific technological operations, e.g., in thin film forma-
tion using the PECVD process [7].
For technological purposes, a compact design of the
source with a planar driving antenna located behind a
flat dielectric window seems to be preferable (e.g., [8]).
Our previous experiments on the research [8] and tech-
nological [9] sources of this type have shown that their
characteristics depend considerably on both the strength
and configuration of the magnetic field. This factor, in
combination with other discharge control methods, can
be used for developing the flexible technological tools.
In this paper, we study how the plasma flux parameters
can be controlled under combined action of various ex-
ternal factors, such as the magnetic configuration, bot-
tom electrode (substrate holder) potential, rf power, and
working gas pressure. To draw some universal regulari-
ties, we performed the experiments using two helicon
sources mentioned above.
EXPERIMENTS ON THE RESEARCH
SOURCE
The discharge chamber of the research source
(Fig. 1) is a 20-cm-diam, 30-cm-long grounded metal
cylinder closed on top by a quartz window. A 11.5-cm-
diam double-turn planar antenna supplied from an rf
generator of frequency 13.56 MHz and up to 2 kW
power is located above the window. The chamber is
confined from below by a 15-cm-diam metal electrode
(substrate holder) that was either at a floating potential,
or negatively biased down to −100 V. The magnetic
field of various configurations and maximum strength
up to 250 G was produced by three solenoids with inde-
pendent power supplies. The working gas was argon at
pressures 1…10 mTorr. The parameters of plasma and
ion fluxes were measured by two movable probes in-
serted into the chamber in its upper (below the antenna)
and lower (above the bottom electrode) parts, and by a
five-electrode ion energy analyzer with a 12-mm-diam
case and a 6-mm-diam entrance aperture. The analyzers
resolution was about 3 eV.
Fig. 1. A scheme of the research source
It was found that, over the whole examined range,
the bottom electrode floating potential possessed nega-
tive values, Ufloat = −5 to −20 V, and decreased with
magnetic field increase. Such a behavior is in qualitative
agreement with that of a local floating potential in the
discharge volume, as was formerly ascertain from the
probe measurements [10], and is apparently determined
by presence in plasma volume of a population of ener-
getic non-maxwellian electrons detected previously us-
ing the probe with a low-frequency bias potential modu-
lation [10].
Measured with the lower probe (see Fig. 1) depend-
ences of ion saturation current on the magnetic field,
which was varied by proportional current changing in
all the solenoids, is shown in Fig. 2, under conditions
when the bottom electrode was either grounded of float-
ing. As seen, the electrode grounding decreases the
plasma density, especially in the range of lower mag-
netic fields. Positive electrode biasing resulted in the
discharge disruption. The discontinuous dependences in
Fig. 2 evidence that the way to control plasma parame-
ters by changing the magnetic field over the whole dis-
charge volume is problematic for the technological
processes.
ISSN 1562-6016. ВАНТ. 2013. №4(86) 180
Fig. 2. Dependences of ion current onto the probe
on magnetic field, at floating (solid curve) and ground
(broken curve) substrate holder potentials
Fig. 3. Volt-ampere characteristics of the substrate
holder, at various magnetic fields
For controlling the ion flux energy onto the elec-
trode (substrate holder), the range of its negative biases
is most interesting. Fig. 3 shows the volt-ampere charac-
teristics of the electrode with a bias in the range from
the floating potentials down to −120 V, at various mag-
netic fields related to different discharge regimes (see
Fig. 2). As seen, the ion current onto the electrode in-
creases with decreasing bias potential and then saturates
at a level that depends non-monotonically on the mag-
netic field. In most intense discharge regimes, the ion
current onto the electrode reaches 3 A.
Fig. 4. Radial profiles of (a) ion current onto the probe
and (b) probe floating potential
Negative electrode biasing gives rise to substantial
plasma density increase (Fig. 4,a), especially around the
axis, where a floating potential sags (Fig. 4,b). As long
as a population of energetic electrons exists just in this
region, it is natural to interpret the density increase as a
result of that the negative potential reflects the energetic
electrons back to the discharge volume thus increasing
the ionization efficiency.
EXPERIMENTS ON THE
TECHNOLOGICAL SOURCE
The technological device (Fig. 5) consists of a heli-
con source discharge chamber, 20 cm in diameter and
length, and an adjoint drift chamber, 35 cm in diameter
and 25 cm long. The discharge in argon at a pressure
7…8 mTorr was excited by a 11-cm-diam single-turn
planar antenna fed from an rf generator of frequency
13.56 MHz and up to 1 kW power. The magnetic field
is created by a set of solenoids. A solenoid surrounding
the discharge chamber generates the main field that pro-
vides the helicon discharge operation in the required
mode. One more solenoid with independent power feed
(not shown in Fig. 5) is located below the substrate
holder and generates the control field which extends
only into the drift chamber and has no substantial influ-
ence on the main field in the discharge chamber. In the
lower part of the drift chamber, there is a subdivided
electrode (substrate holder) of 25-cm total diameter.
Plasma parameters were measured by two cylindrical
probes, the upper (15 cm below the antenna) and the
lower (5 cm above the substrate holder) ones.
Fig. 5. A scheme of the technological source
Fig. 6 shows the radial profiles of the ion saturation
current onto the upper probe. Curves 1 and 2 were taken
with no control magnetic field and relate, respectively,
to the rf power of 300 and 600 W. Curve 3 was also
taken with 600 W power, but with control field turned
on. It is seen from this figure that the plasma density in
the discharge chamber is approximately proportional to
the rf power, and that the control magnetic field has a
minor influence upon the conditions in the discharge
chamber.
a
b
ISSN 1562-6016. ВАНТ. 2013. №4(86) 181
Fig. 6. Radial profiles of ion current onto the upper
probe, at rf power of 300W (curve 1) and 600 W
(curves 2 and 3)
Fig. 7. Radial profiles of ion current onto the upper
(curve 1) and lower (curves 2 and 3) probes, at rf power
of 500W
Fig. 8. Radial profiles of the probe floating potential
with (curve 1) and without (curve 2) the control
magnetic field
Fig. 7 shows the radial profiles of the ion saturation
current onto the lower probe measured without and with
the control magnetic field (curves 2 and 3, respectively),
at the rf power of 500 W. The profile measured by the
upper probe with no control field is also shown there
(curve 1). As seen from comparison of curves 1 and 2,
the plasma density drops an order of magnitude to the
drift chamber bottom, apparently, as a result of strong
plasma flux flaring in a divergent magnetic field of the
upper solenoid. With the control field turned on, the
plasma density rises by 2.5 times near the axis, but its
profile becomes nonuniform (cf. curves 2 and 3). This
effect is thought to result from improved plasma trans-
portation from the discharge chamber to the substrate
holder and, probably, from spreading of the helicon dis-
charge into the drift chamber.
With the pressure increase, the density drop at the
substrate holder increases, whereas the radial density
profiles smooth over.
Fig. 9. Retarding characteristics of the energy analyzer,
at various Ar pressures. Rf power 450 W, main
and control coils currents Im = 1.5 A and Ic = 1 A
In the presence of the control field, the density in-
crease in the central part of the drift chamber is accom-
panied by a considerable decrease there of the floating
probe potential (Fig. 8). This effect arises, apparently,
due to increase in this region of the number of energetic
electrons that were detected earlier in experiments on
the research source [8] and are thought to exist in the
technological source as well.
An important technological characteristic of the
source, along with the plasma density, is the ion flux en-
ergy. In the helicon sources, it is possible to combine high
density plasma production with independent ion energy
control, which makes these sources well suitable for vari-
ous applications. Fig. 9 shows retarding characteristics of
the ion energy analyzer, I(U), for various argon pressures,
at a fixed input rf power of 450 W. As seen, the plasma
potential, which is determined from maximum of dI/dU,
changes only slightly in the pressure range. In general,
the helicon source operating range was found to extend
up to 40…50 mTorr; the ion flux density drops drasti-
cally at higher pressures. An optimal pressure range, as
seen from Fig. 9, lies within 1…5 mTorr.
Fig. 10. The same as in Fig. 9, but at various main coil
currents. Rf power 525 W, Ar pressure 5 mTorr
and Ic = 1 A
Fig. 10 shows analyzer characteristics measured at
argon pressure of 5 mTorr and input rf power of 525 W,
at various currents in the main field solenoid surround-
ing the discharge chamber. (Its magnetic field is evalu-
ated as 15 G/A). With the main field increase, the dis-
charge grows in intensity and extends further from the
antenna, which results in the analyzer current increase.
The retardation curves related to lower pressures in
Fig. 10 evidence the presence of a fast ion “tail” extend-
ing up to 30…35 eV.
ISSN 1562-6016. ВАНТ. 2013. №4(86) 182
Fig. 11. The same as in Fig. 9, but at various control
coil currents. Rf power 525 W, Ar pressure 5 mTorr
and Im = 1.5 A
The effect of the control magnetic field on the ion
current is shown in Fig. 11 taken at various control coil
currents (the magnetic field is evaluated as 25 G/A) and
the same other parameters. The data comparison in
Figs. 10 and 11 evidences that the increase of the con-
trol field gives rise to ion current increase whereas the
ion flux energy distribution changes only slightly. When
the plasma density increases with the rf power, the con-
tent of energetic ions in the flux grows.
CONCLUSIONS
In experiments on two helicon sources driven by a
planar antenna, it was found that the magnetic system,
which is placed nearby the substrate holder and varies
the magnetic field only locally, can effectively control
the magnitude and profile of the ion current onto the
substrate holder whereas the ion energy spectrum
changes only slightly. At that, the conditions in the dis-
charge chamber do not change considerably which per-
mits to eliminate the discharge regimes jumps that arise
when the magnetic field changes globally, on the scale
of the whole system. By changing the substrate holder
potential, one can not only control the ion flux energies
but also control the ion flux current through changing
the plasma density around the substrate holder. The lat-
ter effect is thought to arise from energetic electrons
whose reflection back to the discharge volume increases
the ionization efficiency.
This work was performed by the joint project
№ 5713 of the National Academy of Sciences of
Ukraine and the Science and Technology Center in
Ukraine.
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Article received 15.04.2013.
УПРАВЛЕНИЕ ПАРАМЕТРАМИ, ОПРЕДЕЛЯЮЩИМИ ТЕХНОЛОГИЧЕСКИЕ СВОЙСТВА
ГЕЛИКОННОЙ РАЗРЯДНОЙ СИСТЕМЫ
В.Ф. Семенюк, В.Ф. Вирко, И.В. Короташ, Л.С. Осипов, Д.Ю. Полоцкий, Э.М. Руденко, В.М. Слободян,
К.П. Шамрай
Экспериментами на двух геликонных источниках с плоской возбуждающей антенной показано, что
плотностью плазмы в дрейфовой камере и энергиями и плотностью ионного потока на подложкодержатель
можно эффективно управлять изменением локального магнитного поля и потенциала держателя.
КЕРУВАННЯ ПАРАМЕТРАМИ, ЩО ВИЗНАЧАЮТЬ ТЕХНОЛОГІЧНІ ВЛАСТИВОСТІ
ГЕЛИКОННОЇ РОЗРЯДНОЇ СИСТЕМИ
В.Ф. Семенюк, В.Ф. Вірко, І.В. Короташ, Л.С. Осипов, Д.Ю. Полоцький, Е.М. Руденко, В.М. Слободян,
К.П. Шамрай
Експериментами на двох геліконних джерелах з плоскою збуджуючою антеною показано, что густиною
плазми в дрейфовій камері та енергіями і густиною іонного потоку на підкладинкотримач можна ефективно
керувати зміненням локального магнітного поля і потенциалу тримача.
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