Modified helicon discharge excited by a linear inductive antenna
A new modification of the helicon discharge capable of producing linearly uniform plasma is investigated. The discharge is excited in magnetic field by an inductive antenna consisting of two parallel linear conductors with antiphase RF currents, similar to a two-wire transmission line. The wave natu...
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України
2014
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| Цитувати: | Modified helicon discharge excited by a linear inductive antenna / A.G. Borisenko, M.A. Beloshenko, V.F. Virko, Yu.V. Virko, V.M. Slobodyan // Вопросы атомной науки и техники. — 2014. — № 6. — С. 153-156. — Бібліогр.: 4 назв. — англ. |
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irk-123456789-819512015-05-23T03:01:33Z Modified helicon discharge excited by a linear inductive antenna Borisenko, A.G. Beloshenko, M.A. Virko, V.F. Virko, Yu.V. Slobodyan, V.M. Низкотемпературная плазма и плазменные технологии A new modification of the helicon discharge capable of producing linearly uniform plasma is investigated. The discharge is excited in magnetic field by an inductive antenna consisting of two parallel linear conductors with antiphase RF currents, similar to a two-wire transmission line. The wave nature of the discharge is demonstrated. It is shown that there exist some discharge conditions in which plasma density is homogenous along a significant part of the antenna length. A convenient for realization discharge system with the linear antenna immersed into plasma is proposed. Provided further improvement this discharge may be used for uniform plasma processing of large surfaces. Исследована новая разновидность геликонного разряда, способного генерировать линейно однородную плазму. Разряд возбуждается в магнитном поле индукционной антенной, состоящей из двух параллельных проводников с противофазными ВЧ-токами, подобно двухпроводной передающей линии. Продемонстрирована волновая природа разряда. Показано, что существуют некоторые разрядные условия, в которых плотность плазмы однородна на значительной части длины антенны. Предложена удобная в реализации разрядная система с линейной антенной, погружённой в плазму. При дальнейшем усовершенствовании такой разряд может быть использован для однородной плазменной обработки больших поверхностей. Досліджено новий різновид геліконного розряду, здатного утворювати лінійно однорідну плазму. Розряд збуджується в магнітному полі індукційною антеною, що складається з двох паралельних провідників з протифазними ВЧ-струмами, подібно до двопровідної передавальної лінії. Продемонстровано хвильову природу розряду. Показано, що існують деякі розрядні умови, в яких густина плазми є однорідною на значній частині довжини антени. Запропонована зручна в реалізації розрядна система з лінійною антеною, зануреною в плазму. При подальшому удосконаленні такий розряд може бути використано для однорідної плазмової обробки великих поверхонь. 2014 Article Modified helicon discharge excited by a linear inductive antenna / A.G. Borisenko, M.A. Beloshenko, V.F. Virko, Yu.V. Virko, V.M. Slobodyan // Вопросы атомной науки и техники. — 2014. — № 6. — С. 153-156. — Бібліогр.: 4 назв. — англ. 1562-6016 PACS: 52.50.Qt, 52.75.Di http://dspace.nbuv.gov.ua/handle/123456789/81951 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
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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 Borisenko, A.G. Beloshenko, M.A. Virko, V.F. Virko, Yu.V. Slobodyan, V.M. Modified helicon discharge excited by a linear inductive antenna Вопросы атомной науки и техники |
| description |
A new modification of the helicon discharge capable of producing linearly uniform plasma is investigated. The discharge is excited in magnetic field by an inductive antenna consisting of two parallel linear conductors with antiphase RF currents, similar to a two-wire transmission line. The wave nature of the discharge is demonstrated. It is shown that there exist some discharge conditions in which plasma density is homogenous along a significant part of the antenna length. A convenient for realization discharge system with the linear antenna immersed into plasma is proposed. Provided further improvement this discharge may be used for uniform plasma processing of large surfaces. |
| format |
Article |
| author |
Borisenko, A.G. Beloshenko, M.A. Virko, V.F. Virko, Yu.V. Slobodyan, V.M. |
| author_facet |
Borisenko, A.G. Beloshenko, M.A. Virko, V.F. Virko, Yu.V. Slobodyan, V.M. |
| author_sort |
Borisenko, A.G. |
| title |
Modified helicon discharge excited by a linear inductive antenna |
| title_short |
Modified helicon discharge excited by a linear inductive antenna |
| title_full |
Modified helicon discharge excited by a linear inductive antenna |
| title_fullStr |
Modified helicon discharge excited by a linear inductive antenna |
| title_full_unstemmed |
Modified helicon discharge excited by a linear inductive antenna |
| title_sort |
modified helicon discharge excited by a linear inductive antenna |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2014 |
| topic_facet |
Низкотемпературная плазма и плазменные технологии |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/81951 |
| citation_txt |
Modified helicon discharge excited by a linear inductive antenna / A.G. Borisenko, M.A. Beloshenko, V.F. Virko, Yu.V. Virko, V.M. Slobodyan // Вопросы атомной науки и техники. — 2014. — № 6. — С. 153-156. — Бібліогр.: 4 назв. — англ. |
| series |
Вопросы атомной науки и техники |
| work_keys_str_mv |
AT borisenkoag modifiedhelicondischargeexcitedbyalinearinductiveantenna AT beloshenkoma modifiedhelicondischargeexcitedbyalinearinductiveantenna AT virkovf modifiedhelicondischargeexcitedbyalinearinductiveantenna AT virkoyuv modifiedhelicondischargeexcitedbyalinearinductiveantenna AT slobodyanvm modifiedhelicondischargeexcitedbyalinearinductiveantenna |
| first_indexed |
2025-07-06T07:44:26Z |
| last_indexed |
2025-07-06T07:44:26Z |
| _version_ |
1836882721243136000 |
| fulltext |
ISSN 1562-6016. ВАНТ. 2014. №6(94)
PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2014, №6. Series: Plasma Physics (20), p. 153-156. 153
MODIFIED HELICON DISCHARGE EXCITED BY A LINEAR
INDUCTIVE ANTENNA
A.G. Borisenko, M.A. Beloshenko, V.F. Virko, Yu.V. Virko, V.M. Slobodyan
Institute for Nuclear Research NAS of Ukraine, Kyiv, Ukraine
E-mail: slava.slobodyan@gmail.com
A new modification of the helicon discharge capable of producing linearly uniform plasma is investigated.
The discharge is excited in magnetic field by an inductive antenna consisting of two parallel linear conductors
with antiphase RF currents, similar to a two-wire transmission line. The wave nature of the discharge is
demonstrated. It is shown that there exist some discharge conditions in which plasma density is homogenous
along a significant part of the antenna length. A convenient for realization discharge system with the linear
antenna immersed into plasma is proposed. Provided further improvement this discharge may be used for
uniform plasma processing of large surfaces.
PACS: 52.50.Qt, 52.75.Di
INTRODUCTION
Further development of plasma technologies
demands uniform processing of still larger area
surfaces (as displays, solar batteries, light panels and
so on). The use for these purposes of well known
transformer coupled plasmas (TCP – discharges) [1]
is limited for unacceptable increase thickness of the
quartz window, capable to stand against the
atmospheric pressure. A possible solution is to create
plasma which is uniform along a single coordinate.
Then, moving the surface in the transversal direction
one can uniformly treat a sufficiently large area.
To produce linearly homogeneous plasma the
application of distributed sources was proposed. Since
the helicon discharge is one of the most efficient
technological plasma sources, F.Chen et al [2] in
USA developed a linear array of multiple small
helicon discharges. The discharges were situated in
such a way, that their density profiles, overlapping,
gave approximately uniform plasma along this line.
But the full solution of the problem was not yet
achieved.
Another approach consists in such modification of the
discharge that it itself can produce the linearly
uniform plasma. For this aim the two-turn flat circular
antenna (so called “planar” antenna), which in the
magnetic field is known to excite the azimuthally
symmetric m = 0 mode of helicon waves, was
deformed in a long, highly stretched narrow loop.
Therefore, the modified helicon discharge was excited
in the magnetic field by a linear inductive antenna,
consisted of two parallel conductors with counter-
streaming RF currents, similar to a two-wire
transmission line. The questions are whether it is
possible to excite the discharge using such antenna
and to obtain sufficient plasma uniformity along it.
1. EXPERIMENTAL SETUP 1
Preliminary experiments were performed in a
quartz discharge chamber, of 14 cm in diameter and
40 cm long (Fig. 1). On the left end the quartz tube was
closed with a metal flange, the opposite end was
attached to a metal chamber of the same diameter,
through which the system was pumped out. On the upper
side wall along the quartz cylinder the linear antenna
30 cm long and 3 cm in width was placed. Transversal to
the axis magnetic field was created by a rectangular
electromagnet coil placed underneath the quartz chamber,
close to it, or by a flat set of permanent magnets. The
schematic drought of the device is shown in Fig.1. The
magnetic field was divergent in vertical direction and in
case of the electromagnet use the field decreased from
0.3 mT/A in the coil region to 0.1 mT/A near the antenna.
Inside the chamber, along its bottom a grounded stainless
strip of 8 cm in width was placed which imitated action
of the wafer-holder in a technological device (not shown
see in Fig. 1).
Fig. 1. Schematic diagram of experimental device with
linear antenna upon quartz discharge chamber.
1 – quartz chamber 40 cm long and 14 cm in diameter;
2 − rectangular magnetic coil; 3 – two-turn linear
antenna 30 cm long and 3 cm in width; 4 – movable flat
Langmuir probe 12 cm below the antenna
Trough a conventional matching circuit the antenna
was connected to the RF generator of frequency
13.56 MHz and output power up to 1 kW. Experiments
were carried out in Argon gas at a pressure 0.65 Pa.
mailto:-mail: slava.slobodyan@gmail.com
154 ISSN 1562-6016. ВАНТ. 2014. №6(94)
A flat Langmuir probe moved near the chamber
bottom parallel to the axis at a distance of 12 cm from
the inductive antenna. Distributions of ion saturation
current to the probe, proportional to plasma density,
were measured along the antenna.
2. PRELIMINARY PESULTS
The experimental results obtained using the
coil and with use of the permanent magnet sets are
shown in Fig. 2,a,b correspondingly. It was found that
in both cases the linear antenna could produce a stable
discharge of sufficient density, RF power was
absorbed in plasma well enough and there existed
some discharge regimes in which plasma density was
approximately uniform along essential part of the
antenna length.
Fig. 2. Distributions of ion saturation current along
the linear antenna; pAr = 0.65 Pa, W = 750 W.
a) Elektromagnet. Magnetic coil current: 1 – I = 0;
2 – I = 7 A; 3 – I = 20 A.
b) Permanent magnets. Magnetic field on the set’s
surface: 1 – B0 = 63 mT; 2 – B0 = 42 mT; 3 – B0 = 0
It is seen that at certain conditions the ion current (and
consequently the plasma density) is approximately
constant on the distance of about 20 cm along the
antenna. Some deviation of the density profile at
X = 30 cm may be caused by proximity of the metal
section and the magnetic field inhomogenity. At the
same time any changes of discharge conditions led to
loss of uniformity and in the most cases the density
profile was not uniform.
3. EXPERIMENTAL DEVICE 2
Since in the quartz chamber the measurements
were possible only along one coordinate, the
subsequent experiments were performed in a metal
discharge chamber of cubic shape with dimensions
22×22×20 cm. The two-turn linear antenna
conductors passed through two quartz tubes of 16 mm
diameter separated by 2 cm distance one from another in
the upper part of discharge volume, at 5 cm below the top
plane (Fig. 3). Three magnetic (or Langmuir) probes
moved along mutually perpendicular directions,
intersecting in the chamber center at 5 cm under the
antenna (X – in parallel to the antenna and Z – along the
external magnetic field). Uniform external magnetic field
B0 was created by two rectangular coils above and below
the discharge chamber (not shown see in Fig. 3). The
antenna plane was perpendicular to the external magnetic
field lines.
Fig. 3. Scheme of metal discharge chamber with the
linear antenna immersed into plasma. The antenna
conductors passed inside two quartz tubes at a distance of
5 cm below the upper plane of the chamber. Two
rectangular magnetic coils – upper and lower – are not
shown
The discharge volume was pumped out through an
aperture, closed with the dense metal grid in the rear wall
of the chamber.
4. RF FIELDS AND DENSITY
DISTRIBUTIONS
It was found that increase of the magnetic field caused
several step-like jumps in plasma density and ended with
the full cease of discharge (Fig. 4). The critical magnetic
fields corresponding to the density jump and to the
discharge break down grow with increasing the RF power
and gas pressure.
Fig. 4. Ion saturation current to the probe in the chamber
center vs magnetic field. On curves 1-5 the RF power was
gradually increasing from 180 to 750 W
After the discharge brake-down the reflected power
highly increased, while the plasma density and absorbed
power decreased. The final signals see in Fig. 4 are not
the ion currents but the stray signals resulted from a
strong breach of matching conditions. Thereupon the
discharge may be restored only by decreasing of the
magnetic field. This behavior is characteristic of the
а
b
ISSN 1562-6016. ВАНТ. 2014. №6(94) 155
helicon discharge in a bounded volume at limited RF
power and usually is connected with formation of the
longitudinal standing helicon waves [3].
For measurements of spatial distributions of the
wave RF magnetic fields the moveable magnetic
probes were used. The probe tip represented itself 6-
turn coil 8 mm in diameter from bare stainless wire of
0.3 mm diameter oriented to receive the component
BZ of RF magnetic field. After detecting the probe
signal, proportional to amplitude of RF magnetic
field, was registered by the XY-recorder. To X input of
the recorder a voltage proportional to the probe
position or to magnetic coil current (i.e. to the
magnetic field strength) was applied. For phase
measurements the reference signal was picked up by a
small inductive loop situated near the antenna
conductors. A continuously variable spiral delay line
(0…0.25 μs) was used as a phase shifter.
Magnetic probe measurements revealed that along
the external magnetic field (Z-axis) the standing
waves really settled. Oscillations in every two
adjacent maximums had the opposite phases. The
standing wave patterns changed with the density
jumps. With increasing the magnetic field B0 the
standing wave length also increased in accordance
with the helicon waves’ dispersion.
For plasma parameter measurements the X-probe
was replaced with a flat Langmuir probe. But for
relative estimations of spatial density distributions we
used the ion saturation current to the bare magnetic
probe, although its geometry was not defined.
Evidently, from measurements along only three
mutually perpendicular axis it is not possible to fined
out the whole three dimensional structure of the RF
magnetic fields. As a rule, the spatial RF fields
distributions are complicated and their phase relations
are not too clear. Nevertheless, using the magnetic
probes it was revealed that there existed two the most
typical discharge states, differed one from another in
standing waves structure and in density distributions
along the linear antenna, which might be distinctly
interpreted. Both the cases are shown in Fig. 5, a,b.
Fig. 5. Wave RF magnetic fields and ion saturation
current spatial distributions. B0 = 2.5 mT,
pAr = 0,65 Pa. RF power: a) W = 640 W; b) W = 750 W
In the first regime (see Fig. 5,a) the wave RF
magnetic field BZ is approximately constant along the
antenna, except for its ends. In this case the ion
saturation current Ii (i.e. plasma density) also is highly
homogeneous along the antenna (X-direction). BZ
distributions measured along Z (see Fig. 5) and along Y
(Fig. 6, curve 1) axis, passing through the chamber center
5 cm below the antenna, in this case showed the third
(odd) modes having the maximum amplitude in the
center. The phase of oscillations changes to opposite one
in every adjacent maximum. Note, that for small
dimensions of the experimental device the uniform region
is not large (10 cm see in Fig. 5). But the high degree of
uniformity (often about 1 %) implies that the discharge
“forgot” the boundary conditions on the antenna ends.
This makes it possible that with increase the antenna
length the uniformity will remain.
Fig. 6. Transversal distributions of RF magnetic fields.
B0 = 2.5 mT, pAr = 0.65 Pa; 1 – case (a) in Fig.5,
W = 640 W; 2 – case (b), W = 750 W
Another discharge regime is shown in Fig. 5,b. In this
case the BZ amplitude has two maximums along the
antenna, but they are not components of standing wave,
because their phases are the same. Along the external
magnetic field (Z-axis) the standing wave of fourth
(even) mode is observed with zero field in the centre,
while transversely to the antenna, along Y direction,
(see Fig. 6, curve 2) we observe the 5-th (odd) mode, but
with absent the middle maximum. In this case the density
distribution along X is strongly nonuniform as it shows
the curve Ii(X) see in Fig. 5,b. These results demonstrate
that even increasing the RF power can destroy the plasma
uniformity. Generally, any changes in the discharge
parameters – magnetic field, RF power, matching
conditions or gas pressure – cause loss of the uniformity
and, as a rule, the discharge with arbitrary chosen
parameters has inhomogeneous density distribution. The
exact conditions for obtaining the uniform density profile
yet are not clear.
Plasma parameter measurements with the flat probe
showed the electron temperature in the range of 2…4 eV.
The plasma space potential was estimated from the ion
energy distribution measured with a 5-grid retarding field
energy analyzer and was found to be in the range of
15…20 eV. The ion current density at a distance of
10 cm from the linear antenna was about 20 mA/cm
2
that
corresponded to plasma density 8×10
11
cm
–3
. These
parameters are typical for the helicon discharges in
Argon at given levels of RF power, pressure and
magnetic field. So, the investigated discharge
undoubtedly has the helicon nature.
The linear antenna originates from a deformed
“planar” antenna. This antenna excites the azimuthally-
symmetric mode of helicon waves m = 0 (m – the
azimuthal number) by producing RF magnetic field BZ
а
b
156 ISSN 1562-6016. ВАНТ. 2014. №6(94)
parallel to the external field B0. Therefore, we may
expect that the excited waves also are some modified
helicon waves with prevailing longitudinal RF
magnetic field BZ, but with zero wave number along
the antenna direction (kX = 0).
Though the results of preliminary experiments in
the quartz cylindrical chamber were rather hopeful,
the possibility of uniform profile at much longer
linear antenna has to be examined experimentally.
Also the question is the uniformity of plasma flux on
the grounded bottom of the chamber, where in
technological device the treated surface will be
situated, since in our experiments the uniform profiles
were obtained only in between the antenna and the
chamber bottom. These questions will be the matter
of subsequent experiments.
CONCLUSIONS
In the presented work the possibility of discharge
excitation by a linear antenna has been shown and the
wave (helicon) nature of excited discharge was
demonstrated. The existence of some regimes with
uniform plasma density at essential part of the
antenna length was revealed. Standing wave patterns
corresponding to various discharge regimes were
studied. At RF power of 1 kW on frequency
13.56 MHz, at Argon pressure 0.65 Pa and magnetic
field 5 mT the ion current density of 20 mA/cm
2
was
obtained that corresponded to plasma density of
8×10
11
cm
-3
.
A discharge system with the linear antenna
immersed into plasma, that does not need a large area
flat quartz window and is convenient for realization,
is proposed. After increasing its dimensions and more
detail study this type discharge may be used for design of
technological equipment for uniform plasma treatment of
large area products, including the flexible roll materials.
ACKNOWLEDGEMENTS
This work was supported by the Presidium of NAS of
Ukraine and the Scientific Council of program:
“Prospective researches on Plasma physics, Controlled
fusion and Plasma technology” under the project
№ ПЛ 30/14.
REFERENCES
1. M.A. Liberman and A.J. Lichtenberg. Principles of
Plasma Discharges and Materials Processing. New York:
“Wiley”, 1994.
2. F.F. Chen, H. Torreblanca. Large-area helicon plasma
source with permanent magnets // Plasma Phys. Control.
Fusion. 2007, v 49, № 5A, p. A81-A93.
3. V.M. Slobodyan, V.F. Virko, G.S. Kirichenko,
K.P.Shamrai. Helicon discharge excited planar antenna
along the magnetic field // Problems of Аtomic Science
and Technology. Ser.“Plasma Electronics and New
Methods of Acceleration” (3). 2003, № 4, p. 235-240.
4. R.P. Shamrai, S. Shinohara, V.F. Virko,
V.M. Slobodyan, Yu.V. Virko, G.S. Kirichenko. Wave
stimulated phenomena in inductively coupled magnetized
plasmas // Plasma Phys. Control. Fusion. 2005, v. 47,
p. A307-A315.
Article received 24.09.2014
МОДИФИЦИРОВАННЫЙ ГЕЛИКОННЫЙ РАЗРЯД, ВОЗБУЖДАЕМЫЙ ЛИНЕЙНОЙ
ИНДУКЦИОННОЙ АНТЕННОЙ
А.Г. Борисенко, М.А. Белошенко, В.Ф. Вирко, Ю.В. Вирко, В.М. Слободян
Исследована новая разновидность геликонного разряда, способного генерировать линейно однородную
плазму. Разряд возбуждается в магнитном поле индукционной антенной, состоящей из двух параллельных
проводников с противофазными ВЧ-токами, подобно двухпроводной передающей линии.
Продемонстрирована волновая природа разряда. Показано, что существуют некоторые разрядные условия, в
которых плотность плазмы однородна на значительной части длины антенны. Предложена удобная в
реализации разрядная система с линейной антенной, погружённой в плазму. При дальнейшем
усовершенствовании такой разряд может быть использован для однородной плазменной обработки больших
поверхностей.
МОДИФІКОВАНИЙ ГЕЛІКОННИЙ РОЗРЯД, ЗБУДЖУВАНИЙ ЛІНІЙНОЮ ІНДУКЦІЙНОЮ
АНТЕНОЮ
А.Г. Борисенко, М.А. Бєлошенко, В.Ф. Вірко, Ю.В. Вірко, В.М. Слободян
Досліджено новий різновид геліконного розряду, здатного утворювати лінійно однорідну плазму.
Розряд збуджується в магнітному полі індукційною антеною, що складається з двох паралельних
провідників з протифазними ВЧ-струмами, подібно до двопровідної передавальної лінії. Продемонстровано
хвильову природу розряду. Показано, що існують деякі розрядні умови, в яких густина плазми є однорідною
на значній частині довжини антени. Запропонована зручна в реалізації розрядна система з лінійною
антеною, зануреною в плазму. При подальшому удосконаленні такий розряд може бути використано для
однорідної плазмової обробки великих поверхонь.
|