U.S. patent application number 09/750665 was filed with the patent office on 2001-06-28 for ion beam processing apparatus for processing work piece with ion beam being neutralized uniformly.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Hashimoto, Isao, Ichimura, Satashi, Ogura, Satoshi, Ooishi, Shotaro.
Application Number | 20010005119 09/750665 |
Document ID | / |
Family ID | 15711400 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010005119 |
Kind Code |
A1 |
Ogura, Satoshi ; et
al. |
June 28, 2001 |
Ion beam processing apparatus for processing work piece with ion
beam being neutralized uniformly
Abstract
In order to uniformly neutralize a large current and a large
diameter ion beam so as to irradiate an ion beam having a reduced
beam divergence on a process target, an ion beam processing
apparatus comprises an ion source for producing a processing
plasma, a processing chamber as a vacuum chamber for accommodating
a process target, an extract electrode for extracting an ion beam
so as to irradiate on said process target, an annular electrode
disposed in said processing chamber for forming an annular magnetic
field therein, through which said ion beam is irradiated on said
process, and a wave guide for introducing microwave through an
opening provided on a wall forming said processing chamber, into
said annular magnetic field.
Inventors: |
Ogura, Satoshi;
(Hitachi-shi, JP) ; Ooishi, Shotaro; (Hitachi-shi,
JP) ; Hashimoto, Isao; (Hitachi-shi, JP) ;
Ichimura, Satashi; (Hitachi-shi, JP) |
Correspondence
Address: |
MATTINGLY, STANGER & MALUR, P.C.
104 East Hume Avenue
Alexandria
VA
22301
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
15711400 |
Appl. No.: |
09/750665 |
Filed: |
January 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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09750665 |
Jan 2, 2001 |
|
|
|
09327502 |
Jun 8, 1999 |
|
|
|
6184625 |
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Current U.S.
Class: |
315/335 ;
315/339; 315/344 |
Current CPC
Class: |
H01J 27/18 20130101;
H01J 2237/0817 20130101; H01J 2237/3142 20130101; H01J 2237/0041
20130101; H01J 37/08 20130101 |
Class at
Publication: |
315/335 ;
315/344; 315/339 |
International
Class: |
H01J 011/04; H05B
041/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 9, 1998 |
JP |
10-160271 |
Claims
What is claimed is:
1. An ion beam processing apparatus comprising an ion source for
producing a processing plasma, a processing chamber provided as a
vacuum chamber for accommodating a process target being disposed
adjacent to said ion source, an extract electrode for extracting an
ion beam from said processing plasma into the processing chamber so
as to irradiate on said process target, an annular electrode
disposed in said processing chamber for forming an annular magnetic
field therein, through which said ion beam being irradiated on said
process, and a wave guide for introducing microwave through an
opening provided on a wall forming said processing chamber, into
said annular magnetic field.
2. An ion beam processing apparatus as defined in claim 1, said ion
beam processing apparatus further comprising a micro wave
transparent plate being provided on said opening so as to cover
said opening and to transmit said microwave.
3. An ion beam processing apparatus as defined in claim 2, wherein
said micro wave transparent plate is capable of being replaced from
outside of said processing chamber.
4. An ion beam processing apparatus as defined in claim 1, wherein
said wave guide is partially bent.
5. An ion beam processing apparatus as defined in claim 4, wherein
said microwave is deflected in a portion of said wave guide which
is bent so as to be transmitted into said annular magnetic
field.
6. An ion beam processing apparatus as defined in claim 1, said ion
beam processing apparatus further comprising plurality of openings
being provided on said wall, and plurality of wave guides for
introducing microwave respectively through said openings into said
annular magnetic field.
7. An ion beam processing apparatus as defined in claim 1, wherein
an end of said wave guide is inserted so as to fit into an opening
provided on said annular electrode.
8. An ion beam processing apparatus as defined in claim 1, wherein
an end of said wave guide which is connected to said annular
electrode, being formed to be a tapered opening type.
9. An ion beam processing apparatus as defined in claim 1, wherein
said annular magnetic field is formed as a multi ring cusp magnetic
field generated by a line of plural magnets.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention is related to an ion beam processing
apparatus, and in particular, to an ion beam processing apparatus
which is suitable for processing a work piece by etching with a
large current and a large diameter ion beam.
[0002] As a prior art ion beam processing apparatus, there is
known, for example, an etching apparatus for etching a work piece
using an ion beam as disclosed in JPA Laid-Open No. 63-157887. In
this apparatus, in order to prevent for the work piece charged by
the ion beam irradiated thereon from being damaged due to its
charging, an ion beam neutralizing method is employed, wherein a
plasma is generated by a microwave discharge in a neutralizing unit
disposed near to the ion beam, and electrons are supplied from the
plasma through a small opening to the ion beam so as to neutralize
the ion beam. This method assures a longer time of operation
compared to an ion beam neutralizing method which uses a hollow
cathode containing a filament for emitting thermoelectrons, and
thus is suitable for neutralizing a reactive ion beam. Further,
because no filament such as tungsten is used, contamination of the
work piece by heavy metals constituting the filament can be
prevented, thereby providing for a clean ion beam processing.
[0003] However, the conventional neutralizing method has a
limitation in providing for a large current and large diameter ion
beam because of the following reasons to be described below.
[0004] When providing for a large current ion beam, it becomes
necessary also to increase a flow of electrons to be supplied from
the neutralizing unit in order to effectively neutralize the large
current ion beam thus increased. However, according to the
conventional method whereby electrons are supplied from the plasma
produced within the neutralizing unit, a same quantity of ion
current as an increase in the large current ion beam must be
collected within the neutralizing unit. That is, an increase in the
flow of electrons to be supplied means that the ion current to be
collected also increases. In addition, in order for a higher
density plasma to be generated within the neutralizing unit, it
becomes necessary to increase the power of a microwave to be input
into the neutralizing unit, consequently increasing a plasma
potential in the neutralizing unit. This means an increase in
collision energy of ions to be collected in the neutralizing unit.
According to the conventional method as described above, with
increases in the ion current colliding on the internal wall of the
neutralizing unit and in the ion energy, conducting particles
sputtered from the internal wall of the neutralizing unit by ion
bombardment are caused easily to deposit on a microwave inlet
window of the neutralizing unit, thereby substantially limiting a
service life of the neutralizing unit.
[0005] Further, in order to extract a large quantity of electrons
into the processing chamber, it becomes necessary to decrease a
potential of the neutralizing device itself to a negative potential
which is far below compared to that of the processing chamber.
Consequently, the energy of electrons having been extracted from
the neutralizing device becomes greater, thereby distorting a
distribution of potentials in the ion beam, and thereby causing to
diverge the ion beam which inherently must be parallel. Still
further, because the site of supply of electrons to the ion beam is
localized according to the conventional method, its spatial
uniformity effect of neutralization is deteriorated with an
increasing diameter of the ion beam.
[0006] From the reasons described above, it has been difficult
according to the conventional methods to obtain a large current,
large diameter ion beam with a minimized divergence, which is in
excess of 300 mA and 200 mm in diameter, and which is uniformly
neutralized.
[0007] Hence, in order to solve these problems, there has been
proposed a microwave neutralizing device for use in an ion beam
processing apparatus as disclosed in JPA No.8-296069, which
utilizes a multi-cusp magnetic field formed between electron
cyclotron resonance magnetic fields, and into which a microwave is
introduced through a wave guide to form a plasma therein. This
plasma is used as a source of low energy electrons.
SUMMARY OF THE INVENTION
[0008] When using the microwave neutralizing device as disclosed in
JPA No.8-296069, it becomes possible to provide an ion beam
processing apparatus to uniformly neutralize a large current and a
large diameter ion beam so as to irradiate an ion beam having a
reduced beam divergence on a process target.
[0009] However, in such ion beam processing apparatus, an annular
electrode 8 is disposed between a plasma generating chamber 1 and a
processing chamber 23 and the processing chamber 23 is connected to
the plasma generating chamber 1 through the annular electrode
8.
[0010] Therefore, the annular electrode 8 forms a portion of the
vacuum chamber providing the vacuum of the vacuum chamber, and
needs to be constructed with a thick metal to be strong in order to
prevent the vacuum chamber from an atmospheric pressure.
[0011] Here, many permanent magnets 9 for forming an annular
magnetic field inside of the vacuum chamber are arranged outside of
the vacuum chamber.
[0012] Therefore, the thick metal of the annular electrode 8 make
the annular magnetic field generated by the many permanent magnets
9, difficult sufficiently to be formed inside of the vacuum chamber
through the thick metal.
[0013] The present invention is provided referring to this
problem.
[0014] An ion beam processing apparatus in the present invention
comprises an ion source for producing a processing plasma, a
processing chamber provided as a vacuum chamber for accommodating a
process target being disposed adjacent to said ion source, an
extract electrode for extracting an ion beam from said processing
plasma into the processing chamber so as to irradiate on said
process target, an annular electrode disposed in said processing
chamber for forming an annular magnetic field therein, through
which said ion beam being irradiated on said process, and a wave
guide for introducing microwave through an opening provided on a
wall forming said processing chamber, into said annular magnetic
field.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a cross-sectional view of an ion beam processing
apparatus according to one embodiment of the invention;
[0016] FIG. 2 is a cross-sectional view of a wave-guide for
introducing a microwave;
[0017] FIG. 3A is a schematic diagram indicating a method of
generating a neutralizing plasma according to the invention;
[0018] FIG. 3B is a characteristic diagram indicating a
distribution of spatial potentials along line a-b;
[0019] FIG. 4 is a cross-sectional view of the ion beam processing
apparatus of FIG. 1, cut out along line X-X;
[0020] FIG. 5 is a schematic cross-section of a wave-guide
according to a second embodiment of the invention;
[0021] FIG. 6 is a schematic cross-section of a wave-guide
according to a third embodiment of the invention;
[0022] FIG. 7 is a schematic cross-section of a wave-guide
according to a fourth embodiment of the invention;
[0023] FIG. 8 is a cross-section of an ion beam processing
apparatus according to a second embodiment of the invention; FIG.
9A is a cross-section of a wave guide according to a fifth
embodiment of the invention; and
[0024] FIG. 9B is a cross-section of a wave-guide according to a
sixth embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] A first preferred embodiment of the invention will be
described with reference to the accompanying drawings in the
following.
[0026] FIG. 1 is a schematic cross-sectional view of an ion beam
processing apparatus according to a first embodiment of the
invention. FIG. 2 is a schematic cross-sectional view of a main
part of a guide wave indicative of its structure for introducing
the microwave according to the invention. The ion beam processing
apparatus of FIGS. 1 and 2 is comprised of ion source 1,
acceleration electrode 6, deceleration electrode 9, protection
electrode (third electrode) 11, microwave neutralizer 14, and
processing chamber 13. The processing chamber 13, which constitutes
a vacuum container, is disposed in juxtaposition with the ion
source 1, and is connected thereto via insulation spacer 12.
Regarding the microwave neutralizer 14, a part of which that does
not constitute the vacuum container, is disposed outside the
processing chamber 13, and a main part thereof is disposed inside
the processing chamber 13.
[0027] The ion source 1 which is composed as a container for
generating a processing plasma has a plasma gas inlet pipe 3
connected at its upper side, a plasma generation filament 4
disposed therein, and an opening portion 46 formed at its bottom
side. Plasma gas 2 which is introduced into the ion source 1
through gas inlet tube 3 is heated by conduction of filament 4 so
as to obtain a sufficient energy to become a plasma 5. Acceleration
electrode 6 is disposed in the opening portion 46 of the ion source
1 and firmly connected thereto. This acceleration electrode 6 is
connected to an acceleration power supply 7 via ion source 1. Both
the acceleration electrode 6 and ion source 1 are applied a
positive voltage from the acceleration power supply 7. A
deceleration electrode 9 is mounted on the acceleration electrode 6
via an electrode insulation spacer 8. The deceleration electrode 9
is supplied with a negative voltage from a deceleration power
supply 10. Namely, the acceleration electrode 6 and the
deceleration electrode 9 are disposed in juxtaposition with the ion
source 1, and are composed as an extraction electrode for
extracting a processing ion beam 36 from plasma 5 within the ion
source 1 into processing chamber 13 and irradiating the same on a
wafer (process target) 27 placed on a holder 26. Protection
electrode (third electrode) 11 is mounted on the deceleration
electrode 9 via insulation spacer 8, and the protection electrode
11 is further connected to microwave neutralizer 14 via conductor
45. Microwave neutralizer 14 is connected to neutralizing power
supply 25. According to this embodiment of the invention, because
that a potential of processing chamber 13 is set at the earth
potential, a potential of the protection electrode 11 and microwave
neutralizer 14 is maintained at a negative potential relative to a
potential of the processing chamber 13. Namely, by setting the
potential of the protection electrode 11 at a negative potential
relative to the potential of processing chamber 13, the ions in the
neutralizing plasma generated by the microwave neutralizer 14 are
collected by protection electrode 11 before they collide on the
deceleration electrode 9, thereby preventing for the deceleration
electrode 9 to be damaged by ion bombardment.
[0028] The microwave neutralizer 14 of the invention, which
functions as the neutralizing plasma generation means and the ion
collection means, is comprised of external (atmospheric side) wave
guide 24, quartz plate 23, internal (vacuum side) wave guide 21, a
plurality of permanent magnets 16, annular electrode 47, and
deposition prevention plate 28, and wherein the annular electrode
47 is disposed inside the processing chamber 13 aligned with the
center line of ion source 1 and is firmly fixed thereto via
insulation spacer 15. The external (atmospheric side) wave guide 24
disposed outside the processing chamber 13 and with interposition
of quartz plate (microwave transparent plate) 23 which hermetically
seals the opening 22 formed in the processing chamber 13 for
introducing the microwave thereinto is firmly fixed on an outer
wall of processing chamber 13 as an external portion of the wave
guide for guiding microwave 34 generated in a microwave generator
(not shown) to the opening 22. A recess portion 31 and O-ring
groove 32 are formed on the outer surface of processing chamber 13
and in the vicinity of the opening 22. O-ring 33 is mounted in the
O-ring groove 32, and quartz plate 23 is disposed on the O-ring 33.
The quartz plate 23 is coupled to the opening 22 as supported by an
end portion of the wave-guide 24. The end portion of the wave guide
24 is firmly fixed to the outer wall of processing chamber 13 by
means of fixtures such as insulated screws, insulated bolts and the
like (not shown). Namely, by connecting firmly the wave guide 24
outside the opening 22 of processing chamber 13 via O-ring 33 and
quartz plate 23, vacuum in processing chamber 13 is maintained.
[0029] Internal wave guide (on vacuum side) 21 provided for guiding
the microwave passing through quartz plate 23 is firmly fixed at
its one end to an inner wall of processing chamber 13 via
insulation spacer 15, and at the other end thereof coupled to
annular electrode 47 formed into a straight tube integral
therewith. Further, the wave guide 21 is provided with a deflection
portion 20 for reflecting microwave 34 passing through quartz plate
23 toward a direction of annular electrode 47 on its way so as to
prevent for high energy conducting particles from depositing on
quartz plate 23 which serves as the microwave introduction
window.
[0030] Annular electrode 47, which is formed approximately into a
cylindrical shape as an annular member which surrounds a periphery
of a propagation region of processing ion beam 36, is provided with
an opening 19 for introducing microwave 34 into a region inside the
annular member 47. Further, the annular electrode 47, likewise the
protection electrode 11, is connected to neutralizing power supply
27, and the annular electrode 47 is applied with a voltage which is
negative relative to that of the processing chamber 13. A pair of
permanent magnets 16 having their magnetic poles counterposed is
disposed in plural numbers at a predetermined space along an
external periphery of annular electrode 47. Namely, arrays of
plural permanent magnets (magnetic substances) 16 which constitute
the magnetic field forming members of the invention are arranged
with their magnetic polarities counterposed along the outer
periphery of the annular electrode 47. Each pair of permanent
magnets 16 disposed in opposite polarities produces a line of
magnetic force 17, and a magnetic field 18 is allowed to be formed,
on the internal side of annular electrode 47, having a flux density
of electron cyclotron resonance corresponding to a frequency of
microwave 34. Magnetic field 18 is allowed to form a multi ring
cusp magnetic field as will be described later. Further, annular
electrode 47 is connected to a deposition prevention plate 28 via
insulation spacer 29.
[0031] This deposition prevention plate 28 is provided for
preventing a sputter from wafer 27 placed on holder 26 from
depositing on microwave neutralizer 14. This deposition prevention
plate 28 is maintained at the same potential as that of the
processing chamber 13 (which is normally at the earth potential).
Further, an exhaust opening 30 is formed in the processing chamber
13 so as to allow for the inside of the processing chamber 13 to be
vacuum deaerated as required by an exhaust system connected to the
opening 30. By way of example, when connecting respective portions
via insulation spacers, electric connection structures using
insulation screws or the like are employed.
[0032] Now, operation of the ion beam processing apparatus of FIG.
1 will be described in the following with reference to FIGS. 3 and
4. When microwave 34 of 2.45 GHz is introduced from the microwave
generator into the atmospheric side wave guide 24, microwave 34
guided through wave guide 24 is allowed to pass through quartz
plate 23 to enter vacuum side wave guide 21. When this microwave 34
is reflected on the deflector 20 and is introduced into the inner
region of annular electrode 47 through opening 19, this microwave
34 is absorbed by electrons by resonance absorption in the magnetic
field 18 with an electron cyclotron resonance flux density of 875
gauss, thereby generating high energy electrons. This high energy
electrons move along the line of magnetic force 17 reciprocating in
the multi ring cusp magnetic field formed between the juxtaposed
magnets and on the inner surface of annular electrode 47. As a
macro movement, the high energy electrons revolve in a
circumferential direction by a magnetic field grading drift action
as indicated in FIG. 4 along annular (band) electrode 47 so as to
ionize the gas and generate a neutralizing plasma in an uniform
ring shape. Then, a portion of the neutralizing plasma having a
good containment of the plasma is represented as a high-density
plasma portion 35. This plasma portion 35 is in contact with the
annular electrode 47 and the ion beam 36. At this instant, because
the neutralizing plasma is generated in front of the opening 18,
microwave 34 introduced from the wave guide 21 is deflected
outwardly in the directions of electron cyclotron resonance
magnetic fields 18 so as to facilitate its arrival thereto, thereby
ensuring an efficient absorption of microwave 34.
[0033] Still further, when the neutralizing plasma is formed,
because that annular electrode 47 is set at the negative potential
relative to the potential of processing chamber 13, ions 37 in the
neutralizing plasma are captured by the annular electrode 47,
thereby allowing electrons 38 having a same quantity of opposite
charge as that of ions 37 to be supplied uniformly toward the ion
beam 36. In addition, because that the protection electrode 11 is
maintained likewise the annular electrode 47 at the negative
potential relative to the potential of processing chamber 13, it
becomes possible to reduce a probability of direct collision of the
ions 37 of the neutralizing plasma with deceleration electrode 9,
to increase an efficiency of capture of ions 37 from the
neutralizing plasma, and improve a quantity of supply of electrons
38 into ion beam 36 as well. By way of example, even if the
potential of protection electrode 11 is set at the same potential
as that of processing chamber 13, the probability of direct
collision by ions 37 of the neutralizing plasma on the deceleration
electrode 9 can be reduced as well.
[0034] In the above-mentioned embodiment of the invention, because
that the vacuum side wave guide 21 and annular electrode 47 are
disposed inside of the processing chamber 13, no additional
machining is required for maintaining wave guide 21 and annular
electrode 47 in vacuum, and further because that a thickness of
walls of the portions through which the line of magnetic force 17
passes can be made thinner, there is another advantage that a
magnetic strength of each permanent magnet can be made relatively
smaller. In addition, because that the insulation of wave guide 21
can be provided on the side of the internal wall of processing
chamber 13, it is not necessary to provide for an insulation
structure for the wave guide exposed to the atmosphere.
[0035] Still more, in the above-mentioned embodiment of the
invention, because that deflector 20 is provided in the vacuum side
wave guide 21 after quartz plate 23 for introducing microwave 34
into processing chamber 13, a sputtering from wafer 27 under
etching can be prevented from directly flying toward quart plate 23
to deposit thereon, thereby preventing formation of a film on
quartz plate 23 which hinders transmission of microwave 34, and
allowing a more prolonged time of operation for ion beam
processing.
[0036] Although the above-mentioned embodiment of the invention has
been described by way of example, which has a single opening 22 for
introducing the microwave for generating the neutralizing plasma,
it is not limited thereto, and other modifications having a
plurality of openings 22 formed in processing chamber 13 can be
contemplated within the scope of the invention, wherein each
opening connected to each of a plurality of vacuum side wave guides
21 allows for a plurality of microwaves 34 to be introduced therein
through the plurality of vacuum side wave guides 21, thereby
capable of neutralizing a larger current, broader diameter ion beam
36.
[0037] Although the above-mentioned embodiment of the invention has
been described by way of example using an integral assembly of wave
guide 21 and annular electrode 47, wherein the wave guide 21 and
annular electrode 47 are formed integral, but it is not limited
thereto, and other modifications allowing their insert-connection
can be contemplated within the scope of the invention wherein one
end of wave guide 21 is formed into a straight pipe opening type
wave guide 40 which can be inserted into an opening 19 which is
formed in annular electrode 47 at its wave guide connection port
39, thereby allowing for a more simplified process of
manufacture.
[0038] With reference to FIG. 6, as for the structure of wave-guide
21, one end of wave-guide 21 can be formed into a tapered opening
type wave-guide 41, which can be connected integral with annular
electrode 41.
[0039] When the wave guide 21 having tapered opening type wave
guide 41 at its one end is provided, because its microwave is
caused to propagate in wider radial directions, it becomes possible
to irradiate microwave 34 more efficiently into electron cyclotron
resonance magnetic field 18, ensuring for microwave 34 to reach the
electron cyclotron resonance magnetic field 18 more easily.
[0040] With reference to FIG. 7, another structure of wave guide 21
allowing for an insertion fit-in connection method can be provided
wherein one end of wave guide 21 is formed into a tapered opening
type wave guide 41, which can be inserted into the opening 19 for
connection therebetween.
[0041] A schematic block diagram indicating a second embodiment of
the invention is shown in FIG. 8. A feature of the second
embodiment of the invention different from the preceding embodiment
resides in that although the negative voltage is applied to annular
electrode 47 by connecting the same to neutralizing power supply 25
in the preceding embodiment, its negative voltage is applied from
neutralizing power supply 25 to a band electrode 43 which is fixed
via electrode insulation spacer 42 on the internal side of annular
electrode 47, and through opening 48 formed in annular electrode 47
for internal connection therebetween. Other elements for
construction thereof are the same as those in the preceding
embodiment of the invention of FIG. 1.
[0042] The band electrode 43 provided as a second annular electrode
is formed into a cylindrical shape, and allows microwave 34 to be
introduced through opening 49. The same is further connected to
protection electrode 11 via conductor 45.
[0043] According to the second embodiment of the invention, because
that its neutralizing plasma can be generated in a region which is
inside of band electrode 43, the same effect as the preceding
embodiment of the invention can be achieved, and because that
annular electrode 47 as well as wave guide 21 can be maintained at
the same potential as that of processing chamber 13, wave guide 21
and annular electrode 47 can be coupled firmly with processing
chamber 13 without use of insulation spacer 15 and deposition
prevention plate insulation spacer 29, thereby eliminating use of
insulation structure screws for these spacers.
[0044] Further, according to the second embodiment of the
invention, wave guide 21 can be formed integral with annular
electrode 47, otherwise as indicated in FIG. 9(a) the one end of
wave guide 21 can be formed into tapered opening type wave guide 41
having spacer 44 mounted on its end, which can be inserted into
opening 19. Alternatively, as indicated in FIG. 9(b), one end of
wave guide 21 can be formed into a straight tube opening type wave
guide 40 having spacer 44 mounted to this end, which can be
inserted into opening 19 for connection therebetween.
[0045] Further, according to this method whereby insulation spacer
44 is mounted on the end of wave guide 40, 41, the provision of
insulation spacer 15 is not required for connection of wave guide
21 to processing chamber 13, thereby eliminating the use of the
insulation construction screws corresponding to these spacers.
[0046] The aforementioned embodiments 1 and 2 have been described
by way of examples in which annular electrode 47 and protection
electrode 11 are connected via conductor 45, or in which band
electrode 43 is connected to protection electrode 11 via conductor
45, however, it is not limited thereto, and another modification
within the scope of the invention can be adopted in which
protection electrode 11 is connected to a power supply having the
same potential as the potential of processing chamber 13, instead
of its connection to neutralizing power supply 25.
* * * * *