U.S. patent application number 09/738989 was filed with the patent office on 2001-10-04 for plasma processing system.
Invention is credited to Iizuka, Satoru, Nakagawa, Yukito, Numazawa, Yoichiro, Ogawa, Unryu, Sato, Hiroyasu, Sato, Noriyoshi, Tominaga, Yoshio, Yoneyama, Tsukasa.
Application Number | 20010026575 09/738989 |
Document ID | / |
Family ID | 18471504 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010026575 |
Kind Code |
A1 |
Sato, Noriyoshi ; et
al. |
October 4, 2001 |
Plasma processing system
Abstract
A plasma processing system provided with a vacuum chamber for
accommodating a substrate and for generation of plasma in a space
in the front of the same, an antenna provided at the vacuum
chamber, and a high frequency power source for supplying high
frequency power to the antenna. The antenna emits high frequency
power, generates plasma inside the vacuum chamber, and processes
the surface of the substrate by the plasma. In the plasma
processing system, the antenna has a disk-shaped conductor plate
having a predetermined thickness. A coaxial waveguide having a
folded portion is formed around the disk-shaped conductor plate.
The folded portion of the waveguide is provided with a
short-circuit 3 dB directional coupler having an impedance matching
function. The antenna having the above structure prevents the
generation of a standing wave in the high frequency wave
propagation path from the high frequency power source to the vacuum
chamber and generates high density plasma by supply of a large
power. Due to this, processing of a large area substrate becomes
possible.
Inventors: |
Sato, Noriyoshi;
(Sendai-shi, JP) ; Iizuka, Satoru; (Sendai-shi,
JP) ; Yoneyama, Tsukasa; (Sendai-shi, JP) ;
Sato, Hiroyasu; (Sendai-shi, JP) ; Ogawa, Unryu;
(Tokyo, JP) ; Tominaga, Yoshio; (Tokyo, JP)
; Numazawa, Yoichiro; (Machida-shi, JP) ;
Nakagawa, Yukito; (Tokyo, JP) |
Correspondence
Address: |
Oliff & Berridge PLC
P.O. Box 19928
Alexandria
VA
22320
US
|
Family ID: |
18471504 |
Appl. No.: |
09/738989 |
Filed: |
December 19, 2000 |
Current U.S.
Class: |
373/18 ;
219/121.43; 373/25 |
Current CPC
Class: |
H01J 37/32192 20130101;
H05B 7/00 20130101 |
Class at
Publication: |
373/18 ; 373/25;
219/121.43 |
International
Class: |
H05B 007/00; B23K
009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 1999 |
JP |
11-360929 |
Claims
What is claimed is:
1. A plasma processing system comprising: a vacuum chamber in which
plasma is generated in a space at the front of a substrate loaded
inside, an antenna for plasma generation provided in said vacuum
chamber, a high frequency power source for supplying high frequency
power to said antenna, wherein said antenna supplied with the high
frequency power from said high frequency power source emitting the
high frequency power to cause generation of plasma in the space in
said vacuum chamber and the plasma being used to perform
predetermined processing of the surface of said substrate, and
further wherein, said antenna having a disk-shaped conductor having
a predetermined thickness and an electromagnetic wave emitter
facing said substrate and being connected to said high frequency
power source by a coaxial line, said disk-shaped conductor being
connected to an inside conductor of said coaxial line at its center
point, a waveguide of a coaxial type arranged symmetrically with
respect to the center point and provided with a folded portion from
said coaxial line to said electromagnetic wave emitter being
provided around said disk-shaped conductor, and said folded portion
of said waveguide having structure as a short-circuit 3 dB
directional coupler having an impedance matching action.
2. A plasma processing system as set forth in claim 1, wherein the
structure as said short-circuit 3 dB directional coupler is
produced by forming a step difference at one or both of the top
surface and bottom surface of said disk-shaped conductor.
3. A plasma processing system as set forth in claim 1, wherein the
structure as said short-circuit 3 dB directional coupler is
produced by providing dielectric materials at the waveguide around
said disk-shaped conductor.
4. A plasma processing system as set forth in claim 1, wherein in
said antenna, the variables of any elements in the plurality of
elements comprising the structure as said short-circuit 3 dB
directional coupler are determined to give S.sub.22=.GAMMA..sub.A*
(where "*" is a conjugated complex number) in a representation of a
scattering matrix with respect to a reflection coefficient
.GAMMA..sub.A of said antenna.
5. A plasma processing system as set forth in claim 1, wherein in
said antenna, the variables of any elements in the plurality of
elements comprising the structure as said short-circuit 3 dB
directional coupler are determined to give S.sub.22=0 in a
representation of a scattering matrix.
6. A plasma processing system as set forth in claim 1, wherein a
magnetic circuit for generating a magnetic field in the space is
provided at said disk-shaped conductor.
7. A plasma processing system as set forth in claim 1, wherein the
flux density of the magnetic field generated by said magnetic
circuit in a region in proximity to said disk-shaped conductor in
the space is set so that the electron cyclotron frequency
corresponding to the flux density becomes larger than the frequency
of the high frequency power.
8. A plasma processing system as set forth in claim 1, wherein the
frequency of the high frequency power is 0.5 to 10 GHz.
9. A plasma processing system as set forth in claim 1, wherein a
coaxial type impedance matching mechanism is provided at said
coaxial line.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a plasma processing system,
and more particularly, relates to an antenna supplying a large
power and useful for generation of high density plasma without
causing any loss and a plasma processing system efficiently
generating high density plasma using the antenna and performing
predetermined processing on the surface of a substrate.
[0003] 2. Description of the Related Art
[0004] Among the systems for performing predetermined processing on
the surface of a semiconductor wafer or liquid crystal substrate
(hereinafter referred to as a "substrate") using plasma, plasma
enhanced chemical vapor deposition (PCVD) and plasma etching
systems are widely known. In these plasma processing systems, it is
necessary to generate high density plasma in order to increase the
processing rate. In addition, from the viewpoint of preventing
impurities, it is required to form high density plasma by a lower
pressure.
[0005] To generate plasma for the surface processing, from the
viewpoint of obtaining high density plasma with a high efficiency,
a system using the gaseous discharge generated by high frequency
power is used. The inventors of the present patent application have
already proposed a plasma processing system of a type supplying a
high frequency power of 2.45 GHz to a radial slotted antenna
connected to a coaxial high frequency power feed system to generate
plasma (Japanese Patent No. 8-2534219) and have confirmed that good
plasma processing was possible (as document, see for example N.
Sato et al., "Uniform Plasma Produced by a Plane Slotted Antenna ?
plasma processing system using a slotted antenna shown in the above
document. This plasma processing system has a vacuum chamber 102
provided with an evacuating mechanism 101 and generating a
discharge inside for generation of plasma, an antenna device 104
arranged on the upper section of the vacuum chamber 102 and
provided with a slotted antenna 103, a high frequency wet-feed
system 105 for feeding high frequency power to the slotted antenna
103, a discharge gas introduction mechanism 105 for introducing a
discharge gas into the vacuum chamber 102, and a substrate holder
107 arranged at a lower position inside the vacuum chamber 102. A
substrate 108 is loaded on the substrate holder 107 as an object to
be processed. The shape of the slots (or slits) formed in the
slotted antenna 103 is explained in detail in the above-mentioned
patent specification or document. The slotted antenna 103 is
actually provided with a magnetic circuit formed by permanent
magnets etc. for generating a magnetic field near the
electromagnetic wave emitter 103a, but in FIG. 9, its illustration
is omitted. Further, as a result of the addition of the magnetic
circuit, the slotted antenna 103 originally to be produced as the
disk-shaped conductor plate is actually produced as a conductor
having a predetermined thickness being able to house a magnetic
circuit. In FIG. 9, however, for convenience of explanation, it is
shown as a plate material. The high frequency power feed system 104
supplying the high frequency power is comprised of a high frequency
power source 111, a stub tuner 112, a coaxial waveguide converter
113, a coaxial line 114, and a coaxial vacuum window 115.
[0006] The substrate 108 loaded on the substrate holder 107 is
arranged to face the electromagnetic wave emitter 103a in the
slotted antenna 103.
[0007] In the plasma processing system shown in FIG. 9, the vacuum
chamber 102 is evacuated by the evacuating mechanism 101, discharge
gas is introduced into the vacuum chamber 102, and a predetermined
high frequency power is supplied to the slotted antenna 103 by the
high frequency power feed system 105. The introduced discharge gas
starts to discharge by the high frequency wave emitted from the
electromagnetic wave emitter 103a of the slotted antenna 103 and
generates plasma in the space in front of the substrate 108 in the
vacuum chamber 102. The surface of the substrate 108 is processed
by the physical or chemical action of the generated plasma. For
example, if gas having an etching action is introduced as the
discharge gas, the surface of the substrate 108 is etched.
[0008] Note that in the above-mentioned related art, an industrial
frequency of 2.45 GHz is used as the frequency of the high
frequency power. Further, the flux density of the magnetic field
generated near the antenna by the magnetic circuit, corresponding
to the high frequency, is set to be larger than about 875 Gauss so
that the frequency of the electron cyclotron becomes equal to 2.45
GHz.
[0009] In the field of art of general antennas for transmitting an
electromagnetic wave of the microwave to the millimeter wave band,
conventionally, the folded waveguide proposed In Japanese
Unexamined Patent Publication (Kokai) No. 9-199901 is known. This
folded waveguide was proposed to solve the problem of the
conventional folded waveguide shown in FIG. 14 of Japanese
Unexamined Patent Publication (Kokai) No. 9-199901, that is, the
need for formation of reflection surfaces of 45 degrees cuts at the
top and bottom of the folded ends and the attachment of adjustment
screws for canceling out reflection waves at the reflection
surfaces and the resultant complexity of the configuration, the
requirement for high dimensional precision, the high cost and
inability of mass production, the narrow band of the frequency
characteristics, and the troublesome adjustment work. Therefore,
the folded waveguide proposed in Japanese Unexamined Patent
Publication (Kokai) No. 9-199901 is characterized, as defined for
example in claim 1 and claim 2, by setting an "h" satisfying
predetermined conditions in the dimensions a.times.h (shown in FIG.
1) of the opening window of the 180 degrees folded portion.
[0010] In general the substrates processed by plasma processing
systems have become larger in size in recent years. In the process
of production of an LSI by processing of a silicon substrate, it is
necessary to fabricate a large number of devices from a single
substrate, so the size of substrates have become larger. Therefore,
the above-mentioned plasma processing systems have been required to
be increased in the power of the high frequency wave supplied in
order to make the area of the plasma generation region (area of
plane parallel to the substrate) larger and to make the plasma
density higher for increasing the processing rate.
[0011] The antenna device 104 comprised of the above slotted
antenna 103 is predicated on the processing of a substrate of a
diameter of about 200 mm using plasma of a density of 10.sup.11
cm.sup.-3 or so generated by the supply of a high frequency power
of about 1 kW. Therefore, it is not possible to supply a large
power high frequency wave outside of this assumption and therefore
not possible to generate high density plasma suited to the
processing of a large area substrate. The reason why a large power
high frequency wave cannot be supplied is that a standing wave is
generated due to the mismatch of the impedance at the high
frequency wave propagation path formed in the slotted antenna 103
and therefore a locally strong electrical field is generated and
causes insulation breakdown. Further, the electrical field induced
in the slotted antenna 103 due to the standing wave becomes large
and the surface of the slotted antenna 103 is heated by the Joule
effect resulting in a loss of power which in turn obstructs the
realization of a higher density plasma. In this slotted antenna, it
is generally impossible to avoid mismatch of impedance arising due
to the discontinuity in the shape of the high frequency wave
propagation path.
[0012] Further, according to the technology disclosed in Japanese
Unexamined Patent Publication (Kokai) No. 9-199901 explained above,
it is made possible to match the impedance without adjustment in
the folded waveguide of a low loss transmission line of an
electromagnetic wave of the microwave to the millimeter wave band
and thereby eliminate the reflection wave and thus eliminate the
standing wave. This technology, however, is limited to a folded
waveguide comprised of the wide area surface of a rectangular
waveguide folded substantially 180 degrees. When the width of the
wide area surface is made "a" and the width of the narrow wall
surface is "b", these dimensions "a" and "b" may be used to give
conditions for eliminating the standing wave. Therefore, this
technology mainly relates to the structure of the folded portion of
a rectangular waveguide and does not relate to an antenna
structure. Further, the above publication alludes to a folded
radial waveguide (circular waveguide) in its eighth embodiment
(FIG. 12 and paragraph 0049 etc.) and claims 12 and 13 as a
modification of a folded waveguide. In this case, the folded radial
waveguide uses 2.pi.r ("r" being the distance from the center of
the radial waveguide 61 to the center position of the opening of
the folded waveguide 64) as the value corresponding to the width
"a" of the wide area surface. It is possible to realize a plane
array antenna using the folded radial waveguide, but this is only a
modification of the folded waveguide satisfying the predetermined
conditions in the end.
[0013] In particular, in an antenna used in the above plasma
processing system, since a magnetic circuit is provided for forming
a magnetic field of a predetermined distribution in the plasma
generation space, in actuality a space for accommodating the
magnetic circuit is provided and a disk-shaped conductor having a
predetermined thickness is used. When using the antenna comprised
of the disk-shaped conductor having the above thickness to supply a
high frequency power into the vacuum chamber for the processing of
the substrate, it is extremely difficult to have the most suitable
impedance matching. For the impedance matching and efficient
propagation of a high frequency wave without causing a standing
wave, a new concept of antenna design suitable for the type and
structure of the antenna is required.
SUMMARY OF THE INVENTION
[0014] An object of the present invention is to make improvements
to the structure of a plasma generation antenna comprised mainly of
a disk-shaped conductor having a predetermined thickness and
provided with an electromagnetic emitter, while proposing an
innovative antenna design technique, and thereby provide an antenna
able to prevent the generation of a standing wave in a high
frequency wave propagation path and generate high density plasma by
the supply of a large power.
[0015] Another object of the present invention is to provide a
plasma processing system being able to use the antenna to supply a
large power high frequency wave, generating high density plasma by
a large power, and processing the surface of a large area at a high
rate.
[0016] The plasma processing system according to the present
invention is configured as follows so as to achieve the above
objects.
[0017] The plasma processing system of the present invention has,
as a presupposition configuration, a vacuum chamber in which plasma
is generated in a space at the front of a substrate arranged
therein, an antenna for plasma generation provided in the vacuum
chamber, and a high frequency power source for supplying high
frequency power to the antenna. The antenna supplied with the high
frequency power from the high frequency power source emits the high
frequency power to cause generation of plasma in the space in the
vacuum chamber. The plasma is used to perform predetermined
processing of the surface of the substrate. Further, in the plasma
processing system, the antenna has a disk-shaped conductor having a
predetermined thickness and an electromagnetic emitter facing the
substrate. It is connected to the high frequency power source by a
coaxial line or cable. The disk-shaped conductor is connected to an
inside conductor of the coaxial line at its center point. A
waveguide of a coaxial type arranged symmetrically with respect to
the center point and provided with a folded portion from the
coaxial line to the electromagnetic emitter is provided around the
disk-shaped conductor. The folded portion of the waveguide is
structured as a short-circuit 3 dB directional coupler for
impedance matching.
[0018] The above-mentioned plasma processing system has a radial
waveguide including the disk-shaped conductor having the
predetermined thickness due to housing a magnetic circuit and
including the folded portion around it. The high frequency power
supplied from the top side of the disk-shaped conductor is
propagated to the electromagnetic wave emitter at the bottom side
through the radial waveguide and is emitted from the
electromagnetic wave emitter to the space inside the vacuum
chamber. In the antenna having this structure, the waveguide is
given the structure of a short-circuit 3 dB directional coupler.
This is used for impedance matching to prevent generation of a
standing wave.
[0019] Among antennas for supply of the high frequency power used
in plasma processing systems, there has never before been an
antenna having a disk-shaped conductor having a predetermined
thickness which can perform impedance matching. According to the
present invention, structure enabling impedance matching is
realized by this new antenna design technique.
[0020] In the plasma processing system according to the present
invention, preferably the structure of a short-circuit 3 dB
directional coupler is obtained by forming a step difference at one
or both of the top surface and bottom surface of the disk-shaped
conductor. The disk-shaped conductor having a three-dimensional
shape forms a waveguide with the external chamber. The antenna is
provided at, for example, the top of the vacuum chamber used as the
processing chamber. The high frequency propagation conditions of
the waveguide having the folded portion are changed by the
formation of the step difference. The structure of the
short-circuit 3 dB directional coupler is realized by providing a
step difference meeting predetermined conditions regarding the
three-dimensional shape of the disk-shaped conductor. Impedance is
matched by the waveguide.
[0021] Further, in the above configuration, the structure of a
short-circuit 3 dB directional coupler is given by providing a
plurality of dielectric materials in the region of the waveguide
formed around the disk-shaped conductor divided into for example
smaller regions and adjusting the heights or dielectric constants
of the dielectric materials to satisfy predetermined
conditions.
[0022] Further, In the above antenna, the variables (dimensions,
dielectric constant, etc. of parts) of any elements in the
plurality of elements comprising that structure of a short-circuit
3 dB directional coupler are determined to give
S.sub.22=.GAMMA..sub.A* (where "*" is a conjugated complex number)
in the representation of the scattering matrix with respect to the
reflection coefficient .GAMMA..sub.A of the antenna. This condition
is one example of the predetermined conditions. There are various
elements determining the scattering matrix in the above plurality
of elements. Further, similarly, in the antenna, the variables of
any elements in the plurality of elements comprising the structure
of the short-circuit 3 dB directional coupler are determined to
give S.sub.22=0 in the representation of the scattering matrix.
This condition is another example of the predetermined conditions
and is a basic condition with high practicality.
[0023] The plasma processing system according to the present
invention is preferably provided with a magnetic circuit for
generating a magnetic field in the space inside the disk-shaped
conductor. By providing the magnetic circuit, the disk-shaped
conductor is given a predetermined thickness. Since the disk-shaped
conductor has the predetermined thickness, a new unique technique
for antenna design or impedance matching is provided.
[0024] In the above configuration, the flux density of the magnetic
field generated by the magnetic circuit in the region in proximity
to the disk-shaped conductor In the space of the vacuum chamber is
set so that the electron cyclotron frequency corresponding to the
flux density becomes higher than the frequency of the high
frequency power.
[0025] Further, in the above configuration, the frequency of the
high frequency power is 0.5 to 10 GHz.
[0026] In the plasma processing system according to the present
invention, preferably a coaxial type impedance matching mechanism
is provided at the coaxial line connected to the antenna.
[0027] Note that in the above explanation, the explanation was made
focusing on a plasma processing system provided with the new high
frequency feed antenna, but the antenna itself is also highly
valuable technically.
[0028] The present invention exhibits the following effects. It
provides the plasma processing system supplying a high frequency
power into the vacuum chamber to cause discharge and generate
plasma and thereby process the surface of a substrate, when the
disk-shaped conductor supplying high frequency power has the
predetermined thickness, the waveguide surrounding the disk-shaped
conductor is given the structure of a short-circuit 3 dB
directional coupler. Thereby the generation of a standing wave can
be prevented, the high frequency power can be transmitted
efficiently, and the efficiency of plasma generation can be
improved. Therefore, a large power high frequency wave can be
supplied, a high density plasma can be generated, and the surface
of a substrate of a diameter more than 300 mm can be processed.
Further, according to the present invention, the effect is more
remarkable when using discharge resulting from a high frequency
power with a frequency in the range of 0.5 to 10 GHz to generate
plasma with a good uniformity over a large area. It is possible to
improve the practicality of the plasma processing system when
processing a large area substrate by high frequency discharge.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] These and other objects and features of the present
invention will become clearer from the following description of the
preferred embodiments given with reference to the attached
drawings, wherein:
[0030] FIG. 1 is a longitudinal sectional view of a plasma
processing system according to a first embodiment of the present
invention:
[0031] FIG. 2 is a longitudinal sectional view of the basic
structure for supplementing the explanation of the structure of a
plasma generation antenna of the first embodiment;
[0032] FIG. 3 is a view for explaining the action of the
short-circuit 3 dB directional coupler;
[0033] FIG. 4 is a longitudinal sectional view of the practical
structure for supplementing the explanation of the structure of the
plasma generation antenna of the first embodiment;
[0034] FIG. 5 is a view of the appearance of a disk-shaped
conductor plate of the plasma processing antenna of the first
embodiment:
[0035] FIG. 6 is a view representing a scattering matrix when
viewing the plasma generation antenna as a single power feed
system;
[0036] FIG. 7 is a longitudinal sectional view of key parts of a
plasma generation antenna designed applying this antenna design
technique in the first embodiment of the present invention;
[0037] FIG. 8 is a longitudinal sectional view of a plasma
generation apparatus according to a second embodiment of the
present invention; and
[0038] FIG. 9 is a longitudinal sectional view schematically
showing a plasma processing system of the related art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0039] Next, preferred embodiments of the present invention will be
explained with reference to the attached drawings. The plasma
processing system according to the present invention is in general
used for a dry etching system, plasma CVD system, etc. In the
following explanation of the embodiments, a dry etching process for
fabrication of an LSI is envisioned. The present invention aims at
the improvement of the plasma generation mechanism including an
antenna. Its applications are not however limited to a dry etching
process.
[0040] FIG. 1 shows a plasma processing system provided with an
antenna as a characteristic part of the present invention.
Reference numeral 10 is a plasma generation antenna. In the plasma
processing system according to the present invention, the
characteristic part lies in the improved structure of the antenna
10. Therefore, according to this embodiment, the explanation will
be made of mainly the structure and action of the antenna 10
referring to the drawings, The overall structure of the plasma
processing system is drawn schematically.
[0041] The antenna 10 is provided at the top side of a vacuum
chamber 12 having a space 11 for generation of plasma inside it. At
the bottom part of the inside of the vacuum chamber 12 is provided
a substrate holder 13 arranged so as to face the antenna 10. On the
top surface of the substrate holder 13 is loaded a substrate 14 to
be processed. The substrate 14 is for example a large sized
substrate with a large area having a diameter of 300 mm. The
substrate 14 is held horizontally in the figure. The processed
surface of the substrate 14 is brought close to the space. The
space 11 between the antenna 10 and the substrate holder 13 is a
region of generation of plasma. The top surface of the substrate 14
faces the antenna 10 across this space 11.
[0042] In the plasma processing system according to the present
embodiment, a gas introduction pipe 15 is provided at a
cylindrically shaped surrounding wall of the vacuum chamber 12. The
gas introduction pipe 15 is connected to a discharge gas
introduction mechanism 16 through a valve etc. The discharge gas is
introduced into the space 11 in the vacuum chamber 12 through the
gas introduction pipe 15. Under the substrate holder 13 arranged at
the bottom of the vacuum chamber 12 is formed an evacuation port
17. The evacuation port 17 is connected to an evacuating mechanism
18. The inside of the vacuum chamber 12 is held at a required
reduced pressure state by the evacuating mechanism 18. When
electrical power is supplied to the discharge gas of the vacuum
chamber 12 in this state, discharge is started and plasma is
generated. The antenna 10 is provided at its approximate center
position with a disk-shaped conductor plate 19 in a horizontal
state in the figure. The power for generation of the plasma is
supplied as high frequency power from an electromagnetic wave
emitter 20 provided at the bottom surface of the disk-shaped
conductor plate 19. The high frequency power Is supplied from a
high frequency power feed system 30 to the disk-shaped conductor
plate 19 of the antenna 10. The disk-shaped conductor plate 19
houses a magnetic circuit near the electromagnetic wave emitter 20,
so has a predetermined thickness. Therefore, the disk-shaped
conductor plate 19 is actually formed as a disk-shaped conductor
having an inside volume. The thickness of the disk-shaped conductor
plate 19 is determined in accordance with the magnitude etc. of the
magnetic circuit housed.
[0043] In the antenna 10, the above-mentioned disk-shaped conductor
plate 19 is attached at a location outside the opening 12b of the
ceiling 12a of the discharge vacuum chamber 12, so as to plug the
same, through a ring 21 made of a dielectric functioning also to
seal the vacuum. At the bottom surface of the disk-shaped conductor
plate 19, the part through the opening 12b facing onto the space 11
inside the vacuum chamber 12 forms the above-mentioned
electromagnetic wave emitter 204 Also, a thin dielectric plate 22
is attached to the bottom surface of the disk-shaped conductor
plate 19. Further, at the surrounding regions at the upper side,
side directions, and lower side of the disk-shaped conductor plate
19 is provided a portion 24 forming a high frequency propagation
path, that is, a waveguide 24. The waveguide 24 is formed as a
coaxial high frequency wave propagation path around the disk-shaped
conductor plate 19 between the conductor plate 19 and an outside
vessel 24a and has a folded portion. Further, around the upper
peripheral edge of the disk-shaped conductor plate 19 is provided a
ring 23 made of a dielectric in the waveguide 24. The outer shape
of the peripheral edge of the disk-shaped conductor plate 19
forming the waveguide 24 at its inside portion or the structure of
the waveguide 24 formed using a dielectric material such as the
dielectric rings 21 and 23 and the method of design of the same are
the most important points in the present invention.
[0044] Further, the above high frequency power feed system 30 is
comprised of a high frequency power source 31, a stub tuner 32, a
coaxial waveguide converter 33, and a coaxial line 34. The stub
tuner 32 is comprised of three coaxial tuners and is arranged in a
waveguide. Further, the coaxial line 34 is comprised of an inner
conductor 34a and a tubular outer conductor 34b. The inner
conductor 34a of the coaxial line 34 is connected to the center of
the top surface of the disk-shaped conductor plate 19, while the
bottom end of the outer conductor 34b of the coaxial line 34 is
connected to the outside portion of the waveguide 24. The bottom
end of the coaxial line 34 is connected to the top side of the
waveguide 24. Further, the folded portion of the waveguide 24 is
formed as a portion extending from the bottom end of the coaxial
line 34 to the electromagnetic wave emitter 20 at the bottom side
of the disk-shaped conductor plate 19.
[0045] The disk-shaped conductor plate 19 houses a magnetic
circuit, or is provided additionally with the magnetic circuit, or
assembled with the magnetic circuit for the purpose of improving
the efficiency of plasma generation as explained above. The
configuration of the magnetic circuit itself, however, is not the
gist of the present invention, so in FIG. 1, the illustration is
omitted for simplification. As explained above, however, the
disk-shaped conductor plate 19 provided with the magnetic circuit
is shown by hatching in FIG. 1 to show that it has a predetermined
thickness.
[0046] The feature of the present invention lies in the structure
and action of the plasma generation antenna 10 as explained above.
The antenna 10 is provided at the top of the vacuum chamber 12 for
discharge processing and is used for the purpose of emitting high
frequency power to the inside space of the vacuum chamber 12. Here,
in the explanation of the embodiment, the structure and action of
the antenna 10 are the main themes. In the design of the plasma
generation antenna 10 constituting the major part of the present
invention, the setting of the oscillation frequency of the high
frequency power source 31 in the high frequency power feed system
30 is an important requirement. In the present embodiment, in the
same way as the document cited above, a high frequency power source
able to generate a microwave of 2.45 GHz is used. The output power
of the high frequency power source 31 is for example about
2000W.
[0047] Next, the structure and action of the antenna 10 will be
explained in detail with reference to FIG. 2 to FIG. 6. FIG. 2
shows schematically the basic structure of the antenna 10, FIG. 3
illustrates the concept of operation of a short-circuit 3 dB
directional coupler by, for example, an example of the structure of
a rectangular waveguide, FIG. 4 schematically shows the antenna 10
according to the present invention having the function of impedance
matching, FIG. 5 shows a perspective view of the appearance of only
the disk-shaped conductor plate, and FIG. 6 shows a representation
of a scattering matrix (S matrix) when viewing the antenna 10 as a
single power feed system.
[0048] In FIG. 2, the high frequency power introduced through the
high frequency power feed system 30 is guided by the coaxial line
34, passes through the waveguide 24 of the coaxial transmission
line formed around the disk-shaped conductor plate 19 of the
antenna 10, and is emitted from the rear electromagnetic wave
emitter 20 to the space 11 inside the vacuum chamber 12. In this
figure, the disk-shaped conductor plate of the antenna 10 is the
portion shown by reference numeral 19A. It is shown by a shape
different from the above-mentioned conductor plate 19. That is, the
conductor plate 19A does not actually have the above predetermined
thickness and is drawn schematically as a disk-shaped substantially
flat plate. Further, in FIG. 2, the electromagnetic wave emitter 20
designates the opening in the bottom wall. The above high frequency
power is the energy for causing discharge of the discharge gas
supplied to the space 11 to generate the plasma. In the antenna 10,
as shown by the arrow 41 (meaning an energy flow), the high
frequency power is supplied to the electromagnetic wave emitter 20
around the peripheral edge 19A-1 of the disk-shaped conductor plate
19A. In this configuration, for the efficient propagation of the
high frequency power as shown by the energy flow 41, in the present
embodiment, the waveguide 24 of the surrounding region of the
disk-shaped conductor plate 19A is given the structure of a
short-circuit 3 dB directional coupler, the special property
(action) of the short-circuit 3 dB directional coupler is utilized
for impedance matching, and the efficiency of propagation is
improved, The present embodiment indicates as its features the
method of design of the antenna for giving the structure of a
short-circuit 3 dB directional coupler by the waveguide 24 of the
antenna 10 and the antenna 10 having the structure. The properties
of the short-circuit 3 dB directional coupler will be explained in
detail below.
[0049] Note that in FIG. 2, the waveguide 24 of the portion of
propagation of the high frequency power is divided for convenience
into three regions (A), (B) and (C). That is, the waveguide 24 for
propagation of the high frequency power around the disk-shaped
conductor plate 19A is provided with dielectric materials shown as
the three regions (A), (B) and (C). In this example, the structure
of the short-circuit 3 dB directional coupler is given as explained
later using dielectric materials.
[0050] Next, an explanation will be given of the special properties
of the short-circuit 3 dB directional coupler using (1) to (4) of
FIG. 3. In FIG. 3, the short-circuit 3 dB directional coupler is
represented by the block circuit 42 provided with the two left
ports 42a and 42b and the two right ports 42c and 42d. The top left
of the block circuit 42 having the action of the short-circuit 3 dB
directional coupler forms an incident end. In the short-circuit 3
dB directional coupler 42, the left ports 42a and 42b are open,
while the right ports 42c and 42d are short-circuited and form a
short-circuited end 42A.
[0051] (1) in FIG. 3 is a view of the case where an electromagnetic
wave of a unit amplitude is incident to the top right port 42a of
the short-circuit 3 dB directional coupler. The incident wave is
divided by the action of the short-circuit 3 dB directional coupler
42 into two waves of amplitudes of 1/{square root}{square root over
(2)} which appear at the short-circuited end 42A. At this time, due
to the general properties of the coupler, the amplitude at the top
right port 42c becomes 1/{square root}{square root over (2)}, the
phase at the bottom right port 42d differs by 90 degrees, and
therefore the conjugated amplitude becomes j(1/{square root}{square
root over (2)}).
[0052] In the short-circuit 3 dB directional coupler 42, when the
incident wave enters the, port 42a as explained above, reflection
occurs at the short-circuited end 42A. As shown in (2) and (3) of
FIG. 3. the reflection wave again passes through the short-circuit
3 dB directional coupler 42. (2) of FIG. 3 is a view of the case of
reflection of the electromagnetic wave of the amplitude 1/{square
root}{square root over (2)} of the port 42c. As a result, this
becomes the electromagnetic waves of the conjugated amplitudes 1/2
and j(1/2) and appears at the two ports 42a and 42b. On the other
hand, (3) of FIG. 3 is a view of the case of reflection of the
electromagnetic wave of the conjugated amplitude j(1/{square
root}{square root over (2)}) of the port 42d. Electromagnetic waves
of the conjugated amplitudes -1/2 and j(1/2) appear at the ports
42a and 42b. Since the overall phenomenon is based on the
superposition of (2) and (3) of FIG. 3, in the end, the
electromagnetic wave passing through the short-circuit 3 dB
directional coupler 42 and reflected at the short-circuited end 42A
appears as the conjugated amplitude j at the bottom left port 42b
as shown in (4) of FIG. 3. In short, due to the action of the
short-circuit 3 dB directional coupler 42, the electromagnetic wave
incident from the port 42a of the incident end is output as an
electromagnetic wave with an unchanging amplitude and a 90 degrees
different phase at the left port 42b. That is, the electromagnetic
wave incident to the port 42a is transmitted to the port 42b as an
electromagnetic wave shifted in phase by exactly 90 degrees without
generation of a standing wave.
[0053] If configuring the short-circuit 3 dB directional coupler
having the above action by a rectangular waveguide, the port 42a
where the electromagnetic wave is incident becomes the incident
side waveguide, while the port 42b where the electromagnetic wave
is output becomes the emission side waveguide. The portion of the
waveguide from the incident side waveguide to the emission side
waveguide is formed as a folded portion by the provision of the
short-circuit use metal plate portion. If configuring the
short-circuit 3 dB directional coupler having a folded portion
using the structure of the rectangular waveguide in this way, the
high frequency power entering from the incident side waveguide is
output from the emission side waveguide without the generation of a
standing wave.
[0054] The discussion of the short-circuit 3 dB directional coupler
relating to the above rectangular waveguide can be expanded and
applied to the antenna 10 comprised of the disk-shaped conductor
plate 19A and waveguide 24 formed around it, shown in FIG. 2, that
is, the antenna 10 having the radial waveguide including the folded
portion. The basic operating principle of the short-circuit 3 dB
directional coupler 42 relating to the example of the structure
using the rectangular waveguide is the same in the antenna 10 of
the shape shown in the present embodiment. That is, In the antenna
10, if the generation of the standing wave is eliminated by
structural provision (structural realization) of the short-circuit
3 dB directional coupler at the waveguide 24 at the region
surrounding the disk-shaped conductor plate 19A, the power of the
high frequency wave (microwave) introduced to the incident portion
of the top side of the disk-shaped conductor plate 19A is
efficiently propagated without generation of loss as shown by the
energy flow 41 and is emitted from the electromagnetic wave emitter
20 of the lower, side of the disk-shaped conductor plate 19A In the
example of the antenna 10 shown in FIG. 2, the short-circuit 3 dB
directional coupler is realized by arranging dielectric materials
of the regions (A) to (C) so as to satisfy predetermined conditions
at the waveguide 24 formed around the flat disk-shaped conductor
plate 19A. Here, the "predetermined conditions" means finding a
single scattering matrix S as an overall structure for the
waveguide 24 of the antenna 10 and changing the dielectric
constants etc. of the dielectric materials of the regions (A) to
(C) to make the reflection coefficient S.sub.22 of the scattering
matrix 0. In other words, if the dielectric constants etc. of the
dielectric materials are determined so that the reflection
coefficient S.sub.22 of the scattering matrix becomes 0, the
short-circuit 3 dB directional coupler is provided at the waveguide
24 by the structure of the dielectric materials of the regions (A)
to (C) having those dielectric constants.
[0055] Further, since there are various demands in practice on the
structure of the plasma/generation antenna 10, it is not possible
to employ the above ideal structure as it is. In practice, since a
magnetic circuit using permanent magnets is provided close to the
electromagnetic wave emitter 20, when the magnetic circuit is
contained in the disk-shaped conductor plate 19, the disk-shaped
conductor plate 19 is required to have a predetermined thickness in
accordance with the housed magnetic circuit as shown in FIG. 1.
[0056] Further, similarly, as shown in FIG. 1, the distance between
the electromagnetic wave emitter 20 and the disk-shaped conductor
plate 19 is in many cases made several mm. Sometimes it has to be
made extremely small compared with the distance or clearance at the
top side of the disk-shaped conductor plate 19. If such a shape is
employed, however, the impedances at the top and bottom surfaces of
the disk-shaped conductor plate 19 will become considerably
different and therefore microwave reflection will occur.
[0057] Therefore, relating to the outside shape of the disk-shaped
conductor plate, unlike the flat disk-shaped conductor plate 19A
shown in FIG. 2, tie structure shown in FIG. 4 is employed. The
disk-shaped conductor plate shown in FIG. 4 is formed to have an
impedance matching function so as not to cause microwave reflection
by giving a predetermined thickness and making modifications in the
outside shape. The outer shape of the disk-shaped conductor plate
shown in FIG. 4 is the same as the outer shape of the disk-shaped
conductor plate 19 shown in FIG. 1. Therefore, the reference
numeral 19 is assigned to the disk-shaped conductor plate shown in
FIG. 4 as well. According to this structure, as shown in FIG. 4 and
FIG. 5, step differences 19a and 19b are formed at the peripheral
edges of the top and bottom surfaces of the disk-shaped conductor
plate 19 and the dimensions are suitably designed in accordance
with the method of design of the antenna explained below for
impedance matching. In this example, by providing step differences
19a and 19b at the top and bottom surfaces of the disk-shaped
conductor plate 19 under predetermined conditions, propagation
characteristics of the high frequency power the same as the
short-circuit 3 dB directional coupler 42 whose operating principle
was explained in FIG. 3 are realized. That is, the structure of a
short-circuit 3 dB directional coupler is realized by providing the
step differences 19a and 19b meeting predetermined conditions at
the top and bottom surfaces of the disk-shaped conductor plate 19
of the antenna 10. Here, the "predetermined conditions" means
finding one scattering matrix S as an overall structure for the
waveguide 24 of the antenna 10 and changing the heights and other
dimensions of the step differences 19a and 19b to make the
reflection coefficient S.sub.22 of the scattering matrix 0. In
other words, if the heights etc. of the step differences are
determined so that the reflection coefficient S.sub.22 of the
scattering matrix becomes 0, the short-circuit 3 dB directional
coupler is provided at the waveguide 24 by the structure of the
step differences. By providing the step differences 19a and 19b of
the predetermined conditions at the top and bottom surfaces of the
disk-shaped conductor plate 19 in this way, the impedances are
matched, the generation of microwave reflection is prevented, the
microwave is efficiently transmitted, and a microwave can be
efficiently emitted from the electromagnetic wave emitter 20.
[0058] Further, to practically provide the antenna 10 with the
disk-shaped conductor plate having the outer shape as shown in FIG.
4 and FIG. 5, it is necessary to change the outer shape of the
disk-shaped conductor plate 19 and to consider the selection of the
dielectric materials to be arranged around the disk-shaped
conductor plate, design of the vacuum sealing, etc. That is, to
specifically design the antenna 10, it is necessary to design the
microwave propagation path by changing the outer shape of the
disk-shaped conductor plate 19 and select the surrounding
dielectric materials, design the vacuum sealing, etc. Therefore,
the dielectric rings 21 and 23 are arranged around the disk-shaped
conductor plate 19 as explained in FIG. 1. The dielectric rings 21
and 23 form the waveguide 24 and serve also as vacuum seals. When
designing the antenna 10 of the configuration shown in FIG. 1, the
antenna is designed by changing the outer shape by the step
differences of the disk-shaped conductor plate 19, selecting the
dielectric materials (21, 22, 23) provided at the waveguide 24,
etc. and finding one scattering matrix S as the overall structure
and changing a certain portion of the structure to give a
reflection coefficient S.sub.22 of the scattering matrix of 0 and
thereby realize the structure of the short-circuit 3 cm directional
coupler at the waveguide 24 of the antenna.
[0059] Next, the method of antenna design relating to the antenna
10 will be described in detail. Here, the process of calculation
for realizing a waveguide for propagation of a microwave without
reflection is shown for a basic structure obtained by using a
material usable for a plasma surface processing system and giving
consideration to the mechanical strength.
[0060] FIG. 6 is a view for explaining the basic operation of the
plasma generation antenna 10. It shows one scattering matrix (S
matrix) obtained by viewing the antenna 1 as a single power feed
system. The scattering matrix S is comprised of the reflection
coefficients S.sub.11 and S.sub.22 and the transmission
coefficients S.sub.12 and S.sub.21. In FIG. 6, when the reflection
coefficient of the antenna 10 is .GAMMA..sub.A and the scattering
matrix of the antenna 10 when viewed as a power feed system is made
the following equation (1), the reflection coefficient at the
feeding point of the antenna 10 is expressed by the following
equation (2): 1 [ S ] = ( S 11 S 12 S 21 S 22 ) ( 1 ) A = j2 A - S
22 ' 1 - S 22 A ( 2 )
[0061] Note that in equation (2), the symbol * expresses a
conjugated complex number and .phi.=arg(S.sub.11) . . . (3). For
simplification, in the representation of the scattering matrix of
FIG. 6. the reference plane is moved to the position T-T' where
.phi.=0.
[0062] Here, when the reflection coefficient .GAMMA..sub.A of the
antenna 10 is known, if designing the power feed system so that
S.sub.22=.GAMMA..sub.A* . . . (4), .GAMMA..sub.F=0 . . . (5) and
complete matching becomes possible.
[0063] However, the reflection coefficient .GAMMA..sub.A at the
antenna 10, that is, the reflection coefficient .GAMMA..sub.A at
the electromagnetic wave emitter 20, is generally unknown. The
above method of calculation cannot be applied. Therefore, in
equation (2), the antenna is designed to satisfy S.sub.22=0 . . .
(6). If S.sub.11=0, .GAMMA..sub.F=.GAMMA..sub.A . . . (7) stands
and the reflection coefficient of the antenna 10 and the reflection
coefficient of the feeding point become equal. That is, if ensuring
the condition S.sub.22=0 be satisfied while changing a certain
portion of the structure forming the antenna 10, the state of
change gives the structure of the short-circuit 3 dB directional
coupler and impedance matching is achieved.
[0064] Next, the method of finding the elements of the scattering
matrix of equation (1) for the plasma generation antenna 10 shown
in FIG. 2 as an example will be shown. To facilitate the analysis
at this time, the Inside of the cylinder of the inside diameter R
(waveguide 24) is divided into three regions (A), (B) and (C) as
shown in FIG. 2. The heights h.sub.1, h.sub.2 and h.sub.3 and the
dielectric constants .epsilon..sub..gamma..sup.(1),
.epsilon..sub..gamma..sup.(2) and .epsilon..sub..gamma..sup.(3) are
respectively assigned to these regions. The excitation is made the
TM wave and the electromagnetic field is made uniform in the .phi.
direction. At this time, the electrical component E.sub.Z is
obtained by solution of the wave equation in the cylindrical
coordinate system shown in equation (8), while the magnetic wave
component H.phi. is found by equation (9). 2 2 E Z 2 + 1 E Z + k 2
E X = 0 ( 8 ) H = - 1 j E Z ( 9 )
[0065] The electromagnetic fields in the region (A), region (B) and
region (C) are given by the following equations (10) to (16) in
this way: 3 E r ( 1 ) = H 0 ( 2 ) ( k 0 ( 1 ) ) H 0 ( 2 ) ( k 0 ( 1
) ) + n = 0 .infin. A n ( 1 ) - H 0 ( 1 ) ( k n ( 1 ) ) H 0 ( 1 ) (
k n ( 1 ) ) cos ( n h 1 z ) ( 10 ) H ( 1 ) = jH 1 ( 2 ) ( k 0 ( 1 )
) Z 0 ( 1 ) H 0 ( 2 ) ( k 0 ( 1 ) r ) + j n = 0 .infin. A n ( 3 ) H
1 ( 1 ) ( k n ( 1 ) ) Z n ( 1 ) H 0 ( 1 ) ( k n ( 3 ) r ) cos ( n h
1 z ) ( 11 ) E z ( 2 ) = n = 0 .infin. A n ( 5 ) H 0 ( 1 ) ( k n (
2 ) ) H 0 ( 1 ) ( k n ( 2 ) r ) cos [ n h 2 ( z - ( h 3 - h 2 ) ) ]
( 12 ) H ( 2 ) = j n = 0 .infin. A n ( 2 ) H 1 ( 1 ) ( k n ( 2 ) )
Z n ( 2 ) H 0 ( 2 ) ( k n ( 2 ) r ) cos [ n h 2 ( z - ( h 3 - h 2 )
) ] ( 13 ) E z ( 3 ) = n = 0 .infin. A n ( 3 ) [ H 0 ( 2 ) ( k n (
3 ) ) H 0 ( 2 ) ( k n ( 3 ) R ) - H 0 ( 1 ) ( k n ( 3 ) ) H 0 ( 1 )
( k n ( 3 ) R ) ] cos ( n h 3 z ) ( 14 ) H ( 3 ) = j n = 0 .infin.
A n ( 3 ) Z n ( 3 ) [ H 1 ( 2 ) ( k n ( 3 ) ) H 0 ( 2 ) ( k n ( 3 )
R ) - H 1 ( 1 ) ( k n ( 3 ) ) H 0 ( 1 ) ( k n ( 3 ) R ) ] cos ( n h
3 z ) ( 15 ) k n ( i ) = k n 2 r ( i ) - ( n h i ) , Z ( i ) = k n
( i ) 0 r ( i ) , ( i = 1 , 2 , 3 ) ( 16 )
[0066] Here, A.sub.n.sup.(1) is an unknown coefficient,
k.sub.n.sup.(1) is a phase constant, Z.sub.n.sup.(1) is a
characteristic impedance, and n is a mode number. Further, the
first terms on the right sides of equations (10) and (11)
correspond to incident waves, the second terms on correspond to
reflection waves, and equations (12) and (13) correspond to
transmission waves. These must satisfy the boundary condition at
.rho.=.gamma. (following equations (17), (18) and (19)). 4 E z ( 3
) = { E 2 ( 1 ) ( 0 z h 1 ) 0 ( h 1 z h 3 - h 2 ) E z ( 2 ) ( h 3 -
h 2 z h 3 ) ( 17 ) H ( 1 ) = H ( 3 ) ( 0 z h 1 ) ( 18 ) H ( 2 ) = H
( 3 ) ( h 3 - h 2 z h 3 ) ( 19 )
[0067] Here, if equations (10) to (15) are inserted into equations
(17) to (19) and the results multiplied with the following equation
shown below to integrate them in the range where the boundary
conditions stand, equations (20) to (22) are obtained. 5 cos ( m h
3 ) , cos ( m h1 z ) , cos ( m h 2 ( z - ( h 3 - h 2 ) ) ) [ h 3 Z
n ( 3 ) ] [ S n ] ( A n ( 3 ) ) = h 1 Z 0 ( 1 ) [ n ] ( m0 ( 1 ) )
+ [ n ] [ mn ( 1 ) ] [ h 1 Z n ( 1 ) ] ( A n ( 1 ) ) + [ n ] [ mn (
2 ) ] [ h 2 Z n ( 2 ) ] ( A n ( 2 ) ) ( 20 ) ( A m ( 1 ) ) = I ( n
) + [ n ] [ J n ( 1 ) ] [ mn ( 1 ) ] l [ C n ] ( A n ( 3 ) ) ( 21 )
( A m ( 2 ) ) = [ n ] [ J n ( 2 ) ] [ mn ( 2 ) ] r [ C n ] ( A n (
3 ) ) ( 22 )
[0068] Here, the bracketed terms indicate matrixes, while the
parenthesized terms indicate column vectors. A term with a single
element number such a [S.sub.n] is a diagonal matrix. Note that the
elements are given by the following equations (23) to (28): 6 mn (
1 ) = ( - 1 ) n m h 1 h 3 sin ( m h 1 h 3 ) ( m h 2 h 3 ) 2 - ( n )
2 ( 23 ) a mn ( 2 ) = ( - 1 ) H2 m h 2 h 3 - sin ( m h 2 h 3 ) ( m
h 2 h 3 ) 2 - ( n ) 2 ( 24 ) S n = H 0 ( 2 ) ( k n ( 3 ) r ) H 0 (
2 ) ( k n ( 3 ) R ) - H 0 ( 1 ) ( k n ( 3 ) r ) H 0 ( 1 ) ( k n ( 3
) R ) ( 25 ) C n = H 1 ( 2 ) ( k n ( 3 ) r ) H 0 ( 2 ) ( k n ( 3 )
R ) - H 1 ( 1 ) ( k n ( 3 ) r ) H 0 ( 1 ) ( k n ( 3 ) R ) ( 26 ) J
n ( i ) = H 0 ( 1 ) ( k n ( i ) r ) H 1 ( 1 ) ( k n ( i ) r ) , ( i
= 1 , 2 ) ( 27 ) n = { 1 ( n = 0 ) 2 ( n 0 ) , n = { 1 ( n = 0 ) 0
( n 0 ) ( 28 )
[0069] Here, I is expressed by the following equation (29): 7 I = H
1 ( 2 ) ( k 0 ( 1 ) r ) H 0 ( 1 ) ( k 0 ( 1 ) r ) H 0 ( 2 ) ( k 0 (
1 ) r ) H 1 ( 1 ) ( k 0 ( 1 ) r ) ( 29 )
[0070] If equations (21) and (22) are inserted into equation (20),
the following equation (30) is obtained. 8 [ [ h 3 Z n ( 3 ) ] [ S
n ] - [ ] [ mn ( 1 ) ] [ h 1 Z n ( 1 ) ] [ ] [ J n ( 1 ) ] [ mn ( 1
) ] ' [ C n ] - [ ` ] [ mn ( 2 ) ] [ h 2 Z n ( 2 ) ] [ n ] [ J y (
2 ) ] [ mn ( 2 ) ] ' [ C n ] ] ( A ( 3 ) ) = ( 1 + I ) h 1 Z 0 ( 1
) [ n ] ( m0 ( 3 ) ) ( 30 )
[0071] By solving equation (30) for A.sub.m.sup.(3) and inserting
the result into equations (21) and (22), A.sub.m.sup.(1) and
A.sub.m.sup.(2) are found. In the end, the elements S.sub.11,
S.sub.12 and S.sub.21 of the scattering matrix are given by the
following equations (31) and (32): 9 S 12 = A 0 ( 1 ) - H 1 ( 1 ) (
k 0 ( 1 ) r ) H 0 ( 2 ) ( k 0 ( 1 ) r ) H 0 ( 1 ) ( k 0 ( 1 ) r ) H
1 ( 2 ) ( k 0 ( 1 ) r ) ( 31 ) S 12 = S 21 = A 0 ( 2 ) - h 2 Z 0 (
2 ) H 1 ( 1 ) ( k 0 ( 2 ) r ) H 0 ( 2 ) ( k 0 ( 1 ) r ) h 1 Z 0 ( 1
) H 0 ( 1 ) ( k 0 ( 2 ) r ) H 1 ( 2 ) ( k 0 ( 1 ) r ) ( 32 )
[0072] Using the unitary property, S.sub.22 is obtained by the
following equation (33): 10 S 22 = - S 21 S 21 * S 11 * ( 33 )
[0073] By suitably changing a certain portion of the plurality of
variables (heights h.sub.1, h.sub.2 and h.sub.3 and dielectric
constants .epsilon..sub..gamma..sup.(1),
.epsilon..sub..gamma..sup.(2) and .epsilon..sub..gamma..sup.(3)) in
S.sub.22 obtained by equation (33), it is possible to provide the
structure of the short-circuit 3 dB directional coupler at the
antenna 10. In this way, it is possible to obtain elements of the
scattering matrix relating to the plasma generation antenna 10
shown in FIG. 2 and possible to use the reflection coefficient
S.sub.22 among these to precisely find the dimensions or dielectric
constants etc. of the parts of the antenna 10 enabling impedance
matching.
[0074] It is also possible to use the same method of design as
above for analysis to find the elements of the scattering matrix in
the design of the antenna 10 having the disk-shaped conductor plate
19 formed with the step differences 19a and 19b shown in FIGS. 4
and 5. That is, the antenna is designed by multi variable analysis
using as variables the distance between the peripheral edge of the
disk-shaped conductor plate and the outer vessel, the heights of
the step differences, the distance between the peripheral edge of
the disk-shaped conductor plate and the walls of the step
differences, and the distance between the bottom surfaces of the
step differences and the outer vessel. In this way, it is possible
to precisely find the dimensions etc. of the step differences of
the antenna 10 able to perform impedance matching using the
reflection coefficient S.sub.22 of the scattering matrix even for
the plasma generation antenna 10 shown in FIG. 4 etc.
[0075] An example of the folded portion around the peripheral edge
of the disk-shaped conductor plate 19 designed in the above way for
the plasma generation antenna 10 having the step differences 19a
and 19b shown in FIG. 4 is shown in FIG. 7. The antenna 10 shown in
FIG. 7 is designed so that the reflection coefficient .GAMMA..sub.F
at the feeding point of the antenna 10 deemed to be the power feed
system matches with the reflection coefficient .GAMMA..sub.A at the
electromagnetic wave emitter of the antenna 10. In FIG. 7 the
reference numeral 19 indicates the disk-shaped conductor plate of
the antenna 10, while 24a is a conductive outside vessel. The step
difference 19a is formed on the top sur ace of the disk-shaped
conductor plate 19, while the step difference 19b is formed on the
bottom surface. The above waveguide 24 is formed between the
outside vessel 24a and the disk-shaped conductor plate 19
positioned inside it. The dimensions of the parts of the antenna 10
are as follows. The height of the outside vessel 24a is 8 cm. The
distance between the maximum diameter portion (peripheral edge)
positioned at the center of the disk-shaped conductor plate 19 in
the thickness direction and the cylindrical side walls of the
outside vessel 24a is 5 cm. The dimension of width of the step
difference 19a in the diametrical direction is 3 cm, while the
dimension from the surface (bottom surface) 19a-1 in the step
difference l9a to the upper wall of the outside vessel 24a is 2 cm.
The dimension of width of the step difference l9b in the
diametrical direction is 3 cm, while the dimension from the surface
(bottom surface) 19b-1 in the step difference 19b to the bottom
wall of the outside vessel 24a is 1.5 cm.
[0076] According to the antenna 10 designed so that the reflection
coefficient .GAMMA..sub.A and the reflection coefficient
.GAMMA..sub.F of the waveguide 24 match as explained above, by
inserting three stub tuners into the above coaxial line 34, it is
possible to even more easily match the impedance. Note that at this
time, the coaxial waveguide converter 33 must be designed to be
able to substantially completely match the impedance at the
frequency used, that is 2.4 GHz.
[0077] Further, as a result of actual measurement, when it becomes
clear that the reflection coefficient .GAMMA..sub.A is large, it is
sufficient to insert that value into equation (4) and redesign the
plasma generation antenna. By applying this technique to the design
of a plasma generation antenna, it is possible to construct a
plasma processing system which improves the efficiency of
transmission of electromagnetic waves in the antenna power feed
system, a problem in the past, and has advantages never seen in the
past. These advantages are the following (1) to (3):
[0078] (1) A plasma processing system which can emit a large power
electromagnetic wave impossible in the past, and can generate
higher density plasma than ever before can be provided.
[0079] (2) Plasma of the same extent of density as in the past can
be generated using a smaller power than in the past, so the plasma
processing system can be given a smaller power source and be made
smaller in energy consumption. Further, the rate of increase of the
power for dealing with the increasing size of plasma generation
areas accompanying the processing of large area substrates can be
suppressed.
[0080] (3) The method of design of an antenna according to the
present embodiment defines the structure of the electromagnetic
wave transmission path. Optimal design assuming any shape or
material for the desired process becomes possible.
[0081] Note that the design shown in the first embodiment is one
example of the result of calculations. It is of course possible to
calculate other efficient structures using similar calculations.
Due to the above reasons, according to the plasma generation
antenna 10 according to the above embodiment, it is possible to
minimize the power loss in the inside of the plasma generation
antenna and possible to realize a plasma generation system of a
higher efficiency than ever before.
[0082] Next, the routine and features when processing the surface
of a substrate 14 by using the plasma processing system according
to the first embodiment will be explained in brief. The surface
processing is for example a dry etching process of a silicon oxide
film on a silicon wafer.
[0083] In the plasma processing system according to the first
embodiment, discharge gas is supplied from the discharge gas
introduction mechanism 16 through the gas introduction pipe 15 to
the vacuum chamber 12. As the discharge gas used in the dry etching
process of a silicon oxide film, generally use is made of a mixed
gas comprised mainly of a chlorofluorocarbon gas plus argon,
oxygen, hydrogen, etc. On the other hand, the evacuating mechanism
18 provided at the vacuum chamber 12 is provided with a hydraulic
rotary pump or turbo molecular pump or other vacuum pump. The
inside of the vacuum chamber 12 is evacuated through the evacuation
port 17 until reaching for example a pressure of about 10.sup.-4
Pa. Note that the vacuum chamber 12 is also provided with a gate
valve for loading and unloading the substrates 14 and a transport
system for loading and unloading the substrates 14 through the gate
valve, but illustration of these is omitted in FIG. 1.
[0084] Next, an explanation will be given of the operation of the
above plasma processing system. First, the not shown transport
system is used to load the substrate 14 into the vacuum chamber 12
and place it on the substrate holder 13. The evacuating mechanism
18 is then operated to evacuate the inside of the vacuum chamber 12
to about 10.sup.-4 Pa, then the discharge gas introduction
mechanism 16 introduces the discharge gas into the vacuum chamber
12. The pressure of the gas inside the vacuum chamber 12 is
determined by the flow rate of introduction of the gas and the
evacuation rate of the evacuating mechanism 18. The typical gas
pressure in the plasma processing system of the present embodiment
is about 1 Pa. To maintain the predetermined discharge pressure at
the predetermined gas flow rate the general practice has been to
provide the evacuating mechanism 18 with a mechanism for
controlling the evacuation rate.
[0085] Next, the high frequency power feed system 30 operates to
supply high frequency power to the vacuum chamber 12. That is, the
high frequency power generated from the high frequency power
resource 31 is guided by the waveguide to the stub tuner 32 where
the impedance is matched, then is converted by the coaxial
waveguide converter 33 and is supplied through the coaxial line 34
to the plasma generation antenna 10. The high frequency power
supplied to the antenna 10 is emitted from the electromagnetic wave
emitter 20 to the space 11 in accordance with the action of the
antenna 10 to electrically dissociate the discharge gas in the
space 11 and cause discharge. Plasma is generated in the space 11
inside of the vacuum chamber 12 by this discharge. This plasma is
used for the predetermined processing of the surface of the
substrate 14 on the substrate holder 13.
[0086] In the above plasma processing system, the features of the
antenna 10 were used to enable generation of high density plasma,
which had been impossible in the past. The uniformity of the plasma
is within .+-.3% in the case of a diameter in the range of 300 mm.
This value is sufficient for a plasma processing system using
current silicon substrates. Further. from the features of the
plasma generation antenna 10, it becomes easy to generate uniform
plasma by a larger area. The antenna can therefore be applied to a
system for processing of a large-sized substrate of a diameter of
400 mm or a diameter of 450 mm in the future.
[0087] FIG. 8 shows a second embodiment of the present invention
and is similar to FIG. 1. In FIG. 8, the same reference numerals
are assigned to elements substantially the same as the elements
explained in FIG. 1 and explanations are omitted. In particular,
the structure providing the short-circuit 3 dB directional coupler
of the plasma generation antenna 10 in this embodiment is
substantially the same as that explained in the first embodiment.
In the present embodiment, matching even closer to the ideal can be
realized by providing a coaxial stub tuner 51 in the coaxial line
34.
[0088] In the antenna 10 optimally designed in accordance with the
first embodiment, the design is based on the presumption that the
reflection coefficient of the electromagnetic wave emitter is
sufficiently small or known. The impedance of the plasma generated
however changes somewhat according to the input power, gas
pressure, etc., so the reflection coefficient also changes somewhat
in accordance with the impedance of the plasma. The plasma source
shown in the first embodiment is an ECR plasma source provided with
a magnetic circuit at the disk-shaped conductor plate 19 of the
antenna 10 and using the magnetic field as explained above. In this
case, the change of the impedance is small, but when applying the
present invention to a plasma source of the type generating plasma
without using the magnetic field, the change of the reflection
coefficient sometimes becomes a problem. Therefore, to eliminate
the reflection wave caused in the waveguide in the antenna 10 due
to the change of the impedance of the plasma, the coaxial stub
tuner 51 is added to the coaxial line 34 for supplying high
frequency power to the antenna 10. By adding this configuration, it
is possible to cancel out the reflection wave generated due to the
change of the reflection coefficient by the standing wave generated
by the coaxial stub tuner 51 and realize a completely matched state
without relying on a change of the process conditions.
[0089] The structure of the plasma generation antenna 10 used for
the plasma processing system according to the present invention is
not limited to the above embodiment. If the conditions sought for
the above short-circuit 3 dB directional coupler are satisfied, it
is possible to freely change the shape and material of the
dielectric rings and blocks, the outer diameter and thickness of
the disk-shaped conductor plate, the shapes of the step
differences, and other dimensions, since the application of the
plasma generation antenna designed by the system of the present
invention is a plasma source for a semiconductor manufacturing
system, due to the wavelength of the electromagnetic wave, it is
preferable to set the frequency used to a range of 0.5 to 10 GHz.
Further, by designing the antenna predicated on use at a frequency
of 0.915 GHz or 2.45 GHz for which use is permitted as an
industrial frequency, it is possible to realize a more practical
plasma generation antenna.
[0090] In the above embodiments, the example was shown of the use
of the plasma processing system according to the present invention
to dry etching, but the object of the present invention lies in
generating plasma efficiently and with a good uniformity using a
high frequency wave as explained above. Therefore, even when
applying the invention to a plasma processing system meant for all
types of surface processing using plasma such as plasma CVD, plasma
oxidation, and plasma polymerization, the same effect as explained
in the embodiments can be obtained. While the invention has been
described by reference to specific embodiments chosen for purposes
of illustration, it should be apparent that numerous modifications
could be made those skilled in the art without departing from the
basic concept and scope of the invention.
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