U.S. patent application number 10/396381 was filed with the patent office on 2003-10-02 for internal electrode type plasma processing apparatus and plasma processing method.
This patent application is currently assigned to ISHIKAWAJIMA-HARIMA HEAVY INDUSTRIES CO., LTD.. Invention is credited to Takagi, Tomoko, Ueda, Masashi.
Application Number | 20030183169 10/396381 |
Document ID | / |
Family ID | 26542088 |
Filed Date | 2003-10-02 |
United States Patent
Application |
20030183169 |
Kind Code |
A1 |
Ueda, Masashi ; et
al. |
October 2, 2003 |
Internal electrode type plasma processing apparatus and plasma
processing method
Abstract
A plasma processing apparatus is of an internal electrode type,
and an inductive coupling type electrode arranged facing a
substrate 17 has a shape formed by bending back a conductor at its
central portion. A high frequency power is supplied to an end of
the electrode so that a standing wave of half wavelength are
produced at straight portions formed by bending back the electrode
to make an antinode there, and thus a plasma discharge is generated
around the electrode. The controlled standing waves with its
antinodes positively generated at the straight portions of the
electrode are effectively used. The frequency f of the high
frequency power is determined by f=(c/{square root}{square root
over ( )}.epsilon..sub.p)/2L1 , where c is the speed of light, L1
is the length of the portion formed by bending back the electrode,
and .epsilon..sub.p is the relative dielectric constant of plasma
produced around the electrode. The standing waves are positively
used to control distribution of density of the plasma in a good
situation, and the configuration of the electrode is designed
considering the plasma parameters around the electrode.
Inventors: |
Ueda, Masashi; (Fuchu-shi,
JP) ; Takagi, Tomoko; (Tama-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
ISHIKAWAJIMA-HARIMA HEAVY
INDUSTRIES CO., LTD.
Tokyo
JP
|
Family ID: |
26542088 |
Appl. No.: |
10/396381 |
Filed: |
March 26, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10396381 |
Mar 26, 2003 |
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09830879 |
May 2, 2001 |
|
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09830879 |
May 2, 2001 |
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PCT/JP00/06189 |
Sep 11, 2000 |
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Current U.S.
Class: |
118/723I ;
118/723E; 156/345.47; 156/345.48 |
Current CPC
Class: |
H01J 37/32541 20130101;
C23C 16/509 20130101; H01J 37/32082 20130101 |
Class at
Publication: |
118/723.00I ;
118/723.00E; 156/345.48; 156/345.47 |
International
Class: |
C23F 001/00; C23C
016/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 9, 1999 |
JP |
11-255219 |
Mar 2, 2000 |
JP |
2000-56584 |
Claims
1. In a plasma processing apparatus of an internal electrode type,
which is provided with an inductive coupling type electrode in a
vacuum processing chamber, the plasma processing apparatus
characterized in that: said electrode is formed so that a total
length of said electrode is substantially equal to an excitation
wavelength, one end of said electrode is grounded and another end
thereof is connected to a high frequency power source, and a
standing wave of one wavelength is produced along said electrode
when said high frequency power source supplies a high frequency
power to said electrode; and a node of said standing wave produced
along said electrode is formed at a central portion of said
electrode, and an antinode of said standing wave is formed on both
portions respectively corresponding to a half of said electrode,
which existing at both sides of said center point.
2. A plasma processing apparatus of an internal electrode type as
set forth in claim 1, characterized in that said electrode is
formed to be U-shaped by bending it back at said central portion,
and each of the half portions of said electrode corresponds to a
straight portion, and both of the half portions are arranged in
parallel.
3. A plasma processing apparatus of an internal electrode type as
set forth in claim 1, characterized in that a length of the half
portion of said electrode is substantially equal to a half of the
wavelength of said high frequency power.
4. A plasma processing apparatus of an internal electrode type as
set forth in claim 1, characterized in that a plurality of said
electrodes are arranged to make a stratified structure comprising a
plurality of layers within said vacuum processing chamber, a
plurality of film depositing regions are produced using a space
between said electrodes included in said plurality of layers, and
film deposition on a substrate is performed in each of said
plurality of film depositing regions.
5. In a plasma processing apparatus of an internal electrode type,
which is provided with an inductive coupling type electrode in a
vacuum processing chamber, the plasma processing apparatus
characterized in that: said electrode is formed so that a total
length of said electrode is determined to natural number times of a
half of an excitation wavelength, one end of said electrode is
grounded and another end thereof is connected to a high frequency
power source, and standing waves are produced along said electrode
when said high frequency power source supplies a high frequency to
said electrode; and a node of said standing waves produced along
said electrode is formed at a central portion of said electrode,
and at least one antinode of said standing waves is formed on both
portions respectively corresponding to a half of said electrode,
which existing at both sides of said center point.
6. A plasma processing apparatus of an internal electrode type as
set forth in claim 5, characterized in that said electrode is
formed to be U-shaped by bending it back at said central portion,
and each of the half portions of said electrode is a straight
portion, both of the half portions are arranged in parallel, and
said node of said standing wave is consistent with a bending back
point.
7. A plasma processing apparatus of an internal electrode type as
set forth in claim 5, characterized in that a plurality of said
electrodes are arranged to make a stratified structure comprising a
plurality of layers within said vacuum processing chamber, a
plurality of film depositing regions are produced using a space
between said electrodes included in said plurality of layers, and
film deposition on a substrate is performed in each of said
plurality of film depositing regions.
8. A plasma processing apparatus of an internal electrode type,
characterized by: comprising a plurality of electrodes of an
inductive coupling type in a vacuum processing chamber; wherein
each of said plurality of electrodes is formed by bending back a
conductor at its central portion to be U-shaped, a straight
portions formed by said bending back are parallel and are arranged
to be in one plane and further one end of each of said electrodes
is grounded and another end thereof is connected to a high
frequency power source, said plurality of electrodes having a
positional parallel relationship are placed so that a straight
portion at a power supplying side is adjacent to a straight portion
at a grounded side, high frequency powers respectively supplied
into end of said straight portions of power supplying side for said
plurality of electrodes are in phase.
9. A plasma processing apparatus of an internal electrode type as
set forth in claim 8, characterized in that a length of the
straight portion formed by bending back in the plurality of
electrodes is determined to produce an antinode of a standing wave
on said straight portion.
10. A plasma processing apparatus of an internal electrode type as
set forth in claim 9, characterized in that some of said electrodes
arranged to be in one plane is configured as an electrode array, a
plurality of the electrode arrays are placed as a stratified
structure within said vacuum processing chamber, a plurality of
film depositing regions are produced using a space between said
electrode arrays of plural layers, and film deposition on a
substrate is performed in each of said plurality of film depositing
regions.
11. A plasma processing apparatus of an internal electrode type,
characterized by: comprising a electrodes of an inductive coupling
type in a vacuum processing chamber; wherein said electrodes is
formed by bending back a conductor at its central portion to be
U-shaped, a plasma discharge is produced around said electrode by
supplying a high frequency power to an end of said electrode so
that a standing wave of half wavelength is produced at a straight
portion formed by bending back said electrode, and frequency (f) of
said high frequency power at this time is determined by
f=(c/{square root}{square root over ( )}.epsilon..sub.p)/2L1 where
c is the speed of light, L1 is the length of the straight portion
formed by bending back said electrode, and .epsilon..sub.p is the
relative dielectric constant of plasma produced around said
electrode.
12. A plasma processing apparatus of an internal electrode type as
set forth in claim 11, characterized in that the frequency of said
high frequency power is changed according to plasma parameters
around said electrode.
13. A plasma processing apparatus of an internal electrode type as
set forth in claim 11, characterized in that a plasma CVD
processing is performed for depositing a film with a solar cell
function on a large area substrate within said vacuum processing
chamber.
14. A plasma processing apparatus of an internal electrode type as
set forth in claim 11, characterized in that said length L1 of said
electrode is more than 0.8 meter.
15. In a plasma processing apparatus having an electrode of an
inductive coupling type placed within a vacuum processing chamber,
a plasma processing method characterized in that: said electrode is
formed by bending back a conductor at its central portion, a total
length of said electrode is determined to be a natural number times
of a half of an excitation wavelength, a high frequency power is
supplied to end of said electrode, a node of a standing wave
produced in said electrode is consistent with a bending back point,
an antinode of said standing wave is produced in each half portion
of said electrode, and said standing wave makes density
distribution of plasma around said electrode to be uniform.
16. A plasma processing method as set forth in claim 15,
characterizing in that the total length of said electrode is twice
as long as a half of an excitation wavelength.
17. In a plasma processing apparatus comprising an electrodes of an
inductive coupling type in a vacuum processing chamber, a plasma
processing method characterized in that: said electrodes is formed
by bending back a conductor at its central portion to be U-shaped,
a plasma discharge is produced around said electrode by supplying a
high frequency power to an end of said electrode so that a standing
wave of half wavelength is produced at a straight portion formed by
bending back said electrode, and frequency (f) of said high
frequency power at this time is determined by f=(c/{square
root}{square root over ( )}.epsilon..sub.p )/2L1 where c is the
speed of light, L1 is the length of the straight portion formed by
bending back said electrode, and .epsilon..sub.p is the relative
dielectric constant of plasma produced around said electrode.
18. A plasma processing method as set forth in claim 17,
characterized in that the frequency of said high frequency power is
changed according to plasma parameters around said electrode.
Description
TECHNICAL FIELD
[0001] The present invention relates to an internal electrode type
plasma processing apparatus and plasma processing method, more
particularly, relates to a plasma processing apparatus and plasma
processing method provided with an inductive coupling type
electrode suited for deposition of an amorphous silicon thin film
used for solar cells or thin film transistors and the like on a
large-area substrate.
BACKGROUND ART
[0002] The electrodes of internal electrode type plasma CVD
apparatuses have conventionally been of the parallel-plate type or
the inductive coupling type.
[0003] If using the parallel-plate type electrode, when trying to
raise frequency of a high frequency power in order to increase a
film deposition rate and improve film characteristics, the problem
arises that the electric discharge becomes non-uniform. This is
caused by the occurrence of a standing wave on the electrode plate
resulting on non-uniform distribution of plasma density and by the
production of plasma at undesirable locations due to the voltage
created by the feedback current to the ground. Further, as the
substrate holder is made to function as a ground electrode, the
backing plate for the substrate becomes required and there is the
difficulty of maintaining the clearance between the backing plate
and substrate uniform when the size of the electrode plate is
increased so as to form a film on a large-area substrate. Also,
handling of the backing plate becomes difficult generally.
Therefore, a parallel-plate type electrode is not well suited to
the deposition of a film on a large-area substrate.
[0004] As opposed to the above parallel-plate type electrode, an
inductive coupling type electrode is free from the above problems.
Accordingly, the inductive coupling type electrode is well suited
to the deposition of a film on a large-area substrate when used in
an internal electrode type plasma CVD apparatus, for example.
[0005] As an internal electrode type plasma CVD apparatus using an
inductive coupling type electrode, for depositing an amorphous
silicon thin film on a large-area substrate to form a solar cell
etc. there is the apparatus disclosed in Japanese Unexamined Patent
Publication (Kokai) No. 4-236781, for example. In this plasma CVD
apparatus, the electrode for discharge is formed by a flat coil
having a ladder-like structure which is arranged parallel to the
substrate. The ladder-like flat coil is formed by a conductive
wire. The source gas is introduced from a reaction gas introduction
pipe provided at a single location of the reactor, while the inside
of the reactor is evacuated through an evacuation pipe provided at
a single location of the reactor. This flat coil increases the
intensity of the electromagnetic field and improves the uniformity
of the field. Further, as a similar conventional plasma CVD
apparatus, there may be the apparatus disclosed in Japanese Patent
No. 2785442. In this plasma CVD apparatus, as the electrode
arranged facing the substrate, a flat coil electrode formed by a
single conductive wire bent multiple times to form a zigzag
configuration is used. A high frequency power is supplied from a
high frequency generator to the two ends of this electrode.
[0006] Concerning the above inductive coupling type electrode, the
ladder-shaped flat coil electrode according to Japanese Unexamined
Patent Publication (Kokai) No. 4-236781 does not have a uniform
current flowing at each rung of the ladder configuration and
therefore does not give a uniform distribution of the
electromagnetic field, so has the problem of the inability to
deposit a uniform film on the large-area substrate.
[0007] The ladder-shaped flat coil electrode is a distributed
constant circuit in view of an electric circuit. A current flowing
at each section in the distributed constant circuit can not be
calculated simply from resistance and path length of the circuit.
In the ladder type electrode, an impedance of each ladder rung
relative to other ladder rungs and a geometrical relation between
each ladder rung and a feeding point is related to the magnitude of
Poynting vector at each ladder rung. Experimentally, the phenomenon
that most of the current flows at the ladder rung near the feeding
point is observed.
[0008] Further, since the zigzag flat coil electrode according to
Japanese Patent No. 2785442 is produced by bending a single long
conductive wire and the high frequency power is supplied from one
end, the power cannot be fed efficiently. Further, while effort is
made in the design to prevent the generation of a standing wave as
much as possible, it is impossible to prevent the generation of a
standing wave at undesirable locations due to the configuration of
the electrode. Therefore, the film deposition is disturbed. That
is, an unintentional standing wave is produced at the electrode,
and this standing wave disturbs the distribution of plasma and
results in poor uniformity of film deposition.
[0009] Then, in the plasma CVD apparatus and the like of the
internal electrode type and inductive coupling type, it is desired
to generate the plasma around the electrode by positively producing
and utilizing the standing wave along the electrode arranged in the
processing chamber. The plasma generated around the electrode
receives energy for plasma generation from the antinode portion of
the standing wave. Accordingly, it is preferred to control the
standing wave generated along the electrode and the number or the
positions of the antinodes to be formed in a desirable situation.
Thereby, the standing wave can be actively used in a controllable
state so that the antinodes are produced at desirable positions
along the electrode, and therefore it is possible to skillfully
control a distribution of plasma and to deposit a film on a
large-area substrate with a good situation.
[0010] Further, as a general discussion, when proposing an
electrode configuration in the internal electrode type plasma
processing apparatus, concerning the standing wave positively
produced on the electrode, the relationship between the frequency
of the high frequency power supplied to the electrode and plasma
produced around the electrode in the reactor due to the high
frequency power sometimes cannot be ignored. Further, the plasma
exited around the electrode due to the standing wave formed on the
electrode, specifically the plasma parameters, have a major effect
on the standing wave and sometimes make it necessary to reevaluate
the design parameters of the electrode configuration. In this case,
it is required that sufficient consideration be given to the plasma
parameters when designing the electrode.
[0011] The objective of the present invention is to solve the above
problems, positively utilize a standing wave in a controllable
state to achieve a good uniformity of the plasma density, realize a
configuration of the electrode considering the plasma parameters
around the electrode, and to provide an internal electrode type
plasma processing apparatus and plasma processing method which is
suitable for deposition of a film on a large-area substrate for a
solar cell etc.
DISCLOSURE OF INVENTION
[0012] The internal electrode type plasma processing apparatus and
method according to the present invention are configured so as to
achieve the above objects.
[0013] The plasma processing apparatus of the present invention is
the apparatus of the internal electrode type provided with an
inductive coupling type electrode arranged in a vacuum processing
chamber. The above electrode is formed so that the total length
thereof is substantially equal to an excitation wavelength, and one
end of the electrode is grounded and another end is connected to a
high frequency power source. A standing wave of one wavelength is
produced along the electrode when the high frequency power source
supplies a high frequency power to the electrode. When producing
the standing wave on the electrode, a node of the standing wave
along the electrode is formed at a central portion of the
electrode, and antinodes of the standing wave are formed at half
portions of said electrode, which exists at both sides of a center
point.
[0014] Each part of the standing wave, which are produced on the
halves of the electrode, are mutually intensified to supply the
electromagnetic energy to the surrounding space of the electrode,
and the plasma of uniform density is generated in the surrounding
space of the electrode. When generating the plasma within the
processing chamber, active use of the standing wave positively
generated on the electrode is performed.
[0015] In the above plasma processing apparatus, the electrode is
formed to be U-shaped by bending it back at the central portion,
and each of the half portions of the electrode corresponds to a
straight portion, and both half portions are arranged in
parallel.
[0016] In the above plasma processing apparatus, the length of the
half portion of the electrode is substantially equal to a half of
the wavelength of the supplied high frequency power.
[0017] In the above plasma processing apparatus, a plurality of the
electrodes are arranged to make a stratified structure comprising a
plurality of layers within the vacuum processing chamber, a
plurality of film depositing regions are produced using the space
between the electrodes included in the plurality of layers, and
film deposition on a substrate is performed in each of the
plurality of film depositing regions. This structure can increase a
processing efficiency of substrates.
[0018] The plasma processing apparatus of the present invention is
the apparatus of an internal electrode type, which is provided with
an inductive coupling type electrode in a vacuum processing
chamber, and the electrode is formed so that a total length of the
electrode is determined to natural number times of a half of an
excitation wavelength, one end of the electrode is grounded and
another end thereof is connected to a high frequency power source,
and standing waves are produced along the electrode when the high
frequency power source supplies a high frequency power to the
electrode, and further a node of the standing waves produced along
the electrode is formed at a central portion of the electrode, and
at least one antinode of the standing waves is formed at half
portions of the electrode, which exist at both sides of a center
point.
[0019] In the above plasma processing apparatus, the electrode is
formed to be U-shaped by bending it back at the central portion,
and each of the half portions of the electrode is a straight
portion, both of the half portions are arranged in parallel, and
the node of the standing wave is consistent with a bending back
point.
[0020] In the above plasma processing apparatus, a plurality of
electrodes are arranged to make a stratified structure comprising a
plurality of layers within the vacuum processing chamber, a
plurality of film depositing regions are produced using the space
between the electrodes included in the plurality of layers, and
film deposition on a substrate is performed in each of the
plurality of film depositing regions.
[0021] The plasma processing apparatus of the present invention
comprises a plurality of electrodes of an inductive coupling type
in a vacuum processing chamber, and each of the plurality of
electrodes is formed by bending back a conductor at its central
portion to be U-shaped, the straight portions formed by the bending
back are made parallel and are arranged to be in one plane, and
further one end of each of the electrodes is grounded and another
end thereof is connected to a high frequency power source. Further,
the plurality of electrodes positioned parallel to each other are
placed so that a straight portion of a power supplying side is
adjacent to a straight portion of a grounded side, and high
frequency powers respectively supplied into the ends of the
straight portions of power supplying side for the plurality of
electrodes are in phase.
[0022] In the above plasma processing apparatus, the length of each
straight portion formed by bending back the plurality of electrodes
is determined to produce an antinode of a standing wave on the
straight portion.
[0023] In the above plasma processing apparatus, plural electrodes
arranged to be in one plane is configured as an electrode array, a
plurality of the electrode arrays are placed as a stratified
structure within the vacuum processing chamber, a plurality of film
depositing regions are produced using a space between said
electrode arrays of plural layers, and film deposition on a
substrate is performed in each of the plurality of film depositing
regions.
[0024] The plasma processing apparatus of the present invention
comprises an electrode of an inductive coupling type in a vacuum
processing chamber and the electrode is formed by bending back a
conductor at its central portion to be U-shaped. Further, a plasma
discharge is produced around the electrode by supplying a high
frequency power to an end of the electrode so that a standing wave
of half wavelength is produced at a straight portion formed by
bending back the electrode. In this case, frequency (f) of the high
frequency power at this time is determined by f=(c/{square
root}{square root over ( )}.epsilon..sub.p)/2L1, where c is the
speed of light, L1 is the length of the straight portion formed by
bending back the electrode, and .epsilon..sub.pis the relative
dielectric constant of plasma produced around the electrode.
[0025] In the above plasma processing apparatus, the frequency of
the high frequency power is changed according to plasma parameters
around the electrode.
[0026] In the above plasma processing apparatus, a plasma CVD
processing is performed for depositing a film with a solar cell
function on a large area substrate within the vacuum processing
chamber.
[0027] In the above plasma processing apparatus, the length L1 of
the electrode is preferred to be more than 0.8 meter.
[0028] The plasma processing method of the present invention is the
processing method executed in the plasma processing apparatus
having an electrode of an inductive coupling type placed within a
vacuum processing chamber, and the plasma processing method is
characterized in that the electrode is formed by bending back a
conductor at its central portion, a total length of the electrode
is determined to be a natural number times of a half of an
excitation wavelength, a high frequency power is supplied to end of
the electrode, a node of a standing wave produced in the electrode
is consistent with a bending back point, and the standing wave
makes density distribution of plasma around the electrode to be
uniform.
[0029] The plasma processing method of the present invention is the
method executed in a plasma processing apparatus comprising an
electrode of an inductive coupling type in a vacuum processing
chamber, and the electrode is formed by bending back a conductor at
its central portion to be U-shaped, and a plasma discharge is
produced around the electrode by supplying a high frequency power
to an end of the electrode so that a standing wave of half
wavelength is produced at a straight portion formed by bending back
the electrode.
[0030] In the above plasma processing method, frequency (f) of the
high frequency power at this time is determined by f=(c/{square
root}{square root over ( )}.epsilon..sub.p)/2L1, where c is the
speed of light, L1 is the length of the straight portion formed by
bending back the electrode, and .epsilon..sub.p is the relative
dielectric constant of plasma produced around the electrode.
[0031] In the above plasma processing method, the frequency of the
high frequency power is changed according to plasma parameters
around the electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a front view of an electrode showing the internal
structure of a plasma processing apparatus according to a basic
embodiment of the present invention.
[0033] FIG. 2 is a side view of the inside of the basic
embodiment.
[0034] FIG. 3 is a front view of an electrode showing the internal
structure of another embodiment of the present invention.
[0035] FIG. 4 is a front view of an electrode showing the internal
structure of another embodiment of the present invention.
[0036] FIG. 5 is a side view of the inside of the above other
embodiment.
[0037] FIG. 6 is a view of an example of the mechanism for
conveying a substrate.
[0038] FIG. 7 is a side view of the internal structure of another
embodiment of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0039] The preferred embodiments of the present invention will be
described next with reference to the attached drawings.
[0040] The basic embodiment of the present invention will be
explained first with reference to FIG. 1 and FIG. 2. The plasma
processing apparatus according to this embodiment is, for example,
an inductive coupling type plasma CVD apparatus for depositing a
thin film having the function of a solar cell on a substrate.
[0041] The film-deposition chamber 11 is a reactor in which a film
is deposited or grown on a substrate conveyed inside by plasma CVD
and is able to be set to required vacuum conditions. The
film-deposition chamber 11 has a single electrode 12 arranged in a
vertical standing state, for example. The electrode 12 is supplied
with high frequency power as explained later through its one end.
This electrode 12 has the function of an antenna for supplying the
high frequency electric power to the film-deposition chamber 11.
The electrode 12 is preferably formed by a conductive wire
(conductive line-shaped member), which has a requisite length and
diameter with relation to the frequency of the supplied high
frequency power, bent back at its central portion (bent back point)
so as to be in one plane and thereby being given a substantially
U-shape when seen from the front view. The electrode 12 has a bent
back portion with a curved shape and two straight portions to be
substantially parallel.
[0042] In this embodiment, for example, the electrode 12 is
arranged to be vertical with the curved bent portion at the top and
the open ends at the bottom. Note that it is also possible to
arrange it with the curved bent portion at the bottom and the open
ends at the top. The structure supporting the electrode is not
illustrated, but any support structure can be employed.
[0043] By bending the conductive wire into two, a U-shaped
electrode 12 is formed, and the half length is shown by L3 in the
figure as the length between the center point 12a and the ends. The
portion of the length L3 is the length of a straight portion formed
by bending back the electrode 12 (hereinafter referred to as "the
bent back straight portion") and is the portion in which the
antinode of the standing wave is produced.
[0044] In the electrode 12, the high frequency power is supplied to
the end 12b. A high frequency generator or power source 13
supplying the high frequency power is provided at the outside of
the film-deposition chamber 11. The feeder 14 from the high
frequency generator 13 is led through a connection part 15 provided
at the film-deposition chamber 11 into the inside of the
film-deposition chamber 11 and connected to the end 12b of the
electrode 12. By this, the high frequency power is supplied to the
electrode 12. The connection part 15 has a built-in feed-through
structure by which the feeder passes through the wall of the
film-deposition chamber 11. The end 12b of the electrode 12 serves
as the feeding point.
[0045] The other end 12c of the electrode 12 is electrically
connected to the film-deposition chamber 11. The film-deposition
chamber 11 is made of a conductive member (metal member) and is
maintained at the ground potential by being grounded. Therefore,
the other end 12c of the electrode 12 is grounded. The other line
13a of the high frequency generator 13 is grounded.
[0046] The two ends of the U-shaped electrode 12 are supplied by
the high frequency generator 13 with a high frequency power of a
frequency higher than the conventionally used high frequency power
(for example, 13.56 MHz). The high frequency power used here is a
high frequency power having the frequency of 60 MHz or more, for
example. In the case of the present embodiment, however, the
frequency of the high frequency power supplied to the electrode 12
is determined by a specific method, explained later, in
consideration of the plasma parameters around the electrode 12.
[0047] A single backing plate 16 is, for example, arranged in a
state parallel to the plane containing the electrode 12 at one side
of the electrode 12. Also, for example, four disk-shaped substrates
17 are arranged on the surface of the backing plate 16 facing the
electrode. The backing plate 16 has the function of a substrate
holder with a built-in heater. Also, the four substrates 17 are
arranged on the backing plate 16 along the longitudinal direction
of the U-shaped electrode 12. As shown in FIG. 1, in this
embodiment, the four substrates 17 are placed to exist
corresponding to the position of the space between the two straight
portions of the U-shaped electrode 12.
[0048] The plasma CVD apparatus according to the present embodiment
uses the inductive coupling type electrode, so unlike a parallel
plate type electrode, the above backing plate is not necessarily
essential. Use of the backing plate is however preferable to
improve the uniformity of the substrate temperature and to shield
the heater panel from the electromagnetic field. Note that in the
plasma CVD apparatus shown in FIG. 1 and FIG. 2, for convenience in
explanation, the illustrations of the source gas feed mechanism,
the vacuum evacuation mechanism (vacuum pump), the substrate
holder, the detailed structure of the substrate heating mechanism,
the substrate cooling mechanism, etc. are omitted.
[0049] The conductive wire used for the electrode 12 is for example
rod-shaped and is made from a metal material such as stainless
steel or aluminum. When the electrode 12 is rod-shaped, its
diameter is for example at least 5 mm. In FIG. 1, the relationship
between the length of the straight portions L1 formed by bending
back the conductive wire into two and the width between the two
bent back portions L2 is drawn with the length L2 shown exaggerated
larger than it actually is for convenience in the explanation. As
an actual preferable embodiment, L1 is for example 75 cm to 2.0 m
and L2 is for example about 8 cm. Therefore, the degree of
curvature of the upper bent portion of the actual electrode 12 is
also not as large as illustrated. In FIG. 1, as the lengths of the
bent back portions of the electrode, the length L1 of the straight
portion and the length L3 including half of the bent portion are
shown, but the bent portion is considerably smaller than the
straight portions in length, so the length L1 and the length L3 may
be considered to be substantially the same in practice.
[0050] The length L1, in practice, is determined in accordance with
the size of the substrate on which the film is to be deposited and
is set as the length necessary for generating a standing wave, so
is determined by the relation with the frequency of the high
frequency power supplied. For example, when the frequency is 120
MHz, L1 becomes 1.25 m.
[0051] In principle, the length L1 (or length L3) of the bent back
straight portions in the electrode 12 is found by the relationship
of
L1=c/2f=.lambda./2(or f=c/2L1) . . . (1)
[0052] where f is the frequency of the high frequency power
supplied, c is the speed of light, and .lambda. is the wavelength.
According to this relationship if the size (dimensions etc.) of the
electrode is determined in relation to the substrate (glass etc.),
the frequency of the high frequency power supplied to the electrode
is determined. Conversely, if the frequency of the high frequency
power is determined, the dimensions etc. of the electrode are
determined.
[0053] According to the above relationship (1), L1 becomes
substantially equal to half of the wavelength of the high frequency
power, while the total length L0 (=2L1) of the electrode 12 becomes
substantially .lambda..
[0054] If the frequency becomes smaller than 120 MHz, the length L1
becomes larger than 1.25 m and the electrode cannot be provided
inside the film-deposition chamber 11 in some cases. In such a
case, for example, it is possible to reduce the length L1 by adding
a coaxial cable structure to the ends of the electrode in order to
provide a delayed wave structure relating to the electromagnetic
wave. L1 is preferably set to a range of 75 cm to 1.25 m by doing
this as explained above. The lengths L1 and L2 may be freely
changed in accordance with the objective.
[0055] According to the electrode 12 having the above shape, if a
high frequency power is supplied from the high frequency generator
13, standing waves with half of the wavelength can be formed at the
straight portions formed by bending back the electrode, that is,
the two straight portions having the length L1. The standing wave
formed on the electrode is controlled so as to produce the
antinodes of the standing wave at the central part of each of the
two straight portions and the node at the center point 12a which is
the bent back point.
[0056] In other words, the shape and dimentions of the electrode 12
is designed and the frequency of the high frequency power supplied
to the electrode 12 is determined so that the standing waves are
positively created having, for example, one antinode at each of the
two parallel straight portions of the electrode 12. Further, when
supplying the high frequency power from the high frequency power
generator 13 to the U-shaped electrode 12, one end 12b is made to
be the feeding point and the other end 12c is connected to the
ground. By doing this, the standing wave of one wavelength is
generated on the electrode 12 with controlled standing waves
generated at the two straight portions of the electrode 12. In the
standing waves of the half wavelength generated at each of the two
straight portions of the U-shaped electrode 12, their antinodes are
consistent in their positions and they mutually intensifies at the
region between the straight portions. As a result, plasma with a
uniform density is generated in the region between the two straight
portions of the electrode 12 and in the surrounding regions.
[0057] As explained above, by the film-deposition chamber 11
provided with the electrode 12, when the inside of the
film-deposition chamber 11 is evacuated to a required vacuum state
by the vacuum pump, filled with a source gas etc. and a high
frequency power of for example 100 MHz is fed through the end 12b
to the electrode 12, controlled standing waves are produced at the
two straight portions and plasma 18 having a uniform density is
generated in the space surrounding the U-shaped electrode 12. A
film is deposited on the four disk-shaped substrates 17 provided on
the backing plate 16 by the resultant plasma CVD action. The
standing wave is formed at each of the halves of the electrode 12
from the center point 12a, that is, the above-mentioned two
straight portions. The standing waves control the plasma 18 to
achieve a good distribution of the plasma. In particular, as
mentioned above, the electrode 12 is designed so that the standing
waves with half wavelength produced at the two straight portions
are strengthened, so there is no fall in the density of the plasma
18 produced in the space surrounding the electrode 12 and the
plasma 18 is controlled in state to the preferable distribution of
density.
[0058] Note that the number of the antinodes at each of the two
bent back straight portions of the electrode 12 is not necessarily
limited to one. For example, it is possible to produce the standing
waves having plural antinodes by supplying the high frequency power
with the frequency higher than 100 MHz to the electrode 12 with
above-mentioned dimensions. In this case, the relationship between
the total length of the electrode 12 and the wavelength of the
supplied high frequency power used for the excitation, is
maintained, so that the total length of the electrode is a natural
number times of the half of the excitation wavelength, and a node
is formed at the bent back point of the U-shaped electrode 12.
[0059] As the relationship between the total length of the
electrode and the wavelength of the supplied high frequency, by
selecting the wavelength to form a standing wave at the bent back
straight portions of the electrode 12 as mentioned above, a strong
electromagnetic field strength can be generated in the region
surrounding the electrode functioning as the antenna. If a
discharge frequency becomes different from the designed one, a
traveling wave from the feeding point of the electrode and a
reflecting wave returned from the grounding point cancel each other
on the electrode, and consequently effective electromagnetic field
can not be produced around the electrode. This matter can be
experimentally observed as a phenomenon that the electric discharge
does not happen without giving the specific relationship between
the length of the electrode (the length of the antenna) and the
wavelength of the excitation high frequency.
[0060] Especially, if the total length of the electrode is equal to
one wavelength, the node is made at the feeding point, the bent
back point or the grounding point, and the electromagnetic field
having the strength not being zero is produced at the remaining
portions. Therefore, by making use of the electromagnetic field not
being zero, plasma is generated and uniform film deposition can be
performed around the center of the straight portions of the
electrode.
[0061] Further, in the above structure, the bent portion of the
U-shaped electrode 12 does not have to be exactly a curved shape
and it may be bent sharply or in an angled shape. Also, the two
straight portions of the electrode 12 are unnecessary to be
strictly parallel. The shape of the electrode may be of V-shaped,
for example, instead of the U-shaped one.
[0062] Further, it is possible to make the electrode having a shape
similar to the U-shaped one as a whole by arranging the two
different straight conductors in parallel and coupling the ends of
them with another coupling member. That is, it is possible to form
the electrode 12 by making the U-shape with the combination of some
conductors.
[0063] Also, in the above structure, although the electrode 12 is
placed in the vertical standing state to be toward a vertical
direction, it may be placed in a lateral state to be toward a
horizontal direction. In this case, the backing plate and the
substrate are also arranged in the lateral state of the horizontal
direction.
[0064] According to the above embodiment, since an inductive
coupling type electrode is used, there is the advantage that the
plasma density can easily be raised compared with a capacitive
coupling type electrode. Further, by making the electrode U-shaped
and using one of the ends of the electrode as the feeding point,
due to the interaction of the standing waves produced at the two
bent back straight portions, the plasma is strengthned and the
density of the plasma can be kept from becoming nonuniform.
[0065] Further, according to the above embodiment, it is possible
to manufacture the electrode more inexpensively than a parallel
plate type electrode and the electrode is suited to depositing a
film on a large area substrate.
[0066] When using a high frequency power of 100 MHz for example,
the wavelength .lambda. of the high frequency power is 3 m.
Therefore, the size of the electrode 12 becomes about 150 cm
(length).times.12 cm (width), while the area effective for
depositing a film becomes 120 cm.times.10 cm or so. In FIG. 1 and
the like, disk-shaped substrates were drawn as the objects on which
the film is to be deposited, but the plasma CVD apparatus of the
present embodiment is more suited to depositing a film on
rectangular substrates. Further, it is also suited to form films on
not only stationary objects, but also on large-area moving
substrates. By the use of the above internal electrode type plasma
CVD apparatus with high frequency power, the ion bombardment on the
depositing film is reduced, good film characteristics can be
obtained, and a large area, high quality film can be formed.
[0067] Next, the practical conditions of the basic method of
designing the internal electrode explained above will be
considered.
[0068] The following modifications may be considered in the
electrode design (antenna design) in view of the practical
conditions. If the high frequency power is given from the high
frequency generator 13 to the electrode 12, an electric discharge
occurs and plasma is produced around the electrode 12 when an
discharge gas is introduced into the film-deposition chamber 11 and
the requisite vacuum state and other conditions are met. If plasma
is produced around the electrode 12, the value of the relative
dielectric constant of the surrounding space as determined by the
initial basic electrode design (relative dielectric constant
.epsilon..sub.r at free space) becomes different. As a result,
while a standing wave of half the wavelength was supposed to be
produced at the portion of half the length of the electrode in
relation with the length of the electrode, this design no longer
holds true. Therefore, when dimensional conditions of the electrode
12 are given, the occurrence of the discharge around the electrode
12 after supplying the high frequency power should be envisioned
and the frequency of the high frequency power determined
envisioning plasma parameters.
[0069] If the discharge occurs around the electrode 12 and plasma
is generated, the relative dielectric constant of the space around
the electrode 12 is no longer 1. Therefore, the frequency of the
high frequency power supplied to the electrode 12 is determined in
consideration of the discharge conditions around the electrode 12.
That is, if the relative dielectric constant of the plasma around
the electrode 12 is .epsilon..sub.p, the frequency f is determined
by (c/{square root}{square root over ( )}.epsilon..sub.p)/2L1 . . .
(2). Note that the relative dielectric constant .epsilon..sub.p is
given by the formula:
.epsilon..sub.p=1-.omega..sub.p.sup.2/.omega.(.omega.-j.nu.) . . .
(3). Here, .omega..sub.P is the plasma frequency determined by the
electron density, .omega. is the discharge frequency, and .nu. is
the collision cross section determined by the discharge pressure.
The .epsilon..sub.p of the above formula (2) is the value of the
real part of formula (2) and is not necessarily limited to 1 or
more.
[0070] Since the dielectric constant of the plasma differs
depending on the discharge conditions, the determination of the
frequency is extremely difficult. Therefore, in practice, the
optimal discharge frequency is determined by experiments.
[0071] Another embodiment of the present invention will be
explained next with reference to FIG. 3. FIG. 3 is a view similar
to the above-mentioned FIG. 1. In FIG. 3, elements substantially
the same as elements explained with reference to FIG. 1 are
assigned the same reference numerals. In this embodiment, an
inductive coupling type plasma CVD apparatus of the internal
electrode type provided with electrodes having a configuration
suitable for depositing a film on a larger sized rectangular
substrate 21 is shown. The rectangular substrate 21 has a large
area and is preferably a glass substrate on which a film of
amorphous silicon is deposited for used as a solar cell. Plasma
generating area is set over a broad area to face the
film-deposition surface of this large area large-sized rectangular
substrate 21, and therefore, the portion relating to the electrode
is provided with five electrodes which are same as the
above-mentioned U-shaped electrode 12. The five electrodes 22A,
22B, 22C, 22D and 22E are arranged to be included in a single plane
parallel to the film-deposition surface of the rectangular
substrate 21, which is vertical for example, and are provided in a
line so that their straight portions are parallel with each other
and preferably at equal intervals. In the electrode unit comprised
by the electrodes 22A to 22E, the electrodes are arranged with
their bent portions at the top and the ends at the bottom. Each of
the electrodes 22A to 22E is secured to the bottom wall of the
film-deposition chamber 11. One end of each of the electrodes is
provided with a connection portion 15, while the other end is
connected to the film-deposition chamber 11 so as to be grounded.
Further, the film-deposition chamber 11 shown in FIG. 3 is formed
to be larger than the film-deposition chamber shown in FIG. 1 along
with the larger size of the rectangular substrate 21. Note that the
film-deposition chamber 11 is grounded as explained before.
[0072] In the configuration shown in FIG. 3, the five electrodes
22A to 22E are separately attached to the film-deposition chamber
11, but the electrodes array is configured so that the standing
waves are generated at the two parallel straight portions of each
of the electrodes as mentioned above.
[0073] Each of the five electrodes 22A to 22E is supplied through
its connection portion 15 with the high frequency power having a
predetermined frequency from the single high frequency generator 13
provided at the outside of the film-deposition chamber 11 keeping
the same phase relationship. The method of determination of the
frequency of the high frequency power supplied is as explained in
the previous embodiment, and the frequency is determined in
consideration of the discharge conditions. The high frequency power
supplied from the high frequency power generator 13 to each of the
electrodes 22A to 22E is set so that the controlled standing waves
are produced at the straight portions of each of the
electrodes.
[0074] The standing waves produced at the straight portions of the
electrodes 22A to 22E are, as explained above, is controlled so
that the plasma density of the space around the electrodes become
uniform.
[0075] The above technical contents will be explained concretely.
In FIG. 3, the electrode 22C is paid attention. In the electrode
array, the power-supplied side of the straight portion of the
electrode 22C is adjacent to the grounded side of the straight
portion of the electrode 22B at the left side, and the grounded
side of the straight portion of the electrode 22C is adjacent to
the power-supplied side of the straight portion of the electrode
22D at right side. Watching only the electrode 22C, the vectors'
direction of the electromagnetic field is reversed in a phase
aspect between the power-supplied and the grounded straight
portions in the electrode 22C. The electromagnetic field in the
region between the power-supplied and the grounded straight
portions in the electrode 22C is made stronger in its density by
mutual action. As to the outsides of the power-supplied and the
grounded straight portions of the electrode 22C, based on the
relationship of the adjacent electrodes 22B and 22D and the supply
of the high frequency power to the electrodes 22B and 22D, whose
phase is identical to that of the high frequency power supplied to
the electrode 22C, the same relationship of strengthening the
electromagnetic field is also made in the respective regions
between the power-supplied side straight portion of the electrode
22C and the grounded side straight portion of the electrode 22B,
and between the grounded side straight portion of the electrode 22C
and the power-supplied side straight portion of the electrode 22D.
Thereby, the plasma of uniform density is generated in each of
those regions. The above-mentioned characteristics are realized in
the every one of electrodes 22A to 22E.
[0076] Therefore, in the space in front of the film-deposition
surface of the rectangular substrate 21, no unevenness of intensity
of the electromagnetic field is produced, plasma is generated with
a uniform distribution of density, and a film of a uniform
thickness is deposited on the large-area rectangular substrate 21.
By controlling the standing waves generated at the electrodes to
the desired states as mentioned above, the uniformity of film
thickness can be improved.
[0077] In the above embodiment, the number of electrodes may be
freely set in accordance with the size of the substrate on which
the film is being deposited. Further, while use of a single high
frequency generator is preferable, plural generators may also be
used.
[0078] Next, further, another embodiment of the present invention
will be explained with reference to FIG. 4 and FIG. 5. In these
figures, elements substantially the same as elements explained with
reference to the previous embodiments are assigned the same
reference numerals. In this embodiment, three-layered electrode
arrays 33, 34 and 35, each comprised of three electrodes 32A, 32B
and 32C, are provided in a stratified configuration at
predetermined intervals from each other. The individual electrodes
32A to 32C are configured in the same way as the electrode 12
explained in the above-mentioned basic embodiment. In each of the
three-layered electrode arrays 33 to 35, the electrodes 32A to 32C
are arranged to be contained at equal intervals in the same
vertical plane. Further, the three electrode arrays 33 to 35 are
arranged so that the planes they form are parallel. Rectangular
substrates 31 are arranged at the two sides of each of the
electrode arrays 33 to 35 so that their film-deposition surfaces
are parallel to the planes formed by the electrode arrays. The
rectangular substrates 31 are here glass substrates. Further, as
shown in FIG. 5, heaters 36 are arranged at the outside of the
outermost rectangular substrates in the film-deposition chamber 11.
The heaters 36 hold the rectangular substrates 31 at a
predetermined temperature. The film-deposition chamber 11 is
grounded.
[0079] In the above, each of the electrodes 32A to 32C of the
electrode arrays 33 to 35 is supplied with the high frequency power
from the single high frequency generator through the connection
portion 15. The frequency of the high frequency power supplied to
each electrode is, in the same way as explained in the above
embodiments, determined considering the plasma parameters around
the electrodes. As explained above, the controlled standing waves
are produced at each of the electrodes 32A to 32C of the electrode
arrays 33 to 35. Uniform plasma is produced at the two sides of
each of the electrodes 32A to 32C of the electrode arrays 33 to 35
when the film-deposition chamber 11 is held in the required vacuum
state and source gas etc. is introduced. A film is deposited on the
film-deposition surfaces of the six rectangular substrates 31 based
on the plasma CVD action using the high frequency power (for
example, RF). Further, in the configuration of this embodiment,
since the electrodes are inductive coupling types, no backing
plates are required for holding the rectangular substrates 31 at
the ground potential. The same is true of the case of the
embodiment of the configuration shown in FIG. 3. In FIG. 4 and FIG.
5, only the substrates 31 were shown, but in practice the
substrates 31 are held by support frames. The support frames have
window-frame shaped structures.
[0080] FIG. 6 shows a window-frame shaped support frame 37 that
sets and supports two substrates 31. A substrate conveying
mechanism 38 is provided at the bottom of the support frame 37 and
is designed to move the substrates 31 on a guide path. The
substrates 31 are conveyed in a direction vertical to the paper
surface in FIG. 5 or FIG. 6.
[0081] Since the U-shaped electrode is shaped with the feeding end
and ground end positioned in the same plane and a plurality of
U-shaped electrodes can be arranged so as to be in the same plane
as well, a multi-region (or zone) deposition device can be easily
realized by utilizing a layered or stratified structure of
electrodes arranged at predetermined intervals as shown in FIG. 5.
By enabling the multi-region film deposition in this way, films can
be formed on a plurality of substrates simultaneously and the
throughput of film deposition can be improved. If utilizing the
layered structure, further, the ratio of the surface area of the
film-deposition surfaces of the rectangular substrates to the
volume inside the film-deposition chamber becomes larger, so escape
of heat can be suppressed and the power consumption can be
suppressed.
[0082] Further, according to the above embodiment, since the
backing plates of the substrates on which films are to be deposited
can be omitted, the cost of the power used for raising the
temperature of the backing plates, the cost of the cooling water
required for cooling the backing plates, the running costs required
for handling the backing plates, the hardware costs due to the load
on the conveyance mechanism, and other costs conventionally
required can be eliminated. Further, the conventional system
provided with backing plates suffered from the problem of lack of
uniformity of film thickness or poor film characteristics due to
the uneven degree of contact between the backing plates and
substrates, but this problem is eliminated.
[0083] FIG. 7 shows another embodiment of the present invention. In
this embodiment, a structure is shown where the U-shaped electrodes
of the present invention are provided in the plasma CVD apparatus
of the type using substrate carriers for conveyance. The part of
the structure relating to the U-shaped electrodes is substantially
the same as the structure shown in FIG. 5. Therefore, in FIG. 7,
elements substantially the same as the elements shown in FIG. 5 are
assigned the same reference numerals. In this embodiment, a
substrate conveyance mechanism 42 provided with a substrate support
mechanism 41 is provided at the bottom of the film-deposition
chamber 11. Therefore, electrode arrays 33 to 35 having the above
three-layered structure are arranged attached to the top wall of
the film-deposition chamber 11 and hanging down vertically in the
film-deposition chamber 11. The rest of the structure is the same
as that explained in FIG. 5. The plurality of substrates 31
supported by the substrate support mechanism 41 are conveyed in a
direction vertical to the paper surface in FIG. 7 by the substrate
conveyance mechanism 42 after the films are finished being formed
on them.
[0084] In this embodiment as well, it is possible to form a film
simultaneously on a plurality of substrates by multi-region
deposition and there is no need to provide the backing plates for
the substrates on which the films are to be formed, so the effects
explained with respect to the above embodiments are also
exhibited.
[0085] In the above-mentioned embodiments, the bent portions and
ends of the electrodes may be provided with covers formed by a
dielectric (insulator) to cover them. The covers function as
electromagnetic shields blocking the electromagnetic field from the
electrode. The covers may also be given the function of elements
for adjusting the impedance of the electrode. The covers may for
example be given a coaxial cable structure.
[0086] In the above-mentioned embodiments, the total length of the
U-shaped electrode was set to be equal to the excitation wavelength
(.lambda.), but a similar action can be obtained by an electrode
having a general bent back shape where the total length of the
electrode is made natural number (a whole) times of a half of the
excitation wavelength of the high frequency power supplied if in
this case supplying a high frequency power from the end of the
electrode and making the node of the standing wave produced at the
electrode match with the bent back point of the electrode.
[0087] While the invention has been described with reference to
specific embodiment chosen for purpose of illustration, it should
be apparent that numerous modifications could be made thereto by
those skilled in the art without departing from the basic concept
and scope of the invention.
Industrial Applicability
[0088] As mentioned above, the internal electrode type plasma
processing apparatus and method according to the present invention
is suited to deposit the film onto the large area substrate, and is
useful of making the solar cells by depositing the amorphous
silicon thin film on the large substrates, for example.
* * * * *