U.S. patent application number 13/133230 was filed with the patent office on 2011-09-29 for catalytic chemical vapor deposition apparatus.
This patent application is currently assigned to ULVAC, INC.. Invention is credited to Shin Asari, Masanori Hashimoto, Shuji Osono.
Application Number | 20110232573 13/133230 |
Document ID | / |
Family ID | 42242435 |
Filed Date | 2011-09-29 |
United States Patent
Application |
20110232573 |
Kind Code |
A1 |
Osono; Shuji ; et
al. |
September 29, 2011 |
Catalytic Chemical Vapor Deposition Apparatus
Abstract
[Object] To provide a catalytic chemical vapor deposition
apparatus capable of prolonging the service life of a catalyst
wire. [Solving Means] In a catalytic chemical vapor deposition
apparatus (1) according to the present invention, a catalyst wire
(6) including a tantalum wire and a boride layer formed on a
surface of the tantalum wire is used. The boride of the metal
tantalum (tantalum boride) is harder than the metal tantalum.
Therefore, by using the tantalum wire having the boride layer
formed on the surface thereof as a catalyst wire, it is possible to
reduce thermal expansion of the catalyst wire, improve mechanical
strength, and prolong the service life. Further, by performing
energization heating of the catalyst wire (6) by continuous
energization, it is further possible to prolong the service life of
the catalyst wire (6).
Inventors: |
Osono; Shuji; (Chiba,
JP) ; Hashimoto; Masanori; ( Chiba, JP) ;
Asari; Shin; (Chiba, JP) |
Assignee: |
ULVAC, INC.
Sammu-shi, Chiba
JP
|
Family ID: |
42242435 |
Appl. No.: |
13/133230 |
Filed: |
December 9, 2008 |
PCT Filed: |
December 9, 2008 |
PCT NO: |
PCT/JP2008/072353 |
371 Date: |
June 7, 2011 |
Current U.S.
Class: |
118/724 |
Current CPC
Class: |
C23C 16/06 20130101;
C23C 8/08 20130101; C23C 16/4488 20130101; C23C 16/46 20130101;
C23C 16/345 20130101; C23C 18/02 20130101; C23C 16/24 20130101 |
Class at
Publication: |
118/724 |
International
Class: |
C23C 16/00 20060101
C23C016/00 |
Claims
1. A catalytic chemical vapor deposition apparatus, comprising: a
reaction chamber; a gas introduction source to introduce a source
gas to the reaction chamber; a catalyst wire including a tantalum
wire and a boride layer formed on a surface of the tantalum wire,
and arranged to be opposed to a substrate to be processed that is
installed in the reaction chamber; and a heat source to heat the
catalyst wire.
2. The catalytic chemical vapor deposition apparatus according to
claim 1, further comprising a control means for performing
energization heating of the catalyst wire with the heat source by
continuous energization.
Description
TECHNICAL FIELD
[0001] The present invention relates to a catalytic chemical vapor
deposition apparatus that supplies a source gas to a heated
catalyst wire installed in a reaction chamber and deposits
generated decomposition species on a base material to be
film-formed in the reaction chamber, to thereby perform film
formation.
BACKGROUND ART
[0002] Catalytic-chemical vapor deposition (CAT-CVD) is a film
formation method of supplying a reactive gas (source gas) to a
catalyst wire heated to, for example, 1,500 to 2,000.degree. C. and
depositing decomposition species (deposited species) generated
using catalysis or thermal decomposition reaction of the reactive
gas on a base material to be film-formed.
[0003] The catalytic-chemical vapor deposition is similar to plasma
CVD in that decomposition species of a reactive gas are deposited
on a base material to thereby perform film formation. However, in
the catalytic-chemical vapor deposition, decomposition species are
generated using catalysis or thermal decomposition reaction of the
reactive gas on a catalyst wire having a high temperature.
Therefore, the catalytic-chemical vapor deposition has an advantage
that surface damage due to plasma is not caused and a use
efficiency of a source gas is high, as compared to the plasma CVD
in which plasma is formed to generate decomposition species of a
reactive gas.
[0004] For example, the catalytic-chemical vapor deposition is used
when a silicon (Si)-based film is formed. Conventionally, for a
catalyst wire used in the catalytic-chemical vapor deposition, a
tungsten (W) wire is widely used (see, for example, Patent Document
1). However, tungsten is prone to undergo an alloying reaction with
silicon (silicidation). When tungsten is silicided, cracks are
generated on the surface and the mechanical strength is reduced,
which shortens the service life of the catalyst wire.
[0005] On the other hand, examples of a material having a lower
silicidation speed than that of tungsten include tantalum (Ta).
There is a method of using a tantalum wire as a catalyst wire to
form a silicon film (see, for example, Patent Document 2). [0006]
Patent Document 1: Japanese Patent Application Laid-open No.
2003-303780 [0007] Patent Document 2: Japanese Patent Application
Laid-open No. 2003-247062
DISCLOSURE OF THE INVENTION
Problem to be Solved by the Invention
[0008] However, tantalum has lower mechanical strength than that of
tungsten, and particularly has low creep strength when used in high
temperature. Therefore, in the case where metal tantalum is used
for a catalyst wire, there arise problems that thermal expansion is
caused at a time of heating, and accordingly a wire diameter is
made small and wire resistance is made large, a wire temperature is
raised, and blowout is prone to occur. Therefore, it is impossible
to improve productivity.
[0009] Further, Patent Document 2 discloses a catalyst wire
obtained by coating a surface of a tantalum wire with boron nitride
(BN). However, the coating with boron nitride is insufficient to
prolong the service life of the tantalum catalyst wire, and further
improvement is demanded.
[0010] The present invention has been made in view of the problems
described above and has an object to provide a catalytic chemical
vapor deposition apparatus capable of prolonging the service life
of a catalyst wire.
Means for Solving the Problem
[0011] According to an embodiment of the present invention, there
is provided a catalytic chemical vapor deposition apparatus
including a reaction chamber, a gas introduction source, a catalyst
wire, and a heat source. The gas introduction source introduces a
source gas to the reaction chamber.
[0012] The catalyst wire includes a tantalum wire and a boride
layer formed on a surface of the tantalum wire and is arranged to
be opposed to a substrate to be processed that is installed in the
reaction chamber.
[0013] The heat source heats the catalyst wire.
BEST MODES FOR CARRYING OUT THE INVENTION
[0014] According to an embodiment of the present invention, there
is provided a catalytic chemical vapor deposition apparatus
including a reaction chamber, a gas introduction source, a catalyst
wire, and a heat source.
[0015] The gas introduction source introduces a source gas to the
reaction chamber.
[0016] The catalyst wire includes a tantalum wire and a boride
layer formed on a surface of the tantalum wire and is arranged to
be opposed to a substrate to be processed that is installed in the
reaction chamber.
[0017] The heat source heats the catalyst wire.
[0018] According to the structure described above, the boride of
the metal tantalum (tantalum boride) is harder than the metal
tantalum. Therefore, by using the tantalum wire having the boride
layer formed on the surface thereof as a catalyst wire, it is
possible to reduce thermal expansion of the catalyst wire, improve
the mechanical strength, and prolong the service life. Further,
according to the structure described above, the service life can be
prolonged as compared to a catalyst wire obtained by coating the
surface of the tantalum wire with boron nitride or carbon.
[0019] As a method of forming a boride layer on a surface of a
tantalum wire, a tantalum wire is installed in a reaction chamber
and is subjected to energization heating while a diborane
(B.sub.2H.sub.6) gas is introduced in the reaction chamber. A film
thickness of a boride layer is not particularly limited and can be
adjusted as appropriate based on a heating temperature of the
tantalum wire, a gas concentration of the diborane gas, a reaction
time, or the like.
[0020] The catalytic chemical vapor deposition apparatus may
further include a control means for performing energization heating
of the catalyst wire with the heat source by continuous
energization.
[0021] According to the structure described above, the tantalum
wire having the boride layer formed on the surface thereof is used
as a catalyst wire and subjected to energization heating to perform
film formation. At this time, the control means for performing
energization heating of the catalyst wire by continuous
energization is installed and the energization heating of the
catalyst wire is successively performed during film formation, with
the result that a heat shock given to the catalyst wire can be
relieved, the generation of cracks on the boride layer can be
suppressed, and the service life of the catalyst wire can be
prolonged.
[0022] Hereinafter, embodiments of the present invention will be
described with reference the drawings.
[0023] FIG. 1 is a schematic structural view of a catalytic
chemical vapor deposition apparatus according to an embodiment of
the present invention. A catalytic chemical vapor deposition
apparatus 1 includes a vacuum chamber 3 in which a reaction chamber
2 is formed. To the vacuum chamber 3, a vacuum pump 4 is connected
so that the reaction chamber 2 can be evacuated to a predetermined
degree of vacuum. The reaction chamber 2 is formed inside an
anti-adhesive plate 5 installed in the vacuum chamber 3.
[0024] Inside the reaction chamber 2 partitioned by the
anti-adhesive plate 5, a plurality of catalyst wires 6 are
installed. The catalyst wires 6 are each constituted of a tantalum
(Ta) wire. In this embodiment, the plurality of catalyst wires 6
are set parallel to each other so as to cross the inside of the
reaction chamber 2 in a vertical direction. It should be noted that
the installation form of the catalyst wires 6 is not limited to the
above-mentioned vertical direction, and the catalyst wires 6 may be
installed in a form of crossing the reaction chamber 2 in a
horizontal direction.
[0025] The respective catalyst wires 6 are installed so as to pass
through through-holes 5a and 5b formed on a top surface and a
bottom surface of the anti-adhesive plate 5, and both end portions
thereof are connected to a control unit 8 (control means) set
outside the vacuum chamber 3. The control unit 8 includes a heat
source to perform energization heating on the catalyst wires 6. The
control unit 8 is for performing energization heating of the
catalyst wires 6 by continuous energization, and is constituted of
a computer or the like that adjusts a current supply source and
supply current.
[0026] Inside the reaction chamber 2, a substrate S serving as a
base material to be film-formed is set. For the substrate S, for
example, a rectangular glass substrate is used. In this embodiment,
as shown in FIG. 2, two substrates S are opposed to each other so
as to sandwich the catalyst wires 6 therebetween. Here, the
substrates S are installed in the reaction chamber 2 such that a
long side direction of the substrates S is orthogonal to an
extending direction of the catalyst wires 6. It should be noted
that the substrates S are supported by a substrate support means
(not shown). The substrate support means has a structure
incorporating a heat source to heat the substrates S to a
predetermined temperature.
[0027] The anti-adhesive plate 5 has a substantially rectangular
solid shape, and gas introduction pipes 7 are installed at four
side portions of the anti-adhesive plate 5. The gas introduction
pipes 7 are for introducing a source gas or a diborane
(B.sub.2H.sub.6) gas to the reaction chamber 2, and are connected
to a source gas supply unit 9a and a diborane gas supply unit 9b
installed outside the vacuum chamber 3 via a gas supply line. The
source gas or diborane gas ejected from the gas introduction pipes
7 is mainly introduced between the two substrates S. It should be
noted that a gas introduction source is constituted of the source
gas supply unit 9a, the gas introduction pipes 7, and the like.
[0028] The catalytic chemical vapor deposition apparatus 1 is
constituted as described above. Next, the catalytic-chemical vapor
deposition of this embodiment using the catalytic chemical vapor
deposition apparatus 1 will be described.
First Embodiment
[0029] First, the vacuum pump 4 is operated to evacuate the vacuum
chamber 3 and reduce a pressure of the reaction chamber 2 to a
predetermined degree of vacuum (for example, 1 Pa). Next, a
diborane gas is introduced from the diborane gas supply unit 9b to
the reaction chamber 2 and the catalyst wires 6 are energized by
the control unit 8 to be heated to a predetermined temperature (for
example, 1,700.degree. C.) or more. At this time, due to contact of
the diborane gas with a surface of the catalyst wire 6, a tantalum
boride layer as a reaction product is formed on the surface of the
catalyst wire 6.
[0030] Since the tantalum wire having the boride layer formed on
the surface as described above is harder than a metal tantalum
wire, by using the tantalum wire having the boride layer formed on
the surface thereof as a catalyst wire, it is possible to reduce
thermal expansion of the catalyst wires 6 and improve the
mechanical strength to prolong the service life. It should be noted
that a film thickness of the boride layer is not particularly
limited and can be adjusted as appropriate based on a heating
temperature of the tantalum wire, a gas concentration of the
diborane gas, a reaction time, or the like.
[0031] It should be noted that the step of forming a boride layer
on the surface of the tantalum wire may be performed after the
substrates S are installed in the vacuum chamber 3, or may be
performed before the substrates S are installed therein. Further,
in a chamber to which a diborane gas supply line cannot be
provided, a catalyst wire of tantalum boride whose boride layer is
formed in advance somewhere else may be relocated.
[0032] Next, after the introduction of the diborane gas is stopped,
a source gas is introduced from the source gas supply unit 9a to
the reaction chamber 2. In this embodiment, a mixed gas of a silane
(SiH.sub.4) gas and hydrogen (H.sub.2) is used as a source gas to
form a silicon (Si) film on the surface of the substrate S. It
should be noted that a film to be formed on the surface of the
substrate S may be a silicon nitride film (SiN) formed using
silane, hydrogen, and ammonia (NH.sub.3), a silicon nitride film
formed using trisilylamine ((SiH.sub.3).sub.3N), ammonia, and
hydrogen, a silicon nitride film formed using hexamethyldisilazane
((CH.sub.3).sub.3SiNHSi(CH.sub.3).sub.3, abbreviated to HMDS), a
silicon oxide film (SiO) formed using silane, hydrogen, and oxygen
(O2) or dinitrogen monoxide (N.sub.2O), a silicon oxide film formed
using silane and tetraethoxysilane (Si(OC.sub.2H.sub.5).sub.4,
abbreviated to TEOS), a phosphorus-doped silicon film (n+Si film)
or a boron-doped silicon (p+Si film) formed using silane, hydrogen,
and phosphine (PH.sub.3) or diborane, a silicon carbide film formed
using silane, hydrogen, and acetylene or methane, a silicon germane
film formed using silane, hydrogen, and germane, a
polytetrafluoroethylene (registered trademark "Teflon") film formed
using silane and hexafluoropropylene oxide (abbreviated to HFPO),
or the like. It should be noted that in the case of performing
hydrogen treatment using a hydrogen gas, it is possible to achieve
objects to remove a termination of a defect in a silicon film or a
natural oxide film. Further, in the case of performing nitriding
treatment using an ammonia gas, it is possible to nitride
silicon.
[0033] Specifically, in the film formation step of the substrates
S, a DC voltage is applied to the catalyst wires 6 by the by the
control unit 8, and the catalyst wires 6 are heated to high
temperature of, for example, 1,700.degree. C. or more. Further, at
this time, the substrates S are heated to a predetermined
temperature (for example, about 300.degree. C.). The source gas is
introduced between the two substrates S opposed to each other from
the gas introduction pipes 7. Then, the source gas comes into
contact with the catalyst wires 6 heated to high temperature, and
decomposition species of a reactive gas generated by catalysis or
thermal decomposition reaction are deposited on the substrate S so
that a film is formed.
[0034] Here, when the energization heating of the catalyst wires 6
is performed by an on/off operation of applied current, a heat
shock (expansion due to heating or contraction due to cancel of
heating) given to the catalyst wires 6 becomes large. Therefore,
cracks are prone to be generated on the surface of the catalyst
wires 6 and the mechanical strength is lowered. In this regard, in
this embodiment, a heating temperature of the catalyst wires 6 is
controlled while the energization heating of the catalyst wires 6
is successively performed by the control unit 8 at a time of film
formation of the substrate S so that the heat shock given to the
catalyst wires 6 is reduced.
[0035] As the energization control method for the catalyst wire by
the control unit 8, a method of increasing/decreasing temperature
of the catalyst wires 6 in a plurality of steps (lamp-up/down) is
included in addition to a method of continuously controlling a
current amount and keeping the catalyst wires 6 to be heated to a
predetermined temperature. By those methods, it is possible to
suppress the generation of cracks on the boride layer formed on the
surface of the catalyst wire 6 and improve the mechanical
strength.
[0036] As described above, according to this embodiment, by using
the tantalum wire having the boride layer formed on the surface
thereof as the catalyst wire 6, it is possible to reduce the
thermal expansion of the catalyst wire 6, improve the mechanical
strength, prolong the service life, and improve the productivity.
Further, since the catalyst wire is formed of a material mainly
composed of tantalum, it is possible to suppress an alloying
reaction with the source gas (silicidation) and realize stable film
formation.
[0037] In addition, according to this embodiment, by successively
performing the energization heating of the catalyst wire 6 during
film formation, it is possible to relieve the heat shock given to
the catalyst wire, suppress the generation of cracks on the
superficial boride layer, and prolong the service life of the
catalyst wire. FIGS. 3A and 3B are SEM pictures each showing a side
surface of a catalyst wire having a boride layer formed on a
surface thereof. FIG. 3A shows an example in which energization
heating is intermittently performed (by on/off operation), and it
is apparent that surface cracks are generated. Further, FIG. 3B
shows an example in which energization heating is successively
performed, and the generation of surface cracks is not found.
Second Embodiment
[0038] Next, catalytic-chemical vapor deposition according to a
second embodiment of the present invention will be described.
[0039] The substrates S and tantalum wires serving as the catalyst
wires 6 are installed in the reaction chamber 2. Then, the vacuum
pump 4 is operated to evacuate the vacuum chamber 3, and the
pressure of the reaction chamber 2 is reduced to a predetermined
degree of vacuum (for example, 1 Pa). Next, a source gas and a
diborane gas are introduced to the reaction chamber 2 from the
source gas supply unit 9a and the diborane gas supply unit 9b via
the gas introduction pipes 7, and the respective catalyst wires 6
are energized by the control unit 8 and heated to a predetermined
temperature (for example, 1,700.degree. C.) or more.
[0040] The diborane gas introduced to the reaction chamber 2 comes
into contact with the catalyst wires 6 and is decomposed so that a
boride (tantalum boride) layer is formed on the surface of each
catalyst wire 6. Accordingly, the surface of the catalyst wire 6 is
cured, with the result that the thermal expansion is reduced, the
mechanical strength is improved, and the service life is
prolonged.
[0041] On the other hand, the source gas introduced to the reaction
chamber 2 comes into contact with the catalyst wires 6 and is
decomposed so that reaction products thereof (decomposition
species) are deposited on the surface of the substrate S.
Accordingly, a silicon film is formed on the surface of the
substrate S. It should be noted that silicon as decomposition
species of the source gas has a lower vapor pressure than that of
boron (B), and does not adhere to the catalyst wire 6 or adheres
thereto and then evaporates immediately under a reduced-pressure
atmosphere of 1 Pa and a high temperature state of 1,700.degree. C.
or more. Therefore, a silicon film is not deposited on the surface
of the catalyst wire 6 and the boride layer formed on the surface
of the catalyst wire 6 is not affected.
[0042] It should be noted that also in this embodiment, the
energization heating of the catalyst wire 6 by the control unit 8
is successively performed. Accordingly, it is possible to suppress
the generation of surface cracks of the catalyst wire 6 in the step
of forming a boride layer of the catalyst wire 6 and the film
formation step, and improve the mechanical strength and durability
of the catalyst wire 6 to improve the productivity.
[0043] According to this embodiment, the same effect as that of the
first embodiment described above can be obtained. Particularly,
according to this embodiment, it is possible to perform the film
formation step of a silicon film on the substrate S simultaneously
with the step of forming the boride layer on the surface of the
catalyst wire, with the result that the productivity can be
improved more.
EXAMPLES
[0044] Three types of catalyst wires having different structures
were used to perform a film formation test of Si, and the
durability of the respective catalyst wires was evaluated. Results
thereof are shown in FIG. 4. In the figure, the vertical axis
indicates a monitor output (voltage value), and the horizontal axis
indicates an accumulated film thickness. In other words, FIG. 4
shows a relationship between expansion of the catalyst wire and a
time.
[0045] The catalyst wires used in the experiment were a Ta catalyst
wire (Sample 1) formed of a metal tantalum wire (99.5% pure) that
is formed into a U shape and has a diameter of 1 mm and a length of
3,000 mm, a B--Ta catalyst wire (Sample 2) obtained by boriding a
surface of the tantalum wire described above, and a BN--Ta catalyst
wire (Sample 3) obtained by coating the surface of the tantalum
wire described above with boron nitride. As energization methods
for the catalyst wires, intermittent energization was performed for
the Sample 1 (ON-OFF energization), continuous energization and
intermittent energization were performed for the Sample 2, and
continuous energization was performed for the Sample 3.
[0046] Initial conditions for boriding the Sample 2 are as
follows.
[Initial Conditions for Boriding]
[0047] Flow rate of diborane (B.sub.2H.sub.6) gas: 160 sccm
[0048] Applied power: 3 kW (monitor current value: about 30 A)
[0049] Pressure: 2 Pa
[0050] Conditions for a film formation test are as follows.
[Conditions for Film Formation Test]
[0051] Flow rate of monosilane (SiH.sub.4) gas: 32 sccm
[0052] Flow rate of hydrogen (H.sub.2) gas: 16 sccm
[0053] Applied power: 3 kW (monitor current value: about 30 A)
[0054] Pressure: 2 Pa
[0055] As shown in FIG. 4, the Sample 1 (Ta catalyst wire) was
expanded abruptly from the start of film formation and leaded to
rupture. The expansion amount exceeded 20%.
[0056] In contrast to this, as to the Sample 2 (B--Ta catalyst
wire), the durability was largely improved as compared to the
Sample 1. Particularly, at a time of continuous energization,
deformation was hardly found from the start of film formation. On
the other hand, at the time of intermittent energization, expansion
was gradually caused from the start of film formation, which leaded
to rupture eventually. This may be caused because cracks were
generated on the surface due to a heat shock at the time of turning
current ON/OFF. The expansion at the time of rupture exceeded 10%,
but the durability was improved five times or more as compared to
the Sample 1.
[0057] Next, as to the Sample 3 (BN--Ta catalyst wire), expansion
was gradually caused from the start of film formation, which leaded
to rupture eventually. The expansion at the time of rupture exceeds
10%, but the durability was improved about three times as compared
to the Sample 1. However, the durability was inferior to that of
the Sample 2 at the time of intermittent energization. The change
of the expansion is different from that of the Sample 2 at the time
of intermittent energization. This may be because the Sample 3 has
lower surface hardness than that of the Sample 2.
[0058] As is apparent from the results described above, the
catalyst wire (Sample 2) having the boride layer formed on the
surface of the tantalum wire has a largely improved durability
compared to the solid tantalum wire (Sample 1) and the tantalum
wire (Sample 3) having the boron nitride formed on the surface
thereof. Further, it was confirmed that by performing the
energization heating of the catalyst wire by the continuous
energization, the generation of surface cracks is suppressed and
the service life of the catalyst wire can be prolonged.
[0059] Although the embodiments of the present invention have been
described above, but the present invention is not limited thereto
and can be variously modified based on the technical idea of the
present invention.
[0060] For example, in the embodiments described above, the mixed
gas of silane and hydrogen is used as a source gas, but the source
gas is not limited thereto and can be changed as appropriate in
accordance with types of film-formation materials.
[0061] Further, in the embodiments described above, the example has
been described in which two substrates S are opposed to each other
in the reaction chamber 2 and the plurality of catalyst wires 6 are
installed between the two substrates in the vertical direction, but
the structure of the reaction chamber 2 is not limited to the above
example.
[0062] In addition, using the catalytic chemical vapor deposition
apparatus of the present invention, it is possible to perform film
formation for a p-type layer and an n-type layer of a solar
battery.
[0063] As an example, a solar battery is manufactured by, first,
forming a metal electrode formed of a Mo film or the like on a
substrate of glass, aluminum, or the like by sputtering or thermal
CVD, then forming a p-type layer (for example, CuInSe.sub.2 film)
and an n-type layer (for example, CdS film), and forming a
transparent electrode formed of ZnO or the like thereon. In this
example, using this apparatus, it is possible to form a
CuInSe.sub.2 film as the p-type layer and a CdS film as the n-type
layer.
BRIEF DESCRIPTION OF DRAWINGS
[0064] [FIG. 1] A schematic structural view of a catalytic chemical
vapor deposition apparatus according to an embodiment of the
present invention.
[0065] [FIG. 2] A schematic perspective view of a reaction chamber
of the apparatus shown in FIG. 1.
[0066] [FIG. 3] Pictures of a side view (SEM) each showing a
surface condition of a catalyst wire installed in the reaction
chamber, in which A shows a state where surface cracks are
generated and B shows a state where surface cracks are not
generated.
[0067] [FIG. 4] A diagram showing durability of various samples of
catalyst wires described in Examples of the present invention.
DESCRIPTION OF SYMBOLS
[0068] 1 catalytic chemical vapor deposition apparatus [0069] 2
reaction chamber [0070] 3 vacuum chamber [0071] 4 vacuum pump
[0072] 5 anti-adhesive plate [0073] 6 catalyst wire [0074] 7 gas
introduction pipe [0075] 8 control unit [0076] 9a source gas supply
unit [0077] 9b diborane gas supply unit
* * * * *