U.S. patent application number 13/142100 was filed with the patent office on 2011-10-20 for dry vacuum pump.
This patent application is currently assigned to ULVAC, INC.. Invention is credited to Hideaki Inoue, Ryousuke Kita, Yoshifumi Maruyama, Hirokazu Mizushima, Eiichiro Ohtsubo.
Application Number | 20110256003 13/142100 |
Document ID | / |
Family ID | 43126112 |
Filed Date | 2011-10-20 |
United States Patent
Application |
20110256003 |
Kind Code |
A1 |
Ohtsubo; Eiichiro ; et
al. |
October 20, 2011 |
DRY VACUUM PUMP
Abstract
Between an exhaust chamber and a lubrication chamber, a second
seal that seals between a cylinder that partitions the exhaust
chamber and a first shaft and a first seal that seals between a
side cover that partitions the lubrication chamber and the first
shaft are provided. A gas introduction space to which a seal gas is
supplied is provided between the second seal 2 and the first seal.
The second seal and the first seal each have a base part and a pair
of ring-like lips extending from the base part toward the first
shaft. The pair of lips extends such that the distance therebetween
is gradually increased from the base part toward the first shaft,
and the tips of the pair of lips can be brought into elastic
contact with the first shaft.
Inventors: |
Ohtsubo; Eiichiro;
(Nagasaki, JP) ; Maruyama; Yoshifumi; (Nagasaki,
JP) ; Inoue; Hideaki; (Kanagawa, JP) ; Kita;
Ryousuke; (Kanagawa, JP) ; Mizushima; Hirokazu;
(Kanagawa, JP) |
Assignee: |
ULVAC, INC.
Kanagawa
JP
MITSUBISHI HEAVY INDUSTRIES, LTD.
Tokyo
JP
|
Family ID: |
43126112 |
Appl. No.: |
13/142100 |
Filed: |
May 6, 2010 |
PCT Filed: |
May 6, 2010 |
PCT NO: |
PCT/JP2010/057776 |
371 Date: |
June 24, 2011 |
Current U.S.
Class: |
417/410.3 |
Current CPC
Class: |
F04C 23/001 20130101;
F04C 29/02 20130101; F04C 27/009 20130101; F04C 18/123 20130101;
F04B 37/14 20130101; F04C 28/02 20130101; F04C 25/02 20130101; F01C
19/005 20130101 |
Class at
Publication: |
417/410.3 |
International
Class: |
F04B 37/14 20060101
F04B037/14 |
Foreign Application Data
Date |
Code |
Application Number |
May 20, 2009 |
JP |
2009-122499 |
May 20, 2009 |
JP |
2009-122500 |
Claims
1. A dry vacuum pump comprising: a shaft that is rotationally
driven by an electromagnetic motor; and rotors that are attached to
the shaft and provided in an exhaust chamber and that suck an
exhaust gas in a vacuum processing chamber into the exhaust chamber
and discharge the exhaust gas, wherein, between the exhaust chamber
and a next chamber located next to the exhaust chamber, an
exhaust-chamber-side seal that seals between an exhaust-chamber
partitioning wall portion that partitions the exhaust chamber and
the shaft and a next-chamber-side seal that seals between a
next-chamber partitioning wall portion that partitions the next
chamber and the shaft are provided; a gas introduction space to
which a seal gas is supplied is provided between the
exhaust-chamber-side seal and the next-chamber-side seal; the
exhaust-chamber-side seal and the next-chamber-side seal each have
a ring-like base part that is fixed to the exhaust-chamber
partitioning wall portion or the next-chamber partitioning wall
portion and a pair of ring-like lip parts that extends from the
base part toward the shaft; and the pair of lip parts extends such
that the distance therebetween is gradually increased from the base
part toward the shaft, and the tips of the pair of lip parts can be
brought into elastic contact with the shaft.
2. A dry vacuum pump according to claim 1, wherein the base part
and the pair of lip parts are integrally structured.
3. A dry vacuum pump according to claim 1, wherein the pair of lip
parts is formed as individual members, and the base ends of the lip
parts are fixedly combined to form the base part.
4. A dry vacuum pump according to one of claim 1, wherein portions
of the lip parts that are brought into contact with the shaft are
made of polytetrafluoroethylene.
5. A dry vacuum pump according to one of claim 1, wherein an
electromagnetic motor chamber that accommodates the electromagnetic
motor is provided at a position where it sandwiches the next
chamber with the exhaust chamber; the next chamber is a lubrication
chamber in which lubricating oil is stored; and the exhaust gas
includes hydrogen gas.
6. A dry vacuum pump according to claim 5, wherein a gas discharge
passage that is connected to an exhaust line to which the exhaust
gas is discharged from the exhaust chamber is further provided, and
an oil trap that traps the lubricating oil flowing toward the
exhaust line is provided in the gas discharge passage.
7. A dry vacuum pump according to one of claim 1, wherein a gas
discharge passage that is connected to an exhaust line to which the
exhaust gas is discharged from the exhaust chamber is further
provided, and a check valve that permits a flow of gas flowing
toward the exhaust line and prohibits a flow in the opposite
direction is provided in the gas discharge passage.
8. A dry vacuum pump comprising: an electromagnetic motor that is
accommodated in an electromagnetic motor chamber; a shaft that is
rotationally driven by the electromagnetic motor; and rotors that
are attached to the shaft and provided in an exhaust chamber and
that suck an exhaust gas including hydrogen gas in a vacuum
processing chamber into the exhaust chamber and discharge the
exhaust gas including hydrogen gas, wherein purge means for
introducing an inert gas into the electromagnetic motor chamber and
for discharging a gas in the electromagnetic motor chamber is
provided.
9. A dry vacuum pump according to claim 8, wherein a lubrication
chamber in which lubricating oil is stored is provided between the
exhaust chamber and the electromagnetic motor chamber; and the
inert gas introduced into the electromagnetic motor chamber by the
purge means is discharged through the lubrication chamber.
10. A dry vacuum pump comprising: an electromagnetic motor that is
accommodated in an electromagnetic motor chamber; a shaft that is
rotationally driven by the electromagnetic motor; rotors that are
attached to the shaft and provided in an exhaust chamber and that
suck an exhaust gas including hydrogen gas in a vacuum processing
chamber into the exhaust chamber and discharge the exhaust gas
including hydrogen gas; and a lubrication chamber that is provided
between the exhaust chamber and the electromagnetic motor chamber
and in which lubricating oil is stored, wherein purge means for
introducing an inert gas into the lubrication chamber from outside
the electromagnetic motor chamber through a gas introduction
passage formed in the shaft and for discharging a gas in the
lubrication chamber is provided.
11. A dry vacuum pump according to claim 8, wherein a lubrication
chamber in which lubricating oil is stored is provided between the
exhaust chamber and the electromagnetic motor chamber; and the
exhaust gas includes hydrogen gas.
12. A dry vacuum pump according to claim 9, wherein the exhaust gas
includes hydrogen gas.
13. A dry vacuum pump according to claim 11, wherein the purge
means includes a gas discharge passage that is connected to an
exhaust line to which the exhaust gas is discharged from the
exhaust chamber, and an oil trap that traps the lubricating oil
flowing toward the exhaust line is provided in the gas discharge
passage.
14. A dry vacuum pump according to one of claim 8, wherein the
purge means includes a gas discharge passage that is connected to
an exhaust line to which the exhaust gas is discharged from the
exhaust chamber, and a check valve that permits a flow of gas
flowing toward the exhaust line and prohibits a flow in the
opposite direction is provided in the gas discharge passage.
Description
TECHNICAL FIELD
[0001] The present invention relates to a dry vacuum pump for
evacuating a vacuum processing chamber.
BACKGROUND ART
[0002] A dry vacuum pump has a structure in which liquid, such as
oil, is not brought into contact with an exhaust gas and is often
used in the semiconductor manufacturing field etc., for which high
system cleanliness is required. Although there are many types of
dry vacuum pumps, in a general dry vacuum pump, rotors that suck
and discharge an exhaust gas are rotated with rotational power
produced by a power source such as an electromagnetic motor, to
discharge a gas in a system (see PTL 1, for example).
[0003] The development and the manufacture of silicon thin-film
solar cells have been increasing in recent years. A general method
of manufacturing this type of thin film is to use a plasma CVD
technique using silane (SiH.sub.4) and hydrogen gas (H.sub.2) as
main material gases, to form amorphous silicon and crystalline
silicon thin films on a substrate (see PTL 2, for example).
[0004] In order to prevent lubricating oil from flowing out and to
prevent a reactant gas from entering between a gear box and an
exhaust chamber in the vacuum pump, a passage through which an
inert gas etc. flows is provided in a non-contact shaft seal
mechanism, in some cases (see PTL 3, for example).
CITATION LIST
Patent Literature
[0005] {PTL 1} Japanese Unexamined Patent Application, Publication
No. 2005-171766 [0006] {PTL 2} Japanese Unexamined Patent
Application, Publication No. 2006-216921 [0007] {PTL 3} Japanese
Unexamined Patent Application, Publication No. 2003-172261
SUMMARY OF INVENTION
Technical Problem
[0008] In a plasma CVD apparatus for the above-described thin-film
formation, a mixed gas composed of silane gas and hydrogen gas is
mainly used as a material gas to form an amorphous silicon film and
a crystalline silicon thin film. In a vacuum processing chamber
(film forming chamber etc.) of the plasma CVD apparatus, hydrogen
gas is generated also through the cracking reaction of silane.
Therefore, an exhaust-target gas (exhaust gas) discharged from the
vacuum processing chamber includes a large amount of hydrogen
gas.
[0009] On the other hand, the dry vacuum pump, which is used to
suck and discharge the exhaust gas including hydrogen gas from the
vacuum processing chamber, has an electromagnetic motor serving as
its drive source, and the electromagnetic motor contains a
permanent magnet material as a constituent material. As the
permanent magnet material, an iron neodymium material is typically
used. Because rusting easily occurs on the permanent magnet
material due to moisture, the corrosion resistance is improved by
nickel plating etc. Further, it is known that, since the permanent
magnet material absorbs hydrogen to form a hydrogen compound, it
may embrittle through heat generation etc. to cause a reduction in
magnetic force or disintegration and is susceptible to so-called
hydrogen corrosion. Thus, there is a concern that the excitation
power of the electromagnetic motor may be reduced.
[0010] Furthermore, it has become clear that, because the hydrogen
gas has a small molecular size and easily diffuses, the hydrogen
gas passes through a seal portion at a rotary shaft of rotors from
an exhaust chamber of the dry vacuum pump, diffuses into the
electromagnetic motor, and is further transmitted through pin holes
in a thin nickel plating or in a plated layer applied to the
surface of the permanent magnet, thus causing hydrogen
corrosion.
[0011] Therefore, in a case where the dry vacuum pump is used as
exhaust means for the vacuum processing chamber (film forming
chamber etc.) of the plasma CVD apparatus for thin-film formation,
it is a critical issue to avoid malfunction of the permanent magnet
material of the electromagnetic motor caused by a large amount of
hydrogen gas included in the exhaust-target gas (exhaust gas), and
therefore, it is desired to take a countermeasure so as not to
bring the permanent magnet material into direct contact with the
hydrogen gas.
[0012] In particular, when film-formation processing is applied to
a substrate with a large area of more than 1 m.sup.2 under high
dilution-ratio film formation conditions in which silane gas is
diluted with a large amount of hydrogen gas, as in crystalline
silicon thin-film formation, the ratio of hydrogen gas included in
the exhaust gas with respect to the amount in the evacuation pump
is increased, and therefore, there is a concern that malfunction of
the permanent magnet material of the electromagnetic motor may be
further caused by the hydrogen gas.
[0013] Furthermore, in a vacuum pump, such as that shown in PTL 3,
although the passage through which the inert gas flows is provided
in the non-contact shaft seal mechanism in order to prevent the
reactant gas from entering the gear box from the exhaust chamber,
there is a problem in that the introduction of a large amount of
inert gas causes an increase in cost and deterioration in the
exhaust capability. Furthermore, in order to ensure the sealing
property against a pressure fluctuation in the exhaust chamber, the
flow rate of the inert gas needs to be increased more and more.
[0014] As described above, a contact seal mechanism is employed,
and a seal mechanism having a sufficiently superior sealing
property against a pressure fluctuation in the exhaust chamber is
further desired.
[0015] In view of the above-described circumstances, an object of
the present invention is to provide a dry vacuum pump capable of
preventing malfunction of a drive source (electromagnetic motor)
caused by hydrogen gas included in an exhaust-target gas (exhaust
gas) guided from a vacuum processing chamber.
Solution to Problem
[0016] In order to solve the above-described problems, the dry
vacuum pump of the present invention employs the following
solutions.
[0017] According to a first aspect, the present invention provides
a dry vacuum pump including: a shaft that is rotationally driven by
an electromagnetic motor; and rotors that are attached to the shaft
and provided in an exhaust chamber and that suck an exhaust gas in
a vacuum processing chamber into the exhaust chamber and discharge
the exhaust gas, the dry vacuum pump evacuating the vacuum
processing chamber, in which, between the exhaust chamber and a
next chamber located next to the exhaust chamber, an
exhaust-chamber-side seal that seals between an exhaust-chamber
partitioning wall portion that partitions the exhaust chamber and
the shaft and a next-chamber-side seal that seals between a
next-chamber partitioning wall portion that partitions the next
chamber and the shaft are provided; a gas introduction space to
which a seal gas is supplied is provided between the
exhaust-chamber-side seal and the next-chamber-side seal; the
exhaust-chamber-side seal and the next-chamber-side seal each have
a ring-like base part that is fixed to the exhaust-chamber
partitioning wall portion or the next-chamber partitioning wall
portion and a pair of ring-like lip parts that extends from the
base part toward the shaft; and the pair of lip parts extends such
that the distance therebetween is gradually increased from the base
part toward the shaft, and the tips of the pair of lip parts can be
brought into elastic contact with the shaft.
[0018] The exhaust-chamber-side seal and the next-chamber-side seal
are provided between the exhaust chamber and the next chamber, and
a seal gas is supplied between the seals. The seal gas blows out
from the exhaust-chamber-side seal toward the exhaust chamber and
also from the next-chamber-side seal toward the next chamber. Thus,
the exhaust gas in the exhaust chamber can be prevented from
leaking into the next chamber, and a substance (for example,
lubricating oil or its mist) in the next chamber can be prevented
from leaking into the exhaust chamber.
[0019] Furthermore, the exhaust-chamber-side seal and the
next-chamber-side seal each include a pair of lip parts, and the
tips of the lip parts can be brought into elastic contact with the
shaft. Therefore, more reliable sealing can be performed with the
two lip parts.
[0020] Furthermore, each pair of lip parts has a shape in which the
lip parts extend such that the distance therebetween is gradually
increased toward the shaft, and the lip parts are connected to the
base part, which is regarded as a common part. Therefore, when one
of the lip parts is inclined with respect to the base part, the
other lip part is also inclined via the base part and is inclined
in the same direction. Specifically, when the lip part that faces
the exhaust chamber or the next chamber is inclined so as to move
away from the shaft, the lip part that faces the gas introduction
space, to which a seal gas is supplied, moves toward the shaft,
accordingly. Conversely, when the lip part that faces the exhaust
chamber or the next chamber is inclined so as to move toward the
shaft, the lip part that faces the gas introduction space, to which
a seal gas is supplied, moves away from the shaft, accordingly. In
this way, even when one lip part moves away from the shaft to
increase the gap therebetween, the other lip part, located
corresponding to the circumferential positions of this lip part,
moves toward to the shaft to reduce the gap therebetween; thus, the
seal gas outflow is adjusted such that the unevenness at the
circumferential positions is corrected. Therefore, even if a
pressure distribution occurs in the circumferential direction of
the seal, the seal-gas flow rate is adjusted at the respective
circumferential positions, and thus, a high sealing performance is
exerted.
[0021] Note that, in the present invention, the "next chamber"
means a chamber located next to the exhaust chamber and can be, for
example, a lubrication chamber or a bearing chamber. Therefore, the
present invention is appropriate for a seal between the exhaust
chamber and the lubrication chamber or a seal between the exhaust
chamber and the bearing chamber.
[0022] In the dry vacuum pump according to the first aspect of the
present invention, it is assumed that an electromagnetic motor
chamber that accommodates the electromagnetic motor is provided at
a position where it sandwiches the next chamber with the exhaust
chamber; the next chamber is a lubrication chamber in which
lubricating oil is stored; and the exhaust gas includes hydrogen
gas.
[0023] Hydrogen gas corrodes the permanent magnet material of the
electromagnetic motor to degrade the magnetic performance. In the
present invention, since the exhaust-chamber-side seal and the
next-chamber-side seal of the above-described invention are
provided between the exhaust chamber and the next chamber
(lubrication chamber), the exhaust gas is prevented from leaking
into the electromagnetic motor chamber, which is located at the
opposite side of the next chamber (lubrication chamber) from the
exhaust chamber. Therefore, it is possible to avoid a situation in
which the permanent magnet of the electromagnetic motor is corroded
by hydrogen gas.
[0024] Furthermore, in the dry vacuum pump according to the first
aspect of the present invention, it is preferable that the base
part and the pair of lip parts be integrally structured.
[0025] Since the base part and the pair of lip parts are integrally
structured, handling and maintenance become easy.
[0026] Furthermore, in the dry vacuum pump according to the first
aspect of the present invention, it is preferable that the pair of
lip parts be formed as individual members, and the base ends of the
lip parts be fixedly combined to form the base part.
[0027] Since the pair of lip parts is formed as individual members,
each lip part is easily manufactured, and even a lip part having a
complicated shape can be manufactured, thus realizing a reduction
in cost.
[0028] Furthermore, in the dry vacuum pump according to the first
aspect of the present invention, it is preferable that portions of
the lip parts that are brought into contact with the shaft be made
of polytetrafluoroethylene.
[0029] Since the portions of the lip parts that are brought into
contact with the shaft are made of polytetrafluoroethylene, a
friction coefficient with respect to the shaft is reduced, and the
wear amount of the sliding portions of the lip parts can be
reduced. As a result, the reliability of the seals can be ensured
for a long period.
[0030] According to a second aspect of the present invention, there
is provided a dry vacuum pump including: an electromagnetic motor
that is accommodated in an electromagnetic motor chamber; a shaft
that is rotationally driven by the electromagnetic motor; and
rotors that are attached to the shaft and provided in an exhaust
chamber and that suck an exhaust gas including hydrogen gas in a
vacuum processing chamber into the exhaust chamber and discharge
the exhaust gas including hydrogen gas, the dry vacuum pump
evacuating the vacuum processing chamber, in which purge means for
introducing an inert gas into the electromagnetic motor chamber and
for discharging a gas in the electromagnetic motor chamber is
provided.
[0031] Hydrogen gas corrodes the permanent magnet material of the
electromagnetic motor to degrade the magnetic performance. When the
exhaust gas includes hydrogen gas, there is a concern that hydrogen
may enter the electromagnetic motor chamber from the exhaust
chamber because the exhaust chamber and the electromagnetic motor
chamber are connected via the shaft.
[0032] In the dry vacuum pump according to the second aspect of the
present invention, the purge means for introducing an inert gas
into the electromagnetic motor chamber and for discharging a gas in
the electromagnetic motor chamber is provided. Thus, even if
hydrogen gas enters the electromagnetic motor chamber, the hydrogen
gas can be discharged, and, since the introduction of the inert gas
reduces the partial pressure of the hydrogen gas, the permanent
magnet material of the electromagnetic motor is not corroded by a
large amount of hydrogen. Therefore, it is possible to avoid a
situation in which the permanent magnet of the electromagnetic
motor is corroded by hydrogen gas.
[0033] In the dry vacuum pump according to the second aspect of the
present invention, it is preferable that a lubrication chamber in
which lubricating oil is stored be provided between the exhaust
chamber and the electromagnetic motor chamber; and the inert gas
introduced into the electromagnetic motor chamber by the purge
means be discharged through the lubrication chamber.
[0034] The exhaust gas including hydrogen gas first enters the
lubrication chamber, located next to the exhaust chamber. In the
lubrication chamber, an inert gas guided from the electromagnetic
motor chamber is introduced and discharged. In this way, the
hydrogen gas meets the inert gas in the lubrication chamber and is
discharged before entering the electromagnetic motor chamber.
Therefore, it is possible to prevent the hydrogen gas from entering
the electromagnetic motor chamber as much as possible.
[0035] According to a third aspect of the present invention, there
is provided a dry vacuum pump including: an electromagnetic motor
that is accommodated in an electromagnetic motor chamber; a shaft
that is rotationally driven by the electromagnetic motor; rotors
that are attached to the shaft and provided in an exhaust chamber
and that suck an exhaust gas including hydrogen gas in a vacuum
processing chamber into the exhaust chamber and discharge the
exhaust gas including hydrogen gas; and a lubrication chamber that
is provided between the exhaust chamber and the electromagnetic
motor chamber and in which lubricating oil is stored, the dry
vacuum pump evacuating the vacuum processing chamber, in which
purge means for introducing an inert gas into the lubrication
chamber from outside the electromagnetic motor chamber through a
gas introduction passage formed in the shaft and for discharging a
gas in the lubrication chamber is provided.
[0036] Hydrogen gas corrodes the permanent magnet material of the
electromagnetic motor to degrade the magnetic performance. When the
exhaust gas includes hydrogen gas, there is a concern that hydrogen
may enter the electromagnetic motor chamber from the exhaust
chamber via the lubrication chamber because the exhaust chamber,
the lubrication chamber, and the electromagnetic motor chamber are
connected via the shaft.
[0037] In the dry vacuum pump according to the third aspect of the
present invention, the purge means for introducing an inert gas
into the lubrication chamber from the outside of the
electromagnetic motor chamber through the gas introduction passage
formed in the shaft and that discharges a gas in the lubrication
chamber is provided. Thus, even if hydrogen gas enters the
lubrication chamber from the exhaust chamber, the hydrogen gas can
be discharged before entering the electromagnetic motor chamber,
and, since the introduction of the inert gas reduces the partial
pressure of the hydrogen gas, the permanent magnet material of the
electromagnetic motor is not corroded by a large amount of
hydrogen. Therefore, it is possible to avoid a situation in which
the permanent magnet of the electromagnetic motor is corroded by
hydrogen gas.
[0038] Furthermore, since an inert gas is introduced into the
lubrication chamber from the outside of the electromagnetic motor
chamber through the gas introduction passage formed in the shaft,
piping drawing around the electromagnetic motor chamber is
unnecessary to introduce the inert gas into the lubrication
chamber, thus realizing a simple configuration.
[0039] In the dry vacuum pump according to the second aspect or the
third aspect of the present invention, it is preferable that the
purge means include a gas discharge passage that is connected to an
exhaust line to which the exhaust gas is discharged from the
exhaust chamber, and a check valve that permits a flow of gas
flowing toward the exhaust line and prohibits a flow in the
opposite direction be provided in the gas discharge passage.
[0040] By providing the check valve, it is possible to prevent the
exhaust gas discharged from the exhaust chamber to the exhaust line
from entering the lubrication chamber or the electromagnetic motor
chamber via the gas discharge passage.
[0041] Furthermore, in the dry vacuum pump according to the second
aspect or the third aspect of the present invention, it is
preferable that the purge means include a gas discharge passage
that is connected to an exhaust line to which the exhaust gas is
discharged from the exhaust chamber, and an oil trap that traps the
lubricating oil flowing toward the exhaust line be provided in the
gas discharge passage.
[0042] By providing the oil trap, it is possible to prevent the
lubricating oil from leaking into the exhaust line together with
the purge gas and to maintain a clean exhaust system.
Advantageous Effects of Invention
[0043] According to the dry vacuum pump of the present invention,
since the exhaust-chamber-side seal and the next-chamber-side seal
are provided between the exhaust chamber and the next chamber, and
a seal gas is supplied between the seals, it is possible to prevent
the exhaust gas in the exhaust chamber from leaking into the next
chamber and to prevent a substance (for example, the lubricating
oil or its mist) in the next chamber from leaking into the exhaust
chamber.
[0044] Furthermore, since the exhaust-chamber-side seal and the
next-chamber-side seal each have a pair of lip parts, and the tips
of the lip parts can be brought into elastic contact with the
shaft, more reliable sealing can be performed with the two lip
parts.
[0045] Furthermore, since each pair of lip parts has a shape in
which the lip parts extend such that the distance therebetween is
gradually increased toward the shaft, and the lip parts are
connected to the base part, which is regarded as a common part,
even if a pressure distribution occurs in the circumferential
direction of the seal, since the seal-gas flow rate is adjusted
such that the unevenness thereof at the circumferential positions
is corrected, a high sealing performance is exerted.
[0046] Furthermore, since the exhaust-chamber-side seal and the
next-chamber-side seal are provided between the exhaust chamber and
the lubrication chamber, the exhaust gas is prevented from leaking
into the electromagnetic motor chamber, which is located at the
opposite side of the lubrication chamber from the exhaust chamber.
Therefore, it is possible to avoid a situation in which the
permanent magnet of the electromagnetic motor is corroded by
hydrogen gas.
[0047] Alternatively, according to the dry vacuum pump of the
present invention, since the purge means for introducing an inert
gas into the electromagnetic motor chamber and for discharging a
gas in the electromagnetic motor chamber is provided, it is
possible to avoid a situation in which the permanent magnet of the
electromagnetic motor is corroded by hydrogen gas and to prevent
malfunction of the electromagnetic motor.
BRIEF DESCRIPTION OF DRAWINGS
[0048] FIG. 1 is a configuration diagram showing, in outline, a
vacuum processing system in which a dry vacuum pump according to a
first embodiment of the present invention is used.
[0049] FIG. 2 is a sectional plan view showing the internal
structure of the dry vacuum pump shown in FIG. 1.
[0050] FIG. 3 is a sectional side view showing the internal
structure of the dry vacuum pump shown in FIG. 1.
[0051] FIG. 4 is a sectional view showing the structure of an
exhaust chamber of the dry vacuum pump shown in FIG. 1.
[0052] FIG. 5 is an enlarged sectional view showing details of cup
seals of the dry vacuum pump shown in FIG. 1.
[0053] FIG. 6A is a sectional perspective view showing the
structure of a seal member constituting the cup seal shown in FIG.
5.
[0054] FIG. 6B is a sectional view showing the operation of a main
portion of the seal member.
[0055] FIG. 7 is an enlarged sectional view showing details of the
cup seals in FIG. 5.
[0056] FIG. 8 is a table showing a result of a test of ingress of
hydrogen gas into a lubrication chamber, based on the seal-gas flow
rate.
[0057] FIG. 9 is a sectional plan view showing the internal
structure of a dry vacuum pump according to a second embodiment of
the present invention.
[0058] FIG. 10 is a sectional side view showing the internal
structure of the dry vacuum pump shown in FIG. 9.
[0059] FIG. 11 is a sectional side view showing the internal
structure of a dry vacuum pump according to a third embodiment of
the present invention.
DESCRIPTION OF EMBODIMENTS
[0060] Embodiments of the present invention will be described below
with reference to the drawings.
First Embodiment
[0061] FIG. 1 shows the outline of a vacuum processing system using
a dry vacuum pump 1 according to a first embodiment of the present
invention.
[0062] A plasma CVD apparatus (vacuum processing apparatus) 101
includes a film forming chamber 103, and the dry vacuum pump 1 is
provided in a system for evacuating the film forming chamber 103.
In the film forming chamber 103, film formation is applied to a
glass substrate with a large area of more than 1 m.sup.2 (not
shown). The film forming chamber 103 is connected to gas supply
flow paths 104, 105, and 106 that supply silane gas (SiH.sub.4) and
hydrogen gas (H.sub.2), which are the main material gases, and the
cleaning gas (NF.sub.3), respectively, to the film forming chamber
103. The film forming chamber 103 is provided with an exhaust
system 61 that discharges the gas.
[0063] The exhaust system 61 includes an exhaust flow path 110
provided with a high-vacuum turbo-molecular pump (TMP) 109 and a
flow path 112 provided with a flow control valve (CV) 111. The dry
vacuum pump (DP) 1 is provided in a flow path 113 located
downstream of a junction S of the exhaust flow path 110 and the
flow path 112. Further, an exhaust line 62 is provided at a
downstream side of the dry vacuum pump 1. The exhaust line 62 is
branched into a combustible exhaust line 117 through which a
combustible gas, such as silane gas and hydrogen gas, is discharged
and a combustion-supporting exhaust line 118 through which a
combustion-supporting gas, such as nitrogen trifluoride gas
(NF.sub.3), is discharged. A combustible exhaust valve 119a is
provided in the combustible exhaust line 117, and a
combustion-supporting exhaust valve 119b is provided in the
combustion-supporting exhaust line 118.
[0064] To supply silane gas and hydrogen gas that are used as
material gases in order to perform film formation, the combustible
exhaust line 117 is used with the combustible exhaust valve 119a
opened and the combustion-supporting exhaust valve 119b closed.
[0065] To supply nitrogen trifluoride gas that is used as a
cleaning gas in order to perform self-cleaning of the film forming
chamber 103, the combustion-supporting exhaust line 118 is used
with the combustible exhaust valve 119a closed and the
combustion-supporting exhaust valve 119b opened.
[0066] The plasma CVD apparatus 101 is provided with a vacuum gauge
(V) 120 that measures the pressure in the film forming chamber
103.
[0067] In the thus-configured plasma CVD apparatus 101, a
film-formation gas including a material gas composed of SiH.sub.4
is supplied to the film forming chamber 103 that has been
decompressed from atmospheric pressure while rough evacuation is
performed by the dry vacuum pump 1, plasma is produced by
high-frequency power supplied from a high-frequency power source
(not shown), and film formation is applied to a substrate, made of
glass etc., supported and heated in the film forming chamber 103.
As the substrate, a glass substrate with a large area of more than
1 m.sup.2 can be used, for example.
[0068] The material gas is diluted with hydrogen gas. For example,
to form a crystalline silicon film, the material gas is diluted
with 20 times or greater volume of hydrogen gas than that of the
silane gas, thereby improving the film quality.
[0069] Upon reception of an instruction to perform film-formation
processing, the plasma CVD apparatus 101 performs high evacuation
by using the turbo-molecular pump 109 and the dry vacuum pump 1
with an MV 121 and a TV 122 opened and an RV 123 closed.
[0070] The substrate (not shown) is set in the film forming chamber
103, a film-formation recipe is instructed, and the film-formation
processing is performed according to the film-formation recipe.
[0071] For example, in forming the crystalline silicon film, in
order to obtain a film-formation speed of 2.0 to 2.5 nm/s, the
film-formation pressure is set to 1000 to 3000 Pa, the flow rate of
silane gas used as a film-formation material gas is set to 0.5 to
2.0 SLM/m.sup.2 per 1 m.sup.2 of the substrate, and the flow rate
of hydrogen gas is set to 10 SLM/m.sup.2 or more, which is a large
flow rate.
[0072] Next, with the MV 121 and the TV 122 closed and the RV 123
opened, the film-formation material gas is introduced into the film
forming chamber 103 while roughing evacuation is performed by the
dry vacuum pump 1. The flow control valve (CV) 111 is adjusted such
that the pressure in the film forming chamber 103 measured by the
vacuum gauge (V) 120 becomes equal to the instructed value of the
pressure specified in the film-formation recipe for the film
forming chamber 103, to adjust the pressure in the film forming
chamber 103.
[0073] Next, plasma discharge is started, thereby applying film
formation.
[0074] After a predetermined film formation has been applied, the
plasma discharge is stopped, and the supply of the film-formation
material gas is stopped. With the MV 121 and the TV 122 opened and
the RV 123 closed, high evacuation is performed by the
turbo-molecular pump 109 and the dry vacuum pump 1, and the
substrate to which the film-formation processing has been applied
is taken out to finish the film-formation processing.
[0075] Note that the dry vacuum pump 1 may be used with its
evacuation capability being improved by serially combining a
mechanical booster pump, such as a roots-type pump, and the exhaust
system.
[0076] FIG. 2 is a sectional plan view of the dry vacuum pump 1 of
this embodiment, seen from the top. FIG. 3 is a sectional side view
of the dry vacuum pump 1 seen from a lateral side.
[0077] Although the dry vacuum pump 1 of this embodiment is
configured as a roots-type dry vacuum pump, the present invention
is not limited thereto and can also be used for dry vacuum pumps of
other types, such as a scroll type and a rotary vane type, or a
mechanical booster pump, such as a roots-type pump.
[0078] As shown in the figures, the dry vacuum pump 1 includes an
electromagnetic motor 3 serving as a drive source, a lubrication
chamber (next chamber) 12 disposed laterally to the electromagnetic
motor 3, an exhaust chamber 13 disposed laterally to the
lubrication chamber 12, and a first seal mechanism 11 disposed
between the lubrication chamber 12 and the exhaust chamber 13.
[0079] The lubrication chamber 12 is formed by a motor cover
(next-chamber partitioning wall portion) 8 and a side cover 9, and
the exhaust chamber 13 is formed by a cylinder (exhaust-chamber
partitioning wall portion) 7 and the side cover 9. The lubrication
chamber 12 and the exhaust chamber 13 constitute a main chassis
portion of the dry vacuum pump 1.
[0080] The lubrication chamber 12 accommodates a rotation transfer
mechanism 4, and the exhaust chamber 13 accommodates first rotors
(rotors) 6. The electromagnetic motor 3 is disposed adjacent to the
motor cover 8. The rotational axis of the electromagnetic motor 3
is connected to a first shaft (shaft) 5. The first shaft 5
longitudinally passes through the lubrication chamber 12, passes
through the side cover 9, and extends to the exhaust chamber 13. A
portion where the first shaft 5 makes the lubrication chamber 12
communicate with the exhaust chamber 13 is sealed by the first seal
mechanism 11 so as to suppress the movement of a gas between the
lubrication chamber 12 and the exhaust chamber 13 caused by the
rotation of the first shaft 5. In the lubrication chamber 12, the
rotation transfer mechanism 4 is connected to the first shaft 5. In
the exhaust chamber 13, the first rotors 6 are connected to the
first shaft 5. The lubrication chamber 12 accommodates lubricating
oil F (see FIG. 3) used to lubricate the rotation transfer
mechanism 4.
[0081] The dry vacuum pump 1 of this embodiment includes, in
addition to the above-described components, a second shaft (shaft)
14, second rotors (rotors) 15, and a second seal mechanism 16 (see
FIG. 2). The second shaft 14 is connected to the rotation transfer
mechanism 4 in the lubrication chamber 12, passes through the side
cover 9, and extends to the exhaust chamber 13, in parallel to the
first shaft 5. A portion where the second shaft 14 makes the
lubrication chamber 12 communicate with the exhaust chamber 13 is
sealed by the second seal mechanism 16 so as to suppress the
movement of a gas between the lubrication chamber 12 and the
exhaust chamber 13 caused by the rotation of the second shaft 14.
In the exhaust chamber 13, the second rotors 15 are connected to
the second shaft 14.
[0082] Furthermore, the dry vacuum pump 1 of this embodiment
includes a bearing chamber 17 at the other side (right side in FIG.
2) of the exhaust chamber 13 from the lubrication chamber 12. The
bearing chamber 17 is formed by a second side cover 18 that is
attached to the other side of the cylinder 7 from the side cover 9
and a bearing cover 19 that is attached to the second side cover
18. The first shaft 5 and the second shaft 14 pass through the
second side cover 18 and are rotatably supported in the bearing
chamber 17. The bearing chamber 17 accommodates a first bearing 20
that rotatably supports the first shaft 5 and a second bearing 21
that rotatably supports the second shaft 14. The first bearing 20
and the second bearing 21 are ball bearings, for example.
[0083] The electromagnetic motor 3 is accommodated in an
electromagnetic motor chamber 10 and produces rotational power for
rotating the first rotors 6. The electromagnetic motor 3 can have
the general structure of a power source of the dry vacuum pump 1.
The electromagnetic motor 3 typically has a stator and a rotor, and
a permanent magnet material is used for either the stator or the
rotor. It is preferable that the permanent magnet material be
relatively inexpensive and have superior magnetic properties. For
example, a rare-earth magnet is used. As the permanent magnet
material, a rare-earth iron magnetic material, such as iron
neodymium, is used, for example. A layer plated with metal, such as
nickel, is applied to the magnet surface in order to improve
durability against rusting, erosion, and corrosion that occurs when
a hydrogen compound that absorbs hydrogen is formed.
[0084] As shown in FIG. 2 and FIG. 3, the electromagnetic motor 3
and the lubrication chamber 12 are provided at a side where gas is
compressed in exhaust spaces 26 of the exhaust chamber 13 (side
where the pressure is closer to the atmospheric pressure). With the
electromagnetic motor 3 being disposed in this way, the air
tightness of the electromagnetic motor chamber 10 can be easily
managed. Further, there is an effect of making the sealing property
in the first seal mechanism 11 more reliable because the
lubrication chamber 12 and the exhaust chamber 13 have a small
pressure difference when a pressure fluctuation occurs at the start
or stop of the dry vacuum pump 1.
[0085] Note that the number of electromagnetic motors 3 is not
limited to one, and a plurality of electromagnetic motors 3 may be
provided.
[0086] The rotation transfer mechanism 4 is lubricated with the
lubricating oil F, transfers the rotational power produced by the
electromagnetic motor 3 to the first shaft 5 and the second shaft
14, and makes the first rotors 6 and the second rotors 15 rotate
synchronously in directions opposite to each other. The rotation
transfer mechanism 4 includes a first timing gear 22, a second
timing gear 23, a first bearing 24, and a second bearing 25. The
first timing gear 22 is attached to the first shaft 5 and transfers
the rotational power to the second timing gear 23. The first
bearing 24 includes an outer ring fixed to the side cover 9, an
inner ring fixed to the first shaft 5, and bearing balls arranged
therebetween, and rotatably supports the first shaft 5 in the side
cover 9. The second timing gear 23 is attached to the second shaft
14, receives the rotational power from the first timing gear 22,
and rotates the second shaft 14. The second bearing 25 includes an
outer ring fixed to the side cover 9, an inner ring fixed to the
second shaft 14, and bearing balls arranged therebetween, and
rotatably supports the second shaft 14 in the side cover 9. The
configuration of the rotation transfer mechanism 4 is not limited
thereto, and a reduction gear etc. may be included, for
example.
[0087] Through the rotation of the first rotors 6 and the second
rotors 15, an exhaust gas is sucked and discharged. FIG. 4 is a
sectional side view showing the structures of each of the first
rotors 6 and each of the second rotors 15. As shown in FIG. 2 and
FIG. 3, the first rotors 6 are serially arrayed along the first
shaft 5 at multiple stages (six stages in the example shown in the
figure), and the second rotors 15 are serially arrayed along the
second shaft 14 at multiple stages (six stages in the example shown
in the figure).
[0088] The first rotors 6 arrayed at the respective stages and the
second rotors 15 arrayed at the corresponding stages are disposed
in pairs. The first rotors 6 and the second rotors 15 are each
formed in a three-lobed shape, and, when the first shaft 5 and the
second shaft 14 rotate, the first rotors 6 and the second rotors
15, in pairs, can be rotated with a minute space provided
therebetween.
[0089] The first rotor 6 and the second rotor 15, in pair, are
disposed in each of the six exhaust spaces 26 formed in the
cylinder 7, and the exhaust spaces 26 are connected by exhaust
passages 26a that sequentially communicate with the exhaust spaces
disposed at the stages immediately after. The exhaust space 26 that
is provided at the foremost stage (uppermost-stream stage) is
connected to an air-intake hole 7a formed in the cylinder 7, and
the exhaust space 26 that is provided at the last stage
(lowermost-stream stage) is connected to an exhaust hole 7b formed
in the cylinder 7 (see FIG. 3).
[0090] The air-intake hole 7a is connected to the film forming
chamber 103 of the plasma CVD apparatus, serving as a vacuum
processing chamber for thin-film formation, via the exhaust system
61. The exhaust hole 7b is connected to the exhaust line 62. The
film forming chamber 103 is configured as a film forming chamber
used to form an amorphous silicon film and a crystalline silicon
film on a substrate. In the film forming chamber 103, a
film-formation gas including material gases mainly composed of
silane gas (SiH.sub.4) and hydrogen gas (H.sub.2) is supplied to
the film forming chamber that has been decompressed from
atmospheric pressure while roughing evacuation is performed by the
dry vacuum pump 1, plasma is produced by high-frequency power
supplied from a high-frequency power source (not shown), and film
formation is applied to a substrate, made of glass etc., supported
and heated in the film forming chamber 103. At this time, because
silane gas (SiH.sub.4) is cracked and a large amount of hydrogen
gas (H.sub.2) is supplied to the film forming chamber 103, a great
amount of hydrogen gas is discharged to the exhaust line 62 with
the dry vacuum pump 1.
[0091] Since a large amount of hydrogen gas (H.sub.2) is also
supplied to a substrate preheating chamber, in addition to the film
forming chamber 103, the dry vacuum pump 1 of this embodiment can
be used in the same way.
[0092] For example, to form a crystalline silicon film, the
distance d between a plasma discharge electrode that supplies a
high-frequency power of 40 MHz to 100 MHz and the surface of the
substrate is set to 3 mm to 10 mm, and a material gas that is
obtained by dilution with 20 times or greater volume of hydrogen
gas than that of the silane gas is supplied, thereby realizing
improved film-formation speed and improved film quality. When the
crystalline silicon film is formed on a substrate having a large
area of more than 1 m.sup.2, in order to obtain a film-formation
speed of 2.0 to 2.5 nm/s, the film-formation pressure is set to
1000 to 3000 Pa, the flow rate of silane gas used as a material gas
for film formation is set to 0.5 to 2.0 SLM/m.sup.2 per 1 m.sup.2
of the substrate, and the flow rate of hydrogen gas needs to be 20
SLM/m.sup.2 or more, specifically, about 20 to 100 SLM/m.sup.2.
Because part of the silane gas is used for film formation, and
hydrogen gas generated by cracking the silane gas is also added,
the flow rate of hydrogen gas to be discharged to the exhaust line
62 is further increased, and the partial pressure of hydrogen gas
in the exhaust gas is extremely high.
[0093] The first seal mechanism 11 and the second seal mechanism 16
seal the ingress of the lubricating oil F and the exhaust gas at
the portions where the first shaft 5 and the second shaft 14 make
the lubrication chamber 12 communicate with the exhaust chamber 13.
A gas introduction hole 9a that is used to supply a seal gas to
these portions is formed in the side cover 9.
[0094] Next, the first seal mechanism 11 and the second seal
mechanism 16 will be described.
[0095] Since the first seal mechanism 11 and the second seal
mechanism 16 have the same structure, the first seal mechanism 11
will be described.
[0096] FIG. 5 is a sectional view showing the structure of the
first seal mechanism 11 and is an enlarged view of the vicinity of
the first seal mechanism 11 shown in FIG. 3.
[0097] As shown in the figure, the first seal mechanism 11 has a
first seal (lubrication-chamber-side seal) 27 and a second seal
(exhaust-chamber-side seal) 28. The first seal 27 is disposed
between the side cover 9 and the first shaft 5, and the second seal
28 is disposed between the cylinder 7 and the first shaft 5.
[0098] A gap G communicating with the gas introduction hole 9a is
formed between the cylinder 7 and the side cover 9, and a gas
introduction space 29 is formed by the first seal 27 and the second
seal 28. In the dry vacuum pump 1 of this embodiment, portions of
the side cover 9 and the cylinder 7 that face the gas introduction
space 29 serve as partition walls.
[0099] In addition to the above-described components, the first
seal mechanism 11 has a slinger 30 attached to the first shaft 5 in
the lubrication chamber 12.
[0100] The first seal 27 and the second seal 28 have the same
structure and are each configured by a seal member A shown in FIG.
6A, for example. FIG. 6A is a perspective view showing the
structure of the seal member A. The seal member A is configured by
a ring-like cup seal (lip seal) of which an inner circumferential
portion is brought into elastic contact with the outer
circumference of the shaft 5.
[0101] As shown in FIG. 6A, the seal member A includes a fixed part
a, a base part b, and two lip parts c. The fixed part a is formed
at the outer circumference side of the ring-like seal member A, the
base part b is formed so as to protrude from the fixed part a in
the radial direction of the ring, and the two lip parts c are
formed so as to protrude from the base part b in two oblique
directions with respect to the radial direction (such that they
form an inverted V-shape). Specifically, the pair of lip parts c
has a structure in which they project in opposite directions from
each other, along the axial direction of the first shaft 5. The lip
parts c can be elastically deformed such that the lip parts c
become closer to each other or away from each other.
[0102] Note that the seal member A may be constituted by a
plurality of members.
[0103] The fixed part a, the base part b, and the lip parts c are
made of a material, such as a fluoro-rubber, having elasticity and
a tolerance to the lubricating oil F and the exhaust gas including
hydrogen.
[0104] The seal member A further includes sliding members d that
are disposed on the lip parts c at portions that are brought into
contact with the first shaft 5 and supporting members e that are
inserted into the fixed part a and the base part b.
[0105] The sliding members d are made of a material, such as
polytetrafluoroethylene, having a friction coefficient lower than
that of the lip parts c, reduces the contact resistance of the seal
member A and the first shaft 5, and makes uniform the gaps formed
with respect to the first shaft 5. Because of the low friction
coefficient, the wear amount of the sliding members d can be
reduced, and the reliability can be ensured for a long period,
which are preferable. FIG. 6B is a view showing the structure of
one of the sliding members d. As shown in the figure, after the
seal member A is attached to the dry vacuum pump 1 as the first
seal 27 and the second seal 28, when the dry vacuum pump 1 is
idled, the sliding members d slide on the shaft 5 and are used in a
state where the corner portion of each sliding member d, the corner
portion having a high surface pressure, is made flat, as shown in
the lower figure.
[0106] The supporting members e are made of metal, for example, and
keep the strength and the shape of the seal member A. Note that the
supporting members e may be omitted.
[0107] FIG. 7 is a longitudinal sectional view showing the
arrangement of the first seal 27 and the second seal 28.
[0108] As shown in the figure, the first seal 27 is disposed
between the side cover 9 and the first shaft 5 and mainly has a
function of controlling the leakage of the lubricating oil F (or
its mist) from the lubrication chamber 12 into the exhaust chamber
13. The second seal 28 is disposed between the cylinder 7 and the
first shaft 5 and mainly has a function of controlling the ingress
of the exhaust gas (in particular, hydrogen gas) from the exhaust
chamber 13 into the lubrication chamber 12.
[0109] The fixed part a of the first seal 27 is fixed to the side
cover 9, and the fixed part a of the second seal 28 is fixed to the
cylinder 7. The lip parts c of each of the first seal 27 and the
second seal 28 are brought into elastic contact with the first
shaft 5.
[0110] Of the two lip parts c of the first seal 27, the lip part c
that faces the lubrication chamber 12 is referred to as a first lip
31, and the lip part c that faces the gas introduction space 29 is
referred to as a second lip 32. Of the two lip parts c of the
second seal 28, the lip part c that faces the gas introduction
space 29 is referred to as a third lip 33, and the lip part c that
faces the exhaust chamber 13 is referred to as a fourth lip 34.
[0111] The first lip 31 can be elastically deformed toward the
first shaft 5 when the pressure in the lubrication chamber 12 is
higher than that in the gas introduction space 29 and elastically
deformed away from the first shaft 5 when the pressure in the
lubrication chamber 12 is lower than that of the gas introduction
space 29. Similarly, the second lip 32, the third lip 33, and the
fourth lip 34 can be elastically deformed toward the first shaft 5
when the pressure in a space that the corresponding lip faces is
relatively high and elastically deformed away from the first shaft
5 when the pressure therein is relatively low.
[0112] The slinger 30 rotates together with the first shaft 5 and
suppresses a situation in which the lubricating oil F, which is
liquid, centrifugally reaches the first seal 27. Note that
provision of the slinger 30 is optional.
[0113] The dry vacuum pump 1 of this embodiment is configured as
described above. Next, the operation of the dry vacuum pump 1 will
be described.
[0114] When the electromagnetic motor 3 starts rotating, the first
shaft 5 connected to the electromagnetic motor 3 rotates, and the
first timing gear 22 rotates accordingly. The second timing gear 23
is rotated by the first timing gear 22, and the second shaft 14
connected to the second timing gear 23 rotates. Specifically, the
first shaft 5 and the second shaft 14 rotate in the opposite
directions at the same speed. Through the rotation of the first
shaft 5 and the second shaft 14, the first rotors 6 and the second
rotors 15 rotate.
[0115] In the lubrication chamber 12, the first timing gear 22, the
second timing gear 23, the first bearing 24, and the second bearing
25 are lubricated with the lubricating oil F.
[0116] When the first rotors 6 and the second rotors 15 rotate, a
region where the volume is expanded and a region where the volume
is compressed are formed in each of the exhaust spaces 26.
Therefore, gas is sucked from the exhaust passage that is closer to
the region where the volume is expanded, and gas is discharged to
the exhaust passage that is closer to the region where the volume
is compressed. Thus, in the respective exhaust spaces 26, an
exhaust gas including hydrogen is sucked from the exhaust spaces 26
located at the stages immediately before or from the film forming
chamber 103 via the air-intake hole 7a, and this gas is discharged
to the exhaust spaces 26 located at the stages immediately after or
to the exhaust hole 7b. Since the gas is sequentially compressed in
the respective exhaust spaces 26 more than in the exhaust spaces 26
located at the stages immediately before, even when the pressure in
an exhaust-target system becomes sufficiently lower than the
atmospheric pressure, the gas can eventually be pressurized to
atmospheric pressure or more and discharged. At this time,
particularly in a situation where the pressure in the
exhaust-target system is high at the start of discharge, gas is
pressurized to atmospheric pressure or more in the above-described
region where the volume is compressed, in some cases.
[0117] As described above, the film forming chamber 103 is
evacuated to a predetermined degree of vacuum or is kept at the
predetermined degree of vacuum. Since the dry vacuum pump 1 of this
embodiment includes the first seal mechanism 11 and the second seal
mechanism 16, mixing of the lubricating oil F or its mist in the
exhaust gas is suppressed, and contamination in the exhaust-target
system is suppressed, as described later. Further, since the
ingress of the exhaust gas from the exhaust chamber 13 into the
lubrication chamber 12 is suppressed, a situation in which the
electromagnetic motor 3 is exposed to the exhaust gas is
suppressed. As a result, even when a large amount of hydrogen is
contained in the exhaust gas, it is possible to suppress
deterioration of the permanent magnet material of the
electromagnetic motor 3.
[0118] In the first seal mechanism 11 and the second seal mechanism
16, because a seal gas is supplied, and the pair of lip parts c
that projects in opposite directions from each other along the
axial direction of the shaft are provided, a situation in which the
exhaust gas enters the lubrication chamber 12 and the
electromagnetic motor 3 is exposed to the exhaust gas is prevented
more effectively.
[0119] Next, the operation of the first seal mechanism 11 will be
described. Note that the operation of the second seal mechanism 16
is the same as that of the seal mechanism 11.
[0120] When the gas introduction space 29 is filled with a seal
gas, the pressure in the gas introduction space 29 is increased. As
the seal gas (seal-gas supply source), an inert gas that does not
react with gas components in the exhaust gas is used. As the inert
gas, nitrogen gas or argon gas can be used; however, nitrogen gas
is preferable because nitrogen gas is low in price, and, even when
nitrogen gas is mixed in the exhaust chamber 13, a reduction in the
exhaust capability of the dry vacuum pump is suppressed to a low
level because nitrogen gas has a high molecular weight.
[0121] Through introduction of the seal gas, the flow rate of the
seal gas is adjusted such that the gas introduction space 29 has a
pressure (pressure at which a sufficient flow rate of the seal gas
can be obtained) higher than the maximum pressure in the exhaust
spaces 26, to be described later.
[0122] FIG. 8 shows a result obtained when the concentration of
hydrogen gas leaked into the lubrication chamber 12 is measured
with respect to the flow rate of the seal gas, in a case where 100
SLM of hydrogen gas is discharged as the exhaust gas, and nitrogen
gas is used as the seal gas. When the flow rate of the seal gas
(nitrogen gas) was zero (0 SLM), the hydrogen concentration in the
lubrication chamber 12 was 60 ppm. However, when 5 SLM or more of
the seal gas (nitrogen gas) was introduced, the hydrogen
concentration in the lubrication chamber 12 was of the limit of
measurement or less. It was confirmed that hydrogen gas had been
prevented from entering the lubrication chamber 12. If the pressure
in the lubrication chamber 12 is overly increased by increasing the
flow rate of the seal gas, there is a concern that a small amount
of oil mist of the lubricating oil F that passes through a gas
discharge passage 53 and is not trapped by an oil trap 55 may be
discharged to the exhaust line 62. Thus, it is preferable that the
pressure in the lubrication chamber 12 not be increased more than
necessary.
[0123] In forming the crystalline silicon film on the substrate
having a large area of more than 1 m.sup.2, the flow rate of the
seal gas, for example, nitrogen gas, is set to 5 SLM to 10 SLM,
which is about 1/10 to about 1/20 of the flow rate of the exhaust
gas.
[0124] In the first seal 27, when the first shaft 5 rotates, the
seal gas is caught in the sliding portion between the second lip 32
and the first shaft 5 to push up the second lip 32 and then flows
out from a formed gap. The seal gas flowing out is further caught
in the sliding portion between the first lip 31 and the first shaft
5 to push up the first lip 31 and then flows out from a formed gap
to the lubrication chamber 12. Specifically, the seal gas flows out
from the gas introduction space 29, passes through the gaps formed
between the first seal 27 and the first shaft 5, and blows out to
the lubrication chamber 12.
[0125] Also in the second seal 28, when the first shaft 5 rotates,
the seal gas is caught in the sliding portion between the third lip
33 and the first shaft 5 to push up the third lip 33 and then flows
out from a formed gap. The seal gas flowing out is further caught
in the sliding portion between the fourth lip 34 and the first
shaft 5 to push up the fourth lip 34 and then flows out from a
formed gap. Specifically, the seal gas flows out from the gas
introduction space 29, passes through the gaps formed between the
second seal 28 and the first shaft 5, and blows out to the exhaust
chamber 13.
[0126] As described above, with the seal gas blowing out from the
gaps formed between the first seal 27 and the first shaft 5 and
blowing out from the gaps formed between the second seal 28 and the
first shaft 5, a situation in which the lubricating oil F and its
mist in the lubrication chamber 12 pass through the first seal 27
to enter the gas introduction space 29 or a situation in which the
exhaust gas in the exhaust chamber 13 passes through the second
seal 28 to enter the gas introduction space 29 is prevented more
effectively.
[0127] On the other hand, as shown in FIG. 3, one end of the gas
discharge passage 53 may be connected to the motor cover 8, which
partitions the interior space of the electromagnetic motor 3 and
the lubrication chamber 12, and the other end of the gas discharge
passage 53 may be connected to the exhaust line 62. The gas
discharge passage 53 can be used to discharge, to the exhaust line
62, the seal gas introduced from the gas introduction space 29 and
leaking into the lubrication chamber 12 and the exhaust gas leaking
into the lubrication chamber 12.
[0128] Furthermore, the gas discharge passage 53 may be provided
with a check valve 54 and the oil trap 55.
[0129] The check valve 54 permits a flow of gas flowing from the
lubrication chamber 12 toward the exhaust line 62 and prohibits the
opposite flow. As a result, the exhaust gas in the film forming
chamber (vacuum processing chamber) 103 discharged from the exhaust
hole 7b of the exhaust chamber 13 is prevented from entering the
lubrication chamber 12 via the gas discharge passage 53.
[0130] The oil trap 55 is provided at a position in the gas
discharge passage 53, between the lubrication chamber 12 and the
check valve 54. The oil trap 55 prevents the lubricating oil F in
the lubrication chamber 12 from being carried over to enter the
exhaust line 62 together with the seal gas (nitrogen gas)
introduced from the gas introduction space 29 and leaking into the
lubrication chamber 12 and the exhaust gas leaking into the
lubrication chamber 12. As the oil trap 55, an appropriate
component, such as a filter or a water-cooled trap, can be used,
for example.
[0131] There is an important phenomenon in which the pressure in
the exhaust chamber 13 fluctuates when the dry vacuum pump 1 starts
evacuation of the system. As described above, in the dry vacuum
pump 1, through the rotation of the first rotors 6 and the second
rotors 15, regions where the volumes are reduced or increased are
generated in each exhaust space 26. Since the exhaust gas in the
exhaust space 26 located at the last stage is compressed to a
relatively high pressure, and this exhaust space 26 is adjacent to
the second seal 28, the region where the pressure is high
(high-pressure region) and the region where the pressure is low
(low-pressure region) in the exhaust space 26 located at the last
stage are generated around the second seal 28. These regions move
in accordance with the rotation of the first rotors 6 and the
second rotors 15, and the pressures thereof are also increased and
decreased. Thus, from a close consideration of pressure
fluctuations, it was found that the pressure imposed on the
ring-like second seal 28 is not uniform over the whole
circumference of the second seal 28.
[0132] The fourth lip 34 is deformed toward the shaft 5 when the
pressure in the space that the fourth lip 34 faces is high and is
deformed away from the shaft 5 when the pressure in the space that
the fourth lip 34 faces is low. Specifically, a small gap is formed
at a portion of the fourth lip 34 that faces the high-pressure
region, and a large gap is formed at a portion of the fourth lip 34
that faces the low-pressure region. When the flow rate of seal gas
flowing from the portion of the fourth lip 34 that faces the
low-pressure region is getting larger than the flow rate of seal
gas flowing from the portion of the fourth lip 34 that faces the
high-pressure region, the third lip 33, corresponding to the
circumferential position of this portion of the fourth lip 34 that
faces the low-pressure region, is influenced by the deformation of
the fourth lip 34 to reduce a gap formed between the third lip 33
and the shaft 5, thereby restricting the flow rate. In short, there
is an effect in which the flow rate of the seal gas to the
high-pressure region (to which the flow rate of the seal gas is
unlikely to flow out) is relatively increased, thereby making the
flow rate of the seal gas uniform over the whole circumference of
the second seal 28.
[0133] In a structure in which the third lip 33 is not provided,
when the gap formed between the portion of the fourth lip 34 that
faces the low-pressure region and the first shaft 5 becomes larger
than the gap formed between the portion of the fourth lip 34 that
faces the high-pressure region and the shaft 5, the seal gas in the
circumference of the second seal 28 is not restricted according to
the flow rate. Thus, a large amount of seal gas flows out from the
portion facing the low-pressure region, and the flow rate of seal
gas from the portion facing the high-pressure region is reduced or
the seal gas flowing out therefrom is stopped. Thus, there is a
possibility that the sealing property with respect to the exhaust
gas (particularly, hydrogen gas) is reduced. A possibility occurs
that the exhaust gas (particularly, hydrogen gas) flows out from
the high-pressure region, passes through the gas introduction space
29, leaks into the lubrication chamber 12 together with the seal
gas, flows along the surface of the shaft 5, and enters the
electromagnetic motor 3.
[0134] In a structure in which the fourth lip 34 is not provided,
the pressure difference between the high-pressure region and the
gas introduction space 29 is relatively large with respect to the
pressure difference between the low-pressure region and the gas
introduction space 29. Thus, the gap formed between the portion of
the third lip 33 that faces the high-pressure region and the first
shaft 5 is larger than the gap formed between the portion of the
third lip 33 that faces the low-pressure region and the first shaft
5, and the sealing property with respect to the ingress of the
exhaust gas from the high-pressure region is reduced.
[0135] In this way, when the third lip 33 and the fourth lip 34 are
provided in the second seal 28, even when the imposed pressure of
the exhaust gas is not uniform over the whole circumference, the
third lip 33 and the fourth lip 34 can cooperate to further prevent
the exhaust gas from entering the gas introduction space 29.
[0136] Even when the pressure of the exhaust gas is uniform over
the whole circumference of the second seal 28, there is a
conceivable case where the pressure of the exhaust gas is changed
with time according to the progress of evacuation of the system,
for example. In this case, if only one of the third lip 33 and the
fourth lip 34 is provided, the sealing property is reduced or the
pressure in the gas introduction space 29 is reduced, due to a
pressure fluctuation. In contrast, in the seal mechanism 11, in
which the third lip 33 and the fourth lip 34 are provided, it is
possible to prevent the exhaust gas from entering the gas
introduction space 29, according to a pressure fluctuation, as
described above.
[0137] The first lip 31 of the first seal 27 prevents the
lubricating oil F and its mist from reaching the second lip 32. In
a structure in which the first lip 31 is not provided, because the
second lip 32 is brought into contact with the lubricating oil F,
there is a concern that the lubricating oil F infiltrates the
sliding portion of the second lip 32 and the shaft 5, and the
lubricating oil F or its mist enters the gas introduction space 29
through penetration due to surface tension in a minute scratch or
from a portion where the pressure balance is slightly disrupted.
Furthermore, when the pressure balance between the lubrication
chamber 12 and the exhaust chamber 13 is changed, the lubricating
oil F or its mist enters the gas introduction space 29, in some
cases. In contrast, in the seal mechanism 11, in which the first
lip 31 and the second lip 32 are provided, it is possible to
prevent the lubricating oil F or its mist from entering the gas
introduction space 29, according to the pressure fluctuation, as
described above.
[0138] As described above, the seal mechanism 11 and the second
seal mechanism 16 of this embodiment each have a lip structure in
which the lips project in opposite directions from each other,
along the axial direction of the shaft; therefore, the first seal
27 prevents the lubricating oil F and its mist from entering the
gas introduction space 29, and the second seal 28 prevents the
exhaust gas from entering the gas introduction space 29.
Specifically, the lubricating oil F in the lubrication chamber 12
and the exhaust gas in the exhaust chamber 13 can be sealed with
high sealing properties.
[0139] As described above, according to this embodiment, since the
exhaust gas (particularly, hydrogen) can be prevented from entering
the lubrication chamber 12 from the exhaust chamber 13, the
permanent magnet material of the electromagnetic motor 3 is not
exposed to the exhaust gas. Thus, hydrogen corrosion of the
permanent magnet material of the electromagnetic motor 3 by a large
amount of hydrogen gas included in the exhaust gas is effectively
inhibited, and the reliability of the electromagnetic motor 3 is
dramatically improved.
Second Embodiment
[0140] In a second embodiment, a purge mechanism (purge means) 40
is provided in the dry vacuum pump 1 of the first embodiment, and a
description overlapped with the first embodiment will be
omitted.
[0141] The purge mechanism (purge means) 40 will be described
below.
[0142] As shown in FIG. 9 and FIG. 10, the purge mechanism 40 has a
gas introduction section 50 and the gas discharge passage 53. The
purge mechanism 40 is used to dilute hydrogen in the exhaust gas
leaking into the lubrication chamber 12 via the seal mechanisms 11
and 16, with an inert gas, and an inert gas that does not react
with gas components in the exhaust gas is used. As the inert gas,
nitrogen gas and argon gas, are preferable because nitrogen gas is
low in price, and, even when the nitrogen gas is mixed in the
exhaust chamber 13, a reduction in the exhaust capability of the
dry vacuum pump is suppressed to a low level because nitrogen gas
has a high molecular weight. In this embodiment, nitrogen gas is
used.
[0143] The gas introduction section 50 is formed at a portion of
the container of the electromagnetic motor chamber 10, which
accommodates the electromagnetic motor 3, and is introduced into
the interior space of the electromagnetic motor 3. One end of the
gas introduction section 50 is connected to a nitrogen-gas
introduction source 51 that is provided outside the electromagnetic
motor chamber 10. Thus, nitrogen gas introduced from the
nitrogen-gas introduction source 51 is introduced into the
lubrication chamber 12 from the interior space of the
electromagnetic motor 3 via the gas introduction section 50. While
the dry vacuum pump 1 is being operated, the nitrogen gas is always
introduced into the lubrication chamber 12 from the interior space
of the electromagnetic motor 3. As a result, the interior space of
the electromagnetic motor 3 and the lubrication chamber 12 are
always maintained in a nitrogen-gas atmosphere.
[0144] The interior space of the electromagnetic motor 3 having the
gas introduction section 50 is connected to the motor cover 8,
which partitions the lubrication chamber 12, and the other end of
the gas discharge passage 53 is connected to the exhaust line 62.
The gas discharge passage 53 is used to discharge, to the exhaust
line 62, the nitrogen gas (purge gas) introduced into the
lubrication chamber 12, the seal gas introduced from the gas
introduction space 29 and leaking into the lubrication chamber 12,
and the exhaust gas leaking into the lubrication chamber 12.
[0145] The purge mechanism 40 further includes the check valve 54
and the oil trap 55. The check valve 54 and the oil trap 55 are
disposed in the gas discharge passage 53.
[0146] The check valve 54 permits a flow of gas flowing from the
lubrication chamber 12 toward the exhaust line 62 and prohibits the
opposite flow. As a result, the exhaust gas in the film forming
chamber (vacuum processing chamber) 103 discharged from the exhaust
hole 7b of the exhaust chamber 13 is prevented from entering the
lubrication chamber 12 via the gas discharge passage 53.
[0147] The oil trap 55 is provided at a position in the gas
discharge passage 53, between the lubrication chamber 12 and the
check valve 54. The oil trap 55 prevents the lubricating oil F in
the lubrication chamber 12 from being carried over to enter the
exhaust line 62 together with the nitrogen gas (purge gas)
discharged from the lubrication chamber 12, the seal gas introduced
from the gas introduction space 29 and leaking into the lubrication
chamber 12, and the exhaust gas leaking into the lubrication
chamber 12. As the oil trap 55, an appropriate component, such as a
filter or a water-cooled trap, can be used, for example.
[0148] Depending on the pressure relationship between the exhaust
chamber 13 and the gas introduction space 29 or the pressure
relationship between the gas introduction space 29 and the
lubrication chamber 12, there is a possibility that the exhaust gas
including hydrogen sucked into the exhaust chamber 13 from the film
forming chamber 103 may enter the lubrication chamber 12 via the
seal mechanisms 11 and 16. In this case, there is a concern that
the exhaust gas including hydrogen gas entering the lubrication
chamber 12 is brought into contact with the electromagnetic motor
3, and the permanent magnet material of the electromagnetic motor 3
is subjected to hydrogen corrosion through the contact with the
hydrogen gas and is reduced in excitation power due to the damage
thereto. In this case, the function of the dry vacuum pump 1 as the
drive source deteriorates, and malfunction is caused in the worst
case.
[0149] In order to prevent this situation, in this embodiment, the
above-described adverse effect on the electromagnetic motor 3 is
avoided by decreasing the hydrogen concentration of the exhaust gas
entering the lubrication chamber 12, by the purge mechanism 40,
while the dry vacuum pump 1 is being operated. Specifically, in
this embodiment, during the operation of the dry vacuum pump 1,
while a purge gas (nitrogen gas) is introduced from the
nitrogen-gas introduction source 51 into the interior space of the
electromagnetic motor 3 and the lubrication chamber 12 via the gas
introduction section 50, the introduced purge gas is discharged to
the exhaust line 62 via the gas discharge passage 53. Thus, the
interior space of the electromagnetic motor 3 and the inside of the
lubrication chamber 12 can be maintained in the nitrogen-gas
atmosphere, and, even when the exhaust gas including hydrogen gas
enters the lubrication chamber 12 via the seal mechanisms 11 and
16, it is possible to suppress the hydrogen-gas concentration in
the interior space of the electromagnetic motor 3 and the
lubrication chamber 12 to a predetermined level or less.
[0150] In this embodiment, an appropriate flow rate of nitrogen
gas, serving as a purge gas, to be introduced into the interior
space of the electromagnetic motor 3 and the lubrication chamber 12
can be selected by mixing helium into the exhaust gas, connecting a
helium leak detector to the interior space of the electromagnetic
motor 3 or the lubrication chamber 12, and measuring a change in
helium concentration.
[0151] In this embodiment, the helium concentration was measured
with the helium leak detector while the flow rate of nitrogen gas
serving as a purge gas introduced via the gas introduction section
50 was changed in a range from 1 SLM to 3 SLM. When the flow rate
of nitrogen gas was set to 1.0 SLM or more, the helium
concentration became constant at a very low concentration.
Therefore, a flow rate of 1.0 SLM was selected in order to
effectively use nitrogen gas.
[0152] The flow rate of the purge gas is not particularly limited
and can be set to an appropriate value in consideration of the
volumes of the interior space of the electromagnetic motor 3 and
the lubrication chamber 12 and the amount of hydrogen gas entering
the lubrication chamber 12.
[0153] Furthermore, in this embodiment, since the check valve 54,
having the above-described configuration, is provided in the gas
discharge passage 53, the exhaust gas discharged to the exhaust
line 62 from the film forming chamber 103 via the exhaust hole 7b
is prevented from entering the lubrication chamber 12 via the gas
discharge passage 53. Thus, the nitrogen-gas atmosphere in the
lubrication chamber 12 can be maintained.
[0154] Furthermore, in this embodiment, since the oil trap 55 is
provided in the gas discharge passage 53, the lubricating oil F in
the lubrication chamber 12 is prevented from being discharged to
the exhaust line 62 together with the purge gas. Thus,
contamination in the exhaust line 62 caused by the oil is
prevented, and a clean exhaust system can be obtained.
Third Embodiment
[0155] In a third embodiment, a gas introduction passage 52 is
provided in the gas introduction section 50 of the second
embodiment, and a description overlapped with the second embodiment
will be omitted.
[0156] As shown in FIG. 11, the purge mechanism (purge means) 40
has the gas introduction passage 52 and the gas discharge passage
53. The purge mechanism 40 is used to dilute hydrogen in the
exhaust gas leaking into the lubrication chamber 12 via the seal
mechanisms 11 and 16, with an inert gas. A description will be
given of a case where nitrogen gas is used as the inert gas.
[0157] The gas introduction passage 52 is formed in the rotational
axis (rotor) of the electromagnetic motor 3 and a shaft center
portion of the shaft 5. One end of the gas introduction passage 52
is connected to the nitrogen-gas introduction source 51, provided
outside the electromagnetic motor 3, via the gas introduction
section 50, formed at the container of the electromagnetic motor
chamber 10. The other end of the gas introduction passage 52 faces
an outer circumferential portion of the shaft 5 located in the
lubrication chamber 12. Thus, nitrogen gas introduced from the
nitrogen-gas introduction source 51 is introduced into the
lubrication chamber 12 via the gas introduction passage 52. The
nitrogen gas is always introduced into the lubrication chamber 12
while the dry vacuum pump 1 is being operated. As a result, the
lubrication chamber 12 is always maintained in the nitrogen-gas
atmosphere.
[0158] Note that a small gap is provided between the gas
introduction section 50 and the gas introduction passage 52 at the
axial end of the shaft 5 such that the shaft 5 can rotate. Most of
a purge gas introduced from the gas introduction section 50 may be
introduced into the gas introduction passage 52, and part of the
purge gas may be used to purge the inside of the electromagnetic
motor chamber 10.
[0159] One end of the gas discharge passage 53 is connected to the
motor cover 8, which partitions the lubrication chamber 12, and the
other end of the gas discharge passage 53 is connected to the
exhaust line 62. The gas discharge passage 53 is used to discharge,
to the exhaust line 62, the nitrogen gas (purge gas) introduced
into the lubrication chamber 12, the seal gas introduced from the
gas introduction space 29 and leaking into the lubrication chamber
12, and the exhaust gas leaking into the lubrication chamber
12.
[0160] In third embodiment, since the gas introduction passage 52
is provided in the rotational axis of the electromagnetic motor 3
and the shaft center portion of the shaft 5, there is an advantage
that piping is simple because piping drawing around the
electromagnetic motor 3 is unnecessary. Furthermore, since nitrogen
gas is directly introduced from the periphery of the rotating shaft
5 into the lubrication chamber 12, there is an advantage that the
periphery of the shaft 5 can be always covered with the nitrogen
gas, and the ingress of the exhaust gas including hydrogen into the
electromagnetic motor 3 can be effectively prevented. Since the
hydrogen gas in the exhaust gas leaking into the lubrication
chamber from the exhaust chamber via the seal mechanisms 11 and 16
is directly diluted by the purge mechanism, and the hydrogen-gas
partial pressure of the exhaust gas including the hydrogen gas
leaking into the lubrication chamber from the exhaust chamber is
also reduced, hydrogen corrosion of the permanent magnet material
of the electromagnetic motor 3 can be prevented more
effectively.
[0161] In this way, it is possible to prevent malfunction of the
drive source caused by hydrogen included in the exhaust gas.
[0162] Although the embodiments of the present invention have been
described as above, the present invention is not limited to the
above-described embodiments, and various modifications can be made
based on the technical idea of the present invention.
[0163] For example, a description has been given of a case where
the first lip 31 and the second lip 32 of the first seal 27 have an
integral structure, and the third lip 33 and the fourth lip 34 of
the second seal 28 have an integral structure. However, the first
lip 31, the second lip 32, the third lip 33, the fourth lip 34 may
be manufactured as individual units, and then, the first lip 31 and
the second lip 32 may be combined to form the first seal 27, and
the third lip 33 and the fourth lip 34 may be combined to form the
second seal 28.
[0164] At this time, it is preferable that the first lip 31 and the
second lip 32 be in close contact with each other and the third lip
33 and the fourth lip 34 be in close contact with each other, to be
regarded as an integral structure such that a gap formed with
respect to the shaft is adjusted upon reception of an influence of
the deformation of the mating lip. Furthermore, it is more
preferable to provide a structure in which the lips can be embedded
to be mutually positioned when the lips are combined, because the
first seal 27 and the second seal 28 can be precisely
configured.
[0165] In this way, when the lips are manufactured as individual
units, the manufacturing process becomes easy, and the cost can be
reduced.
[0166] Furthermore, for example, the first lip 31 and the second
lip 32 of the first seal 27 and the third lip 33 and the fourth lip
34 of the second seal 28 are not necessarily the same size. The
first lip 31 and the second lip 32, and the third lip 33 and the
fourth lip 34 may be manufactured such that a lip with high
elasticity is provided at a place where the pressure difference is
large, and a lip with flexibility is provided at a place where the
pressure difference is small, according to the operation of the dry
vacuum pump 1.
[0167] At this time, since the respective lips have different
sizes, the first lip 31, the second lip 32, the third lip 33, and
the fourth lip 34 may be manufactured as individual units.
[0168] By providing the lip structures corresponding to the
pressure differences according to the operation of the dry vacuum
pump 1, the sealing property is further improved. Therefore, the
hydrogen corrosion of the permanent magnet material of the
electromagnetic motor 3 caused by a large amount of hydrogen gas
included in the exhaust gas is further inhibited, and the
reliability of the electromagnetic motor 3 is further enhanced.
[0169] Furthermore, for example, in the above-described
embodiments, the first seal mechanism 11 and the second seal
mechanism 16 are used to seal between the lubrication chamber 12
and the exhaust chamber 13; however, the place at which they are
used is not limited thereto, and they may be used to seal between
the bearing chamber (next chamber) 17 and the exhaust chamber 13.
As a result, particularly when the degree of vacuum in the
exhaust-target system is not large, the lubricating oil etc. filled
in the bearing chamber 17 can be prevented from leaking into the
exhaust chamber 13.
[0170] Furthermore, for example, in the above-described
embodiments, the seal mechanisms 11 and 16, having the
above-described structures, are disposed as seals disposed between
the lubrication chamber 12 and the exhaust chamber 13; however, the
structures thereof are not limited to thereto, and the
above-described seal mechanisms may have an O-ring structure in
cross-section. Furthermore, in the seal mechanisms 11 and 16, the
second seal 28, disposed closer to the exhaust chamber 13, may be
omitted.
* * * * *