U.S. patent application number 10/486189 was filed with the patent office on 2004-09-09 for vacuum exhaust apparatus and drive method of vacuum apparatus.
Invention is credited to Aikawa, Junichi, Fukaura, Yuuji, Kanke, Yukio, Shibayama, Kouji, Tanaka, Tomonari, Tashima, Takahiko, Yahagi, Mitsuru, Yamashita, Yuuichi.
Application Number | 20040173312 10/486189 |
Document ID | / |
Family ID | 27531990 |
Filed Date | 2004-09-09 |
United States Patent
Application |
20040173312 |
Kind Code |
A1 |
Shibayama, Kouji ; et
al. |
September 9, 2004 |
Vacuum exhaust apparatus and drive method of vacuum apparatus
Abstract
Pairs of rotors (R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and
R.sub.6) driven rotationally by a motor (22) are disposed in the
body (21) of a main pump (20) comprising a multistage Roots dry
vacuum pump. A suction opening (23) communicating with the rotor
chamber of the rotor R.sub.1 is provided in the upper wall portion
at the left end of the body (21). A delivery section (24)
communicating with the delivery side of the rotor chamber of rotor
R.sub.6 on the final stage is coupled to an exhaust pipe (25) and
is provided with a silencer (26) and further coupled to a check
valve (28) through a pipe (27). The check valve (28) has its
forward direction toward the atmospheric side. The delivery section
(24), or a delivery section (24') at the side intermediate stage,
is coupled to an auxiliary pump (30) having an exhaust capacity
smaller than that of the main pump (20). When the motor (22) is
driven, gas exhausted through rotation of the rotors
(R.sub.1-R.sub.6) is carried sequentially to the downstream side
from the rotor chambers and a vacuum processing chamber coupled to
the suction opening (23) is exhausted. The delivery section (24) on
the final stage is exhausted by driving the auxiliary pump (30),
and the pressure is reduced. Consequently, the burden of the
exhaust action on the rotor (R.sub.6) on the final stage or the
rotor (R.sub.5) on the intermediate stage is lessened, and the
power consumption of the motor (22) can be reduced significantly as
compared with the prior art.
Inventors: |
Shibayama, Kouji; (Kanagawa,
JP) ; Yamashita, Yuuichi; (Kanagawa, JP) ;
Yahagi, Mitsuru; (Kanagawa, JP) ; Tashima,
Takahiko; (Kanagawa, JP) ; Aikawa, Junichi;
(Kanagawa, JP) ; Tanaka, Tomonari; (Kanagawa,
JP) ; Kanke, Yukio; (Kanagawa, JP) ; Fukaura,
Yuuji; (Kanagawa, JP) |
Correspondence
Address: |
Carothers & Carothers
Suite 500
445 Fort Pitt Boulevard
Pittsburgh
PA
15219
US
|
Family ID: |
27531990 |
Appl. No.: |
10/486189 |
Filed: |
February 5, 2004 |
PCT Filed: |
September 5, 2002 |
PCT NO: |
PCT/JP02/09048 |
Current U.S.
Class: |
156/345.29 |
Current CPC
Class: |
F04C 23/001 20130101;
F16K 15/042 20130101; F04C 2220/12 20130101 |
Class at
Publication: |
156/345.29 |
International
Class: |
C23F 001/00 |
Claims
1. A vacuum exhaust apparatus characterized in that an inlet side
of an auxiliary pump is connected to an outlet side of a pump
chamber of a middle stage or last stage, of a main pump.
2. A vacuum exhaust apparatus according to claim 1 in which the
throughput of said auxiliary pump is smaller than that of main
pump.
3. A vacuum exhaust apparatus according to claim 1 or 2 in which at
least one of pump chambers at the latter stage of said main pump is
smaller than the pump chambers of the former stage of said main
pump so that the throughput of the latter stage is smaller than
that of the former stage.
4. A vacuum exhaust apparatus according to any one of claims 1 to 3
in which an exhaust pipe is connected to an outlet side of the pump
chamber of the last stage of said main pump and a check valve
permitting gas to flow only in the direction towards the atmosphere
is connected to said exhaust pipe.
5. A vacuum exhaust apparatus according to claim 4 in which said
check valve consists of plural members serially connected to each
other.
6. A vacuum exhaust apparatus according to claim 5 in which said
check valve includes a first check valve member which includes a
ball valve body floatable in a valve chamber, said valve body
floats up by an exhaust gas pressure of said main pump to open the
valve and it seats on a valve seat by self-weight under said
exhaust gas pressure, to close the valve, and a second check valve
member similar to said first check valve, said first and second
check valve members being serially connected with each other.
7. A vacuum exhaust apparatus according to any one of claims 4 to 6
in which said auxiliary pump is connected in parallel with said
check valve.
8. A vacuum exhaust apparatus according to claim 6 in which a space
between said first and second check valve members is connected to
the suction side of said auxiliary pump.
9. A vacuum exhaust apparatus according to claim 6 in which said
ball valve body consists of a hollow metal ball and is coated with
rubber.
10. A vacuum exhaust apparatus characterized in that said apparatus
includes a main pump, a check valve permitting gas to flow only in
the direction towards the atmosphere, connected to the outlet side
of said main pump and an auxiliary pump of smaller throughput than
that of said main pump connected in parallel with said check valve
at the outlet side of said main pump and said auxiliary pump is
driven at the pumping speed lower than 3% of that of said main pump
at the inlet pressure 400 Pa of said main pump.
11. A vacuum exhaust apparatus according to claim 10 in which said
main pump is a dry vacuum pump of the positive displacement type or
composite type pump consisting of plural dry vacuum pumps connected
serially to each other.
12. A vacuum exhaust apparatus according to claim 10 in which a
plurality of said main pumps are connected in parallel with each
other and the inlet side of said auxiliary pump is connected to the
respective outlets of said main pump.
13. A vacuum exhaust apparatus according to claim 10 in which the
ultimate pressure of said auxiliary pump is under 20 kPa.
14. A vacuum exhaust apparatus according to claim 13 in which said
auxiliary pump is a sliding-vane type (Gede type), a piston type, a
diaphragm type (membrane type) or scroll type.
15. A vacuum exhaust apparatus characterized in that said apparatus
includes a main pump connected to a vacuum processing chamber, a
check valve permitting gas to flow only in the direction towards
the atmosphere, connected to the outlet side of said main pump and
an auxiliary pump of smaller throughout than that of said main pump
connected in parallel with said check valve at the outlet side of
said main pump, whereby, when said vacuum processing chamber is
exhausted form the atmosphere or from near the atmosphere, first
said auxiliary pump is driven and after said vacuum processing
chamber has reached a predetermined pressure, said main pump is
driven.
16. A vacuum exhaust apparatus characterized in that said apparatus
includes a main pump connected to a vacuum processing chamber, a
check valve permitting gas to flow only in the direction towards
the atmosphere, connected to the outlet side of said main pump and
an auxiliary pump of smaller throughput than that of said main pump
connected in parallel with said check valve at the outlet side of
said main pump, whereby, when said vacuum processing chamber is
exhausted from the atmosphere or from near atmosphere, first said
auxiliary pump is driven and before said vacuum processing chamber
reaches a predetermined pressure, said main pump is started to be
driven at the lower speed or the lower pumping speed and the
rotational speed is raised in accordance with the pressure of the
vacuum processing chamber.
Description
[TECHNICAL FIELD]
[0001] This invention relates to a vacuum exhaust apparatus, for
example, for semiconductor manufacturing equipment and more
particularly to a vacuum exhaust apparatus of the energy
conservation type and a driving method for the vacuum exhaust
apparatus to reduce consumed electric power.
[BACKGROUND OF THE TECHNIQUE]
[0002] Oil-sealed rotary vacuum pumps were used in most cases for
early semiconductor manufacturing equipment. Electric power
consumed by the oil-sealed rotary vacuum pump is generally little
and it has a construction by which low ultimate pressure can be
easily obtained. However, the following points should be noted
where the oil-sealed rotary pump is used in semiconductor
manufacturing equipment:
[0003] (1) The gasses used in semiconductor manufacturing equipment
are strongly reactant in most cases. When such gas is exhausted, it
reacts with vacuum pump oil and so produces reaction materials
which sometimes makes the vacuum pump impossible to rotate or the
pump oil is caused to deteriorate in lubrication capability.
[0004] (2) Vapor of the vacuum pump oil diffuses into the vacuum
treatment or processing chamber and contaminates it.
[0005] (3) Used vacuum pump oil contains arsenic compound and
phosphorus compound as toxic material in most cases. Treatment of
such harmful industrial waste requires considerable cost and the
number of management procedures is also considerable. For the above
reasons a recently developed dry vacuum pump (called also a
"dry-sealed vacuum pump" according to the international standard
ISO/DIS3529/.dagger-dbl.U-1975) which does not use sealing oil, is
used instead of the oil-sealed rotary vacuum pump.
[0006] The dry vacuum pump can vacuum-pump a chamber from
atmosphere and dose not contain seal oil in its compression
chamber. It is a so-called mechanical vacuum pump. Positive
displacement types such as a Roots type vacuum pump, a claw type
vacuum pump and a screw type are used as the dry vacuum pump in
most cases. These vacuum pumps all have a construction having two
axes to which a pair of rotors is fixed and spaced a little gap
from each other. The paired rotors are rotated in opposite
directions for the vacuum pumping. The pump life is long because of
non-contact portions. It can also exhaust solid components
contained in the gas sucked from the semiconductor manufacturing
equipment. Further, resistance to corrosive gas can be easily
imparted to the positive displacement type.
[0007] Thus, a dry vacuum pump has been substituted with the
oil-sealed rotary vacuum pump in semiconductor manufacturing
equipment. However, there is a problem that the required electric
power of the dry vacuum pump is larger than that of the oil-sealed
vacuum pump.
[0008] It is required to save consumption of energy from an
ecological standpoint. It is also required to reduce the cost of
manufacture of the semiconductor. From the above requirements, it
is desired to reduce the consumed electric power of the dry vacuum
pump to less than 50% of the present.
[0009] For example, the Roots-type dry vacuum pump is provided with
plural rotors fixed to the axes, adjacent each other. The paired
rotors are spaced by a small gap from each other and rotated in
opposite directions to suck and exhaust gas. The rotors constitute
normally three to six pump chambers. The respective pump chambers
effect pumping actions in regular sequences. The gas to be
exhausted is displaced from the earlier or former stages to the
latter stages. The gas pressure rises with the displacement.
Accordingly, the throughput of the latter stages may be smaller
than that of the earlier stages.
[0010] In the multi-stage Roots-type dry vacuum pump, the external
form of the rotors are all made to be the same from the viewpoint
of simple manufacture and synchronization of the rotations of the
rotors. For the above reason, the thickness of the rotors is
stepwise smaller towards the outlet side from the inlet side so as
to reduce stepwise the throughputs of the pump chambers.
[0011] In the Roots-type dry vacuum pump, gas to be exhausted is
temporarily confined in a space formed by an inner surface of a
casing and a hollow on the surface of the rotor and the space comes
to communicate with the outlet side space, with further rotation of
the rotor. On that communication, the outlet side gas is reversely
flowed into the space. An ultimate pressure of about 1 to 10 Pa can
be obtained by the Roots-type dry vacuum pump. A pressure from the
ultimate pressure to about 3 kPa is a normal pressure. The outlet
pressure is atmospheric pressure. Accordingly, in order to maintain
the inlet side at the reduced pressure, the gas reversed into the
rotor chamber in the compression process should be pushed back.
About 70 to 80 percentage of the total electric power of the pump
is consumed to receive the back flow or push the flow gas from the
atmosphere in the rotor chamber of the last stage.
[0012] In the Roots-type dry vacuum pump, the power for the final
stage becomes smaller with a decrease of the amount of gas to be
pushed back. Accordingly, as above described, the thickness of the
rotor of the latter stage is reduced so as to reduce the
throughput. Thus, when the throughput of the rotor chamber of the
last stage is so set as to be small, the required power of the pump
is reduced in the range of the normal pressure, and therefore
energy conservation is obtained.
[0013] The exhaust principle of the claw-type dry vacuum pump is
quite the same as that of the Roots-type dry vacuum pump, although
the shapes of the rotors are different between the Roots-type and
the claw type. On the other hand, the gas is transported axially
along the space constituted by the two screw grooves, in the screw
type. The gas of the outlet portion is flowed into the space formed
by the screw grooves, to compress the gas. It is equal to the
Roots-type dry vacuum pump.
[0014] Since the screw grooves are continuous, the pitches of the
screw grooves are continuously reduced towards the last stage.
Thus, the throughput is made smaller towards the last stage,
although the throughput is arbitrarily reduced towards the last
stage in the Roots-type dry vacuum pump and the claw-type dry
vacuum pump. However, the pitch changes of the screw grooves are
limited to some extent. Accordingly, blocks different in screw
pitch are prepared, and so combined with each other as to reduce
the throughput of the last stage pump chamber.
[0015] Further description about the above follows.
[0016] When the rotors are equal in size as shown in FIG. 18, the
pumping speed changes with the inlet pressure (Pa) as shown by
letter a in FIG. 21. When the two rotors of the former stage are
equal in size, those of the middle stage are smaller than the
former two, and those of the latter stage are further smaller than
those of the middle stage, as shown in FIG. 19, the pumping speed
changes with the inlet pressure as shown by the letter b in FIG.
21. When the two rotors of the latter stage are further smaller in
comparison with the case of FIG. 19, as shown in FIG. 20, the
pumping speed changes with the inlet pressure, as shown in FIG.
21.
[0017] FIG. 22 shows the relationships between the consumed
electric power and the inlet pressure, in the respective cases of
FIG. 18, FIG. 19 and FIG. 20. Under pressure less than 10.sup.2 Pa,
which is a normal pressure for semiconductor manufacturing
equipment, the consumed electric power is the smallest in the case
of FIG. 20, that is smaller than the case of FIG. 19 and it is the
largest in the case of FIG. 18, as shown by letters c', b' and
a'.
[0018] Throughput of the last stage is designed in accordance the
use object of the pump. For example, in the multi-stage Roots-type
dry vacuum pump, throughput of the pump chamber of the last stage
is so designed as to be about 50% of that of the first stage. Much
compression heat generates within the range of the normal
temperature. In etching equipment and low pressure CVD equipment
for semiconductor manufacturing apparatus, gas generating in its
reaction process contains a component which deposits solid material
at a gas concentration beyond the saturation vapor pressure in the
vacuum exhaust apparatus. In the exhaust of such gas, a dry vacuum
pump should be heated to a high temperature such as about 100 to
160.degree. C., in order to prevent deposit of solid material. For
that purpose, a dry vacuum pump of a pumping speed ratio of about
50%, as above described, can be employed since compression heat can
be utilized to effectively heat the dry vacuum pump. Gas exhausted
from the sputtering apparatus and the vapor deposition apparatus
are mainly inert gas such as argon and helium. That being the case,
it is not necessary to heat the dry vacuum pump. Accordingly, a dry
vacuum pump, the consumed power of which is as little as possible,
is required. In that case, the throughput of the pump chamber of
the last stage is so designed as to be about 20 to 25% of that of
the pump chamber of the first stage. The consumed power in the
ultimate pressure can be reduced to 30 to 60% of that of the dry
vacuum pump in which the throughput of the last stage is about 50%
of that of the first stage.
[0019] When the throughput of the pump chamber of the last stage is
less than 20% of the throughput of the first stage in the dry
vacuum pump, which is not required to be heated at a high
temperature, more energy can be conserved. However, mechanical
trouble is apt to occur. For example, when the throughput of the
pump chamber of the last stage is about 25% of that of the first
stage in the dry vacuum pump of the class which is used at the
maximum pumping speed of 80 m.sup.3/Hr, the thickness of the rotor
of the first stage is generally about 30 mm. In that case, the
thickness of the rotor of the last stage is equal to 7.5 mm. The
mechanical strength of the rotor of the last stage is small. The
correct angle of the rotor side surface to the axis is difficult to
manufacture, and the gap between the rotor side surface and the
partition wall is difficult to maintained at 0.1 mm to 0.2 mm.
[0020] On the other hand, there is disclosed a vacuum exhaust
apparatus in Japanese Patent Opening Gazette No. 129384/1994 in
which a first vacuum pump of a large exhaust amount and a second
vacuum pump of a small exhaust amount, but capable of sufficiently
low pressure, are connected with each other, and by which total
electric power can be reduced. Particularly, as shown in FIG. 23,
an exhaust pipe 7 is connecting a first exhaust port 5 formed at a
middle portion of a connecting portion between the first pump and
the second pump, with a second exhaust port 6 formed at the exhaust
side of the second pump 4. A control valve 8 is arranged for
opening and closing the exhaust pipe 7 at the middle portion, and
it is opened and closed by the pressure of the suction side of the
first pump 3. A vacuum exhaust apparatus 2 is disclosed which can
thereby reduce total consumed power. In FIG. 23, the first vacuum
pump 3 is modeled as a vacuum pump of a direct acting type.
[0021] A reference numeral 9 represents an adsorption tower for
treating reaction gas contained in the exhausted gas.
[0022] The vacuum exhaust apparatus 2 operates as follows: FIG. 23
shows the situation directly after the start of the exhaust. The
control valve 8 is opened. The first and second pumps 3 and 4 are
driven. The inlet pressure of the first pump 3 is about equal to
the level of atmosphere. The amount of exhaust gas is large. While
the outlet portion of the first pump 3 does not become less than
atmosphere, also by the second pump 4 driven at the same time, the
control valve 8 is opened, and gas of sufficiently high density is
exhausted by the first and second pumps 3 and 4.
[0023] Thereafter, when the outlet side of the first pump 3 is
exhausted to a predetermined pressure less than atmosphere by the
second pump 4, the control valve 8 is closed. Thus, only the second
exhaust port 6 formed at the exhaust side of the second pump 4
communicates with the exhaust side of the pump.
[0024] At that time, the outlet side of the first pump 1 is
maintained at sufficiently low pressure.
[0025] The back flow gas to the first pump 3 is greatly reduced.
The power required for pushing the reverse gas backward can be
definitely reduced. Thus, the energy of the consumed electric power
of the first pump 3 can be conserved.
[0026] However, in the vacuum exhaust apparatus 2, the energy of
the whole vacuum exhaust system including the first pump 3 cannot
be always effectively conserved, although the consumed electric
power of the first pump 3 can be definitely reduced.
[0027] FIG. 24 shows a conduit diagram of a vacuum exhaust
apparatus of the prior art connected to a vacuum processing chamber
for manufacturing semiconductor. In a vacuum exhaust apparatus 10
of FIG. 24, a vacuum processing chamber 1 is connected to a dry
vacuum pump 20 of pumping speed 1000 L/min through an exhaust pipe
12.
[0028] A main valve 13 of large diameter is arranged in the exhaust
pipe 12. A by-pass valve 14 of small diameter is arranged in
parallel with the main valve 13. Further, a pressure gauge 19 for
measuring the pressure of the vacuum processing chamber 1 is
attached to the exhaust pipe 12.
[0029] Generally, the vacuum processing chamber 1 of the
semiconductor manufacturing apparatus contains fine particles which
are apt to fly up, and to be attached to a semiconductor wafer
placed in the vacuum processing chamber 1, resulting in a bad
semiconductor.
[0030] When the vacuum processing chamber 1 is exhausted from
atmosphere to vacuum, the main valve 13 and the by-pass valve 14
are closed, and the dry vacuum pump 20 is driven. Slow exhaust is
effected with the opening of the by-pass valve 14. When it is
confirmed that the pressure of the vacuum processing chamber 1
reaches a predetermined pressure, or when it is confirmed that a
predetermined time has lapsed, the main valve 13 is opened. Such a
driving method is adopted.
[0031] When the slow exhaust is effected with the valve operation,
or namely when the slow exhaust is effected with the by-pass valve
14 arranged in parallel with the main valve 14, a control apparatus
for opening the main valve 13 in accordance with the pressure of
the vacuum processing chamber 1 is required in addition to the
by-pass valve 14.
[0032] Further, a butterfly valve capable of control of the valve
opening may be used instead of the main valve 13 and by-pass valve
14 for effecting the slow exhaust. In that case, the valve opening
is made small at the early stage of the exhaust, and then made
larger in accordance with the lowering of the pressure of the
vacuum processing chamber 1. However, the butterfly valve itself
and an opening control apparatus for valve opening are expensive
and raise the cost.
[0033] On the other hand, also when the exhaust is effected with
the first pump 3 and second pump 4 in the vacuum exhaust pump 2 of
Japanese Patent Opening Gazette No.129384/1994 as shown in FIG. 23,
the fine particles fly up in the vacuum processing chamber 1 and
they contaminate the semiconductor wafer.
[0034] The object of the invention is to provide a vacuum exhaust
apparatus by which much energy conservation effect can be obtained
by mere addition with simple construction of a typical dry vacuum
pump.
[0035] A further object of the invention is to provide a drive
method for a vacuum exhaust apparatus which can effect slow exhaust
without any machine or apparatus for slow exhaust.
[DISCLOSURE OF INVENTION]
[0036] A vacuum exhaust apparatus and a drive method of the same
are constructed for achieving the above objects as follows:
[0037] In a vacuum exhaust apparatus of the invention, an inlet
side of an auxiliary pump is connected to an outlet side of a pump
chamber of a middle stage or of a last stage of a main pump.
[0038] It is preferable that the throughput of the auxiliary pump
is smaller than that of the main pump, and that at least one pump
chamber of a latter stage of the main pump is smaller than pump
chambers of a former stage of the main pump. An exhaust pipe is
connected to the outlet side of the pump chamber of the last stage
of the main pump. A check valve which permits gas to flow only in
the direction towards atmosphere, is connected to the exhaust pipe.
It is preferable that the auxiliary pump is connected in parallel
with the check valve. Plural check valves may be connected in
series with each other instead of the one check valve. It is
preferable that it includes a ball valve body floatable in a valve
chamber. When the pressure of the exhaust gas of the main pump
becomes higher than a predetermined value, the ball valve body
floats to open the valve. When the pressure of the exhaust gas of
the main pump becomes smaller than the predetermined value, the
ball valve body seats downwardly on the valve seat by self-weight
to close the valve. The ball valve body consists of a hollow metal
ball. It is preferable that the surface of the metal ball is
covered with rubber. Further, when the two check valves are
connected in series with each other, it is preferable that the
space between the two check valves is connected to the inlet side
of the auxiliary pump.
[0039] A vacuum exhaust apparatus of this invention comprises a
main pump, a check valve connected to the outlet side of the main
pump permitting gas to flow only from the main pump toward the
atmosphere side, and an auxiliary pump arranged in parallel with
the check valve connected to the outlet side of the main pump.
Throughput of the auxiliary pump is smaller than that of the main
pump. It is preferable that the auxiliary pump is driven at less
than 3% of the pumping speed of the main pump under an inlet
pressure of 400 Pa. It is preferable at this case that the main
pump is the positive displacement type dry vacuum pump or a
composite type consisting of plural vacuum pumps of the above type
connected in series with each other. Further, it is preferable that
plural main pumps are connected in parallel with each other, and an
auxiliary pump is connected at the inlet port and to the outlet
ports of the main pumps respectively. Further, it is preferable
that the ultimate pressure of the auxiliary pump is less than 20
kPa and that it is a sliding vane rotary vacuum pump (Gede type),
piston type, diaphragm type (membrane type) or scroll type.
[0040] In a drive for the vacuum exhaust apparatus of the
invention, a main pump is connected to a vacuum processing chamber,
a check valve is connected to the outlet side of the main pump and
an auxiliary pump is connected to the outlet of the main pump in
parallel with the check valve for exhausting the vacuum processing
chamber. When said vacuum processing chamber is exhausted from
atmosphere or nearly from atmosphere, said auxiliary pump is first
driven, and after the pressure of said vacuum processing chamber
has reached the predetermined pressure, said main pump is started
to be driven.
[0041] Thus slow exhaust is effected without using the machine or
apparatus for slow exhaust. Further, it is possible that the
auxiliary pump is first driven and the main pump is started at low
speed or low throughput before the pressure of the vacuum
processing chamber reaches the predetermined pressure, and the
rotational speed of the main pump is gradually raised in accordance
with the pressure of the vacuum processing chamber.
[BRIEF DESCRIPTION OF THE DRAWINGS]
[0042] FIG. 1 is a schematic view of a vacuum exhaust apparatus
according to one embodiment of this invention in which a
multi-stage Roots-type dry vacuum pump is used as a main pump;
[0043] FIG. 2 is a schematic view of a vacuum exhaust apparatus of
one modification according to one embodiment of this invention in
which a multi-stage Roots-type dry vacuum pump is used as a main
pump;
[0044] FIG. 3 is a schematic view of a vacuum exhaust apparatus of
another modification according to one embodiment of this invention
in which a multi-stage Roots-type dry vacuum pump is used as a main
pump;
[0045] FIG. 4 is a schematic view of a vacuum exhaust apparatus of
further modification according to one embodiment of this invention
in which a multi-stage Roots-type dry vacuum pump is used as a main
pump;
[0046] FIG. 5 is a schematic view of a vacuum exhaust apparatus of
a further modification according to one embodiment of this
invention in which a multi-stage Roots-type dry vacuum pump is used
as a main pump;
[0047] FIG. 6 is a cross-sectional view showing one example of a
check valve used in a vacuum exhaust apparatus according to one
embodiment of this invention;
[0048] FIG. 7 is a schematic conduit arrangement view showing a
vacuum exhaust apparatus according to another embodiment of this
invention;
[0049] FIG. 8 is a cross-sectional view showing one example of a
check valve used in the vacuum exhaust apparatus as shown in FIG. 7
according to the other embodiment of this invention;
[0050] FIG. 9 is schematic conduit arrangement view showing one
modification of the vacuum exhaust apparatus according to the other
embodiment of this invention;
[0051] FIG. 10 is a cross-sectional view showing the detail of the
check valve used in the vacuum exhaust apparatus as shown in FIG. 9
according to the other embodiment of this invention;
[0052] FIG. 11 is a schematic conduit arrangement view showing
another modification of the vacuum exhaust apparatus according to
the other embodiment of this invention;
[0053] FIG. 12 is a graph explaining operation of the vacuum
exhaust apparatus of an embodiment of this invention, showing the
relationship between the inlet pressure of the main pump and the
consumed power of the whole apparatus;
[0054] FIG. 13 is a graph explaining operation of the vacuum
exhaust apparatus of an embodiment of this invention, showing the
relationship between the pumping speed ratio of the main pump to
the auxiliary pump and the consumed power ratio of the main pump to
the auxiliary pump;
[0055] FIG. 14 is a graph showing the relationship between the
pumping speed and the consumed power of a typical auxiliary
pump;
[0056] FIG. 15 is a graph showing the consumed power characteristic
of the vacuum exhaust apparatus according to one embodiment of this
invention;
[0057] FIG. 16 is a graph showing the relationship between the
inlet pressure and the pumping speed of the vacuum exhaust
apparatus of one embodiment of this invention;
[0058] FIG. 17 is a schematic conduit arrangement view showing
further modification of vacuum exhaust apparatus according to one
embodiment of this invention;
[0059] FIG. 18 is a schematic view showing a multi-stage Roots-type
dry vacuum pump in which all of the rotors are equal in size;
[0060] FIG. 19 is a schematic view showing a multi-stage Roots-type
dry vacuum pump in which the rotors are different in size at the
former stage, middle stage and latter stage;
[0061] FIG. 20 is a schematic view showing a multi-stage Roots-type
dry vacuum pump in which the latter two are smaller than those of
FIG. 19;
[0062] FIG. 21 is a graph of the relationship between the inlet
pressure and the pumping speed of the multi-stage Roots-type dry
vacuum pump having the rotors of FIG. 18, FIG. 19 and
[0063] FIG. 20, respectively;
[0064] FIG. 22 is a graph of the relationship between the inlet
pressure and the consumed power of the multi-stage Roots-type dry
vacuum pump having the rotors of FIG. 18, FIG. 19 and
[0065] FIG. 20, respectively;
[0066] FIG. 23 is schematic view of a vacuum exhaust apparatus of
the prior art which can reduce consumed power;
[0067] FIG. 24 is a schematic view of a vacuum exhaust apparatus of
the prior art.
[PREFERRED EMBODIMENT OF THE INVENTION]
[0068] First, one embodiment of a vacuum exhaust apparatus
according to this invention will be described with reference to the
drawings of FIG. 1 to FIG. 5, in which a multi-stage dry vacuum
pump is used as a main pump.
[0069] The multi-stage dry vacuum pump is schematically shown in
these figures, In the embodiment of the vacuum exhaust apparatus 10
of FIG. 1, pairs of rotors R.sub.1, R.sub.2, R.sub.3, R.sub.4,
R.sub.5 and R.sub.6 are driven by an electric motor 22 and are
arranged in a main body 21 of a multi-stage dry vacuum pump 20
(main pump). An inlet port 23 is arranged in an upper wall of the
left end of the main body 21. It communicates with a rotor chamber
of the rotor R.sub.1. An exhaust pipe 25 provided with a silencer
26 is connected to an outlet portion 24 which is connected to a
rotor chamber for rotor R.sub.6 of the last stage. Further, a check
valve 28 is connected through pipe 27 to the silencer 26. The check
valve 28 permits gas to flow only in the direction toward
atmosphere. An auxiliary pump 30 which is smaller in throughput
than the main pump, is connected to the outlet portion 24.
[0070] Next, operation of this embodiment will be described.
[0071] With the drive of motor 22, the rotors R.sub.1, R.sub.2,
R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are rotated to exhaust gas.
The gas is transported from the respective rotor chambers towards
the downward side, in order. A vacuum processing chamber (not
shown) connected to the inlet port 23 is exhausted. The pressure of
the outlet portion 24 of the last stage is nearest to
atmosphere.
[0072] According to this invention, the outlet portion 24 is
exhausted to a low pressure by the drive of the auxiliary pump 30.
Thus, the load on the rotor of the last stage for exhaust is
greatly reduced and the consumed electric power of the motor 22 can
be greatly smaller than that of the prior art.
[0073] FIG. 2 shows one modification of the vacuum exhaust
apparatus 10 according to the teachings of this invention. The
parts which correspond to those in FIG. 1, are denoted by the same
reference numerals, the detailed descriptions of which will be
omitted.
[0074] According to this embodiment, the outlet potion 24 of the
last stage of the main pump 20' is connected to an exhaust pipe 25
through an opening of a main body 21. The silencer 26 is arranged
in the exhaust pipe 25 which is further connected through a pipe 27
to a check valve 27, and is connected to atmosphere. A pipe 31 is
connected in parallel with the pipe 25, which is connected to an
auxiliary pump 30. An outlet port of the auxiliary pump 30 is
connected through a pipe 32 to the atmosphere side of the check
valve 28. Also in this embodiment, the energy conservation effect
can be obtained similarly to the embodiment of FIG. 1.
[0075] Further, since the auxiliary pump 30 is connected in
parallel with the exhaust pipe 25 and check valve 28, a large
amount of the gas is flowed through the exhaust pipe 25, even
through some problems occur in the auxiliary pump 30. Thus,
performance of the main pump 20' can be maintained.
[0076] FIG. 3 shows another modification of a vacuum exhaust
apparatus 10 according to the teachings of the invention.
[0077] According to this embodiment, an auxiliary pump 30 is
connected in parallel with the check valve 28 through pipes 31 and
32. It is clear that the same effect as that of the embodiment of
FIG. 2 can be obtained by this embodiment.
[0078] FIG. 4 and FIG. 5 show modifications of the vacuum exhaust
apparatus 10 of FIG. 1 and FIG. 2, respectively. According to these
modifications, other outlet portions 24' and 24" are arranged at
the middle stages of the main pumps 20A and 20B separate from the
outlet portion 24 of the last stage. The auxiliary pump 30' is
connected to the outlet portion 24' or 24".
[0079] The pressure of the middle stage is decreased in the main
pumps 20A and 20B. The load on the rotor of the middle stage for
exhaustion can be reduced. Thus, the consumed power of the motor 22
can be reduced more than that of the prior art.
[0080] In the above embodiments, the rotors R.sub.1, R.sub.2,
R.sub.3, R.sub.4, R.sub.5 and R.sub.6 all are equal to each other
in size. Instead, the sizes of the rotors may be smaller towards
the latter stage. It is then evident that the consumed power can be
smaller than that of the above embodiments.
[0081] Further, the dry vacuum pump is not limited to the
multi-stage Roots-type dry vacuum pump, but it may be, for example,
a screw type or claw type. The same effect can be obtained also by
them.
[0082] Next, construction of the check valve 28 used in the
embodiment will be described referring to FIG. 6.
[0083] The check valve 28 is provided with a housing 40, a valve
chamber 44, an annular valve seat 45, a ball valve body 46 able to
seat on and be separated from the valve seat 45 and a stopper 47.
The housing 40 consists of an upper cylindrical body 41 positioned
at the atmosphere side and a lower cylindrical body 42 positioned
at the side of the main pump 40. The valve chamber 44 is formed
between the upper cylindrical body 41 and the lower cylindrical
body 42. The valve seat 45 is formed at the lower end of the lower
cylindrical body 42. The stopper 47 is formed on the lower end of
the upper cylindrical body 41 for regulating lift of the ball valve
body 46 to a predetermined height.
[0084] An annular seal 48 is interposed between the contacting
surfaces of the upper and lower cylindrical bodies 41 and 42. They
are fixed to each other by plural bolt members. Thus, they are
air-tightly formed as one body. The ball valve body 46 consists of
hollow stainless ball. It is covered with a thin rubber film.
According to this embodiment, the self-weight of the ball valve
body 46 is equal to about 50 grams. When the pressure of the inlet
side of the check valve 28 becomes about 700 Pa beyond atmosphere,
the ball valve body 46 is so designed as to be lifted upwards.
[0085] The stopper 47 is constituted by four protrusions projected
inwardly from the lower end of the upper cylindrical body 41 at the
angular pitches of 90 degrees. The ball valve body 46 is stopped by
the stopper 47. The gas is flowed through the spaces between the
protrusions 47 towards atmosphere.
[0086] The check valve 28 has low resistance to the gas flow. It
can be opened by a small pressure rise at the inlet side.
Accordingly, it can follow rapid pressure change. Generally in the
positive displacement type pump used as the main pump 20, the gas
is pushed out from the pump chamber and reversed into the pump
chamber, repeatedly. Accordingly, gas pressure in the outlet
portion 24 is pulsatingly changing. When the amount of the sucked
gas becomes small, the ball valve body 46 is repeatedly seated, and
separated on and from, the valve seat 45 with the pulsating change
of the gas pressure. When the followability of the ball valve body
46 is deteriorated, the ball valve body seats for a short time. The
inlet side is sometimes maintained opened towards atmosphere. At
that time, the pressure of the inlet of the auxiliary pump 30 is
not reduced.
[0087] In the embodiment, the valve body of the check valve 28 is
the ball valve body 46 and the valve is opened and closed only by
the self-weight of the ball. The followability to the pulsating
pressure is high.
[0088] However, when the rotational speed of the rotor of the main
pump 20 is higher, the check valve cannot sometimes follow the
pulsating pressure. For example, in a dry vacuum pump of the screw
type, when the rotational speed of the rotor is under 3600 r.p.m.,
the check valve can perfectly follow the pulsating pressure.
However, it cannot follow the pulsating pressure at the rotational
speed of 6000 r.p.m. The ball valve body does not seat on the valve
seat 45 perfectly.
[0089] It has been considered that the ball valve body 46 can be
pushed onto the valve seat 45 by a spring having a small spring
constant to provide good followability to the gas pressure.
However, this method requires much pressure loss in the exhaust gas
line due to the spring force of the spring and therefore higher gas
pressure is required to lift the ball valve body 46 for opening the
valve. Also it is has been considered that the gas pressure of the
outlet portion may be more rapidly reduced by an auxiliary pump 30
of higher throughput. However, in this method, the consumed
electric power is increased and the energy conservation effect is
decreased.
[0090] To overcome the disadvantage of the above method, two check
valves 28a and 28b are serially connected to each other as shown in
the vacuum exhaust apparatus 10 of FIG. 7. The number of the
serially connected check valves is here limited to the two. Three
check valves may be connected serially to each other. Each of the
check valves 28a and 28b is constructed similar to the check valve
28 of FIG. 6 as shown in FIG. 8.
[0091] In a vacuum exhaust apparatus 10, the screw type dry vacuum
pump was used as the main pump 20. The rotor was rotated at the
speed of 6000 r.p.m. to exhaust the vacuum processing chamber. The
check valves 28a and 28b were accurately operated, and not
influenced by the pulsating pressure of the outlet chamber of the
screw type dry vacuum pump. The consumed power was reduced to about
70% of the case in which merely the screw type dry vacuum pump was
used.
[0092] In a further modification of the embodiment, a connection
between the first check valve 28a and the second check valve 28b is
connected through a pipe 29 to a suction side of auxiliary pump 30
as shown in FIG. 9 and FIG. 10. Thus the outlet portion of the main
pump can be more stably exhausted.
[0093] FIG. 11 shows a schematic conduit arrangement of a vacuum
exhaust apparatus 10 according to another embodiment of this
invention. The main valve 13 and a pressure gauge 19 for measuring
vacuum pressure are connected to a pipe 12 connecting the vacuum
processing chamber 1 with the main pump 20 constituted by a single
dry vacuum pump. The check valve 28 is connected to the main pump
20 through the exhaust pipe 25. The auxiliary pump 30 is connected
in parallel with the check valve 28. A dry vacuum pump is used for
auxiliary pump 30. The throughput of the auxiliary pump 30 is equal
to about 10% of that of the main pump 20. The check valve is the
same as that used in FIG. 6. It includes a ball valve body
floatable in the valve chamber, which floats from the seat at a
pressure higher by about 700 Pa than that of atmosphere to open the
valve. It seats onto the valve seat by its self-weight to close the
valve. A gas exhaust processing apparatus (not shown) is connected
to the downside of the gas exhaust pipe 15.
[0094] A high vacuum exhaust pump such as a turbo-molecular pump
may be connected to the upper streamside of the main pump 20.
[0095] In the embodiment of this invention, a positive displacement
type dry vacuum pump of the Roots-type is used for the main pump
20. Of course, it is not limited to that type, but a claw type and
a screw type may be used as the dry vacuum pump. A pump of low
consumed electric power and effective construction is used for the
auxiliary pump 30.
[0096] It is preferable that the pump has such a construction that
the volume of the exhaust gas decreases in compression process.
Accordingly, a sliding vane type (Gede), a piston type, a diaphragm
type (membrane type) and a scroll type are suitable. The pumping
speed of the auxiliary pump 30 is suitably selected within the
range of a few percentages to about 20% of the pumping speed of the
main pump 20, in accordance with a necessary capacity of a vacuum
exhaust apparatus 10.
[0097] Next, operations of the vacuum exhaust apparatus 10
according to the embodiment as above-constructed, will be
described.
[0098] The vacuum processing chamber 1 is exhausted from the
atmosphere to a predetermined vacuum level. While the main pump 20
is driven, the auxiliary pump 30 is always driven. When the outlet
side of the main pump 20 is not exhausted to a pressure lower than
atmosphere by the auxiliary pump 30 due to much exhaust gas from
the main pump 20, the check valve 28 is opened, and the exhaust gas
is discharged in the direction shown by letter a. The exhaust of
the vacuum processing chamber 1 processes, and so the inlet
pressure of the main pump 20 decreases. Accordingly, the gas amount
decreases at the outlet port 24 of the main pump 20.
[0099] When the gas flow of the outlet side of main pump 20 starts
to become less than atmosphere by the exhaust action of the
auxiliary pump 30, it starts to become pulsating. The check valve
28 is repeatedly opened and closed. However, the check valve 28 of
the embodiment has a construction which is highly followable to the
pulsating gas flow. Accordingly, the vacuum exhaust apparatus 10 of
this embodiment can be driven with high reliability.
[0100] When the gas pressure of the outlet side of main pump 20
becomes less than atmosphere, the check valve 28 is perfectly
closed and hereafter the gas does not flow in the direction shown
by the arrow a, but flows only in the direction shown by the arrow
b, by the exhaust action of the auxiliary pump 10. Thus the outlet
pressure of the main pump 20 starts to be reduced and the reverse
gas flow into the main pump 20 is reduced. Accordingly the consumed
electric power of the main pump 20 decreases.
[0101] When the exhaust gas amount of the main pump 20 is so much
that the check valve 28 is opened, the auxiliary pump 30 is not so
useful. The total consumed electric power of the vacuum exhaust
apparatus 10 including the consumed electric power of the main pump
20 and that of the auxiliary pump 30 is larger than the case
wherein the auxiliary pump 30 is not driven.
[0102] However, for example, the volume of the vacuum processing
chamber 1 is less than 100 liters in most instances for
semiconductor manufacturing equipment. The time when the outlet
pressure of the main pump 20 reaches the pressure at which the
auxiliary pump 20 becomes useful, is equal to a few minutes.
Accordingly, the above energy loss is negligible in view of the
energy conservation.
[0103] FIG. 12 shows the characteristics of the consumed electric
power (the consumed electric power of the main pump 20 plus that of
the auxiliary pump) to the inlet pressure of the main pump 20.
[0104] In the vacuum exhaust apparatus, the auxiliary pump 30 of
the pumping speed 1.8 m.sup.3/Hr is connected to the latter stage
(the outlet side) of the main pump 20 of the pumping speed 150
m.sup.3/Hr. The main pump 20 is a pump of the energy conservation
type in which the throughput of the last stage is so designed as to
be equal to 25% of that of the first stage. In FIG. 12, a dot-dash
line (._._._) shows the case wherein the auxiliary pump 30 is not
attached.
[0105] The solid line shows the case wherein the auxiliary pump 30
and the check valve 28 are included. The horizontal axis (inlet
pressure) represents logarithm scale.
[0106] Consumed electric power is steeply decreased below the
pressure of 1 kPa with the auxiliary pump 30 as shown in FIG. 12.
Consumed electric power of the main pump 20 without the auxiliary
pump 30 is equal to 1.35 kW ultimate pressure. That of the main
pump 20 with the auxiliary pump 30 is equal to 0.32 kw ultimate
pressure. Energy conservation rate or consumed electric power
reduction rate of about 76% is obtained by the auxiliary pump 30.
At the inlet pressure 400 Pa of the main pump 20, the consumed
electric power of the main pump 20 without the auxiliary pump 30 is
equal to 1.4 kw. That of the main pump 20 with the auxiliary pump
30 is equal to 0.67 kw. The energy conservation rate is equal to
about 52%.
[0107] With the rise of the pumping speed of the auxiliary pump 30,
the pressure at which the consumed electric power of main pump 20
starts to decrease, moves to the right in FIG. 12 from about 1 kPa
or to the higher inlet pressure.
[0108] Accordingly, the pressure range which the energy
conservation is effective, can be widened. However, the consumed
electric power of the auxiliary pump 30 increases with the pumping
speed and the energy conservation effect is reduced.
[0109] Generally in the vacuum exhaust system for semiconductor
manufacturing equipment, a small amount of the process gas is
flowed into the vacuum processing chamber, maintaining a
predetermined pressure, to treat the film forming process or the
like. In that case, the inlet pressure of the main pump 20 is equal
to 1500 Pa at the highest, and so the object of the invention can
be achieved by the fact that the energy conservation effect can be
obtained in the range of inlet pressure of less than about 3000
Pa.
[0110] FIG. 13 illustrates a multi-stage Roots-type dry vacuum pump
as the main pump connected to the latter stage of a turbo-molecular
pump. The relationship between the pumping speed ratio and the
consumed electric power ratio is shown in FIG. 13, where main pumps
and auxiliary pumps which differ from each other in pumping speed
are differently combined with each other. The inlet pressure of the
main pump is equal to 400 Pa. The pumping speed ratio represents
the ratio of the pumping speed of the auxiliary pump to that of the
main pump. The consumed electric power ratio represents the ratio
of the consumed electric power with the auxiliary pump, to that
without the auxiliary pump.
[0111] Accordingly, consumed electric power of 100% means that
there is no effect by the auxiliary pump. The consumed electric
power with the auxiliary pump represents the total of the consumed
electric power of the main pump 20 and auxiliary pump. The consumed
electric power without auxiliary pump means is that of the main
pump.
[0112] It will be understood from FIG. 13 that the consumed
electric power ratio decreases with the raise of the pumping speed
ratio and so the energy conservation effect rises with that. It
will be understood that the reduction rate of the consumed electric
power ratio tends to decrease near the pumping speed ratio of 3%.
The reason will be described later. From the above, it will be
understood that the energy conservation effect can be sufficiently
obtained by an auxiliary pump of a pumping speed lower than 3% of
that of the main pump 20, at the inlet pressure of 400 Pa for the
main pump 20. In the embodiment of this invention, the pumping
speed ratio of the auxiliary pump to the main pump 20 is equal to
1.2%. Accordingly it fulfills the above requirement.
[0113] As above described, the inlet pressure of the main pump 20,
at which the energy conservation effect starts to be obtained,
moves towards a higher pressure with the rise of the pumping speed
ratio of the auxiliary pump to the main pump. However, the consumed
electric power of the auxiliary pump 30 increases with the pumping
speed. The total consumed electric power of the main pump 20 and
the auxiliary pump 30 becomes larger than the consumed electric
power without the auxiliary pump, under the above condition. The
details will be described with reference to FIG. 14 and FIG.
15.
[0114] FIG. 14 shows a typical relationship between the pumping
speed and the consumed electric power, of a vacuum pump usable as
the auxiliary pump. FIG. 15 shows the relationship between the
pumping speed ratio of the pumping speed of the auxiliary pump
having the characteristic shown in FIG. 14 and the pumping speed of
150 m.sup.3/hr of a dry vacuum pump as the main pump at the inlet
pressure of 400 Pa for the main pump 20, and the consumed electric
power. In FIG. 15, a dot-dash line (._._._) shows the consumed
electric power of only the main pump 20. It decreases steeply with
the rise of the pumping speed ratio of the auxiliary pump to main
pump 20. It converges to the power corresponding to the mechanical
loss of the main pump 20b over the pumping speed ratio of 4%. The
dotted line ( . . . ) represents the relationship between the
consumed electric power and the pumping speed ratio of the
auxiliary pump having the characteristic of FIG. 14, to the main
pump 20. The total consumed electric power of the auxiliary pump
and the main pump 20 is represented by the solid line in FIG. 15.
This is the total consumed electric power of the vacuum exhaust
apparatus.
[0115] It will be understood from the solid line of FIG. 15 that
the consumed electric power is smallest at the pumping speed ratio
of about 3% of the auxiliary pump to the main pump 20.
[0116] With reference to FIG. 12 and FIG. 15, the energy
conservation rate of 50% can be obtained at the pumping speed ratio
of 1.2% or 9.4% of the auxiliary pump to the main pump 20 and at an
inlet pressure of 400 Pa for the main pump 20.
[0117] However, the auxiliary pump of the pumping speed ratio of
9.4% is larger in size than the auxiliary pump 30 of the pumping
speed ratio of 1.2% according to the embodiment. The former is
disadvantageous in the arrangement space and energy for
manufacturing the pump. Accordingly, it is preferable to select the
auxiliary pump of a pumping speed ratio which is less than 3%.
Thus, it is possible to obtain a vacuum exhaust apparatus with a
totally high energy conservation rate. On the other hand, the
auxiliary pump of the pumping speed ratio over the ratio of 3%
reduces the energy conservation effect.
[0118] As shown by the solid line in FIG. 12, the consumed electric
power is almost horizontal or constant within the inlet pressure
range below 10 Pa. That means that the compression work in the pump
chamber is negligibly small at such a low outlet pressure of the
main pump 20 and the consumed electric power is equal to the
mechanical loss of the main pump 20.
[0119] The consumed electric power gradually increases with the
gradual increase of the inlet pressure of main pump 20. That means
that the compression work of the last stage of the main pump 20,
which Is the work for pushing the reverse flow back, becomes
remarkable. The consumed electric power of the main pump 20 is
proportional to the outlet pressure. Accordingly, in order to
obtain the low consumed electric power shown by the solid line in
FIG. 12, the capacity to exhaust the gas to the low outlet pressure
is required for the auxiliary pump.
[0120] The suction gas amount required to raise the consumed
electric power by 10% from the consumed electric power on the
ultimate pressure is set. The measured pressure of the auxiliary
pump is equal to 6.5 kPa to 20 kPa. When the auxiliary pump does
not have the capacity to exhaust the gas to a pressure of less than
the 20 kPa, the consumed electric power, which is equal to the
mechanical loss of the main pump 20, cannot be obtained on ultimate
pressure.
[0121] FIG. 16 shows the pumping speed characteristics of the
vacuum exhaust apparatus of the embodiment. The solid line shows
that the auxiliary pump is used. The dot-dash line shows that the
auxiliary pump is not used. The pumping speed of the vacuum exhaust
apparatus with an auxiliary pump is higher by 10% than that without
the auxiliary pump.
[0122] The ultimate pressure of the apparatus with the auxiliary
pump is improved to 1 Pa from 2 Pa in comparison with that of the
apparatus without the auxiliary pump. That means that reverse gas
flow amount decreases with the decrease of the outlet pressure of
the main pump 20 and so the volume efficiency has been raised. The
effective energy conservation can be obtained for the whole vacuum
exhaust apparatus. With the auxiliary pump, the consumed electric
power can be reduced, and further the pumping speed and the
ultimate pressure can be improved.
[0123] While the preferred embodiments of the vacuum exhaust
apparatus have been described, variations thereto will occur to
those skilled in the art within the scope of the present inventive
concepts which are delineated by the following claims.
[0124] For example, a single dry vacuum pump is used as the main
pump 20 in the above embodiment. Plural multi-stage Roots-type dry
vacuum pumps may be serially connected. Such a composite type pump
may be used as the main pump 20. Further in the above embodiment,
the auxiliary pump is connected to the outlet side of the single
main pump 20. However, plural main pumps 20A, 20B and 20C as shown
in FIG. 17 may be connected in parallel with each other. The outlet
sides of the main pumps are connected to one auxiliary pump 30. In
the shown example, check valves 28a, 28b and 28c are connected to
the respective main pumps 20A to 20C. Further valves 11a, 11b and
11c are connected between the auxiliary pump 30 and the check
valves 28a, 28b and 28c, and the main pumps 20A, 20B, and 20C are
connected to different vacuum processing chambers, respectively.
Suction gas amount of the auxiliary pump 30 changes with the number
of the driven main pump 20A 20B and 20C. The pumping speed
(rotational speed) of the auxiliary pump 30 may be changed in
accordance with the number of the driven main pumps 20A to 20C.
[0125] A driving method of the vacuum exhaust apparatus of this
invention will be described in detail, with reference to the vacuum
exhaust apparatus of FIG. 11.
[0126] When the vacuum processing chamber 1 is exhausted from
atmosphere by the vacuum exhaust apparatus 10, first the auxiliary
pump 30 starts to be driven and the main valve 13 is opened to
start the exhaust. When it has been confirmed by the pressure gauge
19 that the vacuum of the chamber 1 has reached 10.sup.s Pa, the
main pump 20 is started and driven to the rotational speed, for
example, of 3600 r.p.m. to exhaust the vacuum processing chamber 1
to the pressure 1 Pa. Fine particles are prevented from flying high
up in the vacuum processing chamber 1 by the above driving method.
Thus the slow exhaust can be effected by the drive of only the
auxiliary pump 30, without the small diameter by-pass valve
connected in parallel with the main valve. After the vacuum has
reached the pressure 1 Pa, the vacuum exhaust apparatus 10 is
sequentially and stationarily driven. At that time, the exhaust gas
flow is small and the check valve 28 closes. The exhaust is
effected only by the auxiliary pump 30. Thus consumed electric
power of the vacuum exhaust apparatus 10 is reduced and noise is
suppressed.
[0127] In FIG. 11, the nominal outside diameter of the exhaust pipe
15 is 40A. The exhaust amount of the auxiliary pump and sequently
that of the main pump 20 are small. Accordingly it can be
substituted with a pipe of a nominal outside diameter pf 10A (bore
10 mm=3/8 inches). The pipe of the above bore can be bent for
manufacturing and so the manufacturing cost of the pipe arrangement
can be reduced.
[0128] There has been described the driving method of the vacuum
exhaust apparatus with reference to the particular embodiment. Of
course, this invention is not limited to the above embodiment, but
various modifications will be possible on the basis of the
technical concept of the invention.
[0129] For example, in the above embodiment, after the vacuum
processing chamber has reached the predetermined pressure by the
auxiliary pump, the main pump is started and the rotor is rotated
at the rotational speed of 3600 r.p.m. However, before the vacuum
processing chamber reaches the predetermined pressure, the
rotational speed of the main pump 20 may be so controlled as to be
gradually increased from the low rotational speed of small
throughput in accordance with the vacuum degree of the vacuum
processing chamber by the inventor.
[0130] Thus the rapid pressure change on the start of the main pump
20 can be avoided. Also the main pump 20 can be started so as not
to impart load to the auxiliary pump.
[INDUSTRIAL APPLICABILITY]
[0131] According to the vacuum exhaust apparatus and the drive
method of the vacuum exhaust apparatus, energy conservation can be
more greatly achieved by a simple construction than that of the
prior art and slow exhaust can be easily effected.
[0132] [Scope of Demand]
* * * * *