JP4438384B2 - Vacuum pump - Google Patents

Description

  The present invention relates to a vacuum pump used for evacuation in a pressure range from a medium vacuum to an ultra-high vacuum in a semiconductor manufacturing apparatus, an analysis apparatus or the like, specifically, for example, a molecular drag pump represented by a turbo molecular pump or a thread groove pump. And so on.

  In such a vacuum pump, a typical turbo molecular pump is such that a turbo mechanism that forms the main body thereof is rotatably held in a cylindrical casing, and molecules, gases, etc. are supplied from an intake port of one side opening of the casing. This gas is sucked in, compressed, and exhausted from the exhaust port of the opening on the other side of the casing. That is, in the turbo mechanism, a rotating body arranged at the central axis of the casing is rotatably held by upper and lower bearings installed on the casing, and the rotating body is also mounted on a motor installed on the casing. Connected to be rotated at high speed. This turbo mechanism is composed of a combination of rotor blades fixed in multiple stages on the outer periphery of the rotating body and multiple stages of fixed blades fixed on the casing, in which the rotor blades are rotated at high speed by a motor. Specifically, it is driven at a rotational speed of several tens of thousands of revolutions per minute, and compresses and exhausts the gas (see, for example, Patent Publication 1).

An example of such a conventional turbo molecular pump TP is as shown in FIG . The turbo mechanism TK, which is the main component of the turbo molecular pump TP, will be described below. A cylindrical body is integrally formed on the upper portion of the rotating shaft 3, and the cylindrical body has a plurality of stages (specifically, on the outer periphery). Are five-stage rotor blades B1 to B5 (in the drawing, only the uppermost rotor blade B1 and the lowermost rotor blade B5 are provided with reference numerals, and the other reference numerals are omitted). The rotor blades B1 to B5 are arranged with a constant interval in the axial direction. The rotary shaft 3 and the rotary blades B <b> 1 to B <b> 5 are integrated, and constitute a rotary body 4. On the other hand, from the inner peripheral side of the casing 5 in which the intake port 6 is formed on the upper side, the fixed blades T1 to T5 (only the uppermost fixed blade T1 and the lowermost fixed blade T5 are denoted by the reference numerals in the drawing, and the other However, the turbo mechanism is configured by alternately providing the rotor blades B1 to B5. In FIG. 5 , S is a spacer for holding the fixed blades T1 to T5 at a constant interval. 7 is an exhaust port.

  The rotary shaft 3 is rotatably held by upper and lower magnetic bearings 8A and 8R installed on the lower casing 1 and is coupled to the motor 2. The magnetic bearings 8A and 8R have a bearing function in the axial direction and the radial direction, and thereby reliably support the rotating shaft 3. On the other hand, a rotor 2M that constitutes one of the motors 2 is installed inside the rotary shaft 3 and is integrally attached thereto. The rotor 2M forms a motor 2 in cooperation with a motor stator coil 1K installed on the lower casing 1. Electric energy is supplied to the motor 2 from an inverter (not shown), and the rotary shaft 3 is rotated at high speed.

  Further, a cylindrical portion 4N is integrally formed at a part of the rotating body 4, that is, specifically below, and the outer periphery of the cylindrical portion 4N is joined to the inner periphery of the casing 5 that also serves as a machine base. It corresponds to the inner peripheral surface of the ring 9 close to it. A thread groove N is formed on the inner peripheral surface of the stator ring 9. The thread groove N is formed such that the groove depth becomes shallower as it goes downward. The combination of the stator ring 9 and the cylindrical portion 4N constitutes a thread groove pump NP. This thread groove pump NP functions as a drag pump (Holbek pump) and draws and exhausts molecules in the viscous flow region.

Such a turbo molecular pump TP is an organic combination of a turbo pump function by the turbo mechanism TK and a thread groove pump function by the thread groove pump NP, and is generally called a hybrid turbo molecular pump. As the turbo molecular pump TP, such a hybrid type has good exhaust characteristics and is often used. As a molecular pump, a thread groove pump NP composed only of a combination of a turbo mechanism TK only and a stator ring 9 and a rotating body (cylindrical body) 4 having a thread groove N formed on the outer periphery, that is, There are drag pumps.
JP 2002-54593 A

In recent years, turbo-molecular pumps have become larger with the size of exhausted chambers and the like, and throttle valves (variable conductance valves) used on the gas inflow side have come to have large diameters. That is, a typical exhaust system conventional vacuum pump for example a turbo molecular pump is used is as shown in FIG. In FIG. 6 , 16 is a chamber of an exhausted chamber, 17 is a vacuum gauge, 18 is a throttle valve (variable conductance valve), and TP is a turbo molecular pump. Reference numeral 19 is an auxiliary pump, 20 is a control means for controlling the opening of the valve, and 21 is a mass flow controller.

  In such a turbo molecular pump TP, the throttle valve 18 is actuated by a signal from the mass flow controller 21, but the throttle valve 18 is large and has a large capacity, so that the open / close speed response is low. Further, there is a problem that particles are generated from the throttle valve 18. Furthermore, the throttle valve 18 is also expensive. It is an object of the present invention to provide a vacuum pump that has a function of controlling exhaust performance that eliminates the need for the throttle valve and that can reduce the cost of the entire vacuum exhaust system.

  In order to solve the above problems, the vacuum pump provided by the present invention has a flow passage through which gas can flow (i.e., reverse flow) from the downstream side to the upstream side in the gas compression stroke of the vacuum pump. An adjustment valve capable of adjusting the opening degree is provided so that the gas flow rate can be adjusted. Specifically, in the vacuum pump that compresses the gas from the intake port of the one side opening of the casing and exhausts the gas from the exhaust port of the other side of the opening, the gas flows from the exhaust port toward the reverse intake port. Establish a road. Further, an adjustment valve for adjusting the gas flow rate is provided in the flow passage. Further, the vacuum pump provided by the present invention is provided with a filter on the flow path and at least one before and after the control valve. The present invention further includes a mechanism for controlling the opening of the control valve in accordance with an opening signal from the outside or a combination of a target pressure signal and a measured pressure signal.

  Therefore, by returning a part of the exhausted gas from the downstream side to the upstream side of the vacuum pump, the compression action of the intermediate stage of the vacuum pump can be exhibited 100% or can be changed to a state where it is not compressed. Thereby, the compression performance of the vacuum pump can be lowered. The compression performance of the vacuum pump can be controlled by adjusting the flow rate of the reverse flow. Since the exhausted gas is not directly returned to the pump inlet or vacuum container, particles generated inside the pump can be contained inside the pump. The filter on the backflow path also functions to contain particles.

The variable conductance valve attached to the intake side of the turbo molecular pump can be omitted, and the cost of the exhaust system can be reduced. In addition, the variable conductance valve attached to the intake side of the turbo molecular pump is generally large in diameter and has a slow opening / closing response speed. However, the control valve of the present invention can be made small in size with a small flow path and can respond quickly. It becomes. The containment of particles facilitates the action of the control valve on the flow path.
If the control valve and filter are installed in an external removable unit with respect to the vacuum pump casing, the pump can be restored quickly by replacing the unit in the field when the valve and filter are clogged. There are also advantages that can be made.

  The best mode of the vacuum pump provided by the present invention is a configuration based on a combination of a turbo mechanism and a thread groove mechanism. This is because the exhaust characteristics are good. That is, a rotating body is supported by a bearing inside a cylindrical casing, a turbo mechanism is disposed above the rotating body, and a thread groove pump as a drag pump is disposed below the rotating body. Specifically, a plurality of rotating blades constituting a turbo mechanism are fixed on the upper portion of the rotating body, and fixed blades are provided on the inner peripheral side of the casing so as to be alternately arranged with the rotating blades. On the other hand, as described above, the drag pump unit is configured in the lower part of the rotating body. Specifically, the outer peripheral surface of the cylindrical portion located in the lower direction of the rotating body is arranged so as to closely correspond to the inner peripheral surface of the stator ring in which a thread groove is formed on the inner peripheral surface.

  In the above configuration, the vacuum pump provided by the present invention forms a flow passage through which gas in a space close to the exhaust port flows to the intake port side. Specifically, this flow passage constitutes a passage formed in the casing to communicate the space close to the exhaust port to the outside, a gap passage formed in the gap between the inner peripheral surface of the casing and the turbo mechanism, and a turbo mechanism The fixed wing to be arranged at a predetermined interval is formed by a unit having a flow hole formed in a spacer and a passage connecting the external opening and the gap of the passage. This unit is ideally formed of a block or box that is detachably attached to the casing of the vacuum pump. The unit is provided with an adjustment valve for adjusting the flow rate of the gas in the inner passage. Further, a filter is interposed on at least one side of the passage before and after the control valve. More preferably, means for heating at least one of the control valve and the filter, for example, a heater is provided.

  FIG. 1 shows a longitudinal section of a hybrid molecular pump embodying the present invention. That is, in FIG. 1, B1 to B8 (in the drawing, only the uppermost rotor blade B1 and the lowermost rotor blade B8 are denoted by reference numerals, and the other reference numerals are omitted), and the rotor blades T1 to T7 (drawings). The uppermost stationary blade T1 and the lowermost stationary blade T7 are provided with reference numerals and other appendices are omitted), and are stationary blades, and a molecular drag pump stage is connected downstream thereof. Reference numerals 9 and 10 denote stator rings disposed in the lower casing 1 in which the casing 5 is fixedly installed. The stator ring 9 is a cylindrical body installed on the upper portion of the lower casing 1 via a fixing screw. The inner peripheral surface has a three-stage inner diameter, and a thread groove N1 is formed on the inner peripheral surface. The other stator ring 10 is a cylindrical body suspended from a middle portion of the lower casing 1 via a fixing screw, and has a thread groove N2 formed on the outer peripheral surface thereof. This outer peripheral surface corresponds to the cylindrical portion 4N of the rotating body 4 in proximity.

  The fixed blades T1 to T7 are sandwiched and fixed by a ring-shaped spacer S. The spacers S are also laminated without any gaps, and gas (gas) does not flow between the inside and outside of the spacers S. The stator rings 9 and 10 have a spiral groove carved on the surface facing the cylindrical portion 4N of the rotating body 4 so that the exhaust function can be exhibited. The rotary blades B1 to B8 are provided on a rotary body 4 that is integral with the rotary shaft 3, and these are supported by magnetic bearings 8A and 8R. The gas exhausted from the pump enters the pump through the intake port 6 and is compressed by the rotary blades B1 to B8 and the fixed blades T1 to T7, and further compressed by the action of the stator ring 9 and the cylindrical portion 4N. Is further compressed by the action of the stator ring 9 and the cylindrical portion 4N, flows through the ring-shaped space portion A, and is discharged from the exhaust port 7 through the exhaust hole 7H.

  In the above-described configuration, the present invention forms a flow passage for allowing the gas to flow backward in the gas compression mechanism, and the configuration is as follows. First, a passage R1 through which gas can flow is formed in the lower casing 1. The passage R1 communicates with the ring-shaped space A and the exhaust hole 7H, and further communicates with the compression portion formed by both the stator rings 9 and 10. The other end of the passage R1 is open to the outer periphery of the lower casing 1. A block 12 is detachably attached to the outer periphery of the lower casing 1 at the opening of the passage R1, and a passage R2 communicating with the passage R1 is formed inside the block 12.

  An adjustment valve 15 capable of adjusting the opening degree is provided on the passage R2 as means for adjusting the gas flow rate, and filters 13 and 14 are provided before and after the adjustment valve 15. The other opening portion of the passage R2 of the block 12 is communicated with a passage R3 that leads to a gap space R4 between the spacer S of the vacuum pump and the casing 5. This passage R3 is also formed on the lower casing 1. Further, one of the spacers S arranged in multiple stages is provided with a flow hole SH. These passages R1, R2, and R3, and the gap space R4 and the flow hole SH form a flow passage through which gas can flow backward.

  Since gas generally flows from the high pressure side to the low pressure side, the gas from the exhaust port side flows in the order of the passage R1, the filter 13, the control valve 15, the passage R2, and the filter 14, and then flows into the passage R3 and the gap space R4. The gap space R4 passes through the flow hole SH of the spacer S and reaches the upstream low pressure part, that is, the exhaust part by the turbo mechanism TK. By adjusting the flow rate of the gas flowing through the passages R1, R2, R3, etc. by adjusting the opening of the control valve 15, the pressure in the vicinity of the circulation hole SH of the exhaust part can be changed. Since the pressure in the vicinity of the flow hole SH and the pressure at the pump inlet 6 are in a proportional relationship, the pressure at the pump inlet 6 can be adjusted. In the compression mechanism portion of the pump turbo mechanism TK, particularly in the downstream portion of the thread groove pump NP, particles formed by condensation of the gas in the exhaust gas may be generated, but the filters 13 and 14 function. This prevents particle backflow and clogging of the control valve 15. In FIG. 1, reference numeral 2 denotes a motor.

By the way, the installation positions on the inlet side and the outlet side of the flow path for the reverse flow are determined in consideration of the following conditions.
(1) Low back flow of gas having a low molecular weight such as hydrogen (2) Pressure of intake port 6 reacts quickly to opening / closing of control valve 15 (3) Linearity of intake port 6 as linearly as possible to open / close control valve 15 The pressure changes (4) The control range of the pressure of the intake port 6 can be widened (5) The pressure inside the pump is kept low, and the increase in gas resistance due to the rotation of the rotating body 4 is avoided as much as possible (6 ) No back flow of particles These conditions may vary depending on various conditions, and are not necessarily limited to these conditions.

  In view of the above condition (1), it is desirable that the inlet and outlet of the backflow channel be located as close as possible to a place where the compression capacity for hydrogen gas is relatively low even in the pump compression mechanism. Further, from the condition (2), it is desirable to set the internal volume of the backflow passage small and particularly to set the conductance from the control valve 15 to the outlet large. Further, from the above condition (3), it is desirable to install the outlet of the reverse flow passage between the exhaust part of the turbo mechanism TK or between the exhaust part of the turbo mechanism TK and the thread groove pump NP. From the condition (4), it is desirable to increase the distance (distance) between the inlet and outlet of the reverse flow passage. From the above condition (5), it is desirable to install the inlet of the reverse flow passage as close to the intake port 6 as possible. Finally, from the condition (6), the outlet of the reverse flow passage is It is desirable to install it as close to the exhaust port 7 as possible.

  From the above consideration, the inlet of the flow passage where gas flows from the downstream side of the compression stroke area, that is, the upstream side from the exhaust port 7, that is, the reverse flow, is located at the middle position of the thread groove pump NP or near the inlet. However, it is considered that it is most effective to install the outlet at an intermediate position of the turbo mechanism TK.

  A typical exhaust system in the case of using the vacuum pump according to the present invention described in detail above is as shown in FIG. In FIG. 4, 16 is a chamber, 17 is a vacuum gauge, 19 is an auxiliary pump, 21 is a mass flow controller, and these are common. In the vacuum pump, that is, the turbo molecular pump TP according to the present invention, no variable conductance valve is required on the side of the intake port 6. Instead, a control valve 15 is provided to provide a mechanism that can automatically adjust the opening. The opening degree of the control valve 15 is controlled so that the chamber pressure approaches the set pressure by comparing the pressure signal of the vacuum gauge 17 with a set pressure set separately. R2 is a passage constituting a part of the flow passage.

  In the vacuum pump having such a function, specifically, in the molecular pump, it is desirable from the viewpoint of production and cost to use as many common parts as possible with the conventional molecular pump. FIG. 2 shows an embodiment configured so that the present invention can be effectively and functionally demonstrated from such a viewpoint. FIG. 2 shows a specific embodiment of the flow path and block 12. A block 12 is detachably attached to the outer peripheral surface of the lower casing 1, and a passage R2 connected to the passage R1 is formed in the block 12. The block 12 is detachably fixed with a bolt (not shown) or the like. As apparent from FIG. 2, the block 12 is formed with a substantially U-shaped passage R2, and chambers K1 and K2 each having a predetermined volume are formed at both corners of the U-shape.

  A filter 13 is attached to one chamber K1. Reference numeral 22 denotes a screw ring for fixing the filter 13. The filter 14 is fixed to the tip of the other chamber K2 in a form in which a valve frame 23 is screwed. The valve frame 23 is provided with an adjustment valve 15 to adjust the opening degree of the passage R2. A screw 24N is provided on the other end side of the valve shaft 24, and a nut 25 is screwed to the screw 24N. The valve shaft 24 is displaced by the rotation of the nut 25 and the flow rate is adjusted. Reference numeral 26 denotes a seal member (ring shape) interposed between the joint surfaces of the lower casing 1 and the block 12 to prevent gas from leaking to the outside. Reference numeral 29 denotes an opening / closing plate for the chamber K1. When the block 12 is removed, the passages R1 and R3 are opened. In this case, the closing plate 27 is attached to be joined as shown in FIG. By attaching the blocking plate 27, the passages R1 and R3 can be closed, and the same use as the conventional molecular pump can be realized.

  The factors that determine the maintenance cycle of the molecular pump as the vacuum pump according to the present invention include clogged states in the filters 13 and 14 and the control valve 15 due to particles formed by condensation of the exhaust gas. In this case, heating the gas passage prevents the gas from condensing and generating particles, thereby extending the maintenance cycle. For example, as clearly shown in FIG. 2, the lower casing 1 is embedded in the heater 30 and can therefore be heated by the heater 30, but the set temperature of the heater 30 is limited to the allowable temperature of the pump itself. Since the temperature can be set independently, a temperature higher than that of the pump can be set to reduce the generation of particles.

The present invention has been described with respect to a pump in which a turbo molecular pump and a drag pump are combined as described above. In particular, in the case of a drag pump, an example in which two stator rings are provided, and an example in which screw grooves are formed in these is shown. . However, the thread groove can also be formed on the outer peripheral surface or the outer peripheral surface of a part of the cylindrical portion of the rotating body. Further, how to install the stator ring with respect to the casing is not limited to the illustrated example.
In this embodiment, the magnetic bearing type turbo molecular pump has been described. However, the same effect can be expected with a ball bearing type molecular pump.

It is a figure which shows the structure of the vacuum pump at the time of applying this invention to a hybrid type molecular pump in longitudinal cross section. It is a figure which shows the structure of the principal part of this invention in the cross section. It is a figure which shows the structure of the principal part of this invention in the cross section. It is a figure which shows the exhaust system of the vacuum pump by this invention. It is a figure which shows the structure of the typical molecular pump of the conventional vacuum pump in a longitudinal section. It is a figure which shows the exhaust system of the conventional vacuum pump.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lower casing 1K Coil 2 Motor 2M Rotor 3 Rotating shaft 4 Rotor 4N Cylindrical part 5 Casing 6 Intake port 7 Exhaust port 7H Exhaust hole 8A, 8R Magnetic bearing 9, 10 Stator ring 12 Block 13, 14 Filter 15 Control valve 16 Chamber 17 Vacuum gauge 18 Throttle valve 19 Auxiliary pump 20 Control means 21 Mass flow controller 22 Screw ring 23 Valve frame 24 Valve shaft 24N Screw 25 Nut 26 Seal member 27 Blocking plate 28 Block 29 Opening / closing plate 30 Heater A Space B1-B8 Rotor blade K1, K2 chamber N, N1, N2 thread groove NP thread groove pump R1-R3 passage R4 gap space S spacer SH flow hole T1-T7 fixed blade TK turbo mechanism TP turbo molecular pump

Claims (5)

A rotating body that is rotatably held in a cylindrical casing via a bearing and is driven to rotate by a motor, and a plurality of stages of rotating blades are attached to the outer periphery of the rotating body. A turbo mechanism based on a combination of the two fixed blades arranged in the casing and a part of the rotating body are arranged close to the inner peripheral surface of the stator ring arranged on the inner peripheral side of the casing. A thread groove pump mechanism in which a thread groove is formed on at least one of the corresponding surfaces of the rotating body and each of the stator rings, and the casing of the casing is activated by the operation of the turbo mechanism and the thread groove pump mechanism. In the vacuum pump that compresses the gas from the intake port of the one side opening and exhausts the gas from the exhaust port of the other side opening, the exhaust of the turbo mechanism or the thread groove pump mechanism A flow passage for circulating the gas on the side of the intake passage is provided, a control valve for adjusting the flow rate of the gas in the flow passage is provided, and an opening on the exhaust port side of the flow passage is provided at an intermediate portion of the screw pump mechanism. Alternatively, the vacuum pump is installed at an inlet site, and an inlet side opening is installed at an intermediate site of the turbo mechanism. 2. The vacuum pump according to claim 1, wherein a filter is provided in a flow passage on at least one side before and after the control valve for adjusting the flow rate of the gas. The vacuum pump according to claim 1 or 2, further comprising a mechanism for controlling an opening degree of the control valve. 4. The vacuum pump according to claim 1, wherein the flow path and the control valve are provided in a unit that can be detachably attached to the outside of the vacuum pump. The vacuum pump according to claim 2, further comprising means for heating at least one of the control valve and the filter.

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