JP3456558B2 - Turbo molecular pump - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a turbo-molecular pump used in a semiconductor manufacturing apparatus such as a dry etching apparatus, and more particularly to an exhaustion of a condensable gas having a deposition property. It relates to a suitable turbo-molecular pump. FIG. 8 is a diagram showing an example of a conventional turbo-molecular pump. In the conventional turbo-molecular pump, a rotor 2 is disposed in an outer cylinder 1 forming a part of a casing C so as to be rotatable at a high speed, and a rotor blade 2a protruding from an outer periphery of the rotor 2 is laminated with a part of the casing C. A turbine T is formed between the stator blade 1a and the stator blade 1a protruding from the inner periphery of the stator spacer 1b provided in the shape of a circle, and gas molecules sucked from the intake port 3 are compressed by the turbine T to the exhaust port 4 side. It is a configuration to discharge. The thread groove rotor 2b of the rotor 2 includes:
A helical screw is engraved on the outer periphery of the lower end of the turbine T to send gas between the rotor 2 and the stator cylinder 1c to the exhaust port side. In general, the rotor 2 and the stator spacer 1b are formed of a metal such as an aluminum alloy. In the illustrated pump, the rotating shaft 5 fixed to the rotor 2 has a pair of upper and lower radial magnetic bearings 6,7.
And by a thrust magnetic bearing 8 at the shaft end in a non-contact manner. Reference numeral 9 denotes a component of the casing C, which is a base for supporting the outer cylinder 1 and can be formed of, for example, an aluminum alloy. M is an induction motor. [0003] In such a turbo molecular pump,
When the process gas is exhausted, there is a problem that a solid reaction product easily adheres and accumulates in the pump. For example, in the turbo-molecular pump shown in FIG. 8, non-contact bearings 6, 7, and 8 are employed as bearings, so that frictional resistance during operation is reduced. In these bearings and the motor M, eddy current loss is reduced by employing a core made of a silicon steel plate. Therefore, 10-3 to 1
0.05 to 0.5 Torr of intake gas of about 0-2 Torr
The frictional resistance between the gas and the turbine T during the process of compression to about r becomes small. Therefore, the molecular pump as shown in the figure has few heat generation factors as a whole, and is usually operated in a state where the temperature is slightly raised from room temperature. However, when this molecular pump is applied to a semiconductor manufacturing apparatus that performs, for example, aluminum dry etching of a semiconductor device and the like, and the reaction product after etching is evacuated, such as aluminum chloride AlCl3, this kind of gas has a vapor pressure characteristic. Since the temperature at which the solid phase is formed is, for example, 50 to 60 °, this gas is taken into a pump near normal temperature and is cooled to a temperature lower than the solid phase temperature. It will adhere to and accumulate on each of the facing parts. When such reaction products adhere to and accumulate in the pump, they may reach 3 to 4 mm when they are large during a certain period of use. [0004] Therefore, when this turbo-molecular pump is used for exhausting gas which causes aluminum chloride or similar phenomenon, disassembly and cleaning work is required more frequently than usual, which is extremely inconvenient in terms of maintenance and operation efficiency. Will occur. In particular, the space between the outer periphery of the rotor 2 and the casing C, such as between the thread groove rotor 2b and the stator cylinder 1c or between the rotor blades 2a and the stator blades 1a, is a very small distance of about 1 mm. The reaction product increases the possibility of solid contact between the two, and may cause a serious accident such as damage or breakage of the pump itself. Conventionally, as means for solving such problems, a method of controlling the temperature of a pump to a high temperature using a heat source such as a nichrome wire heater, a magnetic circuit between a permanent magnet disposed on a rotor and a housing, and the like. And a method utilizing heat generated by eddy current in the magnetic circuit is known. The turbo molecular pump shown in FIG.
Are shown. The magnetic field generated by the permanent magnet 10 penetrates the facing surface of the casing C or a metal component near the casing C to form a magnetic circuit, and generates heat by eddy current accompanying rotation of the rotor 2. However, the method using a heat source such as a heater requires space for the heater and associated wiring, and requires a relay and a power supply for controlling the nichrome wire heater. A controller is required, and it is necessary to provide an earth leakage breaker and an insulation transformer for preventing a heating action from being stopped due to disconnection and preventing an earth leakage accident. In addition, the conventional method using a permanent magnet can solve the problems of the method using a heat source such as a heater, but since the surroundings of the rotating permanent magnet are made of a material having a low magnetic permeability, the casing or the stator is not used. It is necessary to use a large number of permanent magnets with high magnetic flux density to obtain the magnetic flux density that causes the inside of the device to generate heat, and there is a problem that the rotation of the permanent magnet causes fluctuations in the magnetic field and electric field to the surroundings. . Therefore, the present invention solves the above-mentioned problems of the conventional turbo-molecular pump, and heats the gas flow path with a simple configuration. An object of the present invention is to provide a turbo-molecular pump capable of preventing adhesion and deposition. It is another object of the present invention to provide a turbo-molecular pump having a simple configuration that does not require a large number of permanent magnets having a high magnetic flux density, and to provide a turbo-molecular pump in which fluctuations of a magnetic field and an electric field with respect to the surroundings are reduced. According to the present invention, a permanent magnet and a magnetic body adjacent to a magnetic pole of the permanent magnet are arranged in a circumferential direction of a rotor, and a ferromagnetic body forming a magnetic circuit with the permanent magnet is provided. The above object is achieved by providing a turbo-molecular pump in which the fixed cylinder is provided between the rotor and the base and the fixed cylinder is thermally coupled to the stator. In a first embodiment of the present invention, a permanent magnet is disposed on a rotor so that N and S magnetic poles are alternately arranged in the circumferential direction of the rotor.
Variations in the magnetic and electric fields with respect to the surroundings during rotation of the rotor can be reduced. In a second embodiment of the present invention, the fixed cylinder is brought into contact with the stator or the spacer directly or via a heat conductive member, thereby improving the heat conduction to the stator. Can be. In a third embodiment of the present invention, the fixed cylinder and the stator are integrally formed of a ferromagnetic material, thereby improving heat generation efficiency and heat conduction to the stator. it can. According to a fourth embodiment of the present invention, a temperature sensor and a cooling water pipe are provided near the bearing, whereby the temperature rise of the bearing can be controlled. The permanent magnet arranged on the rotor forms a magnetic circuit between the rotor and a fixed ferromagnetic cylinder provided between the base and the rotor. When the rotor is rotated by the driving of the turbo molecular pump, the magnetic field in the magnetic circuit formed on the fixed cylinder moves in the circumferential direction in the fixed cylinder with the rotation of the rotor. In general, when the magnetic field applied to a ferromagnetic material changes, an eddy current is generated in the ferromagnetic material to generate Joule heat. Therefore, the fixed cylinder generates heat due to a change in the magnetic field in the fixed cylinder due to the rotation of the rotor. In a configuration in which the N and S magnetic poles of the permanent magnet are alternated in the circumferential direction of the rotor, a large amount of heat generation can be obtained by changing the magnetic field more. The heat generated in the fixed cylinder is transmitted to the stator, the stator blades and the spacer directly through the fixed cylinder by heat conduction or through a heat conductive member, and the casing,
It is also transmitted to the base and bearing. Further, the heat from the stator blades is transmitted to the rotor blades by heat radiation, and the temperature of the entire pump is increased. By increasing the temperature of the pump, especially by increasing the temperature in the flow path where the reaction products are likely to adhere and accumulate, the adhesion and accumulation of the reaction products can be reduced. The permanent magnet provided on the rotor is surrounded on the inside and outside by a ferromagnetic fixed cylinder and a magnetic member on the rotor side, so that the motor and bearings inside the pump and the outside of the pump can be protected. The effect of leakage flux is reduced. In addition, when the temperature in the bearing section becomes equal to or higher than the allowable temperature of the bearing section by the temperature detection of the temperature sensor arranged near the bearing, cooling water is passed through the cooling water pipe to the vicinity of the bearing section to generate a reaction. The bearing can be cooled while the temperature of the portion where the adhesion and accumulation of the object is prevented is kept high. Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a cross-sectional view for explaining an embodiment of the present invention, FIGS. 2 and 3 are cross-sectional views for explaining the arrangement of permanent magnets, and FIG. It is the perspective view which removed a part for explaining a relation. The turbo molecular pump shown in FIG. 1 has substantially the same configuration as that of the conventional turbo molecular pump shown in FIG. 8, and is different mainly in the arrangement of the permanent magnet and the arrangement of the fixed cylinder. For example, in the turbine T, stator blades 1a are alternately arranged facing rotor blades 2a made of aluminum alloy, and a plurality of permanent magnets 11 are provided on the inner peripheral surface of a thread groove rotor 2b below the rotor blades 2a. Glued. The permanent magnet 11 is, as shown in FIGS.
The magnetic poles are arranged on the inner peripheral surface at a constant angular interval such that the direction of the magnetic poles is the circumferential direction of rotation. The permanent magnets 11 are arranged such that their magnetic poles alternate between N and S. A fixed cylinder 12 made of a ferromagnetic material is provided between the base portion 9 and the thread groove rotor 2b in the vicinity of the permanent magnet 11. The fixed cylinder 12 forms a magnetic circuit together with the permanent magnet 11. The fixed cylinder 12 and the stator cylinder 1c are integrally formed, and the heat generated in the fixed cylinder 12 immediately
Is transmitted to A magnetic bearing including radial magnetic bearings 6 and 7 and a thrust magnetic bearing 8 and a motor M are arranged around the rotating shaft 5. Further, the turbo molecular pump having the configuration shown in FIG. 1 is provided with a purge port 13 for supplying a purge gas from the outside to the radial magnetic bearing 6 via the base portion 9. In FIG. 2 and FIG. 3, after the magnetic flux from the N pole of the permanent magnet 11 passes through the magnetic piece 14,
A magnetic circuit is formed that passes through the air gap between the opposed fixed cylinder 12 and the inside of the fixed cylinder 12 in the circumferential direction, passes through the air gap again, and returns to the S pole of the permanent magnet 11 via the magnetic piece 14. . This magnetic circuit comprises a permanent magnet 1
It is formed every one. Here, when the rotor 2 rotates, the thread groove rotor 2 b and the permanent magnet 11 rotate in the circumferential direction with respect to the fixed cylinder 12 with the rotation of the rotor 2. FIG.
Shows a state rotated from the position of FIG. Due to the rotational movement of the permanent magnet 11, the magnetic field in the fixed cylinder 12 also moves. Due to the movement of the magnetic field in the ferromagnetic material, an eddy current is generated in the ferromagnetic material, and Joule heat is generated. Here, the magnetic flux density of the fixed cylinder 12 is B,
Assuming that the number of the permanent magnets is n and the rotation speed of the rotor blade 2 is f, the amount of heat generated per unit time W generated by the eddy current is expressed by the following equation. W = K · (n · f · B) 2 The magnetic flux density B increases as the gap t between the permanent magnet 11 and the fixed cylinder 12 decreases, and increases as the magnetic permeability of the fixed cylinder 12 increases. Therefore, by making the fixed cylinder 12 a ferromagnetic material having a large magnetic permeability, the magnetic flux density B and the number of the permanent magnets 11 can be reduced with a small magnetic flux density compared with those of a conventional turbo-molecular pump. It can be realized with a number of permanent magnets. Next, the manner of transmitting heat will be described with reference to FIGS. 4 and 5. FIG. In the perspective view of FIG.
The heat generated in 2 is transmitted to the stator cylinder 1c through the connecting portion 15 connecting the fixed cylinder 12 and the stator cylinder 1c, as indicated by the solid arrow in the drawing. Due to this heat, the temperature of the stator cylinder 1c increases, and the temperature of the portion facing the thread groove rotor 2b increases. Further, as shown in FIG. 5, the heat passes through the stator cylinder 1c and passes through the stator spacer 1b and the stator blade 1
a to increase the temperature of the site. Further, the temperatures of the casing C, the base 9 and the bearings 6 and 7 are increased. The rotor blades 2a receive heat transfer from the opposed stator blades 1a by heat radiation, and contribute to the temperature rise of the entire pump. If the temperature of the turbo-molecular pump becomes unduly high, there is a possibility that a dielectric breakdown occurs in a coil portion of a motor or a magnetic bearing or a temperature drift of a gap sensor of the magnetic bearing occurs. Therefore, in the embodiment of the present invention,
By directly connecting the stator cylinder 1c to the fixed cylinder 12, the efficiency of transmitting the heat generated in the fixed cylinder 12 to the stator cylinder 1c is increased, and thereby the temperature of the stator cylinder 1c after the fixed cylinder 12 is increased. In this way, the configuration is such that the temperature of the bearing portion where the temperature rise is not desired is suppressed relatively low. Further, by supplying a purge gas from the purge port 13 to the radial magnetic bearing 6, the invasion of condensable reaction products into the radial magnetic bearing 6 is prevented. (Effects of the Embodiment) According to the embodiment of the present invention, heat can be efficiently generated by the fixed cylinder made of ferromagnetic material, and the generated heat is used to deposit and deposit reaction products. The transmission can be efficiently performed between the stator cylinder and the thread groove rotor, which are easy to perform. The magnetic circuit formed by permanent magnets forms a closed magnetic circuit by the fixed cylinder and the magnetic material on the rotor side, and does not leak magnetic flux to the outside.
It is possible to reduce the influence of the leakage magnetic flux to the bearing and the outside of the pump. Due to the heat generated by the ferromagnetic material, the magnetic flux intensity and the number of permanent magnets required to generate the same amount of heat as in the related art can be reduced as compared with the related art. (Other Embodiments) Another embodiment of the present invention is to prevent dielectric breakdown of a coil portion of a motor or a magnetic bearing due to a rise in temperature of a turbo-molecular pump and temperature drift of a gap sensor of a magnetic bearing. In order to achieve this, a cooling mechanism such as a temperature sensor and a cooling water pipe is disposed near the bearing. FIG. 6 is a sectional view for explaining another embodiment of the present invention, and FIG. 7 is a block diagram for explaining the configuration of a temperature sensor and a cooling water pipe. 6, a temperature sensor 16 for detecting the temperature of the magnetic bearing 8 is installed near the magnetic bearing 8 in the base portion 9, and a cooling water pipe 17 for cooling the magnetic bearing 8 is installed near the magnetic bearing 8. I do. The cooling water pipe 17 is configured to receive cooling water supplied by a three-way valve 18. A cooling water supply source is connected to the inlet side of the three-way valve 18, a cooling water pipe 17 is connected to one outlet side of the three-way valve 18, and a bypass water pipe 19 is connected to the other outlet side. This three-way valve 18
Is a control circuit 20 for inputting a detection signal of the temperature sensor 16.
It is controlled to open and close by. When the temperature detected by the temperature sensor 16 is equal to or higher than the specified temperature, the cooling water flows through the cooling water pipe 17 to cool the bearing portion. When the temperature is equal to or lower than the specified temperature, the cooling water is bypassed by switching the three-way valve 18. Water piping 19
To perform no cooling operation. This makes it possible to control the temperature rise of the bearing. (Effects of Other Embodiments) In a turbo-molecular pump, the temperature of a portion where reaction products are likely to occur is increased to reduce the adhesion and deposition of reaction products, and the temperature of a magnetic bearing portion, a motor, and the like is reduced. It is possible to prevent an increase in temperature at a portion where the increase is not desired. (Other Embodiments) As a ferromagnetic material used in the embodiment of the present invention, it is possible to improve the corrosion resistance by applying a coating of nickel, fluororesin, or the like in addition to iron. it can. As described above, according to the present invention,
It is possible to provide a turbo molecular pump capable of heating a gas flow path with a simple configuration and preventing deposition and deposition of a reaction product in a pump even for a condensable gas that is easily deposited. Further, it is possible to provide a turbo-molecular pump having a simple configuration that does not require a large number of permanent magnets having a high magnetic flux density, and to provide a turbo-molecular pump in which fluctuations of a magnetic field and an electric field with respect to the surroundings are reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view for explaining an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating an arrangement of permanent magnets according to one embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating an arrangement of permanent magnets according to the embodiment of the present invention. FIG. 4 is a perspective view with a part removed for explaining a relationship between a permanent magnet and a fixed cylinder according to the embodiment of the present invention. FIG. 5 is a diagram illustrating how heat is transmitted in one embodiment of the present invention. FIG. 6 is a cross-sectional view for explaining another embodiment of the present invention. FIG. 7 is a block diagram illustrating a configuration of a temperature sensor and a cooling water pipe according to another embodiment of the present invention. FIG. 8 is a cross-sectional view illustrating a conventional turbo-molecular pump. DESCRIPTION OF SYMBOLS 1 ... Stator, 1a ... Stator blade, 1b ... Stator spacer, 1c ... Stator cylinder, 2 ... Rotor, 2a ... Rotor blade, 2b ... Screw groove rotor, 3 ... Inlet, 4 ... Exhaust, 5
... Rotating shaft, 6,7 ... Radial magnetic bearing, 8 ... Thrust magnetic bearing, 9 ... Base part, 10 ... Permanent magnet, 11 ... Permanent magnet, 12 ... Fixed cylinder, 13 ... Purge port, 14 ... Magnetic piece, 15 ... Connection part, 16: temperature sensor, 17: cooling water pipe, 18: three-way valve, 19: bypass water pipe, 20: control circuit, T: turbine, C: casing.

Claims (1)

(57) [Claim 1] A permanent magnet and a magnetic body adjacent to a magnetic pole of the permanent magnet are arranged in a circumferential direction of a rotor, and a permanent magnet and a ferromagnetic body constituting a magnetic circuit are arranged. A turbo-molecular pump, wherein a fixed cylinder is provided between a rotor and a base, and the fixed cylinder is thermally coupled to a stator.