JP3119272U - Molecular pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molecular pump that solves such a problem because the trajectory of an electron beam is affected by a leakage magnetic field from the pump when this molecular pump is used for evacuation of an electron microscope or other device that uses an electron beam. To do.
A magnetic shield member S1 that shields magnetic flux leaking to a portion of a pump intake port 6 in relation to the installation of magnetic bearings 8A and 8R that are provided on a pump machine base and that supports a rotating body 4 is provided on the intake port 6. Provide at the site. Although not shown in FIG. 1, in a molecular pump in which a net 6 </ b> N for preventing foreign matter from entering the intake port 6 is attached, magnetic flux leaks from the axial direction of the rotating body 4 to the site of the intake port 6. A magnetic shield member S1 is provided on the net 6N or in the center of the net 6N. Therefore, the magnetic flux is shielded by these magnetic shield members and is not leaked.
[Selection] Figure 1

Description

  The present invention is a molecular pump used for evacuation in a pressure range from a medium vacuum to an ultra-high vacuum, which is joined to an exhausted part of a semiconductor manufacturing apparatus or an analysis apparatus such as an electron microscope or the like such as an electron microscope. For example, the present invention relates to a turbo molecular pump or a molecular drag pump represented by a thread groove pump.

  In such a molecular pump, a typical turbo molecular pump is configured such that a turbo mechanism that forms a main body thereof is rotatably held in a cylindrical casing, and sucks molecules, gas, and the like from an intake port on one side of the casing. And it has the structure which exhausts to the exhaust port of the other side. That is, in the turbo mechanism, a rotating body arranged at the central axis of the casing is rotatably held by upper and lower magnetic bearings installed in the casing. Connected to be rotated at high speed. And this turbo mechanism is a combination of a rotor blade fixed in a plurality of stages on the outer periphery of the rotating body and a stator blade of a plurality of stages fixed on the casing side, in which the rotor blades are rotated at high speed by a motor. Specifically, it is driven at a rotational speed of tens of thousands of revolutions per minute, and compresses and exhausts gas and molecules.

  FIG. 12 shows a general example of a conventional turbo molecular pump. In addition, this FIG. 12 has shown the state which is not joined to the to-be-exhausted part. Hereinafter, the turbo mechanism TK which is the main body of the turbo molecular pump TP will be described. A cylindrical portion 4N is integrally formed on the upper portion of the rotating shaft 3, and the cylindrical portion 4N has a plurality of stages (specifically, on the outer periphery). 8 stages) of rotor blades B1 to B8 (in the drawing, only the uppermost rotor blade B1 and the lowermost rotor blade B8 are provided with reference numerals, and the other reference numerals are omitted). Yes. The rotor blades B1 to B8 are arranged with a constant interval in the axial direction. The rotating shaft 3 and the rotating blades B <b> 1 to B <b> 8 are integrated, and constitute a rotating 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, fixed blades T1 to T7 (in the drawing, only the uppermost fixed blade T1 and the lowermost fixed blade T7 are denoted by the reference numerals and other However, the turbo mechanism TK is configured by alternately providing the rotor blades B1 to B8. In FIG. 12, S is a spacer for holding the fixed blades T1 to T7 at regular intervals. 7 is an exhaust port.

The rotary shaft 3 is rotatably held by upper and lower magnetic bearings 8A and 8R installed on the pump base 1 and is coupled to the motor 2. That is, 8A is an axial magnetic bearing, and 8R is a radial magnetic bearing, which reliably supports the rotating shaft 3. The N pole and the S pole of the permanent magnet are configured by being equally arranged, for example, every 180 ° or 90 °, and the motor stator is configured by, for example, six or twelve electromagnets being equally arranged. These stator-side electromagnets act on the shaft-side permanent magnets to drive the shaft to rotate.
In the magnetic levitation type turbo molecular pump, an electromagnet is arranged on the base side in the vicinity of a ferromagnetic part such as iron provided on the shaft to constitute a magnetic bearing for position control of the shaft in the radial direction and the axial direction. Yes. 3G is a gap sensor installed at the bottom of the pump base 1. On the other hand, the rotor (not shown) which comprises one side of the motor 2 is installed in this rotating shaft 3, and is attached integrally. This rotor forms a motor 2 in cooperation with an electrode coil 1K installed on the pump base 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 a screw groove (this groove is not clearly disclosed in the drawing) is formed on the outer periphery thereof. Has been. In addition, this thread groove may be formed in the stator ring 10 side. The screw groove is formed on a cone having a shallow groove as it goes downward. Moreover, the outer periphery of the cylindrical portion 4N is close to the inner peripheral surface of the stator ring 10 joined to the inner periphery of the lower casing 9 that also serves as a base. A thread groove pump NP is configured by a combination of the inner peripheral surface of the stator ring 10 and the cylindrical portion 4N. This thread groove pump NP functions as a drag 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 mechanism by the turbo mechanism TK and a thread groove pump function by the thread groove pump NP, and is usually called a hybrid turbo molecular pump. As the turbo molecular pump TP, such a hybrid type has good exhaust characteristics and is often used. In addition, as the molecular pump, there are a pump that uses only the turbo mechanism TK and a thread groove pump NP that includes only a combination of the above-described stator ring and a rotating body (cylindrical body) having a thread groove formed on the outer periphery.
Further, some turbo molecular pumps are provided with a net for preventing foreign substances from entering and dropping inside the intake port, and a large number of holes such as quadrangles and hexagons are opened. In order to ensure conductance, an opening hole is provided on the entire surface of the net, and is made of stainless steel or aluminum alloy for corrosion resistance and rust prevention (see Patent Document 1). Moreover, the device of magnetic shielding is also performed (refer patent document 2).
JP 11-247790 A Japanese Patent Laid-Open No. 2000-200576

There is a problem that a magnetic field generated from a motor and a magnetic bearing part leaks outside the pump for rotational driving and position control of the rotor of the turbo molecular pump. In particular, among the magnetic bearings, the axial magnet for position control in the axial direction is located at the bottom of the molecular pump machine base, so if a magnetic field leaks from the bottom of the pump machine base to other motors or radial magnets. It is thought that there is little attenuation by space compared to the case of the electromagnet of the bearing.
When this molecular pump is used for evacuation of an apparatus using an electron beam such as an electron microscope, the trajectory of the electron beam is affected by the leakage magnetic field from the pump, and there is a demand to reduce the magnetic field leaking from the pump.

As a technique for reducing the leakage magnetic field, a method of enclosing with a magnetic shield member made of a high permeability material such as iron is conceivable, but this method has the following problems.
First, the whole molecular pump device becomes large, resulting in a decrease in operability and an increase in cost due to weight.
Second, since the inlet side of the molecular pump is connected to a chamber or the like to be evacuated, it is difficult to take a magnetic shield measure and it is difficult to reduce the leakage magnetic field from the pump inlet side.
The present invention is intended to provide a molecular pump that can solve such problems.

The molecular pump provided by the present invention is provided with the following means for solving the above problems. In particular, the main ideas are summarized as follows.
The molecular pump first provided by the present invention is provided with a magnetic shield member that shields magnetic flux leaking from the axial direction of the rotating body to the outside of the pump on the axial center of the rotating body and at the inlet portion. Therefore, the leakage of magnetic flux from the rotating body toward the air inlet is eliminated by the presence of the magnetic shield member.
The molecular pump provided by the present invention secondly includes a magnetic shield member provided at the bottom of the pump base for shielding the magnetic flux leaking from the magnetic bearing bearing the rotating body to the outside of the pump bottom. It is provided at the bottom. Therefore, leakage of magnetic flux from the bottom of the pump machine base to the outside of the bottom is eliminated by the magnetic shield member.
A third molecular pump provided by the present invention provides a magnetic pump that shields magnetic flux leaking from the axial direction of the rotating body to the outside of the bottom of the pump in a molecular pump in which a net for preventing foreign matter is attached to the intake port. A shield member is provided on the net or in the center of the net. Therefore, the magnetic flux is shielded by the magnetic shield member and is not leaked.
A molecular pump provided by the present invention in the fourth aspect is a molecular pump in which a net for preventing foreign matter from being mixed in an intake port, and a magnetic shield member is constituted by the net. Therefore, the magnetic flux is shielded by the shield member of this net.
Furthermore, the molecular pump provided by the present invention in the fifth aspect is one in which a magnetic shield member is stretched on the inner peripheral surface of the casing of the pump, and leakage of magnetic flux in the radial direction is also prevented.

The magnetic field generated from the motor part or magnetic bearing part of the molecular pump leaks up and down the axis of the rotation axis by forming the net at the inlet port or the cover at the bottom of the pump machine base with a ferromagnetic material such as iron. The magnetic field that absorbs the magnetic flux and leaks to the outside of the pump can be reduced.
At the same time, magnetic shield members are arranged on the inner peripheral surface of the casing and the inner peripheral surface of the base to absorb the magnetic flux leaking in the radial direction and reduce the magnetic field leaking outside the pump. The trouble is eliminated.

  The molecular pump to which the present invention is applied is a turbo molecular pump consisting only of a turbo mechanism, a thread groove pump formed between a rotating body and a stator ring, or a hybrid based on a combination of a turbo mechanism and a thread groove pump. A molecular pump of the form. The best molecular pump is the hybrid type. 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.

  The present invention is such a hybrid type molecular pump that employs a magnetic bearing mechanism. By forming a net provided at the inlet port with a ferromagnetic material such as iron, the inlet side to the outside of the pump is formed. The leakage magnetic flux is absorbed, and the magnetic field leaking to the outside is reduced. The central portion of the net is not exhausted because the rotor directly below is not the rotor blade portion, and need not be opened. Therefore, by making the center part of the net into a disk shape, the amount of magnetic flux absorbed (saturated magnetic flux) can be increased, and the effect of reducing the leakage magnetic field to the outside can be further increased. Further, since the disc-shaped portion in the center does not affect the opening conductance even if the thickness is increased, the amount of magnetic flux absorbed can be further increased by increasing the thickness.

Furthermore, the present invention absorbs leakage magnetic flux from the bottom of the pump machine base to the outside by forming the bottom cover at the bottom of the pump machine base with a ferromagnetic material such as iron, thereby reducing the magnetic field leaking to the outside. To do.
Furthermore, the present invention reduces the magnetic field leaking to the outside by absorbing the magnetic flux leakage from the outer periphery of the pump to the radially outer side by arranging a magnetic shield member on the inner peripheral surface of the casing or the inner peripheral surface of the base. is there. However, when it is made of iron, surface treatment such as nickel plating is performed to prevent rust. Furthermore, by arranging the magnetic shield member on the inner peripheral surface of the casing or the inner peripheral surface of the base, it is possible to reduce the magnetic field that leaks radially outward from the outer peripheral surface of the pump. A molecular pump with all of these is the best mode.
Hereinafter, the present invention will be described with reference to embodiments shown in the drawings. In each embodiment, specifically, an example of a turbo molecular pump TP will be described to describe the configuration of the molecular pump of the present invention.

  In the first embodiment of the present invention, as shown in FIGS. 1 and 2, a magnetic shield member S1 is provided at the inlet 6 of the molecular pump. That is, as shown in FIG. 2, a support member 6 </ b> S is provided in the central portion from the inner peripheral surface of the air inlet 6, and a disk-shaped magnetic shield member S <b> 1 is disposed in the central portion of the air inlet 6. In this case, the magnetic shield member S1 is formed of a ferromagnetic material such as iron. Thus, by arranging the magnetic shield member S1 at the intake port 6, leakage of the magnetic field from the rotating body 4 is eliminated. The first embodiment is an example in which a net is not attached to the intake port 6, but the material and shape of the support member 6S are not limited to the illustrated example. 1 shows a longitudinal section, and FIG. 2 is a view from above.

  In the second embodiment of the present invention, a member that functions as a lid of an opening formed by providing a magnetic bearing 8A at the bottom of the pump base 1 in the molecular pump, specifically, the bottom is configured as a magnetic shield member S2. In this case as well, the material is made of a ferromagnetic material such as iron. The configuration is shown in FIG.

  In the third embodiment of the present invention, in a molecular pump of a type in which a net 6N for preventing foreign matter from entering the inside of the intake port 6 is provided, the net 6N is provided with a magnetic shield function. In this example, as shown in FIG. 4, the net 6N itself is configured as a magnetic shield member S3. In this embodiment as well, specifically, an iron material, which is a ferromagnetic material, is employed as the magnetic shield member, and nickel plating is applied to the iron material as a rust prevention treatment. In this embodiment, the function is slightly different from that of the first embodiment, but leakage of the magnetic field is prevented. FIG. 4 is a view of the molecular pump as seen from above.

  In the fourth embodiment of the present invention, a disk which is not subjected to the net opening processing at the central portion in the air inlet 6 is disposed as the magnetic shield member S4. This configuration is shown in FIGS. FIG. 6 is a view showing only the net 6N and the magnetic shield member S4 taken out, and FIG. 7 is a view seen from the side. In this embodiment, the magnetic flux absorption effect (saturation magnetic flux) of the net 6N in the molecular pump is enhanced. Furthermore, an embodiment in which the thickness of the magnetic shield member S4 is increased can be given as a modified example. This configuration is as shown in FIG. 8 showing the same configuration as FIG. 7 showing the cross-sectional view of FIG. If the thickness of the net 6N is made uniform, the conductance of the opening on the outer periphery of the net deteriorates, leading to a decrease in exhaust performance. However, even if only the central portion of the magnetic shield member S5 is thickened as shown in FIG. Since it does not affect, the effect of absorbing the leakage magnetic flux can be enhanced without causing a decrease in exhaust performance.

  The fifth embodiment of the present invention is for reducing the radial leakage magnetic field in the molecular pump. The inner peripheral surface of the casing 5 and the outer peripheral surface of the rotating body 4 as well as the holding portion 11 of the rotating body 4 are used. Magnetic shield members S6, S7, and S8 are stretched on the outer peripheral surface, respectively, and the configuration is as shown in FIG.

  In the sixth embodiment of the present invention, a magnetic shield member S9 is installed on a portion and an inner peripheral surface at the bottom of the pump machine base 1. The configuration of this embodiment is shown in FIG.

  As a seventh embodiment of the present invention, a combination of the above embodiments can be considered. For example, in a molecular pump in which a net 6N is provided at the intake port 6, a magnetic shield member S10 is installed at the central portion of the net 6N, a magnetic shield member S9 is also provided at the bottom of the pump machine base 1, and the casing 5 An example of the molecular pump shown in FIG. 11 in which the magnetic shield member S6 is also provided on the inner peripheral surface can be given. In the seventh embodiment, if the magnetic shield member S6 is unnecessary, it is possible not to provide the magnetic shield member S6, and a combination thereof can be appropriately selected depending on the purpose and application.

  As mentioned above, although the Example of this invention was shown from the 1st to 7th and other Examples, it is not limited to these Examples. For example, the example which comprises a magnetic shielding member with ferromagnetic materials other than iron can also be given. 1 to 11 have the same functions as those in FIG. 12, and detailed descriptions thereof are omitted.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the structure of the 1st Example of this invention in the longitudinal cross-section. It is a top view which shows the structure of the principal part of 1st Example of this invention. It is a figure which shows the structure of the 2nd Example of this invention. It is a figure which shows the structure of the 3rd Example of this invention. It is a figure which shows the structure of the 4th Example of this invention. It is a figure which shows the structure of the 4th Example of this invention. It is the figure which looked at the 4th example of the present invention from the side. It is the figure which looked at the 4th example of the present invention from the side. It is a figure which shows longitudinally the structure of the 5th Example of this invention. It is a figure which shows the structure of the 6th Example of this invention in the longitudinal cross-section. It is a figure which shows the structure of the 7th Example of this invention with a longitudinal cross-section. It is a figure which shows the structure of the conventional molecular pump longitudinally.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pump machine base part 1K Electrode coil 2 Motor 3 Rotating shaft 3G Gap sensor 4 Rotating body 4N Cylindrical part 5 Casing 6 Intake port 6N Net 6S Support member 7 Exhaust port 8A, 8R Magnetic bearing 9 Lower casing 10 Stator ring 11 Holding part B1 B8 Rotary blade S1-S10 Magnetic shield member SP Spacer T1-T7 Fixed blade TK Turbo mechanism TP Turbo molecular pump NP Thread groove pump

Claims (12)

  A rotating blade fixed in a plurality of stages to a rotating body rotatably held in a cylindrical casing via a magnetic bearing, a plurality of fixed blades fixed to the inner peripheral side of the casing, and the rotating body at a high speed A turbo mechanism comprising a rotating blade and a fixed blade is provided with a rotating motor, and the turbo mechanism is operated to suck in molecules from the intake port on one end side of the casing and exhaust it to the exhaust port on the other end side. In the molecular pump, a magnetic shield member for shielding magnetic flux leaking from the axial direction of the rotating body to the outside of the pump from the axial direction of the rotating body on the axial center of the rotating body is attached.   2. The molecular pump according to claim 1, wherein the magnetic shield member is made of a ferromagnetic material.   A molecular pump characterized in that a magnetic shield member that shields magnetic flux leaking outward from a pump bottom from a magnetic bearing provided at the bottom of the pump machine base and bearings a rotating body is provided at the bottom of the pump machine base.   4. The molecular pump according to claim 3, wherein the magnetic shield member is made of a ferromagnetic material.   A rotating blade fixed in a plurality of stages to a rotating body rotatably held in a cylindrical casing via a magnetic bearing, a plurality of fixed blades fixed to the inner peripheral side of the casing, and the rotating body at a high speed A turbo mechanism comprising a rotating blade and a fixed blade is provided with a rotating motor, and the turbo mechanism is operated to suck in molecules from the intake port on one end side of the casing and exhaust it to the exhaust port on the other end side. In a molecular pump which is a pump and has a net attached to the intake port to prevent foreign matter from entering, a magnetic flux leaking from the axial direction of the rotating body to the outside of the pump is formed on the axis of the rotating body and on the portion of the net. A molecular pump characterized in that a magnetic shielding member for shielding is installed.   6. The molecular pump according to claim 5, wherein the magnetic shield member is made of a ferromagnetic material.   A rotating blade fixed in a plurality of stages to a rotating body rotatably held in a cylindrical casing via a magnetic bearing, a plurality of fixed blades fixed to the inner peripheral side of the casing, and the rotating body at a high speed A turbo mechanism comprising a rotating blade and a fixed blade is provided with a rotating motor, and the turbo mechanism is operated to suck in molecules from the intake port on one end side of the casing and exhaust it to the exhaust port on the other end side. In the molecular pump, which is a pump and has a net attached to the intake port for preventing foreign matter from being mixed, the magnetic shielding member configured to shield the magnetic flux leaking upward from the axial direction of the rotating body to the pump is configured by the net. Characteristic molecular pump.   8. The molecular pump according to claim 7, wherein the net is made of a ferromagnetic material.   A rotating blade fixed in a plurality of stages to a rotating body rotatably held in a cylindrical casing via a magnetic bearing, a plurality of fixed blades fixed to the inner peripheral side of the casing, and the rotating body at a high speed A turbo mechanism comprising a rotating blade and a fixed blade is provided with a rotating motor, and the turbo mechanism is operated to suck in molecules from the intake port on one end side of the casing and exhaust it to the exhaust port on the other end side. A molecule that is a pump and has a magnetic shield member that shields magnetic flux leaking from the magnetic bearing portion installed at the bottom of the pump base to the bottom of the pump, on the outer surface of the bottom of the pump base. pump.   The molecular pump according to claim 9, wherein the magnetic shield member is made of a ferromagnetic material.   A rotating blade fixed in a plurality of stages to a rotating body rotatably held in a cylindrical casing via a magnetic bearing, a plurality of fixed blades fixed to the inner peripheral side of the casing, and the rotating body at a high speed A turbo mechanism comprising a rotating blade and a fixed blade is provided with a rotating motor, and the turbo mechanism is operated to suck in molecules from the intake port on one end side of the casing and exhaust it to the exhaust port on the other end side. In the pump, a molecular pump characterized in that a magnetic shield member is attached to the inner peripheral surface of the casing and the outer peripheral surface of the rotating body holding portion.   A rotating blade fixed in a plurality of stages to a rotating body rotatably held in a cylindrical casing via a magnetic bearing, a plurality of fixed blades fixed to the inner peripheral side of the casing, and the rotating body at a high speed A turbo mechanism comprising a rotating blade and a fixed blade is provided with a rotating motor, and the turbo mechanism is operated to suck in molecules from the intake port on one end side of the casing and exhaust it to the exhaust port on the other end side. A molecular pump characterized in that a magnetic shield member is attached to a base connected to a casing in the pump.

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