Vacuum pump

Abstract

To provide a vacuum pump that can effectively restrain a decrease in performance caused by thermal expansion.SOLUTION: A vacuum pump comprises an exterior body 203 provided with a suction port 101, a rotating body 103 contained in the exterior body 203, and supported rotatably, a screw groove stator 131 arranged around an outer periphery of the rotating body 103, and having a nearly cylindrical shape, and a screw groove 131a engraved on at least one out of an outer peripheral surface of the rotating body 103 or an inner peripheral surface of the screw groove stator 131, and exhausts gas sucked from the side of the suction port 101 to the outside of the exterior body 203 by rotating the rotating body 103. Binding means 220 formed of a material having a lower coefficient of linear expansion than that of a material of the screw groove stator 131, and for reducing deformation in a radial direction at the time of thermal expansion of the screw groove stator 131 is arranged around an outer periphery of the screw groove stator 131.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a vacuum pump.

Background Art

[0002] Semiconductor manufacturing equipment, liquid crystal manufacturing equipment, electron microscopes, surface analysis equipment, or microfabrication equipment, etc. need to make the environment inside the equipment in a high vacuum state. A vacuum pump is used to make the inside of these devices in a high vacuum state.

[0003] As shown in Patent Document 1, for example, a screw groove pump may be provided on the downstream side of a turbo molecular pump having a rotating blade and a fixed blade. A so-called Holweck type screw groove pump is composed of an outer peripheral surface of a rotating body and a stator arranged on the outer periphery of the rotating body, and screw grooves are engraved on the outer peripheral surface of the rotating body or the inner peripheral surface of the stator.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in order to prevent reaction products generated in semiconductor manufacturing, etc. from depositing, a technique has been devised to keep the stator forming the screw groove pump at a temperature equal to or higher than the sublimation temperature of the reaction products. However, when the stator arranged on the outer periphery of the rotating body becomes hot, the gap amount between the rotating body and the stator expands due to thermal expansion, and the performance of the screw groove pump deteriorates.

[0006] On the other hand, in addition to exhaust performance, vacuum pumps also have specification requirements such as an optimum internal temperature according to various manufacturing processes in the above-mentioned semiconductor manufacturing. In order to reduce inventory, it may be required to change the internal temperature setting specifications for the same pump. In this case, the gap amount between the rotor and the stator caused by the above-mentioned thermal expansion changes due to the change in the internal temperature setting specifications. If this gap amount changes to a larger amount, the exhaust performance of the thread groove pump may decrease, which may cause a problem.

[0007] The present invention has been made to solve the above-mentioned problems, and has an object to provide a vacuum pump that can effectively suppress performance degradation due to thermal expansion. [Means for solving the problem]

[0008] The vacuum pump according to the present invention, which achieves the above object, comprises an exterior body provided with an intake port, a rotor contained in the exterior body and supported rotatably, a substantially cylindrical stator disposed on the outer periphery of the rotor, and a screw groove engraved on at least one of the outer periphery of the rotor or the inner periphery of the stator, and exhausts gas sucked in from the intake port side to the outside of the exterior body by rotating the rotor, The stator extends from the upper end portion on the upstream side toward the lower side which is the downstream side, and the lower end portion is a free end, The outer periphery of the stator and the lower end portion In addition, the rotor is made of a material having a linear expansion coefficient lower than that of the stator, thereby reducing radial deformation caused by thermal expansion of the stator. cylindrical member is provided. Effect of the Invention

[0009] The vacuum pump configured as described above reduces radial deformation of the stator during thermal expansion. cylindrical member Therefore, it is possible to suppress the increase in the gap between the outer circumferential surface of the rotor and the inner circumferential surface of the stator, and therefore the vacuum pump can effectively suppress the deterioration of the performance of the groove pump caused by thermal expansion.

[0010] The above cylindrical memberIt may be disposed at the downstream end of the stator. Thereby, the radial thermal expansion of the downstream end of the stator whose outer peripheral surface is not fixed on the downstream side can be suppressed, and the deterioration of the performance of the screw groove pump can be effectively suppressed.

[0011] The vacuum pump has a plurality of specifications with different internal temperatures, and the gap amount between the outer peripheral surface of the rotating body and the inner peripheral surface of the stator at a predetermined position in the axial direction of the vacuum pump in each of the specifications is the same by the above. cylindrical member It may be made to be the same. Thereby, this vacuum pump can effectively maintain the performance of the screw groove pump in each specification with different internal temperatures.

[0012] When the stator thermally expands, the stress acting on the stator from the above may be less than the yield stress of the material of the stator. Thereby, it can effectively suppress that the stator restrained by the above and receiving stress during thermal expansion is damaged. cylindrical member It may be made to be less than the yield stress of the material of the stator. Thereby, it can effectively suppress that the stator restrained by the above and receiving stress during thermal expansion is damaged. cylindrical member It can effectively suppress that the stator restrained by the above and receiving stress during thermal expansion is damaged.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the dimensions in the drawings may be exaggerated for convenience of explanation and may differ from the actual dimensions. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

[0015] The vacuum pump according to an embodiment of the present invention is a turbo molecular pump 100 that exhausts gas by the rotating blades of a rotating body rotating at high speed hitting and expelling gas molecules. The turbo molecular pump 100 is used, for example, to suck and exhaust gas from a chamber such as a semiconductor manufacturing apparatus.

[0016] A longitudinal sectional view of this turbo molecular pump 100 is shown in FIG. 1. In FIG. 1, in the turbo molecular pump 100, an intake port 101 is formed at the upper end of a cylindrical outer cylinder 127. And inside the outer cylinder 127, a rotating body 103 is provided in which a plurality of rotating blades 102 (102a, 102b, 102c ···), which are turbine blades for sucking and exhausting gas, are formed radially and in multiple stages on the circumferential portion. A rotor shaft 113 is attached to the center of this rotating body 103, and this rotor shaft 113 is levitated and position-controlled in the air by, for example, a magnetic bearing with 5-axis control. The rotating body 103 is generally made of a metal such as aluminum or an aluminum alloy.

[0017] The upper radial electromagnet 104 has four electromagnets arranged in pairs with respect to the X-axis and the Y-axis. Four upper radial sensors 107 are provided in proximity to the upper radial electromagnet 104 and corresponding to each of the upper radial electromagnets 104. As the upper radial sensor 107, for example, an inductance sensor having a conductive winding or an eddy current sensor is used, and the position of the rotor shaft 113 is detected based on the change in the inductance of this conductive winding that changes according to the position of the rotor shaft 113. This upper radial sensor 107 is configured to detect the radial displacement of the rotor shaft 113, that is, the rotating body 103 fixed thereto, and send it to the control device 200.

[0018] In this control device 200, for example, a compensation circuit having a PID control function generates an excitation control command signal for the upper radial electromagnet 104 based on the position signal detected by the upper radial sensor 107. The amplifier circuit 150 (described later) shown in FIG. 2 controls the excitation of the upper radial electromagnet 104 based on this excitation control command signal, thereby adjusting the radial position above the rotor shaft 113.

[0019] The rotor shaft 113 is formed of a high magnetic permeability material (such as iron or stainless steel) and is attracted by the magnetic force of the upper radial electromagnet 104. Such adjustment is performed independently in the X-axis direction and the Y-axis direction. Further, the lower radial electromagnet 105 and the lower radial sensor 108 are arranged in the same manner as the upper radial electromagnet 104 and the upper radial sensor 107, and the radial position below the rotor shaft 113 is adjusted in the same manner as the radial position above.

[0020] Furthermore, axial electromagnets 106A and 106B are arranged so as to sandwich a disk-shaped metal disk 111 provided at the lower part of the rotor shaft 113 from above and below. The metal disk 111 is made of a high magnetic permeability material such as iron. An axial sensor 109 is provided to detect the axial displacement of the rotor shaft 113, and the axial position signal is configured to be sent to the control device 200.

[0021] In the control device 200, for example, a compensation circuit having a PID control function generates respective excitation control command signals for the axial electromagnet 106A and the axial electromagnet 106B based on the axial position signal detected by the axial sensor 109. The amplifier circuit 150 controls the excitation of the axial electromagnet 106A and the axial electromagnet 106B based on these excitation control command signals, so that the axial electromagnet 106A attracts the metal disk 111 upward by magnetic force, and the axial electromagnet 106B attracts the metal disk 111 downward, thereby adjusting the axial position of the rotor shaft 113.

[0022] In this way, the control device 200 appropriately adjusts the magnetic forces exerted by the axial electromagnets 106A and 106B on the metal disk 111, so as to magnetically levitate the rotor shaft 113 in the axial direction and hold it in space in a non-contact manner. Note that the amplifier circuit 150 for controlling the excitation of the upper radial electromagnets 104, the lower radial electromagnets 105, and the axial electromagnets 106A and 106B will be described later.

[0023] On the other hand, the motor 121 includes a plurality of magnetic poles arranged circumferentially so as to surround the rotor shaft 113. Each magnetic pole is controlled by the control device 200 so as to rotationally drive the rotor shaft 113 via the electromagnetic force acting between the magnetic pole and the rotor shaft 113. In addition, the motor 121 is incorporated with a rotational speed sensor such as a Hall element, a resolver, or an encoder (not shown), and the rotational speed of the rotor shaft 113 is detected by the detection signal of this rotational speed sensor.

[0024] Furthermore, for example, a phase sensor (not shown) is attached near the lower radial sensor 108 to detect the rotation phase of the rotor shaft 113. In the control device 200, the detection signals of this phase sensor and the rotational speed sensor are used together to detect the position of the magnetic pole.

[0025] A plurality of fixed blades 123 (123a, 123b, 123c ···) are arranged with a slight gap from the rotary blades 102 (102a, 102b, 102c ···). The rotary blades 102 (102a, 102b, 102c ···) are each inclined by a predetermined angle from a plane perpendicular to the axis of the rotor shaft 113 in order to transfer the molecules of the exhaust gas downward by collision. The fixed blades 123 (123a, 123b, 123c ···) are made of a metal such as aluminum, iron, stainless steel, copper, or an alloy containing these metals as components.

[0026] In addition, the fixed wing 123 is also formed by being inclined by a predetermined angle from a plane perpendicular to the axis of the rotor shaft 113, and is alternately arranged with the stages of the rotary wing 102 toward the inside of the outer cylinder 127. The outer peripheral end of the fixed wing 123 is supported in a state of being inserted between a plurality of stacked fixed wing spacers 125 (125a, 125b, 125c...).

[0027] The fixed wing spacer 125 is a ring-shaped member and is made of, for example, a metal such as aluminum, iron, stainless steel, copper, or an alloy containing these metals as components. The outer cylinder 127 is fixed to the outer periphery of the fixed wing spacer 125 with a slight gap therebetween. A base portion 129 is disposed at the bottom of the outer cylinder 127. An exhaust port 133 is formed in the base portion 129 and communicates with the outside. The exhaust gas that has entered the intake port 101 from the chamber (vacuum chamber) side and has been transferred to the base portion 129 is sent to the exhaust port 133.

[0028] Furthermore, depending on the application of the turbo molecular pump 100, a threaded groove stator 131 (stator) is disposed between the lower part of the fixed wing spacer 125 and the base portion 129. The threaded groove stator 131 is a cylindrical member made of a metal such as aluminum, copper, stainless steel, iron, or an alloy containing these metals as components, and a plurality of spiral threaded grooves 131a are engraved on its inner peripheral surface. The direction of the spiral of the threaded groove 131a is the direction in which the molecules of the exhaust gas are transferred toward the exhaust port 133 when they move in the rotation direction of the rotating body 103. A cylindrical portion 102d hangs down at the lowermost part following the rotary wings 102 (102a, 102b, 102c...) of the rotating body 103. The outer peripheral surface of this cylindrical portion 102d is cylindrical and protrudes toward the inner peripheral surface of the threaded groove stator 131, and is close to the inner peripheral surface of the threaded groove stator 131 with a predetermined gap amount. The exhaust gas transferred to the threaded groove 131a by the rotary wings 102 and the fixed wings 123 is sent to the base portion 129 while being guided by the threaded groove 131a.

[0029] The base portion 129 is a disc-shaped member that constitutes the base of the turbo molecular pump 100 and is generally made of a metal such as iron, aluminum, or stainless steel. The base portion 129 physically holds the turbo molecular pump 100 and also serves as a heat conduction path, so it is desirable to use a metal with high rigidity and high thermal conductivity such as iron, aluminum, or copper.

[0030] In such a configuration, when the rotary blade 102 is rotationally driven by the motor 121 together with the rotor shaft 113, the exhaust gas is sucked from the chamber through the intake port 101 due to the action of the rotary blade 102 and the stationary blade 123. The rotational speed of the rotary blade 102 is usually 20,000 rpm to 90,000 rpm, and the peripheral speed at the tip of the rotary blade 102 reaches 200 m / s to 400 m / s. The exhaust gas sucked from the intake port 101 passes between the rotary blade 102 and the stationary blade 123 and is transferred to the base portion 129. At this time, the temperature of the rotary blade 102 rises due to the frictional heat generated when the exhaust gas contacts the rotary blade 102 and the conduction of the heat generated by the motor 121. This heat is transferred to the stationary blade 123 side by radiation or conduction by the gas molecules of the exhaust gas.

[0031] The stationary blade spacer 125 is joined to each other at the outer peripheral portion and transfers heat received by the stationary blade 123 from the rotary blade 102 and frictional heat generated when the exhaust gas contacts the stationary blade 123 to the outside.

[0032] In the above description, the threaded groove stator 131 is disposed on the outer periphery of the cylindrical portion 102d of the rotating body 103, and the threaded groove 131a is engraved on the inner peripheral surface of the threaded groove stator 131. However, conversely, there may be a case where a threaded groove is engraved on the outer peripheral surface of the cylindrical portion 102d and a spacer having a cylindrical inner peripheral surface is disposed around it.

[0033] Depending on the application of the turbo molecular pump 100, in order to prevent the gas sucked from the intake port 101 from entering the electrical components composed of the upper radial electromagnet 104, the upper radial sensor 107, the motor 121, the lower radial electromagnet 105, the lower radial sensor 108, the axial electromagnets 106A and 106B, the axial sensor 109, etc., the electrical components are covered by the stator column 122 around them, and the inside of this stator column 122 may be maintained at a predetermined pressure with purge gas.

[0034] In this case, a pipe (not shown) is arranged in the base portion 129, and the purge gas is introduced through this pipe. The introduced purge gas is sent to the exhaust port 133 through the gaps between the protective bearing 120 and the rotor shaft 113, between the rotor and the stator of the motor 121, and between the stator column 122 and the inner peripheral cylindrical portion of the rotating blade 102.

[0035] Here, the turbo molecular pump 100 requires control based on the identification of the model and the specific parameters adjusted individually (for example, various characteristics corresponding to the model). In order to store this control parameter, the turbo molecular pump 100 is provided with an electronic circuit unit 141 inside its main body. The electronic circuit unit 141 is composed of electronic components such as a semiconductor memory such as an EEP-ROM and semiconductor elements for accessing it, a substrate 143 for mounting them, etc. This electronic circuit unit 141 is housed below, for example, near the center of a rotation speed sensor (not shown) that constitutes the lower part of the base portion 129 of the turbo molecular pump 100, and is closed by an airtight bottom cover 145.

[0036] By the way, in the semiconductor manufacturing process, among the process gases introduced into the chamber, there are some that have the property of becoming solid when their pressure becomes higher than a predetermined value or their temperature becomes lower than a predetermined value. Inside the turbo molecular pump 100, the pressure of the exhaust gas is the lowest at the intake port 101 and the highest at the exhaust port 133. When the process gas is transferred from the intake port 101 to the exhaust port 133, if its pressure becomes higher than a predetermined value or its temperature becomes lower than a predetermined value, the process gas will become solid and adhere and deposit inside the turbo molecular pump 100.

[0037] For example, when SiCl is used as a process gas in an Al etching apparatus, when the pressure is low (760 [torr] to 10 4 [torr]) and the temperature is low (about 20 [°C]), it can be seen from the vapor pressure curve that solid products (e.g., AlCl -2 ) precipitate and adhere and deposit inside the turbo molecular pump 100. As a result, when deposits of the process gas accumulate inside the turbo molecular pump 100, these deposits narrow the pump flow path, causing a decrease in the performance of the turbo molecular pump 100. And the above-mentioned products were in a situation where they were likely to solidify and adhere at high-pressure parts near the exhaust port 133 and near the screw groove stator 131. 3 )

[0038] Therefore, in order to solve this problem, conventionally, a heater (not shown) or an annular water-cooling pipe 149 is wound around the outer periphery of the base portion 129, etc., and a temperature sensor (e.g., a thermistor, not shown) is embedded in the base portion 129, for example. Based on the signal of this temperature sensor, control of heating by the heater and cooling by the water-cooling pipe 149 (hereinafter referred to as TMS; Temperature Management System) is performed to keep the temperature of the base portion 129 at a constant high temperature (set temperature).

[0039] Next, regarding the turbo molecular pump 100 configured as described above, an amplifier circuit 150 for exciting and controlling the upper radial electromagnet 104, the lower radial electromagnet 105, and the axial electromagnets 106A and 106B will be described. The circuit diagram of this amplifier circuit 150 is shown in FIG. 2.

[0040] In FIG. 2, one end of the electromagnetic coil 151 constituting the upper radial electromagnet 104 etc. is connected to the positive electrode 171a of the power supply 171 via the transistor 161, and the other end is connected to the negative electrode 171b of the power supply 171 via the current detection circuit 181 and the transistor 162. And the transistors 161 and 162 are so-called power MOSFETs and have a structure in which a diode is connected between their source and drain.

[0041] At this time, for transistor 161, the cathode terminal 161a of its diode is connected to the positive electrode 171a, and the anode terminal 161b is connected to one end of the electromagnet winding 151. Also, for transistor 162, the cathode terminal 162a of its diode is connected to the current detection circuit 181, and the anode terminal 162b is connected to the negative electrode 171b.

[0042] On the other hand, for the current regeneration diode 165, the cathode terminal 165a is connected to one end of the electromagnet winding 151, and the anode terminal 165b is connected to the negative electrode 171b. Similarly, for the current regeneration diode 166, the cathode terminal 166a is connected to the positive electrode 171a, and the anode terminal 166b is connected to the other end of the electromagnet winding 151 via the current detection circuit 181. And the current detection circuit 181 is composed of, for example, a Hall sensor type current sensor or an electric resistance element.

[0043] The amplifier circuit 150 configured as described above corresponds to one electromagnet. Therefore, when the magnetic bearing is under 5-axis control and there are a total of 10 electromagnets 104, 105, 106A, 106B, similar amplifier circuits 150 are configured for each of the electromagnets, and 10 amplifier circuits 150 are connected in parallel to the power supply 171.

[0044] Furthermore, the amplifier control circuit 191 is composed of, for example, a digital signal processor section (hereinafter referred to as the DSP section) (not shown) of the control device 200, and this amplifier control circuit 191 is adapted to switch the on / off of transistors 161 and 162.

[0045] The amplifier control circuit 191 is configured to compare the current value detected by the current detection circuit 181 (a signal reflecting this current value is referred to as the current detection signal 191c) with a predetermined current command value. Then, based on this comparison result, the magnitudes of the pulse widths (pulse width times Tp1, Tp2) generated within the control cycle Ts, which is one period of PWM control, are determined. As a result, the gate drive signals 191a, 191b having these pulse widths are output from the amplifier control circuit 191 to the gate terminals of the transistors 161, 162.

[0046] Note that when passing through the resonance point during the acceleration operation of the rotational speed of the rotating body 103 or when a disturbance occurs during the constant speed operation, etc., it is necessary to control the position of the rotating body 103 with high speed and strong force. Therefore, as the power supply 171, a high voltage of about 50 V, for example, is used so that a rapid increase (or decrease) in the current flowing through the electromagnet winding 151 can occur. Also, a normal capacitor is connected between the positive electrode 171a and the negative electrode 171b of the power supply 171 for stabilizing the power supply 171 (not shown in the figure).

[0047] In such a configuration, when both of the transistors 161, 162 are turned on, the current flowing through the electromagnet winding 151 (hereinafter referred to as the electromagnet current iL) increases, and when both are turned off, the electromagnet current iL decreases.

[0048] Also, when one of the transistors 161, 162 is turned on and the other is turned off, a so-called flywheel current is retained. And by flowing the flywheel current through the amplifier circuit 150 in this way, the hysteresis loss in the amplifier circuit 150 can be reduced, and the power consumption of the entire circuit can be kept low. Also, by controlling the transistors 161, 162 in this way, high-frequency noise such as harmonics generated in the turbo molecular pump 100 can be reduced. Furthermore, by measuring this flywheel current with the current detection circuit 181, the electromagnet current iL flowing through the electromagnet winding 151 can be detected.

[0049] That is, when the detected current value is smaller than the current command value, as shown in FIG. 3, both transistors 161 and 162 are turned on only once during the control cycle Ts (for example, 100 μs) for a time corresponding to the pulse width time Tp1. Therefore, during this period, the electromagnetic current iL increases toward the current value iLmax (not shown) that can flow from the positive electrode 171a to the negative electrode 171b through the transistors 161 and 162.

[0050] On the other hand, when the detected current value is larger than the current command value, as shown in FIG. 4, both transistors 161 and 162 are turned off only once during the control cycle Ts for a time corresponding to the pulse width time Tp2. Therefore, during this period, the electromagnetic current iL decreases toward the current value iLmin (not shown) that can be regenerated from the negative electrode 171b to the positive electrode 171a through the diodes 165 and 166.

[0051] And in any case, after the elapse of the pulse width times Tp1 and Tp2, either one of the transistors 161 and 162 is turned on. Therefore, during this period, the flywheel current is held in the amplifier circuit 150.

[0052] In addition to the above-described configuration, the vacuum pump according to the present embodiment includes, as shown in FIG. 5, a high-temperature stator 201 connected to the screw groove stator 131, a heating element 202 housed in the high-temperature stator 201, a lower outer cylinder 210 disposed on the outer periphery of the high-temperature stator 201, and a restraining means 220 disposed on the outer periphery of the screw groove stator 131.

[0053] The lower outer cylinder 210 has an upper end connected to the lower side of the outer cylinder 127 and a lower end connected to the upper side of the base portion 129. The outer cylinder 127, the lower outer cylinder 210, and the base portion 129 constitute an exterior body 203 that rotatably houses the rotating body 103.

[0054] The high-temperature stator 201 has a substantially cylindrical shape. Its lower end is connected to the upper part of the base portion 129 via an O-ring, and its upper end is connected to the inside of the lower outer cylinder 210 via an O-ring. Note that the high-temperature stator 201 in which the heating element 202 is disposed may not have a structure different from that of the threaded groove stator 131, and may have a structure integrated with the threaded groove stator 131.

[0055] The heating element 202 is inserted and fixed inside the high-temperature stator 201. The heating element 202 is connected to a heating element control device (not shown), and the heating element control device controls the temperature of the heating element 202. The heating element 202 is appropriately adjusted so as to maintain the temperatures of the high-temperature stator 201 and the threaded groove stator 131 at a predetermined value higher than the temperature of the rotating body 103.

[0056] The threaded groove stator 131 has a substantially cylindrical shape and has a stator upper end portion 131b located on the upstream side and a stator lower end portion 131c located on the downstream side. The threaded groove stator 131 is connected to the inside of the high-temperature stator 201 at the stator upper end portion 131b. Further, a space serving as a gas flow path up to the exhaust port 133 is provided on the outer peripheral side of the threaded groove stator 131, and the threaded groove stator 131 extends downward from the stator upper end portion 131b such that the stator lower end portion 131c is a free end. The stator lower end portion 131c is spaced apart from the outer peripheral surface of the cylindrical portion 102d of the rotating body 103 disposed on the inner peripheral side and is also spaced apart from the inner peripheral surface of the high-temperature stator 201 disposed on the outer peripheral side. Note that the outer peripheral surface of the stator lower end portion 131c may face the inner peripheral surface of another member (for example, an exterior body 203 such as the outer cylinder 127 or the lower outer cylinder 210, or another stator member disposed inside the exterior body 203).

[0057] The restraining means 220 is cylindrical and is disposed on the outer periphery of the threaded groove stator 131. The inner peripheral surface of the restraining means 220 is in contact with the outer peripheral surface of the stator lower end portion 131c. The restraining means 220 is fixed, for example, by press-fitting the stator lower end portion 131c. Note that the method of fixing the restraining means 220 to the threaded groove stator 131 is not particularly limited, and it may be fixed by, for example, bolts or the like. The outer peripheral surface of the restraining means 220 faces the inner peripheral surface of the high-temperature stator 201 with a gap therebetween. The axially-side edge portions of the inner peripheral surface and the outer peripheral surface of the restraining means 220 are preferably chamfered with a curved surface or a flat surface. Note that the axial direction of the cylindrical restraining means 220 is the direction connecting the centers of the two openings of the cylinder.

[0058] The axial length and the radial thickness of the restraining means 220 are not particularly limited. The restraining means 220 is formed of a material having a lower linear expansion coefficient than the material of the threaded groove stator 131. For example, when the material of the threaded groove stator 131 is aluminum or an aluminum alloy, the material of the restraining means 220 can preferably use, for example, stainless steel, ceramics, titanium alloy, or the like. The stainless steel is not particularly limited, but SUS400 series such as SUS403, SUS405, SUS410, SUS430, etc. can preferably be used.

[0059] Note that the outer peripheral surface of the restraining means 220 may face the inner peripheral surface of other members (for example, the exterior body 203 such as the outer cylinder 127 and the lower outer cylinder 210, or other stator members disposed inside the exterior body 203) instead of facing the inner peripheral surface of the high-temperature stator 201. The shape of the restraining means 220 is a cylindrical shape having a constant inner diameter and outer diameter in the axial direction, but is not limited thereto. For example, the outer diameter of the restraining means 220 may not be constant in the axial direction.

[0060] Next, the operation of the above-described vacuum pump will be described. When the rotating shaft 113 of the vacuum pump is driven by the motor 121 which is a driving mechanism, the rotating body 103 rotates. Thereby, due to the action of the rotating blade 102 and the stationary blade 123, the exhaust gas from the chamber is sucked through the intake port 101.

[0061] The exhaust gas inhaled from the intake port 101 is transferred to the downstream side by a turbo molecular pump mechanism formed by the rotating blade 102 and the stationary blade 123. The exhaust gas transferred to the downstream side is guided to a Holweck type pump mechanism formed by the cylindrical portion 102d of the rotating body 103 and the helical groove stator 131, and then transferred to the exhaust port 133.

[0062] The helical groove stator 131 and the high-temperature stator 201 are heated by the heater 202 to prevent reaction products generated in semiconductor manufacturing or the like from depositing. When the cylindrical portion 102d and the helical groove stator 131 are formed of a material having approximately the same coefficient of linear expansion, the helical groove stator 131, which has a higher temperature than the cylindrical portion 102d, will thermally expand more than the cylindrical portion 102d without the restraining means 220. As an example, the cylindrical portion 102d and the helical groove stator 131 are made of aluminum, and the restraining means 220 is made of stainless steel. Note that the inner cylindrical portion 102d also expands in diameter due to centrifugal force, but even considering the amount of this expansion, the helical groove stator 131 is more likely to thermally expand than the cylindrical portion 102d. Therefore, without the restraining means 220, the gap amount between the outer peripheral surface of the cylindrical portion 102d and the inner peripheral surface of the helical groove stator 131 widens, and the performance of the helical groove pump deteriorates. However, a restraining means 220 formed of a material having a lower coefficient of linear expansion than the material of the helical groove stator 131 is disposed on the outer periphery of the helical groove stator 131. Even when the restraining means 220 is heated to the same temperature as the helical groove stator 131, it does not thermally expand as much as the helical groove stator 131. For this reason, the helical groove stator 131 is restrained from thermally expanding radially outward by the restraining means 220. Therefore, the gap amount between the outer peripheral surface of the cylindrical portion 102d through which the gas flows and the inner peripheral surface of the helical groove stator 131 can be appropriately maintained.

[0063] Since the restraining means 220 has a cylindrical shape, it has a uniform structure in the circumferential direction and its outer periphery is separated from other members. For this reason, the restraining means 220 can restrain the helical groove stator 131 with a uniform restraining force in the circumferential direction, so that the gap amount between the outer peripheral surface of the cylindrical portion 102d and the inner peripheral surface of the helical groove stator 131 can be uniformly maintained at an appropriate amount.

[0064] This vacuum pump may have a plurality of specifications with different internal temperatures. As an example, the internal temperature in the Holbeck type pump mechanism of the vacuum pump is set in the range of 70°C to 200°C. The internal temperature in the Holbeck type pump mechanism refers to the temperature of the components (cylindrical part 102d and / or threaded groove stator 131) that make up the pump mechanism. The gap amount between the outer peripheral surface of the cylindrical part 102d and the inner peripheral surface of the threaded groove stator 131 of this vacuum pump for each specification (internal temperature) is preferably within an appropriate range, more preferably substantially constant, and even more preferably constant. That is, even if the internal temperature changes within the specification range, due to the provision of the restraining means 220 on the outer periphery of the threaded groove stator 131, it is preferable that the gap amount between the outer peripheral surface of the cylindrical part 102d and the inner peripheral surface of the threaded groove stator 131 hardly changes. The appropriate gap amount between the outer peripheral surface of the cylindrical part 102d and the inner peripheral surface of the threaded groove stator 131 is, for example, 200 to 1000 μm. Due to the vibration caused by the rotation of the rotating body 103, the gap amount between the outer peripheral surface of the cylindrical part 102d and the inner peripheral surface of the threaded groove stator 131 can change during one rotation. So that the outer peripheral surface of the cylindrical part 102d and the inner peripheral surface of the threaded groove stator 131 do not come into contact, the vacuum pump may emit a warning sound when the measured vibration of the rotating body 103 reaches a threshold value (for example, 100 μm).

[0065] When the temperatures of the thread groove stator 131 and the restraining means 220 rise, the thread groove stator 131 receives stress from the restraining means 220. The thread groove stator 131 may be made of a material that is more easily deformed than stainless steel, such as aluminum or an aluminum alloy. Therefore, in order to prevent the thread groove stator 131 from plastically deforming, it is preferable that the stress acting on the thread groove stator 131 from the restraining means 220 is less than the yield stress of the material of the thread groove stator 131. In particular, when the vacuum pump has a plurality of specifications in which the internal temperatures of the thread groove stator 131 are different, it is preferable that the stress acting on the thread groove stator 131 from the restraining means 220 in each specification (internal temperature) is less than the yield stress of the material of the thread groove stator 131. In other words, even if the internal temperature changes within the range of the specifications, the stress acting on the thread groove stator 131 is always less than the yield stress, and the plastic deformation of the thread groove stator 131 can be suppressed.

[0066] As described above, the vacuum pump according to this embodiment is a vacuum pump that includes an outer casing 203 having an intake port 101, a rotor 103 that is enclosed within the outer casing 203 and supported for free rotation, an approximately cylindrical threaded stator 131 arranged on the outer periphery of the rotor 103, and a threaded groove 131a engraved on at least one of the outer periphery of the rotor 103 or the inner periphery of the threaded stator 131, and that exhausts gas sucked in from the intake port 101 side to the outside of the outer casing 203 by rotating the rotor 103, and a restraining means 220 is arranged on the outer periphery of the threaded stator 131, the restraining means 220 being made of a material having a lower linear expansion coefficient than the material of the threaded stator 131 and reducing radial deformation of the threaded stator 131 during thermal expansion. As a result, the vacuum pump has the restraining means 220 that reduces radial deformation of the grooved stator 131 during thermal expansion, and can therefore suppress the increase in the gap between the outer circumferential surface of the rotor 103 and the inner circumferential surface of the grooved stator 131. As a result, the vacuum pump can effectively suppress degradation of the performance of the grooved pump due to thermal expansion.

[0067] Further, the restraining means 220 is disposed at the downstream end of the threaded groove stator 131. Thereby, the radial thermal expansion of the downstream end of the threaded groove stator 131 whose outer peripheral surface is not fixed on the downstream side can be suppressed, and the deterioration of the performance of the threaded groove pump can be effectively suppressed.

[0068] Further, the vacuum pump has a plurality of specifications with different internal temperatures, and the gap amount between the outer peripheral surface of the rotating body 103 at a predetermined position in the axial direction of the vacuum pump and the inner peripheral surface of the threaded groove stator 131 in each specification may be made the same by the restraining means 220. Thereby, this vacuum pump can effectively maintain the performance of the threaded groove pump in each specification with different internal temperatures.

[0069] Further, the stress acting on the threaded groove stator 131 from the restraining means 220 during the thermal expansion of the threaded groove stator 131 may be made less than the yield stress of the material of the threaded groove stator 131. Thereby, it is possible to effectively suppress the threaded groove stator 131 that is restrained by the restraining means 220 and receives stress during thermal expansion from being damaged.

[0070] Note that the present invention is not limited to the above-described embodiments, and various modifications can be made by those skilled in the art within the technical idea of the present invention. For example, in the present embodiment, the outer peripheral surface of the cylindrical portion 102d is smooth and a threaded groove is formed on the inner peripheral surface of the threaded groove stator 131, but a threaded groove may be formed on the outer peripheral surface of the cylindrical portion 102d and the inner peripheral surface of the outer stator may be smooth. Further, the threaded groove pump on the downstream side of the vacuum pump may be formed by combining a Sigbahn type pump mechanism and a Holweck type pump mechanism. Further, the threaded groove stator 131 may have a structure connected at the downstream end with respect to the high-temperature stator 201 or a structure connected at the central portion in the flow direction. Therefore, the restraining means 220 may be disposed not at the upstream end of the threaded groove stator 131 but at the upstream end or the central portion in the flow direction.

Explanation of Reference Numerals

[0071] 100 Turbo molecular pump 101 Intake port 102d Cylindrical part 103 Rotating body 131 Thread groove stator (stator) 131a Thread groove 131b Stator upper end part 131c Stator lower end part 133 Exhaust port 201 High-temperature stator 202 Heating element 203 Outer casing 220 Restraining means

Claims

1. An exterior body provided with an air inlet, a rotating body enclosed within the exterior body and rotatably supported, a substantially cylindrical stator disposed on the outer periphery of the rotating body, and a screw groove engraved on at least one of the outer peripheral surface of the rotating body or the inner peripheral surface of the stator. By rotating the rotating body, it is a vacuum pump that exhausts the gas inhaled from the air inlet side to the outside of the exterior body, the stator extends from the upper end portion on the upstream side toward the lower side which is the downstream side, and the lower end portion is a free end, a cylindrical member made of a material having a lower linear expansion coefficient than that of the stator material is disposed on the outer periphery of the stator and at the lower end portion, and the radial deformation of the stator during thermal expansion is reduced. A vacuum pump characterized by this.

2. The vacuum pump has a plurality of specifications with different internal temperatures, and the gap amount between the outer peripheral surface of the rotating body and the inner peripheral surface of the stator at a predetermined position in the axial direction of the vacuum pump in each of the specifications is made the same by the cylindrical member. The vacuum pump according to claim 1, characterized by this.

3. The stress acting on the stator from the cylindrical member during thermal expansion of the stator is made less than the yield stress of the stator material. The vacuum pump according to claim 1 or 2, characterized by this.

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