Vacuum exhaust device

Abstract

To provide a vacuum exhaust device capable of performing excellent plasma cleaning without providing a pressure control valve.SOLUTION: A vacuum exhaust device 10 comprises a turbo molecular pump 100, and a plasma generation device 210, and comprises a throttling unit 244 that can increase an internal pressure of the plasma generation device 210 until it satisfies the relation of P≥0.3 / D. P represents pressure [Pa], and D represents a distance [m] between electrodes in the plasma generation device. Also, the throttling unit can increase the internal pressure of the plasma generation device 210 until it satisfies the relation of P≤1.5 / D.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a vacuum exhaust device equipped with a vacuum pump such as a turbomolecular pump. [Background technology]

[0002] Generally, turbomolecular pumps are known as a type of vacuum pump. These turbomolecular pumps are used, for example, for exhausting gas in manufacturing equipment for semiconductors, flat panels, and the like. In turbomolecular pumps, a motor in the pump body is energized to rotate rotors, which ejects gas molecules (gas molecules) of a gas (process gas) sucked into the pump body, thereby exhausting the gas. Some turbomolecular pumps are equipped with a heater and a cooling tube to appropriately manage the temperature inside the pump.

[0003] In vacuum pumps such as turbomolecular pumps, reaction products generated during the manufacturing process of semiconductors and the like may accumulate inside the vacuum pump. Patent Document 1, which will be described later, discloses a technique for installing a plasma generator in the vacuum pump and cleaning the inside with plasma as a measure against the reaction products. Patent Document 1 also discloses a technique for installing a plasma generator on the side of the vacuum pump. In the invention described in Patent Document 1, the plasma source is installed in an introduction port arranged on the side of the vacuum pump. A valve installed between the plasma source and the vacuum pump controls the supply of radicals. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-017864 Summary of the Invention [Problem to be solved by the invention]

[0005] In a plasma generating device such as that disclosed in Patent Document 1, raw material gas such as NF3 or CF4 is flowed between electrodes that are discharged, and the raw material gas is ionized. In such a case, the discharge voltage between the electrodes has a minimum value near the condition where the value of the electrode distance x pressure is 0.5 Pa·m (Paschen's law). Therefore, in the past, although not shown in the figure, a valve (pressure adjustment valve, valve device) was installed near the exhaust port of the vacuum pump, and the valve was controlled to adjust the pressure between the electrodes of the plasma generating device so that the above condition was met.

[0006] As a result, the following issues arose: (1) Installation space and costs are required for a pressure regulating valve near the exhaust port. (2) Since the pressure control valve is disposed downstream of the vacuum pump, the entire inside of the vacuum pump needs to be kept at high pressure, and the flow rate of the radicals generated by the plasma generator decreases. As a result, the reach of the radicals decreases (becomes shorter). It is expected that the degree of activity of the radicals will be lost by, for example, about 90%, and will drop to about 10%. In addition, since the pressure near the plasma generator will drop due to the exhaust action of the vacuum pump while the vacuum pump is in operation, the method of disposing the valve downstream of the vacuum pump may not be able to increase the pressure near the plasma generator as desired. In order to increase the pressure near the plasma generator to the desired pressure, it is necessary to significantly increase the pressure near the exhaust port of the vacuum pump, and in some cases, the vacuum pump may overheat. Therefore, in the conventional structure, it may be necessary to reduce the rotation speed of the vacuum pump or stop the vacuum pump to weaken the exhaust action of the pump. (3) Unless a valve is provided between the plasma generator and the pump, as in the invention described in Patent Document 1, there is nothing to prevent the reaction products from entering the plasma generator (accumulating in the plasma generator).

[0007] An object of the present invention is to provide a vacuum exhaust system capable of performing plasma cleaning satisfactorily without providing a pressure regulating valve. [Means for solving the problem]

[0008] In order to achieve the above object, a vacuum exhaust apparatus according to the present invention comprises: A vacuum exhaust device including a vacuum pump and a plasma generator, The internal pressure of the plasma generating device is P ≥ 0.3 / D The present invention is characterized in that the pressure is increased until the above relationship is satisfied. Here, P is pressure [Pa], and D is the distance between the electrodes of the plasma generating device [m]. Effect of the Invention

[0009] According to the above invention, it is possible to provide a vacuum exhaust device capable of performing plasma cleaning satisfactorily without providing a pressure regulating valve. [Brief description of the drawings]

[0010] [Figure 1] 1 is an explanatory diagram illustrating a schematic configuration of a vacuum exhaust device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a circuit diagram of an amplifier circuit. [Diagram 3] 6 is a time chart showing control when a current command value is larger than a detection value. [Figure 4] 6 is a time chart showing control when a current command value is smaller than a detection value. [Diagram 5] FIG. 2 is an explanatory diagram showing an enlarged view of a connection portion between a plasma generating device and a turbo molecular pump. [Figure 6] FIG. 4 is an explanatory diagram showing an enlarged view of a narrowed portion and its surrounding area. [Figure 7] 1 is a graph for explaining Paschen's law. [Figure 8] 13A and 13B are explanatory diagrams showing modified examples of the narrowing portion. [Figure 9] 13A is an explanatory diagram showing an enlarged view of a connection portion between a plasma generating device and a turbo molecular pump according to another modified example, and FIG. 13B is an explanatory diagram showing a throttle portion according to the modified example in plan view. [Figure 10] 13A is an explanatory diagram showing an enlarged view of a connection portion between a plasma generating device and a turbo molecular pump according to another modified example, and FIG. 13B is an explanatory diagram showing a throttle portion according to the modified example in plan view. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] <Basic configuration of the vacuum exhaust device 10 according to the embodiment> A vacuum exhaust device 10 according to an embodiment of the present invention will be described below with reference to the drawings. Fig. 1 shows the vacuum exhaust device 10 according to the embodiment of the present invention. The vacuum exhaust device 10 includes a turbomolecular pump 100, which is a vacuum pump, and a plasma generator 210. The turbomolecular pump 100 performs vacuum exhaust, and the plasma generator 210 performs plasma cleaning of reaction products generated in the turbomolecular pump 100.

[0012] <Turbo Molecular Pump 100> 1 shows a longitudinal section of a turbomolecular pump 100. This turbomolecular pump 100 is adapted to be connected to a vacuum chamber (not shown) of a target device such as a semiconductor manufacturing device.

[0013] 1, turbo molecular pump 100 has an intake port 101 formed at the upper end of a cylindrical outer cylinder 127. Inside outer cylinder 127, rotor 103 is provided, which has a plurality of rotors 102 (102a, 102b, 102c, ...) that are turbine blades for sucking in and exhausting gas, formed radially on its periphery in multiple stages. Rotor shaft 113 is attached to the center of rotor 103, and rotor shaft 113 is supported in the air and its position is controlled by, for example, a five-axis controlled magnetic bearing.

[0014] The upper radial electromagnets 104 are arranged in pairs on the X-axis and the Y-axis. Four upper radial sensors 107 are provided adjacent to the upper radial electromagnets 104 and corresponding to each of the upper radial electromagnets 104. The upper radial sensors 107 are, for example, inductance sensors or eddy current sensors having conductive windings, and detect the position of the rotor shaft 113 based on the change in inductance of the conductive windings that changes according to the position of the rotor shaft 113. The upper radial sensors 107 are configured to detect the radial displacement of the rotor shaft 113, i.e., the rotating body 103 fixed thereto, and send the detected displacement to the control device 200.

[0015] In this control device 200, for example, a compensation circuit having a PID adjustment function generates an excitation control command signal for the upper radial electromagnet 104 based on a position signal detected by the upper radial sensor 107, and an amplifier circuit 150 (described later) shown in Figure 2 controls the excitation of the upper radial electromagnet 104 based on this excitation control command signal, thereby adjusting the upper radial position of the rotor shaft 113.

[0016] The rotor shaft 113 is made of a material with high magnetic permeability (iron, stainless steel, etc.) 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. 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 adjust the lower radial position of the rotor shaft 113 in the same manner as the upper radial position.

[0017] Furthermore, axial electromagnets 106A and 106B are arranged above and below a circular metal disk (also called an "armature disk") 111 provided at the bottom of rotor shaft 113. 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 rotor shaft 113, and an axial position signal is sent to control device 200.

[0018] In the control device 200, a compensation circuit having, for example, a PID adjustment function generates an excitation control command signal for each of the axial electromagnets 106A and 106B based on the axial position signal detected by the axial sensor 109, and the amplifier circuit 150 controls the excitation of the axial electromagnets 106A and 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.

[0019] In this way, the control device 200 appropriately adjusts the magnetic force that the axial electromagnets 106A, 106B exert on the metal disk 111, magnetically levitating the rotor shaft 113 in the axial direction and holding it in a non-contact manner in space. The amplifier circuit 150 that controls the excitation of the upper radial electromagnets 104, the lower radial electromagnets 105, and the axial electromagnets 106A, 106B will be described later.

[0020] Meanwhile, motor 121 has a plurality of magnetic poles arranged circumferentially so as to surround rotor shaft 113. Each magnetic pole is controlled by control device 200 so as to rotate rotor shaft 113 via electromagnetic force acting between the magnetic pole and rotor shaft 113. Also, motor 121 incorporates a rotation speed sensor such as a Hall element, resolver, or encoder (not shown), and the rotation speed of rotor shaft 113 is detected by a detection signal from this rotation speed sensor.

[0021] Furthermore, for example, a phase sensor (not shown) is attached near the lower radial sensor 108 to detect the phase of rotation of the rotor shaft 113. The control device 200 detects the position of the magnetic poles using the detection signals of both this phase sensor and the rotation speed sensor.

[0022] A plurality of fixed blades 123 (123a, 123b, 123c...) are disposed at small gaps (predetermined intervals) from the rotor blades 102 (102a, 102b, 102c...). The rotor blades 102 (102a, 102b, 102c...) are formed at a predetermined angle from a plane perpendicular to the axis of the rotor shaft 113 in order to transport exhaust gas molecules downward by collision with them.

[0023] Similarly, the fixed blades 123 are formed at an inclination at a predetermined angle from a plane perpendicular to the axis of the rotor shaft 113, and are arranged alternately with the stages of the rotor blades 102 toward the inside of the outer cylinder 127. The outer peripheral ends of the fixed blades 123 are supported in a state where they are inserted between a plurality of stacked stages of fixed blade spacers 125 (125a, 125b, 125c, etc.).

[0024] The fixed wing spacer 125 is a ring-shaped member and is made of metal such as aluminum, iron, stainless steel, copper, or an alloy containing these metals as components. An outer cylinder 127 is fixed to the outer periphery of the fixed wing spacer 125 with a small 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. Exhaust gas that enters the intake port 101 from the chamber (vacuum chamber) side and is transferred to the base portion 129 is sent to the exhaust port 133.

[0025] Furthermore, depending on the application of the turbo molecular pump 100, a threaded spacer 131 is disposed between the lower part of the fixed vane spacer 125 and the base part 129. The threaded spacer 131 is a cylindrical member made of metal such as aluminum, copper, stainless steel, iron, or an alloy containing these metals, and has a plurality of helical thread grooves 131a engraved on its inner peripheral surface. The helical direction of the thread groove 131a is the direction in which, when exhaust gas molecules move in the rotation direction of the rotor 103, the molecules are transported toward the exhaust port 133. A rotor lower cylindrical part 103b is suspended from the lower part of the rotor main body 103a on which the rotor vanes 102 (102a, 102b, 102c,...) of the rotor 103 are formed. The outer peripheral surface of the rotor lower cylindrical portion 103b is cylindrical and protrudes toward the inner peripheral surface of the threaded spacer 131, and is adjacent to the inner peripheral surface of the threaded spacer 131 with a specified gap therebetween. The exhaust gas transferred to the thread groove 131a by the rotor 102 and the fixed blades 123 is guided by the thread groove 131a and sent to the base portion 129. In this manner, the threaded spacer 131 and the rotor lower cylindrical portion 103b facing it constitute a Holweck type exhaust mechanism 204. The Holweck type exhaust mechanism 204 gives directionality to the exhaust gas by the rotation of the rotor lower cylindrical portion 103b relative to the threaded spacer 131, thereby improving the exhaust characteristics of the turbo molecular pump 100.

[0026] The base portion 129 is a disk-shaped member that constitutes the base of the turbomolecular pump 100, and is generally made of metal such as iron, aluminum, stainless steel, etc. The base portion 129 physically holds the turbomolecular pump 100 and also functions as a heat conduction path, so it is desirable to use a metal that has rigidity and high thermal conductivity, such as iron, aluminum, or copper.

[0027] In this configuration, when the rotor 102 is rotated together with the rotor shaft 113 by the motor 121, the exhaust gas is sucked from the chamber through the intake port 101 by the action of the rotor 102 and the fixed blades 123. The exhaust gas sucked in from the intake port 101 passes between the rotor 102 and the fixed blades 123 and is transferred to the base portion 129. At this time, the temperature of the rotor 102 rises due to frictional heat generated when the exhaust gas comes into contact with the rotor 102 and the conduction of heat generated by the motor 121, and the like, but this heat is transferred to the fixed blades 123 side by radiation or conduction by gas molecules (gas molecules) of the exhaust gas, and the like.

[0028] The fixed blade spacers 125 are joined to each other at their outer peripheries, and transmit heat received by the fixed blades 123 from the rotor blades 102, frictional heat generated when exhaust gas comes into contact with the fixed blades 123, and the like to the outside.

[0029] In the above description, the threaded spacer 131 is disposed on the outer periphery of the rotor lower cylindrical portion 103b of the rotor 103, and the thread groove 131a is engraved on the inner periphery of the threaded spacer 131. However, conversely, there are also cases where a thread groove is engraved on the outer periphery of the rotor lower cylindrical portion 103b, and a spacer having a cylindrical inner periphery is disposed around it.

[0030] Depending on the application of the turbomolecular pump 100, in order to prevent the gas sucked in from the intake port 101 from entering the electrical equipment section consisting 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 equipment section may be surrounded by a stator column 122, and the inside of this stator column 122 may be kept at a predetermined pressure by a purge gas (protective gas).

[0031] In this case, a port purge gas port (also called "purge gas introduction piping") 132 is provided in the base portion 129, and purge gas is introduced through this piping. The introduced purge gas is sent to an exhaust port 133 through gaps 134 between the protective bearing 120 and the rotor shaft 113, between the rotor and stator of the motor 121, and between the inner cylindrical portion of the rotor blades 102 (lower cylindrical portion 103b of the rotor) and the stator column 122 or between the base portion 129 and the protective bearing 120 and the rotor shaft 113.

[0032] Here, the turbomolecular pump 100 requires control based on specific parameters (e.g., various characteristics corresponding to the model) that are individually adjusted and identified as a model. In order to store these control parameters, the turbomolecular pump 100 has an electronic circuit section 141 in its main body. The electronic circuit section 141 is composed of a semiconductor memory such as an EEPROM, electronic components such as semiconductor elements for accessing the memory, and a substrate 143 for mounting these components. The electronic circuit section 141 is housed below a rotational speed sensor (not shown) near the center of a base section 129 that constitutes the lower part of the turbomolecular pump 100, and is closed by an airtight bottom cover 145.

[0033] In the semiconductor manufacturing process, some process gases introduced into the chamber have the property of becoming solid when their pressure exceeds a predetermined value or their temperature falls below a predetermined value. Inside the turbo molecular pump 100, the pressure of the exhaust gas is lowest at the intake port 101 and highest at the exhaust port 133. If the pressure of the process gas becomes higher than a predetermined value or the temperature falls below a predetermined value while the process gas is being transferred from the intake port 101 to the exhaust port 133, the process gas becomes solid and adheres to and accumulates inside the turbo molecular pump 100.

[0034] For example, when SiCl4 is used as the process gas in an Al etching device, low vacuum (760[torr]~10 -2It can be seen from the vapor pressure curve that at a vapor pressure of 100 MPa (100 [torr]) and low temperature (approximately 20 [°C]), solid products (e.g., AlCl3) precipitate and adhere to and accumulate inside the turbomolecular pump 100. As a result, when precipitates of the process gas accumulate inside the turbomolecular pump 100, the deposits narrow the pump flow path, causing a decrease in the performance of the turbomolecular pump 100. The aforementioned products are prone to solidification and adhesion in high pressure areas near the exhaust port 133 and near the threaded spacer 131.

[0035] Therefore, in order to solve this problem, conventionally, a heater (not shown) or an annular (ring-shaped) water-cooled tube 149 is wound around the outer periphery of the base part 129, and, for example, a temperature sensor (e.g., a thermistor) (not shown) is embedded in the base part 129, and heating by the heater and cooling by the water-cooled tube 149 are controlled based on a signal from the temperature sensor to keep the temperature of the base part 129 at a constant high temperature (set temperature) (hereinafter referred to as TMS; Temperature Management System). In this embodiment, the threaded spacer 131 is heated by a heater (not shown) embedded in the threaded spacer 131, and the base part 129 is cooled by the water-cooled tube 149 embedded in the bottom lid 145.

[0036] Next, an amplifier circuit 150 that controls excitation of the upper radial electromagnets 104, the lower radial electromagnets 105, and the axial electromagnets 106A and 106B in the turbo molecular pump 100 configured as described above will be described. A circuit diagram of this amplifier circuit is shown in FIG.

[0037] 2, one end of an electromagnet winding 151 constituting the upper radial electromagnet 104 etc. is connected to a positive electrode 171a of a power source 171 via a transistor 161, and the other end is connected to a negative electrode 171b of the power source 171 via a current detection circuit 181 and a transistor 162. The transistors 161 and 162 are so-called power MOSFETs, and have a structure in which a diode is connected between the source and drain.

[0038] At this time, the transistor 161 has a cathode terminal 161a of the diode connected to the positive electrode 171a, and an anode terminal 161b connected to one end of the electromagnet winding 151. The transistor 162 has a cathode terminal 162a of the diode connected to the current detection circuit 181, and an anode terminal 162b connected to the negative electrode 171b.

[0039] On the other hand, the current regeneration diode 165 has its cathode terminal 165a connected to one end of the electromagnet winding 151 and its anode terminal 165b connected to the negative electrode 171b. Similarly, the current regeneration diode 166 has its cathode terminal 166a connected to the positive electrode 171a and its anode terminal 166b connected to the other end of the electromagnet winding 151 via a current detection circuit 181. The current detection circuit 181 is composed of, for example, a Hall sensor type current sensor or an electric resistance element.

[0040] The amplifier circuit 150 configured as above corresponds to one electromagnet. Therefore, when the magnetic bearing is controlled by five axes and there are a total of ten electromagnets 104, 105, 106A, and 106B, a similar amplifier circuit 150 is configured for each electromagnet, and the ten amplifier circuits 150 are connected in parallel to the power supply 171.

[0041] Furthermore, the amplifier control circuit 191 is configured, for example, by a digital signal processor section (hereinafter referred to as a DSP section) (not shown) of the control device 200, and this amplifier control circuit 191 switches the transistors 161 and 162 on / off.

[0042] The amplifier control circuit 191 is adapted to compare the current value detected by the current detection circuit 181 (a signal reflecting this current value is called a current detection signal 191c) with a predetermined current command value. Then, based on the result of this comparison, the magnitude of the pulse width (pulse width times Tp1, Tp2) to be generated within a control cycle Ts, which is one period of PWM control, is determined. As a result, gate drive signals 191a, 191b having this pulse width are output from the amplifier control circuit 191 to the gate terminals of the transistors 161, 162.

[0043] In addition, when the rotor 103 passes through a resonance point during an accelerating operation of the rotation speed, or when a disturbance occurs during a constant speed operation, it is necessary to control the position of the rotor 103 at high speed and with a strong force. For this reason, a high voltage of, for example, about 50 V is used as the power supply 171 so that the current flowing through the electromagnet winding 151 can be rapidly increased (or decreased). In addition, a capacitor (not shown) is usually connected between the positive pole 171a and the negative pole 171b of the power supply 171 to stabilize the power supply 171.

[0044] In this configuration, when both transistors 161, 162 are turned on, the current flowing through the electromagnet winding 151 (hereinafter referred to as electromagnet current iL) increases, and when both are turned off, the electromagnet current iL decreases.

[0045] Moreover, when one of the transistors 161, 162 is turned on and the other is turned off, a so-called flywheel current is maintained. By passing a flywheel current through the amplifier circuit 150 in this manner, the hysteresis loss in the amplifier circuit 150 can be reduced, and the power consumption of the entire circuit can be kept low. Furthermore, by controlling the transistors 161, 162 in this manner, 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.

[0046] That is, when the detected current value is smaller than the current command value, both of the transistors 161 and 162 are turned on for a time period corresponding to the pulse width time Tp1 only once in a control cycle Ts (e.g., 100 μs) as shown in Fig. 3. Therefore, the electromagnet current iL during this period increases toward a current value iLmax (not shown) that can flow from the positive electrode 171a to the negative electrode 171b via the transistors 161 and 162.

[0047] On the other hand, when the detected current value is larger than the current command value, both of the transistors 161 and 162 are turned off for a time period corresponding to the pulse width time Tp2 only once during the control cycle Ts, as shown in Fig. 4. Therefore, the electromagnet current iL during this period decreases toward a current value iLmin (not shown) that can be regenerated from the negative pole 171b to the positive pole 171a via the diodes 165 and 166.

[0048] In either case, after the pulse width times Tp1 and Tp2 have elapsed, one of the transistors 161 and 162 is turned on. Therefore, a flywheel current is maintained in the amplifier circuit 150 during this period.

[0049] 1 (the side of the intake port 101) serves as an intake section connected to the target device, and the lower side (the side of the base portion 129 on which the exhaust port 133 is provided so as to protrude to the right in the figure) serves as an exhaust section connected to an auxiliary pump (back pump) or the like (not shown). The turbo molecular pump 100 can be used not only in the vertical position shown in Fig. 1, but also in an inverted position, horizontal position, or inclined position.

[0050] In the turbomolecular pump 100, the outer cylinder 127 and the base portion 129 are combined to form one case (hereinafter, both may be collectively referred to as the "main casing"). The turbomolecular pump 100 is electrically (and structurally) connected to a box-shaped electrical equipment case (not shown), and the above-mentioned control device 200 is incorporated in the electrical equipment case.

[0051] The internal configuration of the main body casing of the turbomolecular pump 100 (a combination of an outer cylinder 127 and a base portion 129) can be divided into a rotation mechanism portion that rotates the rotor shaft 113 and the like by the motor 121, and an exhaust mechanism portion that is rotationally driven by the rotation mechanism portion. The exhaust mechanism portion can be considered to be divided into a turbomolecular pump mechanism portion composed of the rotor 102, fixed blades 123, etc., and a threaded pump mechanism portion (Holbeck type exhaust mechanism portion) composed of the rotor lower cylindrical portion 103b, threaded spacer 131, etc.

[0052] The above-mentioned purge gas (protective gas) is used to protect the bearing parts and the rotor 102, etc., to prevent corrosion caused by the exhaust gas (process gas), and to cool the rotor 102. This purge gas can be supplied by a general method.

[0053] For example, the above-mentioned purge gas port 132 extending linearly in the radial direction is provided at a predetermined position (such as a position 90 degrees or 120 degrees away from the exhaust port 133) of the base portion 129. Then, purge gas is supplied to this purge gas port 132 from the outside of the base portion 129 via a purge gas cylinder (such as an N2 gas cylinder) or a flow rate regulator (valve device).

[0054] The aforementioned protective bearings 120 are also called "touch-down (T / D) bearings" or "back-up bearings." These protective bearings 120 prevent the position and attitude of the rotor shaft 113 from changing significantly, and prevent damage to the rotor blades 102 and their surroundings, even in the unlikely event that a problem occurs with the electrical system or atmospheric inrush.

[0055] In FIG. 1 showing the structures of the turbo molecular pump 100 and the rotor 103, hatching showing cross sections of components is omitted to avoid complicating the drawing.

[0056] <Plasma generating device 210 and throttle section 244> As mentioned above, products may accumulate inside the turbomolecular pump 100. In this embodiment, the products are cleaned using a plasma generator 210. Various types of plasma generators 210 can be used. For example, the plasma generator 210 can be one that applies a high-frequency voltage to an electrode provided inside a cylinder 212 to generate plasma (which can also be called "radicals" here) toward the turbomolecular pump 100.

[0057] The plasma generator 210 is connected to a side of the turbomolecular pump 100. In this embodiment, there are a plurality of plasma generators 210. In FIG. 1, two plasma generators 210 are arranged at 180 degree intervals with respect to the turbomolecular pump 100. For example, it is also possible to arrange the number of plasma generators 210 as four and arrange them at 90 degree intervals.

[0058] The boundary between the plasma generator 210 and the turbo molecular pump 100 is a connection part 220. The inside of the plasma generator 210 and the inside of the turbo molecular pump 100 are spatially connected via the connection part 220.

[0059] 5 is an enlarged schematic view of the inside of the connection part 220. In the connection part 220, the flange part 214 of the plasma generator 210 is fixed to the seat surface 194 of the base part 129 of the turbo molecular pump 100 by a hexagon socket head bolt 224. The gap between the flange part 214 of the plasma generator 210 and the seat surface 194 of the turbo molecular pump 100 is air-tightly sealed by a seal member (here, an O-ring) 226.

[0060] A plasma communication port 228 is formed in the base portion 129 of the turbo molecular pump 100. The plasma communication port 228 connects the internal space of the turbo molecular pump 100 and the internal space of the plasma generator 210. The plasma communication port 228 is machined into a stepped hole shape, and has an inlet portion 230 with a relatively large inner diameter and an outlet portion 232 with a relatively small inner diameter. The inlet portion 230 is located on the plasma generator 210 side, and the outlet portion 232 is located on the turbo molecular pump 100 internal space side.

[0061] A disk-shaped throttle member 240 is fixed (screwed) to the bottom of the introduction section 230 by a machine screw 242. A throttle section 244 is formed in the throttle member 240. The throttle section 244 is a circular hole (round hole) that penetrates the throttle member 240 in the thickness direction. Here, after the throttle member 240 is attached to the base section 129, the plasma generation device 210 can be attached to the base section 129.

[0062] The thickness direction of the throttle portion 244 coincides with the radial direction (direction perpendicular to the rotation axis) of the turbo molecular pump 100. Furthermore, the throttle portion 244 is processed so that its diameter d (FIG. 6) is constant throughout the thickness direction of the throttle member 240. The throttle portion 244 functions as an orifice connecting the inlet portion 230 and the outlet portion 232.

[0063] The plasma generated by the plasma generator 210 passes from the inlet 230 through the throttle section 244 and reaches the outlet 232. The plasma passing through the throttle section 244 may reach the outlet 232 by colliding with an inner wall 245 of the throttle section 244 as shown by arrow A in Fig. 6, or may reach the outlet 232 without colliding with the inner wall 245 of the throttle section 244 as shown by arrow B. In Fig. 6, hatching is provided to represent the cross section of the throttle member 240.

[0064] The diaphragm member 240 including the diaphragm portion 244 is subjected to a surface treatment. For example, ceramic coating, alumite treatment, or the like can be adopted as the surface treatment. These surface treatments provide electrical insulation to the diaphragm member 240. The surface treatment can also be performed only on the diaphragm portion 244.

[0065] 5 (and 6), most of the plasma that reaches the outlet portion 232 collides with the threaded spacer 131. In the axial direction of the turbo molecular pump 100, the throttle portion 244 is disposed at approximately the same position as the inclined surface 131b of the threaded spacer 131. For this reason, most of the plasma heading toward the threaded spacer 131 collides with the inclined surface 131b of the threaded spacer 131.

[0066] The throttle section 244 is capable of increasing (boosting) the pressure (pressure around the electrodes) in the internal space of the plasma generation device 210. The throttle section 244 is formed so that the pressure reached by the boost satisfies the following relationship based on Paschen's law. 0.3 / D≦P≦1.5 / D Here, P is pressure [Pa], and D is the distance between the electrodes of the plasma generator [m].

[0067] Paschen's law is a law that describes the relationship between the voltage at which a spark discharge occurs and the gas pressure in the environment and the distance between the electrodes. A spark discharge occurs when a strong electric field is applied to a gas, which eventually leads to dielectric breakdown. The voltage (spark voltage) [V] at which a spark discharge occurs between parallel electrodes can be expressed as a function of the product of the gas pressure [P] and the distance between the electrodes [D].

[0068] FIG. 7 shows the Paschen curve. The vertical axis of the graph in FIG. 7 shows the spark voltage [V], and the horizontal axis shows the product [P×D] of the gas pressure [P] and the electrode distance [D]. Spark discharge occurs when electrons collide with gas molecules and ionize the gas. For this reason, as shown in FIG. 7, there exists a value of [P×D] at which the spark voltage [V] is minimum. If the pressure is too low (if [P] is too small), it becomes difficult for electrons to collide with gas molecules, and conversely, if the pressure is too high, it becomes difficult for electrons to be sufficiently accelerated before colliding. And, as shown in FIG. 7, the spark voltage becomes large whether [P×D] is too large or too small. Therefore, in order to generate a spark discharge at a low voltage, it is effective to set [P×D] within an appropriate range.

[0069] In this embodiment, the relationship between pressure [P] and inter-electrode distance [D] is determined so that the value on the horizontal axis [P×D] is 0.3 to 1.5 [Pa·m], as shown in the two-dot chain line frame G in the graph of Fig. 7. This makes it possible to keep the spark voltage low for various gases.

[0070] For example, if the distance between the electrodes [D] is 5 mm (= 5 × 10 -3 In the case of a plasma pressure of 500 MPa ([m]), the appropriate range of [P] is 60 to 300 [Pa]. Although not shown in Fig. 7, when the source gas is NF3 and this source gas is flowed at 50 [sccm] (Standard Cubic Centimeter per Minute), by installing an orifice (throttling unit 244 in this case) with a diameter of about 2 to 5 "mm", the pressure inside the plasma generator (plasma generator 210 in this case) will be in the appropriate range, and stable discharge will be possible even at a low voltage.

[0071] Here, the relationship between the flow rate at the orifice, the cross-sectional area of ​​the orifice, and the pressure difference can be calculated using various calculation formulas. For example, the relationship can be calculated using the following formula. Q = CA0(2ΔP / ρ) -1 / 2 (1) Here, the symbols used in the above formula (1) have the following meanings. Q:Flow rate [m 3 / s] C: Flow coefficient A O =πD 2 / 4: Cross-sectional area of ​​the orifice hole [m 2 ], D is the diameter of the orifice hole [m] ρ: Fluid density [kg / m 3 ] ΔP: Differential pressure before and after the orifice [Pa]

[0072] According to the vacuum exhaust device 10 of the present embodiment as described above, since the orifice, throttling portion 244, is used to generate discharge at a low voltage, the pressure in the internal space of the plasma generator 210 can be adjusted by simply installing the throttling member 240. In addition, unlike the conventional method, it is not necessary to open and close the flow path by a pressure regulating valve downstream of the turbo molecular pump 100. Therefore, the pressure regulating valve and the control circuit for the pressure regulating valve are not required. Therefore, the space for installing the pressure regulating valve and the cost for the pressure regulating valve are not required. Furthermore, since the installation space for the pressure regulating valve is not required, the degree of freedom of installation related to the vacuum exhaust device 10 and the turbo molecular pump 100 is increased. Furthermore, since it is not necessary to install a pressure regulating valve downstream of the vacuum pump (here, the turbo molecular pump 100), it is easy to increase the pressure near the plasma generator as desired. In addition, it is not necessary to reduce the rotation speed of the vacuum pump or stop the vacuum pump to weaken the pumping action of the pump.

[0073] In addition, since the throttle member 240 is a plate-shaped member, the pressure adjustment mechanism can be easily made smaller in size than, for example, the valve (radical supply valve 201b) described in Patent Document 1. This also makes it possible to reduce the installation space of the vacuum exhaust device 10.

[0074] In addition, since the throttle member 240 is a plate-like body, the thickness can be set to be thin. Therefore, the length of the gas flow path and the length and area of ​​the inner wall 245 in the gas flow path can be made small. As a result, it is possible to minimize the radicals that collide with the wall surface of the inner wall 245 and are deactivated.

[0075] In addition, the downstream side of the throttle portion 244 can be kept at a relatively low pressure, and the radical flow rate can be increased. Therefore, the radicals can easily reach the downstream before being deactivated. As a result, a higher plasma cleaning effect can be obtained.

[0076] Moreover, the throttle portion 244 is formed simply by installing the throttle member 240 at the connection portion 220 between the plasma generator 210 and the turbo molecular pump 100. The throttle member 240 is installed at the connection portion 220 by screwing. Therefore, the throttle member 240 is easy to install, and the throttle portion 244 can be easily formed.

[0077] Moreover, since the throttle member 240 is subjected to surface treatment such as ceramic coating or alumite treatment, the throttle section 244 can be made highly resistant to radicals. Furthermore, when radicals collide with the wall surface of the inner wall 245, the probability of recombination can be kept low.

[0078] Moreover, the throttle portion 244 is an open hole, and the turbo molecular pump 100 and the plasma generator 210 are spatially connected via the throttle portion 244. Therefore, the purge gas of the turbo molecular pump 100 can be easily introduced into the plasma generator 210. Moreover, even if only a small amount of purge gas is supplied to the plasma generator 210, it is possible to prevent the intrusion (accumulation) of reaction products into the plasma generator 210.

[0079] In the above-described embodiment, the throttle portion 244 extends in the thickness direction of the throttle member 240. However, this is not limited thereto, and for example, as shown in FIG. 8, the throttle portion 244 may be formed at an angle to the thickness direction of the throttle member 240. FIG. 8 shows a schematic plan view of the throttle portion 246 from the suction side (upstream side of the exhaust gas) of the turbo molecular pump 100. As in FIG. 5 and the like, hatching is omitted. Arrow C indicates the discharge direction of the plasma (a representative discharge direction), and arrow F indicates the rotation direction of the turbo molecular pump 100. The direction shown by arrow F is approximately the same as the direction of the spiral flow of the exhaust gas.

[0080] 8, the throttle portion 246 is a hole inclined in a direction intersecting the radial direction of the turbomolecular pump 100. Furthermore, the throttle portion 246 faces the rotation direction (the direction of arrow C) of the turbomolecular pump 100 and extends along the rotation direction (the direction of arrow C).

[0081] Here, "inclined in a direction intersecting the radial direction of the turbo molecular pump 100" can also be expressed as, for example, "oriented horizontally and obliquely with respect to the radial direction of the turbo molecular pump 100". Furthermore, "oriented in the rotational direction" and "along the rotational direction" can also be expressed as, for example, "oriented in the rotational direction, and obliquely with respect to both the tangential direction and the normal direction related to the rotational direction". Furthermore, since the exhaust gas flows in a spiral shape from the intake side to the exhaust side, the throttling section 246 may be oriented obliquely with respect to the direction of the rotation axis (obliquely from the intake side to the exhaust side).

[0082] In this case, the direction in which the throttle portion 246 extends is a direction that enables the plasma derived from the throttle portion 246 to smoothly join the gas flowing inside the turbo molecular pump 100. The opening of the throttle portion 246 facing the turbo molecular pump 100 is also obliquely oriented with respect to the inclined surface 131b of the threaded spacer 131.

[0083] By setting the orientation of the throttle portion 246 as in the example of Fig. 8, it becomes possible to efficiently guide the plasma into the turbo molecular pump 100. As a result, the plasma flows smoothly to the downstream of the gas flow path in the turbo molecular pump 100. Thus, a higher plasma cleaning effect can be obtained. In addition, since the throttle portion 246 opens obliquely to the radial direction of the threaded spacer 131 (Fig. 5), it is possible to prevent the plasma from colliding with the threaded spacer 131 (here, the inclined surface 131b) and being deactivated as much as possible.

[0084] 9(a), (b) and 10(a), (b), the shape of the diaphragm members 250, 260 can be a three-dimensional shape, not a flat plate shape as described above. For example, in the example of FIG. 9(a) and (b), the diaphragm member 250 is formed into a shape having a triangular cross section. Examples of shapes having a triangular cross section include a cone shape, a triangular pyramid shape, and a square pyramid shape.

[0085] Fig. 9(b) shows a schematic plan view of the throttle section 256 from the suction side (upstream side of the exhaust gas) of the turbo molecular pump 100, similar to Fig. 8. Arrow C indicates the plasma extraction direction (representative extraction direction), and arrow F indicates the rotation direction of the turbo molecular pump 100, similar to Fig. 8.

[0086] The throttle portion 256 extends so as to penetrate the inclined surface 258 of the throttle member 250 in the thickness direction, and opens in an oblique direction relative to the inclined surface 131b of the threaded spacer 131. In this way, the plasma can be efficiently guided into the turbo molecular pump 100, and the plasma can be made to flow smoothly to the downstream of the gas flow path in the turbo molecular pump 100. This makes it possible to obtain a higher plasma cleaning effect. In addition, it is possible to prevent the plasma from colliding with the threaded spacer 131 (here, the inclined surface 131b) and being deactivated as much as possible.

[0087] Since the exhaust gas flows in a spiral shape from the intake side to the exhaust side, the throttle section 256 may be oriented obliquely with respect to the direction of the rotation axis (obliquely from the intake side to the exhaust side).

[0088] 10(a) and (b), the throttle member 260 is formed in a shape having a rectangular cross section. Examples of shapes having a rectangular cross section include a cylindrical shape, a cubic shape, and a rectangular parallelepiped shape. Although not shown in the drawings, it is also possible to form the throttle member 260 in a tapered (or widened) trapezoid shape.

[0089] 8 and 9(b), Fig. 10(b) shows a schematic plan view of the throttle section 266 from the suction side (upstream side of the exhaust gas) of the turbo molecular pump 100. Arrow C indicates the plasma extraction direction (representative extraction direction), and arrow F indicates the rotation direction of the turbo molecular pump 100, similar to Figs. 8 and 9(b).

[0090] The throttle portion 266 extends so as to penetrate the side surface 268 of the throttle member 260 in the thickness direction, and opens in a direction directly to the side of the inclined surface 131b of the threaded spacer 131. In this way, the plasma can be efficiently guided into the turbo molecular pump 100, and the plasma can be made to flow smoothly to the downstream of the gas flow path in the turbo molecular pump 100. This makes it possible to obtain a higher plasma cleaning effect. In addition, it is possible to prevent the plasma from colliding with the threaded spacer 131 (here, the inclined surface 131b) and being deactivated as much as possible.

[0091] Since the exhaust gas flows in a spiral shape from the intake side to the exhaust side, the throttle section 266 may be oriented obliquely with respect to the direction of the rotation axis (obliquely from the intake side to the exhaust side).

[0092] Although not shown, various types of electrodes may be used inside the plasma generating device 210, such as a disk, a double cylinder, or a parallel plate.

[0093] Furthermore, the location of the throttling member (e.g., throttling members 240, 250, 260) is not limited to a position outside the plasma generation device 210 (e.g., a position inside the turbo molecular pump 100), but may be a position inside the plasma generation device 210, the position of the plasma outlet, etc.

[0094] It is also possible to employ a variable orifice equipped with a mechanism for varying the diameter as the throttling section (e.g., throttling sections 244, 246, 256, 266). However, in the above-described vacuum exhaust device 10, since the flow rate can be changed by changing the pressure, it is not necessary to use a variable orifice with a complex structure.

[0095] Furthermore, the throttling portion is not limited to an orifice, but may be, for example, a hole-like portion formed in a valve device or a hole-like portion formed in a needle-shaped member, as long as a similar effect is obtained.

[0096] <Inventions that can be extracted from each embodiment> From the above-described embodiments, the following inventions can be extracted. (1) A vacuum exhaust device (such as the vacuum exhaust device 10) including a vacuum pump (such as the turbo molecular pump 100) and a plasma generator (such as the plasma generator 210), The internal pressure of the plasma generating device is P ≥ 0.3 / D A vacuum exhaust device characterized by having a throttle (throttle portion 244, 246, 256, 266, a hole-like portion of a valve device, a hole-like portion formed in a needle-like member, etc.) that can increase the pressure until the relationship above is satisfied. Here, P is pressure [Pa], and D is the distance between the electrodes of the plasma generator [m]. (2) The internal pressure of the plasma generating device is P≦1.5 / D The vacuum exhaust device according to (1) above, characterized in that the pressure can be increased by the throttle up to a pressure that satisfies the relationship: (3) The vacuum exhaust device according to (1) or (2) above, characterized in that the throttle is provided at a connection (such as connection 220) between the vacuum pump and the plasma generating device. (4) The vacuum exhaust device according to (1) or (2) above, wherein the throttle is an orifice. (5) The vacuum exhaust device according to (1) or (2) above, wherein the orifice is a hole inclined in a direction intersecting with a radial direction of the vacuum pump. (6) The vacuum exhaust device according to (1) or (2) above, wherein at least the inner wall of the throttle is ceramic coated. (7) The vacuum exhaust device according to (1) or (2) above, wherein at least the inner wall of the throttle is anodized.

[0097] <Other> The present invention is not limited to the above-described embodiments, and various modifications and combinations of the embodiments are possible without departing from the scope of the present invention. [Explanation of symbols]

[0098] 10: Vacuum exhaust device 100: Turbo molecular pump 210: Plasma generator 220: Connection 228: Plasma connection port 230: Introduction 232: Derivation part 240, 250, 260: Aperture parts 244, 246, 256, 266: Squeezing section 245:Inner wall

Claims

1. A vacuum exhaust device including a vacuum pump and a plasma generator, The internal pressure of the plasma generating device is P≧0.3 / D A vacuum exhaust device comprising a throttle capable of increasing the pressure until the above relationship is satisfied. Here, P is pressure [Pa], and D is the distance between the electrodes of the plasma generating device [m].

2. The internal pressure of the plasma generating device is P≦1.5 / D 2. The vacuum exhaust device according to claim 1, wherein the pressure can be increased by the throttle up to a pressure satisfying the relationship:

3. 3. The vacuum exhaust system according to claim 1, wherein the throttle is disposed at a connection between the vacuum pump and the plasma generating device.

4. 3. The vacuum exhaust system according to claim 1, wherein the throttle is an orifice.

5. 3. The vacuum exhaust device according to claim 1, wherein the throttle has a hole inclined in a direction intersecting a radial direction of the vacuum pump.

6. 3. The vacuum exhaust system according to claim 1, wherein the aperture is ceramic-coated.

7. 3. The vacuum exhaust system according to claim 1, wherein the throttle is anodized.

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