Vacuum evacuation device

Abstract

[Problem] To provide a vacuum evacuation device that can favorably perform plasma cleaning without the provision of a pressure adjustment valve. [Solution] A vacuum evacuation device 10 that comprises a turbo molecular pump 100 and a plasma generation device 210 comprises a throttle part 244 that can raise the internal pressure of the plasma generation device 210 to satisfy P≥0.3 / D.　P is the pressure [Pa], and D is the inter-electrode distance [m] inside the plasma generation device.　The throttle part can also raise the internal pressure of the plasma generation device 210 to satisfy P≤1.5 / D.

Description

Vacuum exhaust device

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

[0002] Turbomolecular pumps are commonly known as a type of vacuum pump. These turbomolecular pumps are used, for example, for exhausting gases in manufacturing equipment for semiconductors, flat panels, and the like. Turbomolecular pumps exhaust gases by rotating rotors when a motor inside the pump body is energized, thereby expelling gas molecules (gas molecules) from the gas (process gas) drawn into the pump body. Some turbomolecular pumps are equipped with heaters and cooling tubes to appropriately control 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, listed below, discloses a technique for dealing with the reaction products by installing a plasma generator in the vacuum pump and plasma cleaning the interior. Patent Document 1 also discloses a technique for installing the plasma generator on the side of the vacuum pump. In the invention described in Patent Document 1, a plasma source is installed in an inlet port disposed on the side of the vacuum pump. A valve installed between the plasma source and the vacuum pump controls the supply of radicals.

[0004] Japanese Patent Application Laid-Open No. 2022-017864

[0005] In a plasma generator such as that disclosed in Patent Document 1, a source gas such as NF3 or CF4 is flowed between electrodes that are subjected to electrical discharge, and the source gas is ionized. In such a case, the discharge voltage between the electrodes has a minimum value near the condition where the product of the electrode distance and the pressure is 0.5 Pa m (Paschen's Law). Therefore, in the past, although not shown in the figure, a valve (pressure control 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 generator so that the above condition was met.

[0006] As a result, the following problems were encountered: (1) The installation space and costs for a pressure adjustment valve are required near the exhaust port. (2) Because the pressure adjustment valve is located downstream of the vacuum pump, the entire interior of the vacuum pump must be kept at high pressure, which reduces the flow rate of the radicals generated by the plasma generator. As a result, the range of the radicals is reduced (shortened). It is expected that the activity of the radicals will be lost by, for example, about 90%, or even as little as 10%. Furthermore, since the pressure near the plasma generator decreases due to the exhaust action of the vacuum pump while the vacuum pump is operating, installing a valve downstream of the vacuum pump may not achieve the desired pressure increase near the plasma generator. In order to increase the pressure near the plasma generator to the desired pressure, the pressure near the exhaust port of the vacuum pump must be significantly increased, which may result in the vacuum pump overheating in some cases. Therefore, with conventional structures, it may be necessary to reduce the pump's exhaust action by reducing the vacuum pump's rotation speed or stopping the vacuum pump. (3) Unless a valve is provided between the plasma generator and the pump, as in the invention described in Patent Document 1, there will be 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 that can perform plasma cleaning effectively without providing a pressure adjustment valve.

[0008] In order to achieve the above object, the present invention provides a vacuum exhaust device comprising a vacuum pump and a plasma generator, characterized in that the device is provided with a throttle capable of increasing the internal pressure of the plasma generator until the internal pressure satisfies the relationship P≧0.3 / D, where P is pressure [Pa] and D is the distance between electrodes of the plasma generator [m].

[0009] According to the above invention, it is possible to provide a vacuum exhaust device that can perform plasma cleaning satisfactorily without providing a pressure adjustment valve.

[0010] 1 is an explanatory diagram schematically showing the configuration of a vacuum exhaust device according to an embodiment of the present invention; FIG. 2 is a circuit diagram of an amplifier circuit; FIG. 3 is a time chart showing control when a current command value is greater than a detection value; FIG. 4 is a time chart showing control when a current command value is smaller than a detection value; FIG. 5 is an explanatory diagram showing an enlarged view of a connection between a plasma generator and a turbomolecular pump; FIG. 6 is an explanatory diagram showing an enlarged view of a throttle portion and its surrounding area; FIG. 7 is a graph for explaining Paschen's law; and FIG. 8 is an explanatory diagram showing a modified example of the throttle portion. (a) is an explanatory diagram showing an enlarged view of a connection between a plasma generator and a turbomolecular pump according to another modified example, and (b) is an explanatory diagram showing a plan view of the throttle portion according to the modified example. (a) is an explanatory diagram showing an enlarged view of a connection between a plasma generator and a turbomolecular pump according to another modified example, and (b) is an explanatory diagram showing a plan view of the throttle portion according to the modified example.

[0011] <Basic Configuration of Vacuum Exhaust Apparatus 10 According to Embodiment> A vacuum exhaust apparatus 10 according to an embodiment of the present invention will now be described with reference to the drawings. Fig. 1 shows the vacuum exhaust apparatus 10 according to an embodiment of the present invention. The vacuum exhaust apparatus 10 includes a turbomolecular pump 100, which is a vacuum pump, and a plasma generator 210. The turbomolecular pump 100 performs vacuum evacuation, and the plasma generator 210 performs plasma cleaning of reaction products generated in the turbomolecular pump 100.

[0012] 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, a turbomolecular pump 100 has an intake port 101 formed at the upper end of a cylindrical outer cylinder 127. Inside the outer cylinder 127, a rotor 103 is provided, the rotor 103 having a plurality of rotors 102 (102a, 102b, 102c, ...) which are turbine blades for sucking in and exhausting gas, arranged radially and in multiple stages around its periphery. A rotor shaft 113 is attached to the center of the rotor 103, and the rotor shaft 113 is levitated and 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 upper radial electromagnet 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 changes in the inductance of the conductive windings, which change depending on 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 electromagnets 104. Such adjustment is performed independently in the X-axis direction and the Y-axis direction. In addition, the lower radial electromagnets 105 and the lower radial sensors 108 are arranged in the same manner as the upper radial electromagnets 104 and the upper radial sensors 107, and adjust the radial position of the lower side of the rotor shaft 113 in the same manner as the radial position of the upper side.

[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 highly magnetic permeable material such as iron. An axial sensor 109 is provided to detect the axial displacement of rotor shaft 113, and an axial position signal from the axial sensor 109 is sent to control device 200.

[0018] In the control device 200, a compensation circuit having, for example, a PID adjustment function generates excitation control command signals 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 each 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 forces that the axial electromagnets 106A and 106B exert on the metal disk 111, magnetically levitating the rotor shaft 113 in the axial direction and holding it in space without contact. The amplifier circuit 150 that controls the excitation of the upper radial electromagnet 104, the lower radial electromagnet 105, and the axial electromagnets 106A and 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. Motor 121 also incorporates a rotational speed sensor (not shown), such as a Hall element, resolver, or encoder, and the rotational speed of rotor shaft 113 is detected by the detection signal of this rotational speed sensor.

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

[0022] A plurality of fixed blades 123 (123a, 123b, 123c...) are arranged at small gaps (predetermined intervals) from the rotating blades 102 (102a, 102b, 102c...). Each of the rotating blades 102 (102a, 102b, 102c...) is inclined 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.

[0023] Similarly, the fixed blades 123 are formed at a predetermined angle from a plane perpendicular to the axis of the rotor shaft 113, and are arranged in a staggered manner 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 by being inserted between a plurality of stacked fixed blade spacers 125 (125a, 125b, 125c, ...).

[0024] The fixed vane spacer 125 is a ring-shaped member made of a metal such as aluminum, iron, stainless steel, or copper, or an alloy containing any of these metals. An outer cylinder 127 is fixed to the outer periphery of the fixed vane spacer 125 with a small gap between them. A base 129 is disposed at the bottom of the outer cylinder 127. An exhaust port 133 is formed in the base 129 and communicates with the outside. Exhaust gas that enters the intake port 101 from the chamber (vacuum chamber) and is transferred to the base 129 is sent to the exhaust port 133.

[0025] Furthermore, depending on the application of the turbomolecular pump 100, a threaded spacer 131 is disposed between the lower part of the fixed vane spacer 125 and the base portion 129. The threaded spacer 131 is a cylindrical member made of a metal such as aluminum, copper, stainless steel, iron, or an alloy containing any of these metals, and has a plurality of spiral thread grooves 131a engraved on its inner circumferential surface. The spiral direction of the thread grooves 131a corresponds to the direction in which exhaust gas molecules are transported toward the exhaust port 133 when they move in the rotation direction of the rotor 103. A rotor lower cylindrical portion 103b hangs down 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, with a predetermined gap separating them from the inner peripheral surface of the threaded spacer 131. Exhaust gas transferred to the thread groove 131a by the rotor 102 and fixed blades 123 is guided along the thread groove 131a and sent to the base portion 129. In this manner, the threaded spacer 131 and the opposing rotor lower cylindrical portion 103b constitute a Holweck-type exhaust mechanism 204. The Holweck-type exhaust mechanism 204 imparts 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 turbomolecular pump 100.

[0026] The base portion 129 is a disk-shaped member that forms the base of the turbomolecular pump 100, and is generally made of metal such as iron, aluminum, stainless steel, etc. The base portion 129 not only physically holds the turbomolecular pump 100, but also functions as a heat conduction path, so it is desirable to use a metal that is rigid and has high thermal conductivity, such as iron, aluminum, or copper.

[0027] In this configuration, when the rotor 102 is driven to rotate together with the rotor shaft 113 by the motor 121, the action of the rotor 102 and the stator 123 causes exhaust gas to be drawn from the chamber through the intake port 101. The exhaust gas drawn in through the intake port 101 passes between the rotor 102 and the stator 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 conduction of heat generated by the motor 121, but this heat is transferred to the stator 123 side by radiation or conduction by gas molecules of the exhaust gas.

[0028] The stator spacers 125 are joined together at their outer peripheries and transmit to the outside heat received by the stator 123 from the rotor 102 and frictional heat generated when exhaust gas comes into contact with the stator 123 .

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

[0030] Depending on the application of the turbomolecular pump 100, the electrical equipment section may be covered by a stator column 122 to prevent the gas sucked in from the intake port 101 from entering the electrical equipment section, which is 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., and the interior 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 referred to as "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 body) and the stator column 122 or between the base portion 129.

[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 specific to the model. To store these control parameters, the turbomolecular pump 100 is provided with an electronic circuit unit 141 within its body. The electronic circuit unit 141 is composed of a semiconductor memory such as an EEPROM, electronic components such as semiconductor devices for accessing the memory, and a substrate 143 for mounting these components. The electronic circuit unit 141 is housed below a rotational speed sensor (not shown) near the center of a base unit 129 that constitutes the lower part of the turbomolecular pump 100, and is closed by an airtight bottom lid 145.

[0033] In the semiconductor manufacturing process, some process gases introduced into a chamber have the property of solidifying when their pressure exceeds a predetermined value or their temperature falls below a predetermined value. Inside the turbomolecular pump 100, the pressure of the exhaust gas is lowest at the inlet 101 and highest at the outlet 133. If the pressure of the process gas exceeds a predetermined value or the temperature falls below a predetermined value while the process gas is being transferred from the inlet 101 to the outlet 133, the process gas solidifies and adheres to and accumulates inside the turbomolecular pump 100.

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

[0035] To solve this problem, conventionally, a heater (not shown) or an annular (ring-shaped) water-cooled pipe 149 is wound around the outer periphery of the base portion 129, and a temperature sensor (e.g., a thermistor) (not shown) is embedded in the base portion 129, and heating by the heater and cooling by the water-cooled pipe 149 are controlled based on a signal from the temperature sensor to maintain the temperature of the base portion 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 portion 129 is cooled by the water-cooled pipe 149 embedded in the bottom cover 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 turbomolecular pump 100 will be described. A circuit diagram of this amplifier circuit is shown in FIG.

[0037] 2, one end of the electromagnet winding 151 constituting the upper radial electromagnet 104 and the like is connected to the positive electrode 171a of the power supply 171 via a transistor 161, and the other end is connected to the negative electrode 171b of the power supply 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 diode cathode terminal 161a 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 diode cathode terminal 162a connected to the current detection circuit 181 and an anode terminal 162b connected to the negative electrode 171b.

[0039] Meanwhile, the current regenerating 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 regenerating 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 detecting circuit 181. The current detecting circuit 181 is configured, for example, by a Hall sensor type current sensor or an electrical resistance element.

[0040] The amplifier circuit 150 configured as described above corresponds to one electromagnet. Therefore, if the magnetic bearing is controlled in 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 in the figure of the control device 200, and this amplifier control circuit 191 is configured to switch the transistors 161 and 162 on / off.

[0042] The amplifier control circuit 191 compares 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. Based on the comparison result, the amplifier control circuit 191 determines the magnitude of the pulse width (pulse width times Tp1 and Tp2) to be generated within a control cycle Ts, which is one period of PWM control. As a result, gate drive signals 191a and 191b having these pulse widths are output from the amplifier control circuit 191 to the gate terminals of the transistors 161 and 162.

[0043] It is necessary to control the position of the rotor 103 at high speed and with strong force when, for example, the rotor 103 passes through a resonance point during acceleration of its rotational speed or when a disturbance occurs during constant-speed operation. 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 electrode 171a and the negative electrode 171b of the power supply 171 to stabilize the power supply 171.

[0044] In this configuration, when both the transistors 161 and 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] Furthermore, when one of the transistors 161 and 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, 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 and 162 in this manner, high-frequency noise such as harmonics generated in the turbomolecular 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 transistors 161 and 162 are turned on for a time period corresponding to a pulse width time Tp1 only once during 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, if the detected current value is greater than the current command value, both transistors 161 and 162 are turned off for a time period corresponding to 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 electrode 171b to the positive electrode 171a via 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 turbomolecular pump 100 can be used not only in the vertical position shown in Figure 1, but also in an inverted position, a horizontal position, or an inclined position.

[0050] In the turbomolecular pump 100, the aforementioned outer cylinder 127 and base portion 129 are combined to form a single case (hereinafter, both may be collectively referred to as the "main body casing" or the like). The turbomolecular pump 100 is electrically (and structurally) connected to a box-shaped electrical equipment case (not shown), and the aforementioned control device 200 is incorporated into 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 using the motor 121, and an exhaust mechanism portion that is rotationally driven by the rotation mechanism portion. The exhaust mechanism portion can be divided into a turbomolecular pump mechanism portion that is composed of the rotor blades 102, fixed blades 123, and the like, and a threaded pump mechanism portion (Hollweck-type exhaust mechanism portion) that is composed of the rotor lower cylindrical portion 103b, threaded spacer 131, and the like.

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

[0053] For example, the aforementioned 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 "touchdown (T / D) bearings," "backup bearings," etc. These protective bearings 120 prevent the position and attitude of the rotor shaft 113 from changing significantly, even in the unlikely event of a problem with the electrical system or atmospheric inrush, thereby preventing damage to the rotor blades 102 and their surrounding areas.

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

[0056] <Plasma Generator 210 and Throttle Portion 244> As mentioned above, products may accumulate inside the turbomolecular pump 100. In this embodiment, the products are cleaned using the 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 the cylinder 212 to generate plasma (which can also be referred to as "radicals" here) toward the turbomolecular pump 100.

[0057] The plasma generator 210 is connected to the 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 relative to the turbomolecular pump 100. For example, it is also possible to arrange four plasma generators 210 at 90-degree intervals.

[0058] The boundary between the plasma generator 210 and the turbomolecular pump 100 is a connection part 220. The inside of the plasma generator 210 and the inside of the turbomolecular 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 turbomolecular pump 100 with hexagon socket head bolts 224. The gap between the flange part 214 of the plasma generator 210 and the seat surface 194 of the turbomolecular pump 100 is airtightly sealed with a seal member (here, an O-ring) 226.

[0060] A plasma communication port 228 is formed in the base portion 129 of the turbomolecular pump 100. The plasma communication port 228 connects the internal space of the turbomolecular pump 100 with 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 turbomolecular pump 100 internal space side.

[0061] A disk-shaped throttle member 240 is fixed (screwed) to the bottom of the introduction section 230 with machine screws 242. The throttle member 240 has a throttle portion 244 formed therein. The throttle portion 244 is a circular hole (round hole) that penetrates the throttle member 240 in the thickness direction. After the throttle member 240 is attached to the base section 129, the plasma generator 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 turbomolecular 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 used 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 used 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 turbomolecular pump 100, the throttle portion 244 is disposed at approximately the same position as the inclined surface 131b of the threaded spacer 131. Therefore, most of the plasma that heads 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 generator 210. The throttle section 244 is formed so that the pressure reached as the pressure increases satisfies the following relationship based on Paschen's law: 0.3 / D≦P≦1.5 / D, where 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, the gas pressure in the environment, and the distance between electrodes. A spark discharge occurs when a strong electric field is applied to a gas, eventually leading 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 represents the spark voltage [V], and the horizontal axis represents the product [P×D] of the gas pressure [P] and the inter-electrode distance [D]. Spark discharge occurs when electrons collide with gas molecules and ionize the gas. Therefore, 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), collisions between electrons and gas molecules are unlikely to occur. Conversely, if the pressure is too high, it is difficult for electrons to be sufficiently accelerated before they collide. Furthermore, as shown in FIG. 7, the spark voltage increases 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 the pressure [P] and the 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] To give a specific example, when the inter-electrode distance [D] is 5 mm (= 5 × 10 m), the appropriate range for [P] is 60 to 300 Pa. Although not shown in Fig. 7, when the source gas is NF and this source gas is flowed at 50 sccm (standard cubic centimeter per minute), installing an orifice (throttling portion 244 in this case) with a diameter of about 2 to 5 mm brings the pressure inside the plasma generator (plasma generator 210 in this case) into the appropriate range, enabling stable discharge even at a low voltage.

[0071] Here, the relationship between the flow rate, cross-sectional area of ​​the orifice, and pressure difference at the orifice can be calculated using various formulas. For example, this 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 [m3 / s] C: flow coefficient AO = πD2 / 4: cross-sectional area of ​​the orifice hole [m2], D is the diameter of the orifice hole [m] ρ: fluid density [kg / m3] ΔP: differential pressure before and after the orifice [Pa]

[0072] According to the vacuum exhaust device 10 of this embodiment as described above, the orifice-like throttle portion 244 is used to generate a discharge at a low voltage. Therefore, simply installing the throttle member 240 makes it possible to adjust the pressure in the internal space of the plasma generator 210. Furthermore, unlike the conventional technique, it is not necessary to open and close the flow path using a pressure regulation valve downstream of the turbomolecular pump 100. This eliminates the need for a pressure regulation valve and its control circuit. Therefore, the space and cost required for installing a pressure regulation valve are eliminated. Furthermore, since no installation space for a pressure regulation valve is required, the degree of freedom in installing the vacuum exhaust device 10 and the turbomolecular pump 100 is enhanced. Furthermore, since there is no need to install a pressure regulation valve downstream of the vacuum pump (here, the turbomolecular pump 100), it is easy to increase the pressure near the plasma generator as desired. Furthermore, it is no longer necessary to reduce the pumping action of the vacuum pump by reducing its rotation speed or stopping the vacuum pump.

[0073] Furthermore, because the throttle member 240 is a plate-shaped member, it is easier to reduce the size of the pressure adjustment mechanism compared to, 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] Furthermore, because the throttle member 240 is a plate-like body, it can be designed to be thin. This allows the length of the gas flow path and the length and area of ​​the inner wall 245 in the gas flow path to be reduced. As a result, it is possible to minimize the number of radicals that collide with the wall surface of the inner wall 245 and are deactivated.

[0075] Furthermore, the pressure downstream of the throttle section 244 can be kept relatively low, increasing the radical flow rate. This allows the radicals to easily reach the downstream area before being deactivated, resulting in a higher plasma cleaning effect.

[0076] Furthermore, 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 turbomolecular pump 100. The throttle member 240 is installed at the connection portion 220 by fastening with screws. Therefore, the throttle member 240 is easy to install, and the throttle portion 244 can be easily formed.

[0077] Furthermore, surface treatment such as ceramic coating or alumite treatment is applied to the throttle member 240, which makes the throttle portion 244 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] Furthermore, the throttle portion 244 is an open hole, and the turbomolecular pump 100 and the plasma generator 210 are spatially connected via the throttle portion 244. Therefore, the purge gas of the turbomolecular pump 100 can be easily introduced into the plasma generator 210. Furthermore, even if only a small amount of purge gas is supplied to the plasma generator 210, it is possible to prevent the intrusion (deposition) 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 limiting, 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 schematically shows the throttle portion 244 in a plan view from the suction side (upstream side of the exhaust gas) of the turbomolecular pump 100. As with FIG. 5 and other figures, hatching is omitted. Arrow C indicates the plasma extraction direction (a typical extraction direction), and arrow F indicates the rotation direction of the turbomolecular pump 100. The direction indicated by arrow F substantially coincides with the direction of the spiral flow of the exhaust gas.

[0080] 8, the throttle portion 246 is a hole that is inclined in a direction that intersects with 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 turbomolecular pump 100" can also be expressed as, for example, "oriented horizontally and obliquely with respect to the radial direction of the turbomolecular 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 to the rotational direction." Furthermore, because exhaust gas flows spirally from the intake side to the exhaust side, the throttle section 246 may be oriented obliquely with respect to the direction of the rotational 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 extracted from the throttle portion 246 to smoothly join the gas flowing inside the turbomolecular pump 100. The opening of the throttle portion 246 that faces the turbomolecular pump 100 is also oriented obliquely with respect to the inclined surface 131b of the threaded spacer 131.

[0083] By orienting the throttle portion 246 as shown in the example of Figure 8, it is possible to efficiently guide plasma into the turbomolecular pump 100. As a result, the plasma flows smoothly all the way to the downstream of the gas flow path in the turbomolecular pump 100, thereby achieving a higher plasma cleaning effect. Furthermore, because the throttle portion 246 opens obliquely relative to the radial direction of the threaded spacer 131 (Figure 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) and 9(b) and 10(a) and 10(b), the shape of the diaphragm members 250, 260 can be a three-dimensional shape instead of the flat shape described above. For example, in the example of FIGS. 9(a) and 9(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] 9B, similar to Fig. 8, shows a schematic plan view of the throttle portion 256 from the suction side (upstream side of the exhaust gas) of the turbomolecular pump 100. Arrow C indicates the direction in which the plasma is extracted (a typical extraction direction), and arrow F indicates the direction of rotation of the turbomolecular pump 100, similar to Fig. 8.

[0086] The throttle portion 256 extends through the inclined surface 258 of the throttle member 250 in the thickness direction, and opens obliquely relative to the inclined surface 131b of the threaded spacer 131. This configuration allows the plasma to be efficiently introduced into the turbomolecular pump 100, and allows the plasma to flow smoothly downstream of the gas flow path within the turbomolecular pump 100. This results in a higher plasma cleaning effect. Furthermore, 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 spirally from the intake side to the exhaust side, the throttle portion 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 10(b), the diaphragm 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, a tapered (or widened) trapezoid shape is also possible.

[0089] 8 and 9B, Fig. 10B schematically shows the throttle portion 266 as viewed from the suction side (upstream side of the exhaust gas) of the turbomolecular pump 100. Arrow C indicates the direction in which plasma is extracted (a typical extraction direction), and arrow F indicates the direction of rotation of the turbomolecular pump 100, as in Figs. 8 and 9B.

[0090] The throttle portion 266 extends through the side surface 268 of the throttle member 260 in the thickness direction, and opens directly sideways to the inclined surface 131b of the threaded spacer 131. This allows the plasma to be efficiently introduced into the turbomolecular pump 100, and allows the plasma to flow smoothly downstream of the gas flow path within the turbomolecular pump 100. This results in a higher plasma cleaning effect. Furthermore, 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 spirally from the intake side to the exhaust side, the throttle portion 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 can 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 generating device 210 (e.g., a position inside the turbomolecular pump 100), but may be an internal position in the plasma generating 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 throttle section (e.g., throttle sections 244, 246, 256, 266). However, in the vacuum exhaust device 10 described above, the flow rate can be changed by changing the pressure, so it is not necessary to use a variable orifice with a complex structure.

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

[0096] <Inventions Extractable from Each Embodiment> The following inventions can be extracted from each of the above-described embodiments. (1) A vacuum exhaust device (such as vacuum exhaust device 10) equipped with a vacuum pump (such as turbomolecular pump 100) and a plasma generator (such as plasma generator 210), characterized in that the vacuum exhaust device is equipped with a throttle (such as throttle portion 244, 246, 256, 266, a hole-like portion of a valve device, or a hole-like portion formed in a needle-like member) capable of increasing the internal pressure of the plasma generator until the relationship P≧0.3 / D is satisfied. Here, P: pressure [Pa], and D: distance between electrodes of the plasma generator [m]. (2) The vacuum exhaust device according to (1) above, characterized in that the internal pressure of the plasma generator can be increased by the throttle until the relationship P≦1.5 / D is satisfied. (3) The vacuum exhaust device according to (1) or (2) above, characterized in that the throttle is installed at a connection (such as connection portion 220) between the vacuum pump and the plasma generator. (4) The vacuum exhaust device according to (1) or (2) above, wherein the orifice 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 the 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 orifice is ceramic coated. (7) The vacuum exhaust device according to (1) or (2) above, wherein at least the inner wall of the orifice is anodized.

[0097] <Others> 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 gist of the present invention.

[0098] 10: Vacuum exhaust device 100: Turbo molecular pump 210: Plasma generator 220: Connection part 228: Plasma communication port 230: Inlet part 232: Outlet part 240, 250, 260: Throttle member 244, 246, 256, 266: Throttle part 245: Inner wall

Claims

1. A vacuum exhaust device comprising a vacuum pump and a plasma generator, characterized in that the device is provided with a throttle capable of increasing the internal pressure of the plasma generator until it satisfies the relationship P≧0.3 / D, where P is pressure [Pa] and D is the distance between the electrodes of the plasma generator [m].

2. The vacuum exhaust system according to claim 1, characterized in that the internal pressure of the plasma generating device can be increased by the throttle to a pressure that satisfies the relationship P≦1.5 / D.

3. The vacuum exhaust device according to claim 1 or 2, wherein the throttle is provided at a connection between the vacuum pump and the plasma generating device.

4. The vacuum exhaust system according to claim 1 or 2, wherein the restrictor is an orifice.

5. A vacuum exhaust device according to claim 1 or 2, characterized in that the orifice has a hole inclined in a direction intersecting with the radial direction of the vacuum pump.

6. A vacuum exhaust system according to claim 1 or 2, characterized in that the orifice is ceramic coated.

7. The vacuum exhaust device according to claim 1 or 2, characterized in that the throttle is anodized.

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