Vacuum pump

Abstract

[Problem] To propose a vacuum pump that offers excellent back pressure performance even when the suction gas is hydrogen gas or the like. [Solution] A vacuum pump 100 comprising an exhaust part 114 that includes: a turbine pump section 115 with a plurality of stages of rotary blades 102 and fixed blades 123; and a drag pump section 116 positioned on the exhaust downstream side of the turbine pump section 115. Intake gas sucked in from an intake port 101 by the exhaust part 114 is discharged from an exhaust port 133 via a gas flow passage FP1. The vacuum pump 100 is characterized by comprising an introduction flow passage FP3 for introducing intermediate introduction gas having a higher viscosity than the intake gas. The vacuum pump 100 is also characterized in that the introduction flow passage FP3 is connected to the gas flow passage FP1 on the exhaust downstream side of the rotary blade 102 closest to the intake port 101 among the plurality of stages of rotary blades 102 in the exhaust part 114.

Description

vacuum pump

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

[0002] Known vacuum pumps, such as turbomolecular pumps, include an exhaust section that includes a turbine pump section that primarily aims to compress the molecular flow region and a drag pump section that primarily aims to compress the intermediate flow region to the viscous flow region (see, for example, FIG. 9 of Patent Document 1).

[0003] The vacuum pump disclosed in Patent Document 1 has a cylindrical casing with multiple stages of rotors and fixed blades functioning as a turbine pump section, and also has a threaded section functioning as a drag pump section. The casing has an intake port at the top and an exhaust port at the bottom. When the vacuum pump is driven, gas is drawn in through the intake port, passes through the turbine pump section and the drag pump section in that order, and is then exhausted through the exhaust port.

[0004] Generally, vacuum pumps have a back pressure dependency in which the performance of the pump is affected by the pressure on the exhaust port side (back pressure side). Conventionally, known means for reducing the influence of back pressure (improving back pressure performance) include increasing the diameter of the thread groove portion or increasing the axial length of the thread groove portion, as shown in Patent Document 1.

[0005] Patent No. 5689546

[0006] However, when the gas being sucked into the vacuum pump is hydrogen gas, even if the above-mentioned means for increasing back pressure performance are used, sufficient back pressure performance may not be obtained compared to when, for example, nitrogen gas is sucked in. After extensive research into this point, the inventors of the present application have concluded that hydrogen gas has a lower viscosity than nitrogen gas, which reduces the compression effect in the exhaust section (especially the drag pump section), and that this is one of the causes of the reduced back pressure performance.

[0007] An object of the present invention is to provide a vacuum pump that has excellent back pressure performance even when the suction gas is hydrogen gas or the like.

[0008] The present invention provides a vacuum pump comprising an exhaust section including a turbine pump section having multiple stages of rotors and fixed blades and a drag pump section located downstream of the turbine pump section in the exhaust direction, and exhausting intake gas sucked in from an intake port by the exhaust section through a gas flow path from the exhaust port, the vacuum pump comprising an introduction flow path for introducing an intermediate introduction gas having a higher viscosity than the intake gas, the introduction flow path being connected to the gas flow path downstream of the rotor of the multiple stages of rotors that is closest to the intake port in the exhaust section.

[0009] Such a vacuum pump is provided with a purge gas flow path that supplies purge gas to the inside of a stator column that is provided on the inner periphery of the rotor on which the rotor blades are provided, and the introduction flow path is preferably branched off from the purge gas flow path, and the purge gas is preferably used as the intermediate introduction gas.

[0010] The purge gas flow path is preferably composed of an outer purge gas flow path located outside the vacuum pump and an inner purge gas flow path located inside the vacuum pump, and the introduction flow path is preferably branched from the inner purge gas flow path and connected to the gas flow path.

[0011] The inner diameter of at least a part of the introduction passage is preferably smaller than the inner diameter of the purge gas passage.

[0012] The introduction passage preferably includes a valve capable of adjusting the flow rate of the intermediate introduction gas.

[0013] The introduction passage is preferably connected to the gas passage between the turbine pump section and the drag pump section.

[0014] The vacuum pump of the present invention includes an introduction passage for introducing an intermediate introduction gas having a higher viscosity than the intake gas. The introduction passage is connected to the gas passage downstream of the rotor of the multiple stages of rotors that is closest to the intake port in the exhaust section. With this configuration, when the intake gas sucked in through the intake port by the exhaust section is exhausted through the gas passage from the exhaust port, the intake gas and the intermediate introduction gas flow through the gas passage. In other words, the viscosity of the mixture of the intake gas and the intermediate introduction gas is higher than that of the intake gas alone, thereby improving the compression effect in the exhaust section. Therefore, the vacuum pump of the present invention can achieve excellent back pressure performance even when the suction gas is hydrogen gas or the like.

[0015] 1 is a longitudinal sectional view schematically showing an embodiment of a vacuum pump according to the present invention. FIG. 5 is a circuit diagram of an amplifier circuit of the vacuum pump shown in FIG. 1. FIG. 6 is a time chart showing control when a current command value is larger than a detection value. FIG. 7 is a time chart showing control when a current command value is smaller than a detection value. FIG. 8 is a partial enlarged view of the vacuum pump shown in FIG. 1. FIG. 9 is a partial enlarged view of a first modified example of the vacuum pump shown in FIG. 1. FIG. 10 is a partial enlarged view of a second modified example of the vacuum pump shown in FIG. 1. FIG. 11 is a partial enlarged view of a third modified example of the vacuum pump shown in FIG. 1. FIG. 12 is a partial enlarged view of a fourth modified example of the vacuum pump shown in FIG. 1. FIG. 13 is a graph showing the relationship between back pressure and suction pressure in the vacuum pumps shown in FIGS. 1 and 5.

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A turbomolecular pump, which is an embodiment of a vacuum pump according to the present invention, will be described below with reference to the drawings.

[0017] A longitudinal cross-sectional view of this turbomolecular pump 100 is shown in Figure 1. The turbomolecular pump 100 has an intake port 101 formed at the upper end of a cylindrical outer tube 127. Inside the outer tube 127 is a rotor 103, which has a plurality of rotor blades 102 (102a, 102b, 102c, ...) formed radially and in multiple stages around its periphery as turbine blades for sucking in and exhausting gas (intake gas). A rotor shaft 113 is attached to the center of the rotor 103, and this rotor shaft 113 is levitated and supported in the air and its position is controlled by, for example, a five-axis controlled magnetic bearing. The rotor 103 is generally made of metal such as aluminum or an aluminum alloy.

[0018] 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 that change 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 a control device (not shown).

[0019] In this control device, 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.

[0020] 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.

[0021] Furthermore, axial electromagnets 106A and 106B are arranged above and below a circular metal 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 is sent to the control device.

[0022] In the control device, 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.

[0023] In this way, the control device appropriately adjusts the magnetic forces exerted by the axial electromagnets 106A and 106B 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.

[0024] Meanwhile, motor 121 has a plurality of magnetic poles arranged circumferentially so as to surround rotor shaft 113. Each magnetic pole is controlled by a control device 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.

[0025] 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 uses the detection signals from both this phase sensor and the rotational speed sensor to detect the position of the magnetic pole.

[0026] A plurality of fixed blades 123 (123a, 123b, 123c...) are arranged with a small gap between them and the rotating blades 102 (102a, 102b, 102c...). Each of the rotating blades 102 (102a, 102b, 102c...) is formed at an angle of a predetermined degree from a plane perpendicular to the axis of the rotor shaft 113 in order to transport intake gas molecules downward through collision. The fixed blades 123 (123a, 123b, 123c...) are made of metal such as aluminum, iron, stainless steel, copper, or an alloy containing any of these metals.

[0027] 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, ...).

[0028] 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. Intake 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.

[0029] Furthermore, a threaded spacer 131 is disposed between the lower portion 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 multiple spiral thread grooves 131a engraved on its inner circumferential surface. The spiral direction of the threaded grooves 131a corresponds to the direction in which intake gas molecules are transported toward the exhaust port 133 when they move in the rotational direction of the rotor 103. A cylindrical portion 102d hangs down from the lowest portion of the rotor 103, adjacent to the rotor vanes 102 (102a, 102b, 102c, etc.). The outer circumferential surface of this cylindrical portion 102d is cylindrical and protrudes toward the inner circumferential surface of the threaded spacer 131, and is adjacent to the inner circumferential surface of the threaded spacer 131 with a predetermined gap therebetween. The intake gas transferred to the thread groove 131 a by the rotary blade 102 and the fixed blade 123 is sent to the base portion 129 while being guided by the thread groove 131 a.

[0030] Here, a portion having the function of discharging intake gas from intake port 101 toward exhaust port 133 is referred to as exhaust section 114, and a flow path through which intake gas flows from intake port 101 to exhaust port 133 is referred to as gas flow path FP1. Exhaust section 114 is composed of turbine pump section 115 having multiple stages of rotor blades 102 and fixed blades 123, and drag pump section 116 having thread groove 131a and cylindrical section 102d.

[0031] 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.

[0032] In this configuration, when the rotor 102 is rotated together with the rotor shaft 113 by the motor 121, the action of the rotor 102 and the stator 123 draws gas from the chamber through the intake port 101. The rotational speed of the rotor 102 is typically 20,000 rpm to 90,000 rpm, and the peripheral speed at the tip of the rotor 102 reaches 200 m / s to 400 m / s. The intake gas drawn through the intake port 101 passes between the rotor 102 and the stator 123 and is transported to the base 129. At this time, the temperature of the rotor 102 rises due to frictional heat generated when the intake 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 by radiation or conduction by gas molecules of the intake gas.

[0033] 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 intake gas comes into contact with the stator 123.

[0034] In the above description, the threaded spacer 131 is disposed on the outer periphery of the cylindrical portion 102d of the rotor 103, and the thread groove 131a is formed on the inner circumferential surface of the threaded spacer 131. However, conversely, there are also cases where a thread groove is formed on the outer circumferential surface of the cylindrical portion 102d, and a spacer having a cylindrical inner circumferential surface is disposed around it.

[0035] In the turbomolecular pump 100 of this embodiment, the electrical equipment section is surrounded by a stator column 122 to prevent the intake 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 is maintained at a predetermined pressure by purge gas.

[0036] A purge gas inlet 135 is provided in the base portion 129, and purge gas is introduced from this purge gas inlet 135 into the inside of the stator column 122. The introduced purge gas is sent to the exhaust port 133 through gaps between the protective bearing 120 and the rotor shaft 113, between the rotor and stator of the motor 121, and between the stator column 122 and the inner cylindrical portion of the rotor blades 102. Here, the flow path through which the purge gas flows from the purge gas inlet 135 to the stator column 122 is referred to as a purge gas flow path FP2.

[0037] 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.

[0038] 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 intake gas is lowest at the intake port 101 and highest at the exhaust port 133. If the pressure of the intake gas exceeds a predetermined value or the temperature falls below a predetermined value while the intake gas is being transferred from the intake port 101 to the exhaust port 133, the intake gas solidifies and adheres to and accumulates inside the turbomolecular pump 100.

[0039] 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.

[0040] Therefore, in order to solve this problem, conventionally, a heater (not shown) or a circular water-cooled pipe 149 is wound around the outer periphery of the base portion 129 or the like, and a temperature sensor (not shown, for example, a thermistor) 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 this temperature sensor so as to maintain the temperature of the base portion 129 at a constant high temperature (set temperature) (hereinafter referred to as TMS; TMS; Temperature Management System).

[0041] Furthermore, the turbomolecular pump 100 of this embodiment is provided with an intermediate introduction gas inlet 137 for introducing an intermediate introduction gas into the turbomolecular pump 100. The intermediate introduction gas and the like will be described in detail later.

[0042] 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 150 is shown in FIG.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] Furthermore, the amplifier control circuit 191 is configured, for example, by a digital signal processor section (hereinafter referred to as a DSP section) of the control device (not shown), and this amplifier control circuit 191 switches the transistors 161 and 162 on / off.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Here, the intermediate gas mentioned above will be explained. The intermediate gas is a gas with a higher viscosity than the intake gas. For example, when the intake gas is hydrogen gas, nitrogen gas or argon gas is used as the intermediate gas. Note that the intermediate gas is not limited to a gas of a different type from the intake gas. For example, the intermediate gas may be a gas of the same type as the intake gas but with its viscosity increased by increasing its temperature.

[0056] In the turbomolecular pump 100 of this embodiment, intermediate introduction gas is introduced into the turbomolecular pump 100 through an intermediate introduction gas inlet 137 shown in FIG. 5. The intermediate introduction gas introduced into the turbomolecular pump 100 flows through the illustrated introduction flow path FP3. The stator spacer 125a of this embodiment is provided with a connection port 138 that penetrates the stator spacer 125a in the radial direction, and as shown, the connection port 138 is located downstream of the rotor 102a in the exhaust direction. In other words, the introduction flow path FP3 is connected by the connection port 138 to the gas flow path FP1 downstream of the rotor 102a that is closest to the intake port 101 in the exhaust section 114.

[0057] With the turbomolecular pump 100 configured in this manner, not only the intake gas sucked in from the intake port 101 but also the intermediate introduction gas that has passed through the connection port 138 flows through the gas flow path FP1. In other words, the viscosity of the mixture of the intake gas and the intermediate introduction gas is higher than that of the intake gas alone, and therefore the compression effect in the exhaust section 114 (particularly the drag pump section 116) is improved. Therefore, with the turbomolecular pump 100, even if the intake gas is a low-viscosity gas such as hydrogen gas, it is possible to improve the back pressure performance compared to when the intermediate introduction gas is not introduced.

[0058] Here, the back pressure performance of the turbomolecular pump 100 of this embodiment will be described with reference to Figure 10. In Figure 10, the horizontal axis represents the pressure at the exhaust port 133 (back pressure), and the vertical axis represents the pressure at the intake port 101 (suction pressure). The dashed line in Figure 10 shows the relationship between the back pressure and the suction pressure when only intake gas is sucked in without introducing intermediate introduction gas, and the solid line in Figure 10 shows the relationship between the back pressure and the suction pressure when intake gas is sucked in while intermediate introduction gas is introduced. In Figure 10, the intake gas is hydrogen gas, and the intermediate introduction gas is nitrogen gas.

[0059] As is clear from FIG. 10, when the back pressure increases, the suction pressure also increases. However, when the intermediate introduction gas is introduced, the increase in suction pressure is suppressed even when the back pressure increases, compared to when the intermediate introduction gas is not introduced, and it was confirmed that the back pressure performance is improved.

[0060] Various modifications are possible to the configuration relating to the intermediate gas introduction in the turbomolecular pump 100. For example, the turbomolecular pump 100 may be modified to the configuration shown in FIG.

[0061] 6 includes a valve 139. The connection port 138 is provided at the outlet of a through-hole provided inside the threaded spacer 131. In this embodiment, the introduction flow path FP3 through which the intermediate introduction gas flows is a flow path extending from the valve 139, via the intermediate introduction gas introduction port 137, to the connection port 138. The valve 139 can adjust the flow rate of the intermediate introduction gas flowing through the introduction flow path FP3.

[0062] In the turbomolecular pump 100 shown in FIG. 6 , the introduction flow path FP3 is connected by a connection port 138 to a location near the middle of the drag pump section 116 in the exhaust section 114. That is, downstream of the middle of the drag pump section 116 in the exhaust section 114, a mixture of intake gas and intermediate introduction gas flows, improving the compression effect in this section compared to when only intake gas flows through the gas flow path FP1. Therefore, the turbomolecular pump 100 shown in FIG. 6 also achieves improved backpressure performance compared to when no intermediate introduction gas is introduced. Note that an improvement in compression effect cannot be expected if the amount of intermediate introduction gas introduced into the gas flow path FP1 is too large or too small. On the other hand, by providing a valve 139 as in this embodiment, the amount of intermediate introduction gas can be easily changed, thereby further improving backpressure performance by adjusting the amount of intermediate introduction gas.

[0063] The turbomolecular pump 100 may also be modified to the configuration shown in Fig. 7. The turbomolecular pump 100 shown in Fig. 7 is provided with a connection port 138 between the turbine pump section 115 and the drag pump section 116 in the exhaust section 114. That is, the introduction flow path FP3 is connected to the gas flow path FP1 between the turbine pump section 115 and the drag pump section 116. With this configuration, the mixed gas of the intake gas and the intermediate introduction gas flows through the drag pump section 116, improving the compression effect in the drag pump section 116.

[0064] In the turbomolecular pump 100 shown in Figure 6, the mixed gas of the intake gas and the intermediate introduction gas basically flows downstream from near the middle of the drag pump section 116, while in the turbomolecular pump 100 shown in Figure 7, the mixed gas basically flows throughout the entire drag pump section 116, thereby further improving the compression effect. Furthermore, in the turbomolecular pump 100 shown in Figure 5, the mixed gas of the intake gas and the intermediate introduction gas also flows throughout the entire drag pump section 116, so a further improvement in the compression effect is expected compared to the turbomolecular pump 100 shown in Figure 6. In the turbomolecular pump 100 shown in Figure 5, the number of gas molecules that come into contact with the rotor 102 and the stator 123 when the mixed gas flows through the turbine pump section 115 increases compared to when only intake gas is used. This increases the heat generated by the rotor 102 and the stator 123, making it more likely that the turbomolecular pump 100 will reach its upper limit of allowable temperature. For this reason, it is necessary to limit the allowable flow rate of the intake gas to prevent the temperature rise. On the other hand, in the turbomolecular pump 100 shown in FIG. 7, the mixed gas basically flows downstream of the turbine pump section 115, so the allowable flow rate of the intake gas can be increased compared to the turbomolecular pump 100 shown in FIG. 5.

[0065] The turbomolecular pump 100 may be modified to the configuration shown in FIG. 8 . In the turbomolecular pump 100 shown in FIG. 8 , a purge gas fitting 135a equipped with a purge gas inlet 135 branches into two on the outside of the base portion 129. One of the branched purge gas fittings 135a leads to the inside of the stator column 122, and the other branched purge gas fitting 135a leads to a connection port 138 located between the turbine pump portion 115 and the drag pump portion 116. In this embodiment, the purge gas flow path FP2 is a flow path that runs from the purge gas inlet 135 via one purge gas fitting 135a to the stator column 122, and the introduction flow path FP3 is a flow path that runs from the other purge gas fitting 135a to the connection port 138. That is, the introduction flow path FP3 branches from the purge gas flow path FP2, and purge gas is used as an intermediate introduction gas that flows through the introduction flow path FP3.

[0066] According to the turbomolecular pump 100 shown in FIG. 8 , the purge gas can be used as the intermediate introduction gas, which simplifies the overall configuration of the turbomolecular pump 100, including associated equipment, compared to when separate purge gases and intermediate introduction gases are prepared. Furthermore, when using the turbomolecular pump 100 shown in FIG. 8 , it is particularly preferable that the suction gas be hydrogen gas and the purge gas be nitrogen gas. In other words, because nitrogen gas has a higher viscosity than hydrogen gas, back pressure performance can be improved compared to when nitrogen gas is not introduced as the intermediate introduction gas. Furthermore, because nitrogen gas is an inexpensive inert gas, the turbomolecular pump 100 can be operated safely and costs can be reduced.

[0067] The turbomolecular pump 100 may be modified to the configuration shown in FIG. 9 . The turbomolecular pump 100 shown in FIG. 9 has through holes formed inside the base portion 129 and the threaded spacer 131. The inlet of this through hole communicates with a purge gas flow path FP2. This through hole also communicates with a connection port 138 located between the turbine pump portion 115 and the drag pump portion 116. In this embodiment, the introduction flow path FP3 is a flow path extending from the inlet of this through hole to the connection port 138. Here, with regard to the purge gas flow path FP2 leading from the purge gas introduction port 135 to the inside of the stator column 122, the flow path located outside the turbomolecular pump 100 (i.e., inside the purge gas joint 135b) is referred to as an outer purge gas flow path FP2A, and the flow path located inside the turbomolecular pump 100 is referred to as an inner purge gas flow path FP2B.

[0068] In the turbomolecular pump 100 shown in Fig. 9, the introduction flow path FP3 branches off from the inner purge gas flow path FP2B and is connected to the gas flow path FP1. That is, in this turbomolecular pump 100, the purge gas can also be used as the intermediate introduction gas, so the overall configuration of the turbomolecular pump 100 can be simplified compared to when the purge gas and the intermediate introduction gas are prepared separately. Furthermore, in the turbomolecular pump 100 shown in Fig. 8, the introduction flow path FP3 is provided outside the turbomolecular pump 100, which requires a corresponding amount of space, but in the turbomolecular pump 100 shown in Fig. 9, the introduction flow path FP3 is provided inside the turbomolecular pump 100, so space can be secured around the turbomolecular pump 100.

[0069] When using a purge gas as an intermediate introduction gas as in the turbomolecular pump 100 shown in Figures 8 and 9, it is preferable that the inner diameter of at least a portion of the introduction flow path FP3 is smaller than the inner diameter of the purge gas flow path FP2. In this embodiment, as shown in Figures 8 and 9, a connection port 138 with a relatively small diameter is used, and the inner diameter of at least this portion is smaller than the inner diameter of the purge gas flow path FP2.

[0070] The amount of purge gas used as the intermediate introduction gas is generally less than the amount of purge gas introduced into the stator column 122. Therefore, by making the inner diameter of at least a portion of the introduction flow path FP3 smaller than the inner diameter of the purge gas flow path FP2, it becomes easier to achieve the desired back pressure performance from the beginning. Furthermore, when adjusting the amount of purge gas flowing through the introduction flow path FP3 to improve the back pressure performance, it is easy to increase a small inner diameter, making the adjustment easier. Note that the amount of purge gas flowing through the introduction flow path FP3 may be adjusted using the above-mentioned valve 139 (see FIG. 6).

[0071] Although one embodiment of the present invention has been described above, the present invention is not limited to the specific embodiment, and various modifications, changes, and combinations are possible within the scope of the spirit of the present invention as set forth in the claims unless otherwise specifically limited in the above description. Furthermore, the effects of the above embodiment are merely examples of the effects resulting from the present invention, and do not mean that the effects of the present invention are limited to the above effects.

[0072] For example, the drag pump section 116 is not limited to the Holweck pump mechanism using the screw groove 131a described above, and may be configured with other pump mechanisms, such as a Sigburn pump mechanism.

[0073] 100: Turbo molecular pump (vacuum pump) 101: Inlet port 102: Rotor 103: Rotor 114: Exhaust section 115: Turbine pump section 116: Drag pump section 122: Stator column 123: Fixed blade 133: Exhaust port 139: Valve FP1: Gas flow path FP2: Purge gas flow path FP2A: Outer purge gas flow path FP2B: Inner purge gas flow path FP3: Introduction flow path

Claims

1. A vacuum pump comprising an exhaust section including a turbine pump section having multiple stages of rotors and fixed blades and a drag pump section located downstream of the turbine pump section, and exhausting intake gas sucked in from an intake port by the exhaust section through a gas flow path from the exhaust port, further comprising an introduction flow path for introducing an intermediate introduction gas having a higher viscosity than the intake gas, the introduction flow path being connected to the gas flow path downstream of the rotor among the multiple stages of rotors that is closest to the intake port in the exhaust section.

2. A vacuum pump as described in claim 1, further comprising a purge gas flow passage for supplying a purge gas to the inside of a stator column provided on the inner periphery of a rotor on which the rotor blades are provided, the introduction flow passage being branched off from the purge gas flow passage, and the purge gas being used as the intermediate introduction gas.

3. A vacuum pump as described in claim 2, characterized in that the purge gas flow path is composed of an outer purge gas flow path located outside the vacuum pump and an inner purge gas flow path located inside the vacuum pump, and the introduction flow path branches off from the inner purge gas flow path and is connected to the gas flow path.

4. The vacuum pump according to claim 2, wherein the inner diameter of at least a part of said introduction passage is smaller than the inner diameter of said purge gas passage.

5. The vacuum pump according to claim 1, wherein the introduction passage is provided with a valve capable of adjusting the flow rate of the intermediate introduction gas.

6. The vacuum pump according to claim 1, wherein the introduction passage is connected to the gas passage between the turbine pump section and the drag pump section.

Images