Vacuum pump

Abstract

A vacuum pump is proposed that has favorable back pressure performance even in a case where an intake gas is a hydrogen gas or the like. A vacuum pump 100 includes an exhaust portion 114 constituted of a turbine pump portion 115 that includes a plurality of stages of rotor blades 102 and a plurality of stages of stator blades 123, and a drag pump portion 116 that is located on a further toward exhaust downstream side than the turbine pump portion 115, exhausts from an outlet port 133 through a gas flow passage FP1 an intake gas sucked from an inlet port 101 by the exhaust portion 114, and includes an introduction flow passage FP3 through which an intermediate introduction gas having viscosity higher than that of the intake gas is introduced, and the introduction flow passage FP3 is connected to the gas flow passage FP1 on the further toward exhaust downstream side than the rotor blade 102, from among the plurality of stages of the rotor blades 102, that is closest to the inlet port 101 in the exhaust portion 114.

Description

[Technical Field]

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

[0002] As a vacuum pump such as a turbomolecular pump, there is known a vacuum pump that includes an exhaust portion including a turbine pump portion that mainly intends to compress a molecular flow area and a drag pump portion that mainly intends to compress an area from an intermediate flow area to a viscous flow area (see, for example, Fig. 9 of PTL 1).

[0003] A vacuum pump described in PTL 1 is provided with a plurality of stages of rotor blades and a plurality of stages of stator blades that function as a turbine pump portion inside a cylindrical casing, and is further provided with a thread groove portion that functions as a drag pump portion. Furthermore, an inlet port is provided at an upper portion of the casing, and an outlet port is provided at a lower portion of the casing. Furthermore, when the vacuum pump is driven, a gas is sucked from the inlet port, and this gas passes through the turbine pump portion and the drag pump portion in order, and then is exhausted from the outlet port.

[0004] Generally, a vacuum pump has back pressure dependency that influences performance of the pump due to a pressure on an exhaust ports side (back pressure side). Conventionally, as a means for reducing a back pressure influence (a means for enhancing back pressure performance), it is known to expand a diameter of the thread groove portion or an axial direction length of the thread groove portion as described in PTL 1.[Citation List][Patent Literature]

[0005] [PTL 1] Japanese Patent No. 5689546[Summary of Invention][Technical Problem]

[0006] By the way, in a case where a gas sucked by a vacuum pump is a hydrogen gas, even if the means for enhancing the above-described back pressure performance is used, it may not be possible to obtain sufficient back pressure performance compared to a case where, for example, a nitrogen gas is sucked. The inventors of the present invention have studied this point over and over, and estimated that the hydrogen gas has low viscosity compared to the nitrogen gas, therefore a compression effect at an exhaust portion (in a drag pump portion in particular) becomes low, and is one of factors that lowers back pressure performance.

[0007] An object of the present invention is to provide a vacuum pump that has favorable back pressure performance even in a case where an intake gas is a hydrogen gas or the like.[Solution to Problem]

[0008] The present invention is a vacuum pump including an exhaust portion constituted of a turbine pump portion, which includes a plurality of stages of rotor blades and a plurality of stages of stator blades, and a drag pump portion, which is located on a further toward exhaust downstream side than the turbine pump portion, and exhausting from an outlet port through a gas flow passage an intake gas sucked from an inlet port by the exhaust portion, the vacuum pump further including an introduction flow passage through which an intermediate introduction gas having viscosity higher than viscosity of the intake gas is introduced, and the introduction flow passage is connected to the gas flow passage on the further toward exhaust downstream side than a rotor blade, from among the plurality of stages of the rotor blades, that is the closest to the inlet port in the exhaust portion.

[0009] Preferably, this vacuum pump further includes a purge gas flow passage that supplies a purge gas to an inside of a stator column provided on an inner circumferential side of a rotating body provided with the rotor blades, and the introduction flow passage is branched from the purge gas flow passage, and the purge gas is used as the intermediate introduction gas.

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

[0011] Furthermore, preferably, an inner diameter of at least part of the introduction flow passage is smaller than an inner diameter of the purge gas flow passage.

[0012] Furthermore, preferably, the introduction flow passage includes a valve that can adjust a flow rate of the intermediate introduction gas.

[0013] Furthermore, preferably, the introduction flow passage is connected to the gas flow passage between the turbine pump portion and the drag pump portion.[Advantageous Effects of Invention]

[0014] The vacuum pump according to the present invention includes the introduction flow passage through which the intermediate introduction gas having the higher viscosity than that of the intake gas is introduced, and this introduction flow passage is connected to the gas flow passage on the exhaust downstream side of the rotor blade of the plurality of stages of the rotor blades that is closest to the inlet port in the exhaust portion. According to this configuration, when the intake gas sucked from the inlet port by the exhaust portion is exhausted from the outlet port through the gas flow passage, the intake gas and the intermediate introduction gas flow in the gas flow passage. That is, the viscosity of a mixed gas of the intake gas and the intermediate introduction gas becomes higher than that of the intake gas alone, and therefore a compression effect in the exhaust portion improves. Consequently, the vacuum pump according to the present invention can obtain favorable back pressure performance even in a case where the intake gas is a hydrogen gas or the like.[Brief Description of Drawings]

[0015] [Fig. 1] Fig. 1 is a longitudinal cross-sectional view schematically illustrating an embodiment of a vacuum pump according to the present invention. [Fig. 2] Fig. 2 is a circuit diagram of an amplifier circuit of the vacuum pump illustrated in Fig. 1. [Fig. 3] Fig. 3 is a time chart illustrating control in a case where a current command value is larger than a detection value. [Fig. 4] Fig. 4 is a time chart illustrating control in a case where a current command value is smaller than a detection value. [Fig. 5] Fig. 5 is a partially enlarged view of the vacuum pump illustrated in Fig. 1. [Fig. 6] Fig. 6 is a partially enlarged view illustrating a first modified example of the vacuum pump illustrated in Fig. 1. [Fig. 7] Fig. 7 is a partially enlarged view illustrating a second modified example of the vacuum pump illustrated in Fig. 1. [Fig. 8] Fig. 8 is a partially enlarged view illustrating a third modified example of the vacuum pump illustrated in Fig. 1. [Fig. 9] Fig. 9 is a partially enlarged view illustrating a fourth modified example of the vacuum pump illustrated in Fig. 1. [Fig. 10] Fig. 10 is a graph illustrating a relationship between a back pressure and a suction pressure in the vacuum pump illustrated in Figs. 1 and 5. [Description of Embodiments]

[0016] Hereinafter, with reference to the drawings a turbomolecular pump that is an embodiment of a vacuum pump according to the present invention will be described.

[0017] Fig. 1 illustrates a longitudinal cross-sectional view of this turbomolecular pump 100. The turbomolecular pump 100 includes an inlet port 101 formed at an upper end of a cylindrical outer cylinder 127. Furthermore, the interior of the outer cylinder 127 is equipped with a rotating body 103 including a plurality of rotor blades 102 (102a, 102b, 102c, and ...) that are turbine blades for sucking and exhausting the gas (intake gas), and are formed at a circumferential portion radially and at multiple stages. A rotor shaft 113 is attached to the center of this rotating body 103, and this rotor shaft 113 is supported to float in the air and is subjected to position control by, for example, a magnetic bearing of five-axis control. The rotating body 103 is generally made of a metal such as aluminum or an aluminum alloy.

[0018] Upper radial direction electromagnets 104 are disposed to form pairs of four electromagnets on the X axis and the Y axis. Four upper radial direction sensors 107 are provided in proximity to these upper radial direction electromagnets 104 and in association with the respective upper radial direction electromagnets 104. As the upper radial direction sensor 107, for example, an inductance sensor, an eddy current sensor, or the like that includes a conductive winding is used, and the upper radial direction sensor 107 detects the position of the rotor shaft 113 on the basis of a change in the inductance of this conductive winding that changes according to the position of the rotor shaft 113. This upper radial direction sensor 107 is configured to detect displacement in a radial direction of the rotor shaft 113, i.e., the rotating body 103 fixed to the rotor shaft 113, and sends a detection result to a control device not shown in figures.

[0019] In this control device, for example, a compensation circuit that has a PID adjustment function generates an excitation control command signal of the upper radial direction electromagnets 104 on the basis of a position signal detected by the upper radial direction sensor 107, an amplifier circuit 150 (described later) illustrated in Fig. 2 controls excitation of the upper radial direction electromagnets 104 on the basis of this excitation control command signal, such that a position on the upper side in the radial direction of the rotor shaft 113 is adjusted.

[0020] Furthermore, this rotor shaft 113 is formed using a highly permeable material (such as iron and stainless steel) or the like, and is attracted by the magnetic forces of the upper radial direction electromagnets 104. This adjustment is performed independently in each of an X axis direction and a Y axis direction. Furthermore, lower radial direction electromagnets 105 and lower radial direction sensors 108 are disposed similarly to the upper radial direction electromagnets 104 and the upper radial direction sensors 107 to adjust a position on a lower side in the radial direction of the rotor shaft 113 similar to the position on the upper side in the radial direction.

[0021] Furthermore, axial direction electromagnets 106A and 106B are disposed sandwiching from upper and lower sides a disc-shaped metal disc 111 provided at a lower portion of the rotor shaft 113. The metal disc 111 is made of a highly permeable material such as iron. An axial direction sensor 109 is provided to detect displacement in an axial direction of the rotor shaft 113, and is configured to send an axial direction position signal to the control device.

[0022] Furthermore, in this control device, for example, a compensation circuit that has a PID adjustment function generates an excitation control command signal of each of the axial direction electromagnet 106A and the axial direction electromagnet 106B on the basis of the axial direction position signal detected by the axial direction sensor 109, the amplifier circuit 150 controls excitation of each of the axial direction electromagnet 106A and the axial direction electromagnet 106B on the basis of these excitation control command signals, such that the axial direction electromagnet 106A attracts the metal disc 111 upward by the magnetic force, and the axial direction electromagnet 106B attracts the metal disc 111 downward to adjust the position in the axial direction of the rotor shaft 113.

[0023] Thus, the control device appropriately adjusts the magnetic forces of these axial direction electromagnets 106A and 106B that act on the metal disc 111, causes the rotor shaft 113 to magnetically float in the axial direction, and holds the rotor shaft 113 in space in a non-contact manner. Note that the amplifier circuit 150 that controls excitation of the upper radial direction electromagnets 104, the lower radial direction electromagnets 105, and the axial direction electromagnets 106A and 106B will be described later.

[0024] On the other hand, a motor 121 includes a plurality of magnetic poles disposed in a circular shape to surround the rotor shaft 113. Each magnetic pole is controlled by the control device to drive and rotate the rotor shaft 113 by means of an electromagnetic force that acts between each magnetic pole and the rotor shaft 113. Furthermore, the motor 121 includes an unillustrated rotation speed sensor such as a Hall element, a resolver, or an encoder incorporated therein, and the rotation speed of the rotor shaft 113 is detected on the basis of a detection signal of this rotation speed sensor.

[0025] Furthermore, an unillustrated phase sensor is attached near, for example, the lower radial direction sensors 108 to detect the phase of rotation of the rotor shaft 113. The control device detects positions of the magnetic poles using the detection signals of this phase sensor and the rotation speed sensors.

[0026] A plurality of stator blades 123 (123a, 123b, 123c, and ...) are installed with a slight gap apart from the rotor blades 102 (102a, 102b, 102c, and ...). The rotor blades 102 (102a, 102b, 102c, and ...) are each formed inclining at a predetermined angle from a plane vertical to an axial line of the rotor shaft 113 to transport molecules of an intake gas in a lower direction by causing the molecules to collide against each other. The stator blades 123 (123a, 123b, 123c, and ...) are made of a metal such as aluminum, iron, stainless steel, and copper, or a metal such an alloy containing these metals as components.

[0027] Furthermore, the stator blades 123 are also formed inclining at a predetermined angle from the plane vertical to the axial line of the rotor shaft 113 likewise, and stages of the stator blades 123 and the stages of the rotor blades 102 are installed alternately toward the interior of the outer cylinder 127. Furthermore, the outer circumferential ends of the stator blades 123 are supported in a state where the stator blades 123 are inserted between a plurality of stacked stator blade spacers 125 (125a, 125b, 125c, and ...).

[0028] The stator blade spacer 125 is a ring-shaped member, and is made of a metal such as aluminum, iron, stainless steel, and copper, or a metal such an alloy containing these metals as components. The outer cylinder 127 is fixed to the outer circumferences of the stator blade spacers 125 with a slight gap apart therebetween. A base portion 129 is installed at a bottom portion of the outer cylinder 127. An outlet port 133 is formed in the base portion 129, and continues to an outside. The intake gas transported from a chamber (vacuum chamber) side to the inlet port 101 and then to the base portion 129 is sent to the outlet port 133.

[0029] Furthermore, thread groove spacers 131 are installed between the lower portions of the stator blade spacers 125 and the base portion 129. The thread groove spacer 131 is a cylindrical member made of a metal such as aluminum, copper, stainless steel, iron, or an alloy containing these metals as components, and has the inner circumferential surface in which a plurality of rows of spiral thread grooves 131a are engraved. A direction of the spirals of the thread grooves 131a is a direction in which the molecules of the intake gas are transported toward the outlet port 133 when the molecules move in a rotation direction of the rotor 103. At a lowermost portion of the rotor 103 that continues to the rotor blade 102 (102a, 102b, 102c, and ...), a cylindrical portion 102d hangs. The outer circumferential surface of this cylindrical portion 102d has a cylindrical shape, protrudes toward the inner circumferential surfaces of the thread groove spacers 131, and are in proximity with a predetermined gap apart from the inner circumferential surfaces of these thread groove spacers 131. The intake gas transported by the rotor blades 102 and the stator blades 123 to the thread grooves 131a is sent to the base portion 129 while being guided to the thread grooves 131a.

[0030] Hereinafter, a portion that has a function of exhausting the intake gas from the inlet port 101 to the outlet port 133 will be referred to as an exhaust portion 114, and a flow passage that goes from the inlet port 101 to the outlet port 133 and through which the intake gas flows will be referred to as a gas flow passage FP1. The exhaust portion 114 includes a turbine pump portion 115 that includes a plurality of stages of the rotor blades 102 and a plurality of stages of the stator blades 123, and a drag pump portion 116 that includes the thread grooves 131a and the cylindrical portion 102d.

[0031] The base portion 129 is a disc-shaped member that constitutes a base portion of the turbomolecular pump 100, and is generally made of a metal such as iron, aluminum, and stainless steel. Since the base portion 129 physically holds the turbomolecular pump 100, and also has a function of a heat conduction path, a metal such as iron, aluminum, and copper that has rigidity and a high thermal conductivity is preferably used therefor.

[0032] According to this configuration, when the rotor blades 102 are driven to rotate by the motor 121 together with the rotor shaft 113, the rotor blades 102 and the stator blades 123 function to suck the exhaust gas from the chamber through the inlet port 101. The rotation speed of the rotor blade 102 is generally 20000 rpm to 90000 rpm, and a circumferential speed at a distal end of the rotor blade 102 reaches 200 m / s to 400 m / s. The exhaust gas sucked through the inlet port 101 passes between the rotor blades 102 and the stator blades 123, and is transported to the base portion 129. At this time, frictional heat generated when the exhaust gas contacts the rotor blades 102, or conduction of heat generated by the motor 121 raises the temperatures of the rotor blades 102, and this heat is transmitted to the stator blades 123 side by radiation or conduction of the gaseous molecules of the exhaust gas or the like.

[0033] The stator blade spacers 125 are bonded to each other through the outer circumferential portions, and transmit, to the outside, heat received by the stator blades 123 from the rotor blades 102 and frictional heat generated when the exhaust gas contacts the stator blades 123.

[0034] Note that the case has been described above where the thread groove spacers 131 are installed on the outer circumference of the cylindrical portion 102d of the rotor 103, and the thread grooves 131a are engraved in the inner circumferential surfaces of the thread groove spacers 131. However, by contrast with this, there is also a case where thread grooves are engraved in the outer circumferential surface of the cylindrical portion 102d, and spacers having the cylindrical inner circumferential surfaces are disposed around the thread grooves.

[0035] According to the turbomolecular pump 100 according to the present embodiment, to prevent the intake gas sucked from the inlet port 101 from entering an electrical component including the upper radial direction electromagnets 104, the upper radial direction sensors 107, the motor 121, the lower radial direction electromagnets 105, the lower radial direction sensors 108, the axial direction electromagnets 106A and 106B, the axial direction sensors 109, and the like, the surroundings of the electrical component are covered with a stator column 122, and an interior of this stator column 122 is kept at a predetermined pressure by a purge gas.

[0036] The base portion 129 is provided with a purge gas introduction port 135, and a purge gas is introduced from this purge gas introduction port 135 to an inside of the stator column 122. The introduced purge gas is sent to the outlet port 133 through gaps between a protection bearing 120 and the rotor shaft 113, between a rotor and a stator of the motor 121, and between the stator column 122 and the rotor blades 102. Here, a flow passage that goes from the purge gas introduction port 135 to the stator column 122 and through which a purge gas flows will be referred to as a purge gas flow passage FP2.

[0037] Here, the turbomolecular pump 100 requires that a model is specified, and control is performed on the basis of individually adjusted unique parameters (e.g., some characteristics associated with the model). The above turbomolecular pump 100 includes an electronic circuit unit 141 in a main body to store these control parameters. The electronic circuit unit 141 includes electronic components such as a semiconductor memory such as an EEP-ROM and a semiconductor element for accessing the semiconductor memory, a substrate 143 for mounting these electronic components thereon, and the like. This electronic circuit part 141 is housed at, for example, a lower portion of the unillustrated rotation speed sensor near the center of the base portion 129 that constitutes the lower portion of the turbomolecular pump 100, and is closed by a bottom lid 145 having airtightness.

[0038] By the way, some process gas among process gases to be introduced in a chamber has the property that the process gas becomes a solid when the pressure of the process gas becomes higher than a predetermined value or the temperature of the process gas becomes lower than a predetermined value in a semiconductor manufacturing process. The pressure of the exhaust gas inside the turbomolecular pump 100 is the lowest at the inlet port 101, and is the highest at the outlet port 133. When the pressure of the process gas becomes higher than the predetermined value or the temperature of the process gas becomes lower than the predetermined value in the middle of transportation of the process gas from the inlet port 101 to the outlet port 133, the process gas becomes a solid state, and adheres to and deposits on the interior of the turbomolecular pump 100.

[0039] In a case where, for example, SiCl4 is used as the process gas for an Al etching device, a vapor pressure curve shows that a solid product (e.g., AlCl3) precipitates at a low vacuum state (760 [torr] to 10-2 [torr]) and at a low temperature (approximately 20 [°C]), and adheres to and deposits on the interior of the turbomolecular pump 100. Therefore, when the precipitate of the process gas deposits inside the turbomolecular pump 100, these deposits narrow a pump flow passage, and cause a decrease in performance of the turbomolecular pump 100. Furthermore, the above-described product readily solidifies and adheres at a portion of a high pressure such as the vicinity of the outlet port 133 or the vicinity of the thread groove spacers 131 in this situation.

[0040] Hence, to solve this problem, conventionally, an unillustrated heater and an annular water cooling pipe 149 are wound around the outer circumference of the base portion 129 or the like, and an unillustrated temperature sensor (e.g., thermistor) is buried in, for example, the base portion 129 to control heating of the heater and cooling of the water cooling pipe 149 in order to keep the temperature of the base portion 129 at a certain high temperature (setting temperature) on the basis of a signal of this temperature sensor (hereinafter, referred to as a TMS (Temperature Management System) below).

[0041] Furthermore, the turbomolecular pump 100 according to the present embodiment includes an intermediate introduction gas introduction port 137 for introducing an intermediate introduction gas in the turbomolecular pump 100. Note that details related to the intermediate introduction gas and the like will be described later.

[0042] Next, as for the turbomolecular pump 100 configured as described above, the amplifier circuit 150 that controls excitation of the upper radial direction electromagnets 104, the lower radial direction electromagnets 105, and the axial direction electromagnets 106A and 106B will be described. Fig. 2 illustrates a circuit diagram of this amplifier circuit 150.

[0043] In Fig. 2, an electromagnet winding 151 that constitutes the upper radial direction electromagnet 104 and the like includes one end connected to a positive electrode 171a of a power supply 171 with a transistor 161 interposed therebetween, and an other end connected to a negative electrode 171b of the power supply 171 with a current detection circuit 181 and a transistor 162 interposed therebetween. Furthermore, the transistor 161 and 162 are so-called power MOSFETs, and each adopt a structure that a diode is connected between a source and a drain of the transistor.

[0044] In this case, the transistor 161 includes a cathode terminal 161a of this diode connected to the positive electrode 171a, and an anode terminal 161b connected with the one end of the electromagnet winding 151. Furthermore, the transistor 162 includes a cathode terminal 162a of this diode connected to the current detection circuit 181, and an anode terminal 162b connected with the negative electrode 171b.

[0045] On the other hand, a current regeneration diode 165 includes a cathode terminal 165a connected to the one end of the electromagnet winding 151, and an anode terminal 165b connected to the negative electrode 171b. Furthermore, similar to this, a current regeneration diode 166 includes a cathode terminal 166a connected to the positive electrode 171a, and an anode terminal 166b connected to the other end of the electromagnet winding 151 with the current detection circuit 181 interposed therebetween. Furthermore, the current detection circuit 181 includes, for example, a Hall sensor-type current sensor and an electrical resistance element.

[0046] The amplifier circuit 150 configured as described above is associated with one electromagnet. Hence, in a case where the magnetic bearing performs five-axis control, and the number of the electromagnets 104, 105, 106A, and 106B is 10 in total, the same amplifier circuit 150 is configured for each electromagnet, and the 10 amplifier circuits 150 are connected in parallel to the power supply 171.

[0047] Furthermore, an amplifier control circuit 191 includes, for example, an unillustrated digital signal processor unit (hereinafter, referred to as a DSP unit) of the control device 200, and this amplifier control circuit 191 switches on / off of the transistors 161 and 162.

[0048] The amplifier control circuit 191 compares a current value (a signal that reflects this current value is referred to as a current detection signal 191c) detected by the current detection circuit 181, and a predetermined current command value. Furthermore, the size of a pulse width (pulse width times Tp1 and Tp2) produced in a control cycle Ts that is one cycle of PWM control is determined on the basis of this comparison result. As a result, gate drive signals 191a and 191b having this pulse width are output from the amplifier control circuit 191 to gate terminals of the transistors 161 and 162.

[0049] Note that, when, for example, the rotor 103 passes a resonance point during an operation of accelerating the rotation speed of the rotor 103 or disturbance occurs during a rated operation, it is necessary to control the position of the rotor 103 at a high speed and with a strong force. Hence, the power supply 171 uses, for example, a voltage of approximately 50 V to make it possible to rapidly increase (or decrease) the current flowing in the electromagnet winding 151. Furthermore, a capacitor (not illustrated) is generally connected between the positive electrode 171a and the negative electrode 171b of the power supply 171 to stabilize the power supply 171.

[0050] According to this configuration, when both of the transistors 161 and 162 are turned on, the current (hereinafter, referred to as an electromagnet current iL) flowing in the electromagnet winding 151 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 one is turned off, a so-called flywheel current is held. Furthermore, by causing the flywheel current to flow in the amplifier circuit 150 in this way, it is possible to reduce hysteresis loss in the amplifier circuit 150, and minimize power consumption as the entire circuit. Furthermore, by controlling the transistors 161 and 162 in this way, it is possible to reduce high frequency noise such as a harmonic produced in the turbomolecular pump 100. Furthermore, by measuring this flywheel current by the current detection circuit 181, it is possible to detect the electromagnet current iL flowing in the electromagnet winding 151.

[0052] That is, when a detected current value is smaller than the current command value, both of the transistors 161 and 162 are turned on for a time corresponding to the pulse width time Tp1 only once during the control cycle Ts (e.g., 100 µs) as illustrated in Fig. 3. Hence, the electromagnet current iL during this period increases toward a current value iLmax that can be caused to flow from the positive electrode 171a to the negative electrode 171b via the transistors 161 and 162.

[0053] On the other hand, when the detected current value is larger than the current command value, both of the transistors 161 and 162 are turned off for a time corresponding to the pulse width time Tp2 only once during the control cycle Ts as illustrated in Fig. 4. Hence, the electromagnet current iL during this period decreases toward a current value iLmin that can be regenerated from the negative electrode 171b to the positive electrode 171a via the diodes 165 and 166.

[0054] Furthermore, in the either case, one of the transistors 161 and 162 is turned on after the pulse width times Tp1 and Tp2 pass. Hence, during this period, the flywheel current is held in the amplifier circuit 150.

[0055] Here, the above-described intermediate introduction gas will be described. The intermediate introduction gas is a gas that has higher viscosity than that of the intake gas, and, in a case where, for example, the intake gas is the hydrogen gas, a nitrogen gas or an argon gas is used as the intermediate introduction gas. Note that the intermediate introduction gas is not limited to different types of gases from the intake gas, and may be, for example, a gas that is the same type as the intake gas and whose viscosity is enhanced by raising the temperature.

[0056] In the turbomolecular pump 100 according to the present embodiment, the intermediate introduction gas is introduced from the introduction gas introduction port 137 illustrated in Fig. 5 into the turbomolecular pump 100. The intermediate introduction gas introduced in the turbomolecular pump 100 flows through an illustrated introduction flow passage FP3. The stator blade spacer 125a according to the present embodiment includes a connection port 138 that penetrates the stator blade spacer 125a in the radial direction, and the connection port 138 is located on the exhaust downstream side of the rotor blades 102a as illustrated. That is, the introduction flow passage FP3 is connected via the connection port 138 to the gas flow passage FP1 on the exhaust downstream side of the rotor blade 102a that is the closest to the inlet port 101 in the exhaust portion 114.

[0057] According to the turbomolecular pump 100 configured as described above, not only the intake gas sucked from the inlet port 101, but also the intermediate introduction gas having passed through the connection port 138 flow in the gas flow passage FP1. That is, the viscosity of the mixed gas of the intake gas and the intermediate introduction gas becomes higher than that of the intake gas alone, so that a compression effect in the exhaust portion 114 (the drag pump portion 116 in particular) improves. Consequently, the turbomolecular pump 100 can improve back pressure performance compared to a case where the intermediate introduction gas is not introduced even if the intake gas is a gas such as the hydrogen gas having lower viscosity.

[0058] Hereinafter, the back pressure performance of the turbomolecular pump 100 according to the present embodiment will be described with reference to Fig. 10. In Fig. 10, the horizontal axis indicates a pressure (back pressure) at the outlet port 133, and the vertical axis indicates a pressure (suction pressure) at the inlet port 101. Furthermore, the broken line in Fig. 10 indicates a relationship between a back pressure and a suction pressure in a case where only the intake gas is sucked without introducing the intermediate introduction gas, and the solid line in Fig. 10 indicates a relationship between a back pressure and a suction pressure in a case where the intake gas is sucked while the intermediate introduction gas is introduced. Furthermore, in Fig. 10, the intake gas is a hydrogen gas, and the intermediate introduction gas is a nitrogen gas.

[0059] As is clear from Fig. 10, it has been confirmed that, although the suction pressure also rises when the back pressure rises, a rise in the suction pressure is suppressed even if the back pressure rises in a case where the intermediate introduction gas is introduced compared to a case where the intermediate introduction gas is not introduced, and the back pressure performance improves.

[0060] A configuration related to the intermediate introduction gas in the turbomolecular pump 100 can be variously changed. For example, the turbomolecular pump 100 may be changed to the configuration illustrated in Fig. 6.

[0061] The turbomolecular pump 100 illustrated in Fig. 6 includes a valve 139. Furthermore, the connection port 138 may be provided at an outlet of a through-hole formed inside the thread groove spacer 131. Note that, in the present embodiment, the introduction flow passage FP3 through which the intermediate introduction gas flows is a flow passage that goes from the valve 139 to the connection port 138 via the introduction gas introduction port 137. Furthermore, the valve 139 can adjust the flow rate of the intermediate introduction gas flowing through the introduction flow passage FP3.

[0062] In the turbomolecular pump 100 illustrated in Fig. 6, the introduction flow passage FP3 is connected to the vicinity of the middle of the drag pump portion 116 in the exhaust portion 114 via the connection port 138. That is, the mixed gas of the intake gas and the intermediate introduction gas flows on a downstream side of the vicinity of the middle of the drag pump portion 116 in the exhaust portion 114, and therefore the compression effect improves at this portion compared to a case where only the intake gas flows through the gas flow passage FP1. Consequently, the turbomolecular pump 100 illustrated in Fig. 6 can also improve the back pressure performance compared to a case where the intermediate introduction gas is not introduced. Note that improvement of the compression effect cannot be expected even when the amount of the intermediate introduction gas to be introduced in the gas flow passage FP1 is too large or too little. On the other hand, by providing the valve 139 as in the present embodiment, it is possible to easily change the amount of the intermediate introduction gas, so that it is possible to adjust the amount of the intermediate introduction gas, and further improve the back pressure performance.

[0063] Furthermore, the turbomolecular pump 100 may be changed to the configuration illustrated in Fig. 7. The turbomolecular pump 100 illustrated in Fig. 7 includes the connection port 138 between the turbine pump portion 115 and the drag pump portion 116 in the exhaust portion 114. That is, the introduction flow passage FP3 is connected to the gas flow passage FP1 between the turbine pump portion 115 and the drag pump portion 116. According to this configuration, the mixed gas of the intake gas and the intermediate introduction gas flows to the drag pump portion 116, so that the compression effect at the drag pump portion 116 improves.

[0064] Note that, while the mixed gas of the intake gas and the intermediate gas basically flows on the downstream side of the vicinity of the middle of the drag pump portion 116 in the turbomolecular pump 100 illustrated in Fig. 6, the mixed gas basically flows in the entire drag pump portion 116 in the turbomolecular pump 100 illustrated in Fig. 7, so that the compression effect further improves. Furthermore, the mixed gas of the intake gas and the intermediate introduction gas flows in the entire drag pump portion 116 in the turbomolecular pump 100 illustrated in Fig. 5, so that further improvement of the compression effect is expected compared to the turbomolecular pump 100 in Fig. 6. Note that the number of molecules of a gas that contacts the rotor blades 102 and the stator blades 123 at a time when the mixed gas flows at the turbine pump portion 115 increases in the turbomolecular pump 100 in Fig. 5 compared to a case where only the intake gas flows, thereby the rotor blades 102 and the stator blades 123 generate more heat, and, as a result, the temperature readily reaches an allowable upper limit temperature of the turbomolecular pump 100. Therefore, it is necessary to suppress an allowable flow rate of the intake gas to suppress a rise in the temperature. On the other hand, the mixed gas basically flows on the downstream side of the turbine pump portion 115 in the turbomolecular pump 100 illustrated in Fig. 7, so that it is possible to increase the allowable flow rate of the intake gas compared to the turbomolecular pump 100 in Fig. 5.

[0065] The turbomolecular pump 100 may be changed to the configuration illustrated in Fig. 8. In the turbomolecular pump 100 illustrated in Fig. 8, a purge gas joint 135a including the purge gas introduction port 135 is branched into two outside the base portion 129. The one branched purge gas joint 135a continues to the inside the stator column 122, and the other branched purge gas joint 135a continues to the connection port 138 located between the turbine pump portion 115 and the drag pump portion 116. In the present embodiment, the purge gas flow passage FP2 is a flow passage that goes from the purge gas introduction port 135 to the stator column 122 via the one purge gas joint 135a, and the introduction flow passage FP3 is a flow passage that goes from the other purge gas joint 135a to the connection port 138. That is, the introduction flow passage FP3 is branched from the purge gas flow passage FP2, and the purge gas is used as the intermediate introduction gas that flows through the introduction flow passage FP3.

[0066] The turbomolecular pump 100 illustrated in Fig. 8 can use the purge gas as the intermediate introduction gas, so that it is possible to simplify the entire configuration related to the turbomolecular pump 100 including an ancillary facility compared to a case where the purge gas and the intermediate introduction gas are separately prepared. Furthermore, in a case where the turbomolecular pump 100 in Fig. 8 is used, it is particularly preferable that the intake gas is the hydrogen gas, and the purge gas is the nitrogen gas. That is, the nitrogen gas has higher viscosity than that of the hydrogen gas, so that it is possible to improve the back pressure performance compared to a case where the nitrogen gas is not introduced as the intermediate introduction gas. Furthermore, the nitrogen gas is a low-cost inert gas, so that it is possible to safely operate the turbomolecular pump 100, and suppress cost.

[0067] The turbomolecular pump 100 may be changed to the configuration illustrated in Fig. 9. In the turbomolecular pump 100 illustrated in Fig. 9, through-holes are formed in the base portion 129 and the thread groove spacer 131. An inlet of this through-hole continues to the purge gas flow passage FP2. Furthermore, this through-hole continues to the connection port 138 located between the turbine pump portion 115 and the drag pump portion 116. Note that, in the present embodiment, the introduction flow passage FP3 is a flow passage that goes from the inlet of this through-hole to the connection port 138. Here, as for the purge gas flow passage FP2 that continues from the purge gas introduction port 135 to the inside of the stator column 122, a flow passage located outside the turbomolecular pump 100 (i.e., inside the purge gas joint 135b) will be referred to as an outer purge gas flow passage FP2A, and a flow passage located inside the turbomolecular pump 100 will be referred to as an inner purge gas flow passage FP2B.

[0068] In the turbomolecular pump 100 illustrated in Fig. 9, the introduction flow passage FP3 is branched from the inner purge gas flow passage FP2B, and connected to the gas flow passage FP1. That is, this turbomolecular pump 100 can also use the purge gas as the intermediate introduction gas, so that it is possible to simplify the entire configuration related to the turbomolecular pump 100 compared to a case where the purge gas and the intermediate introduction gas are separately prepared. Furthermore, although the introduction flow passage FP3 is provided outside the turbomolecular pump 100, and therefore the turbomolecular pump 100 illustrated in Fig. 8 requires a space for the introduction flow passage FP3, the introduction flow passage FP3 is provided inside the turbomolecular pump 100, so that the turbomolecular pump 100 in Fig. 9 can secure a space around the turbomolecular pump 100.

[0069] Note that, in a case where the purge gas is used as the intermediate introduction gas as in the turbomolecular pumps 100 illustrated in Figs. 8 and 9, the inner diameter of at least part of the introduction flow passage FP3 is preferably smaller than the inner diameter of the purge gas flow passage FP2. In the present embodiment, as illustrated in Figs. 8 and 9, the connection port 138 of the 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 passage FP2.

[0070] The amount of the purge gas to be used as the intermediate introduction gas is generally less than the amount of the purge gas to be introduced in the stator column 122. Consequently, by making the inner diameter of at least part of the introduction flow passage FP3 smaller than the inner diameter of the purge gas flow passage FP2, it is easy to exhibit the desired back pressure performance from the beginning. Furthermore, it is easy to increase a small inner diameter when the amount of the purge gas flowing through the introduction flow passage FP3 is adjusted to improve the back pressure performance, so that it is easy to perform adjustment. Note that the amount of the purge gas flowing through the introduction flow passage FP3 may be adjusted using the above-described valve 139 (see Fig. 6).

[0071] Although the embodiment of the present invention has been described above, the present invention is not limited to the specific embodiment, and can be variously modified, altered, or combined within the range of the gist of the present invention recited in the claims unless limited in particular in the above description. Furthermore, the effect in the above embodiment is merely an exemplary effect produced by the present invention, and does not mean that the effect according to the present invention is limited to the above effect.

[0072] For example, the drag pump portion 116 is not limited to a Holbeck-type pump mechanism that uses the above-described thread grooves 131a, and may adopt, for example, other pump mechanisms such as a Siegbahn pump mechanism.[Reference Signs List]

[0073] 100Turbomolecular pump (vacuum pump) 101Inlet port 102Rotor blade 103Rotating body 114Exhaust portion 115Turbine pump portion 116Drag pump portion 122Stator column 123Stator blade 133Outlet port 139Valve FP1Gas flow passage FP2Purge gas flow passage FP2AOuter purge gas flow passage FP2BInner purge gas flow passage FP3Introduction flow passage

Claims

1. A vacuum pump comprising an exhaust portion constituted of a turbine pump portion, which includes a plurality of stages of rotor blades and a plurality of stages of stator blades, and a drag pump portion, which is located on a further toward exhaust downstream side than the turbine pump portion, and exhausting from an outlet port through a gas flow passage an intake gas sucked from an inlet port by the exhaust portion, the vacuum pump further comprising an introduction flow passage through which an intermediate introduction gas having viscosity higher than viscosity of the intake gas is introduced, wherein the introduction flow passage is connected to the gas flow passage on the further toward exhaust downstream side than a rotor blade, from among the plurality of stages of the rotor blades, that is the closest to the inlet port in the exhaust portion.

2. The vacuum pump according to claim 1, further comprising a purge gas flow passage that supplies a purge gas to an inside of a stator column provided on an inner circumferential side of a rotating body provided with the rotor blades, the introduction flow passage is branched from the purge gas flow passage, and the purge gas is used as the intermediate introduction gas.

3. The vacuum pump according to claim 2, wherein the purge gas flow passage is constituted of an outer purge gas flow passage located outside the vacuum pump, and an inner purge gas flow passage located inside the vacuum pump, and the introduction flow passage is branched from the inner purge gas flow passage, and is connected to the gas flow passage.

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

5. The vacuum pump according to claim 1, wherein the introduction flow passage includes a valve that can adjust a flow rate of the intermediate introduction gas.

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

Images