JP7566540B2 - Vacuum pump - Google Patents

Description

The present invention relates to a vacuum pump, and in particular to a vacuum pump that can reduce the amount of deposits (commonly known as "deposits") that are generated when gas solidifies inside the vacuum pump and accumulate in gaps.

In recent years, in the process of forming semiconductor elements from wafers, which are the substrates to be processed, a method has been adopted in which the wafers are processed in a processing chamber of semiconductor manufacturing equipment maintained at a high vacuum to create the product semiconductor elements. In semiconductor manufacturing equipment that processes wafers in a vacuum chamber, a vacuum pump equipped with a turbo molecular pump section and a threaded groove pump section is used to achieve and maintain a high degree of vacuum.

The turbomolecular pump section has a rotatable rotor made of thin metal inside the casing and fixed blades fixed to the casing. The rotors are operated at high speeds, for example several hundred meters per second, and the process gas used in the processing that enters from the intake side is compressed inside the pump and exhausted from the exhaust side.

The process gas molecules taken in from the intake side of the vacuum pump are at a high temperature immediately after being sucked in, and are cooled in the compression process that accompanies the movement to the exhaust side as the rotor rotates in the vacuum pump. When the process gas is cooled, it solidifies, and the solidified by-products adhere to the fixed blades and the inner surface of the outer cylinder (casing), etc., and accumulate as deposits. The by-products are generally chlorine-based or sulfur fluorine-based gases. The lower the degree of vacuum and the higher the pressure, the higher the sublimation temperature of these gases, and the more likely the gases are to solidify and accumulate inside the vacuum pump. If reaction products accumulate inside the vacuum pump, the flow path of the reaction products may be narrowed, and the compression and exhaust performance of the vacuum pump may decrease. On the other hand, in gas transfer parts using aluminum or stainless steel for the rotor and fixed blades, if the temperature becomes too high, the strength of the rotor and fixed blades may decrease and break during operation. In addition, there is a risk that the electric motor that rotates the rotor and electrical equipment installed in the vacuum pump may not perform as desired when the temperature becomes high. Therefore, the vacuum pump requires temperature control to maintain a specified temperature.

Therefore, as a vacuum pump that suppresses the accumulation of reaction products, a structure is also known in which a cooling device or a heating device is provided around the stator to control the temperature in the gas flow path, allowing the gas in the gas flow path to be transported without solidifying (see, for example, Patent Document 1).

However, the gas sucked into the vacuum pump has a characteristic that the sublimation temperature increases as the degree of vacuum increases and the pressure increases, making the gas more likely to solidify and accumulate inside the vacuum pump. On the other hand, the gas transfer section, which is made up of rotors, fixed blades, etc., has a problem of losing strength when it becomes too hot, and can have a negative effect on the performance of the electrical equipment and electric motor inside the vacuum pump. Therefore, it is preferable to control the temperature so that the solidification of the gas inside the vacuum pump can be suppressed while the vacuum pump is operating normally, without negatively affecting the performance of the electrical equipment and electric motor inside the vacuum pump and without reducing the strength of the gas transfer section.

For example, as shown in the vacuum pump 10 in Figures 9 and 10, the upper gas transfer section 11 is divided into a cooling side stator 17A, which is located in the cooling range that requires cooling, and a lower gas transfer section 12, which is located in the heating range that requires heating. A gap 15 is provided between the cooling side stator 17A and the heating side stator 17B, making the cooling side stator 17A and the heating side stator 17B independent from each other, so that the temperature of the upper gas transfer section 11 and the temperature of the lower gas transfer section 12 do not affect each other. The cooling side stator 17A and the heating side stator 17B are positioned by holding the fixed blade spacer 14 with a bolt 19.

Japanese Patent Application Publication No. 10-205486

In a structure in which the cooling side stator 17A and the heating side stator 17B are held in position by the bolts 19, the size of the gap 15 between the cooling side stator 17A and the heating side stator 17B (dimension in the axial direction) changes depending on the magnitude of the force tightening the bolts 19, the deformation amount of the O-ring 18 due to tightening, or the type of the fixed blade spacer 14. If the gap 15 is positioned facing the radial circumferential surface of the rotor 16, when the rotor 16 rotates, the process gas molecules transferred in the tangential and downstream directions by the rotor 16 tend to move toward the gap 15 (the number of gas molecules increases). The gas that enters the gap 15 is cooled by the cooling side stator 17A, solidifies in the gap 15, and accumulates as a by-product. This deposit narrows the width of the gap 15, reducing the insulation effect and changing the temperature distribution inside the pump. Therefore, maintenance work is required to remove the deposits accumulated in the gap 15 by periodically disassembling the vacuum pump 10, etc. This maintenance work caused problems such as poor productivity.

Therefore, a technical problem arises that must be solved in order to provide a vacuum pump that can reduce the flow of gas (the number of gas molecules) toward the gap provided for insulation, reduce the amount of by-products that accumulate in the gap, extend the interval between maintenance operations, and improve productivity. The present invention aims to solve this problem.

The present invention has been proposed in order to achieve the above-mentioned object, and the invention described in claim 1 provides a vacuum pump including a casing having an intake port and an exhaust port, a rotor shaft rotatably supported inside the casing, multiple stages of rotors rotatable together with the rotor shaft, multiple stages of fixed blades fixed to the casing and disposed between the multiple stages of rotors, and a cooling-side stator and a heating-side stator which hold the multiple stages of fixed blades at a predetermined interval, wherein an opening of a gap of a predetermined width which insulates between the cooling-side stator and the heating-side stator is provided in a position which does not face the outer circumferential surface of the rotors in the axial direction of the rotor shaft, the opening being provided in a central position between a lowermost rotor of the multiple stages of rotors located within a cooling range cooled by the cooling-side stator and an uppermost rotor of the multiple stages of rotors located within a heating range heated by the heating-side stator, and the width dimension of the opening in the axial direction is set to 0.1 mm to 2.0 mm.

According to this configuration, the opening of the gap with a predetermined width for insulating between the cooling side stator and the heating side stator is provided in a position that does not face the outer peripheral surface of the rotor blade in the axial direction of the rotor shaft. Therefore, even if part of the gas is blown toward the inner peripheral surface of the stator by the centrifugal force caused by the rotation of the rotor blade, the opening of the gap is provided in a shifted position that does not face the outer peripheral surface of the rotor blade, so that the amount of gas that enters the opening of the gap is extremely small, and the amount of deposits that accumulate in the gap can be reduced. This makes it possible to extend the intervals between maintenance work, contributing to improved productivity.

The invention described in claim 2 provides a vacuum pump having the configuration described in claim 1, in which the shape of the gap has a first gap portion that extends horizontally toward the outside in a radial direction perpendicular to the axial direction, and a second gap portion that extends from the outer end of the first gap portion further outward in the radial direction and along the downstream side in the axial direction.

With this configuration, when the process gas that has entered the first gap from the opening attempts to move further in, it hits the wall of the next, second gap, which acts as a resistance to the flow into the gap. This reduces the amount of process gas that enters the gap from the opening, further reducing the amount of deposits generated by the process gas.

The invention described in claim 3 provides a vacuum pump having the configuration described in claim 1 or 2, in which the shape of the gap has a third gap portion that extends along the downstream side in the axial direction.

With this configuration, when the process gas tries to enter the gap from the opening, it hits the third gap portion toward the bottom as a wall immediately in front of the opening, creating resistance to the flow of the process gas toward the gap. This reduces the amount of process gas that enters the gap from the opening, further reducing the amount of deposits generated by the process gas.

The invention described in claim 4 provides a vacuum pump having the configuration described in any one of claims 1 to 3, in which the shape of the gap has a fourth gap portion that extends radially outwardly perpendicular to the axial direction and upstream in the axial direction.

According to this configuration, the shape of the longitudinal section of the gap has a fourth gap portion that extends radially outward perpendicular to the axial direction and upstream in the axial direction. Therefore, the process gas that enters the gap from the opening collides with the fourth gap portion once, which becomes resistance to the flow of the process gas toward the gap. This reduces the amount of process gas that enters the gap from the opening, and further reduces the amount of deposits generated by the process gas.

The invention described in claim 5 provides a vacuum pump having the configuration described in any one of claims 1 to 4, in which the shape of the gap has an eaves portion above the opening that protrudes toward the inside of the casing beyond the opening.

With this configuration, when the casing is cut longitudinally in the axial direction, the shape of the longitudinal section of the gap is such that, at the top of the opening of the gap formed on the inner peripheral surface of the casing, there is an eaves portion that protrudes further inward into the casing than the opening, so the flow of the process gas flowing from the upstream side is controlled by the eaves portion and it can be directed toward the downstream side different from the opening, rather than proceeding in the direction of the opening of the gap. This reduces the amount of process gas that enters the gap from the opening, and further reduces the amount of deposits generated by the process gas.

According to the present invention, the amount of process gas entering the gap provided for thermal insulation can be reduced, and the amount of deposits generated by the process gas that accumulate in the gap can be reduced. This can extend the interval between maintenance work required to remove the deposits in the gap, thereby improving productivity.
In addition, the insulating effect of the gap is improved, making it possible to precisely control the temperature within a range that does not adversely affect the performance of the electrical equipment installed in the vacuum pump or the electric motor that rotates the rotor, and does not affect the strength of the rotor or stator.
Furthermore, the vacuum pump can be operated normally while controlling the solidification of the process gas.

1 is a vertical sectional view of a turbomolecular pump shown as an example of a vacuum pump according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of an amplifier circuit in the turbo molecular pump. 4 is a time chart showing an example of control when a current command value detected by an amplifier circuit in the turbo molecular pump is larger than a detection value. 5 is a time chart showing an example of control when a current command value detected by an amplifier circuit in the turbo molecular pump is smaller than a detection value. 2A is an enlarged cross-sectional view of a portion of the turbo molecular pump shown in FIG. 1 , and FIG. 2B is an enlarged cross-sectional view of a further portion for explaining the shape of a gap. 2A is a partially enlarged view corresponding to part A in FIG. 1 , and FIG. 2B is a further enlarged cross-sectional view of part A for explaining the shape of the gap. 1B is a cross-sectional view showing another modified example of the present invention, in which (a) is a partially enlarged view corresponding to part A in FIG. 1, and (b) is a further enlarged cross-sectional view of (a) for explaining the shape of the gap. 1B is a cross-sectional view showing a further modified example of the present invention, in which FIG. 1B is a further enlarged view of a part of FIG. 1A for explaining the shape of the gap. FIG. 1 is a vertical sectional view of a turbomolecular pump shown as an example of a conventional vacuum pump. FIG. 10 is a partial enlarged view corresponding to part B in FIG. 9 .

In order to achieve the object of providing a vacuum pump that can reduce the flow of gas (the number of gas molecules) toward gaps provided for thermal insulation, reduce the amount of by-products that accumulate in the gaps, and extend the interval between maintenance operations to improve productivity, the present invention provides a vacuum pump that includes a casing having an intake port and an exhaust port, a rotor shaft rotatably supported inside the casing, multiple stages of rotor blades that can rotate together with the rotor shaft, multiple stages of fixed blades that are fixed to the casing and disposed between the multiple stages of rotor blades, a heating side stator and a cooling and a cooling-side stator, wherein an opening of a gap of a predetermined width that insulates between the heating- side stator and the cooling-side stator is provided at a position not facing the outer circumferential surface of the rotor blades in the axial direction of the rotor shaft, the opening being provided at a central position between a lowermost rotor blade of the multiple stages of rotor blades located within a cooling range cooled by the cooling-side stator and an uppermost rotor blade of the multiple stages of rotor blades located within a heating range heated by the heating-side stator, and the width dimension of the opening in the axial direction is set to 0.1 mm to 2.0 mm.

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. In the following embodiment, when the number, numerical value, amount, range, etc. of components is mentioned, the number is not limited to the specific number, and may be more or less than the specific number, unless otherwise specified or when it is clearly limited to a specific number in principle.

In addition, when referring to the shape or positional relationship of components, etc., this includes things that are substantially similar or similar to that shape, etc., unless otherwise specified or considered in principle to be clearly different.

In addition, drawings may exaggerate characteristic parts to make the features easier to understand, and the dimensional ratios of components may not be the same as in reality. In addition, in cross-sectional views, hatching of some components may be omitted to make the cross-sectional structure of the components easier to understand.

In addition, in the following description, expressions indicating directions such as up/down and left/right are not absolute, but are appropriate when each part of the turbomolecular pump of the present invention is in the orientation depicted, but if the orientation changes, they should be interpreted differently depending on the change in orientation. Also, the same symbols are used for the same elements throughout the description of the embodiments.

Figure 1 shows one embodiment of a turbomolecular pump 100 as a vacuum pump according to the present invention, and FIG. 1 is a longitudinal cross-sectional view of the pump.

In FIG. 1, the turbomolecular pump 100 has an intake port 101 formed at the upper end of an outer cylinder 127 serving as a cylindrical housing. Inside the outer cylinder 127 is a rotor 103 having multiple rotors 102 (102a, 102b, 102c, ...) formed radially and in multiple stages around its periphery as turbine blades for sucking in and exhausting gas. A rotor shaft 113 is attached to the center of the rotor 103, and this rotor shaft 113 is supported in the air and its position is controlled by, for example, a five-axis controlled magnetic bearing.

The upper radial electromagnets 104 are arranged in pairs on the X-axis and Y-axis. Four upper radial sensors 107 are provided adjacent to the upper radial electromagnets 104 and corresponding to each of the upper radial electromagnets 104. The upper radial sensors 107 are, for example, inductance sensors or eddy current sensors having conductive windings, and detect the position of the rotor shaft 113 based on the change in inductance of the conductive windings, which changes according to the position of the rotor shaft 113. The upper radial sensors 107 are configured to detect the radial displacement of the rotor shaft 113, i.e., the rotating body 103 fixed thereto, and send the detected displacement to a control device (not shown).

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 the position signal detected by the upper radial sensor 107, and the amplifier circuit 150 (described later) shown in FIG. 2 controls the excitation of the upper radial electromagnet 104 based on this excitation control command signal, thereby adjusting the upper radial position of the rotor shaft 113.

The rotor shaft 113 is made of a material with high magnetic permeability (iron, stainless steel, etc.) and is attracted by the magnetic force of the upper radial electromagnet 104. Such adjustment is performed independently in the X-axis direction and the Y-axis direction. The lower radial electromagnet 105 and the lower radial sensor 108 are arranged in the same manner as the upper radial electromagnet 104 and the upper radial sensor 107, and adjust the lower radial position of the rotor shaft 113 in the same manner as the upper radial position.

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 high magnetic permeability material such as iron. An axial sensor 109 is provided to detect the axial displacement of rotor shaft 113, and the axial position signal is sent to the control device.

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

In this way, the control device appropriately adjusts the magnetic force 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.

On the other hand, the motor 121 has multiple magnetic poles arranged circumferentially to surround the rotor shaft 113. Each magnetic pole is controlled by a control device so as to rotate the rotor shaft 113 via electromagnetic forces acting between the magnetic poles and the rotor shaft 113. In addition, the motor 121 incorporates a rotational speed sensor, such as a Hall element, resolver, or encoder (not shown), and the rotational speed of the rotor shaft 113 is detected by the detection signal of this rotational speed sensor.

In addition, 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 of both this phase sensor and the rotation speed sensor to detect the position of the magnetic poles.

Multiple fixed blades 123 (123a, 123b, 123c, ...) are arranged with a small gap between the rotor blades 102 (102a, 102b, 102c, ...). Each rotor blade 102 is formed at a predetermined angle from a plane perpendicular to the axis of the rotor shaft 113 in order to transport exhaust gas molecules downward by collision.

The fixed blades 123 are also 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 rotor blades 102 toward the inside of the outer cylinder 127. The outer peripheral end of the fixed blades 123 is supported by being inserted between a plurality of stacked fixed blade spacers 125 (125a, 125b, 125c, ...).

The fixed wing spacer 125 is a ring-shaped member, and is made of metals such as aluminum, iron, stainless steel, copper, or alloys containing these metals. An outer cylinder 127 is fixed to the outer periphery of the fixed wing spacer 125 with a small gap between them. A base portion 129 is disposed at the bottom of the outer cylinder 127. An exhaust port 133 is formed in the base portion 129, and is connected to the outside. Exhaust gas that enters the intake port 101 from the chamber side and is transferred to the base portion 129 is sent to the exhaust port 133.

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 part 129. The threaded spacer 131 is a cylindrical member made of metal such as aluminum, copper, stainless steel, iron, or an alloy containing these metals, and has a plurality of helical thread grooves 131a engraved on its inner peripheral surface. The helical direction of the thread groove 131a is the direction in which the molecules of the exhaust gas are transported toward the exhaust port 133 when they move in the rotation direction of the rotor 103. A cylindrical part 102E hangs down from the lowest part of the rotor 103, which is connected to the rotor vanes 102 (102a, 102b, 102c, ...). The outer peripheral surface of the cylindrical part 102E is cylindrical and protrudes toward the inner peripheral surface of the threaded spacer 131, and is adjacent to the inner peripheral surface of the threaded spacer 131 with a predetermined gap therebetween. The exhaust gas transferred to the thread groove 131a by the rotor 102 and the fixed blade 123 is guided by the thread groove 131a and sent to the base portion 129.

The base portion 129 is a disk-shaped member that forms the base of the turbomolecular pump 100, and is generally made of a metal such as iron, aluminum, or stainless steel. 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.

In this configuration, when the rotor 102 is rotated by the motor 121 together with the rotor shaft 113, the rotor 102 and the fixed blades 123 act to draw exhaust gas 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 fixed blades 123 and is transferred to the base portion 129. At this time, the temperature of the rotor 102 rises due to frictional heat generated when the exhaust gas comes into contact with the rotor 102 and the conduction of heat generated by the motor 121, but this heat is transferred to the fixed blades 123 side by radiation or conduction by gas molecules of the exhaust gas.

The fixed blade spacers 125 are joined together at their outer periphery and transmit to the outside heat received by the fixed blades 123 from the rotor blades 102 and frictional heat generated when exhaust gas comes into contact with the fixed blades 123.

In the above description, the threaded spacer 131 is disposed on the outer periphery of the cylindrical portion 102E of the rotor 103, and the thread groove 131a is engraved on the inner periphery of the threaded spacer 131. However, there are also cases where the opposite is true, that is, a thread groove is engraved on the outer periphery of the cylindrical portion 102E, and a spacer having a cylindrical inner periphery is disposed around it.

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 inside of the stator column 122 may be kept at a predetermined pressure by purging gas.

In this case, piping (not shown) is provided in the base portion 129, and purge gas is introduced through this piping. The introduced purge gas is sent to the exhaust port 133 through the gaps between the protective bearing 120 and the rotor shaft 113, between the rotor and stator of the motor 121, and between the stator column 122 and the inner cylindrical portion of the rotor blades 102.

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

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

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

Therefore, in order to solve this problem, conventionally, a heater (not shown) or a circular water-cooled tube 149 is wrapped around the outer periphery of the base portion 129, etc., and a temperature sensor (e.g., a thermistor) (not shown) is embedded in the base portion 129, and the heating of the heater and the cooling by the water-cooled tube 149 are controlled based on the signal from this temperature sensor to keep the temperature of the base portion 129 at a constant high temperature (set temperature) (hereinafter referred to as TMS; TMS; Temperature Management System).

Next, regarding the turbomolecular pump 100 configured in this manner, we will explain 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. A circuit diagram of this amplifier circuit 150 is shown in Figure 2.

In FIG. 2, one end of the electromagnet winding 151 constituting the upper radial electromagnet 104 etc. is connected to the positive pole 171a of the power supply 171 via the transistor 161, and the other end is connected to the negative pole 171b of the power supply 171 via the current detection circuit 181 and the 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.

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

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

The amplifier circuit 150 configured as above corresponds to one electromagnet. Therefore, if the magnetic bearing is controlled on 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.

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 and off.

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. Then, based on the result of this comparison, it determines the size of the pulse width (pulse width times Tp1, Tp2) to be generated within a control cycle Ts, which is one period of PWM control. As a result, gate drive signals 191a, 191b having this pulse width are output from the amplifier control circuit 191 to the gate terminals of transistors 161, 162.

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

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

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

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

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 equivalent to pulse width time Tp2 only once during control cycle Ts, as shown in FIG. 4. Therefore, during this period, the electromagnet current iL decreases from negative pole 171b to positive pole 171a toward a current value iLmin (not shown) that can be regenerated via diodes 165 and 166.

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

Inside the outer cylinder 127 as a casing, there is an upper group gas transfer section having the cooling side stator 110A (fixed blades 123a-123f) and the cooling side rotor 102A (rotor 102a-102g) arranged in the cooling range that requires cooling, and a lower group gas transfer section having the heating side stator 110B (fixed blades 123h-123j) and the cooling side rotor 102B (rotor 102h-102k) arranged in the heating range that requires heating. An O-ring 112 is disposed between the cooling side stator 110A and the heating side stator 110B, and a gap 114 is provided between the cooling side stator 110A and the heating side stator 110B by a predetermined distance, thereby making the cooling side stator 110A and the heating side stator 110B independent from each other, so that the temperature of the cooling side stator 110A and the temperature of the heating side stator 110B do not affect each other. The cooling side stator 110A and the heating side stator 110B are positioned by holding the fixed wing spacer 125 with a bolt 115. Also, in FIG. 1, reference numeral 152 denotes a temperature sensor that detects the temperature on the cooling side stator 110A side, reference numeral 153 denotes a temperature sensor that detects the temperature on the heating side stator 110B side, reference numeral 154 denotes a heater for heating the heating side stator 110B, and reference numeral 155 denotes a cooling pipe that cools the cooling side stator 110A.

On the other hand, between the cooling side rotor 102g of the upper group gas transfer section and the heating side rotor 102h of the lower group gas transfer section, which are close to the opening 114A of the gap 114 between the cooling side stator 110A and the heating side stator 110B, the positions of the rotors 102g and 102h are shifted axially, i.e., vertically, relative to the opening 114A so that neither the outer peripheral surface of the cooling side rotor 102g nor the outer peripheral surface of the heating side rotor 102h faces the opening 114A of the gap 114 directly face-on, and a gap of distance S is provided between the rotors 102g and 102h. It is preferable that the distance S be large enough that when the cooling side stator 110A and the heating side stator 110B are positioned by pressing them with bolts 115, even if either or both of the cooling side stator 110A and the heating side stator 110B move axially, they do not face the opening 114A of the gap 114 directly.
In addition, a preferable position for the opening 114A is considered to be approximately the center of the axial distance between the rotors 102g and 102h, taking into consideration the movement of process gas molecules by the rotors 102g and 102h. However, the position of the opening 114A is not limited to approximately the center, and for example, the opening 114A may be located downstream from the approximately center position, taking into consideration the movement of process gas molecules by the rotors 102g.

The width (axial dimension) of the opening 114A in the gap 114 is set to a predetermined width that makes it as difficult as possible for molecules to enter, taking into consideration the mean free path, which is the average distance that process gas molecules can travel without colliding with other molecules and changing course, and the insulating effect, etc. For example, the size of the gap 114 and the opening 114A is 0.1 mm to 2.0 mm, and more preferably 0.5 mm to 1.0 mm.

In the structure of this embodiment, as shown in FIG. 5, which is an enlarged view of part A in FIG. 1, when the outer cylinder 127, which is the casing, is cut in the axial direction, the shape of the vertical section of the gap 114 is a structure that has a horizontal gap portion 114a as a first gap portion extending horizontally from the opening 114A toward the outside in the radial direction perpendicular to the axial direction, and an inclined gap portion 14b as a second gap portion that is inclined and extends further radially outward from the outer end of the horizontal gap portion 114a and diagonally downward along the downstream side in the axial direction, and has a portion formed in an inverted L shape from the opening 114A. In the following description, the upstream side in the axial direction is the intake port 101 side, and the downstream side in the axial direction is the exhaust port 133 side. The axial direction is the axial direction of the rotor shaft 113, and the radial direction is the direction perpendicular to the axis, that is, the radial direction of the outer cylinder 127.

In the vacuum pump 10 configured as in this embodiment, the opening 14A of the gap 114 of a predetermined width that insulates between the cooling side stator 110A and the heating side stator 110B is provided at a position offset in the axial direction of the rotor 103, not facing the outer circumferential surface of the rotor 102 (rotor 102g and rotor 102h). Therefore, even if a part of the process gas is blown toward the inner circumferential surface of the cooling side stator 110A and the heating side stator 110B of the cylindrical portion 102E by the centrifugal force caused by the rotation of the rotor 102, the amount of process gas that enters the opening 114A of the gap 114 is extremely small, and the amount of deposits that accumulate in the gap 114 can be reduced. This makes it possible to extend the interval at which maintenance work is required to remove deposits, etc., accumulated in the gap 114, which contributes to improving productivity.

In the embodiment shown in Figures 1 and 5, when the outer cylinder 127, which is the casing, is cut in the axial direction, the shape of the vertical cross section of the gap 114 is shown to be roughly an inverted L-shape, with a horizontal gap portion 114a extending horizontally outward from the opening 114A and an inclined gap portion 114b extending diagonally from the outer end of the horizontal gap portion 114a to the radially outer side and downstream in the axial direction.

In the structure shown in Figures 1 and 5, when the process gas enters the horizontal gap portion 114a from the opening 114A, there is an inclined gap portion 114b that bends diagonally downward and extends outward from the outer end of the horizontal gap portion 114a. Therefore, when the process gas enters the horizontal gap portion 114a from the opening 114A and then flows into the inclined gap portion 114b, the inclined gap portion 114b acts as a wall against which the process gas hits, providing resistance to the flow of the process gas further inward. This reduces the amount of process gas that enters the gap 114 from the opening 114A, and further reduces the amount of deposits generated by the process gas.

The structure of the gap 114 is not limited to the structure shown in Figures 1 and 5, and may be, for example, the structure shown in Figures 6, 7, and 8. The inclined gap portion 114b may be a gap portion that extends further radially outward from the outer end of the horizontal gap portion 114a and obliquely upward along the upstream side in the axial direction.

In the structure of the gap 114 shown in FIG. 6, when the outer tube 127, which is the casing, is cut in the axial direction, the shape of the longitudinal section of the gap 114 is such that the vertical gap portion 114c, which serves as a third gap portion that faces the downstream side in the axial direction immediately after entering the opening 114A, and the horizontal gap portion 114a, which extends horizontally from the lower end of the vertical gap portion 114c toward the outside in the radial direction, are integrally provided, forming a portion that is approximately I-shaped from the opening 114A.

In the structure shown in FIG. 6, the cross-sectional shape of the gap 114 is formed into an approximately I-shape, so that when the process gas tries to enter the gap 114 from the opening 114A, the wall of the vertical gap portion 114c facing the axial downstream side is located immediately in front of the opening 114A, and the wall acts as a resistance to the inward flow of the process gas. This reduces the amount of process gas that enters the gap 114 from the opening 114A, and at the same time, the amount of deposits can be further reduced. Note that the vertical gap portion 114c is structured so that it faces the axial downstream side immediately after entering the opening 114A, but it may also be structured so that it faces the axial upstream side immediately after entering the opening 114A.

In the structure of the gap 114 shown in FIG. 7, when the outer tube 127, which is the casing, is cut in the axial direction, the shape of the vertical cross section of the gap 114 is structured to have a portion formed in a roughly inverted V shape from the opening 114A, with an inclined gap portion 114d as a fourth gap portion that extends diagonally from the opening 11A radially outward in a direction perpendicular to the axial direction and toward the upstream side in the axial direction, and an inclined gap portion 114e as a fifth gap portion that extends diagonally from the outer end of the inclined gap portion 114d toward the downstream side in the axial direction.

In the structure of FIG. 7, as soon as the process gas enters the inclined gap portion 114d from the opening 114A, it rises outward and diagonally upward, so the process gas that enters the inclined gap portion 114d from the opening 114A hits the inclined gap portion 114d, which slopes outward and diagonally upward, as a wall, and this acts as resistance to the inward flow of the process gas. This reduces the amount of process gas that enters the gap 114 from the opening 114A, and further reduces the amount of deposits generated by the process gas.

In the configuration of FIG. 7, the inclined gap portion 114d that extends from the opening 114A radially outwardly perpendicular to the axial direction and obliquely toward the upstream side in the axial direction, and the inclined gap portion 114e that extends obliquely from the outer end of the inclined gap portion 114d toward the downstream side in the axial direction are integrally provided, resulting in a structure having a portion that is formed in a roughly inverted V shape from the opening 114A. However, the structure may also have either the inclined gap portion 114d that extends obliquely from the opening 114A toward the upstream side, or the inclined gap portion 114e that extends obliquely from the opening 114A toward the downstream side.

In the structure of the gap 114 shown in FIG. 8, when the outer cylinder 127, which is the casing, is cross-sectioned in the axial direction, the gap 114 formed on the inner peripheral surface of the outer cylinder 127 has an eaves portion 116 that protrudes toward the inside of the outer cylinder 127 beyond the opening 114A. That is, the eaves portion 116 creates a step between the opening 114A and the opening 114A, and can control the flow so that the process gas flowing from the upstream side does not flow toward the opening 114A but flows straight downstream. In addition, the gap 114 has a vertical gap portion 114c as a third gap portion that flows downstream immediately after entering the opening 114A, and a horizontal gap portion 114a that extends horizontally from the lower end of the vertical gap portion 114c toward the outside in the radial direction perpendicular to the axial direction, and is structured to have a portion that is formed in an approximately I-shape from the opening 114A.

In the structure of FIG. 8, the cross-sectional shape of the gap 114 is formed into an approximately I-shape, so that when the process gas tries to enter the gap 114 from the opening 114A, the wall of the vertical gap portion 114c facing downward is present immediately in front of the opening 114A, and the process gas hits the wall, which acts as a resistance to the flow of the process gas toward the inside. This reduces the amount of process gas that enters the gap 114 from the opening 114A, and further reduces the amount of deposits generated by the process gas. In addition, the lower edge portion (lower surface of the eaves tip) 116a of the eaves portion 116 and the lower edge portion 114g of the opening 114A are each subjected to R-chamfering. The R-chamfering process is performed so that when part of the process gas that has bounced off the rotor blades 102 inside the outer cylinder 127 hits the lower edge portion 116a or the lower edge portion 114g, the part of the process gas that has bounced off is directed in a direction toward the rotor shaft 113 that is different from the direction into the opening 114A, so that it does not enter the opening 114A.

The present invention can be modified in various ways without departing from the spirit of the invention, and it goes without saying that the present invention extends to such modifications.

100: turbo molecular pump 101: intake port 102: rotor 102A: cooling side rotor 102B: cooling side rotor 102E: cylindrical portion 102a: rotor 102b: rotor 102c: rotor 102d: rotor 102e: rotor 102f: rotor 102g: rotor 103: rotor 104: upper radial electromagnet 105: lower radial electromagnet 106A: axial electromagnet 106B: axial electromagnet 107: upper radial sensor 108: lower radial sensor 109: axial sensor 110A: cooling side stator (upper group gas transfer section)
110B: Heating side stator (lower group gas transfer section)
111: Metal disk 112: O-ring 113: Rotor shaft 114: Gap 114A: Opening 114a: Horizontal gap portion (first gap portion)
114b: inclined gap portion (second gap portion)
114c: Vertical gap portion (third gap portion)
114d: Inclined gap portion (fourth gap portion)
114e: Inclined gap portion (fifth gap portion)
114g : Lower edge portion 115 : Bolt 116 : Eaves portion 116a : Lower surface edge portion 120 : Protective bearing 121 : Motor 122 : Stator column 123 : Fixed blade 123a : Fixed blade 123b : Fixed blade 123c : Fixed blade 123d : Fixed blade 123e : Fixed blade 123f : Fixed blade 123g : Fixed blade 123h : Fixed blade 123i : Fixed blade 125 : Fixed blade spacer 127 : Outer cylinder 129 : Base portion 131 : Threaded spacer 131a : Thread groove 133 : Exhaust port 141 : Electronic circuit portion 143 : Board 145 : Bottom cover 149 : Water-cooled tube 150 : Amplifier circuit 151 : Electromagnet winding 152 : Temperature sensor 153 : Temperature sensor 154 : Electromagnet winding 155 : Water-cooled tube 161 : Heater 161a : Cathode terminal 161b : Anode terminal 162 : Transistor 162a : Cathode terminal 162b : Anode terminal 165 : Diode 165a : Cathode terminal 165b : Anode terminal 166 : Diode 166a : Cathode terminal 166b : Anode terminal 171 : Power supply 171a : Positive electrode 171b : Negative electrode 181 : Current detection circuit 191 : Amplifier control circuit 191a : Gate drive signal 191b : Gate drive signal 191c : Current detection signal S : Distance Tp1 : Pulse width time Tp2 : Pulse width time Ts : Control cycle iL : Electromagnet current iLmax : Current value iLmin : Current value

Claims (5)

a casing having an intake port and an exhaust port;
a rotor shaft rotatably supported inside the casing;
A rotor shaft is provided with a plurality of rotor stages, the rotor blades being rotatable together with the rotor shaft;
a plurality of stages of fixed blades fixed to the casing and disposed between the plurality of stages of rotor blades;
a cooling side stator and a heating side stator that hold the plurality of stages of fixed blades at a predetermined interval;
A vacuum pump comprising:
an opening of a gap having a predetermined width for insulating the cooling-side stator and the heating-side stator is provided at a position not facing an outer circumferential surface of the rotor blade in an axial direction of the rotor shaft,
the opening is provided at a central position between a lowermost rotor blade among the plurality of stages of rotor blades located within a cooling range cooled by the cooling-side stator and an uppermost rotor blade among the plurality of stages of rotor blades located within a heating range heated by the heating-side stator,
The width dimension of the opening in the axial direction is set to 0.1 mm to 2.0 mm.
A vacuum pump characterized by: The vacuum pump according to claim 1, characterized in that the shape of the gap has a first gap portion that extends horizontally toward the outside in the radial direction perpendicular to the axial direction, and a second gap portion that extends from the outer end of the first gap portion further outward in the radial direction and along the downstream side in the axial direction. The vacuum pump according to claim 1 or 2, characterized in that the shape of the gap has a third gap portion extending along the downstream side in the axial direction. The vacuum pump according to any one of claims 1 to 3, characterized in that the shape of the gap has a fourth gap portion that extends radially outwardly perpendicular to the axial direction and upstream in the axial direction. The vacuum pump according to any one of claims 1 to 4, characterized in that the shape of the gap has an eaves portion at the top of the opening that protrudes toward the inside of the casing beyond the opening.