US20200347851A1 - Turbomolecular pump and method and apparatus for controlling the pressure in a process chamber - Google Patents
Turbomolecular pump and method and apparatus for controlling the pressure in a process chamber Download PDFInfo
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- US20200347851A1 US20200347851A1 US16/771,358 US201816771358A US2020347851A1 US 20200347851 A1 US20200347851 A1 US 20200347851A1 US 201816771358 A US201816771358 A US 201816771358A US 2020347851 A1 US2020347851 A1 US 2020347851A1
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- turbomolecular pump
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- turbomolecular
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- 230000001133 acceleration Effects 0.000 claims description 14
- 238000010926 purge Methods 0.000 claims description 10
- 230000003247 decreasing effect Effects 0.000 claims description 2
- 239000007789 gas Substances 0.000 description 12
- 238000011109 contamination Methods 0.000 description 5
- 230000006870 function Effects 0.000 description 5
- 239000004065 semiconductor Substances 0.000 description 4
- 230000001419 dependent effect Effects 0.000 description 3
- 238000012545 processing Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 238000005086 pumping Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
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- 238000012423 maintenance Methods 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 238000004804 winding Methods 0.000 description 1
Images
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D27/00—Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids
- F04D27/004—Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids by varying driving speed
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D19/00—Axial-flow pumps
- F04D19/02—Multi-stage pumps
- F04D19/04—Multi-stage pumps specially adapted to the production of a high vacuum, e.g. molecular pumps
- F04D19/042—Turbomolecular vacuum pumps
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D19/00—Axial-flow pumps
- F04D19/02—Multi-stage pumps
- F04D19/04—Multi-stage pumps specially adapted to the production of a high vacuum, e.g. molecular pumps
- F04D19/046—Combinations of two or more different types of pumps
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D25/00—Pumping installations or systems
- F04D25/02—Units comprising pumps and their driving means
- F04D25/06—Units comprising pumps and their driving means the pump being electrically driven
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D27/00—Control, e.g. regulation, of pumps, pumping installations or pumping systems specially adapted for elastic fluids
- F04D27/02—Surge control
- F04D27/0261—Surge control by varying driving speed
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D25/00—Pumping installations or systems
- F04D25/02—Units comprising pumps and their driving means
- F04D25/06—Units comprising pumps and their driving means the pump being electrically driven
- F04D25/0606—Units comprising pumps and their driving means the pump being electrically driven the electric motor being specially adapted for integration in the pump
- F04D25/0613—Units comprising pumps and their driving means the pump being electrically driven the electric motor being specially adapted for integration in the pump the electric motor being of the inside-out type, i.e. the rotor is arranged radially outside a central stator
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
- F04D—NON-POSITIVE-DISPLACEMENT PUMPS
- F04D29/00—Details, component parts, or accessories
- F04D29/58—Cooling; Heating; Diminishing heat transfer
- F04D29/582—Cooling; Heating; Diminishing heat transfer specially adapted for elastic fluid pumps
- F04D29/5846—Cooling; Heating; Diminishing heat transfer specially adapted for elastic fluid pumps cooling by injection
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F05—INDEXING SCHEMES RELATING TO ENGINES OR PUMPS IN VARIOUS SUBCLASSES OF CLASSES F01-F04
- F05D—INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS
- F05D2260/00—Function
- F05D2260/85—Starting
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
- Y02B30/70—Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating
Definitions
- the field of the invention relates to turbomolecular pumps and to a method and apparatus for controlling the pressure in a process chamber using such a turbomolecular pump.
- Turbomolecular pumps which provide high and ultrahigh vacuums are known. These pumps are momentum transfer pumps in which gas molecules entering the pump are given momentum by rotating rotor blades.
- the pump comprises multiple angled rotor and stator blade row pairs, the blades of the rotor blade rows are angled to push the gas molecules towards the exhaust end of the pump.
- turbomolecular pumps are often used to evacuate process chambers such as semiconductor processing chambers.
- Various arrangements have been proposed for controlling the pressure in such a semiconductor process chamber.
- a throttle valve is provided between the outlet of the semiconductor processing chamber and the inlet of the turbomolecular pump.
- Such throttle values have cost and reliability issues and perhaps even more importantly can be a cause of contamination in the chamber as particles exiting the chamber via the valves may hit surfaces of the valves and bounce back into the chamber.
- a first aspect provides a turbomolecular pump comprising: a rotor comprising a plurality of blades on a rotatable shaft; a control motor for driving said rotatable shaft; wherein said control motor is sized to output a power that is more than three times larger than a power required to drive said shaft at a constant velocity that is sufficiently high to provide an exhaust pressure of 5 millibars.
- Turbomolecular pumps provide high and ultrahigh vacuums by rotating at extremely high speeds. Furthermore, as they do not operate well with higher exhaust pressures they often have drag stages integral with the turbomolecular pump and these have a significant inertia and weight. Thus, changing the speed of rotation of such a pump requires very high energy and there is a technical prejudice against providing such pumps with sufficient rotational speed control to allow this to be used to control pressure in a chamber.
- turbomolecular pump for a turbomolecular pump is generally sized such that the exhaust pressure is kept to 5 millibars or below as above this the turbomolecular pump will not operate well.
- turbomolecular pumps are often mounted in constrained spaces and the size of the motor is similarly constrained.
- the conventional size of motor used in a turbomolecular pump is dependent on the pump and on its pumping capacity. For any particular pump an engineer would determine the size of motor required to provide the required exhaust pressure which would generally be below 5 millibars. In this case, a motor that is 3 times larger than that required for normal operation of a typical pump of a similar size is provided and in some cases 5 times larger or even 10 times larger and in this way sufficiently fine control of the inlet pressure is achieved without the need to have a throttle valve.
- the acceleration power (short term power) for a standard turbomolecular pump and for a pump according to the application is about 1.5 times the maximum steady state power.
- a 3000 l/s pump would conventionally require a steady state motor power of about 1 KW.
- the turbomolecular pump of the application provides a motor that provides 3 or more times the standard continuous power of a typical turbo pump and 3 or more times the short term power.
- the pump provides 3 times the power for a typical turbo pump of a given inlet speed, so typically one has a 1 KW motor for a 3000 l/s pump and thus, the motor of the pressure control pump would be 4.5 KW or more.
- said turbomolecular pump comprises a drag stage while in other embodiments it comprises no drag stage.
- turbomolecular pumps are often provided with drag stages as they do not function well with higher exhaust pressures and an additional stage on the back of the pump reduces the exhaust pressure.
- they could also be operated with separate backing pumps connected to the exhaust of the turbomolecular pump and where a drag stage is integral with the turbomolecular pump it does necessarily increase the weight and inertia of the rotor.
- reducing the weight and inertia of the rotor by having no drag stage may be advantageous and provide a system where the inlet pressure can be controlled more easily and without the requirement for such a large motor.
- the rotor of the pump As noted previously, a larger motor than is generally used for turbomolecular pumps is required if the inlet pressure is to be controlled by the speed of the rotor.
- One way of providing such a large motor that provides direct driving of the rotor and yet is still relatively compact is for the rotor of the pump to comprise a skirt portion which is coaxial with its shaft and surrounds the shaft. This skirt portion can be used as the rotor of the motor providing direct driving of the motor and providing an increased sized motor rotor.
- said turbomolecular pump comprises a Holweck drag stage, said skirt portion comprising a skirt of said Holweck drag stage.
- turbomolecular pumps it may be advantageous for turbomolecular pumps to have a drag stage and although this increases the inertia of the rotor, where there is such a stage it may be advantageous to use the skirt of the drag stage as the rotor of the control motor. In this way, a large motor can be incorporated into the turbomolecular pump while retaining the drag stage of the turbomolecular pump and providing an effective and efficient pumping system.
- said skirt portion comprises magnets.
- skirt portion may be formed of metal or it may be formed of carbon fibre. Magnets may be mounted on the skirt portion allowing the skirt to be driven in response to the rotational magnetic field produced by the windings of the stator of the motor.
- said skirt portion comprises a smaller cross section adjacent to said blades of said rotor and a larger cross section remote from said blades.
- the skirt may be a cylinder and may be a cylinder with a relatively large cross section, while in others the cross section may be smaller adjacent to the blades to provide a larger path for the gas at this point, the cross section being larger remote from the blades the increase in volume providing an increased space for the motor.
- said stator of said control motor is arranged inside said skirt portion and around said shaft, while in other embodiments, said stator of said control motor is arranged around said skirt portion.
- a skirt with cylinder shape and a relatively small cross section may be advantageous, perhaps similar or slightly larger than that of the inner diameter of the rotor blades.
- said pump comprises a pump housing and said control motor is located within said pump housing.
- control motor may need to be of a relatively large size in order to provide the acceleration and deceleration required to control the pressure in the process chamber it may be advantageous if it is of a size where it can fit within the pump housing.
- the turbomolecular pump may only comprise one motor, that is the control motor which provides the acceleration and the deceleration under steady state operation.
- said turbomolecular pump comprises a further motor for driving said shaft said further motor and shaft forming a drive spindle and said control motor and skirt portion being formed around said drive spindle.
- said further motor is configured to drive said rotor during steady state operation and said control motor is configured to drive said rotor during acceleration and deceleration of said rotor of said turbomolecular pump.
- said pump comprises control circuitry for controlling a pressure at an inlet of said turbomolecular pump, said control circuitry being configured to control said control motor to control a speed of said rotor and thereby a pressure at an inlet of said turbomolecular pump.
- control circuitry may be provided to control the inlet pressure of the pump and in this way the pressure in any chamber being evacuated by controlling the speed of the control motor.
- said turbomolecular pump comprises an exhaust valve, said control circuitry being configured to control said exhaust valve to increase pressure at an exhaust of said turbomolecular pump in conjunction with controlling said control motor to slow said rotor.
- turbomolecular pump In addition to controlling the speed of the rotor of the pump it may be advantageous if there is an exhaust valve on the turbomolecular pump and this may be controlled to increase the pressure at the exhaust of the turbomolecular pump in conjunction with slowing the rotor, as this helps the rotor to slow and improves the efficiency and speed of reaction of the pump.
- the turbomolecular pump may comprise a purge gas inlet at the exhaust, wherein the control circuitry is configured to control addition of purge gas to the exhaust in conjunction with controlling the control motor to slow the rotor.
- valve purge gas may be used to increase the pressure there and help in the slowing of the rotor.
- a valve is a component that can be expensive, requires maintenance and may become contaminated.
- the addition of an inert purge gas inlet may be a more convenient way of controlling pressure at the exhaust of the turbomolecular pump.
- a second aspect of the present invention provides a turbomolecular pump comprising: a rotor comprising a plurality of blades mounted on a rotatable shaft; a control motor for driving said rotatable shaft; wherein said rotor further comprises a skirt portion extending in an axial direction beyond said blades of said rotor and having an annular cross section, said skirt portion forming a rotor of said control motor and being coaxial with and surrounding said shaft.
- Providing pressure control at an inlet of a turbomolecular pump by controlling the speed of rotation of the pump can be problematic due to the high speed of such a pump and its corresponding inertia such that changes in the speed of rotation require high energy and are difficult to manage without significant delay.
- a control motor may be provided with sufficient power then accurate control at the inlet pressure may be provided.
- Such a control motor may be provided in a compact way by using a skirt portion on the rotor on the pump as a the rotor of the control motor such that direct driving of the rotor is provided by a motor with a significant sized rotor.
- said skirt portion comprises a smaller cross section adjacent to said blades of said rotor and a larger cross section remote from said blades.
- said stator of said control motor is arranged inside said skirt portion and around said shaft.
- said stator of said control motor is arranged around said skirt portion.
- said skirt portion has an inner diameter substantially equal to an inner diameter of the most downstream blade of said turbomolecular pump.
- the skirt portion is adjacent to the most downstream blade of turbomolecular pump and extends perpendicular to it away from the other blades.
- said turbomolecular pump comprises a drag stage.
- said turbomolecular pump does not comprise a drag stage.
- said turbomolecular pump comprises a Holweck drag stage, said skirt portion comprising a skirt of a Holweck drag stage.
- said skirt portion comprises magnets.
- said pump comprises a pump housing and said control motor is located within said pump housing.
- said control motor comprises a ring shape, an inner diameter of which is larger than a largest inner diameter of said rotor blades and smaller than an outer diameter of said rotor blades, and an outer diameter of which is greater than 90% of a diameter of said rotor blades.
- said control motor comprises a ring shape, an inner diameter of which is larger than a largest inner diameter of said rotor blades but smaller than 1.2 times said largest inner diameter, and an outer diameter of which is less than or equal to an outer diameter of said rotor blades.
- said turbomolecular pump comprises: a further motor for driving said shaft, said further motor and shaft forming a drive spindle and said control motor and skirt portion being formed around said drive spindle.
- said motor is configured to drive said rotor during steady state operation and said control motor is configured to drive said rotor during acceleration and deceleration of said rotor of said turbomolecular pump.
- said pump comprises control circuitry for controlling a pressure at an inlet of said turbomolecular pump, said control circuitry being configured to control said control motor to control a speed of said rotor and thereby a pressure at an inlet of said turbomolecular pump.
- said turbomolecular pump comprises an exhaust valve, said control circuitry being configured to control said exhaust valve to increase pressure at an exhaust of said turbomolecular pump in conjunction with controlling said control motor to slow said rotor.
- said turbomolecular pump comprises a turbomolecular pump according to any preceding claim, the turbomolecular pump being connected to said process chamber, said pressure of said process chamber being controlled by controlling a speed of rotation of said turbomolecular pump.
- a third aspect provides an apparatus for controlling the pressure in a process chamber, the apparatus comprising a turbomolecular pump according to any preceding claim, the turbomolecular pump being connected to said process chamber, said pressure of said process chamber being controlled by a controller configured to control a speed of rotation of said turbomolecular pump.
- said turbomolecular pump is connected directly to said process chamber.
- Controlling the pressure in the process chamber controlling the speed of rotation of the turbomolecular pump connected to the chamber removes the need for intermediate pressure control such as a throttle valve. This reduces the cost of the apparatus and also reduces the service requirements and contamination that might occur due to contaminates exiting via the throttle valve and being impeded in their exit and perhaps being bounced back into the process chamber.
- a fourth aspect of the present invention provides a method of controlling the pressure in a process chamber, the method comprising: in response to determining a pressure is to be decreased in said process chamber and accelerating a turbomolecular pump connected to said process chamber; and in response to determining a pressure is to be increased in said process chamber decelerating a turbomolecular pump connected to said process chamber; wherein said acceleration and deceleration of said turbomolecular pump is done by a control motor that is sized to output a power that is more than three times larger than a power required to drive said shaft at a constant velocity that is sufficiently high to provide an exhaust pressure of 5 millibars.
- FIG. 1 shows a turbomolecular pump without a drag stage according to first embodiment
- FIG. 2 illustrates a turbomolecular pump according to a second embodiment
- FIG. 3 illustrates a turbomolecular pump according to the second embodiment configured to evacuate a process chamber
- FIG. 4 illustrates a turbomolecular pump with a drag stage and combined control motor according to an embodiment
- FIG. 5 illustrates a further embodiment of a turbomolecular pump with Holweck drag stage and combined control motor.
- a turbomolecular pump with a motor that is significantly larger than is generally required to operate the same sized conventional turbomolecular pump is provided.
- the larger motor is used to provide effective acceleration and deceleration of the rotor of the pump allowing it to be used to control the pressure at the inlet of the pump and thus, the pressure of any chamber to which it is connected.
- the turbomolecular pump may have one large motor or it may have a large motor and an additional motor similar to the usual drive motor on a conventional turbomolecular pump, such an additional motor being used for steady operation.
- This additional motor drives the shaft and is mounted within a drive spindle.
- the additional larger motor is mounted around the drive spindle and provides the acceleration and deceleration required for pressure control.
- the rotor of the large control motor may be a skirt extending from the rotor and comprising magnets such that the rotating magnetic field generated by the stator of the motor causes the rotor of the motor and thus, the rotor of the pump of which it is a part, to rotate.
- the stator of the motor may be within the rotor and in this way be protected from the process gases, or it may be around the rotor in which case it may have a significantly increased size.
- a method and apparatus for controlling the pressure in a process chamber is also provided using such a turbomolecular pump connected to the process chamber with control circuitry operable to determine the pressure in the chamber and the required pressure and to control the speed of the pump accordingly.
- the control circuitry may additionally control a valve at the exhaust of the turbomolecular pump and/or the input of purge gas at or close to this point.
- FIG. 1 shows a turbomolecular pump without a drag stage comprising a rotor 22 mounted on shaft 23 and driven by motor 16 .
- the rotor 22 has a skirt portion 18 extending from the lower part of the rotor, the skirt portion forming the rotor of motor 16 .
- the skirt portion 18 comprises magnets which cause the rotor to rotate under the rotating magnetic field generated by the motor stator 17 .
- the motor stator is located outside and around the shaft 23 of the rotor but within skirt portion 18 . Being in this position helps protect the stator of the motor from the process flow.
- the skirt portion 18 has an increasing cross section such that it meets the lower part at a place close to the inner diameter of that blade, but then extends out to a larger diameter.
- FIG. 2 shows a similar embodiment of a turbomolecular pump without a drag stage but in this embodiment the stator of the motor is outside of the skirt portion 18 .
- the motor stator 17 can be larger than when it is within the skirt portion and thus, a higher power motor may be provided, however, it may be subject to contamination by the process gases. It is advantageous if it still fits within the pump housing of the turbomolecular pump.
- FIG. 3 shows the turbomolecular pump of FIG. 2 evacuating a process chamber 10 in which for example semiconductor processing may be performed.
- Control circuitry 12 is provided for controlling the pressure inside the process chamber.
- the control circuitry 12 controls the pressure inside process chamber 10 by controlling motor 16 and also in this embodiment exhaust valve 14 .
- control circuitry 12 will monitor the pressure in process chamber 10 and also receive control signals indicating the required pressure. It will then control motor 16 to rotate rotor 22 of the turbomolecular pump at a suitable speed to generate the pressure required.
- exhaust valve 14 may also control exhaust valve 14 to increase the pressure at the exhaust where it is required that the pressure in the process chamber increases and the pump is being slowed.
- a purge gas inlet for inputting an inert gas such as nitrogen may be used to increase the pressure at the exhaust of the turbomolecular pump.
- motor 16 The large size of motor 16 and the use of it to directly drive the rotor via the skirt portion extending down from the rotor blades enables sufficient power to be imparted to accelerate and decelerate the rotor and enable the pressure within the process chamber to be accurately controlled and thereby avoid the need for a throttle valve between the input of the pump and the process chamber allowing this input to be wide and without constrictions. This improves performance and reduces contamination that might arise due to contaminates being impeded by the throttle valve.
- FIG. 4 shows an alternative embodiment with a drag stage on the pump. Having a drag stage on the pump may improve performance but increases the inertia of the rotor. Thus, the size of motor required to provide the required acceleration and deceleration is larger than when no drag stage is present.
- the skirt of the Holweck drag stage may also have a dual function as the rotor of the motor and in such case an efficient turbomolecular pump with a large control motor that provides effective pressure control in a process chamber can be provided.
- the stator of the motor is within the skirt of the Holweck drag stage and as such is protected from the process gases.
- the Holweck drag stage will comprise magnets 34 allowing it to be driven by the rotating magnetic field of the stators of the motor.
- the control motor 16 which is a larger motor provides the acceleration and deceleration for controlling changes in the pressure within the process chamber.
- FIG. 5 shows an alternative embodiment where the stator 17 of the motor is outside the Holweck skirt which acts as the rotor of the motor. This is similar to embodiment of FIG. 4 and as for FIG. 4 has the additional motor 30 mounted on the shaft 23 . It will be appreciated that the additional motor 30 may not be present in some embodiments and the driving of the rotor is performed entirely by the control motor both in steady state and during acceleration and deceleration.
- motors have each had a rotor comprising a skirt portion extending from the pump motor, other pump motors may be used provided they are sufficiently large, that is three or more times larger than a conventionally sized motor.
Abstract
Description
- This application is a Section 371 National Stage Application of International Application No. PCT/GB2018/053572, filed Dec. 10, 2018, and published as WO 2019/116012 A1 on Jun. 20, 2019, the content of which is hereby incorporated by reference in its entirety and which claims priority of British Application No. 1720705.1, filed Dec. 12, 2017.
- The field of the invention relates to turbomolecular pumps and to a method and apparatus for controlling the pressure in a process chamber using such a turbomolecular pump.
- Turbomolecular pumps which provide high and ultrahigh vacuums are known. These pumps are momentum transfer pumps in which gas molecules entering the pump are given momentum by rotating rotor blades. The pump comprises multiple angled rotor and stator blade row pairs, the blades of the rotor blade rows are angled to push the gas molecules towards the exhaust end of the pump.
- Owing to their ability to provide these high and ultrahigh vacuums turbomolecular pumps are often used to evacuate process chambers such as semiconductor processing chambers. Various arrangements have been proposed for controlling the pressure in such a semiconductor process chamber. In one such arrangement, a throttle valve is provided between the outlet of the semiconductor processing chamber and the inlet of the turbomolecular pump. Such throttle values have cost and reliability issues and perhaps even more importantly can be a cause of contamination in the chamber as particles exiting the chamber via the valves may hit surfaces of the valves and bounce back into the chamber.
- It would therefore be desirable to be able to dispense with such throttle valves and yet still be able to provide effective pressure control in such chambers.
- The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.
- A first aspect provides a turbomolecular pump comprising: a rotor comprising a plurality of blades on a rotatable shaft; a control motor for driving said rotatable shaft; wherein said control motor is sized to output a power that is more than three times larger than a power required to drive said shaft at a constant velocity that is sufficiently high to provide an exhaust pressure of 5 millibars.
- Turbomolecular pumps provide high and ultrahigh vacuums by rotating at extremely high speeds. Furthermore, as they do not operate well with higher exhaust pressures they often have drag stages integral with the turbomolecular pump and these have a significant inertia and weight. Thus, changing the speed of rotation of such a pump requires very high energy and there is a technical prejudice against providing such pumps with sufficient rotational speed control to allow this to be used to control pressure in a chamber.
- However, the inventors of the present invention recognised that although controlling the pressure in a process chamber using a turbomolecular pump is not straightforward owing to the high speed of rotation and the inertia of the rotor, were the turbomolecular pump to be provided with a large control motor and in this regard not just a slightly larger motor but one that was significantly larger than the motor generally required to generate the necessary pressure differences, then such a control might be possible and the pump would be able to be accelerated and decelerated sufficiently fast to provide the pressure control needed. In this regard, a motor for a turbomolecular pump is generally sized such that the exhaust pressure is kept to 5 millibars or below as above this the turbomolecular pump will not operate well. However, turbomolecular pumps are often mounted in constrained spaces and the size of the motor is similarly constrained. Thus, there is a technical prejudice against increasing the size of the motor and in particular of increasing it by a significant amount.
- However, the inventors recognised that if the pressure control were provided by the pump, intermediate elements such as throttle valves could be dispensed with and a cost saving of these elements would be made as well as an improved system provided, in which contamination due to bounce back of particles on the throttle valve is avoided.
- It should be noted that the conventional size of motor used in a turbomolecular pump is dependent on the pump and on its pumping capacity. For any particular pump an engineer would determine the size of motor required to provide the required exhaust pressure which would generally be below 5 millibars. In this case, a motor that is 3 times larger than that required for normal operation of a typical pump of a similar size is provided and in some cases 5 times larger or even 10 times larger and in this way sufficiently fine control of the inlet pressure is achieved without the need to have a throttle valve. In this regard, the acceleration power (short term power) for a standard turbomolecular pump and for a pump according to the application is about 1.5 times the maximum steady state power. For example a 3000 l/s pump would conventionally require a steady state motor power of about 1 KW. The turbomolecular pump of the application provides a motor that provides 3 or more times the standard continuous power of a typical turbo pump and 3 or more times the short term power. In this regard the pump provides 3 times the power for a typical turbo pump of a given inlet speed, so typically one has a 1 KW motor for a 3000 l/s pump and thus, the motor of the pressure control pump would be 4.5 KW or more.
- In some embodiments, said turbomolecular pump comprises a drag stage while in other embodiments it comprises no drag stage.
- It should be noted that turbomolecular pumps are often provided with drag stages as they do not function well with higher exhaust pressures and an additional stage on the back of the pump reduces the exhaust pressure. However, they could also be operated with separate backing pumps connected to the exhaust of the turbomolecular pump and where a drag stage is integral with the turbomolecular pump it does necessarily increase the weight and inertia of the rotor. In this case, where it is desired to provide control of the inlet pressure by controlling the speed of the rotor, reducing the weight and inertia of the rotor by having no drag stage may be advantageous and provide a system where the inlet pressure can be controlled more easily and without the requirement for such a large motor.
- As noted previously, a larger motor than is generally used for turbomolecular pumps is required if the inlet pressure is to be controlled by the speed of the rotor. One way of providing such a large motor that provides direct driving of the rotor and yet is still relatively compact is for the rotor of the pump to comprise a skirt portion which is coaxial with its shaft and surrounds the shaft. This skirt portion can be used as the rotor of the motor providing direct driving of the motor and providing an increased sized motor rotor.
- In some embodiments, said turbomolecular pump comprises a Holweck drag stage, said skirt portion comprising a skirt of said Holweck drag stage.
- As noted previously, it may be advantageous for turbomolecular pumps to have a drag stage and although this increases the inertia of the rotor, where there is such a stage it may be advantageous to use the skirt of the drag stage as the rotor of the control motor. In this way, a large motor can be incorporated into the turbomolecular pump while retaining the drag stage of the turbomolecular pump and providing an effective and efficient pumping system.
- In some embodiments, said skirt portion comprises magnets.
- It should be noted that the skirt portion may be formed of metal or it may be formed of carbon fibre. Magnets may be mounted on the skirt portion allowing the skirt to be driven in response to the rotational magnetic field produced by the windings of the stator of the motor.
- In some embodiments, said skirt portion comprises a smaller cross section adjacent to said blades of said rotor and a larger cross section remote from said blades.
- Where the stator of the motor is incorporated within the skirt, then it may be advantageous to have a relatively large cross section for the portion of the skirt where the stator is located. In some cases the skirt may be a cylinder and may be a cylinder with a relatively large cross section, while in others the cross section may be smaller adjacent to the blades to provide a larger path for the gas at this point, the cross section being larger remote from the blades the increase in volume providing an increased space for the motor.
- In some embodiments, said stator of said control motor is arranged inside said skirt portion and around said shaft, while in other embodiments, said stator of said control motor is arranged around said skirt portion.
- Where the motor is outside of the skirt, then a skirt with cylinder shape and a relatively small cross section may be advantageous, perhaps similar or slightly larger than that of the inner diameter of the rotor blades.
- In some embodiments, said pump comprises a pump housing and said control motor is located within said pump housing.
- Although, the control motor may need to be of a relatively large size in order to provide the acceleration and deceleration required to control the pressure in the process chamber it may be advantageous if it is of a size where it can fit within the pump housing.
- In some embodiments, the turbomolecular pump may only comprise one motor, that is the control motor which provides the acceleration and the deceleration under steady state operation. In other embodiments, said turbomolecular pump comprises a further motor for driving said shaft said further motor and shaft forming a drive spindle and said control motor and skirt portion being formed around said drive spindle.
- In some embodiments, said further motor is configured to drive said rotor during steady state operation and said control motor is configured to drive said rotor during acceleration and deceleration of said rotor of said turbomolecular pump.
- In some embodiments, said pump comprises control circuitry for controlling a pressure at an inlet of said turbomolecular pump, said control circuitry being configured to control said control motor to control a speed of said rotor and thereby a pressure at an inlet of said turbomolecular pump.
- As noted previously, providing the pump with a large control motor allows the speed of rotation to be accurately controlled and thereby the inlet pressure of the turbomolecular pump. Thus, control circuitry may be provided to control the inlet pressure of the pump and in this way the pressure in any chamber being evacuated by controlling the speed of the control motor.
- In some embodiments, said turbomolecular pump comprises an exhaust valve, said control circuitry being configured to control said exhaust valve to increase pressure at an exhaust of said turbomolecular pump in conjunction with controlling said control motor to slow said rotor.
- In addition to controlling the speed of the rotor of the pump it may be advantageous if there is an exhaust valve on the turbomolecular pump and this may be controlled to increase the pressure at the exhaust of the turbomolecular pump in conjunction with slowing the rotor, as this helps the rotor to slow and improves the efficiency and speed of reaction of the pump.
- Additionally and/or alternatively, the turbomolecular pump may comprise a purge gas inlet at the exhaust, wherein the control circuitry is configured to control addition of purge gas to the exhaust in conjunction with controlling the control motor to slow the rotor.
- Additionally and/or alternatively to increasing the pressure at the exhaust using a valve purge gas may be used to increase the pressure there and help in the slowing of the rotor. In this regard, a valve is a component that can be expensive, requires maintenance and may become contaminated. The addition of an inert purge gas inlet may be a more convenient way of controlling pressure at the exhaust of the turbomolecular pump.
- A second aspect of the present invention provides a turbomolecular pump comprising: a rotor comprising a plurality of blades mounted on a rotatable shaft; a control motor for driving said rotatable shaft; wherein said rotor further comprises a skirt portion extending in an axial direction beyond said blades of said rotor and having an annular cross section, said skirt portion forming a rotor of said control motor and being coaxial with and surrounding said shaft.
- Providing pressure control at an inlet of a turbomolecular pump by controlling the speed of rotation of the pump can be problematic due to the high speed of such a pump and its corresponding inertia such that changes in the speed of rotation require high energy and are difficult to manage without significant delay. However, where a control motor is provided with sufficient power then accurate control at the inlet pressure may be provided. Such a control motor may be provided in a compact way by using a skirt portion on the rotor on the pump as a the rotor of the control motor such that direct driving of the rotor is provided by a motor with a significant sized rotor.
- In some embodiments, said skirt portion comprises a smaller cross section adjacent to said blades of said rotor and a larger cross section remote from said blades.
- In some embodiments, said stator of said control motor is arranged inside said skirt portion and around said shaft.
- In some embodiments, said stator of said control motor is arranged around said skirt portion.
- In some embodiments, said skirt portion has an inner diameter substantially equal to an inner diameter of the most downstream blade of said turbomolecular pump.
- For the sake of this patent application substantially equal is taken to be within 10% of the inner diameter. In some embodiments, the skirt portion is adjacent to the most downstream blade of turbomolecular pump and extends perpendicular to it away from the other blades.
- In some embodiments, said turbomolecular pump comprises a drag stage.
- In other embodiments, said turbomolecular pump does not comprise a drag stage.
- In some embodiments, said turbomolecular pump comprises a Holweck drag stage, said skirt portion comprising a skirt of a Holweck drag stage.
- In some embodiments, said skirt portion comprises magnets.
- In some embodiments, said pump comprises a pump housing and said control motor is located within said pump housing.
- In some embodiments, said control motor comprises a ring shape, an inner diameter of which is larger than a largest inner diameter of said rotor blades and smaller than an outer diameter of said rotor blades, and an outer diameter of which is greater than 90% of a diameter of said rotor blades.
- In some embodiments, said control motor comprises a ring shape, an inner diameter of which is larger than a largest inner diameter of said rotor blades but smaller than 1.2 times said largest inner diameter, and an outer diameter of which is less than or equal to an outer diameter of said rotor blades.
- In some embodiments said turbomolecular pump comprises: a further motor for driving said shaft, said further motor and shaft forming a drive spindle and said control motor and skirt portion being formed around said drive spindle.
- In some embodiments, said motor is configured to drive said rotor during steady state operation and said control motor is configured to drive said rotor during acceleration and deceleration of said rotor of said turbomolecular pump.
- In some embodiments, said pump comprises control circuitry for controlling a pressure at an inlet of said turbomolecular pump, said control circuitry being configured to control said control motor to control a speed of said rotor and thereby a pressure at an inlet of said turbomolecular pump.
- In some embodiments, said turbomolecular pump comprises an exhaust valve, said control circuitry being configured to control said exhaust valve to increase pressure at an exhaust of said turbomolecular pump in conjunction with controlling said control motor to slow said rotor.
- In some embodiments, said turbomolecular pump comprises a turbomolecular pump according to any preceding claim, the turbomolecular pump being connected to said process chamber, said pressure of said process chamber being controlled by controlling a speed of rotation of said turbomolecular pump.
- A third aspect provides an apparatus for controlling the pressure in a process chamber, the apparatus comprising a turbomolecular pump according to any preceding claim, the turbomolecular pump being connected to said process chamber, said pressure of said process chamber being controlled by a controller configured to control a speed of rotation of said turbomolecular pump.
- In some embodiments, said turbomolecular pump is connected directly to said process chamber.
- Controlling the pressure in the process chamber controlling the speed of rotation of the turbomolecular pump connected to the chamber removes the need for intermediate pressure control such as a throttle valve. This reduces the cost of the apparatus and also reduces the service requirements and contamination that might occur due to contaminates exiting via the throttle valve and being impeded in their exit and perhaps being bounced back into the process chamber.
- A fourth aspect of the present invention provides a method of controlling the pressure in a process chamber, the method comprising: in response to determining a pressure is to be decreased in said process chamber and accelerating a turbomolecular pump connected to said process chamber; and in response to determining a pressure is to be increased in said process chamber decelerating a turbomolecular pump connected to said process chamber; wherein said acceleration and deceleration of said turbomolecular pump is done by a control motor that is sized to output a power that is more than three times larger than a power required to drive said shaft at a constant velocity that is sufficiently high to provide an exhaust pressure of 5 millibars.
- Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.
- Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.
- The Summary is provided to introduce a selection of concepts in a simplified form that are further described in the Detail Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.
- Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:
-
FIG. 1 shows a turbomolecular pump without a drag stage according to first embodiment; -
FIG. 2 illustrates a turbomolecular pump according to a second embodiment; -
FIG. 3 illustrates a turbomolecular pump according to the second embodiment configured to evacuate a process chamber; -
FIG. 4 illustrates a turbomolecular pump with a drag stage and combined control motor according to an embodiment; and -
FIG. 5 illustrates a further embodiment of a turbomolecular pump with Holweck drag stage and combined control motor. - Before discussing the embodiments in any more detail, first an overview will be provided.
- A turbomolecular pump with a motor that is significantly larger than is generally required to operate the same sized conventional turbomolecular pump is provided. The larger motor is used to provide effective acceleration and deceleration of the rotor of the pump allowing it to be used to control the pressure at the inlet of the pump and thus, the pressure of any chamber to which it is connected.
- The turbomolecular pump may have one large motor or it may have a large motor and an additional motor similar to the usual drive motor on a conventional turbomolecular pump, such an additional motor being used for steady operation. This additional motor drives the shaft and is mounted within a drive spindle. The additional larger motor is mounted around the drive spindle and provides the acceleration and deceleration required for pressure control.
- The rotor of the large control motor may be a skirt extending from the rotor and comprising magnets such that the rotating magnetic field generated by the stator of the motor causes the rotor of the motor and thus, the rotor of the pump of which it is a part, to rotate. The stator of the motor may be within the rotor and in this way be protected from the process gases, or it may be around the rotor in which case it may have a significantly increased size.
- A method and apparatus for controlling the pressure in a process chamber is also provided using such a turbomolecular pump connected to the process chamber with control circuitry operable to determine the pressure in the chamber and the required pressure and to control the speed of the pump accordingly. The control circuitry may additionally control a valve at the exhaust of the turbomolecular pump and/or the input of purge gas at or close to this point.
-
FIG. 1 shows a turbomolecular pump without a drag stage comprising arotor 22 mounted onshaft 23 and driven bymotor 16. Therotor 22 has askirt portion 18 extending from the lower part of the rotor, the skirt portion forming the rotor ofmotor 16. Theskirt portion 18 comprises magnets which cause the rotor to rotate under the rotating magnetic field generated by themotor stator 17. In this embodiment, the motor stator is located outside and around theshaft 23 of the rotor but withinskirt portion 18. Being in this position helps protect the stator of the motor from the process flow. In effect a motor that has an inside out type arrangement where the stator is provided within the rotor is used. In order for there to be sufficient space for the stator in this embodiment theskirt portion 18 has an increasing cross section such that it meets the lower part at a place close to the inner diameter of that blade, but then extends out to a larger diameter. -
FIG. 2 shows a similar embodiment of a turbomolecular pump without a drag stage but in this embodiment the stator of the motor is outside of theskirt portion 18. In this case, themotor stator 17 can be larger than when it is within the skirt portion and thus, a higher power motor may be provided, however, it may be subject to contamination by the process gases. It is advantageous if it still fits within the pump housing of the turbomolecular pump. -
FIG. 3 shows the turbomolecular pump ofFIG. 2 evacuating aprocess chamber 10 in which for example semiconductor processing may be performed.Control circuitry 12 is provided for controlling the pressure inside the process chamber. Thecontrol circuitry 12 controls the pressure insideprocess chamber 10 by controllingmotor 16 and also in thisembodiment exhaust valve 14. Thus,control circuitry 12 will monitor the pressure inprocess chamber 10 and also receive control signals indicating the required pressure. It will then controlmotor 16 to rotaterotor 22 of the turbomolecular pump at a suitable speed to generate the pressure required. It may also controlexhaust valve 14 to increase the pressure at the exhaust where it is required that the pressure in the process chamber increases and the pump is being slowed. As an alternative to the exhaust valve (not shown) a purge gas inlet for inputting an inert gas such as nitrogen may be used to increase the pressure at the exhaust of the turbomolecular pump. - The large size of
motor 16 and the use of it to directly drive the rotor via the skirt portion extending down from the rotor blades enables sufficient power to be imparted to accelerate and decelerate the rotor and enable the pressure within the process chamber to be accurately controlled and thereby avoid the need for a throttle valve between the input of the pump and the process chamber allowing this input to be wide and without constrictions. This improves performance and reduces contamination that might arise due to contaminates being impeded by the throttle valve. -
FIG. 4 shows an alternative embodiment with a drag stage on the pump. Having a drag stage on the pump may improve performance but increases the inertia of the rotor. Thus, the size of motor required to provide the required acceleration and deceleration is larger than when no drag stage is present. However, it has been recognised that the skirt of the Holweck drag stage may also have a dual function as the rotor of the motor and in such case an efficient turbomolecular pump with a large control motor that provides effective pressure control in a process chamber can be provided. In the embodiment ofFIG. 4 the stator of the motor is within the skirt of the Holweck drag stage and as such is protected from the process gases. The Holweck drag stage will comprisemagnets 34 allowing it to be driven by the rotating magnetic field of the stators of the motor. In this embodiment, in addition to having this large control motor there is anadditional motor 30 provided on the conventional position on theshaft 23 of the pump which acts to drive theshaft 23 during steady state operations. Thecontrol motor 16 which is a larger motor provides the acceleration and deceleration for controlling changes in the pressure within the process chamber. -
FIG. 5 shows an alternative embodiment where thestator 17 of the motor is outside the Holweck skirt which acts as the rotor of the motor. This is similar to embodiment ofFIG. 4 and as forFIG. 4 has theadditional motor 30 mounted on theshaft 23. It will be appreciated that theadditional motor 30 may not be present in some embodiments and the driving of the rotor is performed entirely by the control motor both in steady state and during acceleration and deceleration. - It should be noted that although in the embodiments shown the motors have each had a rotor comprising a skirt portion extending from the pump motor, other pump motors may be used provided they are sufficiently large, that is three or more times larger than a conventionally sized motor.
- Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.
- Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.
- Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.
Claims (32)
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB1720705.1A GB2569314A (en) | 2017-12-12 | 2017-12-12 | A turbomolecular pump and method and apparatus for controlling the pressure in a process chamber |
GB1720705.1 | 2017-12-12 | ||
PCT/GB2018/053572 WO2019116012A1 (en) | 2017-12-12 | 2018-12-10 | A turbomolecular pump and method and apparatus for controlling the pressure in a process chamber |
Publications (1)
Publication Number | Publication Date |
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US20200347851A1 true US20200347851A1 (en) | 2020-11-05 |
Family
ID=61007319
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US16/771,358 Abandoned US20200347851A1 (en) | 2017-12-12 | 2018-12-10 | Turbomolecular pump and method and apparatus for controlling the pressure in a process chamber |
Country Status (5)
Country | Link |
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US (1) | US20200347851A1 (en) |
EP (1) | EP3724510A1 (en) |
CN (1) | CN111527311B (en) |
GB (1) | GB2569314A (en) |
WO (1) | WO2019116012A1 (en) |
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- 2018-12-10 WO PCT/GB2018/053572 patent/WO2019116012A1/en unknown
- 2018-12-10 EP EP18819358.5A patent/EP3724510A1/en active Pending
- 2018-12-10 CN CN201880080603.3A patent/CN111527311B/en active Active
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Also Published As
Publication number | Publication date |
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GB2569314A (en) | 2019-06-19 |
GB201720705D0 (en) | 2018-01-24 |
EP3724510A1 (en) | 2020-10-21 |
WO2019116012A1 (en) | 2019-06-20 |
CN111527311A (en) | 2020-08-11 |
CN111527311B (en) | 2022-01-04 |
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