VARIABLE INLET CONDUCTANCE VACUUM PUMP, VACUUM PUMP ARRANGEMENT AND METHOD

Abstract

A vacuum pump, vacuum pump arrangement and method are disclosed. The vacuum pump includes at least one rotor; and a stator, an inlet for receiving gas during operation; and an exhaust for exhausting the gas. The vacuum pump includes a shaft extending through a centre of said pump and comprising a plate mounted on an end of the shaft towards the inlet. The vacuum pump includes control circuitry configured to control an axial position of the plate, a change in axial position of the plate providing a change in inlet conductance of gas to the vacuum pump. The plate is mounted such that it extends beyond the inlet in at least some axial positions of the rotor such that the plate is not on the same side of the inlet as the stator.

Claims

1. A vacuum pump comprising: at least one rotor; and a stator, an inlet for receiving gas during operation; and an exhaust for exhausting said gas; wherein said vacuum pump comprises a shaft extending through said pump, said shaft comprising impellers mounted to said shaft and a plate mounted on an end of said shaft towards said inlet; said vacuum pump comprising control circuitry configured to control an axial position of said plate, a change in axial position of said plate providing a change in inlet conductance of gas to said vacuum pump; wherein said plate is mounted such that it extends beyond said inlet in at least some axial positions of said shaft such that said plate is not on the same side of said inlet as said stator, wherein said shaft comprises a rotor shaft, said plate comprising a rotor plate configured to rotate with said rotor.

2. The vacuum pump according to claim 1, wherein said plate is configured to close said inlet at a predefined axial position.

3. The vacuum pump according to claim 1, wherein said shaft comprises a rotor shaft, said plate comprising a rotor plate being configured to rotate with said rotor

4. The vacuum pump according to claim 1, said rotor plate comprising surface irregularities on a surface facing towards said inlet, said surface irregularities being configured to divert at least some particles within said gas towards said inlet.

5. The vacuum pump according to claim 1, wherein said rotor comprises an outer cylinder comprising impellers and said stator comprises said shaft to which are mounted said impellers.

6. The vacuum pump according to claim 1, wherein said vacuum pump comprises a turbo pump.

7. The vacuum pump according to claim 6, wherein said vacuum pump comprises a turbo pump stage backed by at least one further stage.

8. The vacuum pump according to claim 7, wherein said at least one further stage comprises at least one of a drag and a regenerative stage.

9. The vacuum pump according to claim 7, wherein said at least one further stage comprises a Siegbahn stage, said rotor comprising at least one rotating plate and said stator comprising at least one fixed plate, a distance between said at least one rotating plate and said at least one fixed plate being dependent upon said relative axial position of said stator to said rotor.

10. The vacuum pump according to claim 7, wherein said turbo pump stage and said at least one further stage are mounted on the rotor shaft.

11. The vacuum pump according to claim 7, wherein said turbo pump stage and said at least one further stage are mounted on different shafts.

12. The vacuum pump according to claim 1, wherein said rotor and stator are mounted to be movable in an axial direction with respect to each other.

13. The vacuum pump according to claim 12, wherein said rotor is positioned within said vacuum pump via electro-magnetic bearings, and said control circuitry is configured to control an axial position of said rotor by controlling a current supplied to electro-magnets associated with said bearings.

14. The vacuum pump according to claim 1, wherein said control circuitry comprises an input configured to receive a signal indicative of a pressure produced by said vacuum pump, said control circuitry being configured to control a relative axial position of said rotor and said stator in dependence upon a value of said signal.

15. The vacuum arrangement comprising an outlet of a vacuum chamber and a vacuum pump according to claim 1, said vacuum pump inlet being connected to said outlet of said vacuum chamber.

16. The vacuum arrangement according to claim 15, said vacuum pump inlet being connected to said outlet of said vacuum chamber, wherein said control circuitry is configured to control said axial position of said plate by changing an axial position of said vacuum pump relative to said outlet of said vacuum chamber.

17. The vacuum arrangement according to claim 15, further comprising a valve plate mounted on a different side of said vacuum chamber outlet than said stator of said vacuum pump, said plate and valve plate being configured for relative axial movement between an open position where gas can pass from said vacuum chamber into said vacuum pump and a closed position where said valve plate completely obscures at least one of said chamber outlet and said pump inlet such that gas cannot pass from said vacuum chamber to said vacuum pump.

18. The vacuum arrangement according to claim 15, wherein said plate is operable to move axially with respect to said chamber outlet to partially obscure said pump inlet by varying amounts and thereby vary said inlet conductance.

19. The vacuum arrangement according to claim 17, wherein said control circuitry is configured to control said axial position of said plate by changing an axial position of said vacuum pump relative to said outlet of said vacuum chamber and said valve plate comprises a recess and said plate is sized to fit within said recess.

20. A method of controlling a pumping capacity of a vacuum pump according claim 1, said method comprising: setting an axial position of said plate in dependence upon a required inlet conductance; operating the vacuum pump; determining a change of inlet conductance is required; and setting a new axial position of said plate to provide a new required inlet conductance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0068] FIG. 1 shows a vacuum pump according to the prior art;

[0069] FIG. 2 shows a vacuum pump comprising a turbo and drag stage according to an embodiment;

[0070] FIG. 3 shows a vacuum pump comprising a turbo and drag stage according to a further embodiment;

[0071] FIG. 4 shows a turbo pump according to an embodiment;

[0072] FIG. 5 shows a turbo vacuum pump and a drag vacuum pump mounted on different spindles according to an embodiment; and

[0073] FIG. 6 shows a turbo vacuum pump and a drag vacuum pump mounted on different spindles according to a further embodiment.

DETAILED DESCRIPTION

[0074] Before discussing the embodiments in any more detail, first an overview will be provided.

[0075] Embodiments provide a vacuum pump where a disc or plate has been added to the top of a pump's rotor for example a turbo rotor, the disc being raised or lowered to provide fine pressure control by altering the inlet conductance via the radial gap around the disc. Embodiments may use the magnetic bearing control already provided in some pumps to control the axial position or height of the disc. Where there is a regenerative and/or drag stage such as a Siegbahn stage mounted on the same spindle as the turbo stage raising/lowering the rotor affects the pumping speed/capacity of the drag/regenerative stage and can be used in conjunction with changes in the disc position to control pumping capacity.

[0076] In some embodiments rather than raising and lowering the rotor to change the axial position of the disc, the whole pump may be raised and lowered with respect to the chamber, whereby the rotor plate can replace the action of the pressure control valve. Inclusion of an O-ring may provide additional sealing. Providing pressure control by changing the axial position of a rotor plate and in some cases, the whole rotor allows additional valve components conventionally used for this to be replaced and thereby reduces the height of the installed pump and eliminates or at least reduces a source of particle shedding.

[0077] The use of a valve plate mounted on the rotor in this way provides a valve with symmetrical flow around the valve reducing non-uniformities in gas flow in the chamber.

[0078] In the above and in the following text, for convenience it is assumed that the pumps are orientated so that the spindle is vertical—in practice pumps can be orientated in any axis, such that where lowering and raising are discussed, this can be equated to changing an axial position, that is moving along an axis running parallel to the shaft of the pump.

[0079] FIG. 1 shows a conventional vacuum pump with a turbo and drag stage for evacuating a vacuum chamber 10. There is a valve plate 12 for controlling pressure in the chamber. In this embodiment the chamber outlet 14 and pressure control valve 12 are placed directly under the centre of the wafer (not shown). This helps improve the flow symmetry seen around the circumference of the wafer. Raising and lowering of the valve plate 12 causes the chamber to be isolated or in fluid communication with the pump.

[0080] FIG. 2 shows a vacuum pump according to an embodiment. In this embodiment the rotor 22 has a rotor plate 24 affixed to the upper end. The rotor 22 is magnetically levitated via magnetic spindle bearings 48 and control circuitry (not shown) in conjunction with the magnetic levitation system is used to control the vertical position of the rotor and thus, the position of the rotor plate 24 and to effect a rapid change in inlet conductance and thus, performance of the pump. The range of vertical movement available will depend on the magnetic design of the bearing, and the mechanical limitations of turbo blade clearance and where there is a Siegbahn drag stage the Seigbahn clearance and performance characteristics.

[0081] The valve plate 12 has been provided with a recess into which the rotor plate 24 can fit. In the embodiment of FIG. 2, both the valve plate 12 and rotor plate 24 are mounted for vertical movement, such that the valve plate 12 may be used to close the inlet and provide a seal via O-ring seal 70 and vacuum chamber floor 16, and provide gross pressure change, while the rotor plate 24 is used to vary the inlet conductance and provide finer pressure change. The valve plate's vertical position may be changed using actuator 30, while the rotor may move vertically by control of the magnetic bearings. Although not shown the rotor plate may have surface irregularities on its lower surface for deflecting particles into the pump inlet as it rotates.

[0082] In this embodiment variation in the axial position of the rotor 22 relative to the stator 25 changes both the inlet conductance due to the rotor plate obscuring the pump inlet to varying degrees, and changes the pumping capacity of the pump by changing the performance of the Siegbahn stage.

[0083] In this regard, turbo performance is relatively insensitive to the clearance between rotating and static blades. The clearance is there to avoid physical clashes between rotor blades 23 and stator blades 27.

[0084] Drag stages can include Siegbahn and/or Holweck types. Whereas Holweck is essentially a cylinder in a cylinder and insensitive to the vertical relationship between rotor and stator, the Siegbahn drag mechanism is a plate 44 rotating above a static plate 42 and performance is very sensitive to vertical clearance.

[0085] In this case, varying the Siegbahn clearance by varying the height of the rotor 22 will affect the backing pressure of the turbo stages and, depending on species and pressure, will affect the pumping speed. Thus, a pump with both a rotor plate 24 and a stage where pumping performance is sensitive to the relative axial position of the rotor 22 and stator 25 allows effective and rapid pressure control to be provided by varying the relative axial position of these components.

[0086] In some embodiments, at least some of the surfaces of the Siegbahn discs have surface irregularities such as grooves which may improve the efficiency of the pumping action. In some cases these may be different on different surfaces and this can amplify the effect on the pumping capacity of axial movement of the rotor.

[0087] In some cases surfaces on the discs on either the rotor or stator facing in one direction may have the same surface irregularities while those facing in the other direction may have different surface irregularities.

[0088] In summary the benefits of the above pump design include rapid pressure change in some cases without moving anything that was not already moving. This can eliminate a source of particle shedding.

[0089] In an alternative embodiment shown in FIG. 3, which can be used in conjunction with either or both of the above, the whole turbo pump is moved vertically relative to the chamber using actuator 30 to vary the conductance and hence performance. In this case the turbo body could incorporate the o-ring seal 70 for isolation. In this case fixed sample mounting means 18 has a recess for the rotor plate 24.

[0090] Advantages of these arrangements are a reduced height of the total package. There may be reduced flutter of the valve plate and reduced cost and improved stability due to the elimination of an interface.

[0091] Challenges may include the need for relatively powerful actuators to move the pump, some kind of bellows seal 72 may be needed between the chamber body and the turbo body. Furthermore the combination of the bellows and the jacking system may need to be capable of withstanding the crash torque of the pump.

[0092] FIG. 4 shows an alternative embodiment, where the pump is a turbo pump with no drag stage on the same spindle. In this case any axial movement of the rotor affects only the pump inlet conductance and this may make the effects easier to predict. In this case there is a bellows seal between the pump and chamber and an O-ring seal at the edge of the pump inlet that is configured to mate with the plate 12 which in this embodiment is fixed. The pump moves up and down in response to actuator 30 to provide gross control of the inlet conductance and to seal the chamber. In some embodiments the rotor may also move axially for fine control of the inlet conductance.

[0093] FIG. 5 shows a further embodiment where the turbo stage is on a different spindle from the drag stage. In this case the turbo spindle height can be varied independently of the drag spindle—thereby controlling inlet conductance independently of backing pressure. Furthermore, the arrangement allows the total height of the pump to be significantly reduced.

[0094] The traditional configuration includes drag stages and potentially regen stages on the same spindle as the turbo stages. Splitting the turbo and drag stages not only allows independent control of the axial position of the two rotors, but it allows them to be formed of different materials.

[0095] In the embodiment of FIG. 5, the turbo may be used in conjunction with the rotor plate and valve plate to seal the chamber and the drag stage is used to back the turbo pump.

[0096] The axial movement of the rotor plate can be done by the turbo part of the pump being jacked vertically—there being a flexible connection to the drag stage which would be fixed relative to the chamber. This would reduce the mass of the unit to be jacked up and down and would reduce the crash torque which the mounting system would need to withstand.

[0097] Alternatively the turbo and drag parts could be fixed together and jacked up and down together—then the drag part would additional leverage to a mounting system to withstand crash torque.

[0098] In some embodiments a plasma source is provided for injecting radicals into the interstage.

[0099] Control circuitry 60 is provided for controlling the relative axial position of the rotor of the turbo pump and thereby the inlet conductance. The control circuitry receives signals from a pressure sensor 50 allowing it to vary the turbo rotor's axial position and thereby the inlet conductance to the chamber to achieve a desired pressure in the chamber.

[0100] FIG. 6 shows a further example of a pump. In this example the turbo and drag stage are again mounted on different spindles. In this case there is a pendulum valve that allows the chamber to be connected to either the turbo pump which in this case is backed by the drag pump, or directly to the drag pump.

[0101] In high pressure operation the turbo pump is sealed by a turbo isolation valve which may comprise a valve plate acting in conjunction with a rotor plate.

[0102] In lower pressure operation where a higher vacuum is required the drag pump is connected to the exhaust of the turbo pump and the combined pump is used to pump the chamber to a high vacuum, control of pressure within the chamber being achieved by axial movement of the rotor of the drag stage and in some cases axial movement of the rotor plate on the turbo pump.

[0103] Allowing the drag stage to be used on its own to pump the chamber where a lower vacuum is required may be advantageous where aggressive or hot fluids are being pumped such as during a cleaning cycle. As the drag stage is mounted on a separate spindle it can be made of different materials to the turbo stage and these materials may be selected to be more resistant to high temperatures and aggressive chemicals. Furthermore, rapid pressure changes may be achieved by switching between the two arrangements using a valve such as a pendulum valve. Switching times of 0.2 seconds or lower may be achieved. Finer pressure control can be achieved by varying the axial position of the rotor of the drag stage and/or the rotor plate of the turbo stage.

[0104] In summary, FIG. 6 provides split flow/differential pumping to provide more than one inlet into the pump giving more than one pressure point. Each inlet can be valved separately to switch from one performance point to the other quickly.

[0105] In all of the above, the control of pump speed and pressure control, together with pump temperature and the control of any plasma source can be handled by a single controller.

[0106] 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.

[0107] 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.