TURBOMOLECULAR PUMP AND METHOD AND APPARATUS FOR CONTROLLING THE PRESSURE IN A PROCESS CHAMBER

Abstract

A turbomolecular pump and method and apparatus for controlling the pressure in a process chamber using such a pump is disclosed. The turbomolecular comprises: a rotor comprising a plurality of blades on a rotatable shaft; a control motor for driving the rotatable shaft; wherein the control motor is sized to output a power that is more than three times larger than a power required to drive the shaft at a constant velocity that is sufficiently high to provide an exhaust pressure of 5 millibars.

Claims

1. 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 three or more 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.

2. The turbomolecular according to claim 1, wherein said turbomolecular pump comprises a drag stage.

3. The turbomolecular according to claim 1, wherein said turbomolecular pump does not comprise a drag stage.

4. The turbomolecular pump according to claim 1, said rotor further comprising a skirt portion extending in an axial direction beyond said blades of said rotor and having an annular cross section coaxial with and surrounding said shaft, said skirt portion forming a rotor of said control motor.

5. The turbomolecular pump according to claim 4, wherein said turbomolecular pump comprises a Holweck drag stage, said skirt portion comprising a skirt of said Holweck drag stage.

6. The turbomolecular pump according to claim 4, wherein said skirt portion comprises magnets.

7. The turbomolecular pump according to claim 4, wherein said skirt portion comprises a smaller cross section adjacent to said blades of said rotor and a larger cross section remote from said blades.

8. The turbomolecular pump according to claim 4, wherein said stator of said control motor is arranged inside said skirt portion and around said shaft.

9. The turbomolecular pump according to claim 4, wherein said stator of said control motor is arranged around said skirt portion.

10. The turbomolecular pump according to claim 4, wherein said pump comprises a pump housing and said control motor is located within said pump housing.

11. The turbomolecular pump according to claim 4, said turbomolecular pump comprising a further motor for driving said shaft, said further motor and shaft forming a drive spindle and said control motor being formed around said drive spindle.

12. The turbomolecular pump according to claim 11, wherein 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.

13. The turbomolecular pump according to claim 4, wherein 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.

14. The turbomolecular pump according to claim 13, wherein 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.

15. The turbomolecular pump according to claim 13, said turbomolecular pump comprising a purge gas inlet at an exhaust, wherein said control circuitry is configured to control addition of a purge gas at said exhaust in conjunction with controlling said control motor to slow said rotor.

16. 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.

17. The turbomolecular pump according to claim 16, wherein said skirt portion comprises a smaller cross section adjacent to said blades of said rotor and a larger cross section remote from said blades.

18. The turbomolecular pump according to claim 16, wherein said stator of said control motor is arranged inside said skirt portion and around said shaft.

19. The turbomolecular pump according to claim 16, wherein said stator of said control motor is arranged around said skirt portion.

20. The turbomolecular pump according to claim 16, wherein said skirt portion has an inner diameter substantially equal to an inner diameter of the most downstream blade of said turbomolecular pump.

21. The turbomolecular pump according to claim 16, wherein said turbomolecular pump comprises a drag stage.

22. The turbomolecular according to claim 16, wherein said turbomolecular pump does not comprise a drag stage.

23. The turbomolecular pump according to claim 21, wherein said turbomolecular pump comprises a Holweck drag stage, said skirt portion comprising a skirt of a Holweck drag stage.

24. The turbomolecular pump according to claim 15, wherein said skirt portion comprises magnets.

25. The turbomolecular pump according to claim 15, wherein said pump comprises a pump housing and said control motor is located within said pump housing.

26. The turbomolecular pump according to claim 15, said turbomolecular pump comprising 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.

27. The turbomolecular pump according to claim 26, wherein 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.

28. The turbomolecular pump according to claim 16, wherein 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

29. The turbomolecular pump according to claim 28, wherein 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.

30. The turbomolecular pump according to claim 28, said turbomolecular pump comprising a purge gas inlet at said exhaust, wherein said control circuitry is configured to add a purge gas at said exhaust in conjunction with controlling said control motor to slow said rotor.

31-32. (canceled)

33. 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 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 a shaft at a constant velocity that is sufficiently high to provide an exhaust pressure of 5 millibars.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0060] FIG. 1 shows a turbomolecular pump without a drag stage according to first embodiment;

[0061] FIG. 2 illustrates a turbomolecular pump according to a second embodiment;

[0062] FIG. 3 illustrates a turbomolecular pump according to the second embodiment configured to evacuate a process chamber;

[0063] FIG. 4 illustrates a turbomolecular pump with a drag stage and combined control motor according to an embodiment; and

[0064] FIG. 5 illustrates a further embodiment of a turbomolecular pump with Holweck drag stage and combined control motor.

DETAILED DESCRIPTION

[0065] Before discussing the embodiments in any more detail, first an overview will be provided.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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. In this embodiment, 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. 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 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.

[0071] 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. In this case, 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.

[0072] 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. Thus, 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. It 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. 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.

[0073] 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.

[0074] 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 of FIG. 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 comprise magnets 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 an additional motor 30 provided on the conventional position on the shaft 23 of the pump which acts to drive the shaft 23 during steady state operations. The control motor 16 which is a larger motor provides the acceleration and deceleration for controlling changes in the pressure within the process chamber.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.