A TURBOMOLECULAR PUMP, A VACUUM PUMPING SYSTEM AND A METHOD OF EVACUATING A VACUUM CHAMBER

Abstract

A turbomolecular pump, vacuum pumping system and method of evacuating a vacuum chamber is disclosed. The turbomolecular pump comprises: a rotor comprising a plurality of rotor blade rows, a stator comprising a plurality of stator blade rows and an outer casing, the rotor being rotatably mounted within the stator; wherein at least a portion of a surface of at least one of the rotor and the stator comprise a non-evaporable getter material.

Claims

1. A turbomolecular pump comprising: a rotor comprising a plurality of rotor blade rows, a stator comprising a plurality of stator blade rows and an outer casing, said rotor being rotatably mounted within said stator; wherein at least a portion of a surface of at least one of said rotor and said stator comprises a non-evaporable getter material; said turbomolecular pump further comprising: a pressure sensor for sensing pressure; a heater configured to heat said at least a portion of said turbomolecular pump such that said non-evaporable getter material is heated to above its activation temperature; and control circuitry for controlling operation of said turbomolecular pump said control circuitry being configured in response to a signal from said pressure sensor indicating a pressure to have fallen below a first predetermined value to activate said heater.

2. The turbomolecular pump according to claim 1, wherein said control circuitry is further configured to activate rotation of a rotor of said pump in response to a signal from said pressure sensor indicating a pressure to have fallen below an initial predetermined value, said first pressure being lower than said initial pressure.

3. The turbomolecular pump according to claim 1, wherein said control circuitry is further configured to deactivate said heater in response to one of: a predetermined time and a temperature sensor indicating a temperature in said turbomolecular pump being at or above a predetermined value.

4. The turbomolecular pump according to claim 1, wherein said control circuitry is configured in response to detecting said pressure reaching a second predetermined level, to generate a rotor deactivation signal for deactivating rotation of said rotor.

5. The turbomolecular pump according to claim 1, wherein said at least a portion comprises at least one of a subset of said rotor blade rows and an inner surface of said outer casing.

6. The turbomolecular pump according to claim 1, further comprising an exhaust conduit for exhausting gas output from said turbomolecular pump, at least a portion of an internal surface of said exhaust conduit being coated with said non-evaporable getter material.

7. The turbomolecular pump according to claim 6, wherein said at least a portion of said exhaust conduit is detachably mounted to said turbomolecular pump.

8. A turbomolecular pump comprising: a rotor comprising a plurality of rotor blade rows, a stator comprising a plurality of stator blade rows and an outer casing, said rotor being rotatably mounted within said stator; wherein at least a portion of at least one of said stator and said outer casing comprises a gas capture structure for capturing gas, said gas capture structure comprising a skeletal framework comprising a non-evaporable getter material, said skeletal framework being formed from an aerogel.

9. The turbomolecular pump according to claim 8, wherein said at least a portion comprises a static portion of said turbomolecular pump close to an inlet of said pump.

10. A vacuum pumping system comprising a turbomolecular pump according to claim 1, and comprising at least one further pump downstream and in series with said turbomolecular pump.

11. The vacuum pumping system according to claim 10, wherein said at least one further pump comprises a further turbomolecular pump.

12. The vacuum pumping system according to claim 10, wherein said at least one further pump comprises a primary pump.

13. A method of evacuating a chamber comprising: attaching a vacuum pumping system according to claim 12 to said chamber; evacuating said chamber to a first pressure using said primary pump; rotating the rotor of the turbmolecular pump; activating a heater to heat said turbomolecular pump to activate said non-evaporable getter material; deactivating said heater.

14. The method according to claim 13, comprising a further step of stopping rotation of said turbomolecular pump and continuing to provide a pumping process using capture by said non-evaporable getter material.

15. The method according to claim 13, wherein said heating step is part of a bakeout process during which the vacuum chamber and turbomolecular pump are heated to encourage outgassing.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0053] FIG. 1 shows a vacuum pumping system according to an embodiment;

[0054] FIG. 2 shows a vacuum pumping system according to a further embodiment; and

[0055] FIG. 3 shows a flow diagram illustrating steps in a method according to an embodiment.

DETAILED DESCRIPTION

[0056] Before discussing the embodiments in any more detail, first an overview will be provided.

[0057] The ultimate pressure achieved by a turbomolecular pump (TMP) even under zero flow conditions, is limited by the partial pressure in the exhaust line and the compression ratio of the TMP for Hydrogen. Furthermore, the vacuum level can be quickly degraded in situations requiring the TMP to be stopped (for example during a vibration sensitive procedure or when a high magnetic field is applied).

[0058] Embodiments of the present invention address these problems with the use of a NEG coating activated at HV/UHV (high vacuum and ultra-high vacuum) pressures, this allows the ultimate and H.sub.2 pumping performance of the TMPs to be significantly enhanced.

[0059] NEGs are known for their high pumping efficiency for H.sub.2. TMPs are however, poor at pumping H.sub.2. Coating at least some of the internal surfaces of the TMP such as the blade rows and the upper envelope with NEG material provides a pump that combines the pumping efficiency of a NEG with that of a TMP. The NEG may be activated at the same time as the bakeout of the vacuum system and TMP.

[0060] With TMPs, at pressures below 1×10.sup.−7 mbar the dominant gas load is increasingly H.sub.2 and this is the limitation for ultimate performance of TMPs in UHV. The pumping speed for H.sub.2 of a NEG coating is @ 0.35 l/s/cm.sup.2 (c.f. 3 l/s cm.sup.2 for a metal strip). For an ISO160 flange TMP with intrinsic H.sub.2 pumping speed of ˜300 l/s each cross-sectional area NEG coating of ˜200 cm.sup.2 would provide ˜70 l/s.

[0061] A coating of ˜3 blade rows+1×the inner envelope would give a NEG H.sub.2 speed of ˜280 l/s.

[0062] The following advantages may be provided by embodiments:

1. Effective doubling of a similar pure TMP's H.sub.2 pumping speed
2. Allows H.sub.2 pumping to continue if the TMP is stopped
3. Effectively reduces the partial pressure of H.sub.2 in the vacuum chamber, TMP and backing line. This will effectively ‘increase’ the H.sub.2 compression ratio of the TMP or in time improve the ultimate pressure rather than degrade the ultimate pressure as currently happens in TMP systems where the H.sub.2 partial pressure in its backing line rises with time

[0063] The NEG/TMP combination pump would be most suited for UHV and XHV (extremely high vacuum) situations where the activation of the NEG is performed during the heating of the chamber and TMP during bakeout.

[0064] The unlimited capacity of the TMP for outgassing and stimulated desorption loads overcomes a limitation of the finite pumping capacity of NEGs

[0065] FIG. 1 show as turbomolecular pump 10 according to an embodiment. This turbomolecular pump comprises a rotor 12 and a stator 14. In this embodiment the upper rotor blade surfaces and the inner surface of the stator 14 are coated with a non-evaporable getter material. In other embodiments, the lower rotor blades and the stator blades may also be coated with the NEG material.

[0066] The turbomolecular pump 10 has flange 15 for attaching to a vacuum chamber. TMP 10 also has a heating band 20 around its upper surface, which is used to activate the NEG material and this is switched on during a bakeout process of the vacuum chamber.

[0067] TMP 10 is attached via a conduit 35 to a valve 38 and then via a further conduit 36 to a primary pump 30. In some embodiments one or more of the conduits 35, 36 are also coated with the NEG material.

[0068] Primary pump 30 acts to evacuate the vacuum chamber to a first pressure, whereupon the TMP 10 is activated and evacuates the vacuum chamber to a second pressure. The primary pump 30 continues to run and operates as a backing pump to the TMP. When the second pressure has been reached, the heater 20 is switched on and the non-evaporable material is activated, whereupon the turbomolecular pump operates both as a pump both as a molecular pump and as a capture pump.

[0069] In this embodiment control circuitry 45 associated with turbomolecular pump 10 receives signals from a pressure sensor 42 and controls the TMP 10 to perform the functions described above. In particular, when pressure sensor 42 indicates the pressure in the TMP 10 has fallen to the first pressure the control circuitry 45 activates the rotor 12 and when the pressure has fallen to the second pressure the control circuitry activates heater band 20. When a temperature sensor (not shown) indicates that the temperature within the pump has risen to the activation temperature of the non-evaporable getter material the control circuitry 20 sends a signal to turn the heater band off. When the pressure sensor 42 indicates that a further low pressure has been reached in some embodiments the control circuitry may control the rotor to stop rotating, at which point the vacuum within the vacuum chamber may be maintained by the activated NEG material.

[0070] In this embodiment conduit 36 connecting the two pumps is itself coated with a getter material which can also be activated by heating. The conduit 36 is removably connected to the turbomolecular pump 10 such that when the non-evaporable getter material of the exhaust is depleted the exhaust conduit 36 can be exchanged for one with fresh non-evaporable getter material on it allowing this material to be activated on heating and provide additional capture. In this regard, conduit 36 is attached via a valve mechanism 38 such that the vacuum within the chamber and turbomolecular pump can be maintained during the exchange of the exhaust conduit 36.

[0071] In other embodiments the NEG material may be coating or formed of an aerogel, which aerogel structure may form portions of the static part of the TMP 10, particularly those adjacent to the inlet of the pump. In some embodiments, portions of the stator, the blade spacers and/or the spider may be formed of an aerogel.

[0072] FIG. 2 shows a further embodiment which is similar to that of FIG. 1 but this has an additional turbomolecular pump 40 arranged downstream of turbomolecular pump 10. Turbomolecular pump 40 is also backed by primary pump 30.

[0073] There are a plurality of valves 38a, 38b, 38c allowing the different pumps to be connected together in different arrangements. In this embodiment, conduit 37 between the two turbomolecular pumps 10, 40 is coated with NEG material and is detachably connected to the vacuum system allowing it to be replaced. Valve 38a can be closed during replacement of the conduit 37 and in some embodiments TMP 10 can continue to operate backed by primary pump 30. Following replacement of conduit 37, valve 38c may be opened and 38b closed allowing pressure in TMP 40 and conduit 37 to be reduced, whereupon TMP 40 can be switched on, and at a certain point conduit 37 heated and valve 38a opened. The additional TMP 40 helps reduce the pressure further and owing to the NEG material in TMP 10 and 37 predominantly pumps gas from which the lighter gases have been substantially removed making for better compression.

[0074] FIG. 3 shows a diagram illustrating steps in a method for evacuating a chamber according to an embodiment. The evacuation of the chamber starts with the primary pump pumping down at step S10. When a pressure sensor senses the pressure to have reached a first pressure at step D05, the first pressure may be between 0.1 and 10.sup.−3 mbar, the TMP is activated at step S20 and pumps the chamber down to a second pressure. When the pressure sensors sense the pressure has fallen to the second pressure at step D15, which second pressure may be in the region of 10.sup.−7 to 10.sup.−9 mbar, the heater is activated at step S30. The getter material is activated by heating the TMP to the activation temperature of the material, this may occur at the same time as bakeout of the vacuum chamber.

[0075] Once the NEG material has been activated and a temperature sensor indicates that a temperature above the activation temperature has been reached at D25, then the heater is switched off at step S40 and the pump continues to pump until a lower pressure is sensed to have been reached at D35. In some embodiments where the vacuum pump is used to evacuate a chamber of an analyser, this third pressure will be the pressure required for the analysis. Such an analyser may be an electron microscope or a mass spectrometer. Once the pressure required for analysis has been reached, in some embodiments the TMP and vacuum chamber may be isolated using a valve 38 of FIG. 1 and the TMP and primary pump may be switched off at step S50. This may occur where the analyser is vibration sensitive. The analyser may then be switched on at step S60, analysis performed and when complete the pumps may be switched on again and valve 38 opened. While the TMP is not rotating it will still be providing some pumping by the capture of gas molecules on the NEG material within the pump.

[0076] It should be noted that the vacuum system may be controlled to perform the steps of this method by the control circuitry 45 of FIG. 1.

[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.