VACUUM ASSEMBLY AND VACUUM PUMP WITH AN AXIAL THROUGH PASSAGE

Abstract

A vacuum pump and vacuum assembly. The vacuum pump comprises: an inlet for receiving gas; and an exhaust for exhausting the gas; a hollow shaft defining an axial passage extending through the pump from an opening in a base of the pump to an opening axially beyond the pump inlet. The shaft comprises an end remote from the base of the pump, the end being configured to attach to a cathode plate within a vacuum chamber evacuated by the vacuum pump. The shaft is configured for axial movement of the end between at least one open position in which the end is remote from the inlet of the vacuum pump and a sealing position in which the end is closer to the inlet.

Claims

1. A vacuum pump comprising: an inlet for receiving gas; and an exhaust for exhausting said gas; a hollow shaft defining at least a portion of an axial passage, said axial passage extending through said pump from an opening in a base of said pump to an opening axially beyond said pump inlet; said shaft comprising an end remote from said base of said pump, said end being configured to attach to a cathode plate within a vacuum chamber evacuated by said vacuum pump, said shaft being configured for axial movement of said end between at least one open position in which said end is remote from said inlet of said vacuum pump and a sealing position in which said end is closer to said inlet.

2. The vacuum pump according to claim 1, said vacuum pump comprising an actuating means for axially driving said end of said shaft between said axial positions.

3. The vacuum pump according to claim 2, comprising control circuitry for controlling said actuating means to position said end of said shaft in a plurality of different open positions in which said end is remote from said inlet of said vacuum pump.

4. The vacuum pump according to claim 1, wherein said end of said shaft is configured to support said cathode plate.

5. The vacuum pump according to claim 1, wherein a portion of said shaft comprises bellows, said bellows being configured to expand or contract in response to said axial movement.

6. The vacuum pump according to claim 1, said vacuum pump comprising a rotor and a stator, said rotor and said stator extending around said shaft.

7. The vacuum pump according to claim 6, said vacuum pump comprising a turbomolecular pump.

8. The vacuum pump according to claim 1, said vacuum pump further comprising said cathode plate mounted on said end of said shaft.

9. The vacuum pump according to claim 8, said cathode plate comprising annular sealing means around a lower surface of said cathode plate towards an outer circumferential edge, said annular sealing means being configured to seal said vacuum chamber from said vacuum pump when said shaft is in said sealing position.

10. The vacuum pump according to claim 8, wherein a lower surface of said cathode plate facing said axial passage comprises connectors for receiving electrical supply cables.

11. The vacuum pump according to claim 1, said vacuum pump further comprising pressure regulating circuitry configured to regulate a pressure within said vacuum chamber.

12. The vacuum pump according to claim 1, said vacuum pump comprising a housing, an opening in said housing comprising said pump inlet.

13. The vacuum pump according to claim 12, said housing comprising a sealing means arranged around said pump inlet, said sealing means being configured to mate with said cathode plate when said cathode plate is in said sealing position.

14. The vacuum pump according to claim 12 said housing comprising at least a portion of said shaft.

15. The vacuum assembly, comprising a vacuum pump according to claim 1, and a vacuum chamber base, said vacuum chamber base comprising an outlet, said vacuum pump being connected to said outlet such that said vacuum pump is operable to evacuate said vacuum chamber through said outlet.

16. A vacuum assembly according to claim 15, said vacuum chamber base comprising a support housing for housing and supporting said vacuum pump against said outlet, said shaft extending from a base of said support means, said base comprising an aperture aligned with said axial passage through said shaft.

17. A vacuum assembly according to claim 15, said vacuum chamber base comprising a sealing means around said outlet, said cathode plate being configured to mate with said sealing means in said sealing position.

18. A vacuum system comprising a vacuum chamber accommodating a cathode for supporting an electrostatic chuck and a vacuum pump according to claim 1, said vacuum pump being connected to an outlet of said vacuum chamber such that said vacuum pump is operable to evacuate said vacuum chamber through said outlet, said axial passage through said vacuum pump comprising a power source supply means for supplying power to said cathode, and at least one of control signal transmission means for transmitting control signals to said cathode and thermal energy supply means for transmitting heating or cooling energy to said cathode.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0049] FIG. 1 shows a vacuum pump, cathode and base of a vacuum chamber according to one embodiment;

[0050] FIG. 2 shows a vacuum pump, cathode and base of a vacuum chamber according to a further embodiment; and

[0051] FIG. 3 shows a vacuum pump, cathode and base of a vacuum chamber according to a still further embodiment.

DETAILED DESCRIPTION

[0052] Before discussing the embodiments in any more detail, first an overview will be provided.

[0053] In a typical conventional plasma etch chamber, a valve (gate, pendulum, or poppet) is installed between the turbo pump and the main chamber, and serves two functions:

1. Automatic Pressure Control (APC): where the movement of the plate of the valve is controlled to operate between a fully open and fully closed position to proportionally throttle gas flow, and therefore allow pressure control with the chamber; and
2. Isolation: where in the fully closed and sealed position, the turbo pump is vacuum sealed from the chamber, and so can remain under vacuum while the chamber is at atmosphere.

[0054] Embodiments provide an arrangement where there is no valve of this type between the pump and the chamber. In such embodiments, pressure control is either not provided or is provided by a different means, (for example by controlling the rotational speed of the turbo pump, or throttling the exhaust of the turbo pump, or with the use of controllable flow restrictors such as baffles further upstream in the chamber.

[0055] The second function of isolation is provided by using a system with a movable cathode plate such that the cathode plate is lowered onto the pump (or chamber housing holding the pump) and forming a vacuum seal. This allows normal maintenance of the chamber to be carried out while the pump remains under vacuum,

[0056] In embodiments a vacuum seal is provided between the top surface of the pump and the bottom surface of the chamber cathode plate such that when sealed the pump can remain under vacuum while the chamber can be vented to atmosphere.

[0057] In another configuration, the chamber housing that holds the hollow pump may be used to seal with the cathode, to again provide the same isolation between the turbo pump at vacuum and the chamber at atmosphere.

[0058] In summary the conventional APC or poppet valve between the chamber and the pump which typically provided isolation between the pump and chamber is dispensed with.

[0059] The isolation function is provided by forming a vacuum seal between the bottom of a movable cathode and the top of the pump or the top of the chamber housing the pump

[0060] FIG. 1 shows a design of a turbo pump with a hole in the middle according to an embodiment. The pump comprises a vacuum seal (H) formed between the top surface of the pump and the bottom surface of the chamber cathode (A) such that when sealed the pump can remain under vacuum while the chamber can be vented to atmosphere.

[0061] In another configuration FIG. 2, the chamber housing that holds the hollow turbo pump is used to seal with the cathode, to again provide the same isolation between the turbo pump at vacuum and the chamber at atmosphere.

[0062] Each embodiment relies on the concept of a movable cathode. In the drawings, this design is shown with a bellows (C) attached between the bottom of the cathode (A) and cathode support rod (or tube) (E), which is moved up and down by a cathode actuator (F). The normal process position is up, while to isolate the turbo pump the position is down.

[0063] Other potential variations of this design would include no bellows, but with the support rod attached directly to the cathode, while the cathode actuator would include a mechanism to extend up and down the support rod.

[0064] The seal (H) is configured to seal the TMP area (at mTorr pressures) from the surrounding chamber area (up to atmospheric pressures)

[0065] In FIG. 1 vacuum pump 5 which in this embodiment is a hollow turbo pump with a drag stage is mounted within a support housing which forms part of the base of vacuum chamber 10.

[0066] Within vacuum chamber 10 there is a cathode (A) which is sealingly attached to shaft (E). Shaft (E) and the cathode mounted thereon are configured to move axially, that is parallel to an axis running through the pump, between one or more open positions where vacuum chamber 10 is in fluid communication with vacuum pump 5 and a closed or sealed position where cathode (A) seals with the upper surface of the pump housing and isolates vacuum chamber 10 from pump 5.

[0067] There are sealing surfaces (H) on the underside of cathode (A) and on the upper side of the pump housing which sealing surfaces mate to form an effective seal and isolate the vacuum pump from the vacuum chamber which can then be vented. In this way, the vacuum pump is protected from pressure rises within the vacuum chamber. A vacuum chamber in a semiconductor manufacturing plant for example may require frequent servicing during which the pressure in the chamber will rise. It is important that this pressure rise is not transmitted to the areas downstream of the vacuum chamber where a vacuum should be maintained.

[0068] By using a movable cathode as a sealing plate to isolate the pump from the chamber, the conventional sealing plate such as that associated with a poppet valve can be dispensed with, reducing hardware and impediments in the flow path thereby improving conductance. Furthermore, as the cathode is mounted on shaft (E) extending through the centre of pump 5 the cathode is symmetrically mounted and asymmetries in gas flow are avoided or at least reduced.

[0069] The use of a hollow vacuum pump allows access to the underside of cathode (A) via an axial passage (D) through the centre of the pump. It is important that this axial passage and the interior of the vacuum chamber are isolated from each other to avoid or at least impede leakage of the higher pressure external to the vacuum chamber into the vacuum chamber. Thus, the shaft (E) that defines the axial passage has an impervious annular wall along its length and is sealed against the underside of cathode (A) and is integral or sealed with the base of the vacuum pump 5 or the base of the chamber 10.

[0070] In this embodiments the base of the chamber (B) comprises a portion extending from the base, this portion housing and supporting vacuum pump 5 and having a base (G) which extends up to form shaft (E) whose upper surface in this embodiment is in the form of bellows (C) and mates with the under surface of cathode (A). In this embodiment, there is an actuator (F) which drives a cylinder (I) that is attached to the underside of cathode (A) and drives the cathode (A) up or down depending on the movement of actuator F. Bellows (C) expands or contracts with the movement of the cathode, thereby maintaining the seal between the chamber and axial passage while the cathode (A) moves between an open position where the vacuum chamber 10 is in fluid communication with vacuum pump 5 and a closed sealed position where the vacuum chamber 10 is isolated from vacuum pump 5. Bellows provide a convenient manner of allowing axial movement while providing a seal. It would be clear to a skilled person though that any means that allows or provides axial movement and can still provide a seal would be appropriate. In this embodiment, the bellows forms the top portion of the shaft, in other embodiments, it may be located towards the base of the shaft or somewhere in the middle of the shaft.

[0071] In some embodiments, the cathode (A) may be axially movable into several different positions in which the pump and chamber are in fluid communication. The position of the wafer within the chamber affects the electric field experienced by the wafer and it may be advantageous to be able to adjust the position of the wafer during different parts of the manufacturing process. Providing a moveable cathode that allows the cathode to move to seal the chamber also allows control of the cathode and thus, the wafer position within the chamber and in this way hardware used to seal the chamber can also be used for positioning the wafer as desired.

[0072] As can be seen, the cathode acts as a seal to the chamber but it is not used to control inlet conductance. Thus, in some embodiments a separate pressure regulator (not shown) may be associated with the vacuum pump 5 which regulator is configured to control at least one of the rotational speed and the outlet conductance of the pump.

[0073] FIG. 2 shows an alternative embodiment, where cathode (A) seals directly with the base of the chamber body (B). In this case the turbo pump 5 is mounted within the support housing in a similar manner to the first embodiment but it is the base of the vacuum chamber (B) that seals with the cathode.

[0074] It should be noted that the seals between the under surface of cathode (A) and the upper surface of the chamber base (B) may have a number of forms, they may for example comprise labyrinthine paths with sealing elastomeric material within them which paths mate as the cathode moves to the sealing position and thereby provide effective sealing means.

[0075] FIG. 3 shows a third embodiment, where the means for driving the cathode is again a cylinder (I) within shaft (E), which cylinder is driven axially by actuating means (F) and provides the force for moving cathode (A) between different axial positions. In this embodiment the bellows (C) portion of the shaft is towards the base of the shaft and adjacent to the actuating means that drives the cylinder (I). In some embodiments, the cylinder (I) may not contact the cathode but may contact a protrusion in the shaft extending in to the axial passage and located above the bellows, such that the cylinder drives the portion of the shaft (E) above bellows (C) up and down.

[0076] 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.

[0077] 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.

[0078] 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.