VACUUM PUMP

Abstract

A vacuum pump comprising: a rotor rotatably mounted within a stator; the rotor comprising a plurality of angled blades arranged along a helical path from an inlet to an outlet; the stator comprising a plurality of perforated elements forming a plurality of perforated discs arranged to intersect the helical path at different axial positions, the perforations allowing gas molecules travelling along the helical path to pass through the perforated elements. Each of the perforated discs comprises an outer curved wall forming an outer circumference of the disc and an inner curved wall forming a portion of an inner circumference of the disc, the inner circumference comprising at least one gap where there is no inner wall.

Claims

1. A vacuum pump comprising: a rotor rotatably mounted within a stator; said rotor comprising a plurality of angled blades arranged along a helical path from an inlet to an outlet; said stator comprising a plurality of perforated elements forming a plurality of perforated discs arranged to intersect said helical path at different axial positions, said perforations allowing gas molecules travelling along said helical path to pass through said perforated elements; wherein each of said perforated discs comprises an outer curved wall forming an outer circumference of said disc and an inner curved wall forming a portion of an inner circumference of said disc, said inner circumference comprising at least one gap where there is no inner wall.

2. The vacuum pump according to claim 1, wherein each of said perforated discs comprises at least two perforated elements, said inner circumference comprising at least two gaps, said two gaps in said inner circumference being between adjacent perforated elements forming said perforated disc.

3. The vacuum pump according to claim 1, wherein said perforated elements are configured to be mounted such that there is substantially no gap between adjacent outer curved walls.

4. The vacuum pump according to claim 1, wherein said perforated elements further comprise side walls extending between said inner curved wall and said outer curved wall at either end of said perforated elements.

5. The vacuum pump according to claim 1, wherein said perforated elements further comprise a plurality of partitions extending from said outer curved wall to said inner curved wall, perforations being formed between said plurality of partitions.

6. The vacuum pump according to claim 1, wherein said inner curved wall of each of said plurality of perforated elements comprises at least one indent extending from said inner curved wall towards said outer curved wall, said at least one indent comprising said one of said at least one gap in said inner circumference.

7. The vacuum pump according to claim 6, wherein said indent extends substantially to said outer curved wall.

8. The vacuum pump according to claim 6 when dependent on claim 5, wherein said a width of a wall surrounding said indent and a width of said inner and said outer curved walls are substantially wider than a width of said partitions.

9. The vacuum pump according to claim 6, wherein said walls of said at least one indent are angled such that when rotating a radius of said rotor crosses a radially outer portion of said wall before said a radially inner portion of said wall.

10. The vacuum pump according to claim 4, wherein said side wall of said perforated element that said rotor crosses first when rotating is angled such that said radius of said rotor crosses a radially outer portion of said side wall before said rotor crosses a radially inner portion of said wall.

11. The vacuum pump according to claim 4, wherein said side wall of said perforated element that said rotor crosses last when rotating comprises a protrusion extending therefrom, said protrusion extending circumferentially beyond said side wall.

12. The vacuum pump according to claim 1, said stator further comprising a cylindrical inner surface formed by a stack of rings each having a cylindrical inner surface, said plurality of perforated elements being mounted on respective rings, such that said plurality of perforated elements form a plurality of perforated discs intersecting said helical path at different axial positions.

13. The vacuum pump according to claim 1, wherein said perforated elements are formed of aluminium.

14. The vacuum pump according to claim 1, wherein said rotor is formed of stainless steel.

15. The vacuum pump according to claim 1, wherein said perforated elements located towards an inlet of said vacuum pump comprise a transparency of more than 50% and said perforated elements located towards an outlet of said vacuum pump comprise a transparency of more than 40%.

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 perforated stator element according to an embodiment;

[0050] FIG. 2 shows a semiconductor chamber and a set of pumps for evacuating the semiconductor chamber according to an embodiment;

[0051] FIG. 3 shows a vacuum pump of a pump according to an embodiment; and

[0052] FIG. 4 shows a rotor for a vacuum pump according to an embodiment.

DETAILED DESCRIPTION

[0053] Before discussing the embodiments in any more detail, first an overview will be provided.

[0054] Embodiments provide an adapted Schofield pump having a rotor with a plurality of angled blades arranged along a helical path. The stator comprises a plurality of perforated discs arranged to intersect the helical path at different axial positions and through which the gas passes on its way from the inlet to outlet. The pump is suitable for pumping in the pressure region of 1 mbar and 5×10.sup.−2 mbar and provides a pumping capacity in the region of 600 l/s. In embodiments the rotor is mounted on magnetically levitated bearings and this makes it suitable for locating in a clean room and for evacuating a semiconductor processing chamber, in particular, when backed by a roots blower and primary pump combination which may be located in the basement.

[0055] However, passing the gas through perforated stator elements presents its own challenges due to the low axial clearance gaps between the perforated elements and the rotor. Embodiments, seek to address these challenges by designing the stator to provide spaces in the inner circumference such that differential expansion of the inner portion relative to the outer portion can generally be accommodated within the spaces reducing the chances of the expansion leading to axial movement of the element which in turn can lead to clashes between the rotor and stator.

[0056] FIG. 1 shows a perforated element 14, that forms a portion of perforated stator disc. In this embodiment the perforated stator disc, is formed in two sections, which comprise the two elements 14, which are joined together (sloping side wall to side wall with protrusion) to form a complete disc. The perforated stator disc has a transparency of more than 30% and each element 14 comprises an inner circumferential wall 18, an outer circumferential wall 16 and side walls 17 which form a frame providing mechanical stability to the perforated element 14.

[0057] In this embodiment, there are radially extending partitions 36 running between the inner 18 and outer 16 walls and between which are formed perforations 38. These radially extending partitions conduct heat from the inner walls forming the central portion of the disc to the outer walls forming the outer portion, thereby reducing the heat increase of the central ring of the disc.

[0058] Indents 37 are provided in the inner wall 18 forming the inner ring of the disc and these provide space for the inner ring to expand into thereby reducing the chances that expansion will cause buckling of the ring with the associated axial movement which can cause clashing between the rotor and stator.

[0059] The perforated element 14 is configured so that one side wall 17 comprises a protrusion 33 that extends circumferentially beyond the side wall, this protrusion, causes there to be a gap between the radially inner parts of the two perforated elements when they are mounted together to form the disc. This gap also provides space for circumferential expansion of the inner wall thereby reducing the chances that the inner wall will buckle on heating and move axially when expanding due to an increase in temperature.

[0060] The perforated element is also configured so that the side walls 17 and indents 37 are sloped away from the oncoming rotor, so that the rotor will cross the junction between elements 14 and the walls of the indents 37 at a radially outer portion. This means that were there to be some axial movement of the inner ring at these gaps, the rotor will meet the radially outer portion of the side wall of the indent or element 14 first and slide along this, pushing against any axial movement and reducing the chances of a catastrophic clash where the perforated element 14 would be damaged.

[0061] FIG. 2 shows a semiconductor chamber 5 located within a clean room or semiconductor fab 70 and with a Schofield vacuum pump 10 according to an embodiment attached to the semiconductor chamber. The vacuum pump 10 has magnetically levitated bearings and as such can be mounted in the clean room 70 and can be attached to the vacuum chamber 5 by a relatively short conduit 12.

[0062] Remote from the vacuum pump 10 and semiconductor chamber 5 is a backing pump combination 90 which comprises a roots blower and a primary pump. These are located in the basement 80. For this reason the conduit 92 between the backing pump combination 90 and the Schofield pump 10 is relatively long and this affects the effectiveness of the backing pump 90 particularly at low pressures.

[0063] The combination of the Schofield pump 10 with relatively high pumping capacity attached close to the semiconductor chamber 5 and with the backing pumps 90 which can pump effectively at the higher pressures of the effective pumping range provide a set of pumps which pump effectively in the pressure range of a conventional drag pump but with increased pumping capacity.

[0064] The Schofield vacuum pump 10 is shown schematically in FIG. 3. Vacuum pump 10 comprises a plurality of perforated stator elements 14 (as shown in FIG. 1) which are mounted together to form perforated discs through which the gas flows from an inlet 26 to an exhaust 28. The perforated discs are mounted at different axial positions on cylindrical rings 40 and extend between rows of blades 30 of rotor 35 which blades 30 form a helical path from the inlet 26 to the outlet 28. The helical rotor 35 is mounted on shaft 42 and rotates during operation. Shaft 42 is mounted on magnetically levitated bearings 45.

[0065] FIG. 4 shows a view of rotor 35 of vacuum pump 10 and shows the helical path formed by rotor blades 30. Rotation of rotor 35 imparts momentum to gas molecules that the blades contact, and sends them towards the outlet 18 through the perforated elements 14. Impact with the non-perforated portions of the stator disks slows the gas molecules and provides the drag of the drag pump, pulling the molecule trajectory towards the output.

[0066] 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.

[0067] 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.

[0068] 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.