CRYOPUMP

Abstract

A cryopump comprising:a pump inlet, a two stage refrigerator; a first stage array thermally coupled to a first stage of said two stage refrigerator; and a cryopanel structure coupled to a second stage of said two stage refrigerator is disclosed. The cryopanel structure comprises at least three flat panels. The first stage array is mounted between the pump inlet and the cryopanel structure, and comprises a plurality of slats, the plurality of slats each being mounted such that a side of each of the plurality of slats closest to the cryopanel structure is substantially aligned and offset longitudinally with respect to a corresponding one of said at least three flat panels.

Claims

1. A cryopump comprising: a pump inlet; a two stage refrigerator; a first stage array thermally coupled to a first stage of said two stage refrigerator; and a cryopanel structure coupled to a second stage of said two stage refrigerator; wherein said cryopanel structure comprises at least three flat panels; said first stage array being mounted between said pump inlet and said cryopanel structure, and comprising a plurality of slats, said plurality of slats each being mounted such that a side of each of said plurality of slats closest to said cryopanel structure is substantially aligned and offset longitudinally with respect to a corresponding one of said at least three flat panels.

2. The cryopump according to claim 1, wherein said plurality of slats are mounted to extend at an angle of between 110° and 160° with respect to said flat panels towards said pump inlet.

3. The cryopump according to claim 1, wherein said plurality of slats are mounted such that at least some of said slats shield one surface of an adjacent flat panel of said cryopanel structure from gas molecules entering said pump through said pump inlet.

4. The cryopump according to claim 1 wherein surfaces of said plurality of flat panels comprise coated portions coated with an adsorbent material and further portions that are not coated with said adsorbent material.

5. The cryopump according to claim 4, wherein one surface of at least some of said panels is coated with said adsorbent and the other surface is not coated.

6. The cryopump according to 5, wherein said plurality of slats are mounted such that at least some of said slats shield one surface of an adjacent flat panel of said cryopanel structure from gas molecules entering said pump through said pump inlet, said coated surface being said surface shielded by an adjacent one of said plurality of slats.

7. The cryopump according to claim 1, wherein said plurality of slats are arranged substantially parallel to each other, and said plurality of flat panels are arranged substantially parallel to each other.

8. The cryopump according to claim 1, wherein said plurality of panels are arranged to extend substantially parallel to a longitudinal axis of said pump.

9. The cryopump according to claim 1, wherein said plurality of slats and said plurality of panels are substantially rectangular.

10. The cryopump according to claim 1, wherein said plurality of slats are configured to overlap when viewed through said pump inlet in a direction parallel to said flat panels.

11. The cryopump according to claim 1, wherein said plurality of panels are all substantially the same size.

12. The cryopump according to claim 1, wherein said plurality of slats are all substantially the same size.

13. The cryopump according to claim 1, wherein said panels and said slats at either edge of the panel or slat array are smaller than those towards a middle.

14. The cryopump according to claim 4, wherein said adsorbent material is configured to adsorb type III gases such as hydrogen, helium and neon.

15. The cryopump according to claim 4, wherein said adsorbent material comprises a molecular sieve that coats said coated surface.

16. The cryopump according to claim 4, wherein said adsorbent material comprises one of: charcoal, activated carbon, zeolite or a porous metal surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0043] FIG. 1 shows a planar cryopanel structure according to an embodiment; and

[0044] FIG. 2 shows the cryopanel structure of FIG. 1 and the frontal array.

DETAILED DESCRIPTION

[0045] Before discussing the embodiments in any more detail, first an overview will be provided.

[0046] A cryopump with a planar frontal array which comprises parallel sloped panels or slats allows the second stage structure when it is also a planar structure to be aligned with the frontal array. This can provide a very high hydrogen pumping speed. The disadvantage is that the full area of the inlet may not be used as effectively as would be the case with a circular arrangement.

[0047] The second stage array panels run across the pump and lie vertically aligned with the longitudinal axis of the pump. The first stage array comprises sloped panels or slats between the second stage array and the pump inlet arranged so that an edge closest to the second stage array is aligned with a corresponding one of the second stage panels. The slats are sloped so that the surfaces slope towards the pump inlet. In some embodiments, one side of the second stage panels are coated in charcoal and this side is fully blocked by the higher temperature (of the order of 80 K) frontal array to direct impact by gas molecules entering the pump. Gases that are condensed at the temperature of the frontal array will impact that array and not proceed further, some may impact the non- charcoal coated surface of the second stage array and again will not proceed further. Type III gases such as hydrogen will bounce off these surfaces and will be adsorbed when they impact the charcoal coated surface. In this way the adsorbent coated surfaces will pump almost exclusively type III gases with the other surfaces collecting the other gases.

[0048] In some embodiments, the slats of the frontal array overlap when viewed along the longitudinal axis perpendicular to the cross section of the pump inlet. The amount of overlap will determine pumping speed and also how well the panels of the second stage array are shielded from first impact by a gas molecule entering the pump inlet. Embodiments of this pump are effective for evacuating semiconductor processing vacuum chambers such as those used for implant applications, and PVD (physical vapour deposition) processes.

[0049] FIGS. 1 and 2 show an embodiment of a cryopump with planar arrays formed of planar elements. FIG. 1 shows the parallel planar elements 25 of the second stage cryopanel structure within a pump having an inlet 5. The first stage frontal array is not shown. The cryopanel structure of the second stage has parallel panels 25 arranged equally spaced from each other in a line. There is a frontal array (not shown) having a set of sloped slats the lower surface of the slats being aligned with a corresponding panel. The frontal array is longitudinally offset from the second stage array to thermally isolate the two arrays to a degree and lies between the second stage array and pump inlet 5.

[0050] In some embodiments, one side of the panels 25 are coated with an adsorbent and the other side not coated. The sloped elements of the frontal array protect the coated surface from initial impact by molecules entering through the pump inlet.

[0051] FIG. 2 schematically shows the frontal array elements 12 relative to the second stage array elements 25 and pump inlet 5. As can be seen slats 12 are mounted between the pump inlet 5 and the cryopanel structure of the second stage array. They are sloped so that they overlap when viewed from the pump inlet 5. The angle Θ between the slats 12 and panels 25 is between 110° and 160°, such that the slats lean towards an adjacent panel and shield the panel from gas molecules entering the pump inlet. There are gaps between the panels 12 that allow gas molecules to enter the pump.

[0052] In some embodiments both surfaces of panel 25 are coated with an adsorbent while in other embodiments, one surface 24 of the panels is coated with an adsorbent while the other surface 22 is not. The only direct path for a molecule travelling between the frontal array slats 12 leads to the uncoated surface 22 of the cryopanel structure, so that molecules entering through the pump inlet either impact a slat 12 first, or the uncoated surface 22 of the second stage array. Thus, initial impact of any molecule is not with coated surface 24 and molecules that condense at the temperature of the first or second stage refrigerator are captured on these surfaces. Other type III molecules bounce off these surfaces towards coated surface 24 where they are captured by the adsorbent coating on impact. In this way the coated surface of the second stage elements are shielded by the sloped first stage array slats 12 from initial impact by molecules entering the pump. Molecules not condensed on the first stage array or on the second stage array will impact the coated surface 22 and be captured by the adsorbent.

[0053] 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.

[0054] 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.

[0055] 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.