CRYOPUMP

Abstract

A cryopump with a pump inlet; a two stage refrigerator; a first stage array arranged thermally coupled to a first stage of the two stage refrigerator; and a cryopanel structure coupled to a second stage of the two stage refrigerator. Surfaces of the cryopanel structure have portions that are coated portion with an adsorbent material and other portions that are not coated with the adsorbent material.

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 and comprising a plurality of cryopanels; wherein said plurality of cryopanels each comprise two surfaces, said two surfaces comprising a coated surface that is coated with an adsorbent material and a further surface that is not coated with said adsorbent material; said first stage array comprises a plurality of elements corresponding to said plurality of cryopanels; said plurality of elements being configured to be mounted between said pump inlet and said plurality of cryopanels; wherein each of said plurality of elements extends from a location between a corresponding cryopanel and said pump inlet towards a neighbouring cryopanel and slopes towards said inlet, such that each of said plurality of elements at least partially shields a coated surface of said neighbouring cryopanel from direct impact of a gas molecule passing through said pump inlet.

2. The cryopump according to claim 1, wherein said cryopanel structure is configured and mounted such that a surface of said cryopanel structure that a molecule entering said cryopump is most likely to impact first is said further portion of said cryopanel structure surface.

3. The cryopump according to claim 1, wherein said first stage array and said cryopanel structure are configured such that there is no line of sight path between said pump inlet and said coated portions of said surfaces of said cryopanel

4. The cryopump according to claim 1, wherein said plurality of cryopanels comprise a plurality of planar cryopanels, one side of said cropanels comprising said coated surface and the other side comprising said further surface.

5. The cryopump according to claim 1, wherein said plurality of cryopanels comprise a plurality of coaxial cylindrical cryopanels of different diameters.

6. The cryopump according to claim 5, wherein an outer surface of said cylindrical cryopanels comprise said coated surface and an inner surface comprise said further surface.

7. The cryopump according to claim 5, wherein said plurality of elements of said first array comprise a plurality of coaxial frustoconical elements of different diameters.

8. The cryopump according to claim 1, wherein said adsorbent material is configured to adsorb type III gases such as while type III gases, such as hydrogen, helium and neon,

9. The cryopump according to claim 1, wherein said adsorbent material comprises a molecular sieve that coats said coated surface.

10. The cryopump according to claim 1, wherein said adsorbent material comprises one of: charcoal, activated carbon, zeolite or a porous metal surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0035] FIG. 1 shows a section through a cryopanel structure of a second stage array and a frontal array of a cryopump of an embodiment;

[0036] FIG. 2 shows a section of the cryopanel and frontal array structure of FIG. 1 from a different angle;

[0037] FIG. 3 shows a planar cryopanel structure according to a further embodiment; and

[0038] FIG. 4 shows the cryopanel structure of FIG. 3 and the frontal array.

DETAILED DESCRIPTION

[0039] Before discussing the embodiments in any more detail, first an overview will be provided.

[0040] A second stage cryopanel structure is provided where adsorbent such as charcoal coats the surface on one side of the panel to collect hydrogen, while the other side is bare of adsorbent and will collect other molecules such as photoresist that condenses at the low temperatures of the cryopanels.

[0041] In some embodiments, there is a higher temperature (of the order of 80K) frontal array comprising elements that are configured to overlap when viewed through the pump inlet. The amount of overlap will determine the maximum hydrogen pumping speed. In this regard, a large overlap will impede gas flow and reduce pumping speed for the gases not pumped by the frontal array, however, it will protect the second stage array and increase its lifetime between regenerations.

[0042] This cryopump will be particularly effective for pumping gases from semiconductor processing such as implant applications, and PVD (physical vapour deposition) applications too.

[0043] Embodiments provide a planar and a circular solution. Conventionally a frontal array structure is circular since the pump inlet and interface to the vacuum chamber is circular. A planar frontal array which comprises parallel sloped panels allows the second stage structure to be aligned with the frontal array and this can provide a very high hydrogen pumping speed. The disadvantage is that the full area of the inlet may not be used effectively.

[0044] A circular frontal array is better adapted to the circular inlet of the pump and vacuum chamber interface. To provide effective shielding of surfaces of the cryopanel structure by a circular frontal array cylindrical cryopanels may be used. The circular frontal array may advantageously be formed of overlapping frustoconical elements. The internal surfaces of the cylindrical cryopanels may be bare and molecules deflected by these surfaces will impact the coated outer surface of the neighbouring coaxial cylindrical structure. This will yield a pump that doesn't degrade or at least has reduced degradation over time for pumping speed.

[0045] FIG. 1 shows a coaxial second stage cylindrical cryopanel structure 20 according to an embodiment, that is shielded by a first stage or frontal array 10.

[0046] Frontal array 10 comprises a plurality of coaxial frusto conical elements 12 which overlap when viewed through the pump inlet 5.

[0047] The plurality of elements 12 which form the frontal array are thermally connected to the first stage refrigerator of the cryopump and are held at a first stage temperature in the range of 40-130K. The upper surface of the frontal array elements 12 that face towards pump inlet 5 are sloped and molecules hitting these surfaces will be captured if they condense at the temperatures of the first stage refrigerator or will be deflected towards the under surface of an outer neighbouring element. The paths between the elements 12 of the first stage array that lead into the pump towards the second stage cryopanel structure are angled towards the inner surface of the cylindrical cryopanels. Thus, molecules travelling along these paths will preferentially impact an inner surface 22 of a cylindrical element of the cryopanel structure when they arrive at the second stage cryopanel structure. If the molecule is a gas that condenses at the temperatures of the second stage array, that is between 4-25 K, such as nitrogen or photoresist the molecule will follow the trajectory shown by arrow 9 and be captured by the inner surface 22. If the molecule is a type III gas molecule that is not condensed at the second stage temperatures then the molecule will follow the trajectory shown by arrow 7 and be deflected by the inner surface 22 of the cylindrical cryopanel element towards an outer surface 24 of a neighbouring inner cylindrical element and will be captured by the adsorbent surface coating the inner surface 24.

[0048] In this way the inner surfaces 24 of the coaxial cylindrical second stage cryopanel elements are shielded from gas molecules other than type III gas molecules and thus, the long term effectiveness of the cryopanel structure is improved and pumping speeds do not degrade unduly due to adsorption of molecules such as photoresist.

[0049] FIG. 2 shows the same cryopanel structure from a different angle. Here the frusto conical elements 12 of the first stage array 10 can be more clearly viewed extending over the coaxial cylindrical elements 25 that form the second stage cryopanel structure.

[0050] FIGS. 3 and 4 show an alternative embodiment where the two arrays are planar and each are formed of planar elements. The cryopanel structure has parallel panels, one side of which are coated with an adsorbent and the other side not coated. The frontal array comprises sloped elements extending from the elements of the second stage array and sloping towards the pump inlet. In this way they protect the coated surface from initial impact by molecules entering through the pump inlet.

[0051] FIG. 3 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.

[0052] FIG. 4 schematically shows the frontal array elements 12 relative to the second stage array elements 25 and pump inlet 5. As can be seen elements 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 and as for the embodiment of FIGS. 1 and 2, the path between the frontal array elements 12 leads to the bare surface 22 of the cryopanel structure, so that molecules entering through the pump inlet are directed towards this uncoated surface. Thus, initial impact is with bare surface 22 and any molecules that condense at the temperature of the second stage refrigerator are captured. Other type III molecules bounce off surface 22 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 element 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 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.