CRYOPUMP

Abstract

A cryopump comprising: a vessel comprising a radiation shield having a frontal opening, said frontal opening forming an inlet to said vessel; a frontal array thermally coupled to said radiation shield and mounted across said frontal opening; a cryopanel structure mounted within said vessel; a two stage refrigerator extending into said vessel, a first stage of said refrigerator being thermally coupled to said radiation shield and a colder second stage of said refrigerator being thermally coupled to said cryopanel structure; wherein said vessel comprises an elongate vessel a distance between a surface of said cryopanel structure closest to said frontal opening and a surface of said frontal array closest to said cryopanel structure comprising between 0.6 and 1.2 times the diameter of said frontal opening.

Claims

1. A cryopump comprising: a vessel comprising a radiation shield having a frontal opening, said frontal opening forming an inlet to said vessel; a frontal array thermally coupled to said radiation shield and mounted across said frontal opening; a cryopanel structure mounted within said vessel; a two stage refrigerator extending into said vessel, a first stage of said refrigerator being thermally coupled to said radiation shield and a colder second stage of said refrigerator being thermally coupled to said cryopanel structure; wherein said vessel comprises an elongate vessel a distance between a surface of said cryopanel structure closest to said frontal opening and a surface of said frontal array closest to said cryopanel structure comprising between 0.6 and 1.2 times the diameter of said frontal opening.

2. The cryopump according to claim 1, wherein said distance is between 0.7 and 0.9 times the diameter of said frontal opening.

3. The cryopump according to claim 1, wherein the diameter of the frontal opening is between 20 and 21 cm (7.8 and 8.2 inches) and said distance between said cryopanel structure and said frontal array is between 12 cm and 25 cm (4.7 and 10 inches).

4. The cryopump according to claim 1, wherein said second stage of said two stage refrigerator is configured to maintain a temperature of said cryopanels to below 9K.

5. The cryopump according to claim 1, wherein said frontal array comprises a disk element and an annular element, said disk element and said annular element being mounted axially displaced from each other said annular element being mounted to be closer to said frontal opening than said disk element, a diameter of said disk element being equal to or greater than a diameter of the aperture in said annular element and smaller than an outer diameter of said annular element, said outer diameter of said annular element being equal to or greater than a diameter of said frontal opening.

6. The cryopump according to claim 5, wherein said frontal array comprises an axially extending cylindrically-shaped element, said cylindrically-shaped element connecting said disk element and annular element, said cylindrically-shaped element comprising a cylindrical surface, said cylindrical surface comprising a plurality of apertures.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0029] FIG. 1 schematically shows the difference between a conventional cryopump and one according to an embodiment; and

[0030] FIG. 2 schematically shows the frontal array according to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

[0031] Before discussing the embodiments in any more detail, first an overview will be provided.

[0032] Cryopumps and in particular, PVD (physical vapour deposition) process cryopumps store large quantities of type II gasses and are required to recover the chamber pressure between wafers. The longer a pump can perform (store gasses and recover pressure) without needing to be regenerated the more valuable the pump is for its user. Enhancements have been made to the conventional array designs and shielding to increase the capacity of the pump and its vacuum stability. These improvements have enabled the usable physical volume available for frost within the pump below the sputter plate to be enhanced. Although these enhancements have had some success in helping to better utilize the volume available to store the gasses they have not been able to significantly increase the litres of gas it can store. To further increase the volume of a pump with a conventional flange size, it is proposed to elongate the pump such that an extra volumetric capacity further from the frontal opening is provided. In some embodiments, to further improve gas storage capacity better radiation shielding is provided and/or a lower temperature second stage cryopanel.

[0033] In effect, the inside volume of a cryopump, the frost temperature and shielding plus how efficiently the frost is formed dictates the amount of gas that can be stored. If the pump's useful gas volume is increased by lengthening the vessel and cylindrical radiation shield then the capacity may be increased. In particular, if the lengthening is performed in conjunction with an improved shielded sputter plate and/or with a refrigerator unit with lower 2nd stage temperature then an increased storage capacity of up to 50% is possible. Increasing the volume of the cryopump is important to allow a significant increase in its capacity for storing type II gasses. To conclude an elongated cryopump improves capacity, and does so particularly effectively when configured with better shielding and/or lower 2nd stage cryopanel temperatures.

[0034] FIG. 1 schematically shows a comparison between a conventional cryopump on the left and a cryopump according to an embodiment on the right. The cryopump according to an embodiment has an elongated vessel 10 when compared to the conventional pump while still utilizing the same vessel flange size. In some embodiments the length of the vessel is increased by between 1 to 6 inches (2.5 to 15 cm). The portion of the vessel that is elongated is the portion surrounded by the radiation shield 12 and is the portion between the cryopanel structure 30 and the frontal array 20. Increasing this length increases the volume available for storing type II gas as frost. It also increases the frost's distance from the very cold cryopanel surfaces 10K to the 100K sputter plate. In this way the distance 40 between the upper surface of the cryopanels structure 30 and the lower surface of the frontal array is lengthened and the volume A available to store frost is increased.

[0035] In the conventional cryopump shown schematically and not to scale in the left-hand figure the distance between the cryopanel structure and the frontal array is about half the diameter 42 of the frontal opening. In embodiments the vessel is elongated so that this distance is increased to about 0.6 to 1.2 times the diameter, preferably between 0.7 and 0.9 times.

[0036] The cryopump comprises a radiation shield 12 that surrounds the region A where frost is stored. The radiation shield extends above the flange 15 by between 0.6 and 1 (1.5 to 2.5 cm) to isolate the cryopump from the vacuum vessel.

[0037] The capacity to capture gas and still recover pressure afterwards of the cryopump according to the embodiment is increased by making the vessel 10 and radiation shield 12 longer with more length/volume inside radiation shield 12. In this embodiment the cryopump also has an improved frontal array plate 20 across the frontal opening 22.

[0038] The cryopump also has a reduced temperature of the second stage refrigerator that cools the cryopanel structure 30. This reduced temperature helps lower the frost temperature at the cryopanel structure and correspondingly along the frost cylinder and thereby compensates to some extent the effect of the increased frost length on the upper surface temperature of the frost.

[0039] Allowing the frost to grow and form a longer cylinder makes keeping the upper surface of the frost at a low enough temperature to inhibit gas molecules escaping more difficult. Decreasing the inlet radiant heat load by improving the shielding performed by the frontal array and/or decreasing the temperature of the cryopanel structure and thus, the temperature of the base of the frost cylinder may each help in keeping the temperature of the upper surface of the frost cylinder at a lower temperature. Where the refrigerator's 2nd stage temperature is lowered below 10K preferably below 9K then this helps avoid or at least reduce the escape of gas molecules.

[0040] A conventional frontal array plate 50 with holes in the form of louvers blocks most radiation but still allows some line of sight preferential pumping to occur. When the gas is being pumped it forms a crystal-like vertical structure that looks to be more like threads than an accumulation of frost layered horizontally. These crystal rods start growth on the cold 10K cryopanel like millions of threads attached to the cryopanel and stretching up to the 100K sputter plate or anything not at or below 25K. Type II gas also pumps below the 10K cryopanel and forms on the lower panels and charcoal arrays but in limited quantities.

[0041] Increasing the length of the available volume for gasses to accumulate, decreasing the 2nd stage cryopanel temperature, and allowing less radiation/preferential pumping of gasses will increase the volume that can be stored. Furthermore, doing so by elongating the vessel is less expensive that would be the case were a larger vessel with a larger flange size manufactured, it is also easily manufactured.

[0042] The length of the extension may be from 1 up to 6 (2.5 to 15 cm).

[0043] The shielding by the improved frontal array and/or the lower 2nd stage temperature although particularly useful in this embodiment are also applicable for use in other cryopumps.

[0044] FIG. 2 shows the frontal arrays of the conventional cryopump and that of an embodiment in more detail. The left hand figure shows the conventional frontal array 50 and the right hand figure a frontal array sputter plate 22 according to an embodiment, when viewed from above (left-hand side) and below (right hand side). As can be seen there is an upper plate 20a that has a disk form, and a lower annular plate 20b. The disk has a larger diameter than the diameter of the opening in the annular plate 20b. There is a cylindrical element 20c with apertures 21 between the upper disc plate 20a and the inner diameter of the lower annular plate 20b. These apertures are in the axially extending wall and in this way there is no direct line of sight between the interior and the exterior of the vessel, providing effective shielding of the frost within the vessel from radiation.

[0045] 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.

[0046] 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.

[0047] 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.