CRYOPUMP

Abstract

A cryopump comprising: a vessel comprising a frontal open area, the frontal open area comprising an inlet to the vessel; a radiation shield; a two stage refrigerator extending into the vessel, a first stage of the refrigerator being thermally coupled to the radiation shield. A first stage array is arranged within the vessel and is also thermally coupled to the first stage of the refrigerator. A cryopanel structure is coupled to a second stage of the refrigerator. The first stage array comprises a plurality of elements arranged at increasing distances from the inlet, the element closest to the inlet being between the cryopanel structure and the inlet and elements further from the inlet having a passage through a central portion. The element closest to the inlet has a smaller outer perimeter than the elements further from the inlet.

Claims

1. A cryopump comprising: a vessel comprising a frontal open area, said frontal open area comprising an inlet to said vessel; a radiation shield; a two stage refrigerator extending into a side wall of said vessel at a portion of said side wall remote from said inlet, that is a point closer to a closed end of said vessel than to said inlet, a first stage of said refrigerator being thermally coupled to said radiation shield; a first stage array arranged within said vessel and thermally coupled to said first stage of said refrigerator; a cryopanel structure coupled to a second stage of said refrigerator; said first stage array comprising a plurality of elements arranged at increasing distances from said inlet, said element closest to said inlet being located between said inlet and said cryopanel structure and having a smaller outer perimeter than said elements further from said inlet, said elements further from said inlet each having a passage through a central portion.

2. The cryopump according to claim 1, wherein said cryopanel structure has a diameter at a widest point that is less than 70% of a diameter of said vessel, preferably, less than 55%.

3. The cryopump according to claim 1, wherein said refrigerator extends into said vessel at a portion of said side wall that is at a distance of at least 60% of a length of said vessel from said inlet.

4. The cryopump according to claim 1, wherein said cryopanel structure has a length that is greater than 70% of a length of said vessel

5. The cryopump according to claim 1, wherein said first stage array is mounted on a mounting element, said mounting element being formed of a thermally conducting material coupled to said first stage refrigerator and to each of said plurality of elements of said first stage array.

6. The cryopump according to claim 1, wherein one end of said cryopanel structure extends into said first stage array, such that at least one of said elements further from said inlet surrounds an outer perimeter of said one end of said cryopanel structure.

7. The cryopump according to claim 1, wherein neighbouring elements of said first stage array are configured such that for at least some of said elements closest to said inlet an outer perimeter of one element is substantially equal to or smaller than an inner perimeter of a subsequent element located further from said pump inlet.

8. The cryopump according to claim 1, wherein said first stage array has a substantially igloo shape, said elements being concentric and said element closest to said inlet having a smallest perimeter, and a plurality of subsequent elements having outer perimeters of an increasing size with distance from said inlet.

9. The cryopump according to claim 1, wherein said elements are substantially planar said element closest to said inlet having a disc shape and subsequent elements comprising rings.

10. The cryopump according to claim 1, wherein said surfaces of said elements facing said inlet are at an angle of between 0° and 30° to a plane of said inlet, such that they are parallel to said plane or slanted such that a surface closest to said inlet faces towards said radiation shield.

11. The cryopump according to claim 1, wherein said first stage array is mounted on a mounting element, said mounting element being formed of a thermally conducting material coupled to said first stage refrigerator and to each of said plurality of elements of said first stage array.

12. The cryopump according to claim 1, wherein said element of said first stage array that is furthest from said inlet is mounted closest to said first stage of said refrigerator, a surface of said first stage array closest to said inlet being between 5 and 15% into said vessel.

13. The cryopump according to claim 12, wherein said first stage array extends from a point between 5 and 15% into said vessel to a point between 25 and 40% into said vessel.

14. The cryopump according to claim 6, wherein said cryopanel structure comprises a plurality of panels extending out from a central axis and having a substantially cylindrical envelope with at least one tapered end, one of said at least one tapered end extending into said first stage inlet array.

15. The cryopump according to claim 14, wherein a portion of said cryopanel structure that extends into said first stage array comprises at least 20%, preferably at least 30% of said cryopanel structure.

16. The cryopump according to claim 1, wherein said radiation shield is substantially cylindrical and comprises a flattened portion extending into said cylinder for coupling to said refrigerator, said flattened portion extending into said cylinder by less than 8% of a diameter of said cylinder, preferably less than 6%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0056] FIG. 1 shows a first stage array according to an embodiment;

[0057] FIG. 2 shows a second stage cryopanel structure mounted on a refrigerator element and extending into a first stage array according to an embodiment;

[0058] FIG. 3 shows a cryopump according to an embodiment;

[0059] FIG. 4 shows a section through a cryopump according to an embodiment; and

[0060] FIG. 5 shows a further cross section through a cryopump according to an embodiment.

DETAILED DESCRIPTION

[0061] Before discussing the embodiments in any more detail, first an overview will be provided.

[0062] The requirements for cryopumps are becoming more challenging as new implant processes are developed and more consistent vacuum environments are needed to keep up with process vacuum conditions.

[0063] The inventors recognised that cryopump array geometry is critical to improving the vacuum conditions provided by cryogenic vacuum pumps. Taking “Implant” processes for example where cryopumps are often used to generate the high vacuums required and hydrogen is the major gas constituent, and contamination from photoresist is a major issue, embodiments extend the contamination resistance and increase the hydrogen pumping speed by providing one or more of three main design improvements. [0064] 1.) Cryopanel optimization; The geometry of the 2nd stage array has been redesigned, providing an array with a longer and narrower profile than the conventional array leading to enhanced hydrogen pumping. The 2.sup.nd stage array panel is protected from exposure to gaseous contamination and radiation with an “Igloo” first stage array. In effect the cryopanel structure and igloo array are geometrically designed to complement each other such that they act together to improve type III gas conductance while also increasing thermal and type I gas shielding. [0065] 2.) The geometric design of the first stage or “Igloo” inlet baffle provides increased hydrogen performance and superior resistance to gaseous contamination of the second stage array. [0066] 3.) Refrigerator location; The refrigerator is strategically lowered in the vessel compared to conventional designs to permit better gas conductance, creating a longer array pumping path with fewer first strike contamination strikes. The refrigerator penetration in addition to being lower in the vessel also has a smaller cross section to improve conductance.

[0067] The above design changes seek to increase type III gas pumping speed in particular, and to limit second stage array contamination, lower second stage radiant load and lower first stage or Igloo array temperatures, these all make for a more stable vacuum pump.

[0068] The refrigerator location closer to the bottom of the vessel is one aspect to the pump overall performance providing: [0069] 1.) Better conductance—there is less interruption to the type II and type III gases such as hydrogen entering the pump and more can reach the cryopanels. [0070] 2.) It allows the 2nd stage cryopanel/mount to be a one-piece design. The symmetry of the cryopanels improves the type II/III gas pumping uniformity over the entire cryopanel surface. This uniformity is crucial to the type II/III speed and capacity, keeping all panels available to pump these gases more evenly so as not to overwhelm any panels with the gases. When cryopanels become locally saturated because of non-uniformity of their design this renders these panels unavailable to more incoming molecules. This provides an unbalanced pumping condition causing the remaining cryopanels to get higher loading and the cryopump pressure rise to be quicker than expected resulting in a rapid reduction in pumping speed for type III gases. [0071] 3.) The refrigerator cylinder being lower in the pump also works with the enhanced Igloo inlet array to shield the cryopanels from unwanted radiation and from most first strike photoresist contamination. The inlet array design is mounted on a thermally conducting element extending from the first stage of the refrigerator enabling the array to be maintained at a colder temperature than a typical inlet array configuration that is connected to the radiation shield.

[0072] FIG. 1 shows an igloo style first stage array 10 according to an embodiment. The array is formed of a plurality of elements 12, 14 that are arranged at increasing distances from an inlet to the pump. The element that is closest to the pump is disc 12 and further elements 14 of increasing size are placed at increasing distances from the inlet to the pump. This igloo style inlet baffle or array is mounted via a thermally conductive member 36 (see FIG. 2) on the first stage of the refrigerating element. This thermally conductive member allows the igloo to be maintained at a temperature that is close to that of the first stage refrigerating element, reduces hot spots on the igloo surfaces and allows the surfaces to be retained at a reduced temperature and thereby provides improved capture for type I gases. The radiation shield also experiences lower temperatures when compared to a radiation shield coupled to a conventional first stage array extending across the inlet and thus, it too may have improved capture for type I gases. In this embodiment, disc 12 is a solid disc, in other embodiments disc 12 may have apertures within the disc to allow passage of some molecules. In some cases, these apertures may be shielded to some extent by flaps extending partially across the apertures and slanted to deflect molecules towards the radiation shield.

[0073] FIG. 2 shows the first stage array 10 coupled to the refrigerator element 30 which extends into a side wall of the pump vessel and supports the second stage cryopanel structure 20. The second stage cryopanel structure 20 extends up into the first stage array 10 such that the elements of the first stage array 10 surround the portion of the second stage cryopanel structure 20 that is closest to the inlet. This provides improved shielding of this portion of the cryopanel structure and reduces the probability of gas molecules contacting the higher portions and improves the uniformity of capture of molecules along the length of the cryopanel structure thereby increasing the lifetime and effectiveness of the cryopanel structure.

[0074] The refrigerator element 30 extends into the vessel and comprises a first stage refrigerator element at the first stage temperature and this is coupled to the first stage array 10 via a thermally conductive mount 36 allowing for the first stage array to be maintained at or close to the temperature of the first stage refrigerator element in a uniform and effective manner. The thermally conductive mount 36 extends around the first stage array contacting each element in two places and providing effective cooling for this array.

[0075] The second stage cryopanel structure is mounted to the second stage refrigerator element and is thus, cooled to the temperatures of the second stage. The refrigerator element 30 extends into the lower portion of the pump vessel remote from the inlet and supports the lower half of the cryopanel structure such that this support does not obscure the upper half of the cryopanel structure from the gas molecules entering the pump. This again leads to better distribution of gas molecules over the cryopanel structure.

[0076] The cryopanel structure 20 is longer and thinner than conventional cryopanel structures and this improves conductance and type II and type III gas capture uniformity allowing better access to the lower portions of the cryopanels. Furthermore, the refrigerator position being lowered relative to the pump inlet also improves conductance and increases pumping speed.

[0077] FIG. 3 shows a view through the pump inlet 40. As can be seen the inner surface of the pump vessel comprises an inner element 42 which is a radiation shield. When viewed through the inlet the first stage array provides effective shielding of the second stage array from a view perpendicularly through the inlet and protects it from radiation load and from process by product contaminants. The spacing between elements in the axial direction allows access to the cryopanels for molecules with a component of velocity parallel to the inlet, such as those deflected by the radiation shield 42. Molecules deflected by the radiation shield will be predominantly type II or type III gases as the radiation shield will capture the type I gases. The lower portions of the cryopanel structure are not surrounded by the frontal array allowing easy access to this portion of the structure for molecules travelling deeper into the pump.

[0078] FIG. 4 shows a side view of the pumping vessel with a portion cut out such the interior can be viewed. As can be seen the refrigerator 30 extends into the lower portion of the pump vessel remote from the inlet and a first stage of the refrigerator element 34 is thermally connected to the radiation shield 42 and to a thermally conductive mount 36 which mounts the first stage array 10.

[0079] The thermally conductive mount 36 extends around the igloo structure contacting each of the elements in two diametrically opposed places and provides a good thermal connection between these elements and the first stage of the refrigerator element. In this way, there is a good thermal path directly from the first stage refrigerator element to each element of the first stage array allowing for the array to be retained at a cold and uniform temperature.

[0080] The second stage of the refrigerator 32 is connected to the second stage cryopanels not shown and maintains these at the lower second stage temperature. The refrigerator element 30 is located towards the base of the pump vessel and in this way any shielding of the gasses by the extension of this refrigerator element into the pump is reduced.

[0081] FIG. 5 shows a cross section of the pump showing the first stage array 10, the refrigerator element 30 and how they are connected. In particular, it shows how the refrigerator element is held within the pump vessel and connects to the radiation shield. The radiation shield is flattened at this point to provide a sealed connection with the flattened flange of the refrigerator element and there is a protrusion 44 in the radiation shield above the connection that reflects this flattening and provides a surface against which molecules may impact and be deflected back towards the inlet. In this embodiment the design is such that the protrusion is decreased in size compared to a conventional cryopump and extends into the cylinder by less than 8% of the cylinder diameter, in many embodiments less than 6%. This provides less of an obstruction to gas molecules entering the pump and improves pumping speeds.

[0082] This figure shows the differences in temperature between the different portions of the first stage. The first stage refrigerator element is the coldest portion at about 65K, the first stage array is maintained at a temperature of between 71 and 72.5K, while the radiation shield is colder towards the refrigerator side, but the opposing side reaches temperatures above 75K. In conventional cryopumps where the first stage array is adjacent to the inlet, this inlet array reflects the temperature of the warmer portion of the radiation shield and is above 75K. Thus, embodiments provide a cooler first stage array of a more uniform temperature than a conventional cryopump improving capture of type I gases.

[0083] In summary with conventional cryopump designs the 2nd stage array is shielded by an inlet mounted planar radiation baffle or frontal array. This baffle is adjacent to the inlet and attached to the top of the radiation shield. As with a large umbrella, gas molecules are intercepted and bounced out of the pump before they can get close to the second stage array. The refrigerator cylinder and 1st stage mount is also conventionally higher in the pump, shielding more type II and type III molecules such as hydrogen from reaching the second stage array.

[0084] Embodiments provide by contrast a second stage array that is shielded with an inlet radiation baffle of multiple elements arranged within the pump at different distances from the inlet. This array configuration blocks fewer molecules at the inlet of the pump, allowing more molecules to arrive in a position to strike a surface of the second stage array. This design also provides improved shielding of the second stage array from type I gases resulting in lower contamination and lower second stage radiation exposure. The second stage array is combined with the first stage array shape and lower refrigerator placement to form a trinity of enhancements.

[0085] 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.

[0086] 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.

[0087] 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.