Cryogenic pump

Abstract

A cryopump is disclosed that includes a pump inlet, a two-stage refrigerator, a first-stage array 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. The cryopanel structure includes at least three flat panels. The first-stage array is mounted between the pump inlet and the cryopanel structure and includes a plurality of slats each mounted so that a side of each of the plurality of slats closest to the cryopanel structure is generally aligned and longitudinally offset with respect to a corresponding one of the at least three flat panels.

Description

TECHNICAL FIELD

[0001] The technology of the present invention relates to cryogenic pumps, and in particular to a two-stage cryogenic pump having a first stage at a temperature for capturing Class I gases such as water vapor, and a second stage at a lower temperature for capturing Class II gases such as nitrogen, and in some embodiments, for cryo-adsorbing Class III gases such as hydrogen. BACKGROUND

[0002] The two-stage cryogenic pump is formed of a cryogenic second stage cryopanel array. It can operate in the range of 4-25K, and can be coated with a capture material such as charcoal. This cryopanel array acts as the main pumping surface and is surrounded by a first stage radiation barrier that operates in a higher temperature range such as 40-130K, and provides radiation shielding to the lower temperature array and shields it from Class I gases by capturing gas molecules such as Class I gases such as water vapor where they come into contact with the array.

[0003] In operation, as gas enters the pump vessel through the inlet, at least some Class I gases such as water vapor condense on the front array forming part of the first stage radiation barrier. Lower boiling point gases pass through the front array and into the volume within the radiation barrier. Class II gases such as nitrogen condense on the second stage array, while Class III gases such as hydrogen, helium and neon that have appreciable vapor pressure at 4K are adsorbed by the adsorbent such as activated carbon, zeolite or molecular sieve coating the second stage cryopanels.

[0004] In this way, gas entering the chamber into the pump is captured, and a vacuum is created within the pump vessel. One problem with cryogenic pumps is that as the gas molecules in the capture surface become saturated during operation, their ability to capture gas molecules decreases. Therefore, cryogenic pumps are periodically regenerated to release the captured gas molecules.

[0005] There are several competing factors to consider when designing a cryogenic pump. High conductance of gas into the pump increases pumping speed, however, it is advantageous to provide some shielding to the second stage cryopanels from thermal radiation to reduce the thermal load on the cryopanels, and from Class I gases. Class I gases reaching the cryopanels condense on them, preventing Class III gases from being cryo-adsorbed. Furthermore, some Class I gases such as large chain hydrocarbons will not leave the array surface during regeneration, resulting in a decrease in pumping performance over the remaining life of the pump. However, shielding the cryopanels from gas molecules does result in a decrease in conductance.

[0006] It would be desirable to provide an improved two-stage cryogenic pump. SUMMARY

[0007] A first aspect provides a cryopump comprising: a pump inlet; a two-stage refrigerator; a first-stage array 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; wherein 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 each mounted so that a side of each of the plurality of slats closest to the cryopanel structure is generally aligned and longitudinally offset with respect to a corresponding one of the at least three flat panels.

[0008] In designing a cryopump, it is desirable to provide a cryopanel structure with significant surface area to capture gas molecules and a first-stage or front array to provide some shielding of the cryopanel structure from thermal radiation and from some gas molecules entering the pump through the inlet. Cryopump inlets conventionally have a circular cross-section and the cryopanel structure typically has a similar configuration, possibly formed by coaxial cylinders. While such an arrangement has the advantages of symmetry and good matching to the vacuum chamber outlet, manufacturing and construction can be challenging. Providing a planar second-stage cryopanel array formed by flat panels and a first-stage array formed by linear slats aligned with and longitudinally offset with respect to at least some of the panels provides an arrangement that is easy to manufacture and easy to assemble. Moreover, having an arrangement in which the slats are generally aligned with the panels provides effective and targeted shielding of the panels. Such an arrangement can also provide very high hydrogen pumping speed.

[0009] In some embodiments, each of the plurality of panels has a corresponding slat aligned and offset longitudinally with respect thereto.

[0010] In some embodiments, the plurality of slats are mounted to extend at an angle of between 110° and 160° with respect to the flat panels towards the pump inlet.

[0011] Angling the slats so that they are inclined towards the pump inlet and adjacent panels provides effective shielding of the cryopanel structure.

[0012] In some embodiments, the plurality of slats are mounted so that at least some of the slats shield one surface of an adjacent flat panel of the cryopanel structure from gas molecules entering the pump through the pump inlet.

[0013] The slats can be arranged to shield the surface of an adjacent panel from direct impact from gas molecules entering the pump. The gas molecules can bounce off another surface and impact the panel, but the panel is shielded from being the first surface to be impacted. This allows certain types of gas molecules, such as Class I gas molecules, to be captured before they reach this surface. It can be that each panel has slats arranged longitudinally aligned therewith. Alternatively, it can be that each panel in the array, except one end panel, has a corresponding slat associated therewith. The end panel is at an end in a direction in which the panels are inclined from close to an edge of the cryogenic panel structure. The slats provide shielding to adjacent panels to which they are angularly directed, so in the absence of a subsequent panel, it can be that such slats are dispensed with.

[0014] In some embodiments, the surfaces of the plurality of flat panels comprise a coated portion coated with a sorbent material and other portions not coated with the sorbent material.

[0015] Class III gases do not condense at the temperature of the first or second stage refrigerator, and to capture these molecules, a sorbent is required. In a cryogenic pump, the second stage array can be coated with a sorbent to sorb these Class III gases and capture Class II gases. The inventors of the present invention have recognised that a problem with sorbent coated surfaces in a cryogenic pump is that over time, they can become less effective as gas molecules are sorbed onto them. The sorbent material is provided to capture Class III gases, and it is important that these gases contact these surfaces and are captured. However, to increase the time between regeneration cycles, it would be desirable to inhibit any other gases from being captured by the sorbent that can condense on other surfaces. Photoresist, for example, is a gas that can be present when a cryogenic pump is used to evacuate a semiconductor processing chamber, and it is sorbed by the sorbent surface on impact, reducing the lifetime of the sorbent surface between regenerations.

[0016] The inventors of the present invention have recognised that if some surfaces of the second stage cryogenic panel are not coated, and if a gas such as photoresist first impacts these surfaces, it will condense on the uncoated surfaces before it reaches the sorbent coated surfaces, and therefore, the lifetime of the sorbent coated surfaces will be increased.

[0017] Thus, by providing some uncoated surface to the pump, non-class III gases can condense as they impact these uncoated surfaces of the sorbent, while class III gases will bounce off the uncoated surfaces and be adsorbed as they impact the coated surfaces of the sorbent. In this way, the sorbent surfaces will primarily adsorb class III gases, and this will increase the lifetime between its effectiveness and regeneration, and maintain a generally stable pumping rate for a longer period of time. In fact, by allowing at least some of the gases to impact uncoated surfaces, some gases, such as photoresist, will never reach the coated surfaces, and the coated surfaces will be protected from these gases, and can be used almost exclusively for pumping class III gases that will bounce off the uncoated surfaces, thereby increasing the time between regeneration, and providing a pump whose pumping rate does not degrade excessively over time.

[0018] In some embodiments, one surface of at least some of the panels is coated with the sorbent, while the other surface is uncoated.

[0019] Coating only one surface provides a system that is easy to manufacture. For some coating techniques, such as where an adhesive coating, such as epoxy, is provided and the sorbent material is attached thereto, it is much easier to coat a single surface by placing the epoxy-coated surface in contact with the sorbent than it is to coat two surfaces.

[0020] In some embodiments, the coated surface is shielded from the sorbent by adjacent slats in the plurality of slats.

[0021] Arranging the slats such that the coated surface is shielded by the slats allows the coated surface and sorbent thereon to be shielded from non-class III gases, such as photoresist, that will first impact and be captured by the other surfaces. This increases the lifetime of the sorbent. The planar geometry provides an efficient system for shielding one surface, while allowing the other surface to capture class III gases.

[0022] Furthermore, by leaving the surface that is so effectively shielded by the first array of slats free of sorbent, a situation where one surface of the pump becomes contaminated over time and loses its adsorptive properties at a higher rate than the other surface is avoided or at least inhibited. Such a situation would result in a change in the pumping rate of the pump over time, which would require recalibration of the system, and is generally undesirable.

[0023] In some embodiments, the plurality of slats are arranged generally parallel to each other, and the plurality of flat panels are arranged generally parallel to each other.

[0024] The planar arrangement where the panels and slats are generally parallel to each other provides a device that is easy to manufacture and where the flow is more predictable.

[0025] In some embodiments, the plurality of slats are tilted in the same direction as one another. In some embodiments, there is the same number of slats as there are panels.

[0026] In some embodiments, the panels and slats are spaced equidistant from one another within the pump. This results in flow channels between the panels and slats having approximately the same size, allowing for more uniform flow and adsorption by the slats.

[0027] In some embodiments, the plurality of panels are arranged to extend approximately parallel to a longitudinal axis of the pump.

[0028] The panels can be arranged approximately parallel to the longitudinal axis of the pump, such that each panel receives a similar amount of gas molecules, and one panel does not overly shield another panel from gas molecules entering the pump.

[0029] In some embodiments, the plurality of slats and the plurality of panels are approximately rectangular.

[0030] While the slats and panels can have many different shapes, in some cases they are rectangular. Rectangular panels are easy to manufacture, install, and coat, and provide an efficient surface.

[0031] In some embodiments, the plurality of slats are configured to overlap when viewed through the pump inlet in a direction parallel to the flat panels.

[0032] The plurality of slats can be configured to overlap when viewed through the pump inlet along the longitudinal axis, and in this way, there is no line of sight between the pump inlet and the panels, such that a gas molecule will typically have already impacted another surface before impacting the surface of the cryogenic panel structure. In this regard, a gas molecule traveling approximately parallel to the angle of the slats can directly impact one surface of the panel, and in some embodiments, it is the surface of the panel that is not coated with adsorbent. In this way, the side of the panel that is coated with adsorbent is protected from direct impact from a gas molecule.

[0033] In some embodiments, the plurality of panels are all approximately the same size.

[0034] In other embodiments, the slats and panels at either end of the array can be smaller than the slats and panels towards the middle. In this regard, the pump inlet has a circular cross-section, and it can be advantageous to increase the size of the panels towards the middle of the pump, where there is a larger diameter. However, having panels and slats with different sizes results in a more complicated manufacturing process, and in some cases, it can be desirable to have them all the same size.

[0035] In some embodiments, the adsorbent material is configured to adsorb Group III gases, such as hydrogen, helium, and neon.

[0036] In some embodiments, the adsorbent material comprises a molecular sieve coating the coated surface.

[0037] In some embodiments, the adsorbent material comprises one of: a biochar, an activated carbon, a zeolite, or a porous metal surface.

[0038] Further particularly and preferably aspects are set out in the dependent claims and the independent claims. The features of the dependent claims can be combined with the features of the independent claims as appropriate and in combinations other than those explicitly set out in the claims.

[0039] Where a device feature is described as being operable to provide a function, this will be understood to include a device feature that provides the function or is adapted or configured to provide the function. BRIEF DESCRIPTION OF DRAWINGS

[0040] Embodiments of the application will now be further described with reference to the drawings in which:

[0041] Figure 1 A planar cryopanel structure according to an embodiment is shown; and

[0042] Figure 2 A front-on array and Figure 1 a cryopanel structure are shown. DETAILED DESCRIPTION

[0043] Before any embodiments are discussed in more detail, a general overview will first be provided.

[0044] A cryopump with a planar front-on array comprising parallel sloping panels or slats allows the second stage structure to be aligned with the front-on array when it is also a planar structure. This can provide very high hydrogen pumping speeds. The disadvantage is that the full area of the inlet can not be used as efficiently as in the case of a circular arrangement.

[0045] The second stage array panel stretches across the pump and is aligned vertically with the longitudinal axis of the pump. The first stage array includes sloped panels or slats between the second stage array and the pump inlet, arranged so that the edges closest to the second stage array are aligned with corresponding ones of the second stage panels. The slats are sloped so that the surfaces are sloped toward the pump inlet. In some embodiments, one side of the second stage panels is coated with biochar, and this side is completely shielded from direct impact from gas molecules entering the pump by the higher temperature (about 80K) front array. Gas that condenses at the temperature of the front array will impact the array and not proceed further, some can impact the surfaces of the second stage array that are not coated with biochar, and likewise will not proceed further. Class III gases such as hydrogen will bounce off these surfaces and will be adsorbed when they impact the surfaces coated with biochar. In this way, the surfaces coated with adsorbent will almost exclusively pump Class III gases, while the other surfaces collect other gases.

[0046] In some embodiments, the slats of the front array overlap when viewed along the longitudinal axis perpendicular to the cross section of the pump inlet. The amount of overlap will determine the pumping speed and also the degree to which the panels of the second stage array are shielded from first impact by gas molecules entering the pump inlet. Embodiments of this pump are effective at evacuating semiconductor processing vacuum chambers, such as those used for implant applications and PVD (physical vapor deposition) processes.

[0047] Figure 1 and Figure 2 An embodiment of a cryopump is shown having a planar array of planar elements. Figure 1 Parallel planar elements 25 of a second stage cryopanel structure within a pump having an inlet 5 are shown. A first stage front array is not shown. The second stage cryopanel structure has parallel panels 25 arranged equidistantly spaced from each other in a row. There is a front array (not shown) having a set of sloped slats, the lower surfaces of which are aligned with corresponding panels. The front array is longitudinally offset from the second stage array to thermally isolate the two arrays to some extent and is located between the second stage array and the pump inlet 5.

[0048] In some embodiments, one side of the panels 25 is coated with an adsorbent and the other side is not coated with an adsorbent. The sloped elements of the front array protect the coated surfaces from initial impact by molecules entering through the pump inlet.

[0049] Figure 2Front array elements 12 are shown schematically with respect to second stage array elements 25 and pump inlet 5. As can be seen, the slats 12 are mounted between the pump inlet 5 and the second stage array of cryopanel structures. The slats are angled so that they overlap when viewed from the pump inlet 5. The angle Θ between the slats 12 and the panels 25 is between 110° and 160° so that the slats are angled towards the adjacent panels and shield the panels from the incoming gas molecules of the pump inlet. There is a gap between the panels 12 which allows gas molecules to enter the pump.

[0050] In some embodiments, both surfaces of the panels 25 are coated with a sorbent; while in other embodiments, one surface 24 of the panels is coated with a sorbent while the other surface 22 is not. The only direct path for molecules travelling between the front array slats 12 is to the uncoated surface 22 of the cryopanel structures so that molecules entering through the pump inlet first impact either the slats 12 or the uncoated surface 22 of the second stage array. Thus, the initial impact of any molecule is not with a coated surface 24 and molecules that condense at the temperature of the first or second stage refrigerator are captured on these surfaces. Other Class III molecules bounce off these surfaces towards the coated surface 24 where they are captured by the sorbent coating upon impact. In this way, the coated surface of the second stage elements is shielded from the initial impact of the molecules entering the pump by the angled first stage array slats 12. Molecules that do not condense on the first or second stage arrays will impact the coated surface 22 and be captured by the sorbent.

[0051] While the illustrative embodiments of the application have been disclosed in detail herein with reference to the attached drawings, it is to be understood that the application is not limited to the precise embodiments disclosed, and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the application as defined by the appended claims and their equivalents.

[0052] Reference Signs

[0053] 5 pump inlet

[0054] 12 slat

[0055] 22 uncoated surface of the panel

[0056] 24 coated surface of the panel

[0057] 25 second stage array panel

Claims

1. A cryopump comprising: a pump inlet; a two-stage refrigerator; a first-stage array 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; wherein 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 arranged parallel to one another, and the at least three flat panels are arranged parallel to one another, each of the plurality of slats is mounted so that a side of each of the plurality of slats closest to the cryopanel structure is longitudinally aligned with respect to a corresponding one of the at least three flat panels, and each of the plurality of slats is tilted with respect to a corresponding one of the at least three flat panels.

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

3. The cryopump of claim 1, wherein the plurality of slats are mounted so that at least some of the slats shield one surface of adjacent flat panels of the cryopanel structure from gas molecules entering the pump through the pump inlet.

4. The cryopump of claim 3, wherein a surface of the at least three flat panels comprises a coated portion coated with a sorbent material and other portions not coated with the sorbent material.

5. The cryopump of claim 4, wherein at least some of the panels are coated with the sorbent on one surface and not coated on another surface.

6. The cryopump of claim 5, the coated surface is a surface shielded by adjacent ones of the plurality of slats.

7. The cryopump of any of claims 1-6, wherein the at least three flat panels are arranged to extend parallel to a longitudinal axis of the pump.

8. The cryopump of any of claims 1-6, wherein the plurality of slats and the at least three flat panels are rectangular.

9. The cryopump of any of claims 1-6, wherein the plurality of slats are configured to overlap when viewed through the pump inlet in a direction parallel to the flat panels.

10. The cryopump of any of claims 1-6, wherein the at least three flat panels are all the same size.

11. The cryopump of any of claims 1-6, wherein the plurality of slats are all the same size.

12. The cryopump of any of claims 1-6, wherein the panels and slats at any edge of the array of panels or slats are smaller than the panels and slats toward the middle.

13. The cryopump of any of claims 4-6, wherein the sorbent material is configured to sorb Group III gases.

14. The cryopump of any of claims 4-6, wherein the sorbent material comprises a molecular sieve that coats the coated surface. ​ 15. The cryopump of any of claims 4-6, wherein the adsorbent material comprises one of: biochar, activated carbon, zeolite, or a porous metal surface.

16. The cryopump of claim 13, wherein the Class III gases comprise hydrogen, helium, and neon.

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