Cryopump

Abstract

The cryopump includes a pump inlet, a two-stage refrigerator, a first stage array thermally coupled to the first stage of the two-stage refrigerator, and a cryopanel structure coupled to the second stage of the two-stage refrigerator. The surface of the cryopanel structure has a portion coated with an adsorbent and another portion not coated with the adsorbent.

Description

Technical Field

[0001] The field of the present invention relates to cryopumps, and more particularly to a two-stage cryopump having a first stage of temperature for capturing type I gases such as water vapor and a second stage of low temperature for capturing type II gases such as nitrogen and in some embodiments cryo-adsorbing type III gases such as hydrogen.

Background Art

[0002] The two-stage cryopump is formed of a low-temperature second-stage cryopanel array operating in the range of 4 - 25K, which can be coated with a capture material such as charcoal. This cryopanel array functions as a primary pump surface, operates in a high-temperature range such as 40 - 130K, provides a radiation shield for the low-temperature array, and is surrounded by a first-stage radiation shield that shields from type I gases such as water vapor by capturing these gas molecules where they contact the shield.

[0003] During operation, when gas enters the pump vessel from the inlet, at least a portion of the type I gas such as water vapor condenses on the front array that forms part of the first-stage radiation shield. The low-boiling gas passes through the front array and enters the volume within the radiation shield. On the other hand, type III gases having a significant vapor pressure at 4K, such as hydrogen, helium, neon, etc., are adsorbed by adsorbents such as activated carbon, zeolite, molecular sieves, etc., covering the cryopanels of the second stage.

[0004] In this way, the gas flowing from the chamber into the pump is captured and a vacuum is generated within the pump vessel. One problem with cryopumps is that during operation, gas molecules saturate the capture surface and the capture capacity decreases. Therefore, cryopumps need to be regenerated periodically to release the captured gas molecules.

Summary of the Invention

Problems to be Solved by the Invention

[0005] It may be desirable to provide a two-stage cryopump with a long operating time during regeneration.

Means for Solving the Problem

[0006] A first aspect provides a cryopump, which includes a pump inlet, a two-stage refrigerator, a first-stage array thermally coupled to the first stage of the two-stage refrigerator, and a cryopanel structure coupled to the second stage of the two-stage refrigerator and including a plurality of cryopanels. Each of the plurality of cryopanels includes two surfaces, and the two surfaces include a surface coated with an adsorbent and a further surface not coated with an adsorbent. The first-stage array includes a plurality of elements corresponding to the plurality of cryopanels. The plurality of elements are configured to be attached between the pump inlet and the plurality of cryopanels. Each of the plurality of elements extends from a position between the corresponding cryopanel and the pump inlet toward the adjacent cryopanel and is inclined toward the pump inlet. Each of the plurality of elements is configured to at least partially shield the coated surface of the adjacent cryopanel from direct collision of gas molecules passing through the pump inlet.

[0007] The inventor of the present invention recognizes that the problem of the adsorbent-coated surface in a cryopump is that gas molecules are adsorbed over time, resulting in a decrease in effectiveness. The adsorbent is provided to capture type III gases, and it is important that these gases come into contact with these surfaces and are captured. However, in order to increase the time between regeneration cycles, it is desirable to suppress the capture of other gases that may condense on other surfaces by the adsorbent. For example, photoresist is a gas that may be present when evacuating a semiconductor process chamber using a cryopump. This is adsorbed onto the adsorbent surface by collision, shortening the time between regeneration cycles.

[0008] The inventor of the present invention has recognized that when a part of the surface of the second-stage cryopanel is not coated and a gas such as photoresist first collides with these surfaces, it condenses on the uncoated surface before reaching the adsorbent-coated surface, resulting in an extended life of the adsorbent-coated surface. Generally, pump designers attempt to coat the entire surface of the cryopanel, which increases the area covered by the adsorbent, increases the pumping speed, and lengthens the time during regeneration. However, since the surface area covered by the adsorbent reflects the amount of hydrogen that can be adsorbed and has the meaning of a safety function, pump design needs to consider the surface area covered by the adsorbent.

[0009] Therefore, by providing an uncoated surface on the pump, gases that are not of type III collide with and condense on the uncoated surface, and type III gases bounce back when they collide with the uncoated surface and are adsorbed. In this way, the adsorbent surface will mainly adsorb type III gases, its effect will be enhanced, and the time during regeneration will be lengthened. In practice, by enabling at least a part of the gas to collide with the uncoated surface, a part of the gas such as photoresist does not reach the coated surface, the coated surface is protected from these gases, and type III gases bouncing back from the uncoated surface can almost invariably be used as a pump, providing a pump with a longer regeneration time and a pumping speed that does not excessively decrease over time.

[0010] Furthermore, by coating an adsorbent on one surface of the panel and not coating the other surface, a configuration with simple manufacturing is provided. In addition, this configuration itself helps well in providing a surface where molecules entering from the inlet may collide and another surface shielded by the front array. In this regard, the coated surface is at least partially shielded from the molecules entering the inlet by arranging the elements of the first-stage array between the cryopanel and the inlet. A part (side or edge) of the first-stage element closest to each cryopanel is in the same longitudinal plane as the cryopanel and can be angled to extend radially towards the radial position of the adjacent cryopanel. In this way, the element spreads between the cryopanel and the inlet over one side (the coated side) of the cryopanel and protects that side from gas molecules entering the inlet.

[0011] The pump has a reduced coated surface area compared to the case where the entire surface of the cryopanel is coated, so the theoretically maximum amount of hydrogen adsorbed on the surface is reduced. Since the pump has a safety function related to the maximum amount of hydrogen that can be adsorbed, reducing this maximum value reduces the burden on the designed safety function. Although the theoretically maximum amount of hydrogen that can be adsorbed decreases, at least a part of gases other than type III such as photoresist will condense on the uncoated surface rather than on the adsorbent surface, so the actual amount of hydrogen adsorbed by the pump during operation may be the same as that of a pump with a fully coated surface.

[0012] Therefore, when only a part of the surface is coated, an improved pump can be provided in which the pumping speed does not decrease excessively over time.

[0013] The first-stage array can be at the same temperature as the second-stage array, but in some embodiments, the first-stage array is at a warmer temperature than the second-stage array and is configured to pump gases such as water vapor, and the second-stage array pumps gases that condense at low temperatures such as nitrogen.

[0014] In some embodiments, the cryopanel structure is configured and attached such that the surface of the cryopanel structure where molecules entering the cryopump are most likely to first collide is a further portion of the surface of the cryopanel structure.

[0015] When the cryopanel structure is arranged such that the surface not coated with the adsorbent is most likely to be first collided by the molecules entering the pump, molecules such as photoresist molecules that condense on this structure will not reach the adsorbent surface, but type III gases will bounce back from the uncoated surface and will then be captured by the adsorbent surface when they collide with the coated surface. In this way, the adsorbent surface can be used to almost invariably capture molecules that do not condense at these temperatures, and the effective life of the adsorbent surface will be lengthened.

[0016] In some embodiments, the first-stage array and the cryopanel structure are configured such that there is no line-of-sight path between the pump inlet and the coated portion of the surface of the cryopanel.

[0017] Advantageously, the cryopanel structure can be arranged such that there is no line-of-sight path between the pump inlet and the coated portion of the surface, and the probability that the first surface that the molecules entering the pump collide with is the coating structure of the cryopanel is very low. Thus, the coating structure will generally receive only molecules that have already collided with the uncoated surface, and in this way, it will be protected from gases that condense on the uncoated surface such as photoresist.

[0018] In some embodiments, the plurality of cryopanels consists of a plurality of planar cryopanels, one surface of the cryopanel consists of a coating surface, and the other surface consists of a further surface.

[0019] In other embodiments, the plurality of cryopanels consists of a plurality of coaxial cylindrical cryopanels of different diameters.

[0020] In some embodiments, the outer surface of the cylindrical cryopanel consists of a coating surface, and its inner surface consists of a further surface.

[0021] The cryopanel structure can be planar. In some embodiments, the planar structure can have one coating surface and one non - coating surface. In other embodiments, the cryopanel structure can form a coaxial cylindrical configuration. In some embodiments, the inner surface of the cylinder is the non - coating surface and the outer surface is the coating surface, and the cryopanel is arranged such that gas molecules entering the pump inlet bounce off the inner surface without condensing and collide with the opposing outer surface of the coaxial cylinder.

[0022] In some embodiments, the plurality of elements are configured to overlap when viewed through the inlet such that gas molecules collide with one of the plurality of elements before colliding with the cryopanel structure. The arrangement of the elements is such that gas molecules rebounding from the elements are directed towards the non - coating surface, providing further protection for the coating surface.

[0023] In some embodiments, the plurality of elements of the first - stage array consists of a plurality of coaxial frustoconical elements of different diameters.

[0024] When the cryopanel structure consists of cylindrical elements, one configuration of the first - stage array provides particularly effective protection for one surface of the cylinder. Further, this configuration fits well with a circular pump inlet.

[0025] In some embodiments, the adsorbent is configured to adsorb type III gases such as hydrogen, helium, neon, etc.

[0026] In some embodiments, the adsorbent consists of a molecular sieve that coats the coating surface.

[0027] In some embodiments, the adsorbent consists of one of charcoal, activated carbon, zeolite, or a porous metal surface.

[0028] The adsorbent can be a metal, and in some embodiments, a porous metal that can be sprayed on the surface, such as sponge aluminum, can be used. Sponge aluminum has a porosity exceeding 90%.

[0029] Further specific and preferred aspects are described in the independent claims and the dependent claims. The features of the dependent claims can be combined with the features of the independent claims as appropriate, or in combinations other than those explicitly specified in the claims.

[0030] When the features of the device are described as being operable to provide a certain function, it should be understood that this includes the features of the device that provide or are adapted or configured to provide that function.

[0031] Embodiments of the present invention are further described below with reference to the accompanying drawings.

Brief Description of the Drawings

[0032]

Figure 1

Figure 2

Figure 3

Figure 4

DETAILED DESCRIPTION OF THE INVENTION

[0033] Before explaining the embodiments in detail, first, an overview will be described.

[0034] A second-stage cryopanel structure is provided, where an adsorbent such as charcoal is coated on the surface on one side of the panel to collect hydrogen, and the other side is not covered with the adsorbent and will collect other molecules such as photoresist that condense at the low temperature of the cryopanel.

[0035] In some embodiments, there is a front array at a higher temperature (about 80K approximately) consisting of elements 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 the gas flow and limit the pumping speed of the gas that is not pumped by the front array, but this will protect the second-stage array and increase the time during regeneration.

[0036] This cryopump is particularly effective for pumping gases from semiconductor processes such as implant applications and PVD (Physical Vapor Deposition) applications.

[0037] The embodiments provide planar and circular solutions. Conventionally, since the pump inlet and the junction to the vacuum chamber are circular, the front array structure was circular. With a planar front array composed of parallel inclined panels, the second-stage structure can be made to coincide with the front array, and a very high hydrogen pumping speed can be achieved. The drawback is that the inlet area cannot be effectively utilized.

[0038] The circular front array fits well into the circular inlet at the junction of the pump and the vacuum chamber. A cylindrical cryopanel can be used to effectively shield the surface of the cryopanel structure by the circular front array. The circular front array can advantageously be formed of overlapping truncated conical elements. The inner surface of the cylindrical cryopanel can be an uncoated inner surface, and the molecules deflected by these surfaces will collide with the coated outer surface of the adjacent coaxial cylindrical structure. This will result in a pump with a pumping speed that does not decrease over time or at least the decrease is suppressed.

[0039] Figure 1 shows a coaxial second stage cylindrical cryopanel structure 20 according to an embodiment, which is shielded by a first stage or front array 10. The front array 10 comprises a plurality of coaxial truncated conical elements 12 that overlap when viewed through the pump inlet 5.

[0040] The plurality of elements 12 forming the front array are thermally coupled to the first-stage refrigerator of the cryopump and are maintained at a first-stage temperature in the range of 40 - 130K. The upper surfaces of the elements 12 of the front array facing the pump inlet 5 are inclined, and molecules colliding with these surfaces will be captured if they condense at the temperature of the first-stage refrigerator or will be deflected towards the lower surfaces of the adjacent outer elements. The path between the elements 12 of the first-stage array entering the pump towards the second-stage cryopanel structure is angled towards the inner surface of the cylindrical cryopanel. Thus, molecules moving along these paths will preferentially collide with the inner surface 22 of the cylindrical elements of the cryopanel structure when they arrive at the second-stage cryopanel structure. If the molecules are a gas that condenses at the temperature of the second-stage array, i.e., between 4 - 25K, such as nitrogen or photoresist, the molecules follow the trajectory indicated by arrow 9 and are captured by the inner surface 22. If the molecules are type-III gas molecules that do not condense at the temperature of the second stage, the molecules follow the trajectory indicated by arrow 7 and are deflected by the inner surface 22 of the cylindrical cryopanel element towards the outer surface 24 of the adjacent inner cylindrical element and are captured by the adsorbent surface coating the inner surface 24.

[0041] In this way, the inner surface 24 of the coaxial cylindrical second-stage cryopanel element is shielded from gas molecules other than type-III gas molecules, thus improving the long-term effectiveness of the cryopanel structure and preventing the pumping speed from decreasing excessively due to the adsorption of molecules such as photoresist.

[0042] Figure 2 shows the same cryopanel structure from another angle. Here, it can be seen more clearly that the frustoconical elements 12 of the first-stage array 10 extend over the coaxial cylindrical elements 25 forming the second-stage cryopanel structure.

[0043] Figures 3 and 4 show an alternative embodiment in which the two arrays are planar and each is formed of planar elements. The cryopanel structure has parallel panels, one side of which is coated with an adsorbent and the other side is uncoated. The front array is composed of elements extending from the elements of the second stage array and inclined towards the pump inlet. In this way, it protects the coating surface from the first collision by molecules entering from the pump inlet.

[0044] Figure 3 shows the parallel planar elements 25 of the second stage cryopanel structure within a pump having an inlet 5. The front array of the first stage is not shown.

[0045] Figure 4 schematically shows the second stage array elements 25 and the front array elements 12 with respect to the pump inlet 5. As shown, the elements 12 are attached between the pump inlet 5 and the cryopanel structure of the second stage array. They are inclined so as to overlap when viewed from the pump inlet 5. Similar to the embodiments of FIGS. 1 and 2, the path between the front array elements 12 leads to the uncoated surface 22 of the cryopanel structure, so that molecules entering from the pump inlet are directed towards this non-coated surface. Thus, the first collision occurs on the uncoated surface 22, and any molecules that condense at the temperature of the second stage refrigerator are trapped. Other type III molecules bounce back from the surface 22 towards the coating surface 24 and are trapped by the adsorbent coating upon collision. In this way, the coating surface of the second stage elements is shielded from the first collision by the molecules entering the pump by the inclined first stage array elements. Molecules that do not condense on the first stage array or the second stage array collide with the coating surface and are trapped by the adsorbent.

[0046] Exemplary embodiments of the present invention are disclosed in detail herein with reference to the accompanying drawings, but the present invention is not limited to the exact embodiments, and it should be understood that various changes and modifications can be made by those skilled in the art without departing from the scope of the present invention defined by the appended claims and their equivalents.

Explanation of Symbols

[0047] 5 Pump Inlet 7 Orbit of Hydrogen Molecule 9 Orbit of Photoresist Molecule 10 First Stage Array 12 First Stage Array Element 20 Cryopanel Structure 22 Non-Coated Surface 24 Adsorbent Coated Surface 25 Cryopanel Element

Claims

1. A cryopump comprising: a pump inlet; a two-stage refrigerator; a first-stage array thermally coupled to the first stage of the two-stage refrigerator; a cryopanel structure coupled to the second stage of the two-stage refrigerator and including a plurality of cryopanels; wherein each of the plurality of cryopanels includes two side surfaces, the two side surfaces including a side surface coated with an adsorbent and a further side surface not coated with the adsorbent; the first-stage array includes a plurality of elements corresponding to the plurality of cryopanels; the plurality of elements are configured to be mounted between the pump inlet and the plurality of cryopanels; each of the plurality of elements extends from a position between the corresponding cryopanel and the pump inlet toward an adjacent cryopanel, is inclined toward the pump inlet, and each of the plurality of elements is configured to at least partially shield the coated side surface of the adjacent cryopanel from direct collision of gas molecules passing through the pump inlet. A cryopump.

2. The cryopump according to claim 1, wherein the cryopanel structure is configured and mounted such that the surface of the cryopanel structure where molecules entering the cryopump are most likely to first collide is the further portion of the surface of the cryopanel structure.

3. The cryopump according to claim 1 or 2, wherein the first-stage array and the cryopanel structure are configured such that there is no line-of-sight path between the pump inlet and the coated portion of the side surface of the cryopanel.

4. The cryopump according to any one of claims 1 to 3, wherein the plurality of cryopanels are composed of a plurality of planar cryopanels, one surface of the cryopanel consists of the coated side surface, and the other surface consists of the further side surface.

5. The cryopump according to any one of claims 1 to 4, wherein the plurality of cryopanels are composed of a plurality of coaxial cylindrical cryopanels having different diameters.

6. The cryopump according to claim 5, wherein the outer surface of the cylindrical cryopanel consists of the coated side surface, and the inner surface of the cylindrical cryopanel consists of the further side surface.

7. The plurality of elements of the first array consists of a plurality of coaxial frustoconical elements of different diameters, the cryopump according to any one of claims 1 to 6 when dependent on claim 5 or 6.

8. The adsorbent is configured to adsorb type III gases such as hydrogen, helium, neon, etc., the cryopump according to any one of claims 1 to 7.

9. The adsorbent consists of a molecular sieve that coats the coated side surface, the cryopump according to any one of claims 1 to 8.

10. The adsorbent consists of one of charcoal, wood charcoal, activated carbon, zeolite, or a porous metal surface, the cryopump according to any one of claims 1 to 9.

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