CRYOPUMP

Abstract

A cryopump includes a cryopump housing and a water absorbing layer mounted on an outer side of the cryopump housing.

Description

BACKGROUND

Technical Field

Certain embodiments of the present invention relate to a cryopump.

Description of Related Art

A cryopump is a vacuum pump which captures gas molecules on a cryopanel cooled to a cryogenic temperature by condensation or adsorption to exhaust the gas molecules. The cryopump is generally used to realize a clean vacuum environment which is required for a semiconductor circuit manufacturing process or the like. Since the cryopump is a so-called gas accumulation type vacuum pump, regeneration to periodically discharge the captured gas to the outside is required.

SUMMARY

According to an embodiment of the present invention, there is provided a cryopump including: a cryopump housing; and a water absorbing layer mounted on an outer side of the cryopump housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side sectional view schematically showing a cryopump according to an embodiment and a dew condensation suppressing structure thereof.

FIG. 2 is a sectional view taken along line II-II, schematically showing the cryopump shown in FIG. 1.

FIG. 3 is a schematic diagram showing another example of the dew condensation suppressing structure according to the embodiment.

FIG. 4 is a schematic diagram showing another example of the dew condensation suppressing structure according to the embodiment.

FIG. 5 is a schematic diagram showing another example of the dew condensation suppressing structure according to the embodiment.

DETAILED DESCRIPTION

If the regeneration of the cryopump is started, the vacuum in a cryopump housing that accommodates a cryopanel is released. The interior of the housing is filled with gas due to-re-vaporization of an accumulated gas or introduction of a purge gas. At the beginning of the regeneration, the cryopanel is still cooled to a cryogenic temperature. Since a vacuum adiabatic effect is lost due to the gas filling, the housing can be cooled through the gas by the cryopanel. Since the housing is exposed to the ambient environment, in some cases, dew condensation may occur on the outer surface thereof. Condensed water may drop.

It is desirable to suppress dew condensation on a cryopump or to suppress dropping of condensed water.

Any combination of the constituent elements described above, or replacement of constituent elements or expressions of the present invention with each other between methods, apparatuses, systems, or the like is also valid as an aspect of the present invention.

According to the present invention, it is possible to suppress dew condensation on the cryopump or to suppress dropping of condensed water.

Hereinafter, modes for carrying out the present invention will be described in detail with reference to the drawings. In the description and the drawings, identical or equivalent constituent elements, members, and processing are denoted by the same reference numerals, and overlapping description is omitted appropriately. The scales or shapes of the respective parts shown in the drawings are set for convenience in order to facilitate description and are not interpreted to a limited extent unless otherwise specified. Embodiments are exemplification and do not limit the scope of the present invention. All features described in the embodiments or combinations thereof are not necessarily essential to the invention.

FIG. 1 is a side sectional view schematically showing a cryopump 10 according to an embodiment. FIG. 2 is a sectional view taken along line II-II, schematically showing the cryopump 10 shown in FIG. 1. FIG. 1 shows a cross section including a cryopump central axis C indicated by a dashed-dotted line. Further, for easy understanding, in FIG. 1, a low-temperature cryopanel part and a cryocooler of the cryopump 10 are shown not in a cross section but in a side view.

As will be described later, the cryopump 10 has a dew condensation suppressing structure.

The cryopump 10 is mounted to a vacuum chamber of, for example, an ion implanter, a sputtering apparatus, a vapor deposition apparatus, or other vacuum process equipment and is used to increase the degree of vacuum in the interior of the vacuum chamber to a level which is required for a desired vacuum process. The cryopump 10 has an intake port 12 for receiving a gas to be exhausted from the vacuum chamber. The gas enters an internal space 14 of the cryopump 10 through the intake port 12.

The cryopump 10 may be intended to be installed at and used in the vacuum chamber in the direction shown in the drawing, that is, in a posture in which the intake port 12 is directed upward. However, the posture of the cryopump 10 is not limited thereto, and the cryopump 10 may be installed at the vacuum chamber in another direction.

In the following, there is a case where the terms “axial direction” and “radial direction” are used in order to express the positional relationship between constituent elements of the cryopump 10 in an easily understandable manner. The axial direction represents a direction passing through the intake port 12 (in FIG. 1, a direction along the cryopump central axis C passing through the center of the intake port 12), and the radial direction represents a direction along the intake port 12 (a direction perpendicular to the central axis C). For convenience, with respect to the axial direction, there is a case where the side relatively close to the intake port 12 is referred to as an “upper side” and the side relatively distant from the intake port 12 is referred to as a “lower side”. That is, there is a case where the side relatively distance from the bottom of the cryopump 10 is referred to as an “upper side” and the side relatively close to the bottom of the cryopump 10 is referred to as a “lower side”. With respect to the radial direction, there is a case where the side close to the center of the intake port 12 (in FIG. 1, the central axis C) is referred to as an “inner side” and the side close to the peripheral edge of the intake port 12 is referred to as an “outer side”. Such expressions are not related to the disposition when the cryopump 10 is mounted to the vacuum chamber. For example, the cryopump 10 may be mounted to the vacuum chamber with the intake port 12 facing downward in the vertical direction.

Further, there is a case where a direction surrounding the axial direction is referred to as a “circumferential direction”. The circumferential direction is a second direction along the intake port 12 and is a tangential direction orthogonal to the radial direction.

The cryopump 10 includes a cryocooler 16, a first-stage cryopanel 18, a second-stage cryopanel assembly 20, and a cryopump housing 70. The first-stage cryopanel 18 may be referred to as a high-temperature cryopanel part or a 100 K part. The second-stage cryopanel assembly 20 may be referred to as a low-temperature cryopanel part or a 10 K part.

The cryocooler 16 is a cryocooler such as a Gifford McMahon type cryocooler (a so-called GM cryocooler), for example. The cryocooler 16 is a two-stage cryocooler. Therefore, the cryocooler 16 includes a first cooling stage 22 and a second cooling stage 24. The cryocooler 16 is configured to cool the first cooling stage 22 to a first cooling temperature and cool the second cooling stage 24 to a second cooling temperature. The second cooling temperature is lower than the first cooling temperature. For example, the first cooling stage 22 is cooled to a temperature in a range of about 65 K to 120 K, preferably, in a range of 80 K to 100 K, and the second cooling stage 24 is cooled to a temperature in a range of about 10 K to 20 K.

Further, the cryocooler 16 includes a cryocooler structure part 21 that structurally supports the second cooling stage 24 on the first cooling stage 22 and structurally supports the first cooling stage 22 on a room temperature part 26 of the cryocooler 16. Therefore, the cryocooler structure part 21 includes a first cylinder 23 and a second cylinder 25 that extend coaxially along the radial direction. The first cylinder 23 connects the room temperature part 26 of the cryocooler 16 to the first cooling stage 22. The second cylinder 25 connects the first cooling stage 22 to the second cooling stage 24. The room temperature part 26, the first cylinder 23, the first cooling stage 22, the second cylinder 25, and the second cooling stage 24 are linearly arranged in this order.

A first displacer and a second displacer (not shown) are reciprocally disposed in the interiors of the first cylinder 23 and the second cylinder 25, respectively. A first regenerator and a second regenerator (not shown) are respectively incorporated into the first displacer and the second displacer. Further, the room temperature part 26 has a drive mechanism (not shown) for reciprocating the first displacer and the second displacer. The drive mechanism includes a flow path switching mechanism that switches a flow path of a working gas (for example, helium) so as to periodically repeat the supply and discharge of the working gas to and from the interior of the cryocooler 16.

The first cooling stage 22 is installed at the first-stage low temperature end of the cryocooler 16. The first cooling stage 22 is a member that encloses an end portion of the first cylinder 23 on the side opposite to the room temperature part 26 and surrounds a first expansion space for the working gas. The first expansion space is a variable volume that is formed between the first cylinder 23 and the first displacer in the interior of the first cylinder 23 and that changes in volume according to the reciprocation of the first displacer. The first cooling stage 22 is formed of a metal material having a higher thermal conductivity than the first cylinder 23. For example, the first cooling stage 22 is formed of copper and the first cylinder 23 is formed of stainless steel.

The second cooling stage 24 is installed at a second-stage low temperature end of the cryocooler 16. The second cooling stage 24 is a member that encloses an end portion of the second cylinder 25 on the side opposite to the room temperature part 26 and surrounds a second expansion space for the working gas. The second expansion space is a variable volume that is formed between the second cylinder 25 and the second displacer in the interior of the second cylinder 25 and that changed in volume according to the reciprocation of the second displacer. The second cooling stage 24 is formed of a metal material having a higher thermal conductivity than the second cylinder 25. The second cooling stage 24 is formed of copper, and the second cylinder 25 is formed of stainless steel. In FIG. 1, a boundary 24b between the second cooling stage 24 and the second cylinder 25 is shown.

The cryocooler 16 is connected to a compressor (not shown) for the working gas. The cryocooler 16 cools the first cooling stage 22 and the second cooling stage 24 by expanding the working gas pressurized by the compressor in the interior thereof. The expanded working gas is recovered to the compressor and pressurized again. The cryocooler 16 generates cold by repeating a heat cycle including the supply and discharge of the working gas and the reciprocation of the first displacer and the second displacer in synchronization with the supply and discharge of the working gas.

The cryopump 10 which is shown in the drawing is a so-called horizontal cryopump. The horizontal cryopump is generally a cryopump in which the cryocooler 16 is disposed so as to intersect (usually, be orthogonal to) the central axis C of the cryopump 10. The first cooling stage 22 and the second cooling stage 24 of the cryocooler 16 are arranged in the direction perpendicular to the cryopump central axis C (the horizontal direction in FIG. 1, or the direction of a central axis D of the cryocooler 16).

The first-stage cryopanel 18 includes a radiation shield 30 and an inlet cryopanel 32 and surrounds the second-stage cryopanel assembly 20. The first-stage cryopanel 18 is a cryopanel provided in order to protect the second-stage cryopanel assembly 20 from radiant heat outside the cryopump 10 or from the cryopump housing 70. The first-stage cryopanel 18 is thermally coupled to the first cooling stage 22. Accordingly, the first-stage cryopanel 18 is cooled to the first cooling temperature. The first-stage cryopanel 18 has a gap between itself and the second-stage cryopanel assembly 20, and the first-stage cryopanel 18 is not in contact with the second-stage cryopanel assembly 20.

The radiation shield 30 is provided to protect the second-stage cryopanel assembly 20 from the radiant heat of the cryopump housing 70. The radiation shield 30 is located between the cryopump housing 70 and the second-stage cryopanel assembly 20 and surrounds the second-stage cryopanel assembly 20. The radiation shield 30 has a shield main opening 34 for receiving gas from the outside of the cryopump 10 into the internal space 14. The shield main opening 34 is located at the intake port 12.

The radiation shield 30 is provided with a shield front end 36 defining the shield main opening 34, a shield bottom portion 38 which is located on the side opposite to the shield main opening 34, and a shield side portion 40 connecting the shield front end 36 to the shield bottom portion 38. The shield front end 36 forms a part of the shield side portion 40. The shield side portion 40 extends in the axial direction from the shield front end 36 to the side opposite to the shield main opening 34, and extends so as to surround the second cooling stage 24 in the circumferential direction. The radiation shield 30 has a tubular (for example, cylindrical) shape closed at the shield bottom portion 38, and is formed in a cup shape. An annular gap 42 is formed between the shield side portion 40 and the second-stage cryopanel assembly 20.

The shield bottom portion 38 may be a member separate from the shield side portion 40. For example, the shield bottom portion 38 may be a flat disk having substantially the same diameter as the shield side portion 40, and may be attached to the shield side portion 40 on the side opposite to the shield main opening 34. Further, at least a part of the shield bottom portion 38 may be open. For example, the radiation shield 30 may not be closed by the shield bottom portion 38. That is, both ends of the shield side portion 40 may be open.

The shield side portion 40 has a shield side portion opening 44 into which the cryocooler structure part 21 is inserted. The second cooling stage 24 and the second cylinder 25 are inserted into the radiation shield 30 from outside the radiation shield 30 through the shield side portion opening 44. The shield side portion opening 44 is a mounting hole formed in the shield side portion 40 and is, for example, circular. The first cooling stage 22 is disposed outside the radiation shield 30.

The shield side portion 40 is provided with a mounting seat 46 for the cryocooler 16. The mounting seat 46 is a flat portion for mounting the first cooling stage 22 to the radiation shield 30, and is slightly depressed when viewed from outside the radiation shield 30. The mounting seat 46 forms the outer periphery of the shield side portion opening 44. The mounting seat 46 is closer to the shield bottom portion 38 than the shield front end 36 in the axial direction. The first cooling stage 22 is mounted to the mounting seat 46, whereby the radiation shield 30 is thermally coupled to the first cooling stage 22.

The inlet cryopanel 32 is provided in the shield main opening 34 in order to protect the second-stage cryopanel assembly 20 from the radiant heat from a heat source outside the cryopump 10. The heat source outside the cryopump 10 is, for example, a heat source in the vacuum chamber to which the cryopump 10 is mounted. The inlet cryopanel 32 can restrict not only the radiant heat but also the entry of gas molecules. The inlet cryopanel 32 occupies a part of the opening area of the shield main opening 34 so as to limit the gas flow into the internal space 14 through the shield main opening 34 to a desired amount. An annular open area 48 is formed between the inlet cryopanel 32 and the shield front end 36.

The inlet cryopanel 32 is mounted to the shield front end 36 by an appropriate mounting member and is thermally coupled to the radiation shield 30. The inlet cryopanel 32 is thermally coupled to the first cooling stage 22 through the radiation shield 30. The inlet cryopanel 32 has, for example, a plurality of annular or linear vanes. Alternatively, the inlet cryopanel 32 may be a single plate-shaped member.

The second-stage cryopanel assembly 20 is mounted to the second cooling stage 24 so as to surround the second cooling stage 24. Accordingly, the second-stage cryopanel assembly 20 is thermally coupled to the second cooling stage 24, and the second-stage cryopanel assembly 20 is cooled to the second cooling temperature. The second-stage cryopanel assembly 20 is surrounded together with the second cooling stage 24 by the shield side portion 40.

The second-stage cryopanel assembly 20 includes a top cryopanel 60 facing the shield main opening 34, a plurality of (in this example, two) cryopanel members 62, and a cryopanel mounting member 64.

Further, as shown in FIG. 1, the cryopump 10 includes a cryopanel positioning member 67. A heat transfer part that thermally couples the second-stage cryopanel assembly 20 to the second cooling stage 24 includes the cryopanel mounting member 64 and the cryopanel positioning member 67. The top cryopanel 60 and the cryopanel members 62 are mounted to the second cooling stage 24 through the cryopanel mounting member 64 and the cryopanel positioning member 67.

Since the annular gap 42 is formed between the top cryopanel 60 and the cryopanel members 62, and the shield side portion 40, neither the top cryopanel 60 nor the cryopanel members 62 are in contact with the radiation shield 30. The cryopanel members 62 are covered by the top cryopanel 60.

The top cryopanel 60 is a portion of the second-stage cryopanel assembly 20 closest to the inlet cryopanel 32. The top cryopanel 60 is disposed between the shield main opening 34 or the inlet cryopanel 32 and the cryocooler 16 in the axial direction. The top cryopanel 60 is located at the central portion of the internal space 14 of the cryopump 10 in the axial direction. Therefore, a main accommodation space 65 for a condensation layer is widely formed between the front surface of the top cryopanel 60 and the inlet cryopanel 32. The main accommodation space 65 for the condensation layer occupies the upper half of the internal space 14.

The top cryopanel 60 is a substantially flat cryopanel disposed perpendicular to the axial direction. That is, the top cryopanel 60 extends in the radial direction and the circumferential direction. As shown in FIG. 2, the top cryopanel 60 is a disk-shaped panel having a dimension (for example, a projected area) larger than that of the inlet cryopanel 32. However, the relationship between the dimensions of the top cryopanel 60 and the inlet cryopanel 32 is not limited to this, and the dimension of the top cryopanel 60 may be smaller than that of the inlet cryopanel 32, or the top cryopanel 60 and the inlet cryopanel 32 may have substantially the same dimension.

The top cryopanel 60 is disposed so as to form a gap region 66 between itself and the cryocooler structure part 21. The gap region 66 is a void formed in the axial direction between the back surface of the top cryopanel 60 and the second cylinder 25.

The cryopanel member 62 is provided with an adsorbent 74 such as activated carbon. The adsorbent 74 is bonded to the back surface of the cryopanel member 62, for example. It is intended that the front surface of the cryopanel member 62 functions as a condensation surface and the back surface functions as an adsorption surface. The adsorbent 74 may be provided on the front surface of the cryopanel member 62. Similarly, the top cryopanel 60 may have the adsorbent 74 on the front surface and/or the back surface thereof. Alternatively, the top cryopanel 60 may not be provided with the adsorbent 74.

The two cryopanel members 62 are disposed on both sides of the second cooling stage 24 with the cryopump central axis C interposed therebetween. The cryopanel members 62 are disposed along a plane perpendicular to the cryopump central axis C. For easy understanding, the cryopanel members 62 and the cryopanel mounting member 64 are shown by broken lines in FIG. 2.

The two cryopanel members 62 are disposed at a height position between the upper end and the lower end of the second cooling stage 24 in the direction of the cryopump central axis C. The two cryopanel members 62 are disposed at the same height. The second cooling stage 24 has a flange portion 24a provided at the end thereof in the direction perpendicular to the cryopump central axis C (the direction of the central axis D of the cryocooler 16). The upper end and the lower end of the second cooling stage 24 in the direction of the cryopump central axis C are defined by the flange portion 24a. That is, the two cryopanel members 62 are disposed at a height position between the upper end and the lower end of the flange portion 24a of the second cooling stage 24 in the direction of the cryopump central axis C.

The two cryopanel members 62 are designed as the same components. The two cryopanel members 62 have the same shape and are made of the same material. The cryopanel member 62 has a bow shape, a half-moon shape, or a semicircular shape. The cryopanel member 62 is formed of a metal material having a high thermal conductivity, such as copper, for example, and may be coated with a plating layer such as nickel, for example.

As shown in FIG. 2, the cryopanel member 62 has an arc portion 78 and a chord 79. When viewed in the direction of the cryopump central axis C, the two cryopanel members 62 are disposed symmetrically to each other with the intermediate line between them (the central axis D of the cryocooler 16) as the axis of symmetry. The arc portions 78 of the two cryopanel members 62 are on the same circumference centered on the cryopump central axis C. Further, each of the cryopanel members 62 has a line-symmetric shape with a line E passing through the midpoint of the chord 79 (or the cryopump central axis C) and perpendicular to the chord 79 as the axis of symmetry.

As shown in FIG. 1, the cryopanel positioning member 67 is fixed to the flange portion 24a of the second cooling stage 24 and is supported by the second cooling stage 24. The cryopanel positioning member 67 is formed in an inverted L shape that is turned upside down. By using the cryopanel positioning member 67, the restriction on the length of the cryocooler 16 in the direction of the central axis D is relaxed. Even if the flange portion 24a of the second cooling stage 24 is located off the cryopump central axis C in the direction of the central axis D of the cryocooler 16, by adjusting the length of an upper side portion 67a of the cryopanel positioning member 67, it is possible to position the second-stage cryopanel assembly 20 on the cryopump central axis C. As a result, an existing cryocooler can be adopted instead of the cryocooler designed exclusively for the cryopump 10. This can help reduce the manufacturing cost of the cryopump 10.

In order to align the second-stage cryopanel assembly 20 with the cryopump central axis C, the upper side portion 67a of the cryopanel positioning member 67 may extend from the flange portion 24a of the second cooling stage 24 so as to be separated from the second cylinder 25 in the direction of the central axis D of the cryocooler 16, contrary to that shown in FIG. 1. With respect to the cryopump 10 having a large-diameter intake port 12, the cryopanel positioning member 67 having such a shape may be suitable.

The cryopump 10 includes a gas flow adjusting member 50 configured to deflect the flow of the gas flowing in from the shield main opening 34, from the cryocooler structure part 21. The gas flow adjusting member 50 is configured to deflect the gas flow, which flows into the main accommodation space 65 through the inlet cryopanel 32 or the open area 48, from the second cylinder 25. The gas flow adjusting member 50 may be a gas flow deflecting member or a gas flow reflecting member disposed above and adjacent to the cryocooler structure part 21 or the second cylinder 25. The gas flow adjusting member 50 is locally provided at the same position as the shield side portion opening 44 in the circumferential direction. The gas flow adjusting member 50 has a rectangular shape when viewed from above. The gas flow adjusting member 50 is, for example, a single flat plate, but may be curved.

The gas flow adjusting member 50 extends from the shield side portion 40 and is inserted into the gap region 66. However, the gas flow adjusting member 50 is not in contact with the top cryopanel 60, the second cylinder 25, and the other portion having the second cooling temperature and surrounding the gap region 66. The gas flow adjusting member 50 is thermally coupled to the first cooling stage 22 through the radiation shield 30. Therefore, the gas flow adjusting member 50 is cooled to the first cooling temperature.

The cryopump housing 70 is a casing of the cryopump 10, which accommodates the first-stage cryopanel 18, the second-stage cryopanel assembly 20, and the cryocooler 16, and is a vacuum container configured to maintain the vacuum tightness of the internal space 14. The cryopump housing 70 includes the first-stage cryopanel 18 and the cryocooler structure part 21 in a non-contact manner. The cryopump housing 70 is mounted to the room temperature part 26 of the cryocooler 16.

The intake port 12 is defined by a front end of the cryopump housing 70. The cryopump housing 70 has an intake port flange 72 extending radially outward from a front end thereof. The intake port flange 72 is provided over the entire circumference of the cryopump housing 70. The cryopump 10 is mounted to a vacuum chamber to be evacuated by using the intake port flange 72.

The cryopump housing 70 includes a cryopanel accommodation part 76 that surrounds the radiation shield 30 in a non-contact with the radiation shield 30, and a cryocooler accommodation part 77 that surrounds the first cylinder 23 of the cryocooler 16. The cryopanel accommodation part 76 and the cryocooler accommodation part 77 are integrally formed.

The cryopanel accommodation part 76 has a cylindrical or dome shape in which the intake port flange 72 is formed at one end and the other end is closed as a housing bottom surface 76a. Separately from the intake port 12, an opening through which the cryocooler 16 is inserted is formed in the side wall of the cryopanel accommodation part 76 that connects the intake port flange 72 to the housing bottom surface 76a. The cryocooler accommodation part 77 has a cylindrical shape extending from the opening to the room temperature part 26 of the cryocooler 16. The cryocooler accommodation part 77 connects the cryopanel accommodation part 76 to the room temperature part 26 of the cryocooler 16.

The cryopump 10 includes a water absorbing layer 80 mounted on the outer side of the cryopump housing 70, and a heat insulating layer 82 disposed between the cryopump housing 70 and the water absorbing layer 80. The dew condensation suppressing structure of the cryopump 10 is formed by the water absorbing layer 80 and the heat insulating layer 82. The dew condensation suppressing structure includes a water absorbing and heat insulating sheet 84 having the water absorbing layer 80 on the outer side and having the heat insulating layer 82 on the inner side. The water absorbing and heat insulating sheet 84 is configured as a sheet in which the water absorbing layer 80 is attached to the outside of the heat insulating layer 82.

The water absorbing and heat insulating sheet 84 covers at least a part, for example, the entire surface, of the outer surface of the cryopump housing 70. The water absorbing and heat insulating sheet 84 is mounted to both the cryopanel accommodation part 76 and the cryocooler accommodation part 77 and covers almost the entire surfaces of them. The water absorbing and heat insulating sheet 84 is wrapped around the side surface of the cryopanel accommodation part 76 and covers the side surface. The water absorbing and heat insulating sheet 84 is also mounted to the housing bottom surface 76a. The water absorbing and heat insulating sheet 84 is also wrapped around the cryocooler accommodation part 77. The water absorbing and heat insulating sheet 84 is mounted to the cryopump housing 70 by using an appropriate bonding method.

However, the intake port flange 72 is not covered with the water absorbing and heat insulating sheet 84. In most cases, even if the intake port flange 72 is exposed, dew condensation does not occur, and therefore, it is not necessary to mount the water absorbing layer 80 and/or the heat insulating layer 82 to the intake port flange 72. In a case of being required, the water absorbing layer 80 and/or the heat insulating layer 82 may be mounted to the intake port flange 72.

The water absorbing layer 80 is formed of a material having an excellent water absorption property compared to a structural material (for example, stainless steel such as SUS304) forming the outer surface of the cryopump housing 70 and/or compared to a heat insulating material forming the heat insulating layer 82. The water absorbing layer 80 is formed of, for example, a water absorbing material such as a water-absorbent resin or a water-absorbent porous material, which chemically and/or physically adsorbs water, or a material containing such a water absorbing material. For the water absorbing layer 80, products commercially available as general names such as a water-absorbent resin, a water absorbing polymer, and water absorbing sheet can be appropriately adopted. Alternatively, the water absorbing layer 80 may be formed of a material such as felt or sponge that retains water at least temporarily.

The heat insulating layer 82 is formed of a material having a smaller thermal conductivity than the structural material forming the outer surface of the cryopump housing 70. The heat insulating layer 82 may be formed of various known heat insulating materials such as a foam-based heat insulating material and/or a fiber-based heat insulating material.

A thickness 86 of the heat insulating layer 82 is determined such that the temperature of the water absorbing layer 80 is maintained at a temperature higher than 0° C. during the regeneration of the cryopump 10. The thickness 86 of the heat insulating layer 82 may be determined such that the temperature of the water absorbing layer 80 is maintained at a temperature higher than 5° C. or higher than 10° C. In other words, the thickness 86 of the heat insulating layer 82 is determined such that the temperature of the outer surface of the heat insulating layer 82 does not fall below the freezing point of water during the regeneration of the cryopump 10.

The operation of the cryopump 10 having the above configuration will be described below. When the cryopump 10 is operated, first, the interior of the vacuum chamber is roughed to about 1 Pa with another appropriate roughing pump before the operation. Thereafter, the cryopump 10 is operated. The first cooling stage 22 and the second cooling stage 24 are respectively cooled to the first cooling temperature and the second cooling temperature by the driving of the cryocooler 16. Accordingly, the first-stage cryopanel 18 and the second-stage cryopanel assembly 20 thermally coupled to these are also respectively cooled to the first cooling temperature and the second cooling temperature.

The inlet cryopanel 32 cools the gas which comes flying from the vacuum chamber toward the cryopump 10. A gas having a sufficiently low vapor pressure (for example, 10⁻⁸ Pa or less) at the first cooling temperature condenses on the surface of the inlet cryopanel 32. This gas may be referred to as a first type gas (also called a type 1 gas). The type 1 gas is, for example, water vapor. In this way, the inlet cryopanel 32 can exhaust the type 1 gas. A part of a gas in which vapor pressure is not sufficiently low at the first cooling temperature passes through the inlet cryopanel 32 or the open area 48 and enters the main accommodation space 65. Alternatively, the other part of the gas is reflected by the inlet cryopanel 32 and does not enter the main accommodation space 65.

The gas that has entered the main accommodation space 65 is cooled by the second-stage cryopanel assembly 20. A gas having a sufficiently low vapor pressure (for example, 10⁻⁸ Pa or less) at the second cooling temperature condenses on the surface of the second-stage cryopanel assembly 20. This gas may be referred to as a second type gas (also called a type 2 gas). The type 2 gas is, for example, nitrogen or argon. In this way, the second-stage cryopanel assembly 20 can exhaust the type 2 gas. A condensation layer for the type 2 gas can grow largely on the front surface of the top cryopanel 60 because it directly faces the main accommodation space 65. The type 2 gas is a gas that does not condense at the first cooling temperature.

A gas in which vapor pressure is not sufficiently low at the second cooling temperature is adsorbed by the adsorbent 74 of the second-stage cryopanel assembly 20. This gas may be referred to as a third type gas (also called a type 3 gas). The type 3 gas is, for example, hydrogen. In this way, the second-stage cryopanel assembly 20 can exhaust the type 3 gas. Therefore, the cryopump 10 can exhaust various gases by condensation or adsorption and can make the degree of vacuum of the vacuum chamber reach a desired level.

An exhaust operation is continued, whereby gas is accumulated in the cryopump 10. In order to discharge the accumulated gas to the outside the regeneration of the cryopump 10 is performed. If the regeneration is completed, the exhaust operation can be started again.

In order to promote the temperature rise of the cryopump 10 and shorten the regeneration time, a purge gas is generally introduced into the cryopump housing 70 at the start of the regeneration. Due to the re-vaporization of the purge gas or the accumulated gas, the interior of the cryopump housing 70 is filled with gas, and therefore, a vacuum adiabatic effect is lost unlike during the exhaust operation. Heat exchange between the cryopanel and the cryopump housing 70 is promoted through the gas. Immediately after the start of the reproduction, the cryopanel is still cooled to a cryogenic temperature, so that the cryopump housing 70 can be cooled.

Further, since the cryopump 10 has the large main accommodation space 65, it is possible to store a large amount of the type 2 gas. At the relatively early stage of the regeneration, the type 2 gas dissolves into a liquid. As described above, since the type 2 gas is nitrogen, argon, or the like, the liquefied gas is very cold. The liquefied gas may flow down to the bottom portion of the radiation shield 30 or the cryopump housing 70 and come into contact with the inner surface of the cryopump housing 70. Then, the cryopump housing 70 is significantly cooled. For this reason, moisture in the ambient air may condense or frost may adhere to the outer surface of the cryopump housing 70. During the regeneration, the cryopump 10 is gradually heated to room temperature, so that the frost will eventually melt. If there is a lot of frost attached, it melts into a lot of water that can drop. It may result in wetting other equipment or items around the cryopump 10 or the floor surface.

The cryopump 10 according to the embodiment includes the water absorbing layer 80 mounted on the outer side of the cryopump housing 70. Moisture that tends to adhere to the outer surface of the cryopump housing 70 is absorbed by the water absorbing layer 80. Therefore, dew condensation on the cryopump 10 can be suppressed. Since the dew condensation is suppressed, the dropping of water to the surroundings of the cryopump 10 or the floor surface is also suppressed.

Further, the heat insulating layer 82 is disposed between the cryopump housing 70 and the water absorbing layer 80. The temperature decrease of the outer surface of the heat insulating layer 82 is smaller than the temperature decrease of the cryopump housing 70. The temperature difference between the outside air temperature and the water absorbing layer 80 can be made smaller than in a case where the water absorbing layer 80 is directly mounted to the cryopump housing 70 without the heat insulating layer 82. Therefore, dew condensation on the cryopump 10 can be suppressed.

If the temperature of the outer surface of the heat insulating layer 82 is lower than room temperature, dew condensation may occur. In order to prevent the dew condensation only by the heat insulating layer 82 without providing the water absorbing layer 80, the thickness 86 of the heat insulating layer 82 has to be sufficiently thick. In this case, the required thickness 86 of the heat insulating layer 82 may be so large that it is difficult to actually mount it on the cryopump housing 70.

However, since the cryopump 10 according to the embodiment has the water absorbing layer 80, it is possible to absorb the moisture that may condense on the outer surface of the heat insulating layer 82. The outer surface of the heat insulating layer 82 may be cooled to a certain degree from room temperature, and thus it is possible to make the heat insulating layer 82 thin. It is expected that the water absorbing layer 80 itself does not need that much thickness. Therefore, by combining the water absorbing layer 80 and the heat insulating layer 82, a dew condensation suppressing structure having a small thickness as a whole can be realized, and the mounting on the cryopump 10 becomes easier.

In a typical cryopump of the related art, an electric heater such as a band heater is wound around a housing in order to suppress dew condensation. The cryopump 10 according to the embodiment also has an advantage that such an electric heater is not required (therefore, the cryopump 10 according to the embodiment does not have an electric heater for heating the cryopump housing 70).

Further, the cryopump 10 according to the embodiment does not require a water receiving tray also called a drain pan.

The cryopump 10 includes the water absorbing and heat insulating sheet 84 having the water absorbing layer 80 on the outer side and having the heat insulating layer 82 on the inner side. In a case where the water absorbing layer 80 and the heat insulating layer 82 are separate layers, a two-step operation is required in which the heat insulating layer 82 is first mounted to the cryopump housing 70 and the water absorbing layer 80 is then mounted to the heat insulating layer 82. In the case of the water absorbing and heat insulating sheet 84, the water absorbing layer 80 and the heat insulating layer 82 can be mounted together to the cryopump housing 70, and therefore, manufacturing becomes easier.

In a case where the temperature of the outer surface of the water absorbing layer 80 is lower than 0° C., the condensed water may be frozen on the outer surface of the water absorbing layer 80. The ice layer is separated from the water absorbing layer 80 and adheres onto the water absorbing layer 80. When the ice layer melts due to the temperature rise of the cryopump 10, water may drop. However, according to the embodiment, the thickness 86 of the heat insulating layer 82 is determined such that the temperature of the water absorbing layer 80 is maintained at a temperature higher than 0° C. during the regeneration of the cryopump 10. Therefore, the formation of the ice layer on the water absorbing layer 80 is suppressed, and the dropping of water is also suppressed.

The present invention has been described above based on the examples. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, various design changes can be made, various modification examples can be made, and such modification examples are also within the scope of the present invention.

In the embodiment described above, the water absorbing and heat insulating sheet 84 is mounted to both the cryopanel accommodation part 76 and the cryocooler accommodation part 77. However, this is not essential. The water absorbing layer 80, the heat insulating layer 82, and/or the water absorbing and heat insulating sheet 84 may be mounted to only one of the cryopanel accommodation part 76 and the cryocooler accommodation part 77.

The water absorbing layer 80, the heat insulating layer 82, and/or the water absorbing and heat insulating sheet 84 may be mounted to the cryopump housing 70 so as to cover only a part of the outer surface of the cryopump housing 70. For example, the water absorbing and heat insulating sheet 84 may be mounted only to the lower portion of the cryopanel accommodation part 76. With this configuration, the dew condensation water flowing down from the upper portion of the cryopanel accommodation part 76 can be absorbed by the water absorbing and heat insulating sheet 84, and thus the dropping of the dew condensation water can be suppressed. Further, there is a case where the cryocooler accommodation part 77 is provided with a constituent element such as a valve or a sensor, which protrudes outward from the tubular portion. Such a constituent element may not be covered by the water absorbing and heat insulating sheet 84.

The water absorbing layer 80 may be disposed between the cryopump housing 70 and the heat insulating layer 82. That is, the water absorbing layer 80 may be disposed inside the heat insulating layer 82. For example, as shown in FIG. 3, the cryopump housing 70 can have corners or curved portions. The thickness 86 of the heat insulating layer 82 is relatively large in order to provide good thermal insulation. For this reason, a case where the heat insulating layer 82 is unlikely to come into close contact with the corners or the curved portions and is difficult to completely cover them is also assumed. In such a case, as shown in the drawing, the corner or the curved portion of the cryopump housing 70 may be covered with the water absorbing layer 80.

Further, as shown in FIG. 4, in a case where it is difficult for the heat insulating layer 82 to completely cover the corners or the curved portions of the cryopump housing 70, the water absorbing layer 80 may cover the heat insulating layer 82 from the outside. In this case, since the heat insulating layer 82 is not provided at the corner or the curved portion of the cryopump housing 70, a gap 87 may be formed between the corner or the curved portion and the water absorbing layer 80.

As shown in FIG. 5, the cryopump 10 may include a drain pan 88. The drain pan 88 is provided as a water receiving tray disposed below the cryopump housing 70, and is configured to prevent the dew condensation water from dripping on a floor surface 94 and/or to receive and store the dropping dew condensation water. The drain pan 88 is mounted to the cryopanel accommodation part 76 of the cryopump housing 70. The drain pan 88 may be fastened together with a caster 90 to the cryopanel accommodation part 76. A heat insulating spacer 92 may be inserted between the drain pan 88 and the cryopanel accommodation part 76. The drain pan 88 may be mounted to the cryopump housing 70 by another method such as being suspended from the intake port flange 72.

The water absorbing layer 80, the heat insulating layer 82, and/or the water absorbing and heat insulating sheet 84 is mounted to the cryocooler accommodation part 77. The water absorbing layer 80, the heat insulating layer 82, and/or the water absorbing and heat insulating sheet 84 may be mounted to the cryopanel accommodation part 76. In this way, the drain pan 88 may be used together with the dew condensation suppressing structure according to the embodiment.

In the above description, the horizontal cryopump has been exemplified. However, the present invention is also applicable to other vertical cryopumps. The vertical cryopump refers to a cryopump in which the cryocooler 16 is disposed along the cryopump central axis C of the cryopump 10. In that case, the cryocooler accommodation part 77 is installed not on the side surface of the cryopanel accommodation part 76 but on the housing bottom surface 76a. Further, the internal configuration of the cryopump, such as the arrangement, the shape, the number, or the like of a cryopanel, is not limited to the specific embodiment described above. Various known configurations can be appropriately adopted.

The present invention can be used in the field of a cryopump.

It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention.

Claims

1. A cryopump comprising: a cryopump housing; anda water absorbing layer mounted on an outer side of the cryopump housing.

2. The cryopump according to claim 1, further comprising: a heat insulating layer disposed between the cryopump housing and the water absorbing layer.

3. The cryopump according to claim 2, further comprising: a water absorbing and heat insulating sheet having the water absorbing layer on an outer side thereof and having the heat insulating layer on an inner side thereof.

4. The cryopump according to claim 2, wherein a thickness of the heat insulating layer is determined such that a temperature of the water absorbing layer is maintained at a temperature higher than 0° C. during regeneration of the cryopump.