US20160097380A1

US20160097380A1 - Cryopump

Info

Publication number: US20160097380A1
Application number: US14/876,424
Authority: US
Inventors: Ken Oikawa
Original assignee: Sumitomo Heavy Industries Ltd
Current assignee: Sumitomo Heavy Industries Ltd
Priority date: 2014-10-07
Filing date: 2015-10-06
Publication date: 2016-04-07
Also published as: CN105484968A; TW201615981A; TWI631280B; CN105484968B; JP2016075218A; KR20160041796A; KR101773888B1; JP6415230B2

Abstract

A cryopump includes: a cryopump vessel that defines an inlet; a refrigerator including a first stage and a second stage housed in the cryopump vessel, the second stage being cooled to a lower temperature than that of the first stage; a first cryopanel thermally connected to the first stage and surrounded by the cryopump vessel; and a second cryopanel thermally connected to the second stage and surrounded by the first cryopanel. The first cryopanel includes a plate member having an inlet aperture at the inlet. The inlet aperture is formed in the plate member such that a ratio of a conductance of the plate member with respect to an aperture conductance of the inlet is 6% or less.

Description

RELATED APPLICATION

Priority is claimed to Japanese Patent Application No. 2014-206158, filed on Oct. 7, 2014, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a cryopump.
2. Description of the Related Art
One application of a cryopump is a vacuum processing apparatus such as a sputtering apparatus. In a vacuum processing apparatus, a certain vacuum process may be repeatedly executed. The main role of a cryopump in such an apparatus is to maintain a degree of vacuum appropriate for the vacuum process. The cryopump may be used to restore the degree of vacuum to a proper level permitted to start the process while the apparatus temporarily stands by between the previous process and the next process. The time required to restore the degree of vacuum may be referred to as the recovery time. The shorter the recovery time, the earlier the next process can be started so that the productivity of the apparatus is increased. Therefore, the shorter the recovery time, the better. In order to reduce the recovery time, the pumping speed of the cryopump may be increased. One generally recognized means to achieve this is to increase the aperture ratio of the cryopump inlet.
A cryopump is a so-called entrapment vacuum pump so that a gas is collected in the cryopump in a vacuum pumping operation of the cryopump. As the gas is collected, the pumping speed of the cryopump is gradually reduced and the recovery time is gradually increased accordingly. To address this, the cryopump is periodically regenerated in order to discharge the collected gas from the cryopump and restore the pumping speed and the recovery time to the initial level. The period for vacuum pumping operation between the completion of the previous regeneration and the subsequent regeneration is called a regeneration interval.

SUMMARY OF THE INVENTION

As described above, it has been recognized in the related art that an increase in the aperture ratio of the cryopump inlet is useful to reduce the recovery time. The inventor has found, however, that such recognition is not quite appropriate in the later phase of the regeneration interval. Contrary to the general notion, a large aperture ratio promotes an increase in the recovery time in the later phase of the regeneration interval.
Embodiments of the present invention address a need to help improve the productivity of a vacuum processing apparatus by reducing or preventing the recovery time in the vacuum processing apparatus from increasing and by extending the regeneration interval of a cryopump, based on new findings different from the related-art conception.
According to an embodiment of the present invention, a cryopump includes: a cryopump vessel that defines a cryopump inlet; a refrigerator including a first stage and a second stage housed in the cryopump vessel, the second stage being cooled to a lower temperature than that of the first stage; a first cryopanel thermally connected to the first stage and surrounded by the cryopump vessel; and a second cryopanel thermally connected to the second stage and surrounded by the first cryopanel. The first cryopanel includes an inlet cryopanel having an inlet aperture at the cryopump inlet. The inlet aperture is formed in the inlet cryopanel such that a ratio of a conductance of the inlet cryopanel with respect to an aperture conductance of the cryopump inlet is 6% or less.
Optional combinations of the aforementioned constituting elements, and implementations of the invention in the form of methods, apparatuses, and systems may also be practiced as additional modes of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described, by way of example only, with reference to the accompanying drawings which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in several Figures, in which:

FIG. 1 is a schematic sectional side view of a main part of a cryopump according to an embodiment of the present invention;

FIG. 2 is a top view schematically illustrating a top panel of a second cryopanel according to an embodiment of the present invention;

FIG. 3 is a top view schematically illustrating a plate member of a first cryopanel according to an embodiment of the present invention;

FIG. 4 schematically illustrates the cryopump during a pumping operation according to an embodiment of the present invention;

FIG. 5 schematically illustrates an example of variation of the recovery time in a given regeneration interval according to an embodiment of the present invention;

FIG. 6 is a top view schematically illustrating a plate member according to an comparative example; and

FIG. 7 is a top view schematically illustrating a plate member of a first cryopanel according to an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described by reference to the preferred embodiments. This does not intend to limit the scope of the present invention, but to exemplify the invention.
A detailed description of an embodiment to implement the present invention will be given with reference to the drawings. Like numerals are used in the description to denote like elements and the description is omitted as appropriate. The structure described below is by way of example only and does not limit the scope of the present invention.
FIG. 1 is a schematic sectional side view of a main part of a cryopump 10 according to an embodiment of the present invention. The cryopump 10 is mounted on a vacuum chamber of, for example, a vacuum processing apparatus and used to increase the degree of vacuum inside the vacuum chamber to a level required for a desired process. The vacuum processing apparatus on which the cryopump 10 is mounted is exemplified by a sputtering apparatus. For example, the process gas pressure in a sputtering apparatus is in a range from 1 mTorr to 10 mTorr.
The cryopump 10 has an inlet 12 to receive gases. Gases to be pumped flow from the vacuum chamber on which the cryopump 10 is mounted, through the inlet 12, into an internal space 14 of the cryopump 10. FIG. 1 shows a view of the cross-section including a central axis A of the internal space 14 of the cryopump 10.
The diameter of the inlet 12 is in a range from 180 mm to 340 mm. Therefore, the nominal diameter of the cryopump 10 may be 8 inches, 10 inches, 12 inches, or 320 mm.
It is to be noted that terms “axial direction” and “radial direction” may be used herein to facilitate understanding of a positional relationship among components of the cryopump 10. The axial direction represents a direction through the inlet 12 (a direction along the dashed-dotted line A in FIG. 1), and the radial direction represents a direction along the inlet 12 (a direction perpendicular to the dashed-dotted line A). For convenience, relative closeness to the inlet 12 in the axial direction may be described by terms such as “upper” and “upward,” and relative remoteness therefrom may be described by terms such as “lower” and “downward.” In other words, relative remoteness from the bottom of the cryopump 10 may be described by terms such as “upper” and “upward,” and relative closeness thereto may be described by terms such as “lower” and “downward”. Relative closeness to a center (the central axis A in FIG. 1) of the inlet 12 in the radial direction may be described by terms such as “inner” and “inside,” and relative closeness to the circumference of the inlet 12 in the radial direction may be described by terms such as “outer” and “outside.” It should be noted here that these terms are not related to the orientation of the cryopump 10 as mounted on a vacuum chamber. For example, the cryopump 10 may be mounted on a vacuum chamber with the inlet 12 facing downward in the vertical direction.
Also, a direction surrounding the axial direction may be described by a term such as “a circumferential direction.” The circumferential direction is a second direction along the inlet 12 and a tangential direction orthogonal to the radial direction.
The cryopump 10 includes a refrigerator 16. The refrigerator 16 is a cryogenic refrigerator, such as a Gifford-McMahon type refrigerator (generally called a GM refrigerator). The refrigerator 16 is a two-stage refrigerator including a first stage 22 and a second stage 24. The refrigerator 16 is configured to cool the first stage 22 to a first temperature level and the second stage 24 to a second temperature level. The second temperature level is lower than the first temperature level. For example, the first stage 22 is cooled to approximately 65 K to 120 K, and preferably to 80 K to 100 K, while the second stage 24 is cooled to approximately 10 K to 20 K.
Also, the refrigerator 16 includes a first cylinder 23 and a second cylinder 25. The first cylinder 23 connects a room temperature portion of the refrigerator 16 to the first stage 22. The second cylinder 25 is a connecting portion connecting the first stage 22 to the second stage 24.
The cryopump 10 illustrated in the figure is a so-called horizontal-type cryopump. A horizontal-type cryopump is generally a cryopump arranged such that the refrigerator 16 intersects (orthogonally in general) with the central axis A of the internal space 14 of the cryopump 10.
The cryopump 10 includes a first cryopanel 18 and a second cryopanel 20 cooled to a lower temperature than that of the first cryopanel 18. The first cryopanel 18 includes a radiation shield 30 and a plate member 32, and encloses the second cryopanel 20. Details of the first cryopanel 18 will be described later. A main accommodating space 21 for a condensed layer 72 is formed between the plate member 32 and the second cryopanel 20 (see FIG. 4).
A description will be given of the second cryopanel 20 first. The second cryopanel 20 is arranged in a center part of the internal space 14 of the cryopump 10. The second cryopanel 20 is attached to the second stage 24 so as to enclose the second stage 24. Hence, the second cryopanel 20 is thermally connected to the second stage 24, and the second cryopanel 20 is cooled to the second temperature level.
FIG. 2 is a top view schematically illustrating a top panel 60 of the second cryopanel 20 according to an embodiment of the present invention. As shown in FIGS. 1 and 2, the top panel 60 is attached directly to an upper surface of the second stage 24 of the refrigerator 16. The second stage 24 is located at the center part of the internal space 14 of the cryopump 10. In this way, the main accommodating space 21 for the condensed layer 72 occupies the upper half of the internal space 14.
The top panel 60 is provided to condense gases on a surface thereof. The top panel 60 is a part of the second cryopanel 20 proximate to the plate member 32 and includes a top panel front face 61 facing the rear surface of the plate member 32. The top panel front face 61 includes a central region 62 and an outside region 63 surrounding the central region 62.
The top panel 60 is substantially a flat cryopanel arranged perpendicularly to the axial direction. The top panel 60 is fixed at the central region 62 to the second stage 24. The central region 62 has a recess, at which the top panel 60 is fixed to the second stage 24 with use of an appropriate fixing member 64 (see FIG. 2). The fixing member 64 is exemplified by a bolt. Around the recess is formed a step 65 extending upward. A height of the step 65 is defined so as to accommodate the fixing member 64 in the recess. The outside region 63 extends outward in the radial direction from the step 65. A radial end of the outside region 63 is bent downward to form an outer circumferential portion 66 of the top panel 60. The top panel 60 is substantially a disk-like panel as illustrated in FIG. 2.
The top panel 60 may not have the recess in the central region 62 accommodating the fixing member 64. In this case, the top panel front face 61 may be a flat surface not having the step 65. Also, although the top panel 60 does not have an adsorbent in the present embodiment, the top panel 60 may be provided with an adsorbent, for example, on a back face of the top panel 60.
The shape of the second cryopanel 20 is adjusted so that the width W1 of a first lateral gap 43 and the width W2 of a second lateral gap 44 may correspond to each other. That is, the width W1 of the first lateral gap 43 is substantially equal to the width W2 of the second lateral gap 44. To this end, the top panel 60 has a cut-out portion 74 widening the first lateral gap 43. This cut-out portion 74 forms a flat portion in the outer circumference of the top panel 60 toward the refrigerator 16. Cryopanels below the top panel 60 may have cut-out portions in a similar manner.
The second cryopanel 20 includes one or more normal panels 67. Each of the normal panels 67 is provided to condense or adsorb gases on a surface thereof. The normal panels 67 are arranged on a lower side of the top panel 60. Each of the normal panels 67 has a different shape from that of the top panel 60. Each of the normal panels 67 has a shape of the side surface of a truncated cone, i.e., an umbrella-like shape. An adsorbent 68 such as activated charcoal is provided on each of the normal panels 67. The adsorbent is, for example, attached to the back face of each of the normal panels 67. The front face of each of the normal panels 67 is intended to function as a condensing surface while the back face is intended to function as an adsorbing surface.
The first cryopanel 18 is a cryopanel provided to protect the second cryopanel 20 from radiant heat emitted from the outside of the cryopump 10 or a cryopump vessel 38. The first cryopanel 18 is thermally connected to the first stage 22. Thus, the first cryopanel 18 is cooled to the first temperature level. A gap is provided between the first cryopanel 18 and the second cryopanel 20, and the first cryopanel 18 does not contact the second cryopanel 20.
The radiation shield 30 is provided to protect the second cryopanel 20 from radiant heat emitted from the cryopump vessel 38. The radiation shield 30 is located between the cryopump vessel 38 and the second cryopanel 20, and encloses the second cryopanel 20. The radiation shield 30 has a diameter slightly smaller than that of the cryopump vessel 38. A gap is provided between the radiation shield 30 and the cryopump vessel 38, and the radiation shield 30 does not contact the cryopump vessel 38.
The radiation shield 30 includes a shield front end 28 defining a shield opening 26, a shield bottom portion 34 opposite to the shield opening 26, and a shield side portion 36 extending from the shield front end 28 to the shield bottom portion 34. The shield opening 26 defines a main opening of the cryopump 10 located at the inlet 12. The radiation shield 30 has a tubular shape (for example, cylindrical) with the shield bottom portion 34 closed, i.e., the radiation shield 30 is formed into a cup-like shape.
The radiation shield 30 includes an attaching pedestal 37 for the refrigerator 16. The attaching pedestal 37 is dented as seen from the outside of the radiation shield 30 and forms on the shield side portion 36 a flat part for attachment of the refrigerator 16 to the radiation shield 30. The attaching pedestal 37 is located lateral to the second cryopanel 20. Since the top panel 60 is attached directly to the upper surface of the second stage 24 of the refrigerator 16 as described above and is thus as high as the second stage 24, the attaching pedestal 37 is located lateral to the top panel 60.
The shield side portion 36 generally forms a closed annular part. The aforementioned first lateral gap 43 is formed between the attaching pedestal 37 of the shield side portion 36 and the top panel 60. The second lateral gap 44 is formed between the remainder of the shield side portion 36 and the top panel 60. The first lateral gap 43 and the second lateral gap 44 are also formed between the shield side portion 36 and the normal panels 67. The second lateral gap 44 is contiguous with the first lateral gap 43 in the circumferential direction, and the first lateral gap 43 and the second lateral gap 44 form a closed annular gap. The second lateral gap 44 has a constant width in the circumferential direction.
As illustrated in FIG. 1, the attaching pedestal 37 has an attaching hole 42 for the refrigerator 16, and the second stage 24 and the second cylinder 25 of the refrigerator 16 are inserted into the radiation shield 30 through the attaching hole 42. The first stage 22 of the refrigerator 16 is arranged outside the radiation shield 30. The radiation shield 30 is connected to the first stage 22 via a heat transfer member 45. The heat transfer member 45 is fixed to an outer circumferential portion of the attaching hole 42 by a flange at one end thereof and is fixed to the first stage 22 by a flange at the other end thereof. The heat transfer member 45 is, for example, a hollow short tube, and extends between the radiation shield 30 and the first stage 22 along a central axis of the refrigerator 16. The radiation shield 30 is thermally connected to the first stage 22 in this way. The radiation shield 30 may be attached directly to the first stage 22.
Between the second cylinder 25 and the attaching hole 42, an upper gap 46 is formed on the side closer to the shield opening 26, and a lower gap 48 is formed on the side further away from the shield opening 26. Since the refrigerator 16 is inserted through the center of the attaching hole 42, a width of the upper gap 46 is equal to a width of the lower gap 48.
In the present embodiment, the radiation shield 30 is formed as a one-piece tube as illustrated in the figure. Alternatively, as for the radiation shield 30, a plurality of parts may form a tubular shape as a whole. The plurality of parts may be arranged so as to have a gap between one another. For example, the radiation shield 30 may be segmented into two parts in the axial direction. In this case, an upper portion of the radiation shield 30 is a tube having ends that are both open and includes the shield front end 28 and a first part of the shield side portion 36. A lower portion of the radiation shield 30 has an open upper end and a closed lower end and includes a second part of the shield side portion 36 and the shield bottom portion 34. A gap extending in the circumferential direction is formed between the first part and the second part of the shield side portion 36. As for the attaching hole 42 for the refrigerator 16, an upper half thereof is formed in the first part of the shield side portion 36 while a lower half thereof is formed in the second part of the shield side portion 36.
The cryopump 10 is provided with a refrigerator cover 70 enclosing the second cylinder 25 of the refrigerator 16. The refrigerator cover 70 is formed in a cylindrical shape having a slightly larger diameter than that of the second cylinder 25, is attached at one end to the second stage 24, and extends through the attaching hole 42 of the radiation shield 30 toward the first stage 22. A gap is provided between the refrigerator cover 70 and the radiation shield 30, and the refrigerator cover 70 and the radiation shield 30 do not contact each other. The refrigerator cover 70 is thermally connected to the second stage 24 and is cooled to the same temperature as the second stage 24. Accordingly, the refrigerator cover 70 is also regarded as part of the second cryopanel 20.
The first cryopanel 18 includes an inlet cryopanel having an inlet aperture in the inlet 12. The inlet cryopanel includes an orifice member placed in the inlet 12. The inlet aperture is implemented by at least one orifice or opening formed in the orifice member. The orifice member may be a single orifice plate (e.g., the plate member 32) covering the shield opening 26. For example, at least one orifice or opening may be implemented by a large number of holes (e.g., the pores 54). The side surface of the inlet cryopanel defining the inlet aperture may be black in color. The rear surface of the inlet cryopanel (the surface facing the second cryopanel 20) may be black.
The inlet aperture is formed in the inlet cryopanel such that the ratio of the conductance of the inlet cryopanel with respect to the aperture conductance of the inlet 12 is 1%-6%. Preferably, the inlet aperture is formed in the inlet cryopanel such that the ratio of the conductance of the inlet cryopanel with respect to the aperture conductance of the inlet 12 is 4%-6%.
The plate member 32 is provided in the shield opening 26 to protect the second cryopanel 20 from radiant heat emitted from a heat source outside the cryopump 10. The heat source outside the cryopump 10 is, for example, a heat source inside the vacuum chamber on which the cryopump 10 is mounted. The entry of molecules of gases, in addition to the radiant heat, is also limited. The plate member 32 occupies a part of the opening area of the inlet 12 so as to limit a flow of gases through the inlet 12 into the internal space 14 to a desired quantity. The plate member 32 covers a major portion of the inlet 12. Gases (for example, moisture) that condense at cooling temperatures of the plate member 32 are trapped on a surface thereof.
There is a slight gap between the shield front end 28 and the plate member 32 in the axial direction. The plate member 32 includes a skirt 33 to cover the gap to restrict a flow of gases. The skirt 33 is a short tube surrounding the plate member 32. The skirt 33 and the plate member 32 form a one-piece structure resembling a circular tray with the plate member 32 as a bottom surface of the tray. This circular tray structure is arranged to cover the radiation shield 30. Hence, the skirt 33 protrudes downward from the plate member 32 in the axial direction and extends in proximity to the shield front end 28 in the radial direction. A distance between the skirt 33 and the shield front end 28 in the radial direction is, for example, about a dimensional tolerance of the radiation shield 30.
The gap between the shield front end 28 and the plate member 32 may vary according to a manufacturing error. Such an error may be reduced by precise machining and assembly of components, which may not be practical, though, because of possible increases in manufacturing costs. The error contributes to an individual difference of the cryopump 10. In a case where the skirt 33 is not provided, a quantity of gases flowing into the inside of the radiation shield 30 changes depending on a size of the gap. The quantity of entry of gases is directly related to the pumping speed of the cryopump 10. A gap which is excessively large or small causes an actual pumping speed to deviate from a design performance thereof. The flow of gases through the gap is restricted by using the skirt 33 to cover the gap between the shield front end 28 and the plate member 32, which reduces the individual difference. This, as a result, also reduces an individual difference in the pumping speed of cryopumps in reference to the design performance.
A shield front end 28 and the plate member 32 are arranged at an upper side in the axial direction over the inlet flange 40 of the cryopump vessel 38. The shield front end 28 and the plate member 32 are located outside the cryopump vessel 38. In this way, the radiation shield 30 extends toward the vacuum chamber on which the cryopump 10 is mounted. By extending the radiation shield 30 upward, the main accommodating space 21 for the condensed layer 72 can be large in the axial direction. However, the length of the extending part in the axial direction is determined so as not to interfere with the vacuum chamber (or a gate valve between the vacuum chamber and the cryopump 10).
The cryopump vessel 38 is a housing of the cryopump 10 accommodating the first cryopanel 18 and the second cryopanel 20 and is a vacuum vessel configured to maintain vacuum gas tightness of the internal space 14. The first stage 22 and the second stage 24 of the refrigerator 16 are housed in the cryopump vessel 38.
A front end 39 of the cryopump vessel 38 defines the inlet 12. The cryopump vessel 38 includes an inlet flange 40 extending outward in the radial direction from the front end 39. The inlet flange 40 is provided along the entire circumference of the cryopump vessel 38. The cryopump 10 is attached to a vacuum chamber with use of the inlet flange 40. A gap is provided between the front end 39 of the cryopump vessel 38 and the plate member 32, and the cryopump vessel 38 does not contact the plate member 32.
FIG. 3 is a top view schematically illustrating the plate member 32 according to an embodiment of the present invention. In FIG. 3, the representative components located below the plate member 32 are illustrated by dashed lines. The plate member 32 includes a single flat plate (for example, a disk) across the shield opening 26. The front surface of the plate member 32 faces a space outside the cryopump 10 and the rear surface of the plate member 32 faces the top panel 60. The axial distance between the plate member 32 and the top panel 60 defines the height of the main accommodating space 21.
A dimension (for example, a diameter) of the plate member 32 is substantially equal to that of the shield opening 26. The plate member 32 includes a plate center portion 50 and a plate outer rim portion 52. The plate center portion 50 is a radially inward portion of the plate member 32 and the plate outer rim portion 52 is a radially outward portion of the plate member 32 surrounding the plate center portion 50.
The plate outer rim portion 52 is attached to plate mounts 29 of the shield front end 28. The plate mounts 29 are each a protrusion extending from the shield front end 28 inward in the radial direction and are formed at regular intervals (for example, every 90°) in the circumferential direction. The plate member 32 is fixed to the plate mounts 29 in an appropriate manner. For example, the plate mounts 29 and the plate outer rim portion 52 each have a bolt hole (not shown) to allow the plate outer rim portion 52 to be bolted onto the plate mounts 29.
A large number of pores 54 are formed in the plate member 32 in order to allow the gases to flow therethrough. The pores 54 are through holes formed in the plate center portion 50. By doing so, gases to be condensed on the second cryopanel 20 can be received through the pores 54 into the main accommodating space 21 between the plate member 32 and the second cryopanel 20. The pores 54 are not formed in the plate outer rim portion 52.
The pores 54 are regularly arranged. In the embodiment, the pores 54 are provided at regular intervals respectively in two orthogonal linear directions to form a lattice of the pores 54. Alternatively, the pores 54 may be provided at regular intervals respectively in the radial and circumferential directions.
The pores 54 are formed, for example, in a circular shape. However, the shape is not limited to this, and the pores 54 may be openings formed in a rectangular or any other shape, slits extending in a linear or curved form, or cut-outs formed at an outer circumference of the plate member 32. Each of the pores 54 is obviously smaller than the shield opening 26.
The pores 54 are formed in the plate member 32 such that the ratio of the total area of the pores 54 with respect to the area of the opening of the inlet 12 (i.e., the aperture ratio of the inlet 12) is 1%-6% (preferably, 4%-6%). Thus, the pores 54 are formed in the plate member 32 such that the ratio of the conductance of the plate member 32 with respect to the aperture conductance of the inlet 12 is 1%-6% (preferably, 4%-6%).
The rear surface of the plate member 32 and the interior surface of the radiation shield 30 may be treated to increase the radiation factor. For example, a black body coating may be applied to the surfaces. This allows the radiation factor of the rear surface of the plate member 32 and the interior surface of the radiation shield 30 to be substantially equal to 1. The plate member side surfaces defining the pores 54 in plate member 32 may also be treated similarly. The black surface of the plate member 32 may be formed by black chromium plating on the surface of a copper base or by painting the surface in black. The black surface is useful to absorb heat entering the cryopump 10.
Meanwhile, the front surface of the plate member 32 may be treated to reduce the radiation factor so as to reflect the radiation heat from outside. The surface of a low radiation factor may be formed by plating the surface of a copper base with nickel.
An explanation on the operations of the cryopump 10 with the aforementioned configuration will be given below. Before activating the cryopump 10, the inside of the vacuum chamber is first roughly evacuated to approximately 1 Pa by using an appropriate roughing pump. The cryopump 10 is then activated. The operation of the refrigerator 16 cools the first stage 22 and the second stage 24, and that also cools the first cryopanel 18 and the second cryopanel 20 thermally connected to these stages. The first cryopanel 18 and the second cryopanel 20 are cooled to the first temperature and the second temperature, which is lower than the first temperature, respectively.
The plate member 32 cools molecules of the gases flowing from the vacuum chamber into the cryopump 10 to cause gases (for example, moisture) having vapor pressures that are sufficiently reduced by a cooling temperature of the plate member 32 to condense on a surface of the plate member 32 for removal. Gases having vapor pressures that are not sufficiently reduced by the cooling temperature of the plate member 32 pass through the large number of pores 54 to enter the main accommodating space 21. Some of the gases that enters the cryopump 10 are reflected by the plate member 32 and do not enter the main accommodating space 21.
Of the molecules of the gases that have entered, gases (for example, argon) having vapor pressures that are sufficiently reduced by a cooling temperature of the second cryopanel 20 are condensed on a surface of the second cryopanel 20 (mainly, the top panel front face 61) for removal. Gases (for example, hydrogen) having vapor pressures that are not sufficiently reduced by this cooling temperature are adsorbed onto the adsorbent 68 for removal. As described above the adsorbent 68 is attached to the surface of the second cryopanel 20 and cooled. In this way, the cryopump 10 can attain a desired degree of vacuum in the vacuum chamber.
FIG. 4 schematically illustrates the cryopump 10 during a pumping operation. As illustrated in FIG. 4, ice or frost made from condensed gases is deposited on the top panel 60 of the cryopump 10. As shown in FIG. 4, a domed or mushroom condensed layer 72 grows on the top panel 60. The condensed layer 72 consists primarily of, for example, argon. This ice layer grows and gets thick with the elapse of the pumping operation time. In FIG. 4, condensed layers deposited on the normal panels 67 and the refrigerator cover 70 are not illustrated for simplicity.
As the condensed layer 72 grows, a temperature gradient is created in the direction of depth of the condensed layer 72. As a result, the surface temperature of the condensed layer 72 becomes higher than the surface temperature of the top panel 60. This means that the gas is directly condensed on the top panel front face 61 at a lower temperature in the initial phase of the regeneration interval. In contrast, the gas is condensed on the surface of the condensed layer 72 at a higher temperature in the later phase of the regeneration interval. Therefore, the pumping speed of the cryopump 10 is gradually decreased as the vacuum pumping operation of the cryopump 10 is continued. As the pumping speed is decreased, the recovery time is extended accordingly.
Therefore, the recovery time is used as one indicator to determine whether the cryopump 10 needs regeneration. If the recovery time is shorter than a prescribed value, the cryopump 10 can continue to be operated. When the recovery time is longer than the prescribed time, however, the vacuum pumping operation of the cryopump 10 is suspended and the cryopump 10 is regenerated. The prescribed value may be defined as a specification of the vacuum process in the vacuum processing apparatus.
Regeneration of the cryopump 10 results in down time of the vacuum processing apparatus. It is therefore desired to prevent the recovery time from increasing and extend the regeneration interval of cryopump 10 in order to improve the productivity of the vacuum processing apparatus.
It is generally recognized that the pumping speed of the cryopump 10 should be increased to reduce the recovery time. One means to achieve this is to increase the ratio of conductance of the plate member 32 with respect to the aperture conductance of the inlet 12 of the cryopump 10. Simply put, the pumping speed of the cryopump 10 can be increased and the recovery time can be reduced by increasing the aperture ratio of the inlet 12.
This is true in the initial phase of the regeneration interval. Considering the growth of the condensed layer 72, however, it is not necessarily true in the later phase of the regeneration interval. This is because, if the aperture ratio is large, the heat load entering the cryopump 10 is increased and temperature gradient of the condensed layer 72 increases accordingly. Also, a larger aperture ratio increases the amount of gas entering the cryopump 10. This also increases the temperature gradient of the condensed layer 72. An increase in the temperature gradient of the condensed layer 72 leads to an increase in the surface temperature of the condensed layer 72 and in the recovery time as well. As shown in FIG. 4, the condensed layer 72 grows large in the later phase of the regeneration interval so that the recovery time may be significantly increased.
To address this, the embodiment of the present invention seeks to prevent an increase in the recovery time by mitigating an increase in the temperature gradient of the condensed layer 72. By keeping the temperature difference between the condensed layer 72 and the top panel 60 small, a drop in the pumping speed of the cryopump 10 associated with the growth of the condensed layer 72 is mitigated. To this end, the conductance ratio according to this embodiment is set to an ultimately small value within the practical limit. For example, the ratio of the conductance of the plate member 32 with respect to the aperture conductance of the inlet 12 is set to 1%-6% (e.g., 4%-6%).
When the domed condensed layer 72 grows further in the radial direction, the outer circumference of the condensed layer 72 may contact the shield side portion 36. If the gap width between the attaching pedestal 37 and the top panel 60 is narrower, the condensed layer 72 contacts the attaching pedestal 37 first. Gases vaporize again at a contacting part and are emitted out from the main accommodating space 21 and the cryopump 10. Thereafter, the cryopump 10 cannot provide a design pumping performance. Thus, the amount of gases accumulated at this time provides a maximum gas capacity of the cryopump 10. A local part of the condensed layer 72 (in this case, the condensed layer 72 around the attaching pedestal 37) determines a gas capacity limit of the cryopump 10.
A cryopump is generally designed to be axisymmetric. However, the horizontal-type cryopump 10 inevitably has an asymmetric part (e.g., the attaching pedestal 37) since the refrigerator 16 is arranged in a horizontal direction. In the present embodiment, the shape of the top panel 60 is conformed to such an asymmetric part to make uniform the width of the gap between the top panel 60 and the radiation shield 30 in the circumferential direction. This prevents a specific portion of the condensed layer 72 on the top panel 60 growing in the radial direction (in this case, the part of the condensed layer 72 proximate to the attaching pedestal 37) from contacting the radiation shield 30 before the other portions of the condensed layer 72 contact the radiation shield 30. This enables the gas capacity of the cryopump 10 to be improved.
FIG. 5 schematically illustrates an example variation of the recovery time in a given regeneration interval according to an embodiment of the present invention. The vertical axis of FIG. 5 represents the recovery time and the horizontal axis represents the operating time of the cryopump 10. It can be said that the horizontal axis represents the cumulative number of times of recoveries performed during the vacuum pumping operation of the cryopump 10. Referring to FIG. 5, the variation in the recovery time according to the embodiment is indicated by the solid line and the variation of the recovery time according to a comparative example is indicated by the broken line. In the comparative example, the aperture ratio of the cryopump inlet is relatively high (e.g., larger than 7%). The regeneration interval according to the embodiment is indicated by arrow B and the regeneration interval according to the comparative example is indicated by arrow C.
FIG. 6 is a top view schematically illustrating a plate member 132 according to the comparative example. As shown in FIG. 6, the plate member 132 is provided with a large number of pores 154 formed not only in the plate center portion 150 but also in a plate outer rim portion 152. If the pores 154 are distributed over the entire region of the plate member 132 as in this case, the aperture ratio of the inlet exceeds 7%.
As shown in FIG. 5, the recovery time of the cryopump 10 according to the embodiment is longer than that of the comparative example to some extent in the initial phase of the regeneration interval. When the vacuum pumping operation of the cryopump 10 is continued, the pumping speed of the cryopump 10 is gradually decreased toward the later phase of the regeneration interval and the recovery time becomes longer in association. When the recovery time reaches the prescribed time T, the regeneration interval ends (i.e., regeneration is started).
According to the embodiment, the aperture ratio of the inlet cryopanel with respect to the opening of the inlet 12 is small. The aperture ratio of the inlet cryopanel is defined as a ratio of the area of the opened part of the inlet cryopanel with respect to the area of the inlet cryopanel as viewed in the axial direction. Because the aperture ratio of the inlet panel is small, the amount of gas flowing into the main accommodating space 21 from outside the cryopump 10 is small. Consequently, the growth speed of the condensed layer 72 is low. The heat load from the gases is also small. Further, the heat load from the entering radiation heat is small. Therefore, the temperature gradient in the condensed layer 72 is small and the surface temperature of the condensed layer 72 is maintained at a low temperature. Accordingly, the recovery time in the later phase of the regeneration interval is prevented from increasing. This extends the regeneration interval B according to the embodiment as compared to the regeneration interval C according to the comparative example.
In accordance with inventor's study and calculation, reduction in the aperture ratio produces the advantage of extended regeneration interval, given that the diameter of the inlet is in a range between 180 mm and 340 mm. In further accordance with inventor's study and calculation, the embodiment is useful for vacuum pumping in a range between 1 mTorr and 10 mTorr, for example.
As described above, the recovery time in a vacuum processing apparatus can be reduced or prevented from increasing and the regeneration interval of the cryopump 10 can be extended, based on new findings different from the related-art conception. Accordingly, the cryopump 10 capable of contributing to improvement in the productivity of a vacuum processing apparatus can be provided.
Described above is an explanation based on an exemplary embodiment. The invention is not limited to the embodiment described above and it will be obvious to those skilled in the art that various design changes and variations are possible and that such modifications are also within the scope of the present invention.
FIG. 7 is a top view schematically illustrating a plate member 232 of the first cryopanel according to an alternative embodiment of the present invention. The plate member 232 is provided with a first plate 234 having at least one gas-permeable opening and a second plate 236 adjacent to the first plate 234 and covering the shield opening in cooperation with the first plate 234. Unlike the first plate 234, the second plate 236 does not have gas-permeable openings.
The first plate 234 is an orifice disc having a diameter smaller than the diameter of the cryopump inlet or the shield opening. The first plate 234 includes a large number of pores 254. The second plate 236 is a circular annular plate covering the inlet along with the first plate 234. The second plate 236 has an outer diameter substantially equal to the diameter of the inlet and the shield opening. The second plate 236 occupies at least 15% of the cryopump inlet.
The first plate 234 may be a plate member 32 that conforms to the cryopump and/or the radiation shield having a first nominal diameter. By combining the first plate 234 and the second plate 236, the plate member 232 that conforms to the cryopump and/or the radiation shield having a second nominal diameter larger than the first nominal diameter can be obtained. For example, the first nominal diameter may be 8 inches and the second nominal diameter may be 10 inches.
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

What is claimed is:

1. A cryopump comprising:

a cryopump vessel that defines a cryopump inlet;

a refrigerator comprising a first stage and a second stage housed in the cryopump vessel, the second stage being cooled to a lower temperature than that of the first stage;

a first cryopanel thermally connected to the first stage and surrounded by the cryopump vessel; and

a second cryopanel thermally connected to the second stage and surrounded by the first cryopanel,

wherein the first cryopanel comprises an inlet cryopanel having an inlet aperture at the cryopump inlet,

wherein the inlet aperture is formed in the inlet cryopanel such that a ratio of a conductance of the inlet cryopanel with respect to an aperture conductance of the cryopump inlet is 6% or less.

2. The cryopump according to claim 1, wherein the inlet aperture is formed in the inlet cryopanel such that the ratio of the conductance of the inlet cryopanel with respect to the aperture conductance of the cryopump inlet is 1% or more or 4% or more.

3. The cryopump according to claim 1, wherein the inlet cryopanel comprises an orifice member located in the cryopump inlet, and the inlet aperture is implemented by at least one opening formed in the orifice member,

wherein an area ratio of the at least one opening with respect to the cryopump inlet is 6% or less.

4. The cryopump according to claim 3, wherein the area ratio is 1% or more or 4% or more.

5. The cryopump according to claim 3, wherein the orifice member is a single orifice plate covering the cryopump inlet.

6. The cryopump according to claim 3, wherein the cryopump inlet is a circular opening having a first diameter,

wherein the orifice member comprises a circular plate having a second diameter smaller than the first diameter and an annular plate covering the cryopump inlet along with the circular plate, and the at least one opening is formed in the circular plate.

7. The cryopump according to claim 3, wherein the at least one opening is implemented by a large number of holes.

8. The cryopump according to claim 1, wherein a diameter of the cryopump inlet is in a range from 180 mm to 340 mm.

9. The cryopump according to claim 1, wherein a side surface of the inlet cryopanel defining the inlet aperture is black.

10. The cryopump according to claim 1, wherein the inlet cryopanel is located above a front end of the cryopanel vessel that defines the cryopanel inlet.