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Cryopump and method of operating the cryopump

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Cryopump and method of operating the cryopump


A cryopump includes a high-temperature cryopanel, a low-temperature cryopanel, and a cooling system. The cooling system has: a refrigerator provided with a first stage for cooling the high-temperature cryopanel and a second stage for cooling the low-temperature cryopanel; and a control unit configured to control a cool-down operation in which the first stage and the second stage are cooled in order to initiate a vacuum pumping operation of the cryopump. The cooling system may be configured to selectively provide a cooling relief effect to the first stage at least temporarily in the cool-down operation.
Related Terms: Elective Tempo Vacuum Pump Control Unit

Browse recent Sumitomo Heavy Industries, Ltd. patents - Tokyo, JP
USPTO Applicaton #: #20140230461 - Class: 62 555 (USPTO) -
Refrigeration > Low Pressure Cold Trap Process And Apparatus

Inventors: Kakeru Takahashi

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The Patent Description & Claims data below is from USPTO Patent Application 20140230461, Cryopump and method of operating the cryopump.

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BACKGROUND

1. Technical Field

The present invention relates to a cryopump and a method of operating the cryopump.

2. Description of Related Art

When a new cryopump is installed on site, the cryopump is cooled from a room temperature to a cryogenic temperature and a vacuum pumping operation is initiated. Further, the cryopump is a gas entrapment vacuum pump, as known, and hence regeneration is performed at a certain interval in order to discharge entrapped gas to the outside. Regeneration processing generally includes a temperature-raising step, a discharge step, and a cooling step. When the cooling step is terminated, the vacuum pumping operation of the cryopump is resumed. The cooling of the cryopump, performed as preparation for such a vacuum pumping operation, may be sometimes referred to as cool-down.

Although the cryopump is one of the major applications of a cryogenic refrigerator, it is different from other applications in that a relatively large temperature difference is required between a high-temperature stage and a low-temperature stage of the refrigerator. However, when the cryopump is cooled, it is not easy to create such a temperature difference in a short period of time. For example, if the temperature of the low-temperature stage does not yet reach its target temperature when the temperature of the high-temperature stage reaches its target cooling temperature, the cooling of the low-temperature stage is required to be still continued, while the high-temperature stage is being maintained at the target temperature. Alternatively, the high-temperature stage can already be cooled to a temperature lower than the target temperature, when the temperature of the low-temperature stage reaches the target temperature. In this case, the temperature of the high-temperature stage is required to be raised to the target temperature. Such temperature adjustment in the end of the cool-down takes a certain period of time. In particular, when a large temperature difference is required between the high-temperature stage and the low-temperature stage, the temperature adjustment takes a long period of time. Since the cool-down is a downtime of the cryopump, it is desirable to carry out the cool down in a short period of time.

SUMMARY

An exemplary object according to an aspect of the present invention, it is desirable to shorten a cooling time of a cryopump and to provide a method of operating such a cryopump.

According to an embodiment of the present invention, a cryopump having a high-temperature cryopanel, a low-temperature cryopanel, and a cooling system is provided. The cooling system includes: a refrigerator provided with a high-temperature stage for cooling the high-temperature cryopanel and a low-temperature stage for cooling the low-temperature cryopanel; and a control unit configured to control a cool-down operation in which the high-temperature stage and the low-temperature stage are cooled in order to initiate a vacuum pumping operation of the cryopump. The cooling system is configured to provide a cooling relief effect selectively to the high-temperature stage at least temporarily in the cool-down operation.

According to an embodiment of the present invention, a method of operating a cryopump is provided. The method includes: cooling a cryopanel from an initial temperature higher than a cryogenic temperature for a vacuum pumping operation to the cryogenic temperature by using a refrigerator; and after the cooling, initiating the vacuum pumping operation, in which the cooling includes providing a cooling relief effect selectively to a high-temperature stage of the refrigerator.

It is noted that any combination of the aforementioned components or any manifestation of certain embodiments of the present invention exchanged between methods, devices, systems and so forth, is effective as an embodiment 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 view illustrating a cryopump according to an embodiment of the present invention;

FIG. 2 is a schematic view illustrating a compressor according to an embodiment of the invention;

FIG. 3 is a flowchart for describing a method of operating a cryopump according to an embodiment;

FIG. 4 is a view illustrating an example of a temperature profile in a typical cool-down operation;

FIG. 5 is a flowchart for describing flow channel switching control in a compressor according to an embodiment of the invention;

FIG. 6 is a view illustrating an example of a temperature profile in a cool-down operation according to an embodiment of the invention; and

FIG. 7 is a schematic view illustrating a cryopump according to another embodiment of the invention.

DETAILED DESCRIPTION

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.

According to an embodiment of the present invention, a cooling relief effect (i.e., an effect that reduces a cooling capability) is selectively provided to a high-temperature stage during a cool-down operation while the cooling of a low-temperature stage continues at the normal level. This enables a larger difference in temperature to be generated rapidly between the high-temperature stage and the low-temperature stage. Accordingly, a temperature deviation of the low-temperature stage (or of the high-temperature stage) from its target temperature when the high-temperature stage (or the low-temperature stage) is finally cooled to its target temperature can be reduced. Therefore, a period of time required for the temperature adjustment in the end of cool-down can be shortened. As a result, a cool-down time of a cryopump can be shortened.

FIG. 1 is a schematic view illustrating a cryopump 10 according to an embodiment of the present invention. The cryopump 10, which is mounted, for example, to a vacuum chamber such as an ion implantation apparatus or a sputtering apparatus, is used to raise the degree of vacuum inside the vacuum chamber to a level required of a desired process.

The cryopump 10 has an inlet 12 for receiving a gas. The inlet 12 is an entrance to an internal space 14 of the cryopump 10. A gas to be pumped enters the internal space 14 of the cryopump 10 through the inlet 12 from the vacuum chamber to which the cryopump 10 is mounted.

It is to be noted that the terms “axial direction” and “radial direction” may be used in the following description to clearly show the positional relationships between the constituent parts of the cryopump 10. The axial direction represents a direction passing through the inlet 12, whereas the radial direction represents a direction along the inlet 12. For convenience, with respect to the axial direction, positions relatively closer to the inlet 12 may be described as “above”, and positions relatively farther from the inlet 12 as “below”. That is, positions relatively farther from the bottom of the cryopump 10 may be described as “above”, and positions relatively closer thereto as “below”. With respect to the radial direction, positions closer to the center of the inlet 12 may be described as “inside”, and positions closer to the periphery of the inlet 12 as “outside”. However, it is to be noted that these descriptions do not limit the locations of the cryopump 10 as mounted to the vacuum chamber. For example, the cryopump 10 may be mounted to the vacuum chamber with the inlet 12 facing downward in the vertical direction.

The cryopump 10 includes a cooling system 15, a low-temperature cryopanel 18, and a high-temperature cryopanel 19. The cooling system 15 is configured to cool the high-temperature cryopanel 19 and the low-temperature cryopanel 18. The cooling system 15 also includes a refrigerator 16 and a compressor 36.

The refrigerator 16 is a cryogenic refrigerator, such as, for example, a Gifford-McMahon refrigerator (so-called GM refrigerator). The refrigerator 16 is a two-stage type refrigerator including a first stage 20, a second stage 21, a first cylinder 22, a second cylinder 23, a first displacer 24, and a second displacer 25. Accordingly, the high-temperature stage of the refrigerator 16 includes the first stage 20, the first cylinder 22, and the first displacer 24. The low-temperature stage of the refrigerator 16 includes the second stage 21, the second cylinder 23, and the second displacer 25. Accordingly, in the following description, the first stage 20 and the second stage 21 can also be referred to as a low-temperature end of the high-temperature stage and that of the low-temperature stage, respectively.

The first cylinder 22 and the second cylinder 23 are connected in series. The first stage 20 is installed in a joint portion between the first cylinder 22 and the second cylinder 23. The second cylinder 23 connects the first stage 20 and the second stage 21. The second stage 21 is installed at the end of the second cylinder 23. The first displacer 24 and the second displacer 25 are arranged inside the first cylinder 22 and the second cylinder 23, respectively, so as to be movable in the longitudinal direction of the refrigerator 16 (the horizontal direction in FIG. 1). The first displacer 24 and the second displacer 25 are connected together so as to be movable integrally. A first regenerator and a second regenerator (not illustrated) are installed within the first displacer 24 and the second displacer 25, respectively.

The refrigerator 16 includes a drive mechanism 17 provided at the high-temperature end of the first cylinder 22. The drive mechanism 17 is connected to the first displacer 24 and the second displacer 25 such that the first displacer 24 and the second displacer 25 can be moved in a reciprocal manner inside the first cylinder 22 and the second cylinder 23, respectively. The drive mechanism 17 includes a flow channel switching mechanism that switches the flow channels of an operating gas such that intake and discharge of the gas are periodically repeated. The flow channel switching mechanism includes, for example, a valve unit and a drive unit for driving the valve unit. The valve unit includes, for example, a rotary valve, and the drive unit includes a motor for rotating the rotary valve. The motor may be, for example, an AC motor or a DC motor. The flow channel switching mechanism may be a mechanism of a direct acting type that is driven by a linear motor.

The refrigerator 16 is connected to the compressor 36 via a high-pressure conduit 34 and a low-pressure conduit 35. The refrigerator 16 generates cold on the first stage 20 and the second stage 21 by expanding, in the inside thereof, the high-pressure operating gas (e.g., helium) supplied from the compressor 36. The compressor 36 recovers the operating gas that has been expanded in the refrigerator 16, and increase the pressure thereof again to supply to the refrigerator 16.

Specifically, the drive mechanism 17 first communicates the high-pressure conduit 34 with the internal space of the refrigerator 16. The high-pressure operating gas is supplied from the compressor 36 to the refrigerator 16 through the high-pressure conduit 34. When the internal space of the refrigerator 16 is filled with the high-pressure operating gas, the drive mechanism 17 switches the flow channel so as to communicate the internal space of the refrigerator 16 with the low-pressure conduit 35. Thereby, the operating gas is expanded. The expanded operating gas is recovered into the compressor 36. In synchronization with such supply and discharge of the operating gas, the first displacer 24 and the second displacer 25 move in a reciprocal manner inside the first cylinder 22 and the second cylinder 23, respectively. The refrigerator 16 generates cold on the first stage 20 and the second stage 21 by repeating such heat cycles.

The refrigerator 16 is configured to cool the first stage 20 to a first temperature level and the second stage 21 to a second temperature level. The second temperature level is lower than the first temperature level. For example, the first stage 20 is cooled to approximately 65 K to 120 K, and preferably to 80 K to 100 K, whereas the second stage 21 is cooled to approximately 10 K to 20 K.

The refrigerator 16 is configured to flow the operating gas to the low-temperature stage through the high-temperature stage. That is, the operating gas flowing in from the compressor 36 flows into the second cylinder 23 from the first cylinder 22. At this time, the operating gas is cooled to the temperature of the first stage 20 (i.e., the low-temperature end of the high-temperature stage) by the first displacer 24 and its regenerator. The operating gas thus cooled is supplied to the low-temperature stage. Accordingly, it is expected that the temperature of the operating gas introduced into the high-temperature stage of the refrigerator 16 from the compressor 36 may not significantly affect the cooling capability of the low-temperature stage.

The refrigerator 16 may be a three-stage type refrigerator in which three cylinders are connected in series, or a multi-stage type refrigerator having more than three cylinders. The refrigerator 16 may be a refrigerator other than the GM refrigerator, such as a pulse tube refrigerator or a Solvay refrigerator.

FIG. 1 illustrates a section including both of the central axis of the internal space 14 of the cryopump 10 and the central axis of the refrigerator 16. The cryopump 10 illustrated therein is a so-called horizontal cryopump. The horizontal cryopump generally means a cryopump in which the refrigerator 16 is so arranged as to intersect (normally intersect perpendicularly) with the central axis of the internal space 14 of the cryopump 10. Similarly, the present invention is applicable also to a so-called vertical cryopump. The vertical cryopump means a cryopump in which a refrigerator is arranged along the axial direction of the cryopump.

The low-temperature cryopanel 18 is provided in the central portion of the internal space 14 of the cryopump 10. The low-temperature cryopanel 18 includes, for example, a plurality of panel members 26. Each of the panel members 26 has, for example, the shape of a side surface of a truncated cone, so to speak, an umbrella-like shape. An adsorbent (not illustrated), such as activated carbon, is normally provided in each panel member 26. The adsorbent is, for example, adhered to the rear surface of the panel member 26. Thus, the low-temperature cryopanel 18 includes an adsorption region for adsorbing gas molecules.

The panel members 26 are mounted to a panel mounting member 28. The panel mounting member 28 is mounted to the second stage 21. Thus, the low-temperature cryopanel 18 is thermally connected to the second stage 21. Accordingly, the low-temperature cryopanel 18 is cooled to the second temperature level.

The high-temperature cryopanel 19 includes a radiation shield 30 and an inlet cryopanel 32. The high-temperature cryopanel 19 is provided outside the low-temperature cryopanel 18 so as to surround the low-temperature cryopanel 18. The high-temperature cryopanel 19 is thermally connected to the first stage 20, and accordingly the high-temperature cryopanel 19 is cooled to the first temperature level.

The radiation shield 30 is provided mainly for protecting the low-temperature cryopanel 18 from the radiant heat from a housing 38 of the cryopump 10. The radiation shield 30 is located between the housing 38 and the low-temperature cryopanel 18 and encloses the low-temperature cryopanel 18. The axial upper end of the radiation shield 30 is opened toward the inlet 12. The radiation shield 30 has a tubular shape (e.g., cylindrical shape) whose axial lower end is closed, and is formed into a cup-like shape. A hole for mounting the refrigerator 16 is provided in a side surface of the radiation shield 30, and the second stage 21 is inserted into the radiation shield 30 therefrom. The first stage 20 is fixed, at the outer circumferential portion of the mounting hole, to the external surface of the radiation shield 30. Thus, the radiation shield 30 is thermally connected to the first stage 20.

The inlet cryopanel 32 is provided axially above the low-temperature cryopanel 18, and is arranged along the radial direction in the inlet 12. The inlet cryopanel 32 is fixed, at the outer circumferential portion thereof, to the open end of the radiation shield 30, and is thermally connected to the radiation shield 30. The inlet cryopanel 32 is formed, for example, into a louver structure or a chevron structure. The inlet cryopanel 32 may be formed into a concentric circle shape whose center is on the central axis of the radiation shield 30, or into another shape, such as a lattice-like shape.

The inlet cryopanel 32 is provided for pumping a gas entering the inlet 12. A gas that condenses at the temperature of the inlet cryopanel 32 (e.g., moisture) is captured on the surface of the inlet cryopanel 32. The inlet cryopanel 32 is provided also for protecting the low-temperature cryopanel 18 from the radiation heat from a heat source outside the cryopump 10 (e.g., a heat source inside the vacuum chamber to which the cryopump 10 is mounted). The inlet cryopanel 32 also restricts the entry of not only the radiation heat but also gas molecules. The inlet cryopanel 32 occupies part of the opening area of the inlet 12, thereby limiting the entry of a gas into the internal space 14 through the inlet 12 to a desired amount.

The cryopump 10 is provided with the housing 38. The housing 38 is a vacuum container separating the inside of the cryopump 10 from the outside. The housing 38 is configured to airtightly hold the pressure in the internal space 14 of the cryopump 10. The housing 38 maintains the high-temperature cryopanel 19 and the refrigerator 16 therewithin. The housing 38, which is provided outside the high-temperature cryopanel 19, encloses the high-temperature cryopanel 19. Also, the housing 38 has the refrigerator 16 therewithin. In other words, the housing 38 is a cryopump container enclosing the high-temperature cryopanel 19 and the low-temperature cryopanel 18.

The housing 38 is fixed to a portion having the ambient temperature (e.g., a high-temperature part of the refrigerator 16) in such a manner that the housing 38 does not touch the high-temperature cryopanel 19 and a low-temperature part of the refrigerator 16. The external surface of the housing 38, which is exposed to the outside environment, has a temperature higher than that of the cooled high-temperature cryopanel 19 (e.g., approximately room temperature).

The housing 38 also has an inlet flange 56 extending radially outward from the opening end thereof. The inlet flange 56 serves as a flange by which the cryopump 10 is mounted to the vacuum chamber. A gate valve (not illustrated) is provided at the opening of the vacuum chamber, and the inlet flange 56 is mounted to the gate valve. Thus, the gate valve is located axially above the inlet cryopanel 32. For example, the gate valve is closed when the cryopump 10 is regenerated, and is opened when the vacuum chamber is evacuated by the cryopump 10.

The cryopump 10 includes a first temperature sensor 90 for measuring the temperature of the first stage 20 and a second temperature sensor 92 for measuring the temperature of the second stage 21. The first temperature sensor 90 is mounted to the first stage 20. The second temperature sensor 92 is mounted to the second stage 21. Alternatively, the first temperature sensor 90 may be mounted to the high-temperature cryopanel 19. The second temperature sensor 92 may be mounted to the low-temperature cryopanel 18.

The cryopump 10 includes a control unit 100. The control unit 100 may be provided integrally with the cryopump 10 or may be configured as a separate controller away from the cryopump 10.

The control unit 100 is configured to control the refrigerator 16 to carry out a vacuum pumping operation, a regeneration operation, and a cool-down operation of the cryopump 10. The control unit 100 is configured to receive measurement results of various sensors including the first temperature sensor 90 and the second temperature sensor 92. Based on such measurement results, the control unit 100 generates an instruction for control to be provided to the refrigerator 16.

The control unit 100 controls the refrigerator 16 such that the stage temperature follows a target cooling temperature. The target temperature of the first stage 20 is usually set to a fixed value. The target temperature of the first stage 20 is defined as a specification in accordance with the process performed in the vacuum chamber to which the cryopump 10 is mounted. Alternatively, the target temperature may be changed, if necessary, during the operation of the cryopump.

For example, the control unit 100 controls the operating frequency of the refrigerator 16 by feedback control, so that a deviation between the target temperature of the first stage 20 and a measured temperature of the first temperature sensor 90 is minimized. That is, the control unit 100 controls the number of heat cycles per unit time, i.e., a heat cycle frequency in the refrigerator 16 by controlling the number of revolutions of the motor in the drive mechanism 17.

When a heat load to the cryopump 10 is increased, the temperature of the first stage 20 may be raised. When the measured temperature of the first temperature sensor 90 is higher than the target temperature, the control unit 100 increases the operating frequency of the refrigerator 16. As a result, the heat cycle frequency in the refrigerator 16 is also increased, thereby allowing the first stage 20 to be cooled toward the target temperature. Conversely, when the measured temperature of the first temperature sensor 90 is lower than the target temperature, the operating frequency of the refrigerator 16 is reduced, thereby allowing the temperature of the first stage 20 to be raised toward the target temperature. Thus, the temperature of the first stage 20 can be retained within a range of temperatures close to the target temperature. Because the operating frequency of the refrigerator 16 can be appropriately adjusted in accordance with a heat load, such control is useful for reducing the power consumption of the cryopump 10.

In the following description, the control of the refrigerator 16, by which the temperature of the first stage 20 is made substantially equal to the target temperature, may be referred to as “first stage temperature control”. While the cryopump 10 is performing the vacuum pumping operation, the first stage temperature control is usually executed. As a result of the first stage temperature control, the second stage 21 and the low-temperature cryopanel 18 are cooled to a temperature determined by the specification of the refrigerator 16 and a heat load from the outside. Similarly, the control unit 100 can also execute, so to speak, “second stage temperature control” in which the refrigerator 16 is controlled such that the temperature of the second stage 21 is made substantially equal to the target temperature.



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stats Patent Info
Application #
US 20140230461 A1
Publish Date
08/21/2014
Document #
14182778
File Date
02/18/2014
USPTO Class
62 555
Other USPTO Classes
International Class
04B37/08
Drawings
8


Elective
Tempo
Vacuum Pump
Control Unit


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