JPH0642459A - Cryopump - Google Patents

Abstract

PURPOSE:To maintain the cooling temperature of a cryopanel even if the refrigeration cycle of a cryopump is brought into stop. CONSTITUTION:The first stage and second stage cryopanels 4 and 5 are arranged inside the pump container 2 of a cryopump 1. The first stage cryopanel 4 on the outside has the thin plate shaped first stage sealed space forming member 4a on the inner surface and has a gap between the cryopanel 4, and the gap forms the sealed space 9 on the first stage side. The inside of the sealed space 9 is filled with nitrogen. Also the second stage cryopanel 5 on the inside is formed to a cup shape, and also on this inner surface, the thin plate shaped second stage sealed space forming member 5a forms a gap between the cryopanel 5, on the inner surface, and the inside of the sealed space 10 forming the gap is filled with hydrogen. These gases are liquefied, and the cooling temperature for the cryopanels 4 and 5 can be maintained by the evaporation latent heat and specific heat.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryopump as a vacuum pump.

[0002]

2. Description of the Related Art A cryopump equipped with a cryopanel composed of a high temperature side cooling section cooled by a small helium refrigerator and a low temperature side cooling section is used for many vacuum exhaust operations. As shown in FIG. 4, in this type of cryopump 30, a tubular pump case 33 is attached to a helium refrigerator 37, and the high temperature side cooling unit inside the pump case 33, that is, the first-stage cryopanel 31 is 50K-. 1
It is cooled to a temperature of 00K, and the low temperature side cooling unit, that is, the second-stage cryopanel 32 is cooled to a temperature of 10K to 20K.

These first-stage and second-stage cryopanels 3
To explain the refrigeration cycle for cooling Nos. 1 and 32, as shown in FIG. 4, a helium refrigerator 37 accommodates a displacer 38 that reciprocates in the direction of arrow a by an electric motor (not shown). A first regenerator 39 and a second regenerator 40 in which metal nets and metal grains are provided
Helium on the high pressure side in the refrigeration cycle, which is compressed by the external helium circulation compressor 36, is filled in the refrigerator 37 by closing the low pressure valve 42 and opening the high pressure valve 41. . Then, the displacer 38 is moved so as to expand the volumes of the first low temperature expansion chamber 43 and the second low temperature expansion chamber 44, and when the maximum volume is reached, the high pressure valve 41 is closed and the low pressure valve 42 is opened.
The helium is discharged to the low-pressure side and is cooled by Simon expansion, cooling the expansion chambers 43 and 44 and simultaneously returning to the compressor 36 while cooling the first and second regenerators 39 and 40. As a result, the inside of the refrigerator 37 becomes the minimum pressure, and here the displacer 38 moves upward so as to reduce the volumes of the first and second low temperature expansion chambers 43 , 44 , and the helium whose temperature has been lowered becomes the first and second. Backflow is performed while cooling the second regenerators 39 and 40. Through the above cycle, the first low-temperature expansion chamber 43 cools the first-stage cryopanel 31 and the second low-temperature expansion chamber 44 cools the second-stage cryopanel 32 to the aforementioned desired temperatures by heat conduction.

[0004]

When a refrigerating cycle is driven, a cryopump receives the above-described reciprocating motion of the displacer and vibration of an electric motor for operating the cryopump. In an observation work in which the vibration of a microscope device is extremely disliked, this vibration is transmitted to the vacuum device, and precise measurement cannot be performed. For this reason, if the operation of the cryopump is stopped and observation is performed, the cryopanel of the cryopump is made of a thin material such as oxygen-free copper or pure aluminum, which has good heat conduction and small specific heat, in order to improve cooling efficiency. Plates are used, which has the drawback that the temperature rise can occur immediately when the cryopanel refrigeration cycle is stopped, the already condensed gas evaporates and can be observed under a suitable environment. could not.

The present invention has been made in view of the above problems, and an object thereof is to provide a cryopump capable of maintaining a predetermined cooling temperature for a long time even when the operation of the cryopump is stopped.

[0006]

In the cryopump having a cooling part cooled by a refrigerator in a pump container, a closed space forming member for contacting the cooling part to form a closed space is provided. And a gas is enclosed in the closed space.

[0007]

Since the closed space is formed in contact with the cooling part and the gas is enclosed in the closed space, the gases are cooled when the cryopump is operated, and even if the cryopump is stopped, the specific heat The latent heat of vaporization can suppress the temperature rise of the cryopanel, and the desired cooling temperature can be maintained in the cryopump for a long time.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A cryopump according to a first embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, the cryopump according to this embodiment is designated by 1 as a whole, and a cylindrical pump container 2 having an opening 2a is attached to a helium refrigerator 3 (having the same structure as the conventional refrigerator 3). The first stage freezing stage 7 and the second stage freezing stage 8 in which the low temperature expansion chamber of the refrigerator 3 is provided are attached so as to be inserted into the pump container 2. Further, in the pump container 2, there are provided a first-stage cryopanel 4 and a second-stage cryopanel 5 which are thin plate-shaped oxygen-free copper or aluminum metal plates cooled by the freezing stages 7 and 8 by heat conduction. It is arranged. The outer first-stage cryopanel 4 is formed in a cup shape, and is arranged upward on the first-stage freezing stage 7,
A baffle 6 is provided at this upper end. Also, the first
On the inner surface of the multi-stage cryopanel 4, a first plate closed space forming member 4a, which is the same member as and has a similar shape, is provided with a gap from the cryopanel 4, and the upper end of this gap is formed into an annular shape. The closing member 4b is closed by silver brazing to form the closed space 9 on the first stage side. The closed space 9 is filled with nitrogen gas.

Inside the first-stage cryopanel 4, a second
The multi-stage cryopanel 5 is formed in a cup shape, and is arranged downward on the second-stage freezing stage 8. On the inner surface of the second-stage cryopanel 5, a thin-plate-shaped second-stage closed space forming member 5a is provided so as to form a gap between the second-stage cryopanel 5 and the cryopanel 5, similarly to the first-stage cryopanel 4. Cage,
An annular closing member 5b closes the lower end of this gap by silver brazing to form a closed space 10 on the second stage side. Hydrogen gas is enclosed in the closed space 10 . An adsorbent 11 such as activated carbon or molecular sieves is provided on the inner peripheral surface of the second-stage closed space forming member 5a.

In the cryopump 1 thus constructed, the opening 2a of the pump container 2 is connected via a main valve to a vacuum device (not shown) to which, for example, a vacuum electron microscope is attached. The inside of the refrigerator 3 of the cryopump 1 has the same structure as the conventional example, and a compressor (not shown) for circulating a refrigerant is connected to the outside of the cryopump 1.

The cryopump 1 according to the first embodiment of the present invention is constructed as described above, and its operation will be described below.

A cryopump 1 is attached,
After the pressure inside the vacuum device (not shown) is reduced to a predetermined pressure, the refrigeration cycle of the cryopump 1 is operated. As a result, the first stage freezing stage 7 and the second stage freezing stage 8 are each cooled to a predetermined temperature. The desired temperature of each cryopanel 4, 5 is 7 for the first-stage cryopanel 4.
0K to 90K, and the second stage cryopanel 5 is 15 to
In the present embodiment, the first-stage cryopanel 4 is cooled to around 77K, and the second-stage cryopanel 5 is cooled to around 22K. Therefore, the nitrogen enclosed in the closed space 9 in contact with the first-stage cryopanel 4 is cooled to the same temperature as the first-stage cryopanel 4 by heat conduction. In addition, the hydrogen enclosed in the closed space 10 in contact with the second-stage cryopanel 5 cools the second-stage cryopanel 5 and is also cooled to almost the same temperature by heat conduction.

FIG. 3 shows the equilibrium vapor pressure curves for various materials. The vertical axis represents pressure and the horizontal axis represents temperature. As is known, nitrogen and hydrogen are gases at atmospheric pressure at room temperature and liquefy when the temperature becomes extremely low, although it depends on the pressure. Therefore, the first-stage cryopanel 4 and the second-stage cryopanel 5
The nitrogen and hydrogen enclosed in the closed spaces 9 and 10 that are in contact with the gas are condensed when the conditions are on the left side of the curves showing nitrogen and hydrogen in the equilibrium vapor pressure curve in FIG. And tends to liquefy. Since the first-stage cryopanel 4 and the second-stage cryopanel 5 are cooled to the temperatures as described above, the pressure is taken into consideration in the condition range for sufficient liquefaction, and those gases are condensed and liquefied. To do.

When the cryopump 1 is operated in this way, water vapor, carbon dioxide, etc. having a high condensation temperature among the gas molecules flowing in from the opening are condensed on the baffle 6 and the first-stage cryopanel 4, and more than this. The second-stage cryopanel 5 condenses a condensable gas such as oxygen, nitrogen, or argon having a low condensing temperature. Since hydrogen and helium having the lowest condensation temperature than these condensable gases cannot be condensed by the cryopanels 4 and 5, they are adsorbed by the adsorbent 11 and exhausted.

When the inside of the vacuum device (not shown) is depressurized to a predetermined pressure, the sample placed in the device is observed with a vacuum microscope. At this time, the operation of the cryopump 1 is stopped so that the vibration of the cryopump 1 is not transmitted to the vacuum device. As a result, the circulation of helium in the refrigeration cycle is stopped, and the first-stage and second-stage cryopanels 4,
5 does not receive the cooling action from the first and second freezing stages 7 and 8, respectively, and the temperature tends to rise.

However, when the temperature of the first-stage and second-stage cryopanels 4 and 5 is about to rise, this heat liquefies the enclosed spaces 9 and 10 in contact with the cryopanels 4 and 5, respectively. Nitrogen and hydrogen tend to exceed the equilibrium state and increase in evaporation. At low temperatures, the specific heat of the substance is much smaller than at room temperature, whereas the latent heats of vaporization of nitrogen and hydrogen are sufficiently large. The first and second cryopanels 4 and 5 maintain a constant temperature due to the latent heat of vaporization of liquid nitrogen and hydrogen, and when the temperature of these liquids and gases is about to rise, the specific heat (in the case of liquid, Heat is taken from the cryopanels 4 and 5 due to the temperature rise up to the boiling point),
Cooling. Therefore, each of the cryopanels 4 and 5 is continuously cooled, is maintained within a predetermined temperature for a long time, and a rapid temperature rise can be prevented even after the predetermined temperature is maintained.

As described above, in this embodiment, even if the operation of the cryopump 1 is stopped, each cryopanel 4,
A temperature of 5 can be maintained. As a result, the vacuum device can perform microscopic observation with high accuracy without being subjected to vibrations due to the operation of the cryopump 1.

The first embodiment is particularly effective for work that is extremely sensitive to vibration, but the cryopanels 4 and 5 are cooled even when the cryopump 1 is operated in a normal state without being stopped. Even if it tries to reach a temperature below a predetermined level, it absorbs heat when nitrogen and hydrogen are liquefied, so
For example, a thermostat works and the refrigeration cycle is ON-O.
Even when the FF is performed, the cryopanels 4 and 5 can be prevented from rapidly increasing in temperature or being cooled, and the predetermined temperature can be maintained.

Next, a cryopump according to a second embodiment of the present invention will be described with reference to FIG. The same components as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 2, the cryopump according to the present embodiment is indicated by 20 as a whole, and a cylindrical pump container 19 having an opening 19a is attached to a helium refrigerator 29.
Inside the pump container 19, first-stage, second-stage, and third-stage cryopanels 13, 14, and 15 made of thin plate oxygen-free copper or aluminum metal plates are arranged. The outer first-stage cryopanel 13 is formed in a cup shape, and a baffle 21 is provided at the upper end thereof. In addition, on the outer peripheral surface of the first-stage cryopanel 13, a thin plate-shaped first-stage closed space forming member 13 made of the same member as the first-stage cryopanel 13 and having a similar shape is formed.
a is provided with a gap from the cryopanel 13, and upper and lower ends of this gap are annular closing members 13b and 13c.
Is closed by silver brazing and the closed space 23 on the first stage side
Is formed. Nitrogen gas is enclosed in the closed space 23 . Further, on the inner peripheral surface of the first-stage cryopanel 13, a thin-walled cooling pipe 26 made of the same material as this is spirally fixed by silver brazing.

The second-stage cryopanel 14 provided inside the first-stage cryopanel 13 is formed into a cup shape, and a baffle 22 is provided at the upper end thereof. On the outer peripheral surface of the second-stage side cryopanel 14, a thin-plate-shaped second-stage closed space forming member 14a is provided with a gap from the cryopanel 14 like the first-stage side cryopanel 13. The ring-shaped closing members 14b and 14c close the upper and lower ends of the gap by silver brazing,
The closed space 24 on the step side is formed. Hydrogen gas is enclosed in the closed space 24 . A thin-walled cooling pipe 27 made of the same material as the second-stage cryopanel 14 is spirally fixed to the inner peripheral surface of the second-stage cryopanel 14 by silver brazing.

The cryopump 20 according to the present embodiment is further provided with a third-stage cryopanel 15 inside the second-stage cryopanel 14, and this cryopanel 15 also
A cup-shaped third-stage cryopanel 15 is provided on the outer peripheral surface thereof with a similar thin plate-shaped third-stage closed space forming member 15a having a similar gap to the cryopanel 15. There is. An annular closing member 15c closes the lower end portion of this gap by silver brazing to form a closed space 25 on the third step side. Helium gas is enclosed in the closed space 25 . Also, the third stage cryopanel 1
A thin cooling pipe 28 made of the same material as that of the third-stage cryopanel 15 is spirally fixed to the inner peripheral surface of 5 by silver brazing.

As shown in FIG. 2, the refrigerator 29 of the cryopump 20 is provided with a first low temperature chamber 46 , a second low temperature chamber 47 and a third low temperature chamber 48 , and among the low temperature chambers 46 , 47 and 48 ,
Both ends of the cooling pipe 26 brazed to the first stage cryopanel 13 are provided in the first low temperature chamber 46 , and the cooling pipe 27 brazed to the second stage cryopanel 14 is provided in the second low temperature chamber 47. Both ends of the cooling pipe 28 brazed to the third cryopanel 15 are provided in the third low temperature chamber 48 . Each low temperature chamber 46 , 4
7 , cooling pipes 26, 2 connected in communication with 48
The low temperature helium gas is supplied to the low temperature chambers 7 and 28 from the low temperature chambers 46 , 47 and 48 , respectively. As a result, the cooling pipes 26, 27, 2 are utilized by utilizing the Simon expansion due to the operation of the refrigerator 29.
Since 8 is cooled, each cryopanel 13, 1
4, 15 are cooled by heat conduction.

The cryopanel 20 according to the second embodiment of the present invention is constructed as described above, and its operation will be described below.

After the pressure inside the vacuum device (not shown) to which the cryopump 20 is attached is reduced to a predetermined pressure, the refrigeration cycle of the cryopump 20 is operated. As a result, the first, second, and third cooling pipes 2
6, 27 and 28 are each cooled to a predetermined temperature. In this embodiment, like the first embodiment, the first-stage cryopanel 1
3 is cooled to around 77K, and the second stage cryopanel 14 is cooled to around 22K. Also, the 3rd stage cryopanel 15 has 3
It is preferable to cool to ~ 10 K, and in this embodiment, it is 4 K.
It is cooled to the neighborhood. The nitrogen gas sealed in the closed space 23 that is in contact with the first-stage cryopanel 13 cools the first-stage cryopanel 13 by the cooling heat of the cooling pipe 26 and at the same temperature due to heat conduction. To be cooled. In addition, the hydrogen sealed in the closed space 24 in contact with the second-stage cryopanel 14 cools the second-stage cryopanel 14 by the cooling heat of the cooling pipe 27, and at the same temperature as that due to heat conduction. To be cooled. Further, the helium sealed in the closed space 25 that is in contact with the third-stage cryopanel 15 is cooled by the cooling pipe 28 to the third-stage cryopanel and is also cooled to almost the same temperature by heat conduction. .

As a result, as in the first embodiment, the first stage,
The nitrogen and hydrogen sealed in the closed spaces 23 , 24 on the second stage side are condensed and liquefied by being cooled. Third
When the condition is on the left side of the curve indicating helium in FIG. 3, the helium sealed in the closed space 25 on the step side tends to condense gas and is liquefied. Since the third-stage cryopanel 15 is cooled to the temperature as described above, the helium gas is liquefied within the condition range for being sufficiently liquefied in consideration of the pressure.

In the present embodiment, when the operation of the refrigeration cycle of the cryopump 20 is stopped with such a configuration, the first and second stage cryopanels 13 and 14 are similar to the first embodiment.
Tries to raise the temperature. Due to this heat, the liquefied nitrogen and hydrogen in the closed spaces 23 and 24 in contact with the cryopanels 13 and 14 tend to increase beyond the equilibrium state, and the evaporation amounts of nitrogen and hydrogen increase. Due to the specific heat, the cryopanels 13 and 14 are continuously maintained at a predetermined temperature and cooled. In the second embodiment, when the temperature of the third-stage cryopanel 15 further increases, the heat causes the helium liquefied in the closed space 25 in contact with the cryopanel 15 to exceed the equilibrium state, The evaporation amount tends to increase, the predetermined temperature of the third-stage cryopanel 15 is maintained by the latent heat of evaporation and specific heat of helium, and a rapid temperature rise can be prevented.

As described above, in this embodiment, even if the operation of the cryopump 20 is stopped, each cryopanel 1 is operated for a long time.
The cooling temperature of 3, 14, 15 can be maintained. As a result, it is possible to perform microscopic observation with high accuracy in a stationary state without being affected by vibrations due to the operation of the refrigeration system of the cryopump 20.

Although the respective embodiments of the present invention have been described above, needless to say, the present invention is not limited to these, and various modifications can be made based on the technical idea of the present invention.

For example, in the above-described first embodiment, different gas is sealed in the closed space on the first step side and the closed space on the second step side, but this is sealed in the closed space. By changing the gas pressure, the same kind of gas can be used for the first and second stages.
The cooling temperature on the stage side may be controlled, and the gas sealed in the closed space is not limited to nitrogen and hydrogen.
Other gases in may be used. In the second embodiment as well, the same kind of gas may be enclosed in the closed spaces on the first, second and third stages, or other gases other than nitrogen, hydrogen and helium may be enclosed. Good.

In the above embodiment, the closed space is formed by the cryopanel and the thin plate-shaped closed space forming member.
In this closed space, the gas described above may be sealed in a sealed pipe, and the pipe may be attached by being wound around the inner or outer peripheral portion of the cryopanel.

In the second embodiment, a cooling pipe is brazed to the inner peripheral portion of each cup-shaped cryopanel, and a closed space forming member is attached to the outer peripheral portion of the cryopanel to form a closed space. However, the closed space forming member may be attached to the inner peripheral portion of each cryopanel to form a closed space, and the cooling pipe may be brazed to the outer peripheral portion of each cryopanel.

Further, in each of the above embodiments, the number of stages of the cryopanel is plural, but the number of stages may be one, and in the second embodiment, the low temperature side cooling unit is plural, but the high temperature side cooling unit. May be plural.

[0035]

As described above, according to the cryopump of the present invention, since the gas is enclosed in the closed space in contact with the cooling part, even if the refrigerator is stopped, the evaporation latent heat and The specific heat keeps the cooling unit at a constant cooling temperature for a long time. Thus, the refrigeration system of the cryopump can be stopped, and the vacuum device can be used for operations such as precise measurement of the surface of the sample without vibration of the vacuum device.

[Brief description of drawings]

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

FIG. 2 is a schematic sectional view of a main part of the cryopump according to the second embodiment.

FIG. 3 is a diagram showing equilibrium vapor pressure curves for various gases.

FIG. 4 is a schematic cross-sectional view showing a conventional cryopump refrigeration system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Cryopump 4 1st stage cryopanel 4a Closed space forming member 5 2nd stage cryopanel 5a Closed space forming member 9 Sealed space 10 Sealed space 13 1st stage cryopanel 13a Closed space forming member 14 2nd stage cryopanel 14a Closed Space forming member 15 Third stage cryopanel 15a Closed space forming member 20 Cryo pump 23 Sealed space 24 Sealed space 25 Sealed space

Claims (1)

[Claims] 1. A cryopump having a cooling part cooled by a refrigerator in a pump container, wherein a closed space forming member for contacting the cooling part to form a closed space is provided, and a gas is provided in the closed space. A cryopump that is characterized by containing.