JPH04342884A - Cryopump - Google Patents

Abstract

PURPOSE:To prevent the lowering of exhaust speed in a cryopump by exposing the activated carbon of a porous solid absorbent in a closed cell into the exposed space of an absorbent forming gas condensing layer in the case where the time differential value of exhaust object gas pressure is above set value. CONSTITUTION:Argon functioning as the first gas is jetted through a leading pipe 16 from a blow off pipe 12 into the second liquid helium reservoir 10, on whose surface an argon condensing layer 14 acting as an absorbent is forned. The helium serving as the second gas of an exhaust object is therefore absorbed. In this case, a cell 25 which has a porous solid absorbent 23 fixed to its inside and an opening part 25 to expose the absorbent 23 into the exposed space of the argon condensing layer 14 is provided. In addition to that, a cell closing valve 27 to seal up the cell 26 from the above exposed space is provided. A closing motion adjusting device 31 gives a closing signal to a drive control device 29 so as to open the valve 27 according to the measured value of helium pressure detected by a pressure gauge 21 and the time differential value of the above measured value.

Description

[Detailed description of the invention]

[Object of the invention]

0002

[Industrial Application Field] The present invention relates to a cryopump used as a vacuum pump, and particularly to a cryopump that suppresses the instability of the exhaust action when exhausting a target gas by the adsorption action of a condensed layer of adsorbent-forming gas. Regarding the cryopump.

0003

2. Description of the Related Art A conventional cryopump that controls the formation of a condensed layer that acts as an adsorbent cooled to an extremely low temperature is disclosed in Japanese Patent Laid-Open No. 1-178781.

In this conventional example, in order to prevent a decrease in the exhaust capacity of the cryopump, the amount of condensation of the first gas, which is an adsorbent-forming gas in which the condensation layer acts as an adsorbent, is controlled by the cryopump intake. Means is taken to change the pressure in response to the pressure of the second gas, which is the gas to be exhausted near the opening.

Here, the first gas which is the adsorbent forming gas is known to include rare gases such as argon (Ar), nitrogen (N2), sulfur hexafluoride (SF6), etc., and the second gas which is the gas to be exhausted is Examples of gases include helium (He), which is difficult to pump out with ordinary cryopumps, and hydrogen (which has a high ultimate pressure).
H2), and hydrogen isotopes (D2, HD, T2, etc.). Hereinafter, explanation will be given using argon as the first gas and helium as the second gas.

[0006]

[Problems to be Solved by the Invention] In cryopumps, due to a sudden increase in the helium load of the gas to be pumped and the desorption of helium adsorbed in the argon condensation layer,
When a sudden pressure rise occurs in the gas to be pumped out, the relative amount of helium required by the argon condensation layer, which acts as an adsorbent, is insufficient, resulting in a temporary decrease in adsorption capacity and a decrease in pumping speed. occurs. Once the relative amount of helium in the argon condensation layer acting as an adsorbent is insufficient, the pressure of the gas to be pumped, such as helium, will further increase due to the reduction in pumping speed.
As a result, the relative amount of the argon condensation layer of the adsorbent relative to the gas to be exhausted such as helium is further insufficient, which leads to a further increase in the pressure of the gas to be exhausted such as helium, which is a serious drawback of falling into a vicious cycle.

[0007] When such a vicious cycle of a relative shortage of adsorbent and a rise in pressure occurs, the thermal load on the cryopump increases rapidly, causing desorption of the adsorbed gas to be evacuated, such as helium. A sudden increase in the pressure inside the vacuum chamber being evacuated by a cryopump,
There was an extremely serious drawback in that a runaway condition such as a sudden increase in the internal pressure of the cryopump's refrigerant reservoir such as liquid helium occurred, making it difficult for the cryopump to operate normally.

The present invention was developed in view of the above-mentioned conventional problems, and in order to prevent the instability of the pumping action of the cryopump caused by the sudden pressure increase of the gas to be pumped, the pumping capacity of the porous solid adsorbent is improved. The purpose of the present invention is to provide a cryopump that additionally utilizes.

[Configuration of the invention]

0010

[Means for Solving the Problems] In order to achieve the above object, the cryopump of the present invention has a condensation layer condensing a first gas acting as an adsorbent on a surface cooled to an extremely low temperature in a vacuum. In a cryopump that exhausts a second gas to be evacuated into or onto a condensation layer of a first gas from a gas phase in a vacuum by adsorption or cryotrapping, a porous adsorbent is used in a cryopump. a compartment fixed therein so as to be coolable to a low temperature and having an opening that allows the porous solid adsorbent to be exposed to the exposed space of the condensed layer of the first gas; and a compartment stop valve that can be sealed from the exposed space of the condensation layer, the second gas pressure measuring device calculates a time differential value of the pressure measurement value output from the pressure measuring device, and and a compartment shutoff valve opening/closing control device that outputs an opening/closing signal to a drive control device for the compartment shutoff valve to open the compartment shutoff valve according to the measured value and the time differential value of the pressure measured value. Features.

[0011]

[Operation] According to the present invention, when the pressure of the second gas to be exhausted is rapidly increased depending on the pressure near the adsorption port of the second gas to be exhausted and the time differential value of the pressure, the pressure of the second gas is increased. a compartment having an opening to the space in which the condensation layer is exposed and in which a porous solid adsorbent cooled to a cryogenic temperature is fixed;
A compartment shutoff valve hermetically closing said opening is opened. The porous solid adsorbent was kept in a sealed compartment so that its adsorption capacity was maintained. The rapid pressure increase of the second gas to be evacuated is caused by the cryogenically cooled porous solid adsorbent being exposed to the space in which this opening is opened and a condensed layer of the first gas is exposed. absorbed by the additional evacuation capacity provided by the medium. This allows the second
This suppresses the rapid pressure rise of the gas, prevents the cryopump from running out of control, and maintains stable pumping operation.

0012

【Example】

(Example 1) Hereinafter, the first cryopump according to the present invention will be described.
An example will be described with reference to FIGS. 1 and 2. In addition, as the first gas of the adsorption medium forming gas, there are single component gases such as rare gases such as argon, nitrogen, and sulfur hexafluoride, or alternate use of mixed component gases or single component gases. The second gas to be exhausted includes helium, hydrogen, and the like. Porous solid adsorbents include activated carbon,
Examples include molecular sieve 5A. Hereinafter, argon will be used as an example of the first gas, helium will be used as the second gas, and activated carbon will be used as the porous solid adsorbent, but the same applies to the other substances mentioned above.

FIG. 1 shows a cryopump according to a first embodiment, and FIG. 2 shows an enlarged view of the main parts thereof. Reference numeral (1) indicates a vacuum container, and this vacuum container (1) has an inlet port (2), and the vacuum container to be evacuated and the inlet valve (3)
), and a radiation shield is housed inside. A liquid nitrogen reservoir (5) is installed at the top of the radiation shield (4), while a first chevron baffle (6) is installed at the bottom to face the air intake port (2). There is. The intake valve (3) is opened during exhaust.

A liquid helium gas-liquid separator (7) is disposed at an upper position inside the radiation shield (3), and the gas-liquid separator (7) supplies the first chevron-shaped baffle (6). ) A second chevron-shaped baffle (8) is vertically installed and cooled by a liquid helium reservoir (9) vertically installed in the gas-liquid separator (7). Reference numeral (10) indicates a second liquid helium reservoir whose outer surface is at an extremely low temperature to form a condensed layer that adsorbs helium.
1) is connected. The second liquid helium reservoir (10) is arranged opposite the second chevron-shaped baffle (8) at a predetermined distance, and between them, argon is introduced into the second liquid helium reservoir. Tame (10)
A blowout pipe (12) is arranged to blow out the air on the outer surface of the tube. The second liquid helium reservoir (10) of this blow-off pipe (12)
A large number of argon blow-off holes (13) are formed on the side. Therefore, the argon blown out from the blow-off hole (13) of the blow-off pipe (12) toward the second liquid helium reservoir (10) is cooled by the liquid helium inside the second liquid helium reservoir (10), and is heated to the surface of the second liquid helium reservoir (10). An argon condensation layer (14) is formed which condenses and adsorbs helium, which is a gas to be exhausted.

[0015] The above-mentioned blowout pipe (12) is connected to the manifold (1
5) to the introduction pipe (16), and this introduction pipe (
16) is connected to an argon supply device (not shown). A flow control valve (17) is disposed in the middle of the introduction pipe (16) coming out of the vacuum container (1). This flow control valve (
A valve drive mechanism (18) attached to 17) adjusts the opening degree of the valve based on a signal output from a drive mechanism control device (19). On the other hand, a pressure detection tube (20) is installed so as to face the intake port (2) of the vacuum container (1), and the pressure detected by this pressure detection tube (20) is transmitted to the detected pressure via a pressure gauge (21). The signal is converted into a signal and introduced into the pressure opening response device (22). This pressure opening adjustment device (22) outputs a signal for adjusting the opening of the flow rate regulating valve (17) to the drive mechanism control device (19) in response to the detected signal value of the pressure gauge (21). Adjust the flow rate of argon through the tube (16).

[0016] At the front of the second liquid helium reservoir (10),
An activated carbon panel (24) to which activated carbon (23) is fixed; this activated carbon panel (24) is fixed inside so that it can be cooled to an extremely low temperature, and the activated carbon (23) can be exposed in the exposed space of the argon condensation layer (14). A compartment (26) is fitted with an opening (25) for opening. A compartment closing valve (27) capable of sealing the interior of the compartment (26) is attached to the opening (25) of the compartment (26).

[0017] The compartment shutoff valve (27) is provided with a drive mechanism extension (28), and is opened and closed by a drive mechanism (29) disposed outside the vacuum vessel (1). Drive mechanism (
29) The electric circuit, gas pressure piping, etc. of the power source are not shown. The drive mechanism (29) uses a power source (not shown) to operate the compartment shutoff valve (
27).

On the other hand, the pressure detected by the pressure detection tube (20) is converted into a detected pressure signal via the pressure gauge (21), and is sent to the compartment shutoff valve opening/closing adjustment device (31) together with the pressure opening adjustment device (22). ) will be introduced. This compartment shutoff valve opening/closing adjustment device (31) calculates the time differential value of the input detection signal, and based on this calculation, the compartment shutoff valve opening/closing adjustment device (31) calculates the time differential value of the input detection signal.
), the drive mechanism control device (30) is connected to the drive mechanism (31).
An opening/closing signal is output to drive the compartment shutoff valve (27) to open and close it.

(Operation of Embodiment 1) Next, the operation of the cryopump constructed as described above will be explained.

Depending on the opening degree of the flow control valve (17),
Argon flows through the introduction pipe (16) from a supply device (not shown), and is ejected from the blow-off hole (13) of the blow-off pipe (12) through the manifold (15) toward the second liquid helium reservoir (10). The argon is condensed under the cooling effect of liquid helium, so that this second liquid helium reservoir (10
) on the outer surface of the argon condensation layer (1
4) will be formed.

On the other hand, the helium introduced into the interior from the inlet (2) of the vacuum container (1) first passes through the first chevron-shaped baffle, which is cooled by the liquid nitrogen stored in the liquid nitrogen reservoir (5). (6) and reaches the vicinity of the second liquid helium reservoir (10). As described above, helium is exhausted by adsorption or cryotrapping by the argon condensation layer (14) formed on the surface of the second liquid helium reservoir (10). In the above exhaust process, components such as hydrogen in the gas to be exhausted are condensed on the surface of the second chevron baffle (8) and exhausted.

[0022] In such an exhaust process, under normal conditions, each member operates according to set conditions. That is, when the pressure of the helium component in the gas to be exhausted that is guided inside from the intake port (2) increases, this pressure increase is detected by the pressure gauge (21) provided in the pressure detection tube (20).
The detection signal is sent to the pressure opening correspondence device (22). In this pressure opening corresponding device (22), a pressure gauge (2
The drive mechanism control device (19) corresponds to the detection signal value of 1).
A signal is issued to adjust the opening degree of the flow control valve (17), and the flow rate of argon flowing through the introduction pipe (16) is controlled in proportion to the pressure rise of the gas to be exhausted.

Furthermore, when the pressure of the gas to be exhausted led inside from the intake port (2) decreases, the drive mechanism controls the opening adjustment signal in response to the detection signal output from the pressure gauge (21) that detects this pressure decrease. The argon flow rate outputted by the device (19) and flowing through the introduction pipe (16) is controlled to decrease in proportion to the decrease in the pressure of the gas to be exhausted.

When the variation in the load amount of the helium component in the gas to be exhausted is relatively gentle, the flow rate of the adsorbent forming gas introduced is controlled as described above. However, if a sudden increase in the helium load of the gas to be exhausted or a sudden increase in the pressure of the gas to be exhausted occurs due to desorption of helium adsorbed in the argon condensation layer, the compartment shutoff valve should be used as described below. (27) is opened and the activated carbon (23), which has been cooled in the compartment, is exposed to the space where the argon condensation layer is exposed.

When the pressure of the helium component in the gas to be exhausted increases rapidly, the compartment shutoff valve opening/closing control device (31) detects that the time differential value of the pressure exceeds a predetermined value. In this case, in order to prevent the helium load on the argon condensation layer from increasing relatively temporarily and making the pumping action of the cryopump unstable, the compartment shutoff valve is driven by the compartment shutoff valve opening/closing control device (31). Mechanism control device (3
At 0), a signal is output to cause the drive mechanism (29) to open the compartment shutoff valve (27) via the drive mechanism extension (28). As a result, the compartment stop valve (27) opens and the activated carbon (23) cooled to an extremely low temperature in the compartment (26) is exposed. Helium, the gas to be exhausted, is removed from this exposed activated carbon (2
The adsorption/evacuation capacity of 3) compensates for the relative shortage of the argon condensation layer. After the activated carbon (23) is exposed, when the helium pressure value and the time differential value of the helium pressure value fall within predetermined values, the compartment shutoff valve (27) is opened and closed by the compartment shutoff valve opening/closing adjustment device (31). , adjusted to close. The activated carbon (23) is sealed from the exposed space of the argon condensation layer (14) and remains in the compartment until the compartment shutoff valve (27) is next adjusted to open by the compartment shutoff valve opening/closing adjustment device (31). Wait in the room (26).

(Effects of Example 1) As explained above,
If the time differential value of the pressure value of the helium to be evacuated exceeds a predetermined value, activated carbon, which is a porous solid adsorbent, is isolated in a sealed compartment to prevent saturation of the adsorption and exhaust capacity. Since the argon condensation layer of the adsorbent forming gas condensation layer is exposed to the exposed space, it is possible to prevent a temporary decrease in the pumping speed of the cryopump. Therefore, it is possible to prevent a runaway state of the pumping operation of the cryopump, such as a sudden pressure increase in the adsorbent-forming gas condensation layer caused by a temporary decrease in the pumping speed.

In the above explanation, it is assumed that the pressure value for opening the compartment closing valve and the time differential value of the pressure value are experimentally determined in advance so that the pumping operation of each cryopump becomes unstable.

Next, an embodiment in which the present invention is applied to a type of pump different from the cryopump described above will be described with reference to FIGS. 3 and 4. In the embodiment shown in FIGS. 3 and 4, the same members as those in the embodiment shown in FIGS. 1 and 2 are given the same reference numerals, and the description thereof will be omitted.

(Embodiment 2) The cryopump shown in FIG. 3 differs from the cryopumps shown in FIGS. 1 and 2 in that a chevron-shaped baffle (8) cooled by liquid helium is not provided. In this type of cryopump, helium is placed on the exhaust surface of the liquid helium reservoir (10).
Since hydrogen and other gases to be exhausted are adsorbed at the same time, this is advantageous when there is no need to distinguish between the helium exhaust surface and other exhaust surfaces.

(Embodiment 3) The embodiment shown in FIG. 4 uses a helium refrigerator (33) to cool the gas exhaust surface (32).
This is an example of application to a cryopump using In this case, the helium refrigerator (33) includes a first-stage cooling section (34) that is cooled to about the boiling point temperature of liquid nitrogen, a second-stage cooling section (35) that is cooled to about 20K, and a second-stage cooling section (35) that is cooled to about the boiling point temperature of liquid nitrogen. A third stage cooling section (36) cooled to the boiling point temperature.
A gas exhaust surface (32) is formed on a cooling plate (37) fixed to the stage cooling section (36). In addition, the first stage cooling section (3
A chevron-shaped baffle (39) is installed on the radiation shield (38) provided to cover the third stage cooling section (3).
A chevron-shaped baffle (41) is arranged on the radiation shield (40) provided in 6).

[0031]

As is clear from the above description, according to the present invention, when the porous solid adsorbent is exposed to the exposed space of the adsorbent-forming gas condensation layer, the second The pressure of the gas inlet is detected and the exposure time is set in correspondence with the gas pressure value and the time differential value of the pressure value, so that the adsorption capacity of the porous solid adsorbent is not saturated. This can be prevented and the stable evacuation ability of the cryopump can be demonstrated regardless of rapid pressure fluctuations of the second gas to be evacuated.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional and partial system diagram showing a first embodiment of a cryopump according to the present invention.

FIG. 2 is an enlarged view of the portions (23) to (27) in FIG. 1;

FIG. 3 is a cross-sectional and partial system diagram showing a second embodiment.

FIG. 4 is a cross-sectional and partial system diagram showing a third embodiment.

[Explanation of symbols]

1...Vacuum container 2...Intake port 3...Intake valve 4...Radiation shield 5...Liquid nitrogen reservoir 6...First chevron-shaped baffle 7... Gas-liquid separator 8...Second chevron baffle 9...First liquid helium reservoir 10...Second liquid helium reservoir 11... Gas-liquid separator 12...Blowout pipe 13...Blowout hole 14...Argon condensation layer 15...Manifold 16...Introduction pipe 17...Flow control valve 18... Drive mechanism 19...Drive mechanism control device 20...Pressure detection tube 21...Pressure gauge 22...Pressure opening corresponding device 23...Activated carbon (porous solid adsorbent) 24...Activated carbon panel 25...Opening part 26…Separate room 27... Compartment shutoff valve 28...Drive mechanism extension part 29... Drive mechanism 30...Drive mechanism control device 31... Compartment shutoff valve opening/closing adjustment device 32...Gas exhaust surface 33...Helium refrigerator 34...First stage cooling section 35...Second stage cooling section 36...Third stage cooling section 37...Cooling plate 38...Radiation shield 39...Chevron-shaped baffle 40...Radiation shield 41...Chevron-shaped baffle

Claims (1)

[Claims] Claim 1: A condensation layer condenses a first gas acting as an adsorbent on a surface cooled to an extremely low temperature in a vacuum, and the first gas is evacuated into or onto the condensation layer. Second
A cryopump is configured to exhaust gas from a vacuum gas phase by adsorption or cryotrapping, in which a porous solid adsorbent is fixed inside so as to be coolable to an extremely low temperature, and a condensation layer of the first gas is provided. a compartment having an opening that allows the porous solid adsorbent to be exposed to an exposed space of the second gas; a compartment shutoff valve that can seal the compartment from the exposed space of the condensed layer of the gas; a pressure measurement device, and calculates a time differential value of a pressure measurement value outputted from the pressure measurement device, and opens the compartment shutoff valve in accordance with the pressure measurement value and the time differential value of the pressure measurement value. A cryopump comprising a compartment shutoff valve opening/closing adjustment device that outputs an opening/closing signal to a drive control device for the compartment shutoff valve.