JP2994075B2 - Cryopump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[Object of the Invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryopump used as a vacuum pump, and more particularly, to suppressing the instability of the evacuation function when exhausting a gas to be exhausted by the adsorption of a condensed layer of an adsorbent forming gas. Cryopump.

[0003]

2. Description of the Related Art As a conventional cryopump for controlling the formation of a condensed layer acting as an adsorbent cooled to an extremely low temperature, there is a cryopump disclosed in Japanese Patent Application 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 condensed layer acts as an adsorbent, is controlled by the cryopump intake air. Means for changing the pressure in response to the pressure of the second gas which is the gas to be exhausted near the mouth is taken.

[0005] Here, as the first gas which is the adsorbent forming gas, a rare gas such as argon (Ar), nitrogen (N ₂ ), sulfur hexafluoride (SF ₆ ) and the like are known. As the second gas, it is common to use helium (He), hydrogen (H ₂ ) having a high ultimate pressure, and hydrogen isotopes (D ₂ , HD, T _2, etc.), which are difficult to evacuate with a normal cryopump. is there. Hereinafter, an example will be described in which argon is used as the first gas and helium is used as the second gas.

[0006]

In a cryopump, the helium load of the gas to be exhausted is rapidly increased, and helium adsorbed on the argon condensed layer is desorbed.
If the pressure of the gas to be exhausted rises sharply, the relative capacity of the argon condensed layer, which acts as an adsorbent, with respect to helium is insufficient, so that the adsorption capacity temporarily decreases and the exhaust speed decreases. Occurs. Once the relative amount of helium in the argon condensed layer acting as an adsorbent becomes insufficient, the pressure of the gas to be exhausted such as helium further increases due to a decrease in the pumping speed. However, the relative amount of the argon condensed layer with respect to the gas to be exhausted such as helium is further insufficient, and the pressure of the gas to be exhausted such as helium is further increased.

[0007] When such a relative shortage of the adsorbent and a vicious cycle of pressure rise occur, the heat load on the cryopump rapidly increases, so that the adsorbed gas such as helium is desorbed. Sudden pressure rise of the pressure inside the vacuum vessel exhausted by the cryopump,
A runaway condition such as a sudden rise in the internal pressure of a refrigerant reservoir such as liquid helium of a cryopump has occurred, which has a very serious drawback that normal operation of the cryopump is difficult.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems. In order to prevent instability of the evacuation operation of a cryopump due to a sudden increase in pressure of an exhaust gas, the evacuation capacity of a porous solid adsorbent is reduced. It is an object of the present invention to provide a cryopump that additionally uses a cryopump.

[Structure of the Invention]

[0010]

In order to achieve the above object, a cryopump of the present invention condenses a first gas in which a condensed layer acts as an adsorbent on a surface cooled to a very low temperature in a vacuum. In a cryopump in which a second gas to be evacuated is exhausted from a gaseous phase in a vacuum by an adsorption action or a cryotrapping action in a condensed layer of a first gas or on a condensed layer, A compartment having an opening fixed to the inside so that it can be cooled to a low temperature and allowing the porous solid adsorbent to be exposed in an exposed space of the condensed layer of the first gas; and the compartment having the first gas. A closing valve that can be closed from the exposed space of the condensed layer, wherein the second gas pressure measuring device calculates a time differential value of a pressure measurement value output from the pressure measuring device, and Time derivative of measured value and pressure measured value Depending on, characterized in that a said compartment closure valve compartment closed valve closing adjustment device for outputting a switching signal to the drive control device of the compartment closed valve to open.

[0011]

According to the present invention, when the pressure of the second gas rises sharply in accordance with the pressure near the adsorption port of the second gas to be evacuated and the time derivative of the pressure, the first gas is discharged. A compartment having an opening to the space where the condensed layer is exposed and fixing a porous solid adsorbent which is cooled to an extremely low temperature inside;
The compartment shut-off valve, which sealably closes the opening, is opened. Since the porous solid adsorbent is held in the closed compartment, the adsorption capacity is maintained. The sudden increase in pressure of the second gas to be evacuated can be caused by the porous solid adsorption cooled to a very low temperature exposed to the space where the opening is opened and the condensed layer of the first gas is exposed. It is absorbed by the additional pumping capacity provided by the medium. This allows the second
The rapid rise in pressure of the gas is suppressed, runaway of the cryopump is prevented, and a stable exhaust operation is maintained.

[0012]

【Example】

(Embodiment 1) Hereinafter, a first cryopump according to the present invention will be described.
Will be described with reference to FIGS. 1 and 2. FIG.
In addition, as the first gas of the adsorbent forming gas, there is a rare gas such as argon, a single component gas of each of nitrogen and sulfur hexafluoride, or a mixed component gas or a single component gas alternately used. The second gas to be exhausted includes helium, hydrogen and the like. Examples of the porous solid adsorbent include activated carbon, molecular sieve 5A and the like. Hereinafter, argon as the first gas, helium as the second gas,
Activated carbon will be described as an example of the porous solid adsorbent, but the same applies to the other substances described above.

FIG. 1 shows a cryopump according to a first embodiment, and FIG. 2 is an enlarged view of a main part thereof. Reference numeral (1) denotes a vacuum vessel, which has an air inlet (2), is connected to a vacuum vessel to be evacuated via an air inlet valve (3) so as to be evacuable, and has an internal space. The radiation shield is housed in. A liquid nitrogen reservoir (5) is provided above the radiation shield (4), and a first chevron baffle (6) is provided below the radiation shield so as to face the intake port (2). I have. The intake valve (3) is opened during exhaust.

A liquid-helium gas-liquid separator (7) is disposed above the radiation shield (3). The gas-liquid separator (7) outputs the first chevron-shaped baffle (6). ), A second chevron-shaped baffle (8) is attached so as to be cooled by a liquid helium reservoir (9) suspended from the gas-liquid separator (7) and vertically suspended. Reference numeral (10) denotes a second liquid helium reservoir in which a condensed layer for adsorbing helium is formed when the outer surface becomes extremely low temperature,
The upper part of the second liquid helium reservoir (10) is connected to the gas-liquid separator (11). Such a second liquid helium reservoir (10) is arranged at a position facing the second chevron-shaped baffle (8) at a predetermined interval, and argon is filled between the second liquid helium reservoir (8) and the second liquid helium. An outlet pipe (12) for ejecting to the outer surface of the reservoir (10) is arranged. On the second liquid helium reservoir (10) side of the outlet pipe (12), a number of argon outlet holes (13) are formed. Therefore, the outlet hole (1) of the outlet pipe (12)
Argon blown out from 3) toward the second liquid helium reservoir (10) is cooled by the liquid helium inside the second liquid helium reservoir (10) and condensed on the surface thereof, and adsorbs helium as a gas to be exhausted. Argon condensing layer (1
4) is formed.

The outlet pipe (12) is connected to the manifold (1).
5) is connected to an introduction pipe (16), and this introduction pipe (16) is connected to an argon supply device (not shown). A flow control valve (17) is provided in the middle of the introduction pipe (16) coming out of the vacuum vessel (1). A valve drive mechanism (18) attached to the flow control valve (17) adjusts the opening of the valve based on a signal output from a drive mechanism control device (19). On the other hand, a pressure detection pipe (20) is provided so as to face the suction port (2) of the vacuum vessel (1), and the pressure detected by the pressure detection pipe (20) is detected via a pressure gauge (21). The signal is converted into a signal, and the pressure opening corresponding device (22)
Will be introduced. The pressure opening corresponding device (22) sends a signal for adjusting the opening of the flow control valve (17) to the drive mechanism control device (19) in response to the detection signal value of the pressure gauge (21), and introduces the signal. The flow rate of argon flowing through the tube (16) is adjusted.

On the front surface of the second liquid helium reservoir (10),
Activated carbon panel (24) to which activated carbon (23) is fixed, and this activated carbon panel (24) is fixed to the inside so that it can be cooled to a very low temperature, and the activated carbon (23) can be exposed to the exposed space of the argon condensed layer (14). A compartment (26) having an opening (25) is provided. A compartment closing valve (27) capable of sealing the inside of the compartment (26) is attached to the opening (25) of the compartment (26).

The compartment closing valve (27) is provided with a drive mechanism extension (28), which is opened and closed by a drive mechanism (29) disposed outside the vacuum vessel (1). The electric circuit of the power source of the drive mechanism (29), the gas pressure piping, and the like are not shown. The drive mechanism (29) drives the compartment closing valve (27) via a drive mechanism extension (28) by a power source (not shown) based on an opening / closing operation signal output from the drive mechanism control device (30). .

On the other hand, the pressure detected by the pressure detecting pipe (20) is converted into a detected pressure signal via a pressure gauge (21), and together with the pressure opening corresponding device (22), the compartment closing valve opening / closing adjusting device (31). ). The compartment closing valve opening / closing adjusting device (31) calculates a time differential value of the input detection signal, and based on this calculation, the compartment closing valve opening / closing adjusting device (3).
1) The drive mechanism control device (30) controls the drive mechanism (3).
An open / close signal is output so as to drive 1) to open / close the compartment close valve (27).

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

In accordance with the opening of the flow control valve (17),
Argon flows from a supply device (not shown) through the introduction pipe (16), and is ejected from the outlet (13) of the outlet pipe (12) through the manifold (15) toward the second liquid helium reservoir (10). The argon is condensed under the cooling action of the liquid helium, so that this second liquid helium reservoir (1
An argon condensed layer (14) acting as an adsorbent is formed on the outer surface of (0).

On the other hand, the helium introduced from the suction port (2) of the vacuum vessel (1) is firstly cooled by the liquid nitrogen stored in the liquid nitrogen reservoir (5) by a first chevron-type baffle. It passes through (6) and reaches near the second liquid helium reservoir (10). Helium is exhausted by the adsorption or cryotrapping action of the argon condensed layer (14) formed on the surface of the second liquid helium reservoir (10) as described above. In the above exhaust process, components such as hydrogen in the exhaust target gas are condensed and exhausted on the surface of the second chevron baffle (8).

In such an evacuation process, each member operates under a set condition in a normal state. That is, when the pressure of the helium component in the gas to be exhausted introduced from the intake port (2) rises, this pressure rise is detected by the pressure gauge (21) provided in the pressure detection pipe (20), and the detection is performed. The signal is sent to the pressure opening corresponding device (22). In the pressure opening degree correspondence device (22), the drive mechanism control device (1) corresponds to the detection signal value of the pressure gauge (21).
A signal for adjusting the opening of the flow control valve (17) is output to 9), and the flow rate of argon flowing through the introduction pipe (16) is controlled so as to be proportional to the pressure rise of the gas to be exhausted.

When the pressure of the gas to be exhausted introduced from the intake port (2) decreases, an opening adjustment signal corresponding to a detection signal output from the pressure gauge (21) which detects the pressure decrease is transmitted to the drive mechanism control. The device (19) is controlled to control the flow rate so as to decrease in proportion to the flow rate of argon flowing through the inlet pipe (16) and the pressure of the gas to be evacuated.

When the variation in the load of the helium component in the gas to be exhausted is relatively gentle, the flow rate of the adsorbent forming gas is controlled as described above. However, if the helium load of the gas to be exhausted suddenly increases or the pressure of the gas to be exhausted suddenly rises due to the desorption of helium adsorbed on the argon condensed layer, the compartment shutoff valve will be described as follows. (27) is opened, and the activated carbon (23) cooled in the compartment is exposed to the space where the argon condensed layer is exposed.

If the pressure of the helium component in the gas to be exhausted rises sharply, it is detected by the compartment closing valve opening / closing adjusting device (31) as a case where the time differential value of the pressure exceeds a predetermined value. In this case, in order to prevent the helium load on the argon condensed layer from being relatively temporarily increased and the evacuation action of the cryopump being unstable, the helium is driven by the compartment closing valve opening / closing adjusting device (31). Mechanism control device (3
At 0), a signal is output so that the drive mechanism (29) is opened via the drive mechanism extension (28) to open the compartment closing valve (27). As a result, the compartment closing valve (27) opens and the compartment (26) opens.
Activated carbon (23) that has been cooled to a very low temperature is exposed. Helium, which is a gas to be exhausted, is exhausted by the adsorption and exhaust capability of the exposed activated carbon (23), and the relative shortage of the argon condensed layer is compensated. After the activated carbon (23) is exposed, when the pressure value of helium and the time derivative of the pressure value of helium fall within predetermined values, the compartment closing valve (27) is opened and closed by the compartment closing valve opening / closing adjusting device (31). Adjusted to close. Activated carbon (23) is an argon condensed layer (1
It is sealed from the exposed space of 4), and waits in the compartment (26) until the compartment close valve (27) is adjusted to open by the compartment close valve opening / closing adjusting device (31).

(Effect of Embodiment 1) As described above,
When the time derivative of the pressure value of the helium to be evacuated exceeds a predetermined value, the activated carbon of the porous solid adsorbent which is isolated in a closed compartment to prevent saturation of the adsorption / exhaust capacity and is on standby. However, since it is exposed to the space where the argon condensed layer of the adsorbent-forming gas condensed layer is exposed, it is possible to prevent a temporary decrease in the pumping speed of the cryopump. For this reason, it is possible to prevent a runaway state of the cryopump exhaust operation such as a sudden increase in pressure of the adsorbent-forming gas condensed layer caused by a temporary decrease in the exhaust speed.

In the above description, 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 exhaust operation of each cryopump becomes unstable.

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

(Embodiment 2) The cryopump shown in FIG. 3 is different from the cryopumps shown in FIGS. 1 and 2 in that a chevron-type baffle (8) cooled by liquid helium is not provided. In this type of cryopump, helium is added to the exhaust surface of the liquid helium reservoir (10).
Since hydrogen and other gases to be evacuated are simultaneously adsorbed, it is advantageous when it is not necessary to distinguish between the helium exhaust surface and the other exhaust surfaces.

(Embodiment 3) In the embodiment shown in FIG. 4, a helium refrigerator (33) is used to cool the gas exhaust surface (32).
This is an example in which the present invention is applied to a cryopump using a cryopump. In this case, the helium refrigerator (33) includes a first-stage cooling unit (34) cooled to approximately the boiling point of liquid nitrogen, a second-stage cooling unit (35) cooled to approximately 20K, A third-stage cooling unit (36) for cooling to a boiling point temperature, and a gas exhaust surface (32) is formed on a cooling plate (37) fixed to the third-stage cooling unit (36). Further, a radiation shield (3) provided so as to cover the first stage cooling portion (34).
8), a chevron-type baffle (39) is provided on the radiation shield (40) provided in the third-stage cooling unit (36), and a chevron-type baffle (41) is provided.

[0031]

As is apparent from the above description, according to the present invention, the porous solid adsorbent is exposed to the space where the adsorbent-forming gas condensed layer is exposed. Since the pressure at the gas inlet is detected and the exposure time is set in accordance with the gas pressure value and the time derivative of the pressure value, the saturation of the adsorption capacity of the porous solid adsorbent is reduced. While being prevented, the cryopump can exhibit a stable pumping ability irrespective of a sudden pressure change of the second gas to be pumped.

[Brief description of the drawings]

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

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

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

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Vacuum cavity 2 ... Inlet 3 ... Inlet valve 4 ... Radiation shield 5 ... Liquid nitrogen reservoir 6 ... 1st chevron type baffle 7 ... Gas-liquid separator 8 ... 2nd chevron type baffle 9 ... 1st liquid helium reservoir DESCRIPTION OF SYMBOLS 10 ... 2nd liquid helium reservoir 11 ... Gas-liquid separator 12 ... Blow-out tube 13 ... Blow-out hole 14 ... Argon condensing layer 15 ... Manifold 16 ... Introduction tube 17 ... Flow control valve 18 ... Drive mechanism 19 ... Drive mechanism control device 20 ... Pressure detecting tube 21 ... Pressure gauge 22 ... Pressure opening corresponding device 23 ... Activated carbon (porous solid adsorbent) 24 ... Activated carbon panel 25 ... Opening 26 ... Separator 27 ... Separator closing valve 28 ... Drive mechanism extension 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 unit 35 Second stage cooling unit 36 Third stage cooling unit 37 Cooling plate 38 ... radiation shield 39 ... chevron baffle 40 ... radiation shield 41 ... chevron baffle

Claims (1)

(57) [Claims] A condensed layer condenses a first gas acting as an adsorbent on a surface cooled to a very low temperature in a vacuum,
In a cryopump in which a second gas to be evacuated is condensed or condensed on a second gas to be evacuated from a gaseous phase in a vacuum by an adsorption action or a cryotrapping action, A compartment having an opening fixed inside so as to be able to cool to a low temperature and allowing the porous solid adsorbent to be exposed in an exposed space of the first gas condensing layer; and the compartment having the gas condensing layer. A second chamber closing valve that can be sealed from the exposed space, a second gas pressure measuring device, and a time differential value of a pressure measurement value output from the pressure measuring device, and the pressure measurement value and the pressure measurement are calculated. A cryopump comprising a compartment closing valve opening / closing control device that outputs an opening / closing signal to a compartment closing valve drive control device so as to open the compartment closing valve in accordance with a time differential value of the value. .