JPH03237277A - Cryopump - Google Patents

Abstract

PURPOSE:To maintain stable exhaust capacity by detecting the inlet pressure of second gas to be exhausted, and setting the intermittent lead-in interval according to the integrated value of this gas pressure at the time of performing the intermittent lead-in of first gas forming a condensed layer acting as absorbent. CONSTITUTION:A liquid nitrogen reservoir 4 is installed at the upper part of a radiation shield 3 accommodated in a vacuum container 1 provided with an inlet 2, and a first liquid helium reservoir 6 provided hangingly with a chevron type baffle 7 is disposed in an upper position in the radiation shield 3. The radiation shield 3 is also provided with a second liquid helium reservoir 8 opposed to the baffle 7 with a gap, and a blow-off pipe 10 for jetting argon gas is interposed between the baffle 7 and the second liquid helium reservoir 8. A flow switching valve 15 interposed at a lead-in pipe 14 communicated with the blow-off pipe 10 is then switched at the time interval set by an intermittent time adjusting device 20 according to the time integrated value of gas pressure in the vicinity of the inlet 2 detected by a pressure detector 18 so as to attain the intermittent lead-in of argon gas.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a cryopump used as an ultra-vacuum pump, and in particular, to a cryopump that can appropriately control the formation of a condensation layer that adsorbs gas to be evacuated. Regarding cryopumps.

[Conventional technology]

In a cryopump, a conventional technique in which a condensation layer that acts as an adsorbent for the gas to be pumped is formed on a surface cooled to an extremely low temperature using, for example, argon gas, and the amount of this condensation layer formed is controlled. For example, JP-A-1-178
There is a cryopump disclosed in Japanese Patent No. 781.

This cryopump is designed to change the flow rate of argon gas that forms a condensation layer in response to changes in the pressure of the gas to be evacuated near the intake port.

[Problem to be solved by the invention]

In a cryopump, the pressure near the inlet of the gas to be discharged, such as helium or hydrogen, fluctuates over a wide range. For example, in the case of helium, the pressure is 1O-1Pa~
It may vary over several orders of magnitude, such as 10-7 Pa. Therefore, it is necessary to control the flow rate of argon in response to the above-mentioned wide range of changes in helium pressure near the cryopump inlet. However, in practice, the ratio of the maximum flow rate to the minimum flow rate that a flow control valve can control while maintaining accuracy and reproducibility is about 1000 times the limit. Therefore, the responsiveness of control to minimize the argon flow rate in a region where the helium pressure is extremely low has been considered to be a difficult point. In this case, even when the load on the cryogenic surface due to helium is small, argon is supplied at a relatively large flow rate without being able to follow the decrease in load, and the condensation layer is formed unnecessarily thick. This brings about disadvantages such as an increase in the heat load on the Cladio pump and a shortening of the regeneration cycle.

Therefore, the present invention solves the problems of the above-mentioned prior art and provides a Cladio pump that can appropriately control the formation amount of a condensation layer that acts as an adsorption medium for the gas to be exhausted and ensure a stable exhaust action. The purpose is to provide.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a flow rate on-off valve disposed in a first gas introduction pipe, a control device for this flow rate on-off valve, and a second gas inlet near the inlet of a cryopump. a measuring device that detects the pressure of the measuring device, and calculates the time integral value of the pressure value outputted by the measuring device, and calculates the time integral of the time interval at which the first gas is intermittently introduced by opening and closing the flow rate opening/closing valve. The present invention is characterized in that it includes an intermittent time interval adjustment device that is set according to the flow rate opening/closing valve and outputs an opening/closing signal to a control device for the flow rate opening/closing valve.

[For production]

According to the present invention, the interval at which the flow rate opening/closing valve is opened is adjusted in response to pressure changes near the intake port of the second gas to be exhausted, and when the pressure of the second gas is low, the introduction interval is longer. ,
When the pressure of the second gas is high, the introduction interval can be shortened. As a result, the introduction flow rate of the first gas is not controlled according to the pressure of the second gas.
The amount of condensation layer is maintained at an appropriate level.

〔Example〕

Hereinafter, an embodiment of a cryopump according to the present invention will be described with reference to the accompanying drawings. Note that argon,
There are nitrogen, sulfur hexafluoride, etc., and the second gas to be exhausted includes helium, hydrogen, etc. Below, we will use argon as the first gas and helium as the second gas. explain.

FIG. 1 shows a Cladio pump according to a first embodiment. Reference numeral 1 indicates a vacuum container, and this vacuum container 1 has an intake port 2 and a radiation shield 3 is housed inside. A liquid nitrogen reservoir 4 is installed above the radiation shield 3, while a first chevron-type baffle 5 is installed below to face the intake port 2.

A first liquid helium reservoir 6 is disposed at an upper position inside the radiation shield 3, and from this first liquid helium reservoir 6, a second chevron-shaped baffle 5 is disposed so as to face the first chevron-shaped baffle 5. A baffle 7 is provided vertically. Reference numeral 8 indicates a second liquid helium reservoir 8 whose outer surface is a cryogenic surface to form a condensed layer that adsorbs helium gas, and the upper part of this second liquid helium reservoir 8 is connected to a gas-liquid separator 9. There is. Such a second liquid helium reservoir 8 is similar to the second liquid helium reservoir 8.
The chevron-shaped baffle 7 is disposed at a position facing the second liquid helium reservoir 8 at a predetermined distance, and a blowout pipe 10 for blowing out argon gas onto the outer surface of the second liquid helium reservoir 8 is disposed between them. The second part of this blow-off pipe 10
There is an argon gas blowout hole 11 on the liquid helium reservoir 8 side.
are formed in large numbers. Therefore, the argon gas blown out from the blow-off hole 11 of the blow-off pipe 10 toward the second liquid helium reservoir 8 is cooled by the liquid helium inside the second liquid helium reservoir 8, condenses on its surface, and becomes the gas to be exhausted. A condensation layer 12 is formed which adsorbs a certain helium gas.

The blowout pipe 10 is connected to an introduction pipe 14 via a manifold 13, and this introduction pipe 14 is connected to an argon gas supply device (not shown).

Next, a flow rate opening/closing valve 15 is disposed in the middle of the introduction pipe 14 coming out of the vacuum container 1 . A valve drive mechanism 16 attached to the flow rate opening/closing valve 15 opens and closes the valve based on a signal output from the control device 17.

On the other hand, a pressure detection tube 1 is placed facing the intake port 2 of the vacuum container 1.
8 is installed, and the pressure detected by this pressure detection tube 18 is
The detected pressure signal is converted into a detected pressure signal proportional to the pressure via the pressure gauge 19 and introduced into the intermittent time interval adjustment device 20 . This intermittent time interval adjustment device 20 calculates the time integral value of the manually input detected pressure signal, and based on this calculation, the control device 17
An opening/closing signal for the flow rate opening/closing valve 15 is outputted to the drive mechanism 16 via.

Next, the operation of the cryopump configured as described above will be explained.

While the flow rate on/off valve 15 is open, argon gas flows through the introduction pipe 14 from a supply device (not shown), and is ejected from the blowout hole 11 of the blowout pipe 10 to the second liquid helium reservoir 8 via the manifold 13. Ru. Argon gas is condensed under the cooling action of liquid helium, resulting in
A condensation layer 12 is formed on the outer surface of the second liquid helium reservoir 8, which acts as an adsorption medium.

On the other hand, the helium gas introduced into the interior from the inlet 2 of the vacuum container 1 is first transferred to the first Chevron-type buffer 5 which is cooled by the liquid nitrogen stored in the liquid nitrogen reservoir 4.
After passing through, it passes through a second Chevron-type baffle 7 which is under the cooling effect of the liquid helium stored in the first liquid helium reservoir 6, and reaches the vicinity of the second liquid helium reservoir 8. As described above, the helium gas is exhausted by the adsorption effect or triode wrapping effect by the condensation layer 12 formed on the surface of the second liquid helium reservoir 8. In the above exhaust process, components other than the gas to be exhausted, such as hydrogen, are condensed on the surface of the second Chevron type buffle 7 and are exhausted.

In such an evacuation process, helium gas is intermittently introduced according to the pressure of helium gas introduced from the intake port 2 of the vacuum container 1, as shown in the time chart of FIG.

FIG. 2(a) shows the timing of intermittent introduction of argon gas when the flow rate on/off valve 15 is opened, and the vertical axis indicates the flow rate of argon gas. FIG. 2(b) shows the change in the pressure of lithium gas near the intake port 2 detected by the pressure detection tube 18, and the vertical axis indicates the pressure. The horizontal axis is the time axis, which is common to FIGS. 2(a) and 2(b).

In FIG. 2(a), the symbols 100.101.102.
103 is a flow rate waveform of helium gas that is intermittently introduced. In this case, the rise of the flow rate and its time constant when gas flows in the pipe are ignored, and the flow rate on/off valve 15 is ignored.
As soon as the valve is opened, argon gas flows through the introduction pipe 14 at a constant flow rate q per unit time, and on the other hand, as soon as the flow rate on/off valve 15 is closed, the flow rate of argon gas becomes zero. Further, it is assumed that the time period Δt during which the flow rate on-off valve 15 is open is set in advance.

During the time Δt, flow! Argon gas introduced via the on-off valve 15 forms a condensation layer 12 . - times of intermittent introduction, an amount of argon gas of q×Δt forms the condensation layer 12.

Therefore, in FIG. 2(b), it is assumed that the pressure value of helium gas changes stepwise with values such as p, 2p, and p/2. The intermittent time interval adjustment device 20 performs a calculation to integrate the pressure value output from the pressure gauge 19 over time, and
The time interval for introducing argon gas, which is intermittently introduced by opening and closing the flow rate on-off valve 15, is set in accordance with the time integral value.

For example, time intervals (to, t+), (t+, t2), (
The time integral value of the pressure at t2r ts ) corresponds to the area of the regions represented by the symbols 104, 105, and 106, respectively. In this case, the intermittent time interval adjustment device 20 adjusts the time tI,
Set t2, t,... and generate waveform 101.1 at that time.
In order to intermittently introduce argon gas as indicated by 02.103, an opening/closing signal for the flow rate opening/closing valve 15 is output to the control device 17.

In this way, helium gas is introduced intermittently at intervals that keep the time integral value of the helium gas pressure near the intake port 2 constant, so if the helium gas pressure is high, The introduction interval becomes faster (j+ r t
2). As a result, the adsorption capacity of the condensation layer 12 reaches saturation and the decrease in its capacity is compensated for, and a stable exhaust action is maintained.

On the other hand, when the pressure of helium gas is low, it takes time for the condensation layer 12 to become saturated and the adsorption capacity continues for a relatively long time. t3), the condensation layer 12 is not formed to be unnecessarily thick, and the condensation heat load on the second liquid helium reservoir 8 is reduced.

In this way, even if the flow rate of argon gas introduced is constant, by adjusting the introduction interval, the condensed layer 12 necessary for stable exhaust gas can be formed with virtually no excess or deficiency, regardless of pressure fluctuations of helium gas. I can do it.

In the above embodiment, a case has been described in which the intermittent introduction time interval of argon gas is adjusted so that the time integral value of the pressure of helium gas is constant; however, the above-mentioned time integral value is limited to being constant. It's not a thing. For example, when the pressure of helium gas is higher than a predetermined value, the time integral value may be set smaller than when it is lower, and the introduction time interval may be set in accordance with this time integral value.

Next, other embodiments of the present invention will be described with reference to FIGS. 3 to 12.

In the embodiment shown in FIG.
An analysis tube 30 is attached to a location near the analysis tube 3.
A quadrupole mass spectrometer 31 is connected to 0. On the other hand, a pulse motor 33 and an encoder 34 are provided in the flow rate control valve 32 provided upstream of the flow rate on/off valve 15 in the introduction pipe 14, and a control device 35 for the pulse motor 33 and a reading device 36 for the encoder 34 are used as an opening adjustment device. It is connected to 37.

The pressure of helium gas passing through the inlet 2 of the vacuum container 1 is detected by a quadrupole mass spectrometer 31 via an analysis tube 30,
The detection signal is output to the opening adjustment device 37 and the intermittent time interval adjustment device 20. The opening adjustment device 37 outputs a signal for adjusting the opening of the flow rate control valve 32 to the drive mechanism control device 35 in response to the detection signal value of the quadrupole mass spectrometer 31, and controls the flow of argon through the introduction pipe 14. The gas flow rate is controlled. The opening degree of the flow rate control valve 32 is determined by the encoder 3
The opening signal is detected by the reading device 36 via the opening signal 4, and this opening signal is fed back to the opening adjustment device 37. This opening adjustment device 37 compares the opening signal with the detection signal output from the quadrupole mass spectrometer 31, and selects the appropriate flow rate adjustment valve 32.
The opening degree is determined.

In this embodiment, not only can the intermittent time interval adjustment device F20 adjust the time interval of intermittent introduction of argon gas, but also the flow rate adjustment valve 32 can adjust the amount of introduction at one time. This makes it possible to finely adjust the amount of argon gas introduced, further improving the ability to follow pressure changes in helium gas.

In the embodiment shown in FIG.
8 is incorporated, and the detection signal of this flowmeter sensor 38 is outputted to the general adjustment device 40 via the flowmeter reading bag at39. This comprehensive adjustment device 40 adjusts the time integral value for the intermittent time interval adjustment device 20 based on the outputs of the pressure gauge 18 and the flow meter sensor 38, and also controls the opening degree of the flow rate control valve 32 for the opening degree adjustment bag jt41. Adjust the setting value. The opening adjustment device 41 controls the opening of the flow rate control valve 32 via the drive mechanism control device 42 and the drive mechanism 43 based on the corrected setting.

According to this embodiment, since the flow rate of argon gas introduced is detected via the flow meter sensor 38 and fed back by the integrated control device 40, it is possible to respond to pressure fluctuations in the argon gas supply device. .

*In the embodiment shown in Fig. 5, the flow opening/closing valve 15 provided in the inlet pipe 14 has a structure equipped with a valve having a mechanism for opening and closing the piping route using a piezoelectric element, and the drive mechanism 44 incorporating the piezoelectric element is It is attached to the flow rate on/off valve 15. According to this embodiment, a faster response speed can be obtained than a mechanism driven by air pressure or electromagnetic force of a solenoid.

In the embodiment shown in FIG. 6, a total pressure gauge detection tube, for example, an ionization vacuum gauge type detection tube 45 is used as the pressure detection tube disposed in the intake port 2. 4
Connected to 6. Based on the pressure value output from the ionization vacuum gauge type detection tube 45, the intermittent time interval adjustment device 20:
The time integral value of the pressure value is calculated. In this embodiment, helium gas accounts for most of the gas to be exhausted,
It can be applied when the partial pressure can be regarded as the total pressure of the gas to be exhausted. According to this, handling becomes easy.

In the embodiment shown in FIG. 7, an analysis tube 47 is attached to a portion of the vacuum container 1 near the inlet 2, and a magnetic field deflection type partial pressure meter 48 is connected to this analysis tube 47.

In the embodiment shown in FIG. 8, four connecting pipes are attached to a portion of the vacuum container 1 near the intake port 2, and a helium leak detector 5o is connected to the four connecting pipes. When the gas to be exhausted is helium, the helium leak detector 5o can be used without any problem as a means for measuring the helium partial pressure as in this embodiment.

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. 9 to 12.

The cryopump shown in FIG. 9 differs from the cryopump shown in FIG. 1 in that a Scheffron-type baffle 7 cooled by liquid helium is not provided. This type of cryopump is advantageous when there is no need to distinguish between the helium pumping surface and other pumping surfaces because helium, hydrogen, and other gases to be pumped are simultaneously adsorbed on the pumping surface of the liquid helium reservoir 8. It is.

The embodiment shown in FIG. 10 is an example in which the present invention is applied to a cryopump that uses a helium refrigerator 52 to cool a gas exhaust surface 51. In this case, the helium refrigerator 52 includes a first stage cooling section 53 that is cooled to approximately the boiling point of liquid nitrogen, and a
The third stage cooling section 54 is provided with a second stage cooling section 54 that is cooled to K, and a third stage cooling section 55 that is cooled to approximately the boiling point temperature of liquid helium.
A gas exhaust surface 51 is attached to a cooling plate 56 fixed to the stage cooling section 55.
is formed. In addition, a chevron-shaped baffle 58 is provided on the radiation shield 57 provided to cover the bottom from the first stage cooling section 53, and a radiation shield 58 provided on the third stage cooling section 55 is provided.
A chevron-shaped baffle 60 is disposed at each of the sections 9 .

The embodiment shown in FIG. 11 is an example in which the present invention is applied to a modification of the cryopump shown in FIG. In this case, the cryopump shown in FIG. 10 has a configuration in which the radiation shield 59 and the chevron-shaped baffle 60 provided in the third stage cooling section 55 are omitted. According to this embodiment, helium, hydrogen, and other gases are simultaneously exhausted from the gas exhaust surface 51 that is cooled by the third stage cooling section 55.

The embodiment shown in FIG.
This is an example in which the present invention is applied to a type of cryopump in which a gas exhaust surface 63 is formed on the inner surface of the cryopump. In this case, the chevron baffle 64 is cooled by a liquid helium reservoir 65. Also, the fins 68 of the louver blind baffle 67 are cooled by the liquid nitrogen reservoir 66.
are arranged to be inclined so as to prevent radiation from the air intake port 61 to the gas exhaust surface 63. According to this embodiment, there is an advantage that the probability that the gas to be exhausted passes through the chevron-shaped baffle 64 and the gas exhaust surface 63 is increased.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, when the first gas forming a condensation layer acting as an adsorption medium is intermittently introduced, the pressure at the inlet of the second gas to be discharged is Since the intermittent introduction interval is set in accordance with the integral value of the gas pressure, the amount of condensation layer formed can be maintained appropriately regardless of the pressure fluctuation of the second gas to be exhausted. The cryopump exhibits stable pumping capacity.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of a cryopump according to the present invention, FIG. 2 is a time chart showing the relationship between the intermittent introduction of the first gas and the pressure value of the second gas, and FIG. 1 to 12 are cross-sectional views showing other embodiments of the cryopump according to the present invention. DESCRIPTION OF SYMBOLS 1... Vacuum container, 2... Inlet port, 3... Radiation shield, 4... Extremity nitrogen reservoir, 5... First Chevron type buffer, 6... First liquid helium reservoir, 7 ...Second
Chevron type Batsuful, 8...2nd? i & body helium reservoir, 9... gas-liquid separator, 10... blowout pipe, 11
...Blowout hole, 12...Condensation layer, 13...Manifold, 14...Introduction pipe, 15...Flow rate opening/closing valve,
16... Drive mechanism, 17... Control device, 18...
Pressure detector, 1...pressure gauge, 20...intermittent time interval adjustment device.

Claims (1)

[Claims] A first gas acting as an adsorbent is condensed on a surface cooled to an extremely low temperature in a vacuum container, and a second gas to be exhausted is evacuated under adsorption or cryotrapping action by the condensed layer of the first gas. In a cryopump configured to exhaust air from the gas phase inside the cryopump, a flow rate on-off valve disposed in a first gas introduction pipe, a control device for this flow rate on-off valve, and a second gas phase in the vicinity of the inlet port of the cryopump are provided. a measuring device that detects the pressure of the first gas; and a measuring device that calculates a time integral value of the pressure value outputted by the measuring device, and determines the time interval at which the first gas is intermittently introduced by opening and closing the flow rate opening/closing valve. A cryopump characterized by comprising an intermittent time interval adjustment device that is set according to a time integral value and outputs an opening/closing signal to a control device of the flow rate opening/closing valve.