JP2822330B2 - Cryopump and vacuum pump - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cryopump capable of reaching an extremely high vacuum, and a vacuum evacuation device using the cryopump.

(Prior Art) At present, as a pumping means for obtaining a so-called ultra-high vacuum of 10 ⁻¹⁰ Pa or less, a method using a pump described below as a main pump for pumping is known.

(1) A method combining a sputter ion pump and a titanium getter pump.

(2) A method combining a diffusion pump and a titanium getter pump.

(3) A cryopump or a method combining a cryopump and some of the above pumps.

Among these methods, the method using the cryopump (3) is the best in terms of pumping speed and pumping capacity, and it can be said that it is the shortest distance for practical use of ultra-high vacuum in the future.

(Problems to be Solved by the Invention) There have been some reports of obtaining an extremely high vacuum by a cryopump to date. However, those cryopumps are all refrigerators that cool (4K) liquid nitrogen,
Alternatively, a He liquefier was used. These refrigerators or liquefiers have the disadvantages that they have complicated structures, are difficult to operate and operate, and are not suitable for constructing a practical ultra-high vacuum exhaust system because of their high cost.

On the other hand, in the vacuum industry, GM, Solvay,
A cryopump using a small refrigerator applying a heat cycle called a name such as Stirling is widely used. These cryopumps have a simple structure, are easy to operate, are inexpensive, and can be easily obtained.However, since the ultimate temperature of liquid nitrogen is about 10K, they can be used in ultra-high vacuum areas of about 10 ^-8 Pa. It was generally thought that although it could be used for evacuation, it could not be used in an extremely high vacuum region below that.

An object of the present invention is to solve the above problems, to have a simple structure, easy to operate, and inexpensive,
An object of the present invention is to provide a cryopump capable of evacuating to an extremely high vacuum region.

Another object of the present invention is to provide a vacuum exhaust device that can reach an extremely high vacuum region by using the cryopump.

(Means for Solving the Problems) Accordingly, the present invention has made it possible to reach an extremely high vacuum region by reducing gas discharge and leakage at the container wall and the seal portion of the pump container, and furthermore, the vacuum container.

That is, the cryopump of the present invention is a cryopump in which a cooling surface for adsorbing and exhausting gas is installed in a metal pump container. (1) The cooling surface has an adsorbent attached thereto. , GM, Solvay, Stirling, etc., are connected to a mechanical refrigerator having a temperature of about 10K, which is known as a cycle name. (2) The pump container has a smooth exposed surface in a vacuum. And (3) the sealing surface of the pump container has a sealing structure with a metal gasket or an auxiliary vacuum structure interposed therebetween.

In the vacuum evacuation apparatus of the present invention, the cryopump is connected to a vacuum vessel. (1) The vacuum vessel is made of metal, and the exposed surface in the vacuum is smoothed and / or dense. (2) The sealing surface of the vacuum vessel has a sealing structure in which a metal gasket or an auxiliary vacuum structure is interposed.

In the above description, activated carbon is mainly used as the adsorbent attached to the cooling surface, but other low-temperature adsorbents (such as molecular sieves) can also be used.

Further, the pump container and the vacuum container are made of an aluminum alloy (for example, A5052 aluminum alloy) from which occluded gas has been sufficiently removed by heat treatment or the like, or a stainless steel (for example, S
US304, SUS316) is desirable.

It is desirable to smooth the exposed surfaces of the pump container and the vacuum container in a vacuum to a super mirror surface by composite electrolytic polishing or electrolytic abrasive polishing. When the exposed surface in the vacuum is covered with a dense oxide film, the oxide film may be formed on the exposed surface in the vacuum by heating in a mixed gas of argon and oxygen or an oxygen gas atmosphere.

Next, as a metal gasket to be interposed between the sealing surfaces of the pump container and the vacuum container, a metal O-ring called Helicflex (manufactured by Helicoflex), an indium wire gasket, an oxygen-free copper plate, or a pure aluminum plate And a gasket formed in an annular shape can be used. Further, in the case of a seal structure in which an auxiliary vacuum structure is interposed on the seal surface, an elastomer gasket can be used instead of a metal gasket, but a metal gasket is preferably used inside the auxiliary vacuum portion.

(Operation) Next, the fact that the cryopump of the present invention can reach the extremely high vacuum region will be described.

The pressure P in the vacuum chamber evacuated by the cryopump is expressed by the following equation (1).

_{P = Q / S + P S} (T G / T S) 1/2 (1) where, Q is leakage into the chamber, the gas penetration rate due to transmission and outgassing, S is the pumping speed, P _S on activated carbon , T _G is the temperature of the gas in the exhaust gas, and T _S is the surface temperature of the activated carbon. Further, P _S in the equation (1) can be expressed as logP _S = −A / T _S + B (2), where A is a constant related to the heat of adsorption and B is a constant related to the gas adsorption amount.

In the equation (1), the pressure P is the first term Q / S determined by the ratio of the flow rate Q at which the gas leaks into the vacuum chamber and the gas enters due to permeation or gas release, and the pumping speed S, and the pressure of the gas on the activated carbon. It is the sum of the second term P _S (T _G / T _S ) ^1/2 determined by the adsorption equilibrium pressure. The first term has a constant value without depending on the surface temperature T _{S of the} activated carbon, but the second term strongly depends on the temperature T _S as shown in the equation (2).

FIG. 4 is a graph showing the pressure of equation (1) as a function of the reciprocal of the activated carbon surface temperature T _S.

The higher the temperature in the equation (1), the higher the proportion of the pressure component represented by the second term becomes, and the first term becomes negligible. Therefore, the pressure expressed in logarithm is shown in FIG.
It rises linearly as indicated by the symbol.

Conversely, when the temperature decreases in equation (1), the second term becomes smaller, and the constant first term becomes dominant irrespective of the temperature.
In FIG. 4, the portion indicated by B where the pressure is constant on the low temperature side corresponds to this.

From the above considerations, the pressure that can be reached by the cryopump has a large gas release, and does not depend on the temperature when the first term of the equation (1) is dominant. In such a case, it can be said that the ultimate pressure does not change even if a 4K refrigerator or a 10K refrigerator is used.

FIG. 5 is an example of the relationship between the temperature and the pressure of a cryopump (using a mechanical refrigerator having an ultimate temperature of about 10 K) measured by the inventors. In contrast to FIG. 4, it can be predicted that the pressure due to the contribution of the second term of the equation (1) is much lower than 10 ⁻¹¹ Pa even at the operating temperature of the refrigerator of about 10 K. If the amount of gas flowing into the chamber, such as leak and leak, is reduced, the contribution of the first term of equation (1) to the pressure decreases and approaches the value of only the contribution of the second term.
Extremely high vacuum of about 10 ^-11 Pa is expected to be sufficiently possible even with a 10K refrigerator. Therefore, in a pressure range of about 10 ⁻¹¹ Pa and about 10 ⁻¹² Pa, even if a 4K refrigerator is used,
The ultimate pressure is determined by using the refrigerator of (1)
This is the first term of the equation, and it can be concluded that it is essential to reduce the gas leaking into the pump container, such as gas release, leak, or permeation represented by the gas inflow rate Q, in order to lower the ultimate pressure. .

In the present invention, in order to reduce outgassing, the exposed surface in the vacuum is processed smoothly and / or a dense oxide film is formed on the surface, using a metal pump container produced under controlled conditions, In order to reduce outgassing and leakage from the atmosphere side, a metal gasket or an auxiliary vacuum structure is interposed in all the seal parts, so that the component of the first term of the equation (1) can be reduced, and the extremely high vacuum region Can be reached. The same applies to the vacuum exhaust device of the present invention.

(Example) In FIG. 1A, reference numeral 10 denotes a cryopump, which has a cooling surface 11 therein. The cooling surface 11 is cooled by a refrigerator 12 of a GM cycle, which is currently most frequently used in the vacuum industry, and the refrigerator 12 is driven by a compressor unit 13. The cryopump 10 has an activated carbon 11a attached to the surface of the cooling surface 11 in order to adsorb and exhaust a gas having a relatively high vapor pressure such as He, H ₂ , and Ne at a low temperature.

Most of the pump vessel 14 and vacuum vessel 20 are made of A5052 aluminum alloy, and the exposed surface in vacuum is smoothed and then covered with a dense oxide film by heating to a high temperature in a mixed gas of argon and oxygen. It has a stable surface with little gas adsorption. Pump container 14, vacuum container 20
It is also possible to use stainless steel such as SUS304 or SUS316 as the material. The surface is finished to a super mirror surface by composite electrolytic polishing, electrolytic abrasive polishing, etc., reducing the gas adsorption execution area, and generating a stable oxide film by heating in oxygen is also effective in reducing gas emission. .

Between the pump container 14 and the vacuum container 20, the mounting part of the refrigerator 12 at the bottom of the pump container, a vacuum gauge attached to the vacuum container 20
In the seal part of the flange 40 such as 34 and the roughing valve 31,
Metallic O-ring called Helicflex
It is tight with 44 in between. The O-ring 44 may be an indium wire gasket or a metal sheet gasket made of a plate of oxygen-free copper or pure aluminum. Alternatively, as shown in FIG. 1 (b), the gaskets 41 and 42 are arranged in a double manner on the sealing portion of the flange 40, and the space between the inner gasket 41 and the outer gasket 42 is set as an auxiliary vacuum region 45, and By evacuating the vacuum region 45 through the intermediate exhaust pipe 43 with a mechanical pump 50 or the like, a structure that prevents leakage from the atmosphere side to the high vacuum side and gas permeation can be achieved. In this case, the gaskets 41 and 42 are not made of metal but may be made of an elastomer gasket. However, from the viewpoint of reducing gas emission, the inner gasket 41 is preferably made of metal.

The roughing valve 31 that shuts off the roughing system of the vacuum vessel 20 when the cryopump 10 is operated uses a metal seal bubble using a metal gasket. Furthermore, an explosion-proof valve 32, which is usually provided to protect the vacuum vessel 20 and the pump vessel 14 from destruction against an increase in internal pressure due to re-release of a large amount of adsorbed gas when the cryopump 10 rises to room temperature, is also a metal. A seal valve is used. This metal seal valve may be a break valve of a type in which a partition wall made of a thin metal or glass breaks when a pressure rises and releases internal pressure. The explosion-proof valve 32 and the roughing valve 31 are shown in FIG.
By exhausting the atmosphere side of the valve 33 with an auxiliary pump such as the mechanical pump 50 as described above, a structure that avoids leakage from the atmosphere side can be adopted. In this case, the seal gasket of the valve 33 may be an elastomer gasket instead of metal, but it is desirable to use a metal gasket from the viewpoint of reducing gas emission.

A main exhaust valve 30 such as a gate valve may be provided between the vacuum vessel 20 and the cryopump 10 in some cases. For the valve body seal of the main exhaust valve 30, an elastomer gasket can be used because there is no possibility of direct leakage from the atmosphere side, but a metal seal is desirable in order to minimize gas emission. Also, as in the case of the pump container 14 and the vacuum container 20, it is preferable that the surface of the main exhaust valve exposed in the vacuum be made of a metal material that emits little gas, and that the surface be subjected to gas emission reduction measures such as oxide film treatment.

FIG. 2 shows the history of the ultimate pressure in the embodiment shown in FIG. 1 (a). On the 70th day from the start of evacuation, a vacuum leak and dark current flowing into the vacuum gauge were found, and as a result of removing these, an extremely high vacuum of 3 to 5 × 10 ⁻¹¹ Pa was repeatedly obtained.

FIG. 3 shows a typical example of the exhaust characteristics from the atmospheric pressure of the vacuum exhaust device of the embodiment shown in FIG. 1 (a). After returning the chamber to atmospheric pressure, leave it for 28 hours,
After baking for 90 hours, the ultimate pressure of 3 × 10 ⁻¹¹ Pa was obtained after 90 hours.

(Effects of the Invention) As described above, according to the cryopump and the vacuum exhaust device of the present invention, a small refrigerator widely used in the vacuum industry at present without using an expensive and complicated 4K refrigerator. Has the effect that it is possible to reach an extremely high vacuum region of 10 ⁻¹¹ Pa or less, and it is also possible to simplify the structure and facilitate the operation.

[Brief description of the drawings]

FIG. 1 (a) is a system diagram of an embodiment of the present invention, and FIG. 1 (b).
Is a sectional view of another embodiment of the flange seal portion, FIG. 1 (c) is a system diagram of another embodiment of the valve seal, and FIG. 2 is a history of the ultimate pressure from the first exhaust in the embodiment of FIG. FIG. 3 is a graph showing an example of the exhaust characteristic in the embodiment of FIG. 1, and FIG. 4 is a conceptual diagram showing a change in the pressure of the cryopump with respect to the cryogenic surface temperature.
FIG. 5 is a graph showing a change in pressure with respect to a cryo-surface temperature in a conventional cryopump measured by the inventor. 10 Cryopump 11 Cooling surface 11a Activated carbon 12 GM refrigerator 13 Compressor unit 14 Pump container 20 Vacuum container 40 Flange 41 Inner gasket 42 …… Outer gasket, 43 …… Middle exhaust pipe 44 …… Gasket, 45 …… Auxiliary vacuum area

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F04B 37/08

Claims (2)

(57) [Claims] 1. A cryopump in which a cooling surface for adsorbing and exhausting gas is provided in a metal pump container. (1) The cooling surface has an adsorbent attached thereto and a G- M, Solvay, Stirling, and other known cycle names are connected to a mechanical refrigerator having a temperature of about 10K, and (2) the pump container has a vacuum-exposed surface that is smoothed, and And / or a dense oxide film, and (3) the sealing surface of the pump container has a sealing structure with a metal gasket or an auxiliary vacuum structure interposed therebetween. 2. The cryopump according to claim 1, wherein the cryopump is connected to a vacuum vessel. (1) The vacuum vessel is made of metal, and an exposed surface in a vacuum is smoothed and / or dense. (2) a vacuum pumping device, wherein the sealing surface of the vacuum vessel has a sealing structure with a metal gasket or an auxiliary vacuum structure interposed.