JPH0658291A - Cryotrap for turbomolecular pump - Google Patents

Abstract

PURPOSE:To provide a cryotrap for turbomolecular pump which can trap water molecules efficiently. CONSTITUTION:A trap 4 consisting of a cylindrical plate member made of metal is arranged along the inner peripheral wall part of the cylindrical casing 2 on a cryotrap 1 connected with the upper part of a turbomolecular pump 6, and a trap 5 consisting of a disc shaped flat plate made of metal is arranged directly over the part where the blade 7a of the cylindrical rotor 13 is not arranged. The traps 4 and 5 are cooled to about 100 deg.k on the cryotrap surface by the cooling heat due to the refrigeration cycle, etc., of a refrigerator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cryotrap for a turbo molecular pump, which traps water molecules among gases exhausted by the turbo molecular pump.

[0002]

2. Description of the Related Art A turbo molecular pump used in combination with a cryotrap in order to improve the evacuation speed of water with a very small evacuation speed of a turbo molecular pump and realize a vacuum with few water molecules I often do it.
Further, a vacuum with few water molecules has become very important recently in manufacturing semiconductors and the like, and a turbo molecular pump with a cryotrap is used to realize this vacuum with few water molecules.

As shown in FIGS. 6 and 7, a conventional turbo-molecular pump cryotrap 30 is connected to a suction port 46 of a turbo-molecular pump 41 with a flange portion 45 in contact with the cryotrap 30. Casing 3
1, a coiled pipe 33 and a tubular trap 34 are provided.
Is provided. An inlet 33a for introducing the refrigerant into the pipe 33 is formed at one end of the coiled pipe 33, and an outlet 3 for letting the refrigerant out of the pipe 33 is provided at the other end.
3b is formed. This pipe 33 is located outside this circumference.
The cylindrical cryotrap 34 described above having a diameter approximately twice the coil diameter is disposed. Cryo trap 3
4 receives heat conduction from the refrigerant flowing in the pipe 33 and is cooled to a temperature of about −200 ° C. to −100 ° C. which is almost the same as this.

A turbo molecular pump 41 connected to the lower end of the cryotrap 30 is placed in a pump container 42 as shown in FIG.
Blade blades 43a having the blade angle α shown in A and B are arranged all around, and fixed disks 44 in which blades 44b having the blade angle opposite to this are arranged alternately. Then, only the blade disk 43 is rotated in the direction of arrow V by a drive motor (not shown).

In the cryotrap 30 having such a structure, the flange portion 32 at the upper end is connected to a vacuum chamber (not shown), and water molecules jumped into the casing 31 from the vacuum chamber through the upper intake port 32a. A part is condensed on the surface of the pipe 33 or the surface of the trap 34 to be removed from the space. Further, a gas such as argon or hydrogen that does not condense at the temperature of water and about -200 ℃ ~-100 ℃ passing through the cryo-trap 30, blade area A disc 4
When flying in three directions and hitting a blade 43a shown in FIGS. 8A and 8B, since the rotor blade disk 43 is rotating in the direction of arrow V, the passage probability from the area A to the area B is the opposite. large next the pass probability going from region B to the region a, the gas molecules to the area B from the area a, the area from the area B
The gas is exhausted to A ′ and further from the area A ′ to the area B ′.

As described above, as a method for trapping water,
Although the cryotrap 30 having the cylindrical trap surface has been described, as another method for trapping water molecules, FIG.
A chevron 37 is provided in a casing 36 shown in FIG. 10, and a chevron-type cryotrap 35 having the chevron 37 as a trap surface, and a louver 40 is provided in a casing 39 shown in FIG. There is a louver type cryotrap 38.

[0007]

In the above-described conventional cryotrap having the trap surface of the cylindrical body, the trap area of the cryotrap of the cylindrical body arranged in the casing is small, and the cylindrical body is arranged in the vertical direction. Since the structure is such that the rotor disk inside the turbo molecular pump can be seen from the vacuum tank, the probability that water molecules that jumped in from the suction port will collide with this cryo surface is low, and most turbo molecular pump blades Clash with. Molecules that collide with the blade row are partially exhausted, but most are not exhausted and are re-emitted in the other direction and return to the vacuum container side. At this time as well, since the area of the cryo surface is small, there is little probability of collision and condensation there, and many water molecules flow back to the vacuum container side. The same applies to the reverse flow of water molecules discharged from the turbo molecular pump body to the vacuum container side. That is, with such a structure, the exhaust speed for water molecules is not high, and it becomes difficult to obtain a clean vacuum with a low water pressure.

On the other hand, in the case of a cryotrap having a structure in which a chevron is used as a cryo surface and cannot be seen through the intake port, the exhaust speed for water molecules becomes the maximum ideal exhaust speed corresponding to the area of the intake port of the cryotrap. However, the existence of this trap becomes a resistance to other argon and hydrogen that should be exhausted by the turbo molecular pump, that is, the conductance is as small as about 1/4, and if the exhaust speed for these gases is made the same, a large turbo molecule will be generated. You will need to use a pump. Further, when the louver is used as the cryo surface, it is intermediate between the case of the tubular body type described above and the chevron type. That is, although the exhaust speed of water molecules is not ideal as in the chevron type, the exhaust speed of argon and hydrogen is inferior to that of the cylinder type.

The present invention has been made in view of the above problems, and provides a cryotrap for a turbo molecular pump that prevents backflow of water molecules, maintains an ideal pumping speed, and has a small decrease in the pumping speed of argon and hydrogen. The purpose is to do.

[0010]

The above object is to provide a tubular body whose cryotrap surface is provided along the inner circumference of a cryotrap casing attached to the inlet of a turbomolecular pump, and the turbomolecular pump. The present invention is achieved by a cryotrap for a turbo molecular pump, which comprises a flat plate disposed immediately above a portion of a cylindrical rotor in which the uppermost blade row is not formed.

For the above-mentioned purpose, the cryotrap surface has a cylindrical body arranged along the inner circumference of the inlet of the turbo molecular pump casing, and the uppermost blade of the cylindrical rotor of the turbo molecular pump. The present invention is achieved by a cryotrap for a turbo molecular pump, characterized in that it comprises a flat plate arranged immediately above a region where no rows are formed.

[0012]

The cryotrap surface is located just above the top of the cylindrical rotor of the turbo molecular pump in the vicinity of the portion where the blade row is not formed, along the inner circumference of the cryotrap casing, or in the cryomolecular pump cryopump. Since it was arranged along the inner circumference of the inlet of the trap casing, the water molecules that jumped into the blade row of the turbo molecular pump and were re-emitted were effectively condensed on the cryotrap surface, and gas other than water molecules Also, the gas is exhausted by the turbo molecular pump without being affected by the cylinder body and the flat plate forming the cryotrap surface.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A cryotrap for a turbo molecular pump according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a turbo molecular pump 6 and a vacuum chamber 3 which are attached with a cryotrap 1 for the turbo molecular pump interposed therebetween. The vacuum chamber 3 and the cryotrap are airtightly attached to each other by the flange portion 2a at the upper end of the cryotrap 1 and the flange portion 3a at the lower end of the vacuum chamber 3, and the cryotrap 1 and the turbo molecular pump 6 are attached to the cryotrap 1. Flange 2b at the bottom of the
And the flange portion 6a at the upper end of the turbo molecular pump 6 are airtightly attached.

In the figure, the cylindrical rotor case 13 of the turbo molecular pump 6 disposed at the lowermost position is entirely machined from a single material into a cylindrical rotor 13.
The cylindrical rotor 13 is provided with
a (including the entire area of the inner diameter), a moving blade disk 7, and a blade 7a formed on this peripheral portion, and the plurality of moving blade disks 7 are fixed to the pump case 14 side. 8 and 8 are alternately arranged in the vertical direction. The cylindrical rotor 13 is fixed to the shaft 11 of the drive motor 10, and when the drive motor 10 is driven, the blade row of the blades 7a of the rotor blade disk 7 of the cylindrical rotor 13 has a speed substantially equal to the thermal motion velocity of molecules. Rotate. Further, the plurality of fixed disks 8 are fixed disk mounting members 12, 12 one by one.
And is fixed to the inner wall of the pump case 14. A suction port D for sucking the gas in the vacuum chamber is provided inside the flange 6a at the upper part of the cylindrical rotor 13, and an exhaust port 9 is provided below the turbo molecular pump 6, which is not shown. Auxiliary vacuum pump is connected.

The cryotrap 1, which is connected to the upper portion of the turbo molecular pump 6, is provided with a trap 4 made of a metallic and tubular plate member along the inner peripheral wall of a cylindrical casing 2 to form a cylindrical body. A trap 5 made of a metal and made of a circular flat plate is arranged immediately above a portion of the rotor 13 where the blades 7a are not arranged. Although not shown, these traps 4 and 5 may cool the cryotrap surface by the cooling heat of the refrigeration cycle of the refrigerator, or a refrigerant such as liquid nitrogen may be circulated in the pipe to cool the liquid. The cryotrap surface may be cooled by the cooling heat of nitrogen. However, the cryotrap surface is cooled to about 100K so that water molecules can be condensed in the traps 4 and 5.

In the vacuum chamber 3 disposed at the top in the figure, a sample is placed in a vacuum chamber C inside the vacuum chamber 3 and operations such as semiconductor manufacturing and microscope observation in a vacuum space are performed.

The structure of the cryotrap for the turbo molecular pump according to the embodiment of the present invention has been described above. Next, its operation will be described.

The traps 4 and 5 in the casing 2 of the cryotrap 1 are cooled by a cooling means (not shown) and are connected to the exhaust port 9 to drive an auxiliary vacuum pump (not shown) and a turbo molecular pump 6 as well. Motor 1
When 0 is driven, the gas in the vacuum chamber C of the vacuum chamber 3 flies from the vacuum chamber C toward the casing 2 of the cryotrap 1. Of the gas that has flown into the casing 2,
The water molecules colliding with the trap surfaces of the traps 4 and 5 are condensed here because these trap surfaces are cooled to about 100K. Hydrogen whose condensation temperature is lower than this temperature,
Gases such as argon are not condensed on this trap surface.

Gases such as water molecules, hydrogen, and argon that have not collided with the trap surface pass through the casing 2 and collide with the upper surface of the rotor blade disk 7 and the inner wall of the pump case 14. Among the gases that have collided with the respective parts in the pump case 14, the gas that has collided with the stationary surface is re-emitted from the collision surface in the direction of each arrow with a directional distribution according to the cosine law, as shown in FIG. On the other hand, of the gas that has collided with the rotor blade disk 7 that is rotating, a part of the gas is exhausted from the gap between the blades 7a and 7a, and the remaining gas is A and B in FIG.
Is emitted from the collision surface with a directional distribution as shown in (when the blade row is rotating at the same speed as the gas molecules). When the gas molecules collide with the point P of the rotor blade disk 7, a large proportion is released above the tangent line of the rotor blade disk 7 in the rotation direction, that is, above the outer peripheral direction of the rotor blade disk 7. Water molecules of the above flow to the trap 4 and are condensed on the trap surface. On the other hand, the water molecules discharged toward the center of the rotor blade disk 7 at the collision point P fly to the trap 5 and are condensed on the trap surface. As a result, most of the water molecules that have flown from the vacuum chamber to the suction port D are condensed on the trap surfaces of the traps 4 and 5. Also,
Water molecules that flow backward from the rotor blade disk 7 and the gaps between the blades 7a and 7a are also discharged in the same directional distribution, and most of them are condensed on the trap surfaces of the traps 4 and 5.

With respect to the exhaust of gas to be exhausted by a turbo molecular pump such as hydrogen and argon, the position where the trap 5 is arranged is immediately above the blade disk 7a of the rotor blade disk 7 without any row of blades. The turbo molecular pump 6 only covers a portion having no exhaust capacity, and the existence of the trap 5 does not affect the exhaust speed of the turbo molecular pump 6 for hydrogen, argon, etc. at all. Furthermore,
Since the trap 4 is arranged along the inner peripheral wall of the casing 2 of the cryotrap 1, the conductance of the cryotrap 1 is almost equal to the conductance of the casing 2 of the cryotrap 1, and a large conductance is given. The conductance is almost inversely proportional to the length of the cylindrical casing 2, but the cryotrap 1 has high performance and does not need to have a large length. Therefore, the large conductance hardly causes deterioration of the exhaust performance of the turbo molecular pump 6 for gases such as hydrogen and argon.

Next, the structure of a cryotrap for a turbo molecular pump according to a second embodiment of the present invention will be described with reference to the drawings. The operating part of the turbo-molecular pump is the same as that of the first embodiment, so a detailed description will be omitted.

FIG. 4 shows the turbo molecular pump 15 as a whole, and the pump case 16 of the turbo molecular pump 15 has a tubular shape, and a flange portion 17 is formed on the upper portion thereof. A suction port portion 17a is provided at the inner opening of the flange portion 17. A trap 18 made of a tubular metal plate is provided along the inner circumference of the pump case 16 in which the suction port 17a is formed. That is, the cryotrap for the turbo molecular pump according to the present embodiment is arranged at the suction port portion 17 a of the turbo molecular pump 15. Also, the rotor blade disk 2 of the cylindrical rotor 27
0, just above the portion where the wing 20a is not formed,
A trap 19 made of a circular metal flat plate is provided. These traps 18 and 19 are cooled to about 100 K at which the trap surfaces condense water molecules by the same method as in the first embodiment.

Next, the structure of a modification of the second embodiment of the cryotrap for a turbo molecular pump of the present invention will be described.
A description will be given with reference to the drawings.

FIG. 5 shows a turbo molecular pump 21 as a whole, and the pump case 22 of the turbo molecular pump 21 is tubular and is formed by bending in a substantially V-shape at the top. The diameter of the suction port portion 23a formed inside the flange portion 23 at the upper end becomes smaller as it goes upward. Further, along the inner peripheral surface of the pump case 22 that is bent in a V shape, a trap 24 made of a tubular metal plate material that is also bent in a V shape is arranged. In addition, the rotor blade disk 2 of the cylindrical rotor 28
A trap 25 made of a circular metal flat plate is arranged immediately above a portion of the blade 6 where the blade 26a is not formed. That is, the cryotrap for the turbo molecular pump according to the modified example of the second embodiment is also arranged at the suction port portion 23 a in the turbo molecular pump 21. Also, these traps 2
Also in Nos. 4 and 25, the trap surface is cooled to about 100K for condensing water by the same method as in the first embodiment.

As described above, FIG. 4 shows the cryotrap for the turbo molecular pump according to the second embodiment of the present invention, and FIG. 5 shows a modified example thereof. In these cryotraps as well as in the first embodiment, moisture is trapped on the trap surface. It is clear that can be efficiently condensed. Furthermore, in the second embodiment and this modification,
The casing 2 of the cryotrap 1 as in the first embodiment
Is not provided, the conductance can be made larger than that of the first embodiment, and the exhausting ability of gases such as hydrogen and argon can be improved.

Although the respective embodiments of the present invention have been described above, 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 first embodiment, the cryotrap 1 for the turbo molecular pump is provided separately from the turbo molecular pump 6, and the trap is provided in the casing 2.
If this is further duplicated and provided at the suction port of the turbo molecular pump as in the second embodiment, water molecules can be condensed more efficiently. Further, only the trap 5 may be provided in the casing 2 of the cryotrap 1 of the first embodiment, and a tubular trap may be provided along the inner peripheral wall of the suction port portion of the turbo molecular pump 6, and the combination thereof may be various. It is in.

In each of the above embodiments, 10 traps are used.
Although the temperature was set to about 0 K, in consideration of the pressure in the vacuum tank and the equilibrium vapor pressure of various gases, the trap cooling temperature is changed so that gases other than water molecules are trapped on the trap surface. Good.

[0030]

As described above, according to the cryotrap for a turbo molecular pump of the present invention, water molecules can be efficiently trapped, and a gas such as hydrogen or argon can be trapped without lowering the conductance. Can exhaust without degrading exhaust performance.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing that a cryotrap for a turbo molecular pump according to a first embodiment of the present invention is attached to a turbo molecular pump.

FIG. 2 is a diagram showing a distribution when gas to be exhausted collides with a stationary portion and is discharged.

FIG. 3A is a plan view showing a directional distribution when gas collides with a blade row of a blade disk and is discharged. B is the same side view.

FIG. 4 is a partially cutaway front view showing that the cryotrap for a turbo molecule according to the second embodiment of the present invention is disposed at the inlet of a turbo molecular pump.

FIG. 5 is a partially cutaway front view showing a modified example of the second embodiment.

FIG. 6 is a plan view of a conventional cryotrap for a turbo molecular pump.

FIG. 7 is a front view of the same.

FIG. 8A is a plan view showing a blade row of a rotor blade disk.
B is the same side view.

FIG. 9 is a cross-sectional view showing a chevron-type cryotrap for a turbo molecular pump.

FIG. 10 is a cross-sectional view showing a louver type cryotrap for a turbo molecular pump.

[Explanation of symbols]

 1 Cryo Trap 2 Casing 4 Trap 5 Trap 6 Turbo Molecular Pump 13 Cylindrical Rotor 15 Turbo Molecular Pump 17a Suction Port 18 Trap 19 Trap 21 Turbo Molecular Pump 23a Suction Port 24 Trap 25 Trap 27 Cylindrical Rotor 28 Cylindrical Rotor

Claims (2)

[Claims] 1. A tubular body having a cryotrap surface arranged along an inner circumference of a cryotrap casing attached to a suction port of a turbo molecular pump, and an uppermost blade row of a cylindrical rotor of the turbo molecular pump. A cryotrap for a turbo molecular pump, comprising: a flat plate disposed immediately above a portion where no is formed. 2. The cryotrap surface is formed with a cylindrical body arranged along an inner circumference of an inlet portion of a casing of a turbo molecular pump and an uppermost blade row of a cylindrical rotor of the turbo molecular pump. A cryotrap for a turbo molecular pump, characterized in that it comprises a flat plate disposed immediately above a portion that is not open.