JP3710584B2 - Turbo molecular pump - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention particularly relates to a turbo molecular pump suitable for use in exhausting a large volume of gas with a relatively low degree of vacuum.
[0002]
[Prior art]
In order to obtain high vacuum or ultra-high vacuum in the manufacturing process of high performance semiconductor devices, rotor blades (axial flow blades) are formed in multiple stages on a rotor that is rotatably supported in a cylindrical casing. In addition, a turbo molecular pump that obtains a high degree of vacuum by moving gas molecules from the intake port to the exhaust port by rotating the rotor at a high speed by providing fixed blades between the rotor blades on the inner wall of the casing is used.
[0003]
In order to achieve a high vacuum state in a semiconductor manufacturing apparatus or the like, it is usually necessary to increase the compression ratio to gas. As described above, the rotor blades and the stationary blades are provided in multiple stages, or the rotor blades of the rotor A screw groove is formed on the rear side. Magnetic bearings are adopted for the main shaft and the rotor from the viewpoint of maintenance and cleanliness.
[0004]
[Problems to be solved by the invention]
However, recently, depending on the semiconductor manufacturing apparatus, it is necessary to evacuate a large amount of gas and maintain the inside of the apparatus chamber below a certain pressure as the wafer diameter increases. However, the ultimate pressure when no gas flows is 10 ⁻³ to 10 ⁻⁴ Torr, and applications that do not require such a high vacuum have begun to appear. In other words, the pump requires an exhaust speed as high as several thousand L / sec, but has a use in which a high compression ratio is unnecessary. When a rotor having multistage rotor blades as described above is used for such applications, the axial length and weight increase.
[0005]
In this case, precise control is required to support the weight and size. For example, two sets of active radial magnetic bearings for controlling the radial two directions are provided above and below the rotor, and further, active axial magnetic bearings for controlling the axial direction are provided. Control is in progress. For this reason, the pump is increasingly enlarged. Furthermore, since these bearings and the motor are arranged in series, the axial length of the pump becomes long. For example, in the case of a pump with an exhaust speed of 3300 L / sec, the size of the pump body is such that the maximum diameter is D = 450 mm. On the other hand, the height H becomes 400 mm.
[0006]
And even in processes that do not require the ultimate pressure to be ultra-high vacuum, pumps that emphasize compression performance long in the axial direction are used in this way, and there is a need for a compact exhaust system and low price. In view of this, there was a need to improve.
[0007]
In recent semiconductor manufacturing apparatuses, a large amount of gas tends to be used to increase the diameter of the wafer and improve the quality of film formation. A part of the gas introduced into the vacuum chamber of the semiconductor manufacturing apparatus only contributes to the reaction, and most of the remaining gas is discharged unreacted.
[0008]
Therefore, in the future, as shown in FIG. 4 , in order to effectively use the gas, a part Q _{2 of} the gas exhausted from the vacuum chamber 31 by the high vacuum pump 35 such as a turbo molecular pump is returned to the vacuum chamber 31 again. There is a possibility that a device for improving the utilization efficiency of the unreacted gas is made.
[0009]
When gas is introduced into the vacuum chamber 31, a gas ejection device 33, which is usually called a shower head, is used in order to uniformly distribute the gas to the wafer 32. The gas to be circulated must also be returned to the vacuum chamber through a gas blowing device 33 such as this shower head. However, since this shower head is provided with several tens of holes having a diameter of 1 mm or less and gas is ejected from these holes, the conductance is very small. For example, the conductance of a shower head provided with 50 holes with a diameter of 0.8 mm is about 1 × 10 ⁻² L / s. Therefore, when returning 1000 sccm of the circulating gas into the vacuum chamber via the shower head 33, the pressure must be compressed to about 20 Torr.
[0010]
However, turbo molecular pumps and composite molecular pumps that are generally used as high vacuum pumps do not have sufficient compression capacity in applications where the gas is circulated as described above. Accordingly, in applications for circulating gas, as shown in FIG. 5, it is necessary to provide a pump 52 for compression downstream of these high-vacuum pump 51.
[0011]
Here, since the compression pump 52 exhausts the gas compressed by the high vacuum pump 51, the pumping speed may be small, so that the pump outer diameter can be reduced. On the other hand, the high vacuum pump 51 requires a large exhaust speed in order to exhaust a large amount of gas, so that the outer diameter of the pump inevitably increases.
[0012]
Therefore, in the exhaust system that circulates the gas, considering the demand for downsizing of the entire apparatus, the compression pump 52 having a small pump outer diameter is enlarged in the axial direction to satisfy the required compression performance, and the outer diameter of the pump It is desired that the high vacuum pump 51 having a large diameter is made as compact as possible in the axial direction.
[0013]
An object of the present invention is to solve these problems and provide a turbo molecular pump that is compact in the axial direction.
[0014]
[Means for Solving the Problems]
A first aspect of the present invention according to claim 1 is a turbo molecular pump in which rotor-side rotor blades and stator-side stationary blades are alternately arranged, and the rotor rotates at high speed to compress and exhaust gas. A rotating shaft and a rotating cylindrical portion; the stator has a fixed cylindrical portion disposed between the rotating shaft and the rotating cylindrical portion; and an outer peripheral portion of the rotating shaft and the fixed cylindrical portion axial magnetic bearing and a radial magnetic bearing is configured between turbomolecular pump, wherein a radial gap type motor is formed between the inner peripheral portion of the rotating tubular portion and the fixed tubular portion It is. Thereby, the bearing and the motor can be incorporated by utilizing the inner and outer peripheral portions of the fixed cylindrical portion, and the axial dimension can be shortened.
[0020]
A second aspect of the present invention according to claim 2 is a turbo molecular pump in which rotor-side rotor blades and stator-side stationary blades are alternately arranged, and the rotor rotates at high speed to compress and exhaust gas. A rotating shaft and a rotating cylindrical portion; the stator has a fixed cylindrical portion disposed between the rotating shaft and the rotating cylindrical portion; and an outer peripheral portion of the rotating shaft and the fixed cylindrical portion A turbo molecular pump characterized in that the axial and radial magnetic bearings are formed between them, and an axial gap type DC brushless motor is formed between the disk-shaped magnetic pole on the rotor side of the axial magnetic bearings and the stator. It is. Thereby, it is not necessary to attach the motor rotor by shrink fitting or the like to the cylindrical portion of the rotor where the internal stress increases while suppressing the axial dimension, and high speed rotation, long life, and the like can be achieved.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows an example of a turbo molecular pump, showing the structure of a pump rotational cylindrical portion 2 has adopted the outer rotor type disposed about the stationary shaft 1. That is, the rotating cylindrical portion 2 is rotatably supported between the cylindrical casing 3 and the fixed shaft 1 protruding from the bottom plate 4. An intake port 5 is opened over almost the entire surface of the casing 3, and an exhaust port 6 is provided at the lower part.
[0022]
Three stages of rotary blades (axial flow blades) 7 a, 7 b, 7 c are formed on the outer surface of the rotating cylindrical portion 2, and these are two fixed blades 8 a, 8 b formed on the inner surface of the cylindrical casing 3. Are sandwiched alternately. In this example, the rotating cylindrical portion 2 constitutes the rotor R, and the fixed shaft 1, the casing 3 and the bottom plate 4 constitute the stator S.
[0023]
Thus, the turbo-molecular pump are those having the three-stage rotor blades 7a, 7b, the 7c, the ratio H / D of the pump body height H and a maximum diameter D of about 0.3, large variations flat It has become.
[0024]
An annular projecting portion 9 is formed on the inner upper portion of the rotating cylindrical portion 2, while a concave portion 10 corresponding to the projecting portion 9 is formed on the upper portion of the fixed shaft 1, and the projecting portion 9 and the concave portion 10 are opposed to each other. An axial magnetic bearing 11 is formed between horizontal surfaces. This performs active control based on a position detection signal obtained by an axial sensor (not shown). A radial magnetic bearing 13 that performs active control based on a position detection signal obtained by the radial sensor 12 is disposed between the opposing cylindrical surfaces on the lower side in the two directions orthogonal to each other in this example. The rotor magnetic poles 13b are provided to face each other.
[0025]
The radial magnetic bearing 13 and the axial magnetic bearing 11 are disposed so as to be positioned so as to sandwich the center of gravity of the entire rotating cylindrical portion 2 including the blades in the axial direction. By arranging in this way, the axial bearing 11 is allowed to bear the action of the radial bearing that is generally installed also on the upper side. Since the turbo-molecular pump rotor has a large aspect ratio as described above, the arrangement as described above makes it necessary to provide only one radial bearing in the axial direction in practice.
[0026]
A DC brushless motor 14 including a permanent magnet 14a and a coil 14b is provided between the lower end of the rotating cylindrical portion 2 and the bottom plate 4. By arranging the motor at such a position, the surface of the rotating cylindrical portion 2 is used to reduce the size especially in the axial direction. Touchdown bearings 15 and 16 are formed at two locations on the upper and lower sides of the fixed shaft 1.
[0027]
This pump is used in applications that do not require high vacuum ultimate pressure and it is sufficient to compress the gas to an exhaust pressure of about 0.3 Torr. In applications where such a relatively high ultimate pressure is sufficient, high compression performance is not required, and the number of stages of the rotary blades 7a, 7b, 7c is 1-6. Therefore, the rotating cylindrical portion 2 can be flattened in the axial direction.
[0028]
Embodiments of the present Application the first invention shown in FIG. 2, the stator S has a fixed tubular portion 17, the rotating cylinder integral with the rotary shaft 18 the rotor R is surrounded by the fixed tubular portion 17 and which An inner rotor system having a shape portion 2 is employed.
[0029]
The implementation of the embodiment of FIG 2, the motor 19 is incorporated between the fixed tubular portion 17 and the rotary shaft 18 adopts the radial gap type, the bearing unit and the motor unit is different positions radially Therefore, the motor 19 does not affect the axial dimension of the pump body, and a compact pump can be provided in the axial direction.
[0030]
Figure 3 is a implementation of the present Application the second invention, the outer periphery of the disc 21 is a rotor-side magnetic pole of the axial magnetic bearing 11, DC brushless motor 14 of the axial cap type comprising a permanent magnet 14a and the coil 14b Is provided. The inner peripheral portion 2a of the rotating cylindrical portion 2 is a portion having the highest stress in the rotating body. However, according to this structure, it is not necessary to shrink-fit the motor rotor in this portion, so that the internal stress can be kept low. As a result, the rotor R can be rotated at a high speed.
[0034]
【The invention's effect】
As described above, according to the present invention, the rotational stability in the radial direction can be improved, and a compact and low-cost turbo molecular pump can be provided by omitting the bearing device.
[Brief description of the drawings]
1 is a diagram showing an example of a turbo molecular pump.
2 is a diagram showing a turbo molecular pump of implementation in the form of the first feature of the present invention.
3 is a diagram showing a turbo molecular pump of implementation in the form of a second invention.
FIG. 4 is a diagram showing an exhaust system expected in the future of a semiconductor manufacturing apparatus.
FIG. 5 is a diagram showing an exhaust system suitable as an application of the turbo molecular pump of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fixed shaft 2 Rotating cylindrical part 2a Inner peripheral part 3 Casing 4 Bottom plate 5 Intake port 6 Exhaust port 7a, 7b, 7c Rotor blade (axial flow blade)
8a, 8b Fixed blade 9 Protruding portion 10 Protruding portion 11 Axial magnetic bearing 12 Radial sensor 13 Radial magnetic bearing 14 DC brushless motor 14a Permanent magnet 14b Coil 15, 16 Touchdown bearing 17 Fixed cylindrical portion 18 Rotating shaft 19 Radial cap type Motor 20 Thread groove 21 Rotor disk for axial magnetic bearing (disk-shaped magnetic pole)
R rotor S stator

Claims (2)

In a turbo molecular pump in which rotor-side rotor blades and stator-side stationary blades are alternately arranged, and the rotor rotates at high speed to compress and exhaust gas,
The rotor has a rotating shaft and a rotating cylindrical part, the stator has a fixed cylindrical part disposed between the rotating shaft and the rotating cylindrical part, and the outer peripheral part of the rotating shaft and the fixed cylinder axial magnetic bearing and a radial magnetic bearing between the Jo portion is configured, turbo, characterized in that the radial gap type motor between the inner peripheral portion of the rotating tubular portion and the fixed tubular portion is configured Molecular pump. In a turbo molecular pump in which rotor-side rotor blades and stator-side stationary blades are alternately arranged, and the rotor rotates at high speed to compress and exhaust gas,
The rotor has a rotating shaft and a rotating cylindrical part, the stator has a fixed cylindrical part disposed between the rotating shaft and the rotating cylindrical part, and the outer peripheral part of the rotating shaft and the fixed cylinder An axial magnetic bearing and a radial magnetic bearing are formed between the cylindrical portions, and an axial gap type DC brushless motor is formed between the disk-shaped magnetic pole on the rotor side of the axial magnetic bearing and the stator. Turbo molecular pump.

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