JP2004116354A - Turbo molecular pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a turbo molecular pump capable of realizing high back-pressure by a rotor with light weight and high rigidity. <P>SOLUTION: The rotor 4 having an outer surface on which a rotor blade 5 is radially disposed and fixed, to a rotor shaft 4a is provided with a boss part 14 of a hollow and approximately conical shape having inner and outer surfaces expanded in diameter toward an exhaust port side. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a turbo molecular pump used as a vacuum pump for a semiconductor manufacturing apparatus or the like.
[0002]
[Prior art]
2. Description of the Related Art Semiconductors are manufactured through various processes such as optical processing and chemical processing. Typical processing examples of optical processing include, for example, exposure processing for printing a circuit pattern on a wafer surface, and typical processing examples of chemical processing include, for example, surface processing for forming a thin film on a wafer surface, Examples include an etching process and a cleaning process.
In the surface treatment, there is a CVD (Chemical Vapor Deposition) technology as a manufacturing technology that has become essential in semiconductor manufacturing. The CVD is a technique in which a raw material gas is supplied to a substrate such as a wafer, and a thin film is formed on the substrate through gas adsorption and chemical reaction on the substrate. This technology is indispensable for realizing high integration of semiconductors.
[0003]
Among the above-mentioned CVDs, low-pressure CVD, plasma CVD, and the like are performed in a vacuum atmosphere, and require a vacuum exhaust device. In this vacuum evacuation apparatus, a configuration in which a plurality of pumps are combined, such as a rotary pump, a diffusion pump, and a turbo molecular pump, capable of performing multi-stage evacuation from the atmospheric pressure is generally used.
[0004]
Next, the turbo molecular pump will be described in detail. As shown in FIG. 2, the turbo molecular pump P has a configuration in which various devices are provided inside a casing 1 including an upper half 1a and a lower half 1b. In the casing 1, an intake port 1c is formed in an upper half 1a, and an exhaust port 1d is formed in a lower half 1b. Inside the casing 1, an axial flow step portion PA is provided at an upper portion, and a thread groove step portion PB is provided at a lower portion. The axial flow step portion PA is mainly composed of moving blades 5 and stationary blades 3 provided in multiple stages described later. In the screw groove step portion PB, a spiral screw groove 13 is formed in the rotor 4 or the stator.
[0005]
More specifically, a rotor 4 is provided in the rotor chamber 2. The rotor 4 has a configuration in which a rotor shaft 4a that stands vertically and a moving blade 5 that is radially arranged around the rotor shaft 4a are provided. Further, a stationary blade 3 is fixed to the casing upper half 1a.
A thread groove 13 is formed below the rotor blade 5 in the rotor 4 or the stator.
[0006]
A thrust magnetic disk 6 is provided at the lower end of the rotor shaft 4a. Thrust magnetic bearings 8 are provided on the upper and lower surfaces of the thrust magnetic disk 6 so as to face the same. Radial magnetic bearings 7a and 7b are provided above and below an opposing surface of the rotor shaft 4a and the lower casing half 1b, respectively. Further, a ball bearing 9 provided as an upper radial protection bearing is provided at the upper end of the rotor shaft 4a, and a ball bearing 10 provided as a lower protection bearing for radial and thrust is provided at the lower end neck. Further, a rotor driving motor 11 is provided in the lower casing half 1b.
At the time of evacuation, the motor 11 is driven to rotate the rotor 4. After the first compression is performed between the rotor blade 5 and the stationary blade 3 by the rotation of the rotor 4, the second compression is performed by the thread groove 13 of the thread groove stepped portion PB, and the second compression is performed in the direction of the exhaust port 1d. Is evacuated.
[0007]
In the turbo molecular pump P, conventionally, in order to improve the exhaust capacity, for example, the length of a rotor blade (moving blade) and the length of a stator blade (static blade) are sequentially reduced to be shorter toward the exhaust port side. In some cases, the radial gap between the stator and the stator is gradually narrowed (for example, see Patent Document 1).
[0008]
[Patent Document 1]
Japanese Patent Publication No. 6-5076 (Page 2, Figure 1)
[0009]
[Problems to be solved by the invention]
Incidentally, an auxiliary pump having a capacity corresponding to the performance of the turbo-molecular pump is generally installed on the back pressure side of such a turbo-molecular pump in order to improve the exhaust capacity. In the turbomolecular pump having the axial flow step and the thread groove step as described above, a high back pressure is obtained by elongating the screw groove step, and the capacity of the auxiliary pump is suppressed to a small value to reduce cost. Is required.
[0010]
However, when the thread groove step length is increased, the rigidity of the rotor is reduced, the natural frequency is reduced, and there is a problem that resonance occurs below the rated rotation speed. To cope with this problem, it is necessary to increase the natural frequency by increasing the rigidity of the rotor itself and to suppress the resonance at or below the rated rotational speed, while the weight of the rotor is also required to be reduced.
[0011]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a turbo-molecular pump that realizes a high back pressure by using a lightweight and highly rigid rotor.
[0012]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above problems.
That is, the turbo-molecular pump according to claim 1 is a turbo-molecular pump including a rotor shaft, and a rotor fixed to the rotor shaft and having rotor blades radially arranged and fixed on an outer surface thereof. It is characterized in that a hollow substantially conical boss portion whose inner and outer surfaces increase in diameter toward the exhaust port side is provided.
According to the turbo-molecular pump according to the first aspect, since the rotor is provided with the hollow substantially conical boss, the rigidity can be improved while the weight of the rotor is reduced, and the natural frequency can be increased.
[0013]
In the turbo-molecular pump according to a second aspect, in the turbo-molecular pump according to the first aspect, the rotor has an axial flow step portion provided with the rotor blades and a thread groove step portion formed with a thread groove. It is characterized by:
According to the turbo molecular pump according to the second aspect, since the rigidity of the rotor is high and the natural frequency is large, the thread groove step can be provided long, and the back pressure is increased to reduce the size of the auxiliary pump and save labor. be able to.
[0014]
According to a third aspect of the present invention, there is provided the turbo-molecular pump according to the first or second aspect, wherein the boss portion is provided at a position other than a fixed portion between the rotor and the rotor shaft. And
According to the turbo-molecular pump according to the third aspect, since the substantially conical boss portion is provided at a position other than the fixed portion having a small moment of inertia, the rigidity of the rotor can be effectively improved.
[0015]
A turbo-molecular pump according to a fourth aspect is characterized in that, in the turbo-molecular pump according to any one of the first to third aspects, the boss portion is provided immediately near the fixed portion.
According to the turbo-molecular pump according to the fourth aspect, since the substantially conical boss portion is provided immediately near the fixed portion where a large bending moment occurs, the rigidity of the rotor can be effectively improved.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the turbo-molecular pump of the present invention will be described below with reference to the drawings, but it is needless to say that the present invention is not limited to these. In the description of the present embodiment, differences from the conventional turbo-molecular pump will be mainly described, and the other parts are the same as the conventional turbo-molecular pump, and description thereof will be omitted (the same configuration as the conventional turbo-molecular pump). Elements are denoted by the same reference numerals and description thereof is omitted).
The turbo-molecular pump according to the present embodiment is provided as a part of an exhaust system together with a rotary pump, a diffusion pump, and the like, for example, in a CVD apparatus (not shown) used in semiconductor manufacturing, and is used for exhausting the inside of a chamber. Device.
[0017]
FIG. 1 is a longitudinal sectional view showing a portion around a rotor blade of the turbo-molecular pump of the present embodiment.
[0018]
The turbo molecular pump of the present embodiment is particularly characterized by the structure of the boss portion of the rotor 4. Therefore, a new reference numeral 14 is given to the boss portion of the rotor 4, and the description will be made focusing on this. I do.
The rotor 4 is a component that compresses the introduced fluid (hereinafter, referred to as exhaust gas g), and is coaxially fixed to the upper end of the rotor shaft 4a by a plurality of set screws, and is radially arranged and fixed to the outer surface of the rotor blade ( (Rotor blades) 5. The rotor 4 has an axial stepped portion PA for compressing exhaust gas g while sending it in the direction of the rotation axis of the rotor shaft 4a (downward in FIG. 1), and an exhaust gas g introduced from the axial flow stepped portion. And a screw groove step portion PB which further compresses the screw groove 13 while feeding it into the flow path of the screw groove 13 formed spirally around the rotation axis CL.
[0019]
The axial flow step portion PA includes a plurality of blades (moving blades 5) radially formed on the outer surface of the rotor 4 around the axis CL in multiple stages, and the flow of the exhaust gas g between the blade and the stator blades 3. By forming a path and rotating together with the rotor shaft 4a, the exhaust gas g is sent out while being compressed in the direction indicated by the arrow f1 in FIG. A part of the rotor blade 5 is provided on an outer surface of a hollow boss portion 14 whose inner and outer surfaces increase in diameter toward the exhaust port 1d side.
[0020]
The screw groove step portion PB has a screw groove 13 on the outer surface, and forms a screw groove flow path between the screw flow path forming members 1b1 and 1b2 attached to the lower casing 1b side. It is configured integrally and coaxially with the unit PA. When the screw groove stepped portion PB rotates together with the rotor shaft 4a, the exhaust gas g in the screw groove 13 is sent out in the arrow f2 direction while being further compressed, and is discharged from the exhaust port 1d (see FIG. 2). It is being discharged.
[0021]
That is, the rotor 4 is provided with a boss portion 14 provided with a part of the moving blades 5, a cylindrical portion provided above the boss portion 14 and provided with the remaining moving blades 5, and provided below the boss portion 14. And is formed on the rotor shaft 4a via a fixed portion at the center.
The weight of the rotor 4 is reduced by the provision of the hollow substantially conical boss portion 14 having a substantially uniform wall thickness at a portion (lower portion) immediately adjacent to the fixed portion, and the rotor 4 has a moment of inertia generated here. Is reduced, and the rigidity against the moment due to the rotation of the rotor shaft 4a is increased.
[0022]
According to the turbo-molecular pump of the present embodiment described above, the provision of the boss portion 14 makes the rotor 4 lightweight and rigid, so that the thread groove step portion PB is formed long and the back pressure is reduced. Can be enhanced.
[0023]
In the embodiment described above, the rotor blades 5 are provided on the outer surfaces of the cylindrical portion and the boss portion 14 as the cylindrical portion having the rotor blade 5 and the boss portion 14 and the cylindrical portion having the thread groove step portion PB in order from the top. However, the present invention is not limited to this. For example, the outermost portion of the boss portion 14 may be provided with a substantially conical portion and a lower cylindrical portion without providing the uppermost cylindrical portion. It goes without saying that the rotor may be configured such that all of the rotor blades are provided in the boss portion.
[0024]
【The invention's effect】
The turbo molecular pump according to claim 1 of the present invention employs a configuration in which a hollow substantially conical boss portion whose inner and outer surfaces expand toward the exhaust port is provided on the rotor.
According to this configuration, the hollow cone having a substantially uniform thickness and a small deformation with respect to a load can improve the rotor rigidity and reduce the moment of inertia by reducing the weight of the rotor, thereby suppressing damage to the rotor. be able to. Further, even when the rotor is broken, the broken pieces are thin and lightweight, so that damage to other members such as the casing due to scattering of the broken pieces can be suppressed.
[0025]
The turbo molecular pump according to claim 2 of the present invention employs a configuration in which the rotor has an axial flow step provided with rotor blades and a screw groove step formed with a screw groove.
According to this configuration, by providing a long thread groove step portion for the rotor having high rigidity and a large natural frequency, a turbo molecular pump with high back pressure can be realized. Therefore, the size of the auxiliary pump provided on the back pressure side of the turbo-molecular pump can be reduced, and the size and cost of the entire vacuum exhaust device can be reduced.
[0026]
The turbo molecular pump according to claim 3 of the present invention employs a configuration in which the boss portion is provided at a position other than the fixed portion between the rotor and the rotor shaft.
According to this configuration, since the substantially conical boss portion is provided at a position other than the fixed portion having high rigidity, the rigidity of the entire rotor is effectively improved and the natural frequency is increased. A rotor having a portion can be employed, and a turbo molecular pump with a high back pressure can be realized. Therefore, the size of the auxiliary pump provided on the back pressure side of the turbo-molecular pump can be reduced, and the size and cost of the entire vacuum exhaust device can be reduced.
[0027]
The turbo molecular pump according to a fourth aspect of the present invention employs a configuration in which the boss is provided immediately adjacent to the fixed portion.
According to this configuration, the substantially conical boss portion is provided in the immediate vicinity of the fixed portion where a large bending moment occurs, so that the rigidity of the entire rotor is effectively improved and the natural frequency is increased, so that a longer screw is used. A rotor having a groove step can be adopted, and a turbo molecular pump with a high back pressure can be realized. Therefore, the size of the auxiliary pump provided on the back pressure side of the turbo molecular pump can be reduced, and the size and cost of the entire vacuum exhaust device can be reduced.
[Brief description of the drawings]
FIG. 1 is a view showing one embodiment of a turbo-molecular pump of the present invention, and is a longitudinal sectional view showing a peripheral portion of a rotor blade.
FIG. 2 is a perspective sectional view showing a conventional turbo-molecular pump.
[Explanation of symbols]
1d exhaust port 4 rotor 4a rotor shaft 5 rotor blade (rotor blade)
13 ... thread groove 14 ... boss part P ... turbo molecular pump PA ... axial flow step part PB ... screw groove step part

Claims (4)

In a turbo molecular pump having a rotor shaft and a rotor fixed to the rotor shaft and having rotor blades radially arranged and fixed on the outer surface thereof,
A turbo-molecular pump, wherein the rotor is provided with a hollow substantially conical boss portion whose inner and outer surfaces increase in diameter toward an exhaust port side. The turbo molecular pump according to claim 1, wherein the rotor has an axial flow step provided with the rotor blades and a screw groove step formed with a screw groove. 3. The turbo-molecular pump according to claim 1, wherein the boss is provided at a position other than a fixed portion between the rotor and the rotor shaft. 4. The turbo-molecular pump according to any one of claims 1 to 3, wherein the boss is provided in the immediate vicinity of the fixed part.

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