JP3943905B2 - Turbo molecular pump - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a structure of a turbo molecular pump used in a semiconductor process or the like.
[0002]
[Prior art]
The semiconductor process is realized by various processes including optical processing and chemical processing. Typical examples of the optical processing include exposure processing for baking a circuit pattern on the wafer surface, and chemical processing includes, for example, surface processing such as forming a thin film on the wafer surface, etching processing, cleaning processing, and the like. It is done. In order to realize these processes, an exposure apparatus is used for optical processing, and various chemicals and various devices for safely handling these are used for chemical processing. In these various processes or various devices and equipment, as the demand for higher integration of semiconductors is increasing, each of them is required to have a high technical level and further development is required. In order to achieve this, intensive research and development are going on at various places concerned.
[0003]
In particular, if a specific technique is mentioned, there is a CVD (Chemical Vapor Deposition) technique as an indispensable technique in the semiconductor process as the above-mentioned thin film manufacturing technique when paying attention to the surface treatment process which is a chemical treatment. . This CVD is a technique for supplying a raw material gas onto a substrate such as a wafer and forming a desired thin film on the substrate through gas adsorption and chemical reaction on the substrate. This technology is indispensable for realizing high integration of semiconductors such as thinning of gates and reduction of inter-wiring capacitance.
[0004]
Among the above CVDs, low pressure CVD, plasma CVD, and the like are performed in a vacuum atmosphere, and an evacuation system is required. As such an evacuation system, a rotary pump that generally reduces pressure from the atmospheric pressure to the low vacuum range, a diffusion pump that reduces pressure from the low vacuum range to the high vacuum range, and a turbo molecular pump are used. Is done.
As is well known, the turbo molecular pump has a configuration in which gas molecules are exhausted while being compressed by a rotor rotating at high speed. Since the rotor is a member that rotates at a very high speed as described above, an aluminum alloy that is lightweight and has high stress strength is generally selected as the material.
[0005]
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 the casing 1 including the upper half 1 a and the lower half 1 b. In the casing 1, an intake port 1c is formed in the upper half 1a, and an exhaust port 1d is formed in the lower half 1b. In the casing 1, an axial flow step portion PA is provided at the upper portion and a thread groove step portion PB is provided at the lower portion. The axial flow step portion PA is mainly composed of a moving blade 5 and a stationary blade 3 provided in multiple stages, which will be described later. In the screw groove step portion PB, a spiral screw groove 13 is formed in the rotor 4 or the stator.
[0006]
More specifically, the rotor chamber 2 is provided with a rotor 4. The rotor 4 has a configuration including a rotor shaft 4a erected vertically and moving blades 5 arranged radially around the rotor shaft 4a. A stationary blade 3 is fixed to the casing upper half 1a.
A thread groove 13 is formed in the rotor 4 or the stator below the rotor blade 5.
[0007]
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 each other. Further, radial magnetic bearings 7a and 7b are respectively provided above and below the opposing surface of the rotor shaft 4a and the casing lower half 1b. Further, a ball bearing 9 provided as a radial upper protective bearing is provided at the upper end portion of the rotor shaft 4a, and a ball bearing 10 provided as a radial and thrust lower protective bearing is provided at the lower end neck portion. A rotor driving motor 11 is provided in the casing lower half 1b.
When evacuating, the motor 11 is driven to rotate the rotor 4. After the first compression is performed between the moving 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 step portion PB and flows in the direction of the exhaust port 1d. And evacuated.
[0008]
[Problems to be solved by the invention]
By the way, in the turbo molecular pump, in order to increase the compression ratio even though it is small, a multi-stage structure is provided by providing a plurality of screw groove step portions (multi-stage), that is, by providing a plurality of rotors from the outside to the inside. There is something. As an example, a turbo molecular pump having a three-stage structure is known in which a rotor is divided into two parts, an outer rotor and an inner rotor, and a cylindrical spacer is inserted into a gap between these rotors.
Conventionally, the outer rotor and the inner rotor in such a turbo molecular pump have been integrally formed so far. Therefore, even if it is attempted to form a thread groove on the outer surface side of the inner rotor, it is extremely difficult to insert a cutting tool such as an end mill into the gap, and in fact, in most cases, no thread groove is formed in the inner rotor. It was. As described above, even though the thread groove stepped portion is formed in a plurality of steps, a step not actually having a thread groove may be included, and therefore the compression ratio cannot be increased so much even if the plurality of steps are provided. There was a problem.
[0009]
This invention is made | formed in view of the said situation, and it aims at providing the turbo-molecular pump which can aim at the improvement of the performance by raising the compression ratio of gas more.
[0010]
[Means for Solving the Problems]
The invention according to claim 1 is a turbo molecular pump comprising: an axial flow step portion including a moving blade and a stationary blade; and a screw groove step portion in which a spiral screw groove is formed in a rotor. By providing a substantially cylindrical first rotor located on the outer peripheral side around the rotation axis as a rotor and a substantially cylindrical second rotor located on the inner peripheral side of the first rotor, the screw The groove step portion has a plurality of steps, and the first rotor and the second rotor are configured by separate members, and these are connected and fixed detachably directly or via another member. Features.
[0011]
As described above, the first rotor located on the outer peripheral side and the second rotor located on the inner peripheral side are configured by separate members, and these are connected and fixed. It is possible to easily and accurately perform the thread groove processing on the second rotor located on the inner peripheral side. Further, even when the required characteristics are different between the first rotor and the second rotor, by making each of them a separate member, a material according to each characteristic can be used. Furthermore, for example, plating with nickel (Ni) or the like can be performed individually, so that it is difficult to peel off and plating can be performed more accurately.
Further, since the first rotor and the second rotor can be attached and detached, one of them can be removed according to the characteristics required for the turbo molecular pump, and the characteristics such as the compression ratio and the displacement can be changed as appropriate. .
[0014]
According to a second aspect of the invention, a turbo-molecular pump according to claim 1, and the second rotor and the first rotor, characterized in that the detachable by bolt fastening.
[0015]
Thus, since the rotating part main body and the second rotor can be attached and detached by bolt fastening, both can be firmly connected and fixed with a simple configuration, and the second rotor can be easily attached and detached. Can be done.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a turbo molecular pump according to the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing an embodiment of the present invention. The turbo molecular pump 20 has a configuration in which various devices are provided inside a casing 21 constituted by an upper casing 21a, a lower casing 21b, and a base 21c. In the casing 21, an air inlet 21d is formed in the upper casing 21a, and an air outlet 21e is formed in the base 21c.
In the casing 21, an axial flow step portion 20a is provided at the upper portion and a thread groove step portion 20b is provided at the lower portion. The axial flow step portion 20a is mainly configured by a moving blade 25 and a stationary blade 23 provided in multiple stages, which will be described later, and the thread groove step portion 20b includes an outer rotor (first rotor) 36, an inner rotor (second rotor). (Rotor) 37 and a spacer 38.
[0017]
More specifically, the rotor chamber 22 is provided with a rotating portion main body 24. The rotating part main body 24 is configured to include a rotor shaft 24a erected substantially vertically and moving blades 25 arranged radially around the rotor shaft 24a, and can rotate around the rotation axis O. It has become. The rotor blade 25 has a strong structure integrally formed with an outer rotor 36 provided below the rotor blade 25, and is integrally connected and fixed to the upper end portion side of the rotor shaft 24a by fastening bolts 25a. A stationary blade 23 is fixed to the upper casing 21a.
[0018]
The outer rotor 36 is a member having a substantially cylindrical shape, and a helical thread groove 36a is formed on the outer peripheral side surface thereof. Further, an inner rotor 37, which is a substantially cylindrical member that is made of a member different from the outer rotor 36 and is slightly smaller than the outer rotor 36, is attached to the inner peripheral side of the outer rotor 36 of the rotating unit body 24. ing. That is, the outer rotor 36 and the outer rotor 36 are formed so as to form a predetermined gap, and are integrally connected and fixed to the rotating portion main body 24 by fastening the bolts 35. A spiral thread groove 37 a is formed on the outer peripheral side surface of the inner rotor 37.
The inner peripheral side has a lower rotational peripheral speed than the outer peripheral side, and therefore the circumferential stress is small. Therefore, the constituent material of the inner rotor 37 has a smaller allowable stress than the constituent material of the outer rotor 36 and is relatively inexpensive. Of course, the same constituent materials may be used.
[0019]
A substantially cylindrical spacer 38 fixed to the casing 21 is located in a gap between the outer rotor 36 and the inner rotor 37. A spiral thread groove 38 a is formed on the outer side surface of the spacer 38. That is, the screw groove step portion 20b has a three-step screw groove structure by the screw grooves 36a, 38a, and 37a, and the gas passage area in each step is reduced to prevent the backflow accurately. Yes.
[0020]
A thrust magnetic disk 26 is provided at the lower end of the rotor shaft 24a. Thrust magnetic bearings 28 are provided on the upper and lower surfaces of the thrust magnetic disk 26 so as to face each other. Further, radial magnetic bearings 27a and 27b are respectively provided above and below the opposing surface of the rotor shaft 24a and the lower casing 21b. Further, a ball bearing 29 provided as a radial upper protective bearing is provided at the upper end portion of the rotor shaft 24a, and a ball bearing 30 provided as a radial and thrust lower protective bearing is provided at the lower end neck portion. A rotor drive motor 31 is provided in the lower casing 21b.
[0021]
In the turbo molecular pump 20 configured as described above, the motor 31 is driven to rotate the rotating portion main body 24 and the inner rotor 37 during vacuum exhaust. The rotation of the rotating body 24 causes gas to be sucked from the air inlet 21d, and after the first compression is performed between the moving blade 25 and the stationary blade 23, the second compression is performed at the thread groove step portion 20b. Is called. That is, the first compressed gas in the axial flow step portion 20a flows downward (first stage) between the outer rotor 36 and the lower casing 21c, and then turns upward to return to the outer rotor 36 and the spacer. The second compression is performed at a high compression ratio by flowing between the spacer 38 and the inner rotor 37 (third stage). The high compressed gas thus obtained is evacuated from the exhaust port 21e.
[0022]
In the turbo molecular pump 20, the inner rotor 37 can be removed and the thread groove step 20b can be used as two stages. That is, if the fastening by the bolt 35 is released, the inner rotor 37 can be detached from the rotating portion main body 24.
With the three-stage structure as described above, the gas compression ratio can be increased. However, when a large displacement auxiliary pump is provided on the downstream side of the turbo-molecular pump 20, the pressure loss at the third stage. May occur, and it may not be possible to secure an appropriate displacement. In such a case, if the screw groove step portion 20b has two steps and the exhaust amount is improved even if the compression ratio is slightly reduced, an appropriate exhaust amount can be ensured according to the application.
[0023]
In the turbo molecular pump 20 according to the present embodiment, the outer rotor 36 positioned on the outer peripheral side and the inner rotor 37 positioned on the inner peripheral side are configured by separate members, and these are connected and fixed. Yes. Therefore, the machining of the thread groove 37a in the inner rotor 37, which has been considered to be very difficult in the past, can be easily and accurately performed using a cutting tool such as an end mill. While being able to carry out rapidly, the compression ratio of gas can be raised.
Further, by forming the screw groove 37a in the inner rotor 37, it becomes possible to enlarge the outer peripheral diameter of the inner rotor 37 by the height of the crest of the screw groove 37a, so that the compression ratio is further increased and the performance is improved. Can be made.
[0024]
Further, the inner rotor 37 having a lower rotational peripheral speed than the outer rotor 36 and thus having a smaller circumferential stress can be made of a material corresponding to the characteristics of the inner rotor 37. Therefore, the material cost or manufacturing cost can be reduced.
[0025]
Furthermore, since the outer rotor 36 and the inner rotor 37 are configured to be detachable, the inner rotor 37 is removed according to the characteristics required of the turbo molecular pump 20 such as the compression ratio and the displacement, and the compression ratio and the displacement are reduced. These characteristics can be changed as appropriate. Therefore, the turbo molecular pump 20 can be widely used for various applications.
[0026]
Furthermore, the rotating part main body 24 and the inner rotor 37 can be attached and detached by fastening bolts 35. For this reason, the rotating part main body 24 and the inner rotor 37 can be firmly connected and fixed with a simple configuration, and the inner rotor 37 can be easily attached and detached. That is, characteristics such as the compression ratio and displacement of the turbo molecular pump 20 can be changed easily and quickly, and workability can be improved.
[0027]
In the above-described embodiment, a three-stage structure including one outer rotor, one inner rotor, and one spacer is provided, but two or more inner rotors or spacers may be provided to further increase the structure.
[0028]
【The invention's effect】
As described above, since the turbo molecular pump according to the present invention has the above-described configuration, it is possible to improve the performance by further increasing the gas compression ratio, and to improve the characteristics according to the application. A turbo molecular pump that can be appropriately changed can be provided.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a turbo molecular pump shown as an embodiment of the present invention.
FIG. 2 is a longitudinal sectional view showing an example of a conventional turbo molecular pump.
[Explanation of symbols]
20 Turbo molecular pump 20a Axial flow stepped portion 20b Thread groove stepped portion 23 Stator blade 24 Rotating portion main body 25 Rotor blade 35 Bolt 36 Outer rotor (first rotor)
37 Inner rotor (second rotor)
38 Spacer 36a, 37a, 38a Thread groove

Claims (2)

In a turbo molecular pump including an axial flow stepped portion including a moving blade and a stationary blade, and a thread groove step portion in which a spiral thread groove is formed in the rotor,
By providing a substantially cylindrical first rotor positioned on the outer peripheral side around the rotation axis as the rotor, and a substantially cylindrical second rotor positioned on the inner peripheral side of the first rotor, While making the thread groove stepped into multiple steps,
A turbo molecular pump characterized in that the first rotor and the second rotor are composed of separate members, and are detachably connected and fixed directly or via separate members. The turbo molecular pump according to claim 1 , wherein the first rotor and the second rotor are detachable by bolt fastening.

Images