JPH10141273A - Combined vacuum pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent whirling of a rotor for a high vacuum pump by supporting the rotor for the high vacuum pump by a reinforcing bearing arranged on an intake side, in a combined vacuum pump. SOLUTION: A rotor 11 for a high vacuum pump is fixed to the top surface of a rotor 7 on an upper part of a second rotary shaft 2, and is housed between a pair of upper housings 12, 13. Drag grooves 14, 15 for transferring gaseous molecule to a relative moving surface of the rotor 11 are formed on the upper housings 12, 13. The rotor 11 is rotatably supported by a reinforcing bearing 30 in its center part. The bearing 30 consists of a fixing side magnetic bearing 24, a bearing housing 25, a lid plate 26, a rotary side magnetic bearing 28, a sleeve 27, and a fastening bolt 29. Since the rotary side magnetic bearing 28 is held by the sleeve 27 and is fixed to the rotor 11, the bearing 28 is rotated concentrically with the second rotary shaft 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a vacuum pump used for semiconductor manufacturing equipment and the like.

[0002]

2. Description of the Related Art A vacuum pump for creating a vacuum environment is indispensable for a CVD apparatus, a dry etching apparatus, a sputtering apparatus, a vapor deposition apparatus and the like in a semiconductor manufacturing process. In recent years, clean semiconductor processes
With the trend of high vacuum and the like, the required level of the vacuum pump is becoming more and more advanced.

[0003] In general, in a semiconductor facility, a vacuum evacuation system comprising a combination of a roughing pump (a positive displacement vacuum pump) and a turbo molecular pump is formed in order to create a high vacuum. In this system, after reaching a certain vacuum pressure from the atmospheric pressure by a roughing pump, a predetermined high vacuum pressure is obtained by switching to a turbo molecular pump.

[0004] However, with the recent compounding of semiconductor processes, a so-called multi-chamber system, in which a plurality of vacuum chambers are independently evacuated and evacuated, has become the mainstream of semiconductor processing equipment. To cope with this multi-chamber system, a vacuum pumping system consisting of a combination of a roughing pump and a turbo molecular pump is required for each chamber, but such a vacuum pumping system is required for all chambers. In such a case, there is a problem that the entire vacuum evacuation system becomes large and complicated.

To solve the above problems, Japanese Patent Application No. Hei.
No. 255798 (Japanese Unexamined Patent Publication No. 4-154991)
A wide-band vacuum pump that can evacuate from atmospheric pressure to ultra-high vacuum with one unit by forming a momentum transfer type vacuum pump on one shaft of the rotor of a positive displacement vacuum pump that synchronously operates two screw rotors by electronic control Is provided.

FIG. 4 shows an example of the vacuum pump. A first rotating shaft 101 and a second rotating shaft 102 are provided in a housing 103.
Are supported by bearings 104a, 104b, 105a, and 105b, and are stored in a state of standing vertically. Cylindrical rotors 106 and 107 are fitted and fixed to the upper ends of the first rotating shaft 101 and the second rotating shaft 102 from the outside, respectively.

[0007] The outer peripheral surfaces of the rotors 106 and 107 are screwed with each other so as to mesh with each other.
Seeds) 108 and 109 are formed. The portion where these two screw grooves 108 and 109 mesh with each other is a positive displacement vacuum pump structure portion A.

Reference numeral 110 denotes the positive displacement vacuum pump structure portion A
Discharge holes.

A small amount of high-pressure N2 gas is always supplied to the inner space inside each of the rotors 106 and 107,
Exhaust gas is prevented from entering the bearing.

A gear 1 for preventing contact between the screw grooves 108 and 109 is provided on the outer peripheral surface of each lower end of the rotors 106 and 107.
20, 121 are provided. These gears 120,
121 does not contact each other when the synchronous operations of the rotating shafts 101 and 102 are smoothly performed. The contact collision between the grooves 108 and 109 is prevented.

Each of the rotors 106 and 107 is driven for one minute by AC servo motors 122 and 123 independently provided below the rotary shafts 101 and 102, while keeping the rotation speed ratio determined by the outer diameter ratio constant. Rotate synchronously at tens of thousands of rotations. This rotation is performed by the rotation position sensors 117, 1
The position is detected by 18, and synchronous operation control of both rotating shafts 101 and 102 is performed by this detection signal. The rotation position sensors 117 and 118 are provided at the lower ends of the first rotation shaft 101 and the second rotation shaft 102, respectively, and are housed in a sensor housing chamber 119 which also serves as an oil tank for storing oil.

At the top of the second rotating shaft 102, a rotor 111 for a high vacuum pump (momentum transfer type) is provided.
Reference numerals 112 and 113 denote fixed housings for accommodating the rotor 111, respectively, and drag grooves 114 and 115 for transporting gas molecules to a relative movement surface of the rotor 111.
Are formed. A portion formed by the drag grooves 114 and 115, the fixed housings 112 and 113, and the rotor 111 is a high vacuum pump structure portion B. The inside of the housing 113 is an intake hole 116.

The above-described vacuum pump has a cantilevered support structure in which rotors for low vacuum (volume type) and for high vacuum (momentum transfer type) are arranged on the end face of each rotary shaft on the side of the intake hole 116.

Therefore, the gas flowing from the intake hole 116 does not come into contact with a bearing which requires oil lubrication or a polluting source such as a motor which is also a gas generating source, and passes through the high vacuum pump rotor 111 and the roughing pump. Rotor 10
6 and 107 are transported to the discharge hole 110 side. Therefore, the vacuum pump having the above structure can perform clean exhaust.

[0015]

However, with the recent increase in the size of the semiconductor substrate, the above-described vacuum pump having a combined structure of the positive displacement type and the momentum transfer type requires the following when increasing the pumping speed in a high vacuum region. There was such a problem.

When the rotation speed of the rotation shaft of each rotor is fixed, in order to increase the pumping speed of the pump, it is necessary to use the rotor 107.
For high vacuum pump provided on the same axis as
It is necessary to increase the outer diameter of 1. In order to obtain a high vacuum ultimate pressure, the rotor 111 needs to have a certain length. However, in order to increase the size of the rotor 111 for the high vacuum pump, it is necessary to increase the weight of the portion overhanging from the bearing support point 105a, and the above-mentioned cantilever support structure has limitations in terms of the rigidity and reliability of the bearing. is there.
That is, the rotation of the high vacuum pump rotor 111 due to a slight imbalance gives an excessively variable load to the bearing portion, resulting in a significant reduction in the life of the bearings 105a and 105b. If the composite structure with the vacuum pump remains unchanged, there is a limit in increasing the pumping speed in a high vacuum region.

The present invention is to solve the above-mentioned problems of a combined vacuum pump in which a positive displacement vacuum pump and a momentum transfer vacuum pump of a synchronous operation type by electronic control are combined.

[0018]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a plurality of roughing rotors housed in a housing and a plurality of roughing rotors fastened to each of these roughing rotors. A rotating shaft, a bearing for supporting the rotation of these rotating shafts, an intake hole and a discharge hole formed in the housing, and a plurality of motors for independently rotating and driving the plurality of rotating shafts; A plurality of motors are synchronously operated by electronic control to form a positive displacement vacuum pump that sucks and exhausts gas by utilizing a volume change of a closed space formed by the roughing rotor and the housing. A composite vacuum pump comprising a high-vacuum rotor arranged coaxially with the rotating shaft and a housing for accommodating the high-vacuum rotor to form a momentum transfer type vacuum pump. In, it relates to a composite vacuum pump, characterized in that a reinforcing bearing between the central portion of the high vacuum rotor and the stationary portion of the suction hole side of the housing.

According to the present invention, it is possible to increase the size of the high vacuum rotor without impairing the reliability and life of the bearing portion.
This has the effect of increasing the displacement in a high vacuum region.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

In the lower housing 3, a first rotating shaft 1 and a second rotating shaft 2 are supported by bearings 4a, 4b, 5a and 5b, respectively, and are accommodated in parallel in a vertically standing state. Cylindrical rotors 6 and 7 are fitted and fixed to the upper ends of the first rotating shaft 1 and the second rotating shaft 2 from the outside, respectively.
The cylindrical rotors 6 and 7 are housed in an intermediate housing 23 which is located above and communicates with the lower housing 3.
Screw grooves (a type of screw groove) 8, 9 are formed on the outer peripheral surfaces of the cylindrical rotors 6, 7 so as to mesh with each other. The portion where these two screw grooves mesh with each other is the positive displacement vacuum pump structure portion A, and the two rotors 6, 7
A discharge hole 10 is provided between the two.

Gears 20 and 21 for preventing the screw grooves 8 and 9 from coming into contact with each other are provided on the outer peripheral surfaces of the lower ends of the rotors 6 and 7. The backlash of the meshing portions of the contact preventing gears 20 and 21 is smaller than the backlash of the meshing portions of the thread grooves 8 and 9 formed on the outer peripheral surfaces of the rotors 6 and 7. Designed.
For this reason, both contact preventing gears 20 and 21 are connected to both rotating shafts 1 and 2.
When the synchronous rotation of No. 2 is performed smoothly, they do not contact each other, but in the unlikely event of this synchronization, by contacting each other prior to the contact between the two screw grooves 8 and 9, It functions to prevent a contact collision between the two screw grooves 8 and 9.

A sensor storage chamber 19 also serving as an oil tank for storing oil is provided below the housing 3. The rotation position sensor 1 is provided in the sensor storage chamber 19.
7, 18 are stored. Each of the rotors 6 and 7 is controlled by AC servo motors 22 and 23 independently provided below the rotating shafts 1 and 2 while keeping the rotation speed constant.
The motor rotates synchronously at a high speed of several tens of thousands of revolutions per minute. The rotation is detected by the rotational position sensors 17 and 18, and the synchronous operation control of the rotating shafts 1 and 2 is performed by the detection signal.

A high vacuum pump rotor 11 is fixed to the top surface of the rotor 7 fitted and fixed to the upper part of the second rotary shaft 2, and a pair of upper housings 12, 1
3. Drag grooves 14 and 15 for transporting gas molecules are formed in the upper housings 12 and 13 on the relative movement surface of the rotor 11, respectively. The portion formed by the drag grooves 14, 15 and the upper housings 12, 13 is a high vacuum pump structure portion B. still,
The inside of the upper housing 13 is an intake hole 16.

The high vacuum pump rotor 11 is rotatably supported at its center by a reinforcing bearing 30. The reinforcing bearing 30 has a cylindrical fixed magnetic bearing 24, a bearing housing 25 for accommodating the fixed magnetic bearing 24 in a central boss 25 a, and closes an upper opening of the boss 25 a of the bearing housing 25. The cover plate 26, a pipe-shaped rotating magnetic bearing 28 that is disposed in the fixed magnetic bearing 24 and that is fitted over the shaft extending above the second rotating shaft 2. Sleeve 27 for fixing to vacuum pump rotor 11, rotating magnetic bearing 2
8 comprises a fastening bolt 29 for fixing to the second rotating shaft 2.

The rotating magnetic bearing 28 is gripped by the sleeve 27 as described above, is fixed to the high vacuum pump rotor 11, and rotates coaxially with the second rotating shaft 2 concentrically. The fixed magnetic bearing 24 facing the rotating magnetic bearing 28 is housed in a boss 25 a of the bearing housing 25 and is fixed by a cover plate 26. As shown in FIG. 2, the bearing housing 25 has an air passage window 25b, and its outer peripheral portion 25c is fixed to the inner housing 13 in the upper housing using bolts 51.

As shown in FIG. 3, the rotating magnetic bearing 28 and the fixed magnetic bearing 24 have a multilayer structure in which thin magnetized rings are stacked in the axial direction, and a radial bearing of a permanent magnet repulsion type is used. Make up. The surfaces of the fixed-side magnetic bearing 24 and the rotating-side magnetic bearing 28 are each coated with a gas generation preventing coating so as not to damage the ultra-high vacuum atmosphere.

As described above, in this embodiment, since the non-contact type bearing is used, a clean atmosphere can be maintained without contamination by oil, grease or the like. In addition, if a permanent magnet type passive magnetic bearing is used, a simple configuration can be achieved as compared with an active control type magnetic bearing.

In the above embodiment, the rotation-side magnetic bearing 28 is located inside the fixed-side magnetic bearing 24, but on the contrary, the rotation-side magnetic bearing 28 is located outside the fixed-side magnetic bearing 24. You may comprise.

In the above embodiment, as a means for giving momentum to gas molecules in the high vacuum pump structure portion B, a drag groove 1 is provided in the upper housings 12 and 13 which are fixed sides.
Although 4 and 15 are provided, a configuration in which a drag groove is provided on the rotation side, that is, on the inner and outer peripheral portions of the high vacuum pump rotor 11 may be provided.

In this embodiment, the positive displacement type vacuum pump structure portion A is provided with thread grooves 8, 9 on the outer peripheral surfaces of the cylindrical rotors 6, 7, and this thread groove rotor is a gear rotor. Unlike a variant rotor such as a roots-type rotor or a roots-type rotor, the cross section perpendicular to the center axis of rotation is relatively circular, and it can be hollowed up to the vicinity of the outer periphery. It can be used for the bearing portion as in the embodiment, which contributes to downsizing of the device.

[0032]

According to the present invention, a rotor for a high vacuum pump which has been conventionally cantilevered can be supported by a reinforcing bearing provided on the intake port side. Since whirling can be prevented and the rotor for the high vacuum pump can be made large without impairing the reliability and life of the bearing portion, the displacement in the ultra-high vacuum region can be increased.

Further, by using a non-contact type magnetic bearing as the reinforcing bearing and arranging each motor on the opposite side of the intake hole, the ultra-high vacuum atmosphere is not polluted and the ultimate pressure in vacuum is not affected. It is possible to provide a vacuum pump in which the displacement is significantly improved.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing an embodiment of a combined vacuum pump according to the present invention.

FIG. 2 is a plan view showing a bearing housing.

FIG. 3 is a diagram illustrating the principle of a magnetic bearing.

FIG. 4 is a front sectional view showing a conventional broadband vacuum pump.

[Explanation of symbols]

 1, 2 Rotary shaft 3 Housing 4a, 4b, 5a, 5b Bearing 6, 7 Rotor 10 Discharge hole 11 High vacuum pump rotor 12, 13 Upper housing 16 Intake hole 22, 23 Motor 25 Bearing housing 30 Reinforcement bearing

Claims (4)

[Claims] 1. A plurality of roughing rotors housed in a housing, a plurality of rotating shafts fastened to each of the roughing rotors, and a bearing for supporting the rotation of these rotating shafts. An intake hole and a discharge hole formed in the housing, a plurality of motors for independently rotating the plurality of rotation shafts, and a synchronous operation by electronic control of the plurality of motors, A high-vacuum pump, which is configured to cooperate with the rotary shaft, constitutes a positive displacement vacuum pump that suctions and exhausts gas by utilizing a change in volume of a sealed space formed by a roughing rotor and the housing. And a housing for accommodating the high-vacuum rotor, a combined vacuum pump comprising a momentum transfer type vacuum pump. A composite vacuum pump, wherein a reinforcing bearing is provided between the central portion of the high vacuum rotor and the high vacuum rotor. 2. The composite vacuum pump according to claim 1, wherein the reinforcing bearing is a non-contact type magnetic bearing. 3. The combined vacuum pump according to claim 1, wherein each of the motors is arranged on a side opposite to the intake hole. 4. The composite vacuum pump according to claim 1, wherein a thread groove is formed on an outer peripheral surface of the high vacuum pump rotor.