JP2589865B2 - Combined vacuum pump - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a combined vacuum pump used for semiconductor manufacturing equipment and the like.

[Conventional technology]

A vacuum pump for creating a vacuum environment is indispensable for a CVD device, a dry etching device, a sputtering device, a vapor deposition device, and the like in a manufacturing process of semiconductors and liquid crystals. In recent years, demands for vacuum pumps have become more and more advanced with the trend of clean and high vacuum semiconductor processes.

In order to create a high vacuum or an ultra-high vacuum, semiconductor equipment usually evacuates using two pumps, a roughing vacuum pump (a positive displacement type) and a turbo molecular pump (a momentum transfer type). First, after reaching a certain vacuum pressure from the atmosphere by the roughing pump, a predetermined vacuum pressure is obtained by switching to the turbo molecular pump.

(1) Roughing Pump FIG. 5 shows a thread groove type vacuum pump which is a kind of a conventional positive displacement vacuum pump (roughing pump). The conventional screw groove type vacuum pump has the unevenness of the screw grooves 106, 107 formed on each of the rotors 104, 105, and by engaging the recess and the protrusion with each other, a sealed space is created between the two. I have. When both rotors 104 and 105 rotate,
With the rotation, the volume of the closed space changes, and a suction action and a discharge action are performed.

In the screw groove type vacuum pump shown in FIG.
The synchronous rotation of 4, 105 depends on the operation of the timing gears 110a, 110b. That is, the rotation of the motor 108
The transmission from 09a to the intermediate gear 109b is transmitted to one of the timing gears 110b provided on the shafts of both rotors 104 and 105 and meshing with each other. The phase of the rotation angle of both rotors 104, 105 is adjusted by the engagement of these two timing gears 110a, 110b. In this type of vacuum pump,
As described above, since the power transmission of the motor and the synchronous rotating gears are used, the lubricating oil 111 filled in the machine working chamber in which the gears are stored is supplied to the gears for lubrication. Has become.

(2) Turbo molecular pump FIG. 6 shows a thread groove type turbo molecular pump having turbine blades, which is a kind of a conventional momentum transfer type vacuum pump. As with the above-described roughing pump, the turbo molecular pump also has a structure capable of coping with a clean semiconductor process. In the case of the turbo-molecular pump shown in FIG. 6, a magnetic bearing is used instead of a ball bearing structure using oil lubrication.

In FIG. 6, 205a and 205b are radial magnetic bearings that support the rotating shaft 207, and 206 is a thrust magnetic bearing.
A cylindrical rotor 202 is housed in a housing 201, and a turbine blade 203 is provided at an upper portion of the cylindrical rotor 202, and a thread groove 204 is provided at a lower portion. The turbo molecular pump obtains a pump action by rotating the moving blade (turbine blade) and the screw groove at a high speed to give a certain direction to the molecular motion of gas.

[Problems to be solved by the invention]

However, the above-described vacuum pump and a vacuum evacuation system combining these vacuum pumps have the following problems.

In a conventional roughing pump (displacement type vacuum pump), air is evacuated in a viscous flow region close to the atmospheric pressure, but the operating range obtained only reaches a vacuum pressure of at most about 10 ⁻³ torr from the atmosphere. On the other hand, in the above-described conventional turbo-molecular pump,
The operating range obtained reaches about 10 ^-8 to 10 ^-10 torr, but gas cannot be exhausted in a viscous flow region near atmospheric pressure. Therefore, conventionally, first, a roughing pump (for example, the above-mentioned screw groove type vacuum pump) is evacuated to about 10 ^-2 to 10 ^-3 torr, and then switched to a turbo molecular pump so as to reach the vacuum pressure of the place. I have.

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. In order to cope with the multi-chamber system, a vacuum evacuation system including a combination of a roughing pump and a turbo molecular pump is required for each chamber. However, if such an evacuation system is applied to all chambers, there is a problem that the entire evacuation system becomes large and complicated.

A proposal of disposing a turbo-molecular pump on one shaft of a positive displacement vacuum pump and integrating the two has conventionally been disclosed in, for example,
See, for example, 279281. However, in order for a turbo-molecular pump to exhibit effective exhaust performance in the molecular flow region, tens of thousands are required.
Need to rotate at rpm. On the other hand, a roughing pump requires a timing gear, which is a means for transmitting torque accompanied by mechanical movement, and the limit is at most several thousand rpm. Therefore, both rotation speeds did not match, and it was difficult to combine both.

SUMMARY OF THE INVENTION In order to solve this problem, an object of the present invention is to provide a combined pump that can draw from atmospheric pressure to high vacuum at a stroke.

[Means for solving the problem]

In order to achieve the above object, a composite vacuum pump according to the present invention includes a plurality of rotors housed in a housing, bearings for supporting the rotation of these rotors, and a fluid inlet formed in the housing. And a motor for independently rotating the plurality of rotors, and a synchronous operation of the plurality of motors by electronic control, thereby changing the volume of the enclosed space formed by the rotor and the housing. To form a positive displacement vacuum pump for sucking and discharging a fluid, and a momentum transfer type vacuum pump is provided coaxially with the plurality of rotors.

With the above-described configuration, the combined vacuum pump of the present invention can evacuate from the atmosphere to a high vacuum or an ultra-high vacuum all at once.

[Action]

The respective rotors constituting the positive displacement pump are driven by independent motors, and the respective rotors are operated synchronously using electronic control. No torque transmission is required. As a result, it is easy to increase the speed of the device. On one axis of the rotor of the positive displacement pump, a momentum transfer type vacuum pump having high exhaust performance in the molecular flow region is formed. By the high-speed synchronous control, the number of rotations can be increased to a range of tens of thousands of rpm in which the gas molecule exhaust operation is effectively performed, that is, an area where the momentum transfer type vacuum pump can exhibit sufficient exhaust performance. On the other hand, there is no limit on the upper limit of the number of revolutions of the positive displacement roughing pump, and the present invention can integrate the positive displacement roughing pump and the momentum transfer high vacuum pump.

Furthermore, by increasing the rotational speed of the roughing pump, which has conventionally been limited to several thousand rpm, to several tens of thousands of rpm, the size of the motor can be reduced. This is because, for example, if the outer diameter of the motor is the same as the power, it is approximately inversely proportional to the rotation speed.

〔Example〕

FIG. 1 shows a first embodiment of a combined vacuum pump according to the present invention. The rotating part of the vacuum pump is housed in a housing 1, and the housing has a first upper part.
It is divided into a chamber 11 and a lower second chamber 12. The first chamber 11 communicates with the second chamber below the first chamber. The first chamber 11 houses the first rotating shaft 2, and the second chamber 12 has the second rotating shaft 3 arranged in parallel with the first rotating shaft. Both rotating shafts 2 and 3
Are supported by magnetic bearings. A thrust magnetic bearing 161 is arranged opposite to the disk-shaped portions 21 and 31 of both rotating shafts. 171 is a radial magnetic bearing. Further, cylindrical rotors 4 and 5 are fitted at upper ends of both shafts 2 and 3, respectively. Screw grooves 42, 52 are formed on the outer peripheral surfaces of the rotors 4, 5 so as to mesh with each other. The portion of the two screw grooves that mesh with each other forms a positive displacement vacuum pump structure portion A, which is housed in the second chamber 12. That is, the closed space formed between the concave portion (groove) and the convex portion of the engaging portion of the two screw grooves 42, 52 and the housing 1 periodically changes in volume with the rotation of the two rotating shafts 2, 3, This volume change provides the suction / exhaust action.

Cylindrical rotor 4 remote from positive displacement vacuum pump structure A
A screw groove 43 is formed on the upper outer peripheral surface of the single shaft.
A momentum transfer type vacuum pump structure B is formed between the screw groove 43 and the inner wall of the housing 1. The vacuum pump structure B is housed in the first chamber 11. By the molecular drag action of the thread groove 43, the gas flowing from the suction hole 14 is exhausted to the space (the second chamber 12) in which the positive displacement vacuum pump is housed. Further, the gas that has flowed into the positive displacement vacuum pump is discharged to the outside through the exhaust hole 15.

The servomotors 6 and 7 for driving the rotating shafts 2 and 3 are both arranged in parallel on the side opposite to the suction side of the pump structure parts A and B.

The first rotary shaft 2 and the second rotary shaft 3 are
Thus, in the embodiment, the motor rotates at a high speed of tens of thousands of rpm. The rotation of both shafts is detected by rotary encoders 8 and 9 provided at the lower ends of the rotating shafts 3 and 2 on the side opposite to the suction side. In this embodiment, the rotors 4 and 5 are rotated in a non-contact manner at high-speed synchronous rotation by the rotation position detection signal.

Each of the rotating shafts 2 and 3 and the sealed portions of the cylindrical rotors 4 and 5 are fitted at the upper end of the rotating shaft. Therefore, the suction side of both the vacuum pump structural parts A and B has a closed structure. Therefore, the gas flowing from the suction hole 14 is transmitted to the vacuum pump structure A
→ During B, there is no direct exposure to motors and bearings. Therefore, with the structure of the embodiment using the present invention, dryness and cleanness of a vacuum pump that can cope with a process using a corrosive gas can be realized simultaneously from low vacuum to ultra-high vacuum evacuation.

Gears 44, 54 for preventing contact between the thread grooves 42, 52 are provided on the outer peripheral surfaces of the lower ends of the cylindrical rotors 4, 5, respectively. These contact preventing gears 44, 54 do not come into contact with each other when the synchronous rotation of both rotating shafts 2, 3 is performed smoothly, but in the unlikely event that the synchronization is deviated, the thread groove 42 Prior to contact between the two, the two thread grooves 4
It works to prevent 2,52 contact collisions.

In the combined vacuum pump according to the present invention, the suction port is
Only the suction port 14 provided on the upstream side of the momentum transfer type vacuum pump structure part B may be used. In this case, it is possible to pull from the atmosphere to an ultra-high vacuum at once without switching valves and the like. If the narrow slit in the momentum transfer type vacuum pump structure part B becomes an exhaust resistance, a second suction hole 19 is provided upstream of the vacuum pump structure part A, and the second suction hole 19 is provided.
You may inhale gas directly from. In this case, the evacuation time can be reduced.

When roughing is performed from the intake port 19, the first intake port
14 may be closed.

FIG. 2 shows a second embodiment of the present invention, and shows a configuration of a pump in which each rotating shaft is supported by a hydrostatic gas bearing. 16,1
Numeral 7 is an orifice provided on the fixed side facing the disk-shaped thrust bearing surfaces 21, 31 and the radial bearing surfaces of both rotating shafts. A high-pressure compressed gas is supplied to the orifice.

By the way, in a momentum transfer type vacuum pump (a turbo molecular pump or a drag pump), generally, a 10
Unless a vacuum pressure of about ^-2 to 10 ^-4 torr is maintained, sufficient exhaust performance cannot be exhibited. However, in this embodiment,
To form a hydrostatic bearing, the internal space 4 of the cylindrical rotors 4, 5 is
Compressed gas is introduced into 5,55, and there is a concern that this may degrade the exhaust performance of the momentum transfer type vacuum pump. However, in this embodiment, since the upper ends 41 and 51 of the cylindrical rotor located on the side of the intake port 14 have a closed structure, the internal spaces 45 and 55 are provided only through the vacuum pump structure portion A. It communicates with the part B. Therefore, the compressed gas that has flowed into these internal spaces 45 and 55 is blocked by the vacuum pump structure part A and does not reach the exhaust side of the vacuum pump structure part B. Therefore, the compressed gas does not hinder the evacuation action by the momentum transfer type vacuum pump structure part B.

In this embodiment, N ₂ gas is used as the compressed gas. As a result, the pressure in the space where the rotating shafts 2 and 3 and the motor are housed increases by a small amount. In this way, even when this pump is used in a process for handling a corrosive gas such as CVD or dry etching, it is possible to prevent the corrosive gas from entering the inside of the motor.

The bearing for supporting the rotating shaft is not particularly limited, but a non-contact type can further increase the speed.

FIG. 3 shows a cylindrical rotor 4, common to the first and second embodiments.
5 is an external view.

FIG. 4 shows a third embodiment of the present invention. In this embodiment, the momentum transfer type vacuum pump is provided with turbine blades so that a lower vacuum ultimate pressure can be obtained. In the vacuum pump structure portion B, in the first and second embodiments, a screw groove type drag pump is used as a means for applying a momentum to gas molecules and exhausting the gas molecules. However, in the case of the screw groove type, a vacuum pressure of about 10 ^-8 torr is the ultimate limit. Lower vacuum pressure, e.g. 10
^In order to obtain an extremely high vacuum pressure of about ^-10 torr, a method using a turbine blade is effective as a means for imparting momentum to gas molecules, but has the following problems.

In the combined vacuum pump according to the present invention, the first chamber 11 in which the vacuum pump structure B is housed starts rotating under the atmospheric pressure or an atmospheric pressure close thereto. In this case, when the device is rotated at high speed, there is a high possibility that the turbine blade is destroyed by the lift applied to the turbine blade,
Cannot use turbine blades.

However, in this embodiment, without causing the above-mentioned concerns,
The turbine blade can be used in the following manner. In FIG. 4, portions denoted by the same reference numerals as in FIG. 1 represent the same structural portions. The third embodiment differs from the first embodiment in the following points. That is, in the momentum transfer type vacuum pump structure part B, a part of the means for giving momentum to gas molecules is a turbine blade 431, and the remaining part is a screw groove 432. In addition, a second intake port 19 is provided in a part of the housing (the middle part of the thread groove type volume pump) in which the volume type vacuum pump structure portion A is stored. A circumferential groove 433 is formed in the outer peripheral portion of each rotor corresponding to the position where the second intake port 19 is provided. The circumferential groove 433 is formed to reduce the inflow path resistance of the gas sucked from the second air inlet 19.

Therefore, the positive displacement pump structure part A is composed of the upper positive displacement pump (A-1) and the lower positive displacement pump (A-
2) can be considered to be connected to the series with the second intake hole 19 interposed in the middle.

In the above configuration, the first intake port 14 is closed and the second intake port 14 is closed.
With 19 open, start pump rotation. At this time, the exhaust side of the momentum transfer type vacuum pump structure portion B is under the atmospheric pressure immediately after the start of rotation.

However, the first intake hole 14 is closed, and the space S in the space in which the momentum transfer type vacuum pump is housed has an extremely small volume. The gas in the space S is immediately discharged by the exhaust function of the upper positive displacement pump (A-1). Therefore, the vacuum side of the vacuum pump structure portion B immediately reaches a vacuum pressure of about 10 ^-2 to 10 ^-3 torr when rotation starts. Thereafter, even if the rotation speed of the pump increases to the level of tens of thousands of rpm, the turbine blades 431 of the vacuum pump structure B
Is not afraid of being destroyed despite high-speed rotation. The pressure on the suction side (vacuum chamber) of the vacuum pump structure portion B, that is, the pressure on the upstream side of the positive displacement pump (A-2) is increased by 10 ^-2 to 10 ^-3 to ^10-3 due to the action of the positive displacement pump (A-2).
After the degree of vacuum reaches about rr, the second intake port 19 is closed and the first intake port 14 is opened. After that, it can reach an extremely high vacuum of 10 ^-10 torr level by the exhaust action of gas molecules by the turbine blade.

Note that all of the means for imparting momentum to the gas molecules in the vacuum pump structure B may be the turbine blade 431.

Further, the detection method by the rotation position detection sensor does not necessarily need to be an absolute angle, and may be a method of detecting a relative position between two rotation axes.

〔The invention's effect〕

A vacuum pump according to the present invention has a positive displacement vacuum pump structure portion composed of a combination of two shaft rotors on one shaft.
Forming a momentum transfer type vacuum pump structure part;
The shaft is operated at high speed synchronously by electronic control. Therefore, the following effects can be obtained.

(1) A single unit can draw from the atmosphere to ultra-high vacuum (10 ^-8 torr or less) at once.

According to the present invention, pumps of the type having the best pumping performance in the low vacuum region and the high vacuum / ultra high vacuum region can be integrated into one pump. That is, it can combine the features of both a positive displacement vacuum pump having high pumping efficiency in a low vacuum region and a Tobo molecular pump having a low vacuum ultimate pressure and a high pumping efficiency in a high vacuum / ultra-high vacuum region.

(2) The size and size of the exhaust system can be significantly reduced.

 This is for the following reason.

The timing gear is omitted, and the speed of the motor can be increased.

In the present invention, since the individual rotors are driven by independent motors, it is not necessary to transmit a large torque using gears as in a conventional screw groove type vacuum pump. In a positive displacement pump or a positive displacement compressor, it is necessary to create a sealed space in which the volume changes by the relative motion of two or more rotors. Conventionally, complicated transmission using a transmission gear, a timing gear, or a link or a cam mechanism is required. The synchronous rotation of the two or more rotors is performed by a mechanism. By supplying lubricating oil to the timing gear and the transmission mechanism, it is possible to increase the speed to some extent, but considering the vibration, noise, and reliability of the device, the upper limit of the rotation speed is at most 10,000 rpm. Was. On the other hand, according to the present invention, the problem of lubrication of a complicated mechanism involving mechanical movement is solved as described above, and the rotating portion of the rotor can be rotated at a high speed of 10,000 rpm or more. The simplification of the device can be realized by omitting the mechanism part.

By increasing the speed of the motor, the motor can be downsized, and the pump body can also be downsized.

The power of the vacuum pump is the product of the torque and the rotation speed, and the higher the rotation speed, the smaller the torque. Therefore, according to the present invention, there is an additional effect that the motor can be downsized by reducing the torque by increasing the speed. Further, according to the present invention, since the individual rotors are driven by independent motors, the torque required for the individual motors is further reduced. As a result, as shown in the embodiment, a pump configuration in which motors are arranged in the same direction and in parallel with each other in a form built in each of the two rotating shafts can be obtained.

In the case of the conventional roughing pump shown in FIG. 5, the outer diameter of the motor 108 is much larger than the outer diameter of each of the rotors 104 and 105 because of the low speed rotation.
It is difficult to arrange the motor directly under 4, 105. Therefore, the vacuum pump using the present invention does not require the installation space for the conventional motor, and can greatly reduce the size of the pump body.

(3) Clean evacuation from low vacuum to ultra-high vacuum is possible.

According to the present invention, as shown in the embodiment, the closed side of the rotor to which the rotating shaft is fastened can be arranged in a vacuum. Therefore, the gas flowing from the suction port is not directly exposed to motors, bearings, etc. on the path from ultra-high vacuum to low vacuum. This configuration is possible because the outer diameters of the two motors provided on the side opposite to the vacuum side can be reduced by high-speed synchronous control.

If the rotor of the displacement type vacuum pump of the present invention is provided with a thread groove on the outer periphery, for example, in the case of a roots type vacuum pump, the working fluid flowing in and out after a single discharge per rotation is a large pulsation. On the other hand, in the case of the thread groove type, the flow becomes almost continuous. Therefore, the fluctuation of the torque applied to the motor of each axis is reduced. The torque fluctuation causes disturbance of the synchronous control rotation of each rotating shaft, but the adoption of a screw groove type with small torque fluctuation facilitates higher-speed and higher-accuracy synchronous control.

In the case of the screw groove type, since the structure between the suction side and the discharge side is hermetically sealed by multi-stage fitting, the adverse effect due to the internal leak is reduced, and the speed of reaching vacuum can be increased.

In addition, the screw groove type rotor is different from the irregular type rotor such as the gear type, roots type and screw type in which uneven vibration is large, and the cross section perpendicular to the rotation center axis is relatively circular, and the outer peripheral part is hollow. Can be Therefore, a large internal space can be taken, and this space can be used for a bearing portion as in the embodiment, and the size of the device can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view of a combined pump according to a first embodiment of the present invention, FIG. 2 is a sectional view of a combined pump according to a second embodiment of the present invention, and FIG. FIG. 4 (a) is a sectional view showing a third embodiment of the present invention, and FIG. 4 (b) is a perspective view showing a part of a turbine blade and a thread groove in the embodiment, FIG. FIG. 6 is a sectional view showing a conventional vacuum pump. 1 ... housing, 2 ... 1st rotating shaft, 3 ... 2nd rotating shaft, 4, 5 ... cylindrical rotor, 8, 9 ... rotary encoder

Claims (7)

(57) [Claims] A plurality of rotors housed in a housing, a plurality of shafts fastened to each of the rotors, a bearing for supporting the rotation of these shafts, and a fluid formed in the housing. A plurality of motors for independently rotating and driving the plurality of shafts; a plurality of motors for independently rotating the plurality of shafts; and the plurality of motors being synchronously operated by electronic control to form the rotor and the housing. In addition to constituting a positive displacement vacuum pump for sucking and discharging a fluid by utilizing a change in volume of the sealed space, a momentum transfer type vacuum pump is arranged coaxially with the plurality of shafts. Composite vacuum pump. 2. A composite type according to claim 1, wherein said motor further comprises a detecting means for detecting rotational position information of said motor, and said plurality of motors are synchronously operated by electronic control based on a signal from said detecting means. Vacuum pump. 3. The combined vacuum pump according to claim 1, wherein said momentum transfer type vacuum pump is a high vacuum pump or an ultra-high vacuum pump partially formed with a thread groove. 4. The combined vacuum pump according to claim 1, wherein said positive displacement vacuum pump is a screw groove type vacuum pump. 5. The combined vacuum pump according to claim 1, wherein all of the plurality of motors are arranged on a side of the shaft opposite to a fluid suction side. 6. In the vicinity of the shaft end on the fluid suction side of the shaft,
2. The roller according to claim 1, wherein the roller is fastened.
The combined vacuum pump as described. 7. The pump according to claim 1, wherein a second suction port is arranged at an intermediate portion of the positive displacement vacuum pump, and the momentum transfer type vacuum pump has turbine blades.
The combined vacuum pump as described.