JPH0720395Y2 - Vacuum exhaust device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention can provide a clean, high-vacuum atmosphere free from pollution in various technical fields such as semiconductor manufacturing, surface analysis, fusion experiments, and accelerators. The present invention relates to a vacuum exhaust device.

(Prior Art) Conventionally, as a means for obtaining a clean high vacuum region mainly at a pressure lower than 10 ^-1 Pa, a so-called oilless gas storage type vacuum pump such as a cryopump, a sputter ion pump, and a sublimation pump, Alternatively, a means using a gas transportation type turbo molecular pump has been put into practical use, but in order to operate these high vacuum pumps normally, it is necessary to pre-evacuate the back pressure to about 10 pa or less by an auxiliary pump.

However, as this auxiliary pump, an oil rotary pump or a roots vacuum pump equipped with an oil-lubricated bearing is applied, so these auxiliary pumps generate oil vapor, and these oil molecules are reversely diffused to the vacuum container side. And it pollutes the inside.

Therefore, conventionally, as means for solving such a difficulty, so-called foreline traps in FIG. 3 and purge gas introduction means in FIG. 4 have been devised.

That is, the means shown in FIG. 3 has an oil condensing trap 40 (cold trap) provided between a high vacuum pump 2e such as a cryopump connected to the vacuum container 1 and an auxiliary vacuum pump 22 in the subsequent stage. Is.

The means shown in FIG. 4 is provided with a purge gas introducing means 30e in front of the auxiliary vacuum pump 22 so that oil molecules do not flow backward from the auxiliary vacuum pump 22.

(Problems to be solved by the invention) However, in the former means for providing the trap 40, the trap 40 containing the oil may be regenerated without accidentally opening the air introduction valve 42 during the period when the vacuum device is stopped. Alternatively, if the pump is operated while the trap 40 is not cooled, there is a risk that oil molecules will be reversely diffused from the trap 40 or the auxiliary vacuum pump 22 to the vacuum container 1 or the high vacuum pump 2e side. Above all, there was a difficulty in its reliable workability.

On the other hand, it is known that the oil molecules usually have a remarkable reverse diffusion in the pipe in a pressure state of about 15 Pa or less, but in order to prevent this by the latter purge gas introduction means, the pipe 3a It is necessary to maintain the internal pressure at least 15 Pa at all times.

However, under such pressure conditions, it becomes difficult to start the operation of the gas storage type high vacuum pump 2e such as the cryopump,
Further, the turbo molecular pump must maintain the back pressure lower than 5 Pa during normal operation, which causes a problem that a desired high vacuum region cannot be obtained.

Incidentally, in order to eliminate such a difficulty associated with the pump operation, a compound molecular pump having a higher preliminary exhaust pressure or maximum allowable back pressure than the cryopump in the means shown in FIG. 4 is used as the high vacuum pump 2e. It is also possible to apply. However, since the composite molecular pump 2e is provided with an oil-lubricated bearing in its drive mechanism, if the valve operation of the exhaust system is mistaken, the interior of the composite molecular pump 2e and the vacuum container 1 are contaminated with oil. Cause Further, from a practical point of view, it is necessary to provide a stop valve 41 in order to prevent oil diffusion from the composite molecular pump 2e to the vacuum container 1 side when the device is stopped, but the diameter of the pipe 3 in the preceding stage of the composite molecular pump 2e is It is considerably larger than the latter pipe 3a. Therefore, the stop valve 41 inevitably becomes large in size and becomes very expensive, which causes a problem in terms of economy.

Therefore, the object of the present invention is to reliably prevent the reverse diffusion of oil molecules to the vacuum container side by a simple means, and to achieve a clean high vacuum atmosphere in the vacuum container with an inexpensive device configuration. To do.

(Means for Solving Problems) The present invention applies an oilless pump that can obtain a large exhaust speed under high back pressure conditions as a high vacuum pump in a device to which a conventional purge gas introducing means is applied. Therefore, it is configured to solve the above-mentioned conventional problems.

That is, the present invention relates to a magnetic bearing decoding molecular pump 2 connected to a vacuum container 1, an auxiliary vacuum pump 22 connected to a rear side of the magnetic bearing composite molecular pump 2, and a gas of the magnetic bearing composite molecular pump 2. In the vacuum evacuation device including the purge gas supply means 30 for supplying the purge gas to the auxiliary vacuum pump 22 side from the middle position of the vacuum evacuation path in the latter stage than the compression position and before the auxiliary vacuum pump 22, the purge gas supply means 30 Is provided with an opening / closing valve 26 for stopping the supply of the purge gas to the vacuum exhaust path, and is a vacuum exhaust path in a stage subsequent to the gas compression position of the magnetic bearing composite molecular pump 2 and in a stage preceding the auxiliary vacuum pump 22. The vacuum gauge 29 is provided in the vacuum gauge 29, and the opening / closing valve 26 is provided in the vacuum gauge 29 when the measured pressure in the vacuum exhaust path is reduced to a preset pressure value or less. It was opened by control means 28 for the valve opening and closing of the purge gas can be supplied into the vacuum exhaust path
Is provided.

(Operation) Therefore, in the vacuum evacuation device characterized by the above structure, since the magnetic bearing composite molecular pump 2 does not need oil for lubrication or the like inside thereof, the magnetic bearing composite molecular pump 2 is vacuumed. No oil pollution is caused on the container 1 side, and a purge gas is supplied to the vacuum evacuation path on the subsequent stage of the magnetic bearing composite molecular pump 2 even when the flow rate of gas sucked from the vacuum container 1 is extremely small. By supplying a purge gas from the means 30 to the auxiliary vacuum pump 22 side to increase the pressure in the exhaust path, it is possible to appropriately prevent the reverse diffusion of oil molecules from the auxiliary vacuum pump 22 such as an oil rotary pump to the preceding stage side. Become.

By the supply of the purge gas, the back pressure of the magnetic bearing composite molecular pump 2 becomes a back pressure region where a large exhaust speed cannot be obtained in the suction pressure region of a normal turbo molecular pump. In No. 2, a large pumping speed can be obtained even under such a back pressure condition. Therefore, by using the small-sized auxiliary vacuum pump 22, it is possible to quickly achieve a clean high vacuum region without oil contamination in the vacuum container 1.

Further, in the case of performing the vacuum exhaust work, the opening / closing valve 26 provided in the purge gas supply means 30 is opened before the pressure in the vacuum exhaust path is reduced to a pressure value that causes the reverse diffusion phenomenon of oil molecules. If the control means 28 is set to a closed state that prevents the introduction of the purge gas when the pressure is equal to or higher than the predetermined pressure value, the reverse diffusion of oil molecules due to the introduction of the purge gas can be automatically prevented. Moreover, when there is no fear of back diffusion of oil molecules, the supply of purge gas can be stopped to save the gas.

(Example) Hereinafter, the Example of this invention is described.

In FIG. 1, 1 is a vacuum container, and 2 is a magnetic bearing composite molecular pump connected to the vacuum container 1 through a pipe 3. As shown in FIG. 2, the pump 2 includes a large number of rotor blades 6 attached to a drive shaft 4 having a motor portion 31 and rotor blades 7 attached to a rotor 5 and the stator vanes 7 attached alternately. A screw groove 8 that exhibits a screw groove pumping action is formed in the gap with the stator 15 on the outer periphery of the rotor 5 at the rear stage of the rotor blade 6, and the gas is compressed and exhausted from the intake port 16 side to the exhaust port 17 side. Although it is a molecular pump, a magnetic bearing is adopted as a rotation support mechanism of the drive shaft 4.

That is, 9 and 9a are radial bearing electromagnets that support the upper and lower magnets 10 and 10a of the drive shaft 4 in a contactless manner. The upper and lower radial sensors 11 and 11a detect the eccentric amount of the drive shaft 4 and the drive shaft 4 The radial load is supported by suppressing the eccentric movement in the radial direction. Reference numeral 12 is a thrust bearing electromagnet which vertically holds a flange portion 13 projecting from the substantially central portion of the drive shaft 4 in a non-contact state. The thrust sensor 14 below the drive shaft 4 displaces the drive shaft 4 in the axial direction. While detecting the amount, the drive shaft 4 is constantly maintained at a predetermined constant height to support the thrust load. 18,1
Reference numeral 8a denotes a touch-down dry bearing which is provided in a non-contact state with the upper and lower parts of the drive shaft 4 and the drive shaft 4 in order to surely prevent an improper contact between the radial bearing electromagnets 9 and 9a and the magnets 10 and 10a.

The magnetic bearing composite molecular pump 2 described above has a drive mechanism section 19
No oil for lubrication is used in any of the above, and it is not necessary to use it. Reference numeral 20 denotes a communication hole through which purge gas can be introduced into the drive mechanism section 19 from the outside via a pipe 33 having an opening / closing valve 27. Reference numeral 32 denotes a connector for electric wiring to the motor section 31 and the like.

Further, in FIG. 1, reference numeral 22 denotes an auxiliary vacuum pump connected to the rear stage of the magnetic bearing composite molecular pump 2 through a pipe 3a, and an oil vacuum pump, a roots vacuum pump or the like is appropriately applied. Reference numeral 23 denotes a vacuum pipe stop valve provided in the middle of the pipe 3a.

30 is connected to the vacuum exhaust path at the latter stage of the stop valve 23, and the inside of the pipe 3a corresponds to the exhaust speed of the auxiliary vacuum pump 22.
A means for supplying a purge gas at a flow rate sufficient to maintain Pa or more, specifically, a pipe 24 having an opening / closing valve 26 connected to the pipe 3a was connected to a gas supply device (not shown) of clean nitrogen or the like. It is a thing. When the room air is used as the purge gas, it can be constituted only by an opening / closing valve 26 and an orifice through which a fixed amount of air is passed.

29 is a vacuum gauge for detecting the pressure in the pipe 3a to which the purge gas is supplied from the pipe 24, which is used for controlling the operation of the pumps 2 and 22, and the pressure set in advance for each of the valves 23, 26 and 27. A control circuit 28 for automatic opening / closing control according to the value is provided.

The vacuum evacuation device according to the present invention has the above-mentioned structure. Next, an example of its use will be described.

First, the auxiliary vacuum pump 22 and the magnetic bearing composite molecular pump 2 are simultaneously activated in an initial state where the vacuum container 1 is at atmospheric pressure and the valves 23 and 26 are closed. As a result, the pressure inside the pipe 3a on the rear side of the stop valve 23 is reduced in an extremely short time, and when the pressure inside the pipe 3a is reduced to, for example, about 15 Pa, the control circuit 28 connected to the vacuum gauge 29 causes a stop. The valve 23 is opened and the evacuation of the vacuum container 1 and the magnetic bearing composite molecular pump 2 in the preceding stage is started. At the same time, the opening / closing valve 26 is opened and the purge gas is supplied from the pipe 24 side to the auxiliary vacuum pump 22 side.

Thus, the purge gas opening / closing valve 26 is installed in the pipe 3a.
If it is set to open and close according to the measurement pressure of the vacuum gauge 29 so as to supply the purge gas into the pipe 3a so as not to reduce the pressure to less than 15 Pa, the auxiliary vacuum pump 22 moves to the magnetic bearing composite molecular pump 2 side. Therefore, the diffusion of the oil molecules is suitably prevented.

On the other hand, the magnetic bearing composite molecular pump 2 has a back pressure of 300 to 500.
Even if the pressure is as high as Pa, a large pumping speed can be obtained.
Even if the pressure is maintained at Pa or higher, its operation is not hindered and the inside of the vacuum container 1 can be evacuated to a predetermined high vacuum. Therefore, a small one may be used as the auxiliary vacuum pump 22.

Further, since the magnetic bearing composite molecular pump 2 does not use oil for any of its drive mechanism portions 19 and the like, it causes back diffusion of oil molecules from the magnetic bearing composite molecular pump 2 to the vacuum container 1 side to cause contamination. There is nothing to do. That is, the reverse diffusion of the oil molecules from the magnetic bearing composite molecular pump 2 does not occur, and the reverse diffusion of the oil molecules through the pipe 3a side in the subsequent stage is prevented by the introduction of the purge gas through the purge gas supply pipe 24. Therefore, the vacuum container 1 as well as the magnetic bearing composite molecular pump 2 is not contaminated with oil.

Further, since the magnetic bearing composite molecular pump 2 itself is oilless, if the stop valve 23 is closed while the vacuum exhaust device is stopped, oil contamination of the composite molecular pump 2 and the vacuum container 1 can be suitably prevented.

Therefore, it is not necessary to provide a large and expensive stop valve in the pipe 3 having a diameter larger than that of the pipe 3a, and the cost of the device can be significantly reduced. This kind of vacuum valve requires extremely high processing accuracy, and the cost of these valves greatly depends on the pipe diameter.
Although the valve provided in the pipe 3 is several times more expensive than the above cost, the present invention does not need to provide this expensive valve at all.

In the above-described embodiment, the purge gas can be separately introduced into the drive mechanism section 19 of the magnetic bearing composite molecular pump 2, but the purge gas intrudes into the drive mechanism section 19 harmful gas sucked by the pump 2 itself. This is to prevent it from being supplied, and this may be supplied constantly or temporarily during operation as occasion demands. Therefore, supplying the purge gas from the pump 2 is not an essential requirement of the present invention.

Further, the present invention is not limited to providing the purge gas supply means for preventing the reverse diffusion of the oil molecules from the auxiliary vacuum pump 22 in the middle of the pipe 3a as in the above embodiment. For example, as described above, the drive mechanism section 19 of the magnetic bearing composite molecular pump 2 is used.
When introducing the purge gas into the inside, the purge gas supply means 30 connected to the pipe 3a can be removed.
At first, the purge gas supplied into the drive mechanism portion 19 of the magnetic bearing composite molecular pump 2 passes through each magnetic bearing portion and flows out to the exhaust port 17 side of the pump 2, thereby forming an auxiliary vacuum pump.
This is because the reverse diffusion of oil molecules from 22 to the upper side can be prevented. The position where the purge gas is introduced must be an auxiliary vacuum pump.
It suffices that the screw groove 8 of the magnetic bearing composite molecular pump 2 is provided on the upstream side of 22 and at any position on the vacuum exhaust path downstream of the gas compression position. At least one purge gas supply means may be provided, and the specific type of purge gas does not matter.

Further, the specific configuration of the magnetic bearing composite molecular pump 2 according to the present invention is not limited to the above embodiment, and the point is that the drive shaft 4 for rotating the rotor 5 having the moving blades 6 is a magnetic bearing. Any complex molecular pump that is supported and configured to be oil-free may be used, and the specific configuration of each part can be arbitrarily changed in design.

Further, in the present invention, the set pressure at which the open / close valve 26 of the purge gas supply means 30 is opened is not limited to about 15 Pa. The reverse diffusion of oil molecules is usually remarkable at about 15 Pa or less, but this pressure value depends on various conditions such as the amount of oil molecules and the pipe diameter.
In order to more surely prevent the reverse diffusion of oil molecules, it is preferable to set the set pressure higher than that. Therefore, the set pressure may be, for example, 20 Pa or 30 Pa, and its specific set value does not matter. The point is that the on-off valve 26 provided in the purge gas supply means can be controlled correspondingly to the vacuum gauge 29 so as to automatically open when the pressure is reduced to a desired set pressure.

In addition, the present invention does not require any specific types of devices such as the auxiliary vacuum pump 22, the vacuum gauge 29, the control circuit 28 for valve opening / closing control, and the valves 23 and 26.

(Effects of the Invention) As described above, the present invention adopts an oilless magnetic bearing composite molecular pump as a high vacuum pump, and evacuates the latter side of the molecular pump and the front side of the auxiliary vacuum pump. Since the purge gas is introduced into the passage to obtain the oil, the magnetic bearing composite molecular pump does not contaminate the vacuum container side with oil, and the purge gas is introduced into the auxiliary vacuum pump side to prevent the oil from the auxiliary vacuum pump from being contaminated. Even under a relatively high back pressure condition where contamination is prevented, there is no difficulty in main vacuuming work unlike the conventional means using a cryopump, and a magnetic bearing composite molecular pump. Can be started smoothly even if its back pressure is relatively high.
It became possible to perform the main pulling work at a high pumping speed.

As a result, according to the present invention, it is possible to achieve a high vacuum region free of oil pollution at high speed and in a short time, and to provide this for a wide variety of applications such as semiconductor manufacturing, and its practical value is extremely high. It came to a high profit.

Further, since the present invention adopts the magnetic bearing composite molecular pump, it is possible to prevent oil contamination without providing a large and expensive stop valve which is required between the conventional vacuum container and the high vacuum pump. Therefore, there is an advantage that the manufacturing cost of the device can be appropriately reduced.

Further, according to the present invention, the on-off valve provided in the purge gas supply means is automatically controlled according to the measurement pressure of the vacuum gauge so as to be opened when the pressure is reduced to a preset predetermined pressure value. Under conditions where reverse diffusion of oil molecules may occur, not only can purge gas be automatically supplied to reliably prevent oil contamination, but useless purge gas supply can also be prevented as much as possible to save purge gas. It also has the effect.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a vacuum exhaust device according to the present invention. FIG. 2 is a sectional view showing an example of a magnetic bearing composite molecular pump. 3 and 4 are explanatory views showing a conventional example. 1 ... Vacuum container, 2 ... Magnetic bearing compound molecular pump 22 ... Auxiliary vacuum pump, 26 ... Open / close valve 28 ... Control means, 29 ... Vacuum gauge

Claims (1)

[Scope of utility model registration request] 1. A magnetic bearing composite molecular pump 2 connected to a vacuum container 1, an auxiliary vacuum pump 22 connected to a rear side of the magnetic bearing composite molecular pump 2, and a gas compression of the magnetic bearing composite molecular pump 2. In the vacuum exhaust device comprising the purge gas supply means 30 for supplying the purge gas to the auxiliary vacuum pump 22 side from the position of the vacuum exhaust path at the stage subsequent to the position and before the auxiliary vacuum pump 22, the purge gas supply means 30 is provided with a vacuum. An on-off valve 26 for stopping the supply of the purge gas to the exhaust path is provided, and the auxiliary vacuum pump 22 is provided after the gas compression position of the magnetic bearing composite molecular pump 2.
A vacuum gauge 29 is provided in the vacuum evacuation path in the preceding stage, and the opening / closing valve 26 is provided in the vacuum gauge 29 when the measured pressure in the vacuum evacuation path is reduced to a predetermined preset pressure value or less. A vacuum exhaust device, characterized in that a control means 28 for opening and closing the valve is provided to open the valve and supply purge gas to the vacuum exhaust path.