JPH09317688A - Turbo-molecular pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a turbo-molecular pump capable of corresponding up to ultra-high vacuum, favourably in an exhaust characteric of gas small in molecular weight, especially steam, in a short period of cooling time, at low initial running cost and with low oscillation. SOLUTION: This pump is constituted by having a rotor 24 furnished with a plural number of moving blades 22 and a stator 28 furnished with a plural number of stationary blades 26 and to take up gas moleculars from a suction port 36, to compress them and to discharge them from an exhaust port 38. A cold trap 50 using liquid nitrogen as a freezing mixture is provided on the suction port 36 of a turbo-molecular pump, a temperature sensor 54 is provided on this cold trap 50, a solenoid valve 56 or a flow rate adjusting valve is provided on a freezing mixture piping 52 to supply liquid nitrogen to the cold trap 50, and the solenoid valve 56 or the flow rate adjusting valve is controlled so that temperature of the cold trap 50 is in a specified region.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combination of a plurality of moving blades and stationary blades, which are relatively rotated under conditions of low pressure such that collisions of gas molecules can be ignored. To obtain a vacuum pump or turbo molecular pump.

[0002]

2. Description of the Related Art In general, a turbo molecular pump has different exhaust performance depending on the molecular weight of the gas molecule to be handled in the exhaust theory. In the case of gas molecules having a small molecular weight, the exhaust performance will be significantly reduced. As the gas having a small molecular weight, the presence of water vapor has a bad influence.

When a part of a system equipped with a turbo molecular pump is opened to the atmosphere and the atmosphere flows into the system, residual gas in a vacuum of about 10 ⁻⁴ Torr to ^{10 −10} Torr created by the turbo molecular pump is Most of it is water vapor. The residual water vapor adversely affects the vacuum degree and the vacuum environment. Therefore, a turbo molecular pump with a cold trap in which a cold trap is provided at the intake port of the turbo molecular pump has been developed and is generally available as a technique for improving the exhaust rate of water vapor.

A conventional turbo molecular pump with a cold trap is described in detail in Japanese Patent Laid-Open No. 25792/1993, but here, it will be briefly described with reference to FIG. The turbo molecular pump 20 includes a rotor 24 having a plurality of moving blades 22 and a stator 28 having a plurality of stationary blades 26 arranged between the moving blades 22. The rotor 24 is attached to the motor shaft 32 of the motor 30, and the stator 28 is provided inside the casing 34.

An intake port 36 and an exhaust port 38 are formed in the casing 34, and a plurality of moving blades 22 and stationary blades 26 are provided on the downstream side of the intake port 36 (the side near the exhaust port in the flow path).
A protection net 40 for protecting this is provided on the upstream side of the. A shut-off valve (not shown) is arranged upstream of the intake port 36. In addition to the above configuration, the turbo molecular pump 20 of FIG. 4 is provided with a cold trap 42 at its intake port 36. This cold trap 42 is connected to a refrigerator 46 via a refrigerant pipe 44.

When the turbo molecular pump with the cold trap performs the exhaust operation, the shutoff valve provided on the upstream side of the intake port 36 is opened and the refrigerator 40 is operated to deliver the refrigerant to the cold trap 42. And cool. Then, the gas is sucked into the pump by rotating the moving blade 22, and at this time, the water vapor contained in the gas is selectively collected by freezing by the cold trap 42. As a result, the exhaust performance of the turbo molecular pump is improved, and a high-quality vacuum with a high degree of vacuum can be created. In other words, by adding this cold trap 42, the exhaust speed of water vapor is dramatically increased, and in our experimental example, a pump with an 8-inch opening diameter has a capacity of 750 L / S to 320.
It became 0L / S.

[0007]

The cooling temperature of the cold trap of the turbo molecular pump with a cold trap is
Depending on the required degree of vacuum, the higher the degree of vacuum, the lower the cooling temperature. Therefore, Japanese Patent Laid-Open No. 2-5792 discloses that the cold trap is cooled by the refrigerator that can obtain −100 ° C. to −190 ° C. Practically, a refrigerator that uses a mixture of five or more kinds of refrigerants as a working refrigerant and obtains an ultralow temperature by a cascade method is used.

However, the above refrigerator has the following drawbacks. The ultimate temperature is about -150 ° C. It is not possible to create the ultra-high vacuum required for high integration of semiconductors. Due to the CFC problem, there are few refrigerants that can be used, and there is a possibility that they cannot be used in the future. For this reason, in order to solve the above-mentioned drawbacks, the number of cold trap traps using a single-stage helium refrigerator has recently increased. However, this refrigerator also has the following drawbacks. The initial cost is expensive. There is vibration. Cooling takes time.

Further, as another cooling method, there is a method of using liquid nitrogen, but since liquid nitrogen was conventionally used as a dripping flow, there was a drawback that the running cost was high.

Further, it is preferable to heat the cold trap in order to shorten the regeneration time. In the above-mentioned prior art, the cold trap is directly provided with a heater for heating. For this reason, the heater was on the vacuum side, which was a major source of contamination, and as a result, an ultrahigh vacuum could not be obtained.

The present invention has been proposed in view of the above-mentioned drawbacks of the prior art, and has a good exhaust characteristic of a gas having a small molecular weight, especially water vapor, a short cooling time, and an inexpensive initial running cost. It is an object of the present invention to provide a turbo molecular pump that can handle ultra-high vacuum with low vibration.

[0012]

A turbo-molecular pump of the present invention has a rotor having a plurality of moving blades and a stator having a plurality of stationary blades, and takes in gas molecules from an intake port and compresses them. In the turbo molecular pump that discharges from the exhaust port,
A cold trap using liquid nitrogen as a cryogen is provided at the intake port, a temperature sensor is provided at this cold trap, and a solenoid valve or a flow rate adjustment valve is provided at the pipe supplying liquid nitrogen to the cold trap. The electromagnetic valve or the flow rate adjusting valve is controlled so that the temperature of the cold trap falls within a predetermined range.

Here, the temperature control range of the cold trap is preferably -150 ° C to -196 ° C during operation exhaust of the turbo molecular pump and during operation exhaust of the cold trap.

According to the turbo molecular pump of the present invention, when performing the exhaust operation, liquid nitrogen is supplied to the cold trap to cool it with the shutoff valve provided upstream of the intake port opened. Initially, the temperature indicated by the temperature sensor provided on the cold trap is higher than a predetermined range, that is, a temperature range of −150 ° C. to −196 ° C., which is preferable for obtaining good exhaust performance, and therefore, the solenoid valve or the flow control valve Is almost the maximum opening, and a large amount of liquid nitrogen is supplied to the cold trap. In this way, the cold trap is rapidly cooled to a predetermined temperature range.

Then, the turbo molecular pump main body sucks gas into the pump by rotating the moving blade, and at this time, the water vapor contained in the gas is selectively collected by freezing by the cold trap. As a result, the exhaust performance of the turbo molecular pump is improved, and a high-quality vacuum with a high degree of vacuum can be formed. Further, a gas having a small molecular weight which is not collected by freezing, such as hydrogen and helium, is also cooled by the cold trap, so that the temperature thereof is lowered, the gas molecule velocity is slowed down, and the exhaust performance of the turbo molecular pump is improved. As a result, it is possible to solve the problem in the conventional turbo molecular pump, that is, the poor exhaust performance of a gas having a small molecular weight, particularly steam.

During normal operation and exhaust of the turbo molecular pump,
For example, the cold trap opens and closes the solenoid valve and adjusts the opening degree of the flow rate adjusting valve so that the temperature falls within the temperature range of −150 ° C. to −196 ° C., so that the flow rate of liquid nitrogen is reduced and running cost is reduced.

On the other hand, after the evacuation operation is performed for a predetermined time, it is necessary to perform a regeneration operation in which the water vapor frozen in the cold trap is thawed and released. In the case of the step of performing such a regeneration operation, the shutoff valve may be closed and the vapor trapped in the cold trap may be sublimated. By providing a heater in the pipe for supplying liquid nitrogen to the cold trap, the regeneration process can be performed easily and quickly.

By providing a heater in a coolant pipe for supplying liquid nitrogen to the cold trap, or by joining a pipe for supplying nitrogen gas to the coolant pipe, the cold trap is heated by the nitrogen gas and a regeneration operation is performed. It can be carried out.

Therefore, since there is no contamination factor such as a heater in the vacuum exhaust system, it is easy to obtain an ultrahigh vacuum. Moreover, if the temperature of the cold trap during regeneration is controlled below 0 ° C,
The steam trapped on the cold trap surface sublimates without liquefying, and the turbo molecular pump promptly discharges this, and since it does not liquefy, droplets do not fall into the turbo molecular pump. It's safe.

As described above, according to the turbo molecular pump of the present invention, water vapor can be efficiently discharged, and further, low vibration, shortening of cooling time, reduction of initial running cost, ultra-high vacuum, and safety. The improvement of sex has been achieved.

In the present invention, the shape of the cold trap and the heat transfer area can be appropriately selected based on the components of the gas to be exhausted, the exhaust operation time, the ultimate vacuum level and other conditions.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. A turbo molecular pump, generally designated by 20, is connected to a vacuum chamber 10 of a semiconductor manufacturing apparatus, for example, via a shutoff valve 15.

The turbo molecular pump 20 includes a plurality of moving blades 22.
And a stator 28 to which a plurality of stationary blades 26 arranged between the moving blades 22 are attached. The rotor 24 is attached to the motor shaft 32 of the motor 30, and the stator 28 is provided inside the casing 34. An intake port 36 and an exhaust port 38 are formed in the casing 34, and a protective net 40 for protecting the moving blades 22 and the stationary blades 26 is provided on the downstream side of the intake port 36.

In addition to the above configuration, the turbo molecular pump 20 of FIG. 1 is provided with a cold trap 50 at its intake port 36. This cold trap 50
Is composed of, for example, a combination of a heat transfer tube and a heat transfer plate for expanding a heat transfer area.
4 are provided. A coolant pipe 52 for supplying liquid nitrogen from the outside to the cold trap 50 is provided, and an electromagnetic valve 56 (which may be a flow rate adjusting valve) and a heater 5 are provided therein.
8 is provided. Further, the controller 6 for controlling the solenoid valve 56 so that the temperature of the cold trap 50 falls within a predetermined range based on the output signal of the temperature sensor 54.
0 is provided.

The operation of the turbo-molecular pump thus constructed will be described below. When the turbo molecular pump is operated with the shutoff valve 15 opened to draw the chamber 10 to a vacuum, the controller 50 opens and closes the solenoid valve 56 based on the output signal of the temperature sensor 54. At first, the temperature sensor 54 indicates the normal temperature, so the electromagnetic valve 56 is almost opened, and the maximum flow rate is flown until the measured value of the sensor falls within a predetermined temperature range for cooling. Therefore, the cold trap 50 enters a predetermined temperature range and starts operating in a short time. Conventionally, it took 1 hour or more to reach a predetermined temperature in cooling with a helium refrigerator, but in the present invention, it takes 15 hours or more.
It was less than a minute.

When the cold trap 50 is cooled to a predetermined temperature, the motor 30 rotates and the turbo molecular pump 2
0 is driven. The gas sucked in through the intake port 36 is guided to the cold trap 50, and the water vapor in the gas is
The cold trap 50 collects ice. As a result, the exhaust efficiency of the turbo molecular pump 20 is improved, and a high-quality vacuum having a high degree of vacuum can be obtained in the chamber 10. In addition, gas molecules having a small molecular weight other than water vapor (hydrogen, helium, etc.) are not collected by freezing, but collide with the cold trap 50 to lower the gas temperature,
As a result, the blade speed ratio is increased, and the exhaust performance of the pump 20 is improved.

Referring to the graph of the saturated vapor pressure of water vapor shown in FIG. 2, the saturated vapor pressure at −85 ° C. is 10 ⁻⁴ Tor.
Since it is 10 ^-10 Torr at r-140 ℃, it is -100 ℃
It will be understood that if the cold trap 50 can be cooled below, the water vapor can be efficiently collected by ice to perform the exhaust operation, and the degree of vacuum is improved. However, the ultimate degree of vacuum in a vacuum chamber of a recent semiconductor manufacturing apparatus becomes higher as the degree of integration of semiconductors becomes higher, and a degree of vacuum higher than 10 ⁻⁹ to 10 ⁻¹⁰ Torr is required. For this reason, it is preferable to cool the cold trap 50 to −150 ° C. or lower, which allows stable and freezing of water vapor.

However, if the cold trap 50 is cooled too much, it is possible that even a gas other than the water vapor which is originally desired to be frozen will be frozen. For example, when the chamber 10 is the process chamber of the sputtering apparatus and the argon gas is supplied as the process gas, the turbo molecular pump 20 constantly exhausts the argon gas. For this reason, as soon as the cold trap 50 freezes and collects the argon gas, the argon is accumulated on the cold trap 50, and the regeneration operation is required at short intervals.

In the apparatus of FIG. 1, the cold trap 5
The temperature of 0 was cooled to -196 [deg.] C., and it was investigated whether or not ice collection was carried out by flowing argon gas, but it was not collected at all. Therefore, the temperature control range of the cold trap 50 is preferably -150 ° C to -196 ° C.

When the turbo molecular pump continuously evacuates, the controller 60 controls the solenoid valve 56 so as to maintain the temperature of the cold trap 50 within a predetermined range. The electromagnetic valve 56 is closed when the temperature of the cold trap 50 is lower than a predetermined value, and is opened when the temperature is higher than the predetermined value. In this manner, the opening / closing of the solenoid valve 56 is repeated to suppress the flow rate of liquid nitrogen to the necessary minimum, so that the running cost can be reduced.

The turbo-molecular pump 20 shown in FIG. 1 needs to be exhausted for a predetermined time and then regenerated to release and release the water molecules trapped in ice. In this case, the shutoff valve 15 on the upstream side of the intake port 36 is closed, and the heater 58 provided in the pipe 52 for supplying liquid nitrogen is operated. As a result, the liquid nitrogen inside the pipe 52 is heated and vaporized, and the nitrogen gas flows into the cold trap 50. As a result, the steam trapped in the cold trap 50 is heated, sublimates, and is discharged by the action of the moving blades 22 and the stationary blades 26.

In this embodiment, the case where the heater 58 is provided in the liquid nitrogen supply line 52 has been described. However, even without the heater 58, the shutoff valve 15 is closed, the solenoid valve 56 is closed, and the turbo molecular pump is operated. By doing so, reproduction is possible. By providing the heater 58, the regeneration time can be shortened, and since the heater 58 is not on the vacuum exhaust side (provided in the liquid nitrogen pipe 52), there is no worry of the released gas and it does not cause contamination. Therefore, an ultrahigh vacuum can be stably obtained.

FIG. 3 shows a turbo molecular pump according to another embodiment of the present invention. In this embodiment, the cold trap 5
A pipe 62 for supplying nitrogen gas to a pipe 52 for supplying liquid nitrogen to 0 is configured to join via a valve 64. In the regeneration operation in this case, the valve 66 is closed to stop the supply of liquid nitrogen, and the valve 64 is opened to supply the nitrogen gas to the cold trap 50 to sublime the ice.

In the regenerating operation, the cold trap 50
The higher the temperature is, the shorter the regeneration time is, but it is very dangerous if the frozen water vapor is liquefied and drops into the turbo molecular pump 20, so the regeneration temperature is 0 ° C.
The following control is preferable.

Further, the pipe 52 for supplying the liquid nitrogen to the cold trap 50 is preferably a vacuum heat insulating pipe having good heat insulating performance in order to reduce the amount of the liquid nitrogen used as much as possible. Further, among these pipes, the device side is shipped with ready-made pipes, but the other parts are constructed on site, so these connections are site-aligned. Therefore, it is preferable that at least a part of the pipe 52 is a flexible vacuum heat insulating pipe.

The controller 60 preferably grasps the operating state of the turbo molecular pump and the state of the chamber 10 to control the cold trap 50. Therefore, in the example of FIG. 3, the controller 60 is connected to the controller 68 of the entire turbo molecular pump and the host computer on the apparatus side of the chamber 10. 1 and 3, the temperature sensor 54 is installed on the vacuum side of the cold trap 50, but the same effect can be obtained by installing it on the liquid nitrogen side of the cold trap 50.

[0037]

As described above, the turbo molecular pump of the present invention has the following effects. Since liquid nitrogen is used as a cryogenic agent, it has a very low vibration. Since a temperature sensor is installed in the cold trap and the solenoid valve or flow rate adjustment valve is controlled so that it falls within a predetermined range during operation exhaust, the maximum liquid nitrogen flows during initial startup and cooling is performed, so the cooling time is very short . During continuous evacuation, the electromagnetic valve or the flow rate adjusting valve is controlled so that the cold trap falls within a predetermined temperature range, so that the flow rate of liquid nitrogen is reduced and the running cost can be reduced. Since the refrigerator is not used, the initial cost is low. It is not affected by the CFC problem (ozone depletion problem). Since the temperature control range of the cold trap is −150 ° C. to −196 ° C. during operation and exhaust of the turbo molecular pump, an ultrahigh vacuum can be obtained at high speed. A heater used to regenerate the cold trap is installed in the pipe supplying the liquid nitrogen, and the liquid nitrogen is heated and supplied to the cold trap for regeneration, so there is no extra thing on the vacuum side and there is no amount of contamination. Therefore, it is easy to obtain an ultra-high vacuum. The temperature control range of the cold trap during regeneration is -50.
Since the temperature is between 0 ° C and 0 ° C, there is no concern that droplets will be formed, and quick and safe regeneration is possible. Even when nitrogen gas is used to regenerate the cold trap, there is no source of contamination and it is easy to obtain an ultra-high vacuum. 〓 The piping that supplies liquid nitrogen to the cold trap is vacuum insulation piping, and part of it is flexible vacuum insulation piping, so the insulation performance is very good, running costs can be reduced, and construction is easy.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a turbo molecular pump according to a first embodiment of the present invention.

FIG. 2 is a graph showing a saturated vapor pressure curve of water vapor.

FIG. 3 is a diagram showing an overall configuration of a turbo molecular pump according to a second embodiment of the present invention.

FIG. 4 is a diagram showing an overall configuration of a conventional turbo molecular pump.

[Explanation of symbols]

 22 rotor blade 24 rotor 26 stator blade 28 stator 36 intake port 38 exhaust port 50 cold trap 52 coolant pipe 54 temperature sensor 56 solenoid valve 58 heater 60 controller 62 pipe 64 valve

Claims (6)

[Claims] 1. A turbo-molecular pump having a rotor having a plurality of moving blades and a stator having a plurality of stationary blades, wherein gas molecules are taken in from an intake port, compressed, and discharged from an exhaust port. A cold trap that uses liquid nitrogen as a cryogen is installed at the inlet of the molecular pump, a temperature sensor is installed in this cold trap, and a solenoid valve or a flow control valve is installed in the coolant pipe that supplies liquid nitrogen to the cold trap. A turbo-molecular pump characterized in that a solenoid valve or a flow control valve is controlled so that the trap temperature falls within a predetermined range. 2. The turbo molecule according to claim 1, wherein the temperature control range of the cold trap is −150 ° C. to −196 ° C. during operation exhaust of the turbo molecular pump and during operation exhaust of the cold trap. pump. 3. The turbo-molecular pump according to claim 1, wherein a heater is provided in the coolant pipe. 4. The turbo-molecular pump according to claim 1, wherein a pipe for supplying nitrogen gas merges with the coolant pipe via a valve. 5. The turbo-molecular pump according to claim 1, wherein the temperature control range of the cold trap is 0 ° C. or lower during cold trap regeneration. 6. The turbo-molecular pump according to claim 1, wherein the coolant pipe is a vacuum heat insulating pipe, and a part thereof is a flexible vacuum heat insulating pipe.