JPH09310696A - Molecular drag pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molecular rag pump which can always prevent the condensation of condensable gas by keeping the temperature of the part coming into contact with exhaust gas of a rotor, a stator and an exhaust pipe at prescribed temperature regardless of the size of process gas load. SOLUTION: A molecular drag pump is equipped with a preheating gas introducing means being controllable in an introduced quantity and a purging gas introducing means being controllable in the introduced quantity, and a stator 3a is locked in a heat insulating manner on an upper cage body 6 through rings, 3b, 3b, and the first thread seal 7 is stuckly connected to the stator 3a, and exhaust pipes 12a, 12b are inserted in a heat insulating manner through a lower cage body 12, and a driving motor 8a is characterized so as to reduce its rotating speed in the case of the increase of gas load exceeding a fixed value, and the temperature regulation of a part coming into contact with the exhaust gas such as the stator 3a and the rotor 5 therefore becomes possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molecular pump used in a pressure range from a medium vacuum to an ultra-high vacuum in an experimental research apparatus, an analytical measuring apparatus, and an industrial vacuum apparatus in the field of film formation in the semiconductor manufacturing industry. .

[0002]

2. Description of the Related Art Molecular pumps include turbo molecular pumps, thread groove vacuum pumps, and composite molecular pumps that combine these two.

Conventional etching equipment, CVD (Chemical Vapor)
As an example of a composite molecular pump used for exhausting a film forming apparatus such as a por deposition apparatus, a turbocharger is installed from a side of the intake port a in a housing c having an intake port a and an exhaust port b as shown in FIG. It is known that the molecular pump part d and the thread groove vacuum pump part e are sequentially arranged.

Incidentally, f is a rotary shaft to which the common rotor g of the turbo molecular pump part d and the screw groove vacuum pump part e is fixed, h is a motor, and i and j are journal magnetic bearings and thrust magnetic bearings, respectively, and X The arrow indicates the suction direction of the process gas, and the Y arrow indicates the discharge direction of the process gas.

A conventional molecular pump is used as an etching device or a CV.
Since the process gas has a condensable property when used for exhausting the D device or the like, there is a problem that the condensable gas condenses and accumulates on the portion of the molecular pump such as the rotor and the stator where the process gas is in contact with and locks the rotor. there were.

Therefore, an example of heating the pump portion by a heater installed on the outer circumference or inside of the molecular pump to prevent the condensable gas from condensing and accumulating on the rotor and the stator (JP-A-3-290092) Alternatively, an example in which the stator of the screw groove pump is supported by a heat insulating material and the stator is self-heated to prevent condensation / accumulation as in the above (JP-A-7-43).
No. 84) is known.

[0007]

Since the rotor of the molecular pump is made of aluminum alloy, it is necessary to keep the temperature of the rotor up to about 120 ° C. due to the restriction on strength. Also, the electric parts such as the magnetic bearing and the motor are required. Also dislikes high temperatures, so a method of heating the pump portion with the above heater (Japanese Patent Laid-Open No. 29929/1993)
(Japanese Patent Laid-Open Publication No. 2003) has a problem that the pump life may be deteriorated or malfunction may occur due to overheating of the pump section.

In the method of supporting the stator with a heat insulating material and raising the temperature by itself (Japanese Patent Laid-Open No. 7-4384), the pump section is overheated when a large flow rate of process gas is applied as a load. There was a problem.

Furthermore, in this method of self-heating the stator, when the process gas load is too small, or the stator temperature does not rise sufficiently for several hours after the start of the process, the exhaust gas flows in the flow path of the pump section. There was a problem that caused condensation.

The present invention solves these problems and always prevents condensation by keeping the temperature of a portion of the rotor, the stator, the exhaust pipe, etc., which comes into contact with exhaust gas, at a predetermined temperature regardless of the size of the process gas load. An object is to provide a molecular pump capable of

[0011]

SUMMARY OF THE INVENTION The present invention is characterized in that the temperatures of a rotor, a stator and an exhaust passage portion are controllably formed in order to achieve the above-mentioned object.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As a first embodiment of the present invention, an example applied to a composite molecular pump will be described with reference to a vertical sectional view of FIG.

The process gas is sucked in through the intake port 1, passes through the turbo molecular pump unit 2 and the thread groove vacuum pump unit 3, and is exhausted through the exhaust port 4.

A common rotor 5 for the turbo molecular pump unit 2 and the thread groove vacuum pump unit 3 is fixed to the rotary shaft 5a and is made of an aluminum alloy.

The stator 3a of the thread groove vacuum pump section 3 is
It is locked to the upper housing 6 via the rings 3b and 3b made of a heat insulating material, and faces the thread portion of the thread groove 3c in the rotor 5 with a slight gap, and A first screw seal 7 is partly adhered to the lower end of the stator 3a.

However, since the stator 3a is not in direct contact with the other parts, the stator 3a is supported adiabatically.

The first screw seal 7 has a thread groove 7a on the outer peripheral portion and an O ring 7b on the inner peripheral portion.
In a, the thread portion is opposed to the inner peripheral portion of the rotor 5 with a slight gap.

The screw groove 7a is formed so that the gas in the rotor inner chamber 5b is exhausted downward (in the direction leading to the exhaust inner pipe 12a) by the rotation of the common rotor 5.

The first screw seal 7 is the O-ring 7
It is slidably mounted on the outer peripheral portion of the motor housing 8 via b.

The first screw seal 7 prevents the process gas discharged from the screw groove vacuum pump portion 3 from leaking to the rotor inner chamber 5b by the action of the screw groove 7a.

Reference numeral 9 denotes a second screw seal, which has a thread groove 9 on its inner peripheral portion.
a and is engaged with the upper end of the motor housing 8 and the thread portion of the thread groove 9a faces the outer peripheral portion of the boss portion of the common rotor 5 with a slight gap.

Due to the rotation of the rotor 5, the thread groove 9a is
It is formed so that the gas in the rotor inner chamber 5b is exhausted downward (inside the motor housing 8).

Reference numeral 10 denotes a purge gas introduction port. The purge gas such as nitrogen gas introduced from the purge gas introduction port 10 fills the inside of the motor housing 8 through the lower housing inner chamber 10a and the purge hole 10b, and the process gas is filled with the process gas. Prevents intrusion into the interior.

The pressure of the purge gas inside the motor housing 8 is higher than the pressure in the rotor inner chamber 5b due to the compression action of the screw groove 9a of the second screw seal 9. The pressure inside the motor housing 8 has a great influence on the heat transfer between the motor housing 8 and the rotary shaft 5a.

That is, Q: heat transfer amount transmitted from the rotary shaft 5a to the motor housing 8 γ: specific heat ratio of the purge gas M: molecular weight of the purge gas R: gas constant T1: temperature of the rotary shaft 5a T2: in contact with the motor housing 8 If the temperature P of the motor stator electromagnet that is present is the pressure inside the motor housing 8, then the relational expression shown in Equation 1 holds.

[0026]

[Equation 1]

By increasing the pressure P in the motor housing 8 in this way, the amount of heat transfer between the rotary shaft 5a and the motor housing 8 can be increased.

The motor housing 8 radiates heat through the lower housing 12 which is air-cooled or water-cooled and is kept at a constant temperature. On the other hand, since the rotor 5 radiates heat by heat transfer via the rotating shaft 5a, when the temperature of the rotor 5 rises due to an increase in the process gas load, the amount of heat transfer from the rotating shaft 5a to the motor housing 8 is increased. Increase Q and rotor 5
It is necessary to prevent overheating.

Therefore, the purge gas pressure in the motor housing 8 is controlled according to the increase / decrease in the process gas load.

Since the increase / decrease in the process gas load is detected as a variation value of the rotation speed from the rated rotation speed from the characteristic of the drive motor 8a described later, the detected value by the rotation speed detector (not shown). By knowing the increase / decrease in the process gas load, the amount of purge gas introduced into the purge gas inlet 10 is automatically controlled, and the pressure of the purge gas in the motor housing 8 linked to this is automatically controlled to bring the temperature of the rotor 5 to a predetermined value. I keep it.

Next, 11 indicates a preheating gas inlet.

In the composite molecular pump of this embodiment,
The preheating gas inlet 11 is provided between the turbo molecular pump unit 2 and the thread groove vacuum pump unit 3.

Nitrogen gas or the like at room temperature is used as the preheating gas, and the preheating gas is introduced from the preheating gas introduction port 11 at the time of starting the apparatus before starting the operation of the process, and the screw groove vacuum pump unit 3 The temperature of the stator 3a and the like is raised by the heat generated by the pump action.

Further, even when the process gas load is not applied for a long time (for example, when the process is interrupted), the temperature of the stator 3a or the like can be maintained at a predetermined high temperature by introducing the preheating gas.

In order to keep the temperature of the stator 3a appropriate, it is necessary to control the amount of the preheating gas introduced, and the control of the amount of the preheating gas introduced is controlled by the drive motor 8a described later. The rotation speed is detected by using.

The introduction port for the preheating gas is provided between the turbo molecular pump unit 2 and the thread groove vacuum pump unit 3 in the case of the composite molecular pump of the present embodiment. If the turbo molecular pump is the only one, the inlet may be provided at the substantially central part of the total number of stages of the rotor blade and the stator blade. The inlet may be provided in the section.

Here, the characteristics of the drive motor 8a, which is one of the features of the present invention, will be described.

The drive motor 8a for driving the rotary shaft 5a is a brushless DC motor and is formed to have the characteristics shown by the solid line in FIG.

In the conventional method of controlling a motor of this type, as shown in FIG.
It had the characteristics shown by the dotted line. That is, when the process gas load increases at the rated rotation speed, the rotation speed slightly decreases, but the rate of decrease is about 1 even at the maximum current value.
As low as about%.

When such a motor is used for driving the molecular pump, the rotor of the molecular pump is overheated during continuous operation at the maximum rated output, such as when the process gas load is increased.
It is expected that the temperature will exceed 0 ° C, and the rotor strength will be extremely dangerous.

Further, in order to avoid overheating of the rotor, when the conventional control method is used in the conventional motor in which the maximum rated output of the drive motor is smaller, the rotor having a large moment of inertia at the start is rated. Since it takes a long time to reach the rotation speed, this is also a problem.

On the other hand, the drive motor 8a of the present invention
Detects an increase in load with an input current value and controls the motor rotation speed to fall below the rated rotation speed accordingly.

That is, 30 to 70% of the rated rotation speed (5
The range of 0% or more is preferable), and the value of the supply current to the drive motor 8a is reduced to obtain the motor input current / rotational speed characteristic shown by the solid line in FIG.

By this control, the maximum output of the drive motor 8a is remarkably reduced, and when an excessive process gas load is applied, the rotation speed of the rotor 5 is reduced and the motor load due to the process gas load is reduced. It is possible to prevent overheating of the rotor 5 and the like. Further, since the motor input current can be known by measuring the rotation speed, the motor output, that is, the magnitude of the process gas load can be immediately known.

Further, since the maximum output of the drive motor 8a is reduced, it takes a longer time than before for the rotor 5 to reach the rated rotation speed. Even with half the rotation speed, it has a sufficient exhaust speed for initial exhaust when starting up the equipment, so even if the time required to increase the rotation speed to the rated rotation speed thereafter increases a little, there is no practical problem. Absent.

In the drive motor 8a of the present invention, the rotation speed is taken into the controller as information together with the current value, and a microcomputer is used for control so that a current corresponding to the rotation speed flows through the motor. A block diagram is shown in FIG. FIG. 4 shows a block diagram of control of a conventional drive motor.

However, I0 is the set maximum current value, I is the current detection value, N is the rotation speed detection value, and K (N)
Is a variable gain using a microcomputer.

The process gas or preheating gas exhausted from the thread groove molecular pump section 3 is exhausted to the outside from the exhaust port 4 via the exhaust inner pipes 12a and 12b, but from these exhaust inner pipes 12a and 12b. In order to prevent heat from being transferred to the lower housing 12, the exhaust inner pipes 12a, 12b are spaced apart from the inner wall 12c of the exhaust hole portion of the lower housing 12.
Is inserted.

Further, a heater 12d for heating is installed around the exhaust inner pipe 12b so that the process gas is exhausted from the inner pipe 12b.
It has a structure that prevents condensation and accumulation in the exhaust passages a and 12b.

Next, the operation of the first embodiment of the present invention,
The effect will be described.

Before starting the operation of the process, warm up the molecular pump. That is, when the apparatus is started up, a preheating gas such as nitrogen gas is introduced into the thread groove pump portion 3 from the preheating gas introduction port 11, and the temperature of the stator 3a and the rotor 5 is raised by the heat generated by the pump action. After that, by switching to the process gas after that,
The process gas is prevented from condensing and accumulating in the flow path.

The introduction of the preheated gas is not limited to the start-up of the apparatus, and also when the apparatus is operated for a long time without a load of the process gas, the preheated gas is similarly introduced and the screw is It is possible to keep the stator 3a of the groove pump portion, the rotor 5 and the like at a high temperature.

Further, since the increase / decrease of the process gas load causes the temperature variation of the rotor 5 during the operation of the process, the increase / decrease of the process gas load is detected by the rotation speed detector and the supply amount of the purge gas is controlled by this signal. By doing so, the temperature of the rotor 5 is controlled.

That is, when the process gas load increases, the amount of purge gas introduced is increased to increase the pressure inside the lower housing inner chamber 10a and the motor housing 8, and the rotor 5 moves to the motor housing 8 via the rotary shaft 5a. To prevent the temperature of the rotor 5 from rising above 120 ° C., and when the process load is reduced, the amount of purge gas introduced is reduced to reduce the heat transfer amount to prevent the rotor 5 from becoming excessive. Prevents temperature drop.

These effects are obtained by controlling the introduction amount of the preheating gas and the introduction amount of the purge gas, as well as the structure of the motor housing 8 and the stator 3a, and the purge gas delivery of the first screw seal 7 and the second screw seal 9. This is realized by the action and the overall action of the above characteristics and the like given to the drive motor 8a.

Further, by heating the exhaust inner pipe 12b to 120 ° C. or higher by the heater 12d for heating, it is possible to prevent the process gas from condensing and accumulating in the exhaust inner pipe.

When the conventional method of heating the auxiliary pipe between the molecular pump and the auxiliary pump is adopted, the heating by the heater 12d for heating is utilized by the heat conduction. You may do it.

Further, in the present embodiment, the molecular pump is a composite molecular pump, but this is similarly performed when the molecular pump is only a turbo molecular pump or when the molecular pump is only a screw groove vacuum pump. It is possible.

The second embodiment of the present invention will be described with reference to FIGS.
This will be described below.

FIG. 5 is a vertical sectional view of the second embodiment,
An example applied to a composite molecular pump as in the first embodiment will be shown.

In the present embodiment, a supply means that serves as both purge gas supply means and preheating gas supply means is provided.

That is, a gas flow rate switching mechanism 13, which will be described later, is installed in front of the purge gas supply port 10 so that the required gas flow rates can be supplied to the purge gas and the preheating gas, and the shaft of the first screw seal 7 can be supplied. It differs from the first embodiment in that the length is formed to be substantially the same as the axial length of the stator 3a of the thread groove vacuum pump portion 3.

In the first embodiment, the preheating gas is introduced from the preheating gas introduction port 11 between the turbo molecular pump unit 2 and the thread groove vacuum pump unit 3, whereas the preheating gas is introduced in the first embodiment. In the second embodiment, the preheating gas introduced into the motor housing 8 from the purge gas introduction port 10 is the second
The thread groove 9a is supplied to the downstream side of the flow path of the thread vacuum pump unit 3 via the thread groove 9a of the thread seal 9 and the thread groove 7a of the first thread seal 7.

Nitrogen gas or the like is used for both the purge gas and the preheating gas.

FIG. 6 shows an example of the gas flow rate switching mechanism.

The gas flow rate switching mechanism 13 connected to the high pressure nitrogen gas line 14 passes through the pressure reducing valve 13a, the purge gas valve 13b, the first pipe having the purge gas orifice 13c, the preheating gas valve 13d and the preheating gas. It branches into a second pipe having an orifice 13e for injection, and the first pipe and the second pipe merge again to form the purge gas introduction port 1
Connected to 0.

Next, the operation and effect of the second embodiment will be described.

The purge gas is supplied to the inside of the motor housing 8 for the purpose of preventing the process gas from entering the inside of the motor housing 8. The supply amount is about 10 SCCM in a standard example. is there.

On the other hand, about 200 is used as the preheating gas.
A supply of SCCM is required. Therefore, by providing the purge gas orifice 6c and the preheating gas orifice 13e separately, the flow rate of the nitrogen gas is immediately switched from the purge gas to the preheating gas by operating the solenoid valve.

FIG. 7 shows a wiring diagram of the gas flow rate switching mechanism 13.

When PB1 is pressed, R1 is excited to excite PV, the purge gas valve 13b is opened, and nitrogen gas of about 10 SCCM is supplied into the motor housing 8 through the purge gas orifice 13c. When the supply of purge gas is stopped, PB2 may be pushed to deactivate R1.

When R1 is energized, pressing PB3 energizes the timer relay T for a certain period of time, further energizes HV to open the preheating gas valve 13d, and to set the flow rate 2
Nitrogen gas of 00 SCCM is supplied into the motor housing 8 through the preheating gas orifice 13e.

The nitrogen gas supplied to the inside of the motor housing 8 passes through the thread groove 9a of the second thread seal 9 to the first groove.
It passes through the thread groove 7 a of the thread seal 7 and is discharged to the downstream side of the flow path of the thread groove vacuum pump unit 3. At this time, the first screw seal 7 and the rotor 5, and the first screw seal 7 are in close contact with each other by frictional heat when nitrogen gas passes through the screw groove 7a formed in the axial direction. The temperature of the stator 3a rises.

Further, the thread groove vacuum pump 3 itself also generates heat by the pumping action on the nitrogen gas discharged to the downstream side thereof, so that the rotor 5 and the stator 3a are further heated and preheated in a short time.

This preheating is carried out while the rotor 5 is rotating at a high speed, and a large flow rate of nitrogen gas is supplied for a fixed time T to carry out preheating, which is compared with the first embodiment. In this embodiment, a troublesome preheating gas introduction port 11 is provided between the turbo molecular pump unit 2 and the thread groove vacuum pump unit 3.
Since there is no need for a preheating gas pipe and the preheating gas is introduced to the downstream side of the thread groove vacuum pump unit 3, there is no disadvantage that the intake pressure on the upstream side of the molecular pump rises significantly. Have.

The influence on the exhaust performance of the composite molecular pump when the preheating gas is introduced to the downstream side of the thread groove vacuum pump section 3 will be examined.

FIG. 8 shows an example of a compression ratio curve of a composite molecular pump having an exhaust speed of 700 L / S class. Auxiliary pump exhaust speed is 1000L / min, which is the standard value, and 200SCCM
When the nitrogen gas of is introduced through the purge gas inlet 10,
The exhaust pressure of the composite molecular pump is 0.15 Torr.

That is, referring to FIG. 8, the amount of pressure increase due to the introduction of the preheated gas is as shown in Equation 2.

[0079]

[Equation 2]

This increase in intake port pressure poses no problem for the background pressure condition before the start of the process.

Further, a comparison is made between the case where the stator of the thread groove vacuum pump is heated by the conventional external heater and the case where the stator 3a of the thread groove vacuum pump unit 3 is heated by the second embodiment. An example is shown in FIG. To set the temperature of the stator 3a to 55 ° C., which is the temperature at which the process gas does not adhere,
It can be seen that the heater heating type requires two hours, whereas the self-heating type according to the second embodiment reaches the required temperature in a shorter time.

In the second embodiment, the gas flow rate switching mechanism 13 is composed of the purge gas orifice 13c and the preheating gas orifice 13e, but this may be replaced by a single mass flow controller. .

The throttle of the purge gas orifice 13c may be variable, and the heat transfer amount Q from the rotary shaft 5a to the motor housing 8 may be controlled by the variable throttle of the purge gas orifice 13c.

Further, in the present embodiment, the molecular pump is a composite molecular pump, but this can also be carried out in the same way even in the case of only the thread groove vacuum pump.

[0085]

As described above, according to the present invention, the process gas is condensed and deposited in the molecular pump by heating the pump unit in a short time by self-heating without using a heater outside or inside the pump unit. It is possible to provide a molecular pump having a structure capable of preventing the temperature increase and keeping the temperature rise of the rotor portion within a safe allowable range even when the gas load of the process gas rapidly increases.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a composite molecular pump according to a first embodiment of the present invention.

FIG. 2 is a diagram showing characteristics of a drive motor.

FIG. 3 is a block diagram of control of a drive motor according to the present invention.

FIG. 4 is a block diagram of control of a conventional drive motor.

FIG. 5 is a vertical sectional view of a composite molecular pump according to a second embodiment of the present invention.

FIG. 6 is a system diagram of a gas flow rate switching mechanism connected to a purge gas introduction port of a composite molecular pump.

FIG. 7 is a wiring diagram of the same gas flow rate switching mechanism as above.

FIG. 8 is a graph showing an example of a compression curve of a composite molecular pump.

FIG. 9 is a graph showing an example of comparison of temperature rising times of an external heater heating type and a self-heating type in a thread groove vacuum pump.

FIG. 10 is a vertical cross-sectional view of a conventional composite molecular pump.

[Explanation of symbols]

 3 Screw groove vacuum pump section 3a Stator 4 Exhaust port 5 Rotor 6, 12 Case 7 First screw seal 7b O-ring 8 Motor housing 8a Drive motor 9 Second screw seal 10 Purge gas inlet 11 Preheating gas inlet 12a, 12b Exhaust inner pipe 12c Exhaust hole inner wall 12d Heating heater 13 Gas flow rate switching mechanism 13c Purge gas orifice 13e Preheating gas orifice

Front page continuation (72) Inventor Masatomo Okamoto 3-2-25 Kitahama, Chuo-ku, Osaka-shi, Osaka Inside the Osaka Vacuum Equipment Manufacturing Co., Ltd. (72) Inventor Ms. Kiyoshi 3-2-25 Kitahama, Chuo-ku, Osaka-shi, Osaka Osaka Vacuum Equipment Manufacturing Co., Ltd.

Claims (14)

[Claims] 1. A molecular pump characterized in that the temperatures of a rotor, a stator, and an exhaust passage portion are controllable. 2. A preheating gas introducing means for preheating the rotor and the stator is provided, and the introduction amount of the preheating gas is controlled in accordance with the magnitude of the gas load applied to the rotor driving motor. The molecular pump according to claim 1, wherein 3. A purge gas introducing means for introducing the purge gas into the motor housing is provided, and the introduction amount of the purge gas is controlled according to the magnitude of the gas load applied to the rotor driving motor. The molecular pump according to claim 1, wherein: 4. The purge gas introducing means operates so as to prevent the process gas from leaking inside the rotor, and a second screw seal that operates so that the purge gas inside the motor housing does not leak outside the motor housing.
The molecular pump according to claim 3, further comprising a screw seal. 5. A molecular pump having a thread groove vacuum pump section, wherein the preheating gas is introduced into the motor housing, and the preheating gas is provided in the first thread seal installed inside the thread groove vacuum pump section. The molecular pump according to claim 2 or 4, wherein the molecular pump is formed so as to be supplied to the downstream side of the flow path of the thread groove vacuum pump section via the thread groove section. 6. The preheating gas introduction means and the purge gas introduction means are formed in common and communicate with the inside of the motor housing to switch the gas flow rate when introducing the purge gas or introducing the preheating gas. The molecular pump according to claim 2 or 3, further comprising a gas flow rate switching mechanism. 7. The molecular pump according to claim 5, wherein the axial length of the first screw seal is formed to be substantially the same as the axial length of the stator of the thread groove vacuum pump section. 8. The molecular pump according to claim 5, wherein the stator is provided with a thread groove vacuum pump portion that is adiabatically locked to the casing of the pump. 9. The molecular pump according to claim 3, wherein the motor housing is formed in a structure that blocks heat conduction from the exhaust passage portion. 10. An exhaust inner pipe in which an exhaust port for exhausting a process gas in the exhaust passage is inserted adiabatically into an exhaust hole of a casing of a pump with a gap from an inner wall of the exhaust hole. 10. The molecular pump according to claim 9, further comprising a heating heater installed in the exhaust inner pipe. 11. The stator of a screw groove vacuum pump unit, wherein the first screw seal is slidably fitted to the outer peripheral portion of the motor housing via an O-ring and is adiabatically locked to the casing of the pump. 5. The molecular pump according to claim 4, wherein the first screw seal is attached to the stator, and the first screw seal is formed so as to have a temperature substantially the same as that of the stator due to heat conduction from the stator. 12. The preheating gas load or the process gas load for preheating the rotor and the stator is formed so as to be detected from the rotation speed of the drive motor. Item 3. The molecular pump according to item 3. 13. The rotor driving motor is a brushless DC motor, and the rotation speed of the motor when the maximum current value of the motor flows is within the range of 30 to 70% or less of the rated rotation speed of the motor. The numerator according to claim 12, wherein the current value supplied to the motor is controlled so as to decrease with the increase of the rotation speed of the motor at a rotation speed of the motor higher than that. pump. 14. The gas flow rate switching mechanism includes: a second pipeline having a purge gas orifice and a preheating gas orifice connected in parallel; and a second pipeline having a preheating gas orifice for a predetermined time. The molecular pump according to claim 6, comprising a valve that switches a gas flow to a gas flow to the second pipeline.