EP1811176A1

EP1811176A1 - Vacuum exhaust device

Info

Publication number: EP1811176A1
Application number: EP05745938A
Authority: EP
Inventors: Manabu Nonaka
Original assignee: BOC Edwards Japan Ltd
Current assignee: Edwards Japan Ltd
Priority date: 2004-06-03
Filing date: 2005-06-01
Publication date: 2007-07-25
Also published as: EP1811176A4; WO2005119060A1; JP2005344610A

Abstract

To improve the isolation rate of vibrations propagating from a vacuum pump to a vacuum device.

A turbo-molecular pump 1 is connected to a main vacuum chamber 2 via a vacuum seal structure 4. Further, a sub-vacuum chamber 3 is provided so as to contain the main vacuum chamber 2, the vacuum seal structure 4, and an inlet 110 of the turbo-molecular pump 1. The roughing evacuation of the sub-vacuum chamber 3 is accomplished by using a roughing vacuum pump 6 to make the sub-vacuum chamber 3 in a medium vacuum state. Since the vacuum seal structure 4 is arranged in the sub-vacuum chamber 3 in a medium vacuum state, a difference in pressure between the main vacuum chamber 2 and the sub-vacuum chamber 3 can be made extremely small. Thereby, the amount of gas leakage to the main vacuum chamber 2 can be kept at a small value. Also, the vacuum seal structure 4 can use, for example, a non-contact seal structure or a highly flexible seal member because it does not perform a function of supporting the turbo-molecular pump 1.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vacuum exhausting device that evacuates a vacuum chamber (vacuum device) used for semiconductor manufacturing equipment, electron microscopes, and the like by using a vacuum pump. More particularly, it relates to a vacuum exhausting device having a mechanism for restraining the propagation of vibrations produced, for example, in the vacuum pump.

2. Description of the Related Art

Equipment that accomplishes evacuation by using, for example, a vacuum pump to keep the interior thereof in a vacuum includes semiconductor manufacturing equipment, an electron microscope, a surface analyzer, and microfabrication equipment.
Also, of various types of vacuum pumps, a turbo-molecular pump is often used to realize a high vacuum environment.
The turbo-molecular pump is configured so that a rotor rotates at a high speed in a casing having a suction port and an exhaust port. On the inner peripheral surface of the casing, stator blades are disposed in multiple stages, and on the other hand, on the rotor, rotor blades are disposed radially in multiple stages. When the rotor rotates at a high speed, gas is sucked through the suction port by the action of the rotor blades and the stator blades, and is exhausted through the exhaust port.
In the turbo-molecular pump, when the rotor rotates at a high speed, vibrations are produced by the cogging torque of a motor. Also, in the case where the rotor is not balanced completely, vibrations may occur due to the oscillation of a shaft.
Also, in the turbo-molecular pump, since a turbine is rotated at a high speed to accomplish evacuation, a high temperature state is sometimes formed by heating caused by the collision heat of gas molecules or heat generated from the motor.
If such vibrations or heat generated by the vacuum pump propagates to the vacuum device side, a hindrance may be constituted.
Thereupon, techniques for restraining the propagation of vibrations or heat from the vacuum pump have conventionally been proposed, for example, in patent documents described below.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2002-295581
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2002-227765
Patent Document 1 discloses a technique in which a vacuum pump and a vacuum device are connected to each other via a damper, and vibrations produced in the vacuum pump are absorbed by the damper, by which the propagation of vibrations to the vacuum device is restrained.
The damper used for absorbing vibrations has a construction such that a rubber etc. are wound on a bellows.
This bellows has a cylindrical shape having a collapsible lantern shaped deep folds at the outer periphery thereof so as to achieve elasticity by means of the expansion and contraction of the folds on the side surface and to absorb (damp) the vibrations.
Also, Patent Document 2 discloses a technique in which a vacuum pump and a vacuum device are joined to each other via a member (pipe) having high thermal conductivity, and this member is cooled by using a cooling method such as water cooling or air cooling, by which the propagation of heat to the vacuum device is restrained.
The damper conventionally used for absorbing vibrations requires a construction such as to withstand a pressure difference between a vacuum exhaust flow path and the atmosphere because it not only performs a function of supporting the vacuum pump but also is arranged in the atmosphere. Therefore, the damper requires rigidity that is high to some degree.
However, the damper having such high rigidity has a low capability for isolating (damping) vibrations propagating to the vacuum device.

SUMMARY OF THE INVENTION

Accordingly, a first object of the present invention is to provide a vacuum exhausting device capable of increasing the isolation rate of vibrations propagating from a vacuum pump to a vacuum device.
Further, a second object of the present invention is to provide a vacuum exhausting device capable of increasing the isolation rate of heat transmitting from a vacuum pump to a vacuum device.
To achieve the first object, the invention described in claim 1 provides a vacuum exhausting device including a main vacuum chamber; a vacuum pump for evacuating the main vacuum chamber; and a sub-vacuum chamber that contains the main vacuum chamber and a suction port of the vacuum pump and is roughingly evacuated, characterized in that the main vacuum chamber and the vacuum pump are joined to each other via a seal structure for preventing or reducing the leakage of gas between the main vacuum chamber and the sub-vacuum chamber.
In the invention described in claim 1, the main vacuum chamber and the sub-vacuum chamber are preferably provided via, for example, a vibration damper or a vibration absorber. The vibration damper or the vibration absorber is preferably a device using, for example, an active control system, which can properly restrain the propagation of external vibrations.
In the invention described in claim 1, the seal structure is preferably formed, for example, by a seal structure having low sealing strength, a seal structure having low sealability, or a brittle seal structure.
To achieve the first or second object, the invention described in claim 2 is characterized in that in the invention described in claim 1, the main vacuum chamber and the vacuum pump are joined to each other via a predetermined gap, a noncontact seal, a seal member, or an elastic member that is deformed according to a difference in pressure between the main vacuum chamber and the sub-vacuum chamber.
In the invention described in claim 2, the predetermined gap preferably takes a value, for example, calculated based on the leakage quantity of gas from the sub-vacuum chamber and the influence that the leakage quantity exerts on the ultimate pressure in the main vacuum chamber.
In the invention described in claim 2, as the noncontact seal, for example, a labyrinth seal in which the gap portion is formed by a complicated flow path is preferably used. The clearance of this flow path preferably takes a value, for example, calculated based on the leakage quantity of gas from the main vacuum chamber and the influence that the leakage quantity exerts on the ultimate pressure in the main vacuum chamber.
In the invention described in claim 2, as the seal member, for example, a member having low rigidity and high flexibility, specifically, a rubber or a polymer material is preferably used. Further, as the seal member, for example a member having low thermal conductivity or thermometric conductivity, that is, a member having high heat insulating properties is preferably used.
In the invention described in claim 2, as the elastic member, for example, a member having a low modulus of elasticity is preferably used, and a metallic plate etc. may be used. Further, as the elastic member, for example, a member having low thermal conductivity or thermometric conductivity, that is, a member having high heat insulating properties is preferably used.
Also, as the elastic member, for example, a thin-sheet valve shaped member having a composite (affixing) structure of a body part and a coating part may be used, and the configuration may be such that the coating part faces to a gas transfer path (exhaust passage) leading from the main vacuum chamber to the vacuum pump. In this case, as the body part, for example, a flexible rubber, polymer material, or the like is preferably used, and on the other hand, as the coating part, for example, a metal having flexibility of such a degree as not to influence the elastic characteristics of the body part, such as stainless steel or aluminum, is preferably used.
In the case where the elastic member is configured as described above, for example, the elastic member is preferably deformed so that when the pressure on the gas transfer path (exhaust passage) side leading from the main vacuum chamber to the vacuum pump is lower than the pressure in the sub-vacuum chamber, the elastic member seals the sub-vacuum chamber and the gas transfer path (exhaust passage), and when the pressure in the gas transfer path (exhaust passage) leading from the main vacuum chamber to the vacuum pump becomes higher than the pressure in the sub-vacuum chamber, the seal is canceled. In such a case, for example, the contact surface (sliding joint surface) on the mating side (the main vacuum chamber side) contacting with the elastic member may be coated with a hard material.
The invention described in claim 3 is characterized in that in the invention described in claim 1 or claim 2, the vacuum exhausting device further includes a roughing vacuum pump for roughingly evacuating the sub-vacuum chamber, and an exhaust port of the vacuum pump communicates with the sub-vacuum chamber.
According to the present invention, the isolation rate of vibrations or heat propagating from the vacuum pump to the vacuum device can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a view showing a general configuration of a vacuum exhausting device in accordance with an embodiment;
Figure 2(a) is a view showing a vacuum seal structure in the case where a gap is used, Figure 2(b) is a view showing the vacuum seal structure in the case where a labyrinth seal is used, and Figure 2(c) is a view showing the vacuum seal structure in the case where a seal member is used;
Figure 3 is a view showing a vacuum seal structure in the case where an elastic body is used;
Figure 4(a) is a view showing a state of an elastic body in the case where the pressure (P1) in a main vacuum chamber is higher than the pressure (P2) in a sub-vacuum chamber, and Figure 4(b) is a view showing a state of the elastic body in the case where the pressure (P1) in the main vacuum chamber is not higher than the pressure (P2) in the sub-vacuum chamber;
Figure 5 is a view showing a first modification of a connecting method for an exhaust port of a turbo-molecular pump in a vacuum exhausting device in accordance with an embodiment;
Figure 6 is a view showing a second modification of a connecting method for an exhaust port of a turbo-molecular pump in a vacuum exhausting device in accordance with an embodiment; and
Figure 7(a) is a view showing a first modification of a fixing method for a main vacuum chamber in a vacuum exhausting device in accordance with an embodiment, and Figure 7(b) is a view showing a second modification of a fixing method for the main vacuum chamber in the vacuum exhausting device in accordance with an embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the present invention will now be described in detail with reference to Figures 1 to 7.
Figure 1 is a view showing a configuration of a vacuum exhausting device in accordance with the embodiment.
In the vacuum exhausting device in accordance with this embodiment, a vacuum chamber has a double vacuum chamber construction (double casing construction) formed by a main vacuum chamber 2 and a sub-vacuum chamber 3 that contains the main vacuum chamber 2.
The vacuum exhausting device in accordance with this embodiment is broadly formed by three elements of a turbo-molecular pump 1, the main vacuum chamber 2, and the sub-vacuum chamber 3. Also, the vacuum exhausting device has a vacuum seal structure 4, which is one feature of this embodiment, provided in a joint (connection) portion between the turbo-molecular pump 1 and the main vacuum chamber 2.
Next, these elements are explained.
The turbo-molecular pump 1 is a vacuum pump for evacuating the main vacuum chamber 2. This turbo-molecular pump 1 is what is called a compound blade type molecular pump having a turbo-molecular pump section and a thread groove pump section.
An upper casing 101 forming an exterior body of the turbo-molecular pump 1 has a substantially cylindrical shape, and constitutes a housing for the turbo-molecular pump 1 together with a lower casing 102 provided under (on the exhaust port 111 side of) the upper casing 101. In this housing, a structure that causes the turbo-molecular pump 1 to perform an exhausting function is housed.
The structure for performing the exhausting function is broadly formed by a rotating part supported pivotally and a fixed part fixed to the housing.
The upper casing 101 and the lower casing 102 constituting the housing for the turbo-molecular pump 1 are connected to each other by fixing attachment portions thereof provided in connecting portions using fastening members such as bolts.
The attachment portions of both of the upper casing 101 and the lower casing 102 each have a flange shape projecting to the outer periphery side of the turbo-molecular pump 1.
Further, the attachment portion of the upper casing 101 is formed with a flange part 118 further projecting to the outer periphery side from the attachment portion of the lower casing 102.
At the other end of the upper casing 101, a suction port 110 for introducing gas into the turbo-molecular pump 1 is formed.
Also, the lower casing 102 is formed with the exhaust port 111 for exhausting gas from the turbo-molecular pump 1.
The rotating part includes a shaft 104, which is a rotating shaft, a rotor 105 disposed on the shaft 104, rotor blades 106 provided on the rotor 105, and a stator column 107 provided on the exhaust port 111 side (thread groove pump section).
The rotor blade 106 consists of a blade that extends radially from the shaft 104 so as to be tilted through a predetermined angle from a plane perpendicular to the axis line of the shaft 104.
Also, the stator column consists of a cylindrical member having a cylindrical shape concentric with the rotation axis line of the rotor 105.
In a middle portion in the axial direction of the shaft 104, a motor part 109 for rotating the shaft 104 at a high speed is provided.
Further, on the suction port 110 side and the exhaust port 111 side of the shaft 104 with respect to the motor part 109, radial magnetic bearing devices 112 and 113 for pivotally supporting the shaft 104 in the radial direction are provided, respectively. Also, at the lower end of the shaft 104, an axial magnetic bearing device 114 for pivotally supporting the shaft 104 in the axial direction is provided.
On the inner periphery side of the housing, the fixed part is formed. This fixed part includes stator blades 115 provided on the suction port 110 side (turbo-molecular pump section) and a thread groove part 116 formed on the inner peripheral surface of the lower casing 102.
The stator blade 115 consists of a blade that extends from the inner peripheral surface of the housing toward the shaft 104 so as to be tilted through a predetermined angle from a plane perpendicular to the axis line of the shaft 104.
The stator blades 115 in stages are separated from each other by a spacer 117 having a cylindrical shape.
In the turbo-molecular pump section, the stator blades 115 are formed in a plurality of stages in the axial direction so as to be alternate with the rotor blades 106.
The thread groove part 116 is formed with a spiral groove in the surface opposed to the stator column 107. The thread groove part 116 is formed so as to face to the outer peripheral surface of the stator column 107 with a predetermined clearance (gap) being provided therebetween. The direction of the spiral groove formed in the thread groove part 116 is a direction such that gas is directed to the exhaust port 111 when the gas is transported in the rotation direction of the rotor 105 in the spiral groove.
Also, the depth of the spiral groove decreases toward the exhaust port 111, so that the gas transported in the spiral groove is compressed as the gas approaches the exhaust port 111.
By the turbo-molecular pump 1 constructed as described above, the evacuation in the main vacuum chamber 2 is carried out.
In the turbo-molecular pump 1, since the rotating part is rotated at a high speed to accomplish evacuation, a high temperature state is sometimes formed by heating caused by the collision heat of gas molecules or heat generated from the motor part 109.
However, the pressure of the suction port 110 portion formed at the end of the upper casing 101 is approximately equal to the pressure in the main vacuum chamber 2, so that heat transmission due to convection (convection heat transmission) is difficult to occur.
Also, in the turbo-molecular pump 1, when the rotating part rotates at a high speed, vibrations may sometimes be produced by cogging torque created by the motor part 109. Also, if the rotor 105 is not balanced completely, vibrations may occur due to the oscillation of the shaft 104.
Such vibrations produced in the turbo-molecular pump 1 are transmitted to the upper casing 101 and the lower casing 102 constituting the housing.
Next, the main vacuum chamber 2 is explained.
The main vacuum chamber 2 forms a vacuum device used, for example, as a chamber for semiconductor manufacturing equipment or a measurement chamber of an electron microscope.
The main vacuum chamber 2 is a vacuum vessel that is formed by a main vacuum chamber wall 21 and has an exhaust port 22. The main vacuum chamber wall 21 is formed of a strong metal, for example, an aluminum alloy thick plate.
The exhaust port 22 functions as an exhaust port when the main vacuum chamber 2 is evacuated. The turbo-molecular pump 1 and the main vacuum chamber 2 are joined (connected) via this exhaust port 22.
Also, the exhaust port 22 in this embodiment is formed in a flange shape projecting to the inside with respect to the main vacuum chamber 2. However, the exhaust port 22 may be formed in a flange shape projecting to the outside with respect to the main vacuum chamber 2.
The area (size) of the opening of the exhaust port 22 has a proper value according to the suction port 110 of the turbo-molecular pump 1 to be connected or the shape of a vacuum seal structure 4.
Although not shown, the main vacuum chamber wall 21 is sometimes provided with a takeoff port for a sample handled in the main vacuum chamber 2, a service entrance of wiring for various devices, and the like. In the case where such an opening is provided, the opening is sealed to avoid the leakage of gas.
Next, the sub-vacuum chamber 3 is explained.
The sub-vacuum chamber 3 is a vacuum device provided so as to contain the region of the main vacuum chamber 2, the vacuum seal structure 4, and the upper casing 101 of the turbo-molecular pump 1.
The sub-vacuum chamber 3 is a vacuum vessel that is formed by a sub-vacuum chamber wall 31 and has a roughing exhaust port 32 and a pump penetrating port 33 for allowing the turbo-molecular pump 1 to penetrate through. Like the main vacuum chamber wall 21, the sub-vacuum chamber wall 31 is formed of a strong metal, for example, an aluminum alloy thick plate.
The sub-vacuum chamber 3 is configured so that roughing evacuation is accomplished by a roughing vacuum pump 6.
A roughing exhaust port 32 functions as an exhaust port for internal gas when the sub-vacuum chamber 3 is roughingly evacuated.
The roughing vacuum pump 6 is connected to the sub-vacuum chamber 3 via a roughing selector valve 7 connected to the roughing exhaust port 32.
One side of the roughing selector valve 7 is connected to the roughing exhaust port 32, and the other side thereof is connected to the exhaust port 111 of the turbo-molecular pump 1. By switching over the roughing selector valve 7, the flow path of gas evacuated by the roughing vacuum pump 6 can be selected. Specifically, by switching over the roughing selector valve 7, the supply source of gas introduced into the roughing vacuum pump 6 can be changed over, for example, to the roughing exhaust port 32 only, to the exhaust port 111 of the turbo-molecular pump 1 only, or both of the roughing exhaust port 32 and the exhaust port 111 of the turbo-molecular pump 1.
In this embodiment, the roughing vacuum pump 6 is connected via the roughing selector valve 7. However, the roughing vacuum pump 6 is not limited to this configuration. For example, the suction port of the roughing vacuum pump 6 may be connected directly to the roughing exhaust port 32.
The upper casing 101 of the turbo-molecular pump 1 is fitted in the pump penetrating port 33. In this fitted state, the sub-vacuum chamber 3 is connected to the turbo-molecular pump 1. The sub-vacuum chamber 3 and the turbo-molecular pump 1 are connected to each other by fixing the flange part 118 provided on the upper casing 101 of the turbo-molecular pump 1 to a flange-shaped attachment portion provided in the outer peripheral portion of the pump penetrating port 33 using fastening members such as bolts.
To avoid the leakage of gas from the joint portion between the turbo-molecular pump 1 and the sub-vacuum chamber 3, the connecting portion is sealed. The sealing is performed by interposing a seal member such as an O-ring.
Thus, the sub-vacuum chamber 3 is joined directly to the housing (specifically, the upper casing 101) of the turbo-molecular pump 1. Therefore, the vibrations of the turbo-molecular pump 1 propagate directly to the sub-vacuum chamber 3 via the flange part 118.
In order to restrain the vibrations propagating to the sub-vacuum chamber 3 from further propagating to the main vacuum chamber 2, in this embodiment shown in Figure 1, the main vacuum chamber 2 is fixed to the sub-vacuum chamber wall 31 with vibration dampers 5 being interposed therebetween. By fixing (supporting) the main vacuum chamber 2 via the vibration dampers 5, the main vacuum chamber 2 and the sub-vacuum chamber 3 can be isolated from each other in terms of mechanical vibration.
To properly restrain (shut off) the propagation of vibrations to the main vacuum chamber 2, the vibration damper 5 is preferably a device using, for example, an active control system. Also, in place of the vibration damper 5, a vibration absorber having high vibration absorption efficiency may be used.
By isolating the main vacuum chamber 2 from the outside (a mounting part) in terms of vibration, the influence exerted on a sample or equipment handled in the main vacuum chamber 2 can be reduced.
Next, the vacuum seal structure 4 is explained.
The vacuum seal structure 4 is a structure that is provided in the connecting (joint) portion between the exhaust port 22 of the main vacuum chamber 2 and the suction port 110 of the turbo-molecular pump 1 to provide a seal between the main vacuum chamber 2 and the sub-vacuum chamber 3.
By providing the vacuum seal structure 4 to restrain or reduce gas leakage developing between the main vacuum chamber 2 and the sub-vacuum chamber 3, the evacuation efficiency of the main vacuum chamber 2 can be improved.
The vacuum seal structure 4 is disposed in the sub-vacuum chamber 3 already having become in a vacuum (medium vacuum) state. Therefore, the difference in pressure between the main vacuum chamber 2 and the sub-vacuum chamber 3 can be made very small. Thereby, the quantity of gas leakage into the main vacuum chamber 2 can be kept at a small value.
Also, since the vacuum seal structure 4 is disposed in the sub-vacuum chamber 3 already having become in a vacuum (medium vacuum) state, the vacuum seal structure 4 can use a seal structure having a relatively simple construction depending on the vacuum ultimate performance required by the main vacuum chamber 2.
Further, since the vacuum seal structure 4 in accordance with this embodiment not only is not disposed in the atmosphere but also does not perform a function of supporting the turbo-molecular pump 1, the vacuum seal structure 4 need not be configured by a member so rigid as the damper as described in the related art.
Successively, the specific configurations of the vacuum seal structure 4 are explained.
Figure 2(a) is a view showing the vacuum seal structure 4 in the case where a gap d is used.
Figure 2(b) is a view showing the vacuum seal structure 4 in the case where a labyrinth seal is used.
Figure 2(c) is a view showing the vacuum seal structure 4 in the case where a seal member 43 is used.
First, an example in which the vacuum seal structure 4 is configured by using the gap d is explained.
In this embodiment, as shown in Figure 2(a), the vacuum seal structure 4 is configured by providing a predetermined gap d between the main vacuum chamber 2 and the turbo-molecular pump 1.
Specifically, the predetermined gap, namely, the gap d is provided between the surface (outside surface) facing to the sub-vacuum chamber 3 of the main vacuum chamber wall 21 forming the outer periphery of the exhaust port 22 and the end face on the suction port 110 side of the upper casing 101 of the turbo-molecular pump 1, by which the vacuum seal structure 4 is configured.
Here, a deriving (calculating) method for the gap d provided between the main vacuum chamber 2 and the turbo-molecular pump 1 is explained.
The gap d is set so that the leakage quantity of gas passing through this gap d takes a desired value.
First, a method for calculating the leakage quantity Q [Pam/s] of gas passing through the gap d is explained.
Herein, it is assumed that the diameter φD of the exhaust port 22 is far larger than the gap d, and the flow rate of gas passing between two rectangular surfaces arranged in parallel is taken as a leakage quantity. The phase "between two rectangular surfaces arranged in parallel" (hereunder referred to as "between two parallel surfaces") corresponds to the phrase "between the surface (outside surface) facing to the sub-vacuum chamber 3 of the main vacuum chamber wall 21 forming the outer periphery of the exhaust port 22 and the end face on the suction port 110 side of the upper casing 101 of the turbo-molecular pump 1".
When the short side 2 of rectangle is taken as L, the long side thereof as A, and the correction factor between two parallel surfaces as K [L/d], the inverse number of exhaust resistance expressing the ease of flow of gas between two parallel surfaces, namely, the conductance C [m/s] is given by the following equation. $C = 309 \cdot K \cdot A \cdot d / L in which K = 3 / 8 \ln (L / d)$
On the other hand, when the pressure in the main vacuum chamber 2 is taken as P1 [Pa], the pressure in the sub-vacuum chamber 3 as P2 [Pa], the pressure at the suction port 110 of the turbo-molecular pump 1 as Pb [Pa], and the exhaust velocity of the turbo-molecular pump 1 as Sb [m/s], the following equations hold from the definition of conductance C (Equation 1). $Q = C (P 2 \cdot P 1)$
$Q = Pb \times Sb$
Here, the steady state is taken as Pb = P1.
Since the exhaust port 22 has the diameter φD, A is equal to πD. Solving the equations under these conditions, the relationship between the gap d and the pressure P1 (ultimate pressure) in the main vacuum chamber 2 can be determined. The quantity of gas released from the main vacuum chamber wall 21 surface is omitted because being sufficiently small with respect to Q.
Therefore, the value of the gap d can be derived based on the relationship between the gap d and the pressure P1 (ultimate pressure) in the main vacuum chamber 2.
Thus, the gap d is a value calculated (determined) based on the leakage quantity of gas from the main vacuum chamber 2 and the influence that the leakage quantity exerts on the ultimate pressure in the main vacuum chamber 2.
Successively, an example of actual calculation of the pressure P1 (ultimate pressure) in the main vacuum chamber 2 is given.
Herein, P1 is calculated under the conditions of Sb = 2.0 [m/s], φD = 0.25 [m], L = 50 [mm], and gap d = 0.5 [mm]. Since φD is 0.25 [m], A is nearly equal to 0.94 [m].
If it is assumed that K = 1.73, from Equation 1, C = 1.60 x 10 [Pa].
On the other hand, the steady state is taken as Pb = P1, and the pressure P2 in the sub-vacuum chamber 3 as 1 x 10 [Pa], from Equation 2 and Equation 3, P1 = 4 x 10 [Pa].
Under these conditions, in the case where gap d = 0.5 [mm], the interior of the main vacuum chamber 2 is in a sufficiently low pressure state. Therefore, it is seen that the noncontact type vacuum seal structure 4 using the gap d functions as a vacuum seal.
Since the vacuum seal structure 4 is disposed in the sub-vacuum chamber 3 already having become in a vacuum (medium vacuum) state as described above, even the seal structure with the interposed gap d can sufficiently satisfy the specifications of the vacuum exhausting device.
As described above, in the case where the vacuum seal structure 4 with the gap d is used, in the vacuum seal structure 4 portion, the main vacuum chamber wall 21 and the turbo-molecular pump 1 do not come into physical (mechanical) contact with each other. Therefore, the vibrations produced in the turbo-molecular pump 1 can properly be restrained from propagating via the vacuum seal structure 4.
Also, not only vibrations but also heat generated in the turbo-molecular pump 1 does not transmit via the vacuum seal structure 4, so that a temperature rise due to heating in the main vacuum chamber 2 can be restrained.
Next, an example in which the vacuum seal structure 4 is configured by using the labyrinth seal shown in Figure 2(b) is explained.
The labyrinth seal is a kind of noncontact seal, and restrains (shuts off) the leakage of gas (fluid) by configuring the gap portion by means of a complicated flow path.
By configuring the vacuum seal structure 4 using this labyrinth seal, the vacuum seal characteristics can further be improved as compared with the case where the above-described gap d is used. That is to say, the leakage quantity can be reduced further. Therefore, the main vacuum chamber 2 can reach a lower-pressure state.
The labyrinth seal in the vacuum seal structure 4 in accordance with this embodiment includes a ring-shaped projecting part 41 projecting from the end face on the suction port 110 side of the upper casing 101 of the turbo-molecular pump 1 and a ring-shaped projecting part 42 projecting from the surface (outside surface) facing to the sub-vacuum chamber 3 of the main vacuum chamber wall 21 forming the outer periphery of the exhaust port 22 of the main vacuum chamber 2.
The projecting part 41 and the projecting part 42 each are formed in plural numbers in the radial direction via a gap. The projecting part 41 and the projecting part 42 are arranged so as to engage with each other in a state in which a clearance is provided therebetween, namely, in a noncontact state.
Thus, a complicated gas flow path is formed by the clearance formed in a zigzag shape by the projecting part 41 and the projecting part 42 that are engaged with each other.
In the case where there is a need for further enhancing the gastightness, the pair of the projecting part 41 and the projecting part 42 is added to make the zigzag flow path formed by the labyrinth seal long and complicated.
As described above, in the case where the vacuum seal structure 4 using the labyrinth seal is used, in the vacuum seal structure 4 portion, the main vacuum chamber wall 21 and the turbo-molecular pump 1 do not come into physical (mechanical) contact with each other. Therefore, the vibrations produced in the turbo-molecular pump 1 can properly be restrained from propagating via the vacuum seal structure 4.
Further, not only vibrations but also heat generated in the turbo-molecular pump 1 does not transmit via the vacuum seal structure 4, so that a temperature rise in the main vacuum chamber 2 can be restrained.
Next, an example in which the vacuum seal structure 4 is configured by using the seal member 43 shown in Figure 2(c) is explained.
In the case where vacuum seal characteristics still higher than that of the above-described vacuum seal structure 4 using the labyrinth seal are required, a contact seal using the seal member 43 must be used.
In such a case as well, since the seal member 43 is disposed in the sub-vacuum chamber 3 already having become in a vacuum (medium vacuum) state, the seal member 43 need not be constructed by a member having high rigidity.
Therefore, the seal member 43 can be formed of a material having low rigidity, namely, having high flexibility and excellent vibration absorbing characteristics.
The vacuum seal structure 4 using the seal member 43 in accordance with this embodiment is configured by the seal member 43 disposed between the surface (outside surface) facing to the sub-vacuum chamber 3 of the main vacuum chamber wall 21 forming the outer periphery of the exhaust port 22 of the main vacuum chamber 2 and the end face on the suction port 110 side of the upper casing 101 of the turbo-molecular pump 1.
The seal member 43 is a ring-shaped member fixed on the end face on the suction port 110 side of the upper casing 101 of the turbo-molecular pump 1.
The seal member 43 is formed by a member having high flexibility, for example, a rubber, a polymer material, or the like having a low modulus of elasticity.
By utilizing the flexible characteristics of the seal member 43, even in the case where a difference in pressure is produced between the main vacuum chamber 2 and the sub-vacuum chamber 3, the shape can be deformed flexibly in response to the force acting due to this pressure difference.
Therefore, the contact (sealing) state between the seal member 43 and the surface (outside surface) facing to the sub-vacuum chamber 3 of the main vacuum chamber wall 21 forming the outer periphery of the exhaust port 22 of the main vacuum chamber 2 can always be held easily.
Also, in place of the ring-shaped seal member 43, a cylindrical bellows having a collapsible lantern shaped deep folds at the outer periphery thereof may be used.
On the vacuum seal structure 4 in this embodiment, the atmospheric pressure does not act directly. In addition, the vacuum seal structure 4 is not required to have a function of supporting the main vacuum chamber 2 or supporting the turbo-molecular pump 1, so that the bellows need not have high rigidity.
Therefore, the bellows can also be formed of a material having high flexibility.
As described above, in the case where the vacuum seal structure 4 using the seal member 43 is used, the main vacuum chamber wall 21 and the turbo-molecular pump 1 can be connected (joined) to each other by a flexible member. Therefore, vibrations produced in the turbo-molecular pump 1 can be absorbed properly by the seal member 43.
Also, by forming the seal member 43 of a material considering not only flexibility but also thermal insulation, not only vibrations but also heat generated in the turbo-molecular pump 1 can be restrained from transmitting via the vacuum seal structure 4.
Thus, according to this embodiment, the damping characteristics of vibrations propagating to the main vacuum chamber 2 and the heat transmitting characteristics can be improved significantly.
Next, another embodiment of the vacuum seal structure 4 is explained.
Figure 3 is a view showing the vacuum seal structure 4 in the case where an elastic body 44 is used.
The vacuum seal structure 4 using the elastic body 44 in accordance with this embodiment includes the elastic body 44 disposed between the surface (outside surface) facing to the sub-vacuum chamber 3 of the main vacuum chamber wall 21 forming the outer periphery of the exhaust port 22 of the main vacuum chamber 2 and the end face on the suction port 110 side of the upper casing 101 of the turbo-molecular pump 1 and a groove 45 for fixing the elastic body 44.
The elastic body 44 is made up of a ring-shaped body part 46 made of a thin sheet, which forms a body part, and a metallic plate 47 affixed to one face of the body part 46.
The body part 46 is formed by a member having high flexibility, for example, a rubber, a polymer material, or the like having a low modulus of elasticity.
The metallic plate 47 is a metallic thin sheet affixed so that one face of the body part 46 is coated, and is formed of a metal having flexibility of such a degree as not to influence the elastic characteristics of the body part 46, such as stainless steel or aluminum.
The ring-shaped elastic body 44 configured by a composite (affixing) structure of the body part 46 and the metallic plate 47 is formed curvedly so that in the region toward the outer peripheral end, the surface of the metallic plate 47 warps to the body part 46 side, that is, the surface of the metallic plate 47 is curved.
On the other hand, the body part 46 is formed into a U shape in cross section in the region toward the inner peripheral end so that the metallic plate 47 forms the outside surface.
This U-shaped portion is engaged with the ring-shaped groove 45 formed in the end portion of the upper casing 101 of the turbo-molecular pump 1.
By engaging and fixing the U-shaped portion of the elastic body 44 with and in the groove 45, the vacuum seal structure 4 is configured.
In this embodiment, the elastic body 44 is disposed so that a part of the surface of the metallic plate 47 makes contact lightly with the main vacuum chamber wall 21 in a state in which the elastic body 44 is installed, namely, in a state in which no force acts on the elastic body 44.
In this vacuum seal structure 4, in the curved portion, the surface of the metallic plate 47 of the elastic body 44 faces to the flow path (gas transfer path) of gas exhausted from the main vacuum chamber 2, and the face of the body part 46 faces to the sub-vacuum chamber 3.
Successively, the operation of the vacuum seal structure 4 configured by the elastic body 44 is explained.
Figure 4(a) is a view showing a state of the elastic body 44 in the case where the pressure (P1) in the main vacuum chamber 2 is higher than the pressure (P2) in the sub-vacuum chamber 3.
Figure 4(b) is a view showing a state of the elastic body 44 in the case where the pressure (P1) in the main vacuum chamber 2 is not higher than the pressure (P2) in the sub-vacuum chamber 3.
As shown in Figure 4(a), in the case where the pressure (P1) in the main vacuum chamber 2 is higher than the pressure (P2) in the sub-vacuum chamber 3 (P1 > P2), the force created by the pressure difference acts in the direction such that the contact portion between the elastic body 44 and the main vacuum chamber wall 21 is pushed to open from the main vacuum chamber 2 side, namely from the gas flow path (gas transfer path) side.
Therefore, by the action of the force created by the pressure difference, the elastic body 44 is deformed so as to be warped (curved) further to the body part 46 side, namely, to the sub-vacuum chamber 3 side, by which a clearance is formed between the elastic body 44 and the main vacuum chamber wall 21.
The clearance formed between the elastic body 44 and the main vacuum chamber wall 21 functions so as to leak gas from the main vacuum chamber 2 to the sub-vacuum chamber 3 and thereby to decrease the pressure in the main vacuum chamber 2.
That is to say, by forming this clearance, the state can be transferred in the direction such that the pressure difference between the main vacuum chamber 2 and the sub-vacuum chamber 3 is eliminated.
On the other hand, as shown in Figure 4(b), in the case where the pressure (P1) in the main vacuum chamber 2 is lower than the pressure (P2) in the sub-vacuum chamber 3 (P1 < P2), the force created by the pressure difference acts in the direction such that the warp of the elastic body 44 is returned from the sub-vacuum chamber 3 side.
Therefore, by the action of the force created by the pressure difference, the elastic body 44 is deformed so that the warp (curved portion) of the elastic body 44 is returned to the metallic plate 47 side, namely, to the main vacuum chamber 2 side, by which the elastic body 44 and the main vacuum chamber wall 21 are brought into contact with each other.
The elastic body 44 and the main vacuum chamber wall 21 make contact with each other to form a seal structure. Thereby, the leakage of gas from the sub-vacuum chamber 3 to the main vacuum chamber 2 is shut off.
That is to say, the main vacuum chamber 2 and the sub-vacuum chamber 3 are sealed by the elastic body 44, by which the low-pressure state in the main vacuum chamber 2 can be held properly. Therefore, the efficiency of evacuation can be improved.
In the vacuum seal structure 4 using the elastic body 44, as described above, both of the contact state and the noncontact state are present. Especially in the contact state, wear chips may be produced from the contact potion by a shock at the time of contact. Such wear chips enter into the main vacuum chamber 2 and may become a hindrance to equipment etc.
Therefore, to restrain the wear of the contact portion surface, as shown in Figure 3, a coating member 48 may be provided on the surface (outside surface) facing to the sub-vacuum chamber 3 of the main vacuum chamber wall 21, which comes into contact with the elastic body 44.
As a material for the coating member 48, a metal etc. having hardness higher than that of the metal forming the sub-vacuum chamber wall 31, which is a parent body part, and the metallic plate 47 are used. For example, in the case where the parent body part is formed of stainless steel or aluminum, as the material for the coating member 48, TiO (titanium oxide), TiN (titanium nitrite), DLC (Diamond Like Carbon), and the like are effective.
By providing the above-described coating member 48, the occurrence of wear chips in the contact portion (sliding portion) of the elastic body 44 can be reduced.
Also, in the case where, unlike a metal, a rubber, a polymer material, or the like is provided in a portion that becomes in a super high vacuum state, gas may be released from the member itself, and the gas released from the member may exert any influence on the vacuum device.
However, in the above-described vacuum seal structure 4 using the elastic body 44, a portion facing to the main vacuum chamber 2 of the elastic body 44 is coated with the metallic plate 47, by which the gas released from the body part 46 can be prevented from flowing out directly to the main vacuum chamber 2.
Therefore, as a member forming the body part 46, a rubber, a polymer material, or the like can be used.
By being configured by the composite (affixing) structure of the body part 46 using a rubber, a polymer material, or the like and the metallic plate 47, the elastic body 44 can be configured so that the rigidity is high and the flexibility is high (the damping characteristics are excellent) as compared with the case where the elastic body 44 is configured by a metallic member only.
Conventionally, a communication port between the main vacuum chamber 2 and the sub-vacuum chamber 3 has been needed only when roughing evacuation of the main vacuum chamber 2 before the start of the turbo-molecular pump 1 is accomplished.
However, by configuring the vacuum seal structure 4 using the elastic body 44, the elastic body 44 is opened at the time of roughing evacuation of the main vacuum chamber 2, so that there is no need for separately providing the communication port.
This results in a reduction in cost of the vacuum exhausting device, and also can simplify the device construction and control sequence.
Next, a modification of a connecting method for the exhaust port 111 (exhaust part) in the turbo-molecular pump 1 is explained.
Figure 5 is a view showing a first modification of the connecting method for the exhaust port 111 of the turbo-molecular pump 1 in the vacuum exhausting device in accordance with this embodiment.
In Figure 5, the same reference numerals are applied to elements that are the same as those in the embodiment shown in Figure 1 (duplicated parts), and the detailed explanation thereof is omitted.
In the first modification of the connecting method in accordance with this embodiment, a connection port 34 is further provided in the sub-vacuum chamber 3 to suck the gas exhausted through the exhaust port 111 of the turbo-molecular pump 1.
The connection port 34 and the exhaust port 111 of the turbo-molecular pump 1 are connected to each other by an exhaust duct 35.
The roughing exhaust port 32 of the sub-vacuum chamber 3 is connected to the roughing vacuum pump 6.
In the first modification of the connecting method, the gas in the main vacuum chamber 2 is introduced to the suction port 110 of the turbo-molecular pump 1, and is exhausted through the exhaust port 111 of the turbo-molecular pump 1.
Next, the gas exhausted from the turbo-molecular pump 1 is introduced into the sub-vacuum chamber 3 through the exhaust duct 35, and is mixed with the gas in the sub-vacuum chamber 3.
The gas in the sub-vacuum chamber 3 passes through the roughing exhaust port 32, and is exhausted from the sub-vacuum chamber 3. The roughing evacuation in the sub-vacuum chamber 3 is accomplished by the roughing vacuum pump 6.
Thus, the gas exhausted from the turbo-molecular pump 1 is roughingly evacuated together with the gas in the sub-vacuum chamber 3, by which the vacuum exhausting device can be configured without the use of the roughing selector valve 7 shown in Figure 1. That is to say, the roughing vacuum pump 6 in the vacuum exhausting device need not be provided in plural numbers for the main vacuum chamber 2 and the sub-vacuum chamber 3.
Figure 6 is a view showing a second modification of the connecting method for the exhaust port 111 of the turbo-molecular pump 1 in the vacuum exhausting device in accordance with this embodiment.
In Figure 6, the same reference numerals are applied to elements that are the same as those in the embodiment shown in Figure 1 (duplicated parts), and the detailed explanation thereof is omitted.
The second modification of the connecting method in accordance with this embodiment is configured so that the exhaust duct 35 used in the first modification of the connecting method is further excluded.
In the second modification of the connecting method, an upper casing 101' forming the housing of the turbo-molecular pump 1 is extended so as to be longer than the axial length of the upper casing 101 shown in Figure 1.
The upper casing 101' is extended to such an extent that the end face on the axis line exhaust direction side thereof is provided near the end portion of the turbo-molecular pump 1. Therefore, the upper casing 101' is configured so that an exhaust port 111' is formed in the side surface of the upper casing 101'.
The turbo-molecular pump 1 is joined to the sub-vacuum chamber 3 in a state in which the upper casing 101' is fitted in the sub-vacuum chamber 3. Therefore, the exhaust port 111' of the turbo-molecular pump 1 is arranged so as to communicate with the sub-vacuum chamber 3.
Thereby, the gas exhausted from the turbo-molecular pump 1 can be introduced into the sub-vacuum chamber 3 through the exhaust port 111'. That is to say, the exhaust duct 35 for connecting the exhaust port 111 of the turbo-molecular pump 1, which is provided in the first modification of the connecting method shown in Figure 5, to the sub-vacuum chamber 3 can be excluded.
According to the second modification of the connecting method, the gas exhausted from the turbo-molecular pump 1 is introduced directly into sub-vacuum chamber 3 and roughingly evacuated together with the gas in the sub-vacuum chamber 3, by which the vacuum exhausting device can be configured without the use of the roughing selector valve 7 shown in Figure 1 and further without the installation of the exhaust duct 35.
Next, modifications of a fixing method of the main vacuum chamber 2 in the vacuum exhausting device in accordance with this embodiment are explained.
Figure 7(a) is a view showing a first modification of the fixing method for the main vacuum chamber 2 in the vacuum exhausting device in accordance with this embodiment.
Figure 7(b) is a view showing a second modification of the fixing method for the main vacuum chamber 2 in the vacuum exhausting device in accordance with an embodiment.
In Figure 7, the same reference numerals are applied to elements that are the same as those in the embodiment shown in Figure 1 (duplicated parts), and the detailed explanation thereof is omitted.
The first modification of the fixing method shown in Figure 7(a) has, in addition to the configuration of this embodiment shown in Figure 1, a configuration in which the sub-vacuum chamber 3 is fixed to the ground surface (fixing surface) with vibration dampers 51 being interposed.
By fixing the sub-vacuum chamber 3 to the ground surface via the vibration dampers 51, the sub-vacuum chamber 3 can further be isolated from the ground surface in terms of mechanical vibration. Thereby, external vibrations such as seismic vibrations that propagate from the ground surface (fixing surface) to the sub-vacuum chamber 3 can be restrained (reduced) properly.
The second modification of the fixing method shown in Figure 7(b) has a configuration in which the sub-vacuum chamber 3 is fixed to the ground surface (fixing surface) with the vibration dampers 51 being interposed, and the main vacuum chamber 2 is fixed to the ground surface(fixing surface) with vibration dampers 52 being interposed.
The vibration damper 52 that supports the main vacuum chamber 2 must be disposed so as to penetrate the sub-vacuum chamber wall 31, so that gas may leak from the location at which the vibration damper 52 penetrates the sub-vacuum chamber wall 31.
Therefore, the location at which the vibration damper 52 penetrates the sub-vacuum chamber wall 31 is sealed by a seal member 53. As the seal member, for example, an O-ring is used.
By fixing the main vacuum chamber 2 to the ground surface via the vibration dampers 52, the influence of vibrations on the main vacuum chamber brought from the sub-vacuum chamber 3 can be reduced.
The vibration damper 51, 52 used in the first and second modifications of the fixing method is preferably a device using, for example, the active control system like the vibration damper 5. Also, in place of the vibration damper, a vibration absorber having high vibration absorption efficiency may be used.
According to this embodiment in which the vacuum chamber has a double construction consisting of the main vacuum chamber 2 and the sub-vacuum chamber 3, and the vacuum seal structure 4 provided between the turbo-molecular pump 1 and the main vacuum chamber 2 is disposed in the sub-vacuum chamber 3, the heat generated in the turbo-molecular pump 1, the vibrations produced by a failure etc. of the turbo-molecular pump 1, or the moment applied to the turbo-molecular pump 1 can be prevented from propagating (transmitting) to the main vacuum chamber 2, or can be damped (reduced).
Therefore, the influence that the vibrations and heat produced in the turbo-molecular pump 1 exert on the main vacuum chamber 2 side can be restrained (reduced).

Claims

A vacuum exhausting device comprising:
a main vacuum chamber;

a vacuum pump for evacuating the main vacuum chamber; and

a sub-vacuum chamber that contains the main vacuum chamber and a suction port of the vacuum pump and is roughingly evacuated, characterized in that

the main vacuum chamber and the vacuum pump are joined to each other via a seal structure for preventing or reducing the leakage of gas between the main vacuum chamber and the sub-vacuum chamber.
The vacuum exhausting device according to claim 1, characterized in that the main vacuum chamber and the vacuum pump are joined to each other via a predetermined gap, a noncontact seal, a seal member, or an elastic member that is deformed according to a difference in pressure between the main vacuum chamber and the sub-vacuum chamber.
The vacuum exhausting device according to claim 1 or 2, characterized in that the vacuum exhausting device further comprises a roughing vacuum pump for roughingly evacuating the sub-vacuum chamber, and
an exhaust port of the vacuum pump communicates with the sub-vacuum chamber.