EXHAUSTING SYSTEM

Abstract

An exhausting system capable of preventing gas condensation and early overheat in a vacuum pump without causing an increase in the costs of the entire exhausting system and suitable for relaxing the operable conditions of the entire exhausting system including a flow rate at which gas is successively exhausted. An exhausting system is predicated on a constitution including: at least a first vacuum pump and a second vacuum pump connected in series; and a connecting portion disposed therebetween, the exhausting system exhausting gas containing a condensable gas via the vacuum pumps and the connecting portion. In the exhausting system, an environment inside the connecting portion is set to an environment having a vapor phase region below a vapor pressure curve of the condensable gas flowing through an inside of the connecting portion by providing the second vacuum pump near the first vacuum pump.

Claims

1. An exhausting system including: as at least two pumps, a first vacuum pump and a second vacuum pump connected in series; and a connecting portion disposed therebetween, the exhausting system exhausting gas containing a condensable gas via the vacuum pumps and the connecting portion, wherein an environment inside the connecting portion is set to be an environment included in a vapor phase region below a vapor pressure curve of the condensable gas flowing through an inside of the connecting portion by providing the second vacuum pump near the first vacuum pump.

2. The exhausting system according to claim 1, wherein the first vacuum pump and the second vacuum pump are connected and integrated with each other.

3. The exhausting system according to claim 1, wherein the connecting portion is provided with a vibration controlling structure.

4. The exhausting system according to claim 1, wherein the first vacuum pump is positioned upstream of the second vacuum pump and composed of a turbomolecular pump.

5. The exhausting system according to claim 4, wherein the turbomolecular pump has a blade exhausting mechanism that exhausts the gas with a rotor blade and a stator blade and is structured so as not to have a drag pump mechanism.

6. The exhausting system according to claim 4, wherein the environment inside the connecting portion is set to be an environment included in the vapor phase region below the vapor pressure curve of the condensable gas flowing through the inside of the connecting portion by decreasing pressure inside the connecting portion without increasing temperature inside the connecting portion.

7. The exhausting system according to claim 1, wherein the second vacuum pump is positioned downstream of the first vacuum pump and composed of a positive displacement pump.

8. The exhausting system according to claim 7, wherein the positive displacement pump has a heater for heating an inside of the positive displacement pump, a temperature sensor for measuring temperature inside the positive displacement pump, and a temperature controlling circuit for controlling heating temperature of the heater by using a measurement value obtained by the temperature sensor.

9. The exhausting system according to claim 7, wherein the positive displacement pump has an inverter circuit and is capable of changing a rotational speed by the inverter circuit.

10. The exhausting system according to claim 7, wherein the positive displacement pump has a low-speed operating function to be capable of operating at a rotational speed lower than a rotational speed in a normal operation thereof.

11. The exhausting system according to claim 2, which has a structure in which a controlling circuit for at least one of the first vacuum pump and the second vacuum pump is accommodated in a housing and the housing is connected and integrated with at least one of the vacuum pumps.

12. The exhausting system according to claim 11, wherein a thermal insulating means is provided at a connecting portion between one of the first vacuum pump and the second vacuum pump and the housing of the controlling circuit.

13. The exhausting system according to claim 1, wherein a third vacuum pump is arranged and connected downstream of the second vacuum pump.

14. The exhausting system according to claim 1, wherein an environment inside the second vacuum pump is set to be an environment included in a solid phase region above the vapor pressure curve of the condensable gas flowing through the inside of the second vacuum pump.

15. The exhausting system according to claim 13, wherein an environment inside a second connecting portion connecting the second vacuum pump with the third vacuum pump is set to be an environment included in a solid phase region above the vapor pressure curve of the condensable gas flowing through the inside of the second connecting portion.

16. The exhausting system according to claim 15, wherein one of a storing tank or a trap for trapping a condensed or coagulated gas component is provided at the second connecting portion connecting the second vacuum pump with the third vacuum pump.

17. A vacuum pump constituting the exhausting system according to claim 1.

18. A component of the vacuum pump according to claim 17.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG. 1 is a configuration diagram of an exhausting system according to an embodiment of the present invention;

[0041] FIG. 2 is a vapor pressure curve diagram for describing the operating principle of the exhausting system to which the present invention is applied;

[0042] FIG. 3 is a cross-sectional diagram of a turbomolecular pump adopted as a first vacuum pump in the exhausting system in FIG. 1;

[0043] FIG. 4 is a cross-sectional diagram for describing vibration controlling structures;

[0044] FIG. 5 is a cross-sectional diagram for describing the vibration controlling structures;

[0045] FIG. 6 is a cross-sectional diagram for describing a thermal insulating unit;

[0046] FIG. 7 is an explanatory diagram of an example in which a trapping unit is applied to the exhausting system in FIG. 1;

[0047] FIG. 8 is a configuration diagram of an exhausting system according to another embodiment of the present invention;

[0048] FIG. 9 is a configuration diagram of an exhausting system according to another embodiment of the present invention;

[0049] FIG. 10 is a cross-sectional diagram of a turbomolecular pump adoptable as a first vacuum pump constituting the exhausting system according to the embodiment of the present invention;

[0050] FIG. 11 is an explanatory diagram of pipe laying constituting the connecting portion between the first vacuum pump and a second vacuum pump;

[0051] FIG. 12 is a configuration diagram of a conventional exhausting system; and

[0052] FIG. 13 is a configuration diagram of a combination pump.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] Hereinafter, referring to the accompanying drawings, the best mode for carrying out the present invention will be described in detail.

[0054] FIG. 1 is a configuration diagram of an exhausting system according to an embodiment of the present invention, and FIG. 2 is a vapor pressure curve diagram for describing the operating principle of the exhausting system to which the present invention is applied.

[0055] An exhausting system S1 in FIG. 1 has, as at least two pumps, first and second vacuum pumps P1 and P2 connected in series and exhausts gas containing a condensable gas via the vacuum pumps P1 and P2 and a connecting portion C1 between the vacuum pumps P1 and P2.

[0056] The gas to be exhausted by the exhausting system S1 exists inside a chamber (not shown) to which the first vacuum pump P1 is connected and transfers in the order of the first vacuum pump P1, the connecting portion C1, and the second vacuum pump P2 from the chamber to be exhausted outside the chamber.

[0057] For example, a process chamber constituting semiconductor manufacturing equipment, flat panel display equipment, solar panel manufacturing equipment, or the like is assumed as the chamber, but the exhausting system S1 in FIG. 1 may be adopted as a device for exhausting the gas from a chamber other than such a process chamber.

[0058] As a basic technological idea of measures to prevent gas condensation inside the connecting portion C1 and near the connecting portion C1 (specifically, near a gas outlet port closest to the connecting portion C1 in the entire first vacuum pump P1), in the exhausting system S1 in FIG. 1 the environment inside the connecting portion C1 is set to be an environment to be included in a vapor phase region below a vapor pressure curve VPC (see FIG. 2) of the condensable gas flowing through the inside of the connecting portion C1 by providing the second vacuum pump P2 near the first vacuum pump P1. The setting of the environment will be called measures against condensing gas in the present invention below.

[0059] The installation of the second vacuum pump P2 near the first vacuum pump P1 as described above results in the shortening of the distance of the connecting portion C1 (for example, connecting pipe laying or a connecting path) connecting the first vacuum pump P1 with the second vacuum pump P2 and also results in a reduction in the fluid frictional resistance of the gas flowing through the connecting portion C1 such as pipe laying resistance and path resistance at the connecting portion C1. Therefore, it is possible to realize the above measures against condensing gas in the present invention since pressure inside and near the connecting portion C1 may be kept low substantially like pressure near the outlet port of the first vacuum pump P1.

[0060] Hereinafter, the measures against condensing gas in the present invention will be described in detail using FIG. 2.

[0061] In a vapor pressure curve diagram in FIG. 2, VPC represents the vapor pressure curve of the condensable gas flowing through the inside of the connecting portion C1.

[0062] In addition, a point A in FIG. 2 represents, in the exhausting system S1 taking the measures against condensing gas in the present invention, the relationship between pressure and temperature inside the connecting portion C1 connecting the two vacuum pumps P1 and P2 to each other and near the outlet port of the first vacuum pump P1 communicating with the connecting portion C1.

[0063] A point B in FIG. 2 is shown as a first comparative example and represents the relationship between pressure and temperature near the outlet port of the first vacuum pump P101 constituting the exhausting system S100 in the conventional exhausting system S100 (see FIG. 12) taking the conventional measures against condensing gas described above.

[0064] A point C in FIG. 2 is shown as a second comparative example and represents the relationship between pressure and temperature near the outlet port of the first vacuum pump P101 constituting the exhausting system S100 in a case in which the conventional exhausting system S100 in FIG. 12 does not take the conventional measures against condensing gas.

[0065] Referring to the point C in FIG. 2 shown as the second comparative example, the environment near the outlet port of the first vacuum pump P101 is included in a solid phase region above the vapor pressure curve VPC of the condensable gas flowing through the inside of the first vacuum pump P101 in a case in which the exhausting system S100 does not take the measures against condensing gas. Therefore, gas condenses near the outlet port of the first vacuum pump P101.

[0066] On the other hand, referring to the point A in FIG. 2, the environment inside the connecting portion C1 connecting the two vacuum pumps P1 and P2 to each other and near the outlet port of the first vacuum pump P1 communicating with the connecting portion C1 is included in the vapor phase region below the vapor pressure curve VPC of the condensable gas flowing through the inside of the connecting portion C1 in a case in which the exhausting system S1 takes the measures against condensing gas in the present invention. Therefore, gas does not condense near the outlet port of the vacuum pump P1.

[0067] Meanwhile, referring to the point B in FIG. 2, the environment near the outlet port of the first vacuum pump P101 is included in the vapor phase region below the vapor pressure curve VPC of the condensable gas flowing through the outlet port even in a case in which the conventional exhausting system S100 takes the conventional measures against condensing gas. Therefore, gas hardly condenses near the outlet port of the vacuum pump P101.

[0068] However, in the conventional measures against condensing gas, the environment near the outlet port of the first vacuum pump P101 is set an environment included in the vapor phase region below the vapor pressure curve VPC by increasing temperature inside the connecting portion C1 without decreasing pressure inside the connecting portion C1 between the two vacuum pumps P101 and P102 in the conventional exhausting system S100 shown in FIG. 12. Therefore, as described in Description of the Related Art, the problem of so-called early overheat is likely to occur in the first vacuum pump P101 in the conventional exhausting system S100 taking the conventional measures against condensing gas.

[0069] On the other hand, in the measures against condensing gas in the present invention, the environment inside the connecting portion C1 and near the outlet port of the first vacuum pump P1 is set to be an environment included in the vapor phase region below the vapor pressure curve VPC of the condensable gas flowing through the inside of the connecting portion C1 and the outlet port in the exhausting system S1 in FIG. 1, and the exhausting system S1 takes a method for decreasing the pressure inside the connecting portion C1 without increasing the temperature inside the connecting portion C1 as a specific method for performing the setting. Therefore, the problem of early overheat hardly occurs in the exhausting system S1 taking the measures against condensing gas in the present invention.

[0070] Note that, as other measures against condensing gas in the present invention, it is also possible to take both measures to increase the temperature inside the connecting portion and measures to decrease the pressure inside the connecting portion C1 described above to set the environment inside the connecting portion C1 to be included in the vapor phase region.

[0071] Referring to FIG. 1, the first vacuum pump P1 is positioned upstream of the second vacuum pump P2, and specifically a turbomolecular pump TP1 shown in FIG. 3 is adopted as the first vacuum pump P1.

[0072] As shown in FIG. 3, the turbomolecular pump TP1 serving as the first vacuum pump P1 has a blade exhausting mechanism 50 exhausting gas with rotor blades 51 and stator blades 52 and is structured so as not to have various types of drag pump mechanisms such as a Holweck type, a Siegbahn type, and a Gaede type.

[0073] A first reason why the turbomolecular pump TP1 is structured so as not to have a drag pump mechanism is that the drag pump mechanism has a narrow flow path and a narrow gap through which gas flows, and that the flow path and the gap are easily blocked with the accumulation of a precipitation portion. In addition, as a second reason for not having a drag pump mechanism, the drag pump mechanism increases the fluid frictional resistance of gas when the gas flows through a narrow flow path and a narrow gap described above and increases the pressure of the gas. Thus, it becomes difficult to set the environment inside the connecting portion C1 to be included in the vapor phase region with a decrease in the pressure of the gas. That is, the measures against condensing gas in the present invention are hardly taken when the turbomolecular pump TP1 has the drag pump mechanism.

[0074] Referring to FIG. 3, the turbomolecular pump TP1 serving as the first vacuum pump P1 has, as its specific pump components, a rotor 54 supported by magnetic bearings 53, the plurality of rotor blades 51 provided on the outer peripheral surface of the rotor 54, and the plurality of stator blades 52 fixed onto the inner peripheral surface of a pump case 55 accommodating the rotor 54. The turbomolecular pump TP1 forms the blade exhausting mechanism 50 with the plurality of rotor blades 51 and the plurality of stator blades 52 arranged in multiple stages. In the turbomolecular pump TP1, the rotor blades 51 integrally rotate with the rotor 54, and the rotating rotor blades 51 and the stationary stator blades 52 impart momentum in a prescribed direction to gas molecules. Thus, the gas molecules inside the chamber not shown are exhausted from a suction port 56 to the outlet port 57.

[0075] In addition, the turbomolecular pump TP1 serving as the first vacuum pump P1 has, at its lower part, a cooling unit 60 for suppressing the temperature of the entire pump due to heat generated by its exhausting operation, the cooling unit 60 being composed of a water cooling plate 59 including a water cooling pipe 58 or the like.

[0076] Referring to FIG. 1, the second vacuum pump P2 is positioned downstream of the first vacuum pump P1 (turbomolecular pump TP1) and composed of a positive displacement pump DP1.

[0077] The exhausting system S1 in FIG. 1 adopts a Roots type pump (see FIG. 3) as a specific example of the positive displacement pump DP1 but is not limited to the same. As other examples of the positive displacement pump, the exhausting system S1 may adopt various types of positive displacement pumps other than the Roots type pump such as a screw type pump and a claw type pump.

[0078] The positive displacement pump DP1 may have a keep-warm function. In this case, the positive displacement pump DP1 has a heater (not shown) for heating the inside of the pump DP1, a temperature sensor (not shown) for measuring temperature inside the pump DP1, and a temperature controlling circuit (not shown) for controlling (for example, feedback control) the heating temperature of the heater using a measurement value obtained by the temperature sensor to realize the keep-warm function.

[0079] In addition, the positive displacement pump DP1 has an inverter circuit not shown (a unit for converting alternate current into alternate current again). With the inverter circuit, the positive displacement pump DP1 is capable of changing its rotational speed.

[0080] Moreover, the positive displacement pump DP1 has a low-speed operating function to be capable of operating at a rotational speed lower than a rotational speed in its normal operation. The low-speed operating function may be realized on the basis of the rotational speed changing function of the inverter circuit.

[0081] As shown in FIGS. 1 and 3, the first vacuum pump P1 and the second vacuum pump P2 are connected and integrated with each other via the connecting portion C1 (pump connecting and integrating structure). In the pump connecting and integrating structure, a communicating hole H (see FIG. 3) is provided in the connecting portion C1 between the vacuum pumps P1 and P2. As shown in FIG. 3, one end of the communicating hole H communicates with the outlet port 57 of the first vacuum pump P1, and the other end thereof communicates with an inlet port 70 of the second vacuum pump P2. Thus, gas exhausted from the first vacuum pump P1 is fed to the side of the second vacuum pump P2 via the communicating hole H of the connecting portion C1.

[0082] The communicating hole H preferably has a large hole diameter over its entirety. Alternatively, a plurality of communicating holes may be provided. This is because it is possible to easily take the measures against condensing gas in the present invention in these cases since the pressure inside the connecting portion C1 and near the outlet port 57 of the first vacuum pump P1 communicating with the connecting portion C1 may be kept low with a reduction in the fluid frictional resistance of gas flowing through the communicating hole H.

[0083] Meanwhile, when the pump connecting and integrating structure is adopted, there is a likelihood of vibrations generated by the second vacuum pump P2 being transmitted to the first vacuum pump P1 and the chamber positioned upstream of the first vacuum pump P1 via the connecting portion C1. For example, when the positive displacement pump DP1 like the Roots type pump is adopted as the second vacuum pump P2, relatively large vibrations are generated from a timing gear for synchronizing the bearing portion of a rotating body and the rotating body, or the like.

[0084] On the other hand, in the turbomolecular pump TP1 adopted as the first vacuum pump P1, a rotating body composed of the rotor 54 and the rotor blades 51 is supported by the magnetic bearings 53 in a non-contact manner as shown in FIG. 3. In the supported state, the gap between the rotating body and a stator portion around the rotating body (specifically, the gap between the rotor blades 51 and the stator blades 52) is controlled to be kept narrow.

[0085] Therefore, when the vibrations generated by the second vacuum pump P2 are transmitted to the operating turbomolecular pump TP1 (first vacuum pump P1) as described above, the rotating body contacts and collides with the surrounding stator portion to be broken inside the turbomolecular pump TP1, which may result in the breakdown of the turbomolecular pump TP1. Accordingly, it is necessary to reliably prevent the vibrations from being transmitted from the positive displacement pump DP1 (second vacuum pump P2) to the turbomolecular pump TP1 (first vacuum pump P1).

[0086] In addition, the suction port 56 of the turbomolecular pump TP1 is connected to the chamber, and precise machining or an operation such as semiconductor etching is performed inside the chamber. Therefore, it is also necessary to reliably prevent the vibrations generated by the positive displacement pump DP1 (second vacuum pump P2) from being finally transmitted to the chamber via the turbomolecular pump TP1 (first vacuum pump P1).

[0087] In order to address the above problems, vibration controlling structures VC in FIG. 4 or FIG. 5 are installed in the connecting portion C1 between the first vacuum pump P1 and the second vacuum pump P2 in the exhausting system S1 in FIG. 1 as units for effectively preventing a phenomenon in which the vibrations generated by the second vacuum pump P2 are transmitted to the first vacuum pump P1 and the chamber positioned upstream of the first vacuum pump P1. Specific examples of the vibration controlling structures VC will be described as the following vibration controlling structures 1-1 to 1-3.

Vibration Controlling Structure 1-1

[0088] In a vibration controlling structure 1-1, as shown in FIG. 4 or FIG. 5, the first vacuum pump P1 and the second vacuum pump P2 are fastened and connected to each other by bolts BT1 and vibration absorbing members DN1 and DN2 such as rubber bushes are interposed at the fastening and connecting portions to absorb the vibrations generated by the second vacuum pump P2.

[0089] When the first vacuum pump P1 and the second vacuum pump P2 are connected to each other via the cooling unit 60, i.e., when the cooling unit 60 is interposed at the connecting portion C1 between the first vacuum pump P1 and the second vacuum pump P2, the vibration absorbing members DN1 and DN2 may be interposed between the first vacuum pump P1 and the cooling unit 60 and between the second vacuum pump P2 and the cooling unit 60, respectively, as shown in FIG. 4 or FIG. 5.

[0090] By the interposition of the vibration absorbing members DN1 and DN2, a prescribed gap G1 is formed between the second vacuum pump P2 and the cooling unit 60. The gap G1 may be provided between the first vacuum pump P1 and the cooling unit 60. Alternatively, it is also possible to remove one of the vibration absorbing members according to a size of the vibrations generated by the second vacuum pump P2.

[0091] The vibration absorbing members DN1 and DN2 of this type are preferably made of a material having high heat resistance and low hardness like, for example, silicon rubber.

Vibration Controlling Structure 1-2

[0092] In a vibration controlling structure 1-2, as shown in FIG. 4 or FIG. 5, stepped bolts are adopted as the bolts BT1 and a crushing degree of the vibration absorbing members DN1 and DN2 is appropriately managed to prevent the excessive fastening of the bolts BT1 and the disappearance of the gap G1 due to the vibrations generated by the second vacuum pump P2 and effectively exhibit a vibration absorbing effect with the gap G1 and the vibration absorbing members DN1 and DN2. This is because, when the gap G1 disappears due to an inappropriate crushing degree of the vibration absorbing members DN1 and DN2, the second vacuum pump P2 and the cooling unit 60 directly contact each other or the first vacuum pump P1 and the cooling unit 60 directly contact each other to wear off the vibration controlling effect with the gap G1 and the vibration absorbing members DN1 and DN2.

Vibration Controlling Structure 1-3

[0093] In a vibration controlling structure 1-3, as shown in FIG. 5, a cylindrical spacer SP is inserted into the communicating hole H provided in the connecting portion C1 between the two vacuum pumps P1 and P2, and annular elastic members RD1 and RD2 such as O-rings are attached to the upper-end outer peripheral surface and the lower-end outer peripheral surface of the spacer SP. In addition, the spacer SP is set to be put in a floating state in the communicating hole H and the outlet port 57 of the first vacuum pump P1 via the annular elastic members RD1 and RD2. Thus, the spring rigidity of a vibration transmitting path via the surrounding of the communicating hole H reduces, whereby the transmission of the vibrations of the second vacuum pump P2 to the first vacuum pump P1 is alleviated. Note that the spacer SP may be replaced by a bellows.

[0094] Specifically, in the alleviation of the transmission of the vibrations by the vibration controlling structure 1-3, the entire second vacuum pump P2 moves, when the vibrations are generated by the second vacuum pump P2, like a conical pendulum with the upper-side annular elastic member RD1 as a base point to alleviate the transmission of the vibrations from the second vacuum pump to the first vacuum pump.

[0095] Note that the vibration controlling structure VC in FIG. 4 includes the vibration controlling structure 1-1 and the vibration controlling structure 1-2, and that the vibration controlling structure VC in FIG. 5 includes the vibration controlling structure 1-3, the vibration controlling structure 1-1, and the vibration controlling structure 1-2.

[0096] Referring to FIG. 3, the first vacuum pump P1 and the second vacuum pump P2 have respective controlling circuits CC as units for controlling the supply of power to the pumps, the number of the rotations of the pumps, or the like. As a specific installation structural example of the controlling circuits CC, a housing BX serving as a circuit accommodating box is installed at a position below the first vacuum pump P1 and next to the second vacuum pump P2, and the controlling circuits CC are accommodated in the housing BX in the exhausting system S1 in FIG. 1. Thus, a structure (hereinafter called a circuit and pump integrated structure) is configured in which the controlling circuits CC are connected and integrated with the first and second vacuum pumps P1 and P2.

[0097] At the connecting portion between the first vacuum pump P1 and the housing BX of the controlling circuits CC, specifically, at the position between the cooling unit 60 provided below the first vacuum pump P1 and the housing BX, a thermal insulating unit DD is provided as shown in FIG. 6 as a unit for preventing the occurrence of water condensation inside the housing BX.

[0098] Meanwhile, in the circuit and pump integrated structure, the housing BX is also cooled by heat conduction when the first vacuum pump P1 is cooled by the cooling unit 60. As a result, water condensation may occur inside the housing BX. In this case, there is a likelihood of a malfunction or a breakdown occurring in the controlling circuits CC due to water droplets caused by the water condensation. Therefore, the thermal insulating unit DD cuts off a heat conducting path to prevent the occurrence of the water condensation.

[0099] As a specific configuration example of the thermal insulating unit DD, the exhausting system S1 in FIG. 1 adopts, as shown in FIG. 6, both a system in which an air space (thermal insulating space) DG for insulation is provided between the water cooling plate 59 constituting the water cooling unit 60 and the housing BX and a system in which a collar (thermal insulating collar) DC for insulation is provided around a bolt BT2 fastening the water cooling plate 59 and the housing BX together. Where necessary, it is also possible to remove one of these systems. The material of the thermal insulating collar DC may include, but not limited to, stainless steel or ceramics.

[0100] The circuit and pump integrated structure is not limited to the above example, but a structure may be adopted in which the controlling circuit CC of at least one of the first vacuum pump P1 and the second vacuum pump P2 is accommodated in the housing BX and the housing BX is connected and integrated with at least one of the vacuum pumps (P1 or P2).

[0101] In the exhausting system S1 in FIG. 1, a third vacuum pump P3 is further arranged and connected downstream of the second vacuum pump P2.

[0102] In the exhausting system S1 in FIG. 1, a connecting portion C2 (second connecting portion) connecting the second vacuum pump P2 with the third vacuum pump P3 is configured to include pipe laying PL1 connecting the vacuum pump P2 with the vacuum pump P3, a valve VL1 provided halfway through the pipe laying PL1, or the like, and gas exhausted from an outlet port 71 of the second vacuum pump P2 transfers to the third vacuum pump P3 via the pipe laying PL1 and the valve VL1.

[0103] In the configuration having the third vacuum pump P3 like the exhausting system S1 in FIG. 1, the following first gas condensing environment or second gas condensing environment may be adopted.

First Gas Condensing Environment

[0104] The first gas condensing environment is an environment in which the environment inside the second vacuum pump P2 is included in the solid phase region above the vapor pressure curve VPC of the condensable gas flowing through the inside of the second vacuum pump P2. For example, the setting of the environment may be realized in such a manner that temperature inside the second vacuum pump P2 is kept at prescribed temperature by the keep-warm function of the second vacuum pump P2 to make pressure corresponding to the prescribed temperature exceed the vapor pressure curve VPC of the condensable gas inside the second vacuum pump P2.

Second Gas Condensing Environment

[0105] The second gas condensing environment is an environment in which the environment inside the connecting portion C2 connecting the second vacuum pump P2 with the third vacuum pump P3 is included in the solid phase region above the vapor pressure curve VPC of the condensable gas flowing through the connecting portion C2. For example, the setting of the environment may be realized in such a manner that temperature inside the connecting portion C2 is kept at prescribed temperature by the keep-warm function of the connecting portion C2 to make pressure corresponding to the prescribed temperature exceed the vapor pressure curve VPC of the condensable gas inside the connecting portion C2.

[0106] When the first gas condensing environment is adopted, gas condenses inside the second vacuum pump P2, specifically inside a gas exhausting flow path formed by the gap between the rotating bodies and the stator portion around the rotating bodies and the condensed gas component adheres to the inside of the gas exhausting flow path. It is possible to quickly and effectively remove the adhering condensed gas component making use of the mechanical structural characteristics of the second vacuum pump P2.

[0107] That is, the second vacuum pump P2 is the positive displacement pump DP1 like the Roots type pump as described above and is so structured that the rotating bodies rotate with a small gap maintained between the rotating bodies and the stator portion around the rotating bodies, or rotate with a small gap maintained between the rotating bodies. Therefore, when the thickness of the adhering condensed gas component becomes larger than the gap around the rotating bodies, the condensed gas component is scraped away by the rotating bodies to be reliably removed. In order to prevent the scraped-away condensed gas component from flowing back to the upstream side, it is preferable to set the temperature of the second vacuum pump P2 so that the pressure exceeds the vapor pressure curve VPC of the condensable gas near the outlet port 71 of the second vacuum pump P2.

[0108] When the first gas condensing environment is adopted, it is assumed to install, as a specific method for collecting the scraped-away condensed gas component described above, a precipitation matter collecting tank TK via straight-type pipe laying PL2 right below the outlet port 71 of the second vacuum pump P2 as shown in, for example, FIG. 1. According to the method, the scraped-away condensed gas component falls in the precipitation matter collecting tank TK under its own weight to be collected by way of the pipe laying PL2 and a valve VL2 halfway through the pipe laying PL2.

[0109] In addition, when the first gas condensing environment is adopted, it is preferable to perform, in stopping the second vacuum pump P2, a so-called idling operation in which the second vacuum pump P2 operates at low speed until its temperature decreases and the heat shrinkage of the components of the pump, i.e., the rotating bodies and the stator member around the rotating bodies completely ends to perform the above scraping-away operation. This is because a problem such as locking of the rotating bodies of the second vacuum pump P2 due to the unscraped-away condensed gas component is prevented by the idling operation.

[0110] On the other hand, when the second gas condensing environment is adopted, gas condenses on the downstream side of the second vacuum pump P2, specifically at the connecting portion C2 connecting the second vacuum pump P2 with the third vacuum pump P3. Therefore, as shown in FIG. 7, a trapping unit TR such as a storing tank and a trap TR1 for trapping the condensed or coagulated (or solidified) gas component is provided halfway through the pipe laying PL1 constituting the connecting portion C2. Thus, the condensed gas component may be trapped.

[0111] That is, when the environment inside the trapping unit TR, for example, inside the trap TR1 or the storing tank is included in the solid phase region above the vapor pressure curve VPC of the condensable gas flowing through the trap TR1 or the storing tank, gas condenses inside the trapping unit TR such as the trap TR1 and the storing tank and the condensed gas component may be trapped by the trapping unit TR.

[0112] The trap TR1 has, as shown in, for example, FIG. 7, a pressure container 80, a plurality of plate-shaped members 81 (trapping plates) installed inside the pressure container 80, and a refrigerant flowing path 82 through which a refrigerant (cooling water or the like) for cooling the inside of the pressure container 80 and the plate-shaped members 81 flows. The trap TR1 may be so configured as to cool the inside of the pressure container 80 and the plate-shaped members 81 with the refrigerant and thus the condense condensable gas inside the pressure container 80 to make the condensed gas component adhere to the plate-shaped members 81. In this case, the plate-shaped members 81 are installed in parallel with the flow of the gas. This is because the inhibition of the flow of the gas by the plate-shaped members 81 is prevented. The storing tank may be configured in the same manner as the trap TR1.

[0113] In the maintenance of the trap TR1, it is only necessary to close a manual valve VL3 provided halfway through the pipe laying PL1 constituting the connecting portion C2 and a magnetic valve VL1 and open the pressure container 80 to extract and replace the plate-shaped members 81. On this occasion, although not shown in the figure, it is possible to doubly provide the valves VL3 to perform the extraction and replacement of the plate-shape members 81 in a state in which the condensed gas component accumulated in the trap TR1 is contained in the pressure container 80.

[0114] FIGS. 8 and 9 are configuration diagrams of exhausting systems according to other embodiments of the present invention.

[0115] The exhausting system S1 in FIG. 1 adopts the configuration in which the first vacuum pump P1 and the second vacuum pump P2 are connected and integrated with each other via the connecting portion C1. Instead of this, a configuration in which a first vacuum pump P1 and a second vacuum pump P2 are separated from each other and the second vacuum pump P2 is connected in series near the separated first vacuum pump P1 via a connecting portion C1 like an exhausting system S2 shown in FIG. 8 may be adopted. In this case, the connecting portion C1 is composed of pipe laying PL4, and gas transfers from the first vacuum pump P1 to the second vacuum pump P2 via the pipe laying PL4.

[0116] The exhausting system S2 in FIG. 8 may adopt a turbomolecular pump TP2 having a large-diameter outlet port 57 shown in FIG. 10 as the first vacuum pump P1. Note that the turbomolecular pump TP2 shown in FIG. 10 has basically the same configurations as those of the turbomolecular pump TP1 shown in FIG. 3. Therefore, the same members will be denoted by the same symbols, and their detailed descriptions will be omitted.

[0117] In a positive displacement pump DP1 adopted as the second vacuum pump P2, rotors long in their rotating axis directions may be used as rotating bodies. In this case, the second vacuum pump P2 (positive displacement pump DP1) has a rectangular suction port 70, or a plurality of suction ports 70 is arranged in a line. Therefore, pipe laying PL4 having a shape shown in, for example, FIG. 11 is preferably adopted as the pipe laying PL4 in the exhausting system S2 in FIG. 8.

[0118] In the exhausting system S2 in FIG. 8 as well, the second vacuum pump P2 is installed near the first vacuum pump P1 as described above. Therefore, like the exhausting system S1 in FIG. 1, the environment inside the connecting portion C1 may be set to be an environment included in the vapor phase region below the vapor pressure curve of the condensable gas flowing through the inside of the connecting portion C1. As a result, the same function and effect as those of the exhausting system S1 in FIG. 1 are obtained.

[0119] In the exhausting system S2 in FIG. 8, the L-type pipe laying PL4 is adopted as the specific configuration of the connecting portion C1. However, when straight-type pipe laying PL5 shown in FIG. 9 is adopted as the connecting portion C1 instead of the L-type pipe laying PL4, a configuration in which the second vacuum pump P2 is installed near a position right below the first vacuum pump P1 may be adopted. A pressure loss caused by the fluid frictional resistance of gas in the straight-type pipe laying PL5 is smaller than that caused in the L-type pipe laying PL4. Therefore, the straight-type pipe laying PL5 is more suitable for taking the measures against condensing gas in the present invention described above.

[0120] The present invention is not limited to the above embodiments but may be modified in many ways by persons having ordinary knowledge in the filed concerned within the technological idea of the present invention.

[0121] The present invention describes an example in which the condensable gas changes its phase from gas to solid in the vapor pressure curve diagram in FIG. 2. However, the present invention also includes a case in which the condensable gas changes its phase from gas to liquid and a case in which the condensable gas changes its phase from gas to solid via liquid to be capable of producing the same effect.

[0122] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0123] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.