JP2009203945A - Multistage vacuum pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably operate a multistage vacuum pump over a long period of time by introducing purging inert gas in a pump according to a flow rate of process gas flowing in the pump without causing an adverse influence on the exhaust performance of the pump, and without increasing running cost. <P>SOLUTION: This multistage vacuum pump includes a pressure sensor 42 detecting pressure on the intake side of the downstream side final stage 34, an inert gas introducing pipe 44 introducing purging inert gas to the intake side of the downstream side final stage 34, a valve element 46 arranged in the inert gas introducing pipe 44, and a control part 48 for controlling the opening/closing of the valve element 46 according to a pressure value detected by the pressure sensor 42. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multistage vacuum pump, and more particularly to a multistage vacuum pump used for exhausting process gases such as condensable gas and corrosive gas.

  For example, an etching apparatus or a CVD apparatus that performs an etching process or a CVD process on a substrate such as a semiconductor wafer or a liquid crystal panel includes a vacuum pump that evacuates the vacuum chamber. When a process gas such as a condensable gas or a corrosive gas is introduced into this type of vacuum pump, the gas may condense and precipitate inside the vacuum pump, or the vacuum pump may corrode.

  In order to prevent such gas condensation inside the vacuum pump and corrosion of the vacuum pump, an inert gas for purging for diluting the suction target gas into the suction target gas (process gas) flowing inside the pump housing. There has been proposed one in which (purge gas) is introduced (see Patent Document 1). In addition, the applicant introduces an inert gas into the pipe immediately after the vacuum pump to reduce the partial pressure of the process gas discharged from the vacuum pump (see Patent Document 2), or in a vacuum region. A vacuum exhaust system has been proposed in which the flow rate of the shaft seal gas supplied to the vacuum pump is controlled based on the pressure detected by the installed pressure sensor (see Patent Document 3).

JP 2004-293466 A JP-A-4-330388 JP 2006-342688 A

  If a large amount of inert gas for purging is introduced into the pump between the stages of the multistage vacuum pump, the apparent exhaust speed in the compression stage on the downstream side where the inert gas has been introduced generally decreases, resulting in a multistage vacuum. The pressure balance of the pump as a whole changes, the pump inlet pressure increases, and the exhaust performance decreases.

For this reason, in the conventional multistage vacuum pump, an inert gas for purge is introduced into the pump within a range that does not affect the pumping performance of the pump, and a large amount of process gas flows inside the pump. In this case, it is not possible to introduce an inert gas for purging that corresponds to the amount inside the pump, and it is also inert inside the pump even during pump idle operation where process gas does not flow inside the pump. Since the gas was introduced, the inert gas was wasted.
When a heated purge inert gas (purge gas) is introduced into the pump as in the vacuum pump described in the cited document 2, the pump temperature rises when the process gas is a corrosive gas, and the pump It is thought that the internal corrosive environment is deteriorated.

  The present invention has been made in view of the above circumstances, and does not adversely affect the exhaust performance of the pump or increase the running cost, and inactive for purging according to the flow rate of the process gas flowing inside the pump. An object of the present invention is to provide a multistage vacuum pump in which gas is introduced into the pump so that the gas can be stably operated for a long period of time.

  In order to solve the above problems, the multistage vacuum pump of the present invention introduces a pressure sensor for detecting the pressure on the intake side of the downstream final compression stage and an inert gas for purging to the intake side of the downstream final compression stage. An inert gas introduction pipe; a valve body installed in the inert gas introduction pipe; and a control unit that controls opening and closing of the valve body according to a pressure value detected by the pressure sensor.

  If a large amount of inert gas for purging is introduced inside the pump between the stages of the multistage vacuum pump, the apparent pumping speed usually decreases in the downstream compression stage where the inert gas is introduced, and the entire multistage vacuum pump The pressure balance changes and the pump inlet pressure increases. However, when a large amount of process gas is sucked into the pump through the pump inlet and a large amount of process gas is flowing inside the pump, a large amount of inert gas for purging is introduced into the pump between the stages of the multistage vacuum pump. Even so, the pressure at the pump inlet is hardly affected by the inert gas introduced from between the stages.

  According to the present invention, the pressure on the intake side of the downstream final compression stage is detected by the pressure sensor, it is determined whether the process gas is introduced into the pump from the pump intake port, and a predetermined amount of process is detected from the pump intake port. Only when the gas is introduced into the pump, a large amount of inert gas can be introduced into the pump by opening the valve body. As a result, when the pump exhausts a large amount (for example, 5 to 100 SLM (Standard Liter / Min)) of a process gas such as a condensable gas or a corrosive gas, the process gas is compressed, and the process gas is the most inside the pump. A large amount of inert gas can be introduced into the pump at the inlet of the downstream final compression stage where the gas is concentrated, and it is possible to suppress solids from adhering to the pump and corrosion of the pump. Moreover, the running cost can be reduced by introducing the inert gas into the pump only when necessary.

  It further has another inert gas introduction pipe for introducing an inert gas in the vicinity of the discharge part of the downstream final compression stage, and the other inert gas introduction pipe according to the pressure value detected by the pressure sensor The controller may control the opening and closing of the valve body installed inside.

  As a result, when the inert gas cannot be introduced into the pump from the intake side of the final compression stage without affecting the pressure at the pump intake port, the inert gas is pumped from the vicinity of the discharge part of the final compression stage. It can be introduced into the interior to dilute only the vicinity of the discharge portion, or to obtain a dilution effect over the entire final compression stage.

It is preferable that at least one of the compression stages located on the upstream side of the inert gas introduction pipe has a screw form of compression.
The compression type of the compression stage may be root type, claw type or screw type, but the screw type (screw pump) is sealed with two rotor outer diameters and casing inner diameter at the intake and exhaust ports. It is a structure which can obtain a high compression ratio in a single stage as compared with other types. Therefore, when an inert gas is introduced into the pump, the exhaust pressure rises in the previous stage, but by making this part a screw-type compression stage, the exhaust performance in the previous stage is further prevented from being affected. Can do.

The total number of compression stages is preferably 3 or more.
In this way, by setting the number of compression stages to three or more, the influence of pressure deterioration (pressure increase) on the pump inlet when the inert gas for purging is introduced into the pump can be suppressed. it can.

  According to the present invention, an inert gas for purging is introduced into the pump from the intake side of the final compression stage in accordance with the flow rate of the process gas flowing inside the pump, thereby adversely affecting the exhaust performance of the pump, Without increasing the running cost, the process gas is compressed, and it is possible to suppress the solid from adhering to the final compression stage where the process gas is most concentrated inside the pump or the occurrence of corrosion.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following examples, the same or corresponding members are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 shows a multistage vacuum pump according to an embodiment of the present invention. As shown in FIG. 1, the multistage vacuum pump of this example is mainly composed of a first vacuum pump 10 having two compression stages and a second vacuum pump 12 having two compression stages. The first vacuum pump 10 is provided with a pump intake port 14, and the second vacuum pump 12 is provided with a pump exhaust port 16. The exhaust port 18 of the first vacuum pump 10 and the intake port 20 of the second vacuum pump 12 are connected to each other by a connecting pipe 22.

  The first vacuum pump 10 is a Roots-type vacuum pump having a pair of Roots-type pump rotors 24 (only one pump rotor is shown in FIG. 1). The first-stage root part 26 and the two-stage root part 28 are compressed in two stages. A step is provided inside. The second vacuum pump 12 is a screw-type vacuum pump having a pair of screw-type pump rotors 30 (only one pump rotor is shown in FIG. 1), and two-stage compression of a first-stage screw part 32 and a second-stage screw part 34. A step is provided inside.

  For example, an intake pipe 36 extending from a vacuum chamber (not shown) incorporated in the substrate processing apparatus is connected to the pump intake port 14 of the first vacuum pump 10. Examples of the substrate processing apparatus include an etching apparatus or a CVD apparatus that performs an etching process or a CVD process on a substrate such as a semiconductor wafer or a liquid crystal panel. An exhaust pipe 38 is connected to the pump exhaust port 16 of the second vacuum pump 12, and gas (process gas) is exhausted to the outside through the exhaust pipe 38. As described above, the multistage vacuum pump of this example includes the first vacuum pump 10 and the second vacuum pump 12 connected in series with each other, and the second vacuum pump 12 is disposed on the downstream side of the first vacuum pump 10. Has been. That is, the first vacuum pump 10 is disposed on the vacuum side with respect to the second vacuum pump 12, and the second vacuum pump 12 is disposed on the atmosphere side with respect to the first vacuum pump 10. The second vacuum pump 12 is configured to be activated under atmospheric pressure.

In the intake side of the second stage screw part 34 of the second vacuum pump 12 that is the final compression stage, that is, the interstage part 40 of the first stage screw part 32 and the second stage screw part 34 of the second vacuum pump 12, the interstage part is provided. A pressure sensor 42 for measuring the pressure in the (intake side of the final compression stage) 40 is installed. Further, an inert gas pipe 44 for introducing an inert gas such as a purge N ₂ gas is connected to the interstage portion 40, and the inert gas introduction pipe 44 is connected to the valve body in the middle thereof. 46. The pressure sensor 42 and the valve body 46 are connected to the control unit 48 via a signal line and / or a power line.

  In the multistage vacuum pump having such a configuration, the second vacuum pump 12 on the downstream side is closer to the atmosphere side than the first vacuum pump 10, so the internal pressure of the second vacuum pump 12 is the internal pressure of the first vacuum pump 10. Higher than pressure. For this reason, when the condensable gas is exhausted, the by-product of the condensable gas is likely to precipitate in the second vacuum pump 12, particularly at the two-stage screw portion 34 of the final compression stage where the pressure is highest. . Similarly, when the corrosive gas is exhausted, the pressure and temperature are increased in the two-stage screw portion 34 of the final compression stage, so that the corrosive environment in the two-stage screw portion 34 becomes severe.

  Therefore, in the multistage vacuum pump of this example, the pressure sensor 42 and the inert gas introduction pipe 44 are provided in the interstage part 40 between the first stage screw part 32 and the second stage screw part 34 of the second vacuum pump 12, and this stage. While measuring the pressure of the interspace 40, the amount of inert gas introduced into the pump through the inert gas introduction pipe 44 is controlled according to the measured pressure value.

  In this type of vacuum vacuum pump, as shown in FIG. 2, when the process gas Q is introduced into the pump and flows through the pump, the exhaust velocity S1 in the first-stage root portion 26, and the first-stage root portion 28 In general, there is a relationship of S1> S2> S3> S4 between the exhaust speed S2, the exhaust speed S3 in the first-stage screw portion 32, and the exhaust speed S4 in the second-stage screw portion 34 from the viewpoint of reducing power consumption. .

  Here, if the exhaust speed of each compression stage in the actual use region is constant regardless of pressure, the effect of diluting the process gas such as condensable gas and corrosive gas, that is, the effect of reducing the partial pressure of the process gas It is only the two-stage screw portion 34 of the second vacuum pump 12 that is the final compression stage. This is because the operating pressure of the compression stage other than the final compression stage is the exhaust capacity of the downstream compression stage, that is, the operating pressure of the first stage root section 26 is the exhaust capacity of the second stage root section 28, and the second stage root section 28. This is because the operating pressure is determined by the exhaust capacity of the first stage screw part 32 and the exhaust pressure of the first stage screw part 32 is determined by the exhaust capacity of the second stage screw part 34, respectively. Since the second screw part (final compression stage) 34 is opened to the atmospheric pressure on the downstream side, it is difficult for pressure to increase due to the introduction of an inert gas inside the pump. It becomes possible to reduce the partial pressure of the process gas by the ratio of the active gas.

  As shown in FIG. 2, when a certain amount of process gas Q is introduced into the pump and flows, the inlet pressure P of the first-stage root section 26, the inlet pressure P2 of the second-stage root section 28, and the first-stage screw section. The inlet pressure P3 of 32, the inlet pressure P4 and the outlet pressure P5 of the stage screw section 34 are P1 = Q / S1, P2 = Q / S2, P3 = Q / S3, P4 = Q / S4, P5 = atmospheric pressure. Become. As described above, the exhaust speed of each compression stage is set to S1> S2> S3> S4 from the viewpoint of reducing power consumption. Therefore, the amount of change in the pressure value when the process gas Q flows inside the pump Is the largest at the inlet pressure P4 of the two-stage screw portion 34 of the second vacuum pump 12. Therefore, the inlet pressure P4 of the second stage screw part 34 of the second vacuum pump 12 having the largest pressure value change inside the pump, that is, the interstage part between the first stage screw part 32 and the second stage screw part 34 of the second vacuum pump 12. By measuring the pressure of 40, it can be determined whether or not the process gas is introduced into the pump from the pump inlet 14.

  FIG. 3 schematically shows the gas flow rate characteristics in the multistage vacuum pump of this embodiment. As shown in FIG. 3, when the inert gas is introduced into the pump from the intake side of the second stage screw portion 34 of the second vacuum pump 2, that is, the interstage portion 40, the pump is compared with the case where the inert gas is not introduced. The pressure at the intake port 14 increases. However, as the amount of process gas introduced from the pump inlet 14 into the pump increases, the influence of the inert gas introduction amount on the pressure of the pump inlet 14 disappears.

  In the multistage vacuum pump of this embodiment, the control unit 48 determines the amount of process gas introduced into the pump through the pump intake port 14 from the measured value of the pressure sensor 42, and the control unit 48 has a predetermined amount. When it is determined that the process gas has been introduced into the pump, the valve body 46 is opened and the inert gas is introduced into the pump from the interstage part 40. Thereby, the pump has a large amount (for example, 5 to 100 SLM (Standard Liter / Min)) of condensable gas or the like without affecting the pressure value to the pump inlet port 14, that is, without affecting the exhaust performance of the pump. When a process gas such as a corrosive gas is exhausted, a large amount of inert gas is compressed at the inlet of the final compression stage where the process gas is compressed and the process gas is most concentrated inside the pump, that is, at the suction side of the two-stage screw portion 34. By introducing gas into the pump, it is possible to prevent solids from adhering to the pump and corrosion of the pump.

  In addition, the inert gas is introduced into the pump only when the process gas is introduced into the pump from the pump intake port 14, so that the condensable gas or the corrosive gas is actually exhausted, that is, the inert gas. Only when it is desired to introduce gas, an inert gas can be introduced into the pump to reduce running costs.

  FIG. 4 shows a multistage vacuum pump according to another embodiment of the present invention.

  As shown in FIG. 4, in the multistage vacuum pump of this example, a branch pipe (another inert gas introduction pipe) 50 branched from the inert gas introduction pipe 44 is provided in the inert gas introduction pipe 44, and this branch pipe. 50, the inert gas can be introduced into the pump from the vicinity of the discharge portion of the two-stage screw portion 34. The branch pipe 50 is provided with a valve body 52. Opening and closing of the valve body 46 installed in the inert gas introduction pipe 44 and the valve body 52 installed in the branch pipe 50 is controlled by a signal from the control unit 48 (see FIG. 1).

  With such a configuration, for example, the amount of process gas such as condensable gas and corrosive gas exhausted by the pump is extremely small, and the pressure inside the pump from the interstage 40 is not affected without affecting the pressure at the pump intake port 14. When the active gas cannot be introduced, the process gas in the vicinity of the discharge portion is diluted by introducing the inert gas into the pump through the branch pipe 50 from the vicinity of the discharge portion of the two-stage screw portion 34. Can do. Further, by switching the opening and closing of the valve bodies 46 and 52 depending on the amount of process gas introduced into the pump, the inert gas is introduced into the pump from one or both of the inert gas introduction pipe 44 and the branch pipe 50. Can be introduced.

  Since the gas is compressed along the axial direction of the pump, the two-stage screw portion 34 preferably sets the amount of inert gas introduced into the pump at each location according to the pressure distribution in the axial direction. . For example, when 50 SLM inert gas can be introduced into the pump, 10 SLM is introduced into the interstage part 40 and 40 SLM is introduced into the vicinity of the discharge of the second stage screw part 34 to introduce the inert gas into the pump. Compared with the case where all of them are introduced into the pump through the interstage part 40, it is difficult to affect the pressure at the pump inlet 14. For this reason, even when the amount of process gas introduced from the pump intake port 14 is small, a dilution effect over the entire two-stage screw portion 34 can be obtained.

  In the example shown in FIG. 4, the number of the inert gas introduction locations is two, but the number of inert gas introduction locations may be two or more in the two-stage screw portion. Further, as shown in FIG. 5, in addition to the inert gas introduction pipe 44, a branch pipe 50 is provided so that the inert gas can be introduced into the interstage portion 40 and the two valve bodies 46 and 52 are controlled. The amount of inert gas introduced into the interstage part 40 may be adjusted. Further, the valve body itself may have a flow rate adjusting function.

  FIG. 6 shows a multistage vacuum pump according to still another embodiment of the present invention.

  In the multistage vacuum pump shown in FIG. 1, the opening and closing of the valve body 46 installed in the inert gas introduction pipe 44 is controlled by a signal input from the pressure sensor 42 to the control unit 48. The multistage vacuum pump is configured so that the opening and closing of the valve body 46 installed in the inert gas introduction pipe 44 can be controlled by a signal input to the control unit 48 from the outside. In this example, in addition to controlling the opening and closing of the valve body 46 installed in the inert gas introduction pipe 44 by a signal input from the pressure sensor 42 to the control unit 48, for example, the pressure sensor 42 controls the valve body 46. Even when the pressure sufficient to control the opening / closing is not detected, a signal can be input from the outside to the control unit 48 to control the opening / closing of the valve body 46 installed in the inert gas introduction pipe 44. it can.

  In the multistage vacuum pump shown in FIG. 1, when a condensable gas or a corrosive gas is introduced into the pump, the pressure increase in the pump is detected by the pressure sensor 42, and the gas is introduced into the pump. , And an inert gas is introduced into the pump to prevent condensation and corrosion of the gas. Here, the fact that the internal pressure of the pump has increased means that these gases have been introduced into the pump, and at least a slight amount of gas condensation or corrosion may occur. According to the multistage vacuum pump shown in FIG. 6, before the gas is introduced into the pump (a situation where sufficient pressure is not detected), an external signal in the sense that the gas has been introduced from the outside into the pump. In this case, the inert gas can be introduced in advance.

  FIG. 7 shows a multistage vacuum pump according to still another embodiment of the present invention. The difference from the example shown in FIG. 4 of this example is that the valve body 46 and / or the inert gas introduction pipe 44 installed in the inert gas introduction pipe 44 is also branched by a signal input to the control unit 48 from the outside. This is in that the opening and closing of the valve body 52 installed in the branch pipe 50 to be controlled can be controlled. Even in this example, the valve body 46 installed in the inert gas introduction pipe 44 and / or the valve body 52 installed in the branch pipe 50 is opened and closed by a signal input to the control unit 48 from the pressure sensor 42. In addition to the control, for example, even when the pressure sensor 42 does not detect a pressure sufficient to control the opening and closing of the valve body 46 and / or the valve body 52 installed in the branch pipe 50, the control unit 48 from the outside. The valve body 46 installed in the inert gas introduction pipe 44 and / or the valve body 52 installed in the branch pipe 50 can be controlled.

  Although one embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea.

It is a schematic diagram which shows the multistage vacuum pump of embodiment of this invention. It is a figure which shows the relationship between the exhaust speed and pressure in each compression stage of the multistage vacuum pump shown in FIG. It is a graph which shows typically the gas flow rate characteristic in the multistage vacuum pump shown in FIG. It is a schematic diagram which shows the multistage vacuum pump of other embodiment of this invention. It is a schematic diagram which shows the multistage vacuum pump of further another embodiment of this invention. It is a schematic diagram which shows the multistage vacuum pump of further another embodiment of this invention. It is a schematic diagram which shows the other multistage vacuum pump of further another embodiment of this invention.

Explanation of symbols

10 First vacuum pump (Roots type vacuum pump)
12 Second vacuum pump (screw type vacuum pump)
14 Pump inlet 16 Pump exhaust 22 Connecting pipe 24 Roots type pump rotor 26 First stage root part 28 Two stage root part 30 Screw type pump rotor 32 First stage screw part 34 Second stage screw part 40 Interstage part 42 Pressure sensor 44 Not Active gas introduction pipe 46 Valve body 48 Control unit 50 Branch pipe 52 Valve body

Claims (4)

A pressure sensor for detecting the pressure on the intake side of the downstream final compression stage;
An inert gas introduction pipe for introducing an inert gas for purging to the intake side of the downstream final compression stage;
A valve body installed in the inert gas introduction pipe;
A multistage vacuum pump comprising a control unit that controls opening and closing of the valve body in accordance with a pressure value detected by the pressure sensor.   It further has another inert gas introduction pipe for introducing an inert gas in the vicinity of the discharge part of the downstream final compression stage, and the other inert gas introduction pipe according to the pressure value detected by the pressure sensor The multistage vacuum pump according to claim 1, wherein opening and closing of a valve body installed in the inside is controlled by the control unit.   The multistage vacuum pump according to claim 1 or 2, wherein the compression form of at least one of the compression stages located upstream of the inert gas introduction pipe is a screw type.   The multistage vacuum pump according to any one of claims 1 to 3, wherein the total number of compression stages is three or more.

Images