Patent Publication Number: US-2022235796-A1

Title: Vacuum pump

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a vacuum pump. 
     2. Background Art 
     A turbo-molecular pump is used as an exhaust pump for various semiconductor manufacturing devices, but a reactive product is accumulated in the pump when pumping is performed at, e.g., an etching process. Generally, a turbo-molecular pump including a turbo pump portion and a screw groove pump portion is used for the semiconductor manufacturing device, but the reactive product is likely to be accumulated on a lower-vacuum side. For this reason, a structure for heating a stator side of the screw groove pump portion to a high temperature is employed in many cases. However, product accumulation in the screw groove pump portion is reduced by stator heating, but there is a problem that the product is accumulated in an exhaust gas passage downstream of the screw groove pump portion. 
     For example, a technique described in Patent Literature 1 (JP-A-2016-176339) employs, for reducing product accumulation in an exhaust pipe as part of a downstream exhaust gas passage, such a configuration that a pipe fixed to a stator is inserted into an exhaust port. Exhaust gas is discharged to the outside of a pump through the pipe, and therefore, product accumulation on an exhaust port inner peripheral surface is prevented. 
     SUMMARY OF THE INVENTION 
     However, it is configured such that gas discharged from a screw groove pump portion flows into the pipe after having been discharged to a downstream flow path of the screw groove pump portion. Thus, there is a problem that a product is accumulated on an inner peripheral surface of the downstream flow path between the pipe and the screw groove pump portion. That is, in the vacuum pump described in Patent Literature 1, product accumulation on the exhaust port inner peripheral surface is prevented, but the product is accumulated on an inner peripheral surface of an exhaust passage (the flow path downstream of the screw groove pump portion) connected from the screw groove pump portion to the exhaust port. 
     A vacuum pump comprises: a rotor formed with multiple stages of rotor blades and a rotor cylindrical portion; a stator formed with multiple stages of stationary blades and a stator cylindrical portion arranged with a predetermined gap from the rotor cylindrical portion; a first heating section configured to heat the stator cylindrical portion to a temperature for reducing product accumulation; an exhaust pipe provided at a housing storing the rotor and the stator to discharge gas discharged by the rotor and the stator to an outside of the housing; a second heating section configured to heat the exhaust pipe to a temperature for reducing product accumulation; and a gas passage container arranged in the housing, having an inlet port into which gas discharged through a gap between the rotor cylindrical portion and the stator cylindrical portion flows and an outlet port from which inflow gas flows to the exhaust pipe, and heated to a temperature for reducing product accumulation. A gas-inflow-side end portion of the exhaust pipe is inserted into the outlet port of the gas passage container through a clearance. 
     The outlet port is a tunnel-shaped hole, and the gas-inflow-side end portion of the exhaust pipe is inserted such that a clearance is formed between the gas-inflow-side end portion and a wall surface of the tunnel-shaped hole. 
     The gas passage container is a ring-shaped container, and the inlet port is a ring-shaped opening facing an entirety of gas exhaust regions of the rotor cylindrical portion and the stator cylindrical portion. 
     The gas passage container is heated by the first heating section. 
     The gas passage container is fixed to the stator cylindrical portion, and is heated by the first heating section through the stator cylindrical portion. 
     The vacuum pump further comprises: a purge gas injection portion for injecting purge gas into a space surrounding the gas passage container. The gas injected into the surrounding space prevents gas discharged from the gap between the rotor cylindrical portion and the stator cylindrical portion from leaking to a periphery of the gas passage container. 
     The exhaust pipe includes, in addition to the gas-inflow-side end portion inserted into the outlet port through the clearance, a raised portion arranged in parallel with the gas-inflow-side end portion and protruding inward of the housing, and part of a wall portion of the gas passage container is arranged between the gas-inflow-side end portion and the raised portion through a clearance. 
     The clearance forms a labyrinth-like structure. 
     The gas passage container is a ring-shaped container, and has an outer peripheral wall fixed to the stator cylindrical portion, an inner peripheral wall, and a bottom wall. 
     Multiple bolt holes having counterbores are formed at the outer peripheral wall, and utilizing the bolt holes, the outer peripheral wall of the gas passage container is fixed to a lower end surface of the stator cylindrical portion. 
     A clearance is formed between the gas-inflow-side end portion of the exhaust pipe and the stator cylindrical portion. 
     The dimension of the clearance is g, the amount of insertion of the gas-inflow-side end portion of the exhaust pipe is L, and L=α·g is satisfied, the degree of α is set to 2 or greater. 
     According to the present invention, product accumulation on a surface of a member forming a gas passage from an exhaust functional section to an exhaust pipe can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing an embodiment of a vacuum pump according to the present invention, and shows the section of a turbo-molecular pump; 
         FIG. 2  is a plan view of a gas passage container; 
         FIG. 3  is a sectional view of an exhaust port; 
         FIG. 4  is a view from an arrow A of  FIG. 3 ; 
         FIG. 5  is an axial sectional view for describing the flow of gas in a region where the gas passage container is arranged; 
         FIG. 6  is a sectional view along a C 1 -C 1  line of  FIG. 5 ; 
         FIG. 7  is an axial sectional view showing a comparative example; 
         FIG. 8  is a sectional view along a C 1 -C 1  line of  FIG. 7 ; and 
         FIGS. 9A to 9C  are views showing first to third variations. 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Hereinafter, a mode for carrying out the present invention will be described with reference to the drawings.  FIG. 1  is a view showing an embodiment of a vacuum pump according to the present invention, and shows the section of a turbo-molecular pump. The turbo-molecular pump  1  includes a rotor  10  formed with multiple stages of rotor blades  12  and a rotor cylindrical portion  13  and a stator formed with multiple stages of stationary blades  21  and a stator cylindrical portion  22 . The multiple stages of the stationary blades  21  are arranged and stacked corresponding to the multiple stages of the rotor blades  12  in a first pump case  23 . The multiple stages of the rotor blades  12  and the multiple stages of the stationary blades  21  form a turbo pump portion. The multiple stages of the stationary blades  21  stacked in a pump axial direction are arranged on a second pump case  20  through spacers  29 . Multiple turbine blades arranged in a circumferential direction are formed at each of the rotor blades  12  and the stationary blades  21 . The first pump case  23  is fixed to the second pump case  20  with bolts, and the second pump case  20  is fixed to a base  30  with a not-shown fixing unit. 
     The stator cylindrical portion  22  in a cylindrical shape is arranged on an outer peripheral side of the rotor cylindrical portion  13  with a predetermined gap. The stator cylindrical portion  22  is placed on the second pump case  20  through a heat insulating member  24  with a low heat conductivity, and is fixed to the second pump case  20  with bolts  25 . A screw groove is formed at either one of an outer peripheral surface of the rotor cylindrical portion  13  or an inner peripheral surface of the stator cylindrical portion  22 , and the rotor cylindrical portion  13  and the stator cylindrical portion  22  form a screw groove pump portion. 
     A gas passage container  40  for preventing product accumulation on the base  30  and the second pump case  20  is fixed to a lower end of the stator cylindrical portion  22  with bolts. A case-side end portion (a right end portion as viewed in the figure) of an exhaust port  41  provided at the second pump case  20  is inserted into the gas passage container  40 . Gas discharged by the turbo pump portion including the rotor blades  12  and the stationary blades  21  and the screw groove pump portion including the rotor cylindrical portion  13  and the stator cylindrical portion  22  is discharged through the exhaust port  41  after having flowed into the gas passage container  40 . 
     A rotor shaft  11  is fixed to the rotor  10 . The rotor shaft  11  is magnetically levitated and supported by radial magnetic bearings MB 1 , MB 2  and an axial magnetic bearing MB 3 , and is rotatably driven by a motor M. When the magnetic bearings MB 1  to MB 3  are not in operation, the rotor shaft  11  is supported by mechanical bearings  35   a ,  35   b . Note that in the present embodiment, the second pump case  20  and the base  30  are separated from each other, but it may be configured such that the second pump case  20  and the base  30  are integrally formed. 
     At the base  30  provided with electrical components such as the motor M and the magnetic bearings MB 1  to MB 3 , a purge gas injection portion  42  for injecting purge gas such as inert gas into the base  30  is provided for preventing an adverse effect such as corrosion due to entry of discharged process gas. Purge gas injected into the base  30  reaches an exhaust side of the screw groove pump portion through a clearance between the base  30  and the rotor  10  by way of a clearance formed by the mechanical bearing  35   a  on the upper side as viewed in the figure, and is discharged to the outside of the pump through the exhaust port  41 . 
     In the present embodiment, the second pump case  20  and the base  30 , the stator cylindrical portion  22 , and the exhaust port  41  are controlled to different temperatures. The second pump case  20  and the base  30  are controlled to a temperature T 1  by a heater H 1  provided at the second pump case  20  and a cooling pipe  43  provided at the base  30 . A heating section  28  including a heater H 2  is provided at the stator cylindrical portion  22 , and the stator cylindrical portion  22  is controlled to a temperature T 2 . The exhaust port  41  is controlled to a temperature T 3  by a heater H 3 . 
     The temperatures T 2 , T 3  of the stator cylindrical portion  22  and the exhaust port  41  facing a passage for process gas to be discharged are controlled to relatively-high temperatures for reducing product accumulation. The temperatures T 2 , T 3  are set considering, e.g., a relationship between the steam pressure and temperature of process gas and creep strain of the rotor cylindrical portion  13  rotating at high speed. Considering the relationship between the steam pressure and temperature of process gas, a component arranged in a higher-pressure (lower-vacuum) region needs to be at a higher temperature. Thus, the temperatures T 2 , T 3  are set as in T 3 &gt;T 2 . 
     Meanwhile, the temperature T 1  of the base  30  and the second pump case  20  not facing the exhaust gas passage is controlled to a lower temperature than the temperatures T 2 , T 3  of the stator cylindrical portion  22  and the exhaust port  41 . Specifically, the electrical components such as the motor M and the magnetic bearings MB 1  to MB 3  are provided at the base  30 , and therefore, the temperature T 1  cannot be set high with no reason and the cooling pipe  43  in which refrigerant flows is provided for suppressing an excessive increase in the temperatures of the electrical components due to influence of heat generation from the electrical components themselves and influence of heating by the heater. 
     The heating section  28  configured to heat the stator cylindrical portion  22  is provided to penetrate the second pump case  20  from the outer peripheral side to an inner peripheral side. A tip end of the heating section  28  inserted into an internal space of the second pump case  20  thermally contacts an outer peripheral surface of the stator cylindrical portion  22 . A back end of the heating section  28  is exposed to the outside of the base  30 , and a clearance between the heating section  28  and the base  30  is sealed by an O-ring  27 . 
       FIG. 2  is a view showing the gas passage container  40  attached to the lower end of the stator cylindrical portion  22 , and is a plan view from a stator side. The gas passage container  40  is a ring-shaped container, and has an outer peripheral wall  402  fixed to the stator cylindrical portion  22 , an inner peripheral wall  403 , and a bottom wall  404 . Multiple bolt holes  406  having counterbores  406   a  are formed at the outer peripheral wall  402 . Utilizing the bolt holes  406 , the outer peripheral wall  402  of the gas passage container  40  is fixed to a lower end surface of the stator cylindrical portion  22 . 
     A ceiling region (a region between the outer peripheral wall  402  and the inner peripheral wall  403 ) of the gas passage container  40  facing the stator cylindrical portion  22  forms a circular ring-shaped opening (hereinafter referred to as an inlet port)  401  into which gas discharged from the screw groove pump portion (the rotor cylindrical portion  13  and the stator cylindrical portion  22 ) flows. At the outer peripheral wall  402 , an outlet port  405  as a tunnel-shaped passage is formed at a position facing the exhaust port  41  (see  FIG. 1 ). Gas having flowed into the gas passage container  40  through the inlet port  401  is discharged to the exhaust port  41  through the outlet port  405 , and is further discharged to the outside of the pump through the exhaust port  41 . 
       FIGS. 3 and 4  are views for describing the shape of the exhaust port  41 ,  FIG. 3  being a sectional view of the exhaust port  41  and  FIG. 4  being a view from an arrow A of  FIG. 3 . Note that in  FIG. 4 , the stator cylindrical portion  22  and the gas passage container  40  into which a tip end portion of the exhaust port  41  is inserted are indicated by chain double-dashed lines. The exhaust port  41  includes a flange  410  for fixing the exhaust port  41  to the second pump case  20 . The exhaust port  41  has a first pipe portion  411  to be inserted into the pump as shown on the right side of the flange  410  as viewed in the figure and a second pipe portion  412  exposed to the outside of the pump as shown on the left side of the flange  410  as viewed in the figure. As shown in  FIG. 1 , the heater H 3  is attached to the second pipe portion  412 . An insertion portion  414  to be inserted into the outlet port  405  of the gas passage container  40  is provided at a tip end of the first pipe portion  411 . 
     As seen from the view of  FIG. 4  from the arrow A, the insertion portion  414  is a portion remaining after hatched portions H 1 , H 2  have been removed from a circular pipe  414 A formed to protrude from the flange  410 . Note that the removed portion H 1  is a portion which is to contact the stator cylindrical portion  22  and the removed portion H 2  is a portion which is to contact the bottom wall  404  of the gas passage container  40 . The insertion portion  414  is inserted with a slight clearance between the insertion portion  414  and a wall portion of the outlet port  405  formed at the outer peripheral wall  402 . A raised portion  415  is formed on the lower side of the insertion portion  414  as viewed in the figure. The raised portion  415  is arranged at a bottom portion of the outlet port  405 , i.e., on the lower side of the bottom wall  404 , with a clearance. 
       FIGS. 5 and 6  are views for describing the flow of gas in the gas passage container  40  and the exhaust port  41 .  FIG. 5  shows an axial section similar to that in the case of  FIG. 1 , and  FIG. 6  is a sectional view along a C 1 -C 1  line of  FIG. 5 . In  FIG. 5 , a solid arrow indicates the flow of exhaust gas G, and a dashed arrow indicates the flow of purge gas PG. The gas passage container  40  is fixed to the stator cylindrical portion  22  controlled to the temperature T 2 , and therefore, has the substantially same temperature as that of the stator cylindrical portion  22 . Note that instead of heating the gas passage container  40  with the gas passage container  40  being fixed to the stator cylindrical portion  22 , the heating section  28  may contact both of the stator cylindrical portion  22  and the gas passage container  40 , and the gas passage container  40  may be directly heated by the heating section  28 . Alternatively, the gas passage container  40  may be heated by another heating section different from the heating section  28  such that the gas passage container  40  reaches the substantially same temperature as that of the stator cylindrical portion  22 . 
     The gas passage container  40  is provided for avoiding exposure of the surfaces of the base  30  and the second pump case  20  to the flow of gas discharged from the screw groove pump portion. The pump-side tip end (the insertion portion  414  of the first pipe portion  411 ) of the exhaust port  41  is inserted into the outlet port  405 . Thus, the exhaust gas G discharged from the screw groove pump portion (the rotor cylindrical portion  13  and the stator cylindrical portion  22 ) flows into the gas passage container  40  through the inlet port  401 , passes through the gas passage container  40  without contacting the base  30  and the second pump case  20 , and flows into the first pipe portion  411  through the insertion portion  414  inserted into the outlet port  405 . 
     The exhaust port  41  and the stator cylindrical portion  22  are controlled to the different temperatures T 3 , T 2  (&lt;T 3 ) by the different heaters. Thus, in regions B 1 , B 2  of  FIGS. 5 and 6 , a slight clearance is formed between the first pipe portion  411  and the insertion portion  414  of the exhaust port  41 , and, the stator cylindrical portion  22  and the gas passage container  40 , such that the first pipe portion  411  and the insertion portion  414  do not contact to the stator cylindrical portion  22  and the gas passage container  40 . With such a configuration, heat transfer between the exhaust port  41  and the stator cylindrical portion  22  at the different temperatures is prevented, and stability in control of the exhaust port  41  and the stator cylindrical portion  22  to the different target temperatures T 3 , T 2  is improved. 
     At a connection portion between the first pipe portion  411  and the gas passage container  40 , the insertion portion  414  of the first pipe portion  411  is, for avoiding contact between the first pipe portion  411  and the gas passage container  40 , inserted into the outlet port  405  formed in a tunnel shape at the outer peripheral wall  402  with a slight clearance. Thus, the gas conductance of the clearance space between the insertion portion  414  and the outlet port  405  can be decreased, and the amount of exhaust gas G leaking from the clearance can be suppressed small. For example, in a case where a clearance dimension is g, the amount of insertion of the insertion portion  414  is L, and L=α·g is satisfied, the degree of α is substantially set to 2 or greater so that the gas leakage amount can be sufficiently decreased (e.g., α=2 and g=1 are set). In the region B 2 , the raised portion  415  is arranged on the lower side of the bottom wall  404  of the gas passage container  40  as viewed in the figure, and a clearance among the insertion portion  414 , the raised portion  415 , and the bottom wall  404  forms a labyrinth-like structure. Thus, leakage of the exhaust gas G to a region surrounding the gas passage container  40  can be further decreased. 
     As described above, the present embodiment employs such a structure that the gas passage container  40  is provided and the insertion portion  414  of the first pipe portion  411  is inserted into the tunnel-shaped outlet port  405  of the gas passage container  40 , and therefore, gas leakage through the clearance formed by the insertion portion can be sufficiently decreased. As a result, contact of the exhaust gas G with inner peripheral surfaces of the base  30  and the second pump case  20  is suppressed as much as possible, and product accumulation on these inner peripheral surfaces can be suppressed small. 
     The purge gas PG injected into the base  30  through the purge gas injection portion  42  flows downwardly in a clearance between the rotor cylindrical portion  13  and the base  30  as indicated by the dashed arrows, and the region surrounding the gas passage container  40  arranged on the exhaust side of the screw groove pump portion is filled with the purge gas PG. Such purge gas PG enters the gas passage container  40  through a clearance between the inner peripheral wall  403  of the gas passage container  40  and the rotor cylindrical portion  13  and the clearances in the regions B 1 , B 2 , and is discharged to the outside of the pump through the exhaust port  41 . Thus, the purge gas PG flowing in through the clearances can prevent the exhaust gas G from leaking to the outside of the gas passage container  40  through the clearances in the regions B 1 , B 2 , and product accumulation on the inner peripheral surfaces of the base  30  and the second pump case  20  can be more effectively prevented. 
       FIGS. 7 and 8  show, as a comparative example, one example in a case where the tip end of the first pipe portion  411  is not inserted into the gas passage container  40 .  FIG. 7  is an axial sectional view similar to that of  FIG. 5 , and  FIG. 8  is a sectional view along a C 1 -C 1  line of  FIG. 7 . In the case of the comparative example, the first pipe portion  411  is not inserted into the gas passage container  40 , and a clearance between the first pipe portion  411  and the gas passage container  40  in a region B 3  is relatively large. Thus, exhaust gas is likely to leak to the base  30  and the second pump case  20  through the clearance. For this reason, a product is accumulated on the inner peripheral surfaces of these components. Specifically, the product is likely to be accumulated on a surface R, which is close to the clearance, of the base  30  cooled by the cooling pipe  43 . Even if the purge gas PG is injected into the exhaust side of the screw groove pump portion as in the case of  FIG. 5 , a leakage prevention effect by the purge gas PG flowing into the exhaust port  41  is degraded due to the large clearance, and for this reason, the product is likely to be accumulated on the inner peripheral surface in the vicinity of the clearance. 
     The embodiment describes such a structure that the purge gas PG injected into a motor arrangement space of the base  30  flows around to the exhaust side of the screw groove pump portion, but the purge gas supply configuration is not limited to such a structure. For example, it may be configured such that the purge gas PG is directly injected into the exhaust side of the screw groove pump portion. 
     (Variations) 
       FIGS. 9A to 9C  are views showing variations of the outlet port  405 . In a first variation shown in  FIG. 9A , the outlet port  405  having a circular sectional shape is formed at the outer peripheral wall  402 , and the tip end portion of the first pipe portion  411  of the exhaust port  41  is inserted into the outlet port  405 . The amount of insertion of the first pipe portion  411  is L as described above, and the dimension of a gap between the first pipe portion  411  and the outlet port  405  is g as described above. 
     In a second variation shown in  FIG. 9B , an insertion portion  407  formed with the tunnel-shaped outlet port  405  is formed to protrude to the outer peripheral side from the thin outer peripheral wall  402 . The outer peripheral wall  402  is formed thin so that the weight of the gas passage container  40  can be reduced. Needless to say, the insertion portion  407  may be formed to protrude to the inner peripheral side of the outer peripheral wall  402 . 
     In a third variation shown in  FIG. 9C , the case of the outlet port  405  not formed in the tunnel shape is shown. The outlet port  405  is formed at the thin outer peripheral wall  402 , and the first pipe portion  411  of the exhaust port  41  is inserted into the outlet port  405  such that the tip end of the first pipe portion  411  protrudes into the container. In the case of the third variation, the gas leakage amount is greater than that in a case where the outlet port  405  is formed in the tunnel shape as in the first and second variations, but due to the insertion structure, can be reduced as compared to the case of the comparative example of  FIGS. 7 and 8 . 
     Those skilled in the art understand that the above-described exemplary embodiment and variations are specific examples of the following aspects. 
     [1] A vacuum pump comprises: a rotor formed with multiple stages of rotor blades and a rotor cylindrical portion; a stator formed with multiple stages of stationary blades and a stator cylindrical portion arranged with a predetermined gap from the rotor cylindrical portion; a first heating section configured to heat the stator cylindrical portion to a temperature for reducing product accumulation; an exhaust pipe provided at a housing storing the rotor and the stator to discharge gas discharged by the rotor and the stator to an outside of the housing; a second heating section configured to heat the exhaust pipe to a temperature for reducing product accumulation; and a gas passage container arranged in the housing, having an inlet port into which gas discharged through a gap between the rotor cylindrical portion and the stator cylindrical portion flows and an outlet port from which inflow gas flows to the exhaust pipe, and heated to a temperature for reducing product accumulation. A gas-inflow-side end portion of the exhaust pipe is inserted into the outlet port of the gas passage container through a clearance. 
     Specifically, the region where gas is discharged through the gap between the rotor cylindrical portion  13  and the stator cylindrical portion  22  is under low vacuum, and for this reason, the product is likely to be accumulated on the inner peripheral surfaces of the base  30  and the second pump case  20 . However, the heated gas passage container is provided so that product accumulation on the inner peripheral surfaces of the base  30  and the second pump case  20  can be reduced. For example, as shown in  FIG. 5 , the insertion portion  414  at the tip end of the first pipe portion  411  is inserted into the outlet port  405  of the gas passage container  40 . With such an insertion structure, leakage of exhaust gas through the clearance between the insertion portion  414  and the outlet port  405  can be reduced, and product accumulation on the inner peripheral surfaces of the base  30  and the second pump case  20  can be reduced. 
     [2] The outlet port is a tunnel-shaped hole, and the gas-inflow-side end portion of the exhaust pipe is inserted such that a clearance is formed between the gas-inflow-side end portion and a wall surface of the tunnel-shaped hole. 
     For example, as shown in  FIGS. 5 and 6 , the outlet port  405  is the tunnel-shaped hole formed to penetrate the thick outer peripheral wall  402 . Thus, in the clearance space, the length dimension L is greater than the gap dimension g, and therefore, the gas conductance can be increased and gas leakage through the clearance can be further reduced. 
     [3] The gas passage container is a ring-shaped container, and the inlet port is a ring-shaped opening facing an entirety of gas exhaust regions of the rotor cylindrical portion and the stator cylindrical portion. 
     The gas passage container is the ring-shaped container, and therefore, is arranged across the entirety of the ring-shaped space downstream of an exhaust functional section. 
     [4] The gas passage container is heated by the first heating section. 
     [5] The gas passage container is fixed to the stator cylindrical portion, and is heated by the first heating section through the stator cylindrical portion. 
     For example, as shown in  FIG. 5 , the gas passage container  40  is fixed to the stator cylindrical portion  22 , and is directly or indirectly heated by the heating section  28 . Thus, another heating section dedicated to the gas passage container  40  is not necessarily prepared. 
     [6] The vacuum pump further comprises: a purge gas injection portion for injecting purge gas into a space surrounding the gas passage container. The gas injected into the surrounding space prevents gas discharged from the gap between the rotor cylindrical portion and the stator cylindrical portion from leaking to a periphery of the gas passage container. 
     For example, as shown in  FIG. 5 , the purge gas PG is injected into the space surrounding the gas passage container  40 , and accordingly, flows into the gas passage container  40  through the clearance among the members (the rotor cylindrical portion  13 , the insertion portion  414 , the stator cylindrical portion  22  and the like) close to the gas passage container  40 . Thus, leakage of exhaust gas (process gas) to the surrounding space through the clearance can be reduced. As a result, product accumulation on the inner peripheral surfaces of the base  30  and the second pump case  20  can be further reduced. 
     [7] The exhaust pipe includes, in addition to the gas-inflow-side end portion inserted into the outlet port through the clearance, a raised portion arranged in parallel with the gas-inflow-side end portion and protruding inward of the housing, and part of a wall portion of the gas passage container is arranged between the gas-inflow-side end portion and the raised portion through a clearance. 
     For example, as shown in  FIG. 5 , the raised portion  415  is arranged on the lower side of the bottom wall  404  of the gas passage container  40  as viewed in the figure, and the clearance among the insertion portion  414 , the raised portion  415 , and the bottom wall  404  forms the labyrinth-like structure. Thus, leakage of the exhaust gas G to the region surrounding the gas passage container  40  can be further reduced. 
     The various embodiments and the variations have been described above, but the present invention is not limited to the contents of these embodiments and variations. The scope of the present invention also includes other aspects conceivable within the scope of the technical idea of the present invention. For example, in the above-described embodiments, the turbo-molecular pump has been described as an example, but the present invention is also applicable to a vacuum pump having only a screw groove pump including a stator and a rotor cylindrical portion.