Patent Publication Number: US-2023160063-A1

Title: Exhaust pipe apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-191125 filed on Nov. 25, 2021 in Japan, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an exhaust pipe apparatus. 
     BACKGROUND 
     In a film forming apparatus represented by a chemical vapor deposition (CVD) apparatus, a source gas is introduced into a film forming chamber to form a desired film on a substrate disposed in the film forming chamber. The source gas remaining in the film forming chamber is exhausted by a vacuum pump through an exhaust pipe. There have been undesirable situations at that time such as closure of the exhaust pipe by deposition of products in the exhaust pipe due to the source gas, and stop of the vacuum pump downstream of the exhaust pipe by deposition of the products in the vacuum pump. In order to remove the deposit, a cleaning process by a remote plasma source (RPS) apparatus is performed. However, since an RPS apparatus generally focuses on cleaning in the film forming chamber, cleaning performance has been insufficient to clean products deposited in the exhaust pipe near the vacuum pump and the vacuum pump that is distant from the RPS apparatus. 
     In addition, a technique is disclosed in which a radio-frequency voltage is applied to a radio-frequency electrode disposed on the outer periphery of a conduit of an insulating material such as ceramics or quartz to generate plasma inside the conduit. Here, unreacted gas and waste gas generated in the steps of asking, etching, vapor deposition, cleaning, and nitriding is removed by the plasma. However, when the contact between the conduit and the radio-frequency electrode is insufficient, a problem that plasma generation inside the conduit becomes uneven may occur. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a configuration diagram illustrating an example of a configuration of an exhaust system of a semiconductor manufacturing apparatus according to a first embodiment; 
         FIG.  2    is a cross-sectional view of an example of an exhaust pipe apparatus according to the first embodiment as viewed from the front side; 
         FIG.  3    is a cross-sectional view of an example of the exhaust pipe apparatus according to the first embodiment as viewed from the upper side; 
         FIG.  4    is a diagram illustrating an example of a configuration of a radio-frequency electrode according to the first embodiment; 
         FIG.  5    is a diagram illustrating an example of how to assemble the radio-frequency electrode in the first embodiment; 
         FIG.  6    is a top view illustrating an example of a plasma generation state in Comparative Example 1 of the first embodiment; 
         FIG.  7    is a top view illustrating an example of a plasma generation state in the first embodiment; 
         FIG.  8    is a graph for explaining the relationship between the inner pipe temperature and the cleaning processing time; 
         FIG.  9    is a diagram illustrating an example of a layout of cooling pipes according to the first embodiment; 
         FIG.  10    is a front view of an example of an exhaust pipe apparatus according to Comparative Example 2 of the first embodiment; 
         FIG.  11    is a cross-sectional view of an example of an exhaust pipe apparatus according to a second embodiment as viewed from the front side; and 
         FIG.  12    is a cross-sectional view of an example of an exhaust pipe apparatus according to a third embodiment as viewed from the front side. 
     
    
    
     DETAILED DESCRIPTION 
     An exhaust pipe apparatus according to an embodiment includes a dielectric pipe; a radio-frequency electrode; and a plasma generation circuit. The exhaust pipe apparatus functions as a part of an exhaust pipe disposed between a process chamber and a vacuum pump that exhausts gas inside the process chamber. The radio-frequency electrode includes a thin metal plate disposed on an outer periphery side of the dielectric pipe, a buffer member disposed on an outer periphery side of the thin metal plate, and a conductive hollow structure disposed on an outer periphery side of the buffer member and a radio-frequency voltage is applied to the radio-frequency electrode. The plasma generation circuit generates plasma inside the dielectric pipe. 
     In addition, hereinafter, the embodiment provides an exhaust pipe apparatus capable of bringing plasma generation close to a uniform state and removing products deposited inside the exhaust pipe near the vacuum pump. 
     First Embodiment 
       FIG.  1    is a configuration diagram illustrating an example of a configuration of an exhaust system of a semiconductor manufacturing apparatus according to a first embodiment. In the example of  FIG.  1   , a film forming apparatus, for example, a chemical vapor deposition (CVD) apparatus  200  is illustrated as a semiconductor manufacturing apparatus. In the example of  FIG.  1   , the CVD apparatus  200  of a multi-chamber type in which two film forming chambers  202  are disposed is illustrated. In the CVD apparatus  200 , semiconductor substrates  204  ( 204   a ,  204   b ) on which a film is formed are disposed in the film forming chambers  202  controlled to a desired temperature. Then, vacuuming is performed through exhaust pipes  150  and  152  by a vacuum pump  400 , and the source gas is supplied into the film forming chambers  202  controlled to a desired pressure by a pressure adjusting valve  210 . In the film forming chambers  202 , desired films are formed on the substrates  204  by chemical reaction of the source gas. For example, a silane (SiH 4 )-based gas is introduced as a main source gas to form a silicon oxide film (SiO film) or a silicon nitride film (SiN film). Alternatively, for example, tetraethoxysilane (TEOS) gas or the like is introduced as a main source gas to form a silicon oxide film (SiO film). When these films are formed, products due to such a source gas are deposited in the film forming chambers  202  and the exhaust pipes  150  and  152 . Therefore, in the film forming process cycle, a cleaning step is performed in addition to the film forming step. 
     In the cleaning step, a cleaning gas or a purge gas is supplied to a remote plasma source (RPS) apparatus  300  disposed on the upstream side of the film forming chamber  202 , and fluorine (F) radicals are generated by plasma. Examples of the cleaning gas include nitrogen trifluoride (NF 3 ) gas. Examples of the purge gas include argon (Ar) gas. Then, by supplying (diffusing) F radicals into the film forming chambers  202  and toward the exhaust pipe  150 , products that are deposited are cleaned. After decomposition of the deposit by cleaning, for example, silicon tetrafluoride (SiF 4 ) is generated. Since silicon tetrafluoride (SiF 4 ) has high volatility, silicon tetrafluoride is exhausted from the vacuum pump  400  through the exhaust pipes  150  and  152 . 
     However, the F radicals hardly reach portions of the exhaust pipes  150 ,  152  away from the film forming chamber  202 . Therefore, cleaning performance is deteriorated. In particular, at positions close to the inlet port of the vacuum pump  400 , the cleaning rate is lower because the pressure is lower. As a result, the inside of the exhaust pipes  150  and  152  may be blocked by the deposited products. In addition, the gap between the rotor and the casing may be filled with the products deposited in the vacuum pump  400 , which causes an overload state and then the vacuum pump  400  may be stopped. Therefore, in the first embodiment, an exhaust pipe apparatus  100  is disposed at a position closer to the inlet port of the vacuum pump  400  than to the film forming chambers  202  as illustrated in  FIG.  1   . 
     In  FIG.  1   , the exhaust pipe apparatus  100  in the first embodiment is used as a part of an exhaust pipe including the exhaust pipes  150  and  152  disposed between the film forming chamber  202  (an example of a process chamber) and the vacuum pump  400  that exhausts the inside of the film forming chamber  202 . The exhaust pipe apparatus  100  includes an outer pipe  102 , an inner pipe  190  (dielectric pipe) made of a dielectric, and a plasma generation circuit  106 . For the outer pipe  102 , for example, a pipe material of the same material as that of the normal exhaust pipes  150  and  152  is used. For example, a stainless steel material such as SUS 304 is used. However, as a material of the outer pipe  102 , SUS 316 steel material is more preferably used from the viewpoint of corrosion resistance against the cleaning gas. In addition, for the outer pipe  102 , for example, a pipe material having the same size as that of the normal exhaust pipes  150  and  152  is used. However, the material and size are not limited to those described above. A pipe having a size larger than that of the exhaust pipes  150  and  152  may be used. Alternatively, a pipe having a smaller size may be used. 
     Flanges are disposed at both end portions of the inner pipe  190  and the outer pipe  102 , one end portions thereof are connected to the exhaust pipe  150  having a flange of the same size, and the other end portions thereof are connected to the exhaust pipe  152  having a flange of the same size. In  FIG.  1   , a clamp and the like for fixing the flanges of the exhaust pipe apparatus  100  and the flanges of the exhaust pipes  150  and  152  are not illustrated. Hereinafter, the same applies to each drawing. In addition, a seal material such as an O-ring used for connection with the exhaust pipes  150  and  152  is not illustrated. Hereinafter, in each embodiment, the exhaust pipe  152  is sandwiched between the exhaust pipe apparatus  100  and the vacuum pump  400 , but it is not limited to this configuration. The exhaust pipe apparatus  100  may be disposed directly at the inlet port of the vacuum pump  400 . The inner pipe  190  made of a dielectric is disposed inside the outer pipe  102 . The plasma generation circuit  106  generates capacitively coupled plasma (CCP) inside the inner pipe  190  made of a dielectric using an electrode, which will be described later, disposed on the outer periphery side of the inner pipe  190 . 
       FIG.  2    is a cross-sectional view of an example of the exhaust pipe apparatus according to the first embodiment as viewed from the front side.  FIG.  3    is a cross-sectional view of an example of the exhaust pipe apparatus according to the first embodiment as viewed from the upper side. In  FIG.  2   , the cross-sectional structure is of the exhaust pipe apparatus  100 , and cross-sectional structures of other components are not illustrated. Hereinafter, the same applies to each cross-sectional view as viewed from the front side. In  FIGS.  2  and  3   , the exhaust pipe apparatus  100  is formed in a double pipe structure of the outer pipe  102  and the inner pipe  190  made of a dielectric and disposed inside the outer pipe  102 . The inner pipe  190  is formed to have a shape similar to that of the outer pipe  102 . In the example of  FIGS.  2  and  3   , corresponding to the cylindrical outer pipe  102  having a circular cross section (annular), the cylindrical inner pipe  190  having a circular cross section (annular) similar to that of the outer pipe  102  is used. Alternatively, corresponding to a cylindrical outer pipe  102  having a rectangular cross section, a cylindrical inner pipe  190  having a rectangular cross section similar to that of the outer pipe  102  may be used. 
     The inner pipe  190  is disposed to be separated from the inner wall of the outer pipe  102  by a space  36 . The material of the dielectric to be the inner pipe  190  may be any material having a dielectric constant larger than that of air. As a material of the inner pipe  190 , for example, quartz, alumina (Al 2 O 3 ), yttria (Y 2 O 3 ), hafnia (HfO 2 ), zirconia (ZrO 2 ), magnesium oxide (MgO), aluminum nitride (AlN), or the like is preferably used. The thickness of the inner pipe  190  may be appropriately set as long as the exhaust performance is not hindered. 
     A radio-frequency electrode  104  is disposed inner than the outer pipe  102  and on the outer periphery side of the inner pipe  190 . The radio-frequency electrode  104  includes a thin metal plate  50  disposed on the outer periphery side of the inner pipe  190  serving as a dielectric pipe, a buffer member  52  disposed on the outer periphery side of the thin metal plate  50 , and a conductive hollow structure  54  disposed on the outer periphery side of the buffer member  52 . The thin metal plate  50  and the hollow structure  54  are disposed so as to be electrically conductive. 
     In a state where the radio-frequency electrode  104  is disposed on the outer periphery side of the inner pipe  190 , the radio-frequency electrode  104  is formed in a shape corresponding to the outer peripheral shape of the inner pipe  190 . For example, the cylindrical (annular) radio-frequency electrode  104  having the same type of circular cross-section is used for the cylindrical (annular) inner pipe  190  having a circular cross-section. As illustrated in  FIG.  2   , the length of the radio-frequency electrode  104  is shorter than the length of the inner pipe  190 . As illustrated in the example of  FIG.  2   , the radio-frequency electrode  104  is disposed at the center in the height direction with a gap left between the upper end side and the lower end side of the inner pipe  190 . 
     Flanges  19  are disposed on the end portion side of the inner pipe  190 . In the example of  FIG.  2   , the flanges  19  for piping are disposed at both end portions of the inner pipe  190 . The flange  19  disposed upstream with respect to the flow of the gas and the flange of the exhaust pipe  150  are fixed to each other. The flange  19  disposed downstream with respect to the flow of the gas and the flange of the exhaust pipe  152  are fixed to each other. For both of the flanges  19 , for example, a pipe material of the same material as that of the normal exhaust pipes  150  and  152  is used. For example, a stainless steel material such as SUS 304 is used. However, as a material of the flanges  19 , SUS 316 steel material is more preferably used from the viewpoint of corrosion resistance against the cleaning gas. 
     In the first embodiment, as illustrated in  FIG.  2   , the space between the outer pipe  102  and the inner pipe  190  is blocked from the ambient atmosphere and the space in the inner pipe  190  by seal mechanisms  16  disposed at the upper and lower end portions of the inner pipe  190  and the outer pipe  102  covering the outer periphery side of the inner pipe  190 . The seal mechanisms  16  are preferably configured as follows, for example. Each of the seal mechanisms  16  includes a protrusion  10 , an O-ring retainer  11 , an O-ring  12 , and an O-ring  14 . Protrusions  10  are provided in a ring shape on the surfaces of the respective flanges  19  at both end portions of the inner pipe  190 , and extend from the surfaces of the respective flanges  19  toward the radio-frequency electrode  104 , on the outer side of the inner pipe  190 . The (upstream) O-ring  14  closer to the exhaust pipe  150  is disposed between the (upstream) flange surface of the outer pipe  102  closer to the exhaust pipe  150  and the flange  19 . The (downstream) O-ring  14  closer to the exhaust pipe  152  is disposed between the (downstream) flange surface of the outer pipe  102  closer to the exhaust pipe  152  and the flange  19 . In such a case, on the upstream side of the exhaust pipe apparatus  100 , the flange of the outer pipe  102  and the flange of the pipe  150  are preferably clamp-connected with the flange  19  interposed therebetween. On the downstream side of the exhaust pipe apparatus  100 , the flange of the outer pipe  102  and the flange of the pipe  152  are preferably clamp-connected with the flange  19  interposed therebetween. The O-ring  14  shields the atmosphere inside the outer pipe  102  from the ambient atmosphere. 
     Each O-ring  12  is disposed in a state of being pressed between the outer peripheral surface of the end portion of the inner pipe  190  and the inner peripheral surface of the protrusion  10 . Therefore, the protrusion  10  is formed to have the inner diameter larger than the outer diameter size of the inner pipe  190  and have the outer diameter smaller than the inner diameter size of the outer pipe  102 . Each O-ring  12  is pressed by the O-ring retainer  11 . The O-ring retainer  11  may be formed as one member, or may be formed as a combination of two members, that is, a ring-shaped member disposed between the outer peripheral surface of the end portion of the inner pipe  190  and the inner peripheral surface of the protrusion  10 , and an outer member supporting the ring-shaped member as illustrated in  FIG.  2   . As a result, the atmosphere in the inner pipe  190  is shielded from the space  36  between the outer pipe  102  and the inner pipe  190  via the O-ring  12 . 
     In the first embodiment, by forming the sealed double pipe structure of the outer pipe  102  and the inner pipe  190  as described above, it is possible to prevent the gas flowing through the exhaust pipe from leaking to the ambient atmosphere even when the inner pipe  190  made of the dielectric is damaged. Similarly, it is possible to prevent atmospheric air from intruding into (inflow to) the exhaust pipe. Even when the space between the outer pipe  102  and the inner pipe  190  is controlled to the atmospheric pressure, it is possible to prevent inflow of the atmospheric air to such an extent that a failure of the vacuum pump  400  occurs because the volume of the space between the outer pipe  102  and the inner pipe  190  is small. 
     In the examples of  FIGS.  2  and  3   , the double pipe structure in which the outer pipe  102  is disposed outside the inner pipe  190  is illustrated, but it is not limited thereto. The absence of the outer pipe  102  is not excluded. 
       FIG.  4    is a diagram illustrating an example of a configuration of a radio-frequency electrode according to the first embodiment. As described above, the radio-frequency electrode  104  includes the thin metal plate  50 , the buffer member  52 , and the hollow structure  54 . 
     The thin metal plate  50  is thinner than the hollow structure  54 . Thus, the thin metal plate can be bent easier than the hollow structure  54 . Specifically, the thin metal plate  50  is formed by bending a thin metal plate into an annular shape, for example, a circular shape. For example, a thin plate having a thickness of about 0.1 mm to 3 mm is used. Flanges folded outward are formed at both ends in a direction in which the thin plate is bent. A bolt hole is formed in the flange. In the example of  FIG.  4   , two upper and lower bolt holes are formed. As the material of the thin metal plate  50 , a soft material having a low resistivity is suitable. For example, it is preferable to use copper (Cu) or aluminum (Al). Since the resistivity is low, even when the thickness is small, the entire surface can be easily electrically at the same potential as the hollow structure  54 . In addition, it can be easily bent by being soft. By using, for example, a copper material that is softer than the stainless material, it can be easily bent even when the thickness is, for example, 3 mm. 
     The hollow structure  54  is formed as a combination of one half hollow structure  54 - 1  and the other half hollow structure  54 - 2  obtained by halving a circumference of a cylindrical shape. A cavity  34  is formed in the hollow structure  54 . Specifically, the cavity  34  is formed in each of the half hollow structure  54 - 1  and the half hollow structure  54 - 2 . The cavity  34  is suitably formed throughout the hollow structure  54 . The hollow structure  54  is formed of a conductive material. In addition, as will be described later, a copper material having high conductivity, for example, is used from the viewpoint of flowing cooling water into the cavity  34 . Alternatively, an aluminum material or a steel material such as SUS 304 or SUS 316 may be used. The hollow structure  54  guides the radio-frequency potential applied from the introduction terminal  111  to the thin metal plate  50  and functions as a heat exchanger that is a part of the cooling mechanism. A flange for attachment is formed at half ends of the half hollow structure  54 - 1  and the half hollow structure  54 - 2 . A bolt hole is formed in the flange. In the example of  FIG.  4   , two upper and lower bolt holes are formed. The bolt holes of the half hollow structure  54 - 1  and the half hollow structure  54 - 2  are formed so as to be displaced from the bolt holes of the thin metal plate  50 . 
     The buffer member  52  is sandwiched between the thin metal plate  50  and the hollow structure  54  and functions as a buffer material for both. The buffer member  52  is formed as a combination of one half buffer member  52 - 1  and the other half buffer member  52 - 2  obtained by halving a circumference of a cylindrical shape. The buffer member  52  is desirably made of a material having high thermal conductivity in order to efficiently transfer heat from the inner pipe  190  serving as the dielectric pipe to the hollow structure  54 . The thermal conductivity is preferably, for example, about 1 to 10 W/mK. In addition, heat resistance that can withstand heat generated in the dielectric is desired. For example, heat resistance of about 100 to 150° C. is preferable. As a material having these functions, for example, a sheet-like silicone polymer is preferably used as the buffer member  52 . Alternatively, as the buffer member  52 , a silicone gel material may be suitably applied to the inner surface of the hollow structure  54 . The thickness of the buffer member  52  is preferably about 0.1 to 0.5 mm, for example. 
       FIG.  5    is a diagram illustrating an example of how to assemble the radio-frequency electrode in the first embodiment. First, the thin metal plate  50  is attached to the outer periphery of the inner pipe  190 . The thin metal plate  50  can bring the thin metal plate  50  into close contact with the outer peripheral surface of the inner pipe  190  by inserting screws  56  into the bolt holes of the flanges and fastening the flanges so as to approach each other. 
     Next, the thin metal plate  50  is attached from the outer periphery side so as to be sandwiched between the half hollow structure  54 - 1  in which the half buffer member  52 - 1  is disposed on the inner surface and the half hollow structure  54 - 2  in which the half buffer member  52 - 2  is disposed on the inner surface. Then, the hollow structure  54  is attached to the outer periphery side of the thin metal plate  50  via the buffer member  52  by inserting screws  58  into the bolt holes of the flanges between the half hollow structure  54 - 1  and the half hollow structure  54 - 2  and fastening the flanges so as to approach each other. At that time, as illustrated in  FIG.  3   , the assembly is performed such that the tips of the screws  56  in contact with the thin metal plate  50  are in contact with the hollow structure  54 . As a result, the hollow structure  54  can be electrically connected to the thin metal plate  50 . Note that the half hollow structure  54 - 1  and the half hollow structure  54 - 2  are electrically connected to each other via the screws  58 . 
     Although the case where the hollow structure  54  is electrically connected to the thin metal plate  50  using the screws  56  has been described, it is not limited thereto. For example, conductive nanoparticles may be added to the silicone polymer serving as the buffer member  52 . As a result, the buffer member  52  may be configured to electrically connect the hollow structure  54  and the thin metal plate  50 . 
     In the example of  FIGS.  2  and  3   , a radio-frequency (RF) electric field is applied to the radio-frequency electrode  104  by the plasma generation circuit  106 . Specifically, an introduction terminal  111  (an example of a radio-frequency introduction terminal) is introduced into the outer pipe  102  from an introduction terminal port  105  connected to the outer peripheral surface of the outer pipe  102 , and the introduction terminal  111  is connected to the radio-frequency electrode  104 . In the first embodiment, the flanges  19  function as ground electrodes. The outer pipe  102  is also grounded. 
     Then, the plasma generation circuit  106  generates plasma inside the inner pipe  190  using capacitive coupling between the radio-frequency electrode  104  and the ground electrodes. Specifically, in a state where the flange  19  is grounded (ground potential is applied) as a ground electrode, the plasma generation circuit  106  applies a radio-frequency (RF) voltage to the hollow structure  54  of the radio-frequency electrode  104  via the introduction terminal  111 . As a result, the thin metal plate  50  electrically connected to the hollow structure  54  has the same potential as the hollow structure  54 . Therefore, capacitively coupled plasma (CCP) is generated in the inner pipe  190  of the dielectric by a potential difference between the radio-frequency electrode  104  (thin metal plate  50 ) and the flange  19 . In addition, since in the cleaning step, the cleaning gas such as the NF 3  gas described above is supplied at an upstream position, F radicals due to plasma are generated inside the inner pipe  190  by using the remaining cleaning gas. Then, the F radicals remove products deposited inside the inner pipe  190 . Thus, high cleaning performance can be exhibited in the exhaust pipe. 
     Thereafter, for example, SiF 4  generated after decomposition of the deposit by F radicals has high volatility, and thus is exhausted by the vacuum pump  400  through the exhaust pipe  152 . In addition, a part of the radicals generated in the exhaust pipe apparatus  100  enters the vacuum pump  400  through the exhaust pipe  152 , and cleans the products deposited in the vacuum pump  400 . As a result, the amount of products deposited in the vacuum pump  400  can be reduced. For example, the F radicals generated by the plasma at a part of the inner wall surface on the lower end portion side of the inner pipe  190  can be caused to enter the vacuum pump  400  in a state where the consumption inside the inner pipe  190  is small. 
       FIG.  6    is a top view illustrating an example of a plasma generation state in Comparative Example 1 of the first embodiment. In Comparative Example 1 illustrated in  FIG.  6   , in the examples of  FIGS.  2  and  3   , the hollow structure  354  is directly disposed on the outer periphery of the inner pipe  190  without disposing the thin metal plate  50  and the buffer member  52 . In Comparative Example 1, when the hollow structure  354  is attached around the inner pipe  190 , a contact portion and a non-contact portion are generated between the inner peripheral surface of the hollow structure  354  and the outer peripheral surface of the inner pipe  190 . In a case where a radio-frequency voltage is applied to the hollow structure  354 , the radio-frequency electric field is strong and plasma emission is strong at a contact portion, whereas the radio-frequency electric field is weak and plasma emission is weak at a non-contact portion. As described above, in the configuration of Comparative Example 1, the plasma does not spread to the non-contact portion, and plasma generation becomes non-uniform. As a result, the cleaning effect is deteriorated. 
       FIG.  7    is a top view illustrating an example of a plasma generation state in the first embodiment. In the first embodiment, since the thin metal plate  50  having a thickness smaller than that of the hollow structure  54  can be brought into close contact with the inner pipe  190 , a non-contact portion can be prevented from being generated between the inner peripheral surface of the thin metal plate  50  and the outer peripheral surface of the inner pipe  190 . When a radio-frequency voltage is applied to the hollow structure  54 , the entire conductive thin metal plate  50  can be electrically set to substantially the same potential as the hollow structure  54 . As a result, as illustrated in  FIG.  7   , it is possible to expect generation of uniform plasma over the circumferential direction without generating a portion where emission is weak. 
     Here, in the above-described example, the double pipe structure is configured in order to avoid leakage and atmospheric air intrusion due to a damage of the inner pipe  190  by the dielectric. Causes of a damage of the inner pipe  190  made of a dielectric may include an increase of the temperature of the inner pipe  190 . 
       FIG.  8    is a graph for explaining the relationship between the inner pipe temperature and the cleaning processing time. In  FIG.  8   , the vertical axis represents the temperature of the inner pipe in the exhaust pipe, and the horizontal axis represents the continuous processing time for the exhaust pipe in the cleaning process. In addition, the graph illustrated in the example of  FIG.  8    illustrates an example of a case where the inner pipe  190  is used without being cooled. In the cleaning step, the radio-frequency voltage is applied to the radio-frequency electrode  104 . Thus, the temperature of the radio-frequency electrode  104  increases. Accordingly, the temperature of the inner pipe  190 , which is a dielectric pipe in which plasma is generated, increases. As illustrated in the graph of  FIG.  8   , if the processing is continued without cooling, the temperature rises as the cleaning processing time increases, and the inner pipe  190  may eventually be damaged. In order to suppress the damage of the inner pipe  190  made of a dielectric due to the temperature increase, it is desirable to cool the inner pipe  190 . Therefore, in the first embodiment, a configuration capable of suppressing a temperature rise of the inner pipe  190  will be described below. 
     In the first embodiment, a cooling mechanism is disposed. The cooling mechanism introduces cooling water (an example of a refrigerant) into the space  34  in the hollow structure  54  to cool the inner pipe  190  (dielectric pipe) via the buffer member  52  and the thin metal plate  50 . 
       FIG.  9    is a diagram illustrating an example of a layout of cooling pipes according to the first embodiment. As illustrated in the examples of  FIGS.  2  and  3   , the cavity  34  is formed in the hollow structure  54 . The cavity  34  is suitably formed throughout the hollow structure  54 . As described above, the hollow structure  54  is formed as a combination of the half hollow structure  54 - 1  and the half hollow structure  54 - 2 . Therefore, a cooling pipe  30  is disposed below the cavity  34  in the half hollow structure  54 - 1 . A cooling pipe  32  is disposed above the cavity  34  in the half hollow structure  54 - 2 . A cooling pipe  37  is disposed between the upper portion of the cavity  34  in the half hollow structure  54 - 1  and the lower portion of the cavity  34  in the half hollow structure  54 - 2 . In order to facilitate assembly of the half hollow structure  54 - 1  and the half hollow structure  54 - 2 , a flexible pipe is preferably used as the cooling pipe  37 . However, it is not limited thereto. After the half hollow structure  54 - 1  and the half hollow structure  54 - 2  are assembled, a fixed cooling pipe  37  that is difficult to bend freely may be attached. 
     In the example of  FIG.  2   , the cavity  31  is formed inside the flange  19  on the exhaust pipe  152  side (downstream side). Similarly, a cavity  33  is formed inside a (upstream) flange  19  closer to the exhaust pipe  150 . The cavities  31  and  33  may be formed over the whole or a part of the inside of the respective flanges  19 . For example, each cavity may be formed to have an L shape including two cylindrical cavities extending linearly that are connected to each other. The cavity  31  has an inflow port formed in a side surface of the flange  19 , and an outflow port formed on the side of the space  36  between the outer pipe  102  and the inner pipe  190 . The cavity  33  has an inflow port formed on the side of the space  36  between the outer pipe  102  and the inner pipe  190 , and an outflow port formed in a side surface of the flange  19 . The cooling pipe  30  connects an outflow port of the cavity  31  and a lower portion of the cavity  34  in the hollow structure  54  (for example, the half hollow structure  54 - 1 ). The cooling pipe  37  connects the upper portion of the cavity  34  of the half hollow structure  54 - 1  and the lower portion of the cavity  34  of the half hollow structure  54 - 2 . In addition, the cooling pipe  32  connects the upper portion of the cavity  34  in the half hollow structure  54 - 2  and the inflow port of the cavity  33 . The flange  19  in which the cavity  31  is formed, the flange  19  in which the cavity  33  is formed, the cooling pipes  30 ,  32 , and  37 , and the hollow structure  54  in which the cavity  34  is formed constitute a part of the cooling mechanism. 
     The cooling water supplied to the side surface of the flange  19  on the exhaust pipe  152  side (downstream side) passes through the cavity  31  in the flange  19  on the exhaust pipe  152  side (downstream side), passes through the cooling pipe  30 , and moves to the lower portion of the cavity  34  in the half hollow structure  54 - 1 . The cooling water supplied to the lower portion of the cavity  34  in the half hollow structure  54 - 1  accumulates in the cavity  34  from the lower portion toward the upper portion. The cooling water overflowing from the upper portion of the cavity  34  in the half hollow structure  54 - 1  is supplied to the lower portion of the cavity  34  in the half hollow structure  54 - 2  through the cooling pipe  37 . The cooling water supplied to the lower portion of the cavity  34  in the half hollow structure  54 - 2  accumulates in the cavity  34  from the lower portion toward the upper portion. The cooling water overflowing from the upper portion of the cavity  34  in the half hollow structure  54 - 2  passes through the cooling pipe  32  and moves to the cavity  33  in the flange  19  on the exhaust pipe  150  side (upstream side). Then, the water passes through the cavity  33  in the flange  19  and is drained from the outflow port in the side surface of the flange  19 . 
     In a state where the cooling water is flowing, the plasma generation circuit  106  generates plasma inside the inner pipe  190  using the radio-frequency electrode  104 . The plasma generation circuit  106  applies a radio-frequency voltage to the radio-frequency electrode  104 . At this time, the cooling water flowing in the hollow structure  54  is used to cool the inner pipe  190 , which is a dielectric pipe whose temperature rises due to plasma generation inside, and the space  36  between the inner pipe  190  and the outer pipe  102 . As a result, the radio-frequency voltage is applied, and the radio-frequency electrode  104  whose temperature rises is directly cooled. In the first embodiment, the buffer member  52  having a high thermal conductivity is sandwiched between the hollow structure  54  and the metal thin film  50  so as to be in close contact with each other without any gap. Therefore, the metal thin film  50  can be efficiently cooled by directly cooling the hollow structure  54 . Furthermore, the inner pipe  190  in close contact with the inner peripheral surface of the metal thin film  50  can be efficiently cooled. Therefore, the temperature rise of the inner pipe  190  can be suppressed. 
       FIG.  10    is a front view of an example of an exhaust pipe apparatus according to Comparative Example 2 of the first embodiment. In Comparative Example 2 of  FIG.  10   , a case where the radio-frequency electrode  304  is disposed in a space between the outer pipe  302  on the outer periphery side of the dielectric pipe  390  and the dielectric pipe  390  is illustrated. At both end portions of the dielectric pipe  390 , pipe flanges  319  that function as ground electrodes are disposed. Then, capacitively coupled plasma (CCP) is generated by applying a radio-frequency (RF) voltage to the radio-frequency electrode  304  using the flanges  319  as ground electrodes. In such a configuration, the flanges  319  and the radio-frequency electrode  304  may be capacitively coupled to cause electric discharge. 
     In the example of  FIG.  10   , it is also conceivable to cool the outer peripheral surface of the outer pipe  302  disposed on the outer periphery side of the dielectric pipe  390  and the radio-frequency electrode  304  by supplying cooling water. However, even if the outside of the outer pipe  302  is cooled, it is difficult to sufficiently cool the space between the outer pipe  302  and the dielectric pipe  390  via the outer pipe  302 . Therefore, the cooling of the outer pipe  302  may result in increase of the temperature of the dielectric pipe  390  and then damage of the dielectric pipe  390 . 
     On the other hand, in the first embodiment, since the outer peripheral surface of the inner pipe  190  is directly cooled by the radio-frequency electrode  104 , the temperature rise of the inner pipe  190  can be suppressed as compared with the case of cooling from the outer side of the outer pipe  102 . In the first embodiment, when the double pipe structure in which the outer pipe is disposed outside the inner pipe is not formed, the hollow structure  54  in which the cavity  34  is formed is cooled as a part of the cooling mechanism, so that the temperature rise of the inner pipe  190  can be suitably suppressed. 
     As described above, according to the first embodiment, plasma generation can be brought close to a uniform state, and a product deposited inside the exhaust pipe near the vacuum pump can be removed. 
     Second Embodiment 
     In the configuration of Comparative Example 2 illustrated in  FIG.  10   , the flange  319  and the radio-frequency electrode  304  are capacitively coupled to cause electric discharge. The electric discharge may occur not only inside the dielectric pipe  390  but also outside the dielectric pipe  390 , for example, on a side where the atmospheric pressure is set. Therefore, it is desirable to increase the distance L 3  between the flange  319  (ground electrode) and the radio-frequency electrode  304  to such an extent that the atmospheric pressure side does not cause electric discharge. In a case where the distance L 3  between the flange  319  (ground electrode) and the radio-frequency electrode  304  is large, increase of the gas flow rate and the pressure in the dielectric pipe  390  makes it difficult to generate plasma, causing unstable electric discharge. On the other hand, by decreasing the electrode size of the radio-frequency electrode  304  in the gas flow direction to increase the voltage or/and decreasing the distance L 3  between the flange  319  (ground electrode) and the radio-frequency electrode  304 , plasma is easily generated, but abnormal discharge (arcing) is easily generated on the atmospheric pressure side. 
     Therefore, in the second embodiment, the ground electrode is disposed such that the distance to the radio-frequency electrode  104  is smaller on the inner side of the inner pipe  190  than on the outer side. 
       FIG.  11    is a cross-sectional view of an example of an exhaust pipe apparatus according to a second embodiment as viewed from the front side. A cross-sectional view of an example of the exhaust pipe apparatus according to the second embodiment as viewed from the upper side is not provided.  FIG.  11    is the same as  FIG.  2    except that ring-shaped protrusions  18  extending from the surfaces of the flanges  19  toward the radio-frequency electrode  104  are disposed on the inner side of the inner pipe  190 . 
     Each protrusion  18  is made of a conductive material and functions as a part of the ground electrode. Each protrusion  18  is formed integrally with the flange  19  to which the protrusion is connected, for example. 
     Alternatively, each protrusion  18  may be formed separately from the flange  19  as long as it is electrically connected to the flange  19 . In addition, when each O-ring retainer  11  is made of a conductive material, each O-ring retainer  11  functions as a part of the ground electrode by being brought into contact with the protrusion  10 . 
     In the example of  FIG.  11   , since the tip of the protrusion  10  or the exposed surface of the O-ring retainer  11  on the side of the radio-frequency electrode  104  is closest to the radio-frequency electrode  104  on the outer side of the inner pipe  190 , the protrusion  18  is formed such that the distance L 1  between the tip of the protrusion  18  and the radio-frequency electrode  104  is smaller than the distance L 2  between the tip of the protrusion  10  on the outer side of the inner pipe  190  or the exposed surface of the O-ring retainer  11  on the side of the radio-frequency electrode  104  and the radio-frequency electrode  104 . When there is no protrusion  10 , the protrusion  18  is disposed such that the distance L 1  between the tip of the protrusion  18  and the radio-frequency electrode  104  is smaller than the distance between the flange surface on the outer side of the inner pipe  190  and the radio-frequency electrode  104 . Accordingly, when a radio-frequency voltage is applied to the radio-frequency electrode  104 , electric discharge occurs first between the protrusion  18  and the radio-frequency electrode  104 . Therefore, for example, plasma by capacitive coupling can be generated inside the inner pipe  190  without applying a voltage that causes abnormal discharge (arcing) on the atmospheric pressure side. Decrease of the distance between the electrodes on the vacuum side can further enhance ignitability and stability of plasma in addition to suppression of arcing. 
     Note that it is desirable that the protrusion  18  be disposed such that the distance L 1  between the tip of the protrusion  18  and the radio-frequency electrode  104  is even smaller than the distance between the grounded outer pipe  102  and the radio-frequency electrode  104 . 
     The rest of the configurations is similar to that in  FIG.  2   . 
     As described above, according to the second embodiment, in addition to the same effects as those of the first embodiment, it is possible to further remove products deposited inside the exhaust pipe near the vacuum pump while avoiding abnormal discharge such as arcing. 
     Third Embodiment 
     In each of the above-described embodiments, the configuration has been described in which the inner pipe  190  in close contact with the radio-frequency electrode  104  is directly cooled by flowing the cooling water into the cavity  34  in the hollow structure  54 . A configuration in which the cooling mechanism of the third embodiment cools the space  36  between the inner pipe  190  and the outer pipe  102  will be further described. 
       FIG.  12    is a cross-sectional view of an example of an exhaust pipe apparatus according to a third embodiment as viewed from the front side. A cross-sectional view of an example of the exhaust pipe apparatus according to the third embodiment as viewed from the upper side is not provided.  FIG.  12    is the same as  FIG.  11    except that a gas introduction port  41 , a valve  40  (or a check valve  42 ), a gas discharge port  43 , and a valve  44  (or a check valve  46 ) are further added. The cooling mechanism in the third embodiment introduces a cooling gas (another example of a refrigerant) into the space  36  between the inner pipe  190  and the outer pipe  102  from the gas introduction port  41  disposed on the lower side of the outer peripheral surface of the outer pipe  102  via the valve  40  (or the check valve  42 ). Then, the cooling gas is discharged to the outside from the gas discharge port  43  provided in an upper portion of the outer peripheral surface of the outer pipe  102  via the valve  44  (or the check valve  46 ). By allowing the cooling gas to flow into the space  36  between the inner pipe  190  and the outer pipe  102 , the inner pipe  190 , which is a dielectric pipe whose temperature rises due to plasma generation inside, and the space  36  between the inner pipe  190  and the outer pipe  102  are cooled. By cooling the inner pipe  190  with the cooling gas, the effect of suppressing a damage of the inner pipe  190  can be further enhanced. As the cooling gas, for example, air is used. 
     The cooling gas is introduced into the space  36  between the inner pipe  190  and the outer pipe  102  at a pressure higher than atmospheric pressure. Therefore, the pressure in the space  36  between the inner pipe  190  and the outer pipe  102  is controlled to be higher than the pressure in the space inside the inner pipe  190  and the atmospheric pressure. The pressure in the space  36  between the inner pipe  190  and the outer pipe  102  is measured by a pressure sensor  48  via a vent  47  disposed on the outer peripheral surface of the outer pipe  102 , and fluctuations in the pressure in the space  36  are monitored. Here, in a case where the inner pipe  190 , which is a dielectric pipe whose temperature rises due to plasma generation inside, is damaged, vacuum breakdown occurs when a large amount of cooling gas flows into the vacuum side. Therefore, the damage of the inner pipe  190  is detected by the pressure sensor  48 . 
     Specifically, when pressure decrease is detected by the pressure sensor  48 , control is performed to block the valves  40  and  44 . As a result, the inflow of the cooling gas into the exhaust line can be minimized. In a case where the check valve  42  is used instead of the valve  40 , the check valve  42  in which the cracking pressure is set such that the check valve  42  is blocked when the pressure difference between the primary pressure and the secondary pressure is higher than 0.1 MPa and lower than the supply pressure of the cooling gas is used. When the supply of the cooling gas is stopped at the supply source, the primary pressure (the primary side of the check valve) is equal to the atmospheric pressure, the secondary pressure (inside the outer pipe  102 ) is equal to or lower than the atmospheric pressure (the pressure decreases to be lower than the atmospheric pressure due to damage), and the differential pressure is equal to or lower than 0.1 MPa. Therefore, when 0.1 MPa&lt;cracking pressure&lt;supply pressure is satisfied, the cooling gas does not flow. Therefore, if the supply of the cooling gas is stopped at the supply source in response to the detection of the damage of the inner pipe  190 , the atmospheric air can be prevented from flowing into the outer pipe  102  even when the primary side is opened to the atmospheric air. In a case where the check valve  46  is used instead of the valve  44 , damage of the inner pipe  190  makes the primary pressure lower than the secondary pressure, so that the flow path can be blocked. Therefore, the atmospheric air can be prevented from flowing into the outer pipe  102 . 
     The rest of configurations is similar to those in  FIG.  11   . 
     As described above, according to the third embodiment, in addition to the same effects as those of the first and second embodiments, the cooling effect of the inner pipe  190  can be further enhanced. 
     The embodiments have been described with reference to the specific examples. However, the present invention is not limited to these specific examples. For example, in the embodiments of the present invention, the exhaust pipe apparatus may be applied to a semiconductor manufacturing apparatus other than the film forming apparatus such as an etching apparatus. 
     In addition, all exhaust pipe apparatuses that include the elements of the present invention and can be achieved by appropriate modification of design by those skilled in the art fall in the scope of the present invention. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and apparatuses described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and apparatuses described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.