Patent Publication Number: US-7901510-B2

Title: Bolt and plasma processing apparatus provided with same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. application Ser. No. 11/263,955, filed Nov. 2, 2005, now U.S. Pat. No. 7,708,834, which claims benefit to U.S. Provisional Application No. 60/635,969, filed Dec. 15, 2004, and which claims priority under 35 U.S.C. 119 to Japanese Patent Application No. 2004-319411, filed Nov. 2, 2004, the entire contents of each of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a bolt and a plasma processing apparatus; and, more particularly, to a bolt which is driven into a female screw portion disposed in a brittle member and a plasma processing apparatus provided therewith. 
     BACKGROUND OF THE INVENTION 
     Conventionally, a parallel plate type plasma processing apparatus is widely employed as a plasma processing apparatus for performing a plasma processing such as an etching or a film forming process on a wafer serving as an object to be processed. The plasma processing apparatus includes a chamber serving as a vacuum processing vessel, and components such as an upper and a lower electrode, a susceptor, a focus ring and a shield ring are disposed in the chamber. 
     In the plasma processing apparatus, a processing gas is introduced into the chamber and, then, is converted into a plasma to generate radicals in, e.g., an etching process. By those radicals, components in the chamber and an inner wall of the chamber as well as a surface of the wafer are etched to be worn away. Further, the processing gas in the etching process contains a halogen element and, thus, the components in the chamber and the inner wall of the chamber tend to undergo an intensive corrosion. Accordingly, the components in the chamber and the inner wall of the chamber are formed of a wear resistant ceramic material, or a thermally sprayed ceramic coating is used on the surface thereof in order to prevent the wear and corrosion thereof. 
     Typically, the components in the chamber are attached to the inner wall of the chamber by using bolts for the maintenance and repair. The surface of the inner wall of the chamber is formed of a ceramic material as described above, so that a female screw portion for coupling to the bolt is formed in a ceramic portion. In this case, since the ceramic material is a brittle material, the female screw portion cannot be shaped accurately. Further, when an attachment bolt is made of, e.g., metal, there occurs galling between the bolt (male screw portion) and the female screw portion of the inner wall of the chamber. Thus, in the conventional plasma processing apparatus, the bolt is formed of a resin having elasticity and plasticity to prevent the galling. For example, as such a bolt, there is known a plastic bolt whose head and body made of a plastic material are in combination with each other (see, e.g., Japanese Utility Model No. 2579389) 
     However, since the plastic material is easily worn away by the radicals, the bolt (male screw portion) is worn away by the radicals that enter into a gap between the bolt (male screw portion) and the female screw portion of the inner wall of the chamber. Consequently, an axial force of the bolt is reduced such that the components in the chamber may fall apart. 
     A fluorine resin, e.g., PTFE, is known as a resin which is not worn away by the radicals, but the fluorine resin has a low hardness. Accordingly, the bolt made of fluorine resin is broken by a clamping torque, resulting in the degradation of the axial force to make the components fall apart. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a bolt for stably coupling a component with a brittle member in the wear and corrosion environment and a plasma processing apparatus provided therewith. 
     To achieve the object, there is provided a bolt which is driven into a female screw portion disposed in a brittle member in a wear environment, the bolt including a head formed of a wear resistant material; a body, formed of a resin having elasticity or plasticity, including a first male screw portion; and a placed member disposed between the head and the body and formed of a wear resistant resin having elasticity or plasticity. 
     In the bolt, the body further includes a second male screw portion disposed along a central axis of the body and the head includes a female screw portion which the second male screw portion is driven into. 
     In the bolt, the placed member is of a plate shape and has a through hole in its central portion, and a diameter of the through hole is smaller than or equal to a nominal diameter of the first male screw portion and larger than or equal to a nominal diameter of the second male screw portion. 
     In the bolt, the placed member is formed of a fluorine resin. 
     In the bolt, the brittle member is formed of the wear resistant material. 
     To achieve the object, there is provided a plasma processing apparatus having a processing chamber in which a wear environment is formed, the apparatus including a component disposed in the processing chamber; and a bolt for attaching the component to a base portion formed of a brittle member, wherein the bolt includes a head formed of a wear resistant material, a body which is formed of a resin having elasticity or plasticity and has a male screw portion, and a placed member which is disposed between the head and the body and formed of a wear resistant resin having elasticity or plasticity. 
     In accordance with the present invention, a bolt, which is driven into a female screw portion disposed in a brittle member in a wear environment, includes a head formed of a wear resistant material; a body, formed of a resin having elasticity or plasticity, including a first male screw portion; and a placed member disposed between the head and the body and formed of a wear resistant resin having elasticity or plasticity. Accordingly, the galling between the male screw portion and the female screw portion provided in the brittle member does not occur. Further, the radicals do not enter into a gap between the male screw portion and the female screw portion, whereby the male screw portion is not worn away. Therefore, the component can be stably attached to the brittle member in the wear environment by using the bolt. 
     In accordance with the present invention, the body further includes a second male screw portion disposed along a central axis of the body and the head includes a female screw portion which the second male screw portion is driven into. Accordingly, although the head and the body are formed of different materials, the head and the body can be stably combined, thereby being handled as a single unit. Therefore, the component can be easily attached to the brittle member. 
     In accordance with the present invention, the placed member is of a plate shape and has a through hole in its central portion, and a diameter of the through hole is smaller than or equal to a nominal diameter of the first male screw portion and larger than or equal to a nominal diameter of the second male screw portion. Accordingly, the head and the body can be combined with the placed member interposed therebetween. Thus, the head, the body and the placed member can be handled as a single unit. Therefore, the component can be more easily attached to the brittle member. 
     In accordance with the present invention, since the placed member is formed of a fluorine resin, the placed member is not worn away by the radicals and, further, it is possible to definitely prevent the radicals from entering into the gap between the male screw portion and the female screw portion. Therefore, the component can be stably attached to the brittle member in the wear environment by using the bolt. 
     In accordance with the present invention, since the brittle member is formed of the wear resistant material, anti-wear measures can be easily executed. 
     In accordance with the present invention, a plasma processing apparatus having a processing chamber in which a wear environment is formed includes a component disposed in the processing chamber; and a bolt for attaching the component to a base portion formed of a brittle member, wherein the bolt includes a head formed of a wear resistant material, a body which is formed of a resin having elasticity or plasticity and has a male screw portion, and a placed member which is disposed between the head and the body and formed of a wear resistant resin having elasticity or plasticity. Accordingly, the galling between the male screw portion and the female screw portion provided in the brittle member does not occur. Further, the radicals do not enter into a gap between the male screw portion and the female screw portion, whereby the male screw portion is not worn away. Therefore, the component can be stably attached to the brittle member in the wear environment by using the bolt. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments, given in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a longitudinal cross sectional view showing a schematic configuration of the plasma processing apparatus in accordance with a preferred embodiment of the present invention; 
         FIG. 2  is an exploded side view showing a schematic configuration of a bolt in accordance with the preferred embodiment of the present invention; 
         FIG. 3  depicts how the bolt shown in  FIG. 2  is used; and 
         FIG. 4  schematically illustrates a modified example of the bolt in the preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A preferred embodiment of the present invention will now be described with reference to the accompanying drawings. 
     Hereinafter, there will be described a plasma processing apparatus in accordance with the preferred embodiment of the present invention. 
       FIG. 1  is a longitudinal cross sectional view showing a schematic configuration of the plasma processing apparatus in accordance with the preferred embodiment of the present invention. 
     A plasma processing apparatus  1  shown in  FIG. 1 , which is used as an etching processing apparatus for performing an etching process on a wafer W, includes a cylindrical chamber (accommodation chamber)  10  made of metal such as aluminum or stainless steel. A cylindrical susceptor  11  serving as a stage for mounting thereon the wafer W having a diameter of, e.g., 300 mm is disposed in a lower portion of the chamber  10 . 
     An annular focus ring  24  is disposed on the susceptor  11  to surround an outer peripheral portion of the susceptor  11 . The focus ring  24  is formed of silicon (Si) and the like and converges a plasma generated above the susceptor  11  toward the wafer W. 
     A circular electrode plate  20 , formed of a conductive film, for electrostatically attracting and holding the wafer W is disposed inside an upper portion of the susceptor  11 . A DC power supply  22  is electrically connected to the electrode plate  20 . The wafer W is adsorbed to be held on the top surface of the susceptor  11  by Coulomb force or Johnsen-Rahbek force produced by a DC voltage applied to the electrode plate  20  from the DC power supply  22 . When the wafer W need not be adsorbed on the top surface, the electrode plate  20  is cut off from the DC power supply  22  to be in a floating state. 
     A coolant chamber  25  of, e.g., a ring shape is provided inside the susceptor  11 . A coolant, e.g., cooling water, kept at a predetermined temperature is supplied to the coolant chamber  25  from a chiller unit (not shown) via a pipe  26  to be circulated therein, whereby the wafer W on the susceptor  11  is controlled to be maintained at a predetermined process temperature by the coolant. 
     In the top surface of the susceptor  11 , thermally conductive gas supply holes  27  and a thermally conductive gas supply groove (not shown) are disposed in a portion to which the wafer is adsorbed (hereinafter, referred to as an “adsorbing surface”). Those thermally conductive gas supply holes  27  and the like are connected to a thermally conductive gas feeding pipe  29  equipped with a valve V 3  via a thermally conductive gas supply line  28  disposed in the susceptor  11 . A thermally conductive gas, e.g., He gas, from a thermally conductive gas supply unit (not shown) coupled to the thermally conductive gas feeding pipe  29  is supplied into a gap between the adsorbing surface and the bottom surface of the wafer W through the thermally conductive gas supply holes  27  and the like. Accordingly, heat transfer is improved between the wafer W and the susceptor  11 . Further, the valve V 3  can isolate the thermally conductive gas supply holes  27  and the like from the thermally conductive gas supply unit. 
     Further, disposed on the adsorbing surface is a plurality of pusher pins  30 , i.e., lift pins, which can be freely moved up and down from the top surface of the susceptor  11 . A rotational movement of a motor (not shown) is converted into a linear movement by ball screws and the like, whereby the pusher pins  30  can be moved vertically. When the wafer W is adsorbed to be held on the adsorbing surface, the pusher pins  30  are accommodated in the susceptor  11 , whereas when the wafer W is unloaded from the chamber  10  after the plasma processing such as an etching process is finished, the pusher pins  30  are protruded from the top surface of the susceptor  11  such that the wafer W is separated to be lifted from the susceptor  11 . 
     A shower head  33  is disposed in an inner upper portion of the chamber  10 . The shower head  33  is connected to a high frequency power supply  18 , which applies a predetermined high frequency power to the shower head  33 . Accordingly, the shower head  33  functions as an upper electrode. 
     The shower head  33  includes a circular electrode plate  35  having a plurality of gas ventholes  34  and an electrode supporting member  36  for supporting the electrode plate  35  which can be attached thereto or detached therefrom. Further, a buffer chamber  37  is provided in the electrode supporting member  36  and connected to a processing gas supply unit (not shown) via a processing gas inlet pipe  38 . A valve V 1  is installed in the middle of the processing gas inlet pipe  38 . The valve V 1  can isolate the buffer chamber  37  from the processing gas supply unit. Here, a distance D between electrodes, i.e., the susceptor  11  and the shower head  33 , is set to be equal to or larger than, e.g., 35±1 mm. 
     Further, an annular quartz guide (shield ring)  39  facing the focus ring  24  is disposed below the electrode plate  35  to cover an outer peripheral portion of the electrode plate  35 . The quartz guide  39  is formed of, e.g., SiO 2  and protects the outer peripheral portion of the electrode plate  35  and an inner peripheral portion of an inner wall  40  of the chamber  10  formed of an insulator from the plasma generated between the susceptor  11  and the shower head  33 . 
     Formed between the sidewall of the chamber  10  and the susceptor  11  is a gas exhaust path  12  that functions as a channel for discharging a gas existing above the susceptor to the outside of the chamber  10 . An annular baffle plate  13  is disposed in the middle of the gas exhaust path  12 , and a lower portion of the gas exhaust path  12 , which is under the baffle plate  13 , is coupled to an automatic pressure control valve  14  (hereinafter, referred to as an “APC”) that is a variable butterfly valve. The APC  14  is connected to a turbo molecular pump  15  (hereinafter, referred to as a “TMP”), which is a gas exhaust pump for vacuum exhaust. Further, the APC  14  is connected to a dry pump  16  (hereinafter, referred to as a “DP”) serving as a gas exhaust pump via the TMP  15 . A gas exhaust channel including the APC  14 , TMP  15 , and DP  16  is hereinafter referred to as a “main pumping line”, wherein the APC  14  controls pressure in the chamber  10  and, additionally, the TMP  15  and DP  16  depressurize the chamber  10  almost to vacuum. 
     Further, the lower portion of the gas exhaust path  12 , which is under the baffle plate  13 , is coupled to another gas exhaust channel (hereinafter, referred to as a “rough pumping line”), which is separate from the main pumping line. The rough pumping line includes a gas exhaust pipe  17 , having a diameter of, e.g., 25 mm, for connecting the lower portion to the DP  16 ; and a valve V 2  installed in the middle of the gas exhaust pipe  17 . The valve V 2  can isolate the lower portion of the gas exhaust path  12  from the DP  16 . A gas in the chamber  10  is discharged to the outside by the DP  16  in the rough pumping line. 
     A gate valve  32  for opening or closing a loading/unloading port  31  for the wafer W is installed on the sidewall of the chamber  10 . In the chamber  10  of the plasma processing apparatus  1 , as describe above, a high frequency power is applied to the shower head  33 , whereby an O 2  single gas serving as a processing gas is converted into a plasma in a space S to produce radicals. 
     When an etching process is performed in the plasma processing apparatus  1 , first, after the gate valve  32  is opened, the wafer W serving as an object to be processed is loaded into the chamber  10  and mounted on the susceptor  11 . Then, a processing gas such as O 2  single gas or gaseous mixture containing O 2  gas (e.g., gaseous mixture containing CF 4  gas and O 2  gas) through the shower head  33  is introduced into the chamber  10  at a predetermined flow rate, and a specified pressure level is maintained in the chamber  10  by the APC  14  and the like. Further, a high frequency power is applied to the shower head  33  from the high frequency power supply  18  and a DC voltage is applied to the electrode plate  20  from the DC power supply  22 , whereby the wafer W is attracted and held on the susceptor  11 . Then, the O 2  single gas introduced through the shower head  33  is converted into a plasma as described above, thereby producing radicals. The radicals are converged on the wafer W by the focus ring  24 , thereby chemically etching the surface of the wafer W. 
     Besides the surface of the wafer W, the components in the chamber, for example, focus ring  24 , the susceptor  11 , the baffle plate  13  and the electrode plate  35 , and the inner wall  40  of the chamber, which are exposed to the atmosphere in the chamber  10 , are etched by the radicals and, thus, they become worn away by repeated etching. Further, a gas containing a halogen element such as fluoride, chloride and bromide in addition to the O 2  single gas may be employed as a processing gas for etching, thereby forming an intensive corrosion environment in the chamber. Then, the components in the chamber and the inner wall  40  of the chamber are getting corroded by repeated etching. Accordingly, the components in the chamber and the inner wall  40  of the chamber are formed of a wear resistant ceramic material or a thermally sprayed ceramic coating is used on the surface thereof in order to prevent the wear and corrosion thereof. At this time, for example, yttrium oxide (Y 2 O 3 ) or aluminum oxide (Al 2 O 3 ) is preferably used as a ceramic material (brittle material). In the plasma processing apparatus  1 , the inner wall  40  of the chamber is formed of aluminum oxide, so that the inner wall  40  is a brittle member. 
     Further, the quartz guide (component)  39  is attached to the inner wall  40  of the chamber by using a bolt  41  to be described later for the maintenance and repair. 
       FIG. 2  is an exploded side view showing a schematic configuration of a bolt in accordance with the preferred embodiment of the present invention. 
     Referring to  FIG. 2 , the bolt  41  includes a cylindrical head  42  having a diameter of, e.g., 5 mm; a body  44  in which a male screw portion  43  having a screw size of, e.g., M4 is formed; and a washer (placed member)  45  shaped like a circular plate having an outer diameter of, e.g., 5 mm. The head  42  is made of, e.g., aluminum oxide having a wear resistance against the radicals and the body  44  is made of a resin having plasticity and heat resistance, for instance, a wholly aromatic polyimide resin. Further, the washer  45  is made of a resin having a wear resistance against the radicals, plasticity and heat resistance, for example, a tetrafluoroethylene resin (PTFE). 
     The body  44  has a male screw portion  46  having a screw size of, e.g., M3, which is disposed along a central axis of the body  44 . The head  42  has a female screw portion  47  having a screw size of, e.g., M3, which is bored along a central axis of the body  44 . In the bolt  41 , the head  42  and the body  44  is coupled mechanically by driving the male screw portion  46  into the female screw portion  47 . 
     In a central portion of the washer  45 , there is a through hole  48  having a diameter of, e.g., 3.5 mm. The diameter of the through hole  48  is larger than or equal to a nominal diameter of the male screw portion  46 , whereby the male screw portion  46  can be inserted into the through hole  48  of the washer  45  when coupling the head  42  with the body  44 . Further, by driving the male screw portion  46  protruded from the through hole  48  into the female screw portion  47 , the male screw portion  46 , the washer  45  and the head  42  are coupled together as a single body. At this time, the washer  45  is interposed between the male screw portion  43  and the head  42 , but the diameter of the through hole  48  is smaller than or equal to a nominal diameter of the male screw portion  43 . Consequently, the washer  45  can be interposed between the male screw portion  43  and the head  42  without being separated therefrom. 
     The head  42  has a groove portion  49  which is engraved in a diametric direction on a surface opposite to the surface on which an opening of the female screw portion  47  is positioned. When the groove portion  49  is engaged with a minus driver (not shown), a clamping torque is transferred to the head by the minus driver to thereby tighten the bolt  41 . 
       FIG. 3  depicts how the bolt shown in  FIG. 2  is used. 
     Referring to  FIG. 3 , the bolt  41  is tightened to the inner wall  40  of the chamber by driving the male screw portion  43  of the body  44  into a female screw portion  50  bored in the inner wall  40  of the chamber. Thus, the head is protruded from the inner wall  40  of the chamber. Further, the protruded head  42  is engaged with a hook groove  52  bored in a side surface  51  of the quartz guide  39 . Accordingly, the quartz guide  39  is supported by the bolt  41  and, then, attached to the inner wall  40  of the chamber. 
     The shape of the female screw portion  50  bored in the inner wall  40  of the chamber is not formed accurately since the inner wall  40  is formed of aluminum oxide that is a brittle material. However, the male screw portion  43  which is driven into the female screw portion  50  is formed of a tetrafluoroethylene resin having plasticity, whereby the male screw portion  43  can accommodate the shape discrepancy of the female screw portion  50 . 
     Further, since the quartz guide  39  is supported by only the head  42 , a gap  53  may be formed between the inner wall  40  of the chamber and the quartz guide  39  and the radicals may enter into the gap  53 . However, when the bolt is tightened to the inner wall  40  of the chamber, the washer  45  interposed between the inner wall  40  of the chamber and the head  42  fills a gap therebetween, whereby the radicals that have entered into the gap  53  cannot enter into a gap between the male screw portion  43  of the body  44  and the female screw portion  50  of the inner wall  40  of the chamber. 
     The bolt in accordance with the preferred embodiment includes the head  42  made of aluminum oxide; the body  44 , formed of a wholly aromatic polyimide resin, having the male screw portion  43 ; and the washer  45  disposed between the heat  42  and the body  44  and formed of a tetrafluoroethylene resin. Since the male screw portion  43  is formed of a tetrafluoroethylene resin having plasticity, the male screw portion  43  can accommodate the shape discrepancy of the female screw portion  50  bored in the inner wall  40  of the chamber that is a brittle member. Accordingly, the galling between the male screw portion  43  and the female screw portion  50  does not occur. Further, since the washer  45  fills a gap between the inner wall  40  of the chamber and the head  42 , the radicals do not enter into a gap between the male screw portion  43  and the female screw portion  50 , whereby the male screw portion is not worn away. Therefore, the quartz guide  39  can be stably attached to the inner wall  40  of the chamber in an environment containing radicals by using the bolt  41 . 
     Further, since the body  44  has the male screw portion  46  disposed along its central axis and the head  42  has the female screw portion  47  into which the male screw portion is driven, although the head  42  and the body  44  are formed of different materials, the head  42  and the body  44  can be stably combined. Accordingly, the head  42  and the body  44  can be handled as a single unit. Further, since the washer  45  has the through hole  48  in its central portion and the diameter of the through hole  48  is smaller than or equal to the nominal diameter of the male screw portion  43  and larger than or equal to the nominal diameter of the male screw portion  46 , the head  42  and the body  44  can be combined with the washer  45  interposed therebetween. Thus, the head  42 , the body  44  and the washer  45  can be handled as a single unit. Therefore, the quartz guide  39  can be easily attached to the inner wall  40  of the chamber. 
     Since the washer  45  is made of a tetrafluoroethylene resin, the washer  45  is not worn away by the radicals and, further, it is possible to definitely prevent the radicals from entering into the gap between the male screw portion  43  and the female screw portion  50 . Additionally, because the tetrafluoroethylene resin has plasticity, the washer  45  can absorb the collapse of the inner wall  40  serving as a washer-placed surface toward the female screw portion  50 , thereby more stably attaching the quartz guide  39  to the inner wall  40  of the chamber. 
     Further, since the inner wall  40  of the chamber is made of aluminum oxide, which is same as the material of the head  42 , anti-wear measures can be investigated by considering only a wear resistance of aluminum oxide and therefore can be carried out easily. 
     Although the bolt is configured by a plurality of members as described above in the preferred embodiment, the bolt can be made as a single unit. For example, as shown in  FIG. 4 , the bolt  54  is formed by combining a head  55 , a body  56  and a flange  57  provided in a peripheral end portion of the head  55  close to the body  56  to be a single unit by a resin having plasticity and heat resistance, e.g., a wholly aromatic polyimide resin. Further, the surfaces of the head  55  and the flange  57  are preferably coated with a radical resistant material, e.g., an aluminum oxide film  58 . 
     The bolt  54  is closely attached to the inner wall  40  of the chamber by a clamping force. Accordingly, the radicals do not enter into a gap between the male screw portion  43  and the female screw portion  50 , whereby the quartz guide  39  can be stably attached to the inner wall  40  of the chamber in an environment containing radicals by using the bolt  54 . Further, since the surfaces of the head  55  and the flange  57  are coated with the aluminum oxide film  58  in an environment containing radicals, the flange  57  and the film  58  are not worn away. Furthermore, since the head  55 , the body  56  and the flange  57  are formed as a single unit, the quartz guide  39  can be easily attached to the inner wall  40  of the chamber. 
     Since the bolt  41  mentioned above is employed in an environment containing radicals (chemical etching), the head  42  is made of aluminum oxide and the washer  45  is made of a tetrafluoroethylene resin. But, materials of the head  42  and the washer  45  are not limited thereto and may be radical resistant materials in an environment containing radicals or ion resistant materials in an environment containing ions (physical etching). 
     Further, although the body  44  is formed of a wholly aromatic polyimide resin having plasticity and heat resistance, the material of the body  44  may be another resin having plasticity and heat resistance or a resin having elasticity and heat resistance without being limited thereto. 
     Moreover, although the washer  45  is formed of a resin having plasticity, the material of the washer  45  is not limited thereto and may be a resin having elasticity. 
     In the embodiment described above, the bolt  41  is used in the etching processing apparatus, but the usage thereof is not limited thereto and it can be applied to another plasma processing apparatus, for example, CVD processing apparatus or a processing apparatus having therein another wear environment. 
     Further, in the above embodiment, when the quartz guide  39  is attached to the inner wall  40  of the chamber, the bolt  41  is used to couple them. However, the bolt  41  can be employed for any component in the chamber which is attached to a brittle member without being limited to the quartz guide  39 . 
     Hereinafter, there will be described an example of the present invention in detail. 
     EXAMPLE 
     First, in the plasma processing apparatus  1  shown in  FIG. 1 , the quartz guide  39  was attached to the inner wall  40  of the chamber by using four bolts  41  shown in  FIG. 2 . 
     Then, an etching process was performed on 2000 sheets of wafers W. After that, the four bolts  41  were loosened and a wear amount and a wear rate thereof were measured. Additionally, a loosening torque of each bolt  41  was also measured. The following Table 1 shows the wear amount, the wear rate and the loosening torque measured in Examples 1, 2, 3 and 4. 
     COMPARISON EXAMPLE 
     First, in the plasma processing apparatus  1  shown in  FIG. 1 , the quartz guide  39  was attached to the inner wall  40  of the chamber by using wholly resin bolts, each having a body and a head formed of a wholly aromatic polyimide resin as a single unit. 
     Then, an etching process was performed on 750 sheets of wafers W. After that, the wholly resin bolts were loosened and a wear amount and a wear rate thereof were measured. The following Table 1 shows the wear amount and the wear rate measured in Comparison example 1. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                   
                 reduced loosening 
               
               
                   
                 wear amount 
                 wear rate 
                 torque 
               
               
                   
                 (g) 
                 (%) 
                 (kgf · cm) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Example 1 
                 0.0005 
                 0.54 
                 0.10 
               
               
                   
                 Example 2 
                 0.0000 
                 0.00 
                 0.20 
               
               
                   
                 Example 3 
                 0.0004 
                 0.42 
                 0.20 
               
               
                   
                 Example 4 
                 0.0005 
                 0.54 
                 0.20 
               
               
                   
                 Comparison 
                 0.0010 
                 1.10 
                 — 
               
               
                   
                 example 1 
               
               
                   
                   
               
            
           
         
       
     
     As shown in Table 1, the wear amount ranges from 0 to 0.0005 g in Examples 1 to 4. Typically, when a male screw portion of a wholly aromatic polyimide resin is driven into a female screw portion of aluminum oxide, the bolt has the wear amount ranging from about 0.0004 g to 0.0008 g. Accordingly, the wear amount is practically zero and the male bolt  43  is not worn away in Examples 1 to 4. Further, since the reduced loosening torque is smaller than or equal to 0.20 kgf·cm, it is found that the axial force of the bolt  41  is not reduced. 
     On the other hand, in Comparison example 1, the wear amount is 0.0010 g. Even considering the wear amount of the male screw portion of a wholly aromatic polyimide resin caused by driving it into the female screw portion, it is found that the male screw portion of the body is worn away. 
     From the results, it is concluded that the quartz guide  39  can be stably attached to the inner wall  40  of the chamber in an environment containing radicals by using the bolt  41  shown in  FIG. 2 . 
     While the invention has been shown and described with respect to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be without departing from the spirit and scope of the invention as defined in the following claims.