Abstract:
A plasma processor electrode includes a support member disposed to face to an electrode that holds a substrate to be treated, an electrode plate fixed to the support member and equipped with gas injection holes and a screw hole open and facing to the support member to supply a processing gas through the gas discharge hole into a processing space formed between the electrode plate and the electrode to generate a plasma in the processing space, and a fastening unit that clamps the electrode plate on the support member by fastening the electrode plate to the support member with a screw driven into the screw hole from the support member.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a plasma processor electrode and a plasma processor employing the electrode; and, more particularly, to a plasma etching processor electrode and a plasma etching processor for executing an etching process for use in semiconductor substrates, e.g., under plasma atmosphere. 
     BACKGROUND OF THE INVENTION 
     Plasma process techniques, including a plasma etching process, a plasma CVD process and the like, have been widely applied in manufacturing semiconductor devices, liquid crystal display devices and the like. A conventional plasma processor employing the plasma process techniques has an upper electrode and a lower electrode so disposed as to face each other in a processing chamber, and causes a processing gas in the processing chamber to become a plasma by applying a high frequency power to the upper electrode, to thereby feed the plasma to a substrate, mounted on the lower electrode, to be processed. Normally, cooling water for cooling the electrode to a desired temperature is supplied to the upper electrode, in addition to the high frequency power and the processing gas. 
     The upper electrode used in the conventional plasma processor will now be described with reference to  FIGS. 8A-8C . As shown in  FIG. 8A , the upper electrode  1  includes an electrode plate  2  made of, e.g., quartz with a plurality of gas holes  2 A dispersedly formed on the surface thereof, a supporting member  3  made of, e.g., aluminum for supporting the electrode plate  2  and executing a heat exchange with the electrode plate  2 , and a shield ring  4 , in the form of a circular ring, disposed to blockade peripheral portions of the electrode plate  2  and the supporting member  3 . 
     When the upper electrode  1  is assembled, as shown in  FIG. 8B , first of all, a lower surface of the supporting member  3  is made to come in contact with an upper surface of the electrode plate  2 , and then both the electrode plate  2  and the supporting member  3  are fixed by using screws  5 . Thereafter, in order to avoid an abnormal discharge or contamination of metal, as shown in  FIG. 8C , the shield ring  4  is disposed around the electrode plate  2 , thereby blocking heads of the screws  5  which are exposed in the processing chamber. 
     However, as the electrode plate  2  is normally made of quartz, it is not desirable to form tapped holes on the electrode plate  2  due to its high strength, poor workability and the like. Thus in the conventional art, through-holes  2 B are normally formed on peripheral portions of the electrode plate  2 , and tapped holes are formed on a side of the supporting member  3  made of, e.g., aluminum. Consequently, the electrode plate  2  should be jointed to the supporting member  3  by driving the screws  5  into the tapped holes on the side of the supporting member  3  from a side of the processing chamber (a side of the lower electrode). Furthermore, the screws  5  are required to be isolated from plasma by attaching the shield ring  4  around the electrode plate  2  as described above. 
     In addition, to avoid abnormal discharge and to execute a desired process, the processing chamber needs to be configured such that surface irregularities are not provided therein as much as possible. For the purpose of it, configuration of the joint portion between the electrode plate  2  and the supporting member  3  become rather complicated, thereby increasing the manufacturing cost thereof. Furthermore, as the through-holes  2 B for allowing the screws  5  to pass through are formed on periphery of the electrode plate  2  or an area therearound, there are limitations in that the configuration is further complicated as described above, and the outermost diameter (effective gas hole diameter), i.e., the diameter of the whole circular area where all the gas holes  2 A are disposed, cannot be increased. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the present invention to provide a novel plasma processor electrode and a novel plasma processor capable of increasing the effective gas hole diameter and concealing a joint portion of the electrode plate from plasma completely, and smoothing the surface area which is in contact with the plasma at low costs. 
     The object is achieved by the novel plasma processor electrode and the plasma processor employing the same, which are described hereinafter. That is, the plasma processor electrode and the plasma processor employing the plasma processor electrode includes: a supporting member arranged to face a supporting electrode for supporting a substrate to be processed; an electrode plate, mounted to the supporting member, including a plurality of gas injection holes and a tapped hole opened toward the supporting member, for providing a processing gas through the gas injection holes into a processing space formed between the electrode plate and the supporting electrode, thereby generating a plasma in the processing space; and a fastening unit for combining the electrode plate with the supporting member by screwing into the tapped hole of the electrode plate from a side of supporting member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a plasma processor in accordance with a first preferred embodiment of the present invention; 
         FIG. 2  is a schematic sectional view of an upper electrode of the plasma processor of  FIG. 1 ; 
         FIG. 3A  is a plan view of an electrode plate of the upper electrode of  FIG. 2 ; 
         FIG. 3B  is a sectional view taken along the line  3 B- 3 B of  FIG. 3A ; 
         FIG. 4A  is a plan view of a socket installed in a receptacle part of the electrode plate of  FIG. 3 ; 
         FIG. 4B  is a side view of the socket of  FIG. 4A ; 
         FIG. 5A  is a plan view of an electrode plate in accordance with a second preferred embodiment of the present invention; 
         FIG. 5B  is a sectional view taken along the line  5 B- 5 B of  FIG. 5A ; 
         FIG. 6A  is a plan view of a holder installed in a receptacle part of the electrode plate of  FIG. 5 ; 
         FIG. 6B  is a cross sectional view of the holder of  FIG. 6A ; 
         FIG. 7A  is a plan view of a socket installed in the holder of  FIG. 6 ; 
         FIG. 7B  is a cross sectional view of the socket of  FIG. 7A ; 
         FIG. 8A  is a cross sectional view showing a configuration of a conventional upper electrode; 
         FIG. 8B  is a cross sectional view showing a configuration of an electrode plate mounted to a supporting member in the conventional upper electrode; 
         FIG. 8C  is a cross sectional view showing a configuration process of a shield ring being mounted in the conventional upper electrode; 
         FIG. 9A  is a plan view of the electrode plate with the socket shown in  FIGS. 4A and 4B  installed in the receptacle part of the electrode plate shown in  FIGS. 3A and 3B ; 
         FIG. 9B  is a side view of the receptacle part with the socket shown in  FIGS. 4A and 4B  installed in the receptacle part shown in  FIGS. 3A and 3B ; and 
         FIG. 10  is a cross sectional view of the receptacle part after the holder shown in  FIGS. 6A and 6B  and the socket shown in  FIGS. 7A and 7B  are installed in the receptacle part shown in  FIGS. 5A and 5B . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, a plasma processor electrode and a plasma processor in accordance with a first preferred embodiment of the present invention are described in detail with reference to  FIGS. 1-7B . 
     In accordance with the first preferred embodiment, the plasma processor, e.g., a plasma etching processor  10 , includes a processing vessel  11  made of a conductive material such as aluminum, as shown in  FIG. 1 . A lower electrode  13 , vertically movable by elevators  12 , such as pneumatic cylinders, is installed in the processing vessel  11 . The lower electrode  13  is configured to support a substrate W to be processed by a plurality of members made of, e.g., aluminum. A temperature controlling unit  14 , such as a cooling jacket, is installed in the lower electrode  13 . The surface temperature of the substrate W, supported on the lower electrode  13 , can be controlled to a desired temperature by the temperature controlling unit  14 . 
     The temperature controlling unit  14  includes an inlet line  15  and a discharge line  16  for circulating a refrigerant in the cooling jacket. The refrigerant, which has been controlled to a desired temperature, is supplied into the cooling jacket through the inlet line  15 . After a heat exchange, the refrigerant is discharged to an outside through the discharge line  16 . Alternatively, a heater, a peltier element or the like, instead of the cooling jacket, can be installed in the lower electrode  13 . 
     An electrostatic chuck  17  for adsorptively holding the substrate W on an upper surface of the lower electrode  13  is mounted. The electrostatic chuck  17  includes a tungsten electrode layer which is interposed between layers made of a sintered or a thermal-sprayed ceramic. By providing a DC high voltage from a variable voltage source  18  to the tungsten electrode layer through a filter  19  and a lead line  20 , the substrate W mounted on the lower electrode  13  is electrostatically adsorbed to the ceramic layers. 
     Moreover, a focus ring  21 , having a ring shape, is so arranged as to encircle the substrate W which is adsorbedly supported on the electrostatic chuck  17 . The focus ring  21  is selectively made of an insulating or a conductive material according to the type of process, and used to confine or diffuse reactive ions. Furthermore, a gas exhaust ring  22  having a plurality of gas exhaust holes thereon is placed to be lower than the surface of the lower electrode  13  in the lower electrode  13  and the processing vessel  11 , thereby encircling the lower electrode  13 . By the gas exhaust ring  22 , the flow rate of the exhaust gas is controlled, while the plasma is suitably confined between the lower electrode  13  and an upper electrode  23  which will be described hereinafter. 
     Above the lower electrode  13 , the upper electrode  23  is installed to be spaced apart from the lower electrode  13  with a gap of 5 mm-150 mm, such that the lower electrode faces the upper electrode  23 . The lower electrode  13 , as described above, is vertically movable towards or away from the upper electrode  23 . The gap can be freely adjusted by driving the elevators  12  depending on the properties or the composition of the substrate W. Furthermore, a high frequency power supply  25  is connected to the lower electrode  13  through an impedance matching unit  24  including a blocking capacitor. A high frequency power (bias) of about 2 to 13.56 MHz is supplied from the high frequency power supply  25  to the lower electrode  13 . A high frequency power supply  27  is connected to the upper electrode  23  through an impedance matching unit  26  including a blocking capacitor. A high frequency power of about 13.56 to 100 MHz is supplied from the high frequency power supply  27  to the upper electrode  23 . 
     A processing gas feeding pipe  28  is connected to the upper electrode  23 . A processing gas of, e.g., bromine is supplied from a processing gas supply source  29  into the processing vessel  11  through a flow rate controlling device  30  and the processing gas feeding pipe  28 . The processing gas provided into the processing vessel  11  becomes a plasma by the high frequency power source  27 , thereby executing an etching process to the substrate W. Moreover, a vacuum preliminary chamber  32  is connected to a side surface of the processing vessel  11  through a gate valve  31 , and the substrate W is transferred between the vacuum preliminary chamber  32  and the processing vessel  11  by driving a transfer arm  33  provided in the vacuum preliminary chamber  32 . 
     Hereinafter, the upper electrode  23  in accordance with the first preferred embodiment of the present invention will be described with reference to  FIG. 2 . 
     The upper electrode  23  has a laminated structure in which an upper member  34 , a cooling plate  35  and an electrode plate  36  are layered in that order from the top as shown in  FIG. 2 , and ring-shaped insulators  37  and  38  made of, e.g., alumina, are placed between the laminated structure and the processing vessel  11 . The upper member  34 , including a gas supplying line  39  and a cooling jacket  40  therein, controls the electrode plate  36  to be at a desired temperature through the cooling plate  35 . The gas supplying line  39  extends downwards from the gas feeding pipe  28 , and the refrigerant circulates in the cooling jacket  40 . The gas supplying line  39  communicates with a space  41  formed between a lower surface of the upper member  34  and an upper surface of the cooling plate  35 . The processing gas supplied from the gas supplying line  39  is diffused in a horizontal direction in the space  41 . 
     The cooling plate  35 , having a disc shape, is made of, e.g., anodic oxidized aluminum. A plurality of gas supplying paths  35 A which communicate with a plurality of gas injection holes  36 A of the electrode plate  36  are disposed in a vertical direction in the cooling plate  35 , as shown in  FIG. 2 . Thus, the processing gas diffused in the space  41  passes through the gas supplying paths  35 A and the gas injection holes  36 A in that order, thereby providing the processing gas to the substrate W in the processing vessel  11  uniformly, when the cooling plate  35  and the electrode plate  36  are combined with each other. 
     Therefore, the electrode plate  36 , having a disk shape, is made of, e.g., quartz, and an outer diameter thereof is adjusted to be approximately equal to that of a lower surface of the cooling plate  35 . The electrode plate  36  can provide the processing gas uniformly into the processing vessel  11  through the gas injection holes  36 A which are dispersedly located on the surface of the electrode plate  36 . Moreover, a plurality of through-holes  35 B are formed outside of an area, which surrounds all the gas supplying paths  35 A on the cooling plate  35 , along a peripheral direction. A screw  42  (a fastening unit) made of aluminum, stainless steel or the like is inserted into each of the through-holes  35 B. The electrode plate  36  and the cooling plate  35  are firmly joined by screwing the screws  42  into sockets additionally provided in the electrode plate  36 . That is, the cooling plate  35  serves as a supporting member for supporting the electrode plate  36 . 
     The upper electrode  23  will be described in more detail with reference to  FIGS. 3A-4B . As shown in  FIG. 3A , a plurality of thin- and long-shaped grooves  43  (receptacle parts) are extended in radial directions from the peripheral portion of the electrode plate  36  to vicinity areas of the gas injection holes  36 A (opened toward a circumferential surface of the electrode plate  36 ). As shown in  FIG. 3B , each of the grooves  43  includes an opening  43 A and a breadth enlarged part  43 B. The opening  43 A is opened toward the upper surface of the electrode plate  36  and the breadth enlarged part  43 B is widely disposed inside of the opening  43 A. A step-attached part  43 C is formed at a boundary portion between the opening  43 A and the breadth enlarged part  43 B. A socket  44  shown in  FIGS. 4A and 4B  is installed in each of the grooves  43  as shown in  FIGS. 9A and 9B . 
     The socket  44 , having a thin and long shape, is made of, e.g., engineering plastic, desirably, polybenzimidazole, such as Cerazole (a product name). As shown in  FIG. 4A , the socket  44  includes one end thereof (a lower end in  FIG. 4A ) having a circular arc shape and the other end thereof (an upper end in  FIG. 4A ) having a straight-line shape. Moreover, a tapped hole  44 A is placed on a side of said one end. Furthermore, as shown in  FIGS. 4A and 4B , a flange  44 B is located, in a longitudinal direction of the socket  44 , at both side surfaces of the socket  44 . The socket  44  has a reversed-T front shape. The sockets  44  can be attachably mounted to the electrode plate  36  by inserting/disjointing the socket  44  into/from the grooves  43  of the electrode plate  36 . Furthermore, the sockets  44  may be made of aluminum, stainless steel or the like, instead of engineering plastic. 
     As described above, a tapped hole  44 A is located on an upper surface of said one end of the socket  44  so that the tapped hole  44 A can be viewed through the opening  43 A of the electrode plate  36 , while the sockets  44  are attached to the grooves  43  (receptacle parts) of the electrode plate  36 . In other words, the upper electrode  23  in accordance with the first preferred embodiment of the present invention is configured such that the tapped holes  44 A are additionally provided on the electrode plate  36  by attaching the sockets  44  having the tapped holes  44 A formed thereon to the electrode plate  36 . 
     When the electrode plate  36  is mounted to the cooling plate  35 , the tapped holes  44 A of the sockets  44  accommodated in the openings  43 A of the electrode plate  36  coincide with the through-holes  35 B of the cooling plate  35  if viewed from a plane figure thereof. Moreover, while bringing the upper surface of the electrode plate  36  into contact with the lower surface of the cooling plate  35 , the screws  42  (the fastening unit) are inserted into the through-holes  35 B from the side of the upper surface of the cooling plate  35 . By driving the screws  42  into the tapped holes  44 A of the sockets  44 , the cooling plate  35  and the electrode plate  36  can be jointed. 
     As described above, since the sockets  44  are attached to the electrode plate  36  such that the tapped holes  44 A are opened toward a side of the upper surface of the electrode plate  36  and since the screws  42  are located at a region which is not exposed to the processing space (the plasma space), the screws  42  (the fastening unit) can be isolated from the plasma space. Furthermore, by directly hitching the flanges  44 B of the sockets  44  to the step-attached part  43 C of the electrode plate  36 , the electrode plate  36  is firmly supported by the cooling plate  35 . 
     A second preferred embodiment of the present invention will now be described with reference to  FIGS. 5A-7B . Same reference numerals are used in the second preferred embodiment as in the first preferred embodiment if they have same functions as those of the first preferred embodiment. 
     Similar to the electrode plate  36  of the first preferred embodiment as shown in  FIGS. 3A and 3B , an electrode plate  36  in accordance with the second preferred embodiment, having a disk shape, is made of, e.g., quartz, and has a plurality of gas injection holes  36 A for supplying the processing gas into the processing vessel  11 . As shown in  FIGS. 5A and 5B , a plurality of holes  45 , with a nearly circular shape if viewed from a plane figure thereof, are formed around a peripheral portion of the electrode plate  36 . As shown in  FIG. 5B , each of the holes  45  includes a circular-shaped opening  45 A and a breadth enlarged part  45 B having a wider breadth in radial directions (an elliptic shape) than that of the opening  45 A. A step-attached part  45 C is formed at a boundary portion between the opening  45 A and the breadth enlarged part  45 B. Both a holder  46  shown in  FIGS. 6A and 6B  and a socket  47  shown in  FIGS. 7A and 7B  are installed in each of the holes  45  as shown in  FIG. 10 . That is, the holes  45  serve as receptacle parts for supporting the sockets  47 . 
     The holder  46  is made of, e.g., engineering plastic, desirably, polybenzimidazole, such as, e.g., Cerazole (a product name). As shown in  FIGS. 6A and 6B , the holder  46  includes a first member  461  and a second member  462 . The first and second members  461  and  462 , having a shape of circular arc if viewed from a plane figure thereof, are disposed symmetrically. Flanges  461 A,  462 A are formed on an outer peripheral portion of the first and second members  461  and  462 , respectively. Step-attached parts  461 B,  462 B and coupling parts  461 C,  462 C composed of nuts are formed on an inner peripheral portion of the first and second members  461  and  462 , respectively. The holder  46  is inserted into the hole  45  of the electrode plate  36 , while the cross section  461 D of the first member  461  faces the cross section  462 D of the second member  462 . Thereafter, the socket  47  shown in  FIGS. 7A and 7B  is inserted into a spatial part  48  which is surrounded by the first and second members  461  and  462 . 
     The socket  47  is formed into a single body, made of the same material as that of the holder  46 , e.g., engineering plastic, desirably, polybenzimidazole, such as Cerazole (a product name). As shown in  FIGS. 7A and 8B , the socket  47 , including both a flange  47 A and a screw part  47 B, has a nearly cylindrical shape. The screw part  47 B is screwed into a tapped hole surrounded by the coupling parts  461 C and  462 C. 
     By inserting the socket  47  into the spatial part  48  (the tapped hole) and by binding a jig, such as a screwdriver, into a groove  47 C of the socket  47  to impose a rotating force in an axial direction, the holder  46  (the first and second members  461  and  462 ) becomes fixed after it is adjusted in a breadth direction in the hole  45 . And, if the screw part  47 B of the socket  47  is coupled with (screwed into) the tapped hole surrounded by the coupling parts  461 C and  462 C, the flange  47 A comes into contact with the step-attached parts  461 B and  462 B, thereby fixing the holder  46  and the socket  47  to the electrode plate  36 . 
     As described above, the socket  47  is indirectly accommodated in the hole  45  (the receptacle part) of the electrode plate  36  through the holder  47 . The holder  46  and the socket  47  can be made of aluminum, stainless steel or the like, instead of engineering plastic. 
     Meanwhile, because a tapped hole  47 D is located in a center portion of the socket  47 , the tapped holes  47 D can be viewed from the upper surface of the electrode plate  36  (from the side of the cooling plate  35 ) while the holders  46  and the sockets  47  are inserted into the holes  45  of the electrode plate  36 . 
     The through-holes  35 B formed on the cooling plate  35  correspond to the holes  45  of the electrode plate  36  (the tapped holes  47 D of the sockets  47 ) if viewed from a plane figure thereof. While the upper surface of the electrode plate  36 , having the holders  46  and the sockets  47  inserted thereinto, comes in contact with the lower surface of the cooling plate  35 , a fastening member (a screw) is inserted into the through-holes  35 B from the upper surface of the cooling plate  35  (the side on which the cooling plate  35  is mounted). The fastening member is tightened into the tapped holes  47 D, thereby jointing the cooling plate  35  and the electrode plate  36 . 
     By coupling the flanges  461 A and  462 A of the holder  46  with the step-attached part  45 C of the electrode plate  36 , i.e., by indirectly coupling the socket  47  with the step-attached part  45 C, the electrode plate  36  can be firmly supported by the cooling plate  35 . 
     As described above, in accordance with the first and the second preferred embodiments, by forming the receptacle parts  43 ,  45  for accommodating the sockets  44 ,  47  on the electrode plate  36 , and by accommodating the sockets  44 ,  47  having tapped holes  44 A,  47 D in the receptacle parts  43 ,  45 , the tapped hole can be additionally disposed on the electrode plate  36  without directly forming the tapped hole on the electrode plate  36 . Since the screws are inserted from the side of the supporting member (opposite side of the plasma space), the screws are not exposed to the plasma space. Thus, no additional member for shielding the screws (shield ring) is required, and no surface irregularties are required in the processing vessel by simplifying a complicated shape. 
     Consequently, the manufacturing costs are reduced and at the same time, the effective gas hole diameter can be increased by forming the gas injection holes at the peripheral portion of the electrode plate. 
     It should be noted that, in accordance with each of the above-mentioned embodiments, the configuration of accommodating the sockets  44 ,  47  in the receptacle parts after forming thin- and long-shaped grooves  43  or circular-shaped holes  45  on the electrode plate  36  serving as the receptacle parts, are explained, but the shape and the number of the receptacle parts, the shape and the construction of the sockets and the like are not confined to the above-mentioned embodiments if the sockets having the tapped holes are opened toward the side where the supporting member (the cooling plate) is mounted. 
     Furthermore, in accordance with each of the above-mentioned embodiments, the upper electrode, having a laminated structure of the upper member, the supporting member (the cooling plate) and the electrode plate, has been described, but the upper member and the supporting member can be integrated into a single body. 
     Moreover, in accordance with each of the above-mentioned embodiments, the configuration of the lower electrode for supporting the substrate and the electrode plate (the upper electrode) facing the lower electrode, arranged in a vertical direction in parallel, has been described, but the present invention can be applied to a processor in which, for example, the two electrodes are placed apart in a horizontal direction. Furthermore, the plasma processor, in which the high frequency power is applied to both the upper electrode and the lower electrode, respectively, has been described, but the present invention can be adapted to a plasma processor in which the high frequency power is applied to one of the electrodes (for example, the lower electrode). 
     Furthermore, in accordance with each of the above-mentioned embodiments, the parallel plate-type plasma etching processor has been explained, but the present invention can be applied to various types of plasma processors, e.g., magnetron-type, inductive coupling-type and the like. In addition, the present invention can be adapted to a variety of plasma processors, such as an ashing processor, a film forming processor, or the like, as well as the etching processor. Furthermore, the present invention can be adapted to a device for processing a glass substrate for LCD. 
     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 made without departing from the spirit and scope of the invention as defined in the following claims.