Patent Publication Number: US-2007113978-A1

Title: Plasma processing apparatus and method

Description:
TECHNICAL FIELD  
      The present invention relates to a plasma processing apparatus and method and, more particularly, to a plasma processing apparatus and method which generate a plasma by using a high-frequency electromagnetic field to process an object to be processed such as a semiconductor, LCD (liquid crystal display), organic EL (electro luminescent panel), or the like.  
     BACKGROUND ART  
      In the manufacture of a semiconductor device or flat panel display, plasma processing apparatuses are used often to perform processes such as formation of an oxide film, crystal growth of a semiconductor layer, etching, and ashing. Among the plasma processing apparatuses, a high-frequency plasma processing apparatus is available which supplies a high-frequency electromagnetic field into a processing vessel to ionize and dissociate a gas in the processing vessel, thus generating a plasma. The high-frequency plasma processing apparatus can perform a plasma process efficiently since it can generate a high-density plasma at a low pressure.  
       FIG. 10  is a view showing the overall structure of a conventional high-frequency plasma processing apparatus. This plasma processing apparatus has a processing vessel  101  having an upper opening. A stage  103  is fixed to the central portion of the bottom surface of the processing vessel  101 . A substrate  104  is placed on the upper surface of the stage  103 . Exhaust ports  105  for vacuum evacuation are formed in the peripheral portion of the bottom surface of the processing vessel  101 . A gas introducing nozzle  106  is arranged in the side wall of the processing vessel  101 .  
      The upper opening of the processing vessel  101  is closed with a dielectric plate  107 . A radial line slot antenna (to be abbreviated as RLSA hereinafter)  113  is disposed above the dielectric plate  107 . A high-frequency power supply  111  which generates a high-frequency electromagnetic field is connected to the RLSA  113  through a waveguide  112 . The outer surfaces of the dielectric plate  107  and RLSA  113  are covered with a shield material  109  which prevents leak of the high-frequency electromagnetic field.  
      The RLSA  113  has two parallel conductive plates  122  and  124  which form a radial waveguide  121 , and a conductive ring  123  which connects the edge portions of the two conductive plates  122  and  124 . The conductive plate  122  which serves as the upper surface of the radial waveguide  121 , and the conductive ring  123  are formed integrally, and the conductive plate  124  which serves as the lower surface of the radial waveguide  121  is fixed to the lower surface of the conductive ring  123  with a plurality of screws  125 . An opening  126  to be connected to the waveguide  112  is formed at the central portion of the conductive plate  122 . The high-frequency electromagnetic field is introduced into the radial waveguide  121  through the opening  126 . A plurality of slots  127 , through which the high-frequency electromagnetic field propagating in the radial waveguide  121  is supplied into the processing vessel  101  through the dielectric plate  107 , are formed in the conductive plate  124 . These slots  127  form a slot antenna, and accordingly the conductive plate  124  which has the slots  127  is called the antenna surface of the RLSA  113 .  
      In the plasma processing apparatus with the above structure, when the high-frequency power supply  111  is driven to generate a high-frequency electromagnetic field, the high-frequency electromagnetic field is introduced into the radial waveguide  121  through the waveguide  112 . The high-frequency electromagnetic field introduced into the radial waveguide  121  is gradually supplied into the processing vessel  101  through the plurality of slots  127  which are formed in the antenna surface  124  corresponding to the lower surface of the radial waveguide  121 , while it propagates radially from the central portion toward the peripheral portion of the radial waveguide  121 . In the processing vessel  101 , a gas introduced from the nozzle  106  is ionized and dissociated by the supplied high-frequency electromagnetic field to form a plasma P, thus processing the substrate  104  (for example, see Japanese Patent Laid-Open No. 2002-217187).  
      When the high-frequency power supply  111  is driven to introduce the high-frequency electromagnetic field into the radial waveguide  121  of the RLSA  113 , a current occurs in the antenna surface  124  corresponding to the lower surface of the radial waveguide  121 , and the resistance of the conductive plate  124  generates the Joule heat. Although the antenna surface  124  is screwed to the lower surface of the conductive ring  123  of the RLSA  113 , the antenna surface  124  is not in tight contact with the lower surface of the conductive ring  123 . Thus, the heat generated in the antenna surface  124  is not easily transferred to the waveguide member including the conductive ring - 123  and conductive plate  122 . As the antenna surface  124  is in contact with none of the processing vessel  101  and shield material  109 , the heat generated in the antenna surface  124  is not transferred to them. Hence, the heat stays in the antenna surface  124  to sometimes heat it to a high temperature of 100° C. or more. When the antenna surface  124  is heated to such a high temperature, it deforms, although a little, and the antenna characteristics change. When the antenna characteristics change and the dose, radiation direction, and the like of the high-frequency electromagnetic field change, the distribution of the plasma which is generated in the processing vessel  101  by the high-frequency electromagnetic field changes. Then, the substrate  104  on the stage  103  cannot be processed uniformly.  
     DISCLOSURE OF INVENTION  
      The present invention has been made to solve the above problems, and has as its object to suppress a change in antenna characteristics which is caused by a temperature change of the antenna surface.  
      In order to achieve the above object, according to the present invention, there is provided a plasma processing apparatus characterized by comprising a stage on which an object to be processed is to be placed, a vessel which houses the stage, a conductive plate which is arranged to oppose the stage, an antenna element which is formed on the conductive plate, a waveguide member which constitutes, together with the conductive plate, a waveguide which guides a high-frequency electromagnetic field to be supplied to the vessel through said antenna element, and cooling means for cooling the conductive plate.  
      According to the present invention, there is also provided a plasma processing method characterized by comprising the steps of guiding a high-frequency electromagnetic field to a waveguide which includes a waveguide member and conductive plate, supplying the high-frequency electromagnetic field into a vessel through an antenna element formed in the conducive plate to generate a plasma in the vessel and cooling the conductive plate, and processing an object to be processed arranged in the vessel by using the plasma. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a view showing the overall structure of a plasma processing apparatus according to the first embodiment of the present invention;  
       FIG. 2  is a plan view of a conductive plate which serves as the upper surface of a radial waveguide;  
       FIG. 3  is a view showing the structure of part of a modification of the plasma processing apparatus shown in  FIG. 1 ;  
       FIG. 4  is a view showing the structure of part of a plasma processing apparatus according to the second embodiment of the present invention;  
       FIG. 5  is a view showing the structure of part of a plasma processing apparatus according to the third embodiment of the present invention;  
       FIG. 6  is a view showing the lower surface of a pipe line;  
       FIG. 7  is a view showing the structure of part of a plasma processing apparatus according to the fourth embodiment of the present invention;  
       FIG. 8  is a view showing the structure of part of a plasma processing apparatus according to the fifth embodiment of the present invention;  
       FIG. 9  is a view showing the structure of part of a modification of the plasma processing apparatus shown in  FIG. 8 ; and  
       FIG. 10  is a view showing the overall structure of a conventional high-frequency plasma processing apparatus. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      The embodiments of the present invention will be described in detail with reference to the drawings.  
     First Embodiment  
       FIG. 1  is a view showing the overall structure of a plasma processing apparatus according to the first embodiment of the present invention. This plasma processing apparatus has a bottomed cylindrical processing vessel  1  having an upper opening. A stage  3  is fixed to the central portion of the bottom surface of the processing vessel  1  through an insulating plate  2 . A substrate  4  such as a semiconductor, LCD or the like is placed as an object to be processed on the upper surface of the stage  3 . Exhaust ports  5  for vacuum evacuation are formed in the peripheral portion of the bottom surface of the processing vessel  1 . A gas introducing nozzle  6  through which a gas is to be introduced into the processing vessel  1  is arranged in the side wall of the processing vessel  1 . For example, when the plasma processing apparatus is to be used as an etching apparatus, a plasma gas such as Ar and an etching gas such as CF 4  are introduced through the nozzle  6 .  
      The upper opening of the processing vessel  1  is closed with a dielectric plate  7  so, while a high-frequency electromagnetic field is introduced through the upper opening, a plasma P generated in the processing vessel  1  does not leak outside. A seal member  8  such as an O-ring is interposed between the upper surface of the side wall of the processing vessel  1  and the lower surface of the peripheral portion of the dielectric plate  7  to ensure the hermeticity in the processing vessel  1 .  
      An RLSA  13  of an electromagnetic field supply device which supplies a high-frequency electromagnetic field into the processing vessel  1  is disposed above the dielectric plate  7 . The RLSA  13  is isolated from the processing vessel  1  by the dielectric plate  7  and accordingly protected from the plasma P. The outer surfaces of the dielectric plate  7  and RLSA  13  are covered with a shield material  9  annularly arranged on the side wall of the processing vessel  1 . Thus, the high-frequency electromagnetic field supplied from the RLSA  13  into the processing vessel  1  will not leak outside.  
      The electromagnetic field supply device has a high-frequency power supply  11  which generates a high-frequency electromagnetic field having a predetermined frequency within the range of, e.g., 0.9 GHz to ten-odd GHz, the RLSA  13  described above, and a waveguide  12  which connects the high-frequency power supply  11  and RLSA  13 . Although not shown, at least one of a circular polarization converter and load matching unit may be provided to the waveguide  12 .  
      The RLSA  13  has two parallel circular conductive plates  22  and  24  which form a radial waveguide  21 , and a conductive ring  23  which connects the edge portions of the two conductive plates  22  and  24  so that they are shielded. The conductive plate  22  which serves as the upper surface of the radial waveguide  21 , and the conductive ring  23  are formed integrally, and the conductive plate  24  which serves as the lower surface of the radial waveguide  21  is fixed to the lower surface of the conductive ring  23  with a plurality of screws  25 . An opening  26  to be connected to the waveguide  12  is formed at the central portion of the conductive plate  22  which serves as the upper surface of the radial waveguide  21 . A high-frequency electromagnetic field is introduced into the radial waveguide  21  through the opening  26 . A plurality of slots  27 , through which the high-frequency electromagnetic field propagating in the radial waveguide  21  is to be supplied into the processing vessel  1  through the dielectric plate  7 , are formed in the conductive plate  24  which serves as the lower surface of the radial waveguide  21 . These slots  27  form a slot antenna (antenna element). Thus, the conductive plate  24  where the slots  27  are formed is called the antenna surface of the RLSA  13 .  
      A bump  28  is provided to the central portion on the antenna surface  24 . The bump  28  is formed to have a substantially circular conical shape projecting toward the opening  26  of the conductive plate  22 , and its distal end is rounded spherically. The bump  28  can be made of either a conductor or dielectric. With the bump  28 , a change in impedance from the waveguide  12  to the radial waveguide  21  is moderated, and accordingly the reflection of the high-frequency electromagnetic field at the connecting portion of the waveguide  12  and radial waveguide  21  can be suppressed.  
      In this structure, when the high-frequency power supply  11  is driven to generate a high-frequency electromagnetic field, the high-frequency electromagnetic field is introduced into the radial waveguide  21  through the waveguide  12 . The high-frequency electromagnetic field introduced into the radial waveguide  21 , while propagating radially from the central portion toward the peripheral portion of the radial waveguide  21 , is gradually supplied into the processing vessel  1  through the plurality of slots  27  formed in the antenna surface  24  which corresponds to the lower surface of the radial waveguide  21 . In the processing vessel  1 , the supplied high-frequency electromagnetic field ionizes and dissociates the plasma gas introduced through the nozzle  6  to generate the plasma P, thus processing the substrate  4 .  
      When the high-frequency electromagnetic field is introduced into the radial waveguide  21  of the RLSA  13 , the antenna surface  24  which corresponds to the lower surface of the radial waveguide  21  is heated by the Joule heat. To cool the heated antenna surface  24 , a cooling means is provided in this embodiment. The cooling means includes a refrigerant supplying means for supplying a refrigerant into the radial waveguide  21 , and a refrigerant discharging means for discharging the refrigerant, circulating in the radial waveguide  21 , outside the radial waveguide  21 .  
      More specifically, the refrigerant supplying means includes the waveguide  12 , a refrigerant supply channel  31  which opens to the waveguide  12 , and a supply opening/closing valve  32  and refrigerant pump  33  which are provided to the refrigerant supply channel  31 . The refrigerant discharging means includes refrigerant discharge channels  34  which open to the radial waveguide  21 , and discharge opening/closing valves  35  respectively provided to the refrigerant discharge channels  34 . As shown in  FIG. 2 , a plurality of openings  34 A of the refrigerant discharge channels  34  are equidistantly formed in the peripheral portion of the conductive plate  22  which serves as the upper surface of the radial waveguide  21 . In  FIG. 1 , the driving operation of the refrigerant pump  33  and the opening/closing operation of the opening/closing valves  32  and  34  are controlled by a controller (not shown). As the refrigerant, normal-temperature air is used.  
      When the opening/closing valves  32  and  34  are opened and the pump  33  sends air, the air is introduced into the waveguide  12  through the refrigerant supply channel  31 . The air flows through the waveguide  12  and is supplied into the radial waveguide  21  through the opening  26  at the central portion of the conductive plate  22  which serves as the upper surface of the radial waveguide  21 . The air supplied into the radial waveguide  21  spreads from the central portion toward the peripheral portion of the radial waveguide  21 . Also, the air partly flows through the plurality of slots  27  formed in the antenna surface  24  and spreads in the space between the antenna surface  24  and dielectric plate  7  in the same manner from the central portion toward the peripheral portion. The air which has reached the peripheral portion is discharged outside the radial waveguide  21  through the plurality of refrigerant discharge channels  34  which open to the peripheral portion of the conductive plate  22  serving as the upper surface of the radial waveguide  21 . Since the seal member  8  is interposed between the lower surface of the peripheral portion of the dielectric plate  7  and the upper surface of the side wall of the processing vessel  1 , the air does not enter the processing vessel  1 .  
      While the antenna surface  24  is cooled as the Joule heat that heats the antenna surface  24  shifts to air having a lower temperature than that of the antenna surface  24 , simultaneously, the air is heated on the other hand. According to this embodiment, the heated air is discharged from the radial waveguide  21 , and low-temperature air is introduced into the radial waveguide  21 , to maintain the temperature difference between the antenna surface  24 , and air, thus promoting heat shift from the antenna surface  24  to the air. As a result, the antenna surface  24  can be cooled efficiently to suppress a temperature change in it.  
      When the temperature change in the antenna surface  24  is suppressed in this manner, a change in antenna characteristics can be prevented. Hence, the distribution of the plasma generated in the processing vessel  1  is not changed by the influence of the change in antenna characteristics, and the substrate  4  arranged on the stage  3  can be processed uniformly.  
      In the plasma processing apparatus shown in  FIG. 1 , the refrigerant supply channel  31  is connected to the waveguide  12 , and the refrigerant discharge channels  34  are connected to the radial waveguide  21 , but this connection can be made in an opposite manner. More specifically, as shown in  FIG. 3 , a refrigerant supply channel  41  may be branched and connected to the radial waveguide  21 , and a refrigerant discharge channel  44  may be connected to the waveguide  12 . In this case, in the same manner as in  FIG. 2 , the openings of the refrigerant supply channel  41  are formed equidistantly in the peripheral portion of the conductive plate  22  which serves as the upper surface of the radial waveguide  21 . A common supply opening/closing valve  42  and refrigerant pump  43  are provided to the refrigerant supply channel  41 . Also, a discharge opening/closing valve  45  is provided to the refrigerant discharge channel  44 .  
      So far a case has been described in which either the refrigerant supply channel  31  or refrigerant discharge channels  34  are connected to the waveguide  12  and the remaining channel  31  or channels  34  are connected to the radial waveguide  21 . Alternatively, both the refrigerant supply channel  31  and refrigerant discharge channels  34  may be connected to the radial waveguide  21 . In this case, the opening of the refrigerant supply channel  31  and the openings of the refrigerant discharge channels  34  are formed at separate positions.  
     Second Embodiment  
       FIG. 4  is a view showing the structure of part of a plasma processing apparatus according to the second embodiment of the present invention. In  FIG. 4 , constituent elements such as a processing vessel  1  are not shown.  
      The plasma processing apparatus according to this embodiment has a refrigerant flow channel  51  formed by connecting the refrigerant supply channel of a refrigerant supplying means and the refrigerant discharge channel of a refrigerant discharging means. The supply port of the refrigerant flow channel  51  opens to a waveguide  12 , and its plurality of discharge ports equidistantly open to the peripheral portion of a conductive plate  22  which serves as the upper surface of a radial waveguide  21 , in the same manner as in  FIG. 2 . A supply opening/closing valve  52  is provided to the supply port side of the refrigerant flow channel  51 , and a discharge opening/closing valve  55  is provided to its discharge port side. A refrigerant pump (refrigerant feeding means)  53  which feeds out a refrigerant and a cooling unit (refrigerant cooling means)  54  which cools the heated refrigerant to the original temperature are provided between the two opening/closing valves  52  and  55 . As the refrigerant, other than air, an inert gas such as N 2  can be used.  
      With this structure, the refrigerant flow channel  52 , waveguide  12 , and radial waveguide  21  form a closed channel. While circulating in this closed channel, the refrigerant deprives an antenna surface  24  of heat to cool it. Thereafter, the cooling unit  54  takes away from the refrigerant the heat that the refrigerant took away from the antenna surface  24  so the refrigerant restores the original temperature. Therefore, the antenna surface  24  can be cooled repeatedly using the same refrigerant.  
      In the same manner as in  FIG. 3 , supply ports for the refrigerant flow channel  51  may be formed in the conductive plate  22  which serves as the upper surface of the radial waveguide  21 , and a discharge port for it may be formed in the waveguide  12 , so the refrigerant is circulated in the opposite direction.  
      In the first and second embodiments described above, a liquid such as cooling water may be used as the refrigerant. In this case, the plasma processing apparatus must be formed such that the refrigerant does not leak from it.  
     Third Embodiment  
       FIG. 5  is a view showing the structure of part of a plasma processing apparatus according to the third embodiment of the present invention. In  FIG. 5 , constituent elements such as a processing vessel  1  are not shown.  
      In the plasma processing apparatus according to this embodiment, a refrigerant spray member  60  which sprays a refrigerant toward an antenna surface  24  is disposed on a conductive plate  22  of an RLSA  13 . The refrigerant spray member  60  has an annular pipe line  61  which surrounds a waveguide  12 . The inner radius of the pipe line  61  is substantially equal to the radius of the waveguide  12 , and its outer radius is substantially equal to the radius of a radial waveguide  21 .  
      As shown in  FIGS. 5 and 6 , a plurality of small-diameter through holes  62  are formed in the entire area of the lower surface of the pipe line  61 . A plurality of small-diameter through holes  29  are also formed in the conductive plate  22  of the RLSA  13  in contact with the lower surface of the pipe line  61 , at positions corresponding to the through holes  62  of the pipe line  61 . The interiors of the pipe line  61  and radial waveguide  21  communicate with each other through the through holes  62  and  29 .  
      A refrigerant supply channel  63  opens to the upper surface of the pipe line  61 . The refrigerant supply channel  63  is provided with a supply opening/closing valve  64  and refrigerant pump  65 .  
      A refrigerant discharge channel  44  opens to the waveguide  12 , in the same manner as in  FIG. 3 , and a discharge opening/closing valve  45  is provided to the refrigerant discharge channel  44 .  
      As the refrigerant, normal-temperature air is used.  
      In the refrigerant spray member  60  as described above, when the pump  65  feeds air to the pipe line  61  to increase the pressure in the pipe line  61  to be sufficiently higher than the pressure in the radial waveguide  21 , the air is sprayed from the pipe line  61  toward the antenna surface  24  of the RLSA  13  through the through holes  62  and  29 . The air introduced into the radial waveguide  21  adiabatically expands instantaneously to decrease its temperature. The temperature-decreased air abuts against the antenna surface  24  directly to cool it efficiently.  
      A refrigerant circulating channel may be formed in the same manner as in the second embodiment, and an inert gas may be used as the refrigerant.  
     Fourth Embodiment  
       FIG. 7  is a view showing the structure of part of a plasma processing apparatus according to the fourth embodiment of the present invention. In  FIG. 7 , constituent elements such as a processing vessel  1  are not shown.  
      As a refrigerant, the plasma processing apparatus according to this embodiment uses air containing an atomized liquid agent. More specifically, in the first embodiment, an atomizer  71  which atomizes a liquid agent and emits it is connected to the refrigerant supply channel  31 .  
      When the atomizer  71  is driven, the atomized liquid agent is dispensed to the refrigerant supply channel  31  and mixed with air flowing in the refrigerant supply channel  31 . The mixture is then supplied to a waveguide  12 . While the air containing the atomized liquid agent spreads from the waveguide  12  into a radial waveguide  21 , when the atomized liquid agent attaches to an antenna surface  24 , during evaporation, it deprives the antenna surface  24  of the heat of evaporation. Thus, the antenna surface  24  can be cooled efficiently.  
      An example of the liquid agent can include water, but a liquid agent having a larger heat of evaporation may be used. Also, an inert gas may be used in place of air. If an atomizer  71  is connected to the refrigerant supply channel  41  in  FIG. 3 , the same operation and effect can be obtained.  
     Fifth Embodiment  
       FIG. 8  is a view showing the structure of part of a plasma processing apparatus according to the fifth embodiment of the present invention. In  FIG. 8 , constituent elements such as a processing vessel  1  are not shown.  
      The plasma processing apparatus according to this embodiment is provided with a heat transfer member  81  which is present between an antenna surface  24  of an RLSA  13  and a conductive plate  22  and connects them to transfer the heat of the antenna surface  24  to the conductive plate  22 . As a whole, the heat transfer member  81  has the same size and shape as those of a radial waveguide  21  of the RLSA  13 , but has a hole at a portion corresponding to an opening  26  of the conductive plate  22 . Accordingly, the heat transfer member  81  is in contact with the entire area of the conductive plate  22  excluding the opening  26  and the opposing region of the antenna surface  24 . The heat transfer member  81  is made of a dielectric material having good heat conductivity, e.g., an alumina ceramic material or boron nitride (BN).  
      A cooling unit  82  is arranged on the conductive plate  22  of the RLSA  13  to be in contact with the conductive plate  22 . The cooling unit  82  can include an electronic refrigerating/heating element such as a Peltier element. Alternatively, a cooling unit may be used in which a flow channel is formed in a plate-like member and a refrigerant such as cooling water is supplied in the flow channel to cool the conductive plate  22 .  
      The heat of the antenna surface  24  of the RLSA  13  is transferred to the conductive plate  22  (or a conductive ring  23 ) through the heat transfer member  81  and dissipated outside from the conductive plate  22  through the cooling unit  82 . When the heat of the antenna surface  24  is dissipated outside in this manner, the antenna surface  24  can be cooled.  
      As the heat transfer member which transfers the heat of the antenna surface  24  to the conductive plate  22 , columnar dielectric columns  83  as shown in  FIG. 9  can be used. The plurality of dielectric columns  83  are evenly arranged on the antenna surface  24 . When the columnar dielectric columns  83  are used as the heat transfer member, the volume proportion of the heat transfer member in the radial waveguide  21  decreases, so that the influence that the heat transfer member exerts on the high-frequency electromagnetic field propagating in the radial waveguide  21  decreases. When an electronic refrigerating/heating element such as a Peltier element is used as the cooling unit  82 , it is arranged immediately above the position where the dielectric columns  81  are connected to the conductive plate  22 , so that heat transferred from the antenna surface  24  can be dissipated outside efficiently.  
      The cooling unit  82  is not always necessary, and the conductive plate  22  can be cooled by spontaneous heat dissipation.  
      In the above description, the antenna surface  24  of the RLSA  13  is cooled. The present invention is useful in cooling the antenna surface of an antenna in which an antenna element is formed on one surface of a waveguide. For example, the present invention can also be applied to a waveguide slot antenna or a slot antenna in which slots are formed in one of two opposing conductive plates that form a waveguide and power is supplied from the side surface of the waveguide.  
      As has been described above, according to the embodiments described above, the cooling means is provided for cooling the conductive plate where the antenna element is formed, to suppress a temperature change which is caused by heat generated by the conductive plate. This can prevent the conductive plate from being deformed by heat to change its antenna characteristics. Hence, the distribution of the plasma generated in the processing vessel does not change due to the influence of a change in antenna characteristics, and an object to be processed arranged in the processing vessel can be processed uniformly.