Patent Publication Number: US-2006005929-A1

Title: Plasma processing device and plasma generating method

Description:
BACKGROUND OF THE INVENTION  
      The present invention relates to a plasma processing device and plasma generating method and, more particularly, to a plasma processing device and plasma generating method which supply an electromagnetic field into a processing vessel by using a slot antenna to generate a plasma.  
      In the manufacture of a semiconductor device or flat panel display, plasma processing devices 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 devices, a high-frequency plasma processing device is available which supplies a high-frequency electromagnetic field into a processing vessel and ionizes and dissociates a gas in the processing vessel by the effect of the electromagnetic field, thus generating a plasma. The high-frequency plasma processing device can perform a plasma process efficiently since it can generate a low-pressure, high-density plasma.  
       FIG. 8  is a view showing an arrangement of an electromagnetic field supply device conventionally used to supply a high-frequency electromagnetic field into a processing vessel. An electromagnetic field supply device  510  shown in  FIG. 8  includes a high-frequency generator  511  which generates a high-frequency electromagnetic field, a cylindrical waveguide  512  having one end connected to the high-frequency generator  511 , a circular polarization converter  513  and load matching unit  514  provided to the cylindrical waveguide  512 , and a radial line slot antenna (to be abbreviated as RLSA hereinafter)  515  connected to the other end of the cylindrical waveguide  512 .  
      The RLSA  515  supplies the high-frequency electromagnetic field introduced from the cylindrical waveguide  512  into a processing vessel (not shown). More specifically, the RLSA  515  has two parallel circular conductor plates  522  and  523  which form a radial waveguide  521 , and a conductor ring  524  which connects the edge portions of the two conductor plates  522  and  523  to shield the high-frequency electromagnetic field. An opening  525 , through which the high-frequency electromagnetic field is introduced from the cylindrical waveguide  512  to the radial waveguide  521 , is formed at the central portion of the conductor plate  522 . A plurality of slots  526 , through which the high-frequency electromagnetic field propagating in the radial waveguide  521  is supplied into the processing vessel, are formed in the conductor plate  523 . The conductor plate  523  and slots  526  form an antenna surface  528 .  
      The high-frequency electromagnetic field generated by the high-frequency generator  511  propagates in the cylindrical waveguide  512  in the TE 11  mode, is converted into a rotating electromagnetic field by the circular polarization converter  513 , and is introduced to the RLSA  515 . The high-frequency electromagnetic field introduced to the RLSA  515  is supplied into the processing vessel through the slots  526  while it propagates in the radial waveguide  521  radically. In the processing vessel, the supplied high-frequency electromagnetic field ionizes the gas to generate a plasma, so that a target object is processed with the plasma.  
      Part of the high-frequency electromagnetic field which is not supplied into the processing vessel returns from the RLSA  515  through the circular polarization converter  513  as a reflected electromagnetic field F 1 . The load matching unit  514  matches the impedance between the supply side and load side. Thus, the reflected electromagnetic field F 1  is reflected by the load matching unit  514  again, and is phase-matched with a traveling wave supplied from the high-frequency generator  511 , so that a power can be additionally supplied to the RLSA  515 .  
      When the power (reflected power) of the reflected electromagnetic field F 1  increases, the load matching unit  514  cannot reflect the total power of the reflected electromagnetic field F 1 , and a standing wave is generated between the high-frequency generator  511  and load matching unit  514 . Consequently, the cylindrical waveguide  512  may be deformed as it is locally heated by the standing wave between the high-frequency generator  511  and load matching unit  514 . Also, the power may not be supplied to the load side of the RLSA  515  efficiently.  
     SUMMARY OF THE INVENTION  
      The present invention has been made to solve these problems, and has as its object to decrease the reflected power from the slot antenna.  
      In order to achieve the above object, according to the present invention, there is provided a plasma processing device characterized by comprising a table for placing a target object thereon, a processing vessel for accommodating the table, and a slot antenna arranged to oppose the table to supply an electromagnetic field into the processing vessel, wherein radiation coefficients of a plurality of slots formed in an antenna surface of the slot antenna increase monotonously in a radial direction of the antenna surface from a central portion of the antenna surface until a first intermediate portion on the way to a peripheral portion, and maintain values obtained at the first intermediate portion from the first intermediate portion toward the peripheral portion.  
      The lengths of the slots may change monotonously from the central portion until the first intermediate portion of the antenna surface, and maintain lengths obtained at the first intermediate portion from the first intermediate portion toward the peripheral portion.  
      When lengths L of the slots satisfy: 
 
 L≦λg /2 
 
 or 
 
      (N/2+¼)×λg≦L≦(N+1)×λg/2 (N is a natural number) where λg is a wavelength of an electromagnetic field in the slot antenna, the lengths of the slots may increase monotonously from the central portion until the first intermediate portion.  
      Alternatively, from an innermost slot of the antenna surface until an arbitrary slot of the antenna surface in the radial direction, a length of each slot may be larger than that of a slot inside each slot, and from the arbitrary slot toward an outermost slot of the antenna surface, the length of each slot may be equal to that of the arbitrary slot.  
      When the lengths L of the slots satisfy:  
      N×λg/2≦L≦(N/2+¼)×λg (N is a natural number), the lengths of the slots may decrease monotonously from the central portion until the first intermediate portion.  
      Alternatively, from an innermost slot of the antenna surface until an arbitrary slot of the antenna surface in the radial direction, a length of each slot may be smaller than that of a slot inside each slot, and from the arbitrary slot toward an outermost slot of the antenna surface, the length of each slot may be equal to that of the arbitrary slot.  
      In the plasma processing device described above, in the radial direction of the antenna surface, the radiation coefficients of the slots may maintain values obtained at the first intermediate portion from the first intermediate portion of the antenna surface until the second intermediate portion on the way to the peripheral portion, and may decrease monotonously from the second intermediate portion until the peripheral portion.  
      Lengths of the slots may change monotonously from the central portion until the first intermediate portion of the antenna surface, may maintain lengths obtained at the first intermediate portion from the first intermediate portion until the second intermediate portion, and may change monotonously from the second intermediate portion until the peripheral portion, inversely to the slots from the central portion until the first intermediate portion.  
      When the lengths L of the slots satisfy: 
 
 L≦λg /2 
 
 or 
 
      (N/2+¼)×λg≦L≦(N+1)×λg/2 (N is a natural number), the lengths of the slots may decrease monotonously from the second intermediate portion until the peripheral portion.  
      Alternatively, from an innermost slot of the antenna surface until a slot at the first intermediate portion of the antenna surface in the radial direction, a length of each slot may be larger than that of a slot inside each slot, from the slot at the first intermediate portion until a slot at the second intermediate portion in the radial direction, the length of each slot may be equal to that of the slot at the first intermediate portion, and from the slot at the second intermediate portion until an outermost slot in the radial direction, the length of each slot may be smaller than that of a slot inside each slot.  
      When the lengths L of the slots satisfy:  
      N×λg/2≦L≦(N/2+¼)×λg (N is a natural number), the lengths of the slots may increase monotonously from the second intermediate portion until the peripheral portion.  
      Alternatively, from an innermost slot of the antenna surface until a slot at the first intermediate portion of the antenna surface in the radial direction, a length of each slot may be smaller than that of a slot inside each slot, from the slot at the first intermediate portion until a slot at the second intermediate portion in the radial direction, the length of each slot may be equal to that of the slot at the first intermediate portion, and from the slot at the second intermediate portion until an outermost slot in the radial direction, the length of each slot may be larger than that of a slot inside each slot.  
      A plasma generating method of the present invention is characterized in that when an electromagnetic field is supplied into a processing vessel by using a slot antenna in which a plurality of slots are formed in an antenna surface thereof, to generate a plasma, radiation coefficients of the slots are increased monotonously from a central portion of the antenna surface until the first intermediate portion on the way to a peripheral portion in a radial direction of the antenna surface, and values of the radiation coefficients obtained at the first intermediate portion are maintained from the first intermediate portion toward the peripheral portion.  
      The values of the radiation coefficients obtained at the first intermediate portion may be maintained from the first intermediate portion of the antenna surface until a second intermediate portion on the way to the peripheral portion in the radial direction of the antenna surface, and the radiation coefficients may be decreased monotonously from the second intermediate portion until the peripheral portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a view showing the overall arrangement of a plasma processing device according to the first embodiment of the present invention;  
       FIG. 2A  is a,plan view showing an arrangement of the antenna surface seen from the direction of a line II-II′ of  FIG. 1 , and  FIG. 2B  is a graph showing a change in the slot length with respect to a radial direction;  
       FIG. 3A  is a view showing an example of an inverted-V-shaped slot, and  FIG. 3B  is a view showing an example of a cross slot;  
       FIGS. 4A  to  4 D are views each showing an example of the shape of a slot formed in the antenna surface;  
       FIG. 5A  is a plan view showing an arrangement of the antenna surface of a slot antenna used in a plasma processing device according to the second embodiment of the present invention, and  FIG. 5B  is a graph showing a change in slot length with respect to a radial direction;  
       FIG. 6A  is a longitudinal sectional view showing the arrangement of a radial line slot antenna having an antenna surface that forms an upwardly projecting circular cone, and  FIG. 6B  is a perspective view showing the arrangement of the antenna surface shown in  FIG. 6A ;  
       FIG. 7  is a perspective view showing the arrangement of an antenna surface that forms a downwardly projecting circular cone; and  
       FIG. 8  is a view showing an arrangement of a conventional electromagnetic field supply device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The embodiments of the present invention will be described with reference to the drawings.  
     First Embodiment  
      A plasma processing device according to the first embodiment of the present invention will be described with reference to FIGS.  1  to  4 .  FIG. 1  is a view showing the overall arrangement of the first embodiment. This plasma processing device has a processing vessel  1  which accommodates a substrate  4 , e.g., a semiconductor or LCD, as a target object and processes the substrate  4  with a plasma, and an electromagnetic field supply device  10  which supplies a high-frequency electromagnetic field F into the processing vessel  1  so that a plasma P is generated in the processing vessel  1  by the operation of the high-frequency electromagnetic field F.  
      The processing vessel  1  is a bottomed cylinder with an upper opening. A substrate table (table)  3  is fixed to the central portion of the bottom surface of the processing vessel  1  through an insulating plate  2 . The substrate  4  is placed on the upper surface of the substrate table  3 .  
      Exhaust ports  5  for vacuum evacuation are formed in the periphery of the bottom surface of the processing vessel  1 . A gas introducing nozzle  6  is arranged in the side wall of the processing vessel  1  to introduce a gas into the processing vessel  1 . For example, when the plasma processing device is used as an etching device, a plasma gas such as Ar and an etching gas such as CF 4  are introduced into the device through the nozzle  6 .  
      The upper opening of the processing vessel  1  is closed with a dielectric plate  7  so the plasma P generated in the processing vessel  1  will not leak outside. An RLSA  15  of the electromagnetic field supply device  10  is disposed on the dielectric plate  7 . The outer surfaces of the dielectric plate  7  and RLSA  15  are covered by a shield member  8  annularly arranged on the side wall of the processing vessel  1 , so that the high-frequency electromagnetic field F will not leak outside.  
      The electromagnetic field supply device  10  includes the RLSA  15  and a power feed unit of the RLSA  15 . The power feed unit includes a high-frequency generator  11 , a cylindrical waveguide  12  connected between the high-frequency generator  11  and RLSA  15 , and a circular polarization converter  13  and load matching unit  14  provided to the cylindrical waveguide  12 .  
      The high-frequency generator  11  generates and outputs the high-frequency electromagnetic field F having a predetermined frequency (e.g., 2.45 GHz) within the range of 1 GHz to ten-odd GHz. The high-frequency generator  11  may output high-frequency waves including a microwave and a frequency band lower than that.  
      The circular polarization converter  13  converts the high-frequency electromagnetic field F, propagating in the cylindrical waveguide  12  in the TE 11  mode, into a rotating electromagnetic field which rotates by one revolution in one period in a plane perpendicular to its traveling direction.  
      The load matching unit  14  matches the impedance of the supply side (high-frequency generator  11  side) and that of the load side (RLSA  15  side) of the cylindrical waveguide  12 .  
      The RLSA  15  supplies the high-frequency electromagnetic field F, introduced from the cylindrical waveguide  12 , into the processing vessel  1  through the dielectric plate  7 . More specifically, the RLSA  15  has two parallel circular conductor plates  22  and  23  which form a radial waveguide  21 , and a conductor ring  24  which connects the outer edges of the two conductor plates  22  and  23  to shield the high-frequency electromagnetic field F. The conductor plates  22  and  23  and the conductor ring  24  are made of a conductor such as copper or aluminum.  
      An opening  25  to be connected to the cylindrical waveguide  12  is formed at the central portion of the conductor plate  22  serving as the upper surface of the radial waveguide  21 . The high-frequency electromagnetic field F is introduced into the radial waveguide  21  through the opening  25 . A plurality of slots  26 , through which the high-frequency electromagnetic field F propagating in the radial waveguide  21  is supplied into the processing vessel  1 , are formed in the conductor plate  23  serving as the lower surface of the radial waveguide  21 . The conductor plate  23  and slots  26  form an antenna surface  28 .  
      A bump  27  made of a conductor or dielectric is arranged at the central portion on the antenna surface  28 . The bump  27  is a substantially circular conical member projecting toward the opening  25  of the conductor plate  22 . The bump  27  moderates a change in impedance from the cylindrical waveguide  12  to the radial waveguide  21 , so that reflection of the high-frequency electromagnetic field F at the connecting portion of the cylindrical waveguide  12  and radial waveguide  21  can be decreased.  
      A wave delay member may be arranged in the radial waveguide  21 . The wave delay member is made of a dielectric having a relative dielectric constant larger than 1. As the wave delay member decreases a wavelength λg in the radial waveguide  21 , the number of slots  26  to be arranged in the antenna surface  28  in the radial direction can be increased, so that the supply efficiency of the high-frequency electromagnetic field F may be improved.  
      The antenna surface  28  of the RLSA  15  will be described in detail. A case will be described wherein the length of each slot  26  is set equal to or less than ½ the wavelength λg in the radial waveguide  21 .  
       FIG. 2A  is a plan view showing an arrangement of the antenna surface  28  seen from the direction of the line II-II′ of  FIG. 1 , and  FIG. 2B  is a graph showing a change in the length of the slot  26  with respect to the radial direction. Referring to  FIG. 2B , the axis of abscissa represents a distance in the radial direction from a center O of the antenna surface  28 , and the axis of ordinate represents a length L of the slot  26 .  
      In  FIG. 2A , the slots  26  extending in the circumferential direction are arranged concentrically.  
      As shown in  FIG. 2B , assume that the central portion and peripheral portion of the antenna surface  28  are denoted by A and B, respectively, and that a predetermined position (to be referred to as the first intermediate portion hereinafter) on the way from the central portion A to the peripheral portion B is denoted by C. In the radial direction of the antenna surface  28 , the lengths L of the slots  26  increase monotonously from L 1  at the central portion A to reach maximal lengths L 2  at the first intermediate portion C. The maximal lengths L 2  are maintained from the first intermediate portion C until the peripheral portion B. Hence, from the innermost slot of the antenna surface  28  until an arbitrary slot in the radial direction, the length of each slot is larger than that of a slot inside it. Also, from the arbitrary slot until the outermost slot of the antenna surface  28 , the length of each slot is equal to that of the arbitrary slot. Note that 0&lt;L 1 &lt;L 2 ≦λg/2.  
      The ratio of the power of the high-frequency electromagnetic field F in the radial waveguide  21  near a slot  26  to the power (radiation power) of the high-frequency electromagnetic field F radiated (or leaking) through the slot  26  is defined as the radiation coefficient of the slot  26 . More specifically, the radiation coefficient is expressed by (radiation power)/(power in the radial waveguide  21 ), and increases gradually as the length L of the slot  26  increases from zero (0) to reach a maximum λg/2.  
      Hence, when the length L of the slot  26  is changed as described above with respect to the radial direction of the antenna surface  28 , the radiation coefficient of the slot  26  increases monotonously from the central portion A of the antenna surface  28  in the radial direction, and reaches the maximal value at the first intermediate portion C. The maximal value is maintained from the first intermediate portion C until the peripheral portion B. In this manner, when compared to a case wherein the radiation coefficient of the slot is increased monotonously, the power radiated (or leaking) from the RLSA  15  while the high-frequency electromagnetic field F propagates from the central portion to the peripheral portion of the radial waveguide  21  increases. Accordingly, the power which is not radiated from the RLSA  15  but remains in the radial waveguide  21  decreases, so that the reflected power of the reflected electromagnetic field F 1  which returns through the cylindrical waveguide  12  from the radial waveguide  21  decreases.  
      Therefore, impedance matching with the load matching unit  14  becomes easy. The total power of the reflected electromagnetic field F 1  can be reflected by the load matching unit  14  again, and is phase-matched with a traveling wave supplied from the high-frequency generator  11 , so that a power can be additionally supplied to the RLSA  15 . Hence, no standing wave is generated between the high-frequency generator  11  and load matching unit  14 , and the cylindrical waveguide  12  will not be deformed by being locally heated between the high-frequency generator  11  and load matching unit  14 . Also, the power will not be consumed except at the load side portion, so that the power can be supplied into the processing vessel  1  efficiently.  
      In the above description, a case is described wherein the length L of the slot  26  is ½ or less the wavelength λg in the radial waveguide  21 . When the length L of the slot  26  falls within the range of relation (1), the radiation coefficient also increases gradually as the length L of the slot  26  becomes larger than (N/2+¼)×λg, and becomes maximum when the length L is (N+1)×λg/2. Thus, when the lengths L of the slots  26  are set in the same manner, the power returning from the radial waveguide  21  to the cylindrical waveguide  12  can be decreased. 
 
( N /2+¼)×λ g≦L≦ ( N +1)×λ g /2   (1) 
 
 where N is a natural number (this applies to the following description). 
 
      When the length L of the slot  26  falls within the range of relation (2), the radiation coefficient of the slot  26  gradually increases as the length L of the slot  26  becomes smaller than (N/2+¼)×λg, and becomes maximal when the length L is N×λg/2. Hence, the length L of the slot  26  is decreased monotonously from the central portion A until the first intermediate portion C in the radial direction of the antenna surface  28 , and the length (the minimal length of L) obtained at the first intermediate portion C is maintained from the first intermediate portion C until the peripheral portion B. In this case, from the innermost slot until an arbitrary slot of the antenna surface  28  in the radial direction, the length of each slot is smaller than that of a slot inside it. From the arbitrary slot to the outermost slot of the antenna surface  28 , the length of each slot is equal to that of the arbitrary slot. 
 
 N×λg /2≦ L≦ ( N /2+¼)×λ g    (2) 
 
      In this manner, when the length L of the slot  26  is changed, the radiation coefficient of the slot  26  increases monotonously from the central portion A of the antenna surface  28  in the radial direction to reach a maximal value at the first intermediate portion C. The maximal value is maintained from the first intermediate portion C until the peripheral portion B. When this RLSA is used, the power returning from the radial waveguide  21  through the cylindrical waveguide  12  can be decreased.  
      In  FIG. 2B , the length L of the slot  26  changes as a linear function between A and C, but the present invention is not limited to this. Regarding the position of the first intermediate portion C, an appropriate position is selected in accordance with the process conditions and the like.  
       FIG. 2A  shows an example in which the slots  26  extending in the circumferential direction are arranged concentrically. Alternatively, the slots  26  may be arranged to form swirls, or slots  26  extending in the radial direction may be formed.  
      The interval of the radially adjacent slots  26  may be set to about λg so that the RLSA  15  forms a radial antenna, or about λg/3 to λg/40 so that the RLSA  15  forms a leakage antenna.  
      A plurality of so-called inverted-V-shaped slots, in each of which the extension line of one slot  26 A intersects the other slot  26 B or the extension line of the other slot  26 B, as shown in  FIG. 3A , or a plurality of cross slots, each including two different-length slots  26 C and  26 D that intersect at their centers, as shown in  FIG. 3B , may be formed in the antenna surface  28 , to radiate a circularly polarized wave into the processing vessel  1 .  
      Regarding the planar shape of the slot  26 , a rectangle as shown in  FIG. 4A  may be employed, or a shape as shown in  FIG. 4B  may be employed in which the two ends on one side of two parallel straight lines are connected to the two ends on the other side with curves such as arcs. Alternatively, a shape as shown in  FIG. 4C  or  4 D may be employed in which the long sides of the rectangle of  FIG. 4A  or the two parallel straight lines of  FIG. 4B  are arcuated. The length L of the slot is the length of each long side of the rectangle in  FIG. 4A , and is the length of each of the two parallel straight lines in  FIG. 4B . A width W of the slot  26  may be set to about 2 mm by considering the influence on the high-frequency electromagnetic field F in the radial waveguide  33  and the wavelength of the radial waveguide  33 .  
     Second Embodiment  
      A plasma processing device according to the second embodiment of the present invention will be described with reference to  FIGS. 5A and 5B .  FIG. 5A  is a plan view showing an arrangement of the antenna surface of an RLSA used in this embodiment, and  FIG. 5B  is a graph showing a change in the length of the slot with respect to the radial direction. In  FIGS. 5A and 5B , the same or identical portions as in  FIGS. 2A and 2B  are denoted by the same reference numerals, and a description thereof will be omitted when appropriate.  FIG. 5A  corresponds to  FIG. 2A .  
      As shown in  FIG. 5 , assume that a predetermined position (to be referred to as the second intermediate portion hereinafter) on the way from a first intermediate portion C to a peripheral portion B of an antenna surface  128  is denoted by D. In the radial direction of the antenna surface  128 , lengths L of slots  126  increase monotonously from lengths L 1  at a central portion A to reach maximal lengths L 2  at the first intermediate portion C. The maximal lengths L 2  are maintained from the first intermediate portion C until the second intermediate portion D, and decrease monotonously from the second intermediate portion D until the peripheral portion B. Hence, from the innermost slot of the antenna surface  128  until the first intermediate portion C in the radial direction, the length of each slot is larger than that of a slot inside it. Also, from the slot at the first intermediate portion C until the slot at the second intermediate portion D in the radial direction, the length of each slot is equal to that of the slot at the first intermediate portion C. From the slot at the second intermediate portion D until the outermost slot in the radial direction, the length of each slot is smaller than that of the slot inside it.  
      Assume that the lengths L of the slots  126  are set equal to or less than ½ a wavelength λg of a radial waveguide  21 . In this case, near the peripheral portion of the antenna surface  128 , the lengths L of the slots  126  are decreased monotonously conversely to the case from the central portion A until the first intermediate portion C. Then, the radiation coefficients of the slots  126  also decrease monotonously, and the radiation power of a high-frequency electromagnetic field F near the peripheral portion decreases. Consequently, the field strength near the side wall of a processing vessel  1  decreases, so that plasma generation by ionization of the plasma gas is suppressed. If the plasma density in the processing vessel  1  near the side wall is high, it is decreased. Then, contamination in the processing vessel  1  caused when a plasma P comes into contact with the side wall of the processing vessel  1  to sputter the metal surface can be decreased.  
      In the above description, the lengths L of the slots  126  are set equal to or less than ½ the wavelength λg in the radial waveguide  21 . This also applies to a case wherein the slots  126  are formed such that their lengths L fall within the range of relation (1).  
      Assume that the slots  126  are to be formed such that their lengths L fall within the range of relation (2). In this case, in the radial direction of the antenna surface  128 , the lengths L of the slots  126  are inversely decreased monotonously from the central portion A until the first intermediate portion C. The lengths (minimal lengths of L) at the first intermediate portion C are maintained from the first intermediate portion C until the second intermediate portion D, and are increased monotonously from the second intermediate portion D until the peripheral portion B. In this case, from the innermost slot of the antenna surface  128  until the slot at the first intermediate portion C in the radial direction, the length of each slot is smaller than that of a slot inside it. Also, from the slot at the first intermediate portion C until the slot at the second intermediate portion D in the radial direction, the length of each slot is equal to that of the slot at the first intermediate portion C. From the slot at the second intermediate portion D until the outermost slot in the radial direction, the length of each slot is larger than that of the slot inside it. When the lengths L of the slots  126  are changed in this manner, the radiation coefficients of the slots  126  decrease monotonously near the periphery of the antenna surface  128 , so that contamination in the processing vessel  1  can be decreased.  
      In  FIG. 5B , the length L of the slot  126  changes as a linear function between D and B, but the present invention is not limited to this. Although the length L of the slot  126  decreases to L 1  at the peripheral portion B, it need not be decreased to L 1 . Regarding the position of the second intermediate portion D, an appropriate position is selected in accordance with process conditions and the like.  
      Referring to  FIGS. 1, 2 , and  5 , the antenna surfaces  28  and  128  are flat plates. Alternatively, as shown in  FIGS. 6A and 6B , an antenna surface  228 A may form a circular cone. A high-frequency electromagnetic field F radiated (or leaking) from the circular conical antenna surface  228 A becomes incident in an oblique direction on a plasma surface defined by a flat plate-like dielectric plate  7 . Hence, the absorption efficiency of a plasma P for the high-frequency electromagnetic field F improves. The standing wave present between the antenna surface  228 A and the plasma surface is weakened, so that the uniformity of the plasma distribution can be improved.  
      The antenna surface  228 A forms an upwardly projecting circular cone. Alternatively, an antenna surface  228 B which forms a downwardly projecting circular cone, as shown in  FIG. 7 , may be used. The antenna surfaces  228 A and  228 B may form projecting shapes other than circular cones.  
      The plasma device according to the present invention can be utilized as an etching device, plasma CVD device, ashing device, or the like.