Patent Publication Number: US-2007119376-A1

Title: Matching device and plasma processing apparatus

Description:
BACKGROUND ART  
      The present invention relates to a matching device and, more particularly, to a matching device for matching the impedances of the supply side and load side of a cylindrical waveguide.  
      The present invention also relates to a plasma processing apparatus and, more particularly, to a plasma processing apparatus for generating a plasma by using a high-frequency electromagnetic field, and processing an object to be processed such as a semiconductor or LCD (Liquid Crystal Display).  
      In the fabrication of semiconductor devices and flat panel displays, plasma processing apparatuses are often used to form oxide films and perform crystal growth, etching, and ashing of semiconductor layers. One of these plasma processing apparatuses is a microwave plasma processing apparatus which generates a plasma by supplying a microwave from a radial line slot antenna (to be abbreviated as an RLSA hereinafter) into a processing vessel, and ionizing and dissociating a gas in the processing vessel by the action of the electromagnetic field of the microwave. This microwave plasma processing apparatus can generate a high-density plasma at a low pressure, and hence can perform efficient plasma processing.  
      Some microwave plasma processing apparatuses use a method which supplies a circularly polarized wave to the RLSA via a cylindrical waveguide. A circularly polarized wave is an electromagnetic wave which is a rotating electric field whose field vector rotates once in one period in a plane perpendicular to the direction of travel. Accordingly, when this circularly polarized wave is supplied, the field strength distribution in the RLSA becomes symmetric with respect to the axis of the traveling direction of the circularly polarized wave on time average. This makes it possible to supply a microwave having the time-average, axially symmetric distribution from the RLSA into the processing vessel, and generate a highly uniform plasma by the action of the electromagnetic field of the microwave.  
      Unfortunately, if the microwave is reflected in the processing vessel or RLSA, enters the cylindrical waveguide form the RLSA, and is reflected again, the axial ratio of the circularly polarized wave increases by the influence of this reflection. This decreases the axial symmetry of the field strength distribution (time average) in the RLSA. The axial ratio is the ratio of the maximum value to the minimum value in the field strength distribution (time average) on the circular section of the circularly polarized wave. The axial ratio of the circularly polarized wave is desirably close to 1. Therefore, a technique which reduces the reflected wave propagating in the cylindrical waveguide by attaching a matching device to the cylindrical waveguide is proposed. This technique will be explained below.  
       FIG. 18  is a view for explaining the conventional matching device. That is,  FIG. 18  shows a sectional arrangement including the axis (Z) of a cylindrical waveguide having the matching device.  FIG. 19  is a sectional view, taken along a line XIX-XIX′ in  FIG. 18 , showing the sectional arrangement of the matching device in a plane (X-Y plane) perpendicular to the axis (Z) of the cylindrical waveguide.  
      A matching device  1017  shown in  FIGS. 18 and 19  is a matching device for a cylindrical waveguide  1014  in which a TE 11 -mode circularly polarized wave propagates. A plurality of stabs project in the radial direction from the inner wall surface of the cylindrical waveguide  1014 . More specifically, three stabs  1071 A to  1071 C are equally spaced in the direction of the axis (Z) of the cylindrical waveguide  1014 , three stabs  1072 A to  1072 C oppose the three stabs  1071 A to  1071 C, three stabs  1073 A to  1073 C are arranged in positions rotated 90°, from the positions of the three stabs  1071 A to  1071 C, in the circumferential direction around the axis of the cylindrical waveguide  1014 , and three stabs  1074 A to  1074 C (stabs  1074 B and  1074 C are not shown) oppose the three stabs  1073 A to  1073 C. In the coordinate system, the stabs  1071 A to  1071 C and stabs  1072 A to  1072 C oppose each other in the X-Z plane, and the stabs  1073 A to  1073 C and stabs  1074 A to  1074 C oppose each other in the Y-Z plane. The stabs  1071 A to  1074 C are metal rods having a circular section. The reactance of the stabs  1071 A to  1074 C changes in accordance with the length of projection, i.e., the length the stabs project in the radial direction from the inner wall surface of the cylindrical waveguide  1014 , thereby changing the reactance of the cylindrical waveguide  1014 .  
      An RLSA  1015  is connected to the load side of the cylindrical waveguide  1014  having the matching device  1017 . The supply side of the cylindrical waveguide  1014  is connected to a high-frequency power supply  1011  for generating a microwave, a circularly polarized wave converter  1016  for converting the microwave into a circularly polarized wave, and a detector  1018  for detecting the internal voltage of the cylindrical waveguide  1014 . The detector  1018  is connected to a controller  1020  which calculates the impedance of the load side on the basis of an output signal from the detector  1018 , and calculates the projection length of the stabs  1071 A to  1071 C, which satisfies the impedance matching conditions between the supply side and load side. The controller  1020  is connected to a driver  1019  which adjusts the projection length of the stabs  1071 A to  1071 C of the matching device  1017  in accordance with instructions from the controller  1020 .  
      In this arrangement, to match the impedances of the supply side and load side of the cylindrical waveguide  1014 , a reflected wave from the RLSA  1015  is canceled by a reflected wave of the matching device  1017 , thereby reducing a reflected wave propagating in the cylindrical waveguide  1014 . Consequently, the field strength distribution in the RLSA  1015  becomes a time-average, axially symmetric distribution, so a highly uniform plasma can be generated.  
      In the conventional matching device  1017 , however, if the projection length of the stabs  1071 A to  1071 C is increased, the proportional relationship between the projection length and reactance of the stabs  1071 A to  1074 C is lost. That is, as shown in  FIG. 20 , when the projection length of the stabs  1071 A to  1071 C and  1072 A to  1072 C in the X-Z plane and the projection length of the stabs  1073 A to  1073 C and  1073 A to  1073 C in the Y-Z plane are equally changed, the reactance changes substantially linearly with the projection length if the projection length is L 0  or less, but the reactance increases exponentially with the projection length if the projection length exceeds L 0 . This is presumably because when the projection length increases and the distance between the stabs  1071 A to  1071 C and  1072 A to  1072 C in the X-Z plane and the stabs  1073 A to  1073 C and  1074 A to  1074 C in the Y-Z plane decreases, the former and latter interfere with each other and increase the reactance. This increase in reactance changes in accordance with various conditions such as the frequency of the microwave.  
      Accordingly, if the reflected wave is large and it is necessary to increase the reactance by increasing the projection length of the stabs  1071 A to  1074 C, the matching device  1017  is difficult to accurately control by taking account of even the increase in reactance.  
      As a consequence, if the reflected wave is large, it is difficult to reduce this reflected wave by the matching device  1017  and generate a highly uniform plasma.  
     DISCLOSURE OF INVENTION  
      The present invention has been made to solve the above problems, and has as its object to provide a matching device capable of easily performing accurate control.  
      It is another object of the present invention to provide a plasma processing apparatus capable of easily generating a highly uniform plasma.  
      To achieve the above objects, a matching device of the present invention is characterized by comprising a plurality of first branched waveguides connected perpendicularly to an axial direction of a cylindrical waveguide or coaxial waveguide, and having one end which opens in the cylindrical waveguide or in an outer conductor of the coaxial waveguide and the other end which is electrically functionally short-circuited, wherein the first branched waveguides are arranged at a predetermined interval in the axial direction of the cylindrical waveguide or coaxial waveguide.  
      This matching device may further comprise a plurality of second branched waveguides connected perpendicularly to the axial direction of the cylindrical waveguide or coaxial waveguide, and having one end which opens in the cylindrical waveguide or in the outer conductor of the coaxial waveguide and the other end which is electrically functionally short-circuited, wherein the second branched waveguides are arranged in positions which make an angle of 90° with positions of the first branched waveguides when viewed from an axis of the cylindrical waveguide or coaxial waveguide, and arranged at a predetermined interval in the axial direction of the cylindrical waveguide or coaxial waveguide.  
      The matching device may further comprise a plurality of third branched waveguides connected perpendicularly to the axial direction of the cylindrical waveguide or coaxial waveguide, and having one end which opens in the cylindrical waveguide or in the outer conductor of the coaxial waveguide and the other end which is electrically functionally short-circuited, wherein the third branched waveguides oppose the first branched waveguides.  
      The matching device may further comprise a plurality of third branched waveguides and a plurality of fourth branched waveguides connected perpendicularly to the axial direction of the cylindrical waveguide or coaxial waveguide, and having one end which opens in the cylindrical waveguide or in the outer conductor of the coaxial waveguide and the other end which is electrically functionally short-circuited, wherein the third branched waveguides oppose the first branched waveguides, and the fourth branched waveguides oppose the second branched waveguides.  
      In the above matching device, the number of the branched waveguides arranged in the axial direction of the cylindrical waveguide or coaxial waveguide may be at least three.  
      In particular, an interval between the branched waveguides in the axial direction of the cylindrical waveguide or coaxial waveguide may be ¼ or ⅛ a guide wavelength of the cylindrical waveguide or coaxial waveguide.  
      Also, all intervals between the branched waveguides arranged in the axial direction of the cylindrical waveguide or coaxial waveguide may be equal or different.  
      In the above matching device, the first and second branched waveguides may be alternately arranged in the axial direction of the cylindrical waveguide or coaxial waveguide.  
      Alternatively, all the first branched waveguides and all the second branched waveguides may be arranged in different regions in the axial direction of the cylindrical waveguide or coaxial waveguide.  
      The above matching device may also have an arrangement in which a short-circuit plate which. electrically functionally short-circuits the other end of the branched waveguide is slidable in the branched waveguide.  
      The matching device may further comprise detecting means for detecting an internal voltage of the cylindrical waveguide or coaxial waveguide, and control means for sliding the short-circuit plate of the branched waveguide on the basis of an output signal from the detecting means.  
      A matching device of the present invention is characterized by comprising a plurality of first stabs and a plurality of second stabs which project in a radial direction from an inner wall surface of a cylindrical waveguide or from an inner wall surface of an outer conductor of a coaxial waveguide, wherein the first stabs are arranged at a predetermined interval in an axial direction of the cylindrical waveguide or coaxial waveguide, the second stabs are arranged in positions which make an angle of 90° with positions of the first stabs when viewed from an axis of the cylindrical waveguide or coaxial waveguide, and arranged at a predetermined interval in the axial direction of the cylindrical waveguide or coaxial waveguide, and the first and second stabs are arranged in different planes perpendicular to the axis of the cylindrical waveguide or coaxial waveguide.  
      The first and second stabs may be alternately arranged in the axial direction of the cylindrical waveguide or coaxial waveguide.  
      Also, all the first stabs and all the second stabs may be arranged in different regions in the axial direction of the cylindrical waveguide or coaxial waveguide.  
      These matching devices may further comprise a plurality of third stabs and a plurality of fourth stabs which project in the radial direction from the inner wall surface of the cylindrical waveguide or from the inner wall surface of the outer conductor of the coaxial waveguide, wherein the third stabs oppose the first stabs, and the fourth stabs oppose the second stabs.  
      A matching device of the present invention is characterized by comprising a plurality of first stabs and a plurality of second stabs which project in a radial direction from an inner wall surface of a cylindrical waveguide or from an inner wall surface of an outer conductor of a coaxial waveguide, wherein the first stabs are arranged at a predetermined interval in an axial direction of the cylindrical waveguide or coaxial waveguide, the second stabs are arranged in positions which make an angle of 90° with positions of the first stabs when viewed from an axis of the cylindrical waveguide or coaxial waveguide, and arranged at a predetermined interval in the axial direction of the cylindrical waveguide or coaxial waveguide, and at least tips of the first and second stabs are made of a dielectric material having a relative dielectric constant of 1 or more.  
      This matching device may further comprise a plurality of third stabs and a plurality of fourth stabs which project in the radial direction from the inner wall surface of the cylindrical waveguide or from the inner wall surface of the outer conductor of the coaxial waveguide, wherein the third stabs oppose the first stabs, the fourth stabs oppose the second stabs, and at least tips of the first and second stabs are made of a dielectric material having a relative dielectric constant of 1 or more.  
      In the above matching device using the stabs, the number of the stabs arranged in the axial direction of the cylindrical waveguide or coaxial waveguide may be at least three.  
      In particular, an interval between the stabs in the axial direction of the cylindrical waveguide or coaxial waveguide may be ¼ or ⅛ a guide wavelength of the cylindrical waveguide or coaxial waveguide.  
      Also, all intervals of the stabs arranged in the axial direction of the cylindrical waveguide or coaxial waveguide may be equal or different.  
      The above matching device using the stabs may also have an arrangement in which a projection length, which is a length of projection from the inner wall surface of the cylindrical waveguide or from the inner wall surface of the outer conductor of the coaxial waveguide, of the stabs is changeable.  
      The matching device may further comprise detecting means for detecting an internal voltage of the cylindrical waveguide or coaxial waveguide, and control means for changing the projection length of the stabs on the basis of an output signal from the detecting means.  
      In all the matching devices described above, a TE 11 -mode circularly polarized wave electromagnetic field may propagate in the cylindrical waveguide, and a TE-mode rotating electromagnetic field may propagate in the coaxial waveguide.  
      To achieve the above objects, a plasma processing apparatus of the present invention is characterized by comprising a processing vessel which accommodates an object to be processed such as a semiconductor or LCD, a slot antenna which supplies an electromagnetic field into the processing vessel, a cylindrical waveguide or coaxial waveguide connected between the slot antenna and a high-frequency power supply, and a matching device attached to the cylindrical waveguide or coaxial waveguide to match impedances of the slot antenna and power supply, wherein the above-mentioned matching device is used as the matching device.  
      To achieve the above objects, a plasma processing apparatus of the present invention comprising a processing vessel which accommodates an object to be processed, a magnetic field generator which generates a magnetic field in the vessel, and a cylindrical waveguide or coaxial waveguide which supplies a microwave into the vessel, the plasma processing apparatus generating a plasma by using electrons heated by electron-cyclotron resonance, characterized by comprising the matching device described above. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a sectional view showing the arrangement of a processing vessel of a plasma processing apparatus according to the first embodiment of the present invention;  
       FIG. 2  is a view showing the mechanical arrangement of an electromagnetic field supply apparatus of the plasma processing apparatus according to the first embodiment of the present invention;  
       FIG. 3  is a view for explaining a matching device and detector of the electromagnetic field supply apparatus.  
       FIG. 4  is a sectional view taken along a line IV-IV′ in  FIG. 2 ;  
       FIG. 5  is a sectional view taken along a line V-V′ in  FIG. 2 ;  
       FIG. 6  is a block diagram showing the configuration of a control system of the electromagnetic field supply apparatus;  
       FIGS. 7A  to  7 E are views showing the sectional shapes of branched waveguides of the matching device;  
       FIGS. 8A and 8B  are perspective views showing examples of the arrangement of a short-circuit plate of the branched waveguide;  
       FIG. 9A  is a graph showing the voltage distribution in a plane perpendicular to the axis of a cylindrical waveguide having no matching device, when an output microwave from a high-frequency power supply is converted into a circularly polarized wave and supplied to a radial line slot antenna via the cylindrical waveguide, and  FIG. 9B  is a graph showing the voltage distribution in the plane perpendicular to the axis of a cylindrical waveguide having a matching device, when the output microwave from the high-frequency power supply is converted into a circularly polarized wave and supplied to the radial line slot antenna via the cylindrical waveguide;  
       FIG. 10A  is a sectional view showing the arrangement of a matching device according to the second embodiment of the present invention, and  FIG. 10B  is a sectional view taken along a line Xb-Xb′ in  FIG. 10A ;  
       FIG. 11  is a sectional view showing the arrangement of a matching device according to the third embodiment of the present invention;  
       FIG. 12  is a sectional view taken along a line XII-XII′ in  FIG. 11 ;  
       FIG. 13A  is a sectional view showing the arrangement of a matching device according to the fourth embodiment of the present invention, and  FIG. 13B  is a sectional view taken along a line XIIIb-XIIIb′ in  FIG. 13A ;  
       FIG. 14  is a sectional view showing the arrangement of a processing vessel of a plasma processing apparatus according to the fifth embodiment of the present invention;  
       FIG. 15  is a view showing the mechanical arrangement of an electromagnetic field supply apparatus of the plasma processing apparatus according to the fifth embodiment of the present invention;  
       FIG. 16  is a view showing an example of the arrangement of an ECR plasma processing apparatus according to the sixth embodiment of the present invention;  
       FIG. 17  is a view showing another example of the arrangement of the ECR plasma processing apparatus according to the sixth embodiment of the present invention;  
       FIG. 18  is a view for explaining the conventional matching device;  
       FIG. 19  is a sectional view taken along a line XIX-XIX′ in  FIG. 18 ; and  
       FIG. 20  is a graph showing the relationship between the projection length and reactance of stabs in the conventional matching device. 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
      Embodiments of the present invention will be described below with reference to the accompanying drawings.  
     First Embodiment  
      A plasma processing apparatus using a matching device of the present invention has a processing vessel which accommodates an object to be processed and performs plasma processing for this object, and an electromagnetic field supply apparatus which supplies a microwave into this processing vessel and generates a plasma in the processing vessel by the action of the electromagnetic field of the microwave. The arrangements of the processing vessel and electromagnetic field supply apparatus of the plasma processing apparatus of the first embodiment of the present invention will be separately described below.  
       FIG. 1  is a sectional view showing the arrangement of the processing vessel.  
      A processing vessel  1  has a closed-end cylindrical shape having an open upper portion. A substrate table  3  is fixed via an insulating plate  2  to a central portion of the bottom surface of the processing vessel  1 . On the upper surface of the substrate table  3 , a substrate  4 , such as a semiconductor or LCD, as an object to be processed is placed. Exhaust ports  5  for evacuation are formed in the periphery of the bottom surface of the processing vessel  1 . A gas supply nozzle  6  for supplying gases into the processing vessel  1  is formed in the circumferential wall of the processing vessel  1 . When this plasma processing apparatus is used as an etching apparatus, for example, the nozzle  6  supplies a plasma gas such as Ar and an etching gas such as CF 4 .  
      The upper opening of the processing vessel  1  is closed with a dielectric plate  7  so as to prevent a leak of the plasma to the outside. On the dielectric plate  7 , a radial line slot antenna (to be abbreviated as an RLSA hereinafter)  15  of the electromagnetic field supply apparatus is mounted. The RLSA  15  is isolated from the processing vessel  1  by the dielectric plate  7  and thereby protected from the plasma generated in the processing vessel  1 . The outer circumferential surfaces of the dielectric plate  7  and RLSA  15  are covered with a shield member  8  placed annularly on the circumferential wall of the processing vessel  1 , thereby preventing a leak of the microwave to the outside.  
       FIG. 2  is a view showing the mechanical arrangement of the electromagnetic field supply apparatus. That is,  FIG. 2  shows a sectional arrangement including the axis (Z) of a cylindrical waveguide having a matching device.  FIG. 3  is a view for explaining the matching device and a detector of this electromagnetic field supply apparatus.  FIG. 4  is a sectional view, taken along a line IV-IV′, showing the sectional arrangement of the matching device in a plane (X-Y plane) perpendicular to the axis (Z) of the cylindrical waveguide.  FIG. 5  is a sectional view, taken along a line V-V′ in  FIG. 2 , showing the sectional arrangement of the detector in a plane (X-Y plane) perpendicular to the axis (Z) of the cylindrical waveguide.  FIG. 6  is a block diagram showing the configuration of a control system of the electromagnetic field supply apparatus.  
      As shown in  FIG. 2 , the electromagnetic supply apparatus has a high-frequency power supply  11  for generating a microwave having a predetermined frequency of, e.g., 1 GHz to ten-odd GHz, a rectangular waveguide  12  whose transmission mode is TE 10 , a rectangle-cylinder converter  13  for converting the transmission mode from TE 10  to TE 11 , a cylindrical waveguide  14  whose transmission mode is TE 11 , and the RLSA  15 .  
      The RLSA  15  is made up of two circular parallel conductor plates  52  and  53  forming a radial waveguide  51 , and a conductor ring  54  which shields the two conductor plates  52  and  53  by connecting their outer circumferential portions. A hole  55  connected to the cylindrical waveguide  14  is formed in a central portion of the conductor plate  52  as the upper surface of the radial waveguide  51 . A microwave is supplied into the radial waveguide  51  through the hole  55 . In the conductor plate  53  as the lower surface of the radial waveguide  51 , a plurality of slots  56  for supplying the microwave, which propagates in the radial waveguide  51 , into the processing vessel  1  are formed.  
      A bump  57  is formed in a central portion of the conductor plate  53 . The bump  57  is formed into a substantially conical shape which projects toward the hole  55  in the conductor plate  52 , and the point of the cone is rounded into a spherical shape. The bump  57  can be made of either a conductor or dielectric material. It is possible by the bump  57  to reduce a change in impedance from the cylindrical waveguide  14  to the radial waveguide  51 , and control the reflection of the microwave in the connecting portion between the cylindrical waveguide  14  and radial waveguide  51 . A dielectric material having a relative dielectric constant of 1 or more may also be placed in the radial waveguide  51 .  
      The cylindrical waveguide  14  has a circularly polarized wave converter  16 , detectors (detecting means)  18 , and a matching device  17  arranged in this order from the rectangle-cylinder converter  13  to the RLSA  15 .  
      The circularly polarized wave converter  16  converts the TE 11 -mode microwave propagating in the cylindrical waveguide  14  into a circularly polarized wave, i.e., into a rotating electric field whose field vector rotates once in one period in a plane perpendicular to the direction of travel. For example, the circularly polarized wave converter  16  is made up of a pair or a plurality of pairs of columnar projections opposing each other on the inner wall surface of the cylindrical waveguide  14 .  
      The matching device  17  matches the impedances of the supply side (i.e., the high-frequency power supply  11 ) and the load side (i.e., the RLSA  14 ) of the cylindrical waveguide  14 . The matching device  17  is characterized by using branched waveguides connected as reactance elements to the cylindrical waveguide  14 . The reactance of the branched waveguides can be changed by a driver  19  shown in  FIG. 6 .  
      The detectors  18  have probes  18 A projecting in the radial direction from the inner wall surface of the cylindrical waveguide  14 . That is, a set of three probes  18 A are arranged at an interval of, e.g., substantially ⅛ a guide wavelength λg1 in the direction of the axis (Z) of the cylindrical waveguide  14 , and four sets are arranged at an angular interval of 90° in the circumferential direction of the cylindrical waveguide  14 ; a total of twelve probes  18 A are arranged. In the coordinate system, two sets of detectors  18  oppose each other in the X-Z plane, and two sets of detectors  18  oppose each other in the Y-Z plane. Note that three or more detectors  18  may also be arranged at an interval other than an N/2 multiple (N is a natural number) of the guide wavelength λg1 in the direction of the axis (Z) of the cylindrical waveguide  14 , or three or more detectors  18  may also be arranged at an angular interval of 45° in the circumferential direction of the cylindrical waveguide  14 . It is also possible to arrange three detectors  18  in the X-Z plane and three detectors  18  in the Y-Z plane, i.e., a total of six detectors  18 . Each detector  18  performs square-law detection on the microwave power, extracted by its probe  18 A, in the cylindrical waveguide  14 , and outputs the detection result to a controller  20  shown in  FIG. 6 .  
      On the basis of the output signal from each detector  18 , the controller  20  controls the driver  19  so as to match the impedances of the supply side and load side of the cylindrical waveguide  14 , thereby adjusting the reactance of the branched waveguides of the matching device  17 .  
      The matching device  17  will be described in more detail below with reference to FIGS.  2  to  4 ,  7 A to  7 E, and  8 A and  8 B.  FIGS. 7A  to  7 E are views showing the sectional shapes of the branched waveguides.  FIGS. 8A and 8B  are perspective views showing examples of the arrangement of a short-circuit plate.  
      The matching device  17  is made up of a plurality of branched waveguides connected perpendicularly to the direction of the axis (Z) of the cylindrical waveguide  14 . More specifically, as shown in  FIGS. 2 and 4 , three branched waveguides (first branched waveguides)  71 A to  71 C are equally spaced in the direction of the axis (Z) of the cylindrical waveguide  14 , three branched waveguides (third branched waveguides)  72 A to  72 C oppose the three branched waveguides  71 A to  71 C, three branched waveguides (second branched waveguides)  73 A to  73 C are arranged in positions which make an angle of 90° with the positions of the three branched waveguides  71 A to  71 C, when viewed from the axis (Z) of the cylindrical waveguide  14 , and equally spaced in the direction of the axis (Z) of the cylindrical waveguide  14 , and three branched waveguides (fourth branched waveguides)  74 A to  74 C (the branched waveguides  74 B and  74 C are not shown) oppose the three branched waveguides  73 A to  73 C. In the coordinate system, the branched waveguides  71 A to  71 C and  72 A to  72 C oppose each other in the X-Z plane, and the branched waveguides  73 A to  73 C and  74 A to  74 C oppose each other in the Y-Z plane.  
      The branched waveguides  71 A to  71 C and  72 A to  72 C in the X-Z plane and the branched waveguides  73 A to  73 C and  74 A to  74 C in the Y-Z plane are alternately arranged in the direction of the axis (Z) of the cylindrical waveguide  14 . That is, these branched waveguides are arranged in the order of the branched waveguides  71 A and  72 A, branched waveguides  73 A and  74 A, branched waveguides  71 B and  72 B, branched waveguides  73 B and  74 B, branched waveguides  71 C and  72 C, and branched waveguides  73 C and  74 C from above. With this arrangement, the openings of the waveguides  71 A to  74 C formed in the inner wall surface of the cylindrical waveguide  14  continue in the same plane, and this prevents an increase in axial ratio of the circularly polarized wave or a decrease in strength of the cylindrical waveguide  14 . The same effect can be obtained when all the branched waveguides  71 A to  71 C and  72 A to  72 C in the X-Z plane and all the branched waveguides  73 A to  73 C and  74 A to  74 C in the Y-Z plane are arranged in different regions in the direction of the axis (Z) of the cylindrical waveguide  14 , e.g., when the former and latter are arranged in upper and lower regions, respectively.  
      As the branched waveguides  71 A to  74 C, it is possible to use, instead of a rectangular waveguide whose section perpendicular to the axis is a rectangle, a cylindrical waveguide having a circular section as shown in  FIG. 7A , a waveguide having an elliptic section as shown in  FIG. 7B , a waveguide having a rectangular section with round corners as shown in  FIG. 7C , or a ridge waveguide having a ridge in its central portion as shown in  FIG. 7D  or  7 E.  
      Each of the branched waveguides  71 A to  74 C has one end which opens in the cylindrical waveguide  14  as described above, and the other end which is electrically functionally short-circuited by a short-circuit plate  75 . As shown in  FIG. 8A , the short-circuit plate  75  has a U-shape, when viewed from the side, having upper and lower ends bent at right angles, and is inserted into each of the branched waveguides  71 A to  74 C such that a portion (to be referred to as a bent portion hereinafter)  75 A which is bent points in a direction opposite to the opening end of the cylindrical waveguide  14 . When the length of the bent portion  75 A of the short-circuit plate  75  is set to substantially ¼ a guide wavelength λg2 of the branched waveguides  71 A to  74 C and an insulating sheet is adhered to form a so-called choke structure, flexibility can be imparted while the reflection of a microwave in the position of the short-circuit plate  75  is ensured. Note that the short-circuit plate  75  may also be given a boxy shape as shown in  FIG. 8B  by bending the upper, lower, left, and right ends at the right angle.  
      The short-circuit plate  75  is attached to the end of a rod  76  extending in the direction of the axis (X or Y) of the branched waveguides  71 A to  74 C. By moving the rod  76  parallel to the direction of the axis (X or Y) of the branched waveguides  71 A to  74 C by the driver  19  shown in  FIG. 6 , the short-circuit plate  75  can be freely slid in the branched waveguides  71 A to  74 C.  
      The reactance of the branched waveguides  71 A to  74 C changes in accordance with an electrical length which is a value obtained by dividing the length from one end to the other of the branched waveguide by the guide wavelength λg2. Accordingly, by changing this electrical length by sliding the short-circuit plate  75  which forms the other end of each of the branched waveguides  71 A to  74 C, the reactance of the branched waveguides  71 A to  74 C can be changed from a sufficiently large − (minus) value to a sufficiently large + (plus) value via 0 (zero).  
      As shown in  FIG. 3 , the intervals between the branched waveguides  71 A to  71 C,  72 A to  72 C,  73 A to  73 C, and  74 A to  74 C in the direction of the axis (Z) of the cylindrical waveguide  14  are substantially ¼ the guide wavelength λg1 of the cylindrical waveguide  14 . Therefore, by changing the reactance of the branched waveguides  71 A to  74 C from 0 (zero) to sufficiently large +/− values, the matching region of the matching device  17  can be the whole region of a Smith chart. Even when the intervals between the branched waveguides  71 A to  71 C are substantially ⅛ the guide wavelength λg1, the matching region can be the whole region of a Smith chart. Accordingly, even when the reflected wave from the load is large, impedance matching can be performed at all phases.  
      Also, the branched waveguides  71 A to  74 C have no members, such as stabs  1071 A to  1074 C, which project into the cylindrical waveguide  14 , so those arranged in the X-Z plane and those arranged in the Y-Z plane do not interfere with each other and hence do not affect the reactance. Therefore, the reactance of the branched waveguides  71 A to  74 C substantially changes in the form of a tangent function in accordance with the electrical length based on the length from one end to the other of each branched waveguide. Consequently, even when the reflected wave from the load is large, a desired reactance can be readily realized. This facilitates accurate control of impedance matching.  
      Furthermore, since the branched waveguides  71 A to  74 C have no members, such as the stabs  1071 A to  1074 C, which project into the cylindrical waveguide  14 , no discharge occurs between the branched waveguides  71 A to  71 C and branched waveguides  72 A to  72 C opposing each other or between the branched waveguides  73 A to  73 C and branched waveguides  74 A to  74 C opposing each other, even when the reflected wave from the load is large.  
      Note that by using only the branched waveguides  71 A to  71 C, only the branched waveguides  71 A to  71 C and branched waveguides  72 A and  72 C opposing each other in the X-Z plane, or only the branched waveguides  71 A to  71 C in the X-Z plane and the branched waveguides  73 A to  73 C in the Y-Z plane, the matching region can be the whole region of a Smith chart, and impedance matching can be performed at all phases. However, when the branched waveguides  71 A to  71 C and  72 A to  72 C are arranged in the X-Z plane and the branched waveguides  73 A to  73 C and  74 A to  74 C are arranged in the Y-Z plane, thereby giving axial symmetry to these branched waveguides, the axial ratio of the circularly polarized wave propagating in the cylindrical waveguide  14  can be brought as near as possible to 1.  
      Note also that even when three or more branched waveguides are arranged in the direction of the axis (Z) of the cylindrical waveguide  14 , impedance matching can be performed at all phases by setting the intervals between these branched waveguides to substantially ¼ or ⅛ the guide wavelength λg1.  
      Furthermore, even when the intervals between the branched waveguides arranged in the direction of the axis (Z) are not equal, impedance matching can be performed at all phases. For example, it is possible to set the interval between the branched waveguides  71 A and  71 B to substantially ¼ the guide wavelength λg1, and the interval between the branched waveguides  71 B and  71 C to substantially ⅛ the guide wavelength λg1.  
      On the other hand, the matching region narrows if the number of the branched waveguides arranged in the direction of the axis (Z) is two, or if the intervals between the branched waveguides arranged in the direction of the axis (Z) of the cylindrical waveguide  14  take values except for N/2, ¼, and ⅛ of the guide wavelength λg1. However, this arrangement can also be used depending on the conditions.  
      The operation of the plasma processing apparatus shown in  FIGS. 1 and 2  will be described below.  
      The high-frequency power supply  11  is driven to generate a microwave. This microwave is guided in the TE 10  mode by the rectangular waveguide  12 , converted into the TE 11  mode by the rectangle-cylinder converter, circularly polarized by the circularly polarized wave converter  16  of the cylindrical waveguide  14 , introduced to the radial waveguide  51 , and supplied into the processing vessel  1  from the plurality of slots  56  formed in the conductor plate  53  which forms the lower surface of the radial waveguide  51 . In the processing vessel  1 , a plasma gas introduced from the nozzle  6  is ionized, or dissociated in some cases, by the electromagnetic field of the microwave, thereby generating a plasma and processing the substrate  4 .  
      At the same time, each of the plurality of detectors  18  of the cylindrical waveguide  14  extracts a portion of the microwave power in the cylindrical waveguide  14  along the X-Z plane and Y-Z plane, performs square-law detection on the extracted power, and outputs the result to the controller  20 . The controller  20  obtains |Γ| cos θ and |Γ| sin θ from the output signal from each detector  18 . |Γ| is the absolute value of the reflection coefficient of the load, and 0 is the phase angle of the reflection coefficient of the load. The controller  20  calculates the impedance of the load on the basis of the obtained |Γ| cos θ and |Γ| sin θ, obtains the conditions of impedance matching between the supply side and load side, and determines the moving amount of the short-circuit plates  75  of the branched waveguides  71 A to  74 C forming the matching device  17 . For example, a voltage having a reflection coefficient value (e.g., when a voltage-to-standing wave ratio VSWR is 1.1, |Γ 0 |=0.048) is set in the controller  20  beforehand, the moving amount of the short-circuit plates  75  is so determined that the voltage of the detected |Γ| is equal to or lower than the voltage of the preset |Γ 0 |. This moving amount is common to all the branched waveguides  71 A to  74 C. The controller  20  moves the short-circuit plates  75  by controlling the driver  19 , thereby performing impedance matching.  
      In this embodiment, the reactances of all the branched waveguides  71 A to  74 C are equally adjusted on the basis of the outputs from all the detectors  18 . However, it is also possible to adjust the reactances of the branched waveguides  71 A to  71 C and  72 A to  72 C in the X-Z plane on the basis of the outputs from the detectors  18  in the X-Z plane, and adjust the reactances of the branched waveguides  73 A to  73 C and  74 A to  74 C on the basis of the outputs from the detectors  18  in the Y-Z plane. In the latter case, the moving amount of the short-circuit plates  75  of the branched waveguides  71 A to  71 C and  72 A to  72 C in the X-Z plane may be different from that of the short-circuit plates  75  of the branched waveguides  73 A to  73 C and  74 A to  74 C in the Y-Z plane.  
      As an example of a method of obtaining impedance matching conditions by equally spacing a plurality of detectors and processing the output signals from these detectors, a four-probe method is described in, e.g., “Bun&#39;ichi Oguchi and Masamitsu Ohta, ‘Microwave•Milliwave Measurements’, Corona, pp. 84-85”.  
      Accordingly, even when a wave reflected in the processing vessel  1  or in the radial waveguide  51  enters the cylindrical waveguide  14 , this wave can be reflected toward the radial waveguide  51  by the matching device  17 , so the reflected wave from the radial waveguide  51  can be canceled by the reflected wave from the matching device  17 . This makes it possible to reduce the reflected wave propagating in the cylindrical waveguide  14 , and prevents the axial ratio of the circularly polarized wave from increasing owing to the influence of the reflected wave. Accordingly, the field strength distribution in the radial waveguide  51  can be made symmetrical with respect to the axis (Z) of the cylindrical waveguide  14  on time average. As a consequently, an electromagnetic field having this time-average, axially symmetrical distribution can be supplied into the processing vessel  1  from the plurality of slots formed in the conductor plate  53  as the lower surface of the radial waveguide  51 , thereby generating a highly uniform plasma.  
      The results of an experiment of the matching device  17  will be described below with reference to  FIGS. 9A and 9B .  
      In this experiment, voltage distributions in the plane (X-Y plane) perpendicular to the axis (Z) of the cylindrical waveguide when the output microwave from the high-frequency power supply  11  was converted into a circularly polarized wave and supplied to the RLSA  15  via the cylindrical waveguide  14  were checked by using the matching device  17  and without using it. More specifically, the inner diameter of the cylindrical waveguide  14  was set to φ90 [mm], rectangular waveguides having dimensions of inner diameter 80 [mm]×27 [mm] were used as the branched waveguides  71 A to  74 C, the intervals (in the direction of the axis (Z) of the cylindrical waveguide  14 ) between these rectangular waveguides were set to (λg1)/4, and microwaves having a frequency of 2.45 [GHz] and power values of 1, 2, and 3 [kW] were converted into circularly polarized waves and supplied to a load having VSWR 3.0 (when no matching was performed).  
      As a consequence, the voltage distributions when the matching device  17  was not used were largely distorted as shown in  FIG. 9A . This means that the circularly polarized wave propagating in the cylindrical waveguide  14  was distorted to increase the axial ratio. In contrast, the voltage distributions when the matching device  17  was used were less distorted as shown in  FIG. 9B . This means that the axial ratio of the circularly polarized wave propagating in the cylindrical waveguide  14  was close to 1. The above experimental results indicate that the use of the matching device  17  makes it possible to bring the axial ratio of the circularly polarized wave close to 1, and thereby generate a highly uniform plasma on time average in the processing vessel  1 .  
     Second Embodiment  
       FIG. 10A  is a sectional view showing the arrangement of a matching device of the second embodiment of the present invention, and shows a sectional arrangement including the axis (Z) of a cylindrical waveguide having this matching device.  FIG. 10B  is a sectional view, taken along a line Xb-Xb′ in  FIG. 10A , showing a sectional arrangement in a plane (X-Y plane) perpendicular to the axis (Z) of the cylindrical waveguide. The same reference numerals as in  FIGS. 2 and 4  denote the same parts in  FIGS. 10A and 10B , and an explanation thereof will be suitably omitted.  
      A matching device  117  shown in  FIGS. 10A and 10B  match the impedances of the supply side and load side of a cylindrical waveguide  14 , and uses a plurality of stabs  171 A to  171 C,  172 A to  172 C,  173 A to  173 C, and  174 A to  174 C (the stabs  174 B and  174 C are not shown) as reactance elements. Each of the stabs  171 A to  174 C is a rod having a circular section and a tip rounded into a substantially spherical shape, and made of a metal such as copper or aluminum.  
      The stabs  171 A to  174 C are arranged as follows. That is, the three stabs (first stabs)  171 A to  171 C are equally spaced in the direction of the axis (Z) of the cylindrical waveguide  14 , the three stabs (third stabs)  172 A to  172 C oppose the three stabs  171 A to  171 C, the three stabs (second stabs)  173 A to  173 C are arranged in positions which make an angle of 90° with the positions of the three stabs  171 A to  171 C, when viewed from the axis (Z) of the cylindrical waveguide  14 , and equally spaced in the direction of the axis (Z) of the cylindrical waveguide  14 , and the three stabs (fourth stabs)  174 A to  174 C oppose the three stabs  173 A to  173 C. In the coordinate system, the stabs  171 A to  171 C and stabs  172 A to  172 C oppose each other in the X-Z plane, and the stabs  173 A to  173 C and stabs  174 A to  174 C oppose each other in the Y-Z plane.  
      The stabs  171 A to  171 C and  172 A to  172 C in the X-Z plane and the stabs  173 A to  173 C and  174 A to  174 C in the Y-Z plane are alternately arranged in the direction of the axis (Z) of the cylindrical waveguide  14 . That is, these stabs are arranged in the order of the stabs  171 A and  172 A, stabs  173 A and  174 A, stabs  171 B and  172 B, stabs  173 B and  174 B, stabs  171 C and  172 C, and stabs  173 C and  174 C from above. Therefore, the stabs  171 A and  172 A and stabs  173 A and  174 A, stabs  171 B and  172 B and stabs  173 B and  174 B, and stabs  171 C and  172 C and stabs  173 C and  174 C are arranged in different planes perpendicular to the axis (Z) of the cylindrical waveguide  14 .  
      The tips of the stabs  171 A to  174 C project in the radial direction from the inner wall surface of the cylindrical waveguide  14 , and the length of projection of these tips of the stabs  171 A to  174 C from the inner wall surface can be freely changed by a driver (not shown). Accordingly, the reactance which is determined by the projection length of the stabs  171 A to  174 C can be changed from 0 (zero) to a sufficiently large value.  
      The intervals between the stabs  171 A to  171 C,  172 A to  172 C,  173 A to  173 C, and  174 A to  174 C in the direction of the axis (Z) of the cylindrical waveguide  14  are substantially ¼ a guide wavelength λg1 of the cylindrical waveguide  14 . Therefore, by changing the reactance of the stabs  171 A to  174 C from 0 (zero) to a sufficiently large value, the matching region of the matching device  117  can be a considerable range at all phases of a Smith chart. Even when the intervals between the stabs  171 A to  171 C or the like are substantially ⅛ the guide wavelength λg1, the matching region can be a wide region of a Smith chart. Accordingly, even when the reflected power from the load is large, impedance matching can be performed at all phases.  
      As in the first embodiment, it is also possible to use detectors for detecting the internal voltage of the cylindrical waveguide  14 , and a controller for controlling the driver on the basis of output signals from the detectors, thereby changing the projection length of the stabs  171 A to  174 C. With this arrangement, the control of impedance matching can be automated.  
      The matching device  117  is made up of the stabs  171 A to  174 C, and the projection length of the stabs  171 A to  174 C must be increased if the reflected wave is large and so the reactance must be increased. Since the stabs  171 A to  171 C and  172 A to  172 C in the X-Z plane and the stabs  173 A to  173 C and  174 A to  174 C in the Y-Z plane are alternately arranged in the direction of the axis (Z) of the cylindrical waveguide  14 , the distance between the stabs in the direction of the axis (Z) of the cylindrical waveguide  14  is larger than when the former and latter are arranged in the same plane. This makes it possible to reduce changes in reactance caused by mutual interference produced when the projection length of the stabs  171 A to  171 C and  172 A to  172 C in the X-Z plane and the stabs  173 A to  173 C and  174 A and  174 C in the Y-Z plane is increased. Accordingly, even when the reflected wave from the load is large, a desired reactance can be realized more easily than in the conventional matching devices. This makes accurate control of impedance matching easier than in the conventional matching devices.  
      Note that by using only the stabs  171 A to  171 C in the X-Z plane and the stabs  173 A to  173 C in the Y-Z plane, the matching region can be a wide region of a Smith chart, and impedance matching can be performed at all phases. However, when the stabs  171 A to  171 C and  172 A to  172 C are arranged in the X-Z plane and the stabs  173 A to  173 C and  174 A to  174 C are arranged in the Y-Z plane, thereby giving axial symmetry to these stabs, the axial ratio of a circularly polarized wave propagating in the cylindrical waveguide  14  can be brought as near as possible to 1.  
      Note also that even when three or more stabs are arranged in the direction of the axis (Z) of the cylindrical waveguide  14 , impedance matching can be performed at all phases by setting the intervals between these stabs to substantially ¼ or ⅛ the guide wavelength λg1.  
      Furthermore, even when the intervals between the stabs arranged in the direction of the axis (Z) are not equal, impedance matching can be performed at all phases. For example, it is possible to set the interval between the stabs  171 A and  171 B to substantially ¼ the guide wavelength λg1, and the interval between the stabs  171 B and  171 C to substantially ⅛ the guide wavelength λg1.  
      On the other hand, the matching region narrows if the number of the stabs arranged in the direction of the axis (Z) is two, or if the intervals between the stabs arranged in the direction of the axis (Z) of the cylindrical waveguide  14  take values except for N/2, ¼, and ⅛ of the guide wavelength λg1. However, this arrangement can also be used depending on the conditions.  
      Note that it is naturally possible to generate a highly uniform plasma by applying the matching device  117  shown in  FIGS. 10A and 10B  to a plasma processing apparatus as in the first embodiment.  
     Third Embodiment  
       FIG. 11  is a sectional view showing the arrangement of a matching device of the third embodiment of the present invention, and shows a sectional arrangement including the axis (Z) of a cylindrical waveguide having this matching device.  FIG. 12  is a sectional view, taken along a line XII-XII′ in  FIG. 11 , showing a sectional arrangement in a plane (X-Y plane) perpendicular to the axis (Z) of the cylindrical waveguide. The same reference numerals as in  FIGS. 2 and 4  denote the same parts in  FIGS. 11 and 12 , and an explanation thereof will be suitably omitted.  
      Similar to the matching device  117  shown in  FIGS. 10A and 10B , a matching device  217  shown in  FIGS. 11 and 12  is made up of stabs (first stabs)  271 A to  271 C, stabs (third stabs)  272 A to  272 C, stabs (second stabs)  273 A to  273 C, and stabs (fourth stabs)  274 A to  274 C (the stabs  274 B and  274 C are not shown).  
      The matching device  217 , however, differs from the matching device  117  shown in  FIGS. 10A and 10B  in that all the stabs  271 A to  271 C and  272 A to  272 C in the X-Z plane and all the stabs  273 A to  273 C and  274 A to  274 C in the Y-Z plane are arranged in different regions in the direction of the axis (Z) of a cylindrical waveguide  14 . That is, in the matching device  217  shown in  FIG. 11 , the former and latter are separately arranged in the upper and lower regions, respectively, of the cylindrical waveguide  14 . Even in this way, the stabs  271 A and  272 A and stabs  273 A and  274 A, stabs  271 B and  272 B and stabs  273 B and  274 B, and stabs  271 C and  272 C and stabs  273 C and  274 C are arranged in different planes perpendicular to the axis (Z) of the cylindrical waveguide  14 . Therefore, compared to a case in which the stabs  271 A to  271 C and  272 A to  272 C in the X-Z plane and the stabs  273 A to  273 C and  274  in the Y-Z plane are arranged in the same plane, the distance between the stabs in the direction of the axis (Z) of the cylindrical waveguide  14  increases, so changes in reactance caused by mutual interference of the former and latter can be reduced. This makes accurate control of impedance matching easier than in the conventional matching devices. Accordingly, a highly uniform plasma can be generated by applying the matching device  217  shown in  FIG. 11  to a plasma processing apparatus as in the first embodiment.  
      The rest is the same as the matching device  117  shown in  FIGS. 10A and 10B .  
     Fourth Embodiment  
       FIG. 13A  is a sectional view showing the arrangement of a matching device of the fourth embodiment of the present invention, and shows a sectional arrangement including the axis (Z) of a cylindrical waveguide having this matching device.  FIG. 13B  is a sectional view, taken along a line XIIIb-XIIIb′ in  FIG. 13A , showing a sectional arrangement in a plane (X-Y plane) perpendicular to the axis (Z) of the cylindrical waveguide. The same reference numerals as in  FIGS. 2 and 4  denote the same parts in  FIGS. 13A and 13B , and an explanation thereof will be suitably omitted.  
      Similar to the matching device  117  shown in  FIGS. 10A and 10B , a matching device  317  shown in  FIGS. 13A and 13B  is made up of stabs (first stabs)  371 A to  371 C, stabs (third stabs)  372 A to  372 C, stabs (second stabs)  373 A to  373 C, and stabs (fourth stabs)  374 A to  374 C (the stabs  374 B and  374 C are not shown).  
      The matching device  317 , however, differs from the matching device  117  shown in  FIGS. 10A and 10B  in that the stabs  371 A to  374 C are made of a dielectric material having a relative dielectric constant of 1 or more. The whole or only the tip of each of the stabs  371 A to  374 C can be made of a dielectric material. When at least the tips of the stabs  371 A to  374 C are made of a dielectric material, no resonance occurs. Therefore, even when the stabs  371 A to  371 C and  372 A to  372 C in the X-Z plane and the stabs  373 A to  373 C and  374 A to  374 C in the Y-Z plane are arranged in the same plane as in the conventional matching devices, it is possible to reduce changes in reactance caused by mutual interference produced when the projection length of the former and latter is increased. Also, even when high power is supplied, it is possible to reduce discharge between the tips of the stabs  371 A to  374 C or between the tips of the stabs  371 A to  374 C and the inner surface of a cylindrical waveguide  14 . Consequently, even if the reflected wave from the load is large, a desired reactance can be realized more easily than in the conventional matching devices. This makes accurate control of impedance matching easier than in the conventional matching devices.  
      Accordingly, a highly uniform plasma can be generated by applying the matching device  317  shown in  FIGS. 13A and 13B  to a plasma processing apparatus as in the first embodiment.  
      Note that at least the tips of the stabs  371 A to  374 C are desirably made of a material, such as beryllia porcelain, ceramic, or alumina, having a small dielectric loss.  
      Note also that these stabs made of a dielectric material can be alternately arranged in the X-Z plane and Y-Z plane as shown in  FIGS. 10A and 10B , or separately arranged in those regions of the X-Z plane and Y-Z plane, which are different in the Z direction as shown in  FIG. 11 .  
      The rest is the same as the matching device  117  shown in  FIGS. 10A and 10B .  
     Fifth Embodiment  
      In the above embodiments, only the propagation of a TE 11 -mode circularly polarized wave electromagnetic field in the cylindrical waveguide  14  is explained. However, the matching device and plasma processing apparatus of the present invention are also applicable to an apparatus in which a TE-mode rotating electromagnetic field propagates in a coaxial waveguide.  FIGS. 14 and 15  illustrate an embodiment in which the present invention is applied to this apparatus.  FIG. 14  is a sectional view showing the arrangement of a processing vessel of a plasma processing apparatus.  FIG. 15  is a view showing the mechanical arrangement of an electromagnetic field supply apparatus of the plasma processing apparatus.  
      This plasma processing apparatus shown in  FIGS. 14 and 15  is the same as the plasma processing apparatus shown in  FIGS. 1 and 2  except that a coaxial waveguide  114  is used instead of the cylindrical waveguide  14 . Therefore, the same reference numerals as in  FIGS. 1 and 2  denote the same parts in  FIGS. 14 and 15 , and an explanation thereof will be suitably omitted.  
      As shown in  FIG. 15 , the coaxial waveguide  114  is made up of a coaxially arranged inner conductor  114 A and outer conductor  114 B. A rotating electromagnetic field generator  116  is connected to one end of the coaxial waveguide  114 . The rotating electromagnetic field generator  116  generates a rotating electromagnetic field of a coaxial waveguide TE mode by connecting, to the outer conductor  114 B of the coaxial waveguide  114 , two rectangular waveguides  112 A and  112 B in which microwaves having phases shifted 90° from each other propagate. Referring to  FIG. 15 , the two rectangular waveguides  112 A and  112 B are juxtaposed in the direction of the axis (Z) of the coaxial waveguide  114 . However, the rectangular waveguides  112 A and  112 B may also be arranged in positions, in the same plane perpendicular to the axis (Z) of the coaxial waveguide  114 , where they make an angle of 90° with the axis (Z). Note that the phase difference between the microwaves propagating in the two rectangular waveguides  112 A and  112 B can be produced by splitting a microwave supplied from a high-frequency power supply  11  via a rectangular waveguide  12 , and delaying one of the split phases by 90° from the other phase by a phase shifter  113 .  
      An RLSA  15  is connected to the other end of the coaxial waveguide  114 . More specifically, the other end of the outer conductor  114 B of the coaxial waveguide  114  is connected to the circumference of an opening  55  of a conductor plate  52  which is the upper surface of a radial waveguide  51 . A bump  157  is connected to the other end of the inner conductor  114 A of the coaxial waveguide  114 , and the bottom surface of the bump  157  is connected to the center of a conductor plate  53  which is the lower surface of the radial waveguide  51 . Note that a dielectric material having a relative dielectric constant of 1 or more may also be placed in the radial waveguide  51 .  
      The coaxial waveguide  114  has detectors  18  and a matching device  17 .  FIG. 15  shows an example of the matching device  17 , similar to the matching device shown in  FIG. 2 , having branched waveguides each having one end which opens in the outer conductor  114 B of the coaxial waveguide  114  and the other end which is electrically functionally short-circuited. However, it is also possible to use the matching devices  117 ,  217 , and  317 , as shown in FIGS.  10  to  13 , having stabs which project in the radial direction from the inner wall surface of the outer conductor  114 B of the coaxial waveguide  114 . Regardless of whether the matching device  17 ,  117 ,  217 , or  317  is used, accurate control of impedance matching can be easily performed while a TE-mode rotating electromagnetic field is propagating in the coaxial waveguide  114 . This makes it possible to obtain effects such as easy generation of a highly uniform plasma.  
      Various embodiments using microwaves have been explained above. However, similar effects can be obtained even when a high frequency containing a frequency band lower than a microwave is used in the matching device and plasma processing apparatus of the present invention.  
     Sixth Embodiment  
      The present invention is applicable not only to the microwave (high-frequency) plasma processing apparatus described above, but also to an electron-cyclotron-resonance (ECR) plasma processing apparatus.  FIG. 16  is a view showing an example of the arrangement of an ECR plasma processing apparatus to which the present invention is applied. The same reference numerals as in  FIGS. 1, 2 , and  6  denote the same parts in  FIG. 16 , and an explanation thereof will be suitably omitted.  
      This ECR plasma processing apparatus shown in  FIG. 16  has a vessel  401  including a plasma chamber  401 A for generating a plasma, and a reaction chamber  401 B for performing processing such as plasma CVD.  
      A main electromagnetic coil  481  for forming a magnetic field having a flux density B of 87.5 mT in the plasma chamber  401 A is formed around the outer circumferential surface of the plasma chamber  401 A. One end of a cylindrical waveguide  14  is connected to the upper end of the plasma chamber  401 A via a dielectric plate  407 . The cylindrical waveguide  14  supplies a microwave MW having the same frequency, 2.45 GHz, as the electron-cyclotron frequency (the frequency when electrons in a plasma rotate around a line of magnetic force).  
      The reaction chamber  401 B which communicates with the plasma chamber  401 A houses a substrate table  403  on the upper surface of which an Si substrate  4  as an object to be processed is placed. Also, an auxiliary electromagnetic coil  482  is formed below the bottom surface of the reaction chamber  401 B. A magnetic field generator made up of the main electromagnetic coil  481  and auxiliary electromagnetic coil  482  forms a mirror magnetic field MM in the reaction chamber  401 B.  
      A nozzle  406 A for supplying a plasma gas such as N 2  is formed in the upper portion of the plasma chamber  401 A, and a nozzle  406 B for supplying a reaction gas such as SiH 4  is formed in the upper portion of the reaction chamber  401 B. In addition, an exhaust port  405  which communicates with a vacuum pump is formed in the lower portion of the reaction chamber  401 B.  
      In an arrangement like this, when a magnetic field having a flux density B of 87.5 mT is formed in the plasma chamber  401 A and the microwave MW having a frequency of 2.45 GHz is introduced into the plasma chamber  401 A, electron-cyclotron resonance occurs, and the energy of the microwave MW efficiently moves to electrons and heats them. These electrons thus heated by the microwave MW allow N 2  ionization in the plasma chamber  401  to continue, thereby generating a plasma.  
      A high-frequency power supply  11  is connected to the other end of the cylindrical waveguide  14 . Also, the cylindrical waveguide  14  has a circularly polarized wave converter  16 , detector  18 , and matching device  17 , a controller  20  is connected to the detector  18 , and a driver  19  of the matching device  17  is connected to the controller  20 . Since accurate control of impedance matching can be easily performed by the use of the matching device  17  as in the first embodiment, effects such as easy generation of a highly uniform plasma can be obtained. Note that instead of the matching device  17 , it is also possible to use the matching device  117  shown in  FIGS. 10A and 10B , the matching device  217  shown in  FIGS. 11 and 12 , or the matching device  317  shown in  FIGS. 13A and 13B .  
      In addition, as shown in  FIG. 17 , a rotating electromagnetic field of a coaxial waveguide TE mode may also be supplied by using a coaxial waveguide  114  in place of the cylindrical waveguide  14 . In  FIG. 17 , the same reference numerals as in  FIGS. 15 and 16  denote the same parts.  
     INDUSTRIAL APPLICABILITY  
      The plasma processing apparatus of the present invention can be used in an etching apparatus, CVD apparatus, ashing apparatus, and the like.  
      Also, the matching device of the present invention can be used not only in the plasma processing apparatus but also in, e.g., a communication apparatus and high-frequency superheater.