Abstract:
A microwave plasma processing apparatus performs plasma processing on a substrate by exciting a gas by electric field energy of microwaves emitted from a radial line slot antenna (RLSA). The microwave plasma processing apparatus includes: a processing container in which plasma processing is performed; a microwave source outputting microwaves; a rectangular waveguide transmitting the microwaves outputted from the microwave source; a coaxial converter converting a mode of the microwaves transmitted to the rectangular waveguide; a coaxial waveguide including an inner conductor slidably and electrically connected to the coaxial converter by a first contact member; the first contact member fixed to the coaxial converter and slidably contacting the inner conductor; and a first spring member absorbing displacement, which is caused by thermal expansion, of the RLSA and a member disposed above the RLSA.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims the benefit of Japanese Patent Application No. 2008-159629, filed on Jun. 18, 2008, in the Japan Patent Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a microwave plasma processing apparatus and a method of supplying microwaves, and more particularly, to a microwave plasma processing apparatus that performs plasma-processing on an object by exciting a gas by electric field energy of microwaves emitted from a radial line slot antenna (RLSA), and a method of supplying microwaves using the microwave plasma processing apparatus. 
     2. Description of the Related Art 
     Microwave plasma is generated by introducing microwaves into a processing container in a depressurized state and by exciting a gas by electric field energy of the introduced microwaves. In microwave plasma processing apparatuses, when an electron density of plasma is higher than a cut-off density, microwaves cannot be introduced into plasma and thus, are propagated between a dielectric plate and plasma, and some of the microwaves are absorbed into plasma and are used to sustain plasma. 
     According to the principle of generating plasma, since microwave plasma has a higher electron density Ne and a lower electron temperature Te than plasma that is generated by a capacitively coupled plasma or inductively coupled plasma processing apparatus, a high-quality product can be manufactured at high speed and with less damage by performing plasma processing. 
     As one of microwave plasma generating apparatuses, a microwave plasma processing apparatus using a radial line slot antenna (RLSA) has been proposed (e.g., see Reference 1). The RLSA is disposed on a dielectric window in a state in which, above a slot plate having a disk shape in which a plurality of slots are formed, a wavelength-shortening plate having the same shape is placed. And the middle part of the RLSA is connected to a coaxial waveguide. 
     In the above-described structure, microwaves of 2.45 GHz, for example, outputted from a microwave source, are propagated into the coaxial waveguide and are propagated to have a radiation shape in a radial direction of the RLSA. As such, microwaves having a high electric field strength can be radiated into the processing container via the dielectric window from the plurality of slots formed in the slot plate.
     [Reference 1] Japanese Laid-Open Patent Publication No. hei 9-63793   

     However, during processes, the processing container is maintained at a high temperature of more than 200° C. Thus, during the processes, even though a circumferential part of an RLSA  905  is cooled by a cooling jacket  210 , the temperature of the RLSA  905  increases to 150° C.-165° C., and the temperature of the cooling jacket  210  placed above the RLSA  905  increases to 80° C.-100° C., and the temperature of an outer conductor  340  increases to 40° C.-60° C., and a temperature of more than 100° C. is maintained even near the outer conductor  340  in some of the processes. As a result, the RLSA  905  and its upper members, such as the cooling jacket  210 , the outer conductor  340  of the coaxial waveguide, a rectangular waveguide  305 , etc., shown in  FIG. 6  are thermally expanded. 
     Among the members, a wavelength-shortening plate  905   a  of the RLSA  905  is formed of a dielectric substance such as alumina (Al 2 O 3 ). Meanwhile, the cooling jacket  210 , the outer conductor  340 , the rectangular waveguide  305 , and a coaxial converter  310 , placed above the RLSA  905 , are formed of metal such as copper (Cu) or aluminum (Al). Compared to the linear expansion coefficient of alumina which is 7.0×10 −6 (/° C.), the linear expansion coefficient of copper is 16.7×10 −6 (/° C.) and the linear expansion coefficient of aluminum is 23.5×10 −6 (/° C.), which are more than twice that of alumina. Thus, after a temperature increase, each of the cooling jacket  210 , the outer conductor  340 , and the rectangular waveguide  305 , which are placed above the RLSA  905 , is expanded and is displaced in an upper direction compared to a state before a temperature increase, as illustrated in  FIG. 6 . 
     In this case, if the coaxial converter  310  and an inner conductor  315  are integrally formed as one body, the inner conductor  315  integrally formed as one body with the coaxial converter  310  is displaced in a vertical upward direction of the processing container  100 , following a displacement of the position of the rectangular waveguide  305  or the coaxial converter  310 . 
     Meanwhile, the inner conductor  315  and the coaxial converter  310  allow a refrigerant to pass through the inner conductor  315  and are cooled even during the process. Thus, the temperature of the inner conductor  315  and the temperature of the coaxial converter  310  during the process are lower than the temperature of the outer conductor  340  and the temperature of the rectangular waveguide  305 . Thus, the thermal expansion rate of the inner conductor  315  and the coaxial converter  310  during the process is lower than the thermal expansion rate of the outer conductor  340  and the rectangular waveguide  305 . 
     As such, after a temperature increase, a taper connector  320  connected to the inner conductor  315  is displaced in an upper direction away from the RLSA  905  together with the inner conductor  315 , and a gap between the taper connector  320  and the wavelength-shortening plate  905   a , a gap between the wavelength-shortening plate  905   a  and the RLSA  905 , and a gap between the wavelength-shortening plate  905   a  and the cooling jacket  210  vary. Thus, a transmission path of the microwaves varies, and a mode of the microwaves is unstable, and plasma becomes non-uniform. As such, the stability and reliability of the microwave plasma processing apparatus are poor. 
     SUMMARY OF THE INVENTION 
     To solve the above and/or other problems, the present invention provides a microwave plasma processing apparatus that prevents scattering of plasma by suppressing variation of a transmission path of microwaves due to thermal expansion when the microwaves are supplied into a processing container by using a radial line slot antenna (RLSA), and a method of supplying the microwaves using the microwave plasma processing apparatus. 
     According to an aspect of the present invention, there is provided a microwave plasma processing apparatus which performs plasma processing on an object using plasma generated by microwaves emitted from a radial line slot antenna (RLSA), the apparatus including: a processing container in which plasma processing is performed; a microwave source outputting microwaves; a rectangular waveguide transmitting the microwaves outputted from the microwave source; a coaxial converter converting a mode of the microwaves transmitted to the rectangular waveguide; and a coaxial waveguide including an inner conductor slidably and electrically connected to the coaxial converter by a first contact member, wherein the first contact member is fixed to the coaxial converter and slidably contact the inner conductor to thereby slidably and electrically connect the coxial converter and the inner conductor. 
     According to this, the inner conductor and the coaxial converter may be formed as separate bodies, and the inner conductor may be connected to the coaxial converter to be slidable. The first contact member may electrically connect the coaxial converter and the inner conductor each other. 
     According to this, after a temperature increase, members, such as the RLSA and the rectangular waveguide disposed above the RLSA, may be expanded and displaced in an upward direction. Also, even though the coaxial converter connected to the rectangular waveguide is displaced in an upward direction, the inner conductor may be connected to the coaxial converter to be slidable, and thus, the inner conductor may not be displaced together with the coaxial converter. Thus, a distance between a front end part of the inner conductor and the cooling jacket may not vary before and after a temperature increase. Also, an electrical connection between the coaxial converter and the inner conductor may be guaranteed by the first contact member. As such, variation of the transmission path of the microwaves propagated into the antenna may be prevented, and a mode of the microwaves may be stabilized, and plasma may be uniformly generated. 
     At least part of a front end of the inner conductor may extend along the surface of the RLSA that faces the object. 
     The RLSA may be held by a taper-shaped connector portion and an outer conductor of the coaxial waveguide, the taper-shaped connector portion extending from the front end of the inner conductor. 
     According to this clamp structure, deviation of a position of the wavelength-shortening plate and positions of internal and outer conductors (coaxial waveguide) may be prevented. As a result, variation of a transmission path of the microwaves is eliminated, and uniform plasma may be stably generated. 
     The processing container may include an opening in a ceiling part thereof, and wherein a dielectric window is disposed in the opening of the ceiling part, the dielectric window has a protrusion formed at the middle of the surface of the dielectric window that faces the object, and the front end of the inner conductor extends within the protrusion. As such, the mechanical strength of the apparatus may be guaranteed. 
     The apparatus may further include a second contact member disposed at a point at which the outer conductor of the coaxial waveguide and the taper-shaped connector portion face each other. As such, an electrical connection between the coaxial waveguide and the RLSA may be supplemented. 
     The apparatus may further include a first spring member disposed between a first member connected to the inner conductor and a second member connected to the coaxial converter, the first spring member absorbing displacement, which is caused by a thermal expansion, of the RLSA and a third member disposed above the RLSA. According to this, since the inner conductor is not affected by expansion of the RLSA and the member disposed above the RLSA, the position of the inner conductor may not vary before and after a temperature increase. As such, variation of the transmission path of the microwaves propagated into the RLSA may be prevented, and a mode of the microwaves may be stabilized, thus plasma may be uniformly generated. 
     The first spring member may be any one of a coil-shaped spring member, a thermostable metal seal, and a plate-shaped spring member (e.g., a spring washer). 
     The apparatus may further include a second spring member formed to be adjacent to the outer conductor of the coaxial waveguide that supports the rectangular waveguide, the second spring member providing a first force directing an inside of the processing container with respect to the outer conductor contrary to a second force by which the RLSA and the third member disposed above the RLSA are thermally expanded toward an outside of the processing container. 
     According to this, the second spring member may provide force directing the inside of the processing container with respect to the outer conductor contrary to thermal expansion of the outer conductor and one or more members disposed nearby the outer conductor. As such, the RLSA and the third member may absorb displacement of a vertical upward direction of the processing container due to expansion. 
     The second spring member may be any one of a coil-shaped spring member and a thermostable metal seal. Also, the first contact member may be a metal elastic body. 
     The inner conductor may be supported by a bearing, fixed to the coaxial converter, to be slidable. According to this, the inner conductor may be guided by the first contact member and the bearing. As such, a central axis of the inner conductor may be prevented from being shaked, and a distance between the edge of the inner conductor and the cooling jacket may be set as a predetermined distance as designed, thus variation of the transmission path of the microwaves may be suppressed. 
     The RLSA may include a conductive layer coated on an upper surface, a lower surface, and an outer circumferential surface of the wavelength-shortening plate by using plating, spraying, or metallizing, in order to use the conductive layer as a transmission path of the microwaves. Also, at a plurality of slots formed in the portion of the conductive layer formed on a lower surface of the wavelength-shortening plate, the microwaves which are propagated from the coaxial waveguide through the wavelength-shortening plate may be radiated into the processing container. 
     According to this, the conductive layer may be coated on the upper surface, the lower surface, and the outer circumferential surface of the wavelength-shortening plate of the RLSA by using a method such as plating, spraying, or metallizing. 
     If the transmission path is deformed, propagation of the microwaves may vary. However, in the above structure, the conductive layer constituting the transmission path may be closely formed to the wavelength-shortening plate and may not be deformed due to rigidity of the wavelength-shortening plate. Thus, the microwaves may be stably propagated without being affected by the state of the microwave plasma processing apparatus so that uniform plasma can be generated. Also, a gap may not exist between the wavelength-shortening plate and the conductive and thus, the conductive layer may be formed of only a high voltage-withstanding material, thus abnormal discharge may not occur. 
     The conductive layer may be formed by spraying Cu, Al, or Ag. In spraying, a thicker layer than in plating may be formed, and the thickness of the conductive layer may be freely controlled. 
     In the apparatus, the conductive layer may include a shield member so as to prevent leakage of the microwaves. According to this, for example, some of the microwaves, which normally leak from the slots through a gap between the top plate and the conductive layer, may be prevented from being leaked into the cooling jacket. 
     According to another aspect of the present invention, there is provided a method of supplying microwaves to a microwave plasma processing apparatus which performs plasma processing on an object using plasma generated by microwaves emitted from a radial line slot antenna (RLSA), the method including: outputting microwaves from a microwave source; transmitting the microwaves outputted from the microwave source to a rectangular waveguide; converting a mode of the microwaves by using a coaxial converter; transmitting the microwaves from the coaxial converter to the coaxial waveguide by connecting an inner conductor of a coaxial waveguide to the coaxial converter to be slidable and electrically connecting the coaxial converter and the inner conductor by using a first contact member fixed to the coaxial converter; and propagating the microwaves, transmitted to the coaxial waveguide, into the RLSA. 
     According to this, since the inner conductor and the coaxial converter are formed as separate bodies and the inner conductor is connected to the coaxial converter to be slidable, the inner conductor may not be displaced in an upward direction due to thermal expansion of the RLSA and the member disposed above the RLSA. Thus, a distance between the front end part of the inner conductor and the cooling jacket may not vary before and after a temperature increase. Also, an electrical connection between the coaxial converter and the inner conductor may be guaranteed by the first contact member. As such, variation of the transmission path of the microwaves propagated into the RLSA may be prevented, and a mode of the microwaves may be stabilized, and plasma may be uniformly generated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a longitudinal cross-sectional view of a microwave plasma processing apparatus according to an embodiment of the present invention; 
         FIG. 2  is a view of a path, on which microwaves are propagated, of the microwave plasma processing apparatus of  FIG. 1 ; 
         FIG. 3  is a view of a state of the microwave plasma processing apparatus of  FIG. 1  before and after a temperature increase; 
         FIGS. 4A and 4B  are views of the result of simulation of distribution of electric field strengths near a gap; 
         FIG. 5  is a view of an engagement structure in which a rectangular waveguide and a coaxial converter are engaged with each other; 
         FIG. 6  is a longitudinal cross-sectional view of a conventional microwave plasma processing apparatus; 
         FIG. 7  is a view of a state of the conventional microwave plasma processing apparatus of  FIG. 6  before and after a temperature increase; and 
         FIG. 8  is a view of level adjustment of a lower surface of a taper connector and a lower surface of a wavelength-shortening plate. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The attached drawings for illustrating exemplary embodiments of the present invention are referred to in order to gain a sufficient understanding of the present invention, the merits thereof, and the objectives accomplished by the implementation of the present invention. Hereinafter, the present invention will be described in detail by explaining exemplary embodiments of the invention with reference to the attached drawings. Like reference numerals in the drawings denote like elements, thus, description thereof will be omitted. 
     [Entire Structure of Microwave Plasma Processing Apparatus] 
       FIG. 1  is a longitudinal cross-sectional view of a microwave plasma processing apparatus  10  according to an embodiment of the present invention. Referring to  FIG. 1 , the microwave plasma processing apparatus  10  according to the present embodiment includes a processing container  100 , a cover  200 , a transmission path  300 , a cooling mechanism  400 , and a gas supply mechanism  500 . 
     The processing container  100  is a cylindrical container which is open at the top, and is formed of a metal such as aluminum (Al). A top plate  105  (which corresponds to a dielectric window) is disposed on the open top of the processing container  100 . The top plate  105  is formed of a dielectric substance. An extension is formed in the central part of a lower surface of the top plate  105 , and an intermediate part of a lower surface of the top plate  105  extends in a circumferential direction of the top plate  105 . An O-ring  110  is disposed at a point at which the processing container  100  and the top plate  105  contact each other. As such, a processing chamber U is sealed. 
     A susceptor (holding table)  115 , on which a wafer W is disposed, is installed on a bottom of the processing container  100  via an insulator  120 . A high frequency power supply source  125   b  is connected to the susceptor  115  via a matcher  125   a , and a predetermined bias voltage is applied to the processing container  100  due to a high frequency power outputted from the high frequency power supply source  125   b . Also, a high voltage direct current (DC) power supply source  130   b  is connected to the susceptor  115  via a coil  130   a , and the wafer W is electrostatically adsorbed due to a DC voltage outputted from the high voltage DC power supply source  130   b . A vacuum pump (not shown) is attached to the processing container  100 , and a gas in the processing container  100  is exhausted via a gas exhaust pipe  135 , thus the processing chamber U is depressurized to a desired vacuum level. 
     The cover  200  includes a radial line slot antenna (RLSA)  205  (hereinafter, simply referred to as an antenna  205 ), a cooling jacket  210 , and a microwave shielding cover  215 . The antenna  205  is disposed directly on the top plate  105 . 
     A radial line slot antenna  205  is a single flat plate which is in shape of a disk. As shown in  FIG. 2  which is an enlarged longitudinal cross-sectional view of a left part of the radial line slot antenna  205 , the radial line slot antenna  205  is covered with a metal layer  205   b  on an upper surface, an outer circumferential surface, and a lower surface of a wavelength-shortening plate  205   a  that is used as a base member. The metal layer  205   b  is closely formed to the wavelength-shortening plate  205   a  and is integrally formed as one body with the wavelength-shortening plate  205   a  by using a method such as plating, spraying, or metallizing. In the present embodiment, the metal layer  205   b  is formed by spraying and melting Al. Also, the metal layer  205   b  may be formed by spraying a metal having a high electrical conductivity such as copper (Cu), gold (Au), or silver (Ag). Also, the metal layer  205   b  is an example of a conductive layer, and the conductive layer is not limited to metal. 
     A plurality of slots St (radiation holes (not shown)) that radiate microwaves are formed in the lower surface of the wavelength-shortening plate  205   a . The wavelength-shortening plate  205   a  is formed of a dielectric substance such as alumina or the like. In the antenna  205 , microwaves are propagated in a radial direction of the antenna  205  and through the slots St to be radiated into the processing chamber U. 
     The cooling jacket  210  is formed above the antenna  205  and is adjacent to the antenna  205 . The cooling jacket  210  is formed of Al and adjusts the temperature near the antenna  205 . The microwave shielding cover  215  covers the antenna  205  and the cooling jacket  210  so as to shield microwaves propagated into the antenna  205  so that the microwaves are not emitted outside the microwave plasma processing apparatus  10 . 
     Shield members  220  and  225  prevent some of the microwaves, which through the slots St, from leaking from a gap between the top plate  105  and the metal layer  205   b  of  FIG. 2  into a gap between sides of the cooling jacket  210  or a gap between the cover  200  and the processing container  100 . 
     The transmission path  300  mainly includes a rectangular waveguide  305 , a coaxial converter  310 , an inner conductor  315 , an outer conductor  340 , a taper connector  320 , and the radial line slot antenna  205 . The microwaves are transmitted to a space (hereinafter, referred to as a transmission path R of the microwaves) that is defined by the transmission path  300 . In this regard, the microwaves are propagated into the wavelength-shortening plate  205   a  and are reflected from an end face of the wavelength-shortening plate  205   a , and are matched with a discharge load and an impedance of the transmission path  300  by using a tuner (not shown), and standing waves are generated in the space of the transmission path  300  due to an interference between progressive waves and reflective waves. 
     The rectangular waveguide  305  is connected to a microwave source  335 . The coaxial converter  310  is formed to have a cone shape and converts a mode of the microwaves from the TE (Traverse Electric) mode into a mixed mode of a TE mode and a TM (Traverse Magnetic) mode. The mode-converted microwaves are transmitted to a coaxial waveguide (inner conductor  315  and outer conductor  340 ). The inner conductor  315  and the outer conductor  340  are formed of silver-plated copper. An upper part of the outer conductor  340  is screw-fixed to the rectangular waveguide  305 . A second spring member  350  is formed on an outer circumference of the outer conductor  340 . During a temperature increase, the second spring member  350  absorbs displacement of the outer conductor  340  or displacement that occurs at or near the outer conductor  340 . The outer conductor  340  and the taper connector  320  hold the metal layer  205   b  and the wavelength-shortening plate  205   a  in place and prevent displacement of the radial line slot antenna  205 . 
     The taper connector  320  is taper-shaped and is screw-fixed to the inner conductor  315  at a lower surface of the inner conductor  315 . The taper connector  320  is formed of gold-plated copper. The lower surface of the taper connector  320  extends in a flange shape in a radial direction of the antenna  205  below the antenna  205 . The extending portion of the taper connector  320  is buried in the top plate  105 . In order to maintain mechanical strength of the microwave plasma processing apparatus  10 , the taper connector  320  extends within a protrusion formed in the central part of the top plate  105 . 
     A first contact member  330  is a finger-type metal elastic body that is brazed to an inner circumference of the coaxial converter  310  in an opening of a lower end part of the coaxial converter  310 . In the above-described structure, the coaxial converter  310  and the inner conductor  315  are separated from each other, the inner conductor  315  is connected to the coaxial conductor  310  to be slidable, and the coaxial converter  310  and the inner conductor  315  can be electrically connected to each other via the first contact member  330 . 
     A bearing  355  is provided between the coaxial converter  310  and the inner conductor  315  along an outer circumference of the inner conductor  315 . An end part of the bearing  355  is fixed to the coaxial converter  310  and guides the inner conductor  315  to be slidable. As such, the inner conductor  315  is prevented from being shaked in a transverse direction, and variation of a gap can be prevented. 
     The microwaves are propagated along a metal surface of a member that defines the transmission path R of the microwaves. In particular, in the radial line slot antenna  205 , the microwaves pass through the slots, which are formed in the metal layer  205   b , from the metal layer  205   b  constituting a transmission path, and are irradiated into the processing container  100 . 
     If the transmission path is deformed, propagation of the microwaves varies. However, in the present embodiment, the metal layer  205   b  constituting the transmission path is closely formed to the wavelength-shortening plate  205   a  and is not deformed due to rigidity of the wavelength-shortening plate  205   a . Thus, the microwaves are stably propagated without being affected by the state of the microwave plasma processing apparatus  10  so that uniform plasma can be generated. Also, the wavelength-shortening plate  205   a  and the metal layer  205   b  does not have a gap between thereof, and are formed of only a high voltage-withstanding material, thus abnormal discharge does not occur. 
     Also, as in the present embodiment, when the metal layer  205   b  is coated on the upper and lower surfaces and an outer circumferential surface of the wavelength-shortening plate  205   a , the metal layer  205   b  that replaces a slot plate is thin and thus, shaves cannot be formed in the metal layer  205   b . Also, unlike the structure of a conventional slot plate, the metal layer  205   b  is not a sheet material and thus cannot be screw-fixed to the taper connector  320 . Also, the metal layer  205   b  has relatively low mechanical strength, and thus, cannot be robustly fixed by using a screw. Thus, the metal layer  205   b  may be sufficiently held by using a spring or the like. Thus, in the present embodiment, the metal layer  205   b  and the wavelength-shortening plate  205   a , which are integrally formed as one body, are held from both sides by the outer conductor  340  and the taper connector  320 . In the above-mentioned clamp structure, deviation of the wavelength-shortening plate  205   a  on which the metal layer  205   b  is coated, and the internal and outer conductors  315  and  340  (coaxial waveguide) can be prevented. As a result, variation of a transmission path of the microwaves is prevented, a radiation characteristic of the microwaves is maintained, and uniform plasma can be stably generated. 
     A second contact member  325  is disposed at the point at which the outer conductor  340  and the taper connector  320  face each other. The second contact member  325  supplements an electrical connection between the coaxial waveguide (inner conductor  315  and outer conductor  340 ) and the metal layer  205   b  by the clamp structure. In particular, the second contact member  325  is formed of a metal shield member. Thus, the reaction of the second contact member  325  is less than that of a spiral shield member, and an electrical connection between the metal layer  205   b  and the coaxial waveguide can be sufficiently obtained without applying an excessive load to the metal layer  205   b.    
     Referring to  FIG. 1 , a refrigerant pipe  360  is inserted in the inner conductor  315 . The rectangular waveguide  305  and the coaxial converter  310  are guided to a cover portion  365 . The first spring member  375  is formed between a fixing member  370  (i.e., a member connected to the inner conductor  315 ) and the cover portion  365  (i.e., a member connected to the coaxial converter  310 ), and absorbs the displacement of the radial line slot antenna  205  and displacement that occurs in an upper portion of the radial line slot antenna  205  due to a temperature increase. As such, after a temperature increase, members, such as the antenna  205  and the rectangular waveguide  305  disposed above the antenna  205 , are expanded and displaced in an upward direction. Also, even though the coaxial converter  310  connected to the rectangular waveguide  305  is displaced in an upward direction, since the inner conductor  315  and the coaxial converter  310  are formed as separate bodies and the inner conductor  315  is connected to the coaxial converter  310  to be slidable, the inner conductor  315  is not displaced together with the coaxial converter  310 . Thus, a distance between a front end part (taper connector  320 ) of the inner conductor  315  and the cooling jacket  210  does not vary before and after a temperature increase. Also, an electrical connection between the coaxial converter  310  and the inner conductor  315  is guaranteed by the first contact member  330 . As such, variation of the transmission path of the microwaves propagated into the radial line slot antenna  205  is prevented, and a mode of the microwaves is stabilized, and plasma can be uniformly generated. 
     Referring to  FIG. 2 , the rectangular waveguide  305  and the coaxial converter  310  have an engagement structure F in which the rectangular waveguide  305  and the coaxial converter  310  are engaged with each other toward an outer circumference of the transmission path  300  from an opening formed in the rectangular waveguide  305  so that a gap G formed between a lateral sidewall of the opening formed in the rectangular waveguide  305  and a lateral sidewall of the coaxial converter  310  that faces the rectangular waveguide  305  is within a predetermined range even in any facing position. The engagement structure F will be described in detail later. 
     In the cooling mechanism  400  of  FIG. 1 , a refrigerant supply source  405  and the refrigerant pipe  360  are connected to each other, and the refrigerant supply source  405  and the cooling jacket  210  are connected to each other. The refrigerant pipe  360  is a double pipe, and a refrigerant supplied from the refrigerant supply source  405  passes through an outside of the refrigerant pipe  360  from an inside of the refrigerant pipe  360  and is circulated, thus the temperature of the inner conductor  315  is adjusted. Also, the refrigerant supplied from the refrigerant supply source  405  is circulated in a flow path  210   a  of the cooling jacket  210  so that the temperature near the cooling jacket  210  is adjusted. 
     In the gas supply mechanism  500 , a gas supply source  505  and a plurality of upper gas supply lines  510  are connected to each other, and the gas supply source  505  and a shower plate  515  are connected to each other. In the shower plate  515 , a plurality of gas supply holes are uniformly formed to face the wafer W. A plasma excitation gas supplied from the gas supply source  505  is supplied in a lateral direction toward the inner space of the processing chamber U from through holes of the plurality of upper gas supply lines  510  that perforate the side wall of the processing container  100 . A process gas supplied from the gas supply source  505  is supplied to the shower plate  515  in a lateral direction and then supplied in a downward direction from the plurality of gas supply holes formed in the shower plate  515  having a lattice shape. 
     Also, in the present embodiment, even though the inner conductor  315  and the taper connector  320  are connected to each other, the inner conductor  315  and the taper connector  320  may be integrally formed as one body so that a front end of the taper connector  320  extends in a flange shape. Also, at least part of a front end of the inner conductor  315  may extend along the surface of the radial line slot antenna  205  that faces the substrate. 
     As such, variation of the transmission path of the microwaves that occurs because the taper connector  320  is not firmly fixed to the inner conductor  315 , such as a screw for connecting the inner conductor  315  and the taper connector  320  becoming loose, can be prevented. As a result, the microwaves can be more stably transmitted. 
     [Separation of the Coaxial Converter from the Inner Conductor] 
     In the present embodiment, the coaxial converter  310  and the inner conductor  315  are separated from each other. The reason why the coaxial converter  310  and the inner conductor  315  are separated from each other will be described by comparing a conventional apparatus in which the coaxial converter  310  and the inner conductor  315  are integrally formed as one body. 
     Referring to  FIGS. 6 and 7 , in a conventional microwave plasma processing apparatus using an radial line slot antenna  905 , a slot plate  905   b  is formed of a metal sheet material and is disposed to be inserted between the top plate  105  (dielectric window) disposed on a ceiling of the processing container  100  and a wavelength-shortening plate  905   a , is screw-fixed to a lower surface of the taper connector  320  and is fixed to the cooling jacket  210  by a screw  910  at an outer circumference of the taper connector  320 . As illustrated in the left and right sides of  FIG. 7 , which shows the states of the conventional microwave plasma processing apparatus after and before a temperature increase, a lower surface of the wavelength-shortening plate  905   a  and a lower surface of the taper connector  320  are displaced on the same plane before a temperature increase. 
     During processes, the processing container is maintained at a high temperature of more than 200° C. Thus, during the process, even though a circumferential part of the radial line slot antenna  905  is cooled by a cooling jacket  210 , the temperature of the radial line slot antenna  905  increases to 150° C.-165° C., the temperature of the cooling jacket  210  disposed above the antenna  905  increases to 80° C.-100° C., and the temperature of an outer conductor  340  increases to 40° C.-60° C. Also, even a region near the outer conductor  340  is maintained at a temperature of more than 100° C. in some of the processes. As a result, members such as the radial line slot antenna  905 , the outer conductor  340  of the coaxial waveguide, the rectangular waveguide  305 , etc., are thermally expanded. 
     Among the members, the wavelength-shortening plate  905   a  of the radial line slot antenna  905  is formed of a dielectric substance such as alumina (Al 2 O 3 ). Meanwhile, the cooling jacket  210 , the outer conductor  340 , and the rectangular waveguide  305  are formed of a metal such as copper (Cu) or aluminum (Al). Compared to the linear expansion coefficient of alumina which is 7.0×10 −6 (/° C.), the linear expansion coefficient of Cu is 16.7×10 −6 (/° C.) and the linear expansion coefficient of Al is 23.5×10 −6 (/° C.), which are more than twice that of alumina. Thus, after a temperature increase, each of the cooling jacket  210 , the outer conductor  340 , and the rectangular waveguide  305  is respectively expanded and displaced. For example, the relationship between a displacement P 1  of the cooling jacket  210 , displacements P 2  (lower part) and P 3  (upper part) of the rectangular waveguide  305  satisfies P 3 &gt;P 2 &gt;P 1 . Displacement of each member is accumulated and thus increases in a vertical upward direction of the microwave plasma processing apparatus  10 . 
     In this case, since the coaxial converter  310  and an inner conductor  315  are integrally formed as one body, if the rectangular waveguide  305  is displaced in an upper direction due to thermal expansion, the coaxial converter  310  and the inner conductor  315  are also displaced in an upper direction, following the displacement of the rectangular waveguide  305 . 
     In particular, the inner conductor  315  allows a refrigerant to pass through the outside of the refrigerant pipe  360  from the inside of the refrigerant pipe  360  that is piped in a double manner in the internal space of the inner conductor  315  and thus is cooled even during the process. Thus, the temperature of the inner conductor  315  and the temperature of the coaxial converter  310  during the process are lower than the temperature of the outer conductor  340  and the temperature of the rectangular waveguide  305 . Thus, the thermal expansion rate of the inner conductor  315  and the coaxial converter  310  during the process is lower than the thermal expansion rate of the outer conductor  340  and the rectangular waveguide  305 . 
     As such, after a temperature increase, the taper connector  320  disposed at a lower end of the inner conductor  315  is displaced to be the same as that of peripheral members (P 4 ). As a result, the taper connector  320  is displaced in an upper direction from the radial line slot antenna  905  so that a distance between the taper connector  320  and the cooling jacket  310  varies from a predetermined distance as designed. As such, the state of propagation of the microwaves varies, and a mode of the microwaves is unstable, thus uniformity of plasma is lost. 
     If the taper connector  320  is displaced in an upper direction from the radial line slot antenna  905 , the slot plate  905   b  that is screw-fixed to the lower surface of the taper connector  320  is also displaced in an upper direction. As such, the transmission path of the microwaves varies due to deviation of the position of the slot plate  905   b , thus plasma is non-uniformly generated. 
     Referring to  FIG. 8 , each of the rectangular waveguide  305 , the coaxial converter  310 , and the taper connector  320  is screw-fixed and assembled, a shim  380  is engaged between the rectangular waveguide  305  and the coaxial converter  310  and level of the shim  380  is adjusted so that the lower surface of the taper connector  320  and the lower surface of the wavelength-shortening plate  205   a  are disposed on the same plane. For example, in  FIG. 8 , two shims  380   a  and  380   b  are engaged so that levels of the lower surface of the taper connector  320  and the lower surface of the wavelength-shortening plate  205   a  are adjusted. Due to this level adjustment, during assembly, a distance between the cooling jacket  210  disposed on the surface of the wavelength-shortening plate  205   a  and the taper connector  320  can be defined as a predetermined distance as designed. However, during the process, if the taper connector  320  is displaced in an upper direction in relation to the radial line slot antenna  905 , fine level adjustment performed during assembly is meaningless, and as described above, the transmission path Ra of the microwaves varies. 
     The variation of the transmission path of the microwaves as described above causes loss of stability and reliability of the microwave plasma processing apparatus during the process. Thus, in the microwave plasma processing apparatus  10  according to the present embodiment, first, as illustrated in  FIGS. 1 and 2 , the coaxial converter  310  and the inner conductor  315  are separated from each other. 
     The inner conductor  315  is connected to the coaxial converter  310  to be slidable. The first contact member  330  for electrically connecting the coaxial converter  310  and the inner conductor  315  is formed between the coaxial converter  310  and the inner conductor  315 . 
     As such, as illustrated in  FIG. 3 , during the process, even though metal members such as the cooling jacket  210 , the outer conductor  340 , and the rectangular waveguide  305  are displaced (P 1 ˜P 3 ) in a vertical upward direction in relation to the processing container  100 , the inner conductor  315  and the coaxial converter  310  are formed as separate bodies and thus, the inner conductor  315  is not displaced due to not being affected by thermal expansion of the rectangular waveguide  305 . 
     [First Spring Member] 
     In addition, the first spring member  375  is attached between a member (fixing member  370 ) connected to the inner conductor  315  and a member (cover portion  365 ) connected to the coaxial converter  310 , and is contracted according to the degree of thermal expansion of the outer conductor  340  and the rectangular waveguide  305 , and thus absorbs displacement in an upper direction of each member. Due to the first spring member  375 , the position of the inner conductor  315  can be maintained at a position before a temperature increase, even after a temperature increase. 
     As such, a gap Ra (see  FIG. 2 ) that exists between the taper connector  320  of the front end part of the inner conductor  315  and the cooling jacket  210  does not vary, and a distance between the taper connector  320  and the cooling jacket  210  is set as a predetermined distance as designed. Thus, variation of the distance between the taper connector  320  and the cooling jacket  210  can be prevented, and variation of the transmission path of the microwaves can be avoided. As such, the mode of the microwaves is stabilized so that plasma can be uniformly generated. Thus, the stability and reliability of the microwave plasma processing apparatus  10  can be improved. 
     [Clamp Structure] 
     In addition, the taper connector  320  includes an extension portion  320   a  disposed at an outer circumference thereof. In other words, the front end of the taper connector  320  extends from a surface, facing a wafer, of the radial line slot antenna  205  in the radial direction of the antenna  205 . In the present embodiment, a flange-shaped extension is formed in the taper connector  320 . 
     The metal layer  205   b  and the wavelength-shortening plate  205   a  may be closely formed to each other and integrally formed, and are held between the extension portion  320   a  of the taper connector  320  and the outer conductor  340  of the coaxial waveguide. Referring to the clamp structure, deviation of positions of the radial line slot antenna  205  and the internal and outer conductors (coaxial waveguide) can be prevented. 
     In addition, the extension portion  320   a  of the taper connector  320  is formed to extend within a diameter of the protrusion portion  105   a  protruding from a side of the wafer W to the wafer W in the middle of the top plate  105  formed in the opening of ceiling of the processing container  100 . 
     Thus, the extension portion  320   a  of the taper connector  320  does not extend to the outside of the protrusion portion  105   a  formed in the central part of the top plate  105 . As such, the mechanical strength of the top plate  105  can be guaranteed. 
     [Second Spring Member] 
     The second spring member  350  is formed to be adjacent to the outer conductor  340  that supports the rectangular waveguide  305 , and forces the processing container  100  in the vertical downward direction with respect to the outer conductor  340  contrary to a force in which the microwave plasma processing apparatus  10  is thermally expanded in the vertical upward direction of the processing container  100 . 
     Thus, the second spring member  350  can absorb displacement of the outer conductor  340  and a peripheral member of the outer conductor  340  in the vertical upward direction of the processing container  100 . As a result, due to the first spring member  375 , the second spring member  350 , and the clamp structure, before and after a temperature increase, a distance between the taper connector  320  and the cooling jacket  210  is maintained as a predetermined distance as designed without varying the gap Ra, thus variation of the transmission path R of the microwaves can be prevented. 
     In addition, the first spring member  375  may be a coil-shaped spring member, a thermostable metal seal or plate-shaped spring member. In addition, the second spring member  350  may be a coil-shaped spring member or a thermostable metal seal. 
     [Prevention of Shake of Inner Conductor] 
     The bearing  355  that is fixed to the coaxial converter  310  and supports the inner conductor  315  to be slidable, is formed at a hollow of the coaxial converter  310 . Thus, the inner conductor  315  is guided by the first contact member  330  and the bearing  355 . Thus, movement of an axis Oc of the inner conductor  315  can be suppressed. 
     [Integrally Forming Metal Layer and Wavelength-Shortening Plate as One Body] 
     In the radial line slot antenna  205 , the metal layer  205   b  is coated on an upper surface, an outer circumferential surface, and a lower surface of the wavelength-shortening plate  205   a  by using a method such as plating, spraying, or metallizing. The antenna  205  uses the metal layer  205   b  as the transmission path of the microwaves and radiates the microwaves that are propagated into the wavelength-shortening plate  205   a  from the coaxial waveguide, into the processing container  100  through the plurality of slots formed in the portion of the metal layer  205   b  formed on the lower surface of the wavelength-shortening plate  205   a.    
     Thus, the metal layer  205   b  constituting the transmission path is closely formed to the wavelength-shortening plate  205   a  and is not deformed due to the rigidity of the wavelength-shortening plate  205   a . Thus, the microwaves are stably propagated without being affected by the state of the microwave plasma processing apparatus  10  so that uniform plasma can be generated. Also, the wavelength-shortening plate  205   a  and the metal layer  205   b  does not have a gap between thereof, and are formed of only a high voltage-withstanding material, thus abnormal discharge does not occur. As a result, uniform plasma can be generated. 
     In addition, the metal layer  205   b  may be formed by spraying Cu, Al, or Ag. A thicker layer can be formed by spaying, compared to by plating, and the thickness of the metal layer  205   b  can be freely controlled. 
     [Gap G] 
     As illustrated in  FIG. 5 , when the mode of the microwaves transmitted to the rectangular waveguide  305  is converted and the transmission path of the microwaves is assembled by inserting the coaxial converter  310  in the opening of the rectangular waveguide  305 , due to crossing over, a gap G is formed between the lateral sidewall of the rectangular waveguide  305  and the lateral sidewall of the coaxial converter  310  that faces the lateral sidewall of the rectangular waveguide  305 . 
     The gap G exists in a position in which the mode of the microwaves is converted from the TE mode into a mixed mode of a TE mode and a TM mode. In addition, the microwaves are reflected from a reflective end  305   a  of the rectangular waveguide  305  in the vicinity of the gap G and thus, the electric field of the microwaves may be scattered. 
     Actually, even though a distance between the reflective end  305   a  of the rectangular waveguide  305  and the gap G is designed as λg/2 so that node of the microwaves may be placed in the reflective end  305   a  and the gap G, abnormal discharge is not suppressed. Thus, in addition to setting the distance between the reflective end  305   a  of the rectangular waveguide  305  and the gap G, an engagement structure is formed in the rectangular waveguide  305  and the coaxial converter  310  so as to set the gap G. 
     [Setting of Gap] 
     First, in order to specifically determine a proper range of the engagement structure F and the gap G, distribution of electric field strengths of the microwaves near the gap G was obtained by simulation. 
     The electric field strengths at positions P 1 ˜P 4  shown in  FIG. 4A  were calculated by simulation and the results are shown in  FIG. 4B . Referring to the results, while the electric field strengths of the microwaves at the positions P 1  and P 3  are high, the electric field strengths of the microwaves at the positions P 2  and P 4  are low. In addition, as the gap (leak path thickness) G increases, electric field strengths increase. If the gap G is uniform, even if the size of the gap G varies by 0.1 mm, electric field strengths do not increase to extremes. 
     According to the Paschen&#39;s Law, as shown in the formula V=f(pd), a discharge firing voltage V between parallel electrodes is expressed as a product of gas pressure ‘p’ and a distance ‘d’ between the electrodes. Since pressure of gas at the gap G is an atmospheric pressure (1 atm=1.013×10 5  Pa), as the distance d between the electrodes decreases, discharge occurs at a lower voltage V. Meanwhile, if a distance (which corresponds to the distance d) between the gaps G is non-uniform, electric field strengths are subject to be biased. Thus, the distance between the gaps G is set to be within the range of (k±n)(n≦0.1) mm with respect to a predetermined reference distance k (k≧0.3) mm so that the gap G may be set in the state where discharge does not easily occur and electric field strengths are not easily biased, and occurrence of abnormal discharge can be prevented. 
     Thus, even though the ring-shaped gaps G are formed in any facing position, a high-degree engagement structure F (see  FIGS. 2 and 5 ) is formed at the rectangular waveguide  305  and the coaxial converter  310  toward an outer circumference of the transmission path  300  from the gaps G so that the gaps G are within a predetermined range. Specifically, the engagement structure F is formed by setting the reference distance k of the gaps G to 0.3 mm so that, even if the ring-shaped gaps G are formed in any facing position, the gaps G are set within a range of (k±n) mm (n≦0.1). A gap (i.e., within about 20% of a maximum of a distance difference of the gaps G) that is sufficiently smaller than the gaps G is allowed in the engagement structure F in consideration of tolerance that occurs during assembling so that any worker can easily set the gaps G within a predetermined distance difference as designed. As such, occurrence of abnormal discharge in the gaps G between the rectangular waveguide  305  and the coaxial converter  310  can be avoided. 
     [Coating with Insulating Material] 
     The rectangular waveguide  305  and the coaxial converter  310  near the gaps G are coated with an insulating material. The insulating material may be polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkylvinylether (PFA) copolymers, alumina (alumite processing, spraying), or the like. As such, a potential difference between gaps can be reduced so that occurrence of abnormal discharge can be more easily suppressed. 
     As described above, referring to the microwave plasma processing apparatus  10  according to the present embodiment, variation of the transmission path of the microwaves due to thermal expansion can be suppressed. As such, the stability and reliability of the microwave plasma processing apparatus  10  can be remarkably improved. 
     In the above embodiment, operations of the elements are related with each other and can be substituted as a series of operations in consideration of the relation. By substituting the operations of the elements in this way, the embodiment of the microwave plasma processing apparatus can be used as an embodiment of a method of supplying the microwaves using the microwave plasma processing apparatus. 
     While this invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 
     For example, the metal layer may be formed by metallizing. In this case, the metal layer such as a Mo—Mn layer formed by metallizing has a high resistance and thus, a metal layer such as an Ag—Cu—Ti layer may be used. 
     In addition, the above-described formation of the slot plate  905   b  and the wavelength-shortening plate  205   a  as one body (i.e., antenna  205  in which the wavelength-shortening plate  205   a  is coated with the metal layer  205   b ) or the engagement structure F may be provided in the microwave plasma processing apparatus  10  together with a structure where the coaxial converter  310  and the inner conductor  315  are separated from each other, but is not an essential condition of the present apparatus. 
     In addition, gas may be supplied only from the upper gas supply lines  510  or the shower plate  515 . Also, instead of the gas supply mechanism  500  or in addition to the gas supply mechanism  500 , a gas path is formed in the top plate  105 , and the top plate  105  may be used as a shower plate. 
     As described above, according to the present invention, when the microwaves are supplied into the processing container  100  by using the antenna  205 , variation of the transmission path of the microwaves due to thermal expansion can be suppressed, and scattering of plasma can be prevented.