Abstract:
In a substrate processing apparatus, a control electrode ( 131 ) separates a process space ( 11 C) including a substrate to be processed and a plasma formation space ( 11 B) not including the substrate. The control electrode includes a conductive member formed in a processing vessel and having a plurality of apertures ( 131   a ) for passing plasma. A surface of the control electrode is covered by an aluminum oxide or a conductive nitride. In the substrate processing apparatus, a gas containing He and N 2  is supplied into the processing vessel. In the plasma formation space, there is formed plasma under a condition in which atomic state nitrogen N* are excited. The atomic state nitrogen N* are used to nitride a surface of the substrate.

Description:
TECHNICAL FIELD  
       [0001]     The present invention generally relates to plasma processing apparatuses and more particularly to a microwave plasma processing apparatus.  
         [0002]     Plasma process and plasma processing apparatus constitute indispensable technology for fabricating ultrafine semiconductor devices such as the one called deep submicron device or deep sub-quarter micron device having a gate length near 0.1 μm or less, or for fabricating high-resolution flat panel display device including a liquid crystal display device.  
         [0003]     Conventionally, various plasma excitation methods have been employed in the plasma processing apparatus used for fabricating semiconductor devices or liquid crystal display devices. Particularly, high-frequency plasma apparatuses of parallel plate type or induction-coupled type plasma apparatus are used commonly. However, such a conventional plasma processing apparatuses suffers from the problem of non-uniform plasma formation in that the region in which high electron density is achieved is substantially limited, and there has been a difficulty in conducting a uniform processing over the entire surface of the substrate with a large processing rate or throughput. This problem becomes particularly serious in the case of processing a substrate of large diameter. Further, such a conventional plasma processing apparatus has inherent problems, associated with its high electron temperature, in that damages are caused in the semiconductor devices formed on the substrate. Further, severe metal contamination may be caused as a result of sputtering of the chamber wall. Thus, it is becoming difficult with conventional plasma processing apparatuses to satisfy the stringent demand of further miniaturization and further improvement of productivity of semiconductor devices or flat display devices.  
         [0004]     Meanwhile, there has been a proposal of a microwave plasma processing apparatus that uses high-density plasma excited, not by d.c. magnetic field, but by a microwave electric field. For example, there is a proposal of a plasma processing apparatus that excites plasma by emitting a microwave into a processing vessel from a planar antenna (radial line slot antenna) having a number of slots arranged so as to produce a uniform microwave, for emitting a microwave into a processing vessel. In this plasma processing apparatus, the microwave electric field induces plasma by causing ionization in the gas in the vacuum vessel. Reference should be made to Japanese Laid-Open Patent Application 9-63793. By using the microwave plasma excited according to such a process, it becomes possible to realize a high-plasma density over a wide area right underneath the antenna, and uniform plasma processing becomes possible with short time period. Further, the microwave plasma thus excited has an advantageous feature of low electron temperature as a result of excitation of the plasma by using a microwave, and it becomes possible to avoid the problem of damages or metal contamination caused in the substrate. Further, it becomes possible to excite uniform plasma over a substrate of large area, and thus, the plasma processing apparatus can easily handle the fabrication of semiconductor devices on a large-diameter semiconductor wafer or fabrication of large flat panel display devices.  
       BACKGROUND ART  
       [0005]      FIG. 1  shows the schematic construction of a conventional induction-coupled plasma processing apparatus  1 .  
         [0006]     Referring to  FIG. 1 , the plasma processing apparatus  1  includes a processing vessel  2  of a quartz dome evacuated by an evacuation line  2 A, and there is provided a stage  3  in a process space  2 B defined by the processing vessel  2  such that the stage  2  is rotated by a rotating mechanism  3 A. Further, a substrate  4  is held on the stage  3 . Further, an inert gas such as Ar and a process gas such as oxygen or nitrogen are supplied to the process space  2 B via a process gas supply line  2 C. Further, there is provided a coil  5  around the top part of the processing vessel  2  at the outside thereof, and high-density plasma  2 D is inducted at the top part of the process space  2 B by driving the coil  5  by a d.c. power source.  
         [0007]     In the plasma processing apparatus  1  of  FIG. 1 , the radicals of the process gas formed with the high-density plasma  2 D reach the surface of the substrate  4  and the substrate processing such as oxidation or nitridation is achieved.  
         [0008]     In such a conventional induction-coupled plasma processing apparatus  1 , on the other hand, there exists a drawback in that the high-density plasma  2 D is localized at the top part of the processing vessel and there appears an extremely non-uniform distribution in the radicals that are formed with the plasma. Particularly, the non-uniformity of the radical concentration in the radial direction of the substrate is not resolved even when the stage  3  is rotated by the rotating mechanism  3 A.  
         [0009]     Thus, in the conventional induction-coupled plasma processing apparatus  1 , the plasma processing apparatus was designed such that the substrate  4  is separated from the region in which the high-density plasma  2 D is formed with a large distance for realizing as uniform radical concentration distribution as possible at the surface of the substrate  4 . As a result of such a construction, on the other hand, the overall size of the substrate processing apparatus  1  is increased inevitably. Further, the amount of the radicals reaching the substrate  4  is reduced. These problems become particularly serious in the technology of current trend of processing a large-diameter substrate.  
         [0010]     On the other hand, there is a proposal of a microwave plasma processing apparatus that uses high-density plasma induced, not by an induction magnetic field but by a microwave electric field. For example, there is proposed a plasma processing apparatus that uses a planar antenna (radial line slot antenna) having a large number of slots arranged so as to produce a uniform microwave, for emitting a microwave into a processing vessel. In this apparatus, the microwave electric field thus induced is used to excite plasma by causing ionization in the gas in the vacuum vessel. Reference should be made to Japanese Laid-Open Patent Application 9-63793. By using the microwave plasma excited according to such a process, it becomes possible to realize a high-plasma density over a wide area right underneath the antenna, and uniform plasma processing becomes possible with short time period. Further, the microwave plasma thus excited has an advantageous feature of low electron temperature as a result of excitation of the plasma by using a microwave, and it becomes possible to avoid the problem of damages or metal contamination caused in the substrate. Further, it becomes possible to excite uniform plasma over a substrate of large area, and thus, the plasma processing apparatus can easily handle the fabrication of semiconductor devices on a large-diameter semiconductor wafer or fabrication of large flat panel display devices.  
         [0011]      FIG. 2  shows the construction of a microwave plasma processing apparatus  10  that uses such a radial line slot antenna as proposed before by the inventor of the present invention.  
         [0012]     Referring to  FIG. 2 , the microwave plasma processing apparatus  10  includes a processing chamber  11  evacuated at a plurality of evacuation ports  11   a , and there is provided a stage  13  inside the processing chamber  11  for supporting a substrate  12  to be processed. In order to achieve uniform evacuation of the processing chamber  11 , there is provided a ring-shaped space  11 A around the stage  13 , and the processing chamber  11  is evacuated uniformly via the space  11 A and further via the evacuation ports  11   a  by arranging the evacuation ports  11   a  communicating with the space  11 A in axial symmetry with respect to the substrate.  
         [0013]     On the processing chamber  11 , there is provided a plate-like shower plate  14  formed of a low-loss dielectric such as Al 2 O 3  or SiO 2  as a part of the outer wall of the processing chamber  11  at a location facing the substrate  12  held on the stage  13 , wherein the shower plate  14  is provided via a seal ring not illustrated and includes a number of apertures  14 A. Further, a cover plate  15  also of a low-loss dielectric such as Al 2 O 3  or SiO 2  is provided at the outer side of the shower plate  14  via another seal ring not illustrated.  
         [0014]     The shower plate  14  is provided with a gas passage  14 B at a top surface thereof, and each of the apertures  14 A are provided so as to communicate with the gas passage  14 B. Further, there is provided a gas supply passage  14 C in the interior of the shower plate  14  in communication with a gas supply port lip provided at an outer wall of the processing vessel  11 . Thus, the plasma-excitation gas such as Ar or Kr supplied to the gas supply port  11   p  is forwarded to the apertures  11 A via the supply passage  14 C and further via the passage  14 B and is released to the process space  11 B right underneath the shower plate  14  inside the processing vessel  11  from the foregoing apertures  14 A.  
         [0015]     On the processing vessel  11 , there is further provided a radial line slot antenna  20  at the outer side of the cover plate  15  with a separation of 4-5 mm from the cover plate  15 . The radial line slot antenna  20  is connected to an external microwave source (not illustrated) via a coaxial waveguide  21  and causes excitation of the plasma-excitation gas released into the process space  11 B by the microwave from the microwave source. It should be noted that the cover plate  15  and the radiation surface of the radial line slot antenna are contacted closely, and there is provided a cooling block  19  on the antenna  20  for cooling the antenna. The cooling block  19  includes a cooling water passage  19 A.  
         [0016]     The radial line slot antenna  20  is formed of a flat, disk-shaped antenna body  17  connected to an outer waveguide tube  21 A of the coaxial waveguide  21  and a radiation plate  16  provided at the opening of the antenna body  17 , wherein the radiation plate  16  is formed with a number of slots and a retardation plate of a dielectric plate having a constant thickness is interposed between the antenna body  17  and the radiation plate  16 .  
         [0017]     In the radial line slot antenna  20  having such a construction, the microwave fed thereto from the coaxial waveguide  21  propagates along a path between the disk-shaped antenna body  17  and the radiation plate  16  in the radial direction, wherein the microwave thus propagating undergoes compression of wavelength as a result of the existence of the retardation plate  18 . Thus, by forming the slots concentrically in correspondence to the wavelength of the microwave thus propagating in the radial direction, and by forming the slots so as to form a perpendicular angle with each other, it becomes possible to emit a plane wave having a circular polarization from the radial line slot antenna  20  in the direction substantially perpendicular to the radiation plate  16 .  
         [0018]     By using such a radial line slot antenna  20 , there is formed uniform high-density plasma in the process space  11 B right underneath the shower plate  14 . The high-density plasma thus formed has a feature of low electron temperature and the occurrence of damages in the substrate  12  to be processed is avoided. Further, there occurs no metal contamination caused by sputtering of the chamber wall of the processing vessel  11 .  
         [0019]     Thus, by supplying a process gas, such as an O 2  gas, an NH 3  gas, or a mixed gas of an N 2  gas and an H 2  gas, to the gas inlet port  11   p  of the substrate processing apparatus  10  of  FIG. 2  in addition to the plasma-excitation gas such as Ar or Kr, there is caused an excitation of active species such as atomic state oxygen O* or hydrogen nitride radicals NH* in the process space  11 B by the high-density plasma, and it becomes possible to conduct oxidation processing, nitridation processing or oxynitridation processing on the surface of the substrate  12 .  
         [0020]     Further, there is proposed a substrate processing apparatus  10 A shown in  FIG. 3  having a construction similar to the substrate processing apparatus  10  of  FIG. 2  except that there is provided a lower shower plate  31  at the lower side of the shower plate  14 . The lower shower plate  31  is provided with a process gas passage  31 A communicating with a process gas inlet port  11   r  formed at the surface of the processing vessel  1  and a large number of process gas inlet nozzle openings  31 B are formed in communication with the process gas passage  31 A. Further, the lower shower plate  31  is provided with large apertures for passing the process gas radicals formed in the space  11 B.  
         [0021]     Thus, in the substrate processing apparatus  10 A of  FIG. 3 , there is defined another process space  11 C underneath the lower shower plate  31 . By forming the lower shower plate  31  by a conductive material such as a stainless steel having a passivation surface by aluminum oxide (Al 2 O 3 ) in such an apparatus, it becomes possible to block the penetration of microwave to the process space  11 C. Thereby, the excitation of plasma is limited in the process space  11 B right underneath the upper shower plate  14 , and the radicals Kr* of Kr or Ar* of Ar penetrate into the process space  11 C through the large apertures formed in the shower plate  31  after excitation in the space  11 B. The radicals Kr* or Ar* thus penetrated into the process space  11 C cause activation of the process gas released from the nozzle apertures  31 B, and the processing of the substrate  12  is achieved by the process gas radicals thus activated.  
         [0022]     In the substrate processing apparatus  10 A of  FIG. 3 , it should be noted that the microwave is expelled from the process space  11 C by forming the lower shower plate  31  by a conductive material, and the damaging of the substrate by microwave is avoided.  
         [0023]     In the substrate processing apparatus  10 A of  FIG. 3 , it is also possible to conduct a plasma CVD process by introducing a CVD source gas from the lower shower plate  31 . Further, it is possible to conduct a dry etching process by introducing a dry etching gas from the lower shower plate  31  and applying a high-frequency bias to the stage  13 .  
         [0024]     Thus, in the substrate processing apparatus of  FIG. 2  of  FIG. 3 , Kr radicals (Kr*) of intermediate excitation state having an energy of about 10 eV are excited at the time of conducting an oxidation processing, by introducing a Kr gas and an oxygen gas into the process space  11 B. The Kr radicals thus excited cause efficient excitation of atomic state oxygen O* according to the reaction
 
O 2 →O*+O*,
 
 while the atomic state oxygen O* thus excited cause the desired oxidation of the surface of the substrate  12 . 
 
         [0026]     In the case of conducting a nitridation processing of the substrate  12 , a Kr gas and an ammonia gas, or a Kr gas and a nitrogen gas and a hydrogen gas are introduced. In this case, the excited Kr radicals (Kr*) or Ar radicals (Ar*) cause the excitation of hydrogen nitride radicals NH* according to the reaction
 
NH 3 →NH*+2H*+ e   − ,
 
or
 
N 2 +H 2 →NH*+NH*,
 
 wherein the hydrogen nitride radicals thus excited cause the desired nitridation processing of the substrate of the surface  12 . 
 
         [0028]     Meanwhile, there are cases in which it is preferable to use atomic state nitrogen (N*), free from hydrogen and having a strong nitriding power, at the time of the nitridation processing of the substrate. The atomic state nitrogen N* are formed according to the reaction
 
N 2 →N*+N*,
 
 wherein it should be noted that such a reaction requires the energy of 23-25 eV. This means that it is not possible to excite the atomic state nitrogen N* according to the foregoing reaction, as long as Kr or Ar plasma is used. As noted previously, the energy of the Kr radicals or Ar radicals obtained by the Kr or Ar plasma is merely in the order of 10 eV. 
 
         [0030]     Thus, even when there is made an attempt to supply a nitrogen gas in the substrate processing apparatus of  FIG. 2  or  FIG. 3  in place of the Kr gas or the Ar gas, merely the reaction
 
N 2 →N 2   +   +e   − ,
 
 is obtained, and there is caused no desired atomic state oxygen N*. 
 
         [0032]      FIG. 4  shows the relationship between the state density of the Kr plasma and the excitation energy of the atomic state nitrogen N*, hydrogen nitride radicals NH* and nitrogen atoms N 2   + .  
         [0033]     Referring to  FIG. 4 , it can be seen that the state density of the Kr plasma is large at the low energy side, while the state density shows a rapid decrease with increase of the energy. Such a plasma cannot achieve efficient excitation of the desired nitrogen radicals.  
       DISCLOSURE OF THE INVENTION  
       [0034]     Accordingly, it is a general object of the present invention to provide a novel and useful substrate processing apparatus wherein the foregoing problems are eliminated.  
         [0035]     Another and more specific object of the present invention is to provide a substrate processing method and apparatus capable of forming nitrogen radicals N* efficiently.  
         [0036]     Another object of the present invention is to provide a method of processing a substrate by using a substrate processing apparatus which has such a construction that a process space, in which a substrate to be processed is contained, is separated from a plasma formation space, in which the substrate to be processed is not contained, by a control electrode in a processing vessel, characterized by the steps of:  
         [0037]     supplying a gas containing He and N 2  to said processing vessel;  
         [0038]     forming plasma in said plasma formation space under a condition such that there is caused excitation of atomic state nitrogen N* in said plasma; and  
         [0039]     nitriding a surface of the substrate to be processed by said atomic state nitrogen N* in said process space.  
         [0040]     Another object of the present invention is. to provide a substrate processing apparatus, comprising:  
         [0041]     a processing vessel defined by an outer wall and having a stage for holding a substrate to be processed thereon;  
         [0042]     an evacuation system coupled to said processing vessel;  
         [0043]     a plasma gas supplying part supplying a plasma excitation gas and a process gas into said processing vessel;  
         [0044]     a microwave window provided on said processing vessel so as to face said substrate to be processed; and  
         [0045]     a control electrode provided between said substrate to be processed on said stage and said plasma gas supplying part so as to face said substrate to be processed and separating a plasma excitation space containing said microwave window and a process space containing said substrate to be processed,  
         [0046]     said control electrode comprising a conductive member having a plurality of apertures for passing plasma formed in said processing vessel therethrough, and  
         [0047]     a surface of said control electrode being covered by any of aluminum oxide or electrically conductive nitride.  
         [0048]     Another object of the present invention is to provide a substrate processing apparatus, characterized by:  
         [0049]     a processing vessel defined by a wall of quartz glass and having a stage for holding a substrate to be processed;  
         [0050]     an evacuation system coupled to said processing vessel;  
         [0051]     a plasma gas supplying part supplying a plasma excitation gas and a process gas to said processing vessel;  
         [0052]     a control electrode provided so as to face said substrate to be processed on said stage and dividing an interior of said processing vessel into a process space containing said substrate to be processed and a plasma excitation space; and  
         [0053]     an induction coil provided outside said quartz glass wall in correspondence to said plasma excitation space,  
         [0054]     said control electrode comprising a conductive member having a plurality of apertures passing therethrough plasma formed in said processing vessel, and  
         [0055]     a surface of said control electrode being covered with any of aluminum oxide or electrically conductive nitride.  
         [0056]     According to the present invention, it becomes possible to form plasma having the energy sufficient for causing excitation of atomic state nitrogen N* in the substrate processing apparatus by using He for the plasma excitation gas, and it becomes possible to conduct an efficient nitridation of the substrate by using the atomic state nitrogen N* thus excited. By separating the plasma excitation space in which the high-density plasma is excited from the process space in which the substrate is included by means of the control electrode, it becomes possible to reduce the plasma energy in the process space to the level suitable for substrate processing. Further, it becomes possible to trap the positive ions formed in the plasma excitation space. In the case of applying the present invention to the substrate processing apparatus that uses microwave-excited plasma, it becomes possible to avoid excessive increase of the plasma energy by conducting the plasma excitation by using a microwave having the frequency of about 28 GHz or more. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0057]      FIG. 1  is a diagram showing the construction of a conventional induction coupled plasma processing apparatus;  
         [0058]      FIG. 2  is a diagram showing the construction of a previously proposed microwave substrate processing apparatus;  
         [0059]      FIG. 3  is a diagram showing the construction of another previously proposed microwave substrate processing apparatus;  
         [0060]      FIG. 4  is a diagram explaining the characteristics of plasma excitation in the microwave substrate processing apparatus of  FIG. 2  or  FIG. 3 ;  
         [0061]      FIG. 5  is a diagram showing the construction of a microwave substrate processing apparatus according to a first embodiment of the present invention;  
         [0062]      FIG. 6  is a diagram showing a part of the microwave substrate processing apparatus of  FIG. 5 ;  
         [0063]      FIG. 7  is a diagram showing the characteristics of plasma excitation in the microwave substrate processing apparatus of  FIG. 5 ;  
         [0064]      FIG. 8  is a diagram showing a modification of the microwave plasma processing apparatus of  FIG. 5 ;  
         [0065]      FIG. 9  is a diagram showing the construction of a microwave plasma processing apparatus according to a second embodiment of the present invention; and  
         [0066]      FIG. 10  is a diagram showing the construction of an induction coupled plasma processing apparatus according to a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [heading-0067]     [First Embodiment] 
         [0068]      FIG. 5  shows the construction of a substrate processing apparatus  100  according to a first embodiment of the present invention. In  FIG. 5 , those parts corresponding to the parts described previously are designated by the same reference numerals and the description thereof will be omitted.  
         [0069]     Referring to  FIG. 5 , the shower plate  14  is mounted on the processing vessel  11  via a seal  11   s , and the cover plate  15  is mounted on the shower plate  14  via a seal  11   t . Further, the radial line slot antenna  20  is mounted on the processing vessel  11  via a seal  11   u.    
         [0070]     Further, in the substrate processing apparatus  100  of  FIG. 5 , the interface between the emission plate  16  and the cover plate  15  is evacuated via a ring-shaped groove  11   g  formed at the top part of the processing vessel  11  in the region where the processing vessel makes an engagement with the emission plate and further via an evacuation port  11 G communicating with the ring-shaped groove  11   g . After evacuation, a He gas is introduced into the foregoing interface with a pressure of about 0.8 atmospheres as a thermal conducting medium. The He gas thus introduced is confined therein by closing the valve  11 V.  
         [0071]     In the substrate processing apparatus  100  of  FIG. 5 , it should be noted that the lower shower plate  31  used in the substrate processing apparatus  10 A of  FIG. 3  is removed and a control electrode  131  of a conductive member is formed, wherein the control electrode  31  has a lattice shape as represented in  FIG. 6  and is formed so as to separate the plasma excitation space  11 B and the process space  11 C.  
         [0072]     Referring to  FIG. 6 , the lattice-shaped control electrode  131  is formed with large number of apertures  132  having a size set such that there occurs free passage of the radicals excited in the plasma excitation spate  11 B, and thus, the plasma excited in the plasma excitation space  11 B cause diffusion freely into the process space  11 C through the control electrode  131 .  
         [0073]     In the construction of  FIG. 5 , it should be noted that the lattice-shaped control electrode  131  is grounded, and thus, the microwave introduced into the plasma excitation space  11 B from the radial line slot antenna  11 B is reflected by the lattice shaped control electrode  131 , and there is caused no invasion of the microwave into the process space  11 C. Thus, the problem of the microwave causing damages in the substrate  12  is not caused in the substrate processing apparatus  100  of  FIG. 5 .  
         [0074]     It should be noted that the lattice-shaped control electrode  131  can be formed by W, Ti, or the like, wherein it is possible to increase the resistance against plasma irradiation by forming a layer  131   a  of a conductive nitride such as WN or TiN on the surface thereof. Further, it is possible to form such a lattice-shaped control electrode  131  by using a quartz glass and provide the conductive nitride layer  131   a  on the surface thereof. Further, in the substrate processing apparatus  100 , it should be noted that the sidewall surface of the processing vessel  11  is covered by a quartz liner  11 D for the part corresponding to the plasma excitation space  11 B  
         [0075]     In the substrate processing apparatus  100  of  FIG. 5 , a He gas and an N 2  gas are introduced to the process gas inlet port  11   p , and a microwave of about 28 GHz is supplied to the radial line slot antenna. Typically, the process pressure in the processing vessel  11  is set to the range of 66.5-266 Pa (0.5-2 Torr), and nitridation processing or oxynitridation processing of the substrate  12  is conducted in the temperature range of 200-500° C.  
         [0076]      FIG. 7  shows the state density of the plasma excited in the substrate processing apparatus  100  of  FIG. 5  for the case He is used for the plasma gas.  
         [0077]     Referring to  FIG. 7 , it should be noted that the use of He having a characteristically small collision cross-section for the plasma gas causes significant acceleration in the excited He radicals He* with the microwave electric field, and as a result, there is caused significant increase of plasma energy to the level suitable for excitation of the atomic state nitrogen N*. On the other hand, it can be seen that the efficiency of excitation of the hydrogen nitride radicals NH* or nitrogen ions N 2   + , which are excited efficiently in the case Kr is used for the plasma gas, is reduced significantly.  
         [0078]     Thus, in the present invention, efficient excitation of the atomic state nitrogen N* is achieved in the substrate processing apparatus  100  at the high plasma energy of 23-25 eV by using He for the plasma gas. In order to avoid excessive increase of the electron temperature in the plasma, the present invention uses a microwave source  22  that produce a microwave of the frequency higher than the previously proposed frequency, such as about 28 GHz or more, for driving the radial line slot antenna  20 . Thereby, it is possible to select the frequency of the microwave source from the frequencies such as about 2.4 GHz or about 8.3 GHz. Further, by separating the plasma excitation space  1 lB and the process space  11 C by the control electrode  131 , it is possible to reduce the electron temperature and the plasma energy to a level suitable for substrate processing.  
         [0079]     Particularly, it should be noted that the control electrode is protected effectively from the high-energy plasma by forming a conductive nitride such as an Al 2 O 3  passivation film on the surface of the control electrode  131  as explained already. Further, the problem of sputtering of the inner wall of the processing vessel by the high-energy plasma and the associated problem of contamination of the substrate are avoided by covering the inner wall of the processing vessel  11  by a quartz liner  11 D for the part corresponding to the plasma excitation region  11 B.  
         [0080]      FIG. 8  shows the construction of a substrate processing apparatus  100 A according to a modification of the present embodiment.  
         [0081]     Referring to  FIG. 8 , it becomes possible in the substrate processing apparatus  100 A to capture the nitrogen ions N 2   +  excited in the plasma excitation space  11 B with the positive electric charge, by controlling the potential of the control electrode  31  to a suitable negative potential value. Thereby, penetration of the nitrogen ions N 2   +  into the process space  11 C is avoided.  
         [0082]     In the substrate processing apparatus  100  or  100 A of the present embodiment, it is possible to conduct an oxynitridation processing of the substrate  12  by supplying a He gas, an N 2  gas and an O 2  gas to the plasma gas supply port  11   p.    
         [heading-0083]     [Second Embodiment] 
         [0084]      FIG. 9  shows the construction of a substrate processing apparatus  200  according to a second embodiment of the present invention. In  FIG. 9 , those parts corresponding to the parts described previously are designated by the same reference numerals and the description thereof will be omitted.  
         [0085]     Referring to  FIG. 9 , it should be noted that the shower plate  14  is removed in the present embodiment, and in place of this, there are provided a plurality of process gas inlet ports lip on the processing vessel  11  such that the process gas inlet ports  11 P are disposed with a symmetric relationship with respect to the substrate  12 . As a result, therefore, the cover plate  15  constituting the dielectric window is exposed at the top part of the plasma excitation space  11 B. Further, the sidewall surface of the processing vessel is covered by the quartz liner  11 D for the part corresponding to the plasma excitation space  11 B similarly to the previous embodiment.  
         [0086]     According to the present embodiment, the construction of the substrate processing apparatus  11  is simplified, and it becomes possible to conduct the nitridation processing of the substrate  12  efficiently with low cost by using the atomic state nitrogen N*, by supplying a He gas and an N 2  gas to the plasma gas supplying port lip and by supplying the microwave of about 28 GHz to the radial line slot antenna  20 . Further, it is possible to conduct an oxynitridation processing by supplying a He gas, an N 2  gas and an O 2  gas to the plasma gas supplying port  11   p.    
         [heading-0087]     [Third Embodiment] 
         [0088]      FIG. 10  shows the construction of a substrate processing apparatus  300  according to a third embodiment of the present invention. In  FIG. 10 , those parts corresponding to the parts described previously are designated by the same reference numerals and the description thereof will be omitted.  
         [0089]     Referring to  FIG. 10 , the substrate processing apparatus  300  has a construction similar to the substrate processing apparatus  1  explained before with reference to  FIG. 1 , except that a control electrode  6  similar to the control electrode  31  is provided in the quartz vessel  2 , and the space inside the quartz vessel  2  is divided by the control electrode  6  into a plasma excitation space  2 B 1  in which the high-density plasma  2 D is excited and a process space  2 B 2  that includes the substrate  4  to be processed.  
         [0090]     In the present embodiment, a He gas and an N 2  gas are introduced into the plasma excitation space  2 B 1  via the process gas supply line  2 C, and there is formed high-density plasma  2 D having a high electron temperature and plasma energy sufficient for exciting atomic state nitrogen N* in the plasma excitation space  2 B 1 .  
         [0091]     The atomic state nitrogen N* thus formed cause diffusion into the process space  2 C through the control electrode  6 , and the surface of the substrate  4  undergoes nitridation. In such a construction, it should be noted that the plasma has a very high electron temperature and energy in the plasma excitation space  2 B 1 , while the electron temperature and the energy of the plasma are reduced to the level suitable for processing the substrate  4  in the process space  2 B 2 .  
         [0092]     In the present embodiment, too, it becomes possible to remove the low energy positive ions such as N 2   +  formed in the plasma excitation space  2 B 1  from the process space  2 B 2  by trapping the same, by controlling the potential of the control electrode  6  by the voltage source  6 A. Further, it becomes possible to control the state of the high-density plasma  2 D in the plasma excitation space  2 B 1  by controlling the potential of the control electrode  6 .  
         [0093]     In the substrate processing apparatus  200  of the present embodiment, it is also possible to conduct an oxynitridation processing of the substrate  4  in the process space  2 B 2  by introducing a He gas and an N 2  gas and an O 2  gas from the process gas supply line  2 C.  
         [0094]     Further, the present invention is not limited to the specific preferred embodiments described heretofore, but various variations and modifications may be made without departing from the scope of the invention recited in the claims.  
       INDUSTRIAL APPLICABILITY  
       [0095]     According to the present invention, it becomes possible to form plasma having the energy sufficient for causing excitation of atomic state nitrogen N* in the substrate processing apparatus by using He for the plasma excitation gas, and it becomes possible to conduct an efficient nitridation of the substrate by using the atomic state nitrogen N* thus excited. By separating the plasma excitation space in which the high-density plasma is excited from the process space in which the substrate is included by means of the control electrode, it becomes possible to reduce the plasma energy in the process space to the level suitable for substrate processing. Further, it becomes possible to trap the positive ions formed in the plasma excitation space. In the case of applying the present invention to the substrate processing apparatus that uses microwave-excited plasma, it becomes possible to avoid excessive increase of the plasma energy by conducting the plasma excitation by using a microwave having the frequency of about 28 GHz or more.