Patent Publication Number: US-2011061814-A1

Title: Microwave introducing mechanism, microwave plasma source and microwave plasma processing apparatus

Description:
FIELD OF THE INVENTION 
     The present invention relates to a microwave introducing mechanism for introducing a microwave into a chamber in which a plasma processing is performed, a microwave plasma source using the microwave introducing mechanism, and a microwave plasma processing apparatus using the microwave plasma source. 
     BACKGROUND OF THE INVENTION 
     In a process of manufacturing a semiconductor device or a liquid crystal display, a plasma processing apparatus such as a plasma etching apparatus and a plasma CVD film forming apparatus is employed to perform a plasma process such as an etching process or a film forming process on a target substrate to be processed such as a semiconductor wafer or a glass substrate. 
     A few methods for generating a plasma in the plasma processing apparatus have been disclosed. According to one of the plasma generating methods, a plasma is generated with a capacitive coupling between parallel plate electrodes arranged in a chamber while a processing gas is supplied to the chamber and a predetermined power is applied to the parallel plate electrodes. According to another plasma generating method, electrons are accelerated by an electric field formed by a microwave and a magnetic field formed by a magnetic field forming unit that is disposed outside the chamber and collide with neutral molecules in the processing gas, to thereby ionize the neutral molecules and generate a plasma. 
     In the case of the latter plasma generating method using the magnetron effect of the magnetic field formed by the magnetic field forming unit and the electric field formed by the microwave, a microwave having a predetermined power is supplied to an antenna disposed in the chamber through a waveguide or a coaxial tube and the microwave is radiated from the antenna to a processing space in the chamber. 
     A conventional and typical microwave introducing unit includes a microwave oscillator having a magnetron for outputting a microwave whose power is regulated to a predetermined level and a microwave generating power supply for supplying a DC anode current to the magnetron. The microwave introducing unit is configured to radiate the microwave to be outputted from the microwave oscillator to the processing space in the chamber through the antenna. 
     Since, however, the magnetron has a short lifespan of about half a year, the microwave introducing device using the magnetron has a drawback in which the cost for the equipment and the maintenance thereof is high. Further, the magnetron has oscillation stability of approximately 1% and output stability of approximately 3%, whose respective deviations are large. For that reason, it is difficult to have a stable microwave oscillation. 
     Accordingly, Japanese Patent Application publication No. 2004-128141 (patent document 1) has disclosed a technique for ensuring a long life of the device and stable microwave output by generating required high power microwaves by amplifying low-power microwaves through the use of amplifiers, i.e., solid state amplifiers, using semiconductor amplifying devices. This technique involves steps of dividing a microwave by a divider; amplifying the microwaves outputted from the divider by the solid state amplifiers; and combining the microwaves amplified by the solid state amplifiers by a combiner. 
     However, the technique in the patent document 1 is disadvantageous in that an accurate impedance matching is required in a combiner; a large-sized isolator is required to transmit to the isolator itself the high-power microwaves outputted from the combiner; and it is difficult to adjust an output distribution of the microwave in the surface of the antenna. 
     In order to mend such drawbacks, Japanese Patent Application publication No. 2004-128385 (patent document 2) has suggested a technique for dividing a microwave into a plurality of microwaves by a divider and amplifying the divided microwaves by amplifiers. Thereafter, the amplified microwaves are radiated from a plurality of antennas without combining the microwaves by a combiner. The radiated microwaves are combined in a space. 
     The technique, however, is disadvantageous in that the apparatus becomes complicated because it is required that two or more large-sized stub tuners are installed in each of the divided channels and a mismatching portion is tuned. Further, it is difficult to adjust the impedance of the mismatching portion with high accuracy. 
     In order to mend such drawbacks, International Patent Application publication No. WO2008/013112 (patent document 3) has disclosed a microwave plasma source which divides a microwave into a plurality of microwaves and transmits the microwaves to the chamber through a plurality of antenna modules, each of which includes a slug tuner and a slot antenna having a planar shape provided as a single unit, and an amplifier arranged to be located close to the slug tuner and the slot antenna. 
     By providing the antenna and the tuner as a single unit, it is possible to significantly scale down the microwave plasma source itself. Further, by providing the amplifier, the tuner and the antenna closely to each other, it is possible to tune the antenna attachment part including an impedance mismatching portion, thereby reducing the affect of the reflection reliably. 
     However, such technique in the patent document 3 is disadvantageous due to the following reasons. In the patent document 3, two slugs made of a dielectric material such as resin or quartz are employed as a best slug tuner and the impedance is adjusted by moving the slugs. The range of motion (ROM) of the slugs is set to be same as a ½ wavelength of the microwave and the distance between the two slugs is set to be same as the ½ wavelength to adjust the impedance in an overall range of the smith chart. Further, when the effective wavelength of the microwave is kg, the thickness of the slug becomes λg/4. 
     However, as necessary, it is required to increase λ and form the slugs thickly depending on the kinds of the material. Besides, since a portion of ¼ wavelength around the antenna becomes a mismatching portion, it is difficult to use the portion to adjust the impedance. Accordingly, it is necessary to obtain the length by adding the ¼ wavelength into the ROM. To that end, since the length of the main chamber in the microwave introducing mechanism including the antenna and the tuner provided as a single unit becomes increased, the scaling-down of the microwave plasma source may be restricted. 
     SUMMARY OF THE INVENTION 
     In view of the above, the present invention provides a microwave introducing mechanism, a microwave plasma source using the same and a microwave plasma processing apparatus, capable of scaling down the microwave plasma source. 
     In accordance with a first aspect of the present invention, there is provided a microwave introducing mechanism used for a microwave plasma source for generating a microwave plasma in a chamber. The mechanism includes: a main body container having a cylindrical shape; an inner conductor, having a cylindrical shape or a rod shape, coaxially provided in the main body container, a microwave transmission path being defined between the main body container and the inner conductor; a tuner for adjusting an impedance of the microwave transmission path; and an antenna section including a microwave radiating antenna for radiating to the chamber a microwave transmitted through the microwave transmission path. The tuner includes a pair of slugs made of a dielectric material, the slugs being movable along the inner conductor; an actuator for moving the slugs; and a controller for controlling the movement of the slugs, and the controller controls the actuator to move both of the slugs together in a range of a ½ wavelength of the microwave while maintaining a same distance between the slugs and to move one of the slugs in a range of a ¼ wavelength of the microwave with regard to the other slug. 
     In the first aspect of the present invention, the slugs are preferably made of a high-purity alumina. Further, the microwave radiating antenna is preferably a planar slot antenna having slots through which a microwave is radiated. 
     In accordance with a second aspect of the present invention, there is provided a microwave introducing mechanism used for a microwave plasma source for generating a microwave plasma in a chamber. The mechanism includes: a main body container having a cylindrical shape; an inner conductor, having a cylindrical shape or a rod shape, coaxially provided in the main body container, a microwave transmission path being defined between the main body container and the inner conductor; a tuner for adjusting an impedance of the microwave transmission path; and an antenna section including a microwave radiating antenna for radiating to the chamber a microwave transmitted through the microwave transmission path. The microwave radiating antenna is a planar slot antenna on which four or more slots for radiating a microwave are uniformly formed, and the tuner includes a pair of slugs made of a dielectric material, the slugs being movable along the inner conductor; and an actuator for moving the slugs. Further, the slugs are made of a high-purity alumina. 
     In accordance with a third aspect of the present invention, there is provided a microwave introducing mechanism used for a microwave plasma source for generating a microwave plasma in a chamber. The mechanism includes: a main body container having a cylindrical shape; an inner conductor, having a cylindrical shape or a rod shape, coaxially provided in the main body container, a microwave transmission path being defined between the main body container and the inner conductor; a tuner for adjusting an impedance of the microwave transmission path; and an antenna section including a microwave radiating antenna for radiating to the chamber a microwave transmitted through the microwave transmission path. The microwave radiating antenna is a planar slot antenna on which four or more slots for radiating a microwave are uniformly formed, and the tuner includes a pair of slugs made of a dielectric material, the slugs being movable along the inner conductor; an actuator for moving the slugs; and a controller for controlling the movement of the slugs. Further, the controller controls the actuator to move both of the slugs together in a range of a ½ wavelength of the microwave while maintaining a same distance between the slugs and to move one of the slugs in a range of a ¼ wavelength of the microwave with regard to the other slug. 
     In accordance with a fourth aspect of the present invention, there is provided a microwave introducing mechanism used for a microwave plasma source for generating a microwave plasma in a chamber. The mechanism includes: a main body container having a cylindrical shape; an inner conductor, having a cylindrical shape or a rod shape, coaxially provided in the main body container, a microwave transmission path being defined between the main body container and the inner conductor; a tuner for adjusting an impedance of the microwave transmission path; and an antenna section including a microwave radiating antenna for radiating to the chamber a microwave transmitted through the microwave transmission path. The microwave radiating antenna is a planar slot antenna on which four or more slots for radiating a microwave are uniformly formed, and the tuner includes a pair of slugs made of a dielectric material, the slugs being movable along the inner conductor; an actuator for moving the slugs; and a controller for controlling the movement of the slugs. Further, the slugs are made of a high-purity alumina, and the controller controls the actuator to move both of the slugs together in a range of a ½ wavelength of the microwave while maintaining a same distance between the slugs and to move one of the slugs in a range of a ¼ wavelength of the microwave with regard to the other slug. 
     In the first to fourth aspect of the present invention, the slots preferably have a fan shape. Moreover, the antenna section preferably includes a ceiling plate made of a dielectric material through which the microwave radiated from the antenna passes; and a wave retardation member provided on an opposite side of the ceiling plate and made of a dielectric material for shortening a wavelength of the microwave transmitted to the antenna. Further, the tuner and the antenna preferably constitute a lumped constant circuit, and the tuner and the antenna preferably serve as a resonator 
     In accordance with a fifth aspect of the present invention, there is provided a microwave plasma source which turns a gas supplied to a chamber into a plasma by introducing a microwave into the chamber. The source includes: a microwave generating mechanism for generating a microwave; and a microwave introducing mechanism for introducing the generated microwave into the chamber. The introducing mechanism includes a main body container having a cylindrical shape; an inner conductor, having a cylindrical shape or a rod shape, coaxially provided in the main body container, a microwave transmission path being defined between the main body container and the inner conductor; a tuner for adjusting an impedance of the microwave transmission path; and an antenna section including a microwave radiating antenna for radiating to the chamber a microwave transmitted through the microwave transmission path. The tuner includes a pair of slugs made of a dielectric material, the slugs being movable along the inner conductor; an actuator for moving the slugs; and a controller for controlling the movement of the slugs, and the controller controls the actuator to move both of the slugs together in a range of a ½ wavelength of the microwave while maintaining a same distance between the slugs and to move one of the slugs in a range of a ¼ wavelength of the microwave with regard to the other slug. 
     In accordance with a sixth aspect of the present invention, there is provided a microwave plasma source which turns a gas supplied to a chamber into a plasma by introducing a microwave into the chamber. The source includes: a microwave generating mechanism for generating a microwave; and a microwave introducing mechanism for introducing the generated microwave into the chamber. The introducing mechanism includes a main body container having a cylindrical shape; an inner conductor, having a cylindrical shape or a rod shape, coaxially provided in the main body container, a microwave transmission path being defined between the main body container and the inner conductor; a tuner for adjusting an impedance of the microwave transmission path; and an antenna section including a microwave radiating antenna for radiating to the chamber a microwave transmitted through the microwave transmission path. The microwave radiating antenna is a planar slot antenna on which four or more slots for radiating a microwave are uniformly formed, and the tuner includes a pair of slugs made of a dielectric material, the slugs being movable along the inner conductor; and an actuator for moving the slugs. Further, the slugs are made of a high-purity alumina. 
     In accordance with a seventh aspect of the present invention, there is provided a microwave plasma apparatus which performs a process on a substrate by using a microwave plasma. The apparatus includes: a chamber for accommodating therein a target substrate to be processed; a gas supply unit for supplying a gas into the chamber; and a microwave plasma source, including a microwave generating mechanism for generating a microwave; and a microwave introducing mechanism for introducing the generated microwave into the chamber, for turning a gas supplied to the chamber into a plasma by introducing the microwave into the chamber. The introducing mechanism includes a main body container having a cylindrical shape; an inner conductor, having a cylindrical shape or a rod shape, coaxially provided in the main body container, a microwave transmission path being defined between the main body container and the inner conductor; a tuner for adjusting an impedance of the microwave transmission path; and an antenna section including a microwave radiating antenna for radiating to the chamber a microwave transmitted through the microwave transmission path. The tuner includes a pair of slugs made of a dielectric material, the slugs being movable along the inner conductor; an actuator for moving the slugs; and a controller for controlling the movement of the slugs, and the controller controls the actuator to move both of the slugs together in a range of a ½ wavelength of the microwave while maintaining a same distance between the slugs and to move one of the slugs in a range of a ¼ wavelength of the microwave with regard to the other slug. 
     In accordance with an eighth aspect of the present invention, there is provided a microwave plasma apparatus which performs a process on a substrate by using a microwave plasma. The apparatus includes: a chamber for accommodating therein a target substrate to be processed; a gas supply unit for supplying a gas into the chamber; and a microwave plasma source, including a microwave generating mechanism for generating a microwave; and a microwave introducing mechanism for introducing the generated microwave into the chamber, for turning a gas supplied to the chamber into a plasma by introducing the microwave into the chamber, wherein the introducing mechanism includes a main body container having a cylindrical shape; an inner conductor, having a cylindrical shape or a rod shape, coaxially provided in the main body container, a microwave transmission path being defined between the main body container and the inner conductor; a tuner for adjusting an impedance of the microwave transmission path; and an antenna section including a microwave radiating antenna for radiating to the chamber a microwave transmitted through the microwave transmission path. The microwave radiating antenna is a planar slot antenna on which four or more slots for radiating a microwave are uniformly formed, and the tuner includes a pair of slugs made of a dielectric material, the slugs being movable along the inner conductor; and an actuator for moving the slugs. Further, the slugs are made of a high-purity alumina. 
     In the first aspect of the present invention, the tuner including the pair of slugs made of a dielectric material, the slugs being movable along the inner conductor and the microwave transmission path being defined between the main body container and the inner conductor; the actuator for moving the slugs; and the controller for controlling the movement of the slugs is used as a slug tuner. Moreover, the controller controls the actuator to move both of the slugs together in the range of the ½ wavelength of the microwave while maintaining the same distance between the slugs and to move one of the slugs in the range of the ¼ wavelength of the microwave with regard to the other slug. Accordingly, it is possible to shorten a moving range of the slugs by a ¼ wavelength as compared with the conventional method, thereby allowing the microwave introducing mechanism to be scaled down. This contributes to the scaling-down of the microwave plasma source. 
     In the second aspect of the present invention, the tuner including the pair of slugs made of a dielectric material, the slugs being movable along the inner conductor and the microwave transmission path being defined between the main body container and the inner conductor; and the actuator for moving the slugs. Moreover, the slugs are made of the high-purity alumina. Since the high-purity alumina has a high dielectric constant, the slugs can be formed to have a thinner thickness than that of a slug made of quartz or resin and, thus, it is possible to scale down the microwave introducing mechanism by the reduced size. Further, due to the high dielectric constant, it is possible to widen the load matching range. Besides, since tan δ is small, this helps to reduce the amount of loss and degree of distortion in the microwave. 
     In the third aspect of the present invention, similar to the first aspect, the controller controls the actuator to move both of the slugs together in the range of the ½ wavelength of the microwave while maintaining the same distance between the slugs and to move one of the slugs in the range of the ¼ wavelength of the microwave with regard to the other slug. Then, as the microwave radiating antenna, the planar slot antenna in which four or more slots are uniformly formed is used. Accordingly, it is possible to shorten the moving range of the slugs by the ¼ wavelength as compared with the conventional method and to remove a mismatching portion near to the antenna. For that reasons, it is possible to scale down the microwave introducing mechanism much further. This contributes to the scaling-down of the microwave plasma source. 
     In the fourth aspect of the present invention, a pair of slugs is made of the high-purity alumina; the planar slot antenna in which four or more slots are uniformly formed is used as the microwave radiating antenna; and the controller controls the actuator to move both of the slugs together in the range of the ½ wavelength of the microwave while maintaining the same distance between the slugs and to move one of the slugs in the range of the ¼ wavelength of the microwave with regard to the other slug. Accordingly, the effects of the first aspect and the second aspect are mixed and, thus, it is possible to scale down the microwave introducing mechanism much further. This contributes to the scaling-down of the microwave plasma source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view showing a schematic configuration of a plasma processing apparatus including a microwave plasma source having a microwave introducing mechanism in accordance with an embodiment of the present invention; 
         FIG. 2  is a block diagram showing a configuration of the microwave plasma source shown in  FIG. 1 ; 
         FIG. 3  shows an example of a circuit configuration of a main amplifier; 
         FIG. 4  is a cross sectional view showing the microwave introducing mechanism in the microwave plasma processing apparatus shown in  FIG. 1 ; 
         FIG. 5  is a plan view showing a preferable shape of a planar slot antenna; 
         FIG. 6  is a perspective view showing an antenna section having a rectangular ceiling plate; 
         FIG. 7  shows a smith chart for explaining a range of motion of a conventional slug when the impedance is adjusted by using the conventional slug; 
         FIG. 8  shows the range of motion of the conventional slug when the impedance is adjusted by using the conventional slug; 
         FIG. 9  shows a smith chart for explaining the range of motion of a slug when the impedance is adjusted by using the slug in accordance with the present invention; 
         FIG. 10  shows the range of motion of the slug when the impedance is adjusted by using the slug in accordance with the present invention; 
         FIG. 11  shows a smith chart showing a matching range depending on the material of the slug; and 
         FIG. 12  shows a mismatching portion near to an antenna section in a conventional microwave inducing mechanism. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     An embodiment of the present invention will now be described with reference to the accompanying drawings which form a part hereof.  FIG. 1  is a cross sectional view showing a schematic configuration of a plasma processing apparatus including a microwave plasma source having a microwave introducing mechanism in accordance with an embodiment of the present invention, and  FIG. 2  is a block diagram showing a configuration of the microwave plasma source shown in  FIG. 1 . 
     A plasma processing apparatus  100  is configured as a plasma etching apparatus for performing on a wafer a plasma process, e.g., an etching process. The plasma processing apparatus  100  includes a substantially cylindrical airtight chamber  1  that is grounded and made of a metal material such as aluminum, stainless steel or the like; and a microwave plasma source  2  for generating a microwave plasma in the chamber  1 . An opening  1   a  is formed at an upper portion of the chamber  1 , and the microwave plasma source  2  is provided in the opening  1   a  to face an inside of the chamber  1 . 
     In the chamber  1 , a susceptor  11  for horizontally supporting a wafer W as a target substrate to be processed is provided while being supported by a cylindrical supporting member  12  provided upwardly at a center of a bottom portion of the chamber  1  via an insulating member  12   a . The susceptor  11  and the insulating member  12   a  are made of, e.g., aluminum, the surface of which is alumite-treated (anodically oxidized), or the like. 
     In addition, the susceptor  11  is provided with an electrostatic chuck for electrostatically attracting the wafer W; a temperature-control mechanism; a gas channel through which a heat-transfer gas is supplied to a backside of the wafer W; an elevating pin which can move up and down to transfer the wafer W, and the like, which are not shown. Further, a high frequency bias power supply  14  is electrically connected to the susceptor  11  via a matcher  13 . Ions are attracted to the wafer W by a high frequency power supplied from the high frequency bias power supply  14  to the susceptor  11 . 
     A gas exhaust line  15  is connected to a bottom portion of the chamber  1 , and a gas exhaust unit  16  having a vacuum pump is connected to the gas exhaust line  15 . By operating the gas exhaust unit  16 , the inside of the chamber  1  is exhausted and depressurized to a predetermined vacuum level at a high speed. Further provided in a sidewall of the chamber  1  are a loading/unloading port  17  through which the wafer W is loaded and unloaded; and a gate valve for opening and closing the loading/unloading port  17 . 
     A shower plate  20  through which a processing gas for plasma etching is injected toward the wafer W is horizontally provided above the susceptor  11  in the chamber  1 . The shower plate  20  includes grid-shaped gas channels  21  and a plurality of gas injection holes  22  formed in the gas channels  21 . Respective spaces  23  are formed between the grid-shaped gas channels  21 . A line  24  extending to the outside of the chamber  1  is connected to the gas channels  21 , and a process gas supply source  25  is connected to the line  24 . 
     In the meantime, a ring-shaped plasma gas introducing member  26  is provided along a chamber wall above the shower plate  20  of the chamber  1 , and a plurality of gas injection holes are formed on an inner periphery of the plasma gas introducing member  26 . A plasma gas supply source  27  is connected to the plasma gas introducing member  26  via a line  28 . As for a plasma gas, it is preferable to use a rare gas such as Ar gas or the like. 
     The plasma gas introduced through the plasma gas introducing member  26  into the chamber  1  is turned into a plasma by a microwave supplied from the microwave plasma source  2 . Thus generated plasma of, e.g., Ar gas, passes through the spaces  23  of the shower plate  20 , so that the processing gas injected through the gas injection holes  22  of the shower plate  20  is excited, thereby generating a plasma of the processing gas. 
     The microwave plasma source  2  is supported by a supporting ring  29  provided at an upper portion of the chamber  1 , and the gap therebetween is airtightly sealed. As shown in  FIG. 2 , the microwave plasma source  2  includes a microwave output section  30  for dividing a microwave into microwaves and outputting the divided microwaves through a plurality of paths; and an antenna unit  40  for guiding the outputted microwaves into the chamber  1  and radiating the guided microwaves into the chamber  1 . 
     The microwave output section  30  includes a power supply unit  31 ; a microwave oscillator  32 ; an amplifier  33  for amplifying an oscillated microwave; and a divider  34  for dividing the amplified microwave into a plurality of microwaves. 
     The microwave oscillator  32  performs a phase locked loop (PLL) oscillation, for example, to generate a microwave of a predetermined frequency (e.g., 2.45 GHz). The divider  34  divides the microwave amplified by the amplifier  33  while matching the impedance between an input side and an output side to minimize the loss of the microwaves. In addition, the frequency of 8.35, 5.8, 1.98 GHz or the like may be used instead of 2.45 GHz as for the frequency of the microwaves. 
     The antenna unit  40  includes a plurality of antenna modules  41  for guiding the microwaves divided by the divider  34 . Each of the antenna modules  41  includes an amplifier section  42  for mainly amplifying the divided microwaves; and a microwave introducing mechanism  43 . The microwave introducing mechanism  43  includes a tuner  44  for matching the impedance; an antenna section  45  for radiating the amplified microwaves into the chamber  1 . The microwaves radiated into the chamber  1  from the antenna section  45  of the microwave introducing mechanism  43  are combined in the space of the chamber  1 . 
     The amplifier section  42  includes a phase shifter  46 ; a variable gain amplifier  47 ; a main amplifier  48  serving as a solid state amplifier; and an isolator  49 . 
     The phase shifter  46  is configured to shift phases of the microwaves by a slug tuner, and it is possible to modulate the radiation characteristics by controlling the phase shifter  46 . For example, it is possible to adjust the directivity by controlling the phase in each of the antenna modules, to thereby change the plasma distribution. Moreover, it is possible to obtain circular polarized waves by shifting the phase by 90° between adjacent antenna modules to be described later. However, the phase shifter  46  need not be provided when it is not necessary to modulate the radiation characteristics. 
     The variable gain amplifier  47  is an amplifier for controlling plasma intensity or deviation in each of the antenna modules by adjusting power levels of microwaves inputted into the maim amplifier  48 . The distribution of the generated plasma can be variably controlled by changing the variable gain amplifier  47  for each of the antenna modules. 
     The main amplifier  48  serving as a solid state amplifier may include an input matching circuit  61 ; a semiconductor amplifying device  62 ; an output matching circuit  63 ; and a high Q resonant circuit as shown in  FIG. 3 , for example. As for the semiconductor amplifying device  62 , it is possible to use GaAs high electron mobility transistor (HEMT), GaN HEMT, laterally diffused (LD)-metal oxide semiconductor (MOS) or the like, capable of performing a class E operation. Especially, when GaN HEMT is used as the semiconductor amplifying device, the variable gain amplifier has a uniform value, and the power is controlled by varying the power voltage of the amplifier for performing a class E operation. 
     The isolator  49  separates microwaves reflected from the antenna section  45  to main amplifier  48 . The isolator includes a circulator and a dummy load (coaxial terminator). The circulator transfers to the dummy load the microwave reflected from the antenna section  45 , and the dummy load converts the reflected microwave transferred from the circulator into heat. 
     In the present embodiment, there is provided a plurality of antenna modules  41 , and the microwaves introduced into the chamber  1  from the microwave introducing mechanism  43  of each of the antenna modules  41  are combined in the space. Accordingly, the isolator  49  is preferably small sized, and can be arranged to be located adjacent to the main amplifier  48 . 
     Next, the microwave introducing mechanism  43  will be described in detail with reference to  FIG. 4 . As shown in  FIG. 4 , the microwave introducing mechanism  43  includes a main body container  50 . The antenna section  45  is arranged at an upper portion of the main body container  50 , and a base end portion of the main body container  50 , below the antenna section  45 , serves as a portion in which the impedance can be adjusted by a tuner  44 . 
     The main body container  50 , which is cylindrical and made of a metal material, constitutes an outer conductor of the coaxial waveguide. Further, in the main body container  50 , an inner conductor  52  of the coaxial tube extends upward vertically. The inner conductor  52  has a rod shape or a cylindrical shape. A microwave transmission path  53  is defined between the main body container  50  and the inner conductor  52 . 
     The antenna section  45  includes a planar slot antenna  51  having a planar shape, and the planar slot antenna  51  has slots  51   a . The inner conductor  52  is connected to a central portion of the planar slot antenna  51 . 
     A power supply conversion unit (not shown) is installed at a base side of the main body container  50  and is connected to the main amplifier  48  via a coaxial cable. The isolator  49  is provided in the middle of the coaxial cable. The main amplifier  48  is a power amplifier dealing with a high power and thus performs a high-efficiency operation of the class E. Since, however, the heat therefrom ranges from several tens to several hundreds of watts, the main amplifier  48  is installed in series to the antenna section  45  in view of heat radiation. 
     The antenna section  45  includes a wave retardation member  55  provided on a top surface of the planar slot antenna  51 . The wave retardation member  55  has a dielectric constant greater than that of vacuum and is made of, e.g., quartz, ceramic, polyimide-based resin or fluorine-based resin polytetrafluoroethylene or the like. The wave retardation member  55  has a function of shortening the wavelength of the microwave as compared with that in the vacuum, to thereby control the plasma. The wave retardation member  55  can adjust the phases of the microwaves depending on its thickness, and its thickness is adjusted such that an antinode of the standing wave is formed at the planar slot antenna  51 . Accordingly, it is possible to maximize the radiation energy of the planar slot antenna  51  while minimizing the reflection. 
     Further, a dielectric member for vacuum sealing, e.g., a ceiling plate  56  made of quartz, ceramic or the like, is arranged on a bottom surface of the planar slot antenna  51 . The microwaves amplified by the main amplifier  48  pass through the space between the inner conductor  52  and a surrounding wall of the main body container  50  are transmitted through the slots  51   a  of the planar slot antenna  51 . Then, the transmitted microwaves are radiated into the chamber through the ceiling plate  56 . 
     In the present embodiment, as shown in  FIG. 5 , four slots  51   a  are evenly formed in a separated arc-shape. Accordingly, since the slots  51   a  are substantially uniformly formed in a circumferential direction, the propagated microwaves can be suppressed from being reflected in the planar slot antenna  51 , thereby reducing or substantially removing the mismatching portion as will be described later. 
     The slots  51   a  preferably have a fan shape to shorten the length of the slots  51   a  or allowing the slots  51   a  to be scaled down. Further, as shown in  FIG. 6 , the ceiling plate  56  preferably has a rectangular parallelepiped shape or a cylindrical shape whose diameter is greater than that of the main body container  50 . Accordingly, it is possible to effectively radiate the microwaves in a TE mode. 
     As shown  FIG. 4 , the tuner  44  includes the two slugs  48  at the base end portion of the main body container  50 , below the antenna section  45  to constitute a slug tuner. The slugs  58  are made of a dielectric material and have a plate shape. Moreover, the slugs  58  are disposed in a ring shape between the inner conductor  52  and an outer wall of the main body container  50 . The impedance is adjusted by vertically moving the slugs  58  by an actuator  59  based on a command from a controller  60 . The controller  60  adjusts the impedance of termination to become, e.g., about 50Ω. When only one of the two slugs  58  is moved, a circular trajectory passing through the origin of the smith chart is drawn. On the other hand, when both of the slugs  58  are moved together, only the phase of the reflection coefficient is rotated. 
     In the present embodiment, as will be described later, the operations of the slugs  58  are controlled by an algorithm of the controller  60  and, thus, the impedance can be adjusted in all ranges by setting the range of a pair of slugs moved together same as λ/2 and the range of the slugs, one of which is fixed and the other slug is moved, same as λ/4 in case that the in-line wavelength (wavelength in waveguide) is set to be same as λ. Accordingly, as will be described later, the total moving range of the two slugs  58  can be determined to be 3λ/4, which is smaller than that of the conventional slugs. 
     In the present embodiment, the slugs  58  are made of a dielectric material, e.g., high-purity alumina. The high-purity alumina has a relative dielectric constant of 10, which is significantly greater than 3.88 of quartz and 2.03 of Teflon (registered trademark). Accordingly, it is possible to enlarge the matching range by making alumina thinner. Further, the high-purity alumina is advantageous in having small tan δ, reducing loss and suppressing distortion as compared with quartz and Teflon (registered trademark). The high-purity alumina also has a high heat resistance. Preferably, an alumina sintered body of the purity of 99.9% or more is employed as the high-purity alumina. As a specific product name, a SAPPHAL made by the Covalent Materials Corp. may be exemplified. A single-crystal alumina (sapphire) may be employed. 
     In the present embodiment, the main amplifier  48 , the tuner  44  and the planar slot antenna  51  are arranged to be located close to one another. Further, the tuner  44  and the planar slot antenna  51  are included in a lumped constant circuit within ½ wavelength and also serve as a resonator. 
     Each unit of the plasma processing apparatus  100  is controlled by a control unit  70  having a micro processor. The control unit  70  includes a storage unit which stores process recipes, an input unit, a display unit and the like and controls the plasma processing apparatus based on a selected recipe. 
     Next, an operation of the plasma processing apparatus having such configuration will be described. First, the wafer W is loaded into the chamber  1  and is mounted on the susceptor  11 . Then, while a processing gas, e.g., Ar gas, is introduced from the plasma gas supply source  27  into the chamber  1  via a line  28  and the plasma gas introducing member  26 , a microwave is introduced from the microwave plasma source  2  into the chamber  1 , thereby generating a plasma. 
     Thereafter, a processing gas, e.g., an etching gas such as Cl 2  gas or the like, is injected from the processing gas supply source  25  into the chamber  1  via the line  24  and the shower plate  20 . The injected processing gas is excited by the plasma that has passed through the spaces  23  of the shower plate  20 , to thereby be turned into a plasma. The plasma of the processing gas thus generated is used to perform a plasma process, e.g., an etching process, on the wafer W. 
     In this case, in the microwave plasma source  2 , the microwave oscillated by the microwave oscillator  32  of the microwave output section  30  is amplified by the amplifier  33  and is then divided into a plurality of microwaves by the divider  34 , and the divided microwaves are guided to antenna modules  41  of the antenna unit  40 . In the antenna modules  41 , the divided microwaves are individually amplified by the main amplifier  48  serving as the solid state amplifier and pass through the microwave transmission path  53 . Then, the microwaves are individually radiated from the planar slot antenna  51  and introduced into the chamber  1 . Thereafter, the introduced microwaves are combined in a space. Accordingly, it becomes unnecessary to use the large-scaled isolator or combiner. In addition, the microwave introducing mechanism  43  is provided compactly since the antenna section  45  and the tuner  44  are provided as a single unit. Further, the main amplifier  48 , the tuner  44  and the planar slot antenna  51  are arranged to be installed close to one another. Especially, the tuner  43  and the planar slot antenna  51  are included in a lumped constant circuit and also serve as a resonator. Accordingly, in a planar slot antenna installation portion where the impedance mismatching exists, the tuning can be performed with high accuracy by the tuner  43 , thereby reliably solving the effects of reflection. 
     Moreover, since the tuner  44  and the planar slot antenna  51  are arranged to be located close to each other and are included in the lumped constant circuit and also serve as the resonator as described above, this makes impedance mismatching up to the planar slot antenna  51  eliminated accurately, thereby allowing the mismatching portion to substantially serve as the plasma space. Accordingly, the plasma control can be performed with high accuracy by the tuner  44 . Further, it is possible to efficiently radiate the microwaves as TE waves by forming in a quadrangular or cylindrical shape the ceiling plate  56  attached to the planar slot antenna  51 . 
     However, since the microwave introducing mechanism  43  adjusts the impedance by moving the slugs  58  of the tuner  44 , it is required to obtain the length corresponding to the moving margin of the slugs  58 . In the conventional method, in case that the in-line wavelength of the microwave is set as λ, it is possible to shift by 360° the phase of the reflection coefficient of a point A on the smith chart, for example, as shown in  FIG. 7  (the dotted-line trajectory of a circle B) by moving both of the slugs  58  together in the range of λ/2; and to draw a circle C which passes through the origin and a point A by moving only one of the slugs  58  in range of λ/2 with regard to the other slug. Accordingly, it is possible to adjust the impedance at all points by using the combinations thereof. Therefore, as shown in  FIG. 8 , the range of motion (ROM) of the slugs  58  becomes λ by adding λ/2 to λ/2. 
     On the other hand, in the present embodiment, the ROM of one of the slugs  58  with regard to the other slug is set to λ/4, which is a half of the range of the conventional method. Specifically, the ROM on the circle C shown in  FIG. 7  is converted into a ROM represented by a shaded area shown in  FIG. 9 , for example. In this case, since the point A is located beyond the ROM of the circle C, the controller  60 , for example, selects a circle C′ as the circle that passes through the origin and the point A. In this way, the point A can be moved to the origin along the ROM of the circle C′, thereby adjusting the impedance in the ROM of λ/4. Accordingly, as shown in  FIG. 10 , the ROM of the slugs  58  becomes 3λ/4 by adding λ/2 and λ/4, which is shorter by λ/4 than that of the conventional method. Therefore, it is possible to shorten the length of the main body container  50  of the microwave introducing mechanism  43  by λ/4, to thereby allowing the microwave plasma source  2  to be scaled down more and more. 
     Moreover, in the present embodiment, since a high-purity alumina having a high dielectric constant is employed as a dielectric material which the slugs  58  are made of, it is possible to make the slugs  58  thinner. Specifically, a thickness d of the slugs  58  is calculated by using an equation, d=λg/4, where λg indicates an equivalent wavelength of the microwave (the wavelength of the microwave in the slugs  58 ). However, when the wavelength of the microwave in the air is referred to as λ and the relative dielectric constant is referred to as ∈ r , it is possible to obtain an equation λg=λ/∈ r   1/2 . 
     Accordingly, the thickness of the slugs  58  can be made thinner as the relative dielectric constant becomes higher. Since the high-purity alumina has a relative dielectric constant of 10, which is significantly greater than 3.88 of quartz and 2.03 of Teflon (registered trademark), it is possible to make the slugs  58  thinner, i.e., with an about ⅔ thickness of the conventional slug made of quartz. To be specific, as compared with the thickness of 16 mm of the slug made of quartz, the slug  58  made of alumina can have the thickness of 10 mm. For that reason, it is possible to shorten the length of the main body container  50  of the microwave introducing mechanism  43  into 12 mm resultantly, thereby allowing the microwave plasma source  2  to be scaled down by the shortened length. 
     Moreover, it is possible to widen the matching range by using a material having a high dielectric constant.  FIG. 11  is the smith chart showing a load matching range in the case of using a slug of each material calculated by employing the calculating method for a distributed constant circuit. In the case of using the high-purity alumina, it is possible to increase the load matching range, thereby widening the adjustment margin, as compared with the case of using quartz or Teflon (registered trademark). 
     Since an increase in the dielectric constant of the slugs  58  leads to an increase in an attenuation constant, the loss may also be increased. However, the thickness itself of the slug can be reduced, thereby balancing the loss. Moreover, since the high-purity alumina has small tan δ, the loss can be reduced more efficiently as compared with the case of using quartz or Teflon (registered trademark). Specifically, in the case of using the conventional slug made of quartz, the voltage standing wave radio (VSWR) has about 20 at the maximum. On the contrary, in the case of using the slug made of the high-purity alumina, the VSWR can be increased to about 70. 
     Since the high-purity alumina has a high resistance compared with quartz or Teflon (registered trademark), the deformation does not occur even at the high temperature of 1500° C. 
     Besides, in the present embodiment, the four slots  51   a  of the slot antenna  51  are uniformly formed and, thus, it is possible to more uniformly radiate the microwave. As a result, it is possible to reduce or remove the mismatching portion near to the antenna section  45 . 
     Specifically, in the case of providing two slots, the radiation uniformity of the microwaves from the planar slot antenna  51  is not necessarily high and, thus, a λ/4 area near to the antenna section  45  of the main body container  50  becomes a mismatching portion as shown in  FIG. 12 . Accordingly, the mismatching portion has not been used for adjusting the impedance by the slugs  58 . However, the mismatching portion can be reduced or removed by uniformly forming the four slots and, thus, the λ/4 area can be used to adjust the impedance by the slugs  58 . Therefore, it is possible to shorten the length of the main body container  50  of the microwave introducing mechanism  43  by λ/4 at the maximum, thereby allowing the microwave plasma source to be scaled down by the shortened length. 
     As such, it is possible to shorten the length of the main body container  50  of the microwave introducing mechanism  43  by controlling the movement of the slugs  58 . By using the high-purity alumina as the material of the slugs  58 , it is also possible to shorten the length of the main body container  50  by about 12 mm as compared with the case of using the conventional slug made of quartz. Further, by uniformly providing four slots  51   a  of the planar slot antenna  51 , it is possible to shorten the length of the main body container  50  by λ/4. 
     Accordingly, by only one of the above methods, it is possible to allow the microwave plasma source  2  to be scaled down. Further, by the synergy effect by using a combination of the above methods, it is possible to allow the microwave plasma source  2  to be scaled down much further. Especially, by combining the three methods, since λ becomes about 12.2 cm, it is possible to shorten the length of the main body container  50  by about 7.3 cm at the maximum. 
     The present invention is not limited to the above embodiments, and can be variously modified within the scope of the present invention. For example, the circuit configurations of the microwave output section  30 , the antenna unit  40 , the main amplifier  47  and the like are not limited to those described in the above embodiments. To be specific, the phase shifter becomes unnecessary when there is no need to control the directivity of the microwave radiated from the planar slot antenna or to obtain the circular polarized waves. Moreover, the antenna unit  40  is not necessarily provided with a plurality of antenna modules  41 , and a single antenna module is sufficient in a small-sized plasma source such as a remote plasma or the like. 
     In the present embodiment, all the shortenings in the length of the main body container  50  are performed by employing three methods of controlling the movement of the slugs  58  by the controller  60 ; using the high-purity alumina as the material of slugs  58 ; and uniformly forming four slots of the planar slot antenna  51 . Alternatively, any one or two of the methods may be used. In this case, the remaining conditions may be set to be identical to that of the conventional method. 
     Although the four slots  51   a  of the antenna  51  is uniformly formed in the present embodiment, five or more slots may be formed; or one to three slots may be formed with a little reduced efficiency. The slot(s) formed in the planar slot antenna  51  preferably has a fan shape so as to be scaled down by shortening the length thereof, but is not limited thereto. 
     Further, although an etching processing apparatus is used as an example of a plasma processing apparatus in the above embodiments, it is not limited thereto. Other plasma processing apparatuses for performing a film forming process, an oxynitride film forming process, an ashing process and the like may be used. Furthermore, the target substrate to be processed is not limited to the semiconductor wafer W. Alternatively, the target substrate may be one of various substrates, which are used in a flat panel display (FPD) including a liquid crystal display (LCD) as a representative example, a ceramic substrate or the like. 
     While the invention has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.