Patent Publication Number: US-2020294766-A1

Title: Plasma generation unit and method of discriminating state of physical quantity which is used for plasma generation

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims the benefit of priority from Japanese Patent Application No. 2019-046808 filed on Mar. 14, 2019 with the Japan Patent Office, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     Exemplary embodiments of the present disclosure relate to a plasma generation unit and a method of discriminating a state of a physical quantity which is used for plasma generation. 
     BACKGROUND 
     In plasma etching, in order to improve productivity even in the miniaturization and increase in diameter of IC manufacturing, there is a case where plasma which is generated by an RLSA (Radial Line Slot Antenna) is used. 
     Japanese Unexamined Patent Publication No. 2013-016443 discloses a technique aimed at improving the in-plane uniformity of a substrate surface processing amount. In this technique, an antenna includes a dielectric window and a slot plate provided on one surface of the dielectric window. The other surface of the dielectric window has a flat surface surrounded by a first recessed portion having an annular shape, and a plurality of second recessed portions formed in the flat surface to surround the position of the centroid of the flat surface. In a case of being viewed from a direction perpendicular to a main surface of the slot plate, the position of the centroid of each of the second recessed portions is located to overlap in each slot of the slot plate. 
     Japanese Unexamined Patent Publication No. 2015-130325 discloses a technique aimed at improving the in-plane uniformity of plasma. In this technique, a slot plate is disposed on the one surface side of a dielectric window. The other surface of the dielectric window includes a flat surface surrounded by a first recessed portion having an annular shape, and a plurality of second recessed portions formed on the bottom surface of the first recessed portion. 
     SUMMARY 
     In an exemplary embodiment, a plasma generation unit which is used in a plasma processing apparatus is provided. The plasma generation unit includes a dielectric window, a slot plate, and a probe group. The slot plate is provided on the dielectric window. The probe group includes a plurality of probes that are electric conductors, is provided in the dielectric window, and is used for detection of a physical quantity which is used for plasma generation and exists around the dielectric window. The dielectric window extends along the slot plate. Each of the plurality of probes is disposed on a circumference of a first circle centered on a reference position of the dielectric window, when viewed from above the dielectric window. 
     The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, exemplary embodiments, and features described above, further aspects, exemplary embodiments, and features will become apparent by reference to the drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing an example of a configuration of a plasma processing apparatus according to an exemplary embodiment. 
         FIG. 2  is a diagram showing an example of a configuration of a probe shown in  FIG. 1 . 
         FIG. 3  is a diagram showing an example of a disposition aspect of the probe. 
         FIG. 4  is a diagram showing an example of another disposition aspect of the probe. 
         FIG. 5  is a diagram showing an example of a configuration of a plasma generation unit according to the exemplary embodiment. 
         FIG. 6  is a diagram showing an example of a distribution of a physical quantity which is acquired by the probe group shown in  FIG. 5 . 
         FIG. 7  is a flowchart showing an example of a method according to an exemplary embodiment. 
         FIG. 8  is a diagram showing an example of disposition of an electromagnet. 
         FIG. 9  is a diagram showing an example of a disposition aspect of the probe in a case where a dielectric window is provided with a recessed portion. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. The exemplary embodiments described in the detailed description, drawing, and claims are not meant to be limiting. Other exemplary embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. 
     Hereinafter, various exemplary embodiments will be described. In an exemplary embodiment, a plasma generation unit which is used in a plasma processing apparatus is provided. The plasma generation unit includes a dielectric window, a slot plate, and a probe group. The slot plate is provided on the dielectric window. The probe group includes a plurality of probes that are electric conductors, is provided in the dielectric window, and is used for detection of a physical quantity which is used for plasma generation and exists around the dielectric window. The dielectric window extends along the slot plate. Each of the plurality of probes is disposed on a circumference of a first circle centered on a reference position of the dielectric window, when viewed from above the dielectric window. In this manner, since the plurality of probes of the probe group are disposed on the circumference of the first circle of the dielectric window, the physical quantity around the dielectric window can be detected by the probes over an in-plane in which the dielectric window extends. 
     In an exemplary embodiment, the slot plate has a circular shape when viewed from above the dielectric window. The reference position overlaps a center of the circular shape of the slot plate when viewed from above the dielectric window. 
     In an exemplary embodiment, the dielectric window has a disk shape centered on the reference position. The probe group is provided on a side surface of the dielectric window. 
     In an exemplary embodiment, the probe group is provided on a main surface or a rear surface of the dielectric window. The main surface and the rear surface extend along the slot plate. The rear surface is on a side opposite to the main surface and faces the slot plate. 
     In an exemplary embodiment, the plurality of probes are disposed at equal intervals on the circumference of the first circle. 
     In an exemplary embodiment, a peripheral end of the slot plate is located inside a peripheral end of the dielectric window when viewed from above the dielectric window. 
     In an exemplary embodiment, each of the plurality of probes is disposed outside the slot plate when viewed from above the dielectric window. 
     In an exemplary embodiment, the dielectric window includes a plurality of recessed portions. The plurality of recessed portions are provided on a main surface of the dielectric window. 
     In an exemplary embodiment, the distance between one line closest to the recessed portion, among a plurality of lines each connecting each of the plurality of probes and the reference position, and the recessed portion is the same in each of the plurality of recessed portions. 
     In an exemplary embodiment, the plurality of recessed portions are disposed on a circumference of a second circle centered on the reference position, when viewed from above the dielectric window. 
     In an exemplary embodiment, the plurality of recessed portions are disposed rotationally symmetrically with respect to the reference position, when viewed from above the dielectric window. 
     In an exemplary embodiment, the number of the plurality of recessed portions is equal to or greater than the number of the plurality of probes included in the probe group. 
     In an exemplary embodiment, the plurality of recessed portions have the same shape as each other. 
     A plasma generation unit according to an exemplary embodiment further includes an acquisition unit. The acquisition unit acquires a distribution of the physical quantity around the dielectric window, based on a plurality of values of the physical quantities detected by the probe group. 
     A plasma generation unit according to an exemplary embodiment further includes a discrimination unit, and an alarm unit. The acquisition unit acquires an index which is used for discrimination of a state of the physical quantity around the dielectric window, based on the acquired distribution of the physical quantity. The discrimination unit determines whether or not the index satisfies one reference set in advance, which indicates the state of the physical quantity, and discriminates the state of the physical quantity, based on a determination result. The alarm unit outputs an alarm signal in a case where the discrimination unit determines that the index does not satisfy the reference. 
     In an exemplary embodiment, the index is acquired by using at least one of an average value, a maximum value, a minimum value, and a standard deviation of a plurality of values of the physical quantities detected by the plurality of probes. 
     A plasma generation unit according to an exemplary embodiment further includes a plurality of electromagnets, and an adjustment unit that adjusts an electric current which is supplied to the electromagnets. Magnetic field intensity of a magnetic field generated by the electromagnet is variable according to the electric current which is supplied to the electromagnet. The adjustment unit adjusts an electric current which is supplied to each of the plurality of electromagnets, based on the distribution of the physical quantity acquired by the acquisition unit. 
     In an exemplary embodiment, the plurality of electromagnets are disposed above a rear surface of the dielectric window facing the slot plate. 
     A plasma generation unit according to an exemplary embodiment includes a plurality of the probe groups. 
     In an exemplary embodiment, a method of discriminating a state of a physical quantity which is used for plasma generation is provided. The method acquires a distribution of a physical quantity which is used for plasma generation and exists around a dielectric window, by using a plurality of probes that are electric conductors provided in the dielectric window in a plasma processing apparatus, at the time of plasma generation in the plasma processing apparatus. An index which is used for discrimination of the state of the physical quantity around the dielectric window is acquired based on the acquired distribution of the physical quantity. The state of the physical quantity is discriminated by determining whether or not the index satisfies one reference set in advance, which indicates the state of the physical quantity. In this manner, the distribution of the physical quantity around the dielectric window is acquired through a plurality of probes disposed over an in-plane where the dielectric window extends. The state of the physical quantity around the dielectric window can be suitably discriminated by using the index which is acquired based on the distribution. 
     According to the present disclosure, a technique for discriminating a state of a physical quantity which is used for plasma generation can be provided. 
     Hereinafter, various exemplary embodiments will be described in detail with reference to the drawings. In each drawing, identical or corresponding parts are denoted by the same reference numerals. 
     A plasma processing apparatus  1  according to an exemplary embodiment is a radial line slot antenna type plasma processing apparatus. The plasma processing apparatus  1  is provided with a cylindrical processing container  2 . A processing space S is provided in the interior of the processing container  2 . The processing container  2  is electrically grounded. The inner wall surface of the processing container  2  is covered with an insulating protective film  2   f  such as alumina (Al 2 O 3 ). The material of the processing container  2  is, for example, aluminum. 
     In the processing space S, a table  3  which is used to place a wafer W thereon is provided at the center of a bottom portion of the processing container  2 . The wafer W is held on the upper surface of the table  3 . The material of the table  3  is a ceramic material such as alumina or aluminum nitride, for example. 
     A heater  5  is embedded in the table  3 . The wafer W can be heated to a predetermined temperature by the heater  5 . The heater  5  is connected to a heater power source  4  through a wire disposed in a support post. 
     An electrostatic chuck CK is provided on the upper surface of the table  3 . The electrostatic chuck CK is provided in the processing space S. The electrostatic chuck CK can electrostatically attract the wafer W placed on the table  3 . 
     A bias power source BV is connected to the electrostatic chuck CK. The bias power source BV can apply bias direct-current power or bias radio frequency power through a matching device MG 
     An exhaust pipe  11  is provided at the bottom portion of the processing container  2 . The exhaust pipe  11  can exhaust a processing gas from an exhaust port  11   a  below the surface of the wafer W placed on the table  3 . 
     An exhaust device  10  such as a vacuum pump is connected to the exhaust pipe  11  through a pressure control valve PCV. The exhaust device  10  communicates with the interior of the processing container  2  through the pressure control valve PCV. The pressure in the processing container  2  can be adjusted to a predetermined pressure by the pressure control valve PCV and the exhaust device  10 . 
     The plasma processing apparatus  1  includes a plasma generation unit PGS. The plasma generation unit PGS includes a dielectric window  16 , a slot plate  20 , a probe group PBG, an arithmetic device CT, and a detection device DT. 
     The dielectric window  16  (a top plate) is provided on a ceiling portion of the processing container  2  with a seal  15  interposed therebetween. The ceiling portion (the processing space S) of the processing container  2  is closed by the dielectric window  16 . The seal  15  can be an O-ring or the like for securing airtightness. The material of the dielectric window  16  is permeable to microwaves and can be a dielectric such as quartz (SiO 2 ), alumina, or aluminum nitride (AlN), for example. 
     The dielectric window  16  has a disk shape centered on a reference position CP of the dielectric window  16 . The reference position CP overlaps a central axis AX of the slot plate  20 . A main surface PS of the dielectric window  16  faces the processing space S. 
     A rear surface RS of the dielectric window  16  is on the side opposite to the main surface PS and faces the slot plate  20 . The dielectric window  16  extends along the slot plate  20 . The main surface PS and the rear surface RS of the dielectric window  16  extend along the slot plate  20 . 
     The peripheral end of the slot plate  20  is located inside the peripheral end of the dielectric window  16  when viewed from above the dielectric window  16 . In other words, the dielectric window  16  covers the slot plate  20  when viewed from above the dielectric window  16 . 
     The slot plate  20  is provided on the dielectric window  16 . The slot plate  20  is provided on the rear surface RS of the dielectric window  16 . The slot plate  20  has a circular shape when viewed from above the dielectric window  16 . 
     The material of the slot plate  20  is a material having conductivity and can be, for example, copper plated or coated with Ag or Au. In the slot plate  20 , a plurality of slots  21  are arranged concentrically with respect to the center of the circular shape of the slot plate  20 , when viewed from above the dielectric window  16 . 
     The probe group PBG includes a plurality of probes PB that are electric conductors, is provided in the dielectric window  16 , and is used for detection of a physical quantity (hereinafter referred to as a physical quantity PV) around the dielectric window  16 . The physical quantity PV described in this specification is a physical quantity which is detected by the probe group PBG is used for plasma generation, and exists to be distributed around the dielectric window  16  at the time of the plasma generation. The physical quantity PV can be, for example, electric field intensity, electric potential, electric power, or the like. As shown in  FIG. 2 , the probe PB includes an inner conductor PB 1 , a coating PB 2 , a base PB 3 , and a connection member PB 4 . 
     The inner conductor PB 1  and the coating PB 2  are fitted in a hole provided in the center of the base PB 3 . The inner conductor PB 1  and the coating PB 2  extend from the inside of the base PB 3  onto the base PB 3 . The inner conductor PB 1  is covered with the coating PB 2 . 
     The base PB 3  is provided in the dielectric window  16 . The inner conductor PB 1  and the coating PB 2  are held by the connection member PB 4  on the base PB 3 . 
     The material of the inner conductor PB 1  has conductivity. The material of the coating PB 2  has insulation properties. The material of the base PB 3  has conductivity. The material of the connection member PB 4  has conductivity. 
     A coaxial cable CB can be connected to the probe PB. The coaxial cable CB is connected to the detection device DT. The probe PB is connected to the detection device DT through the coaxial cable CB. 
     The coaxial cable CB includes an inner conductor CB 1 , a coating CB 2 , a connection member CB 3 , an outer conductor CB 4 , and an outer skin CBS. The inner conductor CB 1  comes into contact with an end portion of the inner conductor PB 1  on the base PB 3 . The inner conductor PB 1  and the inner conductor CB 1  are electrically connected to each other. The inner conductor CB 1  is covered with the coating CB 2 . The inner conductor CB 1  and the coating CB 2  are held by the connection member CB 3  on the probe PB. 
     The connection member CB 3  has a recess shape. The inner conductor CB 1  protruding from the inside of the recess shape of the connection member CB 3  reaches the inner conductor PB 1  and comes into contact with the inner conductor PB 1 . The connection member PB 4  is fitted into the recess shape of the connection member CB 3 , whereby the connection member CB 3  is held on the connection member PB 4 . 
     The probe group PBG (the plurality of probes PB) can be provided on a side surface SS of the dielectric window  16  in an exemplary embodiment. The side surface SS extends to intersect the main surface PS and the rear surface RS, and extends between the peripheral end of the main surface PS and the peripheral end of the rear surface RS. Each of the plurality of probes PB of the probe group PBG is disposed outside the slot plate  20  when viewed from above the dielectric window  16 . 
     An example of an aspect of the disposition of the plurality of probes PB is shown in  FIG. 3 .  FIG. 3  shows an aspect of the main surface PS when viewed from above the dielectric window  16 . The probe group PBG is provided on the side surface SS of the dielectric window  16 . However, there is no limitation thereto, and the probe group PBG may be provided on the main surface PS or the rear surface RS of the dielectric window  16 , as shown in  FIG. 4 . 
     Each of the plurality of probes PB is disposed (for example, at equal intervals) on the circumference of a first circle CCA centered on the reference position CP of the dielectric window  16 , when viewed from above the dielectric window  16 . The main surface PS of the dielectric window  16  shown in  FIG. 3  has a circular shape. 
     In an exemplary embodiment, when viewed from above the dielectric window  16 , the reference position CP (the center of the first circle CCA) of the dielectric window  16  overlaps the center of the circular shape of the main surface PS, and can be located in a central introduction part  55 . The reference position CP overlaps the center of the circular shape of the slot plate  20  when viewed from above the dielectric window  16 . 
     In an exemplary embodiment, the plurality of probes PB can be disposed periodically (for example, at equal intervals) in accordance with the disposition of the plurality of slots  21  on the circumference of the first circle CCA. 
     A reference line SL and a plurality of lines RL are shown in  FIG. 3 . The reference line SL extends along the main surface PS through the reference position CP when viewed from above the dielectric window  16 . The line RL is a line connecting the probe PB and the reference position CP (a line extending from the probe PB to the reference position CP through the probe PB). 
     An angle α 1 , an angle α 2 , and an angle α 3  are shown in  FIG. 3 . The angle α 1  is an angle (an acute angle) formed between the line RL passing through the probe PB closest to the reference line SL and the reference line SL. The angle α 2  is an angle (an acute angle) formed between two lines RL respectively passing through two probes PB adjacent to each other on the first circle CCA. The angle α 3  is an angle (an acute angle) formed between the line RL passing through the probe PB which is first located beyond the reference line SL in a case where the opposite side of the reference line SL is viewed along the first circle CCA from the probe PB closest to the reference line SL, and the reference line SL. 
     The plurality of angles α 2  are all equal to each other (for example, in an aspect in which the plurality of probes PB are periodically disposed on the circumference of the first circle CCA). However, there can also be a case where at least some of the plurality of angles α 2  are different. 
     Description will be made returning to  FIG. 1 . A dielectric plate  25  which is used for compression of the wavelength of a microwave is disposed on the upper surface of the slot plate  20 . The material of the dielectric plate  25  can be, for example, a dielectric such as quartz, alumina, or aluminum nitride. The dielectric plate  25  is covered with a conductive cover  26 . 
     An annular heat medium flow path  27  is provided in the cover  26 . The cover  26  and the dielectric plate  25  can be adjusted to a predetermined temperature by the heat medium flowing through the heat medium flow path  27 . 
     A coaxial waveguide  30  that propagates microwaves is connected to the center of the cover  26 . The coaxial waveguide  30  includes an inner conductor  31  and an outer conductor  32 . The inner conductor  31  penetrates the center of the dielectric plate  25  and is connected to the center of the slot plate  20 . 
     A microwave generator  35  is connected to the coaxial waveguide  30  through a mode converter  37  and a rectangular waveguide  36 . The microwave that can be used in the plasma processing apparatus  1  can be a microwave of 2.45 [GHz], 860 [MHz], 915 [MHz], 8.35 [GHz], or the like. For example, the microwave of 2.45 [GHz] has a wavelength of about 12 [cm] in a vacuum and has a wavelength in a range of about 3 to 4 [cm] in the dielectric window  16  made of alumina. 
     The microwave generated by the microwave generator  35  sequentially propagates through the rectangular waveguide  36 , the mode converter  37 , the coaxial waveguide  30 , and the dielectric plate  25 . The rectangular waveguide  36 , the mode converter  37 , the coaxial waveguide  30 , and the dielectric plate  25  function as a microwave introduction path. 
     The microwave propagating through the dielectric plate  25  is supplied from the plurality of slots  21  of the slot plate  20  into the processing space S through the main surface PS of the dielectric window  16 . An electric field is formed below the dielectric window  16  in the processing space S by the microwave, and the processing gas in the processing space S can be turned into plasma. 
     The lower end of the inner conductor  31  which is connected to the slot plate  20  has a truncated cone shape. Therefore, the microwave can efficiently propagate from the coaxial waveguide  30  to the dielectric plate  25  and the slot plate  20  without a loss. 
     In the plasma processing apparatus  1 , the microwave is supplied by a radial line slot antenna. The radial line slot antenna diffuses plasma having an energy of a relatively high electron temperature generated (in a plasma excitation region) just below the dielectric window  16 , thereby forming plasma having a relatively low electron temperature in a range of about 1 to 2 [eV] (in a diffusion plasma region) just above the wafer W. 
     That is, the distribution of the electron temperature of the plasma which is generated by the radial line slot antenna can be expressed as a function of the distance from the dielectric window  16 , unlike the plasma which is generated by a parallel flat plate or the like. More specifically, an electron temperature in a range of several [eV] to 10 [eV] just below the dielectric window  16  can be attenuated to an electron temperature in a range of about 1 to 2 [eV] in the wafer W. Since the processing of the wafer W is performed in a region where the electron temperature of the plasma is low (the diffusion plasma region), large damage such as a recess cannot occur in the wafer W. 
     In a case where the processing gas is supplied to a region where the electron temperature of the plasma is high (the plasma excitation region), the processing gas is easily excited and dissociated. On the other hand, in a case where the processing gas is supplied to a region where the electron temperature of the plasma is low (the diffusion plasma region), the degree of dissociation can be suppressed compared to a case where the processing gas is supplied near the plasma excitation region. 
     The central introduction part  55  is provided in the center of the dielectric window  16  of the ceiling portion of the processing container  2 . The central introduction part  55  can introduce the processing gas to the central portion of the wafer W. The central introduction part  55  is connected to a supply path  52 . The supply path  52  is provided in the inner conductor  31  of the coaxial waveguide  30 . The central introduction part  55  is connected to a gas supply source  100 . 
     The central introduction part  55  has a block  57  and a gas reservoir  60 . The block  57  is fitted into a cylindrical space portion provided in the center of the dielectric window  16 . The block  57  is electrically installed and has a columnar shape. The material of the block  57  is a conductive material such as aluminum, for example. 
     The gas reservoir  60  is provided between the lower surface of the inner conductor  31  of the coaxial waveguide  30  and the upper surface of the block  57 . A plurality of central introduction ports penetrating in an up-down direction are formed in the block  57 . The planar shape of the central introduction port can be formed into a perfect circle or a long hole in consideration of necessary conductance or the like. The aluminum block  57  can be coated with anodized and coated alumina, yttria (Y 2 O 3 ), or the like. 
     The processing gas which is supplied from the gas supply source  100  to the gas reservoir  60  through the supply path  52  penetrating the inner conductor  31  is diffused into the gas reservoir  60  and then sprayed downward from the plurality of central introduction ports of the block  57  and toward the central portion of the wafer W. 
     A peripheral introduction part  61  is provided in the processing space S inside the processing container  2 . The peripheral introduction part  61  is disposed to surround the periphery on the upper side of the wafer W. The peripheral introduction part  61  is disposed below the central introduction port disposed at the ceiling portion and above the wafer W placed on the table  3 . The peripheral introduction part  61  is connected to the gas supply source  100 . The peripheral introduction part  61  can supply the processing gas from the gas supply source  100  to the peripheral portion of the wafer W. 
     The peripheral introduction part  61  has a ring shape. The peripheral introduction part  61  has the shape of an annular hollow pipe. A plurality of peripheral introduction ports  62  are provided at certain intervals in the circumferential direction on the inner periphery side of the peripheral introduction part  61 . The material of the peripheral introduction part  61  can be, for example, quartz. The peripheral introduction port  62  can have a function of spraying the processing gas toward the center of the peripheral introduction part  61 . 
     A supply path  53  made of stainless steel penetrates the side surface of the processing container  2 . The supply path  53  is provided between the gas supply source  100  and the peripheral introduction part  61  and is connected to the gas supply source  100  and the peripheral introduction part  61 . The processing gas which is supplied from the gas supply source  100  to the interior of the peripheral introduction part  61  through the supply path  53  is diffused into the space in the interior of the peripheral introduction part  61  and then sprayed from the plurality of peripheral introduction ports  62  toward the inside of the peripheral introduction part  61 . The processing gas sprayed from the plurality of peripheral introduction ports  62  is supplied to the upper portion of the periphery of the wafer W. In the plasma processing apparatus  1 , it is also possible to provide the plurality of peripheral introduction ports  62  on the inner side surface of the processing container  2 , instead of providing the ring-shaped peripheral introduction part  61  described above. 
     In an exemplary embodiment, the reference position CP (the center) of the dielectric window  16  and the center of each of the slot plate  20 , the dielectric plate  25 , the cover  26 , the inner conductor  31 , and the supply path  52  can overlap each other when viewed from above the dielectric window  16 . More specifically, the reference position CP (the center) of the dielectric window  16  and the center of each of the slot plate  20 , the dielectric plate  25 , the cover  26 , the inner conductor  31 , and the supply path  52  overlap the central axis AX of the processing container  2 . 
     A control unit Cnt includes a CPU, a RAM, a ROM, and the like, and comprehensively controls the operation of the plasma processing apparatus  1 , for example, by causing the CPU to execute a computer program. The control unit Cnt controls particularly the operations of the microwave generator  35 , the pressure control valve PCV, and the bias power source By. The control unit Cnt may have a configuration including the arithmetic device CT. 
     As shown in  FIG. 5 , each of the plurality of probes PB of the probe group PBG is connected to each of the plurality of detection devices DT through each of the plurality of coaxial cables CB. The plurality of detection devices DT are connected to the arithmetic device CT. 
     The detection device DT detects a signal which is output from the probe PB connected to the detection device DT and sends the detected signal to the arithmetic device CT. The plurality of signals which are output from the plurality of probes PB represent the physical quantities PV around the dielectric window  16 , which are detected by the probe group PBG For example, there can be a case where the detection device DT has a wave detector and an oscilloscope connected to the wave detector. 
     The arithmetic device CT includes a computer having a CPU, a ROM, a RAM, and the like, and analyzes a plurality of signals sent from the plurality of detection devices DT. The arithmetic device CT realizes various functions of an acquisition unit CT 1 , a discrimination unit CT 2 , an alarm unit CT 3 , and the like by driving the computer provided in the arithmetic device CT. 
     The acquisition unit CT 1  acquires the distribution of the physical quantity PV around the dielectric window  16 , based on a plurality of values of the physical quantities PV detected by the probe group PBG The acquisition unit CT 1  acquires an index which is used for the discrimination of the state of the physical quantity PV around the dielectric window  16 , based on the acquired distribution of the physical quantity PV. 
     The index is acquired by using at least one of an average value (Ave), a maximum value, a minimum value, and a standard deviation (σ) of the plurality of values of the physical quantities PV detected by the plurality of probes PB. The index can be, for example, any one of an average value, a maximum value, a minimum value, and a value indicating variation of the physical quantities PV detected by the plurality of probes PB. 
     For example, a value obtained by multiplying a coefficient of variation by an integer (for example, three times) can be used for the value indicating variation of the physical quantities PV. The coefficient of variation is a value (σ/Ave) obtained by dividing the standard deviation by the average value. 
       FIG. 6  shows an example of the values of the physical quantities PV detected by the plurality of probes PB. The horizontal axis of  FIG. 6  represents the position of the probe PB (the angle shown in  FIG. 3  and the angle between the line RL passing through the probe PB and the reference line SL) [°], and the vertical axis represents the physical quantity PV. Each of a plurality of points PT indicates the value of the physical quantity PV detected by each of the plurality of probes PB. A line AL indicates the average value of the values of the physical quantities PV detected by each of the plurality of probes PB. 
     σ is the standard deviation of the values of the physical quantities PV detected by each of the plurality of probes PB. 3σ is a value obtained by tripling σ. In  FIG. 6 , as an example, 3σ is shown. However, there is no limitation thereto, and it can be σ, 2σ (a value obtained by doubling σ), or the like. 
     Description will be made returning to  FIG. 5 . The discrimination unit CT 2  determines whether or not the index satisfies one reference set in advance (hereinafter, referred to as a reference SV), which indicates the state of the physical quantity PV around the dielectric window  16 . The discrimination unit CT 2  discriminates the state of the physical quantity PV around the dielectric window  16 , based on the result of the determination of whether or not the index satisfies the reference SV. The reference SV is a value corresponding to the index which is used by the discrimination unit CT 2 , and is different for each content of the index. The alarm unit CT 3  outputs an alarm signal to an external device (for example, a display, a speaker, or the like) in a case where the discrimination unit CT 2  determines that the index does not satisfy the reference SV. 
     The arithmetic device CT acquires signals (signals indicating the values of the detected physical quantities PV) which are sent from the plurality of detection devices DT at every timing set in advance at the time of plasma generation in the plasma processing apparatus  1 , and executes the method MT shown in  FIG. 7 . The method MT is an exemplary embodiment of the method of discriminating the state of the physical quantity PV which is used for plasma generation. The method MT shown in  FIG. 7  is executed by the computer of the arithmetic device CT (the acquisition unit CT 1 , the discrimination unit CT 2 , and the like shown in  FIG. 5 ). The method MT includes step ST 1  to step ST 3 . 
     First, a plurality of signals which are sent from the plurality of detection devices DT at the time of the plasma generation in the plasma processing apparatus  1  are acquired by the arithmetic device CT. The acquisition unit CT 1  acquires the distribution of the physical quantity PV which is used for plasma generation and exists around the dielectric window  16 , by using the probe group PBG (the plurality of probes PB) provided in the dielectric window  16 , based on the plurality of signals acquired from the plurality of detection devices DT (step ST 1 ). 
     Subsequent to step ST 1 , the acquisition unit CT 1  acquires the index which is used for the discrimination of the state of the physical quantity PV around the dielectric window  16 , based on the distribution of the physical quantity PV acquired in step ST 1  (step ST 2 ). 
     Subsequent to step ST 2 , the discrimination unit CT 2  determines whether or not the index acquired in step ST 2  satisfies one reference SV set in advance, which indicates the state of the physical quantity PV around the dielectric window  16 . By this determination, the state of the physical quantity PV around the dielectric window  16  is discriminated (step ST 3 ). In step ST 3 , in a case where the discrimination unit CT 2  determines that the index does not satisfy the reference SV, the alarm unit CT 3  outputs an alarm signal to an external device. 
     Steps ST 1  to ST 3  described above are executed, whereby the state of the physical quantity PV around the dielectric window  16  is discriminated, and in a case where the state of the physical quantity PV around the dielectric window  16  does not satisfy the reference, an alarm signal is output to the external device as necessary. 
     (Modification Example) As shown in  FIG. 8 , the plasma processing apparatus  1  may further include a driving device DV and a plurality of electromagnets EM. In this case, the arithmetic device CT further includes an adjustment unit CT 4 . The magnetic field intensity of a magnetic field which is generated by the electromagnet EM is variable according to an electric current which is supplied to the electromagnet EM. The driving device DV supplies an electric current to the electromagnet EM. The adjustment unit CT 4  adjusts the electric current which is supplied to each of the plurality of electromagnets EM, based on the distribution of the physical quantity PV which is acquired by the acquisition unit CT 1 . 
     For example, a case where the physical quantity PV (a point PT 1  shown in  FIG. 6 ) is detected outside the range of “the average value (Ave)” ±“3 times the standard deviation (3σ)” (the range of Ave-3σ or more and Ave+3σ or less) is considered. In this case, the adjustment unit CT 4  adjusts the electric current which is supplied to the electromagnet EM which is at the position (or a position closest to the position) of the probe PB in which the physical quantity PV (the point PT 1  shown in  FIG. 6 ) has been detected, thereby adjusting plasma density at the position. 
     The plurality of electromagnets EM are disposed above the rear surface RS of the dielectric window  16 , as shown in  FIG. 8 , for example. More specifically, the plurality of electromagnets EM are disposed, for example, on the surface of the cover  26  which is disposed above the rear surface RS of the dielectric window  16 . The plurality of electromagnets EM are disposed such that the plasma density can be adjusted in detail over the lower part of the dielectric window  16 . 
     The dielectric window  16  can include a plurality of recessed portions DP, as shown in  FIG. 9 . The plurality of recessed portions DP are provided on the main surface PS of the dielectric window  16 . A second circle CCB, a line CL, and an angle β are shown in  FIG. 9 . 
     The plurality of recessed portions DP are disposed on the circumference of the second circle CCB centered on the reference position CP when viewed from above the dielectric window  16 . The line CL shown in  FIG. 9  is a line connecting the recessed portion DP and the reference position CP (a line extending from the recessed portion DP to the reference position CP through the recessed portion DP). 
     The angle β is an angle between a set of line RL and line CL adjacent to each other and closest to each other. The angle β can be in the range of 0 [°] or more and less than an angle α 2  [°]. 
     For example, all the angles β are the same. In this case, the plurality of recessed portions DP are disposed rotationally symmetrically with respect to the reference position CP, when viewed from above the dielectric window  16 . More specifically, the distance between one line RL closest to a specific recessed portion DP among the plurality of lines RL and the specific recessed portion DP (the angle β between the one line RL and the line CL passing through the specific recessed portion DP) is the same in each of the plurality of recessed portions DP. 
     The number of the plurality of recessed portions DP is equal to or greater than the number of the plurality of probes PB included in the probe group PBG The number of the plurality of recessed portions DP can be, for example, a positive integer multiple (one time, two times, or the like) of the number of the plurality of probes PB included in the probe group PBG Further, in an exemplary embodiment, the plurality of recessed portions DP can have the same shape as each other. 
     According to the plasma generation unit PGS as described above, the plurality of probes PB of the probe group PBG are disposed on the circumference of the first circle CCA of the dielectric window  16 . Therefore, the physical quantity PV around the dielectric window  16  can be detected by the probe PB over the in-plane in which the probe PB extends. 
     Further, according to the method MT as described above, the distribution of the physical quantity PV around the dielectric window  16  is acquired through the plurality of probes PB disposed over the in-plane in which the dielectric window  16  extends. The state of the physical quantity PV around the dielectric window  16  can be suitably discriminated by using the index which is obtained based on the distribution. 
     The number of the probe groups PBG is not limited to one and may be plural. In this case, the plurality of probe groups PBG can mutually have a rotationally symmetric relationship with the reference position CP as the center, when viewed from above the dielectric window  16 . 
     Various exemplary embodiments have been described above. However, the present disclosure is not limited to the exemplary embodiments described above and various omissions, substitutions, and changes may be made. Further, elements in different exemplary embodiments can be combined to form other exemplary embodiments. 
     The present disclosure provides a technique for discriminating the state of the physical quantity which is used for plasma generation. 
     Although various exemplary embodiments have been described above, various modified aspect may be configured without being limited to the above-described exemplary embodiments. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the embodiments described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.