Patent Publication Number: US-2021166920-A1

Title: Plasma processing apparatus and measurement method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2019-215428 filed on Nov. 28, 2019, the entire disclosure of which is incorporated herein by reference. 
     FIELD 
     Exemplary embodiments of the present disclosure relate to a plasma processing apparatus and a measurement method. 
     BACKGROUND 
     A plasma processing apparatus is used to perform plasma processing on a substrate. In a chamber in the plasma processing apparatus, the substrate is placed in an area surrounded by an edge ring. The edge ring may also be called a focus ring. 
     The edge ring can wear and become thinner through plasma. processing performed in the plasma processing apparatus. As the edge ring has a smaller thickness, a sheath that forms above the edge ring can have an upper end at a lower position. With the sheath above the edge ring having the upper end at a lower position, ions in the plasma can diagonally strike the edge of the substrate, thus causing tilting of recesses in the edge of the substrate. Tb reduce such tilting of recesses in the edge of the substrate, a direct-current (DC) voltage is applied to the edge ring as described in Japanese Unexamined Patent Application Publication No. 2007-258417. 
     SUMMARY 
     A plasma processing apparatus according to an exemplary embodiment includes a chamber, a substrate support, an electric path, and a measuring device. The substrate support is accommodated in the chamber. The electric path is coupled to or capacitively coupled to an edge ring on the substrate support. The measuring device measures an electrical characteristic value of the edge ring with a voltage applied to the edge ring on the substrate support through the electric path. The electrical characteristic value measured by the measuring device is variable in accordance with a thickness of the edge ring. 
     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 schematic diagram of a plasma processing apparatus according to an exemplary embodiment. 
         FIG. 2  is a diagram of a substrate support, an electric path, and a measuring device according to the exemplary embodiment. 
         FIG. 3  is a plan view of a first electrode and a second electrode in an exemplary layout. 
         FIG. 4  is a diagram of an electric path including a first electrode and a second electrode according to another embodiment. 
         FIG. 5  is a plan view of the first electrode and the second electrode in another exemplary layout. 
         FIG. 6  is a diagram of a substrate support according to another exemplary embodiment. 
         FIG. 7  is a diagram of an electric path including a first electrode and a second electrode according to still another embodiment. 
         FIG. 8  is a plan view of the first electrode and the second electrode in still another exemplary layout. 
         FIG. 9  is a diagram of a substrate support, an electric path, and a measuring device according to still another exemplary embodiment. 
         FIG. 10  is a plan view of a first contact and a second contact in an exemplary layout. 
         FIG. 11  is a diagram of a measuring device according to still another exemplary embodiment. 
         FIG. 12  is a diagram of the measuring device according to the other exemplary embodiment including contacts between the edge ring and electric paths extending from two voltage sensors in the measuring device in an exemplary layout. 
         FIG. 13  is a diagram of an electric path according to still another exemplary embodiment. 
         FIG. 14  is a plan view of the electric path according to the other exemplary embodiment. 
         FIG. 15  is a diagram of an adjuster and an edge ring according to still another exemplary embodiment. 
         FIG. 16  is a diagram of an adjuster and an edge ring according to still another exemplary embodiment. 
         FIG. 17  is a flowchart of a method according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments will now be described. 
     A plasma processing apparatus according to one exemplary embodiment includes a chamber, a substrate support, an electric path, and a measuring device. The substrate support is accommodated in the chamber. The electric path is coupled to or capacitively coupled to an edge ring on the substrate support. The measuring device measures an electrical characteristic value of the edge ring with a voltage applied to the edge ring on the substrate support through the electric path. The electrical characteristic value measured by the measuring device is variable in accordance with a thickness of the edge ring. 
     When the edge ring is on the substrate support, the electric path to be coupled to or to be capacitively coupled to the edge ring forms in the above embodiment. The measuring device applies a voltage to the edge ring through the electric path to measure an electrical characteristic value of the edge ring that varies depending on the thickness of the edge ring. Thus, the technique according to the above embodiment enables determination of a value reflecting the thickness of an edge ring. 
     In one exemplary embodiment, the plasma processing apparatus may further include a temperature controller that controls a temperature of the edge ring. In this embodiment, the measuring device may obtain the electrical characteristic value of the edge ring with the temperature being controlled at a reference temperature by the temperature controller. 
     In one exemplary embodiment, the plasma processing apparatus may further include a temperature sensor that obtains a temperature measurement value of the edge ring. In this embodiment, the electrical characteristic value may include an electrical characteristic value of the edge ring at a reference temperature. In this embodiment, the measuring device may convert an electrical characteristic value of the edge ring at the temperature measurement value obtained by the temperature sensor to an electrical characteristic value of the edge ring at the reference temperature. 
     In one exemplary embodiment, the measuring device may measure the electrical characteristic value with an alternating-current voltage or a radio-frequency voltage applied to the edge ring through the electric path capacitively coupled to the edge ring. 
     In one exemplary embodiment, the electrical characteristic value may include a value of a real part of an impedance of the edge ring. 
     In one exemplary embodiment, the substrate support may include a dielectric portion on which a part of the edge ring is placeable. In this embodiment, the electric path may include a first electrode and a second electrode located in the dielectric portion. In this embodiment, the measuring device may apply the alternating-current voltage or the radio-frequency voltage to the edge ring through the first electrode and the second electrode capacitively coupled to the edge ring. 
     In one exemplary embodiment, the substrate support may further include a lower electrode and an electrostatic chuck. The electrostatic chuck may be located on the lower electrode. In this embodiment, the dielectric portion may extend between the lower electrode and the electrostatic chuck and a side wall of the chamber to surround the lower electrode and the electrostatic chuck. 
     In one exemplary embodiment, the substrate support may include an electrostatic chuck. The dielectric portion may include a part of the electrostatic chuck. 
     In one exemplary embodiment, the first electrode and the second electrode may be electrically coupled to one or more direct-current power supplies to generate an electrostatic attraction between the electrostatic chuck and the edge ring. In other words, in this embodiment, the two electrodes used to generate the electrostatic attraction between the electrostatic chuck and the edge ring are also used to apply a voltage to the edge ring to deter mine the electrical characteristic value of the edge ring. 
     In one exemplary embodiment, the measuring device may measure the electrical characteristic value with a direct-current voltage applied to the edge ring through the electric path coupled to the edge ring. 
     In one exemplary embodiment, the electrical characteristic value may include a resistance of the edge ring. 
     In one exemplary embodiment, the electric path may include a first contact and a second contact in contact with the edge ring at positions symmetric to each other about a central axis of the edge ring. 
     In one exemplary embodiment, the measuring device may include a current sensor and a voltage sensor. In this embodiment, the current sensor may be located on the electric path to measure a current value of a current flowing through the edge ring. In this embodiment, the voltage sensor may measure a potential difference across the edge ring between the first contact and the second contact. In this embodiment, the measuring device may determine the resistance based on the potential difference and the current value. 
     In one exemplary embodiment, the measuring device may include a current sensor, a first voltage sensor, and a second voltage sensor. In this embodiment, the current sensor may be located on the electric path to measure a current value of a current flowing through the edge ring. In this embodiment, the first voltage sensor may measure a first potential difference across a first area of the edge ring extending in a first part of a plane including the first contact, the second contact, and the central axis. In this embodiment, the second voltage sensor may measure a second potential difference across a second area of the edge ring extending in a second part of the plane. In this embodiment, the measuring device may determine the resistance based on an average of the first potential difference and the second potential difference and on the current value. 
     In one exemplary embodiment, the measuring device may determine a thickness of the edge ring or a decrease in the thickness of the edge ring based on the electrical characteristic value. 
     In one exemplary embodiment, the plasma processing apparatus may further include an adjuster and a controller. In this embodiment, the adjuster may adjust an upper end position of a sheath above the edge ring. The controller may control the adjuster to reduce tilting of a recess in an edge of a substrate on the substrate support in accordance with the electrical characteristic value, or a thickness of the edge ring determined based on the electrical characteristic value or a decrease in the thickness of the edge ring determined based on the electrical characteristic value. 
     In one exemplary embodiment, the adjuster may be controlled by the controller to adjust a vertical position of an upper surface of the edge ring or a potential of the edge ring. The vertical position of the upper surface of the edge ring or the potential of the edge ring may be adjusted in accordance with the electrical characteristic value, or the thickness of the edge ring determined based on the electrical characteristic value or the decrease in the thickness of the edge ring determined based on the electrical characteristic value. 
     In one exemplary embodiment, the adjuster may include a power supply electrically coupled to the edge ring to set a potential of the edge ring. In this embodiment, the electric path may include a first switch and a second switch that selectively couple the edge ring to the power supply or to the measuring device. 
     A measurement method according to one exemplary embodiment includes applying a voltage to an edge ring on a substrate support in a chamber in a plasma processing apparatus. The method further includes measuring an electrical characteristic value of the edge ring variable in accordance with a thickness of the edge ring with the voltage applied to the edge ring. 
     Exemplary embodiments will now be described in detail with reference to the drawings. in the drawings, similar or corresponding components are indicated by like reference numerals. The embodiments are illustrated by way of example and not by way of limitation in the accompanying drawings that are not to scale unless otherwise indicated. 
       FIG. 1  is a schematic diagram of a plasma processing apparatus according to an exemplary embodiment. A plasma processing apparatus  1  shown in  FIG. 1  is a capacitively coupled plasma processing apparatus. The plasma processing apparatus  1  includes a chamber  10  having an internal space  10   s  with a central axis AX in the vertical direction. 
     In one embodiment, the chamber  10  includes a chamber body  12 , which is substantially cylindrical and has the internal space  10   s.  The chamber body  12  is formed from, for example, aluminum, and is electrically grounded. The chamber body  12  has an inner wall defining the internal space  10   s,  coated with a plasma-resistant film. The film may be a ceramic film, such as an anodized film or a film formed from yttrium oxide. 
     The chamber body  12  has a side wall having a port  12   p . A substrate W is transferred between the internal space  10   s  and the outside of the chamber  10  through the port  12   p.  A gate valve  12   g  is on the side wall of the chamber body  12  to open and close the port  12   p.    
     The plasma processing apparatus  1  further includes a substrate support  16 . The substrate support  16  supports the substrate W on the substrate support  16  in the chamber  10 . The substrate W is substantially disk-shaped. The substrate support  16  is supported by a support  17 . The support  17  extends upward from the bottom of the chamber body  12 . The support  17  is substantially cylindrical and is formed from an insulating material such as quartz. 
     The substrate support  16  includes a lower electrode  18  and an electrostatic chuck (ESC)  20 . The lower electrode  18  and the ESC  20  are accommodated in the chamber  10 . The lower electrode  18  is substantially disk-shaped and is formed from a conductive material such as aluminum. 
     The lower electrode  18  has an internal channel  18   f  for carrying a heat-exchange medium. Examples of the heat-exchange medium include a liquid refrigerant and a refrigerant to be vaporized (e.g., chlorofluorocarbon) to cool the lower electrode  18 . The channel  18   f  is connected to a supply unit  23  (e.g., chiller unit) for supplying the heat-exchange medium. The supply unit  23  is external to the chamber  10 . The heat-exchange medium is supplied from the supply unit  23  to the channel  18   f  through a pipe  23   a,  and then returns to the supply unit  23  through a pipe  23   b.  The temperature of the substrate W on the substrate support  16  is adjusted through the heat-exchange medium circulating through the supply unit  23  and the channel  18   f.    
       FIG. 2  is a diagram of the substrate support, an electric path, and a measuring device according to the exemplary embodiment. As shown in  FIGS. 1 and 2 , the ESC  20  is on the lower electrode  18 . The substrate W is placed onto and held by the ESC  20  for processing in the internal space  10   s.    
     The ESC  20  includes a body  20   m  and an electrode  20   e.  The body  20   m  is substantially disk-shaped and is formed from a dielectric such as aluminum oxide or aluminum nitride. The ESC  20  has the axis AX as its central axis. The electrode  20   e  is located in the body  20   m . The electrode  20   e  may be a conductive film The electrode  20   e  is electrically coupled to a direct-current (DC) power supply  20   p  via a switch  20   s.  A voltage is applied from the DC power supply  20   p  to the electrode  20   e  to generate an electrostatic attraction between the ESC  20  and the substrate W. The electrostatic attraction causes the ESC  20  to attract and hold the substrate W. 
     In one embodiment, the ESC  20  may include a first portion  201  and a second portion  202 . The first portion  201  can hold the substrate W placed on the first portion  201 . The first portion  201  is substantially disk-shaped and has the axis AX as its central axis. The substrate W is placed onto the upper surface of the first portion  201  for processing in the chamber  10 . The electrode  20   e  is located in the first portion  201  and in the body  20   m.    
     The second portion  202  extends circumferentially about the central axis of the ESC  20 , or about the axis AX, to surround the first portion  201 . An edge ring ER is placed on the upper surface of the second portion  202 . The edge ring ER is substantially annular and is placed on the second portion  202  with its central axis aligned with the axis AX. The substrate W is placed in an area on the first portion  201  surrounded by the edge ring ER. The edge ring ER is formed from, for example, a conductor or a semiconductor such as silicon or silicon carbide, or a dielectric such as quartz. The second portion  202  may be an ESC holding the edge ring ER. For example, the second portion  202  may incorporate a bipolar electrode in the body  20   m  as described later with reference to  FIG. 6 . 
     As shown in  FIG. 1 , the plasma processing apparatus  1  may further include a gas supply line  25 . The gas supply line  25  supplies a heat-transfer gas (e.g., He gas) from a gas supply assembly into a space between an upper surface of the ESC  20  and a back surface (lower surface) of the substrate W. 
     The plasma processing apparatus  1  may further include an insulating portion  27 . The insulating portion  27  is formed from a dielectric such as quartz. The insulating portion  27  extends between a side wall of the chamber  10  and both the lower electrode  18  and the ESC  20  to surround the lower electrode  18  and the ESC  20 . The insulating portion  27  extends circumferentially along the outer peripheral surfaces of the lower electrode  18  and the second portion  202  of the ESC  20 . The insulating portion  27  may be on the support  17 . The edge ring ER is placed on the insulating portion  27  and on the second portion  202 . In other words, a part of the edge ring ER may be placed on the insulating portion  27 . 
     The plasma processing apparatus  1  further includes an upper electrode  30 . The upper electrode  30  is above the substrate support  16 . The upper electrode  30  closes a top opening of the chamber body  12  together with an insulating member  32 . The upper electrode  30  is supported on an upper portion of the chamber body  12  with the member  32 . 
     The upper electrode  30  includes a ceiling plate  34  and a support member  36 . The ceiling plate  34  has its lower surface defining the internal space  10   s . The ceiling plate  34  has multiple gas outlet holes  34   a  that are through-holes in the thickness direction (vertical direction). The ceiling plate  34  is formed from, but is not limited to, silicon. In some embodiments, the ceiling plate  34  may be an aluminum member coated with a plasma-resistant film. The film may be a ceramic film, such as an anodized film or a film formed from yttrium oxide. The plasma processing apparatus  1  may include a mechanism for changing the distance between the lower electrode  18  and the upper electrode  30 . Changing the distance can control the density distribution of plasma. 
     The support member  36  supports the ceiling plate  34  in a detachable manner. The support member  36  is formed from a conductive material such as aluminum. The support member  36  has an internal gas-diffusion compartment  36   a.  Multiple gas holes  36   b  extend downward from the gas-diffusion compartment  36   a.  The gas holes  36   b  communicate with the respective gas outlet holes  34   a.  The support member  36  has a gas inlet  36   c  that connects to the gas-diffusion compartment  36   a  and to a gas supply pipe  38 . 
     The gas supply pipe  38  is connected to a set of gas sources  40  via a set of valves  41 , a set of flow controllers  42 , and a set of valves  43 . The valve set  41 , the flow controller set  42 , and the valve set  43  form a gas supply unit. The gas supply unit may further include the gas source set  40 . The gas source set  40  includes multiple gas sources. The valve sets  41  and  43  each include multiple valves (e.g., open-close valves). The flow controller set  42  includes multiple flow controllers. The flow controllers in the flow controller set  42  are mass flow controllers or pressure-based flow controllers. The gas sources in the gas source set  40  are connected to the gas supply pipe  38  via the respective valves in the valve set  41 , via, the respective flow controllers in the flow controller set  42 , and via, the respective valves in the valve set  43 . The plasma processing apparatus  1  can supply a gas from one or more gas sources selected from the multiple gas sources in the gas source set  40  into the internal space  10   s  at an individually controlled flow rate. 
     A baffle plate  48  is located between the substrate support  16  or the support  17  and the side wall of the chamber body  12 . The baffle plate  48  may include, for example, an aluminum member covered with ceramic such as yttrium oxide. The baffle plate  48  has many through-holes. An exhaust pipe  52  is connected to the bottom of the chamber body  12  below the baffle plate  48 . The exhaust pipe  52  is connected to an exhaust device  50 . The exhaust device  50  includes a pressure controller such as an automatic pressure control valve and a vacuum pump such as a turbomolecular pump to reduce the pressure in the internal space  10   s.    
     The plasma processing apparatus  1  further includes a radio-frequency (RF) power supply  61 . The RF power supply  61  generates RF power HF. The RF power HF is used to generate plasma from a gas in the chamber  10 . The RF power HF has a frequency ranging from 13 to 200 MHz, or for example, 40 or 60 MHz. The RF power supply  61  is coupled to the lower electrode  18  via a matching circuit  63 . The matching circuit  63  has a variable impedance. The impedance of the matching circuit  63  is adjusted to reduce reflection from a load fir the RF power supply  61 . For example, the matching circuit  63  adjusts the impedance of the load (lower electrode  18 ) for the RF power supply  61  to match to the output impedance of the RF power supply  61 . The RF power supply  61  may not be electrically coupled to the lower electrode  18 , and may be coupled to the upper electrode  30  via the matching circuit  63 . 
     The plasma processing apparatus  1  further includes a bias power supply  62 . The bias power supply  62  is electrically coupled to the lower electrode  18 . The bias power supply  62  generates bias power BP, which is used to draw ions toward the substrate W The bias power BP is controlled to periodically change the potential of the substrate W on the ESC  20  in accordance with a second frequency lower than the first frequency. 
     In one embodiment, the bias power BP may be RE power with the second frequency. In this embodiment, the bias power BP has a frequency ranging from 50 kHz to 30 MHz inclusive, or may for example be 400 kHz. In this embodiment, the bias power supply  62  is coupled to the lower electrode  18  via a matching circuit  64 . The matching circuit  64  has a variable impedance. The impedance of the matching circuit  64  is adjusted to reduce reflection from a load for the bias power supply  62 . For example, the matching circuit  64  adjusts the impedance of the load (lower electrode  18 ) for the bias power supply  62  to match to the output impedance of the bias power supply  62 . 
     In another embodiment, the bias power supply  62  may intermittently or periodically apply a pulsed negative DC voltage to the lower electrode  18  as the bias power BP. The pulsed DC voltage may be periodically applied to the lower electrode  18  in accordance with the second frequency. In this embodiment, the second frequency ranges from 50 kHz to 27 MHz inclusive, or may for example be 400 kHz. In this embodiment, the matching circuit  64  may be eliminated. 
     A gas is supplied into the internal space  10   s  for plasma processing, or for example, plasma etching, in the plasma processing apparatus  1 . At least one of the RF power HF or the bias power BP is then provided to excite the gas in the internal space  10   s.  This generates plasma in the internal space  10   s.  The substrate W is processed with a chemical species of, for example, ions or radicals, contained in the generated plasma. 
     In one embodiment, the plasma processing apparatus  1  may further include an adjuster  74 . The adjuster  74  adjusts an upper end position of a sheath above the edge ring ER. The adjuster  74  adjusts the upper end position of the sheath above the edge ring ER to eliminate or reduce a difference between the upper end position of the sheath above the edge ring ER and the upper end position of the sheath above the substrate W. 
     In one embodiment, the adjuster  74  is a power supply for applying a voltage to the edge ring ER to control the potential of the edge ring ER. The adjuster  74  may apply a negative voltage to the edge ring ER. The adjuster  74  may apply a DC voltage or an RF voltage to the edge ring ER. In some embodiments, the adjuster  74  may intermittently or periodically apply a pulsed DC voltage to the edge ring ER. In this embodiment, the adjuster  74  is coupled to the edge ring ER through a filter  75  and a conducting wire  76 . The filter  75  cuts or reduces RF power entering the adjuster  74 . 
     The plasma processing apparatus  1  further includes a measuring device  80  and an electric path  82 . The electric path  82  is coupled to or capacitively coupled to the edge ring ER placed on the substrate support  16 . The measuring device  80  applies a voltage to the edge ring ER placed on the substrate support  16  through the electric path  82  to measure an electrical characteristic value of the edge ring ER. The electrical characteristic value of the edge ring ER measured by the measuring device  80  varies depending on the thickness of the edge ring ER. The measuring device  80  and the electric path  82  according to embodiments will be described in detail later. 
     In one embodiment, the plasma processing apparatus  1  may further include a temperature sensor  84  as shown in  FIG. 2 . The temperature sensor  84  measures the temperature of the edge ring ER. In one example, the temperature sensor  84  may measure the internal temperature of the substrate support  16  as the temperature of the edge ring ER. In this example, the supply unit  23  may adjust at least one of the temperature or the flow rate of the heat-exchange medium in accordance with the temperature measured by the temperature sensor  84 . 
     A controller MC is a computer including a processor, a storage, an input device, and a display, and controls the components of the plasma processing apparatus  1 . The controller MC executes a control program stored in the storage to control the components of the plasma processing apparatus  1  in accordance with recipe data stored in the storage. in response to the control by the controller MC, a process specified by the recipe data is performed in the plasma processing apparatus  1 . The components of the plasma processing apparatus  1  are controlled by the controller MC to allow the plasma processing apparatus  1  to implement a method according to an embodiment (described later). 
     Referring now to  FIG. 2 , the electric path  82  is capacitively coupled to the edge ring ER in one embodiment. The electric path  82  shown in  FIG. 2  includes a first electrode  821  and a second electrode  822 . The first electrode  821  and the second electrode  822  are capacitively coupled to the edge ring ER placed on the substrate support  16 . The first electrode  821  and the second electrode  822  are located in a dielectric portion on which a part of the edge ring ER is placed.  FIG. 3  is a plan view of the first electrode and the second electrode in an exemplary layout. In the example shown in  FIG. 3 , the first electrode  821  and the second electrode  822  are located in the body  20   m  of the second portion  202 . In the example shown in  FIG. 3 , the first electrode  821  and the second electrode  822  are symmetric to each other about the axis X. The first electrode  821  and the second electrode  822 , which each extend circumstantially about the axis AX, are located apart from each other circumferentially. The first electrode  821  and the second electrode  822  may be substantially circular or island electrodes. 
     In one embodiment, the measuring device  80  determines a resistance R ER  of the edge ring ER as the electrical characteristic value of the edge ring ER. As shown in  FIG. 2 , the measuring device  80  may include a power supply  80   p,  a voltage sensor  80   v,  and a current sensor  80   i , The voltage sensor  80   v  is coupled to the power supply  80   p  and the current sensor  80   i  in parallel. The current sensor  80   i  is coupled to the power supply  80   p  in series. The measuring device  80  may further include an arithmetic unit  80   c.  The arithmetic unit  80   c  may include a processor and a memory. 
     The power supply  80   p  is an alternating-current (AC) power supply or an RE power supply. More specifically, the power supply  80   p  applies an AC voltage or an RE voltage to the edge ring ER through the electric path  82 . When the circuit including the electric path  82  and the edge ring ER does not resonate, the electric path  82  may include an inductor  82   i,  The inductance of the inductor  82   i  is adjustable to cause resonance of the circuit including the electric path  82  and the edge ring ER. In some embodiments, the frequency of the RE power may be changed, and the impedance at the frequency may be measured to determine its real part. 
     The arithmetic unit  80   c  determines the real part of the impedance of the edge ring ER as the resistance R ER  of the edge ring ER. The arithmetic unit  80   c  stores an impedance Z 1  of the edge ring ER not on the substrate support  16 . The arithmetic unit  80   c  determines an impedance Z 2  of the edge ring ER on the substrate support  16 . The arithmetic unit  80   c  can determine the impedance based on a voltage V measured by the voltage sensor  80   v  and a current I measured by the current sensor  80   i  with the formula V/I. 
     The arithmetic unit  80   c  can determine the resistance R ER  of the edge ring ER, or in other words, the real part of the impedance of the edge ring ER by Formula 1 below: 
         R   ER   =Re (( Z   2   ×Z   1 )/( Z   2   −Z   1 ))   (1)
 
     where Re( ) is a function that returns the real part of the operational result in parentheses. 
     The controller MC may calculate the resistance R ER  of the edge ring ER in place of the arithmetic unit  80   c.  In this case, the measuring device  80  includes the controller MC and may eliminate the arithmetic unit  80   c.    
     In some embodiments, the measuring device  80  may include a network analyzer. In this case, the resistance R ER  of the edge ring ER can be determined based on the impedance Z 2  measured by the network analyzer and the impedance Z 1  with Formula 1. The controller MC may perform the operation defined by Formula 1. In this case, the measuring device  80  includes the controller MC and may eliminate the power supply  80   p,  the voltage sensor  80   v,  the current sensor  80   i,  and the arithmetic unit  80   c.  The measuring device  80  may be an impedance meter or another meter with similar functions. 
     When the electrical characteristic value of the edge ring ER is highly dependent on temperature, the electrical characteristic value of the edge ring ER at a reference temperature may be used. When the electrical characteristic value of the edge ring ER is highly dependent on temperature, the measuring device  80  obtains an electrical characteristic value (e.g., resistance R ER ) of the edge ring ER with the temperature being controlled at the reference temperature by a temperature controller. The controller MC controls the temperature controller to reduce a difference between the temperature measured by the temperature sensor  84  and the reference temperature. In one embodiment, the temperature controller includes the supply unit  23 . 
     In some embodiments, when the electrical characteristic value of the edge ring ER is highly dependent on temperature, the arithmetic unit  80   c  or the controller MC in the measuring device  80  may convert an electrical characteristic value of the edge ring ER at a temperature measurement value obtained by the temperature sensor  84 . More specifically, the electrical characteristic value of the edge ring ER at the temperature measurement value obtained by the temperature sensor  84  is converted to the electrical characteristic value of the edge ring ER at the reference temperature using a function or a table. The function or table is predefined for converting the electrical characteristic value of the edge ring ER at the temperature measurement value obtained by the temperature sensor  84  to the electrical characteristic value of the edge ring ER at the reference temperature. For example, the arithmetic unit  80   c  or the controller MC in the measuring device  80  converts the operational result from Formula 1 to the resistance R ER  of the edge ring ER at the reference temperature using the predefined function or table. 
     In one embodiment, the arithmetic unit  80   c  or the controller MC in the measuring device  80  may determine the thickness of the edge ring ER based on an electrical characteristic value (e.g., resistance R ER ) of the edge ring ER. The thickness of the edge ring ER can be determined by converting the electrical characteristic value of the edge ring ER to the thickness of the edge ring ER using a function or a table. The function or table is predefined for converting the electrical characteristic value of the edge ring ER to the thickness of the edge ring ER. In one embodiment, the arithmetic unit  80   c  or the controller MC in the measuring device  80  may determine a decrease in the thickness of the edge ring ER from the initial thickness. 
     In one embodiment, the controller MC controls the adjuster  74  to reduce tilting of recesses in the edge of the substrate W on the substrate support  16 . The controller MC controls the adjuster  74  in accordance with the electrical characteristic value (e.g., resistance R ER ) of the edge ring ER, the thickness of the edge ring ER, or the decrease in the thickness of the edge ring ER. For example, the controller MC determines a potential to be set for the edge ring ER in accordance with the electrical characteristic value (e.g., resistance R ER ) of the edge ring ER, the thickness of the edge ring ER, or the decrease in the thickness of the edge ring ER using a function or a table. The function or table is predefined for determining the potential to be set for the edge ring ER corresponding to the electrical characteristic value (e.g., resistance R ER ) of the edge ring ER, the thickness of the edge ring ER, or the decrease in the thickness of the edge ring ER. The controller MC controls the adjuster  74  to apply a voltage for setting the determined potential in the edge ring ER to the edge ring ER. In some embodiments, the density distribution of plasma may be controlled in accordance with the electrical characteristic value (e.g., resistance R ER ) of the edge ring ER, the thickness of the edge ring ER, or the decrease in the thickness of the edge ring ER. The density distribution of plasma may be controlled by adjusting the distance between the upper electrode and the lower electrode in the plasma processing apparatus. 
     A first electrode and a second electrode according to another embodiment will now be described.  FIG. 4  is a diagram of an electric path including the first electrode and the second electrode according to the other embodiment.  FIG. 5  is a plan view of the first electrode and the second electrode in another exemplary layout. The plasma processing apparatus  1  may include an electric path  82  including a first electrode  821  and a second electrode  822  shown in  FIGS. 4 and 5 . As shown in  FIGS. 4 and 5 , the first electrode  821  and the second electrode  822  may be substantially annular and extend circumferentially about the axis AX. In the illustrated example, the first electrode  821  extends outside the second electrode  822 . The first electrode  821  and the second electrode  822  are located in the second portion  202  and the body  20   m  of the ESC  20 . 
       FIG. 6  is a diagram of a substrate support according to another exemplary embodiment. The plasma processing apparatus  1  may include a substrate support  16  shown in  FIG. 6 . In the substrate support  16  shown in  FIG. 6 , a first electrode  821  and a second electrode  822  are in the same layout as the first electrode  821  and the second electrode  822  in the substrate support  16  shown in  FIGS. 4 and 5 . In the substrate support  16  shown in  FIG. 6 , the second portion  202  serves as an ESC holding the edge ring ER. More specifically, the first electrode  821  and the second electrode  822  in the substrate support  16  shown in  FIG. 6  serve as a bipolar electrode in the ESC. In other words, the two electrodes ( 821  and  822 ) used to generate an electrostatic attraction between the second portion  202  and the edge ring ER are also used to apply a voltage to the edge ring ER to determine the electrical characteristic value of the edge ring ER. 
     In the substrate support  16  shown in  FIG. 6 , the first electrode  821  is electrically coupled to a DC power supply  21   p.  A filter  21   f  and a switch  21   s  may be coupled between the first electrode  821  and the DC power supply  21   p.  The filter  21   f  is a low-pass filter. The second electrode  822  is electrically coupled to a DC power supply  22   p.  A filter  22   f  and a switch  22   s  may be coupled between the second electrode  822  and the DC power supply  22   p.  The filter  22   f  is a low-pass filter. 
     The DC power supply  21   p  applies a DC voltage to the first electrode  821  and the DC power supply  22   p  applies a DC voltage to the second electrode  822  to cause a difference in potential between the first and second electrodes  821  and  822 . This generates an electrostatic attraction between the second portion  202  and the edge ring ER. The second portion  202  attracts the edge ring ER under the generated electrostatic attraction and holds the edge ring ER. A single DC power supply may set the potential for the first electrode  821  and the potential for the second electrode  822 . The second portion  202  may serve as a monopolar ESC. More specifically, the first electrode  821  and the second electrode  822  may receive the same voltage from one or more DC power supplies. 
       FIG. 7  is a diagram of an electric path including a first electrode and a second electrode according to still another embodiment.  FIG. 8  is a plan view of the first electrode and the second electrode in still another exemplary layout. The plasma processing apparatus  1  may include an electric path  82  including a first electrode  821  and a second electrode  822  shown in  FIGS. 7 and 8 . As shown in  FIGS. 7 and 8 , the first electrode  821  and the second electrode  822  are located in the insulating portion  27 . A part of the edge ring ER is placed on the insulating portion  27  and above the first electrode  821  and the second electrode  822 . The first electrode  821  and the second electrode  822  shown in  FIGS. 7 and 8  may be symmetric to each other about the axis AX in the same manner as the first electrode  821  and the second electrode  822  shown in  FIG. 3 . In some embodiments, the first electrode  821  and the second electrode  822  may be located in the insulating portion  27 , and substantially annular to extend circumferentially about the axis AX in the same manner as the first electrode  821  and the second electrode  822  shown in  FIGS. 4 to 6 . 
       FIG. 9  is a diagram of a substrate support, an electric path, and a measuring device according to still another exemplary embodiment.  FIG. 10  is a plan view of a first contact and a second contact in an exemplary layout. The plasma processing apparatus  1  may include a substrate support  16 , an electric path  82 , and a measuring device  80  shown in  FIGS. 9 and 10 . In this case, the plasma processing apparatus  1  uses an electrical characteristic value of an edge ring ER determined by the measuring device  80  shown in  FIG. 9  as well. The plasma processing apparatus  1  including the substrate support  16 , the electric path  82 , and the measuring device  80  shown in  FIGS. 9 and 10  will now be described focusing on its differences from the plasma processing apparatuses  1  according to the embodiments described above. 
     The measuring device  80  shown in  FIG. 9  applies a voltage to the edge ring ER through the electric path  82  coupled to the edge ring ER to measure the electrical characteristic value of the edge ring ER. 
     As shown in  FIGS. 9 and 10 , the electric path  82  includes a first contact  82   a  and a second contact  82   b.  The first contact  82   a  and the second contact  82   b  are in contact with the edge ring ER. In one embodiment, the first contact  82   a  and the second contact  82   b  may be in contact with the edge ring ER at positions symmetric to each other about the central axis of the edge ring ER as shown in  FIG. 10 . In other words, the first contact  82   a  and the second contact  82   b  are symmetric to each other about the axis AX. The first contact  82   a  and the second contact  82   b  may be located on the insulating portion  27  or the second portion  202 . 
     As shown in  FIG. 9 , the measuring device  80  may include a power supply  80   p,  a voltage sensor  80   v,  and a current sensor  80   i.  The power supply  80   p  may be a DC power supply. More specifically, the power supply  80   p  applies a DC voltage to the edge ring ER through the electric path  82 . The current sensor  80   i  is located on the electric path  82  and coupled to the power supply  80   p  in series. The current sensor  80   i  measures a current value of the current flowing through the edge ring ER in accordance with the voltage applied from the power supply  80   p  through the electric path  82 . The voltage sensor  80   v  measures a potential difference across the edge ring ER in accordance with the voltage applied from the power supply  80   p.  The potential difference is a difference in potential between the first contact  82   a  and the second contact  82   b.    
     The measuring device  80  shown in  FIG. 9  may further include an arithmetic unit  80   c.  The arithmetic unit  80   c  may include a processor and a memory. In the measuring device  80  shown in  FIG. 9 , the arithmetic unit  80   c  determines the resistance of the edge ring ER as the electrical characteristic value of the edge ring ER. More specifically, the arithmetic unit  80   c  can determine the resistance of the edge ring ER based on a voltage V (potential difference) measured by the voltage sensor  80   v  and a current I measured by the current sensor  80   i  with the formula V/I. The controller MC may calculate the resistance of the edge ring ER in place of the arithmetic unit  80   c.  In this case, the measuring device  80  includes the controller MC and may eliminate the arithmetic unit  80   c . The voltage sensor  80   v  may measure a potential difference between a contact adjacent to the first contact  82   a  and a contact adjacent to the second contact  82   b.  In other words, the measuring device  80  may determine the resistance of the edge ring ER by a four-terminal method. The four-terminal method can measure the resistance of the edge ring ER with a reduced likelihood of being affected by the resistance of the electric path  82  and the resistance of the wiring that interconnects the voltage sensor  80   v  and the edge ring ER. 
       FIG. 11  is a diagram of a measuring device according to still another exemplary embodiment.  FIG. 12  is a diagram of the measuring device according to the other exemplary embodiment including contacts between an edge ring and electric paths extending from two voltage sensors in the measuring device in an exemplary layout. The plasma processing apparatus  1  may include the measuring device and the electric path shown in  FIGS. 11 and 12 . The plasma processing apparatus  1  including the measuring device and the electric path shown in  FIG. 11  will now be described focusing on its differences from the plasma processing apparatus  1  including the measuring device and the electric path shown in  FIG. 9 . 
     The measuring device  80  shown in  FIG. 11  includes a first voltage sensor  80   v   1  and a second voltage sensor  80   v   2  in place of the voltage sensor  80   v.  The measuring device  80  may measure the resistance of the edge ring ER with the first voltage sensor  80   v   1  and the second voltage sensor  80   v   2  by the four-terminal method. 
     The first voltage sensor  80   v   1  measures a first potential difference across a first area of the edge ring ER. The first area extends in a first part of the plane including the first contact  82   a,  the second contact  82   b , and the central axis (axis AX) of the edge ring ER. The second voltage sensor  80   v   2  measures a second potential difference across a second area of the edge ring ER extending in a second part of the plane. 
     The potential difference across the first area is a difference in potential between the contacts  82   c  and  82   d.  The contacts  82   c  and  82   d  are included in the electric path extending from the first voltage sensor  80   v   1  to the edge ring ER. The contacts  82   c  and  82   d  are in contact with the edge ring ER. The contacts  82   c  and  82   d  may be on the insulating portion  27  or the second portion  202 . 
     The potential difference across the second area is a difference in potential between the contacts  82   e  and  82   f . The contacts  82   e  and  82   f  are included in the electric path extending from the second voltage sensor  80   v   2  to the edge ring ER. The contacts  82   e  and  82   f  are in contact with the edge ring ER. The contacts  82   e  and  82   f  may be on the insulating portion  27  or the second portion  202 . The contacts  82   c  and  82   f  may be symmetric to each other about the central axis (axis AX) of the edge ring ER. The contacts  82   d  and  82   e  may also be symmetric to each other about the central axis (axis AX) of the edge ring ER. 
     The contacts  82   c  and  82   d  may be symmetric to each other across a plane including the central axis (axis AX) of the edge ring ER and orthogonal to a straight line connecting the first contact  82   a  and the second contact  82   b.  The contacts  82   e  and  82   f  may also be symmetric to each other across the plane including the central axis (axis AX) of the edge ring ER and orthogonal to the straight line connecting the first contact  82   a  and the second contact  82   b.    
     The arithmetic unit  80   c  or the controller MC in the measuring device  80  determines the resistance of the edge ring ER based on the average of the first potential difference and the second potential difference and on a current value measured by the current sensor  80   i.  The arithmetic unit  80   c  or the controller MC in the measuring device  80  may determine a first resistivity of the edge ring ER based on the first potential difference, a distance (circumferential distance) between the contacts  82   c  and  82   d,  and a current value measured by the current sensor  80   i.  The arithmetic unit  80   c  or the controller MC in the measuring device  80  may determine a second resistivity of the edge ring ER based on the second potential difference, a distance (circumferential distance) between the contacts  82   e  and  82   f  and a current value measured by the current sensor  80   i.  The arithmetic unit  80   c  or the controller MC in the measuring device  80  may determine the average of the first resistivity and the second resistivity as the electrical characteristic value of the edge ring ER. In this case, the contacts  82   c  and  82   f  may be asymmetric to each other about the central axis (axis AX) of the edge ring ER. The contacts  82   d  and  82   e  may also be asymmetric to each other about the central axis (axis AX) of the edge ring ER. 
       FIG. 13  is a diagram of an electric path according to still another exemplary embodiment.  FIG. 14  is a plan view of the electric path according to the other exemplary embodiment. The plasma processing apparatus  1  may include the electric path shown in  FIGS. 13 and 14 . The plasma processing apparatus  1  including the electric path shown in  FIGS. 13 and 14  will now be described focusing on its differences from the plasma processing apparatus  1  including the electric path shown in  FIG. 9 . 
     The electric path  82  shown in  FIGS. 13 and 14  includes a first switch SW 1  and a second switch SW 2 . The first switch SW 1  includes a first terminal, a second terminal, and a third terminal. The first switch SW 1  selectively couples the first terminal to the second terminal or to the third terminal. The controller MC may control the first switch SW 1 . The first terminal of the first switch SW 1  is coupled to a first contact  82   a . The second terminal of the first switch SW 1  is coupled to a power supply  80   p.  The third terminal of the first switch SW 1  is coupled to a conducting wire  76 . 
     The second switch SW 2  includes a first terminal, a second terminal, and a third terminal. The second switch SW 2  selectively couples the first terminal to the second terminal or to the third terminal. The controller MC may control the second switch SW 2 . The first terminal of the second switch SW 2  is coupled to a second contact  82   b . The second terminal of the second switch SW 2  is coupled to the power supply  80   p.  The third terminal of the second switch SW 2  is coupled to the conducting wire  76 . 
     As shown in  FIG. 14 , the conducting wire  76  may be partially annular. More specifically, the conducting wire  76  may include an annular wiring extending circumferentially about the axis AX. The conducting wire  76  may further include one or more switches SW 3  and one or more contacts  76   c.  Each contact  76   c  is a contact of the conducting wire  76  with the edge ring ER. Each switch SW 3  is coupled between the annular wiring and the corresponding contact  76   c.  When each switch SW 3  is turned on, the annular wiring and the corresponding contact  76   c  are coupled to each other. When each switch SW 3  is turned off, the annular wiring and the corresponding contact  76   c  are uncoupled from each other. The controller MC may control the switches SW 3 . 
     The first switch SW 1 , the second switch SW 2 , and the switches SW 3  may be at circumferentially equal intervals about the axis AX. The first contact  82   a,  the second contact  82   b,  and the contacts  76   c  may also be at circumferentially equal intervals about the axis AX. The annular wiring and wires each extending from the first switch SW 1 , the second switch SW 2 , and the switches SW 3  may have nodes between them at circumferentially equal intervals about the axis AX. 
     As shown in  FIGS. 13 and 14 , the adjuster  74  can apply a voltage to the edge ring ER through the first contact  82   a  and the second contact  82   b  on the electric path  82 , which may couple the measuring device  80  to the edge ring ER. 
       FIG. 15  is a diagram of an adjuster and an edge ring according to still another exemplary embodiment. The plasma processing apparatus  1  may include an adjuster  74  shown in  FIG. 15 , in place of the adjuster  74  in the embodiments described above. The adjuster  74  shown in  FIG. 15  may be used with an edge ring ER shown in  FIG. 15 . 
     The edge ring ER shown in  FIG. 15  includes a first annular member ER 1  and a second annular member ER 2 . The first annular member ER 1  and the second annular member ER 2  are separate from each other. The first annular member ER 1  is an annular plate and on the second portion  202  to extend about the axis AX. A substrate W is placed onto the first portion  201  with the edge on or above the first annular member ER 1 . The second annular member ER 2  is an annular plate and on the second portion  202  to extend about the axis AX. The second annular member ER 2  is located outside the first annular member ER 1  in the radial direction. The second annular member ER 2  may have an internal surface facing the peripheral surface of the edge of the substrate W. 
     The adjuster  74  shown in  FIG. 15  is a moving device for moving the edge ring ER upward to adjust the vertical position of the upper surface of the edge ring ER. More specifically, the adjuster  74  moves the second annular member ER 2  upward to adjust the vertical position of the upper surface of the second annular member ER 2 . In one example, the adjuster  74  includes a drive  74   a  and a shaft  74   b.  The shaft  74   b  supports the second annular member ER 2  and extends downward from the second annular member ER 2 . The drive  74   a  generates a driving force to move the second annular member ER 2  in the vertical direction with the shaft  74   b.    
     The controller MC may control the adjuster  74  shown in  FIG. 15 . More specifically, the controller MC controls the adjuster  74  to reduce tilting of recesses in the edge of the substrate W on the substrate support  16 . The controller MC controls the adjuster  74  in accordance with the electrical characteristic value of the edge ring ER, the thickness of the edge ring ER, or the decrease in the thickness of the edge ring ER. For example, the controller MC determines the vertical position of the upper surface of the edge ring ER (second annular member ER 2 ) in accordance with the electrical characteristic value of the edge ring ER, the thickness of the edge ring ER, or the decrease in the thickness of the edge ring ER using a function or a table. The function or table is predefined for determining the vertical position of the upper surface of the edge ring ER (second annular member ER 2 ) corresponding to the electrical characteristic value of the edge ring ER, the thickness of the edge ring ER, or the decrease in the thickness of the edge ring ER. The controller MC controls the adjuster  74  (e.g., drive  74   a ) to set the upper surface of the edge ring ER (second annular member ER 2 ) to the determined vertical position. 
       FIG. 16  is a diagram of an adjuster and an edge ring according to still another exemplary embodiment. An edge ring ER shown in  FIG. 16  is used with the adjuster  74 , in place of the edge ring ER shown in  FIG. 15 . The edge ring ER shown in  FIG. 16  includes a first annular member ER 1  and a second annular member ER 2 . In the edge ring ER shown in  FIG. 16 , the first annular member ER 1  includes an inner peripheral portion and an outer peripheral portion. The inner peripheral portion has its upper surface lower than the upper surface of the outer peripheral portion in the vertical direction. A substrate W is placed onto the first portion  201  with the edge on or above the inner peripheral portion of the first annular member ER 1 . In the edge ring ER shown in  FIG. 16 , the second annular member ER 2  is on the inner peripheral portion of the first annular member ER 1  to surround the edge of the substrate W. In other words, the edge ring ER shown in  FIG. 16  includes the second annular member ER 2  located inside the outer peripheral portion of the first annular member ER 1 . When the edge ring ER shown in  FIG. 16  is used, the shaft  74   b  in the adjuster  74  extends downward from the second annular member ER 2  through the inner peripheral portion of the first annular member ER 1 . When the edge ring ER shown in  FIG. 16  is used, the adjuster  74  sets the vertical position of the second annular member ER 2  to be the position of the upper surface of the edge ring ER. 
     The plasma processing apparatuses according to the above embodiments include the electric path  82  to be coupled to or capacitively coupled to the edge ring ER while the edge ring ER is placed on the substrate support  16 . The measuring device  80  applies a voltage to the edge ring ER through the electric path  82  to measure the electrical characteristic value of the edge ring ER that varies depending on the thickness of the edge ring ER. This allows determination of a value reflecting the thickness of the edge ring ER. 
       FIG. 17  is a flowchart of a method according to an exemplary embodiment. A method MT shown in  FIG. 17  can be implemented by the plasma processing apparatus  1  according to any one of the embodiments described above. The method MT includes steps ST 5  and ST 6 . A measurement method according to an exemplary embodiment includes steps ST 5  and ST 6 . 
     The method MT may include the first step ST 1 . In step ST 1 , the initial thickness of the edge ring ER is measured. The initial thickness of the edge ring ER is measured by, but is not limited to, a measuring device such as a caliper or a micrometer. 
     The method MT may include step ST 2  following step ST 1 . In step ST 2 , an edge ring ER is placed onto the substrate support  16 . The edge ring ER may be transferred into the chamber  10  and placed onto the substrate support  16  by a transfer robot. The controller MC controls the transfer robot. 
     The method MT may include step ST 3  following step ST 2 . In step ST 3 , an initial electrical characteristic value of the edge ring ER is measured. The measuring device  80  measures the initial electrical characteristic value of the edge ring ER on the substrate support  16 . 
     The method MT includes the next step ST 4 . Step ST 4  is performed on the edge ring ER on the substrate support  16  and a substrate W in an area on the substrate support  16  surrounded by the edge ring ER. Plasma processing is performed in step ST 4 . The plasma processing in step ST 4  may include plasma etching. In step ST 4 , plasma is generated from a process gas in the chamber  10 . In step ST 4 , the substrate W is processed (e.g., etched) with a chemical species contained in the generated plasma. In step ST 4 , the controller MC controls the gas supply unit to supply the process gas into the chamber  10 . in step ST 4 , the controller MC controls the exhaust device  50  to maintain the chamber  10  at a specified gas pressure. In step ST 4 , the controller MC controls at least one of the RF power supply  61  or the bias power supply  62  to provide at least one of RF power HF or bias power BP. 
     The method MT includes the next step ST 5 . For example, step ST 5  is performed while no plasma processing in step ST 4  is being performed, or in other words, while the plasma processing apparatus  1  is in an idle state. In step ST 5 , the measuring device  80  applies a voltage to the edge ring ER through the electric path  82 . The measuring device  80  applies a DC voltage, an AC voltage, or an RF voltage to the edge ring ER as described above. Step ST 6  is performed on the edge ring ER receiving a voltage in step ST 5 . In step ST 6 , the measuring device  80  measures the electrical characteristic value of the edge ring ER receiving a voltage. The electrical characteristic value of the edge ring ER on the substrate support  16  is measured. 
     When the electrical characteristic value of the edge ring ER is highly dependent on temperature, steps ST 5  and ST 6  may be performed on the edge ring ER with the temperature being controlled at the reference temperature by the temperature controller as described above. In some embodiments, when the electrical characteristic value of the edge ring ER is highly dependent on temperature, the electrical characteristic value of the edge ring ER at a temperature measurement value obtained by the temperature sensor  84  may be converted to an electrical characteristic value of the edge ring ER at the reference temperature. This conversion uses the predetermined function or table as described above. 
     The method MT may include the next step ST 7 . In step ST 7 , the thickness of the edge ring ER or a decrease in the thickness of the edge ring ER is obtained. The thickness of the edge ring ER is determined by converting the electrical characteristic value of the edge ring ER using the predetermined function or table as described above. The decrease in the thickness of the edge ring ER is determined by subtracting the thickness of the edge ring ER determined in step ST 7  from the initial thickness of the edge ring ER measured in step ST 1  as described above. 
     In subsequent step ST 8 , the determination is performed as to whether the edge ring ER is to be replaced. In step ST 8 , the electrical characteristic value of the edge ring ER measured in step ST 6 , the thickness of the edge ring ER obtained in step ST 7 , or the decrease in the thickness of the edge ring ER obtained in step ST 7  is compared with a threshold value. When the comparison in step ST 8  shows that the edge ring ER has worn and to be replaced, the edge ring ER is replaced and the processing in step ST 1  and subsequent steps are repeated. When the comparison in step ST 8  shows that the edge ring ER is not to be replaced, step ST 9  is performed. The controller MC may perform the determination in step ST 8 . 
     In step ST 9 , the determination is performed as to whether the upper end position of the sheath above the edge ring ER is to be adjusted by the adjuster  74 . In step ST 9 , the electrical characteristic value of the edge ring ER measured in step ST 6 , the thickness of the edge ring ER obtained in step ST 7 , or the decrease in the thickness of the edge ring ER obtained in step ST 7  is compared with another threshold value. When the comparison in step ST 9  shows that the substrate W on the substrate support  16  is expected to form acceptable tilting of recesses at its edge through the plasma processing in step ST 4 , step ST 4  is performed. When the comparison in step ST 9  shows that the substrate W on the substrate support  16  is expected to form unacceptable tilting of recesses at its edge through the plasma processing in step ST 4 , step ST 10  is performed. The controller MC may perform the determination in step ST 9 . 
     In step ST 10 , a correction value is determined. The controller MC may determine the correction value. The correction value is a potential set for the edge ring ER by the adjuster  74  in subsequent step ST 11  or the vertical position of the upper surface of the edge ring ER set by the adjuster  74  in step ST 11 . As described above, the correction value is determined in accordance with the electrical characteristic value (e.g., resistance R ER ) of the edge ring ER, the thickness of the edge ring ER, or the decrease in the thickness of the edge ring ER using the predefined. function or table. 
     In subsequent step ST 11 , the controller MC controls the adjuster  74  using the correction value determined in step ST 10 . For example, the controller MC controls the adjuster  74  to set the potential for the edge ring ER to the potential corresponding to the correction value. In some embodiments, the controller MC controls the adjuster  74  to set the vertical position of the upper surface of the edge ring ER to the vertical position corresponding to the correction value. After step ST 11 , step ST 4  is performed again. Step ST 4  is performed with the adjuster  74  controlled in step ST 11 . 
     Although the exemplary embodiments have been described above, the embodiments are not restrictive, and various additions, omissions, substitutions, and changes may be made. The components in the different exemplary embodiments may be combined to form another exemplary embodiment. 
     A plasma processing apparatus according to another embodiment may be an inductively coupled plasma processing apparatus. A plasma processing apparatus according to still another embodiment may be a plasma processing apparatus that generates plasma using surface waves such as microwaves. The first portion  201  and the second portion  202  may be separate ESCs. 
     A plasma processing apparatus according to another embodiment may include, in place of the adjuster  74 , an adjuster for adjusting plasma density above at least one of the edge ring ER or the substrate W. The controller MC may control the adjuster in accordance with the electrical characteristic value of the edge ring ER, the thickness of the edge ring ER, or the decrease in the thickness of the edge ring ER. 
     The exemplary embodiments according to the present disclosure have been described by way of example, and various changes may be made without departing from the scope and spirit of the present disclosure. The exemplary embodiments disclosed above are thus not restrictive, and the true scope and spirit of the present disclosure is defined by the appended claims.