Patent Publication Number: US-2023138006-A1

Title: Cleaning method, substrate processing method and plasma processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2021-178533 filed on Nov. 1, 2021, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Exemplary embodiments of the present disclosure relate to a cleaning method, a substrate processing method, and a plasma processing apparatus. 
     2. Related Art 
     JP 2014-056928 A discloses a technique for suppressing adsorption due to residual charge in the surface layer of an electrostatic chuck. 
     SUMMARY 
     A cleaning method is provided in an exemplary embodiment of the present disclosure, in which the cleaning method comprises (a) forming a plasma in a chamber of the plasma processing apparatus while a substrate is not being held in place by an electrostatic chuck in the chamber; and (b) supplying voltage to the electrostatic chuck to reduce the charge on the surface of the electrostatic chuck while plasma is being formed in (a). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a figure schematically illustrating a substrate processing apparatus. 
         FIG.  2    is a figure showing an example of a main body with a lift pin. 
         FIG.  3    is a figure schematically illustrating an example of the substrate processing system. 
         FIG.  4    is a figure used to explain an example of a sequence for the substrate processing method. 
         FIG.  5    is a flowchart showing an example of the second cleaning process. 
         FIG.  6    is a figure used to explain an example of the sequence for supplying processing gas, supplying RF power, and supplying voltage to the electrostatic chuck in the second cleaning process. 
         FIG.  7    is a figure used to explain an example of a charged state on the surface of the electrostatic chuck. 
         FIG.  8 A  is a diagram schematically illustrating an example of the charged state on the surface of the electrostatic chuck after the cleaning process when the cleaning process of the present invention is not used. 
         FIG.  8 B  is a diagram schematically illustrating an example of the charged state on the surface of the electrostatic chuck during subsequent plasma processing when the cleaning process of the present invention is not used. 
         FIG.  8 C  is a diagram schematically illustrating an example of the charged state on the surface of the electrostatic chuck after the subsequent plasma processing when the cleaning process of the present invention is not used. 
         FIG.  9 A  is a diagram schematically illustrating an example of the charged state on the surface of the electrostatic chuck after the cleaning process when the cleaning process of the present invention is used. 
         FIG.  9 B  is a diagram schematically illustrating an example of the charged state on the surface of the electrostatic chuck during subsequent plasma processing when the cleaning process of the present invention is used. 
         FIG.  9 C  is a diagram schematically illustrating an example of the charged state on the surface of the electrostatic chuck after the subsequent plasma processing when the cleaning process of the present invention is used. 
         FIG.  10    is a graph showing the relationship between the lift pin torque difference and the supplied voltage. 
         FIG.  11    is a graph showing the relationship between the residual charge difference and the supplied voltage. 
         FIG.  12    is a graph showing the effect of the cleaning method of the present invention on reducing the number of particles. 
         FIG.  13    schematically illustrates an example of a plasma processing apparatus having a measuring device. 
         FIG.  14    is a figure showing an example of correlation data between the charged state (potential V1) and the supplied voltage. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will now be described. 
     A cleaning method is provided in an exemplary embodiment. This cleaning method comprises: (a) forming a plasma in a chamber of the plasma processing apparatus while a substrate is not being held in place by an electrostatic chuck in the chamber; and (b) supplying voltage to the electrostatic chuck to reduce the charge on the surface of the electrostatic chuck while plasma is being formed in (a). 
     In an exemplary embodiment, (a) includes the supplying power for forming plasma, the supply of voltage to the electrostatic chuck in (b) begins after the supply of power for forming plasma has begun in (a), and the supply of voltage to the electrostatic chuck in (b) stops before the supply of power for forming plasma has stopped in (a). 
     In an exemplary embodiment, (a) includes the supplying gas for forming plasma, the supply of voltage to the electrostatic chuck in (b) begins after the supply of gas for forming plasma has begun in (a), and the supply of voltage to the electrostatic chuck in (b) stops before the supply of gas for forming plasma has stopped in (a). 
     An exemplary embodiment further comprises: (c) measuring the charged state on the surface of the electrostatic chuck while plasma is being formed in (a), wherein the voltage to be supplied to the electrostatic chuck in (b) is determined on the basis of the charged state on the surface of the electrostatic chuck measured in (c). 
     In an exemplary embodiment, the voltage to be supplied to the electrostatic chuck in (b) is determined from the measurement results for the charged state on the surface of the electrostatic chuck in (c) on the basis of the relationship between the charged state on the surface of the electrostatic chuck and the voltage to be supplied to the electrostatic chuck in the charged state on the surface of the electrostatic chuck. 
     In an exemplary embodiment, plasma is formed in the chamber in (a) to clean the surface of the electrostatic chuck in the chamber. 
     In an exemplary embodiment, plasma is formed in the chamber in (a) to clean the interior of the chamber. 
     In an exemplary embodiment, the cleaning method comprises: (a1) forming a plasma in a chamber of the plasma processing apparatus while a substrate is not being held in place by an electrostatic chuck in the chamber to clean the interior of the chamber; (b1) supplying voltage to the electrostatic chuck to reduce the charge on the surface of the electrostatic chuck while plasma is being formed in (a1); (a2) forming a plasma in a chamber of the plasma processing apparatus while a substrate is not being held in place by the electrostatic chuck in the chamber to clean the surface of the electrostatic chuck in the chamber; and (b2) supplying voltage to the electrostatic chuck to reduce the charge on the surface of the electrostatic chuck while plasma is being formed in (a2). In an exemplary embodiment, the voltage supplied to the electrostatic chuck in (b1) and in (b2) is different. 
     A substrate processing method is provided in an exemplary embodiment, the substrate processing method comprises: (a) and (b) in the cleaning method and (c) holding a substrate in place with the electrostatic chuck and subjecting the substrate to plasma treatment at least one of before and after (a) and (b). 
      A substrate processing method is provided in an exemplary embodiment. This substrate processing method comprises: (a) forming a plasma in a chamber of the plasma processing apparatus while a substrate is not being held in place by an electrostatic chuck in the chamber; (b) supplying voltage to the electrostatic chuck while plasma is being formed in (a); and (c) holding a substrate in place with the electrostatic chuck in the chamber of the plasma processing apparatus and subjecting the substrate to plasma treatment, wherein (c) is performed at least one of before and after (a) and (b), and the polarity of the voltage supplied to the electrostatic chuck in (b) is the same as the polarity of the voltage supplied to the electrostatic chuck in (c). 
     A plasma processing apparatus is provided in an exemplary embodiment. This plasma processing apparatus comprises: a chamber; an electrostatic chuck for holding a substrate in place in the chamber; a first power source for supplying power for plasma formation to the chamber; a second power supply for supplying voltage to the electrostatic chuck; and a controller, wherein the controller is configured to cause: (a) supplying power for plasma formation to the chamber from the first power source while a substrate is not being held in place by an electrostatic chuck in the chamber to form plasma in the chamber; and (b) supplying voltage to the electrostatic chuck from the second power supply while plasma is being formed in (a) to reduce the charge on the surface of the electrostatic chuck. 
     The following is a detailed description of embodiments of the present disclosure with reference to the drawings. In the drawings, identical or similar elements are denoted by the same reference numbers and redundant descriptions of these elements has been omitted. In the following description, positional relationships such as up, down, left and right are based on the positional relationships shown in the drawings except where otherwise specified. The dimensional ratios in the drawings do not indicate actual ratios, and the actual ratios are not limited to the ratios shown in the drawings. 
     Configuration of Plasma Processing Apparatus  1   
     An example of a configuration for the plasma processing system will now be described.  FIG.  1    is a figure used to describe an example of a configuration for a capacitively coupled plasma processing apparatus. The substrate processing method in this exemplary embodiment (“the processing method” below) is executed by this plasma processing apparatus  1 . 
     The plasma processing system includes a capacitively coupled plasma processing apparatus  1  and a controller  2 . The capacitively coupled plasma processing apparatus  1  includes a plasma processing chamber  10  (“the chamber” below), a gas supply  20 , a power supply  30 , and an exhaust system  40 . The plasma processing apparatus  1  also includes a substrate support  11  and a gas introducer. The gas introducer is configured to introduce at least one processing gas to the plasma processing chamber  10 . The gas introducer includes a shower head  13 . The substrate support  11  is arranged inside the plasma processing chamber  10 . The shower head  13  is arranged above the substrate support  11 . In an exemplary embodiment, the shower head  13  constitutes at least a portion of the ceiling of the plasma processing chamber  10 . The plasma processing chamber  10  has a plasma processing space  10   s  defined by the shower head  13 , the side walls  10   a  of the plasma processing chamber  10 , and the substrate support  11 . The plasma processing chamber  10  has at least one gas supply port for supplying at least one processing gas to the plasma processing space  10   s , and at least one gas exhaust port for exhausting gas from the plasma processing space. The plasma processing chamber  10  is grounded. The shower head  13  and the substrate support  11  are electrically isolated from the plasma processing chamber  10 . 
     The substrate support  11  includes a main body  50  and a ring assembly  51 . The main body  50  has a central region  50   a  for supporting a substrate W and an annular region  50   b  for supporting the ring assembly  51 . A wafer is an example of a substrate W. The annular region  50   b  of the main body  50  surrounds the central region  50   a  of the main body  50  in a plan view. The substrate W is arranged in the central region  50   a  of the main body  50 , and the ring assembly  51  is arranged in the annular region  50   b  of the main body  50  so as to surround the substrate W in the central region  50   a  of the main body  50 . Therefore, the central region  50   a  is also known as the substrate support surface for supporting the substrate W, and the annular region  50   b  is known as the ring support surface for supporting the ring assembly  51 . 
     In one embodiment, the main body  50  includes a base  60  and an electrostatic chuck  61 . The base  60  includes a conductive member. The conductive member of the base  60  can function as a lower electrode. The electrostatic chuck  61  is arranged on the base  60 . The electrostatic chuck  61  includes a ceramic member  61   a  and an electrostatic electrode  61   b  disposed within the ceramic member  61   a . The ceramic member  61   a  has a central region  50   a . In one embodiment, the ceramic member  61   a  also has an annular region  50   b . Note that another member surrounding the electrostatic chuck  61 , such as an annular electrostatic chuck or an annular insulating member, may have the annular region  50   b . In this case, the ring assembly  51  may be disposed on the annular electrostatic chuck or the annular insulating member, or may be disposed on both the electrostatic chuck  61  and the annular insulating member. An RF or DC electrode may also be placed within the ceramic member  61   a , in which case the RF or DC electrode functions as the lower electrode. An RF or DC electrode is also referred to as a bias electrode if bias RF signals or DC signals described below are connected to the RF or DC electrode. Note that both the conductive member of the base  60  and the RF or DC electrode may function as two lower electrodes. 
     The electrostatic electrode  61   b  of the electrostatic chuck  61  is connected via a switch  70   s  to a DC power supply  70   p  serving as a second power supply. When DC voltage is supplied to the electrostatic electrode  61   b  from the DC power supply  70   p , electrostatic attraction (Coulomb force) is generated between the electrostatic chuck  61  and the substrate W. The substrate W is attracted to the electrostatic chuck  61  by the electrostatic attractive force and is held in place on the surface  61   c  of the electrostatic chuck  61 . The surface  61   c  of the electrostatic chuck  61  may be flat or uneven. The electrostatic chuck  61  is not limited to a Coulomb type chuck using the Coulomb force, and may be of the Johnsen-Rahbek type chuck using the Johnsen-Rahbek effect. 
     The ring assembly  51  includes one or more annular members. In one embodiment, the one or more annular members include one or more edge rings and at least one cover ring. The edge ring or rings is made of a conductive material or an insulating material, and the cover ring is made of an insulating material. 
     Also, the substrate support  11  may include a temperature control module configured to keep at least one of the electrostatic chuck  61 , the ring assembly  51 , and the substrate at a target temperature. The temperature control module may include a heater, a heat transfer medium, a channel  60   a , or combinations of these. A heat transfer fluid such as brine or a gas flows through the flow path  60   a . In one embodiment, channels  60   a  are formed in the base  60  and one or more heaters are disposed in the ceramic member  61   a  of electrostatic chuck  61 . The substrate support  11  may also include a heat transfer gas supply configured to supply a heat transfer gas between the back surface of the substrate W and the central region  50   a . 
      As shown in  FIG.  2   , the main body  50  is formed with through holes  50   c  passing through in the vertical direction. In the main body  50 , a lift pin  80  that can move through a through hole  50   c  in the vertical direction is provided in each through hole  50   c . The lift pins  80  support the substrate W. Lift pins  80  are one example of a lifter that is used to support a substrate. The lift pins  80  are driven by a drive device (not shown). The lift pins  80  can lift the substrate W onto the electrostatic chuck  61  or above the electrostatic chuck  61 . The substrate W can be placed on the surface  61   c  of the electrostatic chuck  61  by lowering the lift pins  80 , and the substrate W can be removed from the surface  61   c  of the electrostatic chuck  61  by raising the lift pins  80 . 
     The shower head  13  shown in  FIG.  1    is configured to introduce at least one processing gas from the gas supply  20  to the plasma processing space  10   s . The shower head  13  has at least one gas supply port  13   a , at least one gas diffusion chamber  13   b , and multiple gas introduction ports  13   c . The processing gas supplied to the gas supply port  13   a  passes through the gas diffusion chamber  13   b  and is introduced to the plasma processing space  10   s  via the gas introduction ports  13   c . The shower head  13  also includes an upper electrode. In addition to the showerhead  13 , the gas introducer may include one or more side gas injectors (SGI) attached to one or more openings formed in a side wall  10   a . 
     The gas supply  20  may include at least one gas source  21  and at least one flow controller  22 . In one embodiment, the gas supply  20  is configured to supply at least one processing gas from its respective gas source  21  via its respective flow controller  22  to the shower head  13 . Each flow controller  22  may include, for example, a mass flow controller or a pressure-controlled flow controller. The gas supply  20  may also include one or more flow modulating devices that modulate or pulse the flow rate of at least one processing gas. 
      The power supply  30  includes an RF power supply  31  serving as the first power supply coupled to the plasma processing chamber  10  via at least one impedance matching circuit. The RF power supply  31  is configured to supply at least one RF signal (RF power), such as a source RF signal and a bias RF signal, to at least one lower electrode and/or to at least one upper electrode. In this way, a plasma is formed from at least one processing gas supplied to the plasma processing space  10   s . Thus, the RF power supply  31  may function as at least part of a plasma generator configured to form a plasma from one or more processing gases in the plasma processing chamber  10 . Also, by supplying a bias RF signal to at least one lower electrode, a bias potential is generaed in the substrate W, and ion components in the formed plasma can be attracted to the substrate W. 
     In one embodiment, the RF power supply  31  includes a first RF generator  31   a  and a second RF generator  31   b . The first RF generator  31   a  is coupled to at least one lower electrode and/or to at least one upper electrode via at least one impedance matching circuit and configured to generate a source RF signal (source RF power) for plasma generation. In one embodiment, the source RF signal has a frequency in the range from 10 MHz to 150 MHz. In one embodiment, the first RF generator  31   a  may be configured to generate multiple source RF signals with different frequencies. One or more source RF signals generated are provided to at least one lower electrode and/or to at least one upper electrode. 
     A second RF generator  31   b  is coupled to the at least one lower electrode via at least one impedance matching circuit and configured to generate a bias RF signal (bias RF power). The frequency of the bias RF signal may be the same as or different from the frequency of the source RF signal. In one embodiment, the bias RF signal has a frequency lower than that of the source RF signal. In one embodiment, the bias RF signal has a frequency in the range from 100 kHz to 60 MHz. In one embodiment, the second RF generator  31   b  may be configured to generate multiple bias RF signals with different frequencies. One or more bias RF signals that have been generated are supplied to at least one lower electrode. Also, in various embodiments, at least one of the source RF signal and the bias RF signal may be pulsed. 
     The power supply  30  may also include a DC power supply  32  coupled to the plasma processing chamber  10 . The DC power supply  32  includes a first DC generator  32   a  and a second DC generator  32   b . In one embodiment, the first DC generator  32   a  is connected to at least one lower electrode and configured to generate a first DC signal. A generated first bias DC signal is supplied to at least one lower electrode. In one embodiment, the second DC generator  32   b  is connected to at least one upper electrode and configured to generate a second DC signal. The generated second DC signal is supplied to at least one upper electrode. 
     In various embodiments, at least one of the first and second DC signals may be pulsed. In this case, a sequence of DC-based voltage pulses is supplied to at least one lower electrode and/or at least one upper electrode. The voltage pulses may have rectangular, trapezoidal or triangular pulse waveforms, or some combination of these pulse waveforms. In one embodiment, a waveform generator for generating a sequence of voltage pulses from a DC signal is connected between the first DC generator  32   a  and at least one lower electrode. Thus, the first DC generator  32   a  and the waveform generator constitute a voltage pulse generator. When a second DC generator  32   b  and a waveform generator constitute a voltage pulse generator, the voltage pulse generator is connected to at least one upper electrode. The voltage pulse may have a positive polarity or a negative polarity. Also, the sequence of voltage pulses may include one or more positive voltage pulses and one or more negative voltage pulses in a single cycle. Note that first and second DC generators  32   a ,  32   b  may be provided in addition to the RF power supply  31 , or a first DC generator  32   a  may be provided instead of a second RF generator  31   b . 
     The exhaust system  40  can be connected, for example, to a gas outlet  10   e  provided at the bottom of the plasma processing chamber  10 . The exhaust system  40  may include a pressure regulating valve and a vacuum pump. The pressure regulating valve regulates the pressure inside the plasma processing space  10   s . The vacuum pump may include a turbo molecular pump, a dry pump, or a combination of these. 
     The controller  2  processes computer-executable instructions that get the plasma processing apparatus  1  to perform the steps described in the present disclosure. The controller  2  may be configured to get each element in the plasma processing apparatus  1  to perform the steps described in the present specification. In an exemplary embodiment, some or all of the controller  2  may be provided as part of the plasma processing apparatus  1 . The controller  2  may include, for example, a computer  2   a . The computer  2   a  may include, for example, a central processing unit (CPU)  2   a   1 , a storage unit  2   a   2 , and a communication interface  2   a   3 . The central processing unit  2   a   1  may be configured to perform control operations by retrieving a program from the storage unit  2   a   2  and executing the retrieved program. This program may be stored in the storage unit  2   a   2  in advance or may be acquired via another medium when necessary. The acquired program is stored in the storage unit  2   a   2 , retrieved from the storage unit  2   a   2  and executed by the central processing unit  2   a   1 . The medium may be any storage medium readable by the computer  2   a  or may be a communication line connected to the communication interface  2   a   3 . The storage unit  2   a   2  may include random access memory (RAM), read-only memory (ROM), a hard disk drive (HDD), a solid state drive (SSD), or a combination of these. The communication interface  2   a   3  may communicate with other configurations in the plasma processing apparatus  1  via a communication line such as a local area network (LAN). 
     Configuration of Substrate Processing System PS 
       FIG.  3    is a figure schematically illustrating a substrate processing system PS in an exemplary embodiment of the present disclosure. The substrate processing system PS in this exemplary embodiment includes the plasma processing apparatus  1 . 
     The substrate processing system PS includes substrate processing modules PM1 to PM6 (referred to collectively as “the substrate processing modules PM” below), a transfer module TM, load lock modules LLM 1  and LLM 2  (referred to collectively as “the load lock modules LLM” below), a loader module LM, and load ports LP 1  to LP 3  (referred to collectively as “the load ports LP” below). The controller CT controls each configuration in the substrate processing system PS and executes given processing on the substrate W. 
     The substrate processing modules PM internally perform processing such as etching processing, trimming processing, film formation processing, annealing processing, doping processing, lithography processing, cleaning processing, and ashing processing on the substrate W. A portion of the substrate processing modules PM may be a measuring module for measuring the film thickness of the film formed on the substrate W, the dimensions of the pattern formed on the substrate W, etc. The plasma processing apparatus  1  shown in  FIG.  1    is one example of a substrate processing module PM. 
     The transfer module TM has a transfer device for transferring substrates W, and transfers substrate W between substrate processing modules PM or between a substrate processing module PM and a load lock module LLM. The substrate processing modules PM and the load lock modules LLM are arranged adjacent to the transfer module TM. The transfer module TM, the substrate processing modules PM, and the load lock modules LLM are spatially isolated from or connected to each other via a gate valve that can be opened and closed. 
     The load lock modules LLM 1  and LLM 2  are provided between the transfer module TM and the loader module LM. The pressure inside the load lock module LLM can be switched to atmospheric pressure or to a vacuum. A load lock module LLM transfers a substrate W from an atmospheric pressure loader module LM to a vacuum transfer module TM, and also from a vacuum transfer module TM to an atmospheric pressure loader module LM. 
     The loader module LM has a transfer device for transferring substrates W, and transfers substrates W between a load lock module LLM and a load port LP. A FOUP (front opening unified pod), for example, that can accommodate 25 substrates W or an empty FOUP can be placed inside the load port LP. The loader module LM removes substrates W from the FOUP inside the load port LP and transfers them to a load lock module LLM. The loader module LM also removes substrates W from the load lock module LLM and transfers them to the FOUP inside the load port LP. 
     The controller CT controls each configuration in the substrate processing system PS and executes given processing on substrates W. The controller CT stores recipes for processing procedures, processing conditions, and transfer conditions, etc. and controls each configuration in the board processing system PS to execute predetermined processing on substrates W based on the recipes. The controller CT may also include some or all of the functions of the controller  2  for the plasma processing apparatus  1  shown in  FIG.  1   . 
     Example of the Processing Method 
       FIG.  4    is a figure used to explain an example of a sequence of this processing method performed by the plasma processing apparatus  1 . In this processing method, the plasma processing apparatus  1  performs processing A, which includes plasma processing P 1  of the substrate W, a first cleaning process P 2 , and a second cleaning process P 3 , in this order. The first cleaning process P 2  is also referred to as waferless dry cleaning (WLDC), and the second cleaning process P 3  is also referred to as waferless treatment (WLT). When the plasma processing apparatus  1  is processing multiple substrates W in a single lot, processing A is performed several times. The substrates W to be processed in the first plasma processing P 1  performed on a single lot may be dummy substrates instead of product substrates. In one example, the dummy substrates may be substrates without patterned resist film. 
     Plasma Processing P 1  of Substrate W 
     Plasma processing P 1  includes, for example, etching a film on a substrate W using a plasma. 
     First, the substrate W is carried into the plasma processing chamber  10  by a transfer arm (not shown) and transferred to the lift pins  80  as indicated by dotted lines in  FIG.  2   . Next, the substrate W is lowered by the lift pins  80  onto the surface  61   c  of the electrostatic chuck  61 . Next, DC voltage is supplied to the electrostatic electrode  61   b  of the electrostatic chuck  61  by the DC power supply  70   p  shown in  FIG.  1   . The electrostatic attraction generated between the electrostatic chuck  61  and the substrate W attracts and holds the substrate W in place on the surface  61   c  of the electrostatic chuck  61 . 
     Next, a processing gas is supplied from the shower head  13  to the plasma processing space  10   s . The processing gas supplied at this time contains a gas that generates active species necessary to the substrate W etching process. The RF power supply  31  supplies high RF power to the lower electrode. The atmosphere in the plasma processing space  10   s  may be exhausted from the gas outlet  10   e , and the pressure in the plasma processing space  10   s  reduced to a predetermined pressure. In this way, a plasma is generated in the plasma processing space  10   s  and the substrate W is etched. 
     The etching process is performed for a predetermined amount of time, after which the supply of processing gas to the plasma processing space  10   s  and the supply of high RF power to the lower electrode are stopped to end the etching process. 
     Afterward, the supply of DC voltage to the electrostatic electrode  61   b  is stopped. The substrate W is then lifted by the lift pins  80  away from the surface  61   c  of the electrostatic chuck  61 . The substrate W is removed from the plasma processing chamber  10  by a transport arm (not shown). 
     First Cleaning Process P 2   
     The first cleaning process P 2  includes removing by-products attached or deposited on the interior of the plasma processing chamber  10 , such as the side walls  10   a  or the ceiling wall using plasma without a substrate W on the surface  61   c  of the electrostatic chuck  61 . In the first cleaning process P 2 , by-products attached or deposited on the electrostatic chuck  61  may be removed. 
     First, after a substrate W has been removed from the plasma processing chamber  10  in the plasma processing P 1  described above, a processing gas is supplied from the shower head  13  to the plasma processing space  10   s  while a substrate W is not being held in place on the surface  61   c  of the electrostatic chuck  61 . The processing gas contains a gas that generates active species capable of removing by-products generated in the plasma processing P 1 . For example, if the by-product is a CF-based polymer, the processing gas may be O 2  gas. The processing gas is not limited to O 2  gas, and may be some other oxygen-containing gas such as CO gas, CO 2  gas, or O 3  gas. When the by-products contain silicon or another metal in addition to a CF-based polymer, the processing gas may contain, for example, a halogen-containing gas in addition to an oxygen-containing gas. A halogen-containing gas is, for example, a fluorine-based gas such as CF 4  gas or NF 3  gas. The halogen-containing gas may also be a chlorine-based gas such as Cl 2  gas or a bromine-based gas such as HBr gas. 
     Next, the RF power supply  31  supplies high RF power to the lower electrode. The atmosphere in the plasma processing space  10   s  may be exhausted from the gas exhaust port  10   e , and the pressure in the plasma processing space  10   s  reduced to a predetermined pressure. As a result, a plasma is formed in the plasma processing space  10   s , and by-products inside the plasma processing chamber  10  are removed. The frequency of the high RF power generated by the RF power supply  31  may be, for example, 10 MHz or more and 100 MHz or less, or may be 40 MHz or more and 100 MHz or less. The high RF power may also be, for example, 50 W or more and 10,000 W or less, 100 W or more and 7,000 W or less, or 200 W or more and 2,000 W or less. 
     After the plasma has been formed for a predetermined amount of time, the supply of high RF power and the supply of processing gas are stopped to end the first cleaning process P 2 . 
     Second Cleaning Process P 3   
     The second cleaning process P 3  includes modifying the surface  61   c  of the electrostatic chuck  61  in the plasma processing chamber  10  using a plasma while a substrate W is not on the surface  61   c  of the electrostatic chuck  61 . A cleaning method according to the present embodiment (also referred to as “the cleaning method”) is included in the second cleaning process P 3 .  FIG.  5    is a flowchart showing an example of the second cleaning process P 3 , and  FIG.  6    is a sequence chart showing the timing for supplying processing gas (gas) for plasma formation, supplying the high RF power (RF) for plasma formation, and supplying voltage (ESCDC) to the electrostatic chuck  61 . 
     When the second cleaning process P 3  has started, first, the supply of processing gas from the shower head  13  to the plasma processing space  10   s  is started while a substrate W is not being held in place on the surface  61   c  of the electrostatic chuck  61  (Step S 1  in  FIG.  5   ). The processing gas supplied at this time includes one that formes a plasma necessary for modifying the surface  61   c  of an electrostatic chuck  61  that has been exposed to plasma in the plasma processing P 1  and in the first cleaning processing P 2 . The processing gas may be an inert gas such as N 2  gas. Next, the RF power supply  31  starts supplying high RF power to the lower electrode (forming plasma) (step S 2  in  FIG.  5   ). Thus, a plasma is formed from, for example, N 2  gas in the plasma processing space  10   s , the surface  61   c  of the electrostatic chuck  61  is nitrided, and fluorine on the surface  61   c  is removed. The high RF power supplied in the second cleaning process P 3  may be higher than the high RF power supplied in the first cleaning process P 2 . The timing for starting the supply of processing gas (step S 1 ) and the timing for starting the supply of high RF power (step S 2 ) may be the same. 
     DC voltage is supplied to the electrostatic electrode  61   b  of the electrostatic chuck  61  while a plasma is being formed in the plasma processing space  10   s  (plasma forming step SA in  FIG.  5   ) to lower the charge on the surface  61   c  of the electrostatic chuck  61  (step S 3  in  FIG.  5   ). For example, when a positive charge has been formed on the surface  61   c  of the electrostatic chuck  61  by plasma formation as shown in  FIG.  7   , positive DC voltage, for example, is supplied to the electrostatic electrode  61   b  of the electrostatic chuck  61  from the DC power supply  70   p . As a result, the surface  61   c  of the electrostatic chuck  61  is negatively charged, the charges cancel each other out, and the charge on the surface  61   c  is reduced. Conversely, when a negative charge has been generated on the surface  61   c  of the electrostatic chuck  61 , negative DC voltage is supplied to the electrostatic electrode  61   b  of the electrostatic chuck  61 , for example. As a result, the surface  61   c  of the electrostatic chuck  61  is positively charged, the charges cancel each other out, and the charge on the surface  61   c  is reduced. Note that in the example shown in  FIG.  7   , the surface  61   c  of the electrostatic chuck  61  has an uneven shape. In one exemplary embodiment, the polarity of the voltage supplied to the electrostatic chuck  61  during the cleaning process P 3  is the same polarity as that of the voltage supplied to the electrostatic chuck  61  during the plasma process P 1  for a substrate W. 
     Afterward, for a predetermined amount of time, the processing gas is supplied, the high RF power is supplied, a plasma is formed, and the DC voltage is supplied to the electrostatic chuck  61  (voltage supplying step SB in  FIG.  5   ). 
     Afterward, the supply of voltage to the electrostatic chuck  61  is stopped (step S 4  in  FIG.  5   ). Next, the supply of high RF power is stopped (step S 5  in  FIG.  5   ) and then the supply of processing gas is stopped (step S 6  in  FIG.  5   ). With this, the second cleaning process P 3  ends. Note that in this exemplary embodiment, the plasma forming process SA includes steps (steps S 2  to S 5 ) in which both the processing gas and high RF power are supplied, and a voltage supplying step SB between steps S 4  and S 5 . 
      In this exemplary embodiment, the cleaning method has a step SA of forming plasma in the chamber  10  while a substrate W is not being held in place by the electrostatic chuck  61  in the chamber  10  of the plasma processing apparatus  1  and a step SB of supplying voltage to the electrostatic chuck  61  to reduce the charge on the surface  61   c  of the electrostatic chuck  61  while the plasma is being formed during the plasma forming step SA. This makes it possible to reduce the charge remaining on the surface  61   c  of the electrostatic chuck  61  during the second cleaning process P 3 . As a result, the number of particles adhering to the back surface of substrates W can be reduced in the plasma processing P 1  following the second cleaning process P 3 . In addition, the torque of the lift pins  80  can be reduced when a substrate W is detached from the electrostatic chuck  61 . This point will now be described in greater detail with reference to  FIG.  8    and  FIG.  9   . 
     When this cleaning method is not used, that is, when no voltage is supplied to the electrostatic chuck  61  during the cleaning process P 3 , a positive charge remains on the surface  61   c  of the electrostatic chuck  61  after the cleaning process P 3  as shown in  FIG.  8 A . 
     As a result, when the substrate W is attracted to the electrostatic chuck  61  during subsequent plasma processing P 1 , an excessively negative charge is transferred from the substrate W to the electrostatic chuck  61 , and the attraction force of the electrostatic chuck  61  increases as shown in  FIG.  8 B . In this state, the difference in coefficients of thermal expansion between the substrate W and the electrostatic chuck  61  cause the number of particles generated by friction between the back surface of the substrate W and the surface of the electrostatic chuck  61  to increase. 
      In addition, the residual charge increases after plasma processing P 1 , as shown in  FIG.  8 C , and the pin torque of the lift pins increases when the substrate W is detached from the electrostatic chuck  61 . 
     When the cleaning method is used, that is, when voltage is supplied to the electrostatic chuck  61  during the cleaning process P 3 , a positive charge remaining on the surface  61   c  of the electrostatic chuck  61  after the cleaning process 3 can be reduced as shown in  FIG.  9 A . 
     Therefore, when the substrate W is attracted to the electrostatic chuck  61  during subsequent plasma processing P 1 , the movement of a negative charge from the substrate W to the electrostatic chuck  61  is suppressed as shown in  FIG.  9 B , and an increase in the adsorption force of the electrostatic chuck  61  is suppressed. As a result, the number of particles generated by friction between the back surface of the substrate W and the surface of the electrostatic chuck  61  can be reduced. 
     Also, an increase in the residual charges after plasma processing P 1  is suppressed, as shown in  FIG.  9 C , so an increase in pin torque can be suppressed when the substrate W is detached from the electrostatic chuck  61  by the lift pins. 
     In this exemplary embodiment, the supply of voltage to the electrostatic chuck  61  is started after the supply of high RF power for plasma formation has been started in the plasma formation step SA (after step S 2 ), and the supply of voltage to the electrostatic chuck  61  is stopped before the supply of the high RF power for plasma formation in the plasma formation step SA has been stopped (before step S 5 ). As a result, voltage is supplied to the electrostatic chuck  61  only while plasma is being formed. This makes it possible to prevent discharges that may occur due to the supply of voltage to the electrostatic chuck  61  while no plasma is being formed. 
     In this exemplary embodiment, the supply of voltage to the electrostatic chuck  61  is started after the supply of processing gas for plasma formation has been started in the plasma formation step SA (after step S 1 ), and supply of voltage to the electrostatic chuck  61  is stopped before the supply of processing gas for plasma formation has been stopped in the plasma formation step SA (before step S 6 ). As a result, voltage is supplied to the electrostatic chuck  61  only while plasma is being formed. This makes it possible to prevent discharges that may occur due to the supply of voltage to the electrostatic chuck  61  while no plasma is being formed. 
     In the plasma formation step SA of the cleaning method in this exemplary embodiment, plasma is formed in the chamber  10  to clean the surface  61   c  of the electrostatic chuck  61  in the chamber  10 . In the second cleaning process P 3 , a large charge tends to remain on the surface  61   c  of the electrostatic chuck  61  in a plasma state. Therefore, by supplying voltage to the electrostatic chuck  61  in the second cleaning process P 3 , the residual charge can be effectively reduced. 
     In this exemplary embodiment, the processing method includes a step SA of forming plasma in the chamber  10  while a substrate W is not being held in place by the electrostatic chuck  61  in the chamber  10  of the plasma processing apparatus  1 , a step of supplying voltage to the electrostatic chuck  61  to reduce the charge on the surface  61   c  of the electrostatic chuck  61  while the plasma is being formed during the plasma forming step SA, and a step of holding a substrate W in place on an electrostatic chuck  61  in the chamber  10  of the plasma processing apparatus  1  and subjecting the substrate W to plasma processing (plasma processing P 1 ). As a result, the charge remaining on the surface  61   c  of the electrostatic chuck  61  can be reduced when the electrostatic chuck  61  is not holding a substrate W in place, for example, during the second cleaning process P 3 . The plasma processing P 1  in which a substrate W is held in place on the electrostatic chuck  61  is then performed, for example, subsequent to the second cleaning processing P 3 . In this plasma processing P 1 , particles adhering to the back surface of the substrate W can be reduced. Also, the torque of the lift pins  80  can be reduced for when the substrate W is detached from the electrostatic chuck  61 . In addition, even when a charge generated by the plasma processing P 1  performed prior to the second cleaning processing P 3  remains in the electrostatic chuck  61 , the residual charge from the previous plasma process P 1  and the residual charge generated during the second cleaning process P 3  can be reduced together in the second cleaning process P 3 . 
     In this exemplary embodiment, the plasma processing apparatus  1  includes a chamber  10 , an electrostatic chuck  61  that holds a substrate W in place in the chamber  10 , an RF power supply  31  serving as the first power supply for supplying plasma forming power to the chamber  10 , a DC power supply  70   p  serving as the second power supply for supplying voltage to the electrostatic chuck  61 , and a controller  2 . The controller  2  executes a step SA of forming plasma in the chamber  10  by supplying power for plasma formation to the chamber  10  from the RF power supply  31  while a substrate W is not being held in place by the electrostatic chuck  61  in the chamber  10 , and a step of supplying voltage to the electrostatic chuck  61  from the DC power source  70   p  to reduce the charge on the surface  61   c  of the electrostatic chuck  61  while the plasma is being formed in the plasma forming step SA. This can reduce the charge remaining on the surface  61   c  of the electrostatic chuck  61  during substrate processing using the plasma processing apparatus  1 , for example, during the second cleaning process P 3  when a substrate W is not being held in place by the electrostatic chuck  61 . Plasma processing P 1  in which a substrate W is held in place on the electrostatic chuck  61  is then performed, for example, after the second cleaning processing P 3 . In this plasma processing P 1 , the number of particles adhering to the back surface of the substrate W can be reduced. Also, the torque of the lift pins  80  can be reduced for when the substrate W is detached from the electrostatic chuck  61 . 
     Example 
     In plasma processing P 1  following a cleaning process in which this cleaning method was used, the torque of the lift pins required to detach a substrate W from the electrostatic chuck  61  was measured. The torque of the lift pins required to detach a substrate W from the electrostatic chuck  61  was also measured in plasma processing P 1  performed after a conventional cleaning process in which this cleaning method was not used. The graph in  FIG.  10    shows the difference between the lift pin torque in the plasma processing P 1  after the cleaning process using the cleaning method and the lift pin torque during plasma processing P 1  after a conventional cleaning process. The horizontal axis in the graph shown in  FIG.  10    is the voltage supplied to the electrostatic chuck  61 . It can be seen from these measurement results that the torque of the lift pins during plasma processing P 1  is reduced by supplying voltage properly to the electrostatic chuck  61 . 
     The residual charge on the surface of the electrostatic chuck  61  was measured during plasma processing P 1  performed after a cleaning process using the cleaning method. The residual charge on the surface of the electrostatic chuck  61  was also measured during plasma processing P 1  performed after a cleaning process that did not use the cleaning method. The graph in  FIG.  11    shows the difference between the residual charge in plasma processing P 1  after a cleaning process using the cleaning method and the residual charge in the plasma processing P 1  after a conventional cleaning process. The horizontal axis in the graph shown in  FIG.  11    is the voltage supplied to the electrostatic chuck  61 . It can be seen from these measurement results that the proper supply of voltage to the electrostatic chuck  61  reduces the residual charge during plasma processing P 1 . 
     The number of particles (case C1) on the back surface of substrates (three substrates W1, W2, W3) due to the plasma processing P 1  performed alone, the number of particles (case C2) on the back surface of substrates (three substrates W1, W2, W3) due to the plasma processing P 1  performed after the second cleaning process P 3  using the cleaning method, and the number of particles (case C3) on the back surface of substrates (three substrates W1, W2, W3) due to the plasma processing P 1  performed after the second cleaning process P 3  which did not use the cleaning method were measured. The measurements were then compared. The results are shown in the graph in  FIG.  12   . Note that “Pt” in  FIG.  12    refers to back surface particles. It can be seen from these measurement results that the number of particles on the back surface of substrates is reduced in plasma processing P 1  (case C2) performed after a second cleaning process P 3  using the cleaning method. 
     Another Exemplary Embodiment of the Cleaning Method 
     The voltage supplied to the electrostatic chuck  61  in the cleaning method may be predetermined based on theoretical values or empirical principles. The voltage supplied to the electrostatic chuck  61  in the cleaning method may also be determined based on charged states of the surface  61   c  of the electrostatic chuck  61  that have been measured. For example, the cleaning method may have a step of measuring the charged state of the surface of the electrostatic chuck  61  while plasma is being formed in the plasma formation step SA, and the voltage supplied to the electrostatic chuck  61  may be determined based on the charged state of the surface  61   c  of the electrostatic chuck  61  measured in the charged state measurement step. In addition, the voltage supplied to the electrostatic chuck  61  may be determined from measurement results of the charged state of the surface  61   c  of the electrostatic chuck  61  on the basis of the relationship between the charged state on the surface  61   c  of the electrostatic chuck  61  and the voltage to be supplied to the electrostatic chuck  61  in that charged state. One exemplary embodiment will now be described. 
     Configuration of Measuring Device  100   
     In one exemplary embodiment, the charged state of the surface  61   c  of the electrostatic chuck  61  corresponds to the potential V1 of the electrostatic electrode  61   b  of the electrostatic chuck  61 . For example, when the surface  61   c  of the electrostatic chuck  61  is positively charged, the potential V1 of the electrostatic electrode  61   b  decreases and becomes negative. Also, when the surface  61   c  of the electrostatic chuck  61  is negatively charged, the potential V1 of the electrostatic electrode  61   b  rises and becomes positive. Therefore, as shown in  FIG.  13   , the plasma processing apparatus  1  in one exemplary embodiment includes a measuring device  100  that measures the potential V1 of the electrostatic electrode  61   b  corresponding to the charged state of the surface  61   c  of the electrostatic chuck  61 . 
     The measuring device  100  has, for example, a filter  101 , a copper disk  102 , a copper plate  103 , an acrylic plate  104 , a probe  105 , and a surface potential meter  106 . A probe  105  and the surface potential meter  106  constitute the potential measuring system  107 . 
     In order to simplify the explanation, the switch  70   s  to the electrostatic chuck  61  is shown separately from the measuring device  100 , but the measuring device  100  may include the switch  70   s . The switch  70   s  is used to switch the connection of the electrostatic electrode  61   b  between the DC power source  70   p  and a member of the measuring device  100  having capacitance. The switch  70   s  connects the electrostatic electrode  61   b  to the measuring device  100  when the charged state of the surface  61   c  of the electrostatic chuck  61  is to be measured. An example of a member having capacitance is a member with a configuration in which the acrylic plate  104   is interposed between a copper disc  102  and a copper plate  103 . The member having capacitance is not limited to a configuration with a copper disk  102 , a copper plate  103  and an acrylic plate  104 , and can be configured using an insulated conductor. 
     In the potential measuring system  107 , the potential formed in the acrylic plate  104  between the copper disc  102  and the copper plate  103  is measured by the surface potential meter  106  using the probe  105  provided on the surface of the copper disc  102  without making contact. The potential measuring system  107  is just one example of a measuring unit that measures a value corresponding to the amount of charge accumulated in a member having capacitance. The probe  105  may make contact with the copper disc  102  or not as long as it can measure the potential difference between the copper disc  102  and the copper plate  103 . 
     A filter  101  for removing high RF power is provided between the switch  70   s  and the member having capacitance. This keeps high RF power from propagating to the measurement device  100 . When the switch  70   s  switches from the side connected to the DC power supply  70   p  to the side connected to the member having capacitance in the measuring device  100 , the potential V1 generated in the member having capacitance can be measured. In other words, the potential V1 of the electrostatic electrode  61   b  in a floating state can be measured. 
     Specifically, the copper plate  103  is grounded, and the potential measured by the surface potential meter  106  using the probe  105  provided on the surface of the copper disc  102  in a non-contact state is the potential V1 of the electrostatic electrode  61   b  in a floating state. 
      Information on the potential V1 measured by the surface potential meter  106  is outputted to the controller  2  as information indicating the charged state of the electrostatic chuck  61 , and the controller  2  controls the DC power supply  70   p  based on this information to supply to the electrostatic chuck  61  voltage that reduces the charge on the surface  61   c  of the electrostatic chuck  61 . 
     The controller  2  has correlation data D indicating the relationship between the charged state (for example, the potential V1) shown in  FIG.  14    and the voltage to be supplied to the electrostatic chuck  61  in that charged state. Correlation data D may be created, for example, from data obtained by operating the plasma processing apparatus  1  prior to processing a substrate W, or may be created from theoretical values or calculated values. From measurement results on the charged state of the surface  61   c  of the electrostatic chuck  61  obtained by the measuring device  100 , the controller  2 , on the basis of the correlation data D, determines the voltage to be supplied to the electrostatic chuck  61  in response to the charge generated by the plasma during the measured cleaning process. 
     Second Cleaning Process P 3  Using the Measuring Device  100   
     In the second cleaning process P 3 , the measuring device  100  measures the potential V1 of the electrostatic electrode  61   b . This potential V1 corresponds to the charged state of the surface  61   c  of the electrostatic chuck  61 . During the second cleaning process P 3 , the measurement may be performed continuously, intermittently, or once at a specific time. 
     Specifically, the measuring device  100  measures the potential V1 of the electrostatic electrode  61   b  of the electrostatic chuck  61  using the probe  105  and the surface potential meter  106 . The measured potential V1 is outputted to the controller  2 , and the controller  2 , on the basis of the correlation data D, determines the voltage (positive or negative voltage, value, etc.) to be supplied to the electrostatic chuck  61  in response to the potential V1 (charged state). 
     The controller  2  then controls the DC power supply  70   p  to supply to the electrostatic electrode  61   b  of the electrostatic chuck  61  voltage that reduces the charge on the surface  61   c  of the electrostatic chuck  61 . For example, when the potential V1 of the electrostatic electrode  61   b  of the electrostatic chuck  61  changes in the positive direction, that is, when the surface  61   c  of the electrostatic chuck  61  is positively charged, positive voltage is supplied to the electrostatic electrode  61   b  of the electrostatic chuck  61  in order to supply the surface  61   c  of the electrostatic chuck  61  with a negative charge. A higher positive voltage is supplied to the electrostatic electrode  61   b  of the electrostatic chuck  61  as the positive potential change of the electrostatic electrode  61   b  increases. 
     Conversely, when the potential V1 of the electrostatic electrode  61   b  of the electrostatic chuck  61  changes in the negative direction, that is, when the surface  61   c  of the electrostatic chuck  61  is negatively charged, positive voltage is supplied to the electrostatic electrode  61   b  of the electrostatic chuck  61  in order to supply the surface  61   c  of the electrostatic chuck  61  with a positive charge. A lower negative voltage is supplied to the electrostatic electrode  61   b  of the electrostatic chuck  61  as the negative potential change of the electrostatic electrode  61   b  decreases. 
     In this exemplary embodiment, the charge on the surface  61   c  of the electrostatic chuck  61  can be reduced accurately and reliably. 
      Note that the measuring device for measuring the charged state of the surface  61   c  of the electrostatic chuck  61  is not limited to the configuration of the measuring device  100  described above. The potential V1 of the electrostatic electrode  61   b  does not have to be measured if the charged state of the surface  61   c  of the electrostatic chuck  61  is measured directly or a value corresponding to the charged state is measured. 
     Application of the Cleaning Method to the First Cleaning Process P 2   
     This cleaning method may be applied to the first cleaning process P 2 . 
     Here, when the first cleaning process P 2  has been started, the supply of processing gas from the shower head  13  to the plasma processing space  10   s  is first started while a substrate W is not being held on the surface  61   c  of the electrostatic chuck  61 . The processing gas supplied at this time includes one that formes the plasma necessary for removing by-products formed during plasma processing P 1 . Next, the RF power supply  31  starts supplying high RF power to the lower electrode. As a result, plasma is formed in the plasma processing space  10   s , and by-products inside the plasma processing chamber  10  are removed. Voltage is supplied to the electrostatic chuck  61  while the plasma is being formed, and the charge on the surface  61   c  of the electrostatic chuck  61  is reduced. For example, when a positive charge is generated on the surface  61   c  of the electrostatic chuck  61  due to plasma formation as shown in  FIG.  7   , positive DC voltage is supplied to the electrostatic electrode  61   b  of the electrostatic chuck  61 . As a result, the surface  61   c  of the electrostatic chuck  61  is negatively charged, the charges cancel each other out, and the charge on the surface  61   c  is reduced. Conversely, for example, when a negative charge is generated on the surface  61   c  of the electrostatic chuck  61 , negative DC voltage is supplied to the electrostatic electrode  61   b  of the electrostatic chuck  61 . As a result, the surface  61   c  of the electrostatic chuck  61  is positively charged, the charges cancel each other out, and the charge on the surface  61   c  is reduced. 
     Afterward, for a predetermined time, the processing gas is supplied, the RF power is supplied, plasma is formed, and the DC voltage is supplied to the electrostatic chuck  61 . 
     Afterward, the supply of voltage to the electrostatic chuck  61  is stopped. Next, the supply of high RF power is stopped, and then the supply of processing gas is stopped. With this, the first cleaning process P 2  ends. 
     In this exemplary embodiment, the charge remaining on the surface  61   c  of the electrostatic chuck  61  can be reduced during the first cleaning process P 2 . 
     This cleaning method may be applied to the first cleaning process P 2  alone and not to the second cleaning process P 3 , or may be applied to both the first cleaning process P 2  and the second cleaning process P 3 . In other words, the cleaning method may comprise the steps of: ( a   1 ) forming a plasma in a chamber of the plasma processing apparatus while a substrate is not being held in place by an electrostatic chuck in the chamber to clean the interior of the chamber and (b1) supplying voltage to the electrostatic chuck to reduce the charge on the surface of the electrostatic chuck while plasma is being formed in step ( a   1 ) in the first cleaning method P 2 ; and (a2) forming a plasma in a chamber of the plasma processing apparatus while a substrate is not being held in place by the electrostatic chuck in the chamber to clean the surface of the electrostatic chuck in the chamber and (b2) supplying voltage to the electrostatic chuck to reduce the charge on the surface of the electrostatic chuck while plasma is being formed in step (a2) in the second cleaning method P 3 . In this case, the charge remaining on the surface  61   c  of the electrostatic chuck  61  can be reduced during the first cleaning process P 2  and during the second cleaning process P 3 . 
     When this cleaning method is applied to both the first cleaning process P 2  and the second cleaning process P 3 , the voltage supplied to the electrostatic chuck  61  in the first cleaning process P 2  and in the second cleaning process P 3  may be different. Also, the voltage supplied to the electrostatic chuck  61  may be higher in the second cleaning process P 3  than in the first cleaning process P 2 . In this case, the voltage supplied is increased in the second cleaning process P 3 , in which the charge on the electrostatic chuck  61  is relatively large, so that energy efficiency can be improved. 
     Various modifications may be made to the cleaning method and processing method without departing from the scope and spirit of the present disclosure. For example, some elements in one embodiment can be added to another embodiment within the ordinary range of creativity of those skilled in the art. Also, some elements in one embodiment can be replaced with corresponding elements from another embodiment. 
     For example, some or all of the voltage supplied to the electrostatic chuck  61  in the cleaning method may be supplied while plasma is being formed. Also, the supply of voltage to the electrostatic chuck  61  may be performed while plasma is not being formed. 
     The cleaning method can also be applied to a cleaning process other than the second cleaning process P 3  or the first cleaning process P 2 . 
     The processing method can also be applied in a sequence other than one in which the plasma processing P 1 , the first cleaning process P 2 , and the second cleaning process P 3  are repeated. 
     In addition, the cleaning method and the processing method may be performed using a plasma processing apparatus using a plasma source other than that of a capacitively coupled plasma processing apparatus  1 , such as inductively coupled plasma or microwave plasma. 
     In one exemplary embodiment of the present disclosure, a technique can be provided that is able to reduce the charge on the electrostatic chuck surface. 
     The embodiments described above were provided for illustrative purposes only and are not intended to limit the scope of the present disclosure. Various modifications may be applied to each of these embodiments without departing from the scope and spirit of the present disclosure. For example, some elements in one embodiment can be added to another embodiment. Also, some elements in one embodiment can be replaced with corresponding elements from another embodiment.