Plasma processing apparatus and plasma processing method

Abstract

The plasma processing apparatus includes a chamber, a substrate supporting portion, a plasma generating portion, and a bias power source. The substrate support portion is disposed within the chamber. The plasma generation unit is configured so as to be capable of generating plasma from a gas within the chamber. The bias power supply is configured so as to be able to apply a sequence of a plurality of voltage pulses as an electrical bias to the substrate support part. The bias power supply is configured to adjust a maximum voltage level of each of the plurality of voltage pulses by adjusting a length of an ON period of each of the plurality of voltage pulses.

Description

Technical Field

[0001] Illustrative embodiments of the present invention relate to a plasma processing apparatus and a plasma processing method. Background Art

[0002] A plasma processing device is used to perform plasma processing on a substrate. The plasma processing device includes a chamber and a substrate support. The substrate support is arranged in the chamber. The plasma processing device described in Patent Document 1 below applies a DC negative pulse voltage to the substrate support in order to introduce ions from plasma generated in the chamber into the substrate.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2009-187975 Summary of the invention

[0006] Technical problem to be solved by the invention

[0007] The present invention provides a technology for adjusting the maximum voltage level of each of a plurality of voltage pulses applied as an electrical bias to a substrate support portion of a plasma processing apparatus.

[0008] Technical solutions for solving technical problems

[0009] In an exemplary embodiment, a plasma processing apparatus is provided. The plasma processing apparatus includes a chamber, a substrate support, a plasma generating unit, and a bias power supply. The substrate support is disposed in the chamber. The plasma generating unit is configured to generate plasma from a gas in the chamber. The bias power supply is configured to apply a sequence of multiple voltage pulses as an electrical bias to the substrate support. The bias power supply is configured to adjust the maximum voltage level of each of the multiple voltage pulses by adjusting the length of the ON period (ON time) of each of the multiple voltage pulses.

[0010] Effects of the Invention

[0011] According to an exemplary embodiment, it is possible to adjust the maximum voltage level of each of a plurality of voltage pulses applied as an electrical bias to a substrate supporting portion of a plasma processing apparatus. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a diagram for explaining a configuration example of a plasma processing system.

[0013] Figure 2 It is a diagram for explaining a configuration example of a capacitive coupling type plasma processing apparatus.

[0014] Figure 3FIG. 1 is a timing chart of an example of an electrical bias used in a plasma processing apparatus according to an exemplary embodiment.

[0015] Figure 4 This is a diagram showing an example of the relationship between the voltage level of a voltage pulse and the length of an ON period.

[0016] Figure 5 FIG. 1 is a timing chart of an example of an electrical bias used in a plasma processing apparatus according to an exemplary embodiment.

[0017] Figure 6 This is a diagram for explaining another configuration example of a capacitive coupling type plasma processing apparatus.

[0018] Figure 7 is a flow chart of a plasma processing method according to an exemplary embodiment. DETAILED DESCRIPTION

[0019] Hereinafter, various exemplary embodiments will be described in detail with reference to the accompanying drawings. In addition, in each of the drawings, the same reference numerals are given to the same or corresponding parts.

[0020] Figure 1 : is a diagram for illustrating a structural example of a plasma processing system. In one embodiment, the plasma processing system includes a plasma processing device 1 and a control unit 2. The plasma processing system is an example of a substrate processing system, and the plasma processing device 1 is an example of a substrate processing device. The plasma processing device 1 includes a plasma processing chamber 10, a substrate support portion 11, and a plasma generating portion 12. The plasma processing chamber 10 has a plasma processing space. In addition, the plasma processing chamber 10 has: at least one gas supply port for supplying at least one processing gas to the plasma processing space; and at least one gas exhaust port for exhausting gas from the plasma processing space. The gas supply port is connected to the gas supply portion 20 described later, and the gas exhaust port is connected to the exhaust system 40 described later. The substrate support portion 11 is arranged in the plasma processing space and has a substrate supporting surface for supporting a substrate.

[0021] The plasma generating unit 12 is configured to generate plasma from at least one processing gas supplied into the plasma processing space. The plasma formed in the plasma processing space may be a capacitively coupled plasma (CCP: Capacitively Coupled Plasma), an inductively coupled plasma (ICP: Inductively Coupled Plasma), an ECR plasma (Electron-Cyclotron-Resonance Plasma: Electron Cyclotron Resonance Plasma), a helicon wave excited plasma (HWP: Helicon Wave Plasma) or a surface wave plasma (SWP: Surface Wave Plasma), etc. In addition, various types of plasma generating units including an AC (Alternating Current: Alternating Current) plasma generating unit and a DC (Direct Current: Direct Current) plasma generating unit may also be used. In one embodiment, the AC signal (AC power) used in the AC plasma generating unit has a frequency in the range of 100kHz to 10GHz. Therefore, the AC signal includes an RF (Radio Frequency: Radio Frequency) signal and a microwave signal. In one embodiment, the RF signal has a frequency in the range of 100kHz to 150MHz.

[0022] The control unit 2 processes computer executable commands that cause the plasma processing device 1 to perform the various steps described in the present invention. The control unit 2 can be configured to control the various elements of the plasma processing device 1 to perform the various steps described herein. In one embodiment, a part or all of the control unit 2 can be included in the plasma processing device 1. The control unit 2 can include a processing unit 2a1, a storage unit 2a2, and a communication interface 2a3. The control unit 2 can be implemented, for example, by a computer 2a. The processing unit 2a1 can be configured to perform various control operations by reading a program from the storage unit 2a2 and executing the read program. The program can be stored in the storage unit 2a2 in advance, or it can be obtained via a medium when necessary. The obtained program is stored in the storage unit 2a2, and is read and executed from the storage unit 2a2 by the processing unit 2a1. The medium can be various storage media that can be read by the computer 2a, or it can be a communication line connected to the communication interface 2a3. The processing unit 2a1 can be a central processing unit (CPU). The storage unit 2a2 may include a RAM (Random Access Memory), a ROM (Read Only Memory), a HDD (Hard Disk Drive), an SSD (Solid State Drive), or a combination thereof. The communication interface 2a3 may communicate with the plasma processing device 1 via a communication line such as a LAN (Local Area Network).

[0023] Hereinafter, a configuration example of a capacitive coupling type plasma processing apparatus will be described as an example of the plasma processing apparatus 1 . Figure 2 It is a diagram for explaining a configuration example of a capacitive coupling type plasma processing apparatus.

[0024] A capacitively coupled plasma processing apparatus 1 includes a plasma processing chamber 10, a gas supply unit 20, and an exhaust system 40. In addition, the plasma processing apparatus 1 includes a substrate support unit 11 and a gas inlet unit. The gas inlet unit is configured to be able to introduce at least one processing gas into the plasma processing chamber 10. The gas inlet unit includes a shower head 13. The substrate support unit 11 is disposed in the plasma processing chamber 10. The shower head 13 is disposed above the substrate support unit 11. In one 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 10s defined by the shower head 13, the side wall 10a of the plasma processing chamber 10, and the substrate support unit 11. The plasma processing chamber 10 is grounded. The shower head 13 and the substrate support unit 11 are electrically insulated from the shell of the plasma processing chamber 10.

[0025] The substrate support portion 11 includes a main body 111 and a ring assembly 112. The main body 111 has a central region 111a for supporting a substrate W and an annular region 111b for supporting the ring assembly 112. A wafer is an example of a substrate W. The annular region 111b of the main body 111 surrounds the central region 111a of the main body 111 when viewed from above. The substrate W is arranged on the central region 111a of the main body 111, and the ring assembly 112 is arranged on the annular region 111b of the main body 111 in a manner of surrounding the substrate W on the central region 111a of the main body 111. Therefore, the central region 111a is also referred to as a substrate support surface for supporting the substrate W, and the annular region 111b is also referred to as a ring support surface for supporting the ring assembly 112.

[0026] In one embodiment, the main body 111 includes a base 1110 and an electrostatic chuck 1111. The base 1110 includes a conductive component. The conductive component of the base 1110 can function (play a role) as a lower electrode. The electrostatic chuck 1111 is arranged on the base 1110. The electrostatic chuck 1111 includes a ceramic component 1111a and an electrostatic electrode 1111b arranged in the ceramic component 1111a. The ceramic component 1111a has a central area 111a. In one embodiment, the ceramic component 1111a also has an annular area 111b. In addition, other components surrounding the electrostatic chuck 1111, such as an annular electrostatic chuck and an annular insulating component, may also have an annular area 111b. In this case, the ring assembly 112 may be arranged on the annular electrostatic chuck or the annular insulating component, or on both the electrostatic chuck 1111 and the annular insulating component. In addition, at least one electrode coupled to the high-frequency power supply 31 and / or the bias power supply 32 described later may also be arranged in the ceramic component 1111a. In this case, the at least one electrode functions as a lower electrode. In the case where the electrical bias described later is supplied to at least one electrode, the at least one electrode is also referred to as a bias electrode. In addition, the conductive component and at least one electrode of the base 1110 may also function as a plurality of lower electrodes. In addition, the electrostatic electrode 1111b may function as a lower electrode. Therefore, the substrate support portion 11 includes at least one lower electrode.

[0027] The ring assembly 112 includes one or more ring-shaped components. In one embodiment, the one or more ring-shaped components include one or more edge rings and at least one cover ring. The edge ring is formed of a conductive material or an insulating material, and the cover ring is formed of an insulating material.

[0028] In addition, the substrate support portion 11 may also include a temperature adjustment module, which is configured to adjust at least one of the electrostatic chuck 1111, the ring assembly 112 and the substrate to a target temperature. The temperature adjustment module may include a heater, a heat transfer medium, a flow path 1110a or a combination thereof. A heat transfer fluid such as brine or gas flows in the flow path 1110a. In one embodiment, the flow path 1110a is formed in the base 1110, and one or more heaters are arranged in the ceramic component 1111a of the electrostatic chuck 1111. In addition, the substrate support portion 11 may also include a heat transfer gas supply portion, which is configured to supply a heat transfer gas to the gap between the back side of the substrate W and the central area 111a.

[0029] The showerhead 13 is configured to be able to introduce at least one processing gas from the gas supply part 20 into the plasma processing space 10s. The showerhead 13 has at least one gas supply port 13a, at least one gas diffusion chamber 13b and a plurality of gas introduction ports 13c. The processing gas supplied to the gas supply port 13a is introduced into the plasma processing space 10s from the plurality of gas introduction ports 13c through the gas diffusion chamber 13b. In addition, the showerhead 13 includes at least one upper electrode. In addition, in addition to the showerhead 13, the gas introduction part may also include one or more side gas injection parts (SGI: Side Gas Injector), and the one or more side gas injection parts are installed in one or more openings formed in the side wall 10a.

[0030] The gas supply unit 20 may also include at least one gas source 21 and at least one flow controller 22. In one embodiment, the gas supply unit 20 is configured to supply at least one processing gas from the corresponding gas source 21 to the nozzle 13 via the corresponding flow controller 22. Each flow controller 22 may also include a mass flow controller or a pressure-controlled flow controller. Furthermore, the gas supply unit 20 may also include at least one flow modulation device for modulating or pulsing the flow of at least one processing gas.

[0031] The exhaust system 40 can be connected to the gas exhaust port 10e provided at the bottom of the plasma processing chamber 10, for example. The exhaust system 40 can include a pressure regulating valve and a vacuum pump. The pressure in the plasma processing space 10s can be adjusted by the pressure regulating valve. The vacuum pump can include a turbomolecular pump, a dry pump, or a combination thereof.

[0032] In one embodiment, the plasma processing apparatus 1 may further include a high-frequency power supply 31 as the plasma generating unit 12. The high-frequency power supply 31 is configured to generate a generating source high-frequency power (also referred to as a generating source high-frequency electric power) in order to generate plasma from a gas in the chamber 10. The generating source high-frequency power has a frequency in the range of 10 MHz to 150 MHz. The high-frequency power supply 31 is electrically connected to the lower electrode or the upper electrode via a matcher 31m. The matcher 31m has a matching circuit for matching the impedance of the load of the high-frequency power supply 31 with the output impedance of the high-frequency power supply 31. In addition, the high-frequency power supply 31 may also supply a continuous wave of the generating source high-frequency power. Alternatively, the high-frequency power supply 31 may also periodically supply pulses of the generating source high-frequency power. The pulses of the generating source high-frequency power may also be synchronized with the pulses of the electrical bias described later.

[0033] In one embodiment, the plasma processing apparatus 1 further includes a bias power supply 32. The bias power supply 32 is configured to supply an electrical bias to the substrate support portion 11. The electrical bias can be supplied to the lower electrode. The electrical bias can also be continuously supplied to the substrate support portion 11. Alternatively, pulses of the electrical bias can also be supplied to the substrate support portion 11. The pulses of the electrical bias can also be supplied in a manner synchronized with the pulses of the generation source high frequency power at the same repetition period as the pulses of the generation source high frequency power.

[0034] In one embodiment, the filter 34 may be connected between the bias power supply 32 and the substrate support portion 11. The filter 34 is an electric filter that attenuates or cuts off the high frequency power of the generated source that may flow into the bias power supply 32.

[0035] The following, with Figure 2 Refer to Figure 3 . Figure 3 FIG. 1 is a timing diagram of an example of an electrical bias used in a plasma processing apparatus according to an exemplary embodiment. Figure 3 As shown, the electrical bias and its pulses are a sequence of multiple voltage pulses VP. Each voltage pulse VP of the multiple voltage pulses VP can also be a pulse of a negative voltage or a negative DC voltage.

[0036] The electrical bias and its pulse, that is, the sequence of multiple voltage pulses VP has a waveform period CY. The waveform period CY includes an ON period (opening period) P ON and OFF period (closed period) P OFF During the ON period of the bias power supply 32, P ON Output voltage, during OFF period P OFFThe output of the voltage is stopped. Thus, one voltage pulse VP can be output in the waveform period CY. By repeating the waveform period CY, a sequence of multiple voltage pulses VP can be output. In addition, the bias frequency, which is the reciprocal of the time length of the waveform period CY, is a frequency in the range of 100 kHz to 13.56 MHz, for example, 400 kHz.

[0037] like Figure 2 As shown, in one embodiment, the bias power supply 32 may also include a DC power supply 32p, a first switch 32a, and a second switch 32b. The DC power supply 32p may also be a variable DC power supply. The positive electrode of the DC power supply 32p is grounded. The negative electrode of the DC power supply 32p is electrically connected to the substrate support portion 11 (e.g., the lower electrode) via the first switch 32a. The second switch 32b is connected between a node 33n on the electrical path 33 that electrically connects the DC power supply 32p and the substrate support portion 11 and the ground. The node 33n is provided between the first switch 32a and the substrate support portion 11 in the electrical path 33. The first switch 32a is on during the P ON Closed, during the OFF period (OFF time) P OFF The second switch 32b is turned off during the ON period P ON Disconnect, during the OFF period P OFF closure.

[0038] The bias power supply 32 is configured to be able to Figure 3 As shown in the figure, by adjusting the ON period P of each of the multiple voltage pulses PV ON The maximum voltage level of each of the plurality of voltage pulses VP is adjusted by adjusting the length of the voltage pulses VP. In addition, when the voltage pulse VP is a pulse of a negative voltage or a negative DC voltage, the maximum voltage level is a voltage level whose absolute value is the largest in the voltage pulse.

[0039] Here, refer to Figure 4 . Figure 4 FIG. 1 is a diagram showing an example of the relationship between the voltage level of a voltage pulse and the length of the ON period. Figure 4 As shown, the voltage level of the voltage pulse VP changes from the ON period P ON The voltage changes towards its maximum level from the beginning of the period. Figure 4 As shown in FIG. 1 , the maximum voltage level of the voltage pulse VP depends on the ON period P within a range that does not reach a level corresponding to the maximum absolute value of the voltage that the bias power supply 32 can output. ON Therefore, by adjusting the ON period P ON The length of the voltage pulses VP can adjust the maximum voltage level of each of the multiple voltage pulses VP.

[0040] In one embodiment, the control unit 2 is configured to determine the ON period P according to the maximum voltage level of each of the plurality of voltage pulses VP to be applied to the substrate support unit 11 using a relational expression: ON The relationship between the maximum voltage level of the voltage pulse VP and the ON period P ON The function related to the length of can be prepared in advance. This relationship can also be determined when the substrate W is subjected to plasma treatment.

[0041] Here, refer to Figure 5 . Figure 5 1 is a timing diagram of an example of an electrical bias used in a plasma processing apparatus of an exemplary embodiment. In another embodiment, the control unit 2 obtains the time variation of the voltage level of at least one voltage pulse VP during the period CP. The period CP may be a period during which a substrate W to be processed in the subsequent period AP is placed on the substrate support 11 and the plasma used in the period AP is generated. The time variation of the voltage level of at least one voltage pulse VP is a time variation from the start of applying the at least one voltage pulse VP. The at least one voltage pulse VP has the maximum voltage level that the bias power supply 32 can output.

[0042] The temporal variation of the voltage level of at least one voltage pulse VP can also be detected by the voltage sensor 35 (cf. Figure 2 ) is measured. The voltage sensor 35 measures the voltage of the electrical path 33 or the lower electrode. Alternatively, the time variation of the voltage level of at least one voltage pulse VP may be measured by Figure 6 The voltage sensor 36 shown in the figure measures the potential of the substrate W. The voltage sensor 36 is arranged just below the substrate W and is configured to be able to measure the potential of the substrate W.

[0043] The control unit 2 determines the ON period P according to the time variation of the voltage level of at least one voltage pulse VP. ON The relational expression between the length of the voltage pulse VP and the maximum voltage level of the voltage pulse VP. In addition, the relational expression may also be determined by a control unit different from the control unit 2.

[0044] The bias power supply 32 sets the ON period P of each of the plurality of voltage pulses VP to ON The length of the ON period P is set to the ON period P determined by the control unit 2. ON When the relational expression is determined in the period CP, the bias power supply 32 sets the ON period P of each of the plurality of voltage pulses VP to ON The length of the ON period P is set to the ON period P determined by the control unit 2. ON In one embodiment, the bias power supply 32 sets the length of the period during which the first switch 32a is closed to the ON period P determined by the control unit 2. ONAs described above, during the period when the first switch 32a is closed, the second switch 23b is open. In addition, the ON period P of each of the plurality of voltage pulses VP ON The length of may also be determined in a control unit different from the control unit 2 and specified to the bias power supply 32.

[0045] Below, refer to Figure 7 . Figure 7 FIG. 1 is a flow chart of a plasma processing method according to an exemplary embodiment. Figure 7 In each step of the plasma processing method (hereinafter referred to as "method MT") shown, each part of the plasma processing apparatus 1 can be controlled by the control unit 2. The method MT includes a step STa and a step STb. In the method MT, before the step STa, the substrate W is placed on the substrate support 11.

[0046] In step STa, plasma is generated in the chamber 10. In one embodiment, in order to generate plasma, gas is supplied from the gas supply unit 20 into the chamber 10. In addition, the pressure in the chamber 10 can be adjusted to a specified pressure by the exhaust system 40. In addition, high-frequency power can be supplied from the high-frequency power supply 31. Step STa continues until step STb is completed.

[0047] In one embodiment, the method MT may further include a step STc and a step STd, wherein the step STc is performed during the period CP. In this case, the step STb is performed during the period AP after the period CP. In the step STc, as described above, at least one voltage pulse VP is applied from the bias power supply 32 to the substrate support 11. In the step STd, the above relationship is determined based on the time variation of the voltage level of the at least one voltage pulse VP. The relationship may be determined in the control unit 2 or other control units.

[0048] In step STb, in order to introduce ions from the plasma to the substrate W on the substrate support 11, a sequence of a plurality of voltage pulses PV is applied from the bias power supply 32 to the substrate support 11. Step STb includes step STb1 and step STb2. In step STb1, based on the above relationship, the ON period P of the voltage pulse VP is determined according to the maximum voltage level of the voltage pulse VP to be applied to the substrate support 11. ON The length of ON period P ON The length of the ON period P of the voltage pulse VP can be determined by the control unit 2 or other control units. ON The length of the ON period P is set to the ON period P determined in step STb1. ON The ON period P is set. ON A voltage pulse PV of a length of φ is applied to the substrate supporting portion 11 .

[0049] In step STJ after step STb2, it is determined whether the stop condition is satisfied. The stop condition can be satisfied at the end of the period specified by the processing plan data. In the case where it is determined in step STJ that the stop condition is not satisfied, steps STb1 and STb2 are repeated. By repeating steps STb1 and STb2, a sequence of a plurality of voltage pulses PV can be applied to the substrate support 11. In the case where it is determined in step STJ that the stop condition is satisfied, the method MT ends.

[0050] Although various exemplary embodiments have been described above, the present invention is not limited to the exemplary embodiments described above, and various additions, omissions, substitutions, and changes may be made. In addition, elements in different embodiments may be combined to form other embodiments.

[0051] According to the above description, it should be understood that the various embodiments of the present invention are described in this specification for the purpose of illustration, and various changes can be made without departing from the scope and spirit of the present invention. Therefore, the various embodiments recorded in this specification are not intended to limit the present invention, and the true scope and spirit are represented by the claims.

[0052] Description of Reference Numerals

[0053] 1…Plasma treatment device

[0054] 10…Chamber

[0055] 11…Substrate support portion

[0056] 12…Plasma generation unit

[0057] 32…Bias power supply.

Claims

1. A plasma processing device, characterized in that: include: Chamber; a substrate support portion disposed within the chamber; a plasma generating unit configured to generate plasma from a gas in the chamber; and a bias power supply configured to apply a sequence of a plurality of voltage pulses as an electrical bias to the substrate support portion, The bias power supply is configured to be able to adjust a maximum voltage level of each of the plurality of voltage pulses by adjusting a length of an ON period of each of the plurality of voltage pulses.

2. The plasma processing device according to claim 1, characterized in that: The device further includes a control unit configured to determine the length of the ON period corresponding to the maximum voltage level of each of the plurality of voltage pulses to be applied to the substrate support portion using a previously prepared relationship between the length of the ON period and the maximum voltage level, The bias power supply is configured to be able to set the length of the ON period of each of the plurality of voltage pulses to the length of the ON period determined by the control unit.

3. The plasma processing apparatus according to claim 1, wherein: Also includes a control unit, The control unit is configured to determine a relationship between the length of the ON period and the maximum voltage level based on a time change in the voltage level from the start of applying at least one voltage pulse from the bias power supply to the substrate support unit, and use the relationship to determine the length of the ON period corresponding to the maximum voltage level of each of the plurality of voltage pulses to be applied to the substrate support unit, The bias power supply is configured to be able to set the length of the ON period of each of the plurality of voltage pulses to the length of the ON period determined by the control unit.

4. The plasma processing device according to claim 3, wherein: further comprising a voltage sensor configured to measure a voltage of an electrical path electrically connecting the bias power supply and the substrate support portion to each other, The temporal variation of the voltage level is acquired by the voltage sensor.

5. The plasma processing apparatus according to claim 3, wherein: The device further includes a voltage sensor configured to measure a potential of a substrate placed on the substrate support portion. The temporal variation of the voltage level is acquired by the voltage sensor.

6. The plasma processing apparatus according to any one of claims 1 to 5, characterized in that: The bias power supply comprises: DC power supply; a first switch connected between the DC power supply and the substrate support; and a second switch connected between a node on an electrical path and ground, wherein the electrical path electrically connects the DC power source and the substrate support to each other, The bias power supply adjusts the length of the ON period of each of the plurality of voltage pulses by adjusting the length of the period during which the first switch is closed.

7. The plasma processing apparatus according to claim 6, wherein: The bias power supply is configured to close the second switch when the first switch is open.

8. A plasma treatment method, characterized in that: include: Step a, generating plasma from a gas in a chamber of a plasma processing device; and Step b, in order to introduce ions from the plasma into the substrate support in the chamber, applying a sequence of a plurality of voltage pulses from a bias power supply as an electrical bias to the substrate support, In the step b, the maximum voltage level of each of the plurality of voltage pulses is adjusted by adjusting the length of the ON period of each of the plurality of voltage pulses.

9. The plasma processing method according to claim 8, wherein: In step b, the length of the ON period of each of the multiple voltage pulses corresponding to the maximum voltage level of each of the multiple voltage pulses to be applied to the substrate supporting portion is determined by using a pre-prepared relationship between the length of the ON period and the maximum voltage level.

10. The plasma processing method according to claim 8, wherein: Also includes: determining a relational expression between the length of the ON period and the maximum voltage level based on a time change in the voltage level of the at least one voltage pulse from the start of application of the at least one voltage pulse from the bias power supply to the substrate supporting portion, In the step b, the length of the ON period of each of the plurality of voltage pulses corresponding to the maximum voltage level of each of the plurality of voltage pulses to be applied to the substrate supporting portion is determined using the relational expression.

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