Plasma processing device, RF system, and plasma processing method

Abstract

Provided is a technology that stabilizes an impedance matching operation. Provided is a plasma processing device. The plasma processing device comprises a chamber, an antenna that is provided above the chamber, an RF generation unit that is connected to the antenna, a measurement instrument that is configured to detect the RF reflection characteristics at a node that is between the antenna and the RF generation unit, an analyzer that is configured to determine an RF reflection spectrum for every frequency on the basis of the RF reflection characteristics, and a control unit that is configured to execute a plasma ignition sequence.

Description

Plasma processing apparatus, RF system, and plasma processing method

[0001] SUMMARY OF THE INVENTION Exemplary embodiments of the present disclosure relate to plasma processing apparatuses, RF systems, and plasma processing methods.

[0002] Patent Document 1 discloses a configuration in which an RF power supply that supplies RF power for generating plasma is connected to an antenna provided above the chamber via a matching box.

[0003] Japanese Patent Application Laid-Open No. 2020-12933

[0004] The present disclosure provides a technique for stabilizing impedance matching operation.

[0005] In one exemplary embodiment of the present disclosure, a plasma ignition system includes: a chamber; an antenna disposed above the chamber; an RF generator connected to the antenna; a measuring instrument configured to detect RF reflection characteristics at a node between the antenna and the RF generator; an analyzer configured to determine an RF reflection spectrum for each frequency based on the RF reflection characteristics; and a controller configured to execute a plasma ignition sequence, the plasma ignition sequence including: (a1) controlling the RF generator to output a first modulated RF signal having a plurality of frequency components in a first frequency band; (a2) acquiring from an analyzer an RF reflection spectrum for each frequency corresponding to the first modulated RF signal; (a3) ​​determining an ignition frequency based on the RF reflection spectrum for each frequency acquired in (a2); and (a4) controlling an RF generating unit to output a second modulated RF signal having a plurality of frequency components in a second frequency band, the second frequency band including the ignition frequency and being narrower than the first frequency band, and the second modulated RF signal having a power level capable of generating plasma in the chamber.

[0006] According to one exemplary embodiment of the present disclosure, a technique for stabilizing impedance matching operation can be provided.

[0007] FIG. 1 is a diagram for explaining an example of the configuration of a plasma processing system; FIG. 2 is a diagram for explaining an example of the configuration of an inductively coupled plasma processing apparatus; FIG. 3 is a diagram for explaining an example of an RF system; FIG. 4 is a diagram for explaining another example of an RF system; FIG. 5 is a flowchart for explaining an example of a method MT; FIG. 6 is a diagram for explaining a modulated RF signal and an RF reflection spectrum in each step of the method MT; FIG. 7 is a flowchart for explaining an example of a process ST1; FIG. 8 is a flowchart for explaining an example of a process ST2; and FIG. 9 is a flowchart for explaining an example of a process ST3.

[0008] Hereinafter, each embodiment of the present disclosure will be described.

[0009] In one exemplary embodiment, a plasma ignition system includes a chamber, an antenna disposed above the chamber, an RF generator connected to the antenna, a measuring instrument configured to detect RF reflection characteristics at a node between the antenna and the RF generator, an analyzer configured to determine an RF reflection spectrum for each frequency based on the RF reflection characteristics, and a controller configured to execute a plasma ignition sequence, the plasma ignition sequence including: (a1) controlling the RF generator to output a first modulated RF signal having a plurality of frequency components in a first frequency band; (a2) acquiring from an analyzer an RF reflection spectrum for each frequency corresponding to the first modulated RF signal; (a3) ​​determining an ignition frequency based on the RF reflection spectrum for each frequency acquired in (a2); and (a4) controlling an RF generating unit to output a second modulated RF signal having a plurality of frequency components in a second frequency band, the second frequency band including the ignition frequency and being narrower than the first frequency band, and the second modulated RF signal having a power level capable of generating plasma in the chamber.

[0010] In one exemplary embodiment, the center frequency of the second frequency band is the ignition frequency.

[0011] In one exemplary embodiment, the control unit is configured to execute an impedance matching sequence after the plasma ignition sequence, and the impedance matching sequence includes: (b1) controlling the RF generation unit to output a modulated RF signal having a plurality of frequency components, the modulated RF signal having a power level capable of generating plasma in the chamber; (b2) acquiring an RF reflection spectrum for each frequency corresponding to the modulated RF signal from an analyzer; (b3) determining a target frequency at which the RF reflection spectrum is minimized based on the RF reflection spectrum for each frequency acquired in (b2); and (b4) narrowing the frequency band of the modulated RF signal output from the RF generation unit while adjusting it so that the center frequency of the frequency band is the target frequency.

[0012] In one exemplary embodiment, the impedance matching sequence further includes (b5) repeating (b1) to (b4) until the frequency band of the modulated RF signal output from the RF generator reaches the target width.

[0013] In one exemplary embodiment, the controller is configured to execute a plasma maintenance sequence for maintaining plasma in the chamber after the matching sequence, the plasma maintenance sequence including: (c1) controlling the RF generator to output a third modulated RF signal having a plurality of frequency components and a fourth modulated RF signal having a plurality of frequency components, wherein the third modulated RF signal has a power level capable of generating plasma in the chamber and the fourth modulated RF signal has a power level such that plasma is not generated in the chamber, and the frequency band of the fourth modulated RF signal is wider than the frequency band of the third modulated RF signal; (c2) acquiring RF reflection spectra for each frequency corresponding to the third modulated RF signal and the fourth modulated RF signal from the analyzer; (c3) determining a target frequency at which the RF reflection spectrum is minimized based on the RF reflection spectra for each frequency acquired in (c2); and (c4) setting the frequency band of the third modulated RF signal output from the RF generator so that a center frequency of the frequency band is the target frequency.

[0014] In one exemplary embodiment, the RF reflection characteristic is any one of (a) the ratio or proportion [%] of the power of the forward wave to the power of the reflected wave, (b) the resistive component of the impedance [Ω], (c) the reflection coefficient, (d) the return loss [dB], and (e) the S-parameter [dB] at the node.

[0015] In one exemplary embodiment, the apparatus further comprises an impedance matching circuit connected between the chamber and the measuring device.

[0016] In one exemplary embodiment, the instrument further comprises an impedance matching circuit connected between the RF signal generator and the measuring device.

[0017] In one exemplary embodiment, the RF generator includes a waveform output configured to output a broadband RF signal having multiple frequency components superimposed thereon, and a power amplifier configured to amplify the broadband RF signal to output a modulated RF signal including the multiple frequency components.

[0018] In one exemplary embodiment, the RF signal generation unit includes a waveform output unit configured to sequentially output swept RF signals of different frequencies, and a waveform output unit configured to sequentially amplify the swept RF signals to output a modulated RF signal including a plurality of frequency components.

[0019] In one exemplary embodiment, the power level at which no plasma is generated is less than 10 W.

[0020] In one exemplary embodiment, the first frequency band has a bandwidth less than 20% of the design frequency of the RF generator, and the second frequency band has a bandwidth less than 10% of the design frequency.

[0021] In one exemplary embodiment, the target width is within the range of 0.1 to 1% of the design frequency of the RF generator.

[0022] In one exemplary embodiment, in (b5), the frequency band of the modulated RF signal is narrowed by 0.1 kHz to 500 kHz.

[0023] In one exemplary embodiment, a plasma generation system includes a chamber, an antenna disposed above the chamber, an RF generator connected to the antenna, a measuring instrument configured to detect RF reflection characteristics at a node between the antenna and the RF generator, an analyzer configured to determine an RF reflection spectrum for each frequency based on the RF reflection characteristics, and a controller configured to execute a plasma sustaining sequence for sustaining plasma generated in the chamber, the plasma sustaining sequence including: (c1) controlling the RF generator to output a third modulated RF signal having a plurality of frequency components and a fourth modulated RF signal having a plurality of frequency components, the third modulated RF signal being a signal to be transmitted to the chamber; (c2) acquiring, from an analyzer, RF reflection spectra for each frequency corresponding to the third modulated RF signal and the fourth modulated RF signal; (c3) determining a target frequency at which the RF reflection spectrum becomes minimum based on the RF reflection spectrum for each frequency acquired in (c2); and (c4) setting the frequency band of the third modulated RF signal output from the RF generating unit so that the center frequency of the frequency band becomes the target frequency.

[0024] In one exemplary embodiment, an RF system is provided, comprising: an RF generator coupled to a chamber; a measuring instrument configured to detect RF reflection characteristics at a node between the chamber and the RF generator; an analyzer configured to determine an RF reflection spectrum for each frequency based on the RF reflection characteristics; and a controller configured to execute a plasma ignition sequence, wherein the plasma ignition sequence includes: (a1) controlling the RF generator to output a first modulated RF signal having a plurality of frequency components in a first frequency band, the first modulated RF signal having a power level such that plasma is not generated in the chamber; (a2) acquiring an RF reflection spectrum for each frequency of the first modulated RF signal from the analyzer; (a3) ​​determining an ignition frequency based on the RF reflection spectrum for each frequency acquired in (a2); and (a4) controlling the RF generator to output a second modulated RF signal having a plurality of frequency components in a second frequency band, the second frequency band including the ignition frequency and being narrower than the first frequency band, the second modulated RF signal having a power level capable of generating plasma in the chamber.

[0025] In one exemplary embodiment, a plasma processing method is provided, comprising the steps of: outputting a first modulated RF signal having a plurality of frequency components in a first frequency band to a chamber, the first modulated RF signal having a power level that does not generate plasma in the chamber; detecting RF reflection characteristics from the chamber; acquiring an RF reflection spectrum for each frequency corresponding to the first modulated RF signal based on the acquired RF reflection characteristics; and determining an ignition frequency based on the acquired RF reflection spectrum for each frequency; and outputting a second modulated RF signal having a plurality of frequency components in a second frequency band to the chamber, the second frequency band including the ignition frequency and being narrower than the first frequency band, the second modulated RF signal having a power level that can generate plasma in the chamber.

[0026] Hereinafter, each embodiment of the present disclosure will be described in detail with reference to the drawings. In each drawing, the same or similar elements are designated by the same reference numerals, and redundant explanations will be omitted. Unless otherwise specified, the positional relationships, such as up, down, left, and right, will be described based on the positional relationships shown in the drawings. The dimensional ratios in the drawings do not represent actual ratios, and the actual ratios are not limited to the ratios shown in the drawings.

[0027] <Configuration Example of Plasma Processing System> FIG. 1 is a diagram illustrating a configuration example of a plasma processing system. In one embodiment, the plasma processing system includes a plasma processing apparatus 1 and a control unit 2. The plasma processing system is an example of a substrate processing system, and the plasma processing apparatus 1 is an example of a substrate processing apparatus. The plasma processing apparatus 1 includes a plasma processing chamber 10, a substrate support 11, and a plasma generation unit 12. The plasma processing chamber 10 has a plasma processing space. The plasma processing chamber 10 also 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 a gas supply unit 20 (described later), and the gas exhaust port is connected to an exhaust system 40 (described later). The substrate support 11 is disposed in the plasma processing space and has a substrate support surface for supporting a substrate.

[0028] The plasma generating unit 12 is configured to generate plasma from at least one processing gas supplied into the plasma processing space. The plasma generated in the plasma processing space may be capacitively coupled plasma (CCP), inductively coupled plasma (ICP), electron-cyclotron-resonance plasma (ECR plasma), helicon wave plasma (HWP), surface wave plasma (SWP), or the like. Various types of plasma generators may be used, including alternating current (AC) plasma generators and direct current (DC) plasma generators. In one embodiment, the AC signal (AC power) used in the AC plasma generator has a frequency in the range of 100 kHz to 10 GHz. Thus, AC signals include radio frequency (RF) signals and microwave signals. In one embodiment, the RF signal has a frequency in the range of 100 kHz to 150 MHz.

[0029] The control unit 2 processes computer-executable instructions that cause the plasma processing apparatus 1 to perform various processes described in this disclosure. The control unit 2 may be configured to control each element of the plasma processing apparatus 1 to perform various processes described herein. In one embodiment, part or all of the control unit 2 may be included in the plasma processing apparatus 1. The control unit 2 may include a processing unit 2a1, a storage unit 2a2, and a communication interface 2a3. The control unit 2 may be implemented by, for example, a computer 2a. The processing unit 2a1 may be configured to read a program from the storage unit 2a2 and execute the read program to perform various control operations. This program may be stored in the storage unit 2a2 in advance or may be acquired via a medium when needed. The acquired program is stored in the storage unit 2a2 and read from the storage unit 2a2 by the processing unit 2a1 for execution. The medium may be various storage media readable by the computer 2a or a communication line connected to the communication interface 2a3. The processing unit 2a1 may be a CPU (Central Processing Unit). The storage unit 2a2 may include a random access memory (RAM), a read-only memory (ROM), a hard disk drive (HDD), a solid state drive (SSD), or a combination thereof. The communication interface 2a3 may communicate with the plasma processing apparatus 1 via a communication line such as a local area network (LAN).

[0030] The following describes a configuration example of an inductively coupled plasma processing apparatus as an example of the plasma processing apparatus 1. Fig. 2 is a diagram for explaining a configuration example of an inductively coupled plasma processing apparatus.

[0031] The inductively coupled plasma processing apparatus 1 includes a plasma processing chamber 10, a gas supply unit 20, a power supply 30, and an exhaust system 40. The plasma processing chamber 10 includes a dielectric window 101. The plasma processing apparatus 1 also includes a substrate support 11, a gas inlet, and an antenna 14. The substrate support 11 is disposed within the plasma processing chamber 10. The antenna 14 is disposed on or above the plasma processing chamber 10 (i.e., on or above the dielectric window 101). The plasma processing chamber 10 has a plasma processing space 10s defined by the dielectric window 101, a sidewall 102 of the plasma processing chamber 10, and the substrate support 11. The plasma processing chamber 10 is grounded.

[0032] The substrate support 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 in a plan view. The substrate W is disposed on the central region 111a of the main body 111, and the ring assembly 112 is disposed on the annular region 111b of the main body 111 so as to surround the substrate W on the central region 111a of the main body 111. Therefore, the central region 111a is also called a substrate support surface for supporting the substrate W, and the annular region 111b is also called a ring support surface for supporting the ring assembly 112.

[0033] In one embodiment, the main body 111 includes a base 1110 and an electrostatic chuck 1111. The base 1110 includes a conductive member. The conductive member of the base 1110 can function as a bias electrode. The electrostatic chuck 1111 is disposed on the base 1110. The electrostatic chuck 1111 includes a ceramic member 1111a and an electrostatic electrode 1111b disposed within the ceramic member 1111a. The ceramic member 1111a has a central region 111a. In one embodiment, the ceramic member 1111a also has an annular region 111b. Note that the annular region 111b may also be provided by another member surrounding the electrostatic chuck 1111, such as an annular electrostatic chuck or an annular insulating member. In this case, the ring assembly 112 may be disposed on the annular electrostatic chuck or the annular insulating member, or may be disposed on both the electrostatic chuck 1111 and the annular insulating member. Furthermore, at least one RF / DC electrode coupled to an RF power supply 31 and / or a DC power supply 32, which will be described later, may be disposed within the ceramic member 1111a. In this case, the at least one RF / DC electrode functions as a bias electrode. Note that the conductive member of the base 1110 and the at least one RF / DC electrode may function as multiple bias electrodes. Alternatively, the electrostatic electrode 1111b may function as a bias electrode. Therefore, the substrate support 11 includes at least one bias electrode.

[0034] The ring assembly 112 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 rings are formed of a conductive or insulating material, and the cover rings are formed of an insulating material.

[0035] The substrate support 11 may also include a temperature adjustment module 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 passage 1110a, or a combination thereof. A heat transfer fluid such as brine or a gas flows through the flow passage 1110a. In one embodiment, the flow passage 1110a is formed in the base 1110, and one or more heaters are disposed in the ceramic member 1111a of the electrostatic chuck 1111. The substrate support 11 may also include a heat transfer gas supply configured to supply a heat transfer gas to a gap between the backside of the substrate W and the central region 111a.

[0036] The gas inlet is configured to introduce at least one process gas from the gas supply unit 20 into the plasma processing space 10s. In one embodiment, the gas inlet includes a center gas injector (CGI) 13. The center gas injector 13 is disposed above the substrate support 11 and attached to a central opening formed in the dielectric window 101. The center gas injector 13 has at least one gas supply port 13a, at least one gas flow path 13b, and at least one gas inlet port 13c. The process gas supplied to the gas supply port 13a passes through the gas flow path 13b and is introduced into the plasma processing space 10s from the gas inlet port 13c. Note that the gas inlet may include one or more side gas injectors (SGIs) attached to one or more openings formed in the sidewall 102 in addition to or instead of the center gas injector 13.

[0037] The gas supply unit 20 may 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 process gas from a corresponding gas source 21 to the gas inlet through a corresponding flow controller 22. Each flow controller 22 may include, for example, a mass flow controller or a pressure-controlled flow controller. Additionally, the gas supply unit 20 may include at least one flow modulation device that modulates or pulses the flow rate of the at least one process gas.

[0038] The power supply 30 includes an RF power supply 31 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) to at least one bias electrode and the antenna 14. This causes a plasma to be formed from at least one processing gas supplied to the plasma processing space 10s. Therefore, the RF power supply 31 can function as at least a part of the plasma generating unit 12. Furthermore, by supplying a bias RF signal to the at least one bias electrode, a bias potential is generated on the substrate W, thereby attracting ions in the formed plasma to the substrate W.

[0039] In one embodiment, the RF power supply 31 includes a first RF generating unit 31a and a second RF generating unit 31b. The first RF generating unit 31a is coupled to the antenna 14 via at least one impedance matching circuit and is 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 of 10 MHz to 150 MHz. In one embodiment, the first RF generating unit 31a may be configured to generate multiple source RF signals having different frequencies. The generated one or more source RF signals are supplied to the antenna 14.

[0040] The second RF generator 31b is coupled to at least one bias electrode via at least one impedance matching circuit and is 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 the frequency of the source RF signal. In one embodiment, the bias RF signal has a frequency in the range of 100 kHz to 60 MHz. In one embodiment, the second RF generator 31b may be configured to generate multiple bias RF signals having different frequencies. The generated one or more bias RF signals are supplied to at least one bias electrode. In various embodiments, at least one of the source RF signal and the bias RF signal may be pulsed.

[0041] 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 bias DC generator 32a. In one embodiment, the bias DC generator 32a is connected to at least one bias electrode and configured to generate a bias DC signal. The generated bias DC signal is applied to the at least one bias electrode.

[0042] In various embodiments, the bias DC signal may be pulsed. In this case, a sequence of voltage pulses is applied to at least one bias electrode. The voltage pulses may have a rectangular, trapezoidal, triangular, or combination thereof. In one embodiment, a waveform generator for generating the sequence of voltage pulses from the DC signal is connected between the bias DC generator 32a and at least one bias electrode. Thus, the bias DC generator 32a and the waveform generator constitute a voltage pulse generator. The voltage pulses may have positive or negative polarity. Furthermore, the sequence of voltage pulses may include one or more positive voltage pulses and one or more negative voltage pulses within one cycle. Note that the bias DC generator 32a may be provided in addition to the RF power supply 31 or may be provided instead of the second RF generator 31b.

[0043] The antenna 14 includes one or more coils. In one embodiment, the antenna 14 may include an outer coil and an inner coil arranged coaxially. In this case, the RF power supply 31 may be connected to both the outer coil and the inner coil, or to either the outer coil or the inner coil. In the former case, the same RF generator may be connected to both the outer coil and the inner coil, or separate RF generators may be connected to the outer coil and the inner coil separately.

[0044] The exhaust system 40 may be connected to, for example, a gas exhaust port 10e 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 in the plasma processing space 10s is regulated by the pressure regulating valve. The vacuum pump may include a turbomolecular pump, a dry pump, or a combination thereof.

[0045] <Example of RF System> FIG. 3 is a diagram showing an example of a system configuration (hereinafter also referred to as an "RF system") from the first RF generating unit 31a to the chamber 10. The first RF generating unit 31a is coupled to the plasma processing chamber 10 (hereinafter also referred to as the "chamber 10") via a transmission line TL. In one embodiment, the first RF generating unit 31a may be connected to the antenna 14 (see FIG. 2) of the plasma processing apparatus 1. The transmission line TL is a signal line through which the RF signal (source RF signal) generated by the first RF generating unit 31a propagates. A matching unit 33 and a measuring unit 34 are arranged in this order on the transmission line TL from upstream (the first RF generating unit 31a) to downstream (the chamber 10). That is, the first RF generating unit 31a is coupled to the chamber 10 via the matching unit 33 and the measuring unit 34 on the transmission line TL. An analyzer 35 is connected to the measuring unit 34. The RF system can be controlled by a controller CT.

[0046] The first RF generating unit 31a is configured to generate a modulated RF signal in which multiple frequency components are superimposed. The first RF generating unit 31a includes a waveform output unit 310a and a power amplifier 312a. Note that the first RF generating unit 31a may generate an RF signal consisting of a single frequency component.

[0047] The waveform output unit 310a may be configured to simultaneously output a broadband RF signal on which multiple frequency components are superimposed. The power amplifier 312a adjusts the power of the broadband RF signal output from the waveform output unit 310a and outputs it as a modulated RF signal. The controller CT controls the output of the broadband RF signal from the waveform output unit 310a so that the modulated RF signal has a desired center frequency, bandwidth, and pitch. The controller CT also controls the amplification factor of the broadband RF signal in the power amplifier 312a so that the modulated RF signal has a desired power.

[0048] The waveform output unit 310a may be configured to sequentially output sweep RF signals of different frequencies. The power amplifier 312a sequentially adjusts the power of the sweep RF signals output from the waveform output unit 310a and outputs them as modulated RF signals. The controller CT controls the output of each of the multiple sweep RF signals from the waveform output unit 310a so that the modulated RF signals have desired center frequencies, bandwidths, and pitches. The controller CT also controls the amplification factor of each sweep RF signal in the power amplifier 312a so that the modulated RF signals have desired power.

[0049] The matching unit 33 is configured to match the impedance between the first RF generating unit 31a and the chamber 10. The matching unit 33 may include a matching circuit including a variable reactance element (e.g., a variable capacitor, a variable inductor, etc.). The variable reactance element of the matching circuit may be controlled by the controller CT, thereby controlling the impedance of the first RF generating unit 31a with respect to the chamber 10.

[0050] The measuring instrument 34 is configured to periodically or continuously detect the RF reflection characteristics of the RF signal propagating through the transmission line TL and output the results to the analyzer 35. The RF reflection characteristics are parameters related to the amount of return (power of reflected waves) relative to the output (power of traveling waves) of the RF signal on the transmission line TL. In the example shown in Fig. 3, what is detected by the measuring instrument 34 and output to the analyzer 35 is the reflection characteristics of the RF signal at the output end (node) of the matching circuit 33.

[0051] The RF reflection characteristics may include one or more of the following (a) to (e): (a) the ratio Ra (see Equation 1) or the ratio Rp (Ra×100[%]) of the power of the forward wave (Pf) to the power of the reflected wave (Pr); (b) the resistance component R [Ω] of the impedance (see Equation 2); (c) the reflection coefficient Γ (see Equation 3); (d) the return loss RL [dB] (see Equation 4); and (e) the S parameter S. 11 [dB] (see equation 5)

[0052]

[0053]

[0054]

[0055]

[0056]

[0057] The measuring instrument 34 may include a directional coupler. The directional coupler is configured to separate a portion of the forward wave and a portion of the reflected wave of the RF signal propagating through the transmission line TL. The measuring instrument 34 may use the directional coupler to separate a portion of the forward wave and a portion of the reflected wave of the RF signal propagating through the transport line TL and obtain the power (Pf) of the forward wave and the power (Pr) of the reflected wave. The measuring instrument 34 may also include a VI sensor. The VI sensor is configured to detect electrical characteristics of the RF signal. The measuring instrument 34 may use the VI sensor to obtain the effective value (V) of the voltage, the effective value (I) of the current, and the phase difference (θ) between the voltage and the current of the RF signal propagating through the transport line TL.

[0058] The analyzer 35 is configured to determine an RF reflection spectrum for each frequency based on the RF reflection characteristics detected by the measuring instrument 34. The RF reflection spectrum is data including RF reflection characteristics (amplitude) for each frequency. An example of an RF reflection spectrum will be described later with reference to FIG. 6. In one example, the analyzer 35 is a spectrum analyzer having a fast Fourier transform (FFT) function. The analyzer 35 may be configured as a part of the controller CT.

[0059] The controller CT may include a processor (processing unit), a storage unit, and a communication interface. The controller CT may be configured to control each component of the RF system to execute each process described below. In one embodiment, a part or all of the controller CT may be included in the control unit 2 of the plasma processing system (see FIGS. 1 and 2). In another embodiment, a part of the controller CT may be included in another component of the RF system (the first RF generation unit 31 a, the matching unit 33, the measuring unit 34, and / or the analyzer 35).

[0060] Fig. 4 is a diagram showing another example of an RF system. In the example shown in Fig. 4, the positional relationship between the matching circuit 33 and the measuring device 34 is the opposite of that in the example shown in Fig. 3. That is, in the example shown in Fig. 4, the measuring device 34 and the matching device 33 are arranged in this order from upstream to downstream on the transmission line TL. In the example shown in Fig. 4, what is detected by the measuring device 34 and output to the analyzer 35 is the reflection characteristic of the RF signal at the input end (node) of the matching circuit 33.

[0061] <Example of Plasma Processing Method> FIG. 5 is a flowchart showing an example of a plasma processing method (hereinafter also referred to as "method MT") according to an exemplary embodiment. FIG. 6 is a diagram illustrating the modulated RF signal and RF reflection spectrum in each step of method MT. As shown in FIG. 5, method MT includes step ST1 of igniting plasma, step ST2 of performing a matching operation, and step ST3 of maintaining plasma. The processes in each step may be performed using the plasma processing apparatus 1 ( FIGS. 1 and 2 ) and RF system ( FIGS. 3 and 4 ). The following describes an example in which the control unit 2 and / or the controller CT controls each part of the plasma processing apparatus 1 and the RF system to perform method MT.

[0062] (Process ST1: Plasma Ignition) Fig. 7 is a flowchart showing an example of process ST1. In process ST1, plasma is generated in chamber 10. As shown in Fig. 7, process ST1 includes a process ST11 of outputting a first modulated RF signal, a process ST12 of detecting RF reflection characteristics, a process ST13 of acquiring an RF reflection spectrum, a process ST14 of determining an ignition frequency, and a process ST15 of outputting a second modulated RF signal. Process ST1 is an example of a plasma ignition sequence in the present disclosure.

[0063] At the start of process ST1, a gas for generating plasma may be supplied from the gas supply unit 20 into the chamber 10. At this time, the pressure inside the chamber 10 may be reduced to a given set pressure. At the start of process ST1, a substrate W may be provided on the substrate support unit 11 of the chamber 10. At this time, the temperature of the substrate support unit 11 and / or the substrate W may be adjusted to a given set temperature. Note that process ST1 may be performed in a state where the substrate W is not provided in the chamber 10.

[0064] In step ST11, a first modulated RF signal is output from the first RF generating unit 31a to the chamber 10. The first modulated RF signal may be generated by simultaneously outputting a broadband RF signal on which multiple frequency components are superimposed from the waveform output unit 310a of the first RF generating unit 31a. Alternatively, the first modulated RF signal may be generated by sequentially outputting sweep RF signals of different frequencies from the waveform output unit 310a of the first RF generating unit 31a.

[0065] An example of a first modulated RF signal is shown in column (A) of "Modulated RF Signal" in FIG. 6 . The first modulated RF signal has multiple frequency components in a first frequency band (bandwidth: BD1). The pitch Pt1 between each frequency component of the first modulated RF signal may be constant, or some or all of the frequency components may vary. The first frequency band may be set so that the design frequency of the first RF generator 31a (the design frequency of the source RF signal for plasma generation, e.g., 27 MHz) is the center frequency. In one embodiment, the bandwidth BD1 of the first frequency band is less than 20% of the design frequency (e.g., 5.4 MHz). In one embodiment, the bandwidth BD1 of the first frequency band is less than 10% of the design frequency (e.g., 2.7 MHz).

[0066] The first modulated RF signal has a first power level P1 (W). The first power level P1 is a power level that does not generate plasma in the chamber 10. In one example, the first power level P1 is less than 10 W, less than 5 W, or less than 1 W. The first power level P1 may be determined based on the reflection resistance of the power supply 30 including the first RF generating unit 31 a.

[0067] In step ST12, the RF reflection characteristics are detected. The measuring instrument 34 detects the RF reflection characteristics of the first modulated RF signal propagating through the transmission line TL, and outputs the results to the analyzer 35.

[0068] In step ST13, an RF reflection spectrum is acquired. The analyzer 35 acquires an RF reflection spectrum for each frequency corresponding to the first modulated RF signal based on the RF reflection characteristics of the first modulated RF signal output from the measuring instrument 34.

[0069] 6 shows an example of the RF reflection spectrum acquired in step ST13. In this example, the amplitude of the RF reflection spectrum (RF reflection characteristic) is the ratio Rp [%] of the power of the forward wave (Pf) to the power of the reflected wave (Pr). The frequency band of the RF reflection spectrum is the same as the first frequency band.

[0070] In step ST14, an ignition frequency is determined. The ignition frequency is determined based on the RF reflection spectrum acquired in step ST13. The ignition frequency may be a frequency in the RF reflection spectrum that has the best RF reflection characteristics, i.e., a frequency at which the return loss is minimized. For example, in the example shown in column (A) of "RF reflection spectrum" in FIG. 6, the frequency Fa at which the amplitude (ratio Rp [%]) of the RF reflection spectrum is minimum may be determined as the ignition frequency.

[0071] In step ST15, a second modulated RF signal is output from the first RF generating unit 31a to the chamber 10. The second modulated RF signal may be generated by simultaneously outputting a broadband RF signal on which multiple frequency components are superimposed from the waveform output unit 310a of the first RF generating unit 31a. Alternatively, the second modulated RF signal may be generated by sequentially outputting sweep RF signals of different frequencies from the waveform output unit 310a of the first RF generating unit 31a.

[0072] An example of the second modulated RF signal is shown in column (B) of "Modulated RF Signal" in FIG. 6. The second modulated RF signal has multiple frequency components in a second frequency band (bandwidth: BD2). The bandwidth BD2 of the second frequency band is narrower than the bandwidth BD1 of the first frequency band. The second frequency band may be set so that the ignition frequency (Fa) determined in step ST14 is its center frequency. In one embodiment, the bandwidth BD2 of the second frequency band is less than 10% of the design frequency. In one embodiment, the bandwidth BD2 of the second frequency band is within a range of 1 to 10% of the design frequency. The pitch Pt2 between the frequency components of the second modulated RF signal may be constant, or may be partially or entirely different. The pitch Pt2 between the frequency components of the second modulated RF signal may be smaller than the pitch Pt1 between the frequency components of the first modulated RF signal.

[0073] The second modulated RF signal has a second power level P2 (W). The second power level P2 is a power level capable of generating plasma in the chamber 10. That is, the second power level P2 is greater than the first power level P1. Note that the second modulated RF signal does not have to have the second power level P2 from the start of process ST15, and may be gradually increased from the first power level P1 to the second power level P2.

[0074] In step ST15, plasma is generated from the gas in the chamber 10. This completes step ST1.

[0075] In step ST1, the RF reflection spectrum of the first modulated RF signal is used to determine the ignition frequency with the smallest return loss. Then, the second modulated RF signal is used to generate plasma in the chamber 10. The ignition frequency is a frequency at which plasma is likely to be generated. This can reduce failures in plasma ignition. Furthermore, because the ignition frequency is determined in advance, the bandwidth BD2 of the second modulated RF signal can be narrower than the bandwidth BD1 of the first modulated RF signal. This can reduce the absolute amount of reflected waves (hereinafter also referred to as "RF reflection") propagating through the transmission line TL during plasma ignition.

[0076] Column (B) of "RF Reflection Spectrum" in FIG. 6 shows an example of an RF reflection spectrum at the end of process ST15, i.e., immediately after plasma is generated in the chamber 10. In this example, the frequency Fb with the best RF reflection characteristics is different from the ignition frequency (Fa). This is because the RF reflection characteristics change due to a change in the load on the chamber 10 caused by plasma generation. In such a case, if the source RF signal has a single frequency component, RF reflection increases immediately after plasma generation, potentially reducing stability (robustness). In this regard, in process ST1, plasma is generated using a second modulated RF signal. The second modulated RF signal has a second frequency band (bandwidth: BD2) centered on the ignition frequency (Fa). That is, the second modulated RF signal includes not only the ignition frequency (Fa) but also frequency components surrounding the ignition frequency (Fa). Therefore, even if the load on the chamber 10 changes immediately after plasma ignition and the frequency with the best RF reflection characteristics changes (e.g., from Fa to Fb), the second modulated RF signal may still contain the frequency component after the change. This can improve stability (robustness) immediately after plasma ignition.

[0077] (Process ST2: Matching Operation) FIG. 8 is a flowchart showing an example of process ST2. In process ST2, an impedance matching operation (hereinafter also simply referred to as "matching operation") is performed. The matching operation is an operation for matching the impedance between the first RF generating unit 31a and the chamber 10 to reduce RF reflection. The matching operation enables efficient supply of power to the plasma in the chamber 10. In one embodiment, the matching operation includes changing the frequency of the source RF signal output from the first RF generating unit 31a and / or changing the reactance of the variable reactance element of the matching unit 33. In one embodiment, the matching operation includes setting the impedance seen from the input end of the matching unit 33 to a characteristic impedance (e.g., 50Ω) on the load side.

[0078] 8, step ST2 includes step ST21 of outputting a modulated RF signal, step ST22 of detecting RF reflection characteristics, step ST23 of acquiring an RF reflection spectrum, step ST24 of determining a target frequency, step ST25 of determining a frequency band of the modulated RF signal, and step ST26 of determining whether the bandwidth of the frequency band is within the target width. Steps ST21 to ST26 are repeated multiple times until the determination in step ST26 is affirmative. The duration of one cycle of steps ST21 to ST26 may be, for example, 1 μs to 10 ms. Step ST2 is an example of an impedance matching sequence in the present disclosure.

[0079] In step ST21, a modulated RF signal is output from the first RF generating unit 31a to the chamber 10. The modulated RF signal may be generated by simultaneously outputting a broadband RF signal on which multiple frequency components are superimposed from the waveform output unit 310a of the first RF generating unit 31a. Alternatively, the modulated RF signal may be generated by sequentially outputting sweep RF signals of different frequencies from the waveform output unit 310a of the first RF generating unit 31a. In step ST21, a variable reactance element of the matching circuit of the matching unit 33 may be changed.

[0080] As described above, steps ST21 to ST26 can be repeated multiple times. In the first step ST21, the modulated RF signal may be the same as the second modulated RF signal (column (B) of "Modulated RF Signal" in FIG. 6). Column (C) of "Modulated RF Signal" in FIG. 6 shows an example of a modulated RF signal output in the Nth (N>1) step ST21. As will be described later, the bandwidth of the modulated RF signal output from the first RF generating unit 31a narrows with each repetition of step ST21. The bandwidth BDN of the modulated RF signal output in the Nth step ST21 may be narrower than the bandwidth of the modulated RF signal output in the previous step ST21 (1st to N-1th). The pitch between the frequency components of the modulated RF signal may be constant, or may be partially or entirely different.

[0081] In one embodiment, the power level of the modulated RF signal may be constant (e.g., second power level P2) regardless of the number of times step ST21 is performed. In one embodiment, the power level of the modulated RF signal may be changed one or more times while step ST21 is repeated. For example, if the RF reflection characteristics deteriorate during the matching operation and it becomes difficult to maintain plasma, the power level of the modulated RF signal output in step ST21 may be increased. This may prevent plasma from misfiring.

[0082] In step ST22, the RF reflection characteristics are detected. The measuring instrument 34 detects the RF reflection characteristics of the modulated RF signal propagating through the transmission line TL, and outputs the results to the analyzer 35.

[0083] In step ST23, an RF reflection spectrum is acquired. The analyzer 35 acquires an RF reflection spectrum for each frequency corresponding to the modulated RF signal based on the RF reflection characteristics of the modulated RF signal output from the measuring instrument 34. Column (B) of "RF reflection spectrum" in Fig. 6 shows an example of an RF reflection spectrum acquired in the first step ST23. Column (C) of "RF reflection spectrum" in Fig. 6 shows an example of an RF reflection spectrum acquired in the Nth step ST23 (N>1).

[0084] In step ST24, a target frequency is determined. The target frequency is determined based on the RF reflection spectrum acquired in step ST23. The target frequency may be a frequency in the RF reflection spectrum that has the best RF reflection characteristics, i.e., a frequency at which the return loss is minimized. For example, in the examples shown in columns (B) and (C) of "RF reflection spectrum" in FIG. 6, frequencies Fb and Fn at which the amplitude (ratio Rp [%]) of the RF reflection spectrum is minimized may be determined as the target frequencies.

[0085] In step ST25, the frequency band of the modulated RF signal is determined. This frequency band is set so that the target frequency (e.g., frequency Fb or Fn) determined in step ST24 is used as the center frequency, and the bandwidth is narrower than the bandwidth of the modulated RF signal output in the immediately preceding step ST21. That is, the bandwidth of the modulated RF signal that is determined becomes gradually narrower with each repetition of step ST25. For example, the frequency band may be set so that the bandwidth becomes narrower by 0.1 kHz to 500 kHz with each repetition of step ST25.

[0086] In step ST26, it is determined whether the bandwidth of the frequency band determined in step ST25 is within a target width. In one embodiment, the target width may be within a range of 0.1 to 1% of the design frequency (e.g., 27 MHz) of the first RF generating unit 31a.

[0087] If the bandwidth of the frequency band determined in step ST25 is equal to or greater than the target width (step ST26: NO), the process returns to step ST21. At this time, the modulated RF signal having the frequency band determined in step ST25 is set as the modulated RF signal to be output in the next step ST21.

[0088] If the bandwidth of the frequency band determined in step ST25 is less than the target width (step ST26: YES), the matching operation of step ST2 is terminated. At this time, the modulated RF signal having the frequency band determined in step ST25 is set as the matching modulated RF signal.

[0089] An example of a matched modulated RF signal is shown in column (D) of "Modulated RF Signal" in Figure 6. Also, an RF reflection spectrum corresponding to the matched modulated RF signal is shown in column (D) of "RF Reflection Spectrum." The frequency band (bandwidth: BDL) of the matched modulated RF signal is the frequency band determined in the final step ST25. The power level PL of the matched modulated RF signal is a power level capable of generating plasma in the chamber 10. This power level PL may be the same as or different from the second power level P2. The pitch PtL between each frequency component of the matched modulated RF signal may be constant, or some or all of them may be different.

[0090] In step ST2, a target frequency, i.e., the frequency at which RF reflection (return loss) is smallest at that point in time, is determined, and matching is performed by gradually narrowing the frequency band while setting the target frequency as the center frequency of the modulated RF signal. This can prevent the impedance matching position from suddenly moving from a low RF reflection region to a high RF reflection region, which would otherwise cause a sudden increase in RF reflection. It can also prevent the impedance matching position from moving to a total reflection region where there is no sensitivity to RF reflection, which would cause the matching direction (the direction in which RF reflection decreases with changes in the frequency and / or reactance of the source RF signal) to be lost, or cause plasma to fail. Step ST2 can stabilize the matching operation.

[0091] However, depending on the state of the gas and plasma in the chamber 10, performing the matching operation may not sufficiently reduce RF reflection. In such cases, if the criterion for determining whether the matching operation is complete is whether the RF reflection characteristic has reached a given threshold, the matching operation may never be completed. In this regard, in process ST2, the matching operation is completed if the bandwidth of the frequency band determined in process ST25 is less than the target width. Therefore, even in the above case, the matching operation can be completed by finding the matching position where the RF reflection is minimized. In such cases, the power level PL of the matching modulation RF signal may be set high to increase the power supplied to the plasma.

[0092] (Process ST3: Plasma Maintenance Operation) FIG. 9 is a flowchart showing an example of process ST3. In process ST3, a plasma maintenance operation is performed. The plasma maintenance operation is an operation for maintaining plasma in chamber 10 and performing a desired process using the plasma. As shown in FIG. 9, process ST3 includes a process ST31 for outputting a third modulated RF signal and a fourth modulated RF signal, a process ST32 for detecting RF reflection characteristics, a process ST33 for acquiring an RF reflection spectrum, a process ST34 for determining a target frequency, a process ST35 for determining a frequency band of the modulated RF signal, and a process ST36 for determining a stop condition. Processes ST31 to ST36 are repeated multiple times until the determination in process ST36 is affirmative. Process ST3 is an example of a plasma maintenance sequence in the present disclosure.

[0093] In step ST31, the first RF generating unit 31a outputs a third modulated RF signal and a fourth modulated RF signal to the chamber 10. The third modulated RF signal and the fourth modulated RF signal may be generated by simultaneously outputting a broadband RF signal on which multiple frequency components are superimposed from the waveform output unit 310a of the first RF generating unit 31a. Alternatively, the third modulated RF signal and the fourth modulated RF signal may be generated by sequentially outputting sweep RF signals of different frequencies from the waveform output unit 310a of the first RF generating unit 31a.

[0094] Column (E) of "Modulated RF Signal" in FIG. 6 shows examples of the third modulated RF signal and the fourth modulated RF signal output in process ST31. The third modulated RF signal has multiple frequency components in a third frequency band (bandwidth: BD3). The bandwidth BD3 of the third modulated RF signal may be, for example, within a range of 0.1 to 1% of the design frequency. The pitch Pt3 between the frequency components of the third modulated RF signal may be constant, or may vary partially or entirely. The third modulated RF signal has a third power level P3 (W). The third power level P3 is a power level capable of generating plasma in the chamber 10. The third power level P3 may be the same as or different from the second power level. As described above, processes ST31 to ST36 can be repeated multiple times. The third modulated RF signal output in the first process ST31 may be the matching modulated RF signal determined in process ST26.

[0095] The fourth modulated RF signal has multiple frequency components in a fourth frequency band (bandwidth: BD4). The center frequency of the fourth frequency band coincides with the center frequency of the third frequency band. The bandwidth BD4 of the fourth modulated RF signal may be, for example, within a range of 1 to 10% of the design frequency. The fourth modulated RF signal may have no frequency components in a frequency band overlapping with the third frequency band. The pitch Pt4 between the frequency components of the fourth modulated RF signal in the portion not overlapping with the third frequency band may be constant or may be partially or entirely different. The pitch Pt4 may be larger than the pitch Pt3 between the frequency components of the third modulated RF signal. The fourth modulated RF signal has a fourth power level P4 (W). The fourth power level P4 is a power level that does not generate plasma in the chamber 10. The fourth power level P4 may be the same as or different from the first power level P1. In one example, the fourth power level P4 is less than 10 W, less than 5 W, or less than 1 W. The fourth power level P4 may be determined based on the reflection resistance of the power supply 30 including the first RF generating unit 31 a.

[0096] In step ST32, the RF reflection characteristics are detected. The measuring instrument 34 detects the RF reflection characteristics of the third modulated RF signal and the fourth modulated RF signal propagating through the transmission line TL, and outputs the results to the analyzer 35.

[0097] In step ST33, an RF reflection spectrum is acquired. The analyzer 35 acquires RF reflection spectra for each frequency corresponding to the third modulated RF signal and the fourth modulated RF signal based on the output from the measuring instrument 34. Column (E) of "RF reflection spectrum" in Fig. 6 shows an example of the RF reflection spectrum acquired in step ST23.

[0098] In step ST34, a target frequency is determined. The target frequency is determined based on the RF reflection spectrum acquired in step ST33. The target frequency may be a frequency in the RF reflection spectrum that has the best RF reflection characteristics, i.e., a frequency at which the return loss is minimized. For example, in the example shown in column (E) of "RF reflection spectrum" in FIG. 6, the frequency Fx at which the amplitude (ratio Rp [%]) of the RF reflection spectrum is minimized may be determined as the target frequency.

[0099] In step ST35, the frequency bands of the third modulated RF signal and the fourth modulated RF signal are determined. The frequency bands of the third modulated RF signal and the fourth modulated RF signal are both set so that the target frequency (frequency Fx) determined in step ST34 is the center frequency. That is, the third modulated RF signal and the fourth modulated RF signal are adjusted so that the frequency at which RF reflection (return loss) is smallest at that time is the center frequency. The bandwidth BD3 of the third modulated RF signal may be, for example, within a range of 0.1 to 1% of the design frequency. The bandwidth BD4 of the fourth modulated RF signal may be, for example, within a range of 1 to 10% of the design frequency.

[0100] In step ST36, it is determined whether or not a stop condition is satisfied. If the stop condition is not satisfied, the process returns to step ST31. If the stop condition is satisfied, step ST3 is terminated. The stop condition may be set as appropriate, for example, based on whether or not the process using plasma in chamber 10 has been completed, the time since plasma generation, the number of cycles of step ST3, etc.

[0101] In step ST3, RF reflection spectra corresponding to a third modulated RF signal having a third frequency band and a fourth modulated RF signal having a fourth frequency band are acquired. The third and fourth frequency bands are adjusted as needed so that the frequency at which RF reflection (return loss) is smallest at that time becomes the center frequency. Therefore, even if the RF reflection characteristics change due to a load change during the plasma process in the chamber 10, the change can be detected and followed. This can prevent the impedance matching position from suddenly moving from a low to a high RF reflection region, causing a sudden increase in RF reflection, or from moving to a total reflection region where RF reflection is insensitive, causing the matching direction to be lost, or causing plasma to fail. Furthermore, for frequency bands away from the center frequency (frequency bands with relatively large RF reflection), RF reflection spectra are acquired using a fourth modulated RF signal having a fourth power level at which plasma is not generated. This can reduce the absolute amount of RF reflection. Note that in one embodiment, step ST3 may be performed using only the third modulated RF signal, without using the fourth modulated RF signal.

[0102] As described above, the method MT can stabilize the matching operation.

[0103] The present disclosure may be implemented in a plasma processing apparatus 1 using any plasma source other than an inductively coupled plasma processing apparatus 1, such as a capacitively coupled plasma processing apparatus or a microwave plasma processing apparatus. For example, the RF system (FIGS. 3 and 4) may be coupled to a capacitively coupled plasma processing apparatus. The capacitively coupled plasma processing apparatus includes an upper electrode and a lower electrode. The lower electrode is disposed within a substrate support in a chamber, and the upper electrode is disposed above the substrate support. The first RF generating unit 31a is connected to the upper electrode or the lower electrode via an impedance matching circuit. This allows the RF system to be coupled to a chamber for capacitively coupled plasma processing. Also, for example, the method MT may be implemented in a capacitively coupled plasma processing apparatus.

[0104] Embodiments of the present disclosure further include the following aspects.

[0105] (Supplementary Note 1) A plasma ignition system comprising: a chamber; an antenna disposed above the chamber; an RF generating unit connected to the antenna; a measuring instrument configured to detect RF reflection characteristics at a node between the antenna and the RF generating unit; an analyzer configured to determine an RF reflection spectrum for each frequency based on the RF reflection characteristics; and a control unit configured to execute a plasma ignition sequence, wherein the plasma ignition sequence includes: (a1) controlling the RF generating unit to output a first modulated RF signal having a plurality of frequency components in a first frequency band, the first modulated RF signal having a power level such that plasma is not generated in the chamber; (a2) acquiring an RF reflection spectrum for each frequency corresponding to the first modulated RF signal from the analyzer; and (a3) ​​determining an ignition frequency based on the RF reflection spectrum for each frequency acquired in (a2). (a4) controlling the RF generating unit to output a second modulated RF signal having a plurality of frequency components in a second frequency band, the second frequency band including the ignition frequency and being narrower than the first frequency band, and the second modulated RF signal having a power level capable of generating plasma in the chamber.

[0106] (Supplementary Note 2) The plasma processing apparatus according to Supplementary Note 1, wherein a center frequency of the second frequency band is the ignition frequency.

[0107] (Supplementary Note 3) The plasma processing apparatus according to Supplementary Note 1 or Supplementary Note 2, wherein the control unit is configured to execute an impedance matching sequence after the plasma ignition sequence, and the impedance matching sequence includes: (b1) controlling the RF generation unit to output a modulated RF signal having a plurality of frequency components, the modulated RF signal having a power level capable of generating plasma in the chamber; (b2) acquiring from the analyzer an RF reflection spectrum for each frequency corresponding to the modulated RF signal; (b3) determining a target frequency at which the RF reflection spectrum is minimized based on the RF reflection spectrum for each frequency acquired in (b2); and (b4) narrowing the frequency band of the modulated RF signal output from the RF generation unit while adjusting it so that a center frequency of the frequency band becomes the target frequency.

[0108] (Supplementary Note 4) The plasma processing apparatus according to Supplementary Note 3, wherein the impedance matching sequence further includes (b5) repeating (b1) to (b4) until the frequency band of the modulated RF signal output from the RF generating unit reaches a target width.

[0109] (Supplementary Note 5) The control unit is configured to execute a plasma maintenance sequence for maintaining plasma in the chamber after the matching sequence, and the plasma maintenance sequence includes: (c1) controlling the RF generation unit to output a third modulated RF signal having a plurality of frequency components and a fourth modulated RF signal having a plurality of frequency components, wherein the third modulated RF signal has a power level capable of generating plasma in the chamber and the fourth modulated RF signal has a power level at which plasma is not generated in the chamber, and a frequency band of the fourth modulated RF signal is wider than a frequency band of the third modulated RF signal; (c2) acquiring RF reflection spectra for each frequency corresponding to the third modulated RF signal and the fourth modulated RF signal from the analyzer; and (c3) determining a target frequency at which the RF reflection spectrum is minimized based on the RF reflection spectrum for each frequency acquired in (c2). (c4) Setting the frequency band of the third modulated RF signal output from the RF generating unit so that the center frequency of the frequency band becomes the target frequency.

[0110] (Supplementary Note 6) The plasma processing apparatus according to any one of Supplementary Notes 1 to 5, wherein the RF reflection characteristic is any one of the following at the node: (a) a ratio or proportion [%] of the power of the forward wave to the power of the reflected wave; (b) a resistance component [Ω] of the impedance; (c) a reflection coefficient; (d) a return loss [dB]; and (e) an S parameter [dB].

[0111] (Supplementary Note 7) The plasma processing apparatus according to any one of Supplementary Notes 1 to 6, further comprising an impedance matching circuit connected between the chamber and the measuring device.

[0112] (Supplementary Note 8) The plasma processing apparatus according to any one of Supplementary Notes 1 to 6, further comprising an impedance matching circuit connected between the RF generating unit and the measuring device.

[0113] (Supplementary Note 9) The plasma processing apparatus according to any one of Supplementary Notes 1 to 8, wherein the RF generating unit includes: a waveform output unit configured to output a broadband RF signal on which a plurality of frequency components are superimposed; and a power amplifier configured to amplify the broadband RF signal and output a modulated RF signal including a plurality of frequency components.

[0114] (Supplementary Note 10) The plasma processing apparatus according to any one of Supplementary Notes 1 to 9, wherein the RF generating unit includes: a waveform output unit configured to sequentially output sweep RF signals of different frequencies; and a power amplifier configured to sequentially amplify the sweep RF signals to output a modulated RF signal including a plurality of frequency components.

[0115] (Supplementary Note 11) The plasma processing apparatus according to any one of Supplementary Notes 1 to 10, wherein the power level at which the plasma is not generated is less than 10 W.

[0116] (Supplementary Note 12) The plasma processing apparatus according to any one of Supplementary Notes 1 to 11, wherein the first frequency band has a bandwidth that is less than 20% of a design frequency of the RF generating unit, and the second frequency band has a bandwidth that is less than 10% of the design frequency.

[0117] (Supplementary Note 13) The plasma processing apparatus according to Supplementary Note 4 or 5, wherein the target width is within a range of 0.1 to 1% of a design frequency of the RF generating unit.

[0118] (Supplementary Note 14) The plasma processing apparatus according to Supplementary Note 4 or 5, wherein in (b5), the frequency band of the modulated RF signal is narrowed by 0.1 kHz to 500 kHz.

[0119] (Supplementary Note 15) A plasma generation system comprising: a chamber; an antenna disposed above the chamber; an RF generating unit connected to the antenna; a measuring instrument configured to detect RF reflection characteristics at a node between the antenna and the RF generating unit; an analyzer configured to determine an RF reflection spectrum for each frequency based on the RF reflection characteristics; and a control unit configured to execute a plasma maintenance sequence for maintaining plasma generated in the chamber, wherein the plasma maintenance sequence includes: (c1) controlling the RF generating unit to output a third modulated RF signal having a plurality of frequency components and a fourth modulated RF signal having a plurality of frequency components, wherein the third modulated RF signal has a power level capable of generating plasma in the chamber and the fourth modulated RF signal has a power level such that plasma is not generated in the chamber, and a frequency band of the fourth modulated RF signal is wider than a frequency band of the third modulated RF signal; and (c2) acquiring RF reflection spectra for each frequency corresponding to the third modulated RF signal and the fourth modulated RF signal from the analyzer. (c3) determining a target frequency at which the RF reflection spectrum is minimized based on the RF reflection spectrum for each frequency acquired in (c2); and (c4) setting a frequency band of the third modulated RF signal output from the RF generating unit so that a center frequency of the frequency band is the target frequency.

[0120] (Supplementary Note 16) A plasma ignition system comprising: an RF generating unit coupled to a chamber; a measuring instrument configured to detect RF reflection characteristics at a node between the chamber and the RF generating unit; an analyzer configured to determine an RF reflection spectrum for each frequency based on the RF reflection characteristics; and a control unit configured to execute a plasma ignition sequence, wherein the plasma ignition sequence includes: (a1) controlling the RF generating unit to output a first modulated RF signal having a plurality of frequency components in a first frequency band, the first modulated RF signal having a power level such that plasma is not generated in the chamber; (a2) acquiring an RF reflection spectrum for each frequency of the first modulated RF signal from the analyzer; and (a3) ​​determining an ignition frequency based on the RF reflection spectrum for each frequency acquired in (a2). (a4) controlling the RF generating unit to output a second modulated RF signal having a plurality of frequency components in a second frequency band, the second frequency band including the ignition frequency and being narrower than the first frequency band, and the second modulated RF signal having a power level capable of generating plasma in the chamber.

[0121] (Supplementary Note 17) A plasma processing method comprising the steps of: outputting a first modulated RF signal having a plurality of frequency components in a first frequency band to a chamber, the first modulated RF signal having a power level such that plasma is not generated in the chamber; detecting RF reflection characteristics from the chamber; acquiring an RF reflection spectrum for each frequency corresponding to the first modulated RF signal based on the acquired RF reflection characteristics; determining an ignition frequency based on the acquired RF reflection spectrum for each frequency; and outputting a second modulated RF signal having a plurality of frequency components in a second frequency band to the chamber, the second frequency band including the ignition frequency and being narrower than the first frequency band, the second modulated RF signal having a power level such that plasma can be generated in the chamber.

[0122] (Supplementary Note 18) A plasma generating apparatus comprising: an RF generating unit coupled to a chamber; a measuring instrument configured to detect RF reflection characteristics at a node between the chamber and the RF generating unit; an analyzer configured to determine an RF reflection spectrum for each frequency based on the RF reflection characteristics; and a control unit configured to execute a plasma maintenance sequence for maintaining plasma generated in the chamber, wherein the plasma maintenance sequence includes: (c1) controlling the RF generating unit to output a third modulated RF signal having a plurality of frequency components and a fourth modulated RF signal having a plurality of frequency components, wherein the third modulated RF signal has a power level capable of generating plasma in the chamber and the fourth modulated RF signal has a power level at which plasma is not generated in the chamber, and the frequency band of the fourth modulated RF signal is wider than the frequency band of the third modulated RF signal; (c2) acquiring from the analyzer the RF reflection spectrum for each frequency corresponding to the third modulated RF signal and the fourth modulated RF signal; and (c3) determining a target frequency at which the RF reflection spectrum is minimized based on the RF reflection spectrum for each frequency acquired in (c2). (c4) setting a frequency band of the third modulated RF signal output from the RF generating unit so that a center frequency of the frequency band is the target frequency.

[0123] (Supplementary Note 19) A plasma processing method comprising: a step of outputting to a chamber a third modulated RF signal having a plurality of frequency components and a fourth modulated RF signal having a plurality of frequency components, wherein the third modulated RF signal has a power level capable of generating plasma in the chamber, the fourth modulated RF signal has a power level such that plasma is not generated in the chamber, and the frequency band of the fourth modulated RF signal is wider than the frequency band of the third modulated RF signal; a step of detecting RF reflection characteristics from the chamber; acquiring RF reflection spectra for each frequency corresponding to the third modulated RF signal and the fourth modulated RF signal based on the acquired RF reflection characteristics; determining a target frequency at which the RF reflection spectrum is minimized based on the acquired RF reflection spectra for each frequency; and setting the frequency band of the third modulated RF signal so that a center frequency of the frequency band is the target frequency.

[0124] The above embodiments are described for the purpose of explanation and are not intended to limit the scope of the present disclosure. Various modifications can be made to the above embodiments without departing from the scope and spirit of the present disclosure. For example, some components in one embodiment can be added to other embodiments. Also, some components in one embodiment can be replaced with corresponding components in other embodiments.

[0125] REFERENCE SIGNS LIST 1: plasma processing apparatus, 2: control unit, 10: plasma processing chamber, 14: antenna, 31a: first RF generating unit, 33: matching unit, 34: measuring instrument, 35: analyzer, CT: controller

Claims

1. A plasma ignition system comprising: a chamber; an antenna disposed above the chamber; an RF generator connected to the antenna; a measuring instrument configured to detect RF reflection characteristics at a node between the antenna and the RF generator; an analyzer configured to determine an RF reflection spectrum for each frequency based on the RF reflection characteristics; and a controller configured to execute a plasma ignition sequence, wherein the plasma ignition sequence comprises: (a1) controlling the RF generator to output a first modulated RF signal having a plurality of frequency components in a first frequency band, the first modulated RF signal having a power level such that plasma is not generated in the chamber; (a2) acquiring from the analyzer an RF reflection spectrum for each frequency corresponding to the first modulated RF signal; and (a3) determining an ignition frequency based on the RF reflection spectrum for each frequency acquired in (a2). (a4) controlling the RF generating unit to output a second modulated RF signal having a plurality of frequency components in a second frequency band, the second frequency band including the ignition frequency and being narrower than the first frequency band, and the second modulated RF signal having a power level capable of generating plasma in the chamber.

2. The plasma processing apparatus according to claim 1, wherein the center frequency of said second frequency band is said ignition frequency.

3. The plasma processing apparatus of claim 2, wherein the control unit is configured to execute an impedance matching sequence after the plasma ignition sequence, and the impedance matching sequence includes: (b1) controlling the RF generation unit to output a modulated RF signal having a plurality of frequency components, the modulated RF signal having a power level capable of generating plasma in the chamber; (b2) acquiring from the analyzer an RF reflection spectrum for each frequency corresponding to the modulated RF signal; (b3) determining a target frequency at which the RF reflection spectrum is minimized based on the RF reflection spectrum for each frequency acquired in (b2); and (b4) narrowing the frequency band of the modulated RF signal output from the RF generation unit while adjusting it so that the center frequency of the frequency band becomes the target frequency.

4. The plasma processing apparatus of claim 3, wherein the impedance matching sequence further includes (b5) repeating (b1) to (b4) until the frequency band of the modulated RF signal output from the RF generating unit reaches a target width.

5. The plasma processing apparatus of claim 4, wherein the control unit is configured to execute a plasma maintenance sequence for maintaining plasma in the chamber after the matching sequence, and the plasma maintenance sequence includes: (c1) controlling the RF generation unit to output a third modulated RF signal having a plurality of frequency components and a fourth modulated RF signal having a plurality of frequency components, wherein the third modulated RF signal has a power level capable of generating plasma in the chamber and the fourth modulated RF signal has a power level at which plasma is not generated in the chamber, and the frequency band of the fourth modulated RF signal is wider than the frequency band of the third modulated RF signal; (c2) acquiring RF reflection spectra for each frequency corresponding to the third modulated RF signal and the fourth modulated RF signal from the analyzer; (c3) determining a target frequency at which the RF reflection spectrum is minimized based on the RF reflection spectrum for each frequency acquired in (c2); and (c4) setting the frequency band of the third modulated RF signal output from the RF generation unit so that a center frequency of the frequency band is the target frequency.

6. A plasma processing apparatus according to any one of claims 1 to 5, wherein the RF reflection characteristic is one of the following at the node: (a) the ratio or proportion [%] of the power of the forward wave to the power of the reflected wave; (b) the resistance component of the impedance [Ω]; (c) the reflection coefficient; (d) the return loss [dB]; and (e) the S parameter [dB].

7. The plasma processing apparatus according to any one of claims 1 to 5, further comprising an impedance matching circuit connected between the chamber and the measuring device.

8. The plasma processing apparatus according to any one of claims 1 to 5, further comprising an impedance matching circuit connected between said RF generating section and said measuring device.

9. A plasma processing apparatus according to any one of claims 1 to 5, wherein the RF generating unit includes: a waveform output unit configured to output a broadband RF signal on which a plurality of frequency components are superimposed; and a power amplifier configured to amplify the broadband RF signal and output a modulated RF signal including a plurality of frequency components.

10. A plasma processing apparatus according to any one of claims 1 to 5, wherein the RF generating unit includes: a waveform output unit configured to sequentially output sweep RF signals of different frequencies; and a power amplifier configured to sequentially amplify the sweep RF signals to output a modulated RF signal containing multiple frequency components.

11. The plasma processing apparatus according to any one of claims 1 to 5, wherein the power level at which no plasma is generated is less than 10 W.

12. A plasma processing apparatus according to any one of claims 1 to 5, wherein the first frequency band has a bandwidth that is less than 20% of the design frequency of the RF generating unit, and the second frequency band has a bandwidth that is less than 10% of the design frequency.

13. The plasma processing apparatus according to claim 4 or 5, wherein the target width is within a range of 0.1 to 1% of the design frequency of the RF generating unit.

14. The plasma processing apparatus according to claim 4 or 5, wherein in (b5), the frequency band of the modulated RF signal is narrowed by 0.1 kHz to 500 kHz.

15. A plasma generating apparatus comprising: a chamber; an antenna disposed above the chamber; an RF generating unit connected to the antenna; a measuring instrument configured to detect RF reflection characteristics at a node between the antenna and the RF generating unit; an analyzer configured to determine an RF reflection spectrum for each frequency based on the RF reflection characteristics; and a control unit configured to execute a plasma maintenance sequence for maintaining plasma generated in the chamber, wherein the plasma maintenance sequence comprises: (c1) controlling the RF generating unit to output a third modulated RF signal having a plurality of frequency components and a fourth modulated RF signal having a plurality of frequency components, wherein the third modulated RF signal has a power level capable of generating plasma in the chamber and the fourth modulated RF signal has a power level such that plasma is not generated in the chamber, and the frequency band of the fourth modulated RF signal is wider than the frequency band of the third modulated RF signal; and (c2) acquiring from the analyzer RF reflection spectra for each frequency corresponding to the third modulated RF signal and the fourth modulated RF signal. (c3) determining a target frequency at which the RF reflection spectrum is minimized based on the RF reflection spectrum for each frequency acquired in (c2); and (c4) setting a frequency band of the third modulated RF signal output from the RF generating unit so that a center frequency of the frequency band is the target frequency.

16. A plasma ignition system comprising: an RF generating unit coupled to a chamber; a measuring instrument configured to detect RF reflection characteristics at a node between the chamber and the RF generating unit; an analyzer configured to determine an RF reflection spectrum for each frequency based on the RF reflection characteristics; and a controller configured to execute a plasma ignition sequence, wherein the plasma ignition sequence includes: (a1) controlling the RF generating unit to output a first modulated RF signal having a plurality of frequency components in a first frequency band, the first modulated RF signal having a power level such that plasma is not generated in the chamber; (a2) acquiring an RF reflection spectrum for each frequency of the first modulated RF signal from the analyzer; and (a3) determining an ignition frequency based on the RF reflection spectrum for each frequency acquired in (a2). (a4) controlling the RF generating unit to output a second modulated RF signal having a plurality of frequency components in a second frequency band, the second frequency band including the ignition frequency and being narrower than the first frequency band, and the second modulated RF signal having a power level capable of generating plasma in the chamber.

17. A plasma processing method comprising the steps of: outputting a first modulated RF signal having a plurality of frequency components in a first frequency band to a chamber, the first modulated RF signal having a power level such that plasma is not generated in the chamber; detecting RF reflection characteristics from the chamber; acquiring an RF reflection spectrum for each frequency corresponding to the first modulated RF signal based on the acquired RF reflection characteristics; determining an ignition frequency based on the acquired RF reflection spectrum for each frequency; and outputting a second modulated RF signal having a plurality of frequency components in a second frequency band to the chamber, the second frequency band including the ignition frequency and being narrower than the first frequency band, the second modulated RF signal having a power level sufficient to generate plasma in the chamber.

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