PLASMA PROCESSING APPARATUS AND MATCHING METHOD

A plasma processing apparatus includes a chamber in which a plasma processing is performed, an electrode that supplies a radio-frequency power to the chamber for the plasma processing; a radio-frequency power supply electrically connected to the electrode, and a matching device connected between the radio-frequency power supply and the electrode. The radio-frequency power supply supplies one of a modulated wave and a continuous wave of a radio-frequency power to the electrode. The modulated wave is generated by alternately increasing or decreasing the power level of the radio-frequency power. The matching device gradually changes a load impedance to a target impedance during a period in which the continuous wave is supplied before or after the power supplied from the radio-frequency power supply to the electrode is switched from one of the modulated wave and the continuous wave to the other.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims priority from Japanese Patent Application No. 2020-026391 filed on Feb. 19, 2020 with the Japan Patent Office, the disclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present disclosure relates to a plasma processing apparatus and a matching method.

BACKGROUND

Plasma processing apparatuses are used in the manufacture of electronic devices. A plasma processing apparatus includes a chamber, electrodes, a radio-frequency power supply, and a matching device. Radio-frequency power is applied to the electrodes from the radio-frequency power supply in order to excite the gas supplied in the chamber to generate plasma. The matching device is configured to match the output impedance of the radio-frequency power supply with the impedance on the load side of the radio-frequency power supply, that is, the load impedance.

In a plasma processing apparatus, a technique has been proposed in which the radio-frequency power having an alternately increased or decreased power, that is, the modulated wave of radio-frequency power is supplied to the electrodes. Such a technique is described in, for example, Japanese Patent Laid-Open Publication Nos. 2015-090770 and 2019-186099.

SUMMARY

In an embodiment, a plasma processing apparatus is provided. The plasma processing apparatus includes a chamber, an electrode, a radio-frequency power supply, and a matching device. The radio-frequency power supply is electrically connected to the electrodes. The radio-frequency power supply is configured to generate radio-frequency power supply supplied to the electrode for plasma processing in the chamber. The matching device is connected between the radio-frequency power supply and the electrodes. The matching device is configured to set the load impedance, which is the load-side impedance of the radio-frequency power supply. The radio-frequency power supply is configured to supply the power wave of one of a modulated wave and a continuous wave of radio-frequency power to the electrode in the preceding period of two consecutive periods, and supply the power wave of the other of the modulated wave and the continuous wave to the electrode in the subsequent period of the two consecutive periods. The radio-frequency power supply generates the modulated wave so that the power level of the radio-frequency power in the first sub-period of the alternating first sub-period and second sub-period is higher than the power level of the radio-frequency power in the second sub-period. The matching device is configured to gradually change the load impedance to the target impedance for subsequent periods during a period in which the continuous wave is supplied in the two consecutive periods.

DETAILED DESCRIPTION

Various embodiments will be described below.

In an embodiment, a plasma processing apparatus is provided. The plasma processing apparatus includes a chamber, an electrode, a radio-frequency power supply, and a matching device. The radio-frequency power supply is electrically connected to the electrodes. The radio-frequency power supply is configured to generate radio-frequency power supplied to the electrode for plasma processing in the chamber. The matching device is connected between the radio-frequency power supply and the electrodes. The matching device is configured to set the load impedance, which is the load-side impedance of the radio-frequency power supply. The radio-frequency power supply is configured to supply the power wave of one of the modulated wave and the continuous wave of radio-frequency power to the electrode in the preceding period of two consecutive periods, and supply the power wave of the other of the modulated wave and the continuous wave to the electrode in the subsequent period of the two consecutive periods. The radio-frequency power supply generates the modulated wave so that the power level of the radio-frequency power in the first sub-period of the alternating first sub-period and second sub-period is higher than the power level of the radio-frequency power in the second sub-period. The matching device is configured to gradually change the load impedance to the target impedance for the subsequent period during a period in which the continuous wave is supplied in the two consecutive periods.

In the above embodiment, the matching device gradually changes the load impedance to the target impedance for the subsequent period during the period during which the continuous wave is supplied before or after the power supplied from the radio-frequency power supply to the electrode is switched from one power wave to the other power wave. Therefore, the matching device may follow the load impedance to be set after the power supplied from the radio-frequency power supply to the electrodes is switched from one power wave to the other power wave. Therefore, it is possible to reduce the reflection after the power supplied from the radio-frequency power supply to the electrode is switched from one of the modulated wave and the continuous wave to the other.

In the embodiment, the matching device may gradually change the load impedance during the period in which the continuous wave is supplied so that the absolute value of the reflectance coefficient of the radio-frequency power is gradually changed to the set target value for the subsequent period.

In the embodiment, the matching device may be configured to gradually reduce the load impedance so that the absolute value of the reflectance coefficient of the radio-frequency power is gradually reduced to zero after the power supplied from the radio-frequency power supply to the electrodes is switched from the modulated wave to the continuous wave.

In the embodiment, the matching device may gradually change the load impedance before the power supplied to the electrodes is switched from the continuous wave to the modulated wave so that the absolute value of the reflectance coefficient of the radio-frequency power is gradually increased to a set target value larger than zero. The set target value may be 0.3 or more and 0.5 or less.

In the embodiment, the matching device may be configured to gradually change the absolute value of the reflectance coefficient during the period in which the continuous wave is supplied to the set target value for the subsequent period. The time length of each of a plurality of sub-periods is set to 0.5 seconds or more, and a difference between the target value of the absolute value of the reflectance coefficient in one sub-period and the target value of the absolute value of the reflectance coefficient in the other sub-period of any two consecutive sub-periods included in the plurality of sub-periods is set to 0.2 or less. Alternatively, the time length is set to 0.2 seconds or more, and the difference is set to 0.1 or less. The time length may be set to 0.5 seconds or more, and the difference may be set to 0.05 or less.

In the embodiment, the matching device may be configured to adjust the load impedance of the radio-frequency power supply to a target impedance different from the output impedance of the radio-frequency power supply during the period in which the modulated wave is supplied out of two consecutive periods. The load impedance of the radio-frequency power supply is specified by the measured value of the load impedance during the monitoring period within the first sub-period. According to this embodiment, the reflection from the load on the modulated wave may be reduced during the period in which the modulated wave is supplied.

In the embodiment, the monitoring period may be a period that starts after a predetermined time length has elapsed from the start of the first sub-period.

In the embodiment, the matching device may be configured to specify the target impedance from the set target value of the absolute value of the reflectance coefficient of the modulated wave during the period in which the modulated wave is supplied. In the embodiment, this set target value may be 0.3 or more and 0.5 or less.

In the embodiment, the radio-frequency power supply may be configured to adjust the power level of the radio-frequency power so that the load power level during the period of supply of the modulated wave approaches or matches the target power level. The load power level is the difference between the power level of the traveling wave of the modulated wave and the power level of the reflected wave of the modulated wave. When the target impedance is different from the output impedance of the radio-frequency power supply, a reflection occurs. According to this embodiment, even when the reflection occurs, the modulated wave of the target power level may be coupled to plasma.

In another embodiment, a matching method is provided. The matching method is performed in the plasma processing apparatus. The plasma processing apparatus includes a chamber, electrodes, a radio-frequency power supply, and a matching device. The radio-frequency power supply is electrically connected to the electrodes. The radio-frequency power supply is configured to generate radio-frequency power supplied to the electrodes for plasma processing in the chamber. The matching device is connected between the radio-frequency power supply and the electrode, and is configured to set the load impedance, which is the impedance on the load side of the radio-frequency power supply. The matching method includes a step of supplying the power wave of one of the modulated wave and the continuous wave of radio-frequency power from the radio-frequency power supply to the electrode in a preceding period of two consecutive periods. The modulated wave is generated so that the power level of the radio-frequency power in the first sub-period of the alternating first sub-period and second sub-period is higher than the power level of the radio-frequency power in the second sub-period. The matching method further includes supplying the power wave of the other of the modulated wave and the continuous wave of radio-frequency power to the electrode in the subsequent period of the two consecutive periods. The matching method further includes gradually changing the load impedance to the target impedance for the subsequent period during the period in which the continuous wave is supplied out of two consecutive periods.

In the embodiment, in the process of gradually changing the load impedance, the load impedance may be gradually changed so that the absolute value of the reflectance coefficient of the radio-frequency power is gradually changed to the set target value for the subsequent period.

In the embodiment, after the power supplied to the electrodes is switched from the modulated wave to the continuous wave, the load impedance may be changed gradually so that the absolute value of the reflectance coefficient of the radio-frequency power is gradually reduced to zero.

In the embodiment, before the power supplied to the electrodes is switched from the continuous wave to the modulated wave, the load impedance may be changed gradually so that the absolute value of the reflectance coefficient of the radio-frequency power is gradually increased to the set target value larger than zero. The set target value may be 0.3 or more and 0.5 or less.

In the embodiment, during the period in which the continuous wave is supplied, the load impedance may be changed gradually so that the absolute value of the reflectance coefficient is gradually changed to the set target value for the subsequent period through a plurality of consecutive sub-periods. The time length of each of a plurality of sub-periods is set to 0.5 seconds or more, and a difference between the target value of the absolute value of the reflectance coefficient in one sub-period and the target value of the absolute value of the reflectance coefficient in the other sub-period of any two consecutive sub-periods included in the plurality of sub-periods is set to 0.2 or less. Alternatively, the time length is set to 0.2 seconds or more, and the difference is set to 0.1 or less. The time length may be set to 0.5 seconds or more, and the difference may be set to 0.05 or less.

Hereinafter, various embodiments will be described in detail with reference to the drawings. Further, the same reference numerals are given to the same or corresponding parts in each drawing.

FIG. 1is a diagram schematically illustrating the plasma processing apparatus according to the embodiment. The plasma processing apparatus1illustrated inFIG. 1is a capacitively coupled plasma processing apparatus. The plasma processing apparatus1includes a chamber10. The chamber10provides an internal space10stherein.

The chamber10includes a chamber body12. The chamber body12has a substantially cylindrical shape. The internal space of the chamber10is provided inside the chamber body12. The chamber body12is formed of a material such as aluminum. A plasma-resistant film is formed on the inner wall surface of the chamber body12. The film may be a ceramic film such as a film formed by anodization or a film formed from yttrium oxide. The chamber body12is grounded. An opening12pis formed on the side wall of the chamber body12. A substrate W passes through the opening12pwhen being conveyed between the internal space of the chamber10and the outside of the chamber10. The opening12pmay be opened and closed by a gate valve12g. The gate valve12gis provided along the side wall of the chamber body12.

An insulating plate13is provided on the bottom of the chamber body12. The insulating plate13is formed of, for example, ceramic. A support base14is provided on the insulating plate13. The support base14has a substantially disk shape. The support base14supports a susceptor16provided thereon. The susceptor16is provided in the chamber10. The susceptor16is formed of a conductive material such as aluminum. The susceptor16constitutes a lower electrode.

The susceptor16supports an electrostatic chuck18provided thereon. The electrostatic chuck18is provided in the chamber10. The electrostatic chuck18is configured to hold the substrate W mounted thereon. The electrostatic chuck18has a main body and electrodes20. The main body of the electrostatic chuck18is formed of a dielectric material and has a substantially disk shape. The electrode20is a conductive film and is provided in the main body of the electrostatic chuck18. A DC power supply24is electrically connected to the electrode20via a switch22. When a DC voltage from the DC power supply24is applied to the electrode20, an electrostatic attraction is generated between the substrate W and the electrostatic chuck18. The substrate W is attracted to the electrostatic chuck18by the generated electrostatic attraction and is held by the electrostatic chuck18.

The susceptor16and the electrostatic chuck18constitute a substrate support. The substrate support supports an edge ring26mounted thereon. The edge ring26is arranged so as to surround the edge of the substrate W. That is, the substrate W is arranged in the region surrounded by the edge ring26and on the electrostatic chuck18. The outer peripheral surfaces of the susceptor16and the support base14are each covered with a cylindrical inner wall member28. The inner wall member28is formed of, for example, quartz.

A flow path14fis formed inside the support base14. The flow path14fextends in a spiral shape with respect to the central axis extending in, for example, the vertical direction. A heat exchange medium cw (e.g., a coolant such as cooling water) is supplied to the flow path14ffrom a supply device (e.g., a chiller unit22) provided outside the chamber10via a pipe32a. The heat exchange medium supplied to the flow path14fis recovered by the supply device via the pipe32b. The temperature of the substrate W is adjusted by adjusting the temperature of the heat exchange medium by the supply device. Further, the plasma processing apparatus1provides a gas supply line34. The gas supply line34is provided to supply heat transfer gas (e.g., He gas) to a gap between the upper surface of the electrostatic chuck18and the back surface of the substrate W.

The plasma processing apparatus1may include one or more radio-frequency power supplies. In the embodiment, the plasma processing apparatus1includes a first radio-frequency power supply (i.e., a radio-frequency power supply36) and a second radio-frequency power supply (i.e., a radio-frequency power supply38). The radio-frequency power supply36is connected to the susceptor16(e.g., the lower electrode) via a conductor44(e.g., a feeding rod) and the first matching device (i.e., the matching device40). The radio-frequency power supply38is connected to the susceptor16(e.g., the lower electrode) via the conductor44and the first matching device (i.e., the matching device42). Further, the radio-frequency power supply36may be connected to the upper electrode (to be described later), not to the lower electrode, via the matching device40. The plasma processing apparatus1may not be provided with one of a set of the radio-frequency power supply36and the matching device40and a set of the radio-frequency power supply38and the matching device42.

The radio-frequency power supply36is configured to generate a first radio-frequency power (i.e., radio-frequency power RF1) for plasma processing in the chamber10. The radio-frequency power RF1is mainly used for plasma generation. The fundamental frequency fB1of the radio-frequency power RF1is, for example, 100 MHz. The radio-frequency power supply38is configured to generate a second radio-frequency power (i.e., radio-frequency power RF2) for plasma processing in the chamber10. The frequency of the radio-frequency power RF2is lower than the frequency of the radio-frequency power RF1. The fundamental frequency fB2of the radio-frequency power RF2is, for example, 13.56 MHz.

The matching device40includes a circuit for setting the load impedance, which is the impedance on the load side (e.g., the lower electrode side) of the radio-frequency power supply36. The matching device42includes a circuit for setting the load impedance, which is the impedance on the load side (e.g., the lower electrode side) of the radio-frequency power supply38. Each of the matching device40and the matching device42may be an electronically controlled matching device. Details of each of the matching device40and the matching device42will be described later.

The matching device40and the conductor44form a part of a power feeding line43. The radio-frequency power RF1is supplied to the susceptor16via the power feeding line43. The matching device42and the conductor44form a part of a power feeding line45. The radio-frequency power RF2is supplied to the susceptor16via the power feeding line45.

The plasma processing apparatus1further includes an upper electrode46. The upper electrode46constitutes the top of the chamber10. The upper electrode46is provided to close an opening at the upper end of the chamber body12. The internal space of the chamber10includes a processing region PS. The processing region PS is a space between the upper electrode46and the susceptor16. The plasma processing apparatus1generates plasma in the processing region PS by the radio-frequency electric field generated between the upper electrode46and the susceptor16. The upper electrode46is grounded. Further, when the radio-frequency power supply36is connected to the upper electrode46, not to the lower electrode, via the matching device40, the upper electrode46is not grounded, and the upper electrode46and the chamber body12are electrically separated from each other.

The upper electrode46includes a top plate48and a support50. A plurality of gas discharge holes48ais formed in the top plate48. The top plate48is formed of a silicon-based material such as, for example, Si or SiC. The support50is a member that detachably supports the top plate48, is formed of a conductor such as aluminum, and has a plasma-resistant film formed on its surface.

A gas buffer chamber50bis formed inside the support50. Further, a plurality of gas holes50ais formed in the support50. Each of the plurality of gas holes50aextends from the gas buffer chamber50band communicates with the plurality of gas discharge holes48a. A gas supply pipe54is connected to the gas buffer chamber50b. A gas source56is connected to the gas supply pipe54via a flow rate controller58(e.g., a mass flow controller) and an on-off valve60. The gas from the gas source56is supplied to the internal space of the chamber10through the flow rate controller58, the on-off valve60, the gas supply pipe54, the gas buffer chamber50b, and the plurality of gas discharge holes48a. The flow rate of the gas supplied from the gas source56to the internal space of the chamber10is adjusted by the flow rate controller58.

An exhaust port12eis provided at the bottom of the chamber body12below the space between the susceptor16and the side wall of the chamber body12. An exhaust pipe64is connected to the exhaust port12e. The exhaust pipe64is connected to an exhaust device66. The exhaust device66includes a pressure regulator such as an automatic pressure control valve and a vacuum pump such as a turbo molecular pump. The exhaust device66depressurizes the internal space of the chamber10to a designated pressure.

The plasma processing apparatus1further includes a main control unit70. The main control unit70includes one or more microcomputers. The main control unit70may include a storage device such as a processor and a memory, an input device such as a keyboard, a display device, and a signal input/output interface. The processor of the main control unit70executes software (program) stored in the storage device to control the individual operation of each part of the plasma processing apparatus1and the entire operation (sequence) of the plasma processing apparatus1according to the recipe data. The main control unit70controls, for example, a radio-frequency power supply36, a radio-frequency power supply38, a matching device40, a matching device42, a flow rate controller58, an on-off valve60, and an exhaust device66.

When plasma processing is performed in the plasma processing apparatus1, the gate valve12gis first opened. Next, the substrate W is loaded into the chamber10via the opening12pand placed on the electrostatic chuck18. Then, the gate valve12gis closed. Next, the processing gas is supplied from the gas source56to the internal space of the chamber10, and the exhaust device66is operated to set the pressure in the internal space of the chamber10to the designated pressure. Further, radio-frequency power RF1and/or radio-frequency power RF2is supplied to the susceptor16. Further, a DC voltage from the DC power supply24is applied to the electrode20of the electrostatic chuck18, and the substrate W is held by the electrostatic chuck18. Then, the processing gas is excited by a radio-frequency electric field formed between the susceptor16and the upper electrode46. As a result, plasma is generated in the processing region PS.

In the following descriptions,FIGS. 2 to 3will be referenced together withFIG. 1.FIG. 2is a diagram illustrating an example of a timing chart of the first radio-frequency power and the second radio-frequency power.FIG. 3is a diagram illustrating another example of a timing chart of the first radio-frequency power and the second radio-frequency power. The plasma processing apparatus1is configured to utilize at least one of a modulated wave MW1of the radio-frequency power RF1and a modulated wave MW2of the radio-frequency power RF2for plasma processing in the chamber10during a period P1. The modulated wave MW1is generated by the radio-frequency power supply36. The modulated wave MW2is generated by the radio-frequency power supply38. As illustrated by the dotted line inFIGS. 2 and 3, either a continuous wave CW1of the radio-frequency power RF1or a continuous wave CW2of the radio-frequency power RF2may be used in the period P1. The continuous wave CW1is generated by the radio-frequency power supply36. The continuous wave CW2is generated by the radio-frequency power supply38. The mode in which the modulated wave MW1and the modulated wave MW2are used in the period P1is a first mode. The mode in which the modulated wave MW1and the modulated wave CW2are used in the period P1is a second mode. The mode in which the modulated wave CW1and the modulated wave MW2are used in the period P1is a third mode.

The period P1includes alternating first sub-period SP11and second sub-period SP12. The modulated wave MW1is generated by the radio-frequency power supply36so that the power level of the radio-frequency power RF1in the first sub-period SP11is higher than the power level of the radio-frequency power RF1in the second sub-period SP12. The power level of the radio-frequency power RF1in the second sub-period SP12may be 0 W. The modulated wave MW2is generated by the radio-frequency power supply38so that the power level of the radio-frequency power RF2in the first sub-period SP11is higher than the power level of the radio-frequency power RF2in the second sub-period SP12. The power level of the radio-frequency power RF2in the second sub-period SP12may be 0 W.

The first sub-period SP11and the subsequent second sub-period SP12constitute one cycle CP. The ratio of the first sub-period SP11in one cycle CP, that is, the duty ratio may be any value. For example, the duty ratio may be controlled to a value within the range of 10% or more and 90% or less. Further, the reciprocal of the one-cycle CP, that is, the modulation frequency may be controlled to any frequency. However, the modulation frequency is lower than the fundamental frequency fB1and the fundamental frequency fB2. The modulation frequency may be, for example, a frequency in the range of 0.1 kHz or more and 100 kHz or less.

Further, the plasma processing apparatus1is configured to utilize the continuous wave CW1and the continuous wave CW2in a period P2. That is, the radio-frequency power RF1and the radio-frequency power RF2are continuously supplied between the start time of the period P2and the end time of the period P2. The time length of the period P2is longer than the time length of the one-cycle CP.

The period P1and the period P2are two consecutive periods. As illustrated inFIG. 2, the period P1of the two consecutive periods may be the preceding period PA and the period P2may be the subsequent period PB. Further, as illustrated inFIG. 3, the period P2of the two consecutive periods may be the preceding period PA and the period P1may be the subsequent period PB. The period P1and the period P2may be repeated alternately. That is, the radio-frequency power supply36supplies a power wave W11in the preceding period PA. The power wave W11is one of the modulated wave MW1and the continuous wave CW1. The radio-frequency power supply36supplies the power wave W11or the power wave W12in the subsequent period PB. The power wave W12is the other of the modulated wave MW1and the continuous wave CW1. The radio-frequency power supply38supplies a power wave W21in the preceding period PA. The power wave W21is one of the modulated wave MW2and the continuous wave CW2. The radio-frequency power supply38supplies the power wave W21or a power wave W22in the subsequent period PB. The power wave W22is the other of the modulated wave MW2and the continuous wave CW2. In the subsequent period PB, at least one of the power wave W12and the power wave W22is supplied.

Hereinafter, the radio-frequency power supply36, the matching device40, the radio-frequency power supply38, and the matching device42will be described in detail with reference toFIGS. 4 to 7.FIG. 4is a diagram illustrating a configuration example of the first radio-frequency power supply and the first matching device of the plasma processing apparatus illustrated inFIG. 1.FIG. 5is a diagram illustrating a configuration example of a sensor of the first matching device of the plasma processing apparatus illustrated inFIG. 1.FIG. 6is a diagram illustrating a configuration example of the second radio-frequency power supply and the second matching device of the plasma processing apparatus illustrated inFIG. 1.FIG. 7is a diagram illustrating a configuration example of a sensor of the second matching device of the plasma processing apparatus illustrated inFIG. 1.

As illustrated inFIG. 4, in the embodiment, the radio-frequency power supply36includes an oscillator36a, a power amplifier36b, a power sensor36c, and a power supply control unit36e. The power supply control unit36eincludes a processor such as a CPU. The power supply control unit36egives a control signal to each of the oscillator36a, the power amplifier36b, and the power sensor36cto control the oscillator36a, the power amplifier36b, and the power sensor36c. The power supply control unit36euses the signal given from the main control unit70and the signal given from the power sensor36cto generate a control signal given to each of the oscillator36a, the power amplifier36b, and the power sensor36c.

The signal given from the main control unit70to the power supply control unit36eincludes a first frequency setting signal and a mode setting signal. The first frequency setting signal is a signal that designates the set frequency of the radio-frequency power RF1. The mode setting signal is a signal that designates the selected mode from the first to third modes. When the first mode or the second mode is designated, the signal given from the main control unit70to the power supply control unit36efurther includes a first modulation setting signal. The first modulation setting signal is a signal that designates the modulation frequency and duty ratio of the modulated wave MW1. The first modulation setting signal is also a signal that designates the power level of the modulated wave MW1in the first sub-period SP11and the power level of the modulated wave MW1in the second sub-period SP12. When the third mode is designated, the signal given from the main control unit70to the power supply control unit36efurther includes a first power level setting signal that designates the power of the continuous wave CW1.

The power supply control unit36econtrols the oscillator36ato output a radio-frequency signal having a set frequency (e.g., the fundamental frequency fB1) designated by the first frequency setting signal. The output of the oscillator36ais connected to the input of the power amplifier36b. The power amplifier36bgenerates radio-frequency power RF1by amplifying the radio-frequency signal output from the oscillator36a. The power amplifier36bis controlled by the power supply control unit36e.

When the first mode or the second mode is designated, the power supply control unit36econtrols the power amplifier36bto generate the modulated wave MW1from the radio-frequency signal in response to the first modulation setting signal during the period P1. When the first mode or the second mode is designated, the power supply control unit36econtrols the power amplifier36bto generate the continuous wave CW1from the radio-frequency signal in response to the first power level setting signal during the period P2. When the third mode is designated, the power supply control unit36econtrols the power amplifier36bto generate the continuous wave CW1from the radio-frequency signal in response to the first power level setting signal during the period P1and the period P2.

The power sensor36cis provided at the rear end of the power amplifier36b. The power sensor36cincludes a directional coupler, a traveling wave detector, and a reflected wave detector. The directional coupler gives a part of the traveling wave of the radio-frequency power RF1to the traveling wave detector and the reflected wave to the reflected wave detector. A first frequency specifying signal for specifying the set frequency of the radio-frequency power RF1is given to the power sensor36cfrom the power supply control unit36e. The traveling wave detector generates a measured value of the power level of a component having the same frequency as the set frequency specified from the first frequency specifying signal among all the frequency components of the traveling wave, that is, a measured value Pf11of the power level of the traveling wave. The measured value Pf11is given to the power supply control unit36e.

The first frequency specifying signal is also given to the reflected wave detector from the power supply control unit36e. The reflected wave detector generates a measured value of the power level of a component having the same frequency as the set frequency specified from the first frequency specifying signal among all the frequency components of the reflected wave, that is, a measured value Pr11of the power level of the reflected wave. The measured value Pf11is given to the power supply control unit36e. Further, the reflected wave detector generates a measured value of the total power level of all frequency components of the reflected wave, that is, a measured value of the power level of the reflected wave. The Pr12measured value Pr12is given to the power supply control unit36efor the protection of the power amplifier36b.

In the embodiment, the radio-frequency power supply36may perform a load power control during the period P1. That is, the radio-frequency power supply36may adjust the power level of the radio-frequency power RF1so that the load power level of the radio-frequency power RF1in the period P1approaches or matches the specified target power level. The power supply control unit36emay control the power amplifier36bin the load power control of the radio-frequency power supply36.

In the load power control when the first mode or the second mode is designated, the power supply control unit36emay control the power amplifier36bto adjust the power level of the modulated wave MW1in the first sub-period SP11. The power level of the modulated wave MW1in the first sub-period SP11is adjusted so that the load power level PL11in the monitoring period MP1approaches or matches the specified target power level.

The monitoring period MP1is a period within the first sub-period SP11. The monitoring period MP1may be a period that starts after a predetermined time length has elapsed from the start time of the first sub-period SP11. The monitoring period MP1is designated by the main control unit70. The load power level PL11is a difference between the power level of the traveling wave of the radio-frequency power RF1in the monitoring period MP1and the power level of the reflected wave of the radio-frequency power RF1in the monitoring period MP1. The load power level PL11is obtained as a difference between the measured value Pf11and the measured value Pr11during the monitoring period MP1. The load power level PL11may be obtained as a difference between the average value of the measured value Pf11and the average value of the measured value Pr11during the monitoring period MP1. Alternatively, the load power level Fin may be obtained as a difference between the moving average value of the measured value Pf11and the moving average value of the measured value Pr11in the plurality of monitoring periods MP1.

When the power level of the modulated wave MW1in the second sub-period SP12is not 0 W, the radio-frequency power supply36may execute the load power control of the modulated wave MW1in the second sub-period SP12. In the load power control, the power supply control unit36emay control the power amplifier36bto adjust the power level of the modulated wave MW1in the second sub-period SP12. The power level of the modulated wave MW1in the second sub-period SP12is adjusted so that the load power level PL12in the monitoring period MP2approaches or matches the specified target power level.

The monitoring period MP2may be a period that coincides with the second sub-period SP12. Alternatively, the monitoring period MP2may be a period within the second sub-period SP12, and may be a period that starts after a predetermined time length has elapsed from the start time of the second sub-period SP12. The monitoring period MP2is designated by the main control unit70. The load power level PL12is a difference between the power level of the traveling wave of the radio-frequency power RF1in the monitoring period MP2and the power level of the reflected wave of the radio-frequency power RF1in the monitoring period MP2. The load power level PL12is obtained as the difference between the measured value Pf11and the measured value Pr11during the monitoring period MP2. The load power level PL12may be obtained as the difference between the average value of the measured value Pf11and the average value of the measured value Pr11during the monitoring period MP2. Alternatively, the load power level PL12may be obtained as the difference between the moving average value of the measured value Pf11and the moving average value of the measured value Pr11in the plurality of monitoring periods MP2.

The radio-frequency power supply36may also perform load power control even when the third mode is designated. In the load power control when the third mode is designated, the power supply control unit36emay control the power amplifier36bto adjust the power level of the continuous wave CW1in the period P1. The power level of the continuous wave CW1in the period P1is adjusted so that the average value of the load power level PL11in the monitoring period MP1and the load power level PL12in the monitoring period MP2matches or approaches the specified target power level.

The matching device40is configured to set the load-side impedance of the radio-frequency power supply36, that is, the load impedance. In each of the first and second modes, the matching device40may set the load impedance of the radio-frequency power supply36in the period P1to a target impedance different from the output impedance of the radio-frequency power supply36. The load impedance of the radio-frequency power supply36in the period P1may be specified by the measured value of the load impedance of the radio-frequency power supply36in the monitoring period MP1.

In the third mode, the matching device40may match the load impedance of the radio-frequency power supply36in the period P1with the output impedance of the radio-frequency power supply36. Alternatively, the matching device40sets the load impedance of the radio-frequency power supply36in the period P1to a target impedance different from the output impedance of the radio-frequency power supply36in the third mode as well as in the first and second modes.

The matching device40matching devices the load impedance of the radio-frequency power supply36in the period P2to the target impedance for the subsequent period PB in each of the first mode and the second mode. That is, the matching device40is configured to gradually change the load impedance of the radio-frequency power supply36to the target impedance for the subsequent period PB in the period P2before or after the power generated by the radio-frequency power supply36is switched from the power wave W11to the power wave W12.

As illustrated inFIGS. 8 and 9, in each of the first and second modes, the matching device40gradually changes the load impedance of the radio-frequency power supply36so that the absolute value |Γ1| of the reflectance coefficient Γ1is gradually changed to the set target value for the subsequent period PB in the period P2. As illustrated inFIG. 8, when the subsequent period PB is the period P2in each of the first and second modes, the set target value of the absolute value |Γ1| of the reflectance coefficient Γ1for the subsequent period PB may be zero. As illustrated inFIG. 9, when the subsequent period PB is the period P1in each of the first and second modes, the set target value of the absolute value |Γ1| of the reflectance coefficient Γ1for the subsequent period PB is larger than zero, for example, 0.3 or more and 0.5 or less.

The period P2includes a plurality of consecutive sub-period SPs. The plurality of sub-period SPs include sub-periods SP1, SP2, . . . , SPN. The matching device40may gradually change the load impedance of the radio-frequency power supply36so that the absolute value |Γ1| of the reflectance coefficient Γ1in the period P2is gradually changed through the sub-periods SP1, SP2, . . . , SPNto the set target value for the subsequent period PB. As illustrated inFIG. 8, when the subsequent period PB is the period P2, the matching device40gradually changes the load impedance of the radio-frequency power supply36through the sub-periods SP1, SP2, . . . , SPNin the period P2after the start of the subsequent period PB (period P2). As illustrated inFIG. 9, when the subsequent period PB is the period P1, the matching device40gradually changes the load impedance of the radio-frequency power supply36through the sub-periods SP1, SP2, . . . , SPNin the period P2before the start of the subsequent period PB (period P1). The period P2further includes a sub-period SP(N+1). The sub-period SP(N+1)is a period continuous with the sub-period SPN. The matching device40sets the load impedance of the radio-frequency power supply36so that the absolute value |Γ1| of the reflectance coefficient Γ1in the sub-period SP(N+1)is set as the set target value for the subsequent period PB. Hereinafter, each of the sub-periods SP1, SP2, . . . , SPN, SP(N+1)may be referred to as a sub-period SPi. The symbol “i” refers to an index that is an integer of 1 or more and N+1 or less.

In the third mode, the matching device40may match the load impedance of the radio-frequency power supply36in the period P2with the output impedance of the radio-frequency power supply36. The matching device40may gradually change the load impedance of the radio-frequency power supply36in the period P2to the target impedance for the subsequent period PB in the third mode as well as in the first and second modes.

In the embodiment, as illustrated inFIG. 4, the matching device40includes a matching circuit40a, a sensor40b, a controller40c, an actuator40d, and an actuator40e. The matching circuit40amay include a variable reactance element40gand a variable reactance element40h. Each of the variable reactance element40gand the variable reactance element40his, for example, a variable capacitor. The matching circuit40amay further include an inductor and the like.

The controller40coperates under the control of the main control unit70. The controller40cadjusts the load impedance of the radio-frequency power supply36according to the measured value of the load-side impedance (i.e., the load impedance) of the radio-frequency power supply36given by the sensor40b. The controller40cadjusts the load impedance of the radio-frequency power supply36by controlling the actuator40dand the actuator40eand adjusting the reactance of each of the variable reactance element40gand the variable reactance element40h. The actuator40dand the actuator40eare, for example, motors.

The sensor40bis configured to acquire a measured value of the load impedance of the radio-frequency power supply36. In the embodiment, the measured value of the load impedance of the radio-frequency power supply36is acquired as a moving average value. As illustrated inFIG. 5, the sensor40bmay include a current detector102A, a voltage detector104A, filters106A and108A, average value calculators110A and112A, moving average value calculators114A and116A, and an impedance calculator118A.

The voltage detector104A detects the voltage waveform of the radio-frequency power RF1transmitted on the power feeding line43, and outputs a voltage waveform analog signal representing the voltage waveform. This voltage waveform analog signal is input to the filter106A. The filter106A generates a voltage waveform digital signal by digitizing the input voltage waveform analog signal. The filter106A receives the above-mentioned first frequency specifying signal from the power supply control unit36eand extracts only the frequency component corresponding to the frequency specified by the first frequency specifying signal from the voltage waveform digital signal, thereby generating a filtration voltage waveform signal. The filter106A may be composed of an FPGA (Field Programmable Gate Array).

The filtration voltage waveform signal generated by the filter106A is output to the average value calculator110A. The average value calculator110A receives a monitoring period setting signal from the main control unit70. The average value calculator110A obtains the average value of the voltage within the period specified from the monitoring period setting signal from the filtration voltage waveform signal. The average value calculator110A obtains the average value Vail of the voltage in each monitoring period MP1as the average value of the voltage. When the third mode is designated, the average value calculator110A may further obtain the average value VA12of the voltage in each monitoring period MP2as the average value of the voltage. Further, the average value calculator110A may be composed of, for example, an FPGA.

The moving average value calculator114A obtains the moving average value VMA11of the average value Vail which is obtained from the voltage of the radio-frequency power RF1in the latest and predetermined number of monitoring periods MP1among the plurality of average values VA11already obtained. The moving average value VMA11is output to the impedance calculator118A.

In the third mode, the moving average value calculator114A may further obtain the moving average value VMA12of the average value VA12which is obtained from the voltage of the radio-frequency power RF1in the latest and predetermined number of monitoring periods MP2among the plurality of average values VA12already obtained. The moving average value VMA12is output to the impedance calculator118A.

The current detector102A detects the current waveform of the radio-frequency power RF1transmitted on the power feeding line43, and outputs a current waveform analog signal representing the current waveform. This voltage waveform analog signal is input to the filter108A. The filter108A generates a voltage waveform digital signal by digitizing the input voltage waveform analog signal. The filter108A receives the above-mentioned first frequency specifying signal from the power supply control unit36eand extracts only the frequency component corresponding to the frequency specified by the first frequency specifying signal from the voltage waveform digital signal, thereby generating a filtration voltage waveform signal. The filter108A may be composed of an FPGA.

The filtration voltage waveform signal generated by the filter108A is output to the average value calculator112A. The average value calculator112A receives a monitoring period setting signal from the main control unit70. The average value calculator112A obtains the average value of the voltage within the period specified from the monitoring period setting signal from the filtration voltage waveform signal. The average value calculator112A obtains the average value IA11of the current in the monitoring period MP1in each period P1as the average value of the current. When the third mode is designated, the average value calculator112A may further obtain the average value IA12of the current in each monitoring period MP2as the average value of the current. Further, the average value calculator112A may be composed of, for example, an FPGA.

The moving average value calculator116A obtains the moving average value IMA11of the average value IA11which is obtained from the current of the radio-frequency power RF1in the latest and predetermined number of monitoring periods MP1among the plurality of average values IA11already obtained. The moving average value IMA11is output to the impedance calculator118A.

In the third mode, the moving average value calculator116A may further obtain the moving average value IMA12of the average value IA12which is obtained from the current of the radio-frequency power RF1in the latest and predetermined number of monitoring periods MP2among the plurality of average values IA12already obtained. The moving average value IMA12is output to the impedance calculator118A.

The impedance calculator118A obtains the moving average value ZMA11of the load impedance of the radio-frequency power supply36from the moving average value IMA11and the moving average value VMA11. The moving average value ZMA11is a measured value of the load impedance of the radio-frequency power supply36during the monitoring period MP1. In the third mode, the impedance calculator118A may further obtain the moving average value ZMA12of the load impedance of the radio-frequency power supply36from the moving average value IMA12and the moving average value VMA12. The moving average value ZMA12is a measured value of the load impedance of the radio-frequency power supply36during the monitoring period MP2.

The controller40ccontrols the matching circuit40ain order to set the load impedance of the radio-frequency power supply36. In the embodiment, the controller40csets the load impedance of the radio-frequency power supply36by adjusting the reactances of the variable reactance element40gand the variable reactance element40hthrough the actuator40dand the actuator40e.

In each of the first and second modes, the controller40cadjusts the load impedance of the radio-frequency power supply36in the period P1specified by the moving average value ZMA11to a target impedance different from the output impedance of the radio-frequency power supply36.

In the embodiment, the controller40cmay specify the target impedance from the set target value of the absolute value |Γ1| of the reflectance coefficient Γ1of the radio-frequency power RF1in the period P1. The set target value of the absolute value |Γ1| in the period P1may be a value larger than 0. For example, the set target value of the absolute value |Γ1| in the period P1is 0.3 or more and 0.5 or less. The reflectance coefficient Γ1is defined by the following equation (1).

In the equation (1), Z01is the characteristic impedance of the power feeding line43, and is generally 50Ω. In the equation (1), Z1is the target impedance. The controller40cdetermines the target impedance Z1corresponding to the set target value of the absolute value |Γ1| in the period P1based on the equation (1). The controller40csets the load impedance of the radio-frequency power supply36so that the load impedance of the radio-frequency power supply36during the period P1specified by the moving average value ZMA11approaches or matches the target impedance Z1.

When the third mode is specified, the controller40cmay match the load impedance of the radio-frequency power supply36with the output impedance (matching point) of the radio-frequency power supply36during the period P1. The load impedance of the radio-frequency power supply36may be specified by the average value of the moving average value ZMA11and the moving average value ZMA12. Alternatively, the controller40cmay adjust the load impedance of the radio-frequency power supply36in the period P1to a target impedance different from the output impedance of the radio-frequency power supply36in the third mode as well as in the first and second modes.

As described above, in each of the first and second modes, the matching device40may gradually change the load impedance of the radio-frequency power supply36so that the absolute value |Γ1| of the reflectance coefficient Γ1is gradually changed to the set target value for the subsequent period PB. As described above, the matching device40gradually changes the load impedance of the radio-frequency power supply36through a plurality of sub-period SPs in the period P2. The time length of each of the plurality of sub-period SPs (i.e., SP1, SP2, . . . , SPN) is TL.

The target values of the absolute value |Γ1| of the reflectance coefficient Γ1of the radio-frequency power RF1in the plurality of sub-periods SP1, SP2, . . . , SPNare different from each other. Of any two consecutive sub-periods included in the plurality of sub-periods SP2, the difference between the target value of the absolute value |Γ1| of the reflectance coefficient Γ1in one sub-period and the target value of the absolute value |Γ1| of the reflectance coefficient Γ1in the other period is ΔΓ1. In addition,FIG. 8andFIG. 9illustrate ΔΓ1as ΔΓ. As illustrated inFIG. 8, when the subsequent period PB is the period P2, the target value of the absolute value |Γ1| of the reflectance coefficient Γ1in the sub-period SP(N+1), that is, the set target value is zero. As illustrated inFIG. 9, when the subsequent period PB is the period P1, the target value of the absolute value |Γ1| of the reflectance coefficient Γ1in the sub-period SP(N+1), that is, the set target value is larger than zero, for example, 0.3 or more and 0.5 or less. In the embodiment, the TL may be set to 0.5 seconds or more and the ΔF1may be set to 0.2 or less. Further, the TL may be set to 0.2 seconds or more and the ΔΓ1may be set to 0.1 or less. In addition, the TL may be set to 0.5 seconds or more and the ΔΓ1may be set to 0.05 or less.

The controller40csets the load impedance of the radio-frequency power supply36. Specifically, the controller40cadjusts the load impedance of the radio-frequency power supply36in the sub-period SPifrom the target value of the absolute value |Γ1| of the reflectance coefficient Γ1of the radio-frequency power RF1in the sub-period SPito the target impedance Z1specified based on the equation (1). Further, the controller40cmay specify the load impedance of the radio-frequency power supply36in the sub-period SPifrom the measured value of the load impedance of the radio-frequency power supply36obtained by the sensor40b. The sensor40bmay obtain the measured value of the load impedance of the radio-frequency power supply36from the above-mentioned filtration voltage waveform signal and filtration current waveform signal.

When the third mode is specified, the controller40cmay match the load impedance of the radio-frequency power supply36with the output impedance (matching point) of the radio-frequency power supply36during the period P2. In the third mode as well as in the first and second modes, the controller40cmay gradually change the load impedance of the radio-frequency power supply36to the target impedance for the subsequent period PB in the period P2.

As illustrated inFIG. 6, in the embodiment, the radio-frequency power supply38includes an oscillator38a, a power amplifier38b, a power sensor38c, and a power supply control unit38e. The power supply control unit38eincludes a processor such as a CPU. The power supply control unit38egives a control signal to each of the oscillator38a, the power amplifier38b, and the power sensor38cto control the oscillator38a, the power amplifier38b, and the power sensor38c. The power supply control unit38euses the signal given from the main control unit70and the signal given from the power sensor38cto generate a control signal given to each of the oscillator38a, the power amplifier38b, and the power sensor38c.

The signal given from the main control unit70to the power supply control unit38eincludes a second frequency setting signal and the above-mentioned mode setting signal. The second frequency setting signal designates the set frequency of the radio-frequency power RF2. When the first mode or the third mode is designated, the signal given from the main control unit70to the power supply control unit38efurther includes a second modulation setting signal. The second modulation setting signal designates the modulation frequency and duty ratio of the modulated wave MW2. Further, the second modulation setting signal is also a signal that designates the power level of the modulated wave MW2in the first sub-period SP11and the power level of the modulated wave MW2in the second sub-period SP12. In the first mode, the modulation frequency of the modulated wave MW1and the modulation frequency of the modulated wave MW2may be the same as each other. When the second mode is designated, the signal given from the main control unit70to the power supply control unit38efurther includes a second power level setting signal that designates the power of the continuous wave CW2.

The power supply control unit38econtrols the oscillator38ato output a radio-frequency signal having a set frequency (e.g., the fundamental frequency fB2) designated by the second frequency setting signal. The output of the oscillator38ais connected to the input of the power amplifier38b. The power amplifier38bgenerates radio-frequency power RF2by amplifying the radio-frequency signal output from the oscillator38a. The power amplifier38bis controlled by the power supply control unit38e.

When the first mode or the third mode is designated, the power supply control unit38econtrols the power amplifier38bto generate the modulated wave MW2from the radio-frequency signal in response to the second modulation setting signal during the period P1. When the first mode or the third mode is designated, the power supply control unit38econtrols the power amplifier38bto generate the continuous wave CW2from the radio-frequency signal in response to the second power level setting signal during the period P2. When the second mode is designated, the power supply control unit38econtrols the power amplifier38bto generate the continuous wave CW2from the radio-frequency signal in response to the second power level setting signal during the period P1and the period P2.

The power sensor38cis provided at the rear end of the power amplifier38b. The power sensor38cincludes a directional coupler, a traveling wave detector, and a reflected wave detector. The directional coupler gives a part of the traveling wave of the radio-frequency power RF2to the traveling wave detector and the reflected wave to the reflected wave detector. A second frequency specifying signal for specifying the set frequency of the radio-frequency power RF2is given to the power sensor38cfrom the power supply control unit38e. The traveling wave detector generates a measured value of the power level of a component having the same frequency as the set frequency specified from the second frequency specifying signal among all the frequency components of the traveling wave, that is, a measured value Pf21of the power level of the traveling wave. The measured value Pf21is given to the power supply control unit38e.

The second frequency specifying signal is also given to the reflected wave detector from the power supply control unit38e. The reflected wave detector generates a measured value of the power level of a component having the same frequency as the set frequency specified from the second frequency specifying signal among all the frequency components of the reflected wave, that is, a measured value Pr21of the power level of the reflected wave. The measured value Pf21is given to the power supply control unit38e. Further, the reflected wave detector generates a measured value of the total power level of all frequency components of the reflected wave, that is, a measured value r22of P the power level of the reflected wave. The measured value Pr22is given to the power supply control unit38efor the protection of the power amplifier38b.

In the embodiment, the radio-frequency power supply38may perform a load power control during the period P1. That is, the radio-frequency power supply38may adjust the power level of the radio-frequency power RF2so that the load power level of the radio-frequency power RF2in the period P1approaches or matches the specified target power level. The power supply control unit38emay control the power amplifier38bin the load power control of the radio-frequency power supply38.

In the load power control when the first mode or the third mode is designated, the power supply control unit38emay control the power amplifier38bto adjust the power level of the modulated wave MW2in the first sub-period SP11. The power level of the modulated wave MW2in the first sub-period SP11is adjusted so that the load power level PL21in the monitoring period MP1approaches or matches the specified target power level.

As described above, the monitoring period MP1is a period within the first sub-period SP11. The monitoring period MP1may be a period that starts after a predetermined time length has elapsed from the start time of the first sub-period SP11. The monitoring period MP1is designated by the main control unit70. The load power level PL21is a difference between the power level of the traveling wave of the radio-frequency power RF2in the monitoring period MP1and the power level of the reflected wave of the radio-frequency power RF2in the monitoring period MP1. The load power level PL21is obtained as the difference between the measured value Pf21and the measured value Prat during the monitoring period MP1. The load power level PL21may be obtained as the difference between the average value of the measured value Pf21and the average value of the measured value Prat during the monitoring period MP1. Alternatively, the load power level PL21may be obtained as the difference between the moving average value of the measured value Pr21and the moving average value of the measured value Pr21in the plurality of monitoring periods MP1.

When the power level of the modulated wave MW2in the second sub-period SP12is not 0 W, the radio-frequency power supply38may execute the load power control of the modulated wave MW2in the second sub-period SP12. In the load power control, the power supply control unit38emay control the power amplifier38bto adjust the power level of the modulated wave MW2in the second sub-period SP12. The power level of the modulated wave MW2in the second sub-period SP12is adjusted so that the load power level PL22in the monitoring period MP2approaches or matches the specified target power level.

As described above, the monitoring period MP2may be a period that coincides with the second sub-period SP12. Alternatively, the monitoring period MP2may be a period within the second sub-period SP12, and may be a period that starts after a predetermined time length has elapsed from the start time of the second sub-period SP12. The monitoring period MP2is designated by the main control unit70. The load power level PL22is a difference between the power level of the traveling wave of the radio-frequency power RF2in the monitoring period MP2and the power level of the reflected wave of the radio-frequency power RF2in the monitoring period MP2. The load power level PL22is obtained as the difference between the measured value Pf21and the measured value Pr21during the monitoring period MP2. The load power level PL22may be obtained as the difference between the average value of the measured value Pf21and the average value of the measured value Pr21during the monitoring period MP2. Alternatively, the load power level PL22may be obtained as the difference between the moving average value of the measured value Pf21and the moving average value of the measured value Pr21in the plurality of monitoring periods MP2.

The radio-frequency power supply38may also perform a load power control even when the second mode is designated. In the load power control when the second mode is designated, the power supply control unit38emay control the power amplifier38bto adjust the power level of the continuous wave CW2in the period P1. The power level of the continuous wave CW2in the period P1is adjusted so that the average value of the load power level PL21in the monitoring period MP1and the load power level PL22in the monitoring period MP2matches or approaches the specified target power level.

The matching device42is configured to set the load-side impedance of the radio-frequency power supply38, that is, the load impedance. In each of the first and second modes, the matching device42may set the load impedance of the radio-frequency power supply38in the period P1to a target impedance different from the output impedance of the radio-frequency power supply38. The load impedance of the radio-frequency power supply38in the period P1may be specified by the measured value of the load impedance of the radio-frequency power supply38in the monitoring period MP1.

In the second mode, the matching device42may match the load impedance of the radio-frequency power supply38in the period P1with the output impedance of the radio-frequency power supply38. Alternatively, the matching device42sets the load impedance of the radio-frequency power supply38in the period P1to a target impedance different from the output impedance of the radio-frequency power supply38in the second mode as well as in the first and third modes.

The matching device42gradually changes the load impedance of the radio-frequency power supply38in the period P2to the target impedance for the subsequent period PB in each of the first mode and the third mode. That is, the matching device42is configured to gradually change the load impedance of the radio-frequency power supply38to the target impedance for the subsequent period PB in the period P2before or after the power generated by the radio-frequency power supply38is switched from the power wave W21to the power wave W22.

As illustrated inFIGS. 8 and 9, in each of the first and third modes, the matching device42gradually changes the load impedance of the radio-frequency power supply38so that the absolute value |Γ2| of the reflectance coefficient Γ2is gradually changed to the set target value for the subsequent period PB in the period P2. As illustrated inFIG. 8, when the subsequent period PB is the period P2in each of the first and third modes, the set target value of the absolute value |Γ2| of the reflectance coefficient Γ2for the subsequent period PB may be zero. As illustrated inFIG. 9, when the subsequent period PB is the period P1in each of the first and third modes, the set target value of the absolute value |Γ2| of the reflectance coefficient Γ2for the subsequent period PB is larger than zero, for example, 0.3 or more and 0.5 or less.

As described above, the subsequent period PB includes a plurality of consecutive sub-period SPs. As described above, the plurality of sub-period SPs include sub-periods SP1, SP2, . . . , SPN. The matching device42may gradually change the load impedance of the radio-frequency power supply38so that the absolute value |Γ2| of the reflectance coefficient Γ2in the period P2is gradually changed through the sub-periods SP1, SP2, . . . , SPNto the set target value for the subsequent period PB. As illustrated inFIG. 8, when the subsequent period PB is the period P2, the matching device42gradually changes the load impedance of the radio-frequency power supply38through the sub-periods SP1, SP2, . . . , SPNin the period P2after the start of the subsequent period PB (period P2). As illustrated inFIG. 9, when the subsequent period PB is the period P1, the matching device42gradually changes the load impedance of the radio-frequency power supply38through the sub-periods SP1, SP2, . . . , SPNin the period P2before the start of the subsequent period PB (period P1). The matching device42sets the load impedance of the radio-frequency power supply38so that the absolute value |Γ2| of the reflectance coefficient Γ2in the sub-period SP(N+1)is set as the set target value for the subsequent period PB.

In the second mode, the matching device42may match the load impedance of the radio-frequency power supply38in the period P2with the output impedance of the radio-frequency power supply38. Further, the matching device42may gradually change the load impedance of the radio-frequency power supply38in the period P2to the target impedance for the subsequent period PB in the second mode as well as in the first and third modes.

In the embodiment, the matching device42includes a matching circuit42a, a sensor42b, a controller42c, an actuator42d, and an actuator42e, as illustrated inFIG. 6. The matching circuit42amay include a variable reactance element42gand a variable reactance element42h. Each of the variable reactance element42gand the variable reactance element42his, for example, a variable capacitor. In addition, the matching circuit42amay further include an inductor and the like.

The controller42coperates under the control of the main control unit70. The controller42cadjusts the load impedance of the radio-frequency power supply38according to the measured value of the load-side impedance (i.e., the load impedance) of the radio-frequency power supply38given by the sensor42b. The controller42cadjusts the load impedance of the radio-frequency power supply38by controlling the actuator42dand the actuator42eand adjusting the reactance of each of the variable reactance element42gand the variable reactance element42h. The actuator42dand the actuator42eare, for example, motors.

The sensor42bis configured to acquire a measured value of the load impedance of the radio-frequency power supply38. In the embodiment, the measured value of the load impedance of the radio-frequency power supply38is acquired as a moving average value. As illustrated inFIG. 7, the sensor42bmay include a current detector102B, a voltage detector104B, filters106B and108B, average value calculators110B and112B, moving average value calculators114B and116B, and an impedance calculator118B.

The voltage detector104A detects the voltage waveform of the radio-frequency power RF2transmitted on the power feeding line45, and outputs a voltage waveform analog signal representing the voltage waveform. This voltage waveform analog signal is input to the filter106B. The filter106B generates a voltage waveform digital signal by digitizing the input voltage waveform analog signal. The filter106B receives the above-mentioned second frequency specifying signal from the power supply control unit38eand extracts only the frequency component corresponding to the frequency specified by the second frequency specifying signal from the voltage waveform digital signal, thereby generating a filtration voltage waveform signal. The filter106B may be composed of an FPGA.

The filtration voltage waveform signal generated by the filter106A is output to the average value calculator110B. The average value calculator110B receives a monitoring period setting signal from the main control unit70. The average value calculator110B obtains the average value of the voltage within the period specified from the monitoring period setting signal from the filtration voltage waveform signal. The average value calculator110B obtains the average value VB11of the voltage in each monitoring period MP1as the average value of the voltage. When the second mode is designated, the average value calculator110B may further obtain the average value VB12of the voltage in each monitoring period MP2as the average value of the voltage. Further, the average value calculator110B may be composed of, for example, an FPGA.

The moving average value calculator114B obtains the moving average value VMB11of the average value VB11which is obtained from the voltage of the radio-frequency power RF2in the latest and predetermined number of monitoring periods MP1among the plurality of average values VB11already obtained. The moving average value VMB11is output to the impedance calculator118B.

In the second mode, the moving average value calculator114B may further obtain the moving average value VMB12of the average value VB12which is obtained from the voltage of the radio-frequency power RF2in the latest and predetermined number of monitoring periods MP2among the plurality of average values VB12already obtained. The moving average value VMB12is output to the impedance calculator118B.

The current detector102B detects the current waveform of the radio-frequency power RF2transmitted on the power feeding line45, and outputs a current waveform analog signal representing the current waveform. This voltage waveform analog signal is input to the filter108B. The filter108B generates a voltage waveform digital signal by digitizing the input voltage waveform analog signal. The filter108B receives the above-mentioned second frequency specifying signal from the power supply control unit38eand extracts only the frequency component corresponding to the frequency specified by the second frequency specifying signal from the voltage waveform digital signal, thereby generating a filtration voltage waveform signal. The filter108B may be composed of an FPGA.

The filtration voltage waveform signal generated by the filter108B is output to the average value calculator112B. The average value calculator112B receives a monitoring period setting signal from the main control unit70. The average value calculator112B obtains the average value of the current within the period specified from the monitoring period setting signal from the filtration current waveform signal. The average value calculator112B obtains the average value IB11of the current in the monitoring period MP1in each period P1as the average value of the current. When the second mode is designated, the average value calculator112B may further obtain the average value IB12of the current in each monitoring period MP2as the average value of the current. Further, the average value calculator112B may be composed of, for example, an FPGA.

The moving average value calculator116B obtains the moving average value IMB11of the average value IB11which is obtained from the current of the radio-frequency power RF2in the latest and predetermined number of monitoring periods MP1among the plurality of average values IB11already obtained. The moving average value IMB11is output to the impedance calculator118B.

In the second mode, the moving average value calculator116B may further obtain the moving average value IMB12of the average value IB12which is obtained from the current of the radio-frequency power RF2in the latest and predetermined number of monitoring periods MP2among the plurality of average values IB12already obtained. The moving average value IMB12is output to the impedance calculator118B.

The impedance calculator118A obtains the moving average value ZMB11of the load impedance of the radio-frequency power supply38from the moving average value IMB11and the moving average value VMB11. The moving average value ZMB11is a measured value of the load impedance of the radio-frequency power supply38during the monitoring period MP1. In the second mode, the impedance calculator118B may further obtain the moving average value ZMB12of the load impedance of the radio-frequency power supply38from the moving average value IMB12and the moving average value VMB12. The moving average value ZMB12is a measured value of the load impedance of the radio-frequency power supply38during the monitoring period MP2.

The controller42ccontrols the matching circuit42ain order to set the load impedance of the radio-frequency power supply38. In the embodiment, the controller42csets the load impedance of the radio-frequency power supply38by adjusting the reactances of the variable reactance element42gand the variable reactance element42hthrough the actuator42dand the actuator42e.

In each of the first and third modes, the controller42cadjusts the load impedance of the radio-frequency power supply38in the period P1specified by the moving average value ZMB11to a target impedance different from the output impedance of the radio-frequency power supply38.

In the embodiment, the controller42cmay specify the target impedance from the set target value of the absolute value |Γ2| of the reflectance coefficient Γ2of the radio-frequency power RF2in the period P1. The set target value of the absolute value |Γ2| in the period P1may be a value larger than 0. For example, the set target value of the absolute value |Γ2| in the period P1is 0.3 or more and 0.5 or less. The reflectance coefficient Γ2is defined by the following equation (2).

In the equation (2), Z02is the characteristic impedance of the power feeding line45, and is generally 50Ω. In the equation (2), Z2is the target impedance. The controller42cdetermines the target impedance Z2corresponding to the set target value of the absolute value |Γ2| in the period P1based on the equation (2). The controller42csets the load impedance of the radio-frequency power supply38so that the load impedance of the radio-frequency power supply38during the period P1specified by the moving average value ZMB11approaches or matches the target impedance Z2.

When the second mode is designated, the controller42cmay match the load impedance of the radio-frequency power supply38with the output impedance (matching point) of the radio-frequency power supply38during the period P1. The load impedance of the radio-frequency power supply38may be specified by the average value of the moving average value ZMB11and the moving average value ZMB12. Alternatively, the controller42cmay adjust the load impedance of the radio-frequency power supply38in the period P1to a target impedance different from the output impedance of the radio-frequency power supply38in the second mode as well as in the first and third modes.

As described above, in each of the first and third modes, the matching device42may gradually change the load impedance of the radio-frequency power supply38so that the absolute value |Γ2| of the reflectance coefficient Γ2is gradually changed to the set target value for the subsequent period PB. As described above, the matching device42gradually changes the load impedance of the radio-frequency power supply38through a plurality of sub-periods SPs in the period P2.

The target values of the absolute value |Γ2| of the reflectance coefficient Γ2of the radio-frequency power RF2in the plurality of sub-periods SP1, SP2, . . . , SPNare different from each other. Of any two consecutive sub-periods included in the plurality of sub-periods SP2, the difference between the target value of the absolute value |Γ2| of the reflectance coefficient Γ2in one sub-period and the target value of the absolute value |Γ2| of the reflectance coefficient Γ2in the other period is ΔΓ2. In addition,FIG. 8andFIG. 9illustrate ΔΓ2as ΔΓ. As illustrated inFIG. 8, when the subsequent period PB is the period P2, the target value of the absolute value |Γ2| of the reflectance coefficient Γ2in the sub-period SP(N+1), that is, the set target value is zero. As illustrated inFIG. 9, when the subsequent period PB is the period P1, the target value of the absolute value |Γ2| of the reflectance coefficient Γ2in the sub-period SP(N+1), that is, the set target value is larger than zero, for example, 0.3 or more and 0.5 or less. In the embodiment, the TL may be set to 0.5 seconds or more and the ΔΓ2may be set to 0.2 or less. Further, the TL may be set to 0.2 seconds or more and the ΔΓ2may be set to 0.1 or less. Further, the TL may be set to 0.5 seconds or more and the ΔΓ2may be set to 0.05 or less.

The controller42csets the load impedance of the radio-frequency power supply38. Specifically, the controller42cadjusts the load impedance of the radio-frequency power supply38in the sub-period SPifrom the target value of the absolute value |Γ2| of the reflectance coefficient Γ2of the radio-frequency power RF2in the sub-period SPito the target impedance Z2specified based on the equation (2). Further, the controller42cmay specify the load impedance of the radio-frequency power supply38in the sub-period SPifrom the measured value of the load impedance of the radio-frequency power supply38obtained by the sensor42b. The sensor42bmay obtain the measured value of the load impedance of the radio-frequency power supply38from the above-mentioned filtration voltage waveform signal and filtration current waveform signal.

When the second mode is designated, the controller42cmay match the load impedance of the radio-frequency power supply38with the output impedance (matching point) of the radio-frequency power supply38during the period P2. In the second mode as well as in the first and third modes, the controller42cmay gradually change the load impedance of the radio-frequency power supply38to the target impedance for the subsequent period PB in the period P2.

In the plasma processing apparatus1, the matching device40gradually changes the load impedance to the target impedance for the subsequent period during the period in which the continuous wave CW1is supplied before or after the power supplied from the radio-frequency power supply36is switched from the power wave W11to the power wave W12. Thus, the matching device40may follow the change in the load impedance to be set after the power from the radio-frequency power supply36is switched from the power wave W11to the power wave W12. Therefore, it is possible to reduce the reflection of the power supplied from the radio-frequency power supply36after being switched from the power wave W11to the power wave W12. Further, the matching device42gradually changes the load impedance to the target impedance for the subsequent period during the period in which the continuous wave CW2is supplied before or after the power supplied from the radio-frequency power supply38is switched from the power wave W21to the power wave W22. Thus, the matching device42may follow the change in the load impedance to be set after the power from the radio-frequency power supply38is switched from the power wave W21to the power wave W22. Therefore, it is possible to reduce the reflection of the power supplied from the radio-frequency power supply38after being switched from the power wave W21to the power wave W22.

In the embodiment, the matching device40adjusts the load impedance of the radio-frequency power supply36in the period P1to a target impedance different from the output impedance of the radio-frequency power supply36. According to this embodiment, the reflection from the load on the modulated wave MW1may be reduced during the period P1. In the embodiment, in each of the first and third modes, the matching device42adjusts the load impedance of the radio-frequency power supply38in the period P1to a target impedance different from the output impedance of the radio-frequency power supply38. According to this embodiment, the reflection from the load on the modulated wave MW2may be reduced during the period P1.

In the embodiment, a load power control of the modulated wave MW1may be performed during the period P1. According to this embodiment, even when a reflection occurs due to the target impedance being different from the output impedance of the radio-frequency power supply36in the period P1, the modulated wave MW1of the target power level may be coupled to the plasma. In the embodiment, a load power control of the modulated wave MW2may be performed during the period P1. According to this embodiment, even when a reflection occurs due to the target impedance being different from the output impedance of the radio-frequency power supply38in the period P1, the modulated wave MW2of the target power level may be coupled to the plasma.

Hereinafter,FIG. 10will be referenced.FIG. 10is a flowchart of a matching method according to the embodiment. In the matching method illustrated inFIG. 10(hereinafter, referred to as a “method MT”), the power supplied from at least one of the radio-frequency power supply36and the radio-frequency power supply38is switched from the power wave of one of the continuous wave and the modulated wave to the power wave of the other. That is, in the method MT, the power wave W11is supplied from the radio-frequency power supply36, and the power wave W21is supplied from the radio-frequency power supply38. Next, at least one of the power wave W12from the radio-frequency power supply36and the power wave W22from the radio-frequency power supply38is supplied. The power wave W11may be supplied from the radio-frequency power supply36for two consecutive periods, or the power wave W21may be supplied from the radio-frequency power supply36for two consecutive periods. In the method MT, the power supplied from at least one of the radio-frequency power supply36and the radio-frequency power supply38may be alternately switched from the power wave of one of the continuous wave and the modulated wave to the power wave of the other.

The method MT is started in step ST1. In step ST1, the power wave W11is supplied from the radio-frequency power supply36, and the power wave W21is supplied from the radio-frequency power supply38. During the execution of step ST1, the load impedance of the radio-frequency power supply36is set by the matching device40. When the power wave W11is the modulated wave MW1, the load impedance of the radio-frequency power supply36may be adjusted to a target impedance different from the output impedance of the radio-frequency power supply36as described above during the execution of step ST1. Further, when the power wave W11is the modulated wave MW1, the load power control may be executed by the radio-frequency power supply36as described above during the execution of step ST1.

When the power wave W11is the continuous wave CW1, the load impedance of the radio-frequency power supply36may be matched with the output impedance of the radio-frequency power supply36during the execution of step ST1. Further, when the power wave W11is the continuous wave CW1, similar to the case where the power wave W11is the modulated wave MW1, the load impedance of the radio-frequency power supply36may be adjusted to a target impedance different from the output impedance of the radio-frequency power supply36during the execution of step ST1.

During the execution of step ST1, the load impedance of the radio-frequency power supply38is set by the matching device42. When the power wave W21is the modulated wave MW2, the load impedance of the radio-frequency power supply38may be adjusted to a target impedance different from the output impedance of the radio-frequency power supply38as described above during the execution of step ST1. Further, when the power wave W21is the modulated wave MW2, the load power control may be executed by the radio-frequency power supply38as described above during the execution of step ST1.

When the power wave W21is the continuous wave CW2, the load impedance of the radio-frequency power supply38may be matched with the output impedance of the radio-frequency power supply38during the execution of step ST1. Further, when the power wave W21is the continuous wave CW2, similar to the case where the power wave W21is the modulated wave MW2, the load impedance of the radio-frequency power supply36may be adjusted to a target impedance different from the output impedance of the radio-frequency power supply36during the execution of step ST1.

In step STJa, it is determined whether the power wave supplied in the preceding period PA out of the two consecutive periods is a continuous wave. When the continuous wave CW1is not supplied in the preceding period PA, that is, when the modulated wave MW1is supplied, step STA2is executed in the succeeding period PB of the two consecutive periods. When the modulated wave MW1is supplied in the preceding period PA and the continuous wave CW1is supplied in the subsequent period PB, step STA3is executed in the subsequent period PB. When the continuous wave CW1is not supplied in the preceding period PA, step STAB is executed in the subsequent period PB. When the modulated wave CW1is supplied in the preceding period PA and the continuous wave MW1is supplied in the subsequent period PB, step STA2is executed in the preceding PB.

When the continuous wave CW2is not supplied in the preceding period PA, that is, when the modulated wave MW2is supplied, step STA2is executed in the subsequent period PB. When the modulated wave MW2is supplied in the preceding period PA and the continuous wave CW2is supplied in the subsequent period PB, step STA3is executed in the subsequent period PB. When the continuous wave CW2is not supplied in the preceding period PA, step STB3is executed in the subsequent period PB. When the modulated wave CW2is supplied in the preceding period PA and the continuous wave MW2is supplied in the subsequent period PB, step STB2is executed in the preceding PB.

Step STA2is executed when the modulated wave MW1is supplied in the preceding period PA. In step STA2, the power wave of the subsequent period PB is supplied from the radio-frequency power supply36. When the power wave supplied from the radio-frequency power supply36in step STA2is the continuous wave CW1, the load impedance of the radio-frequency power supply36is gradually changed in step STA3after the start of the subsequent period PB to the target impedance for the subsequent period PB as described above. When the power wave supplied from the radio-frequency power supply36in step STA2is the modulated wave MW1, the load impedance of the radio-frequency power supply36may be set to a target impedance different from the output impedance of the radio-frequency power supply36.

Step STA2is executed when the modulated wave MW2is supplied in the preceding period PA. In step STA2, the power wave of the subsequent period PB is supplied from the radio-frequency power supply38. When the power wave supplied from the radio-frequency power supply38in step STA2is the continuous wave CW2, the load impedance of the radio-frequency power supply38is gradually changed in step STA3after the start of the subsequent period PB to the target impedance for the subsequent period PB as described above. When the power wave supplied from the radio-frequency power supply38in step STA2is the modulated wave MW2, the load impedance of the radio-frequency power supply38may be set to a target impedance different from the output impedance of the radio-frequency power supply38.

When the continuous wave CW1is not supplied in the preceding period PA, step STB3is executed in the subsequent period PB. In step STB3, the power wave of the subsequent period PB is supplied from the radio-frequency power supply36. When the power wave supplied from the radio-frequency power supply36in step STB3is the modulated wave MW1, step STB2is executed in the preceding period PA before the start of the subsequent period PB. In step STB2, the load impedance of the radio-frequency power supply36is gradually changed to the target impedance for the subsequent period PB as described above. When the power wave supplied from the radio-frequency power supply36in step STB3is the modulated wave CW1, the load impedance of the radio-frequency power supply36may be set to a target impedance different from the output impedance of the radio-frequency power supply36.

When the continuous wave CW2is not supplied in the preceding period PA, step STB3is executed in the subsequent period PB. In step STB3, the power wave of the subsequent period PB is supplied from the radio-frequency power supply38. When the power wave supplied from the radio-frequency power supply38in step STB3is the modulated wave MW2, step STB2is executed in the preceding period PA before the start of the subsequent period PB. In step STB2, the load impedance of the radio-frequency power supply38is gradually changed to the target impedance for the subsequent period PB as described above. When the power wave supplied from the radio-frequency power supply38in step STB3is the continuous wave CW2, the load impedance of the radio-frequency power supply38may be matched with the output impedance of the radio-frequency power supply38.

In step STJb, it is determined whether the end condition has been satisfied. The end condition is satisfied when the number of executions of the cycle CY represented inFIG. 10has reached a predetermined number of times. When it is determined that the end condition has not been satisfied, the cycle CY is repeated from step STJa. When it is determined that the end condition has been satisfied, the method MT is ended.

Although various embodiments have been described above, the present disclosure is not limited to the embodiments described above, and various omissions, substitutions, and changes may be made. In addition, it is possible to combine the elements in other embodiments to form other embodiments.

For example, the plasma processing apparatus1was a capacitively coupled plasma processing apparatus. However, the idea of the present disclosure is applicable to any plasma processing apparatus configured to supply the modulated radio-frequency power from the radio-frequency power supply to the electrodes. Examples of such a plasma processing apparatus include an inductively coupled plasma processing apparatus, an electron cyclotron resonance (ECR) plasma processing apparatus, and a plasma processing apparatus that uses a surface wave such as a microwave for generating plasma.

Further, the plasma processing apparatus1is illustrated to use both the radio-frequency power RF1and the radio-frequency power RF2for plasma processing, but only one of the radio-frequency power RF1and the radio-frequency power RF2may be used for the plasma processing.

Hereinafter, an experiment performed using the plasma processing apparatus1will be described. In the experiment, plasma was generated in the plasma processing apparatus1in the third mode. In the experiment, two types of power, 400 W and 1000 W, were used as the power level of the radio-frequency power RF2. Further, in the experiment, different values were set for each of the above-mentioned TL and ΔΓ2. Other conditions in the experiment are as follows.

Frequency of radio-frequency power RF1: 60 MHz

Power of continuous wave CW1: 300 W

Frequency of radio-frequency power RF2: 40.68 MHz

Power of modulated wave MW2in first sub-period SP11and power of continuous wave CW2in period P2: 400 W or 1000 W

Power of modulated wave MW2in second sub-period SP12: 0 W

Duty ratio of modulated wave MW2: 1 kHz

Duty ratio of modulated wave MW2: 90%

In the experiment, the VPP of the susceptor16was measured according to the radio-frequency power RF2. The VPP is a peak-to-peak value of the voltage of the susceptor16according to the radio-frequency power RF2. In the experiment, the ratio (%) of the amount of decrease in VPP caused by changing the power supplied to the susceptor16from the modulated wave MW2to the continuous wave CW2with respect to the VPP when the reflection was substantially not observed (hereinafter, referred to as a “decrease rate”) was calculated. Table 1 represents the decrease rate when the power of the modulated wave MW2in the first sub-period SP11and the power of the continuous wave CW2in the period P2are set to 400 W. Table 2 represents the decrease rate when the power of the modulated wave MW2in the first sub-period SP11and the power of the continuous wave CW2in the period P2are set to 1000 W.

As represented in Tables 1 and 2, as a result of the experiment, when TL is set to 0.5 seconds or more and ΔΓ2is set to 0.2 or less, or when TL is set to 0.2 seconds or more and ΔΓ2is set to 0.1 or less, the decrease rate was 10% or less. Therefore, when TL is set to 0.5 seconds or more and ΔΓ2is set to 0.2 or less, or when TL is set to 0.2 seconds or more and ΔΓ2is set to 0.1 or less, it was confirmed that the reflection was effectively suppressed. Further, when the TL is set to 0.5 seconds or more and the ΔΓ2is set to 0.05 or less, the decrease rate was 0%. Therefore, when the TL is set to 0.5 seconds or more and the ΔΓ2is set to 0.05 or less, it was confirmed that almost no reflection occurred.

According to the embodiment, it is possible to reduce the reflection from the load after switching the power supplied to the electrodes of the plasma processing apparatus from one of the modulated wave and the continuous wave of the radio-frequency power to the other thereof.