Impedance matching device

Abstract

We provide an impedance matcher that starts matching operation after plasma generation. [Solution] The impedance matcher 30 comprises a matching circuit 32 equipped with impedance variable elements 321 and 322, drive units 33 and 34 for changing the variable values ​​of the impedance variable elements, a matching sensor 31 for detecting information for calculating the load side impedance Z or reflection coefficient ρ (load information), a load information calculation unit 37 for calculating load information based on the information detected by the matching sensor 31, a DC voltage detection circuit 38 for detecting the DC voltage downstream of the matching circuit, and a matching control unit 39 that, after the absolute value of the DC voltage detected by the DC voltage detection circuit 38 becomes higher than a predetermined threshold, gives a command signal to the drive units 33 and 34 to change the variable values ​​of the impedance variable elements using the load information so that the reflected wave power becomes smaller.

Description

Technical Field

[0001] The present disclosure relates to an impedance matcher.

Background Art

[0002] For example, a high-frequency power supply system used in a plasma processing apparatus supplies high-frequency power having a fundamental frequency in the RF band (RF: Radio Frequency) from a high-frequency power source to a load (e.g., a plasma processing apparatus).

[0003] Further, an impedance matcher (also sometimes referred to as an impedance matching device) is provided between the high-frequency power source and the load, and the variable value (e.g., capacitance, inductance) of an internal variable impedance element is adjusted so that the power value of the reflected wave power on the high-frequency power source side (e.g., the input end) of the impedance matcher becomes small, thereby performing an operation of matching the impedance between the high-frequency power source and the load. Such an operation of adjusting the impedance by changing the variable value of the variable impedance element is referred to as a matching operation.

[0004] The impedance matcher detects, based on information detected by a sensor disposed on the high-frequency power source side (e.g., the input end), that the high-frequency power source has started supplying high-frequency power to the plasma processing apparatus serving as the load, and starts the matching operation from the time of the detection.

[0005] This matching operation will be further described.

[0006] When a high-frequency power supply begins supplying high-frequency power to a plasma processing device, the high-frequency power output from the high-frequency power supply is supplied to the plasma processing device via an impedance matching circuit. At this time, plasma does not occur simultaneously with the supply of high-frequency power, but rather after a short period of time has elapsed. Furthermore, the time it takes for plasma to occur is not always the same. Sometimes, plasma may not occur even when high-frequency power is supplied. This is because, in order for the gas introduced into the plasma processing device to ionize and become plasma after high-frequency power is supplied to it, it is desirable that conditions such as the voltage at which the gas ignites and the gas concentration are appropriate, and the time it takes for plasma to occur can also vary depending on these conditions.

[0007] However, even when no plasma is being generated in the plasma processing device, power is consumed to ionize the gas. Therefore, the impedance matcher recognizes that high-frequency power has been supplied to the plasma processing device, and thus begins matching operations even before plasma is generated. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2024-095370 [Patent Document 2] Japanese Patent Application Publication No. 5-63604 [Patent Document 3] Japanese Patent Publication No. 2006-166412 [Overview of the project] [Problems that the invention aims to solve]

[0009] During the transient period between the supply of high-frequency power and the generation of plasma, the load impedance changes abruptly. Therefore, if matching operation is initiated only when the start of high-frequency power supply to the plasma processing device is detected, as in conventional systems, the impedance variable element will attempt to abruptly follow the change in impedance even before plasma generation has occurred. This can cause abrupt changes in the relative positions of the electrodes or windings of the impedance variable element, potentially making the load impedance unstable. In some cases, this can even delay plasma generation.

[0010] Furthermore, as mentioned above, if the variable impedance element responds sharply to changes in impedance, mechanical wear of the variable impedance element may accelerate, potentially shortening its mechanical lifespan.

[0011] This disclosure provides an impedance matcher that can initiate matching operation after plasma generation. [Means for solving the problem]

[0012] The impedance matching device according to this disclosure is an impedance matching device provided between a high-frequency power supply that supplies high-frequency power to a plasma processing device as the load and the load, and comprises: a matching circuit having electrodes and windings and at least one variable impedance element in which the positional relationship of the electrodes or the windings is variable; a driving means for changing the positional relationship of the electrodes or the windings; a sensor for detecting information for calculating the load-side impedance as seen from the high-frequency power supply side to the load side in the impedance matching device, or information for calculating the reflection coefficient on the high-frequency power supply side in the impedance matching device; a calculation unit that calculates the reflection coefficient or load-side impedance based on the information detected by the sensor and outputs it as load information; a DC voltage detection circuit for detecting a DC voltage downstream of the matching circuit; and a control unit that, after the absolute value of the DC voltage detected by the DC voltage detection circuit becomes higher than a predetermined threshold, provides the driving means with a command signal to change the positional relationship of the electrodes or the windings using the load information so that the reflected wave power becomes smaller. [Effects of the Invention]

[0013] According to the impedance matcher of this disclosure, the matching operation starts after plasma generation, thus reducing the instability of the load impedance caused by changing the variable value of the impedance variable element before plasma generation. Furthermore, since the impedance variable element does not abruptly follow the change in load impedance before plasma generation, mechanical wear of the impedance variable element is reduced, and the mechanical life of the impedance variable element can be extended. [Brief explanation of the drawing]

[0014] [Figure 1] A diagram showing an example configuration of a high-frequency power supply system. [Figure 2] A diagram showing an example of the circuit configuration of the DC voltage detection unit. [Figure 3] A diagram showing other configuration examples of matching circuits. [Figure 4]A flowchart for explaining the start timing of a matching operation in the present embodiment. [Figure 5] A diagram for performing a comparative explanation between the matching operation in the present embodiment and the matching operation of a comparative example. [Description of Embodiments for Carrying Out the Invention]

[0015] Hereinafter, embodiments of the impedance matcher according to the present disclosure will be described with reference to the drawings.

[0016] (Embodiment) Figure 1 is a diagram showing a configuration example of a high-frequency power supply system.

[0017] The high-frequency power supply system 1 is an apparatus that outputs high-frequency power having a fundamental frequency (frequency of the fundamental wave) in the RF (Radio Frequency) band from a high-frequency power supply 10, and supplies the high-frequency power to a load 50 (for example, a plasma processing apparatus) via an impedance matcher 30.

[0018] In the present specification, the voltage component of the high-frequency power is referred to as high-frequency voltage, and the current component of the high-frequency power is referred to as high-frequency current. Further, the high-frequency voltage traveling from the high-frequency power supply 10 toward the load 50 is defined as traveling wave voltage VF, the high-frequency voltage reflected from the load 50 side and returning to the high-frequency power supply 10 is defined as reflected wave voltage VR, the high-frequency power traveling from the high-frequency power supply 10 toward the load is defined as traveling wave power PF, and the high-frequency power reflected from the load side and returning to the high-frequency power supply 10 is defined as reflected wave power PR. In Figure 1, the reflected wave voltage VR and the reflected wave power PR are represented by broken lines.

[0019] Further, in the present specification, the power value of the traveling wave power PF is defined as traveling wave power value pf, the power value of the reflected wave power PR is defined as reflected wave power value pr, and the power value obtained by subtracting the reflected wave power value pr from the traveling wave power value pf is defined as load-side power value pL.

[0020] Further, in this specification, the reflection coefficient represented by the ratio of the reflected wave voltage VR to the traveling wave voltage VF (reflected wave voltage VR / traveling wave voltage VF) is denoted as ρ, and the absolute value (magnitude) of the reflection coefficient ρ is denoted as Γ. In practice, the reflection coefficient ρ is calculated as reflected wave voltage detection signal vr / traveling wave voltage detection signal vf using the traveling wave voltage detection signal vf and the reflected wave voltage detection signal vr described later.

[0021] Further, the high-frequency power supply 10 can reduce the reflected wave power value pr by changing the frequency of the output traveling wave power PF (traveling wave voltage VF). Hereinafter, this function is referred to as "frequency matching". When the frequency matching operation is performed, the fundamental frequency of the traveling wave voltage VF is not constant but varies, and the term "fundamental frequency" is used to include such cases where the fundamental frequency varies.

[0022] Further, the high-frequency power supply 10 may perform frequency modulation control, for example, to reduce the reflected wave power value pr caused by intermodulation distortion (hereinafter, IMD: InterModulation Distortion). Even when frequency modulation control is performed, the fundamental frequency of the traveling wave voltage VF is not constant but varies, and the term "fundamental frequency" is used.

[0023] The high-frequency power supply 10 performs feedback control so that the error between the traveling wave power value pf and the target power value pt decreases. Such power control is referred to as traveling wave power constant control (PF constant control).

[0024] Note that it is also possible to perform feedback control so that the error between the load-side power value pL and the target power value pt decreases. Such power control is referred to as load-side power constant control (PL constant control). However, in the following description, the case where traveling wave power constant control is mainly performed will be described as an example.

[0025] The traveling wave voltage VF has a relatively high fundamental frequency suitable for plasma generation, for example. The fundamental frequency is, for example, 40.68 MHz. Of course, the fundamental frequency is not limited to 40.68 MHz; it may be a frequency in the industrial RF band, such as 13.56 MHz or 27.12 MHz.

[0026] The traveling wave voltage VF may have a relatively low fundamental frequency suitable for ion acceleration, for example. In this case, the fundamental frequency is, for example, 400 kHz. Of course, the fundamental frequency is not limited to 400 kHz and may be other frequencies. Thus, the fundamental frequency of the traveling wave voltage VF can be various frequencies depending on the application.

[0027] As shown in Figure 1, the high-frequency power supply system 1 includes a high-frequency power supply 10 and an impedance matching unit 30.

[0028] The high-frequency power supply system 1 may use multiple (for example, two) high-frequency power supplies 10. For example, it may use a first high-frequency power supply with a fundamental frequency of 40.68 MHz for the traveling wave power PF (traveling wave voltage VF) and a second high-frequency power supply with a fundamental frequency of 400 kHz for the traveling wave power PF (traveling wave voltage VF). In this case, the first high-frequency power supply will supply high-frequency power to the load 50 via a first impedance matching device, and the second high-frequency power supply will supply high-frequency power to the load 50 via a second impedance matching device. However, in this embodiment, as shown in Figure 1, the case in which the high-frequency power supply system 1 uses one high-frequency power supply 10 will be explained as an example.

[0029] The high-frequency power supply 10 amplifies the high-frequency signal output from an oscillator (not shown) and outputs high-frequency power (forward wave power) having an output frequency in the RF band, which is supplied to the load 50. The high-frequency power output from the high-frequency power supply 10 is supplied to the load 50 via a transmission line 71, an impedance matching unit 30, and a transmission line 72. The transmission line 71 can be, for example, a coaxial cable or coaxial tube. The transmission line 72 can be, for example, a load connection member made of shielded copper plates. The length of the transmission lines 71 and 72 will vary depending on the environment and operating conditions to which the high-frequency power supply system 1 is applied.

[0030] The impedance matching device 30 matches the impedance between the high-frequency power supply 10 and the load 50. More specifically, if the impedance seen from the output terminal of the high-frequency power supply 10 towards the high-frequency power supply 10 side (output impedance) is designed to be, for example, 50Ω, and the high-frequency power supply 10 is connected to the high-frequency power supply side (e.g., input terminal) of the impedance matching device 30 via a transmission line 71 with a characteristic impedance of 50Ω, then the impedance matching device 30 converts the impedance seen from the high-frequency power supply side (e.g., input terminal) towards the load 50 side to 50Ω.

[0031] Load 50 is, for example, a plasma processing apparatus. A plasma processing apparatus is equipped with a processing section and is used to process (etch, CVD, etc.) workpieces such as wafers and liquid crystal substrates that are brought into the processing section. To process the workpiece, load 50 introduces a plasma discharge gas into the processing section and applies high-frequency power (high-frequency voltage) supplied from a high-frequency power supply 10 to the plasma discharge gas, thereby discharging the plasma discharge gas and changing it from a non-plasma state to a plasma state. The workpiece is then processed using the plasma.

[0032] <Details of Impedance Matching Device 30> The impedance matching unit 30 includes a matching unit sensor 31, a matching circuit 32, a first drive unit 33, a second drive unit 34, a first position detection unit 35, a second position detection unit 36, a load information calculation unit 37, a DC voltage detection unit 38, a matching control unit 39, and a storage unit 43. While the input terminal 301 and output terminal 302 of the impedance matching unit 30 are typically provided with input and output terminals, these are not shown in the illustration.

[0033] The matching sensor 31 is located on the high-frequency power supply side of the impedance matching circuit 30 (for example, the input terminal 301 (the stage before the matching circuit 32)) and detects information for calculating the load-side impedance Z as seen from the high-frequency power supply side (for example, the input terminal 301) of the impedance matching circuit 30 to the load 50 side, or information for calculating the reflection coefficient ρ on the high-frequency power supply side (for example, the input terminal 301) of the impedance matching circuit 30. Since the load-side impedance Z and the reflection coefficient ρ are mutually convertible, either one may be detected.

[0034] When calculating the load-side impedance Z, for example, a voltage detector and a current detector are used as the matching sensor 31. In this case, the voltage at the input terminal of the impedance matching device 30 is detected by the voltage detector, and a voltage detection signal vm is output as the detection signal. In addition, the current at the high-frequency power supply side (for example, the input terminal 301) of the impedance matching device 30 is detected by the current detector, and a current detection signal im is output as the detection signal. The voltage detection signal vm and the current detection signal im are output to the load information calculation unit 37.

[0035] When calculating the reflection coefficient ρ on the high-frequency power supply side (e.g., input terminal 301) of the impedance matching unit 30, a directional coupler is used as the matching unit sensor 31, for example. In this case, the forward wave voltage VF output from the high-frequency power supply 10 is detected, and a forward wave voltage detection signal vfm is output as the detection signal. At the same time, the reflected wave voltage VR that is reflected back from the load 50 side is detected, and a reflected wave voltage detection signal vrm is output as the detection signal. The forward wave voltage detection signal vfm and the reflected wave voltage detection signal vrm are output to the load information calculation unit 37.

[0036] An A / D converter (not shown) may be provided between the matching sensor 31 and the load information calculation unit 37. Furthermore, a filter for removing unwanted signal components (e.g., harmonic components) may be provided between the matching sensor 31 and the load information calculation unit 37. The filter type can be selected as appropriate.

[0037] The matching circuit 32 is provided between the matching sensor 31 and the load 50. This matching circuit 32 is equipped with an impedance variable element, such as a variable capacitor (also called a variable capacitor) whose capacitance can be changed, and the variable value of the impedance variable element (capacitance in the case of a variable capacitor, inductance in the case of a variable inductor) is changed by a command from the matching control unit 39, which will be described later, so that the load side impedance Z of the impedance matching unit 30, as seen from the high-frequency power supply side (for example, the input terminal) to the load 50 side, can be adjusted.

[0038] Furthermore, the impedance Z' viewed from the output terminal of the high-frequency power supply 10 towards the load 50 is approximately the same as the load-side impedance Z. Strictly speaking, the two differ depending on the length of the transmission line 71, etc., but in this embodiment, the error is considered to be within an acceptable range for practical purposes.

[0039] In some cases, a variable inductor is provided as an impedance-variable element. Furthermore, a driving means such as a motor is provided to change the variable value of the impedance-variable element according to a command from the matching control unit 39. In addition to the impedance-variable element, an inductor with a fixed inductance is often provided. Also, a capacitor with a fixed capacitance may be provided.

[0040] The matching circuit 32 shown in Figure 1 is an example of a matching circuit. The matching circuit 32 in Figure 1 has a first variable capacitor 321 provided between the output terminal of the matching sensor 31 and ground, a second variable capacitor 322 provided between the output terminal of the matching sensor 31 and the load 50, and an inductor 323 with a fixed inductance provided between the second variable capacitor and the load 50. The capacitance of the first variable capacitor 321 will be represented as C1, and the capacitance of the second variable capacitor 322 will be represented as C2.

[0041] The first variable capacitor 321 and the second variable capacitor 322 are variable capacitors of a type that change capacitance by changing the relative positions of electrodes using a driving means such as a motor. For example, as described in Patent Documents 1 and 2, the electrodes of a variable capacitor are composed of a fixed electrode and a movable electrode, and the opposing area of ​​the electrodes changes when the position of the movable electrode is changed using a driving means such as a motor. Of course, variable capacitors are not limited to this type. For example, there may be a type in which the distance between electrodes changes when the position of the movable electrode is changed.

[0042] In such a first variable capacitor 321 and second variable capacitor 322, the position of the movable electrode changes by rotating a rotating shaft connected to the movable electrode using a driving means such as a motor. Therefore, the position of the movable electrode can be determined by detecting the rotation angle of the rotating shaft. The rotation angle of the rotating shaft can be detected, for example, using an encoder. In other words, the positional relationship of the electrodes can be detected by detecting the rotation angle of the rotating shaft.

[0043] The axis of rotation is designed, for example, to change the capacitance from a minimum to a maximum value in 10 rotations (3,600 degrees). However, in practice, taking into account the variation in the capacitance of the variable capacitor, it is designed to allow 10+α rotations (for example, 12 rotations), and the predetermined capacitance is achieved in 10 of those rotations.

[0044] For example, in the case of a variable capacitor with a catalog value of a minimum capacitance of 100pF and a maximum capacitance of 1,300pF, it is designed so that 10 turns result in a capacitance of 200 to 1,200pF. Therefore, the ranges of 100-200pF and 1,200-1,300pF are not used in matching operation. In other words, when matching operation is performed, 200pF becomes the minimum capacitance and 1,200pF becomes the maximum capacitance.

[0045] Therefore, when performing matching operation, the rotation angle of the rotation axis when the capacitance is 200pF is set as 0 degrees for control purposes. In practical terms, for example, the rotation angle obtained by subtracting one rotation from the rotation angle of the rotation axis when the minimum capacitance of the variable capacitor (100pF) is used is set as 0 degrees for control purposes.

[0046] Similarly, the rotation angle of the axis of rotation when the capacitance is 1,200 pF is set to 3,600 degrees for control purposes. In practical terms, for example, the rotation angle of the axis of rotation when the variable capacitor has its structurally maximum capacitance (1,300 pF) can be set to 3,600 degrees for control purposes by subtracting one rotation from the rotation angle of the axis of rotation when the capacitor has its structural maximum capacitance.

[0047] Because of this relationship, in order to set the rotation angle of the rotation axis to 0 degrees for control purposes, the rotation angle of the rotation axis should first be set to the rotation angle that results in the minimum capacitance structurally (structural 0 degrees), and then rotated to the control-oriented 0 degrees. Note that when the rotation axis is rotated so that the capacitance is the minimum capacitance, the rotation will structurally stop when it reaches the rotation angle corresponding to the minimum capacitance. Therefore, this rotation angle is considered to be the structural 0 degrees.

[0048] Furthermore, to set the rotation angle of the rotating shaft to a controllable 3,600 degrees, the rotation angle of the rotating shaft should first be set to the rotation angle corresponding to the structurally maximum capacitance, and then the rotation angle obtained by subtracting 1 rotation should be set to the controllable 3,600 degrees. Note that when the rotating shaft is rotated to achieve the maximum capacitance, the rotation will structurally stop when it reaches the rotation angle corresponding to the maximum capacitance. Therefore, this rotation angle is set to the structurally maximum rotation angle.

[0049] This allows the capacitance of the variable capacitor to be changed within a predetermined range. This operation is performed after the variable capacitor is initially installed or after it has been replaced. By performing this operation, the relationship between the structural rotation angle of the variable capacitor's rotation axis and the control rotation angle can be set.

[0050] Note that it is sufficient to know either 0 degrees or 3,600 degrees for control purposes. Therefore, in this embodiment, the following explanation will proceed assuming that 0 degrees for control purposes is set.

[0051] Furthermore, the variable capacitor is not limited to those that change capacitance by changing the relative positions of the electrodes. For example, it may also be a variable capacitor of the type that changes the overall capacitance by connecting multiple capacitors in parallel with a switch and changing the state of the switch (ON / OFF).

[0052] The first drive unit 33 changes the position of the movable electrode of the first variable capacitor 321. The second drive unit 34 changes the position of the movable electrode of the second variable capacitor 322. Such a first drive unit 33 and second drive unit 34 are examples of the drive means of the present invention.

[0053] The first drive unit 33 and the second drive unit 34 each consist of a motor and a driver for driving that motor. The output shaft of the motor is connected to the rotating shaft of the variable capacitor, so that when the output shaft of the motor rotates, the rotating shaft of the variable capacitor rotates, and the position of the movable electrode changes as a result of this rotation.

[0054] The motor is, for example, a stepping motor. Of course, other types of motors (such as servo motors) can also be used, but in this embodiment, we will describe the case in which a stepping motor is used. Here, a stepping motor is a motor that rotates by moving in fixed increments of angle, and the corresponding driver receives the pulse signal output from the control unit as a command signal and operates the stepping motor based on that command signal.

[0055] When using a stepping motor in this way, it is easiest to represent the position of the movable electrode in terms of the number of steps corresponding to the number of pulse signals supplied to the stepping motor. For example, if the rotation angle of the rotating shaft rotates from 0 to 3,600 degrees (10 rotations), and the stepping motor needs to be changed by 1,000 steps, the position of the movable electrode can be represented in terms of 0 to 1,000 steps.

[0056] The first position detection unit 35 detects the rotation angle of the first drive unit 33 and includes, for example, an encoder. The detected rotation angle is output to the matching control unit 39 as rotation angle information Dc1. Similarly, the second position detection unit 36 ​​detects the rotation angle of the second drive unit 34 and includes, for example, an encoder. The detected rotation angle is output to the matching control unit 39 as rotation angle information Dc2.

[0057] Such a first position detection unit 35 and a second position detection unit 36 ​​are examples of the position acquisition means of the present invention.

[0058] As described above, the rotation angles of the first drive unit 33 and the second drive unit 34 indirectly represent the position of the movable electrode of the variable capacitor. Therefore, by detecting the rotation angle of the first drive unit 33, the position of the movable electrode of the variable capacitor can be detected. As described above, when using a stepping motor, the position of the movable electrode of the variable capacitor may be managed by the number of steps.

[0059] For example, when the rotation angle of the rotation axis is 0 degrees for control purposes, the capacitance is at its minimum for control purposes, so the position of the movable electrode of the variable capacitor at this time can be set to step 0. Also, when the rotation angle of the rotation axis is 3,600 degrees for control purposes, the capacitance is at its maximum for control purposes, so the position of the movable electrode of the variable capacitor at this time can be set to step 1,000. Of course, the 0 to 1,000 steps exemplified above are just examples, and a configuration with, for example, 0 to 5,000 steps could also be used.

[0060] Furthermore, as can be seen from the above, the position of the movable electrode, the rotation angle of the variable capacitor's rotation axis, and the rotation angle of the motor all correspond to the capacitance of the variable capacitor. Therefore, by detecting any of these, the capacitance of the variable capacitor can be estimated.

[0061] In this embodiment, as an example, the capacitance of the variable capacitor is estimated based on the rotation angle of the motor. The rotation angle of the motor can be expressed in terms of steps. Therefore, if the minimum capacitance for control is set to 0 steps and the maximum capacitance to 1,000 steps, the capacitance of the variable capacitor can be expressed in terms of steps, such as 0 to 1,000 steps.

[0062] Furthermore, in the above example, the structural minimum capacitance is the capacitance at a rotation angle obtained by rotating the motor +1 from a control-defined rotation angle of 0 degrees, which corresponds to -100 steps in the control. Similarly, the structural maximum capacitance is the capacitance at a rotation angle obtained by rotating the motor +1 from a control-defined rotation angle of 3,600 degrees, which corresponds to 1,100 steps in the control.

[0063] The load information calculation unit 37 can calculate the reflection coefficient ρ or the load-side impedance Z based on the detection signal output from the matching sensor 31. When this information is used as load information IFL, the load information calculation unit 37 can output the load information IFL to the matching control unit 39. It is not necessary to calculate all of the load information IFL. For example, if the load-side impedance Z is not used for control, it does not need to be calculated.

[0064] Furthermore, the load information calculation unit 37 can calculate and output the forward wave power value pf, reflected wave power value pr, load-side power value pL, and absolute reflection coefficient Γ based on the detection signal output from the matching unit sensor 31. This information related to high-frequency power is necessary for output control of the high-frequency power supply 10, but it can also be output externally as monitoring information, for example.

[0065] Furthermore, the above-mentioned information related to high-frequency power can be used to control the impedance matcher 30. For example, the impedance matcher 30 may be configured to start matching operation when the forward wave power value pf exceeds a predetermined threshold. Of course, it may also be configured to start matching operation based on other signals (e.g., forward wave voltage detection signal vfm, reflected wave voltage detection signal vrm, etc.). Note that it is not necessary to calculate all of the above-mentioned information related to high-frequency power. For example, if the load-side power value pL is not used for control, it is not necessary to calculate the load-side power value pL.

[0066] The method for calculating the information shown above is publicly known, so a detailed explanation will be omitted, but for example, it can be calculated as follows.

[0067] (1) Reflectance coefficient ρ The reflection coefficient ρ can be calculated, for example, using the reflected wave voltage detection signal vr / forward wave voltage detection signal vf. The absolute value (magnitude) of the reflection coefficient ρ is denoted as the absolute reflection coefficient Γ.

[0068] (2) Load side impedance Z The load impedance Z can be calculated, for example, from the voltage detection signal vm and the current detection signal im. Alternatively, the load impedance Z can be calculated based, for example, on the magnitude of the voltage detection signal vm, the magnitude of the current detection signal im, and the phase difference θm between the voltage detection signal vm and the current detection signal im.

[0069] Note that the reflection coefficient ρ and the load-side impedance Z are mutually convertible. Therefore, in the following, we may explain only the reflection coefficient ρ or the load-side impedance Z.

[0070] (3) Power value of the traveling wave pf The forward wave power value pf can be calculated, for example, using the forward wave voltage detection signal vfm^2 / R (where R is the gain equivalent to the resistance value).

[0071] (4) Reflected wave power value pr The reflected wave power value pr can be calculated, for example, using the reflected wave voltage detection signal vrm^2 / R (where R is the gain equivalent to the resistance value).

[0072] (5) Load-side power value pL The load-side power value pL can be calculated based on the forward wave power value pf and the reflected wave power value pr calculated above. For example, the load-side power value pL can be calculated by subtracting the reflected wave power value pr from the forward wave power value pf.

[0073] (6) Absolute value of the reflection coefficient Γ The absolute value of the reflection coefficient Γ may be calculated based on the forward wave power value pf and the reflected wave power value pr. For example, the absolute value of the reflection coefficient Γ may be calculated by √(reflected wave power value pr / forward wave power value pf).

[0074] Figure 2 shows an example of the circuit configuration of the DC voltage detection unit 38. The DC voltage detection unit 38 detects the DC voltage VDC at the downstream stage of the matching circuit 32 (the output terminal of the impedance matcher 30). This DC voltage detection unit 38 includes an inductor 381, a capacitor 382, ​​and a voltage detection unit 383.

[0075] Inductor 381 is used to limit the AC component of the voltage downstream of the matching circuit 32, and generates a DC voltage at the connection point between inductor 381 and capacitor 382. Voltage detection unit 383 is configured to detect the DC voltage value vdc and output the detected DC voltage value vdc to the matching control unit 39. This allows the matching control unit 39 to detect the DC voltage value vdc downstream of the matching circuit 32. Note that the DC voltage VDC is usually a negative voltage. DC voltage detection unit 38 converts the DC voltage VDC to, for example, 0 to 10V.

[0076] The matching control unit 39 performs matching operations using load information IFL output from the load information calculation unit 37, rotation angle information Dc1 output from the first position detection unit 35, and rotation angle information Dc2 output from the second position detection unit 36. For example, it outputs command signals Sc1 and Sc2 to change the capacitance C1 of the first variable capacitor 321 and the capacitance C2 of the second variable capacitor 322 inside the matching circuit 32 so that the absolute value of the reflection coefficient Γ approaches the target absolute value of the reflection coefficient Γ0 (usually 0). In other words, it outputs command signals Sc1 and Sc2 to change the capacitance C1 of the first variable capacitor 321 and the capacitance C2 of the second variable capacitor 322 so that the reflected wave power is reduced.

[0077] Furthermore, the matching control unit 39 detects that plasma has been generated in the load 50 (plasma processing device) when the DC voltage value vdc acquired by the DC voltage detection unit 38 exceeds a predetermined threshold, and starts the matching operation after this detection.

[0078] The threshold value mentioned above is determined by factors such as the magnitude of the DC voltage VDC. For example, if plasma generation can be determined when the DC voltage VDC reaches approximately -30V, then the threshold value should be set accordingly. In the example above, since the DC voltage VDC is a negative voltage, the threshold value can be considered in absolute terms.

[0079] The first drive unit 33 and the second drive unit 34 rotate the rotation axes of the first variable capacitor 321 and the second variable capacitor 322 based on command signals Sc1 and Sc2 output from the matching control unit 39. By repeating this operation, the absolute value Γ approaches the target reflection coefficient absolute value Γ0 (usually 0). In other words, the reflected wave power decreases. Matching operation is performed by performing this operation.

[0080] There are various methods for matching the operation. For example, the capacitance C1 of the first variable capacitor 321 and the capacitance C2 of the second variable capacitor 322 can be calculated, and command signals Sc1 and Sc2 can be output to the first drive unit 33 and the second drive unit 34, using these capacitances as targets.

[0081] Even when performing such matching operations, there are various ways in which the command signals Sc1 and Sc2 are output. For example, if the difference between the current capacitance and the target capacitance is large, the capacitance between the two may be used as the target capacitance. Various other methods have also been disclosed, but the method of matching operation is not limited in this embodiment. In any case, the absolute value of the reflection coefficient Γ approaches the target absolute value of the reflection coefficient Γ0 (usually 0), in other words, the reflected wave power is controlled to be small.

[0082] The memory unit 43 is a storage means equipped with non-volatile memory, and can retain stored data even when power is not supplied, such as with an EEPROM. Note that the memory unit 43 is an example of a storage means of the present invention.

[0083] The matching control unit 39 can store position information of the movable electrodes and windings of the variable impedance element in the memory unit 43. The matching control unit 39 can also read the position information stored in the memory unit 43. Furthermore, as described above, the position information of the movable electrodes and windings of the variable impedance element can be used as values ​​converted to the number of steps (for example, 0 to 1,000 steps). The impedance matcher 30 is also equipped with a volatile memory (not shown) that can store information for temporary use. Note that the matching circuit is not limited to the configuration shown in Figure 1.

[0084] Figure 3 shows another example of a matching circuit configuration. The matching circuit 32a in Figure 3 has a first variable inductor 324 provided at the output terminal of the matching sensor 31, a second variable inductor 325 provided between the output terminal of the first variable inductor 324 and the load 50, and a capacitor 326 provided between the output terminal of the first variable inductor 324 and ground. The inductance of the first variable inductor 324 is denoted by L1, and the inductance of the second variable inductor 325 is denoted by L2. The capacitance of the capacitor 326 is a fixed value. Thus, it is also possible to use a variable inductor as an impedance variable element. In addition, although Figure 3 shows an example using a capacitor 326 with a fixed capacitance, a variable capacitor may be used instead of capacitor 326.

[0085] A variable inductor, for example, has a fixed winding and a movable winding, and its inductance can be changed by changing the positional relationship of the movable winding relative to the fixed winding. For example, a rotating shaft is connected to the movable winding, and when this rotating shaft is rotated by a driving means such as a motor, the positional relationship of the movable winding relative to the fixed winding changes, and the inductance changes. In other words, although there is a difference between capacitance and inductance, similar to a variable capacitor, the inductance, which is the object of control, can be changed by changing the positional relationship of the windings by a driving means such as a motor.

[0086] Therefore, as shown in Figure 3, the inductance L1 of the first variable inductor 324 can be detected by changing the relative position of the windings of the first variable inductor 324 using the first drive unit 33a and by detecting the rotation angle of the motor of the first drive unit 33a using the first position detection unit 35a. The detected rotation angle is output to the matching control unit 39 as rotation angle information DL1.

[0087] Similarly, the inductance L2 of the second variable inductor 325 can be detected by changing the relative position of the windings of the second variable inductor 325 using the second drive unit 34a and by detecting the rotation angle of the motor of the second drive unit 34a using the first position detection unit 36a. The detected rotation angle is output to the matching control unit 39 as rotation angle information DL2. Note that the first drive unit 33a, the second drive unit 34a, the first position detection unit 35a, and the second position detection unit 36a have the same configuration as the first drive unit 33, the second drive unit 34, the first position detection unit 35, and the second position detection unit 36 ​​shown in Figure 1, except that they control different objects. Therefore, their explanation is omitted.

[0088] Furthermore, similar to variable capacitors, the position of the movable winding, the rotation angle of the variable inductor's rotation axis, and the rotation angle of the motor all correspond to the inductance of the variable inductor. Therefore, by detecting any of these, the inductance of the variable inductor can be estimated. Thus, similar to variable capacitors, the inductance of a variable inductor can be expressed in terms of steps, for example, from 0 to 1,000 steps.

[0089] Although the rotation angle of the rotating shaft differs between variable inductors and variable capacitors, the concepts of minimum structural inductance and minimum controllable inductance are the same as those for minimum capacitance and minimum controllable capacitance of a variable capacitor.

[0090] In Figure 1, an example is shown where there are two variable capacitors in the matching circuit 32, but the number of variable capacitors is not limited. For example, there may be one variable capacitor, or there may be three or more variable capacitors. Similarly, in Figure 3, an example is shown where there are two variable inductors in the matching circuit 32, but the number of variable inductors is not limited. For example, there may be one variable inductor, or there may be three or more variable inductors. Although not shown in the illustration, the matching circuit 32 may also contain a mixture of one or more variable capacitors and one or more variable inductors.

[0091] Next, the start timing of the matching operation in this embodiment will be described.

[0092] Figure 4 is a flowchart illustrating the start timing of the matching operation in this embodiment.

[0093] <step1> The impedance matching unit 30 keeps each of its built-in variable impedance elements in standby mode at their initial positions.

[0094] <step2> The high-frequency power supply 10 outputs a traveling wave power PF.

[0095] <step3> The impedance matching control unit 39 of the impedance matching unit 30 monitors whether the DC voltage value vdc detected by the DC voltage detection unit 38 exceeds a predetermined threshold.

[0096] If it is determined that the DC voltage value vdc exceeds the threshold (Yes in Step 3), proceed to Step 4. If it is determined that the DC voltage value vdc does not exceed the threshold (No in Step 3), continue monitoring by repeating Step 3.

[0097] <step4> The impedance matching control unit 39 of the impedance matching unit 30 determines that plasma has been generated because the DC voltage value vdc has exceeded a threshold and starts the matching operation. Alternatively, a command signal may be given to the driving means (first drive unit 33, second drive unit 34, etc.) to reduce the reflected wave power after a predetermined delay time has elapsed from the time the absolute value of the DC voltage value vdc detected by the DC voltage detection circuit 38 becomes higher than a predetermined threshold. The reason for this will be explained.

[0098] If matching operation is performed while the plasma is unstable, the variable value of the impedance variable element will change while the load impedance is unstable. Therefore, performing matching operation may actually destabilize the plasma. Also, immediately after plasma generation, the plasma state is often unstable, but it can be expected that the plasma state will stabilize over time.

[0099] Therefore, as described above, when the DC voltage detected by the DC voltage detection circuit becomes higher than a predetermined threshold, a predetermined delay time has elapsed, and then a command signal is given to the driving means to start matching operation so that the reflected wave power decreases, thereby stabilizing the plasma.

[0100] Furthermore, if matching operation is performed in an unstable plasma state, the variable impedance element will rapidly follow the changes in load impedance, leading to increased mechanical wear of the variable impedance element and shortening its mechanical lifespan.

[0101] However, as mentioned above, if the matching operation is initiated after the plasma stabilizes, rather than immediately after the plasma is generated, mechanical wear of the impedance variable element can be reduced and the mechanical life of the impedance variable element can be extended.

[0102] Furthermore, when the absolute value of the DC voltage value vdc detected by the DC voltage detection circuit 38 becomes higher than a predetermined threshold, a predetermined delay time may elapse, after which the positional relationship of the electrodes or windings of the impedance variable element may be changed to a predetermined positional relationship, and then a command signal may be given to the driving means (first drive unit 33, second drive unit 34, etc.) so as to reduce the reflected wave power. The reason for this will be explained below.

[0103] As described above, plasma stabilization can be achieved simply by starting the matching operation after a predetermined delay time has elapsed from the moment the absolute value of the DC voltage value vdc detected by the DC voltage detection circuit 38 exceeds a predetermined threshold. However, instead of immediately performing the matching operation after a predetermined delay time has elapsed from the moment the absolute value of the DC voltage value vdc detected by the DC voltage detection circuit 38 exceeds a predetermined threshold, it is expected that plasma stabilization can be further achieved by first changing the positional relationship of the electrodes or windings of the impedance variable element to a predetermined positional relationship (for example, a positional relationship in which impedance is expected to match) and then starting the matching operation.

[0104] Figure 5 is a diagram illustrating a comparison between the matching operation in this embodiment and the matching operation in a comparative example. Figure 5(a) is an example of the operating trajectory of the variable impedance element when the matching operation is performed in this embodiment. Figure 5(b) is an example of the operating trajectory of the variable impedance element when the matching operation is performed in a comparative example.

[0105] In this example in Figure 5, the impedance-variable elements are the variable capacitors 321 and 322 shown in Figure 1, and it shows an example of the operating trajectory of the variable values ​​(C1, C2) of variable capacitors 321 and 322 after the forward wave power PF is output from the high-frequency power supply 10. The vertical axis on the left shows the power values ​​[W] of the forward wave power value pf and the reflected wave power value pr. In this example, the target power value pt of the forward wave power PF is shown as 1,000W. In Figures 5(a) and 5(b), the forward wave power value pf is shown as a solid line, and the reflected wave power value pr is shown as a dashed line.

[0106] The vertical axis on the right shows the variable values ​​(C1, C2) of variable capacitors 321 and 322 from 0 to 100%. In this example, 100% corresponds to 1,000 steps. In Figures 5(a) and 5(b), the variable value C1 of variable capacitor 321 is shown by a dashed line, and the variable value C2 of variable capacitor 322 is shown by a double-dashed line.

[0107] Furthermore, both Figure 5(a) and Figure 5(b) show that at the start (time 0 seconds), the forward wave power PF is not being output from the high-frequency power supply 10, and the variable capacitors 321 and 322 are waiting in their initial positions. This initial position is, for example, a position where plasma is easily generated. Also, in both Figure 5(a) and Figure 5(b), the value of the forward wave power pf begins to rise when the forward wave power PF is output from the high-frequency power supply 10 approximately 0.9 seconds after the start.

[0108] In this embodiment, as shown in Figure 5(a), when the forward wave power PF is output from the high-frequency power supply 10 (approximately 0.9 seconds after the start), the forward wave power value pf begins to rise. However, the variable values ​​of the variable capacitors 321 and 322 do not change immediately, but begin to change approximately 1.0 second after the start. This is because plasma is generated at this timing (approximately 1.0 second later), and the DC voltage value vdc detected by the DC voltage detection unit 38 is determined to have exceeded a predetermined threshold.

[0109] Subsequently, the variable value gradually shifts to one suitable for plasma generation. Then, approximately 9 seconds after the start, the traveling wave power PF begins to decrease, and approximately 9.4 seconds after the start, when the output is stopped, the variable value also changes accordingly.

[0110] In contrast, in the comparative example, as shown in Figure 5(b), when the traveling wave power PF is output from the high-frequency power supply 10 and the traveling wave power value pf begins to rise, the variable values ​​of the variable capacitors 321 and 322 begin to fluctuate almost simultaneously. Moreover, as can be seen by comparing it with Figure 5(a), the values ​​do not move towards a stable variable value after plasma generation, but rather undergo an unstable change. After plasma generation, the operation is substantially the same as in this embodiment (Figure 5(a)).

[0111] In the comparative example, as shown in Figure 5(b), the variable impedance element behaves erratically. This is because, as mentioned above, even though plasma has not yet been generated, the variable impedance element attempts to rapidly adapt to the change in impedance. This causes a sharp change in the relative positions of the electrodes or windings of the variable impedance element, which in turn makes the load impedance unstable. In some cases, this can even delay the generation of plasma.

[0112] Furthermore, as mentioned above, if the variable impedance element responds sharply to changes in impedance, the mechanical wear of the variable impedance element will accelerate, shortening its mechanical lifespan.

[0113] As can be seen from the explanation above, in this embodiment, the timing at which the DC voltage value vdc becomes higher than a predetermined threshold occurs after plasma is generated, and matching operation is started after detecting that plasma has been generated.

[0114] Specifically, after the DC voltage detected by the DC voltage detection circuit exceeds a predetermined threshold, a command signal is given to the driving means to change the variable value of the impedance variable element (for example, the relative position of electrodes or windings) using load information so that the absolute value of the reflection coefficient ρ approaches the target absolute value of the reflection coefficient Γ0 (usually 0), thereby performing a matching operation. In other words, a command signal is given to the driving means to change the variable value of the impedance variable element (for example, the relative position of electrodes or windings) so that the reflected wave power is reduced, thereby performing a matching operation.

[0115] This eliminates the need to change the variable value of the impedance variable element before plasma generation, thereby reducing the instability of the load impedance associated with changing the variable value of the impedance variable element. Furthermore, because the impedance variable element does not abruptly respond to changes in the load impedance before plasma generation, mechanical wear of the impedance variable element is reduced, extending its mechanical lifespan.

[0116] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Explanation of Symbols]

[0117] 1. High-frequency power supply system 10 High frequency power supply 31 Sensor for matching unit 32 Matching circuit 33 First drive unit 34 Second drive unit 35 First position detection unit 36 Second position detection unit 37 Load Information Calculation Unit 38 DC voltage detection unit 39 Control unit for matching unit 43 Storage section 30 Impedance Matching Devices 50 Load (Plasma Processing Equipment)

Claims

1. An impedance matching device is provided between a high-frequency power supply that supplies high-frequency power to a plasma processing apparatus, and the load, A matching circuit comprising at least one impedance-variable element having electrodes and windings, wherein the relative position of the electrodes or windings is variable, A driving means for changing the positional relationship of the electrode or the winding, A sensor for detecting information for calculating the load-side impedance as seen from the high-frequency power supply side to the load side in the impedance matching device, or information for calculating the reflection coefficient on the high-frequency power supply side in the impedance matching device, A calculation unit calculates the reflection coefficient or load-side impedance based on the information detected by the aforementioned sensor and outputs it as load information. A DC voltage detection circuit for detecting the DC voltage in the downstream stage of the matching circuit, A control unit provides the drive means with a command signal to change the relative position of the electrodes or windings using the load information after the absolute value of the DC voltage detected by the DC voltage detection circuit becomes higher than a predetermined threshold, so as to reduce the reflected wave power. An impedance matching device equipped with [specific features / features].

2. The control unit, When the absolute value of the DC voltage detected by the DC voltage detection circuit becomes higher than the predetermined threshold, a predetermined delay time has elapsed, after which the command signal is supplied to the driving means in such a way that the reflected wave power decreases. The impedance matching device according to claim 1.

3. The control unit, When the absolute value of the DC voltage detected by the DC voltage detection circuit becomes higher than the predetermined threshold, after a predetermined delay time has elapsed, the relative positions of the electrodes or windings are changed to a predetermined relative position, and then a command signal is given to the driving means so that the reflected wave power decreases. The impedance matching device according to claim 1.

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