JP2008243670A - High-frequency power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem where, since a directional coupler has a frequency-amplitude characteristic where a reflected level detection level in a high frequency range is set larger than the actual level, when a reflected wave having high frequencies such as higher harmonics is generated, the output of an amplification part 11 is suppressed more than necessary in order to protect an amplification element in a high-frequency power supply. <P>SOLUTION: The high-frequency power supply with an amplification part 11 used as a supply source of high-frequency power to supply the high-frequency power for plasma generation to a load includes: a directional coupler 13 outputting a reflected wave detection signal; an amplification characteristic conversion part 20 having a characteristic reverse to the frequency-amplitude characteristic of the reflected wave detection signal; and an output power control part 19 controlling the output of an high-frequency output means by using a reflected wave detection signal obtained by converting the frequency-amplitude characteristic. Even when a reflected wave in a high-frequency range is detected, the output can be controlled at an appropriate level by bringing the detection level of the reflected wave close to the actual level. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a high-frequency power supply apparatus that supplies power to a load such as a plasma processing apparatus that performs plasma etching and plasma CVD, for example.

  As shown in FIG. 4, as a plasma processing system that performs processing (plasma etching, plasma CVD, etc.) on a workpiece such as a wafer or a liquid crystal substrate using plasma generated using high-frequency power, high-frequency waves with different frequencies are used. There are plasma processing systems that use electrical power.

FIG. 4 is a block diagram showing a connection relationship of a plasma processing system using high frequency power of different frequencies.
In FIG. 4, a conventional first high frequency power supply apparatus 10 includes a first high frequency power (hereinafter referred to as a first high frequency power) applied to a load 5 via a transmission line 2, a first matching unit 3, and a connection unit 4. It is a power supply device for supplying. The output frequency of the first high-frequency power supply device 10 is a first frequency f1, and the period of the first frequency is t1. The second high-frequency power supply device 6 is a power supply for supplying second high-frequency power (hereinafter referred to as second high-frequency power) to the load 5 via the transmission line 7, the matching unit 8, and the load connection unit 9. Device. The output frequency of the second high-frequency power supply device 6 is the second frequency f2, and the period of the second frequency is t2. The first frequency is higher than the second frequency. For example, the first frequency is a frequency such as 13.56 MHz, 27.12 MHz, or 40.68 MHz. The second frequency is a frequency such as 400 kHz or 2 MHz. As described above, generally, this type of high-frequency power supply device outputs high-frequency power having a frequency of several hundred kHz or more. Note that when viewed from the first high-frequency power supply device 10, the first frequency is referred to as a fundamental frequency, and when viewed from the second high-frequency power supply device 6, the second frequency is referred to as a fundamental frequency.

  The first high frequency power output from the first high frequency power supply device 10 is mainly used to generate plasma in the load 5. The second high-frequency power output from the second high-frequency power supply device 6 is used as a bias for efficiently performing processing (plasma etching, plasma CVD, etc.) in the load 5. Two types of high frequencies output from these two high frequency power supply devices are superimposed and applied to the electrodes in the load 5.

  The output control of the high-frequency power supply device is a method of controlling the traveling wave power output by each of them (referred to as traveling wave power constant control) or a method of controlling the load side power obtained by subtracting the reflected wave power from the traveling wave power ( Load side constant power control) is used.

Hereinafter, the first high frequency power supply device 10, the matching unit 3, and the load 5 will be mainly described. In the following description, a case of traveling wave power constant control will be described as an example.
The matching unit 3 has a power source side impedance Zo (usually 50Ω) viewed from the input end 301 of the matching unit 3 via the transmission line 2 and a load 5 side viewed from the input end of the matching unit 3. It is a device used for the purpose of impedance matching between the high frequency power supply device and the load 5 by matching the load side impedance ZL (impedance of the matching device 3, load connecting portion 4 and load 5).

  The matching unit 3 includes a variable impedance element (for example, a variable capacitor, a variable inductor, etc.) (not shown) inside, and the variable impedance element described above so that impedance matching is performed between the high frequency power supply device 10 and the load 5. It has a function of changing the impedance. More specifically, for example, the impedance (output impedance) when the high frequency power supply device 10 side is viewed from the output end 101 of the high frequency power supply device 10 is designed to be 50Ω, for example, and the high frequency power supply device is a transmission line 2 having a characteristic impedance of 50Ω. Assuming that the impedance matching unit 3 is connected to the input end of the impedance matching unit 3, the impedance matching unit 3 changes the load side impedance ZL as viewed from the load 5 side from the input end 301 of the impedance matching unit 3 to 50Ω. Change the impedance of the element.

  The load 5 is generally called a plasma processing apparatus, and includes a chamber having electrodes therein, and processes a workpiece such as a wafer and a liquid crystal substrate carried into the chamber (etching, CVD, etc.). It is a device for. In order to process the workpiece, the load 5 introduces a plasma discharge gas into the chamber and applies high frequency power (voltage) supplied from two high frequency power supply devices to the internal electrodes, thereby A high-frequency electric field is generated between them, and the plasma discharge gas is discharged into a plasma state. The workpiece is processed using this plasma.

Next, the configuration of the high frequency power supply device 10 will be described.
FIG. 5 is a block diagram illustrating a configuration example of a general high-frequency power supply device.
The amplifying unit 11 outputs high-frequency power having an output frequency in the radio frequency band, and the output is controlled by an output power control unit 19 described later. The amplifying unit 11 includes a DC power supply unit, an oscillator, an amplifying element, and the like (not shown). The amplifying unit 11 has various methods, which are omitted here. For example, an FET or a transistor is used as the amplifying element of the amplifying unit 11. The high frequency power amplified in the amplifying unit 11 is supplied to the load 5 mainly through the low-pass filter 12 and the directional coupler 13 for removing harmonics.

  Further, the directional coupler 13 outputs a traveling wave detection signal (a signal related to the traveling wave) and also outputs a reflected wave detection signal (a signal related to the reflected wave). The detection unit 14 on the traveling wave side detects the traveling wave detection signal, converts it to direct current, and outputs it as a traveling wave voltage Vf. Further, the detection unit 15 on the reflected wave side detects the reflected wave detection signal, converts it to direct current, and outputs it as a reflected wave voltage Vr. The traveling wave power calculation unit 16 calculates the traveling wave power value Pf based on the traveling wave voltage Vf, and the reflected wave power calculation unit 17 calculates the reflected wave power value Pr based on the reflected wave voltage Vr.

The output power control unit 19 compares the output power set value Pset of the high frequency power set in the output power setting unit 18 with the traveling wave power value Pf calculated in the traveling wave power calculation unit 16, and both are equal. As described above, the output power of the high-frequency power is controlled to be constant by controlling the output power of the amplifying unit 11.
Further, as will be described later, the output power control unit 19 performs control to suppress the output power of the amplification unit 11 in accordance with the detected level of the reflected wave. The output power set value Pset may be input from an external device. As such a high-frequency power supply device, there is one as described in Patent Document 1.

Next, the reflected wave will be described.
(1) About the reflected wave generated until the completion of the matching operation In the configuration as described above, even if the reflected wave is generated, the reflected wave is reduced by the matching unit 3. The traveling wave voltage is stably detected, and the reflected wave is controlled to be minimum. However, a reflected wave is generated until the matching operation by the matching device 3 is completed. For example, when the impedance of the load greatly changes instantaneously, the matching operation by the matching unit 3 cannot catch up with the change speed of the load impedance, and thus the reflected wave becomes large until the matching operation is completed. In addition, although the reflected wave at this time is mainly due to the fundamental frequency, it is also affected by the reflected wave due to other frequencies.

(2) About reflected waves due to harmonics Further, in a non-linear load such as the above-described plasma processing apparatus, harmonics are generated, and the harmonics return from the load side to the high-frequency power supply device 10 side. High frequency reflected waves are generated.

(3) About reflected waves around the fundamental frequency As shown in FIG. 4, when two high-frequency power supply devices are used, the frequency of the second high-frequency power for bias (second frequency) is usually the frequency of the first high-frequency power. The frequency is lower than (first frequency). In such a case, if there is a large difference between the output frequencies of the two high frequency power supply devices, a large reflected wave is generated on the first high frequency power supply device 10 side due to the second high frequency power.

  This is because the plasma state changes as if it was modulated at the second frequency. In other words, this is because the impedance of the load 5 changes so as to be modulated at the second frequency. Therefore, a part of the traveling wave output from the first high-frequency power supply device 10 is reflected by the influence of the modulation having the same period as the second frequency, so that a reflected wave is generated.

  At this time, it is sufficient that the first matching unit 3 can perform impedance matching following the modulation of the second frequency. However, as described above, the impedance matching is performed by driving a variable impedance element (for example, a variable capacitor, a variable inductor, etc.). Therefore, it is impossible to follow a high-speed change such as the modulation of the second frequency, and the reflected wave cannot be reduced. Therefore, the generated reflected wave returns to the first high frequency power supply device 10 side.

  In addition, since this reflected wave is generated by a phenomenon in which the first high-frequency power is modulated with the second high-frequency power, the frequency component of the reflected wave is mainly composed of the first frequency and the second frequency as the spurious. The components are superimposed. Therefore, the frequency component of the reflected wave occupies most of the first frequency and the frequencies around the first frequency.

  By the way, as shown in FIG. 5, the high frequency power supply device is usually provided with a low pass filter 12 on the output side of the amplifying unit 11. However, since the low-pass filter 12 is a low-pass filter that removes harmonic components for the main first frequency, frequency components around the first frequency cannot be removed. Therefore, it is impossible to remove the second frequency component superimposed as spurious on the first frequency which is the main component.

  Therefore, the generated reflected wave passes through the filter of the first high-frequency power supply device 10 and enters the high-frequency power supply device 10, which adversely affects the amplification element in the high-frequency power supply device. In addition, the generated reflected wave power may be about 30% of the output, so the influence is great.

  On the other hand, when viewed from the second high frequency power supply device 6, the reflected wave having the frequency component of the first frequency returns to the high frequency power supply device 6 side. However, since the filter provided in the high-frequency power supply device 6 is a low-pass filter that removes harmonic components with respect to the main second frequency, the frequency component of the first frequency can be removed. Therefore, the second high frequency power supply device 6 side is hardly affected by the first high frequency power output from the first high frequency power supply device 10.

  Thus, when a plurality of high frequency power supply devices having different output frequencies supply high frequency power to one load 5, the high frequency power supply device having a higher output frequency is affected by the high frequency power supply device having a lower output frequency. Reflected waves are generated.

(4) About reflected wave by frequency mixing action The various frequencies mentioned above generate a new frequency component simultaneously by the frequency mixing action, and the reflected wave of another frequency is generated.

(5) Protection against reflected waves As described above, various reflected waves are generated. When a reflected wave is generated, a traveling wave and a reflected wave are combined on the transmission line to generate a standing wave. At this time, when the reflected wave is large and applied to the amplifying unit 11 in a state where the level of the standing wave is high, the maximum rating (power, voltage, current) of the amplifying element (eg, FET, transistor) in the amplifying unit 11 is large. There is a risk that the amplifying element will be damaged.

Therefore, when a reflected wave is generated in order to protect the amplifying element in the amplifying unit 11, the output power control unit 19 performs output control according to the level of the reflected wave at high speed, and the traveling wave and the reflected wave. As a result, control is performed so as not to exceed the maximum rating of the amplifying element. That is, control for suppressing the output power of the amplifying unit 11 is performed according to the level of the reflected wave.
For example, when the power value obtained by adding the reflected wave power value Pr calculated in the reflected wave power calculation unit 17 to the traveling wave power value Pf calculated in the traveling wave power calculation unit 16 exceeds a predetermined value, In order to protect the amplifying element in the amplifying unit 11, control is performed to reduce the output of the amplifying unit 11 in accordance with a power value exceeding a predetermined value. That is, the output power control unit 19 performs control to suppress the output of the amplification unit 11.

Therefore, the output power control unit 19 depends on the level of the reflected wave in order to protect the function of setting the output of the amplification unit 11 to the output power set value Pset of the high frequency power and the amplification element in the amplification unit 11. Thus, it has two functions of suppressing the output of the amplifying unit 11.
JP 2003-143861 A JP 2002-252207 A

  If a low-pass filter is provided between the amplifying unit 11 and the directional coupler 13 as in the prior art, reflected waves due to harmonics can be removed. Therefore, in order to protect the amplification unit 11 from the reflected wave, it can be considered that the reflected wave that passes through the low-pass filter 12 and reaches the amplification unit 11 may be protected. Therefore, it may be considered that a low-pass filter similar to the low-pass filter 12 is provided in the output stage on the reflected wave side of the directional coupler 13, and the amplifying unit 11 may be protected according to the output level of the low-pass filter. it can. For example, Patent Document 2 discloses a document in which a similar low-pass filter is provided in the output stage on the reflected wave side of the directional coupler 13.

  However, as described above, the reflected wave is generated not only in the vicinity of the first frequency and the first frequency but also in a wide range of frequencies including harmonic frequencies. Therefore, if an abnormality occurs in the low-pass filter 12 on the output side of the amplifying unit 11 and the function of the filter is lost, a reflected wave due to the harmonics affects the amplifying unit 11.

  The low-pass filter basically has a higher attenuation rate as the frequency becomes higher. However, as shown in FIG. 6, the attenuation rate may once increase in the process of increasing the frequency. The expected attenuation factor may not be obtained. Therefore, even if a low-pass filter is provided between the amplifying unit 11 and the directional coupler 13, there is a possibility that the amplifying unit 11 is affected if the reflected wave due to the harmonics is large.

  Therefore, as protection of the amplification unit 11, it is preferable to target reflected waves in a wide range of frequencies including harmonic frequencies. Therefore, a case where protection according to the output of the directional coupler 13 is performed in a configuration in which a similar low-pass filter is not provided in the output stage on the reflected wave side of the directional coupler 13 will be described below.

  The directional coupler 13 outputs a traveling wave detection signal and a reflected wave detection signal according to the frequency amplitude characteristics. Since the directivity is secured around the fundamental frequency, detection of the reflected wave of the fundamental frequency on the traveling wave side is suppressed. Further, detection of the traveling wave of the fundamental frequency on the reflected wave side is suppressed.

  However, the directional coupler 13 (for example, the CM directional coupler 13) generally deteriorates the degree of directional signal separation and the degree of coupling when the frequency exceeds a certain frequency. For this reason, in a frequency component higher than the fundamental frequency such as a harmonic wave, both the traveling wave and the reflected wave are detected at a level larger than the actual level. For example, at a frequency at which the degree of coupling of 20 dB is degraded as compared with the fundamental frequency, it is detected at a level 100 times larger in terms of power than the actual level. Also, when the degree of coupling deteriorates, the directionality also deteriorates at the same time, so the degree to which the reflected wave is detected on the traveling wave side increases. Similarly, the degree to which the traveling wave is detected on the reflected wave side increases, Detection accuracy deteriorates.

FIG. 7 is a diagram illustrating an example of the frequency amplitude characteristic of the reflected wave side output of the directional coupler 13. In FIG. 7, the waveform indicated by “A” indicates the reflected wave detection characteristic of the output on the reflected wave side, and the waveform indicated by “B” indicates the output on the reflected wave side of the directional coupler 13. This shows traveling wave detection characteristics. The amplitude on the vertical axis is expressed in logarithm.
Thus, since the traveling wave component detected on the reflected wave side of the directional coupler 13 is small near the fundamental frequency, the reflected wave can be detected with high accuracy. However, when the frequency becomes higher than the fundamental frequency, the degree of coupling deteriorates, and the traveling wave component is detected regardless of the output on the reflected wave side. When the frequency is further increased, both the reflected wave and the traveling wave are detected at a level larger than the actual level. Therefore, the reflected wave side output of the directional coupler 13 has a waveform indicated by “C” in which “A” and “B” are combined. Note that the waveform indicated by “C” is illustrated as being somewhat smoothed in order to simplify the drawing.

  As described above, the reflected wave detection signal is used for control for protecting the maximum rating of the amplifying element as one of the main roles. For this reason, when the directional coupler 13 has the frequency amplitude characteristics as described above, when output control is performed based on various reflected waves generated on the load side, an appropriate output value of high-frequency power is obtained. Rather, it is controlled in a direction to suppress the output. As a result, there has been a problem that the output is suppressed more than necessary even though there is still a sufficient margin with respect to the maximum rating of the amplifying element.

  For example, in the case of being detected at a level 100 times larger in terms of power than the actual level as exemplified above, a reflected wave of 10 [W] is actually generated in terms of power. Even if it is a case, it may be detected as a reflected wave of 1,000 [W]. In this case, assuming that a reflected wave of 1,000 [W] is generated, output control is performed in the suppression direction, so the output of the amplifying unit 11 becomes smaller than an appropriate output value.

  The present invention has been conceived under the above circumstances, and even when a reflected wave in a frequency region higher than the fundamental frequency is detected, the detection level of the reflected wave is brought close to the actual level. Accordingly, an object of the present invention is to provide a high-frequency power supply device that performs output control at an appropriate level even when a reflected wave is generated.

The high frequency power supply device provided by the first invention is
In a high-frequency power supply device that includes high-frequency output means that serves as a supply source of high-frequency power and supplies high-frequency power to a load.
Reflected wave detection means for outputting a detection signal relating to the reflected wave;
A characteristic converter having a characteristic opposite to the frequency amplitude characteristic of the detection signal relating to the reflected wave detected by the reflected wave detector;
Detection means for detecting a signal related to the reflected wave output from the reflected wave detection means and converted in frequency amplitude characteristics by the characteristic conversion means;
Reflected wave power calculation means for calculating a reflected wave power value based on the output of the detection means;
Output control means for performing control to suppress the output of the high-frequency output means according to the reflected wave power value calculated by the reflected wave power calculation means;
It is characterized by having.

The high frequency power supply device provided by the second invention is
The characteristic conversion means is a passive high-frequency filter.

The high frequency power supply device provided by the third invention is
The reflected wave detecting means is a directional coupler.

  According to the present invention, even when a reflected wave in a high frequency region is detected, the detection level of the reflected wave can be brought close to an actual level. Thereby, even if a reflected wave is generated, it becomes possible to perform output control of high-frequency power at an appropriate level.

  Hereinafter, details of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a high-frequency power supply device 1 according to the present invention.
As shown in FIG. 1, the high-frequency power supply device 1 includes an amplification unit 11, a low-pass filter 12, a directional coupler 13, a traveling wave side detection unit 14, a reflected wave side detection unit 15, a traveling wave power calculation unit 16, A reflected wave power calculation unit 17, an output power setting unit 18, an output power control unit 19, and an amplitude characteristic conversion unit 20 are provided. Then, the high frequency power amplified by the amplifying unit 11 is supplied to the load 5 via the low pass filter 12 and the directional coupler 14. The configuration shown in FIG. 1 is the same as that of the conventional high frequency power supply device 10 shown in FIG.
Similarly to the conventional high-frequency power supply device 10, the first high-frequency power output from the first high-frequency power supply device 1 is the first high-frequency power, the output frequency of the first high-frequency power supply is the first frequency f1, Let the period of the first frequency be t1.

  The amplifying unit 11 is an example of the high-frequency output unit of the present invention, the directional coupler 14 is an example of the reflected wave detecting unit of the present invention, and the detection unit 15 on the reflected wave side is the detection unit of the present invention. The reflected wave power calculation unit 17 is an example of the reflected wave power calculation unit of the present invention, the output power control unit 19 is an example of the output control unit of the present invention, and the amplitude characteristic conversion unit 20 is an example of the means. These are examples of the characteristic conversion means of the present invention.

  The amplitude characteristic conversion unit 20 is a high-frequency filter provided between the directional coupler 13 and the detection unit 15 on the reflected wave side, and converts the characteristic of the reflected wave detection signal output from the directional coupler 13. Is. The output of the amplitude characteristic converter 20 is input to the detector 15 on the reflected wave side.

  FIG. 2 is a diagram illustrating an example of the frequency amplitude characteristic of the amplitude characteristic conversion unit 20. As shown in FIG. 2, the amplitude characteristic converter 20 has characteristics opposite to the frequency amplitude characteristics of the directional coupler 13. Note that FIG. 2 also uses the logarithmic representation of the amplitude on the vertical axis, as in FIG. The amplitude characteristic conversion unit 20 is composed of passive elements such as capacitors and inductors, and is a so-called passive high-frequency filter. The constants of the elements used in the amplitude characteristic conversion unit 20 may be determined so that the frequency amplitude characteristics of the directional coupler 13 are measured or simulated, and the circuit constants are reversed.

  As described above, the reflected wave detected by the directional coupler 13 is detected at a level larger than the actual level when the frequency increases. Therefore, when the reflected wave detection signal of the directional coupler 13 is output via the amplitude characteristic conversion unit 20 having the frequency amplitude characteristic opposite to the frequency amplitude characteristic of the directional coupler 13, the reflected wave detection signal is actually converted. Can be close to the level.

FIG. 3 is a diagram illustrating an example of the output of the amplitude characteristic conversion unit 20. Note that FIG. 3 also uses the logarithmic representation of the amplitude on the vertical axis, as in FIG.
As shown in FIG. 3, when the reflected wave detection signal of the directional coupler 13 is output via the amplitude characteristic converter 20, the level of the reflected wave detection signal is flattened in a high frequency region. Even when a reflected wave in a high frequency region is detected, the detection level of the reflected wave can be brought close to the actual level. Thereafter, as described above, detection is performed by the detection unit 15 on the reflected wave side, the reflected wave power calculation unit 17 calculates the reflected wave power value Pr, and the output is input to the output power control unit 19. Thereby, even if a reflected wave is generated, it becomes possible to perform output control of high-frequency power at an appropriate level. That is, the output power control unit 19 performs a function of performing control to suppress the output of the amplification unit 11 according to the reflected wave detection signal detected by the directional coupler 13 and converted by the amplitude characteristic conversion unit 20 to the frequency amplitude characteristic. Have

FIG. 1 is a block diagram showing a configuration of a high-frequency power supply device 1 according to the present invention. FIG. 2 is a diagram illustrating an example of the frequency amplitude characteristic of the amplitude characteristic conversion unit 20. FIG. 3 is a diagram illustrating an example of the output of the amplitude characteristic conversion unit 20. FIG. 4 is a block diagram showing a connection relationship of a plasma processing system using high frequency power of different frequencies. FIG. 5 is a block diagram illustrating a configuration example of a general high-frequency power supply device. FIG. 6 is an example of the characteristics of the low-pass filter. FIG. 7 is a diagram illustrating an example of the frequency amplitude characteristic of the reflected wave side output of the directional coupler 13.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 High frequency power supply device 2 according to the present invention Transmission line 2
3 First matcher 4 Load connection 5 Load 5
6 Second high frequency power supply 7 Transmission line 2
8 First Matching Unit 9 Load Connection Unit 11 DC Power Supply Unit 11 Amplifying Unit 12 Low Pass Filter 13 Directional Coupler 14 Traveling Wave Side Detection Unit 15 Reflected Wave Side Detection Unit 16 Traveling Wave Power Calculation Unit 17 Reflected Wave Power Calculation Unit 18 output power setting unit 19 output power control unit 20 amplitude characteristic conversion unit

Claims (3)

In a high-frequency power supply device that includes high-frequency output means that serves as a supply source of high-frequency power and supplies high-frequency power to a load.
Reflected wave detection means for outputting a detection signal relating to the reflected wave;
A characteristic converter having a characteristic opposite to the frequency amplitude characteristic of the detection signal relating to the reflected wave detected by the reflected wave detector;
Detection means for detecting a signal related to the reflected wave output from the reflected wave detection means and converted in frequency amplitude characteristics by the characteristic conversion means;
Reflected wave power calculation means for calculating a reflected wave power value based on the output of the detection means;
Output control means for performing control to suppress the output of the high-frequency output means according to the reflected wave power value calculated by the reflected wave power calculation means;
A high frequency power supply device comprising:   The high frequency power supply device according to claim 1, wherein the characteristic conversion means is a passive high frequency filter.   The high-frequency power supply device according to claim 1, wherein the reflected wave detection means is a directional coupler.

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