JP2005269869A - High-frequency power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency power supply unit capable of appropriately supplying discharge voltage to a load. <P>SOLUTION: This high-frequency power supply unit 1 includes: a calculation section 17 for calculating a value of a DC power supply voltage Vdc serving as the center of an amplitude waveform corresponding to a set high-frequency power value; a DC power supply section 21 for producing the DC power supply voltage Vdc calculated by the calculation section 17; and an amplifier section 14 for amplifying high-frequency power on the basis of the DC power supply voltage produced by the DC power supply section 21, and supplies the high-frequency power amplified by the amplifier section 14 to the load L. Furthermore, the high-frequency power supply 1 comprises an initial voltage setting section 18 capable of setting a prescribed initial voltage value, a matching state detecting section 23 for detecting a matching state in the load L side, a switching section 19 for supplying either one of the value of the DC power supply voltage Vdc calculated by the calculation section 17 and the initial voltage value set by the initial voltage setting section 18 to the DC power supply section 21 on the basis of the matching state detected by the matching state detecting section 23. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-frequency power supply apparatus that supplies high-frequency power to a load, such as a plasma processing apparatus that performs plasma etching in a semiconductor wafer process, via an impedance matching device.

Conventionally, as a high frequency power supply device, for example, a device described in Patent Document 1 has been proposed. FIG. 5 is a configuration diagram of the high-frequency power supply device described in Patent Document 1.
JP 2001-197749 A

  This high frequency power supply device includes an output power setting unit 41 for setting a value of high frequency power, an oscillation unit 43 that varies the level of oscillation output based on a signal from a control unit 42 described later, and an oscillation output of the oscillation unit 43. The amplification unit 44 to be amplified, the output power detection unit 45 to detect the output power output from the amplification unit 44, and the set value by the output power setting unit 41 and the detection value by the output power detection unit 45 are compared, and the comparison result Is provided to the oscillating unit 43 to control the high frequency power to be constant.

  In addition, the high frequency power supply apparatus calculates a DC power supply voltage Vdc that is the center of the amplitude waveform of the high frequency power based on a predetermined characteristic graph or a characteristic function with respect to the value set in the output power setting unit 41. And amplifying the error between the calculated value of the DC power supply voltage Vdc calculated by the calculation unit 47 and the detected value of the DC power supply voltage Vdc by the DC voltage detection unit 52, and outputs the amplified error to the DC power supply unit 51. An error amplifier 50, a DC power supply 51 for generating the DC power supply voltage Vdc, and a DC voltage detection unit 52 for detecting the magnitude of the DC power supply voltage Vdc output from the DC power supply 51 are provided. .

  In the above configuration, when the value of the high frequency power is set in the output power setting unit 41, the level of the oscillation output is varied in the oscillation unit 43 based on the value of the high frequency power, and the oscillation output is amplified in the amplification unit 44. The On the other hand, the calculation unit 47 calculates the calculated value of the DC power supply voltage Vdc in accordance with the value of the high frequency power, and the DC power supply unit 51 generates the DC power supply voltage Vdc and sends it to the amplification unit 44. In the amplifying unit 44, the oscillation output is amplified with reference to the DC power supply voltage Vdc, and is supplied to the load with high efficiency through, for example, an impedance converter (not shown).

  By the way, in the high frequency power supply device, when the value of the high frequency power is set in the output power setting unit 41, the DC power supply voltage Vdc corresponding to the high frequency power is calculated in the calculation unit 47, but in the output power setting unit 41, If the set value is too small, the value of the DC power supply voltage Vdc becomes low, and when the supply of the high frequency output to the load is started, the level of the high frequency power output from the amplifying unit 44 to the load causes the load to discharge. There is a problem that the starting voltage value is not reached and plasma discharge may not be started.

  Further, when plasma discharge is started in the load, in order to maintain the plasma discharge, it is necessary to maintain the voltage across the terminals of the load in the plasma discharge to some extent. Once the plasma discharge is started, the variable impedance element (not shown) constituting the impedance matching device changes its reactance (capacitance and inductance) so that impedance matching can be achieved. When it becomes impossible to remove depending on the state, the voltage between the terminals of the load may be lower than the voltage necessary to maintain the plasma discharge, and the plasma discharge may not be maintained.

  The present invention has been conceived under the circumstances described above, and an object thereof is to provide a high-frequency power supply device that can appropriately supply a discharge voltage to a load.

  In order to solve the above problems, the present invention takes the following technical means.

  The high frequency power supply device provided by the present invention comprises a calculation means for calculating a value of a DC power supply voltage that is the center of an amplitude waveform in accordance with a set value of high frequency power, and a DC power supply voltage calculated by the calculation means. And amplifying means for amplifying the high frequency power with reference to a DC power supply voltage generated by the voltage generating means, and the high frequency power amplified by the amplifying means is applied to a load. A high-frequency power supply device for supplying a predetermined voltage setting means capable of setting a predetermined voltage value, a matching state detecting means for detecting a matching state on the load side, and a matching state detected by the matching state detecting means. Based on either the value of the DC power supply voltage calculated by the calculating means or the value of the predetermined voltage set by the predetermined voltage setting means It is characterized in that it comprises a supply means for supplying to said voltage generating means (claim 1).

  According to this configuration, either the value of the DC power supply voltage calculated by the calculation means based on the matching state on the load side or the value of the predetermined voltage set by the predetermined voltage setting means is determined, and the determined value Based on the above, a DC power supply voltage is generated by the voltage generating means. The generated DC power supply voltage becomes the center of the amplitude waveform of the high frequency power, and the high frequency power is supplied to the load. Therefore, for example, when the supply of high-frequency power is started (in a mismatched state), the value of the DC power supply voltage calculated according to the set high-frequency power value is so low that the load is not discharged. For example, the value of the predetermined voltage set by the predetermined voltage setting means is determined, and the DC power supply voltage is generated by the voltage generation means based on this value, so that the load can be discharged appropriately and reliably. it can.

  According to a preferred embodiment, the matching state detection means may detect the matching state of the load based on a traveling wave traveling toward the load side and a reflected wave returning from the load side.

  According to another preferred embodiment, when the matching state detected by the matching state detection unit is mismatched, the supply unit sets the value of the DC power supply voltage to a predetermined voltage set by the predetermined voltage setting unit. It is good to switch and supply to the value of (Claim 3).

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

  Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the accompanying drawings.

  FIG. 1 is a diagram showing an example of a high-frequency power supply system to which a high-frequency power supply device according to the present invention is applied. This system supplies a high-frequency power to a workpiece such as a semiconductor wafer or a liquid crystal substrate, and performs a processing process such as plasma etching. This system includes a high-frequency power supply device 1, a transmission line 2, an impedance matching device 3, a load connection unit 4, and a load L.

  An impedance matching device 3 is connected to the high frequency power supply device 1 via a transmission line 2 made of, for example, a coaxial cable, and the impedance matching device 3 is connected to a load connecting portion 4 made of, for example, a copper plate shielded from leaking electromagnetic waves. A load L (for example, a plasma processing apparatus) is connected via the. The high frequency power supply device 1 may include the impedance matching device 3.

  The high frequency power supply device 1 is a device for supplying high frequency power having a frequency of, for example, several hundred kHz or more to the load L. The high frequency power supply device 1 will be described later.

  The impedance matching unit 3 matches the impedance between the high frequency power supply device 1 and the load L. More specifically, for example, the impedance (output impedance) when the high frequency power supply device 1 is viewed from the output end of the high frequency power supply device 1 is designed to be 50Ω, for example, and the high frequency power supply device 1 is impedanced by the transmission line 2 having a characteristic impedance of 50Ω. Assuming that the impedance matching unit 3 is connected to the input end of the matching unit 3, the impedance matching unit 3 automatically adjusts the impedance viewed from the input end of the impedance matching unit 3 to the load L side to 50Ω as much as possible.

  Although not shown, the impedance matching unit 3 includes an input detection unit that detects a high-frequency voltage and a high-frequency current of high-frequency power (incident wave) input from the high-frequency power supply device 1 and a phase difference therebetween, and a variable capacitor that is a variable impedance element. Matching unit that calculates the input impedance using the high-frequency voltage, high-frequency current, and phase difference input from the matching unit, the input detection unit, etc., and controls the variable capacitor of the matching unit so that this input impedance becomes, for example, 50Ω It is comprised by the device control part etc.

  The load L is a plasma processing apparatus for processing a workpiece such as a semiconductor wafer or a liquid crystal substrate using a method such as etching or CVD. In the plasma processing apparatus, various processing processes are executed according to the processing purpose of the workpiece. For example, when etching a workpiece, a processing process in which the gas type, gas pressure, high-frequency power supply power value, high-frequency power supply time, and the like according to the etching are appropriately set is performed. Is called. In a plasma processing apparatus, a plasma discharge gas is introduced into a container (not shown) in which a workpiece is placed, and the plasma discharge gas is discharged to change from a non-plasma state to a plasma state. And the workpiece is processed using the gas in the plasma state.

  The load L is plasma-discharged when high-frequency power is supplied. That is, when the supply of high-frequency power is started, a predetermined voltage is applied between the terminals of the load L, plasma discharge is performed by the applied voltage, and the above-described machining process is executed. . In the present embodiment, the voltage supplied between the terminals of the load L is controlled so that the plasma discharge is not lowered to some extent.

  As shown in FIG. 2, the high frequency power supply device 1 includes an output power setting unit 11, a control unit 12, an oscillation unit 13, an amplification unit 14, an output power detection unit 15, a calculation unit 17, and an initial voltage setting. A unit 18, a switching unit 19, an error amplifying unit 20, a DC power supply unit 21, a DC voltage detection unit 22, and a matching state detection unit 23 are provided.

  The output power setting unit 11 is for setting output power to be output to the load L by a user or the like, for example. Although omitted in FIG. 2, the output power setting for setting the output value of high-frequency power is performed. An operation unit or the like provided with a switch and an output start switch for instructing start of supply of high-frequency power is provided. Data of the output value of the high frequency power set in the output power setting unit 11 is sent to the control unit 12 and the calculation unit 17.

  The control unit 12 compares the output value of the high-frequency power set by the output power setting unit 11 with the detection value of the high-frequency power detected by the output power detection unit 15, and the oscillation unit 13 so that they match. It controls the level of oscillation output. That is, the control unit 12 controls the output of the high frequency power to be constant by controlling the level of the oscillation output of the oscillation unit 13.

  The oscillation unit 13 has its oscillation output level controlled by a control signal from the control unit 12. The oscillation output signal output from the oscillation unit 13 is sent to the amplification unit 14.

  The amplifying unit 14 amplifies the oscillation output signal from the oscillating unit 13 and outputs a high frequency power signal. The oscillation output signal amplified in the amplifying unit 14 is output to the impedance matching unit 3 through the output power detection unit 15 and the output connector 16, and the matching operation is performed in the impedance matching unit 3 as described above.

  The output power detection unit 15 detects high-frequency power from the amplification unit 14, and is configured by, for example, a directional coupler and travels from the amplification unit 14 to the load L side (hereinafter, traveling wave). ) And high-frequency power reflected from the load L side (hereinafter referred to as a reflected wave), and their values are detected respectively.

  The value of the traveling wave detected by the output power detection unit 15 is returned to the control unit 12, and the control unit 12 compares it with the output value of the high frequency power set by the output power setting unit 11 as described above. A control signal is output to the oscillating unit 13 so that both coincide. That is, the control unit 12, the oscillation unit 13, the amplification unit 14, and the output power detection unit 15 form a feedback loop and are controlled so that the output is constant.

  In the high frequency power supply device 1, the high frequency power is output to the load L with reference to the DC power supply voltage Vdc that is the center of the amplitude waveform of the high frequency power. Hereinafter, a configuration for generating the DC power supply voltage Vdc will be described. To do.

  The calculation unit 17 calculates the set value of the high-frequency power output from the output power setting unit 11 based on a predetermined characteristic graph or characteristic function, and switches the switching unit 19 and the error amplification unit as the calculated value of the DC power supply voltage Vdc. The power is output to the DC power supply unit 21 via 20. Here, the predetermined characteristic graph or characteristic function is obtained in advance by experiments or the like in order to obtain maximum efficiency in a range where the output voltage of the high frequency power is not saturated, in other words, in a range where waveform distortion does not occur. It is what was done.

  FIG. 3 is an example of the above characteristic graph, in which the horizontal axis represents the set power (%) of the high frequency power, the vertical axis represents the DC power supply voltage Vdc (%), and the amplifier 14 has the maximum efficiency at the set power. The value of the DC power supply voltage Vdc for the amplification operation is shown in FIG. FIG. 4 is a waveform diagram of the DC power supply voltage Vdc and the high frequency power, and the amplitude is maximized in a range where the waveform of the high frequency power is not saturated, that is, the high frequency power supply device 1 can operate at the maximum efficiency. The case where the DC power supply voltage Vdc is set is shown. The hatched portion in the figure indicates a loss, and the smaller this portion, the higher the efficiency. The calculating unit 17 may set the output value of the DC power supply voltage Vdc slightly higher than the calculated value.

  The initial voltage setting unit 18 is for setting an initial voltage to be applied between terminals of the load L in order to discharge the load L when supply of high-frequency power is started. The initial voltage is a voltage value that is necessary and sufficient for causing the load L to perform plasma discharge, and is an empirically obtained value. This initial voltage is set to about 60% of the maximum value of the DC power supply voltage, for example. In other words, when the set value of the output power setting unit 11 is small, the initial voltage is larger than the calculated value of the DC power supply voltage Vdc calculated by the calculating unit 17. Although omitted in FIG. 2, the initial voltage setting unit 18 is provided with a setting switch for setting the value of the initial voltage. Data of the initial voltage value set in the initial voltage setting unit 18 is sent to the switching unit 19.

  Based on the detection result from the matching state detection unit 23, the switching unit 19 calculates the error value of the DC power supply voltage Vdc from the calculation unit 17 and the initial voltage setting value from the initial voltage setting unit 18. The power is output to the DC power supply unit 21 via 20. That is, when a detection signal indicating that the load L side is in the matching state is sent from the matching state detection unit 23, the switching unit 19 converts the calculated value of the DC power supply voltage Vdc from the calculation unit 17 to the DC via the error amplification unit 20. Output to the power supply unit 21. On the other hand, when a detection signal indicating that the load L side is in a mismatch state is sent from the matching state detection unit 23, the switching unit 19 uses the initial voltage setting value from the initial voltage setting unit 18 as the error amplification unit 20. To the DC power supply unit 21 via

  The error amplifying unit 20 amplifies an error between the calculated value of the DC power supply voltage Vdc from the calculating unit 17 or the initial voltage setting value from the initial voltage setting unit 18 and the detected value by the DC voltage detecting unit 22. Then, it is output to the DC power supply unit 21.

  The DC power supply unit 21 generates a DC power supply voltage corresponding to the calculated value of the DC power supply voltage Vdc from the calculation unit 17 or the set value of the initial voltage from the initial voltage setting unit 18. It is. The generated DC power supply voltage is output to the amplifying unit 14 via the DC voltage detecting unit 22.

  The DC voltage detection unit 22 detects the magnitude of the DC power supply voltage generated by the DC power supply unit 21. The detection result in the DC voltage detection unit 22 is fed back to the error amplification unit 20, and in the error amplification unit 20, either the calculated value of the DC power supply voltage Vdc from the calculation unit 17 or the set value of the initial voltage from the initial voltage setting unit 18. It has come to be compared with. As a result, the DC power supply voltage Vdc can be controlled to be supplied to the amplifying unit 14, and fluctuations in the DC power supply voltage Vdc due to fluctuations in the load L are suppressed.

  In this high frequency power supply device 1, in order to control the voltage supplied between the terminals of the load L so as not to lower the plasma discharge to some extent, the matching state on the load L side is detected, and based on the detection result. Thus, it is determined whether or not the initial voltage set by the initial voltage setting unit 18 is output, and the configuration for performing the determination will be described below.

  The matching state detection unit 23 is for detecting an impedance matching state on the load L side. The matching state detection unit 23 calculates the reflection coefficient Γ = Vr / Vf from the amplitude Vf of the traveling wave PF and the amplitude Vr of the reflected wave PR input from the output power detection unit 15, and matches the matching state based on the calculation result. It is discriminate | determined whether it is. The matching state detection unit 23 converts the amplitude Vf of the traveling wave PF and the amplitude Vr of the reflected wave PR into digital amplitude values Df and Dr by an A / D converter, and then calculates Dr / Df to calculate the reflection coefficient Γ. Calculate the value. Then, based on the value of the reflection coefficient Γ, it is determined whether or not the matching state is established, and the result is output to the switching unit 19.

  That is, in the present embodiment, the matching state on the load L side is detected, and the calculated value of the DC power supply voltage Vdc calculated in the calculating unit 17 based on this matching state is supplied to the amplifying unit 14 or the initial voltage The switching unit 19 switches whether the initial voltage set in the setting unit 18 is supplied to the amplification unit 14. For example, if the load L side is in a matching state, it is switched to the calculated value of the DC power supply voltage Vdc and supplied to the DC power supply unit 21. On the other hand, if the load L side is in a mismatched state, it is switched to the initial voltage and supplied to the DC power supply unit 21.

  Next, the operation of the above configuration will be described.

  First, when the supply of high-frequency power is started, the matching state detection unit 23 detects a mismatching state. The matching state detection unit 23 sends a detection signal to that effect to the switching unit 19. Thereby, the switching unit 19 switches to the initial voltage set by the initial voltage setting unit 18 and supplies the initial voltage to the DC power supply unit 21 via the error amplifying unit 20.

  That is, when the supply of high-frequency power is started, a voltage necessary for plasma discharge of the load L must be applied between the terminals of the load L to cause the load L to be plasma discharged. If the set value of the high frequency power to be low is small, the DC power supply voltage Vdc becomes small, and this is not a sufficient voltage for causing the load L to plasma discharge, so the load L cannot be plasma discharged. Therefore, in the present embodiment, immediately after the supply of high-frequency power is started, when the plasma discharge has not yet started and is in a mismatched state, the mismatched state detection unit 23 detects the mismatched state, Based on the detection result, the initial voltage value set by the initial voltage setting unit 18 is output to the DC power source unit 21.

  As a result, the value of the initial voltage is generated as a DC power supply voltage in the DC power supply unit 21, further supplied to the amplification unit 14, amplified to an appropriate value in the amplification unit 14, and output to the load L side. That is, the load L is supplied with a voltage necessary and sufficient for plasma discharge, and the load L can be appropriately and reliably plasma discharged.

  Thereafter, when the impedance matching unit 3 adjusts the input impedance so that the magnitude of the input impedance is, for example, 50Ω and the phase difference is approximately 0 °, the matching state detection unit 23 is input from the output power detection unit 15. The reflection coefficient Γ = Vr / Vf is calculated from the amplitude Vf of the traveling wave PF and the amplitude Vr of the reflected wave PR. Then, if the value of the reflection coefficient Γ is within a predetermined range, it is determined as being in a matching state, and the determination result is output to the switching unit 19.

  The switching unit 19 receives the determination result from the matching state detection unit 23, and when the determination result is the matching state, the calculated value of the DC power supply voltage Vdc from the calculation unit 17 is passed through the error amplification unit 20 to the DC power supply unit. 21 to switch to supply. As a result, the load L is supplied with high-frequency power based on the DC power supply voltage Vdc, and a predetermined processing process is performed.

  Note that the switching unit 19 may be switched after a predetermined time has elapsed since the start of the supply of high-frequency power, that is, assuming that impedance matching is performed in the impedance matching unit 3.

  Here, when plasma discharge is started in the load L, in order to maintain the plasma discharge, it is necessary to maintain the voltage across the load L in the plasma discharge. When the impedance changes and impedance matching cannot be achieved, the voltage between the terminals of the load L may be lower than the voltage necessary to maintain the plasma discharge, and the plasma discharge may not be maintained.

  In this embodiment, even in such a case, since the matching state detection unit 23 always detects whether or not the impedance on the load L side is matched, impedance matching cannot be obtained during the processing process of the load L. In addition, the matching state detection unit 23 detects it and outputs a detection signal to that effect to the switching unit 19. As a result, the switching unit 19 outputs the initial voltage set by the initial voltage setting unit 18 to the DC power supply unit 21 based on the detection result. Therefore, plasma discharge in the load L can be maintained.

  Of course, the scope of the present invention is not limited to the embodiment described above. In the above embodiment, the matching state detection unit 23 detects the matching state on the load L side by calculating the reflection coefficient, but impedance, standing wave ratio, etc. may be used instead of the reflection coefficient. .

1 is a configuration diagram of a high frequency power supply system to which a high frequency power supply device according to the present invention is applied. It is a block diagram of the high frequency power supply device which concerns on this invention. It is a figure which shows an example of a characteristic graph. It is a waveform diagram of a DC power supply voltage and a high frequency output. It is a block diagram of the conventional high frequency power supply device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 High frequency power supply device 3 Impedance matching device 11 Output power setting part 14 Amplification part 15 Output power detection part 17 Calculation part 18 Initial voltage setting part 19 Switching part 20 Error amplification part 21 DC power supply part 22 DC voltage detection part 23 Matching state detection part L load

Claims (3)

An arithmetic means for calculating the value of the DC power supply voltage that is the center of the amplitude waveform according to the set value of the high-frequency power;
Voltage generating means for generating a DC power supply voltage calculated by the calculating means;
Amplifying means for amplifying the high-frequency power with reference to the DC power supply voltage generated by the voltage generating means,
A high frequency power supply apparatus that supplies high frequency power amplified by the amplification means to a load,
Predetermined voltage setting means capable of setting a predetermined voltage value;
A matching state detecting means for detecting a matching state on the load side;
Based on the matching state detected by the matching state detecting means, either the value of the DC power supply voltage calculated by the calculating means or the value of the predetermined voltage set by the predetermined voltage setting means is the voltage generating means. Supply means for supplying to,
A high-frequency power supply device comprising:   2. The high frequency power supply device according to claim 1, wherein the matching state detection unit detects a matching state of the load based on a traveling wave traveling toward the load side and a reflected wave returning from the load side.   The supply means switches and supplies the value of the DC power supply voltage to the value of the predetermined voltage set by the predetermined voltage setting means when the matching state detected by the matching state detection means is not matched. The high frequency power supply device according to claim 1 or 2.

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