Patent Application
20240222077
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2022-211567, filed on Dec. 28, 2022, the entire contents of which are incorporated herein by reference.
The present disclosure relates generally to a high-frequency power supply apparatus.
A high-frequency power supply apparatus used for a plasma processing apparatus outputs a voltage toward a load from a power supply (referred to as a first power supply, for convenience) with a higher fundamental frequency and a power supply (as a second power supply) with a lower fundamental frequency.
In such a high-frequency power supply apparatus, intermodulation distortion (IMD) may occur. The relevant art can be found in, for example, patent documents including JP 7045152 B2, JP 2022-105037 A, JP 2022-102688 A, and JP 6785862 B2.
In a case where, for example, the first power supply and the second power supply each generate a sinusoidal high-frequency voltage, reflected wave power caused by the IMD can be reduced by performing frequency modulation on the sinusoidal high-frequency voltage of the first power supply with a sinusoidal modulation signal corresponding to the high-frequency voltage of the second power supply.
On the other hand, in a case where the first power supply generates a sinusoidal high-frequency voltage and the second power supply generates a rectangular negative-polarity voltage, it tends to be difficult to reduce the reflected wave power caused by the IMD even if performing the frequency modulation control on the sinusoidal high-frequency voltage of the first power supply with a rectangular modulation signal corresponding to the negative polarity voltage of the second power supply.
A high-frequency power supply apparatus according to the present disclosure includes a first power supply, a second power supply, a matching circuit, and a low-pass filter. The first power supply is configured to output a high-frequency voltage with a first fundamental frequency toward a load. The second power supply is configured to output, toward the load, a negative polarity voltage with a second fundamental frequency being lower than the first fundamental frequency. The matching circuit is connected between the first power supply and the load. The matching circuit is configured to match impedance on a side of the first power supply and impedance on a side of the load. The low-pass filter is connected between the second power supply and the load. The first power supply is configured to perform frequency modulation control by: performing frequency-modulation on the high-frequency voltage with a trapezoidal modulation signal whose frequency is equal to the second fundamental frequency, and outputting a modulated wave obtained by the frequency-modulation on the high-frequency voltage.
Hereinafter, an embodiment of a high-frequency power supply apparatus according to the present disclosure will be described with reference to the drawings.
The high-frequency power supply apparatus according to the embodiment is used for a plasma processing apparatus. The high-frequency power supply apparatus outputs, toward a load, a voltage from each of a power supply (first power supply) with a higher fundamental frequency and a power supply (second power supply) with a lower fundamental frequency. In the high-frequency power supply apparatus, intermodulation distortion (IMD) corresponding to the frequency of the second power supply is generated in the high-frequency voltage output from the first power supply.
In a case where the first power supply generates a sinusoidal high-frequency voltage and the second power supply generates a rectangular negative-polarity voltage, the reflection power of the first power supply varies with a waveform of the rectangular negative-polarity voltage due to the IMD. Even if the frequency modulation control is performed on the sinusoidal high-frequency voltage of the first power supply with a rectangular modulation signal corresponding to the negative polarity voltage of the second power supply, it tends to be difficult to reduce the reflected wave power caused by the IMD.
In the present embodiment, the reflected wave power caused by the IMD is reduced by the first power supply performing frequency modulation control by performing frequency-modulation on a high-frequency voltage with a trapezoidal modulation signal whose frequency is equal to a second fundamental frequency and then outputting a modulated wave obtained by the frequency-modulation on the high-frequency voltage.
The high-frequency power supply apparatus 1 includes an HF power supply 10 (an example of the first power supply), a −DC (minus DC) power supply 20 (an example of the second power supply), and a matching device 30. The HF power supply 10 generates a high-frequency voltage with a first fundamental frequency F1 in response to a command signal from a host controller (not illustrated). The HF power supply 10 supplies high-frequency power (traveling wave power) to the load by outputting the high-frequency voltage (traveling wave voltage). The high-frequency voltage mainly has the first fundamental frequency F1 that is relatively high and suitable for generating plasma PL. The first fundamental frequency F1 is, for example, 40.68 MHz. The HF power supply 10 is also referred to as a source power supply. Note that the fundamental frequency F1 is not limited to 40.68 MHZ, and may be, for example, a frequency of an industrial RF band (Radio Frequency) such as 13.56 MHz or 27.12 MHz.
The −DC power supply 20 generates a negative polarity voltage in response to a command signal from a host controller (not illustrated). The negative polarity voltage may be in a form of a rectangular wave. The −DC power supply 20 supplies a negative polarity voltage to the load. The negative polarity voltage has a second fundamental frequency F2 that is relatively low and is suitable for ion acceleration. The second fundamental frequency F2 is lower than the first fundamental frequency F1 and is, for example, 400 KHz.
When, for example, the command value changes from zero to H level at a timing t11 illustrated in
When the command value becomes zero from the H level at the timing t12, the −DC power supply 20 causes the level of the negative polarity voltage to transition from the negative potential −Vm to zero. At this time, the −DC power supply 20 generates the negative polarity voltage so as to transition to a rectangular wave, whereas the output negative polarity voltage transitions with a time constant delay due to the influence of the load. The −DC power supply 20 maintains the level of the negative polarity voltage at zero until a timing t13.
Operations similar to those at the timings t11 to t13 are repeated at timings t13 to t15 and timings t15 to t17. The length between the timings t11 and t13, which is a repetition period, corresponds to the second fundamental frequency F2.
Note that the second fundamental frequency F2 is not limited to 400 kHz, and may be another frequency.
The matching device 30 illustrated in
Note that the high-frequency power supply apparatus 1 and the plasma processing apparatus PA are not limited to the configuration illustrated in
The HF power supply 10 performs frequency modulation control by performing frequency-modulation on the high-frequency voltage with a trapezoidal modulation signal (see
The HF power supply 10 functions to calculate the magnitude of a reflection coefficient Γ or the magnitude of reflected wave power Pr on the basis of information detected in the HF power supply 10. As illustrated in
The sensor 15 supplies the modulated wave (traveling wave) output from the amplifier 14 to the matching device 30. The sensor 15 detects a traveling wave voltage from the amplifier 14 and outputs a traveling wave voltage detection signal Vf1 as a detection signal. Additionally, the sensor 15 detects a reflected wave voltage reflected from the plasma processing apparatus PA side via the matching device 30, and outputs a reflected wave voltage detection signal Vr as a detection signal. The sensor 15 supplies the detected traveling wave voltage detection signal Vf and reflected wave voltage detection signal Vr to the processor 16.
The processor 16 performs calculation on the traveling wave voltage detection signal Vf and the reflected wave voltage detection signal Vr by, for example, a super-heterodyne method to perform filtering processing. Thereby, the processor 16 extracts a traveling wave voltage detection signal Vf2, which is a desired component of the traveling wave voltage detection signal Vf1, and a reflected wave voltage detection signal Vr2, which is a desired component of the reflected wave voltage detection signal Vr1.
The processor 16 calculates traveling wave power Pf on the basis of traveling wave voltage detection signal Vf2, and calculates reflected wave power Pr on the basis of reflected wave voltage detection signal Vr2. For example, the traveling wave power Pf can be calculated by Vf2{circumflex over ( )}2/R (R denotes the gain corresponding to resistance value). The reflected wave power Pr can be calculated in a similar manner. Note that, in the above calculation formula, Vf2 represents the magnitude of the traveling wave voltage detection signal Vf2. Of course, the gain for conversion to the actual power value is multiplied.
Moreover, the processor 16 accumulates the calculated traveling wave power Pf and reflected wave power Pr in a predetermined period. The processor 16 averages the traveling wave power Pf and the reflected wave power Pr for a predetermined period. The processor 16 supplies the average power of the traveling wave power Pf to the subtractor 19. The processor 16 also supplies the average power of the traveling wave power Pf and the average power of the reflected wave power Pr to the frequency modulation control block 11. Note that, in the above description, the example in which the averaging is performed after the power is calculated on the basis of the voltage has been described, whereas the power may be calculated after the voltage is averaged.
Target power is preset for the power setting unit 18. The power setting unit 18 supplies the target power to the subtractor 19. The subtractor 19 subtracts the average power of the traveling wave power Pf from the target power, and feeds back a subtraction result as an error ΔP to the controller 12. The controller 12 controls the amplitude of the modulated wave in accordance with the error ΔP. Specifically, for example, the controller 12 obtains the amplitude of the modulated wave so as to decrease the error ΔP, and then supplies, to the DDS 13, the amplitude setting corresponding to the obtained amplitude.
In a case where, for example, the target power is 1,000 W and the average power of the traveling wave power Pf is 950 W, 50 W is short of the target power. In this case, the controller 12 controls the amplitude of the modulated wave so as to increase the traveling wave power Pf to be supplied to the load. A known method such as PI control or PID control can be used for controlling the amplitude of the modulated wave.
In this way, the frequency modulation control block 11 adjusts the start phase of the modulation signal and the frequency shift amount of the modulated wave within respective predetermined adjustment ranges so as to minimize the average power of the reflected wave power Pr. In one example, at the time when the average power of the reflected wave power Pr becomes equal to or less than a predetermined threshold, the frequency modulation control block 11 recognizes that the average power of the reflected wave power Pr becomes minimum. The frequency modulation control block 11 may make determination that the frequency modulation control is completed when the average power of the reflected wave power Pr becomes minimum.
The fundamental wave generation unit 11b generates a signal (generally called a carrier wave) including frequency information (for example, 40.68 MHz), which is obtained before frequency modulation, and outputs the signal to the DDS 13 through the adder 11c. When the output signal from the frequency modulation setting unit 11a indicates zero, the fundamental wave generation unit 11b outputs the fundamental wave.
In the frequency modulation setting unit 11a, the frequency modulation control unit 11a1 can generate a timing signal in accordance with a control cycle.
In the modulation fundamental waveform table 11a2, amplitude information for one cycle of the second fundamental frequency F2 (for example, 400 kHz) is stored at every predetermined phase interval. In the present disclosure, waveform data represented by this amplitude information for one cycle is referred to as a “modulation fundamental waveform”. The modulation fundamental waveform may be in a form of a trapezoidal wave (see
The phase interval of the amplitude information in the modulation fundamental waveform varies with the control cycle of the frequency modulation control unit 11a1. For example, in a case where the frequency modulation control unit 11a1 operates at a control cycle of 100 MHz, the frequency modulation control unit is divided into 250 (100 MHz/400 kHz). In this case, the amplitude information for every phase interval of 1.44 degrees (360/250) is stored in the modulation fundamental waveform table 11a2. In a case where the frequency modulation control unit 11a1 operates at a control cycle of 500 MHz, the frequency modulation control unit is divided into 1250 (500 MHz/400 kHz). In this case, the amplitude information for every phase interval of 0.288 degrees (360/1250) is stored in the modulation fundamental waveform table 11a2. The control cycle is set on the basis of a clock signal output from a fundamental clock oscillator (not illustrated).
The amplitude of the modulation fundamental waveform stored in the modulation fundamental waveform table 11a2 is a predetermined reference amplitude (for example, the magnitude of the amplitude is +1). Note that the waveform data of the modulation fundamental waveform can be stored in advance in the modulation fundamental waveform table 11a2 via the frequency modulation control unit 11a1.
The start phase setting unit 11a3 reads the modulation fundamental waveform from the modulation fundamental waveform table 11a2 in response to the timing signal supplied from the frequency modulation control unit 11a1. Thereafter, the start phase setting unit 11a3 sets a start phase θst at which modulation in the modulation fundamental waveform is to be started. The method of determining the start phase will be described later. Thereafter, the start phase setting unit 11a3 shifts the modulation fundamental waveform in the time direction such that the waveform is started from the start phase θst. For example, in the case of
The shift amount gain setting unit 11a4 sets the frequency shift amount ΔF in response to the timing signal supplied by the frequency modulation control unit 11a1. The frequency shift amount ΔF may vary within a range of −ΔFmax to +ΔFmax. For example, ΔFmax is 1.2 MHz. The method of determining the frequency shift amount ΔF will be described later. The frequency shift amount when the fundamental wave signal of the first fundamental frequency F1 output from the fundamental wave generation unit 11b is frequency-modulated is represented by the amplitude of the modulation fundamental waveform. By multiplying the modulation fundamental waveform by a gain (shift amount gain) corresponding to the frequency shift amount ΔF, the amplitude of the modulation fundamental waveform is changed, and the frequency shift amount ΔF can be set. The frequency shift amount ΔF and the shift amount gain correspond to each other on a one-to-one basis. Setting of the shift amount gain is equivalent to setting of the frequency shift amount ΔF.
In the frequency modulation control unit 11a1, the counter unit 11a11 counts the number of pulses of the external signal (see
The adder 11c receives the fundamental wave signal from the fundamental wave generation unit 11b, and receives the modulation signal from the shift amount gain setting unit 11a4. The adder 11c adds the modulation signal to the fundamental wave signal. The addition result is supplied to the DDS 13 as output waveform data.
At a timing t1 illustrated in
Accordingly, the reflected wave power Pr or the reflection coefficient I′ from the processor 16 decreases or increases. For example, as illustrated in
The frequency modulation control unit 11a1 recognizes that the change in the reflection power Pr or the reflection coefficient Γ is switched from a decreasing tendency to an increasing tendency. The frequency modulation control unit 11a1 sets the value of the start phase θst at this time or a value slightly decreased from the value, to a value Dt of the start phase θst at which the reflection power Pr or the reflection coefficient Γ becomes substantially minimum.
At a timing t2 illustrated in
Note that, in a case where the search processing is repeatedly performed, the frequency modulation control unit 11a1 may count the number of repetitions. In this case, when the number of repetitions reaches the maximum number of times in the search processing and the value of the start phase θst reaches the maximum value Dmax in the search processing, the frequency modulation control unit 11a1 makes determination that the start phase setting unit 11a3 should end the setting of the start phase.
The frequency modulation control unit 11a1 causes the timing signal TS1 to transition from the active level to the non-active level in synchronization with the pulse of the external signal. In response to this, the start phase setting unit 11a3 sets and maintains the value of the start phase θst to Dt, and ends the setting of the start phase θst.
At the same time, the frequency modulation control unit 11a1 makes determination that the shift amount gain setting unit 11a4 should start setting the frequency shift amount ΔF. As illustrated in
Accordingly, the reflected wave power Pr or the reflection coefficient Γ from the processor 16 decreases or increases. For example, as illustrated in
The frequency modulation control unit 11a1 recognizes that the change in the reflection power Pr or the reflection coefficient Γ is switched from a decreasing tendency to an increasing tendency. The frequency modulation control unit 11a1 sets the value of the frequency shift amount ΔF at this time or a value slightly decreased from the value, to a value Et of the frequency shift amount ΔF at which the reflection power Pr or the reflection coefficient Γ becomes substantially minimum.
At a timing t3 illustrated in
Note that, in a case where the search processing is repeatedly performed, the frequency modulation control unit 11a1 may count the number of repetitions. In this case, when the number of repetitions reaches the maximum number of times in the search processing and the value of the frequency shift amount ΔF reaches the maximum value Emax in the search processing, the frequency modulation control unit 11a1 makes determination that the shift amount gain setting unit 11a4 should end the setting of the frequency shift amount ΔF.
The frequency modulation control unit 11a1 causes the timing signal TS2 to transition from the active level to the non-active level in synchronization with the pulse of the external signal. In response to this, the shift amount gain setting unit 11a4 sets and maintains the value of the frequency shift amount ΔF to Et, and ends the setting of the frequency shift amount ΔF.
The period between the timings t1 and t2 is a period in which the search processing for the start phase θst of the modulation signal is performed. The search processing for the start phase θst is also called a start phase sweep.
The period between the timings t2 and t3 is a period in which the search processing of the frequency shift amount ΔF of the modulation signal is performed. The search processing for the frequency shift amount ΔF is also called a shift amount sweep.
After the timing t3, the frequency modulation control block 11 starts frequency modulation control. Specifically, the frequency modulation setting unit 11a generates a trapezoidal modulation signal (see
As described above, in the HF power supply 10 according to the embodiment, the frequency modulation control is performed. In the frequency modulation control, the high-frequency voltage is frequency-modulated with the trapezoidal modulation signal (see
In a case where, for example, power is supplied from the high-frequency power supply apparatus 1 to a load without performing frequency change control by the HF power supply 10, the impedance of the path from the HF power supply 10 to the load may fluctuate with a large amplitude as indicated by a dotted line in
On the other hand, in the HF power supply 10, when power is supplied from the high-frequency power supply apparatus 1 to the load while the frequency modulation control is performed by performing frequency modulation on the high-frequency voltage with a trapezoidal modulation signal whose frequency is equal to the second fundamental frequency F2 and outputting a modulated wave obtained by the frequency modulation, the impedance of the path from the HF power supply 10 to the load can fluctuate with a smaller amplitude as indicated by a solid line in
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms: moreover, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-211567 | Dec 2022 | JP | national |
