JP2007163308A - High frequency measurement system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high frequency measurement system that can be calibrated in a prescribed frequency range by calibration data generated from calibration data to a holding partial frequency even in a plasma treatment system using a high frequency power source device changing a frequency. <P>SOLUTION: The high frequency measurement system comprises: a signal detection means for detecting a high frequency signal; a calibration data storage means for storing the calibration data Cmin, Cmax for calibrating a detection value Amin in a lower limit frequency fmin and a detection value Amax in an upper limit frequency fmax to respective true measuring values ASmin, ASmax; a frequency detection means for detecting the frequency fm of the high frequency signal; a calibration data calculation means for calculating the calibration data Cm to the frequency fm; and a measured value calibration means for calibrating a detection value Am detected by the signal detection means to a true measuring value ASm by using the calibration data Cm calculated with the calibration data calculation means. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a high-frequency measuring device that measures the voltage, current, and phase of a high-frequency signal.

  In a plasma processing system in which high frequency power is supplied from a high frequency power supply device to a plasma processing apparatus and a workpiece such as a semiconductor wafer or a liquid crystal substrate is processed using a method such as etching, the impedance of the plasma processing apparatus is reduced during the plasma processing. Because of the large fluctuation, generally, as shown in FIG. 7, an impedance matching device 20 is interposed between the high frequency power supply device 10 and the plasma processing device 30, and the impedance matching device 20 causes the high frequency power supply device 10 and the plasma processing device 30 to be interposed. Is used for impedance matching.

  In addition, in order to monitor the impedance fluctuation of the plasma processing apparatus 30 during the plasma processing, a high-frequency detector for detecting a high-frequency voltage and / or a high-frequency current is provided between the impedance matching device 20 and the plasma processing apparatus 30. There is also.

  For example, in Japanese Patent Laid-Open No. 10-185960, a sensor for detecting a high frequency voltage and a high frequency current is incorporated in a case as a probe for detecting a high frequency signal applied to a plasma processing system, and a high frequency signal is input into this case. A high-frequency signal detection probe is described in which an input / output terminal for outputting and an output terminal for outputting a detection signal of a sensor are configured by a coaxial connector.

  Since the high-frequency signal detection probe is configured to be connected between the impedance matching device 20 and the plasma processing apparatus 30 by a coaxial connector, it can be applied when a plasma processing system is configured by a coaxial line. It cannot be applied when the impedance matching unit 20 and the plasma processing apparatus 30 are coupled by a waveguide.

  Some plasma processing systems connect the impedance matching device and the plasma processing device directly with a waveguide in order to suppress transmission loss as much as possible. In such an impedance matching device, there is a high frequency near the output end. There may be a high-frequency measuring device for detecting the voltage (effective value) V, the high-frequency current (effective value) I, and the phase θ between the high-frequency voltage V and the high-frequency current I.

  The high-frequency voltage V, the high-frequency current I, and the phase θ detected by this high-frequency measuring device are impedance values according to arithmetic expressions of R = (V / I) · cos (θ) and X = (V / I) · sin (θ). Z = R + jX (corresponding to the impedance of the plasma processing apparatus because the measurement point is in the vicinity of the input end of the plasma processing apparatus), and this impedance Z is used for monitoring the impedance fluctuation of the plasma processing apparatus 30.

  In recent years, a plasma processing system has been put into practical use in which the impedance matching unit 20 does not perform dynamic impedance matching operation during plasma processing, and the output frequency of the high-frequency power supply device 10 is slightly changed.

Japanese Patent Laid-Open No. 10-185960

  Generally, a measurement device or a measurement device has a configuration in which the sensitivity of a sensor varies and the detection value detected by the sensor is different from the correct measurement value, so that the detection value is converted into a correct measurement value and output. Also in the high-frequency measuring device applied to the above-described plasma processing system, calibration data for converting the detected value to the correct measured value is obtained in advance by actual measurement or the like, and in the actual measurement, the detected value is correct with the calibration data. The measurement value is calibrated and output.

  For example, when the effective value V of the high frequency voltage is measured, a high frequency voltage having the same output and frequency is supplied in advance to a reference load (generally a characteristic impedance of the plasma processing system, for example, 50Ω), and generated at the reference load. The calibration data Ca (= Va / Va ′) is obtained from the measured value Va ′ and the correct voltage value Va, and in the actual measurement, the measured value is multiplied by the calibration data. The measured value is output.

  By the way, in the high frequency measuring apparatus applied to the conventional plasma processing system, since the frequency used for the plasma processing is a fixed frequency such as 2 MHz or 13.56 MHz, only calibration data for these frequencies is prepared. It was.

  However, as described above, in a plasma processing system that performs impedance matching by minutely changing the frequency of a high-frequency signal output from a high-frequency power supply device, the frequency during plasma processing is within a predetermined frequency range centered on the fixed frequency. If the conventional high-frequency measuring device is used as it is, the correct measurement value can be obtained at the center frequency, but the calibration data becomes inappropriate at the frequency outside the center frequency, resulting in a problem that a measurement error occurs.

  For this reason, in a high-frequency measuring device applied to such a plasma processing system, it is necessary to measure calibration data in advance for the frequency fluctuation range of the high-frequency signal output from the high-frequency power supply device and hold it in the device. However, if this method is used, a large amount of calibration data is required, depending on the frequency fluctuation range and the number of frequency samples to be calibrated, and the capacity of the memory for storing calibration data in the high-frequency measurement device is large. The problem of increasing arises. There is also a problem that the work load for acquiring the calibration data in advance increases.

  The present invention has been conceived under the circumstances described above, and calibration data is held only for some frequencies within a predetermined frequency range, and calibration data for other frequencies is held. It is an object of the present invention to provide a high-frequency measuring device that can accurately perform high-frequency measurement in a predetermined frequency range with a small amount of calibration data by generating from existing calibration data.

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

  A high-frequency measurement device provided by the present invention is a high-frequency measurement device capable of measuring a high-frequency signal in a predetermined frequency range set in advance, and includes a signal detection unit that detects the high-frequency signal, and the signal detection unit. Calibration data storing calibration data Cmin and Cmax for calibrating the detected value Amin at the lower limit frequency fmin and the detected value Amax at the upper limit frequency fmax of the frequency range to the true measured value ASmin and measured value ASmax, respectively. Storage means; frequency detection means for detecting a frequency fm of the high-frequency signal detected by the signal detection means; a lower limit frequency fmin and an upper limit frequency fmax of the frequency range; and a frequency fm detected by the frequency detection means Using the calibration data Cmin and Cmax stored in the calibration data storage means, the calibration data Cm for the frequency fm Calibration data calculation means for calculating, and measurement value calibration means for calibrating the detection value Am detected by the signal detection means to a true measurement value ASm using the calibration data Cm calculated by the calibration data calculation means. (Claim 1).

  According to a preferred embodiment, the calibration data calculation means calculates the calibration data Cm by an arithmetic expression of Cm = Cmin + (fm−fmin) · (Cmax−Cmin) / (fmax−fmin). The signal detected by the signal detection means is a high-frequency voltage signal or a high-frequency current signal.

  According to another preferred embodiment, in the high-frequency measurement device according to claim 1 or 2, the signal detection means includes a voltage detection means for detecting the high-frequency voltage signal, and a current detection means for detecting the high-frequency current signal. In the calibration data storage means, the detected value Vmin of the high-frequency voltage signal at the lower limit frequency fmin of the frequency range and the detected value Vmax of the high-frequency voltage signal at the upper limit frequency fmax detected by the voltage detecting means. The true measured value VSmin and voltage calibration data Cvmin, Cvmax for calibrating to the measured value VSmax, the detected value Imin of the high-frequency current signal at the lower limit frequency fmin and the upper limit frequency fmax detected by the current detecting means, respectively. Current calibration data Cim for calibrating the detected value Imax of the high-frequency current signal to the true measured value ISmin and the measured value ISmax, respectively. in, Cimax are stored, and the calibration data calculation means is configured to output the lower limit frequency fmin and the upper limit frequency fmax of the frequency range, the frequency fm detected by the frequency detection means, and the voltage stored in the calibration data storage means. The calibration data Cvmin and Cvmax are used to calculate the voltage calibration data Cvm for the frequency fm, the lower limit frequency fmin, the upper limit frequency fmax and the frequency fm, and the current calibration data Cimin stored in the calibration data storage means. , Cimax is used to calculate current calibration data Cim for the frequency fm, and the measured value calibration means uses the voltage calibration data Cvm calculated by the calibration data calculation means to detect the high frequency detected by the voltage detection means. Calibrating the detected value Vm of the voltage signal to the true measured voltage value VSm, and the calibration data calculating means The detected value Im of the high-frequency current signal detected by the current detecting means is calibrated to the true measured current value ISm using the current calibration data Cim calculated in (5).

  According to still another preferred embodiment, in the high-frequency measurement device according to claim 5, the high-frequency signal is detected using the high-frequency voltage signal detected by the voltage detection means and the high-frequency current signal detected by the current detection means. Phase detection means for detecting a phase is further provided, and the calibration data storage means has the phase θmin at the lower limit frequency fmin and the phase θmax at the upper limit frequency fmax detected by the phase detection means as a true phase θSmin, respectively. Phase calibration data Cdmin and Cdmax for calibrating to the true phase θSmax are further stored, and the calibration data calculation means is further detected by the frequency detection means with a lower limit frequency fmin and an upper limit frequency fmax of the frequency range. Using the frequency fm and the phase calibration data Cdmin, Cdmax stored in the calibration data storage means, the frequency f The phase calibration data Cdm is calculated, and the measurement value calibration unit further calibrates the phase θm detected by the phase detection unit to the true phase θSm using the phase calibration data Cdm calculated by the calibration data calculation unit. (Claim 6).

  In the high-frequency measuring device according to claim 6, the voltage calibration data Cvmin and Cvmax are average values of a plurality of voltage calibration data obtained by changing the output of the high-frequency signal within a predetermined range set in advance. The current calibration data Cimin and Cimax are average values of a plurality of current calibration data obtained by changing the output of the high-frequency signal within the predetermined range, and the phase calibration data Cdmin and Cdmax are the predetermined range. The average value of a plurality of phase calibration data obtained by changing the output of the high-frequency signal in (5).

  Further, in the high-frequency measurement device according to any one of claims 1 to 7, it is preferable to enable measurement with respect to high-frequency signals in two or more discrete frequency ranges in which frequency ranges do not overlap each other (claim 8). .

  According to the high frequency measurement device of the present invention, even when the frequency fm of the high frequency signal fluctuates within a predetermined range, it corresponds to the calibration data Cmin and the upper limit frequency fmax corresponding to the lower limit frequency fmin stored in the calibration data storage means. The calibration data Cm corresponding to the measurement frequency fm is calculated by using, for example, a linear interpolation method, and the detected value Am of the measured high-frequency voltage signal or high-frequency current signal is used as the calibration data. Since Cm is used to calibrate to the true measurement value ASm, high-frequency measurement in a predetermined frequency range can be accurately performed with a small amount of calibration data.

  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 drawings.

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

  An impedance matching device 3 is connected to the high frequency power supply device 1 via a transmission line 2 made of a coaxial cable, for example, and a plasma processing device 4 is connected to the impedance matching device 3.

  The high frequency power supply device 1 supplies high frequency power to the plasma processing apparatus 4 and is a power supply device that can output high frequency power having an output frequency of several hundred kHz or more, for example. Generally, since the frequency used in the plasma processing of the plasma processing apparatus 4 is 2 MHz or 13.56 MHz, the high frequency power supply apparatus 1 supplies the plasma processing apparatus 4 with a high frequency power of 2 MHz or 13.56 MHz. It is like that. Further, in the present plasma processing system, the output frequency f of the high-frequency power supply device 1 is set to a predetermined frequency range ± δf (for example, fo = 2 MHz) around the frequency fo with respect to impedance fluctuation of the plasma processing apparatus 4 during the plasma processing. In this case, when δf = 0.2 MHz and fo = 13.56 MHz, δf = 0.68 MHz), impedance matching is performed.

  More specifically, for example, if the plasma processing system is configured with a 50Ω system, that is, the impedance (output impedance) of the high frequency power supply device 1 viewed from the output end 1a of the high frequency power supply device 1 is, for example, 50Ω. If the output end 1a of the high-frequency power supply device 1 is connected to the input end 3a of the impedance matching device 3 by the transmission line 2 having a characteristic impedance of 50Ω, the high-frequency power supply device 1 changes the output frequency to The impedance when the plasma processing apparatus 4 side is viewed from the output end 1a of the high frequency power supply apparatus 1 is matched with 50Ω.

  The impedance matching unit 3 matches impedances of the high-frequency power supply device 1 and the plasma processing device 4, and includes capacitors C1 and C2, which are impedance elements, an inductor L, and the like. Each value of the capacitors C1 and C2 and the inductor L is a fixed value, and does not have a function of performing impedance matching between the high frequency power supply device 1 and the plasma processing device 4 following the impedance variation of the plasma processing device 4. As described above, the dynamic impedance matching operation during the plasma processing is performed by changing the output frequency of the high-frequency power supply device 1 at the center frequency fo ± δf.

  In the above example, the impedance matching unit 3 is connected to the tip of the transmission line 2 so that the impedance viewed from the input end of the impedance matching unit 3 during plasma processing when viewed from the plasma processing apparatus 4 side is approximately 50Ω. Convert load impedance. Note that when plasma processing is started in the plasma processing apparatus 4, the state of the workpiece and the plasma changes with the progress of the plasma processing, and thereby the impedance of the plasma processing apparatus 4 changes. Since the impedance change range of the plasma processing apparatus 4 when the plasma processing is performed in advance can be known in advance, the representative value within the impedance change range is set as the impedance of the plasma processing apparatus 4, and the impedance matching unit 3 The values of the capacitors C1 and C2 and the inductor L are configured to perform impedance matching with respect to the representative value of this impedance.

  Further, a high-frequency measuring device 5 according to the present invention is provided in the vicinity of the output end 3b of the impedance matching device 3. The high-frequency measuring device 5 measures the voltage (effective value) Vm, current (effective value) Im, and phase θm between the voltage and current of the high-frequency signal at the output end 3b of the impedance matching unit 3, and the measured values Vm, Im and θm are output to the outside. In FIG. 1, the output end 3 b of the impedance matching unit 3 and the input end 4 a of the plasma processing apparatus 4 are depicted as being connected by a transmission line, but in an actual configuration, the output end of the impedance matching unit 3 is illustrated. 3b is directly connected to the input terminal 4a of the plasma processing apparatus 4, and the high-frequency measuring apparatus 5 is configured such that the voltage Vm, current Im, and phase θm of the input terminal 4a of the plasma processing apparatus 4, that is, the load terminal voltage Vm, current Im, and The phase θm is measured.

  This high-frequency measuring device 5 is adapted to measure points (FIG. 1) in the frequency range of 2.0 ± 0.2 MHz and the frequency range of 13.56 ± 0.68 MHz in accordance with the impedance matching operation by changing the frequency of the high-frequency power supply device 1. The voltage Vm, current Im, and phase θm of the output terminal 3b of the impedance matching unit 3) can be measured.

  Usually, a measuring instrument uses a reference measurement object to determine the relationship between the detected value and the value that is output as the measured value in order to convert the detected value that is actually detected by the detecting element into a correct measured value and output it. It comes to calibrate. That is, a calibration coefficient for calibrating the detected value to the measured value is actually measured using the reference measurement object, and in the actual measurement, the detected value of the detection element is multiplied by the calibration coefficient and converted to the measured value. . In this case, with respect to the frequency characteristic, for the frequency range to be measured, the calibration coefficient should be measured and prepared in advance for each measurement frequency. However, in the high frequency measurement device 5 according to the present embodiment, The lower limit frequency fmin and the upper limit frequency fmax of the frequency range (in the frequency range of 2.0 ± 0.2 MHz, fmin = 1.8 MHz, fmax = 2.2 MHz, fmin in the frequency range of 13.56 ± 0.68 MHz) = 12.88 MHz and fmax = 14.24 MHz), the calibration coefficients Cmin and Cmax are actually measured, and the calibration coefficient Cm for an arbitrary frequency fm within the frequency range is linearly interpolated with the calibration coefficients Cmin and Cmax. Thus, accurate measurement can be performed with respect to an arbitrary frequency fm within the frequency range with a small calibration coefficient.

の演算式により算出できる。 Specifically, the high-frequency measuring device 5 stores a calibration coefficient Cmin for the lower limit frequency fmin and a calibration coefficient Cmax for the upper limit frequency fmax, but the frequency range Δf = (fmax−fmin) = 2δf is Since the characteristic of the calibration coefficient C in this frequency range Δf is very narrow and can be approximated as changing linearly, as shown in FIG. 2, the calibration coefficient Cm for an arbitrary frequency fm in the frequency range Δf is obtained. The

It can be calculated by the following equation.

  Since the above equation (1) is a general equation for obtaining the calibration coefficient C by linear interpolation, for example, when obtaining the voltage calibration coefficient Cvm, ΔCv = Cvmax−Cvmin and Cvmin are used as ΔC and Cmin, and the current When obtaining the calibration coefficient Cim, ΔCi = Cimax−Cimin and Cimin are used as ΔC and Cmin. Similarly, when obtaining the phase calibration coefficient Cdm, ΔCd = Cdmax−Cdmin and Cdmin are used as ΔC and Cmin.

  As described above, the high-frequency measuring device 5 stores the voltage calibration coefficients Cvmin and Cvmax, the current calibration coefficients Cimin and Cimax, and the phase calibration coefficients Cdmin and Cdmax. In the present embodiment, a frequency range W1 of 2.0 ± 0.2 MHz (hereinafter referred to as “first frequency range W1”) and a frequency range W2 of 13.56 ± 0.68 MHz (hereinafter referred to as “second frequency”). For the first frequency range W1 and the second frequency range W2, voltage calibration coefficients Cvmin, Cvmax, current calibration coefficients Cimin, Cimax, and phase are respectively measured. Calibration coefficients Cdmin and Cdmax are measured and stored in advance.

  In the following description, in order to identify the frequency bands of the calibration coefficients Cv, Ci, and Cd, those for the first frequency band W1 are appended with “1” after C as in C1v, C1i, and C1d. For the second frequency band W2, “2” is added after C as in C2v, C2i, and C2d.

  Here, a method for obtaining the calibration coefficients Cv, Ci, Cd stored in the high-frequency measuring device 5 will be described.

  FIG. 3 is a diagram illustrating an example of a measurement system for acquiring the calibration coefficients Cv, Ci, and Cd.

  In the measurement system shown in the figure, a high frequency measuring device 5 is connected to the input end 6a of the dummy load 6, and a wattmeter 7 is connected to the input end 5a of the high frequency measuring device 5, and the input end 7a of the wattmeter 7 and the high frequency are connected. The power supply device 1 has a configuration in which the output end 1a is connected by the transmission line 2, and the calibration coefficient measuring device 8 composed of a personal computer or the like for controlling the operation of the measurement system is added to the high frequency power supply device 1, the high frequency measuring device 5, and the dummy. A load 6 and a power meter 7 are connected.

  At the stage of acquiring the calibration coefficients Cv, Ci, Cd, “1” is set as the initial value of the calibration coefficients Cv, Ci and “0” is set as the initial value of Cd in the high-frequency measuring device 5. Accordingly, the detected voltage effective value Vm ′, current effective value Im ′, and phase θm ′ are output to the calibration coefficient measuring apparatus 8 as they are.

  The dummy load 6 generates a characteristic impedance Ro (50Ω in the present embodiment) of the plasma processing system in a pseudo manner, and substantially terminates the output terminal 5b of the high-frequency measuring device with the characteristic impedance Ro (= 50Ω). It is. The dummy load 6 is a T-type connection between the inductor L2 and the variable capacitors VC3 and VC4 which are variable reactance elements, and the variable capacitor VC4 is terminated with a resistor R1 of 50Ω. The reason why the termination resistance R1 is 50Ω is that the characteristic impedance of the measurement system is 50Ω.

  Capacitances C3 and C4 of the variable capacitors VC3 and VC4 can be changed stepwise. By changing the capacitances C3 and C4, the impedance of the dummy load 6 can be set to 50Ω in a wide frequency range including the first frequency range W1 and the second frequency range W2.

  The adjustment positions of the variable capacitors VC3 and VC4 (that is, the values of the capacitances C3 and C4) for setting the dummy load 6 to 50Ω for each frequency to be measured are acquired in advance, and the frequency and the variable capacitors VC3 and VC4 are acquired. The table showing the relationship with the adjustment position is set in the calibration coefficient measuring device 8. The calibration coefficient measurement device 8 controls the output frequency of the high-frequency power supply device 1 to the measurement frequency, and outputs data of the adjustment positions of the variable capacitors VC3 and VC4 corresponding to the measurement frequency to the dummy load 6, and sets the dummy load 6 to 50Ω. adjust.

  The wattmeter 7 includes a directional coupler that separates the traveling wave and the reflected wave, and a detector that detects the power of the traveling wave and the reflected wave output from the directional coupler, and the traveling wave from the high frequency power source 1. The power Pf and the reflected wave power Pr from the dummy load 6 are measured. The measured values Pf and Pr are input to the calibration coefficient measuring device 8.

  A signal (frequency control signal) for controlling the output frequency and a signal (output control signal) for controlling the output power are input to the high frequency power supply device 1 from the calibration coefficient measuring device 8. The high frequency power supply device 1 outputs a high frequency signal having the frequency specified by the frequency control signal and the output power specified by the output control signal.

  The calibration coefficient measuring device 8 includes a voltage calibration coefficient C1vmin, a current calibration coefficient C1imin and a phase calibration coefficient C1dmin at the lower limit frequency f1min of the first frequency range W1, and a voltage calibration coefficient C1vmax, a current calibration coefficient C1imax and a phase calibration coefficient at the upper limit frequency f1max. Automatic measurement of C1dmax, voltage calibration coefficient C2vmin, current calibration coefficient C2imin and phase calibration coefficient C2dmin at the lower limit frequency f2min of the second frequency range W2, and voltage calibration coefficient C2vmax, current calibration coefficient C2imax and phase calibration coefficient C2dmax at the upper limit frequency f2max To do.

  Specifically, the calibration coefficient measuring device 8 adjusts the dummy load 6 to 50Ω at each frequency f1min, f1max, f2min, and f1max, and then, for example, changes the frequency of 300W to 2000W at a 100W pitch while changing the frequency at a high frequency power supply device. 1 outputs a high frequency signal, and voltage calibration coefficients Cv (1), Cv (2), Cv (3)... Cv (18), current calibration coefficients Ci (1), Ci (2), Ci (3) at each output. )... Ci (18) and phase calibration coefficients Cd (1), Cd (2), Cd (3)... Cd (18) are calculated. Then, an average value of 18 calibration coefficients is calculated for each voltage, current, and phase, and the average value is set as a calibration coefficient for each frequency f1min, f1max, f2min, and f1max.

For example, in the case of the voltage calibration coefficient C1vmin at the frequency f1min, the calibration coefficient measuring device 8 adjusts the dummy load 6 so as to be 50Ω at the frequency f1min, and then changes the output of the high frequency signal from Pmin = 300W to Pmax = 2000W. Thus, the effective voltage value Vm ′ output from the high frequency measuring device 3 is detected. The calibration coefficient measuring device 8 calculates the effective voltage value Vm from the traveling wave power Pf and the reflected wave power Pr output from the wattmeter 7 according to the following calculation formula (2).

  In the equation (2), (Pf−Pr) is the power input to the dummy load 6 and Ro is the resistance value (50Ω) of the dummy load 6.

  Since the wattmeter 7 is provided in the vicinity of the high frequency measurement device 5, there is little error between the measurement point and the measurement point of the high frequency measurement device 5, and the measured value of the wattmeter 7 is the measurement point 5 a of the high frequency measurement device 5. Is measured theoretically from the effective voltage value Vm ′ by the high-frequency measurement device 5, the traveling wave power Pf and the reflected wave power Pr by the wattmeter 7, at the measurement point 5 a of the high-frequency measurement device 5. Thus, the effective voltage value Vm calculated in (1) is obtained.

  Accordingly, the output characteristics of the voltage effective value Vm and the voltage effective value Vm ′ are shown in FIG. 4A shows the output characteristics of the voltage effective value Vm calculated from the traveling wave power Pf and the reflected wave power Pr, and FIG. 4B shows the output of the voltage effective value Vm ′ directly detected by the voltage detector. It is a characteristic. For example, the voltage effective value Vm calculated from the traveling wave power Pf and the reflected wave power Pr at the output Pm in FIG. 4 is estimated as the true voltage effective value at the measurement point 5a, while the voltage effective value Vm ′. Since this is a directly detected value, a deviation between the detected value Vm ′ of the voltage effective value and the estimated value Vm of the true voltage effective value can be considered as a detection variation.

  Therefore, the voltage calibration coefficient C1vmin for calibrating the detection value Vm ′ of the effective voltage value of the high-frequency measuring device 5 at the output Pm to the correct effective voltage value Vm is obtained by the calculation of Vm / Vm ′. The voltage calibration coefficient C1vmin at other outputs Pm is also obtained by the same method. In the above example, the voltage calibration coefficient C1vmin is obtained for 18 outputs of outputs 300W, 400W,. Then, a voltage calibration coefficient C1vmin (= (C1v (1) + C1v (2) + C1v (3)... + C1v (18)) / 18) with respect to the frequency f1min is set.

  In the same manner, voltage calibration coefficients C1vmax, C2vmin, and C2vmax for other frequencies f1max, f2min, and f2max are also set.

  If the output P of the high-frequency signal is fixed, the voltage calibration coefficients C1vmin, C1vmax, C2vmin, and C2vmax at the fixed output P may be acquired. However, when the output is variable as in this embodiment, It is desirable to obtain the voltage calibration coefficient C1vmin and the like for each output. However, even when the error such as the voltage calibration coefficient C1vmin is relatively small between the outputs, the voltage calibration coefficient C1vmin is acquired for each output only by increasing the data such as the voltage calibration coefficient C1vmin. In this embodiment, the average value of the voltage calibration coefficient C1vmin of each output is calculated, and the calculated value is set as the voltage calibration coefficient C1vmin of the frequency f1min.

In the case of the current calibration coefficient C1imin at the frequency f1min, the calibration coefficient measuring device 8 calculates the current effective value Im from the traveling wave power Pf and the reflected wave power Pr output from the wattmeter 7 by the following calculation formula (3).

  Therefore, the output characteristics of the current effective value Im and the current effective value Im ′ are depicted as shown in FIG. 5A shows the output characteristics of the effective current value Im calculated from the traveling wave power Pf and the reflected wave power Pr, and FIG. 5B shows the output of the effective current value Im ′ directly detected by the current detection unit. It is a characteristic.

  The current calibration coefficient C1imin for calibrating the detection value Im 'of the current effective value of the high-frequency measuring device 5 at the output Pm to the correct current effective value Im is obtained by the calculation of Im / Im'. The current calibration coefficient C1imin at other outputs Pm is also obtained by the same method. In the above example, the voltage calibration coefficient C1imin is obtained for 18 outputs of outputs 300W, 400W,. Then, a current calibration coefficient C1imin (= (C1i (1) + C1i (2) + C1i (3)... + C1i (18)) / 18) with respect to the frequency f1min is set.

  In the same manner, current calibration coefficients C1imax, C2imin, and C2imax for other frequencies f1max, f2min, and f2max are also set. Further, the phase calibration coefficients C1dmin, C1dmax, C2dmin, and C2dmax for the frequencies f1min, f1max, f2min, and f2max are also set by the same method. The reason why the current calibration coefficient C1imin and the like and the phase calibration coefficient C1dmin and the like are average values of 18 calibration coefficients having different outputs is the same as in the case of the voltage calibration coefficient.

  Next, a processing procedure for acquiring a calibration coefficient will be described with reference to a flowchart shown in FIG.

  In the following description, a case where calibration coefficients for the lower limit frequency f1min and the upper limit frequency f1max of the first frequency range W1 are acquired will be described. Further, the minimum value of the variable range of the power P output from the high frequency power supply device 1 is Plow (300 W in the above example), the maximum value is Phigh (2000 W in the above example), and the increase amount of the output voltage P is ΔP ( In the above example, 100 W).

  First, the output frequency f is set to the lower limit frequency f1min of the first frequency range W1 (S1). Subsequently, the dummy load 6 is adjusted to 50Ω at the frequency f1min (S2), and the output P is set to the minimum power Plow (S3).

  Subsequently, high-frequency power having a frequency f1min and an output Plow is output from the high-frequency power supply device 1 (S4), and the effective voltage value Vm ′, the effective current value Im ′, and the phase θm ′ are measured by the high-frequency measuring device 5, and the wattmeter 7 Thus, the traveling wave power Pf and the reflected wave power Pr are measured (S5).

  Subsequently, a voltage calibration coefficient Cv, a current calibration coefficient Ci, and a phase calibration coefficient Cd with respect to the high-frequency power of the frequency f1min and the output Plow are calculated (S6), and the calculation results are stored in the memory in the calibration coefficient measuring device 8 ( S7).

により算出され、電流校正係数Ｃｉは、

により演算される。また、位相校正係数Ｃｄは、

により演算される。 The voltage calibration coefficient Cv is

And the current calibration coefficient Ci is

Is calculated by The phase calibration coefficient Cd is

Is calculated by

  Subsequently, the output P is increased by ΔP (S8), and it is determined whether or not the increased output P exceeds the maximum output Phigh (S9). If P ≦ Phigh (S9: NO), the process goes to step S4. Returning, the calculation process of the voltage calibration coefficient Cv, the current calibration coefficient Ci, and the phase calibration coefficient Cd for the high frequency power of the frequency f1min and the output (Plow + ΔP) is performed (S4 to S7).

  Thereafter, the calculation process of the voltage calibration coefficient Cv, the current calibration coefficient Ci, and the phase calibration coefficient Cd is repeated while increasing the output P by ΔP (S4 to S9 loop), and when P> Phigh (S9: YES), the memory The average value of the voltage calibration coefficient Cv with respect to the outputs Plow, Plow + ΔP, Plow + 2ΔP,... Phigh stored in is calculated (S10), and this average value is stored in the memory as the voltage calibration coefficient C1vmin with respect to the lower limit frequency f1min (S11). Similarly, the average value of the current calibration coefficient Ci and the average value of the phase calibration coefficient Cd for the outputs Plow, Plow + ΔP, Plow + 2ΔP,... Phigh are calculated (S10), and these average values are the current calibration coefficient C1imin and the phase for the lower limit frequency f1min. The calibration coefficient C1dmin is stored in the memory (S11).

  Subsequently, it is determined whether or not the output frequency f is set to the upper limit frequency f1max of the first frequency range W1 (S12). If f = f1max is not satisfied (S12: NO), the output frequency f becomes the upper limit frequency f1max. Once set (S13), the process returns to step S2, and the same processing as described above is repeated to calculate the voltage calibration coefficient C1vmax, current calibration coefficient C1imax, and phase calibration coefficient C1dmax with respect to the upper limit frequency f1max and store them in the memory (S2 to S2). S11).

  When the voltage calibration coefficients C1vmin and C1vmax, the current calibration coefficients C1imin and C1imax, and the phase calibration coefficients C1dmin and C1dmax with respect to the lower limit frequency f1min and the upper limit frequency f1max of the first frequency range W1 are obtained by the above processing, the high frequency measurement device The high-frequency measurement device 5 is completed as a measurement device capable of correct measurement by replacing the calibration coefficient (Cv = Ci = 1, Cd = 0) stored in 5 with the acquired calibration coefficient.

  Returning to FIG. 1, the measurement operation of the high-frequency measuring device 5 in the plasma processing system will be described.

  When high-frequency power is supplied from the high-frequency power supply device 1 to the plasma processing device 4 via the transmission line 2 and the impedance matching device 3, and the plasma processing is performed, the load end 3b is connected to the high-frequency measuring device 5 in the impedance matching device 3. The high frequency signal at is input.

  When a high frequency signal is input, the effective value Vm ′ of the high frequency voltage, the effective value Im ′ of the high frequency current, the phase θm ′ of the high frequency voltage and the high frequency current, and the frequency fm of the high frequency signal are detected. The voltage calibration coefficient Cvm, current calibration coefficient Cim, and phase calibration coefficient Cdm with respect to the frequency fm are calculated by the above-described equation (1).

  The product of the effective value Vm ′ of the input high-frequency voltage and the set voltage calibration coefficient Cvm is calculated, and the calculation result Vm = Cvm · Vm ′ is output as the voltage measurement value. Further, the product of the effective value Im ′ of the input high-frequency current and the set current calibration coefficient Cim is calculated, and the calculation result Im = Cim · Im ′ is output as the current measurement value. Further, the product of the effective value θm ′ of the input high-frequency current and the set phase calibration coefficient Cdm is calculated, and the calculation result θm = Cdm · θm ′ is output as the phase measurement value.

  As described above, according to the high-frequency measuring device 5 according to the present embodiment, the calibration coefficients Cmin and Cmax measured in advance only for the lower limit frequency fmin and the upper limit frequency fmax of the measurement frequency range of the high-frequency signal are stored. At any frequency fm within the measurement frequency range, the calibration coefficient Cm for the frequency fm is set by linearly interpolating the calibration coefficient Cmin for the lower limit frequency fmin and the calibration coefficient Cmax for the upper limit frequency fmax. It is possible to accurately perform high-frequency measurement at an arbitrary frequency within a predetermined frequency range with a coefficient. In addition, the calibration coefficient can be acquired relatively quickly without increasing the burden of the work of actually measuring the calibration coefficient in advance.

  In the high-frequency measuring device 5 according to the present embodiment, the calibration accuracy Cm does not exist for the arbitrary frequency fm within the measurement frequency range, so that the problem of calibration accuracy remains. When the calibration coefficient is actually measured, the measured calibration coefficient is stored in the high-frequency measuring device 5, and then, for example, the known load impedance Zm = Rm + jXm is measured at the center frequency fo in the first frequency range W1, and the high-frequency measuring device is measured. By calculating the impedance Zm from the effective voltage value Vm, the effective current value Im, and the phase θm output from 5, and checking the error between this calculation result and the known impedance value, the calibration accuracy can be easily confirmed. it can.

により算出することができるので、その算出値から得られる負荷インピーダンスＺｍ’＝Ｒｍ’＋ｊＸｍ’と既知の負荷インピーダンスＺｍ＝Ｒｍ＋ｊＸｍとの誤差を確認することにより、校正精度を確認することができる。 That is, in the measurement system of FIG. 3, after setting the dummy load 6 to the load impedance Zm = Rm + jXm at the center frequency fo in the first frequency range W1, the high frequency power of the frequency fo is output from the high frequency power supply device 1 5, the effective voltage value Vm, the effective current value Im, and the phase θm are measured. From these measured values, the resistance component Rm ′ and the reactance component Xm ′ of the load impedance are

Therefore, the calibration accuracy can be confirmed by checking the error between the load impedance Zm ′ = Rm ′ + jXm ′ obtained from the calculated value and the known load impedance Zm = Rm + jXm.

  Therefore, only when the desired calibration accuracy is obtained, the measured calibration coefficients are held only for the upper and lower frequencies in the frequency range, and the other frequencies may be calculated by linear interpolation.

  In the above embodiment, the second frequency range W2 has a fluctuation range of 0.68 MHz (0.05%) with respect to the center frequency fo = 13.56 MHz, and the ratio of the fluctuation range to the center frequency fo is extremely high. Since it is small, it is considered that the linearity of the calibration coefficient is sufficiently ensured in the second frequency range W2. Therefore, the above calibration method can be applied sufficiently.

  On the other hand, the first frequency range W1 has a fluctuation range of 0.2 MHz (10%) with respect to the center frequency fo = 2.0 MHz, and the ratio of the fluctuation range to the center frequency fo is relatively large. In the frequency range with respect to the center frequency lower than the range W1 or 2.0 MHz, the linearity of the calibration coefficient cannot be ensured sufficiently, and if the above calibration accuracy is checked, there may be a problem of calibration accuracy. In this case, for example, an actual calibration coefficient is also prepared for the center frequency fo in the frequency range, and for the frequency fp in the frequency range between the center frequency fo and the lower limit frequency fmin, the calibration coefficient Co for the center frequency fo and the calibration for the lower limit frequency fmin are performed. The calibration coefficient Cp is calculated by linear interpolation of the coefficient Cmin, and the calibration coefficient Cq is calculated by linear interpolation of the calibration coefficient Co for the center frequency fo and the calibration coefficient Cmax for the lower limit frequency fmax for the frequency fq in the frequency range of the center frequency fo and the upper limit frequency fmax. May be calculated. That is, it is preferable to divide the frequency range into a plurality of regions and calculate the calibration coefficient for each region by linear interpolation.

  In the above embodiment, the case where the high frequency measurement device 5 is built in the output end 3b side of the impedance matching device 3 has been described. However, the high frequency measurement device 5 may be built in the input end 3a of the impedance matching device 3, Needless to say, the measuring device may be used alone.

  In the above embodiment, the high-frequency measuring device capable of measuring all of the high-frequency voltage, high-frequency current, and phase has been described. However, the present invention also relates to a high-frequency measuring device that measures only a high-frequency voltage or only a high-frequency current. It goes without saying that a calibration method for measured values can be applied.

  Further, in the above embodiment, the case where the detection value is multiplied by the calibration coefficient when obtaining the true measurement value has been described, but the measurement value according to the present invention is also applied to the case where addition or other calculation is performed on the calibration data. It goes without saying that the calibration method can be applied.

It is a figure which shows an example of the plasma processing system with which the high frequency measuring apparatus which concerns on this invention is applied. It is a figure for demonstrating the method of calculating a calibration coefficient by linear interpolation. It is a figure which shows an example of the measurement system for acquiring calibration coefficient Cv, Ci, Cd. It is a figure which shows the frequency characteristic of the voltage (effective value) computed from the voltage (effective value) directly detected by a voltage detection part, and incident wave electric power and reflected wave electric power. It is a figure which shows the frequency characteristic of the electric current (effective value) calculated from the electric current (effective value) detected directly by an electric current detection part, and incident wave electric power and reflected wave electric power. It is a flowchart which shows the process sequence for acquiring the calibration coefficients Cv, Ci, and Cd in the measurement system of FIG. It is a figure which shows the structure of a general plasma processing system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 High frequency power supply device 2 Transmission line 3 Impedance matching device 4 Plasma processing apparatus 5 High frequency measuring device 6 Dummy load 7 Wattmeter 8 Calibration coefficient measuring device

Claims (8)

A high-frequency measuring device capable of measuring a high-frequency signal in a predetermined frequency range set in advance,
Signal detection means for detecting the high-frequency signal;
Calibration data Cmin, Cmax for calibrating the detected value Amin at the lower limit frequency fmin and the detected value Amax at the upper limit frequency fmax of the frequency range to the true measured value ASmin and measured value ASmax, respectively, detected by the signal detection means. Stored calibration data storage means;
Frequency detecting means for detecting a frequency fm of the high frequency signal detected by the signal detecting means;
Using the lower limit frequency fmin and upper limit frequency fmax of the frequency range, the frequency fm detected by the frequency detection means, and the calibration data Cmin and Cmax stored in the calibration data storage means, the calibration data Cm for the frequency fm Calibration data calculation means for calculating
A measurement value calibration means for calibrating the detection value Am detected by the signal detection means to a true measurement value ASm using the calibration data Cm calculated by the calibration data calculation means;
A high-frequency measuring device comprising: The high-frequency measuring device according to claim 1, wherein the calibration data calculation means calculates the calibration data Cm by the following calculation formula.

  The high-frequency measuring device according to claim 1 or 2, wherein the signal detected by the signal detecting means is a high-frequency voltage signal.   The high-frequency measuring device according to claim 1 or 2, wherein the signal detected by the signal detecting means is a high-frequency current signal. The signal detection means comprises a voltage detection means for detecting the high frequency voltage signal and a current detection means for detecting the high frequency current signal,
In the calibration data storage means, the detected value Vmin of the high-frequency voltage signal at the lower limit frequency fmin of the frequency range and the detected value Vmax of the high-frequency voltage signal at the upper limit frequency fmax detected by the voltage detecting means are respectively true measurements. Voltage calibration data Cvmin, Cvmax for calibrating to the value VSmin and the measured value VSmax, the detected value Imin of the high frequency current signal at the lower limit frequency fmin and the high frequency current signal at the upper limit frequency fmax detected by the current detection means Current calibration data Cimin and Cimax for calibrating the detected value Imax to the true measured value ISmin and the measured value ISmax are stored.
The calibration data calculation means uses the lower limit frequency fmin and the upper limit frequency fmax of the frequency range, the frequency fm detected by the frequency detection means, and the voltage calibration data Cvmin and Cvmax stored in the calibration data storage means. The voltage calibration data Cvm for the frequency fm is calculated, and the lower limit frequency fmin, the upper limit frequency fmax and the frequency fm, and the current calibration data Cimin and Cimax stored in the calibration data storage means are used to calculate the frequency calibration data Cvm. Calculate current calibration data Cim for fm,
The measurement value calibration means calibrates the detection value Vm of the high-frequency voltage signal detected by the voltage detection means to the true voltage measurement value VSm using the voltage calibration data Cvm calculated by the calibration data calculation means, 2. The detection value Im of the high-frequency current signal detected by the current detection unit is calibrated to a true current measurement value ISm using the current calibration data Cim calculated by the calibration data calculation unit. 2. The high frequency measuring apparatus according to 2. And further comprising phase detection means for detecting the phase of the high-frequency signal using the high-frequency voltage signal detected by the voltage detection means and the high-frequency current signal detected by the current detection means,
Phase calibration data for calibrating the phase θmin at the lower limit frequency fmin and the phase θmax at the upper limit frequency fmax detected by the phase detection unit to the true phase θSmin and the true phase θSmax, respectively, in the calibration data storage means. Cdmin and Cdmax are further stored,
The calibration data calculation means further uses the lower limit frequency fmin and the upper limit frequency fmax of the frequency range, the frequency fm detected by the frequency detection means, and the phase calibration data Cdmin and Cdmax stored in the calibration data storage means. Calculating the phase calibration data Cdm for the frequency fm,
6. The measurement value calibration unit further calibrates the phase θm detected by the phase detection unit to a true phase θSm using the phase calibration data Cdm calculated by the calibration data calculation unit. The high frequency measuring device described in 1.   The voltage calibration data Cvmin and Cvmax are average values of a plurality of voltage calibration data obtained by changing the output of the high-frequency signal within a predetermined range set in advance. The current calibration data Cimin and Cimax are the predetermined values. An average value of a plurality of current calibration data obtained by changing the output of the high-frequency signal in a range, and the phase calibration data Cdmin and Cdmax are a plurality of values obtained by changing the output of the high-frequency signal in the predetermined range. The high-frequency measuring device according to claim 6, wherein the high-frequency measuring device is an average value of phase calibration data.   The high-frequency measuring device according to any one of claims 1 to 7, wherein measurement is possible with respect to high-frequency signals in two or more discrete frequency ranges whose frequency ranges do not overlap each other.

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