JPS61176862A - Method and instrument for measuring impedance - Google Patents

Abstract

PURPOSE:To determine an unknown impedance value such as electric discharge impedance by detecting an amplitude ratio and phase difference from the voltage waveform when the end of a high-frequency power source to be connected to load is open and the voltage waveform when the unknown impedance is connected thereto and subjecting the same to arithmetic processing. CONSTITUTION:The sine wave of the high-frequency power source 2 is generated in synchronization with the clock signal of a clock generator 1 and the clock signal is inputted as an external trigger signal to a synchroscope 5. A high-frequency voltage probe 4 is connected to the point A. A coaxial switch 3 is connected to the side (a). The voltage at the point A is the sine wave of the amplitude E0 having no phase deviation with respect to the clock signal. The voltage at the point A is the sine wave of the amplitude V having the phase deviated by psi by the load (unknown impedance Z) 6 when the switch is connected to the side (b). The phase difference psi and amplitude ratio eta(V/E0) are measured and are inputted to an arithmetic means 7 and the value of the load impedance is easily determined by the equation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to impedance measurement, and particularly to an impedance measurement method and apparatus suitable for measuring impedance of discharge plasma using high frequency.

[Background of the invention]

Conventionally, methods for measuring high-frequency impedance are described in the ``Measurement of impedance'' section of ``High-frequency measurement methods'' in the Electrical Engineering Handbook (IEEJ, 1967), and in ``Electronic measurement'' by Shigeo Morisaki (Corona Publishing, 1972). This is explained in detail in the section ``Measurement of impedance of circuit elements'' in ``Measurement''. However, these measurement methods measure the impedance of fixed circuit elements, such as the impedance of discharge plasma in dry process equipment.
A technique that measures fluctuating impedance, which is not intended to physically measure fluctuating impedance.

For example, an "impedance change detection circuit" disclosed in Japanese Patent Laid-Open No. 59-20985 is disclosed, but it detects changes in impedance and does not measure the impedance value itself.

In addition, as a method to measure the impedance of discharge, the high-frequency power source and the load (plasma) are considered as a system, and when the impedance of the entire system is matched (the impedance when looking from the high-frequency power source side to the load side matches the internal resistance of the high-frequency power source). when).

There is a method of determining the impedance value from the circuit constants of the matching circuit, but this is only possible during impedance matching. In other words, it has been impossible to measure discharge impedance in a general impedance mismatched state.

[Object of the Invention] An object of the present invention is to provide an impedance measuring method and device that eliminates the drawbacks of the above-mentioned prior art and can determine the value of unknown impedance such as discharge impedance by a simple method. be.

[Summary of the invention]

In order to achieve the above object, the present invention detects the amplitude ratio η and the phase difference ψ from the voltage waveform when the high-frequency power supply load connection terminal is open and the voltage waveform when the unknown impedance is connected, and calculates the amplitude ratio using η and ψ. The purpose is to find unknown impedance through arithmetic processing.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 is a schematic configuration diagram of the present invention. 1 is a clock generator with a frequency ω; 2 is a high-frequency power supply that generates a sine wave with a frequency ω in synchronization with the clock of the clock generator 1; 5 is a coaxial switch; 4 is a high-frequency voltage probe; 5 is a synchroscope; C load (unknown impedance Z), 7 is a calculation output stage.

Further, FIG. 2 shows the voltage waveforms at points A0 and B in FIG. 1. (1) is the voltage waveform at point A when 4 to 0 of the coaxial switch 5 are connected, and (3J is the voltage waveform at point A when b to c is connected. On the other hand, ( 2) is the voltage waveform at the output terminal (point B) of the clock generator 1.

In FIG. 5, the load 6 is the electrode 12 of the dry etching device 20.
A discharge plasma 16 is formed on the upper electrode 15. The discharge impedance of this discharge plasma 16 is ZP,
Its equivalent circuit is 17.

FIG. 4 is a flowchart showing the calculation procedure of the calculation means 7.

In addition, FIG. 5 shows the components Rp and Cp of the plasma impedance ZP calculated according to the flowchart in FIG.
) The results were measured for discharge time, (reaction gas pressure in the processing chamber, and high-frequency power.)

Next, the present invention will be explained in detail using FIGS. 1 to 5.

In Fig. 1, when the coaxial switch 5 is connected to the b side, the voltage of the high frequency power supply is E = F6 mjωt, and the internal resistance is r.
Then, the current I flowing through the load 6 is i=paddle
('').Therefore, the potential t at point A is V=ZI=MaE (2) On the other hand, when the coaxial switch 3 is connected to the α side, point A is at the open end (Z -oc), and from equation 2, 9=E.

Now, the clock signal of clock generator 1, Fig. 2 (2)
At the same time, a sine wave of the high frequency power source 2 is generated in synchronization, and at the same time, the clock generator is inputted to the synchroscope 5 as an external trigger signal (2), and the high frequency voltage pulse 4 is connected to the point AK.

At this time, when the coaxial switch 5 is connected to the a side, the voltage has an amplitude E with no one phase shift with respect to the clock generator 1.
A sine wave □S of 0 is obtained. (Fig. 2 (1) Door side, when the coaxial switch is connected to side b, the voltage at point A is a sine wave with a phase shift of ψ with respect to the clock signal and an amplitude of V (V < E, ,) is obtained.

(Fig. 2 (3)) (2) Here, if V4=η (amplitude ratio), then E=E, for ajωt. Substituting (3) into (2), °・−1−1−=ηψ (4
)r −)−Z is obtained. The future will be determined.

Therefore, the voltage waveform when the point A is open is measured in advance, and from this waveform and the voltage waveform when the load is connected, the phase difference ψ
, by measuring the amplitude ratio η and inputting it to the calculation means 7, we get (6)
2, the value of the load impedance can be easily determined.

Next, a case where the load 2 is a discharge plasma 16 connected in cascade to the matching circuit 14 will be explained with reference to FIGS. 5 and 4. In this case, we consider the same way and set the load impedance Z as Z = impedance cascade discharge impedance of the matching circuit, and after measuring ψ (step 51 in Figure 4), we calculate Z (step 51 in Figure 4) using equation (5) above. 52) and the circuit of the matching circuit at that time (step 54 in FIG. 4).Furthermore, from this, the resistance component and capacitance component CP of the discharge plasma can be determined by simple calculation. (Step 55 in Figure 4) As described above, simply measure the voltage waveform when the high-frequency power supply is open, and then measure the phase difference ψ and amplitude ratio η from that waveform and the voltage waveform when the load is connected. , the impedance of any state of discharge plasma can be found very easily. An example of measurement according to the present invention is shown in FIG.

In this way, when the resistance and capacitance components of the discharge plasma are measured and monitored with respect to the time during discharge, process pressure, and high frequency power, the value of discharge impedance is IK ~ 10KO for the resistance component and IK ~ 10KO for the capacitance component. is 100P ~ 2
It can be quantitatively understood as 007F, and has an effect Q'- on analysis of discharge state, analysis of etching characteristics, process condition control, and improvement of reproducibility.

Next, an embodiment in which the discharge impedance actually measured in the present invention is applied to the processing and regulation of a plasma processing apparatus will be explained with reference to FIG. 6. In FIG. , 14 is a matching circuit for two different circuits, 41 is a process status recording device, 42 is an alarm device, and 45 is an information etching end point detection device.

First, impedance matching will be explained.

Electric power (traveling wave electric power (reflected wave electric power)
From the measurement, the capacitors 14a and 14c of the matching circuit 14 are set so that the reflected wave power Q"s is the minimum.

Impedance matching was performed by qualitatively adjusting the coil 14A, but in the present invention, the capacitor is The values of 14α, 14C, and coil 1tA can be grasped quantitatively, and η= O, S, ψ=
It is possible to automatically or manually match the discharge zero impedance in a short time so that the discharge impedance becomes zero.

Second, the matching circuits 14, 141, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 22, 22, 22, 22, 32, 22, 22, 23, 23, 23, 23, 23, 23, 3, 3, 3, 3, 3, 3, 3,,,,, 7,,,,,1,,,,10, sm, 14c, s,, ,, and, e.g., the impedance of the discharge plasma. ...
, 143, etc., it is also possible to select and connect an optimal matching circuit according to the impedance value of the discharge plasma obtained by the calculation means 7 to stabilize the air discharge.

Third, the value of the discharge plasma is stored in the process state storage device 41.
By recording and managing the information, stable control of the process can be achieved, and it is also possible to predict the discharge state when the process conditions are changed.

Fourth, by measuring the discharge impedance value over a long period of time and monitoring the amount of change thereof, when the value exceeds a certain threshold, the alarm device 42 is activated to issue an alarm. Example: Processing chamber 1 with repeated &L discharge
It is possible to detect when it is time to clean the dirt on the wall surface.

Fifth, by inputting and monitoring the discharge impedance value during the -th etching process to the etching end point detection device 45, it is also possible to detect the end point of etching.

As explained above, there is a great effect on stabilizing the process of the dry process equipment and improving the controllability of the process.

〔Effect of the invention〕

As explained above, the high-frequency impedance can be easily determined by detecting the amplitude ratio and phase difference from the voltage waveform when the load connection end of the high-frequency power supply is open and the voltage waveform when the load (impedance unknown) is connected. It can be measured.

In a drive process device in which the load is a matching circuit and a cascade connection of discharge plasma, a state of impedance mismatching of the entire system appears even temporarily due to changes in the discharge state during the reaction process. However, even in a state where the impedance of the entire system is mismatched, the impedance of the discharge plasma can be easily measured according to the present invention, making it possible to constantly monitor the impedance of the discharge state, which has a great effect on the analysis of the discharge state. produced.

Incidentally, in the past, the discharge impedance could only be measured when the impedance of the entire system was matched, and impedance monitoring and analysis of the discharge state was insufficient.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of the present invention, Figure 2 is the voltage waveform at points A and B in Figure 1, Figure 5 is an explanatory diagram when the load is a cascade connection of a matching circuit and discharge plasma, and Figure 4 is Arithmetic means 7
FIG. 5 is a diagram showing the measurement of the impedance change of the discharge plasma. Fig. 6 shows the actual discharge impedance measured in the present invention applied to process processing and control of a plasma processing apparatus (actual mfl). 1...Clock generator 2...High frequency power supply 3...Coaxial switch 4...High frequency voltage probe 5...-Synchroscope 6...Load (unknown impedance) 7...Calculating means μ81 island Shodo - Figure 4, 5] Time - Pressure (T, W) - Purity of the drawing (L to change the content) Procedural amendment (method) Indication of the case 1988 Patent Application No. 16558 Invention name of
Name Person in charge of impedance measurement method and device correction Patent applicant name (5101 Tsuji Co., Ltd. Manufactured by Hitachi Co., Ltd.)
Contents of the amendment by the author, agent and agent t “Figure 5” on page 12, line 20 of the specification has been changed to “Figure 3”
Display of the case 1985 Patent Application No. 16538 Title of the invention Person who corrects the impedance measurement method and its device Relationship with the case Name of the patent applicant (Manufactured by Slot Corporation Hitachi Co., Ltd. Manufacture fee)
Target of amendment by the administrator Contents of amendment in the detailed explanation of the invention in the specification t Correct IZJ in line 19 of page 4 of the first specification to IZJ. 2 Correct ra-cl in the second line of page 5 to ra-cl. B Correct rZpJ on page 5, line 12 to r zp J. Correct rZpJ on page 5, line 16 of the same year to rZpJ. that's all

Claims (1)

[Claims] 1. The value of load impedance is determined by measuring the phase difference and amplitude ratio between the open end voltage waveform of a high frequency power source and the voltage waveform at the load connection end when a load is connected to the high frequency power source. An impedance measurement method characterized by calculating. 2. Consists of means for measuring the phase difference and amplitude ratio between the open end voltage waveform of the high frequency power supply and the voltage waveform at the load connection end when a load is connected to the high frequency power supply, and a calculating means, and the phase difference and the amplitude An impedance measurement device characterized by calculating a value of load impedance from a ratio. 3. The impedance measuring method according to claim 1, wherein the load connected to the high frequency power source is discharge plasma, and the impedance value of the discharge plasma is calculated. 4. The impedance measuring device according to claim 2, wherein the load connected to the high frequency power source is discharge plasma, and the impedance value of the discharge plasma is calculated.