WO2019235690A1

WO2019235690A1 - Plasma measurement method and plasma process measurement sensor

Info

Publication number: WO2019235690A1
Application number: PCT/KR2018/010307
Authority: WO
Inventors: 하창승; 임대철; 장윤민; 최익진; 한희성; 홍윤기
Original assignee: 엘지전자 주식회사
Priority date: 2018-06-05
Filing date: 2018-09-04
Publication date: 2019-12-12
Also published as: KR102616493B1; KR20190138454A

Abstract

Disclosed are a plasma measurement method and a plasma process measurement sensor. The plasma measurement method according to an embodiment of the present invention comprises: pairing a first probe and a second probe; generating a signal by the first probe; generating a signal by the second probe; receiving, by the first probe, signals generated by the first probe and the second probe; and analyzing the received signals to measure characteristics of plasma, wherein the signal generated by the first probe and the signal generated by the second probe are different. By comparing and analyzing the two signals, an accurate measurement value can be obtained without increasing a signal power so that low power operation is possible.

Description

Plasma measurement method and plasma process measurement sensor

The present invention relates to a plasma measuring method and a plasma process measuring sensor, and more particularly, to a plasma measuring method using a plasma process measuring sensor in the form of a wafer.

Plasma processes are widely used in deposition, etching, ashing, etc. in various semiconductor production and display panel production.

In the plasma process, since the state of the plasma has a great influence on the result of the process, it is important to maintain the state of the plasma in an optimal state, and for this purpose, it is necessary to accurately measure the state of the plasma.

However, since the plasma process is performed at a high temperature, it is difficult to accurately measure the state of the plasma, the amount of data collected is large, it is difficult to select data to be utilized, and the measurement itself may affect the plasma.

In addition, as equipment for measuring plasma has been developed, it is cumbersome to replace equipment for plasma measurement in the field.

An object of the present invention is a plasma measurement method and plasma process measurement for analyzing harmonics generated by plasma using two probes paired and paired among a plurality of probes To provide a sensor.

Another object of the present invention is to provide a plasma measuring method and a plasma process measuring sensor, which are advantageous for low power driving.

Another object of the present invention is to provide a plasma process measurement sensor capable of accurately measuring plasma, having a wafer shape, and having a thickness similar to that of a wafer, without requiring additional equipment or replacement of existing plasma process equipment.

Another object of the present invention is to provide a plasma measuring method and a plasma process measuring sensor capable of measuring distribution of plasma characteristics in two dimensions.

Another object of the present invention is to provide a plasma measuring method and a plasma process measuring sensor capable of accurately measuring the characteristics of the plasma without affecting the plasma.

According to an embodiment of the present invention, a plasma measuring method using a plurality of probes includes: pairing a first probe and a second probe, generating a signal by the first probe, and generating a signal by the second probe. The method may further include generating a signal, wherein the first probe receives signals generated by the first probe and the second probe to measure characteristics of the plasma, and the first probe and the second probe are adjacent to each other.

Plasma process measurement sensor using a plurality of probes according to another embodiment of the present invention, a lower plate, a ring on the lower plate, a circuit board on the lower plate, not overlapping with the middle plate, the first on the circuit board A probe and a second probe; And a top plate above the first probe and the second probe, wherein the characteristics of the plasma are measured through the interaction between the first probe and the second probe, wherein the first probe and the second probe are connected to each other. It is characterized by the adjoining.

Plasma measurement method according to an embodiment of the present invention has the effect of measuring the plasma density by analyzing the harmonics generated by the plasma using the two probes paired and paired.

Plasma measurement method according to an embodiment of the present invention has the effect that can be driven at low power.

Plasma process measurement sensor according to an embodiment of the present invention, since the thickness of the wafer shape is similar to the conventional wafer, there is an effect that can accurately measure the characteristics of the plasma while using the existing equipment as it is.

Plasma measurement method according to an embodiment of the present invention, there is an effect that can accurately measure the characteristics of the plasma two-dimensional in the plasma process.

Plasma measurement method according to an embodiment of the present invention, while measuring the characteristics of the plasma has an effect that can accurately measure the characteristics of the plasma without affecting the plasma.

1 is a view showing an example of a pull (foup).

FIG. 2 is a flow chart illustrating a process in which a wafer is transferred to a chamber after being processed from a pool to a chamber.

3A is an exploded view of a plasma process measurement sensor according to an exemplary embodiment.

3B is an exploded view of a plasma process measurement sensor according to another exemplary embodiment.

4 is a diagram illustrating a structure of a pad according to an embodiment of the present invention.

5 is a flowchart illustrating a process of manufacturing a pad according to an embodiment of the present invention.

6 is a flowchart illustrating a process of coupling a top plate and a probe according to an embodiment of the present invention.

7 is a flowchart illustrating a process of manufacturing a plasma process measurement sensor according to an embodiment of the present invention.

8 is a diagram illustrating a plane of a plasma process measurement sensor according to an exemplary embodiment of the present invention.

9A, 9B, and 9C are views illustrating aspects of a structure of a plasma process measurement sensor according to an exemplary embodiment of the present invention.

FIG. 10 is a diagram illustrating that a plane of a plasma process measurement sensor according to an exemplary embodiment includes a plurality of probes.

11 is a diagram illustrating a plasma measuring principle according to an embodiment of the present invention.

12 is a graph illustrating signals generated by probes according to an embodiment of the present invention.

13 is a diagram illustrating a plasma measurement principle according to another embodiment of the present invention.

14 is a graph illustrating signals generated by probes according to another exemplary embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the following examples, and the present invention will be described in detail with reference to the accompanying drawings. However, embodiments according to the present invention may be modified in many different forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. Embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

In the description of the embodiment according to the present invention, when described as being formed on the "on" or "on" (under) of each component, the (up) or down (below) (on or under) includes both the two components are in direct contact with each other (directly) or one or more other components are formed indirectly formed between the two (component). In addition, when expressed as "up" or "on (under)" (on or under) it may include the meaning of the downward direction as well as the upward direction based on one component.

Also, the relational terms used below, such as "first" and "second," "upper" and "lower", etc., do not necessarily require or imply any physical or logical relationship or order between such entities or elements. It may be used only to distinguish one entity or element from another entity or element.

In the drawings, the thickness or size of each layer is exaggerated, omitted, or schematically illustrated for convenience and clarity of description. In addition, the size of each component does not necessarily reflect the actual size.

1 is a diagram illustrating an example of the pull 100.

Front Opening Unified Pod (FOUP) 100 is one of the devices typically used in semiconductor manufacturing. In detail, since the wafer 110 passes through various process equipments according to the semiconductor manufacturing process, the wafers 110 are loaded into the pool 100 to facilitate storage and transportation while blocking external variables as much as possible.

After the wafers 110 are loaded into the pool 100, it is checked whether the wafers 110 are correctly positioned. For example, the wafers 110 inside the pool 100 are scanned with a laser to check whether one wafer 110 is loaded in the slot of the pool 100 or loaded at the correct position. For example, when scanning the inside of the pull 100 with a laser, if the thickness of the wafer 110 is measured to be 1.2 mm or more, two wafers are loaded in one slot in which only one wafer 110 should be loaded. It can be judged that.

FIG. 2 is a flowchart illustrating a process in which the wafer 110 is transferred to the chamber 100 after being processed into the chamber from the pool 100 and then processed again.

After the pull 100 is loaded into the load port, the pull 100 door is opened (210). When the pull 100 door is opened, the transfer device selects one of the wafers 100 inside the pull 100 (220). Thereafter, the transfer device transfers the selected wafer 110 to the chamber (230). In the chamber, plasma is generated to perform an etching process, a deposition process, and the like on the wafer 110 (240). After the process is completed, the wafer is transferred to the pool 100 through the transfer device (260). When all of the semiconductors enter the pool 100, the pool 100 door is closed (260).

Among the above steps, the performance and yield of the wafer vary depending on the result of step 240 of processing the wafer using plasma. Therefore, by accurately measuring the state of the plasma it is possible to accurately predict the results of the process.

Previously, single langmuir probes were mainly used to measure the state of plasma. The single volume muir probe method inserts a small metal probe chip into the plasma to measure plasma parameters based on a current curve with a change in voltage applied to the probe. However, the voltage applied to the probe affects the plasma, which causes errors in the plasma measurement. In addition, an error occurs in the plasma measurement even when a dielectric material is deposited on the probe. In addition, when connecting the probe by wire, it is difficult to apply to the actual process equipment because the data line between the probe inside the chamber and the data analysis device located outside the chamber is required.

Therefore, in an embodiment of the present invention, plasma density, ion flux, electron temperature, and the like, which are variables of plasma, are measured using harmonic perturbation.

Specifically, in one embodiment of the present invention, the sensor may be divided into a probe circuit contacting the plasma and a measurement circuit unit capable of generating a sine wave having a constant voltage and sensing a signal. The signal measured by sensing the signal may be divided into a first harmonic component and a second harmonic component using a fast Fourier transform.

In one embodiment of the present invention, the measurement principle of plasma is as follows. First, current flows through the probe, and the current flowing through the probe is classified by frequency using a modified Bessel function. The electronic temperature is measured using the ratio between the fundamental frequency current component and the second harmonic current component. The ion density can then be determined using the measured electron temperature, the variable for the probe, and the first harmonic current.

When the plasma is analyzed using harmonics, since the sinusoidal voltage is applied to the probe, the plasma perturbation is less. As the frequency of the sinusoidal wave is increased, the plasma can be diagnosed even if a dielectric material is deposited on the probe.

In addition, according to an embodiment of the present invention, the plasma process measurement sensor has the form of a wafer. The wafer shape allows the sensor to accurately measure the plasma when the plasma process is performed by incorporating a wafer-like sensor into the wafer processing process without having to replace or upgrade existing semiconductor equipment. In addition, the sensor operates wirelessly, and does not require a separate wired data cable.

In addition, according to an embodiment of the present invention, by configuring a plurality of probes in the sensor in the form of a wafer, it is possible to represent the variables measuring the plasma in a two-dimensional spatial distribution.

Plasma process measurement sensor according to an embodiment of the present invention has the form of a wafer, the upper plate 310a, the pad 320a, the probe 330a, the circuit board 340a, the pad 350a, and the lower plate 360a The middle plate is omitted. In the following, the probe 330a may also be referred to as a sensor or a tip. In addition, the lower plate 360a may also be referred to as a substrate.

The upper plate 310a and the lower plate 360a may be made of a conductive material or a semiconductor material. In addition, the upper plate 310a and the lower plate 360a may be made of the same material as a product processed by plasma. For example, the upper plate 310a and the lower plate 360a may be formed of a silicon-based semiconductor material or an aluminum-based conductor. That is, since the plasma process measurement sensor according to an embodiment of the present invention directly contacts the plasma in the chamber, the upper plate 310a and the lower plate 360a may be made of a material having low reactivity with the plasma.

The

pads

320a and 350a serve as adhesive and insulating EMI shields and are manufactured in a thin form.

The probe 330a is a sensor for measuring plasma and is configured with a diameter of 20 mm or less. The probe 330a may be made of a conductive material or a semiconductor material. In addition, the probe 330a may be made of the same material as a product processed by plasma. For example, the probe 330a may be formed of a silicon-based semiconductor material or an aluminum-based conductor. That is, since the plasma process measurement sensor according to an embodiment of the present invention contacts the plasma directly in the chamber, the probe 330a may be made of a material having low reactivity with the plasma.

The circuit board 340a includes a circuit electrically connected to the probe 330a.

Unlike the plasma process measurement sensor shown in FIG. 3A, the plasma process measurement sensor shown in FIG. 3B further includes a bottom door 370b. That is, the plasma process measurement sensor according to another embodiment of the present invention has a wafer shape, and includes an upper plate 310b, a pad 320b, a probe 330b, a circuit board 340b, a pad 350b, and a lower plate 360b. ), And the lower plate door 370b, and the middle plate is omitted.

The lower door 370b is located at the center area of the lower plate 360b for debugging the plasma process measuring sensor. The lower door 370b is not separated from the lower plate 360b to disassemble the entire plasma process measuring sensor. It is comprised so that the circuit of the circuit board 340b can be confirmed.

The upper plate 310b, the lower plate 360b, and the lower door 370b may be made of a conductive material or a semiconductor material. In addition, the upper plate 310b, the lower plate 360b, and the lower plate door 370b may be made of the same material as a product processed by plasma. For example, the upper plate 310b, the lower plate 360b, and the lower door 370b may be formed of a silicon-based semiconductor material or an aluminum-based conductor. That is, since the plasma process measurement sensor according to another embodiment of the present invention contacts the plasma directly in the chamber, the upper plate 310b, the lower plate 360b, and the lower door 370b are made of a material having low reactivity with plasma. It is preferred to be configured.

The

pads

320b and 350b serve as adhesion, insulation, and EMI shielding, and are manufactured in a thin form.

The probe 330b is a sensor for measuring plasma and is configured with a diameter of 20 mm or less. The probe 330b may be made of a conductive material or a semiconductor material. In addition, the probe 330b may be made of the same material as a product processed by plasma. For example, the probe 330b may be formed of a silicon-based semiconductor material or an aluminum-based conductor. That is, since the plasma process measurement sensor according to an embodiment of the present invention contacts the plasma directly in the chamber, the probe 330b may be made of a material having low reactivity with the plasma.

The circuit board 340b includes a circuit electrically connected to the probe 330b.

The pad performs functions of insulation, EMI shielding, and adhesion, and includes an adhesive layer 410, an insulating layer 420, a metal layer 430, an insulating layer 440, and an adhesive layer 450.

In order to realize the above functions of the pad, the insulating

layers

420 and 440 of the pad have a porous structure or a heat insulating structure, and the metal layer 430 of the pad has a thin film or mesh structure. The adhesive layer 410 and the insulating layer 420 may be combined into one layer, and the adhesive layer 450 and the insulating layer 440 may also be combined into one layer.

Plasma process measurement sensor according to an embodiment of the present invention has a wafer shape, and because the thickness should be similar to the actual wafer, the pad is made as thin as possible. In order to manufacture the pad, an insulating layer is first manufactured (510), a metal layer is prepared (520), an insulating layer is prepared (530), and finally an upper and lower adhesive layers are prepared (540). Hereinafter, the manufacturing method of each layer for manufacturing a thin pad is demonstrated.

In the insulating

layer manufacturing steps

510 and 530, an insulating layer is manufactured through a spray process or a sputter process. When the insulating layer is manufactured by the metal can method, it is thicker than that produced by the spray process or the sputter process, so it is manufactured by the spray process or the sputter process. The insulating layer produced through the spray process or the sputtering process has a porous structure or a heat insulating structure.

In the metal layer manufacturing step 520, a metal layer is manufactured through a spray process or a sputter process. When the insulating layer is manufactured by the metal can method, it is thicker than that produced by the spray process or the sputter process, so it is manufactured by the spray process or the sputter process. The metal layer manufactured through the spray process or the sputter process has a thin film or mesh structure.

In the upper and lower adhesive layer manufacturing step 540, an adhesive layer is manufactured through a spray process or a paste coating process. However, the adhesive layer and the insulating layer may be combined into one layer, and when combined, a separate adhesive layer manufacturing process step may be omitted.

The top plate and the probe are made of a conductive material or a semiconductor material. When both the top plate and the probe are made of a conductive material, the top plate and the probe are energized, and the plasma is not properly measured. In addition, even if the top plate and the probe is made of a semiconductor material, the semiconductor material turns into a conductor when it enters a high-temperature chamber, so that it is also energized and the plasma is not properly measured. Therefore, the top plate and the probe should be composed of one layer but insulated from each other.

Therefore, first, a top plate is prepared (610), and an insulating film or an oxide film is formed on the top plate (620).

However, since the plasma process measurement sensor according to an embodiment of the present invention has a wafer shape and should have a thickness similar to that of an actual wafer, an insulating film or an oxide film should be formed while keeping the top plate as thin as possible.

As a result of the experiment, when the top plate is made of a silicon-based semiconductor material, the thickness of the top plate is formed as an SiO ₂ film in the case of an oxide film and as a SiN film or Y ₂ O ₃ film in the case of an insulating film, so as to prevent cracking. It can be made as thin as 0.5mm.

As a result of the experiment, when the top plate is composed of aluminum-based conductor material, when the top plate is formed of an Alumina (Al ₂ O ₃ ) film as an oxide film, the thickness can be manufactured to 0.5mm or thinner as long as no crack occurs.

When the insulating film or the oxide film is formed on the top plate (620), and then the probe is coupled to the top plate (630), the top plate and the probe are insulated from each other, so that the plasma can be accurately measured by the probe.

First, a substrate is prepared (710). Substrate means another name that refers to the bottom plate. Then, the circuit board is stacked (720) on the substrate, the probe is stacked (730) on the circuit board, and finally, the insulated top plate shown in FIG. 6 is stacked on the substrate and the circuit board (740).

Plasma process measurement sensor 800 according to an embodiment of the present invention is composed of a plurality of probes 810 and the top plate 820 forming a layer with the probe, the position or number of probes 810 Can be changed as necessary.

FIG. 9A illustrates components of the plasma process measurement sensor before coupling according to an embodiment of the present disclosure, and includes an upper plate 910, a probe 920, a circuit board 930, a ring 940, and a lower plate 950. It is shown.

The middle plate 940 is located on the lower plate in the drawing, but may be integrated with the upper plate 910 or the lower plate 950. In addition, the middle plate 940 may be replaced with an epoxy or silicon adhesive in addition to the conductive material and the semiconductor material.

FIG. 9B illustrates that an insulating film or an oxide film is formed on the upper plate 910 before the plasma process measurement sensor is coupled according to an exemplary embodiment. Next, the middle plate 940, the circuit board 930, and the probe 920 are stacked on the lower plate 950, and the upper plate 915 on which the insulating film or the oxide film is formed is covered.

FIG. 9C illustrates a side surface of the plasma process measurement sensor after coupling according to an embodiment of the present invention, and includes an upper plate 915, a probe 920, a circuit board 930, a middle plate 940 formed with an insulating film or an oxide film, and The bottom plate 950 is shown.

10 to 14 specifically describe the measuring principle of the plasma according to an embodiment of the present invention.

The plasma process measurement sensor 1000 illustrated in FIG. 10 has the same structure as the plasma process measurement sensor 800 illustrated in FIG. 8, and each of the plurality of probes has a unique number. Although the plurality of probes are shown as having numbers 1 to 49, the number and location of the probes may be changed according to an embodiment or need.

Conventionally, each probe independently measured plasma, but according to an embodiment of the present invention, two probes are paired and interact to measure plasma. The plurality of probes are all connected to a multiplexer (MUX), and the two probes are paired and driven at a time through the MUX during plasma measurement. For example, among 1 to 49 probes, adjacent probes such as 1 and 2 probes, 2 and 3 probes, 3 and 4 probes, 9 and 2 probes, and 10 and 11 probes are selected and paired.

In addition, the probes perform a calibration operation before measuring the plasma. Although plasma may be used to calibrate probes, this is inefficient, so probes according to an embodiment of the present invention connect specific impedances instead of plasma and adjust the setting values of the probes based on the measured value of the impedance.

The AC power supply 1110 generates a sinusoidal voltage signal, and the sinusoidal voltage signal moves through the signal processor 1130 to the first probe 1140. Hereinafter, the sinusoidal voltage signal may be referred to as a sinusoidal signal.

The GND (ground) 1120 generates a signal grounded signal, and the signal grounded signal moves to the second probe 1150 after passing through the signal processor 1130. Hereinafter, the signal grounded signal may be referred to as a ground signal.

The first probe 1140 generates a sinusoidal signal with respect to the plasma and measures a response signal thereto. The second probe 1150 generates a ground signal for the plasma, and measures a response signal thereto for the first probe 1140. The first probe 1140 sends the two received signals to the signal processor 1130, and the signal processor 1130 analyzes the received two signals to obtain the density of the plasma.

Conventionally, a signal is generated by one probe and measured again to analyze the signal. However, when the measured value is inaccurate, such as noise in the signal, the voltage of the signal was amplified and measured to improve the accuracy. However, amplifying the voltage of the signal increases power consumption, and it is difficult to apply to power-sensitive devices such as wireless devices.

Therefore, according to an embodiment of the present invention, two probes are used, the first probe generates a sinusoidal signal and the second probe generates a ground signal. Therefore, if you compare the plasma measurement of the sinusoidal signal with the plasma measurement of the ground signal rather than analyzing one plasma measurement of the sinusoidal signal, you can obtain accurate analysis results without amplifying the voltage as in the prior art. There is an effect that can reduce.

FIG. 12 is a graph illustrating signals generated by probes according to the circuit of FIG. 11.

By comparing and analyzing the sinusoidal signal 1210 generated by the first probe and the ground signal 1220 generated by the second probe, an effect such as increasing the potential difference without increasing the output power of the sinusoidal wave can be obtained.

13 is a diagram illustrating a plasma measurement principle according to another embodiment of the present invention. Unlike the circuit shown in FIG. 11, FIG. 13 has an additional AC power supply unit instead of signal ground.

The first AC power supply unit 1310 generates a first sinusoidal wave voltage signal, and the first sinusoidal wave voltage signal moves through the signal processor 1330 to the first probe 1340. Hereinafter, the first sinusoidal voltage signal may be referred to as a first sinusoidal signal.

The second AC power supply 1320 generates a second sinusoidal voltage signal whose phase is inverted 180 degrees with the first sinusoidal voltage signal, and the second sinusoidal voltage signal passes through the signal processor 1330 to the second probe 1350. do. Hereinafter, the second sinusoidal voltage signal may be referred to as a second sinusoidal signal. The phase difference between the first sinusoidal voltage signal and the second sinusoidal voltage signal may be changed according to an embodiment or need.

The first probe 1340 generates a first sinusoidal wave signal for the plasma and measures a response signal thereto. The second probe 1350 generates a second sinusoidal wave signal for the plasma, and measures a response signal thereto for the first probe 1340. The first probe 1340 sends the two received signals to the signal processor 1330, and the signal processor 1330 analyzes the received two signals to obtain the density of the plasma.

Therefore, according to another embodiment of the present invention, two probes are used, the first probe generates a first sinusoidal signal, and the second probe generates a second sinusoidal signal whose phase is inverted 180 degrees with the first sinusoidal signal. Let's do it. Therefore, if the plasma measurement value of the first sinusoidal signal and the plasma measurement value of the second sinusoidal wave signal are compared and analyzed rather than the analysis of one plasma measurement value of the first sinusoidal signal, an accurate analysis result is achieved without amplifying the voltage as in the related art. It is possible to obtain an effect that can reduce the power consumption.

FIG. 14 is a graph illustrating signals generated by probes according to the circuit of FIG. 13.

By comparing and analyzing the first sinusoidal signal 1410 generated by the first probe and the second sinusoidal signal 1220 generated by the second probe, the same effect as that of increasing the potential difference without increasing the power output of the sinusoidal wave can be obtained. have.

While specific structures and details of operations have been shown and described herein, these descriptions are illustrative and other embodiments and equivalents can be readily made by those skilled in the art without departing from the spirit and scope of the invention. This makes sense. Accordingly, the present invention is intended to embrace all such alternatives and equivalents falling within the spirit and scope of the claims.

Embodiments of the present invention as described above may be applied to various plasma processes.

Claims

In the plasma measuring method using a plurality of probes,

Pairing the first probe and the second probe;

Generating a signal by the first probe;

Generating a signal by the second probe;

The first probe receives the signals generated by the first probe and the second probe to measure the characteristics of the plasma,

And the first probe and the second probe are adjacent to each other.
The method of claim 1,

Generating the signal by the first probe,

And the first probe generates a first sinusoidal wave signal.
The method of claim 1,

The second probe generating a signal,

And the second probe generates a signal grounded signal.
The method of claim 2,

The second probe generating a signal,

And the second probe generates a second sinusoidal wave signal.
The method of claim 4, wherein

The phase of the first sinusoidal wave signal and the phase of the second sinusoidal wave signal are different, Plasma measuring method using a plurality of probes.
In the plasma process measurement sensor using a plurality of probes,

Lower plate;

A ring on the lower plate;

A circuit board on the lower plate and not overlapping with the middle plate;

A first probe and a second probe on the circuit board; And

A top plate over the first probe and the second probe,

Measure the characteristics of the plasma through the interaction between the first probe and the second probe,

And the first probe and the second probe are adjacent to each other.
The method of claim 6,

The first probe generates a sinusoidal signal,

The second probe generates a signal grounded signal,

The first probe is a plasma process measurement sensor, characterized in that for receiving the signals generated by the first probe and the second probe to measure the characteristics of the plasma.
The method of claim 6,

The first probe generates a first sinusoidal signal,

The second probe generates a second sinusoidal signal,

The first probe is a plasma process measurement sensor, characterized in that for receiving the signals generated by the first probe and the second probe to measure the characteristics of the plasma.
The method of claim 8,

And the phase of the first sinusoidal wave and the phase of the second sinusoidal wave are different.
The method of claim 6,

And the first probe and the second probe are calibrated in connection with an impedance.