KR101225011B1 - Microwave probe by using resonator - Google Patents

Abstract

PURPOSE: A super high frequency probe using resonance structure is provided to measure a plasma density over again by using the cut-off frequency from a measured antenna and a radiating antenna exposed to plasma. CONSTITUTION: A radiating antenna(112) radiates a super high frequency which scans a frequency from the inside of plasma. A receiving antenna(114) receives an electromagnetic wave radiated from the radiating antenna by being inserted inside of the plasma. A resonance structure(116)which is arranged at the surrounding of the radiating antenna and the receiving antenna is formed with an electrical material which resonances with an electromagnetic wave. The resonance structure provides resonant frequency. The resonance structure comprises a mesh structure or a planar structure. The resonance structure has a cylinder type which covers the radiating antenna and the receiving antenna. [Reference numerals] (AA) Plasma

Description

Microwave probe using resonant structure {MICROWAVE PROBE BY USING RESONATOR}

The present invention relates to a very high frequency probe for measuring the plasma density.

Plasma diagnostics can measure the parameters of the plasma (electron density, electron temperature, plasma potential, etc.). The plasma diagnostic apparatus is used in various industries (semiconductor process, display process, solar cell process, etc.) using plasma.

Electron density (plasma density) is analytical information indicating the behavior of the plasma intuitively in various plasma processes and plasma properties. For example, the density of radicals, which play an important role in the etching and deposition processes, is directly related to the electron density. Therefore, accurate diagnosis of the electron density is required.

Plasma density diagnostics include Langmuir probes, Thompson Thomson Scattering, Optical Emission Spectroscopy (OES), and cut-off probes.

Langmuir probes have been the most widely and longest used for plasma physics research. The Langmuir probe is a diagnostic device in which a variety of plasma parameters that can be measured and its mechanism is accurately identified. However, the probe surface of the Langmuir probe may be etched and deposited by a process gas. Thus, the Langmuir probe cannot provide precise plasma density measurements and is not used for real-time process diagnostics.

 OES is a non-contact diagnostic method that does not contact plasma. OES can know the relative change over time of active species in the plasma. However, OES does not provide spatial resolution for active species and cannot provide absolute information about the density of active species.

Thomson scattering is well known for its physical mechanism and high confidence in the measurement of electron density. However, Thomson scattering does not provide spatial resolution for electron density, and the installation of equipment for measurement is too complex. In addition, the equipment for measuring Thompson scattering is expensive.

Various plasma diagnostic equipments using microwaves have been proposed. Cutoff probes using cutoff frequencies, a type of microwave diagnostic, can provide local electron density measurements.

One technical problem to be solved of the present invention is to provide an ultra-high frequency probe capable of measuring a precise electron density.

According to an embodiment of the present invention, an ultra-high frequency probe includes a radiation antenna radiating an ultra-high frequency inserted into a plasma to scan a frequency; A reception antenna inserted into the plasma to receive electromagnetic waves radiated from the radiation antenna; And a resonant structure formed around the radiation antenna and the receive antenna and formed of a conductive material resonating with the electromagnetic wave, wherein the resonant structure provides a resonant frequency.

In one embodiment of the present invention, the frequency of the ultra-high frequency may start scanning at the resonant frequency.

In one embodiment of the present invention, the resonant structure may include a mesh or flat structure.

In one embodiment of the present invention, the resonant structure may be in the form of a cylinder surrounding the radiating antenna and the receiving antenna.

In one embodiment of the present invention, it may be in the form of a rod extending parallel to the radiation antenna and the receiving antenna.

In one embodiment of the present invention, an ultra-high frequency generator capable of changing the frequency connected to the radiation antenna; A first connection unit disposed between the radiation antenna and the microwave generator to fix the radiation antenna and supply microwave power; An impedance measuring unit connected to the ultra-high frequency generator and measuring an output impedance in the direction of the radiating antenna; A transmission wave detector for detecting a received microwave signal of the reception antenna; And a second connection unit disposed between the reception antenna and the microwave detection unit to fix the reception antenna and guide the microwave signal.

In one embodiment of the present invention, the ultra-high frequency generator, the impedance measuring unit, and the ultra-high frequency detecting unit may be integrally a network analyzer.

In one embodiment of the present invention, the first connection portion and the second connection portion is an inner conductor; An insulator surrounding the inner conductor; And an outer conductor surrounding the insulator. The inner lead may be connected to the radiation antenna or the receive antenna, and the outer lead may be grounded.

Ultra-high frequency probe according to an embodiment of the present invention is inserted into the plasma radiation antenna for radiating the ultra-high frequency scanning; A reception antenna inserted into the plasma to receive electromagnetic waves radiated from the radiation antenna; And a resonance structure disposed around the radiation antenna and the reception antenna and formed of a conductive material resonating with the electromagnetic wave. The method of operating the microwave probe comprises the steps of: measuring a first resonant frequency due to the resonant structure in a vacuum without a plasma in a vacuum vessel; Measuring a second resonant frequency attributable to the resonant structure while generating plasma in the vacuum vessel; And calculating a plasma density using a difference between the first resonance frequency and the second resonance frequency, wherein the first resonance frequency and the second resonance frequency are formed in the resonance structure and the output impedance is viewed toward the radiating antenna. The imaginary part of may be the point where it passes through the zep.

In an embodiment of the present disclosure, the method may further include measuring a plasma frequency due to a cutoff in the plasma generation state.

Ultra-high frequency probe according to an embodiment of the present invention can measure the plasma density from the resonance frequency. In addition, the microwave probe can measure the plasma density by using a cutoff frequency from the radiation antenna and the measurement antenna exposed to the plasma.

1 is a conceptual diagram illustrating an ultra-high frequency probe according to an embodiment of the present invention.
2 is a view illustrating an ultra-high frequency probe according to an embodiment of the present invention.
3 is a cross-sectional view taken along line II ′ of FIG. 2.
4 is a perspective view illustrating an ultra-high frequency probe according to another embodiment of the present invention.
FIG. 5 is a cross-sectional view taken along the line II-II 'of FIG. 4.
Figure 6 is a transmission coefficient (S21) in the vacuum in the ultra-high frequency probe according to an embodiment of the present invention.
FIG. 7 is a diagram illustrating an imaginary part Im (Z) of impedance viewed from a radiation antenna and a transmission coefficient S21 in a plasma in an ultra-high frequency probe according to an exemplary embodiment of the present invention.
8 is a transmission coefficient S21 measured using an ultra-high frequency probe according to an exemplary embodiment of the present invention.
9 is an imaginary part of impedance measured using an ultra-high frequency probe according to an exemplary embodiment of the present invention.
10 is a diagram for explaining plasma density using a cutoff frequency and plasma density using a resonant frequency shift.

As wafers and glass substrates become larger in area, in the semiconductor process and the display process, evaluation of plasma uniformity and evaluation of absolute value of electron density are important.

Langmuir probes exhibit weak characteristics against etching or deposition by plasma using an electrostatic method. OES does not provide an absolute value of spatial plasma density.

According to an embodiment of the present invention, the ultra-high frequency waves may enter the plasma to meet and resonate with a resonance structure having a predetermined resonance frequency. The resonant frequency may shift when plasma is present. The shift of the resonant frequency along the medium can provide the plasma density. The resonant frequency contains information about the spatially averaged plasma density of the plasma existing inside the resonant structure. The plasma density due to the shift of the resonant frequency was compared with the plasma density by the cut-off method for measuring the plasma density of a conventional conventional local region. The plasma density due to the shift of the resonance frequency is consistent with the plasma density by the conventional cutoff method.

Accordingly, the method for measuring plasma density by moving the resonance frequency according to an embodiment of the present invention enables real-time monitoring of plasma density.

Ultra-high frequency probe according to an embodiment of the present invention is not affected by the etching or deposition by the process gas. In addition, the presence of the microwave probe has little effect on the process plasma.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosure may be made thorough and complete, and to fully convey the spirit of the invention to those skilled in the art. In the drawings, the components have been exaggerated for clarity. Portions denoted by like reference numerals denote like elements throughout the specification.

1 is a conceptual diagram illustrating an ultra-high frequency probe according to an embodiment of the present invention.

Referring to Figure 1, the microwave probe is a radiation antenna 112 is inserted into the plasma to radiate the ultra-high frequency, a receiving antenna 114 is inserted into the plasma to receive the electromagnetic wave radiated from the radiation antenna 112, and And a resonant structure 116 disposed around the radiation antenna 112 and the reception antenna 114 and formed of a conductive material resonating with the electromagnetic wave.

The receiving antenna 114 and the radiation antenna 112 is inserted into the plasma. The plasma is formed by the energy applying unit 136 inside the chamber. The energy applying unit 136 may be an electrode for generating a capacitively coupled plasma, an induction antenna for generating an inductively coupled plasma, or a waveguide for forming an ultrahigh frequency plasma.

The power source 132 may provide power to the energy applying unit 136. The power source 132 may be a DC power source, an AC power source, an RF power source, or an ultra high frequency power source. When the power source 132 is an RF power source, an impedance matching network 134 may be disposed between the power source and the energy applying unit.

The chamber 131 may include a substrate holder 138 and a substrate 137 mounted on the substrate holder 138. The substrate 137 may be a glass substrate, a plastic substrate, or a semiconductor substrate.

The network analyzer 120 may provide an ultrahigh frequency to the radiating antenna 112 and analyze an ultrahigh frequency signal provided from the receiving antenna 114. The frequency of the ultra high frequency may be swept with time. The sweeping frequency may be between 100 kHz and 6 GHz. The sweeping frequency may be swept continuously or discretely.

The network analyzer may measure the output impedance Z and the transmission coefficient S21 at each sweep frequency. The network analyzer 120 may include an ultra-high frequency generator 122, an impedance measurer 124, and a transmission wave detector 126.

The ultra-high frequency generator 122 may be connected to the radiation antenna 112 and continuously change the frequency.

The first connector 117 is disposed between the radiating antenna 112 and the ultra-high frequency generator 122 to fix the radiating antenna 112 and to supply ultra-high frequency power.

An impedance measuring unit 124 is connected to the ultra-high frequency generator 122 to measure the output impedance of the radiation antenna direction. The impedance measurement unit 124 may include a directional coupler. The output impedance may be an impedance of the microwave generator 122 facing the radiation antenna direction. The impedance measuring unit 124 may calculate the output impedance by measuring the reflection coefficient.

The transmission wave detector 126 detects the received microwave signal of the reception antenna 114. The transmission wave detector 126 may be synchronized with the ultra-high frequency generator 122. The transmission wave detector 126 may measure the transmission coefficient S21.

The second connector 118 is disposed between the reception antenna 114 and the transmission wave detector 126 to fix the reception antenna 114 and guide the ultra-high frequency signal.

The resonance structure 116 is disposed away from the radiating antenna or receiving antenna.

The radiated electromagnetic waves cause wavelength / 4 resonance by the resonant structure. When the size of the chamber is large, a plurality of cavity peaks are generated by looking at the resonant structure and the chamber wall above the cutoff frequency.

The resonance structure 116 has the effect of reducing the size of the chamber. That is, the resonance structure 116 changes the position of cavity peaks excluding the wavelength / 4 resonance to a high frequency region, and the resonance structure 116 can efficiently generate the wavelength / 4 resonance.

2 is a view illustrating an ultra-high frequency probe according to an embodiment of the present invention.

3 is a cross-sectional view taken along the line II ′ of FIG. 2.

2 and 3, the microwave probe 200 may include a radiation antenna 212, a reception antenna 214, and a radiation antenna disposed around the radiation antenna 212 and the reception antenna 214. Resonance structure 216 formed of a conductive material resonating with the electromagnetic wave.

The resonant structure 216 is disposed away from the radiating antenna 212 or the receiving antenna 216. The resonant structure 216 may be grounded electrically. The resonant structure 216 may have a cylindrical shape surrounding a part of the radiation antenna 212 and the reception antenna 214. The radiating antenna 212 and the receiving antenna 214 may be disposed adjacent to each other in parallel with each other. The resonant structure 216 may include a conductive plate and a cyndircal shell. The cylindrical angle is disposed on the conductive plate. One end of the revolving structure 216 may be opened, and the radiation antenna and the reception antenna may be disposed therein.

The first connector 217 includes an inner lead 217a, an insulator 217b surrounding the inner lead 217a, and an outer lead 217c surrounding the insulator 217b. The inner lead 217a is connected to the radiation antenna 212, and the outer lead 217c is grounded. The first connector 217 may have a coaxial cable shape.

The second connector 218 includes an inner lead 218a, an insulator 218b surrounding the inner lead 218b, and an outer lead 218c surrounding the insulator 218b. The inner lead 218a is connected to the receive antenna 214 and the outer lead 218c is grounded. The second connector 218 may have a coaxial cable shape.

The resonant structure 216 may have a grid or flat structure. The resonant structure 216 may be formed of a conductive material and grounded.

Plasma density (n _e ) can be expressed as follows using the resonant frequency caused by the resonant structure.

Here, f ₀ (unit: GHz) is the first resonant frequency in the vacuum state where no plasma exists, and f _r (unit: GHz) is the second resonant frequency when the plasma exists.

4 is a perspective view illustrating an ultra-high frequency probe according to another embodiment of the present invention.

FIG. 5 is a cross-sectional view taken along the line II-II 'of FIG. 4.

4 and 5, the microwave probe 300 is disposed around the radiation antenna 312, the reception antenna 314, and the radiation antenna 312 and the reception antenna 314 to resonate with electromagnetic waves. And a resonant structure 316 formed of a conductive material.

The resonant structure 316 is disposed away from the radiating antenna 312 and the receiving antenna 314. The resonant structure 316 may be grounded electrically. The radiation antenna and the reception antenna may be disposed adjacent to each other in parallel with each other. The resonant structure 316 may include at least one rod disposed side by side around the radiating antenna. The known structure 316 may be disposed in parallel with the radiation antenna 312.

The first connector 317 includes an inner lead 316a, an insulator 317b surrounding the inner lead 317a, and an outer lead 317c surrounding the insulator 317b. The inner lead 317a is connected to the radiation antenna 312, and the outer lead 317c is grounded. The first connector 317 may have a coaxial cable shape.

The second connector 318 includes an inner lead 318a, an insulator 318b surrounding the inner lead 318a, and an outer lead 318c surrounding the insulator 318b. The inner lead 318a is connected to the receive antenna 314 and the outer lead 318c is grounded. The second connector 318 may have a coaxial cable shape.

Figure 6 is a transmission coefficient (S21) in the vacuum in the ultra-high frequency probe according to an embodiment of the present invention.

Referring to FIG. 6, near 2 GHz, the transmission coefficient S21 rapidly decreases and then increases to generate resonance. This is due to the rapidly changing resonant structure of the transmission coefficient S21. If the first resonant frequency (about 2 GHz) is known, the scanning range of the frequency in the microwave probe may be greater than or equal to the first resonant frequency (about 2 GHz). Thus, the network analyzer can significantly reduce the frequency scanning range of the microwave generator. Therefore, cost reduction is therefore possible.

FIG. 7 is a diagram illustrating an imaginary part Im (Z) of impedance viewed from a radiation antenna and a transmission coefficient S21 in a plasma in an ultra-high frequency probe according to an exemplary embodiment of the present invention.

Referring to FIG. 7, a point where the imaginary part Im (Z) of impedance is zero is used as the first resonant frequency f1 and the second resonant frequency f2. The resonant frequency was used as the point where the imaginary part of the impedance formed due to the resonant structure is zero. The power of the RF power source for forming the plasma is 100 watts.

Using a conventional cutoff scheme, the plasma density (n, unit: cm ⁻³ ) between the radiating antenna and the receiving antenna may be given as follows.

The plasma frequency f _{pe in} Hz is the cutoff frequency f_cut_off. In order to find the cutoff frequency (f_cut_off, unit: Hz), the ultra-high frequency generator oscillates for several GHz band at approximately 100 kHz. However, microwave generators that scan a wide range are very expensive.

In the plasma density measurement method according to an embodiment of the present invention, the first resonant frequency f1 is known in a vacuum state. Therefore, the ultra-high frequency generator may oscillate above the first resonant frequency f1. In addition, when there is a plasma, the movement of the second resonance frequency f2 according to the plasma density is small. Therefore, it is very advantageous in cost reduction.

8 is a transmission coefficient S21 measured using an ultra-high frequency probe according to an exemplary embodiment of the present invention.

9 is an imaginary part of impedance measured using an ultra-high frequency probe according to an exemplary embodiment of the present invention.

10 is a diagram for explaining plasma density using a cutoff frequency and plasma density using a resonant frequency shift.

7-10, the power of the RF power supply for forming the plasma was provided with 100 watts, 200 watts, 300 watts, and 400 watts. The output impedance Z is the impedance viewed from the output terminal of the microwave generator. As the external power generating the plasma increases, the cutoff frequency and the second resonant frequency f2 caused by the resonant structure move.

As the external power increases, the cutoff frequency (f _{cut - off} ) is in the range of approximately 0.8 Ghz to 2 Ghz. On the other hand, when the external power is low, since the cutoff frequency (f _{cut - off} ) is lowered to about 0.8 Ghz or less, substantially, the frequency scanning range (dF_cut_off) for measuring the cutoff frequency (f _{cut - off} ) is 0 Hz. Should start from

Meanwhile, as the external power increases, the second resonance frequency f2 is in the range of 2 Ghz to 2.6 Ghz. Therefore, the scanning range dF2 for measuring the second resonance frequency f2 is in the range of f1 to 2.6 Ghz. Therefore, the frequency at which the scanning starts is at a high frequency, and it is easy to change the oscillation frequency at this high frequency. Thus, the price of the microwave generator decreases.

On the other hand, the plasma density due to the _{cut - off} frequency (f _{cut - off} ) and the plasma density due to the resonance frequency shift may be different from each other. The plasma density determined by the resonance frequency is a spatial averaged plasma density inside the resonance structure.

The plasma density obtained from the resonance frequency is about 0.667 times lower than the electron density measured using the cutoff frequency. This difference is interpreted to be due to the spatial distribution of the plasma. That is, the plasma density inside the resonant structure may have the following distribution.

Where r is the distance from the center of the resonant structure and d is the radius of the resonant structure. Therefore, when the plasma density by the resonance frequency is corrected, the corrected plasma density is equal to the electron density measured using the cutoff frequency. That is, the ultra-high frequency probe according to the embodiment of the present invention provides a spatially averaged plasma density of the plasma density inside the resonant structure.

While the invention has been shown and described with respect to certain preferred embodiments thereof, the invention is not limited to these embodiments, and has been claimed by those of ordinary skill in the art to which the invention pertains. It includes all the various forms of embodiments that can be implemented without departing from the spirit.

112: radiation antenna
114: receiving antenna
116: resonant structure
120: network analyzer

Claims (10)

A radiating antenna inserted into the plasma to radiate ultra-high frequency scanning frequency;
A reception antenna inserted into the plasma to receive electromagnetic waves radiated from the radiation antenna; And
A resonance structure disposed around the radiation antenna and the reception antenna and formed of a conductive material resonating with the electromagnetic wave,
And the resonant structure provides a resonant frequency. delete The method according to claim 1,
The resonant structure is a high frequency probe, characterized in that it comprises a mesh or plate structure. The method according to claim 1,
The resonant structure is a high frequency probe, characterized in that the cylindrical shape surrounding the radiation antenna and the receiving antenna. The method according to claim 1,
Ultra-high frequency probe, characterized in that the rod-like extending parallel to the radiation antenna and the receiving antenna. The method according to claim 1,
An ultrahigh frequency generator capable of changing a frequency connected to said radiating antenna;
A first connection unit disposed between the radiation antenna and the microwave generator to fix the radiation antenna and supply microwave power;
An impedance measuring unit connected to the ultra-high frequency generator and measuring an output impedance in the direction of the radiating antenna;
A transmission wave detector for detecting a received microwave signal of the reception antenna; And
And at least one of a second connection part disposed between the reception antenna and the microwave detection unit to fix the reception antenna and guide the microwave signal. The method of claim 6,
The ultra-high frequency probe, the impedance measuring unit, and the ultra-high frequency detecting unit are integrally a microwave analyzer, characterized in that the network analyzer. The method of claim 6,
The first connection portion and the second connection portion:
Internal conductors;
An insulator surrounding the inner conductor; And
An outer lead surrounding the insulator;
The inner lead is connected to the radiating antenna or receiving antenna,
And the external lead is grounded. A radiation antenna which is inserted into the plasma and radiates ultra-high frequencies for frequency scanning; A reception antenna inserted into the plasma to receive electromagnetic waves radiated from the radiation antenna; And a resonant structure disposed around the radiation antenna and the reception antenna and formed of a conductive material which resonates with the electromagnetic wave.
Measuring a first resonant frequency attributable to the resonant structure in a vacuum without a plasma in a vacuum vessel;
Measuring a second resonant frequency attributable to the resonant structure while generating plasma in the vacuum vessel; And
Calculating a plasma density using a difference between the first resonance frequency and the second resonance frequency;
And a first resonant frequency and a second resonant frequency formed at the resonant structure and at a point where an imaginary part of the output impedance facing the radiating antenna passes through zero. 10. The method of claim 9,
And measuring the plasma frequency due to the cutoff in the plasma generation state.

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