KR101918357B1 - Inductively Coupled Plasma System By Using Radio-Frequency Power - Google Patents

Abstract

An impedance mismatching problem caused by a difference between a load impedance of a resonance circuit composed of an induction coil and a capacitor connected in parallel and an internal impedance of an RF power source is measured by a resonance circuit By connecting a grounding tab to the induction coil and connecting it to the ground, and returning the RF current in the resonant circuit to the RF power source using a grounding tap, the load impedance value can be solved without changing the resonant frequency of the resonant circuit. , The power factor is improved and the stable plasma is generated even under the typical impedance mismatching operation conditions such as high output operation, mixed gas and large amount of raw material powder input.

Description

[0001] The present invention relates to an inductively coupled plasma (RF)

The present invention relates to a radio frequency (RF) power inductively coupled plasma generator, and more particularly, to an RF inductively coupled plasma (RF) power generating apparatus which transmits RF AC power of several hundreds kHz to several tens of MHz band in an inductively coupled plasma generating gas to maintain an ionized and ionized plasma state To an RF inductively coupled plasma generator.

Plasma is an ionized thermal fluid, which can be divided into a direct current (DC) plasma and an alternating current (AC) plasma according to a method of supplying electric energy necessary for maintaining the ionization state. Among the above two types of plasma, the present invention relates to an RF inductively coupled plasma generating apparatus which transfers RF AC power of several hundreds kHz to several tens of MHz in an inductively coupled manner to a plasma forming gas to maintain an ionized and ionized plasma state.

1 is a view showing the operation principle of a general RF inductively coupled plasma generator.

As shown in (1) and (2) of FIG. 1, when the RF current Io flows along the induction coil connected to the RF power supply source, the RF inductively coupled plasma generator generates, according to Faraday's law, A time-varying electromagnetic field B is generated.

As shown in (3) and (4) of FIG. 1, the time-varying electromagnetic field B again induces the eddy current Ie in the plasma fluid passing through the hollow confinement tube, The energy required for maintenance is transmitted.

In this case, since the inductively coupled plasma operates close to the cylindrical conductor, which is regarded as one cycle in terms of the electric circuit, it is applied to a load having a low resistance component and a relatively large inductive inductance and coupling inductance component at both ends of the induction coil according to the transformer principle do.

Therefore, the total equivalent impedance felt at both ends of the induction coil having a large number of windings can be greatly changed as compared with the case where no load is applied when the plasma load is generated or maintained. As a result, an impedance mismatching problem occurs in which the total equivalent impedance felt at both ends of the induction coil is significantly different from the internal impedance of the RF power supply source from the plasma generation.

This impedance mismatch phenomenon seriously lowers the power factor of the RF power source used and adversely affects the output of the RF inductively coupled plasma generator, as well as damages to the RF power source due to the inflow of reflected power, Likewise, it can act as a fatal hindrance to the performance of the inductively coupled plasma generator.

Particularly, in the case of a self-excited vacuum tube oscillator commonly used as an RF power source in a high-output RF inductively coupled plasma generator of 100 kVA or more, the equivalent resistance of the inductively coupled plasma generated is usually several to several tens of Ω The impedance mismatching problem becomes serious and power factor reduction phenomenon is remarkably exhibited.

In addition, when a large amount of a material to be treated is injected into a plasma torch such as a metal raw material powder under a high output operating condition of 100 kVA or more, the energy distribution in the plasma and the plasma impedance rapidly change due to the interaction between the raw material powder and the inductively- The oscillation frequency of the self-excited oscillator is continuously changed in response to this, and the oscillation is stopped.

For example, the anode tuning-grid tuning self-excited oscillator can oscillate only when the resonant frequency of the anode tank circuit is smaller than the resonant frequency of the grid tank circuit, and the resonant frequency of the anode tank circuit is close to the resonant frequency of the grid tank circuit The oscillation is stopped when the resonance frequency of the anode tank circuit is equal to or larger than the resonance frequency of the grid tank circuit. When the anodic tuning oscillator with the above characteristics is used as the RF power source, a change in the plasma impedance due to the plasma generation, the mass input of the raw material powders, and the high output operation causes a change in the resonant frequency of the positive electrode tank circuit At this time, if the variation width of the resonance frequency of the anode tank circuit becomes larger than a certain level, the oscillation may be stopped or the amplification factor may be reduced due to the tuning characteristic with the above-mentioned grid tank circuit 314.

On the other hand, when a frequency-locked captive amplifier is used as an RF power source, a separate impedance matching device, such as a variable capacitor, is installed between the RF power source and the induction coil to adjust the impedance value Methods for improving the impedance mismatching problem are well known.

However, in the case of a self-excited oscillator, in which the oscillation frequency varies depending on the load, which is frequently used in a high-power inductively coupled plasma apparatus, the frequency is rapidly changed in the impedance adjustment process using the matching device, It is relatively difficult to use a conventional impedance matching device designed to be used. In addition, since the self-excited oscillator must use the induction coil as a part of the high-frequency oscillation circuit in order to transmit the high frequency power to the plasma load, a matching device for improving the impedance mismatch phenomenon It is also difficult to mount it separately in the internal circuit of the self-excited oscillator.

Thus, most RF inductively coupled plasma generators using self-excited oscillators have a high output oscillator of 200 kVA or higher, for example, for RF power supply of 100 kVA, without any device or alternative to improve the impedance mismatch problem The same inefficiency as that to be used or the same inconvenience that the capacitance and inductance inside the oscillation circuit must be redesigned each time according to the generation conditions of the inductively coupled plasma.

The present invention solves the above-mentioned impedance mismatching problem caused by a difference between an internal impedance of an RF power source and a load impedance including an induction coil without a separate impedance matching device, thereby efficiently transmitting RF power to a plasma, It is an object of the present invention to provide an RF power inductively coupled plasma generator capable of maintaining a stable plasma even under the operating conditions of operation, complex gas, and large amount of raw material powder.

According to an aspect of the present invention, there is provided an RF power inductively coupled plasma generating apparatus including a hollow confinement tube for providing a space in which a plasma is formed,

An induction coil 201 surrounding the confinement tube 100,

A resonant circuit 200 including a capacitor 203 connected in parallel with the induction coil 201,

And an RF power source (300) for supplying RF power to the resonant circuit (200)

A ground tap 202 is formed in the induction coil 201 so that RF current flowing in the induction coil 201 through the resonance circuit 200 is transmitted to the RF To the power supply source (300).

According to one aspect of the present invention, the RF power source is a self-excited oscillator.

According to an aspect of the present invention, the RF power source 300 includes a vacuum tube 301 including an anode 302, a grid 303, and a cathode 304; A DC supply circuit connected between the cathode 304 and the anode 302; A grid tank circuit 305 connected between the grid 303 and the cathode 304; And a positive electrode tank circuit 306 connected between the cathode 304 and the anode 302. The anode tuning circuit 306 may be a positive tuning-grid tuning type self-oscillating oscillator. In this case, the resonance circuit is included in the anode tank circuit 305, and the grounding tab is connected to the cathode 304 by being grounded.

According to an aspect of the present invention, the RF power source 300 includes: a vacuum tube including an anode, a grid, and a cathode; A DC supply circuit connected between the cathode and the anode; A positive electrode tank circuit connected between the negative electrode and the positive electrode, and a feedback circuit connected to the negative electrode of the vacuum tube and the grid so that the voltage phase difference between the grid and the positive electrode is 180 degrees. In this case, the resonant circuit is included in the positive electrode tank circuit, and the grounding tab is grounded and connected to the negative electrode.

According to an aspect of the present invention, when the RF power source is a frequency-locked-type tapping amplifier, the resonance circuit may be included in an impedance matching circuit of the tapping amplifier.

According to an aspect of the present invention, the capacitor is a variable capacitor.

Other specific embodiments of various aspects of the present invention are included in the detailed description below.

The inductively coupled plasma generating device using RF power according to the present invention can relocate the equivalent impedance of the inductively coupled plasma along with the inductance of the induction coil in the parallel resonant circuit depending on the tap position of the parallel resonant circuit, The total impedance of the parallel resonant circuit can be adjusted without changing the resonant frequency.

Accordingly, when the plasma is generated, a large amount of raw material powder is input, and a high output operation is performed, the total impedance of the resonant circuit is adjusted using a tap in a direction in which the difference between the total impedance of the resonant circuit including the internal impedance of the RF power source and the plasma load is reduced, The influence of the impedance mismatch occurring in the RF inductively coupled plasma generating devices can be minimized.

Particularly, since the total impedance value of the resonance circuit can be adjusted by changing only the reactance value of the resonance circuit without affecting the oscillation frequency of the resonance circuit and the equivalent resistance value of the inductively coupled plasma, It is possible to improve the power factor and minimize the impedance mismatching problem without using an additional impedance matching device for conventional RF inductively coupled plasma generators.

In addition, when the resonance circuit is used as a part of the impedance matching circuit in a conventional RF inductively coupled plasma generator using a fixed frequency RF power source, the range of impedance mismatching is reduced and impedance matching is performed in a relatively narrow range The condition can be found, and an efficient and economical matching circuit can be provided.

1 is a diagram showing the operation principle of a general inductively coupled plasma generator.
2 is a conceptual diagram of an RF power inductively coupled plasma generator according to an embodiment of the present invention.
3 is an equivalent circuit of a resonant circuit according to an embodiment of the present invention.
4 is an equivalent circuit according to an embodiment of the present invention when the grounding tap is grounded at a point where the number of turns of the induction coil becomes half.
5 is a conceptual diagram of an RF inductively coupled plasma generator using an oscillator according to an embodiment of the present invention.

For a better understanding of the present invention, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. The embodiments of the present invention may be modified into various forms, and the scope of the present invention should not be construed as being limited to the embodiments described in detail below. The present embodiments are provided to enable those skilled in the art to more fully understand the present invention. Therefore, the shapes of elements and the like in the drawings can be exaggerated to emphasize a clearer description. It should be noted that in the drawings, the same members are denoted by the same reference numerals. Further, detailed descriptions of well-known functions and configurations that may be unnecessarily obscured by the gist of the present invention are omitted.

2 is a conceptual diagram of an RF power inductively coupled plasma generator according to an embodiment of the present invention.

2, the RF inductively coupled plasma generator 1 includes a confinement tube 100, a resonant circuit 200, and an RF power source 300. The resonant circuit 200 includes an induction coil 201, a grounding tap 202, a capacitor 203, and an RF input terminal 205.

The RF power source 300 supplies the RF power to the resonant circuit 200 including the plasma 10 and the confinement tube 100 and may be the self-excited oscillator or the tapping amplifier described above.

The resonant circuit 200 is connected to the RF power source 300, the RF input terminal 205 and the grounding tap 202 and receives RF power from the RF power source 300 through a plasma 10) through the inductive coupling method.

The confinement tube 100 is a hollow shape providing a space in which a plasma is formed.

The grounding tab 202 is connected to the induction coil 201 to control the number of turns of the induction coil and also functions as a ground. The grounding tab 202 may be a copper bus bar and the induction coil 201 may include a plurality of insertion ports into which a grounding tab 202 may be inserted, As shown in FIG. The number of insertion coils of the plurality of insertion ports can be adjusted by the number of steps and the number of winding of the induction coil can be adjusted by inserting the grounding tab 202 into the insertion port. This is only an example, and is not necessarily limited thereto.

The capacitor 203 is connected in parallel to the induction coil 201, and a variable capacitor can be used if necessary.

The resonance circuit 200 generates an inductively coupled plasma 10 in the hollow confinement tube 100 and all of the RF current flowing in the induction coil 201 in the resonance circuit 200 is connected to the ground tab 202 To the RF power supply 300 through the RF power supply 300.

The total impedance of the resonance circuit 200 can be adjusted without changing the resonance frequency according to the position of the grounding tab 202 and the impedance mismatching range .

3 is an equivalent circuit of the resonant circuit 200 according to an embodiment of the present invention.

As shown in Fig. 3, the inductively coupled plasma 10 has a relatively small resistive component of several ohms in magnitude with respect to both ends of the induction coil 201, and an equivalent impedance with a large inductive and coupling inductance component .

Therefore, the resistance component and the inductance component generated in the inductively coupled plasma 10 can be combined with the resistance component and the inductance component of the induction coil 201 to form an equivalent inductance 206 and Le, respectively, 3, respectively.

Assuming that the inductively coupled plasma 10 is generated in a cylindrical shape over the entire length of the induction coil 201, the ground tab 202 of the induction coil 201 is connected to the equivalent inductance 206 Can be expressed by the same ground.

For example, if the grounding tab 202 capable of adjusting the number of turns of the induction coil 201 is positioned at the center of the induction coil 201 and the induction coil 201 is bisected, 10 also divides the coupling inductance applied to both ends of the induction coil 201 so that the equivalent inductance 206 (Le) is also divided into two.

4 is an equivalent circuit according to an embodiment of the present invention when the grounding tap is grounded at a point where the number of turns of the induction coil becomes half.

FIG. 4 is a graph showing the equivalent inductance 206 (Le) centered on the grounding taps when the grounding tab 202 is placed at a position where the number of turns of the induction coil is halved in the equivalent circuit of FIG. 3, And is an equivalent circuit presented for calculating the overall impedance and frequency change effect of the resonant circuit 200. [

For example, the effect of the grounding tab 202 on the resonant frequency of the resonant circuit using the equivalent circuit representation of FIG. 4 can be examined as follows. If the equivalent resistance 204 (Re = 0) is removed and the resonance condition is calculated using only the equivalent inductance 206 on the assumption that there is no load in FIGS. 3 and 4, the resonance frequency is expressed by the following equation (1) .

(1)

(One)

The above mathematical result means that the resonance circuit newly constructed by the ground tab 202 has the same frequency as the resonance circuit in the absence of the ground tab 202 as shown in FIG.

4, when the grounding tab 202 is located at a position where the number of turns of the induction coil 201 is half, the high voltage RF input terminal 205 and the grounding tab 202 are connected to the center The left branch where the equivalent inductances 206 and 0.5Le are connected in series with the capacitor 203 and the equivalent resistance 204 and the equivalent inductance 206 and 0.5Le of the other half are connected in series It is assumed that the right branches connected to each other constitute a new equivalent resonant circuit connected in parallel with each other.

It can be seen from the circuit theory that the total impedance Z4 of FIG. 4 in which the grounding tab 202 bisects the induction coil 201 from the simple circuit theory is represented by the following equation (2).

(2)

(2)

3, the total impedance Z3 of the resonant circuit 200 can be obtained as shown in the following equation (3) when the grounding tab 202 is not provided.

(3)

(3)

) 대략, Z3/Z4≒4 로 평가된다. From the above equations (2) and (3), the magnitude of the above two impedances can be compared as shown in Equation (4) below. As described above, the inductively coupled plasma 10 has the inductance component (Le) is relatively larger than the impedance value

) Approximately, Z3 / Z4? 4.

(4)

(4)

That is, in the case of the equivalent circuit for the resonant circuit 200 divided by the ground tab 202, the total impedance size is reduced to about 1/4 as compared with the case where the ground tab 202 is not present, Accordingly, it can be seen that the current in the resonance circuit 200 is increased about four times under the RF applied voltage of the same magnitude.

Accordingly, the impedance value generated at the high output voltage stage 205 of the RF power supply source 300 can be reduced by at most about 1/4 as compared with the conventional RF inductively coupled plasma generating devices, thereby minimizing the range of impedance mismatching It can also be seen from the above mathematical results that the impedance adjustment of the resonant circuit 200 by the grounding tab 202 does not significantly affect the resonant frequency.

5 is a conceptual diagram of an RF inductively coupled plasma generator using a self-excited oscillator of a bipolar tuning-grid tuning type as an RF power source 300 according to an embodiment of the present invention.

5, the RF power source 300 includes a vacuum tube 301 including an anode 302, a grid 303, and a cathode 304; A DC supply circuit connected between the cathode 304 and the anode 302; A grid tank circuit 305 connected between the grid 303 and the cathode 304; And a positive electrode tank circuit 306 connected between the negative electrode 304 and the positive electrode 302. Further, a high-voltage DC power supply, a high-voltage AC power transformer, an RF choke circuit, and other electric control circuits for applying a high-voltage direct current to the anode of the grid tank circuit 305 and the vacuum tube 301 are added, Is used as the RF power supply 300 in the general anodic tuning-grid tuning scheme according to FIG.

 When the resonance circuit 200 is used in the positive tuning-grid tuning self-excited oscillator, the positive electrode tank circuit 306 is connected to the grid tank circuit 305 via the grounding tab 202, The RF current flowing through the positive electrode tank circuit is returned to the cathode 313 of the vacuum tube 310 through the grounding tab 202 by grounding the connection between the negative electrode 304 and the grounding tab 202 via the grounding tab 202.

When the resonance circuit 200 is coupled to the anode tank circuit 306 in this manner, the equivalent circuit theory as shown in Equations (1) to (4) can be directly applied, The total impedance of the positive electrode tank circuit 306 can be adjusted without changing the resonance frequency by changing the position of the grounding tab 202 and the changed plasma impedance value can be compensated.

That is, when the plasma is generated or the output is increased, the total impedance of the positive electrode tank circuit 306 is increased, so that the resonance frequency of the positive electrode tank circuit is also increased. At this time, when the resonance frequency value of the positive electrode tank circuit continuously increases and becomes equal to or larger than the resonance frequency value of the grid tank circuit 305 due to an increase in output or the like, the resonance frequency of the positive tuning- Due to the characteristics, there is a possibility that the RF oscillation may suddenly stop.

On the other hand, according to the present invention, when the anode tank circuit 306 is constructed using the resonance circuit and the grounding taps as shown in Fig. 5, the anode tank circuit 306 is increased in the positive electrode tank circuit 306 without changing the resonance frequency value of the anode tank circuit 306 Therefore, the problem of impedance mismatch due to the plasma generation and output increase can be greatly improved.

Also, when a frequency-locked captive amplifier is used, when a resonant circuit including the tap, the induction coil, and the capacitor connected in parallel thereto is included in the impedance matching circuit of the tapping-type RF power source, the impedance mismatching range The impedance matching condition can be found in a relatively narrow range.

1: RF Inductively Coupled Plasma Generating Device 100:
200: resonant circuit 201: induction coil
202: grounding tab 203: capacitor
204: equivalent resistor 205: high voltage RF input stage
206: equivalent inductance 300: RF power source
301: vacuum tube 302: anode
303: grid 304: cathode
305: grid tank circuit 306: anode tank circuit

Claims (7)

A shield for providing a space in which a plasma is formed;
A resonance circuit formed on the induction coil and including a grounding tab for controlling the number of turns of the induction coil and performing a grounding function; And
And an RF power source for supplying RF power to the resonant circuit,
All of the RF current flowing through the induction coil through the resonant circuit is returned to the RF power source via the grounding tab,
Wherein the total impedance of the resonant circuit is adjusted without changing the resonant frequency according to the position of the grounding tab.
The method according to claim 1,
Wherein the RF power source is a self-excited oscillator.
The RF power supply of claim 1,
A vacuum tube including an anode, a grid, and a cathode;
A high-voltage DC supply circuit connected between the cathode and the anode;
A grid tank circuit connected between the grid and the cathode; And
A positive electrode tank circuit connected between the negative electrode and the positive electrode,
And wherein the RF inductively coupled plasma generator is a self-excited oscillator of a bipolar tuning-grid tuning system.
The RF power supply of claim 1,
A vacuum tube including an anode, a grid, and a cathode;
A DC supply circuit connected between the cathode and the anode;
A positive electrode tank circuit connected between the negative electrode and the positive electrode; And
And a feedback circuit connected to the cathode of the vacuum tube and the grid so that the voltage phase difference between the grid and the anode is 180 degrees.
Wherein the RF inductively coupled plasma generator is a self-excited oscillator of a positive polarity tuning type.
The method according to claim 3 or 4,
Wherein the resonant circuit is included in the positive electrode tank circuit and the grounding tab is grounded and connected to the negative electrode of the vacuum tube.
The method according to claim 1,
Wherein the RF power supply source is a frequency locked type tapping amplifier,
Wherein the resonance circuit is included in an impedance matching circuit of the tapped type amplifier.
The method according to claim 1,
Wherein the capacitor is a variable capacitor.

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