JPH0712729A - Induction coupled plasma generating device - Google Patents

Abstract

PURPOSE:To provide an efficient induction-coupled plasma generating device which has not to have a large resistance against reflected waves generated upon ignition of plasma and which incorporates an inexpensive transistor type high-frequency power source with a less loss in high-frequency power after ignition of plasma, by facilitating the impedance matching upon or after ignition of plasma so as to decrease the reflected waves upon ignition of plasma. CONSTITUTION:A high-frequency power source 1 is connected to an impedance matching circuit 3 through a directive couple 2 by a coaxial cable 8, and is connected at its output terminal with an output coil 7 including a torch 6. The impedance matching circuit 3 is composed of capacitors C1, C2 which are connected in an inverted L-like configuration, and is connected thereto with a thermistor resistor 11 in series with the output coil 7. The resistance of the thermistor resistor 11 becomes larger upon ignition of plasma 5, and becomes smaller after the ignition of the plasma 5, and accordingly, the impedance matching can be facilitated upon and after the ignition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inductively coupled plasma generator (hereinafter referred to as ICP), and more particularly to an inductively coupled plasma generator capable of easily performing impedance matching during plasma ignition and after plasma ignition. is there.

[0002]

2. Description of the Related Art Conventionally, a high-frequency power source for ICP has been a vacuum tube system, but in recent years, a transistor has been developed for reasons of downsizing, low cost, and easy maintenance. A drawback of the transistorized system is that it has low resistance to reflected wave power.

The impedance matching circuit has a function of efficiently transmitting high frequency power to the plasma, that is, a function of reducing a reflected wave. Generally, in order to maintain the plasma stably, it is easy to perform matching in a stable ignition state. Circuit constants are designed.

Therefore, at the time of plasma ignition, impedance matching cannot be perfectly achieved, and about 80% of the high frequency incident power is reflected to the high frequency power source, and the load of the transistor becomes large. Was destroyed. As measures against this, a method of reducing the reflected wave and a method of increasing the proof stress of the transistor have been proposed. For example, a technique has been proposed in which a transistor is operated in class C and a DC power supply voltage applied to a collector is made variable to allow the transistor a margin and to improve the resistance to reflected waves.

[0005]

The above-mentioned prior art is based on the IC
This is a method of providing a margin by suppressing the output of each P transistor. Therefore, in order to obtain a large output for practical use, for example, an output of 1 kW or more, it is necessary to operate a large number of transistors in parallel, which causes a problem that the circuit scale becomes large, complicated, and expensive. It was

The present invention has been made in order to solve the above-mentioned problems of the prior art. By facilitating impedance matching between plasma ignition and after plasma ignition, a reflected wave during plasma ignition is obtained. To provide a highly efficient ICP that does not require high thermal and electrical resistance of the transistor against the reflected wave, is equipped with an inexpensive high frequency power supply, and has a small loss of high frequency power after plasma ignition. The purpose is to

[0007]

In order to achieve the above object, the structure of the present invention relating to an ICP is an ICP including a high frequency power supply section, a plasma generating section having an output coil, and an impedance matching section. The impedance matching unit is configured to reduce the high frequency reflected power during plasma ignition and reduce the high frequency power loss after plasma ignition.

The impedance matching section is one in which a resistor having a predetermined resistance value having a negative temperature coefficient is inserted in series with the output coil. The impedance matching unit inserts a resistor having a predetermined resistance value in series with the output coil,
After plasma ignition, the resistance value of the series insertion resistor is set to zero. Further, after the plasma ignition, the resistance value of the resistor having the negative temperature coefficient is set to zero.

Next, the above means will be described in more detail with reference to FIGS. FIG. 3 is an impedance matching equivalent circuit including the output coil of the ICP device, and FIG.
5 is a diagram showing C1 and C2 with respect to R in impedance matching in the equivalent circuit of FIG. 3, and FIG. 5 is a diagram showing a relationship between R and a reflection coefficient in the equivalent circuit of FIG.

In FIG. 3, L is the inductance of the output coil, R is the resistance of the output coil and the plasma, C1 and C2 are variable capacitors of the impedance matching circuit, and Z is the input impedance of this circuit. is there. Note that r indicated by a broken line is a resistance that will be inserted later, so it will be omitted at this stage in the description.

C1 is set so that the input impedance Z becomes equal to the impedances of the high frequency power supply and the line.
And C2 are controlled. High frequency power supply, line impedance
Since the dance is generally designed as a pure resistance Ro (= 50Ω), C1 and C at the time of impedance matching
2 is represented as follows.

[0012]

[Equation 1]

[Equation 2]

[Equation 3]

FIG. 4 is an example of a graph showing the relationship between the above equations (1) and (2). In FIG. 4, L = 0.
It is calculated with 58 μH, Ro = 50Ω, and f = 27.12 MHz. When the plasma is lit, the resistance R is
It is about 5Ω, and the range of change is about ± 0.5Ω. The C1 is composed of a 300 pF high frequency ceramic capacitor and a 100 pF air variable capacitor connected in parallel, and the C2 is a 100 pF vacuum variable capacitor.

Under the above configuration conditions, the C1 is 350
It can be seen that impedance matching can be obtained before and after pF and around 70 pF for C2. The resistance R when the plasma is not lit is about 0.1Ω,
Impedance matching is obtained at about 2600 pF for C1 and about 60 pF for C2.

However, before and after plasma ignition, the C
Since the difference of 1 is too large to control C1 while following plasma ignition, in reality, within the range in which fine adjustment in the plasma lighting state is possible (350 ±).
The capacity is about 50 pF.

FIG. 5 shows that C1 = 350 pF, C2
It is a diagram which shows the reflection coefficient with respect to the said resistance R when it is set to = 70pF. When the reflection coefficient is 1.0, the reflection is 100%, and when 0.0, the reflection is 0. In the plasma lighting state, as described above, when R = 5Ω, almost matching can be obtained, so that the reflection coefficient becomes a value close to zero.

When the plasma is not lit, that is, when the resistance R is about 0.1Ω, the reflection coefficient is close to 1.0 and the reflection is large. Here, in order to reduce the reflected wave during the ignition operation, the resistance R during the ignition operation is brought close to the value during plasma lighting.

Specifically, as shown by the broken line in FIG. 3, a resistor r is inserted in series with the output coil. After the ignition operation is completed, the resistance r causes a loss of high frequency power, and therefore its value must be reduced. If a resistor having a negative temperature coefficient is used as the resistance r, the resistance value becomes large before ignition and becomes small after self-heating after ignition operation, so that the above condition can be satisfied. Also, a switch S is provided so that both ends of the resistor r can be short-circuited, and the switch S is opened during the ignition operation, and is closed after the ignition operation is completed. To be done.

[0019]

The function of each of the above technical means is as follows.
According to the configuration of the present invention, by inserting a resistor having a negative temperature coefficient in series with the output coil of the ICP, the resistance value is large at the time of plasma ignition, impedance matching is easy to take, and the reflected wave is small. . Further, after plasma ignition is completed, a negative temperature coefficient acts due to self-heating, and the resistance value of the resistor becomes small, so high frequency loss is small and efficiency is improved. Further, if the resistor inserted in series with the output coil is plasma-ignited and both ends thereof are short-circuited by the switch, the high frequency loss is further reduced and the efficiency is improved.

[0020]

Embodiments of the present invention will be described below with reference to FIGS. [Embodiment 1] FIG. 1 shows an ICP according to an embodiment of the present invention.
It is a basic block diagram of an apparatus. In FIG. 1, 1 is a high frequency power supply, 2 is a directional coupler, 3 is an impedance matching circuit, 4 is a control unit, 5 is a plasma, 6 is a torch, 7 is an output coil, 8 is a coaxial cable. , C1 and C2 are variable capacitors, and 11 is a thermistor resistor.

The high frequency power supply 1 is of a transistor type, for example, and has a frequency of 27.12 MHz and an output of 1.5 kW. The high frequency output of the high frequency power supply 1 is
The signal is input to the impedance matching circuit 3 via the directional coupler 2 by the coaxial cable 8.

The impedance matching circuit 3 is
The two variable capacitors C1 and C2 are formed in an inverted L shape. The capacitor C1 is composed of, for example, a high frequency ceramic capacitor and an air variable capacitor connected in parallel, and the air variable capacitor is drive-controlled by the control unit 4. The capacitor C2 is, for example, a vacuum variable capacitor, and is drive-controlled by the control unit 4. The capacitor C
1 and the opposite L-shaped configuration of the capacitor C2,
The resistor 11 and the output coil 7 are connected in series.

The resistor 11 is a thermistor having a negative temperature coefficient, and the output coil 7 is a copper pipe having three turns and is wound so as to enclose the torch 6. As the resistor 11, for example, its resistance is 25
A thermistor having a rated current of 20 A and a resistance of 5 Ω at 0.1 ° C. This may be commercially available for suppressing surge current when the power source such as a switching power source is turned on. Also, the thermistor
Since it operates as a pure resistance up to about 100 MHz, there is no problem at the frequency of 27.12 MHz of this embodiment, and it operates as a pure resistance, which is preferable.

Next, the operation of this embodiment will be described. The output of the high frequency power supply 1 is input to the output coil 7 by the coaxial cable 8, the directional coupler 2 and the impedance matching circuit 3. Plasma is generated in the torch 6 by the magnetic field induced by the output coil 7.

The directional coupler 2 detects the traveling wave and the reflected wave, and controls the capacitors C1 and C2 by the control unit 4 so as to minimize the reflected wave. Further, the control section 4 controls the high frequency power source 1 for feedback so that the traveling wave output is constant.

Since impedance matching is achieved during plasma ignition, most of the high-frequency power output from the high-frequency power source 1 is input to the output coil 7, so that ignition can be performed reliably even at low output, for example 300W. You can

Further, since the current from the output coil 7 flows through the thermistor resistor 11 as it is, the temperature of the thermistor becomes high in a short time and the resistance value becomes small. As described above, according to the present invention, the reflected wave is small at the time of plasma ignition, and the loss of high frequency power is small after ignition.

[Embodiment 2] Next, another embodiment of the present invention will be described. FIG. 2 shows an impedance matching circuit according to another embodiment of the ICP of the present invention. The ICP of this embodiment has the same configuration as that of [Embodiment 1] except for the impedance matching circuit, and therefore detailed description thereof will be omitted.

In FIG. 2, the same reference numerals as those in FIG. 1 denote the same parts, and thus detailed description thereof will be omitted. Only new codes will be described. Reference numeral 12 is a switch for shorting the resistor, and 13 is a series resistor. A series resistor 13 is inserted in the output coil 7, and a switch 12 is provided so that both ends of the series resistor 13 can be short-circuited.

The switch 12 is controlled by the controller 4. The resistor 13 is, for example, a metal film resistor for high frequency, having a resistance value of 5Ω and a rated power of 200W. In addition, the switch 12 has a mechanical relay.
Can be used. When plasma is ignited, the switch 12 is opened to input high frequency power. After the plasma ignition is completed, the switch 12 is closed.

Since the resistance value of the thermistor resistor 11 in [Embodiment 1] does not become completely zero during plasma ignition, it is more preferable to provide a switch as in [Embodiment 2] and short-circuit. The effect is obtained. As described above, according to the present embodiment, it is possible to obtain an ICP in which the reflected wave is small at the time of plasma ignition and the loss of high frequency power is small after ignition.

[0032]

As described in detail above, according to the present invention, impedance matching between plasma ignition and after plasma ignition is facilitated to reduce the reflected wave during plasma ignition. (EN) An efficient inductively coupled plasma generator that does not require high thermal and electrical resistance of a transistor against reflected waves, is equipped with an inexpensive high frequency power supply, and has little loss of high frequency power after plasma ignition. be able to.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of an ICP device according to an embodiment of the present invention.

FIG. 2 is an impedance matching equivalent circuit including an output coil of an ICP device according to another embodiment of the present invention.

FIG. 3 is an impedance matching equivalent circuit including an output coil in an ICP device.

4 is a diagram showing C1 and C2 with respect to R at the time of impedance matching in the equivalent circuit of FIG.

5 is a diagram showing a relationship between R and a reflection coefficient in the equivalent circuit of FIG.

[Explanation of symbols]

 1 high-frequency power supply 2 directional coupler 3 impedance matching circuit 4 control unit 5 plasma 6 torch 7 output coil 8 coaxial cable 11 thermistor resistor 12 switch 13 series resistor C1 capacitor C2 capacitor r insertion resistance Body s switch

Claims (4)

[Claims] 1. An inductively coupled plasma generator comprising a high frequency power supply section, a plasma generation section having an output coil, and an impedance matching section, wherein the impedance matching section has high frequency reflected power during plasma ignition. An inductively coupled plasma generator characterized in that the high frequency power loss after plasma ignition is reduced. 2. The inductively coupled plasma generator according to claim 1, wherein the impedance matching section has a resistor having a predetermined resistance value having a negative temperature coefficient inserted in series with the output coil. 3. The impedance matching unit is configured such that a resistor having a predetermined resistance value is inserted in series with the output coil so that the resistance value of the resistor becomes zero after plasma ignition. The inductively coupled plasma generator according to claim 1. 4. The inductive coupling according to claim 2, wherein the resistor having a predetermined resistance value having a negative temperature coefficient is configured so that the resistance value of the resistor becomes zero after plasma ignition. Plasma generator.