JPH04368799A - Device for measuring plasma impedance - Google Patents

Abstract

PURPOSE:To measure the plasma impedance without detecting applied voltage and applied current of plasma. CONSTITUTION:An impedance converting circuit 2 is interposed between a high frequency power source 1 and a plasma load 4. High frequency current and high frequency voltage and a phase difference between the current and the voltage are detected at a measuring point set in the input side of the impedance converting circuit 2. Input impedance seen from the measuring point to the load side is computed on the basis of the current, voltage, and a phase difference. Load circuit side impedance seen from an output end of the impedance converting circuit 2 to the plasma load side through a coaxial cable is computed on the basis of a circuit constant and the input impedance. Plasma impedance can be computed on the basis of the load circuit side impedance and the circuit constant of the coaxial cable.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma impedance measuring device for measuring the impedance of a plasma load to which power is supplied from a high frequency power source.

0002

2. Description of the Related Art In the manufacturing process of semiconductor ICs, LCDs (liquid crystal displays), etc., processes using plasma (referred to as plasma processes) are performed when performing etching, sputtering, thin film growth, etc. In a plasma process, high frequency power is supplied to an electrode provided in a chamber in which processing such as etching, sputtering, thin film growth, etc. is performed, thereby generating plasma within the chamber.

[0003] In this way, the load (
This is called plasma load. ), it is important to match the impedance between the high-frequency power source and the plasma load. If the impedance between the two is not matched, the output terminal of the high-frequency power source Since the high frequency power cannot be efficiently supplied to the plasma load due to power reflection, good results cannot be obtained in the process.

[0004] Therefore, when power is supplied from a high frequency power source to a plasma load, it is essential to insert an impedance matching circuit consisting of an L, C circuit, a transformer, etc. between the high frequency power source and the plasma load.

FIG. 4 shows a circuit diagram when power is supplied from the high frequency power source 1 to the plasma load 4 through the automatic impedance matching circuit 2' and the line 3. The impedance matching circuit 2' includes a coil L1 having a constant inductance, a first variable capacitor C1, a coil L2 whose inductance can be adjusted by selecting taps, and a second variable capacitor C2. The first variable capacitor C1
The impedance is matched by changing the capacitance of the second variable capacitor C2 and the second variable capacitor C2.

In order to automatically adjust the first and second variable capacitors C1 and C2, in this type of automatic matching circuit, a detector (not shown) detects the high frequency voltage V and the input terminal of the matching circuit 2'. The high frequency current I and the phase difference θ between the voltage V and current I are detected, and from the ratio of the absolute value of the voltage V and the absolute value of the current I, the impedance when looking at the load side from the input end of the impedance matching circuit is determined. Z1' is detected, and the capacitors C1 and C2 are adjusted so that the impedance Z1' matches the output impedance Zo (=50Ω, constant) of the power supply and the phase difference θ becomes zero.

Among the above adjustments, the adjustment to make the impedance Z' match the absolute value of the output impedance of the power supply is mainly performed by adjusting the capacitance of the first capacitor C1, and the phase difference θ is adjusted by adjusting the capacitance of the first capacitor C1. The adjustment to zero is mainly performed by adjusting the capacitance of the second capacitor C2.

[0008]

[Problem to be Solved by the Invention] In general impedance matching circuits installed in antennas for wireless communication, input circuits of amplifiers, etc., the impedance of the load is known in advance, so it is difficult to create a matching circuit using the known load impedance. circuit constants can be easily set. Further, if the load impedance is constant, the matching state can be maintained by keeping the circuit constant of the matching circuit constant.

[0009] However, in the case of a plasma load, its impedance changes from time to time, so it is not possible to determine the circuit constants of the matching circuit by connecting known impedances. Furthermore, since the plasma impedance changes from time to time, impedance matching cannot be achieved using a matching circuit having fixed circuit constants.

In the impedance matching circuit shown in FIG. 4, in order to perform impedance matching accurately, the circuit constants of the matching circuit (variable range of capacitance of capacitors C1 and C2, inductance of coils L1 and L2) are required. It is necessary to set it to an appropriate value according to the fluctuation range of plasma impedance.

However, in the past, there was no suitable method for measuring plasma impedance, and it was not possible to set the circuit constants of the matching circuit 2' using information regarding the plasma impedance. The circuit constants of the matching circuit were set based only on the measured voltage and current to reduce the reflected power toward the high-frequency power source. Setting these circuit constants requires relying on experience and intuition without information regarding plasma impedance, which not only takes time but also does not necessarily result in optimal settings. There was a problem. If the circuit constants are not set appropriately, it may become impossible to achieve matching under all plasma load conditions, and the control operation of the automatic matching circuit may become impossible.

[0012] In addition, it is preferable to monitor plasma impedance in order to analyze the state of the plasma load and the cause of malfunction of the impedance matching circuit. No method was proposed.

[0013] As a method of measuring plasma impedance, it is possible to measure the voltage and current on the output side of the matching circuit 2'.
There is a standing wave between the Have difficulty.

An object of the present invention is to provide a plasma impedance measuring device that can accurately measure plasma impedance.

[0015]

[Means for Solving the Problems] The present invention provides a high frequency power source 1
This is a plasma impedance measurement device that measures the impedance of a plasma load 4 to which power is supplied from the plasma load 4.

In the plasma impedance measurement apparatus of the present invention, as shown in FIG. 1, an impedance conversion circuit 2 is provided between a high frequency power source 1 and a plasma load 4. This impedance conversion circuit is a circuit that converts input and output impedances, and only needs to have known circuit constants, and can use an L, C circuit or a transformer, but an impedance matching circuit is not provided. In such a case, the impedance matching circuit itself can be used as the impedance conversion circuit 2. Further, a part of the impedance matching circuit can also be used as the impedance conversion circuit 2.

As the impedance matching circuit, a variable capacitor, a variable inductor (an element that can minutely change the inductance value of a coil), or a combination thereof may be used as an impedance adjustment means for adjusting input and output impedance. Can be done.

In the measuring device of the present invention, the measuring point P is set at an arbitrary point on the input side circuit of the impedance conversion circuit 2.
Input voltage detection means 6 for detecting the absolute value of the high frequency voltage at
, a phase difference detection means 7 that detects the phase difference between the high frequency current and the high frequency voltage at the measuring point P, and the absolute value of the high frequency current, the absolute value of the high frequency voltage, and the phase difference at the measuring point P. The impedance conversion circuit 2 is calculated from the input impedance and the input impedance and the circuit constant of the circuit between the measurement point P and the output end of the impedance conversion circuit 2. Load circuit side impedance calculating means 10 is provided for calculating the impedance of the circuit on the plasma load side from the output end of the plasma load circuit as the load circuit side impedance. The plasma impedance calculated by the load circuit side impedance calculation means 10 includes the impedance of the circuit connecting the output end of the impedance conversion circuit 2 and the plasma load 4, but only the impedance of the plasma load is measured as the plasma impedance. In this case, plasma impedance calculation means 11 is further provided for calculating the impedance of the plasma load from the constant of the circuit connecting the output end of the impedance conversion circuit and the plasma load and the impedance on the load circuit side.

When using an impedance matching circuit in which a variable capacitor, a variable inductor, or a combination thereof is used as an impedance adjustment means as an impedance conversion circuit, the position of the adjustment section of the impedance adjustment means is detected and the position of the adjustment section of the impedance adjustment means is detected. Impedance calculating means 9 for calculating impedance is provided. The load circuit side impedance calculation means calculates the load circuit side impedance using the impedance of the impedance adjustment means calculated by the impedance calculation means 9 and other circuit constants.

Further, in order to easily check the calculation results, a display means 12 is provided for displaying the calculation results of the plasma impedance calculation means on the screen of a display device.
It is preferable to further provide.

The measurement point P set on the input side of the impedance conversion circuit 2 can be set at any point in the circuit between the impedance conversion circuit 2 and the output terminal of the high frequency power source 1. When an automatic impedance matching circuit is used as an automatic impedance matching circuit, it is preferable to set the input terminal of the impedance matching circuit as the measurement point P. If the input end of the automatic impedance matching circuit is used as the measurement point in this way, it is possible to use the current detection means, voltage detection means, and phase difference detection means that are originally provided in the automatic impedance matching circuit.

If the measurement point is set closer to the power supply than the input terminal of the impedance conversion circuit 2, the input impedance of the impedance conversion circuit 2 and the impedance of the line between the input terminal of the impedance conversion circuit and the measurement point are The input impedance calculation means 8 calculates the sum of .

[0023]

[Operation] In the plasma impedance measuring device described above, the input impedance calculation means calculates the impedance viewed from the measurement point to the load side as the input impedance Z1. The circuit constants of the circuit between the measurement point and the output end of the impedance conversion circuit are known. Even if a variable element such as a variable capacitor is installed in the impedance conversion circuit, its constant (in the case of a capacitor, the capacitance)
can be easily determined from the position of the controller. The load circuit side impedance calculating means 10 calculates the resistance and reactance of the load circuit side impedance Z2 when looking at the plasma load side circuit from the output terminal of the impedance conversion circuit 2 by using the known circuit constants and calculations as unknown quantities. The resistance component and reactance component of the load circuit side impedance are calculated from the input impedance Z1.

Since the constants of the distributed constant circuit connecting the output end of the impedance matching circuit and the plasma load are known, once the impedance on the load circuit side is determined, the plasma impedance Zp can be determined from the formula of the distributed constant circuit. Can be done.

[0025] Since each of the above calculations can be performed instantaneously using a computer, the plasma impedance, which changes from moment to moment, can be measured almost in real time.

If the plasma impedance is known, the circuit constants of the impedance matching circuit can be set accurately. Furthermore, since the plasma impedance, which changes from moment to moment, can be measured in real time, the state of the load relative to the high frequency power can be monitored.

Furthermore, it is also possible to automatically control the impedance matching circuit using the above measurement results.

[0028]

[Embodiment] Figure 2 shows the configuration of an embodiment of the present invention. In the figure, 1 is a high-frequency power source, and 2 is an impedance conversion circuit. This impedance conversion circuit supplies high-frequency power to a plasma load. It consists of an automatic impedance matching circuit that has been used in the past. The impedance conversion circuit 2 is connected to a plasma load 4 through a coaxial cable 3.

The impedance matching circuit constituting the impedance conversion circuit 2 includes a coil L1 having a constant inductance, a first variable capacitor C1, a second variable capacitor C2, and a tap, similar to the one shown in FIG. It is equipped with a coil L2 whose inductance can be adjusted by selecting . An adjustment section (operation shaft) for adjusting the capacitance of each of the first and second variable capacitors C1 and C2 is connected to an operation mechanism (not shown) using a motor as a drive source. Further, a control unit (not shown) is provided to control a motor that drives the operator of each variable capacitor, and the control unit controls the variable capacitor C1.
By controlling the rotation of the operators C2 and C2, the capacitance of each variable capacitor is adjusted.

In this example, variable capacitors C1 and C
2 constitutes the impedance adjustment means of the impedance matching circuit.

A high frequency current I (
A detector 2A is provided that detects the absolute value |I| of the high-frequency voltage V (vector), the absolute value |V| of the high-frequency voltage V (vector), and the phase difference θ between the current I and the voltage V.

The control section of the impedance matching circuit takes the ratio of the absolute value of the high frequency voltage V and the absolute value of the high frequency current I, and calculates the impedance Z1' when looking at the load side from the input terminal of the matching circuit, Mainly the first capacitor C1
By adjusting the impedance Z1', the absolute value of the output impedance Zo of the power supply (=50Ω,
(constant). The control section also adjusts the phase difference θ between the high frequency current I and the high frequency voltage V to zero by mainly adjusting the second capacitor C2.

In the present invention, the impedance viewed from the impedance matching circuit from a measurement point set at an arbitrary point in the circuit from the impedance conversion circuit 2 to the output end of the power supply is determined as the input impedance Z1, and this is determined as the plasma impedance. However, in this embodiment, the input terminal of the impedance conversion circuit 2 is used as the measurement point,
The current I detected by the detector 2A originally provided in the automatic impedance matching circuit constituting the conversion circuit 2,
The voltage V and the phase difference θ are used to calculate the input impedance Z1. In this case, the input impedance Z1 is the impedance Z calculated by the automatic impedance matching circuit.
It becomes equal to 1'.

In the present invention, the impedance of the circuit on the plasma load side from the output end of the impedance matching circuit 2 is calculated from the circuit constants and input impedance Z1 of the circuit between the measurement point and the output end of the impedance conversion circuit 2. is calculated as the load circuit side impedance Z2.

In this embodiment, the impedance conversion circuit 2
Since the input end of is used as the measurement point, the input impedance Z1 and the circuit constant of the impedance conversion circuit may be used for this calculation.

The circuit constants of the impedance conversion circuit 2 are:
They are the capacitance of the first and second variable capacitors C1 and C2, and the inductance of the coils L1 and L2. Among these, the inductances of the coils L1 and L2 are known, but the capacitances of the first and second variable capacitors C1 and C2, which are impedance adjustment means, change at any time. Therefore, in this embodiment, in order to calculate the capacitance of variable capacitors C1 and C2, variable resistors VR1 and VR2 are provided, and the sliders of these variable resistors are linked with the operators of variable capacitors C1 and C2. It is connected to the drive mechanism of each variable capacitor operator. Variable resistors VR1 and VR2
A constant DC voltage is applied to both ends of the variable resistors VR1 and VR2, and position detection signals Vp1 and Vp1 corresponding to the positions (rotation angles) of the operators of the capacitors C2 and C2 are applied between the sliders of the variable resistors VR1 and VR2 and the ground, respectively. I'm trying to get Vp2. In this example, variable resistors VR1 and VR
2 constitutes an adjustment position detection device that detects the position of the adjustment section of the impedance adjustment means, and the impedances of variable capacitors C1 and C2 as the impedance adjustment means are calculated from detection signals Vp1 and Vp2 of this detection device.

[0037] Absolute value of current |I|, absolute value of voltage |V|
, phase difference θ and position detection signals Vp1 and Vp2 are input to an analog/digital converter (A/D converter) 20 and converted into digital signals, and the respective digital signals are input to a computer 21.

The computer 21 calculates the plasma impedance according to the algorithm shown in FIG. 3, and displays the result on the display device 12.

The processing performed according to the algorithm shown in FIG. 3 is as follows.

First, from the absolute value of current I |I| and the absolute value of voltage V |V|, the input impedance Z is determined by the following equation (1).
The absolute value of 1 |Z1| is calculated. |Z1|=|I|/|V|

(1) Next, the input impedance Z1 is calculated from the absolute value of the impedance and the phase difference θ between voltage and current using the following equation. The resistance component of the impedance Z1 is R, the reactance component is X, and Z1 = R1 +
jX1, R1 and X1 are given by the following formula. R1 = | Z1 | cos θ

...(2)X1 = |Z1|sin θ

...(3) Next, from the position detection signals Vp1 and Vp2, the variable capacitor C1
and C2, and based on the results, impedances -j (1/ωC1) and -j (1/ωC2) of variable capacitors C1 and C2 are calculated.

Next, the load circuit side impedance Z2 when looking at the load side circuit from the output end of the conversion circuit is Z2 = R2
+jX2, and let R2 and X2 be unknowns,
The resistance component R1 and the reactance component X1 of the input impedance Z1, and the reactance 1/of the components of the conversion circuit.
R2 and X2 are determined using ωC1, 1/ωC2, ωL1, and ωL2 as known numbers. These R2
and X2 are given by the following formula. Note that "*" indicates a multiplication symbol.

R2 =R*(ωC1)2/B

...(4)X2 = {R2 *ωC1 +(X+
ωC1) *ωC1 *X}/B+ω(C2 -L2)


...(5) However, X=X1 -ωL1

...(6) B=R2 +(X+ωC1
)2
...(7) Next, the characteristic impedance of the coaxial cable connecting between the conversion circuit 2 and the plasma load is 50Ω, and the length of the coaxial cable is d.
[m], and if β is the phase constant of the distributed constant circuit connecting between the impedance conversion circuit 2 and the plasma load 4,
Plasma impedance Zp is determined by the following equation. Zp =50*zp

...(8) However, zp = {z2 −jtan (βd)}/{1−jz
2 tan (βd)} …(9)z2 =
Z2 /50

...(10) In this embodiment, by the process of calculating the absolute value of impedance Z1 and the process of calculating the vector of impedance Z1 in the flowchart of FIG.
Input impedance calculation means 8 is realized. Also, the process of calculating the impedance of the variable capacitors C1 and C2, and the load circuit side impedance Z2 from the circuit constants of the impedance conversion circuit and the input impedance Z1.
The load circuit side impedance calculation means is realized by the process of calculating . Furthermore, plasma impedance Zp
The plasma impedance calculating means 11 is realized by the process of calculating.

The plasma impedance Zp, input impedance Z1, and load circuit side impedance Z2 are displayed on the screen of a computer display device. Through this process, the display means 12 is realized.

Each of the above impedances is displayed, for example, on a Smith chart showing the impedance matching range of the automatic impedance matching circuit, and whether the output impedance of the automatic impedance matching circuit (determined by the load impedance) is within the matching range. It can be used as a criterion for determining whether Note that instead of using the Smith chart, the impedances Zp, Z1, and Z2 may be displayed using an orthogonal impedance coordinate system.

In the above embodiment, an automatic impedance matching circuit is used as the impedance conversion circuit 2, but the configuration of the automatic impedance matching circuit is not limited to the illustrated example. For example, in FIG. 2, coil L1
may be omitted. Further, in the impedance matching circuit of FIG. 2, the variable capacitor C2 is provided to change the equivalent inductance of the series circuit of the capacitor C2 and the coil L2, and the variable inductor C2 is provided to change the equivalent inductance of the series circuit of the capacitor C2 and the coil L2. If it is possible to use the variable inductor (it may not be possible depending on the frequency band), replace the series circuit of the variable capacitor C2 and the coil L2 with a single variable inductor, and use the variable inductor as the impedance adjustment means of the impedance matching circuit. You can also do it. In that case, the position of the adjusting section of the variable inductor is detected, and the impedance value of the variable inductor is calculated from the detected position.

Innumerable other variations can be considered in the configuration of the impedance matching circuit, and there are cases where both a variable capacitor and a variable inductor are used as impedance adjusting means.

[0047] The impedance conversion circuit used for measuring plasma impedance in the present invention is one that converts input and output impedance, and the circuit constants are known or can be known. Often, a transformer, L, C circuit, etc. can be used as the impedance conversion circuit.

[0048]

As described above, the present invention has the advantage that plasma impedance can be measured almost in real time without measuring the voltage and current applied to the plasma.

By measuring the plasma impedance, it is possible not only to know the state of the load with respect to high frequency power, but also to accurately measure the circuit constant of the impedance matching circuit provided between the high frequency power source and the plasma load. become able to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention.

FIG. 2 is a circuit diagram showing the configuration of an embodiment of the present invention.

FIG. 3 is a flowchart showing a computer software algorithm for realizing each means of the present invention.

FIG. 4 is a circuit diagram schematically showing the configuration of a circuit that supplies power from a high frequency power source to a plasma load.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... High frequency power supply, 2... Impedance conversion circuit, 4... Plasma load, 5... Input current detection means, 6... Input voltage detection means, 7... Phase difference detection means, 8... Input impedance calculation means, 9... Impedance calculation means, 10...Load circuit side impedance calculation means, 11...Plasma impedance calculation means, 12...Display means.

Claims (4)

[Claims] 1. A plasma impedance measuring device for measuring the impedance of a plasma load to which power is supplied from a high-frequency power source, wherein an impedance conversion circuit is inserted between the high-frequency power source and the plasma load, and the impedance conversion circuit comprises: input current detection means for detecting the absolute value of the high frequency current at a measurement point set at an arbitrary point of the circuit on the input side of the circuit; input voltage detection means for detecting the absolute value of the high frequency voltage at the measurement point; A phase difference detection means detects a phase difference between a high frequency current and a high frequency voltage at a measurement point, and a load is detected from the measurement point based on the absolute value of the high frequency current, the absolute value of the high frequency voltage at the measurement point, and the phase difference. input impedance calculation means for calculating the impedance viewed from the side as the input impedance, and the circuit constant of the circuit between the measurement point and the output end of the impedance conversion circuit and the input impedance, from the output end of the impedance conversion circuit. A plasma impedance measuring device comprising load circuit side impedance calculation means for calculating an impedance viewed from the circuit on the plasma load side as a load circuit side impedance. 2. The plasma impedance calculation means further comprises plasma impedance calculation means for calculating an impedance of the plasma load from a constant of a circuit connecting an output end of the impedance conversion circuit and the plasma load and an impedance on the load circuit side. The plasma impedance measuring device according to claim 1. 3. The impedance conversion circuit includes an impedance matching circuit using a variable capacitor, a variable inductor, or a combination thereof as an impedance adjustment means, and detects the position of the adjustment section of the impedance adjustment means to adjust the impedance adjustment means. The load circuit side impedance calculation means calculates the load circuit side impedance using the impedance of the impedance adjustment means calculated by the impedance calculation means and other circuit constants. The plasma impedance measuring device according to claim 1 or 2. 4. The plasma impedance measuring device according to claim 1, further comprising display means for displaying the calculation result of said plasma impedance calculation means on a screen of a display device.