JPH0770944B2 - High frequency impedance matching circuit - Google Patents

Description

Detailed Description of the Invention

 [Object of the Invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a high frequency impedance matching circuit used in an etching apparatus or the like.

[0002]

2. Description of the Related Art In an etching apparatus or the like, a high frequency voltage is applied in order to form plasma in a vacuum chamber and perform etching effectively. That is, as shown in FIG.
High frequency source 1 that outputs high frequency of 00W, 13.5MHz
Is connected to a load 4 via a coaxial cable 2 and an impedance matching circuit 3. In the load 4, a high frequency is supplied between the container 41 forming the vacuum chamber and the backing plate 42 supporting the target in the container 41.

Usually, the coaxial cable 2 has a characteristic impedance of 50 Ω which matches the high frequency source 1, and the load 4 depends on the shape and size of the load 4, for example, other than 50 Ω.
It has a predetermined resistance value such as 00Ω. A matching circuit 3 for impedance matching, which is provided between the high frequency source 1 and the load 4, has a coil 31 and an L and a parallel variable capacitors 32 and 33.
Although it is composed of a C circuit, for high power use, the high-frequency transmission loss in the coil 31 is large and the temperature rise due to heat generation is also large. Therefore, the coil 31 is formed by winding a tubular body in a coil shape and is connected to both ends. The cooling water is supplied by the supplied water supply / drain pipes 31a and 31b to be cooled.

The impedance matching in the matching circuit 3 is performed by the capacitance control of the series and parallel variable capacitors 32 and 33 by the first and second driving sources 5 and 6 composed of a motor. The drive sources 5 and 6 are controlled by signals from the first and second control circuits 7 and 8. As shown in FIG. 3, the first and second control circuits 7 and 8 include detectors 71 and 81 for detecting an output current and an output voltage respectively flowing through the coaxial cable 2, as will be described later. To
The first control circuit 7 takes out a signal proportional to the ratio (Vi / I) of the output voltage Vi and the current I by the high frequency source 1, and the second control circuit 8 outputs the signal of the output voltage Vi (or the current I). A signal proportional to the phase difference is taken out to control the series variable capacitor 32 and the parallel variable capacitor 33, respectively. However, in practice, due to the restriction on the high frequency measurement for transmitting the coaxial cable 2, the first control circuit 7 detects the current I detected by the current detector 71 and the series circuit of the capacitor 91 and the diode 92. A signal proportional to the difference from the voltage Vi is taken out to drive the first drive source 5 via the amplifier 72, and the second control circuit 8 causes the voltage detector 81 to use the voltage Vi from the diode 92 as a reference signal. Then, a signal proportional to the phase difference of the voltage Vi is taken out to drive the second drive source 6 via the amplifier 82. The capacitor 91 and the diode 92 are configured as a shared circuit for the first and second control circuits 7 and 8.

The operating principle of impedance matching performed by the first and second control circuits 7 and 8 is shown in FIGS.
Will be briefly described. The configurations shown in FIGS. 2 and 3 are represented by an equivalent circuit as shown in FIG. That is, the load 4 is represented as a parallel circuit of a resistance component X and a capacitance component Ccs between the container 41 and the backing plate 42. High-frequency currents flowing through the components are Ix and Ics, and a supply voltage to the load 4 is Vx. , If the high frequency current flowing through the coil 31 is IL, the vector relationship of these Ix, Vx, Ics and IL is expressed as shown by the thick line in FIG. Further, the current IL in the coil 31 and the high-frequency voltage VL across the coil 31 are different in phase by 90 degrees (perpendicular to each other), and the high-frequency voltage Vcc of the series variable capacitor 32 is the coil 31.
Of the voltage VL of the
The vector composite value of x, VL, and Vcc becomes the output voltage Vi of the high frequency source 1.

FIG. 5 shows a series and parallel variable capacitors 32 and 33.
3 shows a vector relationship in a state where impedance matching is performed by the capacitance control of. Matching under the condition that the load of the high frequency source 1 is 50Ω pure resistance and the voltage: current is 50: 1 is that the following conditions (1) and (2) are satisfied. (1) The ratio between the high frequency output voltage Vi and the current I is 50. (2) The phase difference of the high frequency output voltage Vi (or the current I) is zero, and the high frequency current Ici flowing through the parallel variable capacitor 33 leads the output voltage Vi by 90 degrees.

Therefore, in order to satisfy the condition (1),
The series variable capacitor 32 is driven by the first drive source 5 and adjusts the voltage Vcc by capacitance control to output the output voltage Vcc.
It is necessary to take out the difference between i and the high frequency current I and control it so that it becomes a preset value. In order to satisfy the condition of (2), the parallel variable capacitor 33 is driven by the second drive source 6 to control the capacitance and adjust the current Ici so that the phase difference of the high frequency voltage Vi becomes zero ( That is, it is necessary to control Ici so that it leads the phase of Vi by 90 degrees.

In order to control the series variable capacitor 32 based on the high frequency detection measurement signal passing through the coaxial cable 2 and satisfy the above condition (1), the first control circuit 7 is actually The ratio of the output voltage Vi and the output current I is calculated, and the first drive source 5 is drive-controlled by the control signal A corresponding to the ratio to control Vcc. Further, in order to control the parallel variable capacitor 33 and satisfy the above condition (2), the phase difference φ of the output voltage Vi (or the output current I) is derived, and the control signal B corresponding to this phase difference φ is used. , The second motor 6 is drive-controlled.

Considering a case where this impedance matching circuit is actually applied to an etching apparatus or the like, a high frequency source 1 having a power capacity actually adapted to the load 4 is adopted and connected.

When the load of the high frequency source 1 is a pure resistance (R), the relationship between the power (P) and the voltage (V) and the current (I) is P = V2 / R = I2 / R. P is voltage V
(Or current I) squared. In other words, voltage (or current) is proportional to the square root of power. As described above, the first and second control circuits 7 and 8 detect the amplitude of the voltage (or current) to drive and control the drive sources 5 and 6. Therefore, the output power of the connected high frequency source 1 The magnitude of the amplitude of the detection signal changes depending on the magnitude of, and the control speed for varying the direct and parallel variable capacitors 32 and 33 changes in proportion to the square root of the output power. Therefore, when the output power of the high frequency source 1 is increased four times from 1 KW to 4 KW, the control speed of the system is doubled (= square root value of 4) and the drive source 5
The control speed by 6 and 6 increased and became unstable. Therefore, if the control system is set so that the system is stable when the output power of the high-frequency source 1 is large, the response of the control system is delayed when the output power is small.

As described above, the conventional impedance matching circuit has the drawback that the response speed of the control system of the impedance matching circuit changes depending on the output power capacity of the connected high frequency source 1.

Further, the impedance changes in accordance with the change in the capacitance value of the series variable capacitor 32 and the change in the capacitance value. Since the impedance is proportional to the reciprocal of the capacitance value, the unit capacitance per unit capacitance is small. The amount of change in impedance becomes large, and the amount of change in impedance becomes small in a region where the capacitance value is large. That is, although the capacitance value of the series variable capacitor 32 is controlled by the rotational driving by the motor 5, the series variable capacitor 32 is temporarily operated at a constant speed.
Even if is driven to rotate, the controlled impedance amount changes due to the difference in the rotation axis angle, that is, the capacitance value. Therefore, the control voltage amount changes the response speed of the control system depending on the rotation angle (that is, the capacitance value) of the drive source 5. To do.

Therefore, when it is attempted to change the capacity of the series variable capacitor 32 to be impedance-matched by driving by the motor 5, the control speed varies depending on the size of the variable value of the variable region, and stable control is always difficult. There was a drawback.

[0014]

The conventional high-frequency impedance matching circuit has the drawback that the control system becomes unstable because the impedance control speed changes depending on the magnitude of the power of the high-frequency source or the capacitance value of the series variable capacitor. It was

The present invention solves the above-mentioned drawbacks of the prior art and makes the control speed almost constant and stable matching regardless of the magnitude of the power supplied from the high frequency source and the magnitude of the capacitance value of the series variable capacitor. An object is to provide a high frequency impedance matching circuit that can operate.

[Constitution of Invention]

[0017]

According to the present invention , there is provided a series variable capacitor connected in series to a high frequency source, a coil for supplying a high frequency to a load connected in series to the series variable capacitor, and the series variable capacitor. And a parallel variable capacitor connected in parallel with the coil, and a first control signal corresponding to the ratio between the output voltage and the output current is detected by detecting the ratio between the high frequency output voltage and the output current from the high frequency power supply. And a first control circuit for controlling the drive source of the series variable capacitor, and a phase difference between the output voltage and the output current from the high frequency source is detected and a second control signal corresponding to the phase difference is derived. A high-frequency impedance matching circuit including a second control circuit that controls a driving source of the parallel variable capacitor ,
Corresponding to the control signal and the capacitance value of the series variable capacitor
A multiplier for multiplying with the correction voltage signal is provided.
Control the drive source of the series variable capacitor by the output signal
Characterized in that it.

[0018]

[0019]

The high frequency impedance matching circuit according to the present invention is provided with a divider for dividing the first and second control signals by the output voltage from the high frequency source, and controls the corresponding drive source by the output signal of the divider. Since it was done, the first
And the second control signal is divided by the high frequency output voltage even if the initial control voltage (or current) due to detection increases or decreases due to the change in the output power of the high frequency source and the control output changes, Not affected by fluctuations in output power,
A system with stable control speed can be obtained.

Also, the first driving a series variable capacitor
Is provided with a multiplier for multiplying the control signal of the serial variable capacitor by a signal corresponding to the capacitance value of the serial variable capacitor, and the drive signal of the serial variable capacitor is controlled by the output signal of the multiplier. A stable matching operation can be performed by obtaining a control signal that is not affected by the magnitude of the capacitance value of.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a high frequency impedance matching circuit according to the present invention will be described in detail below with reference to FIG. The same components as those of the conventional configuration shown in FIGS. 2 to 5 are designated by the same reference numerals and detailed description thereof will be omitted. That is, as shown in FIG. 1, a high frequency source 1 that outputs a high frequency of, for example, 500 W and 13.5 MHz is connected to a load 4 via a coaxial cable 2 having a characteristic impedance of 50Ω and an impedance matching circuit 3. The matching circuit 3 for impedance matching is directly connected to the coil 31 and is connected in parallel with the variable capacitor 3.
2 and 33, and the series and parallel variable capacitors 32 and 33 between the output side (50Ω) of the high frequency source 1 and the input side of the load 4 by the first and second drive sources 5 and 6. Each drive source 5, whose matching operation is performed by adjusting the capacitance of
6 is controlled by the signals from the first and second control circuits 7 and 8, but the first and second control circuits 7 and 8 first output the output current and the output flowing through the coaxial cable 2 as in the conventional case. The first control circuit 7 includes detectors 71 and 81 for respectively detecting a voltage, and the first control circuit 7 extracts a signal A proportional to a difference between the current I detected by the detector 71 and the voltage Vi generated by the capacitor 91 and the diode 92, Divider 73 via amplifier 72
Is supplied to. Since the voltage Vi detected by the diode 92 is supplied to the divider 73 and the signal from the amplifier 72 is divided, the current value detected by the current detector 71 is the output power of the high frequency source 1. Even if it changes in proportion to the square root of the magnitude (that is, the magnitude of the current value), since it is divided by the current value in the divider 73, the signal A ′ that is not affected by the magnitude of the output power is supplied to the multiplier 74. It

In the multiplier 74, the correction voltage signal C synchronized with the rotation angle of the first drive source 5 is supplied from the correction circuit 51. The correction circuit 51 interlocks with the rotation axis of the first drive source 5 and derives the correction voltage signal C corresponding to the rotation angle. The correction voltage signal C corresponds to the capacitance value level corresponding to the rotation axis of the series variable capacitor 32. The correction voltage signal C
Is multiplied with the control signal A ′, the first motor 5
Even if the capacitance value of the series variable capacitor 32 differs depending on the rotation angle and the changing region of the voltage amount Vcc to be changed is different, the control speed is corrected so that it is always constant, and stable matching operation is possible.

Next, the second control circuit 8 originally has the voltage Vi.
The signal that is proportional to the phase difference between the current I and the current I should be taken out and the parallel variable capacitor 33 should be controlled so that the phase difference becomes zero. However, in reality, it is proportional to the phase difference between the voltage Vi (or the current I). The generated signal B is taken out as a control signal and supplied to the amplifier 82. The output signal B of the amplifier 82 is supplied to the divider 83, is divided by the voltage Vi signal via the diode 92, and controls the second motor 6 as the control signal B ′. Therefore, also in this control system, a system having a stable control speed with little influence of the magnitude of the output power of the high frequency source 1 is realized.

As described above, the high-frequency impedance control circuit according to the present invention enables a stable control operation by simply adding a simple circuit to the conventional structure. It is possible to perform automatic impedance matching without being affected by the magnitude of the power supply capacity of the high frequency source 1 to be generated.

Further, the capacitance value of the series variable capacitor 32 in the matching circuit 3 differs depending on the rotation axis angle, but the correction amount by the multiplier 74 makes the amount of change in voltage always constant, and stable control is realized.

[0026]

According to the present invention, the control speed becomes almost constant and stable matching operation is performed regardless of the amount of electric power supplied by the high frequency source and the capacitance value of the series variable capacitor. Therefore, a remarkable effect can be obtained by adopting it to, for example, an etching device.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a high frequency impedance matching circuit according to the present invention.

FIG. 2 is a configuration diagram showing a conventional high frequency impedance matching circuit.

3 is a circuit diagram of the high frequency impedance matching circuit shown in FIG.

FIG. 4 is an equivalent circuit diagram of the high frequency impedance matching circuit shown in FIG.

5 is a vector diagram of a high frequency signal in the equivalent circuit shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... High frequency source 2 ... Coaxial cable 3 ... Matching circuit 31 ... Coil 32 ... Series variable capacitor 33 ... Parallel variable capacitor 4 ... Load 5,6 ... Driving source 51 ... Correction circuit 6 ... Second motor 7 ... First control Circuits 73, 83 ... Divider 74 ... Multiplier 8 ... Second control circuit

Claims (1)

[Claims] 1. A series variable capacitor connected in series to a high frequency power source, a coil for supplying high frequency to a load connected in series to the series variable capacitor, and the series variable capacitor and the coil connected in parallel. A variable capacitor and a drive source for the serial variable capacitor by detecting a ratio between a high frequency output voltage and an output current from the high frequency power source and deriving a first control signal corresponding to the ratio between the output voltage and the output current. And a first control circuit for controlling the phase difference between the output voltage and the output current from the high-frequency source, and a second control signal corresponding to the detected phase difference to derive a drive source for the parallel variable capacitor. in the high-frequency impedance matching circuit comprising a second control circuit for controlling the series variable co
A first control signal for driving a capacitor and the series variable capacitor
Multiply with the correction voltage signal corresponding to the capacitance value of the capacitor
A multiplier is provided, and the output signal of this multiplier can be used to change the series.
High frequency impedance matching circuit characterized by controlling the driving source of the capacitor