JP3048327B2 - Load discriminator in high frequency transmission lines - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load discriminator in a high-frequency transmission line, and more particularly to a high-frequency load discriminator for detecting the magnitude of a load impedance by using a transformer for an instrument.

[0002]

2. Description of the Related Art Typical examples of industries utilizing high-frequency energy include surface modification of metals by induction hardening and dry processes in semiconductor manufacturing processes. Among the semiconductor manufacturing processes, in CVD sputtering and etching, it is important to supply high-frequency energy efficiently and stably to secure reproducibility of the process. Therefore, generally, as shown in FIG.
A matching device (generally 3) for performing impedance matching between a high-frequency power supply (terminal 1) and a load (terminal 2) is used. This matching device has a discriminator 4 for detecting a phase difference and an impedance difference between the high-frequency power supply side and the load side on the transmission line, and the latter impedance detection function (load discrimination function) has its own. The magnitude of the load impedance (resistance) viewed from the input side is determined, and the servo motor 6 is driven via the load servo amplifier 5 to change the load side impedance to the transmission line impedance (generally 50Ω).
The circuit constant (variable capacitor V
C _L ).

In this case, the principle of measuring the impedance difference of the load discriminator is as shown in FIG. 2, while detecting a value corresponding to the current i of the high-frequency transmission line by an instrument transformer CT1 provided on the transmission line 7. Detecting a value corresponding to the voltage e of the transmission line portion on the load side of the transformer,
The magnitude of the load impedance was determined from the value corresponding to the ratio e / i. Specifically, the line current i is detected via the diode D1 as a voltage e ″ generated across the resistor R1 connected to the secondary winding of the transformer CT1, and the voltage e of the transmission line portion is detected at the load terminal 2 Is detected through the diode D1 as the capacitor partial value e 'at a polarity opposite to that of the above e ", and both of them give the potential of e"-e' to the indication terminal 8. Here, the load impedance is the line impedance and the load impedance is the line impedance. Similarly, if it is 50Ω, the relation of e / i ≒ 50 is e ″ −e ′ = 0 (V) at the output terminal 8, and
Ideally, the relationship between the voltage at the output terminal 8 and the load impedance is 25 to 1 which can be controlled as shown in FIG.
A linear gradient is obtained in the range of 00Ω, and a saturated shape is formed on both sides. Thus, the circuit of FIG. 1, when a positive voltage within the control range (less than the load impedance 50 [Omega) is instructed to adjust the direction in which the load impedance apparent VC _L by the servo motor 6 is increased, a negative voltage When (load impedance exceeds 50Ω) is instructed, on the other hand, adjustment is made in a direction in which the apparent load impedance decreases to obtain balance.

[0004]

However, the apparent impedance as viewed from the load discriminator changes according to the insertion position of the discriminator on the transmission line and according to the magnitude of the imaginary component of the load. Therefore, as shown by the curve in FIG. 4, even though the resistance component of the load impedance is considerably low, when an imaginary component is included, the current hardly flows as compared with a load having only the resistance component, and the current flowing from the detector is reduced. The relationship between current and voltage is lost. Therefore, the indication voltage e ″
−e ′ may produce an error region A where the value is negative,
In this case, there is a disadvantage that the servomotor works in a direction (reverse rotation) for further reducing the apparent load impedance. Obviously, this reverse rotation causes a loss of control and prolongs the time to impedance matching. Therefore, conventionally, the length of the transmission line on the load side is adjusted to an appropriate length, the magnitude of the imaginary component of the load is estimated to some extent, and when the e / i ratio corresponds to the expected value, 0 V indicating the equilibrium state is obtained. Means such as offset adjustment to generate an output were taken. However, this offset adjustment is applied only to a specific load, and there is a problem that even if the reflected power can be suppressed within 1% in the process, it cannot be handled if another load is applied.

That is, the sensitivity and accuracy of the detector, here the load discriminator, manifests itself as the time to power supply-to-load matching and the value of the residual reflected power. The level required for these becomes strict according to the recent demand for thinning in the semiconductor manufacturing process, and the time until the process (high-frequency power supply) is completed is within 10 seconds, and the power supply circuit and the load are matched as a guide. It is required that the time required for the supplied power to reach 90% of the set power value is within 1 second, and that the residual reflected power be within 1%.

An object of the present invention is to solve the problem of an error output caused by an imaginary component of a load in a detection circuit by inserting a correction adjustment circuit in a load discriminator.

[0007]

In order to achieve the above-mentioned object, the present invention detects a value corresponding to a current i of a high-frequency transmission line by an instrumentation transformer, and further comprises a transmission line portion on the load side of the transformer. , The magnitude of the load impedance is determined from the value corresponding to the ratio e / i, and the circuit constant immediately before the load is adjusted to match the line impedance. In the transmission line load discriminator, the voltage of the transmission line, which is the primary winding of the instrument transformer, is divided, and the secondary winding of the transformer is provided with an intermediate tap , and the divided voltage is applied to the intermediate tap.
The applied voltage is applied as an offset voltage with gain.

In the above configuration, the error increases as the "apparent impedance" of the load including the imaginary component is lower than the transmission line impedance, and the partial voltage ε (∝ i) is applied to the transformer secondary winding to obtain a corrected detection output in the load discriminator. As a result, the reverse gradient portion that causes the error region A in FIG. 4 is pushed up to the plus side so that the reverse rotation of the servo motor does not occur in the load power supply range. As a result, the phase difference due to the intrinsic inductance of the instrument transformer (current transformer) in the detection unit, the stray capacitance on the circuit, the phase difference caused by the difference in the length of the transmission line, and the like are also compensated. . Such a function makes it possible to keep the residual reflected power to a low value of 1% or less even in processes having different load impedances. Further, since the degree to which the detection circuit generates an error output due to the imaginary component is reduced, a usable detection output is allowed in a wider range in the positive and negative directions with respect to the 0 V point, and a forward / reverse command for instructing the rotation direction in the motor drive unit. Signals do not occur erroneously, and as a result, the matching time can be shortened.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 5 shows an example of a circuit of a load discriminator to which the configuration of the present invention is applied. The secondary circuit of an instrument transformer (current transformer) CT2 provided on a detection line 17 which is a part of a high-frequency transmission line is shown. A resistor R11 is connected to both ends of the winding, and a primary winding of the transformer is connected to a lead wire from an intermediate tap (determined at the midpoint of the winding or at a side shifted to either side according to design). The voltage of the detection line 17 is divided by the capacitor C11 and the variable capacitor VCl, and a voltage corrected by the variable resistor VR11 connected to the voltage dividing point is applied.

One end 20 of the transformer secondary winding is connected to the anode of a diode D11 whose cathode is connected to a check terminal TP1 and a detection potentiometer VR.
Twelve first pole terminals. The second pole terminal of potentiometer VR12 is connected to the anode of a second diode D12, whose cathode is connected to the third diode D12.
Is connected to the sweep terminal of the potentiometer VR13. The first pole terminal of the third potentiometer VR13 is led to the connection point of the series capacitors C12 and C13 inserted between the detection line 17 and the ground potential, and the second pole terminal is grounded. The cathode of diode D11, and thus terminal TP1, is connected to ground via capacitor C14, and the anode of diode D12, and thus terminal TP2, is connected to ground via capacitor C15. A rectified / smoothed value (positive polarity) of the voltage (ground voltage) at the one end of the secondary winding appears, and a capacitor C12─C1 between the detection line 17 and the ground potential is provided at a terminal TP2.
Rectified / smoothed value (negative polarity) of voltage at 3 division points (ground voltage)
Appears.

When a load 19 such as a high-frequency plasma chamber is connected to the output terminal 12 according to the above-described circuit configuration, the value of the load impedance of the terminal 12 with respect to the transmission line impedance is determined. Accordingly, a different voltage is generated (note that this voltage is divided by the C12─C13 voltage divider circuit and the potentiometer VR13), so that if the position of the sweep terminal of the potentiometer VR12 is adjusted appropriately, this sweep terminal The potential of the detection terminal 18 drawn from the terminal can be made zero at the time of load impedance matching.

In the above-described circuit configuration, if there is no offset application circuit with gain from the detection line 17 to the intermediate tap of the transformer CT2, as described above, the value of the load impedance is induced for other reasons in the circuit configuration. In some cases, an imaginary part of the characteristic or the capacitive component is added to generate an error region A in which the indicated voltage e "-e 'becomes a negative value, in which case the servo motor further reduces the apparent load impedance (reverse rotation). However, in the circuit of the present invention, the voltage proportional to the detection line current i is R1.
1 and both C11, CV1, VR1
Since the value obtained by dividing the voltage of the detection line 17 through the circuit 1 is added to the CT2 intermediate tap voltage, a reverse gradient portion that causes an error region A in FIG. (FIG. 6) so as not to cause the reversal of.

[0013]

As described above, the present invention reduces and suppresses a detection error due to the effect of the imaginary part (capacitive or inductive) of the load impedance. It is an object of the present invention to provide a circuit for canceling a residual inductance and a stray capacitance, and for adjusting a phase difference generated due to a difference in length of a transmission line connected to a load.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a matching device for performing impedance matching in a high-frequency transmission line.

FIG. 2 is a schematic diagram illustrating a principle of measuring a load impedance of a load discrimination circuit in a matching device.

FIG. 3 is a graph showing an ideal relationship between a detection terminal voltage and a load impedance of a load discrimination circuit.

FIG. 4 shows a detection terminal voltage in a conventional load discrimination circuit,
It is a graph which shows the relationship of apparent load impedance.

FIG. 5 is a diagram showing an embodiment of a circuit configuration of the present invention.

FIG. 6 is a graph showing a relationship between a detection terminal voltage and an apparent load impedance in the load discrimination circuit of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 High frequency input terminal 12 Output terminal 17 Detection line (high frequency transmission line) 18 Detection terminal 19 Load impedance CT2 Transformer for instrument

Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H03H 7/40 G01R 27/04 G01R 27/28 H03H 7/38

Claims (1)

(57) [Claims] 1. An instrument transformer detects a value corresponding to a current i of a high-frequency transmission line and a value corresponding to a voltage e of a transmission line portion on a load side of the transformer, and detects a ratio e / a load discriminator that determines the magnitude of the load impedance from the value corresponding to i and adjusts the circuit constant immediately before the load to achieve matching with the line impedance, wherein the primary winding of the instrument transformer is Divide the voltage of the transmission line and provide an intermediate tap on the secondary winding of the transformer.
Wherein the divided voltage is applied as an offset voltage with gain to an intermediate tap of the load tap .