JP3007435B2 - RF generator matching control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control circuit for controlling a variable capacitor of a subsequent matching box so as to maintain an output impedance of an RF generator at a constant value.

[0002]

2. Description of the Related Art Conventionally, variable capacitors C1 and C2 for controlling output impedance have been individually controlled by an analog control method and a digital control method.

In the case of the analog control system alone, if the values of the variable capacitors C1 and C2 are significantly different from the matching point, the analog control circuit runs out of control depending on the circuit constant, and the variable capacitors C1 and C2 have the maximum value or the minimum value. In some cases. If the sensor accuracy is not sufficient, the variable capacitors C1 and C2 cannot be controlled up to the matching point.

In the digital control system, since the amount of reflected power depends on the magnitude of the reflected power, the amount of change in the detection value that controls the change and movement of the variable capacitors C1 and C2 is one.
The control to the matching point is not linear, and the trial operation is repeated. For this reason, there is a disadvantage that the required control time is longer than that of the analog control method.

[0005]

2. Description of the Related Art When the output impedance of an RF generator is kept constant and the reflected power is reduced to zero, the power supplied to the load becomes maximum, and the power supplied from the power source becomes the power supplied to the load. Becomes Therefore, it is important to shorten the time until matching is achieved and to always maintain the matching state, because it contributes to improvement of productivity and stabilization of quality when used for semiconductor manufacturing equipment such as sputtering. The present invention has been made to solve these problems.

[0006]

SUMMARY OF THE INVENTION In the present invention, an analog control system and a digital control system are separately operated so that an analog control system and a digital control system can be optimally controlled. This is to solve the above-mentioned conventional disadvantage by arbitrarily switching the system.
Next, the present invention will be described with reference to examples.

[0007]

FIG. 1 shows a main circuit configuration of a power system. 1A is R
The power detector PD is usually built in the F power supply. 2A is a matching box shown in FIG. 2 and the variable capacitors C1 and C2 are connected to the motors M1 and M2 built in the matching box (direct connection or cam connection, clockwise rotation (CW direction) or left rotation (CCW) of the motor. The Zφ sensor S is attached to the input of the matching box, and can be built in.

FIG. 3 shows the detection signals (Pi, Pr,
Z, φ) to detect the variable capacitor C shown in FIG.
1, a circuit example for controlling C2. 3, reference numeral 2 denotes an analog control circuit which detects a signal from the sensor 1 and can linearly control C1 and C2 up to a matching point M shown in FIG. It is connected to the. In FIG. 4, the horizontal axis represents the digital and analog control ranges, and the vertical axis represents the reflected power coefficient.

Reference numeral 8 denotes a signal P from the detector PD shown in FIG.
An arithmetic circuit that detects i and Pr and outputs △ Pr / △ Pi = △ Kr. By calculating the ratio of the change in reflected power Pr (△ Pr) to the change in effective power (△ Pi) at that time, , And the reflected power coefficient △ Kr. That is, since the weight varies depending on the magnitude of △ Pi even with the same variation value of △ Pr, this circuit detects a constant variation amount regardless of the magnitude of the output. The Kr signal is input to the A / D changer 11, the magnitude of which is determined by the CPU 9, and the right / left (CCW) and left (CCW) rotations of the variable capacitor C1 and the right / left (CW) and left rotation of C2 are determined by the I / O port. Rotation (CC
W) are connected to the input of the switching circuit 3 by D signals representing the four signals. At the same time, the I / O port 12 has a switch C for selecting one of the inputs A and D of the switching circuit 3.
It outputs the NT signal.

Reference numeral 4 denotes a driver circuit for the motors M1 and M2 for 5 and 6, which drive the respective CWs and CCWs for M1 and M2.
When none of them is operating, the stop signal STP is input to the I / O port 12.

Reference numeral 7 denotes a position detector (such as a volume) connected to the motors M1 and M2 at an appropriate cam ratio.
The control amount of the motor operated by the output signal D of the port 12, that is, the position (address) of C1 and C2 is detected and the A / D
It is input to the converter 11.

FIG. 4 shows an operation example in the circuit configuration of FIG. At the point Kr (0) where the displacement of the C1 and C2 from the matching point is large and the reflected power coefficient Kr is extremely high, the signal Z and φ of the sensor indicate that the operation direction and rotation to the matching point are reversed. In many cases, the analog control circuit runs away. In such a case, the input signal is switched to the D input by the output signal CNT of the I / O port 12, and the signals of the position detector 7 are C1, C
The value of Kr can be generally reduced to Kr (1) by moving the variable capacitor to an arbitrary point in the variable range of 2 where matching is easy.

After that, by inverting the CNT signal, switching the input of the switching circuit 3 to A and activating the analog control circuit, Kr can be reduced almost linearly. During this time, the digital control circuits (9 to 12) monitor the output signals VC1 and VC2 of the position detector 7 at a short constant cycle time Δt, so that Kr in FIG.
(1), Kr (2)... Kr (n-1) and Kr (n) are detected, and the moving directions of the variable capacitors C1 and C2 can be known.

If the motors M1 and M2 controlled by the output signal of the analog control circuit 2 move to the matching point M shown in FIG. 4, there is no problem. However, if the accuracy of the sensor and the load impedance change, Kr (n) If it stops at the point, the I / O port 12 detects the STP signal, switches the CNT output to the D input, and places Kr (n-1) and Kr (n) on the signal straight line by the digital circuit. Signal D
Is changed and M1 and M2 are controlled to detect the M point.

That is, by monitoring the operation of the analog control system, the digital circuit can know the moving directions of C1 and C2. When the switching circuit 3 is switched to the digital signal input, Kr (n- 1) By controlling M1 and M2 with an approximated linear equation passing through Kr (n),
A matching point can be detected as an extension of control by the analog system.

The output signal EQ of the Kr operation circuit 8 is a discrimination signal for detecting the EQ signal when the point M is shifted from the point M in FIG. 4 to the point N due to fluctuations on the load side, and returning to the point M '. ,
When the CPU 9 detects the EQ signal, the I / O port 12
Can be converged again to the matching point M 'by slightly changing the output signal D.

[0017]

As is apparent from the above, by controlling the combination of the analog control circuit and the digital control circuit, the time can be reduced by linearly controlling the reflected power coefficient Kr of the analog control system, and the locus thereof can be monitored. If the operation is stopped before the matching point is detected, by performing tracking in the digital system, it is possible to perform almost linear control in the digital control system without significantly improving the sensor accuracy. or,
The present invention is extremely effective even when the accuracy of the sensor cannot be improved or becomes useless due to a load.

[Brief description of the drawings]

FIG. 1 is a main circuit configuration diagram of an RF generator.

FIG. 2 is a circuit diagram in a matching box.

FIG. 3 is a configuration diagram of a matching control circuit according to the present invention.

FIG. 4 is a diagram showing a matching characteristic according to the present invention;

[Explanation of symbols]

 1A RF power supply 2A Matching box 3A Load L Matching box inductance C1 Matching box variable capacitor C2 Matching box variable capacitor 1 Sensor 2 Analog control circuit 3 Switching circuit 4 Driver circuit 5 Motor M1 6 Motor M2 7 Position detector 8 Arithmetic circuit 9 CPU 10 Memory 11 A / D converter 12 I / O port 13 Digital control circuit

Continuation of the front page (56) References JP-A-3-105521 (JP, A) JP-A-63-279609 (JP, A) JP-A-63-248225 (JP, A) JP-A-54-153507 (JP) JP-A-54-28544 (JP, A) JP-A-62-155531 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H03H 7/40 H03H 7/38 H04B 1/02 H01L 21/302 H01L 21/203 H02P 5/00 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A variable capacitor (C) for detecting the output impedance and the phase angle of an RF generator so that the output impedance and the phase angle are constant.
1, an analog control system for controlling C2, and the variable capacitor C1, which detects reflected power or a reflected power coefficient from a power detector of the RF generator output and reduces the reflected power or the reflected power coefficient. In a matching control circuit having a digital control system for controlling C2 and a circuit for switching between the analog control system and the digital control system, initial setting of the variable capacitors C1 and C2 is performed by the digital control system, and the sensor is in an active area. A matching control circuit for switching to an analog control system to obtain a matching point, and when the matching cannot be obtained, switching to a digital control system again to obtain a matching point.