JP2775656B2 - Film forming equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film forming apparatus having a matching device for efficiently supplying high frequency power from a high frequency power supply to film forming means such as a plasma film forming apparatus.

[0002]

2. Description of the Related Art For example, in a plasma CVD apparatus, a pair of electrodes are arranged in a chamber so as to face each other. By supplying high-frequency power between these electrodes and introducing a reaction gas into the chamber, plasma discharge occurs between the opposing electrodes, and a thin film is formed on a substrate mounted on one of the electrodes. .

In such a plasma CVD apparatus, a matching device is provided in order to quickly and efficiently supply high frequency power from a high frequency power supply. FIG. 6 shows a conventional film forming apparatus. As shown in FIG.
A matching circuit 3 is provided between the power supply 2 and the high-frequency power supply 2. The matching circuit 3 includes variable capacitors 3a and 3b and a coil 3c. At the entrance of the matching circuit 3, the high-frequency current IIN is detected by the current detection element 4a, and the voltage VIN is detected by the voltage detection element 4b. The outputs of the current detection element 4a and the voltage detection element 4b are output from a phase difference detector 5a and an impedance detector 5a.
b. In each of the detectors 5a and 5b, a matching circuit 3
The impedance phase argZIN and the absolute value | ZIN | These values are input to the control circuit 6. The control circuit 6 drives according to a predetermined logic.
The capacitances of the variable capacitors 3a and 3b are adjusted via the circuits 7a and 7b.

For example, when the phase of the impedance Z _IN is positive, control is performed such that the capacity of the variable capacitor 3b is increased, and conversely, when the phase is negative, control is performed. When the output impedance of the high-frequency power supply 2 is 50Ω, if the absolute value of the impedance at the entrance of the matching circuit 3 | Z _IN | exceeds 50Ω, the capacity of the variable capacitor 3a is increased, and conversely, | Z _IN | If is smaller, control is performed to reduce it. In this manner, automatic matching is performed so that the phase of the impedance Z _{IN at} the entrance of the matching circuit 3 becomes 0 ° and the absolute value becomes 50Ω.

[0005]

In the conventional apparatus, the capacitance of the corresponding variable capacitors 3a and 3b is adjusted according to the detection results of the detectors 5a and 5b. Here, in the period in which the alignment is performed, the initial period in which the film starts growing on the substrate is a particularly important period. In a plasma film forming apparatus without a shutter, the start of matching and the start of discharge are at the same time, so that if the applied high-frequency power (traveling wave power-reflected wave power) at the start of discharge continues for a long time, the film quality will be greatly affected. Influence. Therefore, automatic alignment devices include:
High-speed convergence to the matching point is required.

In a film forming apparatus for production, reproducibility of film thickness and film quality is required. In order to obtain good reproducibility, good reproducibility of film forming conditions such as gas pressure, gas flow rate, substrate temperature, and input high frequency power is required. The traveling wave power is controlled by a high-frequency power source and the reproducibility is sufficiently obtained.
In order to obtain reproducibility of the input high frequency power, it is necessary to make the reflected wave power close to 0 W with good reproducibility. That is, the automatic matching device is required to have high convergence accuracy to the matching point.

However, especially near the matching point, argZ
_IN is not only the capacity of one variable capacitor 3b,
It changes with the increment of both variable capacitors 3a and 3b, and | Z _IN | does not change with the corresponding variable capacitor 3a but changes with the increment of the variable capacitor 3b. That is, in the conventional film forming apparatus, the logic of the control circuit 6 is not appropriate near the matching point. For this reason, it is necessary to increase the threshold value of the dead zone near the matching point, and it is not possible to obtain sufficient speed and convergence accuracy.

An object of the present invention is to improve the controllability in the vicinity of a matching point and to obtain a film forming apparatus capable of realizing high-speed matching and high-precision convergence.

[0009]

According to a first aspect of the present invention, a film forming apparatus includes a film forming unit, a high-frequency power supply, and a matching device. The film forming means is supplied with a high-frequency power supply and forms a film internally. The high-frequency power supply supplies high-frequency power to the film forming means. The matching device is disposed between the film forming means and the high-frequency power supply, and is a device for matching the two.
The matching device includes a matching circuit, a phase difference detector, an impedance detector, a control circuit, and a cable .

[0010] The matching circuit has a first variable capacitance element in series with the load, a second variable capacitance element in parallel with the power supply, and an inductive element in series with the load. The phase difference detector detects the phase of the impedance at the entrance of the matching circuit.
The impedance detector detects a value of impedance at a matching circuit entrance. The control circuit controls the capacitance of the first variable capacitance element based on the detection result of the phase difference detector, and controls the capacitance of the second variable capacitance element based on the detection result of the impedance detector. The cable has a characteristic impedance substantially equal to the output impedance of the high-frequency power supply and an output wavelength of 0.014 to
0.068 times the length at the entrance of the matching circuit.
Detection point of impedance phase difference and absolute value, first variable
Connected between the capacitive element and the connection point of the second variable capacitive element.
Thus, when one of the two variable capacitance elements is controlled by the control circuit, the influence on the phase or absolute value of the impedance corresponding to the other element is reduced. In addition,
Use a reactance value of 5 to 20 ohms instead of a cable.
And the impedance phase difference at the matching circuit entrance and
An absolute value detection point, the first variable capacitance element and the second variable capacitance element;
Both variable capacitance elements are connected between the connection points of the variable capacitance elements.
Element when one of them is controlled by the control circuit
Phase or absolute value of impedance corresponding to
Inductive elements may be used to reduce
No.

A film forming apparatus according to a second aspect of the present invention includes a film forming means, a high-frequency power supply, and a matching device. The matching device includes a matching circuit, a phase difference detector and an impedance detector, and a matching device. It has a state detecting means and a control circuit.
The matching circuit includes a first variable capacitance element in series with a load, a second variable capacitance element in parallel with a power supply, and an inductive element in series with the load.
And The phase difference detector and the impedance detector detect the phase and the absolute value of the impedance at the entrance of the matching circuit. The matching state detecting means detects that the matching circuit has reached the vicinity of the matching point. The control circuit controls the capacitances of the first and second variable capacitance elements according to the first logic based on the detection results of the phase difference detector and the impedance detector when the matching circuit has not reached the vicinity of the matching point, When the matching circuit reaches the vicinity of the matching point, the capacitances of the first and second variable capacitance elements are controlled according to the second logic based on the detection results of the two detectors.

In the film forming apparatus according to the first invention, the phase and the value of the impedance at the entrance of the matching circuit are detected. These detection results are input to the control circuit, and the capacitances of the first and second variable capacitance elements are controlled according to a predetermined logic. At this time, near the matching point, the control of one variable capacitance element affects the other variable capacitance element, but the dependency of both variable capacitance elements is reduced by the cable and the inductive element.

Therefore, the width of the dead zone in the vicinity of the matching point can be reduced, and high-speed matching and high-precision convergence can be realized.
In the film forming apparatus according to the second invention, the phase and absolute value of the impedance at the entrance of the matching circuit are detected. Then, according to these detection results, when the matching circuit has not reached near the matching point, the capacitances of the first and second variable capacitance elements are controlled according to the first logic. When the vicinity of the matching point is reached, the logic for the control operation is changed, and the capacitances of the first and second variable capacitance elements are controlled according to the second logic.

For this reason, it is possible to quickly perform matching near the matching point, and to realize highly accurate convergence.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS High speed and high convergence accuracy near the matching point Here, the problems of the high speed and high convergence accuracy of the conventional matching device will be discussed in more detail. Assuming that the capacitance of the variable capacitor 3a in FIG. 6 is C1, the capacitance of the variable capacitor 3b is C2, the inductance of the coil 3c is L, the resistance of the plasma generator 1 is R, and the capacitance is C, FIG. The complex impedance Z _IN at the entrance of the matching circuit 3 is expressed by the following equation.

[0016]

(Equation 1)

From equation (1), the absolute value of impedance |
Z _IN | and phase argZ _IN are

[0018]

(Equation 2)

## EQU1 ## Matching point (ReZ _IN = 50, I
Each value at (mZ _IN = 0) is represented as follows. _{C1 = C1 M, C2 = C2} M, Xs = Xs M, X1 = X1 M ... (4) Equation (1), (4) from matching condition (ReZ _IN = 50, Im
Z _IN = 0) is given by the following equation.

[0020]

(Equation 3)

│Z _IN │, argZ _IN is first-order approximated near the matching point. However, the dimension is reduced to z _IN = Z _IN / 50 (7).

[0022]

(Equation 4)

With respect to equations (8) and (9),

[0024]

(Equation 5)

In consideration of the above, each term is partially differentiated to obtain the equation (4),
By substituting (5), (6), and (7), the following equation is obtained.

[0026]

(Equation 6)

According to equation (10), the vector A1 is obtained when (C1) is incremented by a unit capacity, and the vector A2 is (| z _IN | -1)-(a) at the matching point when C2 is incremented by a unit capacity.
rgZ _IN ) represents a change on a plane. FIG. 7 shows (| z _IN | −
1) The vector directions in the-(argZ _IN ) plane are θ1, θ2
Displayed as follows.

[0028]

(Equation 7)

In the conventional matching device shown in FIGS. 6 and 2 (within the dashed line), since X0 = 0Ω, the equations (11) and (1)
2)

[0030]

(Equation 8)

In a general plasma film forming apparatus, since R is about several Ω, 0 ° <θ1 conventional <90 °. This is shown in FIG. Here, the logic of automatic matching near the matching point in the conventional matching device is as follows.

Control Logic of Conventional Matching Device (1) (i) | argZ _IN | <Δθ → The capacitance of the variable capacitor 3b is not changed. (Ii) | argZ _IN |> Δθ and (a) argZ _IN <0 → decrease the capacity of the variable capacitor 3b.

(B) argZ _IN > 0 → Increase the capacity of the variable capacitor 3b. (Iii) || Z _IN | / 50-1 | <ΔZ → The capacitance of the variable capacitor 3a is not changed. (Iv) || Z _IN | / 50-1 |> ΔZ and (a) | Z _IN | / 50-1 <0 → decrease the capacity of the variable capacitor 3a.

(B) | Z _IN | / 50-1> 0 → Increase the capacity of the variable capacitor 3a. Here, Δθ, ΔZ: dead zone thresholds for preventing hunting during control. It is clear that the virtual control target that can be most stably controlled near the matching point by applying such control logic (1) is the case where the directions of the vectors A1 and A2 are as shown in FIG. . That is, in the vicinity of the matching point, when the C1 capacitance is increased or decreased, only the absolute value | Z _IN | of the impedance is decreased, and when the C2 capacitance is increased or decreased, only the impedance phase argZ _IN is decreased or increased. In this case, the dead band threshold Δ
θ and ΔZ are determined only by mechanical performance such as backlash generated in a so-called variable condenser drive system constituting the variable capacitors 3a and 3b. Therefore, it can be set to an extremely small value.

However, in the conventional matching device, FIG.
As shown in the figure, argZ _IN is C1, C2 near the matching point.
, And | Z _IN | does not change with C1, but changes with the increment of C2. That is, the logic (1) is not appropriate near the matching point. Therefore, in the conventional apparatus, the thresholds Δθ, ΔZ
Was set to a large value to prevent hunting near the matching point. Therefore, sufficient speed and convergence accuracy cannot be obtained, especially near the matching point.

First Embodiment FIG. 1 shows a schematic configuration of a film forming apparatus according to one embodiment of the present invention. Plasma generator 10 and high frequency power supply 2
Between 0 and 0, a matching circuit 30 is provided. The matching circuit 30 includes a variable capacitor 32 (capacitance C2) and a coil 33 (L) connected in series to the plasma generator 10;
Variable capacitor 31 connected in parallel to high frequency power supply 20
(Capacitance C1). A coaxial cable 34 is connected to the entrance of the matching circuit 30. The coaxial cable 34 is connected between the connection point between the two variable capacitors 31 and 32 and the high-frequency power supply 20, and has a characteristic impedance having the same value as the output impedance of the high-frequency power supply 20,
The cable length is 0.014 to 0.068 wavelength.

At the entrance of the matching circuit 30, a current detecting element 41 for detecting the current I _IN at the entrance of the matching circuit 30 and a voltage detecting element 42 for detecting the voltage V _IN are connected. The outputs of the current detection element 41 and the voltage detection element 42 are the phase arg of the impedance Z _{IN at} the entrance of the matching circuit 30.
A phase difference detector 51 for detecting Z _IN and an absolute value | Z
It is input to an impedance detector 52 that detects _IN |. The outputs of the detectors 51 and 52 are connected to a control circuit 60. The control circuit 60 controls each of these detectors 5
The driving circuits 71 and 72 are controlled in accordance with the values of the variable capacitors 1 and 52, and the capacitances of the variable capacitors 31 and 32 are controlled. The control logic in this case is the same as the logic (1).

In the first embodiment, the ar with respect to the increase in the capacitance of the variable capacitors 31 and 32 near the matching point is determined.
Consider the change in gZ _IN , (| Z _IN | -1). FIG. 2 shows an equivalent circuit of the matching circuit 30 shown in FIG. Hereinafter, the output impedance of the high frequency power supply 20 is assumed to be 50Ω. Also,
Z _INK is the impedance when Z _IN is viewed through a cable having a characteristic impedance of 50Ω and a cable length of k wavelengths.

At this time, the relationship between Z _INk and Z _IN is represented by the following equation.

[0040]

(Equation 9)

From equation (15), | Z _INk |, argZ _INk
The display is obtained as follows.

[0042]

(Equation 10)

| Z _INk |, argZ _INk is first-order approximated near the matching point. However, the dimension is reduced to z _INk = Z _INk / 50 (18). Here, “z _INk is in a matching state”
The fact that “z _IN is in a matched state” is equivalent to the nature of the coaxial line, and is derived as follows.

[0044]

[Equation 11]

When the matrix of equation (19) is further calculated, the following equation is obtained.

[0046]

(Equation 12)

According to the equation (20), the wavelength of the coaxial cable is k
I saw (| z_INk| -1), argz _INkIs (| z_IN|
-1), argz_INRotated clockwise by 4πk
Is converted to Therefore, the expression (10)
Vectors A1 and A2 pass through a coaxial cable of k wavelengths.
10, the vectors A1k, A1
Converted to 2k.

Here, in this embodiment, k = 0.014-
Since it is about 0.068 and the resistance R of the plasma apparatus 10 is about several Ω, θ1 and θ2 in the case of the conventional apparatus and θ1 and θ2 in the case of the present embodiment shown in Expressions (13) and (14) are used.
θ2 has the following relationship. 90 °> θ1 (conventional) = θ1 (present embodiment)> 0 ° 90 ° = θ2 (conventional)> θ2 (present embodiment) = θ2 (conventional) −4πk> 0 ° (θ1 + θ2) is around 90 ° When a coaxial cable having such a length is connected, the vectors A1 and A2 are oriented as shown in FIG.

As is apparent from FIG. 11, compared with the conventional matching device, | vector A1 |
sin θ2, | vector A2 | · cos (θ1 + θ2)
Decreases, and is a component necessary for control | vector A1 |
cos θ2, | vector A2 | sin (θ1 + θ2) increases. That is, controllability is improved near the matching point.

Second Embodiment FIG. 3 shows a second embodiment of the present invention. In the second embodiment, instead of the coaxial cable 34 of the first embodiment, the reactance (X0) is +5 to +20 at the entrance of the matching circuit 30.
A coil 35 of about Ω is connected. Other configurations are the same as those of the first embodiment. FIG. 4 shows an equivalent circuit in this case.

Θ1 and θ2 shown in equations (11) and (12)
The resistance R of the plasma apparatus 10 is about several Omega, also because it is X0 ² << 50 ^2, in the following relationship. 90 °> θ1 (conventional) ≒ θ1 (present embodiment)> 0 ° 90 ° = θ2 (conventional)> θ2 (present embodiment)> 0 ° When the coil 35 is connected so that (θ1 + θ2) is close to 90 ° , As in the first embodiment, the vectors A1,
A2 is oriented as shown in FIG.

Therefore, in the same manner as described above, the | vector A1 | · sin θ2, |
The vector A2 | · cos (θ1 + θ2) decreases, and the vector | A1 | · cos θ2, | vector A2 | · sin (θ1 + θ2), which is a component necessary for control, increases. That is, controllability is improved near the matching point. Third Embodiment A circuit diagram of the device according to the third embodiment is shown in FIG. In this embodiment, the phase difference detector 51 and the impedance detector 5
The output of No. 3 is input to the control circuit 60 and also to the coordinate conversion circuit 90. Coordinate conversion circuit 90
Is a circuit for performing coordinate conversion of the output signals of the detectors 51 and 53. The output of the coordinate conversion circuit 90 is input to the control circuit 60.

The outputs of the current detecting element 41 and the voltage detecting element 42 are input to a voltage standing wave ratio (| VSWR |) detector 80, respectively. Voltage standing wave ratio detector 80
Is for detecting whether or not it is near the matching point. In the third embodiment, it is determined by the voltage standing wave ratio detector 80 whether or not the position is near the matching point, and the control is performed according to the control logic (1) of the conventional device except for the position near the matching point. On the other hand, if the output value of the voltage standing wave ratio detector 80 is, for example, 1.5
In the following cases, it is determined that it is near the matching point, and the control is performed according to the control logic (2).

That is, I. In the case of | VSWR | -1> ΔVSWR, control is performed according to the control logic (1). II. In the case of | VSWR | -1 <ΔVSWR Control is performed according to the control logic (2).

Control logic (2) (i) | (argZ _IN ) '| <Δθ → The capacitance of the variable capacitor 32 is not changed. (Ii) | (argZ _IN ) '|> Δθ and (a) (argZ _IN )'<0 → Decrease the capacity of the variable capacitor 32.

(B) (argZ _IN ) '> 0 → Increase the capacity of the variable capacitor 32. (Iii) | (| Z _IN | / 50-1) ′ | <ΔZ → The capacitance of the variable capacitor 31 is not changed. (Iv) | (| Z _IN | / 50-1) ′ |> ΔZ and (a) (| Z _IN | / 50-1) ′ <0 → Decrease the capacitance of the variable capacitor 31.

(B) (| Z _IN | / 50-1) '> 0 → Increase the capacity of the variable capacitor 31. Here, ΔVSWR: a threshold value (for example, 0.5) that determines the vicinity of the matching point Δθ, ΔZ: threshold values of a dead zone for preventing hunting during control. (ArgZ _IN ) ', (| Z _IN | / 50-1)'

[0058]

(Equation 13)

(| Z _IN | / 50-1), arg
This is a value obtained by performing coordinate conversion on the value in the Z _IN coordinate system. The control logic (2) will be described. The conventional matching device has been described assuming that X0 = 0Ω in the equivalent circuit of FIG. 4. However, since the inductance is actually formed by the wiring copper plate, the following description will be made without limitation to X0 = 0Ω. .

The amount of change of (| z _IN | -1) and argz _IN with respect to the increment of C1 and C2 near the matching point is given by the following equation (1).
0). Also, the vector A1,
The angles θ1 and θ2 representing the direction of A2 are given by Expressions (11) and (1).
It is shown in 2). The vectors A1 and A2 are represented by the following equations using θ1 and θ2.

[0061]

[Equation 14]

Here, as shown in FIG. 12, (| z _IN |
-1), argZ _IN coordinate system is (| z _IN | -1) ', (arg
Z _IN ) 'Convert to coordinate system. The relationship between the two coordinate systems is given by the following equation.

[0063]

(Equation 15)

From equations (23) and (24), (| z _IN | −
1) The relationship between ', (argZ _IN )' and ΔC1, ΔC2 is given by the following equation.

[0065]

(Equation 16)

From equation (25), (| z _IN | -1) ′ is Δ
Only for C1, (argZ _IN ) 'is affected only for ΔC2. In other words, instead of the (| z _IN | -1) and the argZ _IN signals, the signals using the (| z _IN | -1) 'and (argZ _IN )' signals
By controlling C1 and ΔC2, mutual interference can be eliminated. Therefore, the threshold values Δθ and ΔZ of the dead zone shown in the control logic (1) are extremely small values because they are determined only by mechanical performance such as backlash generated in the variable condenser drive system.

[Other Embodiments] In the third embodiment,
Although the voltage standing wave ratio detector is provided as a circuit for detecting the vicinity of the matching point, the means for detecting the vicinity of the matching point is not limited to this. For example, it may be determined whether or not the position is near the matching point by calculating a reflection coefficient using a directional coupler.

[0068]

As described above, according to the present invention, the controllability near the matching point is improved, so that high-speed matching and highly accurate convergence to the matching point can be realized.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram of a film forming apparatus according to a first embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the device.

FIG. 3 is a block circuit diagram of a film forming apparatus according to a second embodiment of the present invention.

FIG. 4 is an equivalent circuit diagram of the second embodiment.

FIG. 5 is a block circuit diagram of a film forming apparatus according to a third embodiment of the present invention.

FIG. 6 is a block diagram of a conventional film forming apparatus.

FIG. 7 is a diagram for explaining a problem in the conventional device.

FIG. 8 is a diagram for explaining a problem in the conventional device.

FIG. 9 is a diagram for explaining a problem in the conventional device.

FIG. 10 is a diagram for explaining the operation of the first and second embodiments.

FIG. 11 is a diagram for explaining the operation of the first and second embodiments.

FIG. 12 is a view for explaining the operation of the third embodiment device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Plasma generator 20 High frequency power supply 30 Matching circuit 31, 32 Variable capacitor 41 Current detection element 42 Voltage detection element 51 Phase difference detector 52 Impedance detector 60 Control circuit 80 Voltage standing wave ratio detector 90 Coordinate conversion circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H05H 1/46 C23C 16/50 H03H 7/40 H03H 11/30

Claims (3)

(57) [Claims] 1. A high-frequency power is supplied, a film forming means for performing film formation inside, a high-frequency power supply for supplying high-frequency power to the film forming means, and a high-frequency power supply between the film forming means and the high-frequency power supply. And a matching device for matching the two, wherein the matching device comprises: a first variable capacitance element in series with the film forming means and a second variable capacitance element in parallel with the power supply; A matching circuit having a series inductive element; a phase difference detector for detecting a phase of impedance at the entrance of the matching circuit; an impedance detector for detecting an absolute value of impedance at the entrance of the matching circuit; and the phase difference detector A control circuit that controls the capacitance of the first variable capacitance element based on the detection result of the above, and controls the capacitance of the second variable capacitance element based on the detection result of the impedance detector; Source output impedance and substantially output wavelength of the characteristic impedance of the same value as the high frequency power source
0.014 to 0.068 times the length of the alignment circuit.
Detection of phase difference and absolute value of impedance at road entrance
An output point, the first variable capacitance element and the second variable capacitance element
And a variable capacitance element connected between the variable capacitance element and one of the two variable capacitance elements for reducing the influence on the phase or absolute value of the impedance corresponding to the other element when one of the variable capacitance elements is controlled by the control circuit. A film forming apparatus comprising: a cable ; 2. A cable of 5 to 20 ohms instead of said cable.
An impedance value at the entrance of the matching circuit.
The detection points of the phase difference and the absolute value of the dance and the first variable capacitor
Connected between a capacitive element and a connection point of the second variable capacitance element
One of the two variable capacitance elements is controlled by the control circuit.
Impedance corresponding to the other element when controlled
The phase or absolute value of the source
Film forming apparatus provided with an inductive element for the purpose . 3. A high-frequency power is supplied, a film forming means for performing film formation therein, a high-frequency power supply for supplying high-frequency power to the film forming means, and between the film forming means and the high-frequency power supply. And a matching device for matching the two, the matching device comprising: a first variable capacitance element in series with the film forming means and a second variable capacitance element in parallel with a power supply; A matching circuit having an inductive element in series with a phase difference detector and an impedance detector for detecting a phase and an absolute value of impedance at an entrance of the matching circuit; and detecting that the matching circuit has reached a vicinity of a matching point. For the matching state detection means for, the detection results of the two detectors and the matching state detection means,
When the matching circuit has not reached the vicinity of the matching point, the capacitances of the first and second variable capacitance elements are controlled in accordance with a first logic. A control circuit for controlling the capacitance of the first and second variable capacitance elements.