JPH0375082B2 - - Google Patents

Description

[Detailed description of the invention] A. Purpose of the invention [Field of industrial application] In recent years, the application fields of microwave heating have been food processing and
It covers a wide range of fields such as sterilization, various drying, and plasma chemical reactions, and the development of new products and new manufacturing methods that apply plasma chemical reactions is becoming more active in various industrial fields, including semiconductor manufacturing. In this case, it is important to stably supply microwave power to the load, which is a heated object, in order to maintain the quality of the product, and for this purpose, some kind of load matching circuit is required.

The present invention aims to automatically perform this load matching.

[Conventional technology]

Conventionally, load matching in the microwave band was performed by manually operating three or more stub matching devices while monitoring the forward wave power to the load and the reflected wave power from the load, and achieved the maximum forward wave power with the minimum reflected wave. It was adjusted to this point.

[Problem that the invention seeks to solve]

Manual load matching requires the presence of personnel at all times, is very cumbersome as it requires three or more stubs to match the load impedance across the entire range, and is difficult to deal with sudden load changes and fluctuations. It is impossible to do so.

In particular, the etching process in the semiconductor manufacturing industry, which has recently attracted attention, and plasma using microwaves.
For CVD equipment and the like, there is a need for new automatic load matching technology that satisfies product quality control standards and demands for lower production costs.

B. Structure of the invention [Means for solving the problem] In the conventional stub matching method, three or more stubs are required for overall impedance matching,
Therefore, even if these adjustments were automated, it would be complicated and time consuming, making it nearly impossible. By using two sets of composite stubs whose insertion lengths are differentially and continuously varied, the present invention can easily and quickly complete automatic load matching by driving two electric motors.

[Effect]

FIG. 2 shows a state in which a stub made of metal or the like is erected at the center of the wide side of a rectangular waveguide, and its insertion length is varied. The figure shows the normalized susceptance that occurs when a round metal stub is inserted into the center of a WRI26 rectangular waveguide.
An insertion length of approximately 1/4 wavelength causes series resonance, and beyond that the polarity reverses and becomes inductive. Therefore, when used as a matching box, the maximum insertion length should be limited to a point where series resonance does not occur even at the lowest frequency used.

Figure 3 shows such stubs 1 ₁ and 1 ₂ as 2
The stubs are placed at the center of the wide side of the waveguide 2, approximately at the center of the frequency band used, and spaced apart by a distance D that is (1/4) of the wavelength inside the waveguide, and when the insertion length of one stub is at its maximum, The other insertion length is zero, and in between,
Figure 3 shows a set of composite stub matchers of the present invention that are differentially and sequentially varied such that an increase in one is a decrease in the other.

Such a change may be made in conjunction with the inclination of the connector 3, for example, as shown in FIG. Alternatively, as shown in FIG. 4, the stubs 1 ₁ and 1 ₂ may be inserted from the opposing wide sides, moved in the same direction by the connector 3, and differentially interlocked.

When the normalized conductance viewed from the load-side stub is Gl, and the normalized susceptance of the load is zero, Figure 5 shows the change in input admittance on the Smith diagram due to differential interlocking of the two stubs. It shows. The solid lines 1, 2, 3,...7 in the figure show the values when Gl=5, 2, 1.25, 1, 0.8, 0.5, 0.2, respectively, and l ₁ in Fig. 4 is the maximum (i.e. l ₂
As l ₁ becomes shorter, the characteristics move from left to right in the figure, and when l ₁ becomes zero and l ₂ becomes maximum, they are concentrated on the arc of the susceptance 10 at the right end. This is because the maximum susceptance indicated by l ₂ is set to 10.

In the present invention, two sets of such composite stub matching devices are arranged at a distance of (1/8) the average tube wavelength (ie, D/2). This second composite stub matching device may be placed in series with the first one, but it can be made smaller if they are placed alternately as shown in FIG.

When the action of this second composite stub matching device is shown on a Smith diagram, as shown in FIG. 5, the dotted line group is obtained by rotating the solid line group by 90 degrees clockwise (ie, in the load direction). In the figure, 1', 2', ...7' are the solid line groups 1, 2, and 7', respectively.
...corresponds to 7, and the solid line and dotted line curve groups are perpendicular to each other in each part.

Although the normalized susceptance of the load is set to zero in FIG. 5, a similar characteristic group can be drawn even when the load admittance is a complex number, and the entire load admittance is eventually matched by two sets of composite stub matchers. That is, matching can be achieved by supplying control power to two motors that drive each composite stub matching device.

In order to detect the degree of mismatching of the load, various methods of detecting the reflected wave power from the load and the traveling wave power to the load can be adopted. That is, the multi-probe method and the directional coupler method. The multi-probe method is used as a direct impedance viewing device, and is described in detail in, for example, "Microwave and Millimeter Wave Measurement" by Bunichi Oguchi and Masamitsu Ota (Corona Publishing Edition), pp. 84-86. Since the needle method has wide and good frequency characteristics, a circuit based on this method is shown in FIG. Probe with detector 6 ₁ , 6 ₂ , 6 ₃ , 6
₄ and ₆₅ are respectively placed at the center of the wide side of the waveguide at a distance of (1/8) of the average guide wavelength. At this time, the tip detection voltage amplitude corresponding to the waveguide input power is
Let Vi be the reflection coefficient when looking at the load from the central probe ₆₃ as Γ. Now ignoring the error due to frequency change,
Further, assuming that each detector has a square-law characteristic, the output voltage of each probe is as shown in the following equation.

V ₁ =k｜Vt｜ ² [1+｜Γ｜ ² −2
|Γ|cos(θ−π)] V ₂ =k|Vt| ² [1+|Γ| ² −2
|Γ|cos(θ−π/2)] V ₃ =k|Vt| ² [1+|Γ| ² −2
|Γ|cosθ] V ₄ =k|Vt| ² [1+|Γ| ² −2
|Γ|cos(θ+π/2)] V ₅ =k|Vt| ² [1+|Γ| ² −2
|Γ|cos(θ+π)] Now, if we add the outputs of the probes ₆₄ and ₆₂ to the input terminal of the differential amplifier ₇₂ and take the difference voltage output, V _A = V ₄ − V ₂ = 4k |Vt| ² | _Γ |sinθ, and ( ₁ /
2) and the output voltage of the probe ₆₃ , the differential amplifier 7
₁ , V _B = 1/2 (V ₁ + V ₅ ) − V ₃ = 4k|Vt| ² |Γ|cosθ. Since V _A and V _B are orthogonal, these voltages are applied to power amplifiers 8 ₁ and 8 ₂ , and their outputs rotate the matching box drive motor.
By adjusting the respective composite stub matching devices 5 ₁ and 5 ₂ , since their matching characteristics are orthogonal, matching is easily achieved, and when both V _A and V _B become zero, the load is reduced. It will be automatically aligned.

In addition, the method of using two directional couplers to obtain voltages corresponding to reflected wave power and traveling wave power and performing automatic matching is applicable to the frequency band below VHF, as proposed by the applicant. Proposal (1977)
There is an automatic load matching device according to No.-50032 (Japanese Utility Model Publication No. 61-30332), which has been put into practical use. It is easy to add the composite stub matching circuit of the present invention to this detection circuit and use it in the microwave band.

This detection circuit is configured as shown in FIG.
That is, the traveling wave power component input through the terminal 9 is extracted by the directional coupler 11, and its output is divided into two by the signal dividing circuit 13 and applied to the composite detectors 15 ₁ and 15 ₂ , respectively.

On the other hand, the reflected wave component reflected from the load is extracted by the directional coupler 12, and this output is divided by the 90-degree component generator 14 into two signals having the same phase and a 90-degree phase difference, and the two signals are combined. It is added to the other input terminals of detectors 15 ₁ and 15 ₂ . This composite detector performs square-law detection and synthesizes the sum and difference voltages of both terminal inputs, and the output voltage of one composite detector is V ₁ = 4k | a | ² | Γ | cos θ and the output voltage of the other composite detector is Since one of the input signals has a phase difference of 90 degrees, the output voltage of the device is V ₂ = 4k | a | ² | Γ | sinθ, which shows the same characteristics as the multi-probe method, so an automatic matching circuit is also used. It can be used as a detection circuit.

〔Example〕

In the embodiment, a five-probe method is adopted as the detection circuit, and in combination with two sets of composite stub matching devices, a microwave automatic load matching circuit is configured as shown in FIG.
As a result of operating at a frequency of 2450 MHz and a traveling wave power of 50 kW (when matched), a load with a voltage standing wave ratio of 10 (i.e., reflected power of 1.65 kW) was automatically matched to a reflected power of 50 W or less within 3 seconds. This consistent state is
The reflection coefficient is 0.1 and the voltage standing wave ratio is 1.22 or less, which is very good.

When this composite stub matching device is used, there are two adjustment points, and the characteristics thereof are orthogonal over almost the entire area, so automatic matching can be easily and quickly performed.

C. Effects of the Invention It is an epoch-making invention that the microwave band load matching, which was conventionally performed manually, can automatically reach a good matching state in a short period of time, within a few seconds.

Therefore, the present invention is expected to find widespread use in many microwave power applications.

[Brief explanation of drawings]

Figure 1 shows the composite matching circuit used in the present invention, Figure 2
is the normalized susceptance characteristic based on the insertion length of one metal stub, Figures 3 and 4 are a set of composite stub matching devices, Figure 5 is a Smith diagram showing the characteristics of the composite stub matching device, and Figure 6 is the five-point probe. Microwave automatic load matching circuit of the present invention using a detection circuit FIG. 7 shows a detection circuit of the present invention using a directional coupler. 1 ₁ , 1 ₂ , 1 ₃ , 1 ₄ are metal stubs, 2 is a waveguide, 3 is a connector, 4 ₁ , 4 ₂ is a driving motor,
5 ₁ , 5 ₂ composite stub matching device, 6 ₁ , 6 ₂ , 6 ₃ , 6
₄ and 6 ₅ are probes with detectors, 7 ₁ and 7 ₂ are differential amplifiers,
8 ₁ and 8 ₂ are motor drive power amplifiers, 9 is an input terminal, 10 is a load terminal, 11 is a directional coupler for traveling wave components, 12 is a directional coupler for reflected wave components, 13
is a signal dividing circuit, 14 is a 90 degree component generator, 15 ₁ ,
15 ₂ is a composite detector.

Claims (1)

[Claims] 1. In the microwave band, a detection circuit and a matching circuit are placed between a high-frequency power supply and a load circuit, and the reflection coefficient of the load is determined based on the intensity and phase difference of the detected traveling wave component and reflected component. Γ｜ and its cosine
In a circuit that obtains a detection circuit output proportional to the product of cos θ and sine sin θ, and uses this to drive a matching circuit to match the load, the output is applied in parallel to the electric field of the waveguide, approximately (1/1/1) of the average tube wavelength.
4) Two stubs are erected at the distance, one and the other are differentially and continuously interlocked, and this is driven by an electric motor. Place it at a distance of about (1/8),
A microwave automatic load matching circuit that drives a motor using the detection circuit output to match the load.