JPH0696477B2 - High frequency power supply output stabilization device and automatic single crystal growth device using this device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an output stabilizing device for a high-frequency source, and more specifically, stabilizes the filament voltage and the anode voltage of an oscillation tube even when the power supply voltage fluctuates. The present invention also relates to an apparatus capable of growing a single crystal, and further relates to an apparatus for automatically growing a single crystal in which the apparatus is applied to a floating zone method (hereinafter referred to as “FZ method”) which is one of the methods for growing a single crystal.

(Prior Art) The FZ method using high-frequency induction heating is an optimal method for growing a single crystal of a high melting point substance because it does not use a crucible and the sample itself becomes a heating element.

Currently, a LaB ₆ (melting point 2600 ° C) single crystal, which is a thermionic emission material, is grown by this method and is widely put to practical use.
In addition, TiC (melting point 3
(100 ° C) single crystal is also grown by this method. Recently, along with the demand for materials that can withstand the harsh conditions of use, the growing method of single crystals by the high frequency heating FZ method is becoming more and more important.

(Problems to be solved by the invention) By the way, since a high-frequency power source is generally used to heat an object whose shape does not change, the induction heating efficiency between the work coil and the sample does not change, and a high-frequency current is generated. Controlled output stabilizers have been used. For example, as shown in FIG. 1, a high frequency current of the high frequency oscillator (oscillation tube) 1 is detected by an analog detector and fed back.

However, in the case of the FZ method, the shape of the melt zone changes with time during growth, and the induction heating efficiency between the work coil and the sample changes, so the conventional output stabilizer that controls the high-frequency current is changed to the FZ method. It could not be used. Therefore, in the case of the FZ method, the high frequency power supply was used in the manual state, that is, without the output stabilizing device. As a result, the output stability of the power supply is poor, and the power supply voltage (200 V, 3
It was necessary to manually correct the heating power for each fluctuation of the phase), and the single crystal was grown while undergoing a large temperature fluctuation, and the quality was remarkably deteriorated.

Such a problem is not limited to the case where the object to be heated is the above-mentioned melt zone, and is the same when heating another object to be heated whose shape changes with heating.

On the other hand, when a single crystal is grown by the high frequency heating FZ method, the shape of the melt zone changes during the growth, and therefore it is difficult to obtain a high quality single crystal unless the shape of the melt zone is controlled.

However, in the conventional single crystal growth method by the FZ method, there was no device that was able to detect the zone shape well, so the experimenter observed the zone shape directly with his / her eyes and manually set the heating power to an appropriate value. It had to be controlled and to grow a single crystal. Therefore, it is difficult to control the temperature gently by manually controlling the temperature, and the quality of the grown single crystal is deteriorated.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and is an output stabilizing device capable of minimizing the output fluctuation of the high frequency power supply despite the fluctuation of the power supply voltage. It is an object of the present invention to provide an apparatus capable of automatically growing a single crystal when applied to the FZ method by high frequency induction heating.

(Means for Solving the Problem) As a result of intensive studies to achieve the above-mentioned object, the inventors of the present invention firstly found the cause of the fluctuation of the output of the high frequency power supply due to the fluctuation of the power supply voltage (200V, three phases). As a result, it was clarified that it depends on the fluctuations of the filament voltage and the anode voltage of the oscillation tube. Therefore, as a result of studying the countermeasures, a method has been found in which a constant voltage power source is installed to make the filament voltage constant and a computer control is performed so that the anode voltage is detected and made constant. As a result, the output stability of the high frequency power supply could be increased by one digit compared to the conventional one. The present inventors have succeeded in developing a new type of output stabilizer that controls the anode voltage based on this finding.

Moreover, when applying this to the growth of a single crystal by the FZ method,
It was found that the shape of the zone during growth can be judged by the high-frequency current heating the zone, and as a result, by detecting the change in the high-frequency current and controlling the heating power or the moving speed of the growth furnace vertical axis, This proves that crystals can be grown automatically.

That is, the present invention uses a constant voltage power supply as a filament voltage power supply of an oscillation tube in a method of stabilizing the output of a high frequency power supply, and also provides an anode voltage control device for detecting and feedback-controlling the anode voltage, The gist of the present invention is a high-frequency power supply output stabilizing device characterized by stabilizing an anode voltage.

Further, the present invention is an apparatus for automatically growing a single crystal using such a high frequency power source output stabilizing apparatus, which controls heating power or the moving speed of the vertical axis of the growth furnace based on the change of the high frequency current during the growth. The gist of the present invention is an automatic single crystal growth apparatus characterized by being provided with a control unit.

The present invention will be described in more detail below.

(Operation) FIG. 1 shows a case where the output control device of the high frequency oscillator provided with the output stabilizing device according to the present invention is applied to the FZ method.

In the figure, 1 is a high frequency oscillator (oscillation tube), 2 is a power source (200V,
(3 phases), 3 is a high frequency current detector (digital voltmeter), 4 is an anode voltage detector (digital voltmeter), 5 is a CPU having an arithmetic unit and a control unit for comparing the detected value with a set value, and 6 is a filament. A stabilizing power source, 7 is a single crystal growth furnace.

As mentioned above, the high frequency power source is generally used to heat the object to be heated whose shape does not change, so the method of controlling the high frequency current is adopted. Feedback control was performed to stabilize the output.

However, in the case where the shape of the object to be heated changes with heating like a single crystal growth zone, such a method cannot be applied, and the anode voltage is manually adjusted every time the power supply 2 changes. Of.

On the other hand, in the present invention, in view of the fact that the stability of the output of the high frequency oscillator (oscillation tube) 1 depends on the fluctuations of the filament voltage and the anode voltage, a constant voltage power source is used as the filament power source and the anode voltage is detected. This is a system in which the machine 4 detects and performs feedback control. In the CPU5, the anode voltage value detected by the detector 4 is compared with the set value, and the result is passed through the D / A converter to the high frequency oscillator (oscillation tube) 1
Feedback to the anode voltage is controlled. It should be noted that the detector is preferably a digital type, which can improve control accuracy.

The present invention can also be applied to the case where a heated object such as a steel wire whose cross section changes is continuously heat-treated.

It is possible to use a stabilized power source as the power source 2, but such a device has a large capacity and is very expensive.
If you want to use the high-frequency oscillator as a power source for heating an object whose shape does not change, you can use a conventional output stabilizer that controls high-frequency current, and you do not need such an expensive power source. In any case, it is not economical. Further, the high frequency current control device for controlling the high frequency current with the digital voltmeter 3 is not essential in the high frequency power supply output stabilizing device of the present invention.

Next, a specific configuration when this high frequency power source output stabilizing device is applied to a single crystal automatic growing device will be described with reference to FIG.

In FIG. 4, 1 to 7 are the same as those in FIG.
Further, 8 is an upper shaft, 8'is a lower shaft, 9 and 9'is a holder, 10 is a sintered rod, 10 'is a melt zone, 11 is a grown single crystal, 12 is a high frequency coil, 13 is an upper shaft drive part, 13 'is a lower shaft drive unit, 14 is a calculation unit, and 15 is a control unit.

The single crystal automatic growth apparatus of the present invention, while manually controlling the heating power while observing the zone shape in the conventional method,
It is a device that automatically controls heating power by utilizing the fact that the high-frequency current changes in accordance with the change in the shape of the zone.

That is, if the melt zone 10 'becomes thinner during the growth, the impedance between the coil 12 and the melt zone 10' becomes smaller and the high frequency current increases. On the other hand, conversely, if the melt zone 10 'becomes thicker, the high frequency current becomes smaller. Therefore, the high frequency current is detected by the detector 3, the anode voltage at that time is detected by the detector 4, the arithmetic unit 14 of the CPU 5 determines the shape of the melted band, and the control unit 15 controls the heating power.

When actually growing a single crystal, how much the zone shape changes and how much heating power should be controlled appropriately depend on the material of the single crystal. Based on the result of the preliminary experiment of the single crystal, it is determined in advance for each material of the single crystal and reflected in the program.

In this way, the method of controlling only the heating power based on the shape of the fusion zone is suitable when the sintered rod 10 has a high density (generally, the density is 70% or more). However, when the density of the sintered rod 10 is low, a part of the melt zone 10 'soaks into the sintered rod 10 during the growth, the melt zone suddenly becomes thin, or the soaked portion melts into the melt zone. When it is inserted, the zone becomes thick, and the shape of the zone changes due to factors other than deviation from the appropriate heating power. In such cases, to grow a single crystal stably,
In addition to controlling heating power, it is necessary to change the moving speed of the upper shaft and the lower shaft from the set value. Whether the melt zone becomes unstable when it becomes thicker than the set shape or becomes unstable when it becomes thin depends on the material of the single crystal to be grown. The moving speed of the upper shaft and the lower shaft is changed from the set value to restore the original shape of the zone. In any case, when the sintered rod 10 does not melt smoothly into the melt zone 10 ', the moving speed of the vertical shaft is changed, and normally only the upper shaft is changed. The control of the moving speed of the upper shaft and the lower shaft is effective for the second and subsequent zone movements. This is a raw material rod (sintering rod) fed into the melt zone 10 '.
This is because the thickness of may not be uniform.

In order to stably perform automatic growth, the CPU 5 needs to have an electric power control ability for an appropriate heating electric power and an output stabilizing ability for holding the anode voltage at the set anode voltage.
That is, it is output stabilization control in which the anode voltage is detected by the detector 4, compared with a set value, and the result is feedback-controlled to the high-frequency oscillator (oscillation tube) 1. Furthermore, it is more effective if the filament voltage is made constant by using a constant voltage power source as the filament power source 6 of the oscillation tube 1.

(Example) Next, an example of the present invention will be described.

Example 1 The following experiment was conducted in order to investigate the output stability of a high frequency power supply.

Set a 100 mmφ × 200 mm Mo rod in the high-pressure single crystal growth furnace (FZ furnace) connected to the high-frequency oscillator shown in FIG.
Heating is performed in a He atmosphere at 5 atm, and the power supply voltage (200 V, 3
The stability of the high frequency power source due to fluctuations in phase) was investigated. The heating conditions were an anode voltage of 5 KV and a high frequency current of 180 A.

FIG. 2 shows the result when the output stabilizer according to the present invention is not installed, that is, the result of the conventional method. Power supply voltage 8V
(4%), the filament voltage of the oscillation tube is 4
%, The anode voltage changed by 5 V (0.1%). As a result, the high frequency current fluctuated by 0.5A (0.3%). With such a variation, it is necessary to manually adjust the heating power when growing the single crystal.

On the other hand, FIG. 3 shows the result when the output stabilizer according to the present invention is installed. The fluctuation of the filament voltage of the oscillation tube could be suppressed to less than 0.1% by using the constant voltage power supply (2KVA). In addition, the anode voltage was detected by a digital voltmeter and controlled by a computer, and the fluctuation could be suppressed to ± 0.5 V or less (<0.01%). as a result,
It was possible to suppress the fluctuation of high-frequency current to ± 0.05 A or less (<0.03%).

Example 2 In this example, the high frequency power supply output stabilizing device according to the present invention is LaB ₆
This is an example applied to a single crystal growing apparatus.

LaB ₆ powder was sintered to prepare a sintered rod having a diameter of about 1 cm and a length of 20 cm. This was fixed to the upper and lower shafts of the FZ furnace via a BN holder. After filling the FZ furnace with He at 8 atm, an initial zone was formed by high frequency heating. The zone transfer was performed by moving the sintered rod and the grown single crystal downward at a speed of 1 cm / hr. After moving the about 0.5 cm zone, automatic growth was started.

In the case of LaB ₆ single crystal growth, the melt zone was likely to fall and it was necessary to adjust the heating power with a small change in high frequency current. That is, when the high frequency current increased by 0.1 A, the anode voltage was lowered by 4V. Also, when the high-frequency current decreases by 0.1 A, that is, when the melt zone becomes thick, the melt zone is likely to fall, so the anode voltage is lowered by 3.5 V and at the same time, the moving speed of the sintered rod is lowered to reduce the original melt rate. It returned to the strip shape. As a result, the heating power decreased as the zone moved. This is because the melting zone composition changed due to evaporation, so that the melting point of the zone decreased as the zone moved.

The heating condition at the end of 5 hours of automatic growth is 5.474V-195.2A.
Met. In this way, LaB ₆ with a diameter of 8 mm and a length of 5.5 cm
A single crystal was obtained. In the manually grown single crystal, the surface is not smooth because the melt zone grows with a tendency to fall, but the single crystal automatically grown in this example has a very fine heating power control, so the surface is very It was smooth. Moreover, the quality of the single crystal was smaller than that of the manually grown single crystal, and the quality was good.

(Effects of the Invention) As described above, according to the present invention, it is possible to reduce the output fluctuation of the high frequency power supply as much as possible, and to increase the stability by one digit, regardless of the fluctuation of the power supply voltage. It is possible.
In addition, the device is much cheaper than the stabilized power supply. Therefore, it is suitable for high frequency heating of an object to be heated whose shape changes with heating.

In particular, when applied to the high frequency heating FZ method, in addition to the above effects, if the heating power or the vertical axis movement speed is controlled based on the change in the high frequency current, the above effects are also superimposed and a high quality single crystal is stabilized. And can be trained automatically.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an output control device of a high frequency oscillator equipped with an output stabilizing device according to the present invention and a case where the output control device is applied to a single crystal growth furnace, and FIG. 2 shows stability of a conventional high frequency power supply. In the figure, the degree of fluctuation of the anode voltage and the high frequency current with respect to the fluctuation of the power supply voltage is shown. FIG. 3 is a diagram showing the stability of the high frequency power supply when the output stabilizing device according to the present invention is provided. The degree of fluctuation of the anode voltage and the high frequency current with respect to the fluctuation of the voltage and the filament voltage are shown, and FIG. 4 is an explanatory diagram showing an example of an automatic single crystal growth apparatus equipped with an output stabilizer. 1 …… High frequency oscillator (oscillation tube) 2 …… Power supply (200V, 3
Phase), 3 ... High frequency current detector (digital voltmeter), 4 ... Anode voltage detector (digital voltmeter), 5 ... CPU, 6 ... Oscillating tube filament stabilizing power supply, 7 ... Single crystal growth Furnace, 8 ... upper axis, 8 '... lower axis,
9, 9 '... Upper shaft Lower shaft holder, 10 ... Sintered rod, 10' ...
… Blend zone, 11 …… single crystal, 12 …… high frequency coil, 13 …… upper axis drive section, 13 ′ …… lower axis drive section, 14 …… calculation section, 15 ……
Control unit, power supply voltage, anode voltage, filament voltage, high frequency current.

Claims (4)

[Claims] 1. In a method for stabilizing the output of a high frequency power supply, a constant voltage power supply is used as a filament voltage power supply for an oscillating tube, and an anode voltage control device for detecting and feedback-controlling the anode voltage is provided to provide a filament voltage and an anode. A high frequency power supply output stabilization device characterized by stabilizing voltage. 2. An apparatus according to claim 1, wherein a digital detector is used for detecting the anode voltage. 3. An apparatus for automatically growing a single crystal using the apparatus according to claim 1, wherein a controller for controlling heating power based on a change in high frequency current during the growth is provided. Automatic crystal growth device. 4. An apparatus for automatically growing a single crystal using the apparatus according to claim 1, further comprising a controller for controlling the heating power and the moving speed of the vertical axis of the growth furnace based on the change of the high frequency current during the growth. An automatic single crystal growth apparatus characterized by being provided.