JPH0733580A - Drawdown type method for growing large-sized single crystal and apparatus therefor - Google Patents

Abstract

PURPOSE:To provide a technology in which the thickness of a melt can be kept constant without any fluctuation of composition and a large-sized single crystal of high quality can be grown at low cost according to a drawdown method. CONSTITUTION:The characteristic of this method for growing a large-sized single crystal comprises controlling the thickness of a melt to a constant value by measuring the distance from a prescribed position in an upper part of this apparatus for growing the single crystal to the melt surface and making the set heating temperature variable corresponding to the fluctuation in the distance thereof in using a heating furnace, a crucible for growing the single crystal arranged on the inside thereof and a device for continuously feeding a raw material from the upper part of an electric furnace into the crucible for growing and growing the single crystal according to a drawdown method. A further characteristic of the method comprises continuously feeding the raw material powder of a shape having a shape ratio of >=1/1 of the major axis/thickness of the raw material and 0.01-0.4g weight of one piece of the raw material from the upper part of the electric furnace into the interior of the crucible for growing the single crystal. Thereby, the large-sized single crystal of high quality with hardly any change in composition can be grown without using a melting crucible.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a continuous filling method for pulling down raw materials.
The present invention relates to a technique for growing a single crystal by the (also referred to as Bridgman method), and more specifically, it relates to a technique for growing a large single crystal by a pull-down method without using a melting crucible. For example, a MnZn ferrite single crystal for a magnetic head, And single crystals of bismuth germanate for surface acoustic waves, lithium borate, lithium tantalate, lithium diobate, etc., particularly suitable for growing a large and long single crystal by the pulling method.

[0002]

2. Description of the Related Art When manufacturing a single crystal of good quality and low production cost, obtaining a large and long single crystal has become an important issue. To manufacture a ferrite single crystal by the Bridgman method,
From the viewpoint of manufacturing cost, it is generally understood that it is preferable that the single crystal is large and long, the composition of iron oxide, manganese oxide, and zinc oxide is constant, and the amount of platinum mixed is small.

Conventionally, in order to grow a particularly large and long single crystal by the Bridgman method, a growing crucible arranged in a heating furnace is provided with a molten crucible suspended from a furnace upper part by a platinum tube. Into this molten crucible, a sintered ferrite raw material having a columnar shape, a disk shape or a ring shape, which is formed by pressing, of about 1 gr is continuously supplied, and after being melted in the molten crucible, it is supplied into the growing crucible. It was By doing so, the composition of each element can be made uniform to some extent by matching the growth amount of the single crystal and the continuous filling amount.

In this method, only the growing crucible is fixed,
There are a method of synchronously driving the melting crucible and the electric furnace, and a method of fixing the melting crucible and the electric furnace and driving the growing crucible.
In any case, in practice, when a long single crystal is grown by the Bridgman method, the thickness of the melt portion changes as the amount of crystal increases, which causes the matching between the single crystal growth amount and the continuous filling amount to gradually collapse. Then, there is a drawback that the composition of each element changes.

Further, in the prior art, since a melting crucible is used in the growing crucible, unless the temperature is maintained at a certain high temperature (about 1630 ° C.), the raw material does not melt. The furnace temperature was set. For example, if the diameter of the raw material is 70 mm and the growth rate is 2 mm / h
In the case of, 1 gr of raw material needs to melt within 93 seconds.

However, when single crystal growth is continued for a long time by such a conventional method, as the crystal amount increases, the temperature inside the melting crucible rises and the temperature inside the melt also rises, and the melt amount increases. There was a tendency that the amount of platinum increased and, as a result, the amount of platinum mixed in increased and the composition of the crystal fluctuated.

The present invention solves the above-mentioned problems of the prior art, makes it possible to make the thickness of the melt constant, does not change the composition, and makes a large single crystal of high quality with few impurities inexpensive by the pulling method. The purpose is to provide technologies that can be nurtured.

[0008]

As a result of intensive studies to solve the above problems, the present inventors have found a method for growing a high quality single crystal without using a melting crucible.

That is, in the conventional method using a molten crucible, the temperature inside the molten crucible needs to be 1630 ° C. or higher, and it is difficult to lower the growth set temperature, and therefore it is not possible to prevent platinum from being mixed. It was In the first place,
The purpose of using a molten crucible is to drop a ferrite-filled raw material having a weight of about 1 gr onto the melt surface in the growing crucible as it is, there is a bounce from the melt surface, and the furnace core tube is contaminated. This is because the crystals could not be used for a magnetic head because they contained bubbles. These bubbles could not be easily removed even if the growth rate was reduced by about 20%. If a smaller powder is supplied, the powder scatters in the furnace core tube, and only the furnace core tube is soiled.

Further, when the melted crucible is used, there is a problem that the thickness of the melt cannot be controlled to be constant because the thickness of the melt in the growing crucible cannot be measured.

Therefore, since the melting crucible is not used, the height of the molten material in the growing crucible is measured from a certain position in the upper part of the electric furnace so that the distance to the surface of the melt can be measured electrically or optically. It was found that the thickness of the melt can be made constant by controlling the heating set temperature by superimposing this fluctuation amount on the control temperature signal.

Further, in contrast to the method in which the shape of the feed material is changed and the conventional cylindrical piece sintered body is fed as the raw material, the powder feeding method lowers the set temperature of the furnace because it is easier to melt. Crucible for melting raw materials
It was also found that a (molten crucible) becomes unnecessary and a high-quality single crystal with few impurities can be grown.

[0013]

The present invention will be described in more detail below.

First, the present inventors have paid attention to the fact that there is a difference in specific gravity between the liquid and solid ferrite. If the growth rate and the continuous supply of the raw materials are matched, the ferrite melt is considered to be constant, but in reality, when growing a large and long single crystal, the melt increases as the ferrite solids increase from a certain point. It was found that, when the amount of the ferrite solids increases and the amount of the ferrite solids further increases, the melt amount decreases.

That is, an increase in the solid content to some extent serves to keep the heat in the furnace, and when it further increases, the heat escapes through the crystallized solid, and the temperature in the furnace decreases. The state of heat in the furnace is changing in this way. Therefore, the melt amount is changing.

The reason for this is that the density of the solid and the density of the liquid are different. Liquid density ρ (L), solid density ρ (S)
Then, the following ratio holds here. ρ (S) ≧ 1.05ρ (L) However, the liquid contains bubbles.

If the thickness of the melt is 80 mm and the distance from the position where the furnace is located to the surface of the melt is increased by 1 mm due to heat being taken away, it means that the liquid part has changed to the solid part, and the thickness of the melt is Is 1 mm ÷ 1.05 = 0.952 mm (converted amount as solid) 1 mm-0.952 mm = 0.048 mm (change amount at 1 mm) 1 mm ÷ 0.048 mm = 20.8 mm (liquid changed to solid) Thickness) 80 mm-20.8 mm = 59.2 mm (thickness after reduction), which means that the thickness has been reduced to about 60 mm.

Therefore, the distance to the surface of the melt is accurately measured and the set temperature is changed, or the shape of the raw material is set to a certain size and the continuous supply amount is controlled to melt the melt. By making the liquid volume constant, it becomes possible to grow a large and long single crystal having a uniform composition.

As the former means, in the present invention, the distance to the surface of the melt is measured by an electrical or optical measuring device, and the fluctuation amount is superposed on the control temperature signal to make the melt thickness constant. Thus, the heating set temperature is changed. Since the thickness of the melt is controlled to be constant, there is no fluctuation in the single composition even when the growth is continued for a long time, and a large single crystal having a uniform composition can be grown.

As the latter means, in the present invention, the granulated raw material powder is selected to a certain size, and then the shape is different from the conventional cylindrical shape, and the ratio of major axis / thickness is 1.
/ 1 or more, and more specifically, it remains spherical, or is made into a disk shape or an elliptical shape by roll forming to increase the surface area and facilitate light melting, and a raw material of this shape is continuously grown from the upper part of the electric furnace. Since it can lower the set temperature of the furnace by supplying it to the inside, it is possible to obtain a high quality large and long ferrite single crystal with few impurities in combination with not using a melting crucible. You can

At this time, the weight of one raw material is 0.01 to 0.
It is necessary to use a light powder raw material that is 4 g. When the weight of one continuous filling material is 0.4 gr or more, small bubbles enter inside the single crystal. On the other hand, when the amount is 0.01 gr or less, the raw material loses the rising airflow from the surface of the melt and soars, and is not supplied into the growing crucible. In addition, when the surface of the melt shakes, an error will occur in the measurement, so be careful not to hunt the drive of the growth crucible.

As a continuous feeding method for raw materials, conventionally, a core sintered in a cylindrical shape or a disk shape is used as a parts feeder.
(Fluctuating type) was used to fill the melting crucibles one by one, and after melting in the melting crucible, they were dropped on the surface of the growing crucible. In this method, since a parts feeder is used, problems often occur unless the dimensions of the sintered core are controlled, and vibrations are transmitted to the furnace body and the surface of the melt becomes delicate during crystal growth. It also shook, causing subgrains to enter the crystal. Further, it takes time and equipment such as a press until the sintered core is manufactured, and a fused crucible made of platinum is also required, which causes a problem of high cost.

On the other hand, in the present invention, in view of the fact that the powder raw material has the above weight and shape, the powder raw material is continuously fed into the growing crucible in a pellet state without pressing, A non-oscillating type continuous feeding device is used. For example, as shown in FIG. 1, a non-oscillating type powder raw material container (16), a filling pipe (15) and a guide pipe.
A raw material supply device having (14) is exemplified.

Preferably, as shown in FIG.
4) A container (31) supported by a support plate (13) for containing the powder raw material (32), and a rotating body (35) having a groove (36) for receiving and discharging the powder raw material. And the powder raw material discharged from the groove of the rotor is filtered by a filter (42) and a guide pipe.
(44), a continuous feed device for raw materials having a device for feeding into the growing crucible with a saucer (45) is used. Rotating body (3
5) is rotatably supported by a fixing plate (37) and a holding jig (38), and is rotationally driven by a motor (41) via a joint (39) and a gear (40). The powder raw material (pellet) stored in the container (31) is a predetermined amount by a predetermined amount in the groove (36) of the rotating body.
And the rotor (35) is rotated to fill the funnel.
(42), and through the guide pipe (43) the saucer
It is supplied to (44) and filled in the growing crucible. If conditions such as the size and speed of the growing crucible and the size and weight of the pellet are changed, the rotation speed of the motor is changed or the rotation of the motor is turned ON / OFF.
The filling amount can be controlled by changing the time. Since it is supplied in pellet form without pressing, no pressing is required and no vibration occurs.

The former means and the latter means described above may be used alone or in combination. It is preferable to use both in combination.

Next, examples of the present invention will be described.

[0027]

【Example】

FIG. 1 shows an example of an apparatus used for implementing the present invention. The platinum growth crucible (11) is supported by an alumina support tube (8), and this support tube is placed on a support table (23), which is driven by a motor with a screw rod (6) and a support (22). It is connected to the part (5). (7) is a flange.
When the motor is driven, the screw rod (6) rotates and the growing crucible (11) moves. Raising crucible (11)
The atmosphere is maintained in the furnace core tube (24), is heated by the heating element (10), and is kept warm by the heat insulating material (9) outside thereof. The electric furnace is supported by supporting stands (2) and (3) provided on an outer frame (1) standing on a substrate (4).

When heated, the ferrite raw material in the growth crucible (11) is melted, and when the growth crucible is lowered and grown, it becomes a solid (12) and a liquid (13) as shown in the figure. Here, the container (16) in which the ferrite raw material (17) of the shape of the present invention, which corresponds to the amount of solid to be grown, is supported by the support table (21)
And is continuously supplied into the growing crucible (11) through the filling pipe (15) and the guide pipe (14). The raw material is formed of granulated powder, and the amount of melt is stable because it is continuously and lightly supplied so as not to be defeated by the rising air current from the surface of the melt. Conventionally, the thickness of the melt fluctuates every about 96 seconds due to the weight of about 1 gr. Further, the distance to the melt surface is accurately measured using the laser length measuring device (18) on the table (20). (19) is a right angle prism that changes the direction of the laser, and (20) is a laser length measuring instrument.
It is the support of (18).

The implementation conditions are as follows. Growing crystal: manganese zinc ferrite (raw materials MnO, Zn
O, Fe ₂ O ₃ ) Growing method: Bridgman method (invention method: using only growing crucible) (Conventional method: using melting crucible and growing crucible) Growing crucible: made of platinum, 70 mmφ × 500 mm or more, growing temperature: 1650 ° C. (Invention method), 1670 ° C (conventional method) Furnace core tube: outer diameter 100 mmφ / inner diameter 90 mmφ × 1000 mm Growth rate: 2 mm / h Temperature gradient: 19 ° C / cm Melt thickness: 80 mm Atmosphere: Oxygen Filling raw material shape: Disc (about 1.0 gr) and powder (about 0.1 gr) Continuous filling amount: 0.64 gr / min (0.1 gr / piece 6.
(Continuous supply at a rate of 4 pieces / min) (Conventional method supplies 1 gr per piece and melts in 93.6 seconds) Length measuring device: LD type (resolution: ± 10μ for 1000 mm)
m) Temperature controller: Digital program temperature controller

A single crystal was grown under the above conditions. In the method of the present invention, the distance from the constant position in the upper part of the drawing to the melt surface is measured by a laser length measuring machine, and the thickness of the melt is constant (80 mm depending on the increase or decrease of the distance). The set temperature was controlled by the temperature controller so that

The relationship between the length of the obtained single crystal and the composition distribution is shown in FIG. According to the method of the present invention, it can be understood that the composition ratio of MnO, ZnO, and Fe ₂ O ₃ hardly changes even when the length of the single crystal becomes long, and the length can be up to 400 mm. On the other hand, according to the conventional method, the composition ratio of MnO and Fe ₂ O ₃ is remarkably changed, and it is difficult to grow a single crystal having a length of 250 mm.
mm is the limit.

[0033]

As described above, according to the present invention,
The thickness of the melt can be kept constant, the composition does not fluctuate, a large single crystal of high quality with few impurities can be grown, and it is inexpensive.

[Brief description of drawings]

FIG. 1 is an external view of a continuous filling type single crystal growing apparatus capable of controlling a melt layer according to the present invention.

FIG. 2 is a composition distribution diagram of ferrite single crystals obtained by a conventional method and an inventive method in Examples.

3A and 3B are diagrams showing an example of a powder raw material continuous supply apparatus used for carrying out the present invention, in which FIG. 3A is a front view and FIG. 3B is a side view.

[Explanation of symbols]

 11 Growing crucible 12 Solid 13 Liquid 16 Powder raw material storage container 18 Laser length measuring device 24 Furnace core tube 31 Powder raw material storage container 35 Rotating body 36 Groove

Claims (4)

[Claims] 1. When growing a single crystal by a pull-down method using a heating furnace, a single-crystal growing crucible arranged inside the heating crucible, and a device for continuously supplying the raw material into the growing crucible from the upper part of the electric furnace. The pull-down type is characterized in that the thickness of the melt is controlled to be constant by measuring the distance from a fixed position on the upper part to the surface of the melt and varying the heating set temperature according to the fluctuation of the distance. Large single crystal growth method. 2. An apparatus for growing a single crystal by a pulling down method using a heating furnace, a single crystal growth crucible arranged inside thereof, and an apparatus for continuously supplying a raw material into the growth crucible from the upper part of the electric furnace. In the above, a large pull-down single unit is equipped with a measuring device for measuring the distance from a certain position on the upper part to the melt surface and a temperature control device for varying the heating set temperature according to the measured distance. Crystal growth equipment. 3. When growing a single crystal by a pulling down method using a heating furnace, a single crystal growth crucible arranged inside thereof, and a device for continuously supplying the raw material into the growth crucible from the upper part of the electric furnace. , A powder raw material having a shape in which the ratio of major axis / thickness of the raw material is 1/1 or more and the weight of one raw material is 0.01 to 0.4 g, is obtained by single crystal from the upper part of the electric furnace. A pull-down large-sized single crystal growing method characterized by continuously supplying into a growing crucible. 4. An apparatus for growing a single crystal by a pulling down method using a heating furnace, a single crystal growth crucible arranged inside the heating furnace, and an apparatus for continuously supplying the raw material into the growth crucible from the upper part of the electric furnace. In the above, a container having a shape in which a ratio of major axis / thickness of the raw material has a shape ratio of 1/1 or more, and a powder raw material in which the weight of one raw material is 0.01 to 0.4 g,
A raw material continuous feeding device having a rotating body having a groove for receiving and discharging the powdery raw material, and a device for feeding the powdery raw material discharged from the groove of the rotating body into a single crystal growing crucible. , A pull-down large-scale single crystal growing device, which is arranged at the upper part of the electric furnace.