TW201829859A - Apparatus for manufacturing lithium tantalate crystal and method for manufacturing lithium tantalate crystal - Google Patents

Abstract

The present invention provides an apparatus for manufacturing lithium tantalate crystal of high quality by using a platinum-made crucible. The apparatus (10) for manufacturing lithium tantalate crystal of the present invention comprises: a main body (12); a tubular furnace body (14) disposed on the main body (12) and having heat resistance; a covering body (18) for covering the furnace body (14); a heat generator (20) disposed inside the furnace body (14); a crucible supporting shaft (24) penetrating the main body (12) to move up and down freely; and a crucible (30) disposed on the crucible supporting shaft (24) and heated by the heat generator (20). The apparatus of the present invention is an apparatus (10) for manufacturing lithium tantalate crystal which has vertical Bridgman furnace or coagulation furnace with a vertical temperature gradient, and has a crucible (30) which is a platinum-made crucible (30).

Description

   Device for manufacturing lithium tantalate crystal and method for manufacturing lithium tantalate crystal   

The present invention relates to a device and method for manufacturing lithium tantalate crystals used in surface acoustic wave devices and the like.

The single crystal system of lithium tantalate (LiTaO ₃ : LT) is used as a non-linear optical material as a laser medium, or as a piezoelectric ceramic for a piezoelectric element, a surface acoustic wave element, or the like.

The most common method for growing LT single crystals is the Chai method (CZ) method, which is made using an iridium crucible in an inert gas environment or a reducing gas environment. In addition, there is also an example in which a crucible made of a platinum-rhodium alloy is used in the oxygen gas environment in the same manner using the firewood method (Patent Documents 1 to 3).

Prior art literature Patent literature

Patent Document 1 Japanese Patent Application Publication No. 2013-23391

Patent Document 2 Japanese Unexamined Patent Publication No. 4-74790

Patent Document 3 Japanese Patent Laid-Open No. 2000-247782

However, in the case of using an iridium manufacturer for the crucible, since iridium is oxidized and cannot be grown in an oxygen gas environment, it is necessary to introduce a gas such as an inert gas into the furnace, and the device becomes large and the manufacturing steps become complicated. In addition, when a platinum-rhodium alloy is used for the crucible, there is a problem that rhodium is melted into the crystal and the quality of the crystal is deteriorated.

If platinum can be used in the crucible, the above-mentioned problem of oxidation and the problem of so-called rhodium fusion can be eliminated.

However, Patent Document 2 describes those made of noble metals such as platinum, rhodium, and iridium in the crucible. However, in the examples, an example in which a crucible made of iridium was used for the growth of the LT single crystal and an example in which a platinum crucible was used for the growth of single crystals of lithium niobate (LN) was not shown. Example using platinum.

Further, in Patent Document 3, it is seen that oxide single crystals such as lithium tantalate and lithium niobate have a high melting point. Therefore, as a crucible using the wood method, precious metals such as platinum, platinum-rhodium, or iridium can be used. Although the description of the crucible is made, only those who use the iridium crucible are shown in the examples.

As described above, Patent Documents 2 and 3 merely describe that a crucible made of platinum can be used in the Chai method, and actually do not disclose an example of using a crucible made of platinum in the production of a single crystal of lithium tantalate.

It is speculated that this is because the temperature difference between the melting point of platinum (1768 ° C) and the melting point of LT (1650 ° C) is only 118 ° C. When the temperature in the incubator is raised, it will adversely affect the platinum crucible, so it is not platinum. Instead, a crucible using iridium was used.

An object of the present invention is to provide a manufacturing device and a manufacturing method of lithium tantalate crystals that can solve the above-mentioned problems by using a platinum crucible.

The manufacturing device of lithium tantalate crystal according to the present invention is a manufacturing device of lithium tantalate crystal including a vertical Bridgmann furnace or a vertical temperature gradient solidification furnace, and has a substrate and heat resistance arranged on the substrate. A cylindrical furnace body, a cover body plugging the furnace body, a heating body arranged in the furnace body, a crucible bearing penetrating through the base body and provided to move up and down freely, and arranged on the crucible bearing and The crucible heated by the heating element is characterized in that the crucible is a crucible made of platinum.

By using a vertical Bridgman (VB) furnace or a vertical temperature gradient solidification (VGF) furnace, the temperature gradient of the incubator can be reduced. Therefore, even a platinum crucible with a small melting point difference from lithium tantalate, It can also be used without being adversely affected by deformation.

In addition, platinum crucibles can be used in the atmospheric environment to prevent the device from increasing in size. In addition, there is no problem with the so-called rhodium melting out, which enables high-quality lithium tantalate single crystals. Manufacturing.

In addition, since the temperature gradient during incubation can be reduced, high-quality lithium tantalate single crystals can be produced.

A platinum crucible with a purity of 95% or more can be used in the crucible.

It is preferable to provide a control part that controls the heating of the crucible by the heating element, so that the heating of the crucible by the heating element is performed at a temperature lower than the temperature at which the crucible is softened and deformed.

The inner wall of the furnace body can be formed into a plurality of laminated heat-resistant walls having a ring-shaped heat-resistant member having a required height, and the ring-shaped heat-resistant member can be formed into a ring by joining a plurality of divided pieces. Since the furnace body having such a heat-resistant wall is manufactured, management as a breeding furnace with a small temperature gradient is easy.

A resistance heating element can be used for the heating element.

As the resistance heating heating element, a resistance heating heating element including MoSi ₂ as a main material can be used.

Alternatively, a heating element that is heated by high-frequency induction can be used for the heating element.

It is possible to use a Pt-Rh alloy made of the heating element by the high-frequency induction heating.

In the furnace body, a support cylinder containing a heat-resistant material can be disposed outside the heat-resistant wall, and a heat insulating material can be disposed between the heat-resistant wall and the support cylinder, so that the cover is supported by the support Tube to support.

The cover is preferably formed of a heat insulating material, and a reinforcing member is disposed in the heat insulating material.

In addition, the method for manufacturing lithium tantalate crystals of the present invention is a method for manufacturing lithium tantalate crystals using a vertical Bridgman (VB) method or a vertical temperature gradient solidification (VGF) method. The crucible of the raw material of lithium acid is arranged in the furnace body, and the crucible is heated by the heating element arranged in the furnace body to melt the raw material, and then the temperature of the crucible is lowered to obtain the crystal of lithium tantalate. In order to use a crucible made of platinum for the crucible, when the crucible is heated by the heating element, the crucible is heated at a temperature lower than a temperature at which the crucible is softened and deformed.

Since the temperature gradient of the incubator can be reduced by using the vertical Bridgman (VB) method or the vertical temperature gradient solidification (VGF) method, even a platinum crucible with a small melting point difference from lithium tantalate It can also be used without being adversely affected by deformation and the like.

In addition, platinum crucibles can be used in the atmospheric environment to prevent the device from increasing in size. In addition, there is no problem with the so-called rhodium melting out, so high-quality lithium tantalate single crystal can be performed. Manufacturing.

In addition, since the temperature gradient during incubation can be reduced, high-quality lithium tantalate single crystals can be produced.

A platinum crucible with a purity of 95% or more can be used in the crucible.

In the case of the vertical temperature gradient solidification (VGF) method, it is preferable to perform the following method: When the crucible is heated by the heating element, when the temperature of the crucible reaches the vicinity of the seed temperature, the The heating of the heating body is performed slowly to prevent the temperature of the crucible from exceeding the seeding temperature.

In the case of the vertical temperature gradient solidification (VGF) method, it is preferable to perform the following method: When the crucible is heated by the heating element, at a stage before the temperature near the seed temperature is reached, the temperature is temporarily fixed by the foregoing. The heating of the heating body keeps the temperature inside the furnace body constant, and makes the temperature inside the furnace body uniform.

In addition, in the case of the vertical temperature gradient solidification (VGF) method, it is advisable to perform in the following manner: When the temperature of the crucible reaches the seed temperature, the seed is maintained at the temperature for the time required to perform the seed addition. After the seeding was completed, the temperature in the furnace body was gradually lowered, and lithium tantalate was solidified and crystallized.

According to the device and method for manufacturing lithium tantalate crystals according to the present invention, the furnace can be reduced by adopting a vertical Bridgman (VB) method or a vertical temperature gradient solidification (VGF) method capable of reducing a temperature gradient. The temperature gradient in the furnace makes it possible to achieve a uniform temperature distribution in the furnace. Since the maximum temperature in the furnace can be reduced, a crucible made of platinum with a small melting point difference from lithium tantalate can be used without softening or deforming. In addition, since a crucible made of platinum can be used, it can be used in the atmospheric environment, which can prevent the enlargement of the device. In addition, the crucible material is hardly melted into the crystal, and the temperature in the furnace can be precisely controlled. The effect of breeding high-quality lithium tantalate single crystal can be achieved.

10‧‧‧lithium tantalate manufacturing equipment

12‧‧‧ substrate

14‧‧‧furnace body

16‧‧‧ Cooling device

18‧‧‧ cover

18a‧‧‧board

20‧‧‧heating body

22‧‧‧ bottom

24‧‧‧ Crucible Bearing

26‧‧‧Thermocouple

28‧‧‧ adapter

30‧‧‧ Crucible

32‧‧‧ heat-resistant wall

32a‧‧‧ split

32b‧‧‧Heat-resistant components

33‧‧‧Insulation material layer

34‧‧‧ support cylinder

34a‧‧‧Annular member

34b‧‧‧ support ring

35‧‧‧Insulation layer

37‧‧‧ Reinforcing member

38‧‧‧ support

40‧‧‧ long hole

41‧‧‧Insulation material layer

44‧‧‧ high frequency coil

46‧‧‧Fever

FIG. 1 is a cross-sectional view showing the configuration of a manufacturing apparatus for a lithium tantalate single crystal.

FIG. 2 is a perspective view showing a ring-shaped heat-resistant member.

Fig. 3 is a perspective view of a furnace body.

Fig. 4 is a perspective view of a heating element.

Fig. 5 is a plan view of the cover.

FIG. 6 is a schematic diagram of a manufacturing device of lithium tantalate single crystal by high-frequency induction heating.

FIG. 7 is an explanatory diagram showing a measurement range of a temperature distribution in a furnace for culturing a lithium tantalate single crystal in a manufacturing apparatus of a high-frequency induction heating method.

FIG. 8 is a graph showing the temperature distribution in the furnace measured in the measurement range shown in FIG. 7.

FIG. 9 is a diagram showing an example of the profile of the furnace temperature when the furnace temperature control is performed by the VGF method.

FIG. 10 is a temperature control flowchart when the temperature control in the furnace shown in FIG. 9 is performed.

FIG. 11 is a graph showing the followability of the furnace temperature to the high-frequency coil output when the furnace temperature control shown in FIG. 9 is performed.

FIG. 12 is a photograph of a lithium tantalate single crystal obtained by using a 100% platinum crucible, using a high-frequency heating furnace shown in FIG. 7, and using the furnace temperature profile shown in FIG. 9 to crystallize by VGF method .

FIG. 13 is a photograph of a lithium tantalate single crystal obtained by using a 100% platinum crucible in a resistance heating furnace shown in FIG. 1 and using the furnace temperature profile shown in FIG. 9 to crystallize by VGF method.

A form for implementing the invention

(Configuration Example of Manufacturing Device)

In the manufacturing device of lithium tantalate (LiTaO ₃ : LT) single crystal of the present embodiment, a crucible material different from Ir is used as a crucible material for cultivating lithium tantalate single crystal, and specifically, platinum系 材料。 Department of materials. It is preferably 100% platinum (the so-called 100% platinum also includes impurities containing less than 1% inevitably mixed during manufacture), and may be a purity of 95% by weight or more. It may be, for example, rhodium (Rh) in which about 5 wt% is included. If it is about 5 wt% of rhodium, the melting out of rhodium in the crystal can be reduced, and the quality of the crystal will not cause such a large adverse effect. In addition, since the melting point of the crucible is increased by mixing rhodium, deformation of the crucible can be effectively suppressed in this regard. In this embodiment, a crucible made of platinum means a platinum made with a purity of 95% by weight or more.

FIG. 1 shows a configuration example of a manufacturing apparatus 10 for growing a lithium tantalate single crystal. This lithium tantalate single crystal manufacturing device 10 is a device for cultivating lithium tantalate single crystal in an oxygen gas environment (in the atmosphere) according to the vertical Bridgeman (VB) method or the vertical temperature gradient solidification (VGF) method. .

First, a schematic configuration example of the lithium tantalate single crystal manufacturing apparatus 10 is shown.

In FIG. 1, a furnace body 14 is disposed on a base body (abutment) 12. The base body 12 is provided with a cooling mechanism 16 through which cooling water flows.

The furnace body 14 has a cylindrical shape as a whole, and has a structure capable of withstanding high temperatures up to about 1850 ° C.

The opening portion can be closed by the cover body 18.

In addition, a lower portion of the furnace body 14 is a bottom portion 22 in which various heat-resistant materials are laminated.

A heating element 20 is arranged in the furnace body 14. The heating element in this embodiment is a resistance heating heating element and generates heat by being energized.

Although not shown, a control unit is provided to control the power supply (output) of the resistance heating heating element 20. The control unit may be a person who changes the energization amount by manual operation, or may automatically control the energization amount every time according to a required input program.

The bottom portion 22 and the base body 12 are provided with a through hole penetrating in the vertical direction, and the through hole is penetrated. The crucible bearing 24 is provided by a drive mechanism (not shown) so as to be freely movable up and down and centered on the axis Free spin. The crucible bearing 24 is also formed of a high-temperature-resistant heat-resistant material such as alumina.

An adapter 28 containing a heat-resistant material such as zirconia is mounted on the upper end of the crucible bearing 24, so that the platinum crucible 30 can be placed in this adapter 28. The crucible 30 is heated by the heating element 20.

A thermocouple 26 is provided at the bottom of the adapter 28 so that the temperature in the furnace body 14 and the temperature at the bottom of the crucible 30 can be measured.

Next, the details of each part will be further described.

The furnace body 14 has a four-layer structure in the embodiment shown in the figure, and includes the heat-resistant wall 32 as the innermost wall, the heat-insulating material layer 33, the support cylinder 34, and the heat-insulating material layer in this order from the inner layer side. 35. The outer side of the heat insulating material layer 35 is surrounded by an outer wall (not shown).

As shown in FIG. 2 and FIG. 3, the heat-resistant wall 32 is formed by joining six divided pieces 32 a into a ring-shaped heat-resistant member 32 b having a required height. As shown in FIG. 3, the heat-resistant members 32 b formed in a ring shape can be arranged so that the divided pieces 32 a of the ring-shaped heat-resistant members 32 b adjacent to each other are laminated in a circumferential direction and staggered from each other.

The heat-resistant member 32b is not particularly limited, but it is preferably made of alumina or zirconia having heat resistance to a temperature of about 2000 ° C.

The support cylinder 34 is disposed outside the heat-resistant wall 32 and is disposed at a distance from the heat-resistant wall 32. The support cylinder 34 is formed by stacking a plurality of annular members 34a having a required height into a cylindrical shape. The ring members 34a adjacent to each other may be fixed by a suitable connecting member (not shown). In addition, a support ring 34b having a portion protruding inward is inserted into the upper portion of the support cylinder 34 to support the cover 18 by the support ring 34b.

The support cylinder 34 is preferably a structure that functions as a structure, and is preferably made of alumina having heat resistance and excellent strength.

A heat-insulating material layer 33 is interposed between the heat-resistant wall 32 and the support cylinder 34. The heat-insulating material layer 33 is made of alumina fibers having a desired density, becomes porous, and is formed to have heat resistance and heat insulation properties.

In addition, the heat-insulating material layer 35 disposed outside the support cylinder 34 is formed by filling alumina fibers.

Next, the cover body 18 is formed by laminating a plate 18a in which alumina fibers are solidified at a desired density in the same manner as the heat insulating material layer 33. Therefore, in order to fill the strength, a reinforcing member 37 including a sapphire tube and the like having heat resistance is inserted into the laminated board.

The lid body 18 is considered to be made of high density zirconia or alumina, but the lithium tantalate single crystal manufacturing apparatus 10 of this embodiment is heated to a high temperature. Lids with high density, made of zirconia, and alumina will not be able to bear their own weight, which may cause problems such as deformation. This problem can be solved by making a lightweight cover body 18 in which alumina fibers are solidified, and filling the insufficient strength with a reinforcing member 37.

FIG. 4 is a diagram showing a specific structure of the heating element 20.

The heating element 20 of this embodiment is a heating element (trade name: KANTHAL Super) 20 formed by forming a resistance heating heating element including molybdenum disilicide (MoSi ₂ ) into a U-shape. As shown in FIG. 4, the four heating elements 20 are fixed to a frame-shaped support 38 and mounted on the furnace body 14. Specifically, as shown in FIG. 5, a long hole 40 is formed in the cover 18 to penetrate the heating element 20, and the heating element 20 is partially penetrated through the long hole 40. The heating element 20 surrounds the furnace body 14 from all directions. The position of the crucible 30 was arranged. Due to the high temperature, the heating element 20 penetrating the portion of the long hole 40 is formed in such a manner that a gap can be formed in the portion so that the heating element 20 does not directly contact the inner wall of the long hole 40.

The support 38 is formed in a suitable place (not shown) as fixed to the furnace body 14.

In addition, a space between the support 38 and the cover 18 is filled with a heat insulating material containing alumina fibers similar to those used for the heat insulating material layer 35, and a heat insulating material layer 41 is provided.

KANTHAL Super (trade name) containing molybdenum disilicide can be heated at a high temperature of about 1,850 ° C. Of course, the heating temperature can be adjusted by adjusting the power supplied to the heating element 20. In addition to KANTHAL Super (trade name), Keramax (trade name) heating elements can also be heated at high temperatures.

The manufacturing device 10 of lithium tantalate single crystal according to this embodiment is configured as described above, and tantalum can be performed in the atmosphere by the vertical Bridgeman (VB) method or the vertical temperature gradient solidification (VGF) method. Breeding of lithium acid single crystals. The crucible 30 uses a platinum crucible 30. Although it is different from Ir alone in the atmosphere, the crucible 30 can be prevented from being oxidized. On the other hand, it can be crystallized in an oxygen-rich atmosphere, so it can be used without Crystallization of high-quality lithium tantalate single crystals such as oxygen defects.

In the above-mentioned embodiment, for example, a resistance heating heating element is used as the heating element, and heating is performed by resistance heating. However, as the heating portion, a heating method by high-frequency induction heating may be used.

FIG. 6 is a schematic diagram of a manufacturing device 10 of lithium tantalate single crystal by a high-frequency induction heating method.

The furnace body 14 shown in FIG. 6 is slightly different from the one shown in FIG. 1 in the drawing, but is actually the same as the one shown in FIGS. 1 to 5.

The difference between this embodiment is that a high-frequency coil 44 is arranged on the outer periphery of the furnace body 14 and a heating element 46 heated by high-frequency induction heating is provided instead of the resistance heating element 20 in the foregoing embodiment. As the heating element 46, a heating element using a Pt-based alloy material, particularly a Pt-Rh-based alloy material can be used. As the crucible material used for cultivating the lithium tantalate single crystal by the VB method or the VGF method, the crucible made of platinum is preferably used as described above. However, as for the material of the heating element 46, more than crucible 30 can be used Pt-Rh-based alloy materials with a high Rh content of about 30wt% can be further endured. The manufacturing device 10 of lithium tantalate single crystal of this embodiment can prevent oxidation of the crucible 30 by the VB method or the VGF method in the atmosphere, and can perform high-quality tantalic acid without oxygen defects or the like. Breeding of lithium single crystals.

FIG. 7 shows the measurement range of the temperature distribution in the furnace for the growth of lithium tantalate single crystals in the manufacturing apparatus 10 by the high-frequency induction heating method. The measurement result is shown in FIG. 8 (A). FIG. 8 (B) is a partially enlarged view of FIG. 8 (A).

The measurement range is a range from 313 to 489 mm in height from a reference position. The position of the heating element 46 covers a height of 402 to 502 mm.

With the manufacturing apparatus 10 having the heat-resistant and heat-insulating structure, as shown in FIG. 8, a soaking zone having a melting temperature of 1650 ° C. in which lithium tantalate is sandwiched can be formed. It is known that such a soaking zone is located at a height of about 440 to 480 mm. In the soaking zone, there is a temperature gradient near 1650 ° C. This temperature gradient is used for crystallization. In addition, if the temperature of the crucible bearing 24 is moved up and down, the temperature of the moving position is measured even if the thermocouple 26 is moved up and down.

The crystal growth of the lithium tantalate single crystal by the VB method is based on the measured output of the high-frequency coil 44 (hereinafter, the output of the high-frequency coil 44 will be described, but in the case of resistance heating, the resistance heating heating body 20 The output of the heating unit) and the internal temperature of the furnace itself (hereinafter referred to as the temperature in the furnace), the high-frequency coil 44 is output with the required output, and the temperature distribution in the furnace as shown in FIG. 8 is used in advance. The temperature in the furnace rises. Then, the crucible 30 containing the seed crystal of lithium tantalate and the raw material of lithium tantalate is placed on the adapter 28, the crucible bearing 24 is raised, the crucible 30 is raised to the soaking zone, and the lithium tantalate is melted. By lowering the crucible bearing 24 and cooling the crucible 30 outside the furnace, the molten lithium tantalate can be solidified and crystallized to obtain a lithium tantalate single crystal.

After that, the temperature in the furnace can be lowered to a suitable temperature, the crucible can be raised into the furnace again, and the crystal annealing treatment can be performed as needed.

In order to take out the lithium tantalate single crystal from the crucible 30, the crucible 30 made of platinum is cut with a knife or the like to take out the crystal. The cut crucible 30 can be melted and reused. In addition, the crucible 30 can be made of platinum having a thickness of 0.5 mm or less (preferably 0.1 to 0.2 mm) to make it easy to cut.

When growing crystals of lithium tantalate single crystals by the VGF method, the output of the high-frequency coil 44 when heating the heating element 46 is grasped in advance so as to have a temperature distribution in the furnace as shown in FIG. 8.

In the crystal growth of lithium tantalate single crystal by the VGF method, the crucible 30 containing the seed crystals of lithium tantalate and the raw materials of lithium tantalate is placed on the adapter 28 to raise the crucible bearing 24 to make the crucible 30 is raised in advance to a height position which should be a soaking zone in the furnace. Next, the high-frequency coil 44 can be actuated with the required output, the temperature in the furnace can be raised to a temperature distribution as shown in FIG. 8, the lithium tantalate can be melted, and then the temperature in the furnace can be lowered to solidify the lithium tantalate. And crystallize to obtain lithium tantalate single crystal. When the VGF method is used, the crucible 30 is fixedly arranged at a required height position to increase and decrease the temperature in the furnace. Therefore, there is an advantage that annealing treatment can be performed simultaneously when the temperature decreases. In addition, since the temperature in the furnace is raised and lowered during the crystallization incubation, the temperature can be controlled finely and accurately, so that a higher quality lithium tantalate single crystal can be obtained.

FIG. 9 shows an example of the outline of the furnace temperature when the furnace temperature control is performed when the VGF method is used. In addition, the temperature control flow at that time is shown in FIG. 10. FIG. 11 is a graph showing the followability of the temperature in the furnace to the output of the high-frequency coil 44.

In step S1, seed crystals of lithium tantalate and raw materials of lithium tantalate are stored in the crucible 30, and the crucible 30 is raised to a predetermined position in the furnace (the position to be the above-mentioned soaking zone). The temperature in the furnace was room temperature.

In step S2, the output of the high-frequency coil 44 is relatively sharply increased, and the temperature in the furnace is rapidly increased until the temperature in the furnace becomes approximately 1295 ° C. The duration of this period is about 600 minutes. This can shorten the production time. Since the output is rapidly increased, the followability of the temperature in the furnace is low (Fig. 11).

In step S3, the output of the high-frequency coil 44 is fixed, the temperature in the furnace is kept constant, and the temperature in the furnace is made uniform. The time during this period is about 650 minutes.

Next, in step S4, the output of the high-frequency coil 44 is rapidly increased again to increase the temperature in the furnace to about 1500 ° C. before the seed temperature. The duration of this period is about 230 minutes. Since the temperature in the furnace has been made uniform in step S3, the follow-up of the temperature rise in the furnace to the output of the high-frequency coil 44 is high (FIG. 11).

Next, in step S5, the output of the high-frequency coil 44 is pushed down, and the temperature is gradually increased to the temperature in the furnace, that is, the temperature of the crucible 30 becomes the seed temperature. The time during this period is about 150 minutes. In this way, the temperature in the furnace can be gradually increased to prevent the temperature of the crucible 30 from exceeding the seeding temperature (about 1586 ° C).

Then, in step S6, the output of the high-frequency coil 44 is fixed, the temperature of the crucible 30 is fixed to 1586 ° C, and lithium tantalate of the raw material is melted and seeded. The duration of this period is about 180 minutes. In addition, since the temperature of the crucible 30 is measured at the bottom of the crucible 30 with the thermocouple 26, the temperature inside the crucible 30 is considered to rise to about 1650 ° C higher than that.

As described above, since the temperature of the crucible 30 is prevented from exceeding the seeding temperature (about 1586 ° C: the actual seeding temperature in the crucible is 1650 ° C), the temperature in the furnace is gradually increased in step S5. Therefore, the single crystallization of lithium tantalate can be performed with high accuracy and efficiency. In addition, since the crucible 30 is not excessively heated, an unfavorable condition such as softening and deformation of the crucible 30 made of platinum does not occur. In addition, the follow-up of the temperature rise in the furnace in steps S5 and S6 to the output of the high-frequency coil 44 is naturally high (FIG. 11).

In this way, a manufacturing apparatus capable of finely and accurately controlling temperature is manufactured, and the follow-up control of the temperature rise in the furnace is performed, whereby the platinum crucible can be used without being softened or deformed.

Moreover, it turned out that what is necessary is just to make the temperature of a platinum crucible about 50 degreeC lower than a platinum melting point (1768 degreeC).

That is, in the manufacturing apparatus of the present invention, in order not to soften or deform the crucible, it is only necessary to have a margin of 50 ° C from the melting point of the crucible.

Next, in step S7, the output of the high-frequency coil 44 is slightly lowered, and the temperature in the furnace is lowered. As a result, the temperature of the crucible 30 is gradually reduced to about 1425 ° C, and the molten lithium tantalate is solidified and crystallized. The time during this period is about 3010 minutes. The follow-up of the temperature rise in the furnace to the output of the high-frequency coil 44 in this step S7 is high (FIG. 11). In this step S7, an annealing process is also performed substantially.

Then, in step S8, the output of the high-frequency coil 44 is reduced sharply, the temperature in the furnace is lowered to room temperature, and crystallization is completed. The time of step S8 is about 2660 minutes. The follow-up of the temperature rise in the furnace in step S8 to the output of the high-frequency coil 44 is low (FIG. 11).

As described above, in the embodiment of the furnace temperature control shown in Figs. 9 and 10, in steps S1, S2, S3, and S8, the output of the high-frequency coil 44 changes, and the furnace temperature follows behind. However, steps S4 to S7 requiring precise temperature control, especially in steps S5 to S7, have high followability of the temperature in the furnace to the output change of the high-frequency coil 44. This means that in steps S5 to S7 that require precise temperature control, the required correct temperature control can be performed, and high-quality lithium tantalate single crystals can be grown. In addition, crystal growth can be performed without deforming the crucible 30. .

FIG. 12 is a photograph of a lithium tantalate single crystal obtained by using a 100% platinum crucible, using a high-frequency heating furnace shown in FIG. 7, and using the furnace temperature profile shown in FIG. 9 to crystallize by VGF method. .

FIG. 13 is a photograph of a lithium tantalate single crystal obtained by using a 100% platinum crucible in a resistance heating furnace shown in FIG. 1 and using the furnace temperature profile shown in FIG. 9 to crystallize by VGF method. In addition, the outline and control flow of the furnace temperature shown in FIG. 9 and FIG. 10 are examples and are not limited thereto.

As described above, in this embodiment, the temperature distribution in the furnace can be made uniform by using the VB method or the VGF method capable of reducing the temperature gradient, and the maximum temperature in the furnace can be reduced, so that it is not softened or deformed. A crucible made of platinum having a small melting point difference from lithium tantalate was used. Therefore, since the crucible made of platinum can be used, almost no crucible material is melted into the crystal, the temperature in the furnace can be precisely controlled, and high-quality lithium tantalate single crystal can be grown.

In addition, since lithium tantalate single crystals can be grown in an oxygen gas environment (in the atmosphere), as in the case of using a crucible made of iridium, there are advantages in that it is not necessary to introduce an inert gas, etc. At the same time as miniaturization, annealing can be easily performed.

Claims (17)

    A manufacturing device for lithium tantalate crystals, which is a manufacturing device for lithium tantalate crystals including a vertical Bridgmann furnace or a vertical temperature gradient solidification furnace, which is provided with a substrate and has heat resistance arranged on the substrate A cylindrical furnace body, a cover body plugging the furnace body, a heating body arranged in the furnace body, a crucible bearing penetrating the base body and arranged to move up and down freely, and arranged on the crucible bearing The crucible heated by the heating element is characterized in that the crucible is a crucible made of platinum.         For example, the apparatus for manufacturing a lithium tantalate crystal according to claim 1, wherein the crucible is a platinum crucible having a purity of 95% or more.         For example, the manufacturing device of the lithium tantalate crystal of claim 1 or 2 has a control unit that controls the heating of the crucible by the heating element so that the heating of the crucible by the heating element is lower than The crucible is heated at a temperature at which the crucible softens and deforms.         For example, the manufacturing device of lithium tantalate crystal of claim 1 or 2, wherein the inner wall of the furnace body is formed as a plurality of heat-resistant walls having a ring-shaped heat-resistant member having a required height, and the ring-shaped heat-resistant member is plural. The divided pieces are joined to form a ring shape.         The manufacturing device of the lithium tantalate crystal according to claim 1 or 2, wherein the heating element is a resistance heating heating element.     For example, the device for manufacturing a lithium tantalate crystal according to claim 5, wherein the resistance heating heating system uses MoSi ₂ as a resistance heating heating element.     The manufacturing device of the lithium tantalate crystal according to claim 1 or 2, wherein the heating system uses a high-frequency induction heating heating element.         The manufacturing device of lithium tantalate crystal according to claim 7, wherein the heating system is made of Pt-Rh alloy by high frequency induction heating.         The manufacturing device of lithium tantalate crystal according to claim 4, wherein in the furnace body, a support cylinder containing a heat-resistant material is arranged outside the heat-resistant wall, and a space between the heat-resistant wall and the support cylinder is arranged. A heat insulation material is provided, and the cover system is supported by the supporting cylinder.         For example, the device for manufacturing a lithium tantalate crystal according to claim 1 or 2, wherein the cover system is formed of a heat insulating material, and a reinforcing member is arranged in the heat insulating material.         A method for manufacturing lithium tantalate crystals, which is a method for manufacturing lithium tantalate crystals using a vertical Bridgman method or a vertical temperature gradient solidification method, and a crucible containing raw materials containing lithium tantalate is arranged in a furnace In the body, the crucible is heated by a heating element arranged in the furnace body to melt the raw material, and then the temperature of the crucible is lowered to obtain crystals of lithium tantalate, which is characterized in that a crucible made of platinum is used in the crucible. When the crucible is heated by the heating element, the crucible is heated at a temperature lower than a temperature at which the crucible is softened and deformed.         The method for producing a lithium tantalate crystal according to claim 11, wherein a platinum crucible having a purity of 95% or more is used in the crucible.         For example, the method for manufacturing a lithium tantalate crystal according to claim 11 or 12, wherein when the crucible is heated by the heating element, when the temperature of the crucible reaches a temperature near the seed temperature, the heating by the heating element is moderated. Proceed to prevent the temperature of the crucible from exceeding the seeding temperature.         For example, the manufacturing method of lithium tantalate crystal according to claim 13 includes the following steps: when the crucible is heated by the heating element, before the temperature near the seed temperature is reached, temporarily fixing the By heating, the temperature inside the furnace body is kept constant, and the temperature inside the furnace body is made uniform.         For example, the method for manufacturing a lithium tantalate crystal according to claim 13, wherein when the temperature of the crucible reaches the seeding temperature, seeding is performed at a time required to maintain the temperature.         For example, the method for manufacturing lithium tantalate crystal according to claim 13, wherein after the seed crystal addition is completed, the temperature inside the furnace body is gradually lowered to solidify the lithium tantalate for crystallization.         The method for producing a lithium tantalate crystal according to claim 11, using the device for producing a lithium tantalate crystal according to any one of claims 1 to 10.