Apparatus and method for growing oxide single crystals

Abstract

To provide an apparatus and method for growing an oxide single crystal, using an oxide crucible formed of the same material as a raw material melt as storing and holding means of the raw material melt.SOLUTION: An apparatus for growing an oxide single crystal includes: an oxide crucible 1 constituted of an oxide crystal material and capable of storing and holding a raw material melt 10; a high frequency induction coil 2 provided around a side wall of the oxide crucible; and a cylindrical metal heater 3 built in the oxide crucible, having a cylindrical shape obtained by opening an upper end part 3b fixed by fixing means provided above the oxide crucible and closing a lower end part 3a arranged to separate upward from an inner bottom surface 1a of the oxide crucible and inductively heated by the high frequency induction coil. A lower end part 2a of the high frequency induction coil is arranged below from the lower end part 3a of the cylindrical metal heater, and prevention of the oxide crucible and cylindrical metal heater from being deformed has an effect capable of repeatedly and stably an oxide single crystal having same quality.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an improvement in a growth apparatus and a growth method for growing an oxide single crystal such as lithium tantalate by the pulling method.

Background Art

[0002] As a method for growing an oxide single crystal, a crucible filled with a raw material that becomes an oxide single crystal is heated to a high temperature to melt the raw material. After bringing a seed crystal into contact with the molten raw material surface in the crucible from above, the seed crystal is rotated and raised to grow an oxide single crystal having the same orientation as the seed crystal (also referred to as the Chochralski method). This pulling method is widely used.

[0003] In an apparatus for growing an oxide single crystal by the pulling method, as shown in FIG. 7, a high-frequency induction coil 101 is arranged around the side wall of a crucible 100. By passing a high-frequency current through the high-frequency induction coil 101, an eddy current is generated in the crucible 100, and thereby the crucible 100 generates heat and the raw material melts. Further, as the pulling progresses, the upper part of the oxide single crystal is cooled through a seed rod (crystal pulling axis) 102. However, when the heating element is only the crucible 100, the temperature distribution in the single crystal during growth becomes large. Therefore, a metal ring-shaped reflector 103 is arranged at the open end of the crucible 100, and a metal after-heater 104 is arranged at the upper end of the crucible 100. In FIG. 7, reference numeral 105 denotes a seed crystal, reference numeral 106 denotes a molten raw material, reference numerals 107 and 108 denote heat insulating materials, reference numeral 109 denotes a CP crucible (porous alumina crucible), and reference numeral 110 denotes a heat insulating crucible stand.

[0004] By the way, in recent years, the market for oxide single crystals, particularly lithium tantalate, as surface acoustic wave device materials has been expanding, and the pulling length and diameter of single crystals have gradually increased in order to ensure production volume. Along with this increase in size, the crucibles used for crystal growth have become larger.

[0005] Furthermore, since crucibles must be conductive to conduct high-frequency currents, and also have a high melting point to withstand high temperatures and do not degrade in an oxidizing atmosphere in order to melt the crystal raw materials, crucibles used for crystal growth are often made of precious metals such as iridium, platinum, and rhodium, or their alloys.

[0006] However, when growing single crystals using a precious metal crucible, there was a problem in that the crucible deformed. This is because the cylindrical precious metal crucible 100 shown in Figure 8(A) expands as shown in Figure 8(B) when the raw material is melted, and when it cools, the solidified part of the raw material molten liquid 106 stretches and deforms as shown in Figure 8(C), which is due to the difference in expansion rates between the precious metal crucible and the oxide molten liquid.

[0007] Therefore, Patent Document 1 proposes a crucible of precious metal in which a reinforced precious metal plate made of a material in which zirconium oxide or the like is added to a precious metal of the same material as the crucible is attached to the outer circumference of the crucible body for reinforcement, and Patent Document 2 proposes a growth device in which the periphery of the crucible is covered with a cylindrical molded insulating material such as alumina to suppress deformation of the crucible. Furthermore, Patent Document 3 proposes a crucible for single crystal growth in which a ring-shaped frame is fitted to the outer circumference of the side wall of the crucible to prevent deformation, and Patent Document 4 proposes an iridium crucible in which the thickness of the plate on the bottom side of the crucible is thinner than the thickness of the plate in the side direction to allow deformation to escape to the bottom side.

[0008] However, even with any of the countermeasures proposed in Patent Documents 1 to 4, it was difficult to prevent deformation of the crucible, and in particular, the amount of deformation of the crucible becomes large when growing large oxide single crystals, so a more effective countermeasure was needed. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 10-338593 [Patent Document 2] Japanese Patent Publication No. 2020-164339 [Patent Document 3] Japanese Patent Publication No. 2019-112240 [Patent Document 4] Japanese Patent Publication No. 2012-250874 [Overview of the project] [Problems that the invention aims to solve]

[0010] As long as a precious metal crucible is used as a means of storing and holding the molten raw material, deformation cannot be suppressed, so an alternative means of storing and holding the molten raw material is needed.

[0011] This invention was made in view of these problems, and its objective is to provide an apparatus and method for growing oxide single crystals using an oxide crucible made of the same material as the raw material molten as a means of storing and holding the raw material molten, as an alternative to a precious metal crucible. [Means for solving the problem]

[0012] In other words, the first invention according to the present invention is, By the Lifting Law One of the following: lithium niobate single crystal, lithium tantalate single crystal, or yttrium aluminum garnet single crystal In an apparatus for growing oxide single crystals, the above oxides An oxide crucible made of materials and capable of storing and holding molten raw materials, A high-frequency induction coil is provided around the side wall of the above-mentioned oxide crucible, A cylindrical metal heater is incorporated into the oxide crucible, has a cylindrical shape with an open upper end and a closed lower end, and is fixed at the upper end by fixing means provided above the oxide crucible, with the lower end positioned above the inner bottom surface of the oxide crucible, and is inductively heated by the high-frequency induction coil. and, A ceramic container made of alumina, zirconia, magnesia, or calcia that covers the outer bottom surface of the oxide crucible, or a ceramic crucible made of alumina, zirconia, magnesia, or calcia that covers the outer bottom surface and the surrounding side walls of the oxide crucible. Equipped with, Furthermore, the lower end of the high-frequency induction coil is located below the lower end of the cylindrical metal heater.

[0013] Furthermore, the second invention according to the present invention is, First invention In the oxide single crystal growth apparatus described above, The cylindrical metal heater is made of any one of platinum, iridium, rhodium, or an alloy thereof. Let's assume .

[0014] Next, the 3 invention according to the present invention is In a method for growing an oxide single crystal using the growth apparatus described in the first invention, One of the following: lithium niobate single crystal, lithium tantalate single crystal, or yttrium aluminum garnet single crystal a crystal raw material is charged into an oxide crucible incorporating a cylindrical metal heater, and the cylindrical metal heater is induction-heated by a high-frequency induction coil to melt the crystal raw material existing inside the cylindrical metal heater and the crystal raw material existing outside the cylindrical metal heater, and a seed crystal is brought into contact with the raw material melt surface in the cylindrical metal heater, and an oxide single crystal is grown by the pulling method.

Advantages of the Invention

[0015] Since an oxide crucible made of the same material as the raw material melt is applied as the storage and holding means for the raw material melt, deformation of the crucible can be suppressed, and since the lower end of the high-frequency induction coil is located below the lower end of the cylindrical metal heater, the lower end of the cylindrical metal heater is also induction-heated, whereby when growing an oxide single crystal, the cylindrical metal heater is sandwiched between the raw material melt existing inside the cylindrical metal heater and the raw material melt existing outside the cylindrical metal heater, so that thermal deformation of the cylindrical metal heater can also be suppressed.

[0016] Therefore, even if crystal growth is repeated, it is possible to prevent changes in growth conditions, and thus there is an effect that oxide single crystals of the same quality can be repeatedly and stably grown.

Brief Description of the Drawings

[0017] [Figure 1] Configuration explanatory diagram of the growth apparatus according to the present invention. [Figure 2] Explanatory diagram showing an example of fixing means provided above the oxide crucible. [Figure 3] An explanatory diagram of a cultivation device according to the first embodiment and a cultivation method using this device. [Figure 4] An explanatory diagram showing the manufacturing process of the cultivation device according to the second embodiment. [Figure 5] An explanatory diagram showing the manufacturing process of the cultivation device according to the second embodiment. [Figure 6] An explanatory diagram of the cultivation device according to the second embodiment. [Figure 7] An explanatory diagram of a conventional growth method using a growth apparatus that utilizes a precious metal crucible as a means of storing and holding the molten raw material. [Figure 8] Figure 8(A) is a cross-sectional view of a precious metal crucible, Figure 8(B) is a cross-sectional view of the precious metal crucible during the melting of the added crystal raw materials, and Figure 8(C) is a cross-sectional view of the precious metal crucible after it has deformed due to the solidification of the molten raw materials. [Modes for carrying out the invention]

[0018] Embodiments of the present invention will be described in detail below with reference to the drawings.

[0019] 1. Conventional cultivation equipment and cultivation methods (1) Conventional cultivation device and cultivation method using this device As a conventional crystal growth apparatus, as described above, a device is known that includes a chamber 200 (see Figure 7) containing a CP crucible (porous alumina crucible) 109, a crucible 100, an insulating crucible stand 110, a ring-shaped reflector 103, an afterheater 104, insulating materials 107 and 108, a seed rod (crystal pulling axis) 102, and a high-frequency induction coil 101. As for the crucible 100 used for high-temperature crystal growth, crucibles of high-melting-point metals such as tungsten and tantalum, precious metal crucibles such as platinum, rhodium and iridium, and non-metallic crucibles such as alumina, magnesia, carbon and PBN (Pyrolytic Boron Nitride) are known.

[0020] By the way, lithium niobate (LiNbO3: hereafter abbreviated as LN), lithium tantalate (LiTaO3: hereafter abbreviated as LT), yttrium aluminum garnet (Y3Al5O 12When growing oxide single crystals such as YAG (hereinafter abbreviated as YAG), tungsten, tantalum, and carbon, which are easily oxidized, cannot be used because an oxygen-containing growth atmosphere is required. Similarly, alumina and magnesia cannot be used because they react with the oxide melt, and PBN is expensive and difficult to use in creating large crucibles.

[0021] For this reason, when growing oxide single crystals, crucibles made of precious metals such as platinum, rhodium, and iridium are used, as these metals are not oxidized and do not crack, preventing the leakage of the raw material molten metal.

[0022] (2) Conventional challenges However, as shown in Figures 8(A) to (C), the precious metal crucible undergoes thermal expansion during the melting of the raw materials, and deforms when the residue of the molten raw materials solidifies due to the different thermal expansion rates of the oxide and the precious metal. This deformation causes a change in the heat generation state in the case of high-frequency induction heating, which alters the growth conditions, and as the deformation of the crucible progresses, it becomes impossible to obtain single crystals.

[0023] 2. The cultivation apparatus and cultivation method of the present invention The crystal growth apparatus of the present invention, which uses the pulling method (Czochralski method), is used for producing oxide single crystals such as LN, LT, and YAG grown in air or an oxygen-containing inert gas atmosphere. The Czochralski method is a method of growing a single crystal with the same orientation as the seed crystal by immersing the tip of a single crystal, usually processed into a rod shape and cut according to a certain crystal orientation, into a raw material molten with the same composition, and gradually pulling it up while rotating it.

[0024] To solve the problems of the past, the inventors have found an apparatus and method for growing oxide single crystals using an oxide crucible made of the same material as the raw material molten, as a means of storing and holding the raw material molten, as an alternative to a deformable precious metal crucible.

[0025] In other words, the cultivation device according to the present invention is as shown in Figure 1, oxides An oxide crucible 1 made of materials and capable of storing and holding a raw material melt 10, A high-frequency induction coil 2 is provided around the side wall of the oxide crucible 1, A cylindrical metal heater 3 is incorporated into the oxide crucible 1, has a cylindrical shape with an open upper end 3b and a closed lower end 3a, and is fixed at the upper end 3b by fixing means (not shown) provided above the oxide crucible 1, with the lower end 3a positioned above the inner bottom surface 1a of the oxide crucible 1, and is inductively heated by the high-frequency induction coil 2. and, A ceramic container 4 made of alumina, zirconia, magnesia, or calcia covers the outer bottom surface of the oxide crucible 1, or a ceramic crucible made of alumina, zirconia, magnesia, or calcia covers the outer bottom surface and the surrounding side walls of the oxide crucible 1. It is equipped with, and The lower end portion 2a of the high-frequency induction coil 2 is located below the lower end portion 3a of the cylindrical metal heater 3.

[0026] (1) A growing apparatus according to the first embodiment and a growing method using this apparatus (1-1) Cultivation device according to the first embodiment As shown in Figure 3, the growth apparatus according to the first embodiment mainly consists of an insulating outer cylinder 13, which is fixed at the bottom by a support base 11 and houses the growth apparatus according to the present invention (equipped with an oxide crucible 1 and a cylindrical metal heater 3), excluding the high-frequency induction coil 2, and has an opening 12 on the upper side for a seed rod (crystal pulling shaft) 20; a heater fixing rod 14 (see fixing means in Figure 2) attached to the approximate center of the insulating outer cylinder 13 and holding the upper end 3b of the cylindrical metal heater 3; a ring-shaped reflector 15 placed on the upper end 3b of the cylindrical metal heater 3 held by the heater fixing rod 14; an after heater 16 placed on the ring-shaped reflector 15; and a rod-shaped seed crystal 21 attached to the lower end of the seed rod (crystal pulling shaft) 20. In Figure 3, reference numeral 4 denotes the outer bottom surface 1b of the oxide crucible 1. the above This shows a ceramic container.

[0027] (1-2) Cultivation method according to the first embodiment Crystallized raw material is placed in an oxide crucible 1 incorporating a cylindrical metal heater 3, and the cylindrical metal heater 3 is induction heated by a high-frequency induction coil 2 to melt the crystallized raw material inside the cylindrical metal heater 3 and the crystallized raw material outside the cylindrical metal heater 3.

[0028] Next, a seed crystal 21 is brought into contact with the surface of the molten raw material 10 inside the cylindrical metal heater 3, and then the seed rod (crystal pulling shaft) 20 is rotated and raised to grow an oxide single crystal 30.

[0029] (1-3) Effects of the cultivation method according to the first embodiment According to the growth method of the first embodiment, an oxide crucible 1 made of the same material as the raw material molten is used as a means of storing and holding the raw material molten, so deformation of the crucible can be suppressed. Furthermore, since the lower end 2a of the high-frequency induction coil 2 is located below the lower end 3a of the cylindrical metal heater 3, the lower end 3a of the cylindrical metal heater 3 is also induction heated. As a result, when growing oxide single crystals, the cylindrical metal heater 3 is sandwiched between the raw material molten 10 inside the cylindrical metal heater 3 and the raw material molten 10 outside the cylindrical metal heater 3, so thermal deformation of the cylindrical metal heater 3 can also be suppressed.

[0030] Therefore, since it is possible to prevent changes in growth conditions even when crystal growth is repeated, it has the effect of being able to repeatedly and stably grow oxide single crystals of the same quality.

[0031] (2) A growth apparatus according to the second embodiment and a method for manufacturing the growth apparatus. (2-1) Cultivation device according to the second embodiment As shown in Figure 6, the growth apparatus according to the second embodiment mainly consists of an insulating outer cylinder 13, which is fixed at the bottom by a support base 11 and houses the growth apparatus according to the present invention (equipped with an oxide crucible 1 and a cylindrical metal heater 3), excluding the high-frequency induction coil 2, and has an opening 12 on the upper side for a seed rod (crystal pulling axis) not shown; a heater fixing rod 14 attached to the approximate center of the insulating outer cylinder 13 and holding the upper end 3b of the cylindrical metal heater 3; a ring-shaped reflector 15 placed on the upper end 3b of the cylindrical metal heater 3 held by the heater fixing rod 14; an after heater 16 placed on the ring-shaped reflector 15; and a rod-shaped seed crystal (not shown) attached to the lower end of the seed rod (crystal pulling axis) not shown. In Figure 6, reference numeral 40 denotes the outer bottom surface 1b and the surrounding side wall of the oxide crucible 1. It is composed of one of the following: alumina, zirconia, magnesia, or calcia. This shows a ceramic container (CP crucible).

[0032] Furthermore, this growth apparatus allows for the growth of oxide single crystals in the same manner as the growth method according to the first embodiment, and also has the effect of repeatedly and stably growing oxide single crystals of the same quality, similar to the growth method according to the first embodiment.

[0033] (2-2) Method for manufacturing a growth apparatus according to the second embodiment The cultivation apparatus according to the second embodiment can be manufactured, for example, as follows.

[0034] First, as shown in Figure 4, the ceramic crucible (CP crucible) 40 incorporated inside the heat-insulating outer cylinder 13 leaves an upper space 41. oxides Add material 10a. oxides As for material 10a oxides Material powder or oxides A material block is shown as an example.

[0035] Next, a cylindrical metal heater 3, with its upper end 3b open and its lower end 3a closed, is incorporated into the upper space 41 of the ceramic crucible (CP crucible) 40, and the upper end 3b of the cylindrical metal heater 3 is fixed by a heater fixing rod 14 (see fixing means in Figure 2) attached to approximately the center of the heat-insulating outer cylinder 13.

[0036] Then, as shown in Figure 5, in the upper space 41 of the ceramic crucible (CP crucible) 40 into which the cylindrical metal heater 3 is incorporated oxides Material 10a is added to the inside of the cylindrical metal heater 3 and the upper space 41 of the ceramic crucible (CP crucible) 40. oxides Fill with material 10a.

[0037] Next, as shown in Figure 6, a ring-shaped reflector 15 is placed on the upper end 3b of the cylindrical metal heater 3, which is held by the heater fixing rod 14, and an afterheater 16 is placed on the ring-shaped reflector 15.

[0038] Then, the cylindrical metal heater 3 is inductively heated by the high-frequency induction coil 2 provided around the side wall of the ceramic crucible (CP crucible) 40, and the inside of the cylindrical metal heater 3 oxides Material 10a and the vicinity of the side wall and lower end 3a of the cylindrical metal heater 3 oxides The material 10a is melted to form a raw material molten liquid 10, and the portion away from the side wall of the cylindrical metal heater 3 and the portion away from the lower end 3a oxides A growth apparatus according to the second embodiment can be manufactured by flowing molten raw material 10 between materials 10a to form a continuous oxide layer 1c, and then forming an oxide crucible 1 having the oxide layer 1c on its inner surface and capable of storing and holding the molten raw material 10.

[0039] Furthermore, in the growth apparatus according to the first embodiment, as shown in Figure 3, a ceramic container 4 is used to cover the outer bottom surface 1b of the oxide crucible 1, and the growth apparatus cannot be manufactured using the manufacturing method that uses the ceramic crucible (CP crucible) 40. In such cases, oxides Material powder or oxides It is possible to manufacture the growth apparatus according to the first embodiment by applying the above manufacturing method after pressure molding a block of material into the shape of an oxide crucible as shown in Figure 3, and then housing a structure in which the ceramic container 4 is incorporated into the bottom side of the molded body inside the heat-insulating outer cylinder 13. At this time, it is necessary to set the wall thickness of the crucible to be pressure molded to be large so that the entire wall does not melt when the cylindrical metal heater 3 is induction heated.

[0040] (3) Constituting the oxide crucible oxides material The above oxide layer 1c is having the inner surface and oxides Regarding the oxide crucible 1 composed of the material, the entire crucible does not need to be composed of a single crystal. It is preferable that the entire crucible be composed of a sintered body or a polycrystalline body, but it may be partially in powder form. In the case where a part of the oxide crucible is in powder form... including , providing the aforementioned ceramic container for holding the powder. required Furthermore, the oxide layer 1c of the oxide crucible 1 is separated from the oxide layer 1c. oxides The unmelted portion of the material functions similarly to the insulating material 108 and insulating crucible stand 110 in the conventional growth apparatus shown in Figure 7.

[0041] Furthermore, the ceramic container covering the outer bottom surface 1b of the oxide crucible 1, or the ceramic crucible covering the outer bottom surface 1b and the surrounding side walls of the oxide crucible 1, may be made of sintered refractories such as alumina, zirconia, magnesia, or calcia. Listed .

[0042] (4) Metal heater The shape of the metal heater, with an open upper end and a closed lower end, can be arbitrary as long as high-frequency induction heating is possible. However, when growing high-quality crystals using the Czochralski method, it is desirable that the raw material melt has rotational symmetry with respect to the seed crystal. For this reason, the metal heater also preferably has a rotationally symmetrical shape and is required to be cylindrical.

[0043] Furthermore, the metal heater is preferably made of a material that does not oxidize in an oxygen-containing atmosphere and does not crack, and is capable of high-frequency heating. Specifically, it is desirable to make it from platinum, iridium, rhodium, or alloys thereof.

[0044] Furthermore, as a means of fixing the upper end of the metal heater, an example is the heater fixing rod 14 (see fixing means in Figure 2) attached to approximately the center of the heat-insulating outer cylinder 13 shown in Figure 3. The upper end of the metal heater is fixed by passing it through the rod 14, and it is preferable that there be two to six heater fixing rods 14.

[0045] Furthermore, it is preferable that the ring-shaped reflector placed on the upper end of the metal heater, and the afterheater placed on the ring-shaped reflector, be made of the same material as the metal heater. [Examples]

[0046] The embodiments of the present invention will be described in detail below with reference to comparative examples (conventional examples).

[0047] [Example 1] 1. Manufacturing of the growth apparatus according to Example 1 Inside the ceramic crucible (CP crucible) 40 with an inner diameter of 270 mm and an internal height of 340 mm, which is incorporated into the heat-insulating outer cylinder 13 shown in Figure 4, lithium tantalate powder is placed, leaving an upper space 41. oxides Material 10a was added. Furthermore, the above ceramic crucible (CP crucible) 40 is composed of one of the following: alumina, zirconia, magnesia, or calcia.

[0048] Next, an iridium cylindrical metal heater 3, with an inner diameter of 170 mm, a height of 170 mm, and a thickness of 2 mm, with an open upper end 3b and a closed lower end 3a, was incorporated into the upper space 41 of the ceramic crucible (CP crucible) 40. The upper end 3b of the cylindrical metal heater 3 was then fixed by a heater fixing rod 14 attached to approximately the center of the heat-insulating outer cylinder 13.

[0049] Then, as shown in Figure 5, lithium tantalate powder is placed in the upper space 41 of the ceramic crucible (CP crucible) 40 into which the cylindrical metal heater 3 is incorporated. oxides Material 10a is added, and lithium tantalate powder is placed inside the cylindrical metal heater 3 and in the upper space 41 of the ceramic crucible (CP crucible) 40. oxides Material 10a was filled in.

[0050] Next, as shown in Figure 6, a ring-shaped reflector 15 was placed on the upper end 3b of the cylindrical metal heater 3, which was held by the heater fixing rod 14, and an afterheater 16 was placed on the ring-shaped reflector 15.

[0051] Then, the cylindrical metal heater 3 is inductively heated by the high-frequency induction coil 2 provided around the side wall of the ceramic crucible (CP crucible) 40, and the lithium tantalate powder inside the cylindrical metal heater 3 ( oxides Materials) 10a and lithium tantalate powder near the side wall and lower end 3a of the cylindrical metal heater 3 ( oxides Material) 10a is melted to make raw material melt 10, and lithium tantalate powder is removed from the portion away from the side wall of the cylindrical metal heater 3 and the portion away from the lower end 3a. oxides A continuous oxide layer 1c was formed by flowing molten raw material 10 between the material 10a, and an oxide crucible 1 having the oxide layer 1c on its inner surface and capable of storing and holding the molten raw material 10 was formed to manufacture the growth apparatus according to Example 1.

[0052] Furthermore, lithium tantalate powder ( oxides When melting material 10a to form oxide layer 1c, the input power of the high-frequency induction coil 2 is set 10% higher than during the growth stage below in order to increase the amount of molten material on the outside of the cylindrical metal heater 3. This allows lithium tantalate powder ( oxides The raw material molten liquid flows into the gap between the materials 10a, forming a continuous oxide layer 1c.

[0053] 2. Growth of lithium tantalate single crystals (1) Next, a seed rod (crystal pulling axis) with a seed crystal (not shown) attached to its tip was lowered through the opening 12 (see Figure 6) of the heat-insulating outer cylinder 13, and crystal growth was performed by the pulling method (Czochralski method), and a lithium tantalate single crystal with a diameter of 4 inches and a straight body length of approximately 50 mm was grown.

[0054] (2) After growing the lithium tantalate single crystal described above, lithium tantalate powder (crystal material) was placed into an oxide crucible 1 incorporating a cylindrical metal heater 3, and the cylindrical metal heater 3 was inductively heated by a high-frequency induction coil 2 to melt the lithium tantalate powder (crystal material) present inside the cylindrical metal heater 3 and the lithium tantalate powder (crystal material) present outside the cylindrical metal heater 3. Furthermore, the lithium tantalate powder introduced into the oxide crucible 1 is referred to as the lithium tantalate powder (crystal raw material) and is distinguished from the lithium tantalate powder (oxide material) 10a used in the manufacturing stage of the growth apparatus.

[0055] Next, a seed rod (crystal pulling axis) with a seed crystal attached was lowered through opening 12, and crystal growth was performed using the pulling method (Czochralski method). As described above, a lithium tantalate single crystal with a diameter of 4 inches and a straight body length of approximately 50 mm was grown.

[0056] Then, after repeating the same crystal growth process 20 times, we were able to grow lithium tantalate single crystals of the same quality, with a diameter of 4 inches and a straight body length of approximately 50 mm, in 18 of the trials.

[0057] [Comparative Example (Conventional Example)] Using the conventional growth apparatus shown in Figure 7, and employing a crucible 100 made of iridium with a diameter of 170 mm and a height of 170 mm, a lithium tantalate single crystal with a diameter of 4 inches and a straight body length of approximately 50 mm was grown using the pulling method (Czochralski method).

[0058] Then, similar to Example 1, when the crystal growth process was repeated 20 times, lithium tantalate single crystals of the same quality were obtained 11 times, and no single crystals were obtained from the 13th time onward.

[0059] This was because the crucible 100 had become significantly deformed after the 13th use. [Industrial applicability]

[0060] According to the present invention, oxide single crystals of the same quality can be repeatedly and stably grown, and therefore has industrial applicability as an apparatus for growing oxide single crystals such as lithium tantalate single crystals used as surface acoustic wave device materials. [Explanation of symbols]

[0061] 1. Oxide Crucible 1a Inner bottom surface 1b Outer bottom surface 1c oxide layer 2. High-frequency induction coil 2a Bottom end 3. Cylindrical metal heater 3a Bottom end 3b Upper end 4. Ceramic container 10 Raw material melt 10a Oxide materials 11 Support stand 12 aperture 13. Insulated outer cylinder 14. Rods for fixing the heater 15 Ring-shaped reflector 16 Afterheater 20 Seed rods (crystal pulling axes) 21 Seed Crystal 30 Oxide single crystals 40 Ceramic Crucibles 41 Upper space 100 Crucible 101 High-frequency induction coil 102 Seed rod (crystal pulling axis) 103 Ring-shaped reflector 104 Afterheater 105 Seed Crystal 106 Raw material melt 107 Insulation 108 Insulation 109 CP Crucible (Porous Alumina Crucible) 110 Insulated Crucible Stand

Claims

1. In an apparatus for growing one of the following oxide single crystals by the pulling method: lithium niobate single crystal, lithium tantalate single crystal, or yttrium aluminum garnet single crystal, An oxide crucible composed of the above oxide material and capable of storing and holding the raw material melt, A high-frequency induction coil is provided around the side wall of the above-mentioned oxide crucible, A cylindrical metal heater is incorporated into the oxide crucible, has a cylindrical shape with an open upper end and a closed lower end, and is fixed at the upper end by fixing means provided above the oxide crucible, with the lower end positioned above the inner bottom surface of the oxide crucible, and is inductively heated by the high-frequency induction coil. A ceramic container made of alumina, zirconia, magnesia, or calcia covers the outer bottom surface of the oxide crucible, or a ceramic crucible made of alumina, zirconia, magnesia, or calcia covers the outer bottom surface and the surrounding side walls of the oxide crucible. An apparatus for growing oxide single crystals, characterized in that the lower end of the high-frequency induction coil is located below the lower end of the cylindrical metal heater.

2. The apparatus for growing oxide single crystals according to claim 1, characterized in that the cylindrical metal heater is made of platinum, iridium, rhodium, or an alloy thereof.

3. A method for growing an oxide single crystal of any of lithium niobate, lithium tantalate, or yttrium aluminum garnet using the growth apparatus described in claim 1, A method for growing an oxide single crystal, characterized by introducing crystalline raw material into an oxide crucible incorporating a cylindrical metal heater, inductively heating the cylindrical metal heater with a high-frequency induction coil to melt the crystalline raw material present inside the cylindrical metal heater and the crystalline raw material present outside the cylindrical metal heater, and growing an oxide single crystal by a pulling method while bringing a seed crystal into contact with the molten raw material surface inside the cylindrical metal heater.

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