Apparatus and method for growing oxide single crystals

Abstract

To provide an apparatus and a 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, inductively heated by the coil and including a lower end part 3a fitted to an inner bottom surface 1a of the oxide crucible. A lower end part 2a of the coil is arranged above from the lower end part 3a of the cylindrical metal heater; the lower end part 2a of the coil positioned above from the lower end part 3a of the cylindrical metal heater and the lower end part 3a having a structure preventing induction heating can stably fix the cylindrical metal heater in the oxide crucible, and prevention of the oxide crucible and cylindrical metal heater from being deformed has an effect capable of repeatedly and stably growing an oxide single crystal having same quality.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to improvements 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 raw material melt 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 disposed 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 disposed at the open end of the crucible 100, and a metal after-heater 104 is disposed at the upper end of the crucible 100. In FIG. 7, reference numeral 105 denotes a seed crystal, reference numeral 106 denotes a raw material melt, 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, In an apparatus for growing oxide single crystals by the pulling method, 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, The system includes a cylindrical metal heater that is incorporated into the oxide crucible, is inductively heated by the high-frequency induction coil, and whose lower end is inserted into the inner bottom surface of the oxide crucible. Furthermore, the lower end of the high-frequency induction coil is located above the lower end of the cylindrical metal heater.

[0013] Furthermore, the second invention according to the present invention is, In the oxide single crystal growth apparatus described in the first invention, The cylindrical metal heater is characterized in that the lower opening is closed or a ring-shaped flat portion is formed in the lower opening. The third invention is, In the oxide single crystal growth apparatus described in the first or second invention, The oxide single crystal is any one of a lithium niobate single crystal, a lithium tantalate single crystal, and a yttrium aluminum garnet single crystal, and is characterized in that The fourth invention is In the oxide single crystal growth apparatus according to any one of the first to third inventions, The cylindrical metal heater is made of any one of platinum, iridium, rhodium, or an alloy thereof, and is characterized in that The fifth invention is In the oxide single crystal growth apparatus according to any one of the first to fourth inventions, It is characterized by including a ceramic container covering the outer bottom surface of the oxide crucible, or a ceramic crucible covering the outer bottom surface and the peripheral side wall of the oxide crucible.

[0014] Next, the sixth invention according to the present invention is In a method for growing an oxide single crystal using the growth apparatus according to the first invention, A crystal raw material is introduced into an oxide crucible incorporated with 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 and outside the cylindrical metal heater, and a seed crystal is brought into contact with the raw material melting surface in the cylindrical metal heater, and an oxide single crystal is grown by a pulling method. It is characterized by this.

Effect of the Invention

[0015] According to the oxide single crystal growth apparatus according to the present invention, Since the lower end portion of the high-frequency induction coil is located above the lower end portion of the cylindrical metal heater and the lower end portion of the cylindrical metal heater is difficult to be induction-heated, the lower end portion of the cylindrical metal heater can be inserted into the inner bottom surface of the oxide crucible, and the cylindrical metal heater can be stably fixed in the oxide crucible.

[0016] In addition, 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, it is possible to suppress deformation of the crucible. Furthermore, since the cylindrical metal heater at the site excluding the lower end portion inserted into the inner bottom surface of the oxide crucible and its vicinity is induction-heated, 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, and it is also possible to suppress thermal deformation of the cylindrical metal heater.

[0017] Therefore, even if crystal growth is repeated, it is possible to prevent changes in the growth conditions due to fluctuations in the fixed cylindrical metal heater or deformation of the crucible, etc., and it has the effect of enabling repeated and stable growth of oxide single crystals of the same quality.

Brief Description of the Drawings

[0018] [Figure 1] Configuration explanatory drawing of the growth apparatus according to the present invention. [Figure 2] Explanatory drawing of the growth apparatus according to the first embodiment and the growth method using this apparatus. [Figure 3] Explanatory drawing of the growth apparatus according to a modification of the first embodiment. [Figure 4] Explanatory drawing showing the manufacturing process of the growth apparatus according to the second embodiment. [Figure 5] Explanatory drawing showing the manufacturing process of the growth apparatus according to the second embodiment. [Figure 6] Explanatory drawing of the growth apparatus according to the second embodiment. [Figure 7] Explanatory drawing of the growth method using a conventional growth apparatus that uses a noble metal crucible as the storage and holding means for the raw material melt. [Figure 8] Fig. 8(A) is a cross-sectional view of the noble metal crucible, Fig. 8(B) is a cross-sectional view of the noble metal crucible at the time of melting the charged crystal raw material, and Fig. 8(C) is a cross-sectional view of the noble metal crucible deformed by solidification of the raw material melt.

Modes for Carrying Out the Invention

[0019] Embodiments of the present invention will be described in detail below with reference to the drawings.

[0020] 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.

[0021] By the way, lithium niobate (LiNbO3: hereafter abbreviated as LN), lithium tantalate (LiTaO3: hereafter abbreviated as LT), yttrium aluminum garnet (Y3Al5O 12 When 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.

[0022] 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.

[0023] (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.

[0024] 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.

[0025] 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.

[0026] In other words, the cultivation device according to the present invention is as shown in Figure 1, oxidation material An oxide crucible 1 composed of materials and capable of storing and holding the raw material melt 10, A high-frequency induction coil 2 is provided around the side wall of the oxide crucible 1, The system includes a cylindrical metal heater 3 which is incorporated into the oxide crucible 1, is inductively heated by the high-frequency induction coil 2, and whose lower end 3a is inserted into the inner bottom surface 1a of the oxide crucible 1. Furthermore, the lower end portion 2a of the high-frequency induction coil 2 is located above the lower end portion 3a of the cylindrical metal heater 3.

[0027] (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 2, the growth apparatus according to the first embodiment consists mainly of a heat-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 ring-shaped reflector 15 placed on the upper end 3b of the cylindrical metal heater 3; 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 2, reference numeral 4 indicates a ceramic container that covers the outer bottom surface 1b of the oxide crucible 1.

[0028] (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.

[0029] 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.

[0030] (1-3) Effects of the first embodiment According to the growth apparatus of the first embodiment, the lower end portion 2a of the high-frequency induction coil 2 is located above the lower end portion 3a of the cylindrical metal heater 3, and the lower end portion 3a of the cylindrical metal heater 3 is less likely to be inductively heated. Therefore, the lower end portion 3a of the cylindrical metal heater 3 can be inserted into the inner bottom surface 1a of the oxide crucible 1, and the cylindrical metal heater 3 can be stably fixed inside the oxide crucible 1.

[0031] Furthermore, since 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, deformation of the crucible can be suppressed. Moreover, the cylindrical metal heater 3, excluding the lower end portion 3a and its vicinity, which is inserted into the inner bottom surface 1a of the oxide crucible 1, is induction heated. Therefore, during the growth of the oxide single crystal, 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, thus suppressing thermal deformation of the cylindrical metal heater 3.

[0032] Therefore, even when crystal growth is repeated, changes in growth conditions caused by fluctuations in the fixed cylindrical metal heater 3 or deformation of the crucible can be prevented, thus enabling the stable and repeated growth of oxide single crystals of the same quality.

[0033] (1-4) Cultivation device relating to a modification of the first embodiment The growth apparatus according to a modified version of the first embodiment is identical to the growth apparatus according to the first embodiment shown in Figure 2, except that a ring-shaped flat portion 3c is formed in the lower open portion of the cylindrical metal heater 3, as shown in Figure 3.

[0034] Furthermore, according to this modified growth apparatus, the cylindrical metal heater 3 becomes more self-supporting due to the action of the ring-shaped flat portion 3c, and the work of fixing the cylindrical metal heater 3 in the oxide crucible 1 becomes easier, making it possible to fix the cylindrical metal heater 3 more stably in the oxide crucible 1.

[0035] Furthermore, instead of the above structure in which a ring-shaped flat portion 3c is formed at the lower open portion of the cylindrical metal heater 3, if the lower open portion of the cylindrical metal heater 3 is closed and the cylindrical metal heater 3 is given a cup shape, the cylindrical metal heater 3 becomes easier to stand on its own, which has the advantage of making the work of fixing the cylindrical metal heater 3 inside the oxide crucible 1 even easier.

[0036] (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 consists mainly of a heat-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 ring-shaped reflector 15 placed on the upper end 3b of the cylindrical metal heater 3; 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 6, reference numeral 40 indicates a ceramic container (CP crucible) that covers the outer bottom surface 1b and the surrounding side walls of the oxide crucible 1.

[0037] 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.

[0038] (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.

[0039] 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.

[0040] Next, a cylindrical metal heater 3, which has a ring-shaped flat portion 3c formed in its lower open portion, is incorporated into the upper space 41 of the ceramic crucible (CP crucible) 40, and the lower end portion 3a of the cylindrical metal heater 3 is attached to the ceramic crucible (CP crucible) 40. oxides Place it on material 10a.

[0041] 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.

[0042] Next, as shown in Figure 6, a ring-shaped reflector 15 is placed on the upper end 3b of the cylindrical metal heater 3, and an afterheater 16 is placed on the ring-shaped reflector 15.

[0043] 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 near the side wall of 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 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.

[0044] Furthermore, in the growth apparatus according to the first embodiment, as shown in Figure 2, 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 2, 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. In this case, 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.

[0045] (3) Constituting the oxide crucible oxides material The above oxide layer 1c is having the inner surface and oxidesRegarding 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. If part of the oxide crucible is in powder form, it is desirable to provide the aforementioned ceramic container for holding the powder. 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.

[0046] 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, is preferably made of a sintered refractory material such as alumina, zirconia, magnesia, or calcia.

[0047] (4) Metal heater The shape of the metal heater described above is 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, it is preferable that the metal heater also has a rotationally symmetrical shape and is cylindrical.

[0048] Furthermore, the metal heater is preferably made of a crack-resistant material that does not oxidize in an oxygen-containing atmosphere and is capable of high-frequency heating. Specifically, it is desirable that it be made of platinum, iridium, rhodium, or alloys thereof.

[0049] Incidentally, one possible method for fixing the cylindrical metal heater is to attach a heater fixing rod to the inner wall surface of the heat-insulating outer cylinder 13, provide a hole near the upper end of the cylindrical metal heater, and insert the heater fixing rod through this hole to support it.

[0050] However, as metal heaters become larger for growing large crystals, their weight also increases. This raises concerns that the holes in the cylindrical metal heater may deform under the high-temperature conditions during growth, making it difficult to stably fix the cylindrical metal heater in place.

[0051] On the other hand, in the present invention, the cylindrical metal heater is fixed by inserting its lower end into the inner bottom surface of the oxide crucible, and the lower end of the high-frequency induction coil is positioned above the lower end of the cylindrical metal heater, so that the lower end of the cylindrical metal heater is less likely to be inductively heated. As a result, the cylindrical metal heater can be stably fixed inside the oxide crucible even under high-temperature conditions during crystal growth.

[0052] 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]

[0053] The embodiments of the present invention will be described in detail below with reference to comparative examples (conventional examples).

[0054] [Example 1] 1. Manufacturing of the growth apparatus according to Example 1 Inside the ceramic crucible (CP crucible) 40 with an inner diameter of 320 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.

[0055] Next, an iridium cylindrical metal heater 3, with an inner diameter of 230 mm, a height of 240 mm, and a thickness of 2 mm, having a ring-shaped flat portion 3c with an opening diameter of 190 mm formed in the lower open portion, is incorporated into the upper space 41 of the ceramic crucible (CP crucible) 40, and the lower end portion 3a of the cylindrical metal heater 3 is attached to the ceramic crucible (CP crucible) 40. oxides It was placed on material 10a. At this time, the lower end 3a of the iridium cylindrical metal heater 3 was adjusted to be 30 mm below the lower end 2a of the high-frequency induction coil 2.

[0056] 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. oxidesMaterial 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.

[0057] Next, as shown in Figure 6, a ring-shaped reflector 15 was placed on the upper end 3b of the cylindrical metal heater 3, and an afterheater 16 was placed on the ring-shaped reflector 15.

[0058] 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 of cylindrical metal heater 3 ( oxides Material) 10a is melted to make raw material melt 10, and lithium tantalate powder ( from the part away from the side wall of the cylindrical metal heater 3) 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.

[0059] 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.

[0060] 2. Growth of lithium tantalate single crystals (1) Next, a seed rod (crystal pulling shaft) 20 with a seed crystal 21 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 6 inches and a straight body length of approximately 150 mm was grown.

[0061] (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.

[0062] Next, the seed rod (crystal pulling shaft) 20 with the seed crystal 21 attached was lowered through the opening 12, and crystal growth was performed using the pulling method (Czochralski method), and a lithium tantalate single crystal with a diameter of 6 inches and a straight body length of approximately 150 mm was grown, as described above.

[0063] Then, after repeating the same crystal growth process 40 times, we were able to grow lithium tantalate single crystals of the same quality, with a diameter of 6 inches and a straight body length of approximately 150 mm, in 38 of the trials.

[0064] [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 230 mm and a height of 200 mm, a lithium tantalate single crystal with a diameter of 6 inches and a straight body length of approximately 150 mm was grown using the pulling method (Czochralski method).

[0065] Similar to Example 1, we planned to perform crystal growth 40 times, but since single crystals could not be obtained after the 24th time, we terminated crystal growth at the 30th time.

[0066] Furthermore, single crystals were obtained in 22 out of 30 attempts.

[0067] The iridium crucible was deformed after growth, and it is thought that the deformation was so significant after the 24th cycle that single crystals could not be obtained. [Industrial applicability]

[0068] 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]

[0069] 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 3c Ring-shaped flat section 4. Ceramic container 10 Raw material melt 10a oxides Material Fee 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 part 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 oxide single crystals by the pulling method, 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, The system includes a cylindrical metal heater that is incorporated into the oxide crucible, is inductively heated by the high-frequency induction coil, and whose lower end is inserted into the inner bottom surface of the oxide crucible. Furthermore, the apparatus for growing oxide single crystals is characterized in that the lower end of the high-frequency induction coil is located above the lower end of the cylindrical metal heater.

2. The apparatus for growing oxide single crystals according to claim 1, characterized in that the lower open portion of the cylindrical metal heater is closed or a ring-shaped flat portion is formed in the lower open portion.

3. The apparatus for growing oxide single crystals according to claim 1 or 2, characterized in that the oxide single crystal is one of lithium niobate single crystal, lithium tantalate single crystal, or yttrium aluminum garnet single crystal.

4. The apparatus for growing oxide single crystals according to any one of claims 1 to 3, characterized in that the cylindrical metal heater is composed of platinum, iridium, rhodium, or an alloy thereof.

5. An apparatus for growing oxide single crystals according to any one of claims 1 to 4, characterized by comprising a ceramic container covering the outer bottom surface of the oxide crucible, or a ceramic crucible covering the outer bottom surface and the surrounding side walls of the oxide crucible.

6. A method for growing an oxide single crystal 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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