Oxide single crystal growth apparatus and oxide single crystal growth method

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; a cylindrical metal heater 3 built in the oxide crucible, inductively heated by the coil and including an upper end part 3b held by fixing means above the oxide crucible and a lower end part 3a arranged to separate upward from an inner bottom surface 1a of the oxide crucible; and material supply means 51 for supplying a crystal raw material to a ring-shaped gap part 50 sandwiched between the inner wall surface of the oxide crucible and an outer wall surface of the heater. The lower end part 2a of the coil is arranged below from the lower end part 3a of the heater; and an oxide single crystal having the same quality and a long size can be repeatedly and stably grown by suppressing the deformations of the oxide crucible and heater and continuously supplying the crystal raw material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] A widely used method for growing oxide single crystals is the pulling method (also known as the Czochralski method), in which a crucible filled with raw materials to become the oxide single crystal is heated to a high temperature to melt the raw materials, a seed crystal is brought into contact with the surface of the molten raw material in the crucible from above, and then the seed crystal is raised while rotating to grow an oxide single crystal in the same orientation as the seed crystal.

[0003] 11, in an apparatus for growing oxide single crystals by the pulling method, a high-frequency induction coil 101 is arranged around the side wall of a crucible 100, and by passing a high-frequency current through the high-frequency induction coil 101, an eddy current is generated in the crucible 100, which in turn heats the crucible 100 and melts the raw material. As the pulling proceeds, the upper part of the oxide single crystal is cooled along a seed rod (crystal pulling shaft) 102. However, if the only heating element is the crucible 100, the temperature distribution within the single crystal during growth will become large. Therefore, a metal ring-shaped reflector 103 is arranged at the open end of the crucible 100, and a metal afterheater 104 is arranged at the upper end of the crucible 100. In FIG. 11, 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] In recent years, the market for oxide single crystals, especially lithium tantalate, as a surface acoustic wave device material has expanded, and the length and diameter of the single crystals pulled have gradually increased to ensure production volume. As a result of this increase in size, the crucibles used for crystal growth have also become larger.

[0005] Furthermore, the crucible must be conductive in order to pass high-frequency current through it, and must be made of a material that can withstand high temperatures, has a high melting point, and does not deteriorate in an oxidizing atmosphere in order to melt the crystal raw material.Crucibles used for crystal growth are often made of precious metals such as iridium, platinum, and rhodium, or their alloys.

[0006] However, when a single crystal is grown using a noble metal crucible, there is a problem that the crucible is deformed. This is because the cylindrical noble metal crucible 100 shown in Fig. 12(A) expands as shown in Fig. 12(B) when the raw material is melted, and when it cools, the solidified part of the raw material melt 106 stretches and deforms as shown in Fig. 12(C). This is due to the difference in expansion coefficient between the noble metal crucible and the oxide melt.

[0007] To prevent this deformation of the precious metal crucible, it is effective to grow a crystal with a long straight body to reduce the number of times the raw material melt solidifies. However, when a crystal with a long straight body is pulled, the melt level in the crucible drops as the crystal grows, causing the raw material melt to solidify at the bottom of the crucible. Furthermore, the crucible generates heat, which can cause distortion and twisting of the crystal during growth due to the influence of radiant heat from the crucible wall.

[0008] Therefore, Patent Document 1 proposes a method for growing single crystals in which a double crucible is formed by an outer crucible made of a precious metal and an inner crucible made of a precious metal that is placed inside the outer crucible and has a melt that is connected at the bottom, and raw materials consumed during crystal growth are supplied to the gap between the outer crucible and the inner crucible to prevent the melt level in the inner crucible from dropping.Patent Document 2 also proposes a double crucible in which an inner crucible made of a precious metal is fitted into an outer crucible made of a precious metal.

[0009] However, when attempting to heat the double crucible using high-frequency heating with a high-frequency induction coil installed around the side wall of the outer crucible, the high-frequency electromagnetic field is blocked by the outer crucible made of precious metal, so the outer crucible is heated but the inner crucible is not, resulting in a low melt temperature in the inner crucible. In particular, when growing large-diameter crystals, the melt is likely to solidify due to weak heat generation at the center of the bottom of the outer crucible. When the melt at the bottom solidifies, fluctuations in the melt level and temperature occur, making it more likely to become polycrystalline. Furthermore, in double crucibles where the melts are connected at the bottom, there is a problem that when the melt at the bottom solidifies, the melt present in the gap between the outer and inner crucibles cannot move to the inner crucible where the crystal is grown. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-344595 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-137985 Summary of the Invention [Problem to be solved by the invention]

[0011] As long as crystals are grown using a double crucible made of precious metal and high-frequency heating, the high-frequency electromagnetic field is blocked by the outer crucible and the inner crucible is not heated, so a growth apparatus using a new outer crucible to replace the outer crucible made of precious metal is needed.

[0012] The present invention has been made in view of these problems, and its object is to provide an apparatus and method for growing oxide single crystals that uses an oxide crucible made of the same material as the raw material melt, instead of an outer crucible made of a precious metal. [Means for solving the problem]

[0013] That is, the first invention according to the present invention is: An apparatus for growing oxide single crystals by the pulling method, an oxide crucible made of the above crystal material and capable of storing and holding a raw material melt; a high-frequency induction coil provided around the side wall of the oxide crucible; a cylindrical metal heater that is incorporated into the oxide crucible, is induction-heated by the high-frequency induction coil, has an upper end held by a fixing means provided above the oxide crucible, and has a lower end disposed above and spaced apart from the inner bottom surface of the oxide crucible; a raw material supply means for supplying a crystal raw material to a ring-shaped gap between the inner wall surface of the oxide crucible and the outer wall surface of the cylindrical metal heater; The lower end of the high frequency induction coil is located below the lower end of the cylindrical metal heater.

[0014] The second invention of the present invention is: In the oxide single crystal growth apparatus according to the first aspect of the present invention, the cylindrical metal heater has a cylindrical shape with an open upper end and a closed lower end, and an opening for introducing the raw material molten liquid in the ring-shaped gap into the cylindrical metal heater is provided in a side wall of the cylindrical metal heater, The third invention is In the oxide single crystal growth apparatus according to the first or second invention, the raw material supply means is comprised of a heat-resistant holding vessel having a raw material supply port at a lower end thereof and a crystal raw material accommodated in the holding vessel, and the raw material supply port of the holding vessel is disposed so as to be in contact with the raw material melt surface in the ring-shaped gap; The fourth invention is In the oxide single crystal growth apparatus according to any one of the first to third inventions, The holding vessel is made of any one of platinum, iridium, rhodium, and tungsten, or an alloy thereof; The fifth invention is In the oxide single crystal growth apparatus according to any one of the first to fourth inventions, 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, The sixth invention is In the oxide single crystal growth apparatus according to any one of the first to fifth inventions, The cylindrical metal heater is made of any one of platinum, iridium, and rhodium, or an alloy thereof, The seventh invention is In the oxide single crystal growth apparatus according to any one of the first to sixth aspects of the present invention, The method is characterized by comprising a ceramic container that covers the outer bottom surface of the oxide crucible, or a ceramic crucible that covers the outer bottom surface and the periphery of the side wall of the oxide crucible.

[0015] Next, the eighth aspect of the present invention is In a method for growing an oxide single crystal using the growth apparatus according to the first aspect of the present invention, The method is characterized in that a crystal raw material is placed in 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 in the cylindrical metal heater and the crystal raw material present in the ring-shaped gap, while a seed crystal is brought into contact with the surface of the raw material melt in the cylindrical metal heater and the raw material melt in the ring-shaped gap is continuously replenished into the cylindrical metal heater, and a long oxide single crystal is grown by a pulling method. [Effects of the Invention]

[0016] According to the oxide single crystal growth apparatus of the present invention, Since the outer crucible of the double crucible is made of an oxide crucible and the inner crucible of the double crucible is made of a cylindrical metal heater, the high-frequency electromagnetic field is not blocked by the oxide crucible (outer crucible), and therefore it is possible to inductively heat the cylindrical metal heater (inner crucible) using a high-frequency heating method.

[0017] In addition, since an oxide crucible made of the same material as the raw material melt is used as a means for storing and holding the raw material melt, deformation of the crucible can be suppressed, and when growing an oxide single crystal, the cylindrical metal heater is sandwiched between the raw material melt present inside the cylindrical metal heater and the raw material melt present outside the cylindrical metal heater, so thermal deformation of the cylindrical metal heater can also be suppressed.Therefore, it is possible to prevent changes in growth conditions due to deformation of the crucible even when crystal growth is repeated.

[0018] Furthermore, since the lower end of the high-frequency induction coil is located below the lower end of the cylindrical metal heater and the lower end of the cylindrical metal heater is also induction heated, it becomes possible to replenish the raw material melt present in the ring-shaped gap between the outer wall surface of the cylindrical metal heater and the inner wall surface of the oxide crucible into the cylindrical metal heater, and since the crystal raw material is continuously supplied to the ring-shaped gap by the raw material supply means, continuous replenishment of the raw material melt becomes possible.

[0019] Therefore, it is possible to repeatedly and stably grow long oxide single crystals of the same quality. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram illustrating the configuration of a growing device according to the present invention. [Figure 2] FIG. 10 is a diagram illustrating the configuration of a growing device according to a modified example of the present invention. [Figure 3] FIG. 2 is an explanatory diagram showing an example of a fixing means provided above the oxide crucible. [Figure 4] 1A and 1B are explanatory diagrams of a growth device according to a first embodiment and a growth method using this device. [Figure 5] FIG. 2 is an explanatory diagram showing the manufacturing process of the growth device according to the first embodiment. [Figure 6] FIG. 2 is an explanatory diagram showing the manufacturing process of the growth device according to the first embodiment. [Figure 7] FIG. 2 is an explanatory diagram showing the manufacturing process of the growth device according to the first embodiment. [Figure 8] FIG. 10 is an explanatory diagram of a cultivation device according to a second embodiment. [Figure 9]FIG. 10 is an explanatory diagram showing the manufacturing process of the growth device according to the second embodiment. [Figure 10] FIG. 10 is an explanatory diagram showing the manufacturing process of the growth device according to the second embodiment. [Figure 11] FIG. 1 is an explanatory diagram of a growth method using a conventional growth apparatus that uses a noble metal crucible as a means for storing and holding the raw material melt. [Figure 12] Figure 12(A) is a cross-sectional view of a noble metal crucible, Figure 12(B) is a cross-sectional view of the noble metal crucible when the crystal raw material introduced into it is melted, and Figure 12(C) is a cross-sectional view of the noble metal crucible that has been deformed as the raw material melt solidifies. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0022] 1. Conventional cultivation equipment and cultivation methods (1) Conventional cultivation device and cultivation method using this device As mentioned above, a known conventional growth apparatus is one that includes, within chamber 200 (see FIG. 11), a CP crucible (porous alumina crucible) 109, 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 shaft) 102, and a high-frequency induction coil 101. Known crucibles 100 used for high-temperature crystal growth include high-melting-point metal crucibles such as tungsten and tantalum, noble metal crucibles such as platinum, rhodium, and iridium, and non-metallic crucibles such as alumina, magnesia, carbon, and PBN (Pyrolytic Boron Nitride).

[0023] By the way, lithium niobate (LiNbO3: hereinafter abbreviated as LN), lithium tantalate (LiTaO3: hereinafter abbreviated as LT), yttrium aluminum garnet (Y3Al5O 12When growing oxide single crystals such as YAG (Yttrium-Yagranide), the growth atmosphere must contain oxygen, so materials that are easily oxidized, such as tungsten, tantalum, and carbon, cannot be used. Similarly, alumina and magnesia cannot be used because they react with the oxide melt. PBN is expensive and requires a large crucible for its manufacture.

[0024] For this reason, when growing oxide single crystals, crucibles made of precious metals such as platinum, rhodium, and iridium are used, which do not oxidize and do not break, causing the raw material melt to leak out.

[0025] (2) Existing issues However, as shown in Figures 12(A) to 12(C), precious metal crucibles thermally expand when the raw materials are melted, and deform when the residue of the raw material melt solidifies due to the difference in thermal expansion coefficients between the oxide and the precious metal. In the case of high-frequency induction heating, this deformation causes changes in the heat generation state, which in turn changes the growth conditions, and as the deformation of the crucible progresses, there is a problem in that it becomes impossible to obtain single crystals.

[0026] Furthermore, when a double crucible made of a precious metal is used to prevent the above-mentioned deformation of the precious metal crucible and an attempt is made to grow a crystal with a long straight body portion using a high-frequency heating method, there is a problem that the high-frequency electromagnetic field is blocked by the outer crucible made of a precious metal, and the inner crucible is not heated.

[0027] 2. The growth device and growth method of the present invention The growth apparatus of the present invention, which uses the pulling method (Czochralski method), is an apparatus used to produce 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 for 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, cut along a certain crystal orientation, called a seed crystal, in a raw material melt of the same composition, and slowly pulling it up while rotating.

[0028] In order to solve the conventional problems, the present inventors have discovered an apparatus and method for growing oxide single crystals that uses an oxide crucible made of the same material as the raw material melt, instead of an outer crucible made of a noble metal.

[0029] That is, the growth device according to the present invention, as shown in FIG. An oxide crucible (corresponding to an outer crucible) 1 made of an oxide crystal material and capable of storing and holding a raw material melt 10; a high-frequency induction coil 2 provided around the side wall of the oxide crucible 1; a cylindrical metal heater (corresponding to the inner crucible) 3 that is incorporated into the oxide crucible 1 and is induction-heated by the high-frequency induction coil 2, and that has an upper end 3b held by a fixing means (not shown) provided above the oxide crucible 1 and a lower end 3a disposed above and spaced apart from the inner bottom surface 1a of the oxide crucible 1; a raw material supply means 51 for supplying a crystal raw material (crystal material 10a) to a ring-shaped gap 50 sandwiched between the inner wall surface of the oxide crucible 1 and the outer wall surface of the cylindrical metal heater 3; In addition, the lower end 2 a of the high frequency induction coil 2 is located below the lower end 3 a of the cylindrical metal heater 3 .

[0030] The raw material supply means 51 of the growth apparatus shown in Figure 1 is composed of a heat-resistant holding container 51a having a raw material supply port 51b at its lower end and a crystal raw material (crystal material 10a) contained in this holding container 51a, and the crystal raw material (crystal material 10a) in the holding container 51a is pushed by a cylinder (not shown) or the like to drop and supply it onto the surface of the raw material melt 10 in the ring-shaped gap portion 50.

[0031] Next, as shown in FIG. 2, a growth apparatus according to a modified example of the present invention is substantially the same as the growth apparatus of the present invention shown in FIG. 1 except that the mounting form of the raw material supply means 51 is different.

[0032] That is, as shown in Figure 2, the raw material supply means 51 of the growth apparatus according to the modified example is composed of a heat-resistant holding container 51a having a raw material supply port 51b at its lower end and a crystal raw material (crystal material 10a) contained in this holding container 51a, and the raw material supply port 51b of the holding container 51a is positioned so that it is in contact with the surface of the raw material melt 10 in the ring-shaped gap portion 50, and the crystal raw material (crystal material 10a) is supplied while being melted at the surface of the raw material melt 10.

[0033] The method of Figure 2, in which the crystal raw material (crystal material 10a) is brought into contact with the surface of the raw material melt 10, has the advantage that there is no impact when the raw material is supplied, compared to the method of Figure 1, in which the crystal raw material (crystal material 10a) is dropped onto the surface of the raw material melt 10, and therefore crystal growth can be performed in the same temperature environment without fluctuations in the surface of the raw material melt 10.

[0034] The crystal raw material (crystal material 10a) may be, for example, a crystal material powder, a crystal material grain, or a crystal material lump.

[0035] (1) A growth device according to the first embodiment and a growth method using this device (1-1) Growth device according to the first embodiment As shown in Figure 4, the growth apparatus according to the first embodiment is mainly composed of an insulating outer casing 13, the bottom of which is fixed to a support base 11, which houses the growth apparatus according to the present invention (comprising the oxide crucible 1 and the cylindrical metal heater 3) excluding the high-frequency induction coil 2, and which has an opening 12 on the upper side for a seed rod (crystal pulling shaft) 20; a heater fixing rod 14 (see the fixing means in Figure 3) attached to approximately the center of the insulating outer casing 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 afterheater 16 placed on this ring-shaped reflector 15; a raw material supply means 51 inserted into the gap formed by the heater fixing rod 14 and the insulating outer casing 13; and a rod-shaped seed crystal 21 attached to the lower end of the seed rod (crystal pulling shaft) 20.

[0036] In the growth apparatus according to the first embodiment, the oxide crucible 1 corresponds to the outer crucible of the double crucible, and the cylindrical metal heater 3 corresponds to the inner crucible of the double crucible. Also, in Fig. 4, reference numeral 40 denotes a ceramic container (CP crucible) that covers the outer bottom surface 1b and the periphery of the side wall of the oxide crucible 1.

[0037] (1-2) Cultivation method according to the first embodiment Crystal raw materials are 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 crystal raw materials in the cylindrical metal heater 3 and those present in a ring-shaped gap 50 sandwiched between the outer wall surface of the cylindrical metal heater 3 and the inner wall surface of the oxide crucible 1.

[0038] Next, a seed crystal 21 is brought into contact with the surface of the raw material melt 10 in the cylindrical metal heater 3, and then the seed rod (crystal pulling shaft) 20 is raised while being rotated to grow an oxide single crystal 30.

[0039] (1-3) Effects of the cultivation method according to the first embodiment According to the growth method of the first embodiment, the outer crucible of the double crucible is composed of an oxide crucible 1, and the inner crucible of the double crucible is composed of a cylindrical metal heater. Therefore, the high-frequency electromagnetic field is not blocked by the oxide crucible (outer crucible) 1, and therefore the cylindrical metal heater (inner crucible) 3 can be induction heated by a high-frequency heating method.

[0040] In addition, since an oxide crucible 1 made of the same material as the raw material melt is used as a means for storing and holding the raw material melt, deformation of the crucible can be suppressed, and when growing an oxide single crystal, the cylindrical metal heater 3 is sandwiched between the raw material melt 10 inside the cylindrical metal heater 3 and the raw material melt 10 outside the cylindrical metal heater 3, so thermal deformation of the cylindrical metal heater 3 can also be suppressed.Therefore, even if the growth of an oxide single crystal is repeated, it is possible to prevent changes in growth conditions due to deformation of the crucible.

[0041] 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, making it possible to replenish the raw material melt 10 present in the ring-shaped gap 50 into the cylindrical metal heater (inner crucible) 3, and since crystal raw material is continuously supplied to the ring-shaped gap 50 by the raw material supply means 51, continuous replenishment of the raw material melt 10 is possible.

[0042] Therefore, the growth method according to the first embodiment has the effect of repeatedly and stably growing oxide single crystals of the same quality and having a long straight body portion.

[0043] (1-4) Manufacturing method of the growth device according to the first embodiment The growth device according to the first embodiment can be manufactured, for example, as follows.

[0044] First, as shown in Fig. 5, a crystal material 10a is placed in a ceramic crucible (CP crucible) 40 incorporated in a heat-insulating outer cylinder 13, leaving an upper space 41. The crystal material 10a may be, for example, a crystal material powder or a crystal material lump.

[0045] Next, the cylindrical metal heater 3 is installed in 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 3) attached to approximately the center of the insulating outer cylinder 13.

[0046] Then, as shown in Figure 6, the crystal material 10a is poured into the upper space 41 of the ceramic crucible (CP crucible) 40 in which the cylindrical metal heater 3 is incorporated, and the crystal material 10a is filled into the inside of the cylindrical metal heater 3 and the upper space 41 of the ceramic crucible (CP crucible) 40.

[0047] Next, as shown in FIG. 7, a ring-shaped reflector 15 is placed on the upper end 3b of the cylindrical metal heater 3 held by the heater fixing bar 14, and an afterheater 16 is placed on the ring-shaped reflector 15.

[0048] Then, the cylindrical metal heater 3 is induction-heated by a high-frequency induction coil 2 provided around the side wall of the ceramic crucible (CP crucible) 40, and the crystal material 10a in the cylindrical metal heater 3 and the crystal material 10a near the side wall and near the lower end 3a of the cylindrical metal heater 3 are melted to form a raw material melt 10.The raw material melt 10 is then allowed to flow between the crystal material 10a at the portion away from the side wall of the cylindrical metal heater 3 and the portion away from the lower end 3a to form a continuous oxide layer 1c.After forming the oxide crucible 1 having the oxide layer 1c on its inner surface and capable of storing and retaining the raw material melt 10, the growth apparatus according to the first embodiment can be manufactured by incorporating the raw material supply means 51 shown in Figure 4.

[0049] In the growth apparatus according to the present invention and the growth apparatus according to the modified example of the present invention, a ceramic container 4 is used to cover the outer bottom surface 1b of the oxide crucible 1, as shown in Figures 1 and 2, and the growth apparatus cannot be manufactured by the manufacturing method using the ceramic crucible (CP crucible) 40. In such a case, it is possible to manufacture the growth apparatus by press-molding a crystal material powder or a crystal material lump into the shape of an oxide crucible as shown in Figures 1 and 2, incorporating the ceramic container 4 on the bottom side of the formed body into the heat-insulating outer cylinder 13, and then applying the manufacturing method described above. In this case, it is necessary to set the wall thickness of the pressure-molded crucible to a large value so that the entire wall does not melt when the cylindrical metal heater 3 is induction-heated.

[0050] (2) The second embodiment of the growth device As shown in Fig. 8, the growth apparatus according to the second embodiment is substantially the same as the growth apparatus according to the first embodiment (see Fig. 4), except that the cylindrical metal heater 3 has a cylindrical shape with an open upper end 3b and a closed lower end 3a, and an opening 3d is provided in the side wall of the cylindrical metal heater 3 for introducing the raw material melt 10 into the cylindrical metal heater 3 from a ring-shaped gap 50 sandwiched between the outer wall surface of the cylindrical metal heater 3 and the inner wall surface of the oxide crucible 1. Note that Fig. 8 does not show the seed rod (crystal pulling shaft) 20 and raw material supply means 51 shown in Fig. 4.

[0051] The cylindrical metal heater 3 of Figure 8, whose lower end 3a is closed, is easier to stand on its own than the cylindrical metal heater 3 of Figure 4, whose lower end 3a is also open, and has the advantage of simplifying the task of placing the cylindrical metal heater 3 on the crystal material 10a (see Figure 9) during the manufacturing stage of the growth apparatus.

[0052] (3) Crystalline material that makes up the oxide crucible Regarding the oxide crucible 1 having the oxide layer 1c on its inner surface and made of a crystalline material, the entire crucible does not need to be made of a single crystal. It is preferable for the entire crucible to be made of a sintered body or polycrystalline body, but a portion of the material may be in a powder state. If a portion of the oxide crucible is in a powder state, it is desirable to provide the aforementioned ceramic container for holding the powder. The unmelted portion of the crystalline material away from the oxide layer 1c of the oxide crucible 1 functions in the same way as the heat insulating material 108 and the heat-insulating crucible stand 110 in the conventional growth apparatus shown in FIG. 11.

[0053] Furthermore, the material constituting 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 periphery of the side wall of the oxide crucible 1, is preferably a sintered refractory material such as alumina, zirconia, magnesia, or calcia.

[0054] (4) Metal heater The metal heater may have any shape as long as it is capable of high-frequency induction heating, but when growing high-quality crystals using the Czochralski method, it is desirable for the raw material melt to have rotational symmetry with respect to the seed (seed crystal). For this reason, the metal heater also preferably has a rotational symmetry shape, and must be cylindrical.

[0055] Furthermore, it is preferable that the metal heater be made of a material that is capable of high-frequency heating, does not oxidize in an oxygen-containing atmosphere, and does not crack. Specifically, it is desirable that the metal heater be made of platinum, iridium, rhodium, or an alloy of these metals.

[0056] Furthermore, as a fixing means for fixing the upper end of the metal heater, a heater fixing rod 14 (see fixing means in FIG. 3) attached to approximately the center of the heat-insulating outer cylinder 13 shown in FIG. 4 is exemplified, and the upper end 3b of the metal heater 3 is fixed by passing it through the rod 14, and the number of heater fixing rods 14 is preferably about two to six.

[0057] Furthermore, the material of the ring-shaped reflector placed on the upper end of the metal heater and the afterheater placed on the ring-shaped reflector is preferably the same as that of the metal heater. [Example]

[0058] Examples of the present invention will be specifically described below with reference to comparative examples (conventional examples).

[0059] [Example 1] 1. Manufacture of the growth device according to Example 1 Lithium tantalate powder (crystal material) 10a was placed in a ceramic crucible (CP crucible) 40 having an inner diameter of 270 mm and an inner height of 340 mm, which was fitted into a heat-insulating outer cylinder 13 shown in FIG.

[0060] Next, a cylindrical metal heater 3 made of iridium, measuring 170 mm in inner diameter, 170 mm in height, and 2 mm in thickness, with an open upper end 3b and a closed lower end 3a, was installed in the upper space 41 of the ceramic crucible (CP crucible) 40, and the upper end 3b of the cylindrical metal heater 3 was fixed with a heater fixing rod 14 attached to approximately the center of the heat-insulating outer cylinder 13. The cylindrical metal heater 3 was provided with an opening 3d with a diameter of 20 mm at a position 100 mm below the upper end 3b, and the raw material melt 10 in a ring-shaped gap 50 sandwiched between the outer wall surface of the cylindrical metal heater 3 and the inner wall surface of the oxide crucible 1 was introduced into the cylindrical metal heater 3.

[0061] Then, as shown in FIG. 10, lithium tantalate powder (crystal material) 10a was poured into the upper space 41 of the ceramic crucible (CP crucible) 40 incorporating the cylindrical metal heater 3, and the inside of the cylindrical metal heater 3 and the upper space 41 of the ceramic crucible (CP crucible) 40 were filled with lithium tantalate powder (crystal material) 10a.

[0062] Next, as shown in FIG. 8, a ring-shaped reflector 15 was placed on the upper end 3b of the cylindrical metal heater 3 held by a heater fixing bar 14, and an afterheater 16 was placed on the ring-shaped reflector 15.

[0063] Then, the cylindrical metal heater 3 is induction-heated by a high-frequency induction coil 2 provided around the side wall of the ceramic crucible (CP crucible) 40, and the lithium tantalate powder (crystal material) 10a in the cylindrical metal heater 3 and the lithium tantalate powder (crystal material) 10a in the vicinity of the side wall and the lower end 3a of the cylindrical metal heater 3 are melted to form a raw material melt 10, and the lithium tantalate powder (crystal material) in the portion away from the side wall and the lower end 3a of the cylindrical metal heater 3 is melted to form a raw material melt 10. A continuous oxide layer 1c was formed by flowing raw material melt 10 between the raw material melt 10a and the oxide crucible 1, which had the oxide layer 1c on its inner surface and was capable of storing and holding the raw material melt 10. After that, a raw material supply means (consisting of an iridium holding vessel 51a having a raw material supply port 51b and a crystal raw material contained in this holding vessel 51a, as shown in Figure 2, and arranged so that the raw material supply port 51b of the holding vessel 51a is in contact with the raw material melt surface) was incorporated to manufacture the growth apparatus of Example 1.

[0064] When the lithium tantalate powder (crystal material) 10a is melted to form the oxide layer 1c, the input power of the high-frequency induction coil 2 is set 10% higher than that during the following growth in order to increase the amount of melt outside the cylindrical metal heater 3. This allows the raw material melt to flow between the lithium tantalate powder (crystal material) 10a, forming a continuous oxide layer 1c.

[0065] 2.Growth of lithium tantalate single crystals Next, a seed rod (crystal pulling shaft, not shown) with a seed crystal (not shown) attached to its tip was lowered through the opening 12 (see FIG. 8) of the heat-insulating outer cylinder 13, and crystal growth was carried out by the pulling method (Czochralski method), successfully growing a lithium tantalate single crystal having a diameter of 4 inches and a straight body length of approximately 200 mm.

[0066] Next, after growing the lithium tantalate single crystal, lithium tantalate powder (crystal raw material) was placed in the oxide crucible 1 incorporating the cylindrical metal heater 3, and the cylindrical metal heater 3 was induction heated by the high-frequency induction coil 2, thereby melting the lithium tantalate powder (crystal raw material) in the cylindrical metal heater 3 and the lithium tantalate powder (crystal raw material) present between the side wall surface of the cylindrical metal heater 3 and the inner wall surface of the oxide crucible 1.

[0067] Next, a seed rod (crystal pulling shaft) with a seed crystal attached was lowered through the opening 12 and crystal growth was carried out 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 200 mm was grown, as described above.

[0068] [Comparative Example (Conventional Example)] Using the conventional growth apparatus shown in FIG. 11 and an iridium crucible 100 having a diameter of 170 mm and a height of 170 mm, a lithium tantalate single crystal having a diameter of 4 inches was grown by the pulling method (Czochralski method).

[0069] However, when the length of the straight body portion reached approximately 180 mm, the melt surface in the crucible 100 dropped, and the lower end of the grown lithium tantalate single crystal contacted the solidified crystal portion at the bottom of the crucible 100, resulting in bottoming out and becoming polycrystalline. [Industrial Applicability]

[0070] According to the present invention, oxide single crystals of the same quality and having a long straight body can be repeatedly and stably grown, and therefore the present invention 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]

[0071] 1 oxide crucible 1a Inner bottom surface 1b Outer bottom surface 2 High frequency induction coil 2a Bottom end 3 Cylindrical metal heater 3a Bottom end 3b Upper end 3d aperture 4. Ceramic containers 10 Raw material melt 10a Crystal material (crystal raw material) powder 11 Support stand 12 aperture 13. Insulating outer tube 14 Heater fixing rod 15 Ring-shaped reflector 16 Afterheater 20 Seed rod (crystal pulling shaft) 21 Seed Crystal 30 Oxide single crystals 40 Ceramic crucible 41 Upper space 50 Ring-shaped gap 51 Raw material supply means 51a Heat-resistant holding container 51b Raw material supply port 100 Crucible 101 High frequency induction coil 102 Seed rod (crystal pulling shaft) 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. An apparatus for growing oxide single crystals by the pulling method, an oxide crucible made of the above crystal material and capable of storing and holding a raw material melt; a high-frequency induction coil provided around the side wall of the oxide crucible; a cylindrical metal heater that is incorporated into the oxide crucible, is induction-heated by the high-frequency induction coil, has an upper end held by a fixing means provided above the oxide crucible, and has a lower end disposed above and spaced apart from the inner bottom surface of the oxide crucible; a raw material supply means for supplying a crystal raw material to a ring-shaped gap between the inner wall surface of the oxide crucible and the outer wall surface of the cylindrical metal heater; and a lower end of the high frequency induction coil is located below a lower end of the cylindrical metal heater.

2. 2. The oxide single crystal growth apparatus according to claim 1, wherein the cylindrical metal heater has a cylindrical shape with an open upper end and a closed lower end, and an opening for introducing the raw material melt from the ring-shaped gap into the cylindrical metal heater is provided in the side wall of the cylindrical metal heater.

3. 3. The oxide single crystal growth apparatus according to claim 1, wherein the raw material supply means comprises a heat-resistant holding vessel having a raw material supply port at its lower end and a crystal raw material contained in the holding vessel, and the raw material supply port of the holding vessel is positioned so as to come into contact with the surface of the raw material melt in the ring-shaped gap.

4. 4. The oxide single crystal growth apparatus according to claim 1, wherein the holding vessel is made of any one of platinum, iridium, rhodium, and tungsten, or an alloy thereof.

5. 5. The oxide single crystal growth apparatus according to claim 1, wherein the oxide single crystal is one of a lithium niobate single crystal, a lithium tantalate single crystal, and an yttrium aluminum garnet single crystal.

6. 6. The oxide single crystal growth apparatus according to claim 1, wherein the cylindrical metal heater is made of any one of platinum, iridium, and rhodium, or an alloy thereof.

7. 7. The oxide single crystal growth apparatus according to claim 1, further comprising a ceramic container that covers the outer bottom surface of the oxide crucible, or a ceramic crucible that covers the outer bottom surface and the periphery of the side wall of the oxide crucible.

8. 2. A method for growing an oxide single crystal using the growth apparatus according to claim 1, A method for growing an oxide single crystal, comprising: placing a crystal 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 crystal raw material in the cylindrical metal heater and the crystal raw material present in the ring-shaped gap; bringing a seed crystal into contact with the surface of the raw material melt in the cylindrical metal heater; and growing a long oxide single crystal by a pulling method while continuously supplying the raw material melt in the ring-shaped gap into the cylindrical metal heater.

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