JP2023132266A - Apparatus and method for growing oxide single crystal - Google Patents

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

The present invention relates to improvements in a growth apparatus and method for growing oxide single crystals such as lithium tantalate by a pulling method.

As a method for growing an oxide single crystal, a crucible filled with raw materials to become an oxide single crystal is heated to a high temperature to melt the raw materials, and a seed crystal is brought into contact with the raw material melt surface in the crucible from above. A pulling method (also referred to as the Czochralski method) is widely used in which an oxide single crystal is grown in the same direction as the seed crystal by raising the crystal while rotating it.

In the apparatus for growing oxide single crystals by the pulling method, as shown in FIG. An eddy current is generated in the crucible 100, which causes the crucible 100 to generate heat and melt the raw material. Additionally, as the pulling progresses, the upper part of the oxide single crystal is cooled down through the seed rod (crystal pulling shaft) 102, but if the only heating element is the crucible 100, the temperature distribution within the single crystal during growth is large. Therefore, a metal ring-shaped reflector 103 is placed at the open end of the crucible 100, and a metal after-heater 104 is placed at the upper end of the crucible 100. In FIG. 11, 105 is a seed crystal, 106 is a raw material melt, 107 and 108 are heat insulating materials, 109 is a CP crucible (porous alumina crucible), and 110 is a heat insulating crucible stand. .

In recent years, the market for oxide single crystals, especially lithium tantalate, as a material for surface acoustic wave devices has expanded, and the pulled length and diameter of single crystals are gradually increasing to ensure production volume. Along with this increase in size, crucibles used for crystal growth are also becoming larger.

In addition, the crucible must be conductive to allow high-frequency current to flow through it, and in order to melt the crystal raw material, it must be made of a material with a high melting point that can withstand high temperatures and that will not deteriorate in an oxidizing atmosphere. The crucible used is often made of noble metals such as iridium, platinum, rhodium, etc., or alloys thereof.

However, when a single crystal is grown using a noble metal crucible, there is a problem in that the crucible is deformed. This is because the cylindrical precious metal crucible 100 shown in FIG. 12(A) expands as shown in FIG. 12(B) when the raw material is melted, and when cooled, the solidified portion of the raw material melt 106 expands and becomes the shape shown in FIG. 12(C). This is because the noble metal crucible and the oxide melt have different expansion coefficients.

In order to prevent this deformation of the precious metal crucible, it is effective to grow crystals with long straight bodies to reduce the number of solidifications of the raw material melt. However, when a crystal with a long straight body is pulled up, the surface of the melt in the crucible decreases as the crystal grows, causing the problem that the raw material melt solidifies at the bottom of the crucible.Furthermore, the crucible generates heat. There is a problem in that the crystal being grown is distorted, twisted, etc. due to the influence of radiant heat from the crucible wall.

Therefore, in Patent Document 1, a double crucible is configured with an outer crucible made of a noble metal and an inner crucible made of a noble metal placed in the outer crucible so that the melt communicates with the bottom, and this is used for crystal growth. A method for growing a single crystal has been proposed in which the raw material consumed by the process is supplied to the gap between an outer crucible and an inner crucible to prevent a drop in the melt surface in the inner crucible. A double crucible has been proposed in which an inner crucible is fitted into an outer crucible made of precious metal.

However, when attempting to heat the double crucible using a high-frequency heating method using a high-frequency induction coil installed around the side wall of the outer crucible, the outer crucible is heated because the high-frequency electromagnetic field is blocked by the outer crucible made of precious metal. However, there was a problem that the inner crucible was not heated and the temperature of the melt in the inner crucible became low. In particular, when growing large-diameter crystals, the melt tends to solidify because the heat generation at the center of the bottom of the outer crucible is weak, and when the melt at the bottom solidifies, melt surface fluctuations and temperature changes occur, making it easy to form polycrystals. A problem existed. Furthermore, in a double crucible in which the melt is in communication at the bottom, when the melt at the bottom solidifies, the melt existing in the gap between the outer crucible and the inner crucible cannot move to the inner crucible where crystal growth is performed. There was a problem that disappeared.

Japanese Patent Application Publication No. 2000-344595 Japanese Patent Application Publication No. 2002-137985

As long as crystal growth is performed using a high-frequency heating method using a double crucible made of precious metal, the high-frequency electromagnetic field is blocked by the outer crucible and the inner crucible is not heated, so a new outer crucible can replace the outer crucible made of precious metal. A cultivation device using this is required.

The present invention was made with attention to these problems, and its object is to produce an oxide single crystal using an oxide crucible made of the same material as the raw material melt instead of an outer crucible made of noble metal. The purpose is to provide a growing device and a growing method.

That is, the first invention according to the present invention is
In an apparatus for growing oxide single crystals by the pulling method,
an oxide crucible made of the crystalline 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;
It is installed in the oxide crucible and is heated by induction by the high-frequency induction coil, and the upper end is held by a fixing means provided above the oxide crucible, and the lower end is separated upward from the inner bottom surface of the oxide crucible. a cylindrical metal heater arranged in a
a raw material supply means for supplying a crystal raw material to a ring-shaped gap sandwiched between an inner wall surface of the oxide crucible and an outer wall surface of the cylindrical metal heater;
Further, the lower end of the high frequency induction coil is located below the lower end of the cylindrical metal heater.

Moreover, the second invention according to the present invention is
In the oxide single crystal growth apparatus according to the first invention,
The cylindrical metal heater has a cylindrical shape with an open upper end and a closed lower end, and the opening for introducing the raw material melt into the cylindrical metal heater in the ring-shaped gap is a cylindrical metal heater. It is characterized by being provided on the side wall,
The third invention is
In the oxide single crystal growth apparatus according to the first invention or the second invention,
The raw material supply means is composed of a heat-resistant holding container having a raw material supply port at the lower end and a crystal raw material accommodated in the holding container, and the raw material supply port of the holding container is configured to melt the raw material in a ring-shaped gap. It is characterized by being placed in contact with the liquid surface,
The fourth invention is
In the oxide single crystal growth apparatus according to any one of the first to third inventions,
The holding container is characterized by being composed of platinum, iridium, rhodium, 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 platinum, iridium, 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 inventions,
It 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 side walls of the oxide crucible.

Next, the eighth invention according to the present invention is
In the method of growing an oxide single crystal using the growth apparatus according to the first invention,
A crystal raw material is put into an oxide crucible in which a cylindrical metal heater is incorporated, and the cylindrical metal heater is heated by induction using a high frequency induction coil to separate the crystal raw material in the cylindrical metal heater and the crystals present in the ring-shaped gap. While the raw material is melted, 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 the material is lengthened by a pulling method. This method is characterized by growing oxide single crystals with a diameter of 100 cm.

According to the oxide single crystal growth apparatus according to the present invention,
Since the outer crucible of the double crucible is composed of an oxide crucible and the inner crucible of the double crucible is composed of a cylindrical metal heater, the high frequency electromagnetic field is not blocked by the oxide crucible (outer crucible). , it becomes possible to induction-heat the cylindrical metal heater (inner crucible) by high-frequency heating.

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 the oxide single crystal is grown, it is present inside the cylindrical metal heater. Since the cylindrical metal heater is sandwiched between the raw material melt existing on the outside of the cylindrical metal heater and the raw material melt existing on the outside of the cylindrical metal heater, thermal deformation of the cylindrical metal heater can also be suppressed. It becomes possible to prevent changes in growth conditions due to deformation of the .

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, the outer wall surface of the cylindrical metal heater and the inside of the oxide crucible are heated. It becomes possible to replenish the raw material melt present in the ring-shaped gap between the wall surface and the cylindrical metal heater, and the crystal raw material is continuously supplied to the ring-shaped gap by the raw material supply means. This makes it possible to continuously replenish raw material melt.

Therefore, it has the effect of repeatedly and stably growing oxide single crystals of the same quality and long size.

FIG. 1 is an explanatory diagram of the configuration of a growing device according to the present invention. FIG. 3 is a configuration explanatory diagram of a growing device according to a modification of the present invention. FIG. 3 is an explanatory diagram showing an example of a fixing means provided above the oxide crucible. FIG. 1 is an explanatory diagram of a growing device according to a first embodiment and a growing method using this device. Explanatory diagram showing the manufacturing process of the growth device according to the first embodiment. Explanatory diagram showing the manufacturing process of the growth device according to the first embodiment. Explanatory diagram showing the manufacturing process of the growth device according to the first embodiment. An explanatory diagram of a growing device according to a second embodiment. Explanatory diagram showing the manufacturing process of the growth device according to the second embodiment. Explanatory diagram showing the manufacturing process of the growth device according to the second embodiment. FIG. 2 is an explanatory diagram of a growth method using a conventional growth apparatus that uses a noble metal crucible as a storage and holding means for a raw material melt. FIG. 12(A) is a cross-sectional view of the noble metal crucible, FIG. 12(B) is a cross-sectional view of the noble metal crucible when the input crystal raw material is melted, and FIG. 12(C) is the precious metal deformed as the raw material melt solidifies. A cross-sectional view of a crucible.

Hereinafter, embodiments of the present invention will be described in detail using the drawings.

1. Conventional growth device and growth method (1) Conventional growth device and growth method using this device As described above, the conventional growth device includes a CP crucible (porous alumina crucible) in the chamber 200 (see FIG. 11). ) 109, a crucible 100, a heat-insulating crucible stand 110, a ring-shaped reflector 103, an after-heater 104, heat insulators 107 and 108, a seed rod (crystal pulling shaft) 102, and a high-frequency induction coil 101. It has been known. The crucible 100 used for high-temperature crystal growth is a high melting point metal crucible such as tungsten or tantalum, a noble metal crucible such as platinum, rhodium or iridium, or a crucible of alumina, magnesia, carbon or PBN (Pyrolytic Boron Nitride). Non-metallic crucibles are known.

By the way, lithium niobate (LiNbO ₃ : hereinafter abbreviated as LN), lithium tantalate (LiTaO ₃ : hereinafter abbreviated as LT), yttrium aluminum garnet (Y ₃ Al ₅ O ₁₂ : hereinafter abbreviated as YAG) When growing oxide single crystals such as oxides, the growth atmosphere contains oxygen, so tungsten, tantalum, and carbon, which are easily oxidized, cannot be used. Similarly, alumina and magnesia cannot be used because they react with the oxide melt, and PBN is expensive and difficult to prepare in large crucibles.

For this reason, when growing oxide single crystals, crucibles of noble metals such as platinum, rhodium, and iridium are used, which are not oxidized and do not crack and cause the raw material melt to flow out.

(2) Conventional issues However, as shown in Figures 12 (A) to (C), noble metal crucibles thermally expand when raw materials are melted, and when the residue of the raw material melt solidifies, the thermal expansion coefficient of the oxide and precious metal increases. are deformed because they are different. Due to this deformation, in the case of high-frequency induction heating, the heat generation state changes, so the growth conditions change, and as the crucible deforms, a single crystal cannot be obtained.

Furthermore, in order to prevent the above-mentioned deformation of the precious metal crucible, when trying to grow a crystal with a long straight body using a high-frequency heating method using a double crucible made of a precious metal, the high-frequency electromagnetic field is blocked by the outer crucible made of a precious metal. There was also the problem that the inner crucible was not heated.

2. Growth apparatus and growth method of the present invention The growth apparatus of the present invention using the pulling method (Czochralski method) is capable of growing oxides such as LN, LT, and YAG in the air or in an inert gas atmosphere containing oxygen. This is a device used to manufacture single crystals. In the Czochralski method, the tip of a single crystal, called a seed crystal, cut out along a certain crystal orientation and usually processed into a rod shape, is soaked in a raw material melt of the same composition and gradually pulled up while rotating. This is a method of growing a single crystal with the same crystal orientation.

In order to solve the conventional problems, the present inventors have discovered an oxide single crystal growth apparatus and method using an oxide crucible made of the same material as the raw material melt instead of the noble metal outer crucible.

That is, the growing 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;
It is incorporated into the oxide crucible 1 and is heated by induction by the high-frequency induction coil 2, while the upper end 3b is held by fixing means (not shown) provided above the oxide crucible 1 and the lower end 3a is oxidized. a cylindrical metal heater 3 (corresponding to the inner crucible) arranged upwardly away from the inner bottom surface 1a of the crucible 1;
A raw material supply means 51 is provided 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,
Further, 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 raw material supply means 51 of the growth apparatus shown in FIG. 1 is composed of a heat-resistant holding container 51a having a raw material supply port 51b at the lower end, and a crystal raw material (crystal material 10a) accommodated in this holding container 51a. The crystal raw material (crystal material 10a) in the holding container 51a is pushed by a cylinder (not shown) or the like and is supplied to fall onto the surface of the raw material melt 10 in the ring-shaped gap 50.

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 attachment form of the raw material supply means 51 is different.

That is, as shown in FIG. 2, the raw material supply means 51 of the growth apparatus according to the modification includes a heat-resistant holding container 51a having a raw material supply port 51b at the lower end, and a crystal raw material (crystal) housed in the holding container 51a. The material 10a) is arranged so that the raw material supply port 51b of the holding container 51a is in contact with the raw material melt 10 side of the ring-shaped gap 50, and the crystal raw material (crystal material 10a) is supplied from the raw material melt 10 side. It is supplied while being melted.

The method shown in FIG. 2 in which the crystal raw material (crystal material 10a) is brought into contact with the raw material melt 10 surface is more effective than the method shown in FIG. Since there is no impact during supply, there is an advantage that crystal growth can be performed in the same temperature environment without fluctuation of the 10 surfaces of the raw material melt.

Incidentally, the crystal raw material (crystal material 10a) is exemplified by crystal material powder, crystal material grains, or crystal material lumps.

(1) Growing device according to the first embodiment and growing method using this device (1-1) Growing device according to the first embodiment The growing device according to the first embodiment has a bottom surface as shown in FIG. The side is fixed with a support stand 11, and the growth apparatus according to the present invention (comprising an oxide crucible 1 and a cylindrical metal heater 3) excluding the high-frequency induction coil 2 is accommodated, and a seed rod (crystal pulling shaft) is installed on the upper side. A heat insulating outer cylinder 13 having an opening 12 for a metal heater 20, and a heater fixing rod 14 (FIG. ), a ring-shaped reflector 15 placed on the upper end 3b of the cylindrical metal heater 3 held by the heater fixing bar 14, and an after-heater placed on the ring-shaped reflector 15. 16, a raw material supply means 51 fitted into the gap formed by the heater fixing rod 14 and the heat insulating outer cylinder 13, and a raw material supply means 51 attached to the lower end side of the seed rod (crystal pulling shaft) 20. The main part is constituted by a rod-shaped seed crystal 21.

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. Further, in FIG. 4, reference numeral 40 indicates a ceramic container (CP crucible) that covers the outer bottom surface 1b and side walls of the oxide crucible 1.

(1-2) Growth method according to the first embodiment A crystal raw material is introduced into an oxide crucible 1 in which a cylindrical metal heater 3 is incorporated, and the cylindrical metal heater 3 is heated by induction using a high frequency induction coil 2 to form a cylindrical material. The crystal raw material in the cylindrical metal heater 3 and the crystal raw material existing in the 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 are melted.

Next, after the seed crystal 21 is brought into contact with the surface of the raw material melt 10 in the cylindrical metal heater 3, the oxide single crystal 30 is grown by raising the seed rod (crystal pulling shaft) 20 while rotating.

(1-3) Effects of the growth method according to the first embodiment According to the growth method according to the first embodiment, the outer crucible of the double crucible is composed of the oxide crucible 1, and the inner crucible of the double crucible Since it is composed of a cylindrical metal heater, the high frequency electromagnetic field is not blocked by the oxide crucible (outer crucible) 1, so it is possible to induction heat the cylindrical metal heater (inner crucible) 3 by the high frequency heating method. Become.

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

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, so that the ring-shaped gap is heated. It becomes possible to replenish the raw material melt 10 existing in the section 50 into the cylindrical metal heater (inner crucible) 3, and the crystal raw material is continuously supplied to the ring-shaped gap 50 by the raw material supply means 51. Therefore, continuous replenishment of the raw material melt 10 becomes possible.

Therefore, the growing method according to the first embodiment has the effect of repeatedly and stably growing an oxide single crystal of the same quality and having a long straight body.

(1-4) Method of manufacturing the growth device according to the first embodiment The growth device according to the first embodiment can be manufactured, for example, as follows.

First, as shown in FIG. 5, a crystal material 10a is put into a ceramic crucible (CP crucible) 40 built into a heat insulating outer cylinder 13, leaving an upper space 41. Incidentally, the crystal material 10a is exemplified by crystal material powder or crystal material lump.

Next, the cylindrical metal heater 3 is assembled into the upper space 41 of the ceramic crucible (CP crucible) 40, and the heater fixing rod 14 (see FIG. The upper end 3b of the cylindrical metal heater 3 is fixed by means of fixing means (see fixing means).

Then, as shown in FIG. 6, the crystal material 10a is put 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 placed inside the cylindrical metal heater 3 and the ceramic crucible (CP The upper space 41 of the crucible 40 is filled with the crystal material 10a.

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 after-heater 16 is placed on the ring-shaped reflector 15. place

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 crystal material 10a inside the cylindrical metal heater 3 and the vicinity of the side wall of the cylindrical metal heater 3 are heated. The crystal material 10a near the lower end 3a is melted to form a raw material melt 10, and the raw material melt 10 is flowed between a portion of the crystal material 10a located away from the side wall of the cylindrical metal heater 3 and a portion away from the lower end 3a. After forming a continuous oxide layer 1c and forming an oxide crucible 1 having the oxide layer 1c on the inner surface and capable of storing and holding the raw material melt 10, the raw material supply means shown in FIG. 51 can be incorporated to manufacture the growth device according to the first embodiment.

In addition, in the growth apparatus according to the present invention and the growth apparatus according to a modification of the present invention, as shown in FIGS. 1 and 2, a ceramic container 4 that covers the outer bottom surface 1b of the oxide crucible 1 is used, and the ceramic crucible (CP crucible) 40 cannot be used to manufacture a growth device. In such a case, a structure in which a crystalline material powder or a crystalline material lump is pressure-molded into the shape of an oxide crucible as shown in FIGS. 1 and 2, and the ceramic container 4 is incorporated on the bottom side of the molded body. After the body is housed in the heat insulating outer cylinder 13, it is possible to manufacture the growth apparatus by applying the manufacturing method described above. At this time, it is necessary to set the wall thickness of the crucible for pressure molding to be large so that the entire wall does not melt when the cylindrical metal heater 3 is heated by induction.

(2) Growing device according to second embodiment As shown in FIG. 8, the growing device according to the second embodiment has a cylindrical metal heater 3 having a cylindrical shape in which the upper end 3b is open and the lower end 3a is closed. The opening 3d for introducing the raw material melt 10 into the cylindrical metal heater 3 in the 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 is made of cylindrical metal. This is substantially the same as the growth device according to the first embodiment (see FIG. 4) except that the heater 3 is provided on the side wall. In FIG. 8, the seed rod (crystal pulling shaft) 20 and raw material supply means 51 shown in FIG. 4 are not shown.

The cylindrical metal heater 3 shown in FIG. 8 whose lower end 3a is closed is easier to stand on its own than the cylindrical metal heater 3 shown in FIG. 4 whose lower end 3a is also open. This has the advantage that the work of placing the cylindrical metal heater 3 thereon (see FIG. 9) can be simplified.

(3) Crystal material constituting the oxide crucible Regarding the oxide crucible 1 having the oxide layer 1c on the inner surface and being made of a crystal material, the entire crucible does not need to be made of one crystal. It is preferable that the entire crucible is composed of a sintered body or a polycrystalline body, but a part of the crucible may be in a powder state. Note that when a part of the oxide crucible is in a powder state, it is desirable to provide the above-mentioned ceramic container for holding the powder. Incidentally, the unmelted portion of the crystal material that is away from the oxide layer 1c of the oxide crucible 1 functions similarly to the heat insulating material 108 and the heat insulating crucible stand 110 in the conventional growth apparatus shown in FIG.

The ceramic container that covers the outer bottom surface 1b of the oxide crucible 1 or the ceramic crucible that covers the outer bottom surface 1b and side walls of the oxide crucible 1 may be made of sintered materials such as alumina, zirconia, magnesia, and calcia. Solid refractories are preferred.

(4) Metal heater The shape of the metal heater mentioned above can be arbitrary as long as high-frequency induction heating is possible, but when growing high-quality crystals using the Czochralski method, the raw material melt is rotationally symmetrical with respect to the seed (seed crystal). It is desirable to have sex. For this reason, it is preferable that the metal heater also have a rotationally symmetrical shape, and it is required that the metal heater has a cylindrical shape.

In addition, the metal heater is preferably made of a material that can be subjected to high-frequency heating without being oxidized or cracked in an oxygen-containing atmosphere. Specifically, it is preferably made of platinum, iridium, rhodium alone or an alloy thereof. is desirable.

Further, 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 the approximate center of the heat insulating outer cylinder 13 shown in FIG. 4 is exemplified. The metal heater 3 is fixed by passing the upper end 3b through a bar 14, and the number of heater fixing bars 14 is preferably about 2 to 6.

Further, it is preferable that the same material as the metal heater be used for the ring-shaped reflector placed on the upper end of the metal heater and the after-heater placed on the ring-shaped reflector.

Hereinafter, examples of the present invention will be specifically explained by citing comparative examples (conventional examples).

[Example 1]
1. Manufacturing of the growth device according to Example 1
Lithium tantalate powder (crystalline material) 10a is placed in a ceramic crucible (CP crucible) 40 with an inner diameter of 270 mm and an inner height of 340 mm, which is built into a heat insulating outer cylinder 13 shown in FIG. 9, leaving an upper space 41. I put it in.

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

Then, as shown in FIG. 10, lithium tantalate powder (crystalline material) 10a is put into the upper space 41 of a ceramic crucible (CP crucible) 40 in which the cylindrical metal heater 3 is installed. The interior and the upper space 41 of the ceramic crucible (CP crucible) 40 were filled with lithium tantalate powder (crystalline material) 10a.

Next, as shown in FIG. 8, 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 after-heater 16 is placed on the ring-shaped reflector 15. I placed it.

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 (crystal material) 10a in the cylindrical metal heater 3 and the cylindrical The lithium tantalate powder (crystalline material) 10a near the side wall of the metal heater 3 and the bottom end 3a is melted to form a raw material melt 10, and a part away from the side wall of the cylindrical metal heater 3 and a part away from the bottom end 3a The raw material melt 10 is made to flow between the lithium tantalate powder (crystalline material) 10a to form a continuous oxide layer 1c, which has the oxide layer 1c on the inner surface and is capable of storing and holding the raw material melt 10. After forming the oxide crucible 1, the raw material supply means (as shown in FIG. A growth apparatus according to Example 1 was manufactured by incorporating the raw material supply port 51b of 51a (arranged so that the raw material supply port 51b was in contact with the surface of the raw material melt).

When melting the lithium tantalate powder (crystalline material) 10a to form the oxide layer 1c, in order to increase the amount of melt outside the cylindrical metal heater 3, the input power of the high-frequency induction coil 2 is adjusted as follows. It is set 10% higher than before. As a result, the raw material melt flows between the lithium tantalate powders (crystalline materials) 10a, forming a continuous oxide layer 1c.

2. Growth of lithium tantalate single crystal Next, a seed rod (not shown) (crystal pulling shaft) with a seed crystal (not shown) attached to the tip is lowered through the opening 12 (see FIG. 8) of the heat insulating outer cylinder 13. Crystal growth was performed by a pulling method (Czochralski method), and a lithium tantalate single crystal with a diameter of 4 inches and a straight body length of about 200 mm was able to be grown.

Next, after growing the lithium tantalate single crystal, lithium tantalate powder (crystal raw material) is put into the oxide crucible 1 in which the cylindrical metal heater 3 is installed, and the cylindrical metal heater is heated by the high frequency induction coil 2. 3 is induction heated, and 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 are heated by induction heating. was melted.

Next, the seed rod (crystal pulling shaft) with the seed crystal attached is lowered from the opening 12 and crystal growth is performed by the pulling method (Czochralski method), and as above, a seed rod with a diameter of 4 inches and a straight body length of approximately A 200 mm lithium tantalate single crystal was grown.

[Comparative example (conventional example)]
A lithium tantalate single crystal with a diameter of 4 inches was grown by the pulling method (Czochralski method) using the conventional growth apparatus shown in FIG. 11 and a crucible 100 made of iridium with a diameter of 170 mm and a height of 170 mm. .

However, when the length of the straight body reaches approximately 180 mm, the melt level in the crucible 100 decreases, and the lower end of the grown lithium tantalate single crystal contacts the solidified crystal part at the bottom of the crucible 100. It became polycrystalline due to adhesion.

According to the present invention, since it is possible to repeatedly and stably grow oxide single crystals of the same quality and a long body, it can be used as a growth device for oxide single crystals such as lithium tantalate single crystals used as surface acoustic wave device materials. It has industrial applicability.

1 Oxide crucible 1a Inner bottom surface 1b Outer bottom surface 2 High frequency induction coil 2a Lower end 3 Cylindrical metal heater 3a Lower end 3b Upper end 3d Opening 4 Ceramic container 10 Raw material melt 10a Crystal material (crystal raw material) powder 11 Support stand 12 Opening 13 Heat-insulating outer cylinder 14 Heater fixing rod 15 Ring-shaped reflector 16 After-heater 20 Seed rod (crystal pulling shaft)
21 Seed crystal 30 Oxide single crystal 40 Ceramic crucible 41 Upper side 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 After heater 105 Seed crystal 106 Raw material melt 107 Insulating material 108 Insulating material 109 CP crucible (porous alumina crucible)
110 Insulating crucible stand

Claims (8)

In an apparatus for growing oxide single crystals by the pulling method,
an oxide crucible made of the crystalline 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;
It is installed in the oxide crucible and is heated by induction by the high-frequency induction coil, and the upper end is held by a fixing means provided above the oxide crucible, and the lower end is separated upward from the inner bottom surface of the oxide crucible. a cylindrical metal heater arranged in a
a raw material supply means for supplying a crystal raw material to a ring-shaped gap sandwiched between an inner wall surface of the oxide crucible and an outer wall surface of the cylindrical metal heater;
An apparatus for growing an oxide single crystal, wherein the lower end of the high-frequency induction coil is located below the lower end of the cylindrical metal heater. The cylindrical metal heater has a cylindrical shape with an open upper end and a closed lower end, and the opening for introducing the raw material melt into the cylindrical metal heater in the ring-shaped gap is a cylindrical metal heater. The oxide single crystal growth device according to claim 1, wherein the oxide single crystal growth device is provided on a side wall. The raw material supply means is composed of a heat-resistant holding container having a raw material supply port at the lower end and a crystal raw material accommodated in the holding container, and the raw material supply port of the holding container is configured to melt the raw material in a ring-shaped gap. 3. The oxide single crystal growth apparatus according to claim 1, wherein the oxide single crystal growth apparatus is arranged so as to be in contact with a liquid surface. 4. The oxide single crystal growth apparatus according to claim 1, wherein the holding container is made of platinum, iridium, rhodium, tungsten, or an alloy thereof. The oxide single crystal according to any one of claims 1 to 4, wherein 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. Cultivation equipment. 6. The oxide single crystal growth apparatus according to claim 1, wherein the cylindrical metal heater is made of platinum, iridium, rhodium, or an alloy thereof. The oxide single crystal 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 side walls of the oxide crucible. Cultivation equipment. A method for growing an oxide single crystal using the growth apparatus according to claim 1,
A crystal raw material is put into an oxide crucible in which a cylindrical metal heater is incorporated, and the cylindrical metal heater is heated by induction using a high frequency induction coil to separate the crystal raw material in the cylindrical metal heater and the crystals present in the ring-shaped gap. While the raw material is melted, 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 the material is lengthened by a pulling method. A method for growing an oxide single crystal, the method comprising growing a large oxide single crystal.

Images