JP6874473B2 - Single crystal growing device - Google Patents

Description

The present invention relates to an oxide single crystal growing device by the Czochralski method, and particularly relates to an improvement of a single crystal growing device using a high frequency induction coil as a heating device.

Conventionally, the Czochralski method has been used as one of the methods for producing an oxide single crystal, and the single crystal growing apparatus shown in Patent Document 1 is used for producing an oxide single crystal by this Czochralski method. (See FIG. 1) applies. In this single crystal growing device, a furnace material b (acting as a heat insulating material) composed of alumina or the like is formed around the crucible a, and a high frequency induction coil c as a heating device is formed on the outside of the furnace material b. Is arranged, and the material charged into the crucible a is melted by high-frequency induction heating. Further, a pulling device d for pulling the single crystal from the material melt while rotating is arranged above the crucible a, and the upper part of the furnace material b is shielded by the shielding plate e and one of the shielding plates e. An observation window f is provided in the section.

In order to grow an oxide single crystal using the single crystal growing apparatus shown in FIG. 1, the material of the oxide single crystal is put into the crucible a, the crucible a is induced and heated by the high frequency induction coil c, and the heat is used to induce and heat the crucible a. The material is melted to obtain a melt. The seed crystal is brought into contact with the obtained melt, and the seed crystal is pulled up in the vertical direction while being rotated by the pulling device d. Then, in order to grow the single crystal, a single crystal having a diameter similar to or smaller than that of the seed crystal called the neck portion is first pulled up, and then the number of rotations and the pulling speed are adjusted to adjust the number of rotations and the pulling speed of the neck portion. A portion called a shoulder is formed by gradually increasing the crystal diameter from the crystal diameter to a desired crystal diameter. After that, a portion called a straight body portion is formed while adjusting the high frequency output of the heating device so as to have a desired crystal diameter. Finally, the grown crystal is separated from the melt and slowly cooled to obtain an oxide single crystal.

By the way, when growing an oxide single crystal using the above-mentioned single crystal growing apparatus, it is the outer peripheral portion of the crucible a side wall that is heated by the high-frequency induction coil c, and the raw material is heated by the outer peripheral portion of the heated crucible a side wall. Therefore, the melt temperature in the vicinity of the side wall of the crucible a becomes high, but the melt temperature in the center of the crucible a becomes low. As a result, a difference in crystal growth rate occurs between the outer peripheral portion and the central portion of the crystal to be grown, and the lower side of the crystal grows in an inverted conical shape toward the bottom of the crucible a. When the lower side of the crystal grows in an inverted conical shape, the growth tip reaches the bottom of the crucible a and comes into contact with the crystal, making it impossible to accurately measure the crystal weight with a weight sensor such as a load cell, resulting in a stable shape. Crystals may not be obtained.

In addition, after the crystal growth is completed, the crystal is pulled up to separate the crystal from the melt, but if the height of the inverted conical portion (hereinafter referred to as "convexity") is high, the pulling distance becomes long, and as a result, high frequency induction The crystal will come off from the crucible area inside the coil. In such a case, there is a problem that the crystal is rapidly cooled and cracked. Further, the substrate cut out from the crystal having a large convexity has a problem that the strain is large because the growth time of the central portion and the outer peripheral portion is different.

In order to pull the grown single crystal straight and long, it is necessary to take a large temperature gradient in the axial direction (the direction of pulling the crystal), but oxide single crystals such as lithium tantalate and lithium niobate are heated by a large temperature gradient. Since cracks are likely to occur due to strain, the crucible should be surrounded by a fireproof material (acting as a heat insulating material), and the temperature gradient on the upper side of the crucible should be appropriately maintained on the end of the crucible or the fireproof material. The structure in which the afterheater is arranged is common (see Patent Document 2). Then, according to Patent Document 2, it is described that when a cylindrical afterheater is arranged on the crucible end, a good quality crystal with few defects can be obtained without cracking in the grown crystal.

Further, when growing an oxide single crystal, the liquid level of the raw material melt decreases as the single crystal grows, so that the contact area between the inner wall surface of the crucible heated by high frequency induction and the raw material melt decreases, and the raw material The amount of heat supplied to the melt is reduced. Since the bottom of the crucible is difficult to be induced and heated, the heat capacity decreases as the raw material liquid level decreases, and the amount of heat supplied also decreases, so that solidification starts from the bottom of the crucible. When solidification starts, the convection of the melt becomes abnormal, the single crystal cannot grow in a homogeneous shape, and the tendency for spiral growth to occur becomes remarkable. Then, when the liquid level of the raw material melt is further lowered and the amount of heat supplied to the raw material is further reduced, the coagulated product becomes large, and finally the growing single crystal collides with the coagulated product from the bottom of the crucible and is being grown. There was also a problem that the single crystal being grown was dropped due to breakage at the seed crystal part of the single crystal in.

Therefore, in order to solve these problems, in Patent Document 3, the precious metal object shown in FIGS. 2 (B) to 2 (C) (hereinafter referred to as “cup”) is attached to the outer bottom surface of the precious metal crucible a shown in FIG. 2 (A). A method of installing (referred to as "shaped cylinder" or "cup-shaped cylinder heating body") g has been proposed. That is, as shown in FIG. 2 (A), when a high frequency is induced in the noble metal crucible a by the high frequency induction coil c to heat and melt the raw material in the crucible a and the single crystal is pulled up, the cup-shaped cylinder g is used. A method of inducing a high frequency to heat the cup-shaped cylindrical g and heating the bottom of the crucible a with the heat to prevent solidification of the raw material melt at the inner bottom of the crucible a and to grow a single crystal having a uniform shape. is suggesting.

Further, in Patent Document 4 relating to the sapphire single crystal growing apparatus, the outer bottom surface of the refractory crucible (acting as a heat insulating material) b shown in FIG. 3 in which the noble metal crystal growing crucible a is housed via the crucible stand h. We have proposed a method in which a metal tubular heater i is installed in a portion and the tubular heater i is heated by high frequency induction to heat the raw material melt in the crystal growing crucible a from the bottom of the crucible. That is, by controlling the amount of heat transferred from the tubular heater i to the crystal growing crucible a, the height of the inverted conical portion on the lower side of the grown sapphire single crystal, that is, the "convexity" is reduced. We are proposing a method.

JP-A-2002-68884 (see FIG. 3) Japanese Unexamined Patent Publication No. 07-33586 (see paragraph 0005) Japanese Unexamined Patent Publication No. 56-88895 (see FIGS. 2 and 3) Japanese Unexamined Patent Publication No. 2005-231958 (see FIG. 1, paragraph 0014).

When a conventional single crystal growing device is used to induce a high frequency to a noble metal crystal growing crucible with a high frequency induction coil to heat and melt the raw material in the crystal growing crucible, the crucible side wall and the afterheater are induced and heated. Since the bottom of the crucible is difficult to be induced and heated, solidification of the raw material from the bottom of the crucible, abnormal convection of the melt caused by the coagulation, heterogeneous growth of the single crystal, collision between the solidified raw material and the single crystal, etc. occur. In order to suppress the occurrence of these, Patent Document 3 proposes a method of installing a cup-shaped cylinder that generates heat by high frequency induction on the outer bottom surface of the crystal growing crucible, and Patent Document 4 accommodates the crystal growing crucible. We are proposing a method of installing a metal tubular heater on the outer bottom surface of the refractory crucible (which acts as a heat insulating material).

Therefore, the present inventors conducted the following "AC magnetic field analysis" and its examination in order to confirm the induction heating effect of the method according to Patent Document 3 in which a cup-shaped cylinder is installed on the outer bottom surface of the crystal growing crucible. In addition, the heating effect of the metal tubular heater according to Patent Document 4 was analyzed.

(1) Analysis of a crucible structure according to a conventional example in which a cup-shaped cylinder or the like is not installed An iridium crystal growing crucible shown in FIG. 1 and an iridium afterheater incorporated through a donut plate-shaped reflector at the open end of the crucible. For the crucible structure according to the conventional example composed of, an AC magnetic field analysis was performed on the effect on the heat generation density distribution when a high frequency is induced by a high frequency induction coil.

Looking at the analysis results, as shown in FIGS. 7A and 7B, at a relatively low frequency induced current of 1 kHz or less, the heat generation distribution of the crucible structure according to the conventional example is almost uniform along the side wall of the crucible. However, at high frequencies of 7 kHz or higher, which are generally used in crystal growth furnaces, the bent part of the crucible structure (the bent part formed by the bottom surface and the side wall of the crucible) and the connection part between the crucible and the afterheater (doughnut plate shape reflector). It was confirmed that the heat generation was concentrated on the edge part of the crucible.

In addition, when AC magnetic field analysis is performed on the heat generation density distribution of the side wall from the bottom of the crucible to the afterheater and the heat generation density distribution in the radial direction from the center at the bottom of the crucible, it reaches from the bottom of the crucible to the afterheater. As shown in FIGS. 8 (A) and 8 (B), the heat generation density distribution of the side wall portion is distributed at the end (bottom) of the crucible and the edge portion such as the connection portion between the crucible and the afterheater (the location of the donut plate-shaped reflector). It was confirmed that heat generation was concentrated, and as shown in FIGS. 8C and 8D, in the crucible structure according to the conventional example in which the cup-shaped cylinder or the like was not installed, there was almost no heat generation at the center of the crucible bottom, and the end of the crucible bottom. It was confirmed that there was only a slight fever in the crucible.

From these circumstances, it is considered that the method of Patent Document 3 in which a cup-shaped cylinder is installed on the outer bottom surface of the crystal growing crucible to assist heating the bottom of the crucible is effective.

(2) Analysis of crucible structure according to Patent Document 3 in which a cup-shaped cylinder is installed A platinum crystal growing crucible, a platinum afterheater incorporated via a donut plate-shaped reflector at the open end of the crucible, and the above platinum. Regarding the crucible structure according to Patent Document 3, which is composed of a platinum cup-shaped cylinder installed on the outer bottom surface of the crucible for growing crystals, the heat generation density distribution when a high frequency is induced by a high frequency induction coil is applied. An AC magnetic field analysis was performed for the effect.

From the crucible and the cup-shaped cylinder described in FIG. 2 of Patent Document 3 (Japanese Unexamined Patent Publication No. 56-88895), the radius of the cup-shaped cylinder R ₁ = (3/4) R ₀ (R ₀ : crystal). The radius of the outer bottom surface of the growing crucible), the height of the cup-shaped cylinder H ₁ = (1/3) H ₀ (H ₀ : the height of the crystal growing crucible), and it was applied in this Example 1. The size of the platinum cup-shaped cylinder was determined by applying the above dimension ratio to the dimensions of the crucible for growing flat-bottomed crystals having an outer diameter of 205 mmφ and a height of 180 mm, and an AC magnetic field analysis was performed.

As shown in FIGS. 9A and 9B, the heat generation density is large at the cylindrical end of the cup-shaped cylinder, and as shown in FIGS. 10A and 10B, the radius of the cup-shaped cylinder is also an induction coil. Although the heat generation density was slightly higher because it was close to, no significant difference was observed in the crystal growing crucible as compared with FIGS. 8 (B) and 8 (D).

On the other hand, looking at the temperature distribution of the melt in the crucible for crystal growth [see FIG. 11 (A)], it is confirmed that the heating effect is not large as compared with the temperature distribution of FIG. 11 (B).

When the cup-shaped cylinder of Patent Document 3 is applied, a disk-shaped plate material g1 as shown in FIG. 2B exists in the cup-shaped cylinder installed on the outer bottom surface of the crystal growing crucible and is used for crystal growing. The thickness of the outer bottom surface of the crucible is increased by the thickness of the plate material g1, and as a result, the thermal resistance of the outer bottom surface of the crystal growing crucible is increased, so that the heating effect of the cup-shaped cylinder is considered to be weak. ..

Therefore, it was confirmed that the cup-shaped cylinder according to Patent Document 3 needs to be improved.

In addition, FIG. 11B shows the melt temperature in the crucible for crystal growth to which the precious metal cylindrical member (cylindrical heating body) of the present invention described later is applied.

(3) Heating effect of the metal tubular heater of Patent Document 4 When the metal tubular heater i of Patent Document 4 (see FIG. 3) is applied, the outer bottom surface of the iridium crucible a and the metal tubular heater described above. Since the fire-resistant crucible (acting as a heat insulating material) b and the heat insulating material j filled in the fire-resistant crucible b are interposed between i, the heat from the metal tubular heater i is generated from the outer bottom surface of the iridium crucible a. It is difficult to convey to the club.

Therefore, it was confirmed that the conventional technique needs to be improved because the heating effect of the metal tubular heater i on the outer bottom surface of the crucible is also weak.

Therefore, an object of the present invention is to modify the crucible structure that can efficiently increase the heat generation of the bottom of the crucible for crystal growth, thereby solidifying the raw material from the bottom of the crucible and convection of the melt caused by the modification. It is an object of the present invention to provide a single crystal growing apparatus in which abnormalities, inhomogeneous growth of a single crystal, collision between a coagulated raw material and a single crystal, etc. are suppressed.

As a result of diligent research to solve the above problems, the present inventors have replaced the structure of the noble metal object (referred to as the cup-shaped cylinder or the cup-shaped cylinder heating body) described in Patent Document 3 with a noble metal. By adopting a cylindrical member made of a product, that is, a tubular structure that does not have the disk-shaped plate material g1 shown in FIG. 2 (B), solidification of the raw material from the bottom of the crucible and convection abnormality of the melt caused by the solidification, single It has been found that inhomogeneous growth of crystals and collision between a solidified raw material and a single crystal can be suppressed.

That is, the first invention according to the present invention is
A refractory crucible with one end open,
A heat insulating material that is arranged on the open end side of the refractory crucible and has a space that communicates with the space of the refractory crucible to form a cylindrical space with the refractory crucible.
A crucible for growing crystals, which is arranged on the lower side in the cylindrical space via a support and has one end open.
The heat insulating material filled in the space between the refractory crucible and the crystal growing crucible and the space between the refractory crucible and the support base,
A cylindrical afterheater placed at the open end of the crystal growing crucible via a reflector,
A high-frequency induction coil arranged around the refractory crucible is provided in the chamber.
In a single crystal growing apparatus in which a seed crystal attached to the tip of a crystal pulling shaft is brought into contact with the raw material melt of the above-mentioned crystal growing crucible to grow a single crystal.
A precious metal cylindrical member heated by a high-frequency induction coil is attached to the outer bottom surface of the crystal growing crucible so that its central axis is aligned with the central axis of the crystal growing crucible.
Radius R ₁ of the noble metal cylindrical member, with respect to the radius R ₀ of the outer bottom surface of the crystal growth crucible,
1/3 ≤ R ₁ / R ₀ ≤ 1
_{The height H 1} of the precious metal cylindrical member is relative _{to the height H 0} of the crystal growing crucible.
1/8 ≤ H ₁ / H ₀ ≤ 1/2
Together meet the relationship,
The support base of the crucible for crystal growth is fitted in the tubular portion of the noble metal cylindrical member .

According to the single crystal growing apparatus according to the present invention.
It is possible to efficiently increase the heat generated at the bottom of the crucible for crystal growth, thereby preventing the temperature of the bottom of the crucible from dropping, so that solidification of the raw material from the bottom of the crucible can be suppressed and the yield of crystal growth can be improved. ..

FIG. 6 is a configuration explanatory view of the single crystal growing apparatus shown in Patent Document 1. FIG. 2A is a configuration explanatory view of the single crystal growing apparatus according to Patent Document 3 in which a precious metal object (cup-shaped cylinder) is installed on the outer bottom surface of the crucible, and FIG. 2B is the precious metal object (cup). A schematic perspective view of (cylindrical cylinder), FIG. 2 (C) is a schematic cross-sectional view of FIG. 2 (B). FIG. 6 is a configuration explanatory view of a single crystal growing device according to Patent Document 4, in which a metal tubular heater is installed on the outer bottom surface of a refractory crucible (acting as a heat insulating material) in which a crucible for crystal growth is housed. The configuration explanatory view of the single crystal growth apparatus which concerns on embodiment of this invention. _{The height H 0 of the crucible for growing crystals and the radius R 0} of the outer bottom surface portion of the single crystal growing crucible of the present invention _{, and the height H 1} and radius of the noble metal cylindrical member attached to the outer bottom surface portion of the crucible. explanatory view showing a R ₁ respectively. The explanatory view which shows the relationship between the bottom surface of the crucible for crystal growth which concerns on the single crystal growth apparatus of this invention, and the center of the lowermost end coil of a high frequency induction coil. FIG. 7 (A) is a schematic cross-sectional view of a conventional crucible structure composed of a crucible for crystal growth and an afterheater arranged at an open end thereof via a donut plate-shaped reflector, and FIG. 7 (B) is the above-mentioned crucible structure. Graph diagram showing the relationship (frequency dependence) between "distance from the bottom of the crucible" and "heat generation density" when a high frequency (selected from 500Hz, 1kHz, 3kHz, 5kHz, and 10kHz) is induced with respect to the body with a high frequency induction coil. .. FIG. 8 (A) is a schematic cross-sectional view of the conventional crucible structure shown in FIG. 7 (A), and FIG. 8 (B) shows a high frequency (7 kHz is selected) induced in the crucible structure with a high frequency induction coil. A graph showing the relationship between "distance from the bottom of the crucible" and "heat generation density", FIG. 8 (C) is a schematic cross-sectional view of a conventional crucible structure, and FIG. 8 (D) is high-frequency induction with respect to the crucible structure. The graph which shows the relationship between the "distance from the center of the crucible bottom" and the "heat generation density" when a high frequency (7 kHz is selected) is induced by a coil. FIG. 9A shows a crucible structure according to Patent Document 3, which is composed of a crucible for growing crystals, an afterheater arranged via a donut plate-shaped reflector, and a cup-shaped cylinder installed on the outer bottom surface of the crucible. A schematic cross-sectional view, FIG. 9B is a graph showing the relationship between the "distance from the bottom of the crucible" and the "heat generation density" when a high frequency (7 kHz is selected) is induced with respect to the crucible structure. .. FIG. 10 (A) is a schematic cross-sectional view of the crucible structure according to Patent Document 3, and FIG. 10 (B) shows a high frequency (7 kHz is selected) induced in the crucible structure according to Patent Document 3 with a high frequency induction coil. Graph diagram showing the relationship between "distance from the center of the bottom of the crucible" and "heat generation density". FIG. 11 (A) is a temperature distribution diagram showing the temperature distribution of the melt in the crucible in the crucible structure according to Patent Document 3 in which the cup-shaped cylindrical heater is installed in the color of “Temperature Contour 1”, FIG. 11 (B). ) Is a temperature distribution diagram showing the temperature distribution of the melt in the crucible in the crucible structure to which the noble metal cylindrical member (cylindrical heating body) of the present invention is attached in the color of "Temperature Contour 1". The above "Temperature Contour 1" showing the temperature in color. FIG. 12A shows the temperature distribution in the vicinity of the crucible and the melt in the crucible of the crucible structure (with a cylindrical heating body) to which the noble metal cylindrical member according to the present invention is attached, in the color of “Temperature Contour 1”. In the distribution map, FIG. 12 (B), the temperature distribution in the vicinity of the crucible and the melt in the crucible of the conventional crucible structure (without the cylindrical heating body) to which the noble metal cylindrical member is not attached is displayed in the color of "Temperature Contour 1". The temperature distribution map, FIG. 12 (C), shows the temperature in color in the above "Temperature Contour 1". FIG. 13A shows a crucible structure composed of a crucible for growing crystals, an afterheater arranged via a reflector, and a noble metal cylindrical member (precious metal member) according to the present invention attached to the outer bottom surface of the crucible. A temperature distribution diagram of the crucible, reflector, afterheater, melt in the crucible, and seed crystal (with a cylindrical heater) displayed in the color of "Temperature Contour 2" (temperature range 1590 ° C to 1720 ° C), FIG. 13 (B). ) Indicates the temperature range of 1590 ° C to 1720 ° C for the crucible, reflector, afterheater, melt in the crucible and seed crystal of the conventional crucible structure (without the cylindrical heater) to which the noble metal cylindrical member is not attached. The temperature distribution map displayed in the color of "2", FIG. 13 (C) is the above-mentioned "Temperature Contour 2" in which the temperature is shown in color. FIG. 14A is composed of a crucible for growing crystals, an afterheater arranged via a donut plate-shaped reflector, and a noble metal cylindrical member (cylindrical heater) according to the present invention attached to the outer bottom surface of the crucible. Schematic cross-sectional view of the crucible structure, FIG. 14 (B) is a schematic cross-sectional view of the crucible structure in which a cup-shaped cylindrical heater is installed instead of the cylindrical heater, and FIG. 14 (C) is for each crucible structure. The graph which shows the relationship between "distance from the crucible bottom" and "heat generation density" when high frequency (7kHz is selected) is induced by a high frequency induction coil. FIG. 15A shows a noble metal cylindrical member (cylindrical heating body) according to the present invention attached to the outer bottom surface of the pit, where the height of the crystal growing pit is H ₀ and the radius of the outer bottom surface is R _0. The height is H ₁ , the radius is R ₁ , and the radius ratio (R ₁ / R ₀ ) and height ratio (H ₁ / H ₀ ) are round 1 (R ₁ / R ₀ = 1, H ₁ /). H ₀ = 1/2), Maru 2 (R ₁ / R ₀ = 1, H ₁ / H ₀ = 1/8), Maru 3 (R ₁ / R ₀ = 1/3, H ₁ / H ₀ = 1) _{/ 2) and (R 1} / R ₀ ) and (H ₁ / H ₀ ) when Maru 4 (R ₁ / R ₀ = 1/3, H ₁ / H ₀ = 1/8) A graph showing the relationship, FIG. 15 (B), shows the temperature distribution of the melt in the radius and the vicinity of the radius of the radius structure (without the cylindrical heater) to which the cylindrical heater is not attached, and the cylindrical heater is attached ( The temperature distributions in the vicinity of the pit and the melt in the pit of the pit structure in which _{R 1} / R ₀ ) and (H ₁ / H _{0) are set to circles 1 to 4 are displayed in the color of "Temperature Contour 2".} The temperature distribution map, FIG. 15 (C) is the above-mentioned "Temperature Contour 2" in which the temperature is shown in color. Figure 16 (A) the relationship between _(R 1 / R ₀₎ and _(H 1 / H ₀₎ is in the case of the above circle 1 Mar 4 _(R 1 / R ₀₎ and _(H 1 / H ₀₎ 16 (B) shows a crucible structure (without a cylinder) to which the noble metal cylindrical member according to the present invention is not attached, and (R ₁ / R ₀ ) and (H _{1) to which a cylindrical heating body is attached.} A graph showing the relationship between the "distance from the center of the crucible bottom to the side surface" and the "temperature of the bottom surface of the melt" of each crucible structure in which / H _{0) is set to circles 1 to 4.}

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the technical matters relating to the present invention are not limited to the following embodiments.

First, the single crystal growing device according to the present embodiment is arranged on the open end side of the fire resistant crucible (acting as a heat insulating material) 6 whose one end side is open and the fire resistant crucible 6 which is open at one end side as shown in FIG. A heat insulating material 9 having a space portion communicating with the space portion of the fire-resistant crucible 6 and forming a cylindrical space with the fire-resistant crucible 6 and a support base 8 are arranged on the lower side in the cylindrical space. Foam filled in the gap space between the crystal growing crucible 4 and the fire resistant crucible 6 and the crystal growing crucible 4 and between the fire resistant crucible 6 and the support base 8 with one end open. A heat insulating material 7 made of zirconia or the like, a cylindrical afterheater 13 arranged at the open end of the crystal growing crucible 4 via a donut plate-shaped reflector 14, and a fire-resistant crucible 6 are wound around. A metal high-frequency induction coil 2 arranged and a support base 12 for a fire-resistant crucible supporting the bottom surface side of the fire-resistant crucible 6 are provided in the chamber 1, and a seed crystal attached to the tip of the crystal pulling shaft 11 is provided. 10 is brought into contact with the raw material melt 3 of the crystal growing crucible 4 to grow a single crystal.

Further, a precious metal cylindrical member 5 induced and heated by a high-frequency induction coil 2 is fused and installed on the outer bottom surface of the crystal growing crucible 4 so that its central axis is aligned with the central axis of the crystal growing crucible 4. Further, the support base 8 of the crystal growing crucible 4 is fitted in the tubular portion of the precious metal cylindrical member 5.

Then, each component will be described.

First, the chamber 1 has a function of blocking heat from the crystal growing crucible 4 and the high-frequency induction coil 2 and accommodating these members. Further, the chamber 1 can be divided in a horizontal direction or the like with a predetermined vertical cross section, whereby the crystal growing crucible 4 and the high frequency induction coil 2 and the like can be exposed.

The refractory crucible support 12 is a support for holding the refractory crucible 6 that acts as a heat insulating material and the heat insulating material 9 that has a space that communicates with the space of the refractory crucible. It is composed of materials such as. Further, as described above, a cylindrical space is formed by the space portion of the refractory crucible 6 and the space portion of the heat insulating material 9. Alumina or the like is used for the refractory crucible 6, and zirconia, alumina or the like is used for the heat insulating material 9.

The crystal growing crucible 4 is a container for holding a crystal raw material in the crucible and growing crystals. The crystal raw material is held in the state of the melt 3 in which the crystallizing metal or the like is melted. The crystal growing crucible 4 is made of heat-resistant platinum, iridium, or the like, although it depends on the crystal raw material.

Further, zirconia, alumina, or the like is used for the support base 8 that supports the crystal growth crucible 4.

In addition, the single crystal grown by the Czochralski method moves away from the crystal growth chamber 4 as the pulling of the single crystal progresses, so that the temperature distribution of the single crystal becomes large and the single crystal causes problems such as cracking. In some cases. In order to avoid this problem, an afterheater 13 is arranged at the open end of the crystal growing crucible 4 via a donut plate-shaped reflector 14, whereby an appropriate temperature distribution is maintained. The shape of the afterheater 13 is set so that the inner diameter thereof is larger than the diameter of the oxide single crystal to be grown and smaller than the diameter of the crystal growing crucible 4. The total length of the afterheater 13 is a cylinder that is longer than half the total length of the oxide single crystal to be grown and shorter than twice the total length. Further, the after heater 13 is made of a metal such as platinum or iridium.

The metal high-frequency induction coil 2 arranged so as to wind around the fire-resistant crucible 6 is for inducing and heating the crystal growing crucible 4, the precious metal cylindrical member 5, the reflector 14, and the afterheater 13. It is a means, and is arranged so as to surround the upper part of the crystal growing crucible 4, the precious metal cylindrical member 5, the reflector 14, and the afterheater 13. The form of the high-frequency induction coil 2 does not matter as long as it can induce and heat the crucible 4 for crystal growth, the cylindrical member 5 made of precious metal, the reflector 14, and the afterheater 13.

Further, the crystal pulling shaft 11 holds the seed crystal 10 at its tip, brings the seed crystal 10 into contact with the surface of the crystal raw material (raw material melt 3) in the crystal growing crucible 4, and pulls the crystal while rotating. Is a means for. The crystal pulling shaft 11 has a seed crystal holding portion for holding the seed crystal 10 at the lower end portion, and has a pulling shaft driving mechanism including a motor which is a rotation mechanism. Further, the motor is provided with a rotation drive mechanism for pulling up the crystal while rotating the crystal when pulling up the crystal.

The feature of the single crystal growing device according to the present embodiment is that the noble metal cylindrical member 5 induced and heated by the high frequency induction coil 2 on the outer bottom surface of the crystal growing crucible 4 has its central axis at the center of the crystal growing crucible 4. The point is that it is attached (fused and installed) in line with the shaft. That is, by optimizing the dimensions of the noble metal cylindrical member 5 with respect to the crystal growing crucible 4, heat generation at the bottom of the crystal growing crucible 4 is efficiently realized, thereby suppressing a temperature drop at the bottom of the crystal growing crucible 4. However, the occurrence of melt solidification from the bottom of the crystal growing crucible 4 is prevented, and the crystal yield is improved.

From the confirmation experiment described later, when the dimensions of the precious metal cylindrical member 5 satisfy the following conditions, it is possible to prevent the occurrence of melt solidification from the bottom of the crystal growing crucible 4.

That is,
Radius R ₁ of the noble metal-made cylindrical member 5, with respect to the radius R ₀ of the outer bottom surface of the crystal growth crucible 4,
1/3 ≤ R ₁ / R ₀ ≤ 1
_{The height H 1} of the precious metal cylindrical member 5 is relative _{to the height H 0} of the crystal growing crucible 4.
1/8 ≤ H ₁ / H ₀ ≤ 1/2
When the above relationship is satisfied, it is possible to prevent the occurrence of melt solidification from the bottom of the crystal growing crucible 4.

Here, when the above (R ₁ / R ₀ ) is less than 1/3, the heat generated at the bottom of the crystal growing crucible 4 is limited to the vicinity of the central portion of the bottom of the crystal growing crucible 4, so that the crystal growing crucible 4 It becomes difficult to realize efficient heat generation at the bottom. On the other hand, when the above (R ₁ / R ₀ ) exceeds 1, the cylindrical wall surface of the precious metal cylindrical member 5 is located outside the side wall surface of the crystal growing crucible 4, so that the bottom of the crystal growing crucible 4 is used. It becomes difficult to heat uniformly.

Further, when the above (H ₁ / H ₀ ) is less than 1/8, the effect of heat generation by the precious metal cylindrical member 5 becomes insufficient, so that efficient heat generation at the bottom of the crystal growing crucible 4 can be realized. It will be difficult. On the other hand, when the above (H ₁ / H ₀ ) exceeds 1/2, the tip of the precious metal cylindrical member 5 generates excessive heat and the end side of the bottom of the crucible 4 for crystal growth generates more heat, so that it is used for crystal growth. It becomes difficult to uniformly heat the bottom of the crucible 4.

Therefore, it is necessary to set so that the conditions of 1/3 ≤ R ₁ / R ₀ ≤ 1 and 1/8 ≤ H ₁ / H _{0 ≤ 1/2 are satisfied.}

The type of single crystal grown using the single crystal growing apparatus according to the present embodiment is not particularly limited, and for example, a lithium niobate raw material or a lithium tantalate raw material is used to grow a lithium tantalate single crystal or niobate. It is possible to grow a lithium acid single crystal. In addition, crystal raw materials for growing various oxide single crystals including sapphire single crystals can be used.

[Confirmation experiment]
The crucible structure according to the embodiment (a crucible structure in which the noble metal cylindrical member of the present invention is attached to the outer bottom surface of the crystal growing crucible so that its central axis is aligned with the central axis of the crystal growing crucible), and , A confirmation experiment to compare and confirm the heat generation state when high-frequency induction heating is performed on the crucible structure according to the conventional example (the conventional crucible structure without the above-mentioned noble metal cylindrical member) by the following simulation. went.

For simulation, as analysis software, finite element analysis software [ANSYS: ANSYS Inc. ] Was used.

(Simulation analysis conditions)
The analysis conditions for induction heating by a high-frequency magnetic field created by a high-frequency induction coil are shown below.

Since the shape of the member in the single crystal growing apparatus according to the present embodiment is axisymmetric as shown in FIG. 4, a two-dimensional axisymmetric model was created.

Iridium's "Crystal Growth Crucible 4", Iridium's "Reflector 14", Iridium's "Afterheater 13", "High Frequency Induction Coil 2", and cylindrical space as components that are induced and heated by a high frequency magnetic field. The "gas" existing in the part was analyzed.

Regarding the present invention, an iridium-made "precious metal cylindrical member 5" attached to the outer bottom surface of the crucible 4 was added as a component to be induced and heated.

The material constants used in the calculation are the electrical resistivity of iridium: 46.6 × 10 ^-8 (Ω · m) and the magnetic permeability of vacuum: 4π × 10 ^-7 (H / m).

From the high-frequency magnetic field analysis, the current density i (A / m ² ) induced in the crystal growth chamber 4, the reflector 14, and the afterheater 13 was obtained, and each element of the model was calculated by the formula of ^{ρi 2 (ρ: electrical resistivity).} The heat generation density q (W / m ³ ) is calculated. Then, the calorific value of each element can be obtained by multiplying the heat generation density by the volume of each element.

On the other hand, the thermo-fluid analysis software CFX (ANSYS Inc.) was used for the calculation of the temperature distribution in the furnace. As the heat generation load conditions, the heat generation densities of the crystal growing crucible 4, the reflector 14, and the afterheater 13 obtained by the above magnetic field analysis were set in the crystal growing crucible, the reflector, and the afterheater in the thermo-fluid analysis model. The temperature distribution in the furnace was obtained by performing a thermo-fluid analysis with the wall of the cooling water region of the chamber (SUS) 1 fixed at 30 ° C.

(Specific structure of single crystal growing device)
As the main structure shown in FIG. 4, the outer bottom surface of the iridium flat-bottomed crystal growing crucible 4 having an outer diameter of 205 mmφ, a height of 180 mm, and a thickness of 2.5 mm has an outer diameter of 135 mmφ, a height of 50 mm, and a thickness of 2. A 5 mm iridium noble metal cylindrical member 5 is fused and arranged, and the support base 8 of the crystal growing crucible 4 is fitted (fitted) into the tubular portion of the noble metal cylindrical member 5.

The high frequency induction coil 2 is wound with a pitch of 30 mm for 12 turns. The cross-sectional shape of the tubular coil is 20 mm × 20 mm, the thickness of the tube is 1.5 mm, and the distance between the bottom surface of the crystal growing pit 4 and the center of the lowermost end of the high frequency induction coil 2 is as shown in FIG. The height position of the high frequency induction coil 2 was adjusted so as to be 80 mm.

The frequency of the coil current in the high frequency induction coil 2 was set to 7 kHz as a standard, and the power was adjusted so that the temperature at the interface between the seed crystal and the melt had a melting point of 1650 ° C.

The height of the melt 3 in the crystal growth crucible 4 is 166 mm, and a seed crystal 10 of 8 mm square × 70 mm is brought into contact with the surface of the melt.

(1) Effect of coil frequency of heat generation density distribution on the crucible structure according to the conventional example (1-1) High frequency induction coil 2 with respect to the crucible structure according to the conventional example to which the noble metal cylindrical member of the present invention is not attached. The frequency of the coil current in the above was changed to 500 Hz, 1 kHz, 3 kHz, 5 kHz, and 10 kHz, and induction heating was performed, and the effect on the heat generation density distribution was investigated.

Further, when the frequency of the coil current in the high frequency induction coil 2 is 7 kHz,
(A) Heat generation density distribution on the side surface of the crystal growing crucible 4.
(B) The heat generation density distribution at the bottom surface of the crystal growing crucible 4 was investigated.

(1-2) Survey results Looking at the analysis results on the effect of coil frequency, as shown in Fig. 7 (B), at a relatively low frequency of 1 kHz or less, the heat generation density distribution of the crystal growing crucible is on the crucible side wall. It is almost uniform along the line, but at high frequencies of 7 kHz or higher, which is generally used in crystal growth furnaces, the corners of the crucible for crystal growth (corners formed by the bottom surface of the crucible and the side walls) and the connection between the crucible and the afterheater It was confirmed that heat generation was concentrated on the edges such as (the location of the donut plate-shaped reflector) and the end of the after-heater.

Further, in the heat generation density distribution of the bottom surface of the crucible for crystal growth, as shown in FIG. 8 (D), there is almost no heat generation from the center to the corner of the bottom of the crucible, and heat is generated at the corner of the bottom of the crucible. confirmed.

Looking at the temperature distribution of the melt in the crucible, when the noble metal cylindrical member of the present invention is not attached (fused and installed), the inside of the crucible for crystal growth is as shown in FIG. 12 (B). Although the temperature is almost the same, the temperature does not rise at the upper part of the crystal growth crucible, the reflector, and the afterheater, and when the crystal is pulled up, the crystal may be rapidly cooled and cracked. Highly sexual.

In addition, FIG. 12A shows the temperature distribution in the vicinity of the crucible and the melt in the crucible when the precious metal cylindrical member of the present invention is attached (fused and installed) in the color of “Temperature Contour 1”. Although it is a figure, the temperature near the crucible (reflector, afterheater) and the upper end of the seed crystal are slightly lower than the temperature distribution diagram of FIG. 12 (B) in which the noble metal cylindrical member is not attached (fused and installed). Has been done. This point will be supplementarily explained in columns (2-2-1) and (2-2-2) below.

(2) When a precious metal cylindrical member is fused and installed on the outer bottom surface of the crystal growing crucible (2-1) In the embodiment in which the noble metal cylindrical member is attached to the outer bottom surface of the crystal growing crucible. When the frequency of the coil current in the high-frequency induction coil 2 is 7 kHz with respect to the crucible structure,
(A) Heat generation density distribution on the side surface of the crystal growing crucible 4.
(B) The heat generation density distribution at the bottom surface of the crystal growing crucible 4 was investigated.

(2-2) Survey Results As for the heat generation density distribution on the side surface of the crystal growing crucible 4, as shown in FIG. 14 (C), it was confirmed that heat was generated at the end of the cylindrical portion of the precious metal cylindrical member 5. The heat generation density distribution of the other side surfaces of the crystal growing crucible 4 is almost the same as that of the structure of the crucible structure according to the conventional example, and the corners of the crystal growing crucible (corners formed by the bottom surface of the crucible and the side wall). It was confirmed that heat generation is concentrated on the edge part such as the part), the connection part between the crucible and the afterheater (the part where the donut plate shape reflector is arranged), and the end part of the afterheater.

On the other hand, as shown in FIG. 11B, the heat generation density distribution at the bottom surface of the crystal growing crucible 4 is such that heat is generated at the end of the cylindrical portion of the noble metal cylindrical member 5, and heat is generated at the noble metal cylindrical member 5 due to heat conduction. It was confirmed that the density was increasing and the bottom surface of the crystal growing crucible 4 was heated.

(2-2-1) By the way, the temperature distribution of the melt in the crucible and the vicinity of the crucible when the noble metal cylindrical member of the present invention is attached, and the vicinity of the crucible and the inside of the crucible when the noble metal cylindrical member is not attached. The temperature distribution of the melt has already been shown in FIGS. 12 (A) and 12 (B) in FIG. 12 (C) “Temperature Contour 1” (temperature range of 30 ° C. to 1720 ° C. is displayed in hue). (A) A precious metal cylinder according to "Temperature Contour 2" (temperature range 1590 ° C to 1720 ° C) shown in FIG. 13 (C) so that the difference in temperature of each part shown in (B) can be easily understood. Temperature distribution in the vicinity of the crucible and the melt in the crucible when the member is attached [see FIG. 13 (A)], and temperature distribution in the vicinity of the crucible and the melt in the crucible when the noble metal cylindrical member is not attached [Fig. 13] (B)] is shown.

(2-2-2) If the precious metal cylindrical member 5 is attached (fused installation), the melt can be heated efficiently, so that the crucible and reflector required to bring the temperature of the tip of the seed crystal to the melting point. , The amount of heat generated by the entire afterheater can be reduced. Therefore, as shown in FIG. 13A, the temperature of the afterheater is low, and the temperature of the upper end of the seed crystal is also low. Therefore, the heat of the melt is easily transferred along the seed crystal and the seed axis, so that the temperature of the melt is lowered and the temperature gradient is increased. It was confirmed that when the temperature gradient is large, the crystals are less likely to grow rapidly, and the effect of improving the controllability of crystal growth can be obtained.

(2-2-3) On the other hand, if the precious metal cylindrical member 5 is not attached (fused installation), it is shown in FIG. 13 (B) as compared with the case where the precious metal cylindrical member 5 is attached (fused installation). It can be seen that the temperature of the afterheater is high and the temperature of the upper end of the seed crystal is high.

As a result, the temperature difference between the temperature of the tip of the seed crystal in contact with the melt and the upper end is small, the heat of the melt is difficult to escape through the seed crystal and the seed shaft, and the temperature of the melt near the tip of the seed crystal does not decrease. It can be seen that the temperature gradient of the melt near the tip of the seed crystal is small.

Therefore, from this state, it was presumed that if the heating power was lowered to lower the temperature, the crystals might grow rapidly.

(3) Analysis of crucible structure according to Patent Document 3 in which a cup-shaped cylinder is installed (3-1) A crucible for growing platinum crystals, a platinum afterheater incorporated via a reflector, and the above-mentioned platinum crystal growing crucible. About the effect on the heat generation density distribution when a high frequency is induced by a high frequency induction coil for the crucible structure according to Patent Document 3 composed of a platinum cup-shaped cylinder installed on the outer bottom surface of the crucible. An analysis was performed.

From the crucible and the cup-shaped cylinder described in FIG. 2 of Patent Document 3 (Japanese Unexamined Patent Publication No. 56-88895), the radius of the cup-shaped cylinder R ₁ = (3/4) R ₀ (R ₀ : crystal). The radius of the outer bottom surface of the growing crucible), the height of the cup-shaped cylinder H ₁ = (1/3) H ₀ (H ₀ : the height of the crystal growing crucible), and it was applied in this Example 1. The size of the platinum cup-shaped cylinder was determined by applying the above dimension ratio to the dimensions of the crucible for growing flat-bottomed crystals having an outer diameter of 205 mmφ and a height of 180 mm, and an AC magnetic field analysis was performed.

(3-2) Survey results From the analysis results of FIGS. 14 (A) to 14 (C), the heat generation density is high at the cylindrical end of the platinum cup-shaped cylinder [see FIG. 14 (C)], and even at the cylindrical portion. Since the radius is close to that of the induction coil, the heat generation density is slightly higher, but no significant difference was observed in the crucible.

On the other hand, looking at the temperature distribution of the melt in the crucible, as shown in FIG. 11 (A), the platinum cup-shaped cylinder is located on the upper part of the cup-shaped cylinder as shown in FIG. 3 of Patent Document 3. The disk-shaped plate material is fused, and when it is placed in contact with the bottom of the crucible, the thickness of the bottom of the crucible becomes thicker by the thickness of the plate, and the thermal resistance to the bottom of the crucible increases, and the effect of heating the bottom of the crucible is It can be seen that it is not large compared to the invention.

Looking at the temperature distribution of the crucible in the crucible, as shown in FIG. 11 (B), since the noble metal cylindrical member 5 of the present invention is fused to the outer bottom surface of the crystal growing crucible 4, it is made of noble metal. The heat generated at the cylindrical end of the cylindrical member 5 is conducted to the bottom of the crucible 4, the bottom of the crucible is heated, and the temperature rises throughout the melt. It is confirmed that the heat generation is efficiently improved as compared with the case where the cup-shaped cylindrical heating body) is arranged.

_{(4) Temperature distribution near the crucible when the radius R 1} and the height H ₁ of the noble metal cylindrical member 5 are changed In the single crystal growing apparatus according to the present invention, the radius R ₁ of the noble metal cylindrical member is the crucible for growing crystals. With respect to _{the radius R 0} of the outer bottom surface of
1/3 ≤ R ₁ / R ₀ ≤ 1
_{The height H 1} of the precious metal cylindrical member is relative _{to the height H 0} of the crystal growing crucible.
1/8 ≤ H ₁ / H ₀ ≤ 1/2
It is a requirement to satisfy the relationship of.

(4-1) In order to confirm the pros and cons of the above requirements, an AC magnetic field analysis was performed on the temperature distribution in the vicinity of the crucible and in the melt when the _{radius R 1} and the height H _{1 of the precious metal cylindrical member 5 were changed.}

That is, as shown in FIG. 5, the height of the crystal growing crucible is H ₀ , the radius of the outer bottom surface portion is R ₀ , and the height of the noble metal cylindrical member (cylindrical heating body) attached to the outer bottom surface portion of the crucible. When the radius is H ₁ and the radius is R ₁ , the AC magnetic field analysis is performed for the four types in which the radius ratio (R ₁ / R ₀ ) and the height ratio (H ₁ / H _{0) are set to the following circles 1 to 4.} went.
Maru 1 (R ₁ / R ₀ = 1, H ₁ / H ₀ = 1/2),
Maru 2 (R ₁ / R ₀ = 1, H ₁ / H ₀ = 1/8)
Maru 3 (R ₁ / R ₀ = 1/3, H ₁ / H ₀ = 1/2),
Maru 4 (R ₁ / R ₀ = 1/3, H ₁ / H ₀ = 1/8)

(4-2) Survey results The crucible structure without the above-mentioned cylindrical heating body (without the cylindrical heating body), and with the cylindrical heating body attached, (R ₁ / R ₀ ) and (H ₁ / H ₀ ) are round. The temperature distributions in the vicinity of the crucible and the melt in the crucible of the crucible structure set in 1 to 4 are displayed in the colors of "Temperature Contour 2" [see FIG. 15 (C)] in FIG. 15 (B). As can be confirmed from the figure, it was found that when the cylindrical heating body was attached, the temperature of the bottom surface of the melt increased as compared with the case without the cylindrical heating body.

The effect of temperature rise, who cylindrical portion radius R ₁ is large, the effect is it is confirmed, it was found circle 1> circle 2> Mar 4> that the order in effect circle 3 is large.

Further, FIG. 16B shows a crucible structure (without a cylinder) to which the cylindrical heating body is not attached, and (R ₁ / R ₀ ) and (H ₁ / H ₀ ) having a cylindrical heating body attached. The temperature distribution of the temperature at the bottom of the melt from the center of the crucible bottom to the side surface is shown for each crucible structure set in ~ circle 4.

Compared to the 坩 堝 structure without a cylindrical heater (without a cylindrical heater), the temperature at the bottom of the melt is in the range other than that, although there is a region where the temperature rise is weak near the cylinder in the case of Maru 3. It was confirmed that the temperature of the melt rose, and that the installation of the cylindrical heater was effective. The effect of temperature rise, who cylindrical portion radius R ₁ is large, the effect is it is confirmed, it was found circle 1> circle 2> Mar 4> that the order in effect circle 3 is large.

Hereinafter, examples of the present invention will be specifically described with reference to comparative examples.

[Example 1]
_{The LiTaO 3} (LT) single crystal was grown using the growing device shown in FIG.

[Crucible for crystal growth 4]
An iridium cylindrical member 5 having an outer diameter of 135 mmφ, a height of 50 mm, and a thickness of 2.5 mm is provided on the outer bottom surface of a flat-bottomed iridium crystal growing crucible 4 having an outer diameter of 205 mmφ, a height of 180 mm, and a thickness of 2.5 mm. The fused crucible structure was applied, and the tubular portion of the iridium cylindrical member 5 was fixed to the zirconia support base 8 of the crystal growing crucible 4 by fitting them together.

[High frequency induction coil 2]
The high frequency induction coil 2 is wound with a pitch of 30 mm for 12 turns. The cross-sectional shape of the tubular coil (cooling water flows inside the tubular tube) is 20 mm × 20 mm, thickness 1.5 mm, and the central portion of the lowermost end of the high-frequency induction coil 2 and the outer bottom surface portion of the crystal growing crucible 4. The height position of the high frequency induction coil 2 was adjusted so that the distance from the coil 2 was 80 mm (see FIG. 6).

[Training conditions]
The frequency of the coil current in the high-frequency induction coil 2 was set to 7 kHz as a standard, and the power was adjusted so that the interface temperature between the seed crystal and the raw material melt had a melting point of 1650 ° C.

The height of the raw material melt in the crystal growing crucible 4 was 166 mm, and a seed crystal of 8 mm square × 70 mm was brought into contact with the surface of the melt _{to grow a LiTaO 3} (LT) single crystal.

[LiTaO ₃ crystal raw material]
_{Lithium carbonate (Li 2} CO ₃ ) and tantalum oxide (Ta ₂ O ₅ ) are weighed so that the ratio of Li to Ta is 48.4: 51.6 (congluent composition) in terms of chemical quantity theory, and these materials are used. after mixing thoroughly by a mixer, the mixed powder was 10 hours and calcined at 800-1650 ° C. the LiTaO ₃ crystal raw material prepared was the LiTaO ₃ crystal raw material was charged into the crystal growth crucible 4.

[Training results]
When the melt temperature distribution in the crystal growing crucible 4 was examined during the growing process, it was confirmed that the temperature drop at the bottom surface of the crystal growing crucible 4 was suppressed as shown in FIG. 11 (B). It was.

As a result, the solidification of the melt did not occur from the bottom surface of the crystal growth crucible 4, and the yield of crystal growth could be improved.

[Comparative Example 1]
_{The LiTaO 3} single crystal was grown under substantially the same conditions as in Example 1 except that the iridium crystal growing crucible 4 having a flat bottom shape without the iridium cylindrical member 5 was applied.

[Training results]
When the melt temperature distribution in the crystal growing crucible 4 during growing was examined, the temperature drop at the center of the bottom surface of the crystal growing crucible 4 was found as shown in "No cylindrical heater" in FIG. 15 (B). confirmed. As a result, solidification of the melt occurred from the bottom surface of the crystal growing crucible 4.

[Comparative Example 2]
[Crucible for crystal growth 4]
An iridium cup-shaped member having an outer diameter of 135 mmφ, a height of 50 mm, and a thickness of 2.5 mm is attached to the outer bottom surface of the flat-bottomed iridium crystal growing crucible 4 having an outer diameter of 205 mmφ, a height of 180 mm, and a thickness of 2.5 mm. _{A LiTaO 3} single crystal was grown under substantially the same conditions as in Example 1 except that a crucible structure in which the top surface portion (closing surface portion) of the cup-shaped member 5 with one end side open was applied.

[Training results]
When the melt temperature distribution in the crystal growing crucible 4 was examined during the growing process, it was confirmed that the temperature drop at the bottom surface of the crystal growing crucible 4 was suppressed as shown in FIG. 11 (A). It was.

However, it was also confirmed that the melt temperature in the crystal growing crucible 4 was lower than that in Example 1 of FIG. 11 (B). Although the crystal length could be made longer than that of Comparative Example 1, solidification of the melt occurred from the bottom surface of the crystal growing crucible 4.

The reason for this is that in Comparative Example 2, an iridium cup-shaped member (a cup-shaped member with one end open) is applied, so that the iridium cup-shaped member has a top surface portion (closing surface portion), which causes crystals. It is considered that the bottom surface of the growing crucible 4 was apparently thicker, and the effect of warming the bottom surface of the crystal growing crucible 4 was smaller than that of Example 1.

As a result, the yield of crystal growth was slightly reduced as compared with Example 1.

According to the single crystal growing apparatus of the present invention, the temperature drop of the bottom of the crucible is prevented by efficiently increasing the heat generation of the bottom of the crucible for crystal growth, so that the solidification of the raw material from the bottom of the crucible is suppressed and the yield of crystal growth is suppressed. Can be improved. Therefore, it has industrial applicability used for producing a lithium tantalate single crystal and a lithium niobate single crystal.

1 Chamber 2 High-frequency induction coil 3 Melt 4 Crucible for crystal growth 5 Precious metal cylindrical member 6 Refractory crucible 7 Insulation material (bubble)
8 Support base 9 Heat insulating material 10 seed crystals 11 Crystal pulling shaft 12 Fire resistant crucible support base 13 After heater 14 Reflector

Claims (1)

A refractory crucible with one end open,
A heat insulating material that is arranged on the open end side of the refractory crucible and has a space that communicates with the space of the refractory crucible to form a cylindrical space with the refractory crucible.
A crucible for growing crystals, which is arranged on the lower side in the cylindrical space via a support and has one end open.
The heat insulating material filled in the space between the refractory crucible and the crystal growing crucible and the space between the refractory crucible and the support base,
A cylindrical afterheater placed at the open end of the crystal growing crucible via a reflector,
A high-frequency induction coil arranged around the refractory crucible is provided in the chamber.
In a single crystal growing apparatus in which a seed crystal attached to the tip of a crystal pulling shaft is brought into contact with the raw material melt of the above-mentioned crystal growing crucible to grow a single crystal.
A precious metal cylindrical member heated by a high-frequency induction coil is attached to the outer bottom surface of the crystal growing crucible so that its central axis is aligned with the central axis of the crystal growing crucible.
Radius R ₁ of the noble metal cylindrical member, with respect to the radius R ₀ of the outer bottom surface of the crystal growth crucible,
1/3 ≤ R ₁ / R ₀ ≤ 1
_{The height H 1} of the precious metal cylindrical member is relative _{to the height H 0} of the crystal growing crucible.
1/8 ≤ H ₁ / H ₀ ≤ 1/2
Together meet the relationship,
A single crystal growing apparatus characterized in that the support base of the crucible for growing crystals is fitted in a tubular portion of a cylindrical member made of precious metal.

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