JP2022025994A - Apparatus and method for growing single crystal - Google Patents

Abstract

To provide an apparatus and method for growing a single crystal, capable of growing a single crystal having a diameter of 8 inches without cracks and bottoming at a low cost even when using a zirconia bubble (a thermal insulation material).SOLUTION: An apparatus for growing a single crystal includes a fire resistant crucible 10; a crystal growth crucible 1 arranged in the crucible 10; a zirconia bubble 30 charged in a space between the fire resistant crucible 10 and the crucible 1; an after heater 40 arranged through a reflector 41 in the upper end of the crucible 1; and a high frequency induction coil 2 arranged in outer peripheries thereof, in a chamber 100. When setting a length from the lower end of the coil to the upper end thereof to Y, a length from the lower end of the crucible 1 to the upper end thereof to X, a length between the upper end of the coil and the upper end of the crucible 1 to A, a length between the lower end of the coil and the lower end of the crucible 1 to B and Y/X to 2-3.5, A/B is set within 1.22-1.42. Since balance between heat generations on the sides of the after heater 40 and crucible 1 is appropriately controlled, a single crystal without cracks and bottoming can be grown.SELECTED DRAWING: Figure 1

Description

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

As a method for growing an oxide single crystal such as lithium tantalate or lithium niobate, conventionally, a crystal growing pit (sometimes abbreviated as a pit) filled with a raw material to be an oxide single crystal is heated to a high temperature. The Czochralski method is widely used in which the raw material is melted, the seed crystal is brought into contact with the raw material melt in the crystal growing chamber from above, and then the seed crystal is raised to grow an oxide single crystal in the same direction as the seed crystal. It's being used.

In the growth of a single crystal by the Czochralski method, an induction coil is arranged around the crucible for crystal growth, and an eddy current is generated in the crucible by passing a high-frequency current through the induction coil, which causes the crucible to generate heat and become a raw material. Melts. In addition, as the pulling progresses, the upper part of the single crystal is cooled along the seed rod (crystal pulling shaft), but if the heating element is only a crucible, the temperature distribution in the single crystal during growth becomes large, so the crucible It has been devised to keep the upper part warm. For example, Patent Document 1 discloses a method for growing an oxide single crystal in which a metal afterheater is arranged at the upper end of a crucible in order to suppress the generation of cracks due to thermal stress due to a temperature difference in the crystal. Patent Document 2 discloses a method for growing an oxide single crystal in which a ring-shaped metal reflector is arranged at an open end of a crucible to keep the upper part of the crucible warm.

In recent years, the market for lithium tantalate single crystal and lithium niobate single crystal has been expanding as surface acoustic wave device materials, and the pull-up length of the single crystal is gradually increasing in order to secure the production amount. However, if the size of the crucible for crystal growth is increased (internal volume is increased) in accordance with the lengthening of the crucible, the amount of the raw material melt in the crucible increases by that amount, which causes the following problems.

That is, the crystal growing crucible is usually arranged in a refractory crucible (alumina crucible), and the gap space thereof is filled with a heat insulating material made of an alumina sintered body. However, when the growth of lithium niobate single crystal or the like is repeated using the same crystal growth crucible, the crystal growth crucible is deformed by the increased load of the raw material melt, and the crystal growth crucible presses the heat insulating material. There was a problem of causing cracks in the fire-resistant crucible (alumina crucible).

To solve this problem, Patent Document 3 uses a granular zirconia bubble (heat insulating material) instead of a heat insulating material made of an alumina sintered body, and the crucible for crystal growth is deformed by the load of the raw material melt. Disclosed a method in which the zirconia bubble (insulation material) absorbs the pressing force and does not cause cracks in the refractory crucible (alumina crucible) even when the crystal growth crucible presses the zirconia bubble (insulation material). There is. By adopting this method, it is certainly possible to avoid the problem of refractory crucible (alumina crucible) due to the increased load of the raw material melt.

However, since the granular zirconia bubble (heat insulating material) has a smaller thermal conductivity than the above alumina sintered body (heat insulating material), it is at the same level as when the alumina sintered body is applied as the heat insulating material. When the high frequency voltage of the above is applied to the induction coil, the temperature of the melt in the crucible for crystal growth becomes higher than the desired condition, which makes it difficult to grow a single crystal. Therefore, when a granular zirconia bubble (heat insulating material) having a low thermal conductivity is applied, it is necessary to make the high frequency voltage applied to the induction coil relatively small.

However, if the high-frequency voltage applied to the induction coil is reduced, the calorific value of the afterheater placed at the upper end of the pit will decrease, and the temperature gradient will increase at the upper and lower ends of the crystal in the afterheater, resulting in cracks due to thermal stress. There was a problem that caused. In particular, in the lithium niobate single crystal, the generation of cracks due to thermal strain was remarkable.

In such a case, as shown in FIG. 1, the high frequency induction coil 2 arranged around the crystal growth crucible 1 is set relatively upward, and between the upper end of the high frequency induction coil 2 and the upper end of the crystal growth crucible 1. If the length A in the crystal pulling direction of the crucible becomes large, it becomes possible to promote the heat generation of the afterheater. However, when the length A in the crystal pulling direction between the upper end of the high frequency induction coil 2 and the upper end of the crystal growing crucible 1 is increased, the crystal pulling direction between the lower end of the high frequency induction coil 2 and the lower end of the crystal growing crucible 1 Since the length B is relatively small, the calorific value of the crystal growing crucible 1 is reduced, and the melt temperature near the bottom of the crucible 1 is lowered. As a result, the melt near the bottom of the crucible solidifies during crystal growth, and the grown crystal collides with the solidified crystal (called bottoming), and the growth of the single crystal is forcibly terminated, and the desired length is obtained. It causes the crucible single crystal to not be obtained.

In Patent Document 4, the first induction coil arranged around the crystal growing pit and the second derivative coil arranged around the afterheater are individually arranged, and a separate high frequency power supply is prepared for each derivative coil. At the same time, a crystal growth apparatus in which the high frequency currents to be supplied are set to be in opposite phase to each other is disclosed. According to this growing device, the degree of heat generation of the afterheater can be finely controlled independently of the crucible for growing crystals, so that the temperature of the single crystal during pulling can be adjusted in a well-controlled manner according to the growth of the single crystal. Become. However, the growing device disclosed in Patent Document 4 requires two power supply facilities, which causes a problem that the facility cost is high and the installation location is wide.

Against such a technical background, the present inventor usually sets the ratio (Y / X) of the length Y of the high frequency induction coil 2 to the length X of the crystal growing crucible 1 arranged in the high frequency induction coil 2. (The length of the high-frequency induction coil is usually set to 2 to 3.5 times the length of the crucible in the crystal pulling direction), and the upper end of the high-frequency induction coil 2 and the crucible for crystal growth are set. 1 The ratio (A / B) of the length A in the crystal pulling direction between the upper end and the length B in the crystal pulling direction between the lower end of the high frequency induction coil 2 and the lower end of the crystal growing crucible 1 (A / B) is 1.00 to 1. By adjusting to the range of .20, the heat generation balance between the afterheater side and the crystal growth crucible side is properly controlled, and even when zirconia bubbles are applied as a heat insulating material, cracks and bottoming are avoided. We have already proposed a growing device and a growing method for the above (see Patent Document 5).

Japanese Unexamined Patent Publication No. 7-187880 Japanese Unexamined Patent Publication No. 7-033586 Japanese Unexamined Patent Publication No. 2019-052067 Japanese Unexamined Patent Publication No. 2014-125404 Japanese Patent Application No. 2019-232872

By the way, the single crystal grown by using the apparatus of Patent Document 5 is assumed to be a single crystal having a diameter of about 6 inches (for example, a lithium niobate single crystal). Therefore, when trying to grow a single crystal having a diameter of more than 6 inches (for example, a lithium niobate single crystal having a diameter of about 8 inches), the crystal pulling direction between the upper end of the high frequency induction coil 2 and the upper end of the crystal growing pit 1 Adjust the ratio (A / B) of the length A and the length B in the crystal pulling direction between the lower end of the high frequency induction coil 2 and the lower end of the crystal growing pit 1 to the above range of 1.00 to 1.20. However, there was a problem that the heat generation balance between the afterheater side and the crystal growth pit side was not properly controlled, and the single crystal to be grown still had cracks.

The present invention has been made by paying attention to such a problem, and the subject thereof is that a single crystal having a diameter of more than 6 inches can be grown and the above-mentioned is applied even when a zirconia bubble is applied as a heat insulating material. It is an object of the present invention to provide a single crystal growing apparatus and a single crystal growing method in which cracks and bottoming are avoided.

Therefore, when the present inventor analyzed the cause of the crack generation, the temperature difference in the crystal increased as the diameter of the single crystal increased from 6 inches to 8 inches, and the thermal strain in the crystal increased during the growth. It was thought that he was doing it. Then, in order to reduce the thermal strain, it is effective to promote the calorific value of the afterheater, and the high frequency induction coil 2 is relatively upward and the ratio (A / B) range is set to 1.00 to 1.20. Need to be bigger. That is, the length A in the crystal pulling direction between the upper end of the high frequency induction coil 2 and the upper end of the crystal growing crucible 1 and the length B in the crystal pulling direction between the lower end of the high frequency guiding coil 2 and the lower end of the crystal growing crucible 1. The appropriate range of the ratio (A / B) differs depending on whether the diameter of the single crystal to be grown is 6 inches or 8 inches. When growing a single crystal with a diameter of 8 inches, the afterheater side and the crucible for crystal growth It was necessary to find a new ratio (A / B) range in which the heat generation balance on the side was properly controlled. The present invention has been completed from such technical knowledge.

That is, the first invention according to the present invention is
A refractory crucible with one end open,
A metal crystal growing crucible placed in the refractory crucible via a crucible stand,
A heat insulating material filled in the gap space between the refractory crucible and the crystal growing crucible and composed of zirconia bubbles,
A metal afterheater placed at the upper end of the crystal growing crucible via a metal reflector,
The chamber is equipped with the above-mentioned refractory crucible and high-frequency induction coils arranged around the outside of the afterheater.
In the single crystal growing apparatus for growing a single crystal by contacting the seed crystal attached to the crystal pulling shaft with the raw material melt of the above-mentioned crucible for growing crystals.
The length in the crystal pulling direction from the lower end side to the upper end of the high frequency induction coil is Y, the length in the crystal pulling direction from the lower end side to the upper end of the crystal growing pit is X, and the upper end of the high frequency induction coil and the crystal growing The length in the crystal pulling direction between the upper end of the pit is A, the length in the crystal pulling direction between the lower end of the high frequency induction coil and the lower end of the pit for crystal growth is B, and Y / X is 2 to 3.5. If so, the A / B is set in the range of 1.22 to 1.42.
The second invention is
In the single crystal growing apparatus according to the first invention,
It is characterized in that it is used for growing lithium niobate crystals having a diameter of 8 inches and a length of 70 mm or more.

Next, the third invention according to the present invention is
The chamber is filled with a fire-resistant crucible, a metal crystal-growing crucible arranged in the fire-resistant crucible via a crucible, and a gap space between the fire-resistant crucible and the crystal growing crucible, and a zirconia bubble. A heat insulating material composed of, a metal afterheater arranged at the upper end of the crystal growing crucible via a metal reflector, and a high frequency induction coil arranged around the outside of the fire resistant crucible and the afterheater. In the single crystal growing method for growing a single crystal by contacting the seed crystal attached to the crystal pulling shaft with the raw material melt of the above-mentioned crucible for growing crystals.
The length in the crystal pulling direction from the lower end side to the upper end of the high frequency induction coil is Y, the length in the crystal pulling direction from the lower end side to the upper end of the crystal growing pit is X, and the upper end of the high frequency induction coil and the crystal growing The length in the crystal pulling direction between the upper end of the pit is A, the length in the crystal pulling direction between the lower end of the high frequency induction coil and the lower end of the pit for crystal growth is B, and Y / X is 2 to 3.5. If so, the A / B is set in the range of 1.22 to 1.42.

According to the present invention, the length in the crystal pulling direction from the lower end side to the upper end of the high frequency induction coil is Y, the length in the crystal pulling direction from the lower end side to the upper end of the crystal growth chamber is X, and the upper end of the high frequency induction coil. 2. The length in the crystal pulling direction between the upper end of the crystal growing pit is A, the length in the crystal pulling direction between the lower end of the high frequency induction coil and the lower end of the crystal growing pit is B, and Y / X is 2 to 3. When it is 5, since the A / B is set in the range of 1.22 to 1.42, even if the diameter of the single crystal exceeds 6 inches and is about 8 inches, the afterheater side and crystal growth The heat generation balance on the crystal side can be properly controlled. For this reason, it is possible to grow a single crystal having a diameter of more than 6 inches, and a single crystal growing device and a single crystal growing method that avoid cracks and bottoming even when a zirconia bubble is applied as a heat insulating material are provided. Has the effect that can be done.

In the explanatory view showing the length dimension of the component in the single crystal growing apparatus, the reference numeral Y is the length in the crystal pulling direction from the lower end side to the upper end of the high frequency induction coil, and the reference numeral X is the lower end side of the crystal growing pit. The length from the upper end to the upper end in the crystal pulling direction, the reference numeral A is the length in the crystal pulling direction between the upper end of the high frequency induction coil and the upper end of the crystal growth chamber, and the reference numeral B is the lower end of the high frequency induction coil and the lower end of the crystal growth chamber. The length in the crystal pulling direction between and is shown respectively. The configuration explanatory drawing of the single crystal growth apparatus which concerns on embodiment.

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

FIG. 2 is a configuration explanatory view of the single crystal growing device according to the embodiment of the present invention. The single crystal growing device according to the present embodiment has a crucible and a fire resistance arranged in the chamber 100 and one end is open. Fill the gap space between the sex crucible (alumina crucible) 10, the platinum crystal growing crucible 1 arranged in the fire resistant crucible 10 via the crucible 11, and the fire resistant crucible 10 and the crystal growing crucible 1. The zirconia bubble (insulation material) 30 and the platinum afterheater 40 arranged at the upper end of the crystal growing crucible 1 via a platinum reflector 41, and the outside of the fire resistant crucible 10 and the afterheater 40. The main part thereof is composed of a high frequency induction coil 2 arranged around the crucible. In FIG. 2, reference numeral 12 is a refractory material made of alumina, reference numeral 31 is a heat insulating material, reference numeral 50 is a seed rod (crystal pulling shaft), reference numeral 51 is a seed crystal, reference numeral 60 is a grown crystal, and reference numeral 61 is a crystal. The raw materials are shown respectively.

Then, in the single crystal growing apparatus according to the present embodiment, as shown in FIG. 1, the length in the crystal pulling direction from the lower end side to the upper end of the high frequency induction coil 2 is Y, and the length in the crystal pulling direction is from the lower end side of the crystal growing crucible 1. The length in the crystal pulling direction to the upper end is X, the length in the crystal pulling direction between the upper end of the high frequency induction coil 2 and the upper end of the crystal growth crucible 1 is A, the lower end of the high frequency induction coil 2 and the lower end of the crystal growth crucible 1. When the length in the crystal pulling direction is B and Y / X is 2 to 3.5, A / B is set in the range of 1.22 to 1.42.

Therefore, even if the diameter of the single crystal to be grown exceeds 6 inches and is about 8 inches, the heat generation balance between the afterheater 40 side and the crystal growing crucible 1 side by the high frequency induction coil 2 is properly controlled, and as a heat insulating material. Even when the zirconia bubble is applied, it is possible to prevent the above-mentioned problems such as cracks and bottoming.

When the above A / B is less than 1.22 (when the length A in the crystal pulling direction between the upper end of the high frequency induction coil 2 and the upper end of the crystal growing pit 1 is set small), the afterheater by the high frequency induction coil 2 is used. Since the amount of heat generated on the 40 side cannot be sufficiently secured, the temperature difference in the crystal 60 in the afterheater 40 becomes large, and a defect of crack occurs during pulling due to thermal strain in the crystal 60 or the like. On the other hand, when the above A / B exceeds 1.42 (the length A between the upper end of the high frequency induction coil 2 and the upper end of the crystal growing crucible 1 in the crystal pulling direction is set large, and the lower end of the high frequency induction coil 2 and the crystal When the length B in the crystal pulling direction between the lower end of the growing crucible 1 is set to be relatively small), the calorific value of the crystal growing crucible 1 by the high frequency induction coil 2 decreases and melting near the bottom of the crucible 1 The liquid temperature becomes low, and the melt near the bottom of the crucible solidifies during crystal growth, causing problems such as bottoming.

On the other hand, when the A / B is set within the range of 1.22 to 1.42, the afterheater 40 by the high frequency induction coil 2 even if the diameter of the single crystal exceeds 6 inches and is about 8 inches. The heat generation balance between the side and the crystal growing crucible 1 side can be appropriately controlled. Therefore, it is possible to grow a single crystal having a diameter of more than 6 inches, and it is possible to prevent problems such as cracks and bottoming even when a zirconia bubble is applied as a heat insulating material.

Hereinafter, the members constituting the single crystal growing apparatus according to the present embodiment will be described.

The crystal growing crucible 1 is a container for storing and holding a melt of a crystal raw material, and has a cylindrical side surface and a circular bottom surface. Further, the crystal growing crucible 1 is made of iridium or platinum having excellent heat resistance, and when the single crystal to be grown is a lithium niobate crystal, a platinum crucible is applied.

The crucible stand 11 is a support stand for supporting the crystal growing crucible 1, and is arranged below the crystal growing crucible 1.

The reflector 41 arranged at the upper end (open end) of the crystal growing crucible 1 is a heat reflecting means for reflecting the heat in the crucible 1 and returning it to the crucible 1, and covers the upper end peripheral portion of the side surface of the crucible 1. As described above, it is provided at the upper end of the side surface of the crucible 1 and has an annular shape. Further, the reflector 41 is made of iridium or platinum having excellent heat resistance, and when the single crystal to be grown is a lithium niobate crystal, a platinum reflector is applied.

The afterheater 40 is a heating means for heating the single crystal pulled up from the crystal growth crucible 1. The afterheater 40 is provided on the reflector 41 and has a cylindrical shape. Further, the afterheater 40 is made of iridium or platinum having excellent heat resistance, and when the single crystal to be grown is a lithium niobate crystal, a platinum afterheater is applied.

The seed rod (crystal pulling shaft) 50 holds the seed crystal 51 at the lower end, and the seed crystal 51 is brought into contact with the raw material melt held in the crystal growth chamber 1 to pull the single crystal. It is a means. The seed rod (crystal pulling shaft) 50 is connected to a motor or the like (not shown) and is configured to be able to pull a single crystal while rotating.

The refractory crucible (alumina crucible) 10 and the refractory material 12 are means for covering the hot zone of the crystal growing crucible 1 and the afterheater 40 from the outside.

The zirconia bubble (heat insulating material) 30 and the heat insulating material 31 are means for covering the periphery of the crystal growing crucible 1 and suppressing heat from being released to the outside. Examples of the heat insulating material 31 include, for example. Heat resistant materials such as alumina (aluminum oxide) and zirconia are used.

The high-frequency induction coil 2 is a means for heating the crystal growing crucible 1, the afterheater 40, the reflector 41, and the like by a high-frequency induction heating method. As shown in FIG. 2, the high-frequency induction coil 2 is formed by forming a conductor such as copper in a coil shape, and is arranged so as to surround the outer periphery of the refractory crucible (alumina crucible) 10 and the refractory material 12 in a non-contact state. Has been done. That is, the high-frequency induction coil 2 is provided outside the radial direction of the refractory crucible (alumina crucible) 10 and the refractory material 12. Further, the number of turns of the high-frequency induction coil 2, the coil interval (winding pitch), the relative position between the high-frequency induction coil 2 and the crystal growing crucible 1, etc. are the material and size of the crystal growing crucible 1 (the crystal pulling direction of the crucible 1). The length in the crucible), the type of crystal to be grown, the length, the diameter, etc. are appropriately set. For example, when the single crystal to be grown is a lithium niobate crystal having a diameter of 8 inches and a straight body length of about 60 mm to 80 mm, the number of turns of the high frequency induction coil 2 is about 8 to 16 turns, and the coil spacing (winding pitch). Is around 30 mm. Further, when the high frequency induction coil 2 is operated, a high frequency voltage is applied to the coil 2 from an external power source (not shown) and a high frequency current is passed through the coil 2. As a result, a magnetic field is generated around the high frequency induction coil 2, and the crystal growing pit 1, the afterheater 40, the reflector 41, etc. surrounded by the high frequency induction coil 2 generate heat. Further, in order to grow a crystal having a desired diameter, the weight of the crystal being grown is detected by a load cell, the diameter of the crystal is calculated from the crystal weight, and the high frequency applied to the high frequency induction coil 2 by ADC (Automatic Diameter Control). It is configured to control the voltage (eg, 165V to 175V).

The chamber 100 is a means for covering the whole including a crystal growing crucible 1, a refractory crucible (alumina crucible) 10, an afterheater 40, a high frequency induction coil 2, a refractory material 12, a crucible stand 11, and the like, and has a crystal growing atmosphere. It plays a role in holding the crucible and suppressing heat from leaking to the outside.

The control means (not shown) is a means for controlling the entire single crystal growth apparatus, and controls the operation of the entire single crystal growth apparatus including the single crystal growth process. The control means may be configured by, for example, a microcomputer including a CPU (Central Processing Unit) and a memory such as a ROM (Read Only Memory) and a RAM (Random Access Memory) and operated by a program. However, it may be configured by an electronic circuit such as an ASIC (Application Specified Integra Circuit) developed for a specific application.

Then, in the growth of the single crystal, the crucible 1 for crystal growth filled with the crystal raw material 61 is heated by high frequency induction heating to obtain a raw material melt. After that, the seed crystal 51 connected to the seed rod (crystal pulling shaft) 50 is brought into contact with the surface of the raw material melt and pulled upward to grow a single crystal. The growing method by the Czochralski method is not particularly limited, and known techniques can be used.

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

That is, a lithium niobate single crystal having a diameter of 8 inches and a straight body length of 70 mm was grown using the single crystal growing device shown in FIG. When growing the shoulder of the lithium niobate single crystal, the rotation speed of the seed rod (crystal pulling shaft) 50 is 10.0 rpm, and the pulling speed is 0.5 mm / hr. The rotation speed of the seed rod (crystal pulling shaft) 50 in the above is 5.0 rpm, and the pulling speed is 1.0 mm / hr.

A copper work coil (total length Y: 480 mm) having a coil spacing (winding pitch) of 30 mm and 16 turns is applied to the high-frequency induction coil 2, and the crystal growing crucible 1 has an inner diameter of 270 mm and a height (that is, that is). A platinum crucible with an X) of 202 mm was applied. That is, the ratio (Y / X) of the length Y of the high frequency induction coil 2 to the length X of the crystal growing crucible 1 is 480/202 = 2.4 (that is, a normal range of 2 to 3.5). It is set. Zirconia bubbles were applied to the heat insulating material 30 filled in the gap space between the refractory crucible (alumina crucible) 10 and the crystal growing crucible 1, and alumina (aluminum oxide) was used for the heat insulating material 31. Further, a platinum afterheater having a length of 140 mm was applied to the afterheater 40. The voltage applied to the high frequency induction coil 2 was set to 165V to 175V.

Further, the length in the crystal pulling direction from the lower end side to the upper end of the high frequency induction coil 2 shown in FIG. 1 is Y (480 mm), and the length in the crystal pulling direction from the lower end side to the upper end of the crystal growth chamber 1 is X (X). 202 mm), the length in the crystal pulling direction between the upper end of the high frequency induction coil 2 and the upper end of the crystal growing pit 1 is A, and the length in the crystal pulling direction between the lower end of the high frequency induction coil 2 and the lower end of the crystal growing pit 1 Let B.

[Example 1]
The length A in the crystal pulling direction between the upper end of the high frequency induction coil 2 and the upper end of the crystal growing crucible 1 is 153 mm, and the length B in the crystal pulling direction between the lower end of the high frequency induction coil 2 and the lower end of the crystal growing crucible 1 is set. When the lithium niobate single crystal was grown 7 times with the setting set to 125 mm, there were no problems such as cracks and bottoming.

In addition, A / B = 153/125 = 1.22.

The growing conditions and results are shown in Table 1 below.

[Example 2]
The length A in the crystal pulling direction between the upper end of the high frequency induction coil 2 and the upper end of the crystal growing crucible 1 is 158 mm, and the length B in the crystal pulling direction between the lower end of the high frequency induction coil 2 and the lower end of the crystal growing crucible 1 is set. When the lithium niobate single crystal was grown 7 times with the setting set to 120 mm as in Example 1, there were no problems such as cracks and bottoming.

In addition, A / B = 158/120 = 1.32.

The growing conditions and results are shown in Table 1 below.

[Example 3]
The length A in the crystal pulling direction between the upper end of the high frequency induction coil 2 and the upper end of the crystal growing crucible 1 is 163 mm, and the length B in the crystal pulling direction between the lower end of the high frequency induction coil 2 and the lower end of the crystal growing crucible 1 is set. When the lithium niobate single crystal was grown 7 times with the setting set to 115 mm as in Example 1, there were no problems such as cracks and bottoming.

In addition, A / B = 163/115 = 1.42.

The growing conditions and results are shown in Table 1 below.

[Comparative Example 1]
The length A in the crystal pulling direction between the upper end of the high frequency induction coil 2 and the upper end of the crystal growing crucible 1 is 148 mm, and the length B in the crystal pulling direction between the lower end of the high frequency induction coil 2 and the lower end of the crystal growing crucible 1 is set. When the lithium niobate single crystal was grown at a setting of 130 mm, no bottoming occurred, but cracks occurred.

The high-frequency induction coil 2 is set relatively downward, and the amount of heat generated on the after-heater 40 side by the high-frequency induction coil 2 cannot be sufficiently secured, and the temperature difference in the crystal 60 in the after-heater 40 becomes large, resulting in a crystal. It is presumed that cracks were generated due to thermal strain or the like in 60.

In addition, A / B = 148/130 = 1.14.

The growing conditions and results are shown in Table 1 below.

[Comparative Example 2]
The length A in the crystal pulling direction between the upper end of the high frequency induction coil 2 and the upper end of the crystal growing crucible 1 is 168 mm, and the length B in the crystal pulling direction between the lower end of the high frequency induction coil 2 and the lower end of the crystal growing crucible 1 is set. When the growth of the lithium niobate single crystal was set to 110 mm, it was forcibly stopped because the bottoming occurred during the growth. However, no cracks were found in the crystals during growth.

The high-frequency induction coil 2 is set relatively upward, the calorific value of the crystal growing crucible 1 by the high-frequency induction coil 2 decreases, and the melt temperature near the bottom of the crucible 1 decreases, resulting in crystal growth. It is presumed that the melt near the bottom of the crucible 1 solidified inside.

In addition, A / B = 168/110 = 1.53.

The growing conditions and results are shown in Table 1 below.

According to the present invention, even when a zirconia bubble is applied as a heat insulating material, a single crystal having a diameter of more than 6 inches without cracks or bottoming can be grown at low cost. Therefore, a single lithium niobate used as a surface acoustic wave device material can be grown. It has industrial applicability to be used as a crystal growing device.

1 Crucible for crystal growth 2 High frequency induction coil 10 Refractory crucible (alumina crucible)
11 Crucible stand 30 Zirconia bubble (insulation material)
31 Insulation material 40 After heater 41 Reflector 50 Seed rod (crystal pulling shaft)
51 Seed crystal 60 Crystal 61 Crystal raw material 100 Chamber Y Length in the crystal pulling direction from the lower end side to the upper end of the high frequency induction coil 2 X Length in the crystal pulling direction from the lower end side to the upper end of the crystal growing yard 1 A High frequency induction Length in the crystal pulling direction between the upper end of the coil 2 and the upper end of the crystal growing pit 1 B Length in the crystal pulling direction between the lower end of the high frequency induction coil 2 and the lower end of the crystal growing pit 1.

Claims (3)

A refractory crucible with one end open,
A metal crystal growing crucible placed in the refractory crucible via a crucible stand,
A heat insulating material filled in the gap space between the refractory crucible and the crystal growing crucible and composed of zirconia bubbles,
A metal afterheater placed at the upper end of the crystal growing crucible via a metal reflector,
The chamber is equipped with the above-mentioned refractory crucible and high-frequency induction coils arranged around the outside of the afterheater.
In the single crystal growing apparatus for growing a single crystal by contacting the seed crystal attached to the crystal pulling shaft with the raw material melt of the above-mentioned crucible for growing crystals.
The length in the crystal pulling direction from the lower end side to the upper end of the high frequency induction coil is Y, the length in the crystal pulling direction from the lower end side to the upper end of the crystal growth crucible is X, and the upper end of the high frequency induction coil and the crystal growth The length in the crystal pulling direction between the upper end of the crucible is A, the length in the crystal pulling direction between the lower end of the high frequency induction coil and the lower end of the crystal growing crucible is B, and Y / X is 2 to 3.5. If so, the single crystal growing apparatus is characterized in that the A / B is set in the range of 1.22 to 1.42. The single crystal growing apparatus according to claim 1, wherein the single crystal growing apparatus is used for growing lithium niobate crystals having a diameter of 8 inches and a length of 70 mm or more. The chamber is filled with a fire-resistant crucible, a metal crystal-growing crucible arranged in the fire-resistant crucible via a crucible, and a gap space between the fire-resistant crucible and the crystal growing crucible, and a zirconia bubble. A heat insulating material composed of, a metal afterheater arranged at the upper end of the crystal growing crucible via a metal reflector, and a high frequency induction coil arranged around the outside of the fire resistant crucible and the afterheater. In the single crystal growing method for growing a single crystal by contacting the seed crystal attached to the crystal pulling shaft with the raw material melt of the above-mentioned crucible for growing crystals.
The length in the crystal pulling direction from the lower end side to the upper end of the high frequency induction coil is Y, the length in the crystal pulling direction from the lower end side to the upper end of the crystal growth crucible is X, and the upper end of the high frequency induction coil and the crystal growth The length in the crystal pulling direction between the upper end of the crucible is A, the length in the crystal pulling direction between the lower end of the high frequency induction coil and the lower end of the crystal growing crucible is B, and Y / X is 2 to 3.5. If so, the single crystal growing method is characterized in that A / B is set in the range of 1.22 to 1.42.

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