KR20130111253A - Sapphire single crystal and process for manufacturing the same - Google Patents

Abstract

PURPOSE: A sapphire single crystal and a manufacturing method thereof are provided to improve productivity by using a molybdenum crucible. CONSTITUTION: A sapphire seed crystal is immersed in alumina melt (21). The sapphire seed crystal is rotated and is upwardly pulled. A sapphire single crystal (20) is grown on the lower part of the seed crystal in a c-axis. The lateral side of the grown part of the sapphire single crystal is formed with a V shape in the alumina melt. The pulling speed of the sapphire seed crystal is between 0.5 and 10mm/hr.

Description

TECHNICAL FIELD [0001] The present invention relates to a sapphire single crystal and a method for manufacturing the sapphire single crystal.

The present invention relates to a sapphire single crystal and a manufacturing method thereof, and more particularly, to a manufacturing method of a sapphire single crystal using a Czochralski method.

In recent years, the demand for a sapphire single crystal substrate as a substrate for manufacturing a light emitting diode (LED) has been expanding. Since a sapphire single crystal substrate is produced by slicing a sapphire single crystal into a wafer shape, in order to produce a large sapphire substrate, it is necessary to use a large sapphire single crystal.

As a method for producing the sapphire single crystal, the Kyropoulos method, the vertical Brigman method, and the like are widely used, but these methods have a problem that it is difficult to enlarge the sapphire single crystal having a desired surface orientation. For this reason, the Czochralski method (CZ method) attracts attention as a method of obtaining a larger sapphire single crystal (refer patent document 1). The CZ method is a method that is also used for pulling up a silicon single crystal and the like, and since it is a mature technology, it is expected that a large size sapphire single crystal can be produced at low cost by applying it to the pulling up of a sapphire single crystal.

However, even in the same CZ method, since the physical properties differ greatly between silicon and sapphire, the recognition obtained by the pulling up of the silicon single crystal cannot be applied as it is to the pulling up of the sapphire single crystal. On the contrary, the impression of the silicon single crystal and the impression of the sapphire single crystal need to be grasped by completely different technologies, and various problems that have not occurred in the impression of the silicon single crystal must be solved.

For example, in Patent Document 1, in the growth of a sapphire single crystal by the CZ method, the temperature at the time of melting and leaving the raw material is finely managed, and the iridium crucible is not heated more than necessary. As a result, a method of suppressing the oxidation thereof, thereby suppressing the occurrence of inclusion and efficiently producing a high quality single crystal is described.

In addition, Patent Document 2 describes a sapphire single crystal growth apparatus using a crucible having a dual structure composed of a molybdenum or tungsten crucible and an iridium crucible disposed on the outside thereof. In addition, Patent Document 3 describes a method of suppressing the generation of micro bubbles by degassing the melt and producing a high quality sapphire single crystal.

Patent Document 4 describes a method of growing single crystal sapphire by tilting the growth axis of the sapphire single crystal within the range of 0.1 to 15 degrees from the c axis. Patent Document 5 also discloses a method of growing a sapphire single crystal in the c-axis direction, when the liquid level of the alumina melt in the crucible reaches the boundary between the bottom inner surface of the crucible and the inner surface of the wall portion, the sapphire single crystal is pulled up. It is described to improve the single crystal yield by separating from the alumina melt.

Japanese Laid-Open Patent Publication No. 2008-169069 Japanese Laid-Open Patent Publication No. 2008-007353 Japanese Laid-Open Patent Publication No. 2008-195575 Japanese Laid-Open Patent Publication No. 2008-056518 Japanese Laid-Open Patent Publication No. 2010-189242

Usually, blue and white LEDs are manufactured by a method of epitaxially growing a GaN-based thin film on a sapphire substrate, but the substrate material has a (0001) plane (c plane) perpendicular to the c axis. A sapphire wafer cut out from the ingot so as to be a main surface is used. Therefore, in consideration of the convenience and material yield in a later step, it is preferable to slice and use a large diameter and long sapphire single crystal ingot grown in the c-axis direction.

However, there are orientations that are easy to grow and orientations that are difficult to grow. In the case of sapphire crystals, single crystals grow relatively easily in the a-axis direction ((1120) orientation), but c-direction ((0001) orientation) It is difficult for single crystals to grow, or bubbles and defects are easily introduced.

The difficulty in cultivating sapphire single crystals is to suppress the introduction of bubbles or defects to cultivate large diameters and long ingots. Bubbles and defects are easily introduced due to irregular shaking, convection, temperature distribution and temperature change of the melt. In order to suppress these irregular factors, it is necessary to apply appropriate and subtle control over the conditions that change with the growth of the ingot. At present, sapphire single crystal is mainly produced and supplied by the key plus method, and there are many problems to develop a large diameter c-axis sapphire single crystal by the CZ method.

An object of the present invention is to provide a method of manufacturing a sapphire single crystal by the CZ method, in which crystal growth is performed in the c-axis direction while suppressing the introduction of bubbles or defects, . Further, another object of the present invention is to provide a high quality sapphire single crystal produced by such a production method.

The present inventors earnestly studied the mechanism of crystal growth of the sapphire single crystal in the c-axis direction, and as a result, in the impression of the sapphire single crystal by the CZ method, the tip portion of the single crystal ingot in contact with the melt grows greatly under the liquid surface, and the interface shape It may be convex toward this downward direction, and it discovered that air bubbles and a defect were not introduce | transduced into this crystal part depending on pulling conditions, and it was found to be high quality. It was also confirmed that the diameter of the crystal part in the liquid can be controlled.

The present invention has been made on the basis of such technical recognition, and in the method for producing sapphire single crystal according to the present invention, the c-axis sapphire seed crystal is immersed in the alumina melt in the crucible, and the top crystal is pulled upward while rotating the seed crystal to terminate it. A method for producing a sapphire single crystal in which a sapphire single crystal is grown in the c-axis direction at the bottom of a positive electrode, wherein the sapphire single crystal is grown under the liquid surface of the alumina melt, and the single crystal growth portion growing in the melt is the bottom surface of the crucible. It is characterized by pulling the seed crystal upwards so as not to reach.

In the method for producing sapphire single crystal according to the present invention, since the sapphire single crystal is actively grown under the liquid level of the alumina melt, the sapphire single crystal is pulled upward at a predetermined pulling speed in accordance with its crystal growth rate. C-axis sapphire single crystal can be grown, large diameter and long single crystal can be grown.

The typical method for growing a single crystal under the liquid level of an alumina melt is the KiroPlus method, but the present invention is greatly different from the Kiroplus method in the following points.

First, crystal growth is carried out in the c-axis direction in the present invention, whereas crystal growth in the a-axis direction is performed in the key plus method. In general, crystal growth in the c-axis direction of sapphire is considered to be very difficult as compared to the a-axis direction. This is because a large number of minute bubbles or defects are likely to occur in crystal growth in the c-axis direction. The a-axis pulling has already been put to practical use by the Keyro Plus method, but a c-axis pulling technique is indispensable for improving the material yield.

Secondly, in the chiroplus method, seed crystals are fixed in a state of being immersed in the melt, and crystal growth proceeds and growth continues as it is even if the bottom surface of the crucible is contacted. In the present invention, the seed crystals are always rotated, and the crystal parts grown in the liquid do not reach the bottom of the crucible so as to be pulled out of the crucible after being brought to a sufficiently large crystal size. It is different in that it continues raising up while raising upwards.

In addition, the present invention differs from the ordinary CZ method in that crystal growth is actively performed under the liquid level of the alumina melt. In the present invention, a large c-axis crystal part of a convex shape is raised downward in the alumina melt, and this part is further upwardly raised before reaching the bottom of the crucible, and the margin from the crystal in the liquid to the bottom of the crucible ( margins and further promote crystal growth.

In this invention, it is preferable that the side shape of the single crystal growth part which grows in the said melt | dissolution is a substantially V shape which protruded downward. Generally, when performing c-axis pulling, although the interface shape of a single crystal often has a surface parallel to a melt surface, since this crystal surface is c surface and is the closest surface, it is contained in melt Countless bubbles are likely to be blown during the crystal.

For example, in the Keyro Plus method, necking is performed initially, but after that, the seed crystals are left in the melt and do not rotate. , Its shape is always U-shaped. In addition, it becomes a trumpet shape from the top to the bottom. When it becomes such a shape, c surface will generate | occur | produce in the bottom face of a crystal | crystallization, and a bubble will be easy to blow in. Therefore, as described above, the a-axis pulling is performed in the key plus method.

However, in the present invention, since the shape of the lower end of the growth portion in the liquid is substantially V-shaped and does not have a c plane, it can be grown while excluding bubbles in the alumina melt from the outside of the single crystal. Therefore, high quality single crystal can be produced.

In this invention, it is preferable that the pulling speed of the said seed crystal is 0.5 mm / hr or more and 10 mm / hr or less. This is because when the pulling speed exceeds 10 mm / hr, crystal growth does not catch up, crystal peeling occurs under the shoulder, and the crystal shape collapses significantly. Moreover, when it is less than 0.5 mm / hr, it is because there exists a possibility that crystal growth may progress too much and the lower end of a crystal may reach | attain the crucible bottom.

In this invention, it is preferable that the diameter of the single crystal growth part which grows in the said melt at the time of pulling out from the said alumina melt is 2/3 times or less of the diameter of the said crucible. When the diameter of the single crystal is larger than 2/3 of the crucible diameter, the liquid retreat rate of the alumina melt in the molybdenum crucible is increased, and the crystal growth cannot be caught and the crystal peels off under the shoulder as in the case where the pulling speed is increased. This is because the crystal shape is greatly collapsed.

In this invention, it is preferable that the rotation speed of the said seed crystal is 8 rpm or more and 25 rpm or less. If the rotational speed is lower than 8 rpm, the shape (interface shape) of the growth part in the liquid becomes U-shaped, and bubbles are introduced at high density during the crystal. If the rotation speed is higher than 25 rpm, bending occurs in the interface shape of the crystal. This is because continuation becomes difficult.

In this invention, it is preferable to heat an alumina melt by resistance heating system. In this case, it is preferable that the said crucible is a molybdenum crucible, and it is preferable to arrange a resistance heating heater around the molybdenum crucible, and to heat the alumina melt by radiant heat from the resistance heating heater. In the case of the resistance heating system, the alumina melt is heated together with the crucible by radiant heat from a resistance heating heater provided around the crucible. As a result, the alumina melt has a temperature gradient in the longitudinal direction. Since the viscosity of the alumina melt is very high and not very stir, the longitudinal temperature gradient is maintained. Thereby, crystal growth in the c-axis direction can be promoted under the liquid level of the alumina melt. In addition, since molybdenum crucibles are inexpensive compared to iridium crucibles, the production cost of sapphire single crystals can be reduced.

In the present invention, the ratio B / A of the crystal length A of the single crystal portion pulled upward from the liquid surface position of the alumina melt and the crystal length B of the single crystal portion grown under the liquid surface of the alumina melt is 0.2 or more and 2 or less. It is preferable to raise the said sapphire single crystal.

In addition, the sapphire single crystal according to the present invention has a ratio B / A of the crystal length A of the single crystal portion from the enlarged diameter portion to the linear motion portion and the crystal length B of the single crystal portion of the shaft diameter portion. Is 0.2 or more and 2 or less. Further, in the sapphire single crystal according to another aspect of the present invention, by immersing the c-axis sapphire seed crystal in the alumina melt and pulling it upward while rotating the seed crystal, the sapphire single crystal grows in the c-axis direction at the bottom of the seed crystal. And the ratio B / A of the crystal length A of the single crystal portion pulled upward above the liquid surface position of the alumina melt and the crystal length B of the single crystal portion grown under the liquid surface of the alumina melt is 0.2 or more and 2 or less. do. According to the present invention, it is possible to provide a high quality sapphire single crystal in which bubbles or defects are not introduced into the crystal portion.

Thus, according to this invention, in the manufacturing method of the sapphire single crystal by the CZ method, crystal growth is carried out in a c-axis direction, suppressing introduction of a bubble and a defect, and can obtain a large diameter and a long single crystal.

1 is a schematic view showing the configuration of an apparatus 10 for producing sapphire single crystal according to a preferred embodiment of the present invention.
2 is a flowchart for explaining a method for producing sapphire single crystal.
3 (a) to 3 (c) are schematic diagrams for explaining a step of manufacturing a sapphire single crystal.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic view showing the configuration of an apparatus for producing sapphire single crystal according to a preferred embodiment of the present invention.

The sapphire single crystal manufacturing apparatus 10 shown in FIG. 1 has the chamber 11, the rotating shaft 12 installed in the perpendicular direction through the center of the bottom part of the chamber 11, and the support stand fixed to the upper end of the rotating shaft 12. As shown in FIG. (13), the molybdenum crucible 14 provided on the support base 13, the resistance heating heater 15 provided around the molybdenum crucible 14, the rotating mechanism 16 for rotating the rotating shaft 12, And a seed rod 18 having seed crystals attached to the tip, an pulling mechanism 19 for raising the seed rod 18, and a controller 23 for controlling each portion.

The observation window 17 is provided in the chamber 11, and the state of the pulling of a sapphire single crystal can be confirmed. Moreover, the thick heat insulating material 22 is provided in the chamber 11, and surrounds the outer periphery of the resistance heating heater 15. As shown in FIG. The melting point of sapphire is very high at about 2050 ° C., and therefore high heat insulating property is required in the chamber 11, but sufficient heat insulating property is provided because the heat insulating material 22 is provided not only on the side of the resistance heating heater 15 but also on the upper side and the lower side. Can be ensured, and the sapphire raw material in the molybdenum crucible 14 can be efficiently heated. Thus, the structure which arrange | positions the heat insulating material 22 not only to the side of the resistance heating heater 15 but also above and below is one of the structures peculiar to the manufacturing apparatus 10 of a sapphire single crystal.

In the upper part of the chamber 11, the gas introduction port 24 for introducing Ar gas into the chamber 11 is provided. Ar gas is introduced into the chamber 11 from the gas inlet 24 via the gas pipe 25, and the introduction amount thereof is controlled by the conductance valve 26.

At the bottom of the chamber 11, a gas outlet 27 for exhausting Ar gas in the chamber 11 is provided. Ar gas in the sealed chamber 11 is discharged | emitted from the gas discharge port 27 via the exhaust gas pipe 28 to the outside. A conductance valve 29 and a vacuum pump 30 are provided in the middle of the exhaust gas pipe 28, and the flow rate is controlled by the conductance valve 29 while sucking Ar gas in the chamber 11 with the vacuum pump 30. The decompression state in the chamber 11 is maintained.

A resistance heating heater 15 is provided around the molybdenum crucible 14. The resistance heating heater 15 may be a combination of a plurality of heaters divided in the vertical direction. For example, when using the molybdenum crucible 14 whose height is 225 mm, it is preferable that the height of the resistance heating heater 15 is about 350 mm. The output of the resistance heating heater 15 is controlled by the controller 23.

In this embodiment, the molybdenum crucible 14 is used. Although iridium crucibles are well known as crucibles used in the production of sapphire single crystals, iridium is very expensive compared to molybdenum and is one of the great factors that raises the cost of sapphire single crystals. However, when molybdenum crucible is used, manufacturing cost can be reduced and mass productivity can be improved.

Moreover, as a heating system, the high frequency induction heating system is also known. In the high frequency induction heating system, an eddy current is generated in a crucible by flowing a current through a heating coil, and the crucible itself generates heat by this eddy current, and the melt in the crucible is heated. Therefore, the temperature gradient of the melt is affected by the shape of the crucible. However, in the case of employing the resistance heating system, since both the crucible and the melt are heated by the radiant heat from the resistance heater, the temperature gradient of the melt is hardly affected by the shape of the crucible. Therefore, a temperature gradient suitable for crystal growth in the c-axis direction in the melt can be easily realized.

In the pulling-up of the sapphire single crystal 20, by the control of the controller 23, the pulling speed of the sapphire single crystal 20 and the temperature gradient between the sapphire single crystal 20 and the sapphire melt 21 are controlled with high precision. . The pulling speed of the sapphire single crystal 20 is controlled mainly by the pulling speed of the seed rod 18 by the pulling mechanism 19 and the temperature gradient is adjusted mainly by the output of the resistance heating heater 15. [

As seed crystals, crystals cut in the c-axis direction (c-axis seed crystals) are used. In the case of sapphire crystal, it grows relatively easily in the a-axis direction, but single crystal hardly grows in the c-axis direction, or bubbles or defects are easily introduced. In addition, the c-axis refers to the direction of (0001), and the a-axis refers to the direction of (1120). This invention uses the C-axis seed crystal which is hard to grow, and raises by a CZ method.

2 is a flowchart for explaining a method for producing a sapphire single crystal according to the present embodiment. 3 (a) to 3 (c) are schematic diagrams for explaining the manufacturing process of the sapphire single crystal.

In the production of sapphire single crystal, first, a sapphire raw material such as alumina powder is put into the molybdenum crucible 14 (step S1), and then degassing treatment of the raw material is performed (step S2). The degassing treatment can be performed by leaving the raw material for a certain time in Ar atmosphere under reduced pressure. By this degassing process, the gas component adsorbed on the surface of raw material powder can be removed, and as a result, the gas bubble in an alumina melt can be reduced. By this effect, the introduction of a large amount of bubbles in the grown sapphire single crystal can be suppressed.

Next, the raw material is heated and melted by the resistance heating heater 15 to produce an alumina melt (step S3). Subsequently, the alumina melt is degassed (step S4). The degassing treatment can be performed by leaving the alumina melt for a certain time in an Ar gas atmosphere under reduced pressure. By this degassing treatment, bubbles remaining in the alumina melt can be released to the outside through the alumina melt surface, and as a result, the introduction of a large amount of bubbles in the grown sapphire single crystal can be further suppressed.

Next, after returning the inside of the chamber 11 to atmospheric pressure atmosphere, as shown in FIG.3 (a), the liquid crystal of seed crystal 20a is performed (step S5), and a seed crystal is molybdenum crucible ( The position is fixed while being immersed in the alumina melt 21 in 14). And the crystal growth under liquid level is advanced, keeping the alumina melt 21 at a predetermined temperature gradient (step S6). In addition, in this invention, a "liquid surface" means a flat liquid surface, and does not include the contact surface (solid-liquid interface) of the single crystal twisted by crystal growth and melt. Therefore, when it says "liquid position", it means the position of the height direction of the flat liquid level.

During crystal growth under liquid level, it is preferable to rotate the seed crystal 20a at a predetermined rotational speed. It is preferable that they are 8 rpm or more and 25 rpm or less, and, as for the rotation speed at this time, it is more preferable that they are 10 rpm or more and 18 rpm or less. If the rotational speed is lower than 8 rpm, the shape (interface shape) of the growth part in the liquid becomes U-shaped, and bubbles are introduced at high density during the crystal. If the rotation speed is higher than 25 rpm, bending occurs in the interface shape of the crystal, resulting in crystal growth. This is because it becomes difficult to continue.

As shown in FIG. 3 (b), when the crystal growth under the liquid level progresses, the growth portion of the sapphire single crystal 20 in the substantially V-shaped liquid grown in the c-axis direction below the liquid level of the alumina melt 21 is grown. Is formed. In addition, with the crystal growth, the liquid surface position of the alumina melt 21 is lowered by ΔL. Thus, the upper part of the seed crystal 20a appearing on the liquid surface is really the tip of the iceberg.

After that, as shown in FIG. 3 (c), the seed rods 18 are raised to raise the seed crystals 20a before the crystal growth of the growth portion in the liquid proceeds further to reach the bottom surface of the molybdenum crucible 14. It raises upwards (step S7). It is preferable that the pulling speed at this time is 0.5 mm / hr or more and 10 mm / hr or less. This is because when the pulling speed exceeds 10 mm / hr, crystal growth does not catch up, crystal peeling occurs under the shoulder, and the crystal shape collapses significantly. When the thickness is less than 0.5 mm / hr, crystal growth proceeds excessively so that the lower end of the crystal reaches the bottom of the crucible. Here, the timing of starting the crystal pulling in the upward direction is a step at which the crystal habit line, which appears as the c-axis pulling, can be confirmed in the crystal after the seed liquid. If the crystal is raised before the wall is visible, there is a risk of polycrystallization or crystal peeling.

The diameter of the single crystal to be pulled is preferably 2/3 or less of the diameter of the molybdenum crucible 14. When the diameter of the single crystal is larger than two thirds of the crucible diameter, the liquid retreat rate of the alumina melt in the molybdenum crucible is increased, and the crystal growth cannot be caught and the crystal peels off under the shoulder as in the case where the pulling speed is increased. This is because the crystal shape is greatly collapsed.

Thereafter, when the single crystal reaches the predetermined length, the single crystal is taken out from the alumina melt and the pulling is finished. At this time, the sapphire single crystal 20 is pulled up by the pulling mechanism 19 to separate the single crystal from the melt (step S8). By the above, the sapphire single crystal 20 is completed.

The sapphire single crystal 20 obtained by this embodiment has the crystal length A of the single crystal part pulled upward above the liquid surface position of an alumina melt, and the single crystal which grows under the liquid surface of the said alumina melt, as shown to FIG. 3 (c). Ratio B / A with the crystal length B of a part is 0.2 or more and 2 or less. In other words, the ratio B / A of the crystal length A of the single crystal portion from the enlarged diameter portion to the linear motion portion and the crystal length B of the single crystal portion of the shaft diameter portion is 0.2 or more and 2 or less. The shape of such a sapphire single crystal ingot is a shape peculiar to the sapphire single crystal with few bubbles produced by the above production method.

As described above, in the method for producing sapphire single crystal according to the present embodiment, since the sapphire single crystal is actively grown under the liquid level of the alumina melt, the sapphire single crystal is pulled upward at a predetermined pulling speed in accordance with its crystal growth rate. High-quality c-axis sapphire single crystal without defects can be produced by the CZ method, and large diameters and elongated single crystals can be grown.

As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to said embodiment, A various change is possible in the range which does not deviate from the main point of this invention, and they also of the invention It goes without saying that it is included in the range.

[Example]

Hereinafter, although the Example of this invention is described, this invention is not limited to this Example at all.

(Example 1)

The sapphire single crystal was grown using the sapphire single crystal manufacturing apparatus 10 shown in FIG. First, the alumina powder used as a raw material was put into the molybdenum crucible, it was installed in the chamber, it heated with the resistance heating heater, and the raw material was melted. As the molybdenum crucible, one having a diameter of 225 mm and a depth of 225 mm was used.

Next, c-axis sapphire seed crystals are immersed in an alumina melt maintained at a temperature equal to or higher than the melting point, and the single crystals are grown in a liquid such that the target crystal length is 200 mm and the target diameter is 100 mm while rotating the seed crystals at a rotation speed of 12 rpm. Done.

After the single crystal reached the crystal length and diameter, the pulling speed of the single crystal was gradually increased to further grow the single crystal. The pulling speed at this time was made into 7 conditions of 0.3, 0.5, 1, 3, 5, 10, 15 (mm / hr). In addition, the application time of each pulling speed was set so that the crystal length of the crystal | crystallization site | part grown at the said pulling speed may be set to about 20 mm.

Then, the presence or absence of the bubble in the single crystal grown using the optical microscope was observed, and it evaluated for every crystal part corresponding to each pulling speed. The results are shown in Table 1.

As apparent from Table 1, there was no bubble when the pulling speed was lower than 10 mm / hr, but when the pulling speed was 15 mm / hr, crystal growth did not catch up, and crystal peeling occurred under the shoulder, resulting in crystal shape. This collapsed greatly. In addition, a large number of bubbles were introduced into the crystal, and the crystal was clouded white. This is considered to be that bubbles are introduced at a high density from the unstable growth of the solid-liquid interface. Further, even when the pulling speed is 0.3 mm / hr, the crystal can grow, but the crystal length per day in this case is 7.2 mm, and the crystal cost is very high.

(Example 2)

Next, the sapphire single crystal was grown on the conditions similar to Example 1 except having changed the target diameter of the single crystal in various ways. The target diameter of the single crystal to grow was made into four conditions of 70, 100, 150, and 180 (mm). In addition, the crystal pulling speed was 3 mm / hr and the crystal rotation speed was 12 rpm.

Then, the presence or absence of the bubble in the single crystal grown using the optical microscope was observed, and it evaluated for every crystal site | part controlled to be a target diameter. The results are shown in Table 2.

As is apparent from Table 2, when the diameter of the single crystal was small to 150 mm or less, there was no bubble. When the crystal diameter was 180 mm, many bubbles were observed inside the crystal. As the diameter of the grown crystals increases, the ratio of the crystal diameters to the crucible diameter increases, and as a result, the liquid retreat speed increases. This is substantially the same as the pulling speed is increased, so that bubbles are easily introduced. From the above results, it was found that the diameter of the single crystal is preferably 150 mm or less, that is, 2/3 or less of the crucible diameter.

(Example 3)

Next, the sapphire single crystal was grown on the conditions similar to Example 1 except having changed the crystal rotation speed in pulling variously. The crystal rotation speed was made into 6 conditions of 6, 8, 10, 18, 25, 30 (rpm). In addition, the crystal pulling speed was 3 mm / hr and the target diameter was 100 mm.

Thereafter, the presence or absence of bubbles in the grown single crystal was observed using an optical microscope, and the evaluation was performed for each crystal site controlled at each rotational speed. The results are shown in Table 3.

As apparent from Table 3, when the crystal rotation speed was low at 6 rpm, the interface shape became U-shaped, and bubbles were introduced at high density. In addition, when the crystal rotation speed was as high as 30 rpm, bending occurred in the interface shape of the crystal, and continuation of crystal growth became impossible. On the other hand, when the crystal rotation speeds were 8 rpm and 25 rpm, the interface shape became V-shaped, and there were few bubbles. In addition, when the crystal rotation speeds were 10 rpm and 18 rpm, the interface shape became V-shaped and there were no bubbles. From the above results, it was found that the crystal rotation speed is preferably 8 rpm or more and 25 rpm or less, and more preferably 10 rpm or more and 18 rpm or less.

10: apparatus for producing sapphire single crystal
11: chamber
12:
13: Support
14 molybdenum crucible
15: resistance heating heater
16: rotating mechanism
17: observation window
18 seed rod
19: impression mechanism
20: sapphire single crystal
21: sapphire melt (alumina melt)
22: heat insulation
23: controller
24 gas inlet
25 gas pipe
26: conductance valve
27 gas outlet
28: exhaust gas pipe
29: conductance valve
30: vacuum pump

Claims (8)

A method of producing a sapphire single crystal in which a c-axis sapphire seed crystal is immersed in an alumina melt in a crucible, the seed crystal is pulled upward while being rotated, and a sapphire single crystal is grown at the bottom of the seed crystal in the c-axis direction.
The sapphire single crystal is grown under the liquid level of the alumina melt, and the seed crystal is pulled upward so that the single crystal growth portion growing in the melt does not reach the bottom of the crucible. Manufacturing method. The method of claim 1,
A method of producing a sapphire single crystal in which the side shape of the single crystal growing portion growing in the melt has a substantially V-shaped shape projecting downward. The method of claim 1,
The manufacturing method of the sapphire single crystal whose pulling speed of the said seed crystal is 0.5 mm / hr or more and 10 mm / hr or less. The method of claim 1,
A method for producing sapphire single crystal, wherein the diameter of the single crystal growth portion growing in the melt when pulled from the alumina melt is 2/3 times or less of the diameter of the crucible. The method of claim 1,
The rotation speed of the said seed crystal is 8 rpm or more and 25 rpm or less, The manufacturing method of the sapphire single crystal. The method of claim 1,
A method of producing a sapphire single crystal in which a molybdenum crucible is used in the crucible, a resistance heating heater is arranged around the molybdenum crucible, and the alumina melt is heated by a resistance heating method. The method of claim 1,
The sapphire single crystal is pulled up so that the ratio B / A of the crystal length A of the single crystal portion pulled up above the liquid surface position of the alumina melt and the crystal length B of the single crystal portion growing under the liquid surface of the alumina melt is 0.2 or more and 2 or less. Sapphire single crystal manufacturing method. The sapphire characterized by the ratio B / A of the crystal length A of the single crystal portion from the enlarged diameter portion to the linear motion portion and the crystal length B of the single crystal portion of the shaft diameter portion being 0.2 or more and 2 or less. Single crystal.

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