JP5011734B2 - Method for producing aluminum oxide single crystal and aluminum oxide single crystal obtained by using this method - Google Patents

Description

  The present invention relates to a method for producing an aluminum oxide single crystal and an aluminum oxide single crystal obtained by using this method. More specifically, the present invention relates to a method for efficiently producing an aluminum oxide single crystal by suppressing generation of pits and microbubbles. And a high-quality aluminum oxide single crystal suitable for electronic component materials and optical component materials obtained by this method.

  Aluminum oxide single crystals are widely used as an epi growth substrate for producing blue LEDs and white LEDs. These LEDs are expected to spread in the lighting field from the viewpoint of energy saving, and are attracting attention from various fields.

  There are various methods for growing oxide single crystals, but most of the oxide single crystal materials such as LN, LT, YAG and aluminum oxide are obtained by melt solidification because their crystal characteristics and large crystal diameters are obtained. It is nurtured. In particular, the Czochralski method (Cz method), which is one of the melt solidification methods, is most widely used because of its versatility and high technical perfection.

In order to produce an oxide single crystal by the Czochralski method, first, an oxide raw material is filled in a crucible, and the raw material is melted by heating the crucible by a high frequency induction heating method or a resistance heating method. After the raw material is melted, the seed crystal cut in a predetermined crystal orientation is brought into contact with the surface of the raw material melt, and the single crystal is grown by pulling upward at a predetermined speed while rotating the seed crystal at a predetermined rotation speed.
However, when an aluminum oxide single crystal is grown by the Czochralski method, innumerable minute bubbles are likely to be generated in the crystal. The microbubbles include a relatively large bubble that causes pits (small pits with a diameter of several μm) and a light scattering laser tomography method (see Non-Patent Document 1). ), There is a so-called microbubble that can be confirmed like a cloud when irradiated with laser light. Among these, although the influence of microbubbles has not been determined yet, it is said that the LED characteristics are adversely affected together with the pits.

Until now, when growing aluminum oxide single crystals, oxygen atoms (O) and oxygen molecules (O ₂ ) generated by decomposition of the raw material at high temperature exist in the supersaturated state in the melt. It is known that it is taken in and becomes a bubble in the single crystal. In order to avoid this, it has been proposed to grow a single crystal in a reducing atmosphere using hydrogen gas or carbon monoxide gas (see Patent Document 1). As a result, oxygen atoms (O) and oxygen molecules (O ₂ ) present in the melt are removed by reaction with hydrogen gas or carbon monoxide gas, so the amount of bubbles taken into the grown single crystal is certain. To decrease. However, when a wafer is cut out from the grown single crystal and polished and polished, a large number of pits exist on the surface of the wafer, and the amount of bubbles taken in cannot be sufficiently suppressed.

In addition, gas components that are in equilibrium with the melt tend to be discharged from the melt at the solid-liquid interface where crystallization occurs, and in the melt near the interface, gas components become supersaturated and bubbles are generated. Cheap. However, it is said that by enhancing the convection of the melt, it is possible to suppress the supersaturation of the gas component that occurs in the vicinity of the interface and to reduce the amount of gas component taken into the crystal (see Non-Patent Document 2).
Therefore, first, the gas component contained in the raw material is removed as much as possible before melting, the supersaturated gas component present in the melt is reduced, and after melting, the convection is strengthened and the effect of stirring is increased. It is thought that the generation of pits and microbubbles can be suppressed by reducing the amount of minute bubbles taken into the crystal during growth.

By the way, although it is a manufacturing method of the aluminum oxide single crystal containing titanium, when the single crystal is grown in a low oxygen concentration atmosphere, it is said that the convection of the melt can be strengthened and the stirring effect can be increased (patent document) 2). Here, when an aluminum oxide single crystal containing titanium is grown in a low oxygen concentration atmosphere where the oxygen partial pressure is 10 ⁻² to 10 ⁻⁷ atm, the melt is reduced on the surface of the melt, and accordingly the surface tension is increased. There is an explanation that the flow in the same direction as the natural convection of the melt is remarkably promoted as a result of the occurrence of the surface tension flow and the induction of the surface tension flow. It can be considered that the effect of stirring is increased by the convection of the melt being promoted.

However, when an aluminum oxide single crystal is grown in a low oxygen concentration atmosphere, the growth interface tends to be significantly convex on the melt side. When crystal growth is performed in such a situation, the tip of the growth interface comes into contact with the bottom of the crucible when the height of the melt in the crucible decreases to some extent due to crystal growth. For this reason, it is impossible to continue crystal growth beyond that, and there is a problem that the crystal obtained cannot be made so large with respect to the amount of raw material filled in the crucible. In addition, as a result of remarkably promoting the flow in the same direction as the natural convection of the melt, the single crystal growth rate in the melt is increased, and crystal defects are likely to occur in the obtained crystal. In order to solve such problems, in Patent Document 2, excessive convection of the melt is suppressed by increasing the number of rotations of the growth crystal to, for example, 20 rotations / minute or more, particularly 30 to 120 rotations / minute. Has proposed. However, with such means, although the crystal yield can be increased, the generation of fine bubbles in the single crystal cannot be sufficiently suppressed.
JP 04-132695 A JP 09-278592 A Applied Physics Vol.55 No.6 1986 P542-569 Proceedings of the 28th National Conference on Crystal Growth, 22pA2 1997 P15

  In view of the above-mentioned problems of the prior art, the object of the present invention is to produce high-quality aluminum oxide single crystals suitable for electronic component materials and optical component materials, and to efficiently generate aluminum oxide single crystals while suppressing the generation of pits and microbubbles. The object is to provide a method for producing crystals.

  The inventors of the present invention have made extensive studies in order to solve the above conventional problems, and have investigated in detail the generation mechanism of gas components that cause bubbles contained in the aluminum oxide single crystal. As a result, gas components are also generated when aluminum oxide is decomposed. In addition, aluminum oxide powder, which is widely used as a raw material, is originally adsorbed or encapsulated, and gas components are present in the melt. It was found that it was taken into the crystal and became pits or microbubbles. And while using the aluminum oxide sintered compact with a small specific surface area with very little gas component which is adsorbed or encapsulated as a raw material, it is heated and melted under a specific oxygen partial pressure, and when the single crystal is grown, the gas component to the single crystal is It has been found that the amount of incorporation can be suppressed and the amount of pits and microbubbles generated can be reduced, and the present invention has been completed.

That is, according to the first invention of the present invention, in a method for producing an aluminum oxide single crystal by a melt solidification method in which a raw material for a single crystal is put into a crucible in a furnace body and heated and melted, and a grown crystal is pulled up from the raw material melt. When the aluminum oxide sintered body containing no titanium with a specific surface area of 1 m ² / g or less is used as the single crystal raw material, and the single crystal raw material is heated and melted to grow the single crystal, There is provided a method for producing an aluminum oxide single crystal, wherein the oxygen concentration in the atmosphere is set to 10 to 500 Pa in terms of oxygen partial pressure to suppress the generation of microbubbles .

According to a second aspect of the present invention, there is provided the method for producing an aluminum oxide single crystal according to the first aspect, wherein the single crystal raw material is gradually heated and melted over 10 hours or more. Provided.
According to a third aspect of the present invention, there is provided the method for producing an aluminum oxide single crystal according to the first or second aspect, wherein the material of the crucible is iridium.

On the other hand, according to the fourth invention of the present invention, there is provided an aluminum oxide single crystal obtained by the production method of any one of the first to third inventions.
Further, according to the fifth aspect of the present invention, in the fourth aspect, the scattered light intensity (irradiated with a laser beam on the side surface of the aluminum oxide single crystal and emitted in a direction of 90 ° with respect to the incident laser beam). The scattered light is taken into a CCD camera , the intensity is processed into 256 gradations from 0 to 255 by an image processing apparatus , and the average intensity of the 40 mm square of the crystal portion in the image is calculated as the scattered light intensity ) is 140 or less An aluminum oxide single crystal is provided.

According to the present invention, an aluminum oxide sintered body having a specific surface area of 1 m ² / g or less is used as a raw material for single crystal, the furnace atmosphere is a mixed atmosphere of oxygen and nitrogen or an inert gas, and a specific oxygen partial pressure ( Since the single crystal raw material is melted under a low oxygen concentration), the incorporation of gas components from the raw material into the melt can be suppressed, and the generation of minute bubbles in the melt can be suppressed. In addition, by controlling the growth rate of the single crystal in the melt while maintaining a low oxygen concentration during the growth of the single crystal, it is possible to suppress the incorporation of minute bubbles into the single crystal.
The single crystal thus obtained has reduced pits, microbubbles, crystal defects, and the like due to minute bubbles, and further has no inclusion from the crucible material. If a single crystal is used, electronic component materials and optical component materials having excellent characteristics can be provided.

  Hereinafter, the aluminum oxide single crystal of the present invention and the production method thereof will be described in detail with reference to the drawings.

1. Method for Producing Aluminum Oxide Single Crystal The method for producing an aluminum oxide single crystal according to the present invention comprises the steps of putting a single crystal raw material in a crucible in a furnace body, melting it by heating, and pulling the grown crystal from the raw material melt. In the method for producing a crystal, an aluminum oxide sintered body not containing titanium having a specific surface area of 1 m ² / g or less is used as the single crystal raw material, and the single crystal raw material is heated and melted to grow a single crystal. In this case, the oxygen concentration in the furnace atmosphere is set to 10 to 500 Pa in terms of oxygen partial pressure to suppress the generation of microbubbles .

In the present invention, the raw material for single crystal is an aluminum oxide sintered body substantially composed of two elements of Al and O and having a specific surface area of 1 m ² / g or less.
The diameter and density of the aluminum oxide sintered body are not particularly limited, but for handling, for example, the diameter is preferably 10 mm or less, preferably 5 mm or less, and the density is 5 g / cm ³ or less, preferably What is ³ g / cm <3> or less is good.

In the present invention, it is important to select a single crystal raw material that can suppress the generation of pits and microbubbles.
The present applicant prepares four types of raw materials A to D having different raw material forms, the inside of the furnace is a mixed atmosphere of oxygen and nitrogen or an inert gas, and the oxygen partial pressure is 1, 30, 100, 300, and 500 Pa. And changing the amount of microbubbles contained in the single crystal by measuring the scattered light intensity of the single crystal grown from these raw materials. investigated.
The raw material A is an aluminum oxide powder having a diameter of 0.3 μm and has a specific surface area of about 5 to 10 m ² / g. The raw material B is an aluminum oxide raw material in the form of a sintered body and has a specific surface area of 0.8 to 0.00. 9 m ² / g. In addition, the raw material C and the raw material D are called crackle, and are obtained by pulverizing an aluminum oxide single crystal manufactured by the Bernoulli method to a diameter of 20 mm or less. The specific surface area of this crackle raw material is less than 0.1 m ² / g.

The degree of minute bubbles taken into the grown single crystal was determined by irradiating the crystal with laser light and observing the scattered light according to the light scattering laser tomography method described in Non-Patent Document 1. FIG. 1 shows an optical system for measuring light scattering. The aluminum oxide single crystal 1 processed into a cylindrical shape is irradiated with a laser beam 2 having a wavelength of 532 nm and an output of 500 mW, and scattered light 3 emitted in a direction of 90 ° with respect to the incident direction of the irradiated laser beam 2 is emitted from the CCD camera 4. Then, the image processing apparatus 5 processed the intensity to 256 gradations from 0 to 255, and the intensity average of the 40 mm square of the crystal portion in the image was calculated as the scattered light intensity. At this time, the polarization direction of the laser light is linearly polarized light that is 90 ° with respect to the direction of the CCD camera.
As a result, as shown in the graph of FIG. 2, the light scattering intensity varies depending on the oxygen partial pressure during growth and the difference in raw materials, and the lower the oxygen partial pressure during growth, the smaller the scattered light intensity tends to be. It was found that the scattered light intensity varies greatly depending on the form of the raw material.

  Next, wafers each having a diameter of 3 inches were obtained from these single crystals and polished to confirm the occurrence of pits. As a result, an average of several thousand wafers obtained from a single crystal using raw material A, an average of several tens of wafers obtained from a single crystal using raw material B, and a single crystal using raw materials C and D were obtained. The average number of wafers obtained was several hundred.

Thus, the single crystal obtained using the raw material B as the single crystal raw material has the smallest scattered light intensity and the smallest number of pits, and the single crystal obtained using the raw material A having a large specific surface area has the largest scattered light intensity. It was found that the number of pits was large and the single crystal obtained using the raw materials C and D was located between the scattering intensity and the number of pits. The scattered light intensity is considered to indicate the amount of microbubbles taken into the grown single crystal, but the difference in the amount of microbubbles and the number of pits depends on the oxygen partial pressure during growth and the form of the raw material. It suggests that the amount of gas component taken in is different. In the raw material A, which is a powder raw material having a large specific surface area, not only a large amount of gas is adsorbed to the raw material, but also innumerable voids are formed by grain growth at the time of temperature rise accompanying dissolution, and gas components are easily confined therein. Is backed up.
As described above, the crackle raw material is obtained by pulverizing an aluminum oxide single crystal produced by the Bernoulli method to a diameter of 20 mm or less using a melt obtained by melting aluminum oxide powder. Therefore, in this crackle raw material, even if the specific surface area is smaller than that of the raw material B, many bubbles are included in the raw material particles. Therefore, the scattered light intensity and the number of pits of the single crystal obtained using both as raw materials are located between those of the single crystal obtained using raw material A and those of the single crystal obtained using raw material B. This result also supports the above interpretation.

From the viewpoint of reducing pits and microbubbles, in the present invention, an aluminum oxide sintered body having a specific surface area of 1 m ² / g or less is used as a single crystal raw material, and the single crystal raw material is heated and melted. When growing a single crystal, it is necessary to set the oxygen concentration in the furnace body atmosphere to 10 to 500 Pa in terms of partial pressure.

Although the aluminum oxide sintered compact used by this invention can use the commercial item for semiconductor manufacture, it can also manufacture by the method as shown below.
For example, α alumina particles are added as seeds to a sol or gel of an α alumina precursor that is converted to α alumina when baked, and after the sol is gelled, the gel of the α alumina precursor to which the seed crystal is added is 900 to Sinter at a temperature of 1350 ° C. and grind the resulting sintered product.

When normal aluminum oxide powder is used as the raw material for single crystal, the specific surface area is as large as about 5 to 10 m ² / g, so that many gas components are adsorbed or encapsulated in the aluminum oxide powder, and the raw material is melted. This is not preferable because it is not completely removed before and remains in the melt and is taken into the crystal to form pits and microvalves. Moreover, even if it is an aluminum oxide sintered compact, when the specific surface area exceeds 1 m < ² > / g, since the gas component adsorbed or included similarly increases, it is not suitable for use.

The specific surface area of the crackle raw material obtained by grinding the aluminum oxide single crystal produced by the Bernoulli method to a diameter of 20 mm or less is very small, less than 0.1 m ² / g, but the adsorbed gas is small, but the aluminum oxide powder is dissolved. Since a single crystal prepared from the obtained melt is pulverized, innumerable bubbles are often included therein. The crackle raw material tries to release the gas component contained at the time of melting, but because the viscosity of the aluminum oxide melt is high and the surface tension is large, it becomes microbubbles and dissolves in the melt. Therefore, it is not suitable as a single crystal raw material because it is difficult to escape from the melt.

  In the present invention, in order to grow an aluminum oxide single crystal, a conventional oxide single crystal growing apparatus based on the Czochralski method can be used. For example, a crucible formed of a noble metal, a furnace material formed of alumina or the like as a heat insulating material around the crucible, and an apparatus in which a high-frequency coil as a heating device is disposed outside the furnace material. Since the melting point of alumina, which is a single crystal raw material, is slightly over 2000 ° C., it is preferable to use an iridium-made crucible. As the heat insulating material, a heat insulating material such as foamed zirconia may be filled. Above the crucible, a pulling device for pulling up the single crystal from the material melt is provided, and the furnace material is shielded by a shielding plate. The furnace body is a mixed atmosphere of oxygen and nitrogen or an inert gas.

First, the above-mentioned specific single crystal raw material is put in the crucible as an oxide single crystal, and then the crucible is heated by a high-frequency coil to melt the raw material to obtain a melt and grow a single crystal. When the single crystal raw material is melted, the oxygen concentration in the furnace atmosphere is preferably 10 to 500 Pa, particularly 100 to 300 Pa in terms of oxygen partial pressure.
According to FIG. 2, as the oxygen partial pressure decreases, the scattered light intensity decreases, and a single crystal is obtained in which the number of microbubbles precipitated in the crystal during single crystal growth is reduced. When the oxygen partial pressure is less than 10 Pa, iridium is easily taken up as inclusions in the crystal. Moreover, since generation | occurrence | production of a microbubble will increase when it exceeds 500 Pa, it is not preferable.

  The heating rate until the raw material reaches the melting point is not particularly limited, but it is possible to suppress the incorporation of bubbles into the single crystal by heating gradually over a long time without rapidly heating. For example, it is desirable to heat gradually over 10 hours, especially over 12 hours.

Next, heating is continued even after the single crystal raw material is melted, and after 3 hours or more, especially 5 hours or more have elapsed from the melting of the raw material, the seed crystal is brought into contact with the obtained melt, and the seed crystal is rotated with a pulling device. Pull up. Even when the single crystal is grown, the oxygen concentration is preferably 10 to 500 Pa, particularly 100 to 300 Pa in terms of oxygen partial pressure.
Single crystal growth is carried out in accordance with a conventional method except that the furnace atmosphere is changed to a low oxygen concentration atmosphere, and the number of rotations and pulling speed are adjusted to form the neck portion and the shoulder portion, and then the straight body portion is formed. At this time, it is preferable to measure the temperature of the melt surface in the vicinity of the interface between the single crystal and the raw material melt using a radiation thermometer or the like. The crystal shape is adjusted by measuring the crystal weight during growth, deriving the diameter, growth rate, and the like by calculation, and adjusting the rotation speed and pulling speed. Also, the melt temperature can be controlled by feeding back the change in crystal weight to the power applied to the high frequency induction coil.

By the way, as described in Patent Document 2, when an aluminum oxide single crystal is grown in a low oxygen concentration atmosphere, the growth interface tends to be remarkably convex on the melt side. When single crystal growth is performed in such a situation, if the height of the raw material melt in the crucible is reduced to some extent by crystal growth, the tip of the growth interface and the bottom of the crucible come into contact with each other. For this reason, it is impossible to continue the crystal growth beyond that, and there arises a problem that the crystal obtained cannot be so large with respect to the amount of raw material filled in the crucible. In addition, as a result of remarkably promoting the flow in the same direction as the natural convection of the melt, the single crystal growth rate in the melt is increased, and crystal defects are likely to occur in the obtained crystal.
Such a problem can be solved, for example, by increasing the number of rotations of the crystal during growth and adjusting the crystal growth rate, as described in Patent Document 2, for example, in Japanese Patent Application Laid-Open No. 2005-231958 by the present applicant. If the convection of the melt is adjusted using a growing furnace having a heater at the bottom of the crucible as disclosed, the problem can be solved without greatly increasing the rotational speed.

  In this way, by selecting a sintered body of aluminum oxide having a small specific surface area as a raw material for a single crystal, and further growing the single crystal by heating and melting the raw material under specific oxygen partial pressure conditions, Due to the effect, the gas adsorbed or encapsulated in the raw material can be easily eliminated, and as a result, the excess gas contained in the melt can be reduced, and the minute bubbles taken into the crystal during single crystal growth can be reduced. The number of pits and microvalves in the obtained single crystal can be reduced.

2. Aluminum oxide single crystal The aluminum oxide single crystal of the present invention is a single crystal containing two elements of aluminum and oxygen obtained by the above production method.
Furthermore, it is a single crystal whose scattered light intensity calculated | required by the following light-scattering laser tomography method reduced to 140 or less. The scattered light intensity is measured by irradiating the side surface of the aluminum oxide single crystal processed into a cylindrical shape with laser light and capturing the scattered light emitted in the direction of 90 ° with respect to the incident laser light into the CCD camera. Calculate with the device.

  By slicing a wafer from this single crystal and polishing it, an epicrystal substrate can be obtained. Since there are very few microbubbles in the single crystal, the number of pits and microbubbles is reduced, and electronic component materials and optical component materials having excellent characteristics can be provided.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[Measurement of minute bubbles]
The minute bubbles taken into the grown single crystal were observed according to the light scattering laser tomography method. Specifically, as shown in FIG. 1, the side surface of the cylindrically processed aluminum oxide single crystal is irradiated with laser light, and the scattered light emitted from the end surface of the aluminum oxide single crystal is taken into the CCD camera, and an image is obtained. The scattered light intensity was calculated by the processing apparatus. As a result, if the scattered light intensity is 140 or less, it is determined that the amount of microbubbles in the grown single crystal is small.

[Evaluation of pits]
Fifty wafers were sliced from the grown single crystal and polished to measure how many pits there were. The smaller the number of pits, the better the single crystal is grown.

[Example 1]
A growth furnace having a heater at the bottom of the crucible disclosed in JP-A-2005-231958 was used, and 10 kg of 4N (99.99%) aluminum oxide raw material (raw material B) was charged as a starting material into the iridium crucible. The raw material is a sintered body having a specific surface area of 0.8 to 0.9 m ² / g. This raw material was gradually heated over 12 hours at an oxygen partial pressure of 100 Pa until reaching the melting point, and this low oxygen concentration was maintained even after the raw material was melted. After 6 hours from the melting of the raw material, an aluminum oxide single crystal cut in the a-axis direction was used as a seed crystal, and the seed crystal was lowered to near the melt. The seed crystal is gradually lowered while rotating at a speed of 2 revolutions per minute, and the seed crystal is pulled at a pulling speed of 2 mm / hr while gradually lowering the temperature by bringing the tip of the seed crystal into contact with the melt. The crystal was grown by raising.
As a result, a single crystal having a diameter of 102 mm and a straight body portion length of 118 mm was obtained. Further, when the growth interface at the bottom of the crystal was measured, it was 32 mm convex. Furthermore, when this single crystal was processed into a cylindrical shape, a laser beam having a wavelength of 532 nm was irradiated to measure the scattered light inside the crystal, the scattered light intensity was 68. When the number of pits was measured, as shown in Table 1, it was 3.2 on average in a 3-inch wafer.

[Example 2]
Crystal growth was performed in the same manner as in Example 1 except that the oxygen partial pressure was 300 Pa. As a result, a single crystal having a diameter of 105 mm and a length of the straight body portion of 120 mm was obtained.
Further, when the growth interface at the bottom of the crystal was measured, it was 26 mm convex. Further, this single crystal was processed into a cylindrical shape, and a laser beam having a wavelength of 532 nm was irradiated to measure the scattered light inside the crystal. As a result, the scattered light intensity was 103. When the number of pits was measured, as shown in Table 1, it was 5.3 on average in a 3-inch wafer.

[Comparative Example 1]
10 kg of 4N (99.99%) Al ₂ O ₃ material (raw material A) was charged as a starting material into an iridium crucible. This raw material is an aluminum oxide powder having a diameter of 0.3 μm and a specific surface area of 5 to 10 m ² / g.
As in Example 1, this raw material was gradually heated for 12 hours at an oxygen partial pressure of 100 Pa until reaching the melting point. After 6 hours had elapsed since the melting of the raw material, an aluminum oxide single crystal cut in the a-axis direction was used as a seed crystal. The seed crystal was lowered to near the melt. The seed crystal is gradually lowered while rotating at a speed of 2 revolutions per minute, and the seed crystal is raised at a pulling speed of 2 mm / h while gradually lowering the temperature by bringing the tip of the seed crystal into contact with the melt. Crystal growth was performed.
As a result, a crystal was obtained in which the diameter was 100 mm, the length of the straight body portion was 115 mm, and no bubbles were observed visually. Further, when the growth interface at the bottom of the crystal was measured, it was 30 mm convex. Furthermore, when this crystal was processed into a cylindrical shape and irradiated with a laser having a wavelength of 532 nm to measure scattered light inside the crystal, the scattered light intensity was 84. When the number of pits was measured, as shown in Table 1, it was 1256 on average.

[Comparative Example 2]
Crystals were grown using a crackle raw material (raw material C) having a small specific surface area as a raw material. The raw material C is obtained by pulverizing an aluminum oxide single crystal produced by the Bernoulli method to a diameter of 20 mm or less, and has a specific surface area of less than 0.1 m ² / g. When the scattered light inside the crystal was measured, the scattered light intensity was 91. When the number of pits was measured, it was 326 on average as shown in Table 1.

[Comparative Example 3]
A crystal was grown using a crackle raw material (raw material D) having a small specific surface area, which is different from that of Comparative Example 2. The raw material D is obtained by pulverizing an aluminum oxide single crystal produced by the Bernoulli method to a diameter of 20 mm or less, and has a specific surface area of less than 0.1 m ² / g. When scattered light inside the crystal was measured, the scattered light intensity was 81. When the number of pits was measured, it was 52 on average as shown in Table 1.

[Comparative Example 4]
Crystal growth was performed in the same manner as in Example 1 except that the oxygen partial pressure was 1 Pa or less. When a crystal having a diameter of 103 mm and a length of the straight body part of 95 mm was obtained, the crystal bottom part was in contact with the crucible bottom, and the growth was stopped. The growth interface at the bottom of the crystal was measured and found to be as large as 88 mm. When the intensity of scattered light inside the crystal was measured, the scattered light intensity was as small as 42. However, a relatively large scatterer was observed, and it was found that there may be inclusions. In addition, when this crystal was sliced into a wafer and polished and polished, no pits (fine pits with a diameter of several μm) were found, but there were several protruding foreign objects with a size of several μm in each wafer. About one piece was observed on the wafer, and it was iridium when analyzed by EPMA.

[Comparative Example 5]
Crystal growth was performed in the same manner as in Example 1 except that the oxygen partial pressure was 600 Pa or less. A crystal having a diameter of 103 mm and a length of the straight body part of 121 mm was obtained. When the growth interface at the bottom of the crystal was measured, it was 30 mm convex. Further, this crystal was processed into a cylindrical shape, and the intensity of scattered light inside the crystal was measured by irradiating with a laser having a wavelength of 532 nm. As a result, the scattered light intensity was 150, exceeding 140, which was considered good. When the number of pits was measured, as shown in Table 1, it was 18369 on average in a 3-inch wafer.

It is explanatory drawing which shows the means to investigate the micro bubble (micro valve | bulb) in a crystal | crystallization using the optical system which irradiates a laser beam to the grown single crystal and measures light scattering. It is a graph which shows the influence which the oxygen partial pressure at the time of single crystal growth has on the light-scattering intensity | strength of the single crystal to grow.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Grown single crystal 2 Laser light 3 Scattered light 4 CCD camera 5 Image processing device

Claims (5)

In a method for producing an aluminum oxide single crystal by a melt solidification method in which a raw material for a single crystal is put in a crucible in a furnace and heated and melted, and a grown crystal is pulled up from the raw material melt,
When the single crystal raw material is a sintered aluminum oxide containing no titanium having a specific surface area of 1 m ² / g or less, and the single crystal raw material is heated and melted to grow the single crystal, the furnace atmosphere A method for producing an aluminum oxide single crystal, characterized by suppressing the generation of microbubbles by setting the oxygen concentration therein to 10 to 500 Pa in terms of oxygen partial pressure.   The method for producing an aluminum oxide single crystal according to claim 1, wherein the crystal raw material is gradually heated and melted over 10 hours or more.   The method for producing an aluminum oxide single crystal according to claim 1 or 2, wherein the material of the crucible is iridium.   The aluminum oxide single crystal obtained by the manufacturing method in any one of Claims 1-3. Scattered light intensity (irradiating the side surface of the aluminum oxide single crystal with laser light, capturing the scattered light emitted in the direction of 90 ° with respect to the incident laser light into the CCD camera, and setting the intensity to 0 to 255 with an image processing apparatus. 5. The aluminum oxide single crystal according to claim 4 , wherein the processing is performed up to 256 gradations, and the average intensity of a 40 mm square portion of the crystal in the image is calculated as scattered light intensity ) is 140 or less.

Images