JP2008031019A - Method for producing sapphire single crystal - Google Patents

Abstract

A method for producing a sapphire single crystal suitable for blue and white LEDs and various electronic devices is provided.
A raw material (aluminum oxide) is melted in a container 3 installed inside a single crystal growth apparatus 1 having an appropriate temperature gradient, and a sapphire seed crystal 5 is brought into contact with the liquid surface of the aluminum oxide melt 4. Thereafter, the seed crystal 5 is rotated at a peripheral speed of 0 to 12 mm / sec, and the pulling distance d of the seed crystal 5 is set to 0 to less than 20% of the liquid level height h1 of the aluminum oxide melt 4 at the initial growth stage. Is brought into contact with the aluminum oxide melt 4 and then grown while lowering the temperature of the furnace 2 at 0.2 to 2 ° C./hr to solidify the molten aluminum oxide to obtain a large, high-quality sapphire single crystal. Get S.
[Selection] Figure 1

Description

  The present invention relates to a method for producing a sapphire single crystal suitable for blue and white LEDs and various electronic devices.

Czochralski method (CZ method), EFG method, heat exchange method (HEM), kiloporous method and the like are known as representative examples of conventional methods for producing sapphire single crystals.
In the CZ method, aluminum oxide is melted in a container, a seed crystal is brought into contact with the liquid surface (surface) of the aluminum oxide melt, and then the seed crystal is pulled up while being rotated. This is a method for growing a crystal ingot (JP 2002-68884 A and JP 2005-231958 A, etc.).
In the EFG method, aluminum oxide is melted in a container, a seed crystal is brought into contact with the aluminum oxide melt that has risen in the slit set in the container, and then the seed crystal is pulled up, whereby plate-like sapphire This is a method for growing a single crystal.
HEM is a method of growing a sapphire single crystal by melting aluminum oxide in a container and crystallizing all the aluminum oxide melt in the container while cooling the seed crystal set at the bottom of the container.
The kiloporous method is known as a method in which a seed crystal is brought into contact with an aluminum oxide melt and the crystal is grown from the seed crystal as a starting point.
Kristall und Technik, 14, 6, (1979) pp. 661-664 JP 2002-68884 A JP-A-2005-231958

Since the diameter of a sapphire single crystal ingot manufactured by the CZ method is about 50% of the diameter of the container used, a larger apparatus or container is required when manufacturing a large single crystal ingot, and the crystal manufacturing cost There was a problem that would be expensive. This method has a low crystal weight ratio (solidification rate) of about 50% with respect to the weight of the charged raw material, so the remaining raw material in the container must be used repeatedly. There is a problem of causing deterioration.
According to the CZ method and the EFG method, the melting point of sapphire is 2000 ° C or higher, so there are restrictions on the heating method and the furnace configuration, and when trying to produce a sapphire single crystal within those restrictions, the temperature gradient is tight. Crystals had to be manufactured in an environment, and it was difficult to obtain good quality crystals.
HEM crystallizes the aluminum oxide melt inside the container, so there is an advantage that it is easy to produce large crystals, but there is a difference in thermal expansion between the container and the sapphire single crystal, so contact with the container There are problems that distortion and crystal defects are likely to occur in the vicinity of the part, and that the manufacturing cost is high due to the short life of the container used.
The kiloporous method is similar to the CZ method, and is characterized by a higher rate of crystal growth inside the aluminum oxide melt than the CZ method. When trying to obtain it, the apparatus becomes large and the temperature distribution tends to be non-uniform. In particular, since sapphire has a high melting point of 2000 ° C. or higher, there are many restrictions on furnace components, refractories, and heating methods, making it very difficult to produce practically large crystals.
An object of the present invention is to produce a large and high quality sapphire single crystal at low cost.

A first feature of the present invention is a method of growing a sapphire single crystal in an aluminum oxide melt by melting aluminum oxide in a container and bringing a seed crystal into contact with the surface of the aluminum oxide melt in the container. The pulling distance of the seed crystal is 0 to less than 20% of the height of the aluminum oxide melt at the initial stage of growth, and after bringing the seed crystal into contact with the aluminum oxide melt, the furnace temperature is set to 0. 2. To grow while lowering at 2-2 ° C / hr.
A second feature of the present invention is that the first feature is provided, and the seed crystal is rotated at a rotational peripheral speed of 0 to 12 mm / sec.
A third feature of the present invention is that the first or second feature is provided and a seed crystal having a diameter of 10 to 20 mm is used.
A fourth feature of the present invention is that any one of the first to third features is provided, and crystal growth is continued until the solidified rate of molten aluminum oxide in the container reaches 80% by weight or more.
A fifth feature of the present invention is any one of the first to fourth features described above, wherein the temperature gradient in the vertical direction in the furnace is 3 ° C./cm or less between the upper end and the lower end of the vessel. There is.
A sixth feature of the present invention is any one of the first to fifth features, wherein the container is made of iridium, molybdenum, tungsten, or an alloy thereof, and the height / diameter is 1.0. The shape is as described above.
A seventh feature of the present invention is that any one of the first to sixth features is provided, and the atmosphere is Ar, Ar + CO _2, Ar + CO + CO _2, or Ar + H ₂ + H ₂ O.
The eighth feature of the present invention is that the seventh feature is provided, and the oxygen partial pressure is 1E-14 to 3E-5.

  According to the present invention, it is possible to manufacture a large sapphire single crystal without increasing the size of the apparatus or the container, the number of wafers can be increased, the manufacturing cost of the final product can be reduced, and the manufactured sapphire single crystal is A high-quality sapphire single crystal can be manufactured as compared with a conventional manufacturing method with little internal strain and high purity.

In order to manufacture the sapphire single crystal according to the present invention, a single crystal growth apparatus 1 shown in FIG. 1 is used.
The single crystal growth apparatus 1 will be described as follows: a furnace 2 whose inside is heated from outside by a heating means, a container 3 disposed in the furnace, and an aluminum oxide melt 4 accommodated in the container. And a seed crystal 5. The container 3 is heated using a resistance heater as a heating means. The material of the container 3 is made of iridium, molybdenum, tungsten, or an alloy thereof. The height / diameter of the container 3 is preferably 1.0 or more. If it is less than 1.0, the temperature gradient becomes so tight that the growth inside the aluminum oxide melt 4, that is, the growth in the height direction may be hindered.

In the production method of the present invention, the aluminum oxide as a raw material is melted in the container 3 using a heating means, and then a seed crystal is formed on the liquid surface (surface) of the aluminum oxide melt 4 as shown in FIG. 5 is brought into contact with each other, and the sapphire single crystal S is grown in the aluminum oxide melt as shown in FIG. The liquid level height of the aluminum oxide melt in the manufacturing process changes from the liquid level height h1 at the initial stage of growth to the liquid level height h2 after the growth.
The pulling distance d of the seed crystal 5 in the manufacturing process is set to 0 to less than 20% of the liquid level height h1 of the initial stage aluminum oxide melt, and the temperature of the furnace 2 is lowered at 0.2 to 2 ° C./hr. It is to nurture while.
The minimum value 0 of the pulling distance d of the seed crystal 5 means that the seed crystal 5 is manufactured without being pulled up, and depending on the setting conditions, it is desirable to grow the crystal without pulling up the seed crystal 5 as much as possible. By setting the pulling distance d of the seed crystal 5 to the above condition, crystallization at the liquid surface of the aluminum oxide melt hardly occurs, and crystallization becomes dominant inside the aluminum oxide melt.
Further, regarding the temperature of the furnace 2, if the temperature drop rate is less than 0.2 ° C / hr, it takes too much time for crystal growth, and thus costs such as manufacturing, and when it exceeds 2 ° C / hr. The crystal growth rate is too high, and bubbles and impurities are taken up more, and the quality of the crystal deteriorates. For this reason, the temperature drop rate range described above is good.

In the manufacturing method of the present invention, in order to obtain a large sapphire single crystal S, the vertical temperature gradient in the furnace 2 is set to 3 ° C./cm or less between the upper end and the lower end of the vessel 3, and the furnace 2 The whole is cooled at the temperature drop rate of 0.2 to 2 ° C./hr described above, so that the crystallization inside the aluminum oxide melt 4 proceeds.
If this manufacturing method is used, the crystal grows in an environment with a gentle temperature gradient and the thermal strain and stress strain are reduced, so that the crystal quality of sapphire is improved. This is because if the temperature gradient exceeds 3 ° C./cm, the crystal grows only near the surface of the aluminum oxide melt 4, so that the crystal cannot be grown unless the crystal is actively pulled up.

In the manufacturing method of the present invention, the seed crystal 5 is rotated when the sapphire single crystal S is grown.
When the seed crystal 5 is rotated, for example, a uniform cylindrical sapphire single crystal S is easily obtained by rotating at a low rotation speed of 12 mm / sec or less. If the rotation speed exceeds 12 mm / sec, it becomes difficult to control the shape of the sapphire single crystal S, or bubbles are taken into the crystal and adversely affect the quality.
Of course, in the manufacturing method of the present invention, rotating the seed crystal 5 is not an indispensable requirement, and includes a case where the crystal is grown without rotating the seed crystal as another embodiment. This is because it is not necessary to forcibly generate convection by reducing the temperature gradient of the aluminum oxide melt 4. As a result, growing in an environment where natural convection is dominant is preferable for improving quality because entrainment of bubbles is reduced.

In the manufacturing method of the present invention, sapphire having a diameter of 10 to 20 mm is used as the seed crystal 5.
This promotes heat exchange via the seed crystal 5.
The size of the seed crystal 5 is not limited to the above range, but if the diameter of the seed crystal is smaller than 10 mm, the heat exchange via the seed crystal is not promoted, resulting in non-uniform crystal growth, resulting in a crystal It is presumed that the quality improvement is adversely affected, and if the diameter of the seed crystal is larger than 20 mm, the temperature difference on the surface of the seed crystal becomes too large to perform optimum seeding.

  In the manufacturing method of this invention, the growth of the sapphire single crystal in the aluminum oxide melt 4 is promoted by actively depriving the seed crystal 5 of heat. For this purpose, the shaft holding the seed crystal 5 is cooled by water or gas, and at this time, the distance from the cooling part to the seed crystal 5 is set as short as possible.

In the manufacturing method of this invention, crystal growth is continued until the solidification rate of the molten raw material (aluminum oxide) in the container 3 is 80% by weight or more.
When the crystal solidification rate of the molten aluminum oxide is at least 80% by weight or more, the sapphire single crystal S can be efficiently grown in one growth, and the manufacturing cost can be reduced. And since an old raw material does not remain in the container 3 and crystal growth can always be started from a new raw material, a high-purity crystal can be grown.

In the manufacturing method of the present invention, the container 3 for containing the raw material (aluminum oxide) of the aluminum oxide melt 4 is made of iridium, molybdenum, tungsten, or an alloy thereof, and has an elongated shape with a height / diameter of 1.0 or more. It is good to use.
This is because by using an elongated container as the container 3, the temperature gradient can be set loosely. Further, since more raw materials of the aluminum oxide melt 4 can be set in the container 3 at once, it is not necessary to operate the furnace only for charging the raw materials, and the types of aluminum oxide melt raw materials that can be used (for example, powder) A wide range of materials, ceramic materials, crystal materials, etc. can be selected. As the container 3, a cylindrical or cone-shaped heat shield plate may be installed on the container instead of using an elongated container.

  In the manufacturing method of the present invention, the heating method for the container 3 by the heating means is preferably an indirect heating method through the furnace 2. This is because in the direct heating method in which the container 3 is directly heated, the temperature gradient in the container becomes large and high quality crystals cannot be obtained. Further, in the direct heating method, the growth of the sapphire single crystal S into the aluminum oxide melt 4 is hindered, so that a large-diameter crystal cannot be obtained.

In the manufacturing method of the present invention, it is preferable to use any of Ar, Ar + CO ₂ , Ar + CO + CO _{2, and} Ar + H ₂ + H ₂ O as an atmosphere during crystal growth.
These atmospheres may cause crystals to grow without oxidizing the furnace material such as molybdenum or carbon that is the material of the furnace 2 and without reducing sapphire. With the above atmosphere, a carbon heater can be used as the heating means, and a refractory material or a heat insulating material can be used as the furnace material of the furnace 2, thereby reducing the equipment cost.
In the above atmosphere, it is presumed that the oxygen partial pressure is preferably 1E-14 to 3E-5 for crystal growth.

  Embodiments of the present invention will be described below with reference to Table 1.

(Example 1)
A container made of molybdenum having a diameter (inner diameter) of 230 mm was used as the container 3, and a sapphire seed crystal having a diameter of 20 mm was used as the seed crystal 5.
After melting aluminum oxide as a raw material in the vessel 3 in an Ar atmosphere, the sapphire seed crystal 5 is brought into contact with the surface of the aluminum oxide melt 4 while controlling the temperature gradient in the aluminum oxide melt. The temperature drop rate of No. 2 was set to 0.2 ° C./hr to uniformly cool the entire inside of the furnace.
The pulling rate of the seed crystal 5 in the manufacturing process was 0.3 mm / hr. However, at the time of pulling up the seed crystal 5, the rotational peripheral speed was set to 0.0 mm / sec (not rotating).
As a result, as shown in Table 1, a large sapphire ingot having a maximum crystal diameter of 165 mm and a crystal length (height) of 205 mm could be grown.
The sapphire single crystal S grown by this example was colorless and transparent and had very few macroscopic defects such as bubbles. When the dislocation (defect) density (EPD) was measured on the sapphire wafer prepared from the sapphire single crystal S, it was 3500 / cm ^{2 on} average.
A sapphire ingot having a diameter of 165/230 mm (about 72% crystal diameter) with respect to the diameter of the container 3 could be produced, and 70% or more of the charged raw material (aluminum oxide) could be crystallized.

(Example 2)
The same container 3 and seed crystal 5 as in Example 1 were used.
The test was carried out under the same conditions as in Example 1. However, the temperature drop of the furnace 2 was set to 0.4 ° C./hr, the entire furnace was cooled uniformly, and the pulling speed of the seed crystal 5 was set to 0.2 mm / hr.
As a result, as shown in Table 1, a large sapphire ingot having a maximum crystal diameter of 210 mm and a crystal length (height) of 200 mm could be grown.
The sapphire single crystal S grown in this example was colorless and transparent, had very few macroscopic defects such as bubbles, and had an average dislocation density (EPD) of 2200 / cm ² .
A sapphire ingot having a diameter of 210/230 mm (about 91% crystal diameter) with respect to the diameter of the container 3 could be produced, and 90% or more of the charged raw material (aluminum oxide) could be crystallized.

(Example 3)
The same container 3 and seed crystal 5 as in Example 1 were used.
The test was carried out under the same conditions as in Example 1. However, the pulling speed of the seed crystal 5 was set to 0.1 mm / hr.
As a result, as shown in Table 1, a large sapphire ingot having a maximum crystal diameter of 165 mm and a crystal length (height) of 200 mm could be grown.
The sapphire single crystal S grown in this example was colorless and transparent, had very few macroscopic defects such as bubbles, and had an average dislocation density (EPD) of 8700 / cm ² .
A sapphire ingot having a diameter of 165/230 mm (about 72% crystal diameter) with respect to the diameter of the container 3 could be produced, and 70% or more of the charged raw material (aluminum oxide) could be crystallized.

Example 4
The same container 3 and seed crystal 5 as in Example 1 were used.
The test was carried out under the same conditions as in Example 1. However, the temperature drop of the furnace 2 was set to 0.6 ° C./hr, and the pulling speed of the seed crystal 5 was set to 0.1 mm / hr.
As a result, as shown in Table 1, a large sapphire ingot having a maximum crystal diameter of 215 mm and a crystal length (height) of 180 mm could be grown.
The sapphire single crystal S grown in this example was colorless and transparent, had very few macroscopic defects such as bubbles, and had an average dislocation density (EPD) of 5100 / cm ² .
A sapphire ingot having a diameter of 215/230 mm (about 93% crystal diameter) with respect to the diameter of the container 3 could be produced, and 90% or more of the charged raw material (aluminum oxide) could be crystallized.

(Example 5)
The same container 3 and seed crystal 5 as in Example 1 were used.
After melting the aluminum oxide raw material in the vessel 3 in an Ar atmosphere, the sapphire seed crystal 5 is brought into contact with the liquid surface of the aluminum oxide melt 4 while controlling the temperature gradient in the aluminum oxide melt. The temperature drop was set to 2.0 ° C./hr, and then the entire inside of the furnace was cooled uniformly while rotating the seed crystal at a rotational peripheral speed of 3 mm / sec. The pulling speed of the seed crystal 5 in the manufacturing process was set to 0.1 mm / hr.
As a result, as shown in Table 1, a large sapphire ingot having a maximum crystal diameter of 195 mm and a crystal length (height) of 185 mm could be grown.
The sapphire single crystal S grown in this example was colorless and transparent, had very few macroscopic defects such as bubbles, and had an average dislocation density (EPD) of 9100 / cm ² .
A sapphire ingot having a diameter of 195/230 mm (about 85% crystal diameter) with respect to the diameter of the container 3 could be produced, and 80% or more of the charged raw material (aluminum oxide) could be crystallized.

(Example 6)
The same container 3 and seed crystal 5 as in Example 1 were used.
The test was carried out under the same conditions as in Example 1. However, the pulling speed of the seed crystal 5 was set to 0.0 mm / hr. That is, the pulling distance d of the seed crystal 5 is zero.
As a result, as shown in Table 1, a large sapphire ingot having a maximum crystal diameter of 168 mm and a crystal length (height) of 196 mm could be grown.
The sapphire single crystal S grown in this example was colorless and transparent, had very few macroscopic defects such as bubbles, and had an average dislocation density (EPD) of 2700 / cm ² .
A sapphire ingot having a diameter of 168/230 mm (about 73% crystal diameter) with respect to the diameter of the container 3 could be produced, and 70% or more of the charged raw material (aluminum oxide) could be crystallized.

(Example 7)
The same container 3 and seed crystal 5 as in Example 1 were used.
After melting the aluminum oxide raw material in the vessel 3 in an Ar atmosphere, the sapphire seed crystal 5 is brought into contact with the liquid surface of the aluminum oxide melt 4 while controlling the temperature gradient in the aluminum oxide melt. The temperature drop was set to 0.4 ° C./hr, and then the entire inside of the furnace was cooled uniformly while rotating the seed crystal at a rotating peripheral speed of 11 mm / sec.
The pulling rate of the seed crystal 5 was set to 0.0 mm / hr.
As a result, as shown in Table 1, a large sapphire ingot having a maximum crystal diameter of 215 mm and a crystal length (height) of 180 mm could be grown.
The sapphire single crystal S grown by this example was colorless and transparent and had very few macroscopic defects such as bubbles. The dislocation density (EPD) of the sapphire single crystal S was 2200 / cm ^{2 on} average. Impurities in the crystal were 10 ppm or less.
A sapphire ingot having a diameter of 215/230 mm (about 93% crystal diameter) with respect to the diameter of the container 3 could be produced, and 90% or more of the charged raw material (aluminum oxide) could be crystallized.

(Example 8)
The same container 3 and seed crystal 5 as in Example 1 were used.
The test was performed under the same conditions as in Example 7. However, the temperature drop of the furnace 2 was set to 0.6 ° C./hr, and the rotational peripheral speed of the seed crystal 5 was set to 9 mm / sec.
As a result, as shown in Table 1, a large sapphire ingot having a maximum crystal diameter of 215 mm and a crystal length (height) of 180 mm could be grown. At this time, about 98% of the aluminum oxide raw material could be crystallized.
The sapphire single crystal S grown in this example was colorless and transparent, had very few macroscopic defects such as bubbles, and had an average dislocation density (EPD) of 3100 / cm ² .
A sapphire ingot having the same crystal diameter as in Example 7 could be produced, and 90% or more of the charged raw material (aluminum oxide) could be crystallized.

Example 9
The same container 3 and seed crystal 5 as in Example 1 were used.
The test was performed under the same conditions as in Example 8. However, to set the atmosphere Ar + CO _2.
As a result, as shown in Table 1, the same sapphire single crystal S as in Example 7 could be grown.
The sapphire single crystal S grown in this example was colorless and transparent, had very few macroscopic defects such as bubbles, and had an average dislocation density (EPD) of 5100 / cm ² .
A sapphire ingot having the same crystal diameter as in Example 7 could be produced, and 90% or more of the charged raw material (aluminum oxide) could be crystallized.

In Examples 1 to 9, a high-quality sapphire (aluminum oxide; Al ₂ O ₃ ) single crystal S having a diameter of 165 mm or more could be produced.
In all the examples except Example 1, Example 3, and Example 6, a sapphire single crystal S having a crystal diameter of 80% or more of the container diameter can be obtained, and the molten aluminum oxide melt 4 The crystal solidification rate of at least 80% by weight or more could be achieved.

It is a figure which shows the manufacturing process of the sapphire single crystal which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Single crystal growth apparatus 2 Furnace 3 Container 4 Aluminum oxide melt 5 Seed crystal d Seed crystal pulling distance h1 Liquid surface height of aluminum oxide melt at the initial stage of growth S Sapphire single crystal

Claims (8)

A method in which aluminum oxide is melted in a container, a seed crystal is brought into contact with the surface of the aluminum oxide melt in the container, and a sapphire single crystal is grown in the aluminum oxide melt,
The pulling distance of the seed crystal is 0 to less than 20% of the liquid surface height of the aluminum oxide melt at the initial growth stage,
A method for producing a sapphire single crystal, wherein the seed crystal is brought into contact with the aluminum oxide melt and then grown while lowering the furnace temperature at 0.2 to 2 ° C./hr.   The method for producing a sapphire single crystal according to claim 1, wherein the seed crystal is rotated at a rotational peripheral speed of 0 to 12 mm / sec.   The method for producing a sapphire single crystal according to claim 1 or 2, wherein a seed crystal having a diameter of 10 to 20 mm is used.   The method for producing a sapphire single crystal according to any one of claims 1 to 3, wherein crystal growth is continued until the solidification rate of molten aluminum oxide in the container reaches 80 wt% or more.   The method for producing a sapphire single crystal according to any one of claims 1 to 4, wherein a vertical temperature gradient in the furnace is 3 ° C / cm or less between an upper end and a lower end of the vessel.   The sapphire according to any one of claims 1 to 5, wherein the container is made of iridium, molybdenum, tungsten, or an alloy thereof and has a height / diameter of 1.0 or more. A method for producing a single crystal. 7. The method for producing a sapphire single crystal according to claim 1, wherein the atmosphere is Ar, Ar + CO _2, Ar + CO + CO _2, or Ar + H ₂ + H ₂ O. 8. The method for producing a sapphire single crystal according to claim 7, wherein the oxygen partial pressure is 1E-14 to 3E-5.

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