JP2007001805A - Method for producing aluminum nitride single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method which can efficiently manufacture a high quality single crystal with a large diameter as a result of preventing the introduction of defects into the single crystal to be obtained when manufacturing a nitride single crystal by a sublimation method. <P>SOLUTION: When growing aluminium nitride on a seed crystal 7 by heating and sublimating a raw material powder 9 of the aluminium nitride in a heating furnace 1, the manufacturing method uses as the raw material powder 9 of the aluminium nitride one that has an average particle diameter of 10 μm or larger or a specific surface area of 0.02 m<SP>2</SP>/g or smaller. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an aluminum nitride single crystal.

  A single crystal material of aluminum nitride (AlN) is expected as a semiconductor device using gallium nitride (GaN), for example, a substrate of a semiconductor light emitting device. This is because a single crystal material of sapphire is conventionally used for the substrate of a gallium nitride optical semiconductor device, but the aluminum nitride has a higher thermal conductivity than sapphire and This is because the incompatibility of the lattice is small, and the band gap has a size larger than the extent of no light absorption in the visible region as in the case of sapphire.

  An aluminum nitride single crystal material having such advantageous characteristics does not have a stable liquid phase under industrially used temperature and pressure conditions. It cannot be produced by a method such as the CZ method for pulling up the crystal. For this reason, various methods have been proposed.

  For example, Non-Patent Document 1 outlines a sublimation method and other crystal grain growth techniques for crystal growth of high-purity AlN. Among these, for a sublimation method, a carbon crucible charged with AlN is used. It is stated that an AlN single crystal can be produced by heating. However, the AlN single crystal disclosed in this non-patent document is a fine single crystal in a powdery or granular form, and does not disclose a single crystal of a size that can be used as a substrate of a semiconductor light emitting device.

  Non-Patent Document 2 describes that the growth of AlN single crystals could be confirmed by evaporating aluminum in a nitrogen atmosphere.

  In recent years, the sublimation method has come to be regarded as promising as a method for producing a nitride single crystal, and technical development of this sublimation method is underway. For example, in Patent Document 1, a nitride powder and an oxide powder that reacts with the nitride to decompose and vaporize the nitride are mixed and heated in a nitrogen atmosphere or the like at a temperature lower than the sublimation temperature. Describes that a nitride single crystal having a size that can be practically used as a bulk material is obtained.

  FIG. 1 is a schematic diagram showing an example of a general nitride single crystal manufacturing apparatus using a sublimation method. In the figure, reference numeral 1 denotes a heating furnace, and the heating furnace 1 includes an induction heating coil 2 as a heating means and a heating furnace body 3 provided inside the induction heating coil. A graphite crucible 4 that accommodates the raw material 9 is provided at the inner lower portion of the heating furnace body 3. In addition, the heating furnace body 3 is provided with an inlet 5 and an outlet 6 for the atmospheric gas, and the atmospheric gas is introduced from the inlet 5 while being discharged from the outlet 6 so that the inside of the heating furnace body 3 A predetermined gas atmosphere can be adjusted to a predetermined gas pressure.

  A susceptor 8 to which a nitride single crystal seed crystal 7 is attached is fixed to the inside upper portion of the heating furnace body 3. The susceptor 8 is a plate-shaped member made of graphite or the like, and the surface to which the seed crystal 7 is attached is disposed horizontally so as to face the graphite crucible 4 containing the raw material 9. Further, the surface of the seed crystal 7 is also arranged horizontally so as to be parallel to the surface of the susceptor 8 (sometimes referred to as a just direction).

  When a nitride single crystal is manufactured by a sublimation method using such a nitride single crystal manufacturing apparatus, first, a nitride powder or a sintered body as a raw material 9 is placed inside the graphite crucible 4. Insert. Next, after the inside of the heating furnace 1 is evacuated by an exhaust pump (not shown) connected to the discharge port 6, an atmosphere gas such as nitrogen is introduced from the atmosphere gas inlet 5. Then, by operating the induction heating coil, the nitride powder or sintered body, which is the raw material 9 accommodated in the graphite crucible 4, is heated to a predetermined sublimation temperature, and the susceptor 8 and the seed crystal 7 are Heat to deposition temperature. During heating, the atmospheric gas in the heating furnace 1 is exhausted from the discharge port 6 at the upper part of the heating furnace 1 while the atmospheric gas is supplied into the heating furnace 1 from the lower inlet 5. The gas pressure and flow rate are adjusted appropriately.

By heating in the furnace, the nitride powder as the raw material 9 accommodated in the graphite crucible 4 is melted and sublimated, and the sublimated nitride raw material gas is deposited on the surface of the seed crystal 7, so that the nitride single substance is obtained. Crystal grows. During this crystal growth, in order to control the crystallization speed of crystal growth on the seed crystal 7, the temperature of the seed crystal 7 and the sublimation speed of the sublimation gas sublimated from the raw material 9 (sublimation amount per unit time) are set. Control to optimize each is performed.
Glen A. SLACK and T.W. F. McNELLY, Journal of Crystal Growth 34 (1976), p. 263-279 R. Shelesser, Z. et al. Sital, Journal of Crystal Growth 234 (2002), p. 349-353 Japanese Patent Laid-Open No. 10-53495

  In the crystal growth by the sublimation method, the sublimation rate of aluminum nitride described above is correlated with the surface area of the raw material to be sublimated, and it is known that the sublimation rate increases as the surface area of the raw material increases. Therefore, if the particle size of the raw material powder is reduced in order to increase the surface area of the raw material charged in the crucible in the manufacturing apparatus described above, the sublimation rate increases, so the productivity when manufacturing the aluminum nitride single crystal is increased. It is advantageous to improve. However, when an aluminum nitride single crystal is produced using a raw material with a large raw material surface area or a small raw material powder particle size, the aluminum nitride raw material heated at a high temperature in the crucible is As sublimation occurs, sintering of the raw material powders occurs, and the sintering proceeds, so that the sublimation rate changes with the passage of time. Such a change in the sublimation rate has a great influence on the quality of the aluminum nitride single crystal to be produced, and a good quality aluminum nitride single crystal may not be obtained in some cases.

  The present invention advantageously solves the above problems, and when producing a single crystal by a sublimation method, it is ensured that no defects are introduced into the resulting single crystal, resulting in a high quality, large diameter. An object of the present invention is to provide a method for producing an aluminum nitride single crystal capable of efficiently producing a single crystal.

The present invention relates to a method for producing an aluminum nitride single crystal in which an aluminum nitride raw material powder is heated and sublimated in a heating furnace to grow aluminum nitride on a seed crystal. A method for producing an aluminum nitride single crystal characterized by using a material having a surface area of 10 μm or more or a specific surface area of 0.02 m ² / g or less.

In the production method of the present invention, it is more preferable to use the aluminum nitride raw material powder having an average particle size of 20 μm or more or a specific surface area of 0.01 m ² / g or less.

According to the method for producing a nitride single crystal of the present invention, the average particle diameter of the aluminum nitride raw material is 10 μm or less, or the specific surface area of the aluminum nitride raw material is 0.02 m ² / g or less. A single crystal can be manufactured with a stable sublimation speed while suppressing fluctuations in speed. Therefore, the obtained aluminum nitride single crystal has no defects, and a high-quality and large-diameter single crystal can be produced efficiently.

  Sublimation from the raw material powder of aluminum nitride occurs from the surface of the raw material powder. Therefore, the sublimation of the aluminum nitride raw material powder charged in a container of a predetermined size is the same as other conditions, the larger the surface area of the raw material, that is, the smaller the particle size of the raw material powder. Or, the greater the specific surface area, the higher the sublimation rate.

  On the other hand, the aluminum nitride raw material powder charged in a container of a predetermined size in the heating furnace sinters the particles that are in contact with each other by high-temperature heating for sublimation. Therefore, considering the sintering of the raw material powder, if the other conditions are the same, the sublimation rate decreases with the passage of time from the initial stage of sublimation and becomes substantially constant. And since sintering temperature falls, so that the particle size of raw material powder is small, the fall of the sublimation speed in the initial stage of sublimation is large.

  In order to produce an aluminum nitride single crystal, it is necessary to control to certain sublimation conditions (temperature, pressure, etc.) so that the single crystal can be obtained. In this regard, when the particle size of the aluminum nitride raw material powder is small or the specific surface area is large, the sublimation rate is high at the initial stage of sublimation, and the sublimation rate decreases with time, resulting in a substantially constant sublimation rate. The fluctuation amount of the sublimation speed becomes large, and if the particle size of the raw material powder is small, the sintering temperature is lowered, so that the sublimation speed fluctuates in a short time. Therefore, control for obtaining a single crystal is difficult. Even in this case, in the initial stage of sublimation, if measures are taken to prevent crystal growth on the seed crystal until the sublimation rate becomes substantially constant, control for obtaining a single crystal is facilitated. In such a measure, there is a possibility that raw materials, time and energy for sublimation are wasted in the initial stage of sublimation.

Therefore, in the present invention, as the aluminum nitride raw material powder for producing an aluminum nitride single crystal by the sublimation method, an average particle diameter of 10 μm or more or a specific surface area of 0.02 m ² / g or less is used. According to the present invention, by using a raw material powder having a large average particle size or a small specific surface area, sintering does not proceed so much, the amount of fluctuation in the sublimation rate from the initial stage of sublimation is reduced, and a single crystal is stably produced. can do.

  The reason why the average particle size is limited to 10 μm or more is that, according to the research by the inventors, a single crystal may not be obtained if the average particle size is less than 10 μm. Is obtained. An average particle size of 20 μm or more is more preferable because the quality of the obtained aluminum nitride single crystal becomes even better. The upper limit of the average particle diameter is not particularly limited from the viewpoint of stably obtaining a good single crystal by reducing fluctuations in the sublimation rate. From the viewpoint of easy accommodation in containers of various shapes and sizes, for example, it is preferably set to 1000 μm or less.

In addition, the specific surface area of the raw material powder in the present invention is limited to 0.02 m ² / g or less, and the inventors have studied that if it exceeds 0.02 m ² / g, a single crystal may not be obtained. This is because an aluminum nitride single crystal can be stably obtained at 0.02 m ² / g or less. A specific surface area of 0.01 m ² / g or less is more preferable because the quality of the obtained aluminum nitride single crystal becomes even better. The lower limit of the specific surface area is not particularly limited from the viewpoint of stably obtaining a good single crystal by reducing fluctuations in the sublimation rate. From the standpoint of ease of accommodation in containers of various shapes and sizes, for example, it is preferably set to 0.0002 m ² / g or more.

  There are several production methods for aluminum nitride powder currently on the market, all of which are suitable for use as raw materials for engineering ceramics (polycrystals) or as additives for rubber and plastics. The particle size is on the order of submicron less than 1 μm. A powder having such a particle size does not satisfy the requirements of the present invention. As the aluminum nitride powder having a particle size or specific surface area according to the present invention, the commercially available aluminum nitride is once sintered and then pulverized and classified into an average particle size within the range of the present invention. be able to.

  An AlN single crystal was manufactured using the manufacturing apparatus shown in FIG. The raw material 9 is made of AlN powder (particle size: 0.2 μm) with an AlN purity of 99% by mass, and is sequentially sintered, pulverized, and classified to prepare raw material powders having various average particle sizes. did.

These powders are accommodated in a graphite crucible 4, while a seed crystal 7 is attached to a susceptor 8, and sublimation is performed at a furnace pressure of 0.4 atm and a furnace temperature of 2000 ° C. Crystal growth was performed. Regarding the amount of sublimation (gram) per hour during sublimation, the initial stage of sublimation (1 hour after the start of sublimation) and 5 hours after are shown in Table 1, and the obtained aluminum nitride products are also shown in Table 1. did.

  As shown in Table 1, when the average particle size of the AlN raw material powder was 0.2 μm and 5 μm, only polycrystals were formed. In any case, since the initial sublimation rate is too high, the nucleation rate on the seed crystal becomes faster than the crystal growth rate, and it is considered that a single crystal could not be formed.

  On the other hand, when the average particle diameter of the AlN raw material was 10 μm or more, single crystals grew in all cases. This is probably because the nucleation rate on the seed crystal was below the crystal growth rate. In addition, when the average particle diameter of the AlN raw material is 10 μm or more, it is clear that as the average particle diameter increases, the X-ray rocking curve half-value width decreases and the quality of the aluminum nitride single crystal improves.

  An AlN single crystal was produced using the same heating furnace as in Example 1. As the raw material 9, raw material powders having various specific surface areas were prepared by using an AlN powder (particle size: 0.2 μm) with an AlN purity of 99 mass% as a raw material, followed by sintering, pulverization, and classification. .

These powders are accommodated in a graphite crucible 4, while a seed crystal 7 is attached to a susceptor 8, and sublimation is performed at a furnace pressure of 0.4 atm and a furnace temperature of 2000 ° C. Crystal growth was performed. About the amount of sublimation (gram) per hour during sublimation, the initial stage of sublimation (1 hour after the start of sublimation) and after 5 hours are shown in Table 2, and the obtained aluminum nitride product is also shown in Table 2. did.

As shown in Table 2, when the specific surface area of the AlN raw material powder was 1.0 m ² / g and 0.04 m ² / g, only polycrystals were produced. In any case, since the initial sublimation rate is too high, the nucleation rate on the seed crystal becomes faster than the crystal growth rate, and it is considered that a single crystal could not be formed.

On the other hand, when the specific surface area of the AlN raw material was 0.02 m ² / g or less, single crystals grew in all cases. This is probably because the nucleation rate on the seed crystal was below the crystal growth rate. In addition, when the specific surface area of the AlN raw material is 0.02 m ² / g or less, it is clear that as the specific surface area becomes smaller, the half width of the X-ray rocking curve becomes smaller and the quality of the aluminum nitride single crystal is improved. .

It is a schematic diagram which shows an example of the manufacturing apparatus of the nitride single crystal using a sublimation method.

Explanation of symbols

1 Heating furnace 2 Induction heating coil 3 Heating furnace body 4 Graphite crucible 7 Seed crystal 8 Susceptor 9 Raw material

Claims (2)

In the method for producing an aluminum nitride single crystal, the aluminum nitride raw material powder is heated and sublimated in a heating furnace to grow aluminum nitride on the seed crystal.
A method for producing an aluminum nitride single crystal, wherein the aluminum nitride raw material powder has an average particle size of 10 μm or more or a specific surface area of 0.02 m ² / g or less. ^{2. The} method for producing an aluminum nitride single crystal according to claim 1, wherein the aluminum nitride raw material powder has an average particle diameter of 20 μm or more or a specific surface area of 0.01 m ² / g or less.

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