JP2017218370A - Seed crystal for aluminum nitride single crystal production, and production method of aluminum nitride single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a seed crystal for producing stably an aluminum nitride single crystal usable suitably for a field of a semiconductor device, having little dislocation, namely, having a small dislocation density; and to provide a production method of the aluminum nitride single crystal.SOLUTION: In a seed crystal for an aluminum nitride single crystal production, which is a seed crystal 4 for growing a single crystal of aluminum nitride, a surface roughness Ra of at least one surface of the seed crystal 4 is 10 nm or less, preferably 2 nm or less, especially preferably 1 nm or less. In the seed crystal for an aluminum nitride single crystal production, a surface having the surface roughness Ra is a crystal growth surface.SELECTED DRAWING: Figure 1

Description

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

  Aluminum nitride has a wide energy band gap, and also has a high thermal conductivity and a large electric resistance. Therefore, the single crystal is used as a substrate material for various semiconductor devices (for example, optical devices, electronic devices, etc.). Attention has been paid.

  A conventional general manufacturing technique for manufacturing the aluminum nitride single crystal is a technique called a sublimation method. For example, as described in Patent Document 1, aluminum nitride powder housed in a crucible is heated. The sublimated aluminum undergoes a vapor phase reaction with nitrogen in an atmospheric gas, and further deposits on a seed crystal and recrystallizes to form a single crystal. It is known that an aluminum nitride single crystal produced by such a sublimation method has crystal defects (for example, domains, dislocations, etc.).

  In particular, dislocations are linear lattice defects present in the crystal, and if an aluminum nitride single crystal having a large dislocation distribution density (hereinafter referred to as dislocation density) is used as a substrate for a semiconductor device, only a reduction in operating efficiency can be obtained. It causes a decrease in durability. Therefore, it is necessary to use an aluminum nitride single crystal having a low dislocation density. However, since the sublimation method is a thermally non-equilibrium process, there is a problem that dislocations are likely to occur.

  As a technique for producing a seed crystal by the sublimation method, Non-Patent Document 1 discloses a technique for producing an aluminum nitride single crystal by hetero-epi growth using a heterogeneous single crystal substrate (such as a SiC substrate) as a seed crystal. However, this technique is not preferable as a technique for manufacturing an aluminum nitride single crystal used in the field of semiconductor devices because different elements (that is, impurities) are easily mixed into the aluminum nitride single crystal from the different single crystal substrate.

  Thus, a technique for industrially and stably producing a large-area and high-quality aluminum nitride single crystal that can be suitably used in the field of semiconductor devices has not yet been established.

Japanese Patent Laid-Open No. 10-53495

SEI Technical Review No. 168 (103) published in March 2006

  The present invention eliminates the problems of the prior art and is suitable for use in the field of semiconductor devices, a seed crystal for stably producing an aluminum nitride single crystal having a low dislocation, that is, a low dislocation density, And it aims at providing the manufacturing method of an aluminum nitride single crystal.

  The present inventor has studied a technique for producing an aluminum nitride single crystal with few dislocations using the sublimation method because the sublimation method is an effective technique for stably producing various single crystals. Then, the relationship between the surface properties of the seed crystal used and the dislocation density of the produced aluminum nitride single crystal was investigated in detail. As a result, it has been found that the growth due to aluminum migration becomes unstable and the epitaxial growth is hindered with the surface roughness (Ra: about several μm) of the seed crystal used conventionally. That is, since the aluminum nitride single crystal grows while reflecting the irregularities on the surface of the seed crystal, dislocations are likely to occur starting from the irregularities. Therefore, if a seed crystal having a reduced surface roughness Ra is used, an aluminum nitride single crystal with few dislocations can be produced by a sublimation method.

  However, since the surface treatment for reducing the surface roughness Ra is a precise operation, if the surface treatment is performed on the entire surface of the seed crystal, the production cost of the seed crystal increases, and consequently the production cost of the aluminum nitride single crystal increases. Invite. Therefore, surface treatment is applied only to the surface on which the aluminum nitride single crystal grows from the seed crystal (hereinafter referred to as crystal growth surface), and the seed crystal with reduced surface roughness Ra is used for the production experiment of the aluminum nitride single crystal. As a result, it was found that an aluminum nitride single crystal having a low dislocation density grows stably from the crystal growth surface.

The present invention has been made based on such knowledge.
That is, the present invention is a seed crystal for growing an aluminum nitride single crystal, and is a seed crystal for producing an aluminum nitride single crystal having a surface roughness Ra of 10 nm or less on at least one surface of the seed crystal. The surface roughness Ra is more preferably 2 nm or less, and particularly preferably 1 nm or less.

In the seed crystal of the present invention, the surface having the surface roughness Ra is preferably a crystal growth surface.
The present invention is also a method for producing an aluminum nitride single crystal using the above-mentioned seed crystal as a seed crystal in a method for producing an aluminum nitride single crystal by a sublimation method.

  According to the present invention, an aluminum nitride single crystal having a small number of dislocations (that is, having a low dislocation density) suitable for use in the field of semiconductor devices can be stably produced.

It is sectional drawing which shows typically the example of the apparatus which manufactures the aluminum nitride single crystal using the seed crystal of this invention.

  In the seed crystal of the present invention, the surface roughness Ra of the crystal growth surface is 10 nm or less. When the surface roughness Ra of the crystal growth surface exceeds 10 nm, it is not possible to suppress the occurrence of dislocations starting from the unevenness of the crystal growth surface in the process of growing the aluminum nitride single crystal. The surface roughness Ra means the arithmetic average roughness. From the roughness curve, a reference length is extracted in the direction of the average line, and the absolute value of the deviation from the average line of the extracted portion to the measurement curve is calculated. The sum is the average value.

  The surface roughness Ra can be measured with an atomic force microscope (so-called AFM). An AFM is a type of scanning probe microscope (so-called SPM), which scans the surface of a sample with a very fine and sharp metal needle (so-called probe), while acting between the probe and the sample (ie, the attractive force and the force). It is a microscope that detects a change in the repulsive force and measures the surface shape of the sample, and it is possible to observe the surface roughness of the sample almost at the atomic level.

  The means for performing the surface treatment for setting the surface roughness Ra to 10 nm or less is not particularly limited, and a conventionally known technique is used. For example, chemical mechanical polishing (so-called CMP), in which polishing slurry in which chromium oxide is dispersed is used as loose abrasive grains and is rubbed with a polishing cloth, is a common technique.

Alternatively, polishing may be performed using an aqueous polishing liquid. This technique is suitable for surface treatment of the crystal growth surface of the seed crystal because the time required for polishing becomes long but generation of wrinkles on the polished surface can be suppressed.
It is also possible to perform surface treatment by applying heat to the crystal growth surface of the seed crystal.
Such a surface treatment may be performed on the entire surface of the seed crystal or only on the crystal growth surface. However, it is preferable to perform surface treatment only on the crystal growth surface from the viewpoint of reducing the production cost of the seed crystal and thus the production cost of the aluminum nitride single crystal.
Note that an aluminum nitride single crystal is used as a seed crystal.
Here, a method of growing an aluminum nitride single crystal from the crystal growth surface using the above-described seed crystal will be described.

FIG. 1 is a cross-sectional view schematically showing an example of an apparatus (hereinafter referred to as a crystal growth furnace) for producing an aluminum nitride single crystal using the seed crystal of the present invention.
In producing an aluminum nitride single crystal, a mixed powder 3 as a raw material is stored in a crucible 2 in a crystal growth furnace 1. The mixed powder 3 is a powder obtained by mixing aluminum nitride powder and oxide powder. The oxide powder serves as a supply source of oxygen necessary for the decomposition reaction of aluminum nitride, which will be described later, and is preferably a powder of Al ₂ O ₃ or the like suitable for growing an aluminum nitride single crystal.

  The seed crystal 4 is subjected to surface treatment so that a predetermined crystal orientation appears on the crystal growth surface and the surface roughness Ra of the crystal growth surface is 10 nm or less. Then, the crystal growth surface is exposed, and the seed crystal 4 is fixed to the inner surface of the upper lid of the seed crystal placement tool 5. The temperature of the inner surface of the upper lid of the seed crystal placement tool 5 is set lower than that below the seed crystal placement tool 5.

  Next, the air in the crystal growth furnace 1 is discharged from the gas discharge port 6, the inside of the crystal growth furnace 1 is decompressed, and the atmospheric gas is supplied from the gas introduction port 7. Circulate the atmosphere gas. The atmospheric gas is preferably a gas composed of simple nitrogen (that is, a nitrogen content in the gas of 100% by volume), or a mixed gas of hydrogen and / or carbon and nitrogen.

  Subsequently, the whole crucible 2 is heated to 1700-2300 ° C. using the heating means 8 while measuring the temperature from the temperature measurement hole 9. As a result, the aluminum nitride in the mixed powder 3 is decomposed into aluminum and nitrogen, and rises in the seed crystal placement tool 5. Then, aluminum and nitrogen are deposited and recrystallized on the crystal growth surface of the seed crystal 4 to grow an aluminum nitride single crystal having a predetermined orientation.

At this time, since the surface roughness Ra of the crystal growth surface is 10 nm or less, the unevenness that tends to be the starting point of dislocation generation in the growth layer of the aluminum nitride single crystal is extremely small, and the generation of dislocation can be effectively suppressed. That is, since the height difference between the concave portion (groove) and the convex portion (mountain) on the crystal growth surface is small, the regularity of atomic arrangement in the growth layer of the aluminum nitride single crystal is improved, and the occurrence of dislocation is suppressed.
The surface roughness Ra of the crystal growth surface is more preferably 2 nm or less, and further preferably 1 nm or less.
As described above, since the aluminum nitride single crystal obtained by applying the present invention has few dislocations (that is, low dislocation density), it can be suitably used as a substrate for semiconductor devices.

An aluminum nitride single crystal was manufactured using the crystal growth furnace shown in FIG. The procedure will be described.
The crucible 2 was made of tungsten, and a mixed powder 3 of aluminum nitride powder and aluminum oxide powder was stored in the crucible 2. As the seed crystal 4, an aluminum nitride single crystal, which is the same kind of single crystal, was used, and its crystal growth surface was subjected to chemical mechanical polishing (CMP) and fixed to the inner surface of the upper cover of the seed crystal placement tool 5. The measurement result of measuring the surface roughness of the crystal growth surface by AMF showed that the surface roughness Ra was 0.11 nm (measured value in a region of 2 μm × 2 μm).

  Then, while measuring the temperature from the temperature measurement hole 9, the crucible 2 is heated to 1700 to 2300 ° C. using the heating means 8, the mixed powder stored is decomposed into aluminum and nitrogen, and the crystal growth of the seed crystal 4 is further performed. The aluminum nitride single crystal was manufactured by depositing and recrystallizing on the surface.

Next, the manufactured aluminum nitride single crystal was cut into a predetermined crystal orientation and a predetermined thickness to manufacture a wafer. The cut wafer was subjected to chemical mechanical polishing (CMP). The polished wafer was placed in an equal amount of sodium hydroxide and potassium hydroxide in a container and immersed in a melt melted at 300 ° C. for 10 minutes, then taken out, washed with water, and further dried. The surface of the sample for microscope observation thus obtained was photographed with an optical microscope, and the dislocation density was measured from the image. As a result, the dislocation density was 5.6 × 10 ⁵ pieces / cm ² . This is an invention example.

On the other hand, as a comparative example, an aluminum nitride single crystal was obtained by using the seed crystal 4 having a surface roughness Ra of 27.3 nm (measured value in the region of 2 μm × 2 μm) and the same procedure as the above invention example. And the dislocation density was measured. As a result, the dislocation density of the comparative example was significantly increased as compared with the inventive example, and was 4.8 × 10 ⁶ pieces / cm ² .

DESCRIPTION OF SYMBOLS 1 Crystal growth furnace 2 Crucible 3 Mixed powder 4 Seed crystal 5 Seed crystal arrangement tool 6 Gas discharge port 7 Gas inlet 8 Heating means 9 Temperature measurement hole

Claims (5)

  A seed crystal for growing an aluminum nitride single crystal, wherein the seed crystal has a surface roughness Ra of 10 nm or less on at least one surface of the seed crystal.   The seed crystal for producing an aluminum nitride single crystal according to claim 1, wherein the seed crystal has a surface roughness Ra of 2 nm or less.   2. The seed crystal for producing an aluminum nitride single crystal according to claim 1, wherein the seed crystal has a surface roughness Ra of 1 nm or less.   The seed crystal for producing an aluminum nitride single crystal according to any one of claims 1 to 3, wherein the surface having the surface roughness Ra is a crystal growth surface.   In the manufacturing method of the aluminum nitride single crystal by a sublimation method, the seed crystal as described in any one of Claim 1 thru | or 4 is used as a seed crystal. The manufacturing method of the aluminum nitride single crystal characterized by the above-mentioned.

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