JP2010150110A - Nitride single crystal and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an aluminum nitride single crystal by which the growth rate of the aluminum nitride single crystal is enhanced. <P>SOLUTION: In the method for producing a nitride single crystal, comprising depositing the nitride single crystal on a seed substrate arranged on a susceptor by a sublimation method by using a production apparatus of the nitride single crystal, equipped with at least: a growth container having a raw material vessel for accommodating a raw material and a susceptor; and a heating means for adjusting the temperature of an internal space of the growth container, a first step for growing the nitride single crystal at a growth rate of ≤100 μm/h and a second step for growing the nitride single crystal at a growth rate of ≥100 μm/h in such a state that the temperature of the internal space of the growth container is raised are included. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a single crystal such as aluminum nitride (AlN), and more specifically, production of a nitride single crystal capable of preventing a silicon carbide (SiC) substrate as a seed substrate from being carbonized or etched. Regarding the method.

Aluminum nitride semiconductors are expected as deep ultraviolet laser diodes and high-efficiency, high-frequency electronic devices. As a substrate for growing this semiconductor, an aluminum nitride single crystal is optimal, and therefore, development of aluminum nitride single crystal is under development.
A feature of the aluminum nitride single crystal is that it has a very high thermal conductivity of 290 Wm ⁻¹ K ⁻¹ , which is very advantageous for dissipating heat generated during device operation.

As a method for producing an aluminum nitride single crystal, the flux method is used in the solution method, the metal-organic vapor phase epitaxy (MOVPE) is used in the vapor phase method, the hydride vapor deposition method (Hydride Vapor Phase Epitaxy, HVPE) and sublimation methods. Among these, the sublimation method is a powerful method for producing a bulk crystal because the growth rate is generally high. This sublimation method is a method of producing a single crystal by sublimating aluminum nitride as a raw material and recondensing it in a temperature range lower than the sublimation temperature.
In particular, the present application relates to a sublimation method (an improved Rayleigh method) using a seed substrate.

As a method for producing an aluminum nitride single crystal by an improved Rayleigh method, Patent Document 1 discloses that a mixed powder of nitride and oxide is lower than the sublimation temperature of nitride by utilizing the reaction of nitride and oxide. A method is described in which vaporization is performed by heating at a temperature, and a nitride single crystal is grown on the substrate in this nitrogen atmosphere.
Patent Document 2 describes a method in which an SiC single crystal is used as a seed substrate and an aluminum nitride single crystal is grown thereon.
In Non-Patent Document 1, an aluminum nitride single crystal is grown on a SiC substrate to a single crystal length of 200 to 400 nm by MOCVD, and grown at a growth rate of 10 to 30 μm / h in the first stage. Thereafter, a method is described in which the temperature is increased at the second stage to grow at a growth rate of 70 μm / h.
Japanese Patent Laid-Open No. 10-53495 JP-T-2002-527343 Journal of Crystal Growth 281 (2005) 68-74

However, in the conventional method for producing an aluminum nitride single crystal by the sublimation method, when the aluminum nitride single crystal is grown using the SiC single crystal as a seed substrate, the experiment is performed under the condition that the growth rate of the aluminum nitride single crystal exceeds 100 μm / h. The present inventor has found that the SiC surface is easily carbonized or etched when performing.
In the case of the growth conditions for growing at a high growth rate, SiC is in an environment where it can be easily sublimated because the growth temperature is high and the atmospheric pressure is low. Furthermore, since SiC is exposed to a high flux aluminum nitride sublimation gas, it is susceptible to such damage. Further, once the SiC surface is carbonized / etched, the damage of the portion further proceeds, the damage also reaches SiC covered with aluminum nitride, and finally SiC is lost. As a result, the unsupported aluminum nitride is resublimated, and the subsequent growth of the aluminum nitride single crystal becomes difficult.
Therefore, in order to grow an aluminum nitride single crystal on a SiC substrate, growth has to be performed under a low growth rate condition, and there is a problem that it takes a lot of time to grow a bulk crystal.

The method for producing a nitride single crystal of the present invention includes:
A growth container having a raw material container for storing the raw material therein and a susceptor facing the raw material container;
Heating means for adjusting the temperature of the internal space of the growth vessel;
Using a nitride single crystal production apparatus comprising at least a nitride single crystal produced by depositing the nitride single crystal on a seed substrate disposed on the susceptor by a sublimation method,
A first stage of growing the nitride single crystal at a growth rate of 100 μm / h or less;
A second stage of growing the nitride single crystal at a growth rate of 100 μm / h or more with the temperature of the internal space of the growth vessel raised;
It is characterized by having.

  Preferably, the nitride is aluminum nitride and the seed substrate is a silicon carbide substrate.

  Furthermore, the present invention provides a nitride single crystal obtained by using the method for producing a nitride single crystal.

According to the present invention, in the aluminum nitride single crystal growth on the SiC seed substrate, in the first stage, after growing the aluminum nitride single crystal on the entire surface of the SiC seed substrate at a growth rate of 100 μm / h or less, By raising the temperature of the internal space and growing aluminum nitride at a growth rate of 100 μm / h or more in the second stage, the entire seed substrate is covered with aluminum nitride single crystal at the initial stage of growth, so that the SiC surface is carbonized or etched. Thus, it is possible to obtain a bulk aluminum nitride single crystal with improved quality.
By using the method for producing an aluminum nitride single crystal of the present invention, an aluminum nitride single crystal with improved quality can be obtained at a higher growth rate and in a shorter time compared to the conventional method.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an example of an apparatus for producing an aluminum nitride single crystal according to the present invention.

The aluminum nitride production apparatus 1 of the present embodiment includes a growth vessel 2 made of a graphite crucible, a raw material vessel 3 arranged at the inner bottom of the growth vessel 2, and a susceptor 4 attached to the ceiling of the growth vessel 2. It is prepared for. The raw material container 3 has an opening 3a at the top, and stores a raw material 11 such as aluminum nitride powder at the bottom.
An introduction portion 5 such as nitrogen gas is formed at the bottom of the growth vessel 2 and around the raw material vessel 3, and a ceiling portion of the growth vessel 2 and around the susceptor 4 is filled with nitrogen gas and the like. A discharge portion 6 is formed. Thereby, the inside of the growth vessel 2 can be adjusted to a predetermined gas pressure.

Further, the susceptor 4 is a plate made of graphite or the like, and is fixed to the upper center (ceiling part) inside the growth vessel 2, and the lower surface of the susceptor 4 faces the raw material 11 such as aluminum nitride powder. A seed substrate 12 is attached to the substrate.
The seed substrate 12 for crystal growth is, for example, a 6H—SiC single crystal plate having a diameter of 1 inch, and the deposition surface of the aluminum nitride single crystal 13 on the seed substrate 12 is a (0001) Si surface.
Further, heating means 7 for heating the raw material 11, the susceptor 4, and the seed substrate 12 disposed inside the growth container 2 is provided along the outer periphery of the growth container 2 main body. Such heating means 7 is not particularly limited, and conventionally known ones such as high-frequency induction heating (high-frequency coil) or resistance heating (the heater material is carbon, tungsten, etc.) can be used.

Next, the manufacturing method of the aluminum nitride single crystal 13 using the manufacturing apparatus 1 of the present invention will be described.
First, an unillustrated import port provided in the growth vessel 2 is opened, a raw material 11 such as aluminum nitride powder is set at the bottom of the raw material vessel 3, and the seed substrate 12 is arranged on the susceptor 4. Is closed to seal the main body of the growth vessel 2.
Next, after the inside of the growth vessel 2 is evacuated by the gas discharge unit 6, a process gas such as nitrogen gas is introduced into the internal space 2 a in the growth vessel 2 by the gas introduction unit 5 to adjust the pressure. The pressure here can be set to 10 to 1000 Torr.
Then, using the heating means 7, the growth container 7 is heated so that the lower part (raw material part) of the raw material container 3 in which the raw material 11 is arranged is at a higher temperature than the susceptor 4 (growth part) in which the seed substrate 12 is arranged. 2 The raw material 11, the susceptor 4 and the seed substrate 12 in the main body are heated. Here, the temperature of a raw material part can be set to 1800-2400 degreeC. Moreover, the temperature of the growth part can be set to 1700-2200 degreeC.
The temperature of the raw material part is determined, for example, by measuring the temperature of the inner bottom part of the growth container 2 in which the raw material container 3 is installed with a radiation thermometer. The temperature of the growth part is determined, for example, by measuring the temperature of the upper part of the growth vessel 2 where the susceptor 4 is installed with a radiation thermometer.

Further, during the heating, the nitrogen gas in the growth vessel 2 is exhausted from the gas discharge unit 6 at the upper part of the growth vessel 2 and the nitrogen gas is supplied into the growth vessel 2 from the lower gas introduction unit 5. 2. Adjust the nitrogen gas pressure and flow rate in 2 appropriately.
The raw material 11 sublimated by heating and decomposed and vaporized is crystal-grown on the seed substrate 12 in a nitrogen gas atmosphere, and grows as an aluminum nitride single crystal 13 on the (0001) Si surface of the seed substrate 12. In the present invention, during the crystal growth, in order to control the crystallization speed of crystal growth on the seed substrate 12, temperature control is performed to optimize the temperature of the susceptor 4 and the sublimation speed of the sublimation gas sublimated from the raw material 11. .

  In the present invention, at this time, the growth stage of the aluminum nitride single crystal 13 is grown in two stages. The first stage is a stage in which the aluminum nitride single crystal 13 is grown at a low growth rate, and the aluminum nitride single crystal is grown on the entire surface of the seed substrate 12. The second stage is a stage in which the aluminum nitride single crystal 13 is grown at a high growth rate, and the temperatures of the growth part and the raw material part in the internal space of the growth vessel 2 are raised as compared with the first stage. The temperature of the raw material part here can be set to 2000-2500 degreeC. Moreover, the temperature of the growth part can be set to 1800-2300 degreeC.

By the above method, an aluminum nitride single crystal obtained by growing the aluminum nitride single crystal 13 on the deposition surface of the seed substrate 12 is obtained.
According to the above method, since the entire seed substrate 12 is covered with the aluminum nitride single crystal 13 in the initial stage of growth, carbonization / etching of the seed substrate 12 can be suppressed in the subsequent growth of the aluminum nitride single crystal 13.

  An aluminum nitride single crystal was produced on one surface of the seed substrate 12 using the apparatus having the configuration shown in FIG. This production was performed under the experimental conditions 1 to 8 shown in Table 1 below.

  In this experimental condition, conditions 1, 3 and 5 are conditions for allowing the conventional growth of only one stage, and conditions 2, 4 and 6 are the second stage and the growth is compared with the temperature of the first stage. The conditions are such that the temperature of the raw material portion in the internal space 2a of the container 2 is increased by 50 ° C. to 100 ° C., and the temperature of the growth portion is increased by 70 ° C. to 130 ° C. to grow the aluminum nitride single crystal. Condition 7 is a condition for growing in one stage using substantially the same condition as the second stage of condition 4, and condition 8 is a condition for growing in one stage using the second stage condition of condition 2.

<Experimental example 1>
Using a (0001) Si surface of 6H—SiC with a diameter of 1 inch as a seed substrate, using the manufacturing apparatus shown in FIG. It was set to 1. The growth time was 0.5 hour.

<Experimental example 2>
Except that an aluminum nitride single crystal was produced under the condition 3 shown in Table 1, this was performed in the same manner as in Experimental Example 1, and this was designated as Experimental Example 2. The growth time was 1 hour.

<Experimental example 3>
Except that an aluminum nitride single crystal was produced under the condition 4 shown in Table 1, it was carried out in the same manner as in Experimental Example 1, and this was designated as Experimental Example 3. The growth time was 1 hour for the first stage and 20 hours for the second stage where the temperature was increased compared to the first stage. The internal space pressure was constant at each stage.

<Experimental example 4>
Except that an aluminum nitride single crystal was produced under the condition 5 shown in Table 1, it was carried out in the same manner as in Experimental Example 1, and this was designated as Experimental Example 4. The growth time was 0.2 hours.

<Experimental example 5>
Except that an aluminum nitride single crystal was produced under the condition 6 shown in Table 1, this was performed in the same manner as in Experimental Example 1, and this was designated as Experimental Example 5. The growth time was 0.2 hours for the first stage and 20 hours for the second stage where the temperature was increased compared to the first stage. The internal space pressure was constant at each stage.

<Experimental example 6>
Except that an aluminum nitride single crystal was produced under the condition 2 shown in Table 1, this was performed in the same manner as in Experimental Example 1, and this was designated as Experimental Example 6. The growth time was 0.2 hours for the first stage and 20 hours for the second stage where the temperature was increased compared to the first stage. The internal space pressure was constant at each stage.

<Comparative Example 1>
Except that an aluminum nitride single crystal was produced under the condition 7 shown in Table 1, this was performed in the same manner as in Experimental Example 1, and this was designated as Comparative Example 1. The growth time was 1 hour.

<Comparative example 2>
This was carried out in the same manner as in Experimental Example 1 except that an aluminum nitride single crystal was produced under the condition 8 shown in Table 1, and this was designated as Comparative Example 2. The growth time was 1 hour.

<Comparative Example 3>
Except that an aluminum nitride single crystal was produced under the condition 8 shown in Table 1, it was carried out in the same manner as in Experimental Example 1, and this was designated as Comparative Example 3. The growth time was 10 hours.

<Comparative example 4>
This was carried out in the same manner as in Experimental Example 1 except that an aluminum nitride single crystal was produced under the condition 2 shown in Table 1, and this was designated as Comparative Example 4. The growth time was 0.1 hour for the first stage and 20 hours for the second stage where the temperature was increased compared to the first stage. The internal space pressure was constant at each stage.

Table 2 shows the single crystal lengths and growth rates of the grown aluminum nitride single crystals obtained in Experimental Examples 1 to 6 and Comparative Examples 1 to 4 prepared above. The grown aluminum nitride single crystal length is measured by cross-sectional observation.
In this table, the off-angle is a substrate having a surface cut at a certain angle with respect to a certain direction with respect to the (0001) plane, and the off-angle is the angle. Just means that the seed substrate has no off-angle, and 3.5 ° / [11-20] means a seed having an off-angle of 3.5 ° in the [11-20] direction. It shows that a substrate was used.

(Experimental example)
In Experimental Examples 1, 2, and 4, an aluminum nitride single crystal grew on the entire surface of the SiC single crystal serving as the seed substrate, and the growth rate was 35 to 90 μm / h. As a result, the grown aluminum nitride single crystal length was 18 to 35 μm.
In Experimental Example 3, following the first stage under the same conditions as in Experimental Example 2, the temperature was increased (2220 ° C.) with respect to the raw material part temperature (2140 ° C.) in the first stage while keeping the internal space pressure constant. In addition, the temperature was raised (2100 ° C.) with respect to the growth temperature (2000 ° C.) of the first stage, and an attempt was made to grow a single-stage aluminum nitride single crystal. Similarly, in Experimental Example 5, following the conditions of Experimental Example 4, the temperature of the internal space was raised in the second stage to try to grow an aluminum nitride single crystal.

As a result, in the experimental examples 3 and 5 in which the temperature of the internal space was raised in the second stage and the growth of the aluminum nitride single crystal was attempted, damage caused by the carbonization or etching of SiC as the seed substrate An aluminum nitride single crystal could be obtained without being subjected to heat treatment. In addition, the growth rate of the second stage aluminum nitride single crystal could be increased to about 5 times the first stage. As a result, the grown aluminum nitride single crystal length was 3 to 10 mm.
In Experimental Example 6, the aluminum nitride single crystal length in the first stage was 10 μm, but the aluminum nitride single crystal could be grown by increasing the temperature in the second stage. If the aluminum nitride single crystal length of the first stage is 10 μm or more, even if it becomes easy to resublimate when the temperature is raised in the second stage, the aluminum nitride layer is not completely lost. Crystals can be obtained.

(Comparative example)
In Comparative Example 1, the surface of SiC as the seed substrate was carbonized, and the aluminum nitride single crystal did not grow.
In Comparative Example 2, an aluminum nitride single crystal was grown in the central portion of SiC, but the surrounding portion was etched, and hexagonal pits were observed.
In Comparative Example 3, SiC was carbonized, and no aluminum nitride single crystal was deposited on the SiC.
In Comparative Example 4, an aluminum nitride single crystal was partially grown on SiC. The SiC in the region where the aluminum nitride single crystal has not grown has been carbonized. This is because the aluminum nitride single crystal length of the first stage is as thin as 5 μm, and the aluminum nitride grown on the SiC surface at the time of temperature rise to the second stage is re-sublimed, and all of the aluminum nitride is sublimated. This is because of carbonization.

  As described above, by growing the aluminum nitride single crystal at a growth rate of 100 μm / h or more in the second stage in which the internal temperature is increased, the aluminum nitride single crystal is obtained without damaging the SiC as the seed substrate. I was able to get it. Therefore, a higher quality aluminum nitride single crystal can be obtained in a shorter time.

It is the schematic block diagram which showed typically the manufacturing apparatus of the aluminum nitride single crystal of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Manufacturing apparatus of aluminum nitride single crystal, 2 ... Growth container, 2a ... Internal space, 3 ... Raw material container, 3a ... Opening part, 4 ... Susceptor, 5 ... Gas introduction part, 6 ... Gas discharge part, 7 ... Heating means 11 ... Raw material, 12 ... Seed substrate, 13 ... Aluminum nitride single crystal.

Claims (3)

A raw material container for storing the raw material inside, and a growth container equipped with a susceptor facing it,
Heating means for adjusting the temperature of the internal space of the growth vessel;
Using a nitride single crystal production apparatus comprising at least a nitride single crystal deposited on a seed substrate disposed on the susceptor by a sublimation method,
A first stage of growing the nitride single crystal at a growth rate of 100 μm / h or less;
A second stage of growing the nitride single crystal at a growth rate of 100 μm / h or more with the temperature of the internal space of the growth vessel raised;
A method for producing a nitride single crystal, comprising:   The method for producing a nitride single crystal, wherein the nitride is aluminum nitride and the seed substrate is a silicon carbide substrate.   A nitride single crystal obtained by using the production method according to claim 2.

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