JPH07277897A - Synthesis of aluminum nitride single crystal - Google Patents

Abstract

PURPOSE:To cost economically obtain a high-grade aluminum nitride single crystal by heating an aluminum alloy contg. alkali (alkaline earth) metals in a non-oxidizing atmosphere contg. nitrogen. CONSTITUTION:The desired aluminum nitride single crystal is obtd. by heating the aluminum alloy totally contg. one or >=2 kinds among the alkali metals or alkaline earth metals in a range of 0.001 to 2wt.% in the non-oxidizing atmosphere contg. the nitrogen at 700 to 1300 deg.C. The alkali metals and the alkaline earth metals are more particularly preferable as alloy element of the aluminum alloy. the atoms of a high vapor pressure, such as Li, react with impurity oxygen and form Li2O when the allay contg. these elements is heated in the nitrogen atmosphere. Since the Li2O evaporates from the surface, the Li migrates from the inside to the surface and the nitrogen in the atmosphere penetrates the inside as its counter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing an aluminum nitride single crystal.

[0002]

2. Description of the Related Art ALN is a very useful material because of its high thermal conductivity and excellent piezoelectricity due to its bond and crystal structure, but its crystal structure is wurtzite type, 2200 ° C.
Since it decomposes at a high temperature and has a strong covalent bond and a strong bond, it is difficult to produce a sintered compact that is difficult to sinter. Further, it is extremely difficult to synthesize a single crystal because a high temperature melt cannot be obtained. As methods of synthesizing ALN single crystals that have been attempted so far, methods of decomposing ALN at high temperature and recombining, methods by CVD, etc. have been carried out, but the former is small and expensive, and the latter is expensive. In addition to this, the present situation is that satisfactory crystals have not been obtained due to poor orientation.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide a novel method for producing a high-quality aluminum nitride single crystal at an economical cost.

[0004]

The above-described problems can be solved by the following means. 1. The total amount of one or more elements selected from alkali metals or alkaline earth metals is 0.001.
~ 2 wt. %, The aluminum alloy contained in the range of 700 is heated to 700 to 1300 ° C. in a non-oxidizing atmosphere containing nitrogen, and a method for synthesizing an aluminum nitride single crystal. 2. 2. The synthesis method according to 1 above, wherein the alkali metal is Li. 3. 2. The synthesis method according to 1 above, wherein the alkaline earth metal is Ca. 4. The total amount of the above elements is 0.1 to 1 wt. %, The synthetic method according to claim 1. 5. The heating temperature is 800 to 1200 ° C.
~ 3.

[0005]

The present invention is a method for synthesizing an ALN single crystal by melting an aluminum alloy in a nitrogen-containing atmosphere and slowly diffusing nitrogen into an aluminum melt.

In the aluminum alloy, as an alloying element, an alkali metal and an alkaline earth metal are particularly preferable. When an alloy containing these elements is heated in a nitrogen atmosphere, atoms having a high vapor pressure such as Li are surfaced. Then, Li reacts with the impurity oxygen to generate Li ₂ O and evaporates from the surface, so that Li moves from the inside to the surface, and nitrogen in the atmosphere permeates inside as a counter.

Since the nitriding reaction of aluminum is an exothermic reaction, the progress of the nitriding reaction is very effective from the viewpoint of energy saving because self-heating causes the temperature of the sample to rise. However, the self-heating causes the sample to become the original form. Since it deforms so as not to stop, it is usually impossible to make a molded body or a single crystal by utilizing the nitriding reaction of aluminum.

Further, the idea of reducing the amount of an alloy such as Li in order to suppress or eliminate the exothermic reaction has been conventionally overlooked as the reaction itself does not sufficiently proceed, but the present invention is not limited to this. Contrary to my thoughts, I discovered that the nitriding reaction was promoted without self-heating in a very limited range of a small amount of alloy components. In addition, they have found that a single crystal of ALN is synthesized with this reaction.

A nitriding reaction is achieved without causing self-heating. This is the most important point of the present invention.

Alkali metals and alkaline earth metals are effective as alloying elements.
Alternatively, two or more kinds of elements may be appropriately mixed and added.

The most preferable elements among these are Li and Ca.
Is.

The amount of alloying elements is 0.001 to 2 wt.% Of the total amount of the above-mentioned alkali metals and alkaline earth metals. % Range,
Especially 0.05-1 wt. % Range is preferred.

If it exceeds 2 wt%, an exothermic reaction occurs, which is not preferable. If it is less than 0.001%, the reaction does not proceed sufficiently, which is not preferable.

The temperature is about 700 to about 1 atm.
The range of 1300 ° C., particularly 800 to 1200 ° C. is preferable. When the atmosphere is pressurized (HIP several thousand atmospheric pressure or ultra-high pressure of tens of thousands atmospheric pressure), the temperature may further be as high as 2000 ° C.

The atmosphere is required to be a non-oxidizing atmosphere containing nitrogen, and it is effective to use nitrogen alone gas, nitrogen mixed gas such as N2-H2, and nitrogen compound gas such as ammonia.

As described above, the pressure of the atmosphere is effective from atmospheric pressure to tens of thousands of atmospheric pressure. In particular, high pressure is effective for preventing decomposition, so that vaporization of Li can be prevented.

In the present invention, it is essential that the atmosphere contains a very small amount of oxygen, and although it is difficult to strictly define the amount, it is preferably 10 ⁻³ or less.

Nucleation is necessary for crystal growth, and if seed crystals or ALN powder to serve as nuclei are placed, crystal growth is accelerated.

The time for crystallization is, for example, 5 ×
5 × 5 mm, Li 0.5 wt. %, The reaction is completed at 1000 ° C. in about 40 hours. In this case, a hexagonal single crystal of about 100 μm is obtained inside.

[0020]

The present invention will be described with reference to examples. Example 1 Li was added at 0.5 wt. % AL-Li alloy containing 5%
It was cut into a size of 5 × 3 mm, placed on an alumina plate and inserted into a tubular electric furnace. 0.5L / m in this tubular furnace
While flowing in nitrogen gas, the temperature was raised to 1000 ° C. over 3 hours, heated for 35 hours, and then allowed to cool. It was confirmed that the obtained block had been completely nitrided and was converted into ALN by X-ray analysis.

Example 2 Experiments according to Example 1 were conducted using alloys having various compositions, and single crystals of various sizes could be obtained by adjusting the conditions. The results are shown in Table 1.

[0022]

[Table 1]

Example 3 An AL-Li alloy containing 0.2 and 0.3 wt% of Li was cut into a plate of φ15 × 5 mm, and ALN powder as shown in FIG. 1 was laid on the bottom. It was put in an ALN crucible and inserted into a tubular electric furnace. 0.5L / in this tubular furnace
The temperature was raised to 1000 ° C. over 3 hours while flowing a nitrogen gas of min, heated for further 54 hours, and then allowed to cool. It was confirmed that the obtained block had been completely nitrided and was converted into ALN by X-ray analysis. As a result of cutting and observing the inside, formation of single crystals of 480 and 350 μm was confirmed.

Example 4 An AL-Li-based alloy containing 1.0 and 2 wt% of Li and an AL-Ca-based alloy containing 2 wt% of Ca were 5 × 5.
Each piece was cut into a size of 3 mm and mounted in a HIP firing furnace. In 1000 nitrogen nitrogen gas,
After heating at 1400 ° C. for 6 hours, it was allowed to cool. It was confirmed that the obtained block had been completely nitrided and was converted into ALN by X-ray analysis. As a result of cutting and observing the inside, generation of hexagonal columnar single crystals of 0.5 to 1 mm was confirmed.

[0025]

As described in detail above, the present invention has the feature that a high-quality single crystal can be produced at an economical cost, and its size can be adjusted arbitrarily.
This will greatly contribute to the future spread of N single crystals.

Claims (5)

[Claims] 1. A total amount of one or more elements selected from alkali metals or alkaline earth metals of 0.001 to 2 wt. % Aluminum alloy containing 700 to 1300 in a non-oxidizing atmosphere containing nitrogen.
A method for synthesizing an aluminum nitride single crystal, which comprises heating to ℃. 2. The alkali metal is Li.
The synthetic method described in. 3. The synthetic method according to claim 1, wherein the alkaline earth metal is Ca. 4. The total amount of the above elements is 0.1 to 1 wt. %, The synthetic method according to claim 1. 5. The synthesis method according to claim 1, wherein the heating temperature is 800 to 1200 ° C.