JP2003119099A - Method of producing aluminum nitride single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing an aluminum nitride single crystal, by which the aluminum nitride single crystal having a large diameter can be produced at a low cost. SOLUTION: In the method of producing the aluminum nitride single crystal, the aluminum nitride single crystal is grown by melting an aluminum alloy containing at least one transition metal element in an amount of 1 to 50 atom.% in total, in a non-oxidizing atmosphere containing nitrogen and maintaining the alloy in a molten state for a predetermined time so as to accelerate nitriding of aluminum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum nitride single crystal which can be preferably used as a substrate material for a semiconductor light emitting element capable of emitting light in the ultraviolet region or a semiconductor device for which high heat dissipation characteristics are desired. Is.

[0002]

2. Description of the Related Art At present, with the rapid growth of the information technology industry, the amount of information that can be handled on a daily basis is increasing. In order to support such information technology innovation, development of a recording medium and a recording device having a high-density recording capacity is indispensable, and research and development have been promoted from various fields. Among them, a recording device using a blue semiconductor laser element as a light source can have a recording density three times or more that of a device before that, and is attracting attention as a next-generation recording device.

However, it is presumed that the demand for higher recording density will further increase in the future. In that case, as the simplest measure for improving the recording density, it is conceivable to further shorten the wavelength of light used for recording. For that purpose, development of a semiconductor laser device capable of emitting light of a shorter wavelength is desired. Here, aluminum nitride has a large direct transition type band gap of 6.2 eV at room temperature and can be preferably used as a semiconductor material for a short wavelength laser device capable of emitting light in the ultraviolet region.

A semiconductor laser device is generally formed by depositing a high quality multi-layered single crystal thin film on a single crystal substrate by CVD (chemical vapor deposition) or the like. However, when the materials of the substrate and the deposited thin film are different from each other, the dislocation density in the deposited thin film increases due to the crystal lattice mismatch between the two, and the life of the obtained laser element is shortened. The simplest method to solve such a problem is to use the same material for the substrate and the deposited thin film.

That is, in order to form an ultraviolet laser device using an aluminum nitride deposited film, it is optimal to use an aluminum nitride single crystal substrate.

[0006]

Solid aluminum nitride has a wurtzite-type crystal structure having a strong covalent bond and forms a strong chemical bond. Therefore, solid aluminum nitride is very stable up to high temperatures and decomposes at 2400 ° C. under normal pressure without forming a liquid phase. As is clear from this, it is extremely difficult to grow the single crystal from the liquid phase of aluminum nitride.

[0007] To date, as a method for producing an aluminum nitride single crystal, (1) a sublimation method in which aluminum nitride is decomposed in a high temperature portion and precipitated and crystallized in a low temperature portion in a nitrogen atmosphere, and (2) nitrided by CVD Attempts have been made to deposit an aluminum film over a long period of time.

However, in the sublimation method (1), the aluminum nitride single crystal obtained is minute and expensive due to the limitation in the sublimation precipitation apparatus and the like, and many nitrogen defects occur in the crystal. On the other hand, in the CVD method (2), it takes a long time to deposit the aluminum nitride film and the cost is high, and the orientation of the single crystal contained in the thin film is poor. That is, at present, a satisfactory aluminum nitride single crystal has not been obtained as a substrate for a semiconductor laser device.

By the way, the solubility of nitrogen in the aluminum liquid phase under normal pressure is extremely small. Further, since the aluminum nitride film is dense and strong, if the aluminum nitride film is formed on the surface of the aluminum liquid phase, the progress of further nitriding inside the liquid phase is hindered. Under such circumstances, the use of the alloy liquid phase in which other elements are added to aluminum is considered as one of the methods for continuously supplying a large amount of nitrogen into the aluminum liquid phase.

Japanese Unexamined Patent Publication No. 7-277897 discloses a method of synthesizing an aluminum nitride single crystal by slowly diffusing nitrogen into a molten aluminum alloy containing an alkali metal or an alkaline earth metal. According to the teaching of this publication, the atoms of alkali metal or alkaline earth metal having a high vapor pressure react with the impurity oxygen in the atmosphere on the surface of the molten alloy to form an oxide, which evaporates. This means that the nitrogen in the alloy diffuses and penetrates into the molten alloy. As a result, it is taught that under normal pressure, an aluminum nitride single crystal having a maximum diameter of 450 μm was synthesized.

However, in the invention of the publication, the additive element of alkali metal or alkaline earth metal is limited to a maximum of 2% by weight or less in order to suppress a rapid exothermic reaction. Therefore, if all of the small amount of additive elements are oxidized and evaporated from the surface of the molten aluminum alloy, it becomes difficult to diffuse and permeate nitrogen into the molten metal.

In view of the situation in the prior art as described above, the present invention provides a method for inexpensively producing a large-diameter aluminum nitride single crystal by continuously permeating nitrogen into an alloy liquid phase containing aluminum. It is intended to be provided.

[0013]

In the method for producing an aluminum nitride single crystal according to the present invention, the total amount of one or more transition metal elements is 1 in a non-oxidizing atmosphere containing nitrogen element.
It is characterized in that an aluminum nitride single crystal is grown from a melt of an aluminum alloy contained in the range of ˜50 atomic%.

The aluminum alloy may be prepared by mixing one or more transition metals or their nitrides with aluminum.

As the transition metal, for example, Ti, Zr,
V, Cr, Mn, Fe, Co, Ni, Cu, etc. may be mentioned. In particular, it is preferable to contain at least one selected from Fe, Mn and Cr.

The non-oxidizing atmosphere containing nitrogen element preferably contains nitrogen gas and reducing gas and / or inert gas. In this case, the proportion of nitrogen gas is preferably 1 to 50% by volume. Further, ammonia can be included as the non-oxidizing atmosphere containing the nitrogen element.

Aluminum alloys containing transition metal elements are
It is preferable to melt and maintain for a predetermined time at a temperature higher than the liquidus temperature by 50 to 200 ° C. In addition, it is preferable that the time for maintaining the melting at a temperature higher than the liquidus temperature by 50 to 200 ° C. is usually 10 hours or more.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Nitrogen solubility is very small in a liquid phase of aluminum alone, and even if the temperature of the liquid phase is raised, the nitrogen solubility is not significantly increased. Furthermore, when considering the vapor pressure of aluminum and trying to suppress its evaporation, 2
It is desired to perform nitriding at a temperature of 000 ° C or lower.

Therefore, the present inventors first pay attention to a transition metal which has a higher nitrogen solubility in the liquid phase than aluminum and is stable in the liquid phase even at a high temperature, and a transition metal nitride which can also serve as a nitrogen supply source. Also paid attention.

That is, it can be expected that the nitrogen solubility can be increased in the liquid phase of the aluminum alloy containing the transition metal element as compared with the liquid phase of simple aluminum. Further, it is expected that an aluminum nitride single crystal can be formed at a relatively low temperature near the liquidus of an aluminum alloy containing a transition metal element without heating the liquidus temperature to a high temperature such as around 2000 ° C. obtain.

The total amount of one or more transition metal elements contained in the aluminum alloy may be in the range of 1 to 50 atom%, and more preferably in the range of 5 to 30 atom%. The reason why the content of the transition metal element is 50 atomic% or less is to suppress the amount of the transition metal element taken into the formed aluminum nitride single crystal and improve the crystal quality.
Further, in order to increase the diameter of the obtained single crystal, it is desired that the crystal growth temperature be relatively low, but since the liquidus temperature of the aluminum alloy containing a transition metal element increases as the amount of addition increases, From this viewpoint, the transition metal element is 5
It is preferably 0 atomic% or less. On the contrary, the transition metal element concentration of 1 atomic% or more is to improve the nitrogen solubility in the aluminum alloy liquid phase.

Among the transition metals, the particularly preferred element is F
e, Mn and Cr. That is, Fe, Mn, and Cr can increase the nitrogen solubility in the aluminum alloy liquid phase more than other transition metal elements. Also,
The nitride formation energies of Fe, Mn, and Cr are not only higher than the formation energies of aluminum nitride over the entire temperature range, but also higher than the nitride formation energies of other transition metal elements.

Therefore, in the aluminum alloy liquid phase containing Fe, Mn and Cr as the transition metal elements, the transition metal elements themselves do not form a nitride, and the nitrogen dissolved in the alloy liquid phase is converted into aluminum. Aluminum nitride may be formed to form aluminum nitride. Further, these transition metal elements can easily form an alloy liquid phase together with aluminum. Further, since nitrides of these transition metal elements can easily dissociate nitrogen, they can also act as a nitrogen supply source, and can be preferably used as an additive for preparing an aluminum alloy.

As the transition metal nitride, Fe, Cr, M
n-nitride (Fe_xN (x = 2-4), Cr₂N, Mn_x
N (x = 2 to 4)) or the like may be used. Especially Fe and M
The n-nitride is unstable and easily decomposed. Does not decompose due to high melting point
However, vanadium nitride (V ₂N, VN) and molybdenum
Nitride (Mo₂N) and the like can also be used.

As described above, the mechanism of the method for producing an aluminum nitride single crystal according to the present invention is to supply nitrogen into the aluminum alloy through the transition metal liquid phase having high nitrogen solubility.

In the present invention, with respect to the control of the atmosphere containing the nitrogen element, it is preferable to be non-oxidizing, especially to reduce the oxygen concentration. Therefore, it is preferable to use a reducing atmosphere containing a mixed gas of nitrogen and hydrogen, an ammonia, or the like, rather than mixing a simple substance gas of nitrogen into the atmosphere gas. Then, it is preferable to reduce the oxygen concentration in the atmosphere as much as possible by utilizing dew point management or the like.

This is because when the atmosphere contains oxygen,
This is because aluminum oxide (alumina) is easily generated. This is because, particularly when an aluminum alloy containing a transition metal element or a mixture of a transition metal and aluminum is melted and the alumina is thickly formed on the surface of the aluminum, there is a problem that the melting does not proceed smoothly.

Further, it is preferable to introduce an inert gas such as Ar into the atmosphere containing the nitrogen element and adjust the nitrogen partial pressure appropriately. This is because the nitriding reaction of aluminum is an exothermic reaction, and the reaction rapidly progresses on the surface of the aluminum alloy melt in nitrogen gas at normal pressure, which affects the supply of nitrogen into the aluminum alloy. As another method of suppressing this rapid nitriding reaction, the time for starting the supply of the atmosphere gas containing the nitrogen element to the aluminum alloy melt or the supply time may be adjusted.

When nitrogen gas is mixed in the atmosphere gas,
The concentration of the nitrogen gas is preferably 1 to 50% by volume. The concentration of 1% by volume or more is preferable in order to secure the supply amount of nitrogen into the aluminum alloy liquid phase.
Further, the concentration of 50% by volume catabolism is preferable in order to prevent the nitriding reaction on the surface of the aluminum alloy melt from becoming too violent and hindering the growth of the aluminum nitride single crystal. The concentration of nitrogen gas is more preferably 2 to 20% by volume.

The aluminum alloy liquid phase is preferably heated to a temperature higher than the liquidus of the alloy within the range of 50 to 200 ° C. The reason why the temperature higher than the liquidus line by 200 ° C. is limited is that the growth temperature of the aluminum nitride single crystal is preferably not too high in order to increase the size of the single crystal, and the evaporation of aluminum is suppressed. In addition, heating to a temperature 50 ° C or more higher than the liquidus
This is to obtain a sufficient liquid phase of the alloy. Further, the time for maintaining the melting is preferably 10 hours or more.

(Example 1) Al-containing 50 atomic% Fe
A predetermined amount of Fe alloy was filled in an alumina crucible having an inner diameter of 20 mm and a length of 100 mm and inserted into a vertical tubular furnace. Argon gas containing 5% hydrogen gas and high-purity nitrogen gas having a purity of 99.9999% were introduced into this tubular furnace via a dew point control system. The flow rates of these hydrogen-containing argon gas and high-purity nitrogen gas are both 400 ml / m.
It was in. The alloy is 145 at a heating rate of 5 ° C / min
Heated to 0 ° C. and held at that temperature for 30 hours. After that, the alloy was cooled to 1250 at a cooling rate of 1250 / min.
After being gradually cooled to ℃, it was cooled in the furnace.

When a cross-section was observed inside the alloy sample that had been subjected to the above treatment, a hexagonal plate-shaped single crystal with a diameter of 100 to 200 μm was observed. This single crystal was confirmed to be an aluminum nitride single crystal from the X-ray diffraction measurement and the diffraction pattern of an electron microscope.

Example 2 Example 2 is different from Example 1 only in that the flow rate of nitrogen gas introduced into the tubular furnace was variously changed. That is, in Example 2, the partial pressure of nitrogen in the tubular furnace was variously changed.

With respect to the alloy samples thus treated under various nitrogen partial pressures, the internal cross section was observed in the same manner as in Example 1, and the diameters shown in Table 1 were obtained. Aluminum nitride single crystal was formed. In addition, in Table 1, the results of Example 1 also show the sample No. Included as 1.

[0035]

[Table 1]

As is clear from Table 1, the larger the flow rate of nitrogen gas, the larger the diameter of the aluminum nitride single crystal does not necessarily become. It is considered that this is because if the nitrogen gas flow rate becomes too large, the nitriding reaction on the surface of the alloy liquid phase becomes too intense.
Of course, if the flow rate of nitrogen gas is too small,
Nitriding within the alloy liquid phase does not proceed sufficiently, and the diameter of the aluminum nitride single crystal becomes small.

(Embodiment 3) Embodiment 3 is also similar to Embodiment 1, and the matters not particularly mentioned are the same as those in Embodiment 1. As a matter different from Example 1, in Example 3, the alloy composition was variously changed, and accordingly, the heat treatment temperature was also variously changed. In each case, the flow rate of 50 ml / min of nitrogen gas and the flow rate of 1
Argon gas containing 5% hydrogen at 00 ml / min was introduced.

When the internal cross-sections of the alloy samples of various compositions were observed in the same manner as in Example 1, aluminum nitride single crystals having the diameters shown in Table 2 were formed. It was

[0039]

[Table 2]

In each of the above various examples, the maximum temperature holding time of the aluminum alloy liquid phase was 30 hours, but it goes without saying that it is not limited to this time. Generally, in order to obtain an aluminum nitride single crystal, it is preferable that the maximum temperature holding time of the alloy liquid phase is about 10 hours or more. Then, an increase in the diameter of the single crystal can be observed with the extension of the holding time. But,
After the growth of the single crystal has progressed to some extent, almost no increase in the diameter of the single crystal is observed even if the maximum temperature holding time is extended. Therefore, the maximum temperature holding time of the aluminum alloy liquid phase is preferably set to about 10 hours or more, and may be set in consideration of the growth of the diameter of the aluminum nitride single crystal and cost and time efficiency.

[0041]

As described above, according to the present invention, since an aluminum nitride single crystal is grown by utilizing the aluminum alloy liquid phase, it becomes easy to produce a large single crystal, and the aluminum alloy is inexpensive. Since it is obtained by using a transition metal or its nitride, the cost can be reduced.
It can greatly contribute to the future production of aluminum nitride single crystal substrates.

Claims (4)

[Claims] 1. Growing an aluminum nitride single crystal from a melt of an aluminum alloy containing one or more transition metal elements in a total amount of 1 to 50 atomic% in a non-oxidizing atmosphere containing nitrogen element. A method for producing an aluminum nitride single crystal, comprising: 2. The method for producing an aluminum nitride single crystal according to claim 1, wherein the transition metal contains at least one selected from Fe, Mn, and Cr. 3. The non-oxidizing atmosphere containing the nitrogen element,
The method for producing an aluminum nitride single crystal according to claim 1 or 2, which contains a nitrogen gas and a reducing gas and / or an inert gas. 4. The aluminum alloy according to any one of claims 1 to 3, wherein the aluminum alloy is melted and maintained for a predetermined time at a temperature higher than a liquidus temperature of the aluminum alloy within a range of 50 to 200 ° C. Manufacturing method of aluminum nitride single crystal.