JP2003335600A - PROCESS FOR PREPARING AlN SINGLE CRYSTAL - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily prepare a relatively large AlN single crystal at a low cost. <P>SOLUTION: In the process for preparing the AlN single crystal, an abc alloy melt containing at least one chosen from Cr, Mn, Fe, Co, Cu and Ni as metal a, at least one chosen from Sc, Ti, V, Y, Zr and Nb as metal b and Al as component c is prepared in a nitrogen-containing atmosphere, and the AlN single crystal is crystallized either by cooling the melt or by evaporating at least one of metal a and metal b. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an aluminum nitride (AlN) single crystal. The AlN single crystal can be preferably used as a substrate for a compound semiconductor light emitting device or a substrate with high thermal conductivity that can emit light in the blue or ultraviolet region.

[0002]

2. Description of the Related Art AlN, which is a compound semiconductor, has 6.2 eV.
Since it has a large bandgap, if a pn junction is realized in an AlN semiconductor, a new light emitting element such as a light emitting diode or laser in the ultraviolet region can be manufactured. Further, the AlN semiconductor having a large band gap can be applied to a high breakdown voltage power element that operates under radiation or high temperature. Furthermore, AlN semiconductors are known to exhibit a negative electron affinity, and are expected to be applied to highly efficient electron-emitting devices. Furthermore, AlN is about 30
Since it has a good thermal conductivity of 0 W / m · K, its polycrystalline body has already been put into practical use as a heat-radiating substrate. Recently, the AlN layer is used as a buffer layer at the interface with the GaN layer because the AlN crystal lattice has a good matching with gallium nitride (GaN) used in blue light emitting elements. It is an indispensable material for improving the brightness of the.

[0003]

When utilizing AlN having excellent characteristics as described above, it is naturally desirable to use it as a single crystal wafer as in the case of semiconductor silicon. However, at present, a method for producing an AlN single crystal wafer has not been developed yet, and at most, an AlN thin film is synthesized and used on a different substrate by a method such as CVD (chemical vapor deposition) or MBE (molecular beam epitaxy). It's just that. It is difficult to obtain a bulk wafer of AlN because AlN does not show a definite melting point, and the
This is because it decomposes at a temperature as high as ˜2450 ° C. and a simple technique of solidification from a melt cannot be used. Under such circumstances, a method utilizing a sublimation method, a nitriding treatment, or the like has been studied as a method other than the simple solidification from the melt. However, those studies are still at the basic research level,
At present, the method for obtaining a large AlN single crystal has not been developed.

For example, as a method for producing AlN whiskers, Japanese Patent Publication No. 3-23519 has already disclosed a method of reducing Al ₂ O ₃ . However,
According to the disclosed method, only minute AlN whiskers having a diameter of at most several μm and a length of about 100 μm can be obtained, and such whiskers cannot be used as a substrate for semiconductor devices. A method for producing an AlN single crystal by using an alkaline earth metal oxide as a flux for AlN is also disclosed in Japanese Patent Publication No. 5-12320, but the heating temperature for melting is high. Since an oxide that is present and highly reactive with water is used, it is expected that practical application will be difficult in the process. Further, a vapor phase growth method of an AlN single crystal is also proposed in Japanese Patent Laid-Open No. 10-53495, but it is difficult to grow a large crystal continuously by the vapor phase growth method.

In view of such a state of the art, the present invention is
It is an object of the present invention to provide a method capable of easily producing a relatively large AlN single crystal at low cost.

[0006]

[Patent Document 1] Japanese Patent Publication No. 3-23519

[0007]

[Patent Document 2] Japanese Patent Publication No. 5-12320

[0008]

[Patent Document 3] Japanese Patent Laid-Open No. 10-53495

[0009]

In the method for producing an AlN single crystal according to one embodiment of the present invention, C is used as the metal a.
It contains at least one selected from r, Mn, Fe, Co, Cu, and Ni, and Sc, Ti, V, Y as the metal b.
A melt of an abc alloy containing at least one selected from Zr and Nb and further containing Al as a component c is prepared under a nitrogen-containing atmosphere, and the melt of the abc alloy is cooled or the metal a It is characterized in that an AlN single crystal is crystallized by evaporation of at least one of and b.

In this case, the AlN single crystal may be epitaxially crystallized on the SiC single crystal substrate.

When the AlN single crystal is crystallized,
It is preferable that the supersaturated state of AlN is generated in the melt of the abc alloy.

Further, the melt of the abc alloy has a mass Ma of the powder of metal a, a mass Mb of the powder of metal b, and a mass Mc of the Al powder of 0.0075 ≦ Mb / Ma ≦ 0.075.
And 0.02 ≦ Mc / (Ma + Mb) ≦ 0.13 are mixed and dissolved in a nitrogen-containing atmosphere.

The melt of the abc type alloy may be prepared by re-melting the preliminary alloy ingot previously melted and solidified in an inert atmosphere other than nitrogen in a nitrogen-containing atmosphere. Is the molar concentration Ca of metal a, the molar concentration Cb of metal b, and the molar concentration C of Al.
c is 0.01 ≦ Cb / Ca ≦ 0.1 and 0.2 ≦ Cc /
It is preferable that the relationship of (Ca + Cb) ≦ 1 is satisfied.

When crystallizing an AlN single crystal, a melt of an abc type alloy is heated to a temperature not lower than 2000 ° C. above the liquidus of the alloy in a nitrogen-containing atmosphere and then solidified with the liquidus. It is preferable to gradually cool to a predetermined temperature between the phase lines or cool to a predetermined temperature and hold the same temperature for a predetermined time there.

The melt of the abc alloy can also be prepared by immersing and dissolving solid AlN as the component c in the melt containing the metals a and b.

The SiC single crystal substrate is inserted and fixed in the seed crystal fixing space provided at the bottom of the divisible crucible, and then the divisible crucible is assembled integrally, and the abc alloy is melted in a nitrogen-containing atmosphere. The AlN single crystal layer can also be formed by applying the liquid above the SiC single crystal substrate in the crucible.

In the method for producing an AlN single crystal according to another aspect of the present invention, a metal a having a wide primary solid solubility limit with respect to Al immediately below the solidus and a metal a incorporated into the melt. Ab containing a metal b having a function of increasing the concentration of the obtained N atoms and a component c constituting the AlN single crystal
A melt of the c-based alloy was prepared under a nitrogen-containing atmosphere, and a
cooling the melt of the bc alloy or evaporating at least one of the metals a and b to bring the abc alloy between its liquidus and solidus lines to crystallize an AlN single crystal I am trying.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have found that Al or AlN
The metallurgical investigation of the formation behavior of AlN crystals from various synfinial liquids containing Al, and the final prediction based on the prediction by calculation of the ternary phase diagram of Al-N-X (X is various metallic elements) It has been found that AlN can be obtained as a single crystal from a specific synergistic liquid. First, from such a specific combined financial liquid A
The principle of obtaining an 1N crystal will be described by taking the case where the metal element X is Cu or Ni as an example.

9 and 10 are ternary phase diagrams of Al-N-Cu and Al-N-Ni in a cross section at a temperature of 1800K, respectively. The numerical values in these phase diagrams represent atomic%. 9 and 10, AlN +
The region indicated by L represents a coexisting region of solid phase AlN and the synthetic financial liquid L, and the region indicated by L represents a region in which only the synthetic financial liquid exists. From these phase diagrams, it can be seen that AlN crystals directly crystallize from the synergistic liquid L. Also, the lines PQ and RS are between Cu-AlN and N, respectively.
It represents a tie line (connection line) between i-AlN. 11 and 12 show tie lines PQ and R, respectively.
FIG. 6 shows a portion of a Cu-AlN and Ni-AlN pseudo-binary phase diagram along S. FIG.

With reference to these FIGS. 9 to 12, it is clearly understood that there is a liquidus line representing the upper limit temperature at which AlN begins to appear as primary crystals from the combined financial liquid. That is, Cu-AlN or Ni containing an appropriate concentration of AlN
The AlN appears as a primary crystal by holding the combined financial liquid of AlN at a temperature higher than the liquidus temperature thereof, sufficiently dissolving the AlN and then cooling the liquid below the liquidus temperature. Further, instead of AlN, a Cu alloy or a Ni alloy containing Al is melted, and N is removed from the atmosphere.
The same effect can be obtained by supplying the molten metal to the melt. However, in that case, as described later, it is necessary to add a different kind of metal for sufficiently incorporating N into the financial liquid. This is because when AlN is generated by reacting with N in the atmosphere, the dense Al
This is because it tends to form an N film and tends to hinder the penetration of N into the synergistic liquid.

In order to clarify the AlN crystallization behavior from the Al-N-X combined financial liquid, the present inventors cooled the mixed financial liquid with various starting compositions from various initial temperatures at various cooling rates. After cooling to room temperature, the microstructure of the alloy was observed. As a result, first, in order to uniformly disperse and dissolve Al atoms until the reaction with N can be sufficiently promoted,
It has been found that it is optimum to use a melt of each metal of Cr, Mn, Fe, Co, Cu, and Ni (referred to as metal a) or an alloy thereof. Further, as a result of attempting to add the fourth element for sufficiently incorporating nitrogen into the financial liquid, by adding each element of Sc, Ti, V, Y, Zr, and Nb (referred to as metal b), It was found that even under normal pressure, the N in the atmosphere can be sufficiently incorporated into the combined financial liquid.

Here, it is considered that the melt of the metal a acts to disperse and dissolve Al atoms in a sufficiently uniform manner and to sufficiently promote the reaction between Al and N. This is
It can be estimated from the binary phase diagram of metal a and Al. For example, the Al—Cr phase diagram shown in FIG. 13 is characterized in that Cr has a very wide primary solid solubility limit with respect to Al immediately below the solidus line. This is
It is shown that even in the melted state above the primary solid solution limit region, Al atoms are homogeneously dispersed and dissolved, and there is a tendency to form a homogeneous primary solid solution as it is during solidification.

That is, Cr-A has a very wide primary solid solubility limit for Al immediately below the solidus.
It is considered to be an index for producing a dissolved state in which Al atoms are homogeneously dispersed in the combined financial liquid. Further, although the presentation of the further phase diagram is omitted, Mn, Fe, Co, Cu,
Since each of the metals and Ni has a wide primary solid solubility limit with respect to Al immediately below the solidus line, it can be used as the metal a for uniformly dispersing and dissolving Al atoms.

Next, as a criterion for selecting the metal b that acts to increase the concentration at which N atoms can be incorporated into the melt of the metal a in which Al and / or AlN is dissolved, the affinity with N is an important factor. It is thought to get. Therefore,
Examining the free nitridation energy of various metal elements (ΔG _N : Gibbs free nitridation energy), the absolute value is only from the viewpoint of increasing the concentration of N atoms in the melt of the metal a. Metals with large and negative ΔG _N are considered preferred. However, a metal whose absolute value is much larger than ΔG _N of Al and has a negative ΔG _N can certainly be expected to have an effect of remarkably increasing the concentration of N atoms incorporated in the melt of the metal a. In addition, it is considered that the nitriding of the metal preferentially has an action of inhibiting the nitriding of Al.

[0025] Thus, as the metal b that act to increase the concentration can incorporate N atoms in the melt of the metal a dissolved Al and / or AlN, a metal having a .DELTA.G _N and comparable .DELTA.G _N of Al Is considered to be preferable.
The results of the investigation conducted by the present inventors on such metals are
It is shown in FIG.

As shown in the graph of FIG. 14, the V, Nb, Y, Sc, Ti, and Z listed therein are listed.
r is a negative Δ with a large absolute value up to around 2000 ° C.
G _N is shown, and the value of ΔG _N thereof is about the same as the generation energy of AlN, and it can be seen that it has a large affinity for N. Here, as will be seen from the examples described below, Ti has a large absolute value and a negative ΔG even compared with Al.
_It has _N , but Al if the Ti concentration is not too high.
Does not hinder the nitriding of. Further, Zr has a negative ΔG _N with a considerably larger absolute value than that of Al.
When r is used as the metal b, its concentration should be limited so as not to hinder the nitridation of Al.

Finally, these metals a (Cr, Mn,
Fe, Co, Cu, Ni), metal b (Sc, Ti, V,
Y, Zr, Nb), and Al or AlN in powder or sintered form are mixed and heated to prepare a combined liquid under a nitrogen-containing atmosphere, and the melt is cooled or metal a It has been found that AlN single crystals can be crystallized by bringing the alloy to a state between the liquidus and solidus lines by evaporation of at least one of b and b. When the AlN single crystal is crystallized, it is preferable that AlN is substantially supersaturated in the combined financial liquid.

The obtained AlN single crystal shows a needle-shaped or plate-shaped morphology depending on the production conditions, and a large needle-shaped crystal reaches a length of several mm after crystallization treatment for about 5 to 10 hours. was gotten. Further, in the present invention, 6H is added to the seed crystal.
When using a -SiC substrate, we succeeded in epitaxially growing an AlN single crystal on the substrate.
In this case, the AlN single crystal wafer can be obtained by forming the AlN single crystal layer having a sufficient thickness by long-time or repeated crystal growth and then removing the SiC substrate by grinding or the like.

Here, there is a preferable combination between the respective concentrations of metal a, metal b, and Al or AlN (referred to as component c) which is a constituent component of the AlN single crystal, and the melt of the abc alloy is , The mass Ma of the metal a powder,
The mass Mb of the powder of the metal b and the mass Mc of the Al powder are 0.0075 ≦ Mb / Ma ≦ 0.075 and 0.02 ≦ M.
It is preferably prepared by blending so as to satisfy the relationship of c / (Ma + Mb) ≦ 0.13 and dissolving in a nitrogen-containing atmosphere. That is, Mc / (Ma + M
If b) is smaller than 0.02, the amount of Al is insufficient and only fine AlN is obtained, and conversely, if it is larger than 0.13,
Al atoms do not disperse and dissolve homogeneously in the financial solution, and AlN
Single crystal cannot be obtained. If Mb / Ma is less than 0.0075, the N concentration in the synergistic liquid will be insufficient and a fine A
If only 1N crystal can be obtained, and if it is larger than 0.075, the metal b forms a nitride and hinders crystallization of the AlN single crystal.

The melt of the abc type alloy may be prepared by remelting in a nitrogen-containing atmosphere a preliminary alloy ingot previously melted and solidified in an inert atmosphere other than nitrogen. The mass has a molar concentration Ca of metal a, a molar concentration Cb of metal b, and a molar concentration Cc of Al of 0.01 ≦ Cb / Ca ≦ 0.1 and 0.2 ≦ Cc /.
It is preferable that the relationship of (Ca + Cb) ≦ 1 is satisfied.

There is also a preferable range of temperature conditions for crystallization of AlN single crystal. First, it is necessary to heat the alloy to a temperature in the range from the liquidus line to 2000 ° C. in a nitrogen-containing atmosphere. This is to prepare a uniform melt of an alloy containing metal a, metal b, and component c. After that, if the combined financial liquid is kept at a temperature between the liquidus line and the solidus line, N is taken into the melt from the atmospheric gas and the N reacts with Al one after another to form an AlN single crystal. Crystallize. However, solid-phase reaction occurs at a temperature below the solidus of the alloy, and almost no growth of AlN single crystal is observed. In addition, when the combined financial liquid is heated to 2000 ° C or higher,
Depending on the metal element, the evaporation from the combined financial liquid becomes severe, and stable growth of the AlN single crystal is not observed, which is economically unfavorable.

In the above-mentioned method, since the AlN single crystal is obtained by directly crystallizing from the combined financial liquid in the nitrogen-containing atmosphere, by performing the crystallization for a long time, a large A
1N whiskers can be obtained. Also, the obtained Al
It is possible to obtain an even larger single crystal by taking out the N single crystal, and again feeding it into the combined financial liquid to grow the crystal further, and repeating this process. In the method for producing an AlN single crystal according to the present invention, the Bridgman growth method, which is a single crystal growth method by solidification from one direction under a temperature gradient, can also be applied.

The Bridgman method can be roughly classified into a static temperature change type and a mobile type. In the static temperature change type, the thin growth container at the bottom is fixed in a furnace having a temperature gradient in which the bottom is relatively low, and the temperature of the entire furnace is lowered at a certain rate while the container is left stationary. By doing so, the lower end of the container is brought into a supersaturated or supercooled state to crystallize an AlN single crystal.
At this time, by sharpening the lower end of the container, the crystal having a specific orientation first crystallized at the lower end is increased in size to be a single crystal. On the other hand, in the moving Bridgman method, first, in a furnace having a temperature gradient, the lower end of the container is kept at a temperature equal to or higher than the liquidus of the alloy, and the container is maintained while maintaining the temperature distribution in the furnace. The characteristic is that the lower end of the container is cooled by lowering it and AlN is supersaturated at the lower end.

Both the static temperature change type and the mobile type in the Bridgman method are considered to have exactly the same effect. That is, in the Bridgman method,
If AlN is crystallized as a primary crystal from the synergistic liquid and the tip of the container where the crystallization begins is sharpened, only the crystal grains in a specific orientation grow and become a single crystal. Further, at this time, if the 6H-SiC substrate is fixed as a seed crystal to the tip of the container, an AlN crystal having the same hexagonal crystal structure grows epitaxially on this substrate, and if the substrate is removed later, the AlN crystal will grow. A single crystal is obtained.

(Example 1) FIG. 1 is a schematic sectional view showing a graphite container used in Example 1. The container 1 includes a graphite crucible 1a and a graphite pressing lid 1b. The crucible 1a had an inner diameter of 20 mm and a height of 25 mm. As the alloy raw material 2, powders of Cu, Ti, and Al were weighed out to 10.32 g, 0.408 g, and 1.630 g, respectively, and inserted into the crucible 1a.
The pressing lid 1b was put on the crucible 1a.

As shown in the schematic cross-sectional view of FIG. 2, the graphite container 1 in which the alloy raw material 2 is inserted is a closed type soaking furnace including a graphite heating element 3 (manufactured by Fuji Denpa Kogyo KK, Hi-Multi). Furnace) 4. Then, the heat treatment was performed while flowing the pure N ₂ gas into the closed soaking furnace 4 at normal pressure.

As shown in the heat pattern of FIG. 3, first, the alloy raw material 2 was heated to 1850 ° C. at a heating rate of 11.7 ° C./min to be melted, and after reaching that temperature, isothermal holding was performed for 5 hours. did. This is a treatment for sufficiently dissolving AlN in the combined financial liquid, and of course the holding time is not limited to 5 hours. That is, the holding time may be shorter, but a large AlN
In order to obtain a single crystal, it is desirable to hold it for 5 hours or more. The melted alloy raw material 2 had a thickness of 4 mm at the bottom of the crucible 1, as shown in FIG.

Then, as shown in FIG.
The financial liquid 2 was cooled to 1650 ° C. at a cooling rate of 2 ° C./min. This is a process for cooling the AlN in the financial liquid to a supersaturated state to easily crystallize the AlN single crystal. Furthermore, in order to increase the size of the crystallized AlN single crystal, Alloy 2 was held for 10 hours in this supersaturated state. Finally, Alloy 2 was furnace cooled to room temperature (RT) at a cooling rate of 1.2 ° C / min. After taking out the solidified ingot from the graphite crucible 1a at room temperature, metallic elements other than AlN were dissolved in a boiling nitric acid aqueous solution. After the dissolution residue containing AlN was filtered and separated, an AlN single crystal was taken out.

As shown in the optical photograph of FIG. 4 (a), the obtained AlN single crystal was a needle crystal, that is, a whisker. The length of the scale shown in the lower right of the photograph in FIG. 4A represents 0.5 mm. The average size of such whiskers was about 30 μm in diameter and about 0.5 mm in length, but the maximum reached 0.1 mm in diameter and 2 mm in length. The result of TEM (transmission electron microscope) observation of such a largest whisker in a cross section perpendicular to its longitudinal direction is shown in the TEM photograph of FIG. 4 (b). In this TEM photograph, it can be seen that dislocations and grain boundaries do not exist in the AlN whiskers, and a single crystal with good crystallinity is obtained. Further, from the electron diffraction pattern of FIG. 4C corresponding to FIG. 4B, this AlN whisker is a hexagonal system of 2H structure (wurtzite structure), and the longitudinal direction of the whisker is crystallographically <0001. It was found to match the c-axis along the> direction.

(Embodiment 2) FIG. 5 is a schematic sectional view showing a graphite container used in Embodiment 2. The container 11 includes a graphite crucible 11a and a graphite pressing block 11b. As alloy raw material 12, powders of Cu and Ti were weighed to 10.33 g and 0.410 g, respectively, and inserted into the crucible 11a.

Next, the rod (5) obtained by processing the AlN sintered body was used.
(mm × 5 mm × 25 mm) 13 was inserted into the container 11 as a supply source of AlN. The upper end of the rod 13 is pressed by the graphite block 11b so that the lower end of the rod 13 is always immersed in the melt even if the rod 13 is dissolved in the financial liquid 12. In the second embodiment thus raw material set containers 11 is inserted into the sealed soaking furnace in the case of a similar embodiment in FIG 1, a pure N ₂ gas similar to normal pressure Example 1 The following heat treatment was performed while flowing.

Similar to the heat pattern of FIG.
1850 the alloy raw material 12 at a heating rate of 1.7 ° C./min
The mixture was heated to 0 ° C. to be melted, and after reaching that temperature, it was kept isothermal for 5 hours. This is a process for sufficiently dissolving AlN in the combined financial liquid 12. The combined financial liquid 12 at that time is, as shown in FIG. 5, a crucible 11b.
Had a thickness of about 4 mm at the bottom. Thereafter, the combined financial liquid 12 in the present Example 2 is not kept isothermally at 1650 ° C. as in the case of Example 1, but is continuously cooled from 1850 ° C. to room temperature at a cooling rate of 0.7 ° C./min. Chilled

In FIG. 6, the Al obtained in Example 2 was used.
An optical picture of N single crystal is shown, which has the form of plate crystals, the diameter of which reaches 0.4 mm.
The scale shown in FIG. 6 also represents a length of 0.5 mm as in the case of FIG.

(Example 3) In Example 3, 6H-SiC was used.
A using heteroepitaxial growth using Al as a seed crystal
A production example of the 1N single crystal will be described. First, as shown in the schematic perspective view of FIG. 7, a seed crystal 6H-S, which is a seed crystal, is formed below the vertical graphite crucibles 21a and 21b which can be divided into two.
A seed chamber 21c capable of fixing the iC (5 mmφ) single crystal substrate 22 was provided. At this time, it is necessary to reduce the diameter of the upper part of the seed chamber 21c in order to prevent the SiC seed crystal 22 having a small specific gravity from floating above the synthetic financial liquid. Therefore, the crucibles 21a and 21b are half-divided bodies that are half-divided along the vertical direction, and the seed 22 can be easily filled.

A half-cracked crucible 21a in which a seed 22 is inserted,
21b were united and further inserted into the graphite container 23 holding them. Then, powder C as an alloy raw material
u, Ti, and Al are 516.5 g and 20.
5 g and 97.3 g were weighed, and the graphite crucible 21a,
21b was inserted. It should be noted that the graphite crucible 2 which can be divided into two
1a, 21b had an outer diameter of 20 mm, a wall thickness of 3 mm, and a length of 200 mm. And the graphite container 23
Had an inner diameter of 20 mm.

As shown in the schematic sectional view of FIG. 8, the graphite container 23 in which the alloy raw material 24 is set is inserted into a high frequency furnace 30 having a temperature gradient (maximum 10 ° C./cm). It was placed on the jig 32. That is, this high-frequency furnace 30 included a quartz tube 31 in an N ₂ atmosphere, a graphite jig 32 installed inside the tube, and an induction heating coil 33 arranged outside the tube.

At the time when the high-frequency furnace 30 reaches the maximum temperature state, the temperature in the central part of the furnace is 1900 ° C.
The temperature of the furnace end corresponding to the position of the upper surface of the seed 22 is 18
It was 50 ° C. In order to melt the alloy raw material 24 sufficiently uniformly, this temperature state was maintained for 2 hours. After that, until the temperature of the lower end of the container 23 reaches 1650 ° C., 3 ° C./h
It was cooled at a cooling rate of r for 50 hours. Further, after the isothermal holding at 1650 ° C. for 50 hours, the coil output of the high frequency furnace 30 was cut off, and the container 23 was cooled to room temperature in the furnace.

Graphite crucibles 21a, 21b cooled to room temperature
The AlN crystal 25 grown on the seed 22 together with the seed 22 was taken out from the lower part of, and the solvent metal component was dissolved and removed with a boiling nitric acid aqueous solution. As a result of microscopic observation of the cross section, it was found that an AlN crystal 25 having a thickness of 350 μm was grown on the 6H—SiC substrate 22. It was also found from X-ray diffraction and TEM observation that the obtained AlN crystal was a single crystal having a crystal orientation parallel to the SiC single crystal substrate.

Example 4 Example 4 is similar to Example 1, but in Example 4 Ni was used instead of Cu as the metal a. That is, powdered Ni, Ti, and Al as the alloy raw materials are each 9.53 g,
Weighed 0.408 g and 1.630 g, and inserted into the graphite container 1 of FIG. The container was inserted into the closed type soaking furnace shown in FIG. 2, and heat treatment was performed while flowing pure N ₂ gas under normal pressure.

As the heat pattern of the heat treatment, similar to FIG. 3, first, up to 1800 ° C., 11.7 ° C./min.
The temperature was raised at a heating rate of, and after reaching 1800 ° C., the temperature was kept isothermal for 5 hours. Then 1 at a cooling rate of 1.2 ° C / min
It was cooled to 650 ° C. and kept isothermally at 1650 ° C. for 10 hours. After that, the furnace was cooled to room temperature at a cooling rate of 1.2 ° C./min.

The obtained AlN single crystal was a needle-like crystal similar to that shown in FIG. 4 (a), and the average size was about 50 mm in diameter and about 0.8 mm in length. However, the maximum diameter was 0.2 mm and the length reached 3 mm.

Example 5 In Example 5, an attempt was made to produce an AlN single crystal by a method similar to that of Example 1. However, in Example 5, the metal a in the abc alloy raw material was used.
Mass concentration Ma, M of Cu powder as a metal, Ti powder as a metal b, and Al powder as a component c, respectively.
The effects of b and Mc (mass%) on the crystallization behavior of AlN single crystals were investigated. The results are shown in Table 1.
Are summarized in.

[0053]

[Table 1]

In Table 1, as a heat pattern for heat treatment of an abc alloy, the alloy powder raw material is first melted by heating to a temperature T1 at a temperature rising rate of 10 ° C./min in a nitrogen atmosphere, and the temperature is maintained for 5 hours. Was done. After that, the alloy was cooled to a temperature T2 at a cooling rate R (° C./min) and kept at that temperature for 10 hours. The obtained Al
Regarding the evaluation of the N single crystal, the case where a large single crystal having a diameter of 0.5 mm or more is obtained is indicated by a double circle, and the case where a single crystal having a diameter of 0.3 mm or more is obtained is a good condition. The mark is shown, and the case where only a single crystal with a diameter of less than 0.3 mm was obtained is shown with a mark.

From the evaluation results in Table 1 as described above,
0.0075 ≦ Mb / in powder raw material for abc alloy
Ma ≦ 0.075 and 0.02 ≦ Mc / (Ma + Mb) ≦
It can be seen that it is desirable to satisfy the relationship of 0.13. For example, powder raw material No. 23 and 25 are 0.0
The relationship of 075 ≦ Mb / Ma ≦ 0.075 is not satisfied, and the evaluation is x. In addition, powder raw material No. 22
And 26 are 0.02 ≦ Mc / (Ma + Mb) ≦ 0.13
The relationship is not satisfied and the evaluation is x. Powder raw material No. No. 28 does not satisfy both concentration relational expressions, and the evaluation is x. Powder raw material No. Nos. 1-21 all satisfy the relation of 0.0075 ≦ Mb / Ma ≦ 0.075 and 0.02 ≦ Mc / (Ma + Mb) ≦ 0.13, and the evaluation is ◎ or ○. There is.

Powder raw material No. having a rating of ⊚. Further studying, 0.037 ≦ Mb / Ma ≦
0.046 and 0.050 ≦ Mc / (Ma + Mb) ≦ 0.
It is understood that it is more preferable to satisfy the relationship of 075.

Further, among the examples given the evaluation of x, the powder raw material No. No. 24 (not containing Ti) does not contain Ti, so that only very fine AlN is produced and it is difficult to form a single crystal. Powder raw material No. No. 27 (not containing Al) does not contain Al and does not crystallize AlN. On the other hand, powder raw material No. For 22, 23, 25, 26 and 28, it is substantially possible to obtain a large single crystal by giving an evaluation of x, but by giving sufficient growth time.

Further, regarding the initial temperature T1, 185
It can be seen that setting the temperature to 0 ° C. or higher is preferable to setting the temperature lower than that. In addition, in Table 1, since the nitrogen concentration in the high-temperature alloying liquid is unknown, only the concentrations of Cu, Ti, and Al in the powder raw material state are considered.

(Example 6) In Example 6, 68.07 g of Cu pellets, 2.70 g of titanium sponge,
A prealloy mass was prepared by arc melting and solidifying 13.69 g of Al pellets in an Ar atmosphere. This Cu—Ti—Al prealloy lump was inserted into the graphite crucible 1a of FIG. Then, the graphite crucible 1a containing the preliminary alloy ingot (without using the graphite lid 1b)
It was inserted into the closed soaking furnace 4 of FIG. 2 and heat treatment was carried out while flowing pure N ₂ gas at normal pressure.

As for the heat pattern of the heat treatment, as shown in FIG.
Heating at a temperature rising rate of / min, and after reaching 1500 ° C, 1
It was kept isothermal for 0 hr. This is a treatment for sufficiently dissolving AlN in the combined financial liquid, and of course the holding time is not limited to 10 hours. That is, the holding time may be shorter, but a large AlN
In order to obtain a single crystal, it is desirable to hold at 1500 ° C. for 10 hours or more.

Then, as shown in FIG. 15, the combined financial liquid was cooled to room temperature at a cooling rate of 1 ° C./min. This is a process for cooling the AlN in the financial liquid to a supersaturated state to easily crystallize the AlN single crystal. Then, the alloy lump cooled to room temperature and solidified was taken out from the container 1, and its cross section was observed by SEM (scanning electron microscope).

FIG. 16 shows the SEM photograph.
The scale represented by 11 white dots in the lower right of this photograph represents 1 μm between each point, that is, the scale as a whole represents 10 μm. As can be seen from FIG.
It was confirmed that an AlN single crystal having a hexagonal cross section with a diameter of about 10 μm was crystallized. The small numbers 1, 2, 3, and 4 in the photograph of FIG. 16 indicate the composition analysis points by the radiant X-rays.

(Example 7) In Example 7 as well, a Cu-Ti-Al preliminary alloy ingot was prepared in exactly the same manner as in Example 6. However, in Example 7, similar to Example 3, an AlN single crystal was manufactured by utilizing heteroepitaxial growth using 6H—SiC as a seed crystal.

However, in Example 7, as shown in FIG. 17, 6H—SiC was formed on the bottom of the graphite crucible 41.
The seed crystal 42 was installed, and the graphite partition plate 43 was inserted on it. The partition plate 3 had a hole 43a exposing the upper surface of the seed crystal 42. Then, the Cu—Ti—Al preliminary alloy ingot 44 was inserted on the partition plate 42 in the crucible 41. After that, the graphite crucible 41 was placed in the closed soaking furnace 4 of FIG. 2, and heat treatment was performed while flowing pure N ₂ gas at normal pressure.

In the heat treatment, the temperature was raised to 1500 ° C. at a rate of 10 ° C./min according to the heat pattern shown in FIG. After reaching 1500 ° C., the temperature was maintained for 10 hours, and then cooled to room temperature at a rate of 1 ° C./min. After reaching the room temperature, the 6H—SiC substrate 42 and the crystals grown on the 6H—SiC substrate 42 were taken out from the graphite crucible 41, and a cross section orthogonal to the substrate surface was observed by TEM.

FIG. 18 shows the TEM observation photograph. The scale bar at the bottom right of this photo is 2μ
It represents the length of m. Analysis of the crystal and orientation in this TEM observation revealed that an AlN single crystal having a thickness of about 2 μm was grown on the 6H—SiC substrate, and the directions of the c-axis and the a-axis thereof were the same as those of the 6H—SiC substrate. It was confirmed that it was consistent with the direction. That is, 6H-S
It can be seen that the AlN single crystal was grown in liquid phase heteroepitaxially on the iC substrate.

Example 8 In Example 8, an attempt was made to produce an AlN single crystal by a method similar to that of Example 6. However, in Example 8, the molar concentrations Ca, Cb, and Cc (mol%) of the respective elements in the Cu—Ti—Al preliminary alloy ingot prepared by arc melting and solidification in an Ar atmosphere were AlN single crystals. The effect on the crystallization behavior of was investigated. The results are summarized in Table 2 and shown.

[0068]

[Table 2]

In Table 2, as a heat pattern for heat treatment of an abc alloy, a preliminary alloy is melted by heating to 1500 ° C. or 1400 ° C. at a temperature rising rate of 10 ° C./min in a nitrogen atmosphere, and the temperature is 5 hours. Retained After that, the alloy is cooled at a cooling rate of 1 ° C / min or 15
It was cooled to room temperature at ° C / min. Regarding the evaluation of the obtained AlN single crystal, the case where the crystallization of the AlN single crystal is confirmed three-dimensionally is shown as a good condition with a circle, and the other cases are shown as a bad condition with a cross.

From the evaluation results in Table 2 as described above,
In the preliminary alloy, 0.01 ≦ Cb / Ca ≦ 0.1 and 0.
It can be seen that it is desirable to satisfy the relationship of 2 ≦ Cc / (Ca + Cb) ≦ 1. For example, the preliminary alloy No.
40 and 44 do not satisfy the relationship of 0.01 ≦ Cb / Ca ≦ 0.1, and are evaluated as x. In addition, the preliminary alloy No. 35-39 is 0.2 ≦ Cc / (Ca + Cb)
The relationship of ≦ 1 is not satisfied, and the evaluation is x.
Prealloy No. Nos. 41-43 do not satisfy both concentration relational expressions, and the evaluation is x.

If the preferable mass concentration ratio range derived from Table 1 above is converted into the molar concentration ratio range and compared with the preferable molar concentration ratio range derived from Table 2,
In addition to ranges that overlap each other, there are ranges that are significantly offset from each other. This is abc
It is considered that this is due to the difference in the starting material form when preparing the combined financial liquid in a nitrogen atmosphere. That is, when the mixed powder raw material is directly melted in a nitrogen atmosphere, it is considered that nitriding of the Al powder partially occurs before the powder raw material is melted. On the other hand, when preparing the abc-based financial solution by remelting the preliminary alloy in which the powder raw material is melted and solidified in an inert atmosphere other than the nitrogen atmosphere in the nitrogen atmosphere, Al is already solid-solved in the preliminary alloy. Therefore, nitriding of Al does not proceed in a nitrogen atmosphere before the prealloy is remelted. As described above, it is considered that the above-mentioned deviation of the preferable range of the raw material composition occurs due to the difference in the preparation process of the abc compound financial liquid in the nitrogen atmosphere.

By the way, in the above-mentioned embodiments, the preliminary alloy was produced by melting and solidifying with an arc in an Ar atmosphere, but it may be produced by melting and solidifying with another heat source in an atmosphere other than nitrogen. Needless to say. For example, a He atmosphere or vacuum may be used as an inert atmosphere other than nitrogen, and induction heating or electron beam heating may be used as a heat source.

[0073]

As described above, according to the present invention, it is possible to provide a method capable of easily producing a relatively large AlN single crystal at low cost.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a graphite container that can be used in the method for producing an AlN single crystal of the present invention.

FIG. 2 is a schematic cross-sectional view showing an example of a closed soaking furnace that can be used in the method for producing an AlN single crystal of the present invention.

FIG. 3 is a diagram showing an example of a heat pattern of alloy heat treatment in the method for producing an AlN single crystal of the present invention.

4 (a) is an optical photograph showing an example of an AlN single crystal obtained by the present invention, and FIG. 4 (b) is a transmission electron micrograph showing a cross section of an AlN whisker obtained by the present invention. And (c) is an electron diffraction pattern diagram corresponding to the whisker cross section of (b).

FIG. 5 is a schematic cross-sectional view showing another example of a graphite container that can be used in the method for producing an AlN single crystal of the present invention.

FIG. 6 is an optical photograph showing another example of the AlN single crystal obtained by the present invention.

FIG. 7 is a schematic perspective view showing still another example of a graphite container that can be used in the method for producing an AlN single crystal of the present invention.

FIG. 8 is a schematic cross-sectional view showing an example of a high-frequency furnace that can be used in the method for producing an AlN single crystal of the present invention.

FIG. 9 is a phase diagram of a Cu—Al—N ternary alloy in a 1800K cross section.

FIG. 10 is a phase diagram of a Ni—Al—N ternary alloy in a 1800K cross section.

11 is a pseudo binary system state diagram corresponding to the cross section along the line PQ in FIG. 9. FIG.

12 is a pseudo binary system state diagram corresponding to the cross section along the line RS in FIG.

FIG. 13 is a Cr-Al binary system phase diagram.

FIG. 14 is a graph showing the nitride formation energies of other metal elements having the same nitride formation energies as Al.

FIG. 15 is a diagram showing another example of a heat pattern of alloy heat treatment in the method for producing an AlN single crystal of the present invention.

FIG. 16 is a scanning electron micrograph showing a cross section of another example of the AlN single crystal obtained by the present invention.

FIG. 17 is a schematic cross-sectional view showing another example of the graphite crucible that can be used in the method for producing an AlN single crystal of the present invention.

FIG. 18 is a transmission electron micrograph showing a cross section of another example of the AlN single crystal obtained by the present invention.

[Explanation of symbols]

1 Graphite Container, 1a Graphite Crucible, 1b Graphite Lid, 2
Synthetic finance liquid, 3 graphite heating element, 4 closed type soaking furnace, 11
Graphite container, 11a graphite crucible, 11b graphite pressing block, 12 alloy financial liquid, 13 AlN sintered rod,
21a, 21b split graphite crucible, 21c crystal seed chamber,
22 SiC single crystal seed, 23 graphite container, 24 synthetic financial liquid, 25 AlN single crystal, 30 high frequency furnace, 31
Quartz tube, 32 graphite jig, 33 induction heating coil, 41
Graphite crucible, 42 SiC single crystal seed, 43 graphite partition plate, 43a hole, 44 preliminary alloy ingot.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kamei Kazuto             4-53 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture             Sumitomo Metal Industries, Ltd. F-term (reference) 4G077 AA03 AA04 BE13 CC04 CC05                       CG01 CG06 EA02 EA06 EC08                       ED06 HA02 QA12 QA38                 5F053 AA03 AA25 BB14 BB24 DD20                       FF04 GG01 HH01 HH04 LL01                       RR20

Claims (7)

[Claims] 1. The metal a is Cr, Mn, Fe, Co,
An abc-based alloy containing at least one selected from Cu and Ni, at least one selected from Sc, Ti, V, Y, Zr, and Nb as the metal b, and further containing Al as the component c. A melt is prepared in a nitrogen-containing atmosphere, and the melt of the abc alloy is cooled or the metal a
A method for producing an AlN single crystal, characterized in that the AlN single crystal is crystallized by evaporation of at least one of b and b. 2. The method for producing an AlN single crystal according to claim 1, wherein the AlN single crystal is epitaxially crystallized on a SiC single crystal substrate. 3. The production of an AlN single crystal according to claim 1, wherein a supersaturated state of AlN is generated in the melt of the abc alloy when the AlN single crystal is crystallized. Method. 4. The melt of the abc alloy is the metal a.
Mass of the powder b, the mass Mb of the powder of the metal b, and the mass Mc of the Al powder are 0.0075 ≦ Mb / Ma ≦.
0.075 and 0.02 ≦ Mc / (Ma + Mb) ≦ 0.1
The method for producing an AlN single crystal according to any one of claims 1 to 3, characterized in that the AlN single crystal is prepared by being blended so as to satisfy the relationship of 3 and dissolved in a nitrogen-containing atmosphere. 5. The abc-based alloy melt is prepared by remelting, in a nitrogen-containing atmosphere, a preliminary alloy ingot previously melted and solidified in an inert atmosphere other than nitrogen. Is the molar concentration C of the metal a
a, the molar concentration Cb of the metal b, and the molar concentration Cc of Al are 0.01 ≦ Cb / Ca ≦ 0.1 and 0.2 ≦ Cc /
4. The Al according to any one of claims 1 to 3, which has a composition satisfying a relationship of (Ca + Cb) ≦ 1.
Method for producing N single crystal. 6. The ab under the nitrogen-containing atmosphere
The preparation of the c-type synthetic financial liquid is 2000 or more above the liquidus of the alloy.
It is performed by heating to a temperature of ℃ or less, and then gradually cooled to a predetermined temperature between the liquidus and solidus lines, or cooled to a predetermined temperature and kept isothermal for a predetermined time there The method for producing an AlN single crystal according to any one of claims 1 to 5. 7. A wide area with respect to Al immediately below the solidus line.
A metal a having a second solid solubility limit, and a metal b having an action of increasing the concentration of N atoms that can be taken into the melt of the metal a
A melt of an abc alloy containing a component c constituting an AlN single crystal is prepared in a nitrogen-containing atmosphere, and the melt of the abc alloy is cooled or the metal a
A method for producing an AlN single crystal, characterized in that the alloy is brought between a liquidus line and a solidus line of the alloy by vaporization of at least one of (1) and (2) to crystallize the AlN single crystal.