JP2019189479A - Method for manufacturing group iii nitride crystal - Google Patents

Abstract

To provide a method for manufacturing a group III nitride crystal, capable of obtaining a group III nitride single crystal formed by suppressing stress during cooling from a base substrate to the group III nitride single crystal while suppressing the corrosion of an apparatus.SOLUTION: The method for manufacturing a group III nitride crystal comprises the steps of: (i) using sapphire as a base substrate to prepare a seed substrate having a group III nitride layer on the base substrate; (ii) preparing lithium or a lithium compound in a tool formed of tantalum; (iii) growing a group III nitride crystal on the group III nitride layer provided on the seed substrate using a mixed melt of a group III element and alkali metal; and (iv) putting the lithium or the lithium compound into the mixed melt to react the molten mixture with the base substrate.SELECTED DRAWING: Figure 1A

Description

  The present invention relates to a method for producing a group III nitride crystal.

  Group III nitride single crystal semiconductors such as gallium nitride are attracting attention as materials for heterojunction high-speed electronic devices such as power semiconductors and semiconductor elements that emit blue and ultraviolet light. Blue laser diodes (LD) are applied to high-density optical discs and displays, and blue light-emitting diodes (LEDs) are applied to displays and lighting. In addition, ultraviolet LD is expected to be applied to biotechnology and the like, and ultraviolet LED is expected to be an ultraviolet light source for fluorescent lamps.

A substrate of a group III nitride single crystal semiconductor (for example, gallium nitride) is usually formed by vapor phase epitaxial growth. For example, a substrate obtained by heteroepitaxially growing a group III nitride crystal on a base substrate made of sapphire is used. However, the sapphire substrate and the gallium nitride single crystal have a difference of 13.8% in the lattice constant and a difference of 25.8% in the linear expansion coefficient. For this reason, the gallium nitride single crystal thin film obtained by vapor phase epitaxial growth has insufficient crystallinity. The dislocation density of the crystal obtained by this method is usually 1e + 8 cm ^{−2 to} 1e + 9 cm ⁻² , and the reduction of the dislocation density is an important issue. In order to solve this problem, efforts have been made to reduce the dislocation density, and for example, an ELOG (Epitaxial Lateral Overgrowth) method has been developed. According to this method, the dislocation density can be lowered to about 1e + 5 cm ⁻² to 1e + 6 cm ^−2, but the manufacturing process is complicated.

  On the other hand, a method of performing crystal growth in a liquid phase instead of vapor phase epitaxial growth has been studied. Conventionally, the equilibrium vapor pressure of nitrogen at the melting point of a group III nitride single crystal such as a gallium nitride single crystal or an aluminum nitride single crystal is 1000 MPa or more. Therefore, in order to grow gallium nitride in a liquid phase, 800 MPa at 1200 ° C. Conditions have been needed. On the other hand, it has been proposed to use a sodium flux method in which nitrogen is dissolved using a mixed melt with a sodium melt. It has been clarified that the gallium nitride single crystal can be synthesized by this sodium flux method under relatively low temperature and low pressure conditions of 870 ° C. and 4 MPa.

  In addition, a mixture of gallium and sodium was melted at 800 ° C. and 5 MPa in a nitrogen gas atmosphere containing ammonium, and a single crystal having a maximum crystal size of about 1.2 mm was grown using this melt for 96 hours. It is obtained (for example, refer to Patent Document 1).

  In addition, after a gallium nitride single crystal layer is formed on a sapphire substrate by metal organic chemical vapor deposition (MOCVD), a single crystal is grown by liquid phase epitaxy (LPE). A method has also been reported.

  In these methods, there is a difference in thermal expansion coefficient between the base substrate made of sapphire and the group III nitride single crystal. For this reason, when a group III nitride single crystal is grown using a base substrate made of sapphire, the group III nitride single crystal may be distorted or warped in the cooling step after the growth. As a result, the obtained group III nitride single crystal substrate is easily damaged, and it is difficult to manufacture a device using the same. Also, the stress in this case increases as the substrate becomes larger in diameter. Therefore, a manufacturing method including a step of creating a gap between a base substrate made of sapphire and a group III nitride single crystal substrate has been reported. As a result, it is possible to manufacture a group III nitride single crystal substrate made of only a high-quality group III nitride single crystal and having a small warp.

  As another method for reducing the warpage, a method of dissolving a base substrate made of sapphire by a chemical reaction between a base substrate made of sapphire and metallic lithium before a stress due to a difference in thermal expansion coefficient occurs is also reported. (For example, refer nonpatent literature 1.). As a result, the stress acting between the grown group III nitride single crystal substrate and the base substrate made of sapphire is reduced. In this method, inside a crucible containing a mixed melt of a metal raw material placed in a temperature and pressure environment (870 ° C., 40 atm., Etc.) for crystal growth and in a place where the mixed melt of the raw material is not touched. Metal lithium is arranged. Thereafter, after the group III nitride crystal growth step, metallic lithium is charged into the raw material mixed melt containing the group III nitride crystal substrate grown on the sapphire base substrate before cooling. As a result, metallic lithium reacts with sapphire constituting the base substrate to separate the group III nitride crystal substrate from the base substrate.

FIG. 2 shows a configuration example of a conventional method for producing a group III nitride single crystal.
(A) In the conventional method for producing a group III nitride single crystal by the sodium flux method, a mixed melt 101 of a group III element melt and a sodium melt is placed in a crucible container 100 made of alumina. The seed crystal substrate 104 is disposed in the mixed melt. The seed crystal substrate 104 is provided with a group crystal nitride single crystal seed crystal layer 103 on a base substrate 102 made of sapphire.
(B) The crucible container 100, the mixed melt 101, and the seed crystal substrate 104 in the manufacturing apparatus having the above configuration are placed in an environment of 840 ° C. to 900 ° C. and nitrogen gas 40 atm. Thus, nitrogen dissolved in the mixed melt 101 reacts with gallium in the mixed melt 101 in the group III nitride single crystal layer 103 on the base substrate 102 to generate a gallium nitride single crystal (the following formula) (See (I).)
Ga + N → GaN (I)

(C) In order to reduce the stress on the grown group III nitride crystal substrate by dissolving sapphire constituting the base substrate 102 with lithium, during the crystal growth, the mixed melt 101 is formed inside the crucible container 100. The metal lithium 111 is held by a jig (jig, metal lithium holder) 110 without touching it.
(D) After the gallium nitride single crystal is formed on the base substrate 102 and before cooling, the inside of the crucible container 100 containing the group III nitride crystal substrate grown on the sapphire base substrate and the mixed melt 101 is contained. Is charged with metal lithium 111. Thereby, the metal lithium 111 is reacted with sapphire constituting the base substrate 102 to separate the group III nitride crystal substrate from the base substrate 102.

JP 2009-234800 A

Takumi Yamada et al 2016 Appl. Phys. Express 9 071002

In the above-described conventional method of melting sapphire with lithium metal, lithium in standby in the crucible containing the mixed melt cannot be stably present in the growth environment during the growth of the group III nitride single crystal. A part of lithium and the lithium compound is vaporized at the growth temperature. Further, there is a problem that vaporized lithium corrodes a member made of alumina (Al ₂ O ₃ ) or yttria (Y ₂ O ₃ ) present in the crucible. This is thought to be due to the high reactivity of metallic lithium.

  Accordingly, the present invention provides a method for producing a group III nitride crystal that obtains a group III nitride single crystal that suppresses stress during cooling from the base substrate to the group III nitride single crystal while suppressing corrosion of the apparatus. For the purpose.

In order to achieve the above object, in the method for producing a group III nitride crystal according to the present invention, (i) a step of preparing a seed substrate in which sapphire is used as a base substrate and a group III nitride layer is provided on the base substrate. When,
(Ii) preparing lithium or a lithium compound in a jig composed of tantalum;
(Iii) growing a group III nitride crystal on the group III nitride layer provided on the seed substrate using a mixed melt of a group III element and an alkali metal;
(Iv) introducing the lithium or lithium compound into the mixed melt and reacting with the base substrate;
including.

Further, the group III nitride crystal production apparatus according to the present invention includes a tantalum crucible container capable of holding a mixed melt of a group III element and an alkali metal,
A tantalum lithium holder capable of holding lithium or a lithium compound above the liquid surface of the mixed melt in the crucible container;
Is provided.

  With the method for producing a group III nitride crystal according to the present invention, it is possible to grow a group III nitride single crystal while suppressing corrosion of the apparatus.

FIG. 3 is a schematic diagram illustrating an example of a group III nitride crystal growth step in the method for producing a group III nitride crystal according to the first embodiment. In the manufacturing method of the group III nitride crystal which concerns on Embodiment 1, it is the schematic which shows an example of the process of throwing lithium oxide into a mixed melt and making it react with a base substrate. In the manufacturing method of the group III nitride crystal concerning Embodiment 1, it is the schematic which shows an example of the state which the base substrate peeled from the group III nitride crystal. 3 is a schematic diagram illustrating an example of a main part of an apparatus configuration of a method for producing a group III nitride crystal described in Non-Patent Document 1. 1 is a schematic diagram illustrating an example of a main part of a device configuration of Example 1. FIG.

The manufacturing method of the present invention according to the first aspect includes
(I) preparing a seed substrate having sapphire as a base substrate and having a group III nitride layer provided on the base substrate;
(Ii) preparing lithium or a lithium compound in a jig composed of tantalum;
(Iii) growing a group III nitride crystal on the group III nitride layer provided on the seed substrate using a mixed melt of a group III element and an alkali metal;
(Iv) introducing the lithium or lithium compound into the mixed melt and reacting with the base substrate;
including.

For the order of the above steps, for example,
(1) A step of preparing a seed substrate in which sapphire is used as a base substrate and a group III nitride layer is provided on the base substrate;
(2) a step of preparing the metal and additive constituting the raw material mixed melt in the crucible;
(3) preparing lithium or a lithium compound in a lithium holder made of tantalum in the upper part of the crucible;
(4) preparing a crucible in the apparatus;
(5) A step of bringing the inside of the apparatus into an environment of the temperature and pressure of the growth conditions,
(6) Crystal growth process,
(7) A step of introducing lithium or a lithium compound prepared in the upper part of the crucible into the raw material mixed melt,
(8) a reaction (dissolution) step of lithium and sapphire,
(9) cooling process,
In the order.

The method for producing a group III nitride crystal according to a second aspect is the above-described first aspect, wherein in the step (iii),
The group III element may be gallium, the alkali metal may be at least one selected from sodium and potassium, and the group III nitride crystal may be a GaN crystal.

The method for producing a group III nitride crystal according to a third aspect is the above-described first or second aspect, wherein in the step (ii),
The amount of the lithium or the lithium compound may be 4% by weight or more and 15% by weight or less of the weight of the seed substrate in terms of mass of lithium atoms.

In the method for producing a group III nitride crystal according to the fourth aspect, in any one of the first to third aspects, in the step (iii),
The mixed melt may further contain an alkaline earth metal.

  According to the said structure, the effect which suppresses polycrystallization may be acquired by including an alkaline-earth metal.

  The method for producing a group III nitride crystal according to a fifth aspect may further include the step of (iv) cooling the grown group III nitride crystal in any one of the first to fourth aspects. Good.

An apparatus for producing a group III nitride crystal according to a sixth aspect includes a tantalum crucible container capable of holding a mixed melt of a group III element and an alkali metal,
A tantalum lithium holder capable of holding lithium or a lithium compound above the liquid surface of the mixed melt in the crucible container;
Is provided.

  The apparatus for producing a group III nitride crystal according to a seventh aspect may further comprise a tantalum crucible lid covering the opening of the tantalum crucible container in the sixth aspect.

  In the Group III nitride crystal production apparatus according to an eighth aspect, in the sixth or seventh aspect, the tantalum crucible container may be a product cut from a bulk material or an electric discharge machined product.

  Hereinafter, a method for producing a group III nitride crystal according to an embodiment will be described with reference to the accompanying drawings. In the drawings, substantially the same members are denoted by the same reference numerals. In all the drawings, the size, ratio, and the like of each component may be different from actual ones.

(Embodiment 1)
<Method for Producing Group III Nitride Crystal>
Hereinafter, the method for producing a group III nitride crystal according to the first embodiment will be described with reference to an example. 1A is a schematic diagram illustrating an example of a group III nitride crystal growth step in the method for producing a group III nitride crystal according to Embodiment 1. FIG. FIG. 1B is a schematic diagram showing an example of a step of introducing lithium or lithium compound 111 into mixed melt 101 and reacting with base substrate 102 in the method for producing a group III nitride crystal according to Embodiment 1. FIG. 1C is a schematic diagram illustrating an example of a state in which the base substrate 102 is separated from the group III nitride crystal 112 in the method for manufacturing the group III nitride crystal according to the first embodiment.

(A) In this method, first, a composition formula Al _u Ga _v In _{1 -uv} N (where 0 ≦ u ≦ 1, 0 ≦ v ≦ 1) is formed on a base substrate 102 made of sapphire. The first group III nitride single crystal layer 103 is formed. A seed crystal substrate 104 is constituted by the base substrate 102 and the first group III nitride layer 103 provided thereon (FIG. 1A). The first group III nitride single crystal layer 103 can be formed by, for example, MOCVD (Metal Organic Chemical Deposition), MBE (Molecular Beam Epitaxy), or HVPE (Hydrogen Vapor Phase Epitaxy). The first group III nitride layer 103 is preferably a single crystal having a main surface (upper surface) of (0001) plane (+ c plane).

(B) Next, a group III nitride crystal is formed on the first group III nitride single crystal layer 103 using the mixed melt 101 in an atmosphere containing nitrogen (preferably a pressurized atmosphere of 100 atm or less). A growth step is performed (FIG. 1A). The mixed melt 101 contains at least one group III element selected from gallium, aluminum, and indium and an alkali metal. In this step, the growth surface side surface of the group III nitride single crystal layer 103 made of the nitride of the selected group III element is brought into contact with the mixed melt 101. As a result, at least one group III element in the mixed melt 101 is reacted with nitrogen dissolved under pressure to grow a group III nitride crystal on the group III nitride single crystal layer 103. As the atmosphere containing nitrogen, for example, a nitrogen gas atmosphere or a nitrogen gas atmosphere containing ammonium can be applied. As the alkali metal, at least one selected from sodium and potassium, that is, one of them or a mixture thereof is used, and these are usually used in a flux state. Nitrogen molecules in the nitrogen gas supplied by pressurization are separated into nitrogen atoms for the crystal growth reaction and dissolved in the mixed melt 101. Therefore, as an alkali metal constituting the mixed melt 101, for example, sodium May be used. In the first embodiment, a group III nitride crystal is grown using a sodium flux method.

The mixed melt 101 in FIG. 1A is prepared, for example, by charging a raw material into the crucible container 100 and heating. At this time, since crucible container 100 is charged with lithium in the step of melting base substrate 102 made of sapphire, crucible container 100 is preferably made of a member that is not corroded by lithium. The first embodiment is characterized in that, for example, tantalum is used as the material of the crucible container 100.
Note that tungsten and molybdenum are also conceivable as materials that are not easily corroded by lithium. However, the present inventors have found that a group III nitride substrate cannot be grown by the sodium flux method when tungsten or molybdenum is used as a crucible container. That is, it is preferable to use tantalum as a material for the crucible container. Further, at this time, the method for producing the tantalum crucible is preferably not a spatula drawing process from a tantalum plate material but a cutting process from a bulk material such as a bar or an electric discharge process. Although the cause has not been specified, a result that group III nitride crystals cannot grow is obtained in a crucible container prepared by spatula drawing (Comparative Example 4). When a tantalum crucible prepared by spatula drawing from a tantalum plate was evaluated by EDX, it was found from the evaluation that the oxygen concentration on the crucible surface was high. That is, it is considered that there is an influence that the tantalum surface is oxidized during the spatula drawing process or impurities including oxygen are attached. Therefore, the crucible container 100 is preferably a product cut from a bulk material or an electric discharge machined product.

  The mixed melt 101 in the heated tantalum crucible container 100 may perform a rocking motion or a rotational motion in the crucible container 100 or a combination of both in order to promote mixing. After producing the mixed melt 101, a group III nitride single crystal grows by bringing the mixed melt 101 into a supersaturated state. In order to promote the supply of nitrogen and improve the reaction rate, the atmosphere containing nitrogen is preferably a pressurized atmosphere. The melting and crystal growth of the material are performed, for example, in an environment where the temperature is about 700 ° C. to 1100 ° C. and the pressure is about 0.1 to 5 megapascals. The mixed melt 101 may further contain an alkaline earth metal. As the alkaline earth metal, for example, calcium, magnesium, strontium, barium, beryllium and the like can be used. Use of these alkaline earth metals has an effect of suppressing the formation of polycrystals.

In this way, the base substrate 102 in configured to formula _{Al s Ga t In 1-st} N ( provided that 0 ≦ s ≦ 1,0 ≦ t ≦ 1) III -nitride crystal 112 represented by sapphire Grow (FIG. 1B). In the group III nitride crystal 112 to be grown, the crystal orientation (0001) plane (+ c plane) is the growth plane (principal plane). The thermal expansion coefficient between the III-nitride crystal represented by sapphire and the composition formula of the base substrate _{102 Al s Ga t In 1-} st N ( provided that 0 ≦ s ≦ 1,0 ≦ t ≦ 1) There is a big difference. When the temperature is lowered to take out the substrate from this step, stress is applied to the group III nitride crystal from the base substrate made of sapphire due to the difference in thermal expansion coefficient. As a result, the group III nitride crystal is warped, and when the stress is large, cracks and cracks are caused.

(C) Therefore, before cooling, lithium or a lithium compound 111 is charged into the mixed melt 101 to react sapphire constituting the base substrate 102 with lithium or the lithium compound 111 (FIG. 1B). For example, all or part of the base substrate 102 can be dissolved. Thus, the base substrate 102 can be peeled off from the group III nitride crystal, or the bond between the base substrate 102 and the group III nitride crystal 112 can be weakened (FIG. 1C).

  At this time, it is desirable that the amount of lithium or lithium compound to be added is 4% by weight or more and 15% by weight or less in terms of the mass of lithium atoms with respect to the weight of the base substrate 102 made of sapphire to be reacted. When the amount is less than 4% by weight, the reaction (dissolution) amount of sapphire is not sufficient, and the group III nitride crystal is not peeled off from the base substrate 102 composed of sapphire, and the group III nitride crystal is composed of sapphire. Stress from the base substrate 102 is generated, and the group III nitride crystal is warped. When the amount is more than 15% by weight, the effect of reducing the stress on the group III nitride substrate by melting the base substrate composed of sapphire can be expected, but the amount larger than that is the base substrate 102 composed of sapphire. This is not desirable because it is excessive for the reaction (dissolution) of In order to accelerate the sapphire dissolution reaction, it is possible to raise the environmental temperature above the growth temperature of the group III nitride crystal. In addition, the result that the influence by lithium concentration was not seen was obtained in the range whose lithium concentration with respect to a mixed melt is 5 mol% to 15 mol%. Therefore, it is speculated that the total amount of lithium to be dissolved should be in the above range regardless of the lithium concentration.

In this construction method, in order to prevent in-furnace contamination due to evaporation of the mixed melt at the time of pressurization and temperature rise with nitrogen, the crucible container 100 containing the mixed melt for crystal growth is contained in the mixed melt 101. No gap is provided except for a vent hole with a diameter of about 1 millimeter (1 mm) for supplying nitrogen to the seed crystal substrate 104.
A crucible lid 108 is provided to cover the opening of the crucible container 100. The crucible lid 108 is also preferably made of a material that is poorly reactive with lithium or a lithium compound. The crucible lid 108 may be made of tantalum, for example.

  Further, in order to put lithium or lithium compound 111 into mixed melt 101, as shown in FIG. 1A, lithium or lithium compound 111 is placed in the vicinity of mixed melt 101 inside crucible container 100 containing mixed melt 101. Is placed. The lithium or lithium compound 111 may be at least one selected from the group consisting of metal lithium, an alloy of metal lithium and gallium, lithium oxide, and lithium nitride, for example. Note that the lithium or the lithium compound 111 is not limited to the above examples. Then, after growing the group III nitride crystal, lithium or a lithium compound 111 is introduced into the mixed melt 101. Specifically, during crystal growth, lithium or a lithium compound 111 is held by a jig (lithium holder) 110 on the upper part of the mixed melt 101 (FIG. 1A). Thereafter, in the step of melting the base substrate 102 made of sapphire, the jig 110 is tilted or the jig 110 is submerged in the mixed melt 101 to introduce lithium or the lithium compound 111 into the mixed melt 101. Is possible (FIG. 1B). At this time, the jig 110 is preferably made of a material having low reactivity with respect to lithium or the lithium compound 111. The first embodiment is characterized in that, for example, tantalum is used as the material of the jig (lithium holder) 110 that can be corroded by lithium vapor during the reaction (dissolution) step with sapphire. Further, the crucible container and the substrate holder (not shown) that are in contact with the mixed melt 101 charged with lithium are made of tantalum.

According to this method, the composition formula _{Al s Ga t In 1-st} N ( However, 0 ≦ s ≦ 1,0 ≦ t ≦ 1) III Group represented by nitride crystals are obtained. For example, a gallium nitride crystal can be obtained by using only gallium as a group III element as a material. For example, by using gallium and aluminum as a group III element as a material, a crystal represented by a composition formula Al _s Ga _1-s N (where 0 ≦ s ≦ 1) is obtained.

<Group III nitride crystal production apparatus>
As shown in FIG. 1A, the Group III nitride crystal manufacturing apparatus according to Embodiment 1 includes, for example, a tantalum crucible container and a tantalum lithium holder. The tantalum crucible container can hold a mixed melt of a group III element and an alkali metal. Moreover, the lithium holder made of tantalum can hold lithium or a lithium compound above the liquid level of the mixed melt in the crucible container. Furthermore, a tantalum crucible lid that covers the opening of the tantalum crucible container may be provided. The tantalum crucible container may be a product cut from a bulk material or an electric discharge machined product.
According to this group III nitride crystal manufacturing apparatus, using a tantalum crucible container and a tantalum lithium holder which are poorly reactive with lithium or a lithium compound to be charged in a reaction (dissolution) step with a sapphire base substrate. Therefore, corrosion due to lithium can be suppressed.

  In addition, this Group III nitride crystal production apparatus includes a pressurized nitrogen source, a pressure vessel, and a pressure control device that place the inside of the crucible container under a pressure of 0.1 Pa to 5 Mega Pascal in a nitrogen atmosphere. May be. Furthermore, you may provide the heating apparatus which heats a crucible container to the temperature of 700 to 1100 degreeC.

  Furthermore, in order to inject lithium or the lithium compound 111 into the mixed melt 101 before cooling, a lithium holder moving device that tilts the lithium holder 110 or sinks the lithium holder 110 into the mixed melt 101 may be provided. Good.

(Example 1)
The configuration of the first embodiment is shown in FIG. The manufacturing method of Example 1 will be described below.
(1) In Example 1, a tantalum crucible container (outer diameter 19 mm, inner diameter 17 mm, inner depth 49 mm) 100 was used. The aforementioned crucible container 100 was charged with 2.0 g of gallium as a raw material for the mixed melt and 2.6 g of sodium, pressurized with 4.0 megapascals of nitrogen, and held at 870 ° C. for 24 hours. Thereby, the raw material became a mixed melt in the crucible container 100.
(2) Thereafter, a seed substrate (10 mm short side, 20 mm long side, sapphire base substrate 102 (thickness 1 mm), gallium nitride epifilm 103 (5 μm)) 104 was prepared. As shown in FIG. 3, the seed crystal substrate 104 was held at a position where only half of the long side was immersed in the mixed melt 101. The gallium nitride crystal was grown by holding for 48 hours.
(3) Thereafter, 0.15 g of metallic lithium (111) was added to the mixed melt 101, heated to 900 ° C. and held for 24 hours.

The manufacturing process of the tantalum crucible container used in Example 1 will be described.
(I) The crucible container made of tantalum used in Example 1 has a tantalum purity of 3N (99.9%) and a 50 mm long bar material turned to an outer diameter of 19 mm by lathe processing. A lathe was used to cut 49 mm, and the inner diameter was 17 mm. That is, the tantalum crucible container is a product cut from a bulk material.
(Ii) Further, the lithium holder 110 was produced by processing a plate material having a tantalum purity of 3N (99.9%) and a thickness of 100 micrometers into a crucible shape by drawing.

(Comparative Example 1)
As the lithium holder, an alumina container was used instead of a tantalum lithium holder, and the other conditions were the same as in Example 1.

(Comparative Example 2)
As the crucible container, an alumina crucible container was used instead of a tantalum crucible container, and the other conditions were the same as in Example 1.

(Comparative Example 3)
As a lithium holder, not a tantalum lithium holder but an yttria container was used, and the other conditions were the same as in Example 1.

  Table 1 shows the results of evaluating the corrosion of the alumina member by lithium under the conditions of Example 1 and Comparative Examples 1 to 3.

  From the above experiments, it was confirmed that corrosion of the crucible container and corrosion of the lithium holder could be prevented by using a tantalum crucible container and a tantalum lithium holder.

(Comparative Example 4)
In this comparative example 4, a tantalum crucible container (outer diameter 19 mm, inner diameter 17 mm, inner depth 30 mm) was used. The crucible container of this comparative example 4 was created by spatula drawing a tantalum plate material having a thickness of 1 millimeter instead of processing from the bar material of Example 1. The other conditions were the same as in Example 1.

  Table 2 shows the results of evaluating the influence of the tantalum crucible container manufactured by spatula drawing under the conditions of Comparative Example 4.

  From this result, it was found that there was a condition in the manufacturing method of the tantalum crucible container, and crystals were not grown in the crucible container manufactured by spatula drawing. Although the cause of this is not clear, it is known from the evaluation that the oxygen concentration on the surface of the crucible processed by spatula drawing is high. That is, it is considered that there is an influence that the tantalum surface is oxidized during the spatula drawing process or impurities including oxygen are attached.

  The group III nitride single crystal substrate cooled without melting sapphire has a radius of curvature of 1 meter, whereas the curvature of the group III nitride single crystal substrate that has been successfully peeled is the radius of curvature. Converted to 20 meters.

  It should be noted that the present disclosure includes appropriately combining any of the various embodiments and / or examples described above, and each of the embodiments and / or examples. The effect which an Example has can be show | played.

  As described above, when the method for producing a group III nitride crystal according to the present invention is used, a group III nitride crystal applicable to heterojunction high-speed electronic devices such as power semiconductor fields and optoelectronic devices such as LEDs and laser fields. Can be obtained.

100 crucible container 101 mixed melt 102 base substrate 103 group III nitride single crystal layer 104 seed crystal substrate 105 mixed melt 108 containing lithium 108 crucible lid 110 lithium holder 111 metal lithium or lithium-gallium alloy 112 group III nitride crystal 120 crucible container 121 lithium holder 122 crucible lid

Claims (8)

(I) preparing a seed substrate having sapphire as a base substrate and having a group III nitride layer provided on the base substrate;
(Ii) preparing lithium or a lithium compound in a jig composed of tantalum;
(Iii) growing a group III nitride crystal on the group III nitride layer provided on the seed substrate using a mixed melt of a group III element and an alkali metal;
(Iv) introducing the lithium or lithium compound into the mixed melt and reacting with the base substrate;
A method for producing a group III nitride crystal comprising: In the step (iii),
The group III nitride according to claim 1, wherein the group III element is gallium, the alkali metal is at least one selected from sodium and potassium, and the group III nitride crystal is a GaN crystal. Crystal production method. In the step (ii),
The method for producing a group III nitride crystal according to claim 1 or 2, wherein the amount of the lithium or the lithium compound is 4 wt% or more and 15 wt% or less of the weight of the seed substrate in terms of mass of lithium atoms. . In the step (iii),
The method for producing a group III nitride crystal according to any one of claims 1 to 3, wherein the mixed melt further contains an alkaline earth metal. The method for producing a group III nitride crystal according to any one of claims 1 to 4, further comprising (v) a step of cooling the grown group III nitride crystal. A tantalum crucible container capable of holding a mixed melt of a group III element and an alkali metal;
A lithium holder made of tantalum capable of holding lithium or a lithium compound above the liquid level of the mixed melt in the crucible container;
An apparatus for producing a group III nitride crystal.   The apparatus for producing a group III nitride crystal according to claim 6, further comprising a tantalum crucible lid that covers an opening of the tantalum crucible container.   The said tantalum crucible container is a III-nitride crystal manufacturing apparatus according to claim 6 or 7, wherein the tantalum crucible container is a cut product or an electric discharge machined product from a bulk material.

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