JP2014062023A - Method for producing nitride crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently producing a nitride crystal excellent in quality and conductivity through enhancing a growth rate and improving a utilization efficiency in raw materials by controlling a condition of crystalline raw materials used for producing the nitride crystal by an ammonothermal process.SOLUTION: The method for producing a nitride crystal in which a nitride crystalline raw material 8 is charged in a raw material charging area 9 in a reaction vessel 20 and a crystal growth is carried out in the reaction vessel 20 in the presence of a supercritical and/or subcritical solvent, in which the crystal growth is carried out by charging the nitride crystalline raw material 8 in the raw material charging area 9 in a bulk density of 0.7 to 4.5 g/cm.

Description

  The present invention relates to a method for producing a nitride crystal. The present invention also relates to a manufacturing method for growing a nitride crystal using a nitride crystal raw material having an oxygen concentration within a certain range.

Known methods for producing nitride crystals include hydride vapor phase epitaxy (HVPE) and ammonothermal. The HVPE method is a method in which Ga chloride and a hydride of group V element (NH ₃ ) are introduced into a furnace in a hydrogen gas stream, thermally decomposed, and crystals generated by thermal decomposition are deposited on a substrate or the like. is there. On the other hand, the ammonothermal method is a method for producing a desired material by using a dissolution-precipitation reaction of raw materials using a solvent containing nitrogen such as ammonia in a supercritical state and / or a subcritical state. . When applied to crystal growth, crystals are precipitated by generating a supersaturated state due to a temperature difference utilizing the temperature dependence of the raw material solubility in a solvent such as ammonia. Specifically, a crystal raw material or seed crystal is placed in a pressure-resistant container such as an autoclave and sealed, and heated with a heater or the like to form a high-temperature region and a low-temperature region in the pressure-resistant container. The desired crystals can be produced by dissolving and growing the crystals on the other hand. It is known that the ammonothermal method has advantages in that the raw material utilization efficiency is better than the HVPE method and the manufacturing cost can be suppressed.

  As a crystal raw material used for the ammonothermal method, a polycrystal or a single crystal of the same kind as the nitride crystal to be grown by the ammonothermal method is used. For this reason, after first producing a nitride microcrystal raw material corresponding to the raw material as the first stage, nitride crystals are grown using this as a second stage (see, for example, Patent Document 1). At this time, since it is difficult to obtain a lump-shaped raw material in the first stage, it is common to use a nitride polycrystal having a small particle size, that is, a powdery form, as a raw material in the second stage. Patent Document 1 (Japanese Patent Laid-Open No. 2003-277182) describes that in the second stage, it is preferable to grow a GaN crystal using a GaN microcrystalline powder having an average particle diameter of about 1 to 5 μm as a raw material. (See paragraph numbers [0009] to [0010]).

  In Patent Document 2 (Japanese Patent Laid-Open No. 2007-238347), the crucible containing the powdered GaN crystal raw material is multi-staged, and the contact area between the raw material and the solvent is increased to increase the raw material dissolution rate. It describes that GaN crystals can be produced efficiently. Here, it is described that it is preferable to use a box-shaped crucible having one opening only on the upper surface. Patent Document 2 describes that a crystal raw material having a particle size of 10 nm to 10 mm can be used, but it is possible to fill a gap between the raw materials using a powder crystal raw material having a particle size of 50 nm to 1 mm. Particularly recommended (see [0061]).

  Patent Document 3 (Japanese Patent Laid-Open No. 2006-83055) and Patent Document 4 (Japanese Translation of PCT International Publication No. 2005-508822) describe a method for producing a nitride polycrystal as a raw material. According to Patent Document 3, a needle-like, columnar or prismatic crystal having a primary particle diameter of 0.1 μm to several tens of μm and a maximum length in the major axis direction of 0.05 μm to 1 mm is obtained. Is used as a raw material for producing nitride crystals. Patent Document 4 describes that a GaN crystal containing equiaxed grains having an average grain size of about 0.01 to 50 μm is produced and used as a raw material for producing a nitride crystal. In Example 1 of Patent Document 4, several crystal grains having a diameter of about 10 to 20 μm are produced together with a large number of crystal grains having a diameter of about 1 μm or less. In Example 2, a large number of crystal grains having a diameter of about 1 to 3 μm are manufactured. A smooth crystal grain slightly larger than that is produced.

Nitride crystals such as gallium nitride (GaN) obtained by the method described above are used for substrates of various semiconductor devices such as light emitting elements, electronic elements, and semiconductor sensors. In order for the nitride crystal to function as a substrate of a semiconductor device, the nitride crystal needs to have appropriate conductivity depending on the use of various semiconductor devices. In general, the conductivity of a nitride crystal is controlled by the carrier concentration and carrier mobility in the nitride crystal. In order for the nitride crystal to function as a substrate of a semiconductor device, it is important to have an appropriate carrier concentration.
In the nitride crystal produced by the HVPE method, when oxygen is used as an n-type dopant, the activation rate is known to be almost 100% (see Patent Document 5 (Japanese Patent Laid-Open No. 2000-44400)). In the nitride crystal produced by the ammonothermal method, the activation rate was not clear when oxygen was used as the n-type dopant.

JP 2003-277182 A JP 2007-238347 A JP 2006-83055 A JP 2005-508822 A JP 2000-44400 A

  The present inventors have examined the production of a nitride crystal using a nitride crystal raw material obtained according to the method described in Patent Document 1, and found that a nitride crystal can be produced at a high growth rate. It became clear that it was not easy. In addition, as described in Patent Document 2, when a nitride crystal was manufactured by filling a raw material so as to fill a gap between the nitride crystal raw materials, the nitride crystal was formed at a sufficiently high growth rate. It became clear that it was not easy to manufacture and the utilization efficiency of raw materials was poor. Furthermore, even if an attempt is made to produce a nitride crystal by simply using the nitride polycrystal produced by the method described in Patent Document 3 or Patent Document 4 as a nitride crystal raw material, the nitride crystal is produced at a desired growth rate. It became clear that it was difficult to do.

  As described above, it is known that a nitride crystal manufactured by the HVPE method has an activation rate of approximately 100% when oxygen is used as an n-type dopant. However, in the nitride crystal produced by the ammonothermal method, the activation rate when oxygen is used as an n-type dopant was not clear. That is, in the ammonothermal method, basic crystal growth conditions have been studied, and a method for obtaining high-quality crystals having desired conductivity has not been established. In addition, since the ammonothermal method uses dopants supplied from various dopant supply sources, oxygen doping conditions for obtaining a nitride crystal having a desired carrier concentration cannot be established. For this reason, there has been a problem that it is difficult to obtain a nitride crystal having a desired carrier concentration.

  Furthermore, in the ammonothermal method, since oxygen doping conditions for obtaining a nitride crystal having a desired carrier concentration have not been established, precise oxygen doping cannot be performed, and a high-quality nitride crystal is obtained. There was a problem that I could not. Furthermore, in order to obtain a nitride crystal having a target carrier concentration by the ammonothermal method, it was necessary to make trial production examinations of various conditions, and there was a problem that production efficiency did not increase.

  In view of such conventional problems, the present inventors have improved the growth rate by controlling the conditions of the crystal raw material used when producing the nitride crystal in the ammonothermal method, thereby improving the raw material utilization efficiency. With the aim of increasing the efficiency and producing nitride crystals with excellent quality, we have made extensive studies. Furthermore, the present inventors have improved the growth rate and controlled the nitride crystal having excellent conductivity by controlling the conditions of the crystal raw material used in producing the nitride crystal in the ammonothermal method. We studied for the purpose of producing efficiently.

  As a result, the present inventors have found that the growth rate of the nitride crystal can be easily improved by controlling the bulk density of the crystal raw material filled when the crystal is grown by the ammonothermal method. Furthermore, the present inventors succeeded in producing a nitride crystal with excellent quality efficiently by controlling the conditions of the crystal raw material, and completed the present invention. Specifically, the present invention has the following configuration.

[1] A method for producing a nitride crystal in which a nitride crystal raw material is filled in a raw material filling region of a reaction vessel, and crystal growth is performed in the presence of a supercritical and / or subcritical solvent in the reaction vessel, A method for producing a nitride crystal, wherein the nitride crystal raw material is filled in a raw material filling region at a bulk density of 0.7 to 4.5 g / cm ³ to perform crystal growth.
[2] The method for producing a nitride crystal according to [1], wherein the bulk density is 0.8 to 3.6 g / cm ³ .
[3] The method for producing a nitride crystal according to [1] or [2], wherein the crystal raw material has a maximum diameter of 0.5 μm to 120 mm.
[4] The nitride crystal raw material particles are any one of [1] to [3], which are tertiary particles having a maximum diameter of 1 to 120 mm formed by agglomerating secondary particles having a maximum diameter of 100 to 1000 μm. 2. A method for producing a nitride crystal according to item 1.
[5] The method for producing a nitride crystal according to any one of [1] to [4], wherein an oxygen concentration in the nitride crystal raw material is 10 to 500 ppm.
[6] A nitride crystal raw material having a bulk density of 0.7 to 4.5 g / cm ³ and an oxygen concentration in the crystal of 10 to 500 ppm is filled in the raw material filling region of the reaction vessel, And nitride crystal growth in the presence of a supercritical and / or subcritical solvent.
[7] The method for producing a nitride crystal according to [6], wherein the bulk density is 0.8 to 3.6 g / cm ³ .
[8] The method for producing a nitride crystal according to [6] or [7], wherein the nitride crystal raw material has a maximum diameter of 0.5 μm to 120 mm.
[9] The nitride crystal raw material particles are any one of [6] to [8], wherein secondary particles having a maximum diameter of 100 to 1000 μm are aggregated and are tertiary particles having a maximum diameter of 1 to 120 mm. 2. A method for producing a nitride crystal according to item 1.
[10] The method for producing a nitride crystal according to any one of [1] to [9], wherein a network structure is installed in the raw material filling region.
[11] The method for producing a nitride crystal according to [10], wherein the nitride crystal raw material is filled in a network structure and then installed in the raw material filling region.
[12] The method for producing a nitride crystal according to any one of [1] to [11], wherein the nitride crystal raw material has a dissolution rate of 40% or more.
[13] The method for producing a nitride crystal according to any one of [1] to [12], wherein the growth rate of the nitride crystal in the c-axis direction is 100 μm / day or more.
[14] A nitride crystal produced by the method for producing a nitride crystal described in any one of [1] to [13].

  According to the first aspect of the present invention, a high-quality nitride crystal is efficiently manufactured by controlling the bulk density of a crystal raw material to be filled in crystal growth by an ammonothermal method within a specific range. be able to. Therefore, according to the present invention, the manufacturing time can be greatly reduced by shortening the growth time and making the crystal raw material a nitride crystal with high efficiency. Moreover, the nitride single crystal manufactured by the method of the present invention can be effectively used for a device as a high-quality crystal.

  According to the second aspect of the present invention, it is possible to efficiently produce a nitride crystal having excellent quality. Further, a nitride crystal having a desired carrier concentration can be obtained by producing a nitride crystal by an ammonothermal method using a nitride crystal raw material having an oxygen concentration within a certain range.

In the second invention of the present invention, by using a nitride crystal raw material having an oxygen concentration within a certain range, a correlation between the oxygen concentration in the raw material and the carrier concentration in the crystal is found in the ammonothermal method. succeeded in. Thereby, it was possible to establish oxygen doping conditions for obtaining a nitride crystal having a desired carrier concentration. For this reason, in the present invention, precise oxygen doping can be performed, and a high-quality nitride crystal can be obtained.
Furthermore, according to the second invention of the present invention, it is possible to drastically reduce the time and effort required for the trial production of conditions for obtaining a nitride crystal having a target carrier concentration by the ammonothermal method. Production efficiency can be increased.

It is a schematic diagram of the crystal manufacturing apparatus by the ammonothermal method which can be used by this invention. It is a schematic diagram of the crystal manufacturing apparatus by another ammonothermal method which can be used by this invention. It is a graph which shows the relationship between the oxygen concentration in a nitride crystal raw material, and the carrier concentration of a growth crystal. It is a graph which shows the relationship between the oxygen concentration in the grown nitride crystal, and carrier concentration.

  Hereinafter, the nitride single crystal annealing method of the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.

(Definition)
In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
First, the relationship between the axes and planes of the hexagonal crystal structure will be described. In this specification, the “principal surface” of the seed crystal or nitride crystal refers to the widest surface of the seed crystal or nitride crystal, and usually the surface on which crystal growth is to be performed. In this specification, the “C plane” is a plane equivalent to the {0001} plane in a hexagonal crystal structure (wurtzite type crystal structure), and is a polar plane. For example, it refers to the (0001) plane and the (000-1) plane that is the opposite plane. In Group III nitride crystals (Group 13 metal nitride crystals of the periodic table), the C plane is a Group III (Group 13 metal) plane or nitrogen plane, and in gallium nitride (GaN), it corresponds to a Ga plane or N plane, respectively. To do. Further, in this specification, the “M plane” refers to {1-100} plane, {01-10} plane, [−1010] plane, {−1100} plane, {0-110} plane, {10-10 } Non-polar planes comprehensively represented as planes, specifically (1-100) plane, (01-10) plane, (-1010) plane, (-1100) plane, (0-110). ) Plane and (10-10) plane. Further, in this specification, the “A plane” means {2-1-10} plane, {-12-10} plane, {-1-120} plane, {-2110} plane, {1-210} plane. , {11-20} plane which is comprehensively represented as a plane. Specifically, (11-20) plane, (2-1-10) plane, (-12-10) plane, (-1-120) plane, (-2110) plane, (1-210) plane, Means. In this specification, “c-axis”, “m-axis”, and “a-axis” mean axes perpendicular to the C-plane, M-plane, and A-plane, respectively.
In the present specification, the “nonpolar plane” means a plane in which both a group III element and a nitrogen element are present on the surface and the abundance ratio is 1: 1. Specifically, the M surface and the A surface can be cited as preferable surfaces. In the present specification, the “semipolar plane” means, for example, a plane other than the [0001] plane and not m = 0 when the group III nitride is hexagonal and the principal plane is represented by (hklm). Say. That is, it refers to a plane that is inclined with respect to the (0001) plane and is not a nonpolar plane. It means a surface having both a group III element and a nitrogen element or only one surface such as the C surface, and the abundance ratio is not 1: 1. h, k, l and m are each independently preferably an integer of -5 to 5, more preferably an integer of -2 to 2, and preferably a low index surface. . Examples of the semipolar plane that can be preferably used as the main surface of the nitride crystal include (10-11) plane, (10-1-1) plane, (10-12) plane, (10-1-2) plane, (20 -21) plane, (202-1) plane, (20-2-1) plane, (10-12) plane, (10-1-2) plane, (11-21) plane, (11-2-1) ) Plane, (11-22) plane, (11-2-2) plane, (11-24) plane, (11-2-4) plane, etc., and in particular, the (10-11) plane, ( 202-1) surface.
In this specification, “ppm” means weight ppm.

(First invention)
Hereinafter, the method for producing a nitride crystal of the first invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.

(Method for producing nitride crystal of the first invention)
The method for producing a nitride crystal of the first invention (hereinafter also referred to as the production method of the first invention) is a method in which a nitride crystal raw material is filled in a raw material filling region of a reaction vessel and is supercritical and / or in the reaction vessel. A method for producing a nitride crystal in which crystal growth is performed in the presence of a subcritical solvent, wherein the nitride crystal raw material is filled in a raw material filling region at a bulk density of 0.7 to 4.5 g / cm ³ Perform crystal growth. In other words, a nitride crystal is filled from a crystal raw material by an ammonothermal method by filling the raw material filling region with a crystal raw material so as to have a bulk density of 0.7 to 4.5 g / cm ³ . It is a manufacturing method.

  Usually, in the ammonothermal method, a raw material filling region in which a crystal raw material is filled in a reaction vessel and a crystal growth region in which a seed crystal is placed are provided, and the raw material is dissolved in the raw material filling region. A crystal is grown on the seed crystal. At this time, a temperature difference is provided between the raw material filling region and the crystal growth region so that the raw material is more dissolved in the raw material filling region and high-quality crystals are more likely to precipitate in the crystal growth region. The “raw material filling region” as used in the present invention refers to the horizontal plane including the lowermost end of the filled nitride crystal raw material and the filled nitride when the long axis of the reaction vessel before the start of the reaction is installed in the vertical direction. A region inside the reaction vessel sandwiched between a horizontal plane including the uppermost end of the crystal raw material. The “bulk density” of the nitride crystal raw material in the raw material filling region is the weight per unit volume of the nitride crystal raw material filled in the raw material filling region, and the weight of the crystal raw material is divided by the free volume of the raw material filling region. Can be obtained. Here, the free volume of the raw material filling region is a volume obtained by subtracting the solid volume other than the nitride crystal raw material existing in the raw material filling region from the internal volume of the raw material filling region of the reaction vessel. Examples of such solids include baffle plates and support frames that support seed crystal support frames, crucibles for installing raw materials, baskets, and structures such as network structures, and their volumes within the raw material filling region. The free volume can be obtained by removing.

The specific example of calculation of the bulk density of the nitride crystal raw material in the raw material filling area | region of this invention is shown. For example, when 100 g of GaN crystal raw material is installed in the lower region of a cylindrical reaction vessel having an inner diameter of 20 mm, and the height from the lowermost end (bottom surface inside the cylinder) to the uppermost end of the region containing the raw material is 100 mm The bulk density can be calculated at 100 g / (314 mm ² × 100 mm), and is calculated to be about 3.18 g / cm ³ . It can also be analyzed by performing a CT scan (computed tomography) in a container.
The bulk density can be converted into the filling rate of the nitride crystal raw material. The filling rate (unit%) can be calculated by dividing the bulk density by the specific gravity of the nitride crystal raw material and multiplying by 100. For example, in the above specific example, since the specific gravity of the GaN crystal is 6.1 g / cm ³ , the filling rate is calculated to be 52%.

When the bulk density of the nitride crystal raw material in the raw material filling region is too large, the volume of the space generated between the nitride crystal raw materials is reduced, so that the convection of the solvent is inhibited and the dissolution rate of the raw material is reduced. For this reason, it becomes difficult to grow high-quality grown crystals with high productivity. On the other hand, if the bulk density of the nitride crystal raw material is too small, the nitride crystal raw material can be sufficiently dissolved, but the input amount of the raw material per volume is reduced, and a sufficient amount of the dissolved raw material is efficiently supplied to the crystal growth region. Thus, it becomes difficult to quickly grow a nitride crystal having a sufficient size. In the present invention, by controlling the bulk density of the crystal raw material in the raw material filling region within the range of 0.7 to 4.5 g / cm ³ , the dissolution rate of the raw material is improved without inhibiting the convection of the solvent, Good quality crystals can be grown efficiently.

In the production method of the present invention of the first invention, the bulk density of the nitride crystal raw material in the raw material filling region is preferably 0.8 g / cm ³ or more, more preferably 0.9 g / cm ³ or more. 1.0 g / cm ³ or more is more preferable, and 1.1 g / cm ³ or more is particularly preferable. Further, the bulk density of the nitride crystal raw material in the raw material filling region is preferably 4.0 g / cm ³ or less, more preferably 3.6 g / cm ³ or less, and 3.2 g / cm ³ or less. More preferably, it is particularly preferably 3.0 g / cm ³ or less. By setting the bulk density of the nitride crystal raw material in the raw material filling region within the above range, the dissolution rate of the raw material can be improved and high-quality crystals can be efficiently grown without inhibiting the convection of the solvent.

(Method for adjusting bulk density)
The bulk density of the nitride crystal raw material in the raw material filling region can be controlled, for example, by selecting the particle size, particle size distribution, shape, and the like of the nitride crystal raw material to be used. In other words, when a nitride crystal raw material is placed in the raw material filling region in the reaction vessel, a nitride crystal raw material having a particle size or shape that allows the individual nitride crystal raw material particles to easily overlap with each other having a gap is selected. , The bulk density can be increased. For example, it is possible to reduce the bulk density by using a nitride crystal material having a large particle size or using a nitride crystal material having an asymmetric and irregular particle shape. Conversely, when a nitride crystal raw material is selected in the raw material filling region in the reaction vessel, a nitride crystal raw material having a particle size or shape in which individual nitride crystal raw material particles tend to closely overlap each other is selected. The bulk density can be increased. For example, a nitride crystal raw material with a small particle diameter, a nitride crystal raw material with a large particle diameter and a nitride crystal raw material with a small particle diameter that can enter the gap, or a particle shape that is easy to pack closely It is possible to increase the bulk density by using a uniform nitride crystal raw material having

If the bulk density of the nitride crystal raw material in the raw material filling region can be in the above range, the bulk density of the nitride crystal to be used is not particularly limited, but the nitride has a bulk density in the range of 0.7 to 4.5 g / cm ³ . It is preferable to use a crystal raw material. More preferably, it is 1.5 g / cm ³ or more, more preferably 1.8 g / cm ³ or more, more preferably 4.0 g / cm ³ or less, and further preferably 3.0 g / cm ³ or less. It is. It is preferable to adjust the solubility of the nitride raw material in the raw material filling region by using a nitride crystal raw material having such a bulk density alone or in combination. The “bulk density” of each of the nitride crystal raw materials having different bulk densities means a weight per unit volume of the filled crystal raw material in a suitable container, and the filled nitride crystals. It can be determined by dividing the weight of the raw material by the volume of the container. Usually, aggregates of nitride crystal raw materials that are said to have the same bulk density have similar shapes, and aggregates that have a maximum value of 100 times or less with respect to the minimum value of the grain size are substantially equivalent. It is called “one kind of nitride crystal raw material” having a bulk density of One nitride crystal raw material preferably has a small variation in weight per particle, and the standard deviation in the weight per particle varies depending on the size of the reaction vessel used, but generally 8.0. Is preferably 7.0 or less, more preferably 7.0 or less, and still more preferably 6.0 or less. In particular, when the diameter of the reaction vessel is about 26 mm, it is preferable to use a raw material having an average weight of 0.6 to 1.2 g / 1 particle and a standard deviation of 0.35 to 0.48. When the diameter of the reaction vessel is about 60 mm, it is preferable to use a raw material having an average weight of 5.0 to 8.5 g / 1 particle and a standard deviation of 5.4 or less. When the diameter of the reaction vessel is about 130 mm, it is preferable to use a raw material having an average weight of 5.0 to 10.5 g / 1 particle and a standard deviation of 7.0 or less.

The bulk density of the nitride crystal raw material in the raw material filling region can also be controlled by applying energy after the nitride crystal raw material is put in the raw material filling region. For example, after the nitride crystal raw material is placed in the raw material filling region, the bulk density is increased by applying vibration, rotating the reaction vessel, or mixing the filled nitride crystal raw material using a stirring rod or a rotating blade. Can be controlled. The vibration may be applied by directly swinging the reaction container or by non-contact means such as ultrasonic waves.
The bulk density of the nitride crystal raw material in the raw material filling region can be controlled by installing a structure in the raw material filling region. For example, a network structure which can pass a solvent but does not allow a nitride crystal raw material to pass through can be preferably employed. By such a network structure, the bulk density can be controlled by limiting the existence region of the nitride crystal raw material in the raw material filling region. That is, the bulk density can be controlled to be low by restricting the region where the nitride crystal raw material exists to a narrow region and ensuring a wide region where the nitride crystal raw material cannot exist. For example, the bulk density can be reduced by filling a nitride crystal raw material into a network structure having a smaller volume than the raw material filling region and then putting the same into the raw material filling region. Conversely, the bulk density may be controlled by installing a hollow network structure not filled with the nitride crystal raw material in the raw material filling region. For example, such a network structure can be mixed with a nitride crystal raw material and filled in the raw material filling region. At this time, the bulk density can be controlled by adjusting the mixing ratio of the two. The network structure may be fixed in advance in the raw material filling region. Moreover, you may use multiple network structures of such various aspects. Furthermore, it is also possible to employ a non-reticulated structure that allows a solvent to pass through.

(Nitride crystal raw material)
In the present invention, a nitride crystal raw material containing atoms constituting the nitride crystal to be grown by the ammonothermal method is used. For example, when a nitride crystal of a Group 13 metal of the periodic table (hereinafter sometimes referred to as a Group 13 nitride crystal) is to be grown, a raw material containing a Group 13 metal of the periodic table is used. Preferably, a polycrystalline raw material or a single crystal raw material of a Group 13 nitride crystal is used, and this may be used as a raw material in combination with a Group 13 metal. The polycrystalline raw material does not need to be a complete nitride, and may contain a metal component in which the Group 13 atom is in a metal state (zero valence) depending on conditions. For example, when the crystal is gallium nitride, a mixture of gallium nitride and metal gallium can be used. Examples of the group 13 nitride crystal include GaN, InN, AlN, InGaN, AlGaN, and AllnGaN. Preferred is GaN, AlN, AlGaN, AllnGaN, and more preferred is GaN.

  The manufacturing method of the polycrystalline raw material used as a raw material in the present invention is not particularly limited. For example, a nitride polycrystal produced by reacting a metal or an oxide or hydroxide thereof with ammonia in a container in which ammonia gas is circulated can be used. In addition, as a metal compound raw material having higher reactivity, a compound having a covalent MN bond such as a halide, an amide compound, an imide compound, or galazan can be used. Furthermore, a nitride polycrystal produced by reacting a metal such as Ga with nitrogen at a high temperature and a high pressure can also be used.

  The amount of water and oxygen contained in the polycrystalline raw material used as the raw material in the present invention is preferably small. The oxygen content in the polycrystalline raw material is usually 1.0% by weight or less, preferably 0.1% by weight or less, particularly preferably 0.0001% by weight or less. The ease of mixing oxygen into the polycrystalline raw material is related to the reactivity with water or the absorption capacity. The worse the crystallinity of the polycrystalline raw material, the more active groups such as NH groups exist on the surface, which may react with water and partially generate oxides or hydroxides. For this reason, it is usually preferable to use a polycrystalline material having as high crystallinity as possible. The crystallinity can be estimated by the half width of powder X-ray diffraction. The half width of the (100) diffraction line (2θ = about 32.5 ° for hexagonal gallium nitride) is usually 0.25 ° or less, preferably It is 0.20 ° or less, more preferably 0.17 ° or less.

The nitride crystal raw material in the first invention is preferably particles having a maximum diameter of 0.5 μm to 120 mm. The preferable range of the particle size of the nitride crystal raw material used in the present invention varies depending on the size of the reaction vessel from the viewpoints of easy adjustment of bulk density and ease of handling. Specifically, if the size of the reaction vessel is larger, the grain size of the crystal raw material may be larger. In addition, the maximum diameter of a particle here means the linear distance of the maximum length of a particle. In addition, for tertiary particles formed by agglomerating secondary particles described later, the maximum diameter of the tertiary particles coincides with the “particle size” of the nitride crystal raw material.
For example, when using a reaction vessel having a diameter of about 26 mm or about 30 mm, the particle diameter is preferably 0.5 μm or more, more preferably 1 μm or more, and more preferably 10 μm or more. It is more preferable to use a material that is 20 mm or less, more preferably a material that is 15 mm or less, more preferably a material that is 10 mm or less. For example, when using a reaction vessel having a diameter of about 60 mm, the particle diameter is preferably 0.5 μm or more, more preferably 1 μm or more, and more preferably 10 μm or more. It is more preferable to use a material that is 50 mm or less, more preferably 30 mm or less, and even more preferably 20 mm or less.
For example, when using a reaction vessel having a diameter of about 130 mm, the particle diameter is preferably 0.5 μm or more, more preferably 1 μm or more, and more preferably 10 μm or more. It is more preferable to use a material that is 120 mm or less, more preferably 60 mm or less, and even more preferably 30 mm or less.

  The nitride crystal raw material used in the first invention preferably has a structure in which the nitride crystal raw material particles are aggregated. Specifically, it is preferable to use tertiary particles obtained by agglomerating secondary particles. The particle size of the secondary particles is preferably 100 μm or more, more preferably 200 μm or more, further preferably 300 μm or more, more preferably 1000 μm or less, and more preferably 900 μm or less. Preferably, it is 800 μm or less. The particle size of the tertiary particles is 1 mm or more, more preferably 5 mm or more, further preferably 10 mm or more, preferably 120 mm or less, more preferably 60 mm or less, 50 mm More preferably, it is more preferably 30 mm or less, and particularly preferably 20 mm or less. The particle size of the secondary particles can be measured with an optical microscope or the like. If it is 1 mm or more as in the case of tertiary particles, it can be visually confirmed, and can be measured, for example, with calipers or a ruler. Furthermore, when the shape of the nitride crystal raw material used in the present invention is a bowl shape as will be described later, the maximum diameter of the particles is determined including the protrusions on the surface. In the nitride crystal having a structure in which the above-mentioned nitride crystal raw material particles are aggregated, the primary particle means a nano-unit single crystal, and these single crystals are aggregated and bonded to each other to form a polycrystal. Secondary particles are formed. Usually, primary particles cannot be discriminated as particles because they are combined and integrated with each other.

  Regarding the particle size distribution of the nitride crystal raw material used in the first invention, the nitride crystal raw material having a particle size of 0.01 μm or more accounts for 20% or more, more preferably 30% or more of the entire volume of the nitride crystal raw material. It is preferable to occupy because the gaps between the nitride crystal raw materials are sufficiently vacant and the solvent can be convected. Further, the nitride crystal raw material having a particle size of 1.0 mm or more accounts for 10% or more, more preferably 30% or more, further preferably 50% or more, particularly preferably 80% or more of the entire volume of the nitride crystal raw material. This is preferable because the gap between the nitride crystal raw materials is sufficiently vacant and the solvent can be convected.

(Shape of nitride crystal raw material)
The shape of the nitride crystal raw material used in the present invention is spherical, granular with an elliptical cross section, plate shape, rectangular shape, triangular shape, bowl shape (in this specification, bowl shape is 5% of the maximum diameter on the surface) It may be a shape having a protruding portion having the above length (preferably in a state where there is unevenness over the entire surface and the surface area is increased). The preferred shape is that there is a certain gap between the crystal raw materials so as not to greatly inhibit the convection of the solvent, so that the bulk density can be easily adjusted. is there.
In addition, in this specification, the shape represented by words and phrases, such as dendritic shape (dendritic), confetti shape, is generally contained in a bowl shape. Examples of the bowl-like shape include the shape of particles described in JP2011-206866A, the shape of particles described in JP2011026666A, and the like. Among these, it is preferable that the nitride crystal raw material is bowl-shaped because the raw material can be dissolved at a higher rate and large nitride crystals can be obtained efficiently.

  There is no restriction | limiting in particular as an acquisition method of such a cage-like nitride crystal raw material, You may acquire commercially and you may obtain by crystal growth under specific conditions. As a commercially available method, for example, it can be obtained from Kyma as a trade name Poly GaN. In addition, as a method of growing a crystal into a bowl-like shape, a material supply partial pressure or a growth temperature is adjusted so as to increase a crystal growth rate by a generally known HVPE method or a seed crystal is not used. In another example, crystal growth is performed to promote the growth of polycrystals.

  As the nitride crystal raw material used in the first invention, it is preferable to use a material that has a surface that is easily dissolved in a solvent and a surface that is not easily dissolved in a solvent. For example, when a GaN crystal is grown using an ammonia solvent by an ammonothermal method, the + C plane (Ga plane) and the M plane are relatively insoluble in the ammonia solvent, and other planes appear on the surface. It is preferable to use raw materials.

(Crystal growth by ammonothermal method)
In the manufacturing method of the first invention, after filling a raw material filling region with a nitride crystal raw material at a bulk density of 0.7 to 4.5 g / cm ³ , the nitride crystal raw material is nitride-crystallized by an ammonothermal method. Manufacturing.
The ammonothermal method uses a nitrogen-containing solvent such as an ammonia solvent in a supercritical state and / or a subcritical state, and a desired nitride single crystal using a dissolution-precipitation reaction of a nitride crystal raw material. It is a method of manufacturing. Crystal growth is performed by using the temperature dependence of the solubility of the nitride crystal raw material in a solvent such as ammonia to cause a supersaturated state due to a temperature difference and precipitating the crystal.

  According to the manufacturing method of the first invention, a nitride crystal having high quality can be efficiently manufactured at a high growth rate with high raw material utilization efficiency. According to the present invention, as the growth rate in the c-axis direction, 100 μm / day or more can be achieved, further 300 μm / day or more can be achieved, and still 600 μm / day or more can be achieved. . Further, as the growth rate in the m-axis direction, 30 μm / day or more can be achieved, further 100 μm / day or more can be achieved, and still 300 μm / day or more can be achieved. Furthermore, as the growth rate in the a-axis direction, 50 μm / day or more can be achieved, further 600 μm / day or more can be achieved, and still 1500 μm / day or more can be achieved.

  Details of the method for producing nitride crystals by the ammonothermal method will be described below.

(Mineralizer)
In the growth of nitride crystals by the ammonothermal method in the present invention, a mineralizer is preferably used. Since the solubility of the nitride crystal raw material in a solvent containing nitrogen such as ammonia is not high, a mineralizer is used to improve the solubility.

The mineralizer used in the first invention may be a basic mineralizer or an acidic mineralizer. Basic mineralizers include alkali metals, alkaline earth metals, compounds containing rare earth metals and nitrogen atoms, alkaline earth metal amides, rare earth amides, alkali nitride metals, alkaline earth metal nitrides, azide compounds, and other hydrazines. Class of salts. Preferably, it is an alkali metal amide, and specific examples include sodium amide (NaNH ₂ ), potassium amide (KNH ₂ ), and lithium amide (LiNH ₂ ). Moreover, as an acidic mineralizer, the compound containing a halogen element is preferable. Examples of mineralizers containing halogen elements include ammonium halide, hydrogen halide, ammonium hexahalosilicate, and hydrocarbyl ammonium fluoride, tetramethylammonium halide, tetraethylammonium halide, benzyltrimethylammonium halide, halogen Examples thereof include alkylammonium salts such as dipropylammonium halide and isopropylammonium halide, alkyl metal halides such as sodium alkyl fluoride, alkaline earth metal halides and metal halides. Of these, an additive (mineralizing agent) containing a halogen element is preferably an alkali halide, an alkaline earth metal halide, a metal halide, an ammonium halide, or a hydrogen halide, more preferably a halogenated. Alkalis, ammonium halides and halides of Group 13 metals of the periodic table are particularly preferred, ammonium halides and gallium halides. Examples of the ammonium halide include ammonium chloride (NH ₄ Cl), ammonium iodide (NH ₄ I), ammonium bromide (NH ₄ Br), and ammonium fluoride (NH ₄ F).

For use in the first invention, it is particularly preferable to use an acidic mineralizer containing ammonium halide. Moreover, a mineralizer may be used individually by 1 type, and may mix and use multiple types suitably.
The combination and concentration ratio (molar concentration ratio) of the mineralizers used in the present invention are the type, shape and size of the nitride crystal to be grown, the type, shape and size of the seed crystal, and the reactor used. It can be determined appropriately depending on temperature conditions, pressure conditions, and the like.

  In the present invention, it is preferable to select an acidic mineralizer as a mineralizer, and in particular, a mineralizer containing an elemental fluorine and at least one element selected from other halogen elements composed of chlorine, bromine and iodine. Is preferably used. The combination of halogen elements contained in the mineralizer may be a combination of two elements such as chlorine and fluorine, bromine and fluorine, iodine and fluorine, chlorine and bromine and fluorine, chlorine and iodine and fluorine, bromine and A combination of three elements such as iodine and fluorine may be used, or a combination of four elements such as chlorine, bromine, iodine and fluorine may be used. Preferred are a combination containing at least chlorine and fluorine, a combination containing at least bromine and fluorine, and a combination containing at least iodine and fluorine. The combination and concentration ratio (molar concentration ratio) of the halogen elements contained in the mineralizer used in the first invention are the type, shape and size of the nitride crystal to be produced, the type, shape and size of the seed crystal, and the reaction used. It can be determined appropriately depending on the apparatus, the temperature conditions and pressure conditions to be employed, and the like.

In the manufacturing method, it is possible to use a mineralizer containing no halogen element together with a mineralizer containing a halogen element. For example, it is used in combination with an alkali metal amide such as NaNH ₂ , KNH ₂ or LiNH ₂ You can also.

  In order to prevent impurities from being mixed into the nitride crystal grown by the above production method, the mineralizer can be used after being purified and dried as necessary. The purity of the mineralizer is usually 95% or higher, preferably 99% or higher, more preferably 99.99% or higher.

  The amount of water and oxygen contained in the mineralizer is desirably as small as possible, and the content thereof is preferably 1000 ppm or less, more preferably 10 ppm or less, and further preferably 1.0 ppm or less. preferable.

When performing the crystal growth, aluminum halide, phosphorus halide, silicon halide, germanium halide, zinc halide, arsenic halide, tin halide, antimony halide, bismuth halide, etc. are used in a reaction vessel. May be present.
The molar concentration of the halogen element contained in the mineralizer with respect to the solvent is preferably 0.1 mol% or more, more preferably 0.3 mol% or more, and further preferably 0.5 mol% or more. The molar concentration of the halogen element contained in the mineralizer is preferably 30 mol% or less, more preferably 20 mol% or less, and even more preferably 10 mol% or less. If the concentration is too low, the solubility tends to decrease and the growth rate tends to decrease. On the other hand, when the concentration is too high, the solubility tends to be too high and the generation of spontaneous nuclei increases, or the degree of supersaturation becomes too high and control tends to be difficult.

(solvent)
As a solvent used in the production method, a solvent containing nitrogen can be used. Examples of the solvent containing nitrogen include a solvent that does not impair the stability of the grown nitride single crystal. Examples of the solvent include ammonia, hydrazine, urea, amines (for example, primary amines such as methylamine, secondary amines such as dimethylamine, tertiary amines such as trimethylamine, and ethylenediamine. Diamine) and melamine. These solvents may be used alone or in combination.

  In order to reduce the supply of oxygen from other than the nitride crystal raw material, it is desirable that the amount of water and oxygen contained in the solvent is as small as possible, and the content thereof is preferably 1000 ppm or less, and preferably 10 ppm or less. Is more preferable, and it is still more preferable that it is 0.1 ppm or less. When ammonia is used as a solvent, the purity is usually 99.9% or more, preferably 99.99% or more, more preferably 99.999% or more, and particularly preferably 99.9999% or more. .

(Reaction vessel and installation components)
The method for producing a nitride crystal of the first invention can be carried out in a reaction vessel.
The reaction vessel can be selected from those capable of withstanding high temperature and high pressure conditions when growing nitride crystals. “Reaction vessel” means a vessel for producing nitride crystals in the presence of a solvent in a supercritical and / or subcritical state. Preferred examples include capsules to be used. Examples of the reaction vessel include those described in JP-T-2003-511326 (International Publication No. 01/024921 pamphlet) and JP-T-2007-509507 (International Publication No. 2005/043638 pamphlet). A mechanism that adjusts the pressure applied to the reaction vessel and its contents from the outside may be provided, or an autoclave that does not have such a mechanism may be used.

  The reaction vessel is preferably selected from those that can withstand the high-temperature and high-pressure conditions when the nitride crystal is grown. The reaction vessel is preferably made of a material having high temperature strength and pressure resistance and corrosion resistance. In particular, a Ni-based alloy having excellent corrosion resistance against solvents such as ammonia, Stellite (Delloro Stellite Company, Inc.) It is preferable to use a Co-based alloy such as More preferably, it is a Ni-based alloy. Specifically, Inconel 625 (Inconel is a registered trademark of Huntington Alloys Canada Limited, the same applies hereinafter), Nimonic 90 (Nimonic is a registered trademark of Special Metals Wiggin Limited, the same applies hereinafter), RENE41 (Teledyne). Allvac, Inc.), Inconel 718 (Inconel is a registered trademark of Huntington Alloys Canada Limited), Hastelloy (registered trademark of Haynes International, Inc.), Waspaloy (registered trademark of United Technologies, Inc.).

  The composition ratio of these alloys depends on the temperature and pressure conditions of the solvent in the system, and the reactivity with the mineralizers and their reactants contained in the system and / or the oxidizing power / reducing power, pH conditions, What is necessary is just to select suitably. In order to use these as materials constituting the inner surface of the reaction vessel, the reaction vessel itself may be manufactured using these alloys, and a thin film is formed as an inner cylinder and placed in a pressure resistant vessel as a reaction vessel. Alternatively, the inner surface of any reaction vessel material may be plated.

  In order to further improve the corrosion resistance of the reaction vessel, the inner surface of the reaction vessel may be lined or coated using the excellent corrosion resistance of the noble metal. Moreover, the material of the reaction vessel can be a noble metal. Examples of the noble metal herein include Pt, Au, Ir, Ru, Rh, Pd, Ag, and alloys containing these noble metals as a main component, and among these, it is preferable to use Pt or a Pt alloy having excellent corrosion resistance. .

  A specific example of a crystal production apparatus including a reaction vessel that can be used in the method for producing a nitride crystal of the first invention is shown in FIG. FIG. 1 is a schematic view of a crystal manufacturing apparatus that can be used in the present invention. In the crystal manufacturing apparatus shown in FIG. 1, crystal growth is performed in a capsule 20 loaded as an inner reaction container in an autoclave 1 (pressure-resistant container). The capsule 20 includes a raw material filling region 9 for dissolving the raw material and a crystal growth region 6 for growing crystals. The raw material filling region 9 can contain a solvent and a mineralizer together with the raw material 8, and the crystal growth region 6 can be installed by suspending the seed crystal 7 with a wire. Between the raw material filling region 9 and the crystal growth region 6, a partition baffle plate 5 is installed in two regions. The baffle plate 5 has a hole area ratio of preferably 2 to 60%, more preferably 3 to 40%. The material of the surface of the baffle plate is preferably the same as the material of the capsule 20 that is a reaction vessel. Further, in order to give more corrosion resistance and to purify the crystal to be grown, the surface of the baffle plate is Ni, Ta, Ti, W, Mo, Ru, Nb, Pd, Pt, Au, Ir, pBN. Of these, W, Mo, Ti, Pd, Pt, Au, Ir, and pBN are more preferable, and Pt, Mo, and Ti are particularly preferable. In the crystal manufacturing apparatus shown in FIG. 1, the gap between the inner wall of the autoclave 1 and the capsule 20 can be filled with the second solvent. Here, ammonia can be filled as the second solvent while filling the nitrogen gas from the nitrogen cylinder 13 through the valve 10 or confirming the flow rate from the ammonia cylinder 12 with the mass flow meter 14. In addition, the vacuum pump 11 can perform necessary pressure reduction. In the crystal manufacturing apparatus used when carrying out the method for manufacturing a nitride crystal of the first invention, valves, mass flow meters, and conduits do not necessarily have to be installed.

  As in the crystal production apparatus shown in FIG. 2, the lining 4 can be used to provide corrosion resistance with the autoclave 1 without using capsules, and it can be used as a reaction vessel. The lining material is preferably at least one metal or element of Pt, Ir, Ag, Pd, Rh, Cu, Au and C, or an alloy or compound containing at least one metal, More preferably, it is an alloy or compound containing at least one or more metals or elements of Pt, Ag, Cu and C, or at least one or more metals because it is easy to line. For example, Pt simple substance, Pt-Ir alloy, Ag simple substance, Cu simple substance, graphite, etc. are mentioned. Note that the lining described above can also be used in combination when using a capsule as shown in FIG.

(Manufacturing process)
An example of the method for producing a nitride crystal of the first invention will be described. When carrying out the method for producing a nitride crystal of the first invention, first, a seed crystal, a nitrogen-containing solvent, a raw material, and a mineralizer are put in a reaction vessel and sealed. Here, as the seed crystal, the plane orientation of the main surface is not particularly limited, but by cutting a crystal grown with the C plane as the main surface in a desired direction, the main surface becomes a nonpolar plane or a semipolar plane. A substrate can be obtained. Thereby, a seed crystal having a nonpolar plane such as an M plane and a semipolar plane such as (10-11) or (20-21) can be obtained.

  Prior to introducing the material such as the nitride crystal raw material, mineralizer, baffle plate or seed crystal into the reaction vessel, the reaction vessel may be deaerated. Moreover, you may distribute | circulate inert gas, such as nitrogen gas, at the time of introduction | transduction of material. The seed crystal is usually placed in the reaction vessel at the same time or after filling the raw material and the mineralizer. The seed crystal is preferably fixed to a noble metal jig similar to the noble metal constituting the inner surface of the reaction vessel. After installation of the seed crystal, heat deaeration may be performed as necessary.

  When the production apparatus shown in FIG. 1 is used, a capsule 20 that is a reaction vessel is sealed with a seed crystal, a nitrogen-containing solvent, a raw material, and a mineralizer, and then the capsule 20 is sealed in a pressure-resistant container (autoclave). ) 1 is loaded, and preferably the second solvent is filled in the space between the pressure vessel and the reaction vessel to seal the pressure vessel.

  Thereafter, the whole is heated to bring the inside of the reaction vessel into a supercritical state and / or a subcritical state. In the supercritical state, the viscosity is generally low and it is more easily diffused than the liquid, but has the same solvating power as the liquid. The subcritical state means a liquid state having a density substantially equal to the critical density near the critical temperature. For example, in the raw material filling part, the raw material is melted as a supercritical state, and in the crystal growth part, the temperature is changed so as to be in the subcritical state, and crystal growth utilizing the difference in solubility between the supercritical state and the subcritical state raw material is also performed. Is possible.

  When in the supercritical state, the reaction mixture is generally maintained at a temperature above the critical point of the solvent. When an ammonia solvent is used, the critical point is a critical temperature of 132 ° C. and a critical pressure of 11.35 MPa. However, if the filling rate with respect to the volume of the reaction vessel is high, the pressure far exceeds the critical pressure even at a temperature below the critical temperature. In the present invention, the “supercritical state” includes such a state exceeding the critical pressure. Since the reaction mixture is enclosed in a constant volume reaction vessel, the increase in temperature increases the pressure of the fluid. In general, if T> Tc (critical temperature of one solvent) and P> Pc (critical pressure of one solvent), the fluid is in a supercritical state.

  Under supercritical conditions, a sufficient growth rate of nitride crystals can be obtained. The reaction time depends in particular on the reactivity of the mineralizer and the thermodynamic parameters, ie temperature and pressure values. During the synthesis or growth of the nitride crystal, the pressure in the reaction vessel is preferably 120 MPa or more, more preferably 150 MPa or more, and further preferably 180 MPa or more, from the viewpoint of crystallinity and productivity. . The pressure in the reaction vessel is preferably 700 MPa or less, more preferably 500 MPa or less, further preferably 350 MPa or less, and particularly preferably 300 MPa or less from the viewpoint of safety. The pressure is appropriately determined depending on the filling rate of the solvent volume with respect to the temperature and the volume of the reaction vessel. Originally, the pressure in the reaction vessel is uniquely determined by the temperature and the filling rate, but in practice, the raw materials, additives such as mineralizers, temperature heterogeneity in the reaction vessel, and free volume Depending on the presence of

  From the viewpoint of crystallinity and productivity, the lower limit of the temperature range in the reaction vessel is preferably 500 ° C. or higher, more preferably 515 ° C. or higher, and further preferably 530 ° C. or higher. From the viewpoint of safety, the upper limit value is preferably 700 ° C. or less, more preferably 650 ° C. or less, and further preferably 630 ° C. or less. In the method for producing a nitride crystal of the first invention, the temperature of the raw material filling region in the reaction vessel is preferably higher than the temperature of the crystal growth region. The temperature difference (| ΔT |) is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, preferably 100 ° C. or lower, and 90 ° C. or lower from the viewpoints of crystallinity and productivity. More preferably, 80 ° C. or lower is particularly preferable. The optimum temperature and pressure in the reaction vessel can be appropriately determined depending on the type and amount of mineralizer and additive used during crystal growth.

  The injection ratio of the solvent into the reaction vessel to achieve the temperature range and pressure range in the reaction vessel, that is, the filling rate, is the free volume of the reaction vessel, i.e. If used, subtract the volume of the seed crystal and the structure on which it is installed from the volume of the reaction vessel, and if a baffle plate is installed, further add the volume of the baffle plate from the volume of the reaction vessel. The liquid density at the boiling point of the solvent remaining after subtraction is usually 20 to 95%, preferably 30 to 80%, more preferably 40 to 70%. When the capsule 20 as shown in FIG. 1 is used as the reaction vessel, it is preferable to appropriately adjust the amount of the solvent so that the pressure is balanced inside and outside the capsule 20 in the supercritical state of the solvent.

  Nitride crystal growth in the reaction vessel is maintained in a subcritical or supercritical state of a solvent such as ammonia by heating and heating the reaction vessel using an electric furnace with a thermocouple. Is done. The heating method and the rate of temperature increase to a predetermined reaction temperature are not particularly limited, but are usually performed over several hours to several days. If necessary, the temperature can be raised in multiple stages, or the temperature raising speed can be changed in the temperature range. It can also be heated while being partially cooled.

  The “reaction temperature” is measured by a thermocouple provided so as to be in contact with the outer surface of the reaction vessel and / or a thermocouple inserted into a hole having a certain depth from the outer surface. It can be estimated in terms of temperature. The average value of the temperatures measured with these thermocouples is taken as the average temperature. Usually, an average value of the temperature of the raw material filling region and the temperature of the crystal growth region is defined as the average temperature.

In the method for producing a nitride crystal of the first invention, a pretreatment can be added to the seed crystal. Examples of the pretreatment include subjecting the seed crystal to a meltback process, polishing the growth surface of the seed crystal, and washing the seed crystal.
In the method for producing a nitride crystal of the first invention, when raising the temperature of the autoclave, a constant temperature may be maintained, and the growth crystal growth surface of the seed crystal may be subjected to a meltback treatment. By the meltback treatment, the crystal growth surface of the seed crystal and the crystal nucleus attached to the member in the apparatus can be dissolved. As conditions for the meltback treatment, the average temperature difference between the crystal growth region (growth region) and the raw material filling region (raw material region) is preferably 0 ° C. or higher, more preferably 10 ° C. or higher, and particularly preferably 20 ° C. or higher. Moreover, 100 degrees C or less is preferable, 80 degrees C or less is more preferable, and 60 degrees C or less is especially preferable. The temperature of the crystal growth region during the meltback treatment is preferably 500 ° C. or higher, more preferably 550 ° C. or higher, and further preferably 600 ° C. or higher. Moreover, 650 degrees C or less is preferable and 630 degrees C or less is more preferable. The temperature of the raw material filling region is preferably 500 ° C. or higher, more preferably 550 ° C. or higher, and further preferably 590 ° C. or higher. Moreover, 650 degrees C or less is preferable and 630 degrees C or less is more preferable.

  The pressure in the reaction vessel during the meltback treatment is preferably 100 MPa or more, more preferably 150 MPa or more, and particularly preferably 180 MPa or more. In addition, the meltback treatment time is preferably 1 hour or longer, more preferably 5 hours or longer, and particularly preferably 10 hours or longer. Moreover, 200 hours or less are preferable, 100 hours or less are more preferable, and 50 hours or less are especially preferable.

  In the pretreatment, the surface of the seed crystal (nitride crystal growth surface) can be polished by, for example, chemical mechanical polishing (CMP). The surface roughness of the seed crystal is, for example, 1.0 nm or less from the viewpoint that the root mean square roughness (Rms) measured by an atomic force microscope performs meltback and subsequent crystal growth uniformly. Preferably, 0.5 nm is more preferable, and 0.3 nm is particularly preferable.

  The reaction time after reaching a predetermined temperature varies depending on the type of nitride crystal, the raw material used, the type of mineralizer, and the size and amount of the crystal to be produced, but is usually several hours to several hundred days. be able to. During the reaction, the reaction temperature may be constant, or the temperature may be gradually raised or lowered. After a reaction time for producing desired crystals, the temperature is lowered. The temperature lowering method is not particularly limited, but the heating may be stopped while the heating of the heater is stopped and the reaction vessel is installed in the furnace as it is, or the reaction vessel may be removed from the electric furnace and air cooled. If necessary, quenching with a refrigerant is also preferably used.

After the temperature of the outer surface of the reaction vessel or the estimated temperature inside the reaction vessel is below a predetermined temperature, the reaction vessel is opened. The predetermined temperature at this time is not particularly limited, and is usually −80 ° C. to 200 ° C., preferably −33 ° C. to 100 ° C. Here, the valve may be opened by pipe connection to the valve connection port of the valve attached to the reaction vessel, leading to a vessel filled with water or the like. Furthermore, if necessary, remove the ammonia solvent in the reaction vessel sufficiently by applying a vacuum, etc., then dry, open the reaction vessel lid, etc., and generate nitride crystals and unreacted raw materials and mineralization. Additives such as agents can be removed.
When manufacturing gallium nitride according to the method for manufacturing a nitride crystal of the first invention, refer to JP 2009-263229 A for details of materials, manufacturing conditions, manufacturing apparatus, and processes other than those described above. Can do. The entire disclosure of this publication is incorporated herein by reference.

  In the method for producing a nitride crystal of the first invention, after the nitride crystal is grown on the seed crystal, post-treatment may be added. The type and purpose of the post-processing are not particularly limited. For example, the crystal surface may be melted back in the cooling process after growth so that crystal defects such as pits and dislocations can be easily observed.

  In the method for producing a nitride crystal according to the first invention, if the nitride crystal raw material is completely dissolved while maintaining the temperature and pressure in the crystal growth conditions, the grown crystal is dissolved. There is a fear. From the viewpoint that it is preferable that a very small amount of the nitride crystal raw material remains after the crystal growth step, the dissolution rate of the nitride crystal raw material is preferably 40% to 96%, more preferably 50% to 85%. 70% to 80% is particularly preferable. The dissolution rate can be obtained by (raw material input before crystal growth step−raw material remaining after crystal growth step) / (raw material input before crystal growth step).

(Second invention)
According to a second aspect of the present invention, a nitride crystal raw material having a bulk density of 0.7 to 4.5 g / cm ³ and an oxygen concentration in the crystal of 10 to 500 ppm is provided in the raw material filling region of the reaction vessel. After filling, nitride crystal growth is performed in a reaction vessel in the presence of a supercritical and / or subcritical solvent.

In the method for producing a nitride crystal of the second invention of the present invention (hereinafter also referred to as the production method of the second invention), a nitride crystal raw material having an oxygen concentration of 10 to 500 ppm is used, and an ammonothermal method is used. A nitride crystal is produced from the nitride crystal raw material. Specifically, in the production method of the second invention, a nitride crystal raw material having an oxygen concentration of 10 to 500 ppm is filled in a raw material filling region of a reaction vessel, and is in a supercritical and / or subcritical state in the reaction vessel. A growth step of growing a nitride crystal in the presence of a nitrogen-containing solvent;
The nitride crystal material that can be used in the second invention and a nitride crystal growth method using this nitride crystal material will be described below.

(Crystal raw material)
In the second invention, a nitride crystal raw material containing atoms constituting the nitride crystal to be grown by the ammonothermal method is used. For example, when a nitride crystal of Group 13 metal of the periodic table is to be grown, a raw material containing Group 13 metal of the periodic table is used. Preferably, a polycrystalline raw material or a single crystal raw material of a group 13 nitride crystal is used, and this may be used as a raw material in combination with a metal of group 13 atom (metal). The polycrystalline raw material does not need to be a complete nitride, and may contain a metal component in which the Group 13 atom is in a metal state (zero valence) depending on conditions. For example, when the nitride crystal to be grown is gallium nitride, examples of the nitride crystal raw material include a mixture of gallium nitride and metal gallium. Examples of the type of nitride crystal obtained in the second invention include GaN, InN, AlN, InGaN, AlGaN, AllnGaN, and the like. Preferred is GaN, AlN, AlGaN, AllnGaN, and more preferred is GaN. Therefore, as the nitride crystal raw material, the above-mentioned polycrystalline raw material of crystals and / or these metals can be used in combination.

(Oxygen concentration of crystal raw material)
In the method for producing a nitride crystal of the second invention, a nitride crystal raw material having an oxygen concentration of 10 to 500 ppm is used in the presence of a nitrogen-containing solvent in a supercritical and / or subcritical state in a reaction vessel. A growth step of performing nitride crystal growth.
The oxygen concentration of the nitride crystal raw material is 10 ppm or more, preferably 15 ppm or more, more preferably 16 ppm or more, and further preferably 20 ppm or more in order to ensure a sufficient amount as a dopant. The oxygen concentration of the nitride crystal raw material is 500 ppm or less, preferably 150 ppm or less, more preferably 120 ppm or less, and 80 ppm or less in order to obtain high-quality crystals with few impurities. Particularly preferred. By setting the oxygen concentration of the nitride crystal raw material within the above range, the carrier concentration of the obtained nitride crystal can be set to 5 × 10 ^{17 to} 5 × 10 ¹⁹ atoms / cm ^3, and a high-quality nitride crystal is obtained. Can be obtained.
The method for producing a nitride crystal raw material having an oxygen concentration of 10 to 500 ppm is not particularly limited. As the nitride crystal raw material having an oxygen concentration of 10 to 500 ppm, one produced by a normal HVPE method may be used, or one produced by an ammonothermal method may be used. For example, when producing a nitride crystal raw material by the HVPE method, a nitride crystal raw material can be produced by mixing water vapor into the reaction vessel and appropriately adjusting the oxygen concentration. As the water vapor, it is preferable to use one produced by mixing diluted oxygen and water in a reaction vessel.

  In the second invention, the relationship between the oxygen concentration in the nitride crystal raw material and the carrier concentration in the grown nitride crystal can be clarified using the relational expression described below. Thereby, oxygen doping with high reproducibility becomes possible.

  In the second invention, the activation rate of the nitride crystal formed by the ammonothermal method can be expressed by the following formula. In the second invention, the activation rate indicates a ratio at which the dopant functions as a carrier in the nitride crystal.

In the above formula, η is the dopant activation rate (unit:%), [CC] is the carrier concentration (unit: cm ⁻³ ), and [D] is the dopant concentration (unit: cm ⁻³ ). Usually, the carrier concentration can be measured by performing hole measurement, Raman spectroscopy, CV characteristic analysis, mobility measurement using eddy current, and the like on the obtained crystal. In some cases, it is preferable to measure the carrier concentration after annealing the obtained nitride crystal to activate the carrier. The dopant concentration can be determined by performing SIMS on the obtained nitride crystal and totaling the concentration of atoms that can function as an n-type dopant such as oxygen or Si. However, when the amount of dopant other than oxygen, such as Si or a halogen element, incorporated in the crystal is very small compared to oxygen, the concentration of oxygen, which is a representative dopant, can be considered as the dopant concentration.

It is known that in a nitride crystal produced by the HVPE method, when oxygen is used as an n-type dopant, the activation rate is almost 100%. However, the dopant activation rate calculated by the above formula for the nitride crystal obtained by the ammonothermal method is not 100% as in the nitride crystal obtained by the HVPE method, but is 10 to 90%. The average of the ammonothermal crystals obtained under various growth conditions was found to be about 45% dopant activation. Thus, it has been found that the oxygen concentration to be doped in the nitride crystal obtained by the ammonothermal method is in the range of 1.1 to 10 times the target carrier concentration. Specifically, the oxygen concentration to be doped in the obtained nitride crystal is preferably 1.5 × 10 ^{18 to} 2.5 × 10 ¹⁹ atoms / cm ³ , and in order to dope such an amount, The oxygen concentration contained in the nitride crystal raw material is preferably in the range of 10 to 500 ppm.

  According to the manufacturing method of the second invention, it is preferable that 40 to 60 wt% of the oxygen amount contained in the nitride crystal raw material is taken into the obtained nitride crystal, and about 50 wt% of the oxygen amount is taken in. More preferred. The amount of oxygen taken into the nitride crystal from the nitride crystal raw material can be controlled by appropriately adjusting the crystal growth conditions. Specifically, as the amount of halogen uptake in the nitride crystal increases, the amount of oxygen uptake increases. It tends to decrease. Therefore, it can be adjusted by appropriately changing the amount of halogen used as the mineralizer and the ratio of halogen species.

  The amount of oxygen to be doped in order for the nitride crystal to have a desired carrier concentration can be derived from the calculation formula for the activation rate described above, and further, the amount of oxygen to be contained in the nitride crystal raw material can be derived from this. Can do.

Furthermore, in the second invention, the relationship between the oxygen concentration in the nitride crystal raw material and the carrier concentration in the crystal can be expressed by the following equation using the linear approximation equation shown in FIG.
Y = 0.7346X-2 × 10 ¹⁸

In the above formula, X represents the oxygen concentration in the nitride crystal raw material, Y represents the carrier concentration in the obtained nitride crystal, and the carrier concentration in the obtained crystal can be estimated from the oxygen concentration in the raw material.
In the second invention, it is possible to perform oxygen doping with high reproducibility in the ammonothermal method by using the above correlation equation. Thereby, nitride crystals having various carrier concentrations can be easily manufactured according to the use of the semiconductor device.

In the second invention, by using the above-described correlation formula, it is possible to establish the manufacturing conditions for the nitride crystal having a desired carrier concentration. Thereby, it becomes possible to perform precise oxygen doping in the ammonothermal method, and a high-quality nitride crystal can be obtained.
Furthermore, by using the above correlation formula, it is possible to increase the production efficiency of a nitride crystal having a target carrier concentration.

  In the production method of the second invention, the amount of the n-type dopant other than oxygen contained in the nitride crystal raw material is preferably 1000 ppm or less, more preferably 100 ppm or less, and further preferably 10 ppm or less. preferable. When producing the nitride crystal raw material, it is preferable not to mix a certain amount or more of the n-type dopant with the nitride crystal raw material. By setting the amount of n-type dopant other than oxygen in the nitride crystal raw material to the upper limit value or less, it is possible to more accurately set conditions for obtaining a nitride crystal having a desired carrier concentration.

Examples of n-type dopants other than oxygen include Si, Ge, Se, S, F, I, Cl, and C. These dopants are added to the nitride crystal as n-type dopants and serve as carriers in the nitride crystal. Si is the most commonly used dopant in gallium nitride crystals.
Since oxygen has a high activation rate, oxygen is useful as an n-type dopant. For this reason, in the second invention, it is preferable to dope oxygen to contain the target concentration of carriers in the nitrided crystal. Also, by doping the nitride crystal with oxygen, the workability of the nitride crystal can be improved compared to the case where Si is doped. In the second invention, in order to dope the nitride crystal with oxygen, the content of Si as the n-type dopant is preferably set to a certain amount or less.

In the second invention, it is preferable to use a nitride crystal raw material in which oxygen is uniformly mixed, and the carrier concentration in the nitride crystal obtained thereby can be made uniform.
In the crystal growth method of the second invention, the nitride crystal raw material is dissolved in the reaction vessel, and at the same time, the nitride crystal is grown. Oxygen uniformly mixed with the nitride crystal raw material is gradually released into the reaction vessel when dissolved, and sequentially taken into the nitride crystal. Since oxygen is uniformly mixed in the nitride crystal raw material, the amount of oxygen taken in during the growth process of the nitride crystal is constant, and the carrier concentration contained in the nitride crystal is uniform. As described above, in the second invention, mainly by limiting the dopant supply source to the nitride crystal raw material, the oxygen dopant can be uniformly added to the nitride crystal. It is preferable for the nitride crystal to have a uniform carrier concentration as a whole because the conductivity of the crystal can be stabilized and the quality of the nitride crystal can be improved.

  The nitride crystal obtained by the ammonothermal method preferably activates the dopant by annealing. By annealing, the dopant contained in the nitride single crystal can be activated to make the carrier activation rate 10 to 90%, and in addition, the mobility can be sufficiently improved. The annealing time is not particularly limited, but is preferably 5.5 hours or more, more preferably 8 hours or more, further preferably 10 hours or more, and particularly preferably 12 hours or more. . Further, it is preferably within 300 hours, more preferably within 150 hours, further preferably within 120 hours, and particularly preferably within 100 hours.

  The annealing temperature is preferably 750 ° C. or higher, more preferably 800 ° C. or higher, further preferably 850 ° C. or higher, and particularly preferably 900 ° C. or higher. The annealing temperature is preferably 1250 ° C. or less, more preferably 1200 ° C. or less, further preferably 1100 ° C. or less, and particularly preferably 1050 ° C. or less. If it is 1250 degrees C or less, it is easy to suppress the mass reduction by annealing treatment. The temperature during the annealing process may be kept constant, may be changed stepwise, or may be changed continuously. Moreover, you may implement combining these suitably.

  The annealing treatment is preferably performed in an atmosphere in which one or more selected from the group consisting of ammonia, nitrogen, oxygen, and hydrogen exists. Preference is given to carrying out in an atmosphere in which at least nitrogen is present. At this time, the ratio of nitrogen is preferably 50% or more, more preferably 60% or more, and further preferably 70% or more. Furthermore, it can be suitably performed even in an atmosphere of 100% nitrogen.

(Bulk density of crystal raw material)
Usually, in the ammonothermal method, a raw material filling region for filling a nitride crystal raw material and a crystal growth region for installing a seed crystal are provided in a reaction vessel, and the nitride crystal raw material is dissolved in the raw material filling region. A nitride crystal is grown on the seed crystal in the crystal growth region. At this time, a temperature difference is provided between the raw material filling region and the crystal growth region, and control is performed so that the nitride crystal raw material is more dissolved in the raw material filling region and high-quality nitride crystals are more likely to precipitate in the crystal growth region. It is preferable. For this reason, a nitride crystal raw material having a bulk density in the range of 0.7 to 4.5 g / cm ³ is used. More preferably, it is 1.5 g / cm ³ or more, more preferably 1.8 g / cm ³ or more, more preferably 4.0 g / cm ³ or less, and further preferably 3.0 g / cm ³ or less. It is. It is preferable to use a nitride crystal raw material having a bulk density in such a range alone or in combination because the solubility of the nitride crystal raw material in the raw material filling region described later can be adjusted. Furthermore, since the solubility of the nitride crystal raw material can be improved and the dissolution can proceed uniformly, oxygen contained in the nitride crystal raw material can be uniformly and efficiently doped into the resulting nitride crystal, It is preferable because a good quality nitride crystal can be obtained.

  The “bulk density” of each of the nitride crystal raw materials having different bulk densities means a weight per unit volume of the filled crystal raw material in a suitable container, and the filled nitride crystals. It can be determined by dividing the weight of the raw material by the volume of the container. Usually, aggregates of nitride crystal raw materials that are said to have the same bulk density have similar shapes, and aggregates that have a maximum value of 100 times or less with respect to the minimum value of the grain size are substantially equivalent. It is called “one kind of nitride crystal raw material” having a bulk density of One nitride crystal raw material preferably has a small variation in weight per particle, and the standard deviation in the weight per particle varies depending on the size of the reaction vessel used, but generally 8.0. Or less, more preferably 7.0 or less, and even more preferably 6.0 or less. In particular, when the diameter of the reaction vessel is about 26 mm, it is preferable to use a raw material having an average weight of 0.6 to 1.2 g / 1 particle and a standard deviation of 0.35 to 0.48. When the diameter of the reaction vessel is about 60 mm, it is preferable to use a raw material having an average weight of 5.0 to 8.5 g / 1 particle and a standard deviation of 5.4 or less. When the diameter of the reaction vessel is about 130 mm, it is preferable to use a raw material having an average weight of 5.0 to 10.5 g / 1 particle and a standard deviation of 7.0 or less.

In the production method of the second invention, as long as a nitride crystal raw material having a bulk density in the range of 0.7 to 4.5 g / cm ³ is used, even if one kind of nitride crystal raw material is used alone, Two or more types of nitride crystal raw materials having different bulk densities may be used. It is preferable to use one kind of nitride crystal raw material alone because uniform solubility can be achieved and the resulting nitride crystal can be made uniform.

A specific calculation example of the bulk density of the nitride crystal raw material in the second invention will be shown. For example, when 100 g of GaN crystal raw material is installed in the lower region of a cylindrical container having an inner diameter of 20 mm, and the height from the lowermost end (bottom surface inside the cylinder) to the uppermost end of the region containing the raw material is 100 mm The bulk density can be calculated at 100 g / (314 mm ² × 100 mm), and is calculated to be about 3.18 g / cm ³ . It can also be analyzed by performing a CT scan (computed tomography) in a container. For example, when the porosity in the container filled with the raw material was measured by CT scan, it was 70%. Therefore, since the solid volume is about 30%, the density can be calculated from the following equation when the density of gallium nitride is 6.1 g / cm ³ .
6.1 g / cm ³ × 0.3 = 1.83 g / cm ³ (bulk density)

In the production method of the second invention, the convection of the solvent is carried out by controlling the bulk density of the nitride crystal raw material in the raw material filling region in the reaction vessel within a range of 0.7 to 4.5 g / cm ^3. This is preferable because the dissolution rate of the raw material can be improved and high-quality crystals can be efficiently grown without hindering.
The “raw material filling region” as used in the second invention refers to the horizontal plane including the lowest end of the filled crystal raw material and the filled crystal raw material when the long axis of the reaction vessel before starting the reaction is in the vertical direction. The region in the reaction vessel sandwiched between the horizontal plane including the uppermost end of the.

  The “bulk density” of the nitride crystal raw material in the raw material filling region is the weight per unit volume of the nitride crystal raw material filled in the raw material filling region, and the weight of the nitride crystal raw material is divided by the free volume of the raw material filling region. Can be obtained. Here, the free volume of the raw material filling region is a volume obtained by subtracting the solid volume other than the crystal raw material existing in the raw material filling region from the internal volume of the raw material filling region of the reaction vessel. Examples of such solids include baffle plates and support frames that support seed crystal support frames, crucibles for installing nitride crystal raw materials, baskets, and structures such as network structures, The free volume can be obtained by removing these volumes.

  The bulk density of the nitride crystal raw material in the raw material filling region can be converted into the filling rate of the nitride crystal raw material. The filling rate (unit%) can be calculated by dividing the bulk density by the specific gravity of the nitride crystal raw material and multiplying by 100.

When the bulk density of the nitride crystal raw material in the raw material filling region is too large, the volume of the space generated between the crystal raw materials is reduced, so that the convection of the solvent is inhibited and the raw material dissolution rate is reduced. For this reason, it becomes difficult to grow high-quality grown crystals with high productivity. On the other hand, if the bulk density of the nitride crystal raw material is too small, the crystal raw material can be sufficiently dissolved, but the input amount of the raw material per volume is reduced, and a sufficient amount of the dissolved raw material is efficiently supplied to the crystal growth region. It becomes difficult to quickly grow a nitride crystal of sufficient size. The bulk density of the nitride crystal raw material in the raw material filling region is preferably 0.7 g / cm ³ or more, more preferably 0.8 g / cm ³ or more, and 0.9 g / cm ³ or more. More preferably, it is more preferably 1.0 g / cm ³ or more, and particularly preferably 1.1 g / cm ³ or more. Further, the bulk density of the nitride crystal raw material in the raw material filling region is preferably 4.5 g / cm ³ or less, more preferably 4.0 g / cm ³ or less, and 3.6 g / cm ³ or less. More preferably, it is more preferably 3.2 g / cm ³ or less, and particularly preferably 3.0 g / cm ³ or less. By setting the bulk density of the nitride crystal raw material in the raw material filling region within the above range, the dissolution rate of the raw material can be improved and high-quality crystals can be efficiently grown without inhibiting the convection of the solvent.

  The bulk density of the nitride crystal raw material in the raw material filling region can be controlled, for example, by selecting the particle size, particle size distribution, shape, and the like of the nitride crystal raw material to be used. In other words, when a nitride crystal raw material is placed in the raw material filling region in the reaction vessel, a nitride crystal raw material having a particle size or shape that allows the individual nitride crystal raw material particles to easily overlap with each other having a gap is selected. , The bulk density can be lowered. For example, it is possible to reduce the bulk density by using a nitride crystal material having a large particle size or using a nitride crystal material having an asymmetric and irregular particle shape. Conversely, when a nitride crystal raw material is selected in the raw material filling region in the reaction vessel, a nitride crystal raw material having a particle size or shape in which individual nitride crystal raw material particles tend to closely overlap each other is selected. The bulk density can be increased. For example, a nitride crystal raw material with a small particle diameter, a nitride crystal raw material with a large particle diameter and a nitride crystal raw material with a small particle diameter that can enter the gap, or a particle shape that is easy to pack closely It is possible to increase the bulk density by using a uniform nitride crystal raw material having

  The bulk density of the nitride crystal raw material in the raw material filling region can also be controlled by applying energy after putting the crystal raw material in the raw material filling region. For example, the bulk density can be controlled by applying vibration, rotating the reaction vessel, or mixing the filled crystal raw material using a stirring rod or rotating blade after putting the crystal raw material into the raw material filling region. it can. The vibration may be applied by directly swinging the reaction vessel or by non-contact means such as ultrasonic waves.

  The bulk density of the crystal raw material in the raw material filling region can be controlled by installing a structure in the raw material filling region. As the structure, for example, a network structure capable of allowing the solvent to pass through but not allowing the crystal raw material to pass through can be preferably employed. With such a network structure, the bulk density can be controlled by limiting the existence area of the crystal raw material in the raw material filling region. That is, the bulk density can be controlled to be low by restricting the existence area of the crystal raw material to a narrow area and ensuring a wide area where the crystal raw material cannot exist. For example, the bulk density can be reduced by filling a crystal structure in a network structure having a volume smaller than that of the raw material filling region and then putting the crystal raw material in the raw material filling region.

  Conversely, the bulk density may be controlled by installing a hollow network structure not filled with a crystal raw material in the raw material filling region. For example, such a network structure can be mixed with the crystal raw material and filled in the raw material filling region. At this time, the bulk density can be controlled by adjusting the mixing ratio of the two. The network structure may be fixed in advance in the raw material filling region. Moreover, you may use multiple network structures of such various aspects. Furthermore, it is also possible to employ a non-network structure that allows the solvent to pass therethrough.

(Grain size of nitride crystal raw material)
The preferable range of the particle size of the nitride crystal raw material used in the second invention varies depending on the size of the reaction vessel in terms of ease of adjusting the bulk density and ease of handling. Specifically, if the size of the reaction vessel is larger, the particle size of the nitride crystal raw material may be larger. For example, when using a reaction vessel having a diameter of about 26 mm or about 30 mm, the particle diameter is preferably 0.5 μm or more, more preferably 1 μm or more, and more preferably 10 μm or more. It is more preferable to use a material that is 20 mm or less, more preferably a material that is 15 mm or less, more preferably a material that is 10 mm or less. For example, when using a reaction vessel having a diameter of about 60 mm, the particle diameter is preferably 0.5 μm or more, more preferably 1 μm or more, and more preferably 10 μm or more. It is more preferable to use a material that is 50 mm or less, more preferably 30 mm or less, and even more preferably 20 mm or less.

  For example, when using a reaction vessel having a diameter of about 130 mm, the particle diameter is preferably 0.5 μm or more, more preferably 1 μm or more, and more preferably 10 μm or more. It is more preferable to use a material that is 120 mm or less, more preferably 60 mm or less, and even more preferably 30 mm or less.

  The nitride crystal raw material used in the second invention preferably has a structure in which the nitride crystal raw material particles are aggregated. Specifically, it is preferable to use tertiary particles obtained by agglomerating secondary particles. The particle size of the secondary particles is preferably 100 μm or more, more preferably 200 μm or more, and further preferably 300 μm or more. Moreover, it is preferable that it is 1000 micrometers or less, It is more preferable that it is 900 micrometers or less, It is further more preferable that it is 800 micrometers or less. The particle size of the tertiary particles is preferably 1 mm or more, more preferably 5 mm or more, further preferably 10 mm or more, and preferably 120 mm or less, more preferably 60 mm or less. Preferably, it is 50 mm or less, more preferably 30 mm or less, and particularly preferably 20 mm or less. The particle size of the secondary particles can be measured with an optical microscope or the like. If it is 1 mm or more as in the case of tertiary particles, it can be visually confirmed, and can be measured, for example, with calipers or a ruler. Further, for tertiary particles formed by agglomeration of secondary particles, the maximum diameter of the tertiary particles coincides with the “particle diameter” of the nitride crystal raw material described above.

  In the nitride crystal having a structure in which the above-mentioned nitride crystal raw material particles are aggregated, the primary particle means a nano-unit single crystal, and these single crystals are aggregated and bonded to each other to form a polycrystal. Secondary particles are formed. Usually, primary particles cannot be discriminated as particles because they are combined and integrated with each other. Furthermore, when the shape of the nitride crystal raw material used in the present invention is a bowl shape as will be described later, the maximum diameter of the particles is determined including the protrusions on the surface.

  Regarding the particle size distribution of the nitride crystal raw material used in the second invention, the crystal raw material having a particle size of 0.01 μm or more occupies 20% or more, more preferably 30% or more of the total volume of the crystal raw material. It is preferable because the gap between the raw materials is sufficiently vacant and the solvent can be convected. Further, the nitride crystal raw material having a particle size of 1.0 mm or more accounts for 10% or more, more preferably 30% or more, further preferably 50% or more, particularly preferably 80% or more of the entire volume of the nitride crystal raw material. This is preferable because the gap between the nitride crystal raw materials is sufficiently vacant and the solvent can be convected.

(Shape of nitride crystal raw material)
The shape of the nitride crystal raw material used in the second invention is spherical, granular with an elliptical cross section, plate shape, rectangular shape, triangular shape, and bowl shape (refers to a state in which the surface is uneven and the surface area is large). There may be. It is preferable that a certain gap is provided between the crystal raw materials so as not to greatly inhibit the convection of the solvent. Moreover, since adjustment of a bulk density becomes easy, it is more preferable that they are elliptical granular form, a rectangular shape, a triangular shape, a bowl shape, and a confetti shape. The shape of the nitride crystal raw material used in the second invention may be the same as that in the first invention.

  As the nitride crystal raw material used in the second invention, it is preferable to use a material that has a surface that is easily dissolved in a solvent and a surface that is not easily dissolved in a solvent. For example, when a GaN crystal is grown using an ammonia solvent by the ammonothermal method, the + C plane (Ga plane) and the M plane are relatively insoluble in the ammonia solvent, and therefore a material on which other planes appear is used. It is preferable to use it.

(Crystal growth by ammonothermal method)
In the manufacturing method of the second invention, after filling the raw material filling region with a crystal raw material, a nitride crystal is manufactured by an ammonothermal method.
The ammonothermal method is a method for producing a desired nitride single crystal using a solvent containing nitrogen such as an ammonia solvent in a supercritical state and / or a subcritical state and a dissolution-precipitation reaction of a crystal raw material. It is. Crystal growth is performed by using the temperature dependence of the solubility of the crystal raw material in a solvent such as ammonia to precipitate a crystal by generating a supersaturated state due to a temperature difference.

  According to the manufacturing method of the second invention, a nitride crystal having high quality can be efficiently manufactured at a high growth rate with high raw material utilization efficiency. According to the second invention, as the growth rate in the c-axis direction, 100 μm / day or more can be achieved, further 300 μm / day or more can be achieved, and still 600 μm / day or more can be achieved. Can do. Further, as the growth rate in the m-axis direction, 30 μm / day or more can be achieved, further 100 μm / day or more can be achieved, and still 300 μm / day or more can be achieved. Furthermore, as the growth rate in the a-axis direction, 50 μm / day or more can be achieved, further 600 μm / day or more can be achieved, and still 1500 μm / day or more can be achieved.

(Mineralizer)
In the second invention, it is preferable to use a mineralizer when growing the nitride crystal by the ammonothermal method. The mineralizer is used to improve the solubility of the crystal raw material in a solvent containing nitrogen such as ammonia. As the mineralizer, the same mineralizers as described in the first invention can be used, and the same applies to preferred embodiments.

In the production method of the second invention, it is preferable to use the mineralizer after purification and drying as necessary in order to prevent impurities from being mixed into the nitride crystal to be grown. The purity of the mineralizer is usually 95% or higher, preferably 99% or higher, more preferably 99.99% or higher.
In order to reduce the supply of oxygen from other than the nitride raw material, it is desirable that the amount of water and oxygen contained in the mineralizer is as small as possible, and the content thereof is preferably 1000 ppm or less, and is preferably 10 ppm or less. More preferred is 1 ppm or less.

In order to remove water and oxygen from the atmosphere in the reaction vessel, the inside of the reaction vessel is sealed and heated to 200 ° C. or higher, and the moisture adhering to the surface of the member is vaporized as 1 × 10 ⁻⁷ Pa using a pump or the like. A method of degassing is conceivable. Furthermore, a method of introducing a mineralizer with a high purity gas is also conceivable. There is also a method in which members and raw materials are stored in advance in a dry atmosphere with a dew point of 0 ° C. or less, and the reaction vessel and the members and raw materials to be placed in the reaction vessel are assembled therein.

(solvent)
As the solvent used in the production method of the second invention, a solvent containing nitrogen can be used. As the solvent, the same solvents as described in the first invention can be used, and the same applies to preferred embodiments.
In order to reduce the supply of oxygen from other than the nitride raw material, it is desirable that the amount of water and oxygen contained in the solvent is as small as possible, and the content thereof is preferably 1000 ppm or less, and preferably 10 ppm or less. More preferred is 0.1 ppm or less. When ammonia is used as a solvent, the purity is usually 99.9% or more, preferably 99.99% or more, more preferably 99.999% or more, and particularly preferably 99.9999% or more. .

(Reaction vessel and installation components)
The nitride crystal growth step of the second invention is carried out in a reaction vessel. “Reaction vessel” means a vessel for producing nitride crystals in the presence of a solvent in a supercritical and / or subcritical state. Preferred examples include capsules to be used. The reaction vessel used in the second invention is described in JP-T-2003-511326 (International Publication No. 01/024921 pamphlet) and JP-T-2007-509507 (Patent Publication of International Publication No. 2005/043638). Thus, an autoclave having a mechanism for adjusting the pressure applied to the reaction vessel and its contents from the outside of the reaction vessel may be used, or an autoclave without such a mechanism may be used.

  The reaction vessel is preferably selected from those that can withstand the high-temperature and high-pressure conditions when the nitride crystal is grown. A material composed of a material having high temperature strength and corrosion resistance is preferable. Particularly, a Ni-based alloy having excellent corrosion resistance to a solvent such as ammonia, and Co-based materials such as Stellite (registered trademark of Deloro Stellite Company, Inc.). What is comprised with the alloy is preferable. More preferably, it is a Ni-based alloy. Specifically, Inconel 625 (Inconel is a registered trademark of Huntington Alloys Canada Limited, the same applies hereinafter), Nimonic 90 (Nimonic is a registered trademark of Special Metals Wiggin Limited, the same applies hereinafter), RENE41 (Teledyne). Allvac, Inc.), Inconel 718 (Inconel is a registered trademark of Huntington Alloys Canada Limited), Hastelloy (registered trademark of Haynes International, Inc.), Waspaloy (registered trademark of United Technologies, Inc.).

  The composition ratio of these alloys depends on the temperature and pressure conditions of the solvent in the system, and the reactivity with mineralizers contained in the system and their reactants and / or the oxidizing power / reducing power, pH, etc. It may be selected as appropriate. Although the alloys used for these pressure resistant containers have high corrosion resistance, they do not have such high corrosion resistance that they have no influence on the crystal quality. In these alloys, in a supercritical solvent atmosphere, particularly in a more severe corrosive environment containing a mineralizer, components such as Ni, Cr and Fe are dissolved in the solution and taken into the crystal. Since these may affect the carrier concentration of the obtained crystal, it is preferable to reduce the incorporation of these impurities as much as possible. Therefore, in the second invention, in order to suppress the inner surface corrosion of these pressure resistant containers, a method of directly lining or coating the inner surface with a material having further excellent corrosion resistance, or a capsule made of a material having further excellent corrosion resistance in the pressure resistant container. It is preferable to form the reaction container by a method of arranging the reaction container.

The reaction container has an installation member in the reaction container. The installation member means a generic name for members included in the reaction vessel. Examples of the installation member include structures such as a wire, a baffle plate, a support frame that supports a seed crystal support frame, a crucible for installing a nitride crystal raw material, a basket, and a net-like structure.
The reaction vessel and the installation member preferably have a structure in which the n-type dopant is not exposed on the surface. In order not to expose the n-type dopant on the surface, the reaction vessel and the installation member may be formed of a constituent material having a low content of the n-type dopant, and the surface of the reaction vessel and the installation member may be coated or lined. By preventing the n-type dopant from being exposed to the surface, it is possible to prevent a dopant not derived from the nitride crystal raw material from being taken into the nitride crystal in the growth process.

In the case where the reaction vessel and the installation member are formed of a constituent material having a low n-type dopant content, the reaction vessel and the installation member are preferably formed of a constituent material having an n-type dopant content of 1000 ppm or less. The amount of the n-type dopant in the constituent material may be 1000 ppm or less, more preferably 100 ppm or less, and even more preferably 10 ppm or less.
Moreover, when coating or lining the surfaces of the reaction vessel and the installation member, it is preferable that the n-type dopant is coated with a coating material or a lining material having an amount of 1000 ppm or less. The amount of the n-type dopant in the coating material or lining material may be 1000 ppm or less, more preferably 100 ppm or less, and even more preferably 10 ppm or less. By setting the amount of the n-type dopant to the upper limit value or less, it is possible to more accurately set conditions for obtaining a nitride crystal having a desired carrier concentration.

The performance required for the constituent material of the reaction vessel and the installation member, the lining material and the coating material is required to have a low dissolution rate in the crystal growth atmosphere in the ammonothermal method. The dissolution rate may be 3 × 10 ⁻² wt% / day or less, more preferably 3 × 10 ⁻³ wt% / day or less.

The constituent material and the coating material forming the reaction vessel and the installation member preferably contain a platinum group or a platinum group alloy.
Examples of the platinum group include Pt, Au, Ir, Ru, Rh, Pd, and Ag. The platinum group alloy refers to an alloy mainly composed of these noble metals. Among platinum group alloys, it is preferable to use Pt or an alloy containing Pt and Ir having excellent corrosion resistance.
When the inner wall of the reaction vessel is a platinum group or a platinum group alloy, or when the reaction vessel and the surface of the installation member are coated with a platinum group or a platinum group alloy, the coating material should be an alloy containing Pt and Ga. It is preferable to use an alloy containing Ir. These platinum group-containing alloys are suitable for coating and can have excellent corrosion resistance.
The Ir content in the alloy is preferably 30% by weight or less of the total weight of the alloy, and more preferably 25% by weight or less. By making the Ir content not more than the above upper limit value, the reaction vessel can have excellent corrosion resistance.

  As the lining material, it is possible to use at least one metal or element of Pt, Ir, Ag, Pd, Rh, Cu, Au, and C, or an alloy or compound containing at least one metal. In order to make lining easier, more preferably, at least one or more kinds of metals or elements of Pt, Ag, Cu and C, or an alloy or compound containing at least one kind of metals can be used. As a lining material, for example. Pt simple substance, Pt-Ir alloy, Ag simple substance, Cu simple substance, graphite, etc. are also mentioned.

The reaction vessel and the installation member preferably have pressure resistance and corrosion resistance. In order to further improve the corrosion resistance of the reaction vessel and the installation member, it is preferable to use the excellent corrosion resistance of the platinum group or platinum group alloy. The reaction vessel and the installation member can be made of a platinum group or a platinum group alloy, and the inner wall of the reaction vessel can be made of a platinum group or a platinum group alloy.
Furthermore, the reaction vessel is preferably a pressure resistant vessel. In particular, when the inner wall of the reaction vessel is made of a platinum group or a platinum group alloy, or when the reaction vessel and the surface of the installation member are coated or lined with a platinum group or a platinum group alloy, the pressure resistance of other materials forming the reaction vessel It is preferable to ensure the property.
Ti, W, Ni, Mo, Ru, Nb and alloys thereof can be used as materials having pressure resistance and corrosion resistance other than the platinum group. Preferably, Mo, W, and Ti.

(manufacturing device)
As a crystal manufacturing apparatus that can be used in the method for manufacturing a nitride crystal of the second invention, the same apparatus as that described in the first invention can be used, and the same applies to the preferred embodiments.

(Manufacturing process)
An example of the method for producing a nitride crystal of the second invention will be described. When carrying out the method for producing a nitride crystal of the second invention, first, a seed crystal, a nitrogen-containing solvent, a raw material, and a mineralizer are put in a reaction vessel and sealed. Here, as the seed crystal, the plane orientation of the main surface is not particularly limited, but the main surface becomes a nonpolar plane or a semipolar plane by cutting a crystal grown with the C plane as the main plane in a desired direction. A substrate can be obtained. Thereby, a seed crystal having a nonpolar plane such as an M plane and a semipolar plane such as (10-11) or (20-21) can be obtained.

  In the production process of the second invention, it is preferable to further provide a dopant source isolation step prior to introducing the nitride crystal raw material, mineralizer, baffle plate, seed crystal and other materials into the reaction vessel. The dopant source isolation step refers to a step of removing oxygen, oxide, or water vapor present in the reaction vessel. The dopant source isolation step includes a step of coating or lining the surface of a member containing oxygen, oxide, or water vapor among the reaction vessel and various members installed in the reaction vessel. Coating or lining the surface of the member can prevent the dopant from being exposed and incorporated into the nitride crystal.

In the second invention, unintentional doping occurs when an n-type dopant other than that derived from the nitride crystal raw material is incorporated into the nitride crystal. In the second invention, unintentional doping can be suppressed by providing a dopant source isolation step before the growth step.
In order to remove oxygen, oxides or water vapor present in the reaction vessel, the reaction vessel is filled with a nitride crystal raw material, and then the reaction vessel is evacuated, or an inert gas is contained in the reaction vessel. A method that satisfies the above can be adopted. In addition, oxygen, oxides, or water vapor can be removed by drying the reaction vessel and various members included in the reaction vessel.

  At the time of introducing the material, an inert gas such as nitrogen gas may be circulated. Usually, the seed crystal is placed in the reaction vessel at the same time or after the filling of the nitride crystal raw material and the mineralizer. The seed crystal is preferably fixed to a noble metal jig similar to the noble metal constituting the inner surface of the reaction vessel. After installation of the seed crystal, heat deaeration may be performed as necessary.

When the production apparatus shown in FIG. 1 is used, the capsule 20 is sealed in the capsule 20 which is a reaction vessel by putting the seed crystal 7, a nitrogen-containing solvent, a raw material, and a mineralizer, and then sealing the capsule 20 with an autoclave (pressure resistance). Container) 1, and preferably, the space between the pressure-resistant container and the reaction container is filled with the second solvent to seal the pressure-resistant container.
Thereafter, the whole is heated to bring the inside of the reaction vessel into a supercritical state or a subcritical state. In the supercritical state, the viscosity of a substance is generally low and it diffuses more easily than a liquid, but has a solvating power similar to that of a liquid. The subcritical state means a liquid state having a density substantially equal to the critical density near the critical temperature. For example, in the raw material filling part, the raw material is melted as a supercritical state, and in the crystal growth part, the temperature is changed so as to be in the subcritical state, and crystal growth utilizing the difference in solubility between the supercritical state and the subcritical state raw material is also performed. Is possible.

  In the supercritical state, the reaction mixture is generally maintained at a temperature above the critical point of the solvent. When an ammonia solvent is used, the critical point is a critical temperature of 132 ° C. and a critical pressure of 11.35 MPa. However, if the filling rate with respect to the volume of the reaction vessel is high, the pressure far exceeds the critical pressure even at a temperature below the critical temperature. In the second invention, the “supercritical state” includes such a state exceeding the critical pressure. Since the reaction mixture is enclosed in a constant volume reaction vessel, the increase in temperature increases the pressure of the fluid. In general, if T> Tc (critical temperature of one solvent) and P> Pc (critical pressure of one solvent), the fluid is in a supercritical state.

  Under supercritical conditions, a sufficient growth rate of nitride crystals can be obtained. The reaction time depends in particular on the reactivity of the mineralizer and the thermodynamic parameters, ie temperature and pressure values. During the synthesis or growth of the nitride crystal, the pressure in the reaction vessel is preferably 30 MPa or more, more preferably 60 MPa or more, and further preferably 100 MPa or more, from the viewpoint of crystallinity and productivity. . The pressure in the reaction vessel is preferably 700 MPa or less, more preferably 500 MPa or less, further preferably 350 MPa or less, and particularly preferably 300 MPa or less from the viewpoint of safety. The pressure is appropriately determined depending on the filling rate of the solvent volume with respect to the temperature and the volume of the reaction vessel. Originally, the pressure in the reaction vessel is uniquely determined by the temperature and the filling rate. However, in practice, raw materials, additives such as mineralizers, temperature heterogeneity in the reaction vessel, and free volume Depending on the presence of

  From the viewpoint of crystallinity and productivity, the lower limit of the temperature range in the reaction vessel is preferably 320 ° C or higher, more preferably 370 ° C or higher, and further preferably 450 ° C or higher. From the viewpoint of safety, the upper limit value is preferably 700 ° C. or less, more preferably 650 ° C. or less, and further preferably 630 ° C. or less. In the method for producing a nitride crystal of the second invention, the temperature of the raw material filling region in the reaction vessel is preferably higher than the temperature of the crystal growth region. The temperature difference (| ΔT |) is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, preferably 100 ° C. or lower, and 90 ° C. or lower from the viewpoints of crystallinity and productivity. More preferably, 80 ° C. or lower is particularly preferable. The optimum temperature and pressure in the reaction vessel can be appropriately determined depending on the type and amount of mineralizer and additive used during crystal growth.

  In order to achieve the temperature range and pressure range in the reaction vessel, the injection rate of the solvent into the reaction vessel, that is, the filling rate is the free volume of the reaction vessel, that is, when crystal raw materials and seed crystals are used in the reaction vessel. Subtract the volume of the seed crystal and the structure on which the seed crystal is installed from the volume of the reaction vessel, and if a baffle plate is installed, subtract the volume of the baffle plate from the volume of the reaction vessel to remain. Based on the liquid density at the boiling point of the solvent of volume, it is usually 20 to 95%, preferably 30 to 80%, more preferably 40 to 70%. When the capsule 20 as shown in FIG. 1 is used as the reaction vessel, it is preferable to appropriately adjust the amount of the solvent so that the pressure is balanced inside and outside the capsule 20 in the supercritical state of the solvent.

The growth of nitride crystals in the reaction vessel is maintained in a subcritical or supercritical state of a solvent such as ammonia by heating and heating the reaction vessel using an electric furnace having a thermocouple. Is done. The heating method and the rate of temperature increase to a predetermined reaction temperature are not particularly limited, but are usually performed over several hours to several days. If necessary, the temperature can be raised in multiple stages, or the temperature raising speed can be changed in the temperature range. It can also be heated while being partially cooled.
The above-mentioned “reaction temperature” is measured by a thermocouple provided so as to be in contact with the outer surface of the reaction vessel and / or a thermocouple inserted into a hole having a certain depth from the outer surface, and It can be estimated in terms of internal temperature. The average value of the temperatures measured with these thermocouples is taken as the average temperature. Usually, an average value of the temperature of the raw material filling region and the temperature of the crystal growth region is defined as the average temperature.

  In the method for producing a nitride crystal of the second invention, a pretreatment can be added to the seed crystal. Examples of the pretreatment include subjecting the seed crystal to a meltback process, polishing the growth surface of the seed crystal, and washing the seed crystal.

  In the method for producing a nitride crystal of the second invention, when raising the temperature of the autoclave, a constant temperature may be maintained, and the growth crystal growth surface of the seed crystal may be subjected to a meltback treatment. By the meltback treatment, the crystal growth surface of the seed crystal and the crystal nucleus attached to the member in the apparatus can be dissolved. The same explanation as in the first invention can be applied to the conditions, pressure and treatment time of the meltback treatment.

  In the pretreatment, in order to polish the surface of the seed crystal capable of crystal growth, for example, chemical mechanical polishing (CMP) can be performed. The surface roughness of the seed crystal should be, for example, 1.0 nm or less from the viewpoint that the root mean square roughness (Rms) measured by an atomic force microscope performs meltback and subsequent crystal growth evenly. Is preferable, 0.5 nm is more preferable, and 0.3 nm is particularly preferable.

  The reaction time after reaching a predetermined temperature also varies depending on the type of nitride crystal, the raw material used, the type of mineralizer, and the size and amount of the crystal to be produced, but is usually several hours to several hundred days. be able to. During the reaction, the reaction temperature may be constant, or the temperature may be gradually raised or lowered. After a reaction time for forming the desired crystal, the reaction temperature is lowered. The temperature lowering method is not particularly limited, but the heating may be stopped while the heating of the heater is stopped and the reaction vessel is installed in the furnace as it is, or the reaction vessel may be removed from the electric furnace and air cooled. If necessary, quenching with a refrigerant is also preferably used.

After the temperature of the outer surface of the reaction vessel or the estimated temperature inside the reaction vessel is below a predetermined temperature, the reaction vessel is opened. The predetermined temperature at this time is not particularly limited, and is usually −80 ° C. to 200 ° C., preferably −33 ° C. to 100 ° C. Here, the valve may be opened by pipe connection to a valve connection port of the valve attached to the reaction vessel, passing through a vessel filled with water or the like. Furthermore, if necessary, remove the ammonia solvent in the reaction vessel sufficiently by applying a vacuum, etc., then dry, open the reaction vessel lid, etc., and generate nitride crystals and unreacted raw materials and mineralization. Additives such as agents can be removed.
When manufacturing gallium nitride according to the method for manufacturing a nitride crystal of the second invention, preferably refer to Japanese Patent Application Laid-Open No. 2009-263229 for details of materials, manufacturing conditions, manufacturing equipment, and processes other than those described above. Can do. The entire disclosure of this publication is incorporated herein by reference.

  In the method for producing a nitride crystal of the second invention, after the nitride crystal is grown on the seed crystal, post-treatment may be added. The type and purpose of post-processing are not particularly limited. For example, the crystal surface may be melted back in the cooling process after growth so that crystal defects such as pits and dislocations can be easily observed.

(Nitride crystals)
The nitride crystal according to the second invention can be obtained by the manufacturing method described above. The oxygen concentration of the nitride crystal obtained in the second invention is 1.5 × 10 ^{18 to} 2.5 × 10 ¹⁹ atoms / cm ³ , and the dopant activation rate η determined by the following formula is 10 to 90%. It is.
The oxygen concentration of the nitride crystal is preferably 2 × 10 ¹⁸ atoms / cm ³ or more, more preferably 2.5 × 10 ¹⁸ atoms / cm ³ or more, and preferably 2 × 10 ¹⁹ atoms / cm ³ or less. More preferably, it is 1.5 × 10 ¹⁹ atoms / cm ³ or less. Further, the dopant activation rate η is preferably 20% or more, more preferably 30% or more, preferably 85% or less, and more preferably 80% or less.

In the above formula, η is the dopant activation rate (unit:%), [CC] is the carrier concentration (unit: cm ⁻³ ), and [D] is the dopant concentration (unit: cm ⁻³ ).
The carrier concentration of the nitride crystal obtained in the second invention is 5 × 10 ¹⁷ to 2 × 10 ¹⁹ atoms / cm ³ . When the carrier concentration is in the range of 5 × 10 ¹⁷ to 2 × 10 ¹⁹ atoms / cm ³ , a nitride crystal exhibiting appropriate conductivity can be obtained. The carrier concentration is preferably 8 × 10 ¹⁷ atoms / cm ³ or more, more preferably 1 × 10 ¹⁸ atoms / cm ³ or more, and preferably 1.5 × 10 ¹⁹ atoms / cm ³ or less. Preferably it is 1 × 10 ¹⁹ atoms / cm ³ or less.

Further, the Si concentration of the nitride crystal obtained in the second invention is 1.5 × 10 ¹⁶ atoms / cm ³ or less. Preferably, it is 1 × 10 ¹⁶ atoms / cm ³ or less. By making the Si concentration of the nitride crystal within the above range, it is possible to suppress the yield reduction due to cracks by suppressing the distortion of the entire crystal. The Si concentration is preferably 1 × 10 ¹⁶ atoms / cm ³ or less, and more preferably 2 × 10 ¹⁵ atoms / cm ³ or less.

When the halogen content of the nitride crystal obtained in the second invention is increased, the carrier activity is lowered, and therefore it is preferable to control at a low concentration. Examples of the halogen element include F, Cl, Br, and I.
The concentration of F in the obtained nitride crystal is preferably 1 × 10 ¹⁸ atoms / cm ³ or less, more preferably 5 × 10 ¹⁷ atoms / cm ³ or less. The concentration of Cl is preferably 1 × 10 ¹⁹ atoms / cm ³ or less, more preferably 3 × 10 ¹⁸ atoms / cm ³ or less. The concentration of Br is preferably 1 × 10 ¹⁷ atoms / cm ³ or less, and more preferably 1 × 10 ¹⁶ atoms / cm ³ or less. The concentration of I is preferably 1 × 10 ¹⁷ atoms / cm ³ or less, more preferably 3 × 10 ¹⁵ atoms / cm ³ or less.

  In the method for producing a nitride crystal of the second invention, if the nitride crystal raw material is completely dissolved while maintaining the temperature and pressure in the crystal growth conditions, the grown crystal is dissolved. In view of the possibility that a small amount of the nitride crystal raw material remains after the completion of the crystal growth step, the dissolution rate of the nitride crystal raw material is preferably 40% to 96%, preferably 50%. ˜85% is more preferable, and 70% to 80% is particularly preferable. The dissolution rate can be obtained by (the raw material input before the crystal growth step-the raw material remaining after the crystal growth step) / the raw material input before the crystal growth step.

<Nitride crystals>
The nitride crystal of the present invention (first to second inventions) is produced by the method for producing a nitride crystal of the present invention.

(Wafer)
A wafer (semiconductor substrate) having an arbitrary crystal orientation can be obtained by cutting a nitride crystal layer grown by the nitride crystal manufacturing method of the present invention (first to second inventions) in a desired direction. it can. When a nitride crystal having a large and large-diameter M-plane is produced by the production method of the present invention, a large-diameter M-plane wafer can be obtained by cutting in a direction perpendicular to the m-axis. Further, when a nitride crystal having a large-diameter semipolar plane is manufactured by the manufacturing method of the present invention, a large-diameter semipolar plane wafer can be obtained by cutting in parallel to the semipolar plane. These wafers are also characterized by being uniform and of high quality.

(device)
The nitride crystals and wafers of the present invention (first and second inventions) are suitably used for devices such as light emitting elements and electronic devices. Examples of the light-emitting element in which the nitride crystal or wafer of the present invention is used include a light-emitting diode, a laser diode, and a light-emitting element obtained by combining these with a phosphor. In addition, examples of the electronic device using the nitride crystal or wafer of the present invention include a high frequency element, a high withstand voltage high output element, and the like. Examples of the high frequency element include a transistor (HEMT, HBT), and an example of the high breakdown voltage high output element includes a thyristor (IGBT). Since the nitride crystal and wafer of the present invention are characterized by being uniform and of high quality, they are suitable for any of the above applications. Especially, it is suitable for the electronic device use for which high uniformity is especially required.

  The features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[Preparation Example 1]
<Preparation of nitride crystal raw materials used in Examples 1, 3, 6, and 8>
In Example 1, Example 3, Example 6, and Example 8, the bulk density of the GaN polycrystal used as a raw material for the nitride crystal production method was controlled by the following method.
The GaN polycrystals (maximum diameter of tertiary particles 0.5 to 50 mm) produced without using a seed crystal by hydride vapor phase epitaxy (HVPE) are collided with each other. The bulk density was controlled by pulverizing until the maximum diameter of the secondary particles became 0.5 mm to 20 mm. The pulverization at this time was performed by a method of pulverizing GaN polycrystals by colliding with each other at about 26 ° C. in an atmosphere of an atmospheric gas atmosphere and a relative humidity of 50% or less. Note that the crushed GaN polycrystal also maintained a bowl-like shape.
Further, when observed with an optical microscope, the obtained GaN polycrystal is a tertiary particle having a maximum diameter of 0.5 to 20 mm formed by agglomeration of secondary particles having a maximum diameter of 0.5 to 1 mm. I understood it. As the particle size distribution of the tertiary particles, 0.1 to 1.0 mm particles were 1.7% by mass, and 1.0 to 20 mm particles were 98.3% by mass. The bulk density of the obtained GaN polycrystalline material was 1.8 g / cm ³ .

<Example 1>
Crystal growth was performed using the RENE41 autoclave 1 (internal volume of about 345 cm ³ ) as a pressure-resistant container and the Pt—Ir capsule 20 as a reaction container. The inner diameter of the Pt-Ir capsule was 2.5 cm. Capsule filling was performed in a sufficiently dry nitrogen atmosphere glove box. The raw material 8 is weighed 130.36 g of the GaN polycrystal obtained in Preparation Example 1, and a Pt network structure (not shown; 30.4 g, volume 1.39 cm ³⁾ for supporting the burf plate and the seed crystal support frame. ) In the capsule lower region (raw material filling region 9). At this time, the height from the lowermost end (lower part of the capsule) to the uppermost end of the region containing the GaN polycrystal was about 15 cm. Further, about two-thirds of the Pt structure was buried in the region containing the GaN polycrystalline raw material. From the above, the bulk density of the GaN polycrystal in the raw material filling region of the reaction vessel is (GaN polycrystal particle weight 130.36 g) / ((inner capsule circular area 4.9 cm ² ) × (height 15 cm) − (Pt structure) Of 1.39 cm ³ × 2/3)), and was about 1.8 g / cm ³ . In addition, the size of the used polycrystal was 0.5-20 mm on one side, and was a bowl shape.
In addition, when the oxygen concentration of the GaN polycrystal raw material used above was measured by SIMS using Ims-4f manufactured by CAMECA, it was found to be 4.6 × 10 ¹⁸ cm ⁻³ .

Next, a platinum baffle plate 5 was installed between the lower raw material filling region 9 and the upper crystal growth region 6. As the seed crystal 7, a hexagonal GaN single crystal C-plane wafer and M-plane wafer grown by the HVPE method were used. These seed crystals 7 were suspended from a platinum seed crystal support frame by a platinum wire having a diameter of 0.4 mm and placed in the crystal growth region 6 above the capsule.
Next, after a cap made of Pt—Ir was connected to the top of the capsule 20, the weight was measured. A valve similar to the valve 10 in FIG. 1 was connected to a tube attached to the upper part of the cap, and a valve was installed so as to communicate with the vacuum pump 11 and vacuum deaeration was performed. Thereafter, the valve was operated so as to pass through the nitrogen cylinder 13 and the inside of the capsule was purged with nitrogen gas. The vacuum degassing and nitrogen purging were performed five times, and then heating was performed while connected to a vacuum pump to degas the moisture and attached gas in the capsule. Subsequently, HCl gas as an acidic mineralizer was charged at a liquid nitrogen temperature so that the concentration with respect to ammonia was 3 mol% based on flow rate control. Next, after filling with NH ₃ , the capsule 20 was sealed.

Subsequently, after the capsule was inserted into the autoclave equipped with the valve 10, the lid was closed and the weight of the autoclave 1 was measured. Subsequently, the conduit was connected to the vacuum pump 11 through the valve 10 attached to the autoclave, and the valve was opened to perform vacuum deaeration. Nitrogen gas purging was performed several times as in the capsule. Thereafter, the autoclave 1 was cooled with a dry ice ethanol solvent while maintaining the vacuum state, and the valve 10 was once closed. Next, after the conduit was operated to lead to the NH ₃ cylinder 12, the valve 10 was opened again, and NH ₃ was filled in the autoclave 1 without continuously touching the outside air, and then the valve 10 was closed again. The temperature of the autoclave 1 was returned to room temperature, the outer surface was sufficiently dried, and the weight of the autoclave 1 was measured. The weight of NH ₃ was calculated from the difference from the weight before filling with NH ₃ to confirm the filling amount.

Subsequently, the autoclave 1 was housed in an electric furnace composed of a heater divided into two parts in the vertical direction. Thereafter, the temperature difference ΔT between the crystal growth region 6 and the raw material filling region 9 was set to the value shown in Table 1, and the temperature was maintained for 14.7 days. The pressure in the autoclave was about 260 MPa. Further, the variation in the control temperature of the outer surface of the autoclave during the holding was ± 0.3 ° C. or less.
Then, it cooled naturally until the temperature of the outer surface of the autoclave 1 returned to room temperature, the valve 10 attached to the autoclave was opened, and NH ₃ in the autoclave was removed. Thereafter, the autoclave 1 was weighed to confirm the discharge of NH ₃ , the lid of the autoclave was opened, and the capsule 20 was taken out. A hole was made in the tube attached to the upper part of the capsule to remove NH ₃ from the inside of the capsule. When the inside of the capsule was confirmed, gallium nitride crystals were uniformly deposited on the entire surface of the seed crystal on either the C plane or the M plane.

The growth rates in the m-axis, c-axis, and a-axis directions were calculated from the growth thickness and growth days, and the results are shown in Table 1. The weight of the undissolved raw material was confirmed to be 40.88 g. The dissolution rate of the raw materials was calculated and listed in Table 1. Further, when the recovered GaN polycrystalline raw material was confirmed, it was confirmed that the GaN polycrystalline material was totally dissolved and formed into small particles. From this, it is considered that the solvent convected in the raw material filling region 9 and NH ₃ was in contact with the entire GaN polycrystalline raw material.

<Example 2>
In Example 2, as described in Table 1, the same procedure as in Example 1 above was used except that a triangular single crystal GaN obtained by pulverizing a single crystal having a larger bulk density was used as a raw material. A gallium nitride crystal was deposited on the seed crystal.

<Example 3>
In Example 3, NH ₄ I having a purity of 99.999% and GaF ₃ having a purity of 99.999% were used as acidic mineralizers instead of HCl, and the concentrations of I concentration and F concentration with respect to the amount of NH ₃ charged were combined. Each mineralizer was weighed and placed in a capsule so that the amount of the solution was 2.25 mol%, and the growth temperature and pressure were changed as shown in Table 1. The bulk density of the raw materials and other procedures were the same as in Example 1, and gallium nitride crystals were deposited on the seed crystals under the conditions shown in Table 1.
When the weight of the undissolved raw material after the completion of growth was confirmed, it was 82.19 g. From this, the dissolution rate of the GaN polycrystalline raw material was calculated and listed in Table 1. When the recovered GaN polycrystal raw material was confirmed, it was confirmed that it was dissolved as a whole into small particles. This is probably because NH ₃ was in contact with the entire GaN polycrystalline material.

<Example 4>
In Example 4, as described in Table 1, the same procedure as in Example 3 was used, except that a plate-like GaN polycrystalline raw material having a smaller bulk density of 0.8 g / cm ³ was used as the raw material. A gallium nitride crystal was deposited on the seed crystal under the condition of 1.
When a GaN polycrystalline raw material having a relatively small particle size and bulk density is used to fill the raw material filling region 9 so that the bulk density of the GaN polycrystalline raw material becomes 0.8 g / cm ³ , the crystal growth region of the capsule 20 is obtained. The raw material reached a range close to. As a result, the GaN polycrystal raw material near the crystal growth region was not sufficiently dissolved, and a gallium nitride crystal was deposited in a portion other than the seed crystal using this as a nucleus. Therefore, Table 1 shows the predicted values of the growth rate including these spontaneous nucleation crystals.

  From this result, when using a GaN polycrystal raw material with a small bulk density, it is considered preferable to use a reaction vessel that can secure a sufficient distance between the raw material filling region and the crystal growth region.

<Example 5>
In Example 5, as described in Table 1, the same procedure as in Example 3 was used, except that a small granular GaN polycrystalline material having a larger bulk density of 3.2 g / cm ³ was used. A gallium nitride crystal was deposited on the seed crystal under the condition of 1.
The dissolution rate of the GaN polycrystalline raw material was calculated by measuring the weight of the undissolved raw material after completion of the growth. When the recovered GaN polycrystal raw material was confirmed, it was confirmed that it was melted as a whole and further reduced in size. This is probably because NH ₃ was in contact with the entire GaN polycrystalline material. However, it was considered that the dissolution rate was low because the convection of the solvent was somewhat suppressed because the raw material used was small and had a relatively small particle size.

<Example 6>
In Example 6, as described in Table 1, a mixture of the bowl-shaped GaN polycrystal and powdered GaN polycrystal used in Example 1 so that the bulk density in the raw material filling region of the reaction vessel is further increased Was used. The bulk density measured for the powdery polycrystalline GaN used here was 1.8 g / cm ³ .
The raw material mixing procedure of this example was as follows. First, a bowl-like GaN polycrystal having a large bulk density was added. Thereafter, powdery polycrystalline GaN was charged, but the raw material was charged so as to fill the gaps between the candy-like GaN polycrystals by shaking the capsule.

First, 74.2 g of a cage-shaped GaN polycrystal having a bulk density of 1.8 g / cm ³ alone is introduced into a Pt-Ir capsule having an inner diameter of 2.5 cm. When 55.8 g of powdery GaN polycrystal having a particle size of 1.8 g / cm ³ is added, the capsule is shaken, and the powdery GaN polycrystal is packed into the gaps between the bowl-shaped GaN polycrystals, the height is 8.8 cm. Became. The bulk density of the filled GaN polycrystal is (GaN particle weight 130 g) / ((capsule circular area 4.9 cm ² ) × (height 8.8 cm) − (volume of Pt structure 1.39 cm ^3). × 2/3)) = about 3.0 g / cm ³ .
This is because the bulk density of the ridge-shaped GaN polycrystal is 1.8 g / cm ³ , and the density of gallium nitride, which is the maximum theoretical bulk density, is about 6.1 g / cm ³ . This corresponds to about 3.0 g / cm ³ calculated by occupying 30% volume and filling the remaining 70% with powdery GaN polycrystals.
A gallium nitride crystal is deposited on the seed crystal under the conditions shown in Table 1 in the same manner as in Example 3 except that the GaN polycrystal is filled as described above. Since the bulk density in the raw material filling region is increased, the growth rate on the seed crystal is somewhat slow, but the crystal can be grown for a long time.

<Example 7>
In Example 7, as described in Table 1, the triangular GaN single crystal obtained by pulverizing the single crystal used in Example 2 so that the bulk density in the raw material filling region of the reaction vessel was further increased, What mixed the powdery GaN polycrystal used in Example 6 was used. The bulk density measured alone for the triangular GaN single crystal used here was 2.5 g / cm ³ .

  The raw material mixing procedure of this example was as follows. First, a triangular GaN single crystal having a large bulk density was added. Thereafter, powdery polycrystalline GaN was added, and the raw material was charged so as to fill the gaps in the triangular GaN single crystal by shaking the capsule.

The bulk density of the triangular GaN single crystal alone is 2.5 g / cm ³ , and the density of gallium nitride, which is the maximum theoretical bulk density, is about 6.1 g / cm ^3. The GaN single crystal occupies about 40% of the volume and the remaining 60% agreed with the bulk density of 3.6 g / cm ³ calculated by filling the gap with powdery GaN polycrystal.
A gallium nitride crystal is deposited on the seed crystal under the conditions shown in Table 1 in the same manner as in Example 3 except that the GaN polycrystal is filled as described above. Since the bulk density in the raw material filling region is further increased, the growth rate on the seed crystal is remarkably slow, but crystal growth for a long period is possible.

<Example 8>
(Crystal growth)
Preparation using platinum-lined inner diameter of 20 mm, length of 350 mm, Inconel 625 autoclave (about 110 ml), fully dried into pBN crucible with inner diameter of 12 mm, length of 120 mm, wall thickness of 1-2 mm 7.23 g of the GaN polycrystalline material obtained in Example 1 was put and placed at the bottom of the autoclave. The bulk density of the raw material filling region was 0.8 g / cm ³ . Then, by using the well-dried 99.99% of the NH ₄ Cl 2.6 g as a mineralizer, the reaction vessel was weighed mineralizer to Cl concentration of 1.92 mol% with respect to the filling amount of NH ₃ Was put into an autoclave. Thereafter, two baffle plates and two seed crystals were installed. The installed seed crystal had a weight with 218.1 mg as the principal plane of the c-plane and a weight of 28.1 mg with the m-plane as the principal plane. After installing the seed crystal, the autoclave lid fitted with the valve was quickly closed and the autoclave was weighed. Subsequently, the conduit was operated to be connected to a vacuum pump through a valve attached to the autoclave, and the valve was opened to perform vacuum deaeration. Thereafter, the autoclave was cooled with a dry ice methanol solvent while maintaining the vacuum state, and the valve was once closed. Next, after the conduit was operated to lead to the NH ₃ cylinder, the valve was opened again, and NH ₃ was filled in the autoclave without continuously touching the outside air, and then the valve was closed again. The temperature of the autoclave was returned to room temperature, and the increased amount of NH ₃ filled after the outer surface was sufficiently dried was measured.

Subsequently, the autoclave was housed in an electric furnace composed of a heater divided into two parts in the vertical direction. The temperature of the lower outer surface of the autoclave is raised to 475 ° C. and the temperature of the upper outer surface is increased to 425 ° C. over 5 hours with a temperature difference. After reaching 425 ° C., it was held at that temperature for an additional 96 hours. The pressure in the autoclave was about 144 MPa. Further, the temperature range during holding was ± 5 ° C. or less.
Thereafter, the temperature was lowered for about 8 hours until the temperature of the lower outer surface of the autoclave reached 150 ° C., and then the heating by the heater was stopped and the mixture was naturally cooled in an electric furnace. After confirming that the temperature of the lower outer surface of the autoclave had dropped to almost room temperature, first, the valve attached to the autoclave was opened, and NH ₃ in the autoclave was removed. Thereafter, the autoclave was weighed to confirm the discharge of NH ₃ , and then the valve was once closed and operated so as to communicate with the vacuum pump.

The valve was then opened again and the autoclave NH ₃ was almost completely removed. Thereafter, the lid of the autoclave was opened and the inside was confirmed.
When the weight of the c-plane seed crystal (c-plane seed) was measured, a weight increase of 107.3 mg was confirmed at 325.4 mg, and the m-plane seed crystal (m-plane seed) was A weight increase of 34.7 mg and 6.6 mg was confirmed. This confirmed the precipitation of the gallium nitride crystal. In addition, 1.10 g of GaN powder crystals remained undissolved in the crucible containing the GaN polycrystalline raw material, and the amount of the raw material dissolved was 6.13 g. As shown in Table 1, 85% of the raw material was dissolved. Was dissolved.

<Example 9>
In this example, a nitride crystal was grown using the reactor shown in FIG.
Crystal growth was performed using the RENE41 autoclave 1 as a pressure resistant container and the Pt-Ir capsule 20 as a reaction container. A raw material 8 having a bulk density of 1.8 g / cm ³ obtained in the same manner as in Preparation Example 1 and an oxygen concentration of 20 ppm was weighed and 130 g of polycrystalline GaN particles were weighed and placed in the capsule lower region (raw material filling region 9). Installed. Next, NH ₄ F having a purity of 99.999% sufficiently dried as a mineralizer was weighed so that the F concentration was 0.5 mol% with respect to the amount of NH ₃ charged, and charged into the capsule. Further, a platinum baffle plate 5 was installed between the lower raw material filling region 9 and the upper crystal growth region 6. As the seed crystal 7, three hexagonal GaN single crystals having an m-plane as a main surface and one c-plane wafer were used. The surface of the seed crystal having the m-plane as the main surface is subjected to CMP finish, and the main surface of the c-plane wafer is subjected to LAP treatment. These seed crystals 7 were suspended from a platinum seed crystal support frame by a platinum wire 7 having a diameter of 0.3 mm, and placed in the crystal growth region 6 above the capsule.

Next, a cap made of Pt—Ir was connected to the top of the capsule 20. Next, the tube was connected to the HI gas line, and the valve was operated so as to communicate with the vacuum pump 11 to perform vacuum deaeration. Thereafter, the valve was operated so as to pass through the nitrogen cylinder 13 and the inside of the capsule was purged with nitrogen gas. After performing vacuum degassing and nitrogen purging, it was left overnight while connected to a vacuum pump.
Next, the lower part of the capsule was cooled with liquid nitrogen, and the valve was opened and filled with HI without touching the outside air. Based on the flow rate control, HI was charged as a mineralizer so that the concentration of I was 1.5 mol% with respect to the amount of NH ₃ charged, and then the valve was closed again. The capsule was then removed from the HI line and connected to the NH ₃ gas line. The gas line was evacuated and purged with nitrogen, and then evacuated with a vacuum pump. Thereafter, the valve of the NH ₃ line was operated, and based on the flow rate control, an equimolar amount of HI gas previously filled with NH ₃ was filled, and the valve was closed. The capsules were then removed from the liquid nitrogen and cooled with dry ice ethanol solvent. Subsequently, the valve was opened again and charged with NH ₃ without touching the outside air, and then the valve was closed again. Thereafter, the tube at the top of the cap was sealed with a welder.

Subsequently, the capsule was inserted into the autoclave and the autoclave was sealed. The conduit was connected to the vacuum pump 11 through the valve 10 attached to the autoclave, and the valve was opened to perform vacuum deaeration. Nitrogen gas purging was performed several times as in the capsule. Thereafter, the autoclave 1 was cooled with a dry ice methanol solvent while maintaining the vacuum state, and the valve 10 was once closed. Next, after the conduit was operated to lead to the NH ₃ cylinder 12, the valve 10 was opened again, NH ₃ was filled in the autoclave 1 without continuously touching the outside air, and then the valve 10 was closed again.
Subsequently, the autoclave 1 was housed in an electric furnace composed of a heater divided into two parts in the vertical direction. The temperature was raised while controlling the autoclave outer surface temperature so that the average temperature inside the autoclave was 600 ° C. and the temperature difference inside was 20 ° C. After reaching the set temperature, it was held at that temperature for 16.8 days. The pressure in the autoclave was 215 MPa. Further, the variation in the control temperature of the outer surface of the autoclave during the holding was ± 0.3 ° C. or less.

Thereafter, the temperature of the outer surface of the autoclave 1 was cooled to 400 ° C., a valve 10 which is supplied with the autoclave was opened to remove NH ₃ in the autoclave. At this time, the capsule was divided using the pressure difference between the autoclave and the capsule, and NH ₃ filled in the capsule was also removed.
After the autoclave 1 was weighed to confirm that NH ₃ was discharged, the lid of the autoclave was opened and the capsule 20 was taken out. When the inside of the capsule was confirmed, gallium nitride crystals were grown on both the m-plane and c-plane seed crystals. When observed with the naked eye, it was a yellow to brown transparent crystal, and in particular, no visible defects such as cracks and voids were found in the m-plane gallium nitride crystal. As a result of X-ray diffraction measurement of the gallium nitride crystal grown on the seed crystal, it was confirmed that the crystal system was hexagonal and contained no cubic GaN. The growth rate ((crystal thickness−seed crystal thickness) / growth days) was 220 μm / day in the m-axis direction. As shown in Table 1, the dissolution rate was 51%, and when the recovered GaN polycrystalline raw material was confirmed, it was confirmed that the whole was dissolved into small particles. This is probably because NH ₃ was in contact with the entire GaN polycrystalline material.

When the grown crystal is analyzed by SIMS, the oxygen concentration is 2.20 × 10 ¹⁸ atoms / cm ³ , the Si concentration is 1.14 × 10 ¹⁵ atoms / cm ³ , and the F concentration is 1.15 × 10 ¹⁷ atoms / cm ³ . The cm ³ and I concentration was 2.60 × 10 ¹⁷ atoms / cm ³ .
The obtained gallium nitride crystal was annealed at 1060 ° C. for 24 hours in a nitrogen 90% -ammonia 10% atmosphere, and then hole measurement was performed. As a result of the hole measurement of the annealed GaN crystal, the carrier concentration is 1.90 × 10 ¹⁸ atoms / cm ³ , the mobility is 288 cm ² / V · s, and the specific resistance is 1.08 × 10 ⁻² Ωcm. It was confirmed.

<Example 10>
The conditions shown in Table 1 are as shown in Table 1 except that GaN polycrystalline particles having a bulk density of 2.2 g / cm ³ and an oxygen concentration of 13 ppm obtained by the method according to Preparation Example 1 were used as the raw material 8. The same as for 9. As shown in Table 1, the dissolution rate was 70%, and when the recovered GaN polycrystalline raw material was confirmed, it was confirmed that it was dissolved as a whole into small particles. This is probably because NH ₃ was in contact with the entire GaN polycrystalline material.
When the grown gallium nitride crystal was analyzed by SIMS, the oxygen concentration was 1.50 × 10 ¹⁸ atoms / cm ³ and the Si concentration was 2.06 × 10 ¹⁴ atoms / cm ³ .
The obtained gallium nitride crystal was annealed at 1060 ° C. for 24 hours in a nitrogen 90% -ammonia 10% atmosphere, and then hole measurement was performed. As a result of hole measurement of the GaN crystal after annealing, the carrier concentration is 6.7 × 10 ¹⁷ atoms / cm ³ , the mobility is 335 cm ² / V · s, the specific resistance is 2.40 × 10 ⁻² Ωcm, and the F concentration. it was confirmed that the 4.30 × 1017atoms / cm ^3, I concentration is ^{2.86 × 10 17 atoms / cm 3} .

<Example 11>
The conditions shown in Table 1 are as shown in Table 1, except that GaN polycrystalline particles having a bulk density of 1.8 g / cm ³ and an oxygen concentration of 20 ppm obtained by the method according to Preparation Example 1 are used as raw material 8. The same as for 9. As shown in Table 1, the dissolution rate was 68%, and when the recovered GaN polycrystalline raw material was confirmed, it was confirmed that the whole was dissolved into small particles. This is probably because NH ₃ was in contact with the entire GaN polycrystalline material.
When the grown gallium nitride crystal was analyzed by SIMS, the oxygen concentration was 4.80 × 10 ¹⁸ atoms / cm ³ .
The obtained gallium nitride crystal was annealed at 1060 ° C. for 24 hours in a nitrogen 90% -ammonia 10% atmosphere, and then hole measurement was performed. As a result of the hole measurement of the annealed GaN crystal, the carrier concentration is 2.44 × 10 ¹⁸ atoms / cm ³ , the mobility is 343 cm ² / V · s, and the specific resistance is 2.33 × 10 ⁻² Ωcm. It was confirmed.

<Example 12>
The conditions shown in Table 1 are as in Example 1 except that polycrystalline GaN particles having a bulk density of 1.8 g / cm ³ and an oxygen concentration of 20 ppm obtained by the method according to Preparation Example 1 are used as the raw material 8. The same as for 9. As shown in Table 1, the dissolution rate was 64%, and when the recovered GaN polycrystalline raw material was confirmed, it was confirmed that the whole was dissolved into small particles. This is probably because NH ₃ was in contact with the entire GaN polycrystalline material.
When the grown gallium nitride crystal was analyzed by SIMS, the oxygen concentration was 6.90 × 10 ¹⁸ atoms / cm ³ and the Si concentration was 1.5 × 10 ¹⁶ atoms / cm ³ .
The obtained gallium nitride crystal was annealed at 1060 ° C. for 24 hours in a nitrogen 90% -ammonia 10% atmosphere, and then hole measurement was performed. As a result of hole measurement of the annealed GaN crystal, the carrier concentration is 1.69 × 10 ¹⁸ atoms / cm ³ , the mobility is 330 cm ² / V · s, the specific resistance is 2.11 × 10 ⁻² Ωcm, and the F concentration. Was 2.7 × 10 ¹⁷ atms / cm ³ , the I concentration was 2.5 × 10 ¹⁵ atms / cm ³ or less, and the Cl concentration was 1.5 × 10 ¹⁵ atms / cm ³ or less.

<Example 13>
The conditions shown in Table 1 are as shown in Table 1, except that polycrystalline GaN particles having a bulk density of 2.6 g / cm ³ and an oxygen concentration of 61 ppm obtained by the method according to Preparation Example 1 were used as raw material 8. The same as for 9. As shown in Table 1, the dissolution rate was 46%, and when the recovered GaN polycrystalline raw material was confirmed, it was confirmed that it was dissolved as a whole into small particles. This is probably because NH ₃ was in contact with the entire GaN polycrystalline material.
The obtained gallium nitride crystal was annealed at 1060 ° C. for 24 hours in a nitrogen 90% -ammonia 10% atmosphere, and then hole measurement was performed. From the result of hole measurement of the GaN crystal after annealing, it was confirmed that the carrier concentration was 1.70 × 10 ¹⁸ atoms / cm ³ .

<Example 14>
The conditions shown in Table 1 are as shown in Table 1, except that polycrystalline GaN particles having a bulk density of 1.9 g / cm ³ and an oxygen concentration of 78 ppm obtained by the method according to Preparation Example 1 were used as raw material 8. The same as for 9. As shown in Table 1, the dissolution rate was 84%, and when the recovered GaN polycrystalline raw material was confirmed, it was confirmed that the whole was dissolved into small particles. This is probably because NH ₃ was in contact with the entire GaN polycrystalline material.
When the grown gallium nitride crystal was analyzed by SIMS, the oxygen concentration was 9.9 × 10 ¹⁸ atoms / cm ³ and the Si concentration was 7.4 × 10 ¹⁴ atoms / cm ³ .
The obtained gallium nitride crystal was annealed at 1060 ° C. for 24 hours in a nitrogen 90% -ammonia 10% atmosphere, and then hole measurement was performed. As a result of hole measurement of the GaN crystal after annealing, the carrier concentration is 3.09 × 10 ¹⁸ atoms / cm ³ , the mobility is 226 cm ² / V · s, the specific resistance is 0.90 × 10 ⁻² Ωcm, and the F concentration. Was 2.94 × 10 ¹⁷ atms / cm ³ and the I concentration was 2.35 × 10 ¹⁵ atms / cm ³ or less.

<Example 15>
The same procedure as in Example 9 was performed as the conditions shown in Table 1, except that polycrystalline GaN particles having a bulk density of 1.8 g / cm ³ obtained by the method according to Preparation Example 1 were used as raw material 8. As shown in Table 1, the dissolution rate was 61%, and when the recovered GaN polycrystalline raw material was confirmed, it was confirmed that it was dissolved as a whole into small particles. This is probably because NH ₃ was in contact with the entire GaN polycrystalline material.
When the grown gallium nitride crystal was analyzed by SIMS, the oxygen concentration was 9.00 × 10 ¹⁸ atoms / cm ³ and the Si concentration was 3.00 × 10 ¹⁴ atoms / cm ³ .
The obtained gallium nitride crystal was annealed at 1060 ° C. for 24 hours in a nitrogen 90% -ammonia 10% atmosphere, and then hole measurement was performed. From the results of hole measurement of the annealed GaN crystal, the carrier concentration is 3.90 × 10 ¹⁸ atoms / cm ³ , the mobility is 181 cm ² / V · s, and the specific resistance is 8.86 × 10 ⁻³ Ωcm. It was confirmed.

<Example 16>
The same procedure as in Example 9 was performed as the conditions shown in Table 1, except that polycrystalline GaN particles having a bulk density of 1.8 g / cm ³ obtained by the method according to Preparation Example 1 were used as raw material 8.
When the grown gallium nitride crystal was analyzed by SIMS, the oxygen concentration was 2.00 × 10 ¹⁹ atoms / cm ³ and the Si concentration was 5.00 × 10 ¹⁴ atoms / cm ³ .
The obtained gallium nitride crystal was annealed at 1060 ° C. for 24 hours in a nitrogen 90% -ammonia 10% atmosphere, and then hole measurement was performed. From the result of hole measurement of the annealed GaN crystal, the carrier concentration is 9.54 × 10 ¹⁸ atoms / cm ³ , the mobility is 158 cm ² / V · s, and the specific resistance is 4.09 × 10 ⁻³ Ωcm. It was confirmed.

<Example 17>
The conditions shown in Table 1 are as in Example 1 except that polycrystalline GaN particles having a bulk density of 1.8 g / cm ³ and an oxygen concentration of 148 ppm obtained by the method according to Preparation Example 1 are used as the raw material 8. 9 was performed to obtain a gallium nitride crystal. The obtained gallium nitride crystal was colored black as a whole.

<Comparative Example 1>
In Comparative Example 1, as described in Table 1, a fume-like GaN polycrystal having the smallest bulk density as a raw material (20-30 μm powdery GaN aggregates with a gap between 0.1-20 mm. Gallium nitride is deposited on the seed crystal in the same manner as in Example 3 except that it is used. The bulk density of the GaN polycrystal in the raw material filling region is 0.6 g / cm ³ .

<Comparative example 2>
In Comparative Example 2, as shown in Table 1, gallium nitride was formed on the seed crystal in the same manner as in Example 3 except that the wafer-like single crystal GaN having the largest bulk density was stacked as the raw material and used as the raw material. To precipitate.
The bulk density of the GaN crystal in the raw material filling region is such that the gap when the disk-shaped GaN single crystals having a diameter of 0.4 cm and a thickness of 0.5 cm are stacked is 0.1 cm, and the raw material is 100 kg in a capsule having an inner diameter of 24 cm. The trial calculation when adding is 4.9 g / cm ³ .

  Comparing Example 1 and Example 2 using a chlorine-based mineralizer, the growth rate was the same in each growth direction regardless of the type of GaN raw material (polycrystal or single crystal).

Comparing Example 3 and Example 5 using a fluorine- and iodine-based mineralizer, the growth rate of Example 5 grown using a raw material of GaN polycrystalline particles having a higher bulk density is approximately in the m-axis direction. 1/3, about 1/4 in the c-axis direction, and about 1 / 2.5 in the a-axis direction. This is thought to be due to the fact that the bulk density of the raw material is increased, thereby inhibiting convection of the ammonia solvent and reducing the amount of the raw material dissolved in the ammonia solvent. Furthermore, although it is considered that the growth rate decreases as the bulk density of the raw material increases as in Example 7, the growth rate is a value that can be said to be sufficiently productive. Further, when the bulk density of the raw material is increased to 4.9 g / cm ³ as in Comparative Example 2, the GaN crystal hardly grows. Further, when the bulk density of the raw material is reduced to 0.6 g / cm ³ as in Comparative Example 1, the raw material is depleted in a short period of time, making it difficult to produce GaN crystals.

In Examples 9 to 12, crystals are grown using a GaN crystal raw material having a bulk density of 1.8 to 2.2 g / cm ² and an oxygen concentration of 13 to 20 ppm. In Examples 9 to 12, grown crystals having a carrier concentration of 6.70 × 10 ^{17 to} 2.44 × 10 ¹⁸ atoms / cm ³ are obtained. In Examples 9-12, the activation rate was in the range of 22-86%.
In Example 17, crystals were grown using a GaN crystal raw material having a bulk density of 1.8 g / cm ² and an oxygen concentration of 148 ppm. As estimated from the relationship between the oxygen concentration in the nitride crystal raw materials of Examples 9 to 12 and the carrier concentration of the grown crystal shown in FIG. 3, in Example 17, the carrier concentration is about 2.50 × 10 ¹⁹ atoms / cm ³ . It is considered that a gallium nitride crystal was obtained.
In Example 4, crystals were grown using a GaN crystal raw material having a bulk density of 0.8 g / cm ² and an oxygen concentration of 130 ppm. As estimated from the relationship between the oxygen concentration in the nitride crystal raw materials of Examples 7 to 10 and the carrier concentration of the grown crystal shown in FIG. 3, in Example 4, the carrier concentration is about 1.50 × 10 ¹⁹ atoms / cm ^3. It is considered that a gallium nitride crystal was obtained.

A summary of the results in Table 1 is shown in FIGS.
FIG. 3 is a graph showing the relationship between the oxygen concentration in the nitride crystal raw material and the carrier concentration of the grown gallium nitride crystal. The points represented by diamonds are the results of Examples 9 to 12 and 14, and the points represented by squares are the results of Examples 17 and 4. As shown by the approximate line in FIG. 3, it was found that there is a correlation between the oxygen concentration in the raw material and the carrier concentration of the grown crystal.
FIG. 4 is a graph showing the relationship between the oxygen concentration and the carrier concentration in the grown gallium nitride crystal. Each point of Drawing 4 shows the result of Examples 9-12 and 14-16. From FIG. 4, it was found that the average activation rate was 45%.

In addition, in order to calculate the dopant activation rate in the GaN crystal obtained by the ammonothermal method, the carrier concentration and oxygen concentration of the GaN crystal obtained by the method according to Example 11 were measured. In Example 15, the carrier concentration in the obtained crystal was 3.90 × 10 ¹⁸ atoms / cm ³ , and the oxygen concentration in the obtained crystal was 9.00 × 10 ¹⁸ atoms / cm ^3. It was. In Example 16, the carrier concentration in the obtained crystal was 9.54 × 10 ¹⁸ atoms / cm ³ , and the oxygen concentration in the obtained crystal was 2.00 × 10 ¹⁹ atoms / cm ^3. Met.

  According to the first invention, a high quality nitride crystal can be produced efficiently by controlling the bulk density of the crystal raw material to be filled in the crystal growth by the ammonothermal method within a specific range. . Therefore, according to the present invention, the manufacturing time can be greatly reduced by shortening the growth time and making the crystal raw material a nitride crystal with high efficiency. Moreover, the nitride single crystal manufactured by the method of the present invention can be effectively used for a device as a high-quality crystal. For this reason, the manufacturing method of the first invention can be used for manufacturing nitride crystals using the ammonothermal method, and has high industrial applicability.

  According to the second invention, a nitride crystal having a desired carrier concentration can be obtained by producing a nitride crystal using a nitride crystal raw material having an oxygen concentration within a certain range. Further, precise oxygen doping can be performed by using the oxygen doping conditions of the second invention. For this reason, the manufacturing method of the second invention can be used for manufacturing a nitride crystal using an ammonothermal method, and has high industrial applicability.

DESCRIPTION OF SYMBOLS 1 Autoclave 2 Autoclave inner surface 3 Lining 4 Lining inner surface 5 Baffle plate 6 Crystal growth area 7 Seed crystal 8 Raw material 9 Raw material filling area 10 Valve 11 Vacuum pump 12 Ammonia cylinder 13 Nitrogen cylinder 14 Mass flow meter 20 Capsule 21 Inner surface of capsule

Claims (12)

A method for producing a nitride crystal, comprising filling a nitride crystal raw material in a raw material filling region of a reaction vessel and performing crystal growth in the presence of a solvent in a supercritical and / or subcritical state in the reaction vessel. A method for producing a nitride crystal, wherein crystal growth is performed by filling a crystal raw material in a raw material filling region with a bulk density of 0.7 to 4.5 g / cm ³ . The method for producing a nitride crystal according to claim 1, wherein the bulk density is 0.8 to 3.6 g / cm ³ .   The manufacturing method of the nitride crystal | crystallization of Claim 1 or 2 whose maximum diameter of the said nitride crystal raw material is 0.5 micrometer-120 mm.   4. The nitride crystal raw material particles according to claim 1, wherein secondary particles having a maximum diameter of 100 to 1000 μm are agglomerated secondary particles having a maximum diameter of 1 to 120 mm. A method for producing a nitride crystal.   The manufacturing method of the nitride crystal | crystallization of any one of Claims 1-4 whose oxygen concentration in the said nitride crystal raw material is 10-500 ppm. A nitride crystal raw material having a bulk density of 0.7 to 4.5 g / cm ³ and an oxygen concentration in the crystal of 10 to 500 ppm is filled in the raw material filling region of the reaction vessel, and is supercritical in the reaction vessel. And / or nitride crystal growth in the presence of a subcritical solvent.   The method for producing a nitride crystal according to claim 6, wherein the particles of the nitride crystal raw material are tertiary particles having a maximum diameter of 1 to 120 mm formed by agglomerating secondary particles having a maximum diameter of 100 to 1000 µm. .   The method for producing a nitride crystal according to claim 1, wherein a network structure is installed in the raw material filling region.   The method for producing a nitride crystal according to claim 8, wherein the nitride crystal raw material is filled in a network structure and then installed in the raw material filling region.   The method for producing a nitride crystal according to any one of claims 1 to 9, wherein a dissolution rate of the nitride crystal raw material is 40% or more.   The method for producing a nitride crystal according to any one of claims 1 to 10, wherein a growth rate in a c-axis direction of the nitride crystal is 100 µm / day or more.   A nitride crystal produced by the method for producing a nitride crystal according to any one of claims 1 to 11.