JP2014062029A - Manufacturing method of nitride crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a nitride crystal having a desired carrier concentration in an ammonothermal method.SOLUTION: A manufacturing method of a nitride crystal includes a growth step of loading a nitride crystal raw material 8 of an oxygen concentration of 10-120 wt.ppm in a raw material loading region 9 of a reaction vessel 20 and growing a nitride crystal in the presence of a nitrogen-containing solvent under a supercritical state and/or a subcritical state in the reaction vessel, and further includes a step of isolating a dopant supply source before the growth step. A concentration of n-type dopants other than oxygen is 1,000 wt.ppm or less in the nitride crystal raw material.

Description

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

  Nitride crystals such as gallium nitride (GaN) 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.

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 the thermal decomposition are deposited on the substrate. 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 approximately 100% (see, for example, cited document 1).

  The ammonothermal method is a method for producing a desired crystal material using a solvent containing nitrogen such as ammonia in a supercritical state and / or a subcritical state and a dissolution-precipitation reaction of raw materials. 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 nitrogen-containing 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. A crystal can be produced by melting and growing the crystal on the other side (see, for example, Patent Document 2). The ammonothermal method is advantageous in that the raw material utilization efficiency is better than that of the HVPE method, and the manufacturing cost can be suppressed.

JP 2000-44400 A JP 2003-277182 A

  However, 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. 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. 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.

  In addition, 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 order to solve the problems of the conventional technique, the inventors of the present application have studied for the purpose of providing a method for producing a nitride crystal having a desired carrier concentration in the ammonothermal method.

As a result of diligent studies to solve the above problems, the inventors of the present invention have produced nitride crystals by an ammonothermal method using a nitride crystal raw material having an oxygen concentration within a certain range. Thus, it has been found that a nitride crystal having a desired carrier concentration can be obtained. That is, the present inventors succeeded in finding the correlation between the oxygen concentration in the nitride crystal raw material and the carrier concentration in the crystal in the ammonothermal method, and completed the present invention.
Specifically, the present invention has the following configuration.

（上式において、ηはドーパント活性化率（単位：％）であり、［ＣＣ］はキャリア濃度（単位：ｃｍ^-3）であり、［Ｄ］はドーパント濃度（単位：ｃｍ^-3）である。）
［１９］キャリア濃度が５×１０¹⁷〜２×１０¹⁹ａｔｏｍｓ／ｃｍ³である、［１７］又は［１８］に記載の窒化物結晶。
［２０］Ｓｉ濃度が１．５×１０¹⁶ａｔｏｍｓ／ｃｍ³以下である、［１７］〜［１９］のいずれかに記載の窒化物結晶。 [1] A nitride crystal raw material having an oxygen concentration of 10 to 120 wtppm is filled in a raw material filling region of a reaction vessel, and nitride is contained in the reaction vessel in the presence of a supercritical and / or subcritical nitrogen-containing solvent. A method for producing a nitride crystal, comprising a growth step for growing the crystal.
[2] The method for producing a nitride crystal according to [1], wherein an amount of an n-type dopant other than oxygen contained in the nitride crystal raw material is 1000 wtppm or less.
[3] The method for producing a nitride crystal according to [1] or [2], further including a dopant source isolation step before the growth step.
[4] The reaction container includes an installation member in the reaction container, and the reaction container and the installation member are formed of a constituent material having an n-type dopant amount of 1000 wtppm or less. 3] The method for producing a nitride crystal according to any one of [3].
[5] The method for producing a nitride crystal according to [4], wherein the constituent material includes a platinum group or a platinum group alloy.
[6] The method for producing a nitride crystal as described in [5], wherein the platinum group alloy is an alloy containing Pt and Ir.
[7] The method for producing a nitride crystal as described in [6], wherein the Ir content of the platinum group alloy is 30% by weight or less of the total weight of the platinum group alloy.
[8] The reaction container includes an installation member in the reaction container, and the reaction container and the installation member are covered with a coating material or a lining material having an n-type dopant amount of 1000 wtppm or less. ] The manufacturing method of the nitride crystal | crystallization of any one of [7].
[9] The method for producing a nitride crystal as described in [8], wherein the coating agent contains a platinum group or a platinum group alloy.
[10] The method for producing a nitride crystal according to [9], wherein the platinum group alloy is an alloy containing Pt and Ga.
[11] The method for producing a nitride crystal as described in [9] or [10], wherein the platinum group alloy is an alloy containing Ir.
[12] The n-type dopant contained in the nitride crystal contains one or more elements selected from the group consisting of Si, O, C, F, I, Cl, Br, S, and Ge. [11] The method for producing a nitride crystal according to any one of [11].
[13] The method for producing a nitride crystal according to any one of [1] to [12], wherein in the growth step, the nitride crystal is grown using an acidic mineralizer.
[14] The method for producing a nitride crystal according to [13], wherein the acidic mineralizer includes a halide.
[15] The method for producing a nitride crystal according to any one of [1] to [14], wherein the growth step is a step of growing the nitride crystal under a temperature condition of 320 to 700 ° C.
[16] The method for producing a nitride crystal according to any one of [1] to [15], wherein the growth step is a step of growing a nitride crystal under a pressure condition of 30 to 700 MPa.
[17] A nitride crystal produced by the production method according to any one of [1] to [16].
[18] The oxygen concentration is 1.5 × 10 ^{18 to} 2.5 × 10 ¹⁹ atoms / cm ³ , and the dopant activation rate η represented by the following formula is 10 to 90%, Nitride crystals.

(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 ). .)
[19] The nitride crystal according to [17] or [18], wherein the carrier concentration is 5 × 10 ¹⁷ to 2 × 10 ¹⁹ atoms / cm ³ .
[20] The nitride crystal according to any one of [17] to [19], wherein the Si concentration is 1.5 × 10 ¹⁶ atoms / cm ³ or less.

  According to the present invention, 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. it can.

  Further, in the present invention, by limiting the main dopant supply source to the nitride crystal raw material, the present inventors have succeeded in finding a correlation between the oxygen concentration in the raw material and the carrier concentration in the crystal in the ammonothermal method. 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 present invention, it is possible to drastically reduce the time and effort to study the conditions for obtaining a nitride crystal having a target carrier concentration by the ammonothermal method, and to improve the production efficiency of the nitride crystal. Can do.

FIG. 1 is a schematic view of a crystal manufacturing apparatus that can be used in the present invention. FIG. 2 is a graph showing the relationship between the oxygen concentration in the nitride crystal raw material and the carrier concentration of the grown crystal. FIG. 3 is a graph showing the relationship between the oxygen concentration and the carrier concentration in the grown nitride crystal.

(1. Definition)
Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value. Moreover, in this specification, wtppm means weight ppm.

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 opposite to it, and gallium nitride corresponds to the Ga plane or N plane, respectively. In this specification, the “M plane” refers to {1-100} plane, {01-10} plane, {-1010} plane, {−1100} plane, {0-110} plane, {
10-10} plane, which is comprehensively represented as a plane, specifically, a (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 the Group 13 metal element and the nitrogen element are present on the surface, and the abundance ratio thereof is 1: 1. Specifically, the M surface and the A surface can be mentioned. In this specification, the “semipolar plane” means, for example, when the periodic table group 13 metal nitride is a hexagonal crystal and the principal plane is represented by (hklm), except for the {0001} plane, m = A surface that is not zero. 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 in which only one of the group 13 metal element and nitrogen element or the C surface is present on the 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] ], [11-22] plane, [11-2-2] plane, [11-24] plane, [11-2-4] plane, etc., particularly [10-11] plane, 202-1] plane can be mentioned as a preferable plane.

(2. Manufacturing method of nitride crystal)
In the method for producing a nitride crystal of the present invention, a nitride crystal raw material having an oxygen concentration of 10 to 120 wtppm is used, and a nitride crystal is produced from the nitride crystal raw material by an ammonothermal method. Specifically, in the production method of the present invention, a nitride crystal raw material having an oxygen concentration of 10 to 120 wtppm is filled in a raw material filling region of a reaction vessel, and nitrogen content in a supercritical and / or subcritical state is contained in the reaction vessel. A growth step of growing a nitride crystal in the presence of a solvent.
Hereinafter, a nitride crystal raw material that can be used in the present invention and a nitride crystal growth method using this nitride crystal raw material will be described.

(3. 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 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. 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 raw material include a mixture of gallium nitride and metal gallium. Examples of the type of nitride crystal obtained in the present 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.

(3-1. Oxygen concentration of crystal raw material)
The method for producing a nitride crystal according to the present invention uses a nitride crystal raw material having an oxygen concentration of 10 to 120 wtppm in the presence of a nitrogen-containing solvent in a supercritical and / or subcritical state in a reaction vessel. And a growth step of growing the crystal.
The oxygen concentration of the nitride crystal raw material is 10 wtppm or more in order to ensure a sufficient amount as a dopant, preferably 15 wtppm or more, more preferably 16 wtppm or more, and further preferably 20 wtppm or more. Further, the oxygen concentration of the nitride crystal raw material is 120 wtppm or less, preferably 100 wtppm or less, more preferably 80 wtppm or less, and 80 wtppm or less in order to obtain high-quality crystals with few impurities. Further 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 2 × 10 ¹⁹ atoms / cm ^3, and a high-quality nitride crystal can be obtained. Can be obtained.

The method for producing a nitride crystal raw material having an oxygen concentration of 10 to 120 wtppm is not particularly limited. As the nitride crystal raw material having an oxygen concentration of 10 to 120 wtppm, a material produced by a normal HVPE method may be used, or a material 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 addition, when growing by the HVPE method, the oxygen concentration can be adjusted by lowering the growth temperature or changing the molar ratio of the group V source gas and the group III source gas. Increasing the molar ratio of the group V source gas can increase the oxygen concentration.

  In the present invention, the correlation 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 present invention, the activation rate of the nitride crystal formed by the ammonothermal method can be expressed by the following formula. In the present 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.

According to the study by the present inventors, 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. 10 to 90%, and the average of the ammonothermal crystals obtained under various growth conditions was found to be about 45%. From this, it was 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 can be in the range of 10 to 120 wtppm. According to the production method of the present invention, 40 to 60 wt% of the amount of oxygen contained in the nitride crystal raw material is preferably taken into the obtained nitride crystal, more preferably about 50 wt% is taken in. . The amount of oxygen incorporated into the nitride crystal from the crystal raw material can be controlled by appropriately adjusting the crystal growth conditions. Specifically, the amount of oxygen incorporated decreases as the amount of halogen incorporated in the nitride crystal increases. There is a tendency. 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 present 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.

  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 present 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.
Further, in the present invention, by using the above-described correlation formula, it is possible to establish a manufacturing condition for a 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 present invention, the amount of the n-type dopant other than oxygen contained in the nitride crystal raw material is preferably 1000 wtppm or less, more preferably 100 wtppm or less, and even more preferably 10 wtppm or less. 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 present invention, it is preferable to dope oxygen so that the nitride crystal contains a target concentration of carriers. 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 present 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 present 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 present invention, a nitride crystal raw material is dissolved in a reaction vessel, and at the same time, a 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 present 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.

(3-2. 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, it is preferable to use a nitride crystal raw material having a bulk density in the range of 0.7 to 4.5 g / cm ³ . 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 6.0. The following is preferable. In particular, when the diameter of the reaction vessel is 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 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 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 present 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, the bulk density Two or more types of nitride crystal raw materials having different values 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.

The specific example of calculation of the bulk density of the nitride crystal raw material in this invention is 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 . Moreover, it can analyze also by CT scan (computed tomography) in the state put into the container. For example, when the porosity in the container filled with the raw material measured by CT scan is 70%, the solid volume is about 30% by weight. Therefore, when the density of gallium nitride is 6.1 g / cm ³ , The bulk density can be calculated from the formula:
6.1 g / cm ³ × 0.3 = 1.83 g / cm ³ (bulk density)

Further, in the production method of the present invention, the convection of the solvent is performed by controlling the bulk density of the nitride crystal raw material in the raw material filling region in the reaction vessel to be within the 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.

In the present invention, the “raw material filling region” refers to the horizontal plane including the lowest end of the filled crystal raw material and the uppermost of the filled crystal raw material when the long axis of the reaction vessel before the start of the reaction is in the vertical direction. A region inside the reaction vessel sandwiched between a horizontal plane including the upper end portion.
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 the seed crystal support frame, crucibles for installing nitride crystal raw materials, baskets, and structures such as a net-like structure. The free volume can be obtained by removing these volumes. In the specific example described above, if the container is a reaction container, the bulk density of the nitride crystal raw material in the raw material filling region can be calculated in the same manner.

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. 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 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. In the present invention, it is preferable to control the bulk density of the crystal raw material in the raw material filling region within a range of 0.7 to 4.5 g / cm ³ . The bulk density of the nitride crystal raw material in the raw material filling region is more preferably 0.8 g / cm ³ or more, more preferably 0.9 g / cm ³ or more, and 1.0 g / cm ³ or more. More preferably, it is 1.1 g / cm ³ or more. Further, the bulk density of the nitride crystal raw material in the raw material filling region is more 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.

  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 easily overlaps each other while having gaps between the individual nitride crystal raw material particles 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 a solvent to pass through but not allowing a 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 region 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 the crystal material in a network structure having a volume smaller than that of the raw material filling region, and then putting this into 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.
In order to set the bulk density of the nitride crystal raw material in the raw material filling region within the above range, it is preferable to use a nitride crystal raw material having a bulk density in the range of 0.7 to 4.5 g / cm ³ . 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.

(3-3. Color difference of nitride crystal raw material)
The nitride crystal raw material in the present invention preferably has a certain range of L ^* value, a ^* value and b ^* value when expressed in the L ^* a ^* b ^* color system. Here, in the L ^* a ^* b ^* color system, the L ^* value indicates the brightness of the crystal, and the higher the value (closer to 100), the higher the brightness. The a ^* value indicates red-green, and the smaller value indicates green and the larger value indicates red. The b ^* value indicates yellow-blue, and the smaller numerical value is blue and the larger numerical value is yellow. In other words, the larger the L ^* value, the brighter the color, and the larger the absolute value of the a ^* and b ^* values, the clearer the color.

The L ^* value of the group III nitride crystal obtained by the production method of the present invention is preferably 50 or more, more preferably 55 or more, and further preferably 60 or more. Further, the a ^* value of the group III nitride crystal is preferably −10 or more, more preferably −5 or more, and preferably 10 or less, more preferably 5 or less. . Furthermore, the b ^* value is preferably −20 or more, more preferably −10 or more, more preferably 20 or less, and even more preferably 15 or less. By setting the color difference (L ^* value, a ^* value, b ^* value) of the nitride crystal raw material within the above range, a growth crystal with little coloring can be obtained. The color difference (L ^* value, a ^* value, b ^* value) of the nitride crystal raw material is, for example, Nippon Denshoku ZE-2000 colorimetric colorimeter (standard white plate Y = 95.03, X = 95.03). , Z = 112.02).

(3-4. Grain size of nitride crystal raw material)
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 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, the particle diameter is preferably 0.5 μm or more, more preferably 1 μm or more, more preferably 10 μm or more. It is further preferable to use a material having a diameter of 20 mm or less, more preferably a material having a diameter of 15 mm or less, and still more preferably a material having a thickness of 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 present invention is preferably one having a structure formed by agglomerating nitride crystal raw material particles. 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 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 present invention, the crystal raw material having a particle size of 0.01 μm or more occupies 20% or more of the total volume of the crystal raw material, more preferably 30% or more. This is preferable because the gap is sufficiently open and convection of the solvent becomes possible.

(3-5. 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, and bowl shape (refers to a state where the surface is uneven and the surface area is large). Also good. 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.

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

(3-6. Angle of repose of nitride crystal raw material)
In the present invention, it is preferable to use a nitride crystal raw material having an angle of repose of less than 45 °. Specifically, among the nitride crystal raw materials containing atoms constituting the nitride crystal to be grown, those having a repose angle in a specific range can be used.

The “rest angle” of the nitride crystal material used in the present invention refers to the angle of the slope that maintains stability without spontaneous collapse when the nitride crystal material is stacked. Specifically, it refers to the angle of the slope when the nitride crystal raw material is dropped from above the horizontal floor surface, piled up like a cone-shaped sand pile, and piled up at least once until the cone slope collapses. . The angle of the inclined surface is measured as an angle formed by the skirt portion of the cone and the bottom surface in a substantially triangular projection view when the cone is observed from the horizontal direction. As the angle of repose of the nitride crystal raw material used in the present invention, a value measured in an environment of a relative humidity of 50% or less and 30.0 ° C. is used.
In the present invention, the height at which the nitride crystal material is dropped is about 20 cm from the floor at the start of dropping. When the nitride crystal raw material starts to have a conical shape, the dropping position is changed so that it becomes 20 cm from the top of the cone, and this nitride crystal raw material is dropped to pile up the nitride crystal raw material like a sand pile and pile up The value at the time when the slope of the nitride crystal material collapsed twice was adopted. Further, when the angle of repose can be measured by a powder tester (product number PT-N) manufactured by Hosokawa Micron, the value can be used as the angle of repose.

The angle of repose of the nitride crystal raw material used in the present invention is preferably less than 45 ° and more preferably less than 40 ° from the viewpoint of improving the crystal growth rate. When the angle of repose of the nitride crystal raw material is less than 45 °, moderate friction occurs due to the shape and size of the raw material, and an appropriate space is formed between the nitride crystal raw materials when the reaction vessel is filled. It is thought that it becomes easy to come into contact with the solvent. Thereby, dissolution of the nitride crystal raw material in the solvent is promoted, and the crystal growth rate can be increased.
Further, the angle of repose of the nitride crystal raw material used in the present invention is preferably 15 ° or more, more preferably 20 ° or more, from the viewpoint of ease of handling when filling the reaction vessel. It is particularly preferable that the angle is 25 ° or more. When the angle of repose of the nitride crystal raw material is too small, friction due to the shape and size of the raw material is reduced, and diffusion becomes easy. Thereby, it is considered that the handling becomes difficult because the nitride crystal raw material rises at the time of handling such as filling the reaction vessel.

  Examples of the method for controlling the angle of repose of the nitride crystal material within the above range include a method using a nitride crystal material having a specific shape, a method using a nitride crystal material having a specific particle diameter, A method of pulverizing a nitride crystal raw material so that it can be filled in a reaction vessel used for crystal growth described later while feedback controlling to be in a range, a method of controlling the moisture content of the nitride crystal raw material, Si of the nitride crystal raw material, Examples thereof include a method for controlling the content of impurities such as S and Mg. Adjustment of the grain size of the nitride crystal raw material and adjustment of the moisture content of the nitride crystal raw material are particularly effective for controlling the angle of repose. Increasing the particle size of the nitride crystal raw material or increasing the amount of water tends to increase the friction between the particles and increase the angle of repose.

  As a method of controlling the moisture content of the nitride crystal raw material, there is a method of lowering the particle size of the nitride crystal raw material particle or the relative humidity of the atmosphere in which the nitride crystal raw material is handled. Further, by increasing the particle diameter of the nitride crystal raw material particles to some extent, it is possible to suppress the adsorption of moisture in the air as compared with the case where the particle diameter is small.

  As a method for performing feedback control so that the angle of repose of the nitride crystal raw material falls within a specific range, for example, the relationship between the grain size of the obtained nitride crystal raw material and the angle of repose is obtained in advance, and nitriding of a specific shape is performed. A method of pulverizing a nitride crystal raw material so as to have a specific particle diameter when using a material crystal raw material can be mentioned.

The method for pulverizing the nitride crystal raw material is not particularly limited, and for example, there is a method in which the pulverization is divided into a plurality of steps such as a coarse pulverization step, a medium pulverization step, and a fine pulverization step as necessary. In this case, the entire pulverization process can be pulverized using the same apparatus, but the apparatus used may be changed depending on the process. Here, the coarse pulverization step is a step of pulverizing so that approximately 90% by mass of the nitride crystal raw material has a particle size of 1 cm or less. Can be used. The medium pulverization step is a step of pulverizing so that approximately 90% by mass of the nitride crystal raw material has a particle diameter of 1 mm or less. For example, a pulverizer such as a cone crusher, a crushing roll, a hammer mill, or a disk mill is used. can do. The fine pulverization step is a step of pulverizing the nitride crystal raw material to have a finer particle size, such as a ball mill, tube mill, rod mill, roller mill, stamp mill, edge runner, vibration mill, jet mill, etc. A grinding device can be used. In addition, it is preferable to grind | pulverize by making a nitride crystal collide with each other from a viewpoint of suppressing mixing of the impurity originating in a grinder.
On the other hand, if it is a massive nitride crystal raw material, it can be machined or sliced to obtain a desired shape. In particular, by providing a slicing step and making it into a plate shape, pulverization can be performed more easily.
Further, when the nitride crystal raw material is etched with an acid or alkali solution after performing processing such as mechanical grinding, slicing, and pulverization, contamination of impurities derived from the processing can be removed.

The pulverization step is preferably performed in an inert gas atmosphere in order to prevent oxygen, oxides, hydrates and the like from adhering to the nitride crystal raw material. Although there is no restriction | limiting in particular in the kind of inert gas, Usually, 1 type can use 2 or more types among gases, such as nitrogen, argon, and helium. Among these, nitrogen is preferably used from the viewpoint of economy.
In addition, you may cool as needed so that the temperature of a nitride crystal raw material may not rise during a grinding | pulverization process.

(4. Crystal growth by ammonothermal method)
In the manufacturing method of the present invention, after filling a 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 single crystal of nitride 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 production method of the present invention, a high-quality nitride crystal can be efficiently produced 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.

(4-1. Mineralizer)
In the present invention, it is preferable to use a mineralizer when growing a 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.
The mineralizer used 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. A preferred example 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 used preferably. Examples of mineralizers containing halogen elements include ammonium halide, hydrogen halide, ammonium hexahalosilicate, and hydrocarbyl ammonium fluoride, tetramethylammonium halide, tetraethylammonium halide, benzyltrimethylammonium halide, halogenated Illustrative examples include alkylammonium salts such as dipropylammonium and isopropylammonium halides, halogenated alkyl metals such as alkyl sodium fluoride, halogenated alkaline earth metals, 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 listed, and ammonium halides, gallium halides, and hydrogen halides are particularly preferable. 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).

  In the present 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 be used in mixture of 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 iodine. And a combination of three elements such as fluorine and fluorine, or a combination of four elements such as chlorine, bromine, iodine and fluorine. 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 present invention are the type and shape and size of the nitride crystal to be produced, the type and shape and size of the seed crystal, the reactor used, It can be determined as appropriate depending on the temperature conditions and pressure conditions to be employed.

  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.

In the production method of the present invention, a mineralizer containing no halogen element can be used together with a mineralizer containing a halogen element. For example, in combination with an alkali metal amide such as NaNH ₂ , KNH ₂ or LiNH _2. It can also be used.

In the production method of the present 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 wtppm or less, and preferably 10 wtppm or less. More preferred is 1 wtppm 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.

(4-2. Solvent)
As the solvent used in the ammonothermal method, a solvent containing nitrogen can be used. As the solvent containing nitrogen, it is preferable to use a solvent that does not impair the stability of the nitride single crystal to be grown. 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 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 wtppm or less, and preferably 10 wtppm or less. More preferably, it is 0.1 wtppm 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. .

(4-3. Reaction vessel and installation member)
The nitride crystal growth step of the present 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. As a reaction vessel used in the present invention, as described in JP-T-2003-511326 (International Publication No. 01/024921 pamphlet) and JP-T-2007-509507 (Patent International Publication No. 2005/043638 pamphlet). 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 having no such 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 present invention, in order to suppress internal 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 is disposed in the pressure resistant container. It is preferable to form a reaction vessel by a method or the like.

  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 wtppm or less. The amount of the n-type dopant in the constituent material may be 1000 wtppm or less, more preferably 100 wtppm or less, and still more preferably 10 wtppm 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 lining material having a weight of 1000 wtppm or less. The amount of the n-type dopant in the coating material or lining material may be 1000 wtppm or less, more preferably 100 wtppm or less, and still more preferably 10 wtppm 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 made of 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 the lining easier to perform, it is more preferable to use at least one metal or element of Pt, Ag, Cu and C, or an alloy or compound containing at least one metal. As a lining material, for example. Pt simple substance, Pt-Ir alloy, Ag simple substance, Cu simple substance, graphite, etc. are also mentioned.

It is preferable that the reaction vessel and the installation member 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 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, other materials forming the reaction vessel can be pressure resistant. 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.

(5. Manufacturing equipment)
A specific example of a crystal manufacturing apparatus that can be used in the nitride crystal manufacturing method of the present invention is shown in FIG. The crystal production apparatus used in the present invention includes a reaction vessel. 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 (inner cylinder) 20 loaded as a reaction vessel in an autoclave 1 (pressure-resistant vessel). The capsule 20 includes a raw material filling region 9 for dissolving the raw material and a crystal growth region 6 for growing crystals. In the raw material filling area 9, a solvent and a mineralizer can be put together with the raw material 8. A seed crystal 7 can be installed in the crystal growth region 6 by suspending it with a wire 4. 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. Note that a valve, a mass flow meter and the like are not necessarily installed in the crystal manufacturing apparatus used when the nitride crystal manufacturing method of the present invention is carried out.

(6. Manufacturing process)
An example of the method for producing a nitride crystal of the present invention will be described. In carrying out the method for producing a nitride crystal of the present 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 is cut into a desired direction by cutting a nitride crystal grown with the C-plane as the main surface 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 present invention, it is preferable to further provide a dopant source isolation step prior to introducing the material 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 reaction vessel or a member containing oxygen, oxide, or water vapor among 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 present invention, unintentional doping occurs when an n-type dopant other than that derived from a nitride crystal raw material is incorporated into the nitride crystal. In the present 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 filling 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, after encapsulating the seed crystal 7, a solvent containing nitrogen, a raw material, and a mineralizer in a capsule 20 that is a reaction vessel, the capsule 20 is autoclaved (pressure resistant). 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 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 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, 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 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 present 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.

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 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 present 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 present invention, when the temperature of the autoclave is raised, a constant temperature may be maintained, and the grown 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 the conditions for the meltback treatment, the average temperature difference between the crystal growth region and the raw material filling 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. In addition, 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, 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 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.

  In the nitride crystal manufacturing method of the present 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. From the viewpoint that it is preferable that a small amount of the nitride crystal raw material remains after the crystal growth step is finished, the dissolution rate of the nitride crystal raw material is preferably 40% to 96%, preferably 50% to 85 is more preferable, and 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).

  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.

  In addition, when manufacturing gallium nitride according to the method for manufacturing a nitride crystal of the present invention, JP 2009-263229 A can be preferably referred to for details of materials, manufacturing conditions, manufacturing apparatuses, and processes other than those described above. . The entire disclosure of this publication is incorporated herein by reference.

  In the method for producing a nitride crystal of the present 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.

(7. Nitride crystals)
The nitride crystal according to the present invention can be obtained by the manufacturing method described above. The oxygen concentration of the nitride crystal obtained in the present 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%.
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 present 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.

Furthermore, the Si concentration of the nitride crystal obtained in the present 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 present invention is increased, the carrier activity rate is lowered, so that 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.

(8. Wafer)
By cutting a nitride crystal layer grown by the nitride crystal manufacturing method of the present invention in a desired direction, a wafer (semiconductor substrate) having an arbitrary crystal orientation can be obtained. 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.

(9. Device)
The nitride crystal and wafer of the present invention 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.

Example 1
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. Polycrystalline GaN particles having a bulk density of 1.8 g / cm ³ as raw material 8, a color difference of L ^* value 63.99, a ^* value of 0.26, b ^* value of 11.71, and oxygen concentration of 20 wtppm 130 g was weighed and placed in the capsule lower area (raw material filling area 9). The color difference measurement was performed in the following manner using a Nippon Denshoku ZE-2000 colorimetric color difference meter (standard white board Y = 95.03, X = 95.03, Z = 112.02). About 2 cc of the gallium nitride polycrystal powder pulverized to 100 micrometers or less was packed in the bottom of the 35 mmφ transparent round cell attached to the color difference meter, and loaded from the top without any gap. The sample was placed on a powder / paste sample stage and covered with a cap, and then the reflection was measured for a sample area of 30 mmφ.
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, 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 is connected to the top of the capsule 20 by TIG welding, the tube on the top of the cap is connected to an Ar gas line, and a pressure of 0.8 MPa is applied, confirming that there are no pinholes at the weld location. did. Next, after releasing Ar gas, 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 5 times, it was left overnight with it 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 five times, 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.
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 2)
The raw material 8 has a bulk density of 2.2 g / cm ³ , a color difference of L ^* value 63.85, a ^* value of 0.48, b ^* value of 11.65, and an oxygen concentration of 13 wtppm. Except for using particles, the same conditions as in Example 1 were used as the conditions shown in Table 1. 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 3)
Polycrystalline GaN particles having a bulk density of 1.8 g / cm ³ as raw material 8, a color difference of L ^* value 63.99, a ^* value of 0.26, b ^* value of 11.71, and oxygen concentration of 20 wtppm Except that was used, the conditions shown in Table 1 were used in the same manner as in Example 1. 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 hole measurement of the GaN crystal after annealing, the carrier concentration is 2.44 × 10 ¹⁷ 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 4
Polycrystalline GaN particles having a bulk density of 1.8 g / cm ³ as raw material 8, a color difference of L ^* value 63.99, a ^* value of 0.26, b ^* value of 11.71, and oxygen concentration of 20 wtppm Except that was used, the conditions shown in Table 1 were used in the same manner as in Example 1. 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 the hole measurement of the GaN crystal after annealing, the carrier concentration is 6.90 × 10 ¹⁷ 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 5>
Polycrystalline GaN particles having a bulk density of 2.6 g / cm ³ as raw material 8, a color difference of L ^* value of 58.77, a ^* value of 0.64, b ^* value of 11.38, and oxygen concentration of 61 ppm Except that was used, the conditions shown in Table 1 were used in the same manner as in Example 1. 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 6>
Polycrystalline GaN particles having a bulk density of 1.9 g / cm ³ as raw material 8, color difference of L ^* value 58.77, a ^* value of 0.64, b ^* value of 11.38, and oxygen concentration of 78 ppm Except that was used, the conditions shown in Table 1 were used in the same manner as in Example 1. 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.

(Comparative Example 1)
A gallium nitride crystal was produced in the same manner 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 wtppm were used as the raw material 8. Got. The obtained gallium nitride crystal was colored black as a whole, and was estimated to be a crystal containing an extremely large amount of impurities such as oxygen.

(Comparative Example 2)
A gallium nitride crystal was produced in the same manner as in Example 1 except that polycrystalline GaN particles having a bulk density of 0.8 g / cm ³ and an oxygen concentration of 130 wtppm were used as the raw material 8. Got. The obtained gallium nitride crystal was slightly colored brown to black as a whole, and was estimated to be a crystal containing impurities such as oxygen.

In Examples 1 to 6, crystals are grown using a GaN crystal raw material having a bulk density of 1.8 to 2.6 g / cm ² and an oxygen concentration of 13 to 78 wtppm. In Examples 1 to 6, a grown crystal having a carrier concentration of 6.70 × 10 ^{17 to} 2.44 × 10 ¹⁸ atoms / cm ³ is obtained. In Examples 1 to 6, the activation rate was in the range of 12 to 86%.

Comparative Example 1 is a crystal grown using a GaN crystal raw material having a bulk density of 1.8 g / cm ² and an oxygen concentration of 148 wtppm. As estimated from the relationship between the oxygen concentration in the nitride crystal raw materials of Examples 1 to 4 and the carrier concentration of the grown crystal shown in FIG. 2, in Comparative Example 1, the carrier concentration is about 2.50 × 10 ¹⁹ atoms / cm ³ . It is considered that a gallium nitride crystal was obtained, and a crystal having a high carrier concentration and appropriate conductivity could not be obtained. Further, the grown gallium nitride crystal had a color which seems to be derived from oxygen, and the quality was poor.
In Comparative Example 2, 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 wtppm. As estimated from the relationship between the oxygen concentration in the nitride crystal raw materials of Examples 1 to 4 and the carrier concentration of the grown crystal shown in FIG. 2, in Comparative Example 2, the carrier concentration is about 1.50 × 10 ¹⁹ atoms / cm ^3. The gallium nitride crystal was considered to be obtained, and a crystal having a high carrier concentration and appropriate conductivity could not be obtained. Further, the grown gallium nitride crystal had a coloring which seems to be slightly derived from oxygen, and the quality was inferior.

A summary of the results in Table 1 is shown in FIGS.
FIG. 2 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 1 to 6, and the points represented by squares represent the results of Comparative Examples 1 and 2. As shown by the approximate line in FIG. 2, 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. 3 is a graph showing the relationship between oxygen concentration and carrier concentration in the grown gallium nitride crystal. The two points on the right side of FIG. 3 show the results of Reference Examples 1 and 2. From FIG. 3, 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 1 were measured. In Reference Example 1, 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 Reference Example 2, the carrier concentration in the obtained crystal is 9.54 × 10 ¹⁸ atoms / cm ³ , and the oxygen concentration in the obtained crystal is 2.00 × 10 ¹⁸ atoms / cm ^3. Met.

  According to the present 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, if the oxygen doping conditions of the present invention are used, precise oxygen doping can be performed. For this reason, the manufacturing method of this invention can be utilized for manufacture of the nitride crystal using the ammonothermal method, and its industrial applicability is high.

1 Autoclave (pressure-resistant container)
4 Wire 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 (inner cylinder)

Claims (16)

  Nitride crystal raw material having an oxygen concentration of 10 to 120 wtppm is filled in the raw material filling region of the reaction vessel, and nitride crystals are grown in the presence of a supercritical and / or subcritical nitrogen-containing solvent in the reaction vessel. A method for producing a nitride crystal comprising a growth step of performing the step.   The manufacturing method of the nitride crystal | crystallization of Claim 1 whose quantity of n-type dopants other than oxygen contained in the said nitride crystal raw material is 1000 wtppm or less.   The method for producing a nitride crystal according to claim 1, further comprising a dopant source isolation step before the growth step. The reaction vessel has an installation member in the reaction vessel,
The said reaction container and the said installation member are the manufacturing methods of the nitride crystal | crystallization of any one of Claims 1-3 currently formed with the structural material whose quantity of n-type dopant is 1000 wtppm or less.   The said constituent material is a manufacturing method of the nitride crystal | crystallization of Claim 4 containing a platinum group or a platinum group alloy. The reaction vessel has an installation member in the reaction vessel,
The said reaction container and the said installation member are the manufacturing methods of the nitride crystal | crystallization of any one of Claims 1-5 covered with the coating material or lining material whose quantity of n-type dopant is 1000 wtppm or less.   The method for producing a nitride crystal according to claim 6, wherein the coating material or the lining material includes a platinum group or a platinum group alloy.   The n-type dopant contained in the nitride crystal includes one or more elements selected from the group consisting of Si, O, C, F, I, Cl, Br, S, and Ge. 2. A method for producing a nitride crystal according to item 1.   The method for producing a nitride crystal according to any one of claims 1 to 8, wherein in the growth step, the nitride crystal is grown using an acidic mineralizer.   The method for producing a nitride crystal according to claim 9, wherein the acidic mineralizer includes a halide.   The said growth process is a manufacturing method of the nitride crystal | crystallization of any one of Claims 1-10 which is a process of growing a nitride crystal on the temperature conditions of 320-700 degreeC.   The method for producing a nitride crystal according to any one of claims 1 to 11, wherein the growth step is a step of growing a nitride crystal under a pressure condition of 30 to 700 MPa.   The nitride crystal manufactured by the manufacturing method of any one of Claims 1-12. A nitride crystal having an oxygen concentration of 1.5 × 10 ^{18 to} 2.5 × 10 ¹⁹ atoms / cm ³ and a dopant activation rate η represented by the following formula of 10 to 90%: .

(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 nitride crystal according to claim 13 or 14, wherein the carrier concentration is 5 × 10 ¹⁷ to 2 × 10 ¹⁹ atoms / cm ³ . The nitride crystal according to any one of claims 13 to 15, wherein the Si concentration is 1.5 × 10 ¹⁶ atoms / cm ³ or less.

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