JP2016121064A - GaN single crystal and wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride single crystal having low resistance and high mobility even when grown in an ammonothermal method, and a production method thereof.SOLUTION: Provided is an annealing treatment method in which a nitride single crystal that has grown in an ammonothermal method in the presence of a solvent containing nitrogen at a supercritical state and/or a subcritical state is subjected to annealing treatment at 750°C or higher for 5.5 hours or more. The nitride single crystal obtained in the annealing treatment has an n-type carrier concentration of 1×10-1×10cm-3, a specific electric resistance (ρ) of (1×10)-(1×10) Ωcm, a ratio of 1 or more of a maximum peak emission intensity of a band end emission peak in a wavelength between 330 nm and 400 nm to a maximum peak emission intensity of a yellow band peak in a wavelength between 450 nm and 750 nm in an emission spectrum analysis, and a hydrogen (H) concentration of 5×10atoms/cmor more.SELECTED DRAWING: None

Description

  The present invention relates to a method for annealing a nitride single crystal grown by an ammonothermal method, and a nitride single crystal subjected to the treatment method.

  The ammonothermal method is a method for producing a desired material by using a raw material dissolution-precipitation reaction using a solvent containing nitrogen such as ammonia in a supercritical state and / or a subcritical state. When applied to crystal growth, a crystal is precipitated by generating a supersaturated state due to a temperature difference using the temperature dependence of the raw material solubility in an ammonia solvent. Specifically, raw materials and seeds are placed in a pressure-resistant container such as an autoclave and sealed, and heated with a heater installed outside the pressure-resistant container to form a high-temperature region and a low-temperature region in the pressure-resistant container. The desired crystal can be produced by dissolving the raw material on one side and growing the crystal on the other side.

Almost no attempt has been made to heat and anneal the nitride single crystal grown by the ammonothermal method. Further, there are very few documents that describe annealing treatment of nitride single crystals grown by the ammonothermal method.
For example, Patent Document 1 describes that annealing is performed at 500 to 1300 ° C. for about 15 to 60 minutes in order to reduce the coloration of a nitride single crystal grown by an ammonothermal method. Patent Document 1 also notes that the annealing time is not excessively long in order to avoid deterioration of crystal quality.

  Patent Document 2 describes that in order to evaluate the stability of a crystal, a GaN single crystal grown by an ammonothermal method was annealed at 750 ° C. for 30 minutes in high-purity nitrogen. Passivation of gallium vacancies in GaN single crystals grown by the ammonothermal method is extremely stable by measuring infrared spectra before and after annealing to confirm that there is almost no change in absorbance at a specific peak. It leads the evaluation result that there is.

  Patent Document 3 describes that a Zn-doped GaN single crystal grown by an ammonothermal method is annealed at 600 to 900 ° C. for 5 hours in a nitrogen atmosphere containing a small amount of oxygen. This annealing process is performed while a Zn-doped GaN single crystal is processed into a substrate, but its purpose and effect are not described.

  As described above, the annealing process for the nitride single crystal grown by the ammonothermal method is performed only for a limited purpose such as reduction of coloration of the crystal and evaluation of stability in the conventional method. There has been no detailed study of the effects of annealing treatment on crystals and their conditions.

Special table 2011-509231 gazette JP-T-2006-513122 US Patent Publication No. 2006/054076

Nitride single crystals grown by the ammonothermal method generally have a problem that they are semi-insulating crystals with high resistance and low mobility. In device applications such as optical devices, a conductive GaN substrate is required, so crystals with low resistance and high mobility can be easily produced even when crystals are grown using the ammonothermal method. It is desirable to do so. However, so far, no technology has been developed for simply providing a nitride single crystal having a low resistance and high mobility to a satisfactory level, although the crystal has been grown by the ammonothermal method.
Therefore, the inventor has intensively studied for the purpose of producing a nitride single crystal having low resistance and high mobility by a simple method even when the crystal is grown by an ammonothermal method.

As a result, the inventors surprisingly significantly improved the dopant activation rate by annealing the nitride single crystal grown by the ammonothermal method to satisfy specific conditions. Thus, the inventors have found that it is possible to easily obtain a nitride single crystal having low resistance and high mobility, and have come to provide the present invention having the following configuration.
[1] Annealing treatment of a nitride single crystal in which a nitride single crystal grown in the presence of a supercritical and / or subcritical nitrogen-containing solvent is annealed at 750 ° C. or more for 5.5 hours or more Method.
[2] The nitride single crystal annealing method according to [1], wherein the annealing temperature is 750 to 1250 ° C.
[3] The nitride single crystal annealing method according to [1] or [2], wherein the form of the nitride single crystal is bulk.
[4] The nitride single crystal annealing method according to any one of [1] to [3], wherein the nitride single crystal is a wafer.
[5] The nitride single crystal annealing method according to any one of [1] to [4], wherein at least part of the surface of the nitride single crystal after the annealing treatment is removed.
[6] The nitride single crystal annealing method according to any one of [1] to [5], wherein the nitride single crystal is grown using an acidic mineralizer.
[7] The nitride single crystal according to any one of [1] to [6], wherein an impurity concentration other than hydrogen of the nitride single crystal before the annealing treatment is 1 × 10 ²⁰ / cm ³ or less. Annealing method.
[8] The n-type dopant concentration of the nitride single crystal before the annealing treatment is any one of [1] to [7], in which the n-type dopant concentration is 1 × 10 ¹⁶ / cm ³ to 1 × 10 ²⁰ / cm ^3. An annealing method for nitride single crystal.
[9] The nitride single crystal annealing treatment according to [8], wherein the n-type dopant is one or more selected from the group consisting of oxygen, sulfur, selenium, tellurium, silicon, germanium, tin, and a halogen element. Method.
[10] Any one of [1] to [9], wherein the nitride single crystal after the annealing treatment has a hydrogen (H) concentration of 5 × 10 ¹⁶ atoms / cm ³ to 1 × 10 ²¹ atoms / cm ^3. The method for annealing a nitride single crystal according to the item.
[11] The main surface of the nitride single crystal is a Ga plane, an N plane, an M plane, a semipolar plane, or a plane inclined within a range of ± 15 ° from these planes. The annealing method for a nitride single crystal according to any one of the above items.
[12] The nitride single crystal annealing method according to any one of [1] to [11], wherein the nitride single crystal is GaN.
[13] A nitride single crystal subjected to the annealing method according to any one of [1] to [12].
[14] The nitride single crystal according to [13], wherein the carrier concentration is 1 × 10 ¹⁶ cm ⁻³ or more.
[15] n-type carrier concentration is less than 1 × 10 ¹⁹ cm ^-3 at 1 × 10 ¹⁷ cm ^-3 greater mobility (mu) is 150 cm ² / Vs greater than [13] or [14] The nitride single crystal as described.
[16] The n-type carrier concentration is more than 1 × 10 ¹⁶ cm ⁻³ and less than 1 × 10 ²⁰ cm ⁻³ , and the specific resistance (ρ) is more than 1 × 10 ⁻⁴ Ωcm and less than 1 × 10 ⁻¹ Ωcm. The nitride single crystal according to any one of [13] to [15].
[17] The nitride single crystal according to any one of [13] to [16], wherein a dopant activation rate η represented by the following formula is 10 to 100%.
[CC]
η (%) = ――――― x 100
[D]
(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 ). .)
[18] In the emission spectrum analysis, the ratio of the maximum peak emission intensity of the band edge emission peak at 330 to 400 nm to the maximum peak emission intensity of the yellow band peak at a wavelength of 450 to 750 nm is 1 or more. ] The nitride single crystal of any one of [17].
[19] The nitride single crystal according to any one of [13] to [18], wherein the hydrogen (H) concentration is 5 × 10 ¹⁶ atoms / cm ³ or more.
[20] A wafer comprising the nitride single crystal according to any one of [13] to [19].

  According to the present invention, a nitride single crystal grown by an ammonothermal method is easily annealed for a predetermined time or more in an annealing furnace to easily produce a nitride single crystal having low resistance and high mobility. be able to. Moreover, the nitride single crystal manufactured by the method of the present invention can be effectively used for a device as a high-quality crystal.

It is a figure explaining the axis | shaft and surface of a hexagonal crystal structure. It is a schematic diagram of an annealing furnace that can be used in the present invention. It is a schematic diagram of the crystal manufacturing apparatus by the ammonothermal method which can be used by this invention. It is a graph which shows the relationship between the carrier concentration of a GaN crystal, and a specific resistance. It is a graph which shows the carrier concentration of a GaN crystal, and the relationship of a mobility. It is a graph which shows the relationship between the emitted light intensity of a GaN crystal, and a wavelength.

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

  First, the relationship between the axis and the plane of the hexagonal crystal structure will be described with reference to FIG. FIG. 1 is a diagram for explaining axes and planes of a hexagonal crystal structure. In this specification, the “principal surface” of a seed or nitride crystal refers to the widest surface of the seed 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 shown in [2-1] in FIG. 1 and the (000-1) plane that is the opposite plane. In the group III nitride crystal, the C plane is a group III plane or a group V plane, and in gallium nitride, it corresponds to a Ga plane or an N plane, respectively. Further, in this specification, the “M plane” refers to {1-100} plane, {01-10} plane, [−1010] plane, {−1100} plane, {0-110} plane, {10-10 } Non-polar planes comprehensively represented as planes, specifically, the (1-100) plane, (01-10) plane, (-1010) plane shown by [2-2] in FIG. (-1100) plane, (0-110) plane, and (10-10) plane are meant. 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, the (11-20) plane, (2-1-10) plane, (-12-10) plane, (-1-120) plane, as shown in [2-3] in FIG. -2110) plane, (1-210) plane. In this specification, “c-axis”, “m-axis”, and “a-axis” mean axes perpendicular to the C-plane, M-plane, and A-plane, respectively.

  In the present specification, the “nonpolar plane” means a plane in which both a group III element and a nitrogen element are present on the surface and the abundance ratio is 1: 1. Specifically, the M surface and the A surface can be cited as preferable surfaces. In the present specification, the “semipolar plane” means, for example, a plane other than the [0001] plane and not m = 0 when the group III nitride is hexagonal and the principal plane is represented by (hklm). Say. That is, it refers to a plane that is inclined with respect to the (0001) plane and is not a nonpolar plane. It means a surface having both a group III element and a nitrogen element or only one surface such as the C surface, and the abundance ratio is not 1: 1. h, k, l and m are each independently preferably an integer of -5 to 5, more preferably an integer of -2 to 2, and preferably a low index surface. . Examples of the semipolar plane that can be preferably used as the main surface of the nitride crystal include (10-11) plane, (10-1-1) plane, (10-12) plane, (10-1-2) plane, (20 -21) plane, (202-1) plane, (20-2-1) plane, (10-12) plane, (10-1-2) plane, (11-21) plane, (11-2-1) ) Plane, (11-22) plane, (11-2-2) plane, (11-24) plane, (11-2-4) plane, etc., and in particular, the (10-11) plane, ( 202-1) surface.

[Annealing method of nitride single crystal]
(Feature)
The nitride single crystal annealing method of the present invention is characterized in that a nitride single crystal grown by an ammonothermal method is annealed at 750 ° C. or more for 5.5 hours or more.
Although the mechanism of the nitride single crystal grown by the ammonothermal method by annealing treatment is not yet known in detail, the following may be considered. In general, it is known that in order for a dopant to be activated in a crystal, an atom serving as a dopant must enter a lattice point of the crystal. For example, in the case of gallium nitride grown by the ammonothermal method, even though there are a large number of atoms such as oxygen as dopants inside the crystal before annealing, they are not activated because they are not activated. It has been confirmed that. As a factor that is not activated, the dopant atoms are in a state of being interstitial at a temperature lower than 750 ° C., which is a growth temperature in a general ammonothermal method, and the state in which the atoms are replaced with atoms at the lattice points. It is possible that it is not. Therefore, in the present invention, the nitride single crystal grown by the ammonothermal method is annealed at a temperature of 750 ° C. or higher, so that the dopant atoms in the interstitial state are replaced with the atoms at the lattice points. As a result, it is expected that the dopant atoms are activated.
In addition, under the above-described annealing temperature conditions, activation is considered to proceed slowly. Therefore, if the annealing time is not sufficiently long, it is considered that the entire crystal cannot be activated sufficiently. Therefore, in the present invention, it is expected that the dopant atoms can be sufficiently activated by annealing for a long time of 5.5 hours or more under a temperature condition of 750 ° C. or more.

By setting the annealing time to 5.5 hours or longer according to the present invention, the carrier of the nitride single crystal can be activated and the mobility can be sufficiently improved. If the annealing time is insufficient, the carrier can be activated, but the mobility cannot be sufficiently improved. The annealing time is preferably 5.5 hours or more, It is more preferably 8 hours or longer, further preferably 10 hours or longer, and particularly preferably 12 hours or longer. 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. It is preferable to maintain a constant temperature because it satisfies the necessary and sufficient temperature and time. When the temperature is raised, the rate of temperature rise is preferably 10 ° C./hour or more, more preferably 50 ° C./hour or more, still more preferably 100 ° C./hour or more, and 2000 ° C./hour. It is preferable to set it below, More preferably, it is 1500 degrees C / hour or less, More preferably, it is 1000 degrees C / hour or less. In addition, the temperature lowering rate when the temperature is lowered is preferably 10 ° C./hour or more, more preferably 20 ° C./hour or more, further preferably 50 ° C./hour or more, and 1000 ° C./hour. It is preferable to set it below, It is more preferable to set it as 800 degrees C / hour or less, It is more preferable to set it as 500 degrees C / hour or less. Thermal shock due to rapid temperature rise and / or temperature drop induces strain in the crystal and the generation of cracks. Therefore, it is preferable to adjust appropriately within the range of the temperature rise / fall rate. The larger the crystal size, the greater the damage to the crystal due to thermal shock. Therefore, it is preferable to apply a relatively low temperature increase / decrease rate for a crystal with a larger size than for a crystal with a smaller size.

  The annealing treatment of the present invention may be performed only once or a plurality of times. In the case of performing a plurality of times, the time for the plurality of annealing treatments may be 5.5 hours or more in total. That is, the total time for maintaining the temperature at 750 ° C. or higher may be 5.5 hours or longer. Usually, it is preferable to perform one annealing process for 5.5 hours or more in consideration of time efficiency and cost.

(Annealing environment)
Since the annealing treatment of the present invention is performed at a high temperature for a long time, it is preferably performed in a space where the atmosphere can be controlled. For example, it may be performed in an annealing furnace that can be used for crystal annealing, or may be performed in a reaction vessel in which a nitride single crystal to be annealed is grown by an ammonothermal method. . In the latter case, after the crystal growth by the ammonothermal method is completed, the reaction vessel may be opened once, or may be carried out after the crystal growth without opening.
The installation mode of the nitride single crystal grown by the ammonothermal method is not particularly limited. For example, it may be carried on a pedestal such as a susceptor, or may be carried out in a state of being suspended by a wire.

  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. Another preferred form is when it is carried out in an atmosphere in which at least nitrogen and ammonia are present. The ratio of nitrogen at this time is preferably 50% or more, more preferably 60% or more, further preferably 70% or more, and preferably 99% or less, and 97% or less. It is more preferable that it is 95% or less. Further, the proportion of ammonia is preferably 1% or more, more preferably 3% or more, further preferably 5% or more, more preferably 50% or less, and 40% or less. More preferably, it is more preferably 30% or less. Further, when oxygen is present, it is preferably 0.1% or more, preferably 30% or less, more preferably 25% or less, and further preferably 20% or less. The presence of oxygen is presumed to have an effect of suppressing the decomposition of the nitride crystal by forming an oxide film on the surface of the nitride crystal during the annealing process. When hydrogen is present, it is preferably at least 0.1%, more preferably at most 10%, more preferably at most 5%, further preferably at most 3%. Moreover, it can also carry out in an atmospheric condition more simply. In this case, atmosphere control is not necessary, but it may be in the range of 70 to 90% nitrogen and 10 to 30% oxygen.

Furthermore, the annealing treatment may be performed in an atmosphere in which an inert gas such as helium, neon, or argon exists. In this case, ammonia, nitrogen, oxygen, and hydrogen may not be present.
When performing the annealing treatment, it may be performed while circulating the atmosphere gas controlled as described above.
The pressure at the time of annealing treatment can be 0.001-10 MPa. Preference is given to atmospheric pressure (0.1 MPa) that does not require pressure control because it can be carried out easily at low cost. Since the nitride single crystal is decomposed by raising the temperature, the decomposition may be suppressed by applying ammonia pressure above the temperature at which the decomposition starts. For example, in the case of a GaN single crystal, decomposition starts when the temperature exceeds about 800 ° C. under atmospheric pressure. Therefore, ammonia pressure may be applied when the temperature reaches at least 800 ° C. or higher. The ammonia pressure is preferably 0.1 MPa or more, more preferably 0.2 MPa or more, and preferably 0.3 MPa or less, more preferably 10 MPa or less.

  Cap annealing may be performed to suppress the decomposition of the nitride crystal due to annealing. The term “cap annealing” as used herein refers to annealing by covering the surface of the nitride crystal with a thin film or the like in order to suppress surface alteration due to decomposition of the nitride crystal in a high-temperature annealing environment. As the cover method, a thin film forming method such as vapor deposition or sputtering can be used. As the cover material, noble metal elements such as Au and Pt, carbon, nitrides such as silicon nitride and aluminum nitride, and oxides such as silicon dioxide and aluminum oxide are preferably used.

Heating can be performed by a heating means used in a normal annealing process. A lamp can be used to increase or decrease the temperature in a short time. In addition, an electric furnace can be used to increase or decrease the temperature over time. These heating means may be used in combination.
The structure of the annealing furnace that can be used in the present invention is not particularly limited, and a muffle furnace, a vertical tubular furnace, a horizontal charge furnace, etc. can be used, but a horizontal tubular furnace as shown in FIG. 2 is used. Is preferred.

The annealing procedure of nitride crystals in the apparatus shown in FIG. 2 is as follows. First, a soaking tube is installed in a horizontal annular furnace capable of zone control, and a quartz tube is further installed therein, A susceptor 102 on which nitride crystals 101 are placed in a tube 100 is installed at the center of the furnace, and heat shield plates 103 are placed at both ends of the quartz tube. Further, both ends of the quartz tube are sealed with water cooling flanges 104, an introduction tube 105 is installed on the gas introduction side, and an exhaust tube 106 is connected on the exhaust side. The gas flow rate control on the gas introduction side can be performed by a flow meter with a flow rate adjusting function or a mass flow controller. The horizontal tubular furnace can be controlled by setting the temperature of the heater 108 to the target temperature while monitoring the temperature of the thermocouple 110 with a monitor, and setting the heaters 107 and 109 to offset control with respect to the center temperature. it can. Further, the gas flow rate control and heater control can be implemented by program control.
Since the horizontal tubular furnace as shown in FIG. 2 is excellent in heat uniformity, it is preferable because annealing of a large bulk crystal and a plurality of wafers and bulk crystals can be annealed at the same time in the same furnace, Since gas can be introduced and discharged, the internal cleanliness is increased and the atmosphere can be controlled, which is preferable.

(Nitride single crystal to be annealed)
The nitride single crystal to be annealed in the present invention is a nitride single crystal grown by an ammonothermal method.
The nitride single crystal is preferably a group III nitride single crystal. Examples of the nitride single crystal include GaN, InN, AlN, InGaN, AlGaN, AllnGaN, and the like. Preferred is GaN, AlN, AlGaN, AllnGaN, and more preferred is GaN.

  In the present invention, the processing and surface treatment conditions of the nitride single crystal to be annealed are not particularly limited. The nitride single crystal to be annealed may be an as-grown nitride single crystal after crystal growth by the ammonothermal method, or may be a sliced as-sliced nitride single crystal. Further, it may be a nitride single crystal subjected to surface polishing. As the slicing and polishing methods here, a method used for slicing or polishing a nitride single crystal can be widely employed. If the annealing treatment of the present invention is performed after slicing, the annealing time can be shortened and the internal quality can be confirmed in advance. In addition, it is preferable to perform the annealing treatment of the present invention after performing surface polishing because it is easy to check the quality after annealing. Further, it is preferable that the annealing treatment of the present invention is performed after crystal growth by the ammonothermal method, so that contamination by impurities can be prevented.

  In the present invention, the shape of the nitride single crystal to be annealed is not particularly limited. For example, it may be a bulk or a wafer. When the nitride single crystal after the annealing treatment is used as a substrate or a device, the nitride single crystal having a desirable main surface is preferable. The type of main surface may be a polar surface such as a C surface, a nonpolar surface such as an M surface or an A surface, or a semipolar surface. Further, it may be a surface inclined from these surfaces, and is not particularly limited. Examples of preferred main surfaces include a + C plane, a −C plane, an M plane, a semipolar plane, or a plane inclined by ± 15 ° from these planes. The shape of the main surface may be any of a circle, an ellipse, a square, a rectangle, and the like.

In the present invention, the quality of the nitride crystal to be annealed is not particularly limited, but from the viewpoint of providing resistance to thermal shock due to annealing, it is preferable that the residual strain in the crystal is small. As parameters affecting the residual strain in the crystal, the dislocation density in the main surface and the radius of curvature of the crystal lattice can be mentioned. The dislocation density in the crystal is preferably 1 × 10 ⁷ / cm ² or less, more preferably 1 × 10 ⁶ / cm ² or less, further preferably 1 × 10 ⁵ / cm ² or less, and 1 × 10 ⁴ / cm ² or less. Particularly preferred. The radius of curvature is preferably 1 m or more, more preferably 5 m or more, further preferably 10 m or more, and particularly preferably 20 m or more.

  In the present invention, the size of the nitride single crystal to be annealed is not particularly limited. In the case of a wafer, the thickness is preferably 1 mm or less, more preferably 0.5 mm or less, and the lower limit can be set to, for example, 0.1 mm or more from the viewpoints of economy and wafer processability. In the case of a bulk, the thickness is preferably 2 mm or more, more preferably 5 mm or more, and preferably 100 mm or less, more preferably 75 mm or less. If it is too thick, there is a possibility that the crystal will be damaged by the thermal shock due to annealing. Therefore, the damage can be suppressed by adjusting the heating rate and the cooling rate.

In the present invention, the concentration of impurities other than hydrogen in the nitride single crystal to be annealed is preferably 1 × 10 ²⁰ atoms / cm ³ or less, more preferably 5 × 10 ¹⁹ atoms / cm ³ or less, and 1 × More preferably, it is 10 ¹⁸ atoms / cm ³ or less. Further, the hydrogen (H) concentration of the nitride single crystal to be annealed may be, for example, 5 × 10 ¹⁶ atoms / cm ³ or more, and may be 5 × 10 ¹⁷ atoms / cm ³ or more. Further, the hydrogen (H) concentration is preferably 1 × 10 ²¹ atoms / cm ³ or less, and more preferably 5 × 10 ²⁰ atoms / cm ³ or less.

Further, the n-type dopant concentration of the nitride single crystal to be annealed is preferably 1 × 10 ¹⁶ / cm ³ or more, more preferably 1 × 10 ¹⁷ / cm ³ or more, and 1 × 10 ¹⁸ / cm 3. More preferably, it is ³ or more. When it is at least the above lower limit, a nitride single crystal having low resistance and high mobility tends to be obtained after annealing. The n-type dopant concentration is preferably 1 × 10 ²⁰ / cm ³ or less, more preferably 8 × 10 ¹⁹ / cm ³ or less, and further preferably 5 × 10 ¹⁹ / cm ³ or less. . Examples of the n-type dopant include oxygen, sulfur, selenium, tellurium, silicon, germanium, tin, and a halogen element. The n-type dopant preferably includes oxygen and silicon, and more preferably includes oxygen.
The oxygen concentration of the nitride single crystal to be annealed is preferably 1 × 10 ¹⁶ / cm ³ or more, more preferably 1 × 10 ¹⁷ / cm ³ or more, and 1 × 10 ¹⁸ / cm ³ or more. More preferably. When it is at least the above lower limit, a nitride single crystal having low resistance and high mobility tends to be obtained after annealing. Furthermore, the oxygen concentration is preferably 1 × 10 ²⁰ / cm ³ or less, more preferably 8 × 10 ¹⁹ / cm ³ or less, and further preferably 5 × 10 ¹⁹ / cm ³ or less.

Further, the total halogen element concentration of chlorine, bromine, iodine and fluorine in the nitride crystal to be annealed is preferably 1 × 10 ²⁰ atoms / cm ³ or less, and preferably 1 × 10 ¹⁹ atoms / cm ³ or less. Is more preferably 5 × 10 ¹⁸ atoms / cm ³ or less, more preferably 1 × 10 ¹⁴ atoms / cm ³ or more, and more preferably 1 × 10 ¹⁵ atoms / cm ³ or more. It is preferably 1 × 10 ¹⁶ atoms / cm ³ or more.
The ammonothermal method used in the production of a nitride single crystal uses a solvent-containing precipitation reaction using a nitrogen-containing solvent such as an ammonia solvent in a supercritical state and / or a subcritical state. Thus, a desired nitride single crystal is produced. Crystal growth is performed by using the temperature dependence of the solubility of the raw material in the ammonia solvent to generate a supersaturated state due to a temperature difference and precipitating the crystal. Crystal growth by the ammonothermal method is a reaction in a supercritical ammonia environment at high temperature and high pressure. Furthermore, since the solubility of a single crystal nitride in pure ammonia in a supercritical state is extremely small, A mineralizer is preferably used to promote growth. In the present invention, since an alkali metal is not taken as an impurity and excellent in semiconductor characteristics, an annealing treatment is preferably performed particularly on a nitride single crystal grown by an ammonothermal method using an acidic mineralizer. Can be implemented.

The acidic mineralizer is a compound containing a halogen atom, and examples thereof include ammonium halide. For example, ammonium chloride (NH ₄ Cl), ammonium iodide (NH ₄ I), ammonium bromide (NH ₄ Br), fluorine Ammonium chloride (NH ₄ F). In the present invention, since the quality of the obtained nitride single crystal is good, it is preferable to contain at least two or more of chlorine, bromine, iodine and fluorine as an acidic mineralizer, more preferably at least It contains one of chlorine, bromine and iodine and fluorine.
Instead of adding ammonium halide as a mineralizer, it may be added as hydrogen halide gas. The hydrogen halide gas reacts with ammonia in the reaction vessel to produce ammonium halide. Note that the present invention can also be applied to a nitride single crystal grown using a basic mineralizer.

(Amonothermal method)
Hereinafter, a method for producing a nitride single crystal using an ammonothermal method will be described in detail, but the crystal growth step that can be employed in the present invention is not limited to this.
1) Use of mineralizer The amount of mineralizer used in the ammonothermal method is preferably such that the molar concentration of the halogen element contained in the mineralizer relative to ammonia is 0.1 mol% or more. It is more preferable to set it to 3 mol% or more, and it is more preferable to set it to 0.5 mol% or more. In addition, the molar concentration of the halogen element contained in the mineralizer with respect to ammonia is preferably 30 mol% or less, more preferably 20 mol% or less, and more preferably 10 mol% or less. Is more preferable. 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.

2) Solvent As the solvent used in the ammonothermal method, a solvent containing nitrogen can be used. Examples of the solvent containing nitrogen include a solvent that does not impair the stability of the grown nitride single crystal. Examples of the solvent include ammonia, hydrazine, urea, amines (for example, primary amines such as methylamine, secondary amines such as dimethylamine, tertiary amines such as trimethylamine, and ethylenediamine. Diamine) and melamine. These solvents may be used alone or in combination.
The amount of water and oxygen contained in the solvent is desirably as small as possible, and the content thereof is preferably 1000 ppm or less, more preferably 10 ppm or less, and further preferably 0.1 ppm or less. When ammonia is used as a solvent, the purity is usually 99.9% or more, preferably 99.99% or more, more preferably 99.999% or more, and particularly preferably 99.9999% or more. .

3) Raw material As the raw material, a raw material containing an element constituting the nitride single crystal to be grown on the seed is used. Preferred is a polycrystalline raw material of nitride single crystal and / or gallium, and more preferred is gallium nitride and / or gallium. The polycrystalline raw material need not be a complete nitride, and may contain a metal component in which the group III element is in a metal state (zero valence) depending on conditions. For example, when the crystal is gallium nitride Is a mixture of gallium nitride and metal gallium.
The method for producing the polycrystalline raw material is not particularly limited. For example, a nitride polycrystal produced by reacting a metal or an oxide or hydroxide thereof with ammonia in a reaction vessel in which ammonia gas is circulated can be used. In addition, as a metal compound raw material having higher reactivity, a compound having a covalent MN bond such as a halide, an amide compound, an imide compound, or galazan can be used. Furthermore, a nitride polycrystal produced by reacting a metal such as Ga with nitrogen at a high temperature and a high pressure can also be used.

  The amount of water and oxygen contained in the polycrystalline raw material used as the raw material in the present invention is preferably small. The oxygen content in the polycrystalline raw material is usually 10,000 ppm or less, preferably 1000 ppm or less, particularly preferably 1 ppm or less. The ease of mixing oxygen into the polycrystalline raw material is related to the reactivity with water or the absorption capacity. The worse the crystallinity of the polycrystalline raw material, the more active groups such as NH groups exist on the surface, which may react with water and partially generate oxides or hydroxides. For this reason, it is usually preferable to use a polycrystalline material having as high crystallinity as possible. The crystallinity can be estimated by the half width of powder X-ray diffraction. The half width of the (100) diffraction line (2θ = about 32.5 ° for hexagonal gallium nitride) is usually 0.25 ° or less, preferably It is 0.20 ° or less, more preferably 0.17 ° or less.

4) Reaction vessel The ammonothermal method can be carried out in a reaction vessel.
The reaction vessel can be selected from those capable of withstanding high temperature and high pressure conditions when growing a nitride single crystal. Examples of the reaction vessel include those described in JP-T-2003-511326 (International Publication No. 01/024921 pamphlet) and JP-T-2007-509507 (International Publication No. 2005/043638 pamphlet). A mechanism that adjusts the pressure applied to the reaction vessel and its contents from the outside may be provided, or an autoclave that does not have such a mechanism may be used.

The reaction vessel is preferably made of a material having pressure resistance and erosion resistance, and in particular, a Ni-based alloy, stellite (Deroro Stellite Company, Inc.) having excellent erosion resistance against solvents such as ammonia. It is preferable to use a Co-based alloy such as More preferably, it is an Ni-based alloy. Specifically, Inconel 625 (Inconel is a registered trademark of Huntington Alloys Canada Limited, the same shall apply hereinafter), Nimonic 90 (Nimonic is a registered trademark of Special Metals Wiggin Limited, hereinafter the same), RENE41 (Teledyne Allvac, Inc.), Inconel 718 (Inconel is a registered trademark of Huntington Alloys Canada Limited), Hastelloy (registered trademark of Haynes International, Inc.), Waspaloy (registered trademark of United Technologies, Inc.).
The composition ratio of these alloys depends on the temperature and pressure conditions of the solvent in the system, and the reactivity with the mineralizers and their reactants contained in the system and / or the oxidizing power / reducing power, pH conditions, What is necessary is just to select suitably. In order to use these as materials constituting the inner surface of the reaction vessel, the reaction vessel itself may be manufactured using these alloys, or may be installed in the reaction vessel as an inner cylinder, and any reaction vessel material A plating treatment may be applied to the inner surface of the substrate.

  In order to further improve the erosion resistance of the reaction vessel, the inner surface of the reaction vessel may be lined or coated using the excellent erosion resistance of the noble metal. Moreover, the material of the reaction vessel can be a noble metal. Examples of the noble metal herein include Pt, Au, Ir, Ru, Rh, Pd, Ag, and alloys containing these noble metals as a main component. Among them, Pt and Pt alloys having excellent corrosion resistance are used. Is preferred.

  A specific example of a crystal manufacturing apparatus including a reaction vessel that can be used in a method for manufacturing a nitride single crystal is shown in FIG. FIG. 3 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. 3, crystal growth is performed in a capsule 20 loaded as an inner cylinder in the autoclave 1. The capsule 20 includes a raw material dissolution region 9 for dissolving the raw material and a crystal growth region 6 for growing crystals. A solvent and a mineralizer can be placed in the raw material dissolution region 9 together with the raw material 8, and a seed 7 can be installed in the crystal growth region 6 by suspending it with a wire. Between the raw material dissolution 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. Moreover, in order to give more erosion resistance and to purify the crystal to be grown, the surface of the baffle plate is Ni, Ta, W, Mo, Ti, Nb, Pd, Pt, Au, Ir, and pBN. Pd, Pt, Au, Ir, and pBN are more preferable, and Pt is particularly preferable. In the crystal manufacturing apparatus shown in FIG. 3, the space 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. It should be noted that a valve, a mass flow meter, and a conduit do not necessarily have to be installed in the crystal manufacturing apparatus used when the nitride single crystal manufacturing method is carried out.

  A lining can also be used to provide corrosion resistance by the autoclave. The lining material is preferably at least one metal or element of Pt, Ir, Ag, Pd, Rh, Cu, Au and C, or an alloy or compound containing at least one metal, More preferably, it is an alloy or compound containing at least one or more metals or elements of Pt, Ag, Cu and C, or at least one or more metals because it is easy to line. For example, Pt simple substance, Pt-Ir alloy, Ag simple substance, Cu simple substance, graphite, etc. are mentioned.

5) Manufacturing process A procedure for growing a nitride single crystal by the ammonothermal method will be described. First, a seed, a nitrogen-containing solvent, a raw material, and a mineralizer are put in a reaction vessel and sealed. Prior to introducing them into the reaction vessel, the reaction vessel may be deaerated. Moreover, you may distribute | circulate inert gas, such as nitrogen gas, at the time of introduction | transduction of material. The seed is normally loaded into the reaction vessel at the same time as or after filling the raw material and the mineralizer. The seed is preferably fixed to a noble metal jig similar to the noble metal constituting the inner surface of the reaction vessel. After loading, heat deaeration may be performed as necessary.
When the production apparatus shown in FIG. 3 is used, a capsule, which is a reaction vessel, is sealed with a seed, a nitrogen-containing solvent, a raw material, and a mineralizer, and then the capsule 20 is sealed in a pressure-resistant container (autoclave). 1 is filled, 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 is generally low and it is more easily diffused than the liquid, but has the same solvating power as the liquid. The subcritical state means a liquid state having a density substantially equal to the critical density near the critical temperature. For example, in the raw material filling part, the raw material is melted in a supercritical state, and in the crystal growth part, the temperature is changed so that it becomes a subcritical state, and crystal growth using the difference in solubility between the supercritical state and the subcritical state raw material Is possible.
When in the supercritical state, the reaction mixture is generally maintained at a temperature above the critical point of the solvent. When an ammonia solvent is used, the critical point is a critical temperature of 132 ° C. and a critical pressure of 11.35 MPa. However, if the filling rate with respect to the volume of the reaction vessel is high, the pressure far exceeds the critical pressure even at a temperature below the critical temperature. In the present invention, the “supercritical state” includes such a state exceeding the critical pressure. Since the reaction mixture is enclosed in a constant volume reaction vessel, the increase in temperature increases the pressure of the fluid. In general, if T> Tc (critical temperature of one solvent) and P> Pc (critical pressure of one solvent), the fluid is in a supercritical state.

  Under supercritical conditions, a sufficient growth rate of the nitride single crystal 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 single crystal, the pressure in the reaction vessel is preferably 120 MPa or more, more preferably 150 MPa or more, and further preferably 180 MPa or more. 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. 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 reality, additives such as raw materials and mineralizers, temperature non-uniformity in the reaction vessel, and free volume Depending on the presence of

  The lower limit of the temperature range in the reaction vessel is preferably 500 ° C or higher, more preferably 515 ° C or higher, and further preferably 530 ° C or higher. The upper limit value is preferably 700 ° C. or lower, more preferably 650 ° C. or lower, and further preferably 630 ° C. or lower. When producing a nitride single crystal, it is preferable that the temperature of the raw material dissolution region in the reaction vessel is higher than the temperature of the crystal growth region. The temperature difference (| ΔT |) is preferably 5 ° C. or more, more preferably 10 ° C. or more, and preferably 100 ° C. or less from the viewpoint of maintaining crystal quality and controlling spontaneous nucleation crystals. Preferably, it is 80 degrees C or less, and 60 degrees C or less is especially 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 above 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 the polycrystalline raw material and seed are used in the reaction vessel Subtract the volume of the seed and the structure in which it will be 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. Based on the liquid density at the boiling point of the solvent of the volume to be used, it is usually 20 to 95%, preferably 30 to 80%, more preferably 40 to 70%.

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

The reaction time after reaching a predetermined temperature varies depending on the type of nitride single 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. can do. During the reaction, the reaction temperature may be constant, or the temperature may be gradually raised or lowered. Moreover, you may change the temperature difference of a raw material melt | dissolution area | region and a crystal growth area | region during reaction. After a reaction time for producing desired crystals, the temperature is lowered. The temperature lowering method is not particularly limited, but the heating may be stopped while the heating of the heater is stopped and the reaction vessel is installed in the furnace as it is, or the reaction vessel may be removed from the electric furnace and air cooled. If necessary, quenching with a refrigerant is also preferably used.
After the temperature of the outer surface of the reaction vessel or the estimated temperature inside the reaction vessel is below a predetermined temperature, the reaction vessel is opened. The predetermined temperature at this time is not particularly limited, and is usually −80 ° C. to 200 ° C., preferably −33 ° C. to 100 ° C. Here, the valve may be opened by connecting a pipe to the pipe connection port of the valve attached to the reaction vessel, leading to a vessel filled with water or the like. Furthermore, if necessary, the ammonia solvent in the reaction vessel is sufficiently removed by making a vacuum or the like, and then dried, and the nitride single crystal formed by opening the reaction vessel lid and the like and unreacted raw materials and minerals. Additives such as an agent can be taken out.

  In addition, when manufacturing a gallium nitride by an ammonothermal method, Unexamined-Japanese-Patent No. 2009-263229 can be referred preferably for the detail of materials other than the above, manufacturing conditions, a manufacturing apparatus, and a process. The entire disclosure of this publication is incorporated herein by reference.

[Nitride single crystal after annealing]
(Feature)
The nitride single crystal after the annealing treatment of the present invention has various good characteristics.
The hydrogen (H) concentration of the nitride single crystal after the annealing treatment of the present invention is 5 × 10 ¹⁶ atoms / cm ³ to 1 × 10 ²¹ atoms / cm ³ .
The dopant is activated after the annealing treatment of the present invention, the mobility is greatly improved, and the specific resistance is greatly reduced. Therefore, a nitride single crystal having good electrical characteristics can be obtained by the annealing treatment of the present invention. In addition, the N—H absorption of the infrared absorption spectrum observed in the nitride single crystal before annealing is reduced or eliminated.

The carrier concentration of the nitride single crystal after the annealing treatment is preferably 1 × 10 ¹⁶ cm ⁻³ or more,
It is more preferably 1 × 10 ¹⁷ cm ⁻³ or more, and further preferably 1 × 10 ¹⁸ cm ⁻³ or more. The annealing treatment method of the present invention can be preferably applied particularly to an n-type nitride single crystal. For example, when n-type carrier concentration is less than 1 × 10 ¹⁹ cm ^-3 at 1 × 10 ¹⁷ cm ^-3 greater mobility single crystal of a nitride after annealing (mu) Achieved 150 cm ² / Vs greater It is also possible to achieve more than 200 cm ² / Vs, and still more than 300 cm ² / Vs. In the present invention, since the annealing process is performed for a sufficient time, the mobility can be sufficiently increased. On the other hand, for example, when the n-type carrier concentration is more than 1 × 10 ¹⁶ cm ⁻³ and less than 1 × 10 ¹⁹ cm ⁻³ , the specific resistance (ρ) of the nitride single crystal after annealing is 1 × 10 ^−4. It is possible to be in the range of more than Ωcm and less than 1 × 10 ⁻¹ Ωcm, moreover in the range of more than 1 × 10 ⁻³ Ωcm and less than 7 × 10 ⁻² Ωcm, Incidentally it is also possible to 5 × 10 at ^-3 [Omega] cm than 5 × 10 ^-2 in the range of less than [Omega] cm.

It is desirable for use that the nitride single crystal dopant after annealing is sufficiently activated. Insufficient activation, for example, when using a nitride single crystal at a high temperature, the carrier concentration of the nitride single crystal,
Specific resistance and mobility change and cannot be used stably.
FIG. 4 and FIG. 5 show the carrier concentration and the ratio of the nitride single crystal grown by the vapor phase growth method known that the dopant is sufficiently activated and the nitride single crystal grown by the method of the present invention. The relationship between resistance and the relationship between carrier concentration and mobility are shown. From the viewpoint of sufficiently activating the dopant, it is preferable that the carrier concentration and the specific resistance satisfy the following formula (1) in the carrier concentration range of 1 × 10 ¹⁶ to 1 × 10 ²⁰ cm ^−3. It is more preferable to satisfy the formula (2), and it is more preferable to satisfy the following formula (3).
y ≦ 1.3 × 10 ¹¹ × c ^(-0.678) (1)
y ≦ 6.2 × 10 ¹⁰ × c ^(-0.678) (2)
y ≦ 5.1 × 10 ¹⁰ × c ^(-0.678) (3)
Here, c is the carrier concentration [cm ⁻³ ], and y is the specific resistance [Ωcm].
The carrier concentration and mobility preferably satisfy the following formula (4), more preferably satisfy the following formula (5), and most preferably satisfy the following formula (6).
z ≧ 3.3 × 10 ⁸ × c ^(−0.369) (4)
z ≧ 4.3 × 10 ⁸ × c ^(−0.369) (5)
z ≧ 7.7 × 10 ⁸ × c ^(−0.369) (6)
Here, c is the carrier concentration [cm ⁻³ ], and z is the mobility [cm ² / V * s].

By performing the annealing treatment of the present invention, it is possible to make the dopant activation rate within a range of 10 to 100%. The dopant activation rate here is defined by the following equation.
[CC]
η (%) = ――――― x 100
[D]
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 dopant activation rate is preferably 10% or more, more preferably 20% or more, and further preferably 25% or more.

  By performing the annealing treatment of the present invention, the maximum peak emission intensity of the yellow band peak can be reduced. Specifically, the maximum peak emission intensity of the yellow band peak observed at 530 to 630 nm of the nitride single crystal after the annealing treatment can be reduced as compared with that before the annealing treatment. This is because light emission at the impurity level (yellow band light emission) due to point defects existing in the crystal before the annealing treatment is reduced as a result of the reduction of point defects due to annealing. Along with such a reduction in the emission intensity of the yellow band, the intensity of the band edge emission of a nitride single crystal such as GaN becomes relatively large. Specifically, for example, in SEM-CL spectrum analysis, the ratio of the maximum peak emission intensity of the band edge emission peak at 330 to 400 nm to the maximum peak emission intensity of the yellow band peak at a wavelength of 450 to 750 nm is Although it was about 0.1 before the annealing treatment, it is possible to achieve 0.5 or more when the annealing treatment is performed, and it is also possible to achieve 1 or more. It is also possible to achieve the above. The maximum peak light emission intensity indicates the light emission intensity at a wavelength at which the light emission intensity is maximum among the yellow band peak or the band edge emission peak. The same applies to the emission intensity of the PL spectrum.

By performing the annealing treatment of the present invention, coloring before the annealing treatment can be reduced. For example, a deep yellow to brown nitride single crystal can be turned into a light yellow transparent nitride single crystal by annealing. By the annealing treatment of the present invention, the light transmittance can be improved by 10% or more, further improved by 15% or more, and further improved by 20% or more. In addition, if the nitride single crystal before annealing is excessively colored and the impurity concentration is too high, the carrier concentration becomes too high, the mobility becomes low, the coloration does not improve so much, and it does not become transparent. May become cloudy. For this reason, the concentration of impurities other than hydrogen in the nitride single crystal before annealing is preferably controlled to be less than 1 × 10 ²⁰ / cm ^3, and preferably controlled to be less than 1 × 10 ¹⁹ / cm ^3. Is more preferable, and it is still more preferable to control to less than 1 × 10 ¹⁸ / cm ³ .

(Processing of nitride single crystal after annealing)
The nitride single crystal annealed according to the present invention may be used as it is or after being processed. In the case of processing, for example, processing such as removing at least a part of the surface of the annealed nitride single crystal can be performed. The part to be removed may be the surface of the main surface or another surface. For example, the aspect which removes Ga surface in the case of a GaN crystal can be illustrated.
Examples of processing means include slicing, polishing, chemical etching, and dry etching. Specific procedures for these processes can be appropriately selected from those known as crystal processing methods.

[Wafer]
In the case of a bulk nitride single crystal, a wafer (plate-like crystal) having an arbitrary crystal orientation can be obtained by cutting in a desired direction. For example, when a nitride single crystal having a thick and large-diameter M-plane is manufactured, a large-diameter M-plane wafer can be obtained by cutting in a direction perpendicular to the m-axis. Further, when a nitride single crystal having a large-diameter semipolar surface is produced, a large-diameter semipolar surface wafer can be obtained by cutting in parallel to the semipolar surface.
Nitride single crystals and wafers are suitably used for devices such as light emitting elements and electronic devices. Examples of the light-emitting element in which the nitride single 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. Moreover, examples of the electronic device using the nitride single crystal or the 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).

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.
In each example and comparative example, annealing was performed using the crystal samples described in Table 1. First, a method for preparing crystal samples used in Examples and Comparative Examples will be described.

<Preparation example of crystal sample>
Using the apparatus shown in FIG. 3, a GaN crystal sample was prepared by an ammonothermal method according to the following procedure.
Crystal growth was performed using a RENE41 autoclave as a pressure vessel and a Pt-Ir capsule as a reaction vessel. Polycrystalline GaN particles were placed as raw materials in the capsule lower region (raw material dissolution region 9 in FIG. 3). Next, 99.999% purity NH ₄ I and 99.99% purity GaF ₃ which were sufficiently dried as mineralizers were charged into the capsule.
Further, a platinum baffle plate was installed between the raw material dissolution region at the bottom of the capsule and the crystal growth region at the top. The seed was hung on a platinum seed support frame by a platinum wire and placed in the crystal growth region on the top of the capsule. Next, a cap made of Pt—Ir was connected to the top of the capsule by TIG welding.
A valve was connected to a tube attached to the upper part of the cap, and after vacuum deaeration through a vacuum pump, the capsule was repeatedly purged with nitrogen gas by operating so as to pass through a nitrogen cylinder. Then, it deaerated by heating in the state connected to the vacuum pump. After naturally cooling the capsule to room temperature, the valve was closed and the capsule was cooled with a dry ice ethanol solvent while maintaining the vacuum state. Subsequently, the valve of the conduit was operated so as to pass through the NH ₃ cylinder, the valve was opened again, NH ₃ was filled without touching the outside air, and then the valve was closed again. The filling amount was confirmed from the difference in weight before and after filling NH ₃ .

Subsequently, the capsule was inserted into an autoclave equipped with a valve, the lid was closed, and the weight of the autoclave was measured. Subsequently, the conduit was operated to be connected to a vacuum pump through a valve attached to the autoclave, and the valve was opened to perform vacuum deaeration. After performing nitrogen gas purging several times as in the capsule, the autoclave was cooled with dry ice ethanol solvent while maintaining the vacuum state, and the valve was once closed. Next, after the conduit was operated to lead to the NH ₃ cylinder, the valve was opened again and NH ₃ was charged into the autoclave (autoclave 1 in FIG. 3) without continuously touching the outside air. Based on flow control, after filling the amount of NH ₃ to NH ₃ amount and the balance in the capsule as a liquid, once again closing the valve.
Subsequently, the autoclave was housed in an electric furnace composed of a heater divided vertically. The temperature was raised until the average temperature in the crystal growth region was 617 ° C. and the temperature in the raw material dissolution region was 635 ° C., and then held at that temperature for 20 days. The pressure in the autoclave was about 210 MPa.
Thereafter, the temperature of the outer surface of the autoclave was naturally cooled to return to room temperature, to open the valve comes to the autoclave to remove NH ₃ in the autoclave. Thereafter, the autoclave 1 was weighed to confirm the discharge of NH ₃ , the lid of the autoclave was opened, and the capsule was taken out. A hole was made in the tube attached to the upper part of the capsule to remove NH ₃ from the inside of the capsule. As a result, crystals having a thickness of 3 to 8 mm were obtained.

  A GaN crystal sample having the M surface as the main surface was obtained by performing the above process using a seed having the M surface as the main surface. Moreover, the GaN crystal sample which makes a C surface a main surface was obtained by performing using the seed which made the C surface the main surface.

  In the following examples and comparative examples, the obtained as-grown GaN crystal is used as it is as a bulk crystal, or the obtained as-grown GaN crystal is used as a sliced wafer, or after the obtained as-grown GaN crystal is sliced. Further, the surface was polished by mechanochemical polishing and used. These three types of crystals are shown in Table 1 as having surface states of “as-grown”, “slice”, and “polishing”.

<Example 1>
A surface-polished GaN crystal sample having a main surface of M-plane and a thickness of 300 to 800 μm was placed on a graphite-based surface-coated susceptor and placed in an annealing furnace. Thereafter, the atmosphere in the annealing furnace was switched from air to nitrogen.
Thereafter, the atmosphere gas in the furnace was 90% nitrogen-10% ammonia, the heater was turned on, the temperature control system program was started, and the temperature was raised to 1000 ° C. The temperature rising rate at that time was set to a range of 100 to 1000 ° C./hour. After reaching 1000 ° C., it was held for 50 hours, and then cooled at a cooling rate of 100 to 300 ° C./hour. The atmosphere gas in the furnace was maintained at the same composition from the start of temperature increase until it was cooled to 300 ° C. When the temperature of the annealing furnace showed 300 ° C., the supply of ammonia was stopped, and when the temperature in the furnace reached room temperature, the annealing furnace was opened and the GaN crystal was taken out.
Before annealing, it was confirmed that crystals that had been visually colored yellow were light in color, increased in transparency, and had a coloring improvement effect. Further, from the results of hole measurement of the annealed GaN crystal (Hall measuring instrument manufactured by Toyo Technica Co., Ltd.), the carrier concentration is 1.69 × 10 ¹⁸ / cm ³ , the mobility is 232 cm ² / V · s, and the specific resistance is 1. It was confirmed that the carrier was activated with .59 × 10 ⁻² Ωcm.

The concentrations of H, Si, O, F, and I in the gallium nitride crystals before and after annealing were quantitatively analyzed by SIMS analysis. The apparatus used was a secondary ion mass spectrometer (SIMS) IMS4f manufactured by CAMECA. As analysis conditions, the primary ion beam was Cs, the primary ion energy was 14.5 keV, and the secondary ion polarity was negative. The detection limits under these conditions are as follows: H is 2 × 10 ¹⁷ atoms / cm ³ , Si is 5 × 10 ¹⁴ atoms / cm ³ , O is 2 × 10 ¹⁶ atoms / cm ³ , and F is 1 × 10 ¹⁵ atoms / cm ^3. , I was 2 × 10 ¹⁵ atoms / cm ³ .
Before annealing, H is 3 × 10 ¹⁸ atoms / cm ³ , Si is 1.5 × 10 ¹⁵ atoms / cm ³ , O is 8 × 10 ¹⁹ atoms / cm ³ , and F is 2 × 10 ¹⁷ atoms / cm ^3. , I was below the detection limit, but after annealing, H was 1.3 × 10 ¹⁹ atoms / cm ³ , Si was 1.5 × 10 ¹⁵ atoms / cm ³ , and O was 6.9 × 10 ¹⁸ atoms. / Cm ³ , F was 8.3 × 10 ¹⁷ atoms / cm ³ , and I was below the detection limit. The above results indicate that the carrier is activated by annealing.

It was also confirmed that the intensity of the N—H peak observed at 3050 to 3300 cm ⁻¹ measured by FT-IR decreased before and after annealing.
Furthermore, from the SEM-CL (JEOL Thermal Field Emission Scanning Electron Microscope JSM-7000F-Cathodeluminescence) measurement results at room temperature, the yellow band peak that showed a large peak before annealing decreased after annealing, while GaN The peak intensity showing the band edge emission increased. The maximum peak emission intensity at 450 to 750 nm where the yellow band peak exists is 2000 cps at about 730 nm, and the maximum peak emission intensity at 330 to 400 nm where the band edge emission peak exists is 8000 cps at about 360 nm. When the ratio of luminescence intensity was taken, it increased to about 4 times.

<Examples 2 to 21>
In Examples 2 to 21, using the same annealing furnace as in Example 1, the annealing temperature, annealing time, and crystal form were changed as shown in Table 1 to perform annealing. A bulk crystal having a thickness of about 4 mm was used, and a wafer having a thickness of 300 to 800 μm was used. As for the wafer, the annealing process was performed for the main surface of the M surface and the C surface.
Among Examples 2 to ^17, it was confirmed that the carrier concentration was 1.0 × 10 ¹⁷ cm ⁻³ or more for all the samples subjected to Hall measurement, and the improvement in mobility was confirmed. did it. Moreover, the coloring improvement effect by visual observation was also confirmed. In addition, the evaluation result of the coloring improvement effect in Table 1 is based on the following criteria.
◎ The color becomes light and the transparency increases, and a remarkable coloring improvement effect is recognized with the naked eye.
○ The color is lighter and the transparency is increased, and coloring improvement effect is recognized with the naked eye.
Δ Slightly clouded but weak coloring improvement effect is observed.
× No change is seen with the naked eye and there is no coloring improvement effect.

For Example 2, the concentration of H, O, F, and C in the annealed gallium nitride crystal was quantitatively analyzed by SIMS analysis. The apparatus used was a secondary ion mass spectrometer (SIMS) IMS4f manufactured by CAMECA. As analysis conditions, the primary ion beam was Cs, the primary ion energy was 14.5 keV, and the secondary ion polarity was negative. The detection limits under these conditions are as follows: H is 2 × 10 ¹⁷ atoms / cm ³ , O is 2 × 10 ¹⁶ atoms / cm ³ , F is 1 × 10 ¹⁵ atoms / cm ³ , and C is 1 × 10 ¹⁶ atoms / cm ^3. Met. After annealing, H is 6.3 × 10 ¹⁸ atoms / cm ³ , O is 4.8 × 10 ¹⁸ atoms / cm ³ , F is 2.1 × 10 ¹⁶ atoms / cm ³ , and the carrier concentration is 2.44 ×. It was 10 ¹⁸ / cm ³ .
As shown in Table 1, the activation of the carrier could be confirmed after annealing even in the crystal having a relatively deep coloring. However, the coloration is only weakly improved after annealing as compared with a crystal with relatively thin coloration, the carrier concentration is relatively high at about 1.0 × 10 ¹⁹ cm ^−3, and the mobility is compared with 160 or less. There was a tendency to lower.

<Examples 22 to 24>
In Examples 22 to 24, a nitride crystal was heat-treated in the atmosphere using a muffle furnace (Thermo Scientific, Model: FB1415M).
After placing the sample in the muffle furnace, the annealing temperature was set and heating was started. The sample was heated to a predetermined temperature in about 3 hours, and after 14 hours, the heater was turned off to perform natural cooling, and a sample was taken out. The temperature was performed under the conditions shown in Table 1.
In all cases, it was found that coloring after the annealing was improved compared with that before the annealing. After annealing, there was a substance that appeared to be an oxide on the surface, so hole measurement could not be performed, but the surface was etched with KOH (concentration 48%) and the surface was removed by 5 μm. Then, it turned out that the carrier is activated similarly to Examples 1-21.

<Examples 25-57>
In Examples 25 to 48, the same annealing furnace as in Examples 1 to 21 was used, and annealing treatment was performed by changing the annealing temperature and annealing time as shown in Table 2. When hole measurement was carried out after the annealing treatment, it was found to be activated in the same manner as in Examples 1-24.

  In Examples 49-57, annealing treatment was performed in a nitrogen atmosphere using a muffle furnace (manufactured by ASONE Corporation, Model: HPM-1G). First, a GaN crystal sample was placed on a quartz rack, and then a quartz rack on which the crystal sample was placed was placed in a furnace. Thereafter, the temperature was raised to a predetermined set temperature at 100 ° C./h to 200 ° C./h while flowing nitrogen at 3 L / min., And the temperature was maintained for a predetermined time when the predetermined temperature was reached. After elapse of a predetermined time, the temperature was lowered to 100 ° C. at 100 ° C./h to 150 ° C./h, and then the heater was turned off and naturally cooled while flowing nitrogen to 50 ° C. or less. Thereafter, the crystal sample was taken out from the furnace, and hole measurement was performed in the same manner as in Examples 1 to 24. As a result, it was found that carriers were activated in the same manner as in Examples 1 to 24 inside the crystal.

For the GaN crystal samples after annealing in Examples 38, 39, and 43, the concentrations of H, Si, O, F, and I were quantitatively analyzed by SIMS analysis in the same manner as in Example 1. The detection limits under these conditions are as follows: H is 1 × 10 ¹⁷ atoms / cm ³ , Si is 3 × 10 ¹⁴ atoms / cm ³ , O is 1 × 10 ¹⁶ atoms / cm ³ , and F is 1 × 10 ¹⁵ atoms / cm ^3. , I was 3 × 10 ¹⁵ atoms / cm ³ . As shown in Table 3, the hydrogen ^{concentration, 3.4 × 10 18 cm -3,} 1.4 × 10 19 cm -3, it became 4.3 × 1018 cm ^-3. Further, when comparing the carrier concentration and the analysis result, it was considered that O was the main dopant of n-type. Since Si and F can also be an n-type dopant, the sum of the concentrations of O and Si and F was used as the dopant concentration, and the activation rate was calculated. In Example 1, Example 38, Example 39, and Example 43, , 22%, 37%, 41% and 79%, respectively.

FT-IR analysis was performed on the annealed GaN crystal samples of Examples 32-36 and the unannealed GaN crystal samples cut out from the same crystals as the crystal samples used in Examples 32-36.
The measurement was performed by a microscopic FT-IR method, and a MAGNA-IR560 manufactured by Nicolet was used as an apparatus. The conditions were a wavelength resolution of 4 cm ⁻¹ and an integration count of 1024. Table 4 shows the results of normalization of the peak intensity after annealing, with the intensity before annealing set to 1 for the peak intensity measured at a wave number of 3100 to 3200 cm ⁻¹ . After annealing, it was confirmed that the peak intensity was reduced compared to before annealing.

  The absorption coefficient was measured for the annealed GaN crystal samples of Examples 35, 36, and 41 and the unannealed GaN crystal samples divided from the same sample as the crystal samples used in Examples 35, 36, and 41. First, a sample is placed in a 20 inch integrating sphere (manufacturer: LabSphere, model number: LMS-200) and driven outside the integrating sphere (manufacturer: audio-technica, model number: (405 nm) SU-62. -405, (445nm) SU-62-445) was introduced into the integrating sphere. Next, the sample was irradiated with the laser, and the case where the sample was not irradiated with the laser was used as a reference, and the absorption coefficient was obtained from the thickness of the substrate and the laser intensity reduction rate. Table 5 shows the measurement results at wavelengths of 405 nm and 445 nm. When the absorption coefficient in the case of annealing is divided by the absorption coefficient in the case without annealing, the crystal samples used in Example 35, Example 36, and Example 41 are 0.60 and 0.45 at a wavelength of 405 nm, respectively. 0.34, wavelength 455 nm, the crystal samples used in Example 35, Example 36, and Example 41 have small absorption coefficients of 0.51, 0.46, and 0.18, respectively, with annealing. It was confirmed that it improved. Further, in the transmittance when the substrate thickness is assumed to be 350 μm, when the transmittance with annealing is subtracted by the transmittance with no annealing, in the wavelength of 405 nm, in Example 35, Example 36, and Example 41, The crystal samples used were 7.8%, 11.4%, 32.8%, and the wavelength 455 nm, respectively, and the crystal samples used in Example 35, Example 36, and Example 41 were 3.1. %. It was confirmed to improve to 3.7% and 21.1%.

<Example 58>
With respect to the crystal sample cut out from the same GaN crystal as the GaN crystal sample used in Example 42, SEM-CL measurement of the annealed sample and the sample not annealed was performed in the same manner as in Example 1. The sample with annealing and the sample without annealing were prepared by dividing the same sample. Annealing was performed in the same annealing furnace and the same conditions as in Examples 52-57. From the measurement results shown in FIG. 6, the peak of the yellow band, which showed a large peak before annealing, decreased after annealing, while the peak intensity indicating GaN band edge emission increased. Further, the maximum peak emission intensity at 450 nm to 750 nm where the yellow band peak exists is 36147 cps at 544 nm, and the maximum peak emission intensity at 330 nm to 400 nm present at the band edge emission peak is 110849 cps at 366 nm. When the intensity ratio was taken, it increased to about 3 times.

<Comparative Examples 1 and 2>
In Comparative Examples 1 and 2, the surface-polished GaN crystal sample obtained by the above ammonothermal method was tried to perform hole measurement without annealing.
In Comparative Example 1, it did not have conductivity and could not be measured. When SEM-CL spectrum analysis was performed at room temperature, the maximum peak emission intensity at 450 to 750 nm where the yellow band peak was present was 9000 cps at about 570 nm, and at 330 to 400 nm where the band edge emission peak was present. A certain maximum peak emission intensity was 1000 cps at about 360 nm, and it was about 0.1 times when the ratio of emission intensity was taken.
Also in Comparative Example 2, hole measurement was not possible. When the measurement was performed with a non-contact type sheet resistance measuring device (model number: LEI1510, manufactured by Reheighton) instead of the hole measurement, the carrier concentration was 5.59 × 10 ¹² / cm ³ and the mobility was 5.4 cm ² / V. S and specific resistance was 2.09 × 10 ⁻⁴ Ωcm, and the carrier was not activated and the resistance was high.

<Comparative Example 3>
A GaN crystal sample whose main surface was M-surface polished was subjected to heat generation gas analysis (TPD-MS). The equipment used was Shimadzu TPD-MS equipment.
The GaN crystal is put in a TPD-MS analyzer, and the GaN crystal is heated to 1000 ° C. at 20 ° C./min in a helium gas atmosphere with a helium gas flow rate of 50 mL / min (upper) and 0 mL / min (bottom). After heating, when the temperature reached 1000 ° C., the heater power supply was turned off and the mixture was naturally cooled to take out the GaN crystal.
In TPD-MS analysis, generation of hydrogen was confirmed. Thereby, it is estimated that hydrogen is generated from the crystal by heating. Further, when the hole measurement of GaN used for the measurement was performed, the carrier concentration was 1.20 × 10 ¹⁸ cm ⁻³ , the mobility was 72.2 cm ² / V · s, and the specific resistance was 7.12 × 10 ^{−. Although} the carrier was activated at ² Ωcm, it was confirmed that the mobility was insufficiently improved. This indicates that the annealing time is insufficient.

<Comparative example 4>
Using the same annealing furnace as in Examples 49 to 57, the GaN crystal sample with the main surface sliced into the M plane was annealed in a nitrogen atmosphere at 750 ° C. for 5 hours.
After that, Hall measurement was carried out, but measurement was not possible. This indicates that the annealing time is insufficient and the dopant is not fully activated.

DESCRIPTION OF SYMBOLS 1 Autoclave 2 Autoclave inner surface 3 Lining 4 Lining inner surface 5 Baffle plate 6 Crystal growth region 7 Seed 8 Raw material 9 Raw material melting region 10 Valve 11 Vacuum pump 12 Ammonia cylinder 13 Nitrogen cylinder 14 Mass flow meter 20 Capsule 21 Capsule inner surface 100 Quartz tube 101 Nitride Crystal 102 Susceptor 103 Heat shield plate 104 Water cooling flange 105 Introduction pipe 106 Exhaust pipe 107 Heater 108 Heater 109 Heater 110 Thermocouple

Claims (20)

A nitride single crystal annealing method in which a nitride single crystal grown in the presence of a supercritical and / or subcritical nitrogen-containing solvent is annealed at 750 ° C. or more for 5.5 hours or more. 2. The method for annealing a nitride single crystal according to claim 1, wherein the annealing temperature is 750 to 1250 ° C. 3. The nitride single crystal annealing method according to claim 1 or 2, wherein the nitride single crystal is in a bulk form. The nitride single crystal annealing method according to claim 1, wherein the nitride single crystal is in the form of a wafer. The nitride single crystal annealing method according to claim 1, wherein at least part of the surface of the nitride single crystal after the annealing treatment is removed. The method for annealing a nitride single crystal according to claim 1, wherein the nitride single crystal is grown using an acidic mineralizer. The nitride single crystal annealing method according to any one of claims 1 to 6, wherein a concentration of impurities other than hydrogen in the nitride single crystal before the annealing treatment is 1 × 10 ²⁰ / cm ³ or less. The nitride single crystal according to any one of claims 1 to 7, wherein an n-type dopant concentration of the nitride single crystal before the annealing treatment is 1 × 10 ¹⁶ / cm ³ to 1 × 10 ²⁰ / cm ^3. Annealing treatment method. The nitride single crystal annealing method according to claim 8, wherein the n-type dopant is one or more selected from the group consisting of oxygen, sulfur, selenium, tellurium, silicon, germanium, tin, and a halogen element. The nitridation according to any one of claims 1 to 9, wherein a hydrogen (H) concentration of the nitride single crystal after the annealing treatment is 5 × 10 ¹⁶ atoms / cm ³ to 1 × 10 ²¹ atoms / cm ^3. An annealing method for a single crystal. The main surface of the nitride single crystal is a Ga plane, an N plane, an M plane, a semipolar plane, or a plane inclined within a range of ± 15 ° from these planes. The nitride single crystal annealing method described. The nitride single crystal annealing method according to claim 1, wherein the nitride single crystal is GaN. The nitride single crystal which performed the annealing method of any one of Claims 1-12. The nitride single crystal according to claim 13, wherein the carrier concentration is 1 × 10 ¹⁶ cm ⁻³ or more. 15. The nitride unit according to claim 13 or 14, wherein the n-type carrier concentration is greater than 1 × 10 ¹⁷ cm ⁻³ and less than 1 × 10 ¹⁹ cm ⁻³ and the mobility (μ) is greater than 150 cm ² / Vs. crystal. The n-type carrier concentration is more than 1 × 10 ¹⁶ cm ⁻³ and less than 1 × 10 ²⁰ cm ⁻³ , and the specific resistance (ρ) is more than 1 × 10 ⁻⁴ Ωcm and less than 1 × 10 ⁻¹ Ωcm Item 15. The nitride single crystal according to any one of Items 13 to 15. The nitride single crystal according to any one of claims 13 to 16, wherein a dopant activation rate η represented by the following formula is 10 to 100%.
[CC]
η (%) = ――――― x 100
[D]
(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 ). .) In the emission spectrum analysis, the ratio of the maximum peak emission intensity of the band edge emission peak at 330 to 400 nm to the maximum peak emission intensity of the yellow band peak at a wavelength of 450 to 750 nm is 1 or more. The nitride single crystal according to any one of the above. 19. The nitride single crystal according to claim 13, wherein the hydrogen (H) concentration is 5 × 10 ¹⁶ atoms / cm ³ or more. A wafer comprising the nitride single crystal according to any one of claims 13 to 19.