JP2019196294A - Production method of group iii nitride crystal - Google Patents

Abstract

To provide a production method of a group III nitride crystal containing less oxygen impurities in a crystal.SOLUTION: The production method of a group III nitride crystal is provided that is configured to produce the group III nitride crystal l using: a crucible which stores alkali metal, a group III element-containing raw material, and a seed substrate 11; a reaction container which stores the crucible; a pressure container which stores the reaction container 15; a gas supply pipe which introduces a nitrogen-containing gas and/or an argon gas into the pressure container; a lid which seals the pressure container; a heater which heats the pressure container; an insulating material which insulates the heater and reaction container from each other; and a heat insulating material which prevents a thermal leak in the reaction container. The production method of a group III nitride crystal comprises the steps of: separating the lid from the pressure container to store the reaction container in the pressure container and sealing the pressure container with the lid, then filling the pressure container with the argon gas; heating and holding the argon gas; discharging the heated argon gas from the pressure container; and introducing the nitrogen element-containing gas into the pressure container thereby reacting the alkali metal with the group III element-containing raw material and thus growing the group III nitride crystal on the seed substrate.SELECTED DRAWING: Figure 1

Description

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

  In recent years, Group III nitride crystals such as GaN crystals and InGaAlN-based crystals are materials used for light emitting devices such as blue LEDs, white LEDs, and blue-violet LDs used as Blu-ray (registered trademark) reading and writing light sources. As such, its development has been actively conducted. In order to realize the above light emitting device having high luminance and high reliability, a group III nitride crystal serving as a base substrate of the device includes a metal element such as Fe, Zn, Mg, Al, O or C. Thus, there is a demand for crystals with few light elements such as impurities.

  Currently, most of group III nitride crystals used in these semiconductor devices are MOCVD (metal organic chemical vapor deposition) or MBE (molecular beam crystal growth) using sapphire or SiC as a seed substrate. ) And the like. As part of the vapor phase method, in the HVPE method (halogenated vapor phase epitaxy method), sapphire or GaAs is used as a seed substrate, GaN is grown on the seed substrate, and then a GaN crystal is grown from the seed substrate. By separating the GaN crystal, a GaN crystal is obtained.

On the other hand, as a method for producing a GaN crystal by a liquid phase method, nitrogen (N ₂ ) is dissolved in a mixed melt of alkali metal sodium (Na) and a group III element gallium (Ga) to grow the GaN crystal. There is a flux method.

  The flux method allows crystal growth under low temperature and low pressure as compared with other liquid phase growth, and the obtained group III nitride crystal has an advantage of low dislocation density. Development for practical use is being actively conducted.

  However, the flux method has two problems for practical use. The alkali metal sodium (Na) used in the mixed melt has the effect of causing nitride crystal growth on the seed substrate under low temperature and low pressure. On the other hand, due to the oxidizability and hygroscopic properties that are characteristic of metallic sodium, when it touches the atmosphere even slightly, it reacts rapidly with oxygen and moisture in the atmosphere to produce sodium oxide and sodium hydroxide. Sodium oxide and sodium hydroxide in the mixed melt produced by the reaction with the atmosphere become a hindrance to crystal growth, and group III nitride crystals have oxygen in the atmosphere as an impurity. There is a possibility of taking in large quantities. When oxygen is taken into a nitride crystal by a flux method using a mixed melt, the obtained group III nitride single crystal is colored black and cannot be used as a base substrate of a device. This is the first problem of the flux method.

The flux method has another problem. If the mixed melt is not stirred uniformly during crystal growth, macro defects (inclusions) in which alkali metal is taken into the crystal occur. In addition, a large amount of miscellaneous crystals are generated at the boundary between the mixed melt and nitrogen (N ₂ ). Therefore, the group III raw material is consumed for the growth of miscellaneous crystals, and the nitride crystals cannot be grown thick. In addition, a nitride crystal having a macro defect cannot be used as a base substrate of a device because the macro defect is ruptured when heat treatment is performed in a subsequent subsequent process. This is the second problem of the flux method.

  In order to uniformly agitate the mixed melt, for example, as devised and implemented by the present inventor, a plurality of heaters are arranged in the reaction vessel, and the plurality of heaters are strictly controlled independently during crystal growth. There is a measure to provide a temperature distribution by controlling to. By utilizing the thermal convection of the mixed melt generated thereby, the mixed melt can be stirred uniformly and the occurrence of macro defects and miscellaneous crystals can be suppressed.

  In the above measures, in order to realize the temperature distribution condition with high accuracy, for example, carbon is used as the material of the heater arranged in the reaction vessel, and a plurality of heaters are controlled independently. BN (boron nitride) is used as a material for insulating the independent carbon heaters, and a fibrous ceramic is used as a heat insulating material for preventing heat escape inside the pressure vessel. It is known that both BN and fibrous ceramic materials have hygroscopicity and oxidation properties, and particularly BN has high hygroscopicity.

  Since the flux method uses easily oxidizable and easily hygroscopic metallic sodium as a raw material, oxygen is easily taken into the nitride crystal. Therefore, in the flux method, it is necessary to reduce moisture absorption and oxidation of the mixed melt. On the other hand, in order to suppress the macro defects of the above-described nitride crystal and to suppress miscellaneous crystals, a temperature distribution that causes the mixed melt to be convective is necessary. Therefore, it is said that a device configuration in which a plurality of hygroscopic carbon heaters, an insulating material, and a heat insulating material are combined in the pressure vessel is necessary. The flux method has a trade-off relationship with respect to the problem of oxygen impurities and macro-defects in nitride crystals, and the countermeasures of both have a negative effect if one is taken and the other gets worse. Yes.

  The flux method performed by the present inventors also had the same problem. The inside of the crystal growth apparatus developed by the present inventor could not generate appropriate thermal convection in the mixed melt because the heater structure was simple at the beginning. As a result, a macro defect always occurred in the obtained nitride crystal, and a thick nitride crystal could not be obtained due to generation of miscellaneous crystals. As described above, the present inventor has complicated the heater structure and strictly controlled the temperature condition. As a result, the macro defects were improved, but the resulting nitride crystal was colored due to oxygen. In particular, the coloration of nitride crystals may occur suddenly even with the same procedure and the same material. Moreover, there was a case where it suddenly improved without a clear reason. Therefore, the present inventor has been troubled by the problem of the coloration of nitride crystals lacking in stability, that is, the problem of oxygen impurities.

  Therefore, in the flux method, a plurality of inventions relating to the structure of the manufacturing apparatus, the pressure vessel, and the reaction vessel are disclosed as disclosed in Patent Literature 1 and Patent Literature 2 in order to solve the above-described problem with respect to coloring of the nitride crystal.

Patent No. 4968708 Patent No. 4963108

  In both Patent Documents 1 and 2, the reaction vessel is hermetically sealed before heating and pressurizing treatment, and communicated by deformation or melting of the hermetic portion during heating or pressurizing treatment or during the treatment. The reaction container is not exposed to moisture.

  However, in the above-described method, the water discharged from the member in the pressure vessel after being communicated has a possibility of oxidizing the alkali metal of the mixed melt in the reaction vessel and affecting the crystal growth. .

  An object of the present disclosure has been made in view of the problems of the flux method, and is to provide a method for producing a group III nitride crystal with less oxygen impurities in the crystal.

In order to achieve the above-described object, a Group III nitride crystal manufacturing method according to the present disclosure includes an alkali metal, a Group III element-containing raw material, a crucible for storing a seed substrate, a reaction container for storing the crucible, and the reaction container. A pressure vessel containing nitrogen, a gas supply pipe for introducing nitrogen-containing gas and / or argon gas into the pressure vessel, a lid for sealing the pressure vessel, a heater for heating the reaction vessel, the heater and the reaction vessel, A method for producing a group III nitride crystal by using an insulating material for insulating a heat insulating material for preventing heat leakage in the reaction vessel,
Separating the lid from the pressure vessel, storing the reaction vessel in the pressure vessel, sealing the pressure vessel with the lid, and then filling the pressure vessel with argon gas;
Heating and holding the argon gas;
Discharging the heated argon gas from the pressure vessel;
Introducing the nitrogen element-containing gas into the pressure vessel, reacting the alkali metal and the group III element-containing raw material to grow a group III nitride crystal on the seed substrate;
Have

  According to the method for producing a group III nitride crystal according to the present invention, prior to the growth process of the group III nitride crystal, the pressure vessel is filled with argon, the argon is heated and held, and then the heated argon Is discharged from the pressure vessel. As a result, it is possible to remove moisture absorbed by the insulating material and the heater inside the pressure vessel, which is a problem in the flux method. Further, a hygroscopic heater, a heat insulating material, and an insulating material can be freely arranged inside, and a temperature distribution that generates convection can be realized. Therefore, according to the method for producing a group III nitride crystal according to the present invention, there is an effect that a group III nitride crystal with few oxygen impurities can be produced.

1 is a schematic cross-sectional view showing a group III nitride crystal manufacturing apparatus according to Embodiment 1. FIG. FIG. 2 is a flowchart showing the order of the crystal growth method according to the first embodiment. FIG. 3A is a schematic cross-sectional view showing a state in the pressure vessel in the process of S07 in which a reaction vessel is installed in the pressure vessel in the method for producing a group III nitride crystal according to Embodiment 1. FIG. 3B is a schematic cross-sectional view showing the inside of the pressure vessel in the process of S08 in which the inside of the pressure vessel is evacuated in the method for producing a group III nitride crystal according to Embodiment 1. FIG. 3C shows the state in the pressure vessel in the steps S09 and S10 in which argon gas is sealed in the pressure vessel and pressurization and high temperature are continued in the method for producing a group III nitride crystal according to the first embodiment. It is a schematic sectional drawing shown. FIG. 3D is a schematic diagram illustrating a state in the pressure vessel in the step of S12 in which argon gas is discharged from the pressure vessel when the dew point is −38 ° C. or lower in the method for producing a group III nitride crystal according to the first embodiment. It is sectional drawing. FIG. 3E is a schematic cross-sectional view showing a state in the pressure vessel in the step of S13 in which nitrogen gas is sealed in the pressure vessel in the method for producing a group III nitride crystal according to Embodiment 1. FIG. 4 is a diagram showing the quality of the group III nitride crystal obtained when the crystal growth is performed three times according to the first embodiment. FIG. 5 is a flowchart showing the order of the crystal growth method in Comparative Example 1. FIG. 6A is a schematic cross-sectional view showing a state in the pressure vessel in the process of S07 in which a reaction vessel is installed in the pressure vessel in the method for producing a group III nitride crystal according to Comparative Example 1. FIG. 6B is a schematic cross-sectional view showing a state in the pressure vessel in the process of S08 in which the inside of the pressure vessel is evacuated in the method for producing a group III nitride crystal according to Comparative Example 1. FIG. 6C is a schematic cross-sectional view showing the state in the pressure vessel in the step of S13 in which nitrogen gas is sealed in the pressure vessel in the method for producing a group III nitride crystal according to Comparative Example 1. FIG. 7 is a diagram showing the quality of the Group III nitride crystal obtained when the crystal growth is performed three times in Comparative Example 1. FIG. 8 is a diagram showing the relationship between the dew point of nitrogen gas discharged 20 hours after the start of heating and the degree of coloration of the group III nitride crystal in Comparative Example 2. FIG. 9 is a list of results obtained by measuring impurities in the nitride crystals obtained in Example 1 and Comparative Example 1 by D-SIMS.

A method for producing a Group III nitride crystal according to the first aspect includes an alkali metal, a Group III element-containing raw material, a crucible for storing a seed substrate, a reaction container for storing the crucible, a pressure container for storing the reaction container, nitrogen Gas supply pipe for introducing element-containing gas and / or argon gas into the pressure vessel, lid for sealing the pressure vessel, heater for heating the reaction vessel, insulating material for insulating the heater and the reaction vessel A method for producing a group III nitride crystal using a heat insulating material that prevents heat leakage in the reaction vessel,
Separating the lid from the pressure vessel, storing the reaction vessel in the pressure vessel, sealing the pressure vessel with the lid, and then filling the pressure vessel with argon gas;
Heating and holding the argon gas;
Discharging the heated argon gas from the pressure vessel;
Introducing the nitrogen element-containing gas into the pressure vessel, reacting the alkali metal and the group III element-containing raw material to grow a group III nitride crystal on the seed substrate;
It is characterized by having.

  A method for producing a group III nitride crystal according to a second aspect is the method according to the first aspect, wherein the step of filling the argon gas, the step of heating and holding the argon gas, and the step of heating the argon gas The step of discharging may be repeated.

  The method for producing a group III nitride crystal according to the third aspect may include a step of measuring a dew point of the exhausted gas in the first or second aspect.

  In the method for producing a group III nitride crystal according to the fourth aspect, in any one of the first to third aspects, the dew point of the exhausted gas may be −38 ° C. or lower.

  In the method for producing a group III nitride crystal according to a fifth aspect, in any one of the first to fourth aspects, the insulating material is made of boron nitride, and the argon gas is heated at 200 to 700 ° C. You may heat and hold | maintain.

  In the method for producing a group III nitride crystal according to a sixth aspect, in any one of the first to fifth aspects, a carbon heater may be used as the heater.

(Embodiment 1)
1 is a schematic cross-sectional view showing a group III nitride crystal manufacturing apparatus according to Embodiment 1. FIG. With reference to FIG. 1, the example of a structure of the manufacturing method of the group III nitride crystal which concerns on Embodiment 1, and the group III nitride crystal manufacturing apparatus used is demonstrated.

<Group III nitride crystal production equipment>
Since group III nitride crystal production apparatus 10 according to the first embodiment grows group III nitride crystal 12 on seed substrate 11, mixed melt 13 containing an alkali metal and at least a group III element, seed substrate 11. The crucible container 14 and the reaction container 15 in which they are stored can be installed on the reaction container installation table 16. The reaction vessel 15 is detachable from the reaction vessel installation base 16.

  In order to keep the pressure inside the pressure vessel 28 constant, the group III nitride crystal production apparatus 10 is composed of a pressure vessel 28 having a closed shape made of stainless steel and a lid 27. The pressure vessels 28 and 27 are sealed by an O-ring (not shown).

  In order to suppress the occurrence of the macro defects, the inside of the group III nitride crystal manufacturing apparatus 10 includes a bottom heater 17 to an upper stage heater 20 supported by a heater support tube 25. Furthermore, the heat insulating material 26 and the insulating materials 21 to 24 for independently controlling the heaters 17 to 20 are configured.

The group III nitride crystal production apparatus 10 includes a nitrogen (N ₂ ) gas 32 and a pressure regulator 31 for supplying a group III nitride crystal raw material, and moisture adsorbed inside the apparatus, which is the gist of the present disclosure. Are provided with an argon (Ar) gas 34 and a pressure regulator 33 thereof. Nitrogen (N ₂ ) and argon (Ar) can be supplied to the pressure vessel 28 by the mass flow controller 30 and the gas supply pipe 29. The nitrogen element dissolved in the mixed melt is sufficient if it becomes a nitrogen source for growing a group III nitride crystal. For example, in addition to nitrogen (N ₂ ) gas, nitrogen element-containing gas such as ammonia (NH ₃ ) hydrazine (N ₂ H ₄ ) sodium azide (NaN ₃ ) can be applied.

During crystal growth, it is desirable to supply nitrogen (N ₂ ) at a constant flow rate (for example, 1000 sccm) by the mass flow controller 30. In order to make the set pressure constant during crystal growth, the pressure regulator 40 connected by the pressure gauge 39 and the communication cable 41 discharges nitrogen (N ₂ ) and maintains the pressure of the pressure gauge 39 constant. Adjust the pressure. Further, the nitrogen (N ₂ ) argon (Ar) discharged can be measured for moisture by the dew point measuring device 42.

  The group III nitride crystal production apparatus 10 includes an exhaust pipe 35, a valve 36, and a vacuum pump 38 for expelling the air that enters when the pressure vessel 28 and the lid 27 are separated. Further, the degree of vacuum in the pressure vessel 28 can be measured by the vacuum gauge 37.

<Method for Producing Group III Nitride Crystal>
While referring to the flow chart up to the start of crystal growth in FIG. 2 and the schematic cross-sectional views shown in stages until the crystal growth in FIGS. 3A to 3E, the method for producing a group III nitride crystal according to the first embodiment This will be described in detail.

(1) The group III nitride crystal production apparatus 10 closes the mass flow controller 30 and the pressure regulator 40, opens the valve 36, operates the vacuum pump 38 connected to the exhaust pipe 35, and evacuates the pressure vessel 28. Do. At the same time, the heaters 17 to 20 are energized to heat the inside of the furnace (S01). After the previous crystal growth, vacuum baking is performed for the purpose of expelling moisture adsorbed at the time of opening. During vacuum baking, the degree of vacuum in the furnace is monitored by the vacuum gauge 37, and the degree of vacuum is desirably 1 × 10 ⁻¹ Pa or less. If it is 1 × 10 ⁻¹ Pa or higher, either an O-ring (not shown) for sealing the pressure vessel 28 and the lid 27 or a joint (not shown) used in the gas supply pipe 29 and the exhaust pipe 35 There is a possibility that a leak has occurred or a large amount of moisture is adsorbed on the internal member. Since both affect the crystal growth, it is desirable to record the degree of vacuum shown by the vacuum gauge 37 with respect to the elapsed time of evacuation, and periodically inspect for leaks in the joint with a snoop solution. . In order to reduce the load of the heaters 17 to 20 and perform effective vacuum baking, the heating temperature is 900 ° C. or more and 1000 ° C. or less, and the vacuum baking is performed until the vacuum degree indicated by the vacuum gauge 37 is saturated. It is desirable to carry out for 12 hours or more.

(2) Non-oxidation (not shown) of seed substrate 11, crucible vessel 14, reaction vessel 15, group III element material, and alkali metal used for crystal growth when group III nitride crystal production apparatus 10 is performing vacuum baking It is carried into a glove box with a sex atmosphere (S02). The purpose is to remove moisture adsorbed on the surface of these members and materials in an inert gas atmosphere in the glove box.

(3) Stop the heaters 17 to 20 and close the valve 36 and stop the vacuum pump 38 so that the reaction vessel 15 can be installed in the pressure vessel 28 at a temperature of 100 ° C. or less (S03). If the crystal growth apparatus is cooled while the evacuation is continued, the time for which the temperature becomes 100 ° C. or less is about 30 hours.
(4) In order to shorten the temperature lowering time, it is desirable to shorten the cooling time within 8 hours by sealing nitrogen (N ₂ ) in the pressure vessel 28 at 3.0 MPa (S04). If the reaction vessel 15 is installed and evacuated at 100 ° C. or higher, the vapor pressure of the alkali metal is lowered and the alkali metal is liable to vaporize.

(5) A seed substrate 11, a group III element material, and an alkali metal are placed in the crucible container 14 in a non-oxidizing glove box (not shown) one hour before the pressure vessel 28 becomes 100 ° C. or less. . The crucible container 14 is further accommodated in the reaction container 15 (S05). During work, make sure that the oxygen concentration in the glove box is maintained at 1 ppm or less and that the alkali metal is not discolored. When the easily oxidizable alkali metal is oxidized, that is, discolored in the glove box, the oxidized alkali metal is removed using a ceramic knife.

(6) After storing the crucible container 14 in which the group III element, alkali metal, and seed substrate 11 are installed in the reaction container 15, the nitrogen gas in the pressure container 28 is discharged, the pressure container lid 27 is removed, and the inside of the pressure container 28 Open to the atmosphere.

(7) After removing the pressure vessel lid 27, the reaction vessel 15 is taken out of the glove box (S06), the reaction vessel 15 is installed on the installation base 16 of the pressure vessel 28, and the pressure vessel lid 27 is closed (S07). FIG. 3A is a schematic cross-sectional view showing a state in the pressure vessel in step S07 in which a reaction vessel is installed in the pressure vessel in the method for producing a group III nitride crystal according to Embodiment 1. The inside of the pressure vessel 28 is an atmospheric atmosphere 43, and moisture 44 derived from atmospheric components is adsorbed to the internal insulating materials 22 and 23 and the carbon heater 19. In order to explain the outline, all members are not shown. Regarding the time for installing the reaction vessel 15 on the installation table 16 from the inside of the glove box, there is a description that the nitride crystal is colored even in the time required for 5 minutes in the prior literature, and it is said that the shorter the better. This is intended to prevent moisture present in the atmospheric component from adsorbing to the member, but in the present disclosure, the same effect can be obtained even if the time is 30 minutes.

(8) After closing the pressure vessel lid 27, the valve 36 is opened, the vacuum pump 38 is operated, and evacuation is performed to exhaust the internal atmosphere 45 (S08). FIG. 3B is a schematic cross-sectional view showing the inside of the pressure vessel in the step S08 in which the inside of the pressure vessel 28 is evacuated in the method for producing a group III nitride crystal according to Embodiment 1. Although the inside of the pressure vessel 28 is evacuated, the moisture 44 adhering to the insulating material 23 and the carbon heater 19 remains in the apparatus. When evacuating, it is desirable to monitor the degree of vacuum of the vacuum gauge 37, and the vacuum 46 in the pressure vessel 28 is equal to or less than 1 × 10 ⁻¹ Pa, which is the same as the degree of vacuum obtained by vacuum baking before loading. More desirably.

(9) The vacuum pump 38 is stopped and the valve 36 is closed. Thereafter, the pressure regulator 33 and the mass flow controller 30 are opened, and argon (Ar) gas is sealed at 1.0 MPa (S09), the inside of the pressure vessel 28 is heated to 200 ° C., and the argon gas atmosphere is pressurized and heated. The state is continued for 1 hour (S10). FIG. 3C shows a method for producing a group III nitride crystal according to Embodiment 1, in which argon gas is sealed in the pressure vessel 28 and the pressure vessel 28 in the steps S09 and S10 in which pressurization and high-temperature conditions are continued. It is a schematic sectional drawing which shows a state. By heating the enclosed argon gas 47, the moisture 44 absorbed by the insulating material 23 and the heater 19 can be removed. The heating temperature is desirably set to a temperature at which moisture is most removed by conducting a degassing test of the insulating material 23 and the heater 19 in advance under an argon atmosphere. When BN is used as the material of the insulating material 23, the effect of removing moisture is highest at 200 to 700 ° C. In order to prevent the alkali metal disposed in the pressure vessel 28 from being vaporized, the set pressure of argon is preferably 0.1 MPa or more, and more preferably 1.0 MPa or more. Here, the reason for using argon gas is its specific heat. The specific heat of argon is 519 J / kg ° C., nitrogen is 1043, J / kg ° C., and helium is 5,195 J / kg ° C., which is the lowest specific heat among the inert gases. That is, it can be said that argon is an inert gas that is easily heated and has a high effect of removing moisture. By utilizing this feature, the moisture absorbed by the insulating material and heater inside the pressure vessel, which is a problem in the flux method, can be taken into the argon atmosphere 47 as moisture 48 and removed. Further, a hygroscopic heater, a heat insulating material, and an insulating material can be freely arranged inside, and a temperature distribution that generates convection can be realized. Therefore, according to the method for producing a group III nitride crystal according to the present invention, a group III nitride crystal with few oxygen impurities and few macro defects can be produced.

(10) After maintaining the pressurization with argon gas and the high temperature state, the pressure regulator 40 is emptied for 1 minute. A part of the argon gas in the furnace is discharged, and the moisture contained in the exhaust gas is measured by the dew point measuring device 42 connected to the exhaust pipe 35 (S11). In order to solve this problem, the dew point is desirably −38 ° C. or less from the data of Example 2 described later. If the temperature is -38 ° C or higher, the adsorbed moisture may not be completely removed. After cooling to 100 ° C, cycle purge is performed by performing vacuuming and argon filling multiple times. Thus, the dew point can be -38 ° C or lower.

(11) Since argon gas is not required for crystal growth, after the temperature in the furnace becomes 100 ° C. or lower, the valve 36 is opened, the vacuum pump 38 is operated, and the argon gas 49 inside the pressure vessel 28 and adsorption are performed. The drained water 50 is discharged (S12). FIG. 3D shows the state of the pressure vessel 28 in the step S12 in which argon gas 49 is discharged from the pressure vessel 28 when the dew point is −38 ° C. or lower in the method for producing a group III nitride crystal according to the first embodiment. It is a schematic sectional drawing which shows. Thereafter, the pressure vessel 28 is evacuated 46.

(12) The valve 36 is closed, the vacuum pump 38 is stopped, the pressure regulator 31 and the mass flow controller 30 are opened, nitrogen gas 32 is sealed inside the pressure vessel 28, and the pressure is set to 3.4 MPa. FIG. 3E is a schematic cross-sectional view showing a state in pressure vessel 28 in the step S13 in which nitrogen gas is sealed in pressure vessel 28 in the method for producing a group III nitride crystal according to Embodiment 1. As shown in FIG. 3E, almost no moisture remains in the pressure vessel 28 and a nitrogen atmosphere 51 is formed.

(13) The heaters 17 to 20 are energized, and the temperatures of the middle heater 19 and the lower heater 18 are set to 870 ° C. so that the center temperature of the reaction vessel 15 becomes 870 ° C. (S 13). In order to generate thermal convection to prevent the occurrence of macro defects and miscellaneous crystals, if the temperature inside the reaction vessel 15 is 875 ° C. on the lower side and 865 ° C. on the upper side, the upper heater 20 is 865 ° C. The heater 17 is set to 875 ° C. When the crystal growth time exceeds 100 hours, the diameter of the nitride crystal is 4 inches or more, and a more uniform stirring of the mixed melt 13 is required, the middle heater 19 and the lower heater 18, the upper heater 20 and the bottom Fine adjustments can be made between the heaters 17 to prevent problems with the macro defects and miscellaneous crystals.

(14) Maintaining the set pressure of 3.4 MPa with the pressure regulator 40 connected to the pressure gauge 39 and the communication cable 41, and further setting the heaters 17 to 20 to control the temperature of the reaction vessel at 870 ° C. When maintained, nitrogen (N ₂ ) dissolves in the mixed melt 13, and soluble species of GaN · Na are formed in the mixed melt. In the supersaturated region on the seed substrate 11, nuclei of GaN single crystals are generated from GaN / Na, and then continuous GaN crystals without macro defects are grown by thermal convection. This state is maintained for 50 hours (S14).

(15) The heaters 17 to 20 are stopped, and the pressure of nitrogen is maintained until the furnace temperature reaches 100 ° C. or lower.

(16) After the nitrogen is discharged and the pressure in the furnace reaches 0.1 MPa, the pressure vessel lid 27 is opened. From there, the reaction vessel 15 is taken out, and the group III nitride crystal 12 grown on the seed substrate 11 placed in the crucible vessel 14 is taken out (S16). After the group III nitride crystal 12 is taken out, the group III nitride crystal production apparatus 10 can perform maintenance such as replacement of deteriorated parts, the installation base 16 of the highly nitriding stainless steel member, and the heater support tube 25. It is desirable from the viewpoint of maintaining the apparatus and preventing the adhesion of contaminants other than moisture. For example, after the maintenance is performed, the lid 27 is closed, and the vacuum baking operation of the above S01 is performed in preparation for the next crystal growth.

(Example 1)
Using the group III nitride crystal manufacturing apparatus 10 shown in FIG. 1, gallium nitride (GaN) crystal growth was performed three times as a group III nitride crystal according to the method shown in FIGS. 2 and 3A to 3E.

(1) First, the group III nitride crystal production apparatus 10 closes the mass flow controller 30 and the pressure regulator 40, opens the valve 36, and exhausts the piping 36 hours before the reaction vessel 15 is placed on the reaction vessel mounting table 16. The vacuum pump 38 connected to 35 was operated to evacuate the pressure vessel 28. At the same time, the heaters 17 to 20 were energized, the inside of the furnace was heated to 900 ° C., and vacuum baking was performed for 24 hours (S01). Since the degree of vacuum 12 hours after the start of vacuum baking was 7 × 10 ⁻² Pa, it was determined that there was no problem with leakage of piping and joints and moisture adsorption in the apparatus.

(2) 24 hours before setting the reaction vessel 15 on the reaction vessel setting table 16, a seed substrate 11 obtained by dividing a 75 mm diameter wafer obtained by growing a GaN thin film by 5 μm on a 1 mm sapphire substrate into two pieces, having a diameter of 140 mm and a purity of 5N The crucible container 14 made of alumina, the stainless steel reaction container 15 having a diameter of 180 mm, and gallium (Ga) as a group III element were carried into the glove box (S02). As the alkali metal, metallic sodium (Na) that was always stored in the glove box was used after delivery.

(3) The heaters 17 to 20 are stopped 12 hours before the reaction vessel 15 is set on the reaction vessel setting table 16 (S03), and nitrogen gas is sealed at 3.0 MPa, so that a group III nitride crystal production apparatus is provided. The temperature was lowered to 10 ° C. over 12 hours (S04).

(5) One hour before installing the reaction vessel 15 on the reaction vessel mounting table 16, the seed substrate 11, group III element gallium (Ga), and alkali metal sodium (Na) are placed in the crucible vessel 14 in the glove box. ) And installed. The ratio of the number of moles of sodium to the total number of moles of sodium and gallium in the mixed melt 13, Na / (Na + Ga) is 0.73, and the liquid surface height of the mixed melt 13 at a high temperature is the crucible container 14. The weights of Ga and Na were weighed so as to be 20 mm from the bottom of each. During the installation work, it was confirmed that the oxygen concentration in the glove box was 1 ppm or less, and the alkali metal Na had no white, light red, or small gold discoloration caused by peroxidation. In each of the three crystal growths, it took 30 minutes to work in the glove box.

(6) After the seed substrate 11, gallium (Ga), and sodium (Na) are completely stored in the reaction vessel 15, the nitrogen gas in the pressure vessel 28 is discharged, the pressure vessel lid 27 is removed, and the group III nitride crystal is removed. The manufacturing apparatus 10 was opened.

(7) After removing the pressure vessel lid 27, the reaction vessel 15 was removed from the glove box (S06), the reaction vessel 15 was installed, and the pressure vessel lid 27 was closed (S07). In all three crystal growths, it took 30 minutes to close the lid.

(8) After closing the pressure vessel lid 27, the valve 36 was opened, the vacuum pump 38 was operated, and the inside was evacuated for 2 hours (S08). In all three crystal growths, the degree of vacuum of the vacuum gauge 37 was 7 × 10 ⁻² Pa, so it was determined that there was no problem.

(9) The vacuum pump 38 was stopped and the valve 36 was closed. Thereafter, the pressure regulator 33 was opened, argon gas was sealed at 1.0 MPa (S09), the inside was heated to 200 ° C., and the argon gas atmosphere was pressurized and kept at a high temperature for 1 hour (S10). Thereafter, the heaters 17 to 20 were stopped.

(10) A part of the argon gas in the furnace was discharged, and the dew point measuring device 42 connected to the exhaust pipe 35 showed −70 ° C. (S11). In any of the three crystal growths, a cycle purge of argon gas was not performed.

(11) After the temperature in the furnace became 100 ° C. or lower, the valve 36 was opened again to operate the vacuum pump 38, and the argon (Ar) gas inside the pressure vessel 28 was discharged (S12).

(12) The valve 36 is closed, the vacuum pump 38 is stopped, the pressure regulator 31 and the mass flow controller 30 are opened, nitrogen gas is sealed in the pressure vessel 28, and the pressure inside the pressure vessel 28 is set to 3.2 MPa. Set.

(13) The heaters 17 to 20 were operated, and the temperature of the middle heater 19 and the lower heater 18 was set to 870 ° C. so that the temperature inside the reaction vessel 15 became 870 ° C. The upper heater 20 was set to 865 ° C., and the bottom heater 17 was set to 875 ° C. (S13).

(14) The flow rate of the mass flow controller 30 was set to 1000 sccm, and the set pressure of 3.2 MPa was maintained by the pressure gauge 39 and the pressure regulator 40 connected by the communication cable 41. Furthermore, the state which controlled the temperature of the reaction container at 870 degreeC by the setting of the heaters 17-20 was maintained for 50 hours (S14). It was confirmed that the reaction vessel had a temperature distribution of 865 to 875 ° C. with a monitor thermocouple (not shown) installed in the apparatus. Furthermore, when the dew point of nitrogen discharged from the exhaust pipe 35 for maintaining the pressure was measured 20 hours after the temperature reached a steady state by the dew point measuring device 42, it was −50 ° C. or lower.

(15) The heaters 17 to 20 were stopped, and the pressurized state of nitrogen was maintained until the furnace temperature reached 100 ° C. or lower.

(16) After the nitrogen gas was discharged and the pressure in the furnace reached 0.1 MPa, the pressure vessel lid 27 was opened. From there, the reaction vessel 15 was taken out, the group III nitride crystal 12 which was placed inside the crucible vessel 14 and grown on the seed substrate 11 was dissolved in ethanol with the mixed melt 13 and taken out (S15). After the group III nitride crystal 12 is taken out, the group III nitride crystal manufacturing apparatus 10 is a spare part in which the reaction vessel installation table 16 of a highly nitriding stainless steel member is blasted or acid cleaned in advance in the atmosphere. BN damaged by heat was also replaced. At the same time, the group III nitride crystal production apparatus 10 was inspected for 6 hours to confirm that there was no disconnection or deterioration of the heater. Thereafter, the pressure vessel lid 27 was closed (S16), and crystal growth was performed for the second and third times from the vacuum baking in S01.

The obtained group III nitride crystal had a thickness in the range of 0.9 to 1.0 mm in all three crystal growths, and was a white crystal as shown in FIG. When both surfaces of the group III nitride crystal obtained in Example 1 were polished, a colorless and transparent group III nitride crystal was obtained. The amount of oxygen impurities in the group III nitride crystal obtained by the first crystal growth was measured by D-SIMS and found to be 7.00 × 10 ¹⁶ atoms / cm ³ . There was no macro defect in the group III nitride crystal, and generation of miscellaneous crystals at the interface of the mixed melt 13 could not be confirmed.

(Comparative Example 1)
The Group III nitride crystal manufacturing method according to Comparative Example 1 is a stepwise process using the Group III nitride crystal manufacturing apparatus shown in FIG. 1 to represent the flowchart of FIG. 5 and the crystal growth start of FIGS. 6A to 6C. Based on the cross-sectional view. That is, in Comparative Example 1, the same method as in Example 1 except that the steps from S09 to S12 of argon gas encapsulation and heating to discharge of argon gas of Example 1, which is the gist of the present disclosure, are not performed. Crystal growth was performed three times.

The difference from Example 1 was that when the dew point of nitrogen discharged after 20 hours was measured in the pressurized high temperature state of nitrogen of S14, it was in the range of -20 ° C to -25 ° C.
That is, as shown in the schematic cross-sectional view showing the state in the pressure vessel 28 in the step S13 in which the nitrogen gas is enclosed in the pressure vessel 28 in FIG. 6C, the insulating material 23 and the carbon heater 19 are provided in addition to the enclosed nitrogen 51. The adhering moisture 44 remained in the pressure vessel 28 as it was.

The obtained nitride crystal has a thickness in the range of 0.4 to 0.5 mm in any of the three crystal growths, and there is a tendency for the crystal growth to be inhibited by moisture adsorbed inside the apparatus. It was. As shown in FIG. 7, the group III nitride crystals obtained in the first, second and third crystal growths were black and colored, and remained colored even after polishing. It was. Although the nitride crystal had no macro defects, the amount of oxygen impurities in the nitride crystal obtained in the first crystal growth of Comparative Example 1 was measured by D-SIMS, and found to be 6.60 × 10 ¹⁹ atoms. / Cm ³ . Compared with Example 1, the oxygen impurity concentration was about three orders of magnitude higher.

  As shown in FIG. 9, the impurities in the group III nitride crystals obtained in Example 1 and Comparative Example 1 were also compared with those other than oxygen. In Example 1, aluminum and sodium tended to be less than Comparative Example 1 in addition to oxygen. However, the difference as remarkable as oxygen was not seen. It is assumed that the alumina crucible container 14 during crystal growth is etched with an alkali metal, and aluminum is eluted and taken into the nitride crystal as an impurity. In contrast, the amount of impurities in aluminum in Example 1 was small, but the amount of elution was the same, but the amount of incorporation was increased because the crystal growth rate in Example 1 was higher than that in Comparative Example 1. Seems to have changed little.

(Comparative Example 2)
FIG. 8 is a diagram showing the relationship between the dew point of nitrogen gas discharged 20 hours after the start of heating and the degree of coloration of the group III nitride crystal in Comparative Example 2.
Before the idea of the present invention, there was a time when the crystal growth was not stabilized at all by repeating the crystal growth by the method of Comparative Example 1. Therefore, the present inventor pulled out a record of the dew point of nitrogen exhausted after 20 hours, and made an association with the quality of the obtained nitride crystal. As a result, as shown in FIG. 8, when the dew point deteriorates, that is, when the dew point increases, the crystal tends to be colored accordingly. Specifically, when the dew point was −15 ° C., the result was that nitride crystals did not grow on the seed substrate 11 at all. When the dew point was −38.0 ° C. or lower, there was no coloration and crystal growth was normal (Example 1). When the dew point exceeds −38 ° C. and less than −15 ° C., crystals grow, but there is a tendency that the degree of coloring becomes stronger as the dew point increases.

(Summary)
The group III nitride crystal obtained in Example 1 did not show macro defects or coloring due to oxygen impurities, and even if the crystal growth was performed several times, the quality was stable. This is considered to be nothing but the effect of removing the moisture in the pressure vessel 28 by filling the pressure vessel 28 with argon gas and maintaining the high temperature heating state. The dew point value of the discharged gas shown in Example 1, the dew point value of FIG. 9 and the quality of the group III nitride crystal also support the hypothesis. Therefore, it can be seen that the method of manufacturing the group III nitride crystal according to the present disclosure has solved the problems of the flux method with a simple apparatus configuration and method.

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

  The semiconductor substrate made of a group III nitride crystal obtained by the method for producing a group III nitride crystal according to the present invention can be used for making a light emitting device such as an LED or an LD. The obtained group III nitride crystal has excellent light emission characteristics and high reliability. That is, the method for producing a group III nitride crystal according to the present invention is useful for improving the light emission characteristics and reliability of the group III nitride crystal. It can also be useful for other general semiconductor devices such as FETs.

10: Group III nitride crystal production apparatus 11: Seed substrate 12: Group III nitride crystal 13: Mixed melt 14: Crucible vessel 15: Reaction vessel 16: Reaction vessel installation table 17: Bottom heater 18: Lower heater 19: Middle step Heater (carbon heater)
20: Upper heater 21: Bottom insulation material 22: Lower insulation material 23: Middle insulation material 24: Upper insulation material 25: Heater support pipe 26: Heat insulation material 27: Pressure vessel lid 28: Pressure vessel 29: Gas supply piping 30: Mass flow controllers 31, 33: Pressure regulator 32: Nitrogen gas 34: Argon gas 35: Exhaust piping 36: Valve 37: Vacuum gauge 38: Vacuum pump 39: Pressure gauge 40: Pressure regulator 41: Communication cable 42: Dew point measurement Apparatus 43: Air atmosphere 44: Water 45: Air 46: Vacuum 47: Argon atmosphere 48: Water 49: Argon 50: Water 51: Nitrogen atmosphere

Claims (6)

Alkali metal, Group III element-containing raw material, crucible containing seed substrate, reaction vessel containing the crucible, pressure vessel containing the reaction vessel, gas introducing nitrogen element-containing gas and / or argon gas into the pressure vessel Use a supply pipe, a lid for sealing the pressure vessel, a heater for heating the reaction vessel, an insulating material for insulating the heater and the reaction vessel, and a heat insulating material for preventing heat leakage in the reaction vessel. A method for producing a group III nitride crystal comprising:
Separating the lid from the pressure vessel, storing the reaction vessel in the pressure vessel, sealing the pressure vessel with the lid, and then filling the pressure vessel with argon gas;
Heating and holding the argon gas;
Discharging the heated argon gas from the pressure vessel;
Introducing the nitrogen element-containing gas into the pressure vessel, reacting the alkali metal and the group III element-containing raw material to grow a group III nitride crystal on the seed substrate;
A method for producing a group III nitride crystal, comprising:   The group III nitriding according to claim 1, wherein the step of filling the argon gas, the step of heating and holding the argon gas, and the step of discharging the heated argon gas are repeated. Method for producing physical crystals.   The method for producing a group III nitride crystal according to claim 1 or 2, further comprising a step of measuring a dew point of the exhausted gas.   The method for producing a group III nitride crystal according to any one of claims 1 to 3, wherein a dew point of the exhausted gas is -38 ° C or lower.   The group III nitride crystal according to any one of claims 1 to 4, wherein the insulating material is made of boron nitride and holds the argon gas heated at 200 to 700 ° C. Production method.   The method for producing a group III nitride crystal according to any one of claims 1 to 5, wherein a carbon heater is used as the heater.