JP6989924B2 - Method for Producing Group III Nitride Crystal - Google Patents

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 have been used for light emitting devices such as blue LEDs, white LEDs, and blue-purple LDs used as a light source for reading and writing Blu-ray (registered trademark). As a result, its development is being actively carried out. In order to realize the above-mentioned light emitting device having high brightness and high reliability, the group III nitride crystal used as the base substrate of the device contains metal elements such as Fe, Zn, Mg and Al, and O and C. There is a demand for crystals having few impurities of light elements such as.

Most of the group III nitride crystals currently used in these semiconductor devices use sapphire or SiC as a seed substrate, and the MOCVD method (metalorganic chemical vapor phase growth method) or MBE method (molecular beam crystal growth method). ) Etc. are manufactured by the vapor phase method. Further, as a part of the gas phase method, in the HVPE method (halogenated gas phase epitaxy method), sapphire or GaAs is used as a seed substrate, GaN is crystal-grown on the seed substrate, and then the GaN crystal is formed from the seed substrate. A GaN crystal is obtained by separating the above.

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

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 the nitride crystals to grow on the seed substrate under low temperature and low pressure. On the other hand, due to the characteristics of metallic sodium, which are easily oxidized and easily hygroscopic, when it is exposed to the atmosphere even a little, it rapidly reacts 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 are factors that inhibit crystal growth, and Group III nitride crystals use oxygen derived from water in the atmosphere as an impurity. There is a possibility of taking in a large amount. When oxygen is incorporated into the nitride crystal by the flux method using a mixed melt, the obtained Group III nitride single crystal is colored black and cannot be used as a base substrate for the device. This is the first problem of the flux method.

The flux method has another problem. If the mixed melt is not uniformly agitated during crystal growth, macro defects (inclusions) in which alkali metals are incorporated 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 crystal cannot be grown thickly. Further, the nitride crystal having a macro defect cannot be used as a base substrate of a device because the macro defect bursts when the heat treatment is performed in the subsequent post-process. This is the second problem of the flux method.

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

In the above measures, in order to accurately realize the temperature distribution conditions, for example, carbon is used as the material of the heaters arranged in the reaction vessel, and a plurality of heaters are independently controlled. BN (Boron Nitride) is used as the material that insulates the independent carbon heaters, and fibrous ceramic is used as the heat insulating material that prevents heat from escaping inside the pressure vessel. It is known that both BN and fibrous ceramics have hygroscopicity and oxidizing property, and BN has particularly high hygroscopicity.

Since the flux method uses easily oxidizing and 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 the moisture absorption and oxidation of the mixed melt. On the other hand, in order to suppress the macro defects of the above-mentioned nitride crystals and the suppression of miscellaneous crystals, a temperature distribution in which the mixed melt is thermally convected is required. Therefore, it is required to have 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. In the flux method, there is a trade-off relationship between the problems of oxygen impurities and macro defects in the nitride crystal, in which the countermeasures for both are worse if one is countermeasured and the other is affected by the countermeasure. There is.

The flux method carried out by the present inventor had the same problem. Initially, the inside of the crystal growth apparatus developed by the present inventor had a simple heater structure, so that appropriate heat convection could not be generated in the mixed melt. As a result, macro defects always occurred in the obtained nitride crystals, and thick nitride crystals could not be obtained due to the generation of miscellaneous crystals. As a countermeasure, the present inventor has complicated the heater structure and strictly controlled the temperature conditions as described above. As a result, the macro defects were improved, but the obtained nitride crystals were colored due to oxygen. In particular, coloring of nitride crystals may occur suddenly even with the same procedure and the same material. In addition, there were cases of sudden improvement for no apparent reason. Therefore, the present inventor has been troubled by the problem of coloring of nitride crystals lacking stability, that is, 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 in Patent Document 1 and Patent Document 2 in order to solve the above-mentioned problem of coloring the nitride crystal.

Patent No. 49668708 Patent No. 4963108

In both Patent Documents 1 and 2, the reaction vessel is airtightly sealed before the heating and pressurizing treatment, and the reaction vessel is communicated with each other by deformation or melting of the airtight portion during the heating and pressurizing treatment or during the treatment. It is characterized in that the reaction vessel is not exposed to water.

However, in the above method, the water discharged from the member in the pressure vessel after the communication may oxidize the alkali metal of the mixed melt in the reaction vessel and affect the crystal growth. ..

An object of the present disclosure is to provide a method for producing a Group III nitride crystal having a small amount of oxygen impurities in the crystal, which has been made in view of the problems of the flux method.

In order to achieve the above-mentioned object, the method for producing a Group III nitride crystal according to the present disclosure includes an alkali metal, a group III element-containing raw material, a cell for accommodating a seed substrate, a reaction vessel for accommodating the gas, and the reaction vessel. A pressure vessel for accommodating, a gas supply pipe for introducing nitrogen element-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 using an insulating material for insulating the gas and a heat insulating material for preventing heat leakage in the reaction vessel.
A step of separating the lid from the pressure vessel, storing the lid in the reaction vessel in the pressure vessel, sealing the pressure vessel with the lid, and then filling the pressure vessel with argon gas.
The step of heating and holding the argon gas and
The step of discharging the heated argon gas from the pressure vessel and
A step of introducing the nitrogen element-containing gas into the pressure vessel and reacting the alkali metal with the group III element-containing raw material to grow group III nitride crystals 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 step of the Group III nitride crystal, the pressure vessel is filled with argon, and the argon is heated and held, and then heated argon. Is being discharged from the pressure vessel. This makes it possible to remove the moisture absorbed in the insulating material and the heater inside the pressure vessel, which is a problem in the flux method. In addition, a heater having hygroscopicity, 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 having a small amount of oxygen impurities can be produced.

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

The method for producing a Group III nitride crystal according to the first aspect is a method for producing an alkali metal, a group III element-containing raw material, a cell for accommodating a seed substrate, a reaction vessel for accommodating the cell, a pressure vessel for accommodating the reaction vessel, and nitrogen. A gas supply pipe for introducing an element-containing gas and / or an argon gas into the pressure vessel, a lid for sealing the pressure vessel, a heater for heating the reaction vessel, and an insulating material for insulating the heater and the reaction vessel. , A method for producing a Group III nitride crystal using a heat insulating material for preventing heat leakage in the reaction vessel.
A step of separating the lid from the pressure vessel, accommodating the reaction vessel in the pressure vessel, sealing the pressure vessel with the lid, and then filling the pressure vessel with argon gas.
The step of heating and holding the argon gas and
The step of discharging the heated argon gas from the pressure vessel and
A step of introducing the nitrogen element-containing gas into the pressure vessel and reacting the alkali metal with the group III element-containing raw material to grow group III nitride crystals on the seed substrate.
It is characterized by having.

The method for producing a Group III nitride crystal according to the second aspect is the step of filling the argon gas, the step of heating and holding the argon gas, and the step of heating and holding the heated argon gas in the first aspect. 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 the dew point of the discharged gas in the first or second aspect.

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

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 composed of boron nitride, and the argon gas is used at 200 to 700 ° C. It may be heated and held.

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

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view showing a Group III nitride crystal manufacturing apparatus according to the first embodiment. With reference to FIG. 1, a method for producing a Group III nitride crystal according to the first embodiment and a configuration example of a Group III nitride crystal production apparatus used will be described.

<Group III nitride crystal manufacturing equipment>
In the group III nitride crystal manufacturing apparatus 10 according to the first embodiment, in order to grow the group III nitride crystal 12 on the seed substrate 11, the mixed melt 13 containing an alkali metal and at least a group III element, the seed substrate 11 , The elemental container 14, and the reaction container 15 in which they are housed can be installed on the reaction container installation table 16. The reaction vessel 15 is removable from the reaction vessel installation table 16.

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

For the purpose of suppressing the occurrence of the macro defect, the inside of the group III nitride crystal manufacturing apparatus 10 has a bottom heater 17 to an upper heater 20 supported by the heater support tube 25. Further, it is composed of the heat insulating material 26 and the insulating materials 21 to 24 for independently controlling the heaters 17 to 20.

The group III nitride crystal manufacturing apparatus 10 is a nitrogen (N ₂ ) gas 32 for supplying a raw material for the group III nitride crystals, a pressure regulator 31 thereof, and moisture adsorbed inside the apparatus, which is the purpose of the present disclosure. It is provided with an argon (Ar) gas 34 for removing the gas 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 to be dissolved in the mixed melt is sufficient as long as it is a nitrogen source for growing Group III nitride crystals. 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 a constant flow rate (for example, 1000 sccm) of nitrogen (N ₂ ) by the mass flow controller 30. In order to keep the set pressure during crystal growth constant, the pressure regulator 40 connected by the pressure gauge 39 and the communication cable 41 discharges nitrogen (N ₂ ) and keeps the pressure of the pressure gauge 39 constant. Adjust the pressure. Further, the discharged nitrogen (N ₂ ) argon (Ar) can be measured for moisture by the dew point measuring instrument 42.

The Group III nitride crystal manufacturing apparatus 10 includes an exhaust pipe 35, a valve 36, and a vacuum pump 38 for expelling the entering atmosphere 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.

<Manufacturing method of Group III nitride crystal>
The method for producing a group III nitride crystal according to the first embodiment is described with reference to the flow chart up to the start of crystal growth in FIG. 2 and the schematic cross-sectional view showing the steps up to the crystal growth in FIGS. 3A to 3E. It will be explained in detail.

(1) The group III nitride crystal manufacturing apparatus 10 closes the mass flow controller 30, 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. conduct. 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 the moisture adsorbed at the time of opening. During vacuum baking, it is desirable that the degree of vacuum in the furnace is monitored by a vacuum gauge 37, and the degree of vacuum is 1 × 10 ^-1 Pa or less. If it is 1 × 10 ^-1 Pa or more, either an O-ring (not shown) that seals 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 in the pipe, or a large amount of water has been adsorbed on the internal member. Since both of them affect the crystal growth, it is desirable to record the degree of vacuum indicated by the vacuum gauge 37 with respect to the elapsed time of evacuation, and periodically check the joint with snoop liquid for leaks. .. In order to reduce the load on the heaters 17 to 20 and perform effective vacuum baking, the heating temperature should be 900 degrees or more and 1000 degrees or less, and the vacuum bake should be performed until the vacuum degree indicated by the vacuum gauge 37 is saturated. It is desirable to do it for 12 hours or more.

(2) The seed substrate 11, the crucible container 14, the reaction vessel 15, the group III element material, and the alkali metal used for crystal growth when the group III nitride crystal manufacturing apparatus 10 is vacuum-baked are not shown. Carry it into a glove box with a sexual atmosphere (S02). The purpose is to remove the moisture adsorbed on the surface of these members and materials in the atmosphere of the inert gas in the glove box.

(3) The heaters 17 to 20 are stopped, the valve 36 is closed, and the vacuum pump 38 is stopped so that the reaction vessel 15 can be installed in the pressure vessel 28 at a temperature of 100 ° C. or lower (S03). If the crystal growth apparatus is cooled while evacuation is continued, the time required to reach 100 ° C. or lower 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 enclosing 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 may decrease and the alkali metal may be vaporized. Therefore, the temperature should be 100 ° C. or lower.

(5) One hour before the time when the inside of the pressure vessel 28 becomes 100 ° C. or lower, the seed substrate 11, the group III element material, and the alkali metal are installed in the crucible container 14 in the non-oxidizing glove box (not shown). .. The crucible container 14 is further stored in the reaction container 15 (S05). During the work, it is confirmed that the oxygen concentration in the glove box is maintained at 1 ppm or less and that the alkali metal is not discolored. If the easily oxidizable alkali metal is oxidized, that is, discolored in the glove box, use a ceramic knife to remove the oxidized alkali metal.

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

(7) After removing the pressure vessel lid 27, the reaction vessel 15 is taken out from the glove box (S06), the reaction vessel 15 is installed on the installation table 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 the step of S07 in which the reaction vessel is installed in the pressure vessel in the method for producing a Group III nitride crystal according to the first embodiment. The inside of the pressure vessel 28 is an atmospheric atmosphere 43, and moisture 44 derived from an atmospheric component is adsorbed on the insulating materials 22 and 23 and the carbon heater 19 inside. In addition, for the purpose of explaining the outline, all the members are not shown. The time required for installing the reaction vessel 15 from inside the glove box on the installation table 16 is described in the prior art as being colored with the nitride crystals even in the required time of 5 minutes, and it is said that the shorter the time, the better. This is intended to prevent the 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 a vacuum is drawn to discharge the internal atmosphere 45 (S08). FIG. 3B is a schematic cross-sectional view showing the state inside the pressure vessel in the step of S08 in which the inside of the pressure vessel 28 is evacuated in the method for producing a group III nitride crystal according to the first embodiment. 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 should be 1 × 10 ^-1 Pa or less, which is the same as the degree of vacuum obtained by vacuum baking before carrying in. It is even more desirable to be.

(9) The vacuum pump 38 is stopped and the valve 36 is closed. After that, the pressure regulator 33 and the mass flow controller 30 are opened, argon (Ar) gas is filled at 1.0 MPa (S09), the inside of the pressure vessel 28 is heated to 200 ° C., the atmosphere of the argon gas is pressurized, and the temperature is high. The state is continued for 1 hour (S10). FIG. 3C shows the inside of the pressure vessel 28 in the steps of S09 and S10 in which argon gas is sealed in the pressure vessel 28 and the pressurization and the high temperature state are continued in the method for producing the Group III nitride crystal according to the first embodiment. It is a schematic cross-sectional view which shows the state. By heating the enclosed argon gas 47, the moisture 44 absorbed in the insulating material 23 and the heater 19 can be removed. As for the heating temperature, it is desirable to perform a degassing test of the insulating material 23 and the heater 19 in advance in an argon atmosphere and set the temperature at which moisture is most removed. When BN is used as the material of the insulating material 23, the effect of removing water is highest at 200 to 700 ° C. In order to prevent the alkali metal arranged in the pressure vessel 28 from vaporizing, the set pressure of argon is preferably 0.1 MPa or more, 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, that of nitrogen is 1043, J / kg ° C, and that of 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 water. By utilizing this feature, the moisture absorbed in the insulating material inside the pressure vessel and the heater, which is a problem in the flux method, can be taken into the argon atmosphere 47 as the moisture 48 and removed. In addition, a heater having hygroscopicity, 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, it is possible to produce a Group III nitride crystal having few oxygen impurities and few macro defects.

(10) After pressurizing with argon gas and maintaining a high temperature state, the pressure regulator 40 is opened for 1 minute. A part of the argon gas in the furnace is discharged, and the water content contained in the exhaust gas is measured by the dew point measuring instrument 42 connected to the exhaust pipe 35 (S11). In order to solve this problem, it is desirable that the dew point is −38 ° C. or lower from the data of Example 2 described later. If the temperature is -38 ° C or higher, the adsorbed water may not be completely removed. Therefore, after cooling to 100 ° C, perform cycle purging in which vacuuming and argon filling are performed multiple times. Therefore, the dew point can be obtained at −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 and adsorption inside the pressure vessel 28 are adsorbed. The water 50 is discharged (S12). FIG. 3D shows the state inside the pressure vessel 28 in the step of S12 in which the 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 cross-sectional view which shows. After that, the inside of the pressure vessel 28 becomes a vacuum 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, the 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 inside the pressure vessel 28 in the step of S13 in which nitrogen gas is sealed in the pressure vessel 28 in the method for producing a group III nitride crystal according to the first embodiment. As shown in FIG. 3E, there is almost no residual water in the pressure vessel 28, and the 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. (S13). If the temperature conditions inside the reaction vessel 15 are 875 ° C on the lower side and 865 ° C on the upper side for the generation of heat convection to prevent the generation of macro defects and miscellaneous crystals, the upper heater 20 has a temperature of 865 ° C and the bottom. 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 more uniform stirring of the mixed melt 13 is required, the middle heater 19 and the lower heater 18 and the upper heater 20 and the bottom are required. Fine adjustment can be performed between the heaters 17 to prevent the above-mentioned problems with macro defects and miscellaneous crystals.

(14) The set pressure of 3.4 MPa is maintained by the pressure gauge 39 and the pressure regulator 40 connected to the communication cable 41, and the temperature of the reaction vessel is controlled at 870 ° C. by setting the heaters 17 to 20. When maintained, nitrogen (N ₂ ) dissolves in the mixed melt 13 to form soluble species of GaN / Na 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 thermal convection causes continuous growth of GaN crystals without macro defects. This state is maintained for 50 hours (S14).

(15) The heaters 17 to 20 are stopped, and the nitrogen pressurization state is maintained until the temperature inside the furnace becomes 100 ° C. or lower.

(16) After the nitrogen is discharged and the pressure in the furnace becomes 0.1 MPa, the pressure vessel lid 27 is opened. From there, the reaction vessel 15 is taken out, and the group III nitride crystals 12 grown on the seed substrate 11 installed in the crucible vessel 14 are taken out (S16). After taking out the Group III nitride crystal 12, the Group III nitride crystal manufacturing apparatus 10 may perform maintenance such as replacing deteriorated parts, an installation base 16 for a stainless steel member with severe nitriding, and a heater support tube 25. It is desirable from the viewpoint of equipment maintenance and prevention of adhesion of contaminants other than moisture. For example, after performing maintenance, the lid 27 is closed, and the vacuum baking operation of S01 described above 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) was crystal-grown three times as a group III nitride crystal according to the methods shown in FIGS. 2 and 3A to 3E.

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

(2) Twenty-four hours before installing the reaction vessel 15 on the reaction vessel installation table 16, a seed substrate 11 having a diameter of 75 mm in which a GaN thin film was grown by 5 μm on a 1 mm sapphire substrate was divided into two parts, having a diameter of 140 mm and a purity of 5N. A crucible container 14 made of alumina, a reaction container 15 made of stainless steel having a diameter of 180 mm, and glove (Ga) as a group III element were carried into the glove box (S02). After delivery, the alkali metal used was metallic sodium (Na), which is always stored in the glove box.

(3) Heaters 17 to 20 are stopped 12 hours before the reaction vessel 15 is installed on the reaction vessel installation table 16 (S03), and nitrogen gas is sealed at 3.0 MPa to form a group III nitride crystal manufacturing apparatus. The temperature of 10 was lowered to 100 ° C. over 12 hours (S04).

(5) One hour before the reaction vessel 15 is installed on the reaction vessel installation table 16, the seed substrate 11, the group III element gallium (Ga), and the alkali metal sodium (Na) are placed in the glove container 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 level height of the mixed melt 13 at high temperature is the container 14 The weights of Ga and Na were weighed so as to be 20 mm from the bottom of the. During the installation work, it was confirmed that the oxygen concentration in the glove box was 1 ppm or less, and that the alkali metal Na had no discoloration of white, light red due to oxidation, or small golden color due to peroxidation. Each of the three crystal growths required 30 minutes to work in the glove box.

(6) After the seed substrate 11, gallium (Ga), and sodium (Na) have been stored in the reaction vessel 15, the nitrogen gas inside 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 taken out from the glove box (S06), the reaction vessel 15 was installed, and the pressure vessel lid 27 was closed (S07). In each of the 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 internal vacuum was evacuated for 2 hours (S08). Since the degree of vacuum of the vacuum gauge 37 was 7 × 10 ⁻² Pa in all three crystal growths, it was judged that there was no problem.

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

(10) A part of the argon gas in the furnace was discharged, and the dew point measuring instrument 42 connected to the exhaust pipe 35 showed −70 ° C. (S11). No cycle purging of argon gas was performed in any of the three crystal growths.

(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 3.2 MPa. I set it.

(13) The heaters 17 to 20 were operated, and the temperatures of the middle heater 19 and the lower heater 18 were set to 870 ° C. so that the temperature inside the reaction vessel 15 was 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. Further, by setting the heaters 17 to 20, the temperature of the reaction vessel was maintained at 870 ° C. for 50 hours (S14). It was confirmed that the reaction vessel had a temperature distribution of 865 to 875 ° C. with a thermocouple for monitoring (not shown) installed in the apparatus. Further, the dew point of nitrogen discharged from the exhaust pipe 35 for maintaining the pressure was measured with a dew point measuring instrument 42 20 hours after the temperature became a steady state, and was found to be −50 ° C. or lower.

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

(16) After the nitrogen gas was discharged and the pressure inside the furnace became 0.1 MPa, the pressure vessel lid 27 was opened. From there, the reaction vessel 15 was taken out, placed inside the crucible vessel 14, and the Group III nitride crystals 12 grown on the seed substrate 11 were mixed with ethanol to dissolve the melt 13 and taken out (S15). After taking out the Group III nitride crystal 12, the Group III nitride crystal manufacturing apparatus 10 is a spare part in which the reaction vessel setting table 16 of a stainless steel member having severe nitriding is preliminarily blasted and pickled in the atmosphere. The BN damaged by heat was also replaced. At the same time, the Group III nitride crystal manufacturing apparatus 10 was inspected for 6 hours to confirm that the heater was not broken or deteriorated. Then, the pressure vessel lid 27 was closed (S16), and crystal growth was carried out from the vacuum baking of S01 to the second and third times.

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 sides 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 in the first crystal growth was measured by D-SIMS and found to be 7.00 × 10 ¹⁶ atoms / cm ³ . The Group III nitride crystals had no macro defects, and no miscellaneous crystals could be confirmed at the interface of the mixed melt 13.

(Comparative Example 1)
The method for producing a group III nitride crystal according to Comparative Example 1 is a stepwise method showing the flowchart of FIG. 5 and the start of crystal growth of FIGS. 6A to 6C using the group III nitride crystal production apparatus shown in FIG. This was done based on the cross-sectional view. That is, in Comparative Example 1, the same method as in Example 1 is used except that the steps from the filling and heating of the argon gas of S09 to S12 of Example 1 which are the main points of the present disclosure to the discharge of the argon gas are not carried out. Crystal growth was carried out 3 times.

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

The obtained nitride crystal had a thickness in the range of 0.4 to 0.5 mm in all three crystal growths, and there was a tendency that the crystal growth was inhibited by the water adsorbed inside the apparatus. rice field. As shown in FIG. 7, the group III nitride crystals obtained in any of the first, second, and third crystal growths were black and colored, and remained colored even after polishing. rice field. The nitride crystal had no macro defects, but when the amount of oxygen impurities in the nitride crystal obtained in the first crystal growth of Comparative Example 1 was measured by D-SIMS, it was 6.60 × 10 ¹⁹ atoms. It was / ^cm3 . Compared with Example 1, the concentration of oxygen impurities was about 3 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 respect to other than oxygen. In Example 1, aluminum and sodium tended to be less than in Comparative Example 1 in addition to oxygen. However, no significant difference was seen as with oxygen. It is assumed that the alumina-made pit container 14 during crystal growth is etched with an alkali metal, and aluminum is eluted and incorporated as impurities into the nitride crystal. On the other hand, the amount of impurities in the aluminum of Example 1 was small because the elution amount was the same, but the crystal growth rate of Example 1 was higher than that of Comparative Example 1, so that the amount was taken in. Seems to have changed less.

(Comparative Example 2)
FIG. 8 is a diagram showing the relationship between the dew point of the nitrogen gas discharged 20 hours after the start of heating and the degree of coloring of the group III nitride crystal in Comparative Example 2.
Prior to the idea of the present invention, there was a period in which crystal growth was not stable at all due to repeated crystal growth by the method of Comparative Example 1. Therefore, the present inventor drew a record of the dew point of nitrogen discharged after 20 hours and carried out the 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 rises, the crystals tend to be colored accordingly. Specifically, when the dew point was −15 ° C., the result was that the 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 coloring and the crystals grew normally (Example 1). When the dew point was above −38 ° C. and below −15 ° C., crystal growth was observed, but the degree of coloring tended to increase as the dew point increased.

(summary)
The group III nitride crystal obtained in Example 1 did not show macro defects or coloring due to oxygen impurities, and the workmanship was stable even when the crystal growth was carried out a plurality of times. It is considered that this is nothing but the effect of removing the water content 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 performance of the Group III nitride crystal also support the hypothesis. Therefore, it can be seen that the problem of the flux method has been solved by the method for producing the Group III nitride crystal according to the present disclosure by a simple device configuration and method.

It should be noted that the present disclosure includes appropriately combining any of the various embodiments and / or embodiments described above, and the respective embodiments and / or embodiments. The effects of the examples can be achieved.

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 producing a light emitting device such as an LED or LD. The obtained Group III nitride crystal has excellent 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 manufacturing equipment 11: Seed substrate 12: Group III nitride crystal 13: Mixed melt 14: Cave container 15: Reaction vessel 16: Reaction vessel installation stand 17: Bottom heater 18: Lower heater 19: Middle stage 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 tube 26: Insulation material 27: Pressure vessel lid 28: Pressure vessel 29: Gas supply pipe 30: Mass flow controller 31, 33 ,: Pressure regulator 32: Nitrogen gas 34: Argon gas 35: Exhaust pipe 36: Valve 37: Vacuum gauge 38: Vacuum pump 39: Pressure gauge 40: Pressure regulator 41: Communication cable 42: Dew point measurement Vessel 43: Atmospheric atmosphere 44: Moisture 45: Atmosphere 46: Vacuum 47: Argon atmosphere 48: Moisture 49: Argon 50: Moisture 51: Nitrogen atmosphere

Claims (6)

An alkali metal, a group III element-containing raw material, a cell for storing a seed substrate, a reaction vessel for accommodating the cell, a pressure vessel for accommodating the reaction vessel, a gas for introducing a nitrogen element-containing gas and / or an argon gas into the pressure vessel. A supply pipe, a lid for sealing the pressure vessel, a plurality of heaters for heating the reaction vessel, between the plurality of heaters and / or for insulating at least one of the plurality of heaters from the reaction vessel. A method for producing a Group III nitride crystal using a plurality of insulating materials and a heat insulating material for preventing heat leakage in the reaction vessel.
A step of separating the lid from the pressure vessel, accommodating the reaction vessel in the pressure vessel, sealing the pressure vessel with the lid, and then filling the pressure vessel with argon gas.
The step of heating and holding the argon gas and
The step of discharging the heated argon gas from the pressure vessel and
A step of introducing the nitrogen element-containing gas into the pressure vessel and reacting the alkali metal with the group III element-containing raw material to grow group III nitride crystals on the seed substrate.
Have,
The plurality of heaters include a bottom heater arranged on the bottom side of the reaction vessel and two or more side heaters arranged on the lower and upper sides of the reaction vessel.
A method for producing a Group III nitride crystal, which comprises controlling each of the plurality of heaters independently . The group III nitride 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 repeatedly performed. Method for manufacturing physical crystals. The method for producing a Group III nitride crystal according to claim 1 or 2, further comprising a step of measuring the dew point of the discharged gas. The method for producing a Group III nitride crystal according to any one of claims 1 to 3, wherein the dew point of the discharged 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 composed of boron nitride and heats and holds the argon gas 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.

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