JP2018177587A - Method and apparatus for producing group III nitride crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a group III nitride crystal, capable of manufacturing a high quality group III nitride crystal having less impurities in the crystal and a small dislocation density.SOLUTION: The method for manufacturing a group III nitride crystal comprises the steps of: preparing a mixed melt including alkali metal and a group III element in a reaction vessel; supplying gas including a nitrogen element into the reaction vessel; preparing a seed substrate separated from the surface of the mixed melt; heating the mixed melt to change a part thereof into vapor; and coating the seed substrate with a liquid film obtained by condensing the vapor of the mixed melt to grow a group III nitride crystal on the seed substrate.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method and apparatus 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 blue LEDs, white LEDs, and light emitting devices such as blue-violet LDs used as a light source for reading and writing Blu-ray (registered trademark). As, its development is actively done. In order to realize the above-described light emitting device having high brightness and high reliability, metal elements such as Fe, Zn, Mg, Al, O, C, etc. can be used as a group III nitride crystal to be a base substrate of the device. There is also a need for a crystal quality that is low in any impurities such as light elements of the above, and has a dislocation density of 10 ⁴ cm ⁻² or less in the crystal.

  At present, most of the group III nitride crystals used in these semiconductor devices are MO-CVD (metal organic chemical vapor deposition) or MBE (molecular beam crystal) using sapphire or SiC as a seed substrate. It is manufactured by vapor phase methods such as growth method). As part of the gas phase method, in the HVPE method (halogenated vapor phase epitaxy method), GaN crystal is grown on a sapphire substrate or a GaAs substrate and then a GaN crystal is obtained by separating the GaN crystal from the substrate. ing.

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

  The flux method has advantages such as crystal growth under low temperature and pressure as compared with other liquid phase growth, and the obtained crystal also has a low dislocation density.

  However, while the mixed melt of the alkali metal has the effect of causing the crystal growth of nitride on the seed substrate, it is used from the high reactivity of the seed substrate, the reaction container containing the mixed melt, and the inside of the container. Has an effect of etching the member to be That is, the flux method has a problem that when impurities derived from the seed substrate or the reaction container material are dissolved in the mixed melt, nitride crystals grown from the melt also incorporate impurities derived from the seed substrate or the reaction container material into the crystal. doing.

  Therefore, the invention related to the material of the reaction container and the processing method is disclosed in the flux method as in Patent Documents 1 to 3.

  Further, in order to obtain a stable nitride crystal without limiting the reaction container of the flux method, in Patent Document 4, the mixed melt containing Group III nitride as the raw material is wettable to the mixed melt A method of growing a group III nitride crystal is disclosed by coating a thin liquid film on a seed substrate along a good alumina member.

Patent No. 4398762 Patent No. 5046490 Patent No. 5496071 Patent No. 5375690

However, in the flux method described in Patent Document 4, the melt is present as a thin film on the seed substrate through the wettability of the alumina member. The film on the seed substrate is difficult to be replaced with another melt, and the film remaining on the seed substrate not only contributes to crystal growth, but also has the side effect of etching the surface and side of the seed substrate. Therefore, impurities derived from the constituent elements of the reaction vessel, the members and the seed substrate are mixed in the obtained GaN crystal. For example, when ScAlMgO ₄ is used for the seed substrate, magnesium (Mg) is taken into the crystal as an impurity. When sapphire (Al ₂ O ₃ ) is used for the seed substrate and alumina (Al ₂ O ₃ ) is used for the member, impurities such as aluminum (Al) and oxygen (O) are taken into the crystal. In these crystals, the above-mentioned impurities can be an obstacle to the improvement of reliability and characteristics in the manufacture of optical devices.

  SUMMARY OF THE INVENTION The object of the present invention is made in view of the problems of the flux method, and is a group III nitride crystal which produces a group III nitride crystal with few impurities and a small transition density more easily than before. It is to provide a manufacturing method.

In order to achieve the above-described object, the method for producing a group III nitride crystal according to the present invention comprises the steps of: preparing a mixed melt containing an alkali metal and a group III element in a reaction vessel;
Supplying a gas containing nitrogen element into the reaction vessel;
Placing a seed substrate spaced from the surface of the mixed melt;
Heating the mixed melt to partially vaporize it;
Covering the seed substrate with a liquid film in which the vapor of the mixed melt is condensed to grow a group III nitride crystal on the seed substrate;
including.

The group III nitride crystal production apparatus according to the present invention comprises a reaction vessel for storing a mixed melt containing an alkali metal and a group III element, and a seed substrate disposed apart from the liquid surface of the mixed melt. When,
A gas supply pipe for supplying a gas containing nitrogen element into the reaction vessel;
A heating unit which heats the mixed melt and makes a part of it into a vapor;
Equipped with

  According to the method and apparatus for producing a group III nitride crystal according to the present invention, a group III element of a liquid film on a seed substrate generated from a condensation phenomenon due to a temperature difference between a vapor generated from a mixed melt and the seed substrate Crystal growth of a group III nitride crystal can be performed by reaction with nitrogen dissolved in a liquid film. Further, by utilizing the effect that the liquid film is replaced before etching the seed substrate, there is an effect that it is possible to manufacture a group III nitride crystal with few impurities and few dislocation defects.

It is a schematic sectional drawing which shows the structure of the group III nitride crystal production apparatus based on Embodiment 1 of this invention. FIG. 3 is a perspective view showing an arrangement example of a reaction vessel, a mixed melt, and a seed substrate in the group-III nitride crystal production apparatus of FIG. 1. FIG. 5 is a schematic cross-sectional view showing the manner in which crystal growth is performed in the group III nitride crystal production apparatus according to Embodiment 1 in a stepwise manner. FIG. 5 is a schematic cross-sectional view showing the manner in which crystal growth is performed in the group III nitride crystal production apparatus according to Embodiment 1 in a stepwise manner. FIG. 5 is a schematic cross-sectional view showing the manner in which crystal growth is performed in the group III nitride crystal production apparatus according to Embodiment 1 in a stepwise manner. FIG. 5 is a schematic cross-sectional view showing the manner in which crystal growth is performed in the group III nitride crystal production apparatus according to Embodiment 1 in a stepwise manner. In the form of Example 1, it is a schematic sectional drawing which shows the example of arrangement | positioning which makes a seed board | substrate and mixed melt solution contact.

The method for producing a group III nitride crystal according to the first aspect comprises the steps of: preparing a mixed melt containing an alkali metal and a group III element in a reaction vessel;
Supplying a gas containing nitrogen element into the reaction vessel;
Preparing a seed substrate by separating from the liquid surface of the mixed melt;
Heating the mixed melt to make part of it into a vapor;
Covering the seed substrate with a liquid film in which the vapor of the mixed melt is condensed to grow a group III nitride crystal on the seed substrate;
including.

  In the method for producing a group III nitride crystal according to the second aspect, in the step of preparing the seed substrate by separating from the liquid surface of the mixed melt in the first aspect, the bottom surface of the reaction vessel is a horizontal surface The mixed melt covers a portion of the bottom surface of the reaction vessel, and the seed substrate is disposed on the bottom surface of the reaction vessel at a distance from the liquid surface of the mixed melt May be

  In the method for producing a group III nitride crystal according to the third aspect, in the first or second aspect, the seed substrate may be a sapphire substrate.

In the method for producing a group III nitride crystal according to a fourth aspect, in the first or second aspect, the seed substrate may be a ScAlMgO ₄ substrate.

  In the method for producing a group III nitride crystal according to the fifth aspect, in the first or second aspect, the seed substrate may be a GaN substrate.

  In the method for producing a group III nitride crystal according to a sixth aspect, in any of the first to fifth aspects, the alkali metal may be Na.

  In the method of producing a group III nitride crystal according to a seventh aspect, in any of the above first to sixth aspects, the group III element may be gallium.

  In the method for producing a group III nitride crystal according to an eighth aspect, in any of the above first to seventh aspects, the gas containing the nitrogen element may be nitrogen.

  In the method for producing a group III nitride crystal according to a ninth aspect, in any of the first to eighth aspects, the wettability of the seed substrate to the mixed melt is determined by the reaction vessel to the mixed melt. It may be higher than the wettability of

  In the method of producing a group III nitride crystal according to a tenth aspect, in the step of growing the group III nitride crystal according to any one of the first to ninth aspects, the liquid film etches the seed substrate It may be flowed into the mixed melt prior to

In the method for producing a group III nitride crystal according to an eleventh aspect, in the second aspect, the inclination angle of the bottom surface of the reaction vessel is 13 ° or more and 30 ° or less,
The mixed melt and the seed substrate may be separated by 10 mm or more.

  In the method for producing a group III nitride crystal according to a twelfth aspect, in any one of the first to eleventh aspects, the surface temperature of the seed substrate may be lower by 10 ° C. or more than the temperature of the vapor.

A group III nitride crystal production apparatus according to a thirteenth aspect stores a mixed melt containing an alkali metal and a group III element, and a seed substrate disposed apart from the liquid surface of the mixed melt. A reaction vessel,
A gas supply pipe for supplying a gas containing nitrogen element into the reaction vessel;
A heating unit which heats the mixed melt and makes a part of it into a vapor;
Equipped with

  In the group-III nitride crystal production apparatus according to a fourteenth aspect, in the thirteenth aspect, the reaction container is disposed such that the bottom surface is inclined with respect to a horizontal surface, and the mixed melt is a bottom surface of the reaction container The seed substrate may be disposed on the bottom surface of the reaction vessel at a distance from the liquid surface of the mixed melt.

  The group III nitride crystal production apparatus according to a fifteenth aspect is the group III nitride crystal production apparatus according to the thirteenth or fourteenth aspect, wherein the reaction container is accommodated, the gas supply pipe is provided, and the pressure resistant container which can be sealed is further provided. Good.

  Hereinafter, the method for producing a group III nitride crystal and the apparatus for producing a group III nitride crystal according to the embodiment will be described with reference to the attached drawings. In the drawings, substantially the same members are denoted by the same reference numerals.

Embodiment 1
<Configuration of Group III Nitride Crystal Production Device>
With reference to FIG. 1, a method of manufacturing a group III nitride crystal according to the first embodiment of the present invention and a configuration example of a group III nitride crystal manufacturing apparatus 10 used therefor will be described. FIG. 1 is a schematic cross-sectional view showing the configuration of a group III nitride crystal production apparatus 10 according to Embodiment 1 of the present invention.
The group III nitride crystal production apparatus 10 according to the first embodiment includes a reaction vessel 12 storing a mixed melt 28 containing an alkali metal and a group III element and a seed substrate 29, and a nitrogen element in the reaction vessel 12. A nitrogen gas supply pipe 15 for supplying the contained gas, and a heating unit which heats the mixed melt 28 and makes a part of it a vapor. In the reaction vessel 12, the seed substrate 29 is disposed apart from the liquid surface of the mixed melt 28. The bottom surface 33 of the reaction vessel 12 is arranged to be inclined with respect to the horizontal plane. Thus, the mixed melt 28 covers a part of the bottom surface 33 of the reaction vessel 12, and the seed substrate 29 is disposed on the bottom surface 33 of the reaction vessel 12 so as to be separated from the liquid surface of the mixed melt 28. In addition, the reaction vessel 12 may be stored, a nitrogen gas supply pipe 15 may be provided, and the pressure resistant vessel 11 may be further provided.

  According to the group III nitride crystal manufacturing apparatus, the group III element of the liquid film on the seed substrate 29 and the liquid film generated from the condensation phenomenon due to the temperature difference between the vapor 30 generated from the mixed melt 28 and the seed substrate 29 Crystal growth of group III nitride crystals can be carried out by reaction with nitrogen dissolved therein. Further, by utilizing the effect that the liquid film 31 is replaced before etching the seed substrate 29, it is possible to manufacture a group III nitride crystal with few impurities and few dislocation defects.

  Hereinafter, a method for producing a group III nitride crystal and a group III nitride crystal production apparatus 10 will be described.

  The group III nitride crystal production apparatus 10 shown in FIG. 1 is equipped with a closed pressure-resistant container 11 made of stainless steel. The reaction vessel 12 is installed on the reaction vessel installation base 14 in the pressure resistant vessel 11. The reaction container 12 is attachable to and detachable from the reaction container installation table 14.

<Reaction container>
The reaction vessel 12 holds a mixed melt 28 having an alkali metal and a substance containing at least a group III element, and a seed substrate 29 disposed so as not to contact the mixed melt 28 inside the vessel, It is a container for performing crystal growth.

It is desirable that the material of the reaction vessel 12 be a material whose wettability of the reaction vessel 12 to the mixed melt 28 is lower than the wettability of the mixed melt 28 to the seed substrate 29. In Embodiment 1 of the present invention, the material of the reaction vessel 12 is not particularly limited because it is sufficient to satisfy that the wettability of the mixed melt 28 with the seed substrate 29 is lower. For example, boron nitride (BN) sintered body, nitride such as P-BN, alumina (Al ₂ O ₃ ), yttria (Y ₂ O ₃ ), oxide such as yttrium aluminum garnet (YAG), SiC etc. Carbides can be used. The present invention can also be realized by subjecting the inner wall surface of the reaction vessel 12 to a hydrophobization treatment such as washing with an acid.

<Mixed melt>
The mixed melt 28 contains an alkali metal and a substance containing at least a group III element. For example, sodium (Na) or a sodium compound (for example, sodium azide) is used as a source of the mixed melt 28. In addition, as a raw material of the mixed melt 28, lithium (Li), potassium (K), or a compound of the alkali metal may be used as the alkali metal.

  Moreover, as a material containing a Group III element (in the long period table, a Group 13 element) which is a raw material of the mixed melt 28, for example, gallium (Ga) is used. In addition, it is also possible to use boron (B), aluminum (Al), indium (In), group III chlorine, or a mixture thereof as the material of the group III element which is the raw material of the mixed melt 28.

  There are no particular limitations on the quantitative ratio of the alkali metal (for example, sodium (Na)) and the Group III element (for example, gallium (Ga)) to be introduced into the reaction vessel 12 as a raw material of the mixed melt 28.

  In a desirable embodiment for crystal growth, the ratio of the number of moles of alkali metal to the total number of moles of alkali metal (for example, sodium) and the Group III element (for example, gallium) is in the range of 0.6 to 0.8. Is desirable.

<Pressure resistant container>
The pressure container 11 includes a nitrogen gas supply pipe 15 for supplying nitrogen (N ₂ ) gas, which is a raw material of group III nitride crystals, to the internal space thereof, and a nitrogen gas exhaust pipe 21 for exhausting a predetermined amount of nitrogen gas. An evacuation tube 25 for evacuating the internal space is connected.

Nitrogen gas is supplied from a nitrogen gas supply pipe 15 connected to a nitrogen gas cylinder 20 filled with nitrogen (N ₂ ) gas. The pressure of the reaction vessel 12 is set to the pressure necessary for crystal growth (for example, 4.0 MPa) using the nitrogen gas supply pipe 15, the pressure regulator 16, and the valve 19. During crystal growth, it is desirable to supply nitrogen at a constant flow rate (for example, 1000 sccm) by a mass flow controller 18 attached to the nitrogen gas supply pipe 15. In order to make constant the set pressure during crystal growth, the pressure regulator 22 installed in the nitrogen gas exhaust pipe 21 performs pressure regulation so as to maintain the pressure of the pressure gauge 17 constant.

  Further, as shown in FIG. 1, a heater 13 is installed on the outer periphery of the pressure resistant container 11. The heater 13 can adjust the temperature of the mixed melt 28 by heating the pressure-resistant vessel 11 and the reaction vessel 12. Moreover, since the heater 13 is comprised from several independent heaters, it is also possible to attach temperature distribution to an up-down direction.

  The crystal growth temperature of the mixed melt 28 in the method for producing a group III nitride crystal according to the first embodiment is preferably 700 ° C. or more.

  More preferably, the crystal growth temperature is 870 ° C., and the nitrogen pressure in the pressure container 11 at the temperature is more preferably 3.2 MPa.

  Whether or not the vapor of the mixed melt 28 is filled in the reaction vessel 12 varies depending on the pressure in the pressure-resistant vessel 11 and the temperature, amount of the mixed melt 28, and the volume of the reaction vessel. Therefore, preferably, the volume is set by the input amount of the mixed melt 28 and the inner diameter and height of the reaction vessel 12 so that the vapor of the mixed melt 28 is filled in the reaction vessel 12 under the crystal growth conditions described above. . Since the setting required for crystal growth depends on the combination of the above settings, the pressure in the pressure resistant container 11 and the temperature of the mixed melt 28 are not particularly limited in the present embodiment.

<Installation method of seed substrate and mixed melt>
Next, a method of installing the seed substrate 29 and the mixed melt 28 necessary for crystal growth of the group III nitride crystal in the group III nitride crystal production apparatus 10 will be described.

  The operation of charging the raw material into the reaction vessel 12 is carried out by housing the reaction vessel 12 in a glove box having an inert gas atmosphere such as argon gas, for example.

  The bottom surface 33 of the reaction vessel 12 is inclined and disposed, and to the lower side of the bottom surface 33 of the reaction vessel 12, the alkali metal and the Group III element, which are the raw materials of the mixed melt 28, are charged.

  The seed substrate 29 is disposed on the upper side of the bottom surface 33 of the inclined reaction vessel 12. Here, in order to prevent movement of the seed substrate 29 during crystal growth, it is desirable that the bottom surface of the reaction vessel 12 be processed such as counterbore slightly larger from the outer diameter of the seed substrate 29. . As a result, the seed substrate 29 can be fixed to the bottom surface 33 of the reaction container 12, and the surface of the seed substrate 29 and the bottom surface 33 of the reaction container 12 can be made substantially flush.

  The bottom surface 33 of the reaction vessel 12 is horizontal to the horizontal surface so that the mixed melt 28 does not contact the seed substrate 29 during crystal growth, and the liquid film 31 flows to the mixed melt 28 before etching the seed substrate 29. Is set to be inclined.

  Whether the liquid film 31 on the seed substrate 29 flows down to the mixed melt 28 before etching the seed substrate 29 depends on the angle θ at which the bottom surface 33 of the reaction vessel 12 is inclined to the horizontal surface, and the seed substrate 29 It is determined by the temperature difference of the vapor 30 generated from the mixed melt. For example, when the temperature of the vapor of the mixed melt is set to 870 ° C. and the surface temperature of the seed substrate 29 is set to 800 ° C., the bottom 33 of the reaction vessel 12 in the pressure container 11 is at least 13 ° to 30 ° with respect to the horizontal plane. It is desirable to incline at an angle θ less than or equal to °.

  The amount of the mixed melt 28 is set so that the mixed melt 28 does not generate the liquid film 31 on the seed substrate 29 due to the wettability of the reaction vessel 12 during crystal growth. When the temperature of the mixed melt 28 is set to 870 ° C., the distance between the seed substrate 29 and the mixed melt 28 is preferably 10 mm or more.

The above installation method is an example of the installation method of the mixed melt 28 and the seed substrate 29 for realizing the group III nitride crystal production apparatus 10 according to the first embodiment of the present invention.
In addition, since the setting temperature of the mixed melt 28 and the diameter of the reaction vessel 12 also affect the angle at which the bottom surface 33 of the reaction vessel 12 is inclined, the distance between the seed substrate 29 and the mixed melt 28 is limited to the above example. It is not something to be done.

  By installing the seed substrate 29 and the mixed melt 28, the seed substrate 29 and the reaction vessel 12 in which the mixed melt 28 containing an alkali metal and a group III element is placed are taken out from the glove box, and the group III nitride crystal manufacturing apparatus It is installed in the pressure container 11 of ten.

<Nitrogen gas supply to the reaction vessel>
The supply of nitrogen gas from the nitrogen (N ₂ ) gas supply pipe 15 and the exhaust from the vacuum pipe 25 are repeated in the pressure resistant container 11 of the group III nitride crystal production apparatus 10 (purge operation). As a result, the inside of the reaction vessel 12 installed in the pressure resistant vessel 11 is filled with nitrogen gas with few impurities.

  Furthermore, in order to achieve a clean nitrogen gas atmosphere in the reaction vessel 12, the pressure-tight vessel 11 may be evacuated for a certain period of time using a vacuum pump 27 from an evacuation pipe 25.

<Crystal growth method>
A method of growing a group III nitride crystal will be described with reference to FIGS. 3-1 to 3-4. FIGS. 3-1 to 3-4 are schematic cross-sectional views showing the crystal growth process (the state of crystal growth being performed) of the group III nitride crystal in Embodiment 1 in a stepwise manner.

  3-1 is a figure which shows the mode inside reaction container 12 before setting temperature and pressure to crystal growth conditions. In FIG. 3-1, the reaction vessel 12, the mixed melt 28, and the seed substrate 29 are arranged as already described in the installation method described above in conjunction with FIG. 3-1.

  The stage of FIG. 3-1 is a figure which shows a mode at the time of setting temperature and pressure to crystal growth conditions, and shows a mode that temperature and pressure are maintained constant.

  In the stage of FIG. 3B, the vapor 30 is generated from the mixed melt 28 in the high temperature state, and the reaction vessel 12 is filled. At this time, the inner wall of the reaction vessel 12 is not wetted. Or it is slightly wet.

At this time, nitrogen (N ₂ ) is dissolved in the vapor 30 of the mixed melt 28 from the gas phase in the reaction vessel 12.

  At the stage of FIG. 3-3, settings such as lowering the temperature on the lower side of the heater 13 are performed. This allows the surface temperature of the seed substrate 29 to be lower than the temperature of the vapor 30 of the mixed melt 28. For example, the condensation phenomenon occurs from the vapor 30 of the mixed melt 28 on the seed substrate 29 whose surface temperature is lower by 10 ° C. or more than the temperature of the vapor 30 of the mixed melt 28, whereby the mixture is mixed onto the seed substrate 29. The liquid film 31 of the melt is coated.

  At the stage of FIG. 3-4, the nitrogen in the reaction vessel 12 has already been dissolved in the liquid film 31 on the seed substrate 29, and the raw material necessary for crystal growth is present. Growth of the nitride crystal 32 is performed.

  In this case, since the bottom surface 33 of the reaction container 12 is inclined, the surface of the seed substrate 29 is also inclined. Therefore, the liquid film 31 on the seed substrate 29 flows to the mixed melt 28 before eroding the surface and the side surface of the seed substrate 29. Furthermore, since the liquid film 31 is not in contact with the inner wall of the reaction vessel 12, the surface of the reaction vessel 12 is not eroded as well. Therefore, impurities derived from the seed substrate 29 and the reaction vessel 12 are not taken into the mixed melt 28. Since crystal growth is performed on the seed substrate 29 with the clean mixed melt 28, crystals with few impurities can be obtained.

  With the temperature maintained at 870 ° C. and the pressure maintained at 3.2 MPa, the steps of FIGS. 3-3 and the steps of FIGS. 3-4 are repeated in the reaction vessel 12. Crystal growth can be continued by this.

  As described above, in the first embodiment, the condensation phenomenon in which the vapor 30 of the mixed melt 28 present in the reaction vessel 12 generates the liquid film 31 on the surface of the seed substrate 29, and the liquid film 31 on the seed substrate 29. And the phenomenon of flowing down from the surface of the seed substrate 29 and returning to the mixed melt 28 due to the inclination of the seed substrate 29 caused by the inclination of the bottom surface 33 of the reaction vessel 12. Thus, the clean liquid film 31 is continuously supplied to the crystal growth surface of the seed substrate 29. As a result, it is possible to grow a crystal with few impurities.

Example 1
Crystal growth of gallium nitride (GaN) as nitride crystal 32 was performed using group III nitride crystal production apparatus 10 shown in FIG.

  First, the reaction vessel 12 was removed from the pressure resistant vessel 11, and the reaction vessel 12 was housed in a glove box under an argon atmosphere.

By closing the pressure regulators 16 and 22 and the valve 26 connected to the group III nitride crystal production apparatus 10, the pressure resistant container 11 is made into a closed space. Next, the valve 26 was opened and the vacuum pump 27 was operated. As a result, the atmosphere is expelled from the pressure-resistant container 11 and the inside of the pressure-resistant container 11 is evacuated to 1.0 × 10 ^-3 Pa or less, whereby impurities such as oxygen and water remain in the pressure-resistant container 11. It can be prevented.

Alumina (Al ₂ O ₃ ) was used as the material of the reaction vessel 12 housed in the glove box. Gallium (Ga) of Group III element and sodium (Na) of alkali metal were put into the reaction vessel 12 in the glove box. The ratio of the number of moles of sodium to the total number of moles of sodium and gallium in the mixed melt 28, Na / (Na + Ga), was 0.73.

The seed substrate 29 used was obtained by growing a GaN crystal to 5 μm by MO-CVD on a single crystal of ScAlMgO ₄ which is a base material. The seed substrate 29 was placed on the upper substrate holding portion of the inclined reaction vessel 12, as shown in FIG.

The nitrogen pipe and the valve 19 and the pressure regulator 16 were opened, and nitrogen (N ₂ ) gas was supplied to set the inside of the pressure resistant container 11 to about 0.1 MPa, and then the valve 19 was closed.

  The reaction container 12 in which Na (sodium) and Ga (gallium) which are raw materials of the seed substrate 29 and the mixed melt 28 were placed was taken out of the glove box.

  The reaction vessel 12 was placed on the reaction vessel installation stage 14 in the group III nitride crystal production apparatus 10.

  The valve 26 was opened and the vacuum pump 27 was operated for a fixed time. By the operation of the vacuum pump 27, the atmospheric component mixed in the pressure resistant container 11 was expelled to the outside in the installation work of the reaction container 12. After operating the vacuum pump 27 for a fixed time, the valve 26 was closed and the operation of the vacuum pump 27 was stopped.

  Again, the valve 19 and the pressure regulator 16 were opened, nitrogen gas was introduced into the pressure container, and the nitrogen pressure in the pressure container 11 was set to 3.2 MPa.

Next, the flow rate of the mass flow controller 18 was set to 1000 sccm. By adjusting the pressure regulator 22 on the exhaust side, an environment was maintained in which the pressure in the container was maintained at 3.2 MPa while supplying clean nitrogen (N ₂ ) gas.

  Thereafter, the heater 13 was energized to raise the temperature of the mixed melt 28 to 870 ° C., which is the crystal growth temperature.

  After the crystal growth was performed by maintaining the inside of the pressure container at 870 ° C. and 3.2 MPa for 50 hours, energization of the heater 13 was turned off, and the temperature of the reaction container 12 was lowered to around room temperature. After the valve 26 was opened and the pressure in the vessel was returned to 0.1 MPa, the reaction vessel 12 was taken out of the group III nitride crystal production apparatus 10. In the seed crystal 29 taken out of the reaction vessel 12, a single crystal of GaN having a thickness of about 0.5 mm with the C plane as the main surface was grown.

The crystal cross-sections obtained in Example 1 were measured by secondary ion mass spectrometry (SIMS) at the two impurity concentrations on the seed substrate 29 side and on the surface side of the GaN crystal. The impurity concentration of 1) was 1 × 10 ¹⁵ atoms / cm ³ . The impurity concentration of Mg (magnesium) of the obtained GaN crystal showed the measurement lower limit in D-SIMS. The impurity concentration of aluminum (Al) was 1 × 10 ¹⁷ atoms / cm ³ , and the impurity concentration of oxygen (O) was 1 × 10 ¹⁷ atoms / cm ³ . In particular, it was confirmed that Mg can prevent mixing of Mg impurities derived from ScAlMgO _{4 of the} seed substrate 29 to Comparative Example 1 described later.

When the dislocation density on the crystal surface obtained in Example 1 was evaluated, it was 3.0 × 10 ⁵ cm ⁻² , and a high quality nitride GaN crystal with few dislocation defects was obtained.

(Example 2)
In Example 2, crystal growth was performed with the same configuration as in Example 1 except that sapphire (Al ₂ O ₃ ) was used as a base material of the seed substrate 29. Also in this case, a single crystal of GaN having a thickness of 0.5 mm with the C plane as the main surface was grown on the seed substrate 29.

When the impurity concentration in the crystal obtained in Example 2 was measured by secondary ion mass spectrometry (SIMS), both of the measurement points on the surface side of the GaN crystal as in Example 1 were impurities of magnesium (Mg). The concentration was 1 × 10 ¹⁵ Atoms / cm ³ . The impurity concentration of Mg (magnesium) of the obtained GaN crystal showed the measurement lower limit in D-SIMS. The impurity concentration of the aluminum (Al), the surface side of 3.0 × ¹⁰ 16 Atoms / cm ³ of GaN crystal, the seed substrate 29 side ^{is, 2.5 × 10 17 Atoms / cm} 3, the impurity concentration of oxygen (O) is Both measurement points were 1 × 10 ¹⁷ atoms / cm ³ . In particular, aluminum (Al) taken into the crystal is capable of preventing contamination of aluminum (Al) derived from sapphire (Al ₂ O ₃ ) of the seed substrate 29 as compared with Comparative Example 2 described later. confirmed.

The dislocation density in the GaN crystal obtained in Example 2 was evaluated to be 1.0 × 10 ⁷ cm ⁻² . In addition, as compared with Example 1, it was confirmed that dislocation defects which are considered to be caused by the difference in thermal expansion coefficient between the seed substrate 29 and the nitride crystal 32 were generated.

  In order to judge the usefulness of Example 1 and Example 2 in the present invention, as a comparative example, growth of a GaN crystal was performed with the configuration shown below.

(Comparative example 1)
As shown in FIG. 4, the mixed melt 28 and the seed substrate 29 are placed in contact with each other, and a single crystal of ScAlMgO ₄ is used as a base material of the seed substrate 29 as in the first embodiment. Crystal growth of crystals was carried out. A single crystal of GaN with a thickness of 0.5 mm was obtained. However, when the amount of impurities in the crystal is measured by secondary ion mass spectrometry (SIMS) at two points on the surface side of the same GaN crystal as in Example 1, the impurity concentration of magnesium (Mg) in both measurement points is The impurity concentration was 3.0 × 10 ¹⁹ atoms / cm ³ , the impurity concentration of aluminum (Al) was 1 × 10 ¹⁷ atoms / cm ³ , and the impurity concentration of oxygen (O) was 1 × 10 ¹⁷ atoms / cm ³ . From the difference in the impurity concentration of magnesium (Mg) of Example 1 and Comparative Example 1, the mixed melt 28 of FIG. 4 etches ScAlMgO ₄ of the seed substrate 29 and magnesium (Mg) which is a constituent element of the seed substrate 29 It can be seen that they are taken into the GaN crystal as impurities.

(Comparative example 2)
As shown in FIG. 4, the mixed melt 28 and the seed substrate 29 were placed in contact with each other, and III-nitrided using sapphire (Al ₂ O ₃ ) as a base material of the seed substrate 29 as in the second embodiment. Crystal growth was carried out. A single crystal of GaN with a thickness of 0.5 mm was obtained. The amount of impurities in the crystal was measured by secondary ion mass spectrometry (SIMS) at two points on the surface side of the same GaN crystal as in Example 1. As a result, the impurity concentration of magnesium (Mg) was 1 at both measurement points. It was .0 × 10 ¹⁵ Atoms / cm ³ . The impurity concentration of Mg (magnesium) of the obtained GaN crystal showed the measurement lower limit in D-SIMS. The impurity concentration of aluminum (Al) was 7.0 × 10 ¹⁷ atoms / cm ³ on the seed substrate 29 side and 2.6 × 10 ¹⁷ atoms / cm ³ on the surface side. The impurity concentration of oxygen (O) was 1 × 10 ¹⁷ atoms / cm ³ at both measurement points. As compared with Example 2, it was confirmed that aluminum (Al) had a significant difference between the interface of the seed substrate 29 and the surface of the GaN crystal. From this, the mixed melt 28 of FIG. 4 etches sapphire (Al ₂ O ₃ ) of the seed substrate 29 and aluminum (Al) which is a constituent element of the seed substrate 29 is taken into the crystal as an impurity. Recognize.

  When GaN is used as the material of the seed substrate 29, the effect of reducing the amount of impurities in the crystal is hardly obtained. However, it is expected that the impurity concentrations of oxygen (O) and aluminum (Al) in the GaN crystal of the seed substrate 29 are easily dispersed at the time of production on the premise of mass production of the GaN crystal. According to the method of manufacturing a group III nitride crystal according to the first embodiment of the present invention, it is possible to stably obtain a GaN single crystal with few impurities even when gallium nitride (GaN) is selected as the material of seed substrate 29. Can.

As shown in Table 1, the comparison of Example 1 and Comparative Example 1 in which ScAlMgO ₄ is used for the material of the seed substrate 29 shows the following about the result of the impurity concentration of the obtained nitride crystal. That is, in a configuration in which the seed substrate 29 and the mixed melt 28 are not in contact with each other, crystal growth utilizing the condensation phenomenon on the seed substrate 29 can obtain a nitride crystal having a low impurity concentration of Mg derived from the seed substrate 29. . Further, with regard to the result of the impurity concentration of the obtained crystal, the following can be understood when Example 2 and Comparative Example 2 in which Al ₂ O ₃ is used for the material of the seed substrate 29 are compared. That is, in a configuration in which the seed substrate 29 and the mixed melt 28 are not in contact with each other, crystal growth utilizing the condensation phenomenon on the seed substrate 29 can obtain a nitride crystal having a low impurity concentration of Al derived from the seed substrate 29. . Further, comparing the results of dislocation density of the crystals obtained from Example 1 and Example 2, the configuration of Example 1 is the thermal expansion coefficient of the nitride crystal 32 and the seed substrate 29 in comparison with Example 2. Since the difference is small, it is possible to obtain a nitride crystal with a low dislocation density.

In ScAlMgO ₄ used as the material of the seed substrate 29 in Example 1, the difference in thermal expansion coefficient with the GaN crystal is small, but on the other hand, the effect obtained with the material having physical properties that are easily etched with respect to the alkali metal melt Is large. Therefore, the material of the seed substrate 29 is not particularly limited in the present invention.

  Note that the present disclosure includes appropriate combinations of any of the various embodiments and / or examples described above, and the respective embodiments and / or examples. The effects of the embodiment can be exhibited.

  The semiconductor substrate comprising a group III nitride crystal obtained by the method and apparatus for producing a group III nitride crystal according to the present invention can be used to create a light emitting device such as an LED or LD, and It is useful to improve the reliability. It can also be useful for other common semiconductor devices such as FETs.

10: Group III nitride crystal production apparatus 11: Pressure vessel 12: reaction vessel 13: heater 14: reaction vessel installation table 15: nitrogen gas supply pipe 16: pressure regulator 17: pressure gauge 18: mass flow controller 19, 26: valve 20: nitrogen gas cylinder 21: nitrogen gas exhaust pipe 22: pressure regulator 23: air outside the apparatus 24: communication cable 25 for pressure control: vacuum tube 26 of pressure container 26: valve 27: vacuum pump 28: mixed melt 29: Seed substrate 30: Vapor of mixed melt generated from mixed melt 31: Liquid film of mixed melt on seed substrate 32: GaN single crystal 33: Bottom surface

Claims (13)

Preparing a mixed melt containing an alkali metal and a group III element in a reaction vessel;
Supplying a gas containing nitrogen element into the reaction vessel;
Preparing a seed substrate by separating from the liquid surface of the mixed melt;
Heating the mixed melt to make part of it into a vapor;
Covering the seed substrate with a liquid film in which the vapor of the mixed melt is condensed to grow a group III nitride crystal on the seed substrate;
A method for producing a group III nitride crystal, comprising   In the step of preparing the seed substrate by separating it from the liquid surface of the mixed melt, the bottom surface of the reaction container is inclined with respect to a horizontal plane, and the mixed melt covers a part of the bottom surface of the reaction container The method for producing a group III nitride crystal according to claim 1, wherein the seed substrate is disposed on the bottom surface of the reaction vessel at a distance from the liquid surface of the mixed melt.   The method for producing a group III nitride crystal according to claim 1, wherein the seed substrate is a sapphire substrate. The method for producing a group III nitride crystal according to claim 1, wherein the seed substrate is a ScAlMgO ₄ substrate.   The method for producing a group III nitride crystal according to claim 1, wherein the seed substrate is a GaN substrate.   The method for producing a group III nitride crystal according to any one of claims 1 to 5, wherein the alkali metal is Na.   The method for producing a group III nitride crystal according to any one of claims 1 to 6, wherein the group III element is gallium.   The method for producing a group III nitride crystal according to any one of claims 1 to 7, wherein the gas containing nitrogen element is nitrogen.   The method for producing a group III nitride crystal according to any one of claims 1 to 8, wherein the wettability of the seed substrate to the mixed melt is higher than the wettability of the reaction container to the mixed melt.   10. The method for producing group III nitride crystals according to any one of claims 1 to 9, wherein in the step of growing group III nitride crystals, the liquid film is allowed to flow through the mixed melt before etching the seed substrate. Method. A reaction vessel for storing a mixed melt containing an alkali metal and a group III element, and a seed substrate disposed apart from the liquid surface of the mixed melt;
A nitrogen gas supply pipe for supplying a gas containing elemental nitrogen into the reaction vessel;
A heating unit which heats the mixed melt and makes a part of it into a vapor;
A group III nitride crystal production apparatus comprising:   The bottom surface of the reaction container is arranged to be inclined with respect to the horizontal plane, and the mixed melt covers a part of the bottom surface of the reaction container, and the seed substrate is the mixed melt on the bottom surface of the reaction container The group III nitride crystal production apparatus according to claim 11, which is disposed apart from the liquid surface of   The group III nitride crystal production apparatus according to claim 11, further comprising a pressure resistant container that houses the reaction container, has the nitrogen gas supply pipe, and is sealable.

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