JP7169585B2 - Group III nitride crystal production method and production apparatus - Google Patents

Description

The present invention relates to a method and apparatus for producing group III nitride crystals.

Substrates of group III nitride single crystal semiconductors (gallium nitride, for example) are usually formed by vapor phase epitaxial growth. For example, a substrate obtained by heteroepitaxially growing a Group III nitride crystal on a base substrate made of sapphire is used. However, the sapphire substrate and the gallium nitride single crystal have a lattice constant difference of 13.8% and a linear expansion coefficient difference of 25.8%. Therefore, a gallium nitride single crystal thin film obtained by vapor phase epitaxial growth does not have sufficient crystallinity. The dislocation density of the crystal obtained by this method is usually 1e+8 cm ⁻² (1×10 ⁸ cm ⁻² ) to 1e+9 cm ⁻² (1×10 ⁹ cm ⁻² ), and the reduction of the dislocation density is an important issue. It's becoming In order to solve this problem, efforts have been made to reduce the dislocation density, and for example, the ELOG (Epitaxial Lateral Overgrowth) method has been developed. According to this method, the dislocation density can be lowered to about 1e+5 cm ⁻² (1×10 ⁵ cm ⁻² ) to 1e+6 cm ⁻² (1×10 ⁶ cm ⁻² ), but the manufacturing process is complicated.

On the other hand, methods of growing crystals in a liquid phase instead of vapor phase epitaxial growth have also been investigated. Conventionally, the equilibrium vapor pressure of nitrogen at the melting point of group III nitride single crystals such as gallium nitride single crystals and aluminum nitride single crystals is 1000 MPa or higher. conditions have been required. In contrast, it was clarified that gallium nitride single crystals can be synthesized at a relatively low temperature and low pressure of 870° C. and 4 MPa by using a sodium flux method that dissolves nitrogen by utilizing a mixed melt with a sodium melt. (For example, see Patent Document 1.)

In addition, a mixture of gallium and sodium is melted at 800° C. and 5 MPa in a nitrogen gas atmosphere containing ammonia, and a single crystal having a maximum crystal size of about 1.2 mm is grown in a growth time of 96 hours using this melt. have been obtained (see, for example, Patent Document 2).

Further, after forming a gallium nitride single crystal layer on a sapphire substrate by a metal organic chemical vapor deposition (MOCVD) method, a single crystal is grown by a liquid phase epitaxy (LPE) method. A method has also been reported (see, for example, Patent Documents 3 and 4).

In these methods, when the seed crystal substrate is present in the melt before the mixture of gallium and sodium reaches a state satisfying the growth conditions of the group III nitride single crystal, the seed crystal substrate is in the melt. The gallium nitride single-crystal layer of the unintentionally decomposes to deteriorate the flatness of the surface. In order to avoid this problem, a method is known in which the seed crystal substrate is immersed in the mixture of gallium and sodium after the mixture of gallium and sodium has reached a state that satisfies the growth conditions for group III nitride single crystals. (For example, Non-Patent Document 1.).

Japanese Patent No. 4538596 Japanese Patent Application Laid-Open No. 2009-234800 Japanese Patent No. 4588340 Japanese Patent No. 5904421

Taro Sato et al 2015 Jpn. J. Appl. Phys. 54 105501

In the method of Non-Patent Document 1, in order to estimate the time at which the seed crystal substrate should be immersed, the immersion start time is predicted in advance, and the immersion time is changed around the predicted immersion time, and multiple preliminary experiments are performed. need. This method is expensive both in terms of time and material, and the immersion start time derived by this method is estimated from the conditions of the immersion time obtained during the preliminary experiment. depends on the set experimental conditions (setting of immersion start time and its step size). In addition, when the growth conditions change and the optimal immersion time changes, it is required to repeat the above preliminary experiments a plurality of times.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a group III nitride crystal that achieves the completion of mixing of a mixed melt of raw metals by a simple method and produces a high quality group III nitride single crystal. do.

In order to achieve the above object, in the present disclosure, a mixed melt is obtained by mixing a melt containing at least one group III element selected from gallium, aluminum, and indium and an alkali metal,
measuring the relationship between time and electrical resistance in the mixed melt;
A group III nitride single crystal manufacturing method is provided in which it is determined that mixing is completed when the electrical resistance reaches a constant value, and the group III nitride single crystal is grown.

The present disclosure also provides a reaction chamber,
a crucible that is provided in the reaction chamber and holds a mixed melt of raw materials for group III nitride crystals;
a heater for heating the crucible;
a nitrogen supply line for supplying nitrogen gas into the reaction chamber;
a substrate holding mechanism that holds a group III nitride crystal seed crystal substrate movably between a position above the liquid surface of the mixed melt and a position within the mixed melt in the crucible;
an electrical resistance measuring unit that is immersed in the mixed melt in the crucible and measures the electrical resistance of the mixed melt;
a mixing completion determination unit that determines whether or not mixing of the mixed melt is completed based on whether or not the measured electrical resistance reaches a constant value;
a control unit that controls the substrate holding mechanism and the mixing completion determination unit;
with
The control unit causes the substrate holding mechanism to move the seed crystal substrate in response to the determination of completion of mixing of the mixed melt by the mixing completion determination unit to bring the seed crystal substrate into contact with the mixed melt. An apparatus for manufacturing group III nitride crystals is provided.

With the group III nitride crystal production method and the group III nitride crystal production apparatus according to the present disclosure, it is possible to determine the completion of mixing of a mixed melt of at least one group III element selected from gallium, aluminum, and indium and an alkali metal. It is realized by a simple method, and it becomes possible to produce a high-quality Group III nitride single crystal. Further, when the slope of the relationship between the time of the mixed melt and the electric resistance is within a predetermined range, it becomes possible to determine that the degree of supersaturation suitable for the growth of the Group III nitride single crystal has been reached.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an example of a main part of a configuration of a Group III nitride crystal manufacturing apparatus according to Embodiment 1 of the present disclosure; FIG. 2 is a schematic diagram showing the configuration of a four-terminal electrode in the group III nitride crystal manufacturing apparatus of FIG. 1; FIG. 2 is a schematic diagram showing the configuration of a seed crystal substrate in which a first Group III nitride single crystal layer is formed on a base substrate; 4 is a graph showing the results of the relationship between time and electrical resistivity (time is based on completion of immersion) in Experimental Example 1. FIG. 1 is a flow chart of a method for producing a group III nitride crystal according to Embodiment 1;

A method for producing a group III nitride crystal according to a first aspect comprises mixing a melt containing at least one group III element selected from gallium, aluminum and indium and an alkali metal to form a mixed melt,
measuring the relationship between time and electrical resistance in the mixed melt;
When the electrical resistance becomes a constant value, it is determined that the mixing is complete, and the Group III nitride single crystal is grown.

A method for producing a Group III nitride crystal according to a second aspect, in the first aspect, when the slope, which is the time change of the electrical resistance in the relationship between the time and the electrical resistance, is within a predetermined range, the mixing is completed. can be determined.

In the method for producing a Group III nitride crystal according to the third aspect, in the first aspect, a four-terminal electrode may be used for measuring the electrical resistance.

In the method for producing a Group III nitride crystal according to the fourth aspect, in the first aspect, electrodes made of tantalum may be used for measuring the electrical resistance.

A method for producing a Group III nitride crystal according to a fifth aspect is the method for producing a group III nitride crystal according to the second aspect, in which the change in electrical resistivity with respect to time is linearly approximated by the least squares method for the measurement results of the electrical resistivity for arbitrary 30 minutes. Mixing may be determined to be completed when the absolute value of the gradient is 2e-9 ohm·meters/hour or less.

A method for producing a group III nitride crystal according to a sixth aspect is the second aspect, wherein nitrogen is supplied in response to the determination of the completion of mixing,
Even if the group III nitride single crystal is grown when the time change of the electric resistivity of the mixed melt is 3.9e-9 ohm m/h or more and 2.0e-8 ohm m/h or less good.

A group III nitride crystal manufacturing apparatus according to a seventh aspect comprises a reaction chamber,
a crucible that is provided in the reaction chamber and holds a mixed melt of raw materials for group III nitride crystals;
a heater for heating the crucible;
a nitrogen supply line for supplying nitrogen gas into the reaction chamber;
a substrate holding mechanism that holds a group III nitride crystal seed crystal substrate movably between a position above the liquid surface of the mixed melt and a position within the mixed melt in the crucible;
an electrical resistance measuring unit that is immersed in the mixed melt in the crucible and measures the electrical resistance of the mixed melt;
a mixing completion determination unit that determines whether or not mixing of the mixed melt is completed based on whether or not the measured electrical resistance reaches a constant value;
a control unit that controls the substrate holding mechanism and the mixing completion determination unit;
with
The control unit causes the substrate holding mechanism to move the seed crystal substrate in response to the determination of completion of mixing of the mixed melt by the mixing completion determination unit to bring the seed crystal substrate into contact with the mixed melt.

An apparatus for producing a Group III nitride crystal according to an eighth aspect is the apparatus for producing a group III nitride crystal according to the seventh aspect, in which nitrogen is supplied from the nitrogen supply line into the reaction chamber in response to the mixing completion determination made by the mixing completion determination unit. ,
Furthermore, when the change over time of the electrical resistivity of the mixed melt is 3.9e-9 ohm m/h or more and 2.0e-8 ohm m/h or less, the nitrogen supersaturation is within an appropriate range Determining that there is a nitrogen supersaturation determination unit,
The control unit causes the substrate holding mechanism to move the seed crystal substrate in response to the determination by the nitrogen supersaturation determination unit that the nitrogen supersaturation is within an appropriate range, thereby moving the seed crystal substrate to the mixed melt. may come into contact with

Hereinafter, a group III nitride crystal manufacturing method and a group III nitride crystal manufacturing apparatus according to embodiments will be described with reference to the accompanying drawings. In addition, the same code|symbol is attached|subjected about the substantially same member in drawing.

Hereinafter, a method for producing a group III nitride crystal according to an embodiment of the present disclosure will be described by taking an embodiment in which a gallium nitride single crystal substrate is produced as a group III nitride crystal substrate. In all the drawings, the size, ratio, etc. of each component are different from the actual ones.

(Embodiment 1)
In the method for producing a group III nitride crystal according to the first embodiment, a melt containing at least one group III element selected from gallium, aluminum and indium and an alkali metal is mixed to form a mixed melt, and the mixed The relationship between the time in the melt and the electric resistance is measured, and when the electric resistance reaches a constant value, it is determined that the mixing is complete, and the Group III nitride single crystal is grown. More specifically, as shown in FIG. 5, the method for producing a Group III nitride crystal according to Embodiment 1 includes:
(1) electrode, seed crystal substrate, raw material metal, alkali metal preparation step (S01),
(2) step of melting raw material metal and alkali metal by raising temperature (S02);
(3) a resistance measurement step (S03) for judging completion of mixing of the mixed metal melt;
(4) Mixing completion determination (S04),
(5) nitrogen dissolution step (S05),
(6) a resistance measurement step (S06) for determining the nitrogen supersaturation state;
(7) Determination of nitrogen supersaturation (S07),
(8) Crystal growth step (S08)
including.
In addition, if it is determined as NG in the mixing completion determination step (S04), the process returns to the melting step (S02). Further, if NG is determined in the supersaturated state determination step (S07), the process returns to the nitrogen dissolution step (S05).

FIG. 2 is a schematic diagram showing the configuration of a four-terminal electrode in the group III nitride crystal manufacturing apparatus of FIG. A four-terminal measurement method was used to eliminate the influence of the resistance change of the electrode material for measuring the electric resistance of the metal melt (Fig. 2). Although the electrode material is not limited, tantalum was used in this example as a material that is resistant to the raw metal melt and alkali metal melt used and has little effect on nitridation and gallium nitride single crystal growth. Other possible electrode materials for resistance measurements include tungsten, tungsten rhenium, and molybdenum. In addition, an alumina member was machined to prepare a jig so that the distance between terminals at four locations would not change during the experiment. Hereinafter, the alumina jig through which the four tantalum electrode wires 203 are passed will be referred to as a four-terminal electrode 204 .

FIG. 3 is a schematic diagram showing the configuration of seed crystal substrate 100 in which first group III nitride single crystal layer 301 is formed on base substrate 300 . In the method for producing a group III nitride crystal according to the first embodiment, the group III nitride crystal is grown using the flux method.
Therefore, the preparation of the seed crystal substrate 100 used for growth will be described. A sapphire substrate, for example, can be used as the base substrate 300 (FIG. 3) of the seed crystal substrate for growing the gallium nitride crystal as the group III nitride crystal. Sapphire is used because the difference in lattice constant and thermal expansion coefficient from gallium nitride is relatively small. Besides sapphire, for example, SiC, GaAs, _ScAlMgO4 , etc. can be used. Also, the thickness of the base substrate 300 is preferably about 100 to 3000 micrometers, more preferably 400 to 1000 micrometers. When the thickness of the base substrate 300 is within this range, the strength is sufficiently high, and cracks and the like are less likely to occur during fabrication of the gallium nitride single crystal substrate.

Next, a Group III nitride single crystal layer represented by a composition formula of Al _u Ga _v In _1-uv N (where 0≦u≦1 and 0≦v≦1) is formed on the base substrate 300 . 301 is formed. The Group III nitride single crystal layer can be formed, for example, by MOCVD, MBE (Molecular Beam Epitaxy), or HVPE (Hydrogen Vapor Phase Epitaxy). The group III nitride layer is desirably a single crystal with a (0001) plane as the main surface (upper surface). The thickness of the thin film is preferably about 0.5 to 20 micrometers, more preferably 1 to 5 micrometers. When the thickness of the thin film is 0.5 μm or more, the formed thin film becomes a good single crystal, and lattice defects and the like are less likely to occur in the resulting gallium nitride crystal. The dislocation density of a gallium nitride thin film formed on sapphire by MOCVD is generally about 1e+7 to 1e+9 per square centimeter. A buffer layer (not shown) may be formed between the base substrate 300 and the thin film.

The buffer layer is a layer for buffering the lattice constant difference between sapphire and gallium nitride in order to form a high quality gallium nitride single crystal thin film 301 on the base substrate 300 made of sapphire. The buffer layer is preferably made of materials with lattice constants close to those of sapphire and gallium nitride, and can be a layer made of a group III nitride such as aluminum nitride. Also, the buffer layer is preferably an amorphous or polycrystalline layer grown by MOCVD at a relatively low temperature of 400° C. or higher and 700° C. or lower. When such a buffer layer is used, lattice defects and the like are less likely to occur in the gallium nitride single crystal thin film formed on the buffer layer. The thickness of the buffer layer is preferably 10 nm or more and 50 nm or less, more preferably 20 nm or more and 40 nm or less. When the thickness of the buffer layer is 10 nanometers or more, the effect of buffering the difference in lattice constant is exhibited, and lattice defects and the like are less likely to occur in the obtained gallium nitride crystal. On the other hand, if the thickness of the buffer layer is excessively thick, the information on the crystal lattice of the base substrate is lost, making good epitaxial growth impossible. The sapphire base substrate 300 on which the group III nitride single crystal layer 301 is formed by the MOCVD method is referred to as a seed crystal substrate 100 .

A step of processing the group III nitride single crystal layer formed on the base substrate by MOCVD may be included.

Subsequently, a Group III nitride single crystal is formed by a flux method on the seed crystal substrate 100 on which the Group III nitride single crystal layer has been formed. In the present embodiment, nitrogen molecules supplied under pressure in the flux method are separated into nitrogen atoms and dissolved in the melt for the crystal growth reaction, so sodium is used as the alkali metal constituting the mixed melt. Here's an example of how it's used. Alkali metals include at least one selected from sodium, lithium and potassium, ie one or mixtures thereof. Also, the mixed melt may further contain an alkaline earth metal or carbon. Examples of alkaline earth metals that can be used include calcium, magnesium, strontium, barium, and beryllium. In some cases, the effect of suppressing polycrystallization can be obtained by containing minute additives composed of these alkaline earth metals and carbon.
Nitrogen gas and ammonia, for example, can be used as the gas containing nitrogen. In this embodiment mode, an example using nitrogen gas is shown.

<Device for manufacturing Group III nitride single crystal>
FIG. 1 is a schematic diagram of an apparatus 10 for producing group III nitride crystals. The group III nitride single crystal growth step can be carried out as follows, for example, using the reaction apparatus 101 and the control unit 30 which are the group III nitride crystal manufacturing apparatus 10 shown in FIG.

<Reactor>
The reaction device 101 has a reaction chamber 103 made of stainless steel, a heat insulating material, or the like, and a crucible 102 is installed in the reaction chamber 103 . The crucible can be made of boron nitride (BN), alumina (Al ₂ O ₃ ), or the like. A heater 110 is arranged around the reaction chamber 103 , and the heater 110 is designed to adjust the temperature inside the reaction chamber 103 , especially inside the crucible 102 . A four-terminal electrode holding mechanism 120 is installed in the reactor 101 to hold the four-terminal electrode 204 so that it can move up and down. The electrode wires 203 of the four-terminal electrode are connected through a sealed mechanism 202 to a current source 200 and a voltmeter 201 in the out-of-core atmospheric space 109 outside the pressure vessel. A substrate holding mechanism 114 for holding the group III nitride seed crystal substrate 100 so as to be able to move up and down is installed in the reactor 101 as well. In addition, a nitrogen supply line 113 for supplying nitrogen gas is connected to the reaction chamber 103 (not shown, but connected to a nitrogen cylinder or the like outside the reaction chamber).

<Control unit (computer device)>
The control unit 30 is, for example, a computer device. A general-purpose computer device can be used as this computer device, and includes, for example, a processing unit 31, a storage unit 32, and a display unit 33, as shown in FIG. Furthermore, an input device, a storage device, an interface, etc. may be included.
The control unit 30 controls the substrate holding mechanism 114, the mixing completion determination unit 35a, and the nitrogen supersaturation determination unit 35b.

<Processing part>
The processing unit 31 may be, for example, a central processing operator (CPU), a microcomputer, or any other processing device capable of executing computer-executable instructions.

<Memory part>
The storage unit 32 may be, for example, at least one of ROM, EEPROM, RAM, flash SSD, hard disk, USB memory, magnetic disk, optical disk, magneto-optical disk, and the like.
The storage unit 32 contains a program 35 . In addition, when the control unit 30 is connected to a network, the program 35 may be downloaded from the network as necessary.

<Program>
The program 35 may include a mixing completion determination section 35a. The mixing completion determination unit 35a is read from the storage unit 32 and executed by the processing unit 31 at the time of execution. The mixing completion determining unit 35a determines whether or not the mixing of the mixed melt is completed based on whether or not the measured electric resistance of the mixed melt reaches a constant value. Control unit 30 moves seed crystal substrate 100 by substrate holding mechanism 114 in response to determination of completion of mixing of the mixed melt by mixing completion determining unit 35a, and brings seed crystal substrate 100 into contact with the mixed melt. Thereby, the crystal growth process of the group III nitride crystal can be advanced.
Further, the program 35 may include a nitrogen supersaturation determination section 35b. The nitrogen supersaturation determination unit 35b determines the nitrogen supersaturation when the time change of the electrical resistivity of the mixed melt is 3.9e-9 ohm m/h or more and 2.0e-8 ohm m/h or less. is within the appropriate range. Control unit 30 causes substrate holding mechanism 114 to move seed crystal substrate 100 in response to determination by nitrogen supersaturation determination unit 35b that the nitrogen supersaturation is within an appropriate range, thereby moving seed crystal substrate 100 into the mixed melt. come into contact with Thereby, the crystal growth process of the group III nitride crystal can be advanced.

<Display section>
The display unit 33 may, for example, display the determination of the completion of mixing by the mixing completion determination unit 35a. Also, the position of the seed crystal substrate 100 by the substrate holding mechanism 114 may be indicated.

<Method for Producing Group III Nitride Crystal>
FIG. 5 is a flow chart of a method for producing a Group III nitride crystal. A method for producing this group III nitride crystal will be described below.
(1) When the group III nitride single crystal to be grown is gallium nitride, first, an alkali metal as a flux and gallium as a group III element are put into the crucible 102 in the reaction chamber 103 of the reactor 101 (S01). . The amount of alkali metal and gallium charged is, for example, about 85:15 to 50:50 in terms of molar ratio. At this time, if necessary, a trace additive may be added. Trace additives include, for example, boron, thallium, calcium, compounds containing calcium, silicon, sulfur, scandium, selenium, tellurium, carbon, oxygen, aluminum, indium, alumina, indium nitride, silicon nitride, silicon oxide, indium oxide, Zinc, magnesium, zinc oxide, lithium oxide, lithium, magnesium oxide, germanium, and the like. Only one kind of these trace additives may be added, or two or more kinds thereof may be added.

If these operations are carried out in the air, the alkali metals will oxidize and contain oxygen as an impurity, resulting in a significant drop in the quality of the grown crystals. is preferably filled with an inert gas.

(2) Next, the inside of the reaction chamber 103 is sealed, and the temperature of the crucible is adjusted to 800° C. or higher and 1000° C. or lower, more preferably 850° C. or higher and 950° C. or lower (S02). This melts the raw material metal and the alkali metal.

The mixed melt 121 of alkali metal and group III source metal in FIG. 1 is prepared, for example, by charging the material into the crucible 102 and heating it. A rocking or rotating motion, or a combination of both, may be used in crucible 102 to promote uniform mixing of the alkali metal, Group III source metal, and trace additives.

(3) After confirming that the inside of the crucible 102 exceeds the melting point of the alloy of the alkali metal and the group III source metal (around 700° C. in the case of gallium and sodium), the four-terminal electrode 204 is completely lifted using the elevating mechanism. is immersed in the mixed melt (S03). This time, the magnet 122 was used as the lifting mechanism. After confirming the energization, a voltage is applied from the current source 200 to monitor the electrical resistivity of the mixed melt.

(4) Determine whether mixing of the mixed melt is completed. Specifically, it is determined whether or not the mixing of the mixed melt is completed based on whether or not the electrical resistance of the mixed melt reaches a constant value (S04). When argon is used as the inert gas, the electrical resistance increases until the mixing of the alkali metal, group III raw metal, and trace additive is completed, but the mixed melt 121 is completely mixed and the state is uniform. Then the electrical resistance does not change. The same can be said for other inert gases such as helium and neon besides argon gas. That is, when the measured electrical resistance becomes a constant value, it is determined that the mixing is completed.
By this method, it is possible to confirm the completion of the mixing of the mixed melt of the alkali metal and the Group III raw metal and the trace additive by in-situ observation. In this case, it may be determined that mixing is completed when the slope of the relationship between the measured time and the electrical resistivity is within a predetermined range. As for the result, it can be determined that the mixing is completed when the absolute value of the slope is 2e-9 ohm·meters/hour or less when linearly approximating the change in electrical resistivity with respect to time by the method of least squares.
Note that if the mixed melt 121 of the alkali metal and the group III source metal that is not uniformly mixed comes into contact with the seed crystal substrate 100, the group III nitride seed crystal 100 may be etched or the quality of the group III nitride crystal may be poor. Precipitation may occur. Therefore, when it is not determined that the mixing is completed, the process returns to the melting step (S02).

(5) Next, after determining that the mixing is complete, nitrogen gas is supplied from the nitrogen supply line 113 into the reaction chamber 103 (S05). If the gas to be pressurized contains nitrogen, the electric resistance of the mixed melt continues to increase even after the mixing is completed. This is because nitrogen in the gas dissolves in the mixed melt to form Ga—N bonds, thereby reducing free electrons in the mixed melt. In other words, the phenomenon that the electrical resistance continues to increase when nitrogen gas is pressurized means that the mixed metal melt is in a state of nitrogen supersaturation, and the rate of increase (gradient) of the electrical resistance with respect to time is relatively nitrogen It is an index that expresses the degree of supersaturation.

(6) Measure the electrical resistivity of the mixed melt after supplying the nitrogen gas (S06).
(7) Next, it is determined whether the degree of nitrogen supersaturation of the mixed melt is within an appropriate range (S07). Specifically, when the gradient of the electric resistivity of the mixed melt with respect to time is 3.9e-9 ohm m/h or more and 2.0e-8 ohm m/h or less, the nitrogen supersaturation is appropriate. Determined to be within range. In this case, the substrate holding mechanism 114 moves the seed crystal substrate 100 into the mixed melt to immerse the seed crystal substrate 100 in the mixed melt.
When evaluating the mixing completion time and determining the nitrogen supersaturation state at the same time, first, the mixing completion is determined in a state of pressurization with an inert gas other than nitrogen gas, and then nitrogen gas is supplied. to dissolve nitrogen in the melt. In the mixing process, the electric resistivity of the mixed melt converged to a constant value, but the electric resistivity increased when the nitrogen gas was supplied.

At this time, when seed crystal substrate 100 is brought into contact with mixed melt 121 of alkali metal and group III source metal which are lower than a predetermined temperature and have low nitrogen supersaturation or are not uniformly mixed, group III nitride seed crystal 100 etching, precipitation of group III nitride crystals of poor quality, and the like may occur. Therefore, when it is determined in the nitrogen supersaturated state determining step (S07) that the nitrogen saturation of the mixed melt is not within the appropriate range, the substrate holding mechanism 114 moves the seed crystal substrate 100 to the upper portion of the reaction chamber 103. preferably retained.

The nitrogen gas pressure in the reaction chamber 103 is 1×10 ⁶ Pa or more and 1×10 ⁷ Pa or less, more preferably 3×10 ⁶ Pa or more and 5×10 ⁶ Pa or less. By increasing the gas pressure in the reaction chamber 103, nitrogen becomes easier to dissolve in Na melted at a high temperature, and the Group III nitride crystal can be grown at the above temperature and pressure at a high speed.

(8) Confirming completion of mixing of the mixed melt 121 of the alkali metal, group III raw metal and trace additives, and appropriate nitrogen supersaturation, the mixed melt 121 is formed with a group III nitride single crystal layer A group III nitride single crystal is grown by bringing the growing surface side surface of 301 into contact (S08).

An example will be described. In this example, a four-terminal electrode was prepared using a tantalum electrode (cross-sectional diameter of 0.5 mm) and an alumina insulator tube. The inter-electrode distance of the four-terminal electrodes was set to 20 mm. Electrode wires of the four-terminal electrodes are led out of the reaction chamber through sealing terminals and connected to a current source. In all the experimental examples this time, the power supply setting was set to 10 volts and 1 ampere. A crucible made of alumina was used, sodium was used as an alkali metal, and gallium was used as a Group III source metal, so that the atomic weight ratio of sodium to gallium was 27:73.

(Example 1)
In the melt-forming step, the inside of the reaction chamber was pressurized with argon gas of 4 MPa, and the temperature inside the crucible was raised to 870°C. When the temperature reached 870°C, the four-terminal electrode was completely immersed in the metal melt. This experiment evaluates the completion time of mixing of the metal melt.

FIG. 4 is a graph showing the results of the relationship between the time and the electrical resistivity in Experimental Example 1 (the time is based on the completion of immersion). From this result, it was confirmed that the electrical resistance became stable without change over time after 10 hours, and the mixing was completed. The resistivity at this time was less than 2e-9 ohm-meters/hour. Under the conditions of this time, it was found that the substrate should be immersed in the metal melt 10 hours after the temperature inside the crucible reached 870°C. When crystal growth was actually carried out under the conditions of Example 1 with the mixing waiting step set to 10 hours, good gallium nitride crystals could be grown. The fact that a good gallium nitride crystal was grown means that the mixing was sufficiently completed, so when 10 hours passed from the start of mixing and the electrical resistance reached a stable state without change over time. It can be judged that the mixing is completed at .

(Example 2)
In the nitrogen dissolution process, the inside of the reaction chamber was pressurized with nitrogen gas, and the change in electrical resistivity over time was measured when the internal pressure was changed from 1 MPa, 2 MPa, 3 MPa, 4 MPa, and 5 MPa, and supersaturated. Evaluate degree indicators. The change in electrical resistivity over time is obtained by the least squares method from the electrical resistivity measurement results for the final 16 minutes when each of the above pressures is applied and the four-terminal electrode is immersed in the melt and held for 4.6 hours. Obtained by linear approximation. The temperature inside the crucible was set at 900° C., and the change in electrical resistivity with time was evaluated after the completion of mixing. Table 1 below shows the relationship between the change in electrical resistivity over time and the growth results when the nitrogen gas pressure is changed.

From the results of Table 1 for Example 2, the change in electrical resistivity with time after stabilizing the mixing of the metal melt under nitrogen gas pressurization was 3.9e-9 ohm-meter/hour or more and 2.0e-8 ohm-meter. It was found that a rate of m/h or less is favorable for growth. It is considered that the reason why the poor growth occurs when the nitrogen gas pressure is high is that the degree of supersaturation in the melt is too high, and unintended miscellaneous crystals are generated in the melt and on the crucible wall.

That is, when the electrical resistivity becomes constant, it is judged that the mixing of the metal melt has been completed, and by measuring the electrical resistance even during the subsequent dissolution of nitrogen, the optimum timing for starting crystal growth can be determined. Measure. Specifically, the time change of the electrical resistivity of the metal melt is measured when the nitrogen gas is supplied after the completion of mixing. When the measurement result is 3.9e-9 ohm-meters/hour or more and 2.0e-8 ohm-meters/hour or less, it is determined that the nitrogen supersaturation is the optimum value for crystal growth, and crystal growth is started. Start. Starting crystal growth means immersing the seed crystal substrate in the metal melt.

Some or all of the components in the above embodiments may be controlled by a control device composed of one system LSI (Large Scale Integration) or a plurality of dedicated electronic circuits. For example, the methods described above may be implemented by a system LSI or a plurality of dedicated electronic circuits. Also, the method of controlling each component of the apparatus described above may be implemented by a processor executing instructions or a software program stored in a non-transitory memory.

A system LSI is an ultra-multifunctional LSI manufactured by integrating multiple components on a single chip, and specifically includes a microprocessor, ROM (Read Only Memory), RAM (Random Access Memory), etc. A computer system comprising A computer program is stored in the ROM. The system LSI achieves its functions by the microprocessor operating according to the computer program.

Although system LSI is used here, it may also be called IC, LSI, super LSI, or ultra LSI depending on the degree of integration. Also, the method of circuit integration is not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor. An FPGA (Field Programmable Gate Array) that can be programmed after the LSI is manufactured, or a reconfigurable processor that can reconfigure connections and settings of circuit cells inside the LSI may be used.

Furthermore, if an integration technology that replaces the LSI appears due to advances in semiconductor technology or another derived technology, the technology may naturally be used to integrate the functional blocks. Application of biotechnology, etc. is possible.

Also, one aspect of the present disclosure may be a computer program that causes a computer to execute each characteristic step included in the method. Also, one aspect of the present disclosure may be a computer-readable non-transitory recording medium on which such a computer program is recorded.

In each of the above-described embodiments, each component may be configured by dedicated hardware, or realized by executing a software program suitable for each component. Each component may be realized by reading and executing a software program recorded in a recording medium such as a hard disk or a semiconductor memory by a program execution unit such as a CPU or processor.

It should be noted that the present disclosure includes appropriate combinations of any of the various embodiments and / or examples described above, and each embodiment and / or The effects of the embodiment can be obtained.

As described above, by using the method for producing a Group III nitride crystal according to the present invention, a Group III nitride crystal that can be applied to heterojunction high-speed electronic devices such as power semiconductors and optoelectronic devices such as LEDs and lasers. can be obtained.

10 III-nitride crystal manufacturing apparatus 30 control unit 31 processing unit 32 storage unit 33 display unit 35 program 35a mixing completion determination unit 35b nitrogen supersaturation determination unit 100 seed crystal substrate 101 reaction device 102 crucible 103 reaction chamber 109 outer air space 110 heater 111 metal lithium or metal lithium added with gallium 113 nitrogen supply line 114 substrate holding mechanism 120 four-terminal electrode holding mechanism 121 mixed melt 122 magnet 200 current source 201 voltmeter 202 sealing mechanism 203 electrode wire 204 four-terminal electrode 300 Base substrate 301 Group III nitride crystal thin film

Claims (6)

mixing a melt containing at least one Group III element selected from gallium, aluminum and indium and an alkali metal to form a mixed melt;
measuring the relationship between time and electrical resistance in the mixed melt;
Mixing is completed when the absolute value of the gradient when linearly approximating the change in electrical resistivity with respect to time by the least squares method is 2e-9 ohm meters / hour or less for the measurement results of electrical resistivity for an arbitrary 30 minutes. and growing a group III nitride single crystal. 2. The method for producing a Group III nitride crystal according to claim 1, wherein a four-terminal electrode is used for measuring said electrical resistance. 2. The method for producing a Group III nitride crystal according to claim 1, wherein a tantalum electrode is used for measuring said electrical resistance. Nitrogen is supplied according to the determination of the completion of mixing,
Growing a Group III nitride single crystal when the time change of the electric resistivity of the mixed melt is 3.9e-9 ohm m/h or more and 2.0e-8 ohm m/h or less Item 1. A method for producing a Group III nitride crystal according to Item 1. a reaction chamber;
a crucible that is provided in the reaction chamber and holds a mixed melt of raw materials for group III nitride crystals;
a heater for heating the crucible;
a nitrogen supply line for supplying nitrogen gas into the reaction chamber;
a substrate holding mechanism that holds a group III nitride crystal seed crystal substrate movably between a position above the liquid surface of the mixed melt and a position within the mixed melt in the crucible;
an electrical resistance measuring unit that is immersed in the mixed melt in the crucible and measures the electrical resistance of the mixed melt;
Regarding the measurement result of electrical resistivity for arbitrary 30 minutes, whether the absolute value of the slope when linearly approximating the change in electrical resistivity with respect to time by the least squares method is 2e-9 ohm meter / hour or less a mixing completion determination unit that determines whether or not mixing of the mixed melt is completed based on
a control unit that controls the substrate holding mechanism and the mixing completion determination unit;
with
The control unit causes the substrate holding mechanism to move the seed crystal substrate into the mixed melt in response to the determination of completion of mixing of the mixed melt by the mixing completion determination unit, thereby moving the seed crystal substrate into the mixed melt. A Group III nitride crystal manufacturing apparatus that is brought into contact with a melt. supplying nitrogen into the reaction chamber from the nitrogen supply line in response to the determination of the completion of mixing by the mixing completion determination unit;
Furthermore, when the change over time of the electrical resistivity of the mixed melt is 3.9e-9 ohm m/h or more and 2.0e-8 ohm m/h or less, the nitrogen supersaturation is within an appropriate range Determining that there is a nitrogen supersaturation determination unit,
The control unit controls the supersaturation degree determination unit, and moves the seed crystal substrate by the substrate holding mechanism in accordance with the determination by the nitrogen supersaturation degree determination unit that the nitrogen supersaturation degree is within an appropriate range. 6. The apparatus for producing group III nitride crystals according to claim 5 , wherein the seed crystal substrate is brought into contact with the mixed melt.

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