JP4528806B2 - GaN crystal growth method - Google Patents

Description

The present invention also relates to the growth how of GaN crystal by a liquid phase method.

  Group III nitride crystals are widely used for substrates of various semiconductor devices. In recent years, in order to efficiently manufacture various semiconductor devices, a large group III nitride crystal has been demanded.

  As a method for growing a group III nitride crystal, there are a gas phase method such as HVPE (hydride vapor phase epitaxy) method, MOCVD (metal organic chemical vapor deposition) method, a liquid phase method such as high pressure solution method and flux method. is there. Here, the liquid phase method is superior to the gas phase method in terms of environmental protection because no toxic gas is used in crystal growth.

  For example, M. Bockowski, “Growth and Doping of GaN and AlN Single Crystals under High Nitrogen Pressure”, Cryst. Res. Technol., Vol. 36, (2001) , 8-10, p. 771-787 (Non-Patent Document 1) discloses a method for growing a GaN crystal by a high-pressure solution method. H. Yamane and three others, “Preparation of GaN Single Crystals Using a Na Flux”, Chem. Mater., Vol. 9, No. 2, (1997), p. 413-416 (Non-patent Document 2) Discloses a method for growing GaN crystals by the Na flux method. Japanese Patent Laying-Open No. 2003-206198 (Patent Document 1) discloses a GaN crystal growth method using a plate-like group III nitride seed crystal by the Na flux method.

However, the growth method disclosed in Non-Patent Document 1 increases the manufacturing cost of crystals because the crystal growth conditions are 1 GPa and 1 GPa at 1500 ° C., and grows large crystals because seed crystals are not used. Is difficult. The growth method disclosed in Non-Patent Document 2 is a crystal growth condition that is relatively easy to carry out at 800 ° C. and 10 MPa, but it is difficult to grow a large crystal because no seed crystal is used. Moreover, since the diameter of the plate-shaped seed crystal used in the growth method disclosed in Patent Document 1 is not large, large crystals are not obtained.
JP 2003-206198 A M. Bockowski, “Growth and Doping of GaN and AlN Single Crystals under High Nitrogen Pressure”, Cryst. Res. Technol., Vol.36, (2001), 8-10, p.771-787 H. Yamane and 3 others, “Preparation of GaN Single Crystals Using a Na Flux”, Chem. Mater., Vol.9, No.2, (1997), p.413-416

However, high pressure solution method, in the growth of I that GaN crystal in a liquid phase method such as a flux method, a plate-like GaN seed crystal substrate having a large diameter, even when the substrate and chemical composition are the same GaN crystal homoepitaxially grown Cracks occur in the substrate and the GaN crystal grown on the substrate, and it is difficult to obtain a large GaN crystal substrate.

An object of this invention is to provide the growth method of the GaN crystal which can grow a large crystal | crystallization in a liquid phase method.

As a result of examining the cause of the crack of the substrate and the GaN crystal in detail, it was found that there is a correlation between the crack of the substrate and the GaN crystal and the curvature radius of the warp of the substrate. Further, by proceeding with the study, in the homoepitaxial growth of the GaN crystal on the substrate by the liquid phase method, the curvature radius of the predetermined crystal plane of the substrate is 2 m or more, preferably 5 m or more, more preferably 10 m or more, It has been found that cracking of the substrate and the GaN crystal grown on the substrate is suppressed, and a large GaN crystal can be grown.

The present invention is a method for growing a GaN crystal by a liquid phase method, which is a self-supporting substrate having a flat main surface and formed entirely of a GaN seed crystal having the same chemical composition as the GaN crystal, A substrate having a curvature radius of curvature of 2 m or more on the hkil plane closest to the main surface (where i = − (h + k), h, k, and l are integers of −9 to 9) is prepared. step and the main surface of the substrate, the growth method of a GaN crystal and a step, the growing GaN crystal by contacting a solution of a nitrogen-containing gas in a solvent containing a Ga metal and alkali metal on the main surface of It is.

In the GaN crystal growth method according to the present invention, the radius of curvature can be 5 m or more, and further 10 m or more . Also, the area of the main surface of the substrate may be a 1 cm ² or more. Further, the main surface of the substrate can be one type of surface selected from the group consisting of (0001) plane, (10-10) plane, and (10-11) plane .

According to the present invention, a large GaN crystal can be grown in a liquid phase method.

(Embodiment 1)
One embodiment of a method for growing a group III nitride crystal according to the present invention is a method for growing a group III nitride crystal 10 by a liquid phase method with reference to FIGS. And a group III nitride seed crystal 1a having the same chemical composition as that of the group III nitride crystal 10 at least on the main surface 1m side, and is closest to the main surface 1m (hkil) surface 1n (where i = − ( h + k), and h, k, and l are integers of −9 or more and 9 or less, respectively, and a step of preparing a substrate having a curvature radius of 2 m or more; Contacting a solution containing the nitrogen-containing gas 5 with the solvent 3 containing a metal to grow a group III nitride crystal 10 on the main surface 1 m.

  In the method for growing a group III nitride crystal of the present embodiment, the group III nitride crystal 10 is formed on the main surface 1m of the substrate 1 whose curvature radius of curvature of the surface 1n closest to the main surface 1m (hkil) is 2 m or more. By homoepitaxially growing, cracking of the substrate and the group III nitride crystal grown on the substrate is suppressed, and a large crystal is obtained.

  The growth apparatus used in the method for growing a group III nitride crystal of the present embodiment includes, for example, an outer container 29 and a heat insulating material 27 disposed inside the outer container 29, with reference to FIGS. A heater 25 disposed inside the heat insulating material 27 and an inner container 21 disposed inside the heater 25 are provided. In the inner vessel 21, a crystal growth vessel 23 for growing the group III nitride crystal 10 is disposed. Here, the material of the crystal growth vessel 23 is not particularly limited as long as it does not react with the solvent 3 and the nitrogen-containing gas 5 and has high mechanical strength and heat resistance, but BN (boron nitride) or the like is preferable. The material of the inner container 21 is not particularly limited as long as it has high mechanical strength and heat resistance, but stainless steel, heat resistant steel, and the like are preferable. The material of the outer container 29 is not particularly limited as long as it has high mechanical strength and heat resistance, but stainless steel is preferable. The material of the heat insulating material 25 is not particularly limited as long as it has high mechanical strength, heat resistance, and heat insulating properties, but stainless steel, heat resistant steel, and the like are preferable.

  The growth apparatus used in the present embodiment is a pressurization device connected to the outer container 29 by the nitrogen-containing gas supply device 31 connected to the inner container 21 by the first pipe 41 and the second pipe 43. A gas supply device 33 and a vacuum exhaust device 35 connected to the outer container 29 by a third pipe 45 are provided. Here, the first pipe 41 is provided with a valve 41v for adjusting the supply flow rate of the nitrogen-containing gas 5, and the first pressure gauge 41p is provided in the portion 41b on the nitrogen-containing gas supply device 31 side from the valve 41v. Is provided. The second pipe 43 is provided with a valve 43v for adjusting the supply flow rate of the pressurizing gas 7, and a second pressure gauge 43p is provided at the portion 43b on the pressurizing gas supply device 33 side from the valve 43v. Is provided. The third pipe 45 is provided with a valve 45v for adjusting the exhaust flow rate.

  Furthermore, a fourth pipe 47 is provided that connects a portion 41 a closer to the inner container 21 than the valve 41 v of the first pipe 41 and a portion 45 a closer to the outer container 29 than the valve 45 v of the third pipe 45. The fourth pipe 47 is provided with a valve 47v. For reference, FIG. 1 also shows a portion 43a on the outer container 29 side from the valve 43v of the second piping 43 and a portion 45b on the vacuum exhaust device 35 side of the valve 45v of the third piping 45.

  With reference to FIG. 1 to FIG. 3, the growth method of the group III nitride crystal of this embodiment first has a flat main surface, and at least the main surface side has the same chemical composition as the group III nitride crystal. Curvature radius of curvature of group III nitride seed crystal and closest to main surface (hkil) (where i = − (h + k), and h, k, and l are each an integer of −9 to 9) Includes a step of preparing a substrate having a length of 2 m or more (substrate preparation step).

  The substrate 1 prepared in the present embodiment has a flat main surface 1m. The flat main surface 1m can be formed by at least one method selected from smoothing methods such as grinding, polishing and etching. By planarizing the main surface, it becomes easy to epitaxially grow a group III nitride crystal on the main surface.

Substrate 1 includes group III nitride seed crystal 1a having the same chemical composition as group III nitride crystal 10 at least on the principal surface 1m side. Such a substrate 1 can homoepitaxially grow a group III nitride crystal 10 on its main surface 1 m. Here, the substrate 1 is not particularly limited as long as it has a group III nitride seed crystal having the same chemical composition as that of the group III nitride crystal to be grown on the main surface 1m side. For example, a group III is formed on the base substrate 1b. Examples include a template substrate on which the nitride seed crystal 1a is formed, and a free-standing substrate that is entirely formed of a group III nitride seed crystal 1a. For example, when an Al _x Ga _y In _1-xy N crystal (0 ≦ x, 0 ≦ y, x + y ≦ 1) is homoepitaxially grown as the group III nitride crystal 10, the group III nitride seed crystal 1a of the substrate 1 is used. An Al _x Ga _y In _1-xy N seed crystal (0 ≦ x, 0 ≦ y, x + y ≦ 1) is used.

  The substrate 1 has a curvature radius of curvature of 2 m or more on the (hkil) plane closest to the main surface 1 m (i = − (h + k), and h, k and l are integers of −9 to 9). is there. Here, the (hkil) plane is a plane index in the hexagonal system. In this aspect, between h, k, i, and l, h, k, and l are independent from each other, and i is dependent on h and k, i = − (h + k). The (hkil) plane in the present embodiment is a low index plane in which h, k, and l are -9 or more and 9 or less, respectively. Further, the (hkil) surface closest to the main surface 1m means a (hkil) surface that most closely fits the main surface 1m, that is, a surface that is closest to the main surface 1m (hkil).

  In the present embodiment, calculation of the curvature radius of the curvature of the (hkil) surface of the substrate 1 is not particularly limited, but for example, (hkil) at a measurement point provided at a predetermined pitch in the cross direction on the main surface 1m of the substrate. ) From the distribution of diffraction angles measured by X-ray diffraction originating from the surface. Therefore, the (hkil) plane that is the object of X-ray diffraction is i = − (h + k), and h, k, and l are − from the viewpoint of obtaining a high-intensity X-ray diffraction peak that is easy to analyze. It is preferably an integer of 5 or more and 5 or less.

  The substrate 1 having a curvature radius of 2 m or more on the (hkil) plane suppresses cracking of the group III nitride crystal homoepitaxially grown on the substrate and the main surface of the substrate because the internal strain of the substrate 1 is small. Large crystals can be obtained. The curvature radius of the warp of the (hkil) surface 1n of the substrate 1 is preferably 5 m or more from the viewpoint of suppressing the internal strain of the substrate 1 and suppressing the cracking of the substrate and the group III nitride crystal grown on the substrate. The above is more preferable.

  The substrate 1 is not particularly limited as long as it has a group III nitride seed crystal having the same chemical composition as the group III nitride crystal to be grown on the main surface 1m side, and the group III nitride seed crystal on the base substrate 1b. Examples thereof include a template substrate on which la is formed and a free-standing substrate entirely formed of a group III nitride seed crystal 1a. Here, in the crystal growth by the liquid phase method, even if a free-standing substrate formed entirely of the group III nitride seed crystal 1a is used as the substrate, it occurs in the group and the group III nitride crystal grown on the substrate. The crack which has been suppressed is suppressed by using the growth method of this embodiment. From this point of view, the growth method of the present embodiment is highly useful when a self-supporting substrate that is entirely formed of a group III nitride seed crystal 1a is used as the substrate.

The area of the main surface 1m of the substrate 1 is not particularly limited, but is preferably 1 cm ² or more, and more preferably 10 cm ² or more. In crystal growth by the conventional liquid phase method, as the area of the main surface of the substrate increases, the substrate and the grown crystal are more likely to break, whereas in crystal growth by the growth method of the present embodiment, the area of the main surface. Even if it is large, cracks of the substrate and the crystal grown on the substrate are suppressed. From this point, the growth method of the present embodiment is more useful as the area of the main surface of the substrate increases.

  Further, the main surface 1m of the substrate 1 is not particularly limited, but is preferably one type of surface selected from the group consisting of a (0001) plane, a (10-10) plane, and a (10-11) plane. In the growth of group III nitride crystals by the liquid phase method, the (0001) plane, the (10-10) plane, and the (10-11) plane are stable crystal growth planes. Irregularities are formed on the surface, crystal defects are introduced, and the crystal is easily broken.

  The substrate 1 prepared in the present embodiment has a flat main surface 1m, includes a group III nitride seed crystal 1a having the same chemical composition as the group III nitride crystal 10 on at least the main surface 1m side, and includes a main surface 1m. Especially when the curvature radius of the curvature of the hkil plane closest to (where i = − (h + k), h, k and l are integers of −9 to 9) is 2 m or more. There is no limit. The group III nitride seed crystal 1a of the substrate 1 may be grown by any method such as a vapor phase method such as HVPE method or MOCVD method, a liquid phase method such as solution method or flux method. .

  In other words, the substrate preparation step is a substrate for growing a group III nitride crystal by a liquid phase method, regardless of how the substrate is formed. A group III nitride seed crystal 1a having the same chemical composition as the group III nitride crystal 10 on the surface 1m side, the (hkil) plane closest to the main surface 1m (where i = − (h + k), h, It is significant that k and l are each selected from the substrate 1 having a curvature radius of curvature of 2 m or more.

  1 to 3, next, a nitrogen-containing gas 5 is dissolved in a solvent 3 containing a group III metal and an alkali metal on the main surface of the substrate 1. And a step of growing the group III nitride crystal 10 on the main surface 1 m (group III nitride crystal growth step).

  In the growth process of the group III nitride crystal in the present embodiment, a solvent 3 containing a group III metal and an alkali metal is used. When such a solvent 3 containing a group III metal and an alkali metal is used, a solvent containing a group III metal and containing no alkali metal at an impurity concentration (for example, a concentration of less than 1 mol% with respect to the whole solvent) is used. As compared with the above, it is possible to reduce the growth temperature and growth pressure of the group III nitride crystal and increase the crystal growth rate. This is presumably because the alkali metal contained in the solvent 3 promotes the dissolution of the nitrogen-containing material 5 in the solvent 3.

The molar ratio of the Group III metal M _III an alkali metal M _A contained in the solvent 3, the growth temperature of the group III nitride crystal, to reduce the growth pressure, particularly as long as the can increase the crystal growth rate limit _{rather, M III: M A = 90} : 10~10: 90 are _{preferred, M III: M A = 50} : 50~20: 80 is more preferred. Even if the molar ratio of the group III metal M _III is larger than M _III : M _A = 90: 10 or the molar ratio of the alkali metal M _A is larger than M _III : M _A = 10: 90, the crystal growth rate decreases. To do.

  Such a group III nitride crystal growth step is performed, for example, by the following plurality of sub-steps. First, the substrate 1 is placed on the bottom of the crystal growth vessel 23 with the flat main surface 1m facing upward (substrate placement sub-step). Although there is no restriction | limiting in particular in the crystal growth container 23, From a heat resistant viewpoint, the crucible made from BN (boron nitride) etc. are used preferably. Substrate 1 includes a group III nitride seed crystal 1a having the same chemical composition as group III nitride crystal 10 at least on the principal surface 1m side.

  Next, the solvent 3 containing a group III metal and an alkali metal is placed in the crystal growth vessel 23 on which the substrate 1 is placed (solvent placement sub-step). This solvent 3 is solid at room temperature (about 25 ° C.), but is liquefied by subsequent heating. Although there is no restriction | limiting in the solvent 3 containing a group III metal and an alkali metal, From a viewpoint of growing a group III nitride crystal with high purity, the thing with high purity of each of a group III metal and an alkali metal is preferable. For example, in order to grow a high purity GaN crystal, it is preferable to use a high purity metal Ga and a high purity metal Na. In this case, the purity of the metal Ga is preferably 99% by mass or more, and more preferably 99.999% by mass or more. The purity of the metal Na is preferably 99% by mass or more, and more preferably 99.999% by mass or more. Here, the amount of the solvent 3 containing the group III metal and the alkali metal is not particularly limited, but the depth of the liquefied solvent 3 (melt) may be 1 mm or more and 50 mm or less from the main surface 1 m of the substrate 1. preferable. If the depth is less than 1 mm, the surface of the substrate may not be covered with the solvent 3 (melt) due to the surface tension of the solvent 3 (melt). If the depth is greater than 50 mm, the surface of the solvent 3 (melt) may not be covered. This is because the supply of nitrogen is insufficient.

  Next, the crystal growth vessel 23 containing the solvent 3 containing III metal and alkali metal and the substrate 1 is placed in the inner vessel 21 (crystal growth vessel placement sub-step). In FIG. 1 and FIG. 2, for example, five crystal growth vessels 23 are arranged. By disposing a plurality of crystal growth vessels 23 in the inner vessel 21, a plurality of group III nitride crystals 10 can be grown simultaneously.

  Next, the inside of the inner container 21 and the outer container 29 is evacuated using the evacuation apparatus 35 (evacuation sub-process). This is for removing impurities inside the inner container 21 and the outer container 29. At this time, the valves 41v and 43v are closed, and the valves 47v and 45v are opened. The degree of vacuum of the inner container 21 and the outer container 29 after evacuation is not particularly limited, but is preferably 1 Pa or less from the viewpoint of reducing residual impurities.

  Next, the nitrogen-containing gas 5 and the pressurizing gas 7 are supplied into the inner container 21 and the outer container 29 so that the internal pressure of each container is 0.5 MPa or more and 5 MPa or less (nitrogen-containing gas supply sub-process). . At this time, the nitrogen-containing gas 5 supplied into the inner vessel 21 is not particularly limited, but it is preferable that the purity of nitrogen is high from the viewpoint of growing a high-purity group III nitride crystal. From this viewpoint, the nitrogen-containing gas 5 is preferably nitrogen gas having a purity of 99.999 mol% or more. On the other hand, the pressurizing gas 7 supplied to the outer container 29 is not used for growing a group III nitride crystal because it is used for maintaining the pressure in the outer container 29 and is not necessarily a nitrogen-containing gas. However, since the heater 25 is disposed in the outer container 29, an inert gas that does not react with the heater 25, such as nitrogen gas or argon gas, is preferably used for the pressurizing gas 7.

  Next, the inside of the inner container 21 and the outer container 29 is heated using the heater 25, and the temperature inside the inner container 21 is set to 700 ° C. or higher and 900 ° C. or lower (heating sub-step). By such heating, the solvent 3 containing the group III metal and the alkali metal disposed in the inner container 21 changes from a solid to a liquid (melt), covers the main surface 1m of the substrate 1, and contains nitrogen in the solvent 3 (melt). Gas 5 dissolves. In this manner, a solution obtained by dissolving the nitrogen-containing gas 5 in the solvent 3 containing a group III metal and an alkali metal can be brought into contact with the main surface 1 m of the substrate 1. Here, the heater 25 is not particularly limited as long as it is suitable for heating the inside of the inner container 21 and the outer container 29. However, from the viewpoint of easy control of the temperature distribution inside the inner container and the outer container, the heater 25 is resistant. A heating system is preferably used.

  During the heating sub-process, the nitrogen-containing gas 5 is further supplied to the inner container 21 so that the inner pressure of the inner container 21 becomes larger in the range of 0.01 MPa to 0.1 MPa than the inner pressure of the outer container 22. . That is, 0.01 MPa ≦ {(inner pressure of inner container) − (inner pressure of outer container)} ≦ 0.1 MPa. This is because the pressurizing gas 7 in the outer container 29 is prevented from being mixed into the inner container 21 and the purity of nitrogen in the outer container 29 is kept high.

  Next, the supply amount and heating amount of the nitrogen-containing gas 5 to the inner container 21 are adjusted, and the inner pressure of the inner container 21 is set to 0.5 MPa while maintaining the temperature inside the inner container 21 at 700 ° C. or more and 900 ° C. or less. The group III nitride crystal 10 is grown on the main surface 10m of the substrate 1 for a predetermined time at a pressure of 5 MPa or less (crystal growth sub-step). At this time, the supply amount of the pressurizing gas 7 to the outer container 29 is adjusted so that the inner pressure of the outer container 29 becomes smaller than the inner pressure of the inner container 21 in the range of 0.01 MPa to 0.1 MPa. . That is, during the crystal growth, as in the heating, 0.01 MPa ≦ {(internal pressure of the inner container) − (internal pressure of the outer container)} ≦ 0.1 MPa.

  Next, while maintaining the relationship of 0.01 MPa ≦ {(inner pressure of inner container) − (inner pressure of outer container)} ≦ 0.1 MPa, the inside of each of inner container 21 and outer container 29 is cooled and reduced in pressure. Then, the group III nitride crystal 10 grown on the substrate 1 is taken out from the crystal growth vessel 27 of the inner vessel 21 (crystal removal sub-step).

(Embodiment 2)
One embodiment of a Group III nitride crystal according to the present invention is obtained by the growth method of Embodiment 1 with reference to FIG. Since the group III nitride crystal 10 of this embodiment is grown by the method of Embodiment 1, it becomes a large crystal. Further, by using a high-purity group III metal and a nitrogen-containing gas as a crystal raw material, a high-purity group III nitride crystal is obtained.

1. Preparation of Substrate As a substrate 1, a number of self-supporting GaN substrates having a flat (0001) Ga surface with a polished main surface of 1 m and a diameter of 2 inches (50.8 mm) and a thickness of 350 μm prepared by the HVPE method were prepared. . In any GaN substrate, the central portion of the main surface has an off angle of 0.5 ° or less with respect to the (0001) plane from the measurement result by X-ray diffraction. From such a large number of GaN substrates, a GaN substrate having a curvature radius of (0001) plane of 1 m or more and less than 2 m, a GaN substrate having a curvature radius of 2 m or more and less than 5 m, a GaN substrate having a curvature radius of 5 m or more and less than 10 m, and a curvature radius of Ten GaN substrates each having a length of 10 m or more were selected.

  Here, the measurement of the radius of curvature of the (0001) plane of the GaN substrate was performed by measuring the diffraction angle by X-ray diffraction at a pitch of 5 mm in the cross direction of the substrate, and calculating the radius of curvature from the distribution of the diffraction angles. Here, the values of two radii of curvature are calculated from two directions of the cross for one substrate, and the average value thereof is taken as the radius of curvature of the substrate. In many GaN substrates for which the curvature radii were calculated, there was no significant difference in the numerical values of the two curvature radii of each substrate, and the (0001) plane of each substrate had a bowl-like shape.

  Hereinafter, an example in which a GaN crystal is grown using a GaN substrate having a curvature radius of curvature of (0001) plane of 1 m or more and less than 2 m is referred to as Comparative Example 1, and a GaN substrate having a curvature radius of 2 m or more and less than 5 m is used. An example of growing a crystal is referred to as Example 1, and an example of growing a GaN crystal using a GaN substrate having a curvature radius of 5 m or more and less than 10 m is referred to as Example 3, and using a GaN substrate having a curvature radius of 10 m or more, GaN An example of growing crystals is referred to as Example 4.

2. 3. Growth of GaN Crystal Referring to FIG. 3, each GaN substrate (substrate 1) is placed in a BN crucible (crystal growth vessel 23) having an inner diameter of 60 mm and a depth of 20 mm with the flat main surface 1 m facing upward. Placed on the bottom. Next, in a BN crucible (crystal growth vessel 23) on which a GaN substrate (substrate 1) is placed, 15 g of 99.9999% by mass of metal Ga and 11g of 99% by mass of metal Na (solvent) 3) was added. The metal Ga and metal Na (solvent 3) are solid at room temperature (about 25 ° C.), but are liquefied by subsequent heating to form metal Ga (group III metal M _III ) and metal Na (alkali metal M _A ). _A metal Ga—Na melt with a molar ratio of M _III : M _A = 31: 69 is obtained, and the depth from the surface of this metal Ga—Na melt (solvent 3) to the main surface 1m of the GaN substrate (substrate 1) is It became 5 mm.

  Next, a BN crucible (crystal growth vessel 23) containing a GaN substrate (substrate 1) and a metal Ga—Na melt (solvent 3) was placed in the inner vessel 21 in five stages.

Next, the inside of the inner container 21 and the outer container 29 was evacuated using a vacuum pump (evacuation apparatus 35). The degree of vacuum of the inner container 21 and the outer container 29 after evacuation was 1 × 10 ⁻³ Pa.

  Next, the nitrogen-containing gas 5 and the pressurizing gas 7 were supplied into the inner container 21 and the outer container 29 so that the inner pressure of each container was 1 MPa. At this time, high purity nitrogen gas having a purity of 99.99999 mol% was used as the nitrogen-containing gas 5 supplied into the inner vessel 21. On the other hand, nitrogen gas having a purity of 99.9999 mol% was used as the pressurizing gas 7 supplied to the outer container 29.

  Next, the inside of the inner container 21 and the outer container 29 was heated using a resistance heating type heater 25, and the temperature inside the inner container 21 was set to 800 ± 5 ° C. By such heating, the metal Ga and metal Na (solvent 3) disposed in the inner container 21 are liquefied to cover the main surface 1m of the GaN substrate (substrate 1), and the liquefied metal Ga and metal Na, that is, metal Ga— High purity nitrogen gas (nitrogen-containing gas 5) is dissolved in the Na melt (solvent 3). In this way, the main surface 1m of the GaN substrate (substrate 1) can be brought into contact with a solution obtained by dissolving high purity nitrogen gas (nitrogen-containing gas 5) in a metal Ga—Na melt (solvent 3). It was. During heating, nitrogen gas of higher purity (nitrogen-containing gas 5) is supplied to the inner container 21 so that the inner pressure of the inner container 21 is in the range of 0.01 MPa or more and 0.1 MPa or less compared to the inner pressure of the outer container 22. I tried to get bigger. That is, 0.01 MPa ≦ {(internal pressure of the inner container) − (internal pressure of the outer container)} ≦ 0.1 MPa.

  Next, the supply amount and heating amount of the nitrogen-containing gas 5 to the inner container 21 are adjusted, and the internal pressure of the inner container 21 is set to 3 MPa while maintaining the temperature inside the inner container 21 at 800 ± 5 ° C. A GaN crystal (Group III nitride crystal 10) was grown on the main surface 10m of (Substrate 1) for 100 hours. At this time, the supply amount of nitrogen gas (pressurizing gas 7) to the outer container 29 is adjusted so that the internal pressure of the outer container 29 is smaller than the internal pressure of the inner container 21 in the range of 0.01 MPa to 0.1 MPa. It was made to become. That is, during the crystal growth, as in the heating, 0.01 MPa ≦ {(inner pressure in the inner container) − (inner pressure in the outer container)} ≦ 0.1 MPa.

  Next, while maintaining the relationship of 0.01 MPa ≦ {(inner pressure of inner container) − (inner pressure of outer container)} ≦ 0.1 MPa, the inside of each of inner container 21 and outer container 29 is cooled and reduced in pressure. The GaN crystal (Group III nitride) grown on the GaN substrate (substrate 1) from the metal Ga—Na melt (solvent 3) in the BN crucible (crystal growth vessel 27) of the inner vessel 21 cooled to 30 ° C. Crystal 10) was removed with tweezers. The thickness of the obtained GaN crystal was 850 μm to 1050 μm.

  All of the GaN crystals grown on the 10 GaN substrates of Comparative Example 1 (the curvature radius of warpage is 1 m or more and less than 2 m) were cracked. On the other hand, GaN crystals grown on 10 GaN substrates of Example 1 (the curvature radius of warpage was 2 m or more and less than 5 m) were cracked in 10 out of 6 sheets. In addition, GaN crystals grown on 10 GaN substrates of Example 2 (the curvature radius of warpage was 5 m or more and less than 10 m) were cracked in 10 pieces, and two pieces. In addition, none of the GaN crystals grown on each of the 10 GaN substrates of Example 3 (the curvature radius of warpage was 10 m or more) was cracked in 10 pieces. The results are summarized in Table 1.

  As apparent from Table 1, in the growth of the group III nitride crystal by the liquid phase method, the (hkil) plane closest to the main surface (where i = − (h + k), where h, k, and l are −9 or more and an integer of 9 or less) using a substrate having a curvature radius of warpage of 2 m or more, preferably 5 m or more, more preferably 10 m or more, the substrate and the group III nitride crystal grown on the substrate It was found that cracking was suppressed and a large group III nitride crystal was obtained.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  Group III nitride crystals obtained by the growth method according to the present invention include light-emitting elements such as light-emitting diodes and laser diodes, electronic elements such as rectifiers, bipolar transistors, field-effect transistors, and HEMTs (high electron mobility transistors), temperature For sensors, pressure sensors, radiation sensors, semiconductor sensors such as visible-ultraviolet light detection, SAW devices (surface acoustic wave elements), vibrators, resonators, oscillators, MEMS (microelectromechanical system) components, piezoelectric actuators, etc. It is used for the substrate.

It is a schematic sectional drawing which shows one Embodiment of the growth method and growth apparatus of the group III nitride crystal concerning this invention. It is the schematic sectional drawing to which the II part of FIG. 1 was expanded. It is the schematic sectional drawing to which the III part of FIG. 2 was expanded.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Substrate, 1a Group III nitride seed crystal, 1b Base substrate, 1m main surface, 1n (hkil) surface, 3 solvent, 5 nitrogen-containing gas, 7 gas for pressurization, 10 Group III nitride crystal, 21 inner vessel, 23 Crystal growth vessel, 25 heater, 27 heat insulating material, 29 outer vessel, 31 nitrogen-containing gas supply device, 33 gas supply device for pressurization, 35 vacuum exhaust device, 41 first pipe, 41a, 43a portion closer to inner vessel than valve 41b, nitrogen-containing gas supply device side, 41p, 43p pressure gauge, 41v, 43v, 45v, 47v valve, 43 second piping, 43b valve, pressurization gas supply device side, 45 third Piping, part on the outer container side from the 45a valve, part on the vacuum exhaust device side from the 45b valve, 47 fourth piping.

Claims (5)

A method for growing a GaN crystal by a liquid phase method,
Has a flat main surface, a substrate free standing formed of GaN seed crystal whole has the same chemical composition as the GaN crystal, the nearest (hkil) plane to the principal plane (here, i = - (H + k), and h, k, and l are integers of −9 or more and 9 or less, respectively, and a step of preparing a substrate having a curvature radius of 2 m or more;
On the main surface of the substrate, by contacting a solution of a nitrogen-containing gas in a solvent containing a Ga metal and alkali metal, growth of GaN crystal and a step of growing said GaN crystal on the main surface Method. The method for growing a GaN crystal according to claim 1, wherein the radius of curvature is 5 m or more. The method for growing a GaN crystal according to claim 1, wherein the radius of curvature is 10 m or more. The method for growing a GaN crystal according to any one of claims 1 to 3, wherein an area of the main surface is 1 cm ² or more. The main surface is (0001) plane, GaN according to claim 1 which is one type of a surface selected from the group of (10-10) plane and (10-11) plane to claim 4 Crystal growth method.

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