JP2017036178A - Manufacturing method of group xiii nitride single crystal, and manufacturing apparatus of group xiii nitride single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a group XIII nitride single crystal by a flux method that achieves both of low dislocation density and reduction of cracks.SOLUTION: A manufacturing method of a group XIII nitride single crystal includes an arrangement step for arranging a seed crystal 30 made of a group XIII nitride crystal and having a surface roughness Ra of a crystal growth surface of 0.1 μm or more and 5 μm or less and a raw material containing an alkali metal and a group XIII metal in a reactor 52; a crystal growth step for dissolving nitrogen in mixed melt 24 of the raw material and growing a group XIII nitride crystal 32 on the seed crystal 30 arranged in the mixed melt 24 of a crystal growth temperature; and a temperature adjustment step. The temperature adjustment step is at least one of a heating step for heating the raw material to the crystal growth temperature at a heating rate of 150°C per hour or less between the arrangement step and the crystal growth step and a cooling step for cooling the mixed melt 24 at a cooling rate of 150°C per hour or less after the crystal growth step.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a group 13 nitride single crystal and an apparatus for producing a group 13 nitride single crystal.

  As one of the methods for manufacturing a GaN substrate using the liquid phase growth method, a flux method is disclosed in which nitrogen is dissolved in a mixed melt of metallic sodium and metallic Ga to grow GaN. The flux method is capable of crystal growth at a relatively low temperature of 700 ° C. to 900 ° C., and the pressure inside the container is relatively low at about 2 MPa to 8 MPa.

A manufacturing method using this flux method is disclosed (for example, see Patent Documents 1 and 2). In Patent Document 1, a nitride crystal is grown on the concavo-convex surface of a base substrate having a surface roughness R _P-V of 0.5 μm to 10 μm, which is the maximum value of the height difference between the convex and concave portions on the concavo-convex surface. A manufacturing method is disclosed. Patent Document 2 discloses a manufacturing method in which a nitride crystal is grown using a seed crystal having a c-plane surface area of 25% or less.

  However, the conventional manufacturing method cannot realize both reduction of dislocation density and reduction of cracks.

  In order to solve the above-described problems and achieve the object, the method for producing a group 13 nitride single crystal of the present invention comprises a group 13 nitride crystal, and the surface roughness Ra of the crystal growth surface is 0.1 μm or more and 5 μm or less. A seed crystal and a raw material containing an alkali metal and a group 13 metal in a reaction vessel, and in a state where the raw material is melted to form a mixed melt, nitrogen is dissolved in the mixed melt A crystal growth step of growing a group 13 nitride crystal on the seed crystal placed in the mixed melt at a crystal growth temperature, and 150 ° C./hour or less between the placement step and the crystal growth step At least one of a temperature raising step for raising the temperature of the raw material to the crystal growth temperature at a rate of temperature rise and a temperature lowering step for lowering the temperature of the mixed melt at a temperature lowering rate of 150 ° C./hour or less after the crystal growth step. Temperature adjusting step.

  According to the present invention, both reduction of dislocation density and reduction of cracks can be realized.

FIG. 1 is a diagram showing an example of an apparatus for producing a group 13 nitride single crystal. FIG. 2 is a schematic diagram illustrating an example of a stirring mechanism. FIG. 3 is a schematic diagram illustrating an example of a stirring mechanism. FIG. 4 is an explanatory diagram of a seed crystal used in this embodiment. FIG. 5 is a diagram illustrating an example of a group 13 nitride single crystal including cracks generated before crystal growth. FIG. 6 is a diagram illustrating an example of a group 13 nitride single crystal including cracks generated after crystal growth. FIG. 7 is a flowchart illustrating an example of the procedure of the manufacturing process executed by the control unit. FIG. 8 is a hardware configuration diagram of the control unit.

  A group 13 nitride single crystal manufacturing method and a group 13 nitride single crystal manufacturing apparatus according to the present embodiment will be described below with reference to the accompanying drawings. In the following description, the drawings merely show the shapes, sizes, and arrangements of the components to the extent that the invention can be understood, and the present invention is not particularly limited thereby. In addition, similar components shown in a plurality of drawings are denoted by the same reference numerals, and redundant description thereof may be omitted.

  In the following, the method for producing a group 13 nitride single crystal according to the present embodiment may be simply referred to as the production method of the present embodiment.

  In the method for producing a group 13 nitride single crystal of the present embodiment, a group 13 nitride single crystal is produced by growing a group 13 nitride crystal from a seed crystal by a flux method.

  That is, in the manufacturing method of the present embodiment, nitrogen is dissolved in a mixed melt containing an alkali metal and a group 13 metal held in a reaction vessel, and the group 13 is added to the seed crystal disposed in the mixed melt. This is a method for producing a group 13 nitride single crystal by growing a nitride crystal.

  And the manufacturing method of this Embodiment contains an arrangement | positioning process, a crystal growth process, and a temperature adjustment process. An arrangement | positioning process is a process of arrange | positioning a seed crystal and the raw material containing an alkali metal and a group 13 metal in reaction container.

  The seed crystal used in the present embodiment is made of a group 13 nitride crystal, and the surface roughness Ra of the crystal growth surface is 0.1 μm or more and 5 μm or less. The crystal growth surface is a main surface on which a group 13 nitride crystal grows.

  In the crystal growth step, in a state where the raw material is melted to form a mixed melt, nitrogen is dissolved in the mixed melt, and a group 13 nitride crystal is grown on the seed crystal disposed in the mixed melt at the crystal growth temperature. It is a process to make. The crystal growth temperature is the crystal growth temperature of the group 13 nitride crystal.

  The temperature adjustment step includes at least one of a temperature raising step and a temperature lowering step. The temperature raising step in the manufacturing method of the present embodiment is a step in which the temperature of the raw material is raised to the crystal growth temperature at a temperature raising rate of 150 ° C./hour or less, which is performed between the arrangement step and the crystal growth step. The temperature lowering step in the manufacturing method of the present embodiment is a step that is performed after the crystal growth step and lowers the temperature of the mixed melt at a temperature lowering rate of 150 ° C./hour or less.

  In the method for producing a group 13 nitride single crystal according to the present embodiment, by using the above production method, it is possible to produce a group 13 nitride single crystal in which both reduction of dislocation density and reduction of cracks are realized. it can.

  The reason why the above effect can be achieved is estimated as follows. The present invention is not limited by the following estimation.

  In the manufacturing method of the present embodiment, a seed crystal having a surface roughness Ra of 0.1 μm or more and 5 μm or less is used as a seed crystal. That is, the crystal growth surface of the seed crystal used in the present embodiment has irregularities in the range of the surface roughness Ra.

  Here, the dislocations existing in the seed crystal proceed in the crystal growth direction as the group 13 nitride crystal grows on the seed crystal. If the crystal growth surface of the seed crystal is flat (surface roughness Ra is less than 0.1 μm), crystal growth proceeds in a direction perpendicular to the flat crystal growth surface. For this reason, in the group 13 nitride crystal that grows on the crystal growth surface of the seed crystal, the dislocations existing in the seed crystal proceed with the crystal growth, and the dislocations in the seed crystal are inherited as they are. . For this reason, it is considered that when the crystal growth surface of the seed crystal is flat (surface roughness Ra is less than 0.1 μm), the dislocation density of the manufactured group 13 nitride single crystal is increased.

  On the other hand, when a seed crystal having an uneven crystal growth surface with a surface roughness Ra of 0.1 μm or more and 5 μm or less is used, the crystal growth surface includes a flat flat region (for example, a flat region of + c plane) and the above-mentioned There will be a convex region (for example, a non-c surface region) formed by a plurality of convex portions that realize the surface roughness Ra. The surface of this convex part area | region is arrange | positioned non-parallel with respect to a flat area | region, and a plane orientation differs mutually. For this reason, when a group 13 nitride crystal grows on the crystal growth surface having irregularities, crystal growth proceeds in a non-perpendicular direction with respect to the flat region on the convex region. For this reason, dislocations that have reached the surface of the convex region from within the seed crystal proceed in a non-perpendicular direction with respect to the flat region and are orthogonal to the flat region in the group 13 nitride crystal in which the crystal grows. Taking over in the direction is suppressed.

  For this reason, it is presumed that a group 13 nitride single crystal having a reduced dislocation density can be produced by using a seed crystal having a crystal growth surface having irregularities in the range of the surface roughness Ra.

  Further, the present inventors raise the temperature of the mixed melt to the crystal growth temperature when crystal growth is performed by a flux method using a seed crystal having a crystal growth surface having irregularities indicated by the surface roughness Ra. When at least one of the rate of temperature rise and the rate of temperature drop when the temperature is lowered after the crystal growth step is 150 ° C./hour or less, it is possible to achieve both reduction of dislocation density and reduction of cracks. I found out that I can do it.

  It is considered that the temperature distribution is more likely to occur on the crystal growth surface of the seed crystal as the temperature increase rate in the temperature increase process exceeds 150 ° C./hour. Such a temperature distribution is considered to be particularly likely to occur at the uneven portion of the crystal growth surface of the seed crystal. For this reason, it is presumed that the strain of the group 13 nitride crystal in which the crystal grows easily concentrates on the concavo-convex portion, and cracks are generated starting from the strain concentration portion. For this reason, it is estimated that the rate of occurrence of cracks can be suppressed by setting the temperature rising rate to 150 ° C./hour or less.

  Further, the present inventors have found that cracks are generated even when the temperature is lowered after crystal growth. Cracks occur after crystal growth because distortion due to the difference in thermal expansion coefficient and anisotropy between the interface between the seed crystal and the group 13 nitride crystal that has grown and the group 13 nitride crystal that has grown. Possible cause.

  When the temperature lowering rate in the temperature lowering step after crystal growth is 150 ° C./hour or less, the thermal expansion between the interface between the seed crystal and the group 13 nitride crystal grown and the group 13 nitride crystal grown. It is considered that distortion caused by coefficient difference and anisotropy can be suppressed. Since this distortion can be suppressed, it is considered that the generation of cracks due to the distortion can be suppressed.

  Therefore, it is considered that the method for producing a group 13 nitride single crystal of the present embodiment can realize both reduction of dislocation density and reduction of cracks.

  In the case where the crystal growth is performed by the flux method using a seed crystal having a flat + c-plane crystal growth surface that does not have the unevenness indicated by the surface roughness Ra, It has been found that cracks are unlikely to occur even when the rate of temperature increase or the rate of temperature decrease is outside the scope of the present application.

  That is, when the present inventors perform crystal growth by a flux method using a seed crystal having a crystal growth surface having irregularities indicated by the surface roughness Ra, the temperature of the mixed melt is increased to the crystal growth temperature. It has been found that when at least one of the rate of temperature increase and the rate of temperature decrease when the temperature is lowered after the crystal growth step is 150 ° C./hour or less, both reduction of dislocation density and reduction of cracks can be realized. It was.

  Details will be described below.

  FIG. 1 is a diagram showing an example of a group 13 nitride single crystal manufacturing apparatus 1 for performing an arrangement step, a crystal growth step, and a temperature adjustment step in the embodiment. In the following description, the “group 13 nitride single crystal manufacturing apparatus” may be simply referred to as a manufacturing apparatus.

  The manufacturing apparatus 1 includes a control unit 10 and a main body unit 12. The control unit 10 controls the main body unit 12.

  The main body 12 includes an external pressure resistant container 50. The external pressure vessel 50 is made of stainless steel, for example. An internal container 51 is installed in the external pressure resistant container 50. The inner container 51 has a closed shape. The inner container 51 is made of stainless steel, for example. The internal container 51 can be detached from the external pressure resistant container 50.

  A reaction vessel 52 is disposed in the inner vessel 51. That is, the reaction vessel 52 is disposed inside a double-structured vessel composed of the external pressure vessel 50 and the internal vessel 51.

  The reaction vessel 52 holds the raw material or the mixed melt 24 in which the raw material is melted. The mixed melt 24 is obtained by heating the raw material. The reaction vessel 52 holds the seed crystal 30. That is, the reaction vessel 52 is a vessel for crystal growth of the group 13 nitride crystal 32 from the seed crystal 30. In the example shown in FIG. 1, the reaction vessel 52 is provided with a lid 53 and functions as a lid that closes the opening of the reaction vessel 52.

  The mixed melt 24 contains at least an alkali metal as a flux and a group 13 metal.

  The flux is, for example, metallic sodium, a sodium compound (for example, sodium azide), or the like. In this embodiment, the case where sodium (Na), which is an alkali metal, is used as the flux will be described as an example.

  The purity of sodium contained in the mixed melt 24 is preferably 99.95% or more. When the purity of sodium contained in the mixed melt 24 is 99.95% or more, it is possible to suppress generation of miscellaneous crystals on the surface of the mixed melt 24. Further, when the purity of sodium contained in the mixed melt 24 is 99.95% or more, it is possible to suppress a decrease in the crystal growth rate of the group 13 nitride crystal 32 that grows on the seed crystal 30.

  In the present embodiment, a case where at least gallium is used as the group 13 metal contained in the mixed melt 24 will be described. For this reason, in this Embodiment, the mixed melt 24 demonstrates as what is a melt which has sodium (Na) and a gallium (Ga) as a main component.

  As the group 13 metal, another group 13 metal such as boron, aluminum, or indium may be used, or a mixture of a plurality of metals selected from the group 13 metal may be used.

  Further, the group 13 nitride single crystal 40 manufactured in the present embodiment means gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof.

  The molar ratio of the Group 13 metal and the alkali metal contained in the mixed melt 24 is not particularly limited, but the ratio of the number of moles of alkali metal to the total number of moles of Group 13 metal and alkali metal is 40. It is preferable to set it as mol%-95 mol%.

  Note that an additive having an effect of expanding a metastable region in which nucleation is suppressed, boron oxide, gallium oxide, or the like serving as an n-type dopant material may be appropriately added to the mixed melt 24.

  For example, the additive has a role of changing carbon (C), which forms CN ions in the flux to increase the nitrogen concentration in the mixed melt 24, and the amount of nitrogen taken up and the solubility of nitrogen in the mixed melt 24. Some alkaline metals such as Li and K, and alkaline earth metals such as Mg, Ca, and Sr.

  The n-type dopant is, for example, germanium (Ge).

  In addition, the mixed melt 24 is obtained by heating a raw material as mentioned above. In other words, the raw material is a raw material of the mixed melt 24. For this reason, the components of the raw material and the mixed melt 24 are the same. That is, in this embodiment, the case where the raw material contains gallium as a group 13 metal and sodium as an alkali metal will be described.

  The material of the reaction vessel 52 is not particularly limited. The material of the reaction vessel 52 is, for example, a BN sintered body, a nitride such as P-BN, an oxide such as alumina or YAG, or a carbide such as SiC. The inner wall surface of the reaction vessel 52, that is, the portion where the reaction vessel 52 is in contact with the mixed melt 24 is preferably made of a material that does not easily react with the mixed melt 24. When the group 13 nitride crystal 32 is a gallium nitride crystal, examples of the material of the reaction vessel 52 include nitrides such as boron nitride (BN), pyrolytic BN (P-BN), aluminum nitride, alumina, Examples thereof include oxides such as yttrium, aluminum, and garnet (YAG), stainless steel (SUS), and the like.

  In the present embodiment, the manufacturing apparatus 1 includes a stirring mechanism 42. The stirring mechanism 42 is a mechanism for stirring the mixed melt 24 in the reaction vessel 52.

  The stirring mechanism 42 agitates the mixed melt 24 held in the reaction vessel 52 by rotating or swinging the reaction vessel 52.

  FIG. 2 is a schematic diagram illustrating an example of a stirring mechanism 42 </ b> A as the stirring mechanism 42 that rotates the reaction vessel 52.

  The stirring mechanism 42 </ b> A includes a turntable 81, a support member 82, and a drive unit 80.

  The turntable 81 is a plate-like member having a plate surface along a horizontal plane. The turntable 81 supports the reaction vessel 52 via the bottom surface outside the reaction vessel 52. The support member 82 supports the center of the plate surface of the turntable 81. The support member 82 is a member that is long in the vertical direction, one end in the longitudinal direction is connected to the center of the plate surface of the turntable 81, and the other end is connected to the drive unit 80. The drive unit 80 is a drive unit that rotationally drives the turntable 81 with the support member 82 as a rotation axis. The drive unit 80 is electrically connected to the control unit 10 and rotates the turntable 81 under the control of the control unit 10.

  Note that, from the viewpoint of suppressing the occurrence of contamination, the drive unit 80 is preferably disposed outside the internal container 51 or the external pressure resistant container 50.

  The control unit 10 controls the drive unit 80 to control the rotation direction and the rotation speed of the turntable 81. For this reason, by driving the drive unit 80 under the control of the control unit 10, the driving force of the drive unit 80 is transmitted to the reaction vessel 52 installed on the turntable 81 via the support member 82 and the turntable 81, The reaction vessel 52 rotates (in the direction of arrow A in FIG. 2). As the reaction vessel 52 rotates, the mixed melt 24 held in the reaction vessel 52 rotates. Thereby, the mixed melt 24 is agitated.

  FIG. 3 is a schematic diagram showing an example of a stirring mechanism 42B as the stirring mechanism 42 that swings the reaction vessel 52. As shown in FIG.

  The stirring mechanism 42B includes a bending member 86, a drive unit 80, and a support member 84. One end of the support member 84 is connected to the bottom of the reaction vessel 52, for example. The other end of the support member 84 is held by a curved bending member 86 that holds the support member 84 so as to be swingable in a predetermined direction (see arrow B in FIG. 3). In this case, the drive unit 80 swings the support member 84 along the longitudinal direction of the bending member 86. The drive unit 80 is connected to the control unit 10 so as to be able to exchange signals.

  By driving the drive unit 80 under the control of the control unit 10, the reaction vessel 52 supported by the support member 84 swings in the arrow B direction along the longitudinal direction of the bending member 86. Thereby, the mixed melt 24 in the reaction vessel 52 is stirred.

  In addition, the structure of the stirring mechanism 42 which stirs the mixed melt 24 is not limited to the form shown in FIG. 2 and FIG.

  Returning to FIG. 1, the manufacturing apparatus 1 includes a supply unit 48. The supply unit 48 supplies nitrogen into the reaction vessel 52.

  The supply unit 48 includes a gas supply pipe 65, a gas supply pipe 66, a nitrogen supply pipe 57, a pressure control device 56, a valve 55, a gas supply pipe 54, a gas supply pipe 60, a pressure control device 59, a valve 58, a valve 63, and a valve. 61 and a valve 62 are included.

The gas supply pipe 65 and the gas supply pipe 66 are connected to the external pressure resistant container 50 and the internal container 51. Each of the gas supply pipe 65 and the gas supply pipe 66 includes nitrogen (N ₂ ) gas, which is a raw material of the group 13 nitride single crystal 40, in each of the internal space 67 of the external pressure resistant container 50 and the internal space 68 of the internal container 51. And a dilution gas for adjusting the total pressure is supplied.

  These nitrogen gas and dilution gas are supplied to the gas phase 22 in the reaction vessel 52.

  As the diluent gas, it is desirable to use an argon (Ar) gas that is an inert gas, but the present invention is not limited to this, and other inert gases such as helium (He) may be used as the diluent gas.

  Nitrogen gas is supplied from a nitrogen supply pipe 57 connected to a gas cylinder or the like of the nitrogen gas, the pressure is adjusted by the pressure control device 56, and then supplied to the gas supply pipe 54 through the valve 55. On the other hand, a gas for adjusting the total pressure (for example, argon gas) is supplied from a gas supply pipe 60 for adjusting the total pressure, which is connected to a gas cylinder for adjusting the total pressure, and the pressure is controlled by the pressure controller 59. After the adjustment, the gas is supplied to the gas supply pipe 54 through the valve 58. The nitrogen gas whose pressure is adjusted in this way and the gas for adjusting the total pressure are respectively supplied to the gas supply pipe 54 and mixed.

  A mixed gas of nitrogen and dilution gas is supplied from the gas supply pipe 54 through the valve 63, the gas supply pipe 65, the valve 61, and the gas supply pipe 66 into the external pressure resistant container 50 and the internal container 51. The inner container 51 can be detached from the manufacturing apparatus 1 at the valve 61 portion. Further, the gas supply pipe 65 communicates with the outside through a valve 62.

  The gas supply pipe 54 is provided with a pressure gauge 64. In the manufacturing apparatus 1, the control unit 10 adjusts the pressures in the external pressure resistant container 50 and the internal container 51 while monitoring the total pressure in the external pressure resistant container 50 and the internal container 51 with the pressure gauge 64.

  In the present embodiment, the manufacturing apparatus 1 adjusts the pressures of the nitrogen gas and the dilution gas with the valve 55 and the valve 58, the pressure control device 56, and the pressure control device 59 in this way, thereby adjusting the nitrogen partial pressure. Can be adjusted. Moreover, since the total pressure of the external pressure-resistant container 50 and the internal container 51 can be adjusted, the total pressure in the internal container 51 can be increased and evaporation of the flux (for example, sodium) in the reaction container 52 can be suppressed. That is, it is possible to separately control the nitrogen partial pressure, which is a nitrogen raw material that affects the crystal growth conditions of gallium nitride, and the total pressure that affects the evaporation suppression of flux such as sodium.

  The nitrogen partial pressure in the inner vessel 51 during the growth of the group 13 nitride crystal 32 is determined by the size of the group 13 nitride crystal 32 to be manufactured, and the value is not limited. The nitrogen partial pressure in the inner container 51 is preferably in the range of 0.1 MPa to 8 MPa, for example.

  A first heating unit 70 and a second heating unit 72 are disposed on the outer periphery of the inner container 51 in the outer pressure resistant container 50. In the present embodiment, the first heating unit 70 is disposed along the side surface of the inner container 51. The second heating unit 72 is disposed on the bottom surface side outside the reaction vessel 52.

  The first heating unit 70 and the second heating unit 72 heat the reaction vessel 52. As a result, the raw material in the reaction vessel 52 or the mixed melt 24 in which the raw material is melted is heated. It is also possible to form a desired temperature distribution in the mixed melt 24 by adjusting the heating temperature by the first heating unit 70 and the second heating unit 72.

  In the present embodiment, the control unit 10 heats the raw material to the crystal growth temperature, the temperature rising rate of the raw material (and / or the mixed melt 24 in which the raw material is melted) when heating to the crystal growth temperature, and Each of the first heating unit 70 and the second heating unit 72 is controlled so as to adjust the temperature drop rate of the mixed melt 24 when the temperature is lowered from the crystal growth temperature after crystal growth.

―Manufacture of group 13 nitride crystals―
Hereinafter, the manufacturing method of the group 13 nitride single crystal 40 using the manufacturing apparatus 1 will be described in detail.

―Placement process―
In the method for manufacturing group 13 nitride single crystal 40 of the present embodiment, first, the arranging step is executed.

  The arranging step is a step of arranging the seed crystal 30 and the raw material in the reaction vessel 52. In the present embodiment, a seed crystal 30 made of a group 13 nitride crystal and having a surface roughness Ra of 0.1 μm or more and 5 μm or less is used.

  FIG. 4 is an explanatory diagram of the seed crystal 30 used in the present embodiment.

  4A is an electron micrograph of the crystal growth surface C of the seed crystal 30. FIG. FIG. 4B is an electron micrograph of the crystal growth surface C of the seed crystal 30 having a higher magnification than that in FIG. FIG. 4C is an electron micrograph of the crystal growth surface C in the cross section of the seed crystal 30. FIG. 4D is a schematic diagram showing a crystal growth surface C in the cross section of the seed crystal 30.

  As shown in FIG. 4, the crystal growth surface C of the seed crystal 30 has irregularities. Specifically, the crystal growth surface C of the seed crystal 30 has irregularities with a surface roughness Ra in the range of 0.1 μm to 5 μm. As the surface roughness Ra, a value measured according to JIS B0601 is used.

  The surface roughness Ra of the crystal growth surface C is indispensable within the above range, but is preferably in the range of 0.2 μm to 2 μm, and more preferably in the range of 0.5 μm to 1.0 μm.

  By setting the surface roughness Ra of the crystal growth surface C in the above range, the dislocation density of the group 13 nitride single crystal 40 can be reduced. Specifically, when the surface roughness Ra of the crystal growth surface C is 0.1 μm or more, the dislocation density of the group 13 nitride crystal 32 that grows from the seed crystal 30 having the crystal growth surface C is reduced. Can do. Further, when the surface roughness Ra of the crystal growth surface C is 5 μm or less, it is possible to suppress the generation of cracks in the group 13 nitride crystal 32 where the crystal grows.

  In the present embodiment, as shown in FIG. 4, the crystal growth surface C of the seed crystal 30 includes a flat flat region 30A (for example, a flat region of the + c plane) and a plurality of protrusions that realize the surface roughness Ra. And a convex region 30 </ b> B.

  The flat region 30A is, for example, a + c plane region. The convex region 30B is a region composed of convex portions protruding from the flat region 30A. That is, the surface of the convex region 30B includes a non- + c surface having a plane orientation different from the + c surface that is the flat region 30A. The inclined surface that continues in the direction non-orthogonal to the flat region 30A on the surface of the convex region 30B is, for example, a {10-11} surface.

  The height of each of the plurality of convex portions constituting the convex region 30B (the shortest distance from the flat region 30A to the apex of the convex portion) may be any height that can realize the surface roughness Ra. For example, the height of the highest convex portion among the plurality of convex portions constituting the convex region 30B is preferably 0.5 μm or more and 100 μm or less, for example, 1.0 μm or more and 50 μm or less. More preferably.

  The method for manufacturing seed crystal 30 used in the present embodiment is not limited. The seed crystal 30 is obtained by, for example, growing a group 13 nitride crystal on the c-plane of a sapphire substrate using a HVPE (Hydride Vapor Phase Epitaxy) method and adjusting the crystal growth conditions, thereby adjusting the surface of the crystal growth surface C. A seed crystal 30 having a roughness Ra that satisfies the above range may be produced.

  In the arrangement step in the manufacturing method of the present embodiment, the seed crystal 30 is arranged in the mixed melt 24 held in the reaction vessel 52.

  Specifically, the raw material of the mixed melt 24 described above is charged into the reaction vessel 52. The operation of charging the raw material into the reaction vessel 52 is performed by placing the inner vessel 51 in a glove box having an inert gas atmosphere such as argon gas. This operation may be performed with the reaction vessel 52 placed in the internal vessel 51. Then, the seed crystal 30 is installed in the reaction vessel 52.

  At this time, the crystal growth surface C faces the gas-liquid interface A side with the gas phase 22 in the mixed melt 24 when the raw material charged into the reaction vessel 52 is heated to become the mixed melt 24. The seed crystal 30 is disposed on the bottom B inside the reaction vessel 52.

―Crystal growth process―
In the crystal growth step, in a state where the raw material in the reaction vessel 52 is melted to form the mixed melt 24, nitrogen is dissolved in the mixed melt 24 from the gas phase 22 and placed in the mixed melt 24 at the crystal growth temperature. A group 13 nitride crystal 32 is grown on the seed crystal 30.

  Specifically, the reaction vessel 52 in which the raw material and the seed crystal 30 are arranged is arranged in the manufacturing apparatus 1. And it supplies with electricity to the 1st heating part 70 and the 2nd heating part 72, the internal container 51 and the reaction container 52 of the inside are heated, and a raw material is heated to crystal growth temperature. The heating to the crystal growth temperature is performed in a temperature raising process described later. The crystal growth temperature is, for example, 750 ° C. or higher. In addition, it is preferable that the nitrogen partial pressure in the inner container 51 is in a range of 0.1 MPa to 8 MPa, for example.

  Then, in the temperature raising step described later, the raw material group 13 metal, alkali metal, other additives and the like are melted in the reaction vessel 52, and the mixed melt 24 is formed. In the crystal growth step, nitrogen is supplied to the mixed melt 24 by the supply unit 48 in a state where the raw material is melted by the temperature raising step to become the mixed melt 24. Thereby, nitrogen which is a raw material of the group 13 nitride crystal 32 is supplied into the mixed melt 24.

  Then, the raw material dissolved in the mixed melt 24 is supplied to the seed crystal 30, and the group 13 nitride crystal 32 is grown from the crystal growth surface C of the seed crystal 30 by the raw material. Thus, the group 13 nitride crystal 32 is grown from the crystal growth surface C of the seed crystal 30, whereby the group 13 nitride single crystal 40 is obtained.

  The crystal growth process is performed by controlling the main body 12 by the controller 10. That is, the control unit 10 dissolves nitrogen in the mixed melt 24 and supplies the supply unit 48 so that the group 13 nitride crystal 32 is grown on the seed crystal 30 disposed in the mixed melt 24 at the crystal growth temperature. And crystal growth control for controlling the heating units (the first heating unit 70 and the second heating unit 72). As a result, the group 13 nitride crystal 32 grows from the seed crystal 30 and the group 13 nitride single crystal 40 is obtained.

―Temperature adjustment process―
The temperature adjustment step includes at least one of a temperature raising step and a temperature lowering step.

  The temperature adjustment process is performed under the control of the control unit 10. The control unit 10 controls the heating units (the first heating unit 70 and the second heating unit 72) so as to perform at least one of temperature increase control and temperature decrease control.

―Temperature raising process―
The temperature raising step is performed between the placement step and the crystal growth step. In the heating step of the present embodiment, the temperature of the raw material is raised to the crystal growth temperature at a heating rate of 150 ° C./hour or less.

  The temperature increase rate in the temperature increasing step is essential to be the above temperature increase rate, but is preferably 20 ° C./hour or more and 150 ° C./hour or less, preferably 25 ° C./hour or more and 100 ° C./hour or less. More preferably, it is more preferably 25 ° C./hour or more and 50 ° C. or less.

  By including the temperature raising step of the temperature raising rate, it is possible to suppress the concentration of strain on the uneven portion of the crystal growth surface C, and to suppress the generation of cracks starting from the strain concentration location. Conceivable.

  The temperature increase rate in the temperature increase process may be adjusted by adjusting the heating rate of the raw material by the first heating unit 70 and the second heating unit 72. That is, the control unit 10 controls the heating unit (the first heating unit 70 and the second heating unit 72) so as to increase the temperature of the raw material to the crystal growth temperature at a temperature increase rate of 150 ° C./hour or less. Control may be performed. In this temperature raising step, the raw material group 13 metal, alkali metal, other additives and the like are melted to form a mixed melt 24.

  In addition, it is preferable to perform the temperature raising process in the present embodiment while stirring the mixed melt 24.

  The mixed melt 24 may be stirred by the control of the stirring mechanism 42 by the control unit 10. For example, the control unit 10 controls the drive unit 80 to rotate or swing the reaction vessel 52 to stir the mixed melt 24 in the reaction vessel 52. That is, if the control part 10 controls the heating part (the 1st heating part 70, the 2nd heating part 72) and the drive part 80 so that stirring control which stirs the mixed melt 24 may be performed in temperature rising control. Good.

  The stirring speed in the temperature raising step is not limited. Specifically, the stirring speed indicates a rotational speed difference (relative speed) between the mixed melt 24 and the seed crystal 30 and the group 13 nitride crystal 32 grown from the seed crystal 30.

  When the mixed melt 24 is vigorously stirred, miscellaneous crystals may be generated. For this reason, it is preferable that the stirring speed of the mixed melt 24 be a speed at which generation of miscellaneous crystals can be suppressed.

  Further, the stirring speed in the temperature raising step may be constant or variable. However, the stirring speed in the temperature raising step is preferably variable. By changing the stirring speed in the temperature raising step, there is a state in which there is a difference in the rotational speed between the seed crystal 30 and the group 13 nitride crystal 32 grown from the seed crystal 30 and the mixed melt 24. It is preferable to agitate the mixed melt 24 by rotation control including acceleration, deceleration, inversion, and the like of the reaction vessel 52 so as to be maintained. In addition, the stirring is preferably performed by controlling the rotation of the reaction vessel 52 so that the mixed melt 24 is stirred when the mixed melt 24 is formed in the reaction vessel 52 by heating the raw materials and the like. .

  Further, when the stirring speed in the temperature raising step is variable, the stirring speed in the temperature raising step during the period in which the temperature of the mixed melt 24 is in the vicinity of the melting point of the alkali metal contained in the mixed melt 24 is other than the vicinity of the melting point. It is preferable to adjust so that it may become slower than the stirring speed of the period which is this temperature.

  The vicinity of the melting point indicates, for example, the melting point of the alkali metal contained in the mixed melt 24 ± 5 ° C.

  By performing the temperature raising step while stirring the mixed melt 24, the temperature distribution in the mixed melt 24 becomes uniform, and the generation of cracks in the group 13 nitride crystal 32 in which crystals grow can be further suppressed. it is conceivable that.

―Cooling process―
The temperature lowering step is a step of lowering the temperature of the mixed melt 24 at a temperature lowering rate of 150 ° C./hour or less after the crystal growth step.

  The temperature lowering rate in the temperature lowering step is essential to be the above-mentioned temperature lowering rate, preferably 20 ° C./hour to 150 ° C./hour, more preferably 25 ° C./hour to 100 ° C./hour. It is particularly preferably 25 ° C./hour or more and 50 ° C. or less.

  By including the temperature lowering step at the temperature lowering rate, the thermal expansion coefficient difference and anisotropy between the interface between the seed crystal 30 and the group-grown group 13 nitride crystal 32 and the group-grown nitride crystal 32 having the crystal growth are increased. The distortion which generate | occur | produces can be suppressed.

  For example, when the crystal growth surface C of the seed crystal 30 exhibits the surface roughness Ra, and includes a flat region 30A having a + c plane and a convex region 30B having a non- + c plane, the initial stage of crystal growth Is a crystal growth in which {0001} growth and {10-11} growth are complicated.

  A crystal region in which the {0001} growth and {10-11} growth are complicatedly grown is assumed to be an interface layer between the seed crystal 30 and the group 13 nitride crystal 32. This interface layer is formed in the order of several μm to 100 μm depending on crystal growth conditions. Then, if the crystal growth is continued, {0001} growth becomes dominant, and finally a group 13 nitride single crystal 40 grown {0001} except for the end of the crystal is obtained. On the other hand, {10-11} crystal grows at the crystal edge.

  Here, it is known that when the crystal growth direction is changed, the concentration of impurities taken into the crystal is also different. For this reason, it is expected that the interface layer and the layer of {0001} -grown group 13 nitride crystal 32 have different thermal expansion coefficients and anisotropy.

  On the other hand, by including the temperature lowering step at the temperature lowering rate, the interface layer (that is, the interface between the seed crystal 30 and the group 13 nitride crystal 32 that has grown crystal) and the group 13 nitride crystal 32 that has grown crystal have It is thought that distortion generated by the difference in thermal expansion coefficient and anisotropy can be suppressed. For this reason, it is thought that generation | occurrence | production of the crack resulting from distortion can be suppressed.

  The temperature lowering rate in the temperature lowering step may be adjusted by adjusting the heating rate (cooling rate) of the mixed melt 24 by the first heating unit 70 and the second heating unit 72. That is, if the control unit 10 performs the temperature lowering control to control the heating unit (the first heating unit 70 and the second heating unit 72) so as to lower the temperature of the mixed melt 24 at a temperature lowering rate of 150 ° C./hour or less. Good.

  The temperature lowering step in the present embodiment is preferably performed while stirring the mixed melt 24.

  The mixed melt 24 may be stirred by the control of the stirring mechanism 42 by the control unit 10. For example, the control unit 10 controls the drive unit 80 to rotate or swing the reaction vessel 52 to stir the mixed melt 24 in the reaction vessel 52. That is, the control unit 10 may control the heating unit (the first heating unit 70 and the second heating unit 72) and the driving unit 80 so as to execute the stirring control for stirring the mixed melt 24 in the temperature lowering control. .

  The stirring speed of the mixed melt 24 in the temperature lowering step is not limited.

  When the mixed melt 24 is vigorously stirred, miscellaneous crystals may be generated. For this reason, it is preferable that the stirring speed of the mixed melt 24 be equal to or lower than a threshold value of a speed at which generation of miscellaneous crystals can be suppressed.

  In addition, the stirring speed in the temperature lowering step may be constant or variable. However, the stirring speed in the temperature lowering step is preferably variable. By making the stirring speed in the temperature lowering process variable, a state in which a difference occurs in the rotational speed between the seed crystal 30 and the group 13 nitride crystal 32 grown from the seed crystal 30 and the mixed melt 24 is maintained. As described above, it is preferable to agitate the mixed melt 24 by rotation control including acceleration, deceleration, inversion, and the like of the reaction vessel 52.

  When the stirring speed in the temperature lowering step is variable, for example, the temperature of the mixed melt 24 in the temperature lowering step is at least one of the freezing point of the mixed crystal of Ga and Na contained in the mixed melt 24 and the freezing point of Na. It is preferable that the stirring speed during the period near the temperature is lower than the stirring speed during the period other than the temperature. The vicinity of the temperature indicates, for example, the above freezing point ± 5 ° C.

  By performing the temperature lowering step while stirring the mixed melt 24, the temperature uniformity in the group 13 nitride crystal 32 in which the temperature of the mixed melt 24 in the reaction vessel 52 is improved and the crystal grows is reduced. It is thought that you can. For this reason, it is considered that generation of cracks in the group 13 nitride crystal 32 can be further suppressed.

  Next, the flow of the manufacturing process executed by the control unit 10 in the manufacturing apparatus 1 of the present embodiment will be described.

  FIG. 7 is a flowchart illustrating an example of a manufacturing process procedure executed by the control unit 10 according to the present embodiment. In FIG. 7, as an example, a case where the temperature raising step, the crystal growth step, and the temperature lowering step are executed is shown. In addition, the arrangement | positioning process using the said seed crystal 30 of this Embodiment and the raw material shall be performed by the user before the temperature rising process.

  First, the control unit 10 performs temperature increase control (step S100). In step S100, the control unit 10 controls the heating units (the first heating unit 70 and the second heating unit 72) so as to raise the temperature of the raw material to the crystal growth temperature at a temperature rising rate of 150 ° C./hour or less.

  Next, the control unit 10 performs crystal growth control (step S102). In step S102, the control unit 10 dissolves nitrogen from the gas phase 22 in the mixed melt 24 in a state where the raw material is melted to form the mixed melt 24, and arranges it in the mixed melt 24 at the crystal growth temperature. The supply unit 48 and the heating unit (the first heating unit 70 and the second heating unit 72) are controlled so that the group 13 nitride crystal is grown on the seed crystal 30 thus formed.

  Next, the control part 10 performs temperature fall control (step S104). In step S104, the controller 10 lowers the temperature of the mixed melt 24 at a temperature lowering rate of 150 ° C./hour or less.

  Then, this routine ends. By performing the processing of step 100 to step 104, the manufacturing apparatus 1 of the present embodiment can manufacture the group 13 nitride single crystal 40 in which both the reduction of dislocation density and the reduction of cracks are realized. it can.

  As described above, the method for manufacturing group 13 nitride single crystal 40 of the present embodiment includes the placement step, the crystal growth step, and the temperature adjustment step.

  In the arranging step, a seed crystal 30 made of a group 13 nitride crystal and having a crystal growth surface C with a surface roughness Ra of 0.1 μm or more and 5 μm or less, and a raw material containing an alkali metal and a group 13 metal are placed in the reaction vessel 52. It is a process of arranging. In the crystal growth step, nitrogen is dissolved in the mixed melt 24 in a state where the raw material is melted to form the mixed melt 24, and the seed crystal 30 disposed in the mixed melt 24 at the crystal growth temperature is subjected to group 13 nitridation. This is a process of growing the physical crystal 32. The temperature adjustment step includes at least one of a temperature raising step and a temperature lowering step. The temperature raising step is a step of raising the temperature of the raw material to the crystal growth temperature at a temperature raising rate of 150 ° C./hour or less between the arrangement step and the crystal growth step. The temperature lowering step is a step of lowering the temperature of the mixed melt 24 at a temperature lowering rate of 150 ° C./hour or less after the crystal growth step.

  Thus, in the manufacturing method of group 13 nitride single crystal 40 of the present embodiment, seed crystal 30 having a crystal growth surface C with a surface roughness Ra of 0.1 μm or more and 5 μm or less is used as a seed crystal by a flux method. Crystal growth is performed, and includes at least one of a temperature raising step with a temperature rising rate of 150 ° C./hour or less and a temperature lowering step with a temperature lowering rate of 150 ° C./hour or less.

  Therefore, in the manufacturing method of group 13 nitride single crystal 40 of the present embodiment, group 13 nitride single crystal 40 that realizes both a reduction in dislocation density and a reduction in cracks can be manufactured.

  The crystal growth surface C of the seed crystal 30 preferably includes a + c plane flat region 30A and a convex region 30B composed of a plurality of convex portions protruding from the flat region 30A.

  The temperature raising step may be a step of raising the temperature to the crystal growth temperature at a rate of temperature rise of 150 ° C./hour or less while stirring the mixed melt 24 between the arrangement step and the crystal growth step. preferable.

  The temperature lowering step is preferably a step of lowering the temperature of the mixed melt 24 at a temperature lowering rate of 150 ° C./hour or less while stirring the mixed melt 24 after the crystal growth step.

  Moreover, it is preferable that the temperature increase rate in a temperature increase process is 100 degrees C / hr or less. Moreover, it is preferable that the temperature-fall rate in a temperature-fall process is 100 degrees C / hour or less.

  Further, the surface roughness Ra of the crystal growth surface C of the seed crystal 30 is preferably 0.2 μm or more and 2.0 μm or less.

  Moreover, the manufacturing apparatus 1 of the group 13 nitride single crystal 40 of the present embodiment includes a reaction vessel 52, a supply unit 48, a heating unit (first heating unit 70, second heating unit 72), and the control unit 10. And comprising. The reaction vessel 52 holds a seed crystal 30 made of a group 13 nitride crystal and having a surface roughness Ra of 0.1 μm or more and 5 μm or less on the crystal growth surface C, and a raw material containing an alkali metal and a group 13 metal inside. . The supply unit 48 supplies nitrogen into the reaction vessel 52. The heating units (the first heating unit 70 and the second heating unit 72) heat the reaction vessel 52.

  The control unit 10 dissolves nitrogen in the mixed melt 24 in a state where the raw material is melted to form the mixed melt 24, and the group 13 is added to the seed crystal 30 arranged in the mixed melt 24 at the crystal growth temperature. Crystal growth control for controlling the supply unit 48 and the heating unit (the first heating unit 70 and the second heating unit 72) to grow the nitride crystal 32, and a temperature increase of 150 ° C./hour or less before the crystal growth control A heating section (at least one of temperature raising control for raising the temperature of the raw material to the crystal growth temperature at a speed and temperature lowering control for lowering the temperature of the mixed melt 24 at a temperature lowering speed of 150 ° C./hour or less after the crystal growth control ( Temperature adjustment control for controlling the first heating unit 70 and the second heating unit 72) is performed.

  FIG. 8 is a hardware configuration diagram of the control unit 10 in the manufacturing apparatus 1 of the present embodiment.

  The control unit 10 includes, as a hardware configuration, a CPU 501 that controls the entire apparatus, a ROM 502 that stores various data and various programs, and an interface unit (I / F unit) 504 that are connected via a bus 505. The hardware configuration uses a normal computer. The I / F unit 504 is connected to the main body unit 12, a known display device, an operation unit such as a keyboard, and the like.

  A program for executing the above-described processing in the control unit 10 of the above-described embodiment is a file in an installable format or an executable format, such as a CD-ROM, a floppy (registered trademark) disk (FD), a CD-R, a DVD. It is recorded on a computer-readable recording medium such as (Digital Versatile Disk) and provided as a computer program product.

  In addition, the program for executing the above-described processing in the control unit 10 of the above-described embodiment may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network. Good. In addition, a program for executing the above processing in the control unit 10 of the above embodiment may be provided or distributed via a network such as the Internet.

  In addition, a program for executing the above-described processing in the control unit 10 of the above-described embodiment may be configured to be provided by being incorporated in advance in a ROM or the like.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the components without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiments. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined. Various modifications are possible.

  Examples are shown below to describe the present invention in more detail, but the present invention is not limited to these Examples. In addition, the code | symbol respond | corresponds with the structure of the manufacturing apparatus 1 demonstrated in the said embodiment.

-Preparation of seed crystals and comparative seed crystals-
A seed crystal 30 was produced. First, a φ2 inch sapphire substrate was prepared, and a GaN crystal was grown on the c-plane of the sapphire substrate by the HVPE method. After crystal growth, the sapphire substrate was peeled off to produce a seed crystal 30 of crystal-grown GaN crystal.

  When the crystal growth surface C of the produced seed crystal 30 was observed with an electron microscope, a flat region 30A composed of a flat + c surface and a convex region 30B composed of a plurality of convex portions including a non- + c surface were formed ( (See FIG. 4).

  It should be noted that by adjusting the crystal growth conditions of the GaN crystal on the sapphire substrate, a plurality of types of seed crystals 30 in which the surface roughness Ra of the crystal growth surface C is in the range of 0.1 μm to 5 μm are obtained. A plurality of types of comparative seed crystals having a surface roughness Ra outside the range (range of 0.1 μm or more and 5 μm or less) were prepared. It is desirable that Ra satisfies this range over the entire crystal growth surface C.

  It should be noted that the plurality of types of seed crystals 30 and comparative seed crystals produced with different surface roughness Ra were processed into a disk shape of φ2 inches, and a plurality of types of seeds produced with different surface roughness Ra. The off-angle (tilt angle) with respect to the m-axis <10-10> at the center of the crystal growth surface of each of the crystal 30 and the comparative seed crystal was 0.3 °. The thickness of the seed crystal 30 and the comparative seed crystal was 300 μm to 400 μm.

  The surface roughness Ra of the crystal growth surface C of each of a plurality of types of seed crystals 30 and comparative seed crystals having different surface roughness Ra is a contact film thickness meter (tencor stylus type surface roughness meter P10, JIS B0601). Measured with The measurement length of Ra was 10 mm, and five locations on the crystal growth surface C of the seed crystal 30 were measured. Based on the measured Ra, seed crystals having surface roughness Ra at five locations satisfying the range of Ra as shown in Table 1 were selected. Ten seed crystals were prepared for each range classified by Ra. In the following examples and comparative examples, 10 seed crystals were tested under the same conditions.

Example 1
In Example 1, the group 13 nitride single crystal 40 is manufactured by using the manufacturing apparatus 1 provided with the stirring mechanism 42A that stirs the mixed melt 24 by rotating the reaction vessel 52 as the stirring mechanism 42. It was.

―Placement process―
The placement process was performed by the manufacturing apparatus 1 shown in FIG. In the arrangement step, sodium was used as the alkali metal and gallium was used as the group 13 metal. Then, a GaN (gallium nitride) single crystal was manufactured as a group 13 nitride single crystal.

  First, the inner container 51 was separated from the manufacturing apparatus 1 at the valve 61 portion and placed in a glove box having a high-purity Ar atmosphere. Next, as the reaction vessel 52 in the inner vessel 51, a first reaction vessel 52A made of alumina having an inner diameter of 92 mm and a depth of 120 mm was prepared.

  And among the produced seed crystal 30 and the comparative seed crystal, the seed crystal 30 having a surface roughness Ra in the range of 0.1 μm or more and 0.2 μm or less at five locations on the crystal growth surface C is placed in the reaction vessel 52. did.

  Next, as a flux, sodium (Na) was heated to be a liquid and placed in the reaction vessel 52. After sodium solidified, gallium (Ga), carbon (C), and germanium (Ge) were added.

  In this example, the molar ratio of gallium to sodium was 0.30: 0.70. Carbon was 1.0 at% relative to the number of moles of gallium and sodium. Germanium was set to 2.0 at% with respect to the number of moles of gallium. This adjusted the raw material. That is, seed crystals 30 having a surface roughness Ra in a range of 0.1 μm or more and 0.2 μm or less at five locations on the crystal growth surface C were arranged in the reaction vessel 52.

―Temperature raising process―
Next, the reaction vessel 52 was accommodated in the inner vessel 51, taken out from the glove box, and incorporated in the outer pressure resistant vessel 50. The reaction vessel 52 was installed on the turntable 81. And the valve | bulb 61 was closed and the inner container 51 filled with Ar gas was sealed, and the inside of the reaction container 52 was interrupted | blocked from external atmosphere. Next, the inner container 51 was taken out of the glove box and incorporated in the manufacturing apparatus 1. That is, the reaction vessel 52 was installed at a predetermined position with respect to the first heating unit 70, the second heating unit 72, and the turntable 81, and connected to the gas supply pipe 54 at the valve 61 portion.

  By attaching the internal container 51 to the external pressure resistant container 50, the inside of the external pressure resistant container 50 was shut off from the external atmosphere.

  Next, the evacuation in the piping between the valve 61 and the valve 63 and the external pressure vessel 50 and the introduction of nitrogen were repeated 10 times via the valve 62. The valve 63 was closed in advance. Thereafter, the valve 62 was closed, the valve 61, the valve 63, and the valve 58 were opened, and Ar gas was introduced from the gas supply pipe 60 for adjusting the total pressure. Further, the pressure was adjusted by the pressure control device 59, the total pressure in the external pressure resistant container 50 and the internal container 51 was set to 1.1 MPa, and the valve 58 was closed.

  Then, nitrogen gas was introduced from the nitrogen supply pipe 57, the pressure was adjusted by the pressure control device 56, the valve 55 was opened, and the total pressure in the external pressure vessel 50 and the internal vessel 51 was set to 2.1 MPa. That is, the nitrogen partial pressures of the internal space 67 of the external pressure vessel 50, the internal space 68 of the internal vessel 51, and the gas phase 22 that is the internal space of the reaction vessel 52 were 1.0 MPa.

  Next, each of the first heating unit 70 and the second heating unit 72 was energized to raise the temperature of the mixed melt 24 in the reaction vessel 52 to the crystal growth temperature (890 ° C.).

  At this time, the temperature increase rate of the mixed melt 24 by the first heating unit 70 and the second heating unit 72 is adjusted to 150 ° C./hour under the control of the control unit 10, up to the crystal growth temperature (890 ° C.). The raw material was heated at the rate of temperature increase.

  The nitrogen partial pressures in the external pressure vessel 50 and the internal vessel 51 at the crystal growth temperature were 3.8 MPa.

  In Example 1, the mixed melt 24 was stirred in the temperature raising step. Specifically, the reaction vessel 52 was rotated by controlling the rotation of the turntable 81 by the control unit 10. At this time, during crystal growth, the turntable 81 is accelerated, rotated, decelerated so that a relative speed is generated between the mixed melt 24 and the seed crystal 30 (that is, a rotational speed difference is generated). The stop was repeated.

―Crystal growth process―
Next, the valve 55 was opened and the pressure was set to 8 MPa. Thereby, nitrogen consumed by crystal growth is supplied into the reaction vessel 52, and the nitrogen partial pressure can always be kept constant (3.8 MPa in this embodiment). In this state, the reaction vessel 52 was held for 80 hours (the crystal growth time was 80 hours), and the group 13 nitride crystal 32 was grown on the seed crystal 30.

  In this example, the mixed melt 24 was continuously stirred by the stirring mechanism 42 even in the crystal growth step. Stirring is the same as in the temperature raising step.

―Cooling process―
Next, the temperature of the mixed melt 24 was decreased at a temperature decrease rate of 100 ° C./hour. The temperature drop rate of the mixed melt 24 is adjusted to the temperature drop rate of 100 ° C./hour by adjusting the temperature drop rate of the mixed melt 24 by the first heating unit 70 and the second heating unit 72 under the control of the control unit 10. Adjusted.

  In the present example, the mixed melt 24 was continuously stirred by the stirring mechanism 42 in the temperature lowering step. Stirring is the same as in the temperature raising step.

  After the temperature of the mixed melt 24 was lowered to room temperature by the temperature lowering step, the group 13 nitride single crystal 40 was taken out from the reaction vessel 52. The taken out group 13 nitride single crystal 40 had a diameter of 52 mm and a thickness of about 1.1 mm.

―Evaluation―
The group 13 nitride single crystal 40 produced in this example was evaluated for cracks and dislocation density.

--Crack before crystal growth--
The produced group 13 nitride single crystal 40 was evaluated for cracks generated before crystal growth of the group 13 nitride crystal 32.

  “Before crystal growth” means immediately before the crystal growth of the group 13 nitride crystal 32 from the seed crystal 30 is started. The “crack generated before crystal growth” means a crack generated in the seed crystal 30 before crystal growth of the group 13 nitride crystal 32 from the seed crystal 30 is started. The “crack generated before crystal growth” generated in the seed crystal 30 is inherited by the group 13 nitride crystal 32 grown from the seed crystal 30.

  FIG. 5 is a diagram showing an example of a group 13 nitride single crystal 40 including cracks K generated before crystal growth. As shown in FIG. 5, the group 13 nitride single crystal 40 has a large crack K that crosses the vicinity of the center. Since a black crystal grows around the crack K, this black crystal portion is the same as the side surface of the seed crystal 30 or the group 13 nitride crystal 32 crystal-grown from the seed crystal 30 {10-11. } Presumed to be a grown crystal.

  It is known that {10-11} growth grows from an end face of the seed crystal 30 (a side face continuous with the crystal growth face C in the seed crystal 30). For this reason, it can be judged that such a crack K in which black crystal growth is seen in the periphery is a crack generated before crystal growth.

  Of the 10 Group 13 nitride single crystals 40 produced, the number of substrates with cracks before crystal growth was taken as the crack rate, and the crack rate was 0% when the crack reduction effect was highest (crack The evaluation of “1” with the smallest and most favorable) is “1” and the crack rate is greater than 0% and 20% or less. The case of exceeding 3 was evaluated as “3”, which is the lowest evaluation of the crack reduction effect. The evaluation results are shown in Table 1.

--Crack after crystal growth--
The produced group 13 nitride single crystal 40 was evaluated for cracks generated after crystal growth of the group 13 nitride crystal 32.

  Note that “after crystal growth” means after the crystal growth step. The term “crack generated after crystal growth” means a crack generated in the group 13 nitride crystal 32 that has been crystal-grown in the crystal growth step after the crystal growth step.

  FIG. 6 is a diagram illustrating an example of a group 13 nitride single crystal 40 including a crack K ′ generated after crystal growth. As shown in FIG. 6, the group 13 nitride single crystal 40 has a crack K ′ entering in the lateral direction. Unlike the crack K generated before crystal growth described with reference to FIG. 5, the crack K ′ does not show any trace of {10-11} growth. That is, it is inferred that this crack K 'has entered after crystal growth.

  For this reason, it can be determined that such a crack K ′ in which no black crystal grows in the vicinity is a crack generated after crystal growth.

  Of the 10 Group 13 nitride single crystals 40 produced, the number of substrates with cracks after crystal growth was defined as the crack rate, and the crack rate was 0% when the crack reduction effect was highest (crack The evaluation of “1” with the smallest and most favorable) is “1” and the crack rate is greater than 0% and 20% or less. The case of exceeding 3 was evaluated as “3”, which is the lowest evaluation of the crack reduction effect. The evaluation results are shown in Table 1.

―Dislocation density―
About the produced group 13 nitride single crystal 40, when there was a crack, the part which does not have a crack was cut out. Then, both surfaces of the cut group 13 nitride single crystal 40 are ground and flattened, and then polished using diamond abrasive grains. Finally, CMP is performed, and the group 13 nitride single crystal having the c-plane as the main surface is obtained. Crystal 40 was obtained.

  Then, the dislocation density of the main surface of the group 13 nitride single crystal 40 (the + c surface in the seed crystal 30 substantially parallel to the crystal growth surface C) was evaluated using a CL (Cathode Luminescence) method. Observation was performed at a magnification at which one visual field of CL was about 100 μm × 100 μm larger, and the dislocation density was calculated from the number of dark spots of 100 μm × 100 μm. And the average value of the dislocation density of 10 visual fields at different positions on the main surface was calculated as the dislocation density of the produced group 13 nitride single crystal 40. The calculation results are shown in Table 1.

(Example 2 to Example 17, Comparative Example 1 to Comparative Example 13)
The combination of the seed crystal 30 or the comparative seed crystal to be used, the temperature rising rate in the temperature raising step, the presence / absence of stirring in the temperature raising step, the temperature lowering rate in the temperature lowering step, and the presence or absence of stirring in the temperature lowering step was changed to the combinations shown in Table 1. Except for the above, a group 13 nitride single crystal was produced in the same manner as in Example 1, and the crack and dislocation density were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1.

  As shown in Table 1, when the seed crystal 30 having a surface roughness Ra of the crystal growth surface C of 0.1 μm to 5 μm is used (Example 1 to Example 17), the surface roughness of the crystal growth surface C The dislocation density was small as compared with the case of using a comparative seed crystal in which Ra was outside this range (Comparative Examples 2, 4, 6, 8, 10, 12).

  Further, when a comparative seed crystal having a surface roughness Ra of the crystal growth surface C exceeding 5 μm is used (Comparative Examples 1, 3, 7, 9, 11, and 13), the crystal is larger than those of Examples 1 to 17. The evaluation of at least one of the pre-growth crack and the post-growth crack was the lowest evaluation “3”. That is, when a comparative seed crystal having a surface roughness Ra of the crystal growth surface C exceeding 5 μm is used (Comparative Examples 1, 3, 5, 7, 9, 11, 13), compared to Examples 1 to 17. The crack rate was high.

  Further, in Examples (Examples 1 to 17) using the seed crystal 30 having a surface roughness Ra of 0.1 μm or more and 5 μm or less on the crystal growth surface C, the rate of temperature increase is 70 ° C./hour to 130 ° C. In the examples (Examples 4 to 12) that are / hour, no occurrence of cracks before crystal growth was observed regardless of the presence or absence of stirring in the heating step. That is, the evaluation of cracks before crystal growth in these Examples (Examples 4 to 12) was an evaluation “1” indicating the best evaluation.

  Further, in Examples (Examples 1 to 17) in which the seed crystal 30 having a surface roughness Ra of the crystal growth surface C of 0.1 μm or more and 5 μm or less was used, the temperature rising rate was 135 ° C./hour to 150 ° C. Among the examples (Examples 1 to 3 and Examples 13 to 15) that are per hour, the examples (Examples 1 to 3) in which the stirring is “present” in the temperature raising step (Examples 1 to 3) Pre-cracking was not observed. That is, the evaluation of cracks before crystal growth in these examples (Examples 1 to 3) was an evaluation “1” indicating the best evaluation.

  On the other hand, in Examples (Examples 1 to 17) in which the seed crystal 30 having a surface roughness Ra of the crystal growth surface C of 0.1 μm or more and 5 μm or less is used, the rate of temperature increase is 135 ° C./hour to 150 ° C. / Examples (Examples 1 to 3 and Examples 13 to 15) that are stirring / hours, Examples (Examples 13 to 15) in which no stirring is performed in the temperature raising step (Examples 13 to 15) are comparative examples. Although the crack generation rate was low compared to, cracks before crystal growth occurred slightly. That is, the evaluation of cracks before crystal growth in these Examples (Examples 13 to 15) was an evaluation “2” indicating a moderate evaluation.

  Further, in Examples (Examples 1 to 17) in which the seed crystal 30 having a surface roughness Ra of the crystal growth surface C of 0.1 μm or more and 5 μm or less was used, the cooling rate was 50 ° C./hour or less. In the examples (Examples 7 to 9), no cracks were observed after crystal growth, despite no stirring in the temperature lowering step. That is, the evaluation of the crack after crystal growth in these examples (Examples 7 to 9) was evaluation “1” indicating the best evaluation.

  In Examples (Examples 1 to 17) in which the seed crystal 30 having a surface roughness Ra of the crystal growth surface C of 0.1 μm or more and 5 μm or less is used, the rate of temperature decrease is 100 ° C./hour or more and 150 ° C./hour. In Examples (Examples 1 to 3 and Examples 10 to 15) that were set to be less than or equal to the time, Examples 1 to 3 and Examples 10 to 12 of stirring “present” in the temperature lowering step were: The occurrence of cracks before crystal growth and cracks after crystal growth was suppressed as compared with Examples 13 to 15 where stirring was “none”.

  That is, as shown in Table 1, when the seed crystal 30 having a surface roughness Ra of the crystal growth surface C of 0.1 μm or more and 5 μm or less is used and at least one of the heating rate and the cooling rate is 150 ° C./hour It was confirmed that both crack reduction and dislocation density reduction were realized as compared with (Example 1 to Example 17) and Comparative Example (Comparative Examples 1 to 13).

  Further, in Example 1 to Example 17, when satisfying at least one of the stirring “present” in the temperature raising step or the stirring “present” in the temperature lowering step, the case of “no” stirring in the temperature raising step and the temperature lowering step It was confirmed that the crack can be further reduced as compared with the above.

30 seed crystal 32 group 13 nitride crystal 40 group 13 nitride single crystal

JP 2005-281677 A JP 2011-073894 A

Claims (8)

An arrangement step of arranging a seed crystal made of a group 13 nitride crystal and having a surface roughness Ra of a crystal growth surface of 0.1 μm or more and 5 μm or less and a raw material containing an alkali metal and a group 13 metal in a reaction vessel;
In a state where the raw material is melted to form a mixed melt, nitrogen is dissolved in the mixed melt, and a group 13 nitride crystal is grown on the seed crystal disposed in the mixed melt at a crystal growth temperature. A crystal growth process;
A temperature raising step of raising the temperature of the raw material to the crystal growth temperature at a temperature raising rate of 150 ° C./hour or less between the arrangement step and the crystal growth step, and 150 ° C./hour after the crystal growth step. At least one temperature adjustment step of lowering the temperature of the mixed melt at the following temperature drop rate;
A method for producing a group 13 nitride single crystal.   2. The group 13 nitride single crystal according to claim 1, wherein the crystal growth surface of the seed crystal includes a + c plane flat region and a convex region including a plurality of convex portions protruding from the flat region. Production method.   The temperature raising step raises the temperature to the crystal growth temperature at a temperature rise rate of 150 ° C./hour or less while stirring the mixed melt between the arrangement step and the crystal growth step. A method for producing a group 13 nitride single crystal according to claim 1 or 2.   4. The temperature lowering step, after the crystal growth step, lowers the temperature of the mixed melt at a temperature lowering rate of 150 ° C./hour or less while stirring the mixed melt. A method for producing a group 13 nitride single crystal as described in 1.   The said temperature increase rate is a manufacturing method of the group 13 nitride single crystal of any one of Claims 1-4 which is 100 degrees C / hr or less.   The method for producing a group 13 nitride single crystal according to any one of claims 1 to 5, wherein the temperature decrease rate is 100 ° C / hour or less.   The method for producing a group 13 nitride single crystal according to any one of claims 1 to 6, wherein a surface roughness Ra of the crystal growth surface of the seed crystal is 0.2 µm or more and 2.0 µm or less. . A reaction vessel holding a seed crystal made of a group 13 nitride crystal and having a surface roughness Ra of 0.1 μm or more and 5 μm or less on a crystal growth surface, and a raw material containing an alkali metal and a group 13 metal;
A supply unit for supplying nitrogen into the reaction vessel;
A heating unit for heating the reaction vessel;
In a state where the raw material is melted to form a mixed melt, nitrogen is dissolved in the mixed melt, and a group 13 nitride crystal is grown on the seed crystal disposed in the mixed melt at a crystal growth temperature. A crystal growth control for controlling the supply unit and the heating unit, a temperature increase control for increasing the temperature of the raw material to a crystal growth temperature at a temperature increase rate of 150 ° C./hour or less before the crystal growth control, and A control unit for performing temperature adjustment control for controlling the heating unit so as to perform temperature lowering control for lowering the temperature of the mixed melt at a temperature lowering rate of 150 ° C./hour or less after crystal growth control;
An apparatus for producing a group 13 nitride single crystal.