JP2017193465A - Method for producing group 13 element nitride crystal and seed crystal substrate - Google Patents

Abstract

The present invention provides a growth method capable of reducing the average tilt angle of a group 13 element nitride crystal when growing a group 13 element nitride crystal on an oriented polycrystalline sintered body.
A seed crystal layer 17 made of a group 13 element nitride and having a crystal growth surface 17a is provided on an oriented polycrystalline sintered body 11. At this time, a recess recessed from the crystal growth surface 17a is provided, and the surface 11a of the oriented polycrystalline sintered body 11 is exposed from the recess. Next, a group 13 element nitride crystal 19 is grown on the crystal growth surface.
[Selection] Figure 4

Description

  The present invention relates to a method for producing a group 13 element nitride crystal and a seed crystal substrate usable for the method.

  According to Patent Document 1, a laser lift-off method is disclosed in which a gallium nitride (GaN) layer is formed on a sapphire substrate and then the gallium nitride layer is irradiated with a laser to separate the gallium nitride layer from the sapphire substrate. .

  In Patent Document 2, when a gallium nitride layer is provided on a sapphire substrate, voids are generated along the interface between the sapphire substrate and the gallium nitride layer, and the difference in thermal expansion coefficient after growth by the flux method results in the gallium nitride layer. Discloses a method of naturally peeling off the sapphire from the sapphire substrate.

  However, since a sapphire substrate is expensive, Patent Document 3 discloses a growth method using a substrate made of an oriented polycrystalline sintered body. That is, an oriented alumina substrate which is a substrate obtained by sintering polycrystalline alumina and orienting the c-axis of alumina crystal particles in the normal direction of the substrate is prepared. A method for producing a GaN free-standing substrate in which a gallium nitride crystal is oriented in the c-axis direction by forming a gallium nitride crystal on the oriented alumina substrate is disclosed.

  In addition, in the patent document 4, the present applicant further proposed an oriented GaN free-standing substrate having an average inclination angle of 0.1 ° to 1 °.

  Further, according to Non-Patent Document 1, it is known that in InGaN crystal growth, the amount of In atoms taken in varies with the angle (tilt angle) between the c-plane of the GaN substrate and the substrate surface.

JP 2004-087775 A WO 2009/011407 WO 2014/192911 Japanese Patent Application No. 2016-034005

M. Krysko et al., “Correlation between luminescence and compositional striations in InGaN layers grown on miscut GaN substrates”, Applied Physics Letters, 91, 211904 (2007)

  However, the technique for growing GaN crystals on an oriented polycrystalline alumina sintered body still has the following problems. That is, if the average inclination angle of the oriented polycrystalline alumina sintered body is reduced to some extent, the production cost may increase. Further, the tilt angle of the oriented polycrystalline alumina sintered body also varies depending on manufacturing conditions. For this reason, the growth method which can further reduce the average inclination angle of the group 13 element nitride crystal grown on the oriented polycrystalline alumina sintered body is required.

  An object of the present invention is to provide a growth method capable of reducing the average inclination angle of a group 13 element nitride crystal when the group 13 element nitride crystal is grown on an oriented polycrystalline sintered body.

In the present invention, a seed crystal layer made of a group 13 element nitride and having a crystal growth surface is provided on an oriented polycrystalline sintered body, and at this time, a recess recessed from the crystal growth surface is provided. The present invention relates to a method for producing a group 13 element nitride crystal, comprising a step of exposing a surface of the bonded body; and a step of growing a group 13 element nitride crystal on a crystal growth surface.

  The present invention also comprises an oriented polycrystalline sintered body and a group 13 element nitride, and includes a seed crystal layer having a crystal growth surface, provided with a recess recessed from the crystal growth surface. The laminate is characterized in that the surface of the oriented polycrystalline sintered body is exposed.

  When the present inventors grow a group 13 element nitride crystal on an oriented polycrystalline sintered body, when providing a seed crystal layer, the inventor provides a recess recessed from the crystal growth surface of the seed crystal layer, and the orientation is formed from this recess. The surface of the polycrystalline sintered body was exposed. By providing the group 13 element nitride crystal on the seed crystal layer, the average tilt angle of the nitride crystal is reduced as compared with the case where the group 13 element nitride crystal is grown on the uniform seed crystal layer. The present invention has been found.

(A) is a schematic diagram showing a cross section in which a group 13 element nitride crystal layer 2 is formed on an oriented polycrystalline sintered body 1, and (b) is a plan view of the group 13 element nitride crystal layer 2. It is the seen schematic diagram. (A) is a schematic diagram showing an inclination angle distribution of single crystal particles in the oriented polycrystalline sintered body 11, and (b) is a group 13 element nitride film 15 on the surface 11 a of the oriented polycrystalline sintered body 11. , 16 are shown. (A) schematically shows a state in which the group 13 element nitride film 15 on the surface 13a of the single crystal particle 13 having a large tilt angle has been eliminated by sublimation, and (b) shows a single crystal particle having a small tilt angle. 14 shows a state in which the group 13 element nitride film 16 remaining on the surface 14a of 14 is used as a buffer layer, and a seed crystal layer 17 is provided on the buffer layer. (A) schematically shows a state in which the group 13 element nitride crystal 19 is grown on the seed crystal layer 17, and (b) shows a state in which the group 13 element nitride crystal 19 is separated from the substrate. In Example 1, the state which observed the surface of the seed crystal substrate with the laser microscope is shown. In Example 1, the phase map of GaN and alumina obtained by measuring the surface of the seed crystal substrate by the EBSD method is shown. In Example 2, the state which observed the surface of the seed crystal substrate with the laser microscope is shown. In Example 2, the phase map of GaN and alumina obtained by measuring the surface of the seed crystal substrate by the EBSD method is shown.

The present invention will be further described below with reference to the drawings as appropriate.
First, a typical example of the state of the group 13 element nitride crystal layer grown on the oriented polycrystalline sintered body will be described.

  As schematically shown in FIG. 1A, the oriented polycrystalline sintered body 1 is composed of a large number of single crystal particles 3, and there are grain boundaries 5 between adjacent single crystal particles 3. In the oriented polycrystalline sintered body, the crystal orientations of the single crystal particles 3 are not random and are aligned in a specific direction to some extent. That is, as shown in FIG. 1A, the crystal orientations A of the single crystal particles 3 are aligned to some extent. Preferably, single crystal particle 3 extends between first main surface 1a and second main surface 1b of the oriented polycrystalline sintered body. In this example, the first main surface 1a is a crystal growth surface.

  Next, the group 13 element nitride crystal layer 2 is epitaxially grown on the growth surface 1 a of the oriented polycrystalline sintered body 1. That is, the group 13 element nitride crystal layer 2 is grown so as to have a crystal orientation substantially following the crystal orientation of the oriented polycrystalline sintered body. 2b is a growth start surface of the crystal layer 2, and 2a is a surface of the crystal layer 2. The crystal layer 2 is composed of a large number of single crystal particles 4, and there are grain boundaries 6 between adjacent single crystal particles 4. In the crystal layer 2, the crystal orientation B of the single crystal particles 4 is not random, but generally follows the orientation A of each single crystal particle 3 constituting the oriented polycrystalline sintered body as a base.

  However, in the cross section shown in FIG. 1A, the crystal orientations B of the single crystal grains 4 constituting the group 13 element nitride crystal 2 are aligned, but the other crystal orientations of the single crystal grains 4 are aligned. You don't have to. That is, as shown in FIG. 1B, when each single crystal particle 4 is viewed planarly (from a direction parallel to the growth direction), the crystal orientations C and D are particularly random. Has no orientation. However, it is also possible to impart orientation to the crystal orientation of the single crystal particles 4 when viewed in plan.

  Here, in order to reduce the average inclination angle of the oriented polycrystalline alumina sintered body to a certain degree or more, the production cost may increase. Further, the tilt angle of the oriented polycrystalline sintered body also varies depending on manufacturing conditions. For example, in the example shown in FIG. 2A, the inclination angles of a large number of single crystal particles 13 and 14 constituting the oriented polycrystalline sintered body 11 vary. For example, it is assumed that single crystal particles 13 having a relatively large inclination angle and single crystal particles 14 having a relatively small inclination angle are arranged together. Arrows D and E are the crystal orientations of the single crystals constituting each single crystal particle. 11b is a bottom surface.

  When a seed crystal layer is grown on such an oriented polycrystalline sintered body 11 and further a group 13 element nitride crystal is further grown thereon, the tilt angle of the group 13 element nitride crystal is the orientation of the underlying oriented polycrystal sintered. Inheriting the inclination angle α of the knot, it was difficult to lower the average inclination angle, and the inclination angle was likely to vary.

  On the other hand, in the embodiment of the present invention, as shown in FIG. 3B, for example, group 13 element nitride films 15 and 16 are formed on the oriented polycrystalline sintered body 11. At this time, a group 13 element nitride film is formed on the surface 13a of each single crystal particle 13 and the surface 14a of the single crystal particle 14, but the group 13 element nitride film 15, depending on the inclination angle of the single crystal particle, The thickness of 16 changes. That is, the group 13 element nitride film 15 is thin on the single crystal particle 13 having a relatively large inclination angle α, and the film 16 is thicker than the film 15 on the single crystal particle 14 having a relatively small inclination angle α. Become.

  Here, when the laminate of FIG. 2B is heated in a reducing atmosphere, the group 13 element nitride films 15 and 16 are sublimated in order from the respective surfaces. Here, the group 13 element nitride film 15 disappears by sublimation, and the group 13 element nitride film 16 remains. Then, as shown in FIG. 3A, the buffer layer 16 remains on the single crystal particles 14, and the surface 13 a of the single crystal particles 13 is exposed from between the buffer layers 16.

  In this state, a seed crystal layer is formed on the buffer layer 16. As a result, as shown in FIG. 3B, the seed crystal layer 17 is formed on the film 16, and the surface 13 a of the single crystal particle 13 is exposed in the recess 23 between the seed crystal layers 17.

  Next, as shown in FIG. 4A, a group 13 element nitride crystal 19 is grown on the seed crystal layer 17. At this time, since the surface 13a of the single crystal particle 13 having a relatively large inclination angle is exposed, the group 13 element nitride crystal 19 is not grown on the single crystal particle 13, and a void 18 is generated. On the other hand, a group 13 element nitride grows on the seed crystal layer 17, and eventually grows in the horizontal direction and is connected in layers to form a group 13 element nitride crystal 19. The group 13 element nitride crystal 19 is composed of a large number of single crystal particles 21 connected in the horizontal direction. Reference numeral 20 denotes a grain boundary.

  At this time, since the inclination angle of the seed crystal layer 17 inherits the inclination angle of the single crystal particle 14, the inclination angle of the seed crystal layer 17 becomes close to the inclination angle of the single crystal particle 14. And since the inclination angle of each single crystal particle 21 of the group 13 element nitride crystal also takes over the inclination angle of the seed crystal layer 17, these inclination angles are close to each other. As a result, the average inclination angle of each single crystal particle 21 of the group 13 element nitride crystal is the inclination angle of the single crystal particle 14 having a small inclination angle among the single crystal particles 13 and 14 of the oriented polycrystalline sintered body 11. Will be taken over. That is, the orientation F of the single crystal particles in the group 13 element nitride crystal 19 inherits the orientation E of the single crystal particles in the oriented polycrystalline sintered body 11. As a result, the average inclination angle of each single crystal particle 21 constituting the group 13 element nitride crystal 19 can be reduced as compared with the average inclination angle of the oriented polycrystalline sintered body 11.

  Next, as shown in FIG. 4B, by separating the group 13 element nitride crystal 19 from the oriented polycrystalline sintered body 11, it is possible to obtain a self-supporting substrate of group 13 element nitride crystal.

Hereinafter, each component of the present invention will be further described.
(Oriented polycrystalline sintered body)
An oriented polycrystalline sintered body used as a base substrate has a growth surface and a bottom surface. The average inclination angle of the surface of the oriented polycrystalline sintered body is preferably 1 ° to 20 °, more preferably 3 ° to 12 °, from the viewpoint of forming voids.

  However, the inclination angle means an angle from the specific crystal orientation L of the crystal orientations D, E, and F of each single crystal particle measured on the target surface by the electron beam backscatter diffraction method (EBSD method). This indicates α in the case of a single crystal particle having the crystal orientation D shown in FIG. The specific crystal orientation L is normally a normal to the surface of the oriented polycrystalline sintered body 11. The average tilt angle is the average value of the tilt angles from the specific crystal orientation L of the crystal orientations D and E of each single crystal particle measured on the target surface by the EBSD method, or the crystal orientation of each single crystal particle. It means the average value of the tilt angle of F from the specific crystal orientation L.

  The thickness of the oriented polycrystalline sintered body is preferably 250 μm or more and 2 mm or less. By making this thickness 250 μm or more, handling during manufacture becomes easy. From this point of view, the thickness of the oriented polycrystalline sintered body is more preferably 300 μm or more.

  The material of the oriented polycrystalline sintered body is not particularly limited, but oriented polycrystalline alumina, oriented polycrystalline zinc oxide, or oriented polycrystalline aluminum nitride is preferable.

  The oriented polycrystalline sintered body is composed of a sintered body including a large number of single crystal particles, and a large number of single crystal particles are oriented to some extent or highly in a certain direction. By using the polycrystalline sintered body oriented in this way, it is possible to produce a free-standing substrate of a group 13 element nitride crystal having a crystal orientation substantially aligned in a substantially normal direction.

  As a manufacturing method for obtaining an oriented polycrystalline sintered body, in addition to a normal atmospheric pressure sintering method using an air furnace, a nitrogen atmosphere furnace, a hydrogen atmosphere furnace, etc., a hot isostatic pressing method (HIP), a hot press method (HP), pressure sintering methods such as spark plasma sintering (SPS), and a combination thereof can be used.

  The average particle size of the single crystal particles constituting the oriented polycrystalline sintered body on the sintered body surface is preferably 0.3 to 1000 μm, more preferably 3 to 1000 μm, still more preferably 10 μm to 200 μm, and particularly preferably. Is 14 μm to 200 μm.

  In addition, the average particle diameter in the plate | board surface of sintered compact particle | grains is measured by analysis software using EBSD method. OIM Data Analysis was used as analysis software.

  The orientation plane of the oriented polycrystalline sintered body is not particularly limited, and may be a c-plane, a-plane, r-plane, m-plane, or the like.

As a sintering aid for the oriented polycrystalline sintered body, oxides such as MgO, ZrO ₂ , Y ₂ O ₃ , CaO, SiO ₂ , TiO ₂ , Fe ₂ O ₃ , Mn ₂ O ₃ , La ₂ O ₃ , Examples thereof include at least one selected from fluorides such as AlF ₃ , MgF ₂ and YbF ₃ . From the viewpoint of translucency, the amount of the additive should be kept to the minimum necessary, and is preferably 5000 ppm or less, more preferably 1000 ppm or less, and still more preferably 700 ppm or less.
The oriented polycrystalline sintered body is preferably smoothed by lapping using diamond abrasive grains after the surface is flattened by grinding with a grindstone.

(Seed crystal layer)
In the present invention, a seed crystal layer made of a group 13 element nitride and having a crystal growth surface is provided, and a recess recessed from the crystal growth surface is provided. At this time, the surface of the oriented polycrystalline sintered body is exposed from the recess. For example, in the example of FIG. 3, the crystal growth surface 17 a is provided in the seed crystal layer 17, and the recess 23 is provided between the seed crystal layers 17. The surface 11a of the oriented polycrystalline sintered body 11 is exposed from the recess.

  In a preferred embodiment, for example, as shown in FIGS. 2 and 3, group 13 element nitride films 15 and 16 are provided on the surface 11 a of the oriented polycrystalline sintered body 11. Next, by heating the oriented polycrystalline sintered body 11 and the films 15 and 16 in a reducing atmosphere, a part of the group 13 element nitride film disappears by sublimation, and the buffer layer 16 made of the group 13 element nitride is formed. In addition, the surface 11 a of the oriented polycrystalline sintered body 11 is exposed between the buffer layers 16. Next, a seed crystal layer 17 is provided on the buffer layer 16.

The group 13 element nitride constituting the seed crystal layer and the group 13 element nitride film is a nitride of a group 13 element defined by IUPAC. Specifically, it is one or more nitrides of group 13 elements defined by IUPAC. This group 13 element is preferably gallium, aluminum, or indium. Further, Group 13 element nitride crystal, _{specifically, GaN, AlN, InN, Ga} x Al 1-x N (1>x> 0), Ga x In 1-x N (1>x> 0) _{, Ga x Al y InN 1-} x-y (1>x>0,1>y> 0) are preferable.

  Each planar pattern of the recess and the seed crystal layer is not particularly limited. In the group 13 element nitride crystal in which a part of the group 13 element nitride film is eliminated by sublimation by heating in a reducing atmosphere, these planar patterns are formed by a single crystal on the surface of the oriented polycrystalline sintered body. Since it depends on the distribution of the tilt angle of the particles, it becomes relatively random.

  When a group 13 element nitride film is formed on the oriented polycrystalline sintered body by MOCVD, when GaN, AlN, GaAlN is used as the material of the group 13 element nitride film, the film forming temperature is 500 to 600 ° C. Preferably, when InGaN is used, the temperature is preferably 500 to 750 ° C. Thereby, the film thickness of the group 13 element nitride film is likely to be thinner on the single crystal grains having a large tilt angle than on the single crystal grains having a small tilt angle. Therefore, a part (thin part) of the group 13 element nitride film can be easily lost by sublimation by heating in a reducing atmosphere thereafter.

  In a preferred embodiment, InGaN is used as the material of the group 13 element nitride film. In this case, there is a characteristic that the amount of In atoms taken into the group 13 element nitride film during epitaxial growth decreases as the single crystal grain has a larger tilt angle. As a result, the total amount of group 13 elements (Ga atoms and In atoms) in the nitride constituting the group 13 element nitride film is reduced. As a result, the thickness of the group 13 element nitride film is thin and the In composition is reduced. Formation of a low InGaN layer is promoted.

When GaN is used as the material of the group 13 element nitride film, the formation temperature is preferably 500 ° C. to 550 ° C., and it is particularly preferable to form in a hydrogen atmosphere. Further, the thickness of the group 13 element nitride film is preferably set to 4 nm to 8 nm in terms of the thickness when formed on the sapphire substrate.
The film thickness of the seed crystal film and the group 13 element nitride film on the oriented polycrystalline sintered body is the same on the sapphire substrate because the film thickness differs for each single crystal particle constituting the oriented polycrystalline sintered body. The film thickness when the film is produced under the film forming conditions is defined as “designed film thickness”.

  When AlN is used as the material of the group 13 element nitride film, the formation temperature is preferably 550 ° C. to 650 ° C. and is preferably formed in a hydrogen atmosphere. Further, the thickness of the group 13 element nitride film is preferably set to 4 nm to 8 nm in terms of the thickness when formed on the sapphire substrate.

  When InGaN is used as the material of the group 13 element nitride film, the formation temperature is preferably 500 ° C. to 750 ° C. and is preferably formed in a nitrogen atmosphere. The thickness of the group 13 element nitride film is particularly preferably set to 8 nm to 20 nm in terms of the thickness when formed on the sapphire substrate.

  In order to efficiently sublimate the group 13 element nitride film on the alumina single crystal particles having a relatively large tilt angle in the oriented polycrystalline sintered body, it is preferable to heat in a reducing atmosphere. Such a reducing atmosphere is preferably a hydrogen-containing atmosphere and may also contain an inert gas such as nitrogen gas.

In a preferred embodiment, after forming a group 13 element nitride film using a group 13 element source (trimethylgallium, trimethylaluminum, trimethylindium, etc.) and ammonia gas, the supply of the group 13 element source is stopped. The supply of ammonia gas and nitrogen gas is also stopped, and only the hydrogen gas atmosphere is provided. Next, after raising the temperature to the film formation temperature of the seed crystal film, before forming the seed crystal film, the substrate is held in a hydrogen gas atmosphere and a part of the group 13 element nitride film is sublimated. It is preferable. This sublimation temperature depends on the material,
1000-1200 degreeC is preferable and 1050-1150 degreeC is still more preferable. The time for this sublimation step is preferably 5 to 60 minutes.

  The method for producing the seed crystal layer is not particularly limited, but a vapor phase method such as MOCVD (metal organic chemical vapor deposition), MBE (molecular beam epitaxy), HVPE (halide vapor deposition), sputtering, Na flux method, etc. Preferred examples include liquid phase methods such as ammonothermal method, hydrothermal method and sol-gel method, powder method utilizing solid phase growth of powder, and combinations thereof.

(Growth of group 13 element nitride crystals)
Next, a group 13 element nitride crystal layer is formed on the seed crystal layer. This group 13 element nitride crystal layer is formed so as to have a crystal orientation substantially following the crystal orientation of the oriented polycrystalline sintered body. The method for forming the group 13 element nitride crystal layer is not particularly limited as long as it has a crystal orientation generally following the crystal orientation of the oriented polycrystalline sintered body, and is a gas phase method such as MOCVD or HVPE, a Na flux method, an ammono Preferable examples include a liquid phase method such as a thermal method, a hydrothermal method, a sol-gel method, a powder method using solid phase growth of powder, and a combination thereof, but the Na flux method is particularly preferable.

  The formation of a group 13 element nitride crystal by the Na flux method is performed using a crucible provided with a seed crystal substrate, such as a group 13 metal, metal Na, and optionally a dopant (eg, germanium (Ge), silicon (Si), oxygen (O), etc. filling an n-type dopant or a melt composition containing beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn), cadmium (Cd), etc. It is preferable to carry out by rotating while maintaining the temperature and pressure after raising the temperature and pressure to 830 to 910 ° C. and 3.5 to 4.5 MPa in a nitrogen atmosphere. The holding time varies depending on the target film thickness, but may be about 10 to 100 hours.

  Further, it is preferable to smooth the surface by lapping using diamond abrasive grains after grinding the GaN polycrystal thus obtained by the Na flux method with a grindstone to flatten the surface.

The nitride constituting the group 13 element nitride crystal is one or more types of nitrides of group 13 elements defined by IUPAC. This group 13 element is preferably gallium, aluminum, or indium. Further, Group 13 element nitride crystal, _{specifically, GaN, AlN, InN, Ga} x Al 1-x N (1>x> 0), Ga x In 1-x N (1>x> 0) _{, Ga x Al y InN 1-} x-y (1>x>0,1>y> 0) are preferable.

  The group 13 element nitride crystal layer may not contain a dopant. Alternatively, the group 13 element nitride crystal layer may be doped with an n-type dopant or a p-type dopant. Preferable examples of the p-type dopant include one or more selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), zinc (Zn), and cadmium (Cd). It is done. Preferable examples of the n-type dopant include one or more selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn), and oxygen (O).

  In a preferred embodiment, the average tilt angle on the surface of the group 13 element nitride crystal is smaller than the average tilt angle on the surface of the oriented polycrystalline sintered body. This average inclination angle is measured by the EBSD method as in the case of the above-mentioned oriented polycrystalline sintered body.

  According to the present invention, it is possible to grow a group 13 element nitride crystal having an average inclination angle reduced from the average inclination angle of the surface of the oriented polycrystalline sintered body on the oriented polycrystalline sintered body. . The group 13 element nitride crystal thus obtained can be used in an integrated form with the oriented polycrystalline sintered body. However, in a preferred embodiment, by separating the group 13 element nitride crystal from the oriented polycrystalline sintered body, a free-standing substrate including the group 13 element nitride crystal can be obtained.

(Separation of group 13 element nitride crystal from oriented polycrystalline sintered body)
In the method of the present invention, when the temperature is lowered after the growth of the group 13 element nitride crystal, natural peeling due to the generation of stress due to the difference in coefficient of thermal expansion can be caused. In this case as well, the bonding strength at the interface is low, so the group 13 Damage to element nitride crystals is unlikely to occur. However, since natural peeling is generally difficult to occur, it is preferable to employ another separation method. This is because, unlike the case of a void of several μm size produced at the interface with single crystal sapphire or single crystal GaN as in the method described in Patent Document 2, for example, it is about the size of a single crystal particle of an oriented polycrystalline sintered body. It is considered that the stress at the interface is relieved because the void of the size is formed.

  Furthermore, even if the method described in Patent Document 2 is applied to the case where a group 13 element nitride crystal is grown on an oriented polycrystalline sintered body, the effect of reducing the average tilt angle cannot be obtained.

  This separation method is not particularly limited. In a preferred embodiment, the oriented polycrystalline sintered body and the group 13 element nitride are separated by irradiating laser light from the oriented polycrystalline sintered body side.

  Unlike the sapphire substrate, the oriented polycrystalline sintered body scatters laser light at the grain boundaries inside the oriented polycrystalline sintered body when irradiated with laser light from the oriented polycrystalline sintered body side. The laser beam cannot be focused on the interface between the crystal and the group 13 element nitride crystal, and the density cannot be increased. For this reason, it was difficult to uniformly decompose the group 13 element nitride crystal at the interface, and there was a problem that breakage such as cracks or cracks occurred.

  On the other hand, in the present invention, since the voids are formed at the interface between the group 13 element nitride crystal and the oriented polycrystalline sintered body, the bonding strength is lowered. Therefore, even when the laser lift-off method is applied, the group 13 element nitride crystal Is easy to peel off. Furthermore, since the stress at the interface can be reduced, it is possible to reduce cracks and cracks during peeling.

  Alternatively, the group 13 element nitride crystal layer can be separated from the oriented polycrystalline sintered body by chemical etching. In the present invention, since a large number of voids 18 are formed at the interface between the oriented polycrystalline sintered body and the group 13 element nitride crystal layer, the etchant is easily impregnated along the interface through the void. Separation of the physical crystal layer can be promoted.

  As an etchant for performing chemical etching, a strong acid such as sulfuric acid or hydrochloric acid, or a strong alkali such as a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution is preferable. The temperature at which chemical etching is performed is preferably 70 ° C. or higher.

(Independent substrate)
A free-standing substrate can be obtained by separating the group 13 element nitride crystal from the oriented polycrystalline sintered body. In the present invention, the “self-supporting substrate” means a substrate that is not deformed or broken by its own weight when handled, can be handled as a solid, and is composed of a large number of Group 13 element single crystal particles. That is, the self-supporting substrate is composed of a large number of single crystal particles that are two-dimensionally connected in the horizontal plane direction, and therefore has a single crystal structure in a substantially normal direction. Therefore, the self-supporting substrate is not a single crystal as a whole, but has a single crystal structure in a local domain unit, and thus can have high crystallinity sufficient to ensure device characteristics such as a light emitting function. Nevertheless, the free standing substrate of the present invention is not a single crystal substrate.

  Preferably, a large number of single crystal particles constituting the self-standing substrate have crystal orientations that are substantially aligned in a substantially normal direction. “The crystal orientation that is generally aligned in the normal direction” is not necessarily the crystal orientation that is perfectly aligned in the normal direction. As long as a device using a self-supporting substrate can secure desired device characteristics, It means that the crystal orientation may be aligned to some extent in similar directions. In terms of the expression derived from the manufacturing method, the group 13 element nitride single crystal particles have a structure grown substantially following the crystal orientation of the oriented polycrystalline sintered body. The “structure grown substantially following the crystal orientation of the oriented polycrystalline sintered body” means a structure brought about by crystal growth affected by the crystal orientation of the oriented polycrystalline sintered body, and is not necessarily oriented. The crystal of the oriented polycrystalline sintered body is not necessarily a structure that has grown completely following the crystal orientation of the crystalline sintered body, as long as a device such as a light-emitting element using a self-supporting substrate can ensure the desired device characteristics. It may be a structure grown to some extent along the direction. That is, this structure includes a structure that grows in a different crystal orientation from the oriented polycrystalline sintered body. In that sense, the expression “a structure grown substantially following the crystal orientation” can also be rephrased as “a structure grown substantially derived from the crystal orientation”. This paraphrase and the above meaning are similar to those in this specification. The same applies to expression. Therefore, although such crystal growth is preferably by epitaxial growth, it is not limited to this, and various forms of crystal growth similar thereto may be used. In any case, by growing in this way, the free-standing substrate can have a structure in which the crystal orientations are substantially uniform with respect to the substantially normal direction.

  Therefore, this self-supporting substrate is regarded as an aggregate of columnar-structured single crystal particles that are observed as single crystals when viewed in the normal direction and grain boundaries are observed when viewed in a cut surface in the horizontal plane direction. It is also possible. Here, the “columnar structure” does not mean only a typical vertically long column shape, but includes various shapes such as a horizontally long shape, a trapezoidal shape, and a shape in which the trapezoid is inverted. Defined as meaning. However, as described above, the free-standing substrate may be a structure having a crystal orientation aligned to some extent in a normal line or a similar direction, and does not necessarily have a columnar structure in a strict sense. The reason for the columnar structure is that, as described above, a large number of single crystal grains grow while associating with adjacent single crystal grains while forming an interface under the influence of the crystal orientation of the oriented polycrystalline sintered body. it is conceivable that. For this reason, the average particle diameter of the cross section of the single crystal single crystal particles, which can be said to be a columnar structure (hereinafter referred to as the average cross section diameter) depends not only on the film forming conditions but also on the average particle diameter of the surface of the oriented polycrystalline sintered body. It is considered a thing.

  A large number of single crystal grains constituting the self-standing substrate are oriented in a specific crystal orientation in a substantially normal direction. The specific crystal orientation may be any crystal orientation (for example, c-plane, a-plane, etc.) that the group 13 element nitride may have. For example, when a large number of single crystal particles are oriented in the c-axis in a substantially normal direction, each constituent particle on the substrate surface has the c-axis directed in a substantially normal direction (that is, with the c-plane exposed to the substrate surface). ) Will be placed. A large number of single crystal particles constituting the self-standing substrate are oriented in a specific crystal orientation in a substantially normal direction, but each constituent particle is slightly inclined at various angles. That is, the substrate surface as a whole exhibits an orientation toward a predetermined specific crystal orientation in a substantially normal direction, but the crystal orientations of the single crystal grains are distributed at various angles from the specific crystal orientation. The crystal orientation of each single crystal particle can be evaluated by measurement by the EBSD method on the substrate surface as described above. That is, it is possible to observe the state in which the crystal orientation of each single crystal particle is distributed at various angles from the specific crystal orientation by the EBSD method, and the average inclination angle is 0 ° to 5 °. preferable.

  Preferably, the average cross-sectional diameter of the single crystal particles on the outermost surface of the self-supporting substrate is 0.3 μm or more, more preferably 3 μm or more, still more preferably 20 μm or more, particularly preferably 50 μm or more, and most preferably 70 μm or more. Moreover, the upper limit of the cross-sectional average diameter of the single crystal particles on the outermost surface of the self-supporting substrate is not particularly limited, but 1000 μm or less is realistic, more practically 500 μm or smaller, and more practically 200 μm or smaller. .

  The free-standing substrate preferably has a diameter of 50.8 mm (2 inches) or more, more preferably has a diameter of 100 mm (4 inches) or more, and more preferably has a diameter of 200 mm (8 inches) or more.

  There is no particular limitation on the structure of the light-emitting element using the self-standing substrate of the present invention and the manufacturing method thereof. Typically, a light-emitting element is manufactured by providing a light-emitting functional layer on a free-standing substrate, and the formation of the light-emitting functional layer has a substantially normal direction so as to have a crystal orientation that substantially follows the crystal orientation of the free-standing substrate. It is preferable to form one or more layers composed of a large number of semiconductor single crystal particles having a single crystal structure.

  The self-supporting substrate of the present invention can be preferably used for various applications such as various electronic devices, power devices, light receiving elements, solar cells as well as the above-described light emitting elements.

(Example 1)
According to the method described with reference to FIGS. 2 to 4, a free-standing substrate (oriented GaN free-standing substrate) made of GaN oriented in the c-axis direction was obtained.
(Preparation of substrate made of oriented alumina sintered body oriented in c-axis)
As a raw material, a plate-like alumina powder (manufactured by Kinsei Matec Co., Ltd., grade 00700) was prepared. 7 parts by weight of a binder (polyvinyl butyral: product number BM-2, manufactured by Sekisui Chemical Co., Ltd.) and a plasticizer (DOP: di (2-ethylhexyl) phthalate, Kurokin Kasei Co., Ltd.) per 100 parts by weight of the plate-like alumina particles (Manufactured) 3.5 parts by weight, a dispersant (Rheidol SP-O30, manufactured by Kao Corporation) 2 parts by weight, and a dispersion medium (2-ethylhexanol) were mixed. The amount of the dispersion medium was adjusted so that the slurry viscosity was 20000 cP. The slurry prepared as described above was formed into a sheet shape on a PET film by a doctor blade method so that the thickness after drying was 20 μm. The obtained tape was cut into a circular shape having a diameter of 50.8 mm (2 inches), and then 150 sheets were laminated and placed on an Al plate having a thickness of 10 mm, followed by vacuum packing. This vacuum pack was hydrostatically pressed in warm water at 85 ° C. at a pressure of 100 kgf / cm 2 to obtain a disk-shaped molded body.

  The obtained molded body was placed in a degreasing furnace and degreased at 600 ° C. for 10 hours. The obtained degreased body was fired in a nitrogen atmosphere at 1600 ° C. for 4 hours under a surface pressure of 200 kgf / cm 2 using a graphite mold. The obtained sintered body was fired again at 1700 ° C. for 2 hours in argon at a gas pressure of 1500 kgf / cm 2 by a hot pressure-pressing method (HIP).

  The sintered body thus obtained was fixed on a ceramic surface plate and ground to # 2000 using a grindstone to flatten the surface. Next, the surface was smoothed by lapping using diamond abrasive grains to obtain a substrate 1 made of an oriented alumina sintered body having a diameter of 50.8 mm (2 inches) and a thickness of 400 μm. The flatness was improved while gradually reducing the size of the abrasive grains from 3 μm to 0.5 μm. The surface roughness Ra after processing was 0.5 nm.

(Evaluation of substrate made of oriented alumina sintered body)
A substrate made of an oriented alumina sintered body was measured by the EBSD method. That is, a processed surface of a substrate made of an oriented alumina sintered body with a SEM (JEOL JSM-7001F) equipped with an electron beam backscatter diffraction (EBSD) apparatus (manufactured by TSL Solutions, OIM) has a field of view of 500 μm × 500 μm. Observed at. The conditions for this EBSD measurement were as follows.
<EBSD measurement conditions>
・ Acceleration voltage: 15 kV
Sample tilt angle: 70 °
・ Step width: 1.5μm

  From the measurement result by the EBSD method, the frequency distribution of the c-axis inclination angle, the average inclination angle and the average particle diameter of the surface constituent particles were calculated. In this calculation, analysis software OIM Data Analysis was used.

  As for each particle which comprises the board | substrate which consists of an oriented alumina sintered compact, c-axis was orientated in the normal line direction of the board | substrate in general. The inclination angle of each particle constituting the surface was a frequency distribution approximated to a Gaussian distribution, and the average inclination angle was 6 °. The average particle size was 40 μm.

(Group 13 element nitride film deposition and sublimation)
The substrate 11 made of this oriented alumina sintered body is placed on a susceptor in the MOCVD furnace, the temperature is raised to 1200 ° C. in a hydrogen atmosphere and cleaning is performed in a hydrogen atmosphere, and then the temperature is lowered to 500 ° C. Was used as a carrier gas, and TMG (trimethylgallium) and ammonia were used as raw materials, and a GaN layer corresponding to a design film thickness of 8 nm was formed as the group 13 element nitride films 15 and 16. Thereafter, the supply of TMG and ammonia gas was stopped, the substrate temperature was raised to 1100 ° C. using hydrogen as a carrier gas, and the system was kept in that state for 5 minutes, and the group 13 element nitride film 15 was eliminated by sublimation.

  Next, an n-type GaN layer is designed using the group 13 element nitride film 16 remaining on the surface 14a as a buffer layer, using hydrogen gas and nitrogen gas as carrier gases, TMG and ammonia as raw materials, and using silane gas as a dopant. A seed crystal substrate 22 shown in FIG. 3B was formed by forming a film corresponding to a thickness of 2 μm.

  The produced seed crystal substrate was taken out from the MOCVD furnace, and the surface was observed with a laser microscope. As a result, a large number of particles were formed on the flat substrate as shown in FIG. 5, and the cross-sectional shape between the arrows shown in FIG. As a result, the height of the particles was about 3 μm. In addition, when the surface of the seed crystal substrate was observed using the EBSD method and a phase map of GaN and alumina was created, the flat portion was not formed with GaN, the alumina was exposed, and the particles were in the form of islands. It was confirmed that the GaN layer 17 was formed (FIG. 6).

  As a result of calculating the average inclination angle by measurement by the EBSD method for each particle on GaN and alumina, the average inclination angle of the GaN particles in FIG. 6 is 3 °, and the average inclination of the alumina particles exposed between the GaN layers 17 is The angle was 8 °. Since the alumina particles were covered with the GaN layer at the place where the GaN layer was formed, the inclination angle of the alumina particles could not be measured, but when the GaN layer grew on the oriented alumina substrate, the growth was epitaxial, and the GaN layer Since the inclination angle is substantially the same as the inclination angle of the alumina particles, it is considered that a GaN layer having an average inclination angle of about 3 ° was formed on the alumina particles having an average inclination angle of about 3 °. On the other hand, it is considered that the group 13 element nitride film 15 formed on the alumina particles having an average inclination angle of 8 ° disappeared by sublimation.

(Growth of GaN crystals)
A GaN crystal 19 was grown on the seed crystal substrate 22 provided with the island-shaped GaN layer by a flux method. An alumina crucible is filled with 20 g of metal Ga and 40 g of metal Na. Further, this alumina crucible is sealed in a refractory metal growth vessel. The furnace temperature was 850 ° C., nitrogen gas was introduced, and the furnace pressure was 4 MPa. The GaN crystal 19 was grown on the seed crystal substrate 22 to a thickness of about 500 μm by holding the growth vessel for 20 hours while horizontally rotating in a heat-resistant and pressure-resistant crystal growth furnace. After cooling to room temperature, the substrate on which the GaN crystal was grown was taken out from the alumina crucible.

  The surface and back surface (peeled surface) of the taken-out thick film GaN crystal are flattened by polishing with diamond abrasive grains so as to have a thickness of 300 μm, and the oriented alumina substrate and the thick film GaN crystal are formed by a laser lift-off method. By separating, an oriented GaN free-standing substrate was obtained. No cracks or cracks were found on the free-standing substrate. Further, when the surface of the self-supporting substrate was measured by the EBSD method, an average inclination angle of 3 ° and a cross-sectional average diameter of 80 μm were obtained.

(Example 2)
The design film thickness of the group 13 element nitride films 15 and 16 made of GaN in Example 1 was changed to 4 nm. A seed crystal substrate 22 was produced in the same manner as in Example 1 except for this.

  When the surface of the obtained seed crystal substrate was observed with a laser microscope, a large number of particles were formed on the flat substrate as shown in FIG. 7, and the cross-sectional shape was acquired between the arrows shown in FIG. The height of the particles was about 6 μm. In addition, when the surface of the seed crystal substrate was observed using the EBSD method and a phase map of GaN and alumina was created, GaN was not formed on the flat portion, and the alumina particles were exposed, and the particles were island-shaped. It was confirmed that the GaN layer 17 was formed (FIG. 8).

  Subsequently, when an oriented GaN free-standing substrate was produced to a thickness of 300 μm by the flux method in the same manner as in Example 1, no cracks or cracks were found in the free-standing substrate. When the surface of the self-supporting substrate was measured by the EBSD method, an average inclination angle of 2 ° and a cross-sectional average diameter of 120 μm were obtained.

(Example 3)
The group 13 element nitride films 15 and 16 in Example 1 were formed of InGaN.
As a substrate made of an oriented alumina sintered body, a substrate having a diameter of 2 inches, a thickness of 400 μm, a surface roughness Ra of 0.5 nm, an average inclination angle of 6 °, and an average particle size of 40 μm was prepared.
The substrate made of this oriented alumina sintered body is placed on a susceptor in the MOCVD furnace, the substrate temperature is raised to 1200 ° C. in a hydrogen atmosphere and cleaning is performed in a hydrogen atmosphere, and the temperature is lowered to 700 ° C. Was used as a carrier gas, and TMG, TMI (trimethylindium), and ammonia were used as raw materials, and an InGaN layer having a designed film thickness of 10 nm was formed as the group 13 element nitride films 15 and 16. Thereafter, the substrate temperature was raised to 1100 ° C. using hydrogen as a carrier gas, and the substrate was kept in that state for 15 minutes, and the group 13 element nitride film 15 made of InGaN was eliminated by sublimation. Next, the InGaN layer remaining on the surface 14a is used as a group 13 element nitride film 16, an n-type GaN layer is grown to a thickness of 2 μm using TMG and ammonia as raw materials and silane gas as a dopant, and a seed crystal substrate 22 was produced.

  Using the obtained seed crystal substrate 22, an oriented GaN free-standing substrate was produced in the same manner as in Example 1. The average inclination angle of the surface was 2 °. In addition, no cracks or cracks were found on the self-supporting substrate.

  As described above, according to the present invention, it is possible to reduce the average inclination angle of the oriented GaN free-standing substrate, and it is possible to reduce the wavelength half width of the emission spectrum when the LED structure is formed thereon.

Claims (11)

On the oriented polycrystalline sintered body, a seed crystal layer made of a group 13 element nitride and having a crystal growth surface is provided. At this time, a recess recessed from the crystal growth surface is provided, and the oriented polycrystalline sintering is performed from the recess. A method for producing a group 13 element nitride crystal, comprising: a step of exposing a surface of a body; and a step of growing a group 13 element nitride crystal on the crystal growth surface. Providing a group 13 element nitride film on the surface of the oriented polycrystalline sintered body;
By heating the oriented polycrystalline sintered body and the group 13 element nitride film in a reducing atmosphere, a part of the group 13 element nitride film disappears by sublimation, and a buffer layer is provided and the buffer layer 2. The method according to claim 1, comprising: exposing the surface of the oriented polycrystalline sintered body in between; and providing the seed crystal layer on the buffer layer.   The method according to claim 2, wherein the reducing atmosphere is an atmosphere containing hydrogen.   The average inclination angle on the surface of the group 13 element nitride crystal is reduced more than the average inclination angle on the surface of the oriented polycrystalline sintered body. The method according to item.   The freestanding substrate containing the group 13 element nitride crystal is obtained by separating the group 13 element nitride crystal from the oriented polycrystalline sintered body. The method of claim.   6. The method according to claim 5, wherein the oriented polycrystalline sintered body and the group 13 element nitride crystal are separated by irradiating laser light from the oriented polycrystalline sintered body side.   The method according to claim 2, wherein the group 13 element nitride film is made of gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof.   The method according to claim 7, wherein the group 13 element nitride film is made of gallium indium nitride.   An oriented polycrystalline sintered body, and a seed crystal layer having a crystal growth surface, which is made of a group 13 element nitride, is provided with a recess recessed from the crystal growth surface, and the orientation polycrystal from the recess A seed crystal substrate, wherein the surface of the sintered body is exposed.   The seed crystal substrate according to claim 9, wherein the seed crystal layer is made of gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof. The seed crystal substrate according to claim 9 or 10, wherein an average tilt angle of the seed crystal layer is reduced from an average tilt angle of the surface of the oriented polycrystalline sintered body.

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