JP6639317B2 - Method for producing group 13 element nitride crystal and seed crystal substrate - Google Patents

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.

  Patent Literature 1 discloses a laser lift-off method 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 gallium nitride layer is formed by a difference in the coefficient of thermal expansion after growth by a flux method. A method of spontaneously peeling from a sapphire substrate is disclosed.

  However, since a sapphire substrate is expensive, Patent Document 3 discloses a growing method using a substrate made of an oriented polycrystalline sintered body. That is, an oriented alumina substrate is prepared by sintering polycrystalline alumina and orienting the c-axis of the alumina crystal particles in the normal direction of the substrate. A method is disclosed in which a gallium nitride crystal is formed on an oriented alumina substrate to produce a freestanding GaN substrate in which the gallium nitride crystal is oriented in the c-axis direction.

  Note that, in Patent Document 4, the present applicant further proposed an oriented GaN free-standing substrate having an average inclination angle of 0.1 ° to 1 °.

  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-A-2004-087775 WO 2009/011407 WO 2014/192911 Japanese Patent Application No. 2006-034005

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 technology for growing a GaN crystal 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 a certain degree or more, the production cost may increase. In addition, the inclination angle of the oriented polycrystalline alumina sintered body varies depending on the manufacturing conditions. For this reason, a growth method that can further reduce the average tilt 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 tilt angle of a Group 13 element nitride crystal when growing a Group 13 element nitride crystal on an oriented polycrystalline sintered body.

The present invention is directed to an oriented polycrystalline sintered body having a single crystal particle having a relatively large inclination angle and a single crystal particle having a relatively small inclination angle, comprising a Group 13 element nitride, and having a crystal growing surface. A seed crystal layer is provided, and at this time, a concave portion recessed from the crystal growth surface is provided, and when the surface of the oriented polycrystalline sintered body is exposed from the concave portion , the inclination angle is relatively small on the single crystal particles. further comprising the step of growing a and on the crystal growth surface group 13 element nitride crystal; in the seed crystal layer provided, the inclination angle is relatively large the single crystal particles Ru is exposed from the recess step The present invention relates to a method for producing a group 13 element nitride crystal.

Also, the present invention
An oriented polycrystalline sintered body having a single crystal particle having a relatively large inclination angle and a single crystal particle having a relatively small inclination angle , and a seed crystal layer comprising a group 13 element nitride and having a crystal growth surface. A seed crystal substrate ,
The seed crystal layer is provided with a concave portion that is depressed from the crystal growth surface , and the seed crystal layer is provided on the single crystal particles having a relatively small inclination angle, and the inclination angle is relatively small. The present invention relates to a seed crystal substrate in which the large single crystal particles are exposed from the recess .

  The present inventor, when growing a group 13 element nitride crystal on an oriented polycrystalline sintered body, when providing a seed crystal layer, provides a recess recessed from the crystal growth surface of the seed crystal layer, 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 a case where the group 13 element nitride crystal is grown on a uniform seed crystal layer. And reached the present invention.

(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 showing the group 13 element nitride crystal layer 2 in a plan view. FIG. (A) is a schematic diagram showing a tilt angle distribution of single crystal particles in the oriented polycrystalline sintered body 11, and (b) is a group 13 element nitride film 15 on a surface 11 a of the oriented polycrystalline sintered body 11. , 16 are provided. (A) schematically shows a state in which the group 13 element nitride film 15 on the surface 13a of the single crystal particle 13 with a large inclination angle has disappeared by sublimation, and (b) shows a single crystal particle with a small inclination angle. 14 shows a state in which a group 13 element nitride film 16 remaining on the surface 14a of the substrate 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 a 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. 4 shows a phase map of GaN and alumina obtained by measuring the surface of the seed crystal substrate by the EBSD method in Example 1. In Example 2, the state which observed the surface of the seed crystal substrate with the laser microscope is shown. 4 shows a phase map of GaN and alumina obtained by measuring the surface of a seed crystal substrate by the EBSD method in Example 2.

Hereinafter, the present invention will be further described with reference to the drawings as appropriate.
First, a typical example of a state of a group 13 element nitride crystal layer grown on an 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 is a grain boundary 5 between adjacent single crystal particles 3. In the oriented polycrystalline sintered body, the crystal orientation of the single crystal particles 3 is not random, but is aligned in a specific direction to some extent. That is, as shown in FIG. 1A, the crystal orientation A of each single crystal particle 3 is uniform to some extent. Preferably, single crystal particles 3 extend 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, a 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 similar to 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 grains 4, and there is a grain boundary 6 between adjacent single crystal grains 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 serving 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 uniform, but the other crystal orientations of the single crystal grains 4 are uniform. You don't have to. That is, as shown in FIG. 1B, when each single crystal particle 4 is viewed in a plane (from a direction parallel to the growth direction), the crystal orientations C and D are random, and Has no orientation. However, it is also possible to impart orientation to the crystal orientation of the single crystal particles 4 when viewed in a plan view.

  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. In addition, the inclination angle of the oriented polycrystalline sintered body varies depending on the 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. Arrows D and E indicate the crystal orientations of the single crystals constituting each single crystal particle, respectively. 11b is a bottom surface.

  When a seed crystal layer is grown on such an oriented polycrystalline sintered body 11 and a Group 13 element nitride crystal is further grown thereon, the inclination angle of the Group 13 element nitride crystal is set to the orientation polycrystalline firing of the base. Since the inclination angle α of the body is taken over, it is difficult to reduce the average inclination angle, and the inclination angle tends to vary.

  On the other hand, in the embodiment of the present invention, for example, as shown in FIG. 3B, the 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, and the group 13 element nitride film 15, 16 changes in thickness. That is, the group 13 element nitride film 15 becomes thinner on the single crystal grain 13 having a relatively large inclination angle α, and the film 16 becomes thicker than the film 15 on the single crystal grain 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 sublime in order from each surface. Here, the group 13 element nitride film 15 is made to disappear by sublimation, and the group 13 element nitride film 16 is left. 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, a 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 13 a 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 then grows in the horizontal direction and is connected in layers to generate a group 13 element nitride crystal 19. The group 13 element nitride crystal 19 is composed of a large number of single crystal grains 21 connected in the horizontal direction. 20 is a grain boundary.

  At this time, since the inclination angle of the seed crystal layer 17 takes over the inclination angle of the single crystal particles 14, the inclination angle of the seed crystal layer 17 is close to the inclination angle of the single crystal particles 14. Since the inclination angle of each single crystal particle 21 of the group 13 element nitride crystal also inherits the inclination angle of 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 single crystal particles 14 having a small inclination angle among single crystal particles 13 and 14 of 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 takes over 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 group 13 element nitride crystal 19 can be reduced as compared with the average inclination angle of 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 freestanding substrate of the group 13 element nitride crystal.

Hereinafter, each component of the present invention will be further described.
(Oriented polycrystalline sintered body)
The oriented polycrystalline sintered body used as the 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 tilt angle means the angle of the crystal orientations D, E, and F of each single crystal particle measured from the target surface by the electron beam back scattering diffraction method (EBSD method) from the specific crystal orientation L. 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 usually a normal to the surface of the oriented polycrystalline sintered body 11. The average tilt angle is an average value of the tilt angles of the crystal orientations D and E of each single crystal particle measured from the target surface by the EBSD method from the specific crystal orientation L, and the crystal orientation of each single crystal particle. It means the average value of the inclination angles of F from the specific crystal orientation L.

  It is preferable that the thickness of the oriented polycrystalline sintered body be 250 μm or more and 2 mm or less. By setting the thickness to 250 μm or more, handling during manufacture becomes easy. From this viewpoint, it is further preferable that the thickness of the oriented polycrystalline sintered body be 300 μm or more.

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

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

  As a 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), a pressure sintering method such as spark plasma sintering (SPS), or a combination thereof.

  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, further preferably 10 μm to 200 μm, and particularly preferably. Is 14 μm to 200 μm.

  The average particle diameter of the sintered body particles on the plate surface is measured by analysis software using the 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, or m-plane.

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 as sintering aids for the oriented polycrystalline sintered body; At least one selected from fluorides such as AlF ₃ , MgF ₂ , and YbF _{3 is} exemplified. From the viewpoint of translucency, the amount of the additive should be kept to a necessary minimum, and is preferably 5000 ppm or less, more preferably 1000 ppm or less, and further preferably 700 ppm or less.
It is preferable that the surface of the oriented polycrystalline sintered body is flattened by grinding with a grindstone, and then the surface is smoothed by lapping using diamond abrasive grains.

(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 concave portion which is 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, a crystal growth surface 17 a is provided on the seed crystal layer 17, and a concave portion 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 is eliminated by sublimation, and the buffer layer 16 made of the group 13 element nitride is removed. At the same time, 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 forming the seed crystal layer and the group 13 element nitride film is a group 13 element nitride specified by IUPAC. Specifically, it is a nitride of one or more of Group 13 elements defined by IUPAC. The 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 concave portion and the seed crystal layer is not particularly limited. In a group 13 element nitride crystal in which a part of the group 13 element nitride film disappears 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. It is relatively random because it depends on the distribution of the tilt angles of the particles.

  When a group 13 element nitride film is formed on an oriented polycrystalline sintered body by MOCVD, and when GaN, AlN, and GaAlN are used as the material of the group 13 element nitride film, the film forming temperature is set to 500 to 600 ° C. When InGaN is used, the temperature is preferably set to 500 to 750 ° C. Thereby, the film thickness of the group 13 element nitride film tends to be thinner on the single crystal particles having a large inclination angle than on the single crystal particles having a small inclination angle. Therefore, it becomes easy to remove a part (thin part) of the group 13 element nitride film 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 on the single crystal particle having a large inclination 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, and as a result, the thickness of the Group 13 element nitride film is reduced and the In composition is reduced. The formation of a low InGaN layer is promoted.

When GaN is used as the material of the group 13 element nitride film, it is particularly preferable to form the film at a temperature of 500 ° C. to 550 ° C. in a hydrogen atmosphere. It is desirable that the thickness of the group 13 element nitride film be set to 4 nm to 8 nm in terms of the thickness when formed on a sapphire substrate.
Note that the 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 thickness is different for each single crystal particle constituting the oriented polycrystalline sintered body. The film thickness when formed under the film forming conditions is referred to as “design film thickness”.

  When AlN is used as the material of the group 13 element nitride film, it is preferable to form the film in a hydrogen atmosphere at a temperature of 550 ° C. to 650 ° C. It is desirable that the thickness of the group 13 element nitride film be set to 4 nm to 8 nm in terms of the thickness when formed on a sapphire substrate.

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

  In order to efficiently sublimate the group 13 element nitride film on the alumina single crystal particles having a relatively large inclination 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 material (such as trimethylgallium, trimethylaluminum, and trimethylindium) and ammonia gas, the supply of the Group 13 element material is stopped. The supply of ammonia gas and nitrogen gas is also stopped, and only the hydrogen gas atmosphere is once used. Next, after raising the temperature to the seed crystal film forming temperature, before forming the seed crystal film, the substrate is held in a hydrogen gas atmosphere to partially sublimate a group 13 element nitride film. Is preferred. The temperature during this sublimation depends on the material,
1000-1200 ° C is preferred, and 1050-1150 ° C is more preferred. Further, the time of the sublimation step is preferably 5 to 60 minutes.

  The method of forming 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 phase epitaxy), sputtering, or a Na flux method Preferred examples include a liquid phase method such as an ammonothermal method, a hydrothermal method, and a sol-gel method, a powder method utilizing solid phase growth of powder, and a combination thereof.

(Growth of Group 13 element nitride crystal)
Next, a group 13 element nitride crystal layer is formed on the seed crystal layer. The 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 of forming the group 13 element nitride crystal layer is not particularly limited as long as it has a crystal orientation substantially similar to the crystal orientation of the oriented polycrystalline sintered body, such as a gas phase method such as MOCVD and HVPE, a Na flux method, A liquid phase method such as a thermal method, a hydrothermal method, and a sol-gel method, a powder method utilizing solid phase growth of powder, and a combination thereof are preferably exemplified, but the method is particularly preferably performed by a Na flux method.

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

  Also, it is preferable that the GaN polycrystal obtained by the Na flux method is ground with a grindstone to flatten the surface, and then the surface is smoothed by lapping using diamond abrasive grains.

The nitride constituting the Group 13 element nitride crystal is a nitride of one or more of Group 13 elements specified in IUPAC. The 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. Preferred 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). Can be Preferred 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 at the surface of the group 13 element nitride crystal is smaller than the average tilt angle at the surface of the oriented polycrystalline sintered body. This average inclination angle is measured by the EBSD method as in the case of the oriented polycrystalline sintered body described above.

  According to the present invention, it is possible to grow a group 13 element nitride crystal in which the average tilt angle is smaller than the average tilt 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 a form integrated with the oriented polycrystalline sintered body. However, in a preferred embodiment, a free-standing substrate containing a Group 13 element nitride crystal can be obtained by separating the Group 13 element nitride crystal from the oriented polycrystalline sintered body.

(Separation of Group 13 element nitride crystal from oriented polycrystalline sintered body)
In the method of the present invention, spontaneous peeling due to stress generation due to a difference in thermal expansion coefficient can be caused at the time of temperature decrease after growing the group 13 element nitride crystal. In this case, too, the bonding strength at the interface is low. The element nitride crystal is hardly damaged. However, in general, spontaneous peeling is unlikely to occur, so it is preferable to employ another separation method. This is because unlike the case of a void having a size of several μm produced at the interface with single-crystal sapphire or single-crystal GaN as in the method described in Patent Document 2, for example, the size of a single-crystal grain of an oriented polycrystalline sintered body is small. It is considered that the formation of voids of a size alleviates the stress at the interface.

  Furthermore, even if the method described in Patent Document 2 is applied to growing a Group 13 element nitride crystal 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 a laser beam from the oriented polycrystalline sintered body side.

  Unlike a sapphire substrate, an oriented polycrystalline sintered body is different from a sapphire substrate in that when laser light is irradiated from the oriented polycrystalline sintered body side, the laser light is scattered at grain boundaries inside the oriented polycrystalline sintered body. 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 is difficult to uniformly decompose the group 13 element nitride crystal at the interface, and there has been a problem of causing breakage such as cracks and cracks.

  On the other hand, in the present invention, since a void is formed at the interface between the Group 13 element nitride crystal and the oriented polycrystalline sintered body, the bonding strength is reduced. Therefore, even when the laser lift-off method is applied, the Group 13 element nitride crystal is used. Is easy to peel off. Further, since the stress at the interface can be reduced, cracks and cracks at the time of peeling can also be reduced.

  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 voids, and therefore the group 13 element nitride Separation of the material 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 an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution is preferable. The temperature at which the chemical etching is performed is preferably 70 ° C. or higher.

(Independent board)
A self-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 which 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 nitride single crystal particles. That is, the self-standing substrate is composed of a large number of single crystal particles connected two-dimensionally in the horizontal plane direction, and therefore has a single crystal structure in a substantially normal direction. Therefore, the self-standing substrate is not a single crystal as a whole, but has a single crystal structure in a local domain unit, and thus can have a sufficiently high crystallinity to secure device characteristics such as a light emitting function. Nevertheless, the freestanding 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 substantially aligned in a substantially normal direction. "A crystal orientation substantially aligned in a substantially normal direction" is not necessarily a crystal orientation completely aligned in a normal direction, and as long as a device using a free-standing substrate can secure desired device characteristics, the normal or This means that the crystal orientation may be somewhat uniform in a similar direction. 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 an oriented polycrystalline sintered body. The structure does not necessarily grow completely following the crystal orientation of the crystal sintered body. As long as a device such as a light emitting device using a self-standing substrate can secure desired device characteristics, the crystal of the oriented polycrystalline sintered body It may be a structure grown to some extent according to the orientation. That is, this structure includes a structure that grows in a crystal orientation different from that of the oriented polycrystalline sintered body. In that sense, the expression "structure grown substantially following the crystal orientation" can also be rephrased as "structure grown substantially derived from the crystal orientation". The same applies to expressions. Therefore, such crystal growth is preferably performed by epitaxial growth, but 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 self-standing substrate can have a structure in which the crystal orientations are substantially aligned in the substantially normal direction.

  Therefore, the self-supporting substrate is regarded as a single crystal when viewed in the normal direction, and as an aggregate of single crystal particles having a columnar structure in which a grain boundary is observed when viewed in a horizontal plane. It is also possible. Here, the term “columnar structure” does not only mean a typical vertical columnar shape, but includes various shapes such as a horizontally long shape, a trapezoidal shape, and a shape obtained by inverting a trapezoidal shape. Defined as meaning. However, as described above, the free-standing substrate may have a structure having a crystal orientation that is aligned to some extent in the direction of the normal or a similar direction, and does not necessarily have to be a columnar structure in a strict sense. As described above, the cause of the columnar structure is that a large number of single crystal particles grow while each forming an interface with an adjacent single crystal particle 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 size 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 cross section average diameter), depends on not only the film forming conditions but also the average particle size of the surface of the oriented polycrystalline sintered body. It is considered something.

  Many single crystal particles constituting the self-supporting 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 can have. For example, when a large number of single crystal particles are oriented along the c-axis in a substantially normal direction, each constituent particle on the substrate surface has the c-axis oriented substantially in the normal direction (ie, exposing the c-plane to the substrate surface). ). While a large number of single crystal particles constituting the self-supporting substrate are oriented in a specific crystal orientation in a substantially normal direction, the individual constituent particles are slightly inclined at various angles. In other words, the substrate surface as a whole exhibits an orientation in a substantially normal direction to a predetermined specific crystal orientation, but the crystal orientation of each single crystal grain is distributed at various angles from the specific crystal orientation. As described above, the crystal orientation of each single crystal particle can be evaluated by measuring the substrate surface by the EBSD method. That is, a state in which the crystal orientation of each single crystal grain is distributed at various angles from the specific crystal orientation can be observed by the EBSD method, and the average inclination angle is 0 ° to 5 °. preferable.

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

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

  The structure of a light-emitting element using the self-standing substrate of the present invention and a method for manufacturing the light-emitting element are not particularly limited. Typically, a light-emitting element is manufactured by providing a light-emitting functional layer on a self-supporting substrate, and the formation of the light-emitting functional layer is performed in a direction substantially normal to the self-standing substrate so as to have a crystal orientation substantially similar to that of the self-standing substrate. It is preferable to form at least one layer composed of a large number of semiconductor single crystal particles having a single crystal structure.

  The self-standing substrate of the present invention can be preferably used not only for the above-described light emitting element but also for various uses such as various electronic devices, power devices, light receiving elements, and solar cells.

(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.
(Production of Substrate Consisting of Oriented Alumina Sintered with c-Axis)
As a raw material, a plate-like alumina powder (grade 00110, manufactured by Kinsei Matech Co., Ltd.) 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 Chemical Co., Ltd.) are added to 100 parts by weight of the plate-like alumina particles. 3.5 parts by weight), 2 parts by weight of a dispersant (Reodol SP-O30, manufactured by Kao Corporation) and a dispersion medium (2-ethylhexanol) were mixed. The amount of the dispersion medium was adjusted so that the slurry viscosity became 20,000 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 thereafter, 150 sheets were laminated, placed on an Al plate having a thickness of 10 mm, and vacuum-packed. The vacuum pack was subjected to isostatic pressing in hot water of 85 ° C. at a pressure of 100 kgf / cm 2 to obtain a disk-shaped compact.

  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 press 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 in argon at 1700 ° C. for 2 hours under a gas pressure of 1500 kgf / cm 2 by a hot isostatic 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 oriented alumina sintered body having a diameter of 50.8 mm (2 inches) and a thickness of 400 μm. The flatness was improved while the size of the abrasive grains was gradually reduced 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)
The substrate made of the 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 was viewed in a 500 μm × 500 μm field by an SEM (JSM-7001F, manufactured by JEOL Ltd.) equipped with an electron backscatter diffraction (EBSD) device (OIM, manufactured by TSL Solutions). Was observed. Various conditions for this EBSD measurement were as follows.
<EBSD measurement conditions>
・ Acceleration voltage: 15 kV
・ Sample tilt angle: 70 °
・ Step width: 1.5 μm

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

  Each particle constituting the substrate made of the oriented alumina sintered body had a substantially c-axis oriented in the normal direction of the substrate. The inclination angle of each particle constituting the surface was a frequency distribution approximating a Gaussian distribution, and the average inclination angle was 6 °. Further, an average particle size of 40 μm was obtained.

(Formation and sublimation of Group 13 element nitride film)
The substrate 11 made of the oriented alumina sintered body is placed on a susceptor in a MOCVD furnace, the temperature is increased to 1200 ° C. in a hydrogen atmosphere, and a cleaning process is performed in a hydrogen atmosphere. Was used as a carrier gas, and TMG (trimethyl gallium) and ammonia were used as raw materials, and GaN layers were formed as Group 13 element nitride films 15 and 16 to a design film thickness of 8 nm. 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 on standby 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, hydrogen gas and nitrogen gas as carrier gases, TMG and ammonia as raw materials, and silane gas as a dopant. A seed crystal substrate 22 shown in FIG. 3B was formed by forming a film having a thickness of 2 μm.

  The prepared seed crystal substrate was taken out from the MOCVD furnace, and the surface was observed with a laser microscope. As shown in FIG. 5, a large number of particles were formed on the flat substrate, and the cross-sectional shape was defined between the arrows shown in FIG. As a result, the height of the particles was about 3 μm. 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 in the flat portion, alumina was exposed, and the particles were in an island shape. It was confirmed that the GaN layer 17 was formed (FIG. 6).

  As a result of calculating the average inclination angle of each particle on GaN and alumina by the EBSD method, the average inclination angle of the GaN particles in FIG. 6 is 3 °, and the average inclination angle of the alumina particles exposed from between the GaN layers 17 is 3 °. The angle was 8 °. At the position where the GaN layer was formed, the inclination angle of the alumina particles could not be measured because the alumina particles were covered by the GaN layer. However, when the GaN layer was grown on the oriented alumina substrate, the growth was epitaxial growth. Is almost 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 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 crystal)
On the seed crystal substrate 22 provided with the island-shaped GaN layer, a GaN crystal 19 was grown in a thick film 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 placed in a growth container made of a heat-resistant metal and hermetically sealed. The furnace temperature was set to 850 ° C., and nitrogen gas was introduced to set the furnace pressure to 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 container horizontally for 20 hours in a heat and pressure resistant crystal growth furnace. After cooling to room temperature, the substrate on which the GaN crystal had grown was taken out of the alumina crucible.

  The surface and the back surface (peeled surface) of the removed thick-film GaN crystal are flattened by polishing using diamond abrasive grains to have a thickness of 300 μm, and the oriented alumina substrate and the thick-film GaN crystal are separated by a laser lift-off method. By separation, an oriented GaN free-standing substrate was obtained. No cracks or cracks were found on the freestanding substrate. When the surface of the self-standing substrate was measured by the EBSD method, the average inclination angle was 3 ° and the average cross-sectional diameter was 80 μm.

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

  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 result of obtaining the cross-sectional shape between the arrows shown in FIG. The height of the particles was about 6 μm. 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 became island-shaped. It was confirmed that the GaN layer 17 was formed (FIG. 8).

  Next, when a free-standing oriented GaN substrate was formed 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, the average inclination angle was 2 ° and the average cross-sectional diameter was 120 μm.

(Example 3)
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 the oriented alumina sintered body is placed on a susceptor in a MOCVD furnace, the substrate temperature is increased to 1200 ° C. in a hydrogen atmosphere, and a cleaning process is performed in a hydrogen atmosphere. Was used as a carrier gas, and TMG, TMI (trimethylindium), and ammonia were used as raw materials, and an InGaN layer having a designed 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 system was kept on standby for 15 minutes, and the Group 13 element nitride film 15 made of InGaN was eliminated by sublimation. Next, using the InGaN layer remaining on the surface 14a as the 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 to form a seed crystal substrate. No. 22 was produced.

  Using the seed crystal substrate 22 thus obtained, an oriented GaN free-standing substrate was manufactured in the same manner as in Example 1. The average inclination angle of the surface was 2 °. No cracks or cracks were found on the freestanding 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 an LED structure is formed thereon.

Claims (13)

A seed crystal layer made of a Group 13 element nitride and having a crystal growth surface is formed on an oriented polycrystalline sintered body having a single crystal particle having a relatively large inclination angle and a single crystal particle having a relatively small inclination angle. Providing, at this time, a concave portion depressed from the crystal growth surface, and when exposing the surface of the oriented polycrystalline sintered body from the concave portion, the seed crystal is formed on the single crystal particles having a relatively small inclination angle. characterized by having a step of growing a and on the crystal growth surface group 13 element nitride crystal; the layer is provided, the inclination angle is relatively large the single crystal particles Ru is exposed from the recess step A method for producing a Group 13 element nitride crystal. A group 13 element nitride film is provided on the surface of the oriented polycrystalline sintered body, and at this time, the group 13 element nitride film is thick on the single crystal particles having a relatively small inclination angle, and the inclination angle is small. Thinning the group 13 element nitride film on the relatively large single crystal particles;
By removing the group 13 element nitride film on the single crystal particles having a relatively large tilt angle, a buffer layer is provided and the surface of the oriented polycrystalline sintered body is exposed between the buffer layers. Causing; and
Providing the seed crystal layer on the buffer layer
The method of claim 1, comprising: By heating the oriented polycrystalline sintered body and the group 13 element nitride film under a reducing atmosphere, a part of the group 13 element nitride film is eliminated by sublimation, and the buffer layer is provided. 3. The method according to claim 2 , wherein the surface of the oriented polycrystalline sintered body is exposed during the step. The method according to claim 3 , wherein the reducing atmosphere is an atmosphere containing hydrogen. The average tilt angle on the surface of the group 13 element nitride crystal is made smaller than the average tilt angle on the surface of the oriented polycrystalline sintered body, The method according to any one of claims 1 to 4 , wherein The method described in the section. The self-standing 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 according to any one of Claims 1 to 5 , The method according to claim. The method according to claim 6 , wherein the oriented polycrystalline sintered body and the group 13 element nitride crystal are separated by irradiating a laser beam from the oriented polycrystalline sintered body side. 5. 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 . 9. The method according to claim 8 , wherein said Group 13 element nitride film comprises gallium indium nitride. An oriented polycrystalline sintered body having a single crystal particle having a relatively large inclination angle and a single crystal particle having a relatively small inclination angle , and a seed crystal layer comprising a group 13 element nitride and having a crystal growth surface. A seed crystal substrate ,
The seed crystal layer is provided with a concave portion that is depressed from the crystal growth surface , and the seed crystal layer is provided on the single crystal particles having a relatively small inclination angle, and the inclination angle is relatively small. A seed crystal substrate, wherein the large single crystal particles are exposed from the recess . The seed crystal substrate according to claim 10, further comprising a buffer layer made of a Group 13 element nitride between the single crystal particle having a relatively small tilt angle and the seed crystal layer . The seed crystal substrate according to claim 10 , wherein the seed crystal layer is made of gallium nitride, aluminum nitride, indium nitride, or a mixed crystal thereof . The average tilt angle of the seed crystal layer is smaller than the average tilt angle of the surface of the oriented polycrystalline sintered body, The claim according to any one of claims 10 to 12 , wherein. Seed crystal substrate.

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