JP4182935B2 - Method for growing gallium nitride crystal and method for manufacturing gallium nitride substrate - Google Patents

Description

  The present invention relates to a crystal growth method of gallium nitride used as a substrate of a light emitting device such as a blue light emitting diode (LED) or a blue semiconductor laser (LD) made of a group 3-5 nitride compound semiconductor. Further, the present invention relates to a gallium nitride crystal used for a substrate of a blue light emitting device such as a light emitting diode or a semiconductor laser.

  Light emitting devices using nitride-based semiconductors have already been put into practical use, including blue LEDs. Most blue light emitting devices using nitride semiconductors still use sapphire as a substrate. On the sapphire substrate, nitride semiconductor GaN, InGaN, and AlGaN layers are grown to produce blue-blue-green LEDs and LDs using InGaAs as an active layer. Sapphire is a chemically stable substrate and is suitable as a substrate for light emitting devices. The lattice misfit between gallium nitride and sapphire is large. However, this does not mean that defects will multiply due to dislocations. The device is stable. One is an excellent characteristic of sapphire, and the other is that in the case of an LED, the current density is low, so that deterioration such as defect growth is difficult to proceed.

  Sapphire substrates also have drawbacks. That is, there is no cleavage, an insulator, and a large mismatch.

  In the case of an InGaN-based light emitting diode fabricated on a sapphire substrate, the sapphire wafer is mechanically diced and cut into chips. Since sapphire is not cleaved, yield was low and cost was high. In the case of a blue semiconductor laser, it cannot be said that the resonator surface is a cleavage plane. It was a problem in terms of quality, such as the characteristics of a semiconductor laser that could easily make the resonator surface.

  Since the sapphire is an insulating substrate, it is not possible to provide an n-electrode on the bottom surface of the substrate like ordinary LEDs and LDs. After depositing an epi layer of n-type p-type GaN or InGaN, a part is etched to expose a part of the n-type GaN film, which is used as an n-electrode. It is necessary to connect the lead pin and the n electrode by wire bonding. Since current flows in the lateral direction, the n-type GaN film must be thick. For this reason, the number of processes and the process time increase, resulting in high costs.

  Since the p-electrode and n-electrode are taken out from the upper surface, the chip area must be increased. That also raised the cost.

When a nitride thin film is laminated on a sapphire substrate, there is a problem that defects such as a large number of dislocations are generated in the epi layer due to lattice mismatch. It is said that a dislocation density as high as about 10 ⁹ to 10 ¹⁰ cm ⁻² exists in a GaN epilayer produced on a sapphire substrate that is currently commercially available. The same high density of dislocation density is seen even in a GaN-based epilayer using a SiC substrate having a smaller lattice mismatch than sapphire, and there seems to be no significant difference.

  However, this high density dislocation density is hardly a problem in the case of a light emitting diode (LED). This is because defects do not multiply from there. In the case of a semiconductor laser (LD) with a high current density, defects may grow from dislocations, which is considered to be a cause of limiting the life of the semiconductor laser. Sapphire substrates are still mainstream as substrates for blue and ultraviolet light emitting devices (LEDs, LDs).

  Nevertheless, the present inventor considers that the most ideal substrate of the GaN-based light emitting device is a gallium nitride (GaN) substrate.

  If a high-quality GaN single crystal substrate is obtained, the problem of lattice mismatch with epilayers such as GaN, InGaN, and AlGaN does not occur.

  Unlike sapphire, gallium nitride has a clear cleavage. When cutting chips, they can be cut cleanly by natural cleavage. This makes it possible to manufacture a semiconductor laser resonator with high yield.

  Since gallium nitride can be doped, a conductive n-type substrate can be made by doping an n-type impurity. Then, the bottom can be made an n electrode. An n electrode can be formed on the lower surface and a p electrode can be formed on the upper surface. Since the upper and lower electrodes are provided, the chip size can be reduced. Moreover, one wire bonding process can be reduced.

  As such, a gallium nitride single crystal substrate is desired. However, there is still no technology for producing a large, high-quality single crystal gallium nitride substrate.

  It is said that crystallization from a liquid phase in an equilibrium state is possible in an environment of ultra high pressure and high temperature. However, it is not practical because only a small amount of small crystal grains can be produced.

  On the other hand, the present inventor attempted a method of obtaining a single substrate of gallium nitride by thickly vapor-phase-growing a gallium nitride layer on an underlying substrate of a different material and then removing the underlying substrate. It has been.

  Vapor phase growth of gallium nitride (GaN) is a technique originally used for growing a GaN thin film of about 0.1 μm to 2 μm on a sapphire substrate. It is still used for InGaN, GaN, and AlGaN thin film growth. The MOCVD method is the mainstream. In this method, a reaction product is laminated on a sapphire substrate by reacting an organometallic Ga and ammonia in a gas phase and reacting them on heated sapphire. Doping can be easily performed by adding an organometallic gas as a dopant.

  Further, when a GaN thin film is grown on a sapphire substrate, the dislocation density increases. Therefore, a method called epitaxial lateral overgrowth (ELO) is sometimes used to reduce the dislocation density. This is a device that attaches the mask to the substrate and grows in the horizontal direction on the mask so that the growth in the horizontal direction collides and changes the growth direction from the horizontal direction to the vertical direction, reducing the dislocation density at that time. is there. As a result of thin film growth, when the thickness is as thin as about 0.1 μm to 0.5 μm, the growth direction is changed to reduce dislocations, and thereafter growth is performed with a C-plane. Originally, this is a technique for reducing the dislocation density of the thin film.

However, the GaN substrate by the C-plane growth method still has a high dislocation density (about 10 ¹⁰ cm ⁻² ). A nitride-based thin film is laminated thereon, but when the substrate itself has a large number of dislocation densities, a large number of defects starting from the original dislocations are inherited by the epilayer. Therefore, if the substrate itself is not of high quality, a good light emitting device cannot be made on it. ELO originally reduces dislocations in thin films (about 0.1 μm to 1 μm) and is not very effective for thick substrates (several hundred μm). Even if dislocations decrease primarily in the early stages of growth, they increase thereafter.

  Therefore, the present inventor further researched for the purpose of manufacturing a GaN substrate having a low dislocation density. Patent Document 4 proposes a new and excellent gallium nitride crystal growth method that should be called a facet growth method. It is completely different from the conventional C-plane growth. The inventor has created a three-dimensional facet structure on the crystal surface, for example, creating a structure in which a large number of pits composed of inverted hexagonal pyramid facets are arranged, and maintaining the pits without embedding them. The vapor phase growth is continued, and the dislocation density is effectively reduced by sweeping the dislocations to the bottom of the pits by normal growth of the inclined surface of the facet.

  On the average, it grows in the C-axis direction, but the surface includes many facet surfaces that are not C-planes. It can be called the facet growth method. This will be described with reference to FIGS. FIG. 1A is a partially enlarged perspective view including pits on the surface of a gallium nitride crystal 4 grown with a three-dimensional facet. There are also flat portions 7 (C-plane growth portions) on the surface of the crystal 4, but there are a large number of inverted hexagonal pyramid pits 5. Six faces of the pit 5 are facet faces 6. This is often the {11-22} plane. Although the average growth direction is upward (c-axis direction (0001)), dislocations existing in the facet plane that grows in the normal direction of the facet 6 are inclined toward the ridgeline 8 because the inclined surface rises in the normal direction. Move to. The dislocation slides further down the ridgeline 8 and accumulates at the bottom of the pit 5. Here, {...} is a comprehensive expression of a surface, (...) is an individual expression of a surface, <...> is a comprehensive expression of a direction, and [...] is an individual expression of a direction. FIG. 2 is a plan view of a pit, which is a projection of dislocation movement on a horizontal plane. When growing while maintaining the facet 6, the dislocation moves to the ridgeline 8, and further travels along the ridgeline 8 to gather at the central multiple point D.

  The three-dimensional facet structure may be an inverted 12-pyramidal pit. Many of these facet planes 6 are {11-22} planes and {1-101} planes. The facet growth method creates a large number of these facet pits 5 and continues the growth without embedding them. As the crystal grows, the facet surface 6 also lifts upward. Then, the dislocation existing on the facet plane 6 moves in a direction in which the normal of the facet plane is projected onto the C plane. In other words, dislocations are collected under the ridgeline and in the center of the pit.

Those accumulated under the ridgeline are six surface defects 10 (FIG. 1B). What gathers at the bottom of the pit becomes a linear defect 11. The dislocations swept up are collected in linear defects (dislocation aggregate bundle) 11 and planar defects 10. In this way, a large number of dislocations gather and gather at the defects 10 and 11 at the center of the pit. Since dislocations that have been dispersed to people are swept up to the bottom of the pit, the dislocation density in the other parts decreases. The part where the dislocations at the bottom of the pit gather is called the dislocation gathering part. This is a method having an excellent effect of reducing dislocations in other portions. This is the facet growth method described in Patent Document 4 by the present inventor. This is an extremely innovative method. Unlike ELO, dislocations do not collide and reduce only at the initial stage of growth. Since the dislocation continues to be collected at the bottom of the pit (linear defect 11, planar defect 10) throughout the growth, the effect continues. The degree of reduction in dislocation density is high, and the dislocation density in other parts may be reduced to about 10 ⁻⁵ to 10 ⁻⁷ .

  This facet growth method was an excellent new method, but it still proved problematic. The disadvantages of the facet growth method of Patent Document 4 will be clarified with reference to FIGS. FIG. 3 (1) shows the dislocations collected in the linear dislocation gathering portion 11 at the bottom of the pit 5 by facet growth.

(1) As the GaN film grows thicker, dislocations once gathered at the dislocation gathering portion 11 (linear dislocation gathering portion) at the center of the facet pit 6 begin to spread. As shown in FIG. 3B, dislocations 13 tend to be distributed and spread from the bottom of the pit. That is, the linear dislocation gathering portion 11 does not have a force to permanently restrain the dislocation. Therefore, the dislocation density in the peripheral part cannot be further reduced. When the haze-like dislocation spread 13 expands toward the facet growth portion, the dislocation at that portion increases again.

(2) The generation position of the pits 5 composed of facets is random. Dominated by chance. It cannot be actively controlled. The position of the dislocation aggregate bundle 11 where the dislocations are concentrated is also random and cannot be determined in advance. Where can pit 5 be made? That is controlled by chance. Probabilistic. If it is necessary to avoid dislocation density concentrating parts when making a device, it is inconvenient that the location of facet pits is random. Where are the pits and dislocations gathered? It is better to decide in advance. These new challenges have emerged in the facet growth method. In order to solve these problems, the present inventor considered the following devices.

  The present inventors have found that dislocation haze 13 occurs from the bottom of the pit even if the dislocation is concentrated at the center bottom of the pit consisting of facets (linear dislocation gathering portion 11). I guessed that it was because the repulsive force was exerted between the dislocations just by staying temporarily, and when the growth further progressed, it began to disperse and spread like a haze. It is not possible to keep the dislocations collected once by simply maintaining the facets and growing them.

  Therefore, the present inventor newly created a dot mask facet growth method shown in Patent Document 6. In this method, a dot mask is formed so that isolated circular and rectangular covering portions are regularly arranged at a pitch p on a base substrate, and gallium nitride is epitaxially grown thereon.

  This will be described with reference to FIG. A mask (covering portion) 23 is formed on the base substrate 21. Crystal growth starts immediately at the underlying substrate exposed portion 29, and a thin film is laminated. Growth on the covering 23 is delayed, and a facet 26 is generated at the boundary. Since the covering portion 23 is formed in a dot shape, a pit 25 composed of facets 26 is always formed around the covering portion 23. A defect accumulation region H is formed on the covering portion 23. The portion Z that grows following the facet surface 26 of the exposed portion becomes a single crystal, but the dislocations that originally existed gather at the bottom of the pits 25, so the portion Z that facet grows becomes low dislocations. Since the facet growth region exists with H, it is also referred to as a single crystal low dislocation associated region Z. Since the entire portion Z cannot be covered with the geometrically faceted portion Z, the portion Y where the C-plane (27) grows remains. The C-plane growth region Y is also low in dislocation because the dislocation is attracted to the facet region. The region that cannot be completely covered with Z is also referred to as a single crystal low dislocation residual region Y. Thus

Immediately above the mask covering portion = defect collecting region H
Single crystal low dislocation-accompanying zone Z
C-plane growth part = single crystal low dislocation residual region Y

This is a gallium nitride substrate having a composite structure. In the facet growth method of Patent Document 4, there is only a distinction between a part where defects are gathered and another part, but in Patent Document 5, a part that is facet grown (other than a single crystal low dislocation accompaniment). It was recognized for the first time that there was a region Z) and a C-plane grown portion (single crystal low dislocation residual region Y). In other words, it became clear for the first time that there were three distinct parts instead of two parts. And the cylindrical body which extended the peripheral part of the mask upwards becomes a boundary of H and Z, and it becomes a crystal grain boundary K. Dislocations are collected in the defect gathering region H and the crystal grain boundary K, where they partially disappear and the rest are trapped and are not dispersed again. The haze-like spread 13 is thereby eliminated. Such a clear dislocation annihilation trapping mechanism was created by the defect gathering region H and the grain boundary K.

  As described above, in Patent Document 5, a mask is formed on a base substrate in advance and a defect collecting region H is formed on the mask. Therefore, the position of the linear dislocation collecting portion 11 that collects dislocations in Patent Document 4 is determined. become. This also determines the positions of the low dislocation single crystal regions Z and Y at the same time. Dislocation restraint is permanent and no haze redispersion occurs. In Japanese Patent Laid-Open No. 2004-228561, a mask is attached to create a positioned defect assembly region H in place of the unstable dislocation assembly portion 11, thereby making the dislocation capture permanent. This is a significant improvement over the facet growth method of Patent Document 5, which was controlled by chance and allowed dislocation redispersion.

  In Patent Document 6, a mask having parallel-line-shaped covering portions is formed on a base substrate, and gallium nitride is facet grown. Since the mask is parallel lines, it is convenient when manufacturing a device such as a semiconductor laser.

  Patent Document 7 is an application claiming the priority of Patent Document 5 of the Dodd Mask Facet Growth Method. Patent Document 8 is an application claiming the priority of Patent Document 6 of the stripe mask facet growth method.

JP 2001-102307 A Japanese Patent Application 2001-284323 (dot) Japanese Patent Application No. 2001-284323 (Stripe) JP, 2003-165799, A Japanese Patent Application No. 2002-230925 Japanese Patent Application Laid-Open No. 2003-183100 Japanese Patent Application No. 2002-269387

  The mask facet growth method in which the mask 23 is attached to the base substrate 21 and facet growth is performed thereon is an excellent method. Unlike the ELO mask, what can be formed on the covering portion (H region) and the exposed portion (Z, Y) is different in the first place. The H region in which dislocations are concentrated is uniquely determined by the mask position. The dislocation once collected by the H region is permanently restrained. Dislocation haze 13 is not possible.

  However, it has been found that such a precise method still has problems. This means that the identity of the defect gathering region H formed on the mask is not clearly determined. The defect assembly region H may be polycrystalline, may be a single crystal whose crystal orientation is slightly inclined in the positive direction, or may be a single crystal whose crystal orientation is slightly inclined in the negative direction (near 180 degrees). is there.

  It is a problem that the essence of the defect gathering region H is indefinitely diverse. Gallium nitride has different properties in the c-axis direction and the a-axis, b-axis, and d-axis (represented by four axes) directions. The coefficient of thermal expansion is also greatly different between the c-axis direction and the a-axis direction. In the vapor phase growth method, the c-axis shrinkage and the a-axis shrinkage are quite different because they are grown at a high temperature of 1000 ° C. and cooled to room temperature. Since the temperature changes as much as 1000 ° C., even if there is a slight difference in thermal expansion coefficient, the difference in thermal expansion coefficient in the c-axis and a-axis directions (thermal expansion coefficient anisotropy) causes a large stress.

  If the defect assembly region H is polycrystalline, the coefficient of thermal expansion becomes an average value. Therefore, the anisotropy of the thermal expansion coefficient between the defect assembly region H and the surrounding low defect single crystal region Z is different. Therefore, when cooled, a strong internal stress is generated and microcracks are generated. If the base substrate is removed, the gallium nitride crystal will fall apart or it will break easily.

  When the defect gathering region H is a single crystal whose axis is inclined in the positive direction, the orientation is different from that of the surrounding low-defect single crystal region Z, so that stress is also generated due to a temperature change and a crack is generated. Even if a bent gallium nitride substrate is made, it breaks and cannot be used.

  The same is true when the defect gathering region H is a single crystal whose axis is inclined in the negative direction, and the anisotropy of the thermal expansion coefficient becomes inconsistent inside and outside, and cracks are generated.

  It is necessary to match the thermal expansion coefficient anisotropy between the defect assembly region H and the single crystal low dislocation region Z. In order to do so, the orientation must be either completely matched or fully reversed. In other words, single crystals with different axial directions always cause a crack due to a difference in thermal expansion anisotropy.

  If the orientations of the defect assembly region H and the low defect single crystal region Z match, the thermal expansion coefficient anisotropy matches, and no cracks are generated. That's fine, but if it is, the whole becomes a single crystal and there is no discontinuity at the boundary, so it is impossible to capture and collect dislocations permanently. Unable to prevent haze re-diffusion.

  The boundary must confine the dislocations and close the space where the dislocations are concentrated. In order to make the thermal expansion coefficient anisotropy coincident and to give some discontinuity to the boundary, there is no other way than the orientation of the defect assembly region H and the single crystal low dislocation region Z are reversed. If both H and Z are single crystals and their orientations are reversed, it is obvious that there is a defect at the boundary. Nevertheless, since the thermal expansion coefficient anisotropy of the a-axis and c-axis coincides, even if the temperature changes at 1000 ° C., the difference in thermal expansion coefficient does not become apparent. That is, the a-axis, b-axis, d-axis, and c-axis of the low defect single crystal region Z become the -a-axis, -b-axis, -d-axis, and -c-axis of the defect assembly region H (FIG. 15). Since the coefficient of thermal expansion is the same in both the a-axis direction and the -a-axis direction, the anisotropy is completely consistent.

  When the orientation is reversed, there is always a grain boundary at the boundary. If there is a grain boundary, the dislocation can be permanently captured and constrained. For this reason, it can be understood that the defect gathering region H formed on the mask covering portion must be reversed in order not to generate cracks.

  However, in the techniques of Patent Documents 5 to 8, the defect collecting region H is not constant because it becomes polycrystalline, becomes a tilted single crystal, or has a reversed orientation.

  A more advanced technique that always generates a defect gathering region H having a reverse orientation is desired. An object of the present invention is to provide a growth method for forming a defect assembly region H whose orientation is always reversed on a mask in the mask facet method.

  The present inventor has realized that the closed defect gathering region H must have a reversal orientation different from the surrounding by 180 degrees so that cracks do not occur due to the anisotropy of the thermal expansion coefficient. However, the growth of the closed defect gathering region H is not determined and the reversal orientation is not obtained only by growing while holding the facet. When the crystal is grown with the mask attached to the base substrate in advance, the position of the closed defect gathering region H is determined, but it is not in the reverse orientation. Even if it becomes a polycrystal or a single crystal, it is often inclined at an angle, and cracks cannot be prevented. The fact that the azimuth is inverted 180 degrees is sometimes referred to as azimuth inversion or polarity inversion in this specification.

  The inventor thoroughly analyzed the difference between the case where the closed defect gathering region H was not in the reverse orientation and the case where the closed defect gathering region H was in the reverse orientation. And we were able to elucidate the mechanism of the orientation inversion region.

  The present inventors examined many experimental results and found that the reversal orientation was formed in the closed defect gathering region H only when a specific phenomenon occurred at the beginning of growth.

In the reversal orientation area, the reversal orientation crystal is generated in the shape of a lateral protrusion from the vicinity of the lower part of the inclined surface near the boundary between the mask covering portion and the exposed portion, and merges on the mask covering portion to cover the covering portion. Inverted crystals grow on the seeds. From the vicinity of the lower part of the slope rising from the boundary between the mask covering part and the exposed part, a large number of inversion-oriented crystals are suddenly generated in a protruding shape. Such a unique phenomenon occurs. Reversal orientations already exist in the projections, and they are combined and joined together, and those extending from both sides of the mask covering part are joined together to form a seed crystal with a reverse orientation directly above the covering part. It is. Naturally, what grows on the reverse orientation seed crystal becomes a defect assembly region H of reverse orientation.
When such a protrusion does not occur and the crystal grows in the lateral direction while contacting the mask covering portion, the inversion orientation cannot be performed. It will be the same as ELO.

  The inventors of the present invention have studied the conditions of the mask covering portion and the exposed portion, the crystal growth conditions, the progress of crystal growth, and the like using a scanning electron microscope or the like. As a result, it has been found that the following conditions are necessary to stably form the orientation inversion region on the mask covering portion.

(1) The mask material is a material that inhibits epitaxial growth.

(2) The lateral progress of the gallium nitride crystal grown on the covering portion is held for a relatively long time while being damped at the edge of the mask. At that time, the inclined surface blocked at the edge of the mask is often the {11-22} plane. The facet surface is widened because it is dammed up at the edge of the mask and does not cover the mask. With such a wide facet, the following phenomenon occurs:

(3) Projections such as claws begin to protrude in places from the facet surfaces that are prevented from advancing in the lateral direction at the edge of the mask. The protrusion is an azimuth reversal region in which the azimuth is reversed by 180 degrees with respect to other portions. This is important, and protrusions occur above the mask rather than riding on the mask as in ELO.

(4) The number of inversion-oriented protrusions that have started to be formed increases and the growth proceeds, and each increases.

(5) The claw-like projections having the reverse orientation are facet surfaces having a low inclination angle on the upper surface and are {11-2-6} or {11-2-5} surfaces. The lower surface of the protrusion is floating from the mask and is not in contact with the mask. The lower surface of the protrusion is parallel to the facing facet, but the normal direction is opposite and is an antiparallel surface. However, the face index is {11-21}. This is because the direction is reversed.

(6) A plurality of protrusions extend from the periphery of the mask or from both sides to the upper part of the mask and merge at the center of the mask. The merged result is an orientation reversal region.

(7) The bumped portion grows thick with an inversion orientation with a lattice mismatch boundary (K '). A crystal grain boundary (K) associated with the orientation inversion is formed between the normal orientation region and the reverse orientation region where the facet growth is performed.

(8) Since gallium nitride is grown while maintaining the facet, dislocations are collected toward the center of the facet butt by the facet slope. The collected dislocations partially disappear, and the rest are trapped and restrained by the orientation inversion region H, the surrounding crystal grain boundaries (K), and the crystal grain boundaries (K ′) due to mismatch. The dislocations in the other normal orientation parts are significantly reduced. The part (H, K, K ′) where the dislocation density gathers can be determined in advance. The portion (Z, Y) that becomes low dislocation can also be determined in advance.

  In the gallium nitride crystal grown by such a mechanism, it was confirmed that the inversion orientation region clearly exists on the mask, and that the crystal orientation is inverted throughout. Since the defect gathering region H having the reverse orientation is surrounded by the single crystal having the positive orientation, the anisotropies of the thermal expansion coefficients are matched inside and outside. Therefore, cracks do not occur even when there is a temperature change, and a high yield and low dislocation high quality gallium nitride substrate can be manufactured. Although it is not a single crystal, it has a wide range of low dislocation single crystal parts (Z).

  As described above, the azimuth inversion region of the present invention is generated from the middle of the inclined facet surface extending from the end of the covering portion, and is stretched and united to form an azimuth inversion portion above the mask and associated with the mask in a non-contact position. Then, since it grows upward as a seed crystal, a region having an inverted orientation is formed above the mask covering portion. That is, the defect gathering region H formed on the mask has a reverse orientation. Such a phenomenon is new and has not yet been known in Patent Documents 5 to 8 of the present inventors.

  In the present invention, the defect gathering region H formed on the mask can always be an orientation-reversed single crystal. Since the azimuth is only rotated 180 degrees from the other portions, the thermal expansion coefficient has the same anisotropy. Even if the temperature change from the temperature during growth (about 1000 ° C.) to room temperature is large, the thermal expansion coefficient anisotropy does not change and the generation of internal stress is small. For this reason, even if the base substrate is taken, it is not separated and cracks do not occur when the substrate is used. Since there is no crack, it can be obtained as a stable free-standing substrate. A large-sized gallium nitride substrate that has not existed so far can be manufactured with high yield.

The mask facet inversion orientation growth method of the present invention will be described with reference to FIG.
As shown in FIG. 5A, a mask covering portion 63 is provided on the base substrate 61 by CVD, sputtering, or the like. The mask inhibits epitaxial growth. The mask may be in the form of isolated dots or parallel line stripes. The covering part 63 and the exposed part 69 can be distinguished. Gallium nitride is vapor-phase grown at a low temperature (300 ° C. to 700 ° C.).

  The polycrystalline GaN fine particles 70 adhere to both the exposed portion 69 and the covering portion 63. This is important. When grown at a high temperature, GaN is not attached to the coating portion, but polycrystalline particles 70 are attached to the coating portion because of the low temperature. The polycrystalline fine particles 70 play an important role in forming the reversal orientation on the facet plane.

  In FIG. 5B, the epitaxial growth is performed at a high temperature (900 ° C. to 1200 ° C.). A thin film of (0001) single crystal 64 of GaN grows on the exposed portion. However, gallium nitride is not deposited on the mask covering portion 63. Therefore, inclined surfaces are formed on both sides of the covering portion. It is a facet 66 with a low Miller index, often the {11-22} plane. In the case of a stripe mask, the mask is formed in the <1-100> direction so that the {11-22} plane appears on the inclined surface. In the case of a dot mask, it is an inverted hexagonal pyramid pit consisting of a {11-22} plane. Although referred to as {11-22} plane, this is a comprehensive expression that includes six individual planes.

  A C-plane growth region Y that grows with a flat surface 67 is formed outside the facet growth region. It depends on the shape of the mask. In the case of a stripe mask, it can be narrowed, but in the case of a dot mask, the C-plane growth portion Y may occupy a considerable area. Since the mask blocking force is strong and crystals do not easily accumulate on the covering portion 63, the area of the facet surface 66 is considerably widened.

  As shown in FIG. 5 (3), a large number of claw-like protrusions 68 are generated inward from the widened facet surface 66. The protrusion 68 has an inverted orientation and is a (000-1) single crystal. The upper surface of the protrusion 68 is a gently inclined surface, and the lower surface of the protrusion 68 is parallel to the inclination of the facing facet 66 and opposite in direction. The left facet surface is A, the upper surface of the left protrusion is B, the lower surface is C, the right facet surface is D, the upper surface of the right protrusion is E, and the lower surface is F.

A (11-22) D (-1-122)
B (-1-12-6) E (11-2-6)
C (-1-122) F (11-22)

It becomes. The reason why A = F and D = C although they are antiparallel is that B, C, E, and F are direction-inverted (FIG. 15). The reason why the fourth index of the upward surfaces B and E is negative is also due to the direction reversal. The protrusion 68 is not in contact with the covering portion 63 and is floating. This is because minute polycrystal 70 exists in the covering portion, which prevents contact.

  As shown in FIG. 5 (4), the protrusion 68 extending from the facet 66 further extends. Many protrusions 68 are generated and each extends toward the center. Do not touch the mask 63 while stretching.

  The protrusions 68 and 68 extending opposite to each other are united at the central portion. As shown in FIG. 5 (5), the merged portion becomes a crystal grain boundary K 'due to lattice mismatch. Combined to form a gently inclined cone (in the case of dots) or V-groove (in the case of stripes). The portion that grows on the protrusion uniting portion becomes a double-inclined cone or V-groove. The protrusions are originally inverted in orientation to become (000-1), and an orientation inversion crystal grows on the seed crystal as a seed crystal. That is the defect gathering region H. The internal grain boundary K 'also grows. Since the crystal grain boundary K ′ fluctuates left and right, it is not always at the center of the mask.

  The facet grown portion becomes a single crystal with a normal orientation (0001) and low dislocations. That is the single crystal low dislocation region Z. The C-plane grown portion is a single crystal low dislocation residual region Y. There are thus three areas. This is the same as in Patent Documents 5 to 8, but in the present invention, the defect gathering region H always has a reverse orientation. A grain boundary K is generated between the defect assembly region H and the single crystal low dislocation region Z by inversion. The crystal grain boundary K has the effect of annihilating and capturing the collected dislocations.

  FIG. 6 is a perspective view of a part of a crystal showing a state after growth when a dot mask is formed on a base substrate and gallium nitride is grown by the method of the present invention. There is a gallium nitride crystal 64 epitaxially grown on the base substrate 61. Many pits with inverted hexagonal pyramids can be seen. The bottom corresponds to the position of the dot mask. A portion under the facet 66 is a low defect single crystal region Z. Below the flat part (C plane (0001)) without pits is the C plane growth region Y. These three regions H, Z, and Y are greatly different physically, optically, and chemically.

FIG. 9 is a perspective view showing a state after growth when a stripe mask is formed on a base substrate and gallium nitride is grown by the method of the present invention. There is a gallium nitride crystal 64 epitaxially grown on the base substrate 61. The gallium nitride crystal 64 shows a parallel mountain-valley structure. The bottom of the valley corresponds to the position of the stripe mask 63. Between the mask and the valley is an orientation reversal defect assembly region H. There are facets 66 on both sides of the valley. A portion under the facet 66 is a low defect single crystal region Z. In this case, there is no C-plane growth portion Y. As will be described later, the C-plane growth portion Y has a high electrical resistance, and when a light emitting element is manufactured, it may be better not to have a Y region. By skillfully adjusting the facet growth conditions, the facet 66 can be enlarged and the Y region can be made zero. FIG. 9 shows such a case. The ridgeline of the mountain is sharp. In that case, ... HZHZ ... a repeating structure.
Some stripe masks have a C-plane growth region Y. This is shown in FIG. There is a C-plane growth region Y between the single crystal low dislocation associated regions Z and Z. The ridgeline of the mountain becomes flat. In this case, a repetitive structure of... HZYZHZYZ.
In the case of a dot mask and a stripe mask, these three regions H, Z and Y are greatly different physically, optically and chemically.

In order for the azimuth reversal protrusion to protrude from the facet plane, the mask edge must prevent the crystals from climbing up until the facet plane is sufficiently wide.
When crystal growth of gallium nitride is stopped at the edge of the mask (covering portion), the facet surface of gallium nitride is often the {11-22} plane.
At this time, when the crystal is prevented from stretching in the lateral direction by the facet surface {11-22}, the polycrystalline particles of gallium nitride are isolated on the mask (covering portion). . The polycrystalline fine particles seem to suppress the lateral movement of the crystal onto the mask.

  Why does the reversal of the protrusion protrude from the facet surface? I'm still not sure. Details are unknown. The presence of polycrystalline fine particles on the mask seems to play an important role. It appears that the polycrystalline particles on the mask have an inducing effect on the appearance of inversion oriented crystals.

  The essence of the present invention is that, in epitaxial growth of gallium nitride, a mask having an action of inhibiting epitaxial growth is provided on a base substrate in the form of dots (isolated dots) or stripes (parallel lines), and an exposed portion and a covering portion In this case, the positively oriented (0001) single crystal gallium nitride is grown on the exposed portion, but the mask covering portion prevents the growth of the gallium nitride film, and at the beginning of the growth, a thick crystal is formed only in the exposed portion, The facet surface extends from the mask edge (boundary) to the exposed part, the facet surface widens, and from the opposite facet surface, the protrusions that float from the mask and start to reverse are extended, and the protrusions cover the mask. The reversal orientation crystal is formed as a seed crystal, and a reversal orientation region is formed above the mask covering portion, and the reversal orientation crystal is formed on the covering portion. Position single crystal generates a positive orientation, over time transfer onto the crystal inversion orientations simultaneously, produce crystals of complex gallium nitride. A grain boundary K is generated between the orientation inversion region and the positive orientation region due to the orientation inversion. This grain boundary K has an effect of restraining dislocations by disappearance.

  The base substrate may be used as it is. A composite in which a gallium nitride thin film is previously grown may be used as the base substrate. A mask is formed on the GaN / substrate composite as a base substrate.

  Since the facet grows in the normal direction without embedding the facet surface, the dislocations existing on the facet surface and its adjacent parts move toward the bottom of the facet surface and move between the mask cover and the exposed part. It reaches the boundary. There is the crystal grain boundary K described above, and the crystal grain boundary K captures dislocations and partially eliminates them. Restrain the remaining dislocations so that they do not dissipate again. Thus, the crystal grain boundary K is prevented from re-emission 13 (FIG. 3 (2)) of haze-like dislocations. Dislocations are also accumulated inside the orientation inversion crystal H. Therefore, the direction inversion region can also be referred to as a defect assembly region H. Since dislocations are concentrated here, dislocations in other parts can be reduced.

  The crystal grown on the exposed portion is a single crystal of (0001) positive orientation. Its upper surface is a Ga surface. The crystal H that grows on the covering portion is a single crystal whose orientation is reversed (000-1). Its upper surface is a nitrogen surface.

  The gallium nitride formed on the exposed portion and in the vicinity of the covering portion grows with a facet surface so that the facet surface does not disappear during the growth.

  The facet plane is a {11-22} plane facet in the case of a stripe mask. In this way, the mask is formed in parallel lines in the <1-100> direction (FIGS. 9 and 10).

  In the case of a dot mask, the {11-22} plane appears naturally with the covering portion as the bottom, and an inverted hexagonal pyramid (funnel-shaped) pit is formed around it (FIG. 6). Even though the {11-22} plane has three-fold symmetry, it includes six individual planes. An inverted 12-pyramid may appear around the mask. They are {11-22} plane and {1-101} plane. The inclination of these surfaces is about 55 ° to 65 ° and is strong. The portion that grows as the facet plane is called a facet growth region Z.

  Protrusions with a reverse orientation from the facets are generated laterally. The upper surface of the protrusion whose direction has been reversed has a gentler slope than the slope of the facet region Z. It has an inclination of 25 ° to 35 ° with respect to the horizontal. It is a {11-2-5} plane, a {11-2-6} plane, or a facet plane tilted slightly (within 5 °).

  The lower surface of the orientation reversal protrusion has the same inclination as the opposing facet surface, which is the {11-22} plane (FIG. 15). The reason why the mirror index is the same even though the orientation of the surface is opposite is because the orientation is reversed.

  Protrusions with reversed orientations merge on the cover, but even though the orientations are reversed, they occur separately on the slope of the facet surface, so the orientations may slightly differ . Due to the discrepancy between the directions, the inverted azimuth protrusion extends from both sides and bridges, and when they are joined, there is a case where there is a mismatch at the joint. The mismatch generates a grain boundary K ′. The crystal grain boundary K ′ is formed in the middle of the orientation inversion region H. This is different from the peripheral grain boundary K. The causes that occur are also different. As the reversal orientation grows, the crystal grain boundary K 'also grows upward.

  The mask formed first may be a dot mask in which a large number of isolated points are periodically arranged, or may be a stripe mask in which a covering portion and an exposed portion are formed on parallel lines.

  In the case of a dot mask, the dot may be any circle, rectangle or the like, but the diameter d is preferably about 5 μm to 100 μm. The pitch of the periodic array is in the range of p = 100 μm to 1000 μm, and preferably about p = 300 μm to 500 μm.

  In the case of a stripe mask, the width of the wide covering portion is set to w = 5 μm to 100 μm. The pitch is about p = 100 μm to 1000 μm. The exposed portion width is about s = 200 μm to 400 μm.

  In the case of a dot mask, a portion where no facet can exist between the facet growth regions Z and Z remains. It is a flat C-plane growth region Y. Both the C-plane growth region Y and the facet growth region have the same orientation and are single crystals, but have different electrical, optical, and chemical properties. Therefore, the part that has grown on the exposed part should be considered in two (Z, Y). Therefore, it becomes a repeating structure of ... HZYZH ....

  Also in the case of a stripe mask, there may be a C-plane growth region Y where no facet exists between the facet growth regions Z and Z. In that case, the structure is ... HZYZH. However, since the mask is a parallel line, the C-plane growth region Y is not always formed. The Y region can be erased by expanding the facet growth region. In that case, a structure without Y such as... HZHZH.

  In order to generate the protrusions with the reverse orientation, it seems that the condition that fine polycrystalline particles are distributed in advance on the mask is necessary.

Mask material _{is, SiO 2, SiN, Al 2} O 3, AlN, ZrO 2, Y 2 O 3, MgO and the like are suitable.

  As the base substrate, sapphire, Si, SiC, MgO, ZnO, GaAs, InP, GaP, GaN, AlN single crystal, or the like is suitable.

  Alternatively, a thin GaN thin film may be grown on a single crystal such as sapphire, Si, SiC, MgO, ZnO, GaAs, InP, GaP, GaN, or AlN, and the surface may be coated with GaN.

  The gallium nitride thus obtained is not a single crystal but consists of three distinct regions. The definition and properties of these areas are described below. Some of the properties have not yet been described, so we will elaborate later.

  Defect gathering region H: Inversion orientation region. Grows from crystals with protrusions combined. Can be formed on the cover. (000-1) single crystal. Contains a lot of oxygen. Electrical resistance is low.

  Low defect single crystal region Z: A region formed in a faceted portion. A portion adjacent to the covering portion can be formed on the exposed portion. Also referred to as single crystal low dislocation associated region Z or facet growth region Z. It contains a lot of oxygen and has a low electrical resistance.

  Single crystal low dislocation residual region Y: A region formed in a C-plane grown portion. It always occurs in the case of a dot mask. In the case of a stripe mask, it may or may not exist. Also referred to as C-plane growth region Y. Does not contain much oxygen. Electrical resistance is high. Contains a lot of carbon.

  A crystal grain boundary K is formed between H and Z, and a crystal grain boundary K ′ is formed inside H. This is also important.

  The grain boundary K at the boundary is formed between H / Z because the direction is reversed. The dislocations gathered by facet growth are captured and partly disappeared, and the rest are restrained.

  Internal crystal grain boundary K '... is a crystal grain boundary formed at the center of the defect gathering region H due to misalignment of protrusions, and it grows with growth, but it may move to the edge of the defect gathering region H and fluctuate left and right.

  Gallium nitride is transparent and cannot be distinguished by the naked eye. There is no difference even with an optical microscope. It can be distinguished by fluorescence microscope and cathodoluminescence (CL).

  The present invention can be implemented by adopting a parallel line (stripe) mask or an isolated dot (dot) mask. A device using a stripe mask will be described as a first embodiment, and a device using a dot mask will be described as a second embodiment.

[Example 1 (stripe mask pattern)]
A 2-inch diameter sapphire substrate (S1), a GaAs substrate (S2), and a sapphire substrate (S3) in which a gallium nitride film having a thickness of 1.5 μm was previously epitaxially grown by MOCVD were prepared as the base substrate. The sapphire substrate (S1) has a C surface as a main surface. The main surface of the GaAs substrate (S2) is the (111) A plane. The (111) A plane is the Ga plane, and the (111) B plane is the As plane. The gallium nitride film grown on the sapphire substrate is a mirror-like film with C-plane orientation.

S1: 2-inch sapphire substrate
S2: 2 inch (111) A-plane GaAs substrate S3: 2 inch GaN / sapphire substrate

An SiO ₂ film having a thickness of 0.1 μm was formed on three types of substrates by plasma CVD. The following four types of parallel comb patterns (called stripes) were formed by photolithography. The stripe pattern is regularly provided so as to be parallel to the <1-100> orientation of GaN to be grown.

  On the GaAs (111) A plane, the GaN <11-20> direction grows parallel to the GaAs <1-10> direction, and the GaN <1-100> direction grows with the same axis as the GaAs <11-2> direction. I know that. The upper direction means that a stripe mask is formed parallel to the <11-2> direction of the GaAs (111) A plane.

A1: Line width w 5 μm, pitch p 300 μm, exposed portion width s 295 μm
A2: line width w 20 μm, pitch p 300 μm, exposed part width s 280 μm
A3: Line width w 50 μm, pitch p 300 μm, exposed part width s 250 μm
A4: Line width w 200 μm, pitch p 500 μm, exposed part width s 300 μm

A1 to A4 stripe masks were provided on the S1 to S3 substrates. A GaN film was grown on the 12 types of masked substrates by the HVPE method (Hydride Vapor Phase Epitaxy). The HVPE method in this example is provided with a Ga boat containing Ga metal inside the reactor, and the entire furnace can be heated from the outside, and the Ga boat is maintained at 800 ° C. Then, HCl + H ₂ gas is blown from above to synthesize GaCl. A heated base substrate is installed below the Ga boat, and ammonia gas (NH ₃ + H ₂ ) is blown onto GaCl flowing from above to synthesize GaN to form a GaN film on the substrate. It has become. Hydrogen (H ₂ ) is supplied most in the carrier gas. The inside of the furnace is approximately 1 atm as a whole.

[Formation of buffer layer]
Substrate temperature: 490 ° C
HCl partial pressure: 0.002 atm (200 Pa)
NH ₃ partial pressure: 0.2 atm (20000 Pa)
Growth time: 15 minutes

[Epitaxial layer formation]
Substrate temperature: 1010 ° C
HCl partial pressure: 0.02 atm (2000 Pa)
NH ₃ partial pressure: 0.25 atm (25000 Pa)
Growth time: 15 minutes,
30 minutes,
60 minutes,
600 minutes

The growth time was the above four types, and when the growth time passed, the sample was taken out of the furnace and observed and evaluated. In particular, the sample grown for 600 minutes (10 hours) was observed and evaluated, and then the ground substrate and mask were scraped off by grinding and the surface was ground to obtain a flat substrate. Thereafter, polishing was performed to obtain a substrate having a flat surface. This is a transparent flat and smooth substrate. Although it has various different partial structures, it cannot be distinguished with the naked eye because it is transparent.

(1) Observation of crystal growth 15 minutes, 30 minutes, and 60 minutes for a sample (S2 * A3) provided with a mask (exposed portion width 280 μm) provided with parallel lines 20 μm wide at a pitch of 300 μm on a GaAs base substrate The crystal was taken out in 600 minutes, and the state of initial crystal growth was examined with an optical microscope and a scanning electron microscope.

  When the sample taken out 15 minutes after the start of the growth of the gallium nitride film was observed, there was no continuous film on the mask, and only a few fine polycrystalline particles were on it. A thick epitaxial crystal growth film of GaN was observed in the GaAs exposed portion not covered with the mask. The GaN film thickness of the exposed part was about 25 μm. Since the mask is a space and a thick film is formed on the GaAs exposed portion, the mask is depressed.

  The crystal has a mountain groove shape in which a number of peaks and valleys are arranged in parallel (FIG. 5 (2)). Around the mask, the crystal forms an oblique wall. The diagonal walls were {11-22} facets. In order to do so, the direction of the stripe mask is determined in advance in the <1-100> direction.

  Looking at the sample taken out 30 minutes after the start of growth, the crystal growth has not started since only a few fine polycrystalline particles are on the mask. In the non-mask part (exposed part), the thickness of the gallium nitride film increased and the film thickness was about 50 μm. The height difference at the periphery of the mask is about 50 μm, and the facet surface at the periphery of the mask is widened. On the {11-22} facet surface, a large number of protrusions ruggedly formed on the slope faced inwardly in parallel (FIG. 5 (3)). This protrusion extends almost in parallel from the facet surface to the mask groove. The upper surface of the protrusion had an inclination of about 25 ° to 35 ° with respect to the horizontal plane, and was continuous with the {11-22} facet surface at the root.

  Looking at the sample taken out 60 minutes after the start of growth, the crystal growth has not started since the fine polycrystalline particles are still on the linear mask. Crystal growth in the non-mask portion (exposed portion) progressed, and the film thickness reached about 100 μm. The Yamatani structure has become clearer. On the left and right sides of the mask, inclined grooves made of {11-22} facets are generated. The opposing facets are expressed as individual indices (11-22) and (-1-122). The rugged protrusion that appeared during the 30-minute growth further extends (FIG. 5 (4)). A part of the protrusion is bonded above the mask (groove). Protrusions extending from adjacent parts are also bonded above the mask.

  A combination of protrusions covers the stripe mask. A space remained between the coupling protrusion and the mask. Since the extension speeds of the protrusions are not the same, the connecting portion is not necessarily on the mask center line. When the dominant protrusion and the inferior protrusion are combined, they are displaced from the mask center toward the inferior protrusion. The combined protrusions form a loosely inclined V groove (BE in FIG. 5 (5)). The inclination angle of the V-groove was about 25 ° to 35 ° with respect to the horizontal.

  Therefore, a two-step inclined V-groove is formed on the mask. The outer steep inclination is about {tilde (60)} with respect to the horizontal plane at {11-22} and {1-101} facets. The inner inclined surface that continues from the lower end has a gentle inclination of 25 ° to 35 ° and is formed by the combination of the projections. In this way, the V groove and the mountain are arranged in parallel at a constant pitch p.

  When the sample taken out 600 minutes after the start of growth was seen, the average thickness reached about 1 mm. The vicinity of the linear (stripe) mask was almost the same as the sample for 60 minutes, and there was a V-groove with a double inclined surface. That is, a V-groove is formed by a strong inclined surface (facet surface) of about 60 ° and a shallow inclined surface of about 25 ° to 35 ° inside thereof. The V-groove at the top of the mask was maintained without being buried. Immediately above the mask is a shallow inclined surface caused by the projection coupling, and a parallel inclined surface made of {11-22} facet surfaces of about 60 ° is formed in a portion off the mask (FIGS. 9 and 10).

  This V-groove expands with growth. Between adjacent V grooves is a flat surface (C surface). A parallel straight line portion immediately above the linear (striped) mask and below the shallow inclined surface is the defect accumulation region H. The portions under the facets on both sides of the mask are low defect single crystal regions Z. A flat surface between adjacent Z regions is a C-plane growth region Y. That is, this GaN is a crystal having a parallel ... ZHZYZHZ ... structure. Since the exposed portion has a high mountain and the top of the mask has a low V-groove, it has a shape in which a large number of triangular prisms having a ridge line at the center of the mask are laid in parallel. The ridge line of the prism may be a sharp line. It lacks Y and has a structure in which H and Z alternate as... ZHZHZHZH... (FIG. 9). Some prisms have a flat ridgeline. The flat surface is the C plane, which is the C plane growth region Y. In that case, the above-described... ZHZYZHZ... Structure is obtained (FIG. 10).

  Although the partial structures are different, they cannot be distinguished by visual inspection because they are transparent. Although there were parts with different structures, no cracks were generated.

  The GaN / GaAs substrate grown for 10 hours was ground and polished. The GaAs base substrate and the mask were removed by grinding. Surface irregularities were also removed by grinding. Next, both surfaces were polished to obtain a flat and transparent GaN free-standing substrate. The substrate has a diameter of 2 inches and a thickness of about 1 mm. Although the surface was observed with a microscope, no cracks occurred on the entire surface.

(2) Crystal evaluation
The GaN free-standing substrate thus obtained was evaluated by various means such as a transmission electron microscope (TEM), electron beam diffraction, CBED, and CL.

  The V-groove portion was analyzed with a transmission electron microscope (TEM) at a shallow angle covering the mask. As evaluated by electron diffraction, there was no difference in the diffraction pattern between the V-groove on the mask and the other peaks.

  Furthermore, it analyzed by the method called CBED (Convergent Beam Electron Diffraction). According to this, it was found that the crystal orientation of the V-groove was just 180 degrees reversed with respect to the other portions. The other part is a part grown on the base substrate exposure part not covered with the mask.

  In addition, the surface of the polished GaN substrate was etched by raising the temperature in an aqueous KOH solution. It was found that the portion corresponding to the mask on the front side was selectively etched. It has been found that the Ga face of GaN is not etched by KOH and the N face is etched.

  From this result, it can be seen that the growth portion (H) on the mask is a single crystal in which the C axis is just 180 ° reversed with respect to the other portions (Y, Z). That is, the portion (Z, Y) grown on the exposed portion other than the mask is a (0001) crystal whose upper surface is a Ga plane, and the portion (H) grown on the mask is a nitrogen surface (000-1). ) It was found to be a single crystal. The reverse is the opposite. FIG. 8 shows such a structure.

  The regions H and Z whose directions are reversed are adjacent to each other on the surface extending the mask boundary. Since the orientation is reversed, the boundary becomes the grain boundary (K). The grain boundary (K) forms a closed space where some of the collected dislocations disappear and the dislocations are captured and dispersed. This eliminates the haze of dislocations. The generation of grain boundaries (K) is extremely effective in reducing dislocations. Moreover, since the orientation is reversed by 180 degrees, there is an excellent advantage that a difference in thermal anisotropy does not become obvious and cracks do not occur.

  The rugged claw-like projections that are centripetally generated laterally from the slope of the {11-22} facet surface at the mask edge are reversed orientation crystals whose C-axis direction is reversed from the beginning. Crystal growth is performed on the protrusions, the inverted orientation crystal spreads over the entire mask, and the entire region on the mask becomes the inverted orientation single crystal. By such a mechanism, the orientation-reversed single crystal (H) is formed only on the mask. The boundary with the facet region Z is a crystal grain boundary (K).

Furthermore, crystal evaluation was continued using cathodoluminescence and a fluorescence microscope.
The substrate obtained by the double-side polishing is a substrate having the surface of most (Z, Y) as the (0001) plane, that is, the C plane. Only the portion grown on the portion where the stripe mask was present (H), and the surface is the (000-1) plane (nitrogen surface).

  Crystal evaluation was performed by cathodoluminescence (CL) image. The surface of the gallium nitride substrate itself appears flat and transparent and uniform, but when a CL image is taken with a measurement wavelength of 360 nm at the band edge, the growth history appears as various contrasts, so the above regions can be distinguished and observed.

  According to the CL image, a plurality of regions having a dark contrast of about 50 μm width correspond to the stripe mask positions and are regularly arranged in parallel at a pitch of 300 μm. It was found that the dark contrast region corresponding to the stripe mask is an orientation reversal region. The part on the mask looks dark contrast, but part of it has bright contrast.

  The outer ({11-21}) facet grown part has a bright contrast. The region (H) grown on the mask can be clearly distinguished from the outer faceted region (Z). The boundary between the mask upper region (H) and the outside (Z) corresponds to the crystal grain boundary (K). The part of the crystal grain boundary (K) is observed as a clear dark linear contrast. Between the bright contrast (Z) and (Z), a dark contrast portion was linearly present. This is the C-plane grown part (Y). Those having the same orientation but having a history of growth with {11-21} facets are bright in the CL image, and the history of growth on the (0001) C plane is dark in the CL image.

  Further, when the inside of the orientation inversion region (H) on the stripe mask is observed, a clear dark linear contrast corresponding to the crystal grain boundary (K ′) is also recognized inside. That is, a crystal grain boundary (K ′) formed by joining nail-like protrusions (orientation reversal regions) extending from facets on both sides of the linear mask above the linear mask. Since it grows from different facets, the crystal orientations do not always coincide and are somewhat shifted, so grain boundaries are formed. The position of the grain boundary (K ′) corresponds to the bottom of the V groove having a shallow angle.

  Further, the position of the grain boundary (K ′) in the reverse orientation region (H) also changes depending on the crystal growth thickness. In the sample grown for 60 minutes at the initial stage of crystal growth, the grain boundary (K ′) was located at the approximate center of the stripe mask width. However, when a CL image is observed for a GaN substrate with a crystal growth time of 10 hours, there may be a grain boundary (K ′) at the center of the mask width, but it may be biased. This is because the position of the grain boundary (K ′) varies from side to side as the crystal growth proceeds. For example, there may be a case where it is greatly deviated from the center of the mask width and overlaps with the boundary grain boundary (K). The grain boundary (K ′) formed by combining the protrusions is not always in the center of the orientation inversion region.

  The grain boundary (K ′) inside the inversion orientation region (H) can be observed not only by CL but also by using a fluorescence microscope.

  A sample including the reversed orientation region (H) was cut out, and the internal grain boundary (K ′) was analyzed with a transmission electron microscope. A comparison was made by electron beam diffraction from both sides of the grain boundary (K ′) in the reversed orientation region (H). As a result of measurement at 20 points or more, it was found that the crystal planes were misaligned on the both sides of the grain boundary (K ′) as a boundary. Of course, the orientations may match exactly in special cases. There are also variations from place to place. There are differences depending on the sample. Although there was a slight difference in the orientation, the difference in crystal orientation between the both sides of the grain boundary (K ′) was still within 5 °.

  Samples (15 minutes, 30 minutes, 60 minutes) taken out at the initial stage of growth were again observed in detail. When viewed from the side, the claw-like protrusions appearing in the sample taken out 30 minutes after the start of growth have a wedge-shaped cross section surrounded by the upper and lower slopes. The problem is what this is.

  The inclination angle of the upper slope of the protrusion with respect to the horizontal is 25 to 35 degrees, which is a gentle slope. The slope of the lower slope has a strong slope of 55 to 65 degrees. It is just parallel to the slope of the opposing facet surface {11-22}. It can be said that it is just antiparallel because the normal direction is opposite. If the crystal axes are the same, the lower slope should be {-1-12-2} by multiplying the index by minus 1 because it is antiparallel to the opposing facet plane. However, as already explained, it is known that the protrusion is a single crystal whose orientation is reversed by 180 degrees from the surroundings and is an orientation reversal region. Therefore, the lower slope is the {11-22} plane by multiplying the plane index by minus 1. The lower slope of the protrusion is parallel to the opposing facet surface and opposite in the normal direction, but the orientation (reverse) is reversed, so the mirror (Miller index) is the same.

  Since the direction is reversed, the fourth index of the upward surface of the protrusion is negative, and the fourth index of the downward surface is positive. The gentle upward inclined surface of the protrusion can be written as {11-2-6}, {11-2-5}, and generally {11-2-n} (n ≧ 3).

  In the sample grown for 30 minutes, a group of protrusions obliquely parallel to the facet surface is generated and extends inward above the mask without contacting the mask. In the sample grown for 60 minutes, the inward claw-like projections merge at the middle portion to form a shallow inclined pit. Stronger slopes will continue on the outside of the shallow pits. It becomes a two-step inclined V-groove. After the growth for 60 minutes, an orientation reversal crystal grows on the protrusion merged portion on the mask, and a positive orientation crystal grows on the facet portion while maintaining the facet. The C-plane growth portion (Y) also grows upward and increases in thickness.

  Make such a complex growth. The dislocation density was measured by cathodoluminescence (CL) for a sample grown, ground and polished near 1 mm in 600 minutes. According to cathodoluminescence, if there are threading dislocations, they appear as black spots. The number of threading dislocations can be determined by counting the number of sunspots.

In the orientation inversion region (H), the dislocation density was high at 10 ⁶ cm ⁻² to 10 ⁹ cm ⁻² . This is because the dislocations in other parts are swept up and accumulated in the direction inversion region (H). The dislocation density in the facet grown region (Z) and the C plane grown portion (Y) is 10 ⁵ to 10 ⁷ cm ⁻² , and the dislocations in the Z and Y regions (non-inverted; positively oriented single crystal) portions It was confirmed that the density was greatly reduced.

Usually, when a gallium nitride thin film is grown on a sapphire substrate, high-density dislocations of 10 ⁸ cm ⁻² to 10 ¹⁰ cm ⁻² are generated in the gallium nitride thin film. In contrast, it can be seen that the present invention can greatly reduce the dislocation density in the gallium nitride crystal and has a significant dislocation reduction effect.

(3) Influence of mask pattern type In the above example, an A3 mask (parallel; line width w = 50 μm; pitch p = 300 μm) has been described. Similar results were obtained with the A1, A2, and A4 masks. However, in the case where the mask A1 (line width w = 5 μm, pitch p = 300 μm) was produced and GaN was grown thereon, the orientation inversion region (H) generated thereon was narrow because the mask was narrow, There was a tendency that the grain boundaries (K ′) that should be generated in the interior were difficult to understand. In the case of the A1 mask, when the GaN layer is thickened (by increasing the growth time), the inverted orientation region (H) itself may disappear. Although the A1 mask is not the best, the effect expected by the present invention can be increased, and it is considered that the lower limit of the mask dimension is given.

  The mask A2 (line width w = 20 μm, pitch p = 300 μm) was almost the same as the A3 mask, and good results could be obtained.

  In the case of the mask A4 (line width w 200 μm, pitch 500 μm), the covering portion has a width of 200 μm and a half width of 100 μm. Therefore, the protrusion has to be extended by 100 μm until bonding and it takes time to bond. Thereafter, since the orientation inversion region (H) grows, dislocation accumulation and annihilation may be incomplete. Further, the mask covering portion cannot be used as an important portion of the device, and the ratio increases, which is not desirable. Therefore, a desirable value of the line width w of the stripe mask is about 5 μm to 100 μm.

(4) Influence of board type
The case where GaAs is used as the base substrate (S2) has been described. However, when the sapphire substrate (S1) is used as the base substrate, or a GaN / GaN layer having a 1.5 μm-thick GaN layer coated on the sapphire substrate by MOCVD. Similar results were obtained when the same masks A1 to A4 were formed on the sapphire composite substrate (S3) and the GaN was facet grown.

  When the sapphire substrate was used as the base substrate (S1), the GaN buffer layer and the GaN epi layer were grown using the same mask and the same growth conditions as those of the GaAs substrate (S2) described above. The growth time was also 15 minutes, 30 minutes, 60 minutes, and 600 minutes. Initially, the growth occurs only on the exposed portion of the base substrate and does not occur on the stripe (parallel line) mask. A crystal peak is formed in the exposed portion, and the mask becomes a valley, so that a parallel ridge structure in which the peaks and valleys alternate is formed. Parallel facet surfaces are created on both sides of the mask. When the facet is sufficiently high, the claw-like projections (reversal orientation region (H)) extend from the facet and merge at the center, and the reversal orientation region (H) grows thereon, and the single crystal low dislocation region Z is formed in the facet region. The C-plane growth portion Y grew on the flat surface at the boundary between the facet and the facet. A grain boundary (K) was generated between the inversion orientation region (H) and the single crystal low dislocation region Z. It was also found that the reversal direction (H) was a defect assembly region. It was also confirmed that there was a grain boundary (K ′) inside the reverse orientation region (H). It is a grain boundary (K ′) in which the misalignment when the claw-like projections are bonded and united continuously extends upward.

  Similarly, when a sapphire substrate (S3) coated with a 1.5μm GaN film by MOCVD is used as a base substrate, a linear (stripe) mask is formed, and a low-temperature buffer layer and a high-temperature epi layer are grown thereon. I let you. The increment of the growth time was also set to 15 minutes, 30 minutes, 60 minutes, and 600 minutes. Initially, GaN crystal growth occurred only in the exposed portion, and only a small amount of fine particles adhered to the mask portion. Oblique facets are formed around the mask. The facets spread and nail-like projections are generated from the side surfaces, which are united. What is combined is an orientation reversal region, and what has grown on it is orientation reversed. That is the defect gathering region H. A single crystal low dislocation region Z is grown following the facet portion, and a C-plane grown portion Y is formed in the flat portion. A crystal grain boundary (K) is formed between the inversion orientation region (H) and the single crystal low dislocation region (Z) by orientation inversion. A grain boundary (K ′) is also formed inside the reverse orientation region (H). It was the same as in the case of the GaAs substrate (S2).

[Example 2 (dot mask pattern)]
As in Example 1, a 2-inch sapphire substrate (S1), a GaAs substrate (S2), and a sapphire substrate (S3) in which a gallium nitride film having a thickness of 1.5 μm is epitaxially grown in advance by MOCVD are prepared. did. The sapphire substrate (S1) has a C surface as a main surface. The main surface of the GaAs substrate (S2) is the (111) A plane. The gallium nitride film grown on the sapphire substrate is a mirror-like film with C-plane orientation.

S1: 2-inch sapphire substrate
S2: 2 inch (111) A-plane GaAs substrate S3: 2 inch GaN / sapphire substrate

An SiO ₂ film having a thickness of 0.1 μm was formed on three types of substrates by plasma CVD. The following four types of dot patterns were formed by photolithography. The dot pattern is different from ELO in that a single continuous coating film is not provided with a window, but a large number of isolated coating portions are regularly arranged in a continuous exposed portion.

B1: dot diameter d 5 μm, pitch p 300 μm
B2: dot diameter d 20 μm, pitch p 300 μm
B3: dot diameter d 50 μm, pitch p 300 μm
B4: dot diameter d 200 μm, pitch p 500 μm

B1-B4 dot masks were provided on the S1-S3 substrates. A GaN film was grown on the 12 types of masked substrates by the HVPE method (Hydride Vapor Phase Epitaxy). The HVPE method in this example is provided with a Ga boat containing Ga metal inside the reaction furnace, maintaining the Ga boat at 800 ° C., and blowing HCl + H ₂ gas from above to the Ga metal melt. Is synthesized. A heated base substrate is installed below the Ga boat, and ammonia gas (NH ₃ + H ₂ ) is blown onto GaCl flowing from above to synthesize GaN to form a GaN film on the substrate. It has become. Hydrogen (H ₂ ) is supplied most in the carrier gas. The inside of the furnace is approximately 1 atm as a whole.

[Formation of buffer layer]
Substrate temperature: 490 ° C
HCl partial pressure: 0.002 atm (200 Pa)
NH ₃ partial pressure: 0.2 atm (20000 Pa)
Growth time: 15 minutes

[Epitaxial layer formation]
Substrate temperature: 1010 ° C
HCl partial pressure: 0.02 atm (2000 Pa)
NH ₃ partial pressure: 0.25 atm (25000 Pa)
Growth time: 15 minutes,
30 minutes,
60 minutes,
600 minutes

The growth time was the above four types, and when the growth time passed, the sample was taken out of the furnace and observed and evaluated. In particular, the sample grown for 600 minutes (10 hours) was observed and evaluated, and then the ground substrate and mask were scraped off by grinding and the surface was ground to obtain a flat substrate. Thereafter, the substrate was polished to obtain a flat surface. This is a transparent flat and smooth substrate.

(1) Observation of crystal growth As in Example 1, for a sample (S2 * B3) provided with a mask in which dots of 50 μm diameter are provided on a GaAs base substrate at a pitch of 300 μm, 15 minutes, 30 minutes, 60 minutes The crystal was taken out in 600 minutes, and the state of initial crystal growth was examined with an optical microscope and a scanning electron microscope.

  When the sample taken out 15 minutes after the start of the growth of the gallium nitride film was observed, there was no continuous film on the mask, and only fine polycrystalline particles were thinly ridden. A thick epitaxial crystal growth film of GaN was observed in the GaAs exposed portion not covered with the mask. The film thickness was about 25 μm. Since the mask is a space and a thick film is formed at the exposed portion of GaAs, the shape is depressed by the mask. An oblique wall is formed around the mask. The diagonal walls were {11-22} facets or {1-101} facets.

  Looking at the sample taken out 30 minutes after the start of growth, the crystal growth has not started since only a few fine polycrystalline particles are on the mask (FIG. 5 (2)). In the non-mask part (exposed part), the thickness of the gallium nitride film increased and the film thickness was about 50 μm. The height difference at the periphery of the mask is about 50 μm, and the facet surface at the periphery of the mask is widened. On the {11-22} facet surface, a large number of projections rugged on the slope faced inward (FIG. 5 (3)). This protrusion extends centripetally from the facet surface. The upper surface of the protrusion had an inclination of about 25 ° to 35 ° with respect to the horizontal plane and was continuous to the {11-22} facet surface at the root.

  When the sample taken out 60 minutes after the start of growth is seen, the crystal growth has not started since the fine polycrystalline particles are still slightly on the mask. Crystal growth in the non-mask portion (exposed portion) progressed, and the film thickness reached about 100 μm. Around the dot, pits of a hexagonal pyramid and a 12 pyramid consisting of a {11-22} plane or a facet plane consisting of the {11-22} plane and the {1-101} plane are generated. The protrusions appearing during the 30-minute growth are further extended and bonded above the mask. Protrusions extending from adjacent parts are also bonded above the mask. A combination of protrusions covered the mask. A space remained between the coupling protrusion and the mask.

  Since the extension speeds of the protrusions are not the same, the connecting portion is not always at the center of the mask. When the dominant protrusion and the inferior protrusion are combined, they are displaced from the mask center toward the inferior protrusion. The combined protrusions have a loosely inverted inverted spindle shape. The angle was about 25 ° to 35 ° with respect to the horizontal.

  Therefore, a two-step inclined hole is made on the mask. The outer holes are {11-22} and {1-101} facets and have a strong inclination of about 60 ° with respect to the horizontal plane. The inner inclined hole that continues from the lower end has a gentle inclination of 25 ° to 35 ° and is formed by the combination of protrusions.

  When the sample taken out 600 minutes after the start of growth was seen, the average thickness reached about 1 mm. The vicinity of the dot mask was almost the same as the sample for 60 minutes, and there was a hole with a double inclined surface. In other words, a strong inclined surface (facet surface) of about 60 ° and a shallow inclined surface of about 25 ° to 35 ° are formed on the inside thereof, and the hole is maintained without being embedded in the upper hole of the mask. Immediately above the mask is a shallow inclined surface formed by the protrusion coupling, and a hole made of a {11-22} {1-101} facet surface of about 60 ° is formed in a portion off the mask. This hole expands with growth. It becomes a bowl-shaped hole (FIG. 6).

  A space between adjacent holes is a flat surface (C surface). A portion immediately below the mask and below the shallow inclined surface is a defect accumulation region H. The lower part of the facet is a low defect single crystal region Z. A flat surface between adjacent holes is a C-plane growth region Y. That is, this GaN is a crystal composed of H, Z, and Y. Although the structure is different, it cannot be distinguished by visual inspection because it is transparent. Although there were parts with different structures, no cracks were generated.

  The GaN / GaAs substrate grown for 10 hours was ground and polished. The GaAs base substrate and the dot mask were removed by grinding. Surface irregularities were also removed by grinding. Next, both sides were polished to obtain a flat and transparent GaN free-standing substrate. The substrate has a diameter of 2 inches and a thickness of about 1 mm. Although the surface was observed with a microscope, no cracks occurred on the entire surface.

(2) Evaluation of crystal The GaN free-standing substrate thus obtained was evaluated by various means.
According to the same evaluation method as in Example 1 using a transmission electron microscope (TEM), electron beam diffraction, and CBED, the growth part (H) on the mask has a C axis of exactly 180 with respect to the other (Y, Z) parts. It was found to be a single crystal that was inverted. That is, the portion (Z, Y) grown on the exposed portion other than the mask is a (0001) crystal whose upper surface is a Ga plane, and the portion (H) grown on the mask is a nitrogen surface (000-1). ) It was found to be a single crystal. Since the regions whose orientations are reversed are adjacent, the boundary is the grain boundary (K). The grain boundary forms a closed space where some of the collected dislocations disappear and the dislocations are captured and dispersed. This eliminates the haze of dislocations.

  Even when a dot mask is used, the rugged claw-like projections centripetally generated laterally from the slope of the {11-22} facet surface at the end of the mask are inverted orientation crystals whose C-axis direction is reversed from the beginning. Crystal growth is performed on the protrusions, the inverted orientation crystal spreads over the entire mask, and the entire region on the mask becomes the inverted orientation single crystal. By such a mechanism, the orientation-reversed single crystal (H) is formed only on the mask. The boundary is the grain boundary (K).

Furthermore, crystal evaluation was continued using cathodoluminescence and a fluorescence microscope.
The substrate obtained by the double-side polishing is a substrate having the surface of most (Z, Y) as the (0001) plane, that is, the C plane. However, only the portion (H) grown on the portion where the dot mask was present has a (000-1) surface.

  In the same manner as in Example 1, crystal evaluation was performed using a CL image. According to the CL image, the regions of the dot shape clearly distinguished by dark contrast correspond to the mask position, and are regularly arranged at positions of 6 times symmetry at a pitch of 300 μm. It was found that the area corresponding to the dark contrast dot mask is an orientation reversal area (polarity reversal). The boundary between the region and the outside corresponds to the crystal grain boundary (K). The part of the crystal grain boundary (K) is observed as a clear dark linear contrast.

  Further, when the inside of the dot-like orientation inversion region (H) is observed, there are many places where a clear dark linear contrast corresponding to the crystal grain boundary (K ′) is recognized. It is a crystal grain boundary formed by the nail-like projections (orientation reversal regions) extending from the facets around the dot mask uniting above the mask. Since it grows from different facets, the crystal lattices do not necessarily coincide and are somewhat displaced, so grain boundaries are formed. If there are two reversal orientation regions that have grown preferentially, one grain boundary (K ′) is observed by coalescence. There is little regularity with respect to the position of the grain boundary formed inside the inverted orientation region (H).

  Further, the position of the grain boundary (K ′) in the reverse orientation region (H) also changes depending on the crystal growth thickness. In particular, when a CL image is observed for a GaN substrate having a crystal growth time of 10 hours, a grain boundary may not be seen in the orientation inversion region. The reason for this is that the position of the grain boundary changes with the progress of crystal growth. For example, there may be a case where the boundary portion of the orientation inversion region and the grain boundary (K ′) coincide with each other by shifting from the center of the mask. In that case, there is no grain boundary (K ′) inside the inverted orientation region.

  The grain boundary (K ′) inside the inverted orientation region (H) is analyzed with a transmission electron microscope, and electron beam diffraction is performed from both sides of the grain boundary in the inverted orientation region (H) for comparison. Went. As a result of measurement at a large number of points, as in the case of the stripe mask (Example 1), it was found that the surface was a mismatched surface where the crystal orientation was slightly shifted on both sides of the grain boundary (K ′). It was. Of course, the orientations may match exactly in special cases. There are also variations from place to place. There are differences depending on the sample. Although there was a slight difference in the orientation, the difference in crystal orientation between the both sides of the grain boundary (K ′) was still within 5 °.

  Samples (15 minutes, 30 minutes, 60 minutes) taken out at the initial stage of growth were again observed in detail. When viewed from the side, the claw-like protrusions appearing in the sample taken out 30 minutes after the start of growth have a wedge-shaped cross section surrounded by the upper and lower slopes. The problem is what this is. The angle of inclination of the upper slope with respect to the horizontal is 25 to 35 degrees, which is a gentle slope.

  The slope of the lower slope is a strong slope of 55 to 65 degrees. It is just parallel to the slope of the opposing facet surface {11-22}. It can be said that it is just antiparallel because the normal direction is opposite. If the crystal axes are the same, the lower slope should be {-1-12-2} by multiplying the index by minus 1 because it is antiparallel to the opposing facet plane. However, as already explained (FIG. 15), it is known that the protrusion is a single crystal whose orientation is inverted by 180 degrees from the surroundings and is an orientation reversal region.

  Therefore, the lower slope is the {11-22} plane by multiplying the plane index by minus 1. The lower slope of the protrusion is parallel to the opposing facet surface and opposite in the normal direction, but the orientation (reverse) is reversed, so the mirror (Miller index) is the same. Since the direction is reversed, the fourth index on the upward surface is negative, and the fourth index on the downward surface is positive. The gentle upward inclined surface of the protrusion can be written as {11-2-6}, {11-2-5}, and generally {11-2-n} (n ≧ 3). In the case of a Dodd mask, the facet surface may be {1-101}, and in the case of a protrusion facing it, the lower slope is {1-101} and the upper slope is {1-10-m} (m ≧ 2). I can write.

  In the sample grown for 30 minutes, a group of protrusions is generated obliquely from the facet surface and extends inward above the mask without contacting the mask. In the sample grown for 60 minutes, the inward claw-like projections merge at the middle portion to form a shallow inclined pit. Stronger slopes will continue on the outside of the shallow pits. It becomes a two-step inclined hole. After the growth for 60 minutes, an orientation reversal crystal grows on the protrusion merged portion on the mask, and a positive orientation crystal grows on the facet portion while maintaining the facet. The C-plane growth portion (Y) also grows upward and increases in thickness.

Make such a complex growth. The dislocation density was measured by cathodoluminescence (CL) for a sample grown, ground and polished near 1 mm in 600 minutes. In the orientation inversion region (H), the dislocation density was high at 10 ⁶ cm ⁻² to 10 ⁹ cm ⁻² . This is because the dislocations in other parts are swept up and accumulated in the direction inversion region (H). The dislocation density in the facet-grown region (Z) and the C-plane grown part (Y) was 10 ⁴ to 10 ⁷ cm ⁻² , and there were many parts of 10 ⁶ cm ⁻² or less. It was confirmed that the dislocation density in the Z and Y regions (positively oriented single crystal) was greatly reduced.

Usually, when a gallium nitride thin film is grown on a sapphire substrate, high-density dislocations of 10 ⁸ cm ⁻² to 10 ¹⁰ cm ⁻² are generated in the gallium nitride thin film. In contrast, the present invention can greatly reduce the dislocation density at Z and Y of the gallium nitride crystal, and it can be seen that there is a significant dislocation reduction effect.

(3) Influence of Mask Pattern Type In the above example, a B3 mask (dot diameter 50 μm, pitch 300 μm) has been described. Similar results were obtained with the B1, B2, and B4 masks.
However, when the mask B1 (dot diameter 5 μm, pitch 300 μm) was grown and GaN was grown on it, the azimuth inversion region (H) generated on it was narrow because the mask was narrow, and it was generated inside it. There was a tendency that the grain boundary (K ′) that should be made is difficult to understand. In the case of the B1 mask, when the GaN layer is thickened (by increasing the growth time), the inversion orientation region (H) itself may disappear.
Although the B1 mask is not the best, the effect expected by the present invention can be increased, and it is considered that the lower limit of the mask dimension is given.

  The mask B2 (dot diameter 20 μm, pitch 300 μm) was almost the same as the B3 mask and was able to give good results.

  In the case of the mask B4 (dot diameter 200 μm, pitch 500 μm), since the dot diameter is 200 μm and the radius is 100 μm, it takes 100 μm to grow until the protrusions grow and bond, and it takes time to bond. Thereafter, since the orientation inversion region (H) grows, dislocation accumulation and annihilation may be incomplete. Also, the dot portion cannot be used for an important portion of the device, and the ratio increases, which is not desirable. Therefore, the desirable diameter d of the dots is about 5 μm to 100 μm.

(4) Influence of substrate type Although the case where GaAs is used as the base substrate (S2) has been described, when a sapphire substrate (S1) is used as the base substrate, or a GaN layer having a thickness of 1.5 μm is sapphire by MOCVD. Similar results were obtained when GaN was facet grown by forming similar masks B1 to B4 on the GaN / sapphire composite substrate (S3) coated on the substrate.

  When the sapphire substrate was used as the base substrate (S1), the GaN buffer layer and the GaN epi layer were grown using the same mask and the same growth conditions as those for the GaAs substrate (S2) described above. The growth time was also 15 minutes, 30 minutes, 60 minutes, and 600 minutes. Initially, the growth occurs only on the exposed portion of the base substrate and does not occur on the dot mask. Facet pits are formed around the mask, and claw-like projections (reversal orientation region (H)) extend from the facet and merge at the center, and a reversal orientation region (H) grows on it. The dislocation region Z grew, and the C-plane growth portion Y grew on the flat surface at the boundary between the facets. A grain boundary (K) was generated between the inversion orientation region (H) and the single crystal low dislocation region Z. It was also found that the reversal direction (H) was a defect assembly region. It was also confirmed that there was a grain boundary (K ′) inside the reverse orientation region (H). It is a grain boundary (K ') in which the misalignment when the claw-like projections are joined and extended continuously upward.

  Similarly, when a sapphire substrate (S3) coated with a 1.5 μm GaN film by MOCVD was used as a base substrate, a dot mask was formed, and a low temperature buffer layer and a high temperature epi layer were grown thereon. The increment of the growth time was also set to 15 minutes, 30 minutes, 60 minutes, and 600 minutes. Initially, GaN crystal growth occurred only in the exposed portion, and only a small amount of fine particles adhered to the mask portion. Oblique facets are formed around the mask. The facets spread and nail-like projections are generated from the side surfaces, and they are united. What is combined is an orientation reversal region, and what has grown on it is orientation reversed. That is the defect gathering region H. A single crystal low dislocation region Z is grown following the facet portion, and a C-plane grown portion Y is formed in the flat portion. A crystal grain boundary (K) is formed between the inversion orientation region (H) and the single crystal low dislocation region (Z) by orientation inversion. A grain boundary (K ′) is also formed inside the reverse orientation region (H). It was the same as in the case of the GaAs substrate (S2).

[Example 3 (effect of mask type)]
In Examples 1 and 2 so far, SiO ₂ is used as the mask material. Other mask materials were examined. A thin film of Si ₃ N ₂ , Al ₂ O ₃ , AlN, ZrO ₂ , Y ₂ O ₃ , MgO is deposited to a thickness of 0.1 μm on the sapphire substrate, and an A3 mask (w = 50 μm, p = 300 μm; Stripe). As described in Example 1, a GaN buffer layer and an epi layer were grown. The epi layer was grown for 30 minutes.

  In that experiment, whatever mask was used, a ridge / valley structure was formed, and {11-22} facets were formed on both sides of the groove. It was also confirmed that protrusions were generated inward from the {11-22} facet in parallel. It was confirmed for all the mask samples that it was also an inverted orientation region. That is, the present invention can be implemented using any of the above masks.

[Example 4 (absorption coefficient for light of 300 nm to 2000 nm)]
The GaN substrate of the present invention comprises a defect assembly region (protrusion growth portion; reversal orientation) H, a low defect single crystal region (facet growth portion; positive orientation) Z, and a single crystal low dislocation residual region (C-plane growth portion; positive orientation). ) And has a repetitive structure of ZHZYZHZYZ ... or ZHZHZ. The difference between the crystal orientation and the cause of formation has been explained in detail so far. These three regions have not only differences in crystal orientation and history, but also differences in optical, physical and physical properties.

  Here, the results of measuring the absorption of ultraviolet to near infrared light of 300 nm to 2000 nm will be described. Actually, the absorption was measured using light sources of 350 nm band, 450 nm band, 550 nm band, and 650 nm band. There is no non-uniformity among H, Z, and Y for light of 650 nm or more.

The sample GaN substrate has a thickness d = 0.4 mm, a test light of 0.1 mmφ is applied to the sample, and the intensities of incident light Pi, reflected light Pf, and transmitted light Pt are measured,
α = log {Pi / (Pi−Pt−Pf)} / d
The absorption coefficient was calculated by The absorption coefficients of the defect assembly region H, the single crystal low dislocation region Z, and the single crystal low dislocation residual region Y are α _H , α _Z , and α _Y.

The reason why the absorption is large with respect to 350 nm ultraviolet light is that bandgap transition occurs with energy larger than that of GaN. Green 550nm, is the degree of H against the red of 650nm, Z, Y both ^{1cm -1 ~10cm} -1. Compared to the blue 450 nm band, the H and Z regions have a small absorption ( ^{1 to} 10 cm ⁻¹ ), whereas the Y region has a large absorption (10 to 100 cm ⁻¹ ). The ratio is 5 to 20 times. This means that the C-plane growth region Y contains more carbon.

[Example 5 (phosphoric acid: sulfuric acid = 1: 1 etching rate with respect to 1: 1 etching solution)]
The GaN substrate of the present invention was immersed in phosphoric acid: sulfuric acid = 1: 1 etching solution, and was kept at 270 ° C. and etched for 10 minutes. The etching rate of the defect assembly region (protrusion growth portion; reverse orientation) H was 10 μm / hour or more at a high speed. The etching rate for the low defect single crystal region (facet growth portion; positive orientation) Z and the single crystal low dislocation residual region Y (C plane growth portion; positive orientation) was less than 0.1 μm / hour. The ratio between the etching rate in the H region and the etching rate in the Y and Z regions is 100 or more. The surfaces of the Z and Y regions are Ga planes and can hardly be etched. However, the H region with many defects has a nitrogen surface and a high etching rate.

[Example 6 (XRD)]
X-ray source: Cu-Kα1 ray Spectroscope: Two crystals (Ge (220)) + mirror
Slit: 0.5mm x 0.2mm
Incident direction: <11-20>
Diffraction surface: (0004)

The X-ray spectrum of X-rays incident from the direction <11-20> perpendicular to the (11-20) plane of the sample and diffracted in the <-1-120> direction on the opposite side is obtained, and the half width of the peak (FWHM) (Full width at half maximum)) was measured. This is a diffraction peak from the (0004) plane. A large peak half-value width means that the regularity of the (0004) plane is weak, and a narrow half-value width means a good quality single crystal. The unit is arc second, which is 1/60 of a degree.

  In any region, the peak of diffracted X-rays from the (0004) plane is sharp. That is, the H, Z, and Y regions are high quality single crystals. However, since the defect gathering region H has a large crystal disorder, the full width at half maximum is increased. That is 3 to 10 times that of other parts. The lattice constant in the c-axis direction can be measured by X-ray (0004) diffraction. According to this, in the H, Z, and Y regions, the (0004) plane spacing was 0.5185 nm ± 0.0001 nm. That is, the c-axis length is 2.074 nm. The result is that all three regions have the same crystal system and the same lattice constant.

[Example 7 (electric resistance)]
The local electrical resistance was measured using the three-terminal guide method (FIG. 7).
As shown in FIG. 7, an electrode 52 is attached to the entire bottom surface of the target substrate. The periphery of the upper surface is covered with a guard electrode 53 (inner diameter 90 μm). A measuring electrode 55 (outer diameter 70 μm) is attached to the center of the upper surface. There is a 10 μm gap (average diameter 80 μm) between the two electrodes on the top surface. The guard electrode 53 is grounded, and the measurement electrode 55 is grounded through an ammeter 57. A voltage V is applied from the variable power source 56 to the bottom electrode 52. The current I flowing through the ammeter 57 is obtained. The resistance R of the ring gap (10 μm) is obtained by dividing V by I.

ρ (Ωcm) = R (Ω) × S (cm ² ) / L (cm)

Thus, the local resistivity ρ of the substrate can be obtained. Thereby, the resistivity of H, Z, and Y was measured.

The non-uniformity of the etching rate and XRD described so far was unique in the defect assembly region H, but with respect to the resistivity ρ, the C-plane growth region Y (single crystal low dislocation residual region) was particularly unique. High resistivity. This is probably because oxygen is not doped in the C-plane growth region Y while H and Z are heavily doped with oxygen.

[Example 8 (photoluminescence; PL)]
The light of a He-Cd laser having a wavelength of 325 nm was focused on the H, Z, and Y regions of a GaN substrate (0.4 mm thickness) sample with a diameter of 0.1 mmφ, and the photoluminescence spectrum emitted from those regions was examined. .

  FIG. 11 is a photoluminescence spectrum of the defect gathering region H. The horizontal axis represents wavelength (nm) and the vertical axis represents luminescence intensity. There is a sharp and high (1730) peak at 360 nm corresponding to the band gap. There are broad peaks that are low (180) over the green-yellow-orange wavelength.

  FIG. 12 is a photoluminescence spectrum of the low defect single crystal region Z. The band gap of 360 nm also has a high and narrow (1750) peak. There is a low peak (90) over the yellow-orange wavelength.

  FIG. 13 shows the photoluminescence of the single crystal low dislocation residual region (C-plane growth region) Y. The vertical axis is about 1/3 of the previous scale. The peak at 360 nm is remarkably low (70), and a broad yellow-orange peak around 560 nm is raised and high (160). It is estimated that this is because a large amount of carbon is contained in the C-plane growth region. The intensity of the band gap transition can be expressed by a value obtained by dividing the height of the 360 nm peak by the height of the 560 nm peak.

The H region is 1730/180 = 9.6
Z region is 1750/90 = 19.4
Y region is 70/160 = 0.44

It is. In terms of photoluminescence, the Y region (C-plane growth) is a unique region.

The etching rate and XRD non-uniformity described so far are unique in the defect assembly region H, but the C-plane growth region Y (single crystal low dislocation residual region) is unique in the photoluminescence. This is probably because carbon does not enter H and Z, but carbon enters the C-plane growth region Y.

[Example 9 (warpage)]
The warpage of the substrate is an important evaluation criterion when a device is fabricated thereon. It is not a local property and there is no distinction between H, Z and Y. When the curvature of the GaN free-standing substrate made according to the present invention is expressed by the curvature radius R, the minimum is Rmin = 600 mm and the maximum is 50000 mm. The GaN substrate made according to the present invention usually has a curvature radius of warpage of 1500 mm or more. The curvature radius of the substrate according to the example described above was measured, and it can be seen that the curvature radius is in a range of 1000 mm to 50000 mm and the substrate is a good substrate with little warpage. The warpage was measured by the stylus method. In this method, the height is obtained by placing the needle on the center of the substrate.

[Example 10 (measurement of impurity concentration)]
For the H, Z, and Y regions of the polished GaN substrate, the impurity concentration was measured by SIMS (Secondary Ion Mass Spectrometer). It accelerates Cs ⁺ ions, strikes the target with internal atoms as ions, curves the trajectory of ions coming out of the surface with a mass analysis magnet, counts the number of ions coming to a certain bending angle, and exists on the surface The impurity concentration to be obtained is obtained.
Since this is a destructive inspection in which the surface is etched, the impurity concentration up to a certain depth can be examined. The measurement depth of the object is 0 to 5 μm. The measurement area is a local range of 50 μmφ. The concentrations of oxygen (O), silicon (Si), and arsenic (As) were measured for H, Z, and Y.

There is no difference between H, Z, and Y in the concentration of silicon and arsenic. Of note is oxygen. The oxygen concentration is particularly low in the C-plane growth part Y. Oxygen is not easily taken in by C-plane growth. Oxygen easily enters Z and H from the facet growth surface. The Y / Z ratio and Y / H ratio of oxygen are as low as 10 ⁻¹ to 10 ⁻⁵ . It is consistent with the non-uniformity of electrical conductivity that the resistance in the Y region is particularly high.

Example 11 (Substrate dimensions)
The GaN free-standing substrate produced by the method of the present invention has the following size range.
Rectangular substrate: 10 mm ≦ 1 side ≦ 160 mm
Circular substrate: 10 mm ≦ diameter ≦ 160 mm
Thickness: 5μm ≦ thickness ≦ 2000μm
In the case of a rectangular wafer, it is easy to confirm the orientation of the resonator surface when manufacturing a semiconductor laser. In the case of a circular wafer, since the gas flow becomes uniform during epitaxial growth, abnormality in epitaxial growth is unlikely to occur.

  When the diameter is 10 mm or less and one side is 10 mm or less, the throughput in the wafer process is low. If the diameter is 160 mm or more and one side is 160 mm or more, the warpage may increase, and the gas flow during epitaxial growth becomes non-uniform. In the case of using GaAs as a base substrate, the maximum size of commercially available GaAs is 6 inches (160 mm), which also limits the diameter.

[Example 12 (three-dimensional structure: Fig. 14)]
By observation with a fluorescence microscope, it is possible to know the variation in the width of each region in the thickness direction. The widths of the H, Z, and Y regions change slightly with growth. The widths of the H region and the Y region decrease with the progress of epitaxial growth. Conversely, the width of the Z region increases. Therefore, the widths of the H and Y regions on the Ga surface (upper surface) are narrower than the width on the nitrogen surface (lower surface). FIG. 14 shows variations in the widths of the H, Z, and Y regions. When the thickness is t, the variation in width is about 0.001 t to 0.1 t.

  A GaN substrate having a thickness of 400 μm, a diameter of 50 mm, and a pitch of 400 μm (between H and H) was produced by the method of the present invention. The average width of the H region on the N surface (lower surface) was about 20 μm, and the average width of the H region on the Ga surface (upper surface) was 15 μm. The Z region had a width of 385 μm on the bottom surface and a width of about 380 μm on the top surface. The Y region had a width of 10 μm to 40 μm.

  It is advantageous that the Z region expands in the Ga plane as such. When manufacturing a semiconductor laser, a current confinement region must be formed in a Z region with few defects and high electrical conductivity, avoiding the H region with many defects and the Y region with high electrical resistance. A wider Z region is more convenient for design purposes. Since the device is made on the Ga surface, it is convenient that the Z region expands on the Ga surface side.

[Example 13 (dislocation density)]
The dislocation density in each region can be measured by observation with a transmission electron microscope (TEM) or cathodoluminescence (CL).

  Take 10 fields in the <1-100> direction from the target point with a TEM having a field of 10 μm × 10 μm, scan the field in the <11-20> direction between H and H, and count the dislocations. The density was determined.

The defect aggregation region H has a high dislocation density, and the facet growth region (single crystal low dislocation associated region) Z and the C-plane growth (single crystal low dislocation residual region) Y have a low dislocation density. Even with the same GaN substrate, there are variations depending on the location.
Next, an example of dislocation density measurement for two GaN substrate samples 1 and 2 is shown.

[Dislocation density measurement; GaN substrate sample 1 (TEM)]
H; 1 × 10 ⁷ cm ⁻² to 2 × 10 ⁷ cm ⁻²
Z; 1 × 10 ⁵ cm ⁻² to 1 × 10 ⁷ cm ⁻²
Y; 2 × 10 ⁴ cm ⁻² to 2 × 10 ⁵ cm ⁻²

[Dislocation density measurement; GaN substrate sample 2 (TEM)]
H; 5 × 10 ⁷ cm ⁻² to 1 × 10 ⁸ cm ⁻²
Z; 3 × 10 ⁵ cm ^{−2 to} 3 × 10 ⁷ cm ⁻²
Y; 2 × 10 ⁵ cm ⁻² to 1 × 10 ⁶
cm ^-2

Although the dislocation density varies depending on the sample, it can always be said that it is high in the defect assembly region H and low in the facet growth region Z and the C-plane growth region Y (H> Y, H> Z). The dislocation density in the defect assembly region H is in the range of 5 × 10 ^{6 to} 5 × 10 ⁸ cm ⁻² . The dislocation density in the Z region is lower than 5 × 10 ⁶ cm ^{−2 in} the region of 50% or more. The dislocation density in the Y region is lower than 5 × 10 ⁶ cm ^{−2 in} the region of 60% or more.

[Example 14 (heat conduction)]
Thermal conductivity was measured using a 15 mm × 15 mm × 0.8 mm square GaN substrate fabricated and polished by the method of the present invention. This is for examining the presence or absence of anisotropy of heat conduction. Therefore, the dot type without anisotropy was not measured from the beginning.

  In the case of the stripe type, there is a possibility that there is a difference between heat conduction in a direction parallel to the stripe and heat conduction in a direction crossing the stripe. It is relatively easy to measure the heat conduction in the direction perpendicular to the substrate. However, it is difficult to measure the lateral and local heat conduction. The heat conduction cannot be measured directly. The thermal conductivity was determined by inductive means.

The thermal diffusion coefficient D (m ² / s) was measured by a laser flash method. Specific heat C (J / kgK) was measured by differential scanning calorimetry (DSC). The density ρ (kg / m ³ ) was measured by the Archimedes method. The thermal conductivity Q (W / mK) can be calculated by the following formula (W = J / s).

Q (W / ms) = ρ (kg / m ³ ) × C (J / kgK) × D (m ² / s)

The density ρ and specific heat C have no directionality. The thermal diffusion coefficient D has directionality. For the five substrates of GaN substrate samples 3 to 7, the Dp parallel to the stripe and the Dt crossing the stripe were measured. Thereby, the thermal conductivity Qp parallel to the stripe and the thermal conductivity Qt perpendicular to the stripe can be obtained.

Although there are variations depending on the sample, there are some of the former (samples 4 and 7) that are large with respect to Qt and Qp (samples 3, 5, and 6). The difference is smaller than the variation between samples. It is considered that the thermal conductivity has no anisotropy. Although other samples were also measured, the range of thermal conductivity of the GaN substrate of the present invention is 150 W / mK to 220 W / mK.

[Example 15 (Vickers hardness Hv)]
For the samples 3 to 7 (15 mm × 15 mm × 0.8 mm square GaN substrate) prepared and polished by the method of the present invention, the individual Vickers hardness Hv in the H, Z, and Y regions was measured. A diamond square indenter was applied to the target point and a test load P (kgf) was applied to form a depression on the sample surface. The diagonal length a of the formed depression was measured, and the Vickers hardness Hv was calculated from the test load P at that time (based on JIS Z2244) by the following formula.

Hv = 1.8544 × P / a ²

The range of the test load P is 50 to 200 kgf.

In Samples 4, 5, 6, and 7, the hardness of the defect gathering region H is the lowest. It seems that the H region has a nitrogen surface on the top and a lower hardness than the Ga surface. Some of the samples 3 have the lowest hardness, such as sample 3, and vary. The C-plane growth region Y has the highest hardness. It is unclear whether this is due to the high regularity of the crystal structure, a large amount of carbon contamination, or other causes.

  The H region has a Vickers hardness of 1200 to 1500 Hv, the Z region has a Vickers hardness of 1200 to 1800 Hv, and the Y region has a Vickers hardness of about 1300 to 1800 Hv.

[Example 16 (measurement of scratch density)]
The above-mentioned samples 3 to 7 (15 mm × 15 mm × 0.8 mm square GaN substrate) fabricated and polished by the method of the present invention were subjected to individual flaw density measurements in the H, Z, and Y regions. Scratches are generated during polishing and are not directly related to crystal growth. A substrate having too many scratches is not suitable as a substrate for a light-emitting device, but the GaN substrate of the present invention is satisfactory because of its low scratch density.

  A differential interference microscope was used to inspect the scratch. The magnification of the objective lens is 40 times. Photograph a rectangular area of 300 μm in length × 400 μm in width with a differential interference microscope, draw a test line in an arbitrary direction on the photographic surface in an arbitrary direction, count the number of scratches crossing the test line, and length it 1 mm The flaw density (lines / mm) was calculated in terms of the number.

Scratch density is greatly affected by polishing. The flaw density variation between samples is large. Most as in Sample 4 some are 0 lines / mm, and some exceed 10 ⁴ lines / mm as in Sample 3. However, there seems to be no variation between the H, Z, and Y regions. In any region, the scratch density is 0 to 1 × 10 ⁵ pieces / mm. It is sufficient as a substrate for device fabrication.

  Using the sapphire substrate of Example 1, an A3 stripe pattern is formed, a buffer layer is formed under the same conditions as in Example 1, and then the temperature is raised to 1000 ° C. After partial growth, the formation state of the polarity inversion region (orientation inversion region) H on the mask protective layer was confirmed.

  As a result of the growth, the formation of the polarity inversion region H was not sufficiently formed under the conditions 1 and 5, and was not continuous, or a region where the polarity inversion region H was not formed was observed or was insufficient. However, Condition 2, Condition 3, and Condition 4 were good. From this, it is considered that the growth rate is preferably in the range of 30 to 100 μm / h.

The perspective view for demonstrating the concentration mechanism of the dislocation which concentrates a dislocation to a ridgeline and a pit bottom by the facet in the facet growth method proposed by patent document 4 growing in a normal line direction. FIG. 1A illustrates the early stage of growth, and FIG. 1B illustrates that linear dislocation collective defects and planar dislocation collective defects are formed after the growth proceeds.

The top view for demonstrating the concentration mechanism of the dislocation which concentrates a dislocation to a ridgeline and a pit bottom by the facet in the facet growth method proposed in patent document 4 growing in the normal direction.

In the facet growth method proposed by the present inventor, a bundle of dislocations is once formed on the bottom of the pit, but the bundle disperses with growth and the dislocations diffuse again to the surroundings to explain the dislocation spreading. Figure. FIG. 3 (1) shows a linear dislocation aggregate bundle in which dislocations are once collected at the bottom of the pit, and FIG. 3 (2) shows a state in which it disperses like a haze as the growth proceeds.

The present inventor invented in order to solve the problems of dislocation aggregation portion indetermining and dislocation re-diffusion in Patent Document 4 (Patent Documents 5 to 8). A mask is formed on a base substrate, and facet growth is performed thereon. FIG. 6 is a diagram for explaining that a mask is used as a dislocation gathering portion to form a closed defect region H in which dislocations are confined. FIG. 4A shows how dislocations gather in the closed defect gathering region H by facet growth. 4 (2) shows that when the growth is continued so as not to fill the facet, the defect gathering region H grows as it is, and the low-defect single crystal region Z grows on the facet surface as it is, and the single crystal low dislocation residue that grows the C plane. The region Y is shown to grow in the same way.

1 is a partial cross-sectional view of a crystal showing a method for growing gallium nitride according to the present invention. FIG. 5A is a view for explaining that when a mask (covering part) is provided on a base substrate and gallium nitride is vapor-phase grown at a low temperature, polycrystalline fine particles are also deposited on the covering part. FIG. 5 (2) shows that when epitaxial growth is performed at a high temperature, gallium nitride grows only on the exposed portion and becomes a single crystal of the positive orientation (0001), and the covering portion cannot be formed, so that a facet surface rising from the mask covering portion is formed. Figure. FIG. 5 (3) is a diagram showing that a projection with inversion of orientation protrudes from the facet surface to the horizontal mask in a non-contact manner. FIG. 5 (4) shows the projection further extending from both. FIG. 5 (5) is a diagram showing that the extended protrusions are bonded directly above the covering portion to become a seed crystal having a reversed orientation, and a single crystal having a reversed orientation is grown thereon.

1 is a perspective view of a part of a composite substrate after growth in which a dot mask is formed on a base substrate and gallium nitride is grown from the dot mask by the method of the present invention. FIG. A gallium nitride crystal is formed on the underlying substrate, but many hexagonal pyramid facet pits are formed. The bottom of the pit is the defect gathering region H, the portion below the facet is the low defect single crystal region Z, and the portion where the C plane growth between the low defect single crystal regions Z and Z is the single crystal low dislocation residual region Y is there.

The figure which shows the electrode formation for measuring the local electrical resistivity of a gallium nitride substrate.

In the gallium nitride substrate of the present invention, as the growth proceeds, the widths of the defect assembly region H and the single crystal low dislocation residual region Y are reduced, and the width of the single crystal low dislocation region Z is increased.

1 is a perspective view of a part of a composite substrate after growth in which a stripe mask is formed on a base substrate and gallium nitride is grown from the stripe mask by the method of the present invention. FIG. Although a gallium nitride crystal is formed on the underlying substrate, a large number of ridges and valleys (V-grooves) can be formed because the mask is parallel. The prisms are arranged in parallel. The bottom of the upper V groove of the mask is a defect collecting region H, and the lower portion of the facet is a low defect single crystal region Z. The portion where the C-plane growth between the low defect single crystal regions Z and Z is the single crystal low dislocation residual region Y, but here Z is dominant and Y disappears.

1 is a perspective view of a part of a composite substrate after growth in which a stripe mask is formed on a base substrate and gallium nitride is grown from the stripe mask by the method of the present invention. FIG. Although a gallium nitride crystal is formed on the underlying substrate, a large number of ridges and valleys (V-grooves) can be formed because the mask is parallel. The bottom of the upper V groove of the mask is a defect collecting region H, and the lower portion of the facet is a low defect single crystal region Z. The portion where the C-plane growth between the low-defect single crystal regions Z and Z is a single crystal low dislocation residual region Y, which has a repeating structure HZYZHZY.

The spectrum figure of the photoluminescence when 350 nm ultraviolet rays are applied to the defect gathering area | region H of the gallium nitride board | substrate produced by this invention. The horizontal axis is the photoluminescence wavelength (nm), and the vertical axis is the photoluminescence intensity. The emission intensity ratio of 360 nm / 560 nm obtained by dividing the peak value of 360 nm by the peak value of 560 nm is 1730/180 = 9.6.

FIG. 4 is a spectrum diagram of photoluminescence when an ultraviolet ray of 350 nm is applied to a single crystal low dislocation associated region Z (facet growth region) of a gallium nitride substrate manufactured according to the present invention. The horizontal axis is the photoluminescence wavelength (nm), and the vertical axis is the photoluminescence intensity. The emission intensity ratio of 360 nm / 560 nm obtained by dividing the peak value of 360 nm by the peak value of 560 nm is 1750/90 = 19.4.

FIG. 6 is a spectrum diagram of photoluminescence when an ultraviolet ray of 350 nm is applied to a C-plane growth region (single crystal low dislocation residual region) Y of a gallium nitride substrate manufactured according to the present invention. The horizontal axis is the photoluminescence wavelength (nm), and the vertical axis is the photoluminescence intensity. The 360/560 nm emission intensity ratio obtained by dividing the 360 nm peak value by the 560 nm peak value is 70/160 = 0.44.

FIG. 5 is a plan view of pits for explaining how facet pits are generated and a large number of inward projections are generated from the facet surface when a dot mask is formed and crystals are grown by the method of the present invention.

The crystal main axes inside the positive orientation (0001) crystals Z and Y inside the facet plane, the reverse orientation (000-1) projection outside the facet plane (11-22), and the defect gathering region H are completely opposite to each other. FIG.

Explanation of symbols

H Defect assembly area (reversal orientation area)
Z single crystal low dislocation associated region (faceted growth region)
Y single crystal low dislocation residual region (C-plane growth region)
Grain boundary between K Z and H
Grain boundary formed inside H due to misalignment when K 'protrusions are bonded 4 Gallium nitride crystal
5 pits
6 Faceted surface
7 C surface ((0001) surface)
8 Pit edge
11 Linear dislocation aggregate bundle
13 Moya dislocation spread
23 Mask (coating part)
24 Gallium nitride crystal
25 pits
26 Faceted surface
27 C surface ((0001) surface)
29 Exposed area
63 Mask (coating part)
64 Gallium nitride crystal
65 pits
66 Faceted surface
67 C surface ((0001) surface)
68 Direction reversal protrusion
69 Exposed area
70 polycrystalline microparticles

Claims (21)

In epitaxial growth of gallium nitride, a base substrate is prepared, and a predetermined mask pattern that is parallel lines (stripes) or isolated dots (dots) is partially formed on the base substrate with a material that inhibits epitaxial growth. And a gallium nitride buffer layer is formed at a first temperature which is a low growth temperature from 400 ° C. to 600 ° C., and the gallium nitride is formed on the mask. Then, nitriding is performed at a second temperature of 900 ° C. to 1100 ° C. and an initial growth rate of 30 μm / h to 100 μm / h by HVPE at a second temperature of 900 ° C. to 1100 ° C. Gallium is epitaxially grown, and at the initial stage of the epitaxial growth, epitaxial growth occurs at the exposed portion, but epitaxial growth occurs at the covered portion. A slope formed of a facet of gallium nitride is formed from the end of the covering portion to the exposed portion without being subjected to the axial growth, and from the inclined surface, the gallium nitride protrusion having a polarity 180 degrees different from that of the exposed portion of gallium nitride is inverted. Formed above the fine polycrystalline grains of the mask cover, the thickness of the gallium nitride in the exposed portion increases with growth, while the protrusion grows without contacting the mask cover, and further grows on both sides of the cover. As the growth of the protrusion proceeds, a plurality of protrusions are combined in the vicinity of the upper center of the mask covering portion to cover the entire surface of the mask covering portion. A method for growing a crystal of gallium nitride, comprising forming a polarity reversal region H which is a single crystal having a 180-degree polarity different from that of an exposed portion only on the region. A base substrate is prepared, and a mask having parallel lines (stripes) or isolated dots (dots) is formed on the base substrate by a material that inhibits epitaxial growth, and the mask is covered with the covering portion and the mask. An exposed portion is provided, and a gallium nitride buffer layer is formed thereon at a first temperature which is a low temperature of 400 ° C. to 600 ° C., so that fine polycrystalline grains of gallium nitride are deposited on the mask, After that, the furnace pressure is set to 1 atm and gallium nitride is epitaxially grown by the HVPE method at a second temperature of 900 ° C. to 1100 ° C., the gallium nitride thin film cannot be formed on the mask covering portion, and the c-axis is directly above the exposed portion. the face (0001) GaN single crystal film to generate, a facet is formed which rises inclined toward the exposed portion from the end of the covering portion, the initial growth The projection c-axis growth in the growth rate to the upper cover portion not in contact with the mask covering portions beginning of epitaxial growth as 30μm / h~100μm / h is facing downward (000-1) inverted orientation single crystal It is generated above the fine polycrystalline grains of the mask covering part so as to protrude from the facet surface, and while growing the normal orientation (0001) gallium nitride while maintaining the facet of the exposed part, the protrusion is extended to above the covering part. A plurality of protrusions extending from both sides of the covering portion are combined to form a reverse orientation (000-1) single crystal region H above the covering portion so that the facet surface of the exposed portion is not buried, And a single crystal low dislocation Z region following the facet surface of the normal orientation (0001) and a C plane of the positive orientation (0001) that grows while maintaining a flat C plane between the adjacent single crystal low dislocation regions Z and Z. Completion When the region Y is generated, and the grain boundary K accompanying the inversion is generated between the inversion-oriented single crystal H and the facet-grown single crystal low-dislocation region Z, and the protrusion is united inside the inversion-oriented single crystal H The crystal grain boundary K ′ is generated due to the mismatch, and the vapor phase growth is continued and the facets are not embedded so that the Z, Y, and H regions are increased in thickness, and the ... HZYZH ... structure or ... HZHZ ... structure gallium nitride and A method of manufacturing a gallium nitride substrate, comprising: forming a composite substrate of a base substrate, removing the base substrate and mask, polishing the surface, and obtaining a gallium nitride self-supporting substrate having a ... HZYZH ... structure or a ... HZHZ ... structure. 3. The method for producing a gallium nitride substrate according to claim 2 , wherein a base substrate is formed by epitaxially growing a thin gallium nitride thin film on a substrate made of a material other than gallium nitride. As the facet plane grows upward, the dislocations that existed on the facet plane are gathered to the bottom of the facet plane aggregate, gathered at the inversion-oriented single crystal H and the crystal grain boundary K, partially disappeared, and the rest are inversion-oriented crystals. Permanently constrained by H and the grain boundary K, the dislocations in the single crystal low dislocation associated region Z and the C-plane growth region Y are reduced, and the inversion-oriented single crystal H functions as a defect assembly region. The method for manufacturing a gallium nitride substrate according to claim 2 or 3 . A single crystal Z and Y having a positive orientation (0001) whose upper surface is a gallium surface is continuously formed on the exposed portion that is not covered with the mask on the base substrate, and an upper surface is formed on the mask covering portion. The method for producing a gallium nitride substrate according to any one of claims 2 to 4 , wherein the inversion-oriented single crystal H which is a plane is continuously grown. The facet growth region Z grown on the exposed portion adjacent to the covering portion grows while keeping the {11-22}, {1-101} facet surface on the upper surface, and is sandwiched between the facet growth regions Z and Z. The plane growth region Y grows while keeping the flat C-plane (0001) on the upper surface, and the reverse orientation region H grown on the projection combined on the covering portion grows while keeping the upper surface with a lower inclination angle. The method for producing a gallium nitride substrate according to any one of claims 2 to 4 . The method of manufacturing a gallium nitride substrate according to claim 6 , wherein the lower inclined upper surface of the inversion azimuth region H is a facet surface inclined by 25 to 35 degrees with respect to a horizontal plane. The lower-inclined facet surface of the reverse orientation region H is the {11-2-6} plane or the {11-2-5} plane, or another facet plane tilted slightly (within 10 degrees) therefrom. 8. The method of manufacturing a gallium nitride substrate according to claim 7 , wherein The protrusion extending from the facet plane in the early stage of growth has a reversal orientation, and the upper surface is a {11-2-6} plane or {11-2-5} plane with a low inclination angle, or slightly (within 10 degrees) The method of manufacturing a gallium nitride substrate according to claim 6 , wherein the gallium nitride substrate is another facet surface inclined to (), and the lower surface is a {11-22} facet surface having a larger inclination angle. The crystal grain boundary (K ′) continuously extending from the mismatch plane formed by the combination of the protrusions having the reversal orientation in the initial stage of growth grows while maintaining the inside of the reversal orientation region H, and the internal grain boundary ( The method for producing a gallium nitride substrate according to any one of claims 2 to 4 , wherein K ') also cancels a part of the collected dislocations and captures and restrains the rest. Formed on the underlying substrate mask according to any one of claims 2-4, characterized in that a parallel line shape arranged in parallel at a pitch p of the covering portion having a predetermined width w (stripe type mask) A method for manufacturing a gallium nitride substrate. 12. The method for manufacturing a gallium nitride substrate according to claim 11 , wherein the width of the covering portion of the stripe mask is w = 5 μm to 100 μm and the pitch is p = 100 μm to 1000 μm. 12. The method for manufacturing a gallium nitride substrate according to claim 11 , wherein the covering portion and the exposed portion of the stripe mask extend in the <1-100> direction of the GaN crystal. The mask according to claim 2, characterized in that a constant dimension d orphaned covering portion pitch p in regularly aligned was isolated point set shape having (dot type mask) to be formed on the underlying substrate Manufacturing method of gallium nitride substrate. The method of manufacturing a gallium nitride substrate according to claim 14 , wherein the size of the isolated covering portion of the dot mask is d = 5 μm to 100 μm, and the pitch is p = 100 μm to 1000 μm. A buffer layer of gallium nitride is formed at a first temperature which is a low temperature of 400 ° C. to 600 ° C. , fine polycrystalline grains are deposited on the mask, and a second temperature of 900 ° C. to 1100 ° C. is grown. Epitaxial growth of gallium nitride, and at the beginning of the epitaxial growth, a slope made of gallium nitride facets is formed from the edge of the covering portion to the exposed portion, and the protrusions of gallium nitride are formed above the mask so as not to contact the mask from the facet slope. method of manufacturing a gallium nitride substrate according to claim 2, characterized in that the formation. In a growth temperature 400 ° C. buffer layer formed of 600 ° C. from, on a mask, a manufacturing method of the gallium nitride substrate according to claim 2, wherein the layer consisting of fine polycrystalline grain of gallium nitride is deposited. Depositing a small gallium nitride polycrystalline particles on the cover portion by forming a buffer layer of gallium nitride at a low temperature of 600 ° C. from 400 ° C. in the early growth, it deposited fine gallium nitride polycrystalline grains, 900 In the epitaxial growth from ℃ to 1100 ℃, it prevents crystals with the same orientation as the facets from extending horizontally from the bottom of the facet to the coating, and has the effect that the projections whose orientation is reversed are separated from the coating and extend from the middle of the facet The method for producing a gallium nitride substrate according to claim 2 . In the initial stage of epitaxial growth of gallium nitride, the crystal growth rate at the stage where the inversion orientation (000-1) single crystal region H having a different polarity of gallium nitride covers the entire surface of the mask covering portion is 30 to 100 μm / h. The method for producing a gallium nitride substrate according to claim 2 . 5. The gallium nitride substrate according to claim ₂ , wherein the mask material is any one of SiO ₂ , SiN, Al ₂ O ₃ , AlN, ZrO ₂ , Y ₂ O ₃ , and MgO. Production method. The base substrate is one of sapphire single crystal, Si single crystal, SiC single crystal, MgO single crystal, ZnO single crystal, GaAs single crystal, InP single crystal, GaP single crystal, GaN single crystal, and AlN single crystal. The method for producing a gallium nitride substrate according to any one of claims 2 to 4 .

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