Method for producing group iii nitride semiconductor and seed substrate

Abstract

To provide a method for producing a Group III nitride semiconductor that enables suppression of shape variation of initial nuclei.SOLUTION: A method for producing a Group III nitride semiconductor includes a crystal growth step of supplying a nitrogen-containing gas to a mixed melt obtained by mixing a Group III metal and a flux to grow a Group III nitride semiconductor on a seed substrate 9, wherein the seed substrate 9 includes a substrate 1 and a plurality of seed crystals 2 made of a Group III nitride semiconductor and provided on the substrate 1, and a side surface 2a of each of the seed crystals 2 has a (10-11) plane.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a Group III nitride semiconductor and a seed substrate. [Background technology]

[0002] The Na flux method is a well-known method for producing GaN. In the Na flux method, nitrogen is dissolved in a molten mixture of Ga and Na to grow GaN in the liquid phase. In the Na flux method, a seed substrate is generally placed in the molten mixture and GaN is grown on the seed substrate.

[0003] In the Na flux method, a method using a multi-point seed (MPS) substrate as a seed substrate is known as a method for growing large-area GaN crystals with low dislocation density and warpage. An MPS substrate has many tiny dot-shaped seed crystals periodically arranged on a substrate such as sapphire.

[0004] Patent Document 1 describes that the planar pattern of the seed crystals on the MPS substrate is circular or hexagonal. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-151519 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when seed crystals that are circular or hexagonal in plan view are formed as in Patent Document 1, the shapes of the initial nuclei growing from the various crystals are unstable and vary, resulting in failure to form GaN uniformly.

[0007] The present invention has been made in view of the above background, and aims to provide a method for producing a Group III nitride semiconductor and a seed substrate that can suppress variations in the shape of the initial nuclei. [Means for solving the problem]

[0008] One aspect of the present invention is a crystal growth step of growing a Group III nitride semiconductor on a seed substrate by supplying a nitrogen-containing gas to a mixed melt obtained by mixing a Group III metal and a flux; the seed substrate includes a substrate and a plurality of seed crystals made of a Group III nitride semiconductor provided on the substrate; In the method for producing a Group III nitride semiconductor, the side surface of the seed crystal has a (10-11) plane.

[0009] Another aspect of the present invention is A substrate; a plurality of seed crystals made of a Group III nitride semiconductor provided on the substrate, The side of the seed crystal is on the seed substrate, which has a (10-11) plane. [Effects of the Invention]

[0010] In the above embodiment, the side surface of the seed crystal has a (10-11) plane, which makes it possible to suppress variations in the shape of the initial nuclei.

[0011] As described above, according to the above aspects, it is possible to provide a method for manufacturing a Group III nitride semiconductor and a seed substrate that can suppress variations in the shape of the initial nuclei. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view showing the configuration of a seed substrate in Embodiment 1, taken along a plane perpendicular to a main surface of the substrate. [Figure 2] FIG. 1 is a plan view showing the configuration of a seed substrate in Embodiment 1. [Figure 3] FIG. 2 is a cross-sectional view showing the configuration of a seed crystal, the cross-sectional view being perpendicular to the main surface of the substrate. [Figure 4] FIG. 2 is a plan view showing the configuration of a seed crystal. [Figure 5] 1A to 1C are diagrams showing the manufacturing process of a Group III nitride semiconductor according to the first embodiment. [Figure 6] A diagram showing the FFC process. [Figure 7] SEM image of the seed substrate viewed from an angle. [Figure 8] Enlarged SEM image of the seed crystal. [Figure 9] SEM image showing the cross section of the seed crystal. [Figure 10] An oblique overhead SEM image of the initial nucleus. [Figure 11] Fluorescence microscope image of grown crystals. [Figure 12] 1A and 1B are diagrams showing the configuration of a seed crystal in a first modified example of the first embodiment, where (a) is a cross-sectional view perpendicular to the main surface of the substrate, and (b) is a plan view. [Figure 13] 1A and 1B are diagrams showing the configuration of a seed crystal in a second modified example of the first embodiment, where (a) is a cross-sectional view perpendicular to the main surface of the substrate, and (b) is a plan view. [Figure 14] 10A and 10B are diagrams showing the configuration of a seed crystal in a third modified example of the first embodiment, where (a) is a cross-sectional view perpendicular to the main surface of the substrate, and (b) is a plan view. [Figure 15] 10A and 10B are diagrams showing the configuration of a seed crystal in a fourth modified example of the first embodiment, where (a) is a cross-sectional view perpendicular to the main surface of the substrate, and (b) is a plan view. [Figure 16] 10A and 10B are diagrams showing the configuration of a seed crystal in a fifth modified example of the first embodiment, where (a) is a cross-sectional view perpendicular to the main surface of the substrate, and (b) is a plan view. [Figure 17] FIG. 2 is a cross-sectional view showing the configuration of a seed crystal, the cross-sectional view being perpendicular to the main surface of the substrate. DETAILED DESCRIPTION OF THE INVENTION

[0013] The method for producing a Group III nitride semiconductor includes a crystal growth step of growing a Group III nitride semiconductor on a seed substrate by supplying a nitrogen-containing gas to a mixed melt of a Group III metal and a flux, the seed substrate including a substrate and a plurality of seed crystals made of a Group III nitride semiconductor provided on the substrate, the side surfaces of the seed crystals having a (10-11) plane.

[0014] In the method for producing a Group III nitride semiconductor, the side surface of the seed crystal may have a ridge formed by (10-11) planes, which can further suppress variation in the shape of each initial nucleus.

[0015] In the method for producing a Group III nitride semiconductor, the side surface of the seed crystal may be formed solely from the (10-11) plane, which can further suppress variations in the shape of each initial nucleus.

[0016] In the method for producing a Group III nitride semiconductor, the height of the seed crystal may be 0.01 to 0.6 times the diameter of the seed crystal in a plan view, and the height of the seed crystal may be 30 μm or more. This makes it easier for the initial nucleus to grow from the side surface of the seed crystal.

[0017] In the method for producing a Group III nitride semiconductor, the seed crystal may have a diameter in plan view of 10 μm or more and 500 μm or less.

[0018] In the method for producing a Group III nitride semiconductor, the seed crystal may have a regular hexagonal pyramid truncated portion having a regular hexagonal pyramid shape. This makes it possible to further suppress variation in the shape of each initial nucleus. Furthermore, the seed crystal may have a disk portion having a disk shape and located in contact with the substrate, and a regular hexagonal pyramid truncated portion located in contact with the disk portion and having a regular hexagonal pyramid shape. By having the disk portion, stress can be dispersed when the substrate is peeled off after growth is completed, and the occurrence of cracks in the grown crystal can be suppressed.

[0019] In the method for producing a Group III nitride semiconductor, the seed crystal may have a recess in the center, which can suppress dislocation propagation to the upper part of the seed crystal.

[0020] In the method for manufacturing a Group III nitride semiconductor, the recess may have a depth that reaches the substrate.

[0021] In the method for manufacturing a Group III nitride semiconductor, the diameter of the recess may be set so that the seed crystal has no upper surface.

[0022] In the method for manufacturing a Group III nitride semiconductor, the recess may have an uneven side surface.

[0023] In the method for producing a Group III nitride semiconductor, the seed crystal may be formed by forming a mask with openings on the substrate and selectively growing the Group III nitride semiconductor through the openings, which allows the shapes of various crystals to be uniform.

[0024] The seed substrate includes a substrate and a plurality of seed crystals made of a group III nitride semiconductor provided on the substrate, and the side surfaces of the seed crystals have a (10-11) plane.

[0025] In the seed substrate, the side surface of the seed crystal may have a ridge formed by the (10-11) planes, which can further suppress variation in the shape of each initial nucleus.

[0026] In the seed substrate, the side surface of the seed crystal may be formed only of the (10-11) plane, which can further suppress variation in the shape of each initial nucleus.

[0027] In the seed substrate, the height of the seed crystal may be 0.01 to 0.6 times the diameter of the seed crystal in a plan view, and the height of the seed crystal may be 30 μm or more, which makes it easier for the initial nucleus to grow from the side surface of the seed crystal.

[0028] In the seed substrate, the diameter of the seed crystal in a plan view may be 10 μm or more and 500 μm or less.

[0029] In the seed substrate, the seed crystal may have a regular hexagonal pyramid truncated portion having a regular hexagonal pyramid truncated shape. This can further suppress variation in the shape of each initial nucleus. Furthermore, the seed crystal may have a disk portion that is in contact with the substrate and has a disk-like shape, and a regular hexagonal pyramid truncated portion that is in contact with the disk portion and has a regular hexagonal pyramid truncated shape. By having the disk portion, stress can be dispersed when the substrate is peeled off after growth is completed, and the occurrence of cracks in the grown crystal can be suppressed.

[0030] The seed substrate may have a recess in the center of the seed crystal, which can suppress dislocation propagation to the top of the seed crystal.

[0031] In the seed substrate, the depth of the recess may be deep enough to reach the substrate.

[0032] The diameter of the recess in the seed substrate may be set so that the seed crystal has a shape that does not have an upper surface.

[0033] In the seed substrate, the side surface of the recess may have an uneven surface.

[0034] (Embodiment 1) 1. Overview of the flux method Embodiment 1 is a method for producing a Group III nitride semiconductor by a flux method, in which a Group III nitride semiconductor is grown by supplying and dissolving a nitrogen-containing gas into a mixed melt containing an alkali metal flux and a Group III metal raw material, thereby epitaxially growing a Group III nitride semiconductor in the liquid phase.

[0035] The Group III metal raw material is at least one of gallium (Ga), aluminum (Al), and indium (In), and the composition of the Group III nitride semiconductor to be grown can be controlled by adjusting the ratio thereof, allowing for the growth of GaN, AlN, InN, AlGaN, InGaN, AlGaInN, etc. The present invention is particularly suitable for growing GaN.

[0036] The alkali metal used as the flux is usually sodium (Na), but potassium (K) may also be used, or a mixture of Na and K. Furthermore, lithium (Li) or an alkaline earth metal may also be mixed.

[0037] Carbon (C) may be added to the mixed melt. The addition of C can increase the crystal growth rate. Dopants other than C may also be added to the mixed melt for the purposes of controlling the conductivity type, magnetism, and other physical properties of the group III nitride semiconductor to be grown, promoting crystal growth, suppressing miscellaneous crystals, and controlling the growth direction. For example, germanium (Ge) can be used as an n-type dopant, and magnesium (Mg), zinc (Zn), calcium (Ca), and the like can be used as p-type dopants.

[0038] The nitrogen-containing gas is a gas of nitrogen molecules or a compound such as ammonia that contains nitrogen as a constituent element, or may be a mixed gas thereof, or may be a gas in which the nitrogen-containing gas is mixed with an inert gas such as a rare gas.

[0039] 2. Seed Substrate Structure In the first embodiment, a seed substrate 9 is placed in the mixed melt, and a Group III nitride semiconductor is grown on the seed substrate 9. The seed substrate 9 may be placed in the mixed melt before heating and pressurizing, but it is preferable to place the seed substrate 9 in the mixed melt after heating and pressurizing to reach the growth temperature and growth pressure. This can prevent the seed crystal 2 on the seed substrate 9 from melting back.

[0040] An MPC (multi-point seed) substrate is used as the seed substrate 9. The MPC substrate is a substrate 1 on which a plurality of dot-shaped seed crystals 2 are periodically arranged. FIG. 1 is a cross-sectional view of the seed substrate 9, which is a cross-section perpendicular to the main surface of the substrate. FIG. 2 is a plan view of the seed substrate 9 as viewed from above.

[0041] Substrate 1 can be made of a group III nitride semiconductor, sapphire, aluminum oxynitride, SiC, Si, spinel, ZnO, gallium oxide, etc. In the case of a sapphire substrate, the main surface is, for example, the c-plane or the a-plane.

[0042] A plurality of seed crystals 2 are provided on the substrate 1 via a buffer layer (not shown). The seed crystals 2 are arranged in a regular triangular lattice pattern. The buffer layer and the seed crystals 2 are made of a group III nitride semiconductor of any composition, such as GaN, AlGaN, or AlN. An appropriate material for the buffer layer is selected depending on the material of the seed crystals 2. For example, if the seed crystals 2 are made of GaN, the buffer layer is preferably made of GaN. The material for the seed crystals is usually a group III nitride semiconductor of the same composition as the group III nitride semiconductor to be grown by the flux method. The seed crystals 2 may be grown by any method, such as MOCVD, HVPE, or MBE, but MOCVD or HVPE is preferred in terms of crystallinity, growth time, etc.

[0043] As shown in FIG. 2, the seed crystals 2 are arranged in a regular triangular lattice pattern. Any periodic arrangement is possible, not limited to a regular triangular lattice pattern, but highly symmetrical patterns such as a square lattice pattern or a regular triangular lattice pattern are preferred. This allows the Group III nitride semiconductors grown from the various crystals 2 to be uniformly combined, enabling the growth of a Group III nitride semiconductor with fewer dislocations and warpage. When a regular triangular lattice pattern is used, it is preferable that the arrangement direction coincide with the a-axis direction or m-axis direction of the seed crystals 2. Here, "match" does not mean perfect match; an angular deviation of about 10 degrees is acceptable as an error. An angular deviation of 1 degree or less is preferred.

[0044] The distance L1 between the centers of adjacent seed crystals 2 is preferably 100 to 2000 μm. Within this range, a Group III nitride semiconductor with fewer dislocations and warpage can be grown. It is more preferably 200 to 1500 μm, and even more preferably 300 to 1000 μm.

[0045] Next, the shape of the seed crystal 2 will be described in detail. Fig. 3 is a cross-sectional view showing the configuration of the seed crystal 2, which is a cross-sectional view perpendicular to the main surface of the substrate. Fig. 4 is a plan view showing the configuration of the seed crystal 2. As shown in Figs. 3 and 4, the seed crystal 2 has a disk portion having a disk shape and a regular hexagonal pyramid truncated portion having a regular hexagonal pyramid truncated shape located on and in contact with a cylindrical portion, with a recess 2d provided in the center of the regular hexagonal pyramid truncated portion.

[0046] As will be described later, the seed crystal 2 is formed by selective growth using a mask, and the crystal grows laterally from the opening in the mask. The opening pattern of the mask is circular. Therefore, after removing the mask, the mask opening portion remains in the shape of a disk. This remaining portion is the disk portion.

[0047] The shape of the disk portion is equal to the shape of the mask opening used for selectively growing the seed crystal 2. Therefore, the thickness of the disk portion is approximately equal to the thickness of the mask. The diameter of the disk portion is approximately equal to the diameter of the mask opening. Furthermore, the diameter D1 of the regular hexagonal pyramid truncated portion is larger than the diameter of the disk portion. Because the disk portion is circular in plan view, stress can be dispersed when the substrate 1 is separated after growing the Group III nitride semiconductor by the flux method, and the occurrence of cracks in the grown crystal can be suppressed.

[0048] Depending on the opening pattern of the mask, the disk portion may be replaced with a regular hexagonal plate or other shape, but a disk is preferred from the viewpoint of dispersing stress as described above.

[0049] The base of the frustum of the regular hexagonal pyramid of the seed crystal is a regular hexagon. In particular, a regular hexagon with each side aligned with the m-plane of the seed crystal 2 (each side aligned with the a-axis direction) is preferred. Because Group III nitride semiconductors are hexagonal crystals, a regular hexagonal shape allows the Group III nitride semiconductors grown from the frustum of the regular hexagonal pyramid of each type of crystal 2 to be uniformly combined. However, it is not necessary to completely align the base with the a-axis, and an angle deviation of about 10 degrees is permissible. An angle deviation of 1 degree or less is preferred.

[0050] The six side faces 2a of the hexagonal truncated pyramid portion of the seed crystal 2 are (10-11) planes of the Group III nitride semiconductor. The (10-11) plane is a stable plane in the mixed melt of the Na flux method. Therefore, the Group III nitride semiconductor grows from the side faces 2a of the hexagonal truncated pyramid portion of the seed crystal 2 while maintaining the (10-11) plane. As a result, the shape of each initial nucleus 3 can be made uniform. Note that the entire side faces 2a do not need to be (10-11) planes, but it is preferable that 95% or more of the entire side faces are (10-11) planes. In addition, the (10-11) plane referred to here includes planes that form angles of -5 to 5 degrees with respect to the (10-11) plane as an error.

[0051] The diameter D1 (diameter of the circumscribed circle in plan view) of the regular hexagonal pyramid portion of the seed crystal 2 is preferably 10 to 500 μm. Within this range, a Group III nitride semiconductor with fewer dislocations and warpage can be grown. Furthermore, the area of ​​the side surface 2a of the regular hexagonal pyramid portion of the seed crystal 2 can be increased, facilitating the growth of the initial nuclei 3 from the side surface 2a. A diameter of 50 to 300 μm is more preferred, and a diameter of 100 to 200 μm is even more preferred.

[0052] Furthermore, the height H1 of the seed crystal 2 is preferably 30 μm or more. Within this range, the area of ​​the side surface 2a can be made sufficiently large, allowing crystals to grow uniformly from each side surface 2a. As a result, the shapes of the initial nuclei 3 growing from the various crystals 2 can be made uniform. However, if H1 is too high, problems such as the long time required to form the seed crystal 2 can occur, so it is preferable to set it to 100 μm or less. It is more preferably 20 to 60 μm, and even more preferably 30 to 50 μm.

[0053] For the same reasons as above, the height H1 of the seed crystal 2 is preferably 0.01 to 0.6 times the diameter D1 of the seed crystal 2, more preferably 0.1 to 0.35 times, and even more preferably 0.15 to 0.3 times.

[0054] A recess 2d is provided in the center of the seed crystal 2. Providing the recess 2d prevents the initial nuclei 3 grown from the seed crystal 2 from filling the recess 2d, forming a void 7. The formation of the void 7 prevents dislocations in the seed crystal 2 from propagating upward, enabling the growth of a high-quality Group III nitride semiconductor.

[0055] The bottom surface 2b of the recess 2d is flat and is the (0001) plane (c-plane) of the group III nitride semiconductor. The bottom surface 2b is approximately circular in plan view. The bottom surface 2b does not need to be flat and may have irregularities. The shape of the bottom surface 2b in plan view does not need to be circular.

[0056] The side surface 2c of the recess 2d has many irregularities formed thereon, and has an overall inclination similar to that of the (10-11) plane. By forming the side surface 2c in such an irregular shape, the side surface 2c becomes a starting point for crystal growth of the Group III nitride semiconductor, making it easier to fill the upper part of the seed crystal 2 with the Group III nitride semiconductor. Note that the side surface 2c may also be a flat surface.

[0057] The depth H2 of the recesses 2d is preferably 10 to 100 μm. By setting the depth H2 in this range, voids 7 are more easily formed, and a higher quality Group III nitride semiconductor can be grown. The depth H2 is more preferably 20 to 60 μm, and even more preferably 30 to 50 μm. For the same reason, the depth H2 of the recesses 2d is preferably 0.3 to 1.0 times the height H1 of the seed crystal 2, and more preferably 0.6 to 0.8 times.

[0058] The diameter of the top surface of the recess 2d is within a range such that the top surface does not exist on the seed crystal 2, and the side surface 2c of the recess 2d and the side surface 2a of the seed crystal 2 are connected at an angle. Therefore, the c-plane does not exist in the upper part of the seed crystal 2. The c-plane may be etched in the mixed melt of the Na flux method, which may cause variations in the shape of each initial nucleus 3. Furthermore, crystal growth from the c-plane may cause dislocations in the seed crystal 2 to propagate upward. Therefore, if the shape does not have a c-plane in the upper part, variations in the shape of each initial nucleus 3 can be suppressed, and the upward propagation of dislocations in the seed crystal 2 can be suppressed.

[0059] 3. Method for manufacturing seed substrate The seed substrate 9 can be fabricated, for example, as follows. First, a mask having a plurality of openings is formed on the substrate 1. The plurality of openings are arranged in a pattern of a regular triangular lattice. The openings are circular. Although shapes other than circular, such as regular hexagons, are also acceptable, circular openings are preferred as in the embodiment in order to form disk portions and suppress cracks when the substrate is peeled off. The mask may be made of any material that can suppress the growth of a Group III nitride semiconductor on the mask, such as SiO2.

[0060] Next, a buffer layer (not shown) and a seed crystal 2 are selectively grown in this order on the substrate exposed in the opening by a method such as MOCVD or HVPE. Next, the mask is removed by wet etching using hydrofluoric acid or the like. In this way, a seed substrate 9 can be produced.

[0061] Here, when the seed crystals 2 are selectively grown through the openings in the mask, facet growth of the Group III nitride semiconductor can be achieved by appropriately controlling the growth conditions, and the shape of the seed crystals 2 can be made to have the shapes shown in Figures 3 and 4. For example, the growth temperature can be set to 1120 to 1145°C and the V / III ratio to 970 to 1020. Furthermore, because the shape is determined by selective growth, the shapes of various crystals 2 can be made uniform.

[0062] 4. Method for manufacturing Group III nitride semiconductors Next, a method for manufacturing a Group III nitride semiconductor according to the first embodiment will be described with reference to the drawings.

[0063] First, the atmosphere inside the furnace is replaced with an inert gas, the inside of the furnace is heated, and then the furnace is evacuated to a vacuum, thereby sufficiently reducing outgas components such as oxygen inside the furnace.

[0064] Next, predetermined amounts of alkali metal and Group III metal are weighed in a glove box where the atmosphere, including oxygen and dew point, is controlled. Then, the weighed predetermined amounts of alkali metal and Group III metal are charged into the crucible 100. If necessary, an additive element such as carbon may be charged.

[0065] Next, the crucible 100 containing the raw materials and the seed substrate 9 are placed in a reaction vessel, which is then evacuated, and a nitrogen-containing gas is supplied to the reaction vessel. When the pressure inside the reaction vessel reaches the crystal growth pressure, the temperature inside the furnace is raised to the crystal growth temperature. The crystal growth temperature is, for example, 700°C or higher and 1000°C or lower, and the crystal growth pressure is, for example, 2 MPa or higher and 10 MPa or lower. During the temperature increase process, the solid alkali metal and solid Group III metal in the crucible 100 melt and become liquid, forming a mixed melt 101. At this stage, the seed substrate 9 is not yet introduced into the mixed melt 101.

[0066] When the temperature and pressure inside the reaction vessel reach the crystal growth temperature and pressure, and the nitrogen dissolved in the mixed melt 101 becomes supersaturated, the seed substrate 9 is placed into the mixed melt 101 in the crucible 100. Then, crystals (initial nuclei 3) of a Group III nitride semiconductor begin to grow from the various crystals 2 on the seed substrate 9. The growth of the initial nuclei 3 continues until adjacent initial nuclei 3 begin to coalesce (see FIG. 5(a)). Note that a gap remains between the initial nuclei 3 and the substrate 1.

[0067] Here, the (10-11) plane, which is the side surface 2a of the regular hexagonal pyramid truncated portion of the seed crystal 2, exists stably in the mixed melt 101 without being etched. In addition, the height H1 of the seed crystal 2 is 30 μm or more, and the side surface 2a has a sufficiently large area. Therefore, the initial nuclei 3 grow from the side surface 2a while maintaining the (10-11) plane. Since the shapes of the various crystals 2 are uniform and grow uniformly from the seed crystal 2 while maintaining the (10-11) plane, variation in the shape of each initial nucleus 3 can be suppressed, and the shape of each initial nucleus 3 can be made uniform.

[0068] Furthermore, since a recess 2d is formed in the center of the seed crystal 2, the initial nucleus 3 does not completely fill the recess 2d, and a void 7 is formed. The mixed melt 101 is confined within the void 7. Since the void 7 is formed in the upper part of the seed crystal 2, it is possible to prevent dislocations in the seed crystal 2 from being carried over to the upper part.

[0069] Furthermore, by making the diameter of the recess 2d large, the seed crystal 2 is shaped so that it does not have an upper surface (c-plane). The c-plane is an unstable surface that may be etched in the mixed melt 101. Because there is no crystal growth from such an unstable surface, variation in the shape of each initial nucleus 3 can be further suppressed. Furthermore, because there is no crystal growth from the c-plane, it is possible to further suppress the transfer of dislocations in the seed crystal 2 to the upper part.

[0070] When adjacent initial nuclei 3 begin to coalesce, crystal growth is performed using the FFC (flux film coating) method. The FFC method is a method in which a seed substrate 9 is repeatedly removed from and placed into a mixed melt 101 at a predetermined cycle (see Figure 6). When adjacent initial nuclei 3 begin to coalesce, depressions 4 appear on the coalesced surface. When the seed substrate 9 is removed from the mixed melt 101, the mixed melt 101 accumulates in the depressions 4 between the adjacent initial nuclei 3. This allows crystals 5 to grow along the depressions 4 (see Figure 5(b)).

[0071] Here, the mixed melt 101 accumulated in the recess 4 is thin, so it is prone to nitrogen supersaturation. This can speed up the crystal growth. On the other hand, because the amount of accumulated mixed melt 101 is small, the amount of Group III metal is also small, and crystal growth stops after a while. Therefore, the seed substrate 9 is again placed in the mixed melt 101 and the substrate is removed from the mixed melt 101, so that the mixed melt 101 containing the Group III metal is intermittently supplied to the recess 4. The FFC method is performed until the growth of the crystal 5 fills the recess 4. This allows the growth of a crystal with a flat c-plane.

[0072] Although it is not always necessary to perform the FFC growth step, it is preferable to perform the FFC growth step in order to further improve the flatness of the crystal and further reduce warpage.

[0073] Once the depressions 4 are filled and a flat crystal surface is formed, the seed substrate 9 is again placed in the mixed melt 101. Then, the Group III nitride semiconductor crystal 6 is grown and thickened. Because the shape of each initial nucleus 3 is uniform, the crystal 6 can also be formed uniformly within the plane. Furthermore, because the inheritance of dislocations in the seed crystal 2 to the upper part is suppressed, the crystal 6 can be formed with high quality.

[0074] Once the crystal 6 has grown to the desired thickness, the temperature is lowered to room temperature, and the pressure is also lowered to atmospheric pressure, completing the growth of the Group III nitride semiconductor. At this point, the gap between the initial nuclei 3 and the substrate 1 remains unfilled. Therefore, the substrate 1 can naturally peel off when the temperature is lowered due to the difference in thermal expansion coefficients.

[0075] As described above, according to the method for producing a Group III nitride semiconductor in embodiment 1, the side surface of the seed crystal 2 is configured as the (10-11) plane, which makes it possible to suppress variations in the shape of each initial nucleus 3, and to grow a uniform, high-quality crystal 6.

[0076] In addition, a recess 2d is provided in the center of the seed crystal 2, resulting in a shape without an upper surface. Therefore, when the initial nucleus 3 grows, the upper part of the seed crystal 2 is not filled, and a void 7 is formed. As a result, it is possible to prevent dislocations in the seed crystal 2 from propagating upward, and a high-quality crystal 6 can be grown.

[0077] Next, experimental results relating to the first embodiment will be described.

[0078] Experiment 1 A mask made of SiO2 was formed on a substrate 1 made of c-plane sapphire by CVD. The mask had a pattern of circular openings arranged in a regular triangular lattice. The center-to-center distance between adjacent openings was 550 μm, and the diameter of each opening was 175 μm. Next, a buffer layer was formed on the bottom of the openings by MOCVD, and then a seed crystal 2 made of GaN was formed on the buffer layer. The seed crystal 2 was grown at a temperature of 1140°C and a V / III ratio of 720.

[0079] Figure 7 is an SEM image of a seed crystal 2 on a substrate 1, and Figure 8 is an enlarged SEM image of the seed crystal 2. Figure 9 is a cross-sectional SEM image of the seed crystal 2. As shown in Figures 7 to 9, the seed crystal 2 has a disk portion located on the substrate 1 and a regular hexagonal pyramidal truncated portion located on the disk portion and having a central recess 2d. Six side surfaces 2a of the regular hexagonal pyramidal truncated portion are exposed. The angle of the side surface 2a indicates that it is a (10-11) plane. Furthermore, the diameter of the recess 2d is wide, and the side surface 2c of the recess 2d and the side surface 2a of the seed crystal 2 form an apex angle. Therefore, it can be seen that the shape does not have a top surface. It can also be seen that the side surface 2c of the recess 2d has many irregularities. Figure 7 also indicates that the shapes of the various crystals 2 are uniform and consistent.

[0080] Experiment 2 GaN crystals were grown by the Na flux method using the seed substrate 9 prepared as in Experiment 1. The growth was carried out by growing initial nuclei 3 from the seed crystal 2 until the initial nuclei 3 from adjacent seed crystals 2 coalesced.

[0081] Figure 10(a) is an SEM image of the grown initial nuclei 3, and (b) is a further enlarged SEM image. As shown in Figure 10, the initial nuclei 3 are in the shape of a regular hexagonal truncated pyramid, with the side faces being the (10-11) plane and the top face being the (0001) plane (c-plane). Also, as shown in Figure 10, it can be seen that the initial nuclei 3 grown from the various crystals 2 are uniform in shape. Therefore, it can be seen that the initial nuclei 3 can be uniformly coalesced, and flat, uniform crystals 6 can be grown on the initial nuclei 3.

[0082] Experiment 3 GaN crystals were grown by the Na flux method using seed substrates 9 prepared as in Experiment 1. Growth was continued until the initial nuclei 3 from various crystals 2 coalesced, filling the depressions 4 between the initial nuclei 3 using the FFC method, and then growing crystals 6 on the coalesced initial nuclei 3.

[0083] FIG. 11 is a fluorescent X-ray image of a cross section of the seed substrate 9 after GaN crystal growth, showing the location of oxygen. As shown in FIG. 11, it can be seen that the recesses 2d of the seed crystal 2 are not filled with the initial nuclei 3, and voids 7 are formed. The mixed molten liquid (mainly containing sodium and gallium) used in the Na flux method is trapped in the voids 7. As described above, it can be seen that the use of the seed substrate 9 of the first embodiment allows the formation of voids 7, thereby preventing the propagation of dislocations toward the upper part of the seed crystal 2.

[0084] (Modification 1 of Embodiment 1) In the first embodiment, the depth of the recess 2d of the seed crystal 2 is set to a depth that does not expose the substrate 1. However, as shown in FIG. 12, the depth of the recess 2d may be set to a depth that exposes the substrate 1 at the bottom. FIG. 12 shows the shape of the seed crystal 2 in a first modified example of the first embodiment, where FIG. 12(a) is a cross-sectional view perpendicular to the main surface of the substrate, and FIG. 12(b) is a plan view. By making the recess 2d deep in this manner, there is no region in the seed crystal 2 where the c-plane is exposed. This prevents the c-plane growth of a crystal from the seed crystal 2, and further suppresses the propagation of dislocations from the seed crystal 2 to the crystal above. Furthermore, the deeper recess 2d makes it easier to form voids 7.

[0085] In addition, in order to form the seed crystal 2 shown in Figure 12, a mask having a ring-shaped (e.g., annular) opening can be used to selectively grow the seed crystal 2 in a ring shape, thereby forming the seed crystal 2 as shown in Figure 12.

[0086] (Modification 2 of Embodiment 1) In the first embodiment, a recess 2d is provided in the center of the seed crystal 2, but as shown in Fig. 13, a regular hexagonal pyramidal portion without a recess 2d may be used. Fig. 13 shows the shape of the seed crystal 2 in a second modified embodiment of the first embodiment, with Fig. 13(a) being a cross-sectional view perpendicular to the main surface of the substrate, and Fig. 13(b) being a plan view. Because the side surface of the regular hexagonal pyramidal portion of the seed crystal 2 is the (10-11) plane, the shape of each initial nucleus 3 can be made uniform.

[0087] (Variation 3 of Embodiment 1) In the first embodiment, the seed crystal may have any shape with its side surface being a (10-11) plane. For example, as shown in FIG. 14, instead of the truncated hexagonal pyramidal portion, a regular hexagonal pyramidal portion having a side surface 12a in the (10-11) plane may be used. FIG. 14 shows the shape of the seed crystal 12 in a third modified embodiment of the first embodiment, where FIG. 14(a) is a cross-sectional view perpendicular to the substrate main surface, and FIG. 14(b) is a plan view. Because the side surface 12a is a (10-11) plane, the shape of the initial nuclei 3 can be made uniform. Furthermore, because it is a pyramidal shape, there is no top surface. Therefore, dislocations in the seed crystal 2 can be prevented from continuing to the upper part of the seed crystal 2.

[0088] (Fourth Variation of the First Embodiment) In the first embodiment, the seed crystal 2 may have any shape having a recess in the center. An example is shown in FIG. 15 . FIG. 15 shows the shape of the seed crystal 22 in a fourth modified embodiment of the first embodiment, where FIG. 15( a) is a cross-sectional view perpendicular to the substrate main surface, and FIG. 15( b) is a plan view. As shown in FIG. 15 , the seed crystal 22 in the fourth modified embodiment of the first embodiment has a truncated cone shape instead of the regular hexagonal pyramid shape in the first embodiment, and has a recess 22 d in the center. The bottom surface 22 b of the recess 22 d is flat. Furthermore, the side surface 22 c of the recess 22 d is uneven. Because of the recess 22 d, voids can be formed in the initial nucleus 3, as in the first embodiment. Furthermore, the recess prevents the c-plane from existing. Therefore, dislocations in the seed crystal 2 can be prevented from continuing to the upper part of the seed crystal 2.

[0089] (Variation 5 of Embodiment 1) In the first embodiment, the seed crystal 2 has a shape without an upper surface, but it may have a shape with an upper surface. FIG. 16 shows the shape of the seed crystal 32 in a fifth modified embodiment of the first embodiment, where FIG. 16(a) is a cross-sectional view perpendicular to the substrate main surface and FIG. 16(b) is a plan view. As shown in FIG. 16, the seed crystal 32 in the fifth modified embodiment of the first embodiment has a small diameter of the recess 32d so that the upper surface 32e is formed. The side surface 32a of the frustum of the regular hexagonal pyramid of the seed crystal 32 is a (10-11) plane. The bottom surface 2b of the recess 2d is flat, and the side surface 2c is uneven. The difference from the first embodiment is that the upper surface 32e is formed. Since the seed crystal 32 has the upper surface 32e, the effect of suppressing dislocation propagation toward the upper part of the seed crystal 32 is lower than in the first embodiment. However, the same effects as the seed crystal 2 in the first embodiment can otherwise be obtained.

[0090] (Other variations) Although the side surface of the seed crystal 2 may have a plane other than the (10-11) plane, it is preferable that the side surface is formed only of the (10-11) plane. Also, it is preferable that the side surface has a shape having a ridge line formed by the (10-11) planes.

[0091] In the first embodiment, the seed crystal has a disk portion located on and in contact with the substrate 1, and a regular hexagonal pyramid portion on the disk portion, but as shown in Fig. 17, the regular hexagonal pyramid portion may be in direct contact with the substrate 1 without the disk portion. The same applies to the first to fifth modified embodiments of the first embodiment. [Explanation of symbols]

[0092] 1: Circuit board 2: Seed crystal 2a: Side 2b: Bottom 2c: Side 2d: Recess 3: Initial nucleus 4: Depression 5, 6: Crystal 9: Seed substrate

Claims

1. a crystal growth step of growing a Group III nitride semiconductor on a seed substrate by supplying a nitrogen-containing gas to a mixed melt obtained by mixing a Group III metal and a flux; the seed substrate includes a substrate and a plurality of seed crystals made of a Group III nitride semiconductor provided on the substrate; The method for producing a Group III nitride semiconductor, wherein the side surface of the seed crystal has a (10-11) plane.

2. 2. The method for producing a Group III nitride semiconductor according to claim 1, wherein the side surface of the seed crystal has a ridge line formed by (10-11) planes.

3. 2. The method for producing a Group III nitride semiconductor according to claim 1, wherein the side surface of the seed crystal is composed only of a (10-11) plane.

4. 4. The method for producing a Group III nitride semiconductor according to claim 1, wherein the height of the seed crystal is 0.01 to 0.6 times the diameter of the seed crystal in a plan view.

5. The method for producing a Group III nitride semiconductor according to claim 1 , wherein the height of the seed crystal is 30 μm or more.

6. 4. The method for producing a Group III nitride semiconductor according to claim 1, wherein the seed crystal has a diameter in a plan view of 10 μm or more and 500 μm or less.

7. The method for producing a Group III nitride semiconductor according to claim 1 , wherein the seed crystal has a regular hexagonal pyramidal truncated portion having a regular hexagonal pyramidal truncated shape.

8. 2. The method for producing a Group III nitride semiconductor according to claim 1, wherein the seed crystal has a disk portion located on and in contact with the substrate and having a disk shape, and a regular hexagonal pyramid truncated portion located on and in contact with the disk portion and having a regular hexagonal pyramid truncated shape.

9. The method for producing a Group III nitride semiconductor according to claim 1 , wherein the seed crystal has a recess in the center.

10. The method for producing a Group III nitride semiconductor according to claim 9 , wherein the recess has a depth that reaches the substrate.

11. The method for producing a Group III nitride semiconductor according to claim 9 , wherein the diameter of the recess is set so that the seed crystal has no upper surface.

12. The method for producing a Group III nitride semiconductor according to claim 9 , wherein the recess has an uneven side surface.

13. 2. The method for producing a Group III nitride semiconductor according to claim 1, wherein the seed crystal is formed by forming a mask having an opening on the substrate and selectively growing the Group III nitride semiconductor through the opening.

14. A substrate; a plurality of seed crystals made of a Group III nitride semiconductor provided on the substrate, A seed substrate, wherein the side surface of the seed crystal has a (10-11) plane.

15. The seed substrate according to claim 14, wherein the side surface of the seed crystal has a ridge formed by (10-11) planes.

16. The seed substrate according to claim 14, wherein the side surface of the seed crystal is composed only of a (10-11) plane.

17. 17. The seed substrate according to claim 14, wherein the height of the seed crystal is 0.01 to 0.6 times the diameter of the seed crystal in a plan view.

18. 17. The seed substrate according to claim 14, wherein the height of the seed crystal is 30 μm or more.

19. 17. The seed substrate according to claim 14, wherein the seed crystal has a diameter in a plan view of 10 μm or more and 500 μm or less.

20. The seed substrate according to claim 14 , wherein the seed crystal has a regular hexagonal pyramidal truncated portion having a regular hexagonal pyramidal truncated shape.

21. The seed substrate according to claim 14, wherein the seed crystal has a disk portion located on and in contact with the substrate and having a disk-like shape, and a regular hexagonal pyramid truncated portion located on and in contact with the disk portion and having a regular hexagonal pyramid truncated shape.

22. The seed substrate of claim 14 , wherein the seed crystal has a recess in the center.

23. The seed substrate of claim 22 , wherein the recess has a depth that reaches the substrate.

24. The seed substrate according to claim 22 , wherein the diameter of the recess is set so that the seed crystal has no top surface.

25. The seed substrate according to claim 22 , wherein the recess has an uneven side surface.

Images