Substrate for group iii nitride epitaxial growth, method for producing the same, and method for producing epitaxial film and semiconductor device using the same

Abstract

To provide a substrate for group III nitride epitaxial growth capable of suppressing meltback during a device manufacturing process in a composite substrate in which a seed crystal layer is bonded to a support substrate having a ceramic core, and to provide a method of manufacturing the same, and a method of manufacturing an epitaxial film and a semiconductor device using the same.SOLUTION: The growth substrate 1 includes a support substrate 10 in which a ceramic core is wrapped with a sealing layer, and a single-crystal seed layer 30 bonded to the support substrate 10 via a planarization layer 20, and further includes an aluminum nitride film 40 having a thickness of 3 to 250nm and continuously covering a region of the seed layer 30 and a region of the planarization layer 20 in a top view. The aluminum nitride film 40 is formed by a sputtering method or an ALD method. An epitaxial film and a semiconductor device are manufactured by using the growth substrate 1.SELECTED DRAWING: Figure 4C

Description

Technical Field

[0001] The present invention relates to a substrate for epitaxial growth of group III nitride single crystals for use in epitaxial growth of group III nitride single crystals such as aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), aluminum gallium nitride (Al x Ga 1-x N (where 0 < x < 1.0), indium gallium nitride (In y Ga 1-y N (where 0 < y < 1.0), etc., a method for manufacturing the same, and a method for manufacturing an epitaxial film and a semiconductor device using the same.

Background Art

[0002] Currently, single crystal Si substrates are widely used as semiconductor substrates. However, due to their characteristics, they are not necessarily suitable for recent high breakdown voltage and high frequency applications, so expensive single crystal SiC and single crystal GaN substrates have begun to be used. For example, by using semiconductor devices made of silicon carbide (SiC) and nitrides (AlInGaN-based), which are semiconductor materials with a wider bandgap than silicon (Si), to construct power conversion devices such as inverters and AC / DC converters, a reduction in power loss that cannot be achieved with semiconductor devices made of silicon has been realized. By using semiconductor devices made of SiC and nitrides, not only are the losses associated with power conversion reduced compared to the conventional case, but the weight reduction, miniaturization, and high reliability of the devices are promoted.

[0003] Since nitrides centered on GaN are excellent in anti-insulation characteristics and high-frequency characteristics compared to SiC, GaN has attracted attention as a next-generation device. As a substrate for growing a GaN epitaxial film, there is a composite substrate in which a Si single crystal seed layer is bonded to a support substrate having a ceramic core with a thermal expansion coefficient substantially the same as that of the crystal to be formed. Patent Documents 1 and 2 show examples of using single crystals such as SiC, aluminum nitride (AlN), GaN, aluminum gallium nitride (AlGaN), and aluminum oxide (Al2O3) as the seed layer on the support substrate having a ceramic core in addition to Si. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-012558 [Patent Document 2] Japanese Patent Application Publication No. 2023-098137 Summary of the Invention [Problem to be solved by the invention]

[0005] In epitaxial growth of a group III nitride single crystal such as GaN on a Si seed crystal, meltback of the Si seed crystal due to group III elements such as Ga can be suppressed by providing a cover layer made of AlN on the Si seed crystal. In addition, in vapor phase growth methods such as metalorganic chemical vapor deposition (MOCVD) generally used for epitaxial growth, an epitaxial film is deposited on the Si(111) surface, which is the epitaxial growth surface.

[0006] However, in a composite substrate in which a Si seed crystal is bonded to a support substrate, a region where the Si seed crystal is not attached is formed on the surface of the support substrate, such as the outer periphery, and the end face of the Si seed crystal is formed on the surface of the support substrate. Although epitaxial growth is performed on the Si(111) plane, there is a portion of the end face of the seed crystal where the Si(111) plane is not exposed.

[0007] 1 shows a composite substrate in which a Si single-crystal seed crystal layer 130 is bonded to a support substrate 110 via a planarizing layer 120. If the support substrate 110 has an end face 131 of the seed crystal layer 130 that does not have a Si(111) surface, even if a buffer layer 150 is formed in an area corresponding to the flat surface 134 of the seed crystal layer 130, which is the Si(111) surface, the GaN epitaxial film 160 will be deposited over an area wider than the periphery of the flat surface 134 of the seed crystal layer 130. Even if a cover layer 140 is formed by MOCVD to cover the seed crystal layer 130 to prevent meltback, the cover layer 140 formed by such a vapor phase growth method will have poor coverage when the seed crystal layer 130 has an end face 131, and such epitaxial growth will further deteriorate the coverage of the end face of the seed crystal layer 130 by the cover layer 140.

[0008] When fabricating semiconductor devices, device structures are stacked on a composite substrate, and then the element structure is formed on the wafer. The element formation process requires high-temperature heat treatment. For example, after dopant ion implantation to fabricate vertical GaN devices, high-temperature heat treatment at temperatures above 1200°C is required to diffuse and activate the implanted atoms and repair crystal damage caused by the ion implantation. During this heat treatment, at the end faces of Si seed crystals where the cover layer coverage is poor, the heat causes GaN to decompose, resulting in the precipitation of Ga, which then causes Si meltback, which can lead to peeling of the epitaxial film from these points.

[0009] 2A and 2B show images of actual examples of epitaxial film peeling. As shown in Fig. 2A, epitaxial wafer 100 has GaN epitaxial film 160 formed on support substrate 110. In Fig. 2B, which is an enlarged view of epitaxial wafer 100, peeling was observed at the edge of GaN epitaxial film 160 located on the end face of the Si seed crystal, as indicated by the arrow.

[0010] When a Group III element such as Ga precipitates on the end face of a seed crystal layer such as a Si single crystal, melt-back of the seed crystal occurs, and the Group III nitride epitaxial film peels off from the melt-back portion, which causes a significant decrease in the yield of the device manufacturing process and an increase in manufacturing costs.

[0011] In view of the above problems, the present invention aims to provide a substrate for Group III nitride epitaxial growth, which is a composite substrate in which a seed crystal layer such as a Si single crystal is bonded to a support substrate having a ceramic core, and which is capable of suppressing meltback of the seed crystal during the device manufacturing process; a method for manufacturing the same; and a method for manufacturing an epitaxial film and a semiconductor device using the same. [Means for solving the problem]

[0012] In order to solve the above problems, one aspect of the present invention provides a substrate for III nitride epitaxial growth, the substrate for III nitride epitaxial growth comprising: a support substrate having a structure in which a ceramic core is surrounded by a sealing layer; a planarizing layer provided on at least one surface of the support substrate; and a single-crystal seed crystal layer provided on the surface of the planarizing layer, wherein, when viewed from above from the seed crystal layer side, there is a region of the seed crystal layer and a region of the planarizing layer, the seed crystal layer has an end face at the boundary with the region of the planarizing layer, and the substrate further comprises an aluminum nitride film having a film thickness of 3 to 250 nm that continuously covers the surface of the seed crystal layer, the end face, and the surface of the planarizing layer adjacent to the end face.

[0013] In the substrate for III nitride epitaxial growth of the present invention, the seed crystal layer is preferably silicon (111).

[0014] When the aluminum nitride film is a sputtered film, it is preferable that the end face of the seed crystal layer has a portion tapered in a direction parallel to the bottom surface of the seed crystal layer, and that the taper angle (θ) of the tapered portion is 75° or less.

[0015] When the aluminum nitride film is a sputtered film, it is preferable that the end face of the seed crystal layer has a portion tapered in a direction parallel to the bottom surface of the seed crystal layer and a portion approximately perpendicular to the bottom surface of the seed crystal layer, the taper angle (θ) of the tapered portion is 75° or less, and the film thickness of the aluminum nitride film is thicker than the height (h) of the end face approximately perpendicular to the surface of the planarization layer in the region of the planarization layer when viewed from above, including the approximately perpendicular portion of the seed crystal layer.

[0016] The aluminum nitride film is preferably an atomic layer deposition (ALD) film.

[0017] Another aspect of the present invention is a method for producing a III-nitride-based epitaxial film or semiconductor device using such a substrate for III-nitride epitaxial growth.

[0018] In yet another aspect, the present invention provides a method for manufacturing a substrate for Group III nitride epitaxial growth, the method comprising the steps of: preparing a ceramic core; depositing a sealing layer to encase the core to obtain a support substrate; depositing a planarizing layer on at least one surface of the support substrate; and providing a single-crystal seed crystal layer on the surface of the planarizing layer, the seed crystal layer being provided so as to leave a region where the planarizing layer is exposed when viewed from above from the seed crystal layer side, and forming an end face at the boundary with the region where the planarizing layer is exposed; and forming an aluminum nitride film having a film thickness of 3 to 250 nm that continuously covers the surface of the seed crystal layer, the end face, and the surface of the planarizing layer adjacent to the end face.

[0019] In the method of the present invention for producing a substrate for III nitride epitaxial growth, the seed crystal layer is preferably silicon (111).

[0020] In the step of providing the seed crystal layer, it is preferable that the end face of the seed crystal layer has a portion tapered in a direction parallel to the bottom surface of the seed crystal layer, and that the taper angle (θ) of the tapered portion is 75° or less, and that in the step of forming the aluminum nitride film, the aluminum nitride film is formed by a sputtering method.

[0021] In the step of providing the seed crystal layer, it is preferable that the end face of the seed crystal layer has a portion tapered in a direction parallel to the bottom surface of the seed crystal layer and a portion approximately perpendicular to the bottom surface of the seed crystal layer, and that the taper angle (θ) of the tapered portion is 75° or less, and that in the step of forming the aluminum nitride film, the aluminum nitride film is formed by a sputtering method and the thickness of the aluminum nitride film is thicker than the height (h) of the end face approximately perpendicular to the surface of the planarization layer in the region of the planarization layer when viewed from above, including the approximately perpendicular portion of the seed crystal layer.

[0022] In the step of forming the aluminum nitride film, the aluminum nitride film is preferably formed by atomic layer deposition (ALD). [Effects of the Invention]

[0023] According to the present invention, the coverage of the aluminum nitride film can be improved even on the end face of the seed crystal layer, and therefore, meltback of the seed crystal at the end face of the seed crystal layer can be suppressed even under high-temperature heat treatment in the device manufacturing process. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of an epitaxial wafer using a conventional composite substrate. [Figure 2A] This is a top view of the epitaxial wafer of Figure 1 after high-temperature heat treatment. [Figure 2B] 2B is an enlarged image of the wafer outer periphery within the dotted frame B in FIG. 2A, showing film peeling due to meltback. [Figure 3] 1 is a cross-sectional view schematically showing an example of an epitaxial wafer using an embodiment of a substrate for III nitride epitaxial growth according to the present invention. [Figure 4A] 1 is a cross-sectional view schematically showing one embodiment of a substrate for group III nitride epitaxial growth according to the present invention. [Figure 4B] FIG. 2 is a cross-sectional view schematically showing another embodiment of a substrate for group III nitride epitaxial growth according to the present invention. [Figure 4C] FIG. 1 is a cross-sectional view schematically showing yet another embodiment of a substrate for group III nitride epitaxial growth according to the present invention. [Figure 5A] FIG. 4D is an enlarged cross-sectional view of a portion of the substrate for III nitride epitaxial growth shown in FIG. 4C. [Figure 5B] FIG. 10 is a partially enlarged cross-sectional view of a substrate for group III nitride epitaxial growth according to still another embodiment. [Figure 6] FIG. 1 is a cross-sectional view schematically showing an epitaxial wafer of an example. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, an embodiment of a substrate for Group III nitride epitaxial growth, a method for manufacturing the same, and a method for manufacturing an epitaxial film and a semiconductor device using the same according to the present invention will be described with reference to the accompanying drawings, but the present invention is not limited thereto.

[0026] [1. Substrates and epitaxial wafers for group III nitride epitaxial growth] 3 is a cross-sectional view schematically illustrating an example of an epitaxial wafer fabricated using an embodiment of the Group III nitride epitaxial growth substrate according to the present invention. As shown in FIG. 3, the Group III nitride epitaxial growth substrate 1 (hereinafter simply referred to as "growth substrate") of this embodiment includes a support substrate 10, a planarization layer 20 provided on one surface of the support substrate 10, a seed crystal layer 30 provided on the surface of the planarization layer 10, and an aluminum nitride (AlN) film 40 covering the seed crystal layer 3. The epitaxial wafer 3 of this embodiment is obtained by epitaxial growth using this growth substrate 1, and includes the growth substrate 1, a buffer layer 50 on the aluminum nitride film 40, and a Group III nitride epitaxial film 60 (hereinafter simply referred to as "epitaxial film") on the buffer layer 50.

[0027] The support substrate 10 is a support member for preventing deformation of the epitaxial film 60, and has a structure in which a ceramic core (not shown) is enclosed in a sealing layer (not shown). The core is a layer forming the base of the support substrate 10, and examples of ceramics include polycrystalline AlN, polycrystalline GaN, polycrystalline AlGaN, polycrystalline boron nitride (BN), polycrystalline silicon nitride (Si3N4), polycrystalline SiC, Al2O3, polycrystalline zinc oxide (ZnO), polycrystalline gallium trioxide (Ga2O3), and mixtures thereof. The thickness of the core is preferably in the range of 200 to 1500 μm, for example. The size of the core can be, for example, 2 to 12 inches in diameter. The core is preferably polished on both sides.

[0028] The sealing layer is a layer that covers the periphery of the core to prevent the diffusion of impurities. For example, silicon oxide (SiO2), Si3N4, or a mixture thereof can be used as the sealing layer, with Si3N4 being more preferred. The thickness of the sealing layer that covers the core is preferably in the range of 50 to 1500 nm, for example. The sealing layer is not limited to a single layer, and multiple layers of different compositions may be stacked. For example, a QST (USA registered trademark) substrate from Qromis can be suitably used as the support substrate 10 in which the entire core is wrapped in a sealing layer.

[0029] The planarization layer 20 is a layer that flattens unevenness resulting from the outer shape of the support substrate 10. The planarization layer 20 is also a portion that is removed by etching when separating the device from the growth substrate 1 after forming the device on the epitaxial film 60. The planarization layer 20 contains, for example, any of SiO2, Si3N4, silicon oxynitride (SiON), SiC, Al2O3, Si, gallium arsenide (GaAs), and aluminum arsenide (AlAs), with SiO2 being more preferred.

[0030] 3, the planarization layer 20 is provided only on the surface of the support substrate 10 on which the seed crystal is provided, but the present invention is not limited to this. For example, the planarization layer 20 may be provided so as to enclose the entire support substrate 10, or may be provided on both surfaces of the support substrate 10. The thickness of the planarization layer 20 may be, for example, 0.5 to 3.0 μm. The arithmetic mean roughness Ra of the surface of the planarization layer 20 may be 0.02 to 2 nm.

[0031] The seed crystal layer 30 is a layer that serves as a base on which the epitaxial film 60 grows, and may be made of, for example, single crystals of Si, SiC, AlN, AlGaN, or Al2O3. Si is particularly preferred, and Si having a (111) crystal orientation is even more preferred. The film thickness t(sc) of the seed crystal layer 30 may be, for example, 0.1 to 1.5 μm. The size of the seed crystal layer 30 is smaller than the size of the core of the support substrate 10, and may be, for example, 2 to 12 inches in diameter.

[0032] The seed crystal layer 30 is not disposed over the entire surface of the planarizing layer 20 on one surface of the support substrate 10, and when viewed from above from the seed crystal layer 30 side of the growth substrate 1, there are two regions: a region of the seed crystal layer 30 and a region of the planarizing layer 20. The region of the planarizing layer 20 is located on the outer periphery of the growth substrate 1, and the region of the seed crystal layer 30 is located on the center side of the growth substrate 1. The seed crystal layer 30 has an end face at the boundary between the region of the seed crystal layer 30 and the region of the planarizing layer 20. Note that due to defects that occur when attaching the seed crystal layer 30 to the planarizing layer 20 of the support substrate 10, the region of the planarizing layer 20 may also be partially formed in areas other than the outer periphery of the growth substrate 1.

[0033] The end face of the seed crystal layer 30 will be described in detail with reference to Figures 4A to 4C. As shown in Figure 4A, the end face 31 of the seed crystal layer 30 may be approximately perpendicular to the bottom face of the seed crystal layer 30. As shown in Figure 4B, the end face 32 of the seed crystal layer 30 may be tapered in a direction parallel to the bottom face of the seed crystal layer 30. As shown in Figure 4C, the end face 33 of the seed crystal layer 30 may have a portion 33a tapered in a direction parallel to the bottom face of the seed crystal layer 30 and a portion 33b approximately perpendicular to the bottom face of the seed crystal layer.

[0034] The end face in the case of FIG. 4C will be described in more detail with reference to FIGS. 5A and 5B. As shown in FIG. 5A, the bottom surface of the seed crystal layer 30 may be flush with the surface 21 of the outer periphery of the planarizing layer 20 (the region of the planarizing layer 20 in the above-described top view). Alternatively, as shown in FIG. 5B, the bottom surface of the seed crystal layer 30 may be higher than the surface 22 of the outer periphery of the planarizing layer 20. In the latter case, a step surface 24 is formed between the surface 22 of the outer periphery of the planarizing layer 20 and the bonding surface 23 of the planarizing layer 20 with the seed crystal layer 30. The formation and height of the step surface 24 of the planarizing layer 20 can be controlled by changing the substrate surface treatment method after the attachment of the seed crystal layer 30.

[0035] In the case of FIG. 5A , the only end face that is substantially perpendicular to the surface 21 of the outer periphery of the planarizing layer 20 is the substantially perpendicular portion 33b of the end face of the seed crystal layer 30. Therefore, the height of the end face that is substantially perpendicular to the surface 21 of the outer periphery of the planarizing layer 20 (hereinafter referred to as the "substantially perpendicular end face height h") is the same as the length of the substantially perpendicular portion 33b of the end face of the seed crystal layer 30. In the case of FIG. 5B , the end face that is substantially perpendicular to the surface 22 of the outer periphery of the planarizing layer 20 is formed by the substantially perpendicular portion 33b of the end face of the seed crystal layer 30 and the above-mentioned step face 24 of the planarizing layer 20. Therefore, the substantially perpendicular end face height h is the sum of the length of the substantially perpendicular portion 33b of the end face of the seed crystal layer 30 and the length of the step face 24 of the planarizing layer 20.

[0036] As shown in FIGS. 5A and 5B , the taper angle θ of the tapered portion 33a of the end face 33 of the seed crystal layer 30 is the angle between the corner between the tapered portion 33a of the end face 33 of the seed crystal layer 30 and the substantially vertical portion, which is defined as starting point A, and the direction parallel to the bottom surface of the seed crystal layer 30 (direction AB in the figure) and the direction toward point C on the surface of the tapered portion 33a. Note that point C is located at a distance w of 50 nm from starting point A in the direction parallel to the bottom surface of the seed crystal layer 30. When the end face of the seed crystal layer 30 does not have a substantially vertical portion as shown in FIG. 4B , the taper angle θ is defined as the angle between the edge of the tapered end face 32 of the seed crystal layer 30 as starting point A, the direction parallel to the bottom surface of the seed crystal layer 30, and the direction toward point C on the surface of the tapered end face. In this case, point C is also defined as the angle w of 50 nm from starting point A in the parallel direction.

[0037] The AlN film 40 is a cover layer that continuously covers the surface of the seed crystal layer 30, end faces 31, 32, and 33, and surfaces 21 and 22 of the planarizing layer 20 adjacent to the end faces. The AlN film 40 is a sputtered film formed by a sputtering method or an ALD film formed by an atomic layer deposition (ALD) method.

[0038] When the AlN film 40 is a sputtered film, the taper angle θ at the end face of the seed crystal layer 30 is preferably 75° or less, regardless of whether or not there is a substantially vertical portion. If the taper angle is greater than 75°, the end face of the seed crystal layer 30 becomes acute, which reduces the coverage of the AlN film 40 at the end of the seed crystal layer 30. Cracks may also occur in the AlN film 40. By setting the taper angle θ to 75° or less, the coverage of the end face of the seed crystal layer 30 with the AlN film 40 can be improved.

[0039] When the AlN film 40 is an ALD film, there is no limitation on the taper angle θ at the end face of the seed crystal layer 30. That is, as shown in Fig. 4A, all of the end faces of the seed crystal layer 30 may be approximately perpendicular to the bottom face. This is because, due to the film formation principle, an ALD film has higher coverage of the AlN film at the end face of the seed crystal layer 30 than a sputtered film.

[0040] The thickness t(AlN) of the AlN film 40 near the center of the growth substrate 1, i.e., at a position on the flat surface of the seed crystal layer 30, is within a range of 3 to 250 nm, preferably 5 to 200 nm, and more preferably 10 to 150 nm. If the thickness of the AlN film 40 is thinner than 3 nm, there is a concern that the AlN film 40 may evaporate during the temperature rise process during epitaxial growth thereon. Furthermore, if the thickness is thinner than 3 nm, the AlN film 40 becomes discontinuous, particularly at the end face of the seed crystal layer 30, and the entire periphery of the end face of the seed crystal layer 30 may not be covered. On the other hand, if the thickness of the AlN film 40 is thicker than 250 nm, there is a concern that the crystallinity of the epitaxial film 60 grown thereon may deteriorate. This is because the thicker the AlN film 40, the greater the strain on the growing epitaxial film 60.

[0041] 4B , when there is no end face that is approximately perpendicular to the surface 21 of the outer periphery of the flattening layer 20, i.e., when the height of the approximately perpendicular end face h = 0, the film thickness t(AlN) of the AlN film 40 on the end face of the seed crystal layer 30 is preferably the same as that near the center of the growth substrate 1. That is, the film thickness of the AlN film 40 on the end face of the seed crystal layer 30 is in the range of 3 to 250 nm.

[0042] On the other hand, when the height h of the substantially vertical end face is greater than 0, if the AlN film 40 is a sputtered film, the film thickness t(AlN) of the AlN film 40 at the end face of the seed crystal layer 30 is preferably greater than the height h of the substantially vertical end face. Due to the film formation principle of the sputtered film, when the film thickness of the AlN film 40 is the same as or less than the height h of the substantially vertical end face, at the end face substantially perpendicular to the surface 21 of the outer peripheral portion of the planarization layer 20, there will be a location where the coverage by the AlN film 40 is missing. When the AlN film 40 is a sputtered film, the relationship between the film thickness t(AlN) of the AlN film 40 at the end face of the seed crystal layer 30 and the height h of the substantially vertical end face is preferably as follows. t(AlN)>h, and 3 nm ≤ t(AlN) ≤ 250 nm

[0043] When the AlN film 40 is an ALD film, due to its film formation principle, the coverage for the substantially vertical end face is better than that of the sputtered film. Therefore, even when the height h of the substantially vertical end face is greater than 0 and t(AlN) < h, at the end face substantially perpendicular to the surface 21 of the outer peripheral portion of the planarization layer 20, a continuous coverage by the AlN film 40 without missing can be formed.

[0044] An epitaxial wafer 3 is obtained by growing an epitaxial film 60 on the AlN film 40 of the growth substrate 1 having such a structure. As shown in FIG. 3, a buffer layer 50 may be provided on the AlN film 40, and an epitaxial film 60 may be laminated thereon. The buffer layer 50 can be provided as needed when it is desired to relieve the mismatch due to the difference in lattice constants between the seed crystal layer 30 and the epitaxial film 60 and the stress on the epitaxial film 60. As the buffer layer 50, for example, AlN, GaN, AlGaN, or a multilayer film thereof can be used. Also, these may be doped with an N-type dopant. As the dopant, Si, Ge, C, etc. can be used. The thickness of the buffer layer 50 can be, for example, 50 to 1500 nm.

[0045] When the AlN film 40 is a sputtered film or an ALD film, the AlN film 40 also serves as the buffer layer 50, so there are cases where it is not necessary to provide the buffer layer 50. When the AlN film 40 is a sputtered film or an ALD film, the AlN film 40 also functions as a high-quality buffer layer when depositing the Group III nitride single crystal, so that the crystallinity of the Group III nitride single crystal can also be improved.

[0046] The epitaxial film 60 is a single crystal layer on which a semiconductor device is formed. The epitaxial film 60 is not particularly limited as long as it is a group III nitride, but for example, GaN, InN, or AlN is preferred, and it may also be a mixed crystal of different group III nitrides. The composition, structure, and conductivity type of the epitaxial film 60 may be appropriately selected depending on the device to be formed, and it may also be a multilayer of different group III nitrides. Specific devices include optical devices such as LEDs (light-emitting diodes) and LDs (laser diodes), power devices such as transistors and Schottky barrier diodes, and RF devices (radio frequency devices).

[0047] [2. Methods for Manufacturing Substrates for Group III Nitride Epitaxial Growth, Epitaxial Films, and Semiconductor Devices] An embodiment of a method for manufacturing a substrate for III-nitride epitaxial growth according to the present invention will be described. This manufacturing method includes the steps of preparing a ceramic core, forming a sealing layer to encase the core to obtain a support substrate, forming a planarizing layer on at least one surface of the support substrate, providing a single-crystal seed crystal layer on the surface of the planarizing layer, and forming an AlN film to cover the surface and end faces of the seed crystal layer. Each step will be described in more detail with reference to Figure 3, but the configuration and materials of each layer of the growth substrate have already been explained above and will not be repeated here.

[0048] The core preparation step involves first preparing a green sheet by mixing ceramic powder such as AlN with a sintering aid, an organic binder, a solvent, etc. Then, after degreasing, the green sheet is sintered at a temperature of 1600 to 2200°C in an inert gas atmosphere such as N2. The sintered body thus obtained can be processed, for example by polishing, to obtain a ceramic core (not shown) with a predetermined thickness and size.

[0049] In the step of obtaining the support substrate, a sealing layer (not shown) is formed by low pressure chemical vapor deposition (LPCVD) so as to enclose the prepared core, thereby obtaining the support substrate 10. The support substrate may be produced in this manner, or a QST (USA registered trademark) substrate from Qromis may also be used.

[0050] 3, the step of depositing the planarization layer involves first depositing a planarization layer 20 by a plasma CVD method or the like on at least one surface of the support substrate 10. The planarization layer 20 may be deposited so as to encase the entire support substrate 10. After densifying at a temperature of, for example, 800 to 1200°C, the surface of the planarization layer 20 is polished and planarized by chemical mechanical polishing (CMP) or the like to a predetermined thickness and arithmetic mean roughness Ra.

[0051] The step of providing the seed crystal layer 30 involves first bonding a single-crystal seed crystal substrate that will become the seed crystal layer 30 to the surface of the planarization layer 20 of the support substrate 10. Ions are implanted in advance into the surface of the seed crystal substrate that will be bonded to the planarization layer 20. For the ion implantation, for example, hydrogen ions are implanted into the bonding surface of the seed crystal substrate at an acceleration voltage of 50 KeV to 200 KeV. The depth of the ion-implanted layer can be changed by adjusting the acceleration voltage. The depth of the ion-implanted layer is preferably 0.1 μm to 1.5 μm.

[0052] Next, the seed crystal substrate bonded to the planarization layer 20 of the support substrate 10 is separated and peeled at the depth of the ion-implanted layer, and the remaining portion can be thin-film transferred to the support substrate 10 as the seed crystal layer 30. The transferred seed crystal layer 30 is then thinned by CMP polishing, hydrofluoric acid etching, or the like until it reaches a predetermined thickness t(sc). In particular, by adjusting the CMP polishing conditions, it is possible to set the taper angle θ of the end face of the seed crystal layer 30 to a predetermined angle, or to make the approximately vertical end face a predetermined height. Thereafter, to repair damage to the seed crystal layer 30 caused by ion implantation, the seed crystal layer 30 can be heat-treated, for example, at a temperature of 800 to 1000°C in a hydrogen atmosphere. The seed crystal substrate separated and peeled by thin-film transfer can be re-implanted with ions into the bonding surface and bonded to another support substrate, allowing it to be reused for thin-film transfer of the seed crystal layer.

[0053] The step of forming the AlN film is preferably performed by sputtering or ALD, and the AlN film 40 is deposited so as to cover the entire surface and end faces of the seed crystal layer 30. When depositing the AlN film 40 by sputtering, an Al target and nitrogen gas are used as raw materials. The substrate temperature during deposition is preferably, for example, 500 to 800°C. When depositing the AlN film 40 by ALD, for example, trimethylaluminum (TMA) is used as the aluminum source and ammonia (NH3) is used as the nitrogen source. The deposition temperature is preferably, for example, 100 to 750°C. Prior to depositing the AlN film 40, the composite substrate in which the seed crystal layer 30 is bonded to the support substrate 1 is preferably cleaned by reverse sputtering, in which plasma such as argon gas or nitrogen gas acts on the substrate surface, or by cleaning with hydrofluoric acid or the like. In this manner, the AlN film 40 having a predetermined thickness t(AlN) can be formed.

[0054] By carrying out each step in this manner, a Group III nitride epitaxial growth substrate 1 can be obtained. Then, by using this growth substrate 1, a Group III nitride epitaxial film 60 can be produced, and a semiconductor device can be manufactured. The epitaxial film 60 can be formed on the AlN film 40 of the growth substrate 1, or on a buffer layer 50 provided on the AlN film 40. Both the epitaxial film 60 and the buffer layer 50 can be formed by MOCVD.

[0055] In the manufacture of semiconductor devices, for example, in the case of vertical power devices, an epitaxial wafer 3 having an epitaxial film 60 formed on a growth substrate 1 is first prepared. A trench structure having a predetermined pattern is then formed in the epitaxial film 60 by photolithography and dry etching, and a gate insulating film, source electrode, and gate electrode are then formed in the predetermined locations to fabricate the device. A heat treatment of 1200°C or higher is then performed for activation. Next, the devices are separated by dry etching to expose the planarization layer 20. A temporary support substrate is then bonded to the upper surface of the device, and the planarization layer 20 is dissolved using an HF solution or the like to separate the support substrate 10. An ohmic electrode is then formed on the seed crystal layer 30, and a back electrode is then formed on the surface of that electrode to obtain a semiconductor device. [Example]

[0056] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0057] [Example 1] (Preparation of support substrate) First, AlN powder was mixed with Y2O3 as a sintering aid, an organic binder, a solvent, etc. to create a green sheet, which was then degreased and sintered at 1900°C under N2 to form a double-sided polished AlN substrate (AlN polycrystalline ceramic substrate) with a diameter of 8 inches and a thickness of 725 μm.

[0058] Next, the entire core was covered with a 0.2 μm thick SiON layer using the LPCVD method, and then a 0.6 μm thick Si3N4 layer was covered on top of that using another LPCVD apparatus to seal the entire core (total thickness of the sealing layer = 0.8 μm), and this was used as a support substrate.

[0059] (Lamination of planarization layers) A 7 μm thick SiO2 layer was deposited on the Si3N4 layer on one side (top surface) of the support substrate using plasma CVD (ICP-CVD equipment). After that, this SiO2 was baked at 1000°C, and then polished and flattened to a thickness of 3 μm using CMP polishing, creating a flattened layer with a surface with an arithmetic mean roughness Ra of 0.15 nm.

[0060] (Thin film transfer of seed crystal layer) A φ8-inch Si(111) single crystal seed substrate was prepared, which was pulled up by a commercially available CZ method and bonded to a support substrate. Hydrogen ions were irradiated onto this Si single crystal substrate at 100 keV with a dose of 6 × 10 to a depth of 0.7 μm. 17 cm -2 Ion implantation was performed under the conditions shown above. The ion-implanted surface of the seed crystal substrate was then bonded to the surface of the planarization layer of the support substrate. The seed crystal substrate was then separated and peeled at the peeling position (the position at a depth of 0.7 μm where the ions were implanted), and a portion of the seed crystal substrate was transferred onto the support substrate as a thin film seed crystal layer. The transferred seed crystal layer was then thinned to a thickness of 0.38 μm by CMP polishing and hydrofluoric acid etching. By adjusting the CMP polishing conditions, the end faces of the seed crystal layer were tapered with a taper angle θ of 30° and no approximately vertical portions (i.e., the approximately vertical end face height h = 0 nm). Furthermore, the damaged portions of the seed crystal layer due to ion implantation were restored by heat treatment at 1000°C in a hydrogen atmosphere.

[0061] (AlN film deposition) Next, an AlN film was formed using RF sputtering. The composite substrate, in which the seed crystal layer was bonded to the support substrate, was placed in the chamber of the sputtering device. The target used was metallic Al. Before film formation, the chamber was depressurized and a 1.0 × 10 -3The internal pressure was reduced to below 100 Pa, and impurities in the chamber were removed. Next, prior to film deposition, reverse sputtering was performed, in which plasma such as argon gas or nitrogen gas was applied to the substrate surface to clean the substrate surface. After that, the substrate temperature was raised to 500°C to 800°C, and an AlN film was deposited.

[0062] First, only argon gas was introduced into the chamber, and a high-frequency bias was applied to the metal Al target to form an Al seed layer for 3 seconds. Then, 28 sccm of argon gas and 84 sccm of nitrogen gas were introduced, and a 5000 W high-frequency bias was applied to the metal Al target to generate plasma and deposit an AlN film. When the AlN film reached a thickness of 10 nm, the plasma operation was stopped, the temperature of the composite substrate was lowered, and the growth substrate with the AlN film formed on the composite substrate was then removed from the chamber. The above series of processes was repeated multiple times to produce multiple growth substrates.

[0063] (Observation of AlN film coverage on the seed crystal layer end surface) Using one of the prepared growth substrates, the thickness and coverage of the AlN film near the center of the substrate and near the edge of the seed crystal layer on the periphery of the substrate were confirmed by cross-sectional transmission electron microscope (TEM) observation. The observation results showed that the thickness of the AlN film near the center of the substrate was approximately 10 nm. Furthermore, observation near the edge of the seed crystal layer showed that the taper angle θ was approximately 30°, and the edge was also covered with an AlN film of approximately 10 nm, with no cracks or other defects observed in the AlN layer.

[0064] (epitaxial growth) On the prepared growth substrate, an epitaxial film having a device structure for fabricating a vertical MOSFET was formed in an MOCVD apparatus to produce an epitaxial wafer. The structure is shown in Figure 6. First, a Si-doped buffer layer 50 was grown on the AlN film 40 of the growth substrate 1. The buffer layer 50 was an AlGaN layer with a thickness of 150 nm, and the buffer layer 50 was doped with Si as an N-type dopant. The doping amount was 1 x 10 18 cm -3 It was decided.

[0065] Next, as the first layer of the epitaxial film 60, a silicon concentration of 5×10 18 cm -3 n + GaN was grown. + The thickness of the GaN layer was set to 1 μm. 16 cm -3 Then, Mg-doped GaN (Mg concentration 5×10 18 cm -3 , 0.2 μm) and Si-doped GaN (Si concentration 2 × 10 18 cm -3 6, n + GaN, nGaN, PGaN, n + An epitaxial film 60 having a vertical power device structure in which GaN is stacked was fabricated.

[0066] The crystallinity of the epitaxial film 60 thus formed on the vertical device structure was evaluated using an X-ray diffractometer (XRD). As a result, the half-width of the X-ray rocking curve for the GaN (0002) plane was 425 arcsec. This value was better than the half-width of the X-ray rocking curve of 550 arcsec obtained when an epitaxial film with a similar device structure was formed on a Si substrate.

[0067] (Element fabrication) Next, this vertical device epitaxial wafer 3 was processed using the following device manufacturing process to fabricate a vertical MOSFET. First, a mask with a predetermined pattern was formed on the top surface of the wafer using photolithography, and a trench structure was formed by dry etching. Furthermore, Mg ions were implanted into the epitaxial film using an ion implanter. After that, a high-temperature heat treatment was performed at 1300°C in a nitrogen atmosphere for 5 minutes to diffuse and activate the Mg. After the high-temperature heat treatment, the wafer was observed to check the process. As a result of the observation, no meltback due to Ga occurred over the entire wafer surface, and no peeling of the film was confirmed. After that, a gate insulating film (SiO2) was formed in the trench portion. After that, a mask with a predetermined pattern was formed using photography, and a n-type SiO2 film was formed on the surface. + A part of the GaN layer was etched to form a pattern. Then, a mask with a predetermined pattern was formed by photography, and a source electrode and a gate electrode were formed to fabricate the device. The electrodes were made of Al and Ti.

[0068] (Isolation between elements, peeling off of supporting substrate) The elements were separated by dry etching, exposing the planarization layer. A temporary support substrate was attached to the top of the element and immersed in an HF solution. This dissolved the SiO2 planarization layer, separating the element into an upper and lower portion above the planarization layer.

[0069] (removal of buffer layer, formation of back electrode) The buffer layer on the rear surface of the part having the separated device structure is dry etched to form an n + The GaN layer was exposed, and then an ohmic metal such as Al or Ti was formed on the seed crystal layer, and RTA (rapid thermal annealing) was performed in an argon atmosphere to form an ohmic electrode. After that, a back electrode made of Au or Ag was formed on the surface by sputtering, and then heat treatment was performed in an N2 or H2 atmosphere.

[0070] (mounting on device mounting boards, inspection) Then, each element was mounted on a device mounting board to complete the semiconductor device. When mounting the device, we were careful not to mount any defective products that had been inspected after the element was mounted. The completed semiconductor device was inspected for vertical continuity. As a result, good results were obtained for the IdVd characteristics, IdVg characteristics, and off-state IdVd and IdVg characteristics of the semiconductor device.

[0071] [Example 2] Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that the thickness of the AlN film was changed to 3 nm, and various observations and inspections were performed. As a result, observation of the coverage of the AlN layer on the seed crystal layer end face of the growth substrate confirmed that the end face was also covered with an AlN film. Furthermore, XRD evaluation revealed a good GaN (0002) plane half-width of 445 arcsec. No meltback due to Ga was observed even after high-temperature heat treatment during the device fabrication process.

[0072] [Example 3] Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that the thickness of the AlN film was changed to 25 nm, and various observations and inspections were performed. As a result, observation of the coverage of the AlN layer on the seed crystal layer end face of the growth substrate confirmed that the end face was also covered with an AlN film. Furthermore, XRD evaluation revealed a good GaN (0002) plane half-width of 420 arcsec. No meltback due to Ga was observed even after high-temperature heat treatment during the device fabrication process.

[0073] [Example 4] Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that the thickness of the AlN film was changed to 75 nm, and various observations and inspections were performed. As a result, observation of the coverage of the AlN layer on the seed crystal layer end face of the growth substrate confirmed that the end face was also covered with an AlN film. Furthermore, XRD evaluation revealed a good GaN (0002) plane half-width of 455 arcsec. No meltback due to Ga was observed even after high-temperature heat treatment during the device fabrication process.

[0074] [Example 5] Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that the thickness of the AlN film was changed to 150 nm, and various observations and inspections were performed. As a result, observation of the coverage of the AlN layer on the seed crystal layer end faces of the growth substrate confirmed that the end faces were also covered with an AlN film. Furthermore, XRD evaluation revealed a good GaN (0002) plane half-width of 460 arcsec. No meltback due to Ga was observed even after high-temperature heat treatment during the device fabrication process.

[0075] [Example 6] Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that the thickness of the AlN film was changed to 250 nm, and various observations and inspections were performed. As a result, observation of the coverage of the AlN layer on the seed crystal layer end face of the growth substrate confirmed that the end face was also covered with an AlN film. Furthermore, XRD evaluation revealed a good GaN (0002) plane half-width of 500 arcsec. No meltback due to Ga was observed even after high-temperature heat treatment during the device fabrication process.

[0076] [Example 7] Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 3, except that the taper angle θ of the end face of the seed crystal layer was changed to 55°, and various observations and inspections were performed. As a result, observation of the AlN layer coverage on the end face of the seed crystal layer of the growth substrate confirmed that the end face was also covered with an AlN film. Furthermore, XRD evaluation revealed a good GaN (0002) plane half-width of 422 arcsec. No meltback due to Ga was observed even after high-temperature heat treatment during the device fabrication process.

[0077] [Example 8] Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 3, except that the taper angle θ of the end face of the seed crystal layer was changed to 75°, and various observations and inspections were performed. As a result, observation of the AlN layer coverage on the end face of the seed crystal layer of the growth substrate confirmed that the end face was also covered with an AlN film. Furthermore, XRD evaluation revealed a good GaN (0002) plane half-width of 425 arcsec. No meltback due to Ga was observed even after high-temperature heat treatment during the device fabrication process.

[0078] [Example 9] Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that the end faces of the seed crystal layer were modified to have a tapered portion and a substantially vertical portion, with a taper angle θ of 30° and a height of the substantially vertical portion of 8 nm (the substantially vertical end face height h was also 8 nm). Various observations and inspections were performed. Observation of the AlN layer coverage on the end faces of the seed crystal layer of the growth substrate confirmed that the end faces were also covered with an AlN film. Furthermore, XRD evaluation revealed a favorable GaN (0002) plane half-width of 423 arcsec. No meltback due to Ga was observed even after high-temperature heat treatment during the device fabrication process.

[0079] [Example 10] Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that the end faces of the seed crystal layer were changed to end faces having a tapered portion and a substantially vertical portion, with a taper angle θ of 30° and a height of 5 nm (the substantially vertical end face height h was also 5 nm). Various observations and inspections were performed. As a result, observation of the AlN layer coverage on the end faces of the seed crystal layer of the growth substrate confirmed that the end faces were also covered with an AlN film. Furthermore, XRD evaluation revealed a favorable GaN (0002) plane half-width of 430 arcsec. No meltback due to Ga was observed even after high-temperature heat treatment during the device fabrication process.

[0080] [Example 11] Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that the end faces of the seed crystal layer were modified to have a tapered portion and a substantially vertical portion, with a taper angle θ of 75° and a height of the substantially vertical portion of 8 nm (the substantially vertical end face height h was also 8 nm). Various observations and inspections were performed. Observation of the AlN layer coverage on the end faces of the seed crystal layer of the growth substrate confirmed that the end faces were also covered with an AlN film. Furthermore, XRD evaluation revealed a favorable GaN (0002) plane half-width of 432 arcsec. No meltback due to Ga was observed even after high-temperature heat treatment during the device fabrication process.

[0081] [Example 12] Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 3, except that the end faces of the seed crystal layer were modified to have a tapered portion and a substantially vertical portion, with a taper angle θ of 30° and a height of 50 nm (the substantially vertical end face height h was also 50 nm), and the AlN film was deposited by the ALD method. Various observations and inspections were performed. The ALD deposition used trimethylaluminum (TMA) as the aluminum source and ammonia (NH3) as the nitrogen source. The deposition temperature was 300°C to 400°C. Observation of the AlN layer coverage on the end faces of the seed crystal layer on the growth substrate confirmed that the end faces were also covered with the AlN film. Furthermore, XRD evaluation revealed a favorable GaN (0002) plane half-width of 436 arcsec. No meltback due to Ga was observed even after high-temperature heat treatment during the device fabrication process.

[0082] [Example 13] Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 12, except that the end faces of the seed crystal layer were changed to approximately vertical end faces with a height of 300 nm (i.e., a taper angle θ of 90° and an approximately vertical end face height h of 300 nm), and various observations and inspections were performed. As a result, observation of the AlN layer coverage on the end faces of the seed crystal layer of the growth substrate confirmed that the end faces were also covered with an AlN film. Furthermore, XRD evaluation revealed a favorable GaN (0002) plane half-width of 431 arcsec. No meltback due to Ga was observed even after high-temperature heat treatment during the device fabrication process.

[0083] [Comparative Example 1] Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that the thickness of the AlN film was changed to 1.5 nm, and various observations and inspections were performed. Observation of the AlN layer coverage on the seed crystal layer end faces of the growth substrate revealed that the AlN film was discontinuous and insufficient. XRD evaluation revealed a poor result of 750 arcsec, the half-width of the GaN (0002) plane. Furthermore, after high-temperature heat treatment during the device fabrication process, meltback due to Ga was observed, especially on the end faces of the seed crystal layer.

[0084] Comparative Example 2 Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that the thickness of the AlN film was changed to 300 nm, and various observations and inspections were performed. As a result, observation of the coverage of the AlN layer on the seed crystal layer end faces of the growth substrate confirmed that the end faces were also covered with an AlN film. On the other hand, XRD evaluation showed a poor result of 866 arcsec, the half-width of the GaN (0002) plane. No meltback due to Ga was observed after high-temperature heat treatment during the device fabrication process.

[0085] Comparative Example 3 Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that the end faces of the seed crystal layer were changed to approximately vertical end faces with a height of 380 nm (i.e., a taper angle θ of 90° and an approximately vertical end face height h of 380 nm), and various observations and inspections were performed. As a result, observation of the AlN layer coverage on the end faces of the seed crystal layer of the growth substrate confirmed that there were portions of the approximately vertical end faces that were not covered with the AlN film. On the other hand, XRD evaluation revealed a good GaN (0002) plane half-width of 423 arcsec. After high-temperature heat treatment during the device fabrication process, meltback due to Ga was confirmed, especially on the end faces of the seed crystal layer.

[0086] Comparative Example 4 Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that the end faces of the seed crystal layer had tapered and nearly vertical portions, with a taper angle θ of 30° and a height of 8 nm for the nearly vertical portions. A stepped surface was formed on the outer periphery of the planarization layer, resulting in a nearly vertical end face height h of 10 nm. Various observations and inspections were performed. Observation of the AlN layer coverage on the end faces of the seed crystal layer of the growth substrate revealed that there were portions of the end faces of the seed crystal layer, particularly the stepped surfaces, that were not covered by the AlN film. Meanwhile, XRD evaluation revealed a favorable GaN (0002) plane full width at half maximum of 430 arcsec. After high-temperature heat treatment during the device fabrication process, meltback due to Ga was observed, particularly on the end faces of the seed crystal layer.

[0087] Comparative Example 5 Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that the end faces of the seed crystal layer had tapered and nearly vertical portions, with a taper angle θ of 75° and a height of 8 nm for the nearly vertical portions. A stepped surface was formed on the outer periphery of the planarization layer, resulting in a nearly vertical end face height h of 10 nm. Various observations and inspections were performed. Observation of the AlN layer coverage on the seed crystal layer end faces of the growth substrate confirmed that there were portions of the seed crystal layer end faces, particularly the stepped surfaces, that were not covered by the AlN film. Meanwhile, XRD evaluation revealed a favorable GaN (0002) plane FWHM of 422 arcsec. After high-temperature heat treatment during the device fabrication process, meltback due to Ga was observed, particularly on the end faces of the seed crystal layer.

[0088] Comparative Example 6 Growth substrates, epitaxial wafers, and semiconductor devices were fabricated in the same manner as in Example 1, except that an AlN film was deposited by MOCVD and the thickness of the AlN film was 150 nm. Various observations and inspections were then performed. As a result, it was confirmed that the AlN film was discontinuous at the end face of the seed crystal layer, resulting in poor end face coverage. Furthermore, XRD evaluation revealed that the GaN (0002) plane half-width was 492 arcsec, which was relatively good, but was worse than the results in Example 5, where the AlN film thickness was the same 150 nm. After high-temperature heat treatment during the device fabrication process, meltback due to Ga was observed, particularly at the end face of the seed crystal layer.

[0089] The fabrication conditions and evaluation results of the above-mentioned Examples 1 to 13 and Comparative Examples 1 to 6 are shown in Table 1. As shown in Table 1 and described above, according to the present invention, meltback due to Group III nitrides at the end faces of the seed crystal layer can be suppressed even under high-temperature heat treatment during the device fabrication process, and peeling of the epitaxial film can be prevented, thereby enabling a reduction in manufacturing costs.

[0090] [Table 1] [Explanation of symbols]

[0091] 1. Substrates for Group III nitride epitaxial growth 3 Epitaxial wafer 10 Support substrate 20 Planarization layer 21, 22 Peripheral surface 24 Step surface 30 seed crystal layer 31, 32, 33 End face of seed crystal layer 40 Aluminum nitride (AlN) film 50 buffer layer 60 Group III nitride epitaxial films

Claims

1. A substrate for Group III nitride epitaxial growth, comprising: a support substrate having a structure in which a ceramic core is surrounded by a sealing layer; a planarization layer provided on at least one surface of the support substrate; and a single-crystal seed crystal layer provided on a surface of the planarization layer, a seed crystal layer region and a planarizing layer region when viewed from above from the seed crystal layer side, the seed crystal layer having an end face at the boundary with the planarizing layer region, and further comprising an aluminum nitride film having a film thickness of 3 to 250 nm that continuously covers a surface of the seed crystal layer, the end face, and a surface of the planarizing layer adjacent to the end face.

2. 2. The substrate for III-nitride epitaxial growth of claim 1, wherein said seed layer is silicon (111).

3. 2. The substrate for Group III nitride epitaxial growth according to claim 1, wherein the aluminum nitride film is a sputtered film, the end face of the seed crystal layer has a portion tapered with respect to a direction parallel to a bottom surface of the seed crystal layer, and the taper angle (θ) of the tapered portion is 75° or less.

4. 2. The substrate for Group III nitride epitaxial growth according to claim 1, wherein the aluminum nitride film is a sputtered film, an end face of the seed crystal layer has a portion tapered with respect to a direction parallel to a bottom surface of the seed crystal layer and a portion substantially perpendicular to the bottom surface of the seed crystal layer, the tapered portion having a taper angle (θ) of 75° or less, and the thickness of the aluminum nitride film is greater than a height (h) of an end face substantially perpendicular to a surface of the planarizing layer in a region of the planarizing layer when viewed from above, the end face including the substantially perpendicular portion of the seed crystal layer.

5. 2. The substrate for III-nitride epitaxial growth according to claim 1, wherein the aluminum nitride film is an atomic layer deposition (ALD) film.

6. A method for producing a Group III nitride epitaxial film or a semiconductor device using the substrate for Group III nitride epitaxial growth according to any one of claims 1 to 5.

7. providing a ceramic core; forming a sealing layer to surround the core to obtain a support substrate; forming a planarization layer on at least one surface of the support substrate; providing a single-crystal seed crystal layer on the surface of the planarizing layer, the seed crystal layer being provided so that an end face is formed at a boundary with the exposed region of the planarizing layer, leaving a region where the planarizing layer is exposed when viewed from above from the seed crystal layer side; forming an aluminum nitride film having a film thickness of 3 to 250 nm that continuously covers the surface of the seed crystal layer, the end face, and the surface of the planarizing layer adjacent to the end face; A method for producing a substrate for epitaxial growth of Group III nitrides, comprising:

8. 8. The method for producing a substrate for III-nitride epitaxial growth according to claim 7, wherein the seed crystal layer is silicon (111).

9. In the step of providing the seed crystal layer, an end surface of the seed crystal layer has a portion tapered with respect to a direction parallel to a bottom surface of the seed crystal layer, and a taper angle (θ) of the tapered portion is 75° or less; 8. The method for producing a substrate for III-nitride epitaxial growth according to claim 7, wherein in the step of forming the aluminum nitride film, the aluminum nitride film is formed by sputtering.

10. In the step of providing the seed crystal layer, an end face of the seed crystal layer has a portion tapered in a direction parallel to a bottom surface of the seed crystal layer and a portion substantially perpendicular to the bottom surface of the seed crystal layer, and a taper angle (θ) of the tapered portion is 75° or less; 8. The method for producing a substrate for Group III nitride epitaxial growth according to claim 7, wherein in the step of forming the aluminum nitride film, the aluminum nitride film is formed by a sputtering method, and the thickness of the aluminum nitride film is made thicker than a height (h) of an end face that is approximately perpendicular to a surface of the planarization layer in a region of the planarization layer as viewed from above, the end face including the approximately perpendicular portion of the seed crystal layer.

11. 8. The method for producing a substrate for III-nitride epitaxial growth according to claim 7, wherein in the step of forming the aluminum nitride film, the aluminum nitride film is formed by atomic layer deposition (ALD).

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