Substrate for group iii nitride epitaxial growth, method for manufacturing same, and epitaxial film manufacturing method and semiconductor device manufacturing method each using same

Abstract

This substrate 1 for growth comprises: a support substrate 10 in which a ceramic core is enclosed by a sealing layer; and a single crystal seed crystal layer 30 which is bonded to the support substrate by the intermediary of a planarization layer 20. In a top view of this substrate 1 for growth, there are a region of the seed crystal layer 30 and a region of the planarization layer 20, and the seed crystal layer 30 has an end surface 33 at the boundary between the two regions. This substrate 1 for growth additionally comprises an aluminum nitride film 40 which has a film thickness of 3 nm to 250 nm and continuously covers the region from the surface of the seed crystal layer 30 to the surface of the planarization layer 20 adjacent to the end surface 33. The aluminum nitride film 40 is formed by a sputtering method or an ALD method. An epitaxial film and a semiconductor device are manufactured using this substrate 1 for growth.

Description

Substrate for epitaxial growth of III-nitrides, method for manufacturing the same, and method for manufacturing epitaxial film and semiconductor device using the same

[0001] The present invention relates to 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 The present invention relates to a substrate for epitaxial growth of Group III nitrides, such as N (where 0<y<1.0), for use in the epitaxial growth of single crystals of Group III nitrides, a method for producing the same, and methods for producing epitaxial films and semiconductor devices using the same.

[0002] Currently, single-crystal Si substrates are widely used as semiconductor substrates. However, due to their characteristics, they are not necessarily suitable for the recent high voltage and high frequency requirements. Therefore, although they are expensive, single-crystal SiC and single-crystal GaN substrates have begun to be used. For example, by constructing power conversion devices such as inverters and AC / DC converters using semiconductor elements made of silicon carbide (SiC) or nitrides (AlInGaN-based), which are semiconductor materials with a wider bandgap than silicon (Si), power loss reductions that cannot be achieved with semiconductor elements made of silicon have been realized. The use of semiconductor elements made of SiC or nitrides not only reduces losses associated with power conversion compared to conventional devices, but also promotes weight reduction, miniaturization, and high reliability of the devices.

[0003] GaN nitrides, primarily GaN, have superior insulating properties and high-frequency characteristics compared to SiC, and as such, GaN is attracting attention as a next-generation device. Substrates for growing GaN epitaxial films include composite substrates in which a seed crystal layer of Si single crystal is bonded to a support substrate having a ceramic core with approximately the same thermal expansion coefficient as the crystal to be grown. Patent Documents 1 and 2 disclose examples in which, in addition to Si, single crystals such as SiC, aluminum nitride (AlN), GaN, aluminum gallium nitride (AlGaN), and aluminum oxide (AlO) are used as seed crystal layers on support substrates with ceramic cores.

[0004] JP 2022-012558 A JP 2023-098137 A

[0005] In epitaxial growth of a Group III nitride single crystal such as GaN on a Si seed crystal, providing a cover layer made of AlN on the Si seed crystal can suppress meltback of the Si seed crystal due to Group III elements such as Ga. In addition, in general, in vapor phase growth methods such as metalorganic chemical vapor deposition (MOCVD) 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 a part of 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 part 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, which is the Si(111) surface of the seed crystal layer 130, 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 suppress 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 seed crystal layer end face 131 by the cover layer 140.

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

[0009] 2A and 2B show images of actual examples of peeled epitaxial film. 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, meltback of the seed crystal occurs, and the Group III nitride epitaxial film peels off from that portion as a starting point, which results in 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 has an object to provide a substrate for Group III nitride epitaxial growth that is capable of suppressing meltback of the seed crystal during the device manufacturing process in a composite substrate formed by bonding a seed crystal layer such as a Si single crystal to a support substrate having a ceramic core, a method for manufacturing the same, and methods for manufacturing epitaxial films and semiconductor devices using the same.

[0012] In order to solve the above problems, one aspect of the present invention is a substrate for Group III nitride epitaxial growth, the 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 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 with respect to 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 Group III nitride-based epitaxial film or semiconductor device using such a substrate for Group 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; 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 in a top view 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 an 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. In the step of forming the aluminum nitride film, it is preferable that the aluminum nitride film is formed by a sputtering method and that the thickness of the aluminum nitride film is thicker than a 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).

[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.

[0024] 2A , 2B , 2C , 2D , 2E , 2F , 2G , 2G , 2H ...

[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 to this.

[0026] 1. Group III Nitride Epitaxial Growth Substrate and Epitaxial Wafer] Figure 3 is a cross-sectional view schematically showing an example of an epitaxial wafer produced using an embodiment of a Group III nitride epitaxial growth substrate according to the present invention. As shown in Figure 3, Group III nitride epitaxial growth substrate 1 of this embodiment (hereinafter simply referred to as "growth substrate") comprises a support substrate 10, a planarization layer 20 provided on one surface of support substrate 10, a seed crystal layer 30 provided on the surface of planarization layer 20, and an aluminum nitride (AlN) film 40 covering seed crystal layer 30. Furthermore, epitaxial wafer 3 of this embodiment is obtained by performing epitaxial growth using this growth substrate 1, and comprises growth substrate 1, a buffer layer 50 on aluminum nitride film 40, and a Group III nitride epitaxial film 60 (hereinafter simply referred to as "epitaxial film") on 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 that forms the base of the support substrate 10, and the ceramic is preferably made of, for example, 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), or a material containing a mixture thereof. The thickness of the core is preferably in the range of, for example, 200 to 1500 μm. 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. Examples of materials that can be used as the sealing layer include silicon oxide (SiO2), Si3N4, and mixtures thereof, 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. A suitable example of a support substrate 10 that encases the entire core in a sealing layer is the QST (USA registered trademark) substrate from Qromis.

[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 SiO, SiN, silicon oxynitride (SiON), SiC, AlO, Si, gallium arsenide (GaAs), and aluminum arsenide (AlAs), with SiO 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 that is tapered in a direction parallel to the bottom face of the seed crystal layer 30 and a portion 33b that is approximately perpendicular to the bottom face of the seed crystal layer 30.

[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 planarization layer 20 (the region of the planarization 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 planarization layer 20. In the latter case, a step surface 24 is formed between the surface 22 of the outer periphery of the planarization layer 20 and the bonding surface 23 of the planarization layer 20 with the seed crystal layer 30. The formation and height control of the step surface 24 of the planarization layer 20 can be achieved by changing the substrate surface treatment method after the attachment of the seed crystal layer 30.

[0035] In the case of Figure 5A, the only end face that is approximately perpendicular to the surface 21 of the outer periphery of the planarizing layer 20 is the approximately perpendicular portion 33b of the end face of the seed crystal layer 30. Therefore, the height of the end face that is approximately perpendicular to the surface 21 of the outer periphery of the planarizing layer 20 (hereinafter referred to as the "approximately perpendicular end face height h") is the same as the length of the approximately perpendicular portion 33b of the end face of the seed crystal layer 30. In the case of Figure 5B, the end face that is approximately perpendicular to the surface 22 of the outer periphery of the planarizing layer 20 is formed by the approximately 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 approximately perpendicular end face height h is the sum of the length of the approximately 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 33 a of the end face 33 of the seed crystal layer 30 is an angle formed by a direction parallel to the bottom surface of the seed crystal layer 30 (direction A-B in the figures) and a direction toward point C on the surface of the tapered portion 33 a, with the corner between the tapered portion 33 a of the end face 33 of the seed crystal layer 30 and a substantially vertical portion as starting point A. 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 formed by a direction parallel to the bottom surface of the seed crystal layer 30 and a direction toward point C on the surface of the tapered end face, with the edge of the tapered end face 32 of the seed crystal layer 30 as starting point A. In this case, point C is also defined as a position at a distance 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, the end faces 31, 32, and 33, and even the 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. Furthermore, cracks may 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 the 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 will evaporate during the temperature rise process during epitaxial growth thereon. Furthermore, if the thickness is thinner than 3 nm, the AlN film 40 will be discontinuous, particularly at the end face of the seed crystal layer 30, and will not be able to completely cover the outer periphery of the end face of the seed crystal layer 30. 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 will be deteriorated. 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 planarizing 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 of the substantially vertical end face h>0, if the AlN film 40 is a sputtered film, it is preferable that the film thickness t(AlN) of the AlN film 40 on the end face of the seed crystal layer 30 be thicker than the height h of the substantially vertical end face. Due to the film formation principle of a sputtered film, if the film thickness of the AlN film 40 is equal to or thinner than the height h of the substantially vertical end face, there will be portions where the coverage by the AlN film 40 is missing on the end face that is substantially vertical to the surface 21 of the outer periphery of the planarizing layer 20. When the AlN film 40 is a sputtered film, it is preferable that the relationship between the film thickness t(AlN) of the AlN film 40 on the end face of the seed crystal layer 30 and the height h of the substantially vertical end face be as follows: t(AlN)>h and 3 nm≦t(AlN)≦250 nm

[0043] When the AlN film 40 is an ALD film, due to the film formation principle, it has better coverage on approximately vertical end faces than a sputtered film, so even when the approximately vertical end face height h>0 and t(AlN)<h, a continuous coating of AlN film 40 without any defects can be formed on the end faces that are approximately vertical to the surface 21 of the outer periphery of the planarization layer 20.

[0044] The epitaxial wafer 3 is formed by growing an epitaxial film 60 on the AlN film 40 of the growth substrate 1 having such a configuration. Alternatively, as shown in FIG. 3 , a buffer layer 50 may be provided on the AlN film 40, and the epitaxial film 60 may be stacked on top of that. The buffer layer 50 may be provided as needed to alleviate mismatch due to the difference in lattice constant between the seed crystal layer 30 and the epitaxial film 60, or to alleviate stress on the epitaxial film 60. The buffer layer 50 may be made of, for example, AlN, GaN, AlGaN, or a multilayer film thereof. These may also be doped with an N-type dopant. Examples of the dopant that may be used include Si, Ge, and C. The thickness of the buffer layer 50 may 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, and therefore 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, and therefore 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 a Group III Nitride Epitaxial Growth Substrate, an Epitaxial Film, and a Semiconductor Device] One embodiment of a method for manufacturing a Group III nitride epitaxial growth substrate according to the present invention will be described. The manufacturing method of this embodiment includes 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, 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 described here.

[0048] The core preparation step involves first preparing a green sheet by mixing ceramic powder such as AlN with sintering aids, organic binders, solvents, 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 10, 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 (US registered trademark) substrate from Qromis may also be used.

[0050] 3, the step of forming the planarization layer 20 involves first forming the planarization layer 20 on at least one surface of the support substrate 10 by a plasma CVD method or the like. The planarization layer 20 may be formed so as to enclose the entire support substrate 10. Then, after densification 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 bonding surface of the seed crystal substrate to 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, the taper angle θ of the end face of the seed crystal layer 30 can be set to a predetermined angle, or the approximately vertical end face can be set to a predetermined height. Thereafter, to recover the damaged portion of the seed crystal layer 30 due to ion implantation, the seed crystal substrate 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 40 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, trimethylaluminum (TMA) is used as the aluminum source and ammonia (NH) 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 10 is preferably cleaned by reverse sputtering, in which a plasma of argon gas or nitrogen gas is applied to 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 a semiconductor device, for example, in the case of a vertical power device, an epitaxial wafer 3 having an epitaxial film 60 formed on a growth substrate 1 is first fabricated. 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 predetermined positions to fabricate the device. Heat treatment at 1200°C or higher is then performed for activation. Next, dry etching is performed to separate the devices, exposing the planarization layer 20. A temporary support substrate is then bonded to the upper surface of the device. The planarization layer 20 is then dissolved using an HF solution or the like, and the support substrate 10 is then separated. An ohmic electrode is then formed on the seed crystal layer 30, and a backside electrode is then formed on the surface of the ohmic electrode, thereby completing the semiconductor device.

[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, YO as a sintering aid, an organic binder, a solvent, etc. were mixed to prepare a green sheet, which was then degreased and sintered in N at 1900°C to prepare 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 by the LPCVD method, and then a 0.6 μm thick SiN 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 layer) A 7 μm thick SiO2 was laminated on the Si3N4 layer on one side (upper surface) of the support substrate by plasma CVD (ICP-CVD apparatus). After that, this SiO2 was baked at 1000°C, and then polished and planarized to a thickness of 3 μm by CMP polishing to produce a planarization layer with a surface having an arithmetic mean roughness Ra of 0.15 nm.

[0060] (Thin film transfer of seed crystal layer) A commercially available Si (111) single crystal seed crystal substrate, pulled up by the CZ method, with a diameter of 8 inches was prepared for bonding to a support substrate. Hydrogen ions were irradiated onto this Si single crystal substrate at 100 KeV to a depth of 0.7 μm with a dose of 6×10 17 cm -2 Ion implantation was performed under the conditions shown in Table 1. The ion-implanted surface of the seed crystal substrate was then bonded to the planarized layer surface 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), thereby transferring a portion of the seed crystal substrate to the support substrate as a thin film seed crystal layer. The transferred seed crystal layer was then thinned by CMP polishing and hydrofluoric acid etching until the thickness of the seed crystal layer reached 0.38 μm. 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 substantially vertical portions (i.e., the substantially vertical end face height h = 0 nm). Furthermore, the damaged portions of the seed crystal layer due to the ion implantation were restored by heat treatment at 1000°C in a hydrogen atmosphere.

[0061] (Formation of AlN film) Next, an AlN film was formed by RF sputtering. The composite substrate in which the seed crystal layer was bonded to the support substrate was introduced into the chamber of a sputtering device. A target made of metallic Al was used. Before film formation, the pressure inside the chamber was reduced, and a 1.0 × 10 -3 The internal pressure was reduced to 100 Pa or less, 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. Thereafter, the substrate temperature was increased to 500°C to 800°C, and an AlN film was deposited.

[0062] First, argon gas alone 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 circulated, and a 5000 W high-frequency bias was applied to the metal Al target to generate plasma and deposit an AlN film. The plasma operation was stopped when the AlN film reached a thickness of 10 nm, 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 seed crystal layer end face) Using one of the prepared growth substrates, the thickness and coverage of the AlN film near the center of the substrate and near the seed crystal layer end face on the periphery of the substrate were confirmed by cross-sectional transmission electron microscope (TEM) observation. As a result of the observation, the thickness of the AlN film near the center of the substrate was approximately 10 nm. Furthermore, when observing the vicinity of the end face of the seed crystal layer, the taper angle θ was approximately 30°, and the end face was also covered with an AlN film of approximately 10 nm, and no cracks were observed in the AlN layer.

[0064] (Epitaxial Growth) An epitaxial film having a device structure for fabricating a vertical MOSFET was formed on the fabricated growth substrate using an MOCVD apparatus to fabricate an epitaxial wafer. The structure is shown in FIG. 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 1×10 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 having a similar device structure was formed on a Si substrate.

[0067] (Device Fabrication) Next, this vertical device epitaxial wafer 3 was processed using the following device fabrication 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. Then, 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 confirm the process. As a result of the observation, no meltback due to Ga occurred over the entire wafer surface, and no film peeling was observed. Thereafter, a gate insulating film (SiO2) was formed in the trench portion. Then, 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. A mask with a predetermined pattern was then 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 of support substrate) The elements were separated by dry etching, exposing the planarization layer. A temporary support substrate was attached to the top surface of the element and immersed in an HF solution. This dissolved the SiO2 planarization layer, separating the element into an upper portion and a lower portion above the planarization layer.

[0069] (Removal of buffer layer, formation of backside electrode) The buffer layer on the backside 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 heat treatment was performed in an N or H atmosphere.

[0070] (Mounting on device mounting board and inspection) Then, each element was mounted on the device mounting board to complete the semiconductor device. When mounting the device, we made sure 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 characteristics 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 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 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 of 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 layers were modified to have tapered and substantially vertical portions, with a taper angle θ of 30° and a height of the substantially vertical portions of 8 nm (the substantially vertical end face height h was also 8 nm). Various observations and inspections were then performed. Observation of the AlN layer coverage on the end faces of the seed crystal layers of the growth substrates 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 modified to have 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 then performed. Observation of the coverage of the AlN layer 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 then performed. Observation of the coverage of the AlN layer 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 then performed. The ALD deposition used trimethylaluminum (TMA) as the aluminum source and ammonia (NH) 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 of the growth substrate confirmed that the end faces were also covered with an AlN film. Furthermore, XRD evaluation revealed a favorable half-width of 436 arcsec for the GaN (0002) plane. No Ga meltback 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 coverage of the AlN layer 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: A growth substrate, epitaxial wafer, and semiconductor device 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. 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 AlN film on the end face was discontinuous and insufficient. Furthermore, XRD evaluation revealed a poor result of 750 arcsec for the GaN (0002) plane half-width. Furthermore, after high-temperature heat treatment during the device fabrication process, meltback due to Ga was observed, particularly on the end face of the seed crystal layer.

[0084] Comparative Example 2: A growth substrate, epitaxial wafer, and semiconductor device 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 face of the growth substrate confirmed that the end face was also covered with an AlN film. Meanwhile, XRD evaluation revealed a poor result of 866 arcsec for the GaN (0002) plane half-width. 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). Various observations and inspections were then performed. As a result, observation of the coverage of the AlN layer 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. Meanwhile, XRD evaluation revealed a favorable GaN (0002) plane half-width of 423 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.

[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 substantially vertical portions, with a taper angle θ of 30° and a height of 8 nm for the substantially vertical portions. A stepped surface was formed on the outer periphery of the planarization layer, resulting in a substantially vertical end face height h of 10 nm. Various observations and inspections were then performed. Observation of the coverage of the AlN layer on the end faces of the seed crystal layer of the growth substrate confirmed 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 half-width 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 substantially vertical portions, with a taper angle θ of 75° and a height of 8 nm for the substantially vertical portions. A stepped surface was formed on the outer periphery of the planarization layer, resulting in a substantially vertical end face height h of 10 nm. Various observations and inspections were then performed. Observation of the coverage of the AlN layer 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 half-width 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] A growth substrate, epitaxial wafer, and semiconductor device were fabricated in the same manner as in Example 1, except that an AlN film was formed 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 of Example 5, where the AlN film had the same thickness of 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]

[0091] REFERENCE SIGNS LIST 1 Substrate for 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 film

Claims

1. A 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 for III-nitride epitaxial growth further comprises an aluminum nitride film having a 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.

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

3. 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 in a direction parallel to the bottom surface of the seed crystal layer, and the taper angle (θ) of the tapered portion is 75° or less.

4. 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 in a direction parallel to the bottom surface of the seed crystal layer and a portion substantially perpendicular to the bottom surface of the seed crystal layer, the taper angle (θ) of the tapered portion being 75° or less, and the film thickness of the aluminum nitride film is greater than a height (h) of the end face substantially perpendicular to the surface of the planarizing layer in a region of the planarizing layer when viewed from above, the height (h) including the substantially perpendicular portion of the seed crystal layer.

5. 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 semiconductor device using the substrate for Group III nitride epitaxial growth according to any one of claims 1 to 5.

7. A method for manufacturing a substrate for Group III nitride epitaxial growth, comprising: 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; providing a single-crystal seed crystal layer on the surface of the planarizing layer, the seed crystal layer being provided so as to leave an area 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 area where the planarizing layer is exposed; and forming an aluminum nitride film having a thickness of 3 to 250 nm, continuously covering the surface of the seed crystal layer, the end face, and the surface of the planarizing layer adjacent to the end face.

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. A method for producing a substrate for Group III nitride epitaxial growth according to claim 7, wherein, in the step of providing a 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, the tapered portion having a taper angle (θ) of 75° or less, and, in the step of forming an aluminum nitride film, the aluminum nitride film is formed by a sputtering method.

10. A method for producing a substrate for Group III nitride epitaxial growth as set forth in claim 7, wherein in the step of providing a seed crystal layer, an 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 tapered portion having a taper angle (θ) of 75° or less, and in the step of forming an 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 approximately perpendicular to the surface of the planarizing layer in a region of the planarizing layer as viewed from above, including the approximately perpendicular portion of the seed crystal layer.

11. 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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