Nitride semiconductor substrate and method for producing same

Abstract

To provide nitride semiconductor substrate which barely undergoes the cloudiness of a specular edge surface after epitaxial growth and, as a result, does not undergo the generation of dusts or reaction impressions and undergoes little failures during a process and a method for producing the nitride semiconductor substrate.SOLUTION: The present invention provides a nitride semiconductor substrate comprising: a composite substrate that is composed of a plurality of layers laminated on each other; a silicon oxide layer or a TEOS layer that is laminated on the composite substrate and has a flat surface located at the center part thereof and a side surface surrounding the flat surface; a single-crystal silicon layer that is laminated on the silicon oxide layer or the TEOS layer; and a nitride semiconductor thin film that is formed on the single-crystal silicon layer. The whole of the flat surface located at the center part of the silicon oxide layer or the TEOS layer is covered by the single-crystal silicon layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a nitride semiconductor substrate and a method for manufacturing the same. [Background technology]

[0002] Nitride semiconductors such as GaN and AlN can be used to fabricate high electron mobility transistors (HEMTs) that use two-dimensional electron gas and high-voltage electronic devices.

[0003] It is difficult to produce nitride wafers by growing these nitride semiconductors on a substrate, so sapphire or SiC substrates are used as the substrate. However, epitaxial growth by vapor phase growth on silicon substrates is used to increase the diameter and reduce the cost of substrates. The production of epitaxially grown films by vapor phase growth on silicon substrates allows the use of larger diameter substrates than sapphire or SiC substrates, which is advantageous in terms of heat dissipation and high device productivity. However, stress due to differences in lattice constants and thermal expansion coefficients can easily cause increased warping and plastic deformation, so stress reduction is being carried out by adjusting growth conditions and using relaxation layers.

[0004] In high-voltage electronic devices, it is necessary to stack a thick epitaxial layer to improve the high-voltage characteristics. However, stacking a thick epitaxial layer causes warping of the wafer due to the difference in thermal expansion coefficient between the silicon substrate that serves as the substrate and the epitaxial layer.

[0005] For this reason, a large-diameter substrate for growing a nitride semiconductor epitaxial film, which has a large diameter and a thermal expansion coefficient close to that of a nitride semiconductor (hereinafter, a composite substrate), has been developed. This composite substrate is composed of a composite substrate including a polycrystalline ceramic core, a first adhesive layer bonded to the entire polycrystalline ceramic core, a conductive layer bonded to the entire first adhesive layer as required, a second adhesive layer bonded to the entire conductive layer or to the entire first adhesive layer, and a barrier layer bonded to the entire second adhesive layer, a silicon oxide layer bonded to only one side of the composite substrate, and a single-crystal silicon layer bonded to the silicon oxide layer (Patent Document 1).

[0006] By using this composite substrate, it is possible to fabricate a nitride semiconductor epitaxial growth substrate that is large in diameter, has a thick epitaxial layer, and is free of cracks. In addition, because the difference in thermal expansion coefficient between the composite substrate and the nitride semiconductor is small, warping is unlikely to occur during nitride semiconductor growth or cooling, and warping of the substrate after film formation can be controlled to a minimum. Furthermore, because the composite substrate is mostly ceramic, not only is the substrate itself very hard and resistant to plastic deformation, but wafer cracking, which has not been solved with GaN / Si, does not occur.

[0007] However, when a nitride semiconductor substrate having a HEMT structure is manufactured by epitaxially growing a nitride semiconductor using a growth substrate composed of a silicon oxide layer bonded to only one side of such a composite substrate and a single crystal silicon layer bonded to the silicon oxide layer, clouding occurs on the mirror edge surface after epitaxial growth. Reaction marks are often generated at the interface between the mirror surface and the cloudy part, which becomes a source of dust generation during the process. In addition, residues of chemicals and the like remaining in the cloudy part during the process may cause defects during the process. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2021-502701 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve the above-mentioned problems, and has an object to provide a nitride semiconductor substrate which has a clear mirror edge surface after epitaxial growth, and therefore which is free from dust generation and reaction marks and which has few defects during processing, and a method for manufacturing the same. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides A composite substrate having multiple layers stacked together; a silicon oxide layer or a TEOS layer laminated on the composite substrate, the silicon oxide layer having a flat surface in the center and a side surface around the flat surface; a single crystal silicon layer laminated on the silicon oxide layer or the TEOS layer; and A nitride semiconductor thin film formed on the single crystal silicon layer. A nitride semiconductor substrate comprising: The present invention provides a nitride semiconductor substrate in which the entire flat surface at the center of the silicon oxide layer or TEOS layer is covered with the single crystal silicon layer.

[0011] In this way, if the nitride semiconductor substrate has a flat surface of the silicon oxide layer or TEOS layer not exposed at the end of the monocrystalline silicon layer, which is the growth surface of the nitride semiconductor thin film, the nitride semiconductor thin film will not grow as a polycrystal on the flat surface of the silicon oxide layer or TEOS layer, and therefore a nitride semiconductor substrate can be obtained that has a mirror edge surface that is free of cloudiness, dust generation, reaction marks, and few defects during processing.

[0012] It is also preferable that the side surfaces of the silicon oxide layer or the TEOS layer are covered with a silicon nitride film.

[0013] Such a nitride semiconductor substrate can more reliably prevent the occurrence of clouding.

[0014] It is also preferable that the composite substrate includes a polycrystalline ceramic core, a first adhesive layer laminated over the polycrystalline ceramic core, a second adhesive layer laminated over the first adhesive layer, and a barrier layer laminated over the second adhesive layer.

[0015] In this case, the composite substrate may have a conductive layer between the first adhesive layer and the second adhesive layer, the conductive layer being laminated over the entire first adhesive layer.

[0016] A nitride semiconductor substrate using such a composite substrate can be obtained that is suppressed in warping of the substrate after film formation.

[0017] It is also preferable that the conductive layer includes a polysilicon layer.

[0018] It is also preferable that the first adhesive layer and the second adhesive layer contain TEOS or silicon oxide, and the barrier layer contains silicon nitride.

[0019] With such a nitride semiconductor substrate, the warp of the substrate after film formation can be controlled to be even smaller, and it is also possible to form a thick nitride semiconductor thin film.

[0020] The polycrystalline ceramic core preferably contains aluminum nitride.

[0021] Such a nitride semiconductor substrate can reduce warpage of the substrate after film formation.

[0022] The present invention also provides a method for producing a nitride semiconductor substrate, comprising the steps of: (1) preparing a composite substrate having a plurality of layers stacked thereon and a single crystal silicon substrate; (2) bonding the single crystal silicon substrate onto the composite substrate via a silicon oxide layer or a TEOS layer; (3) thinning the bonded single crystal silicon substrate to form a single crystal silicon layer; (4) forming the silicon oxide layer or TEOS layer and the edge of the single crystal silicon layer so that the entire flat surface of the central portion of the silicon oxide layer or TEOS layer is covered with the single crystal silicon layer; (5) growing an AlN film on the single crystal silicon layer; and (6) growing one or more films selected from a GaN film, an AlGaN film, and an AlN film on the AlN film; The present invention provides a method for producing a nitride semiconductor substrate, comprising the steps of:

[0023] According to this manufacturing method, it is possible to relatively easily manufacture a nitride semiconductor substrate that has no cloudiness on the mirror edge surface, no dust generation or reaction marks, and few defects during the process.

[0024] The step (4) is preferably a chamfering step.

[0025] In this way, manufacturing can be achieved without increasing the number of steps required compared to the conventional method.

[0026] It is preferable to further include, between the step (4) and the step (5), a step (4') of covering at least the side surface of the silicon oxide layer or the TEOS layer with a silicon nitride film.

[0027] In this way, the silicon oxide layer or the TEOS layer can be reliably prevented from being exposed.

[0028] It is also preferable that the composite substrate includes a polycrystalline ceramic core, a first adhesive layer laminated over the polycrystalline ceramic core, a second adhesive layer laminated over the first adhesive layer, and a barrier layer laminated over the second adhesive layer.

[0029] In this case, it is preferable that the composite substrate has a conductive layer between the first adhesive layer and the second adhesive layer, the conductive layer being laminated over the entire first adhesive layer.

[0030] Such a manufacturing method can further reduce warping of the substrate after film formation. Effect of the Invention

[0031] As described above, the present invention can provide a nitride semiconductor substrate and a manufacturing method thereof which have a clear mirror edge surface after epitaxial growth and therefore have no dust or reaction marks and few defects during processing. [Brief description of the drawings]

[0032] [Figure 1] 1 is a schematic cross-sectional view showing an example of a film-formation substrate in which a composite substrate, a silicon oxide layer, and a single crystal silicon layer are laminated in a nitride semiconductor substrate of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view for explaining in detail a silicon oxide layer in the nitride semiconductor substrate of the present invention. [Diagram 3] FIG. 2 is a schematic cross-sectional view showing an example of a film-formation substrate in which a composite substrate in which a silicon nitride film is formed on the side surface of a silicon oxide layer in the nitride semiconductor substrate of the present invention, a silicon oxide layer, and a single crystal silicon layer are laminated. [Figure 4] FIG. 1 is a schematic cross-sectional view showing an example of a film-formation substrate in which a composite substrate, a silicon oxide layer, and a single crystal silicon layer are laminated in a conventional nitride semiconductor substrate. [Diagram 5] 1 is a schematic diagram showing an example of an MOCVD apparatus that can be used in the method for producing a nitride semiconductor substrate of the present invention. [Figure 6] 1 is a schematic diagram showing an example of a film-forming substrate for a nitride semiconductor substrate according to the present invention. [Figure 7] 1A to 1C are explanatory diagrams of an example of a method for producing a nitride semiconductor substrate according to the present invention. [Figure 8] FIG. 1 is a cross-sectional view of a conventional nitride semiconductor substrate in which a polysilicon layer is grown on the edge of the substrate. [Figure 9] FIG. 9 is a close-up of the boundary between the single crystal layer and the poly layer of FIG. 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] As described above, when a nitride semiconductor substrate with a HEMT structure is manufactured by epitaxially growing a nitride semiconductor using a deposition substrate composed of a silicon oxide layer laminated on only one side of a composite substrate and a single crystal silicon layer laminated on the silicon oxide layer, the mirror edge surface after epitaxial growth becomes cloudy. Reaction marks often occur at the interface between the mirror surface and the cloudy part, which causes dust generation during the process.

[0034] When the inventors observed the cross-sections of the mirror and cloudy parts using SEM, they found that the mirror part was a nitride semiconductor thin film that had grown as a single crystal, while the cloudy part was a polycrystalline grown (Figure 8). They also found that the mirror part had grown on a single crystal silicon layer, while the cloudy part had grown on a silicon oxide layer. Figure 9 shows the interface between the single crystal and polycrystalline grown parts. Furthermore, residues of chemicals and other materials from the process remain in the polycrystalline parts, which can cause defects during the process.

[0035] The inventors then discovered that a nitride semiconductor substrate having a nitride semiconductor thin film formed on a film-formation substrate in which a single crystal silicon layer is bonded via a silicon oxide layer onto a composite substrate in which multiple layers are stacked, and in which the flat surface of the silicon oxide layer is not exposed from the edge of the single crystal silicon layer, which is the growth surface of the nitride semiconductor thin film, can have a substrate with no clouding at the edges, and thus completed the present invention.

[0036] That is, the present invention provides a nitride semiconductor substrate including a composite substrate having a plurality of layers stacked on top of one another, a silicon oxide layer or a TEOS layer stacked on the composite substrate, the silicon oxide layer or the TEOS layer having a central flat surface and side surfaces surrounding the flat surface, a single crystal silicon layer stacked on the silicon oxide layer or the TEOS layer, and a nitride semiconductor thin film formed on the single crystal silicon layer, wherein the entire central flat surface of the silicon oxide layer or the TEOS layer is covered with the single crystal silicon layer.

[0037] The present invention also provides a method for manufacturing a nitride semiconductor substrate, comprising the steps of: (1) preparing a composite substrate having a plurality of stacked layers and a single crystal silicon substrate; (2) bonding the single crystal silicon substrate onto the composite substrate via a silicon oxide layer or a TEOS layer; (3) thinning the bonded single crystal silicon substrate to form a single crystal silicon layer; (4) forming ends of the silicon oxide layer or TEOS layer and the single crystal silicon layer so that the entire flat surface in the center of the silicon oxide layer or TEOS layer is covered with the single crystal silicon layer; (5) growing an AlN film on the single crystal silicon layer; and (6) growing one or more films selected from a GaN film, an AlGaN film, and an AlN film on the AlN film.

[0038] The present invention will be described in detail below, but the present invention is not limited thereto.

[0039] First embodiment The nitride semiconductor substrate of the present invention includes a composite substrate, a bonding layer made of a silicon oxide layer (SiO2 layer) or a TEOS (tetraethyl orthosilicate) layer, a deposition substrate including a single crystal silicon layer, and a nitride semiconductor thin film deposited on the deposition substrate, and the entire flat surface of the bonding layer is covered with a single crystal silicon layer. In the following description, the case where the bonding layer is a silicon oxide layer will be described as an example, but the present invention can also be applied to the case where the bonding layer is a TEOS layer.

[0040] Fig. 1 shows an example of a film-formation substrate including a composite substrate, a silicon oxide layer, and a single crystal silicon layer in the nitride semiconductor substrate of the present invention. In this film-formation substrate, a single crystal silicon layer 3 is laminated on a composite substrate 1 via a silicon oxide layer 2. The difference from the prior art is that the entire flat surface of the silicon oxide layer 2 in Fig. 1 is covered with the single crystal silicon layer 3. In other words, the silicon oxide layer is not exposed at the end 4 of the flat surface of the silicon oxide layer. In other words, the entire flat surface in the center of the silicon oxide layer 2 is covered with the single crystal silicon layer 3.

[0041] 4, in a conventional nitride semiconductor substrate, the end 4 of the flat surface of the silicon oxide layer 2 is not covered with the single crystal silicon layer 3. Therefore, when a nitride semiconductor thin film is grown on a film-formation substrate, the polysilicon layer of the nitride semiconductor thin film grows on the exposed silicon oxide layer 2 at the end 4 of the flat surface. In contrast, in the present invention, since the silicon oxide layer 2 is not exposed at the end 4 of the flat surface, the polysilicon layer of the nitride semiconductor thin film does not grow on the silicon oxide layer 2.

[0042] Here, the configuration of the silicon oxide layer in the present invention will be described in more detail with reference to FIG. 2. As shown in (a) and (b) of FIG. 2, in the nitride semiconductor substrate of the present invention, the silicon oxide layer 2 has a flat surface 21 (surface indicated by a dotted line) in the center and a side surface 22 (surface indicated by a thick line) around the flat surface. In the present invention, the entire flat surface 21 is covered with the single crystal silicon layer 3. On the other hand, the side surface 22 around the flat surface 21 may or may not be covered with the single crystal silicon layer 3, but it is preferable that it is not covered with the single crystal silicon layer 3 in terms of ease of manufacture. In addition, as shown in (a), the side surface 22 may be perpendicular to the flat surface 21, or as shown in (b), the side surface 22 may be inclined. In addition, although the side surface 22 is drawn as a straight line (plane) in the figure, the side surface 22 may be curved. In addition, the side surface 22 may be a chamfered surface.

[0043] In the present invention, the nitride semiconductor thin film formed on the film-forming substrate may be an AlN film and a GaN film or an AlGaN film, or both, formed thereon. For example, an AlN film, an AlGaN film, and a GaN film may be epitaxially grown on the film-forming substrate using a self-rotating MOCVD reactor as shown in FIG. 5.

[0044] The film formation substrate may be composed of a composite substrate including a polycrystalline ceramic core 6, a first adhesive layer 7 laminated over the entire polycrystalline ceramic core, a conductive layer 8 laminated over the entire first adhesive layer 7, a second adhesive layer 9 laminated over the entire conductive layer 8, and a barrier layer 10 laminated over the entire second adhesive layer 9, a silicon oxide layer 2 laminated on only one side of the composite substrate, and a single crystal silicon layer 3 laminated on the silicon oxide layer 2, as shown in FIG. 6, for example.

[0045] Here, the polycrystalline ceramic core 6 may contain aluminum nitride, and is preferably sintered at a high temperature of, for example, 1800° C. with a sintering aid, and has a thickness of about 300 to 1150 μm. Basically, it is often formed to a thickness that meets the SEMI standard for single crystal silicon substrates.

[0046] The first adhesion layer 7 and the second adhesion layer 9 may be layers containing tetraethylorthosilicate (TEOS) or silicon oxide (SiO2), and are deposited, for example, by an LPCVD process or a CVD process, and preferably have a thickness of 100 nm.

[0047] The conductive layer 8 may include a polysilicon layer, and is preferably deposited by, for example, an LPCVD process, and has a thickness of about 300 nm. This layer is for imparting electrical conductivity, and may be doped with, for example, boron (B) or phosphorus (P). In some cases, the conductive layer 8 may not be deposited.

[0048] The barrier layer 10 may comprise silicon nitride and is preferably deposited by, for example, an LPCVD process, with a thickness of 400 nm to 500 nm to prevent the diffusion and outgassing of elements present in the ceramic core, such as yttrium, yttrium oxide, oxygen, metallic impurities, and other trace elements, into the environment of the semiconductor processing chamber during the high temperature epitaxial growth process.

[0049] The silicon oxide layer 2 is deposited by, for example, an LPCVD process or the like, and preferably has a thickness of about 1.5 μm. The single crystal silicon layer 3 preferably has a thickness of 300 to 500 nm. This layer is used as a growth surface for epitaxial growth of nitride semiconductors such as AlN and GaN.

[0050] The thickness of each layer is not limited to the above values, and not all layers are necessarily present, but the film-formation substrate in the present invention has at least a single crystal silicon layer, a silicon oxide layer or a TEOS layer, and a composite substrate in which multiple layers are stacked.

[0051] The nitride semiconductor substrate of the first embodiment of the present invention can be manufactured by the method for manufacturing a nitride semiconductor substrate of the present invention, for example, as follows.

[0052] First, the above-mentioned composite substrate and a single crystal silicon substrate are prepared (step (1)). The single crystal silicon substrate may have an oxide film (silicon oxide layer) attached thereto.

[0053] Next, a single crystal silicon substrate is bonded onto the composite substrate via a silicon oxide layer (step (2)). The silicon oxide layer is deposited on the composite substrate, for example, by an LPCVD process or the like, and preferably has a thickness of about 1.5 μm. Alternatively, the silicon oxide layer may be a combination of the silicon oxide layer deposited on the composite substrate and the silicon oxide layer attached to the single crystal silicon substrate. The single crystal silicon substrate can be bonded to the silicon oxide layer by, for example, a layer transfer process.

[0054] Next, the bonded single crystal silicon substrates are thinned to form a single crystal silicon layer (step (3)). The single crystal silicon layer preferably has a thickness of 300 to 500 nm. There is no particular limitation on the method for thinning the single crystal silicon layer, and conventional methods can be applied. For example, after bonding the composite substrate and the single crystal silicon substrate via a silicon oxide layer, the single crystal silicon substrate can be thinned by grinding, polishing or etching from the surface. Alternatively, a so-called ion implantation peeling method may be used in which an ion implantation layer is formed in advance on the single crystal silicon substrate, and peeled off at the ion implantation layer after bonding.

[0055] Next, the edges of the silicon oxide layer and the single crystal silicon layer are formed so that the entire flat surface of the center of the silicon oxide layer is covered with the single crystal silicon layer (step (4)). Step (4) can be a step of chamfering the outer periphery of the single crystal silicon. At that time, for example, the chamfering is performed so that the flat portion of the silicon oxide layer is not exposed, as shown in FIG.

[0056] Next, a nitride semiconductor thin film is formed on the single crystal silicon layer. This process can be, for example, a process (5) of growing an AlN film on the single crystal silicon layer, and a process (6) of growing one or more films selected from a GaN film, an AlGaN film, and an AlN film on the AlN film.

[0057] 5 shows a schematic diagram of an example of an MOCVD apparatus that can be used in the method for manufacturing a nitride semiconductor substrate of the present invention. The MOCVD apparatus includes a satellite 52 having a pocket for placing a film-formation substrate 51, a quartz ceiling 53 and quartz 54, and a ring-shaped member 55 placed so as to cover the inside of the edge of the film-formation substrate 51. 56 indicates the direction of the carrier gas flow, and 57 indicates the direction in which the lid is opened.

[0058] The substrate for film formation can be placed in a wafer pocket called a satellite, as shown in FIG. 5. During epitaxial growth, trimethylaluminum (TMAl) can be used as an Al source, TMGa can be used as a Ga source, and NH3 can be used as an N source, but is not limited to these. The carrier gas can be N2 and / or H2, and the process temperature is preferably about 900 to 1200°C.

[0059] At this time, a substrate for film formation is placed on the satellite, and then the lid is closed to perform epitaxial growth. At this time, the epitaxial layer can be formed by forming, for example, an AlN film and an AlGaN film in the growth direction from the substrate side, and then epitaxially growing a GaN film. The structure of the epitaxial layer is not limited to this, and there are also cases where an AlGaN film is not formed, and cases where an AlN film is further formed after the AlGaN film is formed.

[0060] Second Embodiment As shown in Fig. 3, the nitride semiconductor substrate of the present invention may be a film-formation substrate including a composite substrate 1, a silicon oxide layer 2, and a single crystal silicon layer 3, with the side surface of the silicon oxide layer 2 covered with a silicon nitride film 5. Such a nitride semiconductor substrate can more reliably prevent the polysilicon layer of the nitride semiconductor thin film from growing on the edge of the growth substrate. The silicon nitride film 5 may cover only the side surface of the silicon oxide layer 2, or may cover the side surfaces of the silicon oxide layer 2 and the single crystal silicon layer 3, or may even cover the edge of the epitaxial growth surface of the single crystal silicon layer 3.

[0061] In the second embodiment, a part of the silicon oxide layer is exposed by chamfering (i.e., the side surface of the silicon oxide layer is exposed), and a silicon nitride film is coated on the exposed silicon oxide layer (step (4')). Specifically, as shown in FIG. 7, a CVD-SiN film is first deposited on the entire surface of the chamfered wafer (FIG. 7(1)). After that, in a photolithography process, the exposed silicon oxide layer is protected with a resist (FIG. 7(2)), and then the active layer portion is exposed. This wafer is dry etched in a dry etching device to remove the SiN film in the active layer portion (FIG. 7(3)). Thereafter, the resist of the protective film is removed and washed. Thereafter, epitaxial growth is performed in the same manner as in the first embodiment (FIG. 7(4)). EXAMPLES

[0062] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0063] Example 1 A silicon oxide film was applied to a 100 nm TEOS layer encasing a 300 μm polycrystalline ceramic core, a 300 nm polysilicon layer encasing the TEOS layer, a 100 nm TEOS layer encasing the polysilicon, and a 400 nm silicon nitride layer (barrier layer) encasing the TEOS layer, and then the substrate was bonded to a single crystal silicon substrate with an oxide film applied, and the surface of the single crystal silicon substrate was polished to a thin film (400 nm). Next, when the edges were chamfered, the single crystal silicon layer was not cut more than necessary by the chamfering, so that the flat surface of the silicon oxide layer was not exposed on the wafer surface, as shown in Figure 1. After that, epitaxial growth of the HEMT structure (GaN 3 nm / AlGaN 25 nm / GaN 5000 nm / graded AlGaN 200 nm / AlN 150 nm / n-Si) was performed.

[0064] The yield in the manufacturing method of Example 1 was improved by 4% compared to the comparative example described later.

[0065] Example 2 As shown in Figure 7, after attaching the single crystal silicon layer, the edges were chamfered, the sides of the silicon oxide film were exposed, and a CVD-SiN film was deposited over the entire surface of the wafer, after which the exposed oxide film was covered with a protective layer in a photolithography process, exposing the active layer, and the wafer was dry etched in a dry etching device to remove the SiN film in the active layer, and the protective resist was removed and washed. Through the above steps, a nitride semiconductor substrate was produced in which the sides of the silicon oxide layer were covered with a silicon nitride film.

[0066] The yield by the manufacturing method of Example 2 was improved by 6% compared to the comparative example described later.

[0067] (Comparative Example) A nitride semiconductor substrate was manufactured under the same conditions as in Example 1, except that the flat surface of the silicon oxide film was partially exposed on the wafer surface as shown in Figure 4. As a result, the yield was lower than in Examples 1 and 2.

[0068] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention. [Explanation of symbols]

[0069] 1...composite substrate; 2...silicon oxide layer; 3...single crystal silicon layer; 4...edge of flat surface; 5...silicon nitride film; 6...polycrystalline ceramic core; 7...first adhesive layer; 8...conductive layer; 9...second adhesive layer; 10...barrier layer; 21...flat surface; 22...side surface; 51...film formation substrate, 52...satellite, 53...ceiling, 54...quartz, 55...Ring-shaped member, 56...Direction of carrier gas flow, 57...Direction for opening the lid.

Claims

1. A composite substrate having multiple layers stacked thereon; a silicon oxide layer or a TEOS layer laminated on the composite substrate, the silicon oxide layer or the TEOS layer having a flat surface in the center and side surfaces around the flat surface; a single crystal silicon layer laminated on the silicon oxide layer or the TEOS layer; and A nitride semiconductor thin film formed on the single crystal silicon layer. A nitride semiconductor substrate comprising: the entire flat surface of the central portion of the silicon oxide layer or the TEOS layer is covered with the single crystal silicon layer; and A nitride semiconductor substrate, wherein the side surfaces of the silicon oxide layer or the TEOS layer are covered with a silicon nitride film.

2. The nitride semiconductor substrate according to claim 1, characterized in that the composite substrate includes a polycrystalline ceramic core, a first adhesive layer laminated over the entire polycrystalline ceramic core, a second adhesive layer laminated over the entire first adhesive layer, and a barrier layer laminated over the entire second adhesive layer.

3. 3. The nitride semiconductor substrate according to claim 2, wherein the composite substrate has a conductive layer between the first adhesive layer and the second adhesive layer, the conductive layer being laminated over the entire first adhesive layer.

4. 4. The nitride semiconductor substrate according to claim 3, wherein the conductive layer includes a polysilicon layer.

5. 5. The nitride semiconductor substrate according to claim 2, wherein the first adhesive layer and the second adhesive layer contain TEOS or silicon oxide, and the barrier layer contains silicon nitride.

6. 6. The nitride semiconductor substrate according to claim 2, wherein the polycrystalline ceramic core contains aluminum nitride.

7. A method for manufacturing a nitride semiconductor substrate, comprising the steps of: (1) preparing a composite substrate having a plurality of layers stacked thereon and a single crystal silicon substrate; (2) bonding the single crystal silicon substrate onto the composite substrate via a silicon oxide layer or a TEOS layer; (3) thinning the bonded single crystal silicon substrate to form a single crystal silicon layer; (4) forming an end portion of the silicon oxide layer or the TEOS layer and the single crystal silicon layer so that the entire flat surface of the central portion of the silicon oxide layer or the TEOS layer is covered with the single crystal silicon layer; (5) growing an AlN film on the single crystal silicon layer; and (6) A step of growing one or more films selected from a GaN film, an AlGaN film, and an AlN film on the AlN film. and A method for producing a nitride semiconductor substrate, wherein the step (4) is a chamfering step.

8. 8. The method for producing a nitride semiconductor substrate according to claim 7, further comprising, between the steps (4) and (5), a step (4') of covering at least a side surface of the silicon oxide layer or the TEOS layer with a silicon nitride film.

9. 9. The method for manufacturing a nitride semiconductor substrate according to claim 7 or 8, characterized in that the composite substrate includes a polycrystalline ceramic core, a first adhesive layer laminated over the entire polycrystalline ceramic core, a second adhesive layer laminated over the entire first adhesive layer, and a barrier layer laminated over the entire second adhesive layer.

10. 10. The method for manufacturing a nitride semiconductor substrate according to claim 9, wherein the composite substrate has a conductive layer between the first adhesive layer and the second adhesive layer, the conductive layer being laminated over the entire first adhesive layer.

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