Epitaxial substrate and method for manufacturing the same, and method for manufacturing a vertical device substrate

Abstract

To provide an epitaxial substrate in which a nitride semiconductor layer is formed on a Si substrate and in which both shortening of etching time and ensuring of the load resistance of a Si support substrate are achieved, and consequently both shortening of etching time and a reduction in warpage of an epitaxial wafer due to the stress of a heteroepitaxial film are achieved, and a method for producing the same.SOLUTION: An epitaxial substrate comprises a nitride semiconductor epitaxial layer on a main surface of a Si substrate, wherein a rear surface of the Si substrate has recesses in which a substrate thickness of a region other than an outer peripheral part is less than a substrate thickness of the outer peripheral part, a width of the outer peripheral part in a radial direction is 1 / 15 to 1 / 6 of a diameter of the Si substrate, an average thickness of the region other than the outer peripheral part is 1 / 3 to 1 / 2 of a thickness of the outer peripheral part, and a warpage of the epitaxial substrate is 50 μm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an epitaxial substrate, a method for producing the same, and a method for producing a vertical device substrate. Background Art

[0002] In general, GaN-on-Si epitaxial wafers are produced for the purpose of being used in lateral devices. When producing a GaN-on-Si epitaxial wafer for devices, when TMG or TEG, which are GaN raw materials, come into contact with Si, a eutectic reaction occurs, causing melt-back of the substrate. Therefore, in order to prevent direct contact between the Ga raw material and Si, an initial AlN layer is grown on a Si substrate, then an AlGaN layer or a GaN layer serving as a buffer layer is stacked thereon, and a GaN device layer is stacked. Prior Art Literature Patent Literature

[0003] Patent Literature 1 Japanese Patent Laid-Open No. 2018-107431 Patent Literature 2 Japanese Patent Laid-Open No. 2020-031175 Summary of the Invention Problem to be Solved by the Invention

[0004] The initial AlN layer has a large band gap, is non-doped, makes it difficult for current to flow in the vertical direction, and is unfavorable as an epitaxial layer for vertical devices. When attempting to fabricate a vertical device using a general GaN-on-Si epitaxial wafer, even if an initial AlN layer is stacked on a low-resistance Si substrate, a buffer layer is stacked, a device is fabricated on the epitaxial substrate having a stacked nitride semiconductor layer, and current is caused to flow in the vertical direction, the flow of current is almost blocked by the initial AlN layer.

[0005] The goal is to remove the Si substrate, which serves as the growth substrate, and then remove the initial AlN layer. However, removing a typical Si substrate requires a long etching time. Simply thinning the Si substrate to shorten the etching time reduces its load-bearing capacity, making it unable to withstand the stress of the heteroepitaxial film, resulting in warping, cracking, and fracture.

[0006] Patent Document 1 discloses a laminate containing a nitride semiconductor layer in which cracking is suppressed. Patent Document 2 discloses a laminate that can obtain high luminescence brightness over a large area. Patent Documents 1 and 2 also state that a TAIKO substrate may be used as a support substrate, but they do not describe removing the support substrate by etching.

[0007] The present invention has been made to solve the above problems, and aims to provide an epitaxial substrate in which a nitride semiconductor layer is formed on a Si substrate and a method for manufacturing the same, which achieves both a reduction in etching time and ensuring the load-bearing capacity of the Si support substrate, and consequently achieves both a reduction in etching time and a reduction in warping of the epitaxial wafer due to stress of the heteroepitaxial film. [Means for solving the problem]

[0008] The present invention has been made to achieve the above objective, and provides an epitaxial substrate comprising a nitride semiconductor epitaxial layer on the main surface of a Si substrate, wherein the back surface of the Si substrate has a recess in which the substrate thickness in the region other than the outer periphery is thinner than the substrate thickness of the outer periphery, the radial width of the outer periphery is 1 / 15 or more and 1 / 6 or less of the diameter of the Si substrate, the average thickness of the region other than the outer periphery is 1 / 3 or more and 1 / 2 or less of the thickness of the outer periphery, and the warpage of the epitaxial substrate is 50 μm or less.

[0009] With such an epitaxial substrate, the back surface of the Si substrate, which is the growth substrate, has depressions within the shape range of the present invention, thereby appropriately maintaining the maximum load-bearing capacity, which is the strength of the substrate, and keeping warpage to ±50 μm or less even when heteroepitaxial growth is performed. Furthermore, the Si substrate can be easily etched and removed, and vertical devices can be easily fabricated.

[0010] In this case, the maximum load-bearing capacity of the Si substrate can be set to 200N or more.

[0011] This allows the Si substrate to properly maintain its appropriate maximum load-bearing capacity.

[0012] In this case, the resistivity of the Si substrate can be set to 10 mΩcm or less.

[0013] This makes it possible to use it in high-performance vertical device substrates.

[0014] In this case, the substrate can be a vertical device substrate having electrodes on the main surface of the nitride semiconductor epitaxial layer of the epitaxial substrate.

[0015] This results in a vertical device substrate that appropriately maintains the maximum load-bearing capacity of the substrate, suppresses warping to ±50 μm or less even during heteroepitaxial growth, and allows for easy etching and removal of the Si substrate.

[0016] The present invention has also been made to achieve the above objective, and provides a method for manufacturing an epitaxial substrate in which a nitride semiconductor epitaxial layer is formed on the main surface of a Si substrate, the method for manufacturing the epitaxial substrate comprising: a depression formation step of forming a depression on the back surface of the Si substrate in which the substrate thickness in a region other than the outer periphery is thinner than the substrate thickness of the outer periphery; and an epitaxial layer formation step of forming a nitride semiconductor epitaxial layer on the main surface of the Si substrate, wherein in the depression formation step, the depression is formed in which the radial width of the outer periphery is 1 / 15 or more and 1 / 6 or less of the diameter of the Si substrate, and the average thickness of the region other than the outer periphery is 1 / 3 or more and 1 / 2 or less of the thickness of the outer periphery; and in the epitaxial layer formation step, the thickness and / or composition of the nitride semiconductor epitaxial layer is adjusted so that the warpage of the epitaxial substrate is 50 μm or less, and epitaxial growth is performed.

[0017] According to this method for manufacturing epitaxial substrates, by forming depressions within the shape range of the present invention on the back surface of the Si substrate which serves as the support substrate, the maximum load-bearing capacity, which is the strength of the substrate, can be appropriately maintained, and even with heteroepitaxial growth, the warpage can be kept to ±50 μm or less. Furthermore, the Si substrate can be easily etched and removed, making it possible to manufacture epitaxial substrates that can be easily fabricated into vertical devices.

[0018] In this case, the manufacturing method for a vertical device substrate is obtained by forming electrodes on the main surface of the nitride semiconductor epitaxial layer of the epitaxial substrate obtained by the manufacturing method for the epitaxial substrate, thereby manufacturing a substrate for a vertical device.

[0019] This makes it possible to manufacture a substrate for vertical devices that appropriately maintains the maximum load-bearing capacity of the substrate, resists epitaxial film stress even during heteroepitaxial growth, keeps warpage to ±50 μm or less, and allows for easy etching and removal of the Si substrate.

[0020] In this case, the method may be a method for producing a vertical device substrate, in which at least the Si substrate is removed by etching from the vertical device substrate obtained by the method for producing a vertical device substrate to obtain a vertical device substrate.

[0021] Thereby, a vertical device substrate can be produced by the method for producing a vertical device substrate in which the etching time is shortened compared to the prior art.

[0022] In this case, in the etching, the etching can be performed in a time that is not more than 3 / 5 of the time required for removing the Si substrate by etching when the recess forming step is not performed.

[0023] Thereby, a vertical device substrate can be produced by the method for producing a vertical device substrate in which the etching time is significantly shortened compared to the prior art.

Effects of the Invention

[0024] As described above, according to the epitaxial substrate of the present invention, since the back surface of the Si substrate serving as a support substrate has a recess within the shape range of the present invention, the maximum load resistance, which is the strength of the substrate, is appropriately maintained, warpage is suppressed to ±50 µm or less even after heteroepitaxial growth, and the Si substrate can be easily removed by etching, whereby a vertical device can be easily produced.

[0025] Furthermore, according to the method for producing an epitaxial substrate of the present invention, by forming a recess within the shape range of the present invention on the back surface of the Si substrate serving as a support substrate, the maximum load resistance, which is the strength of the substrate, is appropriately maintained, warpage is suppressed to ±50 µm or less even after heteroepitaxial growth, and the Si substrate can be easily removed by etching, thereby providing a method for producing an epitaxial substrate that allows easy production of a vertical device.

Brief Description of Drawings

[0026] [Figure 1] A schematic cross-sectional view of an example of the epitaxial substrate according to the present invention is shown. [Figure 2] An example of the back surface of a Si substrate with a recess is shown. [Figure 3] A schematic cross-sectional view of an example of an epitaxial substrate for a vertical device according to the present invention is shown. [Figure 4] A flowchart of an example of a method for manufacturing a vertical device substrate according to the present invention is shown. [Modes for carrying out the invention]

[0027] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0028] As described above, there was a need for an epitaxial substrate in which a nitride semiconductor layer is formed on a Si substrate, and a method for manufacturing the same, which would simultaneously achieve a reduction in etching time and ensure the load-bearing capacity of the Si support substrate, and consequently, a reduction in etching time and a reduction in warping of the epitaxial wafer due to stress in the heteroepitaxial film.

[0029] As a result of diligent research into the above-mentioned problems, the present inventors have found that an epitaxial substrate comprising a nitride semiconductor epitaxial layer on the main surface of a Si substrate, wherein the back surface of the Si substrate has a depression in which the substrate thickness in the region other than the outer periphery is thinner than the substrate thickness of the outer periphery, the radial width of the outer periphery is 1 / 15 to 1 / 6 of the diameter of the Si substrate, the average thickness of the region other than the outer periphery is 1 / 3 to 1 / 2 of the thickness of the outer periphery, and the warpage of the epitaxial substrate is 50 μm or less, and by having a depression within the above shape range on the back surface of the Si substrate which is the supporting substrate, the maximum load-bearing capacity, which is the strength of the substrate, is appropriately maintained, the warpage is kept to ±50 μm or less even when heteroepitaxial growth occurs, the Si substrate can be easily etched and removed, and vertical devices can be easily manufactured, thus completing the present invention.

[0030] The present inventors have also conducted extensive research on the above problem and have come up with a method for manufacturing an epitaxial substrate in which a nitride semiconductor epitaxial layer is formed on the main surface of a Si substrate, wherein the method for manufacturing the epitaxial substrate comprises a recess formation step of forming a recess on the back surface of the Si substrate in which the substrate thickness in a region other than the outer periphery is thinner than the substrate thickness of the outer periphery, and an epitaxial layer formation step of forming a nitride semiconductor epitaxial layer on the main surface of the Si substrate, wherein in the recess formation step, the radial width of the outer periphery is 1 / 15 or more and 1 / 6 or less of the diameter of the Si substrate, and the average thickness of the region other than the outer periphery is 1 / 3 or more and 1 / 2 or less of the thickness of the outer periphery. The present invention was completed by a method for manufacturing an epitaxial substrate, characterized by forming a certain depression and adjusting the thickness and / or composition of the nitride semiconductor epitaxial layer in the epitaxial layer formation step so that the warpage of the epitaxial substrate is 50 μm or less, thereby enabling the production of an epitaxial substrate that can easily be etched and removed, and that can easily be used to fabricate vertical devices.

[0031] [Epitaxial substrate] Figure 1 shows a schematic cross-sectional view of an example of an epitaxial substrate according to the present invention, which comprises a nitride semiconductor heteroepitaxial (hereinafter also simply referred to as "epitaxial") layer on the main surface of a Si substrate.

[0032] The epitaxial substrate 1 includes a Si substrate 2, which is a support substrate, and a nitride semiconductor epitaxial layer 3. The back surface of the Si substrate 2 has a recess 4 in which the substrate thickness in areas other than the outer periphery is thinner than the substrate thickness in the outer periphery.

[0033] The recess 4 can be cylindrical or bowl-shaped. By making the back surface of the Si substrate 2 on which the nitride semiconductor epitaxial layer 3 is laminated thin, the Si substrate 2 can be easily removed by etching.

[0034] To maintain the strength of the Si substrate 2, the outer periphery of the back surface of the Si substrate 2 is left unprocessed, retaining the thickness of the Si substrate 2. In other words, the outer periphery can be considered a reinforcement portion of the Si substrate. The radial width of the outer periphery is between 1 / 15 and 1 / 6 of the diameter of the Si substrate 2. If it is less than 1 / 15, the Si substrate 2 cannot maintain adequate substrate strength, and if it is greater than 1 / 6, an effective reduction in etching time cannot be achieved.

[0035] Note that if an orientation flat is present, the radial width of the outer perimeter is constant, including the orientation flat portion, just like the other outer perimeter portions. If the shape of the recess 4 on the back surface of the Si substrate 2 is circular, the width of the orientation flat portion will be narrower than the width of other areas, and the maximum load-bearing capacity of the Si substrate 2 will be reduced by about 5 to 20 N. Figure 2 shows an example of the back surface of the Si substrate 2 with a recess 4.

[0036] Furthermore, in order to maintain the strength of the Si substrate 2, the average thickness of the region other than the outer periphery is between 1 / 3 and 1 / 2 of the thickness of the outer periphery. If it is less than 1 / 3, the Si substrate 2 will not be able to maintain adequate substrate strength, and if it is greater than 1 / 2, an effective reduction in etching time cannot be achieved.

[0037] Furthermore, the warpage of the epitaxial substrate 1 is 50 μm or less. If the warpage after epitaxial growth is greater than 50 μm, problems will occur in the device process, especially during photolithography.

[0038] In this case, the maximum load-bearing capacity of the Si substrate 2 can be set to 200N or more. This allows the Si substrate 2 to maintain its appropriate maximum load-bearing capacity.

[0039] Furthermore, the resistivity of the Si substrate 2 can be set to 10 mΩcm or less. This makes it possible to use it in high-performance vertical device substrates.

[0040] The structure of the nitride semiconductor epitaxial layer 3 is not particularly limited and can be made suitable for any desired vertical device application.

[0041] For example, for LED applications, an epitaxial layer structure for LEDs can be formed on a Si substrate 2, in order: an AlN initial layer 5, an n-type AlGaN buffer layer 6, an n-type superlattice buffer layer 7 made of AlGaN and GaN, an MQW structure (not shown) as a light-emitting layer, and a p-type GaN layer 8.

[0042] Another example of the epitaxial layer 3 is a Schottky barrier diode (SBD) structure. For example, the structure up to the n-type superlattice buffer layer 7 is the same as the LED structure described above, and the GaN element layer above it can be configured with stacked layers such as a carbon-doped breakdown layer, an undoped layer, and a p-type layer.

[0043] The epitaxial layer formed on the Si substrate 2 is not limited to nitride semiconductors; the epitaxial substrate may include, for example, GaAs on Si, InP on Si, Diamond on Si, SiC on Si, Ge on Si, or perovskite on Si.

[0044] [Matrix board for vertical devices] Figure 3 shows a schematic cross-sectional view of an example of an epitaxial substrate for a vertical device according to the present invention. As shown in Figure 3, the epitaxial substrate 9 for a vertical device has electrodes 10 on the main surface of the nitride semiconductor epitaxial layer 3 of the epitaxial substrate. This results in a vertical device substrate that appropriately maintains the maximum load-bearing capacity of the substrate, suppresses warping to ±50 μm or less even during epitaxial growth, and allows for easy etching and removal of the Si substrate.

[0045] [Method for manufacturing epitaxial substrates] Next, an example of a method for manufacturing an epitaxial substrate according to the present invention will be described with reference to Figure 1. The method for manufacturing an epitaxial substrate 1 according to the present invention includes a recess formation step of forming a recess 4 on the back surface of a Si substrate 2 in an area other than the outer periphery where the substrate thickness is thinner than the substrate thickness of the outer periphery, and an epitaxial layer formation step of forming a nitride semiconductor epitaxial layer 3 on the main surface of the Si substrate 2.

[0046] In the recess formation process, for example, the main surface of the Si substrate 2 is protected with a UV sheet or resist, the back surface is mechanically drilled into a recess shape using a lathe, and processing distortion is removed by etching. For protecting the main surface, resist is preferred because it is easier to clean after resist processing. UV sheets tend to leave adhesive residue.

[0047] The recess 4 is formed such that the radial width of the outer periphery is between 1 / 15 and 1 / 6 of the diameter of the Si substrate 2, and the average thickness of the area other than the outer periphery is between 1 / 3 and 1 / 2 of the thickness of the outer periphery. If the radial width of the outer periphery is less than 1 / 15 of the diameter of the Si substrate 2, the Si substrate 2 cannot maintain adequate substrate strength, and if it is greater than 1 / 6, an effective reduction in etching time cannot be achieved. Similarly, if the average thickness of the area other than the outer periphery is less than 1 / 3 of the thickness of the outer periphery, the Si substrate 2 cannot maintain adequate substrate strength, and if it is greater than 1 / 2, an effective reduction in etching time cannot be achieved.

[0048] The structure of the nitride semiconductor epitaxial layer 3 is not particularly limited, and a layer with a structure suitable for the desired vertical device application can be formed.

[0049] For example, for LED applications, an epitaxial layer structure for LEDs can be formed on a Si substrate 2 by sequentially forming an AlN initial layer 5, an n-type AlGaN buffer layer 6, an n-type superlattice buffer layer 7 made of AlGaN and GaN, an MQW structure (not shown) as a light-emitting layer, and a p-type GaN layer 8.

[0050] Another example of the epitaxial layer 3 is a Schottky barrier diode (SBD) structure. For example, the structure up to the n-type superlattice buffer layer 7 can be the same as the LED structure described above, and the GaN element layer above it can be configured with a stacked structure of a C-doped breakdown layer, an undoped layer, a p-type layer, etc.

[0051] In manufacturing the epitaxial substrate 1, the thickness and / or composition of the nitride semiconductor epitaxial layer 3 are adjusted so that the warpage of the epitaxial substrate 1 is 50 μm or less, and then epitaxial growth is performed.

[0052] [Manufacturing method for substrates for vertical devices] Electrodes are formed on the main surface of the epitaxial substrate obtained by the epitaxial substrate manufacturing method, for example, by photolithography, to manufacture a substrate for vertical devices (see Figure 3).

[0053] This makes it possible to manufacture vertical device substrates that appropriately maintain the maximum load-bearing capacity of the substrate, suppress warping to ±50 μm or less even during heteroepitaxial growth, and allow for easy etching and removal of the Si substrate.

[0054] [Manufacturing method for vertical device substrates] Based on the flowchart of an example of a vertical device substrate manufacturing method according to the present invention shown in Figure 4, the manufacturing method for a vertical device substrate according to the present invention will be explained.

[0055] The present invention relates to a method for manufacturing a vertical device substrate, which involves removing at least a Si substrate from a vertical device substrate obtained by a method for manufacturing a vertical device substrate by etching to obtain a vertical device substrate. This makes it possible to manufacture vertical device substrates using a manufacturing method for vertical device substrates that shortens the etching time compared to conventional technologies.

[0056] For example, separately from the manufacturing of substrates for vertical devices, an acid-resistant substrate (sapphire substrate) 11 is placed on a hot plate and heated to over 120°C, and a solvent-resistant protective resin (Protect Wax manufactured by Nichika Seiko Co., Ltd.) is applied to the entire surface of the sapphire substrate 11. A temperature of 100-140°C for the sapphire substrate 11 is preferable because the wax melts well, the substrate becomes smooth, and there are no air bubbles when bonding, resulting in good adhesion.

[0057] Once the wax has adhered to the sapphire substrate 11, it is preferable to bond the sapphire substrate 11 and the vertical device substrate together, aligning the orientation flat or notch (see Figure 4(a)). Bonding them together with the orientation flat or notch aligned results in a clean bond. After that, flipping the substrate over so that the Si substrate is on the hot plate side and the sapphire is on the top side improves heat conduction and increases the adhesion of the substrates. At this point, the temperature of the sapphire substrate will be 140-200°C.

[0058] The vertical device substrate and the sapphire substrate are handled together, the Si substrate (which serves as the growth substrate) is removed by wet etching, and the exposed AlN initial layer is then removed by dry etching to obtain the vertical device substrate (see Figure 4(b)).

[0059] Thus, vertical device substrates can be manufactured using a method for manufacturing vertical device substrates that shortens the etching time compared to conventional technologies.

[0060] In this case, etching can be performed in 3 / 5 or less, more preferably 1 / 2 or less, the time required to remove the Si substrate by etching when the recess formation process is not performed.

[0061] This results in a manufacturing method for vertical device substrates with significantly reduced etching time compared to conventional technologies, enabling the production of high-performance vertical device substrates.

[0062] By removing the initial AlN layer, an ohmic electrode 12 can be formed on the back surface of the exposed AlGaN buffer layer (see Figure 4(c)). This electrode can then be bonded to a conductive heat dissipation substrate (support substrate) 13 using, for example, a metal bond using Au or a conductive resin (see Figure 4(d)). Subsequently, the chip can be formed by dicing and then molded. [Examples]

[0063] The present invention will be described in detail below with reference to examples, but this is not intended to limit the present invention.

[0064] (Examples) As a growth substrate, a Si substrate was prepared, which was a polished wafer with a diameter of 150 mm, resistivity of 8 mΩcm, a pressure of 10.47 ppm (JEIDA), and a thickness of 1 mm. The main surface of the Si substrate was protected with resist (SIPR-3251, manufactured by Shin-Etsu Chemical Co., Ltd.), and a recess was mechanically formed on the back surface, excluding the outer periphery, using a lathe. Processing distortion was removed by etching, and the average thickness of Si in the recessed area was set to 500 μm. In addition, the radial width of the outer periphery, which was used to reinforce the substrate, was set to 10 mm, 15 mm, and 25 mm.

[0065] For Si substrates with backside processing, the maximum load capacity was investigated using a three-point bending test on an Instron 5567 universal testing machine.

[0066] Furthermore, the warpage of an epitaxial substrate was measured after growing an epitaxial layer of approximately 1.8 μm in total. This was achieved by forming an initial AlN layer of 150 nm on the main surface of a similarly processed Si substrate, then forming a buffer layer of approximately 1000 nm consisting of GaN and AlGaN layers on top of that, and finally stacking a GaN layer of approximately 820 nm on top of that.

[0067] The main surface of an epitaxial substrate was bonded to a sapphire substrate coated with protective wax. The Si substrate was then etched using a solvent of 50%HF:61%HNO3=1:1, and the time required to remove the Si substrate was investigated.

[0068] The results are shown in Table 1.

[0069] [Table 1]

[0070] (Reference example) Epitaxial growth was performed under the same conditions as in the example, except that no depressions were formed on the back surface of the Si substrate. Etching was then performed, and the time required to remove the Si substrate was 5 minutes and 47 seconds.

[0071] As shown in Table 1, the results of the examples indicate that if the thickness of the region other than the outer periphery is half the thickness of the outer periphery, and the radial width of the outer periphery is between 1 / 15 and 1 / 6 of the diameter of the Si substrate 2, the load-bearing capacity of the Si substrate can be 200 N or more, and the warpage of the substrate after epitaxial growth can be kept to ±50 μm or less. Furthermore, etching of the Si substrate could be completed in less than 3 / 5 of the time required for etching the Si substrate in the reference example.

[0072] (Comparative example) The same Si substrate as in the example was prepared and depressions were formed in the same manner, with the average Si thickness of the depression-forming portion set to 675 μm, 500 μm, and 250 μm. In addition, the radial width of the outer periphery where the substrate is reinforced was set to 5 m The sizes were set to m, 10mm, 15mm, and 25mm.

[0073] For Si substrates with backside processing, the maximum load capacity was investigated using a three-point bending test on an Instron 5567 universal testing machine.

[0074] Furthermore, the warpage of an epitaxial substrate, on which an epitaxial film of approximately 1.8 μm was grown on the main surface of a similarly processed Si substrate, was measured, similar to the example.

[0075] The main surface of an epitaxial substrate was bonded to a sapphire substrate coated with protective wax. The Si substrate was then etched using a solvent of 50%HF:61%HNO3=1:1, and the time required to remove the Si substrate was investigated.

[0076] The results are shown in Table 2.

[0077] [Table 2]

[0078] As shown in Table 2, the comparative example results showed that even with a substrate warp of ±50 μm or less after epitaxial growth and appropriate load-bearing capacity, the etching time was long (greater than 3 / 5 of the reference example), and a sufficient reduction effect could not be obtained.

[0079] As described above, according to the embodiments of the present invention, by forming a recess within the shape range of the present invention on the back surface of the Si substrate which serves as the support substrate, the maximum load-bearing capacity, which is the strength of the substrate, is appropriately maintained, and even when heteroepitaxial growth occurs, the warpage is kept to ±50 μm or less, and the Si substrate can be easily etched and removed, making it possible to easily fabricate a vertical device.

[0080] This specification includes the following embodiments: [1]: An epitaxial substrate comprising a nitride semiconductor epitaxial layer on the main surface of a Si substrate, wherein the back surface of the Si substrate has a depression in which the substrate thickness in the region other than the outer periphery is thinner than the substrate thickness of the outer periphery, the radial width of the outer periphery is 1 / 15 or more and 1 / 6 or less of the diameter of the Si substrate, the average thickness of the region other than the outer periphery is 1 / 3 or more and 1 / 2 or less of the thickness of the outer periphery, and the warpage of the epitaxial substrate is 50 μm or less. [2]: The epitaxial substrate according to [1], wherein the maximum load capacity of the Si substrate is 200 N or more. [3]: The epitaxial substrate according to [1] or [2] above, wherein the resistivity of the Si substrate is 10 mΩcm or less. [4]: A substrate for a vertical device, comprising having electrodes on the main surface of the nitride semiconductor epitaxial layer of the epitaxial substrate described in [1], [2], or [3] above. [5]: A method for manufacturing an epitaxial substrate in which a nitride semiconductor epitaxial layer is formed on the main surface of a Si substrate, the method for manufacturing the epitaxial substrate comprising: a depression forming step of forming a depression on the back surface of the Si substrate in which the substrate thickness of a region other than the outer periphery is thinner than the substrate thickness of the outer periphery; and an epitaxial layer forming step of forming a nitride semiconductor epitaxial layer on the main surface of the Si substrate, wherein in the depression forming step, the depression is formed in which the radial width of the outer periphery is 1 / 15 or more and 1 / 6 or less of the diameter of the Si substrate, and the average thickness of the region other than the outer periphery is 1 / 3 or more and 1 / 2 or less of the thickness of the outer periphery; and in the epitaxial layer forming step, the method for manufacturing an epitaxial substrate comprising adjusting the thickness and / or composition of the nitride semiconductor epitaxial layer so that the warpage of the epitaxial substrate is 50 μm or less and performing epitaxial growth. [6]: A method for manufacturing a vertical device substrate, comprising forming electrodes on the main surface of the nitride semiconductor epitaxial layer of the epitaxial substrate obtained by the method for manufacturing an epitaxial substrate described in [5] above, thereby manufacturing a vertical device substrate. [7]: A method for manufacturing a vertical device substrate, comprising removing at least the Si substrate from the vertical device substrate obtained by the method for manufacturing a vertical device substrate described in [6] above by etching to obtain a vertical device substrate. [8]: The method for manufacturing a vertical device substrate according to [7], comprising, in the etching, performing the etching for a time of 3 / 5 or less of the time required to remove the Si substrate by etching when the recess formation step is not performed.

[0081] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of Symbols]

[0082] 1…Epitaxial substrate, 2…Si substrate, 3…Nitride semiconductor epitaxial layer 4...depression, 5...AlN initial layer, 6...n-type AlGaN buffer layer, 7...n-type superlattice buffer layer, 8...p-type GaN layer, 9...substrate for vertical devices, 10, 12... Electrodes, 11... Acid-resistant substrate (sapphire substrate), 13…Conductive heat dissipation substrate (support substrate).

Claims

1. An epitaxial substrate comprising a nitride semiconductor epitaxial layer on the main surface of a Si substrate, The back surface of the Si substrate has a recess in which the substrate thickness in areas other than the outer periphery is thinner than the substrate thickness of the outer periphery. The radial width of the outer periphery is 1 / 15 to 1 / 6 of the diameter of the Si substrate, and the average thickness of the region other than the outer periphery is 1 / 3 to 1 / 2 of the thickness of the outer periphery. The warpage of the epitaxial substrate is 50 μm or less. The maximum load capacity of the Si substrate is 200 N or more. An epitaxial substrate characterized in that the resistivity of the Si substrate is 10 mΩcm or less.

2. A substrate for a vertical device, characterized in that the epitaxial substrate described in claim 1 has electrodes on the main surface of the nitride semiconductor epitaxial layer.

3. A method for manufacturing an epitaxial substrate, wherein a nitride semiconductor epitaxial layer is formed on the main surface of a Si substrate with resistivity of 10 mΩcm or less, the method for manufacturing the epitaxial substrate is: A recess formation step is performed on the back surface of the Si substrate, in which a recess is formed in a region other than the outer periphery where the substrate thickness is thinner than the substrate thickness of the outer periphery. The process includes an epitaxial layer formation step of forming a nitride semiconductor epitaxial layer on the main surface of the Si substrate, In the recess formation step, the recess is formed such that the radial width of the outer periphery is 1 / 15 or more and 1 / 6 or less of the diameter of the Si substrate, and the average thickness of the region other than the outer periphery is 1 / 3 or more and 1 / 2 or less of the thickness of the outer periphery, thereby making the maximum load-bearing capacity of the Si substrate 200 N or more. A method for manufacturing an epitaxial substrate, characterized in that, in the epitaxial layer formation step, the thickness and / or composition of the nitride semiconductor epitaxial layer is adjusted so that the warpage of the epitaxial substrate is 50 μm or less, and epitaxial growth is performed.

4. A method for manufacturing a vertical device substrate, characterized by forming electrodes on the main surface of the nitride semiconductor epitaxial layer of the epitaxial substrate obtained by the method for manufacturing an epitaxial substrate described in claim 3.

5. A method for manufacturing a vertical device substrate, characterized in that at least the Si substrate is removed by etching from the vertical device substrate obtained by the method for manufacturing a vertical device substrate described in claim 4 to obtain a vertical device substrate.

6. The method for manufacturing a vertical device substrate according to claim 5, characterized in that the etching is performed in a time of 3 / 5 or less of the time required to remove the Si substrate by etching when the recess formation step is not performed.

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