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

Abstract

The present invention pertains to an epitaxial substrate comprising a nitride semiconductor epitaxial layer on a main surface of a Si substrate, the epitaxial substrate being characterized in that: the rear surface of the Si substrate has recesses in which the substrate thickness of a region other than an outer peripheral part is less than the substrate thickness of the outer peripheral part; the width of the outer peripheral part in the radial direction is 1 / 15 to 1 / 6 of the diameter of the Si substrate; the average thickness of the region other than the outer peripheral part is 1 / 3 to 1 / 2 of the thickness of the outer peripheral part; and the warpage of said epitaxial substrate is at most 50 μm. Consequently, provided are: 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 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 manufacturing the same.

Description

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

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

[0002] GaN-on-Si epitaxial wafers are generally manufactured for use in lateral devices. When manufacturing GaN-on-Si epitaxial wafers for devices, if the GaN raw materials TMG or TEG come into contact with Si, a eutectic reaction occurs, causing the substrate to melt back. Therefore, to prevent direct contact between the Ga raw material and Si, an initial layer of AlN is grown on the Si substrate, and then an AlGaN layer or GaN layer is stacked on top of that as a buffer layer, and then the GaN device layer is laminated.

[0003] JP 2018-107431 A JP 2020-031175 A

[0004] The initial layer of AlN has a large band gap, is undoped, and does not allow current to flow easily in the vertical direction, making it unsuitable as an epitaxial layer for vertical devices. Even if an attempt is made to fabricate a vertical device using a typical GaN-on-Si epitaxial wafer by stacking an initial layer of AlN on a low-resistivity Si substrate, stacking a buffer layer, and stacking a nitride semiconductor layer on the epitaxial substrate, and then fabricating a device on the epitaxial substrate and passing a current in the vertical direction, the flow of current is almost entirely blocked by the initial layer of AlN.

[0005] Although it is possible to remove the Si substrate, which is the growth substrate, and then remove the initial AlN layer, removing a typical Si substrate requires a long etching time. Simply thinning the Si substrate to shorten the etching time reduces the load-bearing capacity of the Si substrate, making it unable to withstand the stress of the heteroepitaxial film, resulting in warping, cracks, and breakage.

[0006] Patent Document 1 discloses a stack including a nitride semiconductor layer in which cracks are suppressed. Patent Document 2 discloses a stack that can achieve high luminance over a large area. Patent Documents 1 and 2 also state that a TAIKO substrate may be used as the support substrate, but do not disclose 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, which achieves both a reduction in etching time and an assurance of the load-bearing capacity of the Si support substrate, and ultimately achieves both a reduction in etching time and a reduction in warpage of the epitaxial wafer due to stress in the heteroepitaxial film, and a method for manufacturing the same.

[0008] The present invention has been made to achieve the above-mentioned object, and provides an epitaxial substrate comprising a nitride semiconductor epitaxial layer on a main surface of a Si substrate, wherein the back surface of the Si substrate is provided with a depression in which the substrate thickness in a region other than the outer periphery is thinner than the substrate thickness in 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.

[0009] With such an epitaxial substrate, the rear surface of the Si substrate, which is the growth substrate, has a depression within the shape range of the present invention, thereby appropriately maintaining the maximum load-bearing capacity, which is the strength of the substrate, and suppressing warpage to ±50 μm or less even during heteroepitaxial growth.In addition, the Si substrate can be easily etched and removed, and vertical devices can be easily fabricated.

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

[0011] This makes it possible to appropriately maintain the appropriate maximum load capacity of the Si substrate.

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

[0013] This allows the substrate to be used for a high-performance vertical device.

[0014] In this case, the epitaxial substrate may be provided with an electrode on the main surface of the nitride semiconductor epitaxial layer, to form a substrate for a vertical device.

[0015] This results in a substrate for vertical devices that can adequately maintain the maximum load capacity, which is the strength of the substrate, and suppresses warping to ±50 μm or less even during heteroepitaxial growth, while allowing the Si substrate to be easily removed by etching.

[0016] The present invention has also been made to achieve the above-mentioned object, and provides a method for manufacturing an epitaxial substrate in which a nitride semiconductor epitaxial layer is formed on a main surface of a Si substrate, the method comprising: a recess formation step of forming a recess on a back surface of the Si substrate, in which the substrate thickness in a region other than a peripheral portion is thinner than the substrate thickness in the peripheral portion; 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 recess is formed so that the radial width of the peripheral portion is from 1 / 15 to 1 / 6 of the diameter of the Si substrate and the average thickness in the region other than the peripheral portion is from 1 / 3 to 1 / 2 of the thickness of the peripheral portion; and the epitaxial layer formation step comprises epitaxially growing the nitride semiconductor epitaxial layer while adjusting the thickness and / or composition thereof so that warpage of the epitaxial substrate is 50 μm or less.

[0017] According to this method for manufacturing an epitaxial substrate, by forming a recess within the shape range of the present invention on the back surface of a Si substrate, which is a support substrate, the maximum load capacity, which is the strength of the substrate, can be appropriately maintained, and warpage is kept to ±50 μm or less even during heteroepitaxial growth.In addition, the Si substrate can be easily etched and removed, and an epitaxial substrate on which a vertical device can be easily fabricated can be manufactured.

[0018] In this case, the method for manufacturing a vertical device substrate may be such that an electrode is formed on a main surface of the nitride semiconductor epitaxial layer of the epitaxial substrate obtained by the method for manufacturing an epitaxial substrate, thereby manufacturing a vertical device substrate.

[0019] This makes it possible to manufacture a substrate for a vertical device that can appropriately maintain the maximum load capacity, which is the strength of the substrate, and that can resist epitaxial film stress even during heteroepitaxial growth, suppressing warpage to ±50 μm or less, and that allows the Si substrate to be easily removed by etching.

[0020] In this case, the method for manufacturing a vertical device substrate may be such 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 to obtain a vertical device substrate.

[0021] This allows the vertical device substrate to be manufactured by a method for manufacturing a vertical device substrate that requires less etching time than conventional techniques.

[0022] At this time, the etching can be carried out in a time period of 3 / 5 or less of the time required to remove the Si substrate by etching if the recess forming step is not carried out.

[0023] This allows the vertical device substrate to be manufactured by a method for manufacturing a vertical device substrate in which the etching time is significantly shorter than that of the prior art.

[0024] As described above, according to the epitaxial substrate of the present invention, the rear surface of the Si substrate, which is the support substrate, has a depression within the shape range of the present invention, thereby appropriately maintaining the maximum load-bearing capacity, which is the strength of the substrate, and suppressing warpage to ±50 μm or less even during heteroepitaxial growth.In addition, the Si substrate can be easily removed by etching, and vertical devices can be easily fabricated.

[0025] Furthermore, according to the method for manufacturing an epitaxial substrate of the present invention, by forming a recess within the shape range of the present invention on the back surface of a Si substrate, which is a support substrate, the maximum load capacity, which is the strength of the substrate, is appropriately maintained, and warpage is suppressed to ±50 μm or less even during heteroepitaxial growth, and the Si substrate can be easily removed by etching, resulting in a method for manufacturing an epitaxial substrate that allows for easy fabrication of vertical devices.

[0026] 1 shows a schematic cross-sectional view of an example of an epitaxial substrate according to the present invention; 2 shows an example of the backside of a Si substrate having a depression; 3 shows a schematic cross-sectional view of an example of an epitaxial substrate for a vertical device according to the present invention; and 4 shows a flow chart of an example of a method for manufacturing a vertical device substrate according to the present invention.

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

[0028] As described above, there has been a demand for an epitaxial substrate in which a nitride semiconductor layer is formed on a Si substrate, which can shorten the etching time while ensuring the load-bearing capacity of the Si support substrate, and which can thereby shorten the etching time while reducing warpage of the epitaxial wafer due to stress in the heteroepitaxial film, and a method for manufacturing the same.

[0029] As a result of extensive research into the above-mentioned problems, the present inventors have found that an epitaxial substrate comprising an Si substrate and a nitride semiconductor epitaxial layer on a main surface thereof, the back surface of the Si substrate is provided with a depression in which the substrate thickness in a region other than the outer periphery is thinner than the substrate thickness in the outer periphery, the radial width of the outer periphery is from 1 / 15 to 1 / 6 of the diameter of the Si substrate, the average thickness of the region other than the outer periphery is from 1 / 3 to 1 / 2 of the thickness of the outer periphery, and the epitaxial substrate has a warpage of 50 μm or less, and that by the back surface of the Si substrate serving as a support substrate having a depression of the above-mentioned shape range, the maximum load-bearing capacity, which is the strength of the substrate, is appropriately maintained, and warpage is limited to ±50 μm or less even during heteroepitaxial growth, the Si substrate can be easily etched and removed, and a vertical device can be easily fabricated, thereby completing the present invention.

[0030] The present inventors have also conducted extensive research into the above-mentioned problems, and as a result have discovered a method for manufacturing an epitaxial substrate in which a nitride semiconductor epitaxial layer is formed on a main surface of a Si substrate, the method comprising: a recess forming step of forming a recess on a 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 in 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 recess forming step, the radial width of the outer periphery is from 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 from 1 / 3 to 1 / 2 of the thickness of the outer periphery. and in the epitaxial layer formation step, performing epitaxial growth by adjusting the thickness and / or composition of the nitride semiconductor epitaxial layer so that warpage of the epitaxial substrate is 50 μm or less. By forming a recess having the above-mentioned shape range on the back surface of a Si substrate serving as a support substrate, it has been found that it is possible to appropriately maintain the maximum load-bearing capacity, which is the strength of the substrate, and suppress warpage to ±50 μm or less even during heteroepitaxial growth, and the Si substrate can be easily removed by etching, thereby making it possible to easily produce an epitaxial substrate on which a vertical device can be fabricated, and the present invention has been completed.

[0031] [Epitaxial Substrate] FIG. 1 shows a schematic cross-sectional view of an example of an epitaxial substrate according to the present invention, which has 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 serving as a support substrate and a nitride semiconductor epitaxial layer 3. The back surface of the Si substrate 2 is provided with a recess 4 in which the substrate thickness in the region other than the periphery is thinner than the substrate thickness in the periphery.

[0033] The depression 4 may be cylindrical or bowl-shaped. By thinning the back surface of the Si substrate 2 on which the nitride semiconductor epitaxial layer 3 is deposited, 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 rear surface of the Si substrate 2 is not processed and has the same thickness as the Si substrate 2. In other words, the outer periphery can also be considered a reinforcing portion of the Si substrate. The radial width of the outer periphery is 1 / 15 to 1 / 6 of the diameter of the Si substrate 2. If it is less than 1 / 15, the Si substrate 2 will not maintain an appropriate substrate strength, and if it is more than 1 / 6, the etching time will not be effectively reduced.

[0035] It should be noted that if an orientation flat is present, the radial width of the outer periphery is the same constant width as the other outer periphery. If the shape of the depression 4 on the back surface of the Si substrate 2 is circular, the width of the orientation flat will be narrower than the width of the other parts, reducing the maximum load capacity of the Si substrate 2 by approximately 5 to 20 N. Figure 2 shows an example of the back surface of a Si substrate 2 equipped with a depression 4.

[0036] Furthermore, in order to maintain the strength of the Si substrate 2, the average thickness of the region other than the peripheral portion is set to 1 / 3 or more and 1 / 2 or less of the thickness of the peripheral portion. If it is less than 1 / 3, the Si substrate 2 cannot maintain an appropriate substrate strength, and if it is more than 1 / 2, the etching time cannot be effectively reduced.

[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, particularly in the implementation of photolithography processing. The smaller the warpage, the better, so the lower limit is 0 μm.

[0038] In this case, the maximum load capacity of the Si substrate 2 can be set to 200 N or more. The upper limit of the maximum load capacity is not particularly limited, but can be set to, for example, 2400 N or less. This allows the Si substrate 2 to maintain an appropriate maximum load capacity.

[0039] The resistivity of the Si substrate 2 can be 10 mΩcm or less. The lower limit of the resistivity is not particularly limited, but can be, for example, 1 mΩcm or more. This allows the substrate to be used as a high-performance vertical device substrate.

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

[0041] For example, in the case of an LED application, an epitaxial layer structure for an LED can be formed in which 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, a p-type GaN layer 8, and the like are formed in this order on a Si substrate 2.

[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 can be the same as the LED structure, and the device layer made of GaN thereon can be configured by laminating a C-doped voltage-resistant layer, a non-doped layer, a p-type layer, and the like.

[0043] The epitaxial layer formed on the Si substrate 2 is not limited to nitride semiconductors, and 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] [Vertical Device Substrate] 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 for a vertical device 9 includes an electrode 10 on the main surface of the nitride semiconductor epitaxial layer 3 of the epitaxial substrate. This provides a vertical device substrate that appropriately maintains the maximum load capacity, which is the strength of the substrate, and suppresses warpage to ±50 μm or less even during epitaxial growth, while allowing the Si substrate to be easily removed by etching.

[0045] [Method for Manufacturing Epitaxial Substrate] Next, an example of a method for manufacturing an epitaxial substrate according to the present invention will be described with reference to Fig. 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 which the substrate thickness in an area other than the peripheral portion is thinner than the substrate thickness in the peripheral portion, 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 excavated using a lathe to form a recess, and processing distortion is removed by etching. Note that resist is preferable for protecting the main surface because it is easier to clean after resist processing. UV sheets tend to leave adhesive residue.

[0047] The recess 4 is formed so that the radial width of the outer periphery is 1 / 15 to 1 / 6 of the diameter of the Si substrate 2, 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. 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 appropriate substrate strength, and if it is more than 1 / 6, the etching time cannot be effectively reduced. If the average thickness of the region other than the outer periphery is less than 1 / 3 of the thickness of the outer periphery, the Si substrate 2 cannot maintain appropriate substrate strength, and if it is more than 1 / 2, the etching time cannot be effectively reduced.

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

[0049] For example, in the case of an LED application, 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, a p-type GaN layer 8, and the like can be formed in this order on a Si substrate 2 to form an epitaxial layer structure for an LED.

[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 may be the same as the LED structure, and the device layer made of GaN thereon may be configured by laminating a C-doped voltage-resistant layer, a non-doped layer, a p-type layer, and the like.

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

[0052] [Method for Manufacturing Vertical Device Substrate] A vertical device substrate is manufactured by forming electrodes on the main surfaces of the epitaxial substrate obtained by the epitaxial substrate manufacturing method, for example, by photolithography (see FIG. 3).

[0053] This makes it possible to manufacture a substrate for a vertical device that can adequately maintain the maximum load capacity, which is the strength of the substrate, and suppresses warping to ±50 μm or less even during heteroepitaxial growth, while allowing the Si substrate to be easily removed by etching.

[0054] [Method for Manufacturing a Vertical Device Substrate] A method for manufacturing a vertical device substrate according to the present invention will be described with reference to a flow chart of an example of the method for manufacturing a vertical device substrate according to the present invention shown in FIG.

[0055] The method for manufacturing a vertical device substrate according to the present invention is a method for manufacturing a vertical device substrate in which at least the Si substrate is removed by etching from a vertical device substrate obtained by the method for manufacturing a vertical device substrate, thereby obtaining a vertical device substrate. This method for manufacturing a vertical device substrate allows for a shorter etching time than conventional techniques.

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

[0057] Once the wax has soaked into 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)). Aligning the orientation flat or notch allows for a neater bond. Then, flip the substrate over so that the Si substrate is on the hotplate side and the sapphire is on top, improving heat conduction and increasing the adhesion of the substrates. At this point, the temperature of the sapphire substrate reaches 140-200°C.

[0058] The vertical device substrate and the sapphire substrate are handled in a bonded state, and the Si substrate, which is the growth substrate, is removed by wet etching. The exposed AlN initial layer is then removed by dry etching to form a vertical device substrate (see FIG. 4(b)).

[0059] In this way, a vertical device substrate can be manufactured by a method for manufacturing a vertical device substrate in which the etching time is shorter than that of the conventional technique.

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

[0061] This results in a method for manufacturing a vertical device substrate in which the etching time is significantly shorter than that of the prior art, and a high-performance vertical device substrate can be manufactured.

[0062] An ohmic electrode 12 is formed on the back surface of the AlGaN buffer layer exposed by removing the AlN initial layer (see FIG. 4( c)), and the AlGaN buffer layer is bonded to a conductive heat dissipation substrate (support substrate) 13 by metal bonding using Au or by using a conductive resin (see FIG. 4( d)), after which the AlGaN buffer layer is diced into chips and molded.

[0063] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0064] (Example) A Si substrate was prepared as a growth substrate, which was a polished wafer with a diameter of 150 mm, a resistivity of 8 mΩcm, and a resistivity of 10.47 ppma (JEIDA), and a thickness of 1 mm. The main surface of the Si substrate was protected with a resist (SIPR-3251 manufactured by Shin-Etsu Chemical Co., Ltd.), and the area on the back surface other than the outer periphery was mechanically dug using a lathe to form a recess. Processing strain was removed by etching, and the average thickness of the Si in the recessed portion was set to 500 μm. The radial width of the outer periphery, which reinforced the substrate, was set to 10 mm, 15 mm, and 25 mm.

[0065] The Si substrate with the rear surface processed was subjected to a three-point bending test using an Instron Model 5567 universal testing machine to examine the maximum load capacity.

[0066] In addition, an initial layer of AlN was formed to a thickness of 150 nm on the main surface of a similarly processed Si substrate, and a buffer layer made of GaN and AlGaN layers was formed to a thickness of approximately 1000 nm on top of that, and a GaN layer was stacked to a thickness of approximately 820 nm on top of that, resulting in an epitaxial layer of approximately 1.8 μm in total. The warpage of this epitaxial substrate was measured.

[0067] The main surface of the epitaxial substrate was bonded to a sapphire substrate coated with protective wax, and the Si substrate was then coated with 50% HF: 61% HNO ３ Etching was carried out using a solvent with a ratio of 0.01:0.1, and the time required to remove the Si substrate was investigated.

[0068] The results are shown in Table 1.

[0069]

[0070] Reference Example Epitaxial growth was performed under the same conditions as in the example, except that no recess was formed on the rear surface of the Si substrate. When etching was performed, the time required to remove the Si substrate was 5 minutes and 47 seconds.

[0071] As a result of the example, as shown in Table 1, if the thickness of the region other than the outer periphery is 1 / 2 of the thickness of the outer periphery and the radial width of the outer periphery is 1 / 15 to 1 / 6 of the diameter of Si substrate 2, the load 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, the Si substrate could be etched in 3 / 5 or less 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 recesses were formed in the same manner, with the average Si thickness of the recessed portion being 675 μm, 500 μm, or 250 μm, and the radial width of the outer periphery where the substrate was reinforced being 5 mm, 10 mm, 15 mm, or 25 mm.

[0073] The Si substrate with the rear surface processed was subjected to a three-point bending test using an Instron Model 5567 universal testing machine to examine the maximum load capacity.

[0074] In addition, an epitaxial film of approximately 1.8 μm was grown on the main surface of a similarly processed Si substrate, as in the example, and the warpage of the epitaxial substrate was measured.

[0075] The main surface of the epitaxial substrate was bonded to a sapphire substrate coated with protective wax, and the Si substrate was then coated with 50% HF: 61% HNO ３ Etching was carried out using a solvent with a ratio of 0.01:0.1, and the time required to remove the Si substrate was investigated.

[0076] The results are shown in Table 2.

[0077]

[0078] As a result of the comparative example, as shown in Table 2, even though the warpage of the substrate after epitaxial growth was ±50 μm or less and the load resistance was appropriate, the etching time was long (longer than 3 / 5 of the reference example), and a sufficient reduction effect was not obtained.

[0079] As described above, according to the examples 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 is the support substrate, the maximum load capacity, which is the strength of the substrate, is appropriately maintained, and warpage is suppressed to ±50 μm or less even during heteroepitaxial growth.In addition, the Si substrate can be easily etched and removed, and a vertical device can be easily fabricated.

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

[0081] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

1. An epitaxial substrate comprising a nitride semiconductor epitaxial layer on a main surface of a Si substrate, wherein the rear surface of the Si substrate is provided with a depression in which the substrate thickness in an area other than the outer periphery is thinner than the substrate thickness in the outer periphery, the radial width of the outer periphery is between 1 / 15 and 1 / 6 of the diameter of the Si substrate, 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, and the warpage of the epitaxial substrate is 50 μm or less.

2. The epitaxial substrate according to claim 1, wherein the Si substrate has a maximum load capacity of 200N or more.

3. The epitaxial substrate according to claim 1, wherein the resistivity of said Si substrate is 10 mΩcm or less.

4. A substrate for a vertical device, characterized in that the epitaxial substrate according to any one of claims 1 to 3 has an electrode on the main surface of the nitride semiconductor epitaxial layer.

5. A method for manufacturing an epitaxial substrate in which a nitride semiconductor epitaxial layer is formed on a main surface of a Si substrate, the method comprising: a recess formation step of forming a recess on the back surface of the Si substrate, in which the substrate thickness in an area other than the outer periphery is thinner than the substrate thickness in 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 recess is formed so that the radial width of the outer periphery is from 1 / 15 to 1 / 6 of the diameter of the Si substrate and the average thickness of the area other than the outer periphery is from 1 / 3 to 1 / 2 of the thickness of the outer periphery, and wherein in the epitaxial layer formation step, the thickness and / or composition of the nitride semiconductor epitaxial layer is adjusted and epitaxial growth is performed so that the warp of the epitaxial substrate is 50 μm or less.

6. A method for manufacturing a substrate for a vertical device, comprising forming an electrode on the main surface of the nitride semiconductor epitaxial layer of the epitaxial substrate obtained by the method for manufacturing an epitaxial substrate according to claim 5, thereby manufacturing a substrate for a vertical device.

7. A method for manufacturing a vertical device substrate, comprising removing at least the Si substrate by etching from the vertical device substrate obtained by the method for manufacturing a vertical device substrate according to claim 6, to obtain a vertical device substrate.

8. The method for manufacturing a vertical device substrate according to claim 7, characterized in that the etching is carried out in a time period that is 3 / 5 or less of the time that would be required to remove the Si substrate by etching if the recess formation step were not carried out.

Images