Epitaxial substrate manufacturing method and epitaxial substrate

Abstract

To provide an epitaxial substrate that has a high breakdown voltage characteristic and satisfies |warp|≤50 μm, and a method for manufacturing this epitaxial substrate.SOLUTION: A method for manufacturing an epitaxial substrate 100 includes: a step in which, by using a single crystal Si substrate 1 in thickness of 1500 μm or greater, and adopting the resistivity of the single crystal Si substrate and the ratio a of the thickness of the single crystal Si substrate to the group-III nitride epitaxial layer 2 as parameters, the epitaxial growth of the group-III nitride epitaxial layer on the single crystal Si substrate and a warp of the obtained epitaxial substrate are measured changing the parameters, and the correlation of the ratio a and the warp of the epitaxial substrate is calculated for each resistivity of the single crystal Si substrate; a step in which a manufacturing parameter where the absolute value of the warp of the epitaxial substrate is 50 μm or less is determined from the correlation; and a step in which the group-III nitride epitaxial layer is grown on the single crystal Si substrate by using the determined manufacturing parameter.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an epitaxial substrate and an epitaxial substrate. [Background technology]

[0002] Group III nitride semiconductors, including GaN and AlN, are expected to be next-generation semiconductor materials that overcome the limitations of silicon (Si) as a material. Group III nitride semiconductors can be used to fabricate high electron mobility transistors (HEMTs) using two-dimensional electron gas, and are therefore expected to be used in semiconductor devices for high-frequency applications. In addition, the above-mentioned group III nitride semiconductors are also piezoelectric with excellent mechanical properties, and are expected to be used in high-frequency filters for communications, sensors, energy harvesters, and more. In recent years, high-frequency devices have been manufactured by epitaxially growing group III nitrides on single-crystal Si substrates. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-176936 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-216474 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-103380 [Patent Document 4] Japanese Patent Application Laid-Open No. 2003-063897 Summary of the Invention [Problem to be solved by the invention]

[0004] To increase the breakdown voltage of an epitaxial substrate having an epitaxial layer of a group III nitride on a single crystal Si substrate, such as a GaN-on-Si substrate, known methods include increasing the thickness of the epitaxial layer of the group III nitride, such as GaN, or doping it with C (Patent Document 1).However, increasing the thickness of the epitaxial layer increases the warpage of the epitaxial substrate, which is a problem.

[0005] Patent Document 2 describes the relationship between the B dopant concentration and the epitaxial layer thickness and warpage, but does not mention the relationship between the Si substrate thickness and warpage, nor does it mention the (substrate / epi) thickness ratio suitable for each resistivity.

[0006] Patent Document 3 states that the warpage of a nitride semiconductor substrate was 24 μm when the epitaxial layer thickness was 8 μm, but the diameter of the Si substrate was 4 inches (100 mm). Because warpage increases with increasing substrate diameter, further measures are required to achieve an absolute value of warpage of 50 μm or less (sometimes expressed as "|warpage|≦50 μm") at larger diameters. For example, when the inventors conducted tests using a Si substrate with a diameter of 300 mm and a thickness of 1.5 mm, they found that even within the oxygen concentration and resistivity ranges specified in claim 2 of Patent Document 3, excessive stress caused the substrate to crack at an epitaxial thickness of 5.7 μm.

[0007] Furthermore, Patent Document 4 discloses a technique for suppressing warpage, in which the ratio of epitaxial layer thickness to substrate thickness is ≦0.011 and the substrate thickness is ≧450 μm. However, the diameter of the substrate in the example of Patent Document 4 is 5 cm, and the GaN layer thickness is up to 7 μm. The inventor's investigation confirmed that if the thickness of the III nitride epitaxial layer is further increased beyond 7 μm, the breakdown voltage is further improved. For example, if the leakage current is 1×10 -6 A / mm 2When the bias voltage at which the voltage reaches 1000 V is defined as the breakdown voltage, the Group III nitride epitaxial layer with a thickness of 6.5 μm exhibited a breakdown voltage of 900 V, whereas the Group III nitride epitaxial layer with a thickness of 7.5 μm exhibited a breakdown voltage of 1000 V. In the latter case, the substrate thickness was also increased to keep the absolute value of warpage below 50 μm. However, the substrate used had a low resistivity of 5 mΩcm, so increasing the substrate thickness did not have any effect on the breakdown voltage; the increase in breakdown voltage was due to the increase in the epitaxial layer thickness. Thus, by increasing the thickness of the Group III nitride epitaxial layer beyond 7 μm, nitride semiconductor substrates suitable for even higher breakdown voltage devices can be obtained. Therefore, there has been a demand for epitaxial substrates with a Group III nitride epitaxial layer with a thickness of more than 7 μm and an absolute value of warpage below 50 μm.

[0008] The present invention has been made to solve the above problems, and an object of the present invention is to provide an epitaxial substrate for semiconductor devices that can suppress the absolute value of warpage of the epitaxial substrate to 50 μm or less (|warpage|≦50 μm) while increasing the thickness of the Group III nitride epitaxial layer to more than 7 μm in order to achieve a higher breakdown voltage, and a manufacturing method by which such an epitaxial substrate can be easily and stably obtained. [Means for solving the problem]

[0009] The present invention has been made to achieve the above-mentioned object, and provides a method for producing an epitaxial substrate including a single crystal Si substrate and a Group III nitride epitaxial layer on the single crystal Si substrate, the method comprising: using a single crystal Si substrate having a thickness of 1500 μm or more, epitaxially growing a Group III nitride epitaxial layer on the single crystal Si substrate and forming a Group III nitride epitaxial layer on the single crystal Si substrate using the resistivity of the single crystal Si substrate and the ratio a of the thickness of the single crystal Si substrate to the thickness of the Group III nitride epitaxial layer (thickness of the single crystal Si substrate / thickness of the Group III nitride epitaxial layer) as parameters; The method for manufacturing an epitaxial substrate includes a correlation acquisition step of measuring the warpage of the plate while changing the parameters and determining, for each resistivity of the single crystal Si substrate, the correlation between the ratio a and the warpage of the epitaxial substrate; a manufacturing parameter determination step of determining, from the correlation, the resistivity and ratio a of the single crystal Si substrate such that the absolute value of the warpage of the epitaxial substrate is 50 μm or less; and an epitaxial substrate manufacturing step of epitaxially growing a Group III nitride epitaxial layer on the single crystal Si substrate using the determined manufacturing parameters.

[0010] According to this method for manufacturing an epitaxial substrate, it is possible to easily and stably obtain an epitaxial substrate with |warpage|≦50 μm by suppressing warpage while improving the breakdown voltage characteristics.

[0011] The present invention has been made to achieve the above-mentioned object, and provides an epitaxial substrate having a diameter of 150 mm or less, comprising a single crystal Si substrate and a Group III nitride epitaxial layer on the single crystal Si substrate, wherein the single crystal Si substrate has a thickness of 1500 μm or more and the Group III nitride epitaxial layer has a thickness of more than 7 μm, and wherein, when the ratio of the thickness of the single crystal Si substrate to the thickness of the Group III nitride epitaxial layer (thickness of the single crystal Si substrate / thickness of the Group III nitride epitaxial layer) is defined as a, the epitaxial substrate satisfies at least one of the following (A) to (C): (A) The resistivity of the single crystal Si substrate is 2 mΩcm or less and the ratio a is 125 or more. (B) The resistivity of the single crystal Si substrate is 3 mΩcm or less and the ratio a is 135 or more. (C) The resistivity of the single crystal Si substrate is 5 mΩcm or less and the ratio a is 137 or more.

[0012] Such an epitaxial substrate has high breakdown voltage characteristics and is suppressed from warping, with |warping|≦50 μm.

[0013] In this case, the single crystal Si substrate can be an epitaxial substrate having an oxygen concentration of 11 to 18 ppma (JEIDA).

[0014] This makes it possible to more stably suppress warpage. [Effects of the Invention]

[0015] As described above, the epitaxial substrate manufacturing method of the present invention makes it possible to easily and stably obtain epitaxial substrates with high breakdown voltage characteristics while suppressing warpage, and with |warpage|≦50 μm. The epitaxial substrate of the present invention has high breakdown voltage characteristics and suppresses warpage, resulting in |warpage|≦50 μm. [Brief explanation of the drawings]

[0016] [Figure 1] 1 shows an example of the structure of an epitaxial substrate according to the present invention. [Figure 2] The graph shows the relationship between the ratio a of the thickness of the single-crystal Si substrate 1 to the thickness of the Group III nitride epitaxial layer 2 (thickness of the single-crystal Si substrate / thickness of the Group III nitride epitaxial layer) and the absolute value of the warpage of the epitaxial substrate 100, obtained for each resistivity of the single-crystal Si substrate 1 (thickness 1500 μm). [Figure 3] FIG. 3 is an enlarged view of a part of FIG. 2. [Figure 4] The relationship between the ratio a and warpage due to differences in the thickness of the single-crystal Si substrate is shown. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below, but the present invention is not limited thereto.

[0018] As described above, there has been a demand for an epitaxial substrate with high breakdown voltage characteristics and suppressed warpage, |warpage|≦50 μm, and a manufacturing method by which such an epitaxial substrate can be easily and stably obtained.

[0019] As a result of intensive research into the above-mentioned problems, the present inventors have discovered a method for producing an epitaxial substrate including a single crystal Si substrate and a Group III nitride epitaxial layer on the single crystal Si substrate, the method comprising: using a single crystal Si substrate having a thickness of 1500 μm or more; measuring the epitaxial growth of the Group III nitride epitaxial layer on the single crystal Si substrate and the warpage of the resulting epitaxial substrate while varying the resistivity of the single crystal Si substrate and the ratio a of the thickness of the single crystal Si substrate to the thickness of the Group III nitride epitaxial layer (thickness of the single crystal Si substrate / thickness of the Group III nitride epitaxial layer); the resistivity of the single crystal Si substrate and the ratio a, which will result in an absolute value of the warpage of the epitaxial substrate being 50 μm or less, based on the correlation; and an epitaxial substrate manufacturing step of epitaxially growing a Group III nitride epitaxial layer on the single crystal Si substrate using the determined manufacturing parameters. The inventors have found that this method of manufacturing an epitaxial substrate includes a correlation obtaining step of obtaining a correlation between the ratio a and the warpage of the epitaxial substrate for each resistivity of the single crystal Si substrate, and a manufacturing parameter determining step of epitaxially growing a Group III nitride epitaxial layer on the single crystal Si substrate using the determined manufacturing parameters, thereby easily and stably obtaining an epitaxial substrate having a warpage of |warpage|≦50 μm while improving the breakdown voltage characteristics, and have completed the present invention.

[0020] The present inventors have also discovered that an epitaxial substrate having a diameter of 150 mm or less includes a single crystal Si substrate and a Group III nitride epitaxial layer on the single crystal Si substrate, wherein the single crystal Si substrate has a thickness of 1500 μm or more and the Group III nitride epitaxial layer has a thickness of more than 7 μm, and wherein, when the ratio of the thickness of the single crystal Si substrate to the thickness of the Group III nitride epitaxial layer (thickness of single crystal Si substrate / thickness of Group III nitride epitaxial layer) is defined as a, an epitaxial substrate that satisfies at least one of the following (A) to (C) has high breakdown voltage characteristics and suppresses warpage so that |warpage|≦50 μm, and thus completed the present invention: (A) The resistivity of the single crystal Si substrate is 2 mΩcm or less and the ratio a is 125 or more. (B) The resistivity of the single crystal Si substrate is 3 mΩcm or less and the ratio a is 135 or more. (C) The resistivity of the single crystal Si substrate is 5 mΩcm or less and the ratio a is 137 or more.

[0021] The following description will be made with reference to the drawings.

[0022] [Epitaxial substrate] First, an epitaxial substrate according to the present invention will be described with reference to the example of Fig. 1. As shown in Fig. 1, the epitaxial substrate 100 according to the present invention comprises a single crystal Si substrate 1 and a group III nitride epitaxial layer 2. The epitaxial substrate 100 according to the present invention has a diameter of 150 mm (6 inches) or less.

[0023] The thickness of the single crystal Si substrate 1 is 1500 μm (1.5 mm) or more. A single crystal Si substrate 1 with such a thickness is highly effective in suppressing warpage. Furthermore, the thickness of the group III nitride epitaxial layer 2 is greater than 7 μm. A group III nitride epitaxial layer 2 with such a thickness has high breakdown voltage characteristics.

[0024] FIG. 2 shows the relationship between the ratio a (thickness of single crystal Si substrate 1 / thickness of III nitride epitaxial layer 2) of the thickness of single crystal Si substrate 1 (1500 μm thick) and the absolute value of warpage (|warpage|) of epitaxial substrate 100, obtained for each resistivity of single crystal Si substrate 1 (thickness 1500 μm). As shown in FIG. 2, when the resistivity of single crystal Si substrate 1 is constant, the absolute value of warpage of epitaxial substrate 100 decreases as the ratio a (hereinafter simply referred to as "ratio a") of the thickness of single crystal Si substrate 1 to the thickness of III nitride epitaxial layer 2 increases. FIG. 3 is an enlarged view of a portion of FIG. 2. It can be seen from FIG. 3 that an epitaxial substrate with |warpage|≦50 μm can be obtained when the resistivity and ratio a of single crystal Si substrate 1 are within an appropriate range.

[0025] Specifically, from Figure 3, (A) The resistivity of the single crystal Si substrate is 2 mΩcm or less and the ratio a is 125 or more. (B) The resistivity of the single crystal Si substrate is 3 mΩcm or less and the ratio a is 135 or more. (C) The resistivity of the single crystal Si substrate is 5 mΩcm or less and the ratio a is 137 or more. In this case, the epitaxial substrate will have a warpage of 50 μm or less.

[0026] Furthermore, as can be seen from FIG. 2, when the resistivity exceeds 5 mΩcm, the change in |warpage| with respect to the change in ratio a becomes extremely large, and the correlation curve between ratio a and |warpage| becomes steep. Therefore, the range of ratio a that can be set to achieve |warpage|≦50 μm is narrow, i.e., the adjustable range of the epitaxial layer is narrow. Furthermore, with such a gradient of the correlation curve, the variation in warpage due to the change in ratio a tends to become large, making it difficult to stably control. For these reasons, the epitaxial substrate of the present invention uses a single-crystal Si substrate 1 with a resistivity of 5 mΩcm or less.

[0027] According to the inventors' research, the influence of the thickness of the single crystal Si substrate on the correlation is small when the thickness of the single crystal Si substrate is 1500 μm (1.5 mm) or more. Figure 4 compares the thicknesses of the single crystal Si substrates, 1500 μm (1.5 mm) and 2000 μm (2.0 mm), with the resistivity of the single crystal Si substrate set to 3 mΩ cm. As shown in Figure 4, when the condition |warpage|≦50 μm is met, the influence of the thickness of the single crystal Si substrate on the correlation is negligible.

[0028] Hereinafter, each component of epitaxial substrate 100 according to the present invention will be described in more detail, again with reference to FIG.

[0029] (single crystal Si substrate) Next, the single crystal Si substrate 1 will be described. The single crystal Si substrate may be made of a single wafer, or may be a bonded substrate made by bonding multiple single crystal Si wafers together to ensure a thickness of 1500 μm or more. The bonded substrate may be in the form of substrates directly bonded together, or may be a bonded substrate bonded with an oxide film interposed therebetween.

[0030] The oxygen concentration of the single crystal Si substrate 1 is not particularly limited, but is preferably 11 to 18 ppma (JEIDA).Within this range, warpage is stably suppressed.In this specification, the oxygen concentration values ​​are based on the JEIDA-61-2000 standard.

[0031] (III nitride epitaxial layer) Next, the Group III nitride epitaxial layer 2 will be described. The Group III nitride epitaxial layer 2 according to the present invention is not particularly limited as long as it is a Group III nitride epitaxial layer, and may include, for example, a buffer layer 3 and a device layer 4. The buffer layer 3 may include an initial layer 5 or another layer 6, and may further include a superlattice layer 7. The device layer 4 may include, for example, a GaN layer 8, a barrier layer 9, a cap layer 10, etc.

[0032] When the III-nitride epitaxial layer 2 contains GaN, the buffer layer is, for example, an initial layer of AlN and an AlGaN layer or GaN layer formed thereon. 1-x Ga x An example is a repeating N / GaN structure.

[0033] [Method for manufacturing epitaxial substrate] Next, a method for manufacturing an epitaxial substrate according to the present invention will be described. The method for manufacturing an epitaxial substrate according to the present invention is a method for manufacturing an epitaxial substrate having a warpage of ≦50 μm, which includes a single-crystal Si substrate and a Group III nitride epitaxial layer thereon. Each step will be described below.

[0034] (Correlation acquisition process) In the correlation acquisition step, a single-crystal Si substrate 1 having a thickness of 1500 μm or more is used. Then, a III nitride epitaxial layer is epitaxially grown on the single-crystal Si substrate, using the resistivity of the single-crystal Si substrate 1 and the ratio a of the thickness of the single-crystal Si substrate to the thickness of the III nitride epitaxial layer (thickness of the single-crystal Si substrate / thickness of the III nitride epitaxial layer) as parameters. The above parameters are changed and the epitaxial growth is repeated. For example, if the thickness and resistivity of the single-crystal Si substrate used in the actual epitaxial substrate manufacturing process are fixed, the thickness and resistivity of the single-crystal Si substrate can be fixed and the thickness of the III nitride epitaxial layer can be changed to perform epitaxial growth. Of course, epitaxial growth can also be performed by changing all of the conditions. The warpage of the epitaxial substrate obtained by epitaxial growth is then measured.

[0035] In an example of standard conditions for epitaxial growth, an initial layer of AlN (150 nm thick), an AlGaN layer (50 nm thick), and a GaN layer (50 nm thick) are layered as buffer layers on a Si substrate of a predetermined thickness, and a superlattice layer (SLs structure: Al 1-x Ga xA 6.6 μm thick layer (a 2-10 nm thick AlGaN / 2-15 nm thick GaN layer repeat structure) is grown on the buffer layer, and then a 4.4 μm thick GaN layer, a 23 nm thick AlGaN barrier layer, and a 3 nm thick GaN-Cap layer are grown on the buffer layer as the device layer. When adjusting the thickness (total film thickness) of the III-nitride epitaxial layer to obtain a correlation, the total thickness is adjusted while maintaining the same ratio between the buffer layer and the device layer, using the standard III-nitride epitaxial layer described above as the reference. In particular, it is preferable to adjust the film thickness of the superlattice layer in the buffer layer and the GaN layer in the device layer, since these layers account for a large proportion of their film thickness.

[0036] From the above parameters and measurement results, the correlation between the ratio a and the warpage of the epitaxial substrate can be obtained. For example, the correlation between the ratio a and the absolute value of the warpage of the epitaxial substrate can be obtained as shown in Figures 2 and 3.

[0037] (Manufacturing parameter determination process) Using the correlation obtained as described above, the conditions under which the absolute value of the warpage of the epitaxial substrate is 50 μm or less, i.e., the resistivity and ratio a of the single-crystal Si substrate, are determined. For example, the conditions under which |warpage| ≦ 50 μm can be selected from Figures 2 and 3 and easily determined as manufacturing parameters.

[0038] (epitaxial substrate manufacturing process) By epitaxially growing a group III nitride epitaxial layer on a single crystal Si substrate using the manufacturing parameters determined as described above, an epitaxial substrate with |warpage|≦50 μm can be obtained.

[0039] The device used to measure the warpage is not particularly limited, but for example, an OPTM manufactured by Otsuka Electronics Co., Ltd. may be used.

[0040] The epitaxial growth method is not particularly limited as long as it can form a Group III nitride film, and examples thereof include thermal CVD, MOVPE, and MBE. The epitaxial growth conditions are also not particularly limited. For example, temperatures of 1050 to 1200°C are used to grow an initial AlN layer as part of a buffer layer in the epitaxial layer, 1150 to 1050°C are used to grow an AlGaN layer, 1100 to 1000°C are used to grow a superlattice layer, and 900 to 1000°C are used to grow a GaN layer as part of a device layer. [Example]

[0041] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0042] Example 1 First, Si substrates with a diameter of 150 mm (6 inches) and a thickness of 1500 μm were prepared. The resistivities of the Si substrates were set to levels of 2, 3, 5, 8, and 16 mΩcm. A Group III nitride epitaxial layer was grown on the prepared Si substrates to obtain epitaxial substrates. At this time, the thickness of the Group III nitride epitaxial layer was changed to vary the parameter ratio a between the thickness of the Si substrate and the thickness of the Group III nitride epitaxial layer (thickness of single-crystal Si substrate / thickness of Group III nitride epitaxial layer).

[0043] More specifically, the III nitride epitaxial layer includes a buffer layer (initial layer AlN), an AlGaN layer, a GaN layer, a superlattice layer (Al 1-x Ga x We grew a repeating structure of GaN layer (2-10 nm thick) and GaN layer (2-15 nm thick), and then the device layer (GaN layer, AlGaN barrier layer, GaN-Cap layer) on top of that. When changing the thickness of the group III nitride epitaxial layer, we changed the total thickness while keeping the ratio of the buffer layer to the device layer the same.

[0044] The warpage of the epitaxial substrates thus fabricated was measured, and the ratio a and the warpage (absolute value) were obtained to determine the correlation between them, resulting in the correlation shown in Figures 2 and 3.

[0045] Based on the correlation obtained as described above, the conditions for |warpage|≦50 μm were adopted, that is, the Si substrate with a resistivity of 3 mΩcm and a ratio a exceeding 135 were adopted. Specifically, a Si substrate with a resistivity of 3 mΩcm, an oxygen concentration of 14.7 ppma (JEIDA), and a thickness of 1500 μm was prepared. Regarding the growth of the epitaxial layer, an AlGaN layer (50 nm thick) and a GaN layer (50 nm thick) were grown on an initial AlN layer (150 nm thick). A superlattice layer (SLs structure: Al 1-x Ga x A GaN layer (6.5 μm thick) with a repeating structure of 2-10 nm thick AlGaN / 2-15 nm thick GaN was grown on the epitaxial layer. A GaN layer (4.2 μm thick) and an AlGaN barrier layer (23 nm thick) were grown on top of the GaN layer, and a GaN-Cap layer (3 nm thick) was grown on top of that. The epitaxial layer had a thickness of 11.0 μm, and the ratio a was 136.4. The thickness of the epitaxial layer was changed from these conditions as shown in Table 1, and epitaxial substrates were manufactured and their warpage was evaluated. In Example 1, the warpage of the epitaxial substrate was ±50 μm or less (|warpage|≦50 μm).

[0046] (Comparative Example 1) The same Si substrate with a resistivity of 3 mΩcm as in Example 1 was used, but when the epitaxial layer thickness was set to 11.5 μm, the warpage exceeded ±50 μm. In this case, the ratio a was 130.4, which was below 135.

[0047] (Comparative Example 2) The same Si substrate with a resistivity of 3 mΩcm as in Example 1 was used, but when the epitaxial layer thickness was set to 12.0 μm, the warpage exceeded ±50 μm. In this case, the ratio a was 125.0, which was below 135.

[0048] (Comparative Example 3) A Si substrate with a resistivity of 16 mΩcm and an oxygen concentration of 17.0 ppma (JEIDA) was prepared. When the epitaxial layer thickness was 10 μm, the warpage increased to -208 μm.

[0049] Comparative Example 4 A 1000μm thick Si substrate with a resistivity of 8mΩcm and an oxygen concentration of 10.5ppm (JEIDA) was prepared, and a 7.47μm thick epitaxial layer was grown on it. The warpage was large, at -209μm. The ratio a at this time was 134.

[0050] Table 1 summarizes the conditions and results of Example 1 and Comparative Examples 1 to 4.

[0051] [Table 1]

[0052] As described above, according to the examples of the present invention, it was possible to obtain an epitaxial substrate having high breakdown voltage characteristics and suppressed warpage to |warpage|≦50 μm. I was able to do that.

[0053] 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. [Explanation of symbols]

[0054] 1...single crystal Si substrate, 2...group III nitride epitaxial layer, 3...buffer layer, 4...device layer, 5...initial layer, 6...layer, 7...superlattice layer, 8...GaN layer, 9...barrier layer, 10...cap layer, 100...epitaxial substrate.

Claims

1. A method for manufacturing an epitaxial substrate including a single crystal Si substrate and a Group III nitride epitaxial layer on the single crystal Si substrate, comprising: a correlation obtaining step of using a single crystal Si substrate having a thickness of 1500 μm or more, measuring the epitaxial growth of a Group III nitride epitaxial layer on the single crystal Si substrate and the warpage of the resulting epitaxial substrate while varying the resistivity of the single crystal Si substrate and the ratio a of the thickness of the single crystal Si substrate to the thickness of the Group III nitride epitaxial layer (thickness of the single crystal Si substrate / thickness of the Group III nitride epitaxial layer) as parameters, and obtaining a correlation between the ratio a and the warpage of the epitaxial substrate for each resistivity of the single crystal Si substrate; a manufacturing parameter determination step of determining, from the correlation, the resistivity and the ratio a of the single crystal Si substrate such that the absolute value of the warpage of the epitaxial substrate is 50 μm or less; a method for producing an epitaxial substrate, comprising: an epitaxial substrate production step of epitaxially growing a Group III nitride epitaxial layer on a single crystal Si substrate using the determined production parameters;

2. An epitaxial substrate having a diameter of 150 mm or less, comprising: a single crystal Si substrate; and a Group III nitride epitaxial layer on the single crystal Si substrate, the single crystal Si substrate has a thickness of 1500 μm or more, and the III nitride epitaxial layer has a thickness of more than 7 μm; An epitaxial substrate characterized in that, when the ratio of the thickness of the single crystal Si substrate to the thickness of the Group III nitride epitaxial layer (thickness of the single crystal Si substrate / thickness of the Group III nitride epitaxial layer) is defined as a, the epitaxial substrate satisfies at least one of the following (A) to (C): (A) The resistivity of the single crystal Si substrate is 2 mΩcm or less and the ratio a is 125 or more. (B) The resistivity of the single crystal Si substrate is 3 mΩcm or less and the ratio a is 135 or more. (C) The resistivity of the single crystal Si substrate is 5 mΩcm or less and the ratio a is 137 or more.

3. 3. The epitaxial substrate according to claim 2, wherein the single crystal Si substrate has an oxygen concentration of 11 to 18 ppma (JEIDA).

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