Nitride semiconductor substrate and method for manufacturing nitride semiconductor substrate

Abstract

This invention relates to a nitride semiconductor substrate, specifically a nitride semiconductor substrate for high-frequency applications. It is characterized by comprising: an SOI substrate, which is formed by forming a single-crystal silicon thin film on a single-crystal silicon substrate with a silicon oxide layer as a buffer; and a nitride semiconductor layer formed on the SOI substrate and comprising a GaN layer; wherein the single-crystal silicon thin film contains nitrogen at a concentration of 2.0 × 10¹⁴ atoms / cm³ or higher and has a resistivity of 100 Ωcm or higher; the resistivity of the single-crystal silicon substrate is 50 mΩcm or lower; and the thickness of the silicon oxide layer is 10–400 nm. This provides a nitride semiconductor substrate formed by growing a nitride semiconductor layer on an SOI substrate used for manufacturing high-frequency devices, thereby suppressing plastic deformation of the nitride semiconductor substrate.

Description

Technical Field

[0001] This invention relates to a nitride semiconductor substrate and a method for manufacturing the nitride semiconductor substrate. Prior Technology

[0002] Metal-organic vapor deposition (MOCVD), one of the methods for manufacturing semiconductor thin films, is widely used due to its excellent large-diameter and mass production capabilities, and its ability to form homogeneous thin-film crystals. Nitride semiconductors, represented by GaN, are expected to be next-generation semiconductor materials that surpass the limits of silicon (Si). As substrates for the epitaxial growth of GaN and other materials in MOCVD, GaN, SiC, sapphire, and Si are used.

[0003] In recent years, substrates formed by bonding a single-crystal silicon substrate to an insulating layer (such as SiO2), exemplified by silicon-on-insulator (SOI), have been practically used as substrates for the epitaxial growth of GaN. The growth of nitride semiconductors on SOI substrates has been disclosed, for example, in Patent Documents 1-4. GaN / SOI allows for the electrical separation of individual discrete components, demonstrating that this insulation method can eliminate the back-gate effect (the threshold voltage of a MOSFET varies due to the voltage of the substrate) or reduce switching noise. These characteristics are advantages not found in silicon substrates and GaN substrates. SOI substrates can be obtained, for example, by bonding substrates as described in Patent Documents 5 and 6.

[0004] On the other hand, in recent years, high-frequency devices have been manufactured by epitaxial growth of nitride semiconductors in a single-crystal silicon seed layer, as disclosed in Patent Document 7.

[0005] In high-frequency devices, characteristic degradation caused by the substrate, losses due to the substrate, and degradation of second and third harmonic characteristics were observed.

[0006] Generally speaking, high-frequency devices are fabricated by epitaxial growth of GaN layers on high-resistivity substrates.

[0007] High-frequency device substrates utilize high-resistivity substrates to prevent signal flow from the epitaxial layer to the underlying silicon substrate. Furthermore, when a nitride semiconductor epitaxial layer is stacked on a high-resistivity silicon substrate, a buffer layer is designed as a stress-relieving layer. However, the high-resistivity silicon substrate undergoes plastic deformation due to stress during epitaxial growth. To address this issue, it is preferable to use an SOI substrate, which is fabricated from a stress-resistant, low-resistivity substrate (a hard single-crystal silicon substrate specifically for nitride semiconductor epitaxial growth) and a high-resistivity silicon substrate bonded together by a silicon oxide layer.

[0008] However, even nitride semiconductor substrates prepared in this way for manufacturing high-frequency devices sometimes undergo plastic deformation during the epitaxial growth of the nitride semiconductor. [Previous Technical Documents] (Patent Documents)

[0009] Patent Document 1: Japanese Patent Application Publication No. 2010-40737 Patent Document 2: Japanese Patent Application Publication No. 2011-97062 Patent Document 3: Japanese Patent Application Publication No. 2019-208022 Patent Document 4: Japanese Patent No. 5396369 Specification Patent Document 5: Japanese Patent No. 5233111 Specification Patent Document 6: Japanese Patent Application Publication No. 2010-278339 Patent Document 7: Japanese Patent Application Publication No. 2021-100087 Summary of the Invention

[0010] [The problem the invention aims to solve]

[0011] The present invention was made to solve the above-mentioned problems, and its purpose is to provide a nitride semiconductor substrate and a method for manufacturing the same. The nitride semiconductor substrate is formed by growing a nitride semiconductor layer on an SOI substrate used to manufacture high-frequency devices, and the plastic deformation of the nitride semiconductor substrate is suppressed. [Technical means to solve the problem]

[0012] To address the above problems, the present invention provides a nitride semiconductor substrate, specifically a high-frequency nitride semiconductor substrate, characterized in that it comprises: SOI substrate, which is formed by forming a single-crystal silicon thin film on a single-crystal silicon substrate with a silicon oxide layer in between; and, A nitride semiconductor layer is formed on the SOI substrate and includes a GaN layer; The aforementioned single-crystal silicon thin film contains nitrogen at a concentration of 2.0 × 10¹⁴ atoms / cm³ or higher, and has a resistivity of 100 Ωcm or higher; The resistivity of the aforementioned single-crystal silicon substrate is below 50 mΩcm; The thickness of the aforementioned silicon oxide layer is 10~400 nm.

[0013] If a nitride semiconductor substrate is formed on an SOI substrate containing a GaN layer on a single-crystal silicon thin film with a nitrogen concentration of 2.0 × 10¹⁴ atoms / cm³ or higher, a resistivity of 100 Ωcm or higher for the single-crystal silicon thin film, a resistivity of 50 mΩcm or lower for the single-crystal silicon substrate, and a silicon oxide layer thickness of 10–400 nm, then a nitride semiconductor substrate with suppressed plastic deformation can be manufactured. Furthermore, by using this nitride semiconductor substrate, a high-frequency device with excellent high-frequency characteristics can be manufactured.

[0014] Preferably, the thickness of the aforementioned silicon oxide layer is 10~200 nm.

[0015] If the thickness of the silicon oxide layer is 10~200nm, a nitride semiconductor substrate in which plastic deformation is further suppressed can be fabricated.

[0016] Furthermore, the present invention provides a method for manufacturing a nitride semiconductor substrate, specifically a method for manufacturing a high-frequency nitride semiconductor substrate, characterized by comprising the following steps: The steps for preparing two single-crystal silicon substrates for bonding the wafer and the base wafer; The step of bonding the two monocrystalline silicon substrates together with a silicon oxide layer in between; The steps involve thinning the aforementioned bonding wafer to form a single-crystal silicon thin film, thereby obtaining an SOI substrate formed on the aforementioned substrate wafer with the aforementioned silicon oxide layer in between; and, The step of growing a nitride semiconductor layer including a GaN layer on the aforementioned single-crystal silicon thin film of the aforementioned SOI substrate to obtain a nitride semiconductor substrate formed by forming the aforementioned nitride semiconductor layer on the aforementioned SOI layer; The aforementioned single-crystal silicon substrate used as the bonding wafer is a single-crystal silicon substrate containing nitrogen at a concentration of 2.0 × 10¹⁴ atoms / cm³ or higher and having a resistivity of 100 Ωcm or higher; The aforementioned single-crystal silicon substrate, which serves as the aforementioned base wafer, is a single-crystal silicon substrate with a resistivity of 50 mΩcm or less; As the aforementioned silicon oxide layer, a silicon oxide layer with a thickness of 10~400 nm is used.

[0017] If such a method for manufacturing nitride semiconductors is used, it is relatively simple and reliable to manufacture a nitride semiconductor substrate in which plastic deformation is suppressed. Furthermore, by using a nitride semiconductor substrate prepared in this manner, it is possible to manufacture a high-frequency device with excellent high-frequency characteristics.

[0018] Preferably, a silicon oxide layer with a thickness of 10 to 200 nm is used as the aforementioned silicon oxide layer.

[0019] If a silicon oxide layer with a thickness of 10~200nm is used as the silicon oxide layer, it is possible to manufacture a nitride semiconductor substrate in which plastic deformation is further suppressed.

[0020] The aforementioned single-crystal silicon substrate, which can be prepared as the aforementioned bonding wafer, can be manufactured by the floating zone melting method (FZ method) or the magnetic field Czochralski method (MCZ method).

[0021] For example, single-crystal silicon substrates that serve as bonding wafers can be manufactured using the FZ or MCZ methods. [Effects of the invention]

[0022] As described above, if the nitride semiconductor substrate of the present invention is used, a nitride semiconductor substrate in which plastic deformation is suppressed can be manufactured. Furthermore, if the nitride semiconductor substrate of the present invention is used, a high-frequency device with excellent high-frequency characteristics can be manufactured.

[0023] Furthermore, the manufacturing method of the nitride semiconductor substrate of the present invention can relatively easily and reliably manufacture a high-frequency nitride semiconductor substrate with suppressed plastic deformation. Moreover, if the nitride semiconductor substrate obtained by the manufacturing method of the present invention is used, a high-frequency device with excellent high-frequency characteristics can be manufactured. Simple Explanation of the Diagram

[0024] Figure 1 is a schematic cross-sectional view showing an example of a nitride semiconductor substrate of the present invention. Figure 2 is a schematic diagram of an example of the structure of the nitride semiconductor substrate of the present invention. Figure 3 is a graph showing the changes in warpage state during the epitaxial growth process in the embodiments and comparative examples. Figure 4 is a graph showing the relationship between the thickness of the silicon oxide layer and warpage in the embodiments and comparative examples. Implementation

[0025] As mentioned above, when nitride semiconductors are epitaxially grown on SOI substrates with high resistivity single-crystal silicon thin films for the purpose of manufacturing high-frequency devices, plastic deformation sometimes occurs during the epitaxial growth process.

[0026] The inventors have repeatedly studied nitride semiconductor substrates with suppressed plastic deformation and their manufacturing methods. As a result, they have found that by using a single-crystal silicon thin film as an SOI substrate containing nitrogen at a concentration of 2.0 × 10¹⁴ atoms / cm³ or higher, a resistivity of 100 Ωcm or higher for the single-crystal silicon thin film, a resistivity of 50 mΩcm or lower for the single-crystal silicon substrate, and a silicon oxide layer thickness of 10 to 400 nm for the SOI substrate, a nitride semiconductor substrate with suppressed plastic deformation can be manufactured, thus completing the present invention.

[0027] That is, the present invention is a nitride semiconductor substrate, specifically a high-frequency nitride semiconductor substrate, characterized in that it comprises: SOI substrate, which is formed by forming a single-crystal silicon thin film on a single-crystal silicon substrate with a silicon oxide layer in between; and, A nitride semiconductor layer is formed on the SOI substrate and includes a GaN layer; The aforementioned single-crystal silicon thin film contains nitrogen at a concentration of 2.0 × 10¹⁴ atoms / cm³ or higher, and has a resistivity of 100 Ωcm or higher; The resistivity of the aforementioned single-crystal silicon substrate is below 50 mΩcm; The thickness of the aforementioned silicon oxide layer is 10~400 nm.

[0028] Furthermore, this invention provides a method for manufacturing a nitride semiconductor substrate, specifically a method for manufacturing a nitride semiconductor substrate for high-frequency applications, characterized by comprising the following steps: The steps for preparing two single-crystal silicon substrates for bonding the wafer and the base wafer; The step of bonding the two monocrystalline silicon substrates together with a silicon oxide layer in between; The steps involve thinning the aforementioned bonding wafer to form a single-crystal silicon thin film, thereby obtaining an SOI substrate formed on the aforementioned substrate wafer with the aforementioned silicon oxide layer in between; and, The step of growing a nitride semiconductor layer including a GaN layer on the aforementioned single-crystal silicon thin film of the aforementioned SOI substrate to obtain a nitride semiconductor substrate formed by forming the aforementioned nitride semiconductor layer on the aforementioned SOI layer; The aforementioned single-crystal silicon substrate used as the bonding wafer is a single-crystal silicon substrate containing nitrogen at a concentration of 2.0 × 10¹⁴ atoms / cm³ or higher and having a resistivity of 100 Ωcm or higher; The aforementioned single-crystal silicon substrate, which serves as the aforementioned base wafer, is a single-crystal silicon substrate with a resistivity of 50 mΩcm or less; As the aforementioned silicon oxide layer, a silicon oxide layer with a thickness of 10~400 nm is used.

[0029] The present invention will now be described in detail with reference to the accompanying drawings, but the present invention is not limited to these descriptions.

[0030] [Nitride semiconductor substrate] Figure 1 shows a schematic cross-sectional view of an example of the nitride semiconductor substrate of the present invention. Figure 2 shows a schematic diagram of the structure of an example of the nitride semiconductor substrate of the present invention.

[0031] The nitride semiconductor substrate 1 shown in Figure 1 includes an SOI substrate 2 and a nitride semiconductor layer (nitride semiconductor thin film) 3.

[0032] SOI substrate 2 is formed by forming a single crystal silicon thin film 23 on a single crystal silicon substrate 21 with a silicon oxide layer 22 in between.

[0033] The nitride semiconductor layer 3 includes the GaN layer 34 shown in FIG2. The nitride semiconductor layer 3 shown in FIG2 includes the GaN layer 34, the AlN layer 31, the AlGaN layer 32, and the superlattice layer (SLs) 33. If the nitride semiconductor layer 3 includes the GaN layer 34, it is not limited to the configuration shown in FIG2.

[0034] The single-crystal silicon thin film 23 of the SOI substrate 2 of the nitride semiconductor substrate 1 contains nitrogen with a concentration of 2.0 × 10¹⁴ atoms / cm³ or higher, and has a resistivity of 100 Ωcm or higher. Furthermore, the resistivity of the single-crystal silicon substrate 21 is 50 mΩcm or lower. Moreover, the thickness of the silicon oxide layer 22 is 10 to 400 nm.

[0035] Even with a high-resistivity SOI layer 23, such an SOI substrate 2 can still exhibit high strength. By including such an SOI substrate 2, the nitride semiconductor substrate 1 of the present invention can suppress plastic deformation.

[0036] On the other hand, if the nitrogen concentration in the monocrystalline silicon film 23 is less than 2.0 × 10¹⁴ atoms / cm³, plastic deformation cannot be sufficiently suppressed. There is no particular upper limit to the nitrogen concentration in the monocrystalline silicon film 23; for example, it can be set to 1.0 × 10²⁰ atoms / cm³.

[0037] Furthermore, if the thickness of the silicon oxide layer 22 exceeds 400 nm, plastic deformation cannot be sufficiently suppressed. Conversely, when the thickness of the silicon oxide layer 22 is less than 10 nm, bonding cannot be achieved smoothly, resulting in voids. If the thickness of the silicon oxide layer 22 is 10~400 nm, a nitride semiconductor substrate 1 in which plastic deformation is further suppressed can be fabricated.

[0038] Furthermore, when the resistivity of the monocrystalline silicon substrate 21 exceeds 50 mΩcm, it is also impossible to sufficiently suppress plastic deformation. There is no particular limitation on the lower limit of the resistivity of the monocrystalline silicon substrate 21; for example, it can be set to 2 mΩcm.

[0039] Furthermore, by using the resistivity of the monocrystalline silicon thin film 23, which is above 100 Ωcm, it is possible to manufacture a high-frequency device with excellent high-frequency characteristics. There is no particular upper limit to the resistivity of the monocrystalline silicon thin film 23; for example, it can be set to 30,000 Ωcm.

[0040] [Manufacturing method of nitride semiconductor substrate] The method for manufacturing the nitride semiconductor substrate of the present invention includes the following steps: The steps for preparing two single-crystal silicon substrates for bonding the wafer and the base wafer; The step of bonding the two monocrystalline silicon substrates together with a silicon oxide layer in between; The steps involve thinning the aforementioned bonding wafer to form a single-crystal silicon thin film, thereby obtaining an SOI substrate formed on the aforementioned substrate wafer with the aforementioned silicon oxide layer in between; and, The step of growing a nitride semiconductor layer including a GaN layer on the aforementioned single-crystal silicon thin film of the aforementioned SOI substrate to obtain a nitride semiconductor substrate formed by forming the aforementioned nitride semiconductor layer on the aforementioned SOI layer.

[0041] In the step of preparing two monocrystalline silicon substrates, the monocrystalline silicon substrate used as the bonding wafer is a monocrystalline silicon substrate containing nitrogen at a concentration of 2.0 × 10¹⁴ atoms / cm³ or higher and having a resistivity of 100 Ωcm or higher. There is no particular upper limit to the nitrogen concentration of the monocrystalline silicon substrate used as the bonding wafer; for example, it can be set to 1.0 × 10²⁰ atoms / cm³. Similarly, there is no particular upper limit to the resistivity of the monocrystalline silicon substrate used as the bonding wafer; for example, it can be set to 30000 Ωcm.

[0042] The preferred single-crystal silicon substrate for bonding wafers is a single-crystal silicon substrate with a face orientation of (111) prepared by the FZ or MCZ method. For example, nitrogen can be doped during the fabrication of single-crystal silicon by the FZ or MCZ method to achieve a nitrogen concentration of 2.0 × 10 14 atoms / cm 3 or higher.

[0043] Furthermore, the single-crystal silicon substrate used as the base wafer is prepared to have a resistivity of 50 mΩcm or less. There is no particular limitation on the lower limit of the resistivity of the single-crystal silicon substrate used as the base wafer; for example, it can be set to 2 mΩcm.

[0044] The preferred single-crystal silicon substrate for use as the substrate wafer is a single-crystal silicon substrate prepared by the CZ method with a face orientation of (100).

[0045] Furthermore, for example, thermal oxidation is performed on the single-crystal silicon substrate used as a bonding wafer to form a silicon oxide layer with a thickness of 10 to 400 nm on the surface. Preferably, a silicon oxide layer with a thickness of 10 to 200 nm is formed.

[0046] Subsequently, a single-crystal silicon substrate serving as a bonding wafer is overlapped with a single-crystal silicon substrate serving as a base wafer through a silicon oxide layer with a thickness of 10~400nm to bond them together, for example, by performing a bonding heat treatment at 1150°C for about 2 hours to bond them together.

[0047] The bonding wafer is then processed to achieve a thickness of approximately 100-200 nm, thus obtaining a single-crystal silicon thin film. This processing method is not particularly limited; however, a method involving hydrogen ion implantation followed by peeling and polishing is easier and better.

[0048] By means of this processing, an SOI substrate 2 as shown in FIG1 can be obtained, which is formed by forming a single crystal silicon thin film 23 on a substrate wafer (single crystal silicon substrate) 21 with a silicon oxide layer 22 in between.

[0049] Using an SOI substrate 2 prepared in this manner as the starting substrate, a nitride semiconductor layer including a GaN layer is grown on this SOI substrate 2. For example, as shown in FIG2, an AlN layer 31 is initially formed with a thickness of, for example, 150 nm, followed by an AlGaN layer 32 with a thickness of, for example, 160 nm. Next, a superlattice layer (SLs) 33 is formed, which is composed of 40 to 60 groups of GaN and AlN layers interleaved. Then, a GaN layer 34 with a thickness of, for example, 800 to 1200 nm is formed. Next, a barrier layer composed of, for example, an AlGaN layer 32 with a thickness of 3 nm is formed, and a capping layer composed of, for example, a GaN layer 34 with a thickness of 3 nm is formed on it. In this way, a nitride semiconductor substrate 1 (GaN-HEMT epitaxial growth substrate) 1 as shown in FIG2 can be manufactured, which is formed by forming a nitride semiconductor layer 3 on an SOI substrate 2.

[0050] According to the method for manufacturing the nitride semiconductor substrate of the present invention, the nitride semiconductor substrate of the present invention can be manufactured. However, the method for manufacturing the nitride semiconductor substrate of the present invention is not limited to the manufacturing method described above.

[0051] Thus, the manufacturing method of the nitride semiconductor substrate of the present invention involves forming a nitride semiconductor thin film comprising an AlN layer 31, a GaN layer 34, and an AlGaN layer 32 on an SOI substrate 2. The SOI substrate 2 is formed by forming a single-crystal silicon thin film on a single-crystal silicon substrate serving as a substrate wafer, with a silicon oxide layer in between. The single-crystal silicon substrate serving as the bonding wafer is a single-crystal silicon substrate containing nitrogen at a concentration of 2.0 × 10¹⁴ atoms / cm³ or higher and having a resistivity of 100 Ωcm or higher; the single-crystal silicon substrate serving as the substrate wafer is a single-crystal silicon substrate with a resistivity of 50 mΩcm or lower; and the silicon oxide layer is a silicon oxide layer with a thickness of 10 to 400 nm, preferably 10 to 200 nm. In this way, a nitride semiconductor substrate can be manufactured that can improve relative strength even with high resistivity, and is particularly suitable for high-frequency devices with good high-frequency characteristics, while suppressing plastic deformation. [Example]

[0052] The present invention will now be specifically described using examples and comparative examples, but the present invention is not limited to these examples.

[0053] (Example 1) As shown in Figure 2, a nitride semiconductor layer 3 with a thickness of 1.8 μm is epitaxially grown on SOI substrate 2 to obtain the nitride semiconductor substrate (GaN-HEMT substrate) 1 of Example 1.

[0054] At this point, an SOI substrate with a diameter of 150 mm is used as SOI substrate 2 under the following conditions.

[0055] The single-crystal silicon substrate (Bond substrate) used as the bonding wafer is a single-crystal silicon substrate prepared to be manufactured by the MCZ method with nitrogen doping, having a surface orientation of (111), containing nitrogen at a concentration of 5×10 14 atoms / cm 3, and a resistivity of 1200Ωcm.

[0056] The single-crystal silicon substrate (Base substrate) used as the substrate wafer is a single-crystal silicon substrate to be manufactured by the CZ method with a face orientation of (100), a resistivity of 8mΩcm, and a thickness of 675μm.

[0057] The prepared bonding wafer is thermally oxidized to form a silicon oxide layer with a thickness of 200 nm on the surface of the bonding wafer.

[0058] Subsequently, hydrogen ions are implanted into the bonding wafer through an oxide film to form a bubble layer. Then, the wafer is overlapped with a single-crystal silicon substrate, which serves as the base wafer, through a silicon oxide layer for bonding. After heat treatment to peel off the bonding wafer with the bubble layer, a bonding heat treatment is performed at 1150°C for 2 hours to achieve bonding.

[0059] In this manner, a single-crystal silicon thin film (SOI layer) with a nitrogen concentration of 5 × 10¹⁴ atoms / cm³, a resistivity of 1200 Ωcm, and a thickness of 100 nm is obtained.

[0060] By means of this processing, an SOI substrate 2 as shown in FIG1 is obtained, which is formed by forming a single crystal silicon thin film 23 on a substrate wafer (single crystal silicon substrate) 21 with a silicon oxide layer (BOX layer) 22 in between.

[0061] Example 1 involves forming a nitride semiconductor layer 3 on an SOI substrate 2 obtained in the manner described above, while referring to Figure 2 and following the previously described sequence, by epitaxial growth.

[0062] (Comparative Example 1) Except that the single-crystal silicon substrate used as the bonding wafer is a single-crystal silicon substrate manufactured by the FZ method in a nitrogen-free manner with a face orientation of (111) and a resistivity of 5535 Ωcm, the nitride semiconductor substrate of Comparative Example 1 was obtained in the same order as in Example 1.

[0063] (Comparative Example 2) In addition to thermally oxidizing the prepared bonding wafer to form a silicon oxide layer with a thickness of 400 nm on the surface of the bonding wafer, the nitride semiconductor substrate of Comparative Example 2 was obtained in the same order as Comparative Example 1.

[0064] (Example 2) Except for thermal oxidation of the prepared bonding wafer to form a silicon oxide layer with a thickness of 400 nm on the surface of the bonding wafer, the nitride semiconductor substrate of Example 2 was obtained in the same order as in Example 1.

[0065] (Comparative Example 3) In addition to thermally oxidizing the prepared bonding wafer to form a silicon oxide layer with a thickness of 650 nm on the surface of the bonding wafer, the nitride semiconductor substrate of Comparative Example 3 was obtained in the same order as Comparative Example 1.

[0066] (Comparative Example 4) Except for thermal oxidation of the prepared bonding wafer to form a silicon oxide layer with a thickness of 650 nm on the surface of the bonding wafer, the nitride semiconductor substrate of Comparative Example 4 was obtained in the same order as in Example 1.

[0067] (Comparative Example 5) Except that the single-crystal silicon substrate used as the substrate wafer is a single-crystal silicon substrate manufactured by the CZ method with a face orientation of (100), a resistivity of 8 mΩcm, a thickness of 675 μm, and a 600 nm back CVD oxide film formed on the face opposite to the face to which it is bonded to the bonding wafer, the nitride semiconductor substrate of Comparative Example 5 was obtained in the same order as Comparative Example 4.

[0068] (Comparative Example 6) Except for making the thickness of the single-crystal silicon thin film 200 nm, the nitride semiconductor substrate of Comparative Example 6 was obtained in the same order as Comparative Example 4.

[0069] Table 1 below shows details of the SOI substrates of Examples 1 and 2, and Comparative Examples 1 to 6, as well as the warpage after epitaxial growth of the nitride semiconductor layer.

[0070] [Table 1]

[0071] As shown in Table 1, the warpage of the nitride semiconductor substrates in Examples 1 and 2 after epitaxial growth is within the general equipment input specification of ±50μm, and the plastic deformation is sufficiently suppressed.

[0072] On the other hand, it can be seen that the nitride semiconductor substrates of Comparative Examples 1 and 2 did not use a single-crystal silicon substrate containing nitrogen at a concentration of 5×10 14 atoms / cm 3 as the single-crystal silicon substrate for bonding wafers. The warpage after epitaxial growth exceeded ±50μm, and plastic deformation was not sufficiently suppressed.

[0073] Furthermore, it can be seen that the nitride semiconductor substrates of Comparative Examples 3 to 6 used silicon oxide layers with a thickness of more than 400 nm as silicon oxide layers, and the warpage after epitaxial growth exceeded ±50 μm, and the plastic deformation was not sufficiently suppressed.

[0074] (Example 3) Except that the single-crystal silicon substrate used as the base wafer is a single-crystal silicon substrate manufactured by the CZ method with a face orientation of (100), a resistivity of 8 mΩcm, and a thickness of 1000 μm, the nitride semiconductor substrate of Example 3 is obtained in the same order as in Example 1.

[0075] (Example 4) Except that the single-crystal silicon substrate used as the bonding wafer is a nitrogen-doped single-crystal silicon substrate manufactured by the FZ method with a face orientation of (111), containing a nitrogen concentration of 5 × 10¹⁴ atoms / cm³, and a resistivity of 3552 Ωcm, the nitride semiconductor substrate of Example 4 was obtained in the same order as in Example 1. That is, in Example 4, a silicon oxide layer with a thickness of 200 nm was used in the same manner as in Example 1.

[0076] (Example 5) Except for thermal oxidation of the prepared bonding wafer to form a silicon oxide layer with a thickness of 400 nm on the surface of the bonding wafer, the nitride semiconductor substrate of Example 5 was obtained in the same order as in Example 4.

[0077] (Comparative Example 7) Except for thermal oxidation of the prepared bonding wafer to form a silicon oxide layer with a thickness of 650 nm on the surface of the bonding wafer, the nitride semiconductor substrate of Comparative Example 7 was obtained in the same order as in Example 4.

[0078] Table 2 below shows details of the SOI substrates of Examples 3-5 and Comparative Example 7, as well as the warpage after epitaxial growth of the nitride semiconductor layer.

[0079] [Table 2]

[0080] Figure 3 shows a portion of the log data obtained by utilizing curvature to obtain the warping state during the epitaxial growth process of Examples 1 and 3, and Comparative Examples 3 and 6.

[0081] As shown in Figure 3, Comparative Examples 3 and 6, with a silicon oxide layer thickness of 650 nm, exhibited significant plastic deformation after approximately 2 hours and 40 minutes.

[0082] On the other hand, as shown in Figure 3, compared with Comparative Examples 3 and 6, Examples 1 and 3 are able to suppress substrate warping during epitaxial growth.

[0083] Furthermore, the relationship between the thickness of the silicon oxide layer and warpage in the examples and comparative examples is shown in Figure 4.

[0084] Specifically, the approximate curves of the quadrilateral and the dotted lines represent the warping changes when the thickness of the silicon oxide (BOX) layer is changed to 200 nm (Example 1), 400 nm (Example 2), and 650 nm (Comparative Example 4) using a bonding wafer manufactured and prepared by the MCZ method.

[0085] Furthermore, the circular curve and the approximate curve of the discontinuous line represent the warping changes when the bonding wafer, which is manufactured and prepared by the FZ method, is changed to 200 nm (Example 4), 400 nm (Example 5), and 650 nm (Comparative Example 7).

[0086] As shown in Figure 4, regardless of whether the bonding wafer is manufactured using the MCZ method or the FZ method, in the embodiment where the silicon oxide layer (BOX layer) thickness is less than 400 nm, the warpage is less than 50 μm, which significantly suppresses warpage compared to the comparative example where the silicon oxide layer thickness is 650 nm.

[0087] Furthermore, this invention is not limited to the embodiments described above. The embodiments described above are examples; any invention that has a substantially similar structure and performs the same function as the technical concept described in the claims of this invention is included within the technical scope of this invention.

[0088] 1: Nitride semiconductor substrate 2:SOI substrate 3: Nitride semiconductor layer 21: Monocrystalline silicon substrate 22: Silicon oxide layer 23: Monocrystalline silicon thin films 31: AlN layer 32: AlGaN layer 33: Superlattice layer 34:GaN layer

[0089] Domestic storage information (please note in order of storage institution, date, and number) none Overseas storage information (please note in the order of storage country, institution, date, and number) none

Claims

1. A nitride semiconductor substrate, a high-frequency nitride semiconductor substrate, characterized in that it comprises: an SOI substrate, which is formed by forming a single-crystal silicon thin film on a single-crystal silicon substrate with a silicon oxide layer in between; and a nitride semiconductor layer formed on the SOI substrate and comprising a GaN layer; wherein the single-crystal silicon thin film contains nitrogen with a concentration of 2.0 × 10¹⁴ atoms / cm³ or more and has a resistivity of 100 Ωcm or more; wherein the resistivity of the single-crystal silicon substrate is 50 mΩcm or less; and wherein the thickness of the silicon oxide layer is 10 to 400 nm.

2. The nitride semiconductor substrate as described in claim 1, wherein, The thickness of the aforementioned silicon oxide layer is 10–200 nm.

3. A method for manufacturing a nitride semiconductor substrate, specifically a method for manufacturing a high-frequency nitride semiconductor substrate, characterized by comprising the following steps: preparing two single-crystal silicon substrates as a bonding wafer and a substrate wafer; bonding the two single-crystal silicon substrates with a silicon oxide layer between them; thinning the bonding wafer to form a single-crystal silicon thin film, thereby obtaining an SOI substrate formed on the substrate wafer with the single-crystal silicon thin film between them; and growing a nitride semiconductor layer including a GaN layer on the single-crystal silicon thin film of the SOI substrate, thereby obtaining a nitride semiconductor substrate formed on the single-crystal silicon thin film; wherein the single-crystal silicon substrate used as the bonding wafer is a single-crystal silicon substrate containing nitrogen at a concentration of 2.0 × 10¹⁴ atoms / cm³ or higher and having a resistivity of 100 Ωcm or higher. The aforementioned single-crystal silicon substrate, which serves as the aforementioned base wafer, is a single-crystal silicon substrate with a resistivity of 50 mΩcm or less; the aforementioned silicon oxide layer is a silicon oxide layer with a thickness of 10 to 400 nm.

4. A method for manufacturing a nitride semiconductor substrate as described in claim 3, wherein, As the aforementioned silicon oxide layer, a silicon oxide layer with a thickness of 10 to 200 nm is used.

5. A method for manufacturing a nitride semiconductor substrate as described in claim 3 or 4, wherein, The aforementioned single-crystal silicon substrate, which serves as the aforementioned bonding wafer, is prepared by manufacturing using either the floating zone melting method or the magnetic field Czochralski method.

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