Silicon-on-insulator wafer and preparation method thereof

Abstract

The invention provides a silicon-on-insulator wafer and a preparation method thereof. The silicon-on-insulator wafer comprises a first substrate, a first buried oxide layer arranged on the first substrate, a silicon nitride intermediate layer arranged on the first buried oxide layer, a second buried oxide layer arranged on the silicon nitride intermediate layer, and a second substrate arranged on the second buried oxide layer. The invention has the beneficial effects that the silicon nitride intermediate layer with high refractive index is introduced between the first buried oxide layer and the second buried oxide layer, and the buried oxide layer with asymmetric refractive index distribution is matched to form a gradient refractive index structure, so that stronger light field limitation, better broadband performance and better process compatibility are realized; the method is suitable for high-density integrated optoelectronic devices.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, and in particular relates to a silicon-on-insulator wafer and its preparation method. Background Technology

[0002] Silicon-on-insulator (SOI) wafers are key substrate materials for fabricating silicon-based photonic devices and planar waveguide circuits (PLCs). Traditional SOI structures typically consist of a top silicon layer, a buried oxide layer, and a silicon substrate. Their optical performance is mainly limited by the finite refractive index difference between silicon and silicon dioxide, resulting in insufficient light field confinement and a large mode field size, posing challenges in terms of device integration and coupling efficiency.

[0003] In the prior art, Chinese patent CN112002672A discloses a novel silicon-on-insulator wafer and its manufacturing method, employing a double-layer buried oxide layer structure to modulate the optical field. While this structure improves the optical field distribution by adjusting the refractive indices of the two buried oxide layers, it still has the following shortcomings:

[0004] (1) Relying solely on the refractive index difference between the two buried oxide layers makes it difficult to achieve optimal optical field confinement and mode field matching over a wide wavelength range;

[0005] (2) The refractive index matching accuracy of the two buried oxide layers in the preparation process is extremely high, which increases the complexity of the process and the manufacturing cost, and is prone to introducing defects at the bonding interface.

[0006] Therefore, there is an urgent need for an SOI wafer structure and its fabrication method that combines excellent optical field confinement capability, wide band adaptability, and good process compatibility. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a silicon-on-insulator wafer and its fabrication method, overcoming the shortcomings of existing technologies.

[0008] The technical solution adopted in this invention is: a silicon-on-insulator wafer, comprising:

[0009] First substrate;

[0010] A first buried oxide layer is disposed on the first substrate;

[0011] A silicon nitride intermediate layer is disposed on the first buried oxide layer;

[0012] The second buried oxide layer is disposed on the silicon nitride intermediate layer;

[0013] The second substrate is disposed on the second buried oxide layer.

[0014] Furthermore, the refractive index of the first buried oxide layer is 1.44 to 1.46, and the thickness is 5 to 20 μm.

[0015] Furthermore, the refractive index of the silicon nitride intermediate layer is 2.0 to 2.2, and the thickness is 0.5 to 2 μm.

[0016] Furthermore, the refractive index of the second buried oxide layer is 1.46 to 1.48, and the thickness is 2 to 6 μm.

[0017] Furthermore, the thickness of the first substrate is 400–600 μm, and the thickness of the second substrate is 0.1–1 μm.

[0018] This invention also provides a method for preparing a silicon-on-insulator wafer, comprising the following steps:

[0019] A first substrate is provided, and a first buried oxide layer is grown on the first substrate;

[0020] A silicon nitride intermediate layer is grown on the first buried oxide layer;

[0021] A second substrate is provided, and a second buried oxide layer is grown on the second substrate;

[0022] The second buried oxide layer is bonded to the silicon nitride interlayer;

[0023] The second substrate is then thinned.

[0024] Furthermore, the refractive index of the first and second buried oxide layers is adjusted by doping.

[0025] Furthermore, the first and second buried oxide layers are formed by thermal oxidation or chemical vapor deposition.

[0026] Furthermore, the silicon nitride intermediate layer is formed by plasma-enhanced chemical vapor deposition.

[0027] Furthermore, the step of bonding the second buried oxide layer to the silicon nitride interlayer includes the following steps:

[0028] Clean and activate the silicon nitride intermediate layer and the second buried oxide layer;

[0029] The activated silicon nitride intermediate layer and the second buried oxide layer are bonded together for pre-bonding.

[0030] The pre-bonded structure is annealed at high temperature in an oxygen- or nitrogen-containing atmosphere to complete the bonding.

[0031] The advantages and positive effects of this invention are:

[0032] 1. Enhanced optical field confinement: The high-refractive-index silicon nitride interlayer and the upper and lower buried oxide layers form a significant refractive index difference, which more tightly confines the light energy to the core region of the waveguide and effectively reduces radiation loss.

[0033] 2. Wideband performance optimization: The asymmetric gradient refractive index design enables optimized mode matching and coupling for wideband optical signals from visible light to near-infrared, solving the problem of poor adaptability of a single structure to different wavelengths.

[0034] 3. Process Compatibility and Reliability: All fabrication steps utilize mature semiconductor manufacturing processes, fully compatible with standard CMOS production lines, facilitating large-scale, low-cost manufacturing. The bonding interface is formed through chemical bonding, exhibiting high mechanical strength and good thermal stability.

[0035] 4. Novel structure and improved performance: Compared with the traditional double-layer buried oxide layer structure, the multi-layer gradient refractive index structure of this invention provides a more flexible means of optical field control and significantly improves performance. Attached Figure Description

[0036] The above and other objects, features, and advantages of the present invention will become more apparent from the more detailed description of the embodiments of the invention in conjunction with the accompanying drawings. The drawings are provided to further illustrate the embodiments of the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings, the same reference numerals generally represent the same parts or steps.

[0037] Figure 1 This is a schematic diagram of the structure of a silicon-on-insulator wafer according to an embodiment of the present invention.

[0038] Figure 2 This is a flowchart of a method for preparing silicon-on-insulator wafers according to an embodiment of the present invention.

[0039] Figure 3 This is a manufacturing process diagram of a method for preparing silicon-on-insulator wafers according to an embodiment of the present invention.

[0040] In the figure: 1. First substrate; 2. First buried oxide layer; 3. Silicon nitride intermediate layer; 4. Second buried oxide layer; 5. Second substrate. Detailed Implementation

[0041] This invention provides a silicon-on-insulator wafer and a method for fabricating the same. The embodiments of this invention are described below with reference to the accompanying drawings.

[0042] In the description of the embodiments of this invention, it should be understood that the terms "top," "bottom," etc., indicating orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, it should be noted that unless otherwise explicitly specified and limited, the terms "set" and "connected" should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication of two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention through specific circumstances.

[0043] like Figure 1 As shown, an embodiment of the present invention discloses a silicon-on-insulator wafer, comprising, from bottom to top, a first substrate 1, a first buried oxide layer 2, a silicon nitride interlayer 3, a second buried oxide layer 4, and a second substrate 5. The first buried oxide layer 2 is disposed on the first substrate 1. The silicon nitride interlayer 3 is disposed on the side of the first buried oxide layer 2 away from the first substrate 1. The second buried oxide layer 4 is disposed on the side of the silicon nitride interlayer 3 away from the first buried oxide layer 2. The second substrate 5 is disposed on the side of the second buried oxide layer 4 away from the silicon nitride interlayer 3.

[0044] Specifically, the first substrate 1 is made of silicon material with a thickness of 400-600 μm, and is used to provide mechanical support.

[0045] Specifically, the first buried oxide layer 2 is silicon dioxide with a thickness of 5 to 20 μm and a refractive index of 1.44 to 1.46, and the refractive index is adjusted by germanium or phosphorus doping.

[0046] Specifically, the silicon nitride intermediate layer 3 is made of silicon nitride with a thickness of 0.5 to 2 μm and a refractive index of 2.0 to 2.2, serving as a high refractive index light field confinement layer.

[0047] Specifically, the second buried oxide layer 4 is silicon dioxide with a thickness of 2-6 μm and a refractive index of 1.46-1.48, and the refractive index is adjusted by germanium or phosphorus doping.

[0048] Specifically, the second substrate 5 is made of silicon material with a thickness of 0.1 to 1 μm, and is used to fabricate silicon-based photonic devices.

[0049] In this structure, a high-refractive-index silicon nitride intermediate layer 3 is introduced to form a gradient refractive index distribution. The silicon nitride intermediate layer 3 serves as an optical field enhancement layer, which more effectively confines light energy to the waveguide core region. The first buried oxide layer 2 and the second buried oxide layer 4 have different refractive indices and thicknesses. The asymmetric buried oxide layer and the silicon nitride intermediate layer 3 form a gradual change in refractive index, reducing interface reflection and mode loss.

[0050] A method for fabricating silicon-on-insulator wafers, such as... Figure 2 and Figure 3 As shown, the method includes the following steps: providing a first substrate 1, growing a first buried oxide layer 2 on the first substrate 1; growing a silicon nitride intermediate layer 3 on the first buried oxide layer 2; providing a second substrate 5, growing a second buried oxide layer 4 on the second substrate 5; bonding the second buried oxide layer 4 to the silicon nitride intermediate layer 3; and thinning the second substrate 5.

[0051] S1. Provide a first substrate 1, and grow a first buried oxide layer 2 on the first substrate 1;

[0052] A double-sided polished silicon wafer was selected as the first substrate 1 and subjected to standard RCA cleaning to ensure the cleanliness of the surface of the first substrate 1. The RCA cleaning process is existing technology, and the specific process will not be described in detail here. The thickness of the first substrate 1 is 400-600 μm.

[0053] A silicon dioxide layer with a thickness of 5 to 20 μm is grown on the first substrate 1 by thermal oxidation or chemical vapor deposition as the first buried oxide layer 2. During the growth process, the refractive index of the first buried oxide layer 2 is adjusted by germanium or phosphorus doping, and its refractive index is 1.44 to 1.46.

[0054] S2. A silicon nitride intermediate layer 3 is grown on the first buried oxide layer 2;

[0055] A silicon nitride intermediate layer 3 with a thickness of 0.5–2 μm and a refractive index of 2.0–2.2 is deposited and grown on the side of the first buried oxide layer 2 away from the first substrate 1 by plasma-enhanced chemical vapor deposition.

[0056] S3. Provide a second substrate 5, and grow a second buried oxide layer 4 on the second substrate 5;

[0057] Another silicon wafer with double-sided polishing was selected as the second substrate 5, and standard RCA cleaning was performed to ensure the cleanliness of the surface of the second substrate 5.

[0058] A silicon dioxide layer with a thickness of 2 to 6 μm is grown on the second substrate 5 as a second buried oxide layer 4 by thermal oxidation or chemical vapor deposition. During the growth process, the refractive index of the second buried oxide layer 4 is adjusted by germanium or phosphorus doping, and its refractive index is 1.46 to 1.48.

[0059] S4. Bond the second buried oxide layer 4 to the silicon nitride intermediate layer 3;

[0060] S41. Clean and activate the silicon nitride intermediate layer 3 and the second buried oxide layer 4;

[0061] The first substrate 1 with the first buried oxide layer 2 and the silicon nitride intermediate layer 3 and the second substrate 5 with the second buried oxide layer 4 are cleaned and polished, and then immersed in an alcohol solution such as isopropanol for surface activation treatment, so that the side of the silicon nitride intermediate layer 3 away from the first buried oxide layer 2 and the side of the second buried oxide layer 4 away from the second substrate 5 are hydrolyzed to form Si-OH bonds.

[0062] S42. The activated silicon nitride intermediate layer 3 and the second buried oxide layer 4 are bonded together for pre-bonding.

[0063] The activated silicon nitride intermediate layer 3, the side away from the first buried oxide layer 2, and the side of the second buried oxide layer 4, the side away from the second substrate 5, are bonded together in a clean environment and heated to a temperature of 110–150°C to form Si-OH+Si-OH bonds between them for pre-bonding.

[0064] S43. The pre-bonded structure is subjected to high-temperature annealing in an oxygen- or nitrogen-containing atmosphere to complete the bonding.

[0065] The pre-bonded multilayer structure is placed in an annealing furnace and annealed at high temperature in an oxygen- or nitrogen-containing atmosphere at 800–1000°C to form strong Si-O-Si chemical bonds and complete permanent bonding.

[0066] S5. Thin the second substrate 5.

[0067] The bonded second substrate 5 is thinned using etching, polishing, or smart stripping techniques, resulting in a thickness of 0.1–1 μm.

[0068] Example 1: A method for fabricating silicon-on-insulator wafers, comprising the following steps:

[0069] S1. Provide a first substrate 1, and grow a first buried oxide layer 2 on the first substrate 1;

[0070] A double-sided polished silicon wafer was selected as the first substrate 1 and subjected to standard RCA cleaning. The thickness of the first substrate 1 was 400 μm.

[0071] A silicon dioxide layer with a thickness of 5 μm was grown on the first substrate 1 by thermal oxidation as the first buried oxide layer 2. During the growth process, the refractive index of the first buried oxide layer 2 was adjusted by germanium doping, and its refractive index was 1.44.

[0072] S2. A silicon nitride intermediate layer 3 is grown on the first buried oxide layer 2;

[0073] A silicon nitride intermediate layer 3 with a thickness of 0.5 μm and a refractive index of 2.0 is deposited and grown on the side of the first buried oxide layer 2 away from the first substrate 1 by plasma-enhanced chemical vapor deposition.

[0074] S3. Provide a second substrate 5, and grow a second buried oxide layer 4 on the second substrate 5;

[0075] Another double-polished silicon wafer was selected as the second substrate 5 and subjected to standard RCA cleaning.

[0076] A silicon dioxide layer with a thickness of 2 μm was grown on the second substrate 5 as the second buried oxide layer 4 by thermal oxidation. During the growth process, the refractive index of the second buried oxide layer 4 was adjusted by germanium doping, and its refractive index was 1.46.

[0077] S4. Bond the second buried oxide layer 4 to the silicon nitride intermediate layer 3;

[0078] S41. Clean and activate the silicon nitride intermediate layer 3 and the second buried oxide layer 4;

[0079] The first substrate 1 with the first buried oxide layer 2 and the silicon nitride intermediate layer 3 and the second substrate 5 with the second buried oxide layer 4 are cleaned and polished, and then immersed in isopropanol for surface activation treatment, so that the side of the silicon nitride intermediate layer 3 away from the first buried oxide layer 2 and the side of the second buried oxide layer 4 away from the second substrate 5 are hydrolyzed to form Si-OH bonds.

[0080] S42. The activated silicon nitride intermediate layer 3 and the second buried oxide layer 4 are bonded together for pre-bonding.

[0081] The activated silicon nitride intermediate layer 3, the side away from the first buried oxide layer 2, and the side of the second buried oxide layer 4, the side away from the second substrate 5, are bonded together in a clean environment and heated to 110°C to form Si-OH+Si-OH bonds between them for pre-bonding.

[0082] S43. The pre-bonded structure is annealed at high temperature in an oxygen-containing atmosphere to complete the bonding.

[0083] The pre-bonded multilayer structure is placed in an annealing furnace and annealed at high temperature in an oxygen-containing atmosphere at 800°C to form strong Si-O-Si chemical bonds, thus completing the permanent bonding.

[0084] S5. Thin the second substrate 5.

[0085] The second substrate 5 after bonding was thinned using etching technology, and the thickness of the second substrate 5 after thinning was 0.1 μm.

[0086] Example 2: A method for fabricating a silicon-on-insulator wafer, comprising the following steps:

[0087] S1. Provide a first substrate 1, and grow a first buried oxide layer 2 on the first substrate 1;

[0088] A double-sided polished silicon wafer was selected as the first substrate 1 and subjected to standard RCA cleaning. The thickness of the first substrate 1 was 500 μm.

[0089] A silicon dioxide layer with a thickness of 15 μm was grown on the first substrate 1 by chemical vapor deposition as the first buried oxide layer 2. During the growth process, the refractive index of the first buried oxide layer 2 was adjusted by phosphorus doping, and its refractive index was 1.45.

[0090] S2. A silicon nitride intermediate layer 3 is grown on the first buried oxide layer 2;

[0091] A silicon nitride intermediate layer 3 with a thickness of 1 μm and a refractive index of 2.1 is deposited and grown on the side of the first buried oxide layer 2 away from the first substrate 1 by plasma-enhanced chemical vapor deposition.

[0092] S3. Provide a second substrate 5, and grow a second buried oxide layer 4 on the second substrate 5;

[0093] Another double-polished silicon wafer was selected as the second substrate 5 and subjected to standard RCA cleaning.

[0094] A silicon dioxide layer with a thickness of 4 μm was grown on the second substrate 5 as the second buried oxide layer 4 by chemical vapor deposition. During the growth process, the refractive index of the second buried oxide layer 4 was adjusted by phosphorus doping, and its refractive index was 1.47.

[0095] S4. Bond the second buried oxide layer 4 to the silicon nitride intermediate layer 3;

[0096] S41. Clean and activate the silicon nitride intermediate layer 3 and the second buried oxide layer 4;

[0097] The first substrate 1 with the first buried oxide layer 2 and the silicon nitride intermediate layer 3 and the second substrate 5 with the second buried oxide layer 4 are cleaned and polished, and then immersed in isopropanol for surface activation treatment, so that the side of the silicon nitride intermediate layer 3 away from the first buried oxide layer 2 and the side of the second buried oxide layer 4 away from the second substrate 5 are hydrolyzed to form Si-OH bonds.

[0098] S42. The activated silicon nitride intermediate layer 3 and the second buried oxide layer 4 are bonded together for pre-bonding.

[0099] The activated silicon nitride intermediate layer 3, the side away from the first buried oxide layer 2, and the side of the second buried oxide layer 4, the side away from the second substrate 5, are bonded together in a clean environment and heated to 130°C to form Si-OH+Si-OH bonds between them for pre-bonding.

[0100] S43. The pre-bonded structure is subjected to high-temperature annealing in a nitrogen-containing atmosphere to complete the bonding.

[0101] The pre-bonded multilayer structure is placed in an annealing furnace and annealed at a high temperature of 900°C in a nitrogen-containing atmosphere to form strong Si-O-Si chemical bonds, thus completing the permanent bonding.

[0102] S5. Thin the second substrate 5.

[0103] Polishing technology was used to thin the bonded second substrate 5, and the thickness of the second substrate 5 after thinning was 0.5 μm.

[0104] Example 3: A method for fabricating silicon-on-insulator wafers, comprising the following steps:

[0105] S1. Provide a first substrate 1, and grow a first buried oxide layer 2 on the first substrate 1;

[0106] A double-sided polished silicon wafer was selected as the first substrate 1 and subjected to standard RCA cleaning. The thickness of the first substrate 1 was 600 μm.

[0107] A silicon dioxide layer with a thickness of 20 μm was grown on the first substrate 1 by chemical vapor deposition as the first buried oxide layer 2. During the growth process, the refractive index of the first buried oxide layer 2 was adjusted by germanium doping, and its refractive index was 1.46.

[0108] S2. A silicon nitride intermediate layer 3 is grown on the first buried oxide layer 2;

[0109] A silicon nitride intermediate layer 3 with a thickness of 2 μm and a refractive index of 2.2 is deposited and grown on the side of the first buried oxide layer 2 away from the first substrate 1 by plasma-enhanced chemical vapor deposition.

[0110] S3. Provide a second substrate 5, and grow a second buried oxide layer 4 on the second substrate 5;

[0111] Another double-polished silicon wafer was selected as the second substrate 5 and subjected to standard RCA cleaning.

[0112] A silicon dioxide layer with a thickness of 6 μm was grown on the second substrate 5 as the second buried oxide layer 4 by chemical vapor deposition. During the growth process, the refractive index of the second buried oxide layer 4 was adjusted by germanium doping, and its refractive index was 1.48.

[0113] S4. Bond the second buried oxide layer 4 to the silicon nitride intermediate layer 3;

[0114] S41. Clean and activate the silicon nitride intermediate layer 3 and the second buried oxide layer 4;

[0115] The first substrate 1 with the first buried oxide layer 2 and the silicon nitride intermediate layer 3 and the second substrate 5 with the second buried oxide layer 4 are cleaned and polished, and then immersed in isopropanol for surface activation treatment, so that the side of the silicon nitride intermediate layer 3 away from the first buried oxide layer 2 and the side of the second buried oxide layer 4 away from the second substrate 5 are hydrolyzed to form Si-OH bonds.

[0116] S42. The activated silicon nitride intermediate layer 3 and the second buried oxide layer 4 are bonded together for pre-bonding.

[0117] The activated silicon nitride intermediate layer 3, the side away from the first buried oxide layer 2, and the side of the second buried oxide layer 4, the side away from the second substrate 5, are bonded together in a clean environment and heated to 150°C to form Si-OH+Si-OH bonds between them for pre-bonding.

[0118] S43. The pre-bonded structure is annealed at high temperature in an oxygen-containing atmosphere to complete the bonding.

[0119] The pre-bonded multilayer structure is placed in an annealing furnace and annealed at high temperature in an oxygen-containing atmosphere at 1000°C to form strong Si-O-Si chemical bonds, thus completing the permanent bonding.

[0120] S5. Thin the second substrate 5.

[0121] The bonded second substrate 5 is thinned using intelligent stripping technology, and the thickness of the second substrate 5 after thinning is 1 μm.

[0122] The advantages and positive effects of this invention are:

[0123] 1. Enhanced optical field confinement: The high-refractive-index silicon nitride interlayer and the upper and lower buried oxide layers form a significant refractive index difference, which more tightly confines the light energy to the core region of the waveguide and effectively reduces radiation loss.

[0124] 2. Wideband performance optimization: The asymmetric gradient refractive index design enables optimized mode matching and coupling for wideband optical signals from visible light to near-infrared, solving the problem of poor adaptability of a single structure to different wavelengths.

[0125] 3. Process Compatibility and Reliability: All fabrication steps utilize mature semiconductor manufacturing processes, fully compatible with standard CMOS production lines, facilitating large-scale, low-cost manufacturing. The bonding interface is formed through chemical bonding, exhibiting high mechanical strength and good thermal stability.

[0126] 4. Novel structure and improved performance: Compared with the traditional double-layer buried oxide layer structure, the multi-layer gradient refractive index structure of this invention provides a more flexible means of optical field control and significantly improves performance.

[0127] The embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. It should be noted that implementations not illustrated or described in the drawings or the main text of the specification are forms known to those skilled in the art and have not been described in detail. Furthermore, the definitions of the various components described above are not limited to the specific structures, shapes, or methods mentioned in the embodiments, and those skilled in the art can easily modify or substitute them.

[0128] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made in accordance with the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A silicon-on-insulator wafer, characterized in that, include: First substrate; A first buried oxide layer is disposed on the first substrate; A silicon nitride intermediate layer is disposed on the first buried oxide layer; The second buried oxide layer is disposed on the silicon nitride intermediate layer; The second substrate is disposed on the second buried oxide layer.

2. The silicon-on-insulator wafer according to claim 1, characterized in that: The first buried oxide layer has a refractive index of 1.44 to 1.46 and a thickness of 5 to 20 μm.

3. A silicon-on-insulator wafer according to claim 1 or 2, characterized in that: The silicon nitride interlayer has a refractive index of 2.0 to 2.2 and a thickness of 0.5 to 2 μm.

4. A silicon-on-insulator wafer according to claim 1, characterized in that: The refractive index of the second buried oxide layer is 1.46 to 1.48, and the thickness is 2 to 6 μm.

5. A silicon-on-insulator wafer according to any one of claims 1-2 and 4, characterized in that: The thickness of the first substrate is 400–600 μm, and the thickness of the second substrate is 0.1–1 μm.

6. A method for fabricating a silicon-on-insulator wafer, characterized in that, Includes the following steps: A first substrate is provided, and a first buried oxide layer is grown on the first substrate; A silicon nitride intermediate layer is grown on the first buried oxide layer; A second substrate is provided, and a second buried oxide layer is grown on the second substrate; The second buried oxide layer is bonded to the silicon nitride interlayer; The second substrate is then thinned.

7. The method for fabricating a silicon-on-insulator wafer according to claim 6, characterized in that: The refractive index of the first and second buried oxide layers is adjusted by doping.

8. A method for fabricating a silicon-on-insulator wafer according to claim 6 or 7, characterized in that: The first and second buried oxide layers are formed by thermal oxidation or chemical vapor deposition.

9. The method for fabricating a silicon-on-insulator wafer according to claim 6, characterized in that: The silicon nitride intermediate layer is formed by plasma-enhanced chemical vapor deposition.

10. A method for fabricating a silicon-on-insulator wafer according to any one of claims 6-7 and 9, characterized in that, The step of bonding the second buried oxide layer to the silicon nitride interlayer includes the following steps: Clean and activate the silicon nitride intermediate layer and the second buried oxide layer; The activated silicon nitride intermediate layer and the second buried oxide layer are bonded together for pre-bonding. The pre-bonded structure is annealed at high temperature in an oxygen- or nitrogen-containing atmosphere to complete the bonding.

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