Composite substrate, semiconductor wafer, preparation method and semiconductor device

Abstract

The invention relates to the technical field of semiconductor manufacturing, in particular to a composite substrate, a semiconductor wafer, a preparation method and a semiconductor device. The composite substrate comprises a first substrate, wherein the first substrate comprises an aluminum nitride layer; a second substrate, wherein the second substrate is a sapphire substrate; the bonding layer is positioned between the first substrate and the second substrate; and the thickness h1 of the first substrate is greater than or equal to the thickness h2 of the second substrate. Through the design of the composite substrate, the uniformity of the epitaxial wavelength can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor, in particular to a composite substrate, a semiconductor wafer and a preparation method, and a semiconductor device. BACKGROUND

[0002] In the field of semiconductor devices, especially in the preparation of optoelectronic devices, the selection of the substrate and the epitaxial layer growth process play a decisive role in the performance of the device. At present, the substrate of many semiconductor devices uses sapphire (Al2O3) as the base, and an epitaxial layer is grown on its surface by metal organic chemical vapor deposition (MOCVD) method to prepare it. This process is widely used because of its strong controllability, suitability for mass production, and other characteristics.

[0003] However, in the prior art, the epitaxial layer grown on the sapphire wafer always has the problem of poor uniformity of the epitaxial wavelength. Therefore, how to improve the uniformity of the epitaxial wavelength is still a difficult problem for technical personnel to solve. SUMMARY

[0004] The embodiments of the present application provide a composite substrate, a semiconductor wafer and a preparation method, and a semiconductor device, which can solve at least one problem in the background art to effectively improve the symmetric uniformity of the epitaxial wavelength.

[0005] In a first aspect, the embodiments of the present application provide a composite substrate, comprising a first substrate, a second substrate and a bonding layer, wherein the first substrate comprises an aluminum nitride layer; the second substrate is a sapphire substrate; the bonding layer is located between the first substrate and the second substrate; the thickness h1 of the first substrate is greater than or equal to the thickness h2 of the second substrate.

[0006] In a second aspect, the embodiments of the present application provide a semiconductor wafer, comprising a composite substrate as described in the first aspect above, and an epitaxial layer on the second substrate.

[0007] In a third aspect, the embodiments of the present application provide a preparation method of a semiconductor wafer, comprising the following steps: providing a first substrate, wherein the first substrate comprises an aluminum nitride layer; forming a bonding layer on the first substrate; bonding a second substrate on the bonding layer, wherein the second substrate is a sapphire substrate; the thickness h1 of the first substrate is greater than or equal to the thickness h2 of the second substrate; growing an epitaxial layer on the second substrate; stripping the first substrate by a debonding process.

[0008] In a fourth aspect, the embodiments of the present application further provide a semiconductor device, comprising a composite substrate provided by the first aspect of the embodiments above, and an epitaxial layer on the second substrate, or a semiconductor wafer provided by the second aspect of the embodiments above, or a semiconductor wafer prepared by the third aspect of the embodiments above.

[0009] The composite substrate provided by the present application can effectively improve the uniformity of the epitaxial wavelength on the composite substrate by designing the first substrate and the second substrate, thereby improving the consistency of light emission when the composite substrate is applied to epitaxial growth.

[0010] Other features and advantages of the present application will be described in the following description, and some will become apparent from the description, or will be understood from the practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0012] Figure 1 is a cross-sectional view of a composite substrate provided by an embodiment of the present application; Figure 2 is a cross-sectional view of a semiconductor wafer provided by an embodiment of the present application; Figure 3 is a flow chart of a preparation method of a semiconductor wafer provided by an embodiment of the present application; Figure 4 、 Figure 5 is a structural process diagram of the preparation method of the semiconductor wafer provided by an embodiment of the present application.

[0013] Reference signs: 10, first substrate; 20, bonding layer; 30, second substrate; 40, epitaxial layer. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be described clearly and completely below in combination with the drawings of the embodiments of the present application. The technical features designed in different embodiments of the present application can be combined with each other as long as they do not conflict with each other.

[0015] It should also be noted that the structural schematic diagram provided by the present application is to more clearly express the structural features of the composite substrate, but is not made in proportion.

[0016] The embodiment of the present application provides a composite substrate, which comprises: a first substrate 10, the first substrate 10 comprising an aluminum nitride layer; a second substrate 30, the second substrate 30 being a sapphire substrate; a bonding layer 20 between the first substrate 10 and the second substrate 30; the thickness h1 of the first substrate 10 being greater than or equal to the thickness h2 of the second substrate 30. Through the above arrangement, the problem of poor wavelength uniformity of the chip can be effectively solved, and the subsequent chip thinning cost can be significantly reduced.

[0017] In an embodiment, the thickness h1 of the first substrate 10 is between 300-1500 μm, or the thickness h1 of the first substrate 10 is between 300-800 μm.

[0018] In an embodiment, the thickness h2 of the second substrate 30 is between 50-500 μm, or the thickness h2 of the second substrate 30 is between 50-300 μm.

[0019] In an embodiment, the thickness h3 of the bonding layer 20 is between 0.1-10 μm, and the bonding layer 20 comprises one or more layers of SiO2, AlN, Al2O3, Ga2O3.

[0020] In an embodiment, the thermal conductivity of the first substrate 10 is greater than or equal to 170 W / m·K. That is, the high thermal conductivity of the first substrate 10 is effectively utilized to reduce the temperature gradient from the root, and further improve the wavelength uniformity.

[0021] In an embodiment, the surface roughness Ra of the first substrate 10 on the side close to the bonding layer 20 is less than 100 nm, and the surface roughness Ra of the second substrate 30 on the side away from the bonding layer 20 is less than or equal to 0.2 nm.

[0022] The embodiment of the present application also provides a semiconductor wafer, which comprises the composite substrate according to any one of the above, and an epitaxial layer 40 on the second substrate 30.

[0023] The embodiment of the present application also provides a preparation method of a semiconductor wafer, which comprises the following steps: providing a first substrate 10, the first substrate 10 comprising an aluminum nitride layer; forming a bonding layer 20 on the first substrate 10; bonding a second substrate 30 on the bonding layer 20, the second substrate 30 being a sapphire substrate; the thickness h1 of the first substrate 10 being greater than or equal to the thickness h2 of the second substrate 30; growing an epitaxial layer 40 on the second substrate 30; stripping the first substrate 10 through a debonding process.

[0024] The present invention also provides a semiconductor device comprising a composite substrate as described in any of the above embodiments and an epitaxial layer 40 located on the second substrate 30, or a semiconductor wafer as described in the above embodiments, or a semiconductor wafer fabrication method as described in the above embodiments.

[0025] In one embodiment, the standard deviation of the emission wavelength of the epitaxial layer 40 is less than or equal to 1 nm.

[0026] The technical solution of the present invention will now be described and explained in detail through various specific embodiments and accompanying drawings.

[0027] Example 1 In traditional substrate structures, the typical process involves directly growing epitaxial structures on a sapphire substrate. Furthermore, to meet the requirements of device packaging or subsequent processes (such as reducing thermal resistance and improving heat dissipation), the sapphire substrate usually needs to be thinned. However, this process has at least the following problems: Firstly, the uniformity of the epitaxial wavelength is poor. Specifically, when growing the epitaxial layer 40 directly on the sapphire substrate, the poor thermal conductivity of the sapphire substrate itself negatively impacts the growth of the epitaxial layer 40. During growth, the nucleation and growth rate of the epitaxial material vary due to different local temperature conditions on the substrate, resulting in uneven thickness and composition distribution of the epitaxial layer 40. This leads to poor overall epitaxial wavelength uniformity, severely affecting the color consistency of semiconductor devices (such as LEDs). Secondly, sapphire has high hardness, making it difficult to machine. The thinning process requires multiple steps, including rough grinding, fine grinding, and polishing. Each step requires precise control of process parameters (such as polishing slurry particle size, polishing pressure, and rotation speed) to avoid substrate cracking or the formation of new defects. Furthermore, since the initial thickness of sapphire substrates is usually quite large, it takes a lot of time and effort to reduce them to the target thickness, which leads to a longer process cycle, reduced production efficiency, and increased production costs, which is not conducive to large-scale industrial production.

[0028] Please see Figure 1 , Figure 1 This is a cross-sectional schematic diagram of the composite substrate provided in Embodiment 1 of the present invention. To address the above-mentioned problems, Embodiment 1 of the present invention provides a composite substrate that improves the uniformity of epitaxial wavelength through its design. Specifically, the composite substrate includes at least a first substrate 10, a second substrate 30, and a bonding layer 20. The size of the composite substrate is between 2 and 12 inches.

[0029] The first substrate 10 includes an aluminum nitride layer, which provides stable support for the subsequent formation of the bonding layer 20 and the growth of the second substrate 30. Of course, the first substrate 10 may also include other layer structures. In particular, the aluminum nitride layer has high thermal conductivity, more than five times that of conventional sapphire substrates. Using it as the first substrate 10 can quickly dissipate localized heat generated during epitaxial growth, significantly reducing the temperature gradient on the surface of the composite substrate, thereby improving the wavelength uniformity of the epitaxial layer 40. Simultaneously, the aluminum nitride layer has relatively low hardness, which can greatly improve the efficiency of subsequent mechanical polishing.

[0030] The second substrate 30 is a sapphire substrate. Due to its excellent chemical and thermal stability, sapphire substrates can withstand harsh process environments such as high temperatures and acids / alkalis during subsequent semiconductor device fabrication, effectively ensuring the quality of the functional layers grown on its surface. Furthermore, the fabrication process is mature and low-cost, and its lattice constant matches the GaN epitaxial layer 40 well, reducing dislocation density in the epitaxial layer 40 and improving the performance of the semiconductor device. Therefore, it is one of the important substrate choices for semiconductor devices. Optionally, in the composite substrate used for LED chips, the sapphire substrate can be a patterned substrate to effectively improve the light extraction efficiency of the semiconductor device. The specific design should be tailored to actual needs, and this embodiment does not impose any limitations.

[0031] In this embodiment, the thickness h1 of the first substrate 10 is greater than or equal to the thickness h2 of the second substrate 30. Preferably, h1 is 1.2 to 2 times the thickness of h2. By ensuring h1 ≥ h2, it avoids the situation where h1 is too thin relative to h2, which could lead to warping due to insufficient support during high-temperature epitaxy, affecting the epitaxial quality. This ensures the support strength of the first substrate 10, preventing breakage during bonding and providing sufficient processing allowance for subsequent mechanical polishing / chemical etching. It also ensures that the first substrate 10 has sufficient thermal conductivity to quickly dissipate epitaxial heat, reduce the temperature gradient, and avoid material waste caused by excessive thickness. Furthermore, the thinner thickness of h2 relative to h1 allows the thinner sapphire substrate to shorten the heat transfer path from the epitaxial layer 40 to the first substrate 10, preventing heat accumulation.

[0032] The bonding layer 20 is located between the first substrate 10 and the second substrate 30, serving as a buffer and connection. It ensures the support of the first substrate 10 for the entire structure and provides a suitable interface environment for the growth of the second substrate 30. Simultaneously, it effectively buffers thermal stress and prevents cracking of the epitaxial layer 40. As an example, the bonding layer 20 may include one or more layers of SiO2, AlN, Al2O3, and Ga2O3, the specific composition depending on the bonding temperature and debonding method. In this embodiment, a material with high thermal conductivity is preferred to reduce thermal resistance. It should be understood that the bonding layer 20 may also use other materials capable of bonding between the first substrate 10 and the second substrate 30, all of which fall within the scope of this invention.

[0033] Preferably, the thickness h3 of the bonding layer 20 is between 0.1 and 10 μm. For a single-layer film, the thickness is preferably between 0.5 μm and 5 μm, such as 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, etc. For a multilayer composite film, the thickness of each layer needs to be allocated according to functional requirements. For example, in a composite structure of "SiO2 (1 μm) - AlN (2 μm)," the total thickness is 3 μm, which ensures bonding strength while avoiding thermal stress accumulation due to excessive thickness.

[0034] Based on the above, by bonding a first substrate 10 with higher thermal conductivity below the second substrate 30, the poor uniformity of the epitaxial wavelength caused by temperature differences during epitaxial growth due to the poor thermal conductivity of sapphire can be effectively avoided, thus significantly improving the wavelength uniformity of the composite substrate during the epitaxial process. Simultaneously, due to the composite design of the first substrate 10 and the second substrate 30 having a certain thickness, the second substrate 30 does not require thinning or requires only minimal thinning (for example, traditional sapphire single substrate thinning requires removing 650 μm, while this embodiment only requires removing 0~200 μm), thereby effectively eliminating or reducing thinning costs and improving thinning efficiency.

[0035] Preferably, the thickness h1 of the first substrate 10 is between 300 and 1500 μm, more preferably between 300 and 800 μm; for example, 300 μm, 500 μm, 600 μm, 800 μm, 1000 μm, 1200 μm, 1500 μm, etc. By limiting the thickness range of h1 as described above, the epitaxial heat can be quickly dissipated through the high thermal conductivity of aluminum nitride (temperature gradient ≤ 3℃), while avoiding material waste and increased debonding time caused by excessive thickness.

[0036] Preferably, the thickness h2 of the second substrate 30 is between 50 and 500 μm, more preferably between 50 and 300 μm; for example, 50 μm, 60 μm, 80 μm, 100 μm, 120 μm, 150 μm, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, etc. By limiting the thickness range of h2 as described above, subsequent thinning losses can be reduced, and breakage during bonding due to excessive thinness (<50 μm) can be avoided, while also meeting the lattice matching requirements of the epitaxial layer 40.

[0037] It should be understood that the specific thickness design of the first substrate 10 thickness h1 and the second substrate 30 thickness h2 can be reasonably selected according to the actual composite substrate size, and this embodiment does not limit it here.

[0038] Furthermore, the thermal conductivity of the first substrate 10 is greater than or equal to 170 W / m·K. In specific implementations, the first substrate 10 may contain only an aluminum nitride layer, or it may contain other functional layers besides the aluminum nitride layer. Regardless of whether it is a single-layer or multi-layer structure, by limiting the thermal conductivity of the first substrate 10, its high thermal conductivity can be utilized to fundamentally reduce the temperature gradient (≤3℃) and improve wavelength uniformity. In this embodiment, the first substrate 10 preferably uses a high-purity aluminum nitride layer, and satisfies a thermal conductivity greater than or equal to 170 W / m·K.

[0039] Optionally, the surface roughness Ra of the first substrate 10 on the side near the bonding layer 20 is less than 100 nm to ensure a stable bonding interface with the bonding layer 20 and avoid affecting the bonding effect. Specifically, a double-sided polishing machine can be used for rough polishing to reduce the initial roughness to a certain range, followed by a chemical mechanical polishing (CMP) machine for fine polishing to reduce the roughness to Ra < 100 nm.

[0040] Optionally, the surface roughness Ra of the side of the second substrate 30 away from the bonding layer 20 is less than or equal to 0.2 nm. By limiting the surface roughness of the side of the second substrate 30 away from the bonding layer 20, dislocation defects during epitaxial growth can be reduced, while wavelength uniformity can also be effectively improved. Specifically, a suitable polishing method can be used to reduce the roughness; precision chemical mechanical polishing (CMP) can be used to reduce the roughness to Ra ≤ 0.2 nm.

[0041] The composite substrate design described in Example 1 effectively solves the problem of poor chip wavelength uniformity and significantly reduces the cost of subsequent chip thinning. Furthermore, this composite substrate structure design exhibits strong corrosion compatibility of the bonding layer (e.g., if SiO2 is used, it can be rapidly removed by HF solution), making it suitable for subsequent low-cost debonding techniques.

[0042] Example 2 Based on Embodiment 1, this invention also provides a semiconductor wafer. Please refer to [link to Embodiment 1]. Figure 2 The semiconductor wafer includes a composite substrate as described in Embodiment 1 above, and also includes an epitaxial layer 40 located on the second substrate 30.

[0043] In a specific implementation, when the semiconductor wafer is used to fabricate an LED chip, the epitaxial layer 40 sequentially includes an N-side layer, a P-side layer, and an active layer located between them, for example, by MOCVD (metal-organic chemical vapor deposition) of semiconductor materials. It should be understood that, depending on the functional requirements of the actual semiconductor device, the epitaxial layer 40 can also be other layer structures or contain other functional layer structures; this embodiment does not limit this.

[0044] The semiconductor wafer in this second embodiment can be directly used to fabricate high-brightness GaN-based LED chips. This not only significantly reduces the cost of subsequent chip thinning but also improves the uniformity of the epitaxial wavelength of GaN-based LEDs, making it particularly suitable for scenarios with stringent requirements for wavelength uniformity (such as Mini LED backlighting and automotive lighting).

[0045] Example 3 Embodiment 3 of the present invention also provides a method for preparing a semiconductor wafer; please refer to [link to embodiment 3]. Figure 3 This includes the following steps: A first substrate 10 is provided, the first substrate 10 including an aluminum nitride layer. Preferably, the aluminum nitride layer is a pure aluminum nitride (AlN) ceramic substrate as the first substrate 10, ensuring a thermal conductivity ≥170W / m. K. Wherein, the thickness h1 of the first substrate 10 is between 300 and 1500 μm. Preferably, it further includes chemical mechanical polishing (CMP) of the bonding surface of the first substrate 10 to be bonded, controlling its surface roughness Ra to be less than 100 nm, then removing surface abrasive residue by ultrasonic cleaning, and using plasma cleaning (O2 / N2 mixed gas) to remove organic impurities and activate the surface to increase surface adhesion.

[0046] A bonding layer 20 is formed on the first substrate 10; wherein the bonding layer 20 is selected from one or more of SiO2, AlN, Al2O3, and Ga2O3 thin films, and its thickness h3 is between 0.1 and 10 μm.

[0047] A second substrate 30 is bonded onto the bonding layer 20 to form a composite substrate; the second substrate 30 is a sapphire substrate; wherein the thickness h1 of the first substrate 10 is greater than or equal to the thickness h2 of the second substrate 30. In this embodiment, the thickness of the second substrate 30 is preferably between 50 and 500 μm. Simultaneously, the side of the second substrate 30 near the bonding layer 20 is polished until its surface roughness Ra is less than or equal to 0.2 nm. In this embodiment, the bonding layer 20 is preferably made of SiO2, and the first substrate 10 and the second substrate 30 can be bonded using a vacuum hot-press bonding process. The preferred bonding conditions are a temperature between 200°C and 1000°C, a pressure between 10 MPa and 300 MPa, and a vacuum degree ≤10. -3 The bonding time is approximately 10-200 minutes. Specifically, it utilizes the softening and flow of SiO2 at high temperature to fill interfacial gaps, and high pressure promotes atomic diffusion to form stable covalent bonds. Furthermore, this bonding process is compatible with MOCVD equipment, requiring no additional equipment and effectively reducing costs.

[0048] Please see Figure 4An epitaxial layer 40 is grown on the second substrate 30. Specifically, the epitaxial layer 40 with a multilayer structure can be grown using MOCVD epitaxial growth process. In this embodiment, the epitaxial layer 40 is preferably a GaN-based multilayer structure. Based on the high thermal conductivity of aluminum nitride used in the first substrate 10 of the composite substrate, the temperature gradient can be effectively controlled within ≤3℃ and the wavelength uniformity deviation can be ≤0.8nm during the epitaxial process, thereby effectively improving the performance of the epitaxial layer.

[0049] Please see Figure 5 The first substrate 10 is peeled off using a debonding process. Specifically, the first substrate 10 is peeled off by mechanical grinding (e.g., using a diamond grinding wheel) or chemical etching (e.g., using an HF / HNO3 mixture). Then, it is quickly removed from a high temperature of 300°C to 600°C and placed in a nitrogen atmosphere to achieve thermal shock debonding. Since the first substrate 10 is made of aluminum nitride, the debonding process takes ≤20 minutes, which can greatly improve the debonding speed.

[0050] Preferably, the first substrate 10 after stripping is subjected to high-temperature annealing (nitrogen atmosphere, heat preservation for 60 min) to release stress, and then the residual bonding layer 20 is removed by CMP polishing to restore the surface roughness Ra < 100 nm. It can be recycled ≥ 10 times, reducing material costs.

[0051] To effectively illustrate the advantages of the above-mentioned Example 3, the table below shows the key process parameters and performance indicators of Schemes 1 to 5 under different parameter conditions. Through the synergistic optimization of the composite substrate, it achieves the technical breakthrough of "wavelength uniformity ≤ 1nm and debonding time ≤ 20min", which is far superior to the data of 5.2nm wavelength uniformity and 65min thinning time obtained by the comparative achievement of traditional sapphire single substrate under the same conditions.

[0052]

[0053] Based on Schemes 1 to 5 in the table above and the comparison with traditional sapphire single substrates, we can see that: (1) In Schemes 1 to 5, the uniformity of all wavelengths is ≤1nm (minimum is 0.5nm), which is more than 80% higher than the 5.2nm of the traditional sapphire single substrate. This shows that the composite substrate structure with aluminum nitride layer as the first substrate can effectively reduce the temperature gradient during epitaxial growth, solve the problem of wavelength non-uniformity from the root, and improve the consistency of light emission when the composite substrate is applied to LED chips.

[0054] (2) In Schemes 1 to 5, the debonding time is ≤20min (the shortest is 10min), which is more than 3 times more efficient than the traditional sapphire thinning time of 65min. It can be seen that the low hardness of the aluminum nitride layer combined with the adaptive design of different bonding layer materials greatly reduces the process difficulty and time cost of debonding (cost reduction of 70%).

[0055] (3) In Scheme 1 to Scheme 5, the first substrate with different thicknesses from 300μm to 800μm, together with the corresponding bonding temperature, pressure and intermediate layer material, can be adapted to the wafer requirements of different sizes from 2 to 12 inches, especially to the substrate mass production requirements of large-size chips; and the bonding strength is ≥18MPa, which can stably support high-temperature epitaxial processes.

[0056] In summary, the innovative composite structure design of "a first substrate 10 with an aluminum nitride layer + a bonding layer 20 + a second substrate 30 using a sapphire substrate" adopted in Schemes 1 to 5 achieves significant improvements in wavelength uniformity, debonding efficiency, and structural adaptability, far surpassing traditional sapphire single substrates. Furthermore, the aforementioned performance improvements can be achieved by adjusting the thickness of the first substrate 10 to accommodate chips of different sizes, or by using different materials for the bonding layer 20, demonstrating strong versatility and flexible application.

[0057] Example 4 This fourth embodiment provides a semiconductor device, which includes a composite substrate as described in Embodiment 1 above, and an epitaxial layer 40 grown on the composite substrate to effectively improve the uniformity of the emission wavelength. The semiconductor device can be a light-emitting device with the epitaxial layer 40, such as a light-emitting diode or a semiconductor laser. Alternatively, the semiconductor device may utilize a semiconductor wafer as described in Embodiment 2 above or a semiconductor wafer fabrication method as described in Embodiment 3 above.

[0058] In one optional embodiment, the standard deviation of the emission wavelength of the epitaxial layer 40 is less than 1 nm. More preferably, the standard deviation of the emission wavelength of the epitaxial layer 40 is less than or equal to 0.5 nm. Through the above settings, the uniformity of the emission wavelength of the epitaxial layer can be effectively guaranteed, thereby effectively improving the optical efficiency and uniformity of the emitted light brightness of the semiconductor device.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite substrate, characterized in that, include: A first substrate, the first substrate comprising an aluminum nitride layer; The second substrate is a sapphire substrate; A bonding layer is located between the first substrate and the second substrate; The thickness h1 of the first substrate is greater than or equal to the thickness h2 of the second substrate.

2. The composite substrate according to claim 1, characterized in that: The thickness h1 of the first substrate is between 300 and 1500 μm, or the thickness h1 of the first substrate is between 300 and 800 μm.

3. The composite substrate according to claim 1, characterized in that: The thickness h2 of the second substrate is between 50 and 500 μm, or the thickness h2 of the second substrate is between 50 and 300 μm.

4. The composite substrate according to claim 1, characterized in that: The thickness h3 of the bonding layer is between 0.1 and 10 μm, and the bonding layer includes one or more layers of SiO2, AlN, Al2O3, and Ga2O3.

5. The composite substrate according to claim 1, characterized in that: The thermal conductivity of the first substrate is greater than or equal to 170 W / m·K.

6. The composite substrate according to claim 1, characterized in that: The surface roughness Ra of the first substrate on the side closer to the bonding layer is less than 100 nm, and the surface roughness Ra of the second substrate on the side farther from the bonding layer is less than or equal to 0.2 nm.

7. A semiconductor wafer, characterized in that: It includes a composite substrate as described in any one of claims 1 to 6, and an epitaxial layer located on the second substrate.

8. A method for fabricating a semiconductor wafer, characterized in that, Includes the following steps: A first substrate is provided, the first substrate comprising an aluminum nitride layer; A bonding layer is formed on the first substrate; A second substrate is formed by bonding on the bonding layer, the second substrate being a sapphire substrate; wherein the thickness h1 of the first substrate is greater than or equal to the thickness h2 of the second substrate; An epitaxial layer is grown on the second substrate; The first substrate is removed by a debonding process.

9. A semiconductor device, characterized in that: This includes using a composite substrate as described in any one of claims 1 to 6 and an epitaxial layer located on the second substrate, or using a semiconductor wafer as described in claim 7, or using a semiconductor wafer fabrication method as described in claim 8.

10. The semiconductor device according to claim 9, characterized in that: The standard deviation of the emission wavelength of the epitaxial layer is less than or equal to 1 nm.

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