Method for producing a single crystal substrate

Abstract

The present application provides a method for preparing a single crystal substrate, comprising the steps of: 1) providing a substrate, and forming a porous structure on the surface of the substrate; 2) depositing a barrier layer, the barrier layer covering the top surface of the porous structure and the inner surface of the porous structure; 3) removing the barrier layer on the top surface of the porous structure to expose the top surface of the porous structure; and 4) performing epitaxial growth of a single crystal layer on the porous structure and separating the substrate, wherein the single crystal layer grows from the top surface of the porous structure, and the barrier layer is used to inhibit the growth of the single crystal layer on the inner surface of the porous structure. By applying the porous structure, the epitaxially grown single crystal layer can form a weak connection with the substrate through the porous structure, so that the single crystal layer and the substrate have a higher separation yield.

Description

Technical Field

[0001] This invention belongs to the field of gallium nitride substrate manufacturing, and in particular relates to a method for preparing a single crystal substrate. Background Technology

[0002] Gallium nitride (GaN) and its alloys, representing third-generation semiconductor materials, have garnered significant international attention in the past decade. They possess numerous superior properties, including a large bandgap, high electron saturation drift velocity, low dielectric constant, good thermal conductivity, and structural stability, making them highly promising for applications in optoelectronics and microelectronics. In optoelectronics, the continuously tunable bandgap of Group III nitrides, ranging from 0.7 to 6.2 eV and covering the wavelengths from red to ultraviolet, allows for the fabrication of green, blue, and even ultraviolet light-emitting devices, as well as white light illumination. Furthermore, the recently emerging ultraviolet LEDs have demonstrated unique applications in screen printing, polymer curing, and environmental protection, greatly stimulating researchers' interest. GaN lasers also hold great promise in information storage and can be applied to various fields such as medical diagnostics, underwater exploration, and communications.

[0003] Fabricating bulk GaN single crystals is challenging, making it difficult to obtain large-size and high-quality GaN bulk single crystal substrates. Therefore, GaN epitaxial growth is typically performed using heteroepitaxial methods. However, both theoretical and experimental results demonstrate that using GaN as the substrate for homoepitaxial devices significantly improves device performance. Consequently, the fabrication of self-supporting GaN bulk single crystal substrates has become a focus of attention.

[0004] Currently, large-area GaN self-supporting substrates are typically obtained by vapor-phase growth of thick GaN films on heterogeneous substrates, followed by separation of the original heterogeneous substrates. Sapphire substrates are the most commonly used. To obtain a self-supporting substrate, the sapphire substrate must be removed. Sapphire is hard and chemically stable, making it difficult to remove by chemical etching or mechanical polishing. Currently, laser lift-off is commonly used to separate GaN and the sapphire substrate. However, laser lift-off technology is expensive; and during the laser lift-off process, the high-pressure gas generated after the high-temperature decomposition of GaN at the interface can easily damage the prepared GaN bulk single-crystal self-supporting substrate. This damage can range from generating numerous dislocations and microcracks on the GaN bulk single-crystal self-supporting substrate, affecting the quality of subsequent devices, to completely shattering the GaN bulk single-crystal self-supporting substrate, significantly reducing the yield.

[0005] In general, when heteroepitaxial growth is carried out, the thickness of heteroepitaxial gallium nitride is limited due to lattice mismatch and thermal mismatch. At the same time, the process of dissociating gallium nitride single crystals is quite difficult, which is particularly evident on large-size sapphire / gallium nitride thick film composite substrates (HVPE primary epitaxial wafers).

[0006] It should be noted that the above introduction to the technical background is only for the purpose of providing a clear and complete explanation of the technical solutions of this application and facilitating understanding by those skilled in the art. It should not be assumed that these technical solutions are known to those skilled in the art simply because they have been described in the background section of this application. Summary of the Invention

[0007] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for preparing a single crystal substrate, which solves the problems of limited thickness of heteroepitaxial gallium nitride single crystals and / or the high difficulty of dissociating gallium nitride single crystals in the prior art.

[0008] To achieve the above and other related objectives, the present invention provides a method for preparing a single-crystal substrate, the method comprising the steps of: 1) providing a substrate and forming a porous structure on the surface of the substrate; 2) depositing a barrier layer covering the top surface and the inner surface of the porous structure; 3) removing the barrier layer from the top surface of the porous structure to expose the top surface of the porous structure; 4) performing epitaxial growth of a single-crystal layer on the porous structure and separating the substrate, wherein the single-crystal layer grows from the top surface of the porous structure, and the barrier layer is used to inhibit the growth of the single-crystal layer on the inner surface of the porous structure.

[0009] Optionally, the pore size of each pore in the porous structure is in the nanometer range, and the spacing between two adjacent pores is in the nanometer range.

[0010] Optionally, the substrate is a sapphire substrate, and the porous structure includes a gallium nitride porous layer. The preparation of the gallium nitride porous layer includes the steps of: forming an n-type gallium nitride layer on the sapphire substrate by chemical vapor deposition; and forming multiple pores in the n-type gallium nitride layer by electrochemical etching to form the gallium nitride porous layer.

[0011] Optionally, each hole in the gallium nitride porous layer penetrates the gallium nitride porous layer, resulting in a weak connection between the gallium nitride porous layer and the sapphire substrate, which facilitates subsequent separation.

[0012] Optionally, the process for separating the substrate is self-separation or laser lift-off. The self-separation includes: when the single crystal layer is epitaxially grown to the self-separation thickness, the weak connection between the gallium nitride porous structure and the sapphire substrate breaks, resulting in self-separation. The laser lift-off includes: after the single crystal layer is epitaxially grown to a preset thickness, the gallium nitride porous structure is separated from the sapphire substrate by a laser lift-off process.

[0013] Optionally, the substrate is a sapphire substrate, and the porous structure includes a porous sapphire layer formed on the surface of the sapphire substrate.

[0014] Optionally, the top surface of the porous sapphire layer further includes a deposition buffer layer, which includes a low-temperature gallium nitride layer.

[0015] Optionally, the process for separating the substrate is self-separation or laser lift-off, wherein the self-separation includes: when the single crystal layer is epitaxially grown to a self-separation thickness, the single crystal layer and the porous sapphire layer undergo self-separation; the laser lift-off includes: when the single crystal layer is epitaxially grown to a preset thickness, the single crystal layer and the porous sapphire layer are separated by a laser lift-off process.

[0016] Optionally, the barrier layer is formed by a vapor deposition process, the barrier layer comprising one of silicon nitride, silicon oxide, and graphene, the vapor deposition process including atomic layer deposition.

[0017] Optionally, the single crystal layer is a gallium nitride single crystal. Based on the longitudinal (three-dimensional) epitaxial growth of gallium nitride on the top surface of the porous structure, voids are formed in the gallium nitride single crystal above each of the holes. At the same time, based on the lateral (two-dimensional) growth of gallium nitride, the width of the hole structure gradually decreases and the gallium nitride above the voids merges into a complete gallium nitride single crystal. This epitaxial growth method also helps to reduce the dislocation density of the gallium nitride single crystal.

[0018] Optionally, it also includes step 5), which involves epitaxially growing the single crystal layer to form a single crystal layer of the target thickness.

[0019] Optionally, it also includes step 6), polishing and chamfering both sides of the single crystal layer to obtain an Epi-ready single crystal layer surface.

[0020] As described above, the method for preparing the single-crystal substrate of the present invention has the following beneficial effects:

[0021] This invention utilizes a porous structure to enable the epitaxially grown single crystal layer to form a weak connection with the substrate, thereby achieving a higher separation yield between the single crystal layer and the substrate.

[0022] This invention deposits a barrier layer inside the pores, keeping each pore as a void during epitaxial growth, which greatly reduces the connection area between the single crystal layer and the substrate, making the separation between the single crystal layer and the substrate easier. Subsequently, grinding and polishing can be used to make the porous structure surface smooth, forming an Epi-ready single crystal layer surface.

[0023] This invention can obtain high-quality single crystal layers through two-dimensional and three-dimensional epitaxial growth of single crystal layers. Furthermore, epitaxial thickening can be performed after separation from the substrate, thereby overcoming the limitation on the thickness of single crystal layers caused by heteroepitaxial growth between the single crystal layer and the substrate, and obtaining high-quality single crystal substrates with the target thickness. Attached Figure Description

[0024] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the embodiments of this application and to illustrate the implementation of this application, together with the textual description, to explain the principles of this application. Obviously, the drawings described below are merely some embodiments of this application.

[0025] Figures 1 to 7 The diagram shows the structural schematics of each step in the preparation method of the single-crystal substrate according to Embodiment 1 of the present invention.

[0026] Figures 8-12 The diagram shows the structural schematics of each step in the preparation method of the single-crystal substrate according to Embodiment 2 of the present invention.

[0027] Component designation explanation

[0028] 101 substrate

[0029] 102 Porous Structure

[0030] 103 holes

[0031] 104 Barrier Layer

[0032] 105 Top surface of porous structure

[0033] 106 monocrystalline layer

[0034] 107 gaps

[0035] 201 Deposition Buffer Layer Detailed Implementation

[0036] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0037] It should be emphasized that the term "including / comprises" as used herein refers to the presence of a feature, whole, step, or component, but does not exclude the presence or addition of one or more other features, wholes, steps, or components.

[0038] Features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0039] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0040] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for devices in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or there may be one or more layers in between.

[0041] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0042] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0043] Example 1

[0044] like Figures 1 to 7 As shown, this embodiment provides a method for preparing a single-crystal substrate, the method comprising the following steps:

[0045] like Figure 1 As shown, step 1) is performed first, a substrate 101 is provided, and a porous structure 102 is formed on the surface of the substrate 101.

[0046] In one embodiment, the pore size of each pore 103 in the porous structure 102 is in the nanometer range, and the spacing between two adjacent pores 103 is in the nanometer range. For example, the pore size of each pore 103 in the porous structure 102 is 10–200 nanometers, and the spacing between two adjacent pores 103 is 10–200 nanometers. The pores 103 can be arranged in a periodic array or non-uniformly, etc.

[0047] In one embodiment, the substrate 101 is a sapphire substrate, and the porous structure 102 includes a gallium nitride porous layer, the fabrication of which includes the steps of:

[0048] Step 1-1): An n-type gallium nitride layer is formed on the sapphire substrate by chemical vapor deposition; for example, an n-type gallium nitride layer can be formed on the sapphire substrate by metal-organic chemical vapor deposition (MOCVD) or hydride vapor phase epitaxy (HVPE).

[0049] Steps 1-2) involve forming multiple pores 103 in the n-type gallium nitride layer using an electrochemical etching process to form the gallium nitride porous layer.

[0050] Of course, in other embodiments, the substrate 101 may also be made of other materials, such as silicon, silicon carbide, etc., and is not limited to the examples listed herein.

[0051] In one embodiment, each hole 103 in the gallium nitride porous layer penetrates the gallium nitride porous layer, resulting in a weak connection between the gallium nitride porous layer and the sapphire substrate, which facilitates subsequent separation.

[0052] In one embodiment, the total area of ​​the holes 103 accounts for 40% to 80% of the total area of ​​the n-type gallium nitride layer. The holes 103 can, on the one hand, reduce the connection area between the gallium nitride porous layer and the substrate 101, thereby forming a weak connection between the gallium nitride porous layer and the sapphire substrate; on the other hand, by forming a barrier layer 104 on the inner surface of the holes 103, the epitaxial growth of the single crystal layer 106 can include vertical growth, lateral growth, and merging processes, improving the growth quality of the single crystal layer 106.

[0053] like Figure 2 As shown, then step 2) is performed, depositing a barrier layer 104, which covers the top surface 105 of the porous structure 102 and the inner surface of the porous structure 102.

[0054] In one embodiment, the barrier layer 104 is formed by a vapor deposition process, including atomic layer deposition (ALD). ALD effectively prevents the growth of a single crystal layer 106 due to incomplete coverage of the inner wall of the hole 103, thus improving process stability. Of course, for larger holes 103, processes such as chemical vapor deposition can also be used to form the barrier layer 104. Furthermore, the barrier layer 104 can either completely fill the hole 103 or only cover the inner surface of the hole 103.

[0055] In one embodiment, the barrier layer 104 may be silicon nitride.

[0056] In another embodiment, the barrier layer 104 may also be silicon oxide.

[0057] In yet another embodiment, the barrier layer 104 may also be graphene.

[0058] The barrier layer 104 is used to suppress the growth of the single crystal layer 106 in the hole 103. It can be selected from materials such as gallium nitride, which are difficult for the single crystal layer 106 to nucleate and grow on its surface, and is not limited to the examples listed above.

[0059] like Figure 3 As shown, then step 3) is performed to remove the barrier layer 104 on the top surface 105 of the porous structure 102 to expose the top surface 105 of the porous structure 102.

[0060] For example, the barrier layer 104 on the top surface 105 of the porous structure 102 can be removed by chemical mechanical polishing (CMP) to obtain a high-quality top surface 105 of the porous structure 102, thereby improving the growth quality of the subsequent single crystal layer 106.

[0061] like Figures 4-6 As shown, step 4) is then performed, in which a single crystal layer 106 is epitaxially grown on the porous structure 102 and the substrate 101 is separated. The single crystal layer 106 grows from the top surface 105 of the porous structure 102, and the barrier layer 104 is used to suppress the growth of the single crystal layer 106 on the inner surface of the porous structure 102.

[0062] In one embodiment, the single crystal layer 106 is a gallium nitride single crystal. Based on the epitaxial growth of gallium nitride on the top surface 105 of the porous structure 102, voids 107 are formed in the gallium nitride single crystal above each of the voids 103. At the same time, based on the lateral growth of gallium nitride, the width of the void 107 structure gradually decreases and the gallium nitride above the voids 107 merges into a complete gallium nitride single crystal. This epitaxial growth method also helps to reduce the dislocation density of the gallium nitride single crystal.

[0063] As an example, the process for separating the substrate 101 is self-separation or laser ablation.

[0064] In one embodiment, the process for separating the substrate 101 is self-separation, which includes: when the single crystal layer 106 is epitaxially grown to the self-separation thickness, the weak connection between the gallium nitride porous structure 102 and the sapphire substrate breaks, resulting in self-separation. Figures 5-6 As shown, self-separation can greatly simplify the process and help save on process costs.

[0065] In another embodiment, the process for separating the substrate 101 is laser lift-off, which includes: after the single crystal layer 106 has been epitaxially grown to a preset thickness, the gallium nitride porous structure 102 is separated from the sapphire substrate by laser lift-off.

[0066] Next, step 5) can be performed to epitaxially grow the single crystal layer 106 to form a single crystal layer 106 of the target thickness. The present invention can perform epitaxial thickening after separation from the substrate 101, thereby overcoming the limitation on the thickness of the single crystal layer 106 caused by heteroepitaxial growth between the single crystal layer 106 and the substrate 101, and obtaining a high-quality single crystal substrate with the target thickness.

[0067] like Figure 7 As shown, step 6) is performed last to polish and chamfer both sides of the single crystal layer 106 to obtain an Epi-ready surface.

[0068] Example 2

[0069] like Figures 1-3 and Figures 8-12 As shown, this embodiment provides a method for preparing a single-crystal substrate, the method comprising the following steps:

[0070] like Figure 1 As shown, step 1) is performed first, a substrate 101 is provided, and a porous structure 102 is formed on the surface of the substrate 101.

[0071] In one embodiment, the pore size of each pore 103 in the porous structure 102 is in the nanometer range, and the spacing between two adjacent pores 103 is in the nanometer range. For example, the pore size of each pore 103 in the porous structure 102 is 10–200 nanometers, and the spacing between two adjacent pores 103 is 10–200 nanometers. The pores 103 can be arranged in a periodic array or non-uniformly, etc.

[0072] In one embodiment, the substrate 101 is a sapphire substrate, and the porous structure 102 includes a porous sapphire layer formed on the surface of the sapphire substrate.

[0073] In one embodiment, the total area of ​​the pores 103 accounts for 40% to 80% of the total area of ​​the porous sapphire layer. By forming a barrier layer 104 on the inner surface of the pores 103, the connection area between the single crystal layer 106 and the porous structure 102 can be reduced, and the epitaxial growth of the single crystal layer 106 can include vertical growth, lateral growth, and merging processes, thereby improving the growth quality of the single crystal layer 106.

[0074] like Figure 2 As shown, then step 2) is performed, depositing a barrier layer 104, which covers the top surface 105 of the porous structure 102 and the inner surface of the porous structure 102.

[0075] In one embodiment, the barrier layer 104 is formed by a vapor deposition process, including atomic layer deposition (ALD). ALD effectively prevents the growth of a single crystal layer 106 due to incomplete coverage of the inner wall of the hole 103, thus improving process stability. Of course, for larger holes 103, processes such as chemical vapor deposition can also be used to form the barrier layer 104. Furthermore, the barrier layer 104 can either completely fill the hole 103 or only cover the inner surface of the hole 103.

[0076] In one embodiment, the barrier layer 104 may be silicon nitride.

[0077] In another embodiment, the barrier layer 104 may also be silicon oxide.

[0078] In yet another embodiment, the barrier layer 104 may also be graphene.

[0079] The barrier layer 104 is used to suppress the growth of the single crystal layer 106 in the hole 103. It can be selected from materials such as gallium nitride, which are difficult for the single crystal layer 106 to nucleate and grow on its surface, and is not limited to the examples listed above.

[0080] like Figure 3 As shown, then step 3) is performed to remove the barrier layer 104 on the top surface 105 of the porous structure 102 to expose the top surface 105 of the porous structure 102.

[0081] For example, the barrier layer 104 on the top surface 105 of the porous structure 102 can be removed by chemical mechanical polishing (CMP) to obtain a high-quality top surface 105 of the porous structure 102, thereby improving the growth quality of the subsequent single crystal layer 106.

[0082] like Figures 8-11As shown, step 4) is then performed, in which a single crystal layer 106 is epitaxially grown on the porous structure 102 and the substrate 101 is separated. The single crystal layer 106 grows from the top surface 105 of the porous structure 102, and the barrier layer 104 is used to suppress the growth of the single crystal layer 106 on the inner surface of the porous structure 102.

[0083] In one embodiment, a buffer layer 201 is further deposited on the top surface 105 of the porous sapphire layer, such as... Figure 8 As shown, the deposition buffer layer 201 includes a low-temperature gallium nitride layer to facilitate the growth of the single crystal layer 106 and improve the growth quality of the single crystal layer 106.

[0084] In one embodiment, the single crystal layer 106 is a gallium nitride single crystal. Based on the epitaxial growth of gallium nitride on the top surface 105 of the porous structure 102, voids 107 are formed in the gallium nitride single crystal above each of the voids 103. At the same time, based on the lateral growth of gallium nitride, the width of the voids 107 gradually decreases and the gallium nitride merges into a complete gallium nitride single crystal above the voids 107. This epitaxial growth method also helps to reduce the dislocation density of the gallium nitride single crystal.

[0085] As an example, the process for separating the substrate 101 is self-separation or laser ablation.

[0086] In one embodiment, the process for separating the substrate 101 is self-separation, which includes: when the single crystal layer 106 is epitaxially grown to a self-separation thickness, the single crystal layer 106 and the porous sapphire layer undergo self-separation. Figures 10-11 As shown, self-separation can greatly simplify the process and help save process costs.

[0087] In another embodiment, the process for separating the substrate 101 is laser lift-off, which includes: after the single crystal layer 106 has been epitaxially grown to a preset thickness, the single crystal layer 106 is separated from the porous sapphire layer by laser lift-off.

[0088] Next, step 5) can be performed to epitaxially grow the single crystal layer 106 to form a single crystal layer 106 of the target thickness. The present invention can perform epitaxial thickening after separation from the substrate 101, thereby overcoming the limitation on the thickness of the single crystal layer 106 caused by heteroepitaxial growth between the single crystal layer 106 and the substrate 101, and obtaining a high-quality single crystal substrate with the target thickness.

[0089] like Figure 12 As shown, step 6) is performed last to polish and chamfer both sides of the single crystal layer 106 to obtain an Epi-ready surface.

[0090] As described above, the method for preparing the single-crystal substrate of the present invention has the following beneficial effects:

[0091] This invention utilizes a porous structure to enable the epitaxially grown single crystal layer to form a weak connection with the substrate, thereby achieving a higher separation yield between the single crystal layer and the substrate.

[0092] This invention deposits a barrier layer inside the pores, keeping each pore as a void during epitaxial growth, which greatly reduces the connection area between the single crystal layer and the substrate, making the separation between the single crystal layer and the substrate easier. Subsequently, grinding and polishing can be used to make the porous structure surface smooth, forming an Epi-ready single crystal layer surface.

[0093] This invention can obtain high-quality single crystal layers through two-dimensional and three-dimensional epitaxial growth of single crystal layers. Furthermore, epitaxial thickening can be performed after separation from the substrate, thereby overcoming the limitation on the thickness of single crystal layers caused by heteroepitaxial growth between the single crystal layer and the substrate, and obtaining high-quality single crystal substrates with the target thickness.

[0094] Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0095] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method of producing a single crystal substrate, characterized by, The preparation method comprises the steps of: 1) providing a substrate, and forming a porous structure on the surface of the substrate; 2) depositing a barrier layer, the barrier layer covering the top surface of the porous structure and the inner surface of the porous structure; 3) removing the barrier layer on the top surface of the porous structure to expose the top surface of the porous structure; 4) performing epitaxial growth of a single crystal layer on the porous structure and separating the substrate, wherein the single crystal layer is grown from the top surface of the porous structure, and the barrier layer is used to inhibit the growth of the single crystal layer on the inner surface of the porous structure. The substrate is a sapphire substrate, and the porous structure comprises a porous gallium nitride layer, and the porous gallium nitride layer is prepared by the steps of: forming an n-type gallium nitride layer on the sapphire substrate by a chemical vapor deposition process; and forming a plurality of holes in the n-type gallium nitride layer by an electrochemical etching process to form the porous gallium nitride layer; each hole in the porous gallium nitride layer penetrates the porous gallium nitride layer, so that the porous gallium nitride layer is weakly connected to the sapphire substrate, facilitating subsequent separation. The barrier layer is formed by a vapor deposition process, and the barrier layer comprises one of silicon nitride, silicon oxide and graphene. The single crystal layer is a gallium nitride single crystal, and based on three-dimensional vertical epitaxial growth of gallium nitride on the top surface of the porous structure, voids are formed in the gallium nitride single crystal above each hole, and based on two-dimensional horizontal growth of the gallium nitride, the width of the hole structure gradually decreases and the gallium nitride is merged above the voids into a complete gallium nitride single crystal, which is also conducive to reducing the dislocation density of the gallium nitride single crystal.

2. The method of producing a single crystal substrate according to claim 1, wherein: The pore size of each hole of the porous structure is nanoscale, and the spacing between adjacent two holes is nanoscale.

3. The method of producing a single crystal substrate according to claim 1, wherein: The separation process of the substrate is self-separation or laser lift-off, wherein the self-separation comprises: when the single crystal layer is epitaxially grown to a self-separation thickness, the weak connection between the porous gallium nitride structure and the sapphire substrate is broken to cause self-separation; and the laser lift-off comprises: when the single crystal layer is epitaxially grown to a preset thickness, the porous gallium nitride structure and the sapphire substrate are separated by a laser lift-off process.

4. The method of producing a single crystal substrate according to claim 1, wherein: The substrate is a sapphire substrate, and the porous structure comprises a porous sapphire layer formed based on the surface layer of the sapphire substrate.

5. The method of producing a single crystal substrate according to claim 4, wherein: The top surface of the porous sapphire layer further comprises a deposition buffer layer, and the deposition buffer layer comprises a low-temperature gallium nitride layer.

6. The method of producing a single crystal substrate according to claim 4, wherein: The separation process of the substrate is self-separation or laser lift-off, wherein the self-separation comprises: when the single crystal layer is epitaxially grown to a self-separation thickness, the single crystal layer and the porous sapphire layer cause self-separation; and the laser lift-off comprises: when the single crystal layer is epitaxially grown to a preset thickness, the single crystal layer and the porous sapphire layer are separated by a laser lift-off process.

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