Epitaxial structure and method of manufacturing the same

Abstract

The application provides an epitaxial structure and a preparation method thereof. The preparation method of the epitaxial structure comprises the following steps: providing a substrate; forming a buffer layer on one side of the substrate; and forming an epitaxial layer on the side of the buffer layer away from the substrate. In the process of preparing the buffer layer and / or the epitaxial layer, magnesium and / or antimony are doped to promote lateral growth of crystals, reduce the thickness of the buffer layer and / or the epitaxial layer, and achieve the surface roughness and crystal quality required by a device by using an epitaxial layer with a sub-micron thickness, so as to meet the requirements of a specific device structure with limited thickness of the epitaxial layer and effectively improve the preparation efficiency and reduce the production cost.

Description

Technical Field

[0001] This application belongs to the field of semiconductor technology, specifically relating to epitaxial structures and their fabrication methods. Background Technology

[0002] In the field of semiconductor technology, thin films are typically fabricated epitaxially to meet device design requirements. During heteroepitaxial growth, due to differences in lattice constants and coefficients of thermal expansion, thicker epitaxial layers are more prone to cracking and cannot meet the specific device epitaxial structure requirements where epitaxial layer thickness is limited. Summary of the Invention

[0003] In view of this, the first aspect of this application provides a method for preparing an epitaxial structure, the method comprising:

[0004] Provide substrate;

[0005] A buffer layer is formed on one side of the substrate;

[0006] An epitaxial layer is formed on the side of the buffer layer opposite to the substrate;

[0007] In the process of forming the buffer layer and / or the epitaxial layer, at least one of a magnesium source and an antimony source is added.

[0008] The first aspect of this application provides a method for fabricating an epitaxial structure, which is simple and highly operable. First, a buffer layer is formed on one side of a substrate to provide a basis for the subsequent formation of the epitaxial layer. Then, an epitaxial layer is formed on the side of the buffer layer opposite to the substrate.

[0009] Specifically, during the formation of the buffer layer and / or epitaxial layer, at least one of a magnesium source and an antimony source is added, so the buffer layer and / or epitaxial layer contains at least one of magnesium and antimony elements. The doping of magnesium and / or antimony elements promotes the lateral growth of the buffer layer and inhibits the longitudinal growth. Longitudinal growth refers to epitaxial growth parallel to the alignment direction of the substrate and the epitaxial layer; lateral growth refers to epitaxial growth perpendicular to the alignment direction of the substrate and the epitaxial layer. In other words, the doping of magnesium and / or antimony elements promotes the aggregation of atoms on the surface perpendicular to the alignment direction of the substrate and the epitaxial layer, thereby causing the buffer layer and / or epitaxial layer to grow first along the alignment direction perpendicular to the substrate and the epitaxial layer, and inhibiting the longitudinal growth of the buffer layer and / or epitaxial layer, thus reducing the thickness of the buffer layer and / or epitaxial layer. Compared to related technologies, because the thickness of the buffer layer and / or the epitaxial layer in this application is smaller, it occupies less space.

[0010] Therefore, this application introduces magnesium and / or antimony sources during the preparation of buffer and / or epitaxial layers to promote lateral crystal growth, thereby reducing the thickness of buffer and / or epitaxial layers and reserving more growth space for subsequent device structure layers grown on one side of the epitaxial layer. The submicron-thick epitaxial layer achieves the surface roughness and crystal quality required by the device, which facilitates the device structure layer to better perform its function and improves the working performance of the epitaxial structure.

[0011] The step of forming a buffer layer located on one side of the substrate includes:

[0012] A buffer layer is formed on one side of the substrate; wherein, during the formation of the buffer layer, at least one of the magnesium source and the antimony source is added;

[0013] The buffer layer is subjected to high-temperature annealing.

[0014] The buffer layer includes multiple interconnected first core islands; the multiple first core islands are subjected to high-temperature annealing, and parts of the multiple first core islands are merged into multiple spaced second core islands, and the height of the first core islands is less than the height of the second core islands; wherein the height h1 of the first core islands and the height h2 of the second core islands satisfy the following conditions: 15nm≤h1≤35nm, 50nm≤h2≤250nm.

[0015] In this process, a plurality of third core islands are epitaxially formed on the side of the buffer layer opposite to the substrate;

[0016] The plurality of third nuclear islands are epitaxially grown to obtain the epitaxial layer, wherein at least one of the magnesium source and the antimony source is added during the formation of the epitaxial layer.

[0017] The step of extending the plurality of third nuclear islands includes:

[0018] The plurality of third nuclei islands are epitaxially extended, and the plurality of third nuclei islands are merged together; during the process of merging the plurality of third nuclei islands, at least one of the magnesium source and the antimony source is added.

[0019] The merged plurality of third core islands are epitaxially extended to obtain the epitaxial layer.

[0020] During the lateral growth process to form the epitaxial layer, the molar flow ratio of the group V source and the group III source satisfies the following condition: 500≤V / III≤1000, and the reaction chamber pressure satisfies the following condition: 50torr≤P≤100torr.

[0021] In the process of forming the buffer layer and / or the epitaxial layer, the magnesium source includes, but is not limited to, dicyclopentadienyl magnesium and dimethylcyclophenyladienyl magnesium, and the antimony source includes, but is not limited to, triethylantimony and tri-diethylamine antimony.

[0022] A second aspect of this application provides an epitaxial structure comprising a substrate, and a buffer layer and an epitaxial layer sequentially stacked on one side of the substrate, wherein the buffer layer and / or the epitaxial layer contains at least one of magnesium and antimony.

[0023] The epitaxial structure provided in the second aspect of this application comprises a substrate, a buffer layer, and an epitaxial layer. The buffer layer is doped with magnesium and / or antimony to promote lateral crystal growth, thereby reducing the thickness of the buffer layer and / or the epitaxial layer. This allows for more growth space for the subsequent device structure layer grown on one side of the epitaxial layer. The sub-micron thickness of the epitaxial layer achieves the surface roughness and crystal quality required by the device, facilitating better performance of the device structure layer and improving the overall performance of the epitaxial structure.

[0024] The root mean square (RMS) of the surface roughness on the side of the epitaxial layer away from the substrate satisfies the following condition: 0.2 nm ≤ RMS ≤ 5 nm.

[0025] Wherein, the epitaxial structure satisfies at least one of the following conditions:

[0026] In the extension direction of the (0002) plane in the epitaxial structure, the half-width at half-maximum of the rocking curve under the XRD diffraction angle of the epitaxial layer is no greater than 200 arcseconds;

[0027] In the extension direction of the (10-12) plane in the epitaxial structure, the half-width at half-maximum of the rocking curve under the XRD diffraction angle of the epitaxial layer is no greater than 400 arcseconds.

[0028] The doping concentration c of magnesium and / or antimony in the buffer layer satisfies the following condition: 1×10 17 cm -3 ≤c≤3×10 19 cm -3 . Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments of this application will be described below.

[0030] Figure 1 This is a process flow diagram of the method for preparing the epitaxial structure in one embodiment of this application.

[0031] Figure 2 for Figure 1A schematic diagram of the epitaxial structure corresponding to S300.

[0032] Figure 3 This is a process flow diagram of S200 in one embodiment of this application.

[0033] Figure 4 for Figure 3 A schematic diagram of the epitaxial structure corresponding to S210.

[0034] Figure 5 for Figure 3 A schematic diagram of the epitaxial structure corresponding to S220.

[0035] Figure 6 This is a process flow diagram of S300 in one embodiment of this application.

[0036] Figure 7 for Figure 6 A schematic diagram of the epitaxial structure corresponding to S310.

[0037] Figure 8 This is a process flow diagram of S320 in one embodiment of this application.

[0038] Figure 9 This is a schematic diagram of the extensional structure in one embodiment of this application.

[0039] Label Explanation:

[0040] Epitaxial structure-1, substrate-11, buffer layer-12, second core island-121, epitaxial layer-13, first core island-141, third core island-151. Detailed Implementation

[0041] The following are preferred embodiments of this application. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

[0042] This application provides a method for preparing the epitaxial structure 1. Please refer to it as well. Figure 1 and Figure 2 , Figure 1 This is a process flow diagram of the method for preparing the epitaxial structure in one embodiment of this application. Figure 2 for Figure 1 A schematic diagram of the epitaxial structure corresponding to S300 is shown. This embodiment provides a method for preparing an epitaxial structure 11, which includes steps S100, S200, and S300. Detailed descriptions of S100, S200, and S300 are as follows.

[0043] S100 provides substrate 11.

[0044] In this embodiment, the substrate 11 provided by the epitaxial structure 1 can provide a support base for the fabrication of other layers. This application does not limit the shape, material, or thickness of the substrate 11. Optionally, the material of the substrate 11 includes, but is not limited to, sapphire, silicon, silicon carbide, gallium nitride, aluminum nitride, etc.

[0045] Alternatively, the substrate 11 can be made of sapphire. When the substrate 11 is made of sapphire and the epitaxial layer 13 is made of gallium nitride, the lattice mismatch between gallium nitride and sapphire is relatively low, which can reduce defects in the epitaxial layer 13. Furthermore, sapphire has wide availability, good thermal stability, mature manufacturing process, and relatively low cost. Therefore, choosing sapphire as the substrate 11 material and gallium nitride as the epitaxial layer 13 material can both obtain an epitaxial structure 1 with high crystal quality and reduce the preparation cost.

[0046] It should be noted that the epitaxial growth mentioned below in this application includes lateral growth and longitudinal growth. Longitudinal growth refers to epitaxial growth in a direction parallel to the arrangement direction of the substrate 11 and the buffer layer 12 (e.g., Figure 2 (As shown in the D direction); Lateral growth refers to the epitaxial growth direction being perpendicular to the arrangement direction of the substrate 11 and the buffer layer 12.

[0047] S200, a buffer layer 12 is formed on one side of the substrate 11.

[0048] In this embodiment, the buffer layer 12 provided by the epitaxial structure 1 provides a basis for the subsequent formation of the epitaxial layer 13. This application does not limit the shape, material, or thickness of the buffer layer 12. Optionally, the material of the buffer layer 12 includes, but is not limited to, GaN, AlN, InN, etc. Preferably, the material of the buffer layer 12 is GaN. In one embodiment, the GaN buffer layer 12 containing magnesium can also be understood as a P-GaN buffer layer 12.

[0049] Optionally, in the arrangement direction of the substrate 11 and the buffer layer 12, the thickness d1 of the buffer layer 12 satisfies the following condition: 120nm ≤ d1 ≤ 200nm. Preferably, the thickness d1 of the buffer layer 12 satisfies the following condition: 140nm ≤ d1 ≤ 190nm. More preferably, the thickness d1 of the buffer layer 12 satisfies the following condition: 160nm ≤ d1 ≤ 180nm.

[0050] Designing the thickness of the buffer layer 12 within the aforementioned range not only provides a basis for the subsequent formation of the epitaxial layer 13, allowing for the growth of a thinner epitaxial layer 13, but also shields the defects of the substrate 11, acting as a buffer. If the thickness of the buffer layer 12 is too small, the distribution of the core islands will be loose, which is not conducive to the lateral growth and merging of GaN seed crystals. This would prevent the buffer layer 12 from effectively shielding the defects of the substrate 11 and fulfilling its buffering role between the substrate 11 and other layers, which would be detrimental to the fabrication of subsequent layers. If the thickness of the buffer layer 12 is too large, the fabrication efficiency of the buffer layer 12 will be too low, increasing production costs. Therefore, a thickness of 120nm-200nm for the buffer layer 12 provides a basis for the subsequent formation of the epitaxial layer 13, allowing for the growth of a thinner epitaxial layer 13, while also shielding the defects of the substrate 11, acting as a buffer.

[0051] like Figure 2 As shown, in S300, an epitaxial layer 13 is formed on the side of the buffer layer 12 opposite to the substrate 11; wherein, during the formation of the buffer layer 12 and / or the epitaxial layer 13, at least one of a magnesium source and an antimony source is added.

[0052] The magnesium source in this embodiment includes at least one of magnesium ions and magnesium atoms. The antimony source in this embodiment includes at least one of antimony ions and antimony atoms.

[0053] In this embodiment, the epitaxial layer 13 provided by the epitaxial structure 1 can have a small thickness to meet the specific device process requirements where the thickness of the epitaxial layer 13 is limited. This application does not limit the shape, material, or thickness of the epitaxial layer 13. Optionally, the epitaxial layer 13 includes III-V nitride. The material of the epitaxial layer 13 includes, but is not limited to, GaN, AlN, InN, etc. Preferably, the material of the epitaxial layer 13 is GaN.

[0054] Optionally, in the alignment direction of the substrate 11 and the buffer layer 12, the thickness of the epitaxial layer is 200 nm-990 nm. Optionally, the thickness d2 of the epitaxial layer 13 satisfies the condition: 300 nm ≤ d2 ≤ 900 nm. Preferably, the thickness d2 of the epitaxial layer 13 satisfies the condition: 400 nm ≤ d2 ≤ 800 nm. More preferably, the thickness d2 of the epitaxial layer 13 is 600 nm.

[0055] Designing the thickness of epitaxial layer 13 within the aforementioned range not only meets the specific device process requirements where the thickness of epitaxial layer 13 is limited, but also ensures high crystal quality of epitaxial layer 13 to meet user or product needs. If the thickness of epitaxial layer 13 is too small, it will not be able to completely cover buffer layer 12, and the crystal quality of epitaxial layer 13 will be low, which is not conducive to the fabrication of subsequent layers. If the thickness of epitaxial layer 13 is too large, it will occupy too much space and is not conducive to the fabrication of subsequent device structure layers, increasing fabrication costs. Therefore, the thickness of epitaxial layer 13 is 200nm-990nm, which can meet the specific device process requirements where the thickness of epitaxial layer 13 is limited, and also ensure high crystal quality of epitaxial layer 13 to meet user or product needs.

[0056] The epitaxial structure 1 includes a device structure layer disposed on the side of the epitaxial layer 13 opposite to the buffer layer 12. The device structure layer includes, but is not limited to, an active layer, a confinement layer, and a refractive layer. The device structure layer can be fabricated according to user or product requirements.

[0057] This embodiment provides a method for preparing an epitaxial structure 1, which is simple and highly operable. First, a buffer layer 12 is formed on one side of a substrate 11. Then, an epitaxial layer 13 is formed on the side of the buffer layer 12 facing away from the substrate 11. During the formation of the buffer layer 12 and / or the epitaxial layer 13, at least one of a magnesium source and an antimony source is added, so the buffer layer 12 contains at least one of magnesium and antimony elements.

[0058] Specifically, the doping of magnesium and / or antimony promotes the lateral growth of the buffer layer 12 and / or the epitaxial layer 13. In other words, the doping of magnesium and / or antimony promotes the aggregation of atoms on the surface along the alignment direction perpendicular to the substrate 11 and the epitaxial layer 13, thereby causing the buffer layer 12 and / or the epitaxial layer 13 to preferentially grow along the alignment direction perpendicular to the substrate 11 and the epitaxial layer 13, and suppressing the longitudinal growth of the buffer layer 12 and / or the epitaxial layer 13, thus reducing the thickness of the buffer layer 12 and / or the epitaxial layer 13. Compared with related technologies, since the buffer layer 12 and / or the epitaxial layer 13 in this application has a smaller thickness, it can meet the specific device process requirements where the thickness of the epitaxial layer 13 is limited.

[0059] Therefore, this embodiment introduces a magnesium source and / or an antimony source during the preparation of the buffer layer 12 and / or the epitaxial layer 13 to promote lateral crystal growth, thereby reducing the thickness of the buffer layer 12 and / or the epitaxial layer 13. This leaves more growth space for the device structure layer subsequently grown on one side of the epitaxial layer 13, achieving the surface roughness and crystal quality required by the device with a submicron-thick epitaxial layer 13. This facilitates the device structure layer to better perform its function and improves the working performance of the epitaxial structure 1.

[0060] Optionally, during the formation of the buffer layer 12 and / or the epitaxial layer 13, the magnesium source includes at least one of dicyclopentadienyl magnesium (Cp2Mg) and dimethylcyclophenyladienyl magnesium (MeCp)2Mg, and the antimony source includes at least one of triethylantimony (TESb) and tri-diethylammonium antimony [(CH3)2N]3Sb.

[0061] Please refer to this as well. Figures 3-5 , Figure 3 This is a process flow diagram of S200 in one embodiment of this application. Figure 4 for Figure 3 A schematic diagram of the epitaxial structure corresponding to S210. Figure 5 for Figure 3 A schematic diagram of the epitaxial structure corresponding to S220. In one embodiment, step S200, forming the buffer layer 12 located on one side of the substrate 11, includes:

[0062] like Figure 4 As shown, in S210, the buffer layer 12 is formed on one side of the substrate 11; wherein, during the formation of the buffer layer 12, at least one of the magnesium source and the antimony source is added.

[0063] Optionally, during the formation of the buffer layer 12, the reaction temperature is 510℃-560℃, the reaction chamber pressure is 380 torr-420 torr, and the flow rate of the magnesium source and / or antimony source is 130 sccm-170 sccm.

[0064] Preferably, during the formation of the buffer layer 12, the reaction temperature is 520-550°C, the reaction chamber pressure is 390 torr-410 torr, and the flow rate of the magnesium source and / or antimony source is 140 sccm-160 sccm.

[0065] More preferably, during the formation of the buffer layer 12, the reaction temperature is 535°C, the reaction chamber pressure is 400 torr, and the flow rate of the magnesium source and / or antimony source is 150 sccm.

[0066] Designing the reaction temperature of the buffer layer 12 within the aforementioned range not only ensures a high carrier mobility but also a low surface roughness, meeting the requirements for subsequent fabrication. If the reaction temperature is too high or too low, the carrier mobility of the buffer layer 12 will decrease, and the surface roughness will be too high, which is detrimental to the subsequent fabrication of the epitaxial layer 13.

[0067] Designing the reaction chamber pressure of buffer layer 12 within the aforementioned range not only ensures high atomic migration ability but also high crystal quality of buffer layer 12 to meet subsequent preparation requirements. If the reaction pressure is too high or too low, it will lead to reduced atomic migration ability, increased dislocations in buffer layer 12, and decreased crystal quality.

[0068] Designing the flow rates of the magnesium and / or antimony sources within the aforementioned range not only ensures sufficient amounts of magnesium and / or antimony sources to promote the lateral growth of the buffer layer 12, but also saves costs. If the flow rates of the magnesium and / or antimony sources are too low, their effectiveness in promoting the lateral growth of the buffer layer 12 will be affected, and may even hinder the subsequent fabrication of the thinner epitaxial layer 13. If the flow rates of the magnesium and / or antimony sources are too high, the fabrication cost will increase.

[0069] Optionally, when the material of the buffer layer 12 is gallium nitride, a nitrogen source and a gallium source are added during the formation of the buffer layer 12. The nitrogen source includes nitrogen gas, and the gallium source includes trimethylgallium.

[0070] like Figure 5 As shown, in step S220, the buffer layer 12 is subjected to high-temperature annealing.

[0071] Optionally, during the high-temperature annealing process of the buffer layer 12, the annealing temperature is 1040℃-1080℃ and the annealing time is 2min-5min.

[0072] Designing the annealing temperature and annealing time of the buffer layer 12 within the aforementioned range not only reduces the crystal defect density of the buffer layer 12 but also ensures a low surface roughness to meet the requirements of subsequent fabrication. If the reaction temperature is too high or too low, or the annealing time is too long or too short, it will result in a high crystal defect density and a large surface roughness of the buffer layer 12, which is not conducive to the subsequent fabrication of the epitaxial layer 13.

[0073] In this embodiment, a buffer layer 12 is first formed, followed by high-temperature annealing. Firstly, during the formation of the buffer layer 12, magnesium and / or antimony elements can be doped into the buffer layer 12, promoting its lateral growth, reducing defects, and improving its crystal quality, thus providing a foundation for the subsequent fabrication of a high-quality epitaxial layer 13. Then, the buffer layer 12 undergoes high-temperature annealing, during which the amorphous structure of the buffer layer 12 recrystallizes, further reducing the crystal defect density and improving its crystal quality, further providing a foundation for the subsequent fabrication of a high-quality epitaxial layer 13. Therefore, this allows the buffer layer 12 to have both a low thickness and high crystal quality, providing a basis for the subsequent fabrication of the epitaxial layer 13.

[0074] Optionally, during the formation of the epitaxial layer 13 located on the side of the buffer layer 12 opposite to the substrate 11, the reaction temperature is the same as the annealing temperature. More preferably, during the formation of the epitaxial layer 13 located on the side of the buffer layer 12 opposite to the substrate 11, the reaction temperature is 1040℃-1080℃.

[0075] In this embodiment, annealing not only allows the amorphous structure to recrystallize, thus improving crystal quality, but also, because the annealing temperature is the same as the temperature at which the epitaxial layer 13 is formed, the process of high-temperature annealing after the formation of the buffer layer 12, followed by high-temperature formation of the epitaxial layer 13, involves a temperature increase from low to high. This allows the epitaxial structure 1 to better adapt to temperature changes, thereby improving crystal quality.

[0076] Please refer to this again. Figure 4 and Figure 5 In one implementation, such as Figure 4 As shown, the buffer layer 12 includes a plurality of interconnected first core islands 141.

[0077] like Figure 5 As shown, the plurality of first core islands 141 are subjected to high-temperature annealing treatment, so that parts of the plurality of first core islands 141 merge with each other and are transformed into a plurality of second core islands 121 arranged at intervals. Furthermore, the height of the first core islands 141 is less than the height of the second core islands 121.

[0078] In this embodiment, the buffer layer 12 includes a plurality of first core islands 141. The size, dimensions, and arrangement of the first core islands 141 are not limited in this embodiment. Since the plurality of first core islands 141 are closely connected, the plurality of first core islands 141 can also be approximated as a plane.

[0079] Specifically, designing the reaction chamber pressure of buffer layer 12 to 380 torr-420 torr not only ensures high atomic migration ability but also high crystal quality of buffer layer 12 to meet subsequent preparation requirements. If the reaction chamber pressure is too low, the size of the nuclei islands will be too small and the density too high in the early stage of nucleation. When the nuclei islands merge, the merging rate will be too fast, generating a large number of edge dislocations and reducing the crystal quality of buffer layer 12. If the reaction chamber pressure is too high, i.e., the reaction chamber pressure is relatively increased, although it can increase the size of the nuclei islands, resulting in a decrease in nuclei island density, the merging rate of the nuclei islands will be slowed down. The generated edge dislocations will interact with mixed dislocations and annihilate, improving the crystal quality of buffer layer 12. However, ordinary MOCVD equipment cannot operate normally under excessive reaction chamber pressure.

[0080] In one embodiment, the height h1 of the first core island 141 satisfies the following condition: 15nm ≤ h1 ≤ 35nm. Preferably, the height h1 of the first core island 141 satisfies the following condition: 20nm ≤ h1 ≤ 30nm.

[0081] Designing the height of the first core island 141 within the aforementioned range ensures that the high-temperature annealing process produces a second core island 121 of appropriate size to meet the requirements of subsequent epitaxial layer 13 fabrication. If the height of the first core island 141 is too large or too small, the crystal quality will be reduced, failing to meet the requirements of subsequent epitaxial layer 13 fabrication. A first core island 141 that is too small results in a thinner buffer layer 12, which is not conducive to lateral growth and merging, and the nucleation centers are more scattered and incompletely covered after annealing. A first core island 141 that is too large results in a thicker buffer layer 12, which is not conducive to subsequent epitaxial layer 13 growth. Therefore, designing the height of the first core island 141 to be 15nm-35nm ensures that the high-temperature annealing process produces a second core island 121 of appropriate size to meet the requirements of subsequent epitaxial layer 13 fabrication.

[0082] Optionally, the spacing between two adjacent first core islands 141 is no greater than 91 nm.

[0083] In this embodiment, the buffer layer 12 after high-temperature annealing includes multiple second core islands 121. The size, dimensions, and arrangement of the second core islands 121 are not limited in this embodiment. After the buffer layer 12 undergoes a return process, the multiple first core islands 141 transform into multiple second core islands 121. The second core islands 121 are formed by the merging and growth of some of the first core islands 141. For example, three first core islands 141 merge to form one second core island 121.

[0084] In one embodiment, the height h2 of the second core island 121 satisfies the following condition: 50nm ≤ h2 ≤ 250nm. Preferably, the height h2 of the second core island 121 satisfies the following condition: 100nm ≤ h2 ≤ 150nm.

[0085] Designing the height of the second core island 121 within the aforementioned range ensures high crystal quality of the buffer layer 12 after high-temperature annealing, meeting the requirements for subsequent epitaxial layer 13 fabrication. If the height of the second core island 121 is too large or too small, the crystal quality will decrease, failing to meet the requirements for subsequent epitaxial layer 13 fabrication. An excessively small or large second core island 121 will result in a thin or thick buffer layer 12 after high-temperature annealing, leading to a higher crystal defect density and thus reducing the crystal quality of the buffer layer 12, which is detrimental to the subsequent fabrication of the epitaxial layer 13. Therefore, designing the height of the second core island 121 to be between 50nm and 250nm ensures a suitable size for the second core island 121, resulting in high crystal quality of the buffer layer 12, thus meeting the requirements for subsequent epitaxial layer 13 fabrication.

[0086] Designing the size of the second core island 121 within the aforementioned range ensures high crystal quality of the buffer layer 12, meeting the requirements for subsequent epitaxial layer 13 fabrication. If the size of the second core island 121 is too large or too small, the crystal quality will decrease, failing to meet the requirements for subsequent epitaxial layer 13 fabrication. Conversely, an excessively small or large second core island 121 will result in a high crystal defect density in the buffer layer 12, further reducing its crystal quality and hindering the fabrication of the epitaxial layer 13. Therefore, designing the size of the second core island 121 to be between 50nm and 250nm ensures a suitable size, resulting in high crystal quality of the buffer layer 12, thus meeting the requirements for subsequent epitaxial layer 13 fabrication.

[0087] In one embodiment, the density of the first core island 141 is greater than the density of the second core island 121.

[0088] Optionally, the density ρ1 of the first core island 141 and the density ρ2 of the second core island 121 satisfy the following condition: 4.2 × 10⁻⁶ 10 cm -2 ≤ρ1≤4.8×10 10 cm -2 4.2×10 6 cm -2 ≤ρ2≤4.8×10 8 cm -2 .

[0089] During the high-temperature annealing process of the buffer layer 12, some of the first core islands 141 merge and transform into the second core islands 121. Therefore, as the high-temperature annealing process proceeds, the density component of the first core islands 141 of the buffer layer 12 decreases, so as to obtain the buffer layer 12 after high-temperature annealing composed of the second core islands 121, which provides a basis for the next step of growing an epitaxial layer 13 with higher crystal quality.

[0090] Optionally, the distance between two adjacent second nuclear islands 121 is no greater than 1 μm.

[0091] Optionally, the spacing between at least some of the adjacent second core islands 121 is not equal.

[0092] Specifically, in one embodiment, during the formation of the buffer layer 12, the inclusion of magnesium and / or antimony elements promotes lateral growth due to the presence of the nuclear island sidewalls. These sidewalls can be considered as highly inclined small planes composed of high-density basal step surfaces, each step acting as an effective site for capturing and adsorbing atoms, thus allowing epitaxial growth to preferentially occur in this direction. The addition of magnesium and / or antimony elements promotes the adsorption of atoms on the R-plane (1011) of the sidewall of the C-plane (0001). This phenomenon promotes the growth of the buffer layer 12 along the R-plane (1011), i.e., lateral growth. The C-plane (0001) and R-plane (1011) are perpendicular to each other. Growth along the C-plane (0001) is longitudinal growth, and growth along the R-plane (1011) is lateral growth.

[0093] Please refer to this again. Figure 2 and references Figures 6-7 , Figure 6 This is a process flow diagram of S300 in one embodiment of this application. Figure 7 for Figure 6 A schematic diagram of the epitaxial structure corresponding to S310.

[0094] In one embodiment, wherein S300, the step of forming the epitaxial layer 13 located on the side of the buffer layer 12 opposite to the substrate 11, includes:

[0095] like Figure 7 As shown, in S310, a plurality of third core islands 151 are epitaxially formed on the side of the buffer layer 12 opposite to the substrate 11.

[0096] This embodiment does not limit the size, dimensions, or arrangement of the third core island 151. Optionally, the third core islands 151 are interconnected. Since multiple third core islands 151 are closely connected, they can also be approximated as a single plane. In one embodiment, the height h3 of the third core island 151 satisfies the following condition: 250nm ≤ h3 ≤ 700nm. Further optionally, the height h3 of the third core island 151 satisfies the following condition: 300nm ≤ h3 ≤ 600nm. Even more optionally, the height h3 of the third core island 151 satisfies the following condition: 350nm ≤ h3 ≤ 550nm.

[0097] Optionally, the third core island 151 in this embodiment can also be understood as a 3D core island, meaning that the growth direction of the third core island 151 can be parallel to the arrangement direction of the substrate and the buffer layer, i.e., longitudinal growth; or perpendicular to the arrangement direction of the substrate and the buffer layer, i.e., transverse growth. Among them, the main growth direction of the third core island 151 is longitudinal.

[0098] Designing the height of the third core island 151 within the aforementioned range ensures that it meets the requirements for subsequent fabrication of the epitaxial layer 13. If the height of the third core island 151 is too small, it will be detrimental to lateral growth and merging. If the height of the third core island 151 is too large, it will increase the thickness of the resulting epitaxial layer 13, increasing the fabrication cost. Therefore, designing the height of the third core island 151 to be between 250nm and 700nm ensures that it meets the requirements for subsequent fabrication of the epitaxial layer 13.

[0099] In one embodiment, a buffer layer 12 is formed on one side of the substrate 11, the buffer layer 12 not containing at least one of magnesium and antimony. That is, during the formation of the buffer layer 12, no magnesium source or antimony source is added. During the formation of the buffer layer 12, the first core island 141 does not contain magnesium or antimony, and the second core island 121 of the buffer layer also does not contain magnesium or antimony.

[0100] like Figure 2 As shown, in S320, the plurality of third core islands 151 are epitaxially grown to obtain the epitaxial layer 13. During the formation of the epitaxial layer 13, at least one of the magnesium source and the antimony source is added.

[0101] In this embodiment, multiple third core islands 151 are first formed, followed by the formation of an epitaxial layer 13. During the formation of the epitaxial layer 13, at least one of the magnesium source and the antimony source is added. This process allows magnesium and / or antimony elements to be doped into the epitaxial layer 13, promoting lateral growth and reducing its thickness. This meets the specific device process requirements where the thickness of the epitaxial layer 13 is limited, facilitating better performance of the device structure layer and improving the operational performance of the epitaxial structure 1.

[0102] Please refer to this again. Figure 8 , Figure 8 This is a process flow diagram of S320 in one embodiment of this application. In one embodiment, S320, the step of epitaxially extending the plurality of third core islands 151, includes:

[0103] S321, the plurality of third core islands 151 are extended, and the plurality of third core islands 151 are merged with each other; during the process of merging the plurality of third core islands 151, at least one of the magnesium source and the antimony source is added.

[0104] S322, the merged plurality of third core islands 151 are epitaxially extended to obtain the epitaxial layer 13.

[0105] In this embodiment, during the merging and flattening of multiple third nucleus islands 151, at least one of the magnesium source and the antimony source is added to promote lateral crystal growth, providing a basis for reducing the thickness of the epitaxial layer 13. Subsequently, after the multiple third nucleus islands 151 are merged and flattened, the addition of at least one of the magnesium source and the antimony source is stopped, and epitaxy continues to obtain an epitaxial layer 13 with a submicron thickness. This preparation method not only ensures the obtaining of an epitaxial layer 13 with a submicron thickness but also saves materials and reduces energy consumption.

[0106] In one embodiment, during the formation of the plurality of third core islands 151, the growth direction of the plurality of third core islands 151 is parallel to the arrangement direction of the substrate 11 and the buffer layer 12; during the formation of the epitaxial layer 13, the growth direction of the epitaxial layer 13 is perpendicular to the arrangement direction of the substrate 11 and the buffer layer 12.

[0107] In this embodiment, during the formation of the plurality of third core islands 151, the main growth direction of the plurality of third core islands 151 is parallel to the arrangement direction of the substrate 11 and the buffer layer 12. In other words, most of the plurality of third core islands 151 are longitudinally epitaxial, and a small portion of the plurality of third core islands 151 are laterally epitaxial. During the formation of the epitaxial layer 13, the main growth direction of the plurality of third core islands 151 is perpendicular to the arrangement direction of the substrate 11 and the buffer layer 12. In other words, most of the epitaxial layer 13 is laterally epitaxial, and a small portion of the epitaxial layer 13 is longitudinally epitaxial.

[0108] By setting multiple third core islands 151 with the primary epitaxial direction being longitudinal, and then continuing to epitaxially grow multiple third core islands 151 with the primary epitaxial direction being transverse, the probability of crystal defects being carried from bottom to top to the epitaxial layer 13 can be reduced, thereby reducing the crystal defect density of the epitaxial layer 13 and improving the crystal quality of the epitaxial layer 13. Simultaneously, since at least one of the magnesium source and the antimony source is added during the formation of the epitaxial layer 13, the thickness of the epitaxial layer 13 is also ensured to be relatively small.

[0109] In one embodiment, during the lateral growth to form the epitaxial layer 13, the molar flow ratio of the group V source and the group III source satisfies the following condition: 500 ≤ V / III ≤ 1000, and the reaction chamber pressure satisfies the following condition: 50 torr ≤ P ≤ 100 torr.

[0110] In this embodiment, epitaxial growth is carried out under the conditions of a V / III ratio of 500-1000 and a reaction chamber pressure of 50-100 torr, which can promote lateral epitaxy and improve the crystal quality of epitaxial layer 13.

[0111] It should be noted that the V / III ratio here can be used when epitaxially forming a third nucleus island 151, and / or epitaxially extending the plurality of third nucleus islands 151, and / or epitaxially extending the merged plurality of third nucleus islands 151, to facilitate lateral epitaxy.

[0112] Optionally, the substrate 11 may be subjected to a decontamination treatment.

[0113] Optionally, during the decontamination process of the substrate 11, the reaction temperature is 1050℃-1100℃, the reaction time is 12min-18min, and the cleaning atmosphere is hydrogen.

[0114] In one embodiment, after the substrate 11 is decontaminated at a high temperature of 1050°C-1100°C, the substrate 11 is allowed to cool naturally to 510°C-560°C. At this time, aluminum oxynitride crystal nuclei are formed on the side of the substrate 11 near the buffer layer 12, providing a basis for the preparation of subsequent layer structures.

[0115] This embodiment removes contaminants from the surface of the substrate 11 by performing a decontamination treatment, which facilitates the formation of aluminum oxynitride crystal nuclei and provides a basis for reducing the mismatch between the substrate 11 and the subsequently prepared epitaxial layer 13, thereby improving the crystal quality of the epitaxial structure 1.

[0116] Furthermore, in related technologies, the second core islands 121 of the buffer layer 12 are relatively dispersed and sparse, and the second core islands 121 can reach up to 615 nm. Therefore, when growing the epitaxial layer 13 on the buffer layer 12, a large number of atoms are required to fill the gaps between the second core islands 121. As the second core islands 121 grow larger, the gaps that need to be filled also become larger. Therefore, the thickness of the epitaxial layer 13 with high crystal quality is relatively large. The epitaxial layer 13 in related technologies needs to reach the micrometer level to meet the fabrication requirements of subsequent device structure layers.

[0117] In one embodiment, during the fabrication of the epitaxial structure 1, a buffer layer 12 is first formed on one side of the substrate 11, i.e., a first core island 141 is formed. The buffer layer 12 is then subjected to high-temperature annealing. During this high-temperature annealing process, most of the first core islands 141 merge and transform into second core islands 121, i.e., smaller first core islands 141 merge and transform into larger second core islands 121. Then, an epitaxial layer 13 is formed. During the formation of the epitaxial layer 13, the second core islands 121 continue to grow and transform into third core islands 151, i.e., larger second core islands 121 grow into even larger third core islands 151. Subsequently, growth continues on the basis of the third core islands 151 to obtain the epitaxial layer 13. During the formation of the epitaxial layer 13, the third core islands 151 are connected into a grid, and the grid is flat to form the epitaxial layer 13.

[0118] However, this embodiment introduces a magnesium source and / or an antimony source during the preparation of the buffer layer 12 to form a buffer layer 12 containing magnesium and / or antimony elements, thereby reducing the thickness of the buffer layer 12 and thus reducing the thickness of the epitaxial layer 13. This reduces the thickness of the epitaxial layer 13, which in related technologies requires a thickness of 2 μm or more to achieve high crystal quality and a smooth and flat surface, to the submicron level. This satisfies the specific device process requirements where the thickness of the epitaxial layer 13 is limited, allowing the device structure layer to better perform its function and improving the working performance of the epitaxial structure 1.

[0119] In addition to the preparation method of epitaxial structure 1 provided above, this application also provides an epitaxial structure 1. Both the preparation method of epitaxial structure 1 and the epitaxial structure 1 provided in the embodiments of this application can achieve the technical effects of this application. They can be used together, or they can be used alone; this application does not have any particular limitations in this regard. For example, as one embodiment, the preparation method of epitaxial structure 1 described above can be used to prepare the epitaxial structure 1 described below.

[0120] Please refer to Figure 9 , Figure 9 This is a schematic diagram of an epitaxial structure according to one embodiment of the present application. The present application also provides an epitaxial structure 1, which includes a substrate 11 and a buffer layer 12 and an epitaxial layer 13 sequentially stacked on one side of the substrate 11. The buffer layer 12 and / or the epitaxial layer 13 have at least one of magnesium and antimony.

[0121] The substrate 11, buffer layer 12, and epitaxial layer 13 have been described in detail above and will not be repeated here. In this embodiment, magnesium includes at least one of magnesium ions and magnesium atoms. In this embodiment, antimony includes at least one of antimony ions and antimony atoms.

[0122] The epitaxial structure 1 provided in this embodiment consists of a substrate 11, a buffer layer 12, and an epitaxial layer 13. The buffer layer 12 and / or the epitaxial layer 13 are doped with magnesium and / or antimony to promote lateral crystal growth, thereby reducing the thickness of the buffer layer 12 and / or the epitaxial layer 13. This meets the specific device process requirements where the thickness of the epitaxial layer 13 is limited, achieving the surface roughness and crystal quality required by the device with a sub-micron thickness epitaxial layer 13. This allows the device structure layer to better perform its function and improves the working performance of the epitaxial structure 1.

[0123] Please refer to this again. Figure 9 In one embodiment, the thickness of the epitaxial layer 13 is 200nm-990nm in the alignment direction of the substrate 11 and the buffer layer 12.

[0124] Optionally, such as Figure 9 As shown, in the arrangement direction D of the substrate 11 and the buffer layer 12, the thickness d1 of the buffer layer 12 satisfies the following condition: 120nm ≤ d1 ≤ 200nm. The thickness d2 of the epitaxial layer 13 satisfies the following condition: 200nm ≤ d2 ≤ 990nm.

[0125] The thicknesses of the buffer layer 12 and the epitaxial layer 13 have been described in detail above and will not be repeated here. Since the thickness of the epitaxial layer 13 in this embodiment is relatively small, it can meet the specific device process requirements where the thickness of the epitaxial layer 13 is limited, making it easier for the device structure layer to better perform its function and improve the working performance of the epitaxial structure 1.

[0126] In one embodiment, the doping concentration c of magnesium and / or antimony in the buffer layer 12 satisfies the following condition: 1 × 10⁻⁶ 17 cm -3 ≤c≤3×10 19 cm -3 .

[0127] Designing the doping concentration of magnesium and / or antimony within the aforementioned range not only ensures sufficient amounts of magnesium and / or antimony to promote the lateral growth of the buffer layer 12, but also saves costs. If the doping concentration of magnesium and / or antimony is too low, it will not fully utilize magnesium and / or antimony to promote the lateral growth of the buffer layer 12, which is detrimental to the subsequent fabrication of the thinner epitaxial layer 13. If the doping concentration of magnesium and / or antimony is too high, it will increase the fabrication cost and may even hinder the growth of the buffer layer 12. Therefore, the doping concentration of magnesium and / or antimony is 1 × 10⁻⁶. 17 cm -3 -3×10 19 cm -3 This ensures that the amount of magnesium and / or antimony is sufficient to promote the lateral growth of the buffer layer 12, while also saving costs.

[0128] In one embodiment, the buffer layer 12 includes a plurality of second core islands 121 spaced apart. Optionally, the density ρ2 of the second core islands 121 satisfies the following condition: 4.2 × 10⁻⁶. 6 cm -2 ≤ρ2≤4.8×10 8 cm -2 Optionally, the spacing between at least some adjacent second core islands 121 is not equal. Optionally, the spacing between two adjacent second core islands 121 is not greater than 1 μm. Optionally, in the alignment direction perpendicular to the substrate and the buffer layer, the size h2 of the second core island 121 satisfies the following condition: 50 nm ≤ h2 ≤ 250 nm. It should be noted that the structural schematic diagram of the buffer layer 12 can be found in [reference needed]. Figure 5 .

[0129] In this embodiment, the second core island 121 is unevenly distributed on one side of the substrate 11, and the density of the second core island 121 is maintained at 4.2 × 10⁻⁶. 6 -4.8×10 8 cm -2 If the density of the second core island 121 is too high or too low, it will reduce the crystal defect density of the buffer layer 12, thereby reducing the crystal quality of the buffer layer 12 and failing to meet the requirements for the subsequent preparation of the epitaxial layer 13.

[0130] Optionally, in one embodiment, the root mean square (RMS) of the surface roughness of the epitaxial layer 13 on the side opposite to the substrate 11 satisfies the following condition: 0.2 nm ≤ RMS ≤ 5 nm. In other words, in this embodiment, the epitaxial structure 1 has both a relatively thin epitaxial layer 13 and a low roughness, providing a foundation for the fabrication of subsequent device structure layers.

[0131] Optionally, the surface roughness r of the epitaxial layer 13 on the side opposite to the substrate 11 satisfies the following condition: 0.20nm ≤ r ≤ 5.50nm.

[0132] Optionally, in one embodiment, the epitaxial structure 1 satisfies at least one of the following conditions:

[0133] In the epitaxial structure 1, the epitaxial structure 1 has a hexagonal crystal system, and the full width at half maximum (FWHM) of the rocking curve of the XRD diffraction angle along the (0002) plane of the hexagonal crystal system is no greater than 200 arcseconds;

[0134] In the epitaxial structure 1, the epitaxial structure 1 has a hexagonal crystal system, and the half-width at half-maximum (FWHM) of the rocking curve of the XRD diffraction angle along the (10-12) plane of the hexagonal crystal system is no greater than 400 arcseconds.

[0135] In other words, in this embodiment, the epitaxial structure 1 has both a thin epitaxial layer 13 thickness and high crystal quality, providing a foundation for the fabrication of subsequent device structure layers.

[0136] Optionally, in one embodiment, the FWHM value of the crystal plane in the epitaxial structure 1 is no greater than 400 arcseconds along the extension direction of the (0002) plane and the (1012) plane in the epitaxial structure 1. Here, FWHM is the full width at half maximum (FWHM). In this embodiment, the FWHM value of the epitaxial structure 1 is no greater than 400 arcseconds; in other words, the epitaxial structure 1 in this embodiment has fewer screw-through dislocations and mixed-type dislocations, thus the crystal quality of the epitaxial structure 1 is higher.

[0137] The above provides a detailed description of the embodiments provided in this application. This document elucidates and explains the principles and implementation methods of this application. The above description is only intended to help understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing an epitaxial structure, characterized in that, The preparation method includes: Provide substrate; A buffer layer is formed on one side of the substrate; An epitaxial layer is formed on the side of the buffer layer opposite to the substrate, and the thickness of the epitaxial layer is 200 nm to 990 nm in the alignment direction of the substrate and the buffer layer; The epitaxial structure has a hexagonal crystal system, and the half-width at half-maximum (WHM) of the rocking curve of the XRD diffraction angle along the (0002) plane of the hexagonal crystal system is no greater than 200 arcseconds, and the half-width at half-maximum (WHM) of the rocking curve of the XRD diffraction angle along the (10-12) plane of the hexagonal crystal system is no greater than 400 arcseconds. In the process of forming the buffer layer and the epitaxial layer, at least one of a magnesium source and an antimony source is added. The step of forming an epitaxial layer located on the side of the buffer layer opposite to the substrate includes: Multiple third core islands are epitaxially formed on the side of the buffer layer opposite to the substrate; The plurality of third nuclear islands are extended; The step of extending the plurality of third nuclear islands includes: The plurality of third nuclei islands are epitaxially extended, and the plurality of third nuclei islands are merged together; during the process of merging the plurality of third nuclei islands, at least one of the magnesium source and the antimony source is added. After the multiple third nuclear islands are merged and stretched, the addition of at least one of the magnesium source and the antimony source is stopped, and epitaxy continues; The merged plurality of third core islands are epitaxially extended to obtain the epitaxial layer; During the lateral growth process to form the epitaxial layer, the molar flow ratio of the group V source and the group III source satisfies the following condition: 500≤V / III≤1000, and the reaction chamber pressure satisfies the following condition: 50torr≤P≤100torr.

2. The preparation method according to claim 1, characterized in that, The step of forming a buffer layer located on one side of the substrate includes: The buffer layer is subjected to high-temperature annealing.

3. The preparation method according to claim 2, characterized in that, The buffer layer includes multiple interconnected first core islands; the multiple first core islands are subjected to high-temperature annealing, and parts of the multiple first core islands are merged into multiple spaced second core islands, and the height of the first core islands is less than the height of the second core islands; wherein, the height h1 of the first core islands and the height h2 of the second core islands satisfy the following conditions: 15nm≤h1≤35nm, 50nm≤h2≤250nm.

4. The preparation method according to claim 1, characterized in that, In the process of forming the buffer layer and the epitaxial layer, the magnesium source includes, but is not limited to, dicyclopentadienyl magnesium and dimethylcyclophenyladienyl magnesium, and the antimony source includes, but is not limited to, triethylantimony and tri-diethylamine antimony.

5. An epitaxial structure, characterized in that, The epitaxial structure is prepared by the method for preparing an epitaxial structure as described in claim 1. The epitaxial structure includes a substrate and a buffer layer and an epitaxial layer sequentially stacked on one side of the substrate. The buffer layer and the epitaxial layer have at least one of magnesium and antimony.

6. The epitaxial structure as described in claim 5, characterized in that, The root mean square (RMS) of the surface roughness on the side of the epitaxial layer away from the substrate satisfies the following condition: 0.2 nm ≤ RMS ≤ 5 nm.

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