A semiconductor device and a method of manufacture
By employing an N-group buffer stack structure in semiconductor devices and adjusting the composition content of the buffer layer, the problem of high surface roughness of SiGe buffer layer was solved, resulting in lower surface roughness and higher epitaxial layer quality.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- INST OF MICROELECTRONICS CHINESE ACAD OF SCI LTD
- Filing Date
- 2023-01-30
- Publication Date
- 2026-05-29
AI Technical Summary
In the prior art, the surface roughness of the SiGe buffer layer is relatively high, which affects the subsequent growth of Si channels and electrical performance, and it is difficult to maintain low surface roughness when growing a thick SiGe buffer layer.
An N-group buffer stack structure is adopted, with the first and second buffer layers made of the same material. The content of the slowly varying component in the first buffer layer gradually increases, while the content of the slowly varying component in the second buffer layer gradually decreases. By gradually adjusting the component content of the buffer layers, lattice mismatch is controlled and tensile stress is provided, thereby reducing surface roughness.
It effectively reduces the surface roughness of the buffer stack, improves the quality of the epitaxial layer, limits dislocations and defects, provides higher relaxation, and promotes the growth of high-quality epitaxial layers.
Smart Images
Figure CN115985946B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductors, and more specifically, to a semiconductor device and a method for its fabrication. Background Technology
[0002] SiGe materials play an important role in heterojunction transistors and strained silicon quantum dot devices, and are commonly used buffer layer materials for realizing strained silicon materials.
[0003] Forming a SiGe buffer layer on a Si substrate can reduce mismatch and facilitate the further growth of a near-relaxed SiGe epitaxial layer; however, such a SiGe buffer layer is often quite thick, for example, when growing a relaxed SiGe epitaxial layer. 0.7 Ge 0.3 The epitaxial layer requires a buffer layer of about 3 μm. Since the surface roughness increases with the growth thickness, growing such a thick SiGe buffer layer will result in a very high surface roughness. In severe cases, other surface treatment methods may be used to reduce the surface roughness. This high roughness will affect subsequent growth, such as forming a surface roughness of more than 1 nm that is not conducive to the growth of Si channels and poor electrical performance. Maintaining a low surface roughness of the SiGe buffer layer while growing a relaxed SiGe epitaxial layer is the key and difficult point in growing high-quality strain devices.
[0004] Therefore, reducing the surface roughness of the buffer layer has become an urgent problem to be solved. Summary of the Invention
[0005] In view of this, to solve the above problems, the present invention provides a semiconductor device and a method for its fabrication, the technical solution of which is as follows:
[0006] A semiconductor device, the semiconductor device comprising:
[0007] Substrate;
[0008] N sets of buffer stacks located on one side of the substrate, wherein N≥1; the N sets of buffer stacks are arranged sequentially in a first direction; the first direction is perpendicular to the substrate and extends from the substrate to the buffer stacks;
[0009] The buffer stack includes: a first buffer layer and a second buffer layer sequentially disposed in the first direction; the first buffer layer and the second buffer layer are made of the same material, and the materials of the first buffer layer and the second buffer layer respectively include a first slowly changing component;
[0010] In the first direction, the content of the first slowly varying component in the first buffer layer gradually increases; and the content of the first slowly varying component in the second buffer layer gradually decreases.
[0011] The epitaxial layer located on the side of the buffer stack opposite to the substrate in the Nth group.
[0012] Optionally, in the above-mentioned semiconductor device, the content of the first slowly varying component is 0%-100%.
[0013] Optionally, in the above-mentioned semiconductor device, the materials of the first buffer layer and the second buffer layer are SiGe materials.
[0014] Optionally, in the above-mentioned semiconductor device, the first slowly varying component is a Ge component.
[0015] A method for fabricating a semiconductor device, the method comprising:
[0016] Provide a substrate;
[0017] N sets of buffer stacks are formed on one side of the substrate, where N≥1; the N sets of buffer stacks are arranged sequentially in a first direction; the first direction is perpendicular to the substrate and points from the substrate to the buffer stacks;
[0018] The buffer stack includes: a first buffer layer and a second buffer layer sequentially disposed in the first direction; the first buffer layer and the second buffer layer are made of the same material, and the materials of the first buffer layer and the second buffer layer respectively include a first slowly changing component; wherein, in the first direction, the content of the first slowly changing component in the first buffer layer gradually increases; and the content of the first slowly changing component in the second buffer layer gradually decreases.
[0019] An epitaxial layer is formed on the side of the buffer stack opposite to the substrate in the Nth group.
[0020] Optionally, in the above preparation method, forming N sets of buffer stacks on one side of the substrate includes:
[0021] Determine the final target content of the first slowly varying component of the first buffer layer and the second buffer layer in the first direction in each group of buffer stacks;
[0022] The first buffer layer is formed, wherein the maximum content of the first slowly varying component in the first buffer layer in the first direction is greater than the target content;
[0023] A second buffer layer is formed, wherein the minimum content of the first slowly varying component in the first direction in the second buffer layer is equal to the target content, and the maximum content of the first slowly varying component in the first direction in the second buffer layer is equal to the maximum content of the first slowly varying component in the first direction in the first buffer layer.
[0024] Optionally, in the above preparation method, the materials of the first buffer layer and the second buffer layer are SiGe materials.
[0025] Optionally, in the above preparation method, the first slowly changing component is a Ge component.
[0026] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:
[0027] In this semiconductor device, the content of the first gradually varying component in the first buffer layer gradually increases in the first direction, thereby gradually reducing the lattice mismatch. At the same time, the content of the first gradually varying component in the second buffer layer gradually decreases in the first direction, thereby providing tensile stress for the subsequently grown epitaxial layer and further reducing the surface roughness of the buffer stack. The combination of the two achieves dislocation containment, confining most dislocations and defects within the buffer stack. Compared with the prior art, growing this buffer stack on the substrate can achieve higher relaxation and lower surface roughness, providing a foundation for the formation of high-quality epitaxial layers in the subsequent semiconductor device. Attached Figure Description
[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.
[0029] Figure 1 This is a schematic diagram of the structure of a semiconductor device provided in an embodiment of the present invention;
[0030] Figure 2 A schematic diagram of another semiconductor device is provided for embodiments of the present invention;
[0031] Figure 3 A schematic diagram of the structure of another semiconductor device is provided for embodiments of the present invention;
[0032] Figure 4 This is a schematic diagram of the structure of the buffer stack provided in an embodiment of the present invention;
[0033] Figure 5 This is a schematic diagram of another buffer stack structure provided in an embodiment of the present invention;
[0034] Figure 6 This is a schematic flowchart of a semiconductor device fabrication method provided in an embodiment of the present invention;
[0035] Figure 7 This is a schematic flowchart of another semiconductor device fabrication method provided in an embodiment of the present invention. Detailed Implementation
[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0037] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0038] refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of a semiconductor device provided in an embodiment of the present invention.
[0039] The semiconductor device includes:
[0040] Substrate 01; N sets of buffer stacks 02 located on one side of the substrate 01, wherein N≥1; the N sets of buffer stacks 02 are sequentially arranged in a first direction M; the first direction M is perpendicular to the substrate 01 and points from the substrate 01 to the buffer stacks 02.
[0041] The buffer stack 02 includes a first buffer layer 03 and a second buffer layer 04 sequentially disposed in the first direction M; the first buffer layer 03 and the second buffer layer 04 are made of the same material, and the materials of the first buffer layer 03 and the second buffer layer 04 respectively include a first slowly changing component.
[0042] In the first direction M, the content of the first gradually changing component in the first buffer layer 03 gradually increases; and the content of the first gradually changing component in the second buffer layer 04 gradually decreases.
[0043] Epitaxial layer 05 located on the side of the buffer stack 02 in the Nth group away from the substrate 01.
[0044] Specifically, in this embodiment of the invention, the substrate 01 can be a Si substrate; N sets of buffer stacks 02 are disposed on one side of the substrate 01, where N ≥ 1, for example, N can be 1, 2, 3, etc.; Reference Figure 2 , Figure 2 A schematic diagram of another semiconductor device is provided for embodiments of the present invention; see reference. Figure 3 , Figure 3 A schematic diagram of the structure of another semiconductor device is provided for embodiments of the present invention; such as Figure 2 As shown, a set of buffer stacks 02 is disposed on one side of the substrate 01, or as... Figure 3As shown, three sets of buffer stacks 02 are disposed on one side of substrate 01; the specific design is based on actual needs. It should be noted that, for example... Figure 2 As shown, the thickness of the buffer stack 02 is relatively low. When the thickness is high, setting it in one set will still result in a high surface roughness. In this case, multiple layers can be set. Each set of buffer stacks 02 includes a first buffer layer 03 and a second buffer layer 04 sequentially arranged in the first direction M. The first buffer layer 03 and the second buffer layer 04 are made of the same material, and the materials of the first buffer layer 03 and the second buffer layer 04 respectively include a first gradually changing component.
[0045] Optionally, in another embodiment of the present invention, the first buffer layer 03 and the second buffer layer 04 are made of SiGe material.
[0046] Optionally, in another embodiment of the present invention, the first slowly changing component is a Ge component.
[0047] Specifically, in this embodiment of the invention, the material of the first buffer layer 03 can be SiGe material. SiGe material contains two components, namely Si component and Ge component. In this embodiment, the Ge component is used as the first slowly varying component. Since the changes of Si component and Ge component in SiGe material are relative, that is, when the Ge component gradually increases, the Si component gradually decreases. At this time, the Si component can be used as the second slowly varying component. When the first slowly varying component in the first buffer layer 03 increases with the increase of thickness, the second slowly varying component gradually decreases. In this embodiment, the semiconductor device is described using the Ge component as the first slowly varying component as an example.
[0048] Similarly, since the material of the second buffer layer 04 is the same as that of the first buffer layer 03, the material of the second buffer layer 04 can also be SiGe material. SiGe material contains two components, namely Si component and Ge component. In this embodiment, the Ge component is used as the first slowly varying component. Since the changes of Si component and Ge component in SiGe material are relative, that is, when the Ge component gradually increases, the Si component gradually decreases. At this time, the Si component can be used as the second slowly varying component. When the first slowly varying component in the second buffer layer 04 increases with the increase of thickness, the second slowly varying component gradually decreases. In this embodiment, the semiconductor device is described using the Ge component as the first slowly varying component as an example.
[0049] It should be noted that the material of the first buffer layer 03 and the first slowly changing component in the first buffer layer 03 can be the same as the material of the second buffer layer 04 and the first slowly changing component in the second buffer layer 04. The materials of the first buffer layer 03 and the second buffer layer 04 can also be other materials, and the first slowly changing component in the first buffer layer 03 and the second buffer layer 04 can also be other components. The specific materials and components are not limited.
[0050] Optionally, in another embodiment of the invention, reference is made to... Figure 4 , Figure 4 This is a schematic diagram of the structure of the buffer stack provided in an embodiment of the present invention; see reference. Figure 5 , Figure 5 This is a schematic diagram of another buffer stack structure provided in an embodiment of the present invention; the content of the first gradually changing component is 0%-100%.
[0051] Specifically, in this embodiment of the invention, the content of the first gradually changing component can be 0%-100%, excluding endpoints. For example, the content of the first gradually changing component can be 12%, 30%, or 69%, etc.; in the first direction M, that is, in the thickness direction of the buffer stack 02, the content of the first gradually changing component in the first buffer layer 03 gradually increases; the content of the first gradually changing component in the second buffer layer 04 gradually decreases; such as Figure 4 As shown, when there is only one set of buffer layers 02, taking Ge composition as an example of the first gradually changing component; when the final required content of the first gradually changing component in the buffer layer 02 is 30%, the content of the first gradually changing component in the first buffer layer 03 gradually increases from 0% to 32% in the thickness direction, mainly to gradually reduce lattice mismatch. Then, the content of the first gradually changing component in the second buffer layer 04 gradually decreases from 32% to 30% in the thickness direction. The tensile stress provided by the second buffer layer 04 can reduce the surface roughness of the buffer layer 02, thereby facilitating the formation of the epitaxial layer 05; or as... Figure 5As shown, when there are three sets of buffer layers 02, the three sets of buffer layers 02 are sequentially set as the first group, the second group, and the third group in the first direction M. Taking Ge component as the first gradually changing component as an example, when the final required content of the first gradually changing component in the three sets of buffer layers 02 is 30%, the content of the first gradually changing component in the first buffer layer 03 of the first set of buffer layers 02 gradually increases from 0% to 12% in the thickness direction, and then the content of the first gradually changing component in the second buffer layer 04 gradually decreases from 12% to 10% in the thickness direction; the content of the first gradually changing component in the first buffer layer 03 of the second set of buffer layers 02 gradually increases from 10% to 2% in the thickness direction. 2%, and then the content of the first gradually changing component in the second buffer layer 04 is gradually reduced from 22% to 20% in the thickness direction; in the third group of buffer stacks 02, the content of the first gradually changing component in the first buffer layer 03 is gradually increased from 20% to 32% in the thickness direction, and then the content of the first gradually changing component in the second buffer layer 04 is gradually reduced from 32% to 30% in the thickness direction. Each second buffer layer 04 can provide tensile stress for the first buffer layer 03 in the next group of buffer stacks 02. Finally, the second buffer layer 04 in the third group provides tensile stress for the subsequent epitaxial layer 05, reducing the surface roughness of the buffer stacks 02, which is beneficial to the formation of the epitaxial layer 05.
[0052] Based on the semiconductor device in the above embodiments, the present invention also provides a method for fabricating the semiconductor device, for use in fabricating the above semiconductor device, with reference to... Figure 6 , Figure 6 This is a schematic flowchart of a semiconductor device fabrication method provided in an embodiment of the present invention; the fabrication method includes:
[0053] S101: Provide a substrate 01.
[0054] In this step, substrate 01 can be a Si substrate.
[0055] S102: N sets of buffer stacks 02 are formed on one side of the substrate 01, where N≥1; the N sets of buffer stacks 02 are sequentially arranged in a first direction M; the first direction M is perpendicular to the substrate 01 and points from the substrate 01 to the buffer stacks 02; the buffer stacks 02 include: a first buffer layer 03 and a second buffer layer 04 sequentially arranged in the first direction M; the first buffer layer 03 and the second buffer layer 04 are made of the same material, and the materials of the first buffer layer 03 and the second buffer layer 04 respectively include a first gradually changing component; wherein, in the first direction M, the content of the first gradually changing component in the first buffer layer 03 gradually increases; the content of the first gradually changing component in the second buffer layer 04 gradually decreases.
[0056] In this step, the buffer stack 02 is the same as the buffer stack 02 of the semiconductor device in the above embodiment, and can be N groups, where N≥1. For example, N can be 1, 2, 3, etc. Figure 2 The middle layer is a buffer stack 02, such as Figure 3 The middle section consists of three sets of buffer stacks 02.
[0057] refer to Figure 7 , Figure 7 This is a schematic flowchart of another semiconductor device fabrication method provided by an embodiment of the present invention; forming N sets of buffer stacks 02 on one side of the substrate 01 further includes:
[0058] S103: Determine the final target content of the first slowly varying component of the first buffer layer 03 and the second buffer layer 04 in the first direction M in each group of buffer stacks 02.
[0059] In this step, the final target content of the first gradually varying component of the first buffer layer 03 and the second buffer layer 04 in each buffer stack 02 in the first direction M is first determined. This target content of the first gradually varying component is the final content of the first gradually varying component in the buffer stack 02 in practical application. For example, the final target content of the first gradually varying component is 30%. Figure 4 As shown, when there is only one set of buffer layers 02, the content of the first slowly varying component in the first buffer layer 03 and the second buffer layer 04 of this set of buffer layers 02 needs to reach 30% in the end; for example Figure 5 As shown, there are three sets of buffer stacks 02. At this time, it is only necessary to design that the content of the first slowly changing component in the first buffer layer 03 and the second buffer layer 04 of the last set of buffer stacks 02 formed in the first direction M eventually reaches 30%.
[0060] S104: Form the first buffer layer 03, wherein the maximum content of the first slowly varying component in the first buffer layer 03 in the first direction M is greater than the target content.
[0061] In this step, when forming the first buffer layer 03, the maximum content of the first gradually changing component in the first buffer layer 03 needs to be greater than the target content. Taking a set of buffer stacks 02 as an example, when the target content of the first gradually changing component in the buffer stack 02 is 30%, the content of the first gradually changing component in the first buffer layer 03 gradually increases from 0% to 32% as the thickness increases; as the content of the first gradually changing component in the thickness direction gradually increases in the first buffer layer 03, the lattice mismatch is reduced.
[0062] S105: Form the second buffer layer 04, wherein the minimum content of the first gradually changing component in the first direction M in the second buffer layer 04 is equal to the target content, and the maximum content of the first gradually changing component in the first direction M in the second buffer layer 04 is equal to the maximum content of the first gradually changing component in the first direction M in the first buffer layer 03.
[0063] In this step, based on the content of the first buffer layer 03 in step S104, when forming the second buffer layer 04, the content of the first gradually changing component in the second buffer layer 04 is gradually reduced from 32% to 30% as the thickness increases. The content of the first gradually changing component in the first buffer layer 03 gradually decreases in the thickness direction, thereby providing tensile stress for the structural layers that grow later.
[0064] It should be noted that in the same group of buffer stacks 02, the maximum content of the first buffer component in the first buffer layer 02 is the same as the maximum content of the first component in the second buffer layer 04. In the same group of buffer stacks, the content of the first slowly changing component gradually increases to exceed the final target content, and then gradually decreases to the final target content. The multi-layer buffer stacks 02 only need to repeat steps S104 and S105.
[0065] S106: An epitaxial layer 05 is formed on the side of the buffer stack 02 in the Nth group away from the substrate 01.
[0066] In this step, after completing the N-group buffer stack 02, the epitaxial layer 05 in the semiconductor device can be grown, such as growing Si, GaAs, or SiGe stacks, or further fabricating devices with strained Si / Ge nanosheets.
[0067] Optionally, in another embodiment of the present invention, the first buffer layer 03 and the second buffer layer 04 are made of SiGe material.
[0068] Optionally, in another embodiment of the present invention, the first slowly changing component is a Ge component.
[0069] Specifically, in this embodiment of the invention, the material of the first buffer layer 03 can be SiGe material. SiGe material contains two components, namely Si component and Ge component. In this embodiment, the Ge component is used as the first slowly varying component. Since the changes of Si component and Ge component in SiGe material are relative, that is, when the Ge component gradually increases, the Si component gradually decreases. At this time, the Si component can be used as the second slowly varying component. When the first slowly varying component in the first buffer layer 03 increases with the increase of thickness, the second slowly varying component gradually decreases. In this embodiment, the semiconductor device is described using the Ge component as the first slowly varying component as an example.
[0070] Similarly, since the material of the second buffer layer 04 is the same as that of the first buffer layer 03, the material of the second buffer layer 04 can also be SiGe material. SiGe material contains two components, namely Si component and Ge component. In this embodiment, the Ge component is used as the first slowly varying component. Since the changes of Si component and Ge component in SiGe material are relative, that is, when the Ge component gradually increases, the Si component gradually decreases. At this time, the Si component can be used as the second slowly varying component. When the first slowly varying component in the second buffer layer 04 increases with the increase of thickness, the second slowly varying component gradually decreases. In this embodiment, the semiconductor device is described using the Ge component as the first slowly varying component as an example.
[0071] It should be noted that the materials of the first buffer layer 03 and the first gradually changing component and the second buffer layer 04 can be the same as the first gradually changing component. The materials of the first buffer layer 03 and the second buffer layer 04 can also be other materials, and the first gradually changing component in the first buffer layer 03 and the second buffer layer 04 can also be other components. The specific materials and components are not limited.
[0072] In this semiconductor device, the content of the first gradually varying component in the first buffer layer 03 gradually increases in the first direction M, thereby gradually reducing the lattice mismatch. At the same time, the content of the first gradually varying component in the second buffer layer 04 gradually decreases in the first direction M, thereby providing tensile stress for the subsequently grown epitaxial layer 05 and further reducing the surface roughness of the buffer stack 02. The combination of the two achieves dislocation containment, confining most dislocations and defects in the buffer stack 02. Compared with the prior art, growing this buffer stack 02 on the substrate 01 can achieve higher relaxation and lower surface roughness, providing a foundation for the formation of a high-quality epitaxial layer 05 in the subsequent semiconductor device.
[0073] The above provides a detailed description of a semiconductor device and its fabrication method provided by the present invention. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. 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 the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.
[0074] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.
[0075] It should also be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that elements inherent to a process, method, article, or apparatus that comprises a list of elements, or elements inherent to such processes, methods, articles, or apparatus, are also included. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.
[0076] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A semiconductor device, characterized in that, The semiconductor device includes: Substrate; N sets of buffer stacks located on one side of the substrate, wherein N≥1; the N sets of buffer stacks are arranged sequentially in a first direction; the first direction is perpendicular to the substrate and extends from the substrate to the buffer stacks; The buffer stack includes: a first buffer layer and a second buffer layer sequentially disposed in the first direction; the first buffer layer and the second buffer layer are made of the same material, and the materials of the first buffer layer and the second buffer layer respectively include a first slowly changing component, the content of the first slowly changing component is 0%-100%, and it does not contain endpoints; In the first direction, the content of the first gradually varying component in the first buffer layer gradually increases to be greater than the final target content in the first direction, so as to gradually reduce lattice mismatch, and the maximum content of the first gradually varying component in the first buffer layer in the first direction is greater than the target content; the content of the first gradually varying component in the second buffer layer gradually decreases to the final target content in the first direction, so as to reduce the surface roughness of the buffer stack, the minimum content of the first gradually varying component in the second buffer layer in the first direction is equal to the target content, and the maximum content of the first gradually varying component in the second buffer layer in the first direction is equal to the maximum content of the first gradually varying component in the first buffer layer in the first direction; The epitaxial layer located on the side of the buffer stack opposite to the substrate in the Nth group.
2. The semiconductor device according to claim 1, characterized in that, The first buffer layer and the second buffer layer are made of SiGe material.
3. The semiconductor device according to claim 2, characterized in that, The first slowly varying component is the Ge component.
4. A method for fabricating a semiconductor device, characterized in that, The preparation method includes: Provide a substrate; N sets of buffer stacks are formed on one side of the substrate, where N≥1; the N sets of buffer stacks are arranged sequentially in a first direction; the first direction is perpendicular to the substrate and extends from the substrate to the buffer stacks; The buffer stack includes: a first buffer layer and a second buffer layer sequentially disposed in the first direction; the first buffer layer and the second buffer layer are made of the same material, and the materials of the first buffer layer and the second buffer layer respectively include a first gradually changing component, the content of the first gradually changing component is 0%-100%, and does not include endpoints; wherein, in the first direction, the content of the first gradually changing component in the first buffer layer gradually increases; the content of the first gradually changing component in the second buffer layer gradually decreases; An epitaxial layer is formed on the side of the buffer stack in the Nth group away from the substrate; Wherein, forming N sets of buffer stacks on one side of the substrate includes: Determine the final target content of the first slowly varying component of the first buffer layer and the second buffer layer in the first direction in each group of buffer stacks; The first buffer layer is formed, wherein the maximum content of the first slowly varying component in the first buffer layer in the first direction is greater than the target content; A second buffer layer is formed, wherein the minimum content of the first slowly varying component in the first direction in the second buffer layer is equal to the target content, and the maximum content of the first slowly varying component in the first direction in the second buffer layer is equal to the maximum content of the first slowly varying component in the first direction in the first buffer layer.
5. The preparation method according to claim 4, characterized in that, The first buffer layer and the second buffer layer are made of SiGe material.
6. The preparation method according to claim 5, characterized in that, The first slowly varying component is the Ge component.