Preparation method of silicon-based germanium epitaxial window structure and semiconductor device

Abstract

The invention discloses a preparation method of a silicon-based germanium epitaxial window structure and a semiconductor device. The method comprises the following steps: forming a first groove on an exposed surface of a top silicon layer of an SOI (Silicon On Insulator); forming a dielectric layer on the exposed surface of the top silicon layer, and filling the first groove; forming a second groove on the surface of the dielectric layer, enabling the bottom of the second groove to be nested in the first groove, and forming a dielectric isolation layer between the second groove and the first groove; the dielectric isolation layer is removed, and a third groove with the bottom located in the top silicon layer is formed in the surface of the dielectric layer; and forming a germanium epitaxial layer in the third groove. According to the invention, the generation of a polymer with Si-C bonds on the silicon surface can be effectively prevented, a good germanium-silicon epitaxial interface is formed, the formation of germanium epitaxial defects can be greatly reduced, and better device detection performance is realized.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor integrated circuit technology, and in particular to a method for preparing a silicon-based germanium epitaxial window structure and a semiconductor device. Background Art

[0002] When preparing silicon-based germanium photodetectors, the epitaxial growth of germanium-silicon is very sensitive to the surface properties of the silicon trench in the epitaxial window. Germanium epitaxy needs to be carried out on a clean silicon surface, otherwise various epitaxial defects are easily formed.

[0003] The existing method for forming a silicon trench generally involves first forming a protective dielectric layer on a silicon layer, and then using a dry etching process for the dielectric (for example, etching the dielectric layer until the surface of the silicon layer is exposed), thereby forming a silicon trench serving as an epitaxial window on the surface of the dielectric layer.

[0004] However, dry etching processes for dielectrics usually require the use of high-energy plasma formed by carbon-fluorine gases (such as CF4) for etching (for example, using a capacitively coupled plasma etching process). During the plasma etching process, the plasma gas discharges and collision dissociates to produce unsaturated molecules (such as CF2). Driven by high ion energy, carbon is easily injected into the silicon around the groove and reacts with the silicon to form a polymer film with Si-C bonds on the epitaxial interface, thereby preventing a pure silicon surface from being obtained, thereby adversely affecting the high-quality epitaxy of germanium.

[0005] Therefore, it is necessary to find a method that can effectively avoid the formation of Si-C bonds on the epitaxial interface to improve the epitaxial defects of germanium silicon. Summary of the Invention

[0006] The purpose of the present invention is to overcome the above-mentioned defects in the prior art and provide a method for preparing a silicon-based germanium epitaxial window structure and a semiconductor device.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] The present invention provides a method for preparing a silicon-based germanium epitaxial window structure, comprising:

[0009] forming a first trench on an exposed surface of a top silicon layer of the SOI;

[0010] forming a dielectric layer on the exposed surface of the top silicon layer and filling the first trench;

[0011] forming a second trench on the surface of the dielectric layer, and making the bottom of the second trench nest in the first trench, and forming a dielectric isolation layer between the second trench and the first trench;

[0012] removing the dielectric isolation layer, and forming a third trench on the surface of the dielectric layer with its bottom portion in the top silicon layer;

[0013] A germanium epitaxial layer is formed in the third trench.

[0014] Furthermore, a first photolithography and dry etching process for silicon is used to form the first groove, and a second photolithography and dry etching process for the medium is used to form the second groove; wherein, the photolithography mask used in the first photolithography and dry etching process is used for the photolithography in the second photolithography and dry etching process, and the photolithography parameters are adjusted so that the critical dimension of the formed second groove is smaller than the critical dimension of the first groove, and the etching parameters are adjusted so that the bottom of the second groove is located above the bottom of the first groove, and the bottom of the formed second groove is nested in the first groove, and the dielectric isolation layer is formed between the second groove and the first groove.

[0015] Furthermore, the first photolithography and dry etching process for silicon includes a first photolithography and inductively coupled plasma dry etching process for silicon, and the second photolithography and dry etching process for the medium includes a second photolithography and capacitively coupled plasma dry etching process for the medium.

[0016] Furthermore, the dielectric isolation layer is removed by using a wet etching process.

[0017] Furthermore, forming a dielectric layer on the exposed surface of the top silicon layer and filling the first trench specifically includes:

[0018] forming a first dielectric layer of silicon dioxide on the exposed surface of the top silicon layer and on the inner wall surface of the first trench by a thermal oxidation process;

[0019] A second dielectric layer of silicon dioxide is formed on the surface of the first dielectric layer by a deposition process, and the first trench is filled; wherein the dielectric layer includes the second dielectric layer and the first dielectric layer, and the dielectric isolation layer is formed of at least the first dielectric layer material.

[0020] Furthermore, after forming the second dielectric layer, the method further includes: forming active devices in the top silicon layer around the first trench using an ion implantation process.

[0021] Furthermore, the method further includes: first patterning the top silicon layer to form a waveguide located on the buried oxide layer of SOI, and then forming the first trench on the exposed surface of the waveguide with the bottom located in the waveguide; when forming the first dielectric layer, the first dielectric layer is also formed on the exposed surface and side surfaces of the waveguide; and when forming the second dielectric layer, the second dielectric layer is also filled on the buried oxide layer around the waveguide, and the formed active device is located in the waveguide around the first trench.

[0022] Furthermore, after forming the second dielectric layer, the method further includes: using a deposition process to form a third dielectric layer of silicon dioxide with a thickness of 10 to 200 nm on the surface of the second dielectric layer to cover the first groove, and then forming the second groove on the surface of the third dielectric layer; wherein the dielectric layer includes the third dielectric layer, the second dielectric layer and the first dielectric layer.

[0023] Furthermore, the etching depth of the first trench is 10-100 nm, the difference between the critical dimension of the first trench and the critical dimension of the second trench is 1-2 nm, and the distance between the bottom of the second trench and the bottom of the first trench is 1-2 nm.

[0024] The present invention also provides a semiconductor device, comprising a silicon-based germanium epitaxial window structure prepared according to the above preparation method.

[0025] It can be seen from the above technical solution that the present invention first performs dry etching on silicon to form a first groove on the exposed surface of the top silicon layer, and fills the first groove with a dielectric layer, and then performs dry etching on the dielectric to form a second groove with a smaller critical dimension nested in the first groove on the dielectric layer, and then wet-removes the dielectric isolation layer on the first groove to form an epitaxial window (third groove). The dielectric layer material retained between the first trench and the second trench can be used as an isolation layer, thereby avoiding direct contact with silicon when forming the second trench, thereby effectively preventing the generation of Si-C bond polymers on the silicon surface and forming a good germanium-silicon epitaxial interface, which can greatly reduce the formation of germanium epitaxial defects to achieve better device detection performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a flowchart of a method for preparing a silicon-based germanium epitaxial window structure according to a preferred embodiment of the present invention.

[0027] Figure 2-Figure 10 A preferred embodiment of the present invention is based on Figure 1 A schematic diagram of the process steps for preparing a silicon-based germanium epitaxial window structure is provided. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meanings understood by people with ordinary skills in the field to which the invention belongs. The words "including" and similar words used in this article mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0029] The following combination Figures 1-10 , the specific implementation methods of the present invention are further described in detail.

[0030] refer to Figure 1 The method for preparing a silicon-based germanium epitaxial window structure of the present invention comprises the following steps:

[0031] Step S1: forming a first trench 16 on the exposed surface of the top silicon layer 13 of the SOI.

[0032] like Figure 2-Figure 3 As shown, an SOI substrate is used, which includes a bottom silicon layer 11, a buried oxide layer 12 and a top silicon layer 13 stacked in sequence.

[0033] First, a first photolithography and dry etching process for silicon is used to form a first trench 16 on the exposed surface of the top silicon layer 13 of the SOI. The first trench 16 serves as a preliminary window for forming a germanium epitaxial window.

[0034] In some embodiments, before forming the first trench 16, the top silicon layer 13 is patterned to form a pattern of the silicon waveguide 14 located on the buried oxide layer 12. A gap 15 is defined between the waveguide 14 and other pattern structures on the top silicon layer 13. Then, the first trench 16 is formed on the exposed surface of the waveguide 14 (i.e., the exposed surface of the top silicon layer 13), with the bottom portion located in the waveguide 14.

[0035] In some embodiments, a first photolithography and inductively coupled plasma (ICP) dry etching process directly targeting silicon is used to form the first trench 16 on the exposed surface of the waveguide 14 (top silicon layer 13 ).

[0036] It's worth noting that, unlike existing methods that use dry etching to form germanium epitaxial windows, the present invention employs a dry etching process that directly targets silicon, forming a first trench 16 on the exposed surface of the top silicon layer 13 (waveguide 14) to serve as a preliminary window for germanium epitaxy. In other words, etching is performed directly on the silicon surface.

[0037] In existing methods for forming germanium epitaxial windows using dry etching, in order to protect the silicon layer surface during ion implantation to form active devices and to prevent the formation of a germanium epitaxial layer on the silicon layer surface outside the epitaxial window, a dielectric layer, such as silicon dioxide, is typically formed on the silicon layer to protect the silicon layer surface. A dry etching process with a high selectivity between silicon dioxide and silicon is then used to form a silicon trench. Because the silicon trench for the epitaxial window must be etched until the silicon layer surface is exposed, and the silicon dioxide dielectric layer, which serves as a protective layer, is relatively thick, a capacitively coupled plasma (CCP) dry etching process for dielectrics is typically used. This not only increases the etch rate but also avoids over-etching the silicon layer surface (only the silicon layer surface needs to be exposed at the bottom of the silicon trench). Carbon-fluorine-containing gases, such as CF4, are used in the CCP etching process for silicon dioxide dielectrics, and high-energy plasma is required to accelerate the etch rate. In this way, during the plasma etching process, the plasma gas discharges and collision dissociation occurs, which will produce unsaturated CF2 molecules. Driven by high ion energy, carbon will be injected into the silicon around the groove and react with silicon to form a polymer film with Si-C bonds on the epitaxial interface. As a result, a pure silicon surface cannot be obtained, which has an adverse effect on the high-quality epitaxy of germanium.

[0038] In the present invention, an inductively coupled plasma dry etching process is used to form the first groove 16 on the exposed surface of the waveguide 14 (top silicon layer 13). This process is characterized by its ability to increase ion density under low ion energy conditions, thereby improving the etching rate while minimizing damage to the silicon surface. It also effectively prevents carbon contained in the photoresist from being excited by the energy and injected into the silicon layer of the waveguide 14. Furthermore, when using inductively coupled plasma for dry etching, the probability of carbon injection into the silicon layer can be further controlled by using a carbon-free etching gas (e.g., SF6, Cl2, SiCl4). During etching, volatile substances are generated through reactions and are extracted from the vacuum line in the form of gas, thereby obtaining a pure silicon surface.

[0039] In some embodiments, the etching depth of the first trench 16 is 10-100 nm, and the bottom of the first trench 16 is located in the waveguide 14 to be isolated from the buried oxide layer 12 thereunder.

[0040] Step S2 : forming a dielectric layer 19 on the exposed surface of the top silicon layer 13 and filling the first trench 16 .

[0041] like Figure 4 As shown, a thermal oxidation process is used to form a first silicon dioxide dielectric layer 17 on the exposed surface of the waveguide 14 (top silicon layer 13) and the inner wall surface of the first trench 16. The silicon dioxide thermal oxide layer is formed on the inner wall surface of the first trench 16 by thermal oxidation to repair the roughness of the inner wall surface of the first trench 16 (the edge of the epitaxial preparation window) caused by etching, thereby further improving the smoothness of the inner wall surface of the first trench 16.

[0042] When forming the first dielectric layer 17 , the first dielectric layer 17 may also be formed on the exposed top surfaces and side surfaces of other graphic structures on the waveguide 14 and the top silicon layer 13 , thereby covering the entire surface of the waveguide 14 graphic.

[0043] Next, ion implantation is performed to form active devices in the waveguide 14 surrounding the first trench 16. Since the first dielectric layer 17 formed by thermal oxidation is relatively thin and cannot meet the dielectric protective layer thickness requirement during ion implantation, a second dielectric layer of a certain thickness needs to be formed on the surface of the first dielectric layer 17.

[0044] like Figure 5 As shown, a second dielectric layer such as silicon dioxide is formed on the surface of the first dielectric layer 17 by a deposition process, and fills the first trench 16. The second dielectric layer and the first dielectric layer 17 form an integrated fourth dielectric layer 18.

[0045] The second dielectric layer may also be filled on the buried oxide layer 12 in the gap 15 around the waveguide 14 , and the gap 15 may be completely filled.

[0046] Afterwards, a chemical mechanical polishing process is used to flatten the surface of the fourth dielectric layer 18 (the second dielectric layer) to obtain a flat surface of the fourth dielectric layer 18, and the final thickness of the fourth dielectric layer 18 is adjusted to meet the requirements for the thickness range of the dielectric protection layer during ion implantation, thereby preventing the total thickness of the first dielectric layer 17 and the second dielectric layer from being too thick.

[0047] like Figure 6 As shown, an active device structure (not shown) is formed in the waveguide 14 around the first trench 16 by an ion implantation process.

[0048] like Figure 7As shown, after the ion implantation, a deposition process is used to further form a third dielectric layer, such as silicon dioxide, on the surface of the fourth dielectric layer 18 (the second dielectric layer) to cover the first trench 16. Thus, a dielectric layer 19 composed of the third dielectric layer, the second dielectric layer, and the first dielectric layer 17 is formed on the exposed surface of the waveguide 14 (the top silicon layer 13), filling the first trench 16.

[0049] In some embodiments, the thickness of the third dielectric layer is 10-200 nm.

[0050] Step S3 : forming a second trench 20 on the surface of the dielectric layer 19 , with the bottom of the second trench 20 nested in the first trench 16 , and forming a dielectric isolation layer 21 between the second trench 20 and the first trench 16 .

[0051] like Figure 8 As shown, a second photolithography and dry etching process for the dielectric is used to form a second trench 20 on the surface of the dielectric layer 19 (the third dielectric layer).

[0052] In some embodiments, the second trench 20 is formed by using a second photolithography and capacitively coupled plasma dry etching process for the dielectric.

[0053] The same photolithography mask used in the first photolithography and dry etching process to form the first trench 16 is also used for the second photolithography and dry etching process to form the second trench 20. By adjusting photolithography parameters, such as photolithography energy and focal length, the width critical dimension of the second trench 20 is made smaller than the width critical dimension of the first trench 16. Furthermore, by adjusting etching parameters, such as etching time, the bottom of the second trench 20 is positioned above the bottom of the first trench 16 and nested within the first trench 16, with a certain gap maintained between the walls of the second trench 20 and the walls of the first trench 16. In this way, a dielectric isolation layer 21 of a certain thickness is formed between the second trench 20 and the first trench 16. In other words, the dielectric isolation layer 21 is located on the inner wall surface of the first trench 16, and the bottom wall of the second trench 20 is formed on the surface of the dielectric isolation layer 21.

[0054] In some embodiments, the difference between the critical width dimension of the first trench 16 and the critical width dimension of the second trench 20 is 1-2 nm. That is, the gap between the walls of the second trench 20 and the walls of the first trench 16 is 0.5-1 nm on one side. Furthermore, the gap between the bottom of the second trench 20 and the bottom of the first trench 16 is 1-2 nm. This defines the thickness of the dielectric isolation layer 21 on the side and bottom surfaces of the first trench 16.

[0055] Theoretically, the dielectric isolation layer 21 is formed of at least the material of the first dielectric layer 17. In this embodiment, the dielectric isolation layer 21 is formed of the first dielectric layer 17 and a portion of the second dielectric layer material remaining after etching.

[0056] It can be seen that because the critical dimension of the width of the second trench 20 is smaller than that of the first trench 16, and the bottom of the second trench 20 is located above the bottom of the first trench 16, the etching process during the formation of the second trench 20 is limited to the silicon dioxide dielectric layer 19 and does not contact the silicon on the surface of the first trench 16. Therefore, a conventional capacitively coupled plasma dry etching process for dielectrics can be used to form the second trench 20, which not only improves the etching rate but also effectively avoids the formation of Si-C bond polymers, laying a good foundation for the subsequent formation of a good germanium-silicon epitaxial interface and reducing germanium epitaxial defects.

[0057] Step S4 : removing the dielectric isolation layer 21 and forming a third trench 22 on the surface of the dielectric layer 19 , with its bottom located in the top silicon layer 13 .

[0058] like Figure 9 As shown, the dielectric isolation layer 21 located on the inner wall surface of the first trench 16 is removed by a wet etching process.

[0059] In some embodiments, when the dielectric layer 19 is made of silicon dioxide, a hydrofluoric acid dilution (DHF) is used to completely remove the silicon dioxide dielectric isolation layer 21. The chemical reaction formula is:

[0060] SiO2+4HF=SiF4↑+2H2O;

[0061] The SiF4 produced by the reaction can be removed through the gas exhaust system.

[0062] A selective wet etching process effectively removes the dielectric layer 19 material while avoiding the consumption of silicon at the walls of the first trench 16. This forms a third trench 22, the final germanium epitaxial window, based on the first trench 16. Therefore, the integrated multi-step etching scheme of the present invention for optimizing the germanium epitaxial interface to form the germanium epitaxial window effectively prevents the formation of Si-C bond aggregates on the silicon surface within the epitaxial window, which could affect the epitaxial interface. This reduces interface defects, improves the quality of the germanium epitaxy, and thereby reduces germanium epitaxial defects.

[0063] The material of the dielectric layer 19 is not limited to silicon dioxide and can be determined according to actual conditions.

[0064] Step S5 : forming a germanium epitaxial layer 23 in the third trench 22 .

[0065] like Figure 10As shown, finally, a germanium epitaxial growth process is used to epitaxially grow germanium in the epitaxial window formed by the third trench 22, and a chemical mechanical polishing process is used to flatten the germanium surface to form a germanium epitaxial layer 23 in the epitaxial window.

[0066] A semiconductor device of the present invention comprises a silicon-based germanium epitaxial window structure prepared according to the above-mentioned method for preparing the silicon-based germanium epitaxial window structure of the present invention, for example Figure 10 The silicon-based germanium epitaxial window structure shown.

[0067] refer to Figure 10 A semiconductor device of the present invention is fabricated on an SOI substrate, wherein the SOI substrate comprises a bottom silicon layer 11, a buried oxide layer 12, and a top silicon layer 13 stacked in sequence.

[0068] A semiconductor device according to the present invention includes a dielectric layer 19 formed on a top silicon layer 13, a third trench 22 formed downward from the surface of the dielectric layer 19, a germanium epitaxial window formed by the third trench 22, and a germanium epitaxial layer 23 formed in the epitaxial window. The bottom of the epitaxial window (third trench 22) is located in the top silicon layer 13 and is isolated from the buried oxide layer 12 below the top silicon layer 13.

[0069] In some embodiments, the top silicon layer 13 is patterned to form a silicon waveguide 14 located on the buried oxide layer 12. A gap 15 is defined between the waveguide 14 and other patterned structures on the top silicon layer 13. A dielectric layer 19 fills the gap 15 and is tightly connected to the buried oxide layer 12. The bottom of the epitaxial window (third trench 22) is located in the waveguide 14 and is isolated from the underlying buried oxide layer 12.

[0070] In some embodiments, active device structures (not shown) are fabricated in the waveguide 14 around the epitaxial window.

[0071] In some embodiments, a semiconductor device of the present invention includes a silicon-based germanium photodetector device having the above-described silicon-based germanium epitaxial window structure, wherein the germanium epitaxial layer 23 formed in the epitaxial window serves as the light absorption layer of the silicon-based germanium photodetector device.

[0072] In summary, the present invention first performs ICP dry etching on silicon to form a first groove 16 on the exposed surface of the top silicon layer 13, and fills the first groove 16 with a dielectric layer 19, and then performs CCP dry etching on the dielectric to form a second groove 20 with a smaller critical dimension nested in the first groove 16 on the dielectric layer 19, and then wet-removes the dielectric isolation layer 21 on the first groove 16 to form an epitaxial window (third groove 22). The dielectric layer 19 material retained between the first groove 16 and the second groove 20 can be used as an isolation layer, thereby avoiding direct contact with silicon when dry etching to form the second groove 20, thereby effectively preventing the generation of Si-C bond polymers on the silicon surface and forming a good germanium-silicon epitaxial interface, which can greatly reduce the formation of germanium epitaxial defects and achieve better device detection performance.

[0073] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations of these embodiments are possible. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as set forth in the appended claims. Furthermore, the invention described herein is susceptible to other embodiments and may be practiced or implemented in a variety of ways.

Claims

1. A method for preparing a silicon-based germanium epitaxial window structure, characterized in that: include: forming a first trench on an exposed surface of a top silicon layer of the SOI; forming a dielectric layer on the exposed surface of the top silicon layer and filling the first trench; forming a second trench on the surface of the dielectric layer, and making the bottom of the second trench nest in the first trench, and forming a dielectric isolation layer between the second trench and the first trench; removing the dielectric isolation layer, and forming a third trench on the surface of the dielectric layer with its bottom portion in the top silicon layer; A germanium epitaxial layer is formed in the third trench.

2. The method for preparing a silicon-based germanium epitaxial window structure according to claim 1, wherein: A first photolithography and dry etching process for silicon is used to form the first groove, and a second photolithography and dry etching process for a medium is used to form the second groove; wherein, the photolithography mask used in the first photolithography and dry etching process is used for the photolithography in the second photolithography and dry etching process, and the photolithography parameters are adjusted so that the critical dimension of the formed second groove is smaller than the critical dimension of the first groove, and the etching parameters are adjusted so that the bottom of the second groove is located above the bottom of the first groove, and the bottom of the formed second groove is nested in the first groove, and the dielectric isolation layer is formed between the second groove and the first groove.

3. The method for preparing a silicon-based germanium epitaxial window structure according to claim 2, wherein: The first photolithography and dry etching process for silicon includes a first photolithography and inductively coupled plasma dry etching process for silicon, and the second photolithography and dry etching process for medium includes a second photolithography and capacitively coupled plasma dry etching process for medium.

4. The method for preparing a silicon-based germanium epitaxial window structure according to claim 1, wherein: The dielectric isolation layer is removed by adopting a wet etching process.

5. The method for preparing a silicon-based germanium epitaxial window structure according to claim 1, wherein: The step of forming a dielectric layer on the exposed surface of the top silicon layer and filling the first trench specifically includes: forming a first dielectric layer of silicon dioxide on the exposed surface of the top silicon layer and on the inner wall surface of the first trench by a thermal oxidation process; A second dielectric layer of silicon dioxide is formed on the surface of the first dielectric layer by a deposition process, and the first trench is filled; wherein the dielectric layer includes the second dielectric layer and the first dielectric layer, and the dielectric isolation layer is formed of at least the first dielectric layer material.

6. The method for preparing a silicon-based germanium epitaxial window structure according to claim 5, characterized in that: After forming the second dielectric layer, the method further includes: forming active devices in the top silicon layer around the first trench using an ion implantation process.

7. The method for preparing a silicon-based germanium epitaxial window structure according to claim 6, characterized in that: Also includes: First, the top silicon layer is patterned to form a waveguide located on the buried oxide layer of the SOI, and then the first trench with its bottom located in the waveguide is formed on the exposed surface of the waveguide; When forming the first dielectric layer, the first dielectric layer is also formed on the exposed surface and side surfaces of the waveguide; and when forming the second dielectric layer, the second dielectric layer is also filled on the buried oxide layer around the waveguide, and the formed active device is located in the waveguide around the first trench.

8. The method for preparing a silicon-based germanium epitaxial window structure according to claim 5, wherein: After forming the second dielectric layer, the method further includes: using a deposition process to form a third dielectric layer of silicon dioxide with a thickness of 10 to 200 nm on the surface of the second dielectric layer to cover the first trench, and then forming the second trench on the surface of the third dielectric layer; wherein the dielectric layer includes the third dielectric layer, the second dielectric layer and the first dielectric layer.

9. The method for preparing a silicon-based germanium epitaxial window structure according to claim 2, wherein: The etching depth of the first trench is 10-100 nm, the difference between the critical dimension of the first trench and the critical dimension of the second trench is 1-2 nm, and the distance between the bottom of the second trench and the bottom of the first trench is 1-2 nm.

10. A semiconductor device, characterized in that: It comprises a silicon-based germanium epitaxial window structure prepared by the preparation method according to any one of claims 1 to 9.

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