SOI (Silicon On Insulator) substrate with embedded cavity and preparation method thereof
By forming and removing the sacrificial layer when preparing the SOI substrate with a pre-embedded cavity, the problem of thin and easy to break is solved, the complexity and cost of the preparation process are reduced, and the manufacturing yield and performance of the substrate are improved.
Patent Information
- Application Number
- CN202411702071.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-26
- Publication Date
- 2025-03-11
AI Technical Summary
In the current process of preparing SOI substrates with embedded cavity, the top layer of silicon is thin and easy to break, resulting in low manufacturing yield. The double-layer SOI preparation process is complex and costly, making it difficult to ensure the uniformity of the top layer of silicon thickness.
By forming a top structure including a top layer of silicon and a sacrificial layer covering its surface, and removing the sacrificial layer after being connected to the support substrate, an SOI substrate with an embedded cavity is formed. This method forms a thinner top silicon before being connected to the support substrate, avoiding the risk of top silicon breaking during subsequent grinding, and removing the sacrificial layer through grinding and chemical corrosion processes, reducing manufacturing cost and process complexity.
The manufacturing yield of SOI substrate with a pre-embedded cavity is improved, the difficulty and cost of the preparation process is reduced, and the uniformity of the thickness of the top silicon is improved, thereby improving the performance of the substrate.
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Figure CN119591050A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of semiconductor manufacturing, and in particular to an SOI substrate with a pre-buried cavity and a preparation method thereof. Background Art
[0002] Cavity SOI (C-SOI) with a pre-buried cavity is an advanced SOI technology, which is a substrate further developed on the basis of SOI (Silicon-On-Insulator). The characteristic of SOI with a pre-buried cavity is that it contains a pre-etched cavity in the supporting substrate wafer. The application of SOI technology with a pre-buried cavity can significantly simplify the manufacturing process of MEMS devices, such as simplifying the manufacturing process of pressure sensors. By integrating the pre-buried cavity in the SOI manufacturing process, the complex steps of etching the cavity in the substrate layer can be omitted, and a complex cavity system can be prefabricated. However, in the current process of preparing SOI with a pre-buried cavity, the biggest difficulty lies in the preparation of the top silicon. Because the supporting substrate has a cavity, part of the top silicon will be suspended, and the thinner the top silicon, the more likely it is to break and fail. With the exploration and deepening of technical research and the continuous development of the semiconductor industry, the demand for top silicon of SOI with a pre-buried cavity is getting thinner and thinner. However, in order to obtain a thinner top silicon, a more expensive double-layer SOI is used to prepare an SOI with a pre-buried cavity. The above process is not only costly and complex, but also difficult to ensure the uniformity of the thickness of the top silicon.
[0003] Therefore, how to reduce the thickness of the top silicon while reducing the difficulty of the preparation process of the SOI substrate with a pre-buried cavity, reduce the manufacturing cost of the SOI substrate with a pre-buried cavity, and improve the uniformity of the thickness of the top silicon, thereby improving the performance and manufacturing yield of the SOI substrate with a pre-buried cavity, is a technical problem that needs to be solved urgently. Summary of the invention
[0004] The present invention provides an SOI substrate with a pre-buried cavity and a preparation method thereof, which are used to reduce the difficulty of the preparation process of the SOI substrate with a pre-buried cavity while reducing the thickness of the top silicon layer, reduce the manufacturing cost of the SOI substrate with the pre-buried cavity, and improve the uniformity of the thickness of the top silicon layer, thereby improving the performance and manufacturing yield of the SOI substrate with the pre-buried cavity.
[0005] According to some embodiments, the present invention provides a method for preparing a SOI substrate with a pre-buried cavity, comprising the following steps:
[0006] Forming a support substrate, the support substrate comprising a bottom silicon layer, a buried oxide layer covering a surface of the bottom silicon layer, and a cavity penetrating the buried oxide layer and extending to the inside of the bottom silicon layer;
[0007] forming a top structure, the top structure comprising a top silicon layer and a sacrificial layer covering a surface of the top silicon layer;
[0008] Connecting the support substrate and the top structure along the direction of the buried oxide layer toward the top silicon layer;
[0009] The sacrificial layer is removed to form the SOI substrate with the embedded cavity including the top silicon layer and the supporting substrate.
[0010] In some embodiments, the specific steps of forming the support substrate include:
[0011] Forming the bottom silicon and the buried oxide layer covering the top surface of the bottom silicon along a first direction, wherein the first direction intersects the top surface of the bottom silicon vertically;
[0012] The buried oxide layer and part of the bottom silicon are etched to form a plurality of cavities which are arranged at intervals along a second direction and penetrate the buried oxide layer along the first direction and extend to the inside of the bottom silicon, wherein the second direction is parallel to the top surface of the bottom silicon.
[0013] In some embodiments, the specific steps of forming the top structure include:
[0014] forming a sacrificial layer, the sacrificial layer comprising a top surface and a bottom surface relatively distributed along the first direction, the sacrificial layer being a single crystal silicon layer including first doping ions;
[0015] The top silicon layer is formed on the top surface of the sacrificial layer, the top silicon layer is a single crystal silicon layer including second doping ions, and the concentration of the first doping ions in the sacrificial layer is different from the concentration of the second doping ions in the top silicon layer.
[0016] In some embodiments, the type of the first doping ions is the same as the type of the second doping ions.
[0017] In some embodiments, a concentration of the first doping ions in the sacrificial layer is greater than a concentration of the second doping ions in the top silicon layer.
[0018] In some embodiments, the thickness of the top silicon layer is less than 10 μm.
[0019] In some embodiments, the specific steps of removing the sacrificial layer to form the SOI substrate with the embedded cavity including the top silicon layer and the supporting substrate include:
[0020] Removing part of the sacrificial layer by a grinding process;
[0021] The remaining sacrificial layer is removed by a chemical etching process.
[0022] In some embodiments, the specific steps of removing part of the sacrificial layer by a grinding process include:
[0023] A grinding process is adopted to remove part of the sacrificial layer, and the thickness of the sacrificial layer is reduced to 50 μm to 60 μm.
[0024] In some embodiments, the specific steps of removing the remaining sacrificial layer by a chemical etching process include:
[0025] A chemical etching process is used to selectively remove all the remaining sacrificial layers to expose the surface of the top silicon layer. The chemical etching agent used in the chemical etching process is a mixed solution including hydrofluoric acid, nitric acid and acetic acid.
[0026] According to some other embodiments, the present invention further provides an SOI substrate with a pre-buried cavity, which is formed by using any of the above methods for preparing an SOI substrate with a pre-buried cavity.
[0027] The SOI substrate with a pre-buried cavity and the preparation method thereof provided by the present invention form a top structure including a top silicon and a sacrificial layer covering the surface of the top silicon, and after the top structure is connected to a supporting substrate, the sacrificial layer is removed to form the SOI substrate with a pre-buried cavity including the top silicon and the supporting substrate, that is, before being connected to the supporting substrate, the top silicon with a relatively thin thickness has been formed, thereby avoiding the problem that the top silicon suspended above the cavity is easily broken and failed during subsequent grinding, and improving the manufacturing yield of the SOI substrate with a pre-buried cavity with a relatively thin top silicon. Moreover, the present invention does not need to use a double-layer SOI wafer for preparation, the preparation cost is low, and the preparation process is simple, thereby improving the manufacturing efficiency of the semiconductor structure. In addition, the present invention also removes the sacrificial layer through a two-step process of grinding and chemical etching, and a mixed solution of hydrofluoric acid, nitric acid and acetic acid with a high etching selectivity is used in the chemical etching process, thereby helping to reduce the roughness of the surface of the top silicon exposed after removing the sacrificial layer, and obtaining the top silicon with uniform thickness, thereby further improving the quality of the prepared SOI substrate with a pre-buried cavity. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] Figure 1 is a flow chart of a method for preparing an SOI substrate with a pre-buried cavity in a specific embodiment of the present invention;
[0029] Figure 2 is a schematic structural diagram of a support substrate formed in a specific embodiment of the present invention;
[0030] Figure 3 is a schematic structural diagram of a top structure formed in a specific embodiment of the present invention;
[0031] Figure 4 is a schematic diagram of the structure after the support substrate and the top structure are connected in a specific embodiment of the present invention;
[0032] Figure 5 is a schematic diagram of the structure of a specific embodiment of the present invention after a portion of the sacrificial layer is removed by a grinding process;
[0033] Figure 6 It is a schematic structural diagram of an SOI substrate with a pre-buried cavity formed according to a specific embodiment of the present invention. DETAILED DESCRIPTION
[0034] The specific implementation of the SOI substrate with a pre-buried cavity and the preparation method thereof provided by the present invention will be described in detail below with reference to the accompanying drawings.
[0035] This specific embodiment provides a method for preparing an SOI substrate with a pre-buried cavity. Figure 1 FIG. 1 is a flow chart of a method for preparing a SOI substrate with a pre-buried cavity in a specific embodiment of the present invention. Figure 1 As shown, the method for preparing the SOI substrate with a pre-buried cavity comprises the following steps:
[0036] Step S11, forming a support substrate, wherein the support substrate includes a bottom silicon layer, a buried oxide layer covering a surface of the bottom silicon layer, and a cavity penetrating the buried oxide layer and extending to the inside of the bottom silicon layer;
[0037] Step S12, forming a top structure, wherein the top structure includes a top silicon layer and a sacrificial layer covering a surface of the top silicon layer;
[0038] Step S13, connecting the support substrate and the top structure along the direction of the buried oxide layer toward the top silicon layer;
[0039] Step S14, removing the sacrificial layer to form the SOI substrate with the embedded cavity including the top silicon layer and the supporting substrate.
[0040] Figure 2 Schematic diagram of the structure of the support substrate formed in a specific embodiment of the present invention. In some embodiments, the specific steps of forming the support substrate include:
[0041] Forming the bottom silicon 20 and the buried oxide layer 21 covering the top surface of the bottom silicon 20 along a first direction D1, wherein the first direction D1 intersects the top surface of the bottom silicon 20 vertically;
[0042] The buried oxide layer 21 and part of the bottom silicon 20 are etched to form a plurality of cavities 22 which are arranged at intervals along the second direction D2 and penetrate the buried oxide layer 21 along the first direction D1 and extend to the inside of the bottom silicon 20, and the second direction D2 is parallel to the top surface of the bottom silicon 20. Figure 2 shown.
[0043] For example, an initial silicon wafer is first provided, and the surface of the initial silicon wafer is thermally oxidized to form the buried oxide layer 21 made of silicon dioxide, and the remaining unoxidized initial silicon wafer serves as the bottom silicon 20. Then, a dry etching process can be used to start etching from the surface of the buried oxide layer 21 away from the bottom silicon 20 to form a plurality of cavities 22 arranged at intervals along the second direction D2, and each of the cavities 22 penetrates the buried oxide layer 21 along the first direction D1 and extends to the inside of the bottom silicon 20, and the cavity 22 does not penetrate the bottom silicon 20 along the first direction D1. The cavity 22 serves as a pre-buried cavity in the SOI substrate with a pre-buried cavity. In one example, the depth of the cavity 22 extending to the bottom silicon 20 can be adjusted by controlling factors such as the etching time of the dry etching process and the amount of dry etchant, thereby further improving the flexibility of the manufacturing process of the SOI substrate with a pre-buried cavity to meet the needs of different process manufacturing. The multiple mentioned in this specific implementation mode refers to more than two.
[0044] Figure 3 Schematic diagram of the top structure formed in a specific embodiment of the present invention. In some embodiments, the specific steps of forming the top structure include:
[0045] forming a sacrificial layer 30, wherein the sacrificial layer 30 includes a top surface and a bottom surface that are relatively distributed along the first direction D1, and the sacrificial layer 30 is a single crystal silicon layer including first doped ions;
[0046] The top silicon layer 31 is formed on the top surface of the sacrificial layer 30, wherein the top silicon layer 31 is a single crystal silicon layer including second doping ions, and the concentration of the first doping ions in the sacrificial layer 30 is different from the concentration of the second doping ions in the top silicon layer. Figure 3 shown.
[0047] Specifically, after using the single crystal silicon layer including the first doping ion as the sacrificial layer 30, a single crystal silicon layer including the second doping ion can be formed on the top surface of the sacrificial layer 30 through a deposition process, and the single crystal silicon layer including the second doping ion is used as the top silicon 31. In one example, the thickness of the sacrificial layer 30 along the first direction D1 is greater than the thickness of the top silicon 31 along the first direction D1, so that the top silicon 31 is supported by the solid sacrificial layer 30. In one example, the thickness of the formed top silicon 31 can be adjusted by adjusting the process parameters when depositing the top silicon 31, so that the top silicon 31 with a thinner thickness (for example, the thickness along the first direction D1) can be directly formed through the deposition process, so as to further simplify the preparation process of the SOI substrate with a pre-buried cavity. In another example, after the top silicon 31 is formed through a deposition process, the top silicon 31 can be thinned to a desired thickness through a grinding process. Since the top silicon 31 is supported by the solid sacrificial layer 30, the top silicon 31 is prevented from being damaged during the thinning process. The concentration of the first doping ions in the sacrificial layer 30 is different from the concentration of the second doping ions in the top silicon layer, so that it is convenient to remove the sacrificial layer 30 through a selective etching process later.
[0048] In some embodiments, the type of the first doping ions is the same as the type of the second doping ions.
[0049] In some embodiments, the concentration of the first doping ions in the sacrificial layer 30 is greater than the concentration of the second doping ions in the top silicon layer 31 .
[0050] For example, the first doping ion and the second doping ion are P-type ions of the same type, for example, the first doping ion and the second doping ion are both indium ions, gallium ions or boron ions. The sacrificial layer 30 is a single crystal silicon layer heavily doped with P-type ions, and the top silicon 31 is a single crystal silicon layer lightly doped with P-type ions. In this specific embodiment, by setting the type of the first doping ion and the type of the second doping ion to be the same, and the concentration of the first doping ion in the sacrificial layer 30 is different from the concentration of the second doping ion in the top silicon, the sacrificial layer 30 and the top silicon 31 can be distinguished in physical and chemical properties, which is convenient for the subsequent removal of the sacrificial layer 30 by a selective etching process, and also helps to further simplify the manufacturing process of the top structure. The concentration of the second doping ion in the top silicon 31 is less than the concentration of the first doping ion in the sacrificial layer 30, so as to facilitate the subsequent formation of a device structure on the top silicon 31.
[0051] In some embodiments, the thickness of the top silicon layer 31 is less than 10 μm. In one example, the thickness of the top silicon layer 31 is less than 4 μm, so that the subsequently formed SOI substrate with the embedded cavity has the top silicon layer 31 with a thinner thickness.
[0052] In some embodiments, the specific steps of removing the sacrificial layer 30 and forming the SOI substrate with the embedded cavity including the top silicon layer and the supporting substrate include:
[0053] Using a grinding process to remove part of the sacrificial layer 30;
[0054] The remaining sacrificial layer 30 is removed by a chemical etching process.
[0055] In some embodiments, the specific steps of removing part of the sacrificial layer 30 by a grinding process include:
[0056] A grinding process is used to remove a portion of the sacrificial layer 30 , and the thickness of the sacrificial layer 30 is reduced to 50 μm to 60 μm.
[0057] In some embodiments, the specific steps of removing the remaining sacrificial layer 30 by chemical etching process include:
[0058] A chemical etching process is used to selectively remove all the remaining sacrificial layer 30 to expose the surface of the top silicon layer 31. The chemical etching agent used in the chemical etching process is a mixed solution including hydrofluoric acid, nitric acid and acetic acid.
[0059] Figure 4 is a schematic diagram of the structure after the support substrate and the top structure are connected in a specific embodiment of the present invention, Figure 5 is a schematic diagram of the structure of a specific embodiment of the present invention after a portion of the sacrificial layer is removed by a grinding process, Figure 6 FIG. 1 is a schematic diagram of the structure of the SOI substrate with a pre-buried cavity formed in a specific embodiment of the present invention. For example, after bonding the support substrate and the top structure along the direction of the buried oxide layer 21 toward the top silicon layer 31, the following is obtained: Figure 4 The structure shown. Figure 4 As shown, the top silicon layer 31 continuously covers a plurality of the cavities 22, thereby forming a pre-buried cavity. Next, a grinding process is used to remove part of the sacrificial layer 30, and the thickness of the sacrificial layer 30 is reduced to 50 μm to 60 μm. Figure 5 Afterwards, a chemical etching process is used to selectively remove all the remaining sacrificial layer 30 to expose the surface of the top silicon layer 31, as shown in FIG. Figure 6As shown. This specific embodiment adopts grinding and chemical etching to remove the sacrificial layer 30, which can not only reduce the amount of the chemical etchant, thereby avoiding damage to the supporting substrate or the top silicon 31, but also help to improve the removal efficiency of the sacrificial layer 30. The chemical etchant used in the chemical etching process is a mixed solution including hydrofluoric acid, nitric acid and acetic acid, that is, the chemical etchant is HNA etchant. On the one hand, it can remove the sacrificial layer 30 doped with heavy P-type ions while avoiding damage to the top silicon 31 doped with light P-type ions; on the other hand, it can also make the surface of the top silicon 31 exposed after removing all the sacrificial layers 30 relatively flat, so as to ensure that the thickness of the top silicon 31 in the SOI substrate with embedded cavities formed in the end (for example, the thickness along the first direction D1) is uniform, for example, the thickness uniformity of the top silicon 31 reaches ±100nm, thereby further improving the quality of the prepared SOI substrate with embedded cavities.
[0060] This specific embodiment also provides an SOI substrate with a pre-buried cavity, using the method for preparing the SOI substrate with a pre-buried cavity as described above (see Figure 1-Figure 6 ) is formed. The structure of the SOI substrate with a pre-buried cavity in this specific embodiment can be seen in Figure 6 .
[0061] The SOI substrate with a pre-buried cavity and the preparation method thereof provided in this specific embodiment form a top structure including a top silicon and a sacrificial layer covering the surface of the top silicon, and after connecting the top structure to a supporting substrate, remove the sacrificial layer to form the SOI substrate with a pre-buried cavity including the top silicon and the supporting substrate, that is, before connecting to the supporting substrate, the top silicon with a relatively thin thickness has been formed, thereby avoiding the problem of the top silicon being easily broken and failed during the subsequent grinding of the top silicon suspended above the cavity, and improving the manufacturing yield of the SOI substrate with a pre-buried cavity with a relatively thin top silicon. Moreover, this specific embodiment does not need to use a double-layer SOI wafer for preparation, the preparation cost is low, and the preparation process is simple, thereby improving the manufacturing efficiency of the semiconductor structure. In addition, this specific embodiment also removes the sacrificial layer through a two-step process of grinding and chemical etching, and a mixed solution of hydrofluoric acid, nitric acid and acetic acid with a high etching selectivity is used in the chemical etching process, which helps to reduce the roughness of the surface of the top silicon exposed after removing the sacrificial layer, and obtain the top silicon with uniform thickness, thereby further improving the quality of the prepared SOI substrate with embedded cavity.
[0062] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.
Claims
1. A method for preparing a SOI substrate with a pre-buried cavity, characterized in that: The steps include: Forming a support substrate, the support substrate comprising a bottom silicon layer, a buried oxide layer covering a surface of the bottom silicon layer, and a cavity penetrating the buried oxide layer and extending to the inside of the bottom silicon layer; forming a top structure, the top structure comprising a top silicon layer and a sacrificial layer covering a surface of the top silicon layer; Connecting the support substrate and the top structure along the direction of the buried oxide layer toward the top silicon layer; The sacrificial layer is removed to form the SOI substrate with the pre-buried cavity including the top silicon layer and the supporting substrate.
2. The method for preparing the SOI substrate with a pre-buried cavity according to claim 1, characterized in that: The specific steps of forming the support substrate include: Forming the bottom silicon and the buried oxide layer covering the top surface of the bottom silicon along a first direction, wherein the first direction intersects the top surface of the bottom silicon vertically; The buried oxide layer and part of the bottom silicon are etched to form a plurality of cavities which are arranged at intervals along a second direction and penetrate the buried oxide layer along the first direction and extend to the inside of the bottom silicon, wherein the second direction is parallel to the top surface of the bottom silicon.
3. The method for preparing the SOI substrate with a pre-buried cavity according to claim 2, characterized in that: The specific steps to form the top structure include: forming a sacrificial layer, the sacrificial layer comprising a top surface and a bottom surface relatively distributed along the first direction, the sacrificial layer being a single crystal silicon layer including first doping ions; The top silicon layer is formed on the top surface of the sacrificial layer, the top silicon layer is a single crystal silicon layer including second doping ions, and the concentration of the first doping ions in the sacrificial layer is different from the concentration of the second doping ions in the top silicon layer.
4. The method for preparing the SOI substrate with a pre-buried cavity according to claim 3, characterized in that: The type of the first doping ions is the same as the type of the second doping ions.
5. The method for preparing a SOI substrate with a pre-buried cavity according to claim 4, characterized in that: The concentration of the first doping ions in the sacrificial layer is greater than the concentration of the second doping ions in the top silicon layer.
6. The method for preparing a SOI substrate with a pre-buried cavity according to claim 1, characterized in that: The thickness of the top silicon layer is less than 10 μm.
7. The method for preparing a SOI substrate with a pre-buried cavity according to claim 6, characterized in that: The specific steps of removing the sacrificial layer to form the SOI substrate with the embedded cavity including the top silicon layer and the supporting substrate include: Removing part of the sacrificial layer by a grinding process; The remaining sacrificial layer is removed by a chemical etching process.
8. The method for preparing a SOI substrate with a pre-buried cavity according to claim 7, characterized in that: The specific steps of removing part of the sacrificial layer by a grinding process include: A grinding process is adopted to remove part of the sacrificial layer, and the thickness of the sacrificial layer is reduced to 50 μm to 60 μm.
9. The method for preparing a SOI substrate with a pre-buried cavity according to claim 7, characterized in that: The specific steps of removing the remaining sacrificial layer by chemical etching process include: A chemical etching process is used to selectively remove all the remaining sacrificial layers to expose the surface of the top silicon layer. The chemical etching agent used in the chemical etching process is a mixed solution including hydrofluoric acid, nitric acid and acetic acid.
10. An SOI substrate with a pre-buried cavity, characterized in that: The method for preparing an SOI substrate with a pre-buried cavity as claimed in any one of claims 1 to 9 is used for forming the SOI substrate.