Preparation method of low-roughness polycrystalline silicon carbide substrate and composite substrate
By amorphizing the surface layer of the polycrystalline silicon carbide substrate and performing chemical mechanical polishing, the problem of difficulty in achieving low roughness for the 3C-SiC polycrystalline substrate grown on a graphite substrate is solved, and the surface of the polycrystalline silicon carbide substrate is achieved. The roughness is reduced to less than 1nm, which meets the preparation requirements of composite silicon carbide substrates, and has good bonding quality and low cost.
Patent Information
- Application Number
- CN202411296163.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-14
- Publication Date
- 2025-01-14
AI Technical Summary
It is difficult to achieve a roughness of less than 1 nm during chemical mechanical polishing of 3C-SiC polycrystalline substrate based on graphite substrate growth, and cannot meet the preparation requirements of composite silicon carbide substrates.
By amorphizing the surface layer of the polycrystalline silicon carbide substrate and using chemical mechanical polishing methods, the surface roughness of the polycrystalline silicon carbide substrate is reduced to less than 1 nm.
The surface roughness of the polycrystalline silicon carbide substrate is reduced to less than 1 nm, which meets the preparation requirements of the composite silicon carbide substrate, and has good bonding quality and low cost.
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Figure CN119314862A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of semiconductor material processing, and in particular to a method for preparing a low-roughness polycrystalline silicon carbide substrate and a composite substrate. Background Art
[0002] Silicon carbide materials have the advantages of high temperature resistance, high pressure resistance, radiation resistance, chemical corrosion resistance, high hardness, and high thermal conductivity. Substrates made of 3C silicon carbide materials can be used to make heating plates, focusing rings, guard rings and other parts in semiconductor processes.
[0003] Since 3C silicon carbide substrates have lower production costs than 4H silicon carbide substrates, recently, thicker 3C silicon carbide substrates have been used as support layers and composited with thinner 4H silicon carbide substrates to form composite silicon carbide substrates with lower costs than substrates containing only 4H silicon carbide. The composite silicon carbide substrate is made into devices such as MOSFET after undergoing steps such as epitaxy, etching, ion implantation, and packaging. Compared with silicon carbide substrates for other purposes, this type of 3C-SiC substrate requires lower surface roughness to meet the preparation requirements of composite silicon carbide substrates.
[0004] Chemical vapor deposition (CVD) is a common method for manufacturing 3C silicon carbide substrates. The main process is that the gaseous substances containing Si and C undergo chemical reactions on the surface of the substrate to form solid 3C silicon carbide, which grows on the surface of the substrate. As time goes on, a 3C silicon carbide substrate of a certain thickness is formed on the substrate. The substrate is peeled off by grinding or chemical reaction to form a single material 3C silicon carbide substrate.
[0005] 3C silicon carbide formed by CVD method generally presents a polycrystalline structure. The reason is that the substrate used to grow 3C-SiC polycrystals is a graphite plate, and the surface of the graphite plate presents various crystal directions, resulting in various grain orientations of SiC polycrystals grown on the graphite plate. During the chemical mechanical polishing process, the 3C-SiC substrate with a polycrystalline structure has a roughness of more than 10nm due to the inconsistent polishing rates of grains in different directions. The 3C-SiC polycrystalline substrate used in the composite silicon carbide substrate requires a roughness of less than 1nm, making it difficult to apply the 3C-SiC polycrystalline substrate grown on a graphite substrate to the composite silicon carbide substrate. Summary of the invention
[0006] The purpose of the present invention is to solve the above problems. The present invention proposes a method for preparing a low-roughness polycrystalline silicon carbide substrate, that is, first amorphizing the surface layer of the polycrystalline silicon carbide substrate, and then chemically mechanically polishing the polycrystalline silicon carbide substrate to make the surface roughness of the polycrystalline silicon carbide substrate reach below 1nm, and the surface roughness of the polycrystalline silicon carbide substrate with this roughness can meet the bonding requirements. The polycrystalline silicon carbide substrate is used as a supporting substrate to bond with a single-crystal silicon carbide substrate, and the bonding quality is good and the cost is low.
[0007] To achieve this object, the present invention adopts the following technical solutions:
[0008] A method for preparing a low-roughness polycrystalline silicon carbide substrate comprises: preparing a polycrystalline silicon carbide substrate, grinding the polycrystalline silicon carbide substrate by a mechanical polishing method, and making the surface roughness of the ground surface of the polycrystalline silicon carbide substrate less than 5nm;
[0009] Ion irradiation is used on the ground surface of the polycrystalline silicon carbide substrate to convert the surface crystals of the ground surface into amorphous to form an amorphous layer;
[0010] The surface of the amorphous layer is polished by a chemical mechanical polishing method until the surface roughness of the amorphous layer is less than 1 nm, thereby obtaining the low-roughness polycrystalline silicon carbide substrate.
[0011] The polycrystalline silicon carbide substrate has a high surface roughness due to the inconsistent corrosion rate of grains with different orientations, making it difficult to achieve atomic-level flatness. The amorphous layer does not have the above problems. In addition, the amorphous layer has no clear grains and grain boundaries, and the atomic arrangement is disordered and the structure is uniform. During polishing, the effect of chemical mechanical polishing can be applied more evenly to the surface of the material, which is easy to achieve a flattening effect and reduce the surface roughness. Its structural disorder makes the internal defects and impurities more evenly distributed, the defect types and effects are smaller, and there is less interference with polishing, which is conducive to obtaining a smooth surface. Moreover, its hardness is relatively uniform, and it is not easy to cause uneven polishing due to local hardness differences, and the polishing process is easier to control. Therefore, the surface of the polycrystalline silicon carbide substrate is first amorphized, and then chemical mechanical polishing is performed, so that the surface roughness of the polycrystalline silicon carbide substrate can be reduced to less than 1nm.
[0012] Furthermore, the ions used in ion irradiation are Si + .
[0013] Furthermore, the energy of the ion irradiation is 100-300 keV.
[0014] Furthermore, the ion irradiation dose was 5.0×10 14 -1.5×10 15 Pieces / cm 2 .
[0015] Furthermore, the temperature of the polycrystalline silicon carbide substrate is maintained at no more than 300K during the ion irradiation process.
[0016] Furthermore, the thickness of the amorphous layer is 30-50 nm.
[0017] Further, in the mechanical polishing method, the abrasive comprises diamond;
[0018] In the chemical mechanical polishing method, the abrasive comprises silicon dioxide.
[0019] A composite substrate comprises the above-mentioned polycrystalline silicon carbide substrate as a supporting substrate, and a material layer is formed on an amorphous layer to obtain a composite substrate.
[0020] Furthermore, the step of forming a material layer on the amorphous layer includes:
[0021] preparing a donor substrate, performing ion implantation in the donor substrate, forming an ion-rich layer in the donor substrate, wherein the ion-rich layer divides the donor substrate into a material layer and a recovery layer;
[0022] bonding the material layer of the donor substrate to the amorphous layer of the support substrate to form a bonded body;
[0023] Stress is applied to the bonding body to cause the ion-rich layer to crack and the recovery layer to separate from the bonding body, thereby obtaining a composite substrate.
[0024] Furthermore, the material layer includes single crystal silicon carbide, lithium niobate, and lithium tantalate.
[0025] Beneficial effects of the present invention:
[0026] The present invention provides a method for preparing a low-roughness polycrystalline silicon carbide substrate, that is, first amorphizing the surface layer of the polycrystalline silicon carbide substrate, and then chemically and mechanically polishing the polycrystalline silicon carbide substrate to make the surface roughness of the polycrystalline silicon carbide substrate reach below 1nm, and the surface roughness of the polycrystalline silicon carbide substrate with this roughness can meet the bonding requirements. The polycrystalline silicon carbide substrate is used as a supporting substrate to bond with a single-crystal silicon carbide substrate, and the bonding quality is good and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Figure 1 It is a schematic diagram of the organization and surface structure of the polycrystalline silicon carbide substrate of the present invention;
[0028] Figure 2 It is a schematic diagram of the structure of an amorphous layer formed on the surface of a polycrystalline silicon carbide substrate of the present invention;
[0029] Figure 3 It is a schematic diagram of the preparation process of the composite substrate of the present invention.
[0030] In the figure: 1, polycrystalline silicon carbide; 2, amorphous layer; 30, donor substrate; 300, ion-rich layer; 3, material layer; 30', recovery layer. DETAILED DESCRIPTION
[0031] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention.
[0032] See also Figure 1-3 The present invention provides a method for preparing low-roughness polycrystalline silicon carbide. First, a polycrystalline silicon carbide substrate is prepared. Along the thickness direction of the polycrystalline silicon carbide substrate, the grain orientation may include multiple directions, such as <111> , <100> , <110> The surface of the polycrystalline silicon carbide substrate is polished by mechanical grinding and polishing to reduce the surface roughness of the polycrystalline silicon carbide substrate to 5nm. If the surface roughness is too high, the amorphous layer to be prepared later will be thicker, and the removal amount of chemical mechanical polishing will also need to be increased, which are all unfavorable factors. Since the silicon carbide substrate is hard, in order to save mechanical grinding and polishing time, a polycrystalline silicon carbide substrate with an initial surface roughness of less than 30nm is preferred. Diamond particles can be used as the main abrasive for mechanical grinding and polishing.
[0033] The polycrystalline silicon carbide substrate with a surface roughness of less than 5nm was irradiated with high-energy ions. The irradiation energy was kept between 100-300keV and the irradiation dose was 5.0×10 14 -1.5×10 15 Pieces / cm 2 Between, ions use Si + , so that the silicon carbide on the ion irradiated surface of the polycrystalline silicon carbide substrate is transformed from crystalline to amorphous, forming an amorphous layer with a depth of 30-50nm.
[0034] Adopt Si + After irradiating the surface of the silicon carbide substrate, the Si + No aggregation will occur, and no voids or second phase problems will occur when used in a high-temperature substrate environment.
[0035] The irradiation energy is maintained between 100-300 keV. If the irradiation energy is too small, the silicon carbide atoms after irradiation cannot be amorphized and the amorphous layer cannot be prepared; if the irradiation energy is too large, it is easy to introduce void defects in the polycrystalline silicon carbide substrate, which is not conducive to reducing the roughness during the subsequent polishing process.
[0036] The irradiation dose was maintained at 5.0×10 14 -1.5×10 15 Pieces / cm 2 If the irradiation dose is too small, an effective amorphous layer cannot be formed.
[0037] When ion irradiating a polycrystalline silicon carbide substrate, the ambient temperature must be monitored and adjusted in real time to ensure that the temperature of the irradiated polycrystalline silicon carbide substrate does not exceed 300 K. When the temperature rises, the polycrystalline silicon carbide substrate is prone to stress relief annealing, which releases stress by adjusting the lattice position without amorphization, thus failing to form an amorphous layer.
[0038] The thickness of the generated amorphous layer can be maintained at 30-50nm, which meets the removal requirements of subsequent chemical mechanical polishing. The preparation of a deeper amorphous layer requires increasing the ion irradiation energy, which will introduce more stress in the substrate and reduce the flatness of the substrate.
[0039] The amorphous layer of the polycrystalline silicon carbide substrate is polished by chemical mechanical polishing, with silicon dioxide as the main abrasive, and polishing is performed through chemical mechanical reaction, with a polishing removal amount of 10nm-15nm. After chemical mechanical polishing, the surface roughness of the polycrystalline silicon carbide substrate is less than 1nm.
[0040] An embodiment of the present application also provides a composite substrate, using the low-roughness polycrystalline silicon carbide substrate prepared as above as a supporting substrate, and bonding a material layer on the amorphous layer of the polycrystalline silicon carbide substrate by bonding, wherein the material layer includes single-crystalline silicon carbide, lithium niobate, and lithium tantalate.
[0041] Preferably, the step of forming a material layer on the amorphous layer includes: preparing a donor substrate, performing ion implantation in the donor substrate, forming an ion-rich layer in the donor substrate, wherein the ion-rich layer divides the donor substrate into a material layer and a recovery layer; bonding the material layer of the donor substrate to the amorphous layer of the support substrate to form a bonded body; applying stress to the bonded body to crack the ion-rich layer and separate the recovery layer from the bonded body to obtain a composite substrate. The recovery layer can be recycled as a new donor substrate until it is exhausted, which can greatly reduce production costs.
[0042] Example 1
[0043] Prepare a 3C-SiC polycrystalline substrate with a diameter of 150 mm, a thickness of 350 μm, and a surface roughness of 25 nm. Use mechanical polishing to grind the surface of the polycrystalline silicon carbide substrate to a surface roughness of 4 nm. Use Si+ to irradiate the polycrystalline silicon carbide substrate with an irradiation energy of 200 keV and an irradiation dose of 1.0×10 15 Pieces / cm 2 During the irradiation process, the temperature of the polycrystalline silicon carbide substrate was maintained at 293K, and the thickness of the amorphous layer was measured by high-resolution transmission electron microscopy. The irradiation was completed when the thickness of the amorphous layer was 30nm.
[0044] The amorphous layer was polished by chemical mechanical polishing, and the polishing removal was 15nm. The polished surface was measured by atomic force microscopy, and the surface roughness was 0.5nm.
[0045] A single-crystal silicon carbide substrate with a diameter of 150 mm and a thickness of 350 μm was prepared. Hydrogen ions were injected into the single-crystal silicon carbide substrate to a depth of 3 μm to form an ion-rich layer. The polycrystalline silicon carbide substrate and the single-crystal silicon carbide substrate were cleaned and surface activated respectively and then bonded to form a bonded body. The bonded body was subjected to a temperature treatment to crack the single-crystal silicon carbide substrate along the ion-rich layer to form a material layer and a recovery layer. At this time, the material layer was bonded to the amorphous layer of the polycrystalline silicon carbide substrate to form a composite substrate. According to microscopic observation, the number of bonding voids larger than 1 μm on the composite substrate was 0.
[0046] The recovered layer is used as a new donor substrate after surface polishing and cleaning.
[0047] Comparative Example 1, compared with Example 1, is different in that polycrystalline silicon carbide is directly subjected to chemical mechanical polishing. Due to the material properties of polycrystalline silicon carbide, the optimal surface roughness obtained by chemical mechanical polishing is 2.5nm. The polycrystalline silicon carbide substrate is bonded to the single crystal silicon carbide substrate to form a composite substrate. Microscopic observation shows that the number of bonding voids larger than 1μm on the composite substrate is 7.1 / cm 2 .
[0048] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, various obvious changes, readjustments and substitutions can be made without departing from the protection scope of the present invention. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.
Claims
1. A method for preparing a low-roughness polycrystalline silicon carbide substrate, characterized in that: Preparing a polycrystalline silicon carbide substrate, grinding the polycrystalline silicon carbide substrate by a mechanical polishing method, so that the surface roughness of the ground surface of the polycrystalline silicon carbide substrate is less than 5nm; Ion irradiation is used on the ground surface of the polycrystalline silicon carbide substrate to convert the surface crystals of the ground surface into amorphous to form an amorphous layer; The surface of the amorphous layer is polished by a chemical mechanical polishing method until the surface roughness of the amorphous layer is less than 1 nm, thereby obtaining the low-roughness polycrystalline silicon carbide substrate.
2. The preparation method according to claim 1, characterized in that: The ions used in ion irradiation are Si + .
3. The preparation method according to claim 1, characterized in that: The energy of ion irradiation is 100-300 keV.
4. The preparation method according to claim 1, characterized in that: The dose of ion irradiation was 5.0×10 14 -1.5×10 15 Pieces / cm 2 .
5. The preparation method according to any one of claims 1 to 4, characterized in that: The temperature of the polycrystalline silicon carbide substrate is maintained at no more than 300K during the ion irradiation process.
6. The preparation method according to claim 1, characterized in that: The thickness of the amorphous layer is 30-50 nm.
7. The preparation method according to claim 1, characterized in that: In the mechanical polishing method, the abrasive comprises diamond; In the chemical mechanical polishing method, the abrasive comprises silicon dioxide.
8. A composite substrate, characterized in that: The polycrystalline silicon carbide substrate according to any one of claims 1 to 7 is used as a supporting substrate, and a material layer is formed on the amorphous layer to obtain a composite substrate.
9. The composite substrate according to claim 8, characterized in that: The step of forming a material layer on the amorphous layer comprises: preparing a donor substrate, performing ion implantation in the donor substrate, forming an ion-rich layer in the donor substrate, wherein the ion-rich layer divides the donor substrate into a material layer and a recovery layer; bonding the material layer of the donor substrate to the amorphous layer of the support substrate to form a bonded body; Stress is applied to the bonding body to cause the ion-rich layer to crack and the recovery layer to separate from the bonding body, thereby obtaining a composite substrate.
10. The composite substrate according to claim 8, characterized in that: The material layer includes single crystal silicon carbide, lithium niobate, and lithium tantalate.