Method for manufacturing semiconductor substrate, semiconductor substrate, and semiconductor device

Abstract

The present invention is a method for manufacturing a semiconductor substrate, the method comprising: an ion implantation step in which at least one of silicon, carbon, and oxygen is implanted into the surface of a 4H-SiC substrate, and an amorphous layer formed by amorphizing silicon and carbon is formed in the 4H-SiC substrate; a bonding step of bonding the 4H-SiC substrate subjected to the ion implantation step and another support substrate via a thin film to obtain a bonded substrate; a peeling step in which the 4H-SiC substrate is peeled off by the amorphous layer of the bonded substrate and separated into a bonded substrate obtained by transferring the surface layer of the 4H-SiC substrate onto the support substrate and a peeled-off substrate obtained by peeling off the surface layer from the 4H-SiC substrate; an etching step of performing plasma etching on the stripping surface of at least one of the bonding substrate and the stripping substrate after the stripping step; and an epitaxy step in which epitaxial growth is performed on at least one of the bonded substrate and the release substrate. As a result, it is possible to provide a method for manufacturing a semiconductor substrate capable of manufacturing a lower-cost and high-quality semiconductor substrate.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for manufacturing a semiconductor substrate, a semiconductor substrate, and a semiconductor device. BACKGROUND

[0002] Silicon carbide (SiC) is a material that is expected to be used as a semiconductor material for various semiconductor devices such as power devices or high-frequency devices, because it has a high dielectric breakdown strength due to a wide energy gap of 2.2 to 3.3 eV, and also has a large thermal conductivity.

[0003] However, it is reported in Non-Patent Literature 1 that a device obtained using SiC accounts for half of the cost in the manufacturing process of the SiC substrate and the subsequent epitaxial process, and that it is important to reduce the cost of the substrate.

[0004] As a countermeasure for this cost reduction, a method has been proposed in which H + ions are implanted to a 4H-SiC substrate to perform substrate peeling. As to the implantation of H + ions into SiC, several prior arts have been reported.

[0005] Patent Literature 1 describes a method in which two SiC single crystal wafers are prepared, an oxide layer is formed on each of the wafers, H ions are implanted into one of the substrates, the substrates are integrated by bonding at room temperature with the oxide layer interposed therebetween, and then the SiC single crystal wafers are divided into two parts at a position where H ions have been implanted by heat treatment at 500°C or higher, thereby manufacturing a substrate for a semiconductor electronic component. In this method, the oxide film is present at the bonding portion, and when a vertical device is manufactured, the oxide film functions as an insulating layer, greatly limiting the function as a power device substrate.

[0006] Further, Patent Literature 2 discloses a method in which a single-crystal SiC substrate into which H + ions have been implanted is bonded to a polycrystal SiC substrate, and then the single crystal and the polycrystal are peeled off respectively. This method involves an increase in cost due to the implementation of peeling twice, and there is a difficulty in peeling in each of the prescribed processes.

[0007] Patent Literature 3 discloses a method that focuses on impurity concentration and defect density, which uses H + ion implantation to transfer a high-resistance substrate having a small defect density. This method is a method for reducing defects present in the original substrate, but does not mention the substrate after peeling.

[0008] Further, Patent Literature 4 describes a basic technology of substrate peeling based on H + ions, and although it mentions a diffusion barrier (oxygen diffusion barrier) function, it does not mention the substrate after peeling.

[0009] Further, Patent Literature 5 also describes a method of using H+ Patent Document 1 describes a method of manufacturing various kinds of substrates by a lift-off technique, which describes a method of epitaxially growing InGaN after polishing or dry etching a surface, but does not describe the operation of peeling off the substrate.

[0010] Furthermore, Patent Document 6 describes a method of manufacturing a device on a silicon carbide substrate, performing ion implantation after forming a protective film, and performing high-temperature annealing after bonding to a support substrate, and reusing the separated substrate, but does not describe the operation of the peeled substrate.

[0011] Furthermore, Patent Document 7 describes a method of applying H + implantation, forming polycrystalline SiC on the opposite surface, performing annealing, and peeling off from the ion implantation surface, and epitaxially growing SiC after polishing the peeled surface. As described above, in the substrate technology using H + implantation, there is no description of a specific method of reusing the peeled substrate.

[0012] Further, as a method of forming a support substrate after ion implantation of H + implantation, Patent Document 8 describes growing polycrystalline SiC on the substrate after H + implantation at 1000 to 1600°C, Patent Document 9 describes growing based on DLI-CVD (Direct Liquid Injection-CVD) on the substrate after H + implantation, and Patent Document 10 describes a method of sintering and liquid deposition on the substrate after H + implantation.

[0013] As described in Patent Document 8, when this method is used, SiC is difficult to bond to each other, and there is a problem of metal interposition through the bonding of W and Mo.

[0014] However, after H + implantation in this way, if deposition is performed on a support substrate at high temperature, peeling of the H + implantation layer can occur during deposition, or the substrate itself having the H + implantation layer is exposed to high temperature, not only the crystallinity changes, but also a polycrystalline layer or the like is formed on the side surface, thereby hindering reuse.

[0015] Prior Art Documents

[0016] Patent Documents

[0017] Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 11-003842

[0018] Patent Literature 2: Japanese Patent Application Publication No. 2016-018890

[0019] Patent Literature 3: Japanese Patent Application Publication No. 2014-022711

[0020] Patent Literature 4: Japanese Patent Application Publication No. 2007-329470

[0021] Patent Literature 5: Japanese Patent Application Laid-Open No. 2013-513963

[0022] Patent Literature 6: Japanese Patent Application Publication No. 2022-140396

[0023] Patent Literature 7: International Publication No. 2022 / 158085

[0024] Patent Literature 8: Japanese Patent Application Laid-Open No. 2022-542224

[0025] Patent Literature 9: Japanese Patent Application Laid-Open No. 2023-502571

[0026] Patent Literature 10: Japanese Patent Application Laid-Open No. 2023-502572

[0027] Non-Patent Literature

[0028] Non-Patent Literature 1: Iwamatsu, “SiC MOSFET high performance and high reliability progress”, Wide Bandgap Semiconductor Society Special Symposium Preprints, Wide Bandgap Semiconductor Society, 2022

[0029] Non-Patent Literature 2: H. Biard, W. Schwarzenbach, S. Odoul, I. Radu, A. Potier, M. Ferrato, E. Guajioty, “Tailored polycrystalline substrate for SmartSiCTM substrates enabling high performance power devices”, ICS CRM2022, 2022

[0030] Non-Patent Literature 3: Suga, “Surface activation by room temperature bonding and its mechanism”, Applied Physics, Applied Physics Society, 89(9), 2020.P498 SUMMARY

[0031] (I) Problem to be Solved by the Invention

[0032] Therefore, 4H-SiC is expected to be a high-voltage-resistant device, but the high cost of the substrate makes reducing the cost of bulk substrates a technical challenge. Thus, a technique has been proposed that performs H... + Ion implantation is used to peel off the substrate. Costs are reduced by reusing the peeled substrate (otherwise, the cost remains high). Therefore, it is crucial to know how to reuse the peeled substrate (to produce high-quality substrates), which involves utilizing H... + The basic technology for the widespread use of substrate stripping techniques such as ion removal.

[0033] On the other hand, implementing H + The release surface of the substrate after ion implantation and peeling is rough, so it cannot be bonded again without planarization, and the bonding of SiCs to each other is inherently difficult. In addition, it is sometimes preferable to planarize the release surface of the SiCs transferred to the support substrate by peeling before performing epitaxial growth on the release surface.

[0034] However, SiC is a high-hardness, difficult-to-machine material, so the cost of planarizing the release surface during polishing processes such as CMP is high, ultimately leading to increased substrate manufacturing costs. Furthermore, in the H-implantation process... + In the subsequent method of growing the support substrate, the reuse may be hindered by peeling of the support substrate during the growth process or by the growth of unexpected polycrystalline SiC on the original substrate.

[0035] In H + In the case of injection, if the usual method is used in H + If deposition is performed on a support substrate at high temperature after implantation, sometimes during the deposition process, H... + The injection layer peels off, or has H that takes reuse into account. + When the substrate of the implanted layer is exposed to high temperatures, not only does its crystallinity change, but polycrystalline layers also form on the sides, thus hindering reuse.

[0036] The present invention was made to solve the above-mentioned problems, and its purpose is to provide a method for manufacturing a semiconductor substrate that can use 4H-SiC stripping technology to manufacture a cheaper and higher quality semiconductor substrate.

[0037] Furthermore, the purpose of this invention is to provide cheaper and higher quality semiconductor substrates and semiconductor devices.

[0038] (II) Technical Solution

[0039] The present application relates to a method for manufacturing a SiC wafer for achieving the above object, and more particularly, to a substrate peeling technique using ion implantation of silicon, carbon, and oxygen, and to bonding to a support substrate, reuse of the substrate after peeling, and provides a cheaper and high-quality SiC substrate. Specifically, the present application is achieved for the above object, and provides a method for manufacturing a semiconductor substrate, characterized by comprising the following steps: an ion implantation step of performing ion implantation of at least one of silicon, carbon, and oxygen to a surface of a 4H-SiC substrate to form an amorphous layer in which silicon and carbon are amorphized in the 4H-SiC substrate; a bonding step of forming a thin film on at least one of the surface of the 4H-SiC substrate on which the ion implantation step is performed and a bonding surface of another support substrate, and performing bonding through the thin film to obtain a bonded substrate and a peeled substrate, the bonded substrate being obtained by transferring a surface layer of the 4H-SiC substrate to the support substrate as a 4H-SiC layer, the peeled substrate being a substrate from which the surface layer is peeled from the 4H-SiC substrate; an etching step of performing plasma etching on a peeling surface of at least one of the bonded substrate or the peeled substrate after the peeling step; and an epitaxial growth step of performing epitaxial growth on at least one of the bonded substrate or the peeled substrate.

[0040] According to such a method for manufacturing a semiconductor substrate, by performing ion implantation of at least one of silicon, carbon, and oxygen to a surface of a 4H-SiC substrate to cut the bonding of silicon and carbon, an amorphous layer is formed, and after bonding to a support substrate, the 4H-SiC substrate is peeled from the amorphous layer to transfer a 4H-SiC layer to a bonded substrate.

[0041] In the ion implantation step in which ion implantation of at least one of silicon, carbon, and oxygen is used in such a manner, damage can be formed at a prescribed depth by adjusting the acceleration energy at the time of implantation. The damage specifically refers to cutting the bonding of silicon and carbon by ion implantation of these ions. The silicon and carbon after the cutting each exist in an amorphized manner.

[0042] The amorphous layer formed in such a manner can be peeled by applying an impact in a manner of inserting a substance such as a thin metal from the side surface. Further, the amorphous layer becomes black due to the influence of carbon, and becomes easy to absorb light, so it is also possible to further excite by irradiating light to this place and peel. Or it is possible to peel by simultaneously using both of light irradiation and impact application.

[0043] In particular, when silicon, carbon, or oxygen is ion implanted, if such a separation layer is provided, even if some high heat is applied, separation does not occur, and the separation process can be performed at any point in the manufacturing process. In addition, when oxygen is ion implanted, the implanted oxygen can be bonded to the carbon of the amorphous layer and gasified by applying heat treatment, thereby separating the same.

[0044] Thus, in the present application, after ion implantation of at least one of silicon, carbon, and oxygen is performed, bonding is performed, and at this time, not only single crystals but also polycrystals and sintered bodies can be made into support substrates, and thus the cost can be greatly reduced.

[0045] In addition, it has been reported that the use of polycrystals can further reduce the substrate resistance and thus be effective (Non-Patent Document 2), and in addition to the cost, it is very effective for high quality when considering vertical devices.

[0046] Furthermore, by sputtering a thin film of silicon or the like on the bonding surface of a substrate ion implanted with silicon or the like and bonding through the thin film, SiC substrates that are difficult to bond can be bonded to each other.

[0047] In particular, by preparing an inexpensive support substrate of a polycrystal and thinly forming a film of silicon or the like on the bonding surface and bonding through the film of silicon or the like, even when the support substrate is SiC, SiC that is difficult to bond can be bonded.

[0048] Further, in the present application, after at least one of the separation substrate or the bonding substrate is subjected to etching of the separation surface using plasma to remove a damage layer and thereby planarize, reuse or epitaxial growth is performed, and thus SiC, which is a difficult-to-machine material, can be planarized at low cost compared to polishing such as CMP, and thus a high-quality substrate can be obtained.

[0049] In addition, generally, SiC is not easily etched by plasma, but can be etched by the effect of surface weakening caused by ion implantation. Thus, by performing epitaxial growth using the CVD method in this manner, as long as one high-quality SiC substrate can be prepared, the surface layer of a 4H-SiC substrate can be transferred to a support substrate by repeatedly performing the ion implantation process, the bonding process, the separation process, the etching process, and the epitaxial process, and a high-quality SiC substrate can be inexpensively manufactured by repeatedly performing epitaxial growth using the CVD method.

[0050] At this time, in the separation process, the 4H-SiC substrate can be separated by irradiating light onto the amorphous layer, or applying an impact, or performing a process that combines the above light irradiation and impact application.

[0051] Thus, by irradiating light onto the amorphous layer to cause it to absorb light, the amorphous layer can be directly subjected to the energy required for separation.

[0052] Further, when the bonded substrate is peeled by applying an impact to the amorphous layer, the peeling can be performed by inserting an instrument such as a metal thin blade only into the amorphous layer, and thus it is advantageous in that the equipment that can be used for the peeling is simple.

[0053] Further, by combining the light irradiation with the impact, the time required for the peeling can be shortened compared to when each of the peeling methods is performed alone.

[0054] At this time, the 4H-SiC substrate can be peeled by performing ion implantation of oxygen in the ion implantation process, and by irradiating light, or applying an impact, or performing heat treatment on the amorphous layer in the peeling process to cause the implanted oxygen to react with carbon of the amorphous layer to generate a gas, thereby peeling the 4H-SiC substrate; or by performing a process that combines the above light irradiation, impact application, and heat treatment, thereby peeling the 4H-SiC substrate.

[0055] Thus, by performing light irradiation on the amorphous layer, the energy required for the peeling can be directly applied to the amorphous layer. Further, when the bonded substrate is peeled by applying an impact to the amorphous layer, the peeling can be performed by inserting an instrument such as a metal thin blade only into the amorphous layer.

[0056] Further, when ions of oxygen are implanted in the ion implantation process, the implanted oxygen can also be caused to react with carbon of the amorphous layer to generate a gas, and the peeling can be performed using the gas pressure. Thus, in addition to the light irradiation and the impact, the peeling can also be performed by heating, and the options of the peeling method are broadened.

[0057] Further, by combining the above light irradiation, impact, and heat treatment, the time required for the peeling can be shortened compared to when each of these methods is performed alone.

[0058] At this time, in the bonding process, a silicon thin film can be formed as the thin film, and the bonding can be performed through the thin film.

[0059] A silicon thin film is sometimes used as a substrate when 4H-SiC is epitaxially grown, and thus it is easy to bond with 4H-SiC, and further easy to bond with a polycrystal and a sintered body of SiC. Thus, by preparing a support substrate of polycrystalline SiC, which is cheaper than a single-crystal SiC, and forming a thin silicon on a bonding surface, the bonding is facilitated by performing the bonding through the silicon.

[0060] At this time, in the bonding process, the silicon thin film can be formed by a sputtering method using silicon as a target material.

[0061] If the silicon thin film is formed by a sputtering method in which silicon is used as a target material, an inactive gas such as argon (Ar) is ionized and irradiated to form a film, the adhesion and the like are favorable. In addition, it is known that the roughness of the bonding surface at this time is preferably 1 nm or less (Non-Patent Document 3).

[0062] Furthermore, if the sputtering method is used, high-temperature processing of the substrate to be subjected to film formation is not required, and the SiC surface of the bonding surface is not roughened.

[0063] At this time, in the etching step, a mixed gas of a fluorocarbon compound gas and oxygen can be used as a raw material gas.

[0064] The mixed gas of the fluorocarbon compound gas and oxygen is a gas for etching silicon or the like, and thus is advantageous in that it does not require a dedicated gas for etching SiC by being used as a raw material gas.

[0065] The separation surface of the bonded substrate or the separation substrate on which the etching step is to be performed is annealed at a temperature of 1000°C or higher in a hydrogen atmosphere.

[0066] If the etching is performed after the hydrogen annealing is performed in the above-described manner, the uneven shape of the separation surface roughened by separation is modified by the hydrogen annealing before the etching, and is flattened to some extent. Thus, in the etching step, it becomes easier to improve the flatness of the separation surface.

[0067] At this time, the separation surface of the bonded substrate can be plasma-etched in the etching step, and an epitaxial step can be further performed on the etched separation surface of the bonded substrate after the etching step.

[0068] If the epitaxial layer is grown on the etched separation surface of the bonded substrate in the above-described manner, a device can be manufactured in higher quality by forming the device on the epitaxial layer.

[0069] Furthermore, the present application provides a semiconductor substrate characterized by including a support substrate of SiC and a 4H-SiC layer bonded to the surface of the support substrate via a silicon thin film, and the surface of the 4H-SiC layer is subjected to etching treatment.

[0070] If it is such a semiconductor substrate, the surface of the 4H-SiC layer of the semiconductor substrate is subjected to etching treatment, and thus the surface is flat, an epitaxial layer can be formed even without performing high-cost flattening treatment such as CMP, and a cheap and high-quality semiconductor substrate can be obtained.

[0071] Further, if the 4H-SiC layer is bonded to the support substrate with a silicon thin film interposed therebetween, the 4H-SiC layer is firmly bonded to the support substrate because the silicon thin film is sometimes used as a substrate for epitaxial growth of 4H-SiC. Therefore, even when the support substrate is a polycrystal or a sintered body of SiC, the 4H-SiC layer can be firmly bonded to the support substrate. Thus, a semiconductor substrate in which the 4H-SiC layer is firmly bonded to the support substrate can be obtained.

[0072] Further, the present application provides a semiconductor device characterized by comprising the semiconductor substrate described above.

[0073] Such a semiconductor device can be a cheaper and higher-quality semiconductor device with high reliability because it comprises the cheaper and higher-quality semiconductor substrate described above.

[0074] (Three) Advantageous Effects

[0075] As described above, the manufacturing method of a semiconductor substrate according to the present application can manufacture a cheaper and higher-quality semiconductor substrate using the exfoliation technique of 4H-SiC, and can reduce the manufacturing cost of the substrate. In addition, the manufacturing method of a semiconductor substrate according to the present application can effectively use the 4H-SiC substrate after the surface layer is exfoliated, and can reduce the manufacturing cost of the semiconductor substrate.

[0076] Further, the semiconductor substrate of the present application is a cheaper and higher-quality semiconductor substrate. In addition, the semiconductor device of the present application is also a cheaper and higher-quality semiconductor device. BRIEF DESCRIPTION OF DRAWINGS

[0077] Figure 1 A schematic view of the semiconductor substrate of the present application is shown.

[0078] Figure 2 A flowchart of the manufacturing method of the semiconductor substrate of the present application is shown. DETAILED DESCRIPTION

[0079] Hereinafter, the present application will be described in detail, but the present application is not limited thereto.

[0080] As described above, there is a need for a manufacturing method of a semiconductor substrate that can manufacture a cheaper and higher-quality semiconductor substrate using the exfoliation technique of 4H-SiC and can reduce the manufacturing cost of the substrate, and for a cheaper and higher-quality semiconductor substrate and a cheaper and higher-quality semiconductor device.

[0081] As a result of intensive studies conducted by the inventors of the present invention in order to solve the above-described problems, a semiconductor substrate manufacturing method was found, which is characterized by comprising the following steps: an ion implantation step of implanting ions of at least one of silicon, carbon, and oxygen into a surface of a 4H-SiC substrate to form an amorphous layer in the 4H-SiC substrate by amorphization of silicon and carbon; a bonding step of forming a thin film on at least one of the surface of the 4H-SiC substrate on which the ion implantation step has been performed and a bonding surface of another support substrate, and performing bonding through the thin film to obtain a bonded substrate; a separation step of separating the 4H-SiC substrate into a bonded substrate obtained by transferring a surface layer of the 4H-SiC substrate to the support substrate as a 4H-SiC layer and a separated substrate which is a substrate from which the surface layer has been separated from the 4H-SiC substrate, by separating the 4H-SiC substrate using the amorphous layer of the bonded substrate; an etching step of performing plasma etching on a separation surface of at least one of the bonded substrate and the separated substrate after the separation step; and an epitaxial growth step of performing epitaxial growth on at least one of the bonded substrate and the separated substrate, by which a cheaper and high-quality semiconductor substrate can be manufactured using a separation technique of 4H-SiC, and the present invention was completed.

[0082] Further, as a result of intensive studies conducted by the inventors of the present invention in order to solve the above-described problems, a semiconductor substrate was found, which is characterized by comprising a support substrate of SiC and a 4H-SiC layer bonded to a surface of the support substrate through a thin film of silicon and subjected to etching treatment, by which a cheaper and high-quality semiconductor substrate can be provided, and the present invention was completed.

[0083] Further, as a result of intensive studies conducted by the inventors of the present invention in order to solve the above-described problems, a semiconductor device was found, which is characterized by comprising the above-described semiconductor substrate, by which a cheaper and high-quality semiconductor device can be provided, and the present invention was completed.

[0084] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0085] First, the configuration of a semiconductor substrate 5 will be described with reference to Figure 1

[0086] As shown in FIG. 1, the semiconductor substrate 5 of the embodiment of the present invention comprises a support substrate 3 and a 4H-SiC layer la bonded to a surface of the support substrate 3 through a thin film 7. Figure 1

[0087] ​​The support substrate 3 is a substrate that supports the 4H-SiC layer la through the thin film 7, and has a strength sufficient to support the 4H-SiC layer la, and the material and size can be appropriately selected as long as no unexpected reaction occurs with the thin film 7. Specifically, a bulk 4H-SiC of the same material as the 4H-SiC layer la can be exemplified, and a sintered SiC substrate or a polycrystal SiC substrate, which is cheaper than the bulk 4H-SiC, can also be used in consideration of the price.

[0088] The 4H-SiC layer la is a single crystal layer of 4H-SiC, and is bonded to the surface of the support substrate 3. In order for this bonding, the thin film 7 is formed on the bonding surface of the 4H-SiC layer la and the support substrate 3, and firm bonding is achieved by bonding through the thin film 7.

[0089] The thin film 7 is a material that can be bonded to the 4H-SiC layer la and the support substrate 3, and is, for example, a silicon thin film. As long as not particularly described, the present application will be described in the following description using a silicon thin film as the thin film 7 as an example.

[0090] Further, the surface 25 of the 4H-SiC layer la is subjected to etching treatment. By subjecting the surface 25 of the 4H-SiC layer la to etching treatment, the surface 25 becomes flat, and even if high-cost flattening treatment such as CMP is not performed, an epitaxial layer can be formed, and a cheaper and high-quality semiconductor substrate 5 can be obtained.

[0091] If the 4H-SiC layer la is a single crystal layer, it can be a bulk 4H-SiC, or an epitaxial layer of 4H-SiC.

[0092] As for the thickness of the 4H-SiC layer la, it is a thickness that can at least maintain the shape as a layer, can form a device, and does not disappear due to etching and polishing at that time. On the other hand, the maximum thickness is, for example, a thickness in which a useless portion that is not used when forming a device does not occur as much as possible. The thickness can be, for example, 0.01 μm to 400 μm.

[0093] Next, the configuration of the semiconductor device 6 will be described while referring to Figure 1 .

[0094] Figure 1 The semiconductor device 6 shown in FIG. 1 has the semiconductor substrate 5.

[0095] As a specific semiconductor device 6, a semiconductor device obtained by forming a desired semiconductor device on the semiconductor substrate 5, particularly the 4H-SiC layer la can be exemplified. Of course, the semiconductor device 6 can also be diced to be chipped.

[0096] By incorporating a cheaper and higher-quality semiconductor substrate 5 into the semiconductor device 6, the semiconductor device 6 will also be cheaper, higher-quality, and more reliable.

[0097] Next, refer to Figure 2 A summary of the method for manufacturing the semiconductor substrate 5 of the present invention will be described.

[0098] First, such as Figure 2 As shown in (a), a 4H-SiC substrate 1 is prepared. A single-crystal bulk 4H-SiC is used as the 4H-SiC substrate 1 in this example, but it can also be a 4H-SiC epitaxial substrate.

[0099] Furthermore, in this embodiment, the surface layer of the 4H-SiC substrate 1 is transferred to the support substrate 3, but the final stripped substrate 11 formed after the transfer can also be reused as the 4H-SiC substrate 1. Ideally, these 4H-SiC substrates 1 are obtained by epitaxial growth performed by CVD.

[0100] Next, ion implantation of at least one of silicon, carbon, and oxygen is performed on the 4H-SiC substrate 1 to sever the silicon-carbon bonds near the surface of the 4H-SiC substrate 1, such as... Figure 2 As shown in (b), an amorphous layer 2 is formed in which silicon and carbon each exist in an amorphous manner (ion implantation process).

[0101] By adjusting the acceleration energy of ion implantation, an amorphous layer 2, in which silicon and carbon exist in an amorphous state, can be formed at a specified depth. Additionally, when oxygen is implanted, both the amorphous layer 2 and an oxygen-containing layer are formed.

[0102] The implanted ions only need to be at least one of silicon, carbon, or oxygen, thus allowing for the implantation of various ions. Furthermore, the choice of which of silicon, carbon, or oxygen ions to implant can be made by appropriately considering the advantages of each.

[0103] For example, when silicon or carbon is ion implanted, it is advantageous because these elements are constituent elements of SiC, and therefore will not become impurities even after implantation. On the other hand, when oxygen is ion implanted, the 4H-SiC substrate 1 can be peeled off by heating in a subsequent process, which is advantageous because it offers a wider range of peeling methods.

[0104] In addition, the acceleration energy during ion implantation varies depending on the depth of the amorphous layer 2 formed. Specifically, the deeper the position in the depth direction, the greater the acceleration energy becomes, for example, around 200 keV.

[0105] The amount of ions implanted is sufficient to form an amorphous layer 2, for example, 1.0 × 10⁻⁶. 17 atoms / cm2 left and right.

[0106] Next, as shown in (c) of Figure 2 , a substrate different from the 4H-SiC substrate 1 is prepared as a support substrate 3. The support substrate 3 can be a single crystal 4H-SiC of the same structure as the 4H-SiC substrate 1, and, in consideration of cost, for example, it is also preferable to use sintered SiC or polycrystalline SiC, or the like, which is made by sintering.

[0107] Next, as shown in (d) of Figure 2 , a thin film 7 of silicon or the like is formed on the bonding surface 8 of the surface 14 of the 4H-SiC substrate 1 on which an ion implantation process of silicon or the like has been performed and the support substrate 3, and then they are bonded, thereby obtaining a bonded substrate 10 (bonding process) shown in (e) of Figure 2

[0108] As the thin film 7, it is preferable to form a silicon thin film and perform bonding through the silicon thin film.

[0109] A silicon thin film is sometimes used as a substrate at the time of epitaxial growth of 4H-SiC, and thus it is easy to bond with 4H-SiC, and it is also easy to bond with polycrystals and sintered bodies of SiC. Therefore, by preparing a support substrate 3 of polycrystalline SiC, which is cheaper than a single crystal SiC, and forming silicon thinly on the bonding surface 8, and performing bonding through the silicon, it becomes possible to bond even SiC which is difficult to bond.

[0110] As a specific film formation method of the thin film 7, a sputtering method in which silicon is used as a target and Ar ions are irradiated to the target to perform film formation is effective because high-temperature heating of the substrate is not required, and the SiC surface of the bonding surface is not roughened.

[0111] Furthermore, as a bonding method of the 4H-SiC substrate 1 and the support substrate 3 through the thin film 7, for example, room-temperature bonding can be exemplified.

[0112] Next, as shown in (f) of Figure 2 , the 4H-SiC substrate 1 is peeled off by using the amorphous layer 2 of the bonded substrate 10, and is separated into a bonded substrate 12 obtained by transferring the surface layer of the 4H-SiC substrate 1 as a 4H-SiC layer la to the support substrate 3, and a peeled substrate 11 which is a substrate from which the surface layer has been peeled off from the 4H-SiC substrate 1 (peeling process).

[0113] Specifically, in the peeling process, the 4H-SiC substrate 1 can be peeled off by performing light irradiation, or applying an impact, or performing a process of combining the above-mentioned irradiation light and the applied impact to the amorphous layer 2.

[0114] ​When the light irradiation is performed, the bonded substrate 10 is subjected to the light irradiation so that the amorphous layer 2 of silicon and carbon formed in the ion implantation step absorbs the light and is peeled off from the 4H-SiC substrate 1 as a starting point, whereby the bonded substrate 12 obtained by transferring the surface layer of the 4H-SiC substrate 1 as the 4H-SiC layer la to the support substrate 3 and the peeled substrate 11 obtained by peeling off the surface layer from the 4H-SiC substrate 1 are separated.

[0115] By the light irradiation to the amorphous layer 2 in the above-described manner, the amorphous layer 2 can directly absorb the light and be subjected to the energy required for the peeling.

[0116] The light source of the irradiated light is not particularly limited as long as it can apply the energy to the amorphous layer 2 to the extent that the 4H-SiC substrate 1 can be peeled off from the amorphous layer 2 as a starting point, and YAG laser can be exemplified. When the YAG laser is used as the light source, the wavelength of the irradiated light can be exemplified by the fundamental wavelength (1064 nm).

[0117] In the peeling step, when the amorphous layer 2 is subjected to the impact, the peeling can be performed without the light irradiation by merely inserting a tool such as a metal thin blade into the amorphous layer 2.

[0118] The method of peeling by the impact applied to the amorphous layer 2 in the above-described manner is advantageous in that the equipment that can be used for the peeling is simple.

[0119] Further, the peeling can also be performed by combining the light irradiation and the impact. Specifically, the peeling can be performed by applying the impact to the amorphous layer 2 of carbon by inserting a tool such as a metal thin blade in addition to the light irradiation. At this time, the time required for the peeling can be shortened compared to when the light irradiation or the impact is performed alone.

[0120] When the ion implantation of oxygen is performed in the ion implantation step, in the peeling step, the 4H-SiC substrate 1 can be peeled off in such a manner that the amorphous layer 2 is irradiated with light, or subjected to the impact, or subjected to the heat treatment to cause the implanted oxygen to react with the carbon of the amorphous layer to generate a gas, or subjected to a treatment of combining the above-described light irradiation, impact, and heat treatment.

[0121] The surface of the peeled surface 23 of the bonded substrate 12 obtained by the peeling in the above-described manner is rough, and thus when an epitaxial layer is to be formed in a subsequent step, it is sometimes preferable to planarize the surface. Further, the peeled substrate 11 can be reused by repeatedly performing the ion implantation step, the bonding step, and the peeling step again to transfer the surface layer to a plurality of support substrates 3, but since the surface of the peeled surface 21 is rough, the surface needs to be planarized in order to be bonded to the support substrate 3. In this regard, the steps of planarizing the peeled surfaces 23 and 21 are described below.

[0122] First, as shown in (h) of FIG. 1, at least one of the separation surface 23 of the bonding substrate 12 or the separation surface 21 of the separation substrate 11 after the separation process is subjected to plasma etching (etching process). Figure 2

[0123] In addition, Figure 2 The case where both the separation surface 23 of the bonding substrate 12 and the separation surface 21 of the separation substrate 11 are etched is exemplified in FIG. 1, but only at least one of them can be etched. For example, when an epitaxial layer can be formed even without planarizing the separation surface 23 of the bonding substrate 12, or when the 4H-SiC layer la is an epitaxial layer without the need for further formation of an epitaxial layer, only the separation surface 21 of the separation substrate 11 can be etched.

[0124] By subjecting at least one of the separation surface 23 of the bonding substrate 12 or the separation surface 21 of the separation substrate 11 to plasma etching, the surface of SiC, which is a difficult-to-machine material, can be planarized more inexpensively than CMP or the like.

[0125] A mixed gas of a fluorocarbon compound gas and oxygen can be used as a raw material gas for etching. As a specific fluorocarbon compound gas, CHF3or CF4is preferable. The mixed gas of a fluorocarbon compound gas and oxygen is a gas for etching of silicon or the like, and thus is advantageous in that it does not need to prepare a gas dedicated for etching of SiC by being used as a raw material gas.

[0126] Further, the plasma form at the etching process can be optimized according to the apparatus, and is not particularly limited, and a radio frequency (RF) plasma or the like can be exemplified. In addition, generally, SiC is not etched by such a mixed gas of a fluorocarbon compound gas and oxygen, but since the separation surfaces 23 and 21 are weakened by the implementation of the ion implantation process, the surface layer is a damaged layer, and thus planarization can be performed by removing the layer including the separation surfaces 23 and 21 by etching. Further, the weakening is not only caused by damage by ion implantation, but can also be formed in plasma processing using hydrogen (H2).

[0127] In addition, after the separation process and before the etching process, as shown in (g) of FIG. 1, the separation surface 23 of the bonding substrate 12 or the separation surface 21 of the separation substrate 11 on which the etching process is to be performed can be annealed at a temperature of 1000°C or higher in a hydrogen atmosphere (annealing process). The upper limit of the annealing temperature is not particularly limited, and can be set to 2000°C or lower. Figure 2

[0128] ​​After the hydrogen annealing in the above-described manner is performed in the annealing step, the etching step is performed, and the unevenness of the separation surface 23 or the separation surface 21 that has become rough due to the separation is modified by the hydrogen annealing before the etching, and is planarized to some extent. Thus, in the etching step, it becomes easier to improve the planarity of the separation surface 23 or the separation surface 21.

[0129] The separation substrate 11 after the separation step can be reused as the 4H-SiC substrate 1 by repeatedly performing the ion implantation step, the bonding step, and the separation step again, and thus can be reused as a substrate for transferring 4H-SiC to the support substrate 3 until the thickness becomes such that the separation cannot be performed.

[0130] Here, when the separation surface 21 of the separation substrate 11 is etched in the etching step, the separation surface 21 is planarized by the etching, and thus the support substrate 3 can be bonded to the separation surface 21 even without performing a high-cost planarization treatment such as CMP.

[0131] Next, epitaxial growth (an epitaxial step) is performed on at least one of the bonded substrate 12 or the separation substrate 11. Specifically, the epitaxial layer 4 is grown by CVD or the like.

[0132] Figure 2 The case where the epitaxial layer 4 of 4H-SiC is grown on the 4H-SiC layer la of the bonded substrate 12 is exemplified in (i) in the above.

[0133] Here, when the separation surface 23 of the 4H-SiC layer la is etched in the etching step, the separation surface 23 is planarized by the etching, and thus the epitaxial layer 4 can be formed on the separation surface 23 even without performing a high-cost planarization treatment such as CMP, and the bonded substrate 12 can be made into a cheaper and higher-quality semiconductor substrate 5.

[0134] In addition, when the 4H-SiC layer la is an epitaxial layer, the thickness of the transferred 4H-SiC layer la is not necessarily required to be a thickness sufficient for forming a device in a subsequent step, and the epitaxial step shown in (i) in the above can not be performed. Figure 2

[0135] On the other hand, when the 4H-SiC layer la is not an epitaxial layer, or when the 4H-SiC layer la is an epitaxial layer but the film thickness at the time point of the transfer in the separation step is not a thickness sufficient for forming a device, it is preferable to perform the epitaxial step on the bonded substrate 12. At this time, it is preferable to smooth the separation surface 23 in the etching step before the epitaxial step is performed on the bonded substrate 12.

[0136] Specifically, it is preferable to perform the epitaxial step on the bonded substrate 12 after the etching step is performed on the separation surface 23 of the 4H-SiC layer la of the separation substrate 11. Figure 2 ​As shown in (h) of FIG. 1, in the etching step, the separation surface 23 of the bonded substrate 12 is plasma-etched, and further, on the etched separation surface 23 of the bonded substrate 12, a device is formed as shown in (i) of FIG. 1. ​ As shown in (i) of FIG. 1, in the epitaxial step, the epitaxial layer 4 is grown on the etched separation surface 23 of the bonded substrate 12.

[0137] If the epitaxial layer 4 is grown on the etched separation surface 23 of the bonded substrate 12 in the above-described manner, a device can be made in higher quality by forming a device on the epitaxial layer 4.

[0138] Embodiment

[0139] Hereinafter, the present application will be specifically described by citing examples, but these examples are not intended to limit the present application.

[0140] After the ion implantation step of silicon, carbon, and oxygen, the bonding step (silicon thin film formation and bonding), the separation step, and the etching step are performed on the 4H-SiC substrate 1, a further ion implantation step and a bonding step are performed to attempt to reuse the separation substrate 11 as the 4H-SiC substrate 1.

[0141] (Embodiment 1)

[0142] First, as the 4H-SiC substrate 1, an n-type 4H-SiC single crystal substrate having a diameter of 200 mm, a thickness of 355 μm, a resistivity of 10 Ω-cm, and a deviation of 4° from the (0001) plane was prepared, and as the ion implantation step, an ion implantation device was used to implant ions of 1 x 1016 atoms / cm2of silicon at an acceleration energy of 200 keV. 17 2

[0143] Next, as the bonding step, the following steps were performed. First, as the support substrate 3, a polycrystalline SiC substrate having the same diameter as the 4H-SiC substrate 1 was prepared, and a silicon thin film as the thin film 7 was formed by sputtering on both the 4H-SiC substrate 1 and the support substrate 3 using silicon as the target material and irradiating Ar ions. The film thickness of the silicon thin film at this time was 20 nm. Then, the 4H-SiC substrate 1 and the support substrate 3 were bonded at room temperature with the silicon thin film interposed therebetween, and a bonded substrate 10 was obtained.

[0144] After the bonding step, as the separation step, the amorphous layer 2 was excited by irradiating light thereto using a YAG laser (wavelength 1064 nm), and the bonded substrate 10 was separated into the bonded substrate 12 and the separation substrate 11.

[0145] ​​As an epitaxial process, a hot-wall CVD apparatus was used on the bonding substrate 12, with H2 as the carrier gas and SiH4 and C3H8 as the raw material gases, to perform 4H-SiC epitaxial growth, resulting in semiconductor substrate 5. The temperature at this time was 1600°C, and the furnace pressure was set to 7 kPa.

[0146] For the stripping surface 21 of the stripped substrate 11 formed when the semiconductor substrate 5 is obtained in the above manner, as an etching process, RF plasma etching is performed under the conditions of raw material gases CHF3 and O2 set to 100 sccm and 10 sccm respectively, pressure of 100 Torr (13332.2 Pa), and RF power of 500 W.

[0147] Furthermore, the silicon ion implantation process and bonding process are performed again on the stripped substrate 11 after the etching process using the previous process. As a result, the support substrate 3 can be bonded on the stripped surface 21 of the stripped substrate 11, and the bonded substrate 10 can be obtained in the same way.

[0148] (Example 2)

[0149] First, as the 4H-SiC substrate 1, an n-type 4H-SiC single crystal substrate with a diameter of 200 mm, a thickness of 355 μm, a resistivity of 10 Ω·cm, and an offset of 4° from the (0001) plane is prepared. As an ion implantation process, an ion implantation device is used to implant 1 × 10⁻¹⁰ crystals of this substrate at an accelerating energy of 200 keV. 17 atoms / cm 2 Carbon ions.

[0150] Next, as a bonding process, the following steps are performed. First, a polycrystalline SiC substrate with the same aperture as the 4H-SiC substrate 1 is prepared as the support substrate 3. Silicon is used as a target material, and Ar ions are irradiated onto both the 4H-SiC substrate 1 and the support substrate 3 to form a silicon thin film 7. At this time, the silicon thin film is 20 nm in size. Then, the 4H-SiC substrate 1 and the support substrate 3 are bonded at room temperature through the silicon thin film to obtain the bonded substrate 10.

[0151] After the bonding process, as a peeling process, a YAG laser (wavelength 1064nm) is used to irradiate the amorphous layer 2 to excite it, and the bonding substrate 10 is separated into the bonding substrate 12 and the peeling substrate 11.

[0152] As an epitaxial process, a hot-wall CVD apparatus was used on the bonding substrate 12, with H2 as the carrier gas and SiH4 and C3H8 as the raw material gases, to perform 4H-SiC epitaxial growth, resulting in semiconductor substrate 5. The temperature at this time was 1600℃, and the furnace pressure was set to 7 kPa.

[0153] As to the separation surface 21 of the separation substrate 11 formed when the semiconductor substrate 5 is obtained in the above-described manner, as an etching step, RF plasma etching processing is performed under conditions in which the raw material gases are CHF3and O2and are set to 100 sccm and 10 sccm, respectively, under conditions in which the pressure is 100 torr (13332.2 Pa), and under conditions in which the RF power is 500 W.

[0154] Further, the separation substrate 11 after the etching step is subjected to the carbon ion implantation step and the bonding step again in the same procedure as the previous recycling procedure, and as a result, the support substrate 3 can be bonded to the separation surface 21 of the separation substrate 11, and the bonded substrate 10 can be obtained in the same manner.

[0155] (Example 3)

[0156] First, as the 4H-SiC substrate 1, an n-type 4H-SiC single crystal substrate having a diameter of 200 mm, a thickness of 355 μm, a resistivity of 10 Ω-cm, and a deviation of 4° from the (0001) plane is prepared, and as the ion implantation step, the substrate is implanted with ions of oxygen at an acceleration energy of 200 keV using an ion implantation device at a dose of 1 x 1016atoms / cm2. 17 2 The silicon thin film at this time has a film thickness of 20 nm. Then, as the bonding step, room-temperature bonding of the 4H-SiC substrate 1 and the support substrate 3 is performed, and a bonded substrate 10 is obtained.

[0157] Next, as the bonding step, the following procedure is performed. First, as the support substrate 3, a polycrystalline SiC substrate having the same diameter as the 4H-SiC substrate 1 is prepared, and silicon is formed as the thin film 7 on both the 4H-SiC substrate 1 and the support substrate 3 by sputtering using silicon as the target material and irradiating Ar ions. The silicon thin film at this time has a film thickness of 20 nm. Then, as the bonding step, room-temperature bonding of the 4H-SiC substrate 1 and the support substrate 3 is performed, and a bonded substrate 10 is obtained.

[0158] After the bonding step, as the separation step, the amorphous layer 2 is excited by irradiating light thereto using a YAG laser (wavelength 1064 nm), and the bonded substrate 10 is separated into a bonded substrate 12 and a separation substrate 11.

[0159] As the epitaxial step, the bonded substrate 12 is subjected to epitaxial growth of 4H-SiC using a hot-wall type CVD device, using H2as the carrier gas and SiH4and C3H8as the raw material gases, and a semiconductor substrate 5 is obtained. The temperature at this time is 1600°C, and the pressure in the furnace is set to 7 kPa.

[0160] As to the separation surface 21 of the separation substrate 11 formed when the semiconductor substrate 5 is obtained in the above-described manner, as an etching step, RF plasma etching processing is performed under conditions in which the raw material gases are CHF3and O2and are set to 100 sccm and 10 sccm, respectively, under conditions in which the pressure is 100 torr (13332.2 Pa), and under conditions in which the RF power is 500 W.​

[0161] Further, the ion implantation process and the bonding process are further performed on the exfoliated substrate 11 after the etching process, and as a result, the support substrate 3 can be bonded to the exfoliation surface 21 of the exfoliated substrate 11, and the bonded substrate 10 can be obtained in the same manner.

[0162] As described above, according to the embodiment of the present application, after the amorphous layer 2 is formed by ion implantation on the 4H-SiC substrate 1, the support substrate 3 is bonded through the thin film 7, and the 4H-SiC substrate 1 is exfoliated using the amorphous layer 2, and thus, the bonded substrate 12 can be obtained, which improves the surface layer of the 4H-SiC substrate 1 as a 4H-SiC layer la to be transferred to the support substrate 3. In addition, the exfoliated substrate 11 can be reused as the 4H-SiC substrate 1.

[0163] The present specification includes the following aspects.

[0164] [1] A method for manufacturing a semiconductor substrate, characterized by comprising the steps of:

[0165] an ion implantation process of performing ion implantation of at least one of silicon, carbon, and oxygen on a surface of a 4H-SiC substrate, thereby forming an amorphous layer of silicon and carbon amorphization within the 4H-SiC substrate;

[0166] a bonding process of forming a thin film on at least one of a surface of the 4H-SiC substrate on which the ion implantation process is performed and a bonding surface of another support substrate, and performing bonding through the thin film, thereby obtaining a bonded substrate;

[0167] an exfoliation process of exfoliating the 4H-SiC substrate by using the amorphous layer of the bonded substrate, thereby separating into a bonded substrate obtained by transferring a surface layer of the 4H-SiC substrate as a 4H-SiC layer to the support substrate and an exfoliated substrate which is a substrate from which the surface layer of the 4H-SiC substrate is exfoliated;

[0168] an etching process of performing plasma etching on an exfoliation surface of at least one of the bonded substrate or the exfoliated substrate after the exfoliation process; and

[0169] an epitaxial growth process of performing epitaxial growth on at least one of the bonded substrate or the exfoliated substrate.

[0170] [2] The method for manufacturing a semiconductor substrate according to the above [1], wherein in the exfoliation process, the 4H-SiC substrate is exfoliated by irradiating light or applying an impact or performing a process of combining the irradiation of light and the application of an impact.

[0171] [3] The method for manufacturing a semiconductor substrate according to any one of [1] to [2], wherein

[0172] In the ion implantation process, ion implantation of oxygen is performed,

[0173] In the peeling process,

[0174] The implanted oxygen is caused to react with carbon of the amorphous layer by irradiating light, or applying an impact, or performing heat treatment, to generate a gas, thereby peeling the 4H-SiC substrate; or

[0175] The 4H-SiC substrate is peeled by performing a process in which the above-mentioned irradiation of light, application of an impact, and heat treatment are combined.

[0176] [4] The method for manufacturing a semiconductor substrate according to any one of [1] to [3], wherein, in the bonding process, a silicon thin film is formed as the thin film, and bonding is performed through the thin film.

[0177] [5] The method for manufacturing a semiconductor substrate according to [4], wherein, in the bonding process, the silicon thin film is formed by a sputtering method using silicon as a target material.

[0178] [6] The method for manufacturing a semiconductor substrate according to any one of [1] to [5], wherein, in the etching process, a mixed gas of a fluorocarbon compound gas and oxygen gas is used as a source gas.

[0179] [7] The method for manufacturing a semiconductor substrate according to any one of [1] to [6], wherein, after the peeling process and before the etching process, annealing is performed on a peeling surface of the bonded substrate or the peeled substrate, on which the etching process is to be performed, at a temperature of 1000°C or higher in a hydrogen atmosphere.

[0180] [8] The method for manufacturing a semiconductor substrate according to any one of [1] to [7], wherein, in the etching process, plasma etching is performed on the peeling surface of the bonded substrate, and further, after the etching process, the epitaxial process is performed on the etched peeling surface of the bonded substrate.

[0181] [9] A semiconductor substrate characterized by comprising a support substrate and a 4H-SiC layer bonded to a surface of the support substrate,

[0182] The support substrate is SiC,

[0183] The 4H-SiC layer is bonded to the support substrate through a silicon thin film, and a surface thereof is subjected to an etching process.

[0184]

[10] A semiconductor device characterized by comprising the semiconductor substrate described in [9] above.

[0185] In addition, the present application is not limited to the above-described embodiments. The above-described embodiments are examples, and any technical solution having substantially the same configuration as the technical concept described in the claims of the present application and exerting the same technical effects is included in the technical scope of the present application.

Claims

1. A method of manufacturing a semiconductor substrate, characterized by, comprising the steps of: an ion implantation step of implanting ions of at least one of silicon, carbon, and oxygen into a surface of a 4H-SiC substrate to form an amorphous layer in the 4H-SiC substrate by amorphization of silicon and carbon; a bonding step of forming a thin film on at least one of the surface of the 4H-SiC substrate on which the ion implantation step is performed and a bonding surface of another support substrate, and performing bonding through the thin film to obtain a bonded substrate; a separation step of separating the 4H-SiC substrate into a bonded substrate obtained by transferring a surface layer of the 4H-SiC substrate as a 4H-SiC layer to the support substrate and a separated substrate obtained by separating the surface layer from the 4H-SiC substrate by using the amorphous layer of the bonded substrate; an etching step of performing plasma etching on a separation surface of at least one of the bonded substrate and the separated substrate after the separation step; and an epitaxial growth step of performing epitaxial growth on at least one of the bonded substrate and the separated substrate.

2. The method according to claim 1, wherein in the separation step, the 4H-SiC substrate is separated by irradiating light, or applying an impact, or performing a process combining the irradiation of light and the application of an impact, to the amorphous layer.

3. The method according to claim 1, wherein in the ion implantation step, ions of oxygen are implanted, in the separation step, the 4H-SiC substrate is separated by irradiating light, or applying an impact, or performing a heat treatment to cause the implanted oxygen to react with carbon in the amorphous layer to generate a gas; or the 4H-SiC substrate is separated by performing a process combining the irradiation of light, the application of an impact, and the heat treatment.

4. The method according to claim 1, wherein in the bonding step, a silicon thin film is formed as the thin film, and bonding is performed through the silicon thin film.

5. The method according to claim 4, wherein in the bonding step, the silicon thin film is formed by a sputtering method using silicon as a target.

6. The method according to claim 1, wherein in the etching step, a mixed gas of a fluorocarbon compound gas and oxygen is used as a source gas.

7. The method according to claim 1, wherein after the separation step and before the etching step, annealing is performed on a separation surface of the bonded substrate or the separated substrate on which the etching step is to be performed, in a hydrogen atmosphere at a temperature of 1000°C or higher.

8. The method according to any one of claims 1 to 7, wherein in the etching step, plasma etching is performed on the separation surface of the bonded substrate, and further, after the etching step, the epitaxial growth step is performed on the etched separation surface of the bonded substrate. ​ 9. A semiconductor substrate, characterized by, It has a support substrate and a 4H-SiC layer bonded to the surface of the support substrate, The support substrate is SiC, The 4H-SiC layer is bonded to the support substrate through a silicon thin film, and the surface has been subjected to etching treatment.

10. A semiconductor device, characterized by comprising: It has the semiconductor substrate described in claim 9.

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