Semiconductor substrate manufacturing method

Abstract

To provide a manufacturing method for a semiconductor substrate, by which a semiconductor substrate with high quality can be manufactured at lower cost using a 4H-SiC separation technique.SOLUTION: A manufacturing method for a semiconductor substrate 5 includes: an ion injection step of performing ion injection of at least one of silicon, carbon, and oxygen for a 4H-SiC substrate 1, thereby forming an amorphous layer 2 in the 4H-SiC substrate; a bonding step of forming a thin film on at least one of the 4H-SiC substrate 1 and a supporting substrate 3, thereby performing bonding through the thin film; a separating step of separating the 4H-SiC substrate 1 at the amorphous layer 2 into a bonding substrate 12, in which a surface layer of the 4H-SiC substrate 1 is transferred to the supporting substrate 3, and a separation substrate 11, in which the surface layer is separated from the 4H-SiC substrate 1; an etching step of plasma-etching at least one separation surface of the bonding substrate 12 and the separation substrate 11; and an epitaxial step of performing epitaxial growth on at least one of the bonding substrate 12 and the separation substrate 11.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a semiconductor substrate, a semiconductor substrate, and a semiconductor device. [Background technology]

[0002] SiC has a wide band gap of 2.2 to 3.3 eV, giving it high dielectric breakdown strength, and also has high thermal conductivity, making it a promising semiconductor material for various semiconductor devices such as power devices and high-frequency devices.

[0003] However, Non-Patent Document 1 reports that in devices using SiC, the manufacturing process of the SiC substrate and the subsequent epitaxial process account for half of the cost, making substrate cost reduction extremely important.

[0004] As a cost reduction measure, H + A method has been proposed in which ion implantation is performed to remove the substrate. + Several prior art techniques have been reported regarding the injection of these into SiC.

[0005] Patent Document 1 describes a method for preparing two SiC single crystal wafers, forming an oxide layer on each, then implanting hydrogen ions into one of the substrates, bonding and integrating them at room temperature via the oxide layer, and then heating to over 500°C to split the SiC single crystal wafer into two at the hydrogen ion implantation site to produce a substrate for semiconductor electronic devices. In this method, an oxide film is present at the bonding site, and when used as a vertical device, this oxide film functions as an insulating layer, severely limiting its function as a power device substrate.

[0006] Furthermore, Patent Document 2 contains H + A method is disclosed in which an injected single crystal and a polycrystalline SiC substrate are bonded together, and then the single crystal and polycrystalline layers are separated. However, this method has drawbacks, such as increased costs due to the two-step separation process and the difficulty of performing each separation step in a predetermined manner.

[0007] Patent Document 3 focuses on the impurity concentration and the defect density, and describes a method of transferring a high-resistance substrate with a low defect density by using H + implantation. Although this method can reduce the defects existing in the original substrate, there is no mention of the substrate after peeling.

[0008] Furthermore, Patent Document 4 describes the technology underlying substrate peeling by H + and mentions the diffusion barrier (oxygen diffusion barrier) function, but there is no mention of the substrate after peeling.

[0009] Furthermore, Patent Document 5 also describes a method of fabricating various substrates by the peeling technology of H + and describes a method of epitaxially growing InGaN after polishing or dry etching the surface, but there is no description about the handling of the peeled substrate.

[0010] In addition, Patent Document 6 describes a method of fabricating a device on a silicon carbide substrate, forming a protective film, then performing ion implantation, bonding to a support substrate, and performing high-temperature annealing, and reusing the substrate after separation, but there is still no description about the handling of the substrate after peeling.

[0011] In addition, Patent Document 7 applies H + peeling. After ion implantation into single-crystalline SiC, polycrystalline SiC is formed on the opposite surface, then annealing is performed, peeling is carried out from the ion implantation surface, and after polishing the peeling surface, SiC is epitaxially grown. As described above, in the substrate technology using H + no mention is made of the specific reuse method of the peeled substrate.

[0012] Furthermore, as a method of forming a support substrate when injecting H + ions and then peeling, Patent Document 8 describes the growth of polycrystalline SiC on the substrate after injection at 1000 - 1600°C, and Patent Document 9 describes H + at +Growth on the substrate after injection by DLI-CVD (Direct Liquid Injection - CVD). Patent Document 10 discloses H + Methods such as sintering method and liquid phase deposition on the substrate after injection are disclosed.

[0013] This method is adopted because, as described in Patent Document 8, it is difficult to bond SiC to each other, and problems have been pointed out in bonding via W or Mo due to the presence of metal.

[0014] However, when deposition is performed on the support substrate at a high temperature after such H + injection, peeling may occur in the H + injection layer during deposition, and considering reuse, the substrate itself with the H + injection layer is exposed to high temperature, resulting not only in a change in crystallinity but also in the formation of polycrystalline layers etc. on the side surface, which hinders reuse.

Prior Art Documents

Patent Documents

[0015]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

[0016] [Non-Patent Document 1] Iwamuro, "Advancements in High-Performance and High-Reliability SiC MOSFETs," Proceedings of the Wide Bandgap Semiconductor Society Special Open Symposium, Wide Bandgap Semiconductor Society, 2022. [Non-Patent Document 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”, ICSCRM2022, 2022 [Non-Patent Document 3] Suga, "Room-temperature bonding by surface activation and its mechanism," Applied Physics, The Japan Society of Applied Physics, 89(9), 2020. p498. [Overview of the Initiative] [Problems that the invention aims to solve]

[0017] Thus, 4H-SiC is expected to be a high-voltage device, but the high cost of the substrate is a problem, and the challenge is how to reduce the cost of the bulk substrate. + A technique has been proposed to remove substrates using ion implantation, but in this case, costs can be reduced by reusing the substrate after removal (otherwise, costs will remain high). Therefore, how to reuse the substrate after removal (to make it a high-quality substrate) is extremely important, H + This is a fundamental technology for the widespread adoption of substrate peeling technology using ions and other means.

[0018] On the other hand, H +After ion implantation and delamination of the substrate, the delaminated substrate has a rough surface, making re-bonding impossible without planarization. Furthermore, bonding SiC to SiC is inherently difficult. In addition, it is sometimes preferable to planarize the delaminated surface of the SiC transferred to the support substrate before performing epitaxial growth or other processes on the delaminated surface.

[0019] However, because SiC is a hard material that is difficult to process, polishing methods such as CMP require high costs to flatten the delaminated surface, which ultimately leads to higher manufacturing costs for the substrate. Furthermore, H + In methods where a support substrate is grown after injection, peeling of the support substrate during its growth or unintended growth of polycrystalline SiC on the original substrate can hinder reuse.

[0020] H + In the case of injection, as mentioned earlier, H + After injection, if the support substrate is deposited at high temperature, H + Delamination in the injection layer can occur during deposition, and H is being considered for reuse. + When the substrate with the injection layer is exposed to high temperatures, not only does its crystallinity change, but polycrystalline layers and other structures can also form on the sides, hindering its reuse.

[0021] This invention was made to solve the above problems, and aims to provide a method for manufacturing semiconductor substrates that can produce lower-cost, high-quality semiconductor substrates using 4H-SiC peeling technology. Furthermore, the present invention aims to provide semiconductor substrates and semiconductor devices that are less expensive and of higher quality. [Means for solving the problem]

[0022] This invention relates to a method for manufacturing SiC wafers to achieve the above objectives, and more specifically to a substrate delamination technology utilizing silicon, carbon, and oxygen ion implantation, relating to bonding with a support substrate and reuse of the substrate after delamination, thereby providing a lower-cost, higher-quality SiC substrate. Specifically, the present invention has been made to achieve the above objective, and provides a method for manufacturing a semiconductor substrate, characterized by including an ion implantation step of implanting at least one of silicon, carbon, and oxygen into the surface of a 4H-SiC substrate to form an amorphous layer in which silicon and carbon are amorphous within the 4H-SiC substrate; a bonding step of forming a thin film on at least one of the surface of the 4H-SiC substrate subjected to the ion implantation step and the bonding surface of another support substrate, and bonding through this thin film to obtain a bonded substrate; a peeling step of peeling the 4H-SiC substrate at the amorphous layer of the bonded substrate to separate it into a bonded substrate in which the surface layer of the 4H-SiC substrate is transferred as a 4H-SiC layer onto the support substrate; a peeling step of separating the 4H-SiC substrate into a peeled substrate, which is the substrate after the surface layer has been peeled off from the 4H-SiC substrate; an etching step of plasma etching the peeled surface of at least one of the bonded substrate or the peeled substrate after the peeling step; and an epitaxial step of performing epitaxial growth on at least one of the bonded substrate or the peeled substrate.

[0023] In this semiconductor substrate manufacturing method, at least one of silicon, carbon, and oxygen is ion-implanted onto the surface of a 4H-SiC substrate to break the silicon-carbon bond and form an amorphous layer. After bonding with a support substrate, the 4H-SiC substrate is peeled off starting from the amorphous layer and transferred to the bonding substrate.

[0024] In this ion implantation process, which utilizes at least one of silicon, carbon, or oxygen ions, it is possible to inflict damage to a predetermined depth by adjusting the acceleration energy during implantation. Specifically, this damage involves breaking the bonds between silicon and carbon due to the implantation of these ions. The broken silicon and carbon then exist in an amorphous state.

[0025] The amorphous layer formed in this way can be peeled off by applying impact from the side, such as by inserting a thin, metal-like object. Furthermore, because the amorphous layer becomes black due to the carbon content and thus absorbs light more easily, it can also be further excited and peeled off by irradiating it with light. Alternatively, peeling can be achieved by a combination of light irradiation and impact.

[0026] In particular, when silicon or carbon is ion-implanted, such a delamination layer will not delaminate even if subjected to moderately high temperatures, allowing the delamination process to be carried out at any point in the manufacturing process. Furthermore, when oxygen is ion-implanted, delamination can be achieved by applying heat treatment to bond the implanted oxygen with the carbon in the amorphous layer and gasify it.

[0027] Thus, in this invention, bonding is performed after ion implantation of at least one of silicon, carbon, and oxygen. At this time, it is possible to significantly reduce costs by using polycrystalline materials or sintered bodies as support substrates, as well as single crystals.

[0028] Furthermore, it has been reported that using polycrystalline materials is more effective in reducing substrate resistance (Non-Patent Literature 2), and when considered as a vertical device, it is very effective in improving quality, in addition to cost.

[0029] Then, by sputtering a thin film of silicon or the like onto the bonding surface between the ion-implanted silicon substrate and the support substrate, and bonding them through this thin film, it becomes possible to bond SiC substrates that are otherwise difficult to bond.

[0030] In particular, by using an inexpensive support substrate such as a polycrystalline material, forming a thin film of silicon or the like on the bonding surface, and performing bonding via the silicon or the like film, it becomes possible to bond SiC, which was previously difficult to bond when the support substrate is SiC.

[0031] Furthermore, in this invention, the damaged layer is removed and the substrate is planarized by plasma etching of the delamination surface of at least one of the delamination substrate or bonding substrate, and then reuse or epitaxial growth is performed. In this way, SiC, which is a difficult material to process, can be planarized at a lower cost compared to polishing such as CMP, and a high-quality substrate can be obtained.

[0032] Although SiC is normally difficult to etch with plasma, it can be etched due to the weakening of the surface by ion implantation. By performing epitaxial growth using the CVD method in this way, if a high-quality SiC substrate can be prepared, it becomes possible to repeatedly transfer the surface layer of the 4H-SiC substrate to a support substrate by repeating the ion implantation, bonding, delamination, etching, and epitaxial processes, and then produce high-quality SiC substrates repeatedly and inexpensively by epitaxial growth using the CVD method.

[0033] In this process, the 4H-SiC substrate can be peeled off by irradiating the amorphous layer with light, applying impact, or performing a combination of these treatments during the peeling process.

[0034] In this way, by irradiating the amorphous layer with light and causing it to absorb the light, the energy required for delamination can be directly supplied to the amorphous layer.

[0035] Furthermore, when delaminating a bonded substrate by impacting the amorphous layer, it is advantageous because the delamination can be achieved simply by inserting something like a thin metal blade into the amorphous layer, thus simplifying the delamination equipment.

[0036] Furthermore, by combining light irradiation and impact for delamination, the time required for delamination can be reduced compared to performing each method individually.

[0037] In this process, the 4H-SiC substrate can be peeled off by performing oxygen ion implantation in the ion implantation step, and by irradiating the amorphous layer with light, applying impact, or performing heat treatment in the peeling step to react the implanted oxygen with the carbon in the amorphous layer to generate a gas, or by performing a combination of these processes.

[0038] By irradiating the amorphous layer with light in this way, the energy required for delamination can be directly applied to the amorphous layer. Furthermore, when delaminating the bonded substrate by impacting the amorphous layer, delamination can be achieved simply by inserting something like a thin metal blade into the amorphous layer.

[0039] Furthermore, when oxygen ions are implanted during the ion implantation process, the implanted oxygen reacts with the carbon in the amorphous layer to generate a gas, which can then be used to perform delamination using the gas pressure. Therefore, delamination can be performed not only by light irradiation and impact, but also by heating, expanding the range of delamination methods available. Furthermore, by combining these methods for peeling, the time required for peeling can be reduced compared to performing each method individually.

[0040] In this case, during the bonding process, a silicon thin film can be formed as the thin film and the bonding can be performed via it.

[0041] Since silicon thin films are sometimes used as a substrate when epitaxially growing 4H-SiC, bonding with 4H-SiC is easy, and bonding with polycrystalline and sintered SiC is also easy. Therefore, by preparing a support substrate that is cheaper than single-crystal SiC, such as polycrystalline SiC, and forming a thin layer of silicon on the bonding surface, bonding via silicon becomes easier.

[0042] In this bonding process, the silicon thin film can be deposited by a sputtering method targeting silicon.

[0043] Thus, depositing a silicon thin film by sputtering, which involves irradiating silicon with an ionized inert gas such as Ar, offers advantages in terms of adhesion and other properties. It has been found that the roughness of the bonding surface in this case is preferably 1 nm or less (Non-Patent Literature 3). Furthermore, using the sputtering method eliminates the need for high-temperature processing of the substrate to be coated, and also avoids roughening the SiC surface of the bonding surface.

[0044] In this case, a mixed gas of carbon fluoride and oxygen can be used as the raw material gas in the etching process.

[0045] Since a mixture of carbon fluoride and oxygen is a gas used for etching silicon and other materials, using it as a raw material gas has the advantage of eliminating the need to prepare a gas specifically for SiC etching.

[0046] In this case, after the peeling step and before the etching step, an annealing step can be performed in which the peeled surface of the bonding substrate or the peeled substrate, which is scheduled to undergo the etching step, is annealed at a temperature of 1000°C or higher in a hydrogen atmosphere.

[0047] By performing hydrogen annealing before etching, the uneven surface of the delamination, which was roughened by the delamination process, is modified by hydrogen annealing before etching, resulting in a degree of flattening. Therefore, it becomes easier to further improve the flatness of the delamination surface during the etching process.

[0048] In this case, the delamination surface of the bonding substrate can be plasma-etched in the etching process, and furthermore, the epitaxial process can be performed on the etched delamination surface of the bonding substrate after the etching process.

[0049] By growing an epitaxial layer on the etched delamination surface of the bonding substrate in this way, the device can be made of higher quality by forming the device on the epitaxial layer.

[0050] The present invention also provides a semiconductor substrate comprising a support substrate and a 4H-SiC layer bonded to the surface of the support substrate, wherein the support substrate is made of SiC, the 4H-SiC layer is bonded to the support substrate via a silicon thin film, and its surface is etched.

[0051] With such a semiconductor substrate, the surface of the 4H-SiC layer is etched, resulting in a flat surface. This allows for the formation of an epitaxial layer without the need for costly planarization processes such as CMP, resulting in a lower cost and higher quality product.

[0052] Furthermore, if the 4H-SiC layer is bonded to the SiC support substrate via a silicon thin film, the silicon thin film can also be used as a base layer when epitaxially growing the 4H-SiC. This strengthens the bond between the 4H-SiC and the support substrate, and the bond can be strengthened even if the support substrate is a polycrystalline or sintered SiC material. Therefore, the bond between the support substrate and the 4H-SiC layer becomes strong.

[0053] Furthermore, the present invention provides a semiconductor device characterized by comprising the semiconductor substrate described above. Such semiconductor devices, equipped with the cheaper, higher-quality semiconductor substrates described above, are therefore cheaper, higher quality, and more reliable. [Effects of the Invention]

[0054] As described above, the semiconductor substrate manufacturing method of the present invention allows for the production of lower-cost, high-quality semiconductor substrates using 4H-SiC peeling technology, thereby reducing the manufacturing cost of the substrate. Furthermore, the semiconductor substrate manufacturing method of the present invention makes it possible to effectively utilize the 4H-SiC substrate after the surface layer has been peeled off, further reducing the manufacturing cost of the semiconductor substrate. Furthermore, the semiconductor substrate of the present invention will be less expensive and of higher quality. Similarly, the semiconductor device of the present invention will also be less expensive and of higher quality. [Brief explanation of the drawing]

[0055] [Figure 1] A schematic diagram of the semiconductor substrate of the present invention is shown. [Figure 2] This shows a flowchart of the method for manufacturing a semiconductor substrate according to the present invention. [Modes for carrying out the invention]

[0056] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0057] As described above, there was a need for a semiconductor substrate manufacturing method that could produce cheaper and higher-quality semiconductor substrates using 4H-SiC peeling technology, thereby reducing the manufacturing cost of the substrates, as well as for cheaper and higher-quality semiconductor substrates and cheaper and higher-quality semiconductor devices.

[0058] As a result of diligent study on the above problems, the present inventors have developed an ion implantation step in which at least one of silicon, carbon, and oxygen is implanted into the surface of a 4H-SiC substrate to form an amorphous layer in which silicon and carbon are amorphous within the 4H-SiC substrate; a bonding step in which a thin film is formed on at least one of the surface of the 4H-SiC substrate on which the ion implantation step was performed and the bonding surface of another support substrate, and bonding is performed via this thin film to obtain a bonded substrate; and by peeling the 4H-SiC substrate off the amorphous layer of the bonded substrate, the 4H-SiC substrate The present invention was completed by discovering that a semiconductor substrate can be manufactured at a lower cost and of higher quality using 4H-SiC peeling technology, through a method for manufacturing a semiconductor substrate characterized by including a bonding substrate in which the surface layer of a 4H-SiC layer is transferred onto the support substrate, a peeling step for separating the 4H-SiC substrate into a release substrate which is the substrate after the surface layer has been peeled off from the 4H-SiC substrate, an etching step for plasma etching the peeled surface of at least one of the bonding substrate or the release substrate after the peeling step, and an epitaxial step for performing epitaxial growth on at least one of the bonding substrate or the release substrate.

[0059] Furthermore, as a result of diligent research into the above-mentioned problems, the inventors have found that a semiconductor substrate comprising a support substrate and a 4H-SiC layer bonded to the surface of the support substrate, wherein the support substrate is made of SiC, the 4H-SiC layer is bonded to the support substrate via a silicon thin film, and its surface is etched, can provide a more inexpensive and high-quality semiconductor substrate, thus completing the present invention.

[0060] Furthermore, after diligently studying the above-mentioned problems, the inventors discovered that a semiconductor device characterized by comprising the semiconductor substrate described above can provide a more inexpensive and high-quality semiconductor device, thus completing the present invention.

[0061] Hereinafter, embodiments preferred for the present invention will be described with reference to the drawings. First, the configuration of the semiconductor substrate 5 will be explained with reference to Figure 1. As shown in Figure 1, the semiconductor substrate 5 according to the embodiment of the present invention comprises a support substrate 3 and a 4H-SiC layer 1a bonded to the surface of the support substrate 3, wherein the 4H-SiC layer 1a is bonded to the support substrate 3 via a thin film 7.

[0062] The support substrate 3 is a substrate that supports the 4H-SiC layer 1a via a thin film 7. The material and dimensions can be appropriately selected as long as it has sufficient strength to support the 4H-SiC layer 1a and does not undergo unintended reactions with the thin film 7. Specifically, bulk 4H-SiC made of the same material as the 4H-SiC layer 1a can be used as an example, but considering the cost, a sintered SiC substrate or a polycrystalline SiC substrate, which are less expensive than bulk 4H-SiC, may also be used.

[0063] The 4H-SiC layer 1a is a single-crystal layer of 4H-SiC and is bonded to the surface of the support substrate 3. For this bonding, a thin film 7 is formed on the bonding surface between the 4H-SiC layer 1a and the support substrate 3, and a strong bond is possible through this thin film 7.

[0064] The thin film 7 is a material that can bond to the 4H-SiC layer 1a and the support substrate 3, and is, for example, a silicon thin film. In the following description, unless otherwise specified, the present invention will be described using the case in which a silicon thin film is used as the thin film 7.

[0065] Furthermore, the 4H-SiC layer 1a has an etched surface 25. Because the 4H-SiC layer 1a has an etched surface 25, the surface 25 becomes flat, allowing the epitaxial layer to be formed without the need for costly planarization treatments such as CMP, resulting in a cheaper and higher-quality semiconductor substrate 5.

[0066] The 4H-SiC layer 1a can be a single crystal layer, such as bulk 4H-SiC, or an epitaxial layer of 4H-SiC.

[0067] The thickness of the 4H-SiC layer 1a should be at least sufficient to maintain its layer shape, allow for device formation, and not be lost during etching or polishing. On the other hand, the maximum thickness should be such that there is as little wasted material as possible that is not used during device formation. The thickness can be, for example, between 0.01 μm and 400 μm.

[0068] Next, the configuration of the semiconductor device 6 will be explained with reference to Figure 1. The semiconductor device 6 shown in Figure 1 includes a semiconductor substrate 5. A specific example of a semiconductor device 6 is one in which a desired semiconductor device is formed on a semiconductor substrate 5, particularly on a 4H-SiC layer 1a. Of course, the semiconductor device 6 can also be made into a chip by dicing.

[0069] By incorporating a less expensive, higher-quality semiconductor substrate 5 into the semiconductor device 6, the semiconductor device 6 itself becomes less expensive, higher quality, and more reliable.

[0070] Next, an overview of the manufacturing method for the semiconductor substrate 5 of the present invention will be described with reference to Figure 2. First, prepare the 4H-SiC substrate 1 as shown in Figure 2(a). Here, a single-crystal bulk 4H-SiC is used as an example for the 4H-SiC substrate 1, but a 4H-SiC epitaxial substrate may also be used.

[0071] In this embodiment, the surface layer of the 4H-SiC substrate 1 is transferred to the support substrate 3, but the peeled substrate 11 that is created last after the transfer may be reused as the 4H-SiC substrate 1. It is preferable that these 4H-SiC substrates 1 are those that have been epitaxially grown by CVD.

[0072] Next, at least one of silicon, carbon, or oxygen is ion-implanted into the 4H-SiC substrate 1 to break the silicon-carbon bond near the surface of the 4H-SiC substrate 1, forming an amorphous layer 2 in which silicon and carbon exist in an amorphous state, as shown in Figure 2(b) (ion implantation process).

[0073] By adjusting the acceleration energy of the ion implantation, an amorphous layer 2 can be formed at a predetermined depth in which silicon and carbon are respectively amorphous. When oxygen is ion-implanted, both the amorphous layer 2 and a layer containing oxygen are formed.

[0074] Only one of silicon, carbon, or oxygen ions needs to be implanted; therefore, multiple types of ions may be implanted. Furthermore, the choice of which of silicon, carbon, or oxygen to implant should be made appropriately, taking into account the advantages of each.

[0075] For example, when ion-implanting silicon or carbon, these elements are advantageous because they are constituent elements of SiC, and therefore do not become impurities when implanted. On the other hand, when ion-implanting oxygen, 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 method options.

[0076] Furthermore, the acceleration energy during ion implantation varies depending on the depth at which the amorphous layer 2 is formed. Specifically, the deeper the position in the depth direction, the greater the acceleration energy, although it is, for example, around 200 keV.

[0077] The amount of ions implanted should be sufficient to form amorphous layer 2, for example, 1.0 × 10 17 atoms / cm 2 It is to that extent.

[0078] Next, as shown in Figure 2(c), a substrate separate from the 4H-SiC substrate 1 is prepared as the support substrate 3. The support substrate 3 may be a single-crystal 4H-SiC with the same structure as the 4H-SiC substrate 1, but considering the cost, it is preferable to use sintered SiC or polycrystalline SiC, for example, which are produced by sintering.

[0079] Next, as shown in Figure 2(d), a thin film 7 such as a silicon thin film is deposited on the bonding surface 8 of the 4H-SiC substrate 1 and the surface 14 of the support substrate 3 after the silicon ion implantation process. These are then bonded together to obtain the bonded substrate 10 shown in Figure 2(e) (bonding process).

[0080] It is preferable to deposit a silicon thin film as the thin film 7 and perform bonding through it. Since silicon thin films are sometimes used as a substrate when epitaxially growing 4H-SiC, bonding with 4H-SiC is easy, and bonding with polycrystalline and sintered SiC is also easy. Therefore, by preparing a support substrate 3 that is cheaper than single-crystal SiC, such as polycrystalline SiC, forming a thin layer of silicon on the bonding surface 8, and bonding via silicon, it becomes possible to bond even SiC, which is difficult to bond.

[0081] As for specific film deposition methods for the thin film 7, the sputtering method, which uses silicon as a target and irradiates this target with Ar ions to deposit the film, is effective because it does not require high-temperature heating of the substrate and does not roughen the SiC surface of the bonding surface.

[0082] Furthermore, a possible method for joining the 4H-SiC substrate 1 and the support substrate 3 via the thin film 7 is, for example, room-temperature bonding.

[0083] Next, as shown in Figure 2(f), the 4H-SiC substrate 1 is peeled off using the amorphous layer 2 of the bonding substrate 10, separating it into a bonding substrate 12, on which the surface layer of the 4H-SiC substrate 1 has been transferred as a 4H-SiC layer 1a onto the support substrate 3, and a release substrate 11, which is the substrate after the surface layer has been peeled off from the 4H-SiC substrate 1 (peeling step).

[0084] Specifically, in the peeling process, the 4H-SiC substrate 1 can be peeled off by irradiating the amorphous layer 2 with light, applying impact, or performing a combination of these treatments.

[0085] When light irradiation is performed, the bonding substrate 10 is irradiated with light, and the amorphous silicon and carbon layer 2 formed in the ion implantation process absorbs the light. Using this as a starting point, the 4H-SiC substrate 1 is peeled off, separating the bonding substrate 10 into a bonding substrate 12 in which the surface layer of the 4H-SiC substrate 1 is transferred onto the support substrate 3 as a 4H-SiC layer 1a, and a peeled substrate 11 which is the substrate after the surface layer has been peeled off from the 4H-SiC substrate 1.

[0086] In this way, by irradiating the amorphous layer 2 with light and causing it to absorb the light, the energy required for peeling can be directly supplied to the amorphous layer 2.

[0087] The light source for irradiation is not particularly limited as long as it can supply enough energy to the amorphous layer 2 to peel off the 4H-SiC substrate 1 starting from the amorphous layer 2, but a YAG laser can be used as an example. When using a YAG laser as the light source, the wavelength of the irradiated light can be exemplified as the fundamental wavelength (1064 nm).

[0088] In the peeling process, if an impact is applied to the amorphous layer 2, it is possible to peel it off without irradiating it with light simply by inserting something like a thin metal blade into the amorphous layer 2. This method of delaminating the amorphous layer 2 by applying impact has the advantage of allowing for a simpler setup of equipment for delamination.

[0089] Furthermore, delamination can also be achieved by combining light irradiation and impact. Specifically, in addition to light irradiation, an impact can be applied by inserting something like a thin metal blade into the amorphous carbon layer 2 to delaminate it. In this case, the time required for delamination can be shortened compared to when light irradiation or impact is applied individually.

[0090] If oxygen ions are implanted in the ion implantation process, the 4H-SiC substrate 1 can be peeled off in the peeling process by irradiating the amorphous layer 2 with light, applying impact, or performing heat treatment to react the implanted oxygen with the carbon in the amorphous layer to generate a gas, or by performing a combination of these processes.

[0091] As the surface of the bonded substrate 12 obtained by delamination is rough, it is preferable to flatten the surface if an epitaxial layer is to be formed in a later process. Furthermore, the delamination substrate 11 can be reused by repeating the ion implantation process, bonding process, and delamination process to transfer the surface layer to multiple support substrates 3, but since the surface of the delamination surface 21 is rough, it is necessary to flatten the surface in order to bond it with the support substrate 3.Therefore, the procedure for flattening the delamination surfaces 23 and 21 is described below.

[0092] First, as shown in Figure 2(h), at least one of the peeled surface 23 of the bonding substrate 12 after the peeling process or the peeled surface 21 of the peeling substrate 11 is plasma etched (etching process).

[0093] Although Figure 2 illustrates the case where both the delamination surface 23 of the bonding substrate 12 and the delamination surface 21 of the release substrate 11 are etched, at least one of them may be etched. For example, if an epitaxial layer can be formed without planarizing the delamination surface 23 of the bonding substrate 12, or if the 4H-SiC layer 1a is an epitaxial layer and there is no need to form another epitaxial layer, then only the delamination surface 21 of the release substrate 11 may be etched.

[0094] By plasma etching at least one of the delamination surface 23 of the bonding substrate 12 or the delamination surface 21 of the delamination substrate 11, the surface of SiC, a difficult-to-process material, can be planarized at a lower cost compared to CMP and other methods.

[0095] A mixture of carbon fluoride and oxygen can be used as the raw material gas for etching. CHF3 and CF4 are preferred as specific carbon fluoride gases. Since this mixture of carbon fluoride and oxygen is used for etching silicon and other materials, using it as a raw material gas is advantageous because it eliminates the need to prepare a gas specifically for SiC etching.

[0096] Furthermore, the plasma morphology during the etching process is not particularly limited, as long as it is optimized for the equipment, but RF plasma can be used as an example. Generally, SiC is not etched with such a mixed gas of carbon fluoride and oxygen, but the delamination surfaces 23 and 21 are weakened by the ion implantation process, and since the surface layer is a damaged layer, planarization can be achieved by removing this layer, including the delamination surfaces 23 and 21, by etching. In addition, weakening can be achieved not only by damaging with ion implantation, but also by plasma treatment using H2 gas.

[0097] Furthermore, after the peeling process and before the etching process, the peeled surface 23 of the bonding substrate 12 or the peeled surface 21 of the peeling substrate 11, which is scheduled to undergo the etching process, may be annealed at a temperature of 1000°C or higher in a hydrogen atmosphere, as shown in Figure 2(g) (annealing process).

[0098] By performing hydrogen annealing in the annealing process before the etching process, the uneven shape of the peeled surface 23 or peeled surface 21, which was roughened by peeling, is modified by hydrogen annealing before etching, and flattened to some extent. Therefore, it becomes easier to further improve the flatness of the peeled surface 23 or peeled surface 21 in the etching process.

[0099] The peeled substrate 11 after the peeling process can be reused as a 4H-SiC substrate 1 by repeating the ion implantation process, bonding process, and peeling process again, until it reaches a thickness that can no longer be peeled off, for transferring 4H-SiC to the support substrate 3.

[0100] In this case, if the release surface 21 of the release substrate 11 is etched in the etching process, the release surface 21 is planarized by etching, so the support substrate 3 can be bonded to the release surface 21 without performing costly planarization treatments such as CMP.

[0101] Next, epitaxial growth is performed on at least one of the bonding substrate 12 or the release substrate 11 (epitaxial process). Specifically, the epitaxial layer 4 can be grown using CVD or the like.

[0102] Figure 2(i) illustrates a case in which a 4H-SiC epitaxial layer 4 is grown on a 4H-SiC layer 1a of the bonding substrate 12. In this case, if the peeled surface 23 of the 4H-SiC layer 1a is etched in the etching process, the peeled surface 23 is planarized by etching, so the epitaxial layer 4 can be formed on the peeled surface 23 without performing costly planarization treatments such as CMP, and the bonded substrate 12 can be made into a cheaper and higher quality semiconductor substrate 5.

[0103] Furthermore, if the 4H-SiC layer 1a is an epitaxial layer, and the thickness of the transferred 4H-SiC layer 1a is sufficient to form the device in a subsequent process, then it is not necessarily required to perform the epitaxial process shown in Figure 2(i).

[0104] On the other hand, if the 4H-SiC layer 1a is not an epitaxial layer, or if the 4H-SiC layer 1a is an epitaxial layer but the film thickness at the time of transfer in the peeling process is not thick enough to form a device, it is preferable to perform an epitaxial process on the bonding substrate 12. In this case, it is preferable to smooth the peeled surface 23 in the etching process before performing the epitaxial process on the bonding substrate 12.

[0105] Specifically, as shown in Figure 2(h), it is preferable to plasma etch the delamination surface 23 of the bonding substrate 12 in the etching process, and further, as shown in Figure 2(i), to grow an epitaxial layer 4 on the etched delamination surface 23 of the bonding substrate 12 in the epitaxial process.

[0106] By growing the epitaxial layer 4 on the etched delamination surface 23 of the bonding substrate 12 in this manner, the device can be made of higher quality by forming the device on the epitaxial layer 4. [Examples]

[0107] The present invention will be described in detail below with reference to examples, but this does not limit the present invention. No. We attempted to reuse the exfoliated substrate 11 as a 4H-SiC substrate 1 by performing ion implantation of silicon, carbon, and oxygen, bonding (silicon thin film formation and bonding), exfoliation, and etching processes on the 4H-SiC substrate 1, followed by repeating the ion implantation and bonding processes.

[0108] (Example 1) First, a 4H-SiC single crystal substrate 1 was prepared, with a diameter of 200 mm, a thickness of 355 μm, n-type, resistivity of 10 Ω·cm, and a 4° offset relative to the (0001) plane. Then, as an ion implantation process, silicon ions were implanted into it using an ion implanter at an acceleration energy of 200 keV, resulting in 1 × 10⁻¹⁶ silicon ions. 17 atoms / cm 2 It was injected.

[0109] Next, the following bonding process was performed. First, a polycrystalline SiC substrate with the same diameter as the 4H-SiC substrate 1 was prepared as the support substrate 3. Using silicon as the target, Ar ions were irradiated to deposit a silicon thin film as thin film 7 onto both the 4H-SiC substrate 1 and the support substrate 3 by sputtering. The thickness of the silicon thin film at this time was 20 nm. After this, room-temperature bonding was performed between the 4H-SiC substrate 1 and the support substrate 3 via the silicon thin film to obtain the bonded substrate 10.

[0110] Following the bonding process, a YAG laser (wavelength 1064 nm) was used in a delamination process to irradiate and excite the amorphous layer 2, separating the bonded substrate 10 into a bonding substrate 12 and a delamination substrate 11.

[0111] On this bonded substrate 12, 4H-SiC was epitaxially grown using a hot-wall type CVD apparatus with H2 as the carrier gas and SiH4 and C3H8 as the source gases to obtain a semiconductor substrate 5. The temperature at this time was 1600°C and the furnace pressure was 7kPa.

[0112] In this way, when the semiconductor substrate 5 was obtained, the peeled surface 21 of the peeled substrate 11 was subjected to an RF plasma etching process under the following conditions: the raw material gases were CHF3 and O2 at 100 sccm and 10 sccm respectively, the pressure was 100 Torr (13332.2 Pa), and the RF power was 500 W.

[0113] When the delamination substrate 11 after the etching process was subjected to the silicon ion implantation and bonding processes again using the same flow, the support substrate 3 could be bonded to the delamination surface 21 of the delamination substrate 11, and a bonded substrate 10 could be obtained in the same way.

[0114] (Example 2) First, a 4H-SiC single crystal substrate 1 was prepared, with a diameter of 200 mm, a thickness of 355 μm, n-type, resistivity of 10 Ω·cm, and a 4° offset relative to the (0001) plane. Then, as an ion implantation process, carbon ions were implanted into it using an ion implanter at an acceleration energy of 200 keV, resulting in 1.0 × 10⁻¹⁶ carbon ions. 17 atoms / cm 2 It was injected.

[0115] Next, the following bonding process was carried out. First, a polycrystalline SiC substrate with the same diameter as the 4H-SiC substrate 1 was prepared as the support substrate 3. Using silicon as the target, Ar ions were irradiated to deposit a silicon thin film 7 onto both the 4H-SiC substrate 1 and the support substrate 3 by sputtering. The silicon thin film at this time was 20 nm thick. After this, the 4H-SiC substrate 1 and the support substrate 3 were bonded at room temperature via the silicon thin film to obtain the bonded substrate 10.

[0116] Following the bonding process, a YAG laser (wavelength 1064 nm) was used in a delamination process to irradiate and excite the amorphous layer 2, separating the bonded substrate 10 into a bonding substrate 12 and a delamination substrate 11.

[0117] On this bonded substrate 12, 4H-SiC was epitaxially grown using a hot-wall type CVD apparatus with H2 as the carrier gas and SiH4 and C3H8 as the source gases to obtain a semiconductor substrate 5. The temperature at this time was 1600°C and the furnace pressure was 7kPa.

[0118] In this way, when the semiconductor substrate 5 was obtained, the peeled surface 21 of the peeled substrate 11 was subjected to an RF plasma etching process under the following conditions: the raw material gases were CHF3 and O2 at 100 sccm and 10 sccm respectively, the pressure was 100 Torr (13332.2 Pa), and the RF power was 500 W.

[0119] When the delamination substrate 11 after the etching process was subjected to a carbon ion implantation process and a bonding process again using the same reuse flow described above, the support substrate 3 could be bonded to the delamination surface 21 of the delamination substrate 11, and a bonded substrate 10 could be obtained in the same way.

[0120] (Example 3) First, a 4H-SiC single crystal substrate 1 was prepared, with a diameter of 200 mm, a thickness of 355 μm, n-type, resistivity of 10 Ω·cm, and a 4° offset relative to the (0001) plane. Then, as an ion implantation process, oxygen ions were implanted into it using an ion implanter at an acceleration energy of 200 keV, resulting in 1.0 × 10¹⁶ oxygen ions. 17 atoms / cm 2 It was injected.

[0121] Next, the following bonding process was performed. First, a polycrystalline SiC substrate with the same diameter as the 4H-SiC substrate 1 was prepared as the support substrate 3. Using silicon as the target, Ar ions were irradiated to deposit a silicon thin film 7 onto both the 4H-SiC substrate 1 and the support substrate 3 by sputtering. The thickness of the silicon thin film at this time was 20 nm. After this, the 4H-SiC substrate 1 and the support substrate 3 were bonded at room temperature to obtain the bonded substrate 10.

[0122] Following the bonding process, a YAG laser (wavelength 1064 nm) was used in a delamination process to irradiate and excite the amorphous layer 2, separating the bonded substrate 10 into a bonding substrate 12 and a delamination substrate 11.

[0123] On this bonded substrate 12, 4H-SiC was epitaxially grown using a hot-wall type CVD apparatus with H2 as the carrier gas and SiH4 and C3H8 as the source gases to obtain a semiconductor substrate 5. The temperature at this time was 1600°C and the furnace pressure was 7kPa.

[0124] In this way, when the semiconductor substrate 5 was obtained, the peeled surface 21 of the peeled substrate 11 was subjected to an RF plasma etching process under the following conditions: the raw material gases were CHF3 and O2 at 100 sccm and 10 sccm respectively, the pressure was 100 Torr (13332.2 Pa), and the RF power was 500 W.

[0125] When the delamination substrate 11 after the etching process was subjected to the oxygen ion implantation and bonding processes again using the flow described above, the support substrate 3 could be bonded to the delamination surface 21 of the delamination substrate 11, and a bonded substrate 10 could be obtained in the same way.

[0126] As described above, according to the embodiment of the present invention, an amorphous layer 2 was formed on the 4H-SiC substrate 1 by ion implantation, then a support substrate 3 was bonded via a thin film 7, and the 4H-SiC substrate 1 was peeled off at the amorphous layer 2, thereby obtaining a bonded substrate 12 in which the surface layer of the 4H-SiC substrate 1 was transferred onto the support substrate 3 as a 4H-SiC layer 1a. Furthermore, the peeled substrate 11 could be reused as the 4H-SiC substrate 1.

[0127] This specification includes the following embodiments: [1]: An ion implantation step in which at least one of silicon, carbon, and oxygen is implanted into the surface of a 4H-SiC substrate to form an amorphous layer in which silicon and carbon are amorphous, A bonding step is to form a thin film on at least one of the surfaces of the 4H-SiC substrate that has undergone the ion implantation step and the bonding surface of another support substrate, and then perform bonding through this thin film to obtain a bonded substrate. A peeling step is performed to separate the bonded substrate from the 4H-SiC substrate by peeling the 4H-SiC substrate with the amorphous layer of the bonded substrate, thereby transferring the surface layer of the 4H-SiC substrate as a 4H-SiC layer onto the support substrate, into a bonded substrate and a peeled substrate which is the substrate after the surface layer has been peeled off from the 4H-SiC substrate. An etching step of plasma etching at least one of the peeled surfaces of the bonding substrate or the peeled substrate after the peeling step, A method for manufacturing a semiconductor substrate, characterized by including an epitaxial step of performing epitaxial growth on at least one of the bonding substrate or the delamination substrate. [2]: The method for manufacturing a semiconductor substrate according to [1], characterized in that, in the peeling step, the 4H-SiC substrate is peeled off by irradiating the amorphous layer with light, applying impact, or a combination thereof. [3]: In the ion implantation step, oxygen is implanted as an ion, A method for manufacturing a semiconductor substrate according to [1] or [2] above, characterized in that in the peeling step, the 4H-SiC substrate is peeled off by irradiating the amorphous layer with light, applying impact, performing heat treatment, reacting injected oxygen with the carbon in the amorphous layer to generate a gas, or performing a treatment in combination thereof. [4]: A method for manufacturing a semiconductor substrate according to any one of [1] to [3] above, characterized in that in the bonding step, a silicon thin film is formed as the thin film and bonding is performed via it. [5]: The method for manufacturing a semiconductor substrate according to [4] above, characterized in that the silicon thin film is formed in the bonding step by a silicon-targeted sputtering method. [6]: A method for manufacturing a semiconductor substrate according to any one of [1] to [5] above, characterized in that a mixed gas of carbon fluoride and oxygen is used as a raw material gas in the etching step. [7]: A method for manufacturing a semiconductor substrate according to any one of [1] to [6] above, characterized in that, after the peeling step and before the etching step, an annealing step is performed in which the peeled surface of the bonding substrate or the peeled substrate that is to be etched is annealed at a temperature of 1000°C or higher in a hydrogen atmosphere. [8]: A method for manufacturing a semiconductor substrate according to any one of [1] to [7] above, characterized in that, in the etching step, the delamination surface of the bonding substrate is plasma etched, and further, after the etching step, the epitaxial step is performed on the etched delamination surface of the bonding substrate. [9]: comprising a support substrate and a 4H-SiC layer bonded to the surface of the support substrate, The aforementioned support substrate is made of SiC. The semiconductor substrate is characterized in that the 4H-SiC layer is bonded to the support substrate via a silicon thin film and its surface is etched.

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

[0128] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0129] 1...4H-SiC substrate, 1a...4H-SiC layer, 2...Amorphous layer, 3...Support substrate, 4...Epitaxial layer, 5...Semiconductor substrate, 6...Semiconductor device, 7...Thin film, 8...Bonding surface, 10...Bonding substrate, 11...Release substrate, 12...Bonding substrate, 14...Surface, 21...Release surface, 23...Release surface, 25...Surface.

Claims

1. An ion implantation step is performed on the surface of a 4H-SiC substrate to implant at least one of silicon, carbon, and oxygen, thereby forming an amorphous layer in which silicon and carbon are amorphous within the 4H-SiC substrate. A bonding step is to form a thin film on at least one of the surfaces of the 4H-SiC substrate that has undergone the ion implantation step and the bonding surface of another support substrate, and then perform bonding through this thin film to obtain a bonded substrate. A peeling step is performed to separate the bonded substrate from the 4H-SiC substrate by peeling the 4H-SiC substrate off the amorphous layer of the bonded substrate, thereby transferring the surface layer of the 4H-SiC substrate as a 4H-SiC layer onto the support substrate, into a bonded substrate and a peeled substrate which is the substrate after the surface layer has been peeled off from the 4H-SiC substrate. An etching step of plasma etching at least one of the peeled surfaces of the bonding substrate or the peeled substrate after the peeling step, A method for manufacturing a semiconductor substrate, characterized by including an epitaxial step of performing epitaxial growth on at least one of the bonding substrate or the delamination substrate.

2. The method for manufacturing a semiconductor substrate according to claim 1, characterized in that, in the peeling step, the 4H-SiC substrate is peeled off by irradiating the amorphous layer with light, applying impact, or performing a treatment in combination thereof.

3. In the aforementioned ion implantation process, oxygen ions are implanted. A method for manufacturing a semiconductor substrate according to claim 1, characterized in that, in the peeling step, the 4H-SiC substrate is peeled off by irradiating the amorphous layer with light, applying impact, performing heat treatment, reacting injected oxygen with the carbon in the amorphous layer to generate a gas, or performing a treatment in combination thereof.

4. The method for manufacturing a semiconductor substrate according to claim 1, characterized in that, in the bonding step, a silicon thin film is formed as the thin film and bonding is performed via the silicon thin film.

5. The method for manufacturing a semiconductor substrate according to claim 4, characterized in that, in the bonding step, the silicon thin film is formed by a silicon-targeted sputtering method.

6. The method for manufacturing a semiconductor substrate according to claim 1, characterized in that a mixed gas of carbon fluoride and oxygen is used as a raw material gas in the etching step.

7. The method for manufacturing a semiconductor substrate according to claim 1, characterized in that, after the peeling step and before the etching step, an annealing step is performed in which the peeled surface of the bonding substrate or the peeled substrate that is to be etched is annealed at a temperature of 1000°C or higher in a hydrogen atmosphere.

8. A method for manufacturing a semiconductor substrate according to any one of claims 1 to 7, characterized in that, in the etching step, the delamination surface of the bonding substrate is plasma etched, and further, after the etching step, the epitaxial step is performed on the etched delamination surface of the bonding substrate.

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