Semiconductor substrate manufacturing method

Abstract

To provide a manufacturing method for a semiconductor substrate, by which a high-quality semiconductor substrate can be manufactured at lower cost by using a separation technique of 4H-SiC.SOLUTION: A manufacturing method for a semiconductor substrate 5 includes: a laser irradiating step of irradiating a 4H-SiC substrate 1 with laser, thereby forming an amorphous layer 2 in the 4H-SiC substrate 1; a bonding step of forming a thin film 7 on at least one of the 4H-SiC substrate 1 and another supporting substrate 3 and bonding the 4H-SiC substrate 1 and the supporting substrate together through the thin film 7, thereby obtaining a bonding substrate 10; a separating step of separating the 4H-SiC substrate 1 at the amorphous layer 2 into a coupling substrate 12 to which a surface layer of the 4H-SiC substrate 1 has been transferred onto the supporting substrate 3 and a separation substrate 11 from which the surface layer has been separated from the 4H-SiC substrate 1; an etching step of performing plasma etching on at least one separation surface of the coupling substrate 12 and the separation substrate 11; and an epitaxial step of performing epitaxial growth on at least one of the coupling 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 discloses a method for producing a substrate for semiconductor electronic devices by preparing two SiC single crystal wafers, forming an oxide layer on each, implanting hydrogen ions into one of the substrates, bonding and integrating them at room temperature via the oxide layer, and then heating them to over 500°C to split the SiC single crystal wafer into two at the hydrogen ion implanted locations. 【0006】 In this method, an oxide film is present at the junction, and when used as a vertical device, this oxide film functions as an insulating layer, severely limiting the functionality of the power device substrate. 【0007】 Furthermore, Patent Document 2 contains H +A method of peeling off a single crystal and a polycrystal after bonding an injected single crystal and a polycrystalline SiC substrate is disclosed. There are problems of increased cost due to performing peeling twice and difficulty in performing peeling in each predetermined step. 【0008】 Patent Document 3 focuses on impurity concentration and defect density, and describes a method of transferring a high-resistance substrate with a low defect density using H + implantation. This method is a method of reducing defects existing in the original substrate, but there is no mention of the substrate after peeling. Furthermore, Patent Document 4 is about 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 manufacturing 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 handling of the peeled substrate. 【0010】 Also, 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, performing high-temperature annealing, and reusing the separated substrate, but there is still no description about handling of the substrate after peeling. 【0011】 Also, Patent Document 7 describes a method of applying H + peeling, performing ion implantation on single-crystalline SiC, forming poly-SiC on the opposite surface, annealing, peeling from the ion-implanted surface, polishing the peeled surface, and then epitaxially growing SiC. As described above, in the substrate peeling technology using H + no mention is made of a specific method of reusing the peeled substrate. 【0012】 Furthermore, as a method of forming a support substrate when peeling after ion injection, Patent Document 8 mentions H + ​+ Growth of polycrystalline SiC on a substrate after injection at 1000-1600°C, Patent Document 9 states H + Growth on a substrate after injection by DLI-CVD (Direct Liquid Injection-CVD), Patent Document 10 states H + Methods such as sintering and liquid-phase deposition on the substrate after injection are disclosed. 【0013】 These methods are employed because, as described in Patent Document 8, joining SiC to SiC is difficult, and problems have been pointed out with joining via W or Mo due to the presence of metal. 【0014】 However, H + After injection, deposition is performed on the support substrate under high temperature conditions, 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. [Prior art documents] [Patent Documents] 【0015】 [Patent Document 1] Japanese Patent Application Publication No. 11-003842 [Patent Document 2] Japanese Patent Publication No. 2016-018890 [Patent Document 3] Japanese Patent Publication No. 2014-022711 [Patent Document 4] Japanese Patent Publication No. 2007-329470 [Patent Document 5] Special Publication No. 2013-513963 [Patent Document 6] Japanese Patent Publication No. 2022-140396 [Patent Document 7] International Publication No. 2022 / 158085 [Patent Document 8] Special Publication 2022-542224 [Patent Document 9] Special Table 2023-502571 [Patent Document 10] Special Table 2023-502572 [Non-Patent Document] 【0016】 [Non-Patent Document 1] Iwashiro, "Advances in High Performance and High Reliability of SiC MOSFETs", Proceedings of the Symposium of the Wide Bandgap Semiconductor Society, 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", Journal of Applied Physics, The Japan Society of Applied Physics, 89(9), 2020. p498 [Summary of the Invention] [Problems to be Solved by the Invention] 【0017】 Thus, 4H-SiC is expected as a high-voltage device, but the problem is that the substrate cost is high, and the issue is how to reduce the cost of the bulk substrate. Therefore, H + Although a technique of performing H ion implantation and peeling the substrate has been proposed, in this case, the cost can be reduced by reusing the substrate after peeling (otherwise the cost will remain high). 【0018】 From this, how to reuse the substrate after peeling (to make it a high-quality substrate) is very important, and H +This is a fundamental technology for the widespread adoption of substrate peeling technology using ions and other means. 【0019】 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. 【0020】 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. 【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 laser irradiation, with respect to bonding to a support substrate and reuse of the substrate after delamination, thereby providing a lower-cost, higher-quality SiC substrate. Specifically, the present invention provides a method for manufacturing a semiconductor substrate, comprising: a laser irradiation step of irradiating the surface of a 4H-SiC substrate with a laser to form an amorphous layer of silicon and carbon 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 that has undergone the laser irradiation step and the bonding surface of another support substrate, and bonding the surface of the 4H-SiC substrate and the bonding surface of the support substrate via this thin film to obtain a bonded substrate; a peeling step of peeling the 4H-SiC substrate with the amorphous layer of the bonded substrate to separate it into a bonded substrate in which the surface layer of the 4H-SiC substrate has been 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, an amorphous layer is formed by irradiating the surface of a 4H-SiC substrate with a laser, and after bonding it 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 laser irradiation process, it is possible to inflict damage to a predetermined depth by adjusting the focal position of the laser from the surface of the substrate. Specifically, this damage involves severing the bonds between silicon and carbon using the laser. The severed silicon and carbon then exist in an amorphous state. This amorphous layer can be peeled off by inserting a thin, metal-like material from the side. Furthermore, the carbon layer becomes black and more absorbent of light, so it can be further excited and peeled off by irradiating it with light, or by using both methods in combination. By using the amorphous layer as the peeling layer, peeling will not occur even if some high heat is applied, and the peeling process can be performed at any point in the manufacturing process. 【0025】 Thus, in this invention, an amorphous layer is formed using a laser, followed by bonding. At this time, not only single crystals but also polycrystalline materials and sintered materials can be used as support substrates for the 4H-SiC layer, making it possible to significantly reduce costs. Furthermore, it has been reported that using polycrystalline materials is more effective in reducing substrate resistance (Non-Patent Literature 2), and in addition to cost, it is very effective in improving quality when considered as a vertical device. 【0026】 Furthermore, by sputtering a thin film of silicon or the like onto the bonding surface between the laser-irradiated 4H-SiC substrate and the support substrate, and bonding them through this thin film, it becomes possible to bond SiC substrates together, which was previously difficult when the support substrate was SiC. 【0027】 Furthermore, in this invention, the delamination surface of the delamination substrate or bonding substrate is etched with plasma to remove the damaged layer and flatten it, after which it is reused or subjected to epitaxial growth. In this way, SiC, which is a difficult material to process, can be flattened at a lower cost compared to polishing methods such as CMP, and a high-quality substrate can be obtained. 【0028】 Although SiC is normally difficult to plasma etch, it can be etched due to the weakening of the peeled surface by laser irradiation. By performing epitaxial growth in this way, if a high-quality SiC substrate can be prepared, the laser irradiation process, bonding process, peeling process, etching process, and epitaxial process can be repeated to transfer the surface layer of the 4H-SiC substrate to a support substrate and form an epitaxial layer by vapor phase growth method such as CVD. This makes it possible to repeatedly and inexpensively produce high-quality SiC substrates until the 4H-SiC substrate reaches a thickness that can no longer be peeled off the surface layer. 【0029】 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. 【0030】 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. 【0031】 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. 【0032】 Furthermore, by combining light irradiation and impact for delamination, the time required for delamination can be reduced compared to performing each method individually. 【0033】 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. 【0034】 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. 【0035】 In this bonding process, the silicon thin film can be deposited by a sputtering method targeting silicon. 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. 【0036】 In this case, etching can be performed using a mixed gas of carbon fluoride and oxygen as the raw material gas in the etching process. 【0037】 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. 【0038】 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. 【0039】 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. 【0040】 In this process, the delamination surface of the bonding substrate can be plasma-etched in the etching step, and furthermore, an epitaxial layer can be grown on the etched delamination surface of the bonding substrate in the epitaxial step. 【0041】 By growing an epitaxial layer on the etched delamination surface of the bonding substrate in this way, the required SiC layer thickness can be secured, and by forming the device on the epitaxial layer, the device can be made of higher quality. 【0042】 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 4H-SiC layer is bonded to the support substrate via a silicon thin film and its surface is etched. 【0043】 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 an inexpensive yet high-quality product. 【0044】 Furthermore, if the 4H-SiC layer is bonded to the 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 can also strengthen the bond when the support substrate is a polycrystalline or sintered SiC material. As a result, the bond between the support substrate and the 4H-SiC layer becomes robust. 【0045】 Furthermore, the present invention provides a semiconductor device characterized by comprising the semiconductor substrate described above. Because such semiconductor devices are equipped with the inexpensive, high-quality semiconductor substrates described above, they are inexpensive, high-quality, and highly reliable. [Effects of the Invention] 【0046】 As described above, the semiconductor substrate manufacturing method of the present invention allows for the production of lower-cost, higher-quality semiconductor substrates using 4H-SiC peeling technology, thereby reducing the manufacturing cost of semiconductor substrates. Furthermore, the semiconductor substrate of the present invention is inexpensive and of high quality. Moreover, the semiconductor device of the present invention is also inexpensive and of high quality. 【0047】 Furthermore, the configuration of the present invention makes it possible to effectively utilize the substrate after peeling, and SiC groups This will allow for a reduction in the cost of the boards. [Brief explanation of the drawing] 【0048】 [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] 【0049】 The present invention will be described in detail below, but the present invention is not limited to these descriptions. 【0050】 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, as well as for cheaper and higher-quality semiconductor substrates and cheaper and higher-quality semiconductor devices. 【0051】 As a result of diligent study on the above problems, the present inventors have developed a laser irradiation step in which a laser is irradiated onto 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 that has undergone the laser irradiation step and the bonding surface of another support substrate, and bonding the surface of the 4H-SiC substrate and the bonding surface of the support substrate via this thin film to obtain a bonded substrate; and peeling off the 4H-SiC substrate with the amorphous layer of the bonded substrate so that the surface layer of the 4H-SiC substrate becomes 4H The present invention was completed by discovering that a method for manufacturing a semiconductor substrate can be provided that allows for the production of a lower-cost, higher-quality semiconductor substrate using 4H-SiC peeling technology, characterized by a method for manufacturing a semiconductor substrate that includes a peeling step of separating a bonding substrate transferred onto a support substrate as a SiC layer, a release substrate which is a 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 bonding substrate or the release substrate after the peeling step, and an epitaxial step of performing epitaxial growth on at least one of the bonding substrate or the release substrate. 【0052】 Furthermore, as a result of diligent research into the above-mentioned problems, the inventors have found that a semiconductor substrate can be provided that is less expensive and of higher quality, by providing a semiconductor substrate comprising a support substrate and a 4H-SiC layer bonded to the surface of the support substrate, wherein the 4H-SiC layer is bonded to the support substrate via a silicon thin film and its surface is etched, and have thus completed the present invention. 【0053】 Furthermore, after diligently studying the above-mentioned problems, the inventors discovered that a semiconductor device comprising the semiconductor substrate described above can provide a more inexpensive and high-quality semiconductor device, thus completing the present invention. Thus, the present invention relates to a method for manufacturing a semiconductor substrate, a semiconductor substrate, and a semiconductor device, and more specifically, to a method for manufacturing a SiC wafer, relating to laser substrate peeling technology, bonding, and reuse of the peeled substrate, and aims to provide high-quality and inexpensive SiC substrates, including 4H-SiC. 【0054】 Preferred embodiments of the present invention will be described below 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. 【0055】 The support substrate 3 is a substrate that supports the 4H-SiC layer 1a. 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 cause 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. 【0056】 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 made of silicon or the like is provided at the bonding surface between the 4H-SiC layer 1a and the support substrate 3. A strong bond is achieved by bonding the 4H-SiC layer 1a and the support substrate 3 via this thin film 7 made of silicon or the like. 【0057】 The thin film 7 is not particularly limited as long as it is made of a material that can bond to the 4H-SiC layer 1a and the support substrate 3, but a silicon thin film can be given as an example. 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. 【0058】 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 an inexpensive and high-quality semiconductor substrate 5. 【0059】 The 4H-SiC layer 1a can be a single crystal layer, such as bulk 4H-SiC, or an epitaxial layer of 4H-SiC. 【0060】 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. 【0061】 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. 【0062】 By incorporating an inexpensive, high-quality semiconductor substrate 5 into the semiconductor device 6, the semiconductor device 6 itself becomes inexpensive, high-quality, and highly reliable. 【0063】 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. 【0064】 In this process, the surface layer of the 4H-SiC substrate 1 is transferred to the support substrate 3, but the peeled substrate 11 that is created 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. 【0065】 Next, a laser is irradiated onto the surface of the 4H-SiC substrate 1 to break the silicon-carbon bonds near the surface of the 4H-SiC substrate 1, as shown in Figure 2(b), and to form an amorphous layer 2 in which silicon and carbon exist in an amorphous state (laser irradiation step). By adjusting the laser irradiation focal depth at this time, an amorphous layer 2 can be formed at a predetermined depth in which silicon and carbon are respectively in an amorphous state. 【0066】 The type of laser used for irradiation is not particularly limited as long as it can form an amorphous layer 2 at the desired depth on the 4H-SiC substrate 1, but a YAG laser can be used as an example. In the case of a YAG laser, the second harmonic generation (SHG, wavelength 532 nm) can be used as an example wavelength for irradiation. 【0067】 Next, as shown in Figure 2(c), a support substrate 3 is prepared, which is a substrate separate from the 4H-SiC substrate 1. 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. 【0068】 Next, as shown in Figure 2(d), a thin film 7 is deposited on at least one of the surfaces 14 of the 4H-SiC substrate 1 that have undergone the laser irradiation process and the bonding surface 8 of the support substrate 3. Then, the surfaces 14 of the 4H-SiC substrate 1 and the bonding surface 8 of the support substrate 3 are bonded via this thin film 7 to obtain a bonded substrate 10 as shown in Figure 2(e) (bonding process). Note that Figure 2(d) illustrates the case where a thin film 7 is deposited on both the 4H-SiC substrate 1 and the support substrate 3. 【0069】 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. 【0070】 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 to be deposited on, and does not roughen the SiC surface of the bonding surface 8. 【0071】 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. 【0072】 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). 【0073】 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. 【0074】 When light irradiation is performed, the bonding substrate 10 is irradiated with light, and the amorphous carbon layer 2 formed in the laser irradiation 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. 【0075】 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. 【0076】 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). 【0077】 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. 【0078】 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. 【0079】 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. 【0080】 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). 【0081】 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. 【0082】 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. 【0083】 In the etching process, etching can be performed using a mixed gas of carbon fluoride and oxygen as the etching raw material gas. CHF3 and CF4 are preferred as specific carbon fluoride gases. Since this mixed gas 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. 【0084】 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 laser irradiation 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, the weakening of the delamination surfaces 23 and 21 can be achieved not only by damaging them with laser irradiation, but also by plasma treatment using H2 gas. 【0085】 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). 【0086】 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. 【0087】 The peeled substrate 11 after the peeling process can be reused as a 4H-SiC substrate 1 by repeating the laser irradiation 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. 【0088】 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. 【0089】 Next, epitaxial growth is performed on at least one of the bonding substrate 12 or the release substrate 11 (epitaxial process). 【0090】 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 peel surface 23 of the 4H-SiC layer 1a is etched in the etching process, the peel surface 23 is planarized by etching, so an epitaxial layer can be formed on the peel surface 23 without performing costly planarization treatments such as CMP, and the bonded substrate 12 can be made into an inexpensive and high-quality semiconductor substrate 5. 【0091】 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, it is not necessarily required to perform the epitaxial process shown in Figure 2(i) on the bonded substrate 12. 【0092】 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. 【0093】 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. 【0094】 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] 【0095】 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 peeled substrate 11 as a 4H-SiC substrate 1 by performing a laser irradiation process, silicon thin film formation and bonding (bonding process), peeling process, and etching process on the 4H-SiC substrate 1, followed by another laser irradiation process and bonding process. 【0096】 (Examples) First, a 4H-SiC single crystal substrate 1 was prepared, with a diameter of 200 mm, a thickness of 355 μm, n-type crystal structure, resistivity of 10 Ω·cm, and a 4° offset relative to the (0001) plane. An amorphous layer 2 was then formed by irradiating this substrate with a laser beam of 1064 nm wavelength, which is a light source with a penetrating wavelength. A YAG laser was used for this process, and the laser irradiation depth was adjusted to irradiate the 4H-SiC substrate 1 with the second harmonic (SHG, wavelength 532 nm) to form the amorphous layer 2 within the substrate. 【0097】 Next, a polycrystalline SiC substrate with the same diameter as the 4H-SiC substrate 1 was prepared as the support substrate 3. As a bonding process, silicon was targeted and Ar ions were irradiated onto it to form a thin film 7, which was then deposited 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. 【0098】 Next, as a delamination step, a YAG laser (wavelength 1064 nm) was used to align the focal point with amorphous layer 2 and irradiate and excite the amorphous layer 2 with light, separating the bonded substrate 10 into a bonding substrate 12 and a delamination substrate 11. 【0099】 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. 【0100】 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. 【0101】 When the peeled substrate 11 after the etching process was subjected to a laser irradiation process and a bonding process again using the reuse flow described above, the support substrate 3 could be bonded to the peeled surface 21 of the peeled substrate 11, and a bonded substrate 10 could be obtained in the same way. 【0102】 As described above, according to the embodiment of the present invention, an amorphous layer 2 was formed on the 4H-SiC substrate 1 by irradiating it with a laser, then a support substrate 3 was bonded to it 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 etched and reused as the 4H-SiC substrate 1. Therefore, the present invention can significantly reduce the manufacturing cost of semiconductor substrates using SiC. 【0103】 This specification includes the following embodiments: [1]: A laser irradiation step in which a laser is irradiated onto 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 is to form a thin film on at least one of the surface of the 4H-SiC substrate that has undergone the laser irradiation step and the bonding surface of another support substrate, and to bond the surface of the 4H-SiC substrate and the bonding surface of the support substrate via 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] above, characterized in that the 4H-SiC substrate is peeled off in the peeling step by irradiating the amorphous layer with light, applying impact, or performing a combination thereof. [3]: A method for manufacturing a semiconductor substrate according to [1] or [2] above, 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. [4]: The method for manufacturing a semiconductor substrate according to [3], characterized in that the silicon thin film is formed in the bonding step by a sputtering method targeting silicon. [5]: A method for manufacturing a semiconductor substrate according to any of the above [1] to [4], characterized in that etching is performed using a mixed gas of carbon fluoride and oxygen as a raw material gas in the etching step. [6]: A method for manufacturing a semiconductor substrate according to any of the above [1] to [5], 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. [7]: A method for manufacturing a semiconductor substrate according to any one of [1] to [6] above, characterized in that, in the etching step, the delamination surface of the bonding substrate is plasma etched, and further, in the epitaxial step, an epitaxial layer is grown on the etched delamination surface of the bonding substrate. [8]: A semiconductor substrate comprising a support substrate and a 4H-SiC layer bonded to the surface of the support substrate, wherein the 4H-SiC layer is bonded to the support substrate via a silicon thin film and its surface is etched. [9]: A semiconductor device comprising the semiconductor substrate described in [8] above. 【0104】 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] 【0105】 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

[Claim 1] A laser irradiation step involves irradiating the surface of a substrate made solely of 4H-SiC with a laser to break the bond between silicon and carbon, thereby forming an amorphous layer within the substrate made solely of 4H-SiC in which silicon and carbon exist in amorphous states. 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 laser irradiation step and the bonding surface of another support substrate, and to bond the surface of the 4H-SiC substrate and the bonding surface of the support substrate via this thin film to obtain a bonded substrate. A peeling step is performed to separate the substrate, which is the substrate consisting solely of 4H-SiC, from the amorphous layer of the bonding substrate, thereby transferring the surface layer of the substrate consisting solely of 4H-SiC as a 4H-SiC layer onto the support substrate, into a bonding substrate and a peeling substrate, which is the substrate after the surface layer has been peeled off from the substrate consisting solely of 4H-SiC. 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, The process includes an epitaxial step of performing epitaxial growth on at least one of the bonding substrate or the delamination substrate, A method for manufacturing a semiconductor substrate, characterized in that, in the peeling step, the amorphous layer is irradiated with light, the amorphous carbon layer within the amorphous layer absorbs the light, and the substrate consisting only of 4H-SiC is peeled off starting from the amorphous carbon layer. [Claim 2] The method for manufacturing a semiconductor substrate according to claim 1, characterized in that, in the peeling step, the amorphous layer is subjected to a treatment combining the light irradiation treatment and the impact treatment to peel off the substrate consisting only of 4H-SiC. [Claim 3] 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 it. [Claim 4] The method for manufacturing a semiconductor substrate according to claim 3, characterized in that, in the bonding step, the silicon thin film is formed by a silicon-targeted sputtering method. [Claim 5] The method for manufacturing a semiconductor substrate according to claim 1, characterized in that etching is performed using a mixed gas of carbon fluoride and oxygen as a raw material gas in the etching step. [Claim 6] 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. [Claim 7] In the etching process described above, the delamination surface of the bonding substrate is plasma-etched, and further, A method for manufacturing a semiconductor substrate according to any one of claims 1 to 6, characterized in that, in the epitaxial step, an epitaxial layer is grown on the etched delamination surface of the bonding substrate.

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