COMPOSITE SUBSTRATE, SiC DEVICE, AND METHOD FOR PRODUCING COMPOSITE SUBSTRATE

Abstract

A composite substrate according to an embodiment of the present invention comprises a base substrate and an SiC single crystal layer bonded to the base substrate. Thickness of the SiC single crystal layer is at least 3 μm. The impurity concentration of the SiC single crystal layer is 5 x 1013 cm-3 to 5 x 1016 cm-3.

Description

Composite substrate, SiC device, and method for manufacturing the composite substrate 【0001】 This disclosure relates to a composite substrate, a SiC device, and a method for manufacturing a composite substrate. 【0002】 Silicon carbide (SiC) has a dielectric breakdown field an order of magnitude larger and a band gap three times larger than silicon (Si). Furthermore, SiC has properties such as a thermal conductivity approximately three times higher than silicon (Si). Therefore, SiC is expected to have applications in power devices, high-frequency devices, and other applications. In addition, devices using SiC can operate at high temperatures of 150°C or higher. For this reason, SiC epitaxial wafers have recently come to be used as substrates for the semiconductor devices mentioned above. 【0003】 SiC epitaxial wafers are obtained by stacking SiC epitaxial layers on the surface of a SiC substrate. High-quality SiC substrates are expensive. On the other hand, the active layer that exhibits the actual functionality of the device is a thin region of a few micrometers to several hundred micrometers on the surface of the SiC epitaxial wafer, while the remaining portion functions as a support to facilitate handling and other processes. 【0004】 In recent years, in order to prevent the high cost of SiC epitaxial wafers, research has been conducted on bonding high-quality SiC substrates to low-cost underlayment substrates. For example, Patent Document 1 discloses a method in which a single-crystal silicon carbide layer is bonded to a support substrate, and then an active layer is epitaxially grown on the single-crystal silicon carbide layer to form a device on the active layer. 【0005】 Japanese Patent Publication No. 2012-146695 【0006】 As described in Patent Document 1, when an active layer is epitaxially grown after bonding single-crystal silicon carbide layers, the process involves many steps and is costly to manufacture. Furthermore, bonding defects may occur between the substrate and the single-crystal silicon carbide layer, and if the active layer is epitaxially grown on top of these bonding defects, defects or dislocations will occur within the active layer. 【0007】The present disclosure has been made in view of the above problems, and provides a composite substrate, a SiC device, and a method for manufacturing a composite substrate that do not require forming an epitaxial layer after bonding. 【0008】 To solve the above problems, the present disclosure provides the following means. 【0009】 (1) The composite substrate according to the first aspect includes a base substrate and a SiC single crystal layer bonded to the base substrate. The film thickness of the SiC single crystal layer is 3 μm or more. The impurity concentration of the SiC single crystal layer is 5 × 10 １３ cm －３ or more and 5 × 10 １６ cm －３ or less. 【0010】 (2) The composite substrate according to the above aspect may have a bonding layer between the base substrate and the SiC single crystal layer. 【0011】 (3) The SiC device according to the second aspect includes a base substrate, a SiC single crystal layer bonded to the base substrate, and an element formed inside the SiC single crystal layer. The impurity concentration of the SiC single crystal layer is 5 × 10 １３ cm －３ or more and 5 × 10 １６ cm －３ or less. 【0012】 (4) The method for manufacturing a composite substrate according to the third aspect includes a film forming step of forming a SiC crystal growth layer on a SiC single crystal substrate, an alteration step of irradiating a laser at a predetermined depth position of the SiC crystal growth layer, a bonding step of bonding the SiC crystal growth layer to a base substrate, and a separation step of separating the SiC crystal growth layer along the position irradiated with the laser to form a SiC single crystal layer on the base substrate. 【0013】 (5) In the method for manufacturing a composite substrate according to the above aspect, the impurity concentration of the SiC crystal growth layer may be 5 × 10 １３ cm －３ or more and 5 × 10 １６ cm －３ or less. 【0014】(6) In the method for manufacturing a composite substrate according to the above embodiment, the thickness of the SiC crystal growth layer may be 50 μm or more. 【0015】 The composite substrate and method for manufacturing the composite substrate according to this disclosure enable the fabrication of a device without the need to deposit an epitaxial layer on the composite substrate. The SiC device according to this disclosure does not require the deposition of an epitaxial layer and is of high quality. 【0016】 This is a plan view of the composite substrate according to the first embodiment. This is a cross-sectional view of the composite substrate according to the first embodiment. This is a cross-sectional view of the SiC device according to the first embodiment. This is a schematic diagram for explaining through-dislocations in the composite substrate according to the first embodiment. This is a diagram for explaining the manufacturing method of the composite substrate according to the first embodiment. 【0017】 This embodiment will now be described in detail with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience to clearly illustrate the features of this embodiment, and the dimensional ratios of each component may differ from those of the actual components. The materials, dimensions, etc., exemplified in the following description are examples only, and this disclosure is not limited to them. It is possible to modify and implement these examples as appropriate without altering the essence of the invention. 【0018】 In this specification, individual orientations are indicated by [], collective orientations by <>, individual planes by (), and collective planes by {}. While crystallography dictates that negative exponents are represented by a "-" (bar) above the number, in this specification, the negative sign is placed before the number. 【0019】 First, let's define the directions. The thickness direction of the composite substrate 10 is defined as the Z direction. The Z direction may be the <0001> direction of the SiC single crystal layer 2, or it may be tilted by an offset angle relative to the <0001> direction. One direction of the plane perpendicular to the Z direction is defined as the X direction. Also, on the plane perpendicular to the Z direction, the direction perpendicular to the X direction is defined as the Y direction. The X direction is, for example, the <11-20> direction of the SiC single crystal layer 2. The Y direction is, for example, the <1-100> direction of the SiC single crystal layer 2. 【0020】Figure 1 is a plan view of the composite substrate 10 according to this embodiment. The composite substrate 10 is a wafer that is approximately circular in plan view. The composite substrate 10 may have notches or orientation flats for determining the direction of the crystal axes. 【0021】 The diameter of the composite substrate 10 is not particularly limited. The diameter of the composite substrate 10 is, for example, 145 mm or more, preferably 149 mm or more. The diameter of the composite substrate 10 is, for example, 155 mm or less, preferably 151 mm or less. The diameter of the composite substrate 10 is, for example, 195 mm or more, preferably 199 mm or more. The diameter of the composite substrate 10 is, for example, 205 mm or less, preferably 201 mm or less. The diameter of the composite substrate 10 is, for example, 245 mm or more, preferably 249 mm or more. The diameter of the composite substrate 10 is, for example, 255 mm or less, preferably 251 mm or less. The diameter of the composite substrate 10 is, for example, 295 mm or more, preferably 299 mm or more. The diameter of the composite substrate 10 is, for example, 305 mm or less, preferably 301 mm or less. 【0022】 Figure 2 is a cross-sectional view of the composite substrate 10 according to this embodiment. The composite substrate 10 has a base substrate 1 and a SiC single crystal layer 2. 【0023】 The base substrate 1 is a support substrate that enhances the handling of the composite substrate 10. The base substrate 1 can be made of, for example, polycrystalline SiC, single-crystal SiC, SiC sintered body, ceramic, single-crystal Si, or SiO ２ It is a film-coated Si. The base substrate 1 is preferably, for example, polycrystalline SiC. Polycrystalline SiC is cheaper to obtain than single-crystal SiC, and problems such as warping are less likely to occur when bonded with a SiC single-crystal layer 2. 【0024】 If the base substrate 1 is single-crystal SiC, the single-crystal SiC of the base substrate 1 may be of lower quality than the SiC single-crystal layer 2. For example, the defect density in the single-crystal SiC of the base substrate 1 is higher than the defect density in the SiC single-crystal layer 2. The base substrate 1 is not limited to a single layer, but may consist of multiple layers. 【0025】The thickness of the lower base substrate 1 is, for example, 100 μm or more and 1000 μm or less. The thickness of the lower base substrate 1 is preferably 150 μm or more and 500 μm or less, more preferably 200 μm or more and 400 μm or less, and even more preferably 325 μm or more and 375 μm or less. 【0026】 When the thickness of the lower base substrate 1 in the state before bonding the SiC single crystal layer 2 can be obtained, it can be measured by a thickness gauge or spectroscopic interference method or the like. When measuring the thickness of the lower base substrate 1 in the state of the composite substrate 10, after measuring the film thickness of the SiC single crystal layer 2 by Fourier transform infrared spectroscopy (FT-IR), it is obtained by subtracting the film thickness of the SiC single crystal layer 2 from the total thickness of the composite substrate 10. 【0027】 The thickness of the lower base substrate 1 is measured, for example, at the center. The center is the center of the circumcircle that circumscribes the outer periphery of the composite substrate 10 when the composite substrate 10 is viewed in plan from the Z direction. 【0028】 The thickness of the lower base substrate 1 may be measured at a plurality of measurement points arranged at equal intervals on a straight line passing through the center when the lower base substrate 1 is viewed in plan. For example, the thickness of the lower base substrate 1 may be measured at each of the center, points arranged at equal intervals in the X direction with the center as a reference, and points arranged at equal intervals in the Y direction with the center as a reference. When the thickness of the lower base substrate 1 is measured at a plurality of measurement points, the average of the measured values at each measurement point may be regarded as the thickness of the lower base substrate 1. 【0029】 The SiC single crystal layer 2 is bonded to the lower base substrate 1. The SiC single crystal layer 2 is in contact with the lower base substrate 1 and joined to the lower base substrate 1. 【0030】 The SiC single crystal layer 2 is composed of, for example, a single crystal of SiC. The polytype of the SiC single crystal layer 2 is not particularly limited and may be any of 2H, 3C, 4H, and 6H. The SiC single crystal layer 2 is, for example, 4H-SiC. The SiC single crystal layer 2 is not limited to a single layer and may be a laminated film in which a plurality of layers are laminated. 【0031】The SiC single crystal layer 2 is doped with a dopant element, for example. The dopant element is an impurity that acts as a carrier, for example, nitrogen. The impurity concentration (doping concentration) in the SiC single crystal layer 2 is, for example, 5×10 １３ cm －３ or more and 5×10 １６ cm －３ or less. 【0032】 The impurity concentration in the SiC single crystal layer 2 can be measured using a mercury probe (Hg-CV) method or secondary ion mass spectrometry (SIMS). The mercury probe method is a type of capacitance-voltage method, and is a method of measuring capacitance (C)-reverse voltage (V) characteristics using a Schottky junction generated by contacting mercury with the wafer surface. The donor concentration can be calculated from the C-V characteristics. 【0033】 Secondary ion mass spectrometry (SIMS) is a method of performing mass spectrometry of secondary ions that pop out while shaving layers in the thickness direction. The impurity concentration can be measured from the mass spectrometry. The measurement position in the depth direction of the impurity concentration is each region obtained by equally dividing the SiC single crystal layer 2 into five parts at equal intervals in the Z direction. 【0034】 The impurity concentration in the SiC single crystal layer 2 is measured, for example, at the center of the SiC single crystal layer 2. The measurement of the impurity concentration may be performed at a plurality of measurement points within the XY plane, and the average value of the measured impurity concentrations may be obtained. For example, points at equal intervals in the cross direction with the center as the origin may be used as a plurality of measurement points. 【0035】The thickness of the SiC single crystal layer 2 may be, for example, 3 μm or more and 500 μm or less. The thickness can be defined, for example, by the design breakdown voltage of the device. For example, the thickness can be set to 8 μm or less when the design breakdown voltage of the device is 700 V or less, to 13 μm or less when the design breakdown voltage of the device is 1.2 kV or less, to 18 μm or less when the design breakdown voltage of the device is 1.7 kV or less, to 35 μm or less when the design breakdown voltage of the device is 3.3 kV or less, to 70 μm or less when the design breakdown voltage of the device is 6.5 kV or less, to 120 μm or less when the design breakdown voltage of the device is 10 kV or less, to 250 μm or less when the design breakdown voltage of the device is 20 kV or less, and to 350 μm or less when the design breakdown voltage of the device is 30 kV or less. The thickness of the SiC single crystal layer 2 can be achieved by separating the SiC crystal growth layer using a laser in the manufacturing process described later. For example, when peeling the layer by implanting hydrogen ions at a high concentration and heat treatment, there is a limit to the penetration depth that hydrogen ions can penetrate, making it difficult to obtain a SiC single crystal layer 2 with sufficient thickness. If the SiC single crystal layer 2 consists of multiple layers, the thickness can also be achieved by bonding a portion of the SiC crystal growth layer multiple times in the manufacturing process described later. The thickness of the SiC single crystal layer 2 is set according to the application, for example, between 3 μm and 500 μm. 【0036】 The thickness of the SiC single crystal layer 2 can be measured, for example, using Fourier transform infrared spectroscopy (FT-IR). 【0037】 The thickness of the SiC single crystal layer 2 is measured, for example, at the center. The thickness of the SiC single crystal layer 2 may also be measured at multiple measurement points arranged at equal intervals along a straight line passing through the center. For example, the thickness of the SiC single crystal layer 2 may be measured at the center, at points arranged at equal intervals in the X direction relative to the center, and at points arranged at equal intervals in the Y direction relative to the center. If the thickness of the SiC single crystal layer 2 is measured at multiple measurement points, the average of the measured values ​​at each measurement point may be considered as the thickness of the SiC single crystal layer 2. 【0038】The first surface of the SiC single crystal layer 2 may or may not have an offset angle with respect to the (0001) plane in the <11-20> direction. The first surface is the surface opposite to the bonding surface where the SiC single crystal layer 2 and the underlying substrate 1 are in contact. It is preferable that the first surface of the SiC single crystal layer 2 has an offset angle in the <11-20> direction, for example. The offset angle is, for example, greater than 0° and 10° or less, preferably 0.1° or more and 8° or less, more preferably 3.5° or more and 4.5° or less, and even more preferably 4°. The first surface of the SiC single crystal layer 2 does not have to have an offset angle with respect to the (0001) plane in the <1-100> direction. 【0039】 The SiC single crystal layer 2 is a high-quality layer grown on a SiC single crystal substrate. Device elements can be fabricated within the SiC single crystal layer 2. The SiC single crystal layer 2 is a drift layer through which drift current flows in a SiC device. Drift current is a current generated by the flow of carriers when a voltage is applied to a semiconductor. 【0040】 Multiple SiC devices can be obtained by chipping a composite substrate 10 in which an element is formed within a SiC single crystal layer 2. Figure 3 is a cross-sectional view of an example of a SiC device according to this embodiment. The SiC device 20 has a base substrate 21, a SiC single crystal layer 22, and an element 23 formed within the SiC single crystal layer 22. The base substrate 21 corresponds to a base substrate 1, and the SiC single crystal layer 22 corresponds to a SiC single crystal layer 2. 【0041】 The impurity concentration of the SiC single crystal layer 22 is the same as before chipping, 5 × 10⁻⁶. １３ cm －３ The above 5 x 10 １６ cm －３ The following applies: The impurity concentration of the SiC single crystal layer 22 can be measured by secondary ion mass spectrometry (SIMS). The impurity concentration may be measured, for example, at the center when the SiC device 20 is viewed in a plan view from the Z direction. For example, the impurity concentration of the SiC single crystal layer 22 is measured in the region closest to the underlying substrate 21 among five regions obtained by dividing the SiC single crystal layer 22 into five equally spaced regions in the Z direction. 【0042】Element 23 is, for example, a combination of transistors, capacitors, inductors, resistors, wiring, etc. Figure 3 illustrates the case where element 23 is a transistor. 【0043】 The SiC single crystal layer 22 can be fabricated by bonding it to the substrate 21, eliminating the need to form an epitaxial layer on the SiC single crystal layer 22. When forming an epitaxial layer on a composite substrate, defects are likely to occur within the epitaxial layer in areas where bonding defects occur. The SiC device 20 according to this embodiment does not require the formation of an epitaxial layer, and since defects that occur during the deposition of an epitaxial layer do not occur, it is of high quality. 【0044】 The composite substrate 10 may have a bonding layer between the base substrate 1 and the SiC single crystal layer 2. The bonding layer is a layer located between the base substrate 1 and the SiC single crystal layer 2, and is a layer containing carbon, silicon, and nitrogen. The bonding layer is formed by bonding the base substrate 1 and the SiC single crystal layer 2 together. The bonding layer contains, for example, elements that constitute the base substrate 1 or the SiC single crystal layer 2. The bonding layer can sometimes be confirmed by observing a cross-section of the composite substrate 10 with a transmission electron microscope (TEM). The thickness of the bonding layer may be, for example, 0.25 nm or more and 10 nm or less. The thickness of the bonding layer can sometimes be measured from a cross-sectional image taken with a transmission electron microscope (TEM). However, the resolution of the transmission electron microscope must be considered. 【0045】 Figure 4 is a schematic diagram illustrating through-dislocations in a composite substrate 10 according to the first embodiment. When the base substrate 1 is single-crystal SiC, the base substrate 1 may have through-dislocations 3. The SiC single-crystal layer 2 may also have through-dislocations 4. Through-dislocations 3 and 4 include through-helical dislocations, through-wavy dislocations, through-mixed dislocations, and micropipes. In the composite substrate 10 according to this embodiment, since the SiC single-crystal layer 2 is bonded to the base substrate 1, the coordinates of the through-dislocations 3 on the bonding surface of the base substrate 1 and the coordinates of the through-dislocations 4 on the bonding surface hardly coincide. For example, of the through-dislocations 3 on the bonding surface of the base substrate 1, the number of whose coordinates coincide with those of the through-dislocations 4 on the bonding surface of the SiC single-crystal layer 2 is 0.5% or less. 【0046】 Next, a method for manufacturing the composite substrate 10 according to this embodiment will be described. Figure 5 is a diagram illustrating the method for manufacturing the composite substrate 10 according to this embodiment. The method for manufacturing the composite substrate 10 according to this embodiment includes a film formation step, a modification step, a bonding step, and a separation step. 【0047】 In the film formation process, a SiC crystal growth layer 12 is formed on the SiC single crystal substrate 11. 【0048】 The SiC single crystal substrate 11 is made of, for example, a single crystal of the same polytype SiC as the SiC single crystal layer 2. The deposition surface of the SiC single crystal substrate 11 on which the SiC crystal growth layer 12 is formed may or may not have an offset angle in the <11-20> direction. The offset angle is, for example, greater than 0° and 10° or less, preferably 0.1° or more and 8° or less, more preferably 3.5° or more and 4.5° or less, and even more preferably 4°. 【0049】 The SiC single crystal substrate 11 can be a commercially available one. The SiC single crystal substrate 11 may be a SiC single crystal having the same quality as a commercially available SiC substrate, or it may be a SiC single crystal with a diameter equal to or greater than the diameter of the SiC crystal growth layer 12. The impurity concentration in the SiC single crystal substrate 11 is, for example, 1 × 10⁻⁶ １３ cm －３ The above 2 x 10 １９ cm －３ The following is the case: The impurity concentration in the SiC single crystal substrate 11 is preferably within ±50% of the impurity concentration in the SiC crystal growth layer 12. When the difference between the impurity concentration of the SiC single crystal substrate 11 and the impurity concentration of the SiC crystal growth layer 12 is small, it is possible to suppress wafer warping after the SiC crystal growth layer 12 is formed. 【0050】The SiC crystal growth layer 12 is laminated on the SiC single crystal substrate 11. The SiC crystal growth layer 12 is a layer obtained by epitaxial growth of SiC on one surface of the SiC single crystal substrate 11. The SiC crystal growth layer 12 is not limited to SiC that has been epitaxially grown; for example, SiC that has been crystal-grown by a method such as the gas method may also be used. The SiC crystal growth layer 12 is the layer that becomes the SiC single crystal layer 2. The crystal growth surface of the SiC crystal growth layer 12 has a plane polarity opposite to that of the exposed surface of the SiC single crystal layer 2. For example, if the exposed surface of the SiC single crystal layer 2 is the Si surface, the crystal growth surface of the SiC crystal growth layer 12 is the C surface, and if the exposed surface of the SiC single crystal layer 2 is the C surface, the crystal growth surface of the SiC crystal growth layer 12 is the Si surface. The planar polarity of the crystal growth surface of the SiC crystal growth layer 12 matches the planar polarity of the film-forming surface of the SiC single crystal substrate 11 on which the SiC crystal growth layer 12 is deposited. The impurity concentration of the SiC crystal growth layer 12 is, for example, 5 × 10⁻⁶. １３ cm －３ The above 5 x 10 １６ cm －３ The following applies: 【0051】 The thickness of the SiC crystal growth layer 12 is, for example, 50 μm or more. The thickness of the SiC crystal growth layer 12 may also be, for example, 100 μm or more. If the thickness of the SiC crystal growth layer 12 is thick, many SiC single crystal layers 2 can be produced by repeatedly separating this SiC crystal growth layer 12. 【0052】 In the alteration process, a laser is irradiated into the interior of the SiC crystal growth layer 12. The laser is irradiated, for example, from the side of the SiC crystal growth layer 12 opposite to the surface in contact with the SiC single crystal substrate 11. For example, by keeping the laser output constant, the laser can be irradiated to a predetermined depth position within the SiC crystal growth layer 12. The portion of the SiC crystal growth layer 12 irradiated with the laser becomes the processed altered layer. The processed altered layer is the portion damaged by processing, for example, the portion where distortion has occurred. The processed altered layer spreads in the XY plane at a predetermined depth position within the SiC crystal growth layer 12. 【0053】For example, a known laser used in laser slicing technology can be used. By using a laser, the position where the processed and altered layer is formed can be set over a wide range in the depth direction of the SiC crystal growth layer 12. By forming the processed and altered layer at a depth from the laser irradiation surface, a SiC single crystal layer 2 of sufficient thickness can be obtained. In contrast, for example, in the case of the hydrogen ion implantation method, the processed and altered layer can only be formed up to a position of about 1 μm from the surface where the hydrogen ions are implanted, making it difficult to obtain a SiC single crystal layer 2 of sufficient thickness. Note that when a portion of the SiC crystal growth layer 12 is bonded to the substrate 1 in multiple stages to obtain a SiC single crystal layer 2 consisting of multiple layers, the hydrogen ion implantation method can also be used. 【0054】 In the bonding process, the SiC crystal growth layer 12 is bonded to the substrate 1. The substrate 1 is as described above. The substrate 1 is bonded to the side of the SiC crystal growth layer 12 opposite to the side in contact with the SiC single crystal substrate 11. The SiC crystal growth layer 12 and the substrate 1 can be bonded by activating the bonding surface and then stacking them and applying pressure. The bonding surface can be activated, for example, by irradiating the bonding surface with ions. Furthermore, it is preferable that the surface roughness of the bonding surface of the SiC crystal growth layer 12 and the substrate 1 be 1 nm or less. 【0055】 In the separation process, a portion of the SiC crystal growth layer 12 is separated along the position where the laser was irradiated. The SiC crystal growth layer 12 is separated in the Z direction. The portion of the SiC crystal growth layer 12 that adheres to the substrate 1 and is separated becomes the SiC single crystal layer 2, and the portion of the SiC crystal growth layer 12 that adheres to the SiC single crystal substrate 11 and is separated becomes the SiC crystal growth layer 14. The SiC crystal growth layer 14 can be reused when producing the SiC single crystal layer 2 on another substrate. The separation surfaces of the SiC single crystal layer 2 and the SiC crystal growth layer 14 may be polished to make the surface roughness below a predetermined value. 【0056】Through the process described above, a composite substrate 10 having a base substrate 1 and a SiC single crystal layer 2 can be fabricated. Furthermore, by creating device elements inside the SiC single crystal layer 2 and forming each element into a chip, multiple SiC devices can be fabricated from the composite substrate 10. 【0057】 The manufacturing method for the composite substrate 10 according to this embodiment involves directly bonding a SiC single crystal layer 2, which can function as an active layer for fabricating devices, to a base substrate 1. Therefore, SiC device elements can be directly fabricated on the SiC single crystal layer 2. The manufacturing method for the composite substrate 10 according to this embodiment does not require the formation of an epitaxial layer on the SiC single crystal layer 2, resulting in fewer process steps. 【0058】 Furthermore, when forming an epitaxial layer on a composite substrate manufactured by bonding, defects are likely to occur within the epitaxial layer in areas where bonding defects occur. The composite substrate 10 according to this embodiment does not require epitaxial growth after bonding, and therefore does not produce such defects, resulting in high quality. 【0059】 While preferred embodiments of this disclosure have been described in detail above, this disclosure is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the gist of this disclosure as described in the claims. 【0060】 1. Substrate 2. SiC single crystal layer 3, 4. Threading dislocations 10. Composite substrate 11. SiC single crystal substrate 12, 14. SiC crystal growth layer 13. Processed and altered layer

Claims

1. The device comprises a base substrate and a SiC single crystal layer bonded to the base substrate, wherein the thickness of the SiC single crystal layer is 3 μm or more, and the impurity concentration of the SiC single crystal layer is 5 × 10⁻¹⁶. １３ cm －３ The above 5 x 10 １６ cm －３ The following is a composite substrate.

2. The composite substrate according to claim 1, wherein a bonding layer is provided between the base substrate and the SiC single crystal layer.

3. The device comprises a base substrate, a SiC single crystal layer bonded to the base substrate, and an element formed inside the SiC single crystal layer, wherein the impurity concentration of the SiC single crystal layer is 5 × 10 １３ cm －３ The above 5 x 10 １６ cm －３ The following are SiC devices.

4. A method for manufacturing a composite substrate, comprising: a film deposition step of forming a SiC crystal growth layer on a SiC single crystal substrate; a modification step of irradiating the SiC crystal growth layer with a laser at a predetermined depth; a bonding step of bonding the SiC crystal growth layer to a base substrate; and a separation step of separating the SiC crystal growth layer along the position irradiated with the laser and forming a SiC single crystal layer on the base substrate.

5. The impurity concentration of the SiC crystal growth layer is 5×10 １３ cm －３ or more and 5×10 １６ cm －３ or less. The method for manufacturing a composite substrate according to claim 4.

6. The method for manufacturing a composite substrate according to claim 4, wherein the thickness of the SiC crystal growth layer is 50 μm or more.

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