SiC substrate and SiC composite substrate

Abstract

The present invention provides a SiC substrate having little warpage. This SiC substrate is provided with a biaxially oriented SiC layer, and the difference between the maximum value (kmax) and the minimum value (kmin) of Raman shift values in the Si plane and the C plane of the SiC substrate is 0.50 cm-1 or less. The Raman shift values are obtained by measuring Raman shift values at an interval of 1 mm on two straight lines passing through the center point of the Si plane and orthogonal to each other in the Si plane of the SiC substrate, and measuring Raman shift values at an interval of 1 mm on two straight lines passing through the center point of the Si plane and corresponding to the transverse wave acoustic branch of the Raman spectrum, and measuring Raman shift values at an interval of 1 mm on two straight lines passing through the center point of the Si plane and corresponding to the transverse wave acoustic branch of the Raman spectrum in the C plane of the SiC substrate. Raman shift values indicating peaks corresponding to the transverse wave acoustic branch of the Raman spectrum are measured at an interval of 1 mm on two straight lines that pass through the center point of the C-plane and are orthogonal to each other.

Description

Technical Field

[0001] This invention relates to SiC substrates and SiC composite substrates. Background Technology

[0002] Silicon carbide (SiC) has attracted considerable attention as a wide-bandgap material capable of controlling high voltage and high power with low loss. In particular, in recent years, power semiconductor devices using SiC materials (SiC power devices) have demonstrated superior miniaturization, low power consumption, and high efficiency compared to power devices using Si semiconductors, thus promising applications in a wide variety of fields. For example, by employing SiC power devices, the efficiency of converters, inverters, and on-board chargers used in electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) can be improved through miniaturization. Therefore, the development of SiC wafers, which constitute the core of SiC power devices, is of great interest.

[0003] To fabricate SiC power devices, SiC single crystals need to be epitaxially grown on a SiC single crystal substrate. However, warping sometimes occurs on the SiC substrate, and it is desirable to suppress this warping. As an example of reducing substrate warping, Patent Document 1 (Japanese Patent Application Publication No. 2022-120059) discloses a SiC substrate in which the maximum value of the half-width of the peak corresponding to the folding mode of the longitudinal optical branch of the Raman spectrum of the SiC substrate is set as Δ. max Let the minimum value be Δ min When Δ is satisfied max -Δ min ≤0.14. Patent Document 2 (WO2021 / 111835A1) discloses a SiC substrate having a first main surface and a second main surface located opposite the first main surface. In a first square region of the first main surface, the average wavenumber of peaks corresponding to the folding mode of the longitudinal optical branch of the SiC Raman spectrum is set as a first wavenumber. In a second square region of the first main surface, the average wavenumber of peaks corresponding to the folding mode of the longitudinal optical branch of the SiC Raman spectrum is set as a second wavenumber. The absolute value of the difference between the first wavenumber and the second wavenumber is 0.2 cm⁻¹. －1 The following is disclosed in Patent Document 3 (Japanese Patent Application Publication No. 2017-75074): a SiC substrate comprising a carbon-side main surface and a silicon-side main surface, having a 4H crystal structure, wherein the nitrogen concentration in the carbon-side main surface is higher than the nitrogen concentration in the silicon-side main surface, and the difference in Raman peak shift between the carbon-side and silicon-side main surfaces is 0.2 cm. －1The following patent document 4 (WO2017 / 057742A1) discloses a SiC single-crystal ingot having SiC single crystals in the seed crystal, wherein the difference (A-B) between the Raman shift value (A) measured at the center of the substrate cut from the ingot and the Raman shift value (B) measured at the periphery, i.e., the Raman index, is 0.20 or less. Patent document 5 (Japanese Patent Application Laid-Open No. 2016-164120) discloses a SiC single-crystal wafer with a diameter of 150 mm or more and 300 mm or less, wherein the basal dislocation density on the surface is 100 dislocations / cm². 2 More than 1000 / cm 2 The density of through-spiral dislocations is 160 / cm³. 2 More than 500 per cm 2 Furthermore, the Raman index is above 0.03 and below 0.2.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2022-120059

[0007] Patent Document 2: WO2021 / 111835A1

[0008] Patent Document 3: Japanese Patent Application Publication No. 2017-75074

[0009] Patent Document 4: WO2017 / 057742A1

[0010] Patent Document 5: Japanese Patent Application Publication No. 2016-164120 Summary of the Invention

[0011] As mentioned above, while methods to reduce substrate warpage have been explored, further improvements are needed. In particular, SiC substrate warpage is a problem during SiC substrate polishing after epitaxial film deposition and during semiconductor device manufacturing. Specifically, it causes cracking when attaching the SiC substrate to the polishing machine, or poor adhesion when the SiC substrate is held in place during semiconductor manufacturing processes.

[0012] The inventors of this invention have recently come to the insight that by controlling the Raman shift value of the peak in the SiC substrate that corresponds to the transverse acoustic branch of the Raman spectrum, the warpage of the SiC substrate can be reduced.

[0013] Therefore, the object of the present invention is to provide a SiC substrate with less warpage.

[0014] According to the present invention, the following solution is provided.

[0015] [Option 1]

[0016] A SiC substrate having a biaxially oriented SiC layer.

[0017] The SiC substrate is characterized in that...

[0018] The maximum value of the Raman shift k within the Si and C surfaces of the SiC substrate. max With minimum value k min The difference is 0.50cm －1 the following,

[0019] The Raman shift values ​​are obtained as follows: Raman shift values ​​corresponding to the transverse acoustic branch of the Raman spectrum are measured at 1 mm intervals on two straight lines passing through the center point of the Si surface and orthogonal to each other within the Si surface of the Si substrate; and Raman shift values ​​corresponding to the transverse acoustic branch of the Raman spectrum are measured at 1 mm intervals on two straight lines passing through the center point of the C surface of the Si C substrate.

[0020] [Option 2]

[0021] The SiC substrate according to Scheme 1 is characterized in that...

[0022] The maximum value k max With the minimum value k min The difference is 0.20cm －1 the following.

[0023] [Option 3]

[0024] The SiC substrate according to scheme 1 or 2 is characterized in that,

[0025] The N concentration of the biaxially oriented SiC layer is 5.0 × 10⁻⁶. 18 atoms / cm 3 above.

[0026] [Option 4]

[0027] The SiC substrate according to any one of claims 1 to 3 is characterized in that,

[0028] The rare earth element concentration of the biaxially oriented SiC layer is 1.0 × 10⁻⁶. 14 ~5.0×10 15 atoms / cm 3 .

[0029] [Option 5]

[0030] A SiC composite substrate, characterized in that it comprises:

[0031] SiC single crystal substrate; and

[0032] The SiC substrate described in any one of Schemes 1 to 4 on the SiC single crystal substrate. Attached Figure Description

[0033] Figure 1 This is a longitudinal cross-sectional view of the SiC composite substrate 10.

[0034] Figure 2 This is a manufacturing process diagram of the SiC composite substrate 10.

[0035] Figure 3 This is a conceptual diagram showing the configuration of an aerosol deposition (AD) device 50.

[0036] Figure 4 This is a top view of the SiC substrate 10 used to illustrate the method for measuring the warpage of the SiC substrate 10.

[0037] Figure 5 This is a simplified cross-sectional view of the SiC substrate 10 used to illustrate the method for measuring the warpage of the SiC substrate 10.

[0038] Figure 6 This is a simplified cross-sectional view of the SiC substrate 10 used to illustrate the method for measuring the warpage of the SiC substrate 10. Detailed Implementation

[0039] SiC substrate

[0040] The SiC substrate of the present invention has a biaxially oriented SiC layer. Regarding this SiC substrate, the maximum value of the Raman shift k within the planes of the Si and C surfaces is... max With minimum value k min The difference is 0.50cm －1The Raman shift values ​​are obtained as follows: In the Si plane of the SiC substrate, Raman shift values ​​corresponding to the transverse acoustic branch of the Raman spectrum are measured at 1mm intervals along two straight lines passing through the center point of the Si plane and orthogonal to each other. Similarly, in the C plane of the SiC substrate, Raman shift values ​​corresponding to the transverse acoustic branch of the Raman spectrum are measured at 1mm intervals along two straight lines passing through the center point of the C plane. It should be noted that the Si plane and C plane of the SiC substrate refer to the Si plane and C plane of the biaxially oriented SiC layer when the SiC substrate is composed of a biaxially oriented SiC layer, and the Si plane and C plane of the composite substrate when the SiC substrate is a composite substrate comprising a biaxially oriented SiC layer and a SiC single-crystal substrate (in which case, the surface of the biaxially oriented SiC layer may be the Si plane and the surface of the SiC single-crystal substrate may be the C plane, or the surface of the biaxially oriented SiC layer may be the C plane and the surface of the SiC single-crystal substrate may be the Si plane). Furthermore, the Raman shift value representing the peak corresponding to the transverse acoustic branch of the Raman spectrum typically refers to: representing FTA(2 / 4)E2 (wavenumber 200cm⁻¹). －1 The Raman shift value of the peak (near the [surface]). By controlling the Raman shift value of the peak in the SiC substrate that corresponds to the transverse acoustic branch of the Raman spectrum in this way, the warpage of the SiC substrate can be reduced.

[0041] As mentioned above, SiC substrates sometimes warp, and it is desirable to suppress this warping. Previous methods have not been sufficiently effective in suppressing warping, and further improvements are needed. In this regard, the present invention effectively eliminates this problem. Specifically, controlling the Raman shift value of the peak corresponding to the transverse acoustic branch of the Raman spectrum in the SiC substrate means reducing the in-plane distribution of nitrogen and the elastic strain distribution in the SiC substrate. By reducing the in-plane distribution of nitrogen and the elastic strain distribution in the SiC substrate, the warping of the SiC substrate can be reduced.

[0042] Regarding the SiC substrate of the present invention, when measuring the Raman shift values ​​representing the peaks corresponding to the transverse acoustic branches of the Raman spectrum within the planes of the Si and C surfaces, the maximum value k of the obtained Raman shift value is... max With minimum value k min The difference is 0.50cm －1 The preferred value is 0.20cm. －1Here, as described above, within the Si plane of the SiC substrate, Raman shift values ​​representing peaks corresponding to the transverse acoustic branch of the Raman spectrum are measured at 1 mm intervals along two straight lines passing through the center point of the Si plane and orthogonal to each other. Similarly, within the C plane of the SiC substrate, Raman shift values ​​representing peaks corresponding to the transverse acoustic branch of the Raman spectrum are measured at 1 mm intervals along two straight lines passing through the center point of the C plane and orthogonal to each other. The maximum value k of the Raman shift values ​​obtained in this way is... max With minimum value k min The difference can be considered as the difference between the maximum and minimum Raman shift values ​​when measured over the entire (all areas) of the SiC substrate.

[0043] When the SiC substrate or even the biaxially oriented SiC layer has an off-angle, the off-angle is preferably 0.1 to 12° relative to the

[0001] axis of the SiC substrate or even the biaxially oriented SiC layer, and more preferably 1 to 5°.

[0044] Examples of rare earth elements contained in biaxially oriented SiC layers include Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and combinations thereof. From the viewpoint of minimizing substrate warping, Y or Ce is preferred, and Y is more preferred.

[0045] The rare earth element concentration of the biaxially oriented SiC layer is preferably 1.0 × 10⁻⁶. 14 ~5.0×10 15 atoms / cm 3 More preferably 5.0×10 14 ~5.0×10 15 atoms / cm 3 More preferably 5.0×10 14 ~1.4×10 15 atoms / cm 3 .

[0046] The preferred N concentration for the biaxially oriented SiC layer is 1.0 × 10⁻⁶. 18 atoms / cm 3 The above, more preferably 5.0×10 18 atoms / cm 3 The above is further preferred to be 8.0×10 18 atoms / cm 3 The above. There is no specific upper limit for the N concentration, but it is preferably 1.0 × 10⁻⁶. 21 atoms / cm 3 Hereinafter, 1.0 × 10 is preferred. 20 atoms / cm3 Hereinafter, 1.0 × 10 is further preferred. 19 atoms / cm 3 the following.

[0047] The biaxially oriented SiC layer is preferably oriented along both the c-axis and a-axis. Furthermore, the SiC substrate is preferably composed of a biaxially oriented SiC layer. The biaxially oriented SiC layer can be oriented along both the c-axis and a-axis, and can be a single crystal, a polycrystalline SiC, or a mosaic crystal. Mosaic crystal refers to a collection of crystals without distinct grain boundaries, but whose orientation along one or both of the c-axis and a-axis is slightly different. There are no particular limitations on the method for evaluating the orientation; for example, known analytical methods such as EBSD (Electron Back Scatter Diffraction Patterns) and X-ray pole figures can be used. For example, when using EBSD, the inverse pole figure mapping of the surface (plate surface) or a cross-section orthogonal to the plate surface of the biaxially oriented SiC layer is measured. In the obtained inverse pole figure mapping, a biaxial orientation along the approximate normal direction and the approximate plate surface direction can be defined when the following four conditions (A) to (D) are met: (A) a specific orientation (first axis) along the approximate normal direction of the plate surface; (B) a specific orientation (second axis) along a direction orthogonal to the first axis and generally within the plate surface; (C) the tilt angle relative to the first axis is distributed within ±10°; and (D) the tilt angle relative to the second axis is distributed within ±10°. In other words, when the above four conditions are met, it is determined to be a biaxial orientation along the c-axis and the a-axis. For example, if the approximate normal direction of the plate surface is oriented along the c-axis, then the orientation along the specific orientation (e.g., the a-axis) orthogonal to the c-axis in the direction generally within the plate surface is sufficient. A biaxial orientation of the SiC layer along the approximate normal direction and the approximate in-plane direction is sufficient; however, it is preferable that the approximate normal direction is oriented along the c-axis. When the tilt angle distribution in the approximate normal direction and / or approximate in-plane direction is small, the mosaicism of the biaxially oriented SiC layer decreases, and the closer it is to zero, the closer it is to a single crystal. Therefore, from the viewpoint of the crystallinity of the biaxially oriented SiC layer, the tilt angle distribution is preferably small in both the approximate normal direction and the approximate in-plane direction, for example, more preferably ±5° or less, and even more preferably ±3° or less.

[0048] SiC composite substrate

[0049] The SiC substrate of the present invention is preferably in the form of a SiC composite substrate. That is, according to a preferred embodiment of the present invention, a SiC composite substrate comprising a SiC single-crystal substrate and the aforementioned SiC substrate on the SiC single-crystal substrate is provided. In this way, by having a SiC composite substrate having a controlled Raman shift value representing the peak corresponding to the transverse acoustic branch of the Raman spectrum, the warpage of the SiC composite substrate can be reduced.

[0050] Typically, the SiC single-crystal substrate is a layer composed of SiC single crystals and has a crystal growth surface. The polytype and deflection angle of the SiC single crystal are not particularly limited, but the polytype is preferably 4H or 6H, and the deflection angle is preferably 0.1 to 12° relative to the

[0001] axis of the single-crystal SiC. More preferably, the polytype is 4H, and the deflection angle is 1 to 5° relative to the

[0001] axis of the single-crystal SiC.

[0051] The SiC substrate of this invention can be a self-standing substrate with only a biaxially oriented SiC layer, or a SiC composite substrate with a SiC single-crystal substrate. Therefore, the biaxially oriented SiC layer can be ultimately separated from the SiC single-crystal substrate as needed. Separation of the SiC single-crystal substrate can be performed using known methods and is not particularly limited. Examples include: methods using a wire saw to separate the biaxially oriented SiC layer, methods using electrical discharge machining to separate the biaxially oriented SiC layer, and methods using a laser to separate the biaxially oriented SiC layer. Furthermore, in the case where the biaxially oriented SiC layer is epitaxially grown on the SiC single-crystal substrate, the biaxially oriented SiC layer can be placed on another support substrate after separating the SiC single-crystal substrate. The material of the other support substrate is not particularly limited; an ideal material can be selected from the viewpoint of material properties. Examples include: metal substrates such as Cu, ceramic substrates such as SiC and AlN, etc., from the viewpoint of thermal conductivity.

[0052] Manufacturing method of SiC composite substrate

[0053] The SiC composite substrate of the present invention can be readily manufactured as follows: (a) forming a predetermined orientation precursor layer on a SiC single-crystal substrate; (b) heat-treating the orientation precursor layer on the SiC single-crystal substrate to transform at least a portion of it near the SiC single-crystal substrate into a SiC substrate (biaxially oriented SiC layer); and (c) performing grinding, polishing, or other processing to expose the surface of the biaxially oriented SiC layer. However, the manufacturing method of the SiC composite substrate is not limited, as long as a SiC substrate in which the Raman shift value representing the peak corresponding to the transverse acoustic branch of the Raman spectrum is controlled is obtained. For example, a method that allows for a treatment that increases the nitrogen flow rate during heat treatment is preferred; in this case, a gas-phase method such as CVD or sublimation, or a liquid-phase method such as a solution method, can be used. The concentration of rare earth elements and / or nitrogen in the SiC substrate (biaxially oriented SiC layer) can be ideally controlled by adding rare earth compounds to the raw materials during the formation of the orientation precursor layer or by changing the heat treatment conditions (gas flow rate, heat treatment temperature, and holding time, etc.). Using such a manufacturing method, SiC substrates with well-controlled Raman shift values ​​representing peaks corresponding to the transverse acoustic branch of the Raman spectrum can be produced, thereby effectively reducing warpage of the SiC substrate and even SiC composite substrates using this SiC substrate.

[0054] The preferred manufacturing method for SiC composite substrates will be described below. Figure 1 It is a longitudinal section view of the SiC composite substrate 10 (a cross-sectional view of the SiC composite substrate 10 when it is longitudinally cut with the surface including the central axis of the SiC composite substrate 10). Figure 2 This is a manufacturing process diagram of the SiC composite substrate 10.

[0055] like Figure 1 As shown, the SiC composite substrate 10 of this embodiment includes: a SiC single crystal substrate 20, and a SiC substrate 30 on the SiC single crystal substrate.

[0056] (a) Formation process of orientation precursor layer

[0057] like Figure 2 As shown in (a), the orientation precursor layer 40 becomes a SiC substrate (biaxially oriented SiC layer) 30 through a heat treatment described later. In the formation process of the orientation precursor layer 40, the orientation precursor layer 40 is formed on the crystal growth surface of the SiC single crystal substrate 20.

[0058] The orientation precursor layer 40 can be formed using known methods. Examples of methods for forming the orientation precursor layer 40 include solid-state film formation methods such as AD (aerosol deposition) and HPPD (high-speed plasma particle deposition), sputtering, evaporation, sublimation, various CVD (chemical vapor deposition) methods, and liquid-state film formation methods such as solution growth. Alternatively, the orientation precursor layer 40 can be formed directly on the SiC single-crystal substrate 20. For CVD methods, examples include thermal CVD, plasma CVD, spray CVD, and MO (metal-organic) CVD. Another method is to use a polycrystalline material pre-fabricated by sublimation, various CVD methods, sintering, etc., as the orientation precursor layer 40, and place it on the SiC single-crystal substrate 20. Alternatively, a pre-fabricated shape of the orientation precursor layer 40 can be prepared and placed on the SiC single-crystal substrate 20. Such an orientation precursor layer 40 can be a cast body made by casting molding or a pressed powder made by pressure molding such as uniaxial pressing.

[0059] When forming the orientation precursor layer 40, it is preferable that the raw material for the orientation precursor layer 40 includes a rare earth compound. This allows for control of the concentration of the rare earth compound in the biaxially oriented SiC layer. The rare earth compound is not particularly limited, and examples include oxides, nitrides, carbides, and fluorides of at least one of the 17 rare earth elements mentioned above. Oxides of rare earth elements are preferred as the rare earth compound.

[0060] It should be noted that in methods for directly forming the orientation precursor layer 40 on a SiC single-crystal substrate 20, when using various CVD, sublimation, solution growth, etc., epitaxial growth sometimes occurs on the SiC single-crystal substrate 20 without the heat treatment process described later, forming a SiC substrate 30 in film form. However, the orientation precursor layer 40 is in an unoriented state during formation, i.e., it is amorphous or unoriented polycrystalline. It is preferable to orient it using a SiC single crystal as a seed crystal in a subsequent heat treatment process. This can effectively reduce crystallization defects reaching the surface of the SiC substrate 30. The reason for this is not yet clear, but it is believed that the rearrangement of the crystal structure of the temporarily formed solid phase orientation precursor layer using a SiC single crystal as a seed crystal is also effective in eliminating crystallization defects. Therefore, when using various CVD, sublimation, solution growth, etc., it is preferable to select a condition in which epitaxial growth does not occur during the formation process of the orientation precursor layer 40.

[0061] However, methods that directly form the alignment precursor layer 40 on the SiC single-crystal substrate 20 using the AD method or various CVD methods are preferred, as are methods that place a separately fabricated polycrystalline material on the SiC single-crystal substrate 20 using sublimation, various CVD methods, sintering, etc. By using these methods, the alignment precursor layer 40 can be formed in a relatively short time. The AD method does not require a high-vacuum process and has a relatively fast film formation speed, making it particularly preferred. In methods using pre-fabricated polycrystalline materials as the alignment precursor layer 40, the surface of the polycrystalline material needs to be sufficiently smoothed beforehand to improve the adhesion between the polycrystalline material and the SiC single-crystal substrate 20. Therefore, from a cost perspective, the method of directly forming the alignment precursor layer 40 is preferred. Additionally, the method of placing a pre-fabricated molded body on the SiC single-crystal substrate 20 is also preferred as a simple method; however, since the alignment precursor layer 40 is composed of powder, a sintering process is required in the heat treatment step described later. Either method can use known conditions; however, the following describes the method of directly forming the orientation precursor layer 40 on the SiC single crystal substrate 20 using the AD method or thermal CVD method, and the method of placing the pre-made molded body on the SiC single crystal substrate 20.

[0062] Algebraic deposition (AD) is a technique that forms a film by mixing microparticles or microparticle raw materials with a gas to form an aerosol, and then ejecting the aerosol at high speed from a nozzle to impact a substrate. It is characterized by its ability to form a film at room temperature. An example of a film-forming apparatus (AD apparatus) used in such an AD method is shown below. Figure 3 . Figure 3 The AD device 50 shown is configured as an apparatus used in the AD process for spraying raw material powder onto a substrate in an atmosphere with a pressure lower than atmospheric pressure. The AD device 50 includes: an aerosol generation unit 52 that generates an aerosol containing raw material components; and a film formation unit 60 that sprays the raw material powder onto a SiC single-crystal substrate 20 to form a film containing the raw material components. The aerosol generation unit 52 includes: an aerosol generation chamber 53 that collects the raw material powder and receives a carrier gas supplied from a gas cylinder (not shown) to generate an aerosol; a raw material supply pipe 54 that supplies the generated aerosol to the film formation unit 60; and a vibration exciter 55 that applies vibration to the aerosol generation chamber 53 and the aerosol therein at a vibration frequency of 10–100 Hz. The film-forming section 60 includes: a film-forming chamber 62 in which aerosol is sprayed onto the SiC single-crystal substrate 20; a substrate holder 64 disposed inside the film-forming chamber 62 and fixing the SiC single-crystal substrate 20; and an X-Y stage 63 that moves the substrate holder 64 in the X-axis-Y-axis direction. Additionally, the film-forming section 60 includes: a spray nozzle 66 with a slit 67 formed at its tip to spray aerosol onto the SiC single-crystal substrate 20; and a vacuum pump 68 that depressurizes the film-forming chamber 62. The spray nozzle 66 is mounted at the tip of the raw material supply pipe 54.

[0063] Regarding the Alignment and Coagulation (AD) method, it is known that there are cases where pores are generated in the film depending on the film formation conditions, or where the film becomes a pressed powder. For example, it is easily affected by factors such as the impact velocity of the raw material powder towards the substrate, the particle size of the raw material powder, the agglomeration state of the raw material powder in the aerosol, and the spraying rate per unit time. Regarding the impact velocity of the raw material powder towards the substrate, it is affected by factors such as the differential pressure between the film formation chamber 62 and the spray nozzle 66, and the opening area of ​​the spray nozzle. Therefore, in order to obtain a dense orientation precursor layer, it is necessary to appropriately control these factors.

[0064] In the thermal CVD method, commercially available film-forming apparatus or other known film-forming apparatus can be used. The feed gas is not particularly limited; silicon tetrachloride (SiCl4) gas or silane (SiH4) gas can be used as the Si supply source, and methane (CH4) gas or propane (C3H8) gas can be used as the C supply source. The film-forming temperature is preferably 1000–2200°C, more preferably 1100–2000°C, and even more preferably 1200–1900°C.

[0065] It is known that when a film is formed on a SiC single-crystal substrate 20 using thermal CVD, epitaxial growth sometimes occurs on the SiC single-crystal substrate 20 to form a SiC substrate 30. However, the orientation precursor layer 40 is in an unoriented state during its fabrication, i.e., it is amorphous or non-oriented polycrystalline. It is preferable to allow it to undergo rearrangement of crystals using the SiC single crystal as a seed crystal during the heat treatment process. For the formation of amorphous or polycrystalline layers on SiC single crystals using thermal CVD, it is known that the film formation temperature, the gas flow rates of the Si source and C source and their ratio, and the film formation pressure are all affected. The film formation temperature has a significant impact. From the viewpoint of forming amorphous or polycrystalline layers, the film formation temperature is preferably lower, preferably less than 1700°C, more preferably less than 1500°C, and even more preferably less than 1400°C. However, if the film formation temperature is too low, the film formation rate itself also decreases. Therefore, from the viewpoint of film formation rate, the film formation temperature is preferably higher.

[0066] When using a pre-made molded body as the orientation precursor layer 40, the raw material powder of the orientation precursor can be molded to produce it. For example, when using compression molding, the orientation precursor layer 40 is a compression molded body. The compression molded body can be produced by compression molding the raw material powder of the orientation precursor based on a known method, for example, by placing the raw material powder into a mold at a pressure of preferably 100 to 400 kgf / cm³. 2 More preferably 150–300 kgf / cm³ 2The material can be manufactured by pressing under pressure. Furthermore, the molding method is not particularly limited; besides pressing, casting, extrusion, casting, scraping, and any combination thereof can be used. For example, in the case of casting, it is preferable to add appropriate additives such as binders, plasticizers, dispersants, and dispersion media to the raw material powder to form a slurry, which is then extruded through a narrow, slit-shaped nozzle and formed into a sheet. The thickness of the sheet is not limited, but from an operational point of view, 5 to 500 μm is preferred. Additionally, if a thicker orientation precursor layer is required, multiple sheets can be stacked and used at the desired thickness. These sheets are then subjected to heat treatment on the SiC single-crystal substrate 20 to transform the portion near the SiC single-crystal substrate 20 into a SiC substrate 30. In this method, the sheet needs to be sintered in the heat treatment process described later. Preferably, the SiC substrate 30 is formed after sintering the sheet and then undergoing a process where it is integrated with the SiC single-crystal substrate 20 as a polycrystalline material. Without sintering the molded body, epitaxial growth using SiC single crystals as seed crystals may not occur sufficiently. Therefore, in addition to SiC raw materials, the molded body may also contain additives such as sintering aids.

[0067] (b) Heat treatment process

[0068] like Figure 2As shown in (b), in the heat treatment process, a laminate on which the orientation precursor layer 40 is stacked or placed on the SiC single crystal substrate 20 is heat-treated to generate the SiC substrate 30. Regarding the heat treatment method, epitaxial growth with the SiC single crystal substrate 20 as a seed crystal occurs; there are no particular limitations, and it can be carried out in a known heat treatment furnace such as a tubular furnace or a hot plate. Furthermore, not only can these atmospheric pressure (non-pressurized) heat treatments be used, but also pressurized heat treatments such as hot pressing and HIP, or combinations of atmospheric pressure heat treatment and pressurized heat treatment can be used. The atmosphere for heat treatment is preferably a nitrogen-containing inert gas atmosphere. The nitrogen-containing inert gas is preferably a mixture of nitrogen and argon, where the nitrogen flow rate is, for example, 0.5–15 L / min, and the argon flow rate is, for example, 3–100 L / min. The heat treatment temperature is preferably 1700–2700 °C. By increasing the temperature, the orientation precursor layer 40 can easily grow along the c-axis and a-axis orientation edges with the SiC single crystal substrate 20 as a seed crystal. Therefore, the heat treatment temperature is preferably 1700°C or higher, more preferably 1800°C or higher, even more preferably 1900°C or higher, and particularly preferably 2200°C or higher. On the other hand, if the temperature is too high, some of the SiC may disappear due to sublimation, or SiC may undergo plastic deformation and warp, resulting in undesirable conditions. Therefore, the heat treatment temperature is preferably 2700°C or lower, more preferably 2500°C or lower. However, the heat treatment conditions affect the rare earth element content in the biaxially oriented SiC layer, so it is preferable to appropriately control these conditions (e.g., heat treatment temperature and holding time). From this point of view, the heat treatment temperature is preferably 1900–2700°C, more preferably 2200–2600°C, and even more preferably 2400–2500°C. In addition, the holding time is preferably 2–30 hours, more preferably 4–20 hours. Furthermore, the heat treatment temperature and holding time are also related to the thickness of the SiC substrate 30 produced during epitaxial growth and can be adjusted appropriately.

[0069] However, when using a pre-formed molded body as the orientation precursor layer 40, it needs to be sintered in a heat treatment process, preferably by high-temperature atmospheric pressure sintering, hot pressing, HIP, or a combination thereof. For example, when using hot pressing, the surface pressure is preferably 50 kgf / cm². 2 The above, more preferably 100 kgf / cm 2 The above is further preferred to be 200 kgf / cm². 2There are no specific upper limits for the above. Similarly, regarding the firing temperature, as long as sintering and epitaxial growth occur, there are no particular limitations. However, the firing conditions affect the rare earth element content in the biaxially oriented SiC layer; therefore, it is preferable to appropriately control these conditions (e.g., firing temperature, holding time). From this perspective, the firing temperature is preferably 1700–2700°C. Furthermore, the holding time is preferably 2–18 hours. The atmosphere during firing can be selected from vacuum, nitrogen, inert gas, or a mixture of nitrogen and inert gas. Furthermore, firing can be carried out in multiple stages, and the firing temperature and total holding time are preferably within the above ranges. The SiC powder constituting the raw material can be composed of at least one of α-SiC and β-SiC, preferably β-SiC. The SiC powder is preferably composed of SiC particles having an average particle size of 0.01–100 μm. It should be noted that the average particle size refers to the average value obtained by observing the powder using a scanning electron microscope and measuring the maximum oriented diameter of 100 primary particles.

[0070] During the heat treatment process, the crystals within the orientation precursor layer 40 grow from the c-axis and a-axis orientation edges of the crystal growth surface of the SiC single crystal substrate 20. Therefore, the orientation precursor layer 40 gradually transforms into the SiC substrate 30 from the crystal growth surface. The SiC composite substrate with the generated SiC substrate 30 becomes a substrate where the Raman shift value representing the peak corresponding to the transverse acoustic branch of the Raman spectrum is controlled, and warpage is reduced. The exact mechanism for this is unknown; however, it is believed that, for example, increasing the nitrogen flow rate during heat treatment increases the nitrogen concentration and heat distribution uniformity, resulting in reduced warpage.

[0071] (c) Grinding and / or polishing processes

[0072] like Figure 2 As shown in (c), in the grinding process, the orientation precursor layer 40 remaining on the SiC substrate 30 after the heat treatment process is removed by grinding, exposing the surface of the SiC substrate 30, and the exposed surface is then ground and / or polished. Thus, the SiC composite substrate 10 is obtained.

[0073] It should be noted that the present invention is not limited to any of the above embodiments. Of course, it can be implemented in various ways as long as it falls within the technical scope of the present invention. For example, in the above embodiments, only one SiC substrate 30 is provided on the SiC single crystal substrate 20, but two or more layers can also be provided. Specifically, an orientation precursor layer 40 is stacked on the SiC substrate 30 of the SiC composite substrate 10. After heat treatment, grinding and / or polishing are performed sequentially, thereby allowing a second SiC substrate 30 to be provided on the SiC substrate 30.

[0074] Example

[0075] The invention will be further illustrated by the following examples.

[0076] Example 1

[0077] (1) Fabrication of orientation precursor layers

[0078] A raw material powder comprising 93.0 wt% commercially available fine β-SiC powder (volume basis D50 particle size: 0.7 μm) and 7.0 wt% yttrium oxide powder (volume basis D50 particle size: 0.1 μm) was prepared. The raw material powder was ball-milled in ethanol for 24 hours using SiC balls and then dried to obtain a mixed powder. As a SiC single crystal layer, a commercially available SiC single crystal substrate (n-type 4H-SiC, diameter 100 mm (4 inches), Si face, (0001) face, 4° offset angle, 0.35 mm thickness, non-orientation flat) was prepared. Figure 3 In the AD device 50 shown, mixed powder is sprayed onto a SiC single crystal substrate to form an AD film (orientation precursor layer).

[0079] The AD film formation conditions are as follows. First, He is used as the carrier gas, and film formation is performed using a ceramic nozzle with a slit formed with a long side of 5 mm and a short side of 0.4 mm. Regarding the nozzle scanning conditions, a repeated scan is performed: moving 105 mm forward in a direction perpendicular to the long side of the slit at a scanning speed of 0.5 mm / s, moving 5 mm along the long side of the slit, moving 105 mm back in a direction perpendicular to the long side of the slit, and moving 5 mm in the opposite direction to the initial position along the long side of the slit. At the moment when moving 105 mm from the initial position along the long side of the slit, a scan is performed in the opposite direction, returning to the initial position. This cycle is considered one cycle, and it is repeated 4000 times. The thickness of the AD film formed in this way is approximately 400 μm.

[0080] (2) Heat treatment of the orientation precursor layer

[0081] The SiC single-crystal substrate with the AD film forming the orientation precursor layer was removed from the AD device and annealed at 2400°C for 10 hours in a mixture of argon and nitrogen. That is, the orientation precursor layer was heat-treated to form a heat-treated layer. During this process, the argon flow rate was 4.5 L / min and the nitrogen flow rate was 0.5 L / min.

[0082] (3) Grinding

[0083] (3a) Surface grinding

[0084] The (0001) surface of the SiC single crystal substrate with the heat treatment layer is ground to a specified thickness using a grinding device (diamond wheel with a grit size of 1000 to 6000) and set as the target thickness and surface condition.

[0085] (3b) Backside grinding

[0086] The (000-1) surface of the SiC single crystal substrate with the heat treatment layer is ground to a specified thickness using a grinding device (diamond wheel with a grit size of 1000-6000) and set as the target thickness and surface condition.

[0087] (4) Grinding

[0088] The (0001) and (000-1) surfaces of a SiC single-crystal substrate with a heat-treated layer are ground with diamond abrasives, and then the (0001) surface is finished by chemical mechanical polishing (CMP) to achieve the target thickness and surface condition. This process yields the SiC substrate.

[0089] (5) Raman spectrophotometry

[0090] Raman shift values ​​corresponding to the transverse acoustic branch of the Raman spectrum were measured at 1 mm intervals along two orthogonal straight lines passing through the center point of the (0001) plane (i.e., the Si plane) of the obtained SiC substrate. Additionally, Raman shift values ​​corresponding to the transverse acoustic branch of the Raman spectrum were measured at 1 mm intervals along two orthogonal straight lines passing through the center point of the (000-1) plane (i.e., the C plane) of the obtained SiC substrate. The measurement conditions are shown below. The maximum value k among the Raman shift values ​​measured along these four straight lines was calculated. max With minimum value k min The difference (k) max -k min The results are shown in Table 1. It should be noted that the Raman shift value representing the peak corresponding to the transverse acoustic branch of the Raman spectrum refers to: representing FTA(2 / 4)E2 (wavenumber 200 cm⁻¹). －1 Raman shift values ​​of peaks (nearby).

[0091] <Raman Spectrophotometry Conditions>

[0092] • Measuring apparatus: LabRAM HR Evolution manufactured by Horiba Corporation

[0093] • Light source: Semiconductor-excited solid-state laser (DPSS, 532nm, 100mW)

[0094] • Diffraction grating: 1800gr / mm

[0095] Optical system: Backscatter configuration

[0096] • Objective lens: 100x

[0097] Laser irradiation time: 5 seconds

[0098] (6) Warpage determination

[0099] The degree of warpage, or warpage amount, was measured on the surface of the obtained SiC substrate using a high-precision laser measuring instrument (LT-9010M manufactured by Keyence Co., Ltd.). Figure 4 As shown, in the top view of the (0001) surface of the SiC substrate 10, two straight lines X and Y, passing through the centroid of the top view (point G) and orthogonal to each other, are drawn. Points A and B on line X, each 45 mm from point G, and points C and D on line Y, each 45 mm from point G, are determined. Next, as... Figure 5 As shown, a point P on curve AB is determined to be the longest among the line segments extending perpendicularly to line segment AB between any point A and point B on the surface of the SiC substrate 10. (For example, ...) Figure 5 In this context, any point on curve AB can be P, O, etc. However, the longest line segment extending from each point perpendicularly to line segment AB is the line segment extending from point P. Furthermore, the distance between line segment AB and point P is defined as the warping amount α. Additionally, as... Figure 6 As shown, a point R on curve CD is determined to be the longest among the line segments extending perpendicularly to line segment CD between any point C and point D on the surface of the SiC substrate 10. (For example, ...) Figure 6 In this method, any point on curve CD can be represented by point R, point O, etc. However, the longest line segment extending from each point perpendicularly to line segment CD is the line segment extending from point R. The distance between line segment CD and point R is defined as the warpage amount β. The average value of the warpage amounts α and β is defined as the warpage amount of the SiC substrate. The results are shown in Table 1. It should be noted that the warpage amount can be measured using the above method for both convex and concave warpage of the SiC substrate 10.

[0100] (7) Determination of the concentration of N and rare earth elements in the heat-treated layer

[0101] The center of the (0001) facet of the SiC substrate was designated as the evaluation site for dynamic secondary ion mass analysis (D-SIMS). For rare earth elements (Y in this example), a CAMECA IMS-7f was used, with O2 as the primary ion species. ＋The determination was performed at an accelerating voltage of 11.0 kV. For N, the analytical apparatus used was a CAMECA IMS-7f, with the primary ion species Cs. ＋ The measurement was performed using an accelerating voltage of 15.0 kV. This method was used to determine the concentration of rare earth elements, C. RE (atoms / cm) 3 ) and the concentration of N C N (atoms / cm) 3 The results are shown in Table 1.

[0102] (8) Evaluation of the biaxial orientation of the heat-treated layer

[0103] Using the EBSD (Electron Back Scatter Diffraction Patterns) method, the inverse pole figure mapping of the surface (plate surface) and the cross section orthogonal to the plate surface of the obtained heat-treated layer was measured under the conditions shown below. The results showed that the tilt angle distribution was less than 0.01° in both the approximate normal direction and the approximate plate surface direction. Therefore, it was determined that the heat-treated layer was a biaxially oriented SiC layer with the same tilt angle as the SiC single crystal substrate.

[0104] <EBSD Measurement Conditions>

[0105] • Measurement apparatus: SEM (Hitachi High Technology Co., Ltd. SU-5000) equipped with electron backscatter diffraction (EBSD) device (Oxford Instruments Nordlys Nano)

[0106] Accelerating voltage: 15kV

[0107] • Spot intensity: 70

[0108] • Working distance: 22.5mm

[0109] • Step size: 0.5μm

[0110] • Sample tilt angle: 70°

[0111] • Measurement procedure: Aztec (version 3.3)

[0112] Example 2

[0113] In (2) above, the flow rate of argon was 45 L / min and the flow rate of nitrogen was 5 L / min. Otherwise, the SiC substrate was fabricated and evaluated in the same manner as in Example 1. It was confirmed that the obtained heat-treated layer was a biaxially oriented SiC layer. The results are shown in Table 1.

[0114] Example 3

[0115] In (2) above, the flow rate of argon was 90 L / min and the flow rate of nitrogen was 10 L / min. Otherwise, the SiC substrate was fabricated and evaluated in the same manner as in Example 1. It was confirmed that the obtained heat-treated layer was a biaxially oriented SiC layer. The results are shown in Table 1.

[0116] Example 4

[0117] In step (2) above, the flow rate of argon was 5 L / min and the flow rate of nitrogen was 0.5 L / min. Otherwise, the SiC substrate was fabricated and evaluated in the same manner as in Example 1. It was confirmed that the obtained heat-treated layer was a biaxially oriented SiC layer. The results are shown in Table 1.

[0118] Example 5

[0119] In (1) above, a raw material powder containing 91.7 wt% commercially available fine β-SiC powder (volume basis D50 particle size: 0.7 μm) and 8.3 wt% yttrium oxide powder (volume basis D50 particle size: 0.1 μm) was used. Otherwise, the SiC substrate was fabricated and evaluated in the same manner as in Example 1. It was confirmed that the obtained heat-treated layer was a biaxially oriented SiC layer. The results are shown in Table 1.

[0120] example 6

[0121] In (1) above, a raw material powder containing 95.2 wt% commercially available fine β-SiC powder (volume basis D50 particle size: 0.7 μm) and 4.8 wt% yttrium oxide powder (volume basis D50 particle size: 0.1 μm) was used. Otherwise, the SiC substrate was fabricated and evaluated in the same manner as in Example 1. It was confirmed that the obtained heat-treated layer was a biaxially oriented SiC layer. The results are shown in Table 1.

[0122] Example 7

[0123] In (1) above, a raw material powder containing 93.0 wt% commercially available fine β-SiC powder (volume basis D50 particle size: 0.7 μm) and 7.0 wt% yttrium oxide powder (volume basis D50 particle size: 0.1 μm) was used. Otherwise, the SiC substrate was fabricated and evaluated in the same manner as in Example 1. It was confirmed that the obtained heat-treated layer was a biaxially oriented SiC layer. The results are shown in Table 1.

[0124] Example 8 (Compare)

[0125] In (2) above, the flow rate of argon was 2.7 L / min and the flow rate of nitrogen was 0.3 L / min. Otherwise, the SiC substrate was fabricated and evaluated in the same manner as in Example 1. It was confirmed that the obtained heat-treated layer was a biaxially oriented SiC layer. The results are shown in Table 1.

[0126] Example 9 (Compare)

[0127] In step (2) above, the flow rate of argon was 0.9 L / min and the flow rate of nitrogen was 0.1 L / min. Otherwise, the SiC substrate was fabricated and evaluated in the same manner as in Example 1. It was confirmed that the obtained heat-treated layer was a biaxially oriented SiC layer. The results are shown in Table 1.

[0128] [Table 1]

[0129]

Claims

1. A SiC substrate having a biaxially oriented SiC layer, The SiC substrate is characterized in that... The maximum value of the Raman shift k within the Si and C surfaces of the SiC substrate. max With minimum value k min The difference is 0.50cm －1 the following, The Raman shift values ​​are obtained as follows: Raman shift values ​​corresponding to the transverse acoustic branch of the Raman spectrum are measured at 1 mm intervals on two straight lines passing through the center point of the Si surface and orthogonal to each other within the Si surface of the Si substrate; and Raman shift values ​​corresponding to the transverse acoustic branch of the Raman spectrum are measured at 1 mm intervals on two straight lines passing through the center point of the C surface of the Si C substrate.

2. The SiC substrate according to claim 1, characterized in that, The maximum value k max With the minimum value k min The difference is 0.20cm －1 the following.

3. The SiC substrate according to claim 1 or 2, characterized in that, The N concentration of the biaxially oriented SiC layer is 5.0 × 10⁻⁶. 18 atoms / cm 3 above.

4. The SiC substrate according to claim 1 or 2, characterized in that, The rare earth element concentration of the biaxially oriented SiC layer is 1.0 × 10⁻⁶. 14 ~5.0×10 15 atoms / cm 3 .

5. A SiC composite substrate, characterized in that, have: SiC single crystal substrate; and The SiC substrate of claim 1 or 2 is described on the SiC single crystal substrate.

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