JP7628960B2 - SiC substrate and its manufacturing method - Google Patents

Description

The present invention relates to a SiC substrate and a method for manufacturing the same.

Silicon carbide (SiC) has been attracting attention as a wide band gap material capable of controlling high voltage and high power with low loss. Representative dislocations present in SiC single crystals include basal plane dislocations, threading screw dislocations, threading edge dislocations, etc., and the total dislocation density of currently commercially available SiC single crystal substrates is said to be approximately 10 ³ to 10 ⁴ cm ^-2 . In recent years, there have been known examples of fabricating SiC single crystal substrates with significantly low crystal defect density by using a solution method (also called liquid phase growth method) (for example, Patent Document 1). Crystal growth by the solution method is a method of forming a SiC layer on a SiC single crystal serving as a seed crystal, and is characterized in that crystal defects contained in the seed crystal are reduced as the crystal grows.

JP 2014-43369 A

However, in the solution method, in order to increase the driving force of crystal growth, it is necessary to create a temperature difference between the seed crystal and the Si melt. For this reason, the general method is to place the back side of the seed crystal on a sample holder, cool the seed crystal by extracting heat from the sample holder, and create a temperature difference with the Si melt. Therefore, crystal growth progresses only on the growth surface (one side) of the SiC single crystal (seed crystal) containing crystal defects and the solution growth layer with few crystal defects. In this film formation state, although there are few penetrating defects that reach the surface of the SiC layer, there is a difference in density of crystal defects in the thickness direction, which causes an internal stress distribution and causes the crystal to warp.

The present invention has been made to solve these problems, and its main objective is to provide a SiC substrate with minimal warping.

The SiC substrate of the present invention is
A first surface; and
a second surface opposite to the first surface;
a central surface that is equidistant from the first surface in a thickness direction and from the second surface in a thickness direction;
A SiC substrate comprising:
a crystal defect density at the first surface and the second surface is less than a crystal defect density at the central surface;
It is something.

In this SiC substrate, the crystal defect density on the first surface and the second surface is less than the crystal defect density on the central surface. Therefore, the SiC substrate of the present invention has less warping than a SiC substrate having the same crystal defect density on the second surface and the central surface, but a lower crystal defect density on the first surface. The amount of warping is not particularly limited, but is preferably 10 μm or less, for example.

In the SiC substrate of the present invention, the crystal defect density in the first surface and the second surface is preferably 1/100 or less of the crystal defect density in the central plane. In this way, the crystal defect density in the first surface and the second surface is sufficiently small, making it suitable for stacking a functional layer on the surface to fabricate a device (e.g., SiC-MOSFET, SiC-SBD, etc.).

In the SiC substrate of the present invention, the difference between the crystal defect density on the first surface and the crystal defect density on the second surface is preferably less than 10%. This reduces the warping of the SiC substrate.

The SiC substrate of the present invention comprises a central layer, a first layer laminated on one side of the central layer, and a second layer laminated on the other side of the central layer, the first surface being a surface of the first layer, the second surface being a surface of the second layer, and the central surface being a surface contained within the central layer.

The method for producing a SiC substrate of the present invention includes the steps of:
(a) forming a SiC oriented precursor layer on both sides of a SiC seed crystal substrate;
(b) simultaneously heat-treating both of the SiC oriented precursor layers to grow crystals in both of the SiC oriented precursor layers while orienting them from the crystal growth surface of the SiC seed crystal substrate;
It includes.

This SiC substrate manufacturing method is suitable for manufacturing the SiC substrate described above.

FIG. 2 is a longitudinal sectional view of a SiC substrate 10. 1A to 1C are manufacturing process diagrams of a SiC substrate 10. FIG. 2 is a conceptual diagram of an AD device 50. 3A and 3B are explanatory diagrams illustrating a method for measuring the amount of warpage of a SiC substrate 10. 3A and 3B are explanatory diagrams illustrating a method for measuring the amount of warpage of a SiC substrate 10. 1 is a conceptual diagram of a single crystal growth apparatus 70. 4A to 4C are manufacturing process diagrams of a SiC substrate 80.

A preferred embodiment of the present invention will be described below with reference to the drawings. Figure 1 is a longitudinal cross-sectional view of a SiC substrate 10 (a cross-sectional view of the SiC substrate 10 cut along a plane including the central axis of the SiC substrate 10), and Figure 2 is a manufacturing process diagram of the SiC substrate 10.

As shown in FIG. 1, the SiC substrate 10 of this embodiment has a central layer 20, a first layer 21, and a second layer 22.

The central layer 20 is a layer made of SiC single crystal, and has crystal growth surfaces on both sides. The polytype and off-angle of the SiC single crystal are not particularly limited, but the polytype is preferably 4H or 6H, and the off-angle is preferably 0.1 to 12° from the [0001] axis of the single crystal SiC. It is more preferable that the polytype is 4H, and the off-angle is 1 to 5° from the [0001] axis of the single crystal SiC.

The first layer 21 is provided on one crystal growth surface of the central layer 20, and the second layer 22 is provided on the other crystal growth surface of the central layer 20. The first layer 21 and the second layer 22 are biaxially oriented SiC layers, in which SiC is oriented in both the c-axis direction and the a-axis direction. The first layer 21 and the second layer 22 are preferably epitaxially grown layers using the central layer 20 as a seed crystal. The biaxially oriented SiC layer may be a SiC single crystal, a SiC polycrystal, or a mosaic crystal, as long as it is oriented in the two axial directions of the c-axis and the a-axis. A mosaic crystal is a collection of crystals that do not have clear grain boundaries, but whose crystal orientations are slightly different in one or both of the c-axis and the a-axis. The method for evaluating the orientation is not particularly limited, and known analytical methods such as EBSD (Electron Back Scatter Diffraction Patterns) method and X-ray pole figures can be used. For example, when the EBSD method is used, inverse pole figure mapping of the surface (plate surface) of the biaxially oriented SiC layer or a cross section perpendicular to the plate surface is measured. In the obtained inverse pole figure mapping, when the following four conditions are satisfied: (A) orientation in a specific direction (first axis) approximately normal to the plate surface, (B) orientation in a specific direction (second axis) approximately in the plate surface direction perpendicular to the first axis, (C) the inclination angle from the first axis is distributed within ±10°, and (D) the inclination angle from the second axis is distributed within ±10°, it can be defined as being oriented in two axes approximately normal to the plate surface direction. In other words, when the above four conditions are satisfied, it is determined that the biaxial orientation is in the c-axis and a-axis. For example, when the approximately normal direction of the plate surface is oriented to the c-axis, the approximately in-plane direction may be oriented in a specific direction (e.g., the a-axis) perpendicular to the c-axis. The biaxially oriented SiC layer may be oriented in two axes, the approximately normal direction and the approximately in-plane direction, but it is preferable that the approximately normal direction is oriented to the c-axis. The smaller the inclination angle distribution in the approximately normal direction and/or the approximately in-plane direction, the smaller the mosaic property of the biaxially oriented SiC layer becomes, and the closer it is to zero, the closer it becomes to a single crystal. Therefore, from the viewpoint of the crystallinity of the biaxially oriented SiC layer, it is preferable that the inclination angle distribution is small in both the approximately normal direction and the approximately in-plane direction, for example, ±5° or less, and more preferably ±3° or less.

The first layer 21 has a first surface 21a. The first surface 21a is the outer surface of the first layer 21 (the surface opposite to the surface in contact with the central layer 20). The second layer 22 has a second surface 22a. The second surface 22a is the outer surface of the second layer 22 (the surface opposite to the surface in contact with the central layer 20). The central layer 20 has a central surface 20a inside. The central surface 20a is a surface in which the distance L1 in the thickness direction from the first surface 21a and the distance L2 in the thickness direction from the second surface 22a are equal (i.e., L1 = L2). The crystal defect density on the first surface 21a and the second surface 22a is less than the crystal defect density on the central surface 20a. The SiC substrate 10 has less warping than a comparative SiC substrate in which the crystal defect density on the second surface 22a and the central surface 20a is equal and the crystal defect density on the first surface 21a is less. The amount of warpage of the SiC substrate 10 is not particularly limited, but is preferably, for example, 10 μm or less, and more preferably 5 μm or less. The first layer 21 and the second layer 22 preferably have reduced crystal defects therein and/or at the interface with the central layer 20. In this way, the crystal defect density at the first surface 21a and the second surface 22a can be reduced below the crystal defect density at the central surface 20a.

The crystal defect density at the first surface 21a and the second surface 22a is preferably 1/100 or less, and more preferably 1/1000 or less, of the crystal defect density at the central surface 20a. If it is 1/100 or less, the crystal defect density at the first surface 21a and the second surface 22a is sufficiently small, so that it is suitable for stacking a functional layer on the first surface 21a or the second surface 22a to fabricate a device. If it is 1/1000 or less, it is even more suitable. The difference between the crystal defect density at the first surface 21a and the crystal defect density at the second surface 22a is preferably less than 10%, and more preferably less than 5%.

The crystal defect density in the first surface 21a and the second surface 22a is typically 10 ³ /cm ² or less, preferably 10 ² /cm ² or less, and more preferably 10 ¹ /cm ² or less. The crystal defect density is measured by etch pit evaluation using a known KOH melt etching. The crystal defect density in the central surface 20a can be calculated by performing the same evaluation as above after exposing the central surface 20a from the first surface 21a or the second surface 22a by grinding and polishing. In this specification, the defect includes threading screw dislocations (TSDs), basal plane dislocations (BPDs), and micropipes (MPs). Threading means that the dislocation line is approximately parallel to the [0001] axis of the hexagonal crystal system. Basal means that the dislocation line is in the basal hexagonal crystal system (0001) plane. A micropipe is a hollow core TSD with a Burgers vector greater than 3c. Here, c is the lattice constant.

The polytype and off-angle of the first surface 21a and/or the second surface 22a are not particularly limited, but the polytype is preferably 4H or 6H, and the off-angle is preferably 0.1 to 12° from the (0001) axis of the single crystal SiC.

It is preferable to form the first layer 21 and the second layer 22 simultaneously. If only one of the first layer 21 and the second layer 22 is formed, a distribution of crystal defect density occurs in the thickness direction, causing warping at that point. If the other layer is formed in a warped state, a homogeneous film cannot be obtained, and there is a risk that the crystal defect density will not be sufficiently reduced.

From the viewpoint of imparting electrical conductivity in the thickness direction to the SiC substrate 10, the central layer 20, the first layer 21, and the second layer 22 are preferably layers with low resistivity, typically 20 mΩcm or less. As a layer with low resistivity, a layer having electrical conductivity, for example, a layer made of nitrogen-doped n-type SiC, is preferable. When a layer having electrical conductivity is adopted as the central layer 20, the first layer 21, and the second layer 22, the SiC substrate 10 has electrical conductivity in the thickness direction and can be used as a substrate for a vertical device (for example, a power device). Depending on the application, the central layer 20, the first layer 21, and the second layer 22 may be p-type SiC. As the p-type SiC, for example, p-type SiC doped with Al and/or B is preferable.

From the viewpoint of imparting insulation in the thickness direction to the SiC substrate 10, the central layer 20, the first layer 21, and the second layer 22 are preferably layers having a high resistivity, typically 1×10 ⁷ Ωcm or more. As a layer having a high resistivity, a layer having insulating properties, such as a SiC layer containing no doping element or a SiC layer containing both an n-type dopant and a p-type dopant, is preferable. When insulating layers are used as the central layer 20, the first layer 21, and the second layer 22, the SiC substrate 10 can be used as a base substrate for a lateral device (for example, a high-frequency power device in which a GaN or AlGaN layer is formed on a SiC substrate) because of its insulating properties.

Next, a method for manufacturing the SiC substrate 10 will be described. Specifically, the method includes (a) a process for forming an oriented precursor layer, (b) a heat treatment process, and (c) a grinding process. The first and second oriented precursor layers 31 and 32 become the first layer 21 and the second layer 22, which are biaxially oriented SiC layers, by a heat treatment described later, and may contain components such as dopants. Below, these processes will be described in order using FIG. 2.

(a) Formation of an alignment precursor layer (see FIG. 2(a))
In the step of forming the orientation precursor layer, a SiC seed crystal substrate 30 (here, a SiC single crystal layer) that will eventually become the central layer 20 is prepared, and a first orientation precursor layer 31 is formed on one crystal growth surface of the SiC seed crystal substrate 30, and a second orientation precursor layer 32 is formed on the other crystal growth surface to obtain a laminate 33. As the SiC single crystal layer, it is preferable to use a 4H or 6H polytype. In addition, as the crystal growth surface of the SiC single crystal layer, a surface having an off angle of 0.1 to 12° from the SiC [0001] axis is preferable. The off angle is more preferably 1 to 5°.

The first and second orientation precursor layers 31, 32 can be formed by known methods. The first and second orientation precursor layers 31, 32 can be formed by solid-phase deposition methods such as AD (aerosol deposition) and HPPD (supersonic plasma particle deposition), vapor-phase deposition methods such as sputtering, vapor deposition, sublimation, and various CVD (chemical vapor deposition) methods, and liquid-phase deposition methods such as solution growth, and can be formed by forming the orientation precursor layer directly on the SiC single crystal substrate. As the CVD method, for example, thermal CVD, plasma CVD, mist CVD, and MO (metal organic) CVD can be used. In addition, a method in which a polycrystalline body prepared in advance by sublimation, various CVD, sintering, or the like is used as the first and second orientation precursor layers 31, 32 and placed on the SiC seed crystal substrate 30 can also be used. Alternatively, a method may be used in which a molded body of the first and second orientation precursor layers 31, 32 is prepared in advance and the molded body is placed on the SiC seed crystal substrate 30. Such first and second orientation precursor layers 31, 32 may be a tape molded body prepared by tape casting, or a green compact prepared by pressure molding such as a uniaxial press. A solid-phase film formation method is preferable as a method for forming the first and second orientation precursor layers 31, 32. For example, the first layer 21 and the second layer 22 can be simultaneously formed by sequentially forming the first and second orientation precursor layers 31, 32 on both sides of the SiC seed crystal substrate 30 by a solid-phase film formation method and then performing a heat treatment.

These first and second alignment precursor layers 31, 32 may contain components that control the electrical properties. For example, when forming an n-type first layer 21, the first alignment precursor layer 31 may contain nitrogen. When forming a p-type first layer 21, the first alignment precursor layer 31 may contain B and/or Al. In addition to nitrogen, the first alignment precursor layer 31 may contain B and/or Al to impart insulating properties to the first layer 21. The same applies to the second alignment precursor layer 32.

In addition, when various CVD methods, sublimation methods, solution growth methods, etc. are used in the method of forming the first and second orientation precursor layers 31, 32 directly on the SiC seed crystal substrate 30, epitaxial growth may occur on the SiC seed crystal substrate 30 without going through the heat treatment process described below, and the first layer 21 and the second layer 22 may be formed. However, the first and second orientation precursor layers 31, 32 are in an unoriented state, that is, in an amorphous or unoriented polycrystalline state, when formed, and it is preferable to orient them using a SiC single crystal as a seed in the subsequent heat treatment process. In this way, crystal defects that reach the first surface 21a and the second surface 22a can be effectively reduced. Although the reason for this is unclear, it is believed that the rearrangement of the crystal structure of the solid phase first and second orientation precursor layers 31, 32 once formed using the SiC single crystal as a seed may also be effective in eliminating crystal defects. Therefore, when using various CVD methods, sublimation methods, solution growth methods, and the like, it is preferable to select conditions under which epitaxial growth does not occur in the process of forming the first and second alignment precursor layers 31 and 32 .

However, the method of forming the first and second orientation precursor layers 31, 32 directly on the SiC seed crystal substrate 30 by the AD method or various CVD methods, or the method of placing a polycrystalline body separately prepared by the sublimation method, various CVD methods, or sintering on the SiC seed crystal substrate 30 is preferable. By using these methods, it is possible to form the first and second orientation precursor layers 31, 32 in a relatively short time. The AD method is particularly preferable because it does not require a high vacuum process and the film formation speed is relatively fast. In the method of using a polycrystalline body prepared in advance as the first and second orientation precursor layers 31, 32, it is necessary to take measures such as making the surface of the polycrystalline body sufficiently smooth in order to increase the adhesion between the polycrystalline body and the SiC seed crystal substrate 30. Therefore, from the viewpoint of cost, the method of directly forming the first and second orientation precursor layers 31, 32 is preferable. In addition, a method of placing a previously prepared molded body on the SiC seed crystal substrate 30 is also preferable as a simple method, but since the first and second orientation precursor layers 31, 32 are composed of powder, a sintering process is required in the heat treatment step described below. Although any of the methods can use known conditions, the following describes a method of forming the first and second orientation precursor layers 31, 32 directly on the SiC seed crystal substrate 30 by the AD method or thermal CVD method, and a method of placing a previously prepared molded body on the SiC seed crystal substrate 30.

The AD method is a technology in which fine particles or fine particle raw material is mixed with a gas to form an aerosol, and this aerosol is sprayed at high speed from a nozzle to collide with a substrate to form a coating, and has the characteristic that the coating can be formed at room temperature. An example of a film formation device (aerosol deposition (AD) device) used in such an AD method is shown in FIG. 3. The AD device 50 shown in FIG. 3 is configured as a device used in the AD method in which raw material powder is sprayed onto a substrate under an atmosphere with a pressure lower than atmospheric pressure. This AD device 50 includes an aerosol generation unit 52 that generates an aerosol of raw material powder containing raw material components, and a film formation unit 60 that sprays the raw material powder onto a SiC seed crystal substrate 30 to form a film containing the raw material components. The aerosol generating section 52 includes an aerosol generating chamber 53 that contains raw material powder and generates an aerosol by receiving a carrier gas from a gas cylinder (not shown), a raw material supply pipe 54 that supplies the generated aerosol to the film forming section 60, and a vibrator 55 that applies vibrations at a frequency of 10 to 100 Hz to the aerosol generating chamber 53 and the aerosol therein. The film forming section 60 includes a film forming chamber 62 that sprays the aerosol onto the SiC seed crystal substrate 30, a substrate holder 64 that is disposed inside the film forming chamber 62 and fixes the SiC seed crystal substrate 30, and an XY stage 63 that moves the substrate holder 64 in the X-axis and Y-axis directions. The film forming section 60 also includes an injection nozzle 66 that has a slit 67 formed at its tip and sprays the aerosol onto the SiC seed crystal substrate 30, and a vacuum pump 68 that reduces the pressure in the film forming chamber 62. The injection nozzle 66 is attached to the tip of the raw material supply pipe 54. First, the first orientation precursor layer 31 is formed on the surface of the SiC seed crystal substrate 30 opposite to the surface that abuts against the substrate holder 64. Next, the SiC seed crystal substrate 30 is removed from the substrate holder 64, and the first orientation precursor layer 31 side of the SiC seed crystal substrate 30 is abutted against the substrate holder 64 and fixed. Then, the second orientation precursor layer 32 is formed on the other surface of the SiC seed crystal substrate 30.

It is known that the AD method may cause pores in the film or the film may become a compact depending on the film formation conditions. For example, it is easily affected by the collision speed of the raw material powder with the substrate, the particle size of the raw material powder, the agglomeration state of the raw material powder in the aerosol, and the amount sprayed per unit time. The collision speed of the raw material powder with the substrate is affected by the pressure difference between the film formation chamber 62 and the spray nozzle 66, the opening area of the spray nozzle, and other factors. For this reason, in order to obtain a dense oriented precursor layer, it is necessary to appropriately control these factors.

In the thermal CVD method, a known deposition apparatus such as a commercially available one can be used. The source gas is not particularly limited, but silicon tetrachloride (SiCl ₄ ) gas or silane (SiH ₄ ) gas can be used as a Si source, and methane (CH ₄ ) gas or propane (C ₃ H ₈ ) gas can be used as a C source. The deposition temperature is preferably 1000 to 2200°C, more preferably 1100 to 2000°C, and more preferably 1200 to 1900°C. In the thermal CVD method, the first orientation precursor layer 31 is first deposited on one surface of the SiC seed crystal substrate 30, and then the second orientation precursor layer 32 is deposited on the other surface of the SiC seed crystal substrate 30.

It is known that when a film is formed on a SiC seed crystal substrate 30 using a thermal CVD method, epitaxial growth may occur on the SiC seed crystal substrate 30, and the first layer 21 and the second layer 22 may be formed instead of the first and second oriented precursor layers 31 and 32. However, the first and second oriented precursor layers 31 and 32 are not oriented when they are produced, that is, they are amorphous or unoriented polycrystalline, and it is preferable to use a SiC single crystal as a seed crystal to cause crystal rearrangement during the heat treatment process. It is known that the film formation temperature, the gas flow rate of the Si source and the C source and their ratio, the film formation pressure, etc. have an effect on the formation of an amorphous or polycrystalline layer on a SiC single crystal using a thermal CVD method. The film formation temperature has a large effect, and from the viewpoint of forming an amorphous or polycrystalline layer, a lower film formation temperature is preferable, preferably less than 1700°C, more preferably 1500°C or less, and particularly preferably 1400°C or less. However, if the film formation temperature is too low, the film formation rate itself also decreases, and therefore, from the viewpoint of the film formation rate, a high film formation temperature is preferable.

When a molded body prepared in advance is used as the first and second alignment precursor layers 31 and 32, the first and second alignment precursor layers 31 and 32 can be prepared by molding the raw material powder of the first and second alignment precursor layers 31 and 32. For example, when press molding is used, the first and second alignment precursor layers 31 and 32 are press molded bodies. The press molded body can be prepared by press molding the raw material powder of the alignment precursor based on a known method, for example, by putting the raw material powder into a mold and pressing it at a pressure of preferably 100 to 400 kgf/cm ² , more preferably 150 to 300 kgf/cm ^2. In addition, there is no particular limitation on the molding method, and in addition to press molding, tape molding, extrusion molding, casting molding, doctor blade method, and any combination thereof can be used. For example, when tape molding is used, it is preferable to appropriately add additives such as binders, plasticizers, dispersants, and dispersion media to the raw material powder to make a slurry, and then pass the slurry through a thin slit-shaped discharge port to discharge and mold it into a sheet. There is no limit to the thickness of the molded body formed into a sheet shape, but from the viewpoint of handling, it is preferable that it is 5 to 500 μm. In addition, if a thick oriented precursor layer is required, a number of these sheet molded bodies may be stacked and used to obtain the desired thickness. These molded bodies (first and second oriented precursor layers 31, 32) are arranged on both the front and back sides of the SiC seed crystal substrate 30, and then heat-treated in a heat treatment process described below, so that the portion of the molded body near the central layer 20 becomes a biaxially oriented SiC layer (first layer 21 and second layer 22). In the heat treatment process, it is preferable to form the biaxially oriented SiC layer after the molded body is sintered and integrated with the central layer 20 as a polycrystalline body. If the molded body does not go through a sintered state, epitaxial growth using the SiC single crystal as a seed may not occur sufficiently. For this reason, the molded body may contain additives such as sintering aids in addition to the SiC raw material.

(b) Heat treatment step (see FIG. 2(b))
In the heat treatment step, the laminate 33 in which the first and second orientation precursor layers 31, 32 are laminated or placed on both the front and back sides of the SiC seed crystal substrate 30 is heat treated to generate the first layer 21 and the second layer 22, which are biaxially oriented SiC layers. That is, the first and second orientation precursor layers 31, 32 are heat treated simultaneously. In this way, the heat treatment body 34 is obtained. The heat treatment method is not particularly limited as long as epitaxial growth occurs with the central layer 20 as a seed, and can be performed in a known heat treatment furnace such as a tubular furnace or a hot plate. In addition to these normal pressure (pressless) heat treatments, pressurized heat treatments such as hot pressing and HIP, or a combination of normal pressure heat treatment and pressurized heat treatment can also be used. The heat treatment atmosphere can be selected from vacuum, nitrogen, and inert gas atmospheres. The heat treatment temperature is preferably 1700 to 2700°C. By increasing the temperature, the first and second orientation precursor layers 31, 32 tend to grow while being oriented to the c-axis and a-axis with the central layer 20 as a seed crystal. Therefore, the temperature is preferably 1700°C or higher, more preferably 1850°C or higher, even more preferably 2000°C or higher, and particularly preferably 2200°C or higher. On the other hand, if the temperature is excessively high, a part of the SiC may be lost due to sublimation, or the SiC may be plastically deformed, resulting in defects such as warping. Therefore, the temperature is preferably 2700°C or lower, more preferably 2500°C or lower. The heat treatment temperature and holding time are related to the thickness of the biaxially oriented SiC layer generated by epitaxial growth, and can be adjusted appropriately.

However, when a molded body prepared in advance is used as the first and second orientation precursor layers 31 and 32, it is necessary to sinter during the heat treatment, and high-temperature atmospheric sintering, hot pressing, HIP, or a combination thereof is suitable. For example, when hot pressing is used, the surface pressure is preferably 50 kgf/cm ² or more, more preferably 100 kgf/cm ² or more, particularly preferably 200 kgf/cm ² or more, and there is no particular upper limit. In addition, the sintering temperature is not particularly limited as long as sintering and epitaxial growth occur. It is preferably 1700°C or more, more preferably 1800°C or more, even more preferably 2000°C or more, and particularly preferably 2200°C or more. The atmosphere during sintering can be selected from vacuum, nitrogen, inert gas atmosphere, or a mixed gas of nitrogen and inert gas. The SiC powder used as the raw material may be either α-SiC or β-SiC. The SiC powder is preferably composed of SiC particles having an average particle size of 0.01 to 5 μm. The average particle size refers to the average value of the maximum diameters in a fixed direction of 100 primary particles measured by observing the powder with a scanning electron microscope.

In the heat treatment process, the crystals in the first and second oriented precursor layers 31 and 32 grow from the crystal growth surface of the central layer 20 while being oriented to the c-axis and a-axis. Therefore, the first and second oriented precursor layers 31 and 32 gradually change from the crystal growth surface into a biaxially oriented SiC layer. The surface of the generated biaxially oriented SiC layer (the surface of the first layer 21 opposite the central layer 20 and the surface of the second layer 22 opposite the central layer 20) has a defect density of 1×10 ¹ /cm ² or less. The reason why the defect density is so significantly low is unclear, but it is thought to be related to the bending of defects accompanying crystal growth, conversion to stacking faults that progress in a direction perpendicular to the c-axis, annihilation of defects, etc. Also, it is thought that thermal stress in the biaxially oriented SiC layer is one of the causes of defects. If crystal growth occurs only on one side, stress is generated due to defect reduction, and there is a risk of defects caused by stress. It is thought that defects caused by stress can be suppressed by simultaneously growing crystals in the first and second oriented precursor layers 31 and 32.

(c) Grinding step (see FIG. 3(c))
In the grinding process, the first orientation precursor layer 31 remaining on the first layer 21 and the second orientation precursor layer 32 remaining on the second layer 22 after the heat treatment process are ground and removed to expose the surfaces of the first layer 21 and the second layer 22, and the exposed surfaces are polished using diamond abrasive grains and further finished by CMP (chemical mechanical polishing). In this manner, the SiC substrate 10 is obtained.

In the SiC substrate 10 of the present embodiment described above, the crystal defect density on the first surface 21a and the second surface 22a is less than the crystal defect density on the central surface 20a. Therefore, the SiC substrate 10 has less warping than a comparative SiC substrate having the same crystal defect density on the second surface 22a and the central surface 20a and a lower crystal defect density on the first surface 21a. The amount of warping is not particularly limited, but is preferably 10 μm or less, for example.

In addition, it is preferable that the crystal defect density on the first surface 21a and the second surface 22a is 1/100 or less of the crystal defect density on the central surface 20a. In this way, the crystal defect density on the first surface 21a and the second surface 22a is sufficiently small, making it suitable for fabricating a device by stacking a functional layer on the surfaces 21a and 22a.

Furthermore, it is preferable that the difference between the crystal defect density on the first surface 21a and the crystal defect density on the second surface 22a is less than 10%. This reduces the warping of the SiC substrate 10.

It goes without saying that the present invention is in no way limited to the above-described embodiments, and can be implemented in various forms as long as they fall within the technical scope of the present invention.

Below, examples of the present invention are described. The following Experimental Example 1 corresponds to an example of the present invention, and Experimental Example 2 corresponds to a comparative example. Note that the following examples do not limit the present invention in any way.

[Experimental Example 1]
1. Preparation of SiC Substrate (1) Formation of Oriented Precursor Layer As the SiC seed crystal substrate 30, a commercially available SiC single crystal substrate (n-type 4H-SiC, diameter 50.8 mm (2 inches), (0001) plane, off angle 4°, thickness 350 μm, no orientation flat) was prepared, and both the Si plane and the C plane were mirror-finished. Using commercially available fine β-SiC powder (volume basis D50: 0.7 μm) as the raw material powder, AD films (first and second orientation precursor layers 31, 32) were formed on the Si plane and C plane of the above-mentioned SiC seed crystal substrate 30 by the AD device 50 shown in FIG. 3. As a result, a laminate 33 was obtained.

The AD film formation conditions were as follows. First, the carrier gas was _N2 , and a ceramic nozzle with a slit of 5 mm long side x 0.4 mm short side was used for film formation. The nozzle scan conditions were a scan speed of 0.5 mm/s, 55 mm movement perpendicular to the long side of the slit and in the forward direction, 5 mm movement in the long side direction of the slit, 55 mm movement perpendicular to the long side of the slit and in the return direction, and 5 mm movement in the long side direction of the slit and in the opposite direction to the initial position, and when it moved 55 mm from the initial position in the long side direction of the slit, a scan was performed in the opposite direction to the previous one, and a cycle of returning to the initial position was defined as one cycle, and this was repeated 900 times. Using this method, an AD film (first alignment precursor layer 31) was first formed on the Si surface, and then an AD film (second alignment precursor layer 32) was formed on the C surface under the same conditions. The thickness of the AD film was 90 μm on both the Si and C surfaces.

(2) Heat Treatment Step The laminate 33 was taken out of the AD device 50 and annealed in an argon atmosphere at 2450° C. for 5 hours. That is, both the first and second alignment precursor layers 31 and 32 were simultaneously heat treated to obtain a sample.

(3) Evaluation of crystal growth layer 1. A sample prepared separately in the same manner as in (1) and (2) was prepared and cut so as to pass through the center of the sample in a direction perpendicular to the plate surface. The cut sample was smoothed by lapping using diamond abrasive grains, and mirror-finished by chemical mechanical polishing (CMP) using colloidal silica. The obtained cross section was photographed with a scanning electron microscope (SU-5000, manufactured by Hitachi High-Technologies). The crystal growth layer was evaluated by the channeling contrast of the reflected electron image of the cross section after polishing, and it was found that almost no polycrystalline parts were observed in both the AD film on the Si surface side and the AD film on the C surface side, and crystals grew over almost the entire area of the formed AD film, forming a biaxially oriented SiC layer with a thickness of 90 μm on both the Si surface side and the C surface side. In other words, it was found that the samples prepared in (1) and (2) were heat-treated bodies 34 in which the entire first and second orientation precursor layers 31, 32 of the laminate 33 were biaxially oriented SiC layers (first layer 21 and second layer 22) except for the regions near the surfaces on the side opposite to the SiC seed crystal substrate 30. Hereinafter, the crystal growth layer on the Si surface will be referred to as the first layer 21, the crystal growth layer on the C surface as the second layer 22, and the SiC seed crystal substrate 30 as the central layer 20.

(4) Grinding and polishing process 1. The sample prepared in (1) and (2) was fixed to a metal platen with the first layer 21 side as the upper surface and the second layer 22 side as the lower surface, and ground to #1200 with a grindstone to expose and flatten the surface of the first layer 21. Next, the surface of the first layer 21 was smoothed by lapping using diamond abrasive grains. Then, it was mirror-finished by chemical mechanical polishing (CMP) using colloidal silica. The total amount of grinding and polishing was processed to 20 μm, and the arithmetic mean roughness Ra after processing was 0.1 nm. This mirror-finished surface corresponds to the first surface 21a. Next, it was removed from the metal platen, and the protected first layer 21 was fixed to a metal platen with the second layer 22 side as the upper surface, and the second layer 22 side was ground and polished in the same manner as the first layer 21 side to give a mirror finish. The total amount of grinding and polishing was 20 μm, and the arithmetic mean roughness Ra after processing was 0.1 nm. This mirror-finished surface corresponds to the second surface 22a. In this way, the SiC substrate 10 was obtained. From the thickness (90 μm) of the crystal growth layer observed in (3) and the total amount of processing (20 μm), the thicknesses of the first layer 21 and the second layer 22 of the SiC substrate 10 were both calculated to be 70 μm. In addition, since the thickness of the central layer 20 is 350 μm, the distance L1 from the first surface 21a to the central surface 20a and the distance L2 from the second surface 22a to the central surface 20a are both 245 μm.

2. Evaluation (1) Crystal orientation of the first layer and the second layer The SiC substrate 10 prepared in 1. was cut so as to pass through the center of the substrate in a direction perpendicular to the plate surface. The cut sample was smoothed by lapping using diamond abrasive grains, and mirror-finished by chemical mechanical polishing (CMP) using colloidal silica. Next, inverse pole figure mapping of the first layer, the second layer, and the central layer was performed using the EBSD (Electron Back Scatter Diffraction Patterns) method. Specifically, using a scanning electron microscope (SU-5000, manufactured by Hitachi High-Technologies Corporation) equipped with an EBSD (Nordlys Nano, manufactured by Oxford Instruments), inverse pole figure orientation mapping of the first layer 21, the second layer 22, and the central layer 20 was performed under the following conditions in a field of view of 50 μm × 100 μm.
<EBSD measurement conditions>
Acceleration voltage: 15 kV
Spot Intensity: 70
Working distance: 22.5 mm
Step size: 0.5 μm
Sample tilt angle: 70°
Measurement program: Aztec (version 3.3)

The inverse pole figure orientation map showed that the first layer 21 and the second layer 22 were oriented in the same direction as the central layer 20 in both the surface normal direction and the plate surface direction. In addition, the inclination angle distribution was ±0.5° or less in both the approximate normal direction and the approximate plate surface direction, confirming that the first layer 21 and the second layer 22 were both biaxially oriented SiC layers.

(2) Crystal defect density evaluation (2-1) First layer (thickness: 70 μm)
The crystal defect density on the surface (first surface 21a) of the first layer 21 of the SiC substrate 10, which was separately prepared by the same method as in 1., was evaluated by the following method. The first layer 21 was processed by the same method as in 1. (4) so that the total amount of grinding and polishing was 30 μm, and was mirror-finished. The arithmetic mean roughness Ra after processing was 0.1 nm. The processed SiC substrate was placed in a nickel crucible together with KOH crystals, and etched in an electric furnace at 500 ° C. for 10 minutes. The evaluation sample after the etching process was cleaned and observed with an optical microscope to count the number of pits. Specifically, for any part of the surface of the evaluation sample, 100 images of a field of view of 2.3 mm long x 3.6 mm wide were taken at a magnification of 50 times to count the total number of pits, and the total number of pits counted was divided by the total area of 8.05 cm ² to calculate the crystal defect density. As a result, the crystal defect density in the mirror-finished surface of the first layer 21 was 9.7×10 ⁰ /cm ^2. Since it is known that the crystal defect density of the first layer 21 decreases with increasing distance from the central layer 20, the crystal defect density in the first surface 21 a was 9.7×10 ⁰ /cm ² or less.

(2-2) Center layer (thickness: 350 μm)
A SiC substrate 10 was prepared separately by the same method as in 1., and the first surface 21a was processed by the same method as in 1. (4) so that the total amount of grinding and polishing was 245 μm, and the substrate was mirror-finished. The arithmetic mean roughness Ra after processing was 0.1 nm. The first layer 21 was removed by processing, and a surface (central surface 20a) of the central layer 20 equidistant from the first surface 21a and the second surface 22a was exposed. The central surface 20a was evaluated for crystal defect density by the same method as in (2-1). As a result, the crystal defect density in the central surface 20a was 2.0×10 ⁴ /cm ² .

(2-3) Second layer (thickness: 70 μm)
A SiC substrate 10 was prepared separately in the same manner as in 1., and the first surface 21a was processed to a total grinding and polishing amount of 460 μm using the same method as in 1. (4), and was mirror-finished. The arithmetic mean roughness Ra after processing was 0.1 nm. The first layer 21 and the central layer 20 were removed by processing, and the inside of the second layer 22 was exposed on the surface. The newly exposed surface of the second layer 22 was evaluated for crystal defect density using the same method as in (2-1). As a result, the crystal defect density on the newly exposed surface of the second layer 22 was 1.0×10 ¹ /cm ^2. It is known that the crystal defect density of the second layer 22 also decreases with increasing distance from the central layer 20, so it was estimated that the crystal defect density on the second surface 22a was 1.0×10 ¹ /cm ² or less, and the difference from the crystal defect density on the second surface 22a was less than 10%.

(2-4) Conclusion The above results show that the crystal defect densities at the first surface 21a and the second surface 22a are 1/100 times or less (1/1000 times or less) the crystal defect density at the central surface 20a, and the difference between the crystal defect densities at the first surface 21a and the second surface 22a is less than 10%.

(3) Warpage Evaluation The amount of warpage of the SiC substrate 10 separately manufactured in the same manner as in 1. was evaluated using a high-precision laser measuring device (LT-9010M manufactured by Keyence Corporation). First, the amount of warpage of the first surface 21a was evaluated by the following method. As shown in FIG. 4, two straight lines X and Y were drawn that pass through the center point G of the plate surface when the SiC substrate 10 manufactured in 1. is viewed in plan, and two points A and B were determined that are 20 mm away from point G on the straight line X, and two points C and D were determined that are 20 mm away from point G on the straight line Y. Next, as shown in FIG. 5, among any points on the curve AB between points A and B on the first surface 21a, point P that is the longest distance to the line segment AB was determined. Then, the distance between the line segment AB and point P was defined as the amount of warpage α. 5, among any points on the curve CD between points C and D on the first surface 21a, point R having the longest distance to the line segment CD was determined, and the distance between the line segment CD and point R was defined as the amount of warping β. The larger of these amounts of warping α and β was defined as the amount of warping of the first surface 21a. The amount of warping of the second surface 22a was also evaluated using a similar method, and the amount of warping of the first surface 21a or the amount of warping of the second surface 22a, whichever had the larger absolute value, was defined as the amount of warping of the SiC substrate 10. As a result, the amount of warping of the SiC substrate 10 manufactured in 1. was 10 μm or less.

[Experimental Example 2]
1. Preparation of SiC Substrate (1) Formation of Crystal Growth Layer A commercially available SiC single crystal substrate (n-type 4H-SiC, diameter 50.8 mm (2 inches), (0001) face, off-angle 4°, thickness 350 μm, no orientation flat) was prepared as a base substrate, and both the Si face and C face were mirror-finished. A single crystal growth apparatus equipped with a high-frequency heating graphite hot zone furnace was used to grow a crystal on the Si face of the SiC single crystal substrate by a top seeded solution growth (TSSG) method. A conceptual diagram of a single crystal growth apparatus 70 is shown in FIG. 6. The single crystal growth apparatus 70 is installed in a chamber not shown. The single crystal growth apparatus 70 comprises a carbon crucible 72, a heating coil conductor 73 (connected to a power source not shown), a SiC solution 74, a drive 76 for rotating the crucible, a sample holding rod 77, and a drive 75 for driving the sample holding rod 77 up and down. The apparatus 70 is heated by the heating coil conductor 73 wound around the crucible 72, and the heating method is an induction heater. The carbon crucible 72 is approximately cylindrical with an open top and a closed bottom.

Specifically, the above-mentioned commercially available SiC single crystal substrate 90 was placed on the tip of the sample holding rod 77 so that the Si surface was exposed to the SiC solution 74. Then, the Si raw material was heated in the carbon crucible 72 by an induction heater composed of a heating coil conductor 73 and the like to form a Si melt, and the C contained in the carbon crucible 72 was dissolved in the Si melt to obtain the SiC solution 74. The set temperature of the single crystal growth apparatus 70 was 1680°C. In the carbon crucible 72, a temperature gradient was formed in the vertical direction (from the liquid surface to the bottom surface of the carbon crucible 72) in FIG. 6. The temperature gradient was 34°C/cm. The SiC solution 74 contained in the carbon crucible 72 was hottest in a portion located near the conductor 73 and adjacent to the inner wall surface of the carbon crucible 72. The temperature of the SiC solution 74 became lower as it approached the center of the carbon crucible 72, as it moved away from the inner wall surface of the crucible, and as it moved away from the lead wire 73 in the axial direction of the carbon crucible 72, i.e., the vertical direction in FIG. 6. In this state where a temperature gradient was formed in the SiC solution 74 in the carbon crucible 72, the sample holding rod 77 holding the SiC single crystal substrate 90 was inserted into the carbon crucible 72 while supplying high purity argon gas into the chamber. As described above, the SiC single crystal substrate 90 was attached to the tip of the sample holding rod 77 so that the Si surface faced the SiC solution 74, and the sample holding rod 77 was advanced toward the inside of the carbon crucible 72 by the driving device 75, and the SiC single crystal substrate 90 was immersed in the SiC solution 4. The SiC solution 74 was cooled near the SiC single crystal substrate 90, which had a low temperature, so that the SiC crystal grew on the Si surface of the SiC single crystal substrate 90. The crystal growth was performed based on the accelerated crucible rotation technique. Specifically, during the crystal growth, the carbon crucible 72 was rotated by the driving device 76, and the carbon crucible 72 and the SiC single crystal substrate 90 were rotated in the opposite directions relative to each other, and the rotation directions were alternately switched. The rotation speed (maximum speed) at this time was about 20 rpm. Four hours after the start of the crystal growth (i.e., after the start of contact between the SiC single crystal substrate 90 and the SiC solution 74), the sample holding rod 77 was moved upward by the driving device 75, and the SiC single crystal substrate 90, on which the crystal had grown on the Si surface, was pulled up from the SiC solution 74. The pulled-up SiC single crystal substrate 90 was washed with a mixture of _HNO3 and HF ( _HNO3 :HF=2:1). Through the above steps, a sample 83 having a crystal growth layer 93 only on the Si face of the SiC single crystal substrate 90 was obtained, as shown in FIG.

(2) Evaluation of crystal growth layer 1. Sample 83 was prepared separately in the same manner as in (1), and cut so as to pass through the center of sample 83 in a direction perpendicular to the plate surface. The cut sample was smoothed by lapping using diamond abrasive grains, and mirror-finished by chemical mechanical polishing (CMP) using colloidal silica. The obtained cross section was photographed with a scanning electron microscope (SU-5000, manufactured by Hitachi High-Technologies). The thickness of the crystal growth was evaluated by the channeling contrast of the reflected electron image of the cross section after polishing, but no polycrystalline part was observed, and the total thickness of sample 83 was 440 μm. Considering the thickness of the SiC single crystal substrate 90 used as the base, which was 350 μm, it was found that the crystal growth layer 93 was 90 μm, forming a biaxially oriented layer.

(3) Grinding and Polishing 1. For the sample 83 prepared in (1), the crystal growth layer 93 was set as the upper surface, and the C-face side of the SiC single crystal substrate 90 was fixed to a metal surface plate, and the surface of the crystal growth layer 93 was flattened by grinding to #1200 using a grindstone. Next, the surface of the crystal growth layer 93 was smoothed by lapping using diamond abrasive grains. Then, a mirror finish was performed by chemical mechanical polishing (CMP) using colloidal silica. The total amount of grinding and polishing was processed to be 20 μm, and the arithmetic mean roughness Ra after processing was 0.1 nm. The sample 83 after mirror finishing is a SiC substrate 80 (see FIG. 7(b)) having a crystal growth layer 91 only on the Si face of the SiC single crystal substrate 90. From the thickness (90 μm) of the crystal growth layer 93 observed in (2) and the total amount of processing (20 μm), the thickness of the crystal growth layer 91 was calculated to be 70 μm.

2. Evaluation (1) Crystal orientation of crystal growth layer The SiC substrate 80 prepared in 1. was cut so as to pass through the center of the substrate in a direction perpendicular to the plate surface. The cut sample was smoothed by lapping using diamond abrasive grains, and mirror-finished by chemical mechanical polishing (CMP) using colloidal silica. Inverse pole figure mapping of the crystal growth layer 91 and the SiC single crystal substrate 90 was performed using a method similar to that in 2(1) of Experimental Example 1. The inverse pole figure orientation map showed that the crystal growth layer 91 was oriented in the same direction as the SiC single crystal substrate 90 in both the surface normal direction and the plate surface direction. In addition, the tilt angle distribution was ±0.5 ° or less in both the approximately normal direction and the approximately plate surface direction, and it was confirmed that the crystal growth layer 91 was a biaxially oriented SiC layer.

(2) Crystal defect density evaluation (2-1) Crystal growth layer (thickness: 70 μm)
The crystal defect density was evaluated on the surface 91a of the crystal growth layer 91 of the SiC substrate 80 separately prepared by the same method as in 1. (3). The surface 91a was processed to a total grinding and polishing amount of 30 μm using the same method as in 1. (3), and was mirror-finished. The arithmetic mean roughness Ra after processing was 0.1 nm. The processed SiC substrate 80 was placed in a nickel crucible together with KOH crystals, and etched in an electric furnace at 500 ° C for 10 minutes. The evaluation sample after the etching process was cleaned and observed with an optical microscope to count the number of pits. Specifically, for any part of the surface of the evaluation sample, 100 images of a field of view of 2.3 mm long x 3.6 mm wide were taken at a magnification of 50 times to count the total number of pits, and the total number of pits counted was divided by the total area of 8.05 cm ² to calculate the crystal defect density. As a result, the crystal defect density in the mirror-finished surface of the crystal growth layer 91 was 1.6×10 ¹ /cm ^2. Since it is known that the crystal defect density of the crystal growth layer 91 decreases with increasing distance from the SiC single crystal substrate 90, the crystal defect density in the surface 91 a was 1.6×10 ¹ /cm ² or less.

(2-2) SiC single crystal substrate (thickness: 350 μm)
A SiC substrate 80 was prepared separately in the same manner as in 1., and the surface 91a of the crystal growth layer 91 was processed to a total grinding and polishing amount of 245 μm using the same method as in 1. (3), and the substrate was mirror-finished. The arithmetic mean roughness Ra after processing was 0.1 nm. The crystal growth layer 91 was removed by processing, and the surface (central surface 90a) at the center of the SiC single crystal substrate 90 was exposed. The central surface 90a was subjected to a crystal defect density evaluation in the same manner as in (2-1). As a result, the crystal defect density in the central surface 90a was 2.0×10 ⁴ /cm ^2. The crystal growth layer 91 was processed to a total grinding and polishing amount of 390 μm from the surface 91a of the crystal growth layer 91, and the crystal defect density in the mirror-finished sample was also evaluated in the same manner, and it was found that the crystal defect density was 2.0×10 ⁴ /cm ² , which was the same as that of the central surface 90a. From this, it was estimated that the crystal defect density in exposed surface 90b (see FIG. 7B) of SiC single crystal substrate 90 on which crystal growth layer 91 is not formed is also approximately 2.0×10 ⁴ /cm ² .

(2-3) Conclusion From the above results, the crystal defect density on one surface (surface 91a of crystal growth layer 91) of SiC substrate 80 was significantly lower than the crystal defect density on the central surface 90a of the SiC single crystal substrate. However, the crystal defect density on the other surface (exposed surface 90b of SiC single crystal substrate 90) of SiC substrate 80 was approximately the same as the crystal defect density on the central surface 90a of the SiC single crystal substrate.

(3) Warpage Evaluation The amount of warpage of one surface (surface 91a of crystal growth layer 91) and the other surface (exposed surface 90b of SiC single crystal substrate 90 on which crystal growth layer 91 is not formed) of SiC substrate 80 separately fabricated in the same manner as in 1 was evaluated in the same manner as in Experimental Example 1. As a result, the amount of warpage of SiC substrate 80 fabricated in 1 reached 62 μm. The above results show that the SiC substrate 80 has a large difference in crystal defect density between one surface and the other surface, and therefore has a large amount of warpage.

This application claims priority from Japanese Patent Application No. 2019-209518, filed on November 20, 2019, the entire contents of which are incorporated herein by reference.

The SiC substrate of the present invention can be used, for example, as a semiconductor material.

10 SiC substrate, 20 central layer, 20a central surface, 21 first layer, 21a first surface, 22 second layer, 22a second surface, 30 SiC seed crystal substrate, 31 first oriented precursor layer, 32 second oriented precursor layer, 33 laminate, 34 heat treatment body, 50 AD device, 52 aerosol generation unit, 53 aerosol generation chamber, 54 raw material supply pipe, 55 vibrator, 60 film formation unit, 62 film formation chamber, 63 X-Y stage, 64 substrate holder, 66 injection nozzle, 67 slit, 68 vacuum pump, 70 single crystal growth device, 72 carbon crucible, 73 heating coil conductor, 74 SiC solution, 75 drive unit, 76 drive unit, 77 sample holding rod, 80 SiC substrate, 83 sample, 90 SiC single crystal substrate, 90a central surface, 90b exposed surface, 91 crystal growth layer, 91a surface, 93 crystal growth layer.

Claims (5)

A first surface; and
a second surface opposite to the first surface;
a central surface that is equidistant from the first surface in a thickness direction to the second surface;
A SiC substrate comprising:
the first surface and the second surface are both surfaces of a biaxially oriented SiC layer oriented in both the c-axis direction and the a-axis direction,
a crystal defect density at the first surface and the second surface is less than a crystal defect density at the central surface;
Defects include threading screw dislocations, basal plane dislocations and micropipes.
The crystal defect density is a value measured by an etch pit evaluation using KOH molten etching,
a crystal defect density on the first surface and the second surface is 1/100 or less of a crystal defect density on the central surface;
SiC substrate. a difference between a crystal defect density at the first surface and a crystal defect density at the second surface is less than 10%;
The SiC substrate according to claim 1 . The amount of warping of the SiC substrate is 10 μm or less.
The SiC substrate according to claim 1 or 2 . The central layer,
a first biaxially oriented SiC layer oriented in both the c-axis direction and the a-axis direction stacked on one surface of the central layer;
a second biaxially oriented SiC layer oriented in both the c-axis direction and the a-axis direction, stacked on the other surface of the central layer;
Equipped with
the first surface is a surface of the first biaxially textured SiC layer;
the second surface is a surface of the second biaxially textured SiC layer;
The central surface is a surface contained within the central layer.
The SiC substrate according to any one of claims 1 to 3 . (a) forming a SiC oriented precursor layer on both sides of a SiC seed crystal substrate by an AD method;
(b) simultaneously heat-treating both of the SiC oriented precursor layers to grow crystals in both of the SiC oriented precursor layers while orienting them from the crystal growth surface of the SiC seed crystal substrate , thereby converting the SiC oriented precursor layers into biaxially oriented SiC layers oriented in both the c-axis direction and the a-axis direction ;
(c) after the step (b), grinding and removing a surface portion of the biaxially-oriented SiC layer to expose a surface of the biaxially-oriented SiC layer;
Including,
a crystal defect density on a surface of the biaxially oriented SiC layer after the step (c) is 1/100 or less of a crystal defect density on a surface of the SiC seed crystal substrate;
Defects include threading screw dislocations, basal plane dislocations and micropipes.
The crystal defect density is a value measured by etch pit evaluation using KOH molten etching.
Manufacturing method of SiC substrate.

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