SiC substrates and SiC composite substrates

Abstract

Provided is an SiC substrate with which breaking and cracking during substrate processing, such as grinding, polishing, cutting, and the like, can be reduced. This SiC substrate includes a biaxially oriented SiC layer. The SiC substrate and the biaxially oriented SiC layer have an off angle. In an X-ray topography (XRT) image of this SiC substrate obtained by performing XRT measurement of a 4 mm square region in the biaxially oriented SiC layer, the ratio of the number of basal plane dislocations (BPD) at which the absolute value of the acute angle side of an angle formed by a BPD progression direction and the [11-20] direction is 15° or less to the total number of the basal plane dislocations is 60% or greater. The BPD progression direction is defined as a direction, in the XRT image, of a line segment that connects an end point of a linearly observed BPD and a point separated from the end point by 150 μm along the linear BPD.

Description

Technical Field

[0001] The present invention relates to a SiC substrate and a SiC composite substrate.

Background Art

[0002] SiC (silicon carbide) has attracted attention as a wide-bandgap material that can control high voltages and high powers with low losses. In particular, in recent years, power semiconductor devices using SiC materials (SiC power devices) are expected to be used in various applications because they are superior to those using Si semiconductors in terms of miniaturization, low power consumption, and high efficiency. For example, by adopting SiC power devices, converters, inverters, in-vehicle chargers, etc. for electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs) can be miniaturized and the efficiency can be increased. Therefore, the development of SiC wafers, which are the basis of SiC power devices, has been attracting great attention.

[0003] To fabricate a SiC power device, it is necessary to epitaxially grow a SiC single crystal on a SiC single crystal substrate. The obtained SiC single crystal substrate has many dislocations, which are roughly classified into three types: screw threading dislocations, edge threading dislocations, and basal plane dislocations (BPDs). Among these dislocations, basal plane dislocations are inherited by the epitaxial growth film. When they exist in the driving region of the device, the basal plane dislocations expand into stacking faults due to energization, which has an adverse effect on the reliability of the SiC device. Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2014-162649) discloses a SiC substrate having a main surface inclined by an off-angle from a plane perpendicular to the c-axis, and for 80% or more of the basal plane dislocations on the surface of the main surface, the angle formed by the dislocation line direction and the off-direction of the off-angle is 45° or more and 90° or less. It is described that when epitaxial growth is performed on the main surface of this SiC substrate, the basal plane dislocations on the surface of the SiC substrate main surface are not inherited by the epitaxial layer, so the basal plane dislocations in the epitaxial layer are suppressed. Also, it is known that cracks and fractures occur when processing a SiC single crystal substrate. Non-Patent Document 1 (Y. Qiusheng, C. Senkai and P. Jisheng, “Surface and subsurface cracks characteristics of single crystal SiC wafer in surface machining,” AIP Conference Proceedings 1653, 020091 (2015)) describes that various processes were performed on a single crystal SiC wafer, and the crack characteristics generated on the wafer surface were analyzed thereby.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

[0006] According to the disclosure of Non-Patent Document 1, since SiC is extremely hard, it is difficult to process, and the reduction in yield due to cracks and fractures generated during grinding, polishing, cutting, etc. of wafers has become a problem. Although the direct cause has not been clarified, it is possible that strains in the crystal such as plastic deformation due to dislocations are involved. That is, simply reducing the basal plane dislocations (BPD) in the substrate is insufficient, and it is desirable to reduce cracks and fractures during substrate processing such as grinding, polishing, and cutting.

[0007] The present inventors have now found that when an X-ray topograph (XRT) measurement or optical microscope observation is performed on an SiC substrate, the ratio of the number of BPDs whose absolute value of the acute angle side of the angle formed by the propagation direction of the BPDs and the [11-20] direction to the total number of BPDs is controlled by providing a biaxially oriented SiC layer, cracks and fractures during substrate processing such as grinding, polishing, and cutting can be reduced.

[0008] Therefore, an object of the present invention is to provide an SiC substrate capable of reducing cracks and fractures during substrate processing.

[0009] According to the present invention, the following aspects are provided. [Aspect 1] An SiC substrate including a biaxially oriented SiC layer, wherein the SiC substrate and the biaxially oriented SiC layer have an off-angle, In an X-ray topograph (XRT) image obtained by measuring a 4 mm square region in the biaxially oriented SiC layer, the ratio of the number of basal plane dislocations (BPDs) with the absolute value of the acute angle between the propagation direction of the BPDs and the [11-20] direction to the total number of BPDs is 60% or more, and the propagation direction of the BPDs is defined as the direction of a line segment connecting the end point of the linearly observed BPDs and a point 150 μm away from the end point along the linear BPDs in the XRT image, SiC substrate. [Aspect 2] An SiC substrate including a biaxially oriented SiC layer, wherein the SiC substrate and the biaxially oriented SiC layer have an off-angle, in an optical microscope image obtained by observing a plane inclined by the off-angle from the (0001) plane after KOH etching in a 4 mm square region in the biaxially oriented SiC layer, the ratio of the number of basal plane dislocations (BPDs) with the absolute value of the acute angle between the propagation direction of the BPDs and the [11-20] direction to the total number of BPDs is 70% or more, and the propagation direction of the BPDs is defined as the major axis direction of the elliptical etch pits specified in the optical microscope image, SiC substrate. [Aspect 3] the rare earth element concentration of the biaxially oriented SiC layer is 1.0×10 14 ~5.0×10 15 atoms / cm 3 and is the SiC substrate according to Aspect 1 or 2. [Aspect 4] the N concentration of the biaxially oriented SiC layer is 1.0×10 18 ~5.0×10 19 atoms / cm 3 and is the SiC substrate according to any one of Aspects 1 to 3. [Aspect 5] the B concentration of the biaxially oriented SiC layer is 1.0×10 15 ~1.0×10 18 atoms / cm 3 and is the SiC substrate according to any one of Aspects 1 to 4. [Aspect 6] In an optical microscope image obtained by observing a plane inclined by the off-angle from the (0001) plane after KOH etching of the biaxially oriented SiC layer, the density of elliptical etch pits that are BPDs is 50 / cm 2 The SiC substrate according to any one of Aspects 1 to 5, including a region of 5 mm square as follows. [Aspect 7] An SiC composite substrate including an SiC single crystal substrate and the SiC substrate according to any one of Aspects 1 to 6 on the SiC single crystal substrate.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0011] SiC substrate The SiC substrate according to the present invention includes a biaxially oriented SiC layer, and the SiC substrate and the biaxially oriented SiC layer have an off-angle. In this biaxially oriented SiC layer, in an XRT image obtained by X-ray topograph (XRT) measurement of a certain 4 mm square region in the biaxially oriented SiC layer, the ratio P of the number of BPDs whose absolute value of the acute angle between the propagation direction of the BPD and the [11-20] direction to the total number of basal plane dislocations (BPDs) is 15° or less BPD,XRT(%) is 60% or more. Here, the progress direction of the BPD is defined as the direction of the line segment connecting the end point of the BPD observed linearly in the XRT image and the point 150 μm away from the end point along the linear BPD. Alternatively, the biaxially oriented SiC layer is, in an optical microscope image obtained by observing a plane tilted by an off-angle from the (0001) plane after KOH etching in a certain 4 mm square region in the biaxially oriented SiC layer, the ratio P of the number of BPDs whose absolute value of the acute angle between the progress direction of the BPD and the [11-20] direction is 15° or less with respect to the total number of basal plane dislocations (BPDs). BPD,KOH (%) is 70% or more. Here, the progress direction of the BPD is defined as the major axis direction of the elliptical etch pit specified in the optical microscope image. Note that the above-mentioned 4 mm square region means a region in the plane direction of the biaxially oriented SiC layer. Also, P BPD,XRT Or P BPD,KOH The region where the ratio becomes the above ratio is defined as the "4 mm square region", but in the present specification, when P BPD,XRT Or P BPD,KOH becomes the above ratio in the "4 mm square region", it can be regarded that P BPD,XRT Or P BPD,KOH becomes the above ratio over the entire biaxially oriented SiC layer. Thus, when the SiC substrate is subjected to X-ray topography (XRT) measurement or optical microscope observation, by providing a biaxially oriented SiC layer in which the ratio of the number of BPDs whose absolute value of the acute angle between the progress direction of the BPD and the [11-20] direction is 15° or less with respect to the total number of BPDs is controlled, cracks and fractures during substrate processing such as grinding, polishing, and cutting can be reduced.

[0012] As described above, since SiC is extremely hard, it is difficult to process, and a reduction in yield due to cracks and fractures generated during wafer grinding, polishing, cutting, etc. has been a problem. That is, it is not sufficient to simply reduce the basal plane dislocations (BPDs) in the substrate, and it is desired to reduce cracks and fractures during substrate processing such as grinding, polishing, and cutting. In this regard, according to the present invention, such a problem is advantageously solved.

[0013] The biaxially oriented SiC layer provided in the SiC substrate of the present invention has a P in an XRT image obtained by performing XRT measurement on a 4 mm square region in the biaxially oriented SiC layer. BPD,XRT of 60% or more. This P BPD,XRT may be 70% or more, may be 80% or more, or may be 90% or more. The upper limit of P BPD,XRT is not particularly limited, but is typically 100%. Alternatively, this biaxially oriented SiC layer has a P in an optical microscope image obtained by observing a plane inclined by an off-angle from the (0001) plane after KOH etching in a 4 mm square region in the biaxially oriented SiC layer. BPD,KOH of 70% or more. This P BPD,KOH may be 80% or more, or may be 90% or more. The upper limit of P BPD,KOH is not particularly limited, but is typically 100%. By setting such P BPD,XRT or P BPD,KOH , cracking and cracking during substrate processing can be more effectively reduced.

[0014] The biaxially oriented SiC layer provided in the SiC substrate of the present invention has an elliptical etch pit density, which is BPD, of 50 / cm or less in an optical microscope image obtained by observing a plane inclined by an off-angle from the (0001) plane after KOH etching of the biaxially oriented SiC layer, and preferably includes a 5 mm square region. The density of this BPD may be 1 to 40 / cm 2 , and may be 1 to 10 / cm 2 , 2It may be. Note that the above-mentioned 5 mm square region means the region in the plane direction of the biaxially oriented SiC layer. Also, although the region where the density of BPD becomes the density described above is defined as the "5 mm square region", in the present specification, when the density of BPD in the "5 mm square region" becomes the density described above, it can be regarded that the density of BPD becomes the density described above over the entire biaxially oriented SiC layer. Thus, the SiC substrate of the present invention can reduce cracks and fractures during substrate processing such as grinding, polishing, and cutting while reducing BPDs in the biaxially oriented SiC layer. Furthermore, it can be said that the SiC substrate (specifically, the biaxially oriented SiC layer) with the above-described BPD density has few BPDs present in the substrate, and since most of the BPDs are aligned such that the absolute value of the acute angle formed between the propagation direction and the [11-20] direction is 15° or less, it is considered that the strain within the crystal is reduced. Thereby, not only can cracks and fractures during substrate processing be reduced, but also the yield during substrate manufacturing can be improved.

[0015] The SiC substrate or the biaxially oriented SiC layer has an off-angle, and the off-angle is preferably 0.1 to 12°, more preferably 1 to 5° from the

[0001] axis of the SiC substrate or the biaxially oriented SiC layer.

[0016] Examples of rare earth elements contained in the biaxially oriented SiC layer include Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, and combinations thereof. This rare earth element is preferably Y or Ce from the viewpoint of reducing cracks and fractures, and more preferably Y.

[0017] The concentration of rare earth elements in the biaxially oriented SiC layer is 1.0×10 14 ~5.0×10 15 atoms / cm 3 is preferable, more preferably 5.0×10 14 ~5.0×10 15 atoms / cm 3 and even more preferably, when containing Y, it is 5.0×10 14 ~1.4×10 15 atoms / cm3 and when containing Ce, it is 5.0×10 14 ~4.0×10 15 atoms / cm 3 . The N concentration of the biaxially oriented SiC layer is 1.0×10 18 ~5.0×10 19 atoms / cm 3 is preferably, more preferably 1.0×10 18 ~2.0×10 19 atoms / cm 3 , still more preferably 1.0×10 18 ~1.0×10 19 atoms / cm 3 . The B concentration of the biaxially oriented SiC layer is 1.0×10 15 ~1.0×10 18 atoms / cm 3 is preferably, more preferably 2.0×10 15 ~1.0×10 17 atoms / cm 3 . By setting the rare earth element, N or B concentration to a concentration within the above range, the progress direction and density of BPD can be effectively controlled.

[0018] The biaxially oriented SiC layer is preferably oriented in the c-axis direction and the a-axis direction. Further, it is preferable that the SiC substrate is composed of a biaxially oriented SiC layer. The biaxially oriented SiC layer may be a single crystal of SiC, a polycrystal of SiC, or a mosaic crystal as long as it is oriented in the biaxial direction of the c-axis and the a-axis. A mosaic crystal refers to a collection of crystals that do not have distinct grain boundaries but have a slightly different orientation in one or both of the c-axis and the a-axis. The method for evaluating the orientation is not particularly limited, and for example, known analysis methods such as the EBSD (Electron Back Scatter Diffraction Patterns) method or the X-ray pole figure can be used. For example, when using the EBSD method, the 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, (A) being oriented in a specific orientation (first axis) in the substantially normal direction of the plate surface, (B) being oriented in a specific orientation (second axis) in the substantially in-plane direction of the plate surface perpendicular to the first axis, (C) the inclination angle from the first axis being distributed within ±10°, and (D) the inclination angle from the second axis being distributed within ±10°. When these four conditions are satisfied, it can be defined that it is oriented in two axes of the substantially normal direction and the substantially plate surface direction. In other words, when the above four conditions are satisfied, it is determined that it is oriented in two axes of the c-axis and the a-axis. For example, when the substantially normal direction of the plate surface is oriented in the c-axis, the substantially in-plane direction may be oriented in a specific orientation (for example, the a-axis) perpendicular to the c-axis. The biaxially oriented SiC layer only needs to be oriented in two axes of the substantially normal direction and the substantially in-plane direction, but it is preferable that the substantially normal direction is oriented in the c-axis. The smaller the inclination angle distribution in the substantially normal direction and / or the substantially in-plane direction, the smaller the mosaicity of the biaxially oriented SiC layer, 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, it is preferable that the inclination angle distribution is smaller in both the substantially normal direction and the substantially plate surface direction. For example, ±5° or less is more preferable, and ±3° or less is even more preferable.

[0019] SiC composite substrate 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 is provided, which includes a SiC single crystal substrate and the above-mentioned SiC substrate on the SiC single crystal substrate. In this way, when X-ray topography (XRT) measurement or optical microscope observation is performed, the ratio of the number of BPDs whose absolute value of the acute angle formed by the propagation direction of the BPD and the [11-20] direction to the total number of BPDs is controlled, and the SiC substrate having a biaxially oriented SiC layer can reduce cracks and fractures during substrate processing.

[0020] The SiC single crystal substrate is typically a layer composed of a SiC single crystal and has a crystal growth surface. The SiC single crystal substrate preferably has an off-angle. The polytype, off-angle, and polarity of the SiC single crystal are not particularly limited, but the polytype is preferably 4H or 6H, the off-angle is preferably 0.1 to 12° from the

[0001] axis of the single crystal SiC, and the polarity is preferably the Si plane. More preferably, the polytype is 4H, the off-angle is 1 to 5° from the

[0001] axis of the single crystal SiC, and the polarity is the Si plane.

[0021] The SiC substrate of the present invention may be in the form of a self-supporting substrate of a biaxially oriented SiC layer alone or in the form of a SiC composite substrate with a SiC single crystal substrate. Therefore, if necessary, the biaxially oriented SiC layer may be finally separated from the SiC single crystal substrate. The separation of the SiC single crystal substrate may be performed by a known method and is not particularly limited. For example, methods such as separating the biaxially oriented SiC layer by a wire saw, separating the biaxially oriented SiC layer by electrical discharge machining, and separating the biaxially oriented SiC layer using a laser can be mentioned. In addition, in the case of epitaxially growing a biaxially oriented SiC layer on a SiC single crystal substrate, after separating the SiC single crystal substrate, the biaxially oriented SiC layer may be installed on another supporting substrate. The material of the other supporting substrate is not particularly limited, but a suitable one may be selected from the perspective of material physical properties. For example, from the perspective of thermal conductivity, metal substrates such as Cu, and ceramic substrates such as SiC and AlN can be mentioned.

[0022] Method for manufacturing SiC composite substrate The SiC composite substrate provided with the SiC substrate of the present invention can be preferably manufactured by: (a) forming a predetermined orientation precursor layer on the SiC single crystal substrate; (b) heat-treating the orientation precursor layer on the SiC single crystal substrate to convert at least the portion near the SiC single crystal substrate into a SiC substrate (biaxially oriented SiC layer); and, if desired, (c) subjecting it to processing such as grinding or polishing to expose the surface of the biaxially oriented SiC layer. However, the manufacturing method of the SiC composite substrate is not limited, and it is sufficient to obtain a SiC substrate in which P BPD,XRT or P BPD,KOH is controlled to a specific ratio. For example, a vapor phase method such as CVD or sublimation method may be used, or a liquid phase method such as a solution method may be used. Rare earth elements, B and / or N may be added by the methods described later. According to such a manufacturing method, P BPD,XRT or P BPD,KOH a SiC substrate provided with a biaxially oriented SiC layer in which is controlled to a specific ratio can be preferably produced, and cracks and fractures during processing of the SiC substrate or the SiC composite substrate using the same can be effectively reduced.

[0023] Hereinafter, a preferred manufacturing method of the SiC composite substrate will be described. FIG. 1 is a longitudinal sectional view of the SiC composite substrate 10 (a sectional view when the SiC composite substrate 10 is longitudinally cut along a plane including the central axis of the SiC composite substrate 10), and FIG. 2 is a manufacturing process diagram of the SiC composite substrate 10.

[0024] As shown in FIG. 1, the SiC composite substrate 10 of the present embodiment includes a SiC single crystal substrate 20 and a SiC substrate 30 (corresponding to the SiC substrate of the present invention) on the SiC single crystal substrate.

[0025] (a) Formation step of the orientation precursor layer As shown in FIG. 2(a), the orientation precursor layer 40 will become a SiC substrate (biaxially oriented SiC layer) 30 by heat treatment described later. In the formation step 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.

[0026] Known methods can be adopted for forming the pre - oriented precursor layer 40. For example, solid - phase film - forming methods such as the AD (aerosol deposition) method and the HPPD (high - speed plasma particle deposition) method, sputtering methods, vapor deposition methods, sublimation methods, vapor - phase film - forming methods such as various CVD (chemical vapor deposition) methods, and liquid - phase film - forming methods such as solution growth methods can be used. A method of directly forming the pre - oriented precursor layer 40 on the SiC single - crystal substrate 20 can be used. As the CVD method, for example, thermal CVD method, plasma CVD method, mist CVD method, MO (metal - organic) CVD method, etc. can be used. Also, as the pre - oriented precursor layer 40, a polycrystalline body prepared in advance by sublimation method, various CVD methods, sintering, etc. can be used and placed on the SiC single - crystal substrate 20. Alternatively, a method of preparing a molded body of the pre - oriented precursor layer 40 in advance and placing this molded body on the SiC single - crystal substrate 20 may be used. Such a pre - oriented precursor layer 40 may be a tape - formed body produced by tape forming or a compacted powder produced by pressure forming such as uniaxial pressing.

[0027] When forming these pre - oriented precursor layers 40, it is preferable that the raw material of the pre - oriented precursor layer 40 contains a rare - earth compound. By doing so, the concentration of the rare - earth compound in the biaxially - oriented SiC layer can be controlled. 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 described above. Oxides of rare - earth elements are preferable as the rare - earth compound, and more preferably oxides of Y (yttrium oxide) and Ce (cerium oxide). Also, the concentration of B in the biaxially - oriented SiC layer can be controlled by adjusting the amount of boron or boron compound (e.g., boron carbide) added to the raw material, calcining the raw material, or depositing metal boron on the SiC single - crystal. Furthermore, by the type of carrier gas (e.g., He or N 2 ) used when forming the pre - oriented precursor layer 40, the angle formed between the progress direction of BPD and the [11 - 20] direction can be effectively controlled.

[0028] In the method of directly forming the pre-oriented precursor layer 40 on the SiC single crystal substrate 20, when various CVD methods, sublimation methods, solution growth methods, etc. are used, epitaxial growth may occur on the SiC single crystal substrate 20 without going through the heat treatment process described later, and the SiC substrate 30 may be formed. However, the pre-oriented precursor layer 40 is in a non-oriented state during formation, that is, it is amorphous or non-oriented polycrystalline, and it is preferable to orient it using the SiC single crystal as a seed in the subsequent heat treatment process. By doing so, crystal defects reaching the surface of the SiC substrate 30 can be effectively reduced. The reason for this is not clear, but it is thought that the once-formed solid-phase pre-oriented precursor layer causing rearrangement of the crystal structure 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, etc., it is preferable to select conditions under which epitaxial growth does not occur in the formation process of the pre-oriented precursor layer 40.

[0029] However, methods such as the AD method, the method of directly forming the pre-oriented precursor layer 40 on the SiC single crystal substrate 20 by various CVD methods, or the method of placing a separately prepared polycrystalline body on the SiC single crystal substrate 20 by sublimation, various CVD methods, sintering, etc. are preferable. By using these methods, it becomes possible to form the pre-oriented precursor layer 40 in a relatively short time. The AD method does not require a high-vacuum process and has a relatively high film formation rate, so it is particularly preferable. In the method of using a previously prepared polycrystalline body as the pre-oriented precursor layer 40, in order to enhance the adhesion between the polycrystalline body and the SiC single crystal substrate 20, measures such as sufficiently smoothing the surface of the polycrystalline body are necessary. Therefore, from a cost perspective, the method of directly forming the pre-oriented precursor layer 40 is preferable. Also, the method of placing a previously prepared molded body on the SiC single crystal substrate 20 is preferable as a simple method, but since the pre-oriented precursor layer 40 is composed of powder, a sintering process is required in the heat treatment process described later. Known conditions can be used for any of these methods, but below, the method of directly forming the pre-oriented precursor layer 40 on the SiC single crystal substrate 20 by the AD method or thermal CVD method and the method of placing a previously prepared molded body on the SiC single crystal substrate 20 will be described.

[0030] The AD method is a technique that mixes fine particles or fine particle raw materials with a gas to form an aerosol, and then injects this aerosol at high speed from a nozzle to collide with a substrate to form a film. It has the characteristic that the film can be formed at room temperature. An example of a film-forming apparatus (AD apparatus) used in such an AD method is shown in FIG. 3. The AD apparatus 50 shown in FIG. 3 is configured as an apparatus used in the AD method of injecting raw material powder onto a substrate in an atmosphere at a pressure lower than atmospheric pressure. This AD apparatus 50 includes an aerosol generation unit 52 that generates an aerosol of raw material powder containing raw material components, and a film-forming unit 60 that injects the raw material powder onto the 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 houses the raw material powder and receives the supply of a carrier gas from a gas cylinder (not shown) to generate an aerosol, a raw material supply pipe 54 that supplies the generated aerosol to the film-forming unit 60, and a vibrator 55 that applies vibration to the aerosol generation chamber 53 and the aerosol therein at a frequency of 10 to 100 Hz. The film-forming unit 60 includes a film-forming chamber 62 that injects an aerosol onto the SiC single crystal substrate 20, a substrate holder 64 disposed inside the film-forming chamber 62 for 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 directions. Further, the film-forming unit 60 includes an injection nozzle 66 having a slit 67 formed at its tip for injecting the aerosol onto the SiC single crystal substrate 20, and a vacuum pump 68 for reducing the pressure in the film-forming chamber 62. The injection nozzle 66 is attached to the tip of the raw material supply pipe 54.

[0031] In the AD method, it is known that pores are generated in the film depending on the film-forming conditions, or the film becomes a compressed powder body. For example, it is easily affected by the collision speed of the raw material powder against the substrate, the particle size of the raw material powder, the aggregation state of the raw material powder in the aerosol, the injection amount per unit time, etc. Regarding the collision speed of the raw material powder against the substrate, it is affected by the differential pressure between the film-forming chamber 62 and the injection nozzle 66, the opening area of the injection nozzle, etc. Therefore, in order to obtain a dense precursor layer with orientation, it is necessary to appropriately control these factors.

[0032] In the thermal CVD method, a commercially available or other known film forming apparatus can be used. The raw material gas is not particularly limited. As a Si source, silicon tetrachloride (SiCl 4 ) gas, silane (SiH 4 ) gas, etc. can be used. As a C source, methane (CH 4 ) gas, propane (C 3 H 8 ) gas, etc. can be used. The film forming temperature is preferably 1000 to 2200 °C, more preferably 1100 to 2000 °C, and even more preferably 1200 to 1900 °C.

[0033] When forming a film on the SiC single crystal substrate 20 using the thermal CVD method, it is known that epitaxial growth may occur on the SiC single crystal substrate 20 to form the SiC substrate 30. However, the pre-orientation precursor layer 40 is in an unoriented state during its fabrication, that is, it is amorphous or polycrystalline without orientation. It is preferable to cause crystal rearrangement using the SiC single crystal as a seed crystal during the heat treatment process. To form an amorphous or polycrystalline layer on a SiC single crystal using the thermal CVD method, it is known that the film forming temperature, the gas flow rates of the Si source and C source, and their ratios, the film forming pressure, etc. have an impact. The influence of the film forming temperature is significant. From the perspective of forming an amorphous or polycrystalline layer, a lower film forming temperature is preferable, less than 1700 °C is preferable, less than 1500 °C is more preferable, and less than 1400 °C is even more preferable. However, if the film forming temperature is too low, the film forming rate itself also decreases. Therefore, from the perspective of the film forming rate, a higher film forming temperature is preferable.

[0034] When using a pre-fabricated molded body as the pre-orientation precursor layer 40, the raw material powder of the pre-orientation precursor can be molded and fabricated. For example, when using press molding, the pre-orientation precursor layer 40 is a press molded body. The press molded body can be fabricated by press molding the raw material powder of the pre-orientation precursor based on a known method. For example, the raw material powder is put into a mold, preferably at 100 to 400 kgf / cm 2 , more preferably 150 to 300 kgf / cm 2It may be produced by pressing at the pressure of . Further, the molding method is not particularly limited, 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, additives such as a binder, a plasticizer, a dispersant, and a dispersion medium are appropriately added to the raw material powder to form a slurry, and it is preferable to discharge and mold the slurry into a sheet shape by passing it through a slit-like thin discharge port. Although there is no limitation on the thickness of the molded body formed into a sheet shape, from the viewpoint of handling, it is preferably 5 to 500 μm. Further, when a thick pre-orientation precursor layer is required, a large number of these sheet-shaped molded bodies may be stacked and used as a desired thickness. These molded bodies become SiC substrates 30 in the portion near the SiC single crystal substrate 20 by heat treatment on the SiC single crystal substrate 20 thereafter. In such a method, it is necessary to sinter the molded body in the heat treatment step described later. After the step in which the molded body is sintered and integrated with the SiC single crystal substrate 20 as a polycrystal, it is preferable to form the SiC substrate 30. When the molded body does not go through the sintered state, epitaxial growth using the SiC single crystal as a seed may not occur sufficiently. Therefore, the molded body may contain additives such as a sintering aid in addition to the SiC raw material.

[0035] (b) Heat treatment step As shown in Fig. 2(b), in the heat treatment step, the SiC substrate 30 is produced by heat-treating a laminate in which the orientation precursor layer 40 is laminated or placed on the SiC single crystal substrate 20. The heat treatment method is not particularly limited as long as epitaxial growth using the SiC single crystal substrate 20 as a seed occurs, and it can be carried out in a known heat treatment furnace such as a tubular furnace or a hot plate. Also, not only heat treatment at these normal pressures (pressures), but also pressure heat treatment such as hot pressing and HIP, and combinations of normal pressure heat treatment and pressure heat treatment can be used. The atmosphere for heat treatment can be selected from atmospheres of vacuum, nitrogen, inert gas, and combinations thereof. At this time, the concentration of N in the biaxially oriented SiC layer can be controlled by adjusting the amount of nitrogen in the atmosphere during heat treatment. The heat treatment temperature is preferably 1700 to 2700 °C. By increasing the temperature, the orientation precursor layer 40 grows while being oriented along the c-axis and a-axis with the SiC single crystal substrate 20 as a seed crystal, making it easier to grow. Therefore, the heat treatment temperature is preferably 1700 °C or higher, more preferably 1800 °C or higher, still more preferably 1900 °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 by sublimation, or the SiC may plastically deform and defects such as warping may occur. Therefore, the heat treatment temperature is preferably 2700 °C or lower, more preferably 2500 °C or lower. However, since the heat treatment conditions affect the concentrations of rare earth elements, N, and B in the biaxially oriented SiC layer, it is preferable to appropriately control the conditions (for example, heat treatment temperature and holding time). From such a viewpoint, the heat treatment temperature is preferably 1900 to 2700 °C, more preferably 2200 to 2600 °C, and still more preferably 2400 to 2500 °C. Also, the holding time is preferably 2 to 30 hours, more preferably 4 to 20 hours. Also, the heat treatment may be carried out in multiple stages. For example, it may be carried out under conditions such as heat treatment at 1950 °C for 3 hours in a nitrogen atmosphere and then heat treatment at 2400 °C for 3 hours in an argon atmosphere. Even in such a case, the heat treatment temperature and the total holding time are preferably within the above ranges. Furthermore, the heat treatment temperature and the holding time are also related to the thickness of the SiC substrate 30 formed by epitaxial growth and can be adjusted as appropriate.

[0036] However, when using a prefabricated molded body as the pre-oriented precursor layer 40, it is necessary to sinter it during the heat treatment, and normal pressure firing at high temperature, hot pressing, HIP, or a combination thereof is suitable. For example, when using hot pressing, the surface pressure is preferably 50 kgf / cm 2 or more, more preferably 100 kgf / cm 2 or more, still more preferably 200 kgf / cm 2 or more, and there is no particular upper limit. Also, the firing temperature is not particularly limited as long as sintering and epitaxial growth occur. However, since the firing conditions affect the concentrations of rare earth elements, N, and B in the biaxially oriented SiC layer, it is preferable to appropriately control the conditions (for example, firing temperature and holding time). From such a viewpoint, the firing temperature is preferably 1700 to 2700 °C. Also, the holding time is preferably 2 to 18 hours. The atmosphere during firing can be selected from a vacuum, nitrogen, inert gas atmosphere, or a mixed gas of nitrogen and inert gas. Also, similar to the above, the firing may be performed in multiple stages, and the firing temperature and total holding time are preferably within the above ranges. The SiC powder used as the raw material may be composed of at least one of α-SiC and β-SiC, but is preferably composed of β-SiC. The SiC powder is preferably composed of SiC particles having an average particle size of 0.01 to 100 μm. The average particle size refers to the average value obtained by observing the powder with a scanning electron microscope and measuring the maximum diameter in a fixed direction for 100 primary particles.

[0037] In the heat treatment step, the crystals in the pre-oriented precursor layer 40 grow while being oriented along the c-axis and a-axis from the crystal growth surface of the SiC single crystal substrate 20. Therefore, the pre-oriented precursor layer 40 gradually changes into the SiC substrate 30 from the crystal growth surface. The SiC composite substrate provided with the generated SiC substrate 30 has reduced cracking and cracking during substrate processing.

[0038] (c) Grinding and / or polishing step As shown in FIG. 2(c), in the grinding process, the orientation precursor layer 40 remaining on the SiC substrate 30 after the heat treatment process is ground and removed to expose the surface of the SiC substrate 30, and the exposed surface is ground and / or polished. By doing so, the SiC composite substrate 10 is obtained.

[0039] Note that the present invention is not limited to the above-described embodiments at all, and it goes without saying that the present invention can be implemented in various modes as long as it belongs to the technical scope of the present invention. For example, in the above-described embodiment, only one layer of the SiC substrate 30 is provided on the SiC single crystal substrate 20, but two or more layers may be provided. Specifically, an orientation precursor layer 40 is laminated on the SiC substrate 30 of the SiC composite substrate 10, and after heat treatment, grinding and / or polishing are performed in this order, whereby a second layer of the SiC substrate 30 can be provided on the SiC substrate 30.

Example

[0040] The present invention will be described more specifically by the following examples.

[0041] Example 1 (1) Preparation of orientation precursor layer Raw material powder containing 90.8% by weight of commercially available fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 8.1% by weight of yttrium oxide powder (volume-based D50 particle size: 0.1 μm), and 1.1% by weight of silicon dioxide powder (volume-based D50 particle size: 0.7 μm) was prepared. These raw material powders were ball-milled in ethanol for 24 hours using SiC balls and dried to obtain a mixed powder. A commercially available SiC single crystal substrate (n-type 4H-SiC, diameter of about 100 mm (4 inches), Si plane, (0001) plane, off angle of 4°, thickness of 0.35 mm, no orientation flat) was prepared as the SiC single crystal layer, and in the AD device 50 shown in FIG. 3, the mixed powder was sprayed onto the SiC single crystal substrate to form an AD film (orientation precursor layer).

[0042] The AD film formation conditions were as follows. First, the carrier gas was He, and film formation was carried out using a ceramic nozzle with a slit of 5 mm in the long side and 0.4 mm in the short side. The scanning conditions of the nozzle were as follows: scanning at a speed of 0.5 mm / s, moving 105 mm in a direction perpendicular to the long side of the slit and advancing, moving 5 mm in the long side direction of the slit, moving 105 mm in a direction perpendicular to the long side of the slit and returning, moving 5 mm in the long side direction of the slit and in the direction opposite to the initial position, and repeating the scan. When moving 105 mm from the initial position in the long side direction of the slit, scanning was performed in the opposite direction to that until then, and one cycle of returning to the initial position was defined as one cycle, and this was repeated 4000 cycles. The thickness of the AD film formed in this way was about 400 μm.

[0043] (2) Heat treatment of the pre-oriented precursor layer The SiC single crystal substrate on which the AD film, which is the pre-oriented precursor layer, was formed was taken out from the AD apparatus and annealed at 2400 °C for 10 hours in an argon atmosphere. That is, the pre-oriented precursor layer was heat-treated to form a heat-treated layer.

[0044] (3) Grinding (3a) Surface grinding The (0001) plane of the SiC single crystal substrate on which the heat-treated layer was formed was surface-ground to a predetermined thickness using a grinder (diamond wheel with 1000 - 6000 grit) to obtain the target thickness and surface state.

[0045] (3b) Back grinding The (000-1) plane of the SiC single crystal substrate on which the heat-treated layer was formed was surface-ground to a predetermined thickness using a grinder (diamond wheel with 1000 - 6000 grit) to obtain the target thickness and surface state. In this way, the SiC substrate was obtained.

[0046] (4) Incidence rate of cracks and fractures after processing An industrial microscope (manufactured by Nikon, ECLIPSE LV150N) was used with an eyepiece magnification of 10x and an objective lens magnification of 5x. The entire surface of the SiC substrate obtained in (3) above was observed in polarized light mode and differential interference contrast mode. If cracks or fissures were confirmed, the substrate was considered to have cracks or fissures. At this time, only those with crack and fissure lengths of 100 μm or more were counted as cracks and fissures. Among 100 SiC substrates fabricated under the same conditions as the SiC substrate fabricated as described above, the occurrence rate P C (%) of cracks and fissures was calculated. By determining this P C , the yield of the substrate was evaluated. The results were as shown in Table 1.

[0047] (5) Cutting process of SiC substrate After the evaluation in (4) above, SiC substrates without cracks and fissures were cut with a diamond cutter and processed into chip shapes of about 5 mm × 5 mm.

[0048] (6) Polishing (6a) Surface polishing The (0001) plane of the chip-shaped SiC substrate obtained in (5) above was polished with diamond abrasive grains and then finished by chemical mechanical polishing (CMP) to obtain the target thickness and surface condition.

[0049] (6b) Backside polishing The (000-1) plane of the chip-shaped SiC substrate obtained in (5) above was polished with diamond abrasive grains to obtain the target thickness and surface condition.

[0050] (7) Evaluation of biaxial orientation of heat treatment layer Using the EBSD (Electron Back Scatter Diffraction Patterns) method, under the conditions shown below, inverse pole figure mapping of the surface (plate surface) of the heat treatment layer obtained in (3) above and the cross-section perpendicular to the plate surface was measured. As the inclination angle distribution was 0.01° or less in both the approximate normal direction and the approximate plate surface direction, it was determined that the heat treatment layer was a biaxially oriented SiC layer oriented in the c-axis and a-axis directions and had the same off-angle as the SiC single crystal substrate.

[0051] <EBSD Measurement Conditions> · Measuring device: SEM (SU-5000, manufactured by Hitachi High-Technologies Corporation) equipped with an electron backscatter diffraction device (EBSD) (Nordlys Nano, manufactured by Oxford Instruments) · 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)

[0052] (8) X-ray topography (XRT) measurement of the heat treatment layer Using the chip (about 5 mm × 5 mm) of the heat treatment layer (biaxially oriented SiC layer) prepared according to (1) to (6) above as an evaluation sample, an XRT image of the evaluation sample was obtained under the conditions shown below.

[0053] <XRT Measurement Conditions> · Measuring device: X-ray topography imaging system (XRTmicron, manufactured by Rigaku Corporation) · Measurement area: 4 mm square area · Observation mode: 3D-XRT · Diffraction plane: (22-40) plane · X-ray source: Cu, Kα · Tube voltage / tube current: 40 kV / 30 mA · Detector: CCD camera

[0054] By superimposing the 3D-XRT data, an XRT image as shown in Fig. 4 was obtained. Among the linear contrasts observed in this XRT image, linear contrasts with an XRT intensity of 5% or more in the upper rank (arrows a and b in Fig. 4) were regarded as BPDs, and the total number of BPDs was counted. Thereby, the density C BPD,XRT ( / cm 2 ) of BPDs in the 4 mm square region was calculated. And the ratio P BPD,XRT (%) of the number of BPDs (arrow a in Fig. 4) whose absolute value of the acute angle formed by the propagation direction of BPDs and the [11-20] direction is 15° or less with respect to the total number of BPDs was calculated. Note that arrow b in Fig. 4 indicates BPDs whose absolute value of the acute angle of the above angle exceeds 15°. Here, the propagation direction of BPDs is defined as the direction of the line segment connecting the end point of the linearly observed BPDs and a point 150 μm away along the linear BPDs in the XRT image. The results were as shown in Table 1.

[0055] (9) Optical Microscopic Observation of Heat Treatment Layer A chip (about 5 mm × 5 mm) of the heat treatment layer (biaxially oriented SiC layer) produced by the above (1) to (6) was used as an evaluation sample. The evaluation sample 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 treatment was washed, and the surface inclined by the off-angle from the (0001) plane of the 4 mm square region of the heat treatment layer (biaxially oriented SiC layer) in the evaluation sample was observed with an optical microscope at a magnification of 50 times. In this optical microscope image, the total number of BPDs identified as elliptical etch pits was counted, and the density C BPD,KOH ( / cm 2 ) of BPDs in the 4 mm square region was calculated. And the ratio P of the number of BPDs whose absolute value of the acute angle formed by the propagation direction of BPDs and the [11-20] direction is 15° or less with respect to the total number of BPDs BPD,KOH(%) was calculated. The results were as shown in Table 1. The progress direction of BPD is defined as the major axis direction of the elliptical etch pit identified in the optical microscope image. Here, an example of the observed BPD is shown in Fig. 5. Arrow a in Fig. 5 indicates a BPD where the absolute value of the acute angle formed between the progress direction of BPD and the [11-20] direction is 15° or less, and arrow b in Fig. 5 indicates a BPD where the absolute value of the acute angle of the above angle exceeds 15°.

[0056] (10) Concentrations of B, N, Y, and Ce in the heat treatment layer (biaxially oriented SiC layer) A chip (about 5 mm × 5 mm) of the heat treatment layer (biaxially oriented SiC layer) produced according to the above (1) to (6) was used as an evaluation sample. Dynamic secondary ion mass spectrometry (D-SIMS) was performed on the (0001) plane, which is the polished surface of this evaluation sample. For the analysis of rare earth elements (Y and Ce in this example) and B, IMS-7f manufactured by CAMECA was used, and the primary ion species was O 2 + , and the measurement was carried out at an acceleration voltage of 11.0 kV. For the analysis of N, IMS-7f manufactured by CAMECA was used, and the primary ion species was Cs + , and the measurement was carried out at an acceleration voltage of 15.0 kV. In this way, the Y concentration C Y (atoms / cm 3 ), Ce concentration C Ce (atoms / cm 3 ), B concentration C B (atoms / cm 3 ), and N concentration C N (atoms / cm 3 ) were measured. The results were as shown in Table 1.

[0057] Example 2 In the above (1), except that a raw material powder containing 82.7 wt% of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 16.2 wt% of yttrium oxide powder (volume-based D50 particle size: 0.1 μm), and 1.1 wt% of silicon dioxide powder (volume-based D50 particle size: 0.7 μm) was used, 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 were as shown in Table 1.

[0058] Example 3 (Comparison) In the above (1), except that a raw material powder containing 74.9 wt% of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 24.0 wt% of yttrium oxide powder (volume-based D50 particle size: 0.1 μm), and 1.1 wt% of silicon dioxide powder (volume-based D50 particle size: 0.7 μm) was used, 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 were as shown in Table 1.

[0059] Example 4 In the above (1), except that a raw material powder containing 94.9 wt% of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 4.0 wt% of yttrium oxide powder (volume-based D50 particle size: 0.1 μm), and 1.1 wt% of silicon dioxide powder (volume-based D50 particle size: 0.7 μm) was used, 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 were as shown in Table 1.

[0060] Example 5 (Comparison) In the above (1), except that a raw material powder containing 97.9 wt% of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 1.0 wt% of yttrium oxide powder (volume-based D50 particle size: 0.1 μm), and 1.1 wt% of silicon dioxide powder (volume-based D50 particle size: 0.7 μm) was used, 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 were as shown in Table 1.

[0061] Example 6 In the above (1), except that a raw material powder containing 90.8 wt% of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 8.1 wt% of cerium oxide powder (volume-based D50 particle size: 0.1 μm), and 1.1 wt% of silicon dioxide powder (volume-based D50 particle size: 0.7 μm) was used, 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 were as shown in Table 1.

[0062] Example 7 In the above (1), except that a raw material powder containing 82.7 wt% of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 16.2 wt% of cerium oxide powder (volume-based D50 particle size: 0.1 μm), and 1.1 wt% of silicon dioxide powder (volume-based D50 particle size: 0.7 μm) was used, 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 were as shown in Table 1.

[0063] Example 8 (Comparative) In the above (1), except that a raw material powder containing 74.9% by weight of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 24.0% by weight of cerium oxide powder (volume-based D50 particle size: 0.1 μm), and 1.1% by weight of silicon dioxide powder (volume-based D50 particle size: 0.7 μm) was used, the production and evaluation of the SiC substrate were carried out 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 were as shown in Table 1.

[0064] Example 9 In the above (1), except that a raw material powder containing 94.9% by weight of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 4.0% by weight of cerium oxide powder (volume-based D50 particle size: 0.1 μm), and 1.1% by weight of silicon dioxide powder (volume-based D50 particle size: 0.7 μm) was used, the production and evaluation of the SiC substrate were carried out 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 were as shown in Table 1.

[0065] Example 10 (Comparative) In the above (1), except that a raw material powder containing 97.9% by weight of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 1.0% by weight of cerium oxide powder (volume-based D50 particle size: 0.1 μm), and 1.1% by weight of silicon dioxide powder (volume-based D50 particle size: 0.7 μm) was used, the production and evaluation of the SiC substrate were carried out 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 were as shown in Table 1.

[0066] Example 11 In the above (1), except that a raw material powder containing 88.8 wt% of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 8.1 wt% of yttrium oxide powder (volume-based D50 particle size: 0.1 μm), 1.1 wt% of silicon dioxide powder (volume-based D50 particle size: 0.7 μm), and 2.0 wt% of boron carbide powder (volume-based D50 particle size: 0.5 μm) was used, 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 were as shown in Table 1.

[0067] Example 12 In the above (1), except that a raw material powder containing 86.8 wt% of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 8.1 wt% of yttrium oxide powder (volume-based D50 particle size: 0.1 μm), 1.1 wt% of silicon dioxide powder (volume-based D50 particle size: 0.7 μm), and 4.0 wt% of boron carbide powder (volume-based D50 particle size: 0.5 μm) was used, 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 were as shown in Table 1.

[0068] Example 13 In the above (1), except that a raw material powder containing 82.8 wt% of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 8.1 wt% of yttrium oxide powder (volume-based D50 particle size: 0.1 μm), 1.1 wt% of silicon dioxide powder (volume-based D50 particle size: 0.7 μm), and 8.0 wt% of boron carbide powder (volume-based D50 particle size: 0.5 μm) was used, 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 were as shown in Table 1.

[0069] Example 14 In the above (1), except that a raw material powder containing 74.8 wt% of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 8.1 wt% of yttrium oxide powder (volume-based D50 particle size: 0.1 μm), 1.1 wt% of silicon dioxide powder (volume-based D50 particle size: 0.7 μm), and 16.0 wt% of boron carbide powder (volume-based D50 particle size: 0.5 μm) was used, the production and evaluation of the SiC substrate were carried out 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 were as shown in Table 1.

[0070] Example 15 (Comparison) In the above (1), except that a raw material powder containing 58.8 wt% of fine β-SiC powder (volume-based D50 particle size: 0.7 μm), 8.1 wt% of yttrium oxide powder (volume-based D50 particle size: 0.1 μm), 1.1 wt% of silicon dioxide powder (volume-based D50 particle size: 0.7 μm), and 32 wt% of boron carbide powder (volume-based D50 particle size: 0.5 μm) was used, the production and evaluation of the SiC substrate were carried out 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 were as shown in Table 1.

[0071] Example 16 In the above (2), except that the heat treatment atmosphere was 99.95% argon and 0.05% nitrogen, the production and evaluation of the SiC substrate were carried out 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 were as shown in Table 1.

[0072] Example 17 In the above (2), except that the heat treatment atmosphere was 99.9% argon and 0.1% nitrogen, the production and evaluation of the SiC substrate were carried out 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 were as shown in Table 1.

[0073] Example 18 In (2) above, the SiC substrate was fabricated and evaluated in the same manner as in Example 1, except that the heat treatment atmosphere was 99.5% argon and 0.5% nitrogen. It was confirmed that the obtained heat treatment layer was a biaxially oriented SiC layer. The results were as shown in Table 1.

[0074] Example 19 In (2) above, the SiC substrate was fabricated and evaluated in the same manner as in Example 1, except that the heat treatment atmosphere was 99.0% argon and 1.0% nitrogen. It was confirmed that the obtained heat treatment layer was a biaxially oriented SiC layer. The results were as shown in Table 1.

[0075] Example 20 (Comparison) In (2) above, the SiC substrate was fabricated and evaluated in the same manner as in Example 1, except that the heat treatment atmosphere was 70.0% argon and 30.0% nitrogen. It was confirmed that the obtained heat treatment layer was a biaxially oriented SiC layer. The results were as shown in Table 1.

[0076]

Table 1

[0077] Although the cause is not clear, it was found that the progress direction and density of BPD can be controlled by the carrier gas and the concentrations of Y, Ce, N, and B in the biaxially oriented SiC layer. Also, it was found that the ratio of the number of BPDs such that the absolute value of the acute angle formed between the progress direction of BPD and the [11-20] direction is 15° or less can control the ratio of cracks and fractures during processing. In particular, when the rare earth element concentration is 5.0×10 14 ~5.0×10 15 atoms / cm 3 , the N concentration is 1.0×10 18 ~2.0×10 19 atoms / cm 3 , and the B concentration is 2.0×10 15 ~1.0×10 17 atoms / cm 3It has been found that when it is [as described], cracks and fractures during processing can be more effectively reduced.

Claims

1. A SiC substrate comprising a biaxially oriented SiC layer, wherein the biaxially oriented SiC layer is oriented in a biaxial direction of the c-axis direction and the a-axis direction such that the c-axis of the crystal is oriented in a substantially normal direction to the plate surface and the a-axis of the crystal is oriented in a substantially in-plane direction of the plate surface, the SiC substrate and the biaxially oriented SiC layer have an off-angle, in an XRT image obtained by measuring a 4 mm square region in the biaxially oriented SiC layer by X-ray topograph (XRT), the ratio of the number of BPDs having an absolute value of the acute angle between the propagation direction of the BPD and the [11-20] direction to the total number of BPDs is 60% or more, where the absolute value of the acute angle is 15° or less, the propagation direction of the BPD is defined as the direction of a line segment connecting the end point of the linearly observed BPD and a point 150 μm away from the end point along the linear BPD in the XRT image, The rare earth element concentration of the biaxially oriented SiC layer is 1.0×10 １４ to 5.0×10 １５ atoms / cm ３ and the N concentration of the biaxially oriented SiC layer is 2.0×10 １９ atoms / cm ３ or less, the B concentration of the biaxially oriented SiC layer is 1.0×10 １８ atoms / cm ３ or less, a SiC substrate including a 5 mm square region having a density of elliptical etch pits, which are BPDs, of 40 / cm2 or less in an optical microscope image obtained by observing a plane inclined by the off-angle from the (0001) plane after KOH etching of the biaxially oriented SiC layer.

2. A SiC substrate comprising a biaxially oriented SiC layer, wherein the biaxially oriented SiC layer is oriented in a biaxial direction of the c-axis direction and the a-axis direction such that the c-axis of the crystal is oriented in a substantially normal direction to the plate surface and the a-axis of the crystal is oriented in a substantially in-plane direction of the plate surface, the SiC substrate and the biaxially oriented SiC layer have an off-angle, in an optical microscope image obtained by observing a plane inclined by the off-angle from the (0001) plane after KOH etching in a 4 mm square region in the biaxially oriented SiC layer, the ratio of the number of BPDs having an absolute value of the acute angle between the propagation direction of the BPD and the [11-20] direction to the total number of BPDs is 70% or more, where the absolute value of the acute angle is 15° or less, the propagation direction of the BPD is defined as the major axis direction of the elliptical etch pit specified in the optical microscope image, The rare earth element concentration of the biaxially oriented SiC layer is 1.0×10 １４ to 5.0×10 １５ atoms / cm ３ and the N concentration of the biaxially oriented SiC layer is 2.0×10 １９ atoms / cm ３ or less, the B concentration of the biaxially oriented SiC layer is 1.0×10 １８ atoms / cm ３ or less, a SiC substrate including a 5 mm square region having a density of elliptical etch pits, which are BPDs, of 40 / cm2 or less in an optical microscope image obtained by observing a plane inclined by the off-angle from the (0001) plane after KOH etching of the biaxially oriented SiC layer.

3. The N concentration of the biaxially oriented SiC layer is 1.0×10 １８ ~2.0×10 １９ atoms / cm ３ , and the SiC substrate according to claim 1 or 2.

4. The B concentration of the biaxially oriented SiC layer is 1.0×10 １５ ~1.0×10 １８ atoms / cm ３ , and the SiC substrate according to claim 1 or 2.

5. In the optical microscope image obtained by observing the surface inclined by the off-angle from the (0001) plane after KOH etching of the biaxially oriented SiC layer, the density of elliptical etch pits that are BPDs is 36 / cm ２ The SiC substrate according to claim 1 or 2, including a region of 5 mm square that is as follows.

6. A SiC composite substrate comprising a SiC single crystal substrate and the SiC substrate according to claim 1 or 2 on the SiC single crystal substrate.

Images