Sic substrate and sic composite substrate

Abstract

Provided is an SiC substrate that is less susceptible to a fracture or crack during processing such as grinding, polishing, etc. and thus can be produced at a high yield. This SiC substrate comprises a biaxially oriented SiC layer, wherein, when multiphoton excitation photoluminescence images are acquired for individual regions on the surface of the biaxially oriented SiC layer that are partitioned in a 440 μm-square lattice pattern excluding the outer peripheral region within 2 mm from the outer edge of the SiC substrate, the proportion P1 of the number of images including an abnormal light emission region to the total number of multiphoton excitation photoluminescence images is not more than 40%.

Description

SiC substrate and SiC composite substrate

[0001] The present disclosure relates to SiC substrates and SiC composite substrates.

[0002] SiC (silicon carbide) has attracted attention as a wide-bandgap material capable of controlling high voltages and high power with low loss. In particular, in recent years, power semiconductor devices using SiC materials (SiC power devices) are expected to be used in a variety of applications because they are more compact, consume less power, and are more efficient than those using Si semiconductors. For example, the adoption of SiC power devices can reduce the size and improve the efficiency of converters, inverters, on-board chargers, etc. for electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs). Therefore, the development of SiC wafers, which form the backbone of SiC power devices, has attracted considerable attention.

[0003] Patent Document 1 (WO 2023 / 008054) discloses a SiC substrate containing a dopant, the SiC substrate having a portion where the resistivity is lower downstream of the center of the SiC substrate in a planar view than the center. In this SiC substrate, the difference between the resistivity of the SiC substrate at the center and the minimum resistivity of the SiC substrate downstream of the center divided by the resistivity of the SiC substrate at the center is 0.015 or less. Furthermore, the resistivity of the SiC substrate increases from the position where the resistivity of the SiC substrate is minimum toward the downstream of the off-state. This SiC substrate is said to be capable of suppressing crack generation, stacking fault generation, and heterogeneous crystal generation.

[0004] WO2023 / 008054

[0005] Because SiC is extremely hard, it is difficult to process, and the reduction in yield due to breakage and cracks that occur during wafer polishing is an issue. Therefore, there is a demand for SiC substrates that are less susceptible to breakage and cracks.

[0006] The present inventors have now discovered that when multiphoton-excited photoluminescence images are acquired for individual regions partitioned into a 440 μm square grid on the surface of a SiC substrate, the ratio of the number of images containing anomalous light emission regions to the total number of multiphoton-excited photoluminescence images is 40% or less (or the ratio P ２ The inventors have found that by configuring the SiC substrate so that the surface roughness is 35% or less, it is possible to provide a SiC substrate or SiC composite substrate that is less likely to break or crack during processing such as grinding and polishing, and that can therefore be manufactured with a high yield.

[0007] Therefore, an object of the present invention is to provide a SiC substrate that is less susceptible to breakage or cracking during processing such as grinding and polishing, and therefore can be manufactured with a high yield.

[0008] The present disclosure provides the following aspects: [Aspect 1] A SiC substrate including a biaxially textured SiC layer, wherein, when multiphoton-excited photoluminescence images are acquired for individual regions on the surface of the biaxially textured SiC layer that are partitioned into a 440 μm square grid, excluding a peripheral region within 2 mm from the outer edge of the SiC substrate, the ratio P of the number of images including anomalous light emission regions to the total number of multiphoton-excited photoluminescence images is １ A SiC substrate in which the ratio P of the number of images including an anomalous emission region having a side parallel to the [1-100] direction to the total number of multiphoton excited photoluminescence images is 40% or less. ２The SiC substrate according to Aspect 1, wherein the ratio of the number of images including anomalous emission regions having sides parallel to the [1-100] direction to the total number of multiphoton-excited photoluminescence images is 35% or less. [Aspect 3] The SiC substrate according to Aspect 1 or 2, wherein the diameter of the SiC substrate is 99 mm or more. [Aspect 4] The SiC substrate according to any one of Aspects 1 to 3, wherein the diameter of the SiC substrate is 149 mm or more. [Aspect 5] The SiC substrate according to any one of Aspects 1 to 4, wherein the diameter of the SiC substrate is 199 mm or more. [Aspect 6] A SiC composite substrate comprising a SiC single crystal substrate and the SiC substrate according to any one of Aspects 1 to 5 on the SiC single crystal substrate. [Aspect 7] A SiC substrate comprising a biaxially textured SiC layer, wherein, when multiphoton-excited photoluminescence images are acquired for individual regions partitioned into a 440 μm square lattice on the surface of the biaxially textured SiC layer, excluding a peripheral region within 2 mm from the outer edge of the SiC substrate, the ratio P ２ A SiC substrate, wherein the SiC substrate has a diameter of 99 mm or more. [Aspect 8] The SiC substrate according to aspect 7, wherein the SiC substrate has a diameter of 99 mm or more. [Aspect 9] The SiC substrate according to any one of aspects 7 or 8, wherein the SiC substrate has a diameter of 149 mm or more. [Aspect 10] The SiC substrate according to any one of aspects 7 to 9, wherein the SiC substrate has a diameter of 199 mm or more. [Aspect 11] A SiC composite substrate comprising a SiC single crystal substrate and the SiC substrate according to any one of aspects 7 to 10 on the SiC single crystal substrate.

[0009] 1 is a longitudinal sectional view of a SiC composite substrate 10. FIG. 2 is a manufacturing process diagram of a SiC composite substrate 10. FIG. 3 is a conceptual diagram showing the configuration of an aerosol deposition (AD) apparatus 50. FIG. 4 is an example of one section (440 μm square) of a multiphoton excitation photoluminescence image including an anomalous light emission region acquired in Example 1.

[0010] The SiC substrate according to the present invention is provided with a biaxially textured SiC layer. When multiphoton-excited photoluminescence images are acquired for each of the regions on the surface of the biaxially textured SiC layer, which are partitioned into 440 μm square grids excluding the peripheral region within 2 mm from the outer edge of the SiC substrate, the ratio P of the number of images containing anomalous light emission regions to the total number of multiphoton-excited photoluminescence images is １ is 40% or less (or the ratio P ２ This makes it possible to provide a SiC substrate or a SiC composite substrate that is less susceptible to breakage or cracking during processing such as grinding or polishing, and that can be manufactured with a high yield.

[0011] As mentioned above, SiC is extremely hard and therefore difficult to process, and reduced yields due to fractures and cracks that occur during wafer polishing have become an issue. While the direct cause of this has not been clarified, it is possible that distortions in the crystal structure due to residual stress within the crystal or stacking faults are involved. Therefore, the inventors focused on multiphoton-excited photoluminescence images. Multiphoton-excited photoluminescence images allow observation of areas with abnormalities in the crystal structure that emit light that differs from the surrounding area, as shown in Figure 4 (described below). For example, in Figure 4, gray or dark areas represent areas without abnormalities, while whitish areas represent areas with abnormalities. Therefore, the quality of a wafer can be determined by examining the number of areas with abnormal light emission that emit light that differs from the surrounding area. In other words, if there is distortion in the crystal structure, it is believed that the area can be observed as an abnormal light emission area. Based on this approach, multiphoton-excited photoluminescence images were acquired and analyzed for each area partitioned into a 440 μm square grid, excluding the peripheral area within 2 mm from the outer edge of the SiC substrate. As a result, it was found that there was a tendency for breakages and cracks to be less likely to occur, and that the proportion of images containing anomalous light emission areas to the total number of multiphoton-excited photoluminescence images was P １ (or the ratio P of the number of images containing anomalous regions with sides parallel to the [1-100] direction) ２Specifically, the ratio P １ is 40% or less (or the ratio P ２ When the strain is 35% or less, breakage or cracking is unlikely to occur during processing such as grinding or polishing. That is, according to the present invention, it is possible to manufacture a SiC substrate that has little internal strain and is unlikely to breakage or cracking during processing such as grinding or polishing, thereby improving the yield rate during production.

[0012] In the SiC substrate of the present invention, when multiphoton-excited photoluminescence images are acquired for each of the areas on the surface of the biaxially oriented SiC layer that are partitioned into a 440 μm square grid, excluding the peripheral area within 2 mm from the outer edge of the SiC substrate, the ratio P of the number of images including anomalous light emission areas to the total number of multiphoton-excited photoluminescence images is １ is 40% or less, preferably 30% or less, more preferably 20% or less, and even more preferably 10% or less. １ The lower the better, but is typically 5% or more, more typically 10% or more.

[0013] In a preferred embodiment (or another embodiment) of the present invention, when multiphoton-excited photoluminescence images are acquired for each of the areas on the surface of the biaxially oriented SiC layer that are partitioned into a 440 μm square grid, excluding the peripheral area within 2 mm from the outer edge of the SiC substrate, the SiC substrate has a surface with a biaxially oriented SiC layer, and the ratio P ２is 35% or less, preferably 30% or less, more preferably 20% or less, and even more preferably 10% or less. An anomalous emission region having a side parallel to the [1-100] direction may have one side roughly parallel to the [1-100] direction, as shown by the right-most side of the anomalous emission region that appears whitish in FIG. 4 (described later). Note that the arrow shown in the lower right of FIG. 4 does not strictly represent the [1-100] direction, but merely indicates a rough direction due to the image resolution of multiphoton-excited photoluminescence. However, because the right-most side of the anomalous emission region shown in FIG. 4 is parallel to the [1-100] direction due to the crystal structure, the direction indicated by this side can be interpreted as the [1-100] direction. Taking into account the tolerance due to the image resolution of multiphoton-excited photoluminescence, in this specification, a side parallel to the [1-100] direction refers to a side that forms an angle with the [1-100] direction within the range of 0 to 10°. The edges parallel to the [1-100] direction are the areas where planar defects (typically progressing obliquely relative to the surface of the SiC substrate) such as stacking faults that cause distortion of the crystal structure are exposed on the outermost surface, and can therefore be a factor that significantly influences the occurrence of breakages and cracks during processing. That is, since the multiphoton excited photoluminescence image acquires information not only on the outermost surface of the SiC substrate but also on its depth direction, the luminescence abnormality region is identified as a region (not an edge) originating from a planar defect, but the edges parallel to the [1-100] direction of the luminescence abnormality region are understood to be the ends of the planar defects that have reached the outermost surface, and can be the starting points for inducing breakages and cracks, and therefore, in this embodiment, attention is focused on their abundance ratio. Therefore, the ratio P of the number of images containing luminescence abnormality regions ２ The lower the better, but is typically 5% or more, more typically 10% or more.

[0014] As described above, to determine whether or not a substrate is a SiC substrate of the present invention, it is necessary to acquire multiphoton-excited photoluminescence images of individual regions partitioned into 440 μm square grids on the surface of the biaxially oriented SiC layer, excluding the peripheral region within 2 mm from the outer edge of the SiC substrate. Multiphoton-excited photoluminescence images can be acquired by surface-grinding and surface-polishing the surface of the SiC substrate, and then using a multiphoton microscope (e.g., Nikon AX R MP) on the polished surface according to the procedures and conditions described in the Examples below. Next, using image processing software (e.g., ImageJ from the National Institutes of Health), histogram flattening and noise removal are performed on each of the acquired multiphoton-excited photoluminescence images according to the procedures described in the Examples below. Then, the proportion P of images containing anomalous emission regions to the total number of multiphoton-excited photoluminescence images is calculated for the obtained images. １ or the ratio P of the number of images containing anomalous luminescence regions with sides parallel to the [1-100] direction ２ It is preferable to determine

[0015] The diameter of the SiC substrate is 99 mm or more (approximately 4 inches or more), preferably 149 mm or more (approximately 6 inches or more), and more preferably 199 mm or more (approximately 8 inches or more). While there is no particular upper limit to the diameter of the SiC substrate, the diameter of the SiC substrate is typically 201 mm or less, more typically 151 mm or less. According to the present invention, even SiC substrates with such large diameters are less likely to break or crack during processing, which is advantageous in that large-diameter SiC substrates can be manufactured with a high yield. Typically, the SiC substrate has a circular shape. In this specification, the term "circular shape" does not necessarily mean a perfect circle, but may be a substantially circular shape that can be recognized as a circle overall. For example, the shape may be a shape in which a portion of the circle is cut out for identifying the crystal orientation or for other purposes (e.g., a circular shape including an orientation flat or a notch).

[0016] The SiC substrate or biaxially oriented SiC layer may have an off-axis angle, which is preferably 0.1 to 12°, more preferably 1 to 5°, from the

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

[0017] The biaxially oriented SiC layer may contain a rare earth element. 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. The rare earth element is preferably Y or Ce from the viewpoint of reducing warpage of the substrate, and more preferably Y. The rare earth element concentration in the biaxially oriented SiC layer is 1.0 × 10 １４ ~5.0 x 10 １５ atoms / cm ３ is preferably 5.0 × 10 １４ ~5.0 x 10 １５ atoms / cm ３ and more preferably 5.0 × 10 １４ ~1.4 × 10 １５ atoms / cm ３ is.

[0018] The biaxially oriented SiC layer is preferably oriented in the c-axis and a-axis directions. Furthermore, the SiC substrate is preferably composed of a biaxially oriented SiC layer. 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 axes 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, along either the c-axis or the a-axis, are slightly different. The method for evaluating the orientation is not particularly limited, and known analytical techniques such as EBSD (Electron Backscatter Diffraction Patterns) and X-ray pole figures can be used. For example, when using the EBSD method, inverse pole figure mapping of the surface (plate surface) of the biaxially oriented SiC layer or a cross section perpendicular to the plate surface can be measured. In the obtained inverse pole figure mapping, when the following four conditions are satisfied, the biaxially oriented SiC layer can be defined as being oriented in two directions, namely, the approximately normal direction and the approximately in-plane direction: (A) the first axis, (B) the second axis, (C) the tilt angle from the first axis is distributed within ±10°; and (D) the tilt angle from the second axis is distributed within ±10°. In other words, when the above four conditions are satisfied, the biaxially oriented SiC layer is determined to be oriented in two directions, namely, the c-axis and the a-axis. For example, when the approximately normal direction to 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 directions, namely, 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 tilt 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, 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 tilt angle distribution be small in both the approximately normal direction and the approximately in-plane direction, for example, ±5° or less is more preferable, and ±3° or less is even more preferable.

[0019] 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, there is provided a SiC composite substrate comprising a SiC single crystal substrate and the above-described SiC substrate on the SiC single crystal substrate. Thus, the ratio P of the number of images containing anomalous emission regions to the total number of multiphoton excited photoluminescence images is １ is 40% or less (or the ratio P ２ By providing the SiC composite substrate with a SiC substrate having a surface roughness of 35% or less, breakage or cracking is less likely to occur during processing, and therefore the SiC composite substrate can be manufactured with a high yield.

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

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

[0001] axis of the single crystal SiC.

[0021] The SiC substrate of the present invention may be in the form of a freestanding substrate of a biaxially oriented SiC layer alone, or in the form of a SiC composite substrate accompanied by a SiC single crystal substrate. Therefore, if necessary, the biaxially oriented SiC layer may finally be separated from the SiC single crystal substrate. Separation of the SiC single crystal substrate may be performed by any known method, without particular limitation. Examples include a method of separating the biaxially oriented SiC layer using a wire saw, a method of separating the biaxially oriented SiC layer by electrical discharge machining, and a method of separating the biaxially oriented SiC layer using a laser. Furthermore, when a biaxially oriented SiC layer is epitaxially grown on a SiC single crystal substrate, the biaxially oriented SiC layer may be placed on a separate support substrate after separation of the SiC single crystal substrate. The material of the separate support substrate is not particularly limited, and a suitable material may be selected from the viewpoint of material properties. For example, from the viewpoint of thermal conductivity, metal substrates such as Cu, and ceramic substrates such as SiC and AlN may be used.

[0022] 2. Manufacturing Method of SiC Composite Substrate The SiC composite substrate comprising the SiC substrate of the present invention can be preferably manufactured by (a) forming a predetermined oriented precursor layer on a SiC single crystal substrate, (b) heat-treating the oriented precursor layer on the SiC single crystal substrate to convert at least a portion thereof near the SiC single crystal substrate into a SiC substrate (biaxially oriented SiC layer), and, if desired, (c) subjecting the layer to processing such as grinding or polishing to expose the surface of the biaxially oriented SiC layer. However, there are no limitations on the manufacturing method of the SiC composite substrate, and the ratio P of the number of images containing anomalous emission regions to the total number of multiphoton excited photoluminescence images can be used. １ and / or the ratio P of the number of images containing anomalous luminescence regions with sides parallel to the [1-100] direction ２ It is sufficient to obtain a SiC substrate in which the ratio P is controlled within a predetermined range. For example, a gas phase method such as CVD or sublimation method, or a liquid phase method such as a solution method may be used. １ and / or P ２ can be controlled, for example, by controlling the average particle size (e.g., D50 particle size) of the SiC powder used to prepare the textured precursor layer, as will be explained in the section on the aerosol deposition (AD) method later.

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

[0024] As shown in FIG. 1, a SiC composite substrate 10 of this embodiment includes a SiC single crystal substrate 20 and a SiC substrate 30 on the SiC single crystal substrate.

[0025] 2(a) Step of Forming Textured Precursor Layer As shown in Fig. 2(a), the textured precursor layer 40 will become the SiC substrate (biaxially textured SiC layer) 30 by heat treatment, which will be described later. In the step of forming the textured precursor layer 40, the textured precursor layer 40 is formed on the crystal growth surface of the SiC single crystal substrate 20.

[0026] The orientation precursor layer 40 can be formed by any known method. Examples of methods for forming the orientation precursor layer 40 include solid-phase deposition methods such as aerosol deposition (AD) and HPPD (supersonic plasma particle deposition), vapor-phase deposition methods such as sputtering, evaporation, sublimation, and various CVD (chemical vapor deposition) methods, and liquid-phase deposition methods such as solution growth. A method in which the orientation precursor layer 40 is formed directly on the SiC single crystal substrate 20 can be used. Examples of CVD methods that can be used include thermal CVD, plasma CVD, mist CVD, and metal-organic CVD. Alternatively, a polycrystalline body previously prepared by sublimation, various CVD, sintering, or the like can be used as the orientation precursor layer 40, and then placed on the SiC single crystal substrate 20. Alternatively, a molded body for the orientation precursor layer 40 can be prepared in advance and then placed on the SiC single crystal substrate 20. Such an alignment precursor layer 40 may be a tape-molded body produced by tape casting, or may be a green compact produced by pressure molding using a uniaxial press or the like.

[0027] When forming these textured precursor layers 40, it is preferable that the raw materials for the textured precursor layers 40 contain a rare earth compound. This allows the concentration of the rare earth compound in the biaxially textured SiC layer to be controlled. The rare earth compound is not particularly limited, but examples include oxides, nitrides, carbides, and fluorides of at least one rare earth element selected from the 17 rare earth elements described above. Oxides of rare earth elements are preferred as the rare earth compound.

[0028] In addition, when various CVD methods, sublimation methods, solution growth methods, etc. are used to form the textured precursor layer 40 directly on the SiC single crystal substrate 20, epitaxial growth may occur on the SiC single crystal substrate 20, resulting in the formation of the SiC substrate 30, without the heat treatment process described below. However, the textured precursor layer 40 is preferably in an unoriented state upon formation, i.e., amorphous or unoriented polycrystalline, and is preferably oriented using the SiC single crystal as a seed in a subsequent heat treatment process. This effectively reduces crystal defects that reach the surface of the SiC substrate 30. Although the reason for this is unclear, it is believed that the reorganization of the crystalline structure of the solid-phase textured precursor layer once formed using the SiC single crystal as a seed may also be effective in eliminating crystal defects. Therefore, when various CVD methods, sublimation methods, solution growth methods, etc. are used, it is preferable to select conditions that do not cause epitaxial growth in the textured precursor layer 40 formation process.

[0029] However, preferred are methods of forming the texture precursor layer 40 directly on the SiC single crystal substrate 20 using the AD method or various CVD methods, or methods of placing a polycrystalline body separately prepared by sublimation, various CVD methods, sintering, or the like on the SiC single crystal substrate 20. These methods enable the texture precursor layer 40 to be formed in a relatively short time. The AD method is particularly preferred because it does not require a high-vacuum process and has a relatively fast film formation rate. When using a pre-prepared polycrystalline body as the texture precursor layer 40, it is necessary to take measures such as sufficiently smoothing the surface of the polycrystalline body to improve adhesion between the polycrystalline body and the SiC single crystal substrate 20. Therefore, from a cost perspective, the method of directly forming the texture precursor layer 40 is preferred. The method of placing a pre-prepared compact on the SiC single crystal substrate 20 is also preferred as a simple method, but because the texture precursor layer 40 is composed of powder, a sintering process is required in the heat treatment step described below. Both methods can use known conditions, but below we will describe a method of forming an orientation precursor layer 40 directly on a SiC single crystal substrate 20 by the AD method or thermal CVD method, and a method of placing a pre-prepared molded body on a SiC single crystal substrate 20.

[0030] The AD method is a technology in which fine particles or fine particle raw material are mixed with a gas to form an aerosol, and this aerosol is then sprayed at high speed from a nozzle to collide with a substrate, forming a coating. The AD method has the advantage of being able to form a coating at room temperature. An example of a film-forming apparatus (AD apparatus) used in this 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, in which raw material powder is sprayed onto a substrate under 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 sprays the raw material powder onto a SiC single crystal substrate 20 to form a film containing the raw material components. The aerosol generation unit 52 includes an aerosol generation chamber 53 that contains raw material powder and generates aerosol by receiving a supply of carrier gas from a gas cylinder (not shown), a raw material supply pipe 54 that supplies the generated aerosol to the film formation unit 60, and a vibrator 55 that applies vibrations at a frequency of 10 to 100 Hz to the aerosol generation chamber 53 and the aerosol therein. The film formation unit 60 includes a film formation chamber 62 that sprays the aerosol onto the SiC single crystal substrate 20, a substrate holder 64 that is disposed inside the film formation chamber 62 and fixes the SiC single crystal substrate 20, and an XY stage 63 that moves the substrate holder 64 in the X-axis and Y-axis directions. The film formation unit 60 also includes an injection nozzle 66 that has a slit 67 formed at its tip and sprays the aerosol onto the SiC single crystal substrate 20, and a vacuum pump 68 that depressurizes the film formation chamber 62. The injection nozzle 66 is attached to the tip of the raw material supply pipe 54.

[0031] It is known that the AD method can cause pores in the film or result in a compacted film 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, the amount sprayed per unit time, etc. 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, etc. Therefore, to obtain a dense oriented precursor layer, it is necessary to appropriately control these factors.

[0032] As described above, the ratio P of the number of images containing anomalous light emission regions １and / or the ratio P of the number of images containing anomalous luminescence regions with sides parallel to the [1-100] direction ２ can be controlled by controlling the average particle size (e.g., D50 particle size) of the raw material powder used in the AD method, i.e., the SiC powder. The volumetric D50 particle size of the SiC powder used in the AD method is typically 10 to 200 μm, more typically 50 to 150 μm, although the preferred range varies somewhat depending on the diameter of the SiC single crystal substrate. For example, when the diameter of the SiC single crystal substrate is less than about 200 mm (less than 8 inches) (e.g., about 100 mm (4 inches) to about 150 mm (6 inches)), the volumetric D50 particle size of the SiC powder is preferably 10 μm or more and less than 200 μm, more preferably 30 to 180 μm, and most preferably 50 to 150 μm. When the diameter of the SiC single crystal substrate is about 200 mm (8 inches) or more, the volume-based D50 particle size of the SiC powder is preferably 10 μm or more and less than 100 μm, more preferably 30 to 90 μm, and even more preferably 50 to 70 μm.

[0033] In the thermal CVD method, a commercially available or other known film forming apparatus can be used. The source gas is not particularly limited, but silicon tetrachloride (SiCl ４ ) gas and silane (SiH ４ ) gas, and methane (CH ４ ) gas and propane (C ３ H ８ The film formation temperature is preferably 1000 to 2200°C, more preferably 1100 to 2000°C, and even more preferably 1200 to 1900°C.

[0034] It is known that when a film is formed on a SiC single crystal substrate 20 using thermal CVD, epitaxial growth may occur on the SiC single crystal substrate 20, forming a SiC substrate 30. However, the orientation precursor layer 40 is not oriented at the time of its formation, i.e., amorphous or non-oriented polycrystalline, and it is preferable to use a SiC single crystal as a seed crystal during the heat treatment process to cause crystalline rearrangement. It is known that the formation of an amorphous or polycrystalline layer on a SiC single crystal using thermal CVD is affected by factors such as the film formation temperature, the gas flow rates of the Si source and the C source and their ratio, and the film formation pressure. The film formation temperature has a significant effect, and from the perspective 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 even more preferably 1400°C or less. However, if the film formation temperature is too low, the film formation rate itself also decreases, so from the perspective of the film formation rate, a higher film formation temperature is preferable.

[0035] When a pre-prepared compact is used as the orientation precursor layer 40, it can be produced by molding raw material powder of the orientation precursor. For example, when press molding is used, the orientation precursor layer 40 is a press-molded body. The press-molded body can be produced by press molding raw material powder of the orientation precursor based on a known method, for example, by placing the raw material powder in a mold and pressing it at a pressure of preferably 100 to 400 kgf / cm. ２ , more preferably 150 to 300 kgf / cm ２The sheet can be fabricated by pressing the SiC single crystal substrate 20 at a pressure of 1000 psi. Furthermore, the molding method is not particularly limited, and in addition to press molding, tape casting, extrusion molding, slip casting, doctor blade molding, and any combination thereof can be used. For example, when using tape casting, additives such as binders, plasticizers, dispersants, and dispersion media are appropriately added to the raw material powder to form a slurry, and this slurry is then discharged and molded into a sheet by passing it through a narrow slit-shaped discharge port. The thickness of the sheet-shaped molded body is not limited, but from the perspective of handling, a thickness of 5 to 500 μm is preferable. Furthermore, if a thick orientation precursor layer is required, multiple sheets of this molded body can be stacked to achieve the desired thickness. These molded bodies are subsequently heat-treated on the SiC single crystal substrate 20, and the portion near the SiC single crystal substrate 20 becomes the SiC substrate 30. In this method, the molded body must be sintered in the heat treatment process described below. The SiC substrate 30 is preferably formed after the molded body is sintered and integrated with the SiC single crystal substrate 20 as a polycrystalline body. If the compact is not sintered, epitaxial growth using the SiC single crystal as a seed may not occur sufficiently. For this reason, the compact may contain additives such as sintering aids in addition to the SiC raw material.

[0036] (b) Heat Treatment Step As shown in FIG. 2(b), in the heat treatment step, a stack in which an orientation precursor layer 40 is stacked or placed on a SiC single crystal substrate 20 is heat-treated to produce a SiC substrate 30. The heat treatment method is not particularly limited as long as epitaxial growth occurs using the SiC single crystal substrate 20 as a seed. It can be performed in a known heat treatment furnace, such as a tubular furnace or a hot plate. In addition to these atmospheric (pressless) heat treatments, pressurized heat treatments such as hot pressing and HIP, or a combination of atmospheric and pressurized heat treatments, can also be used. The heat treatment atmosphere is preferably a nitrogen-containing inert gas atmosphere. The nitrogen-containing inert gas is preferably a mixed gas containing nitrogen and argon. The nitrogen flow rate is, for example, 0.5 to 15 L / min, and the argon flow rate is, for example, 3 to 100 L / min. The heat treatment temperature is preferably 1700 to 2700°C. Increasing the temperature facilitates the growth of the orientation precursor layer 40 while oriented along the c-axis and a-axis, using the SiC single crystal substrate 20 as a seed crystal. Therefore, the heat treatment temperature is preferably 1700°C or higher, more preferably 1800°C or higher, even more preferably 1900°C or higher, and particularly preferably 2200°C or higher. On the other hand, excessively high temperatures can result in partial loss of SiC due to sublimation or plastic deformation of the SiC, resulting in defects such as warping. Therefore, the heat treatment temperature is preferably 2700°C or lower, more preferably 2500°C or lower. However, because the heat treatment conditions affect the content of rare earth elements in the biaxially oriented SiC layer, it is preferable to appropriately control the conditions (e.g., heat treatment temperature and holding time). From this perspective, the heat treatment temperature is preferably 1900 to 2700°C, more preferably 2200 to 2600°C, and even more preferably 2400 to 2500°C. Furthermore, the holding time is preferably 2 to 30 hours, more preferably 4 to 20 hours. Furthermore, the heat treatment temperature and holding time are related to the thickness of the SiC substrate 30 produced by epitaxial growth, and can be adjusted as appropriate.

[0037] However, when a pre-formed compact is used as the orientation precursor layer 40, it is necessary to sinter it during the heat treatment, and high-temperature atmospheric pressure firing, hot pressing, HIP, or a combination thereof is suitable. For example, when using hot pressing, the surface pressure is 50 kgf / cm. ２ More preferably, 100 kgf / cm ２ More preferably, 200 kgf / cm ２ The firing temperature is not particularly limited, as long as sintering and epitaxial growth occur. However, since firing conditions affect the content of rare earth elements in the biaxially oriented SiC layer, it is preferable to appropriately control the firing conditions (e.g., firing temperature and holding time). From this perspective, the firing temperature is preferably 1700 to 2700°C. The holding time is preferably 2 to 18 hours. The firing atmosphere can be selected from vacuum, nitrogen, inert gas, or a mixture of nitrogen and inert gas. Furthermore, firing may be performed in multiple stages, with the firing temperature and total holding time preferably within the above ranges. The raw SiC powder 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 specific direction for 100 primary particles.

[0038] In the heat treatment step, the crystals in the orientation precursor layer 40 grow from the crystal growth surface of the SiC single crystal substrate 20 while being oriented along the c-axis and a-axis, and therefore the orientation precursor layer 40 gradually changes from the crystal growth surface into the SiC substrate 30. The SiC composite substrate including the resulting SiC substrate 30 is less susceptible to breakage and cracks during substrate processing.

[0039] 2(c) Grinding and / or Polishing Step As shown in Fig. 2(c), in the grinding step, the orientation precursor layer 40 remaining on the SiC substrate 30 after the heat treatment step is ground and removed to expose the surface of the SiC substrate 30, and the exposed surface is then ground and / or polished to obtain the SiC composite substrate 10.

[0040] It should be noted that the present invention is not limited to the above-described embodiment, and may be embodied in various forms as long as it falls within the technical scope of the present invention. For example, in the above-described embodiment, only one SiC substrate 30 is provided on the SiC single crystal substrate 20, but two or more layers may be provided. Specifically, a second SiC substrate 30 can be provided on the SiC substrate 30 by stacking an orientation precursor layer 40 on the SiC substrate 30 of the SiC composite substrate 10, performing heat treatment, and then grinding and / or polishing in this order.

[0041] The present invention will be explained in more detail by the following examples, but the present invention is not limited to the following examples.

[0042] Example 1 (1) Preparation of Textured Precursor Layer A raw material powder containing 93.0 wt.% of commercially available β-SiC powder (volume-based D50 particle size: 70 μm) and 7.0 wt.% of yttrium oxide powder (volume-based D50 particle size: 0.1 μm) was prepared. These raw material powders were mixed in ethanol using SiC balls in a ball mill for 24 hours and then dried to obtain a mixed powder. A SiC single crystal substrate (n-type 4H-SiC, circular, approximately 100 mm (4 inches) in diameter, 4° off-angle, approximately 350 μm thick) was prepared as a SiC single crystal layer. The mixed powder was sprayed onto the (0001) plane of the SiC single crystal substrate using the AD device 50 shown in FIG. 3 to form an AD film (textured precursor layer).

[0043] The AD film formation conditions were as follows: First, the carrier gas was N ２ The film was formed using a ceramic nozzle with a 5 mm long x 0.4 mm short slit. The nozzle scanning conditions were a scan speed of 0.5 mm / s, with the nozzle moving 105 mm in a direction perpendicular to the long side of the slit and advancing, 5 mm in the direction of the long side of the slit, 105 mm in a direction perpendicular to the long side of the slit and returning, and 5 mm in the direction of the long side of the slit and in the opposite direction from the initial position, and after moving 105 mm from the initial position in the direction of the long side of the slit, the nozzle was scanned in the opposite direction from the initial position, and this cycle was repeated 6,000 times. The thickness of the AD film formed in this way was approximately 600 μm.

[0044] (2) Heat Treatment of the Orientation Precursor Layer The SiC single crystal substrate on which the AD film serving as the orientation precursor layer was formed was removed from the AD apparatus and annealed in an argon atmosphere at 2400°C for 10 hours. That is, the orientation precursor layer was heat-treated to form a heat-treated layer. In this way, a SiC single crystal substrate on which a heat-treated layer was formed (hereinafter referred to as a SiC composite substrate) was obtained.

[0045] (3) Grinding (3-1) Surface Grinding The (0001) surface of the SiC composite substrate (the heat-treated layer surface opposite to the SiC single crystal substrate) was surface-ground to a predetermined thickness using a grinder (a diamond wheel with a grit of 1000 to 6000) to achieve the target thickness and surface condition.

[0046] (3-2) Backside Grinding The (000-1) surface of the SiC composite substrate (the backside of the SiC single crystal substrate opposite the heat treatment layer) was plane-ground to a predetermined thickness using a grinder (a diamond wheel with a grit of 1000 to 6000) to achieve the target thickness and surface condition.

[0047] (4) Polishing (4-1) Surface Polishing The (0001) surface of the surface-ground SiC composite substrate was polished with diamond abrasive grains, and then finished by chemical mechanical polishing (CMP) to achieve the target thickness and surface condition.

[0048] (4-2) Backside Polishing The (000-1) surface of the surface-ground SiC composite substrate was polished with diamond abrasive grains to the target thickness and surface condition. In this way, a surface-ground and surface-polished SiC composite substrate was obtained.

[0049] (5) Occurrence rate of cracks and fractures during processing Using an industrial microscope (Nikon, ECLIPSE, L200N), the eyepiece was set to 10x and the objective lens to 5x. The entire surface of the SiC composite substrate obtained in (4) above was observed in polarized light mode and differential interference mode, and if cracks or fractures were found, the substrate was considered to have cracks or fractures. At this time, only those with a length of 100 μm or more were counted as cracks and fractures. The crack and fracture incidence rate P was calculated by calculating the number of SiC composite substrates with a length of 100 μm or more out of 100 SiC composite substrates produced under the same conditions as the SiC composite substrate produced as described above.Ｃ (%) was calculated. Ｃ The yield of the substrate was evaluated by determining the following. The results are shown in Table 1.

[0050] (6) Evaluation of biaxial orientation of heat-treated layer Using EBSD (Electron Backscatter Diffraction Patterns), inverse pole figure mapping of the surface (plate surface) of the heat-treated layer of the SiC substrate obtained in (4) above and a cross section perpendicular to the plate surface was measured under the following conditions: <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)

[0051] As a result, the tilt angle distribution was 0.01° or less in both the approximately normal direction and the approximately plate-plane direction, and therefore it was determined that the heat-treated layer was a biaxially oriented SiC layer oriented along the c-axis and the a-axis. In other words, it was confirmed that the SiC composite substrate fabricated in this example consisted of a SiC single crystal substrate and a SiC substrate (biaxially oriented SiC layer) formed thereon.

[0052] (7) Multiphoton excitation microscope observation of the heat-treated layer Using a multiphoton excitation microscope (Nikon, AX R MP), a multiphoton excitation photoluminescence image of each of the areas partitioned into a 440 μm × 440 μm square grid was obtained under the following conditions for the area on the surface of the heat-treated layer (biaxially oriented SiC layer) of the SiC substrate obtained in (4) above, excluding the peripheral area within 2 mm from the outer edge of the SiC composite substrate. <Measurement conditions> Magnification of objective lens: 20x Numerical aperture of objective lens: 0.45 Laser wavelength: 700 nm Detection wavelength: 440 nm

[0053] In a multiphoton excitation photoluminescence image, as shown in Figure 4, it is possible to observe light emission that differs from the surrounding area at locations where there are abnormalities in the crystal structure. Locations that emit light that differs from the surrounding area are identified as areas with abnormal light emission. For example, in Figure 4, gray or dark areas are areas with no abnormalities, and whitish areas are areas with abnormal light emission. It is possible to determine the quality of the wafer by examining the number of areas with abnormal light emission.

[0054] (8) Analysis of Multiphoton Excitation Photoluminescence Images Using image processing software (National Institutes of Health, ImageJ), histogram equalization and noise removal were performed on each of the acquired multiphoton excitation photoluminescence images according to the following procedure.

[0055] (ImageJ operation procedure) - Step 1: Import a multiphoton-excited PL image of a 440 μm square area into the image processing software ImageJ. - Step 2: Select the commands "Process" → "Enhance Contrast" in this order, and the "Enhance Contrast" window will appear. Set "Saturated pixels" to 0.3%, check "Equalize histogram", and click "OK" to perform histogram equalization. - Step 3: Select the commands "Process" → "Filters" → "Median" in this order, and the "Median" window will appear. Set "Radius" to 5.0 pixels and click "OK" to perform noise removal using a median filter. Step 4: Select "Process" → "Filters" → "Gaussian Blur" to display the "Gaussian Blur" window. Set "Sigma (Radius)" to 5.00 and click "OK" to perform noise removal processing using a Gaussian filter.

[0056] For all images that have been subjected to the histogram equalization process and the noise removal process, the number of images containing anomalous luminescence regions is counted, and this number is divided by the number of all images and multiplied by 100 to obtain the ratio P of the number of images containing anomalous luminescence regions to the total number of multiphoton excited photoluminescence images. １ Furthermore, among the images containing anomalous luminescence regions, the number of images in which anomalous luminescence regions with sides parallel to the [1-100] direction were confirmed was counted, and this number was divided by the number of all images, and multiplied by 100 to obtain the proportion P of the number of images containing anomalous luminescence regions with sides parallel to the [1-100] direction to the total number of multiphoton excited photoluminescence images.２ The percentage P (%) was calculated. １ and P ２ was as shown in Table 1.

[0057] Example 2: In the above (1), except that β-SiC powder (volume-based D50 particle size: 50 μm) was used as the raw material powder, an SiC substrate was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0058] Example 3: A SiC substrate was produced and evaluated in the same manner as in Example 1, except that in (1) above, β-SiC powder (volume-based D50 particle size: 100 μm) was used as the raw material powder. The results are shown in Table 1.

[0059] Example 4 A SiC substrate was produced and evaluated in the same manner as in Example 1, except that in (1) above, β-SiC powder (volume-based D50 particle size: 150 μm) was used as the raw material powder. The results are shown in Table 1.

[0060] Example 5 (Comparative) An SiC substrate was produced and evaluated in the same manner as in Example 1, except that in (1) above, β-SiC powder (volume-based D50 particle size: 200 μm) was used as the raw material powder. The results are shown in Table 1.

[0061] Example 6 A SiC substrate was fabricated and evaluated in the same manner as in Example 1, except that in (1) above, a commercially available SiC single crystal substrate (n-type 4H—SiC, circular with a diameter of approximately 150 mm (6 inches), off-angle 4°, sample thickness approximately 350 μm) was used as the SiC single crystal layer. The results are shown in Table 1.

[0062] Example 7 A SiC substrate was produced and evaluated in the same manner as in Example 1, except that in (1) above, β-SiC powder (volume-based D50 particle size: 50 μm) was used as the raw material powder, and a commercially available SiC single crystal substrate (n-type 4H—SiC, circular shape with a diameter of approximately 150 mm (6 inches), off-angle 4°, sample thickness approximately 350 μm) was used as the SiC single crystal layer. The results are shown in Table 1.

[0063] Example 8 A SiC substrate was produced and evaluated in the same manner as in Example 1, except that in (1) above, β-SiC powder (volume-based D50 particle size: 100 μm) was used as the raw material powder, and a commercially available SiC single crystal substrate (n-type 4H—SiC, circular shape with a diameter of approximately 150 mm (6 inches), off-angle 4°, sample thickness approximately 350 μm) was used as the SiC single crystal layer. The results are shown in Table 1.

[0064] Example 9 A SiC substrate was produced and evaluated in the same manner as in Example 1, except that in (1) above, β-SiC powder (volume-based D50 particle size: 150 μm) was used as the raw material powder, and a commercially available SiC single crystal substrate (n-type 4H—SiC, circular shape with a diameter of approximately 150 mm (6 inches), off-angle 4°, sample thickness approximately 350 μm) was used as the SiC single crystal layer. The results are shown in Table 1.

[0065] Example 10 (Comparison) A SiC substrate was produced and evaluated in the same manner as in Example 1 above (1), except that β-SiC powder (volume-based D50 particle size: 200 μm) was used as the raw material powder, and a commercially available SiC single crystal substrate (n-type 4H—SiC, circular shape with a diameter of approximately 150 mm (6 inches), off-angle 4°, sample thickness approximately 350 μm) was used as the SiC single crystal layer. The results are shown in Table 1.

[0066] Example 11 A SiC substrate was fabricated and evaluated in the same manner as in Example 1, except that in (1) above, a commercially available SiC single crystal substrate (n-type 4H—SiC, circular with a diameter of approximately 200 mm (8 inches), off-angle 4°, sample thickness approximately 500 μm) was used as the SiC single crystal layer. The results are shown in Table 1.

[0067] Example 12 A SiC substrate was produced and evaluated in the same manner as in Example 1, except that in (1) above, β-SiC powder (volume-based D50 particle size: 50 μm) was used as the raw material powder, and a commercially available SiC single crystal substrate (n-type 4H—SiC, circular shape with a diameter of approximately 200 mm (8 inches), off-angle 4°, sample thickness approximately 500 μm) was used as the SiC single crystal layer. The results are shown in Table 1.

[0068] Example 13 A SiC substrate was produced and evaluated in the same manner as in Example 1, except that in (1) above, β-SiC powder (volume-based D50 particle size: 100 μm) was used as the raw material powder, and a commercially available SiC single crystal substrate (n-type 4H—SiC, circular shape with a diameter of approximately 200 mm (8 inches), off-angle 4°, sample thickness approximately 500 μm) was used as the SiC single crystal layer. The results are shown in Table 1.

[0069]

[0070] From the above experiment, it was found that the rate P of occurrence of luminescence abnormality regions can be reduced by changing the particle size of the SiC powder used in the heat treatment of the textured precursor layer. １ and P ２ and the rate of crack occurrence P ｃ For example, when the diameter of the SiC substrate is about 100 mm (equivalent to 4 inches) or about 150 mm (equivalent to 6 inches), if the volume-based D50 particle size of the SiC powder is less than 200 μm, the ratio P １ is 40% or less, percentage P ２ When the diameter of the SiC substrate is about 200 mm (equivalent to 8 inches), the ratio P １ is 40% or less, percentage P ２ It was found that the cracks and breakages during processing could be effectively reduced.

Claims

1. A SiC substrate having a biaxially oriented SiC layer, wherein, when multiphoton excitation photoluminescence images are acquired for each region on the surface of the biaxially oriented SiC layer, which is partitioned into a 440 μm square grid, excluding a peripheral region within 2 mm from the outer edge of the SiC substrate, the ratio P of the number of images including anomalous emission regions to the total number of multiphoton excitation photoluminescence images is １ A SiC substrate, wherein the SiC substrate has a surface roughness of 40% or less.

2. The ratio P of the number of images including anomalous luminescence regions having sides parallel to the [1-100] direction to the total number of multiphoton excited photoluminescence images ２ The SiC substrate according to claim 1 , wherein the SiC substrate has a refractive index of 35% or less.

3. The SiC substrate according to claim 1 or 2, wherein the diameter of the SiC substrate is 99 mm or more.

4. The SiC substrate according to claim 1 or 2, wherein the diameter of the SiC substrate is 149 mm or more.

5. The SiC substrate according to claim 1 or 2, wherein the diameter of the SiC substrate is 199 mm or more.

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.

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