Patent Application
20240186380
The present invention relates to a SiC substrate and a SiC composite substrate.
SiC (silicon carbide) has attracted attention as a wide bandgap material capable of controlling large voltage and large electric power with low loss. In recent years in particular, power semiconductor devices using SiC materials (SiC power devices) are superior to those using Si semiconductors in terms of downsizing, low power consumption, and high efficiency, and therefore are expected to be utilized in various applications. For example, by adopting the SiC power devices, a converter, an inverter, an in-vehicle charger, and the like for an electric vehicle (EV) or a plug-in hybrid vehicle (PHEV) can be downsized, making it possible to improve efficiency.
To utilize a SiC power device for high withstand voltage applications, defects in a SiC wafer need to be decreased to the utmost limit in order to cope with a large current, thereby lowering of device characteristics needs to be suppressed. In this respect, a solution growth method is known as a method for decreasing defects in a wafer, particularly threading screw dislocations (TSDs) which are considered to be a cause for deterioration in withstand voltage. For example, Patent Literature 1 (JP2014-043369A) discloses a method for manufacturing a SiC single crystal comprising the steps of forming a macrostep composed of a SiC single crystal and having a height of higher than 70 nm on a (0001) plane of a SiC seed crystal to provide a second seed crystal, and growing a SiC single crystal on a (0001) plane of the second seed crystal in a reaction atmosphere comprising Si and C to cause the macrostep to progress on threading screw dislocations in the second seed crystal. It is stated that according to this manufacturing method, a SiC single crystal in which the threading screw dislocations are small in number is obtained. However, when a SiC substrate is produced by a solution growth method, there are problems that, for example, macrodefects, such as solvent inclusion due to surface roughness and different polymorphic crystal forms, are likely to occur.
On the other hand, as a method other than the solution growth method, a method of forming a SiC epitaxial layer by a chemical vapor deposition method is known. For example, Non-Patent Literature 1 (Lixia Zhao et al. “Surface defects in 4H—SiC homoepitaxial layers” Nanotechnology and Precision Engineering 3 (2020) 229-234) discloses that a SiC epitaxial layer is obtained by a chemical vapor deposition method and the forms and structures of the surface defects have been investigated, and states that the TSD density of a SiC substrate is generally 300 to 500 cm−2.
However, according to the disclosure of Non-Patent Literature 1, most of the TSDs on the substrate are propagated to the epitaxial layer, and therefore it is difficult to allow the TSD density of the substrate surface to fall well below 300 cm−2. Therefore, further decrease in the TSD density at the SiC substrate surface is desired.
The present inventors have now discovered that a biaxially oriented SiC layer that satisfies predetermined conditions when analyzed by photoluminescence (PL) provides a SiC substrate in which the TSD density of the surface is very low.
Therefore, it is an object of the present invention to provide a SiC substrate in which the TSD density of the surface is very low.
The present invention provides the following aspects:
A SiC substrate comprising a biaxially oriented SiC layer, wherein when a surface of the biaxially oriented SiC layer is analyzed by photoluminescence (PL) to obtain a graph by plotting PL intensity I as the vertical axis versus distance (μm) in the [11-20] direction as the horizontal axis,
The SiC substrate according to aspect 1, wherein the distance L is 50 to 150 μm.
A SiC substrate comprising a biaxially oriented SiC layer, wherein when in an image obtained by analyzing a surface of the biaxially oriented SiC layer by photoluminescence (PL), the [11-20] direction of the image is processed with a Prewitt filter to obtain a graph by plotting PL intensity IF as the vertical axis versus distance (μm) in the [11-20] direction as the horizontal axis,
The SiC substrate according to any one of aspects 1 to 3, wherein the biaxially oriented SiC layer is oriented in the c-axis direction and the a-axis direction, and when a graph is obtained for the biaxially oriented SiC layer by plotting threading screw dislocation (TSD) density (cm−2) as the vertical axis versus depth (μm) from a (0001) plane that is a substrate surface to an arbitrary (000-1) plane as the horizontal axis, the graph comprises a TSD sloped region where the TSD density is decreased at a constant slope a as the depth decreases and the absolute value of the slope a is 5.0 cm−2/μm or more.
The SiC substrate according to any one of aspects 1 to 4, wherein the biaxially oriented SiC layer comprises boron in a concentration of 1.0×1016 to 1.0×1017 atoms/cm3.
The SiC substrate according to aspect 4, wherein the absolute value of the slope a is 5.0 to 25 cm−2/μm.
A SiC composite substrate comprising:
A SiC substrate according to the present invention is a Sic substrate comprising a biaxially oriented SiC layer. When a surface of this biaxially oriented SiC layer is analyzed by photoluminescence (PL) to obtain a graph by plotting PL intensity I as the vertical axis versus distance (μm) in the [11-20] direction as the horizontal axis, (i) the graph has a specific shape such that a maximum point and a minimum point are repeated, as shown in
When a SiC substrate comprising a biaxially oriented SiC layer is analyzed by PL, and the biaxially oriented SiC layer satisfies predetermined conditions, as just described above, the biaxially oriented SiC layer can provide a SiC substrate in which the TSD density of the surface is very low. In addition, such a SiC substrate can be produced without using a solution growth method, and therefore a macrodefect on the substrate surface is unlikely to occur.
As described above, with regard to conventional SiC substrates, when a SiC substrate is produced by a solution growth method for example, there are problems that, for example, macrodefects, such as solvent inclusion due to surface roughness and different polymorphic crystal forms, are likely to occur. In addition, even when a SiC epitaxial layer is formed by a chemical vapor deposition method, most of the TSDs on the substrate are propagated to the epitaxial layer, and therefore it has been considered to be difficult to allow the TSD density of the substrate surface to fall well below 300 cm−2. In this respect, according to the SiC substrate of the present invention, the problems can be conveniently solved.
The biaxially oriented SiC layer that forms the SiC substrate of the present invention is such that in the case where a surface of the biaxially oriented SiC layer is analyzed by PL to obtain a graph by plotting PL intensity I as the vertical axis versus distance (μm) in the [11-20] direction as the horizontal axis, when a maximum value of PL intensity I at a given maximum point PM is assumed to be M, and a minimum value of PL intensity I at a minimum point Pm whose distance in the [11-20] direction is longer than that of the maximum point PM, and the minimum point Pm being present at a position nearest to the maximum point PM, is assumed to be m, a ratio of M/m is 1.05 or more (hereinafter, referred to as condition (ii)). Although the upper limit is not particularly limited, this ratio of M/m is preferably 1.05 to 1.80.
Further, in the graph obtained by analyzing the surface of the biaxially oriented SiC layer by PL, the distance L in the [11-20] direction between the maximum point PM and the minimum point Pm is 15 to 150 μm (hereinafter, referred to as condition (iii)), preferably 50 to 150 μm, more preferably 50 to 120 μm, and further preferably 50 to 100 μm.
The graph typically has a regular pattern in which a waveform including a maximum point and a minimum point are repeated at a constant cycle, as shown in
Alternatively, the biaxially oriented SiC layer that forms the SiC substrate of the present invention is such that when in an image obtained by analyzing a surface of the biaxially oriented SiC layer by PL, the [11-20] direction of the image is processed with a Prewitt filter to obtain a graph by plotting PL intensity IF as the vertical axis versus distance (μm) in the [11-20] direction as the horizontal axis, distance LE in the [11-20] direction between a given maximum point PM1 and a maximum point PM2 whose distance in the [11-20] direction is longer than that of the maximum point PM1, the maximum point PM2 being present at a position nearest to the maximum point PM1, is 30 to 300 μm (hereinafter, referred to as condition (v)), preferably 100 to 300 μm, more preferably 100 to 240 μm, and further preferably 100 to 200 μm.
In the graph obtained by Prewitt filter processing, a plurality of maximum points is repeated as shown in
The biaxially oriented SiC layer is preferably oriented in the c-axis direction and the a-axis direction. In addition, the SiC substrate is preferably composed of the biaxially oriented SiC layer. The biaxially oriented SiC layer may be a SiC single crystal, or a mosaic crystal as long as the biaxially oriented SiC layer is oriented in the biaxial directions of the c-axis direction and the a-axis direction. The mosaic crystal refers to an aggregate of crystals not having clear grain boundaries but being such that the orientation directions of the crystals are slightly different from one or both of the c-axis and the a-axis. The method for evaluating the orientation is not particularly limited, but known analysis methods such as an EBSD (Electron Back Scatter Diffraction Patterns) method and an X-ray pole figure can be used. For example, when the EBSD method is used, inverse pole figure mapping of a surface (plate surface) of the biaxially oriented SiC layer or a section orthogonal to the plate surface is measured. When the following four conditions are satisfied in the resultant inverse pole figure mapping, the SiC layer can be defined as being biaxially oriented in an approximate normal direction and an approximate plate surface direction: (A) the SiC layer is oriented in a particular direction (the first axis) in an approximate normal direction of the plate surface; (B) the SiC layer is oriented in a particular direction (the second axis) in an approximate in-plate-surface direction, the direction orthogonal to the first axis; (C) tilt angles from the first axis are distributed within +10°; and (D) tilt angles from the second axis are distributed within +10°. In other words, when the four conditions are satisfied, the SiC layer is determined to be biaxially oriented along the c-axis and the a-axis. For example, when the approximate normal direction of the plate surface is oriented along the c-axis, the approximate in-plate-surface direction only needs to be oriented in a particular direction (for example, the a-axis) orthogonal to the c-axis. The biaxially oriented SiC layer only needs to be biaxially oriented in the approximate normal direction and the approximate in-plate-surface direction, but the approximate normal direction is preferably oriented along the c-axis direction. As a tilt angle distribution in the approximate normal direction and/or the approximate in-plate-surface direction is smaller, the mosaicity of the biaxially oriented SiC layer is smaller, and as the tilt angle distribution is closer to zero, the biaxially oriented SiC layer is closer to a single crystal. Therefore, in view of the crystallinity of the biaxially oriented SiC layer, the tilt angle distribution is preferably smaller in both the approximate normal direction and the approximate plate surface direction, more preferably, for example, +5° or less, and further preferably +3º or less.
As for the biaxially oriented SiC layer oriented in the c-axis direction and the a-axis direction, when a graph is obtained by plotting the TSD density (cm−2) as the vertical axis versus depth (μm) from a (0001) plane that is a substrate surface to an arbitrary (000-1) plane as the horizontal axis, the graph preferably comprises a TSD sloped region in at least a part of thereof, as shown in
The biaxially oriented SiC layer preferably comprises boron in a concentration of 1.0×1016 to 1.0×1017 atoms/cm3, and more preferably 1.0×1016 to 9.5×1016 atoms/cm3. By controlling the boron content in this manner, the distribution of PL intensity can be preferably controlled in the above-described graph obtained by PL, and the SiC substrate in which the TSD density of the substrate surface is decreased can be effectively obtained.
The SiC substrate of the present invention may be a self-supporting substrate consisting of a SiC substrate or may be in the form of a SiC composite substrate. The SiC composite substrate can be one comprising: a SiC single crystal substrate; and the above-described SiC substrate on the SiC single crystal substrate.
The SiC single crystal substrate is typically a layer composed of a SiC single crystal and has a crystal growth surface. 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 axis of single crystal SiC, and the polarity is preferably the Si surface. More preferably, the polytype is 4H, the off angle is 1 to 5° from the axis of single crystal SiC, and the polarity is the Si surface.
As described above, the SiC substrate of the present invention may be in the form of a self-supporting substrate consisting of a biaxially oriented SiC layer or may be in the form of a SiC composite substrate with a SiC single crystal substrate. Therefore, the biaxially oriented SiC layer may be finally separated from the SiC single crystal substrate as necessary. The separation of the SiC single crystal substrate may be performed by a known method and is not particularly limited. Examples of the known method include a method of separating the biaxially oriented SiC layer with a wire saw, a method of separating the biaxially oriented SiC layer by electro discharge machining, and a method of separating the biaxially oriented SiC layer utilizing laser. In an embodiment in which the biaxially oriented SiC layer is epitaxially grown on a SiC single crystal substrate, the biaxially oriented SiC layer may be installed on another support substrate after the SiC single crystal substrate is separated. The material of the another support substrate is not particularly limited and suitable one may be selected in view of physical properties of the material. In view of thermal conductivity for example, examples of the material include metal substrates such as a Cu substrate and ceramic substrates such as a SiC substrate and an AlN substrate.
The SiC composite substrate comprising the SiC substrate of the present invention can be preferably manufactured by (a) forming a predetermined orientation precursor layer on a SiC single crystal substrate, (b) subjecting the orientation precursor layer to heat treatment on the SiC single crystal substrate to convert at least a portion of the orientation precursor layer near the SiC single crystal substrate into a SiC substrate (biaxially oriented SiC layer), and, optionally, (c) performing processing such as grinding or polishing to expose the surface of the biaxially oriented SiC layer. However, the method for manufacturing the SiC composite substrate is not limited as long as it is possible to obtain a SiC substrate such that when a SiC substrate comprising a biaxially oriented SiC layer is analyzed by PL, the particular analysis results as described above are obtained. For example, as the manufacturing method, vapor phase methods such as CVD and a sublimation method may be adopted, liquid phase methods such as a solution method may be adopted, or solid phase methods utilizing grain growth may be adopted. The distribution of PL intensity in the graph obtained by PL can be controlled by, for example, controlling heat treatment conditions in (b); or controlling the amount of boron or the boron compound (for example, boron carbide or the like) to be added in (a) forming an orientation precursor layer. According to such manufacturing methods, it is possible to produce a SiC substrate such that when a SiC substrate comprising a biaxially oriented SiC layer is analyzed by PL, the particular analysis results as described above are obtained, and it is possible to significantly decrease the TSD density on the surface of the siC substrate or the SiC composite substrate using the SiC substrate.
Hereinafter, a preferred method for manufacturing the SiC composite substrate will be described.
As shown in
As shown in
As the method for forming the orientation precursor layer 40, a known method can be adopted. Examples of the method for forming the orientation precursor layer 40 include solid phase film deposition methods such as an AD (Aerosol Deposition) method and a HPPD (Hypersonic Plasma Particle Deposition) method, vapor phase film deposition methods such as a sputtering method, a vapor deposition method, a sublimation method, and various CVD (Chemical Vapor Deposition) methods, and liquid phase film deposition methods such as a solution growth method, and a method of directly forming the orientation precursor layer 40 on the SiC single crystal substrate 20 can be used. As the CVD method, for example, a thermal CVD method, a plasma CVD method, a mist CVD method, and a MO (Metal Organic) CVD method can be used. Further, it is also possible to use a method in which a polycrystalline substance previously produced by a sublimation method, any of various CVD methods, sintering, or the like is used as the orientation precursor layer 40, and the polycrystalline substance is placed on the SiC single crystal substrate 20. Alternatively, the method for forming the orientation precursor layer 40 may also be a method in which a green body of the orientation precursor layer 40 is preliminarily produced, and this green body is placed on the SiC single crystal substrate 20. Such an orientation precursor layer 40 may be tape green body produced by tape casting or a green compact produced by pressure forming such as uniaxial pressing.
In forming these orientation precursor layers 40, a boron compound is preferably contained in the raw materials for the orientation precursor layers 40. Examples of the boron compound include, but not particularly limited to, boron carbide. As described above, the concentration of boron in the biaxially oriented SiC layer to be finally obtained can be controlled by, for example, controlling the amount of the boron compound to be added.
When any of various CVD methods, a sublimation method, a solution growth method, or the like is used in the method of directly forming the orientation precursor layer 40 on the SiC single crystal substrate 20, epitaxial growth may occur on the SiC single crystal substrate 20 without a heat treatment process, which will be described later, so that the SiC substrate 30 may be deposited. However, the orientation precursor layer 40 is preferably not oriented, specifically is preferably an amorphous or non-oriented polycrystal, at the time of formation, and is preferably oriented using a SiC single crystal as a seed in the heat treatment process in a later stage. Thus, crystal defects that reach the surface of the SiC substrate 30 can be effectively reduced. The reason for this is not certain, but it is considered that the solid phase orientation precursor layer once deposited causes rearrangement of the crystal structure using a SiC single crystal as a seed, and this may also have an effect in disappearance of crystal defects. Therefore, when any of various CVD methods, a sublimation method, a solution growth method, or the like is used, it is preferred to select conditions that do not cause epitaxial growth to occur in the process of forming the orientation precursor layer 40. However, it is difficult to decrease the TSD density sufficiently by only selecting such conditions, and therefore it is preferred to control the heat treatment conditions such as firing temperature; the amount of boron to be added; and the like.
However, the method for forming the orientation precursor layer 40 is preferably a method of directly forming the orientation precursor layer 40 on the SiC single crystal substrate 20 by an AD method or any of various CVD methods, or a method of placing a polycrystalline substance on the SiC single crystal substrate 20, wherein the polycrystalline substance is separately produced by a sublimation method, any of various CVD methods, sintering, or the like. The use of these methods makes it possible to form the orientation precursor layer 40 in a relatively short time. The AD method is particularly preferred because a high-vacuum process is unnecessary, and the film deposition rate is relatively high. In the method using a previously produced polycrystalline substance as the orientation precursor layer 40, ingenuity such as making the surface of the polycrystalline substance sufficiently smooth in advance is necessary in order to enhance the adhesion between the polycrystalline substance and the SiC single crystal substrate 20. Therefore, the method of directly forming the orientation precursor layer 40 is preferred in view of cost. The method of placing a previously produced green body on the SiC single crystal substrate 20 is also preferred as a simple method, but the orientation precursor layer 40 is composed of a powder, and therefore a sintering process is necessary in the heat treatment process, which will be described later. Known conditions can be used in any of the methods, but hereinafter, description will be made on the method of directly forming the orientation precursor layer 40 on the SiC single crystal substrate 20 by an AD method or a thermal CVD method and the method of placing a previously produced green body on the SiC single crystal substrate 20.
The AD method is a technique such that fine particles or fine particle raw materials are mixed with a gas to form aerosol, and this aerosol is jetted at a high speed from a nozzle to allow the aerosol to collide with a substrate to form a coat and has a characteristic that the coat can be formed at normal temperature.
The AD method is known to generate pores in a film or make a film into a green compact depending on the film deposition conditions. For example, the AD method is susceptible to the collision speed of the raw material powder onto the substrate, the particle size of the raw material powder, the aggregation state of the raw material powder in the aerosol, the jetting amount per unit time, and the like. The collision speed of the raw material powder onto the substrate is influenced by the differential pressure between the inside of the film deposition chamber 62 and the inside of the jet nozzle 66, the opening area of the jet nozzle, and the like. Therefore, to obtain a dense orientation precursor layer, these factors need to be controlled properly.
In the thermal CVD method, known film deposition apparatuses such as commercially available film deposition apparatuses can be utilized as a film deposition apparatus. The raw material gas is not particularly limited, and a silicon tetrachloride (SiCl4) gas and a silane (SiH4) gas as a supply source of Si, and a methane (CH4) gas, a propane (C3H8) gas, and the like as a supply source of C can be used. The film deposition temperature is preferably 1000 to 2200° C., more preferably 1100 to 2000° C., and further preferably 1200 to 1900° C.
When the orientation precursor layer 40 is deposited 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 orientation precursor layer 40 is preferably not oriented, specifically is preferably an amorphous or non-oriented polycrystal, at the time of production, and it is preferred to allow rearrangement of the crystals to occur using a SiC single crystal as a seed crystal during the heat treatment process.
The film deposition temperature, the flow rates of gases such as a Si source and a C source and the ratio thereof, the film deposition pressure, and the like are known to give influences in forming an amorphous or polycrystal layer on a SiC single crystal using the thermal CVD method. The influence of the film deposition temperature is large, and in view of forming an amorphous or polycrystal layer, the film deposition temperature is preferably lower, preferably lower than 1700ºC, more preferably 1500° C. or lower, and further preferably 1400° C. or lower. However, when the film deposition temperature is too low, the film deposition rate itself is also lowered, and therefore the film deposition temperature is preferably higher in view of the film deposition rate.
When a previously produced green body is used as the orientation precursor layer 40, the green body can be produced by forming a raw material powder for the orientation precursor. For example, when press forming is used, the orientation precursor layer 40 is a press-formed green body. The press-formed green body can be produced by subjecting the raw material powder for the orientation precursor to press forming based on a known method and may be produced by, for example, putting the raw material powder into a metal mold and pressing the raw material powder at a pressure of preferably 100 to 400 kgf/cm2, and more preferably 150 to 300 kgf/cm2. The forming method is not particularly limited, and tape casting, extrusion forming, slip casting, and a doctor blade method, and optional combinations thereof can be used in addition to press forming. For example, when tape casting is used, additives such as a binder, a plasticizer, a dispersant, and a dispersion medium are appropriately added to the raw material powder to make a slurry, and this slurry is preferably allowed to pass through a slit-like thin ejection port to be ejected and formed into a sheet. The thickness of the green body formed into a sheet is not limited but is preferably 5 to 500 μm in view of handling. When a thick orientation precursor layer is necessary, a plurality of the sheet green bodies may be stacked into a desired thickness for use. A portion of these green bodies near the SiC single crystal substrate 20 is made into the SiC substrate 30 by the subsequent heat treatment on the SiC single crystal substrate 20. In such a method, the green bodies need to be sintered in the heat treatment process, which will be described later. The SiC substrate 30 is preferably formed after the green bodies are subjected to the process in which the green bodies are sintered and integrated as a polycrystalline substance with the SiC single crystal substrate 20. When the green bodies do not undergo a sintered state, epitaxial growth using a SiC single crystal as a seed may occur insufficiently. Therefore, the green body may contain an additive such as a sintering aid in addition to the SiC raw material.
As shown in
However, a previously produced green body, when used as the orientation precursor layer 40, needs to be sintered during the heat treatment, and normal pressure firing at a high temperature, hot pressing, HIP, or a combination thereof is suitable. For example, when hot pressing is used, the surface pressure is preferably 50 kgf/cm- or higher, more preferably 100 kgf/cm- or higher, and further preferably 200 kgf/cm2 or higher, and there is no upper limit in particular. In addition, the firing temperature is not particularly limited as long as sintering and epitaxial growth occur. However, the firing conditions give an influence on the distribution of PL intensity in the graph obtained by PL of the surface of the biaxially oriented SiC layer, and therefore it is preferred to appropriately control the conditions (for example, the firing temperature and holding time). From such viewpoints, the firing temperature is preferably 1700 to 2700° C. The holding time is preferably 2 to 18 hours. The atmosphere during the firing can be selected from vacuum, nitrogen, and inert gas atmospheres, or a mixed gas of nitrogen and an inert gas. The SiC powder which is a raw material may be any of an α-SiC powder and a β-SiC powder, but is preferably a β-SiC powder. 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 an average value obtained when the powder is observed with a scanning electron microscope to measure the maximum sizes in a constant direction for 100 primary particles.
In the heat treatment process, the crystals in the orientation precursor layer 40 grow while being oriented along the c-axis and the a-axis from the crystal growth surface of the SiC single crystal substrate 20, and therefore the orientation precursor layer 40 is gradually changed into the SiC substrate 30 from the crystal growth surface. The SiC composite substrate comprising the generated SiC substrate 30 is such that the TSD density of the substrate surface is decreased. The reason for this is not clear, but it is considered that this is because the distribution of PL intensity reflects a step-terrace structure that is generated during crystal growth, and the TSDs have been converted to lamination defects with the crystal growth.
As shown in
The present invention is not limited to the above-described embodiments, and it is needless to say that that the present invention can be conducted in various aspects as long as they belong 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, by laminating the orientation precursor layer 40 on the SiC substrate 30 of the SiC composite substrate 10, and performing heat treatment and grinding in the mentioned order, the SiC substrate 30 as the second layer can be provided on the SiC substrate 30.
The present invention will be more specifically described by the following examples. The present invention is not limited only by the following Examples.
A raw material powder containing 90.8% by weight of a commercially available β-SiC fine powder (volume-based D50 particle size: 0.7 μm), 8.1% by weight of an yttrium oxide powder (volume-based D50 particle size: 0.1 μm), and 1.1% by weight of a silicon dioxide powder (volume-based D50 particle size: 0.7 μm) was mixed with a ball mill using SiC balls in ethanol for 24 hours, and the resultant mixture was dried to obtain a mixed powder. A commercially available SiC single crystal substrate (n-type 4H—SiC, diameter 100 mm (4 inches), Si surface, (0001) plane, off angle 4°, thickness 0.35 mm, without an orientation flat) was provided, and the mixed powder was jetted onto the SiC single crystal substrate with the AD apparatus 50 shown in
Conditions for depositing the AD film were as follows. Firstly, Ne was used as a carrier gas, and the film was deposited using a nozzle made of a ceramic and being such that a slit of 5 mm in long side×0.4 mm in short side was formed. The condition for scanning the nozzle was as follows. The scan speed was set to 0.5 mm/s, the following scans were repeated: moving the nozzle 105 mm in a vertical and advancing direction with respect to the long side of the slit; moving the nozzle 5 mm in the long side direction of the slit; moving the nozzle 105 mm in a vertical and returning direction with respect to the long side of the slit; and moving the nozzle 5 mm in the long side direction of the slit and the opposite direction to the initial position, at the time when the nozzle was moved 105 mm from the initial position in the long side direction of the slit, scans were conducted in directions opposite to the previous directions to return the nozzle to the initial position, and this cycle was defined as one cycle, and this cycle was repeated up to 4000 cycles. The AD film thus formed had a thickness of about 400 μm.
The SiC single crystal substrate on which the AD film, which is the orientation precursor layer was formed was taken out of the AD apparatus, and annealed in an argon atmosphere at 2400° C. for 10 hours. In other words, the orientation precursor layer was subjected to heat treatment to form a heat-treated layer. Thus, a SiC composite substrate including a heat-treated layer formed on a SiC single crystal substrate was produced.
A (0001) plane (that is, heat-treated layer surface) of the SiC composite substrate including a heat-treated layer formed on the SiC single crystal substrate was subjected to polishing using diamond abrasive grains (whose grain sizes are 3.0 μm, 1.0 μm, 0.5 μm, and 0.1 μm respectively) in descending order of grain size into a targeted thickness and surface state.
After (3-1), a (000-1) plane of the SiC composite substrate including a heat-treated layer formed on the SiC single crystal substrate was subjected to surface grinding with a grinder (diamond wheel of #1000 to 6000) to a predetermined thickness. Subsequently, the (000-1) plane was subjected to polishing using diamond abrasive grains (whose grain sizes are 3.0 μm, 1.0 μm, 0.5 μm, and 0.1 μm respectively) in descending order of grain size. Thereby, the whole of the SiC single crystal substrate was ground to obtain a substrate (SiC substrate) consisting of the heat-treated layer.
The SiC composite substrate or the SiC substrate obtained as a sample in (3-1) or (3-2), was cut with a diamond cutter to be processed into a chip shape of 5 mm×6 mm.
Inverse pole figure mapping was measured using the EBSD (Electron Back Scatter Diffraction Patterns) method for the surface (plate surface) and section orthogonal to the plate surface of the heat-treated layer produced in (3-1) and (3-2) under the following conditions to find the tilt angle distribution to be 0.01° or less for both the approximate normal direction and the approximate plate surface direction, and therefore the heat-treated layer was determined to be a biaxially oriented SiC layer oriented along the c-axis and the a-axis.
The sample obtained by processing the heat-treated layer (biaxially oriented SiC layer) produced in (1) to (4) into a chip shape was used as an evaluation sample to obtain a PL image of the evaluation sample surface. At this time, as shown in
Further, in the image obtained by cutting out the arbitrary region of 3.0 mm×2.2 mm in the PL image, the [11-20] direction was processed using image processing software (product name: WinROOF2015) with a Prewitt filter using a kernel of 5×5. The result is shown in
The sample obtained by processing the heat-treated layer (biaxially oriented SiC layer) produced in (1) to (4) into a chip shape was used as an evaluation sample to quantitatively determine the boron concentration inside the biaxially oriented SiC layer by secondary ion mass spectrometry (SIMS). The boron concentration from the (0001) plane that is a substrate surface of the evaluation sample to a depth of 10 μm was measured to find that the boron concentration was almost constant irrespective of the depth of the biaxially oriented SiC layer and the boron concentration was as shown in Table 1. Even though a boron compound was not added in the present example, boron was detected in the biaxially oriented SiC layer, but this merely shows that boron as an inevitable impurity was detected. The analysis conditions at this time were as shown below.
The sample obtained by processing the SiC composite substrate obtained in (1) to (3-1) into a chip shape by (4) was used as an evaluation sample to measure the TSD density (cm−2) of the biaxially oriented SiC layer. The evaluation sample was placed together with a KOH crystal in a crucible made of nickel and was subjected to etching treatment in an electric furnace at 500° C. for 10 minutes. The evaluation sample after the etching treatment was rinsed, and the surface thereof was observed with an optical microscope to determine the kind of dislocation from the shapes of pits. Here, a shell-like shape pit was regarded as a basal plane dislocation, a small hexagonal pit was regarded as a threading edge dislocation, and a middle to large hexagonal pit was regarded as the TSD to measure the TSD density. Subsequently, the surface of this evaluation sample was polished by the same procedure as in (3-1), and the etching treatment and the measurement of the TSD density were repeated a plurality of times in the same manner as described above to obtain the TSD density at a plurality of depths. Thus, a graph was obtained by plotting the TSD density (cm−2) as the vertical axis versus depth (polished thickness) (μm) from the (0001) plane that is a substrate surface of the evaluation sample to an arbitrary (000-1) plane as the horizontal axis, as shown in
A SiC substrate was produced and evaluated as in Example 1 except that the annealing temperature was set to 2200° ° C. in (2). The heat-treated layer of the resultant SiC substrate was confirmed to be a biaxially oriented SiC layer. The results were as shown in Table 1.
A SiC substrate was produced and evaluated as in Example 1 except that a powder containing 85.8% by weight of the β-SiC fine powder (volume-based D50 particle size: 0.7 μm), 8.1% by weight of the yttrium oxide powder (volume-based D50 particle size: 0.1 μm), 1.1% by weight of the silicon dioxide powder (volume-based D50 particle size: 0.7 μm), and 5.0% by weight of a boron carbide powder (volume-based D50 particle size: 0.5 μm) was used as the raw material powder in (1). The heat-treated layer of the resultant SiC substrate was confirmed to be a biaxially oriented SiC layer. The results were as shown in Table 1.
A SiC substrate was produced and evaluated as in Example 1 except that a powder containing 80.8% by weight of the β-SiC fine powder (volume-based D50 particle size: 0.7 μm), 8.1% by weight of the yttrium oxide powder (volume-based D50 particle size: 0.1 μm), 1.1% by weight of the silicon dioxide powder (volume-based D50 particle size: 0.7 μm), and 10.0% by weight of a boron carbide powder (volume-based D50 particle size: 0.5 μm) was used as the raw material powder in (1). The heat-treated layer of the resultant SiC substrate was confirmed to be a biaxially oriented SiC layer. The results were as shown in Table 1.
A SiC substrate was produced and evaluated as in Example 1 except that a powder containing 70.8% by weight of the β-SiC fine powder (volume-based D50 particle size: 0.7 μm), 8.1% by weight of the yttrium oxide powder (volume-based D50 particle size: 0.1 μm), 1.1% by weight of the silicon dioxide powder (volume-based D50 particle size: 0.7 μm), and 20.0% by weight of a boron carbide powder (volume-based D50 particle size: 0.5 μm) was used as the raw material powder in (1). The heat-treated layer of the resultant SiC substrate was confirmed to be a biaxially oriented SiC layer. The results were as shown in Table 1.
A SiC substrate was produced and evaluated as in Example 1 except that a powder containing 60.8% by weight of the β-SiC fine powder (volume-based D50 particle size: 0.7 μm), 8.1% by weight of the yttrium oxide powder (volume-based D50 particle size: 0.1 μm), 1.1% by weight of the silicon dioxide powder (volume-based D50 particle size: 0.7 μm), and 30.0% by weight of a boron carbide powder (volume-based D50 particle size: 0.5 μm) was used as the raw material powder in (1). The heat-treated layer of the resultant SiC substrate was confirmed to be a biaxially oriented SiC layer. The results were as shown in Table 1.
A SiC substrate was produced and evaluated as in Example 1 except that the annealing temperature was set to 2350° C. in (2). The heat-treated layer of the resultant SiC substrate was confirmed to be a biaxially oriented SiC layer. The results were as shown in Table 1.
It was found from Examples 1 to 7 that the distribution of PL intensity versus the distance in the [11-20] direction can be controlled by the annealing temperature and the boron content, although the cause is not certain. In addition, as shown in Examples 1, 3 to 5, and 7, it was found that when the ratio of M/m is 1.05 or more and the distance L is 15 to 150 μm in the graph obtained by PL, or when the distance LE is 30 to 300 μm in the graph obtained by processing, with a Prewitt filter, the image obtained by PL, thereby the TSD density of the (0001) plane of the evaluation sample at a polished thickness of 50 μm, that is, the TSD density of the surface of the biaxially oriented SiC layer can be decreased. Further, it was found that in the SiC substrate including a biaxially oriented SiC layer and being such that in the graph obtained by plotting the TSD density as the vertical axis versus the depth from the (0001) plane that is the substrate surface to an arbitrary (000-1) plane as the horizontal axis, a TSD sloped region where the TSD density decreases at a constant slope a as the depth decreases and the absolute value of the slope a is 5.0 cm−2/μm or more is present, the TSD density of the surface of the biaxially oriented SiC layer can be effectively decreased. It is considered that this is because the distribution of PL intensity versus the distance in the [11-20] direction reflects a step-terrace structure generated during crystal growth, and the TSDs were converted to lamination defects with the crystal growth. On the other hand, as was the case in Examples 2 and 6, when the firing temperature was low and the ratio of M/m fell below 1.05, when the distance L exceeded 150 μm, or when the distance LE exceeded 300 μm, the absolute value of the slope a of the TSD density remarkably decreased, and the TSD density of the surface of the biaxially oriented SiC layer increased. It is considered that this is because the step-terrace structure collapsed, and therefore the TSDs were not converted to lamination defects. In this respect, as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/039155 | Oct 2021 | WO | international |
This is a continuation of PCT/JP2022/039004 filed Oct. 19, 2022, which claims priority to International Application No. PCT/JP2021/039155 filed Oct. 22, 2021, the entire contents all of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2022/039004 | Oct 2022 | WO |
| Child | 18441303 | US |
