Silicon carbide substrate and silicon carbide epitaxial substrate

Abstract

To provide a silicon carbide substrate capable of reducing the warp change of the silicon carbide substrate before and after forming a silicon carbide epitaxial layer.SOLUTION: When setting a wave number showing a peak corresponding to a return mode of a vertical type optical branch in the Raman spectrum of polytype 4H silicon carbide having a stress of 0 as ν0, setting the maximum of wave numbers showing peaks corresponding to the return mode of the vertical type optical branch in the Raman spectrum of the silicon carbide substrate in an area from a first main surface to a second main surface as νmax, setting the minimum of the wave numbers showing the peaks corresponding to the return mode of the vertical mold optical branch in the Raman spectrum of the silicon carbide substrate in the area from the first main surface to the second main surface as νmin, and setting a wave number showing a peak corresponding to the return mode of the vertical mold optical branch in the Raman spectrum of the silicon carbide substrate in the first main surface as ν1, the following expression is satisfied.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a silicon carbide substrate. This application claims priority to Japanese Patent Application No. 2017-236405, filed on December 8, 2017. The entire contents of the Japanese Patent Application are incorporated herein by reference. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2014-210690 (Patent Document 1) describes chemical mechanical polishing being performed on a silicon carbide single crystal substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-210690 A Summary of the Invention

[0004] The silicon carbide substrate according to the present disclosure includes a first main surface and a second main surface opposite to the first main surface, and is made of silicon carbide of polytype 4H. The maximum diameter of the first main surface is 140 mm or more. The silicon carbide substrate has a thickness of 300 μm or more and 600 μm or less. The first main surface is a {0001} plane or a plane inclined at an off angle of more than 0° and not more than 8° with respect to the {0001} plane. The wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of silicon carbide of polytype 4H having zero stress is defined as ν0, and the maximum wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate in the region from the first main surface to the second main surface is defined as ν0. max In the region from the first principal surface to the second principal surface, the minimum wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate is defined as ν min When the wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate on the first main surface is ν1, Formulas 1 to 3 are satisfied.

[0005]

number

[0006]

number

[0007]

number

[0008] [Figure 1] FIG. 1 is a schematic plan view showing the structure of a silicon carbide substrate in accordance with the present embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 3 is a schematic diagram showing the configuration of a Raman spectrum measuring device. [Figure 4] FIG. 4 is a schematic cross-sectional view showing a method for measuring a Raman spectrum. [Diagram 5] FIG. 5 is a diagram showing an example of a Raman spectrum. [Figure 6] FIG. 6 is a diagram showing an example of a Raman spectrum measured at the first position. [Figure 7] FIG. 7 is a diagram showing the relationship between the wave number indicating the peak and the measurement position. [Figure 8] FIG. 8 is a diagram showing the relationship between the half width of the peak and the measurement position. [Figure 9] FIG. 9 is a schematic cross-sectional view showing a first step of the method for manufacturing a silicon carbide substrate in accordance with the present embodiment. [Figure 10] FIG. 10 is a schematic plan view showing a first step of the method for manufacturing a silicon carbide substrate in accordance with the present embodiment. [Figure 11] FIG. 11 is a schematic cross-sectional view showing a second step of the method for manufacturing a silicon carbide substrate in accordance with the present embodiment. [Figure 12] FIG. 12 is a cross-sectional view illustrating a step of forming a silicon carbide epitaxial layer on a silicon carbide substrate according to this embodiment. [Figure 13] FIG. 13 is a schematic plan view showing a method for determining a three-point reference plane. [Figure 14] FIG. 14 is a first schematic diagram for explaining a method for measuring warp and bow. [Figure 15] FIG. 15 is a second schematic diagram for explaining the method of measuring warp and bow. [Figure 16] FIG. 16 is a diagram showing the relationship between Δν(Ne) and the measurement position of Sample 1. [Figure 17] FIG. 17 is a diagram showing the relationship between Δν(Ne) and the measurement position of Sample 2. [Figure 18] FIG. 18 is a diagram showing the relationship between Δν(Ne) and the measurement position of Sample 3. [Figure 19] FIG. 19 is a diagram showing the relationship between Δν(Ne) and the measurement position of Sample 4. [Figure 20] FIG. 20 is a diagram showing the relationship between the FWHM and the measurement position of the sample 1. In FIG. [Figure 21] FIG. 21 is a diagram showing the relationship between the FWHM of sample 2 and the measurement position. [Figure 22] FIG. 22 is a diagram showing the relationship between the FWHM and the measurement position of the sample 3. In FIG. [Diagram 23] FIG. 23 is a diagram showing the relationship between the FWHM and the measurement position of Sample 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] [Problem that this disclosure aims to solve] An object of the present disclosure is to reduce a change in warpage of a silicon carbide substrate before and after formation of a silicon carbide epitaxial layer.

[0010] [Effects of this disclosure] According to the present disclosure, it is possible to reduce the change in warpage of a silicon carbide substrate before and after the formation of a silicon carbide epitaxial layer.

[0011] [Description of the embodiments of the present disclosure] (1) A silicon carbide substrate 10 according to the present disclosure includes a first main surface 1 and a second main surface 2 opposite to the first main surface 1, and is made of silicon carbide of polytype 4H. A maximum diameter 111 of the first main surface 1 is 140 mm or more. The silicon carbide substrate 10 has a thickness of 300 μm or more and 600 μm or less. The first main surface 1 is a {0001} plane or a plane inclined at an off angle of more than 0° and not more than 8° with respect to the {0001} plane. The wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of silicon carbide of polytype 4H having zero stress is defined as ν0, and the maximum wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate 10 in the region from the first main surface 1 to the second main surface 2 is defined as ν0. max In the region from the first main surface 1 to the second main surface 2, the minimum value of the wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate 10 is defined as ν min When the wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of silicon carbide substrate 10 on first main surface 1 is taken as ν1, Formulas 1 to 3 are satisfied.

[0012] (2) In silicon carbide substrate 10 according to the above (1), when a wave number indicating a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of silicon carbide substrate 10 is denoted by ν, formula 4 may be satisfied at any position within a region of 3 μm from first main surface 1 toward second main surface 2.

[0013]

number

[0014] (3) In the silicon carbide substrate 10 according to the above (1) or (2), in the region from the first main surface 1 to the second main surface 2, the maximum half-width of the peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate 10 is Δ maxIn the region from the first main surface 1 to the second main surface 2, the minimum half-width of the peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate 10 is defined as Δ min Then, formula 5 may be satisfied.

[0015]

number

[0016] [Details of the embodiment of the present disclosure] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are given the same reference numerals, and the description thereof will not be repeated. In the crystallographic description in this specification, an individual orientation is indicated by [], a collective orientation by <>, an individual plane by (), and a collective plane by {}. In addition, for negative indices, a "-" (bar) is placed before the number in crystallography, but in this specification, a negative sign is placed before the number.

[0017] First, the configuration of silicon carbide substrate 10 in accordance with the present embodiment will be described. As shown in FIGS. 1 and 2 , silicon carbide substrate 10 according to this embodiment mainly has a first main surface 1, a second main surface 2, and an outer peripheral surface 5. The second main surface 2 is on the opposite side to first main surface 1. Silicon carbide substrate 10 is made of silicon carbide of polytype 4H. Silicon carbide substrate 10 contains n-type impurities such as nitrogen (N). The conductivity type of silicon carbide substrate 10 is, for example, n-type. The concentration of n-type impurities in silicon carbide substrate 10 is, for example, 1×10 17 cm -3 More than 1×10 20 cm -3 The following is the result.

[0018] As shown in FIG. 1, the maximum diameter 111 of the first main surface 1 is 140 mm or more. The maximum diameter 111 of the first main surface 1 is not particularly limited, and may be, for example, 160 mm or less, 200 mm or less, 250 mm or less, or 300 mm or less. As shown in FIG. 2, the thickness 112 of the silicon carbide substrate 10 is 300 μm or more and 600 μm or less. The thickness 112 of the silicon carbide substrate 10 is not particularly limited, and may be, for example, 350 μm or more, or 400 μm or more. The thickness 112 of the silicon carbide substrate 10 is not particularly limited, and may be, for example, 550 μm or less, or 500 μm or less.

[0019] The first main surface 1 is a {0001} plane or a plane inclined at an off angle of more than 0° and not more than 8° with respect to the {0001} plane. The off angle may be, for example, 1° or more, or 2° or more. The off angle may be 7° or less, or 6° or less. Specifically, the first main surface 1 may be a (0001) plane or a plane inclined at an off angle of more than 0° and not more than 8° with respect to the (0001) plane. The first main surface 1 may be a (000-1) plane or a plane inclined at an off angle of more than 0° and not more than 8° with respect to the (000-1) plane. The inclination direction of the first main surface 1 is, for example, the <11-20> direction.

[0020] As shown in FIG. 1 , the outer peripheral surface 5 may have, for example, a first flat 3 and an arc-shaped portion 4. The first flat 3 extends, for example, along a first direction 101. The arc-shaped portion 4 is continuous with the first flat 3. The outer peripheral surface 5 may have, for example, a second flat (not shown) extending, for example, along a second direction 102. The second direction 102 is, for example, a <1-100> direction. The first direction 101 is parallel to the first main surface 1 and perpendicular to the second direction 102. The first direction 101 is, for example, a <11-20> direction.

[0021] The first main surface 1 is, for example, a surface on which an epitaxial layer is formed. From another perspective, a silicon carbide epitaxial layer 20 (see FIG. 12) is provided on the first main surface 1. The second main surface 2 is, for example, a surface on which a drain electrode is formed. From another perspective, a drain electrode (not shown) of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is formed on the second main surface 2.

[0022] Next, the configuration of a Raman spectrometer for measuring the Raman spectrum of silicon carbide substrate 10 will be described.

[0023] As shown in FIG. 3, the Raman spectrometer 30 mainly includes, for example, a light source 32, an objective lens 31, a spectroscope 33, a stage 34, a beam splitter 35, and a detector 38. As the Raman spectrometer 30, for example, LabRAM HR-800 manufactured by HORIBA JOBIN YVON can be used. The light source 32 is, for example, a YAG (Yttrium Aluminum Garnet) laser. The excitation wavelength of the light source 32 is, for example, 532 nm. The laser irradiation intensity is, for example, 10 mW. The measurement method is, for example, backscattering measurement. The magnification of the objective lens 31 is 100 times. The diameter of the measurement area is, for example, 1 μm. The laser irradiation time is, for example, 20 seconds. The number of integrations is, for example, 5 times. The grating is 2400 gr / mm.

[0024] Next, a method for measuring the Raman spectrum of silicon carbide substrate 10 will be described. First, incident light 36 is emitted from a YAG laser of light source 32. As shown by an arrow 61 in Fig. 3, incident light 36 is reflected by beam splitter 35 and directed toward first main surface 1 of silicon carbide substrate 10. Raman spectroscopic device 30 employs, for example, a confocal optical system. In the confocal optical system, a confocal aperture (not shown) having a circular opening is disposed at a position conjugate with the focus of objective lens 31. This makes it possible to detect light only at the focused position (height).

[0025] As shown by arrow 62 in Fig. 3, the Raman scattered light scattered by silicon carbide substrate 10 passes through beam splitter 35 and is introduced into spectrometer 33. In spectrometer 33, the Raman scattered light is resolved into wavenumbers. The Raman scattered light resolved into wavenumbers is detected by detector 38. This results in a Raman spectrum with the horizontal axis representing the wavenumber and the vertical axis representing the intensity of the Raman scattered light. Stage 34 can move in the thickness direction of silicon carbide substrate 10 (in the direction of arrow 63).

[0026] As shown in FIG. 4, incident light 36 is focused on the first main surface 1 of silicon carbide substrate 10, and the Raman spectrum in measurement region 37 is measured. In this case, the position in the height direction of the focus of incident light 36 is first position X1. The focus of incident light 36 is adjusted to the center 6 of first main surface 1 (see FIG. 1). The measurement region 37 of the Raman scattered light is a region with a diameter of about 1 μm including the center 6 of the first main surface 1. Next, stage 34 is moved upward, and the position in the height direction of the focus of incident light 36 is adjusted to second position X2. As a result, the Raman spectrum at second position X2 is measured. As described above, by moving stage 34 along the direction of arrow 63, the measurement region 37 is moved from the first position X1 to the nth position X n In other words, the Raman spectrum is measured in the thickness direction of silicon carbide substrate 10.

[0027] FIG. 5 shows an example of the Raman spectrum of the silicon carbide substrate 10. The horizontal axis of FIG. 5 is the wave number (Raman shift). The vertical axis of FIG. 5 is the intensity of the Raman scattered light (Raman intensity). The wavelength of the excitation light from the light source 32 is 514.5 nm. The Raman shift is the difference between the wave number of the excitation light and the wave number of the Raman scattered light of the object to be measured. When the object to be measured is silicon carbide of polytype 4H, four peaks are mainly observed in the Raman spectrum. The first peak 41 is the Raman scattered light caused by the folded mode of the longitudinal wave optical (LO) branch. The first peak 41 is, for example, at 964 cm -1The second peak 42 is Raman scattered light due to the folded mode of the transverse optical (TO) branch. The second peak 42 appears, for example, at 776 cm -1 The third peak 43 is Raman scattered light caused by the folded mode of the longitudinal acoustic (LA) branch. The third peak 43 appears, for example, at 610 cm -1 The fourth peak 44 is a Raman scattered light caused by the folded mode of the transverse acoustic (TA) branch. The fourth peak 44 appears, for example, at 196 cm -1 appears nearby.

[0028] The Raman profile shown by the solid line in FIG. 6 shows the Raman spectrum measured at the first position X1 (see FIG. 4) of the silicon carbide substrate 10. Using the Raman spectrum, the wave number ν of the peak 41 corresponding to the folding mode of the vertical optical branch is obtained. Similarly, the half-width Δ of the peak 41 is obtained. The peak 41 corresponding to the folding mode of the vertical optical branch is a peak of the Raman profile generated due to the folding mode of the vertical optical branch. The Raman profile 50 shown by the dashed line in FIG. 6 is a peak corresponding to the folding mode of the vertical optical branch in the Raman spectrum of silicon carbide of polytype 4H with zero stress. The wave number ν0 of the peak can be obtained, for example, as follows. The peak of the Raman spectrum obtained by Raman measurement of the Lely crystal (crystal grown by the Lely method) is set as the wave number ν0 of zero stress. The Lely crystal grows by spontaneous nucleation and has few impurities, so it can be considered to have zero stress.

[0029] Tensile stress or compressive stress occurs near the first main surface 1 of the silicon carbide substrate 10 after slicing. Therefore, the wave number indicating the peak due to the folding mode of the vertical optical branch in the Raman profile measured at the first position X1 of the silicon carbide substrate 10 shifts from the wave number ν0 indicating the peak corresponding to the folding mode of the vertical optical branch in the Raman spectrum of silicon carbide of polytype 4H in which the stress is 0. When tensile stress occurs in the measurement region, the wave number indicating the peak corresponding to the folding mode of the vertical optical branch in the Raman profile of the measurement region shifts to the negative side. Conversely, when compressive stress occurs in the measurement region, the wave number indicating the peak corresponding to the folding mode of the vertical optical branch in the Raman profile of the measurement region shifts to the positive side. By obtaining the shift amount S in this way, the stress in the measurement region can be quantitatively evaluated.

[0030] FIG. 7 is a plot of the measurement position of the silicon carbide substrate 10 on the horizontal axis and the wave number of the peak corresponding to the folding mode of the vertical optical branch of silicon carbide on the vertical axis. As shown in FIG. 4, the measurement position of the silicon carbide substrate 10 is changed at a constant interval t from the first main surface 1 to the second main surface 2. The interval t is, for example, 2.75 μm. Specifically, after measuring the Raman spectrum of the silicon carbide substrate 10 at the first position X1, the wave number of the peak of the Raman spectrum corresponding to the folding mode of the vertical optical branch is obtained. Next, the stage 34 is moved in the direction of the arrow 63, and after measuring the Raman spectrum of the silicon carbide substrate 10 at the second position X2, the wave number of the peak of the Raman spectrum corresponding to the folding mode of the vertical optical branch is obtained. Similarly, the Raman spectrum is measured at the third position X3 to the nth position X4. n The Raman spectrum is measured from up to the measurement position, and the wave number of the peak corresponding to the folded mode of the vertical optical branch of the Raman spectrum at each measurement position is obtained. In this manner, the relationship between the wave number and the measurement position shown in FIG. 7 is obtained.

[0031] In the region from the first principal surface 1 to the second principal surface 2, the maximum value of the wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate 10 is ν maxIn FIG. 7, the wave number at the first position X1 is v max Similarly, in the region from the first principal surface 1 to the second principal surface 2, the minimum value of the wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate 10 is ν min In FIG. 7, the mth position X m The wave number at min The wave number indicating a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of silicon carbide substrate 10 on first main surface 1 is determined as ν1.

[0032] If the peak wave number corresponding to the folded mode of the vertical optical branch in the Raman spectrum of silicon carbide of polytype 4H with zero stress is ν0, then ν max satisfies the above formula 1. ν max is (ν0+0.045cm -1 ) or less, or (ν0+0.04cm -1 ) or less. min satisfies the above formula 2. ν min is (ν0-0.045cm -1 ) or more, or (ν0-0.04 cm -1 ) or more. ν1 satisfies the above-mentioned formula 3. ν1 is (ν0-0.015 cm -1 ) or more, or (ν0-0.01cm -1 ) or more. ν1 is (ν0 + 0.03 cm -1 ) or less, or (ν0+0.025cm -1 ) or less.

[0033] 7, the wave number indicating a peak corresponding to the folded mode of the vertical optical branch in the Raman profile measured at the first position X1 may be larger than the wave number v0. In the direction from the first main surface 1 to the second main surface 2, the silicon carbide substrate 10 has a region (for example, from the first position X1 to the m-th position X2) where the wave number indicating a peak corresponding to the folded mode of the vertical optical branch in the Raman profile monotonically decreases. mSilicon carbide substrate 10 may have a region (for example, at m-th position X m From the n-1th position X n-1 The wave number at which the peak corresponding to the folded mode of the vertical optical branch in the Raman profile shows asymptotically to the wave number ν0 toward the second main surface 2.

[0034] If the surface roughness of the second principal surface 2 is large, a lot of noise is introduced into the Raman spectrum on the second principal surface 2, and it is not possible to accurately calculate the wave number showing the peak corresponding to the folding mode of the vertical optical branch. Therefore, when calculating the maximum wave number and the minimum wave number, the wave number showing the peak of the Raman spectrum on the second principal surface 2 corresponding to the folding mode of the vertical optical branch is not taken into consideration. In FIG. 7, the measurement position (nth position X n ) is shown by a white circle. This means that the wave number of the nth position X n may be measured but are not taken into account in calculating the maximum wavenumber and minimum wavenumber values.

[0035] 7, assuming that the wave number indicating a peak corresponding to the folding mode of the vertical optical branch in the Raman spectrum of silicon carbide substrate 10 is ν, ν satisfies the above-mentioned formula 4 at any position in a region within 3 μm from first main surface 1 toward second main surface 2. Specifically, the wave number of the peak corresponding to the folding mode of the vertical optical branch in the Raman spectrum of silicon carbide substrate 10 at first position X1 and the wave number of the peak corresponding to the folding mode of the vertical optical branch in the Raman spectrum of silicon carbide substrate 10 at second position X2 satisfy the above-mentioned formula 4. ν is (ν0-0.015 cm -1 ) or more, or (ν0-0.01cm -1 ) or more. ν is (ν0+0.03cm -1 ) or less, or (ν0+0.025cm -1 ) or less.

[0036] FIG. 8 is a plot of the measurement position of the silicon carbide substrate 10 on the horizontal axis and the half-width of the peak corresponding to the folded mode of the vertical optical branch of silicon carbide on the vertical axis. As in the case of FIG. 7, the measurement position of the silicon carbide substrate 10 is changed at a constant interval t from the first main surface 1 to the second main surface 2, and the Raman spectrum of the silicon carbide substrate 10 is measured at each measurement position. The half-width Δ of the peak corresponding to the folded mode of the vertical optical branch of the Raman spectrum at each measurement position is obtained. The half-width Δ is specifically the full width at half maximum (FWHM). In this manner, the relationship between the half-width and the measurement position shown in FIG. 8 is obtained. The half-width of the peak is an index of the stress distribution in the measurement region parallel to the first main surface 1. If the half-width of the peak is small, the stress distribution in the measurement range is small. Conversely, if the half-width of the peak is large, the stress distribution in the measurement range is large.

[0037] In the region from the first principal surface 1 to the second principal surface 2, the maximum half-width of the peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate 10 is Δ max In FIG. 8, the half-width at the first position X1 is Δ max Similarly, in the region from the first main surface 1 to the second main surface 2, the minimum half-width of the peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate 10 is Δ min In FIG. 8, the (n-1)th position X n-1 The half-width at Δ min In FIG. 8, the measurement position (the nth position X n ) is shown by a white circle. This means that the wave number of the nth position X n This means that the half width at may be measured but is not taken into consideration when calculating the maximum half width and the minimum half width.

[0038] 8, the half-width Δ of the peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum may monotonically decrease from the first principal surface 1 to the second principal surface 2. min According to the silicon carbide substrate 10 of this embodiment, in the region from the first main surface 1 to the second main surface 2, the maximum half-width of the peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate 10 is set to Δ max In the region from the first main surface 1 to the second main surface 2, the minimum half-width of the peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate 10 is defined as Δ min When this is done, the above formula 5 is satisfied. (Δ max -Δ min ) is 0.13 cm -1 May be less than 0.11 cm -1 It may be the following.

[0039] In the above description, the Raman profile is measured along a straight line that passes through center 6 of first main surface 1 and is substantially perpendicular to first main surface 1, but the location where the Raman profile is measured is not limited to the straight line. For example, formulas 1 to 5 may be satisfied in any region of silicon carbide substrate 10 except for a region from outer peripheral surface 5 to a predetermined distance (e.g., 3 mm) inward.

[0040] Next, a method for manufacturing silicon carbide substrate 10 in accordance with the present embodiment will be described. First, a slicing process is performed. Specifically, an ingot made of a silicon carbide single crystal of polytype 4H is formed, for example, by sublimation. After the ingot is shaped, it is sliced ​​by a wire saw device. Thus, the silicon carbide substrate 10 is cut out from the ingot. Diamond abrasive grains are fixed to the surface of the saw wire. The diameter of the diamond abrasive grains is, for example, 15 μm or more and 25 μm or less. The diameter of the saw wire is, for example, 120 μm. The linear speed of the saw wire is, for example, 800 m / min or more and 1500 m / min or less. The tension of the saw wire is, for example, 18 N.

[0041] The silicon carbide substrate 10 is made of hexagonal silicon carbide of polytype 4H. The silicon carbide substrate 10 has a first main surface 1 and a second main surface 2 on the opposite side of the first main surface 1. The first main surface 1 is, for example, a surface that is off-angled in the <11-20> direction by 4° or less with respect to the {0001} plane. Specifically, the first main surface 1 is, for example, a surface that is off-angled in the <11-20> direction by an angle of about 4° or less with respect to the (0001) plane. The second main surface 2 is, for example, a surface that is off-angled in the <11-20> direction by an angle of about 4° or less with respect to the (000-1) plane.

[0042] As shown in FIG. 9, the silicon carbide substrate 10 has a first region 7, an intermediate region 8, and a second region 9. The first region 7 is a region including the first main surface 1. The second region 9 is a region including the second main surface 2. The intermediate region 8 is a region between the first region 7 and the second region 9. In the above-mentioned slicing process, processing damage is applied to each of the first region 7 and the second region 9. Therefore, each of the first region 7 and the second region 9 is more distorted than the intermediate region 8. The first main surface 1 is curved, for example, so that the center approaches the second main surface 2 and the periphery moves away from the second main surface 2. The second main surface 2 is curved, for example, so that the center moves away from the first main surface 1 and the periphery moves toward the first main surface 1. As shown in FIG. 10, the first main surface 1 of the silicon carbide substrate 10 may be dotted with substantially circular distorted regions 51 when viewed from a direction perpendicular to the first main surface 1. The distorted region is a region where processing damage remains. The distorted region 51 has a different stress from the regions around the distorted region 51.

[0043] Next, a first etching step is performed. Specifically, the silicon carbide substrate 10 is etched by being entirely immersed in an etching solution prepared by mixing potassium hydroxide (KOH), potassium permanganate (KMnO4), and pure water. The volume ratio of the etching solution is KOH:KMnO4:pure water=5-15:1-3:20-30. The temperature of the etching solution is, for example, 70°C or higher and 95°C or lower. Next, the silicon carbide substrate 10 is etched by being entirely immersed in an etching solution prepared by mixing hydrofluoric acid (HF) and nitric acid (HNO3). The volume ratio of the etching solution is HF:HNO3=3-5:2-4 (here, the volume of HF is greater than the volume of HNO3). The temperature of the etching solution is, for example, 70°C or higher and 95°C or lower. As a result, the surface of silicon carbide substrate 10 is etched by approximately 1 μm or more and 5 μm or less. The first etching reduces the stress distribution in the thickness direction of silicon carbide substrate 10. As a result, warping of silicon carbide substrate 10 is reduced (see FIG. 11). First main surface 1 becomes approximately parallel to second main surface 2.

[0044] Next, a double-sided mechanical polishing step is performed. Specifically, the silicon carbide substrate 10 is placed between a first platen and a second platen such that the first main surface 1 faces the first platen (not shown) and the second main surface 2 corresponds to the second platen (not shown). Next, a slurry is introduced between the first main surface 1 and the first platen and between the second main surface 2 and the second platen. The slurry contains, for example, diamond abrasive grains. The diameter of the diamond abrasive grains is, for example, 1 μm or more and 3 μm or less. A load is applied to the first main surface 1 by the first platen and a load is applied to the second main surface 2 by the second platen, whereby mechanical polishing is performed on both sides of the silicon carbide substrate 10.

[0045] Next, a second etching step is performed. Specifically, the silicon carbide substrate 10 is etched by being entirely immersed in an etching solution prepared by mixing potassium hydroxide (KOH), potassium permanganate (KMnO4), and pure water. The volume ratio of the etching solution is KOH:KMnO4:pure water=5-15:1-3:20-30. The temperature of the etching solution is, for example, 70°C or higher and 95°C or lower. Next, the silicon carbide substrate 10 is etched by being entirely immersed in an etching solution prepared by mixing hydrofluoric acid (HF) and nitric acid (HNO3). The volume ratio of the etching solution is HF:HNO3=3-5:2-4 (here, the volume of HF is greater than the volume of HNO3). The temperature of the etching solution is, for example, 70°C or higher and 95°C or lower. This etches the surface of silicon carbide substrate 10 by approximately 1 μm or more and 5 μm or less. The second etching reduces the stress distribution in the thickness direction of silicon carbide substrate 10. As a result, warping of silicon carbide substrate 10 is reduced.

[0046] Next, a first chemical mechanical polishing (CMP) is performed on the first main surface 1 of the silicon carbide substrate 10. Specifically, the silicon carbide substrate 10 is held by a polishing head so that the first main surface 1 faces a surface plate. Aluminum oxide is used as the abrasive grains. The average grain size of the abrasive grains is 180 nm. A nitrate-based oxidizing agent is used as the oxidizing agent. The load (surface pressure) on the silicon carbide substrate 10 is, for example, 250 g / cm. 2 More than 500g / cm 2 The rotation speed of the platen is, for example, 60 rpm or more and 90 rpm or less, and the rotation speed of the polishing head is 80 rpm or more and 120 rpm or less.

[0047] Next, a second CMP is performed on the first main surface 1 of the silicon carbide substrate 10. Specifically, colloidal silica is used as the abrasive grains. Hydrogen peroxide solution to which vanadate has been added is used as the oxidizing agent. The load (surface pressure) on the silicon carbide substrate 10 is, for example, 300 g / cm. 2This reduces distortion in first main surface 1 of silicon carbide substrate 10. In this manner, silicon carbide substrate 10 in accordance with the present embodiment is manufactured (see FIG. 1).

[0048] Next, a method of forming a silicon carbide epitaxial layer on silicon carbide substrate 10 according to this embodiment will be described.

[0049] For example, a silicon carbide substrate 10 is placed in a reaction chamber of a hot-wall horizontal CVD (Chemical Vapor Deposition) apparatus. Next, the silicon carbide substrate 10 is heated to, for example, about 1630° C. Next, a mixed gas containing, for example, silane (SiH4), propane (C3H8), ammonia (NH3), and hydrogen (H2) is introduced into the reaction chamber. As a result, a silicon carbide epitaxial layer 20 is formed on the first main surface 1 of the silicon carbide substrate 10 (see FIG. 12). As shown in FIG. 12, the silicon carbide epitaxial layer 20 is in contact with the first main surface 1. The silicon carbide epitaxial layer has a surface 21 facing the first main surface 1. The silicon carbide epitaxial layer 20 has a thickness of, for example, 5 μm or more and 100 μm or less.

[0050] Next, the effects of silicon carbide substrate 10 in accordance with the present embodiment will be described. When the silicon carbide substrate 10 is processed, such as sliced ​​or mechanically polished, using diamond abrasive grains, processing damage is applied to the silicon carbide substrate 10. As a result, a region (specifically, the first region 7 and the second region 9) where the strain (stress) changes is formed in a region from tens to hundreds of μm from each of the first main surface 1 and the second main surface 2 of the silicon carbide substrate 10 toward the inside. It is considered that the region where the strain changes is formed by the rolling of the diamond abrasive grains in the mechanical polishing. Even in the final state after CMP, strain exists in the distorted region 51 shown in FIG. 10 and in the region around the distorted region 51. Compared to the region around the distorted region 51, the distorted region 51 has a deeper (stronger) strain.

[0051] By performing hydrogen etching on the first main surface 1 of the silicon carbide substrate 10, a part of the region where the strain changes is removed. This changes the stress distribution, and the shape of the warpage of the silicon carbide substrate 10 changes. A part of the region where the stress distribution changes remains in the silicon carbide substrate 10. The warpage changes from this point on. Furthermore, when the temperature of the silicon carbide substrate 10 is raised to form the silicon carbide epitaxial layer 20 on the silicon carbide substrate 10, the stress distribution in the region where the stress distribution changes remaining in the silicon carbide substrate 10 changes, and the warpage of the silicon carbide substrate 10 changes even more significantly. In other words, the warpage of the silicon carbide substrate 10 changes significantly before and after the formation of the silicon carbide epitaxial layer.

[0052] According to the silicon carbide substrate 10 of this embodiment, most of the region where the strain changes is removed, and the distribution of stress in the thickness direction is reduced. Specifically, the wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of silicon carbide of polytype 4H, in which the stress is 0, is defined as ν0, and the maximum wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of silicon carbide substrate 10 in the region from first main surface 1 to second main surface 2 is defined as ν1. max In the region from the first main surface 1 to the second main surface 2, the minimum value of the wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate 10 is defined as ν min and a wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of silicon carbide substrate 10 on first main surface 1 is taken as ν1, then formulas 1 to 3 are satisfied. This makes it possible to reduce a change in warpage of silicon carbide substrate 10 before and after the formation of the silicon carbide epitaxial layer.

[0053] If the stress distribution is large in the thickness direction of the silicon carbide substrate 10, linear streaks (protrusions) extending in the <1-100> direction from the strained region 51 may be formed on the first main surface 1 of the silicon carbide substrate 10 when the silicon carbide substrate 10 is heated. When the silicon carbide epitaxial layer 20 is formed on the silicon carbide substrate 10, the linear streaks formed on the first main surface 1 of the silicon carbide substrate 10 are inherited by the silicon carbide epitaxial layer 20 formed on the first main surface 1. As a result, linear streaks are formed on the surface 21 of the silicon carbide epitaxial layer 20. In the silicon carbide substrate 10 according to this embodiment, the stress distribution is reduced in the thickness direction of the silicon carbide substrate 10. This may suppress the formation of linear streaks on the surface 21 of the silicon carbide epitaxial layer 20 formed on the silicon carbide substrate 10. EXAMPLES

[0054] (Sample preparation) The silicon carbide substrates 10 according to Samples 1 to 4 were prepared using the manufacturing process described in Table 2. The silicon carbide substrate 10 according to Sample 1 was used as an example. The silicon carbide substrates 10 according to Samples 2 to 4 were used as comparative examples. Specifically, a silicon carbide ingot of polytype 4H was first sliced ​​by a wire saw device, so that the silicon carbide substrates 10 were cut out from the ingot. Sample 1 was sliced ​​using condition A. Condition A of the slicing process is as follows. The diameter of the diamond abrasive grains was 15 μm or more and 25 μm or less. The diameter of the saw wire was 120 μm. The linear speed of the saw wire was 800 m / min or more and 1500 m / min or less. The tension of the saw wire was 18 N. Samples 2 to 4 were sliced ​​using condition B. Condition B of the slicing process is as follows. The diameter of the diamond abrasive grains was 30 μm or more and 40 μm or less. The diameter of the saw wire was 180 μm. The linear speed of the saw wire was set to 800 m / min or more and 1200 m / min or less. The tension of the saw wire was set to 45 N.

[0055] Next, the first etching step was performed on the silicon carbide substrate 10 of Sample 1. The conditions of the first etching step were as described above. The silicon carbide substrates 10 of Samples 2 to 4 were not subjected to the first etching step.

[0056] Next, a double-sided mechanical polishing process was carried out on the silicon carbide substrates 10 of Samples 1 to 4. The conditions for the double-sided mechanical polishing process were as described above.

[0057] Next, the second etching step was performed on the silicon carbide substrate 10 of Sample 1. The conditions for the second etching step were as described above. The silicon carbide substrates 10 of Samples 2 to 4 were not subjected to the second etching step.

[0058] Next, a first CMP step was performed on the silicon carbide substrates 10 of Samples 1 to 4. Conditions C, D, E and F were used for the silicon carbide substrates 10 of Samples 1 to 4, respectively (see Table 1).

[0059] [Table 1]

[0060] Condition C of the first CMP step is as follows. Specifically, aluminum oxide was used as the abrasive grains. The average grain size of the abrasive grains was 180 nm. A nitrate-based oxidizing agent was used as the oxidizing agent. The load (surface pressure) on the silicon carbide substrate 10 was 250 g / cm. 2 More than 500g / cm 2 The rotation speed of the surface plate was set to 60 rpm or more and 90 rpm or less, and the rotation speed of the polishing head was set to 80 rpm or more and 120 rpm or less.

[0061] Condition D of the first CMP step is as follows. Specifically, aluminum oxide was used as the abrasive grains. The average grain size of the abrasive grains was 250 nm. A nitrate-based oxidizing agent was used as the oxidizing agent. The load (surface pressure) on the silicon carbide substrate 10 was 250 g / cm. 2 More than 500g / cm2 The rotation speed of the platen was set to 60 rpm or more and 90 rpm or less, and the rotation speed of the polishing head was set to 80 rpm or more and 120 rpm or less.

[0062] Condition E of the first CMP step is as follows. Specifically, aluminum oxide was used as the abrasive grains. The average grain size of the abrasive grains was 180 nm. A nitrate-based oxidizing agent was used as the oxidizing agent. The load (surface pressure) on the silicon carbide substrate 10 was 600 g / cm. 2 More than 700g / cm 2 The rotation speed of the platen was set to 60 rpm or more and 90 rpm or less, and the rotation speed of the polishing head was set to 80 rpm or more and 120 rpm or less.

[0063] Condition F of the first CMP step is as follows. Specifically, aluminum oxide was used as the abrasive grains. The average grain size of the abrasive grains was 250 nm. A nitrate-based oxidizing agent was used as the oxidizing agent. The load (surface pressure) on the silicon carbide substrate 10 was 500 g / cm. 2 More than 600g / cm 2 The rotation speed of the platen was set to 60 rpm or more and 90 rpm or less, and the rotation speed of the polishing head was set to 80 rpm or more and 120 rpm or less.

[0064] Next, the second CMP step was performed on the silicon carbide substrates 10 of Samples 1 to 4. The conditions of the second CMP step were as described above. In this manner, the silicon carbide substrates 10 of Samples 1 to 4 were prepared.

[0065] [Table 2]

[0066] (Evaluation method 1) Next, the warp and bow of the first main surface 1 of the silicon carbide substrate 10 of Samples 1 to 4 were measured. The warp and bow of the first main surface 1 were measured using a Flatmaster manufactured by Tropel. As shown in FIG. 13, a three-point reference plane 94 of the first main surface 1 was determined. The three-point reference plane 94 is an imaginary plane including three points (a fifth position 95, a sixth position 96, and a seventh position 97) on the first main surface 1. The triangle formed by connecting the fifth position 95, the sixth position 96, and the seventh position 97 is an equilateral triangle including the center 6 of the first main surface 1 therein.

[0067] As shown in Fig. 14 and Fig. 15, in the direction perpendicular to the three-point reference plane 94, the sum of the distance 154 between the highest position 92 of the first main surface 1 seen from the three-point reference plane 94 and the three-point reference plane 94 and the distance 155 between the lowest position 93 of the first main surface 1 seen from the three-point reference plane 94 and the three-point reference plane 94 is the warp. As shown in Fig. 14 and Fig. 15, in the direction perpendicular to the three-point reference plane 94, the distance between the position 91 of the center 6 of the first main surface 1 and the three-point reference plane 94 is the bow. As shown in Fig. 14, when the position 91 of the center 6 of the first main surface 1 is lower than the three-point reference plane 94, the bow indicates a negative value. As shown in Fig. 15, when the position 91 of the center 6 of the first main surface 1 is higher than the three-point reference plane 94, the bow indicates a positive value.

[0068] (Evaluation result 1) As shown in Table 3, before epitaxial growth, the warps of first main surfaces 1 of silicon carbide substrates 10 in Samples 1 to 4 were 16.4 μm, 23.3 μm, 36.1 μm, and 57.5 μm, respectively. The bows of first main surfaces 1 of silicon carbide substrates 10 in Samples 1 to 4 were −10.9 μm, 8.0 μm, 21.8 μm, and −31.2 μm, respectively.

[0069] [Table 3]

[0070] (Evaluation method 2) In addition, the Raman spectrum of the silicon carbide substrate 10 was measured in the region from the first main surface 1 to the second main surface 2 of the silicon carbide substrate 10 according to the samples 1 to 4 using Raman spectroscopy. The relationship between Δν(Ne) and the measurement position was obtained using the Raman spectrum. Similarly, the relationship between the half width (FWHM) of the peak and the measurement position was obtained. Here, Δν(Ne) is a value obtained by subtracting the wave number of the peak of the neon Raman spectrum from the wave number of the peak corresponding to the folding mode of the vertical optical branch of the silicon carbide of polytype 4H. The wave number of the peak corresponding to the folding mode of the vertical optical branch of the silicon carbide was obtained based on the wave number indicating the peak of the neon Raman spectrum. The measurement direction of the peak corresponding to the folding mode of the vertical optical branch and the half width of the peak are as described above. The value obtained by subtracting the wave number showing the peak of the neon Raman spectrum from the wave number showing the peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of silicon carbide of polytype 4H, which has zero stress (Δν(Ne)0), is, for example, −44.25 cm -1 The measurement position is the distance from first main surface 1. The measurement position on first main surface 1 of silicon carbide substrate 10 is the position at 0 μm.

[0071] [Table 4]

[0072] (Evaluation result 2) As shown in FIG. 16 and Table 4, in silicon carbide substrate 10 according to Sample 1, Δν(Ne) max The absolute value of the difference between and Δν(Ne)0 is 0.032 cm -1 It was. Δν(Ne) min The absolute value of the difference between and Δν(Ne)0 is 0.046 cm -1 The Δν(Ne) at the measurement position of 0 μm was -44.218 cm -1 The value obtained by subtracting Δν(Ne)0 from Δν(Ne) of the first main surface 1 was 0.032 cm -1 It was.

[0073] As shown in FIG. 17 and Table 4, in silicon carbide substrate 10 according to sample 2, Δν(Ne) max The absolute value of the difference between and Δν(Ne)0 is 0.140 cm -1 It was. Δν(Ne) min The absolute value of the difference between and Δν(Ne)0 is 0.069 cm -1 The Δν(Ne) at the measurement position of 0 μm was -44.110 cm -1 The value obtained by subtracting Δν(Ne)0 from Δν(Ne) of the first main surface 1 was 0.140 cm -1 It was.

[0074] As shown in FIG. 18 and Table 4, in silicon carbide substrate 10 according to sample 3, Δν(Ne) max The absolute value of the difference between and Δν(Ne)0 is 0.003 cm -1 It was. Δν(Ne) min The absolute value of the difference between and Δν(Ne)0 is 0.061 cm -1 The Δν(Ne) at the measurement position of 0 μm was -44.247 cm -1 The value obtained by subtracting Δν(Ne)0 from Δν(Ne) of the first main surface 1 was 0.003 cm -1 It was.

[0075] As shown in FIG. 19 and Table 4, in silicon carbide substrate 10 according to Sample 4, Δν(Ne) max The absolute value of the difference between and Δν(Ne)0 is 0.071 cm -1 It was. Δν(Ne) min The absolute value of the difference between and Δν(Ne)0 is 0.028 cm -1 The Δν(Ne) at the measurement position of 0 μm was -44.179 cm -1 The value obtained by subtracting Δν(Ne)0 from Δν(Ne) of the first main surface 1 was 0.071 cm -1 It was.

[0076] As shown in FIG. 20 and Table 4, in silicon carbide substrate 10 according to Sample 1, Δ max From Δ min The value after subtracting is 0.1 cm -1As shown in FIG. 21 and Table 4, in silicon carbide substrate 10 according to Sample 2, Δ max From Δ min The subtracted value is 0.15 cm -1 It was.

[0077] As shown in FIG. 22 and Table 4, in silicon carbide substrate 10 according to Sample 3, Δ max From Δ min The subtracted value is 0.18 cm -1 As shown in FIG. 23 and Table 4, in silicon carbide substrate 10 according to Sample 4, Δ max From Δ min The subtracted value is 0.22 cm -1 It was.

[0078] Next, silicon carbide epitaxial layer 20 was formed by epitaxial growth on first main surface 1 of silicon carbide substrate 10 of Samples 1 to 4, thereby producing silicon carbide epitaxial substrates. The manufacturing conditions for silicon carbide epitaxial substrates were as described above.

[0079] (Evaluation method 3) Next, the warp and bow of the surface 21 of the silicon carbide epitaxial layer 20 formed on the silicon carbide substrate 10 according to Samples 1 to 4 were measured. The warp and bow of the surface 21 were measured in the same manner as described above using a Flatmaster manufactured by Tropel.

[0080] The number of linear streaks on the surface 21 of the silicon carbide epitaxial layer 20 formed on the silicon carbide substrate 10 in each of Samples 1 to 4 was counted. The measurement area was a square area of ​​250 μm×250 μm. Linear protrusions with a height of 0.5 μm or more were identified as streaks.

[0081] (Evaluation result 3) As shown in Table 3, after epitaxial growth, the warps of the surface 21 of the silicon carbide epitaxial layer 20 formed on the silicon carbide substrate 10 of Samples 1 to 4 were 12.3 μm, 89.6 μm, 64.3 μm, and 34.9 μm, respectively. The bows of the surface 21 of the silicon carbide epitaxial layer formed on the silicon carbide substrate 10 of Samples 1 to 4 were -7.8 μm, -65.6 μm, 48.9 μm, and -0.03 μm, respectively. The changes in warp before and after forming the silicon carbide epitaxial layer on the silicon carbide substrate 10 were +4.1 μm, -112.9 μm, +28.2 μm, and +22.6 μm. The change in warp before and after forming a silicon carbide epitaxial layer on silicon carbide substrate 10 was determined by applying the sign of bow to the warp and subtracting the warp of first main surface 1 before epitaxial growth from the warp of surface 21 after epitaxial growth.

[0082] As shown in Table 3, the numbers of linear streaks formed on surface 21 of silicon carbide epitaxial layer formed on silicon carbide substrate 10 in Samples 1 to 4 were 0, 11, 2, and a large number (12 or more), respectively.

[0083] From the above results, it was confirmed that the silicon carbide substrate 10 of Sample 1 can reduce the amount of change in warp compared to the silicon carbide substrates 10 of Samples 2 to 4. It was also confirmed that the silicon carbide substrate 10 of Sample 1 can suppress the occurrence of linear streaks compared to the silicon carbide substrates 10 of Samples 2 to 4.

[0084] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered as limiting. The scope of the present invention is defined by the claims, not the above description, and is intended to include the meaning equivalent to the claims and all modifications within the scope. [Explanation of symbols]

[0085] 1 first main surface, 2 second main surface, 3 first flat, 4 arc-shaped portion, 5 outer peripheral surface, 6 center, 7 first region, 8 middle region, 9 second region, 10 silicon carbide substrate, 20 silicon carbide epitaxial layer, 21 surface, 30 Raman spectroscopy device, 31 objective lens, 32 light source, 33 spectroscope, 34 stage, 35 beam splitter, 36 incident light, 37 measurement region, 38 detector, 41 first peak (peak), 42 second peak, 43 third peak, 44 fourth peak, 50 Raman profile, 51 strain region, 91 position, 92 highest position, 93 lowest position, 94 three-point reference surface, 95 fifth position, 96 sixth position, 97 seventh position, 101 first direction, 102 second direction, 111 maximum diameter, 112 thickness.

Claims

1. A silicon carbide substrate comprising a first main surface and a second main surface opposite to the first main surface, the silicon carbide substrate being made of 4H polytype silicon carbide, The maximum diameter of the first main surface is 140 mm or more, The thickness of the silicon carbide substrate is 300 μm or more and 600 μm or less, the first main surface is a {0001} plane or a plane inclined at an off angle of more than 0° and not more than 8° with respect to the {0001} plane, The wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of silicon carbide of polytype 4H with zero stress is ν ０ year, When the wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate is ν, A silicon carbide substrate, satisfying formula 4 at any position in a region within 3 μm from the first main surface toward the second main surface. [0010]

2. In a region from the first main surface to the second main surface, the maximum half-width of a peak corresponding to a folded mode of a vertical optical branch in a Raman spectrum of the silicon carbide substrate is Δ ｍａｘ year, In a region from the first main surface to the second main surface, the minimum half-width of a peak corresponding to a folded mode of a vertical optical branch in a Raman spectrum of the silicon carbide substrate is Δ ｍｉｎ The silicon carbide substrate according to claim 1 , which satisfies Formula 5 when [0025]

3. Δ ｍａｘ -Δ ｍｉｎ ≦0.10, and Δ ｍａｘ and Δ ｍｉｎ The unit is cm －１ The silicon carbide substrate according to claim 2 ,

4. In the region from the first main surface to the second main surface, the maximum wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate is defined as ν ｍａｘ year, In a region from the first main surface to the second main surface, the minimum value of the wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate is defined as ν ｍｉｎ When The silicon carbide substrate according to claim 1 , which satisfies formulas 1 and 2. [0030] [0045]

5. In a region from the first main surface to the second main surface, the maximum half-width of a peak corresponding to a folded mode of a vertical optical branch in a Raman spectrum of the silicon carbide substrate is Δ ｍａｘ year, In a region from the first main surface to the second main surface, the minimum half-width of a peak corresponding to a folded mode of a vertical optical branch in a Raman spectrum of the silicon carbide substrate is Δ ｍｉｎ The silicon carbide substrate according to claim 4 , which satisfies Formula 5 when [0050]

6. A silicon carbide substrate according to any one of claims 1 to 5; a silicon carbide epitaxial layer in contact with the first main surface.

7. A step of preparing a silicon carbide substrate according to any one of claims 1 to 5; forming a silicon carbide epitaxial layer on the silicon carbide substrate.

8. A silicon carbide substrate comprising a first main surface and a second main surface opposite to the first main surface, the silicon carbide substrate being made of 4H polytype silicon carbide, The maximum diameter of the first main surface is 140 mm or more, The thickness of the silicon carbide substrate is 300 μm or more and 600 μm or less, the first main surface is a {0001} plane or a plane inclined at an off angle of more than 0° and not more than 8° with respect to the {0001} plane, In a region from the first main surface to 200 μm toward the second main surface, the maximum half-width of a peak corresponding to a folded mode of a vertical optical branch in a Raman spectrum of the silicon carbide substrate is Δ ｍａｘ year, In a region from the first main surface to 200 μm toward the second main surface, the minimum half-width of a peak corresponding to a folded mode of a vertical optical branch in a Raman spectrum of the silicon carbide substrate is Δ ｍｉｎ A silicon carbide substrate, which satisfies Formula 5 when [006]

9. Δ ｍａｘ -Δ ｍｉｎ ≦0.10, and Δ ｍａｘ and Δ ｍｉｎ The unit is cm －１ The silicon carbide substrate according to claim 8 .

10. A silicon carbide substrate comprising a first main surface and a second main surface opposite to the first main surface, the silicon carbide substrate being made of 4H polytype silicon carbide, The maximum diameter of the first main surface is 140 mm or more, The thickness of the silicon carbide substrate is 300 μm or more and 600 μm or less, the first main surface is a {0001} plane or a plane inclined at an off angle of more than 0° and not more than 8° with respect to the {0001} plane, The wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of silicon carbide of polytype 4H with zero stress is ν ０ year, In a region from the first main surface to the second main surface of 200 μm, the maximum wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate is defined as ν ｍａｘ year, In a region from the first main surface to 200 μm toward the second main surface, the minimum value of the wave number showing a peak corresponding to the folded mode of the vertical optical branch in the Raman spectrum of the silicon carbide substrate is defined as ν ｍｉｎ When A silicon carbide substrate that satisfies Formula 1 and Formula 2. [0070] [0080]

11. In a region from the first main surface to 200 μm toward the second main surface, the maximum half-width of a peak corresponding to a folded mode of a vertical optical branch in a Raman spectrum of the silicon carbide substrate is Δ ｍａｘ year, In a region from the first main surface to 200 μm toward the second main surface, the minimum half-width of a peak corresponding to a folded mode of a vertical optical branch in a Raman spectrum of the silicon carbide substrate is Δ ｍｉｎ The silicon carbide substrate according to claim 10 , which satisfies Formula 5 when [0097]

12. A silicon carbide substrate according to any one of claims 8 to 11; a silicon carbide epitaxial layer in contact with the first main surface.

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