Method of measuring conversion depth of substrate bpd dislocations in silicon carbide epitaxial layers

Abstract

The application discloses a method for measuring the conversion depth of BPD dislocation in a silicon carbide epitaxial layer, and comprises the following steps: providing an etched silicon carbide epitaxial wafer, and forming etching pits on the silicon carbide epitaxial layer; obtaining an etching pit image, and selecting a first etching pit image with an eccentric shell structure; drawing a measuring line on the first etching pit image, the measuring line passes through a shell tip of the eccentric shell structure and symmetrically divides the eccentric shell structure; determining a scanning path of the first etching pit according to the measuring line; scanning according to the scanning path to obtain a depth curve, the depth curve comprises a bottom section and two side sections; obtaining a mutation point with a sudden change in slope on the side section; and determining the conversion depth according to the position of the mutation point. The conversion depth of the BPD dislocation in the silicon carbide substrate into the TED dislocation in the silicon carbide epitaxial layer is obtained through the mutation point D on the depth curve, and the method plays a guiding role in optimizing the defects of the silicon carbide epitaxial wafer.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide processes, and more particularly to a method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer. Background Technology

[0002] Silicon carbide (SiC) single-crystal materials possess high thermal conductivity and high electron saturation drift velocity, along with a large bandgap and stable chemical properties. Based on these characteristics, they are widely used in power electronics and optoelectronics, and have enormous potential for future applications in photovoltaic power generation and electric vehicles. During the growth of SiC epitaxial wafers, most basal plane dislocations (BPDs) from the substrate are transformed into threading edge dislocations (TEDs) in the epitaxial layer. However, the exact depth at which these BPDs transform within the epitaxial layer cannot be accurately determined. It is generally believed that the closer the transformation depth of the BPDs is to the growth interface between the epitaxial layer and the substrate, the less impact the power devices fabricated on the underlying substrate BPDs will have. If the transformation depth of the BPDs were known, it would be possible to influence this depth by optimizing growth process parameters and further develop growth processes that bring the transformation depth closer to the growth interface, thereby reducing the adverse effects of substrate BPDs on SiC power devices. Summary of the Invention

[0003] The purpose of this invention is to provide a method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer, so as to solve the problem that the depth of the transformation process of BPD dislocations in the epitaxial layer cannot be accurately known in the prior art.

[0004] To achieve the above objective, the present invention provides a method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer, comprising the following steps: providing a silicon carbide epitaxial wafer etched by molten potassium hydroxide, the silicon carbide epitaxial wafer having a silicon carbide substrate and a silicon carbide epitaxial layer disposed on the silicon carbide substrate, wherein etching pits are formed on the silicon carbide epitaxial layer, the etching pits extending from the outer surface of the silicon carbide epitaxial layer towards the interior of the silicon carbide epitaxial layer; acquiring an image of the etching pits of the silicon carbide epitaxial wafer, and selecting a first etching pit image having an eccentric shell-like structure from the etching pit image, the eccentric shell-like structure being the etching pit corresponding to a BPD dislocation. The first etch pit image is divided by drawing a measurement line on it. The measurement line passes through the pointed corner of the eccentric shell-like structure and symmetrically divides the structure. A scanning path for the first etch pit corresponding to the first etch pit image is determined based on the measurement line. The first etch pit is scanned according to the scanning path to obtain a depth curve of the first etch pit on the scanning path. The depth curve includes a bottom segment and two side segments. Abrupt change points where the slope changes abruptly are obtained on the side segments. The transformation depth of the substrate BPD dislocation in the silicon carbide epitaxial layer to TED dislocation is determined based on the position of the abrupt change points.

[0005] Preferably, the step of acquiring the etch pit image of the silicon carbide epitaxial wafer includes: providing a confocal microscope and using the confocal microscope to acquire the etch pit image of the silicon carbide epitaxial wafer; and the step of scanning according to the scanning path to obtain the depth curve of the first etch pit in the scanning path direction includes: using the confocal microscope to scan according to the scanning path to obtain the depth curve of the first etch pit in the scanning path direction.

[0006] Preferably, before the step of providing the silicon carbide epitaxial wafer etched by molten potassium hydroxide, the method further includes: providing the silicon carbide epitaxial wafer; immersing the silicon carbide epitaxial wafer in molten potassium hydroxide and etching it for a first time; removing the silicon carbide epitaxial wafer from the molten potassium hydroxide; and cleaning the silicon carbide epitaxial wafer with deionized water.

[0007] Preferably, the thickness of the silicon carbide epitaxial layer of the silicon carbide epitaxial wafer is greater than or equal to 5 micrometers and less than or equal to 6 micrometers.

[0008] Preferably, the first time is greater than or equal to 9 minutes and less than or equal to 11 minutes.

[0009] Preferably, before acquiring the etching pit image of the silicon carbide epitaxial wafer, the method further includes: providing a circular piece of white paper with the same diameter as the silicon carbide epitaxial wafer; determining a plurality of test points on the white paper; covering the silicon carbide epitaxial wafer with the white paper; and using an oil-based pen to apply ink to each test point on the white paper to transfer each test point onto the silicon carbide epitaxial wafer to form test points.

[0010] Preferably, the step of selecting a first corrosion pit image with an eccentric shell-like structure on the corrosion pit image includes: selecting a plurality of first corrosion pit images that are closest to each of the test points and have an eccentric shell-like structure on the corrosion pit image.

[0011] Preferably, the test points are distributed on the first diameter of the silicon carbide epitaxial wafer and at both ends on a second diameter perpendicular to the first diameter.

[0012] Preferably, the step of determining the transformation depth of the substrate BPD dislocation in the silicon carbide epitaxial layer based on the location of the abrupt change point includes: obtaining a first distance between the abrupt change point and the outer surface of the silicon carbide epitaxial layer; and determining the transformation depth of the substrate BPD dislocation in the silicon carbide epitaxial layer based on the difference between the thickness of the silicon carbide epitaxial layer and the first distance.

[0013] Preferably, the upper part of the first corrosion pit is a first corrosion part corresponding to a TED dislocation, the outer contour of the first corrosion part is a circular contour, and the lower part of the first corrosion pit is a second corrosion part corresponding to a BPD dislocation.

[0014] Compared with the prior art, the present invention divides the first etch pit image by drawing a measurement line on the first etch pit image and obtaining the depth curve of the first etch pit on the scanning path. Thus, the position and depth of the overlapping of BPD dislocation etch pits and TED dislocation etch pits can be determined by the abrupt change point D on the depth curve. In addition, the transformation depth of BPD dislocations in silicon carbide substrates into TED dislocations in silicon carbide epitaxial layers can be obtained, which plays a guiding role in the defect optimization of silicon carbide epitaxial wafers. Attached Figure Description

[0015] Figure 1 This is a structural diagram of a silicon carbide epitaxial wafer in an embodiment of the present invention.

[0016] Figure 2 This is an image of the first corrosion pit in an embodiment of the present invention.

[0017] Figure 3 This is a depth curve diagram from an embodiment of the present invention.

[0018] Figure 4 This is a structural diagram of the white paper in an embodiment of the present invention.

[0019] Figure 5 This is a structural diagram of a silicon carbide epitaxial wafer with test sites set in an embodiment of the present invention.

[0020] Explanation of reference numerals in the attached diagram: 1. Silicon carbide epitaxial wafer; 11. Silicon carbide substrate; 12. Silicon carbide epitaxial layer; 13. Test point; 2. White paper; 21. Test point; 3. Etching pit image; 31. First etching pit image; 311. Eccentric shell-like structure; 3111. First shell tip; 4. Measurement line; 51. Bottom section; 52. Left side section; 53. Right side section. Detailed Implementation

[0021] To illustrate the technical content, structural features, and effects of the present invention in detail, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0022] like Figures 1 to 5 As shown, this embodiment of the invention provides a method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer, comprising the following steps: S1. A silicon carbide epitaxial wafer 1 is provided after being etched by molten potassium hydroxide. The silicon carbide epitaxial wafer 1 has a silicon carbide substrate 11 and a silicon carbide epitaxial layer 12 disposed on the silicon carbide substrate 11. Etching pits are formed on the silicon carbide epitaxial layer 12, extending from the outer surface of the silicon carbide epitaxial layer 12 towards the interior of the silicon carbide epitaxial layer 12. Specifically, silicon carbide single crystal substrates are prone to anisotropic etching in alkaline etchants, and the etching rate varies for different crystal orientations. For silicon carbide single crystals with (0001) orientation, the lattice around dislocations is distorted, the surface strain energy is large, and it is easy to react chemically with the etchant, thus being etched first. At the same time, due to the anisotropy of the etching rate, regularly shaped etching pits appear at the defective locations. Since the silicon carbide epitaxial layer 12 is grown directly on the silicon carbide single crystal substrate, and the thickness of the silicon carbide epitaxial layer 12 is generally much smaller than the thickness of the silicon carbide substrate 11, the dislocations in the silicon carbide substrate 11 will generally extend into the silicon carbide epitaxial layer 12. Therefore, the distribution of dislocation density in the silicon carbide substrate 11 and the silicon carbide epitaxial layer 12 can be obtained by etching with molten potassium hydroxide.

[0023] S2. Obtain the etching pit image 3 of the silicon carbide epitaxial wafer 1, and select the first etching pit image 31 with an eccentric shell-like structure 311 on the etching pit image 3. The eccentric shell-like structure 311 is the etching pit image 3 corresponding to the BPD dislocation; specifically, as shown in... Figure 2As shown, after etching with molten potassium hydroxide, there are two main types of etching pits on the surface of the silicon carbide epitaxial wafer 1. Correspondingly, there are also two types of etching pit images 3. The first type of etching pit image 3 is a circular outline with an eccentric shell-like structure 311 inside. Eccentricity means that the sharp corner of the shell-like structure is not at the center of the corresponding circular outline, such as... Figure 2 Image 3, shown within the blue box A, is the first type of etch pit image 3, also known as the first etch pit image 31. The shell-like tip on image 31 is the first shell-like tip 3111. Image 31 represents the first etch pit. The first etch pit is mainly formed by the transformation of BPD dislocations from the silicon carbide substrate 11 into TED dislocations in the silicon carbide epitaxial layer 12. In each first etch pit, BPD dislocations and TED dislocations overlap vertically. The upper part of the first etch pit is the first etched portion corresponding to the TED dislocation, with a circular outer contour. The lower part of the first etch pit is the second etched portion corresponding to the BPD dislocation, which is shell-shaped. The shell-like tip of the shell-shaped BPD dislocation etch pit is the second shell-like tip. Image 3, the second type of etch pit, is a circular outline with an elliptical interior. This second type of etch pit image 3 represents the second etch pit, formed by the direct extension of TED dislocations from the silicon carbide substrate 11 into the silicon carbide epitaxial layer 12. Figure 2 Image 3 shows the corrosion pits inside the red box B in the image.

[0024] S3. Draw a measurement line 4 on the first corrosion pit image 31 to divide the first corrosion pit image 31. The measurement line 4 passes through the cusp of the eccentric shell-like structure 311 and symmetrically divides the eccentric shell-like structure 311; specifically, as shown... Figure 2 As shown, the measurement line 4 is a straight line segment. The measurement line 4 passes through the first corrosion pit image 31 and divides the eccentric shell-like structure 311 into two symmetrical halves. The measurement line 4 needs to pass through the first shell tip 3111 in order to obtain the mutation point D in step S6.

[0025] S4. Determine the scanning path of the first corrosion pit corresponding to the first corrosion pit image 31 according to the measurement line 4. Specifically, the first corrosion pit image 31 corresponds one-to-one with the first corrosion pit on the silicon carbide epitaxial wafer 1. Selecting a first corrosion pit image 31 means selecting a first corrosion pit. The scanning path of the first corrosion pit can be determined according to the measurement line 4. Thus, the selected first corrosion pit can be scanned along the scanning path so that the scanning path passes through the second shell tip of the first corrosion pit and divides the shell-shaped BPD dislocation corrosion pit.

[0026] S5. Scan according to the scanning path to obtain the depth curve of the first corrosion pit on the scanning path. The depth curve includes the bottom segment 51 and the side segments; specifically, the depth curve is as follows: Figure 3 As shown, the horizontal axis of the depth curve is the distance from the starting position of the scanning path, and the vertical axis of the depth curve is the depth of the first corrosion pit. The depth curve has a concave structure. Taking the bottom segment 51 as a reference, the side segment to the left of the bottom segment 51 is the left segment 52, and the side segment to the right of the bottom segment 51 is the right segment 53. The left segment 52 and the right segment 53 are asymmetrical. The bottom segment 51, the left segment 52, and the right segment 53 are all curved segments. The mutation point D in step S6 appears on the left segment 52 or the right segment 53. If the scanning path first passes through the arc of the shell-shaped BPD dislocation corrosion pit, then the mutation point D will be on the left segment 52. If the scanning path first passes through the second shell tip, then the mutation point D will be on the right segment 53.

[0027] S6. Obtain the abrupt change point D on the side section where the slope changes abruptly; specifically, the abrupt change point D is the intersection of two straight lines with different slopes. Since the corrosion rates are different for different crystal orientations, two different crystal planes will form an intersection line after corrosion, which is represented by an abrupt change point D on the depth curve, such as... Figure 3 As shown in the center of the circle, the curve to the right of the circle is approximately a straight line, while the curve to the left of the circle, from the bottom to the position of the circle, is also approximately a straight line. The curvature between these two approximately straight lines changes significantly. Therefore, the center of the circle is the abrupt change point D.

[0028] S7. Determine the transformation depth of the substrate BPD dislocation into the silicon carbide epitaxial layer 12 based on the location of the mutation point D. Specifically, after obtaining the transformation depth, the transformation depth of the BPD dislocation can be affected by optimizing the growth process parameters. Furthermore, a growth process can be developed to make the transformation depth close to the interface between the silicon carbide substrate 11 and the silicon carbide epitaxial layer 12, thereby reducing the adverse effects of substrate BPD dislocations on SiC power devices.

[0029] In this embodiment of the invention, a measurement line 4 is drawn on the first etch pit image 31 to divide the first etch pit image 31, and the depth curve of the first etch pit on the scanning path is obtained. Thus, the position and depth at which BPD dislocation etch pits and TED dislocation etch pits overlap can be determined by the abrupt change point D on the depth curve. In this way, the transformation depth of the BPD dislocation of the silicon carbide substrate 11 into the TED dislocation in the silicon carbide epitaxial layer 12 can be obtained, which plays a guiding role in the defect optimization of the silicon carbide epitaxial wafer 1.

[0030] In this embodiment of the invention, step S2, the step of obtaining the etching pit image 3 of the silicon carbide epitaxial wafer 1, includes: S21. Provide a confocal microscope and use it to obtain an etching pit image 3 of the silicon carbide epitaxial wafer 1. Specifically, the confocal microscope is a mature product that can be purchased and used directly. The confocal microscope can be used to directly obtain the etching pit image 3. After obtaining the etching pit image 3, a first etching pit image 31 with an eccentric shell-like structure 311 can be manually selected, and a measurement line 4 can be made on the first etching pit image 31 using the confocal microscope.

[0031] Further, in this embodiment of the invention, step S5, the step of scanning according to the scanning path to obtain the depth curve of the first corrosion pit in the scanning path direction, includes: S5. Using a confocal microscope, a scanning path is used to obtain the depth curve of the first corrosion pit along the scanning path direction. Specifically, the confocal microscope directly converts measurement line 4 into a scanning path to scan the first corrosion pit and obtain the depth curve. Of course, in actual use, other equipment can also be selected, as long as it can obtain the depth curve of this embodiment of the invention; no limitation is made here.

[0032] The embodiments of the present invention can obtain the depth curve of the first corrosion pit using only a confocal microscope, which is very convenient to use.

[0033] In this embodiment of the invention, before providing the silicon carbide epitaxial wafer 1 etched by molten potassium hydroxide in step S1, the method further includes: S011. A silicon carbide epitaxial wafer 1 is provided; specifically, the thickness of the silicon carbide epitaxial layer 12 of the silicon carbide epitaxial wafer 1 is greater than or equal to 5 micrometers and less than or equal to 6 micrometers, for example, the thickness of the silicon carbide epitaxial layer 12 can be 6 micrometers.

[0034] S012. Immerse the silicon carbide epitaxial wafer 1 in molten potassium hydroxide and etch it for a first time. Specifically, pour 1500g of potassium hydroxide solid powder into a sealed container, then heat the sealed container until the temperature inside reaches 550°C. Place the silicon carbide epitaxial wafer 1 on a jig, and then insert the jig into the sealed container, with the bottom end of the jig submerged below the surface of the molten liquid, so that the silicon carbide epitaxial wafer 1 is completely immersed in the molten potassium hydroxide. From the moment the silicon carbide epitaxial wafer 1 is completely immersed in the molten liquid, after a first time, remove the jig from the sealed container. The first time is greater than or equal to 9 minutes and less than or equal to 11 minutes, for example, the first time can be 10 minutes to etch away the dislocations in the silicon carbide epitaxial layer 12 of the silicon carbide epitaxial wafer 1.

[0035] S013. Remove the silicon carbide epitaxial wafer 1 from the molten potassium hydroxide.

[0036] S014. Clean the silicon carbide epitaxial wafer 1 with deionized water. Specifically, rinse the surface of the silicon carbide epitaxial wafer 1 with deionized water for 3 minutes. After rinsing, use a nitrogen gun to dry the moisture on the upper and back surfaces of the silicon carbide epitaxial wafer 1.

[0037] In this embodiment of the invention, before step S2, which involves obtaining the etching pit image of the silicon carbide epitaxial wafer 1, the method further includes: S021. A circular piece of white paper 2 is provided, the diameter of which is the same as the diameter of the silicon carbide epitaxial wafer 1.

[0038] S022. Determine a number of test points 21 on the white paper 2; specifically, the test points 21 can be distributed on a third diameter of the white paper 2 and at both ends of a fourth diameter perpendicular to the third diameter, as shown in the figure. Figure 4 As shown.

[0039] S023. Cover the silicon carbide epitaxial wafer 1 with white paper 2. Specifically, cover the silicon carbide epitaxial wafer 1 with white paper 2 and make the edge of white paper 2 flush with the edge of silicon carbide epitaxial wafer 1.

[0040] S024. Using an oil-based pen, apply ink to each test point 21 on the white paper 2 to transfer each test point 21 onto the silicon carbide epitaxial wafer 1 to form the test point 13. Specifically, as follows: Figure 5 As shown, the test points 13 are distributed on the first diameter of the silicon carbide epitaxial wafer 1 and at both ends of the second diameter perpendicular to the first diameter. Further, there are, for example, 10 test points 13, of which seven test points 13 are evenly distributed on the section from the first end of the first diameter to the center of the silicon carbide epitaxial wafer 1, and one of the remaining three test points 13 is located on the second end of the first diameter opposite to the first end, and the other two test points 13 are distributed at both ends of the second diameter perpendicular to the first diameter. Thus, the conversion depth of different regions of the silicon carbide epitaxial wafer 1 can be measured with only a small number of test points 13, effectively saving time.

[0041] Further, in this embodiment of the invention, step S2, selecting the first corrosion pit image 31 with an eccentric shell-like structure 311 on the corrosion pit image 3, includes: S21. Select several first corrosion pit images 31 that are closest to each test point 13 and have an eccentric shell-like structure 311 on the corrosion pit image 3, so that the obtained values ​​of each transformation depth are more comprehensive.

[0042] In this embodiment of the invention, step S7, determining the transformation depth of the substrate BPD dislocation in the silicon carbide epitaxial layer 12 based on the location of the abrupt change point D, includes: S71. Obtain the first distance H1 between the mutation point D and the outer surface of the silicon carbide epitaxial layer 12, specifically, as follows: Figure 3 As shown.

[0043] S72. The transformation depth of the substrate BPD dislocation in the silicon carbide epitaxial layer 12 is determined based on the difference between the thickness of the silicon carbide epitaxial layer 12 and the first distance. Specifically, the thickness of the silicon carbide epitaxial layer 12 can be obtained using a Fourier transform infrared spectrometer. The thickness of the silicon carbide epitaxial layer 12 at the test site 13 corresponding to the transformation depth can be obtained, and the transformation depth can be calculated using the difference between the thickness of the silicon carbide epitaxial layer 12 and the first distance H1. The calculation result is more accurate. This embodiment of the invention can obtain the transformation depth in different regions, and the measurement results are more comprehensive.

[0044] The above-disclosed examples are merely preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer, characterized in that, Includes the following steps: A silicon carbide epitaxial wafer is provided after being etched by molten potassium hydroxide. The silicon carbide epitaxial wafer has a silicon carbide substrate and a silicon carbide epitaxial layer disposed on the silicon carbide substrate. Etching pits are formed on the silicon carbide epitaxial layer, and the etching pits extend from the outer surface of the silicon carbide epitaxial layer to the interior of the silicon carbide epitaxial layer. Obtain an etching pit image of the silicon carbide epitaxial wafer, and select a first etching pit image with an eccentric shell-like structure on the etching pit image, wherein the eccentric shell-like structure is an etching pit image corresponding to a BPD dislocation. A measurement line is drawn on the first corrosion pit image to divide the first corrosion pit image. The measurement line passes through the shell tip of the eccentric shell-like structure and symmetrically divides the eccentric shell-like structure. The scanning path of the first corrosion pit corresponding to the first corrosion pit image is determined based on the measurement line; A scan is performed according to the scan path to obtain the depth curve of the first corrosion pit on the scan path, the depth curve including the bottom segment and the side segments; The abrupt change point where the slope changes abruptly is obtained on the side segment; The transformation depth of the substrate BPD dislocation into the TED dislocation in the silicon carbide epitaxial layer is determined based on the location of the mutation point.

2. The method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer as described in claim 1, characterized in that, The steps for obtaining the etch pit image of the silicon carbide epitaxial wafer include: A confocal microscope is provided, and images of etch pits on the silicon carbide epitaxial wafer are acquired using the confocal microscope; and, The step of scanning according to the scanning path to obtain the depth curve of the first corrosion pit in the direction of the scanning path includes: The confocal microscope is used to scan along the scanning path to obtain the depth curve of the first corrosion pit in the direction of the scanning path.

3. The method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer as described in claim 1, characterized in that, Prior to the step of providing a silicon carbide epitaxial wafer etched with molten potassium hydroxide, the process also includes: Provide silicon carbide epitaxial wafers; The silicon carbide epitaxial wafer is immersed in molten potassium hydroxide and etched for a first time; The silicon carbide epitaxial wafer is removed from the molten potassium hydroxide. The silicon carbide epitaxial wafer was cleaned with deionized water.

4. The method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer as described in claim 3, characterized in that, The thickness of the silicon carbide epitaxial layer of the silicon carbide epitaxial wafer is greater than or equal to 5 micrometers and less than or equal to 6 micrometers.

5. The method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer as described in claim 3, characterized in that, The first time is greater than or equal to 9 minutes and less than or equal to 11 minutes.

6. The method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer as described in claim 1, characterized in that, Before the step of obtaining the etch pit image of the silicon carbide epitaxial wafer, the method further includes: A circular piece of white paper is provided, the diameter of which is the same as the diameter of the silicon carbide epitaxial wafer; Determine several test points on the white paper; The white paper is placed over the silicon carbide epitaxial wafer; An oil-based pen is used to mark each test point on the white paper to transfer each test point onto the silicon carbide epitaxial wafer to form the test points.

7. The method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer as described in claim 6, characterized in that, The step of selecting the first corrosion pit image with an eccentric shell-like structure from the corrosion pit image includes: Select several first corrosion pit images that are closest to each of the test points and have an eccentric shell-like structure from the corrosion pit images.

8. The method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer as described in claim 6, characterized in that, The test points are distributed on the first diameter of the silicon carbide epitaxial wafer and at both ends of the second diameter perpendicular to the first diameter.

9. The method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer as described in claim 1, characterized in that, The step of determining the transformation depth of substrate BPD dislocations in the silicon carbide epitaxial layer based on the location of the abrupt change point includes: Obtain the first distance between the mutation point and the outer surface of the silicon carbide epitaxial layer; The transformation depth of the substrate BPD dislocation in the silicon carbide epitaxial layer is determined based on the difference between the thickness of the silicon carbide epitaxial layer and the first distance.

10. The method for measuring the transformation depth of BPD dislocations in a silicon carbide epitaxial layer as described in claim 1, characterized in that, The upper part of the first corrosion pit is the first corrosion part corresponding to the TED dislocation, and the outer contour of the first corrosion part is a circular contour. The lower part of the first corrosion pit is the second corrosion part corresponding to the BPD dislocation.

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