A nondestructive testing system and method for internal voids in silicon carbide boules

Abstract

This invention discloses a non-destructive testing system for internal voids in silicon carbide crystal rods. The system includes an eddy current probe, a variable frequency AC generator, a first eddy current sensor, a second eddy current sensor, a positioning probe, a terminal, and a sample holder. This invention uses the cooperation of the eddy current probe and the first eddy current sensor to determine the presence of voids below the detection point and to preliminarily determine the void's location. Simultaneously, the cooperation of the positioning probe and the second eddy current sensor confirms the exact location of the void. This invention eliminates the need for slicing microscopy during void detection in silicon carbide crystal rods, thus avoiding damage to the crystal rod. The silicon carbide crystal rod can still be used after detection. Furthermore, the system can determine the void location, facilitating subsequent processing of the void-containing silicon carbide crystal rod.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide crystal rod testing technology, specifically relating to a non-destructive testing device and system for internal voids in silicon carbide crystal rods. Background Technology

[0002] In recent years, silicon carbide crystals have evolved from a high-potential wide-bandgap semiconductor material into one of the most widely recognized and important materials in the field of power electronics. Silicon carbide crystals applicable to electronics were first grown by Lely in 1955 using the vertical vapor phase method. This growth process requires temperatures exceeding 2000°C, and even minute temperature fluctuations can introduce defects of varying degrees into the crystal. Some of these defects are fatal, such as hexagonal voids, which can potentially cause device failure.

[0003] Since hexagonal voids generally do not exist in the form of penetrating or clustering within crystals, the detection of hexagonal voids requires cutting the silicon carbide crystal into slices, polishing the slices smooth, and finally observing the presence of hexagonal voids under a microscope. However, this method is destructive and irreversible, making it unsuitable for detecting hexagonal voids in commercial crystal rods.

[0004] To achieve non-destructive testing, Chinese invention patent CN 115425011A discloses a semiconductor structure and a testing method for the semiconductor structure, employing eddy current testing. However, this method is suitable for detecting the connection status of metal interconnects after wafer bonding and can test wafers with a thickness of several hundred micrometers. Since silicon carbide crystal rods are generally over 10 mm thick, and the defects within the crystal are complex, unprocessed crystals often have numerous defects on their surface, all of which affect eddy current testing. Therefore, ordinary eddy current testing methods cannot detect specific defects in silicon carbide crystals, nor can they pinpoint the precise location of the defects. Summary of the Invention

[0005] The present invention provides a non-destructive testing device and system for internal voids in silicon carbide crystal rods, so as to solve at least one of the above-mentioned technical problems.

[0006] The technical solution adopted in this invention is: a non-destructive testing system for internal voids in silicon carbide crystal rods, wherein the non-destructive testing system includes an eddy current probe that moves at the top of the silicon carbide crystal rod to generate eddy currents in the silicon carbide crystal rod to be tested.

[0007] A first eddy current detection sensor connected to the eddy current probe is used to detect changes in the magnitude of surface eddy currents on the silicon carbide crystal rod to be tested.

[0008] A variable frequency AC generator connected to the eddy current probe is used to change the penetration depth of the eddy current by alternating the frequency of the alternating current.

[0009] A positioning probe moves along the side of the silicon carbide crystal rod to be tested, in conjunction with the eddy current probe, to determine the location of the cavity.

[0010] A second eddy current detection sensor connected to the positioning probe is used to detect the magnitude, current density, and phase change of the eddy current on the side of the silicon carbide crystal rod to be tested.

[0011] The terminal controls the non-destructive testing device to receive and process test signals and output test results.

[0012] A sample holder is used to place and position the silicon carbide crystal rod to be tested.

[0013] Preferably, the sample holder has a positioning area to determine the relative position of the silicon carbide crystal rod to be tested and the sample holder.

[0014] Preferably, the thickness T of the silicon carbide crystal rod to be tested is 10mm-50mm, and the surface undulation is less than 50μm.

[0015] Preferably, the top of the silicon carbide crystal rod to be tested has a test area, the distance between the test area and the edge of the silicon carbide crystal rod to be tested is not less than 3mm, the test area has test points, and the test time for any of the test points is 20-60s.

[0016] Preferably, the radius of the point to be detected is the radius of the eddy current probe, the radius r of the eddy current probe is 10-30mm, and the distance between two adjacent points to be detected is r*√2 and / or 2r.

[0017] This invention also discloses a non-destructive testing method for internal voids in silicon carbide crystal rods using the aforementioned non-destructive testing system, comprising the following steps:

[0018] S1: Sample pretreatment and sample placement;

[0019] S2: Establish a three-dimensional coordinate system with any fixed point on the sample holder as the origin, determine the first and second coordinates of the point to be tested with the location of the eddy current probe, and determine the third coordinate of the point to be tested with the penetration depth of the eddy current.

[0020] S3: The fixed eddy current probe determines the first and second coordinates of the point to be tested, continuously changes the penetration depth of the eddy current, and makes the third coordinate of the point to be tested and the third coordinate of the positioning probe change synchronously to obtain the test results;

[0021] S4: Move the eddy current probe and repeat step S3 until the trajectory of the eddy current probe completely covers the area to be detected.

[0022] Preferably, the third coordinate is determined according to the following formula.

[0023] Z = Tn,

[0024] n = 5δ,

[0025]

[0026] Where Z is the third coordinate, T is the thickness of the silicon carbide crystal rod to be tested, n is the eddy current penetration depth, δ is the eddy current penetration depth, ρ is the resistivity of the silicon carbide crystal rod to be tested, f is the alternating current frequency of the frequency converter, and μ0 is the permeability of the silicon carbide crystal rod to be tested.

[0027] Preferably, step S1 further includes rolling and smoothing the outer surface of the silicon carbide crystal rod to be tested so that its surface undulation is less than 50 μm, and measuring the thickness T and diameter D of the silicon carbide crystal rod to be tested.

[0028] Preferably, step S1 includes placing the silicon carbide crystal rod to be tested in the positioning area of ​​the sample holder, placing the eddy current probe on top of the silicon carbide crystal rod to be tested, and placing the positioning probe on the side of the silicon carbide crystal rod to be tested.

[0029] Preferably, the center of the bottom surface of the silicon carbide crystal rod to be tested coincides with the center of the positioning area.

[0030] Preferably, step S2 includes establishing a three-dimensional coordinate system with the center point of the positioning area as the origin.

[0031] Preferably, the third coordinate of the point to be detected changes continuously between 0 and T.

[0032] Preferably, step S3 includes determining the existence of a cavity based on the eddy current changes detected by the first eddy current detection sensor, and determining the first and second coordinates of the cavity using the first and second coordinates of the eddy current probe; plotting the eddy current phase and / or current density variation curves with penetration depth based on the detection signal of the second eddy current detection sensor, and determining the third coordinates of the cavity using the variation curves.

[0033] Preferably, step S2 further includes establishing a three-dimensional model of the silicon carbide crystal rod to be tested in a three-dimensional coordinate system using the thickness T and diameter D of the silicon carbide crystal rod to be tested.

[0034] Preferably, step S3 further includes marking the location of the void onto the three-dimensional model of the silicon carbide crystal rod to be tested based on the three-dimensional coordinates of the void.

[0035] Preferably, the method further includes step S5: cavity re-inspection, moving the eddy current probe to coincide with the first and second coordinates of the cavity to be confirmed, adjusting the alternating current frequency to make the penetration depth of the eddy current T or T / 2, moving the positioning probe along the third coordinate direction, and plotting the change curve of eddy current phase and / or current density with penetration depth based on the detection signal of the second eddy current detection sensor.

[0036] Due to the adoption of the above technical solution, the beneficial effects achieved by this invention are as follows:

[0037] 1. When eddies are generated in a silicon carbide crystal rod, if the rod is free of voids and defects, the eddies will flow stably, and their size will not change significantly. However, if voids exist, the eddies will bypass them, resulting in irregular flow and detectable unevenness. Furthermore, the penetration depth formula shows a positive correlation between the eddy current depth and the current frequency: lower frequencies result in shallower penetration, while higher frequencies result in greater penetration. This invention utilizes a combination of an eddy current probe and a first eddy current detection sensor to gradually increase the current frequency, thereby increasing the penetration depth. The presence of eddies is determined by the changes detected by the first eddy current detection sensor. More specifically, assuming a cavity exists at a depth of h, when the penetration depth of the eddy current is less than h, the eddy current will flow stably because it has not reached the cavity, and no significant change will be observed in the first eddy current detection sensor. As the penetration depth increases, when the penetration depth is greater than or equal to h, the eddy current will flow irregularly to avoid the cavity because it has reached the cavity, resulting in a significant change in the first eddy current detection sensor. Therefore, the presence of the cavity can be determined based on the changes in the first eddy current detection sensor. Furthermore, the location of the cavity can also be determined based on the penetration depth of the eddy current when it first shows a significant change as the penetration depth gradually increases. This invention achieves non-destructive testing in the inspection of silicon carbide crystal rods and can determine the location of cavities, facilitating subsequent processing of silicon carbide crystal rods containing cavities.

[0038] 2. As a preferred embodiment of the present invention, the present invention can adopt different detection strategies according to the different thicknesses of the silicon carbide crystal rod to be detected. When the thickness of the silicon carbide crystal rod to be detected is small, the penetration depth of the eddy current can be directly made to gradually penetrate from one end of the silicon carbide crystal rod to the other end, thereby achieving scanning of the height direction of the silicon carbide crystal rod to be detected through the eddy current. When the thickness of the silicon carbide crystal rod to be detected is large, a segmented detection method can be used. Even if the maximum penetration depth of the eddy current is half the thickness of the silicon carbide crystal rod, after one half of the silicon carbide crystal rod to be detected is detected, the other half is detected by flipping the silicon carbide crystal rod to be detected. This increases the thickness of the silicon carbide crystal rod that the present invention can detect, thereby expanding the scope of application of the present invention.

[0039] 3. As a preferred embodiment of the present invention, based on the eddy current probe and the first eddy current detection sensor, the present invention, through the cooperation of the positioning probe and the second eddy current detection sensor, and based on the principle that the second eddy current detection sensor will produce obvious phase changes when there are cavities in the eddy current, as the penetration depth increases, the positioning probe changes with the penetration depth. During the movement of the positioning probe, when there is an obvious phase change in the eddy current detected by the second eddy current detection sensor, it indicates that there is irregular movement of the eddy current at that depth, that is, there is a cavity at that depth, so that the accurate location of the cavity can be determined.

[0040] 4. In a preferred embodiment of the present invention, the silicon carbide crystal rod to be tested is positioned using a reference point on the sample holder. Specifically, the reference point can be the center point of the sample holder, aligning it with the center of the bottom surface of the silicon carbide crystal rod to determine the relative position between the two. Alternatively, the reference point can be a point on another sample holder. For example, if the sample holder is square, the reference point can be the vertex of one of its corners. Placing the silicon carbide crystal rod at that corner of the sample holder also determines the relative position between the two. After determining the positions of the sample holder and the silicon carbide crystal rod, by establishing a three-dimensional coordinate system and modeling the silicon carbide crystal rod, the location of the void can be determined using three-dimensional coordinates. The void's location can also be displayed on the three-dimensional model, facilitating observation and judgment by the operator.

[0041] 5. As a preferred embodiment of the present invention, in addition to being applied to the process of detecting voids in silicon carbide crystal rods, the present invention can also be further extended to the process of detecting voids in gemstones that can generate eddies, or to other detection processes that can generate eddies and require determining the location of voids. Attached Figure Description

[0042] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0043] Figure 1 This is a schematic diagram of vortex flow without voids according to one embodiment of the present invention;

[0044] Figure 2 A schematic diagram of vortex flow in the presence of voids according to one embodiment of the present invention;

[0045] Figure 3 This is a schematic diagram of the placement structure of the silicon carbide crystal rod to be tested according to one embodiment of the present invention;

[0046] Figure 4 This is a schematic diagram of a non-destructive testing device according to one embodiment of the present invention;

[0047] Figure 5 This is a schematic diagram of the initial scanning movement path of an eddy current probe according to one embodiment of the present invention;

[0048] Figure 6 This is a schematic diagram of the secondary scanning movement path of an eddy current probe according to one embodiment of the present invention;

[0049] Figure 7 This is a schematic diagram of the movement path of an eddy current probe according to another embodiment of the present invention;

[0050] Figure 8 This is a schematic diagram of the spacing between points to be detected according to one embodiment of the present invention;

[0051] Figure 9 This is a schematic diagram of the current density change when there are no voids at the point to be detected according to one embodiment of the present invention;

[0052] Figure 10 This is a schematic diagram of the eddy current phase change when there are no voids at the point to be detected according to one embodiment of the present invention;

[0053] Figure 11 This is a schematic diagram illustrating the change in current density when there is a void at the point to be detected according to one embodiment of the present invention;

[0054] Figure 12 This is a schematic diagram of the eddy current phase change when there is a cavity at the point to be detected according to one embodiment of the present invention.

[0055] Figure label:

[0056] 1. Eddy current probe; 2. Variable frequency AC generator; 3. First eddy current detection sensor; 4. Second eddy current detection sensor; 5. Positioning probe; 6. Terminal; 7. Sample holder; 8. Silicon carbide crystal rod to be tested; 9. Detection point. Detailed Implementation

[0057] To more clearly illustrate the overall concept of the present invention, a detailed description will be provided below with reference to the accompanying drawings and examples.

[0058] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0059] Furthermore, in the description of this invention, it should be understood that the terms "top," "bottom," "inner," "outer," "axial," "radial," "circumferential," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0060] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0061] In this invention, unless otherwise expressly specified and limited, the first feature "on" or "below" the second feature may be in direct contact with the first and second features, or indirect contact through an intermediate medium. In the description of this specification, references to terms such as "implementation," "example," "aspect," "specific example," or "specific example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0062] In the defect detection process of silicon carbide crystal rods, microscopic observation of silicon carbide crystal rod slices can damage the silicon carbide crystal rods, rendering them unusable. Therefore, a non-destructive testing method is needed to ensure that silicon carbide crystal rods can still be used after defect detection.

[0063] Since eddies are generated in a silicon carbide crystal rod, if there are no voids or defects in the silicon carbide crystal rod, the eddies will flow stably, i.e., as... Figure 1 As shown in the diagram, there is no significant change in the size of the eddy current when it is detected; however, if voids exist in the silicon carbide crystal rod, the eddy current will bypass the voids during its flow, i.e., as shown in the diagram. Figure 2 The flow pattern shown indicates that, due to the irregular flow of the eddies, non-uniform changes in the eddies can be detected. Based on this principle, non-destructive testing of silicon carbide crystal rods can be achieved.

[0064] According to one embodiment of the present invention, such as Figure 3 , Figure 4 As shown, a non-destructive testing system for internal voids in a silicon carbide crystal rod is disclosed. The system includes an eddy current probe 1, a variable frequency AC generator 2, a first eddy current detection sensor 3, a second eddy current detection sensor 4, a positioning probe 5, a terminal 6, and a sample holder 7. The eddy current probe 1 can generate an alternating magnetic field, thereby generating eddy currents in the silicon carbide crystal rod 8 to be tested. The eddy current probe 1 can be made of copper coil and soft magnetic ferrite. The silicon carbide crystal rod 8 to be tested is usually cylindrical. The eddy current probe 1 can be placed on the bottom or top surface of the silicon carbide crystal rod 8 to be tested.

[0065] The variable frequency AC generator 2 provides power to the non-destructive testing system. Since the penetration depth of eddy currents is positively correlated with the current frequency (i.e., the higher the current frequency, the greater the penetration depth), the penetration depth can be changed by altering the frequency of the alternating current. Furthermore, by gradually increasing the frequency of the alternating current, the penetration depth of the eddy current can be gradually increased to be the same as or half the thickness of the silicon carbide crystal rod 8 under test. Specifically, when the thickness of the silicon carbide crystal rod 8 is small, adjusting the alternating current can adjust the penetration depth of the eddy current, allowing it to gradually penetrate from one end of the silicon carbide crystal rod 8 to the other, thus achieving scanning of the height direction of the silicon carbide crystal rod 8 through eddy currents. However, when the thickness of the silicon carbide crystal rod 8 is large... When the thickness is large, if the eddy current penetration depth is to gradually penetrate from one end of the silicon carbide crystal rod 8 to the other end, the penetration depth of the eddy current is positively correlated with the frequency of the alternating current. The greater the penetration depth of the eddy current, the higher the frequency of the alternating current is required. At the same time, when the penetration depth of the eddy current increases, the error in the detection process of the eddy current size will also increase. Therefore, in order to reduce the frequency variation range of the alternating current and reduce the detection error, when the thickness of the silicon carbide crystal rod 8 is large, a segmented detection method can be used. That is, the frequency of the alternating current is adjusted so that the maximum penetration depth of the eddy current is half the thickness of the silicon carbide crystal rod. After one half of the silicon carbide crystal rod 8 is detected, the other half can be detected by flipping the silicon carbide crystal rod 8.

[0066] The first eddy current detection sensor 3 is connected to the eddy current probe 1 to detect the change in the size of the surface eddy current of the silicon carbide crystal rod 8 to be tested.

[0067] The second eddy current detection sensor 4 is used to detect the magnitude, current density, and phase change of the eddy current on the side of the silicon carbide crystal rod 8 to be tested. During the test, at a certain penetration depth, the second eddy current detection sensor 4 can detect the changes in the eddy current phase and eddy current density at different depths. When the current density and phase change abruptly, it indicates that there is a void.

[0068] Positioning probe 5 is placed on the side of silicon carbide crystal rod 8 to be tested, and moves along the axis of silicon carbide crystal rod 8 to cooperate with eddy current probe 1 through position movement.

[0069] Terminal 6 has a controller, processor and display, which plays a control role in the entire non-destructive testing device. It also receives the detection signals of the first eddy current detection sensor 3 and the second eddy current detection sensor 4, processes the detection signals and outputs the detection results in a visual manner.

[0070] The sample holder 7 is used to place and position the silicon carbide crystal rod 8 to be tested. The sample holder 7 has a positioning area to determine the relative position of the silicon carbide crystal rod 8 and the sample holder 7. Specifically, the sample holder 7 has a reference point, which can be the center point of the sample holder 7. When confirming the position of the silicon carbide crystal rod 8, aligning the center point of the sample holder 7 with the center of the bottom surface of the silicon carbide crystal rod 8 determines the relative position of the silicon carbide crystal rod 8 and the sample holder 7. Alternatively, the reference point on the sample holder 7 can also be any other point on the sample holder 7. For example, if the sample holder 7 is square, the reference point can be the vertex of one of its corners. Placing the silicon carbide crystal rod 8 at that corner of the sample holder 7 also determines the relative position of the sample holder 7 and the silicon carbide crystal rod 8.

[0071] In a preferred embodiment, to improve the accuracy of void detection in the silicon carbide crystal rod 8, the thickness T of the silicon carbide crystal rod 8 is 10mm-50mm. Simultaneously, to eliminate the influence of surface defects on the detection results, the surface undulation of the silicon carbide crystal rod 8 needs to be less than 50μm. Therefore, pretreatment is required before detection, by rolling and smoothing the outer surface of the silicon carbide crystal rod 8. Furthermore, since microtubes may exist at the edge of the silicon carbide crystal rod, and the presence of microtubes can affect the eddy currents, thus affecting the accuracy of void detection, void detection is not required at the edge 3mm of the silicon carbide crystal rod 8. Specifically, the following two methods can be selected:

[0072] Method 1:

[0073] A test area is defined on the top of the silicon carbide crystal rod 8 to be tested, and the distance between the test area and the edge of the silicon carbide crystal rod 8 to be tested is not less than 3mm.

[0074] Method 2:

[0075] The silicon carbide crystal rod 8 to be tested is de-skinned, that is, 3mm of the surface layer at the edge of the silicon carbide crystal rod 8 is ground off. The top of the silicon carbide crystal rod after grinding is the area to be tested.

[0076] The area to be tested contains a test point 9, the radius of which is the radius of the eddy current probe 1. To ensure that the test point 9 completely covers the area to be tested, the movement of the eddy current probe 1 can be controlled. Specifically, the test point 9 can completely cover the area to be tested in the following way:

[0077] Method 1:

[0078] Initial scan: such as Figure 5 , Figure 8As shown, with the radius r of the eddy current probe 1, the first test point 9 is selected. The center of the first test point 9 coincides with the center of the test area. After the first test point 9 is tested, using any radial direction of the first test point 9 as the first reference line, the eddy current probe 1 is moved 2r along the first reference line towards the edge of the test area to determine the second test point 9. After the second test point 9 is tested, the eddy current probe 1 is moved another 2r along the first reference line towards the edge of the test area, and so on, until the eddy current probe 1 reaches the edge of the test area. Then, the eddy current probe 1 is moved 2r in a direction perpendicular to the first reference line to determine the next test point 9, and then moved along the first reference line again, and so on. By moving the eddy current probe 1, the test points 9 gradually cover the test area, and the last stop position of the eddy current probe 1 is the end point of the first scan.

[0079] Secondary scan, such as Figure 6 , Figure 8 As shown, since the eddy current probe 1 and the point to be detected 9 are circular, there will be an area that is not covered after moving in the above way. At this time, the second reference line can be used as the first reference line at 45°. The eddy current probe 1 can be moved along the second reference line direction from the end point of the first scan by r*√2 to determine the first point to be detected 9 of the second scan. The second scan is performed in the same way as the first scan until all the points to be detected 9 can completely cover the area to be detected.

[0080] Method 2:

[0081] like Figure 7 , Figure 8 As shown, with the radius of the eddy current probe 1 as r and any radial direction of the area to be tested as the baseline, the first test point 9 is selected. The center of the first test point 9 coincides with the center of the area to be tested. After the first test point 9 is tested, the eddy current probe 1 moves r*√2 in a direction 45° with the baseline to determine the second test point 9. After the second test point 9 is tested, the eddy current probe 1 moves r*√2 in a direction 135° with the baseline to determine the third test point 9. After the third test point 9 is tested, the eddy current probe 1 moves r*√2 in a direction 45° with the baseline to determine the fourth test point 9, and so on. The movement trajectory of the eddy current probe 1 is "M" shaped, and finally the test points 9 completely cover the area to be tested.

[0082] It is understandable that the eddy current probe 1 may have other movement modes besides the two mentioned above. When detecting point 9, the dwell time of the eddy current probe 1 at point 9 is 20-60 seconds. When the thickness of the silicon carbide crystal rod 8 being detected is small, the shorter the time it takes for the eddy current penetration depth to change from the top to the bottom of the silicon carbide crystal rod 8 by changing the frequency of the alternating current, the shorter the detection time. When the thickness of the silicon carbide crystal rod 8 being detected is large, the longer the time it takes for the eddy current penetration depth to change from the top to the bottom of the silicon carbide crystal rod 8 by changing the frequency of the alternating current, the longer the detection time. In addition, since the radius of the eddy current probe 1 directly affects the radius of the point 9 being detected, and the smaller the radius of the point 9 being detected, the more detection points there are, and the higher the accuracy of the detection results, different radii of eddy current probe 1 can be selected according to the requirements of the detection results. Usually, the radius of the eddy current probe 1 can be selected between 10-30 mm.

[0083] The following describes a non-destructive testing method using the above-described non-destructive testing device through specific embodiments. Embodiment 1

[0084] S1: Sample Pretreatment and Placement; First, remove the 3mm thick surface layer of the silicon carbide crystal rod 8 to be tested. Then, roll and smooth the outer surface of the silicon carbide crystal rod 8 to make its surface undulation less than 50μm. Measure the thickness T and diameter D of the silicon carbide crystal rod 8 and input this data into the computer terminal 6. Place the silicon carbide crystal rod 8 on the sample holder 7, ensuring that the center of the sample holder 7 coincides with the center of the bottom surface of the silicon carbide crystal rod 8. Simultaneously, place the eddy current probe 1 at the center of the top surface of the silicon carbide crystal rod 8, and place the positioning probe 5 at the highest point of the side surface of the silicon carbide crystal rod 8. The sample holder 7 can be made of insulating material, such as polytetrafluoroethylene (PTFE), to avoid the sample holder 7 affecting the test results during the testing process.

[0085] S2: As Figure 3 As shown, a three-dimensional coordinate system is established with the center of the sample holder 7 as the origin and the axis of the silicon carbide crystal rod 8 to be tested as the Z-axis. At this time, the coordinates of the position of the eddy current probe 1 are (0,0,T), which are also the initial coordinates of the point to be tested 9. The coordinates of the position of the positioning probe 5 are (0,D / 2,T).

[0086] S3: Fix the eddy current probe to keep the X and Y coordinates of the point to be tested 9 unchanged. Adjust the Z coordinate of the point to be tested 9 by adjusting the frequency of the alternating current, so that the Z coordinate of the point to be tested 9 changes to 0. Specifically, according to the following formula:

[0087] Z = Tn,

[0088] n = 5δ,

[0089]

[0090] Where Z is the third coordinate, T is the thickness of the silicon carbide crystal rod 8 to be tested, n is the eddy current penetration depth, δ is the eddy current penetration depth, ρ is the resistivity of the silicon carbide crystal rod 8 to be tested, f is the alternating current frequency of the frequency converter 2, and μ0 is the permeability of the silicon carbide crystal rod 8 to be tested.

[0091] When the frequency of the alternating current is 0, the Z-axis coordinate of the detection point 9 is T. At this time, by increasing the frequency of the alternating current, the penetration depth of the eddy current gradually increases. When there is no cavity below the eddy current probe 1, the size of the eddy current detected by the first eddy current detection sensor 3 will not change significantly; when there is a cavity below the eddy current probe 1, the size of the eddy current detected by the first eddy current detection sensor 3 will change. At this time, it can be determined that there is a cavity below the detection point 9, and the X-axis and Y-axis coordinates of the cavity are the X-axis and Y-axis coordinates of the eddy current probe.

[0092] As the frequency of the alternating current increases, the positioning probe 5 is moved along the Z-axis, and the Z-axis coordinate of the positioning probe 5 is kept the same as the Z-axis coordinate of the point to be detected 9. Figure 9 , Figure 10 , Figure 11 , Figure 12 As shown, based on the phase change and current density change of the eddy current detected by the second eddy current detection sensor 4, the computer terminal 6 plots the eddy current phase and penetration depth curves, as well as the current density and penetration depth change curves.

[0093] Specifically, when there are no cavities under the eddy current probe 1, the current density and eddy current phase detected by the second eddy current detection sensor 4 are as follows: Figure 9 , Figure 10 As shown, with increasing penetration depth, both current density and eddy current phase gradually decrease, and their curves show no significant fluctuations. When a cavity exists below the eddy current probe, the current density and eddy current phase detected by the second eddy current detection sensor 4 are as follows: Figure 11 , Figure 12 As shown, the current density gradually decreases with increasing penetration depth, but suddenly increases when the penetration depth is around 2.5 mm, and the eddy current phase also suddenly increases in this area. At this point, it can be determined that there is a cavity near 2.5 mm, and the third coordinate of the cavity can be determined according to the aforementioned formula Z = Tn.

[0094] S4: Move eddy current probe 1 and repeat step S3 until the movement trajectory of eddy current probe 1 completely covers the area to be tested. When moving eddy current probe 1, with the radius of eddy current probe 1 as r and any radial direction of the area to be tested as the baseline, move eddy current probe 1 along a 45° direction with the baseline by r*√2 to determine the second point to be tested 9. After the second point to be tested 9 is tested, move eddy current probe 1 along a 135° direction with the baseline by r*√2 to determine the third point to be tested 9. After the third point to be tested 9 is tested, move eddy current probe 1 along a 45° direction with the baseline by r*√2 to determine the fourth point to be tested 9, and so on. The movement trajectory of eddy current probe 1 is "M" shaped, and finally the movement trajectory of eddy current probe 1 completely covers the area to be tested.

[0095] At the same time, after moving the eddy current probe 1, the position of the positioning probe 5 is moved so that the straight-line distance between the positioning probe 5, located on the side of the silicon carbide crystal rod to be tested, and the eddy current probe 1 is minimized.

[0096] Example 2

[0097] Everything else is the same as in Example 1, except that in step S2, based on the thickness T and diameter D of the silicon carbide crystal rod 8 to be tested input into the computer terminal 6, a three-dimensional model of the silicon carbide crystal rod 8 to be tested is drawn on the established three-dimensional coordinate system. After determining the location and three-dimensional coordinates of the void, the void location is marked on the three-dimensional model of the silicon carbide crystal rod 8 to be tested, thereby realizing the visualization of the void location and facilitating observation by the testing personnel.

[0098] Example 3

[0099] The rest is the same as in Example 2, except that after determining the coordinates of the cavity, a second detection is performed for cavity re-inspection. The eddy current probe is moved to coincide with the first and second coordinates of the cavity to be confirmed. The alternating current frequency is adjusted so that the penetration depth of the eddy current is T. The positioning probe is moved along the third coordinate direction so that the third coordinate of the positioning probe changes between 0 and T. The change curve of eddy current phase and / or current density with penetration depth is plotted based on the detection signal of the second eddy current detection sensor. The change curve during the re-inspection process is observed to see whether there is an obvious fluctuation change at the third coordinate with the confirmed cavity. If there is, the existence of the cavity can be verified.

[0100] It is understood that the present invention utilizes the principle of eddy current testing when detecting voids in silicon carbide crystal rod 8. Through the cooperation of multiple eddy current detection sensors, eddy current probe 1, and positioning probe 5, the location of the void is determined by the phase change of the eddy current at the void after the void is detected. In addition to being applied to the void detection process of silicon carbide crystal rods, this method can also be further extended to the void detection process of gemstones that can generate eddy currents, or to other detection processes that can generate eddy currents and require the location of voids to be determined.

[0101] For any parts not mentioned in this invention, existing technologies can be used or referenced.

[0102] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0103] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A non-destructive testing system for internal voids in a silicon carbide boule, comprising: The non-destructive testing system includes an eddy current probe that moves on top of the silicon carbide crystal rod to generate eddy currents in the silicon carbide crystal rod. A first eddy current detection sensor connected to the eddy current probe is used to detect changes in the magnitude of surface eddy currents on the silicon carbide crystal rod to be tested. A variable frequency AC generator connected to the eddy current probe is used to change the penetration depth of the eddy current by alternating the frequency of the alternating current. A positioning probe moves along the side of the silicon carbide crystal rod to be tested, in conjunction with the eddy current probe, to determine the location of the cavity. A second eddy current detection sensor connected to the positioning probe is used to detect the magnitude, current density, and phase change of the eddy current on the side of the silicon carbide crystal rod to be tested. The terminal controls the non-destructive testing system, receives and processes test signals, and outputs test results.

2. The non-destructive testing system for internal voids in silicon carbide crystal rods according to claim 1, characterized in that, The non-destructive testing system also includes a sample holder for placing and positioning the silicon carbide crystal rod to be tested.

3. The non-destructive testing system for internal voids in silicon carbide crystal rods according to claim 2, characterized in that, The thickness T of the silicon carbide crystal rod to be tested is 10mm-50mm, the surface undulation is less than 50μm, the top of the silicon carbide crystal rod to be tested has a test area, the distance between the test area and the edge of the silicon carbide crystal rod to be tested is not less than 3mm, the test area has a test point, and the test time of any test point is 20-60s.

4. The non-destructive testing system for internal voids in silicon carbide crystal rods according to claim 3, characterized in that, The radius of the point to be tested is the radius of the eddy current probe, and the radius r of the eddy current probe is 10-30mm. The distance between two adjacent points to be tested is r*√2 and / or 2r.

5. A non-destructive testing method for internal voids in a silicon carbide crystal rod, characterized in that, The non-destructive testing system for internal voids in silicon carbide crystal rods according to any one of claims 1-4 includes the following steps: S1: Sample pretreatment and sample placement; S2: Establish a three-dimensional coordinate system with any fixed point on the sample holder as the origin, determine the first and second coordinates of the point to be tested with the location of the eddy current probe, and determine the third coordinate of the point to be tested with the penetration depth of the eddy current. S3: The fixed eddy current probe determines the first and second coordinates of the point to be tested, continuously changes the penetration depth of the eddy current, and makes the third coordinate of the point to be tested and the third coordinate of the positioning probe change synchronously to obtain the test results; S4: Move the eddy current probe and repeat step S3 until the trajectory of the eddy current probe completely covers the area to be detected.

6. The non-destructive testing method for internal voids in a silicon carbide crystal rod according to claim 5, characterized in that, Determine the third coordinate using the following formula. Z = Tn, n = 5δ, , Where Z is the third coordinate, T is the thickness of the silicon carbide crystal rod to be tested, n is the eddy current penetration depth, δ is the eddy current penetration depth, ρ is the resistivity of the silicon carbide crystal rod to be tested, f is the alternating current frequency of the frequency converter, and μ0 is the permeability of the silicon carbide crystal rod to be tested.

7. The non-destructive testing method for internal voids in a silicon carbide crystal rod according to claim 5, characterized in that, Step S3 includes determining the existence of a cavity based on the eddy current changes detected by the first eddy current detection sensor, and determining the first and second coordinates of the cavity using the first and second coordinates of the eddy current probe; plotting the eddy current phase and / or current density variation curves with penetration depth based on the detection signal of the second eddy current detection sensor, and determining the third coordinates of the cavity using the variation curves.

8. The non-destructive testing method for internal voids in a silicon carbide crystal rod according to claim 7, characterized in that, Step S2 also includes establishing a three-dimensional model of the silicon carbide crystal rod to be tested in a three-dimensional coordinate system using the thickness T and diameter D of the silicon carbide crystal rod to be tested.

9. The non-destructive testing method for internal voids in a silicon carbide crystal rod according to claim 8, characterized in that, Step S3 also includes marking the location of the void onto the three-dimensional model of the silicon carbide crystal rod to be tested based on the three-dimensional coordinates of the void.

10. The non-destructive testing method for internal voids in a silicon carbide crystal rod according to claim 9, characterized in that, It also includes step S5: cavity re-inspection, moving the eddy current probe to coincide with the first and second coordinates of the cavity to be confirmed, adjusting the alternating current frequency so that the penetration depth of the eddy current is T or T / 2, moving the positioning probe along the third coordinate direction and plotting the eddy current phase and / or current density variation curves with penetration depth based on the detection signal of the second eddy current detection sensor.

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