SiC crystal with small axial and radial optical path difference and SiC substrate

Abstract

The invention discloses a SiC crystal with small axial and radial optical path difference and a SiC substrate, and belongs to the technical field of SiC material preparation. On any horizontal line of the SiC crystal, the maximum value of the optical path difference does not exceed 6.593 nm, and the standard difference does not exceed 1.271 nm; and on any axis of the SiC crystal, the maximum value of the optical path difference does not exceed 9.334 nm, and the standard deviation does not exceed 1.506 nm. The optical path difference between the SiC crystal and the SiC substrate is smaller than that of the existing SiC crystal and SiC substrate, and the difference in the radial direction and the axial direction is small, which means that the SiC crystal and the SiC substrate are good in crystal quality and more uniform in surface internal stress.

Description

Technical Field

[0001] The present application relates to a SiC crystal and a SiC substrate with small axial and radial optical path differences, belonging to the technical field of SiC material preparation. Background Art

[0002] Currently, commercially available SiC single crystal production methods include physical vapor deposition (PVT), solution deposition, and high-temperature chemical vapor deposition (HTCVD). These methods are used to grow SiC crystals. These crystals are then rolled into standard-sized ingots, followed by multiple wafer processing steps such as ingot cutting, grinding, and polishing to obtain SiC substrates.

[0003] However, during the growth of SiC crystals, since they grow in a high-temperature, closed environment throughout the entire process, and as the crystal diameter and thickness continue to increase, the temperature field changes at any time. When the temperature field disturbance causes lattice distortion, residual stress will be generated, inducing various defects such as microtubes, voids, and polycrystals. When such crystals and processed substrates are tested using polarized light, light will be refracted in two different directions when passing through SiC, namely ordinary light (o light) and extraordinary light (e light), and both beams of light are polarized. Due to the residual thermal stress caused by lattice distortion, surface processing stress, external stress, etc., according to the photoelastic effect, the optical path difference of light changes when it passes through the material, causing the polarization direction of the light to change.

[0004] On the one hand, there are radial and axial temperature gradient differences in the growth process of SiC. On the other hand, the center and edge surface shapes of SiC will be different during the processing. Taken together, there will be differences in the axial and radial test optical path difference and stress of the SiC crystal. Summary of the Invention

[0005] In order to solve the above problems, a SiC crystal and a SiC substrate with small axial and radial optical path differences are provided. The optical path difference of the SiC crystal is smaller than that of the existing SiC crystal, and the difference in the radial and axial directions is small, which means that the SiC crystal and the prepared SiC substrate have good crystal quality and more uniform in-plane stress.

[0006] According to one aspect of the present application, a SiC crystal is provided with small differences in axial and radial optical path differences, wherein the mean optical path difference on any horizontal line of the SiC crystal does not exceed 6.5 nm, and the standard deviation does not exceed 2 nm;

[0007] On any axis of the SiC crystal, the mean value of the optical path difference does not exceed 9.5 nm, and the standard deviation does not exceed 2.5 nm.

[0008] Preferably, the standard deviation of any horizontal line of the SiC crystal does not exceed 1.3 nm;

[0009] The standard deviation of the SiC crystal on any axis does not exceed 1.5 nm.

[0010] The optical path difference (OPD) in this application refers to the difference in optical path length caused by different paths when light propagates within a medium. Stress testing of SiC products can result in different test results due to wavelength changes, a drawback that prevents effective feedback on the actual product conditions. This application uses OPD to characterize SiC crystals and SiC substrates. This parameter is unaffected by the test wavelength and is more capable of characterizing the actual product parameters, thereby optimizing production and achieving significantly improved SiC product quality.

[0011] The horizontal line here refers to a horizontal line parallel to the horizontal plane of the SiC crystal, the optical path difference on the horizontal line represents the optical path difference and stress value of the crystal in the horizontal direction, and the standard deviation on the horizontal line represents the degree of fluctuation of the stress of the crystal in the horizontal direction (radial direction); similarly, the axis refers to a line parallel to the central axis of the SiC crystal, the optical path difference on the axis represents the optical path difference and stress value of the crystal in the axial direction, and the standard deviation on the axis represents the degree of fluctuation of the stress of the crystal in the axial direction. The above parameters indicate that the SiC crystal of this application has small stress in the axial and radial directions, and small variability in the axial and radial directions, and the product has high crystallization quality.

[0012] Optionally, on any horizontal line of the SiC crystal, a horizontal optical path difference standard deviation coefficient is ≤1.5, and the horizontal optical path difference standard deviation coefficient refers to a ratio of the optical path difference standard deviation calculated on a horizontal line to the optical path difference mean.

[0013] Preferably, on any horizontal line of the SiC crystal, the horizontal optical path difference standard deviation coefficient is ≤0.5, and the horizontal optical path difference standard deviation coefficient refers to the ratio of the optical path difference standard deviation calculated on a horizontal line to the optical path difference mean.

[0014] Optionally, on any axis of the SiC crystal, a standard deviation coefficient of the vertical optical path difference is ≤1.5, and the standard deviation coefficient of the vertical optical path difference refers to a ratio of the optical path difference standard deviation calculated on one axis to the optical path difference mean.

[0015] Preferably, on any axis of the SiC crystal, the standard deviation coefficient of the vertical optical path difference is ≤0.5, and the standard deviation coefficient of the vertical optical path difference refers to the ratio of the optical path difference standard deviation calculated on one axis to the optical path difference mean.

[0016] The standard deviation coefficient refers to the ratio of the standard deviation of the optical path difference on the tested straight line to the mean value. It can characterize the variability and dispersion of the optical path difference between multiple test points on the tested straight line. This parameter can further prove that the variability of the SiC crystal in the radial and axial directions is small.

[0017] Optionally, on any straight line of the SiC crystal that passes through the center of the circle and has an angle of 0 to 80° with the axis, the mean optical path difference does not exceed 6.5 nm and the standard deviation does not exceed 2 nm;

[0018] Preferably, on any straight line of the SiC crystal passing through the center of the circle and with an angle of 0 to 80° with the axis, the standard deviation coefficient of the angular optical path difference is ≤1.3, and the standard deviation coefficient of the angular optical path difference refers to the ratio of the standard deviation of the optical path difference calculated on the straight line to the mean optical path difference.

[0019] Preferably, the standard deviation coefficient of the angular optical path difference is ≤0.4.

[0020] Generally speaking, the crystal quality at the edge of SiC crystal is slightly worse than that at the center. Therefore, the crystals at the edge of SiC crystal are also counted in the test method of arbitrary horizontal line or arbitrary axis. In actual use, if the edge quality is too poor, downstream applications often choose to cut off the edge area and then reuse it, and only use the SiC crystal with better quality in the center area.

[0021] This application uses any straight line passing through the center of the circle and with an angle of 0 to 80 degrees with the axis to characterize the SiC crystal. This characterization method can remove areas with poor edge quality to characterize the quality and uniformity of our central area. The small parameters mentioned above can further highlight that the optical path difference and stress in the central area of ​​the SiC crystal of this application are smaller and more uniformly distributed.

[0022] Optionally, the maximum value of the optical path difference on any horizontal line within the surface of the SiC substrate does not exceed 10 nm.

[0023] Preferably, the maximum value of the optical path difference on any horizontal line within the surface of the SiC substrate does not exceed 6 nm.

[0024] The maximum value of the optical path difference on any horizontal line in the SiC substrate plane is used to represent the distribution of extreme values ​​in the SiC substrate plane. The smaller the value, the less stress concentration point there is in the SiC substrate, and the more uniform the stress distribution in the plane of the entire substrate is.

[0025] According to another aspect of the present application, a SiC substrate with small differences in axial and radial optical path differences is provided, wherein the mean optical path difference on any horizontal line of the SiC substrate does not exceed 6.5 nm and the standard deviation does not exceed 2 nm.

[0026] Optionally, on any horizontal line of the SiC substrate, OPD1-OPD2<5.5 nm, OPD1 represents the maximum optical path difference on the horizontal line, and OPD2 represents the minimum optical path difference on the horizontal line.

[0027] Similarly, the mean, standard deviation, and OPD1-OPD2 on any horizontal line of the SiC substrate can represent that the in-plane uniformity of the SiC substrate is high.

[0028] Optionally, the maximum value of the optical path difference on any horizontal line in the SiC substrate plane does not exceed 20 nm.

[0029] More preferably, the maximum value of the optical path difference on any horizontal line within the surface of the SiC substrate does not exceed 10 nm, more preferably 6 nm.

[0030] Optionally, for the SiC substrate, 0.1<OPD3 / OPD4<3.5, OPD3 indicates that the SiC substrate is 25mm 2 OPD4 represents the average optical path difference within the region, and represents the average optical path difference of the entire SiC substrate.

[0031] The smaller the OPD1 / OPD2 is, the better the radial uniformity of the SiC substrate is.

[0032] Optionally, the SiC crystal and the SiC substrate are both single crystals.

[0033] Optionally, the crystal type of the SiC crystal and the SiC substrate is selected from one of 4H, 6H, and 3C, preferably 4H.

[0034] Optionally, the size of the SiC crystal and the SiC substrate is selected from one of 4 inches, 6 inches, 8 inches, and 12 inches, preferably 8 inches or 12 inches.

[0035] Optionally, the SiC crystal and the SiC substrate are semi-insulating or conductive.

[0036] The beneficial effects of this application include but are not limited to:

[0037] 1. The SiC crystal of the present application has small differences in axial and radial optical path differences, and the maximum values ​​on any horizontal line and axis are small, and the standard deviations on the horizontal line and axis are less than 2 nm, which proves that the optical path difference of the SiC crystal in the axial direction and in the plane has small fluctuations, indicating that the stress in the axial direction and in the plane of the SiC crystal is small and the crystal quality is uniform.

[0038] 2. The SiC crystal of the present application has small differences in axial and radial optical path differences, and both the horizontal optical path difference standard coefficient and the vertical optical path difference standard coefficient are small, which means that the difference and discreteness of the optical path difference at different positions of the horizontal line and the axis are smaller, which can also prove that the uniformity of the SiC crystal is better.

[0039] 3. The SiC crystal of the present application has a small difference in axial and radial optical path differences. The optical path difference is characterized by a straight line passing through the center of the circle and with an angle of 0 to 80 degrees with the axis. This can eliminate the value with the greatest influence from the edge of the SiC crystal, indicating that the performance of the SiC crystal in the central area is better.

[0040] 4. The SiC substrate of the present application has a small difference in axial and radial optical path differences. The mean and standard deviation of the optical path difference on any horizontal line are used for characterization, which can prove that the stress of the substrate is small and evenly distributed. In addition, the maximum value of the optical path difference on any horizontal line is used for characterization, which can highlight the extreme value and thus provide feedback on whether there is a stress concentration point in the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0042] Figure 1 This is a structural diagram of the induction furnace with precise positioning and installation involved in Example 1 of the present application;

[0043] Figure 2 This is the optical path difference test result on any horizontal line of one of the SiC substrates prepared from SiC crystal 1# involved in Example 1 of the present application.

[0044] List of parts and reference numerals:

[0045] 1-furnace chamber; 2-upper flange; 3-lower flange; 4-crucible body; 5-transition crucible cover; 6-crucible holder; 7-external insulation; 8-lower insulation; 9-movable support rod; 10-movable laser positioner; 11-transverse slide rail; 12-transverse rail; 13-graphitized carbon fiber cloth; 14-transverse moving part; 15-longitudinal moving part; 16-lifting assembly; 17-rotating assembly; 18-temperature measuring hole; 19-induction coil. DETAILED DESCRIPTION

[0046] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0047] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0048] Unless otherwise specified, the methods used in the embodiments of the present application are conventional methods in the prior art.

[0049] Example 1 Crystal Growth Furnace Structure

[0050] like Figure 1As shown, this embodiment provides an induction crystal growth furnace, including a furnace chamber 1 and an upper flange 2 on the top of the furnace chamber 1, and a lower flange 3 on the bottom of the furnace chamber 1. A crucible, external insulation 7 and lower insulation 8 are arranged in the furnace chamber 1. The external insulation 7 and the lower insulation 8 form an insulation layer. The crucible is arranged inside the insulation layer. A movable support rod 9 is fixed to the bottom of the lower insulation 8. A moving mechanism is provided on the top of the lower flange 3. The moving mechanism includes a planar moving component. The planar moving component can drive the movable support rod 9 to drive the insulation layer to move. A closable slide rail is provided on the top of the furnace chamber 1, and a movable laser locator 10 is provided on the closable slide rail.

[0051] The movable laser locator 10 can move along the enclosed slide rail. The laser locator can determine the outer edge of the crucible and the inner edge of the outer insulation 7 by measuring the round-trip time, combining the distance relationship and then comparing the changing trend of the round-trip time, wherein the outer insulation 7 is the insulation felt, thereby determining the cavity width between the outer insulation 7 and the crucible, and controlling the planar moving component in the motion mechanism according to the determined cavity width. The planar moving component can control the movable support rod 9 to drive the insulation layer to move, thereby driving the outer insulation 7 to move, and then the width of the cavity between the inner edge of the outer insulation 7 and the outer edge of the crucible can be adjusted to be similar, thereby ensuring the uniformity of the temperature field, reducing the influence of the temperature field disturbance on the growth of SiC, and thus ensuring the quality of SiC products.

[0052] The present application does not limit the implementation method of the planar moving assembly, as long as it can drive the movable support rod 9 to achieve in-plane movement and adjustment. For example, as an embodiment, the planar moving assembly includes a transverse moving portion 14 and a longitudinal moving portion 15; the longitudinal moving portion 15 is used to control the longitudinal movement of the movable support rod 9; the transverse moving portion 14 is used to control the transverse movement of the movable support rod 9.

[0053] It should be noted that the closable slide rail in the present application is closable and can be used to protect the movable laser locator 10 and the slide rail. It is opened before crystal growth to allow the movable laser locator 10 to work, and is closed during the crystal growth process to protect the movable laser locator 10 and the slide rail, and avoid being affected by the Si atmosphere or SiC atmosphere during the crystal growth process and affecting their subsequent normal operation.

[0054] As a specific embodiment, the lower flange 3 is provided with a longitudinal track, and the longitudinal moving part 15 can move longitudinally along the longitudinal track provided on the lower flange 3 under the action of the driving mechanism. Further, a transverse track 12 is provided on the longitudinal moving part 15, and the transverse moving part 14 can move transversely along the transverse track 12 provided on the longitudinal moving part 15 under the action of the driving mechanism, and then drive the movable support rod 9 to move. Through the cooperation of the transverse moving part 14 and the longitudinal moving part 15, the movable support rod 9 can be moved within the plane, thereby driving the movement of the outer insulation 7 to adjust the relative position with the crucible. In addition, it can be understood by those skilled in the art that the order of setting the longitudinal moving part 15 and the transverse moving part 14 can be reversed. It is only necessary to set the transverse track 12 corresponding to the lower flange 3, and the transverse moving part 14 moves on this transverse track 12. Then, a longitudinal track is set on the transverse moving part 14, and the longitudinal moving part 15 moves on this longitudinal track, which can achieve the same function.

[0055] As an embodiment, the motion mechanism further includes a rotating assembly 17 and a lifting assembly 16; the rotating assembly 17 is used to control the rotation of the movable support rod 9; and the lifting assembly 16 is used to control the movable support rod 9 to rise or fall.

[0056] By setting up the rotating component 17, the rotation of the movable support rod 9 can be realized, thereby driving the rotation of the external insulation 7. Since the external insulation 7 is easily corroded by the Si atmosphere, its inner edge changes, thereby affecting the cavity distance between the inner edge of the external insulation 7 and the outer edge of the crucible. After the external insulation 7 is set to be rotatable, the movable laser locator 10 can measure and adjust more radial directions of the external insulation 7, thereby ensuring that the uniformity of the cavity distance between the inner edge of the external insulation 7 and the outer edge of the crucible is more accurate, thereby further improving the uniformity of the temperature field.

[0057] By providing the lifting assembly 16 , the rise or fall of the thermal insulation layer can be controlled, thereby meeting different requirements for the thermal insulation layer during the SiC crystal growth process.

[0058] The present application does not impose any specific restrictions on the implementation method of the rotating component 17 and the lifting component 16, which can be conventionally selected by those skilled in the art. There is no specific restriction on the connection method of the rotating component 17, the lifting component 16 and the planar moving component. For example, the planar moving component is set at the bottom, the lifting component 16 is set in the middle, and the rotating component 17 is set at the top, or the structural order of the three is swapped as long as the effect required by the present application can be normally met. Those skilled in the art can perform conventional implementation or make adjustments and solutions based on some problems that arise.

[0059] As an embodiment, the enclosable slide rail includes a transverse slide rail 11 and a longitudinal slide rail, and a movable laser locator 10 is provided on both the transverse slide rail 11 and the longitudinal slide rail.

[0060] By setting up two slide rails, the number of movable laser locators 10 thereon can be increased, thereby improving the efficiency of determining the outer edge of the crucible and the inner edge of the outer insulation 7. At the same time, several movable laser locators 10 work at the same time, which can significantly improve the efficiency of adjusting the cavity distance between the outer edge of the crucible and the inner edge of the outer insulation 7.

[0061] As an embodiment, a crucible holder 6 is fixed to the bottom of the upper flange 2, and the crucible includes a transitional crucible cover 5 and a crucible body 4;

[0062] The transitional crucible cover 5 is located between the crucible holder 6 and the crucible body 4 and is connected to the crucible holder 6 and the crucible body 4 respectively through threads.

[0063] As a specific embodiment, the bottom of the crucible holder 6 is provided with an internal thread, the top of the transition crucible cover 5 is provided with an external thread that cooperates with the internal thread at the bottom of the crucible holder 6, the bottom of the transition crucible cover 5 is provided with an internal thread, and the top of the crucible body 4 is provided with an external thread that cooperates with the internal thread at the bottom of the transition crucible cover 5.

[0064] As another specific embodiment, the bottom of the crucible holder 6 is provided with an external thread, the top of the transition crucible cover 5 is provided with an internal thread that cooperates with the external thread at the bottom of the crucible holder 6, the bottom of the transition crucible cover 5 is provided with an external thread, and the top of the crucible body 4 is provided with an internal thread that cooperates with the external thread at the bottom of the transition crucible cover 5.

[0065] Skilled and technical personnel know that since the intermediate transition crucible cover 5 is respectively connected to the upper and lower crucible holders 6 and the crucible body 4 through threads, there are other different implementation methods, and skilled and technical personnel can design according to needs.

[0066] It should be noted that skilled and technical personnel can adjust the shapes of the transition crucible cover 5, the crucible holder 6 and the crucible body 4 according to the circumstances to meet the technical effects to be achieved by the present application. For example, since the movable laser locator 10 needs to meet the positioning of the outer edge of the crucible body 4, the outer edges of the transition crucible cover 5 and the crucible holder 6 cannot block the positioning of the outer edge of the crucible body 4 by the movable laser locator 10, so the corresponding threaded connection structure can be designed as needed. For example, in the case where the bottom of the transition crucible cover 5 is provided with an internal thread, and the top of the crucible body 4 is provided with an external thread that matches the internal thread at the bottom of the transition crucible cover 5, in order to meet the positioning needs of the above-mentioned movable laser locator 10, a narrowed transition structure can be provided on the top of the crucible body 4, and then the outer edge of the transition crucible cover 5 can be set so that it cannot block the outer edge of the crucible body 4.

[0067] By setting a crucible holder 6 to be fixed at the bottom of the upper flange 2, and then connecting the crucible body 4 and the crucible holder 6 respectively through the transition crucible cover 5, after the reaction material is filled into the crucible body 4, the crucible body 4 can be fixed at a fixed position on the upper flange 2, and then the relative position of the external insulation 7 can be adjusted.

[0068] As an embodiment, a graphitized carbon fiber cloth 13 is further arranged between the outer insulation 7 and the crucible. The graphitized carbon fiber cloth 13 includes a matrix and carbon fiber bundles in the matrix. The matrix is ​​tar pitch, and the carbon fiber bundles are graphitized carbon fiber bundles. The graphitized carbon fiber bundles are arranged in parallel in the tar pitch matrix.

[0069] Tar pitch is the binder, while graphitized carbon fiber bundles are the support. Since Si atmosphere is more easily captured by the tar pitch binder, it can effectively reduce the corrosive effect of Si atmosphere on the insulation felt during the PVT method for preparing silicon carbide crystals, thereby ensuring the insulation effect of the insulation felt, ensuring the uniformity and stability of the temperature field during the crystal growth process, and reducing the generation of polymorphs. The support is the graphitized carbon fiber bundle, which can significantly improve the tensile strength and high temperature resistance of the carbon fiber cloth, and can meet the use environment exceeding 2000℃ during the silicon carbide growth process.

[0070] It should be noted that the tar pitch and graphitized carbon fiber bundles used in this application are commonly used materials, and those skilled in the art can choose them according to their needs. In addition, this application does not limit the preparation process of the graphitized carbon fiber cloth 13. The preparation process commonly used in this field can be adopted, and the pre-preg method can also be adjusted as needed.

[0071] It should be noted that the present application mainly describes the main invention points. For other structures in the induction furnace, they can be implemented by referring to the solutions of the induction furnace in this field. This is something that can be routinely determined by those skilled in the art and does not require additional elaboration. For example, those skilled in the art can set the deployment mode of the induction coil 19 as needed, and can also set the temperature measuring hole 18 structure on the upper flange 2 as needed. In addition, those skilled in the art can also adjust and set the position of the closable slide rail and the crucible holder 6 on the upper flange 2 as needed, and adjust the shape of the transition crucible cover 5 as needed to ensure that the movable laser locator 10 on the closable slide rail has sufficient movement space and can detect the outer edge of the crucible body 4 and the inner edge of the outer insulation 7. This is a routine skill of those skilled in the art and does not require additional explanation.

[0072] As an embodiment, the graphitized carbon fiber cloth 13 includes a matrix and carbon fiber bundles in the matrix. The matrix is ​​tar pitch, and the carbon fiber bundles are graphitized carbon fiber bundles. The graphitized carbon fiber bundles are arranged in parallel in the tar pitch matrix.

[0073] Example 2 Preparation of SiC Crystal

[0074] The SiC crystal prepared in this embodiment was grown using the apparatus of Example 1. The specific growth steps included the following:

[0075] (1) Place the raw materials in a crystal growth furnace and heat them up, first heating them to 950-1000°C and maintaining them for 4.5-5 hours, during which the pressure is 100-110 mbar, and introducing 280-300 sccm of Ar gas;

[0076] (2) After 10 hours, the temperature is raised to 1500-2000 ° C, the pressure is 50-55 mAbr, and maintained for 4-5 hours; during this period, 300-310 sccm of Ar gas and 30-35 sccm of N2 gas are introduced;

[0077] (3) After 15 hours, the temperature is raised to 2300-2350 ° C, the pressure is 7-9 mbar, and maintained for 140-150 hours for crystal growth. During this period, 50-60 sccm of Ar gas and 10-15 sccm of N2 gas are introduced. After the crystal growth is completed, the temperature is naturally lowered and the furnace is opened to obtain the crystal.

[0078] SiC crystals 1# to 3# were prepared according to the above-mentioned crystal growth method. The specific crystal growth method is as follows:

[0079] SiC crystal 1#

[0080] (1) The raw materials were placed in a crystal growth furnace and heated to 950°C for 5 h, with a pressure of 110 mbar and 300 sccm of Ar gas introduced;

[0081] (2) After 10 hours, the temperature was raised to 1500 ° C and the pressure was 55 mAbr, and maintained for 4 hours; during this period, 310 sccm of Ar gas and 35 sccm of N2 gas were introduced;

[0082] (3) After 15 hours, the temperature was raised to 2300 ° C, the pressure was 7 mbar, and maintained for 150 hours for crystal growth. During this period, 50 sccm of Ar gas and 10 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0083] SiC crystal 2#

[0084] (1) Place the raw materials in a crystal growth furnace and heat them up, first heating them to 1000°C and maintaining them for 5 hours, during which the pressure is 100 mbar and 280 sccm of Ar gas is introduced;

[0085] (2) After 10 hours, the temperature was raised to 2000 ° C, the pressure was 50mAbr, and maintained for 5 hours; during this period, 300 sccm of Ar gas and 30 sccm of N2 gas were introduced;

[0086] (3) After 15 hours, the temperature was raised to 2350 ° C, the pressure was 9 mbar, and maintained for 140 hours for crystal growth. During this period, 60 sccm of Ar gas and 15 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0087] SiC crystal 3#

[0088] (1) The raw materials were placed in a crystal growth furnace and heated to 950°C for 5 h, with a pressure of 105 mbar and 290 sccm of Ar gas introduced;

[0089] (2) After 10 hours, the temperature was raised to 1700 ° C and the pressure was 55 mAbr, and maintained for 4 hours; during this period, 310 sccm of Ar gas and 35 sccm of N2 gas were introduced;

[0090] (3) After 15 hours, the temperature was raised to 2300 ° C, the pressure was 8 mbar, and maintained for 150 hours for crystal growth. During this period, 55 sccm of Ar gas and 13 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0091] The SiC substrates obtained by cutting, grinding and polishing the SiC crystals prepared above have a surface roughness Ra of no more than 10 nm and a thickness of 500 microns.

[0092] The parameters obtained by polarized light testing of each SiC substrate obtained from each SiC crystal are as follows:

[0093] 1. Convert the light source into polarized light through a polarizer,

[0094] 2. Polarized light is transmitted through a polished, transparent single-crystal SiC substrate using a pre-set optical path. Residual stress in the SiC substrate can cause lattice distortion, including crystal defects such as dislocations and micropipes, as well as processing damage such as edge collapse and scratches. Lattice distortion deflects polarized light, and this deflection angle causes polarized light to undergo birefringence, resulting in the appearance of bipolarized light.

[0095] 3. The polarization camera then analyzes the interference fringes of the two polarized beams in the optical path to qualitatively obtain a polarization stress map. When the stress in the sample plane reaches equilibrium, the two polarized beams completely cancel each other out, producing black interference fringes. When residual stress exists, the two polarized beams do not completely cancel each other out, resulting in bright interference fringes, thus enabling the characterization and analysis of residual stress in SiC single crystal substrates.

[0096]

[0097] in,

[0098] Δ: optical path difference between ordinary light (o light) and extraordinary light (e light);

[0099] d: sample thickness;

[0100] Δn: The difference in refractive index between ordinary light (o light) and extraordinary light (e light);

[0101] λ: wavelength.

[0102] Each of the multiple SiC substrates derived from a single SiC crystal has an optical path difference value. The values ​​marked with "maximum" in Table 1 refer to the maximum value obtained from the tests of the multiple SiC substrates derived from that SiC crystal. Therefore, the multiple SiC substrates derived from the entire SiC crystal are all less than or equal to the values ​​in Table 1. For example, the maximum mean optical path difference on any horizontal line means that each SiC substrate will obtain a maximum mean value for any horizontal line of that substrate. The maximum mean values ​​of multiple SiC substrates are then compared, and the value of the SiC substrate with the largest value is the value in Table 1. The value of any axis in Table 1 is obtained by statistically analyzing the data of multiple SiC substrates tested at the same axis position. Similarly, the value of any line passing through the center of a circle and with an angle of 0 to 80° with the axis is obtained by statistically analyzing the data of multiple SiC substrates tested at that axis position.

[0103] The SiC crystals 1# to 3# prepared above are all 8 inches.

[0104] Table 1

[0105]

[0106]

[0107] Figure 2 This is the optical path difference test result of one of the SiC substrates prepared from SiC crystal 1# on an arbitrary horizontal line. It can be seen that the optical path difference of the SiC substrate is uniformly distributed on the horizontal line.

[0108] The foregoing is merely an embodiment of the present application, and the scope of protection of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc. made within the technical ideas and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A SiC crystal with small axial and radial optical path differences, characterized in that: On any horizontal line of the SiC crystal, the mean value of the optical path difference does not exceed 6.5 nm, and the standard deviation does not exceed 2 nm; On any axis of the SiC crystal, the mean value of the optical path difference does not exceed 9.5 nm, and the standard deviation does not exceed 2.5 nm.

2. The SiC crystal with small axial and radial optical path differences according to claim 1, characterized in that: On any horizontal line of the SiC crystal, the horizontal optical path difference standard deviation coefficient is ≤1.5, and the horizontal optical path difference standard deviation coefficient refers to the ratio of the optical path difference standard deviation calculated on a horizontal line to the optical path difference mean value.

3. The SiC crystal with small axial and radial optical path differences according to claim 1, characterized in that: On any axis of the SiC crystal, the standard deviation coefficient of the vertical optical path difference is ≤1.5, and the standard deviation coefficient of the vertical optical path difference refers to the ratio of the optical path difference standard deviation calculated on one axis to the optical path difference mean.

4. The SiC crystal with small axial and radial optical path differences according to claim 3, characterized in that: On any straight line of the SiC crystal that passes through the center of the circle and has an angle of 0 to 80 degrees with the axis, the mean value of the optical path difference does not exceed 6.5 nm, and the standard deviation does not exceed 2 nm.

5. The SiC crystal with small axial and radial optical path differences according to claim 4, characterized in that: On any straight line of the SiC crystal that passes through the center of the circle and has an angle of 0 to 80 degrees with the axis, the angle optical path difference standard deviation coefficient is ≤1.3, and the angle optical path difference standard deviation coefficient refers to the ratio of the optical path difference standard deviation calculated on the straight line to the optical path difference mean.

6. The SiC crystal with small axial and radial optical path differences according to claim 1, characterized in that: The SiC substrate prepared from the SiC crystal has a maximum optical path difference on any horizontal line within the plane that does not exceed 20 nm.

7. A SiC substrate with small difference in axial and radial optical path differences, characterized in that: On any horizontal line of the SiC substrate, the mean value of the optical path difference does not exceed 6.5 nm, and the standard deviation does not exceed 2 nm.

8. The SiC substrate with small axial and radial optical path differences according to claim 7, characterized in that: On any horizontal line of the SiC substrate, OPD1-OPD2<5.5nm, OPD1 represents the maximum value of the optical path difference on the horizontal line, and OPD2 represents the minimum value of the optical path difference on the horizontal line.

9. The SiC substrate with small axial and radial optical path differences according to claim 7, characterized in that: On any horizontal line of the SiC substrate, the maximum value of the optical path difference does not exceed 10 nm.

10. The SiC substrate with small axial and radial optical path differences according to claim 7, characterized in that: The SiC substrate, 0.1<OPD3 / OPD4<3.5, OPD3 means that the SiC substrate is 25mm 2 OPD4 represents the average value of the optical path difference within the region, and represents the average value of the optical path difference of the entire SiC substrate.

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