Sic crystal and sic substrate having small axial and radial optical path differences

Abstract

Disclosed are a SiC crystal and SiC substrate having small axial and radial optical path differences, belonging to the technical field of SiC material preparation. On any one horizontal line of the SiC crystal, the maximum optical path difference does not exceed 6.503 nm, and the standard deviation does not exceed 1.271 nm; and on any axis of the SiC crystal, the maximum optical path difference does not exceed 9.334 nm, and the standard deviation does not exceed 1.506 nm.

Description

A SiC crystal and SiC substrate with small differences in axial and radial optical path difference

[0001] This application claims priority to Chinese Patent Application No. 202411657190.4, filed on November 19, 2024, entitled "A SiC Crystal and SiC Substrate with Small Axial and Radial Optical Path Difference", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to a SiC crystal and a SiC substrate with small differences in axial and radial optical path difference, belonging to the field of SiC material preparation technology. Background Technology

[0003] Currently available technologies for SiC single crystal preparation include physical vapor deposition (PVT), solution deposition, and high-temperature chemical vapor deposition (HTCVD) to grow SiC crystals. These crystals are then rolled into standard-sized ingots, followed by multiple wafer fabrication processes such as ingot cutting, grinding, and polishing to obtain the SiC substrate.

[0004] However, during the growth of SiC crystals, the entire process takes place in a high-temperature, sealed environment. As the crystal diameter and thickness increase, the temperature field constantly changes. When temperature disturbances cause lattice distortion, residual stress is generated, inducing various defects such as microtubes, voids, and polycrystalline structures. When polarized light is used to test such crystals and the resulting substrates, light passing through SiC undergoes refraction in two different directions: ordinary light (o-ray) and extraordinary light (e-ray), both of which are polarized. Due to residual thermal stress caused by lattice distortion, surface processing stress, and external stress, the optical path difference changes as light passes through the material, according to the photoelastic effect, leading to a change in the polarization direction of the light.

[0005] On the one hand, there are radial and axial temperature gradient differences during the growth of SiC. On the other hand, the processing of SiC can lead to differences in the surface shape between the center and the edge. As a result, there are differences in the axial and radial optical path difference and stress of SiC crystals. Summary of the Invention

[0006] To address the aforementioned issues, a SiC crystal and a SiC substrate with small differences in axial and radial optical path differences are provided. The optical path difference of this SiC crystal is smaller than that of existing SiC crystals, and the differences in radial and axial directions are small, indicating that the SiC crystal and the prepared SiC substrate have good crystal quality and more uniform in-plane stress.

[0007] According to one aspect of this application, a SiC crystal with small differences in axial and radial optical path differences is provided, wherein the mean value of the 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.

[0008] The mean optical path difference on any axis of the SiC crystal does not exceed 9.5 nm, and the standard deviation does not exceed 2.5 nm.

[0009] Optionally, the standard deviation of the SiC crystal on any horizontal line does not exceed 1.3 nm;

[0010] The standard deviation of the SiC crystal on any axis does not exceed 1.5 nm.

[0011] The optical path difference in this application refers to the difference in optical path caused by different paths when light propagates within a medium. In stress testing of SiC products, changes in wavelength can lead to different test results, which makes it difficult to effectively reflect the actual condition of the product. This application uses optical path difference to characterize SiC crystals and SiC substrates. This parameter is not affected by the test wavelength and can better characterize the actual parameters of the product, thereby optimizing production and obtaining SiC products with significantly improved quality.

[0012] The horizontal line here refers to a horizontal line parallel to the horizontal plane of the SiC crystal. The optical path difference on this horizontal line represents the optical path difference and stress values ​​of the crystal in the horizontal direction, and the standard deviation on the horizontal line represents the degree of stress fluctuation 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 values ​​of the crystal in the axial direction, and the standard deviation on the axis represents the degree of stress fluctuation of the crystal in the axial direction. The above parameters indicate that the SiC crystal of this application has low stress in both the axial and radial directions, and small differences between the axial and radial directions, resulting in high crystal quality.

[0013] Optionally, on any horizontal line of the SiC crystal, the standard deviation coefficient of the horizontal optical path difference is ≤1.5. The standard deviation coefficient of the horizontal optical path difference refers to the ratio of the standard deviation of the optical path difference calculated on a horizontal line to the mean of the optical path difference.

[0014] Optionally, on any horizontal line of the SiC crystal, the standard deviation coefficient of the horizontal optical path difference is ≤0.5. The standard deviation coefficient of the horizontal optical path difference refers to the ratio of the standard deviation of the optical path difference calculated on a horizontal line to the mean of the optical path difference.

[0015] Optionally, the standard deviation coefficient of the vertical optical path difference on any axis of the SiC crystal is ≤1.5. The standard deviation coefficient of the vertical optical path difference refers to the ratio of the standard deviation of the optical path difference calculated on an axis to the mean of the optical path difference.

[0016] Optionally, the standard deviation coefficient of the vertical optical path difference on any axis of the SiC crystal is ≤0.5. The standard deviation coefficient of the vertical optical path difference refers to the ratio of the standard deviation of the optical path difference calculated on an axis to the mean of the optical path difference.

[0017] The standard deviation coefficient is the ratio of the standard deviation of the optical path difference to the mean on the test line. It can characterize the difference and dispersion of the optical path difference among multiple test points on the test line. This parameter can further prove that the SiC crystal has small differences in the radial and axial directions.

[0018] Optionally, on any straight line passing through the center of the SiC crystal and making 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.

[0019] Optionally, on any straight line passing through the center of the SiC crystal and making an angle of 0 to 80° with the axis, the standard deviation coefficient of the optical path difference is ≤1.3. The standard deviation coefficient of the optical path difference refers to the ratio of the standard deviation of the optical path difference calculated on the straight line to the mean of the optical path difference.

[0020] Optionally, the standard deviation coefficient of the included optical path difference is ≤0.4.

[0021] Generally speaking, the crystal quality at the edge of a SiC crystal is slightly worse than that at the center. Therefore, the test method using any horizontal line or any axis includes the crystal quality at the edge of the SiC crystal. In actual use, if the edge quality is too poor, downstream applications often choose to cut off the edge region and reuse it, using only the SiC crystal with better quality in the center region.

[0022] This application uses any straight line passing through the center of the circle and making an angle of 0 to 80° with the axis to characterize the SiC crystal. This characterization method can remove regions with poor edge quality, thus characterizing the quality and uniformity of the central region. Smaller parameters further highlight that the SiC crystal of this application has a smaller optical path difference and stress distribution in the central region.

[0023] Optionally, the maximum optical path difference on any horizontal line within the SiC substrate surface does not exceed 10 nm.

[0024] Optionally, the maximum optical path difference on any horizontal line within the SiC substrate surface does not exceed 6 nm.

[0025] The distribution of extreme values ​​in the SiC substrate is represented by the maximum value of the optical path difference on any horizontal line in the SiC substrate. The smaller the value, the less stress concentration points there are in the SiC substrate, and the higher the uniformity of the in-plane stress distribution of the entire substrate.

[0026] According to another aspect of this 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.

[0027] Optionally, on any horizontal line of the SiC substrate, OPD1-OPD2 < 5.5nm, where OPD1 represents the maximum optical path difference on that horizontal line and OPD2 represents the minimum optical path difference on that horizontal line.

[0028] Similarly, the mean, standard deviation, and OPD1-OPD2 along any horizontal line of the SiC substrate can represent the high in-plane uniformity of the SiC substrate.

[0029] Optionally, the maximum optical path difference on any horizontal line within the SiC substrate surface does not exceed 20 nm.

[0030] Optionally, the maximum optical path difference on any horizontal line within the SiC substrate surface does not exceed 10 nm.

[0031] Optionally, the maximum optical path difference on any horizontal line within the SiC substrate surface does not exceed 6 nm.

[0032] Optionally, for the SiC substrate, 0.1 < OPD3 / OPD4 < 3.5, where OPD3 represents the SiC substrate at a thickness of 25 mm. 2 The mean optical path difference within the region, OPD4 represents the mean optical path difference of the entire SiC substrate.

[0033] The smaller the OPD1 / OPD2 ratio, the better the radial uniformity of the SiC substrate.

[0034] Optionally, both the SiC crystal and the SiC substrate are single crystals.

[0035] Optionally, the crystal form of the SiC crystal and the SiC substrate is selected from one of 4H, 6H, and 3C.

[0036] Optionally, the crystal form of the SiC crystal and the SiC substrate is selected from 4H.

[0037] 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.

[0038] Optionally, the size of the SiC crystal and the SiC substrate is selected from 8 inches or 12 inches.

[0039] Optionally, the SiC crystal and SiC substrate are semi-insulating or conductive.

[0040] The beneficial effects of this application include, but are not limited to:

[0041] 1. The SiC crystal with small axial and radial optical path difference in this application has small maximum values ​​on any horizontal line and axis, and the standard deviation on the horizontal line and axis is less than 2nm. This proves that the SiC crystal has small fluctuations in optical path difference in the axial direction and in the plane, which means that the SiC crystal has low stress in the axial direction and in the plane and uniform crystal quality.

[0042] 2. The SiC crystal of this application has small differences in axial and radial optical path difference. The standard coefficients of both horizontal and vertical optical path difference are small, which means that the differences and dispersion of optical path difference at different positions on the horizontal line and the axis are smaller, which also proves that the SiC crystal has good uniformity.

[0043] 3. The SiC crystal with small differences in axial and radial optical path difference in this application is characterized by using a straight line passing through the center of the circle and with an angle of 0 to 80° with the axis. This can eliminate the values ​​with the greatest influence from the edge of the SiC crystal, indicating that the SiC crystal has better performance in the central region.

[0044] 4. The SiC substrate with small axial and radial optical path difference differences in this application can be characterized by the mean and standard deviation of the optical path difference on any horizontal line, which can prove that the stress of the substrate is small and uniformly distributed. In addition, the maximum value of the optical path difference on any horizontal line can be used to highlight the extreme value, thereby providing feedback on whether there are stress concentration points in the substrate. Attached Figure Description

[0045] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0046] Figure 1 is a schematic diagram of the structure of the induction furnace with precise positioning and assembly according to Embodiment 1 of this application;

[0047] Figure 2 shows the optical path difference test results of one of the SiC substrates prepared by SiC crystal 1# according to Embodiment 1 of this application on any horizontal line.

[0048] List of components and reference numerals: 1-Furnace cavity; 2-Upper flange; 3-Lower flange; 4-Crucible body; 5-Transition crucible cover; 6-Crucible holder; 7-External insulation; 8-Lower insulation; 9-Modible support rod; 10-Modible laser positioner; 11-Transverse slide rail; 12-Transverse track; 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 Implementation

[0049] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0050] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0051] Unless otherwise specified, the methods used in the embodiments of this application are conventional methods in the prior art.

[0052] Example 1: Crystal Growth Furnace Structure

[0053] As shown in Figure 1, this embodiment provides an induction crystal growth furnace, including a furnace cavity 1, an upper flange 2 at the top of the furnace cavity 1, and a lower flange 3 at the bottom of the furnace cavity 1. A crucible, an outer heat insulation 7, and a lower heat insulation 8 are arranged inside the furnace cavity 1. The outer heat insulation 7 and the lower heat insulation 8 form a heat insulation layer. The crucible is arranged inside the heat insulation layer. A movable support rod 9 is fixed at the bottom of the lower heat insulation 8. A motion mechanism is provided at the top of the lower flange 3. The motion mechanism includes a planar moving component. The planar moving component can drive the movable support rod 9 to move the heat insulation layer. A closable slide rail is provided at the top of the furnace cavity 1. A movable laser positioner 10 is provided on the closable slide rail.

[0054] The movable laser positioner 10 can move along the enclosed slide rail. By measuring the round-trip time and comparing the trend of the round-trip time with the distance relationship, the laser positioner can determine the outer edge of the crucible and the inner edge of the outer insulation 7, where the outer insulation 7 is the insulation felt. This determines the cavity width between the outer insulation 7 and the crucible. Based on the determined cavity width, the planar moving component in the motion mechanism is controlled. 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. This allows the width of the cavity between the inner edge of the outer insulation 7 and the outer edge of the crucible to be adjusted to be similar, thereby ensuring temperature field uniformity, reducing the impact of temperature field disturbance on SiC growth, and thus ensuring the quality of SiC products.

[0055] This application does not limit the implementation method of the planar moving component, as long as it can drive the movable support rod 9 to move and adjust within the plane. For example, as one embodiment, the planar moving component includes a lateral moving part 14 and a longitudinal moving part 15; the longitudinal moving part 15 is used to control the longitudinal movement of the movable support rod 9; the lateral moving part 14 is used to control the lateral movement of the movable support rod 9.

[0056] It should be noted that the sealable slide rail in this application is sealable and can be used to protect the movable laser positioner 10 and the slide rail. It is opened before crystal growth so that the movable laser positioner 10 can work, and closed during crystal growth, thereby protecting the movable laser positioner 10 and the slide rail and preventing them from being affected by the Si atmosphere or SiC atmosphere during crystal growth so that they can work normally afterwards.

[0057] In one specific implementation, 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 drive mechanism. Furthermore, the longitudinal moving part 15 is provided with a transverse track 12, and the transverse moving part 14 can move laterally along the transverse track 12 provided on the longitudinal moving part 15 under the action of the drive mechanism, thereby driving 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 move in a plane, thereby driving the movement of the outer insulation 7 to adjust its relative position with the crucible. Furthermore, those skilled in the art will understand that the order of the longitudinal moving part 15 and the transverse moving part 14 can be interchanged. Simply provide the transverse track 12 corresponding to the lower flange 3, with the transverse moving part 14 moving on this transverse track 12, and then provide the longitudinal track on the transverse moving part 14, with the longitudinal moving part 15 moving on this longitudinal track, to achieve the same function.

[0058] In one embodiment, the motion mechanism further includes a rotating component 17 and a lifting component 16; the rotating component 17 is used to control the rotation of the movable support rod 9; the lifting component 16 is used to control the raising or lowering of the movable support rod 9.

[0059] By setting the rotating component 17, the movable support rod 9 can be rotated, thereby driving the outer insulation 7 to rotate. Since the outer insulation 7 is easily corroded by the Si atmosphere, causing its inner edge to change, it affects the cavity distance between the inner edge of the outer insulation 7 and the outer edge of the crucible. After setting the outer insulation 7 to be able to rotate, the movable laser positioner 10 can measure and adjust the radial direction of more outer insulation 7, thereby ensuring that the uniformity of the cavity distance between the inner edge of the outer insulation 7 and the outer edge of the crucible is more accurate, thereby further improving the uniformity of the temperature field.

[0060] By setting up the lifting component 16, the rise or fall of the insulation layer can be controlled, thereby meeting the different requirements of the insulation layer during the SiC crystal growth process.

[0061] The present application does not impose specific limitations on the implementation of the rotating component 17 and the lifting component 16, which are conventional choices that can be made by those skilled in the art. Furthermore, the present application does not impose specific limitations on the connection method of the rotating component 17, the lifting component 16, and the planar moving component. For example, the planar moving component can be placed at the bottom, the lifting component 16 can be placed in the middle, and the rotating component 17 can be placed at the top. Alternatively, the structural order of the three components can be changed as long as the desired effect of the present application is achieved. Those skilled in the art can implement this conventionally or adjust and solve it based on the problems that arise.

[0062] As one implementation, the encloseable slide rail includes a transverse slide rail 11 and a longitudinal slide rail, and a movable laser positioner 10 is provided on both the transverse slide rail 11 and the longitudinal slide rail.

[0063] By setting two slide rails, the number of movable laser positioners 10 on them can be increased, thereby improving the determination efficiency of the outer edge of the crucible and the inner edge of the outer insulation 7. At the same time, several movable laser positioners 10 work simultaneously, which can significantly improve the adjustment efficiency of the cavity distance between the outer edge of the crucible and the inner edge of the outer insulation 7.

[0064] In one 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;

[0065] 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 by threads respectively.

[0066] In one specific implementation, the crucible holder 6 has an internal thread at its bottom, the transition crucible cover 5 has an external thread at its top that mates with the internal thread at the bottom of the crucible holder 6, the transition crucible cover 5 has an internal thread at its bottom, and the crucible body 4 has an external thread at its top that mates with the internal thread at the bottom of the transition crucible cover 5.

[0067] As another specific implementation, the crucible holder 6 has an external thread at its bottom, the transition crucible cover 5 has an internal thread at its top that mates with the external thread at the bottom of the crucible holder 6, the transition crucible cover 5 has an external thread at its bottom, and the crucible body 4 has an internal thread at its top that mates with the external thread at the bottom of the transition crucible cover 5.

[0068] Those with expertise and technical knowledge know that, since the intermediate transitional crucible cover 5 is connected to the upper and lower crucible holders 6 and the crucible body 4 by threads, there are other different implementation methods. Those with expertise and technical knowledge can design according to their needs.

[0069] It should be noted that skilled technicians can adjust the shapes of the transitional crucible cover 5, the crucible holder 6, and the crucible body 4 as needed to achieve the technical effects required by this application. For example, since the movable laser positioner 10 needs to position the outer edge of the crucible body 4, the outer edges of the transitional crucible cover 5 and the crucible holder 6 must not obstruct the positioning of the outer edge of the crucible body 4 by the movable laser positioner 10. Therefore, a corresponding threaded connection structure can be designed as needed. For example, if the bottom of the transitional crucible cover 5 has an internal thread, and the top of the crucible body 4 has an external thread that mates with the internal thread at the bottom of the transitional crucible cover 5, a narrowing transition structure can be provided at the top of the crucible body 4 to meet the positioning requirements of the movable laser positioner 10. Then, the outer edge of the transitional crucible cover 5 can be ensured not to obstruct the outer edge of the crucible body 4.

[0070] By setting the 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 in the fixed position of the upper flange 2, and then the relative position of the external insulation 7 can be adjusted.

[0071] In one embodiment, a graphitized carbon fiber cloth 13 is also provided between the external insulation 7 and the crucible. The graphitized carbon fiber cloth 13 includes a matrix and carbon fiber bundles within the matrix. The matrix is ​​tar pitch, and the carbon fiber bundles are graphitized carbon fiber bundles arranged in parallel within the tar pitch matrix.

[0072] In this method, tar pitch serves as the binder, while graphitized carbon fiber bundles act as the support. Because the Si atmosphere is more easily captured by the tar pitch binder, the erosion effect of the Si atmosphere on the insulation felt during PVT crystal preparation is effectively reduced, thus ensuring the insulation effect of the felt, maintaining a uniform and stable temperature field during crystal growth, and reducing polymorph formation. The graphitized carbon fiber bundles as the support significantly improve the tensile strength and high-temperature resistance of the carbon fiber cloth, enabling it to withstand operating environments exceeding 2000℃ during silicon carbide growth.

[0073] 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 as needed. In addition, this application does not limit the preparation process of the graphitized carbon fiber cloth 13. Commonly used preparation processes in the art can be used, and the prepreg method can be adjusted as needed.

[0074] It should be noted that this application mainly describes the main inventive points. Other structures in the induction furnace can be implemented with reference to induction furnace solutions in the field, which is conventionally determined by those skilled in the art and does not require further explanation. For example, those skilled in the art can set the deployment method 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, so that the movable laser positioner 10 on the closable slide rail can have sufficient movement space to detect the outer edge of the crucible body 4 and the inner edge of the outer insulation 7. This is conventional skill for those skilled in the art and does not require further explanation.

[0075] In one embodiment, the graphitized carbon fiber cloth 13 includes a matrix and carbon fiber bundles within the matrix. The matrix is ​​tar pitch, and the carbon fiber bundles are graphitized carbon fiber bundles arranged in parallel within the tar pitch matrix.

[0076] Example 2 Preparation of SiC crystals

[0077] The SiC crystals prepared in this embodiment were grown using the apparatus of Example 1. The specific crystal growth process included the following steps:

[0078] (1) Place the raw material in a crystal growth furnace and heat it up to 950-1000℃ for 4.5-5 hours. During this period, the pressure is 100-110 mbar and Ar gas is introduced at 280-300 sccm.

[0079] (2) After 10 hours, the temperature is raised to 1500-2000℃ and the pressure is 50-55 mabr, and maintained for 4-5 hours; during this period, Ar gas is introduced at 300-310 sccm and N2 gas at 30-35 sccm.

[0080] (3) After 15 hours, the temperature is raised to 2300-2350℃ and the pressure is 7-9mba. The temperature is maintained for 140-150 hours for crystal growth. During this period, Ar gas is introduced at 50-60 sccm and N2 gas at 10-15 sccm. After the crystal growth is completed, the temperature is naturally lowered and the furnace is opened to obtain the crystal.

[0081] SiC crystals #1 to #3 were prepared according to the above crystal growth method. The specific crystal growth method is as follows:

[0082] SiC crystal #1

[0083] (1) Place the raw material in a crystal growth furnace and heat it up to 950℃ and maintain it for 5 hours. During this period, the pressure is 110 mbar and Ar gas is introduced at 300 sccm.

[0084] (2) After 10 hours, the temperature was raised to 1500℃ and the pressure was 55 mabr, and maintained for 4 hours; during this period, Ar gas was introduced at 310 sccm and N2 gas at 35 sccm.

[0085] (3) After 15 hours, the temperature was raised to 2300℃ and the pressure was 7mba. The temperature was 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.

[0086] SiC crystal #2

[0087] (1) Place the raw material in a crystal growth furnace and heat it up to 1000℃ and maintain it for 5 hours. During this period, the pressure is 100mbar and Ar gas is introduced at 280sccm.

[0088] (2) After 10 hours, the temperature was raised to 2000℃ and the pressure was 50 mabr, and maintained for 5 hours; during this period, 300 sccm of Ar gas and 30 sccm of N2 gas were introduced.

[0089] (3) After 15 hours, the temperature was raised to 2350℃ and the pressure was 9mba. The temperature was maintained for 140 hours for crystal growth. During this period, Ar gas was introduced at 60 sccm and N2 gas at 15 sccm. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0090] SiC crystal #3

[0091] (1) The raw material is placed in a crystal growth furnace and heated. The temperature is first raised to 950℃ and maintained for 5 hours. During this period, the pressure is 105mbar and 290sccm of Ar gas is introduced.

[0092] (2) After 10 hours, the temperature was raised to 1700℃ and the pressure was 55 mabr, and maintained for 4 hours; during this period, Ar gas was introduced at 310 sccm and N2 gas at 35 sccm.

[0093] (3) After 15 hours, the temperature was raised to 2300℃ and the pressure was 8mba. The temperature was maintained for 150 hours for crystal growth. During this period, 55sccm of Ar gas and 13sccm 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.

[0094] The SiC substrate obtained by cutting, grinding and polishing the SiC crystals prepared above has a surface roughness Ra of no more than 10 nm and a thickness of 500 micrometers.

[0095] The parameters were obtained by polarization light testing on each SiC substrate obtained from each SiC crystal. The specific testing method is as follows:

[0096] 1. A polarizer converts the light source into polarized light.

[0097] 2. Polarized light is transmitted through a polished, transparent single-crystal SiC substrate via a pre-defined optical path. Residual stress in the SiC substrate causes lattice distortion, including crystal defects such as dislocations and microtubes, as well as processing damage such as edge chipping and scratches. This lattice distortion causes the polarized light to deflect, and the deflection angle results in birefringence, producing light polarized in two directions.

[0098] 3. Subsequently, the interference fringes of the two polarized beams in the optical path are analyzed using a polarization camera to qualitatively obtain the polarization stress map. When the in-plane stress of the sample reaches equilibrium, the polarized beams in the two directions completely cancel each other out, producing black interference fringes; when residual stress exists, the polarized beams in the two directions do not completely cancel each other out, resulting in bright colors, thus enabling the characterization and analysis of residual stress on the SiC single crystal substrate;

[0099] in,

[0100] Δ: Optical path difference between ordinary light (o-ray) and extraordinary light (e-ray);

[0101] d: Sample thickness;

[0102] Δn: The difference in refractive index between the ordinary ray (o ray) and the extraordinary ray (e ray);

[0103] λ: wavelength.

[0104] Several SiC substrates are obtained from a single SiC crystal. Each SiC substrate yields an optical path difference value. The values ​​marked "maximum value" in Table 1 refer to the maximum value measured among the several SiC substrates obtained from that single SiC crystal. Therefore, the values ​​of all SiC substrates obtained from the entire SiC crystal are less than or equal to the values ​​in Table 1. For example, the maximum average optical path difference along any horizontal line means that each SiC substrate will have a maximum average value along any horizontal line of that substrate. The maximum average values ​​of several SiC substrates are then compared, and the value of the SiC substrate with the largest value is the value in Table 1. The values ​​of any axis in Table 1 are obtained by statistically analyzing the data from several SiC substrates tested at the same axis position. Similarly, the values ​​of any straight line passing through the center of a circle and making an angle of 0° to 80° with the axis are obtained by statistically analyzing the data from several SiC substrates tested at that angle along the axis.

[0105] The SiC crystals prepared above, from #1 to #3, are all 8 inches in size.

[0106] Table 1

[0107] Figure 2 shows the optical path difference test results of one of the SiC substrates prepared by SiC crystal 1# on any horizontal line. It can be seen that the optical path difference of the SiC substrate is uniformly distributed on this horizontal line.

[0108] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A SiC crystal with small differences in axial and radial optical path difference, characterized in that, The mean optical path difference along any horizontal line of the SiC crystal does not exceed 6.5 nm, and the standard deviation does not exceed 2 nm. The mean optical path difference on any axis of the SiC crystal 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 difference according to claim 1, characterized in that, The standard deviation coefficient of the horizontal optical path difference on any horizontal line of the SiC crystal is ≤1.

5. The standard deviation coefficient of the horizontal optical path difference is the ratio of the standard deviation of the optical path difference calculated on a horizontal line to the mean of the optical path difference.

3. The SiC crystal with small axial and radial optical path difference 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. The standard deviation coefficient of the vertical optical path difference refers to the ratio of the standard deviation of the optical path difference calculated on an axis to the mean of the optical path difference.

4. The SiC crystal with small axial and radial optical path difference according to claim 3, characterized in that, The mean optical path difference on any straight line passing through the center of the SiC crystal and making an angle of 0 to 80° with the axis 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 difference according to claim 4, characterized in that, On any straight line passing through the center of the SiC crystal and making an angle of 0 to 80° with the axis, the standard deviation coefficient of the optical path difference is ≤1.

3. The standard deviation coefficient of the optical path difference is the ratio of the standard deviation of the optical path difference calculated on the straight line to the mean of the optical path difference.

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

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

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

10. The SiC substrate with small axial and radial optical path difference according to claim 7, characterized in that, For the SiC substrate, 0.1 < OPD3 / OPD4 < 3.5, where OPD3 represents the SiC substrate at a thickness of 25mm. 2 The mean optical path difference within the region, where OPD4 represents the mean optical path difference of the entire SiC substrate.

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