Sic crystal and sic substrate having low defect stress

Abstract

The present application belongs to the technical field of SiC material preparation, and provides an SiC crystal and an SiC substrate having low defect stress. Several SiC substrates are prepared from the SiC crystal. High-pass signals and low-pass signals are distinguished on the basis of the Laplace pyramid principle. Under the high-pass signals, the overall optical path difference of any SiC substrate is less than 6 nm, the maximum value of the optical path difference is less than 12 nm, and the standard deviation of the optical path difference is less than 3 nm.

Description

A SiC crystal with low defect stress and a SiC substrate

[0001] This application claims priority to Chinese Patent Application No. 202411657192.3, filed on November 19, 2024, entitled "A SiC Crystal with Low Defect Stress and a SiC Substrate", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to a SiC crystal with low defect stress and a SiC substrate, belonging to the field of SiC material preparation technology. Background Technology

[0003] During SiC growth, axial and radial temperature gradients exist, and the continuous and gradual change of these temperature gradients, coupled with the continuous surface changes of the SiC substrate during cutting, grinding, and polishing, result in a gradual stress variation from the center to the edge of the SiC substrate. On the other hand, if lattice distortion occurs during SiC growth, inducing in-plane defects such as micropipes, voids, and white spots, these in-plane defects will cause localized stress concentration.

[0004] The stress of SiC substrates is tested by using polarized birefringence. Since the light source penetrates the entire SiC wafer, the optical path difference caused by the lattice distortion in the SiC wafer plane can be measured, and the stress can be characterized by the optical path difference.

[0005] However, when using optical path difference to characterize SiC stress, it can only achieve qualitative characterization of stress. It cannot distinguish optical path difference caused by internal stress or defects, and therefore cannot use optical path difference to provide feedback on the manufacturing process of SiC products in order to obtain SiC crystals and SiC substrates with low defect stress. Summary of the Invention

[0006] To address the aforementioned issues, a SiC crystal and a SiC substrate with low defect stress are provided. The SiC crystal and SiC substrate exhibit a small and uniform optical path difference under high-pass signals, indicating a low number of defects in SiC, less stress concentration caused by in-plane defects, and more uniform crystal quality of SiC.

[0007] According to one aspect of this application, a low-defect-stress SiC crystal is provided, wherein the SiC crystal is used to prepare a plurality of SiC substrates, and high-pass signals and low-pass signals are distinguished based on the Laplace pyramid principle. Under the high-pass signal, the overall optical path difference of any SiC substrate is <6nm, the maximum value of the optical path difference is <12nm, and the standard deviation of the optical path difference is <3nm.

[0008] 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.

[0009] This application is based on the characteristics of stress caused by defects. Stress concentration occurs around defects, which is reflected in the optical path difference of polarized birefringence testing as a localized high-frequency abrupt change. By filtering the measured optical path difference using a high-pass signal (which filters out low-frequency continuous fluctuations in the optical path difference signal), the data representing localized stress concentration caused by in-plane defects is selected for data analysis. The aforementioned distinction between high-pass and low-pass signals based on the Laplace pyramid principle refers to using the Laplace pyramid to differentiate between high-pass and low-pass signals based on spatial curl, which is prior art and will not be elaborated upon here. This method can distinguish between defect stress and intracrystalline stress. Defect stress is mostly caused by microtubes, small-angle grain boundaries, voids, etc. Besides being inherited from seed crystals, these defects can also be induced by temperature field disturbances or uneven thermal and flow fields during crystal growth, leading to lattice distortion or misalignment. Therefore, by obtaining high-frequency fluctuating optical path difference information through the high-pass signal, stress concentration caused by localized defects can be screened out, thereby quantitatively assessing the in-plane defect stress level using the optical path difference. Based on this characterization, the manufacturing process was optimized to obtain the SiC crystal and SiC substrate with low defect stress as described in this application.

[0010] The SiC crystal obtained from this SiC substrate not only has a smaller overall optical path difference, but also a smaller maximum optical path difference and a smaller standard deviation of the optical path difference. Therefore, it indicates that the SiC crystal has less stress concentration caused by defects, making it a low-defect SiC crystal. Furthermore, the defects in the SiC crystal have better uniformity in both the axial and radial directions.

[0011] Optionally, under high-pass signal conditions, |OPD1-OPD2| < 4nm, where OPD1 represents the overall optical path difference of the SiC substrate including the first end face obtained by the SiC crystal, and OPD2 represents the overall optical path difference of the SiC substrate including the second end face obtained by the SiC crystal.

[0012] After the SiC crystal is ground flat at both ends, several SiC substrates are then prepared. In this application, the SiC substrate with the first end face and the SiC substrate with the second end face are the first substrates obtained by processing the two ends of the ground SiC crystal.

[0013] The above parameters further demonstrate the uniform axial distribution of the SiC crystal in this application. Combined with the optical path difference of any SiC substrate, the overall defect density of the SiC crystal in this application is small and uniform.

[0014] Optionally, under high-pass signal conditions, |OPD1-OPD3| < 1.5 nm, |OPD2-OPD3| < 1.5 nm, where OPD3 represents the average value of the overall optical path difference of all SiC substrates obtained by the SiC crystal.

[0015] Optionally, |OPD1-OPD3| < 1.0 nm, |OPD2-OPD3| < 1.0 nm.

[0016] |OPD1-OPD3| and |OPD2-OPD3| can represent the differences between the SiC substrate containing the first end face and the SiC substrate containing the second end face and all SiC substrates obtained from the crystal. The smaller the value, the more uniform the distribution of defects in the crystal can be achieved in the axial direction, thus reflecting the uniform distribution of optical path difference in the axial direction.

[0017] Optionally, for any SiC substrate obtained by the SiC crystal, the values ​​of OPD4 / OPD5 are in the range of 0.8 to 1.2 under high-pass signal, where OPD4 represents the optical path difference of the SiC substrate along the [11-20] direction and OPD5 represents the optical path difference of the SiC substrate along the [1-100] direction.

[0018] The [11-20] and [1-100] directions are two characteristic directions of SiC. The closer the OPD4 / OPD5 ratio is to 1, the better the radial uniformity of the SiC substrate, and the more the uniformity of the in-plane defect distribution is significantly improved.

[0019] Optionally, any SiC substrate obtained from the SiC crystal has a central region and an annular region surrounding the central region, wherein the annular region has a width of no more than 15 mm extending inward from the edge of the substrate.

[0020] Under high-pass signal conditions, the values ​​of OPD6 / OPD7 are in the range of 0.9 to 1.1. OPD6 represents the optical path difference in the central region of the SiC substrate along the [11-20] direction, and OPD7 represents the optical path difference in the central region of the SiC substrate along the [1-100] direction.

[0021] For the SiC crystals currently prepared, due to the influence of the growth temperature field, defects are more likely to occur in the annular region than in the central region, resulting in greater stress in the annular region than in the central region. This application demonstrates that the SiC crystal of this application has higher in-plane uniformity in the central region than in the overall in-plane uniformity by comparing the ratio of the optical path difference in the central region in the [11-20] direction to that in the [1-100] direction, thus obtaining a SiC crystal with better crystal quality.

[0022] According to another aspect of this application, a low-defect-stress SiC substrate is provided, wherein under high-pass signal conditions, the overall optical path difference of the SiC substrate is <6nm, the maximum value of the optical path difference is <12nm, and the standard deviation of the optical path difference is <3nm.

[0023] Optionally, the standard deviation of the optical path difference along any horizontal line of the SiC substrate is <1.5 nm.

[0024] Optionally, the SiC substrate has a central region and an annular region surrounding the central region, wherein the annular region has a width of no more than 15 mm extending inward from the edge of the substrate.

[0025] The standard deviation of the optical path difference on any horizontal line in the central region is <1nm.

[0026] The standard deviation of the optical path difference along any horizontal line of a SiC substrate reflects the data fluctuation of the SiC substrate along that line. The smaller the standard deviation of the optical path difference, the more uniform the product quality is in the radial direction. The smaller the standard deviation of the optical path difference along any horizontal line in the central region, the better the in-plane uniformity of the SiC substrate in the central region.

[0027] Optionally, under high-pass signal conditions, the values ​​of OPD4 / OPD5 of the SiC substrate are in the range of 0.8 to 1.2, where OPD4 represents the optical path difference of the entire SiC substrate along the [11-20] direction and OPD5 represents the optical path difference of the entire SiC substrate along the [1-100] direction.

[0028] Optionally, the SiC substrate has a central region and an annular region surrounding the central region, wherein the annular region has a width of no more than 15 mm extending inward from the edge of the substrate.

[0029] Under high-pass signal conditions, the values ​​of OPD6 / OPD7 are in the range of 0.9 to 1.1. OPD6 represents the optical path difference in the central region of the SiC substrate along the [11-20] direction, and OPD7 represents the optical path difference in the central region of the SiC substrate along the [1-100] direction.

[0030] Optionally, the SiC substrate has a central region and an annular region surrounding the central region, wherein the annular region has a width of no more than 15 mm extending inward from the edge of the substrate.

[0031] Under high-pass signal conditions, |OPD7-OPD8| < 4nm, where OPD7 represents the average optical path difference obtained along the annular region of the <11-20> crystal orientation group, and OPD8 represents the average optical path difference obtained along the central region of the <11-20> crystal orientation group.

[0032] Optionally, under high-pass signal conditions, the SiC substrate has |OPD9-OPD10| < 4nm, where OPD9 represents the average optical path difference obtained along the annular region of the <1-100> crystal orientation group, and OPD10 represents the average optical path difference obtained along the central region of the <1-100> crystal orientation group.

[0033] Optionally, both the SiC crystal and the SiC substrate are single crystals.

[0034] Optionally, the crystal form of the SiC crystal and the SiC substrate is selected from one of 4H, 6H, and 3C.

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

[0036] 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.

[0037] Optionally, the size of the SiC crystal and the SiC substrate is selected from 8 inches or 12 inches.

[0038] Optionally, the SiC crystal and SiC substrate are semi-insulating or conductive.

[0039] Optionally, the thickness of the SiC substrate is <1 mm.

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

[0041] 1. The low-defect-stress SiC crystal and SiC substrate of this application reduce the number of defects generated in the material, avoid lattice distortion or lattice misalignment caused by defects, and improve the quality of SiC single crystal wafers.

[0042] 2. The low-defect-stress SiC crystal and SiC substrate of this application have optical path difference distribution in the axial and radial directions that is the distribution law of stress caused by defects inside the material. The defects of the material are significantly reduced, which can improve the operating quality of downstream devices.

[0043] 3. The low-defect-stress SiC substrate of this application has different physical properties in different characteristic crystal directions, and therefore the optical path difference in different crystal directions will also be different. The difference between the [1-100] direction and the [11-20] direction of this SiC substrate is small, which also means that the performance of this SiC substrate is more uniform. Attached Figure Description

[0044] 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:

[0045] 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;

[0046] Figure 2 shows the optical path difference test results of one of the SiC substrates prepared by SiC crystal 1# in Embodiment 2 of this application after polishing. Figure 2(a) shows the overall optical path difference test results of the SiC substrate, and Figure 2(b) shows the optical path difference test results of the SiC substrate under high-pass signal.

[0047] 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

[0048] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0049] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0050] Unless otherwise specified, the methods used in the embodiments of this application are conventional methods in the prior art.

[0051] Example 1

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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;

[0064] 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.

[0065] 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.

[0066] 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.

[0067] Those skilled in the art will 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, and those skilled in the art can design according to their needs.

[0068] It should be noted that those skilled in the art 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 cannot 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 transitional 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 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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 sealable 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 sealable 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 of those skilled in the art and does not require further explanation.

[0074] 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.

[0075] Example 2

[0076] The SiC crystal prepared in this embodiment was grown using the induction crystal growth furnace of Example 1. The specific crystal growth method is as follows:

[0077] (1) Place the raw material in a crystal growth furnace, heat it to 1000-1500℃ and maintain it for 15 hours, with a pressure of 75-80 mbar; during this period, introduce 290-300 sccm of Ar gas.

[0078] (2) After that, the temperature is raised to 1500-1700℃ in 20-25h, the pressure is 40-45mabr, and it is maintained for 10h. During this period, Ar gas is introduced at 260-270sccm and N2 gas at 25-30sccm.

[0079] (3) After that, the temperature is raised to 2100-2200℃ and the pressure is 25-30mbar for 25h, and maintained for 130-145h. During this period, Ar gas is introduced at 100-120sccm and N2 gas at 20-24sccm. After the crystal growth is completed, the temperature is lowered to room temperature at a rate of 100-150℃ / min, and the furnace is opened to obtain the crystal.

[0080] SiC crystals #1 to #3 were prepared according to the above crystal growth method. The specific crystal growth method is as follows:

[0081] SiC crystal #1

[0082] (1) Place the raw material in a crystal growth furnace, heat it to 1000℃ and maintain it for 15 hours, and pressurize it at 75mbar; during this period, 290sccm of Ar gas is introduced.

[0083] (2) After 25 hours, the temperature was raised to 1500℃ and the pressure was 45 mabr. The pressure was maintained for 10 hours, during which 270 sccm of Ar gas and 30 sccm of N2 gas were introduced.

[0084] (3) After that, the temperature was raised to 2100℃ in 25h, the pressure was 30mbar, and it was maintained for 145h. During this period, Ar gas was introduced at 120sccm and N2 gas at 24sccm. After the crystal growth was completed, the temperature was lowered to room temperature at a rate of 100℃ / min, and the furnace was opened to obtain the crystal.

[0085] SiC crystal #2

[0086] (1) Place the raw material in a crystal growth furnace, heat it to 1200℃ and maintain it for 12 hours, and pressurize it at 75 mbar; during this period, 290 sccm of Ar gas is introduced.

[0087] (2) After that, the temperature was raised to 1600℃ in 23h, the pressure was 45mbar, and it was maintained for 13h. During this period, 265sccm of Ar gas and 25sccm of N2 gas were introduced.

[0088] (3) After that, the temperature was raised to 2150℃ in 25 hours and the pressure was 30mbar. It was maintained for 140 hours. During this period, Ar gas was introduced at 110 sccm and N2 gas at 22 sccm. After the crystal growth was completed, the temperature was lowered to room temperature at a rate of 130℃ / min. The furnace was then opened to obtain the crystal.

[0089] SiC crystal #3

[0090] (1) Place the raw material in a crystal growth furnace, heat it to 1500℃ and maintain it for 10 hours, and pressurize it at 80mbar; during this period, 300sccm of Ar gas is introduced.

[0091] (2) After that, the temperature was raised to 1700℃ in 20h, the pressure was 40mbr, and it was maintained for 15h. During this period, 260sccm of Ar gas and 25sccm of N2 gas were introduced.

[0092] (3) After that, the temperature was raised to 2200℃ in 25h, the pressure was 25mbar, and it was maintained for 130h. During this period, 100sccm of Ar gas and 20sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was lowered to room temperature at a rate of 150℃ / min, and the furnace was opened to obtain the crystal.

[0093] 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.

[0094] The parameters were obtained by polarization light testing on each SiC substrate obtained from each SiC crystal. The specific testing method is as follows:

[0095] 1. A polarizer converts the light source into polarized light.

[0096] 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.

[0097] 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;

[0098] in,

[0099] Δ: Optical path difference between ordinary light (o-ray) and extraordinary light (e-ray);

[0100] d: Sample thickness;

[0101] Δn: The difference in refractive index between the ordinary ray (o ray) and the extraordinary ray (e ray);

[0102] λ: Wavelength.

[0103] The data in Table 1 below are based on the Laplace pyramid principle to distinguish between high-pass and low-pass signals, and the optical path difference is obtained under the high-pass signal condition. For a single SiC crystal, several SiC substrates are obtained, and each SiC substrate yields an optical path difference value. Values ​​marked with "maximum value" in Table 1 refer to the maximum value measured among the several SiC substrates obtained from the same SiC crystal. Therefore, the values ​​for all SiC substrates obtained from the same SiC crystal are less than or equal to the values ​​in Table 1. Similarly, values ​​marked with "minimum value" refer to the minimum value measured among the several SiC substrates obtained from the same SiC crystal. For example, the minimum and maximum values ​​of OPD4 / OPD5 combined represent the overall range of OPD4 / OPD5 values ​​for the SiC crystal.

[0104] The SiC crystals prepared above, from #1 to #3, are all 8 inches in size. The annular region refers to a region with a width of 15 mm extending inward from the edge of the SiC substrate.

[0105] Table 1

[0106] Figure 2 shows the optical path difference test results of one of the SiC substrates obtained by cutting, grinding, and polishing SiC crystal #1. Figure 2(a) shows the overall optical path difference test results of the SiC substrate, and Figure 2(b) shows the optical path difference test results of the SiC substrate under a high-pass signal. According to the results, it can be seen that this application can obtain an optical path difference analysis diagram that can characterize the defect stress by screening the high-pass signal and the low-pass signal, and the low-defect SiC crystal prepared in this application has low internal stress.

[0107] 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 low defect stress, characterized in that, The SiC crystal is used to prepare several SiC substrates. Based on the Laplace pyramid principle, high-pass and low-pass signals are distinguished. Under the high-pass signal, the overall optical path difference of any SiC substrate is <6nm, the maximum value of the optical path difference is <12nm, and the standard deviation of the optical path difference is <3nm.

2. The low-defect-stress SiC crystal according to claim 1, characterized in that, Under high-pass signal conditions, |OPD1-OPD2| < 4nm, where OPD1 represents the overall optical path difference of the SiC substrate including the first end face obtained by the SiC crystal, and OPD2 represents the overall optical path difference of the SiC substrate including the second end face obtained by the SiC crystal.

3. The low-defect-stress SiC crystal according to claim 2, characterized in that, Under high-pass signal conditions, |OPD1-OPD3| < 1.5 nm, |OPD2-OPD3| < 1.5 nm, where OPD3 represents the average value of the overall optical path difference across all SiC substrates obtained from the SiC crystal.

4. The SiC crystal with low defect stress according to any one of claims 1 to 3, characterized in that, For any SiC substrate obtained from the SiC crystal, the values ​​of OPD4 / OPD5 are in the range of 0.8 to 1.2 under high-pass signal conditions. OPD4 represents the optical path difference of the SiC substrate along the [11-20] direction, and OPD5 represents the optical path difference of the SiC substrate along the [1-100] direction.

5. The low-defect-stress SiC crystal according to claim 4, characterized in that, Any SiC substrate obtained from the SiC crystal has a central region and a ring-shaped region surrounding the central region. The ring-shaped region has a width of no more than 15 mm extending inward from the edge of the substrate. Under high-pass signal conditions, the values ​​of OPD6 / OPD7 are in the range of 0.9 to 1.

1. OPD6 represents the optical path difference in the central region of the SiC substrate along the [11-20] direction, and OPD7 represents the optical path difference in the central region of the SiC substrate along the [1-100] direction.

6. A SiC substrate with low defect stress, characterized in that, Under high-pass signal conditions, the overall optical path difference of the SiC substrate is <6nm, the maximum optical path difference is <12nm, and the standard deviation of the optical path difference is <3nm.

7. The low-defect-stress SiC substrate according to claim 6, characterized in that, The standard deviation of the optical path difference along any horizontal line of the SiC substrate is <1.5 nm.

8. The low-defect-stress SiC substrate according to claim 6, characterized in that, The SiC substrate has a central region and an annular region surrounding the central region, wherein the annular region has a width of no more than 15 mm extending inward from the edge of the substrate. The standard deviation of the optical path difference on any horizontal line in the central region is <1nm.

9. The low-defect-stress SiC substrate according to claim 6, characterized in that, The SiC substrate has a central region and an annular region surrounding the central region, wherein the annular region has a width of no more than 15 mm extending inward from the edge of the substrate. Under high-pass signal conditions, |OPD7-OPD8| < 4nm, where OPD7 represents the average optical path difference obtained along the annular region of the <11-20> crystal orientation group, and OPD8 represents the average optical path difference obtained along the central region of the <11-20> crystal orientation group.

10. The low-defect-stress SiC substrate according to claim 9, characterized in that, Under high-pass signal conditions, the SiC substrate has |OPD9-OPD10| < 4nm, where OPD9 represents the average optical path difference obtained along the annular region of the <1-100> crystal orientation group, and OPD10 represents the average optical path difference obtained along the central region of the <1-100> crystal orientation group.

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