SiC crystal with small and uniform in-plane optical path difference and SiC substrate

Abstract

The invention discloses a SiC crystal with small and uniform in-plane optical path difference and a SiC substrate, and belongs to the technical field of SiC material preparation. The optical path difference of any SiC substrate prepared from the SiC crystal is lt; the difference between the optical path difference of the SiC substrate including the first end surface and the optical path difference of the SiC substrate including the second end surface is in the range of-5 to 5 nm. The optical path difference of any SiC substrate obtained by the SiC crystal is relatively small, and the difference value of the optical path difference of the SiC substrate comprising the head part and the SiC substrate comprising the tail part is small, so that the optical path difference of the SiC crystal can be uniformly distributed along the axial direction.

Description

Technical Field

[0001] The present application relates to a SiC crystal and a SiC substrate with a small and uniform in-plane optical path difference, and belongs to the technical field of SiC material preparation. Background Art

[0002] When using polarized birefringence to test the stress of SiC substrate, since the light source penetrates the entire SiC wafer, the optical path difference caused by the lattice distortion within the SiC wafer surface can be measured, so that the optical path difference can be used to characterize its stress and lattice arrangement state.

[0003] At present, the entire SiC growth process is in a high-temperature, closed environment. As the crystal diameter and thickness continue to increase, the temperature field changes at any time. When the temperature field is disturbed, the lattice is distorted, which will produce residual stress and induce various defects such as micropipes, voids, and polycrystals. The above defects will increase the optical path difference inside the crystal and increase the internal variability of the optical path difference.

[0004] In addition, after rolling, cutting, grinding, polishing and other processes, SiC crystals can be processed into SiC substrates with small surface roughness for further use downstream. This process will introduce surface damage into the substrate, which will not only cause changes in the crystal plane spacing within the SiC substrate, but also cause differences between the center and edge of the SiC substrate, thereby increasing the in-plane optical path difference of the SiC substrate and increasing the variability of the in-plane optical path difference.

[0005] Therefore, there is currently a lack of a SiC crystal and SiC substrate with a small and uniform in-plane optical path difference. Summary of the invention

[0006] In order to solve the above problems, a SiC crystal and a SiC substrate with a small and uniform in-plane optical path difference are provided. The optical path difference of any SiC substrate obtained from the SiC crystal is small, and the difference in the optical path difference between the SiC substrate including the head and the SiC substrate including the tail is small, which proves that the optical path difference of the SiC crystal can be uniformly distributed along the axial direction.

[0007] According to one aspect of the present application, a SiC crystal with a small and uniform in-plane optical path difference is provided, wherein the optical path difference of any SiC substrate prepared from the SiC crystal is <10 nm, and the difference between the optical path difference of the SiC substrate including the first end face and the optical path difference of the SiC substrate including the second end face is in the range of -5 to 5 nm.

[0008] The in-plane optical path difference of this application refers to the optical path difference caused by different paths when light propagates inside a medium. The stress test on SiC products will result in different test results due to the change in wavelength. This shortcoming makes it impossible to effectively feedback the actual situation of the product. This application uses the 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 to obtain SiC products with significantly improved quality.

[0009] Preferably, the optical path difference of any SiC substrate obtained from the SiC crystal is less than 5 nm, and the difference between the optical path difference of the SiC substrate including the first end face and the optical path difference of the SiC substrate including the second end face is in the range of -1.5 to 1.5 nm.

[0010] After the SiC crystal is ground flat at both ends, several SiC substrates are prepared. The SiC substrate containing the first end face and the SiC substrate containing the second end face in this application belong to the first substrates obtained by processing the two ends of the ground SiC crystal. The above parameters prove that the SiC crystal with small and uniform in-plane optical path difference in this application is uniformly distributed in the axial direction. Combining the optical path difference of any SiC substrate can obtain that the overall stress of the SiC crystal in this application is small and uniform.

[0011] Optionally, |σ1-σ2|<3 nm, σ1 represents the standard deviation of the optical path difference of the SiC substrate including the first end face, and σ2 represents the standard deviation of the optical path difference of the SiC substrate including the second end face.

[0012] Preferably, |σ1-σ2|<1 nm, σ1 represents the standard deviation of the optical path difference of the SiC substrate including the first end face, and σ2 represents the standard deviation of the optical path difference of the SiC substrate including the second end face.

[0013] The smaller the value of |σ1-σ2| is, the smaller the difference between the head and tail of the SiC crystal is, which can further improve the axial stability of the crystal.

[0014] Optionally, The value range is 0.8~1.2, The value range is 0.8~1.2, It represents the average value of the standard deviation of the optical path difference of all SiC substrates.

[0015] Preferably, The value range is 0.9~1.1, The value range is 0.9~1.1, It represents the average value of the standard deviation of the optical path difference of all SiC substrates.

[0016] The above ratio can represent the difference between the SiC substrate including the first end face, the SiC substrate including the second end face and all SiC substrates obtained from the crystal. The closer the ratio is to 1, the more it indicates that the crystal can achieve uniform stress distribution in the axial direction, which is reflected in the uniform distribution of the optical path difference in the axial direction.

[0017] Optionally, the standard deviation of the optical path difference of any SiC substrate obtained by the SiC crystal is less than 6 nm.

[0018] Preferably, the standard deviation of the optical path difference of any SiC substrate obtained from the SiC crystal is less than 2 nm.

[0019] For any SiC substrate, the calculated optical path difference of the SiC substrate is the average value of all test point values ​​obtained in the entire SiC substrate area, but the average value is easily affected by extreme values. Therefore, the standard deviation of the optical path difference in the SiC substrate of the present application is <6nm, which proves that the optical path difference of the SiC substrate is uniformly distributed in the radial direction, and therefore indicates that the stress is also uniformly distributed in the radial direction.

[0020] Optionally, for any SiC substrate obtained from the SiC crystal, after removing the annular region with a width of 3 mm extending inward from the edge, the optical path difference of the remaining central region is less than 6 nm, and the standard deviation of the optical path difference is less than 3 nm.

[0021] Due to the influence of the growth temperature field, the quality of the annular area is slightly worse than that of the central area. Therefore, after removing the annular area, the optical path difference and the standard deviation of the optical path difference of the SiC substrate are reduced, indicating that the distribution uniformity of the central area is better.

[0022] According to another aspect of the present application, a SiC substrate having a small and uniform in-plane optical path difference is provided, wherein the optical path difference of the SiC substrate is <10 nm and the standard deviation is <6 nm.

[0023] Preferably, the optical path difference of the SiC substrate is less than 5 nm, and the standard deviation is less than 2 nm.

[0024] Optionally, after removing the annular region with a width of 3 mm extending inward from the edge of the SiC substrate, the optical path difference of the remaining central region is less than 6 nm, and the standard deviation of the optical path difference is less than 3 nm.

[0025] Optionally, on any horizontal line in the annular area, the standard deviation of the optical path difference is <4 nm.

[0026] Preferably, on any horizontal line in the annular region, the standard deviation of the optical path difference is <1.5 nm.

[0027] Optionally, on any horizontal line in the central area, the standard deviation of the optical path difference is <2 nm.

[0028] Preferably, on any horizontal line in the central area, the standard deviation of the optical path difference is <1 nm.

[0029] For a certain horizontal line, it can reflect the data volatility of the SiC substrate on this line. The smaller the standard deviation of the optical path difference, the more uniform the product quality is in the radial direction.

[0030] Optionally, for any horizontal line, σ4 / σ5<1.9, σ4 represents the standard deviation of the optical path difference of the annular area on the straight line, and σ5 represents the standard deviation of the optical path difference of the central area on the straight line. Preferably, σ4 / σ5<1.5.

[0031] For a certain horizontal line, the closer the ratio of σ4 / σ5 is to 1, the smaller the difference between the annular area and the central area, which means that the overall uniformity of the SiC substrate is better. The available area of ​​the SiC substrate will increase, thereby increasing the number of devices that can be prepared on a single SiC substrate and reducing the unit production cost.

[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] Optionally, the SiC substrate has a thickness of less than 1 mm.

[0037] The beneficial effects of this application include but are not limited to:

[0038] 1. According to the SiC crystal with a small and uniform in-plane optical path difference of the present application, the difference in the optical path difference between the SiC substrate including the first end face and the SiC substrate including the second end face represents that the optical path difference of the SiC crystal is axially uniform, and |σ1-σ2| is small, which means that the difference in the uniformity of the radial distribution of the optical path difference from front to back of the SiC crystal is small. Therefore, the internal lattice arrangement of the SiC crystal is uniform, with few defects and low stress, and it can be promoted and used commercially.

[0039] 2. According to the SiC crystal with small and uniform in-plane optical path difference of the present application, the optical path difference fluctuation of any SiC substrate obtained is small, and the quality of the central area is more uniform. Therefore, it is possible to greatly increase the available area of ​​the crystal while improving the crystal quality, thereby reducing the unit production cost.

[0040] 3. According to the SiC substrate with a small and uniform in-plane optical path difference of the present application, the optical path difference can be significantly reduced while achieving uniform distribution of the optical path difference in the axial and radial directions, and reducing the difference between the annular area and the central area, thereby meeting the market requirements for high uniformity and high stability of 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 schematic diagram of the structure 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 of one of the SiC substrates prepared from SiC crystal 3# involved in Example 2 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

[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, an external insulation 7 and a 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 arranged 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 closeable slide rail is arranged on the top of the furnace chamber 1, and a movable laser locator 10 is arranged on the closeable 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 and 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 then 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 plane moving assembly, as long as it can drive the movable support rod 9 to move and adjust within the plane. For example, as an implementation method, the plane moving assembly includes a transverse 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 transverse moving part 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 a closable type 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, thereby protecting the movable laser locator 10 and the slide rail and preventing them from being affected by the Si atmosphere or SiC atmosphere during the crystal growth process and affecting their subsequent normal operation.

[0054] As a 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 driving mechanism. Further, the longitudinal moving part 15 is provided with a transverse track 12, 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 in a plane, thereby driving the movement of the outer insulation 7 to adjust the relative position with the crucible. In addition, the skilled and technical personnel can understand that the order of setting the longitudinal moving part 15 and the transverse moving part 14 can be exchanged. 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, and then set the longitudinal track on the transverse moving part 14, and the longitudinal moving part 15 moves on this longitudinal track, so as to achieve the same function.

[0055] As an implementation mode, 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 the rotating component 17, the movable support rod 9 can be rotated, thereby driving the rotation of the external insulation 7. Since the external insulation 7 is easily corroded by the Si atmosphere, its inner edge may change, 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 positioner 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 limitation on the implementation method of the rotating assembly 17 and the lifting assembly 16, which can be conventionally selected by those skilled in the art. There is no specific limitation on the connection method between the rotating assembly 17, the lifting assembly 16 and the planar moving assembly. For example, the planar moving assembly is arranged at the bottom, the lifting assembly 16 is arranged in the middle, and the rotating assembly 17 is arranged 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 implementation mode, the closable slide rail includes a transverse slide rail 11 and a longitudinal slide rail, and a movable laser locator 10 is disposed on both the transverse slide rail 11 and the longitudinal slide rail.

[0060] By setting 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 implementation mode, 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 respectively connected to the crucible holder 6 and the crucible body 4 through threads.

[0063] As a specific implementation manner, the bottom of the crucible holder 6 is provided with an internal thread, the top of the transitional 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 transitional 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 transitional 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] The skilled person and technicians 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 by threads, there are other different implementation methods, and the skilled person and technicians can design them according to needs.

[0066] It should be noted that the 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 situation to meet the technical effect 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 according to the needs. 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] The crucible holder 6 is fixed on the bottom of the upper flange 2, and the crucible body 4 and the crucible holder 6 are respectively connected through the transition crucible cover 5. After the reaction materials are filled into the crucible body 4, the crucible body 4 can be fixed at a fixed position of 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 also 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, and graphitized carbon fiber bundles are the support. Since Si atmosphere is more easily captured by the tar pitch binder, it can effectively reduce the erosion of Si atmosphere on the insulation felt during the preparation of silicon carbide crystals by the PVT method, 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 polymorphism. The support is a 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 of more than 2000°C during the growth of silicon carbide.

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

[0071] It should be noted that the present application scheme mainly describes the main invention points. Other structures in the induction furnace can be implemented by referring to the scheme of the induction furnace in the 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, so that the movable laser positioner 10 on the closable slide rail can have 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, wherein the matrix is ​​tar pitch, and the carbon fiber bundles are graphitized carbon fiber bundles, and the graphitized carbon fiber bundles are arranged in parallel in the tar pitch matrix.

[0073] Example 2

[0074] The SiC crystal prepared in this embodiment is grown using the induction crystal growth furnace of Example 1. The specific crystal growth method is as follows:

[0075] (1) Place the raw materials in a crystal growth furnace and heat them up to 1450-1500°C, adjust the pressure to 50-55 mabr, maintain for 5 hours, and introduce 300-320 sccm of Ar gas and N 2 Gas 30-35sccm

[0076] (2) The temperature was raised to 2000-2100°C within 5 h, and the pressure was reduced to 30-35 mbar and maintained for 10-12 h. During this period, 100-120 sccm of Ar gas and N 2 Gas 20-25sccm

[0077] (3) The temperature was raised to 2200-2250°C within 15 h, the pressure was reduced to 7-8 mbar, and the crystal growth was maintained for 150-160 h. During this period, 50-55 sccm of Ar gas and N 2 Gas is 10-15sccm, and 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# are prepared according to the above-mentioned crystal growth method. The specific crystal growth method is as follows:

[0079] SiC crystal 1#

[0080] (1) Place the raw materials in a crystal growth furnace and heat them up to 1450°C. Adjust the pressure to 55 mAbr and maintain for 5 h. Then introduce 320 sccm of Ar gas and N 2 Gas 35sccm

[0081] (2) The temperature was raised to 2000°C within 5 h, and the pressure was reduced to 35 mbar and maintained for 10 h. During this period, 120 sccm of Ar gas and N 2 Gas 25sccm

[0082] (3) The temperature was raised to 2250°C within 15 h, the pressure was reduced to 7 mbar, and the crystal growth was maintained for 160 h. During this period, 50 sccm of Ar gas and 50 sccm of N 2 The gas is 10sccm, and after the crystal growth is completed, the temperature is naturally lowered and the furnace is opened to obtain the crystal.

[0083] SiC crystal 2#

[0084] (1) Place the raw materials in a crystal growth furnace and heat them up to 1500°C. Adjust the pressure to 50 mAbr and maintain for 5 h. Then introduce 300-sccm Ar gas and N 2 Gas 30sccm

[0085] (2) The temperature was raised to 2100 °C within 5 h, and the pressure was reduced to 30 mbar and maintained for 12 h. During this period, 100 sccm of Ar gas and N 2 Gas 20sccm

[0086] (3) The temperature was raised to 2200°C within 15 h, the pressure was reduced to 8 mbar, and the crystal growth was maintained for 150 h. During this period, 55 sccm of Ar gas and 55 sccm of N 2 The gas is 15sccm, and after the crystal growth is completed, the temperature is naturally lowered and the furnace is opened to obtain the crystal.

[0087] SiC crystal 3#

[0088] (1) Place the raw materials in a crystal growth furnace and heat them up to 1450°C. Adjust the pressure to 53 mabr and maintain for 5 h. Then introduce 310 sccm of Ar gas and N 2 Gas 35sccm

[0089] (2) The temperature was raised to 2050°C within 5 h, and the pressure was reduced to 33 mbar and maintained for 10 h. During this period, 110 sccm of Ar gas and N 2 Gas 22sccm

[0090] (3) The temperature was raised to 2230°C within 15 h, the pressure was reduced to 7 mbar, and the crystal growth was maintained for 150 h. During this period, 50 sccm of Ar gas and 50 sccm of N 2 The gas is 10sccm, and after the crystal growth is completed, the temperature is naturally lowered and the furnace is opened to obtain the crystal.

[0091] The SiC substrates prepared above were cut, ground and polished to obtain a surface roughness Ra of no more than 10 nm and a thickness of 500 micrometers.

[0092] The parameters obtained by performing polarized light testing on 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 and transparent single-crystal SiC substrate through a preset optical path. When there is residual stress in the SiC substrate, the substrate lattice will be distorted, including crystal defects such as dislocations and microtubes, as well as processing damage such as edge collapse and scratches. Lattice distortion causes polarized light to deflect, and the deflection angle causes polarized light to undergo polarization birefringence, presenting polarized light in two directions.

[0095] 3. Then, the polarization camera is used to analyze the interference fringes of the two polarized lights in the optical path, and the polarization stress map can be qualitatively obtained. When the stress in the sample surface reaches equilibrium, the polarized lights in the two directions completely cancel each other out, resulting in black interference fringes; when residual stress exists, the polarized lights in the two directions do not completely cancel each other out, presenting bright colors, thereby achieving the residual stress characterization and analysis of the SiC single crystal substrate;

[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] A number of SiC substrates obtained from a SiC crystal, each SiC substrate has an optical path difference value, the values ​​represented in Table 1 with "maximum value" refer to the maximum value obtained by testing among the several SiC substrates obtained from the SiC crystal, so the several SiC substrates obtained from the entire SiC crystal are less than or equal to the values ​​in Table 1; similarly, the values ​​with "minimum value" refer to the minimum value obtained by testing among the several SiC substrates obtained from the SiC crystal. For example The minimum and The maximum value of the SiC crystal is combined The value range of .

[0103] The SiC crystals 1# to 3# prepared above are all 8 inches in size, and the annular region refers to a region extending inward from the edge of the SiC substrate with a width of 3 mm.

[0104] Table 1

[0105]

[0106] Figure 2 The optical path difference test result of one of the SiC substrates prepared from SiC crystal 3# shows that the overall optical path difference of the SiC substrate is 3.425nm, and the in-plane optical path difference is small, which means that the stress of the SiC substrate is also small.

[0107] The above is only the embodiment of the present application, and the protection scope 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 can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the technical ideas and principles of the present application should be included in the protection scope of the present application.

Claims

1. A SiC crystal having a small and uniform in-plane optical path difference, characterized in that: The optical path difference of any SiC substrate prepared from the SiC crystal is less than 10 nm, and the difference between the optical path difference of the SiC substrate including the first end face and the optical path difference of the SiC substrate including the second end face is within the range of -5 to 5 nm.

2. The SiC crystal with small and uniform in-plane optical path difference according to claim 1, characterized in that: |σ1-σ2|<3 nm, σ1 represents the standard deviation of the optical path difference of the SiC substrate including the first end face, and σ2 represents the standard deviation of the optical path difference of the SiC substrate including the second end face.

3. The SiC crystal with small and uniform in-plane optical path difference according to claim 2, characterized in that: The value range is 0.8~1.2, The value range is 0.8~1.2, It represents the average value of the standard deviation of the optical path difference of all SiC substrates.

4. The SiC crystal with small and uniform in-plane optical path difference according to claim 1, characterized in that: The standard deviation of the optical path difference of any SiC substrate obtained by the SiC crystal is less than 6 nm.

5. The SiC crystal with small and uniform in-plane optical path difference according to claim 1, characterized in that: For any SiC substrate obtained from the SiC crystal, after removing the annular region with a width of 3 mm extending inward from the edge, the optical path difference of the remaining central region is less than 6 nm, and the standard deviation of the optical path difference is less than 3 nm.

6. A SiC substrate having a small and uniform in-plane optical path difference, characterized in that: The optical path difference of the SiC substrate is less than 10 nm, and the standard deviation of the optical path difference is less than 6 nm.

7. The SiC substrate with a small and uniform in-plane optical path difference according to claim 6, characterized in that: After removing the annular region with a width of 3 mm extending inward from the edge of the SiC substrate, the optical path difference of the remaining central region is less than 6 nm, and the standard deviation of the optical path difference is less than 3 nm.

8. The SiC substrate with a small and uniform in-plane optical path difference according to claim 7, characterized in that: On any horizontal line in the annular region, the standard deviation of the optical path difference is <4 nm.

9. The SiC substrate with a small and uniform in-plane optical path difference according to claim 7, characterized in that: On any horizontal line in the central area, the standard deviation of the optical path difference is <2 nm.

10. The SiC substrate having a small and uniform in-plane optical path difference according to any one of claims 7 to 9, characterized in that: σ4 / σ5<1.9, σ4 represents the standard deviation of the optical path difference on any horizontal line in the annular area, and σ5 represents the standard deviation of the optical path difference on any horizontal line in the central area.

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