SiC crystal with low internal stress and SiC substrate

Abstract

The invention discloses a low-internal stress SiC crystal and a SiC substrate, and belongs to the technical field of SiC material preparation. A plurality of SiC substrates are prepared from the SiC crystal, high-pass signals and low-pass signals are distinguished on the basis of the Laplacian pyramid principle, and the optical path difference of any SiC substrate is lt under the low-pass signals; 6 nm, the maximum value of the optical path difference is lt; 10 nm, and the standard deviation of the optical path difference is lt; 2 nm. The optical path difference between the SiC crystal and the SiC substrate is small and uniform under a low pass signal, which represents that the internal stress in SiC is low, and the lattice distortion degree caused by the internal stress is small.

Description

Technical Field

[0001] The present application relates to a SiC crystal and a SiC substrate with low internal stress, and belongs to the technical field of SiC material preparation. Background Art

[0002] During the growth of SiC, due to the presence of axial and radial temperature gradients, the continuous and gradual change of the temperature gradient, and the continuous change of the surface shape of the SiC substrate during the cutting, grinding and polishing process, the stress of SiC changes gradually from the center to the edge. On the other hand, if SiC has lattice distortion during the growth process and induces in-plane defects such as micropipes, voids, and white spots, the in-plane defects will cause local stress concentration.

[0003] Polarized birefringence is used 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 the optical path difference can be used to characterize its stress.

[0004] However, when optical path difference is used to characterize SiC stress, only qualitative characterization of stress can be achieved. It is impossible to distinguish the optical path difference caused by internal stress or defects, and further, it is impossible to use the optical path difference to provide feedback on the production and processing technology of SiC products to obtain SiC crystals and SiC substrates with low internal stress. Summary of the invention

[0005] In order to solve the above problems, a SiC crystal and a SiC substrate with low internal stress are provided. The optical path difference of the SiC crystal and the SiC substrate under a low-pass signal is small and uniform, which means that the internal stress in the SiC is low and the degree of lattice distortion caused by the internal stress is small.

[0006] According to one aspect of the present application, a SiC crystal with low internal stress is provided. Several SiC substrates are prepared from the SiC crystal. High-pass signals and low-pass signals are distinguished based on the Laplace pyramid principle. Under the low-pass signal, the optical path difference of any SiC substrate is <6nm, the maximum value of the optical path difference is <10nm, and the standard deviation of the optical path difference is <2nm.

[0007] The optical path difference of this application refers to the difference in optical path 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.

[0008] Based on the characteristics of internal stress, the present application found that it is a continuous low-frequency change in the optical path difference of the polarized birefringence test. The low-pass data is the optical path difference signal that filters out high-frequency fluctuations, representing the stress caused by the lattice distortion caused by internal stress and surface fluctuations; therefore, based on this theoretical principle, the optical path difference measured in the plane is screened to characterize the stress caused by the lattice distortion of SiC due to internal stress and surface fluctuations, and the production process is optimized based on the characterization, thereby obtaining the SiC crystal and SiC substrate with low internal stress of the present application.

[0009] Any SiC substrate obtained from the SiC crystal not only has a smaller overall optical path difference, but also a smaller standard deviation of the optical path difference, which means that the SiC crystal has better uniformity in the axial and radial directions.

[0010] The above-mentioned distinction between high-pass signals and low-pass signals based on the Laplace pyramid principle refers to the use of the Laplace pyramid to distinguish high-pass signals from low-pass signals based on spatial warping. This is the prior art and will not be repeated in this application.

[0011] Optionally, |OPD1-OPD2|<3nm, OPD1 represents the optical path difference of the entire SiC substrate including the first end face obtained by the SiC crystal, and OPD2 represents the 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 prepared. In the present application, the SiC substrate including the first end face and the SiC substrate including the second end face are the first substrates obtained by processing the two ends of the ground SiC crystal.

[0013] The above parameters further prove that the SiC crystal of the present application is evenly distributed in the axial direction. Combining the optical path difference of any SiC substrate, it can be obtained that the overall internal stress of the SiC crystal of the present application is small and uniform.

[0014] Optionally, |OPD1-OPD3|<1nm, |OPD2-OPD3|<1nm, OPD3 represents the average value of the optical path difference of all SiC substrates obtained by the SiC crystal.

[0015] Preferably, |OPD1-OPD3|<0.5nm, |OPD2-OPD3|<0.5nm.

[0016] |OPD1-OPD3| and |OPD2-OPD3| can represent the differences between the SiC substrate including the first end face and the SiC substrate including the second end face and all SiC substrates obtained from the crystal. The smaller the value is, the more it indicates that the crystal can achieve uniform distribution of internal stress in the axial direction, which is reflected in the uniform distribution of optical path difference in the axial direction.

[0017] Optionally, any SiC substrate obtained from the SiC crystal has a central region and an annular region surrounding the central region, and the annular region is a region extending inward from the edge of the substrate and has a width of no more than 15 mm;

[0018] Under the low-pass signal, |OPD4-OPD5|<4nm, OPD4 represents the optical path difference obtained in the annular area along the [11-20] direction, and OPD5 represents the optical path difference obtained in the central area along the [11-20] direction.

[0019] Optionally, |OPD6-OPD7|<4nm, OPD6 represents the optical path difference obtained in the annular area along the [1-100] direction, and OPD7 represents the optical path difference obtained in the central area along the [1-100] direction.

[0020] Preferably, |OPD4-OPD5|<3nm, |OPD6-OPD7|<3nm.

[0021] For the SiC crystals currently prepared, due to the influence of the growth temperature field, the quality of the annular region is slightly worse than that of the central region. The SiC crystal of the present application can reduce the difference between the annular region and the central region, and achieve the improvement of the uniformity of the internal stress in the plane. The [11-20] direction and the [1-100] direction are two characteristic directions of SiC. The lower the values ​​of |OPD4-OPD5| and |OPD6-OPD7| in the above two directions, the higher the degree of homogenization of the SiC substrate in the [11-20] direction and the [1-100] direction.

[0022] According to another aspect of the present application, a SiC substrate with low internal stress has an optical path difference of <6 nm, a maximum value of the optical path difference of <10 nm, and a standard deviation of the optical path difference of <2 nm under a low-pass signal.

[0023] Optionally, the standard deviation of the optical path difference on any horizontal line of the SiC substrate is <2 nm.

[0024] The standard deviation of the optical path difference on any horizontal line of the SiC substrate 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.

[0025] Optionally, the SiC substrate has a central area and an annular area surrounding the central area, and the annular area extends inward from the edge of the substrate and has a width of no more than 15 mm;

[0026] Under the low-pass signal, for any horizontal line, the value range of σ1 / σ2 is 1.1-5.0, σ1 represents the standard deviation of the optical path difference on the horizontal line in the annular area, and σ2 represents the standard deviation of the optical path difference on the horizontal line in the central area.

[0027] Preferably, the value range of σ1 / σ2 is 1.1 - 3.5.

[0028] σ1 / σ2 refers to the ratio of the standard deviation of the optical path difference of the annular region calculated on a horizontal line to the standard deviation of the optical path difference of the central region. The closer this ratio is to 1, the smaller the difference between the annular region and the central region, which means the better the overall uniformity of the SiC substrate. The available area of the SiC substrate will increase, thereby increasing the number of devices that can be fabricated on a single SiC substrate and reducing the unit manufacturing cost.

[0029] Optionally, the SiC substrate has a central region and an annular region surrounding the central region. The width of the annular region extending inward from the substrate edge is not greater than 15 mm.

[0030] Under a low-pass signal, |OPD4 - OPD5| < 4 nm, where OPD4 represents the optical path difference obtained from the annular region of the SiC substrate along the [11 - 20] direction, and OPD5 represents the optical path difference obtained from the central region of the SiC substrate along the [11 - 20] direction.

[0031] Optionally, under a low-pass signal, |OPD6 - OPD7| < 4 nm, where OPD6 represents the optical path difference obtained from the annular region of the SiC substrate along the [1 - 100] direction, and OPD7 represents the optical path difference obtained from the central region of the SiC substrate along the [1 - 100] direction.

[0032] Optionally, for the SiC substrate under a low-pass signal, 0.7 < OPD8 / OPD9 < 1.4, where OPD8 represents the average value of the optical path differences obtained from the annular region along the <11 - 20> crystal orientation family, and OPD9 represents the average value of the optical path differences obtained from the annular region along the <1 - 100> crystal orientation family.

[0033] Optionally, for the SiC substrate under a low-pass signal, 0.8 < OPD10 / OPD11 < 1.2, where OPD10 represents the average value of the optical path differences obtained from the central region along the <11 - 20> crystal orientation family, and OPD11 represents the average value of the optical path differences obtained from the central region along the <1 - 100> crystal orientation family.

[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, preferably 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, preferably 8 inches or 12 inches.

[0037] Optionally, the SiC crystal and the SiC substrate are semi-insulating or conductive.

[0038] Optionally, the SiC substrate has a thickness of less than 1 mm.

[0039] The beneficial effects of this application include but are not limited to:

[0040] 1. The low internal stress SiC crystal and SiC substrate of the present application realize quantitative characterization of SiC internal stress through optical path difference, and the uniformity of internal stress of the SiC crystal and SiC substrate is improved, which means that there is no internal stress concentration in the SiC product.

[0041] 2. The low internal stress SiC crystal of the present application has a small difference in optical path difference between the SiC substrate including the first end face and the SiC substrate including the second end face, and the difference between the optical path difference of the two SiC substrates and the average optical path difference of all SiC substrates is small, both of which represent that the internal stress of the SiC crystal is uniformly distributed in the axial direction, thereby improving the quality consistency of several SiC substrates obtained from a single crystal.

[0042] 3. The low internal stress SiC substrate of the present application has small differences between the central area and the annular area in the [1-100] direction and the [11-20] direction, which means that the stress fluctuation amplitude of SiC from the center to the edge is small and the in-plane uniformity is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] 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:

[0044] 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;

[0045] Figure 2 This is the optical path difference test result after polishing of one of the SiC substrates prepared from SiC crystal 2# involved in Example 2 of the present application, where Figure 2 (a) is the overall optical path difference test result of the SiC substrate. Figure 2 (b) is the optical path difference test result of the SiC substrate under a low-pass signal.

[0046] List of parts and reference numerals:

[0047] 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

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

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

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

[0051] Example 1

[0052] like Figure 1 As 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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;

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] Example 2

[0076] 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:

[0077] (1) Place the raw materials in a crystal growth furnace, first raise the temperature to 1000-1100°C and maintain for 10-15 hours, the pressure is 100-110 mbar, and 300-350 sccm of Ar gas is introduced;

[0078] (2) Then, the temperature was raised to 1500-1600°C within 20 hours, maintained for 10-15 hours, and the pressure was 50-60mab, during which time 240-260sccm of Ar gas and 30-35sccm of N2 gas were introduced;

[0079] (3) Then, the temperature is raised to 2000-2200°C within 20 hours, the pressure is 30-35 mbar, and maintained for 150-160 hours. During this period, 100-120 sccm of Ar gas and 20-25 sccm of N2 gas are introduced. After the crystal growth is completed, the temperature is lowered to room temperature at a cooling rate of 100-200°C / min, and the furnace is opened to obtain crystals.

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

[0081] SiC crystal 1#

[0082] (1) Place the raw materials in a crystal growth furnace, first heat to 1050°C and maintain for 13 h, the pressure is 110 mbar, and 350 sccm of Ar gas is introduced;

[0083] (2) After that, the temperature was raised to 1550°C in 20 hours and maintained for 12 hours at a pressure of 55 mab, during which time 250 sccm of Ar gas and 35 sccm of N2 gas were introduced;

[0084] (3) The temperature was then raised to 2100°C within 20 h, the pressure was 30 mbar, and maintained for 150 h, during which time 100 sccm of Ar gas and 20 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was lowered to room temperature at a rate of 150°C / min, and the furnace was opened to obtain the crystal.

[0085] SiC crystal 2#

[0086] (1) Place the raw materials in a crystal growth furnace, first raise the temperature to 1000°C and maintain for 15 hours, the pressure is 100 mbar, and 300 sccm of Ar gas is introduced;

[0087] (2) After that, the temperature was raised to 1500°C in 20 hours and maintained for 15 hours at a pressure of 60 mAb, during which time 260 sccm of Ar gas and 35 sccm of N2 gas were introduced;

[0088] (3) The temperature was then raised to 2000°C within 20 h, the pressure was 35 mbar, and maintained for 160 h, during which time 120 sccm of Ar gas and 25 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was lowered to room temperature at a rate of 100°C / min, and the furnace was opened to obtain the crystal.

[0089] SiC crystal 3#

[0090] (1) Place the raw materials in a crystal growth furnace, first heat to 1100°C and maintain for 10 h, the pressure is 100 mbar, and 300 sccm of Ar gas is introduced;

[0091] (2) After that, the temperature was raised to 1600°C in 20 hours and maintained for 10 hours at a pressure of 50 mAb, during which time 240 sccm of Ar gas and 30 sccm of N2 gas were introduced;

[0092] (3) The temperature was then raised to 2200°C within 20 h, the pressure was 30 mbar, and maintained for 150 h, during which time 100 sccm of Ar gas and 20 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was lowered to room temperature at a rate of 200°C / min, and the furnace was opened to obtain the crystal.

[0093] 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.

[0094] The parameters obtained by performing polarized light testing on each SiC substrate obtained from each SiC crystal are as follows:

[0095] 1. Convert the light source into polarized light through a polarizer,

[0096] 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.

[0097] 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;

[0098]

[0099] in,

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

[0101] d: sample thickness;

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

[0103] λ: wavelength.

[0104] The data in the following Table 1 are based on the Laplace pyramid principle to distinguish high-pass signals from low-pass signals, and the optical path difference is obtained under low-pass signals. Several SiC substrates obtained from a SiC crystal, each SiC substrate obtains an optical path difference value. The values ​​represented in Table 1 with "maximum value" refer to the maximum value obtained by testing among 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 several SiC substrates obtained from the SiC crystal. For example, the minimum value of σ1 / σ2 and the maximum value of σ1 / σ2 are combined to obtain the value range of σ1 / σ2 of the entire SiC crystal.

[0105] 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 15 mm.

[0106] Table 1

[0107]

[0108] The optical path difference test result of one of the SiC substrates after polishing obtained by cutting, grinding and polishing SiC crystal 2# Figure 2 , Figure 2 (a) is the overall optical path difference test result of the SiC substrate. Figure 2 (b) is the optical path difference test result of the SiC substrate under a low-pass signal. According to the result, it can be known that the present application can obtain an optical path difference analysis diagram that can characterize the internal stress by screening the high-pass signal and the low-pass signal, and the low-internal stress SiC crystal prepared in the present application has a low internal stress.

[0109] 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 with low internal stress, characterized in that: A number of SiC substrates are prepared from the SiC crystal. Based on the Laplacian pyramid principle, the high-pass signal and the low-pass signal are distinguished. Under the low-pass signal, the optical path difference of any SiC substrate is <6 nm, the maximum value of the optical path difference is <10 nm, and the standard deviation of the optical path difference is <2 nm.

2. The SiC crystal with low internal stress according to claim 1, characterized in that: Under the low-pass signal, |OPD1 - OPD2| < 3 nm, where OPD1 represents the optical path difference of the entire SiC substrate obtained from the SiC crystal and including the first end face, and OPD2 represents the optical path difference of the SiC substrate obtained from the SiC crystal and including the second end face.

3. The SiC crystal with low internal stress according to claim 2, characterized in that: Under the low-pass signal, |OPD1 - OPD3| < 1 nm, |OPD2 - OPD3| < 1 nm, where OPD3 represents the average value of the optical path differences of all SiC substrates obtained from the SiC crystal.

4. The SiC crystal with low internal stress according to claim 1, characterized in that: Any SiC substrate obtained from the SiC crystal has a central region and an annular region surrounding the central region. The annular region extends inward from the substrate edge with a width not greater than 15 mm. Under the low-pass signal, |OPD4 - OPD5| < 4 nm, where OPD4 represents the optical path difference obtained from the annular region along the [11 - 20] direction, and OPD5 represents the optical path difference obtained from the central region along the [11 - 20] direction.

5. The SiC crystal with low internal stress according to claim 4, characterized in that: Under the low-pass signal, |OPD6 - OPD7| < 4 nm, where OPD6 represents the optical path difference obtained from the annular region along the [1 - 100] direction, and OPD7 represents the optical path difference obtained from the central region along the [1 - 100] direction.

6. A SiC substrate with low internal stress, characterized in that: Under the low-pass signal, the optical path difference of the SiC substrate is <6 nm, the maximum value of the optical path difference is <10 nm, and the standard deviation of the optical path difference is <2 nm.

7. The SiC substrate with low internal stress according to claim 6, characterized in that: Under the low-pass signal, the standard deviation of the optical path difference on any horizontal line of the SiC substrate is <2 nm.

8. The SiC substrate with low internal stress according to claim 6, characterized in that: The SiC substrate has a central region and an annular region surrounding the central region. The annular region extends inward from the substrate edge with a width not greater than 15 mm. Under the low-pass signal, for any horizontal line, the value range of σ1 / σ2 is 1.1 - 5.0, where σ1 represents the standard deviation of the optical path difference on this horizontal line in the annular region, and σ2 represents the standard deviation of the optical path difference on this horizontal line in the central region.

9. The SiC substrate with low internal stress according to claim 6, characterized in that: Under the low-pass signal, 0.7 < OPD8 / OPD9 < 1.4, where OPD8 represents the average value of the optical path differences obtained from the annular region along the <11 - 20> crystal direction family, and OPD9 represents the average value of the optical path differences obtained from the annular region along the <1 - 100> crystal direction family.

10. The SiC substrate with low internal stress according to claim 9, characterized in that: Under the low-pass signal, 0.8 < OPD10 / OPD11 < 1.2, where OPD10 represents the average value of the optical path differences obtained from the central region along the <11 - 20> crystal direction family, and OPD11 represents the average value of the optical path differences obtained from the central region along the <1 - 100> crystal direction family.

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