Conductive silicon carbide crystal with good optical path difference uniformity and silicon carbide substrate

Abstract

The invention discloses a conductive silicon carbide crystal with good optical path difference uniformity and a silicon carbide substrate, and belongs to the technical field of silicon carbide material preparation. The resistivity at any position of the silicon carbide crystal is lt; the thickness is 30 m omega.cm; 1-N silicon carbide substrates are prepared from the silicon carbide crystal, N is a positive integer and represents the serial number of the silicon carbide substrates, the value of the first silicon carbide substrate including the first end face from the silicon carbide crystal is 1, the optical path difference of any silicon carbide substrate meets the following formula: = a (N-1) + b, the unit is nm, the value range of a is-0.8 to 0.8, the value range of b is-0.8 to-0.8, and the value range of b is-0.8 to-0.8. The value of b is 0.5-8, and the unit is nm. According to the conductive silicon carbide crystal, the uniformity of the optical path difference can be improved while the conductivity is improved, so that the commercial use requirement of a conductive silicon carbide substrate is met.

Description

Technical Field

[0001] The present application relates to a conductive silicon carbide crystal and a silicon carbide substrate with good uniformity of optical path difference, and belongs to the technical field of silicon carbide material preparation. Background Art

[0002] Conductive silicon carbide substrates are mainly used to manufacture power devices such as Schottky diodes, MOSFETs, and IGBTs. Currently, conductive silicon carbide substrates are mainly grown using the physical vapor phase method (PVT). During preparation, silicon carbide powder is added to a crucible and then doped with nitrogen to reduce the resistivity of the material. The higher the resistivity, the better the conductivity of the material.

[0003] However, if you want to reduce the resistivity of conductive silicon carbide crystals as much as possible, you often use the method of increasing the nitrogen doping amount to achieve this, but this method will increase the residual stress inside the crystal and cause the stress distribution to be uneven. In the presence of this increased and unevenly distributed stress, polarized light will be refracted in two different directions when passing through the silicon carbide substrate, resulting in a certain optical path difference between the two directions of light, so the uniformity of the optical path difference of the silicon carbide substrate is also worse.

[0004] In addition, there will be axial and radial temperature gradients during the growth of silicon carbide, and the temperature gradient will be characterized by continuous gradual change, which will lead to uneven nitrogen doping and make the resistivity in the crystal different. Usually, the resistivity difference of crystals above 30mΩ·cm is not large. However, when the resistivity is further reduced, that is, when the nitrogen doping amount is increased, the unevenness of nitrogen doping will be further increased, thereby exacerbating the problem of uneven resistivity in the axial and radial directions of the crystal, making it difficult to meet the use requirements. Summary of the invention

[0005] In order to solve the above problems, a conductive silicon carbide crystal and a silicon carbide substrate with good optical path difference uniformity are provided. The conductive silicon carbide crystal can improve the uniformity of the optical path difference while improving the conductivity, thereby meeting the commercial use requirements of the conductive silicon carbide substrate.

[0006] According to one aspect of the present application, a conductive silicon carbide crystal with good optical path difference uniformity is provided, wherein the resistivity at any position of the silicon carbide crystal is less than 30 mΩ·cm;

[0007] The silicon carbide crystal is used to prepare 1 to N silicon carbide substrates, where N is a positive integer representing the serial number of the silicon carbide substrate, and the value is 1 from the first silicon carbide substrate of the silicon carbide crystal including the first end face, and the optical path difference of any silicon carbide substrate meets the following formula:

[0008] △=a(N-1)+b, where △ represents the optical path difference, the unit is nm, the value range of a is -0.8 to 0.8, and the value of b is 0.5 to 8, the unit is nm.

[0009] The several silicon carbide substrates obtained from the conductive silicon carbide crystal of the present application all conform to the formula △=a(N-1)+b, which proves that the optical path difference and stress of the crystal are well distributed uniformly in the axial direction of the crystal, and all silicon carbide substrates obtained from the silicon carbide crystal are well consistent.

[0010] However, for different silicon carbide substrates prepared from the same silicon carbide crystal rod, not all a and b are the same. As long as each silicon carbide substrate independently meets the formula, it is the silicon carbide crystal protected by this application.

[0011] After the silicon carbide crystal is ground flat at both ends, 1 to N SiC substrates are prepared. The silicon carbide substrate including the first end face in the present application is the first substrate obtained by processing one end of the ground SiC crystal.

[0012] Optionally, among the 1 to N silicon carbide substrates prepared from the silicon carbide crystal, a and b of at least three adjacent (serial numbered) silicon carbide substrates are the same. In this case, the optical path difference between adjacent silicon carbide substrates is based on the value of b and transitions uniformly according to the slope a, thereby indicating that the axial uniformity of the silicon carbide crystal is good.

[0013] Preferably, among the 1 to N silicon carbide substrates prepared from the silicon carbide crystal, a and b of at least five adjacent (with consecutive numbers) silicon carbide substrates are the same.

[0014] The statistical optical path difference of the silicon carbide substrate is fitted to obtain a fitting curve. The chi-square (R 2 ) needs to be greater than 0.98 to be representative. The above a and b refer to R 2 The values ​​obtained from the fitted curve are greater than 0.98.

[0015] 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 silicon carbide 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 silicon carbide crystals and silicon carbide 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 silicon carbide products with significantly improved quality.

[0016] If a and b of all silicon carbide substrates prepared from silicon carbide crystals are the same, it proves that the silicon carbide crystal as a whole gradually changes according to a constant slope a. At this time, the trend of the optical path difference of the silicon carbide crystal in the axial direction can be gradually decreasing from one end including the first end face to the other end, and the value range of a is -0.002 to -0.8. It can also be gradually increasing from one end including the first end face to the other end, and the value range of a is 0.002 to 0.8. In either case, it represents that the conductive silicon carbide crystal of the present application has a uniform distribution of optical path difference in the axial direction and high overall uniformity.

[0017] Optionally, the value range of a is -0.002 to 0.2 or 0.002 to 0.2.

[0018] Optionally, any silicon carbide substrate is divided into a plurality of positive direction regions with a side length of 5 mm, and each square region obtains an optical path difference of the region;

[0019] OPD1-OPD2≤6.5nm, OPD1 represents the maximum value of the optical path difference in all square areas, and OPD2 represents the minimum value of the optical path difference in all square areas.

[0020] Preferably, 0.15≤OPD1-OPD2≤6.5nm.

[0021] For the entire silicon carbide substrate, each area will have an optical path difference. If all areas are compared, the maximum value minus the minimum value can represent the two extreme values ​​of the silicon carbide substrate. Therefore, the smaller the value of OPD1-OPD2 is, the more uniform the overall quality of the silicon carbide substrate in the radial direction.

[0022] Optionally, for any two adjacent square areas of any silicon carbide substrate, OPD3-OPD4≤5nm, OPD3 represents a larger value of the optical path difference between the two adjacent square areas, and OPD4 represents a smaller value of the optical path difference between the two adjacent square areas.

[0023] Preferably, 0.02≤OPD3-OPD4≤3.5nm.

[0024] By comparing two adjacent square areas, the difference between the adjacent areas can be obtained, which represents the degree of uniform transition of the optical path difference of the silicon carbide substrate. Therefore, OPD3-OPD4 represents the uniformity of the distribution of the optical path difference of the silicon carbide substrate at the microscopic level. This parameter combined with OPD1-OPD2 jointly proves that the optical path difference consistency of the silicon carbide substrate of the present application is high.

[0025] Optionally, any silicon carbide substrate is divided into a plurality of square regions with a side length of 5 mm, and each square region obtains a resistivity of the region;

[0026] R1-R2≤10mΩ·cm, R1 represents the maximum value of the optical path difference in all square areas, and R2 represents the minimum value of the resistivity in all square areas;

[0027] Preferably, 0.2≤R1-R2≤10mΩ·cm.

[0028] This parameter indicates the resistivity distribution uniformity of the silicon carbide substrate. The smaller the value of R1-R2 is, the more uniform the resistivity distribution of the silicon carbide substrate is in the radial direction.

[0029] In summary, the silicon carbide crystal of the present application can not only achieve a dual reduction in resistivity and optical path difference, but also achieve uniform distribution of resistivity and optical path difference in the radial and axial directions, so as to meet the commercial production and use of silicon carbide crystals.

[0030] According to another aspect of the present application, a conductive silicon carbide substrate with good uniformity of optical path difference is provided, wherein the resistivity at any position of the silicon carbide substrate is <30 mΩ·cm, and the optical path difference of the silicon carbide substrate is <9 nm.

[0031] Optionally, a difference between a maximum value and a minimum value of an optical path difference on any horizontal line of the silicon carbide substrate is less than 6.5 nm.

[0032] Optionally, the silicon carbide substrate is divided into a plurality of positive direction regions with a side length of 5 mm, and each square region obtains an optical path difference of the region;

[0033] OPD1-OPD2≤6.5nm, OPD1 represents the maximum value of the optical path difference in all square areas, and OPD2 represents the minimum value of the optical path difference in all square areas.

[0034] Preferably, 0.15≤OPD1-OPD2≤6.5nm.

[0035] Optionally, for any two adjacent square areas of the silicon carbide substrate, OPD3-OPD4≤5nm, OPD3 represents a larger value of the optical path difference between the two adjacent square areas, and OPD4 represents a smaller value of the optical path difference between the two adjacent square areas.

[0036] Preferably, 0.02≤OPD3-OPD4≤3.5nm.

[0037] Optionally, the silicon carbide substrate is divided into a plurality of square regions with a side length of 5 mm, and each square region obtains a resistivity of the region;

[0038] R1-R2≤10mΩ·cm, R1 represents the maximum value of the optical path difference in all square areas, and R2 represents the minimum value of the resistivity in all square areas.

[0039] Preferably, 0.2≤R1-R2≤10mΩ·cm.

[0040] Optionally, the area within a radius of 1 / 5 of the silicon carbide substrate is a central area, the area within a radius of 1 / 5 to 3 / 5 is a first annular area, the area within a radius of 3 / 5 to 4 / 5 is a second annular area, and the area outside a radius of 4 / 5 is a third annular area;

[0041] The standard deviation coefficient of the central area is < the standard deviation coefficient of the first annular area < the standard deviation coefficient of the second annular area < the standard deviation coefficient of the third annular area. The standard deviation coefficient is defined as the ratio of the standard deviation of the optical path difference in the area to the mean of the optical path difference in the area.

[0042] Optionally, the standard deviation coefficient of the central area is <1.1, the standard deviation coefficient of the first annular area is <1.2, the standard deviation coefficient of the second annular area is <1.3, and the standard deviation coefficient of the third annular area is <1.5.

[0043] Optionally, the silicon carbide crystal and the silicon carbide substrate are both single crystals.

[0044] Optionally, the crystal type of the silicon carbide crystal and the silicon carbide substrate is selected from one of 4H, 6H, and 3C, preferably 4H.

[0045] Optionally, the size of the silicon carbide crystal and the silicon carbide substrate is selected from one of 4 inches, 6 inches, 8 inches, and 12 inches, preferably 8 inches or 12 inches.

[0046] Optionally, the thickness of the silicon carbide substrate is less than 1 mm.

[0047] The beneficial effects of this application include but are not limited to:

[0048] 1. The conductive silicon carbide crystal and silicon carbide substrate with good uniformity of optical path difference according to the present application can reduce stress and lattice distortion inside the material on the basis of improving conductivity, thereby reducing the value of the optical path difference and improving the application prospects of silicon carbide crystals and silicon carbide substrates.

[0049] 2. According to the conductive silicon carbide crystal and silicon carbide substrate with good optical path difference uniformity of the present application, it is possible to achieve improved conductivity and uniform distribution of conductivity, thereby increasing the usable area of ​​the material, reducing production costs, and improving the stability and reliability of the material, facilitating downstream production and utilization.

[0050] 3. According to the conductive silicon carbide crystal and silicon carbide substrate of the present application, the internal optical path difference is small and can be evenly distributed in the axial and radial directions, which means that the residual stress and lattice distortion inside the material are small, thereby improving the overall uniformity of the conductive silicon carbide crystal and silicon carbide substrate.

[0051] 4. According to the conductive silicon carbide crystal and silicon carbide substrate of the present application, the synergistic improvement and uniform distribution of the material conductivity and optical path difference performance are achieved to obtain high-quality products, improve the performance uniformity of batch products, and promote their use through industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] 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:

[0053] 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;

[0054] Figure 2 This is an optical path difference test diagram of one of the silicon carbide substrates of silicon carbide crystal 1# prepared in Example 2 of the present application.

[0055] List of parts and reference numerals:

[0056] 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

[0057] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0058] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0059] Unless otherwise specified, the methods used in the embodiments of the present application are conventional methods in the prior art.

[0060] Example 1

[0061] 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.

[0062] 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 silicon carbide, and thus ensuring the quality of silicon carbide products.

[0063] 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.

[0064] 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 silicon carbide atmosphere during the crystal growth process and affecting their subsequent normal operation.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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 silicon carbide crystal growth process.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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;

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] Example 2

[0085] The silicon carbide crystal prepared in this embodiment is grown using the induction crystal growth furnace of Example 1. The specific crystal growth method is as follows:

[0086] (1) Place the raw materials in a crystal growth furnace, first raise the temperature to 800-1200°C within 3-5 hours, maintain for 3-5 hours, and the pressure is 70-80 mbar, during which Ar = 0 sccm, N2 = 0 sccm;

[0087] (2) Then, the temperature is raised to 1500-1800°C within 3-7 hours and maintained for 3-5 hours at a pressure of 35-55 mbar, during which time 200-250 sccm of Ar gas and 20-30 sccm of N2 gas are introduced;

[0088] (3) Then, the temperature is raised to 1900-2100°C within 25-30 hours, the pressure is 20-30 mabr, and maintained for 30-45 hours, during which time 190-220 sccm of Ar gas and 30-40 sccm of N2 gas are introduced.

[0089] (4) Finally, the temperature is raised to 2200-2300°C within 10-15 hours, the pressure is adjusted to 10-15 mabr, and maintained for 100-120 hours for crystal growth. During this period, 50-80 sccm of Ar gas and 20-30 sccm of N2 gas are introduced. After the crystal growth is completed, the temperature is naturally lowered and the furnace is opened to obtain the crystal.

[0090] Silicon carbide crystals 1# to 6# are prepared according to the above-mentioned crystal growth method. The specific crystal growth method is as follows:

[0091] Silicon carbide crystal 1#

[0092] (1) Place the raw materials in a crystal growth furnace, first raise the temperature to 800°C within 3 hours, maintain for 5 hours, and the pressure is 70 mbar, during which Ar = 0 sccm, N2 = 0 sccm;

[0093] (2) The temperature was then raised to 1500°C within 3 hours and maintained for 5 hours at a pressure of 55 mbar, during which time 200 sccm of Ar gas and 30 sccm of N2 gas were introduced;

[0094] (3) The temperature was then raised to 1900°C within 25 hours, the pressure was 30 mabr, and maintained for 45 hours, during which time 200 sccm of Ar gas and 30 sccm of N2 gas were introduced;

[0095] (4) Finally, the temperature was raised to 2200°C within 10 hours, the pressure was adjusted to 12 mabr, and the temperature was maintained for 120 hours for crystal growth. During this period, 50 sccm of Ar gas and 30 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0096] Silicon carbide crystal 2#

[0097] (1) Place the raw materials in a crystal growth furnace, first raise the temperature to 900°C within 3 hours, maintain for 5 hours, and the pressure is 72 mbar, during which Ar = 0 sccm, N2 = 0 sccm;

[0098] (2) The temperature was then raised to 1600°C within 3 h and maintained at a pressure of 50 mbar for 3 h, during which time 240 sccm of Ar gas and 30 sccm of N2 gas were introduced;

[0099] (3) The temperature was then raised to 1900°C within 25 hours, the pressure was 20 mabr, and maintained for 35 hours, during which time 190 sccm of Ar gas and 40 sccm of N2 gas were introduced;

[0100] (4) Finally, the temperature was raised to 2210°C within 15 hours, the pressure was adjusted to 10 mabr, and maintained for 120 hours for crystal growth. During this period, 80 sccm of Ar gas and 30 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0101] Silicon carbide crystal 3#

[0102] (1) Place the raw materials in a crystal growth furnace, first raise the temperature to 1000°C within 4 hours, maintain for 4 hours, and the pressure is 75 mbar, during which Ar = 0 sccm, N2 = 0 sccm;

[0103] (2) The temperature was raised to 1650°C within 5 hours and maintained for 4 hours at a pressure of 45 mbar, during which time 220 sccm of Ar gas and 25 sccm of N2 gas were introduced;

[0104] (3) The temperature was then raised to 2000°C within 28 hours, the pressure was 25 mabr, and maintained for 40 hours, during which time 210 sccm of Ar gas and 35 sccm of N2 gas were introduced;

[0105] (4) Finally, the temperature was raised to 2230°C within 12 hours, the pressure was adjusted to 14 mabr, and maintained for 110 hours for crystal growth. During this period, 60 sccm of Ar gas and 26 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0106] Silicon carbide crystal 4#

[0107] (1) Place the raw materials in a crystal growth furnace, first raise the temperature to 1050°C within 4 hours, maintain for 4 hours, and the pressure is 75 mbar, during which Ar = 0 sccm, N2 = 0 sccm;

[0108] (2) The temperature was then raised to 1700°C within 5 h and maintained for 4 h at a pressure of 45 mbar, during which time 230 sccm of Ar gas and 22 sccm of N2 gas were introduced;

[0109] (3) The temperature was then raised to 1950 °C within 30 h, the pressure was 28 mabr, and maintained for 40 h, during which time 200 sccm of Ar gas and 35 sccm of N2 gas were introduced;

[0110] (4) Finally, the temperature was raised to 2250°C within 12 hours, the pressure was adjusted to 15 mabr, and maintained for 110 hours for crystal growth. During this period, 70 sccm of Ar gas and 25 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0111] Silicon carbide crystal 5#

[0112] (1) Place the raw materials in a crystal growth furnace, first raise the temperature to 1100°C within 5 hours, maintain for 3.5 hours, and the pressure is 78 mbar, during which Ar = 0 sccm, N2 = 0 sccm;

[0113] (2) The temperature was then raised to 1750°C within 6 hours and maintained for 5 hours at a pressure of 40 mbar, during which time 210 sccm of Ar gas and 30 sccm of N2 gas were introduced;

[0114] (3) The temperature was then raised to 2050°C within 28 hours, the pressure was 20 mabr, and maintained for 38 hours, during which time 190 sccm of Ar gas and 30 sccm of N2 gas were introduced;

[0115] (4) Finally, the temperature was raised to 2280°C within 15 hours, the pressure was adjusted to 15 mabr, and maintained for 100 hours for crystal growth. During this period, 80 sccm of Ar gas and 20 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0116] Silicon carbide crystal 6#

[0117] (1) Place the raw materials in a crystal growth furnace, first raise the temperature to 1200°C within 5 hours, maintain for 3 hours, and the pressure is 80 mbar, during which Ar = 0 sccm, N2 = 0 sccm;

[0118] (2) The temperature was then raised to 1800°C within 7 hours and maintained for 3 hours at a pressure of 35 mbar, during which time 250 sccm of Ar gas and 20 sccm of N2 gas were introduced;

[0119] (3) The temperature was then raised to 2100°C within 25 hours, the pressure was 30 mabr, and maintained for 30 hours, during which time 210 sccm of Ar gas and 40 sccm of N2 gas were introduced;

[0120] (4) Finally, the temperature was raised to 2300°C within 15 hours, the pressure was adjusted to 10 mabr, and maintained for 100 hours for crystal growth. During this period, 50 sccm of Ar gas and 20 sccm of N2 gas were introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.

[0121] The silicon carbide substrates are obtained by cutting, grinding and polishing each of the silicon carbide crystals prepared above. All the silicon carbide substrates prepared from each silicon carbide crystal are named 1 to N, where N is a positive integer and represents the serial number of the silicon carbide substrate. The first silicon carbide substrate including the first end face of the silicon carbide crystal is 1. The surface roughness Ra of the silicon carbide substrate after polishing is not greater than 10 nm and the thickness is 500 microns.

[0122] The parameters obtained by performing polarized light testing on each silicon carbide substrate obtained from each silicon carbide crystal are as follows:

[0123] 1. Convert the light source into polarized light through a polarizer,

[0124] 2. Polarized light is transmitted through a polished and transparent single-crystal silicon carbide substrate through a preset optical path. When there is residual stress in the silicon carbide 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.

[0125] 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, and appear bright, thereby achieving the residual stress characterization and analysis of the silicon carbide single crystal substrate;

[0126]

[0127] in,

[0128] Δ: optical path difference between ordinary light (o light) and extraordinary light (e light);

[0129] d: sample thickness;

[0130] Δn: The difference in refractive index between ordinary light (o light) and extraordinary light (e light);

[0131] λ: wavelength

[0132] 1 to N silicon carbide substrates are obtained from a silicon carbide crystal, and each silicon carbide 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 silicon carbide substrates obtained from the silicon carbide crystal, so the several silicon carbide substrates obtained from the entire silicon carbide crystal are less than or equal to the values ​​in Table 1; similarly, the value with "minimum value" refers to the minimum value obtained by testing among several silicon carbide substrates obtained from the silicon carbide crystal. And the optical path differences of 1 to N silicon carbide substrates are statistically analyzed to determine whether they meet △ = a (N-1) + b. The test results are shown in Table 1. In Table 1, "the maximum number of adjacent silicon carbide substrates when the values ​​of a and b are the same" refers to the fitting curve obtained by fitting the optical path differences of these silicon carbide substrates. The chi-square (R 2 ) are greater than 0.98. For example, the curve of the optical path difference fitting of the four adjacent silicon carbide substrates of silicon carbide crystal 1#, chi-square (R 2 ) is greater than 0.98, and a and b at this time are selected as the common a and b of the three adjacent silicon carbide substrates.

[0133] The silicon carbide crystals 1# to 3# prepared above are all 8 inches, the 1 / 5 radius of the silicon carbide substrate is the central area, the 1 / 5 to 3 / 5 radius area is the first annular area, the 3 / 5 to 4 / 5 radius area is the second annular area, and the 4 / 5 radius area is the third annular area. The square area refers to dividing the silicon carbide substrate into several square areas with a side length of 5 mm.

[0134] Table 1

[0135]

[0136]

[0137] Figure 2 This is an optical path difference test diagram of one of the silicon carbide substrates of silicon carbide crystal 1#. According to the diagram, it can be seen that the optical path difference of the silicon carbide substrate is well distributed uniformly in the radial direction, and the overall quality is significantly improved.

[0138] 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 conductive silicon carbide crystal with good uniformity of optical path difference, characterized in that: The resistivity at any position of the silicon carbide crystal is less than 30 mΩ·cm; The silicon carbide crystal is used to prepare 1 to N silicon carbide substrates, where N is a positive integer representing the serial number of the silicon carbide substrate, and the value of the first silicon carbide substrate including the first end face of the silicon carbide crystal is 1. The optical path difference of any silicon carbide substrate meets the following formula: △=a(N-1)+b, where △ represents the optical path difference, the unit is nm, the value range of a is -0.8 to 0.8, and the value of b is 0.5 to 8, the unit is nm.

2. The conductive silicon carbide crystal with good optical path difference uniformity according to claim 1, characterized in that: The value range of a is -0.002 to 0.2 or 0.002 to 0.

2.

3. The conductive silicon carbide crystal with good optical path difference uniformity according to claim 1, characterized in that: Any silicon carbide substrate is divided into a number of square areas with a side length of 5 mm, and each square area obtains an optical path difference of the area; OPD1-OPD2≤6.5nm, OPD1 represents the maximum optical path difference in all square areas, and OPD2 represents the minimum optical path difference in all square areas; Preferably, 0.15≤OPD1-OPD2≤6.5nm.

4. The conductive silicon carbide crystal with good optical path difference uniformity according to claim 3, characterized in that: For any two adjacent square areas of any silicon carbide substrate, OPD3-OPD4≤5nm, OPD3 represents the larger value of the optical path difference between the two adjacent square areas, and OPD4 represents the smaller value of the optical path difference between the two adjacent square areas.

5. The conductive silicon carbide crystal with good optical path difference uniformity according to claim 1, characterized in that: Any silicon carbide substrate is divided into a number of square regions with a side length of 5 mm, and each square region obtains a resistivity of the region; R1-R2≤10mΩ·cm, R1 represents the maximum value of the optical path difference in all square areas, and R2 represents the minimum value of the resistivity in all square areas.

6. A conductive silicon carbide substrate with good optical path difference uniformity, characterized in that: The resistivity of the silicon carbide substrate at any position is less than 30 mΩ·cm, and the optical path difference of the silicon carbide substrate is less than 9 nm.

7. The conductive silicon carbide substrate with good optical path difference uniformity according to claim 6, characterized in that: The difference between the maximum value and the minimum value of the optical path difference on any horizontal line of the silicon carbide substrate is less than 6.5 nm.

8. The conductive silicon carbide substrate with good optical path difference uniformity according to claim 6, characterized in that: The silicon carbide substrate has a central area within a radius of 1 / 5, a first annular area within a radius of 1 / 5 to 3 / 5, a second annular area within a radius of 3 / 5 to 4 / 5, and a third annular area outside a radius of 4 / 5. The standard deviation coefficient of the central area is < the standard deviation coefficient of the first annular area < the standard deviation coefficient of the second annular area < the standard deviation coefficient of the third annular area. The standard deviation coefficient is defined as the ratio of the standard deviation of the optical path difference in the area to the mean of the optical path difference in the area.

9. The conductive silicon carbide substrate with good optical path difference uniformity according to claim 8, characterized in that: The standard deviation coefficient of the central area is <1.1, the standard deviation coefficient of the first annular area is <1.2, the standard deviation coefficient of the second annular area is <1.3, and the standard deviation coefficient of the third annular area is <1.

5.

10. The conductive silicon carbide substrate with good optical path difference uniformity according to claim 6, characterized in that: The size of the silicon carbide substrate is selected from 4 inches, 6 inches, 8 inches, and 12 inches, preferably 8 inches or 12 inches.

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