Semi-insulating silicon carbide crystal with small optical path difference and silicon carbide substrate
By preparing a silicon carbide substrate that conforms to the specific optical path difference formula, the problems of large optical path difference and uneven resistivity distribution in the prior art are solved, the reduction of optical path difference and distribution uniformity are achieved, and the electrical performance uniformity and commercial application prospects of the substrate are improved.
Patent Information
- Application Number
- CN202411665021.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-20
- Publication Date
- 2025-02-25
AI Technical Summary
The existing semi-insulated silicon carbide substrates have problems such as large optical path difference and uneven resistivity distribution, which affects their performance at high temperatures and high breakdown voltages.
By preparing a silicon carbide substrate that conforms to the formula △=a(N-1)+b, the distribution of optical path difference is controlled to make it uniform in the axial and radial directions, and the overall uniformity of the substrate is improved.
The reduction of optical path difference and distribution uniformity are achieved, and the electrical performance uniformity and commercial application prospects of semi-insulated silicon carbide substrates are improved.
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Figure CN119507049A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to a semi-insulating silicon carbide crystal with a small optical path difference and a silicon carbide substrate, belonging to the technical field of silicon carbide material preparation. Background Art
[0002] Due to the design requirements of downstream devices, semi-insulating silicon carbide substrates are not doped to obtain high resistivity, which effectively suppresses parasitic capacitance and parasitic inductance, thus having strong high temperature resistance and high breakdown voltage strength, and is suitable for high-power microwave devices. In order to improve the resistivity, the raw material purity is usually required to be very high. Due to the axial and radial temperature gradients in the current crystal growth temperature field, the residual stress of the semi-insulating silicon carbide crystal will increase and the resistivity distribution will be uneven.
[0003] In addition, the process of obtaining a semi-insulating silicon carbide substrate by cutting, grinding, polishing, etc. of the semi-insulating silicon carbide crystal will also introduce processing stress to the substrate surface. Due to the existence of the above-mentioned growth stress, surface processing stress and external 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. The greater the force on the silicon carbide substrate, the greater the optical path difference.
[0004] Therefore, there is currently a lack of a silicon carbide crystal and a silicon carbide substrate with good semi-insulating properties and small optical path difference. Summary of the invention
[0005] In order to solve the above problems, a semi-insulating silicon carbide crystal and a silicon carbide substrate with a small optical path difference are provided. The semi-insulating silicon carbide crystal can not only meet the semi-insulating performance required for manufacturing radio frequency devices, optoelectronic devices, etc., but also reduce the optical path difference, so as to improve the commercial application prospects of the semi-insulating silicon carbide substrate.
[0006] According to one aspect of the present application, a semi-insulating silicon carbide crystal with a small optical path difference is provided, wherein the resistivity at any position of the silicon carbide crystal is greater than 10 6 Ω·cm;
[0007] The silicon carbide crystal is prepared to obtain 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 -1 to 1, and the value of b is 0.5 to 10.5, the unit is nm.
[0009] The silicon carbide substrates obtained from the semi-insulating silicon carbide crystal of the present application all conform to the formula △=a(N-1)+b, proving 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. 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 conforms to the formula, it is the silicon carbide crystal protected by the present application.
[0010] 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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 -0.004 to -1. 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 0.004 to 1. In either case, it represents that the optical path difference of the semi-insulating silicon carbide crystal of the present application is uniformly distributed in the axial direction, and the overall uniformity is high.
[0016] Optionally, the value range of a is -0.004 to -0.4 or 0.004 to 0.4.
[0017] 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 an optical path difference of the region;
[0018] The standard deviation of the optical path difference calculated for all square areas is less than 3 nm.
[0019] Optionally, the optical path difference standard deviation coefficient of any silicon carbide substrate is ≤1.25 and ≥0.65, and the optical path difference standard deviation coefficient refers to the ratio of the optical path difference standard deviation calculated for all square areas to the optical path difference mean.
[0020] The above parameters indicate that the optical path difference of the semi-insulating silicon carbide crystal of the present application can be uniformly distributed in the radial direction, which, combined with the axial uniformity distribution, allows the silicon carbide substrate obtained from each crystal to have small differences, thereby improving the performance stability of mass-produced silicon carbide substrates.
[0021] Optionally, any silicon carbide substrate is divided into a number of square areas with a side length of 5 mm, and each square area obtains a resistivity of the area. The resistivity standard deviation coefficient of any silicon carbide substrate is ≤1.45 and ≥0.15, and the resistivity standard deviation coefficient refers to the ratio of the resistivity standard deviation calculated for all square areas to the resistivity mean.
[0022] Preferably, 0.65≤resistivity standard deviation coefficient≤1.25.
[0023] While the radial distribution of the optical path difference of the semi-insulating silicon carbide crystal is uniform, the radial uniformity of the silicon carbide substrate prepared from the crystal is also better, which can improve the uniformity of the electrical properties of the crystal.
[0024] According to another aspect of the present application, a semi-insulating silicon carbide substrate with a small optical path difference is provided, wherein the resistivity at any position of the silicon carbide substrate is greater than 10 6 Ω·cm, and the optical path difference of the silicon carbide substrate is less than 10.5nm.
[0025] Preferably, the optical path difference of the silicon carbide substrate is less than 10.5 nm.
[0026] The optical path difference of the silicon carbide substrate of the present application is small, and the standard deviation is also small, which means that the silicon carbide substrate can achieve a uniform distribution of the optical path difference on the basis of reducing the optical path difference, thereby improving the performance consistency of the single silicon carbide substrate, so that the performance of the device prepared using the silicon carbide substrate tends to be consistent, thereby improving the stability and reliability of the device.
[0027] Optionally, a standard deviation of an optical path difference on any horizontal line of the silicon carbide substrate is less than 2 nm.
[0028] 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 an optical path difference of the region;
[0029] The standard deviation of the optical path difference calculated for all square areas is less than 3 nm.
[0030] Optionally, the optical path difference standard deviation coefficient of the silicon carbide substrate is ≤1.25 and ≥0.65, and the optical path difference standard deviation coefficient refers to the ratio of the optical path difference standard deviation calculated for all square areas to the optical path difference mean.
[0031] Optionally, the silicon carbide substrate is divided into a plurality of square areas with a side length of 5 mm, each square area obtains a resistivity of the area, and the resistivity standard deviation coefficient of the silicon carbide substrate is ≤1.45 and ≥0.15, and the resistivity standard deviation coefficient refers to the ratio of the resistivity standard deviation calculated for all square areas to the resistivity mean.
[0032] Preferably, 0.65≤resistivity standard deviation coefficient≤1.25.
[0033] Optionally, the area within a radius of 1 / 3 of the silicon carbide substrate is the central area, the area within a radius of 1 / 3 to 1 / 2 is the first annular area, the area within a radius of 1 / 2 to 5 / 6 is the second annular area, and the area outside a radius of 5 / 6 is the third annular area;
[0034] 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.
[0035] Optionally, the standard deviation coefficient of the central area is <1.2, the standard deviation coefficient of the first annular area is <1.3, the standard deviation coefficient of the second annular area is <1.4, and the standard deviation coefficient of the third annular area is <1.6.
[0036] Optionally, the silicon carbide crystal and the silicon carbide substrate are both single crystals.
[0037] 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.
[0038] 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.
[0039] Optionally, the thickness of the silicon carbide substrate is less than 1 mm.
[0040] The beneficial effects of this application include but are not limited to:
[0041] 1. The semi-insulating silicon carbide crystal of the present application complies with the formula △=a(N-1)+b, which is used to characterize the axial uniformity of the semi-insulating silicon carbide crystal, proving that the optical path difference of the semi-insulating silicon carbide crystal can transition uniformly from one end of the crystal to the other end along a certain slope, and the axial distribution uniformity of stress is good.
[0042] 2. The semi-insulating silicon carbide crystal and silicon carbide substrate with small optical path difference of the present application can reduce the optical path difference while also reducing the variability of the optical path difference, so as to improve the overall uniformity of the semi-insulating silicon carbide.
[0043] 3. The semi-insulating silicon carbide crystal and silicon carbide substrate with small optical path difference according to the present application have higher resistivity and lower residual stress, which can improve the stability and reliability of the material, thereby facilitating downstream production and utilization and facilitating industrial promotion and use.
[0044] 4. According to the semi-insulating silicon carbide crystal and silicon carbide substrate with small optical path difference of the present application, the optical path difference is used for performance characterization, which can eliminate the differences caused by the different wavelengths of polarized light and can more intuitively reflect the lattice distortion or residual stress inside and on the surface of the material. The optical path difference of the above materials is small, which means that the lattice distortion or residual stress inside and on the surface is small. BRIEF DESCRIPTION OF THE DRAWINGS
[0045] 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:
[0046] 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;
[0047] Figure 2 This is an optical path difference test diagram of one of the silicon carbide substrates of silicon carbide crystal 6# prepared in Example 2 of the present application.
[0048] List of parts and reference numerals:
[0049] 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
[0050] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.
[0051] Unless otherwise specified, the raw materials in the examples and comparative examples of the present application were purchased through commercial channels.
[0052] Unless otherwise specified, the methods used in the examples and comparative examples of the present application are conventional methods in the prior art.
[0053] Example 1
[0054] 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.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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;
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
[0073] 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.
[0074] 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.
[0075] 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.
[0076] 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.
[0077] Example 2
[0078] 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:
[0079] (1) placing the raw materials in a crystal growth furnace, first raising the temperature to 800-1200°C within 3-5 hours, maintaining the temperature for 3-4 hours, and the pressure is 80-100 mbar, during which no Ar gas is introduced;
[0080] (2) Then, the temperature is raised to 1200-1800°C within 3-7 hours, maintained for 3-5 hours, and the pressure is 70-80 mbar, during which time 200-250 sccm of Ar gas is introduced;
[0081] (3) Then, the temperature is raised to 1900-2000°C within 5-15 hours, the pressure is 35-40 mAbr, and maintained for 10-15 hours, during which time 150-200 sccm of Ar gas is introduced.
[0082] (4) Finally, the temperature is raised to 2200-2300°C within 30-35 hours, the pressure is adjusted to 5-15 mabr, and maintained for 130-140 hours for crystal growth. During this period, 50-80 sccm of Ar gas is introduced. After the crystal growth is completed, the temperature is naturally lowered and the furnace is opened to obtain the crystal.
[0083] Silicon carbide crystals 1# to 6# are prepared according to the above-mentioned crystal growth method. The specific crystal growth method is as follows:
[0084] Silicon carbide crystal 1#
[0085] (1) The raw materials were placed in a crystal growth furnace, and the temperature was first raised to 800°C within 5 hours, and maintained for 3 hours at a pressure of 80 mbar, during which no Ar gas was introduced;
[0086] (2) The temperature was then raised to 1200 °C within 3 h and maintained for 5 h at a pressure of 70 mbar, during which time 200 sccm of Ar gas was introduced;
[0087] (3) The temperature was then raised to 1900 °C within 5 h, the pressure was 35 mAbr, and maintained for 15 h, during which time 150 sccm of Ar gas was introduced;
[0088] (4) Finally, the temperature was raised to 2200°C within 30 hours, the pressure was adjusted to 5 mabr, and maintained for 140 hours for crystal growth. During this period, 50 sccm of Ar gas was introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.
[0089] Silicon carbide crystal 2#
[0090] (1) The raw materials were placed in a crystal growth furnace, and the temperature was first raised to 900°C within 3 hours, and maintained for 4 hours at a pressure of 85 mbar, during which no Ar gas was introduced;
[0091] (2) The temperature was then raised to 1300 °C within 4 h and maintained for 5 h at a pressure of 75 mbar, during which time 210 sccm of Ar gas was introduced;
[0092] (3) The temperature was then raised to 1920 °C within 7 h, the pressure was 35 mabr, and maintained for 13 h, during which time 160 sccm of Ar gas was introduced;
[0093] (4) Finally, the temperature was raised to 2230°C within 30 hours, the pressure was adjusted to 7 mabr, and the temperature was maintained for 140 hours for crystal growth. During this period, 55 sccm of Ar gas was introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.
[0094] Silicon carbide crystal 3#
[0095] (1) Place the raw materials in a crystal growth furnace, first raise the temperature to 1000°C within 3-5 hours, maintain for -4 hours, and the pressure is 90 mbar, during which no Ar gas is introduced;
[0096] (2) The temperature was then raised to 1400 °C within 7 h and maintained for 5 h at a pressure of 76 mbar, during which time 230 sccm of Ar gas was introduced;
[0097] (3) The temperature was then raised to 1950 °C within 15 h, the pressure was 37 mabr, and maintained for 14 h, during which time 170 sccm of Ar gas was introduced;
[0098] (4) Finally, the temperature was raised to 2240°C within 35 hours, the pressure was adjusted to 9 mabr, and maintained for 130 hours for crystal growth. During this period, 60 sccm of Ar gas was introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.
[0099] Silicon carbide crystal 4#
[0100] (1) Place the raw materials in a crystal growth furnace, first raise the temperature to 1050°C within 3-5 hours, maintain for 3.5 hours, and the pressure is 94 mbar, during which no Ar gas is introduced;
[0101] (2) The temperature was then raised to 1600 °C within 7 h and maintained for 3 h at a pressure of 78 mbar, during which time 235 sccm of Ar gas was introduced;
[0102] (3) The temperature was then raised to 1960 °C within 10 h, the pressure was 38 mabr, and maintained for 13 h, during which time 185 sccm of Ar gas was introduced;
[0103] (4) Finally, the temperature was raised to 2250°C within 30 hours, the pressure was adjusted to 10 mabr, and maintained for 140 hours for crystal growth. During this period, 65 sccm of Ar gas was introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.
[0104] Silicon carbide crystal 5#
[0105] (1) The raw materials were placed in a crystal growth furnace, and the temperature was first raised to 1100°C within 3 hours, and maintained for 4 hours at a pressure of 95 mbar, during which no Ar gas was introduced;
[0106] (2) The temperature was then raised to 1700 °C within 6 h and maintained for 4 h at a pressure of 75 mbar, during which time 240 sccm of Ar gas was introduced;
[0107] (3) The temperature was then raised to 1980 °C within 11 h, the pressure was 38 mabr, and maintained for 10 h, during which time 190 sccm of Ar gas was introduced;
[0108] (4) Finally, the temperature was raised to 2280°C within 35 hours, the pressure was adjusted to 13 mabr, and the crystal growth was maintained for 130 hours. During this period, 75 sccm of Ar gas was introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.
[0109] Silicon carbide crystal 6#
[0110] (1) The raw materials were placed in a crystal growth furnace, and the temperature was first raised to 1200°C within 5 hours, and maintained for 3.5 hours at a pressure of 100 mbar, during which no Ar gas was introduced;
[0111] (2) The temperature was then raised to 1800 °C within 7 h and maintained for 3 h at a pressure of 80 mbar, during which time 250 sccm of Ar gas was introduced;
[0112] (3) The temperature was then raised to 2000 °C within 10 h, the pressure was 40 mAbr, and maintained for 10 h, during which time 200 sccm of Ar gas was introduced;
[0113] (4) Finally, the temperature was raised to 2300°C within 35 hours, the pressure was adjusted to 15 mabr, and maintained for 130 hours for crystal growth, during which 80 sccm of Ar gas was introduced. After the crystal growth was completed, the temperature was naturally lowered and the furnace was opened to obtain the crystal.
[0114] The silicon carbide substrates obtained after cutting, grinding and polishing the silicon carbide crystals prepared as above are respectively named 1 to N, where N is a positive integer representing the serial number of the silicon carbide substrate, and 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.
[0115] The parameters obtained by performing polarized light testing on each silicon carbide substrate obtained from each silicon carbide crystal are as follows:
[0116] 1. Convert the light source into polarized light through a polarizer,
[0117] 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.
[0118] 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;
[0119]
[0120] in,
[0121] Δ: optical path difference between ordinary light (o light) and extraordinary light (e light);
[0122] d: sample thickness;
[0123] Δn: The difference in refractive index between ordinary light (o light) and extraordinary light (e light);
[0124] λ: wavelength
[0125] 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 three 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.
[0126] The silicon carbide crystals 1# to 3# prepared above are all 8 inches, the 1 / 3 radius of the silicon carbide substrate is the central area, the 1 / 3 to 1 / 2 radius area is the first annular area, the 1 / 2 to 5 / 6 radius area is the second annular area, and the 5 / 6 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.
[0127] Table 1
[0128]
[0129]
[0130] Figure 2 This is the optical path difference test diagram of one of the silicon carbide substrates of silicon carbide crystal 6#. Through the analysis of the diagram, it can be seen that this silicon carbide substrate has no obvious optical path difference protruding points, the overall optical path difference is small and the distribution uniformity is good.
[0131] 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 semi-insulating silicon carbide crystal with a small optical path difference, characterized in that: The resistivity at any position of the silicon carbide crystal is>10 6 Ω·cm; The silicon carbide crystal is prepared to obtain 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: △=a(N-1)+b, where △ represents the optical path difference, the unit is nm, the value range of a is -1 to 1, and the value of b is 0.5 to 10.5, the unit is nm.
2. The semi-insulating silicon carbide crystal with a small optical path difference according to claim 1, characterized in that: The value range of a is -0.004 to -0.4 or 0.004 to 0.
4.
3. The semi-insulating silicon carbide crystal with a small optical path difference 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; The standard deviation of the optical path difference calculated for all square areas is less than 3 nm.
4. The semi-insulating silicon carbide crystal with a small optical path difference according to claim 3, characterized in that: The optical path difference standard deviation coefficient of any silicon carbide substrate is ≤1.25 and ≥0.65, and the optical path difference standard deviation coefficient refers to the ratio of the optical path difference standard deviation calculated from all square areas to the optical path difference mean.
5. The semi-insulating silicon carbide crystal with a small optical path difference 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 a resistivity of the area. The resistivity standard deviation coefficient of any silicon carbide substrate is ≤1.45 and ≥0.15, and the resistivity standard deviation coefficient refers to the ratio of the resistivity standard deviation calculated for all square areas to the resistivity mean.
6. A semi-insulating silicon carbide substrate with a small optical path difference, characterized in that: The resistivity of the silicon carbide substrate at any position is>10 6 Ω·cm, and the optical path difference of the silicon carbide substrate is ≤10.5nm.
7. The semi-insulating silicon carbide substrate with a small optical path difference according to claim 6, characterized in that: The standard deviation of the optical path difference on any horizontal line of the silicon carbide substrate is less than 2 nm.
8. The semi-insulating silicon carbide substrate with a small optical path difference according to claim 6, characterized in that: The silicon carbide substrate has a central area within a radius of 1 / 3, a first annular area within a radius of 1 / 3 to 1 / 2, a second annular area within a radius of 1 / 2 to 5 / 6, and a third annular area outside a radius of 5 / 6. 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 semi-insulating silicon carbide substrate with a small optical path difference according to claim 8, characterized in that The standard deviation coefficient of the central area is <1.2, the standard deviation coefficient of the first annular area is <1.3, the standard deviation coefficient of the second annular area is <1.4, and the standard deviation coefficient of the third annular area is <1.
6.
10. The semi-insulating silicon carbide substrate with a small optical path difference 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.