A 4H silicon carbide crystal rod with large and uniform curvature radius, preparation method and application thereof

Abstract

The present application discloses a 4H silicon carbide crystal rod with a large and uniformly distributed curvature radius, a preparation method and an application thereof, and belongs to the technical field of 4H silicon carbide crystal rod preparation. The resistivity of the 4H silicon carbide crystal rod at any position is greater than 12mΩ·cm and less than 15mΩ·cm, the curvature radius of the silicon carbide wafer obtained by cutting is greater than 800m, and the curvature radius distribution function of the silicon carbide wafer obtained by cutting in the axial direction is CR=ey+fy 2 +gy 3 The 4H silicon carbide crystal rod reduces the resistivity while increasing the curvature radius of the silicon carbide wafer obtained by cutting, and the curvature radius of the silicon carbide wafer prepared from the same 4H silicon carbide crystal rod is evenly distributed, which can significantly improve the stability of the device prepared using the material.

Description

Technical Field

[0001] The present application relates to a 4H silicon carbide crystal rod with a large and uniformly distributed curvature radius, a preparation method and an application thereof, and belongs to the technical field of 4H silicon carbide crystal rod preparation. Background Art

[0002] Since silicon carbide has excellent electrical and optical properties, it is widely used in new electronic power devices. The resistivity of the silicon carbide substrate will directly affect the on-resistance of the power device, so the current research focus and difficulty is to reduce the resistivity of the substrate.

[0003] At present, the resistivity of silicon carbide substrates on the market is generally between 15 and 25 mΩ·cm. If the resistivity is further reduced, it means increasing the nitrogen doping content, which will increase the residual stress inside the material and make it unevenly distributed. This stress accumulates on the crystal rod as the thickness increases, making the internal stress distribution of the substrate prepared from the same 4H silicon carbide crystal rod uneven, making it difficult to apply in batches. After silicon carbide crystals are doped with more nitrogen, the ionization rate decreases and the free nitrogen content increases, which will reduce the hardness and rigidity of the crystal. Therefore, it is easier to bend during the crystal processing process, and it is difficult to obtain wafers with a large radius of curvature.

[0004] Therefore, there is an urgent need for a 4H silicon carbide crystal rod that can improve the curvature radius and uniform distribution of the 4H silicon carbide crystal rod while ensuring the resistivity. Summary of the invention

[0005] In order to solve the above problems, a 4H silicon carbide crystal rod with a large and uniform curvature radius, a preparation method and an application are provided. The 4H silicon carbide crystal rod reduces the resistivity while increasing the curvature radius of the cut silicon carbide wafer, and the curvature radius of the silicon carbide wafer prepared from the same 4H silicon carbide crystal rod is evenly distributed, providing a new solution for improving the quality of silicon carbide wafers and device performance.

[0006] According to one aspect of the present application, a 4H silicon carbide crystal rod with a large and uniformly distributed curvature radius is provided, wherein the resistivity of the 4H silicon carbide crystal rod at any position is greater than 12 mΩ·cm and less than 15 mΩ·cm, the curvature radius of the silicon carbide wafer obtained by cutting the 4H silicon carbide crystal rod is greater than 800 m, and the curvature radius distribution function of the silicon carbide wafer obtained by cutting the 4H silicon carbide crystal rod in the axial direction is CR=ey+fy 2 +gy 3 +h;

[0007] Wherein, CR is the radius of curvature of the silicon carbide wafer, in m, y is the wafer number of the silicon carbide wafer, and the naming starts from the silicon surface of the 4H silicon carbide crystal rod to the carbon surface, and the first silicon carbide wafer including the silicon surface of the 4H silicon carbide crystal rod is named 1. The thickness of the silicon carbide wafer is 350-500 μm, the value range of e is -4.1~-3.5, the value range of f is 0.17~0.19, the value range of g is 0.15~0.19, and the value range of h is 830~890.

[0008] The curvature radius of the present application is a good means of characterizing the stress of the crystal rod. It can distinguish the stress difference in different directions of the wafer and can also characterize the change trend of the crystal body stress. The curvature radius is an important indicator of the residual stress of the crystal.

[0009] Optionally, the thickness of the 4H silicon carbide crystal rod is greater than 15 mm.

[0010] Optionally, the ratio of the curvature radii of the silicon carbide wafer obtained by cutting the 4H silicon carbide crystal rod in the [1-100] and [11-20] directions is less than 2, preferably less than 1.5.

[0011] The radius of curvature in the [1-100] direction refers to the average value of the inverse of the curvature at multiple points along the [1-100] direction on the entire diameter, and the radius of curvature in the [11-20] direction refers to the average value of the inverse of the curvature at multiple points along the [11-20] direction on the entire diameter. The smaller the ratio, the higher the uniformity of the in-plane stress.

[0012] Optionally, among the silicon carbide wafers obtained by cutting the 4H silicon carbide crystal rod, the difference in curvature radius between any two silicon carbide wafers is less than 25 m, and the difference in curvature radius between two adjacent silicon carbide wafers is less than 2.5 m.

[0013] The first silicon carbide wafer containing the silicon surface of the 4H silicon carbide crystal rod is the head wafer, and the last silicon carbide wafer containing the carbon surface of the 4H silicon carbide crystal rod is the tail wafer. The difference between the curvature radius of the head wafer and the curvature radius of the tail wafer is less than 25 μm. The smaller the difference in the curvature radius between the head wafer and the tail wafer, the more uniform the stress distribution of the 4H silicon carbide crystal rod. The more uniform the stress of the 4H silicon carbide crystal rod and the silicon carbide wafer obtained by cutting it are, the more conducive to the manufacture of the device and the improvement of the stability of the device.

[0014] Optionally, the ratio of the basal plane dislocation density of the 4H silicon carbide crystal rod in the [1-100] direction to the basal plane dislocation density in the [11-20] direction is 1-3, preferably 1-1.5.

[0015] Optionally, the ratio of the stacking fault of the 4H silicon carbide crystal rod in the [1-100] direction to the stacking fault in the [11-20] direction is 1-3, preferably 1-1.5.

[0016] The basal plane dislocation and stacking fault are obtained by X-ray testing. The basal plane dislocation and stacking fault in the [1-100] direction refer to the basal plane dislocation and stacking fault obtained by testing an area with a total width of 20 mm centered on the [1-100] direction. The basal plane dislocation and stacking fault in the [11-20] direction refer to the basal plane dislocation and stacking fault obtained by testing an area with a total width of 20 mm centered on the [11-20] direction.

[0017] Preferably, the basal plane dislocation of the 4H silicon carbide ingot is less than 600 / cm 2 The stacking faults of any silicon carbide wafer obtained by cutting the 4H silicon carbide crystal rod are less than 25.

[0018] Preferably, the basal plane dislocation of the 4H silicon carbide ingot is less than 400 / cm 2 The stacking faults of any silicon carbide wafer obtained by cutting the 4H silicon carbide crystal rod are less than 11.

[0019] Optionally, a ratio of the resistivity of the 4H silicon carbide crystal rod in a [1-100] direction to the resistivity in a [11-20] direction is 1.01-1.03.

[0020] For 4H silicon carbide crystal rods, the [1-100] direction and the [11-20] direction are their characteristic crystal directions. The physical properties in different characteristic crystal directions are different. Therefore, in different crystal directions, their resistivity, curvature radius, dislocation, and stacking fault will also be different. The ratio of the resistivity, curvature radius, dislocation, and stacking fault in the [1-100] direction and the [11-20] direction of the 4H silicon carbide crystal rod of the present application is very small, which means that the performance of the 4H silicon carbide crystal rod is more uniform.

[0021] Optionally, the single crystal ratio of the 4H silicon carbide crystal rod is 100%.

[0022] According to another aspect of the present application, a silicon carbide wafer having a large and uniformly distributed curvature radius is provided, which is prepared by cutting the 4H silicon carbide crystal rod having a large and uniformly distributed curvature radius as described in any of the above items.

[0023] According to another aspect of the present application, a method for preparing a 4H silicon carbide crystal rod with a large and uniformly distributed curvature radius is provided, comprising the following steps:

[0024] (1) The raw materials are placed in a crucible, wherein the porosity of the bottom of the crucible is greater than that of the side wall of the crucible, and a ventilation plate with the same diameter as the crucible is arranged at the bottom of the crucible, a ventilation pipe is arranged below the ventilation plate, and a plurality of evenly distributed ventilation holes are arranged on the ventilation plate, and the total area of ​​all ventilation holes is 8.5~15cm²;

[0025] (2) Install the seed crystal in the crucible, remove impurities, first heat it to 2100K, then evenly heat it from 2100K to 2300K within 40-60h to continue growing the crystal. During this period, the nitrogen gas pressure is 0.5-0.6MPa and the helium gas pressure is 0.1-0.2MPa.

[0026] (3) Then, uniformly raise the temperature from 2300K to 2400K within 10-15h to continue crystal growth, turn off nitrogen and maintain helium flux;

[0027] (4) Finally, the temperature is uniformly raised from 2400K to 2500K within 50-60h to continue crystal growth. During this period, the pressure of nitrogen introduced is 0.6-1MPa. The helium gas is turned off. After the temperature reaches 2500K and the crystal growth is completed, 1-5g / L of helium gas is introduced to cool down.

[0028] In step (1) of the preparation method, a vent plate is arranged at the bottom of the crucible, so that when the gas in the vent pipe enters the vent plate, the nitrogen can be evenly dispersed to avoid dead zones. The porosity setting at the bottom of the crucible is combined to achieve continuous nitrogen introduction into the crucible. As the raw material sublimates during the heating process, the evenly distributed nitrogen is evenly mixed with the raw material sublimation atmosphere, thereby increasing the nitrogen doping rate and the doping uniformity, thereby reducing the resistivity of the silicon carbide crystal and improving the uniformity of the resistivity distribution. The more uniform the resistivity distribution, the more uniform the residual stress distribution inside the material, thereby increasing the radius of curvature of the silicon carbide wafer obtained by cutting the 4H silicon carbide crystal rod, and the radius of curvature of the silicon carbide wafer prepared from the same 4H silicon carbide crystal rod is evenly distributed. At the same time, avoiding the occurrence of nitrogen dead zones and achieving uniform nitrogen doping can also avoid dislocation accumulation in a certain area, inhibit the expansion of stacking faults, reduce the number of dislocations and stacking faults, and improve the uniformity of the distribution of dislocations and stacking faults, and optimize the uniform distribution of dislocations and stacking faults in different directions.

[0029] In step (2), part of the helium is introduced at the same time as the nitrogen. This is because the helium atom is lighter and is more evenly distributed than the nitrogen at high temperature. Firstly, the nitrogen distribution is more even. Secondly, the temperature difference within the surface of the seed crystal and the newly formed crystal on the seed crystal is less than 1.5K. The above two effects can significantly improve the in-plane uniformity of the resistivity of the 4H silicon carbide crystal rod, so that the curvature radius of the 4H silicon carbide crystal rod conforms to the distribution function CR=ey+fy 2 +gy 3 +h.

[0030] In step (3), the temperature rises by 100K, but the temperature at this time is at the critical temperature point where the absolute nitrogen doping content decreases. In order to prevent uneven nitrogen distribution during continued growth, helium is needed to modify the growth interface at this time to prepare for uniform stress distribution at higher temperatures.

[0031] In step (4), the temperature is raised again, during which higher pressure nitrogen is introduced and helium is turned off, which can ensure the sufficiency of the doping content in the later stage of growth and increase the absolute content of nitrogen in the system. At the same time, since the temperature is very high, helium assistance is no longer needed to ensure temperature uniformity.

[0032] Those skilled in the art will appreciate that the raw material in step (1) refers to a raw material that can be heated and sublimated to grow silicon carbide crystals, including but not limited to silicon carbide powder, carbon powder and silicon powder.

[0033] Optionally, the diameter of the ventilation holes is 4-6 mm, and the spacing between the ventilation holes is 3-5 times the diameter of the ventilation holes.

[0034] The diameter of the vent holes and the spacing between adjacent vent holes can further improve the uniformity of the introduced gas, achieving the technical effect of adjusting the nitrogen distribution amount, thereby reducing the stress of the 4H silicon carbide crystal rod, increasing the curvature radius of the silicon carbide wafer and reducing the difference in curvature radius between adjacent silicon carbide wafers.

[0035] Optionally, the crucible and the ventilation plate are both made of graphite, the porosity of the side wall of the crucible is less than 10%, and the porosity of the bottom of the crucible is 15-18%.

[0036] When the resistivity is low, more nitrogen needs to be doped. The resistivity value and doping content are not in a linear relationship as usually believed. In the resistivity range of 12-28mΩcm, the lower the resistivity, the higher the free nitrogen in the system, which will cause the basal plane of the edge to bend and produce a large number of basal plane dislocations, which will lead to greater stress in the entire crystal and smaller curvature radius of the wafer.

[0037] After the gas is homogenized by the porous ventilation plate in the above-mentioned preparation method, the gas enters the growth area from the bottom of the crucible with high porosity. Different from the traditional crucible, the porosity of the side wall of the crucible in the present invention is relatively low, and the gas is not easy to leak, so that a nitrogen gas flow field with a spiral flow is formed, which avoids the nitrogen concentration area, reduces the concentrated distribution of the edge and center basal plane dislocations, and then increases the radius of curvature and reduces the overall stress. In addition, in order to ensure uniform axial stress, different temperature intervals and gas intakes are set according to the characteristics of nitrogen doping, so that the basal plane dislocation distribution of the entire 4H silicon carbide crystal rod in the radial direction is more uniform, reducing the overall stress. The different nitrogen contents in different temperature intervals are set because the suspension ability of nitrogen atoms on the growth surface is different at different temperatures. Therefore, the gas pressure of the nitrogen element is changed in different temperature intervals, thereby changing the total amount of gas intake, reducing the basal plane dislocations at the edge and center, and being beneficial to inhibiting the proliferation of stacking faults.

[0038] Therefore, the concept of the present preparation method is to achieve resistivity reduction, dislocation and stress reduction, and inhibit stacking fault proliferation through uniform, continuous and efficient doping of nitrogen. After clarifying the technical concept of the present application, those skilled in the art can use other preparation methods to uniformly, continuously and efficiently dope nitrogen to obtain the 4H silicon carbide crystal rod of the present application. The preparation method does not constitute a limitation on the 4H silicon carbide crystal rod.

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

[0040] 1. The 4H silicon carbide crystal rod with a large and uniformly distributed curvature radius of the present application can achieve a dual reduction in resistivity and stress, and can achieve a uniform distribution of resistivity and stress, which is beneficial to reducing the overall on-resistance and performance of the device, and provides a new solution for the quality of silicon carbide wafers and device performance.

[0041] 2. The curvature radius of the silicon carbide wafer obtained by cutting the 4H silicon carbide crystal rod with a large and uniform curvature radius in the present application conforms to the distribution function: CR=ey+fy 2 +gy 3 +h, which proves that the stress distribution in the axial direction of the 4H silicon carbide crystal rod is more uniform, which can reduce the stress inside the crystal.

[0042] 3. The 4H silicon carbide crystal rod with a large and uniformly distributed curvature radius of the present application reduces basal plane dislocations and stacking faults while reducing resistivity, further improving the performance of silicon carbide materials and broadening the application range of silicon carbide materials.

[0043] 4. The 4H silicon carbide crystal rod with a large and uniform curvature radius of the present application distinguishes the stress difference in different directions of the wafer by the ratio of the curvature radius in the [1-100] and [11-20] directions, proving that the body stress distribution of the 4H silicon carbide crystal rod is uniform. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] 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:

[0045] Figure 1 This is a structural arrangement diagram of a crucible, a vent plate and a vent pipe involved in Example 1 of the present application;

[0046] Figure 2 A top view of the ventilation plate involved in Example 1 of the present application;

[0047] Figure 3 This is a fitting distribution curve diagram of the curvature radius of the 4H silicon carbide crystal rod involved in Example 3 of the present application.

[0048] List of parts and reference numerals:

[0049] 1. Crucible; 2. Ventilation plate; 3. Ventilation pipe; 4. Ventilation hole. 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] This embodiment relates to a method for preparing a 4H silicon carbide crystal rod with a large and uniformly distributed curvature radius, which specifically includes the following steps:

[0055] (1) Place silicon carbide powder in a crucible 1, the porosity of the bottom of the crucible 1 is 15%, and the porosity of the side wall of the crucible 1 is less than 10%. Figure 1 A ventilation plate 2 having the same diameter as the crucible is arranged at the bottom of the crucible 1, a ventilation pipe 3 is arranged below the ventilation plate 2, and the ventilation pipe 3 is V-shaped near the ventilation plate 1. A plurality of ventilation holes 4 are evenly distributed on the ventilation plate 2. The top view of the ventilation plate 2 is shown in FIG. Figure 2 , Figure 2 The intersection of the lines in represents the position of the vent holes 4. The diameter of the vent holes 4 is 4 mm. The spacing between the vent holes 4 is 5 times the diameter of the vent holes 4. The total area of ​​all the vent holes 4 is 8.5 cm².

[0056] (2) A seed crystal was installed in crucible 1, and the temperature was first raised to 2100 K after impurities were removed. The temperature was then raised uniformly from 2100 K to 2300 K over 40 h to continue growing the crystal. During this period, the nitrogen gas pressure was 0.5 MPa and the helium gas pressure was 0.1 MPa.

[0057] (3) Then, uniformly raise the temperature from 2300K to 2400K within 10 hours to continue crystal growth, turn off nitrogen and maintain helium flux;

[0058] (4) Finally, the temperature was uniformly raised from 2400 K to 2500 K within 50 h to continue crystal growth. During this period, the pressure of nitrogen gas introduced was 0.6 MPa. The helium gas was turned off. After the temperature reached 2500 K and the crystal growth was terminated, 1 g / L helium gas was introduced to cool down.

[0059] Example 2

[0060] This embodiment relates to a method for preparing a 4H silicon carbide crystal rod with a large and uniformly distributed curvature radius, which specifically includes the following steps:

[0061] (1) Structure diagram and Figure 1 Similarly, this embodiment does not require component marking. Silicon carbide powder is placed in a crucible, the porosity of the bottom of the crucible is 18%, the porosity of the side wall of the crucible is less than 10%, a ventilation plate with the same diameter as the crucible is arranged at the bottom of the crucible, a ventilation pipe is arranged below the ventilation plate, and the ventilation pipe is V-shaped near the ventilation plate. A plurality of evenly distributed ventilation holes are arranged on the ventilation plate, the diameter of the ventilation holes is 6 mm, the spacing between the ventilation holes is 3 times the aperture of the ventilation holes, and the total area of ​​all the ventilation holes is 15 cm²;

[0062] (2) Install the seed crystal in the crucible, remove impurities, first heat it to 2100K, then evenly heat it from 2100K to 2300K within 60h to continue growing the crystal. During this period, the nitrogen gas pressure is 0.6MPa and the helium gas pressure is 0.2MPa.

[0063] (3) Then, the temperature was uniformly raised from 2300 K to 2400 K within 1 h to continue crystal growth, the nitrogen gas was turned off, and the helium gas flux was maintained;

[0064] (4) Finally, the temperature was uniformly raised from 2400K to 2500K within 60 hours to continue crystal growth. During this period, the pressure of nitrogen gas introduced was 1MPa. The helium gas was turned off. After the temperature reached 2500K and the crystal growth was terminated, 5g / L helium gas was introduced to cool down.

[0065] Example 3

[0066] This embodiment relates to a method for preparing a 4H silicon carbide crystal rod with a large and uniformly distributed curvature radius, which specifically includes the following steps:

[0067] (1) Same as Example 2;

[0068] (2) Install the seed crystal in the crucible, remove impurities, first heat it to 2100K, then evenly heat it from 2100K to 2300K within 50h to continue growing the crystal. During this period, the gas pressure of nitrogen is 0.6MPa and the gas pressure of helium is 0.2MPa.

[0069] (3) Then, uniformly raise the temperature from 2300K to 2400K within 12 hours to continue crystal growth, turn off the nitrogen gas, and maintain the helium gas flux;

[0070] (4) Finally, the temperature was uniformly raised from 2400 K to 2500 K within 55 h to continue crystal growth. During this period, the pressure of nitrogen gas was 0.8 MPa. The helium gas was turned off. After the temperature reached 2500 K and the crystal growth was terminated, 3 g / L helium gas was introduced to cool down.

[0071] Example 4

[0072] The difference between this embodiment and embodiment 3 is that the diameter of the vent hole is 3 mm, and the rest is the same as embodiment 3.

[0073] Example 5

[0074] The difference between this embodiment and embodiment 3 is that the diameter of the vent hole is 10 mm, and the rest is the same as embodiment 3.

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 3 is that in step (1), no ventilation plate is provided at the bottom of the crucible, and the Figure 1 The gas is introduced into the crucible through a vent pipe, and the remaining preparation steps are the same as those in Example 3.

[0077] Comparative Example 2

[0078] The difference between this comparative example and Example 3 is that helium is not introduced in step (2), but is introduced only in step (3), and the pressure of the helium introduced is 0.2 MPa. The rest is the same as Example 3.

[0079] Comparative Example 3

[0080] The difference between this comparative example and Example 3 is that in step (4), the temperature is uniformly raised from 2400 K to 2500 K within 5 h, and then the crystal growth is continued at 2500 K for 50 h. Finally, 3 g / L helium is introduced and the temperature is lowered. The rest is the same as Example 3.

[0081] The curvature radius of each silicon carbide wafer was fitted, and the results of the 4H silicon carbide crystal rod prepared in Example 3 are shown in FIG. Figure 3 It can be seen that the curvature radius of each wafer is well matched with the curve, proving that the curvature radius distribution function can characterize the curvature radius distribution of the 4H silicon carbide crystal rod.

[0082] Test Example 1

[0083] The basal plane dislocation and stacking fault of the silicon carbide wafer including the Si surface of the 4H silicon carbide crystal rod prepared as described above, as well as the thickness of the entire crystal rod were tested. The test results are shown in Table 1.

[0084] Table 1. Dislocation, stacking fault and thickness of 4H silicon carbide ingot

[0085]

[0086] According to the data in Table 1, the setting of the vent plate affects the distribution of nitrogen, thereby affecting the dislocation distribution and dislocation density. It can be found that within the range we set, the lowest dislocation density is more evenly distributed, and a crystal rod of more than 15 mm can be obtained. The crystal thickness of Examples 4, 5, 6 and Comparative 4H silicon carbide crystal rods 1 and 2 is reduced compared to that of Example 3 because cracks occur when the crystal continues to grow to a higher thickness. Therefore, the data in Table 1 are the maximum crystal thickness obtained by this method.

[0087] Although the basal plane dislocation and stacking fault in Table 1 are the data obtained by detecting the silicon carbide wafer including the Si surface, the other silicon carbide wafers cut from the 4H silicon carbide crystal rod still conform to the same rules as the Si surface. In addition, the parameter values ​​of the silicon carbide wafer including the Si surface are the worst data of the entire crystal rod, and the data of the other wafers are better than that of the silicon carbide wafer including the Si surface.

[0088] Test Example 2

[0089] The 4H silicon carbide crystal rod prepared above was cut and processed to obtain a plurality of silicon carbide wafers, each of which was 500 μm thick, wherein the silicon carbide wafer containing the silicon surface of the 4H silicon carbide crystal rod was the head wafer, the silicon carbide wafer containing the carbon surface of the 4H silicon carbide crystal rod was the tail wafer, and the middle wafer was the silicon carbide wafer with the lowest resistivity obtained by cutting the 4H silicon carbide crystal rod. The resistivity distribution and curvature radius distribution of the silicon carbide wafer were tested, and the test results are shown in Table 2.

[0090] 1. Resistivity: Use the instrument to test the resistivity of each wafer and obtain the following parameters:

[0091] (1) Minimum resistivity: refers to the minimum resistivity value tested among all silicon carbide wafers cut from the 4H silicon carbide ingot.

[0092] (2) Maximum resistivity: refers to the maximum resistivity value obtained by testing all silicon carbide wafers cut from the 4H silicon carbide ingot.

[0093] (3) Maximum ratio of resistivity in the [1-100] direction to that in the [11-20] direction: Calculate the ratio of the resistivity in the [1-100] direction to the resistivity in the [11-20] direction of each silicon carbide wafer cut from each silicon carbide crystal rod. The values ​​in Table 2 refer to the maximum values ​​calculated among all silicon carbide wafers of the silicon carbide crystal rod.

[0094] 2. Radius of curvature: The radius of curvature of each wafer is tested by an instrument to obtain the following parameters:

[0095] (1) Minimum value of curvature radius: refers to the minimum value obtained by testing all silicon carbide wafers cut from the 4H silicon carbide crystal rod. The smaller the value, the greater the stress of the 4H silicon carbide crystal rod.

[0096] (2) The maximum ratio of the curvature radii in the [1-100] and [11-20] directions: The curvature radius in the [1-100] direction refers to the average value of the inverse curvature of multiple points along the [1-100] direction on the entire diameter, and the curvature radius in the [11-20] direction refers to the average value of the inverse curvature of multiple points along the [11-20] direction on the entire diameter. The smaller the ratio, the higher the uniformity of the in-plane stress.

[0097] (3) The maximum difference in the radius of curvature of any two silicon carbide wafers refers to the difference between the maximum and minimum values ​​of the radius of curvature obtained by testing all silicon carbide wafers cut from the 4H silicon carbide crystal rod. The larger the value, the greater the stress difference in the axial direction of the 4H silicon carbide crystal rod.

[0098] (4) The maximum difference in the radius of curvature of two adjacent silicon carbide wafers refers to the maximum value of the difference in the radius of curvature of all adjacent silicon carbide wafers cut from the 4H silicon carbide crystal rod. The larger the value, the greater the stress difference in the axial direction of the 4H silicon carbide crystal rod.

[0099] (5) According to the resistivity of each silicon carbide wafer, the axial curvature radius distribution function of the entire crystal rod is obtained by fitting, and it is determined whether it conforms to the curvature radius distribution function of CR=ey+fy 2 +gy 3 +h; where CR is the radius of curvature of the silicon carbide wafer, in m, y is the wafer number of the silicon carbide wafer, and the naming starts from the silicon surface of the 4H silicon carbide crystal rod to the carbon surface. The first silicon carbide wafer containing the silicon surface of the 4H silicon carbide crystal rod is named 1. The thickness of the silicon carbide wafer is 350-500μm, the value range of e is -4.1~-3.5, the value range of f is 0.17~0.19, the value range of g is 0.15~0.19, and the value range of h is 830~890. Fitting gives (r2) 2 Value, (r2) 2The closer it is to 1, the closer it is to the curvature radius distribution function of the 4H silicon carbide crystal rod. In this application, a value greater than 0.98 is considered to be in line with the fitting curve.

[0100] Table 2. Resistivity and curvature radius of 4H silicon carbide crystal rod

[0101]

[0102] According to the data in Table 2, the diameter of the vent plate affects the uniformity of nitrogen distribution, thereby affecting the stress distribution of the 4H silicon carbide crystal rod, among which the 4H silicon carbide crystal rod prepared in Example 3 has the lowest stress and the most uniform stress distribution in both the axial and radial directions. The final stage of growth in Comparative Example 3 is constant temperature growth, and the stress of the crystal obtained at the end increases, so the radius of curvature of the tail piece decreases significantly, and the stress difference of the silicon carbide crystal in the axial direction is large.

[0103] 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 4H nitrogen-doped silicon carbide crystal rod with a large and uniformly distributed curvature radius, characterized in that: The resistivity of the 4H silicon carbide crystal rod at any position is greater than 12 mΩ·cm and less than 15 mΩ·cm, the curvature radius of the silicon carbide wafer obtained by cutting the 4H silicon carbide crystal rod is greater than 800m, and the curvature radius distribution function of the silicon carbide wafer obtained by cutting the 4H silicon carbide crystal rod in the axial direction is CR=ey+fy 2 +gy 3 +h; Wherein, CR is the radius of curvature of the silicon carbide wafer, in m, y is the serial number of the silicon carbide wafer, and they are arranged in natural numbers from the silicon surface of the 4H silicon carbide crystal rod to the carbon surface, the serial number of the first silicon carbide wafer containing the silicon surface of the 4H silicon carbide crystal rod is 1, the thickness of the silicon carbide wafer is 350-500 μm, the value range of e is -4.1~-3.5, the value range of f is 0.17~0.19, the value range of g is 0.15~0.19, and the value range of h is 830~890; The first silicon carbide wafer including the silicon surface of the 4H silicon carbide crystal rod is the head wafer, and the last silicon carbide wafer including the carbon surface of the 4H silicon carbide crystal rod is the tail wafer. The difference between the curvature radius of the head wafer and the curvature radius of the tail wafer is less than 25m.

2. The 4H nitrogen-doped silicon carbide crystal rod with a large and uniformly distributed curvature radius according to claim 1, characterized in that: The ratio of the curvature radii of the silicon carbide wafer obtained by cutting the 4H silicon carbide crystal rod in the [1-100] and [11-20] directions is less than 2.

3. The 4H nitrogen-doped silicon carbide crystal rod with a large and uniformly distributed curvature radius according to claim 1, characterized in that: Among the silicon carbide wafers obtained by cutting the 4H silicon carbide crystal rod, the difference in curvature radius between any two silicon carbide wafers is less than 25m, and the difference in curvature radius between two adjacent silicon carbide wafers is less than 2.5m.

4. The 4H nitrogen-doped silicon carbide crystal rod with a large and uniformly distributed curvature radius according to claim 1, characterized in that: The ratio of the basal plane dislocation density of the 4H silicon carbide crystal rod in the [1-100] direction to the basal plane dislocation density in the [11-20] direction is 1-3.

5. The 4H nitrogen-doped silicon carbide crystal rod with a large and uniformly distributed curvature radius according to claim 1, characterized in that: The ratio of the stacking faults in the [1-100] direction to the stacking faults in the [11-20] direction of the 4H silicon carbide crystal rod is 1-3.

6. The 4H nitrogen-doped silicon carbide crystal rod with a large and uniformly distributed curvature radius according to claim 1, characterized in that: The ratio of the resistivity of the 4H silicon carbide crystal rod in the [1-100] direction to the resistivity in the [11-20] direction is 1.01-1.

03.

7. The 4H nitrogen-doped silicon carbide crystal rod with a large and uniformly distributed curvature radius according to claim 1, characterized in that: The thickness of the 4H silicon carbide crystal rod is greater than 15 mm, and the single crystal ratio of the 4H silicon carbide crystal rod is 100%.

8. A method for preparing a 4H nitrogen-doped silicon carbide crystal rod with a large and uniformly distributed curvature radius, characterized in that: The steps include: (1) The raw materials are placed in a crucible, wherein the porosity of the bottom of the crucible is greater than that of the side wall of the crucible, and a ventilation plate with the same diameter as the crucible is arranged at the bottom of the crucible, a ventilation pipe is arranged below the ventilation plate, and a plurality of evenly distributed ventilation holes are arranged on the ventilation plate, and the total area of ​​all ventilation holes is 8.5~15cm²; (2) Install the seed crystal in the crucible, remove impurities, first heat it to 2100K, then evenly heat it from 2100K to 2300K within 40-60h to continue growing the crystal. During this period, the nitrogen gas pressure is 0.5-0.6MPa and the helium gas pressure is 0.1-0.2MPa. (3) Then, uniformly raise the temperature from 2300K to 2400K within 10-15h to continue growing crystals, turn off nitrogen and maintain helium flux; (4) Finally, the temperature is uniformly raised from 2400K to 2500K within 50-60h to continue crystal growth. During this period, the pressure of nitrogen introduced is 0.6-1MPa. The helium gas is turned off. After the temperature reaches 2500K and the crystal growth is completed, 1-5g / L of helium gas is introduced to cool down.

9. The preparation method according to claim 8, characterized in that: The diameter of the ventilation holes is 4-6 mm, and the spacing between the ventilation holes is 3-5 times the diameter of the ventilation holes.

10. Application of a 4H nitrogen-doped silicon carbide crystal rod prepared by the method for preparing a 4H nitrogen-doped silicon carbide crystal rod with a large and uniform curvature radius according to any one of claims 1 to 7 or a 4H nitrogen-doped silicon carbide crystal rod with a large and uniform curvature radius according to any one of claims 8 to 9 in a semiconductor device.

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