4H-SiC single crystal with low resistivity and low stress and single crystal wafer

Abstract

The invention discloses a 4H-SiC single crystal with low resistivity and low stress and a single crystal wafer, and belongs to the technical field of SiC single crystal material preparation. The resistivity of the 4H-SiC single crystal wafer at any position is larger than 6 m omega.cm and smaller than 12 m omega.cm, the resistivity variation coefficient of the 4H-SiC single crystal wafer is smaller than or equal to 3%, and the average value of the surface internal stress of the 4H-SiC single crystal wafer is smaller than or equal to 6 MPa. According to the 4H-SiC single crystal and the single crystal wafer, double reduction of resistivity and stress is achieved, the physical performance of SiC is more stable, the conduction capacity of a device is improved, and the service life of the device is prolonged.

Description

Technical Field

[0001] This application relates to a 4H-SiC single crystal and single crystal wafer with low resistivity and low stress, belonging to the field of SiC single crystal material preparation technology. Background Technology

[0002] Heavy doped 4H-SiC wafers with low resistivity, especially nitrogen-doped N-type wafers, are the cornerstone of many high-performance semiconductor devices. Heavily nitrogen-doped N-type 4H-SiC wafers (typically achieved through nitrogen doping) play two key roles in these devices: 1. Provides a low-resistance path: In vertical power devices (where current passes vertically through the wafer), the resistance of the wafer itself is part of the total on-resistance of the device. Heavy nitrogen doping can greatly reduce this resistance and directly improve energy efficiency.

[0003] 2. Constructing high-quality electrodes: Heavily doped wafers can form excellent ohmic contacts with metal electrodes, ensuring that current can be efficiently injected into or extracted from the device.

[0004] However, introducing a large number of nitrogen atoms into 4H-SiC crystals directly leads to changes in the lattice constant, thereby causing an increase in intrinsic stress. When nitrogen atoms enter the SiC lattice as donor impurities, they preferentially occupy lattice sites of carbon atoms. Due to the differences in covalent radius and electronegativity between nitrogen and carbon atoms, this substitution behavior causes local distortion of the lattice. Simultaneously, the non-uniform nitrogen doping distribution further exacerbates the stress problem. In actual crystal growth, especially in the early stages, improper control of nitrogen flow rate and partial pressure can lead to a spatially uneven distribution of nitrogen concentration in the grown crystal. This non-uniformity induces an internal stress gradient, forming a complex stress field within the crystal, resulting in a significant increase in stress within the 4H-SiC crystal.

[0005] Furthermore, nitrogen doping alters the bonding strength and phonon spectrum of 4H-SiC, thus affecting its thermal expansion behavior. Studies have shown that the thermal expansion coefficient of 4H-SiC undergoes a systematic change with increasing nitrogen doping concentration. This change stems from the modification effect of nitrogen atoms on Si-C bonds—nitrogen atoms, after substituting carbon sites, shorten local bond lengths, enhance bonding strength, and consequently affect the anharmonicity of lattice vibrations, ultimately leading to a change in the thermal expansion coefficient. Notably, the thermal expansion coefficient may respond differently to nitrogen doping in different crystal orientations, and this anisotropic change can further induce lattice distortion and internal stress. Especially under heavy doping conditions, the change in the thermal expansion coefficient may be more pronounced, and its impact on the crystal stress state is more significant.

[0006] Therefore, there is an urgent need for a low-stress and low-resistivity SiC single-crystal wafer to meet current application requirements. Summary of the Invention

[0007] To address the aforementioned issues, a 4H-SiC single crystal and single crystal wafer with low resistivity and low stress are provided. The resistivity is greater than 6 mΩ·cm and less than 12 mΩ·cm, while also exhibiting lower volume stress and surface stress without significant local distortion, thus meeting higher application requirements.

[0008] According to one aspect of this application, a 4H-SiC single crystal with low resistivity and low stress is provided, wherein the resistivity of the 4H-SiC single crystal at any location is greater than 6 mΩ·cm and less than 12 mΩ·cm, the coefficient of variation of resistivity of any cross section of the 4H-SiC single crystal is ≤3%, and the average stress of any cross section of the 4H-SiC single crystal is ≤6 MPa.

[0009] Optionally, the average stress value of any cross section of the 4H-SiC single crystal is ≤4MPa.

[0010] Optionally, the difference between the average resistivity of the silicon surface and the average resistivity of the carbon surface of the 4H-SiC single crystal is less than 1.5 mΩ·cm.

[0011] The small difference between the average resistivity of the carbon face and the average resistivity of the silicon face in 4H-SiC single crystals proves that the crystal is more axially uniform, which can provide a more stable conduction channel, thereby improving the stability of power devices. Furthermore, the high performance consistency of several wafers obtained by cutting a single crystal can improve the performance consistency of mass-produced power devices, which is conducive to industrial promotion and use.

[0012] The stress test method is birefringence stress test, which is a common test method that can characterize volume stress.

[0013] Optionally, the average stress of the 4H-SiC single crystal in the [1-100] and / or [11-20] directions of any cross section is <4.5MPa.

[0014] Optionally, the average stress of the 4H-SiC single crystal in the [1-100] and / or [11-20] directions of any cross section is <3MPa.

[0015] Optionally, the average stress in the [1-100] and / or [11-20] directions of the 4H-SiC single crystal is <3MPa within a region of 3 / 4 of the diameter of any cross-section.

[0016] Optionally, the average stress in the [1-100] and / or [11-20] directions of the 4H-SiC single crystal is <2MPa within a region of 3 / 4 of the diameter of any cross-section.

[0017] Optionally, in any cross-section of the 4H-SiC single crystal, the range where the stress exceeds 4.5 MPa is less than 1 / 10 of the diameter in the [1-100] and / or [11-20] directions.

[0018] Optionally, in any cross-section of the 4H-SiC single crystal, the range where the stress exceeds 3 MPa in the [1-100] and / or [11-20] directions is less than 1 / 10 of the diameter.

[0019] Optionally, in the X-ray test of the 4H-SiC single crystal, the difference between the Ω angle obtained at the same site with a power of 1.6KW and the Ω angle obtained at 9KW is less than 0.2°.

[0020] Optionally, in X-ray testing of any 4H-SiC single crystal wafer obtained by cutting the 4H-SiC single crystal, the difference between the radius of curvature obtained at 1.6KW and the radius of curvature obtained at 9KW is ≤5%.

[0021] Optionally, within 3 / 4 of the diameter of the 4H-SiC single crystal, the average stress on any axis is ≤4.0 MPa.

[0022] Optionally, within 3 / 4 of the diameter of the 4H-SiC single crystal, the average stress on any axis is ≤2.5MPa.

[0023] Optionally, the thickness of the 4H-SiC single crystal is 5 mm or more.

[0024] Optionally, the thickness of the 4H-SiC single crystal is 10 mm or more.

[0025] Optionally, the diameter of the 4H-SiC single crystal is 100 mm or more.

[0026] According to another aspect of this application, a 4H-SiC single crystal wafer with low resistivity and low stress is provided, wherein the resistivity of the 4H-SiC single crystal wafer at any location is greater than 6 mΩ·cm and less than 12 mΩ·cm, the coefficient of variation of the resistivity of the 4H-SiC single crystal wafer is ≤3%, and the average in-plane stress of the 4H-SiC single crystal wafer is ≤6 MPa.

[0027] This 4H-SiC single crystal and wafer can reduce resistivity while simultaneously decreasing its coefficient of resistivity variation. This overcomes the challenge of improving resistivity uniformity while reducing resistivity using traditional methods. Furthermore, it exhibits low in-plane stress, improving the stability of SiC during use, reducing the risk of stress cracking, and extending its service life. The aforementioned coefficient of resistivity variation = (standard deviation / average value) × 100% refers to the coefficient of resistivity calculated by measuring the standard deviation and average value of the 4H-SiC single crystal wafer at several points.

[0028] Optionally, the average in-plane stress of the 4H-SiC single crystal wafer is ≤4MPa.

[0029] Optionally, the diameter of the 4H-SiC single crystal wafer is 150-300 mm.

[0030] Optionally, the average stress of the 4H-SiC single crystal wafer in the [1-100] and / or [11-20] directions is <4.5MPa.

[0031] Optionally, the average stress of the 4H-SiC single crystal wafer in the [1-100] and / or [11-20] directions is <3MPa.

[0032] Optionally, the average stress in the [1-100] and / or [11-20] directions is <3 MPa within a region of 3 / 4 of the diameter of the 4H-SiC single crystal wafer. Optionally, the average stress in the [1-100] and / or [11-20] directions is <2 MPa within a region of 3 / 4 of the diameter of the 4H-SiC single crystal wafer. Optionally, in the [1-100] and / or [11-20] directions of the 4H-SiC single crystal wafer, the range where the stress exceeds 4.5 MPa is less than 1 / 10 of the diameter.

[0033] Optionally, in the [1-100] and / or [11-20] directions of the 4H-SiC single crystal wafer, the range where the stress exceeds 3 MPa is less than 1 / 10 of the diameter.

[0034] The stress is lower in the two crystal orientations mentioned above, and the range of <4.5MPa in both directions is larger, indicating that the stress of the wafer is not only low in value, but also more uniformly distributed. This not only improves the performance of SiC, but also increases the usable area of ​​a single wafer and reduces the manufacturing cost of power devices.

[0035] Optionally, in the X-ray test of the 4H-SiC single crystal wafer, the difference between the Ω angle obtained at the same site with a power of 1.6KW and the Ω angle obtained at 9KW is less than 0.2°.

[0036] Optionally, in the X-ray testing of the 4H-SiC single crystal wafer, the difference between the radius of curvature obtained at 1.6KW and 9KW for the same cross-section is ≤5%.

[0037] The number of photons excited by X-rays varies with power. A higher number of excited photons results in a higher intensity received by the detector, leading to a more detailed characterization of the signal on the material surface and better resolution of defects in small areas. By comparing data from different power levels, it's possible to confirm whether the observed peaks are genuine diffraction signals or background noise. This helps to indirectly characterize surface stress and distinguish whether stress distortion is caused by local dislocations (or lattice distortion). At two different test powers, a smaller difference in the radius of curvature and Ω angle indicates that there is no significant local distortion on the SiC single-crystal wafer surface, suggesting a good surface stress state for silicon carbide.

[0038] Optionally, the absolute value of the Bow of the 4H-SiC single crystal wafer is ≤15μm.

[0039] Optionally, the 4H-SiC single crystal wafer has a 30mm inward region from the edge as a ring region, and the remainder as a central region. The warp value of the ring region is ≤30μm, and the warp value of the central region is ≤15μm.

[0040] In terms of Bow and Warp values, higher values ​​indicate greater stress on the wafer. This 4H-SiC single-crystal wafer maintains low Bow and Warp values ​​even with low resistance, demonstrating low stress, especially in the central region, thus meeting higher quality requirements.

[0041] Optionally, the 4H crystal form of the 4H-SiC single crystal and the 4H-SiC single crystal wafer is 100%.

[0042] Because low-resistivity 4H-SiC substrates require doping with more nitrogen to reduce resistivity, this directly leads to changes in the lattice constant and anisotropy due to altered atomic pairing. These property changes result in non-uniform internal stress in the crystal, as well as non-uniformity between surface and bulk stress. By measuring the overall average stress across the cross-section of the crystal and substrate, the average stress along characteristic crystal directions, and stress values ​​within a certain range, we can effectively prevent stress concentration areas, more reasonably measure the stress of low-resistivity substrates, and avoid warping and cracking that could affect photolithography during epitaxy and device fabrication.

[0043] The above-mentioned method for preparing 4H-SiC single crystals includes the following steps: (1) Place SiC powder in a crucible and cover the crucible with a seed crystal. After removing impurities, heat to 2073-2273K for the first stage of crystal growth. During this period, a first mixed gas of N2, He and Ar is introduced. In the first mixed gas, N2:(N2+He+Ar) = 1:(3-3.5) and He:Ar=(2-2.5):1. The flow rate of the first mixed gas is 30-50 sccm. The growth time is 20h-30h. The rotation speed of the crucible during the first stage of crystal growth is 0.1r / min. (2) Then the temperature is raised to 2273-2373K for the second stage of crystal growth. The second mixture of N2, He and Ar is continued to be introduced. In the second mixture, N2:(N2+He+Ar) = 1:(1-1.5) and He:Ar=1:(1-2). The flow rate of the second mixture is 80-100sccm. The growth time is 30h-40h. The rotation speed of the crucible in the second stage of crystal growth is 0.5r / min. (3) Then the temperature is raised to 2373-2473K for the third stage of crystal growth. The third mixture of N2 and Ar is continued to be introduced. The ratio of N2 to Ar in the third mixture is (3-3.5):1. The flow rate of the third mixture is 120-150 sccm. The growth time is 30h-40h. The rotation speed of the crucible during the third stage of crystal growth is 1.0r / min. (4) Then the temperature is raised to 2473-2573K for the fourth stage of crystal growth. The third mixture of N2 and Ar is continued to be introduced. The ratio of N2 to Ar in the third mixture is (3-3.5):1. The flow rate of the third mixture is 100-150 sccm. The growth time is 30h-40h. The rotation speed of the crucible in the fourth stage of crystal growth is 0.5r / min. (5) Cool down to room temperature to obtain the product.

[0044] The growth method disclosed in this application does not constitute a limitation on 4H-SiC single crystals and single crystal wafers. New preparation methods can also be studied to obtain the 4H-SiC single crystals and single crystal substrates of this application.

[0045] The low resistivity and low stress 4H-SiC single crystal and single crystal wafer of this application are defined by the resistivity range, the coefficient of variation of cross-sectional resistivity, and the difference between the average resistivity of the carbon surface and the average resistivity of the silicon surface. Under this limitation method, the superiority of SiC in terms of resistivity performance can be measured, and the performance becomes better and better as the aforementioned limitation range increases. The stress is defined by the average stress value, the difference in Ω angle and radius of curvature of X-ray test at two power levels, and the average stress value in two directions. Under this limitation method, the superiority of SiC in terms of stress performance can be measured, and the stress performance of SiC becomes better and better as the aforementioned limitation range increases, and the stress distribution uniformity is also better.

[0046] The beneficial effects of this application include, but are not limited to: 1. The low resistivity and low stress 4H-SiC single crystal and single crystal wafer of this application can improve the uniformity of resistivity distribution while reducing resistivity, thereby improving the operating stability of SiC in power devices. 2. The low resistivity and low stress 4H-SiC single crystal and single crystal wafer of this application achieve a dual reduction in resistivity and stress, making the physical properties of SiC more stable, improving the conductivity of the device, and extending the service life of the device.

[0047] 3. Based on the low resistivity and low stress 4H-SiC single crystal and single crystal wafer of this application, the analysis of resistivity, stress values ​​and the difference in radius of curvature and Ω angle under different power shows that SiC has low volume stress and no obvious stress distortion on the surface.

[0048] 4. The low resistivity and low stress 4H-SiC single crystal and single crystal wafer of this application have a smaller average stress in the [1-100] and / or [11-20] directions, which can meet the requirements of downstream processing and thus improve the conductivity, withstand voltage, high temperature stability and switching speed of the device. Attached Figure Description

[0049] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the birefringence test of two crystal orientations of one of the 4H-SiC single crystal wafers prepared in Example 2 of this application.

[0050] Figure 2 The stress test diagram of one of the 4H-SiC single crystal wafers prepared in Example 2 of this application in the [11-20] crystal orientation.

[0051] Figure 3 The stress test diagram of one of the 4H-SiC single crystal wafers prepared in Example 2 of this application in the [1-100] crystal orientation. Detailed Implementation

[0052] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0053] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application were all purchased commercially.

[0054] Unless otherwise specified, the methods used in the embodiments and comparative examples of this application are conventional methods in the prior art.

[0055] Example 1 This embodiment relates to a method for preparing a 4H-SiC single crystal with low resistivity and low stress, comprising the following steps: (1) Place SiC powder in a crucible and cover the crucible with a seed crystal. After removing impurities, heat to 2073K for the first stage of crystal growth. During this period, a first mixed gas of N2, He and Ar is introduced. In the first mixed gas, N2:(N2+He+Ar) = 1:3 and He:Ar = 2:1. The flow rate of the first mixed gas is 30 sccm. The growth time is 30h. The rotation speed of the crucible during the first stage of crystal growth is 0.1r / min. (2) Then the temperature was raised to 2273K for the second stage of crystal growth. The second mixture of N2, He and Ar was introduced. The ratio of N2 to (N2+He+Ar) in the second mixture was 1:1, and the ratio of He to Ar was 1:1. The flow rate of the second mixture was 80 sccm. The growth time was 40 h. The rotation speed of the crucible in the second stage of crystal growth was 0.5 r / min. (3) Then the temperature was raised to 2373K for the third stage of crystal growth. The third mixture of N2 and Ar was continued to be introduced. The ratio of N2 to Ar in the third mixture was 3:1. The flow rate of the third mixture was 120 sccm. The growth time was 40h. The rotation speed of the crucible in the third stage of crystal growth was 1.0 r / min. (4) Then the temperature is raised to 2473K for the fourth stage of crystal growth. The third mixture of N2 and Ar is continued to be introduced. The ratio of N2 to Ar in the third mixture is 3:1. The flow rate of the third mixture is 100 sccm. The growth time is 30h. The rotation speed of the crucible in the fourth stage of crystal growth is 0.5r / min. (5) Cool down to room temperature to obtain the product.

[0056] Example 2 This embodiment relates to a method for preparing a 4H-SiC single crystal with low resistivity and low stress, comprising the following steps: (1) Place SiC powder in a crucible and cover the crucible with a seed crystal. After removing impurities, heat to 2273K for the first stage of crystal growth. During this period, a first mixed gas of N2, He and Ar is introduced. The ratio of N2:(N2+He+Ar) in the first mixed gas is 1:3.5, and the ratio of He:Ar is 2.5:1. The flow rate of the first mixed gas is 50 sccm. The growth time is 20h. The rotation speed of the crucible during the first stage of crystal growth is 0.1r / min. (2) Then the temperature is raised to 2373K for the second stage of crystal growth. The second mixture of N2, He and Ar is continued to be introduced. The ratio of N2:(N2+He+Ar) in the second mixture is 1:1.5, and the ratio of He:Ar is 1:2. The flow rate of the second mixture is 100sccm. The growth time is 30h. The rotation speed of the crucible in the second stage of crystal growth is 0.5r / min. (3) Then the temperature was raised to 2473K for the third stage of crystal growth. The third mixture of N2 and Ar was continued to be introduced. The ratio of N2 to Ar in the third mixture was 3.5:1. The flow rate of the third mixture was 150 sccm. The growth was carried out for 30 h. The rotation speed of the crucible in the third stage of crystal growth was 1.0 r / min. (4) Then the temperature was raised to 2573K for the fourth stage of crystal growth. The third mixture of N2 and Ar was continued to be introduced. The ratio of N2 to Ar in the third mixture was 3.5:1. The flow rate of the third mixture was 150 sccm. The growth time was 40h. The rotation speed of the crucible in the fourth stage of crystal growth was 0.5r / min. (5) Cool down to room temperature to obtain the product.

[0057] Example 3 This embodiment relates to a method for preparing a 4H-SiC single crystal with low resistivity and low stress, comprising the following steps: (1) Place SiC powder in a crucible and cover the crucible with a seed crystal. After removing impurities, heat to 2200K for the first stage of crystal growth. During this period, a first mixed gas of N2, He and Ar is introduced. In the first mixed gas, N2:(N2+He+Ar) = 1:3 and He:Ar = 2:1. The flow rate of the first mixed gas is 45 sccm. The growth time is 30h. The rotation speed of the crucible during the first stage of crystal growth is 0.1r / min. (2) Then the temperature is raised to 2273K. At the initial temperature of 2273K, the temperature is continuously raised to 2373K for 40h to carry out the second stage of crystal growth. The second mixed gas of N2, He and Ar is continuously introduced. In the second mixed gas, N2:(N2+He+Ar) = 1:1 and He:Ar=1:1. The rotation speed of the crucible in the second stage of crystal growth is 0.5r / min. The flow rate of the second mixed gas in the temperature range of 2273K-2323K is 80sccm, and the flow rate of the second mixed gas in the temperature range of 2323K-2373K is 100sccm. (3) Then the temperature was raised to 2473K for the third stage of crystal growth. The third mixture of N2 and Ar was continued to be introduced. The ratio of N2 to Ar in the third mixture was 3:1. The flow rate of the third mixture was 150 sccm. The growth time was 30h. The rotation speed of the crucible in the third stage of crystal growth was 1.0r / min. (4) Then, the temperature was continuously increased from 2473 to 2573 K for 20 hours to carry out the fourth stage of crystal growth. The third mixture of N2 and Ar was continuously introduced. The ratio of N2 to Ar in the third mixture was 3:1. The flow rate of the third mixture was 120 sccm. Then the flow rate of the third mixture was changed to 140 sccm. The crystal was then kept at 2573 K for 20 hours. The rotation speed of the crucible in the fourth stage of crystal growth was 0.5 r / min. (5) Cool down to room temperature to obtain the product.

[0058] Example 4 This embodiment relates to a method for preparing a 4H-SiC single crystal with low resistivity and low stress, comprising the following steps: (1) Place SiC powder in a crucible and cover the crucible with the seed crystal. After removing impurities, heat to 2073K. At the initial temperature of 2073K, continue to heat to 2273K for 30 hours to carry out the first stage of crystal growth. During this period, a first mixed gas of N2, He and Ar is introduced. In the first mixed gas, N2:(N2+He+Ar) = 1:3 and He:Ar = 2:1. The flow rate of the first mixed gas is 40 sccm. During the first stage of crystal growth, the rotation speed of the crucible is 0.1r / min. (2) Then the temperature was raised to 2373K for the second stage of crystal growth. The second mixture of N2, He and Ar was introduced. The ratio of N2 to (N2+He+Ar) in the second mixture was 1:1, and the ratio of He to Ar was 1:1. The flow rate of the second mixture was 90 sccm. The growth time was 35 h. The rotation speed of the crucible in the second stage of crystal growth was 0.5 r / min. (3) Then, the temperature was continuously increased from 2373K to 2473K within 20h for the third stage of crystal growth. The third mixture of N2 and Ar was continuously introduced. The ratio of N2 to Ar in the third mixture was 3:1. The flow rate of the third mixture was 140sccm. After that, the flow rate of the third mixture remained unchanged. The crystal was then kept at 2473K for 10h. The rotation speed of the crucible in the third stage of crystal growth was 1.0r / min. (4) Then the temperature is raised to 2523K for the fourth stage of crystal growth. The third mixture of N2 and Ar is continued to be introduced. The ratio of N2 to Ar in the third mixture is 3:1. The flow rate of the third mixture is 150 sccm. The growth time is 30h. The rotation speed of the crucible in the fourth stage of crystal growth is 0.5r / min. (5) Cool down to room temperature to obtain the product.

[0059] Comparative Example 1 The difference between this comparative example and Example 3 is that steps (1) and (2) are interchanged, while the rest is the same as Example 3.

[0060] Comparative Example 2 The difference between this comparative example and Example 3 is that steps (2) and (3) are interchanged, while the rest is the same as Example 3.

[0061] Comparative Example 3 The difference between this comparative example and Example 3 is that the growth time in step (3) is 50 hours, and step (4) is omitted. The rest is the same as in Example 3.

[0062] Comparative Example 4 4H-SiC crystals were prepared using the preparation method disclosed in Example 1 of JP2008290898A.

[0063] Test Example 1 The thickness of the prepared 4H-SiC single crystal was measured. After cutting and processing, multiple SiC single crystal wafers were obtained, each with a thickness of 350 μm. Resistivity, surface shape, in-plane stress, and X-ray diffraction tests were performed on the single crystal wafers. The test results are shown in Tables 1 and 2. 1. The resistivity of each wafer was measured using instruments, and the following parameters were obtained: (1) Minimum resistivity: refers to the minimum resistivity obtained by testing any test point among all SiC wafers cut from the 4H-SiC single crystal.

[0064] (2) Maximum resistivity: refers to the maximum resistivity obtained by testing any test point among all SiC wafers cut from the 4H-SiC single crystal.

[0065] (3) Average resistivity difference between carbon surface and silicon surface: refers to the difference between the average resistivity of the first wafer obtained by cutting the 4H-SiC single crystal from the carbon surface and the average resistivity of the first wafer obtained by cutting the silicon surface.

[0066] (4) Maximum value of resistivity variation coefficient of any cross section: Each of the SiC wafers obtained by cutting the 4H-SiC single crystal has a resistivity variation coefficient value (resistivity variation coefficient = (standard deviation / average value) × 100%). The maximum value of resistivity variation coefficient refers to the maximum value of resistivity variation coefficient obtained by testing all SiC wafers.

[0067] 2. The Bow and Warp values ​​of each wafer were tested using instruments, and the following parameters were obtained: (1) Maximum absolute Bow value: refers to the maximum absolute Bow value obtained from all SiC wafers cut from the 4H-SiC single crystal; (2) Maximum Warp value in the annular region: refers to the maximum value of the Warp value obtained by testing in the annular region of all SiC wafers cut from the 4H-SiC single crystal. The annular region refers to the region extending 30mm inward from the edge. (3) Maximum Warp value in the central region: refers to the maximum value of the Warp value obtained in the central region of all SiC wafers cut from the 4H-SiC single crystal. The central region refers to the other regions outside the annular region (the region extending 30mm inward from the edge).

[0068] 3. The in-plane stress of each wafer was tested using instruments, and the following parameters were obtained: (1) Maximum value of in-plane stress: refers to the maximum value of the average in-plane stress obtained from all SiC wafers cut from the 4H-SiC single crystal, which means that the average stress of any cross section of the 4H-SiC single crystal is less than the maximum value of the average in-plane stress. (2) The maximum value of the average internal stress in the [11-20] crystal direction: refers to the maximum value of the average in-plane stress obtained by testing all SiC wafers cut from the 4H-SiC single crystal in the [11-20] crystal direction; (3) The maximum value of the average internal stress in the [1-100] crystal direction: refers to the maximum value of the average in-plane stress obtained by testing all SiC wafers cut from the 4H-SiC single crystal in the [1-100] crystal direction; (4) Maximum average stress in the [11-20] direction within the 3 / 4 diameter region: This refers to the maximum value of the in-plane stress in the [11-20] direction within the 3 / 4 diameter region of all SiC wafers cut from the 4H-SiC single crystal. This value can represent the maximum value of the average stress in the [11-20] direction within the 3 / 4 diameter region of any cross-section of the 4H-SiC single crystal. (5) Maximum value of average stress in the [1-100] direction within a 3 / 4 diameter region: This refers to the maximum value of the average in-plane stress obtained by testing the [1-100] direction within a 3 / 4 diameter region of all SiC wafers cut from the 4H-SiC single crystal. This value can represent the maximum value of the average stress in the [1-100] direction within a 3 / 4 diameter region of any cross-section of the 4H-SiC single crystal. (6) Maximum average stress value on any axis within 3 / 4 of the diameter: refers to the maximum average stress value of several axes obtained in the 3 / 4 diameter region of all SiC wafers cut from the 4H-SiC single crystal.

[0069] 4. The Ω angle and radius of curvature of each wafer were tested using X-rays at powers of 1.6KW and 9KW, and the following parameters were obtained: (1) The maximum difference between the Ω angle obtained at 1.6KW and the Ω angle obtained at 9KW at the same site; Several sites of all SiC wafers cut from the 4H-SiC single crystal were tested at 1.6KW and 9KW, and a difference was obtained at each site, which refers to the maximum difference between the Ω angle obtained at 1.6KW and the Ω angle obtained at 9KW at all SiC wafers cut from the 4H-SiC single crystal; (2) Maximum difference in radius of curvature between 1.6KW and 9KW: All SiC wafers cut from the 4H-SiC single crystal were tested at 1.6KW and 9KW. A radius of curvature difference was obtained for each wafer. The maximum difference in radius of curvature between 1.6KW and 9KW refers to the maximum value of the difference in radius of curvature between 1.6KW and 9KW for all SiC wafers cut from the 4H-SiC single crystal. Radius of curvature difference = [2|R1-R2| / (R1+R2)]×100%, where R1 refers to the radius of curvature at 1.6KW and R2 refers to the radius of curvature at 9KW.

[0070] Table 1

[0071] Table 2

[0072] In the 4H-SiC single crystal prepared in this application, the range of stress exceeding 4.5 MPa in any cross-section along the [1-100] and [11-20] directions is less than 1 / 10 of the diameter. Furthermore, according to the data characterized in Tables 1 and 2, the 4H-SiC single crystal and single crystal wafer of this application can simultaneously reduce resistivity and stress, thus meeting the requirements of power devices for good conductivity and stress tolerance. Figure 1 This is a schematic diagram of the birefringence test of two crystal orientations on one of the 4H-SiC single crystal wafers prepared in Example 2, according to... Figure 1 The stress test diagrams for the two crystal orientations obtained from the tests along the two indicated directions (section line A and section line B) are shown below. Section line A represents the [11-20] crystal orientation, and its stress test diagram is shown in [reference needed]. Figure 2 Section line B is in the [1-100] crystal orientation, and its stress test diagram is shown below. Figure 3 ,pass Figure 2 and Figure 3 It can be seen that the average stress of this 4H-SiC single crystal wafer is low, and the average stress in the region of 3 / 4 of the diameter is <3 MPa, while the range where the stress exceeds 4.5 MPa is less than 1 / 10 of the diameter.

[0073] The data characterized above demonstrate that the growth method of this application can prepare 4H-SiC single crystals and single crystal wafers with low resistivity and low stress. The advantages of the growth method of this application are demonstrated by comparing Example 3 and Comparative Examples 1-3. However, this comparison is only for the current growth method and does not imply that new preparation methods cannot be studied to obtain the 4H-SiC single crystals and single crystal wafers of this application. Therefore, this comparison does not constitute a limitation on the 4H-SiC single crystals and single crystal wafers of this application. A comparison of Example 3 and Comparative Example 4 shows that even though it is currently possible to prepare 4H-SiC with resistivity greater than 6 mΩ·cm and less than 12 mΩ·cm, it is difficult to control the coefficient of variation of resistivity of the SiC cross-section to within 3% and to control the average in-plane stress of SiC to within 6 MPa.

[0074] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A 4H-SiC single crystal with low resistivity and low stress, characterized in that, The resistivity of the 4H-SiC single crystal at any location is greater than 6 mΩ·cm and less than 12 mΩ·cm, the coefficient of variation of resistivity of any cross section of the 4H-SiC single crystal is ≤3%, and the average stress of any cross section of the 4H-SiC single crystal is ≤6 MPa.

2. The low resistivity and low stress 4H-SiC single crystal according to claim 1, characterized in that, The difference between the average resistivity of the silicon surface and the average resistivity of the carbon surface of the 4H-SiC single crystal is less than 1.5 mΩ·cm; and / or The average stress of the 4H-SiC single crystal in any cross section along the [1-100] and / or [11-20] directions is <4.5 MPa.

3. The low resistivity and low stress 4H-SiC single crystal according to claim 2, characterized in that, In the 4H-SiC single crystal, within a region of 3 / 4 of the diameter of any cross-section, the average stress in the [1-100] and / or [11-20] directions is <3 MPa; and / or In the 4H-SiC single crystal, the range in which the stress exceeds 4.5 MPa in any cross-section along the [1-100] and / or [11-20] directions is less than 1 / 10 of the diameter.

4. The low resistivity and low stress 4H-SiC single crystal according to claim 1, characterized in that, In the X-ray testing of the 4H-SiC single crystal, the difference between the Ω angle obtained at the same site with a power of 1.6 kW and that obtained with a power of 9 kW is less than 0.2°; and / or In X-ray testing of any 4H-SiC single crystal wafer obtained by cutting the 4H-SiC single crystal, the difference between the radius of curvature obtained at 1.6KW and the radius of curvature obtained at 9KW is ≤5%.

5. The low resistivity and low stress 4H-SiC single crystal according to claim 1, characterized in that, Within 3 / 4 of the diameter of the 4H-SiC single crystal, the average stress on any axis is ≤4.0MPa.

6. A 4H-SiC single crystal wafer with low resistivity and low stress, characterized in that, The resistivity of the 4H-SiC single crystal wafer at any location is greater than 6 mΩ·cm and less than 12 mΩ·cm, the coefficient of variation of the resistivity of the 4H-SiC single crystal wafer is ≤3%, and the average in-plane stress of the 4H-SiC single crystal wafer is ≤6 MPa.

7. The low resistivity and low stress 4H-SiC single crystal wafer according to claim 6, characterized in that, The average stress in the [1-100] and / or [11-20] directions of the 4H-SiC single crystal wafer is <4.5 MPa; and / or The diameter of the 4H-SiC single crystal wafer is 150-300mm.

8. The low resistivity and low stress 4H-SiC single crystal wafer according to claim 7, characterized in that, Within a 3 / 4 diameter region of the 4H-SiC single crystal wafer, the average stress value in the [1-100] and / or [11-20] directions is <3 MPa; and / or In the [1-100] and / or [11-20] directions of the 4H-SiC single crystal wafer, the range where the stress exceeds 4.5 MPa is less than 1 / 10 of the diameter.

9. The low resistivity and low stress 4H-SiC single crystal wafer according to claim 6, characterized in that, In the X-ray testing of the 4H-SiC single crystal wafer, the difference between the Ω angle obtained at the same site under 1.6KW power and the Ω angle obtained under 9KW power is less than 0.2°; and / or In the X-ray testing of the 4H-SiC single crystal wafer, the difference between the radius of curvature obtained at 1.6KW and the radius of curvature obtained at 9KW is ≤5%.

10. The low resistivity and low stress 4H-SiC single crystal wafer according to claim 6, characterized in that, The absolute value of the Bow of the 4H-SiC single crystal wafer is ≤15μm; and / or The 4H-SiC single crystal wafer has a 30mm inward area from the edge as a ring region, and the remainder is the central region. The Warp value of the ring region is ≤30μm, and the Warp value of the central region is ≤15μm.

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