Method for quantitatively characterizing internal stress of substrate defect accumulation region, internal stress of substrate in epitaxial wafer and internal stress of epitaxial layer

Abstract

The invention discloses a method for quantitatively characterizing internal stress of a substrate defect accumulation region, internal stress of a substrate in an epitaxial wafer and internal stress of an epitaxial layer, and belongs to the technical field of semiconductor detection. Comprising the following steps: 1, testing a substrate to obtain peak displacement values and stress values of the substrate at different test points, and calculating to obtain a peak displacement and stress conversion coefficient mu; and 2, carrying out internal scanning test on the substrate defect accumulation area by using a Raman tester to obtain a peak position value, calculating a peak position displacement value, and calculating an internal stress value of the substrate defect accumulation area according to the peak position displacement value and the peak position displacement and stress conversion coefficient mu in the step 1. According to the invention, quantitative testing of the internal stress of the substrate defect accumulation region, the internal stress of the substrate in the epitaxial wafer and the internal stress of the epitaxial layer can be realized, and according to the tested stress information, each process parameter in the growth of the crystal or the growth of the substrate epitaxial layer can be fed back, so that the low-stress substrate or epitaxial wafer can be obtained.

Description

Technical Field

[0001] The present application relates to a method for quantitatively characterizing internal stress in a substrate defect aggregation region, internal stress in a substrate in an epitaxial wafer, and internal stress in an epitaxial layer, and belongs to the technical field of semiconductor detection. Background Art

[0002] Silicon carbide (SiC) planes can cause defects such as microtubes and dislocations due to lattice dislocation, lattice distortion or inclusions. Take microtubes as an example. They are generated due to stress relaxation, and their stress birefringence morphology can be seen under polarized light. Currently, microtubes or stress lines can be observed by polarized light, but it is difficult to quantitatively observe the difference between the defect aggregation area and the surrounding stress area and the normal stress area.

[0003] SiC surface defects such as microtubes and dislocations may be caused by lattice dislocation, lattice distortion or inclusions. Taking microtubes as an example, they are generated due to stress relaxation, and their stress birefringence morphology can be seen under polarized light. Currently, microtubes or stress lines can be observed by polarized light, but it is difficult to quantitatively observe the difference between stress in defect clustering areas and stress in normal areas. In addition, the stress in the substrate is relatively complex. The thermal stress of silicon carbide crystal growth and the residual stress caused by defects in the body are mixed with the surface stress introduced during the processing of the silicon carbide substrate. It is difficult to distinguish between surface stress and body stress. Therefore, there is a lack of a quantitative test method for body stress in the defect clustering area of ​​the silicon carbide substrate.

[0004] Silicon carbide substrates can be further divided into semi-insulating and conductive substrates. According to their physical properties, semi-insulating silicon carbide is mostly used in high-power devices such as 5G base stations and RF chips, while conductive silicon carbide is mostly used in the new energy industry. Based on the differences in their physical properties and application directions, semi-insulating SiC is used as a heteroepitaxial substrate to grow GaN on the Si surface of the SiC substrate, while conductive SiC is used as a homoepitaxial substrate to grow SiC on the Si surface of the SiC substrate.

[0005] Since the epitaxial process is based on the CVD method, an epitaxial film is further grown on the substrate end. Therefore, during the growth of the epitaxial film, due to differences in the epitaxial process, there will be a lattice mismatch between the epitaxial layer and the substrate, thereby introducing stress into the substrate and the epitaxial layer. Among them, the heteroepitaxial lattice mismatch is more serious than that of homoepitaxial. Quantitative characterization of the internal stress of the substrate and the internal stress of the epitaxial wafer in the epitaxial wafer can play a feedback role in the epitaxial process. However, there is still a lack of a quantitative test method for the internal stress of the substrate and the internal stress of the epitaxial layer in the epitaxial wafer. Summary of the invention

[0006] In order to solve the above problems, a method for quantitatively characterizing the internal stress in the defect clustering area of ​​the substrate, the internal stress of the substrate in the epitaxial wafer, and the internal stress of the epitaxial layer is provided. The method can realize the quantitative test of the internal stress in the defect clustering area of ​​the substrate, the internal stress of the substrate in the epitaxial wafer, and the internal stress of the epitaxial layer, and can obtain complete stress information of the substrate or the epitaxial layer. According to the above stress information, it can play a feedback role on the parameters of each process in the growth of the crystal or the growth of the substrate epitaxial layer, thereby optimizing the process parameters of the crystal growth process or the substrate epitaxial layer growth process, reducing the generation of internal defects in the substrate or reducing the internal stress introduced in the growth of the epitaxial layer, thereby obtaining a low-stress substrate or epitaxial wafer.

[0007] According to one aspect of the present application, a method for quantitatively characterizing the internal stress of a defect aggregation region of a substrate is provided, comprising the following steps:

[0008] Step 1: Test the substrate to obtain the actual peak value and stress value of the substrate at different test points, calculate the difference between the actual peak value and the peak value of the standard substrate, that is, obtain the peak displacement value of different test points, and calculate the peak displacement and stress conversion coefficient μ according to the peak displacement value and stress value;

[0009] The second step: use a Raman tester to perform an internal scanning test on the defect clustering area of ​​the substrate, where the diameter of the substrate is greater than 150 mm, the defects in the defect clustering area include at least one of micropipes, dislocations, polytypes, and carbon inclusions, and the interior is an area extending inward from the surface of the substrate to 30%-60% of the substrate thickness, obtain the peak position value, and calculate the peak position displacement value, and calculate the internal stress value of the substrate defect clustering area based on the peak position displacement value and the peak position displacement and stress conversion coefficient μ in the first step.

[0010] The substrate is cut from crystals. Due to different cutting processes, the thickness of the substrate surface damage layer will be different. However, even with the worst cutting process, the thickness of the surface damage layer introduced does not exceed 30% of the substrate thickness. Therefore, the area extending from the substrate surface to 30%-60% of the substrate thickness is the substrate's internal stress zone, which is not affected by factors such as later cutting.

[0011] Optionally, before the second step of using a Raman tester to perform an internal scanning test on the substrate defect clustering area, the Raman tester is first used to perform an axial test on the substrate defect clustering area, and the depth of the surface damage layer and the damage stress extension layer in the substrate defect clustering area is determined based on the stress curve fed back by the axial test.

[0012] Optionally, before the second step of using a Raman tester to perform an internal scanning test on the defect clustering area of ​​the substrate, a curvature test is first performed on the substrate surface to obtain the curvature of the substrate in the defect clustering area, and based on the curvature, in the second step of the scanning test, an equidistant focusing mode and / or an equifocusing plane mode is selected, wherein the distance between the Raman laser spot at each test point in the equidistant focusing mode and the substrate surface is equal, and the Raman laser spot at each test point in the equifocusing plane mode is in the same horizontal plane.

[0013] According to another aspect of the present application, a method for quantitatively characterizing the internal stress of a substrate in an epitaxial wafer is provided, comprising the following steps:

[0014] Step 1: Test the substrate to obtain the actual peak value and stress value of the substrate at different test points, calculate the difference between the actual peak value and the peak value of the standard substrate, that is, obtain the peak displacement value of different test points, and calculate the peak displacement and stress conversion coefficient μ according to the peak displacement value and stress value;

[0015] Step 2: Use a Raman tester to perform internal scanning test on the substrate in the epitaxial wafer, where the interior of the substrate is the area extending inward from the surface of the substrate to 30%-60% of the substrate thickness, obtain the peak value, and calculate the peak displacement value. According to the peak displacement value and the peak displacement and stress conversion coefficient μ in the first step, calculate the internal stress value of the substrate in the epitaxial wafer.

[0016] Optionally, before the second step of using a Raman tester to perform internal scanning testing on the defect clustering area of ​​the substrate, the Raman tester is first used to perform an axial test on the epitaxial wafer, and the depth of the epitaxial layer, the surface damage layer and the damage stress extension layer in the epitaxial wafer is determined based on the stress curve fed back by the axial test.

[0017] Optionally, before the second step of using a Raman tester to perform an internal scanning test on the defect aggregation area of ​​the substrate, a curvature test is first performed on the surface of the epitaxial wafer to obtain the curvature of the surface of the epitaxial wafer. Taking the curvature as a reference, in the second step of the scanning test, an equidistant focusing mode and / or an equifocusing plane mode is selected, wherein the distance between the Raman laser spot at each test point in the equidistant focusing mode and the substrate surface is equal, and the Raman laser spot at each test point in the equifocusing plane mode is in the same horizontal plane.

[0018] According to another aspect of the present application, a method for quantitatively characterizing the stress in an epitaxial layer is provided, characterized in that the method comprises the following steps:

[0019] Step 1: Test the epitaxial layer to obtain the actual peak value and stress value of the epitaxial layer at different test points, calculate the difference between the actual peak value and the peak value of the standard substrate, that is, obtain the peak displacement value of different test points, and calculate the peak displacement and stress conversion coefficient μ according to the peak displacement value and stress value;

[0020] Step 2: Use a Raman tester to scan the inside of the epitaxial layer. The inside of the epitaxial layer is the area extending from the surface of the epitaxial wafer inward to 30% to 60% of the thickness of the epitaxial layer. Obtain the peak value and calculate the peak displacement value. According to the peak displacement value and the peak displacement and stress conversion coefficient μ in the first step, calculate the internal stress value of the epitaxial layer.

[0021] Before the second step of using a Raman tester to perform an internal scanning test on the epitaxial layer, a curvature test is first performed on the surface of the epitaxial wafer to obtain the curvature of the surface of the epitaxial wafer. Taking the curvature as a reference, an equidistant focusing mode is selected in the second step of the scanning test. In the equidistant focusing mode, the distance between the Raman laser spot and the substrate surface at each test point is equal.

[0022] In the above-mentioned in-vivo stress test of the substrate defect clustering area, the in-vivo stress test of the substrate in the epitaxial wafer and the in-vivo stress test of the epitaxial layer, the calculation steps of the peak displacement and the stress conversion coefficient μ are as follows:

[0023] First, the interplane spacing dx in the substrate or epitaxial layer is tested by a test instrument. The interplane spacing dx is subtracted from the theoretical interplane spacing d0 to obtain the interplane spacing difference △d at different test points. Hooke's law σ / S=E×(△d / d0) or stress-strain formula σ=E×△d is used to obtain the stress value of the substrate at different test points.

[0024] Afterwards, the substrate is scanned and tested using a Raman tester to obtain the actual peak position values ​​at different test points, and the difference between the actual peak value and the standard peak position is calculated to obtain the peak displacement values ​​at different test points. The ratio of the peak displacement value to the stress value is the peak displacement and stress conversion coefficient μ;

[0025] Preferably, the testing instrument for testing the interplanar spacing dx in the substrate is selected from any one or more of an XRD diffractometer, a synchrotron radiation tester, a white light tester, a neutron diffractometer, a scanning electron microscope, and a transmission electron microscope.

[0026] When an XRD diffractometer is used to test a substrate or an epitaxial layer, the interplanar spacing dx at different positions of the substrate is calculated using the Bragg diffraction formula.

[0027] In the above-mentioned internal stress test of the substrate defect aggregation area, the internal stress test of the substrate in the epitaxial wafer and the internal stress test of the epitaxial layer, the substrate surface is taken as the zero point, and the test range of the axial test is from -150μm to -30μm inside the substrate to above the surface of the substrate or epitaxial layer.

[0028] Preferably, with the substrate surface as the zero point, the test range of the axial test is from -100 μm to -30 μm inside the substrate to above the surface of the substrate or epitaxial layer.

[0029] In the above-mentioned in-vivo stress test of the substrate defect clustering area, the in-vivo stress test of the substrate in the epitaxial wafer, and the in-vivo stress test of the epitaxial layer, the focus depth (d) and the spot diameter (D) of the Raman spot are determined according to the thickness of the epitaxial layer, the surface damage layer, and the stress extension layer, so that the Raman spot is located inside the substrate or inside the epitaxial layer. The calculation formula for selecting the focus depth (d) is:

[0030] Where Dp is the penetration depth of the Raman laser in the sample, α is the absorption coefficient, λ is the laser wavelength, and k is the extinction coefficient. The appropriate focusing depth (d) is selected according to the calculated penetration depth (Dp). The requirement that needs to be met is that the penetration depth (Dp) is greater than the focusing depth (d). In the in vivo stress test of the substrate defect aggregation area and the in vivo stress test of the substrate in the epitaxial wafer, the Raman laser spot is located inside the substrate. In the in vivo stress test of the epitaxial layer, the Raman laser spot is located inside the epitaxial layer.

[0031] The calculation formula of the spot diameter (D) is:

[0032] Where λ is the laser wavelength and Na is the numerical aperture of the device.

[0033] In the above-mentioned in-vivo stress test of the substrate defect clustering area, the in-vivo stress test of the substrate in the epitaxial wafer and the in-vivo stress test of the epitaxial layer, the diameter of the substrate is greater than 200 mm.

[0034] In the above-mentioned in-vivo stress test of the substrate defect clustering area, the in-vivo stress test of the substrate in the epitaxial wafer and the in-vivo stress test of the epitaxial layer, the specific method of the curvature test is:

[0035] (1) Ensure that the test platform is level and select a fixed origin (0,0,0) on the test platform;

[0036] (2) Use Raman automatic focusing to the position with the strongest test signal on the substrate surface or epitaxial wafer surface, mark this position as (a, b, c), then adjust the Raman laser down by a distance of H and focus on the position (a, b, cH);

[0037] (3) Adjust the Raman laser test position to (0,0,cH) to perform an iso-focal plane test to obtain a peak intensity scan of the substrate surface. Calculate the distance from the focal plane to the substrate surface or epitaxial wafer surface at different positions to determine the curvature of the substrate surface or epitaxial wafer surface.

[0038] Optionally, the value range of H is 5-150 μm, preferably 5-100 μm.

[0039] In the above-mentioned in-vitro stress test of the substrate defect aggregation area, the in-vitro stress test of the substrate in the epitaxial wafer and the in-vitro stress test of the epitaxial layer, the peak value and peak displacement value in the second step are obtained by fitting, and the fitting uses functions including Gaussian, Lorentz, GaussLor, AGauss, Aloren and AgaussLor.

[0040] In the above-mentioned in-vivo stress test of the substrate defect aggregation area and the in-vivo stress test of the substrate in the epitaxial wafer, S1 is recorded as the in-vivo stress value calculated by the equal spacing focusing test mode, and S2 is recorded as the in-vivo stress value calculated by the equal focusing plane mode, -0.2MPa≤S1-S2≤0.2MPa; or

[0041] V1 is recorded as the peak position value obtained after fitting the equal-space focusing mode, and V2 is recorded as the peak position value obtained after fitting the equal-focusing plane mode, -0.0005cm -1 <V1-V2<0.0005cm -1 .

[0042] Preferably, -0.05MPa≤S1-S2≤0.05Mpa; or

[0043] -0.0001cm -1 <V1-V2<0.0001cm -1 .

[0044] According to the curvature of the substrate surface, the influence of the curvature of the substrate surface on the internal stress of the substrate can be eliminated in the internal stress test of the substrate defect clustering area and the internal stress test of the substrate in the epitaxial wafer. According to the curvature of the epitaxial wafer surface, the influence of the curvature of the epitaxial wafer surface on the internal stress of the epitaxial layer can be eliminated in the internal stress test of the epitaxial layer.

[0045] Optionally, the substrate is selected from a silicon carbide substrate;

[0046] Preferably, the crystal form of the silicon carbide substrate is one of 2H-SiC, 4H-SiC, 6H-SiC, 3C-SiC, and 15R-SiC.

[0047] In the above-mentioned in-vivo stress test of substrate defect clustering area, in-vivo stress test of substrate in epitaxial wafer and in-vivo stress test of epitaxial layer, the in-vivo stress value calculated in the second step includes in-vivo absolute stress and in-vivo relative stress;

[0048] Among them, in the calculation of the absolute stress in the body, the calculated peak displacement value is the difference between the actual peak position of the test point and the standard peak position; in the calculation of the relative stress in the body, the calculated peak displacement value is the difference between the actual peak position of the test point and the actual peak position of the relative point.

[0049] The peak value of the relative point can be a reference value obtained in the entire test plane. The value of each test point is correlated with the reference value for obtaining the peak value of the relative point. The reference value includes but is not limited to the mean, median, mode and any one of the results calculated by other statistical functions of all test values ​​in the entire test plane.

[0050] Absolute stress can reflect the difference between the substrate and the perfect SiC crystal without defects, and is used to determine the stress level of the SiC substrate. However, since it is difficult to achieve a perfect SiC substrate with current technology, the relative stress can be used to determine the relative stress distribution within the substrate surface.

[0051] For example, when the absolute stress of the substrate is large and the relative stress is small, it means that there are more in-plane defects, but the stress distribution is uniform, the crystal quality is poor, and the uniformity quality in each area of ​​the substrate is poor; if the absolute stress is small and the relative stress is large, the overall substrate quality is good, but there are abnormal quality deviations in some areas.

[0052] The beneficial effects of this application include but are not limited to:

[0053] 1. This application calculates the interplanar spacing and interplanar spacing difference at different positions of the substrate, uses a formula to calculate the stress value at different positions, and calculates the peak displacement and stress conversion coefficient μ based on the peak displacement value obtained by Raman test, providing a calculation basis for the quantitative test of the stress in the substrate.

[0054] 2. The present application performs axial testing on the substrate to determine the thickness of the surface damage layer and the damage stress extension layer of the substrate. By calculating and selecting the Raman laser penetration depth and the spot diameter, the Raman laser is used to test the inside of the substrate. Based on the obtained peak displacement value and the calculation of the peak displacement and the stress conversion coefficient μ, quantitative testing of the internal stress in the defect aggregation area of ​​the substrate and the internal stress of the substrate in the epitaxial wafer is achieved.

[0055] 3. The present application performs a curvature test on the substrate. Based on the calculated curvature, the use of equal-pitch focusing test or equal-focusing plane test can eliminate the influence of the curvature and warping of the substrate surface, thereby achieving quantitative testing of the internal stress in the defect aggregation area of ​​the substrate or the internal stress of the substrate in the epitaxial layer, thereby improving the test accuracy of the test method.

[0056] 4. The present application provides a method for quantitatively characterizing the internal stress in the defect clustering area of ​​the substrate, which can quantitatively test the difference between the stress in the defect clustering area and the stress in the normal area, and can quantitatively test the stress in the substrate that has not yet been released through defects due to lattice distortion, thereby improving the accuracy of stress detection in the defect clustering area of ​​the substrate.

[0057] 5. According to the method of quantitatively characterizing the internal stress of the substrate and the internal stress of the epitaxial layer in the epitaxial wafer of the present application, the change of the internal stress of the substrate during the epitaxial process and the internal stress of the epitaxial layer can be quantitatively tested, so as to calculate the stress value introduced into the substrate by the lattice adaptation of the epitaxial layer and the substrate, which plays a feedback role on the parameters of each process in the growth of the substrate epitaxial layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] 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:

[0059] Figure 1 This is the axial peak intensity distribution diagram of the Si substrate and the 4H-SiC substrate involved in Example 2 of the present application.

[0060] Figure 2 This is a schematic diagram of the surface shape of a SiC substrate for Raman testing involved in Example 2 of the present application.

[0061] Figure 3 This is a schematic diagram and stress axial distribution diagram of the Raman axial test SiC substrate involved in Example 3 of the present application.

[0062] Figure 4 Schematic diagram of testing the internal stress of a substrate using the Raman equi-pitch focusing mode and the equi-focusing plane mode involved in Example 4 of the present application.

[0063] Figure 5 This is a test diagram of the substrate defect aggregation area involved in Example 5 of the present application.

[0064] Figure 6 This is a diagram of the internal stress test of the substrate involved in Example 6 of the present application before and after the epitaxial layer growth.

[0065] Figure 7 This is a graph showing the in vivo stress test of the epitaxial layer in Example 7. DETAILED DESCRIPTION

[0066] The present application is described in detail below in conjunction with the embodiments, but the present application is not limited to these embodiments. The quantitative testing method of the present application can be used to detect the surface stress and internal stress of the substrate. In the following embodiments, 4H-SiC single crystal is used as an example for illustration, and the type and crystal form of the substrate do not constitute a limitation to the present testing method.

[0067] The principle of using Raman to test the stress of the substrate in the following embodiments is as follows: the Raman spectrometer passes a monochromatic laser of a certain wavelength through a series of optical paths and then converges the laser through an objective lens to irradiate the substrate surface, and the laser photons interact with the substrate lattice to cause photon scattering. The occurrence of Raman scattering is related to the lattice vibration of the substrate itself. When there is residual stress in the sample, the tensile and compressive stresses will cause the atomic bond length to be elongated or shortened accordingly, thereby causing the atomic vibration frequency to decrease or increase, which is reflected in the Raman spectrum as the characteristic peak of the substrate moves to a low frequency or a high frequency, that is, the peak position shift occurs.

[0068] Example 1 Quantitative Testing Method for Substrate Stress

[0069] (1) Calculation of peak displacement and stress conversion coefficient μ

[0070] First, a single crystal XRD diffractometer is used to test the silicon carbide substrate and the substrate is analyzed according to the reciprocal lattice space. The parameters of the standard 4H-SiC substrate are calculated and compared with the standard parameters. Then, according to the Bragg diffraction equation: 2dsinθ=nλ, where d is the interplanar spacing, θ is the diffraction half-angle, n is the diffraction order, and λ is the wavelength, the θ and d of different substrates are tested. It can be seen that the tensile and compressive stress inside the crystal causes the interplanar spacing d to expand and contract accordingly. According to the different interplanar spacings d0 and d x , d x It is divided into d1 and d2, where d0 is the theoretical interplanar spacing, d1 is the interplanar spacing after tensile stress, and d1 is greater than d0, and d2 is the interplanar spacing after compressive stress, and d2 is less than d0. The interplanar spacing dx and the theoretical interplanar spacing d0 are subtracted to obtain the interplanar spacing difference △d at different test points, △d = d1-d0 or △d = d0-d2. Then, the stress value σ of the silicon carbide substrate at different test points is calculated in combination with Hooke's law or stress-strain formula:

[0071] The calculation formula of Hooke's law is σ / S=E×(△d / d0), where S is the area affected by σ, which is a fixed value. When Hooke's law is applicable to microscopic calculations, S is the microscopic area, which can be calculated as unit 1. E is the Young's modulus of the substrate, which is a fixed parameter of the substrate. △d is the difference in crystal plane spacing at different positions, d0 is the theoretical crystal plane spacing, and σ is the stress value that needs to be calculated.

[0072] The calculation formula for stress and strain is σ=E×△d, where E is the Young's modulus of the substrate, which is a fixed parameter of the substrate, △d is the difference in crystal plane spacing at different positions, and σ is the stress value to be calculated.

[0073] The Raman tester is used to scan and test the substrate to obtain the actual peak value of the substrate at different test points, and the difference between the actual peak value and the standard peak value is calculated to obtain the peak displacement value △v at different test points; the ratio of the peak displacement value to the stress value at different test points is the peak displacement and stress conversion coefficient μ, which ranges from -125 to -2500.

[0074] (2) Quantitative test method of substrate stress

[0075] First, set the Raman test points. You can perform single-point testing or Mapping scanning on the entire substrate. Therefore, single-point testing is a sporadic coordinate point setting, and Mapping scanning is 10x10~50x50 and more points. You can choose the appropriate test method according to the properties of the substrate to determine the Raman test coordinates of the silicon carbide substrate.

[0076] The test results are then output, including but not limited to editable peak position, peak intensity data and Mapping.

[0077] The output data is then subjected to peak position fitting, where fitting functions include but are not limited to Gaussian, Lorentz, GaussLor, AGauss, Aloren and AGaussLor, to obtain precise peak position values ​​and peak position shift values, with the peak position accurate to more than one decimal place.

[0078] Finally, according to the peak displacement and stress conversion coefficient μ calculated in (1) and the peak displacement value △v obtained in the Raman test, the stress value of silicon carbide is calculated. The calculation formula is: σ(MPa)=μ×△v(cm -1 ), and finally obtain the stress test image of the substrate.

[0079] Example 2 Testing of curvature of substrate surface or epitaxial wafer surface

[0080] Since SiC is subjected to a lot of external mechanical stress during the process of preparing wafers from crystals through a series of processes, it is difficult to ensure that the surface is completely level, that is, there is a certain degree of curvature. In order to eliminate the influence of substrate surface curvature on substrate surface stress and internal stress test, it is necessary to first perform a curvature test on the substrate. According to the curvature, the substrate surface stress is tested with equal spacing focus, and the substrate internal stress is tested with equal spacing focus or equal focus plane.

[0081] After the curvature test, the tester needs to be calibrated using single crystal silicon. First, a Z-axis mapping test is performed on the single crystal Si to confirm that it is a Gaussian distribution. The surface of the single crystal Si substrate is taken as the zero point, and an axial mapping test is performed from -100μm inside the single crystal Si substrate to +20μm above the single crystal Si substrate to analyze the change in Raman signal intensity. The results are as follows: Figure 1 As shown, Figure 1 (a) is the axial peak intensity distribution diagram of the single crystal Si substrate. The single crystal Si substrate is a non-transparent material, so its peak intensity presents a Gaussian distribution with the surface zero point position as the symmetry axis. Then, the single crystal Si is subjected to a surface focusing single point test, and the single crystal Si Raman peak position is adjusted to 520.70 cm by the correction instrument. -1 , at this time, it means that the instrument optical path has been calibrated.

[0082] The following uses a 4H-SiC substrate as an example to illustrate the test process of surface curvature. The 4H-SiC substrate is tested in the Z direction using a calibrated tester. The Raman laser is transmitted from -100μm inside the 4H-SiC substrate to +20μm above the 4H-SiC substrate. Figure 1 (b) is the axial peak intensity distribution diagram of the 4H-SiC substrate. The 4H-SiC substrate and other silicon carbide are transparent materials, so the Raman laser can penetrate into the silicon carbide substrate, and as the Raman laser incidence depth increases, the feedback signal gradually weakens. Other silicon carbides include semi-insulating, conductive, and 3C, 4H, 15R, 6H and other silicon carbide substrates with different crystal forms. Therefore, the Raman peak intensity of the silicon carbide substrate gradually decreases as the Raman laser penetrates deeper into the silicon carbide substrate.

[0083] The Raman device’s autofocus function can be used to automatically find the strongest peak of the test signal on the substrate surface, so that the curvature of the substrate surface can be measured with the help of this function. The specific method is as follows:

[0084] (1) First, ensure that the test platform is level, select a fixed origin (0,0) on the test platform, and mark the point as the three-dimensional coordinate (0,0,0);

[0085] (2) According to the thickness of the substrate, the objective lens is raised to a height that does not contact the substrate, and any point is automatically focused to the position where the test signal on the substrate surface is the strongest. This position is marked as (a, b, c), and then the Raman laser is adjusted to move down a distance of H and the focusing position is adjusted to (a, b, cH);

[0086] (3) Adjust the Raman laser test position to (0,0,cH) to perform an iso-focal plane test to obtain a two-dimensional peak intensity scan of the substrate surface. Figure 1 The peak intensity distribution relationship of SiC substrate and Figure 2 According to the principle diagram in, the distance between the focal plane of the Raman laser and the surface of the silicon carbide substrate can be obtained, thereby obtaining the in-plane curvature of the substrate and obtaining the in-plane curvature distribution map of the substrate.

[0087] The same steps and operation methods can be used to test the surface curvature of the epitaxial wafer.

[0088] Example 3 Axial test distinguishes substrate surface stress from internal stress

[0089] Since the substrate is affected by the temperature field and the introduction of inclusions during the crystal growth process, thermal stress and residual stress exist inside the crystal, and the substrate is obtained after a series of cutting, grinding and polishing. The above-mentioned processing process of the crystal to form the substrate will cause surface lattice distortion, thereby generating surface stress. In order to further distinguish the surface stress from the body stress of the substrate, the substrate is subjected to axial testing according to the light transmittance characteristics of silicon carbide, namely, Z-direction Mapping, with the substrate surface as the zero point. The test range of the axial test is from -150μm to -30μm inside the substrate to above the substrate surface.

[0090] Test schematic diagram Figure 3 As shown in (a), the laser spot is gradually focused upward from the substrate body to the damaged stress extension layer, further to the surface damaged layer, and then continued to focus upward into the air to determine the thickness of the substrate surface damaged layer and the damaged stress extension layer. With the substrate surface as the zero point, the axial test range is that the Raman laser spot gradually moves upward from -100μm inside the substrate to 30μm above the substrate surface. Figure 3 (b) is the stress axial distribution diagram of 5 points tested on the top, bottom, left and right of the substrate. The 5 points on the substrate show the same trend, and there is only a difference in the maximum negative stress at the surface damage.

[0091] Figure 3 In (b), the stress fluctuates up and down along the horizontal line from -100μm inside the substrate to -30μm, indicating that the internal stress is uniform. When the laser spot is focused on the damaged stress extension layer, the stress curve begins to show a downward trend at -30μm, and the downward trend of stress gradually increases. When it approaches the zero point on the substrate surface, it reaches the maximum negative stress value, which is the stress value of the surface damaged layer. Finally, the laser spot continues to move upward and gradually leaves the substrate surface into the air, and the stress shows a rapid rise to chaotic fluctuations. Therefore, the thickness of the surface damaged layer and the damaged stress extension layer of the substrate can be determined based on the axial test results of the substrate.

[0092] Example 4 Quantitative Testing of Stress in the Substrate

[0093] During the PVT crystal growth process, silicon carbide is affected by temperature gradient changes and the intrusion of inclusions, resulting in residual stress in the crystal. Different from the surface processing stress, the internal stress is located at a certain depth from the surface, reflecting the thermal stress and residual stress of crystal growth. In addition, silicon carbide undergoes a large amount of external mechanical stress in the process of preparing the substrate from the crystal through a series of processing, and it is difficult to ensure that the surface is completely horizontal, that is, there is a certain degree of curvature on the surface of the substrate. According to the measurement method of the curvature of the substrate surface obtained by Raman testing in Example 2, this embodiment, combined with the physical properties of silicon carbide, involves a method for quantitatively characterizing its internal stress that is not affected by surface curvature.

[0094] According to the physical property of silicon carbide being light-transmissive, the method of using Raman to quantitatively characterize the internal stress of the substrate is divided into equal-spacing focusing test and equal-focusing plane test, as follows:

[0095] 1. Equally spaced focus mode

[0096] The test principle of the equidistant focusing mode is as follows: Figure 4 As shown in (a), under this test mode, the focal depth (d) of the Raman laser focused on the inside of the substrate at different positions remains unchanged, and the penetration depth (Dp) and the spot diameter (D) of the Raman laser are calculated according to the formula, and a suitable focal depth (d) is selected. The requirement that needs to be met is that the penetration depth (Dp) is greater than the focal depth (d), and because the test is for internal stress, the focal depth d needs to be greater than the thickness of the surface damage layer and the damage stress extension layer tested in Example 3.

[0097] According to the characteristics of silicon carbide materials, the peak intensity reaches the highest when the laser is focused on the substrate surface. Therefore, the automatic focusing function of the Raman tester can be used to focus the laser on the substrate surface. Then, according to the focusing depth (d) determined above, the equally spaced focusing test is performed on different positions of the substrate, that is, the distance between the focusing plane and the substrate surface is always equal. This method is not affected by the bending and warping of the substrate surface, so that the obtained Raman peak intensity is always maintained at the axial maximum value of the test point. According to the stress quantitative testing method of Example 1, the in-body stress map of the substrate is obtained.

[0098] 2. Equifocal plane mode

[0099] The principle of the isofocal plane mode test is as follows Figure 4 As shown in (b), under this test method, the focus depth (d) of the Raman laser spot focused on the inside of the substrate at different positions changes, and the laser spot at different positions is focused on the same plane inside the substrate. The penetration depth (Dp) of the Raman laser is calculated according to the same formula as the equidistant focusing test, and the appropriate focus depth (d) is selected in the same selection method.

[0100] Since the focal planes are equal in this test method, combined with the characteristics of silicon carbide, such as Figure 1 As shown in (b), when the laser is focused on the substrate surface, the peak intensity reaches the highest and the signal gradually decays with the increase of the focus depth. And according to the effective signal-to-noise ratio tested by the Raman tester, it is found that the effective signal-to-noise ratio is inversely correlated with the Raman laser focus depth (d). Therefore, in this test method, the focus depth (d) at different positions needs to be combined with the curvature of the substrate to obtain the effective peak displacement value through the stress quantitative test method of Example 1, thereby reducing the error of the in vivo stress test. The test method obtains the in vivo stress test diagram of the substrate.

[0101] Through the above two testing methods of equal-spaced focusing mode and equal-focusing plane mode, the peak displacement values ​​inside the substrate are obtained respectively, and the internal stress distribution of the substrate is calculated. S1 is recorded as the internal stress value calculated by the equal-spaced focusing mode, S2 is recorded as the internal stress value calculated by the equal-focusing plane mode, -0.2MPa≤S1-S2≤0.2MPa, V1 is recorded as the peak value obtained after fitting the equal-spaced focusing mode, V2 is recorded as the peak value obtained after fitting the equal-focusing plane mode, -0.0005cm -1 <V1-V2<0.0005cm -1 .

[0102] The internal stress includes the internal absolute stress and the internal relative stress, which is illustrated by taking 4H-SiC as an example:

[0103] The absolute stress in the body is calculated by subtracting the measured 4H-SiC peak position from the standard peak position to determine the simplified wave vector peak position, such as FTO (2 / 4). The absolute stress in the body is calculated as:

[0104] σabsolute=μ×(v 实际 -V FTO(2 / 4) ), σ is in MPa, v 实际 and V FTO(2 / 4) The unit is cm -1 , where v 实际 is the actual FTO(2 / 4) peak position at the substrate test point, V FTO(2 / 4) is the standard peak position of FTO (2 / 4) of the substrate;

[0105] The relative stress in the body is calculated by subtracting the peak position of the 4H-SiC measured on the SiC substrate from the peak position of the relative point. The calculation formula for the relative stress in the body is:

[0106] σrelative=μ×(v (x1,y1) -V (x2,y2) ), σ is in MPa, v (x1,y1) and V (x2,y2) The unit is cm -1 , where v (x1,y1)is the actual FTO(2 / 4) peak position at the substrate test point, V (x2,y2) is the actual FTO (2 / 4) peak position of the substrate relative point. The relative stress value of the test point is calculated according to the above calculation formula. If the relative value of σ is positive, it means that the stress of the test point relative to the relative point is tensile stress. If the relative value of σ is negative, it means that the stress of the test point relative to the relative point is compressive stress.

[0107] Example 5 Quantitative testing of internal stress in the defect aggregation area of ​​the substrate

[0108] According to the axial test of Example 3, the thickness of the surface damage layer and the damage stress extension layer of the substrate is determined. According to the method for measuring the curvature of the substrate surface by Raman testing in Example 2, this embodiment, combined with the physical properties of silicon carbide, involves a method for quantitatively characterizing the stress in the defect aggregation area of ​​the substrate without being affected by surface curvature.

[0109] See Figure 5 (b) is the substrate polarization stress scanning diagram, Figure 5 (c) is the high-density micropipe aggregation area in the third quadrant of the substrate. The two testing methods of the medium-distance focusing mode and the equal-focusing plane mode in Example 4 are used to quantitatively test the substrate defect aggregation area. Since the errors of the two methods are small, the mapping results are retained to 0.1Mpa, so there is no difference in the results. The test results are shown in Figure 5 (a) It can be clearly seen that the difference between the internal stress in the defect clustering area of ​​the substrate and the internal stress in the normal area of ​​the substrate, and the internal stress value in the defect clustering area of ​​the substrate can be quantitatively tested, proving that the testing method of this embodiment can achieve quantitative testing of the internal stress in the defect clustering area of ​​the substrate.

[0110] Example 6 Quantitative Testing of Stress in the Substrate of Epitaxial Wafer

[0111] According to the axial test of Example 3, the thickness of the epitaxial layer, the surface damage layer of the substrate and the damaged stress extension layer are determined. According to the measurement method of the curvature of the epitaxial layer obtained by Raman testing in Example 2, this embodiment, combined with the physical properties of silicon carbide and the epitaxial wafer obtained therefrom, involves a method for quantitatively characterizing the stress in the substrate body of the epitaxial wafer without being affected by surface curvature and warping, so as to detect the stress change of the substrate during the growth of the epitaxial layer.

[0112] Before the epitaxial layer is grown, the test method of Example 4 is used to test the internal stress of the normal silicon carbide substrate from the Si and C surfaces. Through multiple tests, it is found that the internal stress test results of the Si and C surfaces of the same silicon carbide substrate are basically consistent. Figure 6 (a) is the stress distribution diagram of the substrate tested from the Si surface; Figure 6(b) is the stress distribution diagram of the substrate body tested from the C surface. Therefore, it can be seen that for a silicon carbide substrate, the axial residual stress distribution in the body can be considered uniform, and it can be regarded as a stress uniform body, such as Figure 6 (c) as shown.

[0113] The silicon carbide substrate is subjected to epitaxial layer growth. Since the conductive type and semi-insulating type silicon carbide are subjected to homoepitaxial and heteroepitaxial processes respectively, different epitaxial layers are obtained on the Si surface of the silicon carbide substrate, that is, an epitaxial wafer is obtained. After the epitaxial layer is grown, there is a lattice mismatch between the epitaxial layer and the substrate, thereby introducing stress, and the substrate needs to be heat treated during the epitaxial process, so the internal stress in the substrate changes accordingly. The epitaxial wafer obtained after the epitaxial layer growth is tested by the test method of Example 4, and the internal stress of the substrate in the epitaxial wafer is tested from the Si and C surfaces. Figure 6 (e) is the stress distribution diagram of the substrate body tested from the Si surface. Figure 6 (f) is the internal stress distribution diagram of the substrate tested from the C surface. It can be seen that in the process of epitaxy of the substrate on the Si surface to obtain the epitaxial layer, the Si surface substrate and the epitaxial layer show lattice mismatch, which will cause the internal stress of the Si surface of the substrate to increase. In the epitaxy process, the C surface is heat treated, so the stress is released to a certain extent. Therefore, the internal stress of the C surface will be reduced to a certain extent, resulting in the axial internal stress distribution of the substrate increasing as it approaches the Si surface. Figure 6 (d) as shown.

[0114] Example 7 Quantitative Testing of Epitaxial Layer Body Stress

[0115] According to the measurement method of the epitaxial layer surface curvature obtained by Raman testing in Example 2, this embodiment, in combination with the physical properties of silicon carbide and the epitaxial wafer obtained therefrom, involves a method for quantitatively characterizing the internal stress of the epitaxial layer that is not affected by surface curvature and warping, so as to detect the internal stress condition in the epitaxial layer.

[0116] The same test method as in Example 4 is used to quantitatively test the epitaxial layer. The thickness of the epitaxial layer is limited, so only the test method of equal-pitch focusing can be used. The focus of the Raman laser is inside the epitaxial layer, that is, extending from the surface of the epitaxial wafer inward to the 30%-60% area of ​​the epitaxial layer thickness. The test results are shown in FIG. Figure 7 The overall morphology of the epitaxial layer is the same as that of the substrate, but the stress value is increased compared to that of the substrate.

[0117] This application analyzes and simulates the crystal growth stress based on the characteristics of SiC crystals obtained by growing crystals using the PVT method. The in-plane radial relative stress actually measured using the above quantitative test method and the simulated radial relative stress results both show a symmetrical distribution with high edge stress and low center stress, and the simulation results are consistent with the actual measured results; the simulated axial absolute stress and the actual measured in-plane axial absolute stress show a distribution with positive front stress and negative rear stress, and the simulation results are also consistent with the actual measured results. The values ​​of absolute stress and relative stress calculated using the calculation formula of this embodiment are consistent with the magnitude of the simulation results, both of which are 10~10 2 MPa. Since the SiC crystal is thick and the penetration depth of Raman laser is limited, the SiC crystal is cut into multiple substrates. The actual measured axial absolute stress is obtained by testing the in vivo absolute stress of different substrates on the same axis.

[0118] In Example 1 of the present application, the peak displacement and stress conversion coefficient μ of the substrate are obtained according to the different characteristics of the substrate, which provides a basis for the quantitative test of substrate stress; the thickness of the surface damage layer and the damage stress extension layer of the substrate is calculated according to the axial test method of Example 3, and the thickness of the epitaxial layer, the surface damage layer and the damage stress extension layer in the epitaxial wafer can also be calculated; and according to the above-mentioned Example 2, the curvature of the substrate is determined, and the focusing depth (d) and the spot diameter (D) of the Raman laser spot are calculated, so as to eliminate the influence of the curvature of the substrate surface on the substrate internal stress test, and at the same time eliminate the influence of the curvature of the epitaxial wafer surface on the substrate internal stress and epitaxial layer internal stress test, which provides a unified standard for the quantitative test of the internal stress in the substrate defect aggregation area, the substrate internal stress in the epitaxial wafer and the internal stress in the epitaxial layer.

[0119] 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 method for quantitatively characterizing the internal stress of a substrate defect aggregation region, characterized in that: The steps include: Step 1: Test the substrate to obtain the actual peak value and stress value of the substrate at different test points, calculate the difference between the actual peak value and the peak value of the standard substrate, that is, obtain the peak displacement value of different test points, and calculate the peak displacement and stress conversion coefficient μ according to the peak displacement value and stress value; The second step: use a Raman tester to perform an internal scanning test on the defect clustering area of ​​the substrate, where the diameter of the substrate is greater than 150 mm, the defects in the defect clustering area include at least one of micropipes, dislocations, polytypes, and carbon inclusions, and the interior is an area extending inward from the surface of the substrate to 30%-60% of the substrate thickness, obtain the peak position value, and calculate the peak position displacement value, and calculate the internal stress value of the substrate defect clustering area based on the peak position displacement value and the peak position displacement and stress conversion coefficient μ in the first step.

2. The method for quantitatively characterizing the internal stress of the substrate defect aggregation region according to claim 1, characterized in that: Before the second step of using Raman tester to conduct internal scanning test on the substrate defect clustering area, the Raman tester is first used to conduct axial test on the substrate defect clustering area, and the depth of the surface damage layer and the damage stress extension layer in the substrate defect clustering area is determined according to the stress curve fed back by the axial test.

3. The method for quantitatively characterizing the internal stress of the substrate defect aggregation region according to claim 2, characterized in that: Before the second step of using a Raman tester to perform an internal scanning test on the defect clustering area of ​​the substrate, a curvature test is first performed on the substrate surface to obtain the curvature of the substrate in the defect clustering area. Taking the curvature as a reference, in the second step of the scanning test, an equidistant focusing mode and / or an equifocusing plane mode is selected, wherein the distance between the Raman laser spot at each test point in the equidistant focusing mode and the substrate surface is equal, and the Raman laser spot at each test point in the equifocusing plane mode is in the same horizontal plane.

4. A method for quantitatively characterizing the stress in the substrate of an epitaxial wafer, characterized in that: The steps include: Step 1: Test the substrate to obtain the actual peak value and stress value of the substrate at different test points, calculate the difference between the actual peak value and the peak value of the standard substrate, that is, obtain the peak displacement value of different test points, and calculate the peak displacement and stress conversion coefficient μ according to the peak displacement value and stress value; Step 2: Use a Raman tester to perform internal scanning test on the substrate in the epitaxial wafer, where the interior of the substrate is the area extending inward from the surface of the substrate to 30%-60% of the substrate thickness, obtain the peak value, and calculate the peak displacement value. According to the peak displacement value and the peak displacement and stress conversion coefficient μ in the first step, calculate the internal stress value of the substrate in the epitaxial wafer.

5. The method for quantitatively characterizing the internal stress of the substrate in the epitaxial wafer according to claim 4, characterized in that: Before the second step of using Raman tester to conduct internal scanning test on the defect clustering area of ​​the substrate, the Raman tester is first used to conduct axial test on the epitaxial wafer. According to the stress curve fed back by the axial test, the depth of the epitaxial layer, surface damage layer and damage stress extension layer in the epitaxial wafer is determined.

6. The method for quantitatively characterizing the internal stress of the substrate in the epitaxial wafer according to claim 4, characterized in that: Before the second step of using a Raman tester to perform an internal scanning test on the defect clustering area of ​​the substrate, a curvature test is first performed on the surface of the epitaxial wafer to obtain the curvature of the surface of the epitaxial wafer. Taking the curvature as a reference, in the second step of the scanning test, an equidistant focusing mode and / or an equifocusing plane mode is selected, wherein the distance between the Raman laser spot at each test point in the equidistant focusing mode and the substrate surface is equal, and the Raman laser spot at each test point in the equifocusing plane mode is in the same horizontal plane.

7. The method for quantitatively characterizing the internal stress of a substrate defect aggregation region according to any one of claims 1 to 3 or the method for quantitatively characterizing the internal stress of a substrate in an epitaxial wafer according to any one of claims 4 to 6, characterized in that: The calculation steps of the peak displacement and the stress conversion coefficient μ are as follows: First, the interplane spacing dx in the substrate is tested by a test instrument. The interplane spacing dx is subtracted from the theoretical interplane spacing d0 to obtain the interplane spacing difference △d at different test points. Hooke's law σ / S=E×(△d / d0) or stress-strain formula σ=E×△d is used to obtain the stress value of the substrate at different test points. Afterwards, the substrate is scanned and tested using a Raman tester to obtain the actual peak position values ​​at different test points, and the difference between the actual peak value and the standard peak position is calculated to obtain the peak displacement values ​​at different test points. The ratio of the peak displacement value to the stress value is the peak displacement and stress conversion coefficient μ; Preferably, the testing instrument for testing the interplanar spacing dx in the substrate is selected from any one or more of an XRD diffractometer, a synchrotron radiation tester, a white light tester, a neutron diffractometer, a scanning electron microscope, and a transmission electron microscope.

8. The method for quantitatively characterizing the internal stress of a substrate defect aggregation region according to any one of claims 1 to 3 or the method for quantitatively characterizing the internal stress of a substrate in an epitaxial wafer according to any one of claims 4 to 6, characterized in that: S1 is recorded as the in vivo stress value calculated by the equal-interval focusing mode, and S2 is recorded as the in vivo stress value calculated by the equal-focusing plane mode, -0.2MPa≤S1-S2≤0.2MPa; or V1 is recorded as the peak position value obtained after fitting the equal-space focusing mode, and V2 is recorded as the peak position value obtained after fitting the equal-focusing plane mode, -0.0005cm -1 <V1-V2<0.0005cm -1 .

9. The method for quantitatively characterizing the internal stress of a substrate defect aggregation region according to any one of claims 1 to 3 or the method for quantitatively characterizing the internal stress of a substrate in an epitaxial wafer according to any one of claims 4 to 6, characterized in that: The in vivo stress values ​​calculated in the second step include in vivo absolute stress and in vivo relative stress; Wherein, in the calculation of the in vivo absolute stress, the calculated peak displacement value is the difference between the actual peak position of the test point and the standard peak position; in the calculation of the in vivo relative stress, the calculated peak displacement value is the difference between the actual peak position of the test point and the actual peak position of the relative point; and / or The diameter of the substrate is greater than 200 mm.

10. A method for quantitatively characterizing the stress in an epitaxial layer, characterized in that: The steps include: Step 1: Test the epitaxial layer to obtain the actual peak value and stress value of the epitaxial layer at different test points, calculate the difference between the actual peak value and the peak value of the standard substrate, that is, obtain the peak displacement value of different test points, and calculate the peak displacement and stress conversion coefficient μ according to the peak displacement value and stress value; Step 2: Use a Raman tester to scan the inside of the epitaxial layer. The inside of the epitaxial layer is the area extending from the surface of the epitaxial wafer inward to 30% to 60% of the thickness of the epitaxial layer. Obtain the peak value and calculate the peak displacement value. According to the peak displacement value and the peak displacement and stress conversion coefficient μ in the first step, calculate the internal stress value of the epitaxial layer.

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