Stress detection method, device and equipment and computer readable storage medium

Abstract

The invention provides a stress detection method, device and equipment and a computer readable storage medium, relates to the technical field of semiconductor detection, and aims to solve the problem that the comprehensive stress of a substrate cannot be accurately detected. The stress detection method comprises the steps that Raman laser detection is conducted on a detection point of a substrate to be detected, the peak position of a Raman spectrum of the detection point is obtained, and light spots of Raman laser for detecting the detection point are located on a surface layer and a middle layer of the substrate to be detected; determining the peak position offset of the detection point according to the detected peak position and a preset reference peak position; the comprehensive stress of the detection point is determined according to the peak position offset and a predetermined conversion coefficient, and the conversion coefficient is a proportionality coefficient of the peak position offset and the stress.

Description

Technical Field

[0001] The present application relates to the field of semiconductor detection technology, and in particular to a stress detection method, device, equipment and computer-readable storage medium. Background Art

[0002] During the growth process of silicon carbide crystals, due to the imbalance of Si / C ratio, the introduction of impurities and temperature gradient changes, various defects such as polycrystalline, polymorphic, microtubes, dislocations, etc. are easily introduced into the crystals. These defects will cause lattice distortion, and even worse, it will cause the crystal form to change. Lattice distortion releases stress by generating defects, thereby causing internal stress in the silicon carbide crystal. On the other hand, during the process of processing silicon carbide crystals into substrates, they are subjected to external mechanical cutting, grinding, polishing, etc., which will cause incomplete surface lattices, resulting in surface lattice distortion, surface damage layer, and surface stress.

[0003] The above-mentioned internal stress is mixed with the surface stress to form a comprehensive stress. The comprehensive stress will comprehensively reflect the lattice distortion caused by the substrate during the crystal growth and processing, the epitaxial defects in the epitaxial process, the change in the shape and morphology after the epitaxy, etc. Uneven stress distribution or excessive stress will reduce the yield of the prepared device. Therefore, it is necessary to accurately evaluate the stress size of the substrate. However, the current stress detection methods can usually only detect surface stress or internal stress, and cannot accurately measure the comprehensive stress. Summary of the invention

[0004] The present application provides a stress detection method, device, equipment and computer-readable storage medium to improve the problem of being unable to accurately detect the comprehensive stress of a substrate.

[0005] In the first aspect, the embodiment of the present application provides a stress detection method, including: performing Raman laser detection on the detection point of the substrate to be tested, obtaining the peak position of the Raman spectrum of the detection point, and the light spot of the Raman laser used to detect the detection point is located on the surface layer and the middle layer of the substrate to be tested; determining the peak position offset of the detection point according to the obtained peak position and the preset reference peak position; determining the comprehensive stress of the detection point according to the peak position offset and a predetermined conversion coefficient, wherein the conversion coefficient is a proportional coefficient between the peak position offset and the stress, wherein the stress, the peak position offset, and the conversion coefficient satisfy: σ=μ·Δω. In the above formula, σ is the stress, μ is the conversion coefficient, and Δω is the peak position offset of the detection point for Raman detection.

[0006] The method provided in the embodiment of the present application performs Raman laser detection on the substrate to be tested, so that the light spot of the Raman laser covers the surface layer and the middle layer of the substrate to be tested at the same time. The Raman laser is reflected or scattered under the combined effect of the surface layer and the middle layer. In this way, the stress obtained according to the peak position shift of the Raman spectrum obtained by the detection is the comprehensive stress of the combined effect of the surface stress and the internal stress of the substrate to be tested, thereby realizing the quantitative detection of the comprehensive stress and improving the problem that currently only the internal stress and surface stress can be detected but the comprehensive stress cannot be detected.

[0007] In a possible implementation, Raman laser detection is performed on the detection point of the substrate to be measured to obtain the peak position of the Raman spectrum of the detection point, and the spot of the Raman laser used to detect the detection point is located before the surface layer and the middle layer of the substrate to be measured. The method also includes: performing axial Raman laser scanning detection on multiple detection points of the substrate to be measured to obtain the axial stress distribution of the multiple detection points, and the axial stress distribution includes the stress at different axial positions of the detection point; according to the axial stress distribution of the multiple detection points, the surface layer and the middle layer of the substrate to be measured are determined, wherein the change rate of the axial stress of the surface layer is greater than the change rate of the axial stress of the middle layer.

[0008] The embodiment of the present application determines the comprehensive stress by detecting the peak shift formed by the reflection or scattering of the Raman laser under the combined action of the surface layer and the middle layer. Prior to this, the axial stress distribution is determined by axially scanning the substrate to be tested. Since the stress damage to the surface layer is greater and the stress damage to the middle layer is smaller, the rate of change of the axial stress can be used to distinguish the surface layer and the middle layer. The position with a larger rate of change of the axial stress is determined as the surface layer, and the position with a smaller rate of change of the axial stress is determined as the middle layer.

[0009] In a possible implementation, axial Raman laser scanning detection is performed on multiple detection points of the substrate to be tested, and the step of obtaining the axial stress distribution of the multiple detection points includes: performing axial Raman laser scanning detection on the detection points to obtain the peak positions of the Raman spectra at different axial positions of the detection points; determining the peak position offset at different axial positions of the detection points based on the acquired peak position and a preset reference peak position; and determining the stress at different axial positions of the detection points based on the peak position offset and the conversion coefficient.

[0010] In a possible implementation, the method further includes: when detecting the comprehensive stress of multiple detection points, performing Raman laser detection with equal focal distance on multiple detection points of the substrate to be measured, and the equal focal distance means that the focusing depth when performing Raman laser detection on each detection point is the same, and the focusing depth is the distance between the focusing position of the Raman laser when detecting the detection point and the surface of the substrate to be measured.

[0011] In the equal focusing distance detection, when performing Raman laser detection on each detection point, the focusing position of the Raman laser is at the same distance from the surface of the substrate to be tested, so as to avoid the influence of warping or bending of the substrate to be tested on stress detection.

[0012] In a possible implementation, the method further includes: when detecting the comprehensive stress of multiple detection points, performing isofocal plane Raman laser detection on multiple detection points of the substrate to be tested, and the isofocal plane means that the focal axis positioning position of the Raman laser when performing Raman laser detection on each detection point is located in the same horizontal plane.

[0013] When Raman laser detection is performed on each detection point in the isofocusing plane, the focus axis positioning position of the Raman laser is located in the same horizontal plane, and there is no need to reselect or adjust the focus position using automatic focusing, which can improve the detection efficiency.

[0014] In a possible implementation, before performing isofocal plane Raman laser detection on multiple detection points of the substrate to be detected, the method also includes: determining the curvature of the surface of the substrate to be detected, the curvature including the height of protrusions or the depth of depressions on the surface of the substrate to be detected; and determining the focal position of the isofocal plane Raman laser detection according to the curvature so that the light spot of the Raman laser covers the surface layer and the middle layer of the substrate to be detected in the axial direction of the detection point.

[0015] Since the focal axis positioning position of the Raman laser for isofocal plane detection is located in the same horizontal plane, it is necessary to avoid being affected by the curvature of the substrate to be tested. The focusing position is selected according to the curvature of the substrate to be tested to avoid the Raman laser spot falling completely into the surface layer or completely falling into the middle layer, which makes it impossible to accurately detect the comprehensive stress.

[0016] In a possible implementation, determining the curvature of the surface of the substrate to be tested includes: selecting a fixed origin on a test platform to establish a spatial coordinate system, using a Raman spectrometer to automatically focus on any reference point on the surface of the substrate to be tested, adjusting the focus position of the Raman laser to move down a first preset distance from the reference point, performing isofocus plane detection on the substrate to be tested, and obtaining peak intensities of the substrate to be tested at different positions on the focus plane; determining a height difference between the focus position and a position with the maximum axial peak intensity according to the peak intensity of any focus position on the focus plane and a predetermined axial peak intensity distribution of the substrate to be tested; and determining a curvature of the surface of the substrate to be tested corresponding to the focus position according to the first preset distance and the height difference, wherein the curvature satisfies:

[0017] S=Δh-H

[0018] Wherein S is the curvature of the substrate surface relative to the reference point, Δh is the height difference, and H is the first preset distance. When the curvature is positive, the substrate surface corresponding to the focusing position of the surface is convex relative to the reference point. When the curvature is negative, the substrate surface corresponding to the focusing position of the surface is concave relative to the reference point.

[0019] In a possible implementation, before determining the comprehensive stress of the detection point according to the peak position offset and a predetermined conversion coefficient, the method further includes: determining the interplanar spacing difference between the interplanar spacing of the substrate to be measured and the theoretical interplanar spacing; determining the stress of the substrate to be measured according to the interplanar spacing difference and the stress-strain formula; obtaining the peak position of the Raman spectrum of the substrate to be measured, subtracting the peak position from the standard peak position to obtain the peak position offset, and determining the ratio of the peak position offset to the calculated stress as the conversion coefficient.

[0020] In a possible implementation, before determining the comprehensive stress of the detection point according to the peak position offset and the predetermined conversion coefficient, the method also includes: obtaining a first Raman spectrum peak position of the standard sample; obtaining a second Raman spectrum peak position when a preset stress is applied to the standard sample; determining the pressure according to the preset stress applied to the standard sample and the force application area of ​​the preset stress; determining the conversion coefficient according to the first Raman spectrum peak position, the second Raman spectrum peak position and the pressure, and the first Raman spectrum peak position, the second Raman spectrum peak position, the pressure and the conversion coefficient satisfy: μ = (P0-P1) / P, where μ is the conversion coefficient, P0 is the first Raman spectrum peak position, P1 is the second Raman spectrum peak position, and P is the pressure.

[0021] In a possible implementation, when the preset reference peak position is a standard peak position, the measured comprehensive stress is an absolute comprehensive stress; when the preset reference peak position is a peak position of another detection point on the substrate to be measured, the measured comprehensive stress is a relative comprehensive stress of the detection point relative to the other detection point.

[0022] In the second aspect, an embodiment of the present application also provides a stress detection device, which includes: a detection module, configured to perform Raman laser detection on a detection point of a substrate to be tested, and obtain the peak position of the Raman spectrum of the detection point, and the spot of the Raman laser covers the surface layer and the middle layer of the substrate to be tested in the axial direction of the detection point; a processing module, configured to determine the peak position offset of the detection point according to the acquired peak position and a preset reference peak position; the processing module is also configured to determine the comprehensive stress of the detection point according to the peak position offset and a predetermined conversion coefficient, and the conversion coefficient is a proportional coefficient between the peak position offset and the stress.

[0023] In a third aspect, an embodiment of the present application further provides a stress detection device, comprising: a processor and a memory, wherein the processor is coupled to the memory, and the memory is configured to store a computer program; the processor is configured to execute the computer program stored in the memory, so that the stress detection device performs the steps of the method provided in any implementation of the first aspect.

[0024] In a fourth aspect, an embodiment of the present application further provides a computer-readable storage medium, comprising computer instructions, which, when executed on a computer, enable the computer to execute the steps of the method provided in any implementation of the first aspect.

[0025] In a fifth aspect, an embodiment of the present application further provides a substrate, which is a substrate detected by the stress detection method provided by any implementation manner of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of a substrate provided in an embodiment of the present application;

[0027] Figure 2 A schematic diagram of substrate stress distribution provided in an embodiment of the present application;

[0028] Figure 3 A schematic diagram of a stress detection method provided in an embodiment of the present application;

[0029] Figure 4 A schematic diagram of a flow chart of another stress detection method provided in an embodiment of the present application;

[0030] Figure 5 A schematic diagram of a flow chart of another stress detection method provided in an embodiment of the present application;

[0031] Figure 6 A schematic diagram of a flow chart of another stress detection method provided in an embodiment of the present application;

[0032] Figure 7 A schematic diagram of a flow chart of another stress detection method provided in an embodiment of the present application;

[0033] Figure 8 A schematic diagram of an axial scanning test of a substrate to be tested provided in an embodiment of the present application;

[0034] Fig. 9 A schematic diagram of the axial stress distribution of the substrate to be tested provided in an embodiment of the present application;

[0035] Fig.10 A schematic diagram of iso-focal plane detection provided in an embodiment of the present application;

[0036] Fig.11 Another schematic diagram of iso-focal plane detection provided in an embodiment of the present application;

[0037] Fig.12 A schematic diagram of equal focusing distance detection provided in an embodiment of the present application;

[0038] Fig.13 A schematic diagram of a flow chart of another stress detection method provided in an embodiment of the present application;

[0039] Fig.14 A schematic diagram of peak intensity distribution for axial scanning test of single crystal silicon;

[0040] Fig.15 Schematic diagram of peak intensity distribution during axial scanning test of the substrate to be tested;

[0041] Fig.16 A schematic diagram of a flow chart of another stress detection method provided in an embodiment of the present application;

[0042] Fig.17 A schematic diagram of detecting curvature provided in an embodiment of the present application;

[0043] Fig.18 A schematic diagram of determining a height difference provided in an embodiment of the present application;

[0044] Fig.19 A schematic diagram of the comprehensive stress distribution of the substrate to be tested provided in an embodiment of the present application;

[0045] Fig. 20 A schematic diagram of comprehensive stress distribution of another substrate provided in an embodiment of the present application;

[0046] Fig.21 This is a functional module block diagram of the stress detection device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0048] In the following, the terms "first", "second", etc. are used only for convenience of description and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more. For example, a plurality of processing units refers to two or more processing units.

[0049] In addition, in the embodiments of the present application, "upper", "lower", "left" and "right" are not limited to being defined relative to the orientation of the components schematically placed in the drawings. It should be understood that these directional terms can be relative concepts, which are used for description and clarification relative to the components, and can change accordingly according to the change in the orientation of the components placed in the drawings. In the drawings, for the sake of clarity, the thickness of the layers and regions is exaggerated, and the size ratio relationship between the parts in the drawings does not reflect the actual size ratio relationship.

[0050] In the embodiments of the present application, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium.

[0051] In the embodiments of the present application, the term "module" is generally a functional structure divided according to logic, and the "module" can be implemented by pure hardware, or by a combination of software and hardware. In the embodiments of the present application, "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, B exists alone, and A and B exist at the same time.

[0052] In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0053] The substrate is a wafer made of semiconductor single crystal materials, including silicon, silicon carbide, sapphire, silicon nitride and other material types. The substrate is the bottom material of all semiconductor chips and mainly plays the role of physical support, thermal conductivity and electrical conductivity.

[0054] Silicon carbide is one of the ideal materials for making high-temperature, high-frequency, high-power, and high-voltage devices. Semiconductor devices made with silicon carbide (SiC) as a substrate can better meet application requirements under high temperature, high pressure, and high power conditions.

[0055] At present, more than 200 isomorphous crystal structures of silicon carbide have been discovered. Among them, the hexagonal 4H-SiC (4H-SiC) has the advantages of high critical breakdown electric field and high electron mobility. It is an excellent semiconductor material for manufacturing high-voltage, high-temperature, and radiation-resistant power semiconductor devices. In addition, silicon carbide also includes 2H-SiC, 6H-SiC, 3C-SiC, 15R-SiC and other types of crystal structures.

[0056] At present, the methods for preparing SiC single crystals include seed crystal sublimation method, high temperature chemical vapor deposition method (HTCVD) and liquid phase method (LPE). The most widely used method is seed crystal sublimation method, also known as physical vapor transport method (PVT). Its principle is to sublimate carbon powder and silicon powder into gas phase substances such as Si atoms, Si2C molecules and SiC2 molecules at a high temperature of more than 2000℃. Driven by the temperature gradient, these gas phase substances will be transported to the silicon carbide seed crystal with a lower temperature to form 4H silicon carbide crystal. By controlling the temperature field, airflow and other process parameters of PVT, a specific 4H-SiC crystal type can be grown.

[0057] After the silicon carbide single crystal is prepared, the crystal is ground flat and rolled into a round shape to obtain a crystal rod. Figure 1 As shown, the substrate is then processed by cutting, grinding, mechanical polishing (MP), chemical mechanical polishing (CMP) and other processing methods with increasing precision, and finally a conductive or semi-insulating silicon carbide substrate that meets market demand is obtained.

[0058] During the growth process of silicon carbide crystals, due to the imbalance of Si / C ratio, the introduction of impurities and temperature gradient changes, various defects such as polycrystalline, polymorphic, micropipes, dislocations, etc. are easily introduced into the crystals. These defects will cause lattice distortion, and even worse, it will cause the crystal form to change, such as the generation of 4H, 6H, 3C, 15R and other polymorphic symbiosis. Lattice distortion releases stress by generating defects, thereby causing internal stress in the silicon carbide crystal. On the other hand, in the process of processing silicon carbide crystals into substrates, they are subjected to external mechanical cutting, grinding, polishing, etc., which will cause incomplete surface lattices, resulting in surface lattice distortion, surface damage layer, and surface stress.

[0059] The above-mentioned internal stress is mixed with the surface stress to form a comprehensive stress. The comprehensive stress will comprehensively reflect the participating stress caused by lattice distortion in the substrate during crystal growth and processing, epitaxial defects in the epitaxial process, and shape changes after epitaxy. Uneven stress distribution or excessive stress will reduce the yield of the prepared device, so it is necessary to accurately evaluate the stress size of the substrate.

[0060] One possible way to detect substrate stress is to apply an external force to the silicon carbide substrate, detect the strain of the substrate after the stress is applied, and thus calculate the stress of the substrate. However, this method requires applying an external force to the substrate. Due to the application of external force, the stress quantitatively reflected is large, and the large external force will to a certain extent mask the internal stress condition. Therefore, this test method is mainly aimed at the stress caused by defects, and the stress that has not been released by defects due to lattice distortion cannot be characterized, resulting in inaccurate stress detection results.

[0061] The embodiments of the present application provide a method for detecting stress, which utilizes the change in the peak position of Raman scattered light, that is, utilizes the so-called Raman spectroscopy or Raman shift method to detect the stress of a substrate.

[0062] The principle of Raman laser stress detection of substrates is as follows: Raman spectrometer passes a monochromatic laser of a certain wavelength through a series of optical paths and then converges it through an objective lens to irradiate the surface of the substrate to be tested. 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 to be tested. When stress exists in the substrate to be tested, tensile and compressive stresses will cause the atomic bond lengths to be elongated or shortened accordingly, and the distance between atoms will change, thereby causing the atomic vibration frequency to decrease or increase. This is reflected in the Raman spectrum as the peak position of the characteristic peak of the substrate to be tested moves to a low frequency or a high frequency, that is, a peak position offset occurs. Therefore, a Raman spectrometer can be used to detect the substrate to be tested, and the magnitude of the stress can be evaluated based on the movement of the peak position.

[0063] For example, a Raman spectrometer is used to focus on a certain detection point on the surface of the substrate for detection to obtain a Raman spectrum, and the peak position of the Raman spectrum is compared with the standard peak position to obtain a peak position shift. The standard peak position here can be the position of a characteristic peak in the Raman spectrum obtained by detecting a standard substrate. After the peak position shift is obtained, the stress of the detection point can be calculated based on the peak position shift and the conversion coefficient. The conversion coefficient here refers to the proportional coefficient between the peak position shift and the stress. Assuming that the peak position shift is Δω, the stress is σ, and the conversion coefficient is μ, then the peak position shift, stress and conversion coefficient satisfy the following formula:

[0064] σ=μ·Δω

[0065] The Raman spectrometer focuses the Raman laser spot inside the substrate, so the stress detected is the internal stress of the substrate, such as Figure 2 As shown, Figure 2 A schematic diagram of the distribution of the internal stress of the substrate to be tested provided in an embodiment of the present application is shown. The numbers in the figure represent the magnitude of the stress. The Raman spectrometer can also focus the light spot of the Raman laser on the surface of the substrate. According to the same algorithm, the peak offset is obtained and then the stress is calculated based on the peak offset and the conversion coefficient. However, by focusing the Raman laser on the surface of the substrate, the surface stress of the substrate is detected. It can be seen that although this detection method can detect the surface stress and internal stress of the substrate, it cannot accurately detect the comprehensive stress of the substrate, resulting in the inability to accurately evaluate the stress distribution of the substrate.

[0066] In order to improve this situation, the present application embodiment provides a method for testing the comprehensive stress of a substrate based on Raman laser detection. For example, see Figure 3 , the method provided in the embodiment of the present application includes:

[0067] S110, performing Raman laser detection on the detection point of the substrate to be detected, obtaining the peak position of the Raman spectrum of the detection point, and the light spot of the Raman laser used to detect the detection point is located on the surface layer and the middle of the substrate to be detected.

[0068] In the above example, it is mentioned that the substrate includes an intermediate layer and a surface layer. When the Raman spot is focused on the surface, the surface stress is measured; when the Raman spot is focused on the intermediate layer of the substrate, the internal stress of the substrate is measured. The focused spot of the Raman laser is ellipsoidal, with its major axis parallel to the axial direction of the substrate and its minor axis perpendicular to the axial direction of the substrate. In the solution provided in the embodiment of the present application, when the substrate to be tested is subjected to Raman laser detection, the focusing position of the Raman laser (the center point of the spot) can be located between the surface layer and the intermediate layer, or can also be located on the surface layer or the intermediate layer, but it is necessary to make the Raman laser spot cover the surface layer and the intermediate layer of the substrate at the same time, or the Raman laser spot is located at the surface layer and the intermediate layer of the substrate at the same time, so that the peak position of the Raman spectrum is displaced under the combined effect of the stress of the surface layer and the intermediate layer, that is, the peak position offset, so the stress measured in this case can characterize the combined stress of the combined effect of the internal stress and the surface stress.

[0069] S130, determining a peak position offset of the detection point according to the acquired peak position and a preset reference peak position.

[0070] The Raman laser spot covers the surface layer and the middle layer of the substrate at the same time, and the peak position of the Raman spectrum is measured. The measured peak position is compared with the preset reference peak position to obtain the peak position offset of the detection point. Refer to the following formula:

[0071] Δω=ω1-ω0

[0072] Wherein, Δω is the peak position offset, ω1 is the peak position of the Raman spectrum measured when the Raman laser spot covers the surface layer and the middle layer of the substrate to be measured at the same time, and ω0 is the preset reference peak position.

[0073] S150, determining the comprehensive stress of the detection point according to the peak position offset and a predetermined conversion coefficient, where the conversion coefficient is a proportional coefficient between the peak position offset and the stress.

[0074] According to the peak offset and the predetermined conversion coefficient, the comprehensive stress of the detection point is calculated, where the stress, peak offset and conversion coefficient satisfy:

[0075] σ=μ·Δω

[0076] In the above formula, σ is stress, μ is conversion coefficient, and Δω is peak position shift of Raman detection at the detection point.

[0077] The method provided in the embodiment of the present application utilizes a Raman spectrometer to detect the substrate to be tested, so that the light spot of the Raman laser covers the surface layer and the middle layer of the substrate to be tested at the same time. The peak position of the Raman spectrum shifts under the combined effect of the surface stress of the surface layer and the body stress of the middle layer, thereby obtaining the peak position shift under the combined stress. The combined stress of the substrate to be tested can be calculated based on the peak position shift and the conversion coefficient, thereby improving the problem that the current stress detection can only achieve qualitative characterization but cannot achieve quantitative measurement.

[0078] When testing the substrate to be tested, it can be a single-point test, that is, testing a certain test point, or it can be a multi-point scan. For example, a range is selected on the surface of the substrate to be tested. This range can range from 10x10 test points to 50x50 test points and more. The Raman spectrometer is used to scan in sequence from left to right and from top to bottom, and the peak position offset of each test point is measured, so as to calculate the comprehensive stress distribution of this range.

[0079] In practical applications, such as single-point detection or multi-point scanning, the amount of data obtained by detection is small, and the maximum value of the measurement point may not be the actual point with the highest peak position. Therefore, after obtaining the test data, it is necessary to perform peak position fitting on the data output by the Raman spectrometer. The fitting function or model includes but is not limited to Gaussian function (Gaussian), Lorentz function (lorentz), Gauss-Loren function (GaussLoren) for relative values, or also includes Gaussian function (Agauss), Lorentz function (Aloren) and Gauss-Loren function (AGaussLoren) for absolute values, etc., to perform fine fitting on a limited number of data, so as to obtain accurate peak intensity and peak position data. Since the stress of the substrate is small, usually in actual use, the peak position accuracy value needs to be more than one decimal place before the magnitude of the stress can be calculated and distinguished.

[0080] After fitting the peak position and peak intensity data, the peak offset can be further obtained, and the stress magnitude can be determined based on the peak offset and the conversion coefficient. However, before this, the conversion coefficient, that is, the proportional coefficient between the peak offset and the stress, needs to be determined. The present application provides two methods for determining the conversion coefficient. For example, see Figure 4 , Figure 4 A flow chart of a method for determining a conversion coefficient provided in an embodiment of the present application is shown.

[0081] Before determining the comprehensive stress at the detection point according to the peak position shift and the predetermined conversion coefficient, the method further includes:

[0082] S211: Obtaining the interplanar spacing of the substrate to be tested.

[0083] Interplanar spacing refers to the distance between two parallel crystal planes. The greater the distance between the crystal planes, the denser the atomic arrangement on the crystal planes, that is, the greater the surface density. The atoms of the same crystal plane family are arranged in the same way, and the spacing between their crystal planes is also the same. There are many ways to obtain the interplanar spacing of the substrate to be tested. For example, a single crystal diffractometer, a synchrotron radiation tester, a white light tester, a neutron diffractometer, a scanning electron microscope, a transmission electron microscope, and other equipment or methods can be used to detect and obtain the interplanar spacing of the substrate to be tested. The embodiment of the present application takes the determination of the interplanar spacing by a single crystal diffractometer as an example. First, a single crystal diffractometer is used to detect the diffraction angle of the substrate to be tested; the interplanar spacing is calculated according to the diffraction angle, and the interplanar spacing d and the diffraction angle α satisfy the Bragg diffraction formula:

[0084] 2dsinθ=nλ

[0085] Where λ is the wavelength of the ray emitted by the single crystal diffractometer, d is the crystal plane spacing, n is the reflection order, and θ is the diffraction half-angle (2θ is the diffraction angle), that is, the angle between the incident light and the substrate to be measured.

[0086] S212: Determine the interplanar spacing difference between the interplanar spacing of the substrate to be tested and the theoretical interplanar spacing.

[0087] The theoretical interplane spacing is the interplane spacing of the standard substrate, and the interplane spacing difference is calculated based on the interplane spacing and the theoretical interplane spacing, wherein the interplane spacing, the theoretical interplane spacing, and the interplane spacing difference satisfy the following formula:

[0088] Δd=d-d0

[0089] Wherein, d is the interplanar spacing of the substrate to be tested, d0 is the theoretical interplanar spacing, that is, the interplanar spacing of a standard substrate, and Δd is the interplanar spacing difference.

[0090] S213: Determine the stress of the substrate to be measured according to the interplanar spacing difference and the stress-strain formula.

[0091] The stress-strain formula is:

[0092] σ=E·ε

[0093] Where σ is stress, E is Young's modulus, and ε is deformation. Since the interplanar spacing difference Δd is the difference between the interplanar spacing of the substrate to be tested and the theoretical interplanar spacing, it can be regarded as the magnitude of the deformation. Therefore, the interplanar spacing difference Δd calculated above can be substituted into the deformation variable ε to calculate the stress.

[0094] The stress-strain formula analyzes stress from a microscopic perspective. In another possible implementation, the stress of the substrate to be measured can also be calculated from a macroscopic perspective based on Hooke's law, where Hooke's law can be expressed as:

[0095] F=-k·Δx

[0096] Where F is the elastic force (or it can be considered as stress here), k is the elastic coefficient, and Δx is the distance or deformation variable. The difference in the interplanar spacing Δd obtained by the above calculation can be substituted into the deformation variable Δx to calculate the stress.

[0097] S214: Obtain the peak position of the Raman spectrum of the substrate to be tested, subtract the peak position from the standard peak position to obtain a peak position offset, and determine the ratio of the peak position offset to the calculated stress as a conversion coefficient.

[0098] Determine the peak position offset of the substrate to be tested compared with the standard peak position, the standard peak position refers to the peak position obtained by Raman laser detection of a standard sample (without stress), and determine the ratio of the peak position offset to the calculated stress as the conversion coefficient μ.

[0099] In addition, in a possible implementation method, the crystal plane spacing of a detection point can be detected, and the peak position offset can be detected and obtained, and then the conversion coefficient can be calculated according to the steps provided in the aforementioned example; or the crystal plane spacing of multiple detection points can be detected, and multiple detection points can be detected to obtain the peak position offset, and multiple conversion coefficient values ​​can be calculated according to the steps provided in the aforementioned example, and the average of the multiple conversion coefficient values ​​is calculated as the final conversion coefficient.

[0100] The above example introduces a method for obtaining the conversion coefficient based on theoretical calculation. The present application also provides another method for obtaining the conversion coefficient, namely, an experimental determination method. For example, see Figure 5 , Figure 5 A flow chart of another method for determining a conversion coefficient provided in an embodiment of the present application is shown.

[0101] S221: Obtain the first Raman spectrum peak position of the standard sample.

[0102] The standard sample (silicon carbide substrate) refers to a sample without internal stress and surface stress. Raman laser detection is performed on the standard sample to detect the Raman spectrum peak position of the standard sample, which is recorded as the first Raman spectrum peak position P0.

[0103] S222: Obtain a second Raman spectrum peak position when a preset stress is applied to the standard sample.

[0104] A stress F is applied to the standard sample, and the peak position of the Raman spectrum when the stress F is applied to the standard sample is measured, and recorded as the second Raman spectrum peak position P1.

[0105] S223: Determine the pressure according to the preset stress applied to the standard sample and the force application area of ​​the preset stress.

[0106] The pressure is calculated based on the area of ​​force applied to the standard sample, where the stress, force area and pressure satisfy:

[0107] P=F / S

[0108] In the above formula, P is the pressure, F is the stress applied to the standard sample, and S is the area where the stress F is applied to the standard sample.

[0109] S224: determining a conversion coefficient according to the first Raman spectrum peak position, the second Raman spectrum peak position and the pressure.

[0110] Among them, the first Raman spectrum peak position, the second Raman spectrum peak position, the pressure and the conversion coefficient satisfy:

[0111] μ=(P0-P1) / P

[0112] Wherein μ is the conversion coefficient between peak position shift and stress, P0 is the first Raman spectrum peak position of the standard sample obtained by Raman laser detection of the standard sample, P1 is the second Raman spectrum peak position when stress F is applied to the standard sample, and P is the pressure when stress F is applied to the standard sample.

[0113] The embodiments of the present application provide two methods for determining the conversion coefficient between the peak offset and the stress, but are not limited thereto, and other methods may be used to determine the above conversion coefficient.

[0114] The above example mentioned that if the comprehensive stress is to be detected, the Raman laser spot needs to cover the surface layer and the middle layer of the substrate to be tested, that is, the focus position of the Raman laser is located between the surface layer and the middle layer. In this way, on the one hand, it is necessary to determine the distribution of the surface layer and the middle layer of the substrate to be tested, and on the other hand, it is necessary to reasonably set the focus depth of the Raman laser according to the distribution of the surface layer, the middle layer, etc. of the substrate to be tested.

[0115] Here, we need to introduce two concepts: focus depth and penetration depth. Focus depth refers to the distance between the focal position of the Raman laser and the surface of the substrate to be measured. Penetration depth refers to the maximum depth that the laser can penetrate into the substrate to be measured:

[0116]

[0117] In the above formula, Dp is the penetration depth of the Raman laser in the substrate to be measured, α is the absorption coefficient of the substrate to be measured, λ is the laser wavelength, and k is the extinction coefficient of the substrate to be measured. It can be seen that the penetration depth is only related to the material properties and the laser wavelength. Therefore, in order to measure inside the substrate, the penetration depth must be greater than the focusing depth, otherwise the laser cannot penetrate to the required position and cannot be detected.

[0118] Therefore, when performing Raman laser detection on the substrate to be tested, the penetration depth must first be determined based on the material parameters and laser parameters, and then the surface layer or middle layer position of the substrate to be tested must be determined to determine whether it is less than the penetration depth. If it is greater than the penetration depth, it cannot be measured because the Raman laser cannot be focused or cover a position beyond the penetration depth. If the surface layer or middle layer position of the substrate to be tested is less than the penetration depth, then a suitable focusing depth D can be selected. d , so that the Raman laser spot can cover the surface layer and middle layer of the substrate to be tested, realizing comprehensive stress detection.

[0119] Exemplarily, before S110, it is necessary to determine the distribution of the surface layer and the middle layer of the substrate to be tested, that is, the position of the surface layer and the middle layer of the substrate to be tested. For example, the surface of the substrate to be tested is taken as the zero point, the downward depth is marked as negative, and the upward height is marked as positive. As an example, from the surface of the substrate to be tested to -20 μm inside the substrate to be tested is the surface layer, and from -20 microns inside the substrate to be tested to -100 microns inside the substrate to be tested is the middle layer.

[0120] The present application embodiment provides a method for determining the distribution of the surface layer and the intermediate layer of a substrate to be tested. For example, refer to Figure 6 Before S110, the stress detection method further includes:

[0121] S101: performing axial Raman laser scanning detection on multiple detection points of the substrate to be detected to obtain axial stress distribution conditions of the multiple detection points, wherein the axial stress distribution conditions include stresses at different axial positions of the detection points.

[0122] For example, the multiple detection points here can be selected from detection points distributed at different positions such as the upper left, upper right, lower left, lower right and center point of the substrate to be tested. Axial Raman laser scanning detection is performed on each point to be tested to obtain the axial stress distribution of multiple detection points, and the axial stress distribution includes the stress at different positions on the axial direction of the detection point, such as the stress at -20μm, the stress at -30μm, etc.

[0123] S102: Determine the positions of the surface layer and the middle layer of the substrate to be tested according to the axial stress distribution of the plurality of detection points, wherein the change rate of the axial stress of the surface layer is greater than the change rate of the axial stress of the middle layer.

[0124] Since the stress of the middle layer of the substrate to be tested is mainly the thermal stress during crystal growth, the stress variation at different depths of the substrate is small; while the stress of the surface layer is mainly the residual stress of the cutting, grinding, polishing and other processes during crystal processing. The closer to the surface of the substrate to be tested, the greater the stress variation. The distribution of the surface layer and the middle layer can be distinguished based on the rate of change of the axial stress of the substrate to be tested, wherein the rate of change of the axial stress of the middle layer is greater than the rate of change of the axial stress of the middle layer.

[0125] In a possible implementation, the present application embodiment provides a method for obtaining the axial stress distribution of multiple detection points of a substrate to be tested, wherein, referring to Figure 7 , S101 may include the following sub-steps:

[0126] S101 - 1 : Perform axial Raman laser scanning detection on the detection point to obtain the peak positions of the Raman spectrum at different axial positions of the detection point.

[0127] For example, see Figure 8 , so that the laser spot is gradually focused upward from the body of the substrate to be tested to the middle layer, further to the surface layer, and then continues to focus upward into the air, and the peak position of the Raman spectrum of the substrate to be tested at different positions on the axial direction of the detection point.

[0128] Exemplarily, in a possible implementation, the surface of the substrate to be tested is taken as the zero point, and the test range of the axial test is that the Raman laser spot gradually moves upward from -100 μm inside the substrate to 30 μm above the substrate surface.

[0129] S101 - 2: Determine the peak position offset at different axial positions of the detection point according to the acquired peak position and the preset reference peak position.

[0130] The reference peak position here may be a standard peak position.

[0131] S101-3: Determine the stress at different positions of the detection point according to the peak position shift and the conversion coefficient.

[0132] After determining the peak position offset at different axial positions of the detection point, the stress at different axial positions of the detection point can be determined based on the following formula.

[0133] σ=·Δω

[0134] In the above formula, σ is stress, μ is conversion coefficient, and Δω is peak position shift.

[0135] For example, see Fig. 9 , Fig. 9A schematic diagram of the axial stress distribution of multiple detection points of the substrate to be tested provided by the embodiment of the present application is shown. Taking the surface of the substrate to be tested as the zero point, the sign of penetrating downward into the interior of the substrate to be tested is negative, and the sign of entering the air upward is positive. It can be seen that from -100μm to -30μm, it is mainly reflected in the stress of the middle layer, and the stress change trend is relatively gentle, and the rate of change is small; from -30μm to the zero point, the negative stress continues to increase until it reaches the maximum value when it reaches the surface (zero point). This stress distribution is reflected as the stress of the surface layer. From 0 to 20μm, since the focus point of the Raman laser enters the air, the air scatters the Raman laser, resulting in disordered changes in the peak position, and the stress also shows disordered changes.

[0136] Based on this, the distribution of the surface layer and the middle layer of the substrate to be tested can be determined by obtaining the axial stress distribution of the substrate to be tested. For example, Fig. 9 As for the schematic diagram of axial stress distribution shown, 0 to -30 microns is the surface layer, and -30 microns to -100 microns is the middle layer. When detecting the comprehensive stress of the substrate to be tested, it is only necessary to set the Raman laser spot between -100 microns and 0, and at the same time in the middle layer and the surface layer, so as to measure the comprehensive stress of the substrate to be tested.

[0137] After determining the distribution of the surface layer and the middle layer of the substrate to be tested, it can be scanned and tested so that the Raman laser spot covers the surface layer and the middle layer at the same time to detect the comprehensive stress of the substrate to be tested. Generally, there are two ways of scanning detection, one is equal focus plane detection, and the other is equal focus interval detection.

[0138] Exemplarily, when detecting the comprehensive stress of multiple detection points, equal-focal-plane Raman laser detection can be performed on multiple detection points of the substrate to be tested. The equal-focal-plane means that the focal axis positioning position of the Raman laser is located in the same horizontal plane when Raman laser detection is performed on each detection point.

[0139] As the name implies, the Raman laser scans and detects multiple detection points on the same horizontal plane. After the parameters of the Raman spectrometer are adjusted and confirmed, the axial focus position will not be changed, that is, the focus axis positioning position of the Raman laser is located on the same horizontal plane. Fig.10 As shown in the figure, based on the origin selected by the test platform of the Raman spectrometer, the focus position of the Raman laser in the axial direction of the substrate to be tested is set to h1. Then, during the entire test process, this focus position is kept unchanged, and multiple test points of the substrate to be tested are scanned and tested in the horizontal direction (or radial direction of the substrate). After the focus position is set, it is no longer adjusted in the isofocus plane detection, so the scanning and detection speed is faster. However, the isofocus plane detection may be affected by the curvature of the surface of the substrate to be tested, such as Fig.11As shown, if the curvature of the surface of the substrate to be measured is large, the light spot of the Raman laser may fall completely into the surface layer, or completely fall into the middle layer, and the comprehensive stress of the substrate to be measured cannot be accurately detected.

[0140] Exemplarily, when detecting the comprehensive stress of multiple detection points, Raman laser detection with equal focal distance may be performed on multiple detection points of the substrate to be detected.

[0141] See also Fig.12 , equal focus spacing means that the focus depth is the same when performing Raman laser detection on each detection point. The focus depth is the distance between the focus position of the Raman laser and the surface of the substrate to be tested when detecting the detection point. It can be seen that when detecting different detection points, since the surface height of the substrate to be tested may be different, the focus position will also be adjusted up and down with the deformation of the surface of the substrate to be tested. Therefore, equal focus spacing detection will not be affected by the curvature of the substrate surface. When the surface of the substrate to be tested is convex due to curvature, the focus position of the Raman laser also moves upward; when the surface of the substrate to be tested is concave due to curvature, the focus position of the Raman laser also moves downward, ensuring that the focus position of the Raman laser is the same as the distance between the surface of the substrate to be tested for each scanning detection, so that it will not be affected by the curvature of the substrate surface to be tested.

[0142] Usually, the Raman spectrometer has an automatic focusing function, which can automatically focus the Raman laser spot on the position with the strongest stress, that is, the surface of the substrate to be measured. After automatically focusing on the surface of the substrate to be measured, the focus axis of the Raman laser is controlled to move downward. d height, so that the Raman laser covers the surface layer and the middle layer of the substrate to be tested at the same time, and detects the comprehensive stress of the substrate to be tested.

[0143] However, combined with the above introduction, it can be seen that the equal focus spacing detection is not affected by the curvature, and the stress data obtained by the detection is more accurate, but each detection point needs to be automatically focused and then moved down D d Height, so the efficiency is very low when scanning multiple detection points. Therefore, the most commonly used method is still the equal focus plane detection. For some application scenarios that need to ensure detection accuracy, the equal focus interval detection is used.

[0144] Exemplarily, in one possible implementation, the equifocal spacing test or the equifocal plane test can be selected according to the curvature of the substrate to be tested: if the curvature of the surface of the substrate to be tested is relatively severe, the protrusion height and the depression depth are large, resulting in the inability of the equifocal plane test to cover the middle layer and the surface layer. In this case, the equifocal spacing test can be selected; in another possible implementation, if the curvature of the surface of the substrate to be tested is relatively slight, the Raman laser spot can cover the middle layer and the surface layer. In this case, the equifocal plane test can be selected to improve the efficiency of the detection scan.

[0145] The use of equifocal plane detection can improve the efficiency of detection. However, when using the equifocal plane detection method, the influence of curvature should be avoided as much as possible to avoid the Raman laser spot falling completely into the surface layer or completely falling into the middle layer.

[0146] Therefore, before using the iso-focal plane detection, the curvature of the surface of the substrate to be tested should be determined, that is, the degree of undulation of the surface of the substrate to be tested should be determined, and which position of the surface of the substrate to be tested is convex and which position is concave.

[0147] Exemplarily, before performing iso-focal plane Raman laser detection on multiple detection points of the substrate to be detected, refer to Fig.13 , the method further comprises:

[0148] S310: Obtaining the curvature of the surface of the substrate to be measured, where the curvature includes a convex height or a concave depth of the surface of the substrate to be measured.

[0149] The curvature of the surface of the substrate to be tested is manifested as a convexity or a concaveity. Detecting the height of the convexity or the depth of the concaveity on the surface of the substrate to be tested can characterize the curvature of the substrate to be tested. For example, a spatial coordinate system is constructed with a fixed point selected on the test platform as the origin (0, 0, 0). The x-axis and y-axis are parallel to the surface of the test platform, and the z-axis is perpendicular to the surface of the test platform, that is, perpendicular to the substrate to be tested. A point with coordinates (a, b, c) on the substrate is selected as a reference point. If the height of the z-axis of a point on the surface of the substrate to be tested is greater than c, it can be determined that the point is convex relative to the reference point. If the height of the z-axis of a point on the surface of the substrate to be tested is less than c, it can be determined that the point is concave relative to the reference point. Therefore, it is only necessary to obtain the z-axis coordinates of each point on the substrate surface to determine the curvature of the substrate surface.

[0150] S320: Determine the focus position of the Raman laser detection on the isofocal plane according to the curvature, so that the light spot of the Raman laser covers the surface layer and the middle of the substrate to be detected in the axial direction of the detection point.

[0151] After the curvature is determined, the focus position of the Raman laser detection can be determined according to the curvature of the substrate surface to be detected, so that the Raman laser spot covers the surface layer and the middle layer of the substrate to be detected in the axial direction of the detection point.

[0152] Of course, it is also possible that the curvature of the substrate surface to be measured is large, resulting in the Raman laser being unable to cover the surface layer and the middle layer at the same time. In this case, it is necessary to use equal focusing distance detection to improve the accuracy of stress detection.

[0153] Before the curvature test, the Raman spectrometer needs to be calibrated using single crystal silicon. First, the single crystal silicon substrate is scanned in the Z direction (i.e., axial direction) to confirm that its peak intensity is Gaussian distribution. For example, the surface of the single crystal Si substrate is taken as the zero point, and an axial scanning test is performed from -100 μm inside the single crystal silicon substrate to +20 μm above the single crystal silicon substrate to analyze the change in Raman spectrum signal intensity. Fig.14 The peak intensity distribution diagram of the axial scanning test of the single crystal silicon substrate is shown. Since the single crystal Si substrate is a non-transparent material, its peak intensity presents a Gaussian distribution with the surface zero point position as the symmetry axis. Then, the single crystal silicon is subjected to a surface focusing single point test, and the single crystal silicon Raman spectrum peak position is adjusted to the standard peak position of the standard sample (for example, 520.70cm -1 ), which means the Raman spectrometer has been calibrated.

[0154] The calibrated Raman spectrometer is used to perform an axial scanning test on the silicon carbide substrate. The scanning range is from -100 μm inside the silicon carbide substrate to +20 μm above the silicon carbide substrate. The peak intensity distribution diagram of the axial scanning test on the silicon carbide substrate is obtained, as shown in FIG. Fig.15 As shown, the 4H-SiC substrate and other silicon carbide materials have the characteristics of transparent materials, so the Raman laser can penetrate into the interior of the silicon carbide substrate, and as the incident depth of the Raman laser increases, the feedback signal gradually weakens, so the Raman peak intensity of the silicon carbide substrate gradually decreases as the depth of the Raman laser penetrating into the silicon carbide substrate increases. Based on this, when the peak intensity at a certain point of the substrate to be measured is detected, the peak intensity difference between it and the peak intensity of the surface (zero point) of the substrate to be measured when the peak intensity is the largest can be judged, and then the distance between this point and the surface (zero point) of the substrate to be measured can be determined.

[0155] Exemplarily, the present application embodiment provides a method for determining the curvature of the surface of the substrate to be tested, in combination with reference to Figure 16 to Figure 18 , step S310 includes:

[0156] S311: Select a fixed origin on the test platform to establish a spatial coordinate system, use a Raman spectrometer to automatically focus on any reference point on the surface of the substrate to be tested, adjust the Raman laser focus position to move down a first preset distance from the reference point, perform isofocusing plane detection on the substrate to be tested, and obtain the peak intensity of the substrate to be tested at different positions on the focusing plane.

[0157] The Raman spectrometer can automatically focus on the position with the strongest reflection signal intensity, that is, the substrate surface. The Raman spectrometer is used to automatically focus on the surface of the substrate to be measured, and the position coordinates of the point are marked as (a, b, c), which is determined as the reference point of the substrate surface to be measured.

[0158] Combination Fig.17 , based on the reference point on the surface of the substrate to be tested, the Raman laser focus position is adjusted to move down a first preset distance H, that is, an equal focus plane test is performed on the plane where the point (a, b, cH) is located, and the peak intensity scanning results at different positions on this focus plane are obtained. Exemplarily, the range of the first preset distance H is 5-150 μm.

[0159] S312: Determine the height difference between any focus position and the position with the maximum axial peak intensity according to the peak intensity of any focus position on the focus plane and the predetermined axial peak intensity distribution of the substrate to be tested.

[0160] like Fig.18 As shown, if the peak intensity of a certain focusing position A1 is measured, the axial position corresponding to the peak intensity is determined to be x1, and the position with the maximum axial peak intensity (i.e., the substrate surface) is x0, and the height difference △h between the focusing position and the position with the maximum axial peak intensity is calculated, where △h = x0-x1.

[0161] S313: Determine the curvature of the surface of the substrate to be measured corresponding to the focus position according to the first preset distance and the height difference.

[0162] Curvature meets:

[0163] S=Δh-H

[0164] Wherein S is the curvature of the substrate surface relative to the reference point, Δh is the height difference, and H is the first preset distance.

[0165] Assuming that the coordinates of the focus position are (a, b, cH), and the height difference between the focus position and the corresponding substrate surface is △h, the coordinates of the substrate surface corresponding to the focus position are (a, b, c-H+△h), and the coordinates of the reference point selected in the above example are (a, b, c), so the curvature of the substrate surface corresponding to the focus position relative to the substrate surface is:

[0166] S=c-H+Δh-c.

[0167] That is:

[0168] S=Δh-H

[0169] When S is positive, it means that the substrate surface corresponding to the focus position is convex relative to the reference point; when S is negative, it means that the substrate surface corresponding to the focus position is concave relative to the reference point.

[0170] After determining the curvature of the substrate surface to be measured, the focus position of the isofocus plane detection can be reasonably set according to the curvature of the substrate surface to be measured, so as to prevent the Raman laser spot from falling completely into the surface layer or the middle layer.

[0171] For example, according to the curvature of the surface of the substrate to be tested, it is determined that the surface layer and the middle layer of the substrate to be tested are concave to a certain depth. Then, when selecting the focus depth of the iso-focal plane test, the focus plane can also be lowered to a certain depth to ensure that the Raman laser spot can cover the surface layer and the middle layer at the same time. After selecting the focus position, the iso-focal plane Raman laser scanning test is performed on the substrate to be tested, wherein the Raman laser spot covers the middle layer and the surface layer of the substrate to be tested, and the comprehensive stress distribution of the substrate to be tested is measured. For example, refer to Fig.19 , showing a schematic diagram of the distribution of the comprehensive stress of the substrate to be tested provided in an embodiment of the present application.

[0172] In the scheme provided by the embodiment of the present application, the Raman laser spot is made to cover the surface layer and the middle layer of the substrate to be measured, the peak position is obtained, the peak position obtained is subtracted from the preset reference peak position to obtain the peak position offset, and then the comprehensive stress is calculated according to the peak position offset and the stress conversion coefficient μ. Here, when the preset reference peak position is the standard peak position, the measured comprehensive stress is the absolute comprehensive stress, and the absolute comprehensive stress is the comprehensive stress relative to the standard substrate. Absolute stress can reflect the difference between the substrate and the standard SiC crystal, and is used to determine the comprehensive stress level of the SiC substrate. However, the realization of the standard and ideal SiC substrate is relatively difficult. Therefore, the peak position of the Raman laser can be measured at two detection points on the substrate surface, and the difference between the peak positions of the Raman laser at the two detection points can be determined. The relative stress distribution in the substrate surface can be judged by the relative stress.

[0173] Exemplarily, when the preset reference peak position is the peak position of a reference point on the substrate to be tested (ie, another detection point on the substrate to be tested), the measured comprehensive stress is the relative comprehensive stress of the detection point relative to the reference point.

[0174] In a possible implementation, the preset reference peak position may also be any one of the average value, median, mode and other statistical function calculation results of the peak positions of all detection points in the entire substrate to be tested.

[0175] For example, 4H-SiC is used as an example to illustrate: the absolute stress is integrated to determine the simplified wave vector peak position. The measured 4H-SiC peak position is subtracted from the standard peak position, such as FTO (2 / 4). The calculation formula for the comprehensive absolute stress is:

[0176] σabsolute=μ×(ω 实际 -ω FTO(2 / 4))

[0177] The unit of σ is MPa, ω 实际 and ω FTO(2 / 4) The unit is cm -1 , where ω 实际 is the actual FTO(2 / 4) peak position at the detection point of the substrate to be tested, ω FTO(2 / 4) It is the standard peak position of FTO (2 / 4) substrate.

[0178] The comprehensive relative stress is calculated by subtracting the measured values ​​of the same simple wave vector peak position at any two points on the substrate surface, such as the FTO (2 / 4) peak position. The calculation formula for the comprehensive relative stress is:

[0179] σrelative=μ×(ω (x1,y1) -ω (x2,y2))

[0180] The unit of σ is MPa, ω (x1,y1) and ω (x2,y2) The unit is cm -1 , where ω (x1,y1) is the actual FTO(2 / 4) peak position at the detection point of the substrate to be tested, ω (x2,y2) is the actual FTO (2 / 4) peak position of the relative point of the substrate to be tested. The comprehensive relative stress of the detection point is calculated according to the above calculation formula. If the relative value of σ is positive, it means that the stress of the detection point relative to the relative point is tensile stress. If the relative value of σ is negative, it means that the stress of the detection point relative to the relative point is compressive stress.

[0181] In addition, the stress distribution of the substrate to be tested can be jointly evaluated based on the detected absolute comprehensive stress and relative comprehensive stress of the substrate to be tested. For example, when the absolute comprehensive stress of the substrate is large and the relative comprehensive stress is small, it means that there are many defects in the surface, but the stress distribution is uniform, the crystal quality is poor, and the uniformity quality in various regions of the substrate is poor; if the absolute comprehensive stress is small and the relative comprehensive stress is large, the overall substrate quality of the surface is good, but there are abnormal quality deviations in some parts.

[0182] In the above example, the present application uses the detection of the comprehensive stress of the SiC substrate as an example, but is not limited to this. The solution provided in the embodiment of the present application can also be applied to the detection of the comprehensive stress of other materials, such as Si, GaN, AlN, Ga2O3, Diamond and other crystalline and amorphous materials.

[0183] This application analyzes and simulates the crystal growth stress according to the characteristics of SiC crystals obtained by crystal growth using the PVT method. The in-plane radial relative stress actually measured by the above stress detection method and the simulated radial relative stress result both show a symmetrical distribution with high edge stress and low center stress, and the simulation result is consistent with the actual measured result; the simulated axial absolute stress and the actually measured in-plane axial absolute stress show a distribution with positive front stress and negative rear stress, and the simulation result is also consistent with the actual measured result. And 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. Since the SiC crystal is relatively thick and the penetration depth of the Raman laser is limited, the SiC crystal is cut into multiple substrates. The actually measured axial absolute stress is obtained by testing the in-body absolute stress of different substrates on the same axis.

[0184] The embodiment of the present application also provides a substrate, which is a substrate detected by the stress detection method provided in the embodiment of the present application. The stress detection method is used to measure the stress distribution of a SiC single crystal substrate grown by a conventional process, and it is found that the radial stress distribution is too high, which is greater than 60Mpa; according to the stress distribution characteristics obtained by stress scanning, the thermal field and process of crystal growth are simulated and optimized, and a thermal field design and process that can obtain low stress and uniform distribution are obtained; stress testing is performed on the wafers after cutting, grinding, and polishing, and the processes with high surface processing damage stress and additional internal stress are located, and the relevant processing technology is optimized; finally, a substrate with low stress and uniform stress distribution is obtained through multiple rounds of crystal growth thermal field, growth process, processing technology and stress measurement, such as Fig. 20 shown.

[0185] The above describes the process of the method provided in the present application. The following describes the structure of the device provided in the present application in combination with the above method process.

[0186] The present application also provides a stress detection device, such as Fig.21 As shown, the stress detection device 400 includes: a detection module 410 and a processing module 420 .

[0187] The detection module 410 is configured to perform Raman laser detection on the detection point of the substrate to be detected, obtain the peak position of the Raman spectrum of the detection point, and the light spot of the Raman laser used to detect the detection point is located on the surface layer and the middle layer of the substrate to be detected.

[0188] In a possible implementation, the detection module 410 may be used to execute S110 in the aforementioned method embodiment to achieve corresponding technical effects.

[0189] The processing module 420 is configured to determine the peak offset of the detection point based on the acquired peak position and the preset reference peak position; the processing module 420 is also configured to determine the comprehensive stress of the detection point based on the peak offset and a predetermined conversion coefficient, and the conversion coefficient is a proportional coefficient between the peak offset and the stress.

[0190] In a possible implementation, the processing module 420 may be used to execute steps S130 and S150 in the aforementioned method embodiment to achieve corresponding technical effects.

[0191] The detection module 410 is also configured to obtain the crystal plane spacing of the substrate to be tested. For example, the crystal plane spacing of the substrate to be tested can be detected and obtained using a single crystal diffractometer, a synchrotron radiation tester, a white light tester, a neutron diffractometer, a scanning electron microscope, a transmission electron microscope, or other equipment or methods.

[0192] In a possible implementation, the detection module 410 may be used to execute S211 in the aforementioned method embodiment to achieve corresponding technical effects.

[0193] The processing module 420 is also configured to determine the inter-plane spacing difference between the inter-plane spacing of the substrate to be tested and the theoretical inter-plane spacing, determine the stress of the substrate to be tested according to the inter-plane spacing difference and the stress-strain formula, obtain the peak position of the Raman spectrum of the substrate to be tested, subtract the peak position from the standard peak position to obtain the peak position offset, and determine the ratio of the peak position offset to the calculated stress as the conversion coefficient.

[0194] In a possible implementation, the processing module 420 may be used to execute S212 to S214 in the aforementioned method embodiment to achieve corresponding technical effects.

[0195] The detection module 410 is further configured to obtain a first Raman spectrum peak position of the standard sample, and obtain a second Raman spectrum peak position when a preset stress is applied to the standard sample.

[0196] In a possible implementation, the detection module 410 may be used to execute S221 to S222 in the aforementioned method embodiment to achieve corresponding technical effects.

[0197] The processing module 420 is further configured to determine the pressure according to the preset stress applied to the standard sample and the area where the preset stress is applied, and determine the conversion coefficient according to the first Raman spectrum peak position, the second Raman spectrum peak position and the pressure.

[0198] Among them, the first Raman spectrum peak position, the second Raman spectrum peak position, the pressure and the conversion coefficient satisfy:

[0199] μ=(P0-P1) / P

[0200] Wherein μ is the conversion coefficient between peak position shift and stress, P0 is the first Raman spectrum peak position of the standard sample obtained by Raman laser detection of the standard sample, P1 is the second Raman spectrum peak position when stress F is applied to the standard sample, and P is the pressure when stress F is applied to the standard sample.

[0201] In a possible implementation, the processing module 420 may be used to execute S223 to S224 in the aforementioned method embodiment to achieve corresponding technical effects.

[0202] The detection module 410 is further configured to perform axial Raman laser scanning detection on multiple detection points of the substrate to be detected to obtain axial stress distribution of the multiple detection points, where the axial stress distribution includes stress at different axial positions of the detection points.

[0203] In a possible implementation, the detection module 410 may be used to execute S101 in the aforementioned method embodiment to achieve corresponding technical effects.

[0204] The processing module 420 is further configured to determine the positions of the surface layer and the middle layer of the substrate to be tested according to the axial stress distribution of multiple detection points, wherein the change rate of the axial stress of the surface layer is greater than the change rate of the axial stress of the middle layer.

[0205] In a possible implementation, the processing module 420 may be used to execute S102 in the aforementioned method embodiment to achieve corresponding technical effects.

[0206] In one possible implementation, the equifocal spacing test or the equifocal plane test can be selected according to the curvature of the substrate to be tested: if the curvature of the substrate surface to be tested is relatively bad, the convex height and the concave depth are large, resulting in the equifocal plane test being unable to cover the middle layer and the surface layer at the same time, in this case, the equifocal spacing test can be selected; in another possible implementation, if the curvature of the substrate surface to be tested is relatively slight, the Raman laser spot can cover the middle layer and the surface layer, in this case, the equifocal plane test can be selected to improve the efficiency of the detection scan. The use of the equifocal plane test can improve the efficiency of the detection, but when using the equifocal plane test, the influence of the curvature should be avoided as much as possible, and the Raman laser spot should be avoided from falling completely into the surface layer or the middle layer. Therefore, before using the equifocal plane test, the curvature of the substrate surface to be tested should be determined, that is, the degree of undulation of the surface of the substrate to be tested should be determined, and which position of the surface of the substrate to be tested is convex and which position is concave.

[0207] The detection module 410 is further configured to obtain the curvature of the surface of the substrate to be tested, where the curvature includes the height of a protrusion or the depth of a concave depression of the surface of the substrate to be tested.

[0208] Exemplarily, the detection module 410 is configured to select a fixed origin on the test platform to establish a spatial coordinate system, use a Raman spectrometer to automatically focus on any reference point on the surface of the substrate to be tested, adjust the Raman laser focusing position to move down a first preset distance from the reference point, perform equal focusing plane detection on the substrate to be tested, and obtain the peak intensity of the substrate to be tested at different positions on the focusing plane, determine the height difference between the focusing position and the position with the maximum axial peak intensity according to the peak intensity of any focusing position on the focusing plane and the predetermined axial peak intensity distribution of the substrate to be tested, and determine the curvature of the surface of the substrate to be tested corresponding to the focusing position according to the first preset distance and the height difference.

[0209] Curvature meets:

[0210] S=Δh-H

[0211] Wherein S is the curvature of the substrate surface relative to the reference point, Δh is the height difference, and H is the first preset distance.

[0212] In a possible implementation, the detection module 410 may be used to execute S310 in the aforementioned method embodiment to achieve corresponding technical effects.

[0213] The processing module 420 is further configured to determine the focus position of the Raman laser detection on the isofocal plane according to the curvature, so that the light spot of the Raman laser covers the surface layer and the middle of the substrate to be detected in the axial direction of the detection point.

[0214] In a possible implementation, the processing module 420 may be used to execute S320 in the aforementioned method embodiment to achieve corresponding technical effects.

[0215] An embodiment of the present application also provides a stress detection device, which includes: a processor and a memory, wherein the processor is coupled to the memory, and the memory is configured to store a computer program; the processor is configured to execute the computer program stored in the memory, so that the stress detection device performs the steps of the stress detection method provided in the embodiment of the present application.

[0216] The embodiments of the present application also provide a computer program product. When the computer program product is run on a stress detection device, the stress detection device is enabled to execute the above-mentioned related steps to implement each step in the above-mentioned method embodiment.

[0217] A computer-readable storage medium is also provided in an embodiment of the present application. The computer-readable storage medium stores a program (computer instructions). When the program (computer instructions) is run on a computer, the computer executes the steps in the method provided in the above embodiment.

[0218] In the several embodiments provided in the present application, it should be understood that the disclosed devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of the modules or units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another device, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0219] The units described as separate components may or may not be physically separated, and the components shown as units may be one physical unit or multiple physical units, that is, they may be located in one place or distributed in multiple different places. Some or all of the units may be selected according to actual needs to achieve the purpose of the present embodiment.

[0220] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a readable storage medium. The above content is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered by the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

[0221] Although the present invention has been described in conjunction with specific features and embodiments thereof, it is apparent that various modifications and combinations may be made thereto without departing from the spirit and scope of the present invention. Accordingly, this specification and the accompanying drawings are merely exemplary illustrations of the present invention as defined by the appended claims and are deemed to cover any and all modifications, variations, combinations or equivalents within the scope of the present invention. Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, the present invention is intended to include such modifications and variations if they fall within the scope of the claims of the present invention and their equivalents.

Claims

1. A stress detection method, It is characterized in that The method comprises: Performing Raman laser detection on a detection point of the substrate to be detected to obtain a peak position of the Raman spectrum of the detection point, wherein the light spot of the Raman laser used to detect the detection point is located on the surface layer and the middle layer of the substrate to be detected; Determining a peak position offset of the detection point according to the acquired peak position and a preset reference peak position; The comprehensive stress of the detection point is determined according to the peak position offset and a predetermined conversion coefficient, wherein the conversion coefficient is a proportional coefficient between the peak position offset and the stress.

2. The method according to claim 1, It is characterized in that The method further comprises: performing Raman laser detection on the detection point of the substrate to be detected to obtain the peak position of the Raman spectrum of the detection point, and before the light spot of the Raman laser used to detect the detection point is located on the surface layer and the middle layer of the substrate to be detected. Performing axial Raman laser scanning detection on multiple detection points of the substrate to be tested to obtain axial stress distribution conditions of the multiple detection points, wherein the axial stress distribution conditions include stresses at different axial positions of the detection points; The positions of the surface layer and the middle layer of the substrate to be tested are determined according to the axial stress distribution of the plurality of detection points, wherein the change rate of the axial stress of the surface layer is greater than the change rate of the axial stress of the middle layer.

3. The method according to claim 2, It is characterized in that The step of performing axial Raman laser scanning detection on multiple detection points of the substrate to be tested to obtain the axial stress distribution of the multiple detection points includes: Performing axial Raman laser scanning detection on the detection point to obtain the peak positions of the Raman spectrum at different axial positions of the detection point; Determining peak position offsets at different axial positions of the detection point according to the acquired peak position and a preset reference peak position; The stress at different axial positions of the detection point is determined according to the peak position offset and the conversion coefficient.

4. The method according to any one of claims 1 to 3, It is characterized in that The method further includes: when detecting the comprehensive stress of the plurality of detection points, performing Raman laser detection with equal focal distance on the plurality of detection points of the substrate to be detected, wherein the equal focal distance means that the focal depth when detecting each of the detection points is the same, and the focal depth is the distance between the focal position of the Raman laser and the surface of the substrate to be detected when detecting the detection points.

5. The method according to any one of claims 1 to 3, It is characterized in that The method further comprises: when detecting the comprehensive stress of the plurality of detection points, performing iso-focal-plane Raman laser detection on the plurality of detection points of the substrate to be detected, wherein the iso-focal-plane refers to the position of the focal axis of the Raman laser when detecting each of the detection points being located on the same horizontal plane.

6. The method according to claim 5, It is characterized in that Before performing isofocal plane Raman laser detection on a plurality of detection points of the substrate to be detected, the method further comprises: Determining the curvature of the surface of the substrate to be measured, wherein the curvature includes a convex height or a concave depth of the surface of the substrate to be measured; The focusing position of the isofocal plane Raman laser detection is determined according to the curvature, so that the light spot of the Raman laser covers the surface layer and the middle layer of the substrate to be detected in the axial direction of the detection point.

7. The method according to claim 6, It is characterized in that Determining the curvature of the surface of the substrate to be measured includes: Selecting a fixed origin on the test platform to establish a spatial coordinate system, using a Raman spectrometer to automatically focus on any reference point on the surface of the substrate to be tested, adjusting the Raman laser focus position to move down a first preset distance from the reference point, performing an isofocusing plane detection on the substrate to be tested, and obtaining peak intensities at different positions of the substrate to be tested on the focus plane; Determine the height difference between the focus position and the position with the maximum axial peak intensity according to the peak intensity of any focus position on the focus plane and the predetermined axial peak intensity distribution of the substrate to be measured; The curvature of the surface of the substrate to be measured corresponding to the focus position is determined according to the first preset distance and the height difference, wherein the curvature satisfies: S=Δh-H Wherein S is the curvature of the substrate surface relative to the reference point, Δh is the height difference, and H is the first preset distance.

8. The method according to claim 1, It is characterized in that Before determining the comprehensive stress of the detection point according to the peak position offset and the predetermined conversion coefficient, the method further includes: Determining the interplanar spacing difference between the interplanar spacing of the substrate to be tested and the theoretical interplanar spacing; Determining the stress of the substrate to be measured according to the interplanar spacing difference and the stress-strain formula; The peak position of the Raman spectrum of the substrate to be tested is obtained, the peak position is subtracted from the standard peak position to obtain a peak position offset, and the ratio of the peak position offset to the calculated stress is determined as the conversion coefficient.

9. The method according to claim 1, It is characterized in that Before determining the comprehensive stress of the detection point according to the peak position offset and the predetermined conversion coefficient, the method further includes: Obtain the first Raman spectrum peak position of the standard sample; Obtaining a second Raman spectrum peak position when a preset stress is applied to the standard sample; Determining pressure according to the preset stress applied to the standard sample and the area to which the preset stress is applied; The conversion coefficient is determined according to the first Raman spectrum peak position, the second Raman spectrum peak position and the pressure, and the first Raman spectrum peak position, the second Raman spectrum peak position, the pressure and the conversion coefficient satisfy: μ=(P0-P1) / P Wherein μ is the conversion coefficient, P0 is the first Raman spectrum peak position, P1 is the second Raman spectrum peak position, and P is the pressure.

10. The method according to claim 1, It is characterized in that When the preset reference peak position is the standard peak position, the measured comprehensive stress is the absolute comprehensive stress; When the preset reference peak position is the peak position of another detection point on the substrate to be measured, the measured comprehensive stress is the relative comprehensive stress of the detection point relative to the other detection point.

11. A stress detection device, It is characterized in that The stress detection device comprises: The detection module is configured to perform Raman laser detection on a detection point of the substrate to be detected, and obtain the peak position of the Raman spectrum of the detection point, wherein the light spot of the Raman laser covers the surface layer and the middle layer of the substrate to be detected in the axial direction of the detection point; A processing module, configured to determine a peak position offset of the detection point according to the acquired peak position and a preset reference peak position; The processing module is further configured to determine the comprehensive stress of the detection point according to the peak offset and a predetermined conversion coefficient, wherein the conversion coefficient is a proportional coefficient between the peak offset and the stress.

12. A stress detection device, It is characterized in that The stress detection device comprises: a processor and a memory, wherein the processor is coupled to the memory, and the memory is configured to store a computer program; the processor is configured to execute the computer program stored in the memory, so that the stress detection device performs the steps of the method described in any one of claims 1 to 10.

13. A computer-readable storage medium, It is characterized in that The method comprises computer instructions, and when the computer instructions are executed on a computer, the computer is enabled to execute the stress detection method according to any one of claims 1 to 10.

14. A substrate, It is characterized in that The substrate is a substrate to be detected by the stress detection method according to any one of claims 1 to 10.

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