Wide bandgap semiconductor wafer substrate and method for characterizing influence of high-temperature performance on epitaxial film

Abstract

The invention discloses a wide bandgap semiconductor wafer substrate and a characterization method for the influence of high-temperature performance on an epitaxial film. The characterization method comprises the following steps: preparing wide bandgap semiconductor wafer substrates with different masses and growing an epitaxial film; respectively measuring a Raman spectrum, a white light interference spectrum and an ellipsometry spectrum at the same position of the epitaxial thin film by using a multispectral enhanced ellipsometry instrument at different temperatures; extracting initial values of surface physical parameters of the epitaxial film at the corresponding temperature according to the Raman spectrum and the white light interference spectrum; constructing a corresponding optical model according to the type of the epitaxial thin film and the initial value of the surface physical parameter, determining the material characteristics of the epitaxial thin film according to the material composition of the epitaxial thin film, selecting an oscillator model according to the material characteristics and / or temperature of the epitaxial thin film, and performing regression analysis by using the optical model and the oscillator model in combination with an ellipsometry spectrum. And analyzing to obtain a curve that the surface physical parameters of the epitaxial films grown on the substrates with different masses change along with the temperature. The method is uniform in measurement basis and high in characterization precision.

Description

Technical Field

[0001] This invention relates to the field of epitaxial thin film performance characterization, specifically to a wide bandgap semiconductor wafer substrate and a method for characterizing the influence of high-temperature performance on epitaxial thin films. Background Technology

[0002] Wide bandgap semiconductors (bandgap width Eg > 2.3 eV), represented by silicon carbide (SiC), gallium nitride (GaN), gallium oxide (Ga2O3), and diamond, have demonstrated unique advantages in high-frequency and high-power devices using these materials in critical fields such as 5G communications, new energy vehicles, rail transportation, and aerospace, adapting to extreme conditions such as high frequency, high power, and high temperature. However, wide bandgap semiconductor materials often face performance degradation and lifespan reduction due to thermal accumulation during operation under extreme conditions like high frequency and high power. For example, under high-power conditions, overload voltage increases the electric field strength, reducing resistance and increasing heat output, leading to temperature rise and ultimately device performance degradation. Simultaneously, excessively high voltage may exceed the device's breakdown voltage, causing it to fail. Therefore, temperature is one of the key factors affecting the performance, lifespan, and operational safety of wide bandgap semiconductor devices during extreme operating conditions.

[0003] In actual service operations, temperature increases influence macroscopic material properties of wide-bandgap semiconductor materials through induced changes in interface morphology and volumetric thermal expansion, particularly surface and interface morphology, internal stress, and optoelectronic properties (conductivity, dielectric constant, absorptivity, reflectivity). Due to the differentiated coefficients of thermal expansion of different epitaxial thin film materials on the wafer substrate, stress concentration occurs at the substrate-film interface, leading to morphological evolution such as surface roughening or warping, as well as stress caused by surface crack propagation. Simultaneously, temperature changes alter the electronic structure and atomic arrangement of the material, thereby changing its absorption, reflection, scattering, and emission behavior of light. This results in changes in optical properties such as refractive index and extinction coefficient; for perovskite materials, phase transitions may also occur at specific temperatures. Therefore, accurate characterization of the impact of high-temperature performance of wide-bandgap semiconductor wafer substrates on epitaxial thin films can provide fundamental support for performance and safety assessments of wide-bandgap devices during service.

[0004] In existing wide-bandgap semiconductor wafer manufacturing processes, the morphological performance parameters of the process layers are typically measured using dispersed measurement methods and are performed at room temperature. However, precise measurements of the morphological parameters of wide-bandgap semiconductor materials under varying or even high-temperature conditions are rare. Furthermore, for measurements of thin films under high-temperature conditions, the influence of the substrate and high-temperature properties on the thin film is rarely considered. For example, patent publication number CN 104880436B, entitled "A Thin Film High-Temperature Optoelectronic Property Testing Device," can simultaneously generate curves of thin film reflected light intensity and resistance as a function of temperature from room temperature to high temperature, and calculate the optoelectronic related physical parameters of the thin film. However, it does not provide information on the influence of the substrate on the quality of the thin film. Summary of the Invention

[0005] In view of the aforementioned technical problems, the purpose of the embodiments of this application is to provide a method for characterizing the influence of wide bandgap semiconductor wafer substrates and high-temperature properties on epitaxial thin films to solve the technical problems mentioned in the background section.

[0006] In a first aspect, embodiments of this application provide a method for characterizing the influence of wide-bandgap semiconductor wafer substrates and high-temperature performance on epitaxial thin films, comprising the following steps:

[0007] S1, prepare wide bandgap semiconductor wafer substrates of different qualities, and grow epitaxial thin films on wide bandgap semiconductor wafer substrates of different qualities respectively;

[0008] S2, at one of the temperatures, Raman spectrum, white light interference spectrum and ellipsometric spectrum are measured at the same location on an epitaxial thin film on one of the wide bandgap semiconductor wafer substrates using a multispectral enhanced ellipsometer;

[0009] S3. Based on Raman spectroscopy and white light interference spectroscopy, extract the initial values ​​of the surface physical parameters of the epitaxial thin film on one of the wide bandgap semiconductor wafer substrates at the corresponding temperature. The surface physical parameters include material composition, thickness, optical constants, stress, surface morphology and surface micro-defects.

[0010] S4. Based on the type of epitaxial thin film and the initial values ​​of surface physical parameters on one of the wide bandgap semiconductor wafer substrates, construct the corresponding optical model. Determine the material properties of the epitaxial thin film based on its material composition. Select the oscillator model based on the material properties and / or temperature of the epitaxial thin film. Use the optical model and the oscillator model in combination with elliptic spectrum to perform regression analysis and obtain the optical constants, thickness and stress of the epitaxial thin film.

[0011] S5, heat one of the wide bandgap semiconductor wafer substrates and the epitaxial film on it to another preset temperature and hold it, repeat steps S2-S4 to obtain the curve of the surface physical parameters of the epitaxial film grown on one of the wide bandgap semiconductor wafer substrates as a function of temperature;

[0012] S6. Repeat steps S2-S5 for wide bandgap semiconductor wafer substrates of different qualities and their epitaxial films to obtain curves showing the change of surface physical parameters of epitaxial films grown on wide bandgap semiconductor wafer substrates of different qualities with temperature.

[0013] Preferably, the multispectral enhanced ellipsometer includes a high-temperature heating module, an ellipsometric spectroscopy module, and a partially shared white light interference module and Raman spectroscopy module. The white light interference module and the Raman spectroscopy module share the same objective lens and beam splitter in their optical path structures. The white light interference module and the Raman spectroscopy module measure the white light interference spectrum and Raman spectrum at the same measurement position on the surface of the epitaxial thin film, respectively. The light spot formed on the surface of the epitaxial thin film by the light emitted from the ellipsometric spectroscopy module coincides with the light spot formed on the surface of the epitaxial thin film by the light emitted from the white light interference module and the Raman spectroscopy module. The ellipsometric spectrum at the same measurement position on the surface of the epitaxial thin film is measured in the same position by the ellipsometric spectroscopy module.

[0014] Preferably, the white light interferometry module includes a white light source, a collimating lens, a focusing lens group, an imaging tube, a white light detector, a first beam splitter, a second beam splitter, a third beam splitter, a first objective lens, and a second objective lens. The incident light path of the first objective lens is perpendicular to the surface of the epitaxial film, and the incident light path of the second objective lens is parallel to the surface of the epitaxial film. A reference plane is provided at the focal plane of the second objective lens. The second beam splitter is positioned between the first beam splitter and the second objective lens, and the third beam splitter is positioned between the first beam splitter and the first objective lens. The first objective lens is moved perpendicular to the surface of the epitaxial film by a second driving unit, and the second objective lens is moved parallel to the surface of the epitaxial film by a first driving unit. The light emitted from the white light source is converted into a parallel beam after passing through the collimating lens. After passing through the focusing lens group and the first beam splitter in sequence, the parallel beam is split into two coherent light waves, namely a reference beam and a measurement beam. After the beam of light illuminates the surface of the epitaxial thin film, it enters the second objective and the first objective respectively. The two coherent light waves return along the original path and pass through the second beam splitter and the third beam splitter respectively. They then interfere with each other at the first beam splitter and pass through the imaging tube to the white light detector to obtain the white light interference spectrum. The Raman spectroscopy module includes a laser source, a second beam splitter, a dichroic mirror, a confocal mirror group, a first objective, and a Raman detector. The dichroic mirror is placed between the second beam splitter and the confocal mirror group. The monochromatic light emitted by the laser source is reflected by the dichroic mirror and the second beam splitter in sequence and enters the first objective. The first objective focuses the monochromatic light and projects it onto the surface of the epitaxial thin film. It then collects the Raman scattered light and returns it to the second beam splitter. The Raman scattered light is reflected by the second beam splitter and passes through the dichroic mirror to the confocal mirror group. The confocal mirror group filters out stray light in the Raman scattered light and transmits the required Raman spectral information to the Raman detector to obtain the Raman spectrum.

[0015] Preferably, the white light interferometer module includes a white light source, a collimating lens, a focusing lens group, an imaging tube, a white light detector, a first beam splitter, a second beam splitter, a first objective lens, and a second objective lens. The incident light path of the first objective lens is perpendicular to the surface of the epitaxial film, and the incident light path of the second objective lens is parallel to the surface of the epitaxial film. A reference plane is provided at the focal plane of the second objective lens. The first beam splitter is positioned between the second objective lens and the second beam splitter, and the second beam splitter is positioned between the first beam splitter and the imaging tube. The first objective lens is controlled to move in a direction perpendicular to the surface of the epitaxial film by a second driving unit, and the second objective lens is controlled to move in a direction parallel to the surface of the epitaxial film by the first driving unit. The light emitted from the white light source is converted into a parallel beam after passing through the collimating lens. After passing through the focusing lens group and the first beam splitter in sequence, the parallel beam is split into two coherent light waves, namely a reference beam and a measurement beam, which illuminate the light source. After passing through the surface of the epitaxial thin film, the two coherent light waves enter the second objective lens and the first objective lens respectively. After returning along the original path, they are superimposed and interfered at the first beam splitter, and then pass through the second beam splitter and the imaging tube to enter the white light detector to obtain the white light interference spectrum. The Raman spectroscopy module includes a laser source, a first beam splitter, a second beam splitter, a dichroic mirror, a confocal lens group, a first objective lens, and a Raman detector. The second beam splitter is set between the first beam splitter and the first objective lens. The monochromatic light emitted by the laser source is reflected by the dichroic mirror and the second beam splitter in sequence, and then passes through the first beam splitter before entering the first objective lens. The first objective lens focuses the monochromatic light and projects it onto the surface of the epitaxial thin film. It then collects the Raman scattered light and returns it to the second beam splitter. The Raman scattered light is reflected by the second beam splitter and passes through the dichroic mirror to enter the confocal lens group. The confocal lens group filters out stray light in the Raman scattered light and transmits the required Raman spectral information to the Raman detector to obtain the Raman spectrum.

[0016] Preferably, the ellipsometric spectroscopy module includes a broadband light source, a polarizer, a first compensator, a second compensator, an analyzer, and an ellipsometric detector. The light emitted by the broadband light source is transmitted to the polarizer, and after passing through the polarizer and the first compensator, the light emitted by the broadband light source is converted into polarized light and obliquely incident on the surface of the epitaxial thin film. Then, it passes through the second compensator and the analyzer in sequence to collect the polarized light reflected from the surface of the epitaxial thin film and transmit it to the ellipsometric detector to obtain the ellipsometric spectrum of the epitaxial thin film.

[0017] Preferably, the high-temperature heating module includes a sample stage, a protective cavity, a first observation window, a second observation window, and a third observation window, with a temperature control range of 300–1200 K. The sample stage is installed inside the protective cavity, which can be evacuated or filled with inert gas. The first and third observation windows are respectively installed on both sides of the protective cavity, allowing the incident and reflected light from the ellipsometric spectroscopy module to pass through. The second observation window is installed on the surface of the protective cavity and is perpendicular to the sample stage. A six-degree-of-freedom motion displacement stage is provided below the sample stage for adjusting the measurement position or leveling the sample stage according to the white light interference spectrum. A first rotating stage is provided below the polarizer for adjusting the angle between the polarizer and the sample stage, and a second rotating stage is provided below the analyzer for adjusting the angle between the analyzer and the sample stage.

[0018] Preferably, the oscillator model includes the empirical Cauchy model, Gaussian model, Drude model, or Lorentz model. The empirical Cauchy model is used in the transparent region of the epitaxial film, and a combination of one or more of the Lorentz model, Drude model, and Gaussian model is used in the absorption spectral region of the epitaxial film.

[0019] Preferably, the regression evaluation function used in the regression analysis in step S4 is the mean squared error (MSE), and its calculation formula is as follows:

[0020]

[0021] Where mod and exp represent the fitted value and the measured value, respectively, δ is the measurement error, N is the total logarithm of the two ellipsoidal parameters φ and Δ measured simultaneously by the multispectral enhanced ellipsometer, M is the logarithm of the selected fitted parameters, and i = 1, 2, ..., N.

[0022] Preferably, wide bandgap semiconductor wafer substrates of different qualities include wide bandgap semiconductor wafer substrates with different surface roughness, surface defects or subsurface defects.

[0023] Preferably, the wide bandgap semiconductor wafer substrate is a substrate with a bandgap width greater than 2.3 eV, including silicon carbide substrates, diamond substrates, or gallium nitride substrates.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) The method proposed in this invention for characterizing the influence of wide bandgap semiconductor wafer substrate and high-temperature performance on epitaxial thin film uses a multispectral enhanced ellipsometer to detect the wide bandgap semiconductor wafer substrate and the epitaxial thin film on it at different temperatures, and obtains the white light interference spectrum, Raman spectrum and ellipsometric spectrum at the same measurement position on the epitaxial thin film. Based on the material properties of different epitaxial thin films and the surface physical parameters extracted from the in-situ measured Raman spectrum and white light interference spectrum, an optical model and an oscillator model are constructed. The optical model and oscillator model are combined with the ellipsometric spectrum for fitting analysis to obtain the surface morphology, material composition, defects, thickness, optical constants and stress of the epitaxial thin film at different temperatures.

[0026] (2) The wide bandgap semiconductor wafer substrate and the high temperature performance of the epitaxial film proposed in this invention can characterize the influence of the high temperature performance of the semiconductor wafer substrate on the epitaxial film. The measurement benchmark is unified and the characterization accuracy is high. It can simultaneously obtain the surface morphology, thickness, material composition, optical properties and mechanical properties of the epitaxial film at different temperatures, and construct the change curve of the morphological parameters of the epitaxial film under high temperature of the substrate to provide feedback for device optimization design.

[0027] (3) The wide bandgap semiconductor wafer substrate and the high temperature performance characterization method proposed in this invention can simultaneously explore the influence of substrate surface roughness, surface defects and subsurface defects on the quality and performance of epitaxial films at different temperatures. Attached Figure Description

[0028] The accompanying drawings are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the description, serve to explain the principles of the invention. Other embodiments and many anticipated advantages of the embodiments will be readily recognized as they become better understood through reference to the following detailed description. Elements in the drawings are not necessarily to scale. The same reference numerals refer to corresponding similar parts.

[0029] Figure 1 This paper illustrates a flowchart of an embodiment of the present application showing a wide bandgap semiconductor wafer substrate and a method for characterizing the influence of high-temperature performance on epitaxial thin films.

[0030] Figure 2 The diagram shows a schematic of the structure of the wide bandgap semiconductor wafer substrate and the multispectral enhanced ellipsometer used in the method for characterizing the influence of high-temperature performance on epitaxial thin films according to Embodiment 1 of this application.

[0031] Figure 3 The diagram shows a schematic of the structure of the wide bandgap semiconductor wafer substrate and the multispectral enhanced ellipsometer used in the method for characterizing the influence of high-temperature performance on epitaxial thin films in Embodiment 2 of this application.

[0032] Reference numerals: 11. Broadband light source; 12. Polarizer; 13. First compensator; 14. Wide bandgap semiconductor wafer substrate; 15. Second compensator; 16. Analyzer; 17. Ellipsometry detector; 21. White light source; 22. Collimating lens; 23. Focusing lens group; 24. First driving unit; 25. First objective lens; 26. Imaging lens tube; 27. White light detector; 28. Second objective lens; 29. ​​Reference plane; 31. First beam splitter; 32. Second beam splitter; 33. Dichroic mirror; 34. Confocal lens group; 35. Raman detector; 36. Laser source; 37. Third beam splitter. Detailed Implementation

[0033] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the relevant invention and not intended to limit the invention. It should also be noted that, for ease of description, only the parts relevant to the invention are shown in the drawings. It should be observed that the dimensions and sizes of the components in the drawings are not to scale, and the size of certain components may be highlighted for clarity.

[0034] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0035] refer to Figure 1 The present invention provides a method for characterizing the influence of wide bandgap semiconductor wafer substrates and high-temperature performance on epitaxial thin films, comprising the following steps:

[0036] S1, prepare wide bandgap semiconductor wafer substrates 14 of different qualities, and grow epitaxial films on wide bandgap semiconductor wafer substrates 14 of different qualities respectively;

[0037] S2, at one of the temperatures, Raman spectrum, white light interference spectrum and ellipsometric spectrum are measured at the same location on one of the epitaxial films on one of the wide bandgap semiconductor wafer substrates 14 using a multispectral enhanced ellipsometer.

[0038] S3. Based on Raman spectroscopy and white light interference spectroscopy, the initial values ​​of the surface physical parameters of the epitaxial thin film on one of the wide bandgap semiconductor wafer substrates 14 at the corresponding temperature are extracted. The surface physical parameters include material composition, thickness, optical constants, stress, surface morphology and surface micro-defects.

[0039] S4. Based on the type of epitaxial thin film and the initial values ​​of surface physical parameters on one of the wide bandgap semiconductor wafer substrates 14, construct the corresponding optical model. Determine the material properties of the epitaxial thin film based on its material composition. Select the oscillator model based on the material properties and / or temperature of the epitaxial thin film. Use the optical model and the oscillator model in combination with ellipsometric spectroscopy for regression analysis to obtain the optical constants, thickness and stress of the epitaxial thin film.

[0040] S5, heat one of the wide bandgap semiconductor wafer substrates 14 and its epitaxial film to another preset temperature and hold it, repeat steps S2-S4 to obtain the curve of the surface physical parameters of the epitaxial film grown on one of the wide bandgap semiconductor wafer substrates 14 as a function of temperature;

[0041] S6. Repeat steps S2-S5 for wide bandgap semiconductor wafer substrates 14 of different qualities and their epitaxial films to obtain curves showing the surface physical parameters of the epitaxial films grown on wide bandgap semiconductor wafer substrates 14 of different qualities as a function of temperature.

[0042] In specific embodiments, wide bandgap semiconductor wafer substrates 14 of different qualities include wide bandgap semiconductor wafer substrates 14 with different surface roughness, surface defects or subsurface defects.

[0043] In a specific embodiment, the wide bandgap semiconductor wafer substrate 14 is a substrate with a bandgap width greater than 2.3 eV, including a silicon carbide substrate, a diamond substrate, or a gallium nitride substrate.

[0044] In specific embodiments, the oscillator model includes the empirical Cauchy model, Gaussian model, Drude model, or Lorentz model. The empirical Cauchy model is used in the transparent region of the epitaxial film, while the Lorentz model, Drude model, and Gaussian model or a combination of several of these oscillator models is used in the absorption spectral region of the epitaxial film.

[0045] In a specific embodiment, the regression evaluation function used in the regression analysis process of step S4 is the mean squared error (MSE), and its calculation formula is as follows:

[0046]

[0047] Where mod and exp represent the fitted value and the measured value, respectively, δ is the measurement error, and N is the two ellipsometric parameters measured simultaneously by the multispectral enhanced ellipsometer. The total logarithm of Δ, where M is the logarithm of the selected fitting parameters, i = 1, 2, ..., N.

[0048] Specifically, firstly, wide-bandgap semiconductor wafer substrates 14 of varying qualities are prepared. Epitaxial thin films are then grown on these substrates. The wide-bandgap semiconductor wafer substrates 14 are substrates with a bandgap greater than 2.3 eV, such as silicon carbide substrates, diamond substrates, and gallium nitride substrates. The varying qualities of the wide-bandgap semiconductor wafer substrates 14 include surface roughness, surface defects, and subsurface defects. At room temperature, the Raman spectrum, white light interference spectrum, and ellipsometric spectrum of the epitaxial thin film are measured in situ using a multispectral enhanced ellipsometer. Initial values ​​of the surface physical parameters of the epitaxial thin film at room temperature, such as material composition, stress, surface morphology, and surface micro-defects, are extracted based on the in-situ measured Raman and white light interference spectra. An oscillator model can be selected based on the material properties of the epitaxial thin film. Material properties refer to the fact that different material compositions lead to differences in absorption, and that the transparent / absorbed wavelengths change with temperature. Therefore, in the transparent region of the thin film, the empirical Cauchy model can be used as the oscillator model, and the optical constants and thickness of the epitaxial thin film in this wavelength range can be obtained through regression analysis. In the absorption spectrum region of the thin film, other oscillator models are selected, such as the Lorentz model, Drude model, Gaussian model, or a combination of several oscillator models. During the fitting analysis, the amplitude and width of the oscillator model are adjusted according to the measured ellipsometric spectrum, and the initial values ​​of the actual collected surface physical parameters are combined to make the fitting results more consistent with the actual situation. Then, the wide bandgap semiconductor wafer substrate 14 and the epitaxial thin film on it are heated to the preset temperature and held, and the above measurement and analysis process is repeated to obtain the surface physical parameter variation curves of the epitaxial thin film under different temperature changes. The temperature variation range is 300-1200K, and temperature sampling can be performed at intervals of 10K or 100K to meet the device optimization design requirements.

[0049] In the regression analysis, the evaluation function MSE is used to judge the difference between the experimental value and the fitted value, and finally the optical constants (n,k) and thickness d of the epitaxial film at different temperatures are obtained, where n represents the refractive index and k represents the reflectivity.

[0050] The calculation formula for the empirical Cauchy model is as follows:

[0051]

[0052] Where n is the refractive index, A, B, and C are the parameters of the Cauchy model, and λ is the wavelength.

[0053] In a specific embodiment, the multispectral enhanced ellipsometer includes a high-temperature heating module, an ellipsometric spectroscopy module, and a partially shared optical path white light interference module and Raman spectroscopy module. The white light interference module and the Raman spectroscopy module share the same objective lens and beam splitter in their optical path structures. The white light interference module and the Raman spectroscopy module measure the white light interference spectrum and Raman spectrum at the same measurement position on the surface of the epitaxial thin film, respectively. The light spot formed on the surface of the epitaxial thin film by the light emitted from the ellipsometric spectroscopy module coincides with the light spot formed on the surface of the epitaxial thin film by the light emitted from the white light interference module and the Raman spectroscopy module. The ellipsometric spectrum at the same measurement position on the surface of the epitaxial thin film is measured in the same position by the ellipsometric spectroscopy module.

[0054] The following specific embodiments illustrate the specific structure of the multispectral enhanced ellipsometer used in the characterization method of the influence of wide bandgap semiconductor wafer substrates and high-temperature properties on epitaxial thin films in this application.

[0055] Example 1

[0056] In Embodiment 1 of this application, the white light interferometer module includes a white light source 21, a collimating lens 22, a focusing lens group 23, an imaging tube 26, a white light detector 27, a first beam splitter 31, a second beam splitter 32, a third beam splitter 37, a first objective lens 25, and a second objective lens 28; the second beam splitter 32 is disposed between the first beam splitter 31 and the second objective lens 28, and the third beam splitter 37 is disposed between the first beam splitter 31 and the first objective lens 25; the incident light path of the first objective lens 25 is perpendicular to the surface of the epitaxial film, and the incident light path of the second objective lens 28 is parallel to the surface of the epitaxial film; a reference plane 29 is provided at the focal plane of the second objective lens 28; the first objective lens 25 is controlled by a second driving unit to move along the path perpendicular to the surface of the epitaxial film. The vertical movement of the film surface is controlled by the first driving unit 24 to move the second objective lens 28 in a direction parallel to the surface of the epitaxial film. The light emitted by the white light source 21 is converted into a parallel beam after passing through the collimating lens 22. After passing through the focusing lens group 23 and the first beam splitter 31 in sequence, the parallel beam is split into two coherent light waves, namely the reference beam and the measurement beam. The reference beam and the measurement beam illuminate the surface of the epitaxial film and then enter the second objective lens 28 and the first objective lens 25, respectively. The two coherent light waves return along the original path and pass through the second beam splitter 32 and the third beam splitter 37, respectively. After superimposing interference at the first beam splitter 31, they pass through the imaging tube 26 and enter the white light detector 27 to obtain the white light interference spectrum.

[0057] In a specific embodiment, the Raman spectroscopy module includes a laser source 36, a dichroic mirror 33, a second beam splitter 32, a confocal lens group 34, a first objective lens 25, and a Raman detector 35. The dichroic mirror 33 is positioned between the second beam splitter 32 and the confocal lens group 34. Monochromatic light emitted from the laser source 36 is reflected sequentially by the dichroic mirror 33 and the second beam splitter 32 before entering the first objective lens 25. The first objective lens 25 focuses the monochromatic light and projects it onto the surface of the epitaxial thin film, then collects the Raman scattered light and returns it to the second beam splitter 32. The Raman scattered light is reflected by the second beam splitter 32 and passes through the dichroic mirror 33 before entering the confocal lens group 34. The confocal lens group 34 filters out stray light from the Raman scattered light and transmits the required Raman spectral information to the Raman detector 35 to obtain the Raman spectrum. The white light interferometer module and the Raman spectroscopy module share the same first objective lens 25 and second beam splitter 32 in their optical path structures.

[0058] In a specific embodiment, the ellipsometric spectroscopy module includes a broadband light source 11, a polarizer 12, a first compensator 13, a second compensator 15, an analyzer 16, and an ellipsometric detector 17. The light emitted by the broadband light source 11 is transmitted to the polarizer 12. After passing through the polarizer 12 and the first compensator 13, the light emitted by the broadband light source 11 is converted into polarized light and obliquely incident on the surface of the epitaxial film. Then, it passes through the second compensator 15 and the analyzer 16 in sequence to collect the polarized light reflected from the surface of the epitaxial film and transmit it to the ellipsometric detector 17 to obtain the ellipsometric spectrum of the epitaxial film.

[0059] In a specific embodiment, the high-temperature heating module includes a sample stage, a protective cavity, a first observation window, a second observation window, and a third observation window. The temperature control range is 300–1200 K. The sample stage is installed inside the protective cavity, which can be evacuated or filled with inert gas. The first and third observation windows are respectively installed on both sides of the protective cavity, allowing the incident and reflected light from the ellipsometric spectroscopy module to pass through. The second observation window is installed on the surface of the protective cavity and is perpendicular to the sample stage. A six-degree-of-freedom motion displacement stage is provided below the sample stage for adjusting the measurement position or leveling the sample stage according to the white light interference spectrum. A first rotating stage is provided below the polarizer 12 for adjusting the angle between the polarizer 12 and the sample stage. A second rotating stage is provided below the analyzer 16 for adjusting the angle between the analyzer 16 and the sample stage.

[0060] Specifically, such as Figure 2As shown, the multispectral enhanced ellipsometer mentioned in the embodiments of this application uses an ellipsometric spectroscopy module as its core, and integrates a Raman spectroscopy module and a white light interferometer module in situ. The white light interferometer module and the Raman spectroscopy module can share a common optical path to detect the white light interferometer spectrum and Raman spectrum at the same measurement position on the surface of the epitaxial thin film. The spectral range covers the ultraviolet, visible, and near-infrared. Further, through surface three-dimensional morphology reconstruction and Raman spectroscopy analysis, information such as the initial value of surface roughness and material composition can be obtained. Specifically, in-situ measurement can be achieved by using the same first objective lens 25. The first objective lens 25 simultaneously collects the detection beam emitted by the white light interferometer module and the Raman scattered light containing epitaxial thin film information emitted by the Raman spectroscopy module. Simultaneously, the ellipsometric spectroscopy module can be adjusted so that the light emitted by the ellipsometric spectroscopy module and the light emitted by the first objective lens 25 are at the same measurement position on the surface of the epitaxial film. This allows the white light interference spectrum, Raman spectrum, and ellipsometric spectrum at the same measurement position to be obtained, avoiding inconsistencies in the information carried by different measurement positions, which could lead to analytical errors. An optical model and an oscillator model can be established, and the ellipsometric spectral data can be used to calculate the ellipsometric parameters, Mueller matrix, reflection coefficient, and transmission coefficient, etc., and further fitting analysis can be performed to obtain the surface physical parameters of the epitaxial film.

[0061] Furthermore, in the embodiments of this application, a high-temperature heating module is used to heat the wide bandgap semiconductor wafer substrate 14 and the epitaxial film on it. The temperature adjustment range is 300 to 1200K, and temperature sampling can be performed at intervals of 10K or 100K to meet the device optimization design requirements.

[0062] Therefore, the aforementioned multispectral enhanced ellipsometer was used to detect the wide-bandgap semiconductor wafer substrate 14 and the epitaxial thin film at different temperatures, obtaining spectral data that varied with temperature. Based on the material properties of different epitaxial thin films and the surface physical parameters extracted from in-situ measured Raman and white light interference spectra, optical and oscillator models were constructed. These models were then fitted with the ellipsometric spectra to obtain parameters such as surface morphology, material composition, defects, thickness, optical constants, and stress of the epitaxial thin film at different temperatures. This invention can characterize the wide-bandgap semiconductor wafer substrate 14 and the influence of high-temperature performance on the epitaxial thin film. It provides a unified measurement benchmark, high characterization accuracy, and can simultaneously obtain the surface morphology, thickness, material composition, optical properties, and mechanical properties of the epitaxial thin film at different temperatures. It also constructs curves showing the variation of the substrate's morphology and performance parameters at high temperatures, providing feedback for device optimization design.

[0063] Example 2

[0064] The difference between Embodiment 2 and Embodiment 1 of this application lies in the optical path structure of the white light interference module and the Raman spectroscopy module. The white light interference module in Embodiment 2 includes a white light source 21, a collimating lens 22, a focusing lens group 23, an imaging tube 26, a white light detector 27, a first beam splitter 31, a second beam splitter 32, a first objective lens 25, and a second objective lens 28. The incident light path of the first objective lens 25 is perpendicular to the surface of the epitaxial film, and the incident light path of the second objective lens 28 is parallel to the surface of the epitaxial film. A reference plane 29 is provided at the focal plane of the second objective lens 28. The first beam splitter 31 is positioned between the second objective lens 28 and the second beam splitter 32, and the second beam splitter 32 is positioned between the first beam splitter 31 and the imaging tube 26. The first objective lens 25 is moved perpendicular to the surface of the epitaxial film by the second driving unit, and the second objective lens 28 is moved parallel to the surface of the epitaxial film by the first driving unit. The light emitted by the white light source 21 is converted into a parallel beam after passing through the collimating lens 22. After passing through the focusing lens group 23 and the first beam splitter 31 in sequence, the parallel beam is split into two coherent light waves, namely the reference beam and the measurement beam. The reference beam and the measurement beam illuminate the surface of the epitaxial film and then enter the second objective lens 28 and the first objective lens 25, respectively. The two coherent light waves return along the original path and are superimposed and interfered at the first beam splitter 31. Then they pass through the second beam splitter 32 and the imaging tube 26 and enter the white light detector 29 to obtain the white light interference spectrum.

[0065] In a specific embodiment, the Raman spectroscopy module includes a laser source 36, a first beam splitter 31, a second beam splitter 32, a dichroic mirror 33, a confocal lens group 34, a first objective lens 25, and a Raman detector 35. The second beam splitter 32 is positioned between the first beam splitter 31 and the first objective lens 25. Monochromatic light emitted from the laser source 36 is reflected sequentially by the dichroic mirror 33 and the second beam splitter 32, then passes through the first beam splitter 31 and enters the first objective lens 25. The first objective lens 25 focuses the monochromatic light and projects it onto the surface of the epitaxial thin film, collects the Raman scattered light, and returns it to the second beam splitter 32. The Raman scattered light is reflected by the second beam splitter 32, passes through the dichroic mirror 33, and enters the confocal lens group 34. The confocal lens group 34 filters out stray light from the Raman scattered light and transmits the required Raman spectral information to the Raman detector 35 to obtain the Raman spectrum. The optical path structures of the white light interferometer module and the Raman spectroscopy module share the same first objective lens 25, first beam splitter 31, and second beam splitter 32. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-mentioned technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-mentioned technical features or their equivalent features without departing from the above-mentioned inventive concept. For example, technical solutions formed by substituting the above-mentioned features with technical features disclosed in this application (but not limited to) that have similar functions.

Claims

1. A method for characterizing the influence of wide bandgap semiconductor wafer substrates and high-temperature properties on epitaxial thin films, characterized in that, Includes the following steps: S1, prepare wide bandgap semiconductor wafer substrates of different qualities, and grow epitaxial thin films on wide bandgap semiconductor wafer substrates of different qualities respectively; S2, at one of the temperatures, Raman spectrum, white light interference spectrum and ellipsometric spectrum are measured at the same location on an epitaxial thin film on one of the wide bandgap semiconductor wafer substrates using a multispectral enhanced ellipsometer; S3. Based on the Raman spectrum and white light interference spectrum, extract the initial values ​​of the surface physical parameters of the epitaxial thin film on one of the wide bandgap semiconductor wafer substrates at the corresponding temperature. The surface physical parameters include material composition, thickness, optical constants, stress, surface morphology and surface micro-defects. S4. Construct a corresponding optical model based on the type of epitaxial thin film and the initial values ​​of surface physical parameters on one of the wide bandgap semiconductor wafer substrates. Determine the material properties of the epitaxial thin film based on its material composition. Select an oscillator model based on the material properties and / or temperature of the epitaxial thin film. Use the optical model and the oscillator model in conjunction with the ellipsometric spectrum to perform regression analysis and obtain the optical constants, thickness and stress of the epitaxial thin film. S5, heat one of the wide bandgap semiconductor wafer substrates and the epitaxial film on it to another preset temperature and hold it, repeat steps S2-S4 to obtain the curve of the surface physical parameters of the epitaxial film grown on one of the wide bandgap semiconductor wafer substrates as a function of temperature; S6. Repeat steps S2-S5 for wide bandgap semiconductor wafer substrates of different qualities and their epitaxial films to obtain curves showing the change of surface physical parameters of epitaxial films grown on wide bandgap semiconductor wafer substrates of different qualities with temperature.

2. The method for characterizing the influence of wide bandgap semiconductor wafer substrate and high-temperature performance on epitaxial thin films according to claim 1, characterized in that, The multispectral enhanced ellipsometer includes a high-temperature heating module, an ellipsometric spectroscopy module, and a partially shared optical path white light interference module and Raman spectroscopy module. The white light interference module and Raman spectroscopy module share the same objective lens and beam splitter in their optical path structures. The white light interference module and Raman spectroscopy module respectively measure the white light interference spectrum and Raman spectrum at the same measurement position on the surface of the epitaxial thin film. The light spot formed on the surface of the epitaxial thin film by the light emitted from the ellipsometric spectroscopy module coincides with the light spot formed on the surface of the epitaxial thin film by the light emitted from the white light interference module and Raman spectroscopy module. The ellipsometric spectrum at the same measurement position on the surface of the epitaxial thin film is then measured in tandem by the ellipsometric spectroscopy module.

3. The method for characterizing the influence of wide bandgap semiconductor wafer substrates and high-temperature properties on epitaxial thin films according to claim 2, characterized in that, The white light interferometer module includes a white light source, a collimating lens, a focusing lens group, an imaging tube, a white light detector, a first beam splitter, a second beam splitter, a third beam splitter, a first objective lens, and a second objective lens. The incident light path of the first objective lens is perpendicular to the surface of the epitaxial film, and the incident light path of the second objective lens is parallel to the surface of the epitaxial film. A reference plane is provided at the focal plane of the second objective lens. The second beam splitter is disposed between the first beam splitter and the second objective lens, and the third beam splitter is disposed between the first beam splitter and the first objective lens. The first objective lens is controlled by the second driving unit to move in a direction perpendicular to the surface of the epitaxial film, and the second objective lens is controlled by the first driving unit to move in a direction parallel to the surface of the epitaxial film. The light emitted by the white light source is converted into a parallel beam after passing through the collimating lens. After passing through the focusing lens group and the first beam splitter in sequence, the parallel beam is split into two coherent light waves, namely a reference beam and a measurement beam. The reference beam and the measurement beam illuminate the surface of the epitaxial film and then enter the second objective lens and the first objective lens, respectively. The two coherent light waves return along the original path and pass through the second beam splitter and the third beam splitter, respectively. After superimposing interference at the first beam splitter, they pass through the imaging tube and enter the white light detector to obtain the white light interference spectrum. The Raman spectroscopy module includes a laser source, a second beam splitter, a dichroic mirror, a confocal lens group, a first objective lens, and a Raman detector. The dichroic mirror is positioned between the second beam splitter and the confocal lens group. Monochromatic light emitted from the laser source is reflected sequentially by the dichroic mirror and the second beam splitter before entering the first objective lens. The first objective lens focuses the monochromatic light and projects it onto the surface of the epitaxial thin film, then collects the Raman scattered light and returns it to the second beam splitter. The Raman scattered light is reflected by the second beam splitter and passes through the dichroic mirror before entering the confocal lens group. The confocal lens group filters out stray light from the Raman scattered light and transmits the required Raman spectral information to the Raman detector to obtain the Raman spectrum.

4. The method for characterizing the influence of wide bandgap semiconductor wafer substrate and high-temperature performance on epitaxial thin films according to claim 3, characterized in that, The white light interferometry module includes a white light source, a collimating lens, a focusing lens group, an imaging tube, a white light detector, a first beam splitter, a second beam splitter, a first objective lens, and a second objective lens. The incident light path of the first objective lens is perpendicular to the surface of the epitaxial film, and the incident light path of the second objective lens is parallel to the surface of the epitaxial film. A reference plane is provided at the focal plane of the second objective lens. The first beam splitter is positioned between the second objective lens and the second beam splitter, and the second beam splitter is positioned between the first beam splitter and the imaging tube. A second driving unit controls the movement of the first objective lens in a direction perpendicular to the surface of the epitaxial film, and a first driving unit controls the movement of the second objective lens in a direction parallel to the surface of the epitaxial film. The light emitted by the white light source is converted into a parallel beam after passing through the collimating lens. After passing through the focusing lens group and the first beam splitter in sequence, the parallel beam is split into two coherent light waves, namely a reference beam and a measurement beam. The reference beam and the measurement beam illuminate the epitaxial film. After passing through the surface, the two coherent light waves enter the second objective lens and the first objective lens respectively. After returning along the original path, they superimpose and interfere at the first beam splitter, and then pass through the second beam splitter and the imaging tube to enter the white light detector to obtain the white light interference spectrum. The Raman spectroscopy module includes a laser source, a first beam splitter, a second beam splitter, a dichroic mirror, a confocal lens group, a first objective lens, and a Raman detector. The second beam splitter is located between the first beam splitter and the first objective lens. The monochromatic light emitted by the laser source is reflected sequentially by the dichroic mirror and the second beam splitter, and then passes through the first beam splitter before entering the first objective lens. The first objective lens focuses the monochromatic light and projects it onto the surface of the epitaxial film, collects the Raman scattered light, and returns it to the second beam splitter. The Raman scattered light is reflected by the second beam splitter, passes through the dichroic mirror, and enters the confocal lens group. The confocal lens group filters out stray light in the Raman scattered light and transmits the required Raman spectral information to the Raman detector to obtain the Raman spectrum.

5. The method for characterizing the influence of wide bandgap semiconductor wafer substrate and high-temperature performance on epitaxial thin films according to claim 2, characterized in that, The ellipsometric spectral module includes a broadband light source, a polarizer, a first compensator, a second compensator, an analyzer, and an ellipsometric detector. The light emitted by the broadband light source is transmitted to the polarizer, which converts the light emitted by the broadband light source into polarized light and obliquely incident on the surface of the epitaxial thin film. The light then passes through the second compensator and the analyzer in sequence to collect the polarized light reflected from the surface of the epitaxial thin film and transmit it to the ellipsometric detector to obtain the ellipsometric spectrum of the epitaxial thin film.

6. The method for characterizing the influence of wide bandgap semiconductor wafer substrate and high-temperature performance on epitaxial thin films according to claim 5, characterized in that, The high-temperature heating module includes a sample stage, a protective cavity, a first observation window, a second observation window, and a third observation window. The temperature control range is 300–1200 K. The sample stage is installed inside the protective cavity, which can be evacuated or filled with inert gas. The first and third observation windows are respectively installed on both sides of the protective cavity, allowing the incident and reflected light from the ellipsometric spectroscopy module to pass through. The second observation window is installed on the surface of the protective cavity and perpendicular to the sample stage. A six-degree-of-freedom motion displacement stage is provided below the sample stage for adjusting the measurement position or leveling the sample stage according to the white light interference spectrum. A first rotating stage is provided below the polarizer for adjusting the angle between the polarizer and the sample stage. A second rotating stage is provided below the analyzer for adjusting the angle between the analyzer and the sample stage.

7. The method for characterizing the influence of wide bandgap semiconductor wafer substrate and high-temperature performance on epitaxial thin films according to claim 1, characterized in that, The oscillator model includes the empirical Cauchy model, Gaussian model, Drude model, or Lorentz model. The empirical Cauchy model is used in the transparent region of the epitaxial film, while the Lorentz model, Drude model, and Gaussian model or a combination of several of these oscillator models is used in the absorption spectral region of the epitaxial film.

8. The method for characterizing the influence of wide bandgap semiconductor wafer substrate and high-temperature performance on epitaxial thin films according to claim 1, characterized in that, The regression evaluation function used in the regression analysis process of step S4 is the mean squared error (MSE), and its calculation formula is as follows: Where mod and exp represent the fitted value and the measured value, respectively, δ is the measurement error, and N is the two ellipsoidal parameters measured simultaneously by the multispectral enhanced ellipsometer. The total logarithm of Δ, where M is the logarithm of the selected fitting parameters, i = 1, 2, ..., N.

9. The method for characterizing the influence of wide bandgap semiconductor wafer substrate and high-temperature performance on epitaxial thin films according to claim 1, characterized in that, The wide bandgap semiconductor wafer substrates of different qualities include wide bandgap semiconductor wafer substrates with different surface roughness, surface defects or subsurface defects.

10. The method for characterizing the influence of wide bandgap semiconductor wafer substrate and high-temperature performance on epitaxial thin films according to claim 1, characterized in that, The wide bandgap semiconductor wafer substrate is a substrate with a bandgap width greater than 2.3 eV, including silicon carbide substrates, diamond substrates, or gallium nitride substrates.

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