Method and system for detecting residual stress

Abstract

To provide a residual stress detection method and a residual stress detection system for non-contact and non-destructive detection of residual stress.SOLUTION: A residual stress detection method includes the steps of: generating a terahertz emission electromagnetic wave and emitting the terahertz emission electromagnetic wave to a test piece via a first polarizer; detecting, via a second polarizer, a plurality of terahertz reception electromagnetic waves that are reflected, transmitted, or scattered after the terahertz emission electromagnetic wave is incident on the test piece; measuring a plurality of characteristic signals based on the terahertz emission electromagnetic wave and the plurality of terahertz reception electromagnetic waves; analyzing the plurality of characteristic signals to determine a plurality of characteristics of the test piece; and determining residual stress of the test piece based on the plurality of characteristics.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to a residual stress detection method and a residual stress detection system, and more specifically, to a residual stress detection method and a residual stress detection system that enable non-contact and non-destructive detection of residual stress.

Background Art

[0002] Residual stress refers to the stress remaining in a solid material even after the main stress source has been removed. There are several reasons or mechanisms leading to the generation of residual stress, including inelastic (plastic or mechanical) deformation, temperature gradients (due to temperature cycles), or changes in structure (such as phase transitions), which result in non-uniform deformation within the material. The presence of residual stress can affect the strength and other mechanical properties of components and may lead to defects such as deformation and cracks during their application. Ultimately, these defects can affect the condition, accuracy, and service life of the components. For example, in the manufacturing process of wafers, various steps such as crystal growth, cutting, grinding, polishing, and doping can introduce surface or internal residual stress into the wafers, which may even cause the wafers to warp or break during subsequent processing.

[0003] Therefore, in order to ensure the quality of components, it is essential to detect and measure residual stress in a timely manner during the manufacturing process. Generally, the magnitude and direction of residual stress are calculated based on strain or equivalent displacement. Current measurement techniques are classified into two categories: destructive methods and non-destructive methods. These methods can be further classified as surface residual stress and internal residual stress based on the measurement depth.

[0004] In conventional techniques, one common destructive method for measuring surface residual stress is drilling. This approach involves drilling a hole in the surface of the specimen and determining (determining) the residual stress based on the principle of elasticity using strain or displacement measurements. However, it is clear that destructive residual stress measurement methods have limited applicability due to the physical damage to the specimen. In practice, measuring, analyzing, and predicting the internal residual stress state of a material is more important than surface residual stress. Unfortunately, it is often difficult to directly observe or measure internal residual stress. Non-destructive stress measurement techniques typically include methods such as Raman spectroscopy, ultrasonic testing, and X-ray diffraction (XRD). However, these techniques can only measure residual stress on the surface or shallow parts of the specimen and cannot evaluate the residual stress distribution deep within the material or specimen.

[0005] Therefore, the development of effective non-destructive methods for detecting residual stress remains a key objective in the industry. [Overview of the project] [Problems that the invention aims to solve]

[0006] Therefore, the present invention provides a residual stress detection method and a residual stress detection system that enable non-destructive detection of residual stress. [Means for solving the problem]

[0007] One embodiment of the present invention provides a residual stress detection method comprising the steps of: generating terahertz emitted electromagnetic waves and emitting the terahertz emitted electromagnetic waves onto a test piece via a first polarizer; detecting a plurality of terahertz received electromagnetic waves that have been reflected, transmitted, or scattered after the terahertz emitted electromagnetic waves have been incident on the test piece via a second polarizer; measuring a plurality of characteristic signals based on the terahertz emitted electromagnetic waves and the plurality of terahertz received electromagnetic waves; analyzing the plurality of characteristic signals to determine a plurality of characteristics of the test piece; and determining the residual stress of the test piece based on the plurality of characteristics.

[0008] One embodiment of the present invention provides a residual stress detection system comprising: a first polarizer positioned in front of the test piece; a second polarizer positioned behind the test piece; a terahertz electromagnetic wave generator positioned in front of the first polarizer and configured to generate terahertz-emitting electromagnetic waves and emit the terahertz-emitting electromagnetic waves onto the test piece via the first polarizer; a terahertz electromagnetic wave receiver positioned behind the second polarizer and configured to detect a plurality of terahertz-received electromagnetic waves reflected, transmitted, or scattered after the terahertz-emitting electromagnetic waves have been incident on the test piece, via the second polarizer; and a detection device coupled to the terahertz electromagnetic wave generator and the terahertz electromagnetic wave receiver, configured to measure a plurality of characteristic signals based on the terahertz-emitting electromagnetic waves and the plurality of terahertz-received electromagnetic waves, analyze the plurality of characteristic signals to determine a plurality of characteristics of the test piece, and determine the residual stress of the test piece based on the plurality of characteristics.

[0009] These and other objects of the present invention will become undoubtedly apparent to those skilled in the art after reading the following detailed description of preferred embodiments shown in various figures and drawings. [Brief explanation of the drawing]

[0010] [Figure 1] This shows a functional block diagram of a residual stress detection system according to one embodiment of the present invention. [Figure 2]This is a schematic diagram of the time-domain and frequency-domain optical spectra detected by terahertz-emitting electromagnetic waves. [Figure 3] This is a schematic diagram of the time-domain and frequency-domain optical spectra detected by terahertz-emitting electromagnetic waves. [Figure 4] A schematic diagram of a residual stress detection system according to an embodiment of the present invention is shown. [Figure 5] A schematic diagram of a residual stress detection system according to an embodiment of the present invention is shown. [Figure 6A] Figure 5 shows the C-scan detection of the wafer using the residual stress detection system shown. [Figure 6B] Figure 5 shows the C-scan detection of the wafer using the residual stress detection system shown. [Figure 7] Figure 5 shows B-scan detection of a wafer using the residual stress detection system shown. [Figure 8A] This is a schematic diagram illustrating the detection of the electric field and refractive index of a test specimen according to an embodiment of the present invention. [Figure 8B] This is a schematic diagram illustrating the detection of the electric field and refractive index of a test specimen according to an embodiment of the present invention. [Figure 9] This is a schematic diagram of phase detection of a test specimen according to one embodiment of the present invention. [Figure 10] This is a flowchart of the residual stress detection process according to one embodiment of the present invention. [Modes for carrying out the invention]

[0011] Certain terms are used throughout the specification and the claims below to refer to specific components. As those skilled in the art will understand, hardware manufacturers may refer to components by different names. This document is not intended to distinguish between components that have different names but the same function. In the specification and claims below, the terms “include” and “comprise” are used in open-ended form and should be interpreted as “including, but not limited to…”. The term “combined” is intended to mean indirect or direct electrical connection. Thus, when one device is combined with another, the connection may be via a direct electrical connection or via an indirect electrical connection through other devices and connections.

[0012] In particular, to effectively detect residual stress within a material, the present invention utilizes terahertz electromagnetic waves for non-contact and non-destructive testing. Terahertz electromagnetic waves are 10 11 Hz~10 13 It operates in a frequency range of Hz (0.1 THz to 10 THz), thereby enabling the transmission of non-conductive materials and the measurement of highly water-containing substances. The advantages of terahertz testing include its ability to penetrate structures within various materials and sheet materials. It can evaluate optical coefficients, electrical properties, and layer thickness, and detect structural defects. Terahertz testing is also applicable to technical inspections during the manufacturing process, as well as inspections of semi-finished or finished products. When using terahertz electromagnetic waves for material testing, infrared electromagnetic waves (10 13 Hz~10 15 Lower frequencies (compared to the Hz range) ensure minimal photon energy, preventing damage to molecular structure and preserving material integrity. This is suitable for measuring polymer materials and crystalline structures without exacerbating existing damage or defects.

[0013] For details, please refer to Figure 1. Figure 1 shows a functional block diagram of a residual stress detection system 1 according to one embodiment of the present invention. The residual stress detection system 1 includes a terahertz electromagnetic wave generator 10, a terahertz electromagnetic wave receiver 12, a detection device 14, a first polarizer 16, and a second polarizer 18. The residual stress detection system 1 is designed to detect residual stress in a test specimen TS. The terahertz electromagnetic wave generator 10 generates terahertz emitted electromagnetic waves and emits them toward the test specimen TS via the first polarizer 16. The terahertz electromagnetic wave receiver 12 detects a plurality of terahertz received electromagnetic waves that have been reflected, transmitted, or scattered after the terahertz emitted electromagnetic waves have entered the test specimen TS, via the second polarizer 18. The detection device 14 is coupled to a terahertz electromagnetic wave generator 10 and a terahertz electromagnetic wave receiver 12, and is configured to determine the magnitude and distribution of residual stress by measuring multiple characteristic signals based on terahertz emitted electromagnetic waves and terahertz received electromagnetic waves, and by analyzing the three characteristic signals to determine multiple characteristics of the test specimen TS.

[0014] Specifically, the residual stress detection system 1 measures the optical activity of the test specimen TS by performing polarization measurement techniques using a first polarizer 16 and a second polarizer 18. The first polarizer 16 acts as a polarizer, converting the terahertz emitted electromagnetic waves from the terahertz electromagnetic wave generator 10 into linearly polarized or elliptically polarized electromagnetic waves. The second polarizer 18 functions as an analyzer, detecting the polarization state (linear or elliptic) of the received terahertz electromagnetic waves. In practice, polarizers can also be used as analyzers. Except for being placed in different positions to achieve different purposes, polarizers and analyzers are substantially the same and completely interchangeable. According to Malus's law, the transmitted irradiance can be calculated using the angle between the transmission axis of the polarizer and the transmission axis of the analyzer. Therefore, any polarization effect (such as birefringence) can be detected by placing the test specimen TS between two orthogonal polarizers and measuring the change in signal as the terahertz emitted electromagnetic waves pass through the test specimen TS along its optical axis (with a phase difference of 90 degrees). Birefringence refers to the optical property in which light passing through a material receives two different refractive indices in different directions. One light beam is polarized perpendicular to the optical axis (receiving the refractive index of the ordinary ray), and the other light beam is polarized parallel to the optical axis (receiving the refractive index of the extraordinary ray). If residual stress is present in the test specimen TS, the residual stress alters the material properties in a specific region, resulting in a birefringence effect when polarized electromagnetic waves pass through. By detecting these birefringence phenomena, embodiments of the present invention can determine the magnitude and location of the residual stress.

[0015] Furthermore, the relationship between the change in refractive index and the change in stress, measured under different polarizations of terahertz electromagnetic waves, can be expressed as follows. Δn = S·Δσ (Equation 1) Δn represents the change in refractive index, S represents the photoelastic coefficient of the material, and Δσ corresponds to the change in stress. It can be inferred that the photoelastic coefficient of the material can be determined by measurement and the change in stress can be obtained by evaluating the change in refractive index. In one embodiment, when direct refractive index measurement is not feasible, the change in refractive index may be determined based on the phase change induced by the material stress. This relationship is expressed as follows. Δδ=(δ1 - δ2)=(2πfd)·Δn / c (Equation 2) Δδ represents the change in phase, f represents the frequency, d represents the thickness of the material, and c corresponds to the speed of light in a vacuum.

[0016] Therefore, from the above analysis, it can be inferred that information regarding the change in stress (Equation 1) can be obtained by detecting the change in the photoelastic coefficient of the material and the refractive index of the test piece TS. When direct measurement of the change in refractive index is not feasible, the change in refractive index may be determined based on the change in phase and the thickness of the material (Equation 2). In this scenario, when the test piece TS is placed within the residual stress detection system 1, the position or angle of the first polarizer 16 and the second polarizer 18 can be adjusted (e.g., by rotation) to change the polarization of the electromagnetic wave with respect to the optical axis, thereby enabling the terahertz emission electromagnetic wave to pass through the test piece TS along its optical axis and detecting the terahertz reception electromagnetic wave at an angle of 90 degrees with respect to the optical axis. Therefore, the change in the electric field strength and the electric field phase can be detected to determine the magnitude and distribution of the residual stress within the test piece TS.

[0017] In detail, the detection device 14 can compare the signal obtained from the terahertz emitted electromagnetic wave detecting air with the signal obtained from the terahertz emitted electromagnetic wave detecting the test specimen TS, and measure the characteristic signal by analyzing both the time-domain and frequency-domain optical spectra. For example, see Figures 2 and 3. Figures 2 and 3 are schematic diagrams of the time-domain and frequency-domain optical spectra detected by the terahertz emitted electromagnetic wave. In Figure 2, the solid line represents the field-pair optical delay when the terahertz emitted electromagnetic wave detects air (without test specimen TS) in the time-domain optical spectrum, and the dashed line represents the field-pair optical delay when the terahertz emitted electromagnetic wave detects the test specimen TS in the time-domain optical spectrum. In Figure 3, the solid line represents the field-pair frequency when the terahertz emitted electromagnetic wave detects air (without test specimen TS) in the frequency-domain optical spectrum, and the dashed line represents the field-pair frequency when the terahertz emitted electromagnetic wave detects the test specimen TS in the frequency-domain optical spectrum. By analyzing the time-domain and frequency-domain optical spectra, the detection device 14 can measure characteristic signals to determine coefficients or parameters such as the thickness of the test specimen TS, interface shape, optical coefficients, and electrical coefficients. It can also analyze residual stress and identify defects caused by residual stress, or provide criteria for determining defects. Defects may include dislocations, deformations, changes in molecular chain arrangement, or changes in impurity ratios. Specifically, the detection device 14 measures the transient electric field of each terahertz received electromagnetic wave in the time domain to obtain electric field strength, phase, and frequency information of the transient electric field, and measures the spectral electric field between the terahertz received electromagnetic waves in the frequency domain to obtain electric field amplitude and phase information of the spectral electric field. In other words, the characteristic signals measured by the detection device 14 may include the strength, phase, and frequency of the transient electric field of each terahertz received electromagnetic wave in the time domain, and the amplitude and phase of the spectral electric field in the frequency domain.Since the characteristic signals (intensity and phase of the transient electric field, amplitude and phase of the spectral electric field) provide sensitivity to the material properties, by applying a transformation (e.g., Fourier transform), the detection device 14 can directly measure the dielectric constant of the material and calculate its optical coefficients (such as photoelastic coefficient, absorption rate, refractive index, reflectivity, and transmittance), electrical coefficients (such as phase change, conductivity, resistivity, doping concentration, dielectric constant, and charge carrier mobility), and structural properties. Further, the detection device 14 can measure the respective flight times of the terahertz received electromagnetic waves and analyze the flight times to determine the thickness and interface shape of the test piece TS.

[0018] Therefore, by comparing the signal of the terahertz emitted electromagnetic wave for detecting air with the signal of the terahertz emitted electromagnetic wave for detecting the test piece TS, the detection device 14 can measure the characteristic signal regarding the test piece TS to determine a plurality of characteristics of the test piece TS. The characteristic signal may include the electric field strength, electric field phase, and electric field frequency of the time-domain electric field of each terahertz received electromagnetic wave, and / or the electric field amplitude and electric field phase of the spectral electric field between the terahertz received electromagnetic waves. The plurality of characteristics may include the thickness of the test piece TS, interface shape, optical coefficients (such as photoelastic coefficient, absorption rate, refractive index, reflectivity, and transmittance), and electrical coefficients (phase change, conductivity, resistivity, dopant concentration, dielectric constant, and charge carrier mobility). Further, the detection device 14 can further determine whether the test piece TS has residual stress, the magnitude and distribution of the residual stress, and whether any defects are caused by the residual stress, or provide a basis for defect evaluation.

[0019] In Figure 1, it should be noted that the residual stress detection system 1 is represented by a functional block as an essential component of the embodiment of the present invention. However, when implementing the residual stress detection system 1, those skilled in the art can design or select an appropriate architecture based on the actual requirements. For example, Figures 4 and 5 are schematic diagrams of residual stress detection systems 4 and 5 according to embodiments of the present invention, respectively. Residual stress detection systems 4 and 5 are derived from the residual stress detection system 1 and use a transmission and reflection-based terahertz electromagnetic wave detection architecture. For simplicity, Figures 4 and 5 omit the specific location of the detection device 14, which can be inferred by those skilled in the art from Figure 1. Specifically, the residual stress detection system 4 generates terahertz emitted electromagnetic waves I using a terahertz electromagnetic wave generator 40, then incidents them on the test specimen TS via a first polarizer 44, and uses a terahertz electromagnetic wave receiver 42 to detect the terahertz received electromagnetic waves R transmitted through the test specimen TS via a second polarizer 46. The second polarizer 46 is oriented 90 degrees from the optical axis to detect the terahertz received electromagnetic wave R transmitted through the test specimen TS. The first polarizer 44 and the second polarizer 46 may be a combination of linearly polarized or elliptically polarized elements, and both the first polarizer 44 and the second polarizer 46 may be adjusted in position or angle (e.g., by rotation) so that the terahertz emitted electromagnetic wave I passes through the test specimen TS along its optical axis, while being oriented 90 degrees from the optical axis so that the terahertz electromagnetic wave receiver 42 detects the terahertz received electromagnetic wave R. Furthermore, the relative position or angle between the first polarizer 44 and the second polarizer 46 may preferably be adjusted (e.g., by rotation) to ensure the maximum change in the characteristic signal, particularly the electric field strength and electric field phase in the characteristic signal.

[0020] On the other hand, the residual stress detection system 5 uses a reflection-based detection architecture, and the terahertz electromagnetic wave generator and receiver 50 integrate both emission and reception functions. In other words, the terahertz electromagnetic wave generator and receiver 50 generates terahertz emitted electromagnetic waves I directed towards the test specimen TS via a first polarizer 52, and after the terahertz emitted electromagnetic waves I have entered the test specimen TS, detects the terahertz received electromagnetic waves R reflected by the test specimen TS via a second polarizer 54. The first polarizer 52 and the second polarizer 54 may be a combination of linearly polarized or elliptically polarized elements and can be adjusted in position or angle (e.g., by rotation) to ensure that the terahertz emitted electromagnetic waves I emitted by the terahertz electromagnetic wave generator and receiver 50 enter the test specimen TS along its optical axis, while the terahertz received electromagnetic waves R are detected at an angle of 90 degrees to the optical axis. Preferably, the relative positions or angles of the first polarizer 52 and the second polarizer 54 can be adjusted to maximize the characteristic signals, particularly the changes in electric field strength and electric field phase within these signals.

[0021] Furthermore, the operation of residual stress detection systems 4 and 5 can refer to the operation of residual stress detection system 1 described above. Specifically, the detection device (not shown in Figures 4 and 5) analyzes the time-domain and frequency-domain optical spectra of terahertz emitted electromagnetic waves I (which do not pass through the test specimen TS) and terahertz received electromagnetic waves R (which do pass through the test specimen TS) to measure multiple characteristic signals and determine coefficients or characteristics such as the thickness of the test specimen TS, interface shape, optical coefficient, and electrical coefficient. In addition, the detection device 14 can use equations 1 and 2 described above to evaluate residual stress, the magnitude and distribution of residual stress in the test specimen TS, and whether any defects were caused by residual stress, or to provide a basis for defect evaluation.

[0022] Furthermore, embodiments of the present invention are applicable to detecting various test specimens TS containing one or more of compounds, insulators, semiconductors, or metals. For example, if the test specimen TS is a wafer, the material may be selected from silicon (Si), silicon carbide (SiC), gallium arsenide (GaAs), gallium nitride (GaN), aluminum nitride (AlN), gallium oxide (Ga2O3), etc. Furthermore, the detection area in embodiments of the present invention may be a specific point, and single-point measurement will yield results similar to those shown in Figures 2 and 3. Alternatively, the detection area may be achieved by covering a specific area and scanning using a movable detector or sample stage. The detection process may include multiple steps, such as inspecting the front and then the sides. For example, Figures 6A and 6B show C-Scan detection of a wafer by the residual stress detection system 5. In this context, C-Scan represents a planar scan of the wafer. Figure 6A shows a surface image of the wafer, and Figure 6B shows a residual stress image detected by the residual stress detection system 5. Figure 6B clearly shows the presence of residual stress within the wafer. Therefore, further B-scan detection may be performed on the same wafer, resulting in the detection results shown in Figure 7. B-scan represents a cross-sectional scan, and Figure 7 provides insight into the distribution and magnitude of internal residual stress. Thus, by observing Figures 6A, 6B, and 7, a person skilled in the art can determine the presence of residual stress and its distribution and magnitude. In particular, Figure 7 clearly shows the presence of residual stress within the wafer, which cannot be detected using conventional non-destructive microscopy techniques. In other words, the detection results from the residual stress detection system 5 not only indicate the presence of residual stress but also enable the evaluation of internal residual stress. This information helps inspectors identify defective products and researchers understand the causes of defects.

[0023] Figures 6A, 6B, and 7 illustrate possible scenarios for residual stress detection in embodiments of the present invention. It should be noted that, before obtaining these results, information regarding changes in refractive index or phase must be derived based on Equations 1 and 2, which should be well known in the art. For example, Figures 8A and 8B show schematic diagrams of residual stress detection systems 1, 4, and 5 for detecting the electric field and refractive index of a test specimen TS. In Figure 8A, solid lines represent electric field measurements in the stress-free region, and dashed lines represent measurements in the region with residual stress. Similarly, Figure 8B shows refractive index measurements, with solid lines indicating the stress-free region and dashed lines indicating the region with residual stress. Furthermore, Figure 9 is a schematic diagram of phase detection of a test specimen TS using residual stress detection systems 1, 4, and 5. Therefore, based on the information from Figures 8A, 8B, and 9, those skilled in the art can evaluate the magnitude and distribution of residual stress according to Equations 1 and 2.

[0024] Furthermore, residual stress detection systems 1, 4, and 5 are embodiments of the present invention and can be modified accordingly by those skilled in the art. For example, residual stress detection systems 1, 4, and 5 utilize a terahertz electromagnetic wave detection architecture and may be appropriately integrated with other systems that also utilize terahertz electromagnetic waves. For example, the applicant has disclosed a composite structure detection method and system in U.S. Patent Application No. 18 / 813,045 and a semiconductor wafer inspection method and corresponding detection apparatus in Taiwan Patent No. I788105, which can be applied to the present invention with appropriate modifications.

[0025] The operation of the residual stress detection systems 1, 4, and 5 described above can be summarized as a residual stress detection process 100, as shown in Figure 10. The residual stress detection process 100 is used to detect residual stress and includes the following steps.

[0026] Step 102: Start

[0027] Step 104: Terahertz emitted electromagnetic waves are generated and incident on the test specimen via the first polarizer.

[0028] Step 106: After the terahertz emitted electromagnetic wave is incident on the test specimen, multiple terahertz received electromagnetic waves that have been reflected, transmitted, or scattered are detected via a second polarizer.

[0029] Step 108: Measure multiple characteristic signals based on terahertz emitted electromagnetic waves and multiple terahertz received electromagnetic waves.

[0030] Step 110: Analyze multiple characteristic signals to determine multiple characteristics of the test specimen.

[0031] Step 112: Determine the residual stress of the test specimen based on multiple properties.

[0032] Step 114: Finish.

[0033] For detailed information on the operation and deformation of the residual stress detection process 100, please refer to the description above, which will not be repeated below.

[0034] Conventional non-destructive stress measurement techniques can only measure residual stress on the surface or shallow parts of a test specimen, and cannot evaluate residual stress in the deeper parts of the specimen. In contrast, the present invention utilizes polarization measurement technology to measure multiple characteristic signals based on terahertz emitted electromagnetic waves and multiple terahertz received electromagnetic waves, and determines the magnitude and distribution of residual stress by analyzing these characteristic signals. Because terahertz electromagnetic waves have the ability to penetrate various materials and structures, they enable the detection of optical coefficients, electrical properties, layer thickness, and structural defects, and can be applied to different materials and structures, or used for process inspection, testing of semi-finished or finished products, enabling non-contact and non-destructive residual stress evaluation.

[0035] Those skilled in the art will readily see that many modifications and changes can be made to the apparatus and method while maintaining the teachings of the present invention. Accordingly, the above disclosure should be interpreted as being limited only by the boundaries and scope of the appended claims.

Claims

1. The steps include generating terahertz-emitting electromagnetic waves and emitting the terahertz-emitting electromagnetic waves onto a test piece via a first polarizer, The steps include detecting, via a second polarizer, a plurality of terahertz received electromagnetic waves that have been reflected, transmitted, or scattered after the terahertz emitted electromagnetic waves have been incident on the test piece, The steps include measuring the electric field strength, electric field phase, and electric field frequency of each of the multiple terahertz received electromagnetic waves in the time domain, and measuring the spectral electric field amplitude and spectral electric field phase between the multiple terahertz received electromagnetic waves in the frequency domain, thereby measuring multiple characteristic signals based on the terahertz emitted electromagnetic wave and the multiple terahertz received electromagnetic waves, The steps include analyzing multiple characteristic signals to determine multiple characteristics of the test specimen, A method for detecting residual stress, comprising the step of determining the residual stress of a test specimen based on a plurality of the aforementioned characteristics.

2. The frequency of the aforementioned terahertz emitted electromagnetic wave is 10 １１ Hz to 10 １３ The residual stress detection method according to claim 1, wherein the frequency is Hz.

3. The residual stress detection method according to claim 1, wherein the plurality of characteristics include at least one of the thickness of the test specimen, interface shape, optical coefficient, and electrical coefficient.

4. The residual stress detection method according to claim 3, wherein the electrical coefficient is at least one of phase change, conductivity, resistivity, doping concentration, dielectric constant, and charge carrier mobility, and the optical coefficient is at least one of photoelastic coefficient, absorptivity, refractive index, reflectance, and transmittance.

5. The residual stress detection method according to claim 4, wherein the step of determining the residual stress of the test specimen based on a plurality of the above characteristics includes the step of determining a change in the residual stress of the test specimen based on a change in the refractive index and the photoelastic coefficient.

6. The residual stress detection method according to claim 5, further comprising the step of determining the change in refractive index based on the change in phase and thickness of the test specimen.

7. The residual stress detection method according to claim 1, further comprising the step of determining at least one defect in the test specimen based on a plurality of the aforementioned characteristics.

8. The residual stress detection method according to claim 7, wherein at least one of the defects is at least one of dislocation, deformation, change in molecular chain arrangement, and change in impurity ratio.

9. The residual stress detection method according to claim 1, further comprising the step of adjusting the first polarizer and the second polarizer so that the terahertz emitted electromagnetic wave passes through the test piece along the optical axis and a plurality of the terahertz received electromagnetic waves are detected at an angle of 90 degrees from the optical axis.

10. The residual stress detection method according to claim 1, further comprising the step of adjusting the first polarizer and the second polarizer so as to have the greatest change in a plurality of characteristic signals.

11. The residual stress detection method according to claim 1, wherein the first polarizer and the second polarizer are a combination of linearly polarized or elliptically polarized light.

12. A first polarizer placed in front of the test specimen, A second polarizer positioned behind the aforementioned test specimen, A terahertz electromagnetic wave generator is positioned in front of the first polarizer and configured to generate terahertz-emitting electromagnetic waves and emit the terahertz-emitting electromagnetic waves onto a test piece via the first polarizer, A terahertz electromagnetic wave receiver is positioned after the second polarizer and configured to detect, via the second polarizer, a plurality of terahertz received electromagnetic waves that have been reflected, transmitted, or scattered after the terahertz emitted electromagnetic waves have been incident on the test piece, A residual stress detection system comprising: a detection device coupled to the terahertz electromagnetic wave generator and the terahertz electromagnetic wave receiver, configured to measure the electric field strength, electric field phase, and electric field frequency of each of the plurality of terahertz received electromagnetic waves in the time domain, and to measure the spectral electric field amplitude and spectral electric field phase between the plurality of terahertz received electromagnetic waves in the frequency domain, thereby measuring a plurality of characteristic signals based on the terahertz emitted electromagnetic wave and the plurality of terahertz received electromagnetic waves, analyzing the plurality of characteristic signals to determine a plurality of characteristics of the test piece, and determining the residual stress of the test piece based on the plurality of characteristics.

13. The frequency of the aforementioned terahertz emitted electromagnetic wave is 10 １１ Hz to 10 １３ The residual stress detection system according to claim 12, wherein the frequency is Hz.

14. The residual stress detection system according to claim 12, wherein the plurality of characteristics include at least one of the thickness of the test specimen, interface shape, optical coefficient, and electrical coefficient.

15. The residual stress detection system according to claim 14, wherein the electrical coefficient is at least one of phase change, conductivity, resistivity, doping concentration, dielectric constant, and charge carrier mobility, and the optical coefficient is at least one of photoelastic coefficient, absorptivity, refractive index, reflectance, and transmittance.

16. The residual stress detection system according to claim 15, wherein the step of determining the residual stress of the test specimen based on a plurality of the above characteristics includes the step of determining a change in the residual stress of the test specimen based on a change in the refractive index and the photoelastic coefficient.

17. The residual stress detection system according to claim 16, wherein the detection device is further configured to determine the change in refractive index based on the change in phase and thickness of the test piece.

18. The residual stress detection system according to claim 12, wherein the detection device is further configured to determine at least one defect in the test piece based on a plurality of the characteristics.

19. The residual stress detection system according to claim 18, wherein at least one of the defects is at least one of dislocation, deformation, change in molecular chain arrangement and change in impurity ratio.

20. The residual stress detection system according to claim 12, wherein the first polarizer and the second polarizer are adjustable to allow the terahertz emitted electromagnetic wave to pass through the test piece along the optical axis and to detect a plurality of the terahertz received electromagnetic waves at an angle of 90 degrees from the optical axis.

21. The residual stress detection system according to claim 12, wherein the first polarizer and the second polarizer are adjustable to have the greatest change in a plurality of characteristic signals.

22. The residual stress detection system according to claim 12, wherein the first polarizer and the second polarizer are a combination of linearly polarized or elliptically polarized light.

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