An optical non-destructive testing system and method for substrate residual stress

Abstract

The application discloses a kind of optical nondestructive testing system and method of substrate residual stress, system includes light source, modulation module, beam splitter, sample stage, demodulation module, image acquisition module;Light source, modulation module and beam splitter are sequentially arranged along straight line A, beam splitter, demodulation module and image acquisition module are sequentially arranged along straight line B, straight line A is perpendicular to straight line B, the line connecting sample stage and beam splitter is perpendicular to straight line A and straight line B simultaneously.When measuring, the laser emitted by light source reaches image acquisition module after passing through modulation module, beam splitter, material to be measured and demodulation module, is collected to form a series of interference images, and the direction and size of substrate residual stress are calculated by the relationship between light intensity signal, optical component parameter and equal inclination angle and phase difference.The application detects system by perpendicular incidence type reflected photoelastic optical path, improves the system error caused by small-angle incidence of existing reflected photoelastic system, and realizes high-precision detection of substrate residual stress.

Description

Technical Field

[0001] This invention relates to the field of optical inspection technology, and in particular to an optical non-destructive testing system and method for residual stress in a substrate. Background Technology

[0002] Currently, common methods for optical non-destructive testing of residual stress in substrates include Stoney curvature method, Raman spectroscopy, X-ray diffraction, and photoelasticity.

[0003] The Stoney curvature method indirectly measures the overall stress distribution of a substrate by measuring the curvature change before and after coating, combined with a mechanical model of the relationship between curvature and residual stress. It is generally suitable for structures with a single-layer coating on the substrate, but suffers some loss of accuracy for localized stress and small-sized components. Raman spectroscopy infers the distribution of residual stress in a sample by measuring the shift of Raman spectral peaks under residual stress. It can achieve online monitoring of single-point stress in a sample, offering high spatial resolution, but requires point-by-point scanning, has a long detection time, is sensitive to temperature, and has a maximum penetration depth of only 10 micrometers. X-ray diffraction is highly accurate and fast, widely used in residual stress measurement and phase analysis, but its penetration depth is limited. Photoelasticity utilizes the photoelastic effect of the substrate to obtain interference images, and uses phase-shifting techniques to obtain the phase difference distribution and principal stress direction distribution caused by stress. The photoelastic effect refers to the phenomenon where a beam of light incident on a photoelastic model with birefringence produces two polarized beams, which exit from the same point on the upper surface of the model and interfere with each other through an analyzer. Phase-shifting methods involve rotating the angles of certain optical elements in an optical system to obtain several interference images with different phase differences, thereby obtaining the phase of isochordinal lines and the phase of isochromatic lines through a system of equations. Traditional reflective photoelastic systems employ small-angle incident light, and the current national standard GB / T 30020-2023 even uses a 45-degree incident angle for detecting glass defects. In these reflective photoelastic systems, when the incident angle is not zero, the circularly polarized light incident on the material surface will experience phase delay, becoming elliptically polarized light; furthermore, small-angle incident light can cause thin-film interference, resulting in errors that affect detection accuracy. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of errors caused by small-angle incident light in existing reflective photoelastic systems.

[0005] The technical solution adopted by the present invention to solve its technical problem is: to provide an optical non-destructive testing system for substrate residual stress, including a light source, a modulation module, a beam splitter, a sample stage, a demodulation module and an image acquisition module;

[0006] The light source, modulation module, and beam splitter are arranged sequentially along line A, while the beam splitter, demodulation module, and image acquisition module are arranged sequentially along line B. Line A is perpendicular to line B, and the line connecting the sample stage and the beam splitter is perpendicular to both line A and line B. The laser emitted by the light source passes through the modulation module and beam splitter to reach the test material placed on the sample stage. The light reflected from the test material passes through the beam splitter and demodulation module to reach the image acquisition module, where it is acquired to form a photoelastic image.

[0007] Preferably, the modulation module includes a first linear polarizer and a first waveplate, and the light source, the first linear polarizer, the first waveplate and the beam splitter are arranged sequentially along a straight line A.

[0008] Preferably, the demodulation module includes a second waveplate and a second linear polarizer, and the beam splitter, the second waveplate, the second linear polarizer, and the image acquisition module are arranged sequentially along line B.

[0009] Preferably, both the first and second wave plates are quarter-wave plates.

[0010] Preferably, the image acquisition module includes a camera and a matching lens, wherein the camera is a CCD camera or a CMOS camera.

[0011] The present invention also provides an optical non-destructive testing method for residual stress in a substrate, based on any of the optical non-destructive testing systems described above, comprising the following steps:

[0012] Set up the optical non-destructive testing system and place the material to be tested on the sample stage;

[0013] The light source emits a laser, which reaches the material under test and is reflected back to the image acquisition module to form a photoelastic image.

[0014] Extracting phase difference and inclination angle from photoelastic images;

[0015] The magnitude and direction of the principal stress difference are calculated based on the phase difference and the equal inclination angle.

[0016] Preferably, the arrangement detection system specifically comprises:

[0017] The modulation module includes a first linear polarizer and a first waveplate, and the light source, the first linear polarizer, the first waveplate and the beam splitter are arranged sequentially along a straight line A;

[0018] The demodulation module includes a second waveplate and a second linear polarizer. The beam splitter, the second waveplate, the second linear polarizer, and the image acquisition module are arranged sequentially along a straight line B. The polarization angle α of the first linear polarizer and the fast axis angle ζ of the first waveplate are set. The fast axis angle ζ of the first waveplate is the angle between the fast axis of the first waveplate and the reference axis. The reference axis is perpendicular to the direction of light propagation and parallel to the table.

[0019] Set the initial value of the polarization detection angle β of the second linear polarizer and the initial value of the fast axis angle γ of the second waveplate. The fast axis angle γ of the second waveplate is the angle between the fast axis of the second waveplate and the reference axis.

[0020] Set the rotation speed of the second linear polarizer and the second waveplate.

[0021] Preferably, the laser reaches the material under test and is reflected to the image acquisition module to form a photoelastic image. Specifically, the image acquisition module continuously acquires photoelastic images within a certain period of time to form a photoelastic image sequence.

[0022] Preferably, the extraction of phase difference and isoclimax from the photoelastic image specifically involves:

[0023] Six photoelastic images were acquired, and the light intensity signal was extracted from each image. The relationship between the light intensity signal and the phase difference δ and the isoclimax angle θ was obtained as follows:

[0024]

[0025] Among them, I i Let represent the light intensity of the i-th image.

[0026] Preferably, the calculation of the principal stresses of the residual stress based on the phase difference and the equal inclination angle includes:

[0027] The constant inclination angle is converted into the principal stress direction using the stress circle model; the phase difference is converted into the principal stress difference using the stress-optics theorem, expressed as:

[0028]

[0029] Where d is the thickness of the material to be measured; (c1-c2) is the stress optical constant, determined by the material to be measured; Δ represents the optical path difference, δ represents the phase difference, and λ is the wavelength of the laser emitted by the light source. This invention has the following beneficial effects:

[0030] (1) The photoelastic optical path of vertical incident and reflection is adopted, which avoids the systematic error caused by small angle incident in the existing reflective photoelastic system and realizes high-precision detection of substrate residual stress.

[0031] (2) The vertical incident reflective photoelastic system proposed in this invention can avoid the negative impact of other testing systems, does not damage the material under test, and can characterize the stress distribution of the material in the whole field. It is particularly suitable for stress testing of semiconductor substrates.

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the embodiments. Attached Figure Description

[0033] Figure 1 This is a system structure diagram of an embodiment of the present invention;

[0034] Figure 2 This is a diagram illustrating the method steps of an embodiment of the present invention. Detailed Implementation

[0035] See Figure 1 The diagram shown is a system structure diagram of an embodiment of the present invention, including: a light source, a modulation module, a beam splitter, a sample stage, a demodulation module, and an image acquisition module. The sample stage is used to place the material to be tested. The light source, modulation module, and beam splitter are arranged sequentially along line A, and the beam splitter, demodulation module, and image acquisition module are arranged sequentially along line B. Line A is perpendicular to line B, and the line connecting the sample stage and the beam splitter is perpendicular to both line A and line B. The laser emitted by the light source passes through the modulation module, beam splitter, material to be tested, and demodulation module before reaching the image acquisition module, where it is acquired to form a photoelastic image.

[0036] Specifically, the modulation module includes a polarizer P and a first quarter-wave plate Q. P The laser emitted by the light source first passes through the polarizer P-polarized light, and then through the first quarter-wave plate Q. O Circularly polarized light is obtained, which is the modulated light, and is used to measure the residual stress of the substrate of the sample under test.

[0037] Specifically, the demodulation module includes a second quarter-wave plate Q. A The modulated light reaches the test material, is reflected, and then passes through the beam splitter B before entering the demodulation module. Specifically, it first passes through the second quarter-wave plate Q. A The first quarter-wave plate Q in the restoration modulation module P The introduced 90° phase difference is then demodulated by analyzer A to obtain the demodulated light.

[0038] Specifically, the image acquisition module includes a camera and a matching lens. In this embodiment, a CCD camera is used. After demodulation, the light passes through the matching lens to expand the field of view and is then captured by the CCD camera to obtain a photoelastic image.

[0039] See Figure 2 The diagram shows the method steps of an embodiment of the present invention, including the following steps:

[0040] Specifically, the image acquisition module described in S202 acquires photoelastic images. In this embodiment, the second 1 / 4 waveplate Q is used. A With the S201 detector, set up the detection system and place the material to be tested on the sample stage;

[0041] S202, the light source emits laser light, the laser light reaches the material under test and is reflected to the image acquisition module to form a photoelastic image;

[0042] S203, extracting phase difference and inclination angle from photoelastic images;

[0043] S204, calculate the magnitude of the principal stress difference and the direction of the principal stress based on the phase difference and the equal inclination angle.

[0044] Specifically, the arrangement detection system described in S201 includes setting the polarizer P's polarization angle α to 90 degrees, and the first quarter-wave plate Q... P The angle ζ between the fast axis and the reference axis is set to 45 degrees, and the angle θ between the optical axis and the reference axis caused by substrate stress is set to the second quarter-wave plate Q. A The angle γ between the fast axis and the reference axis is initially set to 0 degrees, and the polarization angle β of analyzer A is also initially set to 0 degrees. The second quarter-wave plate Q is rotated at a constant rate ratio of -0.5. A And analyzer A, i.e., the second quarter wave plate Q A If the analyzer A rotates by constants of -π / 12 (radians / frame) and π / 6 (radians / frame) respectively, the camera can record a series of interference images that change over time. The light intensity signal output by the camera is the integral of the instantaneous light intensity with respect to the rotation angle of the analyzer within the exposure time. The upper and lower limits of this integral are the initial and final angles of the analyzer within the exposure time.

[0045] If mirror A rotates 2π for one acquisition cycle, then the camera needs to collect 6 images in one acquisition cycle, and each image has its own output light intensity equation.

[0046] Specifically, in S203, based on the light intensity signal, the polarization angle α of the first linear polarizer, the fast axis angle ζ of the first waveplate, the analysis angle β of the second linear polarizer, and the fast axis angle γ of the second waveplate, equations are derived regarding the light intensity signal, phase difference, and isoclimax angle. The analysis angle β of the second linear polarizer and the fast axis angle γ of the second waveplate corresponding to each photoelastic image are calculated based on the initial values ​​of the analysis angle β and the fast axis angle γ of the second linear polarizer, the rotation speed of the second linear polarizer, the rotation speed of the second waveplate, and the acquisition time of the photoelastic image. The only unknowns are the phase difference caused by stress in the tested material and the isoclimax angle of the interference image. The light intensity equations corresponding to all photoelastic images in the photoelastic image sequence are combined into an overdetermined system of equations. Substituting the known parameters, the final equation system is expressed as follows:

[0047]

[0048] Among them, I i I represents the light intensity of the i-th image. a I represents the light intensity after passing through the polarizer. b δ represents the ambient light intensity, θ represents the phase difference caused by the stress of the material under test, and θ represents the constant tilt angle.

[0049] The relationship between the phase difference and the tilt angle of the interference image caused by stress in the material under test, and the output light intensity of the six images within one acquisition cycle, can be obtained by solving this system of equations as follows:

[0050]

[0051] Specifically, in S204, the constant inclination angle θ can be converted into the principal stress direction of the residual stress of the material under test through the stress circle model, and the phase difference δ can be converted into the principal stress difference of the material under test through the stress-optics theorem.

[0052] Specifically, the phase difference is converted into principal stress difference using the stress-optics theorem, expressed as:

[0053]

[0054]

[0055] Where d is the thickness of the material to be measured; (c1-c2) is the stress optical constant, which is determined by the material to be measured; Δ represents the optical path difference; δ represents the phase difference; and λ is the wavelength of the laser emitted by the light source.

[0056] This allows us to obtain the principal stress difference distribution and principal stress direction distribution of the material under test.

[0057] It can be seen that the vertical incident reflective photoelastic optical path detection system of the present invention can improve the systematic error caused by small-angle incident in the existing reflective photoelastic system and realize high-precision detection of substrate residual stress.

[0058] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for optically non-destructively detecting a residual stress of a substrate using a system for optically non-destructively detecting a residual stress of a substrate, characterized by, The optical nondestructive detection system comprises a light source, a modulation module, a beam splitter, a sample stage, a demodulation module and an image acquisition module; the light source, the modulation module and the beam splitter are arranged in sequence along a straight line A, the sample stage, the beam splitter, the demodulation module and the image acquisition module are arranged in sequence along a straight line B, and the straight line A is perpendicular to the straight line B; the laser emitted by the light source reaches the material to be measured placed on the sample stage after passing through the modulation module and the beam splitter, and the reflected light of the material to be measured reaches the image acquisition module after passing through the beam splitter and the demodulation module, and the image acquisition module forms a photoelastic image. The optical nondestructive detection method comprises the following steps: arranging an optical nondestructive detection system and placing a material to be measured on a sample stage; a light source emits laser, the laser reaches the material to be measured and is reflected to the image acquisition module to form a photoelastic image; extracting a phase difference and an isoclinic angle from the photoelastic image; calculating the size and direction of the principal stress difference according to the phase difference and the isoclinic angle; the modulation module comprises a first linear polarizer and a first wave plate, and the light source, the first linear polarizer, the first wave plate and the beam splitter are arranged in sequence along the straight line A; the demodulation module comprises a second wave plate and a second linear polarizer, and the beam splitter, the second wave plate, the second linear polarizer and the image acquisition module are arranged in sequence along the straight line B; the first linear polarizer is provided with a polarizing angle α and the first wave plate is provided with a fast axis angle ζ, the fast axis angle ζ of the first wave plate is the angle between the fast axis of the first wave plate and a reference axis, and the reference axis is perpendicular to the direction of the detection light propagation and parallel to the tabletop; the second linear polarizer is provided with an initial value of a detection angle β and the second wave plate is provided with an initial value of a fast axis angle γ, and the fast axis angle γ of the second wave plate is the angle between the fast axis of the second wave plate and the reference axis; the second linear polarizer and the second wave plate are provided with a rotating speed; the extraction of the phase difference and the isoclinic angle from the photoelastic image is specifically: six photoelastic images are collected, the light intensity signal of each photoelastic image is extracted, and the relationship between the light intensity signal and the phase difference δ and the isoclinic angle θ is obtained as follows: where I i represents the light intensity of the ith image, i = 1, 2, 3, 4, 5, 6; the calculation of the size and direction of the principal stress difference according to the phase difference and the isoclinic angle comprises: the isoclinic angle is converted into the direction of the principal stress through a stress circle model, and the phase difference is converted into the principal stress difference through a stress-optical theorem and is expressed as: wherein d is the thickness of the material to be measured; Δ represents the optical path difference, δ represents the phase difference, and λ is the wavelength of the laser emitted by the light source.

2. The method of optical non-destructive testing of residual stress in a substrate according to claim 1, wherein, The first wave plate and the second wave plate are both 1 / 4 wave plates.

3. The method of claim 1, wherein the substrate residual stress is measured by optical non-destructive detection. The image acquisition module comprises a camera and a matching lens, and the camera adopts a CCD camera or a CMOS camera.

4. The method of claim 1, wherein the substrate residual stress is measured by optical non-destructive detection. the laser reaches the material to be measured and is reflected to the image acquisition module to form a photoelastic image, specifically: the image acquisition module continuously collects photoelastic images within a certain time to form a photoelastic image sequence.

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