Optical nondestructive testing system for residual stress of substrate

Abstract

The utility model discloses an optical nondestructive testing system for residual stress of a substrate. The optical nondestructive testing system comprises a light source, a modulation module, a spectroscope, a sample table, a demodulation module and an image acquisition module, the light source, the modulation module and the spectroscope are sequentially arranged along a straight line A. The spectroscope, the demodulation module and the image acquisition module are sequentially arranged along a straight line B. The straight line A is perpendicular to the straight line B. The connecting line of the sample table and the spectroscope is perpendicular to the straight line A and the straight line B. During detection, laser emitted by the light source passes through the modulation module, the spectroscope, a to-be-detected material and the demodulation module, then reaches the image acquisition module and is acquired to form a series of interference images, and the direction and the size of the residual stress of the substrate are calculated according to the relationship among light intensity signals, optical component parameters, an equal inclination angle and a phase difference. According to the utility model, the system error caused by small-angle incidence of the existing reflective photoelastic system is improved through the vertical incidence type reflective photoelastic optical path detection system, and high-precision detection of the residual stress of the substrate is realized.

Description

Technical Field

[0001] The utility model relates to the technical field of optical detection, in particular to an optical nondestructive detection system for substrate residual stress. Background Art

[0002] At present, the commonly used methods for optical nondestructive testing of substrate residual stress include Stoney curvature method, Raman spectroscopy, X-ray diffraction method and photoelasticity method.

[0003] The Stoney curvature method detects the curvature change of the substrate before and after coating, and indirectly detects the overall stress distribution of the substrate by combining the mechanical model between curvature and residual stress. It is generally suitable for structures with a substrate plus a single layer of coating, and the accuracy of local stress and small-sized parts is compromised. The Raman spectroscopy method infers the distribution of residual stress of the sample by detecting the movement of the Raman spectrum peak of the sample under the influence of residual stress. It can realize online monitoring of single-point stress of the sample. This method has high spatial resolution, but requires point-by-point scanning, long detection time, and is sensitive to temperature. The penetration depth is only 10 microns at most. The X-ray diffraction method has high accuracy and high speed. It is widely used in residual stress detection, phase analysis and other fields, but the penetration depth is not high. The photoelastic method uses the photoelastic effect of the substrate to obtain interference images, and obtains the phase difference distribution map and the principal stress direction distribution map caused by stress through phase shift technology. The photoelastic effect refers to the phenomenon that a beam of light is incident on a photoelastic model with a birefringence effect, each of which produces two polarized lights, in which the two beams of light with different polarization states are emitted from the same point on the upper surface of the model and interfere with the polarizer. The phase shift method refers to a technique that obtains several interference images with different phase differences by rotating the angles of certain optical elements in the optical system, thereby obtaining the isoclinic line phase and the isotropic line phase through a set of equations. In the traditional reflection photoelastic system, a small angle of incidence is used, and the current national standard GB / T 30020-2023 uses a 45-degree incident angle to detect glass defects. In the reflection photoelastic system, when the incident angle is not 0, the circularly polarized light incident on the surface of the material will be phase delayed and become elliptically polarized light; and the small angle of incidence will cause thin film interference, resulting in errors that affect the detection accuracy. Summary of the invention

[0004] The purpose of the utility model is to solve the problem in the prior art that the reflective photoelastic system may cause errors due to small angle incidence.

[0005] The utility model solves the technical problem by adopting a technical solution: providing an optical nondestructive detection system for residual stress of a substrate, comprising a light source, a modulation module, a spectroscope, a sample stage, a demodulation module and an image acquisition module;

[0006] The light source, modulation module and beam splitter are arranged in sequence along straight line A, the beam splitter, demodulation module and image acquisition module are arranged in sequence along straight line B, straight line A is perpendicular to straight line B, and the line connecting the sample stage and the beam splitter is perpendicular to both straight line A and straight line B; the laser emitted by the light source reaches the material to be tested placed on the sample stage after passing through the modulation module and the beam splitter, and the reflected light of the material to be tested reaches the image acquisition module after passing through the beam splitter and the demodulation module, and is collected to form a photoelastic image.

[0007] Preferably, 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 straight line A.

[0008] Preferably, 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 straight line B.

[0009] Preferably, the first wave plate and the second wave plate are both 1 / 4 wave plates

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

[0011] The utility model has the following beneficial effects:

[0012] (1) The vertical incidence and reflection photoelastic optical path is adopted to avoid the system error caused by small angle incidence in the existing reflective photoelastic system, and realize high-precision detection of substrate residual stress;

[0013] (2) The vertical incidence reflective photoelastic system proposed in the present invention can avoid the negative effects brought by other test systems, is non-destructive to the material to be tested, can characterize the stress distribution of the material in the entire field, and is particularly suitable for stress testing of semiconductor substrates.

[0014] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments, but the present invention is not limited to the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 2 is a system structure diagram of an embodiment of the utility model. DETAILED DESCRIPTION

[0016] See also Figure 1As shown, it is a system structure diagram of an embodiment of the utility model, including: a light source, a modulation module, a spectroscope, a sample stage, a demodulation module, and an image acquisition module, wherein the sample stage is used to place the material to be tested; the light source, the modulation module and the spectroscope are arranged in sequence along a straight line A, the spectroscope, the demodulation module and the image acquisition module are arranged in sequence along a straight line B, the straight line A is perpendicular to the straight line B, and the line connecting the sample stage and the spectroscope is perpendicular to both the straight line A and the straight line B; the laser emitted by the light source passes through the modulation module, the spectroscope, the material to be tested and the demodulation module and reaches the image acquisition module, and is collected to form a photoelastic image.

[0017] Specifically, the modulation module includes a polarizer P and a first 1 / 4 wave plate Q P The laser emitted by the light source first passes through the polarizer P linear polarization light, and then passes through the first 1 / 4 wave plate Q P Circularly polarized light is obtained, and the circularly polarized light is modulated light, which is used to detect the substrate residual stress of the sample to be tested.

[0018] Specifically, the demodulation module includes a second 1 / 4 wave plate Q A and analyzer A; after the modulated light reaches the material to be tested, it is reflected and passes through the beam splitter B before entering the demodulation module. Specifically, it first passes through the second 1 / 4 wave plate Q A , restore the Q of the first quarter wave plate in the modulation module P The introduced 90° phase difference is then demodulated by analyzer A to obtain the demodulated light.

[0019] Specifically, the image acquisition module includes a camera and a matching lens. This embodiment uses a CCD camera. After the demodulated light passes through the matching lens to expand the field of view, the CCD camera captures the photoelastic image.

[0020] When using the embodiment of the utility model to perform detection, the following steps are included:

[0021] Specifically, the image acquisition module in S202 acquires a photoelastic image. In this embodiment, the second quarter wave plate Q A and polarization analysis S201, arranging the detection system, and placing the material to be tested on the sample stage;

[0022] S202, the light source emits laser light, the laser light reaches the material to be tested and is reflected to the image acquisition module to form a photoelastic image;

[0023] S203, extracting phase difference and isoclinic angle from the photoelastic image;

[0024] S204, calculating the magnitude of the principal stress difference and the principal stress direction according to the phase difference and the isoclinic angle.

[0025] Specifically, the arrangement of the detection system in S201 includes setting the polarization angle α of the polarizer P to 90 degrees, the first 1 / 4 wave plate QP The angle ζ between the fast axis and the reference axis is set to 45 degrees, the angle θ between the optical axis generated by the stress of the substrate and the reference axis, and the second quarter wave plate Q A The angle γ between the fast axis and the reference axis is set to an initial value of 0 degrees, and the analyzer angle β of the analyzer A is set to an initial value of 0 degrees. The second 1 / 4 wave plate Q is rotated at a constant rate ratio of -0.5 A and analyzer A, i.e. the second 1 / 4 wave plate Q A The camera can record a series of interference images that change with time when the analyzer A and the analyzer A rotate according to the constants -π / 12 (radians / frame) and π / 6 (radians / frame) respectively. 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 during the exposure time, and the upper and lower limits of the integral are the initial angle and the end angle of the analyzer during the exposure time.

[0026] Mirror A rotates 2π in total for one acquisition cycle, so the camera needs to collect 6 images in one acquisition cycle, and each image has its own output light intensity equation.

[0027] Specifically, in S203, the equations about the light intensity signal, the phase difference and the isoclinic angles are obtained according to the light intensity signal, the polarization angle α of the first linear polarizer, the fast axis angle ζ of the first wave plate, the analyzer angle β of the second linear polarizer and the fast axis angle γ of the second wave plate, wherein the analyzer angle β of the second linear polarizer and the fast axis angle γ of the second wave plate corresponding to each photoelastic image are calculated according to the initial value of the analyzer angle β of the second linear polarizer, the initial value of the fast axis angle γ of the second wave plate, the rotation speed of the second linear polarizer, the rotation speed of the second wave plate and the acquisition time of the photoelastic image. Then the unknowns are only the phase difference and the isoclinic angles of the interference image caused by stress of the material to be tested, and the light intensity equations corresponding to all the photoelastic images in the photoelastic image sequence are formed into an overdetermined system of equations, and the known parameters are substituted to finally obtain the system of equations expressed as:

[0028]

[0029] Among them, I i represents the light intensity of the i-th image, I a Represents the light intensity after passing through the polarizer, I b represents the ambient light intensity, δ represents the phase difference caused by the stress of the material to be tested, and θ represents the isoclinic angle.

[0030] Through this set of equations, the relationship between the phase difference caused by stress in the material to be tested, the iso-inclination angle of the interference image, and the output light intensity of the six images in one acquisition cycle can be solved as follows:

[0031]

[0032] Specifically, in S204, the isoclinic angle θ can be converted into the principal stress direction of the residual stress of the material to be tested by using a stress circle model, and the phase difference δ can be converted into the principal stress difference of the material to be tested by using the stress-optics theorem.

[0033] Specifically, the phase difference is converted into the principal stress difference through the stress-optics theorem, which is expressed as:

[0034]

[0035]

[0036] Wherein, 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.

[0037] Thereby, the principal stress difference distribution and principal stress direction distribution of the material to be tested can be obtained.

[0038] It can be seen that the vertical-incident reflective photoelastic optical path detection system of the utility model can improve the system error caused by small-angle incidence in the existing reflective photoelastic system and realize high-precision detection of substrate residual stress.

[0039] The above are only 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 in the protection scope of the present invention.

Claims

1. An optical nondestructive testing system for substrate residual stress, characterized in that: It includes a light source, a modulation module, a spectroscope, a sample stage, a demodulation module and an image acquisition module; The light source, modulation module and beam splitter are arranged in sequence along straight line A, the beam splitter, demodulation module and image acquisition module are arranged in sequence along straight line B, straight line A is perpendicular to straight line B, and the line connecting the sample stage and the beam splitter is perpendicular to both straight line A and straight line B; the laser emitted by the light source reaches the material to be tested placed on the sample stage after passing through the modulation module and the beam splitter, and the reflected light of the material to be tested reaches the image acquisition module after passing through the beam splitter and the demodulation module, and is collected to form a photoelastic image.

2. The optical nondestructive testing system for substrate residual stress according to claim 1, characterized in that: The modulation module comprises a first linear polarizer and a first wave plate. The light source, the first linear polarizer, the first wave plate and the beam splitter are arranged in sequence along a straight line A.

3. The optical nondestructive testing system for substrate residual stress according to claim 2, characterized in that: The demodulation module includes a second wave plate and a second linear polarizer. The beam splitter, the second wave plate, the second linear polarizer and the image acquisition module are arranged in sequence along a straight line B.

4. The optical nondestructive testing system for substrate residual stress according to claim 3, characterized in that: The first wave plate and the second wave plate are both 1 / 4 wave plates.

5. The optical nondestructive testing system for substrate residual stress according to claim 1, characterized in that: The image acquisition module includes a camera and a matching lens, and the camera adopts a CCD camera or a CMOS camera.

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