CN118243274A - Optical nondestructive testing system and method for residual stress of substrate - Google Patents

Abstract

The present invention discloses an optical nondestructive detection system and method for substrate residual stress. The system includes a light source, a modulation module, a spectroscope, a sample stage, a demodulation module, and an image acquisition module. The light source, the modulation module, and the spectroscope are arranged in sequence along a straight line A, and 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. During measurement, the laser emitted by the light source passes through the modulation module, the spectroscope, the material to be tested, and the demodulation module before reaching the image acquisition module. A series of interference images are collected to form a series of interference images. The direction and magnitude of the substrate residual stress are calculated through the relationship between the light intensity signal, the parameters of the optical components, the isoclinic angle, and the phase difference. The present invention improves the system error caused by the small angle incidence of the existing reflective photoelastic system through a vertical incidence reflective photoelastic optical path detection system, and realizes high-precision detection of substrate residual stress.

Description

Optical nondestructive testing system and method for substrate residual stress

Technical Field

The present invention relates to the field of optical detection technology, and in particular to an optical nondestructive detection system and method for substrate residual stress.

Background technique

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.

The Stoney curvature method measures the curvature change of the substrate before and after coating, and indirectly measures the overall stress distribution of the substrate by combining the mechanical model between curvature and residual stress. It is generally applicable to the structure of substrate plus single-layer 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 measuring the movement of the Raman spectrum peak of the sample under the influence of residual stress. It can realize the online monitoring of the single-point stress of the sample. This method has high spatial resolution, but it needs to scan point by point, the detection time is long, and it is sensitive to temperature reaction. The penetration depth is only 10 microns at most. The X-ray diffraction method has high precision and fast speed. It is widely used in residual stress measurement, 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 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

The purpose of the present invention is to solve the problem in the prior art that the reflective photoelastic system may cause errors due to small angle incidence.

The technical solution adopted by the present invention to solve the technical problem is: to provide an optical nondestructive detection system for residual stress of a substrate, including 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.

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.

Preferably, the demodulation module includes 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.

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

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

The present invention also provides an optical nondestructive testing method for substrate residual stress, based on any of the above optical nondestructive testing systems, comprising the following steps:

Arrange the optical nondestructive testing system and place the material to be tested on the sample stage;

The light source emits laser light, which reaches the material to be tested and is reflected to the image acquisition module to form a photoelastic image;

Extract phase difference and isoclinic angle from photoelastic images;

The magnitude of the principal stress difference and the direction of the principal stress are calculated based on the phase difference and the isoclinic angle.

Preferably, the arrangement detection system is specifically:

The modulation module includes 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 a straight line A;

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. The polarization angle α of the first linear polarizer and the fast axis angle ζ of the first wave plate are set. The fast axis angle ζ of the first wave plate is the angle between the fast axis of the first wave plate and the reference axis. The reference axis is perpendicular to the propagation direction of the detection light and parallel to the desktop.

Setting an initial value of the analyzer angle β of the second linear polarizer and an initial value of the fast axis angle γ of the second wave plate, wherein 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;

Set the rotation speed of the second linear polarizer and the second wave plate.

Preferably, the laser reaches the material to be tested 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.

Preferably, the extracting of the phase difference and the isoclinic angle from the photoelastic image is specifically as follows:

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

Wherein, _Ii represents the light intensity of the i-th image.

Preferably, the calculation of the residual stress and the principal stress according to the phase difference and the isoclinic angle comprises:

The isoclinic angle is converted into the principal stress direction through the stress circle model; the phase difference is converted into the principal stress difference through the stress-optics theorem, which is expressed as:

Wherein, d is the thickness of the material to be measured; (c ₁ -c ₂ ) 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. The present invention has the following beneficial effects:

(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;

(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 material stress distribution in the entire field, and is particularly suitable for stress testing of semiconductor substrates.

The present invention is 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

FIG1 is a system structure diagram of an embodiment of the present invention;

FIG. 2 is a diagram showing steps of a method according to an embodiment of the present invention.

Detailed ways

Referring to FIG1 , which is a system structure diagram of an embodiment of the present invention, the system structure diagram includes: 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, where it is collected to form a photoelastic image.

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 to obtain linear polarized light, and then passes through the first quarter wave plate Q _O to obtain circular polarized light. The circular polarized light is the modulated light, which is used to measure the substrate residual stress of the sample to be tested.

Specifically, the demodulation module includes a second 1/4 wave plate Q _A and an analyzer A; the modulated light reaches the material to be tested, is reflected, and enters the demodulation module after passing through a beam splitter B, specifically, first passes through the second 1/4 wave plate Q _A , restores the 90° phase difference introduced by the first 1/4 wave plate Q _P in the modulation module, and then completes the demodulation function through the analyzer A to obtain the demodulated light.

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.

Referring to FIG. 2 , there is shown a method step diagram of an embodiment of the present invention, which includes the following steps:

Specifically, the image acquisition module in S202 acquires a photoelastic image. In this embodiment, the second quarter wave plate Q _A and the polarization analyzer S201 are used to arrange the detection system, and the material to be tested is placed on the sample stage;

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;

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

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

Specifically, the arrangement detection system in S201 includes setting the polarization angle α of the polarizer P to 90 degrees, the angle ζ between the fast axis of the first 1/4 wave plate Q _P and the reference axis to 45 degrees, the angle θ between the optical axis generated by the stress of the substrate and the reference axis, the angle γ between the fast axis of the second 1/4 wave plate Q _A and the reference axis to 0 degrees, and the analyzer angle β of the analyzer A to 0 degrees. The second 1/4 wave plate Q _A and the analyzer A are rotated at a constant rate ratio of -0.5, that is, the second 1/4 wave plate Q _A and the analyzer A are rotated at constants of -π/12 (radians/frame) and π/6 (radians/frame), respectively, and the camera can record a series of interference images that change with time. At this 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 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.

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.

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 caused by stress of the material to be tested and the isoclinic angles of the interference image. 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:

Wherein, _Ii represents the light intensity of the i-th image, _Ia represents the light intensity after passing through the polarizer, _Ib represents the ambient light intensity, δ represents the phase difference caused by the stress of the material to be measured, and θ represents the isoclinic angle.

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:

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.

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

Wherein, d is the thickness of the material to be measured; (c ₁ -c ₂ ) 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.

Thus, the principal stress difference distribution and principal stress direction distribution of the material to be tested can be obtained.

It can be seen that the vertical-incident reflective photoelastic optical path detection system of the present invention 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.

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 (10)

1. An optical nondestructive testing system for residual stress of a substrate, characterized in that it comprises 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 is characterized in that the modulation module includes 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. 3. The optical nondestructive testing system for residual stress of a substrate according to claim 2 is characterized in that the demodulation module includes 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. 4 . The optical nondestructive testing system for residual stress of a substrate according to claim 3 , wherein 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 comprises a camera and a matching lens, and the camera is a CCD camera or a CMOS camera. 6. An optical nondestructive testing method for residual stress of a substrate, using the optical nondestructive testing system according to any one of claims 1 to 5, characterized in that it comprises the following steps: Arrange the optical nondestructive testing system and place the material to be tested on the sample stage; The light source emits laser light, which reaches the material to be tested and is reflected to the image acquisition module to form a photoelastic image; Extract phase difference and isoclinic angle from photoelastic images; The magnitude of the principal stress difference and the direction of the principal stress are calculated based on the phase difference and the isoclinic angle. 7. The optical nondestructive testing method for residual stress of a substrate according to claim 6, characterized in that the arrangement detection system is specifically: The modulation module includes 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 a straight line A; 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. The polarization angle α of the first linear polarizer and the fast axis angle ζ of the first wave plate are set. The fast axis angle ζ of the first wave plate is the angle between the fast axis of the first wave plate and the reference axis. The reference axis is perpendicular to the propagation direction of the detection light and parallel to the desktop. Setting an initial value of the analyzer angle β of the second linear polarizer and an initial value of the fast axis angle γ of the second wave plate, wherein 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; Set the rotation speed of the second linear polarizer and the second wave plate. 8. The optical nondestructive testing method for residual stress of a substrate according to claim 7 is characterized in that the laser reaches the material to be tested 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. 9. The optical nondestructive testing method for residual stress of a substrate according to claim 8, characterized in that the extraction of phase difference and isoclinic angle from the photoelastic image is specifically: Six photoelastic images were collected, and the light intensity signal was extracted from each photoelastic image. The relationship between the light intensity signal and the phase difference δ and the iso-inclination angle θ was obtained as follows: Wherein, _Ii represents the light intensity of the i-th image. 10. The optical nondestructive testing method for substrate residual stress according to claim 8, characterized in that the calculation of residual stress principal stress according to phase difference and isoclinic angle comprises: The isoclinic angle is converted into the principal stress direction through the stress circle model; the phase difference is converted into the principal stress difference through the stress-optics theorem, which is expressed as: Wherein, d is the thickness of the material to be measured; (c ₁ -c ₂ ) 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.