A surface plasmon resonance enhancement-based defect detection device and method

Abstract

The application provides a kind of defect detection device and method based on surface plasmon resonance enhancement, belongs to the field of optical precision measurement and nondestructive testing.The method forms the base frequency interference light field carrying the phase information of the surface of the measured object by phase shift interference, and the base frequency interference light field is coupled to the prism structure plated with metal film at surface plasmon resonance angle, and the secondary or third harmonic interference light field is generated by using local electric field enhancement;A plurality of phase shift harmonic interference images are collected by filtering and surface array detection, and the harmonic phase is calculated by generalized phase shift algorithm and converted into height distribution.The device comprises a laser light source, a polarization light splitting system, a phase shift interference system, a nonlinear enhancement module, a filtering and detection system and a control processing system, thereby improving the fringe contrast, signal-to-noise ratio and three-dimensional profile reconstruction sensitivity of weak defects.

Description

Technical Field

[0001] This invention relates to the field of optical precision measurement and non-destructive testing technology, specifically to a defect detection device and method based on surface plasmon resonance enhancement, which realizes the reconstruction of the three-dimensional morphology of the surface through phase shift calculation. Background Technology

[0002] In scenarios such as micro-nano manufacturing, semiconductor chip inspection, precision optical component inspection, and biomedical imaging, the surface under test may have nanoscale steps, scratches, pits, or local refractive index changes. Existing optical inspection methods such as white light interferometers, confocal microscopes, and laser interferometric profilometers typically acquire surface information using linear light intensity or linear interference phase. However, these methods are easily limited by signal-to-noise ratio, fringe contrast, and diffraction limit under conditions of weak scattering, low reflectivity, or extremely shallow defects.

[0003] Nonlinear optical detection methods can enhance defect response by utilizing the sensitivity of second or third harmonics to abrupt changes in surface, interface, and refractive index. However, their nonlinear conversion efficiency is low, and harmonic signals are weak during conventional wide-field detection. To enhance harmonic signals, existing technologies have proposed surface plasmon resonance-enhanced nonlinear microscopy methods. For example, patent document WO2009112431A1 utilizes a metal layer in a Kretschmann configuration to excite surface plasmon resonance, thereby enhancing harmonic light intensity and performing sample imaging.

[0004] However, the aforementioned existing technologies mainly focus on harmonic intensity imaging or nonlinear response intensity enhancement, without first encoding the phase-shifting interference information formed by the reflection from the surface under test into the fundamental frequency interference light field, and then converting it into an enhanced nonlinear harmonic interference image at the surface plasmon resonance interface; nor do they provide a multi-step generalized phase-shifting solution and high-resolution reconstruction process for second or third harmonic interference fringes. Therefore, in defect detection scenarios that require simultaneous high sensitivity, high signal-to-noise ratio, and full-field three-dimensional morphology reconstruction, a detection device and method that can combine surface plasmon resonance enhancement, nonlinear interference, and phase-shifting solution is still needed. Summary of the Invention

[0005] The technical problem to be solved by this invention is that existing linear interferometry detection has insufficient fringe contrast and phase sensitivity under weak defect conditions, and existing surface plasmon resonance enhanced nonlinear microscopy techniques are mostly based on light intensity imaging, making it difficult to obtain a high signal-to-noise ratio phase distribution for three-dimensional morphology reconstruction while ensuring high sensitivity.

[0006] To address the aforementioned technical problems, this invention provides a defect detection method based on surface plasmon resonance enhancement. The method includes the following steps: S1. Generate coherent fundamental frequency light, adjust the fundamental frequency light to a p-polarization state, and split it into reference light and signal light; S2. After focusing the signal light and the reference light respectively, the signal light is made to illuminate the surface of the object under test and reflect it, and the reference light is made to be reflected by the reference mirror. The two beams are combined to form a fundamental frequency interference light field carrying the phase information of the surface of the object under test. S3. The fundamental frequency interference light field is coupled and incident on a Kretschmann structure consisting of a coupling prism coated with a metal film, and then incident on the interface region of the metal film at a surface plasmon resonance angle to generate a local electric field enhancement and generate a beam carrying the phase information. The second harmonic interference optical field, in which the target harmonic order It is 2 or 3; the target harmonic wavelength is ,in The center wavelength of the fundamental frequency light; S4. The reference mirror is driven to move along the optical axis to N phase shift positions by the displacement driving component. At the phase shift positions, the fundamental frequency light and non-target harmonics are filtered out, and the target harmonic interference image is acquired. S5. Based on the N target harmonic interferometric images, establish a DC term, a first-order phase term, and a harmonic order relative to the target harmonic for each pixel. corresponding The generalized phase shift equations for the first phase term are obtained, and the target harmonic phase distribution is obtained by solving the equations. S6. Perform phase unwrapping on the target harmonic phase distribution, and obtain the height distribution and defect characteristics of the surface of the object under test according to the pre-calibrated phase-height conversion relationship.

[0007] Furthermore, when When N is 2, N is not less than 5. The adjacent phase shift positions of the displacement driving component cause the fundamental frequency interference optical field to generate a phase step of π / 2, and the second harmonic interference optical field to generate a phase step of π.

[0008] Furthermore, the displacement driving component is a piezoelectric ceramic phase shifter, and the fundamental frequency light center wavelength... The piezoelectric ceramic phase shifter drives a single-step displacement of the reference mirror, ranging from 780nm to 850nm. satisfy ;when At 800nm, It is 100nm.

[0009] Furthermore, when When N is 3, N is not less than 7. The adjacent phase shift positions of the displacement driving component cause the fundamental frequency interference optical field to generate a phase step of π / 2 and the third harmonic interference optical field to generate a phase step of 3π / 2.

[0010] Furthermore, the displacement driving component is a piezoelectric ceramic phase shifter, and the fundamental frequency light center wavelength... The piezoelectric ceramic phase shifter drives a single-step displacement of the reference mirror, ranging from 1050 nm to 1300 nm. satisfy ;when At 1200nm, It is 150nm.

[0011] Furthermore, the metal film is a gold film or a silver film with a thickness of 40nm to 65nm; the surface plasmon resonance angle is determined by scanning the incident angle and making the reflected fundamental frequency light intensity reach a valley value.

[0012] Furthermore, in the reflective interference configuration, the phase-height conversion relationship is as follows: ,in Highly distributed, To determine the target harmonic phase distribution after unwrapping, The target harmonic wavelength.

[0013] The present invention also provides a defect detection device based on surface plasmon resonance enhancement for implementing the above method, the device comprising: Laser light source, used to generate fundamental frequency light; A polarization beam splitting system is disposed after the laser source and includes, in sequence, a polarization element and a polarization beam splitting element. The polarization element is used to adjust the fundamental frequency light to a p-polarization state, and the polarization beam splitting element is used to split the beam. A phase-shifting interferometry system includes a first focusing component, an interferometric beam splitter, a reference arm, and a sample arm, which are sequentially arranged after reflection by the polarization beam splitter. The interferometric beam splitter is used to split the fundamental frequency light into a reference light entering the reference arm and a signal light entering the sample arm. The interferometric beam splitter is located at the intersection of the reference arm and the sample arm and is used to combine the returning reference light and the signal light to form an interferometric light field. The reference arm is provided with a displacement driving component and a reference mirror connected to the displacement driving component. The sample arm is provided with a displacement stage for carrying the object under test. The phase-shifting interferometry system is used to form a fundamental frequency interferometric light field carrying the phase information of the surface of the object under test. The nonlinear enhancement module includes a second focusing component and a coupling prism arranged sequentially after being transmitted through the polarization beam splitter. The inclined surface of the coupling prism is coated with a metal film, which is used to focus the fundamental frequency interference light field and couple it to the metal film interface to excite surface plasmon resonance and generate a target harmonic interference light field. The detection system includes a spectral separation element and an array detector arranged sequentially after the coupling prism, used to filter out the fundamental frequency light and non-target harmonics and acquire target harmonic interference images; The control and processing system is communicatively connected to the displacement drive component, the displacement stage, and the area array detector, and is used to control phase shift acquisition and perform generalized phase shift calculation and three-dimensional reconstruction.

[0014] Furthermore, the laser source is a femtosecond laser or a picosecond laser; the polarization beam splitter is a beam splitter, a dichroic mirror, or a polarization beam splitter prism; the interference beam splitter is a beam splitter or a polarization beam splitter prism; the area array detector is a CCD, CMOS, or EMCCD; the displacement stage is a triaxial displacement stage; the spectral separation element is a short-pass filter, a band-pass filter, a dichroic mirror, or a combination thereof; in the second harmonic detection mode, the spectral separation element transmits spectral components with wavelengths near half the wavelength of the fundamental frequency light; in the third harmonic detection mode, the spectral separation element transmits spectral components with wavelengths near one-third the wavelength of the fundamental frequency light and suppresses the second harmonic.

[0015] Compared with the prior art, the present invention has at least the following technical effects: First, this invention couples the fundamental frequency interference optical field carrying the phase information of the surface under test to the Kretschmann structure of the metal-coated film at the surface plasmon resonance angle. By utilizing the local electric field enhancement effect at the metal film interface, the intensity of the second or third harmonic interference signal is significantly improved. At the same time, the high-order dependence of the nonlinear harmonics on the fundamental frequency electric field makes the edges of the interference fringes sharper, thereby effectively improving the fringe contrast, signal-to-noise ratio and discernibility of weak defects. Second, this invention uses an area array detector to acquire multiple harmonic interferometric images across the entire field at multiple phase shift positions, achieving non-contact full-field three-dimensional topography reconstruction without point-by-point scanning. Simultaneously, by establishing a generalized phase shift equation set including DC terms, fundamental frequency terms, and higher-order harmonic terms corresponding to the target harmonics, the coupling error when traditional linear phase shift algorithms directly process nonlinear harmonic fringes can be effectively reduced. This results in a more accurate target harmonic phase distribution, and non-contact full-field three-dimensional topography reconstruction of the surface under test is achieved according to the phase-height conversion relationship.

[0016] Third, this invention organically combines surface plasmon resonance enhancement, nonlinear harmonic interference, and generalized phase shift phase calculation techniques, overcoming the problem that existing SPR-enhanced nonlinear microscopy techniques cannot directly obtain the full-field three-dimensional morphology. It is applicable to the detection of surface micro-defects in fields such as micro-nano manufacturing, semiconductor chip inspection, and precision optical component inspection. Attached Figure Description

[0017] Figure 1This is a schematic diagram of the optical path structure of the defect detection device based on surface plasmon resonance enhancement according to an embodiment of the present invention. In the figure: 1-laser source; 2-polarization element; 3-polarization beam splitter; 4-first focusing component; 5-interference beam splitter; 6-displacement driving component; 7-displacement stage; 8-second focusing component; 9-coupled prism; 10-spectral separation element; 11-area array detector; 12-control and processing system.

[0018] Figure 2 This is a schematic diagram of the normalized curves of the fundamental frequency interference intensity and the nonlinear harmonic interference intensity, where curve 21 represents the fundamental frequency interference intensity, curve 22 represents the second harmonic interference intensity, and curve 23 represents the third harmonic interference intensity.

[0019] Figure 3 This is a schematic diagram of the detection process in an embodiment of the present invention, wherein 301 represents generating and adjusting the fundamental frequency light, 302 represents forming the fundamental frequency interference light field, 303 represents surface plasmon resonance enhancement, 304 represents target harmonic separation and acquisition, 305 represents multi-step phase shift acquisition, 306 represents generalized phase shift solution, and 307 represents phase unwrapping and height reconstruction.

[0020] Figure 4 This is a schematic diagram of interference in the second harmonic detection mode.

[0021] Figure 5 This is a schematic diagram of interference under the third harmonic detection mode. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Unless otherwise stated, surface plasmon resonance is abbreviated as SPR, second harmonic generation as SHG, third harmonic generation as THG, and piezoelectric ceramic phase shifter as PZT.

[0023] like Figure 1 As shown, laser source 1 outputs coherent fundamental frequency light. Polarization element 2 adjusts the fundamental frequency light to a p-polarized state to meet the polarization requirements of SPR excitation. Polarization beam splitter 3 and first focusing component 4 guide the beam into the phase-shifting interference system. Interference beam splitter 5 splits the fundamental frequency light into signal light entering the sample arm and reference light entering the reference arm respectively; the signal light in the sample arm illuminates and reflects the surface of the object under test placed on the displacement stage 7, and the reference light in the reference arm illuminates and reflects the reference mirror, which is driven by displacement driving component 6 to make a small displacement along the optical axis. The two beams are combined at interference beam splitter 5 to form a fundamental frequency interference light field carrying phase information of the surface of the object under test.

[0024] The fundamental frequency interference light field passes sequentially through the first focusing component 4 and the polarization beam splitter 3, then is transmitted through the polarization beam splitter 3 to the second focusing component 8 for convergence, and subsequently incident on the coupling prism 9. The coupling prism 9 is coated with a metal film to form a Kretschmann structure. The metal film can be gold or silver, with a thickness of 40 nm to 65 nm. This thickness range is determined by the optimization conditions required for surface plasmon resonance, and the specific value is selected based on the fundamental frequency laser wavelength and the refractive index of the coupling prism. By rotating the coupling prism or adjusting the incident light angle, the incident angle is brought close to the SPR resonance angle. When the reflected fundamental frequency light exhibits an intensity trough, the resonance condition is confirmed. At this point, a localized electric field enhancement is generated at the metal film interface, exciting a second or third harmonic interference light field carrying phase information.

[0025] Figure 2 This is a schematic diagram showing the normalized comparison curves of the fundamental frequency interference intensity and the nonlinear harmonic interference intensity in this embodiment. Curve 21 in the figure represents the fundamental frequency interference intensity, curve 22 represents the second harmonic interference intensity, and curve 23 represents the third harmonic interference intensity. Figure 2 It can be seen that the bright fringe width of the second and third harmonic interference fringes is significantly reduced and the edge slope is significantly increased compared with the fundamental frequency interference fringes, indicating that nonlinear harmonic interference has higher recognition and response sensitivity to surface micro-defects.

[0026] The spectral separation element 10 is used to separate the target harmonics from the fundamental light and non-target harmonics. The spectral separation element 10 can be a short-pass filter, a band-pass filter, a dichroic mirror, or a combination thereof. In SHG detection mode, the spectral separation element 10 transmits spectral components near half the wavelength of the fundamental light; in THG detection mode, the spectral separation element 10 transmits spectral components near one-third the wavelength of the fundamental light and suppresses the second harmonic. The area array detector 11 can be a CCD, CMOS, or EMCCD, used to acquire target harmonic interference images. The control and processing system 12 controls the displacement drive assembly 6, the displacement stage 7, and the area array detector 11, and performs image acquisition, phase calculation, and three-dimensional reconstruction. During detection, the control and processing system 12 controls the displacement drive assembly 6 to drive the reference mirror to move along the optical axis to N phase-shift positions, and acquires one target harmonic interference image at each phase-shift position through the area array detector 11, thereby obtaining N target harmonic interference images. Subsequently, based on the N target harmonic interferometric images, the control and processing system 12 establishes a generalized phase-shifting linear equation system for each pixel, including a DC term, a fundamental frequency term, and higher harmonic terms corresponding to the target harmonics. The target harmonic phase distribution is obtained by solving the equation system. Finally, the target harmonic phase distribution is unwrapped, and the height distribution and defect characteristics of the surface of the object under test are obtained according to a pre-calibrated phase-height conversion relationship.

[0027] Let the center wavelength of the fundamental frequency light be... The target harmonic order is The target harmonic wavelength is In reflective phase-shifting interferometry, PZT drives the reference mirror to move. At that time, the phase shift of the fundamental frequency interference optical field is To obtain the fundamental frequency phase shift step size of π / 2, we can let... For SHG detection, the target harmonic phase shift step size is... For THG detection, the target harmonic phase shift step size is: .

[0028] At a pixel position At this location, the target harmonic interferometry image can be represented as containing a DC term, a first-order phase term, and higher-order phase terms. For example, at this pixel location, the first... The intensity of each SHG detection is expressed as follows: ,in, Indicates the first The second harmonic intensity of the second measurement This represents the two-dimensional coordinate position of the displacement stage. , and These are the coefficients of the DC term, first-order phase term, and second-order phase term at that pixel location, respectively. For the phase information of the object surface, For the first Secondary phase shift step size, where Where N represents the number of phase shift steps selected, i.e., the number of phase shift positions moved. Representing the The displacement of the reference arm relative to its initial position during the next measurement; THG detection may further include... Item, of which This represents the third-order phase term coefficient at that pixel location. The control and processing system 12 is based on different... A system of linear equations is established from the corresponding multiple images to solve for the target harmonic phase. Subsequently, on Phase unwrapping is performed. Since this embodiment uses a reflective interference optical path, the relationship between phase difference and height difference is the optical path length for a round trip. Therefore, according to... Alternatively, the phase-to-height conversion coefficient obtained through calibration can be used to convert the phase distribution into a height distribution.

[0029] Specifically, the pre-calibration may include: before formal testing, placing a calibration step sample with a known height difference on the displacement stage, obtaining the harmonic phase distribution of the calibration step sample according to the method described above, and fitting the measured phase difference with the known height difference to determine the phase-height conversion coefficient; or, directly using theoretical formulas. The transformation relationship is highly reconstructed.

[0030] Figure 3 This is a schematic diagram of the detection process according to an embodiment of the present invention. Figure 3 As shown, the detection process includes: generating and adjusting the fundamental frequency light (301) → forming a fundamental frequency interference light field (302) → generating harmonics through surface plasmon resonance enhancement (303) → target harmonic separation and acquisition (304) → multi-step phase shift acquisition (305) → generalized phase shift calculation (306) → phase unwrapping and height reconstruction (307). This process is uniformly scheduled and executed by the control and processing system 12.

[0031] Example 1: Second Harmonic Detection Mode In this embodiment, the laser source 1 uses a center wavelength. The system comprises a femtosecond laser; polarization element 2 is a polarizer; polarization beam splitter element 3 is a polarization beam splitter prism; first focusing component 4 is an objective lens; interference beam splitter element 5 is a beam splitter; displacement driving component 6 is a piezoelectric ceramic phase shifter; displacement stage 7 is a triaxial displacement stage; second focusing component 8 is a focusing lens; coupling prism 9 is a BK7 glass prism; spectral separation element 10 is a short-pass filter; and area array detector 11 is a CCD. The metal film is a 45nm thick gold film; the SPR resonance angle is determined to be approximately 42.2° by angle scanning. The spectral separation element 10 uses a short-pass filter with a cutoff wavelength of approximately 550nm, and can be superimposed with a bandpass filter with a center wavelength of approximately 400nm to suppress the fundamental frequency light and transmit the second harmonic.

[0032] During testing, the PZT-driven reference mirror performs 5-step phase shift acquisition. Because... Take single-step displacement At that time, the fundamental frequency phase shift step size is π / 2, and the second harmonic phase shift step size is π. The array detector 11 acquires SHG interferometric images at five phase shift positions, and the control and processing system 12 establishes a generalized phase shift equation set containing DC, fundamental, and second harmonic terms, and solves the second harmonic phase distribution.

[0033] The detection results of this embodiment are as follows: compared with the fundamental frequency linear interference fringes, the bright fringe width of the SHG interference fringes is reduced and the edge slope is increased; after phase unwrapping, a continuous surface height distribution can be obtained, thereby enabling three-dimensional positioning and morphological reconstruction of the steps, scratches or pits on the surface of the object under test.

[0034] Figure 4 This is a schematic diagram of the interference in the second harmonic generation (SHG) detection mode of this embodiment. In SHG detection mode, the PZT drives the reference mirror to perform 5-step phase shift acquisition, and the short-pass filter transmits the spectral components near half the wavelength of the fundamental frequency light. Figure 4 As can be seen, the SHG interference fringes exhibit a typical circular, equal-thickness interference pattern, and their fringe contrast and spatial resolution are superior to those of the fundamental frequency interference fringes.

[0035] Example 2: Third Harmonic Detection Mode In this embodiment, the laser source 1 uses a center wavelength. The system utilizes a femtosecond or picosecond laser; the polarization element 2 is a polarizer; the polarization beam splitter element 3 is a polarization beam splitter prism; the first focusing assembly 4 is an objective lens; the interference beam splitter element 5 is a beam splitter; the displacement driving assembly 6 is a PZT; the displacement stage 7 is a triaxial displacement stage; the second focusing assembly 8 is a focusing lens; the coupling prism 9 is a BK7 glass prism; the spectral separation element 10 is a bandpass filter; and the area array detector 11 is a CCD. The metal film is a 60nm thick gold film; the SPR resonance angle is determined to be approximately 44° through angle scanning. The spectral separation element 10 uses a bandpass filter with a center wavelength of approximately 400nm and a bandwidth of 10nm to 40nm to transmit the third harmonic and suppress the 1200nm fundamental frequency light and the 600nm second harmonic.

[0036] During testing, the PZT-driven reference mirror performs 7-step phase shift acquisition. Because... Take single-step displacement At that time, the fundamental frequency phase shift step size is π / 2, and the third harmonic phase shift step size is 3π / 2. The array detector 11 acquires THG interferometric images at 7 phase shift positions respectively, and the control and processing system 12 establishes a generalized phase shift equation system containing DC term, fundamental frequency term, second harmonic term and third harmonic term, and solves the third harmonic phase distribution.

[0037] The detection results of this embodiment are as follows: the THG interference fringes are further sharpened compared to the SHG mode, and have a higher response to changes in interface refractive index and small edge defects; after phase unwrapping and height conversion, the three-dimensional morphology and defect distribution of the surface of the object under test can be obtained.

[0038] Figure 5 This is a schematic diagram of the interference in the third harmonic (THG) detection mode of this embodiment. In THG detection mode, the PZT drives the reference mirror to perform 7-step phase-shift acquisition, and the bandpass filter transmits spectral components near one-third of the wavelength of the fundamental light while suppressing the second harmonic. Figure 5 As can be seen, the THG interference fringes are further sharpened compared to the SHG mode, exhibiting higher response sensitivity to changes in interface refractive index and minute edge defects. Table 1 below compares the key parameters of the SHG and THG detection modes in this embodiment: Table 1: Key Parameter Comparison Table Finally, it should be noted that the above embodiments are only used to illustrate the defect detection method, measuring device, and technical solution based on surface plasmon resonance enhancement of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can make equivalent substitutions or adjustments to the laser wavelength, metal film material and thickness, detector type, filter combination, phase shift step number, and algorithm implementation method without departing from the concept of the present invention. Such substitutions or adjustments should not depart from the spirit and scope of the technical solution of the present invention and should be covered within the scope of the claims of the present invention.

Claims

1. A defect detection method based on surface plasmon resonance enhancement, characterized in that, Includes the following steps: S1. Generate coherent fundamental frequency light, adjust the fundamental frequency light to a p-polarization state, and split it into reference light and signal light; S2. After focusing the signal light and the reference light respectively, the signal light is made to illuminate the surface of the object under test and reflect it, and the reference light is made to be reflected by the reference mirror. The two beams are combined to form a fundamental frequency interference light field carrying the phase information of the surface of the object under test. S3. The fundamental frequency interference light field is coupled and incident on a Kretschmann structure consisting of a coupling prism coated with a metal film, and then incident on the interface region of the metal film at a surface plasmon resonance angle to generate a local electric field enhancement and generate a beam carrying the phase information. The second harmonic interference optical field, in which the target harmonic order It is 2 or 3; the target harmonic wavelength is ,in The center wavelength of the fundamental frequency light; S4. The reference mirror is driven to move along the optical axis to N phase shift positions by the displacement driving component. At the phase shift positions, the fundamental frequency light and non-target harmonics are filtered out, and the target harmonic interference image is acquired. S5. Based on N target harmonic interferometric images, establish a structure for each pixel containing a DC term, a first-order phase term, and the harmonic order relative to the target. corresponding The generalized phase shift equations for the first phase term are obtained, and the target harmonic phase distribution is obtained by solving the equations. S6. Perform phase unwrapping on the target harmonic phase distribution, and obtain the height distribution and defect characteristics of the surface of the object under test according to the pre-calibrated phase-height conversion relationship.

2. The method according to claim 1, characterized in that, when When N is 2, N is not less than 5. The adjacent phase shift positions of the displacement driving component cause the fundamental frequency interference optical field to generate a phase step of π / 2, and the second harmonic interference optical field to generate a phase step of π.

3. The method according to claim 2, characterized in that, The displacement driving component is a piezoelectric ceramic phase shifter, and the fundamental frequency optical center wavelength is... The piezoelectric ceramic phase shifter drives a single-step displacement of the reference mirror, ranging from 780nm to 850nm. satisfy ;when At 800nm, It is 100nm.

4. The method according to claim 1, characterized in that, when When N is 3, N is not less than 7. The adjacent phase shift positions of the displacement driving component cause the fundamental frequency interference optical field to generate a phase step of π / 2 and the third harmonic interference optical field to generate a phase step of 3π / 2.

5. The method according to claim 4, characterized in that, The displacement driving component is a piezoelectric ceramic phase shifter, and the fundamental frequency optical center wavelength is... The piezoelectric ceramic phase shifter drives a single-step displacement of the reference mirror, ranging from 1050 nm to 1300 nm. satisfy ;when At 1200nm, It is 150nm.

6. The method according to claim 1, characterized in that, The metal film is a gold or silver film with a thickness of 40 nm to 65 nm; the surface plasmon resonance angle is determined by scanning the incident angle and making the reflected fundamental frequency light intensity reach the valley value.

7. The method according to claim 1, characterized in that, In the reflective interference configuration, the phase-height conversion relationship is as follows: ,in Highly distributed, To determine the target harmonic phase distribution after unwrapping, The target harmonic wavelength.

8. A defect detection device based on surface plasmon resonance enhancement for implementing the method according to any one of claims 1 to 7, characterized in that, include: Laser light source, used to generate fundamental frequency light; A polarization beam splitting system is disposed after the laser source and includes, in sequence, a polarization element and a polarization beam splitting element. The polarization element is used to adjust the fundamental frequency light to a p-polarization state, and the polarization beam splitting element is used to split the beam. A phase-shifting interferometry system includes a first focusing component, an interferometric beam splitter, a reference arm, and a sample arm, which are sequentially arranged after reflection by the polarization beam splitter. The interferometric beam splitter is used to split the fundamental frequency light into a reference light entering the reference arm and a signal light entering the sample arm. The interferometric beam splitter is located at the intersection of the reference arm and the sample arm and is used to combine the returning reference light and the signal light to form an interferometric light field. The reference arm is provided with a displacement driving component and a reference mirror connected to the displacement driving component. The sample arm is provided with a displacement stage for carrying the object under test. The phase-shifting interferometry system is used to form a fundamental frequency interferometric light field carrying the phase information of the surface of the object under test. The nonlinear enhancement module includes a second focusing component and a coupling prism arranged sequentially after being transmitted through the polarization beam splitter. The inclined surface of the coupling prism is coated with a metal film, which is used to focus the fundamental frequency interference light field and couple it to the metal film interface to excite surface plasmon resonance and generate a target harmonic interference light field. The detection system includes a spectral separation element and an array detector arranged sequentially after the coupling prism, used to filter out fundamental frequency light and non-target harmonics and acquire target harmonic interference images; The control and processing system is communicatively connected to the displacement drive component, the displacement stage, and the area array detector, and is used to control phase shift acquisition and perform generalized phase shift calculation and three-dimensional reconstruction.

9. The apparatus according to claim 8, characterized in that, The laser source is a femtosecond laser or a picosecond laser; the polarization beam splitter is a beam splitter, a dichroic mirror, or a polarization beam splitter prism; the interference beam splitter is a beam splitter or a polarization beam splitter prism; the area array detector is a CCD, CMOS, or EMCCD; and the displacement stage is a triaxial displacement stage.

10. The apparatus according to claim 8, characterized in that, The spectral separation element is a short-pass filter, a band-pass filter, a dichroic mirror, or a combination thereof; in the second harmonic detection mode, the spectral separation element transmits spectral components with wavelengths in the range of half the wavelength of the fundamental frequency light; in the third harmonic detection mode, the spectral separation element transmits spectral components with wavelengths in the range of one-third the wavelength of the fundamental frequency light and suppresses the second harmonic.

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