Automatic focusing scanning imaging device and method based on bright and dark field confocal objective lens

Abstract

The invention provides an automatic focusing scanning imaging device and method based on a bright and dark field confocal objective lens. The device comprises a spatial modulation illumination module, the bright and dark field confocal objective lens, an annular light beam differential confocal module, a dark field confocal detection module and a bright field differential interference contrast imaging module. According to the invention, the bright and dark field confocal objective lens based on the combination of the parabolic mirror and the bright field microscope objective lens is arranged, the focus point of the annular light beam reflected by the parabolic mirror coincides with the focus of the bright field microscope objective lens, and the annular light reflected by the surface of the sample realizes automatic focusing through the differential confocal module; dark-field scattering confocal detection is realized by dark-field scattering light reflected by sample surface and subsurface defects through the confocal module, bright-field imaging of a defect area is realized by the bright-field differential interference contrast imaging module, and bright-field and dark-field three-dimensional imaging of the sample surface and subsurface defects can be realized through point-by-point scanning of the sample in x, y and z directions.

Description

Technical Field

[0001] The present invention relates to the field of optical precision measurement technology, and particularly to an autofocus scanning imaging device and method based on a bright and dark field confocal objective lens. Background Art

[0002] In optical manufacturing, the detection of surface and subsurface defects of high-performance optical components and materials is crucial, as these defects may have a significant impact on applications such as precision measurement, optical communication, and biomedical imaging. Due to the extremely high requirements of optical systems for the surface quality of components, any minor defect may seriously affect the performance, accuracy, and lifespan of the system. Therefore, it is of great significance to detect and handle these defects in a timely manner to ensure the efficient and stable operation of optical systems.

[0003] Dark field and bright field defect detection are common surface defect detection methods in microscope imaging technology. Bright field detection has low light loss and can provide clear images, which is helpful for observing the overall morphology and structure of samples. However, the detection sensitivity of bright field detection to surface defects is relatively low, especially for defects with small sizes or smooth surfaces, which are easily masked by background noise. In contrast, dark field detection captures the dark field scattered light caused by defects, significantly improving the detection sensitivity to minor defects. However, due to the weak dark field scattered light signal, the signal-to-noise ratio is low. By introducing confocal technology in dark field detection, optical sectioning can be achieved, reducing the influence of defects in non-target areas.

[0004] In dark field confocal detection, existing methods usually use complementary apertures to irradiate the outer ring part of the light passing aperture of a bright field microscope objective lens with an annular beam, and the scattered light from the surface and subsurface defects of the measured sample is detected through the central part of the light passing aperture of the bright field microscope objective lens. This brings two problems: one is that the annular illumination beam and the defect scattered beam share the same light passing aperture of a bright field objective lens, which is prone to beam crosstalk; the other is that the annular beam occupies a part of the numerical aperture of the bright field objective lens, resulting in a significant reduction in the collection aperture angle of the defect scattered beam. The above two problems cause a reduction in the signal-to-noise ratio of defect detection. Currently, commercial dark field microscope objectives (such as Mitutoyo and Nikon in Japan) can only provide diffused spot dark field illumination for the imaging field of the objective lens and do not have the ability to focus the annular illumination beam to the diffraction limit, making it difficult to meet the strong requirements of dark field confocal detection. Summary of the Invention

[0005] In view of the above problems, the present invention provides an autofocus scanning imaging device and method based on a bright and dark field confocal objective lens, designs a diffraction limit bright and dark field confocal objective lens, develops an autofocus technology based on the bright and dark field confocal objective lens, and integrates bright field differential interference contrast imaging and dark field confocal detection to obtain more comprehensive information about surface and subsurface defects, improve the detection efficiency, and accurately judge the defect characteristics.

[0006] To achieve the above object, the present invention provides an autofocus scanning imaging device of a bright-field and dark-field confocal objective lens, comprising a spatial modulation illumination module, a bright-field and dark-field confocal objective lens, an annular beam differential confocal module, a dark-field confocal detection module and a bright-field differential interference contrast imaging module;

[0007] The spatial modulation illumination module is used to generate a collimated annular light beam;

[0008] The bright and dark field confocal objective is used to focus the collimated annular light beam onto the sample surface to form dark field diffraction-limited illumination and collect dark field scattered light from the sample surface and sub-surface defects;

[0009] The annular beam differential confocal module is used to split the collimated annular beam reflected by the sample surface into two defocused beams to obtain two defocused signals, and obtain an annular light differential confocal signal after differentiation to achieve automatic focusing on the sample surface;

[0010] The dark field confocal detection module is used to receive dark field scattered light of sample surface and sub-surface defects;

[0011] The bright field differential interference contrast imaging module is used to perform bright field imaging on the surface and sub-surface defects detected by the dark field confocal detection module.

[0012] Further technology of the present invention:

[0013] Preferably, the spatial modulation lighting module includes, in order according to the light propagation direction: a laser light source, a collimated homogenization converter and a spatial light modulator; the collimated homogenization converter converts the Gaussian light beam emitted by the laser light source into a collimated flat-top light and irradiates it to the spatial light modulator, and obtains a collimated annular light beam through spatial modulation.

[0014] Preferably, the bright and dark field confocal objective lens includes, in order according to the light propagation direction: a hollow beam splitter, a parabolic lens barrel for mounting the objective lens, and the objective lens; the diameter of the collimated annular light beam generated by the spatial modulation illumination module matches the diameters of the hollow beam splitter and the parabolic reflector.

[0015] Preferably, an annular beam incident hole and an objective lens light hole are arranged on the tube cover of the parabolic lens tube, and the objective lens is fixed in the tube of the parabolic lens tube to form a bright and dark field confocal objective lens; a parabolic reflector is built-in at the bottom end of the parabolic lens tube, and the focal length of the parabolic reflector is the same as the focal length of the objective lens, and the two have overlapping focuses; an annular beam incident hole is arranged on the tube cover; the collimated annular beam reflected by the hollow beam splitter uses the annular beam incident hole in the parabolic lens tube as a light channel; the hollow beam splitter is used to reflect and transmit the dark field illumination light, and does not affect the beam passing through the objective lens.

[0016] Preferably, the annular beam differential confocal module sequentially includes, in the light propagation direction: a compensation sheet, a first lens, a first beam splitter, a first pinhole, a first photodiode, a second pinhole, and a second photodiode; the compensation sheet is used to correct the optical axis shift caused by the perforated beam splitter; the beam focused by the first lens is split into two beams by the first beam splitter and respectively passes through the first pinhole and the second pinhole, different defocus signals are received by the first pinhole and the second pinhole, the pre-focus signal is received by the first photodiode, and the post-focus signal is received by the second photodiode, and the two defocus signals are differentiated to achieve differential confocal.

[0017] Preferably, the dark field confocal detection module sequentially includes, in the light propagation direction: a second beam splitter, a second lens, a third pinhole, and a photomultiplier tube.

[0018] Preferably, the bright field differential interference contrast imaging module sequentially includes, in the light propagation direction: an illumination light source, a third beam splitter, a Wollaston prism, a third lens, and a area array camera;

[0019] The white light beam emitted by the illumination light source is split into two linearly polarized light beams with a certain separation angle and perpendicular vibration directions by the Wollaston prism, and the diameter of the beam after collimation by the third lens is smaller than the diameter of the perforated part of the perforated beam splitter, so as to avoid the interference of the bright field illumination light on the dark field illumination light.

[0020] The present invention also provides an autofocus scanning imaging method based on a bright and dark field confocal objective lens, which uses the autofocus scanning imaging device based on the bright and dark field confocal objective lens and is carried out according to the following steps:

[0021] Step a, the Gaussian beam emitted by the laser light source is adjusted into an annular beam with the same diameter as the diameter of the annular beam incident hole provided on the cover of the parabolic mirror barrel through a collimating and homogenizing converter and a spatial light modulator;

[0022] Step b, the annular beam is reflected by the perforated beam splitter to the bright and dark field confocal objective lens composed of the parabolic mirror barrel and the objective lens, and is focused on the surface of the sample to be measured by the parabolic mirror provided in the parabolic mirror barrel;

[0023] Step c: The bright and dark field confocal objective lens is driven by the z-axis displacement platform to approach the sample to be measured, and a reflected annular beam is generated on the surface of the sample to be measured. After the reflected annular beam is reflected by the parabolic mirror and then passes through the hollow beam splitter, the compensation sheet is used to correct the optical axis offset caused by the hollow beam splitter to obtain a corrected annular light. The corrected annular light is converged by lens 1, and then split into two converging lights by beam splitter 1. The pinhole 1 and pinhole 2 are used to receive different defocus signals. The photodiode 1 receives the pre-focus signal of one of the converging lights, and the photodiode 2 receives the post-focus signal of the other converging light. The two defocus signals are differentiated to form a differential confocal signal, and a straight line passing through the zero point is obtained. The zero point is the focusing position of the sample to be measured, and the defocus position is calculated according to the differential signal. The z-axis displacement platform completes the focusing;

[0024] Step d: The sample moving stage is controlled to perform a horizontal scan on the sample to be measured according to the set scanning strategy. The scattered light generated by the surface and subsurface defects of the sample is collected and collimated by the objective lens and passes through the hollow beam splitter, is reflected by the elliptical mirror and enters the dark field confocal detection module, and then passes through beam splitter 2. After being focused by lens 2, it passes through the pinhole 3 to achieve confocal detection. The scattered light is converted into a voltage signal by the photomultiplier tube (20) to realize dark field scattering defect detection;

[0025] Step e: The sample moving stage drives the sample to be measured to perform bright field imaging observation at the defect position. The white light beam emitted by the illumination light source is reflected by beam splitter 3 and then split into two linearly polarized lights with perpendicular vibration directions by the Wollaston prism. After being collimated by lens 3, it is reflected by beam splitter 2 and the elliptical mirror in turn and enters the objective lens to be focused on the surface of the sample, and bright field illumination light is generated on the surface of the sample;

[0026] Step f: The bright field illumination light passes through the objective lens, the elliptical mirror, beam splitter 2, lens 3, and the Wollaston prism in turn, and then is transmitted by beam splitter 3 to the area array camera to realize bright field differential interference contrast imaging.

[0027] Further: The diameters of the pinhole 1 and the pinhole 2 are set to D0, the diameter of the pinhole 3 is D1,

[0028] wherein, D H is the outer diameter of the annular light incident on lens 1, D B is the diameter of the dark field scattered light incident on lens 2, λ is the laser wavelength, f1 is the focal length of lens 1, and f2 is the focal length of lens 2.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The bright and dark field confocal objective lens structure proposed by the present invention realizes the isolation of the annular beam and the scattered light of the defect dark field on the one hand, which is beneficial to making full use of the numerical aperture of the objective lens; on the other hand, it realizes the diffraction-limited focusing of the annular light, which is beneficial to improving the signal-to-noise ratio of defect detection.

[0031] 2. The present invention sets a bright and dark field confocal objective lens to realize in-situ detection of dark field defect detection and bright field differential interference imaging without changing the working conditions of the objective lens, which is beneficial to greatly improving the detection efficiency and accurately and comprehensively judging the defect characteristics.

[0032] 3. The present invention realizes automatic focusing on the surface of the sample to be measured based on the differential confocal of the annular beam. Compared with the differential confocal signal of the traditional Gaussian beam, the differential confocal curve of the present invention has better linearity. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic structural diagram of an automatic focusing scanning imaging device based on the bright and dark field confocal objective lens of the present invention.

[0034] Figure 2 It is a schematic structural diagram of the assembly of the parabolic mirror and the objective lens in the present invention;

[0035] Figure 3 is Figure 2 a top view schematic diagram;

[0036] Figure 4 It is a schematic diagram of the difference between the differential confocal of the annular beam and the solid beam, where Figure 4 Figure (a) in it is the measured signal of the annular beam, Figure 4 Figure (b) in it is the simulated signal of the solid beam, and the dotted line is their respective differential signals;

[0037] Figure 5 It is the control strategy for z-axis automatic focusing in the present invention;

[0038] Figure 6 It is the movement strategy of the sample moving stage in the present invention;

[0039] Figure 7 It is a flowchart of the automatic focusing scanning imaging method based on the bright and dark field confocal objective lens of the present invention.

[0040] Markings in the figure: 1 Laser light source; 2 Collimating and homogenizing converter; 3 Spatial light modulator; 4 Hollow beam splitter; 5 Parabolic mirror tube; 6 Objective lens; 7 Sample to be measured; 8 Sample moving stage; 9 Compensation plate; 10 Elliptical mirror; 11 First lens; 12 First beam splitter; 13 First pinhole; 14 Second pinhole; 15 First photodiode; 16 Second photodiode; 17 Second beam splitter; 18 Second lens; 19 Third pinhole; 20 Photomultiplier tube; 21 Third lens; 22 Wollaston prism; 23 Third beam splitter; 24 Illumination light source; 25 Area array camera; 26 Z-axis displacement stage; 27 Parabolic mirror; 28 Coincident focus; 29 Annular beam incident hole, 30 Objective lens aperture. Detailed implementation manner

[0041] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. The present invention includes but is not limited to the following embodiments.

[0042] In this embodiment, the autofocus scanning imaging device based on the bright and dark field confocal objective lens includes: a spatial modulation illumination module, a bright and dark field confocal objective lens, an annular beam differential confocal module, a dark field confocal detection module, and a bright field differential interference contrast imaging module; wherein, the spatial modulation illumination module is used to generate a collimated annular beam; the bright and dark field confocal objective lens is used to focus the collimated annular beam on the sample surface to form a dark field diffraction-limited illumination, and collect the dark field scattered light of the sample surface and subsurface defects; the annular beam differential confocal module is used to split the annular beam reflected from the sample surface into two defocused beams, obtain two defocus signals, and obtain an annular light differential confocal signal after differential, which is used to realize the autofocus of the sample surface; the dark field confocal detection module is used to receive the dark field scattered light of the sample surface and subsurface defects; the bright field differential interference contrast imaging module is used to perform bright field imaging on the surface and subsurface defects detected by the dark field confocal detection module to achieve a relief imaging effect, so as to facilitate the judgment of defect characteristics.

[0043] See Figure 1 、 Figure 2 and Figure 3 In this embodiment, the specific implementation measures include:

[0044] The spatial modulation illumination module sequentially includes, in the light propagation direction: a laser light source 1, a collimating and homogenizing converter 2, and a spatial light modulator 3; the collimating and homogenizing converter 2 generates a collimated flat-top light from the Gaussian beam emitted by the laser light source 1 and irradiates it onto the spatial light modulator 3, and obtains a collimated annular beam through spatial modulation for dark field illumination.

[0045] The bright and dark field confocal objective lens sequentially includes, in the light propagation direction: a hollow beam splitter 4, a parabolic mirror tube 5 for installing a parabolic mirror 27, and an objective lens 6; the diameter of the collimated annular beam generated by the spatial modulation illumination module is matched with the diameters of the hollow beam splitter 4 and the parabolic mirror 27.

[0046] An annular beam incident hole 29 and an objective lens light passing hole 30 are provided on the cover of the parabolic mirror barrel 5. The objective lens 6 is fixed inside the parabolic mirror barrel 5 to form a bright and dark field confocal objective lens; a parabolic mirror 27 is built in at the bottom end of the parabolic mirror barrel 5. The focal length of the parabolic mirror 27 is the same as that of the objective lens 6, and they have a coincident focal point 28; the annular beam incident hole 29 provided on the cover; the annular beam reflected by the hollow beam splitter 4 uses the annular beam incident hole 29 in the parabolic mirror barrel 5 as the light path; the hollow beam splitter 4 is used to reflect and transmit the annular beam and does not affect the beam passing through the objective lens 6.

[0047] The annular beam differential confocal module successively includes, in the light propagation direction: a compensating plate 9, a first lens 11, a first beam splitter 12, a first pinhole 13, a first photodiode 15, a second pinhole 14, and a second photodiode 16; the compensating plate 9 is used to correct the optical axis offset caused by the hollow beam splitter 4. The thickness of the compensating plate needs to be consistent with that of the hollow beam splitter 4, and the placement angles are complementary to ensure that the optical axis does not shift; the beam focused by the first lens 11 is split into two beams by the first beam splitter 12 and respectively passes through the first pinhole 13 and the second pinhole 14. Different defocus signals are received by using the first pinhole 13 and the second pinhole 14. The pre-focus signal is received by the first photodiode 15, and the post-focus signal is received by the second photodiode 16. The two defocus signals are differentiated to achieve differential confocal.

[0048] The elliptical mirror 10 is fixed on the compensating plate 9, and the placement position does not affect the annular light. The projection of the dark field scattered light collected by the objective lens 6 on the plane of the compensating plate 9 is elliptical, and this projection is smaller than the aperture of the elliptical mirror 10 to ensure that the dark field scattered light is completely reflected.

[0049] The dark field confocal detection module successively includes, in the light propagation direction: a second beam splitter 17, a second lens 18, a third pinhole 19, and a photomultiplier tube 20.

[0050] The bright field differential interference contrast imaging module successively includes, in the light propagation direction: an illumination light source 24, a third beam splitter 23, a Wollaston prism 22, a third lens 21, and a area array camera 25.

[0051] The white light beam emitted by the illumination light source 24 is split into two linearly polarized lights with a certain separation angle and perpendicular vibration directions by the Wollaston prism 22. The diameter of the beam collimated by the third lens 21 is smaller than the diameter of the hollow part of the hollow beam splitter 4 to avoid the bright field illumination light interfering with the dark field illumination light.

[0052] See Figure 4 、 Figure 5 、 Figure 6 In this embodiment, the specific implementation measures for the automatic focusing and scanning strategy for the annular light include:

[0053] Figure 4 The difference between the measured signal of the annular beam in (a) and Figure 4 the simulated signal of the solid beam in (b) is due to the characteristics of the annular beam. In the same defocus interval, Figure 4 the signal in (a) changes faster and has a narrower peak, making the slope of the differential confocal signal at the zero-crossing point larger than that of the solid beam. According to the principle of differential confocal: the difference ΔI between the two defocus signals is linearly related to the offset z of the focal position, and the expression is ΔI = k*z; where: k is the slope of the straight line in the central part of the differential confocal signal of the annular light, which determines the focusing sensitivity and focusing accuracy.

[0054] As Figure 5 shown, the control of the z-axis motor is based on the linear segment at the zero-crossing point of the differential confocal signal of the annular light. Taking the zero point as the origin, the distance and direction of the defocus position relative to the origin can be calculated, and then the z-axis motor can be controlled to achieve autofocus. Since the parabolic mirror focuses the annular beam to the diffraction limit, the Figure 6 shown scanning strategy can be used to perform point-by-point scanning of the sample, and the scanning interval is 1 / e of the diffraction-limited focused spot 2 diameter.

[0055] As Figure 7 , in this embodiment, the autofocus scanning imaging method based on the bright and dark field confocal objective lens is carried out according to the following steps by using the Figure 1 shown autofocus scanning imaging device based on the bright and dark field confocal objective lens:

[0056] Step a: The Gaussian beam emitted by the laser light source 1 is adjusted into an annular beam with the same diameter as the diameter of the annular beam incident hole 29 provided on the cover of the parabolic mirror barrel 5 through the collimating and homogenizing converter 2 and the spatial light modulator 3;

[0057] Step b: The annular beam is reflected by the hollow beam splitter 4 to the bright and dark field confocal objective lens composed of the parabolic mirror barrel 5 and the objective lens 6, and is focused on the surface of the sample to be measured 7 by the parabolic mirror 27 provided in the parabolic mirror barrel 5;

[0058] Step c: The bright and dark field confocal objective lens is driven by the z-axis displacement platform 26 to approach the sample to be measured 7, and a reflected annular light beam is generated on the surface of the sample to be measured 7. After the reflected annular light beam is reflected by the parabolic mirror and then passes through the hollow beam splitter 4, the compensation plate 9 is used to correct the optical axis offset caused by the hollow beam splitter 4 to obtain the corrected annular light. The corrected annular light is converged by the first lens 11, and then split into two converging light beams by the first beam splitter 12. The pinhole 13 and the pinhole 14 are used to receive different defocus signals. The front focus signal of one of the converging light beams is received by the first photodiode 15, and the rear focus signal of the other converging light beam is received by the second photodiode 16. The two defocus signals are differentiated to form a differential confocal signal, and a straight line passing through the zero point is obtained. The zero point is the focusing position of the sample to be measured. The defocus position is calculated according to the differential confocal signal, and the z-axis displacement platform 26 is used to complete the focusing so that the differential confocal signal is zero;

[0059] Step d: After the focusing is completed, the photomultiplier tube 20 is turned on for dark field detection. The sample moving stage 8 is controlled to scan the sample to be measured 7 point by point according to the set scanning strategy. The scattered light generated by the surface and subsurface defects of the sample 7 is collected and collimated by the objective lens 6, passes through the hollow beam splitter 4, and is reflected by the elliptical mirror 10 and enters the dark field confocal detection module. After passing through the second beam splitter 17, the second lens 18, and the pinhole 19 in sequence, dark field confocal detection is realized. The scattered light is converted into a voltage signal by the photomultiplier tube 20, and the coordinate position and voltage signal of each scanning point are recorded at a certain sampling rate;

[0060] Step e: If it is necessary to observe a specified defect, the laser light source 1 and the photomultiplier tube 20 are turned off, and the illumination light source 24 and the area array camera 25 are turned on. The sample moving stage 8 drives the sample to be measured 7 to perform bright field interference contrast imaging at the defect position. Specifically, a white light beam is emitted by the illumination light source 24, and after being reflected by the third beam splitter 23, it is split into two linearly polarized light beams with perpendicular polarization directions by the Wollaston prism 22. After being collimated by the third lens 21, they are reflected by the second beam splitter 17 and the elliptical mirror 10 in sequence and enter the objective lens 6, and are focused on the surface of the sample 7 to generate bright field illumination light;

[0061] Step f: The bright field illumination light passes through the objective lens 6, the elliptical mirror 10, the second beam splitter 17, the third lens 21, and the Wollaston prism 22 in sequence, and then is transmitted by the third beam splitter 23 to the area array camera 25 to realize bright field differential interference contrast imaging.

[0062] In this embodiment, the wavelength of the laser beam emitted by the laser light source 1 is 532 nm; the diameters of the pinhole 13 and the pinhole 14 are set to D0, the diameter of the pinhole 19 is D1,

[0063] where, D H is the outer diameter of the annular light incident on the first lens 11, DB is the dark-field scattered light diameter incident on the second lens 18, λ is the laser wavelength, f1 is the focal length of the first lens 11, and f2 is the focal length of the second lens 18.

[0064] When the pinhole diameter is equal to the beam waist diameter, the slope of the differential confocal signal is the largest. The focusing of the annular beam is calculated according to the Gaussian beam focusing.

[0065] The above content is only an example and explanation of the structure of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the described specific embodiments or use similar methods for substitution. As long as they do not deviate from the structure of the invention or exceed the scope defined by this claims, they should fall within the protection scope of the present invention.

Claims

1. An automatic focus scanning imaging device for a bright and dark field confocal objective lens, characterized in that: It includes a spatial modulation illumination module, a bright and dark field confocal objective lens, an annular beam differential confocal module, a dark field confocal detection module and a bright field differential interference contrast imaging module; The spatial modulation illumination module is used to generate a collimated annular light beam; The bright and dark field confocal objective is used to focus the collimated annular light beam onto the sample surface to form dark field diffraction-limited illumination and collect dark field scattered light from the sample surface and sub-surface defects; The annular beam differential confocal module is used to split the collimated annular beam reflected by the sample surface into two defocused beams to obtain two defocused signals, and obtain an annular light differential confocal signal after differentiation to achieve automatic focusing on the sample surface; The dark field confocal detection module is used to receive dark field scattered light of sample surface and sub-surface defects; The bright field differential interference contrast imaging module is used to perform bright field imaging on the surface and sub-surface defects detected by the dark field confocal detection module.

2. The automatic focusing scanning imaging device of the bright and dark field confocal objective lens according to claim 1, characterized in that: The spatial modulation illumination module comprises, in order according to the light propagation direction: a laser light source (1), a collimated homogenizing converter (2) and a spatial light modulator (3); the collimated homogenizing converter (2) generates collimated flat-top light from a Gaussian light beam emitted by the laser light source (1) and irradiates the collimated flat-top light to the spatial light modulator (3), thereby obtaining a collimated annular light beam through spatial modulation.

3. The automatic focusing scanning imaging device of the bright and dark field confocal objective lens according to claim 2, characterized in that: The bright and dark field confocal objective lens comprises, in order according to the light propagation direction: a hollow beam splitter (4), a parabolic lens barrel (5) for mounting a parabolic reflector (27), and an objective lens (6); the diameter of the collimated annular light beam generated by the spatial modulation illumination module matches the diameters of the hollow beam splitter (4) and the parabolic reflector (27).

4. The automatic focus scanning imaging device based on bright and dark field confocal objective lens according to claim 3, characterized in that: An annular beam incident hole (29) and an objective lens light hole (30) are arranged on the tube cover of the parabolic lens tube (5), and the objective lens (6) is fixed in the tube of the parabolic lens tube (5) to form a bright and dark field confocal objective lens; a parabolic reflector (27) is built into the bottom end of the parabolic lens tube (5), the focal length of the parabolic reflector (27) is the same as the focal length of the objective lens (6), and the two have overlapping focal points (28); the annular beam incident hole (29) is arranged on the tube cover; the collimated annular beam reflected by the hollow beam splitter (4) uses the annular beam incident hole (29) in the parabolic lens tube (5) as a light channel; the hollow beam splitter (4) is used to reflect and transmit dark field illumination light, and does not affect the beam passing through the objective lens (6).

5. The automatic focus scanning imaging device based on bright and dark field confocal objective lens according to claim 4, characterized in that: The annular beam differential confocal module comprises, in order according to the light propagation direction: a compensation plate (9), a lens 1 (11), a beam splitter 1 (12), a pinhole 1 (13), a photodiode 1 (15), a pinhole 2 (14) and a photodiode 2 (16); the compensation plate (9) is used to correct the optical axis deviation caused by the hollow beam splitter (4); the beam splitter 1 (12) splits the light beam focused by the lens 1 (11) into two beams, which respectively pass through the pinhole 1 (13) and the pinhole 2 (14); the pinhole 1 (13) and the pinhole 2 (14) receive different defocus signals; the photodiode 1 (15) receives the pre-focus signal; the photodiode 2 (16) receives the post-focus signal; the two defocus signals are differentiated to realize differential confocal.

6. The automatic focus scanning imaging device based on bright and dark field confocal objective lens according to claim 5, characterized in that: The dark field confocal detection module comprises, in order according to the light propagation direction: a second beam splitter (17), a second lens (18), a third pinhole (19) and a photomultiplier tube (20).

7. The automatic focus scanning imaging device based on bright and dark field confocal objective lens according to claim 6, characterized in that: The bright field differential interference contrast imaging module comprises, in order according to the light propagation direction: an illumination light source (24), a third beam splitter (23), a Wollaston prism (22), a third lens (21) and a planar array camera (25); The white light beam emitted by the illumination light source (24) is split into two beams of linearly polarized light with a certain separation angle and mutually perpendicular vibration directions by a Wollaston prism (22); the diameter of the white light beam after being collimated by lens three (21) is smaller than the diameter of the hollow portion of the hollow beam splitter (4), thereby preventing the bright field illumination light from interfering with the dark field illumination light.

8. An autofocus scanning imaging method based on a bright and dark field confocal objective lens, characterized in that: The automatic focus scanning imaging device based on the bright and dark field confocal objective lens as described in claim 7 is adopted, and the following steps are performed: Step a, the Gaussian beam emitted by the laser light source (1) is adjusted by the collimating uniform converter (2) and the spatial light modulator (3) to be an annular beam having a diameter equal to the diameter of the annular beam incident hole (29) provided on the tube cover of the parabolic lens tube (5); Step b, the annular light beam is reflected by the hollow beam splitter (4) to a bright and dark field confocal objective lens composed of a parabolic lens barrel (5) and an objective lens (6), and is focused by a parabolic reflector (27) disposed in the parabolic lens barrel (5) to the surface of the sample to be tested (7); Step c, driving the bright and dark field confocal objective lens by the z-axis displacement platform (26) to approach the sample to be measured (7), generating a reflected annular light beam on the surface of the sample to be measured (7), the reflected annular light beam passing through the parabolic reflector and then passing through the hollow beam splitter (4), using the compensation plate (9) to correct the optical axis deviation caused by the hollow beam splitter (4), obtaining a corrected annular light, the corrected annular light is converged by the lens one (11), and then divided into two beams of converged light by the beam splitter one (12), using the pinhole one (13) and the pinhole two (14) to receive different defocus signals, the photodiode one (15) receiving the pre-focus signal of one of the converged lights, the photodiode two (16) receiving the post-focus signal of the other of the converged lights, differentiating the two defocus signals to form a differential confocal signal, obtaining a straight line passing through the zero point, the zero point being the focus position of the sample to be measured, calculating the defocus position according to the differential signal, and completing the focus by the z-axis displacement platform (26); Step d, controlling the sample moving stage (8) to perform a transverse scan on the sample to be tested (7) according to a set scanning strategy, the scattered light generated by the surface and sub-surface defects of the sample (7) is collected and collimated by the objective lens (6) and passes through the hollow beam splitter (4), is reflected by the elliptical reflector (10) and enters the dark field confocal detection module, and then is transmitted through the beam splitter second (17), is focused by the lens second (18), and passes through the pinhole third (19) to realize confocal detection, and the scattered light is converted into a voltage signal by the photomultiplier tube (20) to realize dark field scattering defect detection; Step e, the sample moving stage (8) drives the sample to be tested (7) to perform bright field imaging observation at the defect position. The bright field imaging observation is performed by emitting a white light beam from the illumination light source (24), which is reflected by the third beam splitter (23) and then split by the Wollaston prism (22) into two beams of linear polarized light with mutually perpendicular vibration directions. After being collimated by the third lens (21), the beams are sequentially reflected by the second beam splitter (17) and the elliptical reflector (10) and enter the objective lens (6) to focus on the surface of the sample to be tested (7), and the surface of the sample to be tested (7) generates bright field illumination light; Step f, the bright field illumination light passes through the objective lens (6), the elliptical reflector (10), the second beam splitter (17), the third lens (21), and the Wollaston prism (22) in sequence, and then is transmitted to the area array camera (25) by the third beam splitter (23) to achieve bright field differential interference contrast imaging.

9. The auto-focus scanning imaging method based on bright and dark field confocal objective lens according to claim 8, characterized in that: The diameters of pinhole 1 (13) and pinhole 2 (14) are set to D0, The diameter of pinhole three (19) is D1, Among them, D H is the outer diameter of the annular light incident on lens 1 (11), D B is the diameter of the dark field scattered light incident on lens 2 (18), λ is the laser wavelength, f1 is the focal length of lens 1 (11), and f2 is the focal length of lens 2 (18).

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