Image quality detection system for bright field microscopic imaging

Abstract

The invention provides a bright-field microscopic imaging quality detection system, which belongs to the field of imaging quality detection and comprises an imaging optical module, a bright-field illumination optical module, a carrier and an image quality detection nano-point mechanism. The imaging optical module is arranged above the carrying table, and the imaging optical module collects an image of the image quality detection nano-point mechanism on the carrying table to realize image quality detection; the image quality detection nanodot mechanism comprises a nanostructure scatterer and a substrate. According to the invention, by designing the illumination pupil and the nanodot mechanism, a P polarized light Brewster angle illumination mode is realized, the adverse effect of the secondary reflected light of the substrate on the signal-to-noise ratio of the image is filtered out, the serious influence of the reflected light of the substrate on the signal-to-noise ratio of the image in the point spread function measurement based on nanostructure imaging is reduced, and the measurement accuracy is improved. And the signal-to-noise ratio of online image quality detection is improved. The system can be popularized and applied in the fields requiring on-line image quality detection, such as microscopic imaging, nanoscale semiconductor quantity detection, overlay quantity detection and the like.

Description

Technical Field

[0001] The present invention belongs to the field of imaging quality detection, and in particular relates to a bright field microscopic imaging quality detection system. Background Art

[0002] In the field of image quality testing in microscopic imaging systems, particularly in brightfield microscopy systems with large numerical aperture and wide field of view objectives, online image quality testing faces challenges such as high integration difficulties, weak detection signals, and difficulty filtering out interfering stray light. These issues result in low precision and repeatability in image quality testing results, making online high-throughput testing difficult. This severely limits the industrialization and integration of high-performance brightfield microscopy systems. In microscopic imaging system image quality testing, measurement and analysis of the system's point spread function (PSF) can provide intuitive and highly accurate evaluation results. PSF analysis relies on imaging and measuring a near-ideal point radiation source on the system's object plane. In brightfield microscopy systems, point radiation sources can be realized by illuminating nanostructures, allowing their scattering field to be approximated by that of a point source. This approach also offers the significant advantage of online, real-time measurement. In conventional brightfield microscopy systems, the signal-to-noise ratio (SNR) of such nanostructures is low. This is primarily due to the strong light reflected from the substrate, which acts as an interfering signal and reduces the SNR of the scattered light imaging of the nanostructures. Therefore, in the online measurement of the point spread function of bright-field microscopy systems, it is of great significance to improve the imaging signal-to-noise ratio of nanostructures. Summary of the Invention

[0003] In order to overcome the deficiencies of the prior art, the present invention aims to provide a bright field microscopic imaging image quality detection system that can solve the above-mentioned problems.

[0004] Design principle: In a bright-field microscopy system, a point radiation source on the object surface can be realized by illuminating and exciting the nanostructure. Its scattering field can be approximated as a point source radiation field, and it also has the significant advantage of being able to be measured online in real time. Secondly, the substrate is coated (highly reflective film) in the non-imaging area to reduce interference signals from the nanostructure above. Finally, the image quality of the microscopy system is detected through a bright-field microscopy image quality detection system based on the point spread function high signal-to-noise ratio measurement method.

[0005] A brightfield microscopic imaging image quality detection system includes an imaging optical module, a brightfield illumination optical module, a carrier and an image quality detection nano-dot mechanism; the imaging optical module is arranged above the carrier, the brightfield illumination optical module provides illumination to the image quality detection nano-dot mechanism on the carrier through an illumination light path module, and the imaging optical module realizes online image quality detection by collecting images of the image quality detection nano-dot mechanism.

[0006] Furthermore, the imaging optical module includes an imaging unit, a tube lens group and an objective lens group, and the imaging unit receives the collected light of the tube lens group and the objective lens group to realize image acquisition; a variable illumination pupil diaphragm with adjustable polarization, adjustable aperture position and size is set on the illumination pupil plane of the illumination optical path module.

[0007] Furthermore, the bright field illumination optical module is connected to the imaging optical module through the illumination optical path module; a semi-transparent and semi-reflective mirror is provided in the imaging optical module to achieve coupling of the illumination and imaging optical paths.

[0008] Furthermore, the polarization direction modulated by the variable illumination pupil diaphragm, that is, the polarization state of the illumination pupil plane includes x-direction polarization, y-direction polarization or radial linear polarization.

[0009] Furthermore, the image quality detection nano-dot mechanism includes a nano-structured scatterer and a substrate, high-reflective coatings are provided on the upper and lower surfaces of the substrate, and an imaging area without high-reflective coating is provided in the middle of the upper surface of the substrate, and the nano-structured scatterer is provided in the imaging area.

[0010] Furthermore, one or more imaging areas are provided on the upper surface of the substrate, and one or more nanostructured scatterers are provided in the imaging areas.

[0011] Compared with the existing technology, the beneficial effects of the present invention are: this application realizes the Brewster angle illumination mode of P-polarized light by designing the illumination pupil and the nanodot mechanism, and further filters out the adverse effects of the secondary reflected light of the substrate on the image signal-to-noise ratio, significantly reducing the serious influence of the substrate reflected light on the image signal-to-noise ratio in the point spread function measurement based on nanostructure imaging, and significantly improving the signal-to-noise ratio of the online image quality detection of the bright field microscopy imaging system. The system can be promoted and applied in fields requiring image quality detection, such as microscopy imaging, nano-scale semiconductor quantity detection, and overlay quantity detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Schematic diagram of a bright field microscopy image quality detection system of the present invention; Figure 2 Schematic diagram of the nano-dot mechanism for image quality detection; Figure 3 An example diagram of the layout of a nanostructured scatterer having a circular cross section in the imaging area of ​​the image quality detection nanodot mechanism; Figure 4 An example diagram of the layout of a nanostructured scatterer having a rectangular cross section in the imaging area of ​​the image quality detection nanodot mechanism; Figure 5 Schematic diagram of arranging two imaging areas for a substrate; Figure 6 Schematic diagram of the optical path of the nano-dot mechanism for image quality detection; Figure 7is the scattering far-field three-dimensional distribution diagram of the nanostructure scatterer; Figure 8 is the two-dimensional distribution diagram of the scattering far field of the nanostructure scatterer; Figure 9 is the reflectivity curve of the substrate; Figure 10 Different forms of variable illumination pupil diaphragms.

[0013] In the picture: 1. Imaging unit; 2. Tube lens group; 3. Objective lens group; 4. Variable illumination pupil diaphragm; 5. Bright field illumination optical module; 6. Lighting optical path module; 7. Semi-transparent and semi-reflective mirror; 8. Carrier; 9. Image quality detection nano-dot mechanism; 11. Nanostructured scatterer; 12. Substrate; 13. High-reflective coating; 14. Imaging area. DETAILED DESCRIPTION

[0014] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0015] A bright field microscopy image quality detection system, see Figure 1 The bright field microscopy imaging image quality detection system includes an imaging optical module, a bright field illumination optical module 5, a stage 8 and an image quality detection nano-dot mechanism 9.

[0016] Layout relationship: The imaging optical module is arranged above the carrier 8, the bright field illumination optical module 5 provides illumination to the image quality detection nano-dot mechanism 9 on the carrier 8 through the illumination optical path module 6, and the imaging optical module realizes online image quality detection by collecting images of the image quality detection nano-dot mechanism.

[0017] A processor (not shown) performs high-signal-to-noise image quality measurement on the microscopic imaging system based on the point spread function (PSF). The PSF is collected by the system's imaging optics module as the scattered field of a single nanostructure by the image quality detection nanodot mechanism 9, and imaged for measurement. This measurement is based on the assumption that the scattered field of a single nanostructure can be equivalent to a relatively ideal point source radiation field, exhibiting a near-ideal uniform spherical wavefront within the numerical aperture of the objective lens. Therefore, in this solution, the brightfield microscopic imaging image quality detection system is designed such that the image quality detection nanodot mechanism 9, acting as the sample under test, is integrated into the brightfield microscopic imaging system, and the system's PSF measurement is performed by microscopically imaging the sample under test.

[0018] Among them, the imaging optical module includes an imaging unit 1, a tube lens group 2 and an objective lens group 3. The imaging unit 1 receives the collected light from the tube lens group 2 and the objective lens group 3 to realize image acquisition; a variable illumination pupil diaphragm 4 with adjustable polarization, aperture position and size is set on the illumination pupil plane of the illumination optical path module 6.

[0019] In one example, the bright field illumination optical module 5 is connected to the imaging optical module through the illumination optical path module 6; a semi-transparent and semi-reflective mirror 7 is provided in the imaging optical module to achieve coupling of the illumination and imaging optical paths.

[0020] The bright field illumination optical module 5 uses a wide spectrum ultraviolet and / or deep ultraviolet illumination light source, and realizes uniform bright field illumination through the illumination optical path module 6 and the objective lens group 3. In a specific example, Kohler illumination is used.

[0021] In this scheme, considering the bright field microscopy under Köhler illumination conditions, the illumination pupil is designed to achieve high purity P polarized light illumination of the sample to achieve the illumination conditions described above. In bright field microscopy systems, a specific polarization illumination mode is usually achieved by defining and modulating the polarization state of the light at the illumination pupil position. Figure 10 As shown, the polarization direction of the variable illumination pupil diaphragm 4 can be modulated to x-, y-, or radial polarization. Specifically, the polarization state of the light at the position of the variable illumination pupil diaphragm 4 can be modulated to x-, y-, and radial polarization states, respectively. To achieve high-purity p-polarized light illumination for the sample under test, specific aperture settings are required for the illumination pupil for each of these three polarization states. Figure 10 In the figure, the dotted circle corresponds to the Brewster angle position. The pupil area that satisfies P polarization illumination is determined on this dotted circle. Specifically, corresponding to the x, y, and radial linear polarization pupils, the positions of these areas are located on the x-axis, y-axis, and annular zone, respectively, as shown in Figure 2. Figure 10 The light-transmitting areas marked therein correspond to the variable illumination pupil diaphragms 4 which are light-transmitting aperture diaphragm shapes as shown in the figure.

[0022] The design of the sample under test involves two parameters: the material and shape of the nanostructure, and the material and shape of the substrate on which the nanostructure resides. The material and shape of the nanostructure are determined through physical models or numerical simulations and must satisfy a strong scattering effect and an ideally uniform spherical wavefront at the operating wavelength of the microscopic imaging system. The substrate material and shape must be designed to filter out reflected light from the substrate and prevent it from being collected by the microscopic imaging system. This ensures low substrate background noise in nanostructure imaging, improves the signal-to-noise ratio of the nanostructure scattering field imaging, and thus enhances the measurement and calculation accuracy of the point spread function.

[0023] Therefore, in this solution, the sample to be tested, that is, the image quality detection nano-dot mechanism 9 is designed to include a nano-structured scatterer (nano-scatter) 11 and a substrate 12 with a special coating design.

[0024] The cross section of the nanostructured scatterer 11 is circular ( Figure 3 ),rectangle( Figure 4 ), star or regular polygon, preferably a circle, to form a disk shape that is easy to process ( Figure 3 For disc, Figure 4 The dimensions of the nanostructured scatterer 11 were determined by numerical simulation, with the circumscribed diameter ranging from 100 nm to 180 nm. Currently used circumscribed diameters for the nanostructured scatterer 11 include 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, and 190 nm. Under ultraviolet / deep ultraviolet microscopic imaging wavelengths, diameters of 150 nm and 160 nm are more ideal.

[0025] The substrate 12 is a transparent flat plate. In the example shown, the substrate 12 is a transparent glass plate. In this solution, the most commonly used substrate 12, i.e., the base material is glass (refractive index 1.5). According to Fresnel's law, the reflectivity of P-polarized light and S-polarized light at different incident angles on the air-glass interface can be calculated, as shown in the following example: Figure 9 As shown. Figure 9 The reflectivity curve in Figure 2 shows that within an incident angle range of 50 to 60 degrees (near the Brewster angle), the reflectivity of P-polarized light is approximately 0.18 to 0.33%, which allows for extremely weak reflection from the glass substrate. Furthermore, the glass substrate has a certain thickness (H), and consideration must be given to the secondary reflection of P-polarized light at the glass-air interface on the lower surface after the high transmittance of the upper surface passes through it. This secondary reflection will then be collected again by the microscopic imaging system through the upper surface, where it will still constitute the main background stray light noise in bright-field imaging of nanostructures, affecting the signal-to-noise ratio of bright-field imaging of nanostructures.

[0026] To address this problem, this solution is designed as follows Figure 2 — Figure 6The substrate structure shown, considering the incident angle ( b ), glass substrate thickness (H), nanostructure imaging area size (W), and satisfy the relationship W< 2 *H* tan c ,in c Depend on b According to the law of refraction, b When the temperature is 50-60 degrees, c The range is 30 to 36 degrees. At the same time, it is necessary to coat the entire glass substrate with a high reflective film on the lower and upper surfaces of the glass substrate outside the nanostructure imaging area (W). That is, a high reflective film 13 is provided on the upper and lower surfaces of the substrate 12, and an imaging area 14 is provided in the middle of the upper surface of the substrate 12 without the high reflective film 13, and the nanostructure scatterer 11 is provided in the imaging area 14. In a specific example, the film thickness is marked as follows: Figure 2 As shown. The height of the nanostructured scatterers 11 is equal to the thickness of the high-reflective coating 13 on the upper surface of the substrate 12. Of course, the height of the nanostructured scatterers 11 can also be different from the thickness of the high-reflective coating 13 on the upper surface of the substrate 12. In the illustrated example, the side length of the imaging area 14 is 900 μm, the height of the nanostructured scatterers 11 and the thickness of the high-reflective coating 13 on the upper surface of the substrate 12 are both 100 nm, the thickness of the high-reflective coating 13 on the lower surface of the substrate 12 is 200 nm, the center-to-center spacing between adjacent nanostructured scatterers 11 is 20 μm, and the thickness of the substrate 12 is 775 μm.

[0027] Under the above design, P polarized light is b With the incident angle illumination, near the nanostructure area, the bright field microscopy system will only collect the scattered light of the nanostructure, and the P-polarized light illuminating the substrate area will pass through the upper surface and be guided to the far end in the light guide cavity composed of the high reflective film on the upper surface and the high reflective film on the lower surface, such as Figure 6 The light path is shown by the black arrow.

[0028] The calculated scattered wavefront of the nanostructured scatterer 11 satisfies the requirement that its scattered field angle range covers a wide numerical aperture range, and can be applied to bright field microscopy systems with large numerical aperture objectives. Specifically, when the nanostructured scatterer 11 is illuminated by a variable illumination pupil diaphragm 4 with X-axis polarization, the calculated far-field three-dimensional and two-dimensional distributions of the nanostructured scattering are shown in Figure 1. Figure 7 and Figure 8, with scattered light greater than NA0.9 in the yz plane and scattered light greater than NA0.8 in the xz plane.

[0029] One or more imaging areas 14 are provided on the upper surface of the substrate 12. Figure 5 Two imaging areas 14 are provided on a substrate 12, and the imaging areas 14 are rectangular or circular. Figure 3 and Figure 5 In the example, it is a square. Figure 4 The example is circular, and the nanostructured scatterers 11 with a circular cross section and a disk shape as a whole are arranged in a rectangular matrix in the square imaging area 14.

[0030] One or more nanostructure scatterers 11 are arranged in the imaging area 14. The multiple nanostructure scatterers 11 are arranged in a rectangular matrix ( Figure 3 ), ring matrix arrangement ( Figure 4 ) or randomly arranged, the distance between the multiple nanostructured scatterers 11 meets the near-field no-coupling condition.

[0031] Regarding materials: the nanostructured scatterer 11 is made of chromium (Cr), the substrate 12 is a transparent glass plate with a refractive index of 1.5, and the high-reflective coating 13 is a chromium film. Of course, the nanostructured scatterer 11 and the high-reflective coating 13 can also be made of other highly responsive materials.

[0032] In summary, this solution improves the signal-to-noise ratio (SNR) of online image quality testing using brightfield microscopy systems based on point spread function (PSF) measurements by employing specialized pupil modulation and designing the substrate of the sample being measured. This solution achieves Brewster angle illumination through pupil modulation, while also satisfying P-polarized light illumination. This significantly reduces the severe impact of substrate-reflected light on the image SNR during PSF measurements based on nanostructure imaging. Furthermore, the special design of the sample substrate further eliminates the adverse effects of secondary reflected light on the image SNR.

[0033] This solution is currently used for image quality detection in microscopic imaging systems and can be expected to be applied to scenarios such as semiconductor bright field measurement and overlay alignment measurement.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A bright field microscopic imaging image quality detection system, characterized by: The bright field microscopic imaging image quality detection system comprises an imaging optical module, a bright field illumination optical module (5), a carrier (8) and an image quality detection nano-dot mechanism (9); The imaging optical module is arranged above the carrier (8), and the bright field illumination optical module (5) provides illumination to the image quality detection nano-dot mechanism (9) on the carrier (8) through the illumination light path module (6). The imaging optical module realizes online image quality detection by collecting images of the image quality detection nano-dot mechanism; The imaging optical module comprises an imaging unit (1), a tube lens group (2) and an objective lens group (3), wherein the imaging unit (1) receives collected light from the tube lens group (2) and the objective lens group (3) to realize image acquisition; and a variable illumination pupil diaphragm (4) with adjustable polarization, adjustable aperture position and adjustable size is provided on the illumination pupil plane of the illumination light path module (6).

2. The bright field microscopy image quality detection system according to claim 1, characterized in that: The bright field illumination optical module (5) is connected to the imaging optical module via the illumination optical path module (6); a semi-transparent and semi-reflective mirror (7) is provided in the imaging optical module to achieve coupling of the illumination and imaging optical paths.

3. The bright field microscopy image quality detection system according to claim 1, characterized in that: The bright field illumination optical module (5) adopts an ultraviolet and / or deep ultraviolet broad spectrum illumination light source, and realizes uniform bright field illumination through the illumination light path module (6) and the objective lens group (3).

4. The bright field microscopy image quality detection system according to claim 1, characterized in that: The polarization direction modulated by the variable illumination pupil diaphragm (4), that is, the polarization state of the illumination pupil surface, includes x-direction polarization, y-direction polarization or radial linear polarization.

5. The bright field microscopy image quality detection system according to claim 1 or 4, characterized in that: The aperture stop position of the variable illumination pupil stop (4) corresponds to the modulated illumination direction of the x-direction polarization, y-direction polarization, and radial linear polarization of the illumination pupil plane, thereby realizing the Brewster angle illumination condition of the P-polarized light for the image quality detection nano-dot mechanism (9).

6. The bright field microscopy image quality detection system according to claim 1, characterized in that: The image quality detection nano-dot mechanism (9) comprises a nano-structured scatterer (11) and a substrate (12), wherein high-reflective coatings (13) are provided on the upper and lower surfaces of the substrate (12), and an imaging area (14) without the high-reflective coating (13) is provided in the middle of the upper surface of the substrate (12), wherein the nano-structured scatterer (11) is provided in the imaging area (14).

7. The bright field microscopy image quality detection system according to claim 6, characterized in that: When the nanostructured scatterer (11) is illuminated by the variable illumination pupil diaphragm (4) with X-direction deflection modulation, the nanostructured scatterer (11) has scattered light greater than NA0.9 in the yz plane and scattered light greater than NA0.8 in the xz plane, meeting the point spread function measurement conditions of the large NA microscopic imaging system.

8. The bright field microscopy image quality detection system according to claim 6, characterized in that: The materials of the nanostructured scatterer (11) and the high-reflective coating (13) are chromium.

9. The bright field microscopy image quality detection system according to claim 6, characterized in that: One or more imaging areas (14) are provided on the upper surface of a substrate (12), and one or more nanostructured scatterers (11) are provided in the imaging areas (14).

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