Imaging system and imaging method

Abstract

This invention relates to the field of semiconductor metrology, and more particularly to an imaging system and imaging method. The imaging system includes a beam splitter, a focusing element, a first detector, and a second detector. The beam splitter splits the signal light emitted from a marked area of ​​a sample into a first imaging light and a second imaging light, and guides the first imaging light into the first detector and the second imaging light into the second detector. The focusing element is disposed in the transmission optical path of the second imaging light. The marked area includes a current layer mark and a previous layer mark. While the first detector clearly images one of the current layer mark and the previous layer mark, the focusing element ensures that the second detector clearly images the other of the current layer mark and the previous layer mark. This invention is at least advantageous for achieving high-precision and rapid overlay measurements.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor measurement technology, and particularly relates to an imaging system and imaging method. Background Technology

[0002] Overlay error in wafers refers to the alignment error between the current layer and the previous layer. It is usually measured using a high-powered microscope. However, high-powered microscopes typically have a very small depth of focus, which cannot simultaneously and clearly image two markings with different heights. Therefore, when the height difference between the two markings exceeds a certain threshold, it is impossible to image both markings simultaneously with a single microscope. It is necessary to first use a camera to focus on and clearly image one of the current markings and the previous markings, and then use the camera to focus on and clearly image the other of the current markings and the previous markings. This not only seriously affects the measurement speed, but also places very high demands on the stability of the system. Summary of the Invention

[0003] In view of this, the present invention aims to provide an imaging system and imaging method that at least facilitates high-precision and rapid overlay measurement.

[0004] To achieve the above objectives, the technical solution created by this invention is implemented as follows: This invention provides an imaging system comprising: a beam splitter, a focusing element, a first detector, and a second detector. The beam splitter is used to split the signal light emitted from a marked area of ​​a sample into a first imaging light and a second imaging light, and guide the first imaging light into the first detector and guide the second imaging light into the second detector. The focusing element is disposed in the transmission optical path of the second imaging light. The marked area includes a current layer mark and a previous layer mark. While the first detector clearly images one of the current layer mark and the previous layer mark, the focusing element ensures that the second detector clearly images the other of the current layer mark and the previous layer mark.

[0005] Furthermore, the focusing element is a deformable mirror, and when the radius of curvature of the deformable mirror is the target radius of curvature, it satisfies the requirement that the second detector can clearly image the other of the current layer mark and the previous layer mark.

[0006] Furthermore, the imaging system also includes a telescope. The signal light passes through the telescope and is incident on the beam-splitting element. The radius of curvature of the target satisfies Formula 1, as follows: ; Where R is the target radius of curvature, Δu is the distance between the current layer mark and the previous layer mark in the optical axis direction, u is the object distance, d is the distance between the principal plane of the tube mirror and the principal plane of the deformable mirror object, and f1 is the focal length of the tube mirror.

[0007] Furthermore, the imaging system also includes a mounting structure, on which the beam splitter, focusing element, first detector, second detector, and tube lens are all mounted.

[0008] Furthermore, the optical path length from the tube mirror to the first detector is the same as the optical path length from the tube mirror to the second detector.

[0009] Furthermore, both the first and second detectors are located on the focal plane of the tube mirror on the side away from the sample.

[0010] Furthermore, the imaging system also includes an objective lens mounted on the mounting structure, through which the signal light sequentially passes and enters the beam splitter.

[0011] Furthermore, the deformable mirror is a convex mirror, and the first detector provides a clear image of the current layer marker, while the second detector provides a clear image of the previous layer marker.

[0012] Furthermore, the deformable mirror is a concave mirror, and the first detector provides a clear image of the previous layer marker, while the second detector provides a clear image of the current layer marker.

[0013] Furthermore, the deformable mirror is used to compensate for wavefront aberrations in the imaging optical path corresponding to the second detector.

[0014] This invention provides an imaging method, comprising: providing a sample having a marked region, the marked region including a current layer mark and a previous layer mark; providing the aforementioned imaging system, the imaging system including a beam splitter, a focusing element, a first detector, and a second detector, the beam splitter being used to split signal light emitted from the marked region into a first imaging light and a second imaging light, and guiding the first imaging light into the first detector and guiding the second imaging light into the second detector, the focusing element being disposed in the transmission optical path of the second imaging light; acquiring the interval distance between the current layer mark and the previous layer mark in the optical axis direction; adjusting the focusing element according to the interval distance, so that the first detector clearly images one of the current layer mark and the previous layer mark while the second detector clearly images the other of the current layer mark and the previous layer mark.

[0015] Furthermore, the imaging system also includes a mounting structure, on which the beam-splitting element, focusing element, first detector, and second detector are all mounted. Obtaining the distance between the current layer mark and the previous layer mark in the optical axis direction includes: moving the mounting structure so that one of the current layer mark and the previous layer mark is clearly imaged on the first detector; then moving the mounting structure at equal intervals along the optical axis direction, and during the movement of the mounting structure, the first detector continuously images the other of the current layer mark and the previous layer mark until the other of the current layer mark and the previous layer mark is clearly imaged on the first detector. The distance the mounting structure moves at equal intervals is the distance between the current layer mark and the previous layer mark in the optical axis direction.

[0016] Furthermore, the focusing element is a deformable mirror, and adjusting the focusing element according to the interval distance includes: determining the target radius of curvature according to the interval distance, and adjusting the radius of curvature of the deformable mirror to the target radius of curvature.

[0017] Furthermore, the imaging system also includes a tube mirror mounted on the mounting structure. The signal light passes through the tube mirror and is incident on a beam splitter. The radius of curvature of the target is determined based on the interval distance according to Formula 1, as follows: ; Where R is the target radius of curvature, Δu is the interval distance, u is the object distance, d is the distance between the principal plane of the tube mirror and the principal plane of the deformable mirror object, and f1 is the focal length of the tube mirror.

[0018] Furthermore, the deformable mirror is a convex mirror. After adjusting the focusing element according to the interval distance, the moving mounting structure is used to make the first detector clearly image the current layer mark, while the second detector clearly image the previous layer mark.

[0019] Furthermore, the deformable mirror is a concave mirror. After adjusting the focusing element according to the interval distance, the moving mounting structure is used to make the first detector clearly image the previous layer mark, while the second detector clearly image the current layer mark.

[0020] Compared with the prior art, the present invention can achieve the following beneficial effects: In the imaging system and imaging method provided by the present invention, when there is a height difference between the current layer mark and the previous layer mark, it is not necessary to set up a separate imaging device for the current layer mark and the previous layer mark. Instead, a single imaging system can be used to simultaneously and clearly image the current layer mark and the previous layer mark.

[0021] Specifically, this invention splits the signal light emitted from the marked area into a first imaging light and a second imaging light. A second detector images one of the current layer mark and the previous layer mark based on the second imaging light, and a first detector images the other of the current layer mark and the previous layer mark based on the first imaging light. A focusing element is placed in the transmission optical path of the second imaging light. The focusing element is adjusted according to the distance between the current layer mark and the previous layer mark, and the object distance of the imaging channel in which the focusing element is located is adjusted. This allows the first detector to clearly image one of the current layer mark and the previous layer mark, while the second detector can also clearly image the other of the current layer mark and the previous layer mark, avoiding repeated focusing operations. In other words, the focusing position can be adaptively adjusted according to the height difference between the two layers of marks, thereby achieving high-precision and fast measurement.

[0022] This invention overcomes the limitations of traditional high-magnification microscopes with their shallow depth of focus. It eliminates the need for time-division focusing and, by adjusting the focal length of a single channel using a deformable mirror, allows for simultaneous clear images of the current and preceding layers of the wafer (two thick resist layers with a height difference) from two cameras. This completely changes the traditional separate focusing and time-division acquisition method. Based on the actual height difference between the current and preceding layers (obtained through process menu presets or calibration), the curvature radius of the deformable mirror (and thus its focal length) can be adjusted to precisely adapt to different height difference scenarios. No manual adjustment of the mechanical structure is required, resulting in greater adaptability. Furthermore, the deformable mirror combines focal plane adjustment and aberration correction functions, compensating for wavefront aberrations in the imaging system, particularly addressing aberration degradation during off-focal plane imaging, optimizing image clarity and resolution, and providing a higher-quality image foundation for subsequent overlay error measurements. Attached Figure Description

[0023] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram of the imaging system described in an embodiment of the present invention. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0026] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0027] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] refer to Figure 1 This invention provides an imaging system and an imaging method.

[0030] The imaging system provided by this invention includes: a beam splitter 15, a focusing element 14, a first detector 12, and a second detector 13. The beam splitter 15 is used to split the signal light emitted from the marked area of ​​the sample into a first imaging light and a second imaging light, and guide the first imaging light into the first detector 12 and guide the second imaging light into the second detector 13. The focusing element 14 is disposed in the transmission optical path of the second imaging light. The marked area includes a current layer mark and a previous layer mark. While the first detector 12 clearly images one of the current layer mark and the previous layer mark, the focusing element 14 ensures that the second detector 13 clearly images the other of the current layer mark and the previous layer mark.

[0031] In some embodiments, the beam-splitting element may be a beam-splitting prism.

[0032] Furthermore, the focusing element 14 is a deformable mirror. When the radius of curvature of the deformable mirror is the target radius of curvature, it satisfies the requirement that the second detector 13 can clearly image the other of the current layer mark and the previous layer mark.

[0033] Furthermore, the imaging system also includes a lens 16, through which the signal light is incident on the beam-splitting element, and the radius of curvature of the target satisfies Formula 1, as follows: ; Where R is the target radius of curvature, Δu is the distance between the current layer mark and the previous layer mark in the optical axis direction, u is the object distance, d is the distance between the image principal plane of the tube lens 16 and the object principal plane of the deformable mirror, and f1 is the focal length of the tube lens 16.

[0034] Furthermore, the imaging system also includes a mounting structure 18, on which the beam splitter 15, the focusing element 14, the first detector 12, the second detector 13, and the tube lens 16 are all mounted.

[0035] In some examples, mounting structure 18 can be a mounting plate.

[0036] Furthermore, the optical path length from the lens 16 to the first detector 12 is the same as the optical path length from the lens 16 to the second detector 13.

[0037] Furthermore, both the first detector 12 and the second detector 13 are located on the focal plane of the tube lens 16 away from the sample. Ensuring that both the first and second detectors are on the focal plane of the tube lens away from the sample, and that the image distances of the two imaging channels are completely consistent, avoids the problem of "different imaging sharpness benchmarks for the two channels at the same object distance" caused by image distance differences. If the optical path lengths are different, even for the same mark, the sharp imaging conditions of the two detectors will have inherent deviations, making it impossible to compensate for the height difference between the two layers of marks separately using the focusing element. When the image distances of the two imaging channels are completely consistent, it is only necessary to precisely adjust the focusing element according to the interval between the current layer and the previous layer of marks to adapt to the focusing requirements, without needing to compensate for both the height difference and the image distance deviation. This helps reduce computational complexity and adjustment errors, making the adjustment of the focusing element more direct and faster, and adapting to the needs of rapid overlay measurement. Furthermore, having the same optical path length means that the installation positions of the two detectors can be located based on the same reference (the focal plane position of the tube lens), eliminating the need to separately calibrate the attitude and position of detectors corresponding to different image distances. This helps reduce assembly and adjustment steps and accumulated errors. In addition, the same optical path length makes it easier to keep the optical characteristics (such as magnification and distortion) of the two imaging channels consistent, avoiding measurement deviations caused by differences in characteristics between channels.

[0038] Furthermore, the imaging system also includes an objective lens 17 mounted on the mounting structure 18, and the signal light passes through the objective lens 17 and the tube lens 16 in sequence before entering the beam splitter 15.

[0039] Furthermore, the deformable mirror is a convex mirror, and the first detector provides a clear image of the current layer marker, while the second detector provides a clear image of the previous layer marker.

[0040] Furthermore, the deformable mirror is a concave mirror, and the first detector provides a clear image of the previous layer marker, while the second detector provides a clear image of the current layer marker.

[0041] Furthermore, the deformable mirror is used to compensate for wavefront aberrations in the imaging optical path corresponding to the second detector.

[0042] Using a deformable mirror as the focusing element 14, the focusing position can be changed by adjusting the radius of curvature of the deformable mirror, which can accurately adapt to different working conditions without the need for manual adjustment of the mechanical structure. This achieves adaptive adjustment of the focusing position, reducing operational complexity. In addition, the deformable mirror can compensate for wavefront aberrations in the imaging system, especially improving aberration problems in off-focal plane imaging, making the image clearer. The clear imaging effect is conducive to directly improving the accuracy of overlay error measurement and meeting the requirements of high-precision detection.

[0043] The imaging system provided by this invention significantly improves measurement efficiency. Specifically, it eliminates the repetitive steps of "focusing-acquiring-switching focal planes-refocusing-reacquiring" in traditional time-division imaging, using simultaneous acquisition from two focal planes in a single operation. This significantly shortens the measurement cycle for overlay errors and solves the problem of slow measurement speed. This invention also reduces the requirements for system stability. Traditional time-division imaging relies on repeated mechanical movement for focusing, placing extremely high demands on equipment stability and vibration control. This invention adjusts the focal length using a deformable mirror, reducing the frequency of mechanical movements and decreasing the system's dependence on environmental vibration and mechanical precision, thus improving the stability and repeatability of the measurement process. Finally, this invention improves the accuracy of overlay error measurement, primarily through two aspects: first, simultaneous imaging from two focal planes avoids errors such as mechanical drift and environmental interference that may occur during time-division acquisition; second, wavefront aberration compensation improves image quality, making the edges and details of the markings clearer, providing more accurate image data support for error calculation.

[0044] The imaging method provided by the invention includes: providing a sample having a marked area, the marked area including a current layer mark and a previous layer mark, the current layer mark being the mark located in the current layer 11 and the previous layer mark being the mark located in the previous layer 10; providing the aforementioned imaging system, the imaging system including a beam splitter 15, a focusing element 14, a first detector 12 and a second detector 13, the beam splitter 15 being used to split the signal light emitted from the marked area into a first imaging light and a second imaging light, and guiding the first imaging light into the first detector 12 and guiding the second imaging light into the second detector 13, the focusing element 14 being disposed in the transmission optical path of the second imaging light; obtaining the interval distance between the current layer mark and the previous layer mark in the optical axis direction; adjusting the focusing element 14 according to the interval distance, so that the first detector 12 clearly images one of the current layer mark and the previous layer mark while the second detector 13 clearly images the other of the current layer mark and the previous layer mark.

[0045] Furthermore, the imaging system also includes a mounting structure 18, on which the beam-splitting element 15, focusing element 14, first detector 12, and second detector 13 are all mounted. Obtaining the distance between the current layer mark and the previous layer mark in the optical axis direction includes: moving the mounting structure 18 so that one of the current layer mark and the previous layer mark is clearly imaged on the first detector 12; then moving the mounting structure 18 at equal intervals along the optical axis direction. Specifically, the mounting structure 18 can be controlled to move away from the sample or towards the sample. During the movement of the mounting structure 18, the first detector 12 continuously images the other of the current layer mark and the previous layer mark. Specifically, the first detector 12 performs one image for each step the mounting structure 18 moves, until the other of the current layer mark and the previous layer mark is clearly imaged on the first detector 12. The distance the mounting structure 18 moves at equal intervals is the distance between the current layer mark and the previous layer mark in the optical axis direction. This helps ensure that the imaging channel corresponding to the first imaging light and the imaging channel corresponding to the second imaging light have the same image distance. As a result, the adjustment degree of the focusing element 14 can be determined directly based on the height difference or interval between the current layer mark and the previous layer mark. This helps to improve adjustment efficiency and reduce adjustment difficulty, and also helps to reduce the assembly and adjustment difficulty of the imaging system.

[0046] Furthermore, the imaging system also includes a lens 16 mounted on the mounting structure 18. The signal light passes through the lens 16 and is incident on the beam splitter 15. The optical path length from the lens 16 to the first detector 12 is the same as the optical path length from the lens 16 to the second detector 13. Furthermore, both the first detector 12 and the second detector 13 are located on the focal plane of the lens 16 away from the sample.

[0047] Furthermore, the imaging system also includes an objective lens 17 mounted on the mounting structure 18, and the signal light passes through the objective lens 17 and the tube lens 16 in sequence before entering the beam splitter 15.

[0048] Furthermore, the focusing element 14 is a deformable mirror, and adjusting the focusing element 14 according to the interval distance includes: determining the target radius of curvature according to the interval distance, and adjusting the radius of curvature of the deformable mirror to the target radius of curvature.

[0049] Adjusting the radius of curvature of the deformable mirror is equivalent to adjusting its focal length f2, thereby adjusting the overall focal length f of the imaging channel containing the deformable mirror. This is based on the Gaussian formula. Where f is the overall focal length of the imaging channel where the deformable mirror is located, u is the object distance when the deformable mirror is not set, that is, the distance from objective lens 17 to the sample, and v is the image distance. When the back intercept of the imaging channel where the deformable mirror is located remains unchanged, the image distance v can be approximated as unchanged. When the focal length f is changed, the corresponding object distance u changes, that is, the focusing position changes. It can be seen that the change in focusing position Δu (that is, the aforementioned height difference or interval distance) can be regarded as the dependent variable of the focal length f2 of the deformable mirror, and there is a corresponding relationship between the two.

[0050] The derivation of the relationship between the change in focusing position Δu and the focal length f2 of the deformable mirror is as follows: According to the formula for the optical power of a combined lens, the total optical power P of the system composed of the tube lens 16 and the deformable mirror satisfies the following formula. ,in, , The focal length of the tube lens 16 It is a known quantity. f2 is the focal length of the deformable mirror, and d is the distance between the image-side principal plane of the tube lens 16 and the object-side principal plane of the deformable mirror. When the deformable mirror is being focused... The change occurs, and the amount of change is... The corresponding P also changes, and the change is... The correspondence is as follows: According to Gauss's formula, taking the differential of both sides and simplifying, we get... Combining the aforementioned formula, we can obtain Then, according to the focal length formula of a spherical mirror... This allows us to derive the relationship between the defocusing amount Δu (interval distance) and the radius of curvature R of the deformable mirror. .

[0051] Furthermore, the target radius of curvature is determined based on Formula 1 according to the interval distance. Formula 1 is as follows: ; Where R is the target radius of curvature, Δu is the interval distance, u is the object distance, d is the distance between the image principal plane of the tube lens 16 and the object principal plane of the deformable mirror, and f1 is the focal length of the tube lens 16.

[0052] Furthermore, the deformable mirror is a convex mirror. After adjusting the focusing element 14 according to the interval distance, the moving mounting structure 18 is used to make the first detector 12 clearly image the current layer mark, while the second detector 13 clearly image the previous layer mark.

[0053] Furthermore, the deformable mirror is a concave mirror. After adjusting the focusing element 14 according to the interval distance, the moving mounting structure 18 is used to make the first detector 12 clearly image the previous layer mark, while the second detector 13 clearly image the current layer mark.

[0054] Furthermore, since there is a height difference between the current layer marker and the previous layer marker, they cannot both be located on the focal plane of the objective lens 17. However, the objective lens 17 is usually used for aberration correction on the focal plane. When imaging on a non-focal plane, its aberration performance cannot reach the optimal state. Therefore, in some embodiments, the wavefront aberration of the imaging system can be measured, and at the same time, the wavefront aberration of the imaging channel where the deformable lens is located can be compensated using a deformable lens, thereby ensuring that both imaging channels have high imaging quality.

[0055] The imaging method provided by this invention splits the signal light into two paths using a beam splitter. The first detector directly and clearly images one layer of the marker, while the second detector, with the help of a deformable mirror's precise focusing, simultaneously captures a clear image of the other layer of the marker. This eliminates the need for repeated mechanical focusing movements, significantly reducing the single measurement cycle, making it particularly suitable for wafer batch inspection scenarios. During assembly and adjustment, only the reference position needs to be calibrated once, eliminating the need to calibrate the optical parameters of two separate systems, greatly reducing assembly and adjustment time. Furthermore, the deformable mirror's lack of mechanical wear (compared to traditional mechanical focusing mechanisms) extends the equipment's lifespan, helping to shorten maintenance cycles and reduce maintenance costs. Additionally, environmental temperature fluctuations and mechanical vibrations can cause transmission... Traditional solutions suffer from optical element positional shifts, leading to measurement errors. In this invention, core components such as the beam splitter, deformable mirror, and detector are integrated into the same mounting structure, reducing the impact of relative displacement between components. The dynamic adjustment capability of the deformable mirror can compensate for aberration drift caused by environmental interference in real time, giving the system high stability and accuracy. Frequent mechanical focusing in traditional solutions leads to wear on the stage and lens drive mechanism, and also introduces thermal drift (the heat generated by mechanical movement affects the stability of optical elements). This solution only requires equal-step movement when acquiring the interval distance, and subsequent measurements do not require mechanical adjustment, reducing equipment wear and avoiding measurement interruptions caused by thermal drift.

[0056] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0057] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. An imaging system, characterized in that, include: The system includes a beam splitter, a focusing element, a first detector, and a second detector. The beam splitter is used to split the signal light emitted from the marked area of ​​the sample into a first imaging light and a second imaging light, and guide the first imaging light into the first detector and guide the second imaging light into the second detector. The focusing element is disposed in the transmission optical path of the second imaging light. The marked area includes a current layer mark and a previous layer mark. While the first detector clearly images one of the current layer mark and the previous layer mark, the focusing element satisfies the requirement that the second detector clearly images the other of the current layer mark and the previous layer mark.

2. The imaging system according to claim 1, characterized in that, The focusing element is a deformable mirror. When the radius of curvature of the deformable mirror is the target radius of curvature, the second detector can clearly image the other of the current layer mark and the previous layer mark.

3. The imaging system according to claim 2, characterized in that, The imaging system also includes a tube mirror, through which the signal light enters the beam-splitting element. The radius of curvature of the target satisfies Formula 1, as follows: ； Where R is the target radius of curvature, Δu is the distance between the current layer mark and the previous layer mark in the optical axis direction, u is the object distance, d is the distance between the principal plane of the tube mirror and the principal plane of the deformable mirror object, and f1 is the focal length of the tube mirror.

4. The imaging system according to claim 3, characterized in that, The imaging system also includes a mounting structure, on which the beam splitter, the focusing element, the first detector, the second detector, and the tube lens are all mounted.

5. The imaging system according to claim 3, characterized in that, The optical path length from the tube mirror to the first detector is the same as the optical path length from the tube mirror to the second detector.

6. The imaging system according to claim 3, characterized in that, Both the first detector and the second detector are located on the focal plane of the tube mirror on the side away from the sample.

7. The imaging system according to claim 4, characterized in that, The imaging system also includes an objective lens disposed on the mounting structure, and the signal light passes through the objective lens and the tube lens in sequence before entering the beam splitter.

8. The imaging system according to claim 2, characterized in that, The deformable mirror is a convex mirror. The first detector provides a clear image of the current layer mark, while the second detector provides a clear image of the previous layer mark.

9. The imaging system according to claim 2, characterized in that, The deformable mirror is a concave mirror. The first detector provides a clear image of the previous layer mark, while the second detector provides a clear image of the current layer mark.

10. The imaging system according to claim 2, characterized in that, The deformable mirror is used to compensate for wavefront aberrations in the imaging optical path corresponding to the second detector.

11. An imaging method, characterized in that, include: A sample is provided, the sample having a marked area, the marked area including a current layer mark and a previous layer mark; An imaging system according to any one of claims 1 to 10 is provided, the imaging system comprising a beam splitting element, a focusing element, a first detector and a second detector, the beam splitting element being used to split the signal light emitted from the marked area into a first imaging light and a second imaging light, and to guide the first imaging light into the first detector and to guide the second imaging light into the second detector, the focusing element being disposed in the transmission optical path of the second imaging light; Obtain the distance between the current layer marker and the previous layer marker along the optical axis; The focusing element is adjusted according to the interval distance so that the first detector clearly images one of the current layer mark and the previous layer mark, while the second detector clearly images the other of the current layer mark and the previous layer mark.

12. The imaging method according to claim 11, characterized in that, The imaging system also includes a mounting structure, on which the beam-splitting element, the focusing element, the first detector, and the second detector are all mounted; Obtaining the distance between the current layer marker and the previous layer marker along the optical axis includes: The mounting structure is moved so that one of the current layer marker and the previous layer marker is clearly imaged on the first detector; Then, the mounting structure is moved at equal intervals along the optical axis. During the movement of the mounting structure, the first detector continuously images the other of the current layer mark and the previous layer mark until the other of the current layer mark and the previous layer mark is clearly imaged on the first detector. The distance that the mounting structure moves at equal intervals is the interval distance between the current layer mark and the previous layer mark in the optical axis direction.

13. The imaging method according to claim 11, characterized in that, The focusing element is a deformable mirror. Adjusting the focusing element according to the interval distance includes: determining the target radius of curvature according to the interval distance, and adjusting the radius of curvature of the deformable mirror to the target radius of curvature.

14. The imaging method according to claim 13, characterized in that, The imaging system also includes a tube mirror disposed on the mounting structure. The signal light passes through the tube mirror and enters the beam-splitting element. The target radius of curvature is determined based on the interval distance according to Formula 1, which is as follows: ； Where R is the target radius of curvature, Δu is the interval distance, u is the object distance, d is the distance between the principal plane of the tube mirror and the principal plane of the deformable mirror object, and f1 is the focal length of the tube mirror.

15. The imaging method according to claim 14, characterized in that, The deformable mirror is a convex mirror. After adjusting the focusing element according to the interval distance, the moving mounting structure is used to make the first detector clearly image the current layer mark, while the second detector clearly image the previous layer mark.

16. The imaging method according to claim 14, characterized in that, The deformable mirror is a concave mirror. After adjusting the focusing element according to the interval distance, the mounting structure is moved so that the first detector can clearly image the previous layer mark, while the second detector can clearly image the current layer mark.

Images