Mask detection equipment and detection method based on light path technology

Abstract

The invention relates to the technical field of semiconductor manufacturing, and discloses a mask detection device and method based on a light path technology, and the device comprises an optical imaging system, a dark field illumination system, a reflection coaxial light illumination system, a transmission coaxial light illumination system, and an automatic focusing system. Wherein the dark field illumination system is arranged in the bottom area of the optical imaging system, a mask to be detected is arranged at the bottom of the dark field illumination system, the reflection coaxial light illumination system is arranged in the side edge area of the optical imaging system, and the transmission coaxial light illumination system is arranged in the bottom area of the mask. A transmission light path adopts a four-stage compression design of a light source, a light receiving lens, a field lens and a condensing lens, and is matched with a plane reflector to fold the light path, so that the total length is shortened by 35% compared with that of a Kohler illumination system, and the Kohler illumination system is shorter in light path, smaller in occupied space and convenient to integrate and use compared with a traditional Kohler illumination system.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor manufacturing technology, and more specifically to a mask detection device and detection method based on optical path technology, which are used to solve the problems of integration, illumination uniformity and cost control of multi-mode optical detection. Background Art

[0002] As a core component of the photolithography process, defects in the mask pattern can directly lead to a decrease in the yield of semiconductor devices. As semiconductor technology nodes continue to shrink, the complexity and precision requirements of the mask pattern continue to increase, posing greater challenges to the sensitivity, efficiency, and cost of detection equipment. Currently, the mainstream reticle inspection method on the market employs a single light source, with transmissive and reflective inspection cameras mounted on either side of the reticle. For example, application publication number CN117751284A discloses a method and system for detecting defects on a reticle: The method comprises generating a database reference image of a multi-die mask through simulation and detecting a first defect on the mask by comparing the database reference image with an image of the mask generated by an imaging subsystem for a first die. The method further comprises generating a die reference image of one or more of the plurality of dies other than the first die by applying one or more parameters of the imaging subsystem learned from generating the database reference image to images of the first die generated by the imaging subsystem. Furthermore, the method comprises detecting a second defect on the mask by comparing the die reference image with the image of the mask generated by the imaging subsystem for the first die. While this method can achieve comprehensive reticle inspection, it utilizes a discrete structure: a transmissive inspection camera and a reflective inspection camera are mounted on either side of the reticle. Therefore, this technical solution has the following significant defects during use: 1. System complexity and high cost: Separate inspection cameras on both sides require two independent imaging systems, which not only increases equipment cost but also increases system complexity and maintenance difficulty. Secondly, to address the interference of the mask glass thickness on the imaging effect of the transmitted light path, a special objective lens is required, further increasing the cost. 2. Limitations of Transmitted Illumination: While traditional Köhler illumination provides uniform illumination, the defocused design of the light source results in insufficient illumination intensity, particularly at low magnification and a large field of view, where the brightness decreases significantly. Switching objectives requires re-adjusting the condenser numerical aperture to match the new objective, a cumbersome and time-consuming operation. Köhler illumination also has a complex structure and occupies a large space, making it unsuitable for miniaturization. Therefore, there is an urgent need for a mask detection device based on optical path technology to solve the above-mentioned technical problems. Summary of the Invention

[0003] In order to overcome the above-mentioned defects of the prior art, the implementation regulations of the present invention provide an integrated, uniformly illuminated and low-cost mask inspection device and inspection method to solve the technical problems raised in the background technology.

[0004] To achieve the above-mentioned object, the present invention provides the following technical solutions: a mask inspection device based on optical path technology, comprising an optical imaging system, a dark field illumination system, a reflected coaxial light illumination system, a transmitted coaxial light illumination system and an autofocus system; The dark field illumination system is arranged in the bottom area of ​​the optical imaging system, the mask to be inspected is arranged at the bottom of the dark field illumination system, the reflected coaxial light illumination system is arranged in the side area of ​​the optical imaging system, and the transmitted coaxial light illumination system is configured in the bottom area of ​​the mask; The reflected coaxial light illumination system includes a bright field coaxial light illumination module and a second beam splitter, wherein the autofocus system is connected to the optical path via the second beam splitter; The dark field illumination system, the reflected coaxial light illumination system and the transmitted coaxial light illumination system are independent of each other and do not interfere with each other, and when the mask inspection device inspects the mask, there are two modes: individual illumination and combined illumination; The autofocus system includes an autofocus module.

[0005] Furthermore, the optical imaging system includes a photoelectric detection device, an extinction lens tube, a tube lens, a first beam splitter, an objective lens turret, and an objective lens, wherein: Photoelectric detection device: configured to convert the optical signal into a digital signal; Extinction lens barrel: its inner wall is extinct and connected to the downstream of the photoelectric detection device to suppress stray light interference; Tube lens: coaxially fixedly mounted on the end of the extinction lens tube away from the photoelectric detection device, used to adjust and guide the light path; First beam splitter: vertically and coaxially fixedly installed downstream of the tube lens, used to construct a bright field coaxial illumination light path; Objective lens turret: installed downstream of the first beam splitter, with at least two objective lenses with different magnifications, the objective lenses are coaxially arranged with the photoelectric detection device to achieve fast switching; Objective lens: installed on the objective lens turret and used to image the mask.

[0006] Furthermore, the matte treatment of the inner wall of the matte lens barrel includes matte threads and a light-absorbing material coating.

[0007] Furthermore, the first beam splitter and the second beam splitter are coaxially arranged and arranged horizontally in parallel for coaxial autofocusing and detecting the optical path.

[0008] Furthermore, the dark field illumination system includes a dark field light guide light source, wherein the dark field light guide light source is coaxially mounted with the objective lens and the relative height thereof is adjustable, for providing dark field illumination to enhance the detection capability of tiny particles and scratches; The dark field light guide light source is selected from one of a xenon lamp, a high brightness LED and a laser driven light source.

[0009] Furthermore, the bright field coaxial light illumination module is vertically and coaxially fixedly installed on the top of the second beam splitter to provide bright field illumination. The reflected coaxial light illumination system is connected to the optical imaging system through the first beam splitter and constitutes a Kohler illumination system with the objective lens.

[0010] Furthermore, the transmitted coaxial light illumination system includes a transmitted light illumination module, wherein the transmitted light illumination module includes a light source, a variable aperture, a light collecting lens, a field lens, a plane reflector and a condenser lens in sequence along the light path; The condensing lens is arranged at the bottom area of ​​the mask, and the variable aperture is selected from one of an LED point light source and a light guide fiber light source.

[0011] Furthermore, the light source is located at one focal length to the left of the light-collecting lens, wherein the variable aperture is adjacent to the left of the light-collecting lens and both are located at one focal length to the left of the field lens; The plane reflector is arranged in the bottom area of ​​the condenser lens.

[0012] A detection method based on optical path technology is applied to a mask detection device, and is characterized by comprising the following steps: Step 1: Using an autofocus system to keep the detection surface of the mask conjugate with its photoelectric detection surface in real time; Step 2: activating the dark field illumination system, the reflected coaxial light illumination system, and the transmitted coaxial light illumination system independently or in combination to form a corresponding transmitted illumination mode; Step 3: In transmitted illumination mode, adjust the iris diaphragm to match the current objective magnification and maintain illumination uniformity when switching to other objectives within the magnification range.

[0013] 1. The present invention integrates dark field illumination, reflected coaxial illumination, and transmitted coaxial illumination into a mask inspection device for the first time. Each illumination mode is independently controllable and does not interfere with each other. It can be enabled individually or in combination, which is beneficial to significantly improve inspection efficiency.

[0014] 2. The present invention adopts a four-stage compression design of light source, light-collecting lens, field lens and focusing lens through the transmission light path, and cooperates with the plane reflector to fold the light path. The total length of the transmission light path is shortened by 35% compared with the Köhler illumination system. Therefore, it is shorter than the traditional Köhler illumination light path, occupies less space, and is easy to integrate and use.

[0015] 3. The present invention achieves a light spot uniformity of more than 95% by precisely controlling the light source to be located at one focal length of the light-collecting lens and designing the focal lengths of the field lens and the focusing lens.

[0016] 4. The present invention can achieve uniform illumination for objective lens A (e.g., 5X) by adjusting only a single variable iris. When switching to objective lens B (e.g., 10X) with a magnification of 1-2 times, the uniformity attenuation is ≤3%, which completely solves the industry pain point of repeated adjustment required when switching between objective lenses. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0018] Figure 2 Schematic diagram of the internal structure of the transillumination module of the present invention.

[0019] Figure 3 Schematic diagram of the transmitted light illumination path of the present invention.

[0020] The accompanying drawings are marked as follows: 1. photoelectric detection device; 2. extinction lens tube; 3. tube lens; 4. first beam splitter; 5. objective lens turntable; 6. dark-field light guide light source; 7. objective lens; 8. autofocus module; 9. bright-field coaxial light illumination module; 10. transmitted light illumination module; 11. mask; 12. second beam splitter; 101. light source; 102. variable aperture; 103. light collecting lens; 104. field lens; 105. plane reflector; 106. focusing lens. DETAILED DESCRIPTION

[0021] The technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. In addition, the forms of the various structures described in the following embodiments are merely examples. The mask detection equipment and detection method based on optical path technology involved in the present invention are not limited to the various structures described in the following embodiments. All other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0022] Reference Figure 1 As shown, the present invention provides a mask detection device based on optical path technology, including an optical imaging system, a dark field illumination system, a reflected coaxial light illumination system, a transmitted coaxial light illumination system and an autofocus system; The dark field illumination system is arranged in the bottom area of ​​the optical imaging system, the mask 11 to be inspected is arranged at the bottom of the dark field illumination system, the reflected coaxial light illumination system is arranged in the side area of ​​the optical imaging system, and the transmitted coaxial light illumination system is configured in the bottom area of ​​the mask 11; The reflected coaxial light illumination system includes a bright field coaxial light illumination module 9 and a second beam splitter 12, wherein the autofocus system is connected to the optical path via the second beam splitter 12; The dark field illumination system, the reflected coaxial light illumination system and the transmitted coaxial light illumination system are independent of each other and do not interfere with each other, and when the mask inspection device inspects the mask 11, there are two modes: individual illumination and combined illumination; The auto-focus system includes an auto-focus module 8 .

[0023] Reference Figure 1 As shown, the present invention provides a mask detection device based on optical path technology, wherein the optical imaging system includes a photoelectric detection device 1, an extinction lens barrel 2, a tube lens 3, a first beam splitter 4, an objective lens turret 5, and an objective lens 7, wherein: Photoelectric detection device 1: configured to convert an optical signal into a digital signal; Extinction lens barrel 2: its inner wall is extinct and connected to the downstream of the photoelectric detection device 1, and is used to absorb 99% of visible light to suppress stray light interference; Tube lens 3: coaxially fixedly mounted on the end of the extinction lens tube 2 away from the photoelectric detection device 1, used for adjusting and guiding the light path; First beam splitter 4: vertically and coaxially fixedly installed downstream of the tube lens 3, used to construct a bright field coaxial illumination light path; Objective lens turret 5: installed downstream of the first beam splitter 4, with at least two objective lenses 7 of different magnifications provided thereon, the objective lenses 7 being coaxially arranged with the photoelectric detection device 1 to achieve fast switching; Objective lens 7: mounted on the objective lens turret 5, used for imaging the mask.

[0024] In the embodiment of the present application, the different objective lenses 7 can be distinguished by objective lens A (such as 5X) and objective lens B (such as 10X).

[0025] The matte treatment of the inner wall of the matte lens barrel 2 includes matte threads and a light-absorbing material coating; by providing the inner wall of the matte lens barrel 2 with matte threads and a light-absorbing material coating, it is beneficial to absorb 99% of the light, effectively ensuring uniform imaging illumination when the objective lens turret 5 switches to an objective lens 7 of different magnifications.

[0026] The first beam splitter 4 and the second beam splitter 12 are coaxially arranged and arranged horizontally side by side for coaxial autofocus and optical path detection. The advantage of placing the first beam splitter 4 and the second beam splitter 12 horizontally side by side rather than vertically is that it does not significantly increase the distance between the tube lens 3 and the objective lens 7, thereby avoiding affecting image quality, and provides sufficient space for the autofocus system to adjust the relative distance between the objective lens 7 and the detection surface of the reticle 11.

[0027] Reference Figure 1 As shown, the present invention provides a mask detection device based on optical path technology, wherein the dark field illumination system includes a dark field light guide light source 6, wherein the dark field light guide light source 6 is coaxially mounted with the objective lens 7 and the relative height can be adjusted to provide dark field illumination and enhance the detection capability of tiny particles and scratches.

[0028] The dark field light guide light source 6 is selected from one of a xenon lamp, a high brightness LED and a laser driven light source.

[0029] In the embodiment of the present application, the dark field light guide light source 6 can be a xenon lamp, a high brightness LED, a laser driven light source, etc. but is not limited to these light sources; The optical fiber of the dark field light guide light source 6 can be a ring optical fiber with different angles according to the detection requirements, wherein the relative height of the ring optical fiber and the mask can be adjusted to achieve the best imaging effect; Darkfield imaging achieves a near-zero background brightness while the features to be detected are bright; thus, features smaller than the system's resolution can be detected. In darkfield imaging, the background appears almost completely dark, while the features to be detected appear significantly brighter due to scattered or reflected light. This high-contrast imaging method effectively highlights tiny structures or defects on the surface of the reticle 11, such as cracks, particles, and scratches, even when these features are smaller than the system's resolution.

[0030] Reference Figure 1 As shown, the present invention provides a mask detection device based on optical path technology, wherein the bright field coaxial light illumination module 9 is vertically and coaxially fixedly mounted on the top of the second beam splitter 12 to provide bright field illumination, and the reflected coaxial light illumination system is connected to the optical imaging system through the first beam splitter 4, and forms a Kohler illumination system with the objective lens 7.

[0031] Reference Figures 1 to 2 As shown, the transmitted coaxial light illumination system includes a transmitted light illumination module 10, wherein the transmitted light illumination module 10 includes a light source 101, a variable aperture 102, a light collecting lens 103, a field lens 104, a plane reflector 105 and a condenser lens 106 in sequence along the light path; The condenser lens 106 is disposed at the bottom area of ​​the mask 11, and the variable aperture 102 is selected from one of an LED point light source and a light guide fiber light source; The light source 101 is located at one focal length to the left of the light-collecting lens 103, wherein the variable aperture 102 is adjacent to the left of the light-collecting lens 103 and both are located at one focal length to the left of the field lens 104; The plane reflector 105 is disposed at the bottom region of the condenser lens 106 .

[0032] In the embodiment of the present application, the light source 101 may be an LED point light source, an optical fiber light source, etc., but is not limited to these light sources; the light source 101 is used to provide illumination light; The variable aperture 102 is used to adjust the numerical aperture value of the illumination light path, intercept stray light, improve imaging quality and generate corresponding light, wherein the light receiving lens 103 is used to collect the light emitted by the light source 101 after being adjusted by the variable aperture 102; The light-collecting lens 103 converges the adjusted light into parallel light, the field lens 104 converges the parallel light at its right focus, and the light path is redirected by the plane reflector 105 to converge the parallel light at the focus of the focusing lens 106. At this time, the main light of the parallel light formed by the off-axis point of the light source 101 converges at the focus of the focusing lens 106, and the corresponding light emitted by the light source 101 passes through the transmitted coaxial light illumination system to form a light spot with uniform brightness, and is evenly illuminated on the mask 11.

[0033] In the embodiment of this application, the design of the transmitted coaxial light illumination system has at least the following advantages: compared with other transmitted light illumination systems such as Abbe illumination, this illumination system has better illumination uniformity; compared with the Köhler illumination system in which the field diaphragm is located between the light-collecting lens 103 and the field lens 104, this transmitted coaxial illumination system occupies less space; and adjusting the variable diaphragm 102 can adapt to objective lenses of different magnifications to form uniform illumination.

[0034] Reference Figures 1 to 3 As shown, the present invention provides a detection method based on optical path technology, comprising the following steps: Step 1: Using an autofocus system to keep the detection surface of the mask 11 conjugate with its photoelectric detection surface in real time; Step 2: activating the dark field illumination system, the reflected coaxial light illumination system, and the transmitted coaxial light illumination system independently or in combination to form a corresponding transmitted illumination mode; Step 3: In the transmitted illumination mode, adjust the variable iris 102 to adapt to the current objective lens magnification, and maintain the illumination uniformity when switching to other objective lenses 7 within the 1-2 magnification range.

[0035] The workflow of the present invention is: Autofocus: The autofocus system operates first. The focus detection light path is introduced through the second beam splitter 12. After being reflected by the first beam splitter 4, this light path is illuminated by the objective lens 7 to the detection surface of the mask 11 to be detected. The autofocus system analyzes the returned light signal and determines in real time whether the focal plane of the objective lens 7 coincides with the surface of the object to be detected. If the autofocus system detects defocus, it automatically controls and fine-tunes the relative distance between the objective lens 7 and the detection surface until the two are precisely confocal. Lighting mode selection and operation: Users can choose to enable one or a combination of the following lighting systems based on their inspection requirements, such as the type of feature to be measured, material properties, and required contrast: Darkfield illumination system: Light is provided by a darkfield light source 6. The light passes through a ring-shaped light guide fiber, whose angle and relative height are adjustable, and illuminates the inspection surface of the mask 11 to be inspected at a large angle. The smooth and flat inspection surface reflects the light outside the objective lens's acceptance angle, appearing almost completely black in the image. Small surface defects, particles, edges, or rough structures scatter the light, and some of the scattered light enters the objective lens 7 to assist in the inspection of the mask 11. Reflected coaxial illumination system: Light is provided by the brightfield coaxial illumination module 9. The light is reflected by the second beam splitter 12, then by the first beam splitter 4, and then coaxially illuminates the surface of the object to be measured along the optical axis of the objective lens. Together with the objective lens 7, it forms a Köhler illumination system, providing uniform brightfield illumination. After being reflected by the surface of the object to be measured, the light returns along the original optical path, passes through the first beam splitter 4, and enters the imaging optical path, which is used to assist in the detection of the mask 11. Transmitted coaxial light illumination system: Light is provided by light source 101; the variable aperture 102 is used to adjust the numerical aperture value of the illumination light path, intercept stray light, improve imaging quality and generate corresponding light, wherein the light-collecting lens 103 is used to collect the light emitted by the light source 101 after adjustment by the variable aperture 102; the light-collecting lens 103 converges the adjusted light into parallel light, and the field lens 104 converges the parallel light at its right focus. The light path is deflected by the plane reflector 105 and the parallel light is converged at the focus of the condenser lens 106. At this time, the main light of the parallel light formed by the off-axis point of the light source 101 converges at the focus of the condenser lens 106. The light source 101 forms a light spot with uniform brightness through the transmitted coaxial light illumination system, and evenly illuminates the mask 11 to assist in the detection of the mask 11; Optical imaging and extinction processing: Regardless of the illumination mode used, the light reflected or transmitted by the object is ultimately collected by the objective lens 7; the objective lens is mounted on the objective turret 5, facilitating quick switching between objectives of different magnifications; after passing through the objective lens, the light enters the tube lens 3, which works together with the objective lens to image the object at infinity or at the intermediate image plane; the light then enters the extinction lens barrel 2, the inner wall of which is not only machined with extinction threads but also sprayed with light-absorbing material that can absorb up to 99% of stray light; this greatly suppresses stray light generated by objective lens switching, internal reflections in the barrel, etc., and effectively ensures the illumination uniformity and contrast of imaging under objectives of different magnifications.

[0036] The above embodiments can be implemented in whole or in part by software, hardware, firmware or any other combination thereof; those skilled in the art will appreciate that the units and algorithmic steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application. Those skilled in the art will clearly understand that for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0037] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

[0038] Finally: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A mask inspection device based on optical path technology, characterized by: Including optical imaging system, dark field illumination system, reflected coaxial light illumination system, transmitted coaxial light illumination system and autofocus system; The dark field illumination system is arranged in the bottom area of ​​the optical imaging system, a mask (11) to be detected is arranged at the bottom of the dark field illumination system, the reflected coaxial light illumination system is arranged in the side area of ​​the optical imaging system, and the transmitted coaxial light illumination system is configured in the bottom area of ​​the mask (11); The reflected coaxial light illumination system comprises a bright field coaxial light illumination module (9) and a second beam splitter (12), wherein the autofocus system is connected to the light path via the second beam splitter (12); The dark field illumination system, the reflected coaxial light illumination system, and the transmitted coaxial light illumination system are independent of each other and do not interfere with each other, and when the mask detection device detects the mask (11), there are two modes: individual illumination and combined illumination; The automatic focusing system comprises an automatic focusing module (8).

2. The optical path technology-based mask detection device according to claim 1, characterized in that: The optical imaging system comprises a photoelectric detection device (1), an extinction lens tube (2), a tube lens (3), a first beam splitter (4), an objective lens turret (5), and an objective lens (7), wherein: Photoelectric detection device (1): configured to convert an optical signal into a digital signal; Extinction lens barrel (2): the inner wall of which is subjected to extinction treatment and is connected to the downstream of the photoelectric detection device (1) to suppress stray light interference; Tube lens (3): coaxially fixedly mounted on the end of the extinction lens tube (2) away from the photoelectric detection device (1), and used for adjusting and guiding the light path; A first beam splitter (4): vertically and coaxially fixedly installed downstream of the tube lens (3), used to construct a bright field coaxial illumination light path; An objective lens turret (5) is installed downstream of the first beam splitter (4), and is provided with at least two objective lenses (7) with different magnifications. The objective lenses (7) are coaxially arranged with the photoelectric detection device (1) to achieve rapid switching; Objective lens (7): mounted on the objective lens turntable (5), and used for imaging the mask.

3. The optical path technology-based mask inspection device according to claim 2, characterized in that: The matte treatment of the inner wall of the matte lens barrel (2) includes matte threads and a light-absorbing material coating.

4. The optical path technology-based mask inspection device according to claim 2, characterized in that: The first beam splitter (4) and the second beam splitter (12) are coaxially arranged, and the two are arranged horizontally in parallel, for coaxial automatic focusing and detecting the light path.

5. The mask inspection device based on optical path technology according to claim 2, characterized in that: The dark field illumination system comprises a dark field light guide light source (6), wherein the dark field light guide light source (6) is coaxially mounted with the objective lens (7) and the relative height thereof can be adjusted, and is used to provide dark field illumination and enhance the detection capability of tiny particles and scratches; The dark field light guide light source (6) is selected from one of a xenon lamp, a high brightness LED and a laser driven light source.

6. The mask inspection device based on optical path technology according to claim 1, characterized in that: The bright field coaxial light illumination module (9) is vertically and coaxially fixedly mounted on the top of the second beam splitter (12) to provide bright field illumination. The reflected coaxial light illumination system is connected to the optical imaging system through the first beam splitter (4) and forms a Kohler illumination system with the objective lens (7).

7. The mask inspection device based on optical path technology according to claim 1, characterized in that: The transmitted coaxial light illumination system comprises a transmitted light illumination module (10), wherein the transmitted light illumination module (10) comprises a light source (101), a variable aperture (102), a light collecting lens (103), a field lens (104), a plane reflector (105), and a condensing lens (106) in sequence along the light path; The focusing lens (106) is arranged in the bottom area of ​​the mask (11), and the variable aperture (102) is selected from one of an LED point light source and a light guide fiber light source.

8. The mask inspection device based on optical path technology according to claim 7, characterized in that: The light source (101) is located at one focal length to the left of the light-collecting lens (103), wherein the variable aperture (102) is adjacent to the left of the light-collecting lens (103), and both are located at one focal length to the left of the field lens (104); The plane reflector (105) is arranged in the bottom area of ​​the condenser lens (106).

9. A detection method based on optical path technology, applied to the mask detection device based on optical path technology according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1: Using an automatic focusing system to keep the detection surface of the mask (11) conjugate with its photoelectric detection surface in real time; Step 2: activating the dark field illumination system, the reflected coaxial light illumination system, and the transmitted coaxial light illumination system independently or in combination to form a corresponding transmitted illumination mode; Step 3: In the transmission illumination mode, adjust the variable iris (102) to adapt to the current objective lens magnification, and maintain the illumination uniformity when switching to other objective lenses (7) within the 1-2 magnification range.

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