A photomask inspection device and method based on optical path technology

Abstract

This invention relates to the field of semiconductor manufacturing technology and discloses a mask inspection device and method based on optical path technology, including an optical imaging system, a dark field illumination system, a reflective coaxial illumination system, a transmittance coaxial illumination system, and an autofocus system. The dark field illumination system is located in the bottom region of the optical imaging system, and the mask to be inspected is located at the bottom of the dark field illumination system. The reflective coaxial illumination system is located in the side region of the optical imaging system, and the transmittance coaxial illumination system is located in the bottom region of the mask. This invention employs a four-stage compression design of a light source, a light-collecting lens, a field lens, and a condenser lens in the transmittance optical path. Combined with a planar reflector to fold the optical path, the total length is 35% shorter than that of a Köhler illumination system. Therefore, it has a shorter optical path than traditional Köhler illumination, occupies less space, and is easier to integrate and use.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and more specifically to a mask inspection device and method based on optical path technology, which is used to solve the problems of integration, illumination uniformity and cost control in multi-mode optical inspection. Background Technology

[0002] As a core component of photolithography, the pattern defects of photomasks can directly lead to a decrease in the yield of semiconductor devices. With the continuous miniaturization of semiconductor technology nodes, the complexity and precision requirements of photomask patterns are constantly increasing, posing greater challenges to the sensitivity, efficiency, and cost of inspection equipment.

[0003] Currently, the mainstream mask inspection method on the market uses a single-source transmission and reflection inspection camera mounted on both sides of the mask. For example, application CN117751284A discloses a method and system for detecting defects on a mask: a method includes generating a database reference image of multiple bare masks by 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 of the multiple bare masks. The method further includes generating a bare mask reference image of the first of the multiple bare masks by applying one or more parameters of the imaging subsystem learned by generating the database reference image to an image of one or more of the multiple bare masks generated by the imaging subsystem other than the first multiple bare masks. In addition, the method includes detecting a second defect on the mask by comparing the bare mask reference image with the image of the mask generated by the imaging subsystem for the first of the multiple bare masks. Although this method can achieve comprehensive inspection of the mask, it uses a discrete structure: a transmission inspection camera and a reflection inspection camera are respectively set on both sides of the mask. Therefore, this technical solution has the following significant drawbacks during use:

[0004] First, the system is complex and costly: the separate detection cameras on both sides require two independent imaging systems, which not only increases the equipment cost, but also increases the complexity and maintenance difficulty of the system; secondly, special objective lenses are required to deal with the interference of the thickness of the mask glass on the imaging effect of the transmitted light path, which further increases the cost.

[0005] II. Limitations of Transmitted Illumination: Although traditional Köhler illumination can provide uniform illumination, the defocused design of the light source results in insufficient illumination intensity, especially at low magnification and wide field of view where the brightness drops significantly; when switching objectives, the numerical aperture of the condenser lens needs to be readjusted to match the new objective lens, which is cumbersome and time-consuming; Köhler illumination has a complex structure and occupies a large space, which is not conducive to the miniaturization of equipment.

[0006] Therefore, there is an urgent need for a photomask inspection device based on optical path technology to solve the aforementioned technical problems. Summary of the Invention

[0007] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide an integrated, uniformly illuminated, and low-cost mask inspection device and method to solve the technical problems mentioned in the background art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: 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;

[0009] The dark field illumination system is located in the bottom region of the optical imaging system, and the mask to be detected is located at the bottom of the dark field illumination system. The reflected coaxial light illumination system is located in the side region of the optical imaging system, and the transmitted coaxial light illumination system is located in the bottom region of the mask.

[0010] 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.

[0011] 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. When the mask inspection equipment inspects the mask, it has two modes: individual illumination and combined illumination.

[0012] The autofocus system includes an autofocus module.

[0013] Furthermore, the optical imaging system includes a photoelectric detection device, an extinction mirror tube, a tube mirror, a first beam splitter, an objective lens turret, and an objective lens, wherein:

[0014] Photoelectric detection device: configured to convert optical signals into digital signals;

[0015] Extinction lens tube: Its inner wall is treated with an anti-glare coating and it is connected downstream of the photoelectric detection device to suppress stray light interference;

[0016] Tube mirror: Coaxially fixedly installed at the end of the extinction mirror tube away from the photoelectric detection device, used to adjust and guide the optical path;

[0017] First beam splitter: vertically and coaxially fixedly installed downstream of the tube mirror, used to construct a bright-field coaxial illumination optical path;

[0018] Objective lens turntable: installed downstream of the first beam splitter, with at least two objective lenses of different magnifications on it, the objective lenses being coaxially arranged with the photoelectric detection device to achieve rapid switching;

[0019] Objective lens: mounted on the objective lens turret, used to image the mask.

[0020] Furthermore, the matting treatment of the inner wall of the matting mirror tube includes matting threads and a light-absorbing material coating.

[0021] Furthermore, the first beam splitter and the second beam splitter are coaxially arranged and horizontally side by side for coaxial autofocus and detection of the optical path.

[0022] Furthermore, the dark field illumination system includes a dark field light guide source, wherein the dark field light guide source is coaxially mounted with the objective lens and its relative height is adjustable, for providing dark field illumination and enhancing the ability to detect small particles and scratches;

[0023] The dark field light guide source is selected from one of xenon lamps, high-brightness LEDs, and laser-driven light sources.

[0024] Furthermore, the bright-field coaxial illumination module is vertically and coaxially fixedly mounted on the top of the second beam splitter to provide bright-field illumination. The reflective coaxial illumination system is connected to the optical imaging system through the first beam splitter and forms a Kohler illumination system with the objective lens.

[0025] Furthermore, the transmissive coaxial light illumination system includes a transmissive light illumination module, wherein the transmissive light illumination module includes, in sequence along the optical path, a light source, a variable aperture, a light-collecting lens, a field lens, a plane mirror, and a condenser lens;

[0026] The focusing lens is disposed in the bottom region of the photomask, and the light source is selected from one of the following: an LED point light source or an optical fiber light source.

[0027] 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 side of the light-collecting lens and both are located at one focal length to the left of the field lens.

[0028] The planar reflector is positioned in the bottom region of the condenser lens.

[0029] A detection method based on optical path technology, applied in a photomask inspection device, is characterized by comprising the following steps:

[0030] Step 1: The automatic focusing system keeps the detection surface of the mask conjugate with its photoelectric detection surface in real time;

[0031] Step 2: Activate the dark field lighting system, the reflected coaxial lighting system, and the transmitted coaxial lighting system independently or in combination to form the corresponding transmitted lighting mode;

[0032] Step 3: In transmitted illumination mode, adjust the variable aperture to match the current objective lens magnification, and maintain illumination uniformity when switching to other objectives within the -x magnification range.

[0033] 1. This invention integrates dark field illumination, reflected coaxial light illumination, and transmitted coaxial light illumination into a mask detection device for the first time. Each illumination mode is independently controllable and does not interfere with each other. It supports individual or combined activation, which is beneficial to significantly improve detection efficiency.

[0034] 2. The present invention employs a four-stage compression design of light source, light-collecting lens, field lens and condenser lens in the transmission light path, and with the addition of a plane reflector to fold the light path, the total length of the transmission light path is shortened by 35% compared to the Köhler lighting system. Therefore, it is shorter than the traditional Köhler lighting light path, occupies less space, and is easier to integrate and use.

[0035] 3. This invention achieves a light spot uniformity of over 95% by precisely controlling the light source to be located at one focal length of the light-collecting lens and designing the field lens and condenser lens to have the same focal length.

[0036] 4. This invention enables objective lens A (e.g., 5X) to obtain uniform illumination by adjusting only a single variable aperture, and the uniformity attenuation is ≤3% when switching to objective lens B (e.g., 10X) with a magnification of 1-2x, thus completely solving the industry pain point of repeated adjustment required when switching objectives. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0038] Figure 2 This is a schematic diagram of the internal structure of the transmission illumination module of the present invention.

[0039] Figure 3 This is a schematic diagram of the transmitted light illumination path of the present invention.

[0040] The attached figures are labeled 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 source; 7. Objective lens; 8. Autofocus module; 9. Bright field coaxial illumination module; 10. Transmitted light illumination module; 11. Photomask; 12. Second beam splitter; 101. Light source; 102. Variable aperture; 103. Light-collecting lens; 104. Field lens; 105. Plane mirror; 106. Condensing lens. Detailed Implementation

[0041] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. In addition, the forms of the various structures described in the following embodiments are merely illustrative. The photomask detection device and detection method based on optical path technology involved in the present invention are not limited to the structures described in the following embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Reference Figure 1 As shown, the present invention provides a mask inspection 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;

[0043] The dark field illumination system is located in the bottom region of the optical imaging system, and the mask 11 to be detected is located at the bottom of the dark field illumination system. The reflected coaxial light illumination system is located in the side region of the optical imaging system, and the transmitted coaxial light illumination system is located in the bottom region of the mask 11.

[0044] 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.

[0045] 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. When the mask inspection equipment inspects the mask 11, it has two modes: individual illumination and combined illumination.

[0046] The autofocus system includes an autofocus module 8.

[0047] Reference Figure 1 As shown, the present invention provides a mask inspection device based on optical path technology. The optical imaging system includes a photoelectric detection device 1, an extinction mirror tube 2, a tube mirror 3, a first beam splitter 4, an objective lens turret 5, and an objective lens 7, wherein:

[0048] Photoelectric detection device 1: configured to convert optical signals into digital signals;

[0049] Extinction mirror tube 2: Its inner wall is treated with extinction and connected downstream of the photoelectric detection device 1, used to absorb 99% of visible light to suppress stray light interference;

[0050] Tube mirror 3: Coaxially fixedly installed at the end of the extinction mirror tube 2 away from the photoelectric detection device 1, used to adjust and guide the optical path;

[0051] First beam splitter 4: Vertically and coaxially fixedly installed downstream of the tube mirror 3, used to construct a bright-field coaxial illumination optical path;

[0052] Objective lens turntable 5: installed downstream of the first beam splitter 4, and equipped 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.

[0053] Objective lens 7: Mounted on the objective lens turret 5, used for imaging the mask.

[0054] In this embodiment of the application, the different objectives 7 can be distinguished by objective lens A (e.g., 5X) and objective lens B (e.g., 10X).

[0055] The inner wall of the matting lens barrel 2 is treated with matting threads and a light-absorbing material coating. By providing matting threads and a light-absorbing material coating on the inner wall of the matting lens barrel 2, it is possible to absorb 99% of the light, effectively ensuring uniform imaging illumination when switching between different magnification objective lenses 7 on the objective lens turret 5.

[0056] The first beam splitter 4 and the second beam splitter 12 are coaxially arranged and horizontally side by side for coaxial autofocus and detection optical path. The advantage of placing the first beam splitter 4 and the second beam splitter 12 horizontally side by side instead of vertically is that it does not excessively increase the distance between the tube lens 3 and the objective lens 7, thus avoiding affecting the 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 mask 11.

[0057] Reference Figure 1 As shown, the present invention provides a mask inspection device based on optical path technology. The dark field illumination system includes a dark field light guide source 6, wherein the dark field light guide source 6 is coaxially mounted with the objective lens 7 and its relative height is adjustable, for providing dark field illumination and enhancing the detection capability of small particles and scratches.

[0058] The dark field light guide source 6 is selected from one of xenon lamps, high-brightness LEDs, and laser-driven light sources.

[0059] In this embodiment of the application, the dark field light guide source 6 may be a xenon lamp, a high-brightness LED, a laser-driven light source, or other light sources, but not limited to these.

[0060] The optical fiber of the dark field light guide source 6 can be a ring optical fiber with different angles according to the detection requirements. The relative height between the ring optical fiber and the mask can be adjusted to achieve the best imaging effect.

[0061] The dark-field imaging effect is that the background brightness is almost zero, while the feature to be detected has brightness; therefore, some features smaller than the system resolution can be detected. In dark-field imaging, the imaging effect is that the background is almost completely dark, while the feature to be detected exhibits obvious brightness due to the effect of scattered or reflected light. This high-contrast imaging method can effectively highlight small structures or defects on the surface of the mask 11, such as cracks, particles, scratches, etc., and these features can be detected even if their size is smaller than the system resolution.

[0062] Reference Figure 1 As shown, the present invention provides a mask inspection device based on optical path technology. The bright field coaxial light illumination module 9 is vertically and coaxially fixedly installed on the top of the second beam splitter 12 to provide bright field illumination. The reflective 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.

[0063] Reference Figures 1 to 2 As shown, the transmission coaxial light illumination system includes a transmission light illumination module 10, wherein the transmission light illumination module 10 includes, in sequence along the optical path, a light source 101, a variable aperture 102, a light-collecting lens 103, a field lens 104, a plane mirror 105, and a condenser lens 106.

[0064] The condenser lens 106 is disposed in the bottom region of the mask 11, and the light source 101 is selected from one of the following: LED point light source and optical fiber light source.

[0065] 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 side of the light-collecting lens 103 and both are located at one focal length to the left of the field lens 104.

[0066] The planar reflector 105 is disposed in the bottom region of the condenser lens 106.

[0067] In this embodiment of the application, the light source 101 may be an LED point light source, an optical fiber light source, or other light sources, but not limited to these; the light source 101 is used to provide illumination light.

[0068] The variable aperture 102 is used to adjust the numerical aperture value of the illumination optical 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 being adjusted by the variable aperture 102.

[0069] The light-collecting lens 103 converges the adjusted light into parallel light, and the field lens 104 converges the parallel light to its right focal point. The light path is redirected by the plane mirror 105, and the parallel light is converged to the focal point of the condenser lens 106. At this time, the main rays of the parallel light formed by the off-axis point of the light source 101 converge at the focal point of the condenser lens 106. The corresponding light emitted by the light source 101 forms a uniformly bright light spot through the transmission coaxial light illumination system and uniformly illuminates the mask 11.

[0070] In this embodiment of the application, the design of the transmission coaxial light illumination system has at least the following advantages: compared with other transmission light illumination systems such as Abbe illumination, this illumination system has better illumination uniformity; compared with the Köhler illumination system where the field stop is located between the light-collecting lens 103 and the field lens 104, this transmission coaxial light illumination system occupies less space; adjusting the variable stop 102 can be adapted to objective lenses of different magnifications to form uniform illumination.

[0071] Reference Figures 1 to 3 As shown, the present invention provides a detection method based on optical path technology, comprising the following steps:

[0072] Step 1: The detection surface of the mask 11 is kept conjugate with its photoelectric detection surface in real time by the autofocus system;

[0073] Step 2: Activate the dark field lighting system, the reflected coaxial lighting system, and the transmitted coaxial lighting system independently or in combination to form the corresponding transmitted lighting mode;

[0074] Step 3: In the transmitted illumination mode, adjust the variable aperture 102 to match the current objective lens magnification, and maintain illumination uniformity when switching to other objectives 7 in the 1-2x magnification range.

[0075] The workflow of this invention is as follows:

[0076] Autofocus: The autofocus system operates first; a focus detection optical path is introduced through the second beam splitter 12, and after being reflected by the first beam splitter 4, the optical path illuminates the detection surface of the mask 11 to be detected through the objective lens 7; 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 will automatically control and fine-tune the relative distance between the objective lens 7 and the detection surface until the two are precisely confocal;

[0077] Lighting mode selection and operation: Users can select to enable one or a combination of the following lighting systems based on their testing needs, such as the type of feature to be measured, material properties, and required contrast:

[0078] Dark field illumination system: Light is provided by dark field light guide source 6; the light is tilted at a large angle to illuminate the detection surface of the mask 11 to be inspected through the ring light guide fiber with adjustable angle and relative height; the smooth and flat detection surface reflects the light beyond the objective lens receiving angle, appearing almost completely black in the image; small defects, particles, edges or rough structures on the surface will scatter the light, and some of the scattered light enters the objective lens 7 to assist in the inspection of the mask 11;

[0079] Reflective coaxial illumination system: Light is provided by bright-field coaxial illumination module 9; the light is reflected by the second beam splitter 12, and then reflected by the first beam splitter 4, and then coaxially illuminates the surface of the object to be tested along the optical axis of the objective lens; together with the objective lens 7, it constitutes the Kohler illumination system, providing uniform bright-field illumination; after being reflected by the surface of the object to be tested, the light returns along the original optical path, passes through the first beam splitter 4 and enters the imaging optical path to assist in the detection of the mask plate 11;

[0080] Transmitted coaxial illumination system: Light is provided by light source 101; 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 light-collecting lens 103 is used to collect the light emitted by light source 101 after adjustment by variable aperture 102; light-collecting lens 103 converges the adjusted light into parallel light, field lens 104 converges the parallel light to its right focal point, and the light path is redirected by plane mirror 105 to converge the parallel light to the focal point of condenser lens 106. At this time, the main ray of parallel light formed by the off-axis point of light source 101 converges to the focal point of condenser lens 106. Light source 101 forms a uniform brightness spot through the transmitted coaxial illumination system and uniformly illuminates the mask 11 to assist in the detection of mask 11;

[0081] Optical Imaging and Extinction Processing: Regardless of the illumination mode used, all light reflected or transmitted from the object is ultimately collected by the objective lens 7. The objective lens is mounted on the objective lens turntable 5, facilitating rapid switching between different magnifications. After passing through the objective lens, the light enters the tube lens 3, where the tube lens and objective lens work together to image the object at infinity or the intermediate image plane. The light then enters the extinction lens tube 2, whose inner wall is not only machined with extinction threads but also coated with light-absorbing material, capable of absorbing up to 99% of stray light. This greatly suppresses stray light generated by objective lens switching and reflections within the tube, effectively ensuring the illumination uniformity and contrast of images formed under different magnifications.

[0082] 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 recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0083] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0084] In conclusion, 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 within the protection scope of the present invention.

Claims

1. A photomask inspection device based on optical path technology, characterized in that: It includes optical imaging systems, dark field illumination systems, reflected coaxial illumination systems, transmitted coaxial illumination systems, and autofocus systems; The dark field illumination system is set in the bottom region of the optical imaging system, and the mask to be detected (11) is set at the bottom of the dark field illumination system. The reflected coaxial light illumination system is set in the side region of the optical imaging system, and the transmitted coaxial light illumination system is set in the bottom region 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. When the mask detection equipment detects the mask (11), it has two modes: individual illumination and combined illumination. The autofocus system includes an autofocus module (8); The optical imaging system includes a photoelectric detection device (1), an extinction lens tube (2), a tube mirror (3), a first beam splitter (4), an objective lens turret (5), and an objective lens (7); The dark field illumination system includes a dark field light guide (6), wherein the dark field light guide (6) is coaxially mounted with the objective lens (7) and its relative height is adjustable, for providing dark field illumination and enhancing the ability to detect small particles and scratches; The dark field light guide source (6) is selected from one of xenon lamps, high-brightness LEDs and laser-driven light sources; The bright field coaxial light illumination module (9) is vertically and coaxially fixed on the top of the second beam splitter (12) to provide bright field illumination. The reflective 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). The transmission coaxial light illumination system includes a transmission light illumination module (10), wherein the transmission light illumination module (10) includes, in sequence along the optical path, a light source (101), a variable aperture (102), a light-collecting lens (103), a field lens (104), a plane mirror (105), and a condenser lens (106). The focusing lens (106) is disposed in the bottom region of the mask (11), and the light source (101) is selected from one of the following: an LED point light source and an optical fiber light source.

2. The photomask inspection device based on optical path technology according to claim 1, characterized in that: Photoelectric detection device (1): configured to convert optical signals into digital signals; Extinction mirror tube (2): Its inner wall is treated with extinction and connected downstream of the photoelectric detection device (1) to suppress stray light interference; Tube mirror (3): Coaxially fixed at one end of the extinction mirror tube (2) away from the photoelectric detection device (1), used to adjust and guide the optical path; First beam splitter (4): Vertically and coaxially fixedly installed downstream of the tube mirror (3) to construct a bright field coaxial illumination optical path; Objective lens turntable (5): installed downstream of the first beam splitter (4), on which at least two objective lenses (7) with different magnifications are provided. 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) for imaging the mask.

3. The photomask inspection device based on optical path technology according to claim 2, characterized in that: The matting treatment of the inner wall of the matting mirror tube (2) includes matting threads and a light-absorbing material coating.

4. The photomask inspection device based on optical path technology according to claim 2, characterized in that: The first beam splitter (4) and the second beam splitter (12) are coaxially arranged and horizontally side by side for coaxial autofocus and detection of the optical path.

5. The photomask inspection device based on optical path technology according to claim 1, characterized in that: The light source (101) is located 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 one focal length to the left of the field lens (104). The planar reflector (105) is disposed in the bottom region of the condenser lens (106).

6. A detection method based on optical path technology, applied to the photomask detection equipment based on optical path technology as described in any one of claims 1-5, characterized in that, Includes the following steps: Step 1: The detection surface of the mask (11) is kept conjugate with its photoelectric detection surface in real time by the autofocus system; Step 2: Activate the dark field lighting system, the reflected coaxial lighting system, and the transmitted coaxial lighting system independently or in combination to form the corresponding transmitted lighting mode; Step 3: In the transmission illumination mode, adjust the variable aperture (102) to match the current objective lens magnification, and maintain illumination uniformity when switching to other objectives (7) in the 1-2x magnification range.

Images