Mask defect detection system and method based on fiber laser array

Abstract

The application discloses a kind of multi-beam confocal mask defect detection system and method based on fiber laser array, the present application obtains multi-point scanning light field as illumination light source based on fiber laser array, and can be based on the arrangement of laser array Realize the regulation and control of scanning light field, through the joint action of motion platform and multi-surface rotating mirror, realize fast and accurate mask two-dimensional scanning imaging, and based on confocal microscopic imaging method, with high-power microscope objective and photomultiplier tube Realize high-resolution detection of mask defect.Compared with the traditional point scanning type mask defect detection system, the present application has the advantages of high detection resolution, fast scanning speed, multi-point scanning light field can be freely regulated and controlled, and does not need to introduce additional diffractive optical element.

Description

Technical Field

[0001] The present invention relates to the technical field of photolithography, and in particular to a multi-beam confocal mask defect detection system and method based on an optical fiber laser array. Background Art

[0002] The reticle is an indispensable component of the lithography system, and its quality has a near-deterministic impact on the yield of the final lithographic component. Even tiny defects at the nanometer scale can cause a shift in the amplitude or phase of the light field, ultimately replicating the defect on the wafer surface and significantly affecting the yield of the lithography process. Therefore, reticle defect detection technology is essential, and its detection accuracy and speed have become major challenges restricting the development of the lithography process.

[0003] Although the existing line-scanning mask defect detection system has a relatively fast detection speed, it is limited by its imaging method and only has high detection accuracy in the scanning direction, and cannot accurately locate defects in two dimensions. Although the existing point-scanning mask defect detection system can accurately locate defects, it generally has problems such as slow detection speed and complex system structure.

[0004] Therefore, improving the detection speed while ensuring high detection accuracy is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] The purpose of this application is to provide a multi-beam confocal mask defect detection system and method based on a fiber laser array, which can improve the overall detection accuracy and speed.

[0006] To solve the above technical problems, the present application provides a multi-beam confocal mask defect detection system based on a fiber laser array, comprising:

[0007] A fiber laser array, including a multi-point scanning light field, serves as the system light source;

[0008] A collimating lens, a reflector and a first beam splitter, wherein the fiber laser array is connected to the collimating lens, and the collimated incident light passes through the reflector and is split into two independent light beams by the first beam splitter;

[0009] A polygonal mirror, a second beam splitter, and a third beam splitter, wherein the polygonal mirror is used to deflect one of the incident light beams independently generated by the first beam splitter, so that the light beam passes through the imaging lens and is expanded to the second beam splitter and the third beam splitter;

[0010] a quarter-wave plate, used to modulate the linearly polarized light after being split by the second beam splitter and the third beam splitter into circularly polarized light;

[0011] Microscope objective lens, used to focus circularly polarized light onto the surface of the mask to be tested;

[0012] The motion stage is used to fix the mask to be tested and realize fast two-dimensional scanning of the mask;

[0013] Differential confocal module, used to help the microscope objective lens to accurately focus;

[0014] The photomultiplier tube detector analyzes the reflected light from the surface of the mask to be tested after it returns along the original optical path to the first beam splitter and obtains the intensity information of the corresponding reflected light;

[0015] The clock synchronization module is used to analyze the other beam of linear polarization after the incident light is split by the second beam splitter to obtain the time series of the impulse signal.

[0016] Optionally, the fiber laser array is arranged in an X-shaped cross pattern, and triangular grooves are etched on both sides of the fiber laser array, and the depth and spacing of the etching are determined by the arrangement of the array and the outer diameter of the optical fiber.

[0017] Optionally, the arrangement of the fiber laser array is consistent with the arrangement of the photomultiplier tube detector array.

[0018] Optionally, the method further includes: the multi-faceted rotating mirror realizes fast two-dimensional scanning of the mask through the cooperation with the motion stage, thereby improving the detection speed of the system, specifically including: using the multi-faceted rotating mirror and the imaging lens, the multi-faceted rotating mirror rotates at an angular velocity of β, and the angle between the imaging axial coordinate z and the incident light is Satisfy the corresponding relationship , is the focal length of the imaging lens, and the scanning speed at this point , matched with a polygonal mirror rotating at a constant angular velocity.

[0019] Optionally, the differential confocal module has a built-in detection light source. The emitted light beam is collimated by a collimating lens, reflected by a third beam splitter, and focused by a microscope objective onto the surface of the mask to be measured after passing through a quarter-wave plate. Similarly, the reflected light beam passes through the microscope objective, a quarter-wave plate and a third beam splitter again and returns along the original optical path to be incident on the differential confocal module. The incident light is respectively incident on the back focus optical path and the front focus optical path by a beam splitter, and is collected by corresponding detectors to obtain corresponding back focus signals and front focus signals. After scanning by an actuator, the corresponding axial differential confocal response curve is obtained, and the accurate focusing information of the microscope objective is obtained after fitting the data, so that the microscope objective is always in the ideal fixed focus position.

[0020] The optional differential confocal module features a built-in detection light source, the microscope objective focal plane, and the detector pinhole, all in a conjugate relationship. Scattered light generated at the microscope objective focal plane is collected by the detector pinhole. However, scattered light from non-focal areas is imaged away from the pinhole, allowing only a small amount of scattered light to pass through the pinhole and be collected by the detector. This eliminates interference from out-of-focus light outside the focal plane.

[0021] Optionally, the linearly polarized light in the reflection direction split by the second beam splitter is incident on the clock synchronization module to obtain the time series of the impulse signal, and combined with the reflected light intensity information sequence, the corresponding two-dimensional mask detection icon is obtained to achieve rapid positioning and type identification of defects.

[0022] An embodiment of the present invention further provides a multi-beam confocal mask defect detection method based on a fiber laser array, comprising:

[0023] A fiber laser array is used to obtain a multi-point light beam. The beam is deflected by a collimating lens, a reflector, and a first beam splitter. After deflection, the beam is expanded by an imaging lens and incident on a second beam splitter. At this time, the light beam is divided into linearly polarized light in the transmission direction and linearly polarized light in the reflection direction. The linearly polarized light in the transmission direction is modulated into circularly polarized light after passing through a third beam splitter and a quarter-wave plate. The light is focused by a microscope objective lens placed on an actuator onto a mask sample to be tested, which is fixed on a motion stage. The reflected light from the surface of the mask sample to be tested returns along the original optical path to the first beam splitter through which the incident light passed. The split reflected light is focused by the first lens onto a photomultiplier light detection array, and a sequence of reflected light intensity information at each position is obtained.

[0024] The linearly polarized light in the reflected direction split by the second beam splitter is incident on the clock synchronization module to obtain the time series of the impulse signal. Combined with the reflected light intensity information sequence, the corresponding two-dimensional mask inspection icon is obtained to achieve rapid defect location and type identification.

[0025] The reflected light from the surface of the mask sample to be measured is split along the original optical path through the third beam splitter through which the incident light passes, and then is sent to the differential confocal module. The beam splitter in the differential confocal module splits the light beam into the back-focus optical path and the front-focus optical path respectively. The light beam is collected by the corresponding detectors, and the corresponding back-focus and front-focus signals are obtained. After scanning by the actuator, the corresponding axial differential confocal response curve is obtained. After fitting the data, the accurate focusing information of the microscope objective lens is obtained, so that the microscope objective lens is always in the ideal fixed focus position.

[0026] Optionally, the differential confocal module is used to accurately place the mask sample to be tested at the focal plane of the microscope objective lens, the fiber laser array and the photomultiplier tube detector are both located at the conjugate plane of the sample plane, and a pinhole is placed close to the detector. The pinhole and the fiber laser array are in an imaging relationship with each other, thereby removing out-of-focus light outside the focal plane and improving detection accuracy.

[0027] Optionally, the differential confocal module further includes the following steps to improve the detection accuracy:

[0028] The built-in detection light source point, the focal plane of the microscope objective, and the detector pinhole of the differential confocal module are in a conjugate relationship with each other. The scattered light generated at the focal plane of the microscope objective is normally collected by the detector through the detector pinhole. For the scattered light at the non-focal plane, its imaging position deviates from the pinhole position, and only a small part of the scattered light can be collected by the detector through the pinhole, thereby eliminating the interference of out-of-focus light outside the focal plane.

[0029] This application has the following beneficial effects:

[0030] Using a fiber laser array to acquire a multi-point scanning light field, the scanning light field can be freely controlled based on the arrangement of the laser array, eliminating the traditional system's reliance on diffractive optical elements. This system is simple to manufacture and offers a high degree of adjustment freedom. Through the combined action of a motion stage and a multi-faceted rotating mirror, combined with signals from a clock synchronization module, fast and accurate two-dimensional scanning imaging of the mask is achieved. The present invention uses a differential confocal system to acquire the corresponding differential confocal axial response, enabling real-time, accurate focusing of the microscope objective lens and improving defect detection accuracy. Combining these advantages, the present invention achieves a high-precision, fast mask defect detection system with greater adjustment freedom. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of a multi-beam confocal mask defect detection system based on a fiber laser array provided in an embodiment of the present application;

[0032] Figure 2 A schematic diagram of the structure of a fiber laser array provided in an embodiment of the present application;

[0033] Figure 3 A schematic diagram of the differential confocal response simulation results provided in an embodiment of the present application;

[0034] Figure 4 This is a schematic diagram of the signal detected by the time synchronization module provided in an embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to make the core, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by ordinary technicians in this field without paying creative labor are within the scope of protection of this application.

[0036] At present, although the existing line scanning mask defect detection system has a fast detection speed, it cannot accurately locate the defects in two dimensions. Although the existing point scanning mask defect detection system can accurately locate the defects, it generally has the problem of slow detection speed. This application provides a multi-beam confocal mask defect detection system and method based on a fiber laser array that can comprehensively solve the above problems, such as Figure 1 As shown, the multi-beam confocal mask defect detection system based on the fiber laser array of this embodiment includes:

[0037] A fiber laser array 1 serves as a scanning light field, comprising a freely arrangable multi-point scanning light field. The emitted light beam is collimated by a collimating lens 2 and then transmitted through a first reflector 3 and a first beam splitter 4 to a polygonal mirror 5. The light beam is deflected and expanded by imaging lenses (including a second lens 6 and a third lens 7) before entering a second beam splitter 8. The light beam is then split into linearly polarized light in the transmission and reflection directions. The linearly polarized light in the transmission direction is modulated into circularly polarized light by a third beam splitter 9 and a quarter-wave plate 10. The light is then focused by a microscope objective 11 mounted on an actuator 12 onto a reticle sample to be tested, which is fixed to a motion stage 13. The reflected light from the surface of the reticle sample to be tested, carrying reticle-related information, returns along the original optical path, passing through the microscope objective 11, the quarter-wave plate 10, the third lens 7, and the second lens 6. After being deflected by the polygonal mirror 5, it passes through the first beam splitter 4 and is focused by the first lens 14 onto a photomultiplier light detection array 15, thereby obtaining an intensity information sequence on the reticle surface.

[0038] The linearly polarized light reflected by the second beam splitter 8 enters the clock synchronization module 16, is focused by the lens in the module, and is transmitted to the grating. It is collected by the detector therein to obtain the time series of the impulse signal.

[0039] The differential confocal module 17 has a built-in 632nm laser as a detection light source. The emitted light beam is collimated by a collimating lens, reflected by the third beam splitter 9, and then focused by the microscope objective 11 onto the mask surface to be measured after passing through the quarter-wave plate 10. Similarly, the reflected light beam passes through the microscope objective 11, the quarter-wave plate 10, and the third beam splitter 9 again and returns along the original optical path to be incident on the differential confocal module 17. The incident light is split by a beam splitter into linearly polarized light in the transmission direction and the reflection direction, respectively entering the back-focus optical path and the front-focus optical path. The corresponding detectors collect the corresponding back-focus and front-focus signals, and scan them with the actuator 12 to obtain the corresponding axial differential confocal response curve. After fitting the data, the accurate focusing information of the microscope objective is obtained, so that the microscope objective is always in the ideal fixed focus position.

[0040] Furthermore, the sample to be tested is accurately placed at the focal plane of the microscope objective through a differential confocal module. The fiber laser array and the photomultiplier tube detector are both located at the conjugate plane of the sample plane. A pinhole is placed close to the detector. The scattered light generated at the focal plane can be normally collected by the detector through the pinhole. However, for the scattered light at non-focal planes, its imaging position deviates from the pinhole position. Therefore, only a small amount of scattered light can be collected by the detector through the pinhole, thereby eliminating interference outside the focal plane and improving the accuracy of system detection.

[0041] The differential confocal module is combined with an actuator to achieve accurate focusing of the microscope objective lens. The beam splitter in the differential confocal module divides the reflected light of the mask sample to be measured into two measuring beams, which are received by the two detectors PMT1 and PMT2 after passing through the focusing lens and the pinhole respectively. The offsets of the intersection of the pinhole and the measuring beam are respectively and , then the light intensity signal obtained by the corresponding detector can be expressed as:

[0042]

[0043]

[0044] in and Represents the normalized optical coordinates of the radial and axial directions in the object space, respectively, and the actual radial coordinates and the axial coordinates There is a conversion relationship between them. represents the defocus amount Optical coordinates under normalized conditions. and are the three-dimensional point spread functions of the illumination light path and the collection light path in the differential confocal module, represents the three-dimensional amplitude distribution of the illumination light field, and the operator It represents the convolution operation in three-dimensional space.

[0045] Since the focal length of the system is much larger than the offset , the normalized radius of the available system pupil , system normalized pupil function and the zero-order Bessel function Represents the point spread function of the system and , the formula used is:

[0046]

[0047] Among them, the normalized optical coordinates With actual coordinates The relationship between is determined by formula (4):

[0048]

[0049]

[0050] in To detect the wavelength of the light source, is the effective numerical aperture of the microscope objective lens, when The value of defocus is When the normalized value is calculated, the optical coordinate , represents the additional noise caused by the difference between the two detectors, , which has good linearity in the center of the response curve; based on the above formula, the corresponding differential confocal curve is calculated, and the simulation results are as follows Figure 4 As shown, the central part of the response curve has good linearity. Based on the differential response curve, the fixed focus offset can be calculated by formula (6). Perform an exact calculation:

[0051] Formula (6)

[0052] in Represents the change value of the differential response signal, represents the slope of the linear region; the differential confocal module periodically acquires the differential response signal and calculates the corresponding offset in real time , the corresponding actuator moves a distance , actuator and the calculated offset inter-satisfaction relationship , It is a proportional parameter whose value is determined by the system numerical aperture size and focus rate requirements. It is used to limit the distance of fixed focus movement and achieve real-time and accurate focus tracking of the system.

[0053] Furthermore, when the scanning light field is incident on the surface of the reticle area to be tested, if there are defects such as bumps and depressions on the reticle surface, the intensity of the reflected light collected by the photomultiplier tube detector will change accordingly due to the scattering effect of the defects. By analyzing the intensity information on the detector obtained from different areas, the location of the defect can be determined. At the same time, the type of defect can be distinguished based on the transformation pattern of the detected intensity information. The system uses a multi-faceted rotating mirror and a motion stage to achieve two-dimensional inspection of the mask, and a time synchronization module matches the deflection angle of the light beam with the corresponding scanning area to achieve accurate positioning of the scanning area.

[0054] Furthermore, in order to make the fiber laser array arrangement more compact and firm, Figure 2 As shown, the clamping structure fixes the optical fiber. Triangular grooves are etched on both sides of the structure. The depth and spacing of the etching are determined by the arrangement of the array and the outer diameter of the optical fiber. During preparation, the optical fiber is installed in the corresponding groove to ensure the fixing effect. In particular, the optical fiber used in the device uses an etchant to corrode the outer cladding of the front end of the optical fiber before use, thereby further reducing the spacing between the optical fiber array and improving the scanning speed of the system.

[0055] During the arrangement of the fiber laser array, the actual use requirements of the system are first considered to determine the corresponding microscope objective lens. The arrangement of the fiber laser array is determined based on the field of view size of the microscope objective lens used and the required detection accuracy requirements to optimize the scanning rate of the system. In addition, the arrangement of the photomultiplier tube array should be consistent with the arrangement of the fiber laser array to meet the multi-point confocal relationship to improve the detection resolution.

[0056] Furthermore, for the multi-faceted rotating mirror, if the rotating mirror rotation angular velocity is , the current rotation angle of the mirror is , the imaging distance is , then on the imaging plane, there is an image point scanning speed , the image point scanning speed changes with the current rotation angle changes, and the linear relationship cannot be satisfied; an imaging lens is introduced after the multi-faceted rotating mirror, and its imaging axial coordinate Angle with incident light Satisfy the corresponding relationship , is the focal length of the imaging lens, and the scanning speed is , which matches the rotating mirror rotating at a constant angular velocity, eliminating the need to introduce complex nonlinear compensation algorithms.

[0057] Furthermore, the clock synchronization module is introduced to match the signal collected by the photomultiplier tube detector with the corresponding detection position. When the linearly polarized light in the reflection direction enters the clock synchronization module, it is deflected by the converging lens. A grating is placed behind the converging lens. Only a part of the light at a specific angle can pass through the grating and be collected by the detector. The signal collected by the detector is as follows: Figure 3 As shown, represents the mirror rotation frequency of the polygon mirror, represents the number of faces of the multi-faceted mirror in a single deflection cycle. In the method, the position of the impact signal obtained is the horizontal scanning calibration position, and there is a corresponding relationship between the scanning calibration position in the grating and the horizontal coordinate of the detection area in the mask to be tested. Therefore, according to the horizontal coordinate-time relationship obtained by the time synchronization module and the vertical coordinate-time relationship obtained by the motion stage recording, the defect position can be accurately located. Combined with the light intensity-time signal obtained by the detector array, the scanning position and the light intensity information obtained by detection can be accurately mapped.

[0058] This embodiment also provides a multi-beam confocal mask defect detection method based on fiber laser, including:

[0059] The actuator is adjusted to scan axially, and the front and back focal paths in the differential confocal module are used to acquire light intensity signals at corresponding positions. The axial differential confocal response curve is calculated and used as a basis for real-time positioning of the microscope objective lens to the desired focus. A multi-faceted rotating mirror and a motion stage are used to achieve two-dimensional scanning of the mask to be tested. A photomultiplier tube detector is used to acquire the corresponding light intensity-time series. Combined with the horizontal coordinate-time series obtained by the time synchronization module and the vertical coordinate-time series recorded by the motion stage, a precise mapping relationship between the corresponding scanning position on the mask and the obtained light intensity information is established. Based on the corresponding data processing model, the corresponding mask inspection pattern is obtained. By comparing and analyzing the obtained patterns and combining the corresponding relationships between mask inspection patterns for different defect types, accurate positioning and type differentiation of mask defects are achieved. Furthermore, the obtained mask inspection results can be analyzed using a trained neural network model to accurately locate the defect position and quickly distinguish the defect type.

[0060] The above is a detailed introduction to the multi-beam confocal mask defect detection system and method based on fiber laser provided by the present application; for ordinary technicians in this technical field, several improvements and modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A multi-beam confocal mask defect detection system based on a fiber laser array, characterized in that: include: A fiber laser array, including a multi-point scanning light field, serves as the system light source; A collimating lens, a reflector and a first beam splitter, wherein the fiber laser array is connected to the collimating lens, and the collimated incident light passes through the reflector and is split into two independent light beams by the first beam splitter; A polygonal mirror, a second beam splitter, and a third beam splitter, wherein the polygonal mirror is used to deflect one of the incident light beams independently generated by the first beam splitter, so that the light beam passes through the imaging lens and is expanded to the second beam splitter and the third beam splitter; a quarter-wave plate, used to modulate the linearly polarized light after being split by the second beam splitter and the third beam splitter into circularly polarized light; Microscope objective lens, used to focus circularly polarized light onto the surface of the mask to be tested; The motion stage is used to fix the mask to be tested and realize fast two-dimensional scanning of the mask; Differential confocal module, used to help the microscope objective lens to accurately focus; The photomultiplier tube detector analyzes the reflected light from the surface of the mask to be tested after it returns along the original optical path to the first beam splitter and obtains the intensity information of the corresponding reflected light; The clock synchronization module is used to analyze the other beam of linear polarization after the incident light is split by the second beam splitter to obtain the time series of the impulse signal.

2. The multi-beam confocal mask defect detection system based on a fiber laser array according to claim 1, characterized in that: The fiber laser array is arranged in an X-shaped cross pattern. Triangular grooves are etched on both sides of the fiber laser array. The depth and spacing of the etching are determined by the arrangement of the array and the outer diameter of the optical fiber.

3. The multi-beam confocal mask defect detection system based on a fiber laser array according to claim 2, characterized in that: The arrangement of the fiber laser array is consistent with the arrangement of the photomultiplier tube detector array.

4. The multi-beam confocal mask defect detection system based on a fiber laser array according to claim 1, characterized in that: Also includes: The multi-faceted rotating mirror realizes fast two-dimensional scanning of the mask by cooperating with the motion stage, thereby improving the detection speed of the system. Specifically, the multi-faceted rotating mirror and the imaging lens are used, the multi-faceted rotating mirror rotates at an angular velocity of β, and the angle between the imaging axial coordinate z and the incident light is Satisfy the corresponding relationship , is the focal length of the imaging lens, and the scanning speed at this point , matched with a polygonal mirror rotating at a constant angular velocity.

5. The multi-beam confocal mask defect detection system based on a fiber laser array according to claim 1, characterized in that: The differential confocal module has a built-in detection light source. The emitted light beam is collimated by the collimating lens, reflected by the third beam splitter, and focused by the microscope objective onto the surface of the mask to be tested after passing through the quarter-wave plate. Similarly, the reflected light beam passes through the microscope objective, quarter-wave plate and third beam splitter again and returns to the original optical path to be incident on the differential confocal module. The incident light is respectively incident on the back focus optical path and the front focus optical path by a beam splitter, and is collected by the corresponding detector to obtain the corresponding back focus signal and front focus signal. After scanning by the actuator, the corresponding axial differential confocal response curve is obtained. After fitting the data, the accurate focusing information of the microscope objective is obtained, so that the microscope objective is always in the ideal fixed focus position.

6. The multi-beam confocal mask defect detection system based on a fiber laser array according to claim 5, characterized in that: The built-in detection light source point, the focal plane of the microscope objective, and the detector pinhole of the differential confocal module are in a conjugate relationship with each other. The scattered light generated at the focal plane of the microscope objective is normally collected by the detector through the detector pinhole. For the scattered light at the non-focal plane, its imaging position deviates from the pinhole position, and only a small part of the scattered light can be collected by the detector through the pinhole, thereby eliminating the interference of out-of-focus light outside the focal plane.

7. The multi-beam confocal mask defect detection system based on a fiber laser array according to claim 1, characterized in that: The linearly polarized light in the reflected direction split by the second beam splitter is incident on the clock synchronization module to obtain the time series of the impulse signal. Combined with the reflected light intensity information sequence, the corresponding two-dimensional mask detection icon is obtained to achieve rapid positioning and type identification of defects.

8. A multi-beam confocal mask defect detection method based on a fiber laser array, characterized in that: include: A fiber laser array is used to obtain a multi-point light beam. The beam is deflected by a collimating lens, a reflector, and a first beam splitter. After deflection, the beam is expanded by an imaging lens and incident on a second beam splitter. At this time, the light beam is divided into linearly polarized light in the transmission direction and linearly polarized light in the reflection direction. The linearly polarized light in the transmission direction is modulated into circularly polarized light after passing through a third beam splitter and a quarter-wave plate. The light is focused by a microscope objective lens placed on an actuator onto a mask sample to be tested, which is fixed on a motion stage. The reflected light from the surface of the mask sample to be tested returns along the original optical path to the first beam splitter through which the incident light passed. The split reflected light is focused by the first lens onto a photomultiplier light detection array, and a sequence of reflected light intensity information at each position is obtained. The linearly polarized light in the reflected direction split by the second beam splitter is incident on the clock synchronization module to obtain the time series of the impulse signal. Combined with the reflected light intensity information sequence, the corresponding two-dimensional mask inspection icon is obtained to achieve rapid defect location and type identification. The reflected light from the surface of the mask sample to be measured is split along the original optical path through the third beam splitter through which the incident light passes, and then is sent to the differential confocal module. The beam splitter in the differential confocal module splits the light beam into the back-focus optical path and the front-focus optical path respectively. The light beam is collected by the corresponding detectors, and the corresponding back-focus and front-focus signals are obtained. After scanning by the actuator, the corresponding axial differential confocal response curve is obtained. After fitting the data, the accurate focusing information of the microscope objective lens is obtained, so that the microscope objective lens is always in the ideal fixed focus position.

9. The multi-beam confocal mask defect detection method based on a fiber laser array according to claim 8, characterized in that: The differential confocal module is used to accurately place the mask sample to be tested at the focal plane of the microscope objective lens. The fiber laser array and the photomultiplier tube detector are both located at the conjugate plane of the sample plane. A pinhole is placed near the detector. The pinhole and the fiber laser array form an imaging relationship with each other, thereby removing out-of-focus light outside the focal plane and improving detection accuracy.

10. The multi-beam confocal mask defect detection method based on a fiber laser array according to claim 8, characterized in that: The differential confocal module further includes the following steps to improve detection accuracy: The built-in detection light source point, the focal plane of the microscope objective, and the detector pinhole of the differential confocal module are in a conjugate relationship with each other. The scattered light generated at the focal plane of the microscope objective is normally collected by the detector through the detector pinhole. For the scattered light at the non-focal plane, its imaging position deviates from the pinhole position, and only a small part of the scattered light can be collected by the detector through the pinhole, thereby eliminating the interference of out-of-focus light outside the focal plane.

Images