Integrated bright field and dark field EUV microscope device and mask defect detection method

Abstract

The invention discloses an integrated bright field and dark field EUV microscope device and a mask defect detection method. The EUV microscope device comprises a double-cavity vacuum system, an EUV light source system, a microscope light path system, a nanoscale positioning and automatic film changing system and a double-mode EUV imaging system, and the microscope light path system can converge EUV light radiated by the EUV light source system to the surface of a mask. By adjusting the light beam limiting aperture and the configuration of the central aperture of the secondary mirror in the infinite or finite Schwarzschild objective lens, the device construction switching between the bright field imaging mode and the dark field imaging mode can be realized. According to the invention, not only can the pattern defects of the mask be detected, but also the internal defects caused by deformation of the interior of the MoSi multilayer reflecting film and the substrate material and the like can be detected.

Description

Technical Field

[0001] This invention relates to the fields of optical inspection, mask inspection, and EUV lithography machines, and in particular to an integrated bright-field and dark-field EUV microscope device and a method for detecting mask defects. Background Technology

[0002] With the continuous development of semiconductor technology, chip process nodes are shrinking, from 7nm, 3nm to 2nm. This places higher demands on the quality of EUV lithography masks. Since the mask is the pattern template used in the lithography process, it transfers nanoscale pattern information onto the substrate material using EUV light. Extremely small defects in EUV masks, such as nanoscale depressions, bumps, particles, or slight breaks in the pattern, can be amplified during the lithography process, causing deviations in the circuit pattern on the wafer and leading to a decrease in chip yield. To a certain extent, mask defects affect the quality of chip manufacturing, necessitating the development of higher resolution and more precise defect detection equipment.

[0003] Atomic force microscopy (AFM) can detect defects in mask images over an area of ​​approximately 50 μm, but its detection speed is relatively slow. Stromal electron microscopy (SEM) can provide high-resolution imaging of the microstructure of a mask surface and detect defects at the nanometer scale, but it cannot detect defects inside the mask (Tung-Yaw Kang, et al., Proceedings of SPIE, 2008, 7122: 71221F). However, both AFM and SEM are large and expensive inspection devices that must be mounted on a dedicated desktop. Electron beam microscopy (EB) can detect defects in smaller geometries, but it cannot detect defects with technology nodes smaller than 10 nm.

[0004] To accurately detect defects on EUV masks, Lasertec delivered its first photochemical blank inspection system in 2020 (Harry J. Levinson, SPIE, 2020, Bellingham, Washington 98227-0010USA). EUV inspection equipment offers higher detection accuracy, capable of detecting defects and particles that other inspection methods cannot. In particular, when the mask is covered with a protective film (Pellicle), it can interfere with other inspection equipment. Even in this situation, EUV inspection equipment can still accurately identify minute defects. Therefore, developing EUV inspection equipment suitable for miniaturized benchtop masks has become a key technological challenge for improving chip yield. Summary of the Invention

[0005] To address the need for higher resolution detection equipment for mask defects, this invention aims to construct a bright-field and dark-field EUV microscope device and method for detecting mask defects. A driving laser bombards a target material to generate plasma and emit EUV light. A collecting mirror collects the EUV light emitted from the laser-target interaction point (PF). The microscope's optical path system focuses the collected EUV light onto the mask surface. The reflected / scattered EUV light reaches the EUV imaging system via an infinity Schwarzschild objective and an EUV high-magnification lens. This type of bright-field / dark-field device can detect surface defects in masks. The reflected / scattered EUV light also reaches the EUV imaging system via a microscope optical path system with an infinity Schwarzschild objective. This type of bright-field / dark-field device can also detect internal defects in masks. The EUV microscope detection device constructed using this patent can detect not only surface defects in masks but also nanoscale internal defects.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: An integrated bright-field and dark-field EUV microscope device for simultaneously detecting surface and internal defects of a photomask, characterized by comprising: The dual-chamber vacuum system comprises an EUV light source chamber and an EUV microscope chamber, which are independent of each other and connected by a gate valve. Both chambers are maintained at a vacuum level below 1 × 10⁻⁶ using a dry pump and a molecular pump, respectively. -4 Pa, to ensure efficient EUV light transmission; An EUV light source system is set inside the EUV light source cavity, including a driving laser and a target supply unit. The laser emitted by the driving laser is focused and then bombards the target provided by the target supply unit to generate plasma at the point of interaction (PF) and radiate EUV light. Microscope optical path system: includes optical elements arranged sequentially along the optical path within a dual-cavity vacuum system. - Ellipsoidal collecting mirror: It is set in the EUV source cavity, with its first focal point located at the interaction point (PF) between the laser and the target, and its second focal point located on the focal plane of the Schwarzschild objective lens group, used to focus the EUV light radiated from the PF point onto the surface of the mask. - A 45° EUV plane mirror for receiving and deflecting EUV light from the ellipsoidal collecting mirror; - A replaceable Schwarzschild objective lens assembly, wherein, in surface defect detection mode, an infinity Schwarzschild objective lens is combined with an EUV high-magnification lens; and in internal defect detection mode, a finite-distance Schwarzschild objective lens is combined with a secondary imaging module. The secondary imaging module comprises two types: one is a high-magnification finite-distance Schwarzschild objective lens, and the other includes an EUV plane mirror and a high-magnification ellipsoidal mirror. Nanoscale positioning and automatic lens changing system: including a five-axis (X, Y, Z, Θ and Φ directions) displacement stage, anti-vibration platform, robotic arm and multi-axis laser interferometer located at the focal plane of the Schwarzschild objective lens group, for nanoscale positioning and automatic lens changing of the mask; Dual-mode EUV imaging system: includes a switchable CCD camera and a TDI line array camera, used for static high-resolution imaging and dynamic scanning imaging respectively. The microscope optical path system enables the switching between bright-field and dark-field imaging modes within the same device by adjusting the beam limiting aperture and the aperture configuration of the secondary mirror center in the infinite or finite-distance Schwarzschild objective.

[0007] Furthermore, the microscope optical path system is configured in a first detection mode: when the infinity Schwarzschild objective lens (magnification of 4-40) is installed, the system also includes an EUV high magnification lens to form an optical path for surface defect detection; the reflected / scattered light from the mask passes sequentially through the infinity Schwarzschild objective lens and the EUV high magnification lens to form an image.

[0008] Furthermore, the microscope optical path system is configured in a second detection mode: when the finite-distance Schwarzschild objective is installed, the system also includes a high-magnification finite-distance Schwarzschild objective, and the two are connected in series to form a 4-1000x adjustable secondary imaging optical path, which is used to enhance the collection and resolution of defect signals inside the mask.

[0009] Furthermore, the microscope optical path system is configured in a third detection mode: when the finite-distance Schwarzschild objective lens is installed, the system also includes an EUV plane mirror and a high-magnification ellipsoidal mirror, which are connected in series to form a 4-1000x adjustable secondary imaging optical path, forming a collection optical path for internal micro-defects and improving the detection sensitivity of deep defects.

[0010] Furthermore, the secondary mirrors of the infinity and finite distance Schwarzschild objectives have optional central aperture structures, which, in conjunction with the position adjustment of the beam limiting aperture, enable the switching of the device setup for bright-field imaging and dark-field imaging.

[0011] Furthermore, the target material of the EUV light source system is xenon gas or tin droplets, the surface of the optical elements in the microscope optical path system is coated with a Mo / Si multilayer reflective film, and a Zr filter is provided in the EUV light source cavity to filter out stray light in the non-EUV band.

[0012] Furthermore, the robotic arm, the multi-axis laser interferometer, and the five-axis displacement stage are integrated for control, supporting the maintenance of a vacuum level higher than 1×10⁻⁶. -4 The mask can be automatically picked up, placed, and aligned under the condition of Pa.

[0013] Furthermore, the TDI linear array camera is synchronized with the motion controller of the five-axis displacement stage to achieve continuous scanning imaging of the mask, with the imaging speed matching the scanning speed of the displacement stage.

[0014] A method for detecting mask defects based on the above-mentioned device, characterized in that it includes: Step 1: Select the detection mode and bright-field or dark-field imaging mode according to the type of defect to be detected: - When inspecting surface defects, select the first inspection mode; - When detecting internal defects, select the second or third detection mode; Step 2: The mask is loaded onto the five-axis displacement stage using a robotic arm, and initial positioning is performed using a multi-axis laser interferometer; Step 3: Start the vacuum system and evacuate the dual chambers to the working vacuum level; Step 4: Turn on the EUV light source and adjust the microscope optical path system; Step 5: Drive the displacement stage to scan and acquire images using the EUV imaging system; Step 6: Based on image contrast analysis, identify and locate nanoscale defects on or inside the mask surface.

[0015] Furthermore, when detecting internal defects, the collection of deep-layer scattered signals can be enhanced by using a series high-magnification finite-distance Schwarzschild objective lens or a high-magnification ellipsoidal mirror, thereby improving the detection capability of internal minute defects such as Mo / Si multilayer films in photomasks and substrate material deformation.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: An ellipsoidal collecting mirror was used to collect EUV light emitted from the laser-target interaction point (PF). Different microscope optical path systems were designed, and bright-field EUV and dark-field EUV devices were built to detect surface and internal defects of photomasks. A robotic arm was used to place blank and patterned photomasks, and nanoscale defect information of the photomasks was observed by switching between a CCD camera and a TDI linear array camera. The bright-field EUV and dark-field EUV microscope detection devices built using this patent can detect not only pattern defects in photomasks but also internal defects caused by deformation of the MoSi multilayer reflective film and substrate material. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the EUV microscope device for detecting mask defects according to the present invention; Figure 2 This is an EUV microscope optical path diagram for detecting surface defects of a photomask according to the present invention; Figure 3 This is a schematic diagram of defects in the mask of the present invention; Figure 4 This is an EUV microscope optical path diagram of the present invention using two Schwarzschild objectives of different specifications with finite distance. Figure 5 This is the optical path diagram of the EUV microscope using a finite-distance Schwarzschild objective and a high-magnification ellipsoidal mirror according to the present invention; In the picture: 1-1: EUV light source cavity 1-2: EUV microscope cavity 2: First dry pump; 5: Second dry pump 3: First molecular pump; 6: Second molecular pump; 4: First vacuum gauge; 7: Second vacuum gauge 8: Driving Laser 9: Vacuum cavity viewing window 10: Focusing lens 11: Nozzle 12: Xenon 13: Gas feedthrough components 14, 16: Pipelines 15: Helium 17: Ellipsoidal collecting mirror 18: Zr filter 19: Pinhole 20:45° EUV plane mirror 21: Infinity Schwarzschild objective lens 21-1: Principal lens of the Schwarzschild objective at infinity 21-2: Secondary mirror of the Schwarzschild objective at infinity 22: Incident beam limiting aperture / Outgoing beam limiting aperture (collectively referred to as beam limiting aperture) 23: Mask 24: Five-axis displacement stage 25: Anti-micro-vibration platform 26: Computer (Control System) 27: CCD camera 28: TDI Linear Scan Camera 29: Robotic Arm 30: Multi-axis laser interferometer 31: Slide valve 32: EUV high magnification lens (in) Figure 2 (as shown in the image) 33: EUV plane mirror (in) Figure 5 (as shown in the image) 34: High-magnification ellipsoidal mirror (in) Figure 5 (as shown in the image) 35: High-magnification finite-distance Schwarzschild objectives (in...) Figure 4 (as shown in the image) 35-1: Primary mirror of a high-magnification finite-distance Schwarzschild objective. 35-2: Secondary mirror of a high-magnification finite-distance Schwarzschild objective. 36: Optical path components of an EUV microscope cavity 37: Buffer layer 38: Covering layer 39: MoSi multilayer reflective film 40: Glass substrate (starting substrate / low thermal expansion material substrate) 41: Conductive layer 42: Particle defects inside MoSi multilayer films 43: Depressions inside MoSi multilayer films 44: Finite Distance Schwarzschild Objective 44-1: Principal mirror of a finite-distance Schwarzschild objective 44-2: Secondary mirrors of finite-distance Schwarzschild objectives Detailed Implementation The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] The purpose of this invention is to provide an experimental platform system for detecting defects in EUV microscopes.

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Figure 1 This is a schematic diagram of the bright-field and dark-field EUV microscope apparatus for detecting mask defects according to the present invention, as shown in the figure, including: The dual-cavity vacuum system is designed to minimize the absorption of EUV light, necessitating a vacuum environment for the entire device. EUV light is generated by the excitation of xenon plasma radiation through the bombardment of a xenon target by a driving laser 8. The EUV light source system cavity 1-1 is externally connected to a first dry pump 2 and a first molecular pump 3, which maintain the vacuum chamber at a high vacuum level for an extended period. The pressure value in the EUV light source system cavity 1-1 is displayed by a first vacuum gauge 4, and this value is maintained at 10 for an extended period. -4 Below Pa. The EUV microscope chamber 1-2 is externally connected to a second dry pump 5 and a second molecular pump 6. The vacuum level of the vacuum chamber can be checked with a second vacuum gauge 7. Specifically, a gate valve 31 is installed between the two vacuum chambers. When the EUV light source system chamber 1-1 and the EUV microscope chamber 1-2 require separate maintenance, only the gate valve 31 needs to be closed. When the entire apparatus is operating normally, the gate valve 31 is in the open state.

[0022] The EUV light source system is located within the EUV light source cavity 1-1. This embodiment employs a laser-bombarded xenon gas target to generate plasma (Xe-LPP). The driving laser 8 passes through the vacuum cavity window 9 and is focused by the focusing lens 10 at a position 1 mm from the tip of the nozzle 11. Xenon gas 12 stored in a gas cylinder is introduced into the nozzle 11 from outside the vacuum cavity via the gas feed component 13 and pipe 14. Furthermore, to slow the diffusion of xenon gas 12, it is surrounded by helium gas 15, which is introduced into the nozzle 11 via pipe 16. When the nozzle 11 ejects gas, the driving laser 8 bombards the gas. At the point of interaction between the laser 8 and xenon gas 12, called the plasma (PF) point, EUV light is emitted.

[0023] The microscope optical system employs a modular design, with a multi-functional frame at its core, allowing for easy installation and switching of different optical modules. The basic optical path consists of the EUV beam collected by the ellipsoidal collecting mirror 17, which is first deflected 90° by a 45°-positioned EUV plane mirror 20 before entering the main imaging optical path, followed by the crucial interchangeable objective lens module. The microscope optical system includes the following key optical components.

[0024] - An ellipsoidal collecting mirror 17, mounted on a mirror support and placed inside the EUV source cavity 1-1, is used to collect EUV light emitted from the point of interaction (PF) between the laser 8 and the xenon 12 target. The EUV light is filtered by a Zr filter 18 to remove visible and near-infrared light. A pinhole 19 is placed in the optical path to collimate the light.

[0025] - Surface Inspection Module: Mounts an infinity Schwarzschild objective lens 21. This objective lens consists of a primary mirror 21-1 with a large radius of curvature and a secondary mirror 21-2 with a small radius of curvature, with a typical magnification of 20-40x. It converges the incident collimated light onto the surface of the mask 23.

[0026] - Internal detection module A: Mounts a finite-distance Schwarzschild objective lens 44. This objective lens also consists of a large radius-of-curvature primary mirror 44-1 with a central aperture and a small radius-of-curvature secondary mirror 44-2, with a typical magnification of 20-40x and a finite focal length. A second, higher-magnification (e.g., 400-1000x) finite-distance Schwarzschild objective lens 35 can be mounted in series behind it to form a secondary magnification imaging chain.

[0027] -Internal detection module B: It also installs a finite-distance Schwarzschild objective lens 44, but introduces an EUV plane mirror 33 into its outgoing optical path to redirect the beam, which is then collected and refocused by a high-magnification ellipsoidal mirror 34.

[0028] The optical path also integrates incident and outgoing beam limiting apertures 22. By adjusting the size of the beam limiting aperture and the aperture configuration of the secondary mirror center in the infinite or finite distance Schwarzschild objective, the device setup can switch between bright field and dark field imaging modes in the same device.

[0029] A nanoscale positioning and automated wafer changing system is positioned above a five-axis stage 24. The five-axis stage 24, connected to a computer 26, carries the mask 23 to be inspected and adjusts its X, Y, Z, Θ, and Φ directions. A robotic arm 29, also connected to the computer 26, is used to replace blank and patterned masks. During operation, the robotic arm 29 maintains the vacuum level and high cleanliness of the vacuum chamber. A vibration-damping platform 25, placed below the EUV microscope chambers 1-2, eliminates image blurring and positioning deviations caused by minute vibrations. A multi-axis laser interferometer 30, connected to the computer 26, monitors the relative position of the mask 23 and the silicon wafer stage in real time, ensuring the alignment accuracy of multilayer circuit patterns.

[0030] The dual-mode EUV imaging system observes defects in the mask 23 by switching between a CCD camera 27 and a TDI line scan camera 28. The sensor of the CCD camera 27 converts the captured light signals into electrical signals, thereby generating an image. The TDI line scan camera 28 can be precisely synchronized with the movement speed of the mask 23 on the five-axis displacement stage 24, enabling continuous exposure of the mask 23 and capturing an image of the entire mask 23.

[0031] Figure 2 This is an EUV microscope optical path diagram for detecting surface defects of a photomask according to the present invention.

[0032] See Figure 2(a) Optical path diagram of EUV bright-field microscopy for detecting defects on the mask surface. Ellipsoidal collecting mirror 17 collects EUV light emitted from the laser-xenon target interaction (PF) point. The light passes sequentially through Zr filter 18 and pinhole 19. The EUV microscope cavity optical path element 36 includes a 45° EUV plane mirror 20, an infinity Schwarzschild objective 21 (magnification 40), and an EUV high-magnification lens 32. After passing through the 45° EUV plane mirror 20, the EUV light is reflected and sequentially passes through the incident beam limiting aperture 22, the secondary mirror 21-2 of the infinity Schwarzschild objective, and the primary mirror 21-1 of the infinity Schwarzschild objective before converging on the mask surface 23. The reflected EUV light is sequentially reflected through the primary mirror 21-1 of the infinity Schwarzschild objective and the secondary mirror 21-2 of the infinity Schwarzschild objective. The light is then reflected again through the exit beam limiting aperture 22 and the EUV high-magnification lens 32 before reaching the EUV imaging system. By switching between the CCD camera 27 and the TDI line-scan camera 28 to observe the magnified image of the mask 23, the location and size of defects on the mask surface are identified. This detection device is called bright-field detection. Defect-free areas within the mask reflect EUV light back, appearing bright. However, defective areas reflect relatively less light, appearing as darker areas against a bright background. Therefore, defects in the mask can be detected by comparing the differences in brightness of the pattern.

[0033] See Figure 2 (b) The ellipsoidal collecting mirror 17 collects the EUV light emitted from the point of interaction between the laser and the xenon target. The light then passes through the Zr filter 18 and the pinhole 19. The light path then passes through the 45° EUV plane mirror 20, where it is reflected and converges onto the surface of the mask 23. Alternatively, an infinity Schwarzschild objective (40x magnification) with a secondary mirror 21-2 having a central aperture is used. After reflection by the 45° EUV plane mirror 20, the light passes through the infinity Schwarzschild objective with a secondary mirror 21-2 having a central aperture and converges onto the surface of the mask 23. See [reference needed]. Figure 2 (c) The scattered EUV light passes sequentially through the primary mirror 21-1 of the infinity Schwarzschild objective, the secondary mirror 21-2 of the infinity Schwarzschild objective, and the EUV high-magnification lens 32 before reaching the EUV imaging system. By switching between the CCD camera 27 and the TDI line array camera 28 to observe the magnified image of the mask, the location and size of defects on the mask surface are identified. Figure 2 (b) and Figure 2(c) The detection devices are all dark-field detection. Normal areas of the mask do not scatter light, while defective areas do, thus creating bright areas against a dark background. Dark-field detection is very sensitive for detecting tiny surface defects because these defects cause light scattering, resulting in bright areas in a dark field.

[0034] Figure 3 This is a schematic diagram of defects in the mask of the present invention.

[0035] See Figure 3 The photomask consists of a buffer layer 37, a cover layer 38, a MoSi multilayer reflective film 39, a glass substrate 40, and a conductive layer 41. Figure 2 The constructed EUV microscope setup is feasible for detecting particles and pattern defects on the surface of a photomask, but it cannot detect internal defects, such as particles 42 and depressions 43 in MoSi multilayer films. To accurately detect internal defects in the photomask, this patent... Figure 4 and Figure 5 exist Figure 2 Based on this, improvements and refinements were made to the corresponding optical path design.

[0036] Figure 4 This is an EUV microscope optical path diagram of the present invention using two Schwarzschild objectives of different finite distances.

[0037] See Figure 4(a) The ellipsoidal collecting mirror 17 collects the EUV light emitted from the laser-xenon target interaction (PF) point. The light then passes sequentially through the Zr filter 18 and the pinhole 19. The EUV microscope cavity optical path element 36 includes a 45° EUV plane mirror 20, a finite-distance Schwarzschild objective 44 (magnification 40), and a high-magnification finite-distance Schwarzschild objective 35 (magnification 400-1000). After passing through a 45° EUV plane mirror 20, the EUV light is reflected and then sequentially passes through the incident beam limiting aperture 22, the secondary mirror 44-2 of the finite-distance Schwarzschild objective, and the primary mirror 44-1 of the finite-distance Schwarzschild objective before converging on the surface of the mask 23. The reflected EUV light is sequentially reflected by the primary mirror 44-1 of the finite-distance Schwarzschild objective and the secondary mirror 44-2 of the finite-distance Schwarzschild objective. The light is then reflected again and converged by the exit beam limiting aperture 22 to the focal point of the finite-distance Schwarzschild objective 44. The EUV reflected light at this focal point is reflected by the secondary mirror 35-2 and the primary mirror 35-1 of the high-magnification finite-distance Schwarzschild objective and focused onto the EUV imaging system. By switching between the CCD camera 27 and the TDI line-scan camera 28 to observe the magnified image of the mask 23, the location and size of defects inside the mask can be identified. This detection device is called bright-field detection.

[0038] See Figure 4 (b) The ellipsoidal collecting mirror 17 collects the EUV light emitted from the point of interaction between the laser and the xenon target. The light then passes sequentially through the Zr filter 18 and the pinhole 19. The light path passes through a 45° EUV plane mirror 20, where it is reflected and converges onto the surface of the mask 23. Alternatively, a secondary mirror 44-2 with a central aperture is used with a finite-distance Schwarzschild objective lens. After being reflected by the 45° EUV plane mirror 20, the light passes through the secondary mirror 44-2 with a central aperture and converges onto the surface of the mask 23. See [reference needed]. Figure 4 (c) The scattered EUV light passes sequentially through the primary mirror 44-1 of the finite-distance Schwarzschild objective and the secondary mirror 44-2 of the finite-distance Schwarzschild objective, converging at the focal point of the finite-distance Schwarzschild objective 44. The EUV reflected light at this focal point is reflected by the secondary mirror 35-2 and the primary mirror 35-1 of the high-magnification finite-distance Schwarzschild objective and focused onto the EUV imaging system. By switching between the CCD camera 27 and the TDI line-scan camera 28 to observe the magnified image of the mask, the location and size of internal defects in the mask can be identified. Figure 4 (b) and Figure 4 (c) All detection devices are dark field detection devices.

[0039] Figure 5 This is the optical path diagram of an EUV microscope using a finite-distance Schwarzschild objective and a high-magnification ellipsoidal reflector, as described in this invention.

[0040] See Figure 5 (a) The ellipsoidal collecting mirror 17 collects the EUV light emitted from the laser-xenon target interaction (PF) point. The light then passes sequentially through the Zr filter 18 and the pinhole 19. The EUV microscope cavity optical path element 36 includes a 45° EUV plane mirror 20, a finite-distance Schwarzschild objective 44 (magnification of 40), a plane mirror 33, and a high-magnification ellipsoidal mirror 34 (magnification of 400-1000). After passing through a 45° EUV plane mirror 20, the EUV light is reflected and sequentially passes through the incident beam limiting aperture 22, the secondary mirror 44-2 of the finite-distance Schwarzschild objective, and the primary mirror 44-1 of the finite-distance Schwarzschild objective before converging on the surface of the mask 23. The reflected EUV light is sequentially reflected by the primary mirror 44-1 of the finite-distance Schwarzschild objective and the secondary mirror 44-2 of the finite-distance Schwarzschild objective. The light is then reflected again and converged by the exit beam limiting aperture 22 to the EUV plane mirror 33. The high-magnification ellipsoidal mirror 34 focuses the collected EUV light onto the EUV imaging system. By switching between the CCD camera 27 and the TDI line array camera 28 to observe the magnified image of the mask 23, the location and size of defects inside the mask are identified. This detection device is called bright-field detection.

[0041] See Figure 5 (b) The ellipsoidal collecting mirror 17 collects the EUV light emitted from the point of interaction between the laser and the xenon target. The light then passes sequentially through the Zr filter 18 and the pinhole 19. The EUV microscope cavity optical path element 36 includes a 45° EUV plane mirror 20, a finite-distance Schwarzschild objective lens 44 (magnification 40), an EUV plane mirror 33, and a high-magnification ellipsoidal mirror 34 (magnification 400-1000). After passing through the 45° EUV plane mirror 20, the light is reflected and converged on the surface of the mask. Alternatively, a secondary mirror 44-2 with a central aperture is used with a finite-distance Schwarzschild objective lens. After being reflected by the 45° EUV plane mirror 20, the light passes through the secondary mirror 44-2 with a central aperture and converges on the surface of the mask 23. See [link to documentation]. Figure 5(c) The scattered EUV light passes sequentially through the primary mirror 44-1 of the finite-distance Schwarzschild objective and the secondary mirror 44-2 of the finite-distance Schwarzschild objective, where it is reflected again and converged to the EUV plane mirror 33. The high-magnification ellipsoidal mirror 34 focuses the collected EUV light onto the EUV imaging system. By switching between the CCD camera 27 and the TDI line array camera 28 to observe the magnified image of the mask, the location and size of defects inside the mask are identified. Figure 5 (b) and Figure 5 (c) The detection device is called dark field detection.

[0042] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. An integrated bright-field and dark-field EUV microscope device for simultaneously detecting surface and internal defects of a photomask, characterized in that, include: The dual-chamber vacuum system comprises an EUV light source chamber and an EUV microscope chamber, which are independent of each other and connected by a gate valve. Both chambers are maintained at a vacuum level below 1 × 10⁻⁶ using a dry pump and a molecular pump, respectively. -4 Pa, to ensure efficient EUV light transmission; The EUV light source system is located inside the EUV light source cavity and includes a driving laser (8) and a target supply unit. The laser emitted by the driving laser (8) is focused and then bombards the target provided by the target supply unit to generate plasma at the point of interaction (PF) and radiate EUV light. Microscope optical path system: includes optical elements arranged sequentially along the optical path within a dual-cavity vacuum system. - Ellipsoidal collecting mirror: It is set in the EUV light source cavity, with its first focal point located at the interaction point (PF) between the laser (8) and the target material, and its second focal point located on the focal plane of the Schwarzschild objective lens group, used to focus the EUV light radiated from the PF point onto the surface of the mask (23). - A 45° EUV plane mirror for receiving and deflecting EUV light from the ellipsoidal collecting mirror; - A replaceable Schwarzschild objective lens assembly, wherein, in surface defect detection mode, an infinity Schwarzschild objective lens is combined with an EUV high-magnification lens; and in internal defect detection mode, a finite-distance Schwarzschild objective lens is combined with a secondary imaging module. The secondary imaging module comprises two types: one is a high-magnification finite-distance Schwarzschild objective lens, and the other includes an EUV plane mirror and a high-magnification ellipsoidal mirror. Nanoscale positioning and automatic lens changing system: including a five-axis (X, Y, Z, Θ and Φ directions) displacement stage, anti-vibration platform, robotic arm and multi-axis laser interferometer located at the focal plane of the Schwarzschild objective lens group, for nanoscale positioning and automatic lens changing of the mask (23); Dual-mode EUV imaging system: includes a switchable CCD camera and a TDI line array camera, used for static high-resolution imaging and dynamic scanning imaging respectively. The microscope optical path system enables the switching between bright-field and dark-field imaging modes within the same device by adjusting the beam limiting aperture and the aperture configuration of the secondary mirror center in the infinite or finite-distance Schwarzschild objective.

2. The integrated bright-field and dark-field EUV microscope device according to claim 1, characterized in that, The microscope optical path system is configured in the first detection mode: when the infinity Schwarzschild objective (magnification of 4-40) is installed, the system also includes an EUV high magnification lens to form an optical path for surface defect detection; the reflected / scattered light from the mask passes sequentially through the infinity Schwarzschild objective and the EUV high magnification lens to form an image.

3. The integrated bright-field and dark-field EUV microscope device according to claim 1, characterized in that, The microscope optical path system is configured in a second detection mode: when the finite-distance Schwarzschild objective is installed, the system also includes a high-magnification finite-distance Schwarzschild objective, and the two are connected in series to form a 4-1000x adjustable secondary imaging optical path, which is used to enhance the collection and resolution of defect signals inside the mask.

4. The integrated bright-field and dark-field EUV microscope device according to claim 1, characterized in that, The microscope optical path system is configured in a third detection mode: when the finite-distance Schwarzschild objective lens is installed, the system also includes an EUV plane mirror and a high-magnification ellipsoidal mirror, which are connected in series to form a 4-1000x adjustable secondary imaging optical path, forming a collection optical path for internal micro-defects and improving the detection sensitivity of deep defects.

5. The integrated bright-field and dark-field EUV microscope device according to claim 1, characterized in that, The secondary mirrors of the infinity and finite distance Schwarzschild objectives have optional central aperture structures, which, in conjunction with the position adjustment of the beam limiting aperture, enable the switching of the device setup for bright-field imaging and dark-field imaging.

6. The integrated bright-field and dark-field EUV microscope device according to claim 1, characterized in that, The target material of the EUV light source system is xenon gas or tin droplets. The optical components in the microscope optical path system are all coated with Mo / Si multilayer reflective films, and the EUV light source cavity is equipped with a Zr filter to filter out stray light in the non-EUV band.

7. The integrated bright-field and dark-field EUV microscope device according to claim 1, characterized in that, The robotic arm, the multi-axis laser interferometer, and the five-axis displacement stage are integrated for control, supporting the maintenance of a vacuum level higher than 1×10⁻⁶. -4 The mask can be automatically picked up, placed, and aligned under the condition of Pa.

8. The integrated bright-field and dark-field EUV microscope device according to claim 1, characterized in that, The TDI linear array camera is synchronized with the motion controller of the five-axis displacement stage to achieve continuous scanning imaging of the mask, with the imaging speed matching the scanning speed of the displacement stage.

9. A method for detecting mask defects based on the apparatus according to any one of claims 1-8, characterized in that, include: Step 1: Select the detection mode and bright-field or dark-field imaging mode according to the type of defect to be detected: - When inspecting surface defects, select the first inspection mode; - When detecting internal defects, select the second or third detection mode; Step 2: The mask (23) is loaded onto the five-axis displacement stage (24) by the robotic arm (29), and the initial positioning is performed using a multi-axis laser interferometer (30); Step 3: Start the vacuum system and evacuate the dual chambers to the working vacuum level; Step 4: Turn on the EUV light source and adjust the microscope optical path system; Step 5: Drive the displacement stage to scan and acquire images using the EUV imaging system; Step 6: Based on image contrast analysis, identify and locate nanoscale defects on or inside the mask surface.

10. The mask defect detection method according to claim 9, characterized in that, When detecting internal defects, the collection of deep-layer scattered signals can be enhanced by using a series high-magnification finite-distance Schwarzschild objective or a high-magnification ellipsoidal mirror, thereby improving the detection capability of internal minute defects such as Mo / Si multilayer films in photomasks and substrate material deformation.

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