Defect detection method for extreme ultraviolet lithography mask white board
By combining an extreme ultraviolet light source and a photoemission electron microscope, adjusting the wavelength and angle of the detection light, and acquiring PEEM images to analyze contrast changes, the problem of not being able to identify defect types in existing technologies has been solved, achieving high-sensitivity and high-spatial-resolution defect detection.
Patent Information
- Application Number
- CN202411112659.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-14
- Publication Date
- 2026-03-03
AI Technical Summary
Existing extreme ultraviolet lithography mask inspection technology cannot effectively identify defect types and has a slow inspection speed, which cannot meet the needs of the semiconductor industry.
An extreme ultraviolet light source with a wavelength range of 13.1~13.5nm was combined with a photoemission electron microscope. By adjusting the angle of the reflector and the wavelength of the detection light, PEEM images of different wavelengths were acquired, and the changes in image contrast were analyzed to identify the defect types of the mask white board.
It achieves high-sensitivity and high-spatial-resolution detection of mask whiteboards, accurately identifying phase and amplitude defects, and meeting the testing needs of the semiconductor industry.
Smart Images
Figure CN121595544A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of extreme ultraviolet (EUV) lithography mask technology, and more particularly to a defect detection method for EUV lithography mask white plates. Background Technology
[0002] Extreme ultraviolet (EUV) lithography masks mainly consist of a white mask and an absorption layer structure. The white mask is a blank mask without etched circuit patterns, composed of an ultra-smooth substrate and an EUV multilayer film structure. Defects on the white mask will cause errors in the integrated circuits on the chip, rendering it unusable and ultimately discarding it. However, current mask manufacturing technology cannot completely eliminate reproducible defects on the white mask. Therefore, defect detection technology is needed to inspect the white mask and perform mask repair and defect compensation based on the detection results, thereby achieving the manufacture of "zero-defect" masks.
[0003] Currently, the more mature extreme ultraviolet (EUV) mask defect detection technologies mainly include three types: dark-field detection based on the Schwarzchild optical system, EUV coherent diffraction microscopy, and electron beam microscopy. However, dark-field detection based on the Schwarzchild optical system suffers from problems such as its inability to identify absorption-type nanoscale defects and its detection speed not meeting industrialization requirements. EUV coherent diffraction microscopy, on the other hand, has drawbacks such as high light source intensity requirements, slow detection speed, inability to identify defect types, and inability to accurately locate defects. Electron beam microscopy performs microscopic imaging by receiving electrons emitted from the mask, but single-electron scanning microscopy has a slow detection speed, making it difficult to meet the needs of the semiconductor industry. Furthermore, multi-electron beam simultaneous scanning suffers from numerous problems, including crosstalk between electron beams and space charge effects in the high-density electrons of the scanning beam. Summary of the Invention
[0004] To address the technical bottleneck of existing detection technologies that cannot identify defect types, this invention provides a defect detection method for extreme ultraviolet lithography mask white boards, which can achieve high sensitivity and high spatial resolution detection of defect types in mask white boards.
[0005] The defect detection method for extreme ultraviolet lithography mask white plates provided by the present invention specifically includes the following steps: S1: Construct a defect type detection device, which includes an extreme ultraviolet light source and a photoemission electron microscope; S2: Extreme ultraviolet light source emits detection light with a wavelength range of 13.1~13.5nm. Adjust the reflector of the photoemission electron microscope so that the detection light reflected by the reflector is incident on the white mask to be tested, and the angle between the detection light and the normal of the white mask to be tested is 6°. S3: Set the wavelength adjustment interval, and adjust the collecting mirror of the extreme ultraviolet light source and the reflecting mirror of the photoemission electron microscope according to the wavelength adjustment interval to collect PEEM images formed on the imaging module of the photoemission electron microscope with different wavelengths of detection light. S4: Analyze the image contrast of all PEEM images acquired in step S3, and complete the defect type detection of the white mask to be tested based on the analysis results.
[0006] Preferably, in step S4, the region where the image contrast of all PEEM images acquired in step S3 is reversed is set as the first region, and the defect type of the region corresponding to the white mask to be tested and the first region is a phase defect type. The region with unchanged image contrast in all PEEM images acquired in step S3 is designated as the second region, and the defect type of the region corresponding to the white mask under test and the second region is amplitude defect type.
[0007] Preferably, the photoemission electron microscope further includes an electron objective, a contrast diaphragm, an aberration corrector, an Airy diaphragm, and a projection lens group arranged sequentially along the electron emission direction, wherein, A reflecting mirror is positioned in front of the back focal plane of the photoemission electron microscope (PEEM) objective, reflecting the detection light onto the white mask under test. The electron objective collects electrons emitted from the white mask, forming an electron image, which is then pre-magnified and focused. A contrast diaphragm is positioned at the back focal plane of the electron objective, used to adjust the electron reception angle. An Airy diaphragm is positioned at the first image plane of the electron objective, blocking the labyrinthine electrons in the PEEM and continuously adjusting the observation area. An aberration corrector corrects the aspherical aberrations of the electrons. A projection lens group magnifies the corrected electron image. The imaging module receives the magnified electrons and displays and stores the corresponding PEEM image based on the magnified and enhanced electrons.
[0008] Preferably, the surface of the reflector is deposited with a narrow-band extreme ultraviolet multilayer film.
[0009] Preferably, the imaging module consists of a microchannel plate, a fluorescent screen, and a CCD camera. The microchannel plate amplifies and enhances electrons from the projection lens group; the fluorescent screen receives the amplified and enhanced electrons and displays the PEEM image based on the amplified and enhanced electrons; and the CCD camera stores the PEEM image.
[0010] Preferably, the Airy aperture is adjusted to control the observation area of the photoemission electron microscope, and the diameter of the minimum observation area is 1 micrometer.
[0011] Preferably, the projection lens group includes a first projection lens and a second projection lens.
[0012] Compared with the prior art, the present invention can achieve the following beneficial effects: This invention combines wavelength detection technology with electronic detection technology, leveraging their respective advantages. It fully utilizes the high sensitivity of 13.5nm extreme ultraviolet light to detect internal defects in multilayer films and the high spatial resolution of electronic imaging to achieve highly sensitive and spatially resolved detection of defect types in mask white plates. Simultaneously, based on the operation of photoemission electron microscopy, by adjusting the detection illumination wavelength, the contrast changes between defective and defect-free locations on the mask white plate under different wavelength illumination conditions are observed, enabling defect type identification and overcoming the technical bottleneck of current detection technologies that cannot achieve defect type identification. Attached Figure Description
[0013] Figure 1 This is a schematic diagram of the defect type detection device for extreme ultraviolet lithography mask white plate provided according to an embodiment of the present invention; Figure 2 This is a flowchart illustrating a defect detection method for an extreme ultraviolet lithography mask white plate according to an embodiment of the present invention; Figure 3 The figure shows the IMD simulation results of the amplitude and phase distribution of the standing wave field formed inside the white mask of the test under different detection wavelengths according to the embodiments of the present invention. Figure 4(a) is a PEEM image generated by a photoemission electron microscope with a detection wavelength of 13.1 nm according to an embodiment of the present invention; Figure 4(b) is a PEEM image generated by a photoemission electron microscope with a detection wavelength of 13.3 nm according to an embodiment of the present invention; Figure 4(c) is a PEEM image generated by a photoemission electron microscope with a detection wavelength of 13.5 nm according to an embodiment of the present invention.
[0014] Figure reference numerals: 1. Mask white plate; 2. Electronic objective lens; 3. Reflector; 4. Contrast diaphragm; 5. Aberration corrector; 6. Airy diaphragm; 7. Projection lens group; 8. Imaging module; 9. Extreme ultraviolet light source; 701. First projection lens; 702. Second projection lens; 801. Microchannel plate; 802. Fluorescent screen; and 803. CCD camera. Detailed Implementation
[0015] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.
[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.
[0017] Because different detection wavelengths result in different standing wave field intensity distributions on the surface of the multilayer film of the photomask 1, phase defect-type PEEM (photoemission electron microscopy) images exhibit contrast reversal under detection wavelengths of 13.1 nm and 13.5 nm, while amplitude defect-type PEEM images do not show significant contrast changes due to variations in the light source wavelength. Therefore, by observing the changes in image contrast of PEEM images for different defect types under different light source wavelengths, the defect types of the extreme ultraviolet lithography photomask 1 can be identified.
[0018] Figure 1 The structure of a defect type detection device for an extreme ultraviolet lithography mask white plate 1 provided according to an embodiment of the present invention is shown.
[0019] like Figure 1 As shown, the present invention provides a defect type detection device for an extreme ultraviolet lithography mask white plate 1. The defect type detection device includes an extreme ultraviolet light source 9 and a photoemission electron microscope. The photoemission electron microscope includes a mirror 3 and, arranged sequentially along the electron emission direction, an electron objective lens 2, a contrast aperture 4, an aberration corrector 5, an Airy aperture 6, a projection lens group 7, and an imaging module 8. Extreme ultraviolet light source 9 emits reflected light with a wavelength range of 13.1~13.5nm. Reflector 3 is positioned in front of the back focal plane of the photoemission electron microscope objective, reflecting the detection light onto the white mask 1 under test. Electron objective 2 collects electrons emitted from the white mask 1, forming an electron image, and pre-magnifies and focuses the image. Contrast diaphragm 4 is positioned at the back focal plane of electron objective 2, used to adjust the electron reception angle. Airy diaphragm 6 is positioned at the first image plane of electron objective 2, blocking maze electrons in the photoemission electron microscope and continuously adjusting the observation area. Aberration corrector 5 corrects the aspherical aberration of the electrons. Projection lens group 7 magnifies the corrected electron image. Projection lens group 7 includes a first projection lens 701 and a second projection lens 702. Imaging module 8 receives the magnified electrons and displays and stores the corresponding PEEM image based on the magnified and enhanced electrons.
[0020] The surface of mirror 3 is deposited with a narrow-band extreme ultraviolet multilayer film.
[0021] The imaging module 8 consists of a microchannel plate 801, a fluorescent screen 802, and a CCD camera 803. The microchannel plate 801 amplifies and enhances electrons from the projection lens group 7. The fluorescent screen 802 receives the amplified and enhanced electrons and displays a PEEM image based on the amplified and enhanced electrons. The CCD camera 803 stores the PEEM image.
[0022] To improve imaging resolution and enhance image contrast, and to reduce the impact of the imaging background on image clarity, an Airy stop 6 that can be continuously adjusted is set at the first image plane of the objective lens. The Airy stop 6 adjusts the observation area of the photoemission electron microscope, and the diameter of the minimum observation area obtained is 1 micrometer.
[0023] Figure 2 The flowchart of a defect detection method for an extreme ultraviolet lithography mask white plate 1 provided according to an embodiment of the present invention is shown.
[0024] like Figure 2 As shown, the defect detection method for extreme ultraviolet lithography mask white plate 1 provided by the present invention specifically includes the following steps: S1: Construct a defect type detection device, which includes an extreme ultraviolet light source 9 and a photoemission electron microscope; S2: Extreme ultraviolet light source 9 emits detection light with a wavelength range of 13.1~13.5nm. Adjust the reflector 3 of the photoemission electron microscope so that the detection light reflected by the reflector 3 is incident on the white mask 1 to be tested, and the angle between the detection light and the normal of the white mask 1 to be tested is 6°. The choice of a 6° angle between the detection light and the normal of the mask 1 is based on two factors. First, this angle is the same as the incident angle between the illumination light and the mask in the extreme ultraviolet (EUV) lithography machine, which better matches the lithography conditions. Second, near-normal incident EUV light can propagate longitudinally for hundreds of nanometers within the multilayer film structure of the mask 1, effectively detecting phase defects within the multilayer film. The change in the reflected light phase caused by the phase defect is characterized by the wavefront change of the standing wave field formed by the superposition of incident and outgoing light within the multilayer film. Specifically, this manifests as a change in photoelectron emission intensity, i.e., the difference in intensity between the defective and non-defective regions in the PEEM detection image.
[0025] S3: Set the wavelength adjustment interval, and adjust the collecting mirror of the extreme ultraviolet light source 9 and the reflecting mirror of the photoemission electron microscope according to the wavelength adjustment interval, so as to collect PEEM images formed on the imaging module 8 of the photoemission electron microscope with different wavelengths of detection light. S4: Analyze the image contrast of all PEEM images acquired in step S3, and complete the defect type detection of the white mask 1 to be tested based on the analysis results.
[0026] In step S4, the region where the image contrast of all PEEM images acquired in step S3 is reversed is set as the first region, and the defect type of the region corresponding to the first region of the white mask 1 under test is the phase defect type. The region with unchanged image contrast in all PEEM images acquired in step S3 is designated as the second region, and the defect type of the region corresponding to the white mask 1 under test and the second region is amplitude defect type.
[0027] Figure 3 The figure shows the IMD simulation results of the amplitude and phase distribution of the standing wave field formed inside the white mask 1 under test by different detection wavelengths according to an embodiment of the present invention.
[0028] like Figure 3 As shown, when the detection wavelength is 13.5 nm, the phase defect appears as a bright spot in the PEEM image. However, when the detection wavelength is gradually decreased from 13.5 nm to 13.1 nm (as shown in the image), the phase defect appears as a bright spot. Figure 3 As shown at point B in the image, the electric field intensity at Z=0nm gradually increases, and the standing wave field on the surface of the white mask 1 under test shifts from nodes to antinodes. When PEEM is used to image and detect the white mask 1 under test at a wavelength of 13.1nm, the electron yield is highest in the defect-free area of the white mask 1 under test, which is a bright area with high brightness. The electron yield is lower in the area with defects inside the white mask 1 under test, which is a dark area with low brightness. Therefore, when the detection wavelength is 13.1nm, the phase defect appears as a dark spot in the PEEM image. Compared with the PEEM image at a detection wavelength of 13.5nm, the imaging contrast of the phase defect is reversed.
[0029] For amplitude-type defects, the materials of the defective and defect-free regions differ, resulting in different photoionization cross sections. Therefore, under the premise of irradiation with the same intensity of detection light, materials with larger photoionization cross sections generate more photoelectrons, appearing as brighter bright spots in the PEEM image, while materials with smaller photoionization cross sections generate fewer photoelectrons, appearing as darker dark spots, thus creating contrast in the PEEM image. Generally, the photoionization cross section increases with increasing atomic number. Taking the test mask 1 with a Mo / Si multilayer film structure as an example, the outermost material of the Mo / Si multilayer film is Si, a material with low absorptivity and photoionization cross section near a wavelength of 13.5 nm. When detection light near a wavelength of 13.5 nm irradiates the surface of the mask 1 containing amplitude defects, the outermost Si material in the defect-free region will generate fewer photoelectrons, appearing as darker areas in the PEEM image, while the defective structure will generate more photoelectrons, appearing as brighter areas in the PEEM image. This image contrast does not change with the detection wavelength. Therefore, when the detection wavelength is adjusted from 13.5nm to 13.1nm, the PEEM image of the mask white plate 1 with amplitude defect does not show the phenomenon of image contrast reversal.
[0030] In summary, it is feasible to identify defect types by adjusting the detection wavelength near the center wavelength of 13.5nm and observing the contrast changes of PEEM images under different wavelength conditions.
[0031] To verify the detection effect of the defect detection method for extreme ultraviolet lithography mask white plate 1 proposed in this invention, this invention performs PEEM imaging on the extreme ultraviolet lithography mask white plate 1 containing grating-type phase defects by adjusting the detection wavelength. The mask white plate 1 to be detected first prepared a grating-type phase defect structure with a height of 20nm, a period of 1000nm, and a duty cycle of 1 on a silicon substrate material. Then, a 40-period Mo / Si multilayer film with a center wavelength of 13.5nm was coated on the defect structure. In the experiment, detection wavelengths of 13.1nm, 13.3nm, and 13.5nm were used to perform PEEM imaging on the same area of the sample, respectively.
[0032] As shown in Figures 4(a)-4(c), the vertical stripe structure can be clearly observed, with a distance of 500 nm between adjacent stripes, corresponding to the two sidewalls of the grating structure. As shown in Figure 4(a), when the detection wavelength is 13.1 nm, the sidewall brightness of the grating structure in the PEEM image is low, while the brightness of the top surface and defect-free area of the grating structure is high. As shown in Figure 4(b), when the detection wavelength is 13.3 nm, the visibility of the grating structure in the PEEM image decreases, and the image contrast decreases. As shown in Figure 4(c), further changing the detection wavelength to 13.5 nm significantly improves the contrast of the PEEM image, but the sidewall brightness of the grating structure remains high, while the brightness of the top surface and defect-free area of the grating structure is low. Compared with the PEEM image at a detection wavelength of 13.1 nm, the image contrast has reversed.
[0033] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.
[0034] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.
Claims
1. A defect detection method for extreme ultraviolet lithography mask white plates, characterized in that, Specifically, the steps include the following: S1: Construct a defect type detection device, which includes an extreme ultraviolet light source and a photoemission electron microscope; S2: The extreme ultraviolet light source emits detection light with a wavelength range of 13.1~13.5nm. The reflector of the photoemission electron microscope is adjusted so that the detection light reflected by the reflector is incident on the white mask to be tested, and the angle between the detection light and the normal of the white mask to be tested is 6°. S3: Set the wavelength adjustment interval, and adjust the collecting mirror of the extreme ultraviolet light source and the reflecting mirror of the photoemission electron microscope according to the wavelength adjustment interval, and collect PEEM images formed on the imaging module of the photoemission electron microscope with different wavelengths of detection light. S4: Analyze the image contrast of all PEEM images acquired in step S3, and complete the defect type detection of the white mask to be tested based on the analysis results.
2. The defect detection method for extreme ultraviolet lithography mask white plate according to claim 1, characterized in that, In step S4, the region where the image contrast of all PEEM images acquired in step S3 is reversed is set as the first region, and the defect type of the region corresponding to the first region of the white mask to be tested is a phase defect type. The region with unchanged image contrast in all PEEM images acquired in step S3 is designated as the second region, and the defect type of the region corresponding to the white mask under test and the second region is amplitude defect type.
3. The defect detection method for extreme ultraviolet lithography mask white plate according to claim 1, characterized in that, The photoemission electron microscope also includes an electron objective, a contrast diaphragm, an aberration corrector, an Airy diaphragm, and a projection lens group arranged sequentially along the electron emission direction. The reflecting mirror is positioned in front of the back focal plane of the photoemission electron microscope objective, reflecting the detection light onto the white mask under test. The electron objective collects electrons emitted outward from the white mask under test, forming an electron image, and pre-magnifies and focuses the electron image. The contrast diaphragm is positioned at the back focal plane of the electron objective, and is used to adjust the receiving angle of the electrons. The Airy diaphragm is positioned at the first image plane of the electron objective, and blocks the labyrinthine electrons of the photoemission electron microscope, continuously adjusting the observation area of the photoemission electron microscope. The aberration corrector corrects the aspherical aberration of the electrons. The projection lens group magnifies the corrected electron image. The imaging module receives the magnified electrons and displays and stores the PEEM image according to the magnified and enhanced electrons.
4. The defect detection method for extreme ultraviolet lithography mask white plate according to claim 3, characterized in that, The surface of the reflector is deposited with a narrow-band extreme ultraviolet multilayer film.
5. The defect detection method for extreme ultraviolet lithography mask white plate according to claim 3, characterized in that, The imaging module consists of a microchannel plate, a fluorescent screen, and a CCD camera. The microchannel plate amplifies and enhances electrons from the projection lens group; the fluorescent screen receives the amplified and enhanced electrons and displays a PEEM image based on the amplified and enhanced electrons; and the CCD camera stores the PEEM image.
6. The defect detection method for extreme ultraviolet lithography mask white plate according to claim 3, characterized in that, The Airy aperture adjusts the observation area of the photoemission electron microscope, and the diameter of the minimum observation area obtained is 1 micrometer.
7. The defect detection method for extreme ultraviolet lithography mask white plate according to claim 3, characterized in that, The projection lens group includes a first projection lens and a second projection lens.