Method and system for defect detection of an euv photomask body

Abstract

The application provides a defect detection method and system for an EUV photomask body, which can scan at least one to-be-detected position point of the EUV photomask body (including an EUV mask blank or an EUV photomask plate with a corresponding pattern) by using extreme ultraviolet laser with different incident intensities without damaging the EUV photomask body, obtain corresponding reflectivity, and obtain defect information of the corresponding to-be-detected position point by analyzing the reflectivity, including a distribution range in a transverse direction and deep information.

Description

Technical Field

[0001] This invention relates to the field of photolithography, and in particular to a method and system for detecting defects in EUV photomasks. Background Technology

[0002] Extreme ultraviolet (EUV) lithography is an advanced lithography technology used in the integrated circuit manufacturing industry, employing extreme ultraviolet laser wavelengths (13.5 nm). The EUV photomask is a crucial component in this process. The EUV lithography process typically involves first coating a photoresist layer (such as photoresist) onto the wafer surface. After the photoresist layer dries, the pattern on the EUV photomask is exposed onto the photoresist layer using an extreme ultraviolet laser (EUV) with a wavelength of 1 nm to 100 nm, for example, 13.5 nm). Subsequently, the exposed photoresist layer is developed using a developer. The developed photoresist pattern is then used as a mask to perform etching and other processes on the wafer, ultimately transferring the pattern from the EUV photomask to the wafer.

[0003] In the fabrication of EUV photomasks, including EUV photomask blanks or EUV photomask slabs with corresponding patterns, the presence of defects is unavoidable, and these defects affect the final EUV lithography results. Therefore, defect detection of EUV photomask blanks or EUV photomasks has always been one of the key research issues in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for detecting defects in EUV photomasks, which can detect defects on EUV photomasks including EUV photomask blanks or EUV photomask plates with corresponding patterns.

[0005] To achieve the above objectives, the present invention provides a defect detection method for an EUV photomask, comprising:

[0006] At least one test location point of the EUV photomask under test is scanned using extreme ultraviolet lasers of different incident intensities to obtain the reflectivity of each incident ultraviolet laser at the test location point, wherein the EUV photomask under test is an EUV photomask blank or an EUV photomask plate with a corresponding pattern.

[0007] The reflectivity at the location to be tested is analyzed to obtain defect information at the location to be tested.

[0008] Optionally, extreme ultraviolet lasers of different incident intensities are used to traverse each test location point of the EUV photomask under test to obtain the reflectivity at the defect-free location point of the EUV photomask under test. Using the reflectivity at the defect-free location point as a reference, the reflectivity at the test location points other than the defect-free location point is analyzed to determine the defect information of the test location points other than the defect-free location point.

[0009] Optionally, the defect detection method for the EUV photomask further includes: collecting and analyzing relevant data of historical EUV photomasks to obtain the reflectivity at a defect-free location point of the EUV photomask under different incident intensities.

[0010] Using the reflectance at the defect-free location as a reference, the reflectance at the location to be tested is analyzed to determine the defect information of the location to be tested.

[0011] Optionally, the defect detection method for the EUV photomask further includes:

[0012] The reflectance at the defect-free location points under different incident intensities is plotted as a reflectance-incident intensity curve as a reference.

[0013] The reflectance at each of the test locations under different incident intensities is plotted as a reflectance-incident intensity curve at the test location.

[0014] The reflectivity-incident intensity curves at each of the test locations are compared with the reflectivity-incident intensity curve of the reference reference to obtain the defect information of the test locations.

[0015] Optionally, the defect detection method for the EUV photomask further includes: using extreme ultraviolet lasers of different incident intensities to traverse each test location point of the EUV photomask under test, and obtaining a distribution map of reflectivity on the EUV photomask under test for each incident intensity.

[0016] Optionally, the defect detection method for the EUV photomask further includes: comparing the reflectance at multiple adjacent test locations under the same incident intensity to determine information including the lateral distribution range and / or vertical thickness variation of the corresponding defects.

[0017] Optionally, the extreme ultraviolet lasers with different incident intensities have the same incident angle and wavelength, and the incident angle is 0 to 15°.

[0018] Optionally, the incident angles of the extreme ultraviolet lasers with different incident intensities are all set to be the same as the incident angle of the exposure light preset for the EUV photomask under test, and the wavelengths of the extreme ultraviolet lasers with different incident intensities are all set to be the same as the wavelengths of the exposure light preset for the EUV photomask under test.

[0019] Optionally, among the different incident intensities, the maximum incident intensity is the same as the maximum intensity of the preset exposure light source of the EUV photomask to be tested, and the minimum incident intensity is 1% of the maximum incident intensity.

[0020] Based on the same inventive concept, the present invention also provides a defect detection system for an EUV photomask, comprising:

[0021] A base is used to place the EUV photomask to be tested, move the position of the EUV photomask to be tested, and adjust the tilt angle of the EUV photomask to be tested, wherein the EUV photomask to be tested is an EUV photomask blank or an EUV photomask plate with a corresponding pattern.

[0022] An extreme ultraviolet laser source is used to provide extreme ultraviolet lasers of different incident intensities to the corresponding test locations on the EUV photomask under test.

[0023] A detector is used to collect extreme ultraviolet laser reflected from the location to be tested, to obtain the reflectivity of the location to be tested for each wavelength of extreme ultraviolet laser, and to analyze the reflectivity of the location to be tested to obtain defect information of the location to be tested.

[0024] The controller is used to control and coordinate the movement and operation of the base, the extreme ultraviolet laser source, and the detector.

[0025] Optionally, the incident intensity of the extreme ultraviolet laser provided by the extreme ultraviolet laser source to the corresponding test location point of the EUV photomask under test is such that the maximum incident intensity is the same as the maximum intensity of the preset exposure light source of the EUV photomask under test, and the minimum incident intensity is 1% of the maximum incident intensity.

[0026] Compared with the prior art, the technical solution of the present invention has at least one of the following effects:

[0027] 1. Without damaging the EUV photomask under test (including the EUV photomask blank or the EUV photomask plate with corresponding pattern), at least one test location point of the EUV photomask under test can be scanned using extreme ultraviolet lasers with different incident intensities to obtain the corresponding reflectivity. By analyzing these reflectivities, the defect information of the corresponding test location point can be obtained, including the distribution range in the lateral direction and the information in the depth.

[0028] 2. By analyzing the reflectance of multiple adjacent test locations of the EUV photomask to be tested (including the EUV photomask blank or the EUV photomask plate with the corresponding pattern), a distribution map of the reflectance under each incident intensity on the EUV photomask to be tested can be obtained. Thus, the lateral distribution range of the defects can be intuitively observed from the distribution map. At the same time, by comparing the differences in reflectance of multiple adjacent test locations of the EUV photomask to be tested under the same incident intensity, the vertical thickness difference of these test locations can be obtained.

[0029] 3. Using the reflectance-incident intensity curve of the defect-free location of the EUV photomask under test (including the EUV photomask blank or the EUV photomask plate with the corresponding pattern) as a reference baseline, observe the changes of the reflectance-incident intensity curves of other test locations of the EUV photomask under test relative to this reference baseline. This will allow you to obtain information on the defect distribution at the corresponding test locations of the EUV photomask under test, including lateral distribution and vertical thickness variation (i.e., information within the deeper layers).

[0030] 4. The defect detection system for EUV photomask (including EUV photomask blank or EUV photomask plate with corresponding pattern) of the present invention has an extreme ultraviolet laser source and incident intensity tuning capability, and can be used to automatically realize defect detection of EUV photomask plate. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the cross-sectional structure of an existing EUV photomask.

[0032] Figures 2 to 6 This is a schematic diagram of the structure of five typical defects in existing EUV photomasks or EUV photomask blanks.

[0033] Figure 7 This is a flowchart of a defect detection method for an EUV photomask (including an EUV photomask blank or an EUV photomask plate) according to an embodiment of the present invention.

[0034] Figure 8 This is a schematic diagram of the defect detection method for an EUV photomask (including an EUV photomask blank or an EUV photomask plate) according to a specific embodiment of the present invention, using λ = 13.5 nm.

[0035] Figure 9 This is a schematic diagram of the defect detection system for an EUV photomask (including an EUV photomask blank or an EUV photomask plate) according to a specific embodiment of the present invention.

[0036] Figure 10 This is a schematic diagram of illumination at a location point in a defect detection method for an EUV photomask (including an EUV photomask blank or an EUV photomask plate) according to a specific embodiment of the present invention.

[0037] Figure 11 This is a schematic diagram of the reflection at different locations on an EUV photomask (including an EUV photomask blank or an EUV photomask plate) according to a specific embodiment of the present invention.

[0038] Figure 12 and Figure 13 This is a schematic diagram of reflectivity-incident intensity curves obtained after detecting five typical defects in an EUV photomask body (including an EUV photomask blank or an EUV photomask plate) according to a specific embodiment of the present invention. Detailed Implementation

[0039] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described to avoid confusion with the invention. It should be understood that the invention can be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, for clarity, the dimensions of layers and regions, as well as their relative dimensions, may be exaggerated. The same reference numerals denote the same elements throughout.

[0040] It should be understood that when an element or layer is referred to as "on" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, parts, and / or processes, these elements, components, areas, layers, parts, and / or processes should not be limited by these terms. These terms are only used to distinguish one element, component, area, layer, part, and / or process from another element, component, area, layer, part, and / or process. Therefore, without departing from the teachings of this invention, the first element, component, area, layer, part, and / or process discussed below may be referred to as a second element, component, area, layer, part, and / or process.

[0041] Spatial relation terms such as “below,” “under,” “below,” “below,” “above,” “on the top,” “on the bottom,” “front,” “back,” etc., are used herein for convenience of description to describe the relationship of one element or feature shown in the figure to other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as “below other elements,” “under them,” “on the bottom,” or “on its back” will be oriented “above,” “top,” or “right” of the other elements or features. Therefore, the exemplary terms “below,” “under,” and “on its back” can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0042] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0043] As described in the background section, the EUV photomask is a crucial component of an EUV lithography (EUVL) system. Please refer to [link / reference]. Figure 1 A known method for manufacturing an EUV photomask includes the following steps:

[0044] 1. Manufacturing the EUV mask preform. Specifically, the following operations are performed in sequence:

[0045] 1.1 Provide a substrate 100 and perform wet cleaning on the substrate 100;

[0046] 1.2. Using any suitable deposition method, such as sputtering, chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), plasma enhanced ALD (PEALD), ion beam deposition (IBD), etc., molybdenum (Mo) film and silicon (Si) film are alternately deposited on substrate 100 to form reflective film stack layer 101.

[0047] 1.3, deposit the capping layer 102 on the top surface of the reflective film stack layer 101 using any suitable deposition method such as sputtering, CVD, PECVD, ALD, PEALD;

[0048] 1.4. An absorber layer 103 is deposited on the top surface of the capping layer 102 by any suitable deposition method such as sputtering, CVD, PECVD, ALD, PEALD, IBD, etc. The material is selected as chromium (Cr)-based or tantalum (Ta)-based material. The absorber layer 103 can be a single-layer structure or a multi-layer film stacked structure.

[0049] 1.5 Deposit a hard mask layer (not shown) on the top surface of the absorber layer 103 using any suitable deposition method such as CVD, PECVD, ALD, PEALD, etc.

[0050] 1.6 Deposit the back conductive layer 105 on the bottom surface of the substrate 100 using any suitable deposition method such as CVD, PECVD, ALD, PEALD, IBD, etc.

[0051] 2. Manufacturing of the first pattern 103a. Specifically, the following operations are performed in sequence:

[0052] 2.1 Coating and baking photoresist (PR, not shown), and exposing and developing the photoresist by laser, electron beam or ion beam, etc., to form a patterned photoresist layer;

[0053] 2.2 Using a patterned photoresist layer as a mask, a hard mask layer is plasma etched, with the etching stopping at the top surface of the absorption layer 103;

[0054] 2.3. The photoresist layer is dry-ashed with oxygen (O2) plasma, and then wet-stripped with various organic acids and inorganic sulfuric acid and H2O2 at high temperature. After that, it is rinsed with isopropanol (IPA) and CO2 to remove the photoresist layer.

[0055] 2.4 Dry plasma etching of the absorber layer 103, with etching stopping at the top surface of the capping layer 102, to form a desired first pattern 103a in the absorber layer 103, the first pattern 103a being a pattern of circuits and / or devices required for integrated circuit manufacturing.

[0056] 3. Manufacturing the second pattern 104. Specifically, the following operations are performed in sequence:

[0057] 3.1 Coating and baking photoresist (PR, not shown), and exposing and developing the photoresist by laser, electron beam or ion beam, etc., to form a patterned photoresist layer;

[0058] 3.2 Using a patterned photoresist layer as a mask, wet or dry plasma etching is performed on the absorption layer 103 and the reflective film stack layer 102 surrounding the first pattern 103a. The etching stops on the top surface of the substrate 100 to form a second pattern 104, which is a border pattern required for integrated circuit manufacturing.

[0059] 3.3. The photoresist layer is dry-ashed with oxygen (O2) plasma, and then wet-stripped with various organic acids and inorganic sulfuric acid and H2O2 at high temperature. After that, it is rinsed with isopropanol (IPA) and CO2 to remove the photoresist layer.

[0060] 4. Cleaning, inspection and transportation.

[0061] During the manufacturing process of the aforementioned EUV photomask (including EUV photomask blank or EUV photomask), defects can be introduced by factors such as the surface condition of the substrate 100, deposition process, etching process, and photoresist layer removal process. Therefore, the existence of defects is unavoidable during the manufacturing process of the EUV photomask (including EUV photomask blank or EUV photomask), and these defects will affect the final result of the EUV photomask being used for EUV lithography.

[0062] The inventors discovered that common defects in EUV photomasks (including EUV photomask blanks or EUV photomasks) can be categorized into five types: a) Type 1 defects 101a caused by pre-existing large-sized (>10nm) pits 100a on the substrate 100 surface, such as... Figure 2 As shown, these pit defects 100a on the substrate 100 are formed on the surface of the substrate 100 by processes such as chemical mechanical polishing (CMP) and cleaning, and are induced from the substrate 100 upwards and towards the layers of the reflective film stack 101 deposited above it, thus forming the first type of defect 101a; b) the second type of defect 101b caused by the pre-existing large-sized (>10nm) bump defects on the surface of the substrate 100, such as... Figure 3As shown, these bump defects 101b on the substrate 100 are formed on the surface of the substrate 100 by processes such as chemical mechanical polishing (CMP) and cleaning. They are induced from the substrate upwards towards the layers of the reflective film stack 101 deposited above it. During this upward induction process, the defect size may increase due to factors such as stress and thickness changes, thus forming a second type of defect 101b; c) a third type of defect 101c caused by pre-existing large-sized defects 100c (such as pits, bumps, etc.) on the surface of the substrate 100, such as... Figure 4 As shown, defects 100c on the substrate 100 are induced vertically upwards from the substrate 100 towards the layers of the reflective film stack 101 deposited above. During the upward induction process, the defect may shift laterally due to factors such as stress and thickness changes, thus forming a third type of defect 101c; d) a fourth type of defect 101d temporarily generated during the deposition of the layers of the reflective film stack 101, such as... Figure 5 As shown, the fourth type of defect 101d is mainly caused by temporary particle (or contaminant, etc.) defects generated during the deposition of each film layer of the reflective film stack 101, and these particle (or contaminant, etc.) defects will be induced in the film layer of the reflective film stack 101 above it, thus forming the fourth type of defect 101d; e) the fifth type of defect is caused by the small-sized (>10nm size) defect 100d that already exists on the surface of the substrate 100. This defect mainly affects the uniformity of the film thickness of a few films at the bottom of the reflective film stack 101, and will not be induced upward to the upper film layer of the reflective film stack 101.

[0063] All of these defects will affect the final performance of EUV lithography.

[0064] In existing technologies, defects are typically detected using methods such as AFM (Atomic Force Microscope), SEM (Scanning Electron Microscope), and TEM (Transmission Electron Microscope). However, these defect detection methods can only detect defects on the surface of the EUV photomask, or defects within a few layers of the EUV photomask, and / or, by destroying the EUV photomask, it is impossible to detect and locate defects deep within the EUV photomask.

[0065] Based on this, the present invention provides a defect detection method for an EUV photomask (including an EUV photomask blank or an EUV photomask plate with a corresponding pattern). The method can use extreme ultraviolet lasers of different incident intensities (wavelength λ = 13.5 nm) to scan at least one location point of the EUV photomask to be tested (including an EUV photomask blank or an EUV photomask plate with a corresponding pattern) to obtain the reflectivity of the location point to be tested for these wavelengths of ultraviolet laser. By analyzing these reflectivities, the defect information of the location point to be tested can be obtained.

[0066] Furthermore, by analyzing the reflectance of multiple adjacent test locations of the EUV photomask under test (including the EUV photomask blank or an EUV photomask plate with a corresponding pattern), a distribution map of the reflectance under each incident intensity on the EUV photomask under test can be obtained. Thus, the lateral distribution range of defects (whether the defects are distributed in a point-like or sheet-like manner) can be intuitively observed from the distribution map. At the same time, by comparing the differences in reflectance at the same wavelength among multiple adjacent test locations of the EUV photomask under test, the vertical thickness differences of these test locations can be obtained.

[0067] Furthermore, by using the reflectance-incident intensity curve of the defect-free location point of the EUV photomask under test (including the EUV photomask blank or the EUV photomask plate with the corresponding pattern) as a reference line, and observing the changes of the reflectance-incident intensity curves of other test locations of the EUV photomask under test relative to the reference line, information on the defect distribution at the corresponding test locations of the EUV photomask under test can be obtained, including lateral distribution, vertical thickness variation, etc.

[0068] The following is combined with Figures 1 to 11 The present invention provides a detailed description of the defect detection method for EUV photomasks (including EUV photomask blanks or EUV photomasks with corresponding patterns) using specific embodiments.

[0069] An embodiment of the present invention provides a defect detection method for an EUV photomask, which can be used to detect defects in an EUV photomask under test. The EUV photomask under test can be an EUV photomask blank manufactured without the aforementioned first and second patterns, or an EUV photomask plate having corresponding patterns (i.e., the aforementioned first and / or second patterns). Therefore, depending on the structure of the EUV photomask under test, the defect detection method of this embodiment can be performed after depositing the reflective film stack layer, capping layer, or absorber layer of the EUV photomask blank (including the photomask blank), or after photolithography and etching of the EUV photomask blank to form the required circuit pattern and border pattern. That is, the EUV photomask under test to be defect-detected in this embodiment can be an EUV photomask blank, or an EUV photomask plate finished product with corresponding patterns after photolithography, etching, and other processes. In either case, the EUV photomask under test has at least a substrate 100 and a reflective film stack layer 101 formed on the substrate 100.

[0070] The substrate 100 is preferably made of a material with low thermal expansion and high thermal conductivity, such as low thermal expansion glass or quartz, specifically quartz glass, glass-ceramic (Zerodur), ultra-low expansion coefficient quartz glass (ULE, also known as zero expansion glass), etc. In some embodiments, the low thermal expansion glass can transmit visible wavelengths, a portion of the infrared wavelengths (near-infrared) close to the visible spectrum, and a portion of the ultraviolet wavelengths. Further, the substrate 100 can absorb extreme ultraviolet (EUV) wavelengths and deep ultraviolet wavelengths close to EUV. The reflective film stack layer 101 is mainly formed by alternating layers of a first reflective film (not shown) and a second reflective film (not shown) on the front side of the substrate 100. The number of layers of the first reflective film is, for example, 30 to 80, and preferably 40 to 50, and the film thickness is, for example, 3 nm to 4 nm. The first and second reflective films can be any suitable material capable of having high reflectivity (e.g., higher than 70%) for EUV lasers of a specific wavelength (e.g., 13.5 nm). For example, the material of the first reflective film is silicon (Si), and the material of the second reflective film is molybdenum (Mo). For example, the material of the first reflective film is Mo, and the material of the second reflective film is beryllium (Be).

[0071] It should be understood that when the EUV photomask under test also includes a capping layer 102, an absorption layer 103 and a back conductive layer 105, the capping layer 102 and the absorption layer 103 are sequentially covered on the reflective film stack layer 101, and the back conductive layer 105 is covered on the back side of the substrate 100.

[0072] The capping layer 102 is used to prevent the reflective film stack 102 from being damaged by subsequent processes. Its material may include at least one of ruthenium (Ru), ruthenium alloys (e.g., RuB, RuSi, or RuNb), or ruthenium oxide (e.g., RuO2 or RuNbO). It can be a single-layer film structure or a multi-layer film stack structure. The thickness of the capping layer 202 is, for example, 2 nm to 4 nm. In other embodiments of the present invention, when the top layer of the reflective film stack 101 is silicon, the fabrication of the capping layer 102 may be omitted. Alternatively, when forming the reflective film stack 101, an additional silicon film (i.e., the first reflective film at the top layer) may be deposited as the capping layer 102.

[0073] The absorber layer 103 can be a single-layer film structure or a composite structure composed of multiple stacked films. Its material includes at least one of cobalt (Co), tellurium (Te), hafnium (Hf), nickel (Ni), tantalum (Ta), chromium (Cr), tantalum-based materials, and chromium-based materials. The total thickness of the absorber layer 203 is, for example, 50 nm to 75 nm. When the absorber layer 103 is a composite structure composed of multiple stacked films, the thickness of each single layer is, for example, 3 nm to 6 nm.

[0074] The material of the back conductive layer 105 may include at least one conductive material selected from chromium, chromium-based materials (e.g., chromium nitride CrN or chromium oxynitride CrON), tantalum, or tantalum-based materials (e.g., tantalum boride TaB, tantalum oxide TaO, tantalum nitride TaN, tantalum boron oxide TaBO, or tantalum boron nitride TaBN, etc.). The thickness of the back conductive layer 105 is, for example, 60 nm to 75 nm.

[0075] Please refer to Figure 7 The defect detection method for EUV photomask (including EUV photomask blank or EUV photomask with corresponding pattern) in this embodiment includes:

[0076] S1, using extreme ultraviolet lasers of different incident intensities to scan at least one test location point of the EUV photomask under test, to obtain the reflectivity of the extreme ultraviolet laser at the test location point for each wavelength, wherein the EUV photomask under test is an EUV photomask blank or an EUV photomask plate with a corresponding pattern.

[0077] S2, Analyze the reflectivity at the location to be tested to obtain defect information at the location to be tested.

[0078] In this embodiment, in step S1, the wavelength λ of the extreme ultraviolet laser used to scan each test location point of the EUV photomask to be tested (including the EUV photomask blank or the EUV photomask with the corresponding pattern) can be set to be the same as the wavelength of the exposure light source of the exposure system required by the EUV photomask to be tested, and the incident angles of these extreme ultraviolet lasers with different incident intensities are all the same, and set to be the same as the incident angle of the exposure light emitted by the exposure light source of the exposure system required by the EUV photomask to be tested. This allows it to penetrate more film layers of the EUV photomask to be tested, and it is more conducive to focusing on defects that affect the EUV lithography results. This is beneficial for obtaining the corresponding defect information on the EUV photomask to be tested more directly, obviously, and efficiently when analyzing the reflectivity at each test location point in step S2. Specifically, the exposure light source of the exposure system required for the EUV photomask under test is the exposure light source used in the exposure system when the EUV photomask under test is applied to the EUV lithography process in product manufacturing and the corresponding film layer is exposed using the EUV photomask under test as a mask.

[0079] Taking the most advanced 13.5nm extreme ultraviolet (EUV) lithography technology as an example, the wavelength of the exposure light source used in 13.5nm EUV lithography is 13.5nm, which can be used for chip manufacturing at 7nm, 5nm, and 3nm. Therefore, λ = 13.5nm in this example. After scanning each test location point of the EUV photomask under test using EUV lasers with a wavelength of 13.5nm and different incident intensities, the subsequent reflectivity analysis in step S2 can obtain not only the defect information on the surface of the EUV photomask under test, but also the defect information deep within the EUV photomask. This differs from existing detection methods that can only detect surface defect information of the EUV photomask. This is because:

[0080] Please refer to Figure 7For an EUV photomask (including an EUV photomask blank or an EUV photomask with a corresponding pattern), when a first reflective film and a second reflective film stacked sequentially in the reflective film stack layer 101 are defined as a double-film structure, when an extreme ultraviolet laser with a wavelength of 13.5 nm is incident vertically or approximately vertically on the EUV photomask, at least about 31 double-film structures can be penetrated, and the Bragg reflectivity of the EUV photomask to the 13.5 nm wavelength extreme ultraviolet laser is at least 60%, for example, 70%, 80% or 85%. When 193nm or 199nm deep ultraviolet (DUV) lasers are incident perpendicularly or nearly perpendicularly onto an EUV photomask, they can penetrate only about three double-layer structures; 266nm ultraviolet lasers, when incident perpendicularly or nearly perpendicularly onto an EUV photomask, can penetrate only about two double-layer structures; and 488nm lasers, when incident perpendicularly or nearly perpendicularly onto an EUV photomask, can penetrate up to about 13 double-layer structures; electron beams (e - When incident perpendicularly or nearly perpendicularly onto an EUV photomask, only about one or two double-film structures can penetrate. Clearly, when using 193nm or 199nm deep ultraviolet light, 266nm ultraviolet light, 488nm laser light, and electron beams (e... - Conventional light or electron beams used for detecting defects in photomasks or photomask blanks can only detect defects on the surface of the EUV photomask or a few defects within the top double-film structure. However, an extreme ultraviolet laser with a wavelength of 13.5 nm can effectively detect most or even all defects within the double-film structure of an EUV photomask.

[0081] In this embodiment, in step S1, among the extreme ultraviolet laser incident intensities used to scan each test location point of the EUV photomask to be tested (including an EUV photomask blank or an EUV photomask plate with a corresponding pattern), the maximum incident intensity Imax is the same as the maximum intensity of the preset exposure light source of the EUV photomask to be tested, and the minimum incident intensity Imin is 1% of the maximum incident intensity. The incident intensity of the extreme ultraviolet laser refers to the optical power per unit area, typically expressed in W / cm². 2 Units.

[0082] In step S1, please refer to Figure 10When scanning the EUV photomask (including the EUV photomask blank or an EUV photomask with a corresponding pattern) at various test locations using different incident intensities, the intensity can be continuously adjusted from Imin (smallest) to Imax (largest) or continuously adjusted from Imax (largest) to Imin (smallest) to Imin. This allows for extreme ultraviolet laser scanning of each test location B(X,Y) of the EUV photomask. This yields the reflectivity of each test location under different incident intensities, and consequently, the reflectivity-incident intensity curves for each test location B(X,Y).

[0083] In addition, in step S1, please refer to Figure 8 The EUV photomask 110 to be tested can be placed on the base 111. The base 111 can fix the position of the EUV photomask 110 and adjust the tilt angle of the surface of the EUV photomask 110, and maintain a constant incident angle θ between the surface of the EUV photomask 110 and the optical axis A of the incident extreme ultraviolet laser beam 203 emitted by the extreme ultraviolet laser source 201. θ is 0 to 15°, preferably not greater than 6°. To improve the measurement effect, the spot size of the incident extreme ultraviolet laser beam 203 emitted by the extreme ultraviolet laser source 201 can be adjusted to the minimum by the focuser 202. The detector 205 is fixed in position and is used to detect the reflected extreme ultraviolet laser beam 204 and obtain the corresponding reflectivity. The extreme ultraviolet light source 201 is preferably a point light source or a line light source, which is excited to emit an incident extreme ultraviolet laser beam 203 with adjustable incident intensity. The adjustable range of the incident intensity of the incident extreme ultraviolet laser beam 203 emitted by the extreme ultraviolet light source 201 falls within the adjustable range of the incident intensity of the exposure light source required by the EUV photomask to be tested.

[0084] In a preferred embodiment, in step S1, the base 111 can be controlled by the controller 200 to translate the EUV photomask 110 under test, or the extreme ultraviolet laser source 201 can be controlled by the controller 200 to translate the incident extreme ultraviolet laser beam 203, thereby performing a step-by-step scan on the entire surface of the EUV photomask 110 under test, while maintaining a constant incident angle θ between the normal of the EUV photomask 110 under test and the optical axis of the incident extreme ultraviolet laser beam 203, so as to achieve the purpose of traversing all test positions of the EUV photomask under test with extreme ultraviolet lasers of different incident intensities.

[0085] Specifically, in step S1, please combine Figures 9 to 11First, a test location can be located, and the incident intensity of the extreme ultraviolet laser beam 203 emitted by the extreme ultraviolet laser source 201 can be continuously or selectively adjusted in order of increasing or decreasing incident intensity to complete the scanning and reflectivity measurement of the test location. Then, the process is repeated to the next test location, that is, the incident intensity of the extreme ultraviolet laser is adjusted again in order of increasing intensity to complete the scanning and reflectivity measurement of the next test location. This process is repeated until all test locations of the EUV photomask under test have been traversed.

[0086] Please refer to Figure 10 and Figure 11 Different points (e.g.) on the EUV photomask to be tested (including the EUV photomask blank or an EUV photomask with a corresponding pattern) Figure 11 As shown in the diagram, the reflection of extreme ultraviolet (EUV) lasers of the same incident intensity varies depending on the defect conditions. Therefore, even when using EUV lasers of the same incident intensity, with the same wavelength and incident angle, the reflectivity obtained at different positions of the EUV photomask under test is not exactly the same. The more severe the defect (e.g., the more double-layer film structures involved in the defect), the more severe the drift (both horizontal and vertical axes) of the position relative to the defect-free position in the reflectivity-wavelength curve.

[0087] In step S2, the reflectance of each test location of the EUV photomask to be tested (including EUV photomask blank or EUV photomask plate with corresponding pattern) is analyzed to obtain the defect information of each test location of the EUV photomask to be tested. The defect information includes: whether there is a defect, the lateral distribution range of the defect, the depth and vertical thickness of the defect (i.e., information in the deeper layers), etc.

[0088] Optionally, in this embodiment, in step S2, the means of analyzing the reflectance of each test location point of the EUV photomask to be tested (including an EUV photomask blank or an EUV photomask plate with a corresponding pattern) includes: obtaining a distribution map (which can be a two-dimensional planar map or a three-dimensional stereo map) of the reflectance under different incident intensities on the EUV photomask to be tested. This allows for a direct observation of the defect distribution on the EUV photomask to be tested, as well as the lateral distribution range of each defect (e.g., whether it is a point-like distribution or a sheet-like distribution). Further, by observing the corresponding reflectance contour lines (maximum reflectance contour lines and / or minimum reflectance contour lines) under the same incident intensity, or by observing the degree of reflectance (maximum reflectance and / or minimum reflectance) offset of each test location point relative to a defect-free location point, information such as the vertical thickness and depth of the corresponding defects can be obtained.

[0089] Optionally, in step S2, the means of analyzing the reflectance of each test location point of the EUV photomask to be tested (including EUV photomask blank or EUV photomask plate with corresponding pattern) includes: comparing the reflectance at multiple adjacent test locations under the same incident intensity to determine information such as the lateral distribution range and / or vertical thickness variation of the corresponding defects.

[0090] Optionally, in step S2, the means of analyzing the reflectance at each test location of the EUV photomask (including an EUV photomask blank or an EUV photomask with a corresponding pattern) include: Please refer to Figure 12 and Figure 13 The reflectance-wavelength curves at the defect-free location point A(0,0) of the EUV photomask under different incident intensities are obtained. The reflectance-wavelength curve at the defect-free location point is used as a reference line. The reflectance-incident intensity curves at each test location point are compared with the reference line to obtain the defect information of each test location point.

[0091] Specifically, please combine Figures 2 to 6 as well as Figure 12 , Figure 13 It can be known that:

[0092] (1) When there is a defect at any point in the EUV photomask to be tested (including EUV photomask blank or EUV photomask with corresponding pattern), the reflectivity of the point where the defect is located will be lower than the reflectivity of the point where there is no defect under the same incident light intensity.

[0093] (2) The reflectivity-incident intensity curves of different defect types are different, and the offset of the reflectivity-incident intensity curves relative to the defect-free location is different.

[0094] Specifically, the reflectance-incident intensity curves of the first type of defect (i.e., a defect-induced mechanism that is vertically upward without lateral offset and without size increase), the second type of defect (i.e., a defect-induced mechanism that is vertically upward with size increase and without lateral offset), and the third type of defect (i.e., a defect-induced mechanism that is upward with lateral offset) located on the top surface of the reflective film stack layer 101 are similar in shape, but the degree of offset relative to the reflectance-incident intensity curve of the defect-free location is different. Among them, the reflectance-incident intensity curve corresponding to the third type of defect is closer to the reflectance-incident intensity curve of the defect-free location than the first type of defect and the second type of defect.

[0095] Regarding Type III and Type IV defects, Type IV defects do not exist in the lower middle part of the reflective film stack 101. Assuming the size of the Type IV defect at the initial position is the same as the size of the defect on the substrate surface that causes the Type III defect, initially, in the upper reflective film stack of the same thickness, for the same incident intensity, the reflectivity at the location of the Type IV defect will be lower than the reflectivity at the location of the Type III defect under the same incident intensity. However, once the incident intensity is increased to a value exceeding a certain threshold, since the extreme ultraviolet laser used for scanning can penetrate to the reflective film stack 101 below the Type IV defect, the reflectivity at the location of the Type IV defect will surpass the reflectivity at the location of the Type III defect under the same incident intensity. Moreover, since the Type IV defect is offset laterally, the reflectivity-incident intensity curve at the location of the Type IV defect will show a more obvious inflection point.

[0096] By comprehensively analyzing the curvature changes of the reflectivity-incident intensity curves at different locations where the third type of defect exists, and the degree of offset of the reflectivity-incident intensity curves relative to the defect-free locations, defect information such as the depth of the lateral offset of the third type of defect, the lateral offset distance, and the starting position of the defect can be obtained.

[0097] By comprehensively analyzing the inflection points, curvature changes, and offset of the reflectivity-incident intensity curves at different locations with Type IV defects, relative to the reflectivity-incident intensity curves at defect-free locations, information such as the starting position (i.e., vertical thickness) and lateral range distribution of Type IV defects can be obtained.

[0098] For both the defect-free case and the case with Type 5 defects, when Type 5 defects are mainly located in a few layers at the bottom of the reflective film stack 101, and the incident intensity is low, the extreme ultraviolet laser used for scanning mainly penetrates to the defect-free upper layer of the reflective film stack 101 at the location of the Type 5 defect. The reflectivity is less affected by the Type 5 defect. When the incident intensity increases to a large value (close to the maximum incident intensity), the extreme ultraviolet laser used for scanning penetrates to the layer of the reflective film stack 101 with Type 5 defects, causing a sharp drop in reflectivity. Therefore, the reflectivity-incident intensity curve of the Type 5 defect will show a more obvious inflection point.

[0099] By comprehensively analyzing the inflection points, curvature changes, and offset of the reflectivity-incident intensity curves at different locations with Type 5 defects, relative to the reflectivity-incident intensity curves at defect-free locations, information such as the vertical thickness and lateral range distribution of Type 5 defects can be obtained.

[0100] Obviously, by analyzing the reflectance-incident intensity curves of each test location and defect-free location, the defect information of the EUV photomask to be tested (including the EUV photomask blank or the EUV photomask with the corresponding pattern) can be obtained, including the location of the defects, the lateral distribution range of the defects, the vertical thickness of the defects, etc.

[0101] It should be noted that, in this embodiment, the reflectance-incident intensity curves of defect-free locations of the EUV photomask under test (including an EUV photomask blank or an EUV photomask with a corresponding pattern) can be obtained in the following two ways:

[0102] One approach is to analyze relevant data of historical EUV photomasks (including EUV photomask blanks or EUV photomasks with corresponding patterns) to obtain reflectivity-wavelength curves corresponding to defect-free locations on the EUV photomask to be tested.

[0103] Secondly, in step S1, extreme ultraviolet lasers of different incident intensities are used to traverse each test location point of the EUV photomask to be tested (including the EUV photomask blank or the EUV photomask plate with the corresponding pattern). Among these test locations, there are usually defect-free locations or near-defect-free locations. Therefore, in step S2, the location point with the highest relative reflectivity under each incident intensity can be taken as the defect-free location point of the EUV photomask to be tested, thereby obtaining the reflectivity-wavelength curve at the defect-free location point of the EUV photomask to be tested.

[0104] In subsequent applications, based on the analysis results of step S2, the defective test locations of the EUV photomask to be tested (including the EUV photomask blank or an EUV photomask plate with a corresponding pattern) can be further sliced ​​longitudinally or transversely to conduct a more detailed analysis of the defects at the test locations.

[0105] In summary, the defect detection method for an EUV photomask (including an EUV photomask blank or an EUV photomask plate with a corresponding pattern) of the present invention can scan at least one test location point of the EUV photomask under test using extreme ultraviolet lasers of different incident intensities without damaging the EUV photomask under test, obtaining the corresponding reflectivity. By analyzing these reflectivities, defect information of the corresponding test location point can be obtained. Furthermore, by analyzing the reflectivity of multiple adjacent test location points of the EUV photomask under test, a distribution map of the reflectivity at each incident intensity on the EUV photomask under test can be obtained. This allows for a direct observation of the lateral distribution range of defects from the distribution map. Simultaneously, by comparing the differences in reflectivity at the same wavelength among multiple adjacent test location points of the EUV photomask under test, the vertical thickness differences of these test location points can be obtained.

[0106] Based on the same inventive concept, please refer to Figure 8 An embodiment of the present invention also provides a defect detection system for an EUV photomask, which can be used to implement the defect detection method of the EUV photomask of the present invention. The EUV photomask includes an EUV photomask blank or an EUV photomask plate with a corresponding pattern. The defect detection system includes: a base 111, an extreme ultraviolet laser source 201, a focuser 202, a detector 205, and a controller 200.

[0107] The base 111 is used to place the EUV photomask 110 to be tested, move the position of the EUV photomask 110 to be tested, and adjust the tilt angle of the EUV photomask 111 to keep the incident angle θ between the normal of the EUV photomask 110 to be tested and the optical axis of the incident extreme ultraviolet laser beam 203 emitted by the extreme ultraviolet laser source 201 constant. The EUV photomask 110 to be tested includes an EUV photomask blank or an EUV photomask plate with a corresponding pattern.

[0108] The extreme ultraviolet (EUV) laser source 201 has incident intensity tuning capability, enabling it to provide EUV lasers (incident EUV laser beam 203) of different incident intensities to the corresponding test locations on the EUV photomask 110 under test. The focuser 202 is used to adjust the focal length of the incident EUV laser beam 203 emitted by the EUV laser source 201, thereby changing the light spot on the surface of the EUV photomask 110 under test where the incident EUV laser beam 203 is incident. The wavelength λ of the EUV laser provided by the EUV laser source 201 to the corresponding test locations on the EUV photomask 110 under test is the same as the wavelength of the exposure light required for EUV lithography, for example, 13.5 nm.

[0109] Optionally, the extreme ultraviolet laser source 201 provides extreme ultraviolet laser incident intensity to the corresponding test position point of the EUV photomask 110 under test, wherein the maximum incident intensity is the same as the maximum intensity of the preset exposure light source of the EUV photomask under test, and the minimum incident intensity is 1% of the maximum incident intensity.

[0110] In order to improve the measurement effect, the spot size of the incident extreme ultraviolet laser beam 203 emitted by the extreme ultraviolet laser source 201 can be adjusted to the minimum by the focuser 202.

[0111] The detector 205 is used to collect the reflected extreme ultraviolet laser beam 204 reflected from the test location point of the EUV photomask 110 (including EUV photomask blank or EUV photomask plate with corresponding pattern) to obtain the reflectivity of the corresponding test location point of the EUV photomask 110 to the extreme ultraviolet laser at each incident light intensity, and to analyze the reflectivity of the test location point to obtain the defect information of the test location point. Furthermore, the detector 205 can generate a distribution map of reflectance on the EUV photomask (including the mask blank) under each incident light intensity. This allows for a direct observation of the lateral distribution range of defects from the distribution map and can be used to compare the differences in reflectance at the same wavelength at multiple adjacent test locations of the EUV photomask, thus obtaining the vertical thickness differences at these test locations. And / or, it can form a reflectance-incident intensity curve for each test location of the EUV photomask (including the mask blank), so that defect information such as whether there are defects at each test location can be directly determined through these reflectance-incident intensity curves.

[0112] The controller 200 is used to control and coordinate the movement and operation of the base station 111, the extreme ultraviolet laser source 201 and the detector 205.

[0113] The method of using the defect detection system in this embodiment is as follows:

[0114] The EUV photomask 110 to be tested (including an EUV photomask blank or an EUV photomask plate with a corresponding pattern) is placed on the base 111. The base 111 can fix the position of the EUV photomask 110 to be tested and adjust the tilt angle of the surface of the EUV photomask 110 to be tested, and keep the incident angle θ between the surface of the EUV photomask 110 to be tested and the optical axis A of the incident extreme ultraviolet laser beam 203 emitted by the extreme ultraviolet laser source 201 constant. θ is 0 to 15°, preferably not greater than 6°.

[0115] The controller 200 controls the base 111 to translate the EUV photomask 110 under test, or controls the extreme ultraviolet laser source 201 to translate the incident extreme ultraviolet laser beam 203, thereby performing a step-by-step scan on the entire surface of the EUV photomask 110 under test. Simultaneously, a constant incident angle θ is maintained between the normal of the EUV photomask 110 and the optical axis of the incident extreme ultraviolet laser beam 203, thus achieving the goal of traversing all test locations of the EUV photomask 110 using extreme ultraviolet lasers of different incident intensities. Furthermore, at each test location of the EUV photomask 110, the incident intensity of the extreme ultraviolet laser beam 203 emitted by the extreme ultraviolet laser source 201 is adjusted according to either increasing or decreasing incident intensity to complete the scanning of each test location.

[0116] In summary, the defect detection system for EUV photomasks (including EUV photomask blanks or EUV photomasks with corresponding patterns) of the present invention can automatically detect defects in EUV photomasks (including EUV photomask blanks or EUV photomasks with corresponding patterns) without damaging the structure of the EUV photomask.

[0117] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the scope of the present invention.

Claims

1. A method for defect detection of an EUV photomask, characterized in that, include: At least one test location point of the EUV photomask under test is scanned using extreme ultraviolet lasers of different incident intensities to obtain the reflectivity of each incident ultraviolet laser at the test location point, wherein the EUV photomask under test is an EUV photomask blank or an EUV photomask plate with a corresponding pattern. The reflectance at defect-free locations under different incident intensities is plotted as a reflectance-incident intensity curve as a reference. The reflectance at each of the test locations under different incident intensities is plotted as a reflectance-incident intensity curve at the test location. The reflectivity-incident intensity curves at each of the test locations are compared with the reflectivity-incident intensity curve of the reference reference to obtain defect information at each of the test locations. Compare the reflectivity at multiple adjacent test locations under the same incident intensity to determine information about the corresponding defects, including their lateral distribution range and / or vertical thickness variation.

2. The defect detection method for an EUV photomask as described in claim 1, characterized in that, Extreme ultraviolet lasers of different incident intensities are used to traverse each test location point of the EUV photomask under test to obtain the reflectivity at the defect-free location point of the EUV photomask under test. Using the reflectivity at the defect-free location point as a reference, the reflectivity at the test locations other than the defect-free location point is analyzed to determine the defect information of the test locations other than the defect-free location point.

3. The defect detection method for an EUV photomask as described in claim 1, characterized in that, Also includes: Collect and analyze relevant data of historical EUV photomasks to obtain the reflectivity at a defect-free location point of the EUV photomask under test corresponding to different incident intensities; Using the reflectance at the defect-free location as a reference, the reflectance at the location to be tested is analyzed to determine the defect information of the location to be tested.

4. The defect detection method for an EUV photomask as described in claim 1, characterized in that, Also includes: Using extreme ultraviolet lasers of different incident intensities, the test locations of the EUV photomask under test are traversed to obtain the reflectivity distribution map of the EUV photomask under each incident intensity.

5. The defect detection method for an EUV photomask as described in claim 1, characterized in that, The extreme ultraviolet lasers with different incident intensities have the same incident angle and wavelength, and the incident angle is 0~15°.

6. The defect detection method for an EUV photomask as described in claim 1, characterized in that, The incident angles of the extreme ultraviolet lasers with different incident intensities are all set to be the same as the incident angle of the exposure light preset for the EUV photomask under test, and the wavelengths of the extreme ultraviolet lasers with different incident intensities are all set to be the same as the wavelengths of the exposure light preset for the EUV photomask under test.

7. The defect detection method for an EUV photomask as described in any one of claims 1-6, characterized in that, Among the different incident intensities, the maximum incident intensity is the same as the maximum intensity of the preset exposure of the EUV photomask to be tested, and the minimum incident intensity is 1% of the maximum incident intensity.

8. A defect detection system for an EUV photomask, characterized in that, include: A base is used to place the EUV photomask to be tested, move the position of the EUV photomask to be tested, and adjust the tilt angle of the EUV photomask to be tested, wherein the EUV photomask to be tested is an EUV photomask blank or an EUV photomask plate with a corresponding pattern. An extreme ultraviolet laser source is used to provide extreme ultraviolet lasers of different incident intensities to the corresponding test locations on the EUV photomask under test. A detector is used to collect extreme ultraviolet laser reflected from the location to be tested, to obtain the reflectivity of the location to be tested for each incident intensity of extreme ultraviolet laser, and to plot the reflectivity at defect-free locations under different incident intensities as a reflectivity-incident intensity curve as a reference. The reflectivity at each location to be tested under different incident intensities is plotted as a reflectivity-incident intensity curve at the location to be tested, and the reflectivity-incident intensity curve at each location to be tested is compared with the reflectivity-incident intensity curve of the reference to obtain defect information at each location to be tested. Furthermore, the reflectivity at multiple adjacent locations to be tested under the same incident intensity is compared to determine information including the lateral distribution range and / or vertical thickness variation of the corresponding defects. The controller is used to control and coordinate the movement and operation of the base, the extreme ultraviolet laser source, and the detector.

9. The defect detection system for an EUV photomask as described in claim 8, characterized in that, The incident intensity of the extreme ultraviolet laser provided by the extreme ultraviolet laser source to the corresponding test location point of the EUV photomask under test is such that the maximum incident intensity is the same as the maximum intensity of the preset exposure light source of the EUV photomask under test, and the minimum incident intensity is 1% of the maximum incident intensity.

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