Extreme ultraviolet mask inspection systems

Abstract

To provide an improved system capable of in situ measurement of wave-front aberration of EUV mask inspection systems.SOLUTION: A metrology system for measuring wave-front aberration of an extreme ultraviolet (EUV) mask inspection system is disclosed. The test mask includes a substrate formed from a material having substantially no reflectivity for EUV illumination, and one or more patterns formed on the substrate. The one or more patterns have a reflective portion configured to reflect EUV illumination and positioned in a common plane, and an absorption portion having substantially no reflectivity for EUV illumination and positioned on or above the substrate.SELECTED DRAWING: Figure 1A

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates generally to wavefront aberration metrology, and more specifically, to wavefront aberration metrology through the use of an extreme ultraviolet (EUV) mask inspection system incorporating a test mask. [Background technology]

[0002] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 62 / 856,719, filed June 3, 2019, and entitled “WAVEFRONT ABERRATION METROLOGY FOR EUV MASK INSPECTION SYSTEMS” by Dmitriy Zusin, Rui-fang Shi and Qiang Zhang, which is hereby incorporated by reference in its entirety.

[0003] In general, nanocircuits and their components are becoming increasingly sensitive to defects that can impair the operation of the nanocircuit or adversely affect the nanocircuit. Detection of defects on nanocircuits is typically performed using an EUV inspection system to illuminate a photomask that contains the nanocircuit product patterns. However, because EUV inspection systems rely on an array of optics, the optics often distort the image through wavefront aberrations, which can corrupt the image of the photomask and prevent defect detection.

[0004] Existing methods for measuring and mitigating wavefront aberrations introduced by the optics of an EUV inspection system rely on diagnostic test masks. However, existing diagnostic test masks are prone to defects and undesirable performance as a result of how they are manufactured. For example, existing diagnostic patterns on test masks can introduce shadowing and other unwanted reflective effects into the image. Additionally, existing diagnostic test patterns suffer from short life spans as a result of oxidation.

[0005] Additionally, some existing methods for measuring and mitigating wavefront aberrations introduced by the optics of an EUV inspection system involve identifying the aberrations using systems and procedures separate from the EUV inspection system, which reduces metrology efficiency by not allowing for quantification and mitigation of wavefront aberrations within the EUV inspection system itself. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] U.S. Pat. No. 9,335,206 Summary of the Invention [Problem to be solved by the invention]

[0007] It would therefore be desirable to provide an improved system for in situ measurement of wavefront aberrations in an EUV mask inspection system. [Means for solving the problem]

[0008] A test mask for measuring wavefront aberrations of an EUV mask inspection system is disclosed in accordance with one or more embodiments of the present disclosure. The test mask according to an embodiment includes a substrate formed of a material having substantially no reflectivity with respect to EUV illumination. The test mask according to an embodiment includes one or more patterns formed on the substrate, the one or more patterns including an absorbing portion configured to absorb EUV illumination and a reflective portion configured to reflect EUV illumination, the reflective portion and the absorbing portion being disposed in a common plane on or above the substrate.

[0009] An EUV mask inspection system is disclosed according to one or more embodiments of the present disclosure. The system according to an embodiment includes an EUV illumination source. The system according to an embodiment includes one or more illumination optics configured to direct an EUV beam from the EUV illumination source onto a test mask, the test mask including a substrate formed of a material having substantially no reflectivity with respect to EUV illumination, one or more patterns formed on the substrate, the one or more patterns including an absorbing portion configured to absorb EUV illumination and a reflective portion configured to reflect EUV illumination, the reflective portion and the absorbing portion being located in a common plane above the substrate, and one or more caps disposed on at least one of the absorbing portion and the reflective portion, the one or more caps being formed of a material suitable for reducing oxidation of a portion or portions of the test mask. The system according to an embodiment includes one or more detectors. The system according to an embodiment includes one or more EUV projection optics configured to collect EUV illumination reflected from the test mask and direct the EUV illumination onto the one or more detectors. In one embodiment, the system includes one or more controllers having one or more processors communicatively coupled to the one or more detectors, the one or more processors configured to execute a set of program instructions stored in a memory, the set of program instructions configured to cause the one or more processors to receive one or more signals from the one or more detectors indicative of EUV illumination reflected from the test mask, and to identify one or more wavefront aberrations throughout the EUV beam based on the one or more signals from the one or more detectors indicative of EUV illumination received from the test mask.

[0010] A method of using an EUV mask inspection system is disclosed in accordance with one or more embodiments of the present disclosure. In some embodiments, the method includes illuminating a test mask including a substrate formed of a material having substantially no reflectivity with respect to EUV illumination, one or more patterns formed on the substrate, the one or more patterns including an absorbing portion configured to absorb EUV illumination and a reflective portion configured to reflect EUV illumination, the reflective portion and the absorbing portion being located in a common plane above the substrate, and one or more caps disposed on at least one of the absorbing portion and the reflective portion, the cap being formed of a material suitable for reducing oxidation of a portion or portions of the test mask. In some embodiments, the method includes detecting a reflected beam. In some embodiments, the method includes generating one or more images based on the reflected beam. In some embodiments, the method includes identifying one or more wavefront aberrations across the one or more images. In some embodiments, the method includes providing one or more adjustment amounts to adjust one or more components of the EUV inspection system.

[0011] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily intended to limit the invention as claimed. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the general description, serve to explain the principles of the invention.

[0012] The many advantages of the present disclosure can be better appreciated by those skilled in the art by reference to the following drawings, in which: [Brief description of the drawings]

[0013] [Figure 1A] 2 is a cross-sectional view of a pattern on a test mask for measuring wavefront aberration in an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Figure 1B]2 is a cross-sectional view of a pattern on a test mask for measuring wavefront aberration in an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Figure 1C] 2 is a cross-sectional view of a pattern on a test mask for measuring wavefront aberration in an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Figure 1D] 2 is a cross-sectional view of a pattern on a test mask for measuring wavefront aberration in an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Figure 1E] 2 is a cross-sectional view of a pattern on a test mask for measuring wavefront aberration in an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Diagram 2] FIG. 1 is a schematic block diagram of an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Diagram 3] 1 is a pictorial diagram illustrating the relationship between reflectivity at one or more portions of a test mask for measuring wavefront aberrations of an EUV mask inspection system and the angle of an incident light beam directed at the test mask, in accordance with one or more embodiments of the present disclosure. [Figure 4A] 1 is a plot illustrating intensity contrast in the imaging pupil for one embodiment of a pattern included in a test mask for measuring wavefront aberrations in an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Figure 4B] 11 is a plot illustrating intensity contrast in the imaging pupil for another embodiment of a pattern included in a test mask for measuring wavefront aberrations in an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Figure 4C] 11 is a plot illustrating intensity contrast in the imaging pupil for another embodiment of a pattern included in a test mask for measuring wavefront aberrations in an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Figure 4D]11 is a plot illustrating intensity contrast in the imaging pupil for another embodiment of a pattern included in a test mask for measuring wavefront aberrations in an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Figure 4E] 11 is a plot illustrating intensity contrast in the imaging pupil for another embodiment of a pattern included in a test mask for measuring wavefront aberrations in an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Figure 4F] 11 is a plot illustrating intensity contrast in the imaging pupil for another embodiment of a pattern included in a test mask for measuring wavefront aberrations in an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Figure 4G] 11 is a plot illustrating intensity contrast in the imaging pupil for another embodiment of a pattern included in a test mask for measuring wavefront aberrations in an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Figure 4H] 1A-1C are plots illustrating intensity contrast in the imaging pupil for various embodiments of patterns on a test mask for measuring wavefront aberrations in an EUV mask inspection system in accordance with one or more embodiments of the present disclosure. [Diagram 5] FIG. 1 is a process flow diagram illustrating a method for identifying wavefront aberrations in an EUV inspection system using a test mask in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings. The present disclosure has been specifically shown and described with reference to certain embodiments and specific features thereof. The embodiments described herein should be understood to be illustrative and not limiting. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail may be made therein without departing from the spirit and scope of the present disclosure.

[0015] Embodiments of the present disclosure are directed to wavefront aberration metrology systems and methods that use an EUV mask inspection system incorporating one or more test masks configured to improve performance of the inspection system.

[0016] EUV mask inspection typically involves the detection of one or more defects in an EUV photomask through the use of EUV illumination (e.g., radiation having an EUV wavelength, e.g., 13.5 nm), which may result in one or more unwanted deviations that may affect the yield and performance of chips printed with the photomask. An EUV inspection system typically implements one or more reflective elements (e.g., mirrors) to form an image of the EUV photomask from one or more EUV incident beams directed from the EUV photomask. The one or more reflective elements in the EUV inspection system may introduce aberrations into the wavefront at the imaging pupil. Such aberrations may impair or impair the imaging and inspection of the EUV photomask.

[0017] The test mask includes a pattern 100 and can be configured as a diagnostic photomask for measuring wavefront aberrations in an EUV mask inspection system. For example, the test mask can be used in an EUV mask inspection system for inspecting an EUV photomask. The test mask includes a pattern 100 and can be configured to perform the functions disclosed herein. The test mask can be configured to reflect EUV illumination such that an imaging pupil of the optical system is substantially and uniformly filled. Based on the uniformity and intensity of the imaging pupil fill, the EUV mask inspection system can measure one or more wavefront aberrations of the system and determine one or more adjustments to one or more components of the system. One or more wavefront aberration measurement systems and methods for an EUV mask inspection system are generally described in U.S. Patent Application Publication No. 2016 / 0133634, entitled "WAVE FRONT ABERRATION METROLOGY OF OPTICS OF EUV MASK INSPECTION SYSTEM," which was published on May 10, 2016, and is hereby incorporated by reference in its entirety.

[0018] The test mask can be configured to reflect EUV radiation at reflective portions of the test mask and absorb EUV radiation at absorbing portions of the test mask when the test mask is illuminated with EUV radiation. For example, the test mask can reflect EUV radiation from the reflective portions toward an imaging pupil of an EUV mask inspection system and absorb EUV light at the absorbing portions. The EUV mask inspection system can be configured to generate an image of the test mask based on the reflected EUV light and the absence of reflected EUV light that may correspond to the absorbing portions of the test mask. The test mask can be configured to have a high contrast between the reflective and absorbing portions and to be detectable by the EUV mask inspection system.

[0019] 1A-1E depict cross-sectional views of a pattern 100 on a test mask for measuring wavefront aberrations in an EUV mask inspection system according to one or more embodiments of the present disclosure. Although not shown in its entirety, the test mask may include a substrate 102 formed of a material that is substantially non-reflective with respect to EUV illumination, such as silicon dioxide (SiO 2 ) the substrate 102. The pattern 100 can include an absorbing portion 104 and a reflective portion 106 located in a common plane on or above the substrate 102. The absorbing portion 104 can be configured to absorb EUV illumination. For example, the absorbing portion 104 can be formed of one or more materials configured to absorb EUV illumination. The reflective portion 106 can be configured to reflect EUV illumination. For example, the reflective portion 106 can be formed of one or more materials configured to reflect EUV illumination at an index of about 60%-70% or more.

[0020] According to the embodiment depicted in FIG. 1A, one or more absorbers 110 configured to absorb EUV illumination may be provided in the absorbing portion 104. For example, the one or more absorbers 110 may be formed of a material configured to absorb EUV illumination. The one or more absorbers 110 may be provided with an anti-reflective coating 112 configured to reduce reflection of the incident EUV beam from the one or more absorbers 110. The anti-reflective coating 112 may be formed of a material that has substantially no reflectivity with respect to EUV illumination. For example, the anti-reflective coating 112 may be formed of a transition metal nitride compound such as TaNO. The anti-reflective coating 112 may be configured such that the height of the one or more absorbers 110 together with the anti-reflective coating 112 is uniform with respect to the height of the reflecting portion 106. In some embodiments, the absorbing portion 104 may include one or more pinholes configured to expose the substrate 102.

[0021] In some embodiments, the reflective portion 106 may include one or more multilayer pillars 114 including a plurality of periodically repeating bilayers 116 configured to reflect EUV illumination. For example, the plurality of periodically repeating bilayers 116 may be configured such that the thickness of each of the periodically repeating bilayers 116 and the repeat period of the periodically repeating bilayers 116 may be selected to reflect EUV illumination in a manner that maximizes reflection toward an imaging pupil of an EUV mask inspection system. Each of the periodically repeating bilayers 116 may have a thickness between about 7.0 nm and about 7.5 nm. The one or more multilayer pillars 114 may include between about 5 and about 15 periodically repeating bilayers 116.

[0022] The periodically repeating bilayers 116 may be formed of alternating layers of one or more EUV illumination reflective materials, including, but not limited to, molybdenum and silicon. The multilayer pillars 114 may also include one or more caps 128 formed of a material configured to reduce the likelihood of oxidation of a portion or portions of the multilayer pillars 114 (e.g., due to moisture, oxygen exposure, etc.). For example, the caps 128 may be formed of ruthenium. The caps 128 may also be configured such that the height of the multilayer pillars 114 together with the caps 128 is uniform relative to the height of the absorber 110.

[0023] The one or more multi-layer pillars 114 may include one or more Bragg reflectors configured to maximize reflection of EUV illumination while minimizing absorption of the EUV illumination. The one or more multi-layer pillars 114 may facilitate reflection of EUV illumination due to the interfaces between the layers that make up the periodically repeating bilayer 116. For example, a molybdenum monolayer may be disposed with a silicon monolayer to form a periodically repeating bilayer 116. In one embodiment, an incident EUV illumination beam directed at a test mask including the periodically repeating bilayer 116 pattern 100 is reflected according to the respective refractive indices of molybdenum and silicon, such that a larger refractive index difference between the two monolayers provides a higher EUV illumination reflectance. Since the refractive indices may vary depending on the thickness and period of the periodically repeating bilayer 116, the periodically repeating bilayer 116 may be configured to account for different optical configurations (e.g., different imaging pupil parameters, e.g., numerical apertures, of the EUV inspection system used).

[0024] The pattern 100 may also be formed such that one or more multi-layer pillars 114 are disposed within one or more pinholes in the absorbing portion 104. For example, one or more absorbers 110 may be formed by depositing a material configured to absorb EUV illumination on the substrate 102, forming one or more pinholes in the material that expose the substrate 102, and embedding one or more multi-layer pillars 114 within the pinholes. This configuration of the absorbing portion 104 may facilitate reduced oxidation of one or more portions of the one or more multi-layer pillars 114 by reducing exposure of the portion or portions of the one or more multi-layer pillars 114 to oxidizing agents in the environment. According to an alternative embodiment, the pattern 100 may be formed by depositing one or more multi-layer pillars 114 on the substrate 102, followed by depositing an absorbing portion 104 over the multi-layer pillars 114, and removing the excess absorbing portion 104, e.g., via etching, to form one or more absorbers 110.

[0025] Also, according to the embodiment depicted in Fig. 1B, the pattern 100 can be formed such that the one or more absorbers 110 are disposed within the array of the one or more multi-layer pillars 114. For example, one or more multi-layer pillars 114 can be deposited in an array on the substrate 102, and one or more absorbers 110 can be interstitially deposited on the substrate 102 between the one or more multi-layer pillars 114. According to an alternative embodiment, the pattern 100 can be formed by depositing one or more multi-layer pillars 114 on the substrate 102, followed by depositing an absorbing portion 104 above the multi-layer pillars 114, and removing the excess absorbing portion 104, for example via etching, to form one or more absorbers 110.

[0026] 1C, the one or more pinholes 120 in the reflective portion 106 can be included in the absorbing portion 104. For example, the one or more pinholes 120 can include one or more openings sandwiched between one or more multi-layer pillars 114 and configured to expose the substrate 102, where the substrate 102 is configured to absorb EUV illumination.

[0027] Additionally, according to the embodiment depicted in FIG. 1D and FIG. 1E, one or more pillars of reflective material 124 may be provided in the reflective portion 106. For example, one or more pillars of reflective material 124 may be provided in the reflective portion 106, which may be formed of an EUV illumination reflective material, including, but not limited to, palladium, platinum, and silver. The pillars of reflective material 124 may be formed of a material that exhibits a reflectivity of about 0.5% or greater for EUV radiation. The reflective material 124 may be formed of a material that has a reflectivity that allows the radiation reflected by the reflective material to have a high contrast compared to the absorbing portion 104. The thickness of the pillars of reflective material 124 may vary depending on the desired amount of reflectivity. According to one embodiment, the pillars of reflective material 124 may be formed of a thickness of more than 100 nm. The absorbing portion 104 may include one or more pinholes 120 within the reflective portion, the pinholes 120 configured to expose the substrate 102 .

[0028] Although the embodiments described in this disclosure are described with pillar structures and pinholes, it is noted that other shapes are contemplated. For example, the multi-layer pillar(s) 114 can have any shape suitable for the purposes contemplated herein, including but not limited to cubic, oval, etc. Similarly, the pinhole 120 can be a hole of any shape, including but not limited to square, oval, etc.

[0029] In some embodiments, the reflective portion 104 is comprised of a single piece (e.g., one multi-layer pillar 114 or one pillar made of reflective material 122). In other embodiments, the reflective portion 104 is comprised of multiple pieces (e.g., multiple multi-layer pillars 114 or multiple pillars made of reflective material 122).

[0030] In some embodiments, the absorbing portion 106 is comprised of a single component (e.g., one absorber 110 or one pinhole 120). In other embodiments, the absorbing portion 106 is comprised of multiple components (e.g., multiple absorbers 110 or multiple pinholes 120).

[0031] 2 depicts an EUV mask inspection system 200 according to one or more embodiments of the present disclosure. The EUV mask inspection system 200 may include an EUV illumination source 202, one or more illumination optics 204 for illuminating a test mask 201, one or more projection optics 210, one or more detectors 208, and one or more controllers 212.

[0032] The EUV illumination source 202 may include any illumination source known in the art suitable for the purposes contemplated by this disclosure. An example of an EUV illumination source 202 may be a quasi-continuous wave laser. The EUV illumination source 202 may provide high pulse repetition rates, low noise, high power, stability and reliability.

[0033] The EUV illumination source 202 can be configured to direct an EUV incident beam 206 onto the test mask 201 through one or more illumination optics 204. For example, the EUV illumination source 202 can direct the EUV incident beam 206 onto the one or more illumination optics 204, which can be configured to focus the EUV incident beam 206 onto the test mask 201.

[0034] Any EUV compatible optics known in the art suitable for precisely positioning the EUV incident beam 206 onto the test mask 201 may be included within the illumination optics 204. For example, one or more mirrors configured to reflect EUV radiation may be included within the illumination optics 204. The illumination optics 204 may be configured to direct the EUV incident beam 206 onto the test mask 201 at any suitable angle, including but not limited to orthogonal and oblique angles.

[0035] Upon being focused onto the test mask 201, the EUV incident beam 206 may be reflected and / or scattered as a reflected beam 207. The reflected beam 207 may be collected by one or more detectors 208 via one or more projection optics 210. For example, the one or more projection optics 210 may collect the reflected beam 207 and focus the reflected beam 207 onto a portion or portions of the one or more detectors 208. The one or more detectors 208 may include any detector known in the art suitable for the purposes contemplated by the present disclosure. For example, the one or more detectors 208 may include any CCD type camera.

[0036] Any EUV compatible optics known in the art may be included within the one or more projection optics 210 suitable for projecting the reflected beam 207 onto the one or more detectors 208. For example, the one or more projection optics may include one or more mirrors configured to reflect EUV radiation.

[0037] The controller 212 may include one or more processors and memory. The one or more processors may be communicatively coupled to the one or more detectors 208. The one or more processors may be configured to execute a set of program instructions stored in a memory configured to cause the one or more processors to perform one or more steps of the present disclosure. The components of the EUV mask inspection system 200 may be communicatively coupled via one or more wired connections (e.g., copper wire, fiber optic cable, soldered connections, etc.) or wireless connections (e.g., RF connections, IR connections, data network connections, etc.). The controller 212 may be communicatively coupled to a user interface.

[0038] After the reflected beam 207 is focused onto a portion or portions of the one or more detectors 208, an image based on the reflected beam 207 may be generated by the one or more controllers 212. For example, the intensity, phase, wavefront and / or other characteristics of the reflected beam 207 may be analyzed by one or more processors in the one or more controllers 212. The one or more processors may be configured to convert detected light of the reflected beam 207 into detection signals corresponding to one or more characteristics of the reflected beam 207. For example, the one or more processors may be configured to generate an image exhibiting different intensity values ​​corresponding to different positions or portions of the test mask 201.

[0039] The one or more controllers 212 can be configured to measure one or more wavefront aberrations of the EUV mask inspection system 200 based on the reflected beam 207. For example, the one or more detected signals corresponding to one or more characteristics of the reflected beam 207 can be compared by the one or more controllers 212 to an expected signal based on the particular test mask 201 being used. The expected signal based on the particular test mask 201 can be stored in a memory of the EUV mask inspection system 200 or can be provided through a user input. Based on the one or more wavefront aberrations measured by the EUV mask inspection system 200, the one or more controllers 212 can determine one or more adjustment amounts to adjust one or more components of the EUV mask inspection system 200. For example, the one or more controllers 212 may determine one or more adjustments to the position of the one or more illumination optics 204 and / or the one or more projection optics 210 .

[0040] One or more processors in the one or more controllers 212 may be configured to execute program instructions stored in memory to perform any of the various process steps described elsewhere in this disclosure. The memory may store various data used by various components of the EUV mask inspection system 200. For example, the memory may store wavefront aberration data generated by the EUV mask inspection system 200.

[0041] The one or more processors in the one or more controllers 212 may include any processing element known in the art. In this sense, the one or more processors may include any microprocessor-based device configured to execute algorithms and / or instructions. According to an embodiment, the one or more processors may be a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, or any other computer system (e.g., a networked computer) configured to execute a program, which may be configured to operate the EUV mask inspection system 200 as described elsewhere in this disclosure. It is noted that the term "processor" may be broadly defined to include any device having one or more processing elements that executes program instructions obtained from a non-transitory storage medium.

[0042] The memory may include any storage medium known in the art suitable for storing program instructions executable by one or more associated processors of the one or more controllers 212. For example, the memory may include a non-transitory storage medium. For example, the memory may include, but is not limited to, read-only memory, random access memory, magnetic or optical storage devices (e.g., disks), magnetic tapes, solid state drives, etc. It is noted that the memory may be housed with the one or more processors in a common controller housing. In some embodiments, the memory may be remote to the physical location of one or more processors of the one or more controllers 212. For example, one or more processors of the one or more controllers 212 may access a remote memory (e.g., a server) accessible over a network (e.g., the Internet, an intranet, etc.). Therefore, the above description should be taken as illustrative rather than limiting on the present invention.

[0043] Additionally, the controller(s) 212 and any components associated therewith (e.g., processor, memory, etc.) may comprise one or more controllers housed within a common housing or within multiple housings. Further, the controller(s) 212 may be integrated with and / or perform the functions of any component of EUV mask inspection system 200.

[0044] The one or more controllers 212 may perform any number of processing or analysis steps disclosed herein, including, but not limited to, receiving, generating, or applying a model that relates wavefront aberration data to specified attributes of specimen features, which may involve a number of algorithms, such as, but not limited to, a geometric engine, a process modeling engine, or a combination thereof, to determine wavefront aberrations using any technique known in the art.

[0045] The one or more controllers 212 may further analyze the collected data from the EUV mask inspection system 200 by applying the collected data to a model using any data fitting and optimization technique known in the art, including, but not limited to, libraries, fast order reduction models, regression, machine learning algorithms such as neural networks, support vector machines (SVM), dimensionality reduction algorithms (e.g., principal component analysis (PCA), independent component analysis (ICA), locally linear embedding (LLE), etc.), sparse representations of data (e.g., Fourier or wavelet transforms, Kalman filters, algorithms to facilitate homogeneous or heterogeneous tool matching, etc.).

[0046] In some embodiments, the one or more controllers 212 analyze raw data generated by the EUV mask inspection system 200 using algorithms that do not involve modeling, optimization, and / or fitting. It is noted that the data processing algorithms executed by the controllers can be, but are not required to be, tailored for wavefront aberration metrology applications through the use of parallelization, distributed data processing, load balancing, multi-service support, data processing hardware design and implementation, or dynamic load optimization. Additionally, various implementations of the algorithms can be, but are not required to be, executed by the one or more controllers 212 (e.g., via firmware, software, or a field programmable gate array (FPGA), etc.).

[0047] 3 is a diagram illustrating the reflectivity of unpolarized light at a portion or portions of a pattern 100 versus the angle of an EUV incident beam 206 directed at the test mask 201, in accordance with one or more embodiments of the present disclosure. The EUV mask inspection system 200 may be configured to provide an angle of incidence between approximately 6° and 17°. It is noted that the reflectivity at the reflective portion 106 of the test mask 201 may result from one or more factors, including, but not limited to, the configuration of the reflective portion 106 (e.g., material used, thickness and period of the plurality of periodically repeating bilayers 116, chief ray angle, etc.).

[0048] 4A-4G are diagrams illustrating intensity contrast at the imaging pupil 402 of the projection optics 210 according to one or more embodiments of the present disclosure. It is noted that the diagrams 4A-4G depict specific embodiment representations of the EUV mask inspection system 200, but the EUV mask inspection system 200 is not limited to the embodiments disclosed therein. The diagrams 4A-4E depict intensity contrast at the imaging pupil 402 of the projection optics 210 of the EUV mask inspection system 200, and the EUV mask inspection system 200 has eight periodically repeating bilayers 116, the period of the periodically repeating bilayers 116 is about 7.2 nm, the cap(s) 128 are substantially formed of ruthenium and have a thickness of about 2.5 nm, and the illumination chief ray angle is 8.2°, the illumination coherence parameter is σ=0.7, and the numerical aperture is equal to about 0.16.

[0049] 4A illustrates the intensity contrast of the fill of the imaging pupil 402 of the one or more projection optics 210 for an EUV mask inspection system 200 having a pattern 100 in its reflective portion 106 of an array of multilayer pillars 114 having a plurality of periodically repeating bilayers 116. The one or more multilayer pillars 114 may be provided with a protective material layer deposited on walls of the one or more multilayer pillars 114 and configured to prevent oxidation of the one or more multilayer pillars 114.

[0050] 4B illustrates the intensity contrast of the fill of the imaging pupil 402 of the projection optics 210 of an EUV mask inspection system 200 having a pattern 100 in which an array of multi-layer pillars 114 having a plurality of periodically repeating bilayers 116 are disposed within an array of pinholes in the absorbing portion 104. According to an embodiment, the pinhole array in the absorbing portion 104 may introduce undesirable reflective effects (e.g., shadowing) into the EUV mask inspection system 200 that may reduce the uniformity of the fill of the imaging pupil 402.

[0051] 4C illustrates the fill intensity contrast of the imaging pupil 402 of the projection optics 210 of an EUV mask inspection system 200 having a pattern 100 with a multi-layer pillar 114 having a plurality of periodically repeating bilayers 116 and a cap 128 in its reflective portion 106. The pattern 100 also includes a plurality of absorbers 110 having anti-reflective coatings 112 with the multi-layer pillars 114 disposed inside the plurality of absorbers 110.

[0052] 4D illustrates the fill intensity contrast of the imaging pupil 402 of the projection optics 210 of an EUV mask inspection system 200 having a pattern 100 with a plurality of multilayer pillars 114 having a plurality of periodically repeating bilayers 116 and a cap 128 in its reflective portion 106. The pattern 100 also includes an absorber 110 having an anti-reflective coating 112 disposed inside the plurality of multilayer pillars 114.

[0053] 4E illustrates the fill intensity contrast of the imaging pupil 402 of the projection optics 210 of an EUV mask inspection system 200 having a pattern 100 with a plurality of multilayer pillars 114 and a cap 128 with a plurality of periodically repeating bilayers 116 in the reflective portion 106. The absorbing portion 104 has a pinhole 120 disposed between the plurality of periodically repeating bilayers 116.

[0054] 4F illustrates the fill intensity contrast of the imaging pupil 402 of the projection optics 210 of an EUV mask inspection system 200 having a pattern 100 with pillars of reflective material 124 within the reflective portion 106. The absorbing portion 106 is shown as having a pinhole 120 disposed between the pillars of reflective material 124.

[0055] 4G illustrates the fill intensity contrast of the imaging pupil 402 of the projection optics 210 of an EUV mask inspection system 200 having a pattern 100 with pillars of reflective material 124 within the reflective portion 106. The absorbing portion 104 is shown as having pinholes 120 disposed between the pillars of reflective material 124.

[0056] FIG. 4H is a diagram illustrating various intensities in the coordinate plane of the fill of the imaging pupil 402 of the projection optics 210 of an EUV mask inspection system 200 having a pattern 100 corresponding to the test mask 201 described in FIGS. 4A-4G of this disclosure, where the coordinate position of the imaging pupil along the y-axis is Py (Img) =0.

[0057] FIG. 5 is a process flow diagram illustrating substeps of a method 500 of using an EUV inspection system in accordance with one or more embodiments of the present disclosure.

[0058] An embodiment of the method 500 includes illuminating 502 a test mask, for example by directing an EUV incident beam 206 from an illumination source 202 through the one or more illumination optics 204 onto the test mask 201.

[0059] The method 500 according to an embodiment also includes detecting 504 the beam reflected from the test mask 201. For example, the one or more detectors 208 may receive the reflected beam 207 from the test mask 201 via the one or more projection optics 210.

[0060] The method 500 according to an embodiment also includes generating 506 one or more images based on the reflected beam. For example, the intensity, phase or wavefront and / or other characteristics of the reflected beam 207 may be analyzed by one or more processors in the one or more controllers 212. The one or more processors may be configured to convert detected light of the reflected beam 207 into detection signals corresponding to one or more characteristics of the reflected beam 207. For example, the one or more processors may be configured to generate images exhibiting different intensity values ​​corresponding to different positions or portions of the test mask 201.

[0061] In accordance with an embodiment, the method 500 may also include identifying 508 one or more wavefront aberrations by, for example, comparing an image generated based on the reflected beam 207 with an expected image based on the particular test mask 201 being used by the one or more controllers 212. The expected image based on the particular test mask 201 may be stored in a memory of the EUV mask inspection system 200 or may be provided via user input.

[0062] The method 500 according to the embodiment also includes providing 510 one or more adjustment amounts for adjusting one or more components of the system. For example, the one or more controllers 212 may determine one or more adjustment amounts for the positions of the one or more illumination optics 204 and / or the one or more projection optics 210. The adjustment of one or more components of the EUV mask inspection system 200 by the one or more adjustment amounts may be performed automatically by the EUV mask inspection system 200 or may be alerted to and performed by a user by a suitably configured one or more controllers 212. The adjustment of one or more components of the EUV mask inspection system 200 by the one or more adjustment amounts may compensate for the identified wavefront aberrations. For example, adjusting one or more components of EUV mask inspection system 200 by one or more adjustment amounts can reduce or eliminate deviations from a desired wavefront caused by aberrations and / or provide a mitigation of the effects of one or more identified wavefront aberrations.

[0063] The subject matter described herein is sometimes depicted with various components embedded within or connected to other components. As will be appreciated, the depicted architectures are merely exemplary, and in fact many other architectures can be implemented to achieve the same functionality. Conceptually, if any arrangement of components achieves the same functionality, then the arrangement of components is substantially "associated" with one another to achieve the desired functionality. Thus, any two components in this application that are combined to achieve a particular functionality can be considered to be "associated" with one another to achieve the desired functionality, regardless of the architecture or intervening components. Similarly, any two components so associated can also be viewed as being "connected" or "coupled" to one another to achieve the desired functionality, and any two components that can be so associated can also be viewed as being "combinable" with one another to achieve the desired functionality. Examples of coupleable include, but are not limited to, physically interactable and / or physically interacting components, and / or wirelessly interactable and / or wirelessly interacting components, and / or logically interactable and / or logically interacting components.

[0064] The present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes in the form, construction and arrangement of the parts may be made without departing from the disclosed subject matter or diminishing all of its essential advantages. The form described is merely illustrative, and it is the intent of the following claims to encompass and embrace all such modifications. Moreover, it will be understood that it is the appended claims which define the invention.

Claims

1. 1. An extreme ultraviolet (EUV) mask inspection system, comprising: an EUV illumination source; A test mask and one or more illumination optics configured to direct an EUV beam from the EUV illumination source onto the test mask; the test mask comprises: a substrate formed of a material having substantially no reflectivity with respect to EUV illumination; one or more patterns formed on the substrate, the one or more patterns comprising absorbing portions configured to absorb EUV illumination and reflective portions configured to reflect EUV illumination, the reflective and absorbing portions being located in a common plane above the substrate, the absorbing portions being configured to reveal a portion or portions of the substrate and comprising one or more pinholes in the reflective portions; and one or more caps disposed on at least one of the absorbing and reflective portions, the caps being formed of a material suitable for reducing oxidation of a portion or portions of the test mask. one or more illumination optical systems; one or more detectors; one or more EUV projection optics configured to collect EUV illumination reflected from the test mask and direct the EUV illumination onto the one or more detectors; one or more controllers having one or more processors communicatively coupled to the one or more detectors, the one or more processors configured to execute a set of program instructions retained in a memory; wherein the set of program instructions causes the one or more processors to: receiving one or more signals from the one or more detectors indicative of EUV illumination reflected from the test mask; and identifying one or more wavefront aberrations throughout the EUV beam based on the one or more signals from the one or more detectors indicative of EUV illumination reflected from the test mask; The system being configured.

2. 10. The system of claim 1, wherein the substrate is formed of silicon dioxide.

3. 2. The system of claim 1, wherein the reflective portion comprises one or more multi-layer pillars formed of a plurality of periodically repeating bilayers of molybdenum and silicon, the thickness of each layer of the periodically repeating bilayer and the period of the periodically repeating bilayer being configured to reflect EUV illumination.

4. 10. The system of claim 1, wherein the reflective portion comprises a multi-layer formed of a plurality of repeating bilayers of molybdenum and silicon.

5. 10. The system of claim 1, wherein the reflective portion comprises a layer of reflective material.

6. 6. The system of claim 5, wherein the reflective material comprises at least one of palladium, platinum, and silver.

7. 10. The system of claim 1, wherein the reflective portion comprises one or more pillars formed of a reflective material.

8. 8. The system of claim 7, wherein the one or more pinholes are disposed between the pillars formed of a reflective material.

9. 2. The system of claim 1, wherein the one or more processors are configured to provide one or more adjustment amounts to adjust at least one of the EUV illumination source, one or more illumination optics, and the one or more EUV projection optics, thereby compensating for the identified one or more wavefront aberrations in the EUV beam.

Images