Method and system for cleaning an optical element in an EUV optical system

Abstract

A system and method for cleaning an optical element of an EUV optical system are disclosed. The system and method can include receiving design data of one or more samples. The system and method can include simulating a plurality of irradiance distributions at a surface of an EUV optical subsystem 102 based on the design data and one or more parameters. The system and method can include aggregating the plurality of irradiance distributions to generate an aggregated irradiance distribution. The system and method can include determining a predicted contaminant distribution based on both the aggregated irradiance distribution and a contaminant growth rate. The system and method can include determining a cleaning recipe for one or more optical elements 112 based on the predicted contaminant distribution.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application No. 63 / 356,035, filed on Jun. 28, 2022, the entire disclosure of which is incorporated herein by reference.

[0002] The present disclosure generally relates to extreme ultraviolet (EUV) property evaluation systems, and more particularly, to cleaning of optical elements of EUV property evaluation systems.

Background Art

[0003] As the demand for lithography - based device structures with smaller features continues to increase, there is a growing need for improvements in illumination sources used in lithography and in the inspection of related reticles for lithographically printing these continuously shrinking devices. One such illumination source used in lithography and inspection systems is an extreme ultraviolet (EUV) light source.

[0004] In inspection systems using EUV, it is extremely important to maintain the cleanliness of the environment in order to maintain the reflectivity of the mirrors and the overall EUV photon budget. However, it is impossible to completely remove contaminants that tend to contaminate the vacuum environment from the system. For example, this is the case when inevitable sources of contamination are included in the components of the EUV system, such as adhesives, actuators, cables, etc. As a result, EUV optical elements within the vacuum chamber are exposed to the partial pressures of contaminants such as hydrocarbons and gaseous H2O. When these contaminants are exposed to EUV radiation within the tool, they will cause the growth of carbon and / or oxides on the optical surfaces of the system, such as mirrors. In the case of mirrors, contamination causes a decrease in reflectivity and a phase change of the light incident on the mirror. All of these effects will cause degradation of the optical elements over time if left unattended, leading to malfunctions in the optical system.

[0005] Even with the best multilayer coating technology, EUV mirrors will only be able to reflect about 65% of the light at normal or near-normal angles of incidence. This reflectivity will be reduced by carbon deposition on the optical surface, which is caused by the interaction of volatile organic contaminants (VOCs) with high-energy EUV photons and other wavelengths. For example, in EUV systems, the imaging light also includes vacuum ultraviolet / ultraviolet (VUV / UV) photons with wavelengths less than 300 nm, which can cause the deposition of contaminants.

[0006] The growth rate of contaminants is proportional to the total irradiance of EUV and VUV / UV up to a certain threshold irradiance, beyond which it becomes independent of the irradiance. In the case of a non-uniformly irradiated mirror, in the region of irradiance below this threshold, the carbon growth rate is dose-dependent, while in the region of irradiance above this threshold, the growth rate becomes uniform and independent of the dose. As a result, when the mirror is near the pupil plane of the imaging system, this non-uniform carbon growth increases the wavefront error and further reduces the reflectivity.

[0007] One way to clean the deposited carbon is to expose the mirror surface to UV light in the presence of ozone molecules (UVO). The carbon removal rate is generally proportional to the UV irradiance. Usually, the mirror is uniformly irradiated with UV light. Under such conditions, some areas with non-uniform carbon deposition on the optical element will be over-cleaned to ensure complete cleaning of the areas with the highest level of carbon deposits. As a result, in areas with less carbon deposition, the cleaning time will be longer than necessary, which may cause damage to the mirror surface due to over-cleaning.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

[0009] Therefore, it is desirable to provide a method and a system for cleaning an optical element to solve the above-mentioned drawbacks. MEANS FOR SOLVING THE PROBLEM

[0010] An EUV optical system according to one or more embodiments of the present disclosure is disclosed. In an exemplary embodiment, the EUV optical system includes an EUV optical subsystem configured to clean the optical elements of the EUV optical system. In an exemplary embodiment, the EUV optical subsystem includes a control device communicatively coupled to the EUV optical subsystem. In another exemplary embodiment, the control device may include one or more processors and also include a memory. In another exemplary embodiment, the one or more processors are configured to execute a set of program instructions stored in the memory. In another exemplary embodiment, the one or more processors are configured to execute program instructions that cause the one or more processors to receive design data of one or more samples. In another exemplary embodiment, the one or more processors are configured to execute program instructions that cause the one or more processors to simulate a plurality of irradiance distributions on a surface of the EUV optical subsystem based on the design data and one or more parameters. In another exemplary embodiment, the one or more processors are configured to execute program instructions that cause the one or more processors to aggregate the plurality of irradiance distributions to generate an aggregated irradiance distribution. In another exemplary embodiment, the one or more processors are configured to execute program instructions that cause the one or more processors to determine a predicted contaminant distribution based on both the aggregated irradiance distribution and the contaminant growth rate, where the contaminant distribution indicates a predicted amount of contaminants deposited on one or more optical elements. In another exemplary embodiment, the one or more processors are configured to execute program instructions that cause the one or more processors to determine a cleaning recipe for one or more optical elements based on the predicted contaminant distribution, the cleaning recipe including one or more cleaning processes.

[0011] A method according to one or more embodiments of the present disclosure is disclosed. In an exemplary embodiment, the method may include receiving design data of one or more samples, among other things. In another exemplary embodiment, the method may include simulating a plurality of irradiance distributions on a surface of an EUV optical subsystem based on the design data and one or more parameters. In another exemplary embodiment, the method may include aggregating the plurality of irradiance distributions to generate an aggregated irradiance distribution. In another exemplary embodiment, the method may include determining a predicted contaminant distribution based on both the aggregated irradiance distribution and the contaminant growth rate, where the contaminant distribution indicates a predicted amount of contaminants deposited on one or more optical elements of the EUV optical subsystem. In another exemplary embodiment, the method may include determining a cleaning recipe for one or more optical elements based on the predicted contaminant distribution, where the cleaning recipe includes one or more cleaning processes. In another exemplary embodiment, the method may be performed via an EUV optical subsystem that includes an illumination source configured to generate an illumination beam, where one or more optical elements are configured to reflect a measurement beam, one or more optical elements are disposed within a focusing path of the EUV optical subsystem, and the EUV optical system includes the EUV optical subsystem.

[0012] It should be understood that the foregoing general description and the following detailed description are merely exemplary and explanatory and are not necessarily restrictive of the claimed invention. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the general description, serve to explain the principles of the invention.

[0013] Many advantages of the present disclosure can be better understood by those skilled in the art with reference to the accompanying drawings.

Brief Description of the Drawings

[0014]

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DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, reference will be made in detail to the disclosed subject matter shown in the accompanying drawings. The present disclosure has been specifically shown and described with respect to specific embodiments and their detailed features. The embodiments described in this specification are to be construed as illustrative rather than limiting. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail can be made without departing from the spirit and scope of the present disclosure.

[0016] Embodiments of the present disclosure are directed to systems and methods for performing various cleanings depending on the location of an optical element. For example, an aggregated irradiance distribution approximating the dose of irradiance received by an optical element of an EUV optical system can be determined by simulating and aggregating the irradiance distribution received by the optical element during the scanning of one or more samples. Further, based on the aggregated irradiance distribution, a predicted contaminant distribution can be determined that predicts the amount of thickness of contaminants distributed on the optical element. Further, based on such a predicted contaminant distribution, a cleaning recipe can be determined that uses one or more modulators (such as an aperture, etc.) in one or more processing steps for cleaning the optical element. In this context, based on the predicted contaminant distribution, a location-dependent cleaning recipe can be determined that efficiently cleans the optical element and reduces or eliminates excessive cleaning that may damage the surface of the optical element in some cases.

[0017] In the case of at least carbon, the removal rate of contaminants generally is proportional to the UV irradiance used for the removal.

[0018] One way to clean contaminants (e.g., carbon contaminants on a mirror of an EUV optical system) is to irradiate the contaminants on the optical element with UV light in the presence of ozone, which may also be called UV ozone (UVO) cleaning. In such a method, often a uniform amount of UV light is used to remove the contaminants, regardless of the uniformity of the distribution of the contaminants on the surface. Under these conditions, some areas with a relatively small amount of contaminant deposits on the optical element are over-cleaned to ensure complete cleaning of areas with the highest levels of contaminants. Herein, it is envisioned that as a result of such uniform cleaning, the cleaning time becomes longer and, in some cases, may result in damage to the optical element due to over-cleaning in areas with relatively few contaminant deposits.

[0019] Another challenge in cleaning EUV optical elements is that it can be difficult to determine or measure the amount of contaminants. For example, the optical elements of an EUV system are often in a vacuum chamber, and it may be unrealistic and costly to remove the optical elements to measure the thickness of nanoscale contaminant deposits. Therefore, if the maximum level of contaminants is not accurately estimated, excessive cleaning may be performed more than necessary to ensure that the maximum level of contaminants is reduced to an acceptable level, and the amount of excessive cleaning in areas where the contaminants are at a relatively low level will further increase.

[0020] While it may not be practical to directly measure the contaminant distribution on the optical element, it is contemplated that by simulating the irradiance distribution received by the optical element, determination and cleaning (e.g., precise cleaning) of the contaminant distribution will be possible. Further, rather than performing uniform cleaning, in some embodiments, location-dependent cleaning via one or more light modulators may be used to provide a specific dose of cleaning to a specific area of the optical element. Embodiments of the present disclosure determine the amount of contaminant distribution on the optical element and clean the optical element more precisely and efficiently. Further, some embodiments may contribute to improving the measurement throughput of an actinic EUV optical system by reducing excessive cleaning and damage to the optical element, improving the clarity of measurements (e.g., images) obtained using the optical element, and reducing the downtime required for cleaning.

[0021] Such advantages can be particularly pronounced for optical elements placed within the pupil plane of the condenser path of an EUV optical system. For example, the irradiance distribution received by an optical element, such as a mirror, within or near the pupil plane of the condenser path of an EUV optical system, when aggregated, may have a more variable (i.e., less uniform) value than the aggregated irradiance distribution in other locations (e.g., the field plane) of the EUV optical system. Such higher variability is due, at least in part, to the consistency of the location of the diffraction order of light in the pupil plane.

[0022] FIG. 1 shows a simplified block diagram of an EUV optical system 100 according to one or more embodiments of the present disclosure. In a plurality of embodiments, the EUV optical system 100 includes an EUV inspection system (e.g., an EUV mask inspection system or an EUV wafer inspection system). In a plurality of embodiments, the EUV optical system 100 includes an EUV lithography system.

[0023] In a plurality of embodiments, the EUV optical system 100 includes an EUV optical subsystem 102 and a control device 104. The control device 104 may include one or more processors 106 configured to execute program instructions held in a memory 108. In a plurality of embodiments, the one or more processors 106 are configured to cause the one or more processors to: i) receive design data of one or more samples 124; ii) simulate a set of irradiance distributions on a surface of the EUV optical subsystem 102 based on the design data and one or more parameters; iii) aggregate the set of irradiance distributions to generate an aggregated irradiance distribution; iv) determine a predicted contaminant distribution of the condenser optical element 112 based on both the aggregated irradiance distribution and the contaminant growth rate; and v) determine a cleaning recipe for the condenser optical element 112 based on the predicted contaminant distribution.

[0024] In a plurality of embodiments, the EUV optical subsystem 102 includes an EUV illumination source 114 configured to generate an illumination beam 120 and guide the illumination beam 120 through an illumination path 126 to the sample 124 using one or more illumination optical elements 110. In a plurality of embodiments, the EUV optical subsystem 102 includes a collection path 128 including one or more condenser optical elements 112 configured to guide a measurement beam 122 emitted from the sample 124 to a detector 116.

[0025] The EUV optical subsystem 102 can include any number of optical elements such as the illumination optical element 110 and the condenser optical element 112. The one or more illumination optical elements 110 and the one or more condenser optical elements 112 can include any EUV optical elements known in the art of EUV optics. For example, the one or more illumination optical elements 110 can include, but are not limited to, one or more EUV mirrors configured to be disposed within the illumination path 126 and direct the illumination beam 120 toward the sample 124. As another example, the one or more condenser optical elements 112 can include, but are not limited to, one or more EUV mirrors configured to be disposed within the condenser path 128 and reflect the measurement beam 122 from the sample 124 to the detector 116.

[0026] Furthermore, the components and configurations of the EUV optical system can be better understood in the context of an EUV system as described in U.S. Patent No. 8,916,831, issued December 23, 2014, which is hereby incorporated by reference in its entirety. Additionally, the EUV system is described in U.S. Patent No. 11,293,880, issued April 5, 2022, which is hereby incorporated by reference in its entirety.

[0027] FIG. 2 shows a flowchart of steps performed in method 200, according to one or more embodiments of the present disclosure.

[0028] In step 202, design data for one or more samples 124 is received. The design data can include any type of design data related to the design of one or more layers of the sample 124. For example, FIGS. 3A and 3B are conceptual diagrams of photomask design data 300, 302 including various patterns. In a plurality of embodiments, the one or more processors 106 receive the design data from a design data database. For example, the design data database can include a storage medium (e.g., a server) external to the system, or the design data database can be included in the memory 108 of the EUV optical system 100.

[0029] In step 204, based on the design data and one or more parameters, a set of irradiance distributions on a surface of EUV optical subsystem 102 is simulated. In multiple embodiments, the set of irradiance distributions is simulated using a simulator on a processor. For example, one or more processors 106 may be configured to execute program instructions of a simulator module (e.g., software, application) that is configured to simulate the set of irradiance distributions stored in memory 108 of EUV optical system 100. In multiple embodiments, referring back to FIG. 1, the set of irradiance distributions may be used to simulate (e.g., approximate) the amount of irradiance received by condenser optic 112 based on one or more operations of EUV optical system 100 (e.g., imaging operation, lithography operation). For example, multiple samples 124 can be imaged with EUV optical system 100. In multiple embodiments, the pattern of sample 124 forms a specific diffracted irradiance distribution on the condenser pupil plane of EUV optical system 100 when sample 124 is illuminated. The irradiance distribution emitted from the sample and received by condenser optic 112 of EUV optical system 100 can be simulated based on the design of sample 124.

[0030] In multiple embodiments, the irradiance distribution can be any type of irradiance distribution based on any type of simulation at any simulated location (e.g., surface) of EUV optical system 100 that uses any value of any set of parameters. For example, various non-limiting examples of irradiance distributions 502 for nine different incident angle values are shown in FIG. 5B.

[0031] For the purposes of the present disclosure, the term irradiance is the amount of energy per unit time incident on a unit area and is generally referred to as the luminous flux per unit area. Further, the term dose can be defined as the irradiance multiplied by the residence time. For at least some contaminants, below the saturation threshold, the rate of growth / deposition of the contaminant is proportional to the dose received. However, it is noted that such growth rates may vary depending on the wavelength and other characteristics, and this can also be simulated by embodiments.

[0032] In multiple embodiments, the parameters can include any parameters that can be utilized in the simulation. For example, the parameters can approximate the real-world parameters of the EUV optical subsystem 102 and its elements, although this is not essential. In multiple embodiments, the parameters include, but are not limited to, the angle of incidence of the optical axis of such light with respect to the sample 124 illuminated by the light, the spectral range of the light (e.g., the illumination spectrum based on the spectral range of the light of the illumination beam), the chief ray angle, and the like. Further, or alternatively, the parameters can include various characteristics, features, and configurations of various optical elements. For example, such parameters can include the optical characteristics (e.g., reflectivity, numerical aperture) of one or more elements, material, size, shape, position, orientation, and / or the like. Further, or alternatively, the parameters can include the parameters of the sample measurement recipe. For example, the parameters can include the parameters of the scanning pattern recipe, such as the size of the field of view of the area to be imaged or etched, the direction of the scanning path, the overlap distance of the scanning paths, and / or the like. In another example, the parameters can include the parameters of the movement and measurement recipe, such as, for example, the size of the field of view, the length of time that the location of each field of view will be irradiated for imaging purposes, which location of the sample will be measured, and the like. The parameters can include, additionally or alternatively, the partial pressure and the weight or volume percentage of the VOC surrounding the element. The parameters can include, additionally or alternatively, simulation quality parameters, such as to what extent the geometry of the components is detailed and at what "size" time intervals the simulation is performed. For example, the smaller the time interval size, the more calculations may be required to perform the simulation. For example, each irradiance distribution 502 can be based on where the sample 124 is positioned relative to the illumination beam at a given time, over a given time interval size (e.g., less than 1 nanosecond, less than 1 millisecond, less than 1 second, or any other time) at a given scanning speed (e.g., the speed at which the sample is moved relative to the illumination beam).In this context, during the simulated scan of sample 124, the amount of irradiance received on a surface of the simulated EUV optical system 100 can be simulated over many different time intervals corresponding to many different locations on the illuminated sample 124. In this context, the total dose of illumination received by the optical element during the measurement (e.g., the entire scan) of one or more samples can be simulated.

[0033] In step 206, a set of irradiance distributions is aggregated to generate an aggregated irradiance distribution. The aggregated irradiance distribution can be generated using any method disclosed herein or known in the art. In multiple embodiments, one or more processors 106 aggregate the set of irradiance distributions. For example, one or more processors 106 can be configured to combine the set of irradiance distributions into a set of aggregated data and store such data in the memory 108. As another example, one or more processors 106 can be configured to determine a total irradiance distribution, an average distribution, or any other type of calculated value based on a combination of the set of irradiance distributions. In multiple embodiments, aggregating the irradiance distribution 502 can make it possible to approximate the "dose" received by the condenser optical element 112 during one or more scans of one or more samples 124 over a period of time. A non-limiting illustration of the aggregated irradiance distribution 504 is shown in FIG. 5C. In multiple embodiments, the aggregated irradiance distribution 504 can include an irradiance distribution of aggregated extreme ultraviolet radiation (EUV) corresponding to a simulated scan of one or more samples 124 using light within the EUV spectral range.

[0034] In multiple embodiments, each irradiance distribution 502 can approximate the amount of irradiance directed onto the surface of EUV optical system 100 at a single point in time. By aggregating these irradiance distributions 502, an approximation of the total combined "dose" received over a non-instantaneous time period may be possible. For example, the simulation may be configured to simulate the dose received by the condenser optic 112 when scanning the pattern of the photomask based on the actual scan pattern of the EUV optical system 100. In this context, by aggregating the irradiance distributions 502, it may be possible to simulate the dose received based on such a scan pattern.

[0035] In step 208, a predicted contaminant distribution is determined. For example, the contaminant distribution may be determined (e.g., calculated) based on both the aggregated irradiance distribution of step 206 and the contaminant growth rate. In multiple embodiments, the predicted contaminant distribution is determined by one or more processors 106 and stored in the memory 108. For example, the predicted contaminant distribution may indicate the predicted amount of contaminants deposited on the surface of the condenser optic 112 based on the scan of one or more samples 124. For example, a diagram of the predicted contaminant distribution 506 is shown in FIG. 5D.

[0036] In multiple embodiments, the contaminant growth rate can be any data (e.g., correlation data), knowledge, function, program, etc. For example, the contaminant growth rate may be a curve, function, data table, etc. of the contaminant growth rate. For example, a non-limiting example of a contaminant growth rate curve 402 is shown in plot 400 of FIG. 4. In multiple embodiments, each value at each location of the predicted contaminant distribution 506 is determined by multiplying the respective aggregated irradiance distribution value by the contaminant growth rate (e.g., carbon growth rate) using the contaminant growth rate curve 402.

[0037] The growth rate of contaminants is generally a function of the irradiance at a specific wavelength. The challenge in simulating contaminated deposits is that for a given dose, VUV / UV light produces disproportionately more carbon deposits than EUV light. This effect is significant, and in EUV optical systems where the intensity of EUV light exceeds that of VUV / UV light, VUV / UV light can cause non-negligible amounts of carbon deposition. In multiple embodiments, to address this challenge, different contaminant growth rates are used for each wavelength or wavelength range. For example, the aggregated irradiance distribution for each wavelength may be simulated individually, and each aggregated irradiance distribution may be used with the contaminant growth rate specific to each wavelength to determine the (overall) predicted contaminant distribution.

[0038] For example, the contaminant distributions 506 caused by EUV light and VUV / UV light may be considered (e.g., simulated) individually and then combined. However, as another challenge, the amount of VUV / UV light in the EUV optical system 100 may not always be well understood as much as the amount of EUV light. In multiple embodiments, to address such challenges, the amount of VUV / UV light can be sampled / measured. For example, the range and intensity of the VUV / UV spectrum may be based on discrete sampling using an optical sensor at one or more locations (e.g., any location) of the EUV optical system 100. In this context, VUV / UV measurements may be obtained from the EUV optical system 100 and used to simulate the VUV-based contaminant distribution. On the other hand, the EUV spectral parameters used in the simulation may be more easily determined, such as being determined based on the wavelength and intensity of the known illumination beam 120. Note that such EUV and VUV / UV wavelengths and intensities used in the simulation are examples of illumination spectral parameters.

[0039] It should be noted that such sampling of VUV / UV light can also be utilized in a method for separately determining and combining VUV / UV-based and EUV-based contaminant growth rate distributions, as further described below with respect to FIG. 14.

[0040] In step 210, based on the predicted contaminant distribution 506, a cleaning recipe for the condenser optic 112 is determined. In a plurality of embodiments, the cleaning recipe is determined by one or more processors 106 and stored in the memory 108. For example, the cleaning recipe may be stored, sent to a cleaning subsystem for performing the cleaning, or used by one or more processors 106 of the EUV optical system 100 to instruct the execution of the cleaning. For example, the cleaning recipe may include one or more cleaning processes. For example, each cleaning process can utilize each of one or more modulators, in which case each respective modulator is configured to selectively direct each respective portion of the cleaning illumination to each respective optical element area of the condenser optic 112.

[0041] In a plurality of embodiments, the cleaning recipe for the condenser optic 112 is determined using any method disclosed herein or known in the art and can be stored or transmitted in any format known in the art. For example, the cleaning recipe may be data used by an automatic or semi-automatic cleaning program configured to instruct one or more elements to perform the cleaning of the condenser optic 112. For example, the cleaning recipe may indicate how much intensity of cleaning illumination should be used for how long and / or in which regions it should be applied. Further, for example, the cleaning recipe may include data configured to be used to fabricate one or more modulators or to select one modulator from an inclusive set of one or more modulators.

[0042] In another example, the cleaning recipe may be a transmission configured to display to the user data indicative of information useful for performing the cleaning of the condenser optical element 112. For example, the cleaning recipe may be data that is sent to a program configured to display graphics to the user via a graphical user interface on a display. For example, the cleaning recipe may be one or more texts and / or symbol graphics indicating one or more parameters or steps to be performed in the cleaning. For example, such graphics may indicate which modulator to use, what cleaning dose to use (e.g., what intensity of cleaning illumination for what period of time), and / or which area of the condenser optical element 112 to clean.

[0043] Examples of modulators can include any modulator configured to selectively direct (e.g., block, filter, reflect, diffract, etc.) the cleaning illumination. For example, the modulator may include an aperture and / or a diffractive optical element (DOE) configured to create a far-field diffraction pattern.

[0044] The descriptions in FIGS. 1 to 14 and in this specification are provided for illustrative purposes only and should not be construed as limiting, and it should be noted that they may vary according to one or more embodiments. For example, for cleaning, two or more modulators, such as one inner modulator and one outer modulator, can be used to selectively guide light (e.g., UV cleaning illumination) to the focusing optical element 112. In an additional example, the modulator used for cleaning may be based on a Zernike polynomial, such as by decomposing the contaminant distribution 506 into terms of a Zernike polynomial and selecting one or more modulators based on those terms of the Zernike polynomial. It should be noted that such examples are not necessarily mutually exclusive. For example, the method may utilize in combination the selection of a modulator based on a spectrally resolved range of discretely measured light, a plurality of modulators, and / or terms of a decomposed Zernike polynomial of the contaminant distribution 506.

[0045] Referring to FIGS. 3A to 14, embodiments and various components are described in detail.

[0046] FIG. 3A shows a conceptual diagram of checkerboard-like photomask design data 300 of a sample 124 obtained from a database according to one or more embodiments of the present disclosure.

[0047] FIG. 3B shows a conceptual diagram of complex-pattern photomask design data 302 of a sample 124 obtained from a database according to one or more embodiments of the present disclosure.

[0048] FIG. 4 shows a plot 400 of a carbon contaminant growth rate curve 402 according to one or more embodiments of the present disclosure. The growth rate of carbon contaminants generally depends on the input EUV photon flux until the irradiance reaches the mass-limited region of carbon, at which point the carbon growth rate saturates at a value that depends on the chemical species and partial pressure of volatile organic contaminants (VOCs).

[0049] FIG. 5A shows a schematic diagram of an illumination pupil distribution 500 of a circular (e.g., "flat top") illumination beam according to one or more embodiments of the present disclosure.

[0050] FIG. 5B shows a simulated condenser pupil irradiance distribution 502 based on various incident angle parameter values simulated based on the circular illumination beam of FIG. 5A and the checkerboard photomask design data of FIG. 3A according to one or more embodiments of the present disclosure.

[0051] FIG. 5C shows an aggregated irradiance distribution 504 based on the simulated condenser pupil irradiance distribution of FIG. 5B according to one or more embodiments of the present disclosure.

[0052] FIG. 5D shows a predicted contaminant distribution 506 based on the aggregated irradiance distribution 504 of FIG. 5C according to one or more embodiments of the present disclosure.

[0053] In a plurality of embodiments, FIGS. 5A-5D show a simplified example of determining the predicted contaminant distribution 506 of FIG. 5D. In such an example, the numerical aperture (NA) of the EUV optical system 100 is 0.15 to 0.32, and the coherence of the illumination beam 120 is 0.5. The checkerboard photomask design data of FIG. 3A used to determine the predicted contaminant distribution 506 of FIG. 5D includes a patterned contact array with a pitch along the X direction of 1 um, a pitch along the Y direction of 2 um, and a contact size of 0.6 um×0.6 um. In a plurality of embodiments, the aggregated irradiance distribution 504 is based on the incoherent addition of contributions from the irradiance distributions 502 at different incident angles.

[0054] For example, in multiple ways, various incident angle values corresponding to the illumination conditions of the EUV optical subsystem 102 can be selected. For each incident angle, the diffraction order on a certain surface can be calculated based on design data (e.g., data of the pattern of the sample 124 stored in a database). The calculated diffraction orders can be converted into their irradiance distributions 502 on the pupil plane. In multiple embodiments, the thin mask approximation is utilized (e.g., utilized during the calculation of the diffraction order), which may enable relatively efficient calculations. In multiple embodiments, the diffraction distribution from other incident angles can be interpolated relatively accurately from such a thin mask approximation. In alternative embodiments, more rigorous calculations are performed at the preparation stage of a database configured to process or generate database data.

[0055] Referring now to FIGS. 6A and 6B, a first modulator 602 and a second modulator 604 according to one or more embodiments of the present disclosure are shown. For example, the first modulator 602 and the second modulator 604 can be used in a two-part cleaning process for uniformly cleaning the inner and outer regions. On the other hand, FIG. 6C shows the distribution 606 of the fifth Zernike term that can be used as the far-field diffraction pattern of a diffractive optical element (DOE) for providing non-uniform (e.g., non-binary, intensity-varying) cleaning.

[0056] In multiple embodiments, referring to FIGS. 6A and 6B, the first modulator 602 of two or more modulators is configured to selectively direct a first portion of the cleaning illumination to the inner region of the condenser optical element 112 according to the inner cleaning process, and the second modulator 604 of two or more modulators can be configured to selectively direct a second portion of the cleaning illumination to the outer region of the condenser optical element 112 according to the outer cleaning process.

[0057] FIG. 6A shows a first modulator 602 configured to clean the inner region of the condenser optical element 112, and FIG. 6B shows a second modulator 604 configured to clean the outer region of the condenser optical element 112. For example, the outer region 708 and the inner region 710 are shown in FIG. 7. FIGS. 6A-7 are provided for illustrative purposes only, and it should be noted that any number and shape of regions, such as circular, rectangular, annular, diamond-shaped, radially patterned, etc., and corresponding modulators can be used.

[0058] In multiple embodiments, the cleaning recipe includes two or more cleaning processes configured to utilize two or more modulators. For example, a single DOE placed in the optical path of the UV cleaning illumination can be used to modulate the UV cleaning illumination to be uniform. Further, two apertures (e.g., modulators 602, 604) can be used to direct uniform UV cleaning illumination to clean the inner region 710 and the outer region 708 of the condenser optical element 112. Compared to conventional methods of cleaning the entire mirror simultaneously, the advantage of embodiments having multiple cleaning processes is that overcleaning is avoided or minimized considering the large differences in carbon thickness between different regions.

[0059] FIG. 7 shows a flowchart illustrating a method 700 for a two-part cleaning process of a condenser optical element 112, and FIGS. 702, 704, 706 of the carbon distribution on the condenser optical element 112, according to one or more embodiments of the present disclosure. FIG. 702 of the carbon distribution on the pupil plane before inner region cleaning, FIG. 704 of the carbon distribution after inner region cleaning, and FIG. 706 of the carbon distribution after outer region cleaning are shown.

[0060] In an optional step, referring back to step 210 of FIG. 2, determining the cleaning recipe can include determining an inner cleaning process and an outer cleaning process.

[0061] For example, the inner cleaning process may include instructing a system (e.g., any system or subsystem) to perform cleaning of the inner region 710 of the condenser optic 112 using the first modulator 602 of FIG. 6A. For example, the internal cleaning process may be a step performed using the first modulator 602 between FIGS. 702 and 704. For example, the inner region 710 may be an area of the condenser optic 112 associated with irradiation of the zero diffraction order. The zero diffraction order may be dominant over other diffraction orders and may cause a large accumulation of contaminants, and in some examples, may be caused by the irradiance corresponding to the saturation region of the contaminant growth rate curve 402. In some examples, the inner region 710 has a uniform or substantially uniform contaminant distribution.

[0062] Furthermore, the outer cleaning process may include instructing the system to perform cleaning of the outer region 708 of the condenser optic 112 using the second modulator 604 of FIG. 6B. For example, the outer cleaning process may be a step performed using the second modulator 604 between FIGS. 704 and 706. For example, the outer region 708 may be an area of the condenser optic 112 associated with irradiation of non-zero diffraction orders (e.g., plus and minus first diffraction orders, plus and minus second diffraction orders, etc.).

[0063] In a plurality of embodiments, the inner region 710 can be cleaned multiple times before cleaning the outer region 708, for example, when the contaminant distribution 506 in the outer region 708 is considered to be small enough and the required cleaning frequency is lower.

[0064] In multiple embodiments, any type of condenser optical element 112 at any location can be simulated and / or cleaned according to one or more embodiments. For example, the location of the condenser optical element 112 and / or the location to be simulated can include one or more surfaces. For example, the surface of the EUV optical subsystem 102 may be the location where the condenser optical element 112 is disposed, which may also be the surface where the irradiance distribution 502 is simulated. In this context, the irradiance received by the condenser optical element 112 can be simulated. As an example, such a surface includes a pupil plane. In another example, such a surface includes a field plane.

[0065] For the purposes of the present disclosure, terms such as "pupil" plane, "field" plane, etc. are intended to include locations near such planes. For example, "at the pupil plane" generally includes any pupil plane of the EUV optical system that includes a plane near the pupil plane. For example, in some examples, the exact location of the pupil plane is inaccessible and is disposed within another optical element or subsystem, and any optical element installed near those locations is also considered to be "at" the pupil plane for the purposes of the present disclosure. For example, "at the pupil plane" may mean being adjacent to an element of the pupil plane.

[0066] In multiple embodiments, the contaminant can be any contaminant having a certain growth rate. For example, the contaminant can be a carbon-based molecule, for example, it can contain carbon.

[0067] In an optional step, the system is instructed to perform cleaning of the condenser optical element 112 based on a cleaning recipe. Any system and method may be used to provide cleaning of the condenser optical element 112. For example, the EUV optical system 100 may be configured to clean the condenser optical element 112 itself, or a separate system may be used. In multiple embodiments, the cleaning system may utilize a light source configured to provide a photon energy (e.g., cleaning illumination) that is the same as or slightly higher than the binding energy of the contaminants. Further, to dissociate the contaminants, the photon energy provided by a light source (e.g., the illumination source 114 used as a cleaning illumination source, or another light source) can be combined with a gas mixture. For example, the light source may provide extreme ultraviolet (EUV), vacuum ultraviolet (VUV), deep ultraviolet (DUV), ultraviolet (UV), visible light, infrared (IR), etc. to the surface of the condenser optical element 112. EUV, VUV, or DUV photons can form reactive free radicals in combination with the presence of H2, N2, He, Ar, Xe, H2O, O2, O3, CO2, or other gases near the area to be cleaned, thereby dissociating the contaminants. If the contaminant contains multiple contaminant species, using a gas mixture can target different contaminant species that require cleaning. In multiple embodiments, specific contaminants are targeted by selecting an appropriate gas (or combination of gases) that induces photodissociation. Further, a combination of multiple wavelengths, or of EUV, VUV, DUV, UV, visible light, IR, etc., can be utilized to generate target free radicals from a single gas or a gas mixture. In this way, by combining various types of photons provided by the light source with various types of gases, free radicals that react with the contaminants and as a result clean the surface of the condenser optical element 112 can be effectively supplied.For example, a system and method for cleaning an optical element using illumination are disclosed in U.S. Patent No. 9,335,279, issued on May 10, 2016, and U.S. Patent No. 9,810,991, issued on November 7, 2017, the entireties of which are hereby incorporated by reference into the present application respectively.

[0068] For example, the cleaning recipe may be an ultraviolet radiation ozone (UVO) cleaning recipe configured to be used to direct UV cleaning illumination to the condenser optical element 112 in the presence of ozone molecules. For example, the EUV optical system 100 may include a UV source. The UV source may generate UV cleaning illumination such that the UV cleaning illumination is directed to the condenser optical element 112. For example, the UV source may be configured to direct the UV cleaning illumination along the condenser path 128 in one or more condenser optical elements 112, or along a different path (not shown) in one or more condenser optical elements 112. Further, the EUV optical subsystem 102 may be configured to receive one or more modulators 602, 604. Further, the EUV optical subsystem 102 may be configured to store one or more modulators 602, 604 and move one or more modulators 602, 604 within the path of the UV cleaning illumination via an operating process. For example, the operating process may include modulator translation elements (e.g., an electric motor or any other operating element) for moving the modulators 602, 604 in and out of the path of the UV cleaning illumination.

[0069] In some embodiments, non-uniform cleaning is performed, such as when uniform cleaning is insufficient. For example, when performing non-uniform cleaning, a DOE modulator of terms of Zernike polynomials can be used. In some embodiments, the far-field diffraction pattern of the DOE can be designed / selected such that various areas of the condenser optical element 112 are cleaned in proportion to the amount of contaminants on its surface. For example, the contaminant distribution 506 can be decomposed into one or more Zernike terms to create a distribution based on one or more Zernike polynomials. Further, the far-field diffraction pattern of the DOE can be associated with (e.g., selected based on, designed to match, etc.) a distribution based on one or more Zernike polynomials. For example, in the contaminant distribution 506, terms of low-order Zernike polynomials, such as first-order and second-order terms, may be dominant. The DOE modulator can be based on one or more of these terms of low-order Zernike polynomials such that the number of required modulators is minimized. In some embodiments, an exhaustive set of DOE modulators for each term of low-order Zernike polynomials can be cataloged and stored so that it can be quickly selected for use in cleaning the modulators. FIG. 6C shows a distribution 606 of the fifth Zernike term that can be used as the far-field diffraction pattern of a diffractive optical element (DOE) to provide non-uniform (i.e., non-binary, varying) cleaning.

[0070] The terms of the Zernike polynomials can be determined using any method known in the art or disclosed herein. For example, the carbon thickness distribution (t) on the pupil plane can be defined as t(k), where k is the position on the pupil. Typically, in the degradation of performance (e.g., clarity, reflectivity, etc.) due to the contaminant distribution, low-order Zernike terms, such as first-order and second-order terms, are dominant. The distribution function (i.e., W(k)) can be decomposed into the first several terms of the Zernike polynomials as follows.

[0071]

Number

[0072] In the above formula, for example

Number

[0073] FIG. 8 shows a flow diagram 800 of irradiance distributions 804, 806, 808, 810 for light of different wavelengths (e.g., 13.5 nm, 80 nm, 140 nm, and 200 nm) based on a high-density pattern of design data 802 according to one or more embodiments of the present disclosure. For example, the EUV spectral range of light includes light of 13.5 nm. Such wavelength-specific irradiance distributions can be calculated individually and used to calculate the carbon growth rate distribution and / or the carbon distribution individually.

[0074] FIG. 9 shows a flow diagram 900 illustrating irradiance distributions 906 for different patterns of design data 904 of a single sample 124 based on an illumination pupil distribution 902 according to one or more embodiments of the present disclosure. In a plurality of embodiments, the irradiance distribution 906 is different if the pattern is different. However, when combining the irradiance distributions 906 for different patterns, as may occur when scanning various samples and patterns, the aggregated irradiance distribution 908 may be more uniform in the radial direction but still have an inner portion where the zero-order diffraction order is dominant. In this context, generally, the more diverse the patterns and the more patterns that are aggregated, the more the inner and outer regions can be made uniform in the radial direction.

[0075] FIG. 10 shows a flow diagram 1000 illustrating irradiance distributions 1006 in a field of view for different patterns (not shown) for a circular illumination beam 1002 that images a plurality of samples 1004 according to one or more embodiments of the present disclosure. In a plurality of embodiments, a carbon distribution 1008 of mirrors disposed within the field of view can be determined. In a plurality of embodiments, the carbon distribution 1008 in the field of view rather than the pupil plane is likely to be relatively uniform due to a lack of coherence in the diffraction order, but there can still be some variation. In a plurality of embodiments, one or more DOE modulators can be used to perform cleaning of a condenser optic 112 disposed in the field of view.

[0076] FIG. 11 shows a flow diagram 1100 of carbon distributions 1110, 1116 simulated with and without using an illumination CRA equal to the imaging chief ray angle (CRA) according to one or more embodiments of the present disclosure. The carbon distribution 1110 is based on an aggregated irradiance distribution 1108 simulated using an illumination CRA equal to the imaging CRA. The carbon distribution 1116 is based on an aggregated irradiance distribution 1114 simulated using an illumination CRA not equal to the imaging CRA.

[0077] Generally, the locations of diffraction orders higher than the zero order (e.g., the first diffraction order) of the mask pattern on the pupil plane depend on the shape and layout of the pattern to be inspected, but the locations of all diffraction orders can depend on other parameters such as the illumination CRA and the imaging CRA. In a plurality of embodiments, standard photomasks include simple and / or complex patterns having different pitches and orientations. Thus, after inspection of a plurality of masks, the dose of diffraction orders higher than the aggregated zero order on the pupil plane may become uncertain (e.g., more uniform), while the dose of the aggregated zero order diffraction continues to increase as more masks are imaged. Further, the intensity of the irradiance of the zero order diffraction is generally greater than the intensity of the irradiance of higher order diffractions. As a result, in the aggregated irradiance distribution of the pupil plane after scanning a plurality of masks, the zero order region may become dominant. For example, a plurality of masks can be scanned using an EUV inspection system with a numerical aperture (NA) of 0.15 to 0.32 using a flat top illumination source such as the illumination beam 1104 with a coherence σ = 0.5. In such an example, when the illumination chief ray angle (CRA) is equal to the imaging CRA, assuming they are both 6°, the aggregated irradiance distribution (i.e., the dose map) on the pupil plane may be concentrated in the zero order diffraction region around the center of the pupil. For example, such a concentration can be indicated by a darker portion in the center of the aggregated irradiance distribution 1108. In another example, the illumination CRA may deviate from the imaging CRA, such as when the illumination CRA is 1° and the imaging CRA is 6° as shown by the illumination beam 1112. In such an example, the carbon thickness distribution may deviate from the center of the pupil as shown by the high density contaminant region 1102 of the carbon distribution 1116.

[0078] FIG. 12 shows a Gaussian-shaped illumination beam 1200 and a contaminant distribution 1202 based on the Gaussian-shaped illumination beam 1200, according to one or more embodiments of the present disclosure.

[0079] FIG. 13A shows a plot 1300 of the normalized intensity of light of EUV optical system 100, according to one or more embodiments of the present disclosure. As shown, the amount of EUV is above the peak intensity of the VUV / UV light 1304.

[0080] FIG. 13B shows a plot 1302 of the normalized contaminant growth rate versus the spectrum of light for a given intensity of irradiance, according to one or more embodiments of the present disclosure. As shown, light 1306 in the VUV / UV spectral range produces more contaminant deposits than light in some other spectral ranges for a given intensity.

[0081] FIG. 14 shows a flowchart of a process 1400 for determining a carbon growth rate distribution 1406 based on EUV light and VUV / UV light, according to one or more embodiments of the present disclosure.

[0082] In multiple embodiments, referring again to FIGS. 13A, 13B, and 14, for a specific wavelength, an irradiance distribution is calculated and used to determine a contaminant growth rate distribution that indicates the contaminant growth rate at all locations across the surface of the condenser optic 112. By combining such contaminant growth rate distributions, an overall contaminant growth rate distribution can be obtained. Such an overall contaminant growth rate distribution can be utilized in accordance with one or more embodiments herein, for example, used to determine a predicted contaminant distribution. For example, by combining (e.g., multiplying, integrating, etc.) the intensity of the spectrum of light obtained from FIG. 13A with the corresponding contaminant growth rate in FIG. 13B, a carbon growth rate distribution for a specific wavelength can be generated. For example, an EUV carbon growth rate distribution 1402 can be generated based on the EUV spectrum of light. Next, for example, a composite carbon growth rate distribution 1404 can be determined by combining the EUV carbon growth rate distribution 1402 with a VUV / UV carbon growth rate distribution (not shown). Further, for example, an adjusted carbon growth rate distribution 1406 can be determined by checking and adjusting the composite carbon growth rate distribution 1404 for portions / values that reach and / or exceed a saturation threshold. For example, referring again to FIG. 4, the contaminant growth rate may reach a saturation point such as a mass-limited region, in which case, even if the irradiance further increases, the contaminant growth rate does not increase. For example, the saturation region 1408 can be adjusted / modified to be equal to the saturated (i.e., maximum) contaminant growth rate value based on the saturation threshold.

[0083] Referring again to FIG. 1, embodiments and various components are described in further detail.

[0084] In multiple embodiments, the EUV optical subsystem 102 is configured to capture a measurement beam 122 via a collection path 128. The measurement beam 122 is defined as light that is reflected or diffracted from the sample 124 and passes through the collection path 128 of the EUV optical subsystem 102 such that at least a portion of it can be measured (e.g., imaged) by the detector 116.

[0085] The measurement beam 122 may include the irradiance distribution of the diffraction order received by the focusing optical element 112 at or near the pupil plane of the EUV optical subsystem 102.

[0086] In a plurality of embodiments, the EUV optical system 100 includes the EUV optical subsystem 102. The EUV optical system 100 can include any number of EUV optical subsystems 102, and each EUV optical subsystem 102 can include any number of subsystems (e.g., measurement and / or inspection subsystems). For example, the EUV optical subsystem 102 can be configured to operate within the EUV spectral range of light.

[0087] As already pointed out herein, the EUV optical subsystem 102 may include the detector 116. For example, the detector 116 may be a multi-pixel detector. For example, the detector 116 can be disposed on the field-of-view plane 118 conjugate to the object plane of the sample 124.

[0088] As already pointed out herein, one or more processors 106 of the control device 104 may be communicatively coupled to the memory 108, in which case the one or more processors 106 may be configured to execute a set of program instructions held in the memory 108, and the set of program instructions may be configured to cause the one or more processors 106 to perform the various functions and steps of the present disclosure.

[0089] It is noted that in this specification, one or more components of the EUV optical system 100 can be communicatively coupled to various other components of the EUV optical system 100 in any manner known in the art. For example, one or more processors 106 can be communicatively coupled to each other and to other components via wiring (e.g., copper wire, optical fiber cable, etc.) or wireless connections (e.g., RF coupling, IR coupling, WiMax®, Bluetooth®, 3G, 4G, 4G LTE, 5G, etc.). According to another example, the control device 104 can be communicatively coupled to one or more components of the EUV optical system 100 via any wiring or wireless connection known in the art.

[0090] In multiple embodiments, one or more processors 106 may include any one or more processing elements known in the art. In this sense, one or more processors 106 may include any device of any microprocessor type that is configured to execute software algorithms and / or instructions. In multiple embodiments, one or more processors 106 are configured to execute a program configured to operate EUV optical system 100 as described throughout the present disclosure, and may consist of a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, or other computer systems (e.g., networked computers). It should be recognized that the steps described throughout the present disclosure may be executed by a single computer system or alternatively by multiple computer systems. Further, it should be recognized that the steps described throughout the present disclosure may be executed by any one or more of one or more processors 106. In general, the term "processor" may be broadly defined to include any device having one or more processing elements that execute program instructions from memory 108. Further, various subsystems of EUV optical system 100 (e.g., EUV optical subsystem 102, control device 104, user interface, etc.) may include processors or logic elements suitable for executing at least some of the steps described throughout the present disclosure. Accordingly, the above description should be construed as illustrative rather than as a limitation to the present disclosure.

[0091] Memory 108 may include any storage medium known in the art suitable for storing program instructions executable by one or more associated processors 106 and data received from EUV optical system 100. For example, memory 108 may include a non-transitory memory medium. For example, memory 108 may include, but is not limited to, read-only memory (ROM), random access memory (RAM), magnetic or optical memory (e.g., disk), magnetic tape, solid state drive, and the like. It is further noted that memory 108 may be housed together with one or more processors 106 within a common control device housing. In alternative embodiments, memory 108 may be located remotely with respect to the physical locations of processor 106, control device 104, etc. In another embodiment, memory 108 holds program instructions for causing one or more processors 106 to perform the various steps described throughout this disclosure.

[0092] In a plurality of embodiments, the user interface is communicatively coupled to control device 104. The user interface may include, but is not limited to, one or more desktops, tablets, smartphones, smartwatches, and the like. In another embodiment, the user interface includes a display used to display data of EUV optical system 100 to a user. The display of the user interface may include any display known in the art. For example, the display may include, but is not limited to, a liquid crystal display (LCD), an organic light emitting diode (OLED)-based display, or a CRT display. One of ordinary skill in the art will recognize that display devices such as those that can be integrated with the user interface are also suitable for implementation in this disclosure. In another embodiment, selections and / or commands may be input via a user input device of the user interface in response to data displayed to the user.

[0093] All of the methods described herein may include storing the results of one or more steps of an embodiment of the method in a memory. These results may include any of the results described herein and may be stored in any manner known in the art. The memory may include any of the memories described herein or any other suitable storage medium known in the art. After storing the results, it is possible to access those results in the memory and use them by any of the embodiments of the methods or systems described herein, format them for display to a user, use them by another software module, method, or system, etc. Further, the results can be stored "permanently," "semi-permanently," "transiently," or for a period of time. For example, the memory may be random access memory (RAM), and the results need not necessarily remain in the memory indefinitely.

[0094] It is further contemplated that each of the above-described method embodiments may include any other steps of any other method described herein. Further, each of the above-described method embodiments may be executed by any of the systems described herein.

[0095] Those skilled in the art will recognize that the components, operations, devices, objects, and associated discussions described herein are used as examples for clarity of concepts and that modifications of various configurations are contemplated. As a result, when used herein, the specific examples and associated discussions provided are intended to be representative of their more general classes. In general, the use of any specific example is intended to be representative of its class, and the exclusion of specific components, operations, devices, and objects should not be construed as limiting.

[0096] As used herein, terms related to directions such as "top", "bottom", "above ~", "below ~", "upper", "upward", "lower", "downward", "X direction", etc. are intended to provide relative positions for the purpose of explanation and are not intended to specify an absolute reference system. Various modifications to the described embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments.

[0097] Regarding the use of substantially any plural and / or singular terms herein, those skilled in the art can read and replace them from plural to singular and / or from singular to plural as appropriate according to the context and / or application. Various singular / plural substitutions are not explicitly described herein for clarity.

[0098] The subject matter described in this specification, in some cases, illustrates various components that are included within or connected to other components. It should be understood that the depicted configurations are merely exemplary and that many other configurations that achieve the same functionality can actually be implemented. In a conceptual sense, components that are configured to achieve the same functionality are effectively "associated" so that the desired functionality is achieved. Thus, any two components that are combined to achieve a particular functionality in this specification can be considered to be "associated with" each other so that the desired functionality is achieved, regardless of the configuration or intervening components. Similarly, any two components so associated can also be considered to be "connected" or "coupled" to each other to achieve the desired functionality, and any two components that can be so associated can also be considered to be "couplable" to each other to achieve the desired functionality. Specific examples of being couplable include, but are not limited to, components that are physically joinable and / or physically interact, and / or components that wirelessly interact and / or wirelessly interact, and / or components that logically interact and / or are logically interactable.

[0099] Furthermore, it should be understood that the present invention is defined by the appended claims. In general, it will be understood by those skilled in the art that the terms used herein, particularly in the appended claims (e.g., the main body of the appended claims), are generally intended to be “open” terms (e.g., the term “including” should be construed as “including but not limited to”, the term “having” should be construed as “having at least”, the term “includes” should be construed as “includes but not limited to”, etc.). If a specific number is intended in the description of the introduced claim, such intention will be explicitly described in the claim, and it will be further understood by those skilled in the art that if such description does not exist, such intention does not exist. For example, for the purpose of assistance in understanding, the following appended claims may include the use of introductory phrases “at least one” and “one or more” to introduce the described matters of the claim. However, the use of such phrases should not be construed as suggesting that introducing the described matters of the claim by the indefinite article “a” or “an” limits any particular claim including the described matters introduced in this way to an invention that includes only one such described matter. This also applies when the same claim includes an introductory phrase “one or more” or “at least one” and an indefinite article, e.g., “a” or “an” (e.g., “a” and / or “an” should usually be construed as meaning “at least one” or “one or more”). The same applies to the use of the definite article used to introduce the description of the claim. Furthermore, those skilled in the art will recognize that if the described matters of the introduced claim are explicitly described as being a specific number, such description should usually be construed as meaning at least the described number (e.g., the minimal description of “two described matters” without other modifying phrases usually means at least two described matters, or two or more described matters).Moreover, when conventional expressions similar to "at least one of A, B, and C, etc." are used, generally such a structure is intended in the sense that a person skilled in the art would understand such a conventional expression (e.g., for "a system having at least one of A, B, and C", without limitation, it would include a system having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). When conventional expressions similar to "at least one of A, B, or C, etc." are used, generally such a structure is intended in the sense that a person skilled in the art would understand such a conventional expression (e.g., for "a system having at least one of A, B, or C", without limitation, it would include a system having only A, only B, only C, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). A person skilled in the art will further understand that disjunctive words and / or phrases presenting two or more alternative terms are in fact to be understood as envisioning the possibility of including one of those terms, any of those terms, or both terms, regardless of whether in the specification, claims, or drawings. For example, the phrase "A or B" would be understood to include the possibilities of "A" or "B" or "A and B".

[0100] It is believed that many of the present disclosure and its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the form, structure, and configuration of the components without departing from the disclosed subject matter or sacrificing all of its important advantages. The forms described are for illustrative purposes only, and it is intended that such changes be embraced and included in the following claims. Further, it should be understood that the present invention is defined by the appended claims.

Claims

1. An EUV optical subsystem, comprising: An illumination source configured to generate an illumination beam, and One or more optical elements configured to reflect a measurement beam, said one or more optical elements being disposed within a light-gathering path of said EUV optical subsystem; Said EUV optical subsystem comprising said one or more optical elements; A control device communicatively coupled to said EUV optical subsystem, said control device including one or more processors, said one or more processors causing said one or more processors to: Receive design data of one or more samples; Based on said design data and one or more parameters, simulate a plurality of irradiance distributions on a surface of said EUV optical subsystem; Aggregate said plurality of irradiance distributions to generate an aggregated irradiance distribution; Based on both said aggregated irradiance distribution and a contaminant growth rate, determine a predicted contaminant distribution, said contaminant distribution indicating a predicted amount of contaminants deposited on said one or more optical elements; Based on said predicted contaminant distribution, determine a cleaning recipe for said one or more optical elements, said cleaning recipe including one or more cleaning processes; Said control device being configured to execute program instructions causing said actions; An EUV optical system, characterized by comprising the above components.

2. The EUV optical system according to claim 1, wherein said surface of said EUV optical subsystem includes a pupil plane.

3. The EUV optical system according to claim 1, wherein said surface of said EUV optical subsystem includes a field plane.

4. The EUV optical system according to claim 1, wherein said contaminants deposited on said one or more optical elements contain carbon.

5. The EUV optical system according to claim 1, wherein said cleaning recipe includes an ultraviolet radiation ozone (UVO) cleaning recipe configured to direct UV illumination to said one or more optical elements in the presence of ozone molecules.

6. The EUV optical system according to claim 1, wherein each cleaning process utilizes each of one or more modulators, and each respective modulator is configured to selectively direct each portion of the cleaning illumination to each optical element area of the one or more optical elements. EUV optical system.

7. The EUV optical system according to claim 6, wherein the one or more modulators comprise a diffractive optical element (DOE) configured to create a far-field diffraction pattern. EUV optical system.

8. The EUV optical system according to claim 7, wherein the far-field diffraction pattern is based on one or more Zernike polynomials. EUV optical system.

9. The EUV optical system according to claim 6, wherein the one or more modulators include a modulator based on one or more Zernike polynomials. EUV optical system.

10. The EUV optical system according to claim 6, wherein the cleaning recipe includes two or more cleaning processes that utilize two or more modulators. EUV optical system.

11. The EUV optical system according to claim 10, wherein a first modulator of the two or more modulators is configured to selectively direct a first portion of the cleaning illumination to an inner region of the one or more optical elements according to an inner cleaning process, and a second modulator of the two or more modulators is configured to selectively direct a second portion of the cleaning illumination to an outer region of the one or more optical elements according to an outer cleaning process. EUV optical system.

12. The EUV optical system according to claim 11, wherein the inner region comprises a circular region. EUV optical system.

13. The EUV optical system according to claim 11, wherein the outer region comprises an annular region. EUV optical system.

14. The EUV optical system according to claim 1, wherein determining the cleaning recipe includes decomposing the contaminant distribution into a distribution based on one or more Zernike polynomials. EUV optical system.

15. The EUV optical system according to claim 1, wherein the aggregated irradiance distribution includes an irradiance distribution of aggregated extreme ultraviolet (EUV) radiation corresponding to a simulated scan over the one or more samples.

16. The EUV optical system according to claim 1, wherein the one or more parameters include a plurality of angles of incidence on the optical axis of the EUV optical system.

17. The EUV optical system according to claim 1, wherein the one or more parameters include illumination spectral parameters based on the spectral range of the light of the illumination beam.

18. The EUV optical system according to claim 17, wherein the illumination spectral parameters are further based on vacuum ultraviolet / ultraviolet (VUV / UV) measurements obtained from the EUV optical system.

19. The EUV optical system according to claim 1, wherein the EUV optical system is configured to operate with light in the extreme ultraviolet (EUV) spectral range.

20. The EUV optical system according to claim 1, wherein the one or more samples comprise one or more photomasks.

21. The EUV optical system according to claim 1, wherein the one or more processors are further configured to instruct the system to perform cleaning of the one or more optical elements based on the cleaning recipe.

22. The EUV optical system according to claim 1, wherein the EUV optical system includes an EUV lithography system.

23. Receiving design data of one or more samples; Simulating a plurality of irradiance distributions on a surface of an EUV optical subsystem based on the design data and one or more parameters; Aggregating the plurality of irradiance distributions to generate an aggregated irradiance distribution; ​ Determining a predicted contaminant distribution based on both the aggregated irradiance distribution and the contaminant growth rate, wherein the contaminant distribution indicates a predicted amount of contaminants deposited on one or more optical elements of the EUV optical subsystem, said determining; Determining a cleaning recipe for the one or more optical elements based on the predicted contaminant distribution, wherein the cleaning recipe includes one or more cleaning processes, said determining; comprising; The EUV optical subsystem includes an illumination source configured to generate an illumination beam, the one or more optical elements are configured to reflect a measurement beam, the one or more optical elements are disposed within a condensing path of the EUV optical subsystem, and the EUV optical system comprises the EUV optical subsystem. Method.

24. The method according to claim 23, wherein the surface of the EUV optical subsystem includes a pupil plane.

25. The method according to claim 23, wherein the surface of the EUV optical subsystem includes a field plane.

26. The method according to claim 23, wherein the contaminants deposited on the one or more optical elements include carbon.

27. The method according to claim 23, wherein the cleaning recipe includes an ultraviolet radiation ozone (UVO) cleaning recipe configured to direct UV illumination to the one or more optical elements in the presence of ozone molecules.

28. The method according to claim 23, wherein each cleaning process utilizes a respective one of the one or more modulators, and each respective modulator is configured to selectively direct a respective portion of the cleaning illumination to a respective optical element area of the one or more optical elements.

29. The method according to claim 28, wherein the one or more modulators comprise a diffractive optical element (DOE) configured to create a far-field diffraction pattern.

30. The method according to claim 29, wherein the far-field diffraction pattern is based on one or more Zernike polynomials.

31. The method according to claim 28, wherein the one or more modulators include modulators based on one or more Zernike polynomials.

32. The method according to claim 28, wherein the cleaning recipe includes two or more cleaning processes using two or more modulators.

33. The method according to claim 32, wherein a first modulator of the two or more modulators is configured to selectively direct a first portion of the cleaning illumination to an inner region of the one or more optical elements according to an inner cleaning process, and a second modulator of the two or more modulators is configured to selectively direct a second portion of the cleaning illumination to an outer region of the one or more optical elements according to an outer cleaning process.

34. The method according to claim 33, wherein the inner region comprises a circular region.

35. The method according to claim 33, wherein the outer region comprises an annular region.

36. The method according to claim 23, wherein determining the cleaning recipe includes decomposing the contaminant distribution into a distribution based on one or more Zernike polynomials.

37. The method according to claim 23, wherein the aggregated irradiance distribution includes an irradiance distribution of aggregated extreme ultraviolet (EUV) radiation corresponding to a simulated scan over the one or more samples.

38. The method according to claim 23, wherein the one or more parameters include a plurality of incident angles of the optical axis of the EUV optical subsystem.

39. The method according to claim 23, wherein the one or more parameters include illumination spectral parameters based on the spectral range of the light of the illumination beam.

40. The method according to claim 39, wherein the illumination spectral parameters are further based on vacuum ultraviolet / ultraviolet (VUV / UV) measurements obtained from the EUV optical subsystem.

41. The method according to claim 23, wherein the EUV optical subsystem is configured to operate with light in the extreme ultraviolet (EUV) spectral range.

42. The method according to claim 23, wherein the one or more samples comprise one or more photomasks.

43. The method according to claim 23, further comprising cleaning the one or more optical elements based on the cleaning recipe.

44. The EUV optical system according to claim 1, comprising an EUV lithography system.

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