System and method for optical path coupling of light for in-site photochemical cleaning in projection imaging systems

Abstract

Embodiments of the invention relate to systems and methods for optical path coupling of light for on-site photochemical cleaning in projection imaging systems. A system for cleaning an optical surface covering an inspection system is disclosed. In particular, systems for optical path coupling of light for on-site photochemical cleaning in projection imaging systems are disclosed. A system for cleaning an optical surface covering an inspection system includes a first illumination source, a detector, a set of illumination optics, and a set of imaging optics. In some embodiments, the system may include at least one of a second illumination source and a third illumination source, each of which may be configured to cause or assist in removing contaminants from one or more optical surfaces of the system.

Description

[0001] Information about divisional applications

[0002] This application is a divisional application of the invention patent application with the application date of April 20, 2022, application number "202280017625.1", and invention name "System and method for optical path coupling of light for on-site photochemical cleaning in projection imaging systems". Technical Field

[0003] The present disclosure relates generally to the field of inspection systems, including inspection systems having extreme ultraviolet optical systems, and more particularly to cleaning optical elements of inspection systems. Background Art

[0004] As the demand for lithography-based device structures with smaller features continues to increase, there is a growing need for improved illumination sources for lithography and for inspecting the associated reticles used to lithographically print these ever-shrinking devices. Some such illumination sources utilized in lithography and inspection systems are inspection systems that utilize extreme ultraviolet (EUV), vacuum ultraviolet (VUV) light, deep ultraviolet (DUV) light, or ultraviolet (UV) light.

[0005] In many cases, inspection systems, and in particular their optics, need to operate in a clean, vacuum environment. However, contaminants that tend to contaminate the vacuum environment cannot be completely removed from the system. This is the case, for example, when components of the inspection system (e.g., certain optical surfaces) contain unavoidable contaminants. As a result, the optics of the inspection system (which in many cases are located within a vacuum chamber) are exposed to partial pressures of contaminants, such as hydrocarbons and gaseous HO. When these contaminants are exposed to radiation within the system (e.g., as may be the case during an illumination process), they will result in the growth of carbon and / or oxide optical surfaces (e.g., mirrors) of the system. In the case of mirrors, contamination will result in a decrease in reflectivity, resulting in a phase shift in the light incident on a given mirror. If not controlled, these two effects will cause the optics to degrade over time, leading to failure of the optical system.

[0006] It is therefore desirable to provide a method and system that addresses the deficiencies of the prior art identified above. Summary of the invention

[0007] According to one or more embodiments of the present disclosure, an optical system is disclosed. The optical system may include a first illumination source configured to generate light. In another embodiment, the optical system may include a detector. In another embodiment, the optical system may include a set of illumination optical devices configured to receive at least a portion of the light from the first illumination source and direct at least a portion of the light to one or more sample surfaces of one or more samples along an illumination axis. In another embodiment, the optical system may include a set of imaging optical devices configured to receive at least a portion of the light from the one or more sample surfaces and direct at least a portion of the light from the one or more sample surfaces to the detector along an imaging axis. In another embodiment, the optical system may include a second illumination source configured to generate a first cleaning beam and direct at least a portion of the first cleaning beam to the set of illumination optical devices via at least one of the illumination axis or the imaging axis. In another embodiment, the optical system may include a third illumination source configured to generate a second cleaning beam and direct at least a portion of the second cleaning beam to at least one of the set of imaging optics or the detector via at least one of the illumination axis or the imaging axis. In another embodiment, the optical system may include one or more chambers, wherein the set of illumination optics, the set of imaging optics, and the detector are disposed within the one or more chambers, wherein each of the one or more chambers is configured to contain a selected purge gas, wherein the selected purge gas photo-reacts with at least one of the first cleaning beam or the second cleaning beam, and wherein the selected purge gas photo-reacts with at least one of the first cleaning beam or the second cleaning beam to form at least one of one or more ion species or one or more radical species, and wherein the at least one of the one or more ion species or one or more radical species is capable of converting contaminants from one or more optical surfaces of at least one of the set of illumination optics, the set of imaging optics, or the detector into one or more volatile species.

[0008] According to one or more embodiments of the present disclosure, an optical system is disclosed. The optical system may include a first illumination source configured to generate light. In another embodiment, the optical system may include a detector. In another embodiment, the optical system may include a set of illumination optical devices configured to receive at least a portion of the light from the first illumination source and direct at least a portion of the light to one or more sample surfaces of one or more samples along an illumination axis. In another embodiment, the optical system may include a set of imaging optical devices configured to receive at least a portion of the light from the one or more sample surfaces and direct at least a portion of the light from the one or more sample surfaces to the detector along an imaging axis. In another embodiment, the optical system may include a second illumination source configured to generate a first cleaning beam and direct at least a portion of the first cleaning beam to the set of illumination optical devices via at least one of the illumination axis or the imaging axis. In another embodiment, the optical system may include one or more chambers, wherein the set of illumination optics, the set of imaging optics, and the detector are disposed within the one or more chambers, wherein each of the one or more chambers is configured to contain a selected purge gas, wherein the selected purge gas photo-reacts with the first cleaning beam, and wherein the selected purge gas photo-reacts with the first cleaning beam to form at least one of one or more ion species or one or more free radical species, and wherein at least one of the one or more ion species or one or more free radical species is capable of converting contaminants from one or more optical surfaces of at least one of the set of illumination optics, the set of imaging optics, or the detector to one or more volatile species.

[0009] According to one or more embodiments of the present disclosure, a method for cleaning an optical surface is disclosed. In one embodiment, the method includes providing a selected cleaning gas to one or more chambers. In another embodiment, the method includes directing one or more cleaning light beams to one or more optical surfaces within the one or more chambers, wherein each of the one or more cleaning light beams photoreacts with the selected cleaning gas, and wherein the selected cleaning gas photoreacts with the one or more cleaning light beams to form at least one of one or more ion species or one or more free radical species, and wherein the at least one of the one or more ion species or one or more free radical species is capable of converting contaminants from one or more optical surfaces into one or more volatile species to form gaseous reaction products. In another embodiment, the method includes evacuating the gaseous reaction products from the one or more chambers.

[0010] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Those skilled in the art may better appreciate the numerous advantages of the present disclosure by referring to the accompanying drawings.

[0012] Figure 1A A conceptual diagram illustrating an optical system according to one or more embodiments of the present disclosure.

[0013] Figure 1B A conceptual diagram illustrating an optical system according to one or more embodiments of the present disclosure.

[0014] Figure 1C A block diagram illustrating an optical system according to one or more embodiments of the present disclosure.

[0015] Figure 2 A method of cleaning an optical surface according to one or more embodiments of the present disclosure is depicted.

[0016] Figure 3 Flowchart depicting steps of a method of cleaning an optical surface according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0017] The present disclosure has been shown and described in detail with respect to certain embodiments and specific features thereof. The embodiments set forth herein are considered to be illustrative and not restrictive. It should be readily apparent to those skilled in the art that various changes and modifications may be made in form and detail without departing from the spirit and scope of the present disclosure. Reference will now be made in detail to the disclosed subject matter, which is illustrated in the accompanying drawings.

[0018] Embodiments of the present disclosure relate to systems and methods for cleaning optical surfaces of an overlay inspection system. In particular, systems and methods are disclosed for optical path coupling of light for on-site photochemical cleaning in projection imaging systems.

[0019] It is recognized herein that contamination of optical surfaces within an inspection system can occur when volatile organic contaminant species adsorb on the optical surfaces such that they can interact with high energy radiation (e.g., EUV light or VUV light) to produce carbonaceous deposits in areas exposed to the high energy radiation. The presence of small amounts of deposits (e.g., deposits having a height of only a few nanometers) can result in significant degradation of the performance of optical elements of the inspection system.

[0020] Contaminant deposits on optical surfaces of the inspection system can be removed by one or more photochemical reactions. For example, deposited carbonaceous deposits can be removed via one or more reactions with ionic or radical species, such as oxygen (ID) and other excited states of oxygen, as well as excited states of nitrogen, fluorine, or the like. When a precursor gas, such as ozone, reacts with photons of sufficient energy, such as EUV, VUV, DUV, or UV photons, ionic or radical species can be generated. In this way, irradiating the optical surface with illumination of sufficient energy in the presence of the precursor gas can result in the removal of contaminants deposited on the optical surface.

[0021] Figures 1A to 1C An embodiment of an optical system 100 according to one or more embodiments of the present disclosure is generally described. Figure 1A A conceptual diagram illustrating an optical system 100 according to one or more embodiments of the present disclosure.

[0022] In one embodiment, the system 100 includes a first illumination source 102 configured to generate light 110. In another embodiment, the system 100 includes a set of illumination optics 106 configured to direct at least a portion of the light to one or more sample surfaces 116 of one or more samples 120. For example, the first illumination source 102 may include, but is not limited to, a broadband light source (e.g., a light source suitable for generating EUV, VUV, DUV, and / or UV light), or a narrowband illumination source (e.g., a laser source). The first illumination source 102 may include a laser source configured to generate illumination having a wavelength of at least one of about 355 nanometers, about 266 nanometers, or about 193 nanometers.

[0023] In one embodiment, the illumination optics 106 may be configured to direct illumination 110 emitted from the first illumination source 102 to one or more samples 120 disposed on a stage along an illumination axis 112 (e.g., an illumination path). The one or more samples 120 may include, but are not limited to, a wafer (e.g., a semiconductor wafer) or a mask.

[0024] In another embodiment, the system 100 may include a set of imaging elements 108 configured to receive illumination from a surface of one or more samples 120 and direct the illumination from the one or more samples 120 to the detector 104 via an imaging axis 114 (e.g., an illumination collection path). For example, the imaging optics 108 may include one or more projection optics adapted to collect light scattered, reflected, diffracted, or otherwise emitted from the sample 120 and direct the light to the one or more detectors 104 (e.g., a CCD, TDI-CCD, PMT, and the like). In another embodiment, the system 100 includes a controller (e.g., a controller) for receiving and / or analyzing signals indicative of illumination collected from the sample 120 via the imaging optics 108 and the detector 104. Figure 1C (shown in the).

[0025] It should be noted that Figure 1A As described, embodiments of the present disclosure may be configured to perform one or more inspection processes and one or more cleaning processes. Figure 1A As shown in FIG. 1 , the optical system 100 can be configured to perform one or more inspection processes of the sample 120. As another example, Figure 1B As shown in , the optical system 100 can be configured to perform one or more cleaning processes on one or more optical surfaces of the optical system 100.

[0026] Figure 1B An embodiment of an optical system 100 configured to perform one or more cleaning processes is described.

[0027] In some embodiments, optical system 100 may include a second illumination source 122 configured to generate a first cleaning beam 124. Second illumination source 122 may include, but is not limited to, any illumination source configured to generate EUV, VUV, DUV, and / or UV light. In this regard, first cleaning beam 124 may include, but is not limited to, an EUV, VUV, DUV, and / or UV beam.

[0028] The second illumination source 122 can be configured to direct the first cleaning beam 124 to the illumination optics 106. For example, although not shown, the second illumination source 122 can be configured to direct the first cleaning beam 124 to one or more optical surfaces of the illumination optics 106 via one or more first cleaning optics. The second illumination source 122 (and, in some embodiments, the one or more first cleaning optics) can be configured to direct the first cleaning beam 124 to a point in space corresponding to the mask surface 116. For example, Figure 1B , when configured for cleaning, optical system 100 may not include sample 120. However, second illumination source 122 (and, if applicable, one or more first cleaning optical elements) may be configured to direct first cleaning beam 124 to the point within system 100, to which illumination optics 106 may be configured to direct light 110. In this sense, first cleaning beam 124 may be configured to propagate along illumination axis 112 in the same manner as light 110 propagates along illumination axis 112 (albeit in the opposite direction). It should be noted that first cleaning beam 124 may be configured to propagate entirely along illumination axis 112 (e.g., until first cleaning beam 124 reaches first illumination source 102).

[0029] Second illumination source 122 can be configured to generate first cleaning beam 124 such that first cleaning beam 124 is uniform irradiance illumination. In another embodiment, second illumination source 122 can be configured to generate first cleaning beam 124 such that first cleaning beam 124 includes one or more scanning gratings. First cleaning beam 124 can be configured to illuminate the same field plane as light 110 (e.g., because second illumination source 122 has a numerical aperture value equal to that of first illumination source 102).

[0030] In some embodiments, optical system 100 may include a third illumination source 126 configured to generate a second cleaning beam 128. Third illumination source 126 may include, but is not limited to, any illumination source configured to generate EUV, VUV, DUV, and / or UV light. In this manner, second cleaning beam 128 may include, but is not limited to, EUV, VUV, DUV, and / or UV light beams.

[0031] The third illumination source 126 can be configured to direct the second cleaning beam 128 to the imaging optics 108. For example, although not shown, the third illumination source 126 can be configured to direct the second cleaning beam 128 to one or more optical surfaces of the imaging optics 108 via one or more second cleaning optical elements. The third illumination source 126 (and, in some embodiments, the one or more second cleaning optical elements) can be configured to direct the second cleaning beam 128 to a point in space corresponding to the mask surface 116. For example, Figure 1B , when configured for cleaning, the optical system 100 may not include the sample 120. However, the third illumination source 126 (and, if applicable, one or more second cleaning optical elements) may be configured to direct the second cleaning beam 128 to the point within the system 100 from which the imaging optics 108 may be configured to receive the light 110 from the sample 120. In this sense, the second cleaning beam 128 may be configured to propagate along the imaging axis 114 in the same manner as the light 110 propagates along the imaging axis 114. It should be noted that the second cleaning beam 128 may be configured to propagate entirely along the imaging axis 114 (e.g., until the second cleaning beam 128 reaches the detector 104).

[0032] The third illumination source 126 can be configured to generate the second cleaning beam 128 such that the second cleaning beam 128 is uniform irradiance illumination. In another embodiment, the third illumination source 126 can be configured to generate the second cleaning beam 128 such that the second cleaning beam 128 includes one or more scanning gratings. The second cleaning beam 128 can be configured to illuminate the same field plane as the light 110 (e.g., because the third illumination source 126 has a numerical aperture value equal to the numerical aperture value of the first illumination source 102).

[0033] It should be noted that each of the second illumination source 122 and the third illumination source 126 can be configured to direct illumination (e.g., the first cleaning beam 124 and / or the second cleaning beam 128, as appropriate) to the mask surface 116 through a common aperture (e.g., a viewing hole) of the system 100.

[0034] Specifically contemplated, embodiments of the present disclosure are configured to provide cleaning light (e.g., first cleaning beam 124 and / or second cleaning beam 128) in such a manner that the cleaning light is limited to areas of the optical surface that have been contaminated. For example, embodiments of the present disclosure are configured such that first cleaning beam 124 is configured to propagate along illumination axis 112 in the same manner as light 110. In this manner, first cleaning beam 124 is naturally configured to interact with contaminants only on those areas that may be contaminated (e.g., via deposition catalyzed by light 110 in a detection operation). Similarly, second cleaning beam 128 is configured to propagate along imaging axis 114 in the same manner as light 110. In this manner, second cleaning beam 128 is naturally configured to interact with contaminants only on those areas that may be contaminated (e.g., via deposition catalyzed by light 110 in a detection operation). This approach reduces and / or eliminates the need for additional steering optics, apertures, or beam dumps within optical system 100. Additionally, the need for shielding (e.g., to protect surrounding components from the cleaning light) is reduced. In this sense, the irradiation of the optical surface with the cleaning light is also distributed in a manner equivalent to the distribution of light 110, so that the risk of over- or under-cleaning the optical surface is minimized under the condition that the contamination rate of carbonaceous compounds is proportional to the irradiance of light 110.

[0035] Embodiments of the present disclosure are additionally configured to reduce the amount of cleaning light required to clean all optical surfaces of system 100. For example, because the cleaning light is propagated along the entirety of each of illumination axis 112 and imaging axis 114, the cleaning light is reflected within and along each axis, thereby allowing the cleaning light to be used to clean multiple optical surfaces (rather than being used to clean a single surface and then allowed to dissipate out of optical system 100).

[0036] In some embodiments, the system 100 may include one or more chambers 118. The one or more chambers 118 may include, but are not limited to, one or more vacuum chambers. One or more elements of the system 100 may be disposed in one or more chambers 118. For example, the first illumination source 103, the second illumination source 122, the first cleaning optical element, the third illumination source 126, the second cleaning optical element, the detector 104, the illumination optical device 106, the imaging optical device 108, the sample 120, and / or the stage may be disposed in one or more chambers 118. It should be noted that embodiments of the present disclosure are not limited to a single chamber 118. For example, although not shown, various elements of the system 100 may be disposed in a common chamber, while other elements of the system may be disposed in separate chambers 118. As another example, in some embodiments, certain elements of the present disclosure may not be disposed in a chamber 118.

[0037] One or more chambers may be configured to contain a selected purge gas 202 (e.g. Figure 2 ). The selected cleaning gas (or at least a component of the cleaning gas) may undergo ionization or radicalization in the presence of at least one of the first cleaning beam 124 or the second cleaning beam 128.

[0038] The selected cleaning gas 202 may include any cleaning gas known in the art to be suitable for cleaning one or more optical elements of the present disclosure. For example, the selected cleaning gas may include, but is not limited to, any gas including ozone, oxygen, nitrogen, fluorine, hydrogen, or gaseous water in any proportion. In one embodiment, the cleaning gas includes any gas known in the art that can be ionized by the first cleaning beam 124 and / or the second cleaning beam 128 (e.g., EUV light, VUV light, DUV light, UV light, or the like). In another embodiment, the cleaning gas may include a mixture of any one or more gases.

[0039] It is noted herein that the selected purge gas can be configured to cause or assist in photolysis of contaminants on optical surfaces of system 100. For example, the selected purge gas can be configured such that upon photoreaction with at least one of first cleaning beam 124 or second cleaning beam 128, one or more ions or radical species are formed, wherein the one or more radical species are configured to convert contaminants on one or more optical surfaces into volatile (e.g., gaseous) reaction products that can be evacuated from system 100.

[0040] Figure 1CA block diagram illustrating an optical system 100 in accordance with one or more embodiments of the present disclosure. In some embodiments, the system 100 may include a controller 130 that may be communicatively coupled to one or more other elements of the system 100 (e.g., the first illumination source 102, the detector 104, the pump 136, the second illumination source 122, and / or the third illumination source 126). The controller 130 may include one or more processors 132 that are communicatively coupled to one or more memory units 134. The one or more processors 132 may be configured to execute a set of program instructions stored in the one or more memory units 134 for acquiring detection and / or measurement data from one or more components of the system 100 (e.g., the detector 104) and / or for controlling one or more portions of the system 100 (e.g., the first illumination source 102, the second illumination source 122, the third illumination source 126, the pump 136, or the like).

[0041] Figure 2 A method of cleaning an optical surface according to one or more embodiments of the present disclosure is depicted.

[0042] As previously described, contaminant deposits on optical surfaces can be removed by one or more photochemical reactions. For example, deposited carbonaceous deposits can be removed via one or more reactions with ions or radical species, such as oxygen (ID) and other excited states of oxygen, as well as excited states of nitrogen, fluorine, or the like. When a precursor gas, such as ozone, reacts with photons of sufficient energy, such as EUV, VUV, DUV, or UV photons, ions or radical species can be generated. In this way, irradiating an optical surface with illumination of sufficient energy in the presence of a precursor gas can result in the removal of contaminants deposited on the optical surface.

[0043] The second illumination source 122 can be configured to generate a first cleaning beam 124 and direct the first cleaning beam 124 into one or more chambers 118 of the system 100. Figure 2 For purposes of this disclosure, the embodiments of the present disclosure are not limited to the conceptual descriptions contained therein. For example, specifically considering, Figure 2 The embodiments of the present disclosure shown in Figure 1B Displayed and referenced Figure 1B The illumination and propagation of the first cleaning beam 124 is described (eg, propagating through cleaning optics to the mask surface 116, propagating along an illumination axis, etc.).

[0044] The one or more chambers 118 may contain a selected purge gas 202. Upon irradiating the one or more chambers 118, the selected purge gas 202 may undergo one or more photochemical reactions 208, wherein the first cleaning light beam 124 may excite one or more components of the selected purge gas 202 such that one or more ion species or free radicals 209 are generated.

[0045] The one or more ion species or radicals 209 generated by the photochemical reaction between the first cleaning light beam 124 and one or more components of the selected purge gas 202 may be capable of transforming one or more contaminants 204 present on the optical surface 210 of the system 100 via one or more chemical reactions. For example, the one or more components of the selected purge gas 202 may react with the one or more contaminants to form volatile reaction products 206 that exist in a gaseous state in the one or more chambers 118.

[0046] It should be noted that the one or more optical surfaces 210 of the system may include any portion of any optical element of the system 100. For example, the one or more optical surfaces 210 may include, but are not limited to, any portion of the first illumination source 103, the second illumination source 122, the first cleaning optics, the third illumination source 126, the second cleaning optics, the detector 104, the illumination optics 106, and / or the imaging optics 108.

[0047] The reaction products 206 can be evacuated from the one or more chambers 118. For example, the system 100 can cause the one or more pumps 136 to remove the reaction products 206 from the one or more chambers 118 after the cleaning process is completed.

[0048] The one or more pumps 136 may include any pump known in the art suitable for removing gaseous reaction products formed by the interaction of the ionized and / or radicalized species 209 of the purge gas 202 with the one or more contaminants 204. For example, the one or more pumps 136 may include, but are not limited to, one or more vacuum pumps.

[0049] In another embodiment, the one or more pumps 136 may include a pump system suitable for establishing and maintaining a low pressure or vacuum environment within the one or more chambers 118. For example, the one or more pumps 136 may include a turbo pump and / or a Roots pump that supports a dry pumping unit and is equipped with an exhaust system (not shown).

[0050] It should be noted that in order Figure 2 For purposes of illustration, only the second illumination source 122 is shown. However, embodiments of the present disclosure are not limited to the second illumination source 122. For example, it is specifically contemplated that the cleaning process and accompanying photochemical reactions disclosed herein may be performed using any one of the second illumination source 122 and / or the third illumination source 126, or any combination thereof.

[0051] Figure 3 Depicted is a flow chart illustrating the steps of a method 300 of cleaning an optical surface in accordance with one or more embodiments of the present disclosure.

[0052] In step 302, a selected purge gas is provided to one or more chambers. For example, the selected purge gas 202 may be provided to the one or more chambers 118. The selected purge gas 202 may include any purge gas known in the art suitable for cleaning one or more optical elements of the present disclosure. For example, the selected purge gas may include, but is not limited to, any gas including ozone, oxygen, nitrogen, fluorine, hydrogen, or gaseous water in any proportion. In one embodiment, the purge gas includes any gas known in the art that can be ionized by the first cleaning beam 124 and / or the second cleaning beam 128 (e.g., EUV light, VUV light, DUV light, UV light, or the like). In another embodiment, the purge gas may include a mixture of any one or more gases.

[0053] In step 304, one or more cleaning beams are directed to one or more optical surfaces within one or more chambers, wherein the one or more cleaning beams photoreact with the selected purge gas. For example, second illumination source 122 and / or third illumination source 126 may direct first cleaning beam 124 or second cleaning beam 128, as appropriate, to one or more components of optical system 100. As another example, second illumination source 122 may direct first cleaning beam 124 along illumination axis 112. As yet another example, third illumination source 126 may direct second cleaning beam 128 along imaging axis 114.

[0054] After the one or more cleaning beams are directed to the one or more optical surfaces of the system 100, the selected cleaning gas 202 may undergo one or more photochemical reactions 208, wherein the first cleaning beam 124 and / or the second cleaning beam 128 may excite one or more components of the selected cleaning gas 202, resulting in the generation of one or more ion species or free radicals 209. The one or more ion species or free radicals 209 generated by the photochemical reaction between the first cleaning beam 124 and the one or more components of the selected cleaning gas 202 may transform one or more contaminants 204 present on the optical surface 210 of the system 100. For example, the one or more components of the selected cleaning gas 202 may react with the one or more contaminants to form volatile reaction products 206, which exist in a gaseous state in the one or more chambers 118.

[0055] In step 306, the gaseous reaction products are evacuated from the one or more chambers. For example, the reaction products 206 can be evacuated from the one or more chambers 118. For example, after the cleaning process is completed, the system 100 can cause the one or more pumps 136 to remove the reaction products 206 from the one or more chambers 118 (e.g., via the controller 130).

[0056] It should be noted that the scope of the present disclosure is not limited to optical system 100. Rather, systems incorporating various aspects of the present disclosure may include any other optical system known in the art, including characterization systems, metrology systems, and / or lithography systems.

[0057] For example, in one embodiment, the optical system 100 is configured as a wafer inspection system or a reticle inspection system. In this regard, the optical system 100 may include any wafer or reticle inspection optical architecture known in the art that is suitable for operating in the EUV and / or VUV spectral range. It is further recognized that the optical system 100 may be configured as an EUV blank mask inspection system. EUV-based blank mask inspection is generally described in U.S. Patent No. 8,711,346 to Stokowski, issued on April 29, 2014, the disclosure of which is incorporated herein by reference. EUV-based blank mask inspection is generally described in U.S. Patent Application No. 13 / 417,982 to Xiong et al., filed on March 12, 2012, the disclosure of which is incorporated herein by reference. EUV-based reticle inspection is generally described in US Patent Application No. 13 / 905,449 to Nasser-Ghodsi et al., filed on May 30, 2013, the disclosure of which is incorporated herein by reference.

[0058] As another example, in another embodiment, although not shown, the optical system 100 may be configured as an EUV lithography system. In one embodiment, the optical lithography system (not shown) may include a set of illuminator optics configured to direct output light from the light source 100 to an EUV compatible lithography mask (e.g., an EUV reflective mask). In another embodiment, the lithography system includes a set of projection optics configured to receive illumination reflected from the mask and direct the illumination reflected from the mask to one or more wafers disposed on a wafer stage. The optical lithography system may include any EUV lithography system known in the art. EUV-based lithography is generally described in U.S. Patent Application No. 13 / 419,042 to Wang, filed on March 13, 2012, the disclosure of which is incorporated herein by reference.

[0059] It is contemplated herein that the various embodiments of the present disclosure may be implemented in conjunction or independently. For example, Figure 1A to Figure 2 The embodiments described in should be construed as being applicable in combination with each other.

[0060] The one or more processors 132 of the controller 130 may include any processor or processing element known in the art. For the purposes of this disclosure, the term "processor" or "processing element" may be broadly defined to encompass any device having one or more processing or logic elements (e.g., one or more microprocessor devices, one or more application specific integrated circuit (ASIC) devices, one or more field programmable gate arrays (FPGAs), or one or more digital signal processors (DSPs)). In this sense, the one or more processors 132 may include any device configured to execute algorithms and / or instructions (e.g., program instructions stored in a memory). In one embodiment, the one or more processors 132 may be embodied as a desktop computer, a mainframe computer system, a workstation, an image computer, a parallel processor, a network computer, or any other computer system that is configured to execute a program configured to operate or operate with the metering system 100 as described throughout this disclosure.

[0061] In addition, different subsystems of the system 100 (e.g., devices 102, 104, 122, 126, and 136) may include processors or logic elements suitable for performing at least a portion of the steps described in the present disclosure. Therefore, the above description should not be interpreted as a limitation on the embodiments of the present disclosure, but should only be interpreted as an illustration. In addition, the steps described throughout the present disclosure may be performed by a single controller 130 or alternatively multiple controllers. In addition, the controller 130 may include one or more controllers housed in a common housing or multiple housings. In this way, any controller or combination of controllers can be individually packaged as a module suitable for integration into the metering system 100. In addition, the controller 130 can analyze the data received from the detector 104 and feed the data to additional components within the system 100 or external to the system 100.

[0062] The memory 134 may include any storage media known in the art suitable for storing program instructions that can be executed by the associated one or more processors 132. For example, the memory 134 may include a non-transitory storage medium. As another example, the memory 134 may include, but is not limited to, a read-only memory (ROM), a random access memory (RAM), a magnetic or optical storage device (e.g., a disk), a tape, a solid-state drive, and the like. It should be further noted that the memory 134 may be housed in a common controller housing with the one or more processors 132. In one embodiment, the memory 134 may be remotely located relative to the physical location of the one or more processors 132 and the controller 130. For example, the one or more processors 132 of the controller 130 may access a remote memory (e.g., a server) that is accessible via a network (e.g., the Internet, an intranet, and the like).

[0063] In one embodiment, although not shown, the user interface 135 is communicatively coupled to the controller 130. In one embodiment, the user interface 135 may include, but is not limited to, one or more desktop or laptop computers, tablet computers, and the like. In another embodiment, the user interface 135 includes a display for displaying data of the system 100 to the user. The display of the user interface 135 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. Those skilled in the art will recognize that any display device capable of being integrated with the user interface 135 is suitable for the embodiments of the present disclosure. In another embodiment, the user may enter a selection and / or instruction in response to data displayed to the user via a user input device of the user interface 135.

[0064] In another embodiment, the controller 130 is communicatively coupled to one or more elements of the system 100. In this manner, the controller 130 may transmit and / or receive data from any component of the system 100. Furthermore, the controller 130 may direct or otherwise control any component of the system 100 by generating one or more control signals for the associated component. For example, the controller 130 may be communicatively coupled to the detector 104 to receive one or more images from the detector 104.

[0065] All methods described herein may include storing the results of one or more steps of the method embodiments in the memory 134. The results may include any results described herein and may be stored in any manner known in the art. The memory may include any memory described herein or any other suitable storage medium known in the art. After the results have been stored, the results may be accessed in the memory and used by any of the method or system embodiments described herein, formatted to be displayed to a user, used by another software module, method or system, and the like. In addition, the results may be stored "permanently", "semi-permanently", "temporarily" or for a period of time. For example, the memory may be a random access memory (RAM), and the results may not necessarily exist in the memory indefinitely.

[0066] It is further contemplated that each of the above described method embodiments may include any other steps of any other method described herein.In addition, each of the above described method embodiments may be performed by any of the systems described herein.

[0067] Those skilled in the art will recognize that for conceptual clarity, the components, operations, devices, objects, and their accompanying discussions described herein are used as examples, and various configuration modifications are contemplated. Therefore, as used herein, the specific examples and accompanying discussions set forth are intended to represent their more general classes. In general, the use of any particular illustration is intended to represent its class, and the non-inclusion of specific components, operations, devices, and objects should not be considered limiting.

[0068] As used herein, directional terms such as "top", "bottom", "above", "below", "above", "below", "upper", "lower", and "downward" are intended to provide relative positions for description 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 may be applied to other embodiments.

[0069] Regarding the use of any plural and / or singular terms herein, those skilled in the art may translate the plural into the singular and / or the singular into the plural according to the context and / or application. For the sake of clarity, various singular / plural arrangements may not be explicitly described herein.

[0070] The subject matter described herein sometimes illustrates different components that are contained in other components or connected to other components. It should be understood that the described architecture is only exemplary, and many other architectures that realize the same functionality can actually be implemented. In a conceptual sense, any arrangement of components that realize the same functionality is effectively "associated" so that the desired functionality is realized. Therefore, any two components combined to realize specific functionality herein can be regarded as "associated" with each other so that the desired functionality is realized, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be regarded as "connected" or "coupled" to each other to realize the desired functionality, and any two components that can be so associated can also be regarded as "coupled" to each other to realize the desired functionality. Specific examples of coupling components include but are not limited to physically matching and / or physically interacting components and / or wirelessly interacting and / or wirelessly interacting components and / or logically interacting and / or logically interacting components.

[0071] In addition, it should be understood that the invention disclosed and described herein is defined by the appended claims. Those skilled in the art will understand that, in general, the terms used herein, and especially in the appended claims (e.g., the body of the appended claims), are generally intended as "open" terms (e.g., the term "including" should be interpreted as "including but not limited to", the term "having" should be interpreted as "having at least", the term "includes" should be interpreted as "including but not limited to", and the like). Those skilled in the art will further understand that if a specific number of introductory claim statements is intended, then this intention will be explicitly stated in the claim, and in the absence of such a statement, such intention does not exist. For example, to aid understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim statements. However, the use of these phrases should not be interpreted as implying that the introduction of claim statements by the indefinite article "a" or "an" limits any particular claim containing these introductory claim statements to inventions containing only one such statement, even if the same claim contains the introductory phrases "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a and / or an" should generally be interpreted as meaning "at least one" or "one or more"); the same is true for the use of definite articles to introduce claim statements. In addition, even if a specific number of introductory claim statements is explicitly stated, one skilled in the art will recognize that such statement should generally be interpreted to mean at least the stated number (e.g., the bare statement "two statements" without other modifiers generally means at least two statements, or two or more statements). Furthermore, in examples where a convention similar to “at least one of A, B, and C, and the like” is used, generally speaking, such construction is intended that one of ordinary skill in the art will understand the convention (e.g., “a system having at least one of A, B, and C” will include, but is not limited to, systems having A alone, B alone, C alone, A and B together, A and C together, B and C together, and / or A, B, and C together, and the like). In these examples where a convention similar to “at least one of A, B, or C, and the like” is used, generally speaking, such construction is intended that one of ordinary skill in the art will understand the convention (e.g., “a system having at least one of A, B, or C” will include, but is not limited to, systems having A alone, B alone, C alone, A and B together, A and C together, B and C together, and / or A, B, and C together, and the like). Those skilled in the art will further appreciate that any disjunctive words and / or phrases, whether in the specification, claims or drawings, that actually present two or more alternative terms should be understood to contemplate the possibility of including one of the terms, either of the terms, or both of the terms.For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

[0072] It is believed that the present disclosure and its attendant numerous advantages will be appreciated from the foregoing description, and it will be appreciated that various changes may be made to the form, construction, and arrangement of components without departing from the disclosed subject matter or sacrificing all of its substantial advantages. The forms described are merely illustrative, and it is intended that the appended claims cover and encompass such changes. Furthermore, it should be understood that the invention is defined by the appended claims.

Claims

1. An optical system, comprising: a first illumination source configured to generate light; Detector; a set of illumination optics configured to receive at least a portion of the light from the first illumination source and direct at least a portion of the light along an illumination axis to one or more sample surfaces of one or more samples; a set of imaging optics configured to receive at least a portion of the light from the one or more sample surfaces and direct the at least a portion of the light from the one or more sample surfaces to the detector along an imaging axis; a second illumination source configured to generate a first cleaning beam and direct at least a portion of the first cleaning beam to the set of illumination optics via at least one of the illumination axis or the imaging axis; a third illumination source configured to generate a second cleaning beam and direct at least a portion of the second cleaning beam to at least one of the set of imaging optics or the detector via at least one of the illumination axis or the imaging axis, wherein each of the second illumination source and the third illumination source has a numerical aperture value equal to a numerical aperture value of the first illumination source; and one or more chambers, wherein the set of illumination optics, the set of imaging optics, and the detector are disposed within the one or more chambers, wherein each of the one or more chambers is configured to contain a selected purge gas, wherein the selected purge gas photo-reacts with the first cleaning beam, and wherein the selected purge gas photo-reacts with the first cleaning beam to form at least one of one or more ion species or one or more free radical species, and wherein the at least one of the one or more ion species or one or more free radical species is capable of converting contaminants from one or more optical surfaces of at least one of the set of illumination optics, the set of imaging optics, or the detector into one or more volatile species.

2. The optical system of claim 1, wherein the optical system is configured as a mask inspection system.

3. The optical system of claim 2, wherein each of the first cleaning beam and the second cleaning beam comprises at least one of uniform illumination or one or more scanning gratings.

4. The optical system of claim 2, wherein the first illumination source comprises a broadband illumination source.

5. The optical system of claim 4, wherein the first illumination source comprises an illumination source configured to generate at least one of extreme ultraviolet light, vacuum ultraviolet light, deep ultraviolet light, or ultraviolet light.

6. The optical system of claim 2, wherein the first illumination source comprises a narrow-band illumination source.

7. The optical system of claim 2, wherein each of the second illumination source and the third illumination source is configured to generate at least ultraviolet light.

8. The optical system of claim 2, wherein the first cleaning beam comprises ultraviolet light having a wavelength between about 210 nanometers and about 300 nanometers.

9. The optical system of claim 2, wherein the second cleaning beam comprises ultraviolet light having a wavelength between about 210 nanometers and about 300 nanometers.

10. The optical system of claim 2, wherein the selected purge gas comprises at least one of ozone, fluorine, or nitrogen.

11. The optical system of claim 2, wherein the one or more ion species include one or more ions of at least one of oxygen, nitrogen, or fluorine.

12. The optical system of claim 11, wherein the one or more ions are configured to remove one or more elements of the contaminant from at least one of a set of illumination optics, the set of imaging optics, or the detector via one or more photoreactions between the contaminant and at least one of the first cleaning beam or the second cleaning beam, wherein the one or more photoreactions form gaseous reaction products within the one or more chambers.

13. The optical system of claim 12, further comprising one or more pumps configured to evacuate the gaseous reaction products from the one or more chambers.

14. The optical system of claim 2, wherein the one or more radical species include one or more radicals of at least one of oxygen, nitrogen, or fluorine.

15. The optical system of claim 14, wherein the one or more free radicals are configured to remove one or more elements of the contaminant from at least one of a set of illumination optics, the set of imaging optics, or the detector via one or more photoreactions between the contaminant and at least one of the first cleaning beam or the second cleaning beam, wherein the one or more photoreactions form gaseous reaction products within the one or more chambers.

16. The optical system of claim 15, further comprising one or more pumps configured to evacuate the gaseous reaction products from the one or more chambers.

17. The optical system of claim 2, wherein the selected purge gas comprises a mixture of two or more gases.

18. The optical system of claim 1, wherein each of the first cleaning beam and the second cleaning beam is configured to illuminate the same field plane as the light.

19. The optical system of claim 1, wherein the first illumination source comprises a laser source configured to generate illumination having a wavelength of at least one of approximately 355 nanometers, approximately 266 nanometers, or approximately 193 nanometers.

Images