Systems and methods for coupling light into a projection imaging system for in situ photochemical cleaning

Abstract

A system for cleaning optical surfaces of an overlay inspection system is disclosed. In particular, a system for optical path coupling of light for in situ photochemical cleaning in a projection imaging system is disclosed. The system for cleaning optical surfaces of an overlay 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 the removal of contaminants from one or more optical surfaces of the system.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE 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 technology]

[0002] As the demand for lithography-based device structures with smaller features continues to increase, improved illumination sources continue to be needed for use in lithography and for inspection of the associated reticles that lithographically print these ever-shrinking devices. Particular such illumination sources utilized in lithography and inspection systems are extreme ultraviolet (EUV), vacuum ultraviolet (VUV), deep ultraviolet (DUV), or ultraviolet (UV) light-based inspection systems.

[0003] Inspection systems, particularly their optical components, are often required to operate in a clean vacuum environment. However, contaminants that tend to contaminate a vacuum environment cannot be completely removed from the system. For example, inspection system components, such as certain optical surfaces, inevitably contain contaminants. As a result, the inspection system's optical components (often located within a vacuum chamber) are exposed to partial pressures of contaminants, such as hydrocarbons and gas-phase HO. These contaminants, when exposed to radiation within the system (e.g., as may be the case during the illumination process), can cause carbon and / or oxide growth on the system's optical surfaces, such as mirrors. In the case of mirrors, contamination can cause a decrease in reflectivity, resulting in a phase shift in the light incident on a given mirror. Both of these effects, if left unchecked, can cause degradation of optical components over time, leading to failure of the optical system. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 06-093477 [Patent Document 2] U.S. Patent Application Publication No. 2012 / 0223256 Summary of the Invention [Problem to be solved by the invention]

[0005] It would therefore be desirable to provide a method and system that overcomes the above-identified deficiencies of the prior art. [Means for solving the problem]

[0006] 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 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 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 optics configured to receive at least a portion of the light from one or more sample surfaces and direct at least a portion of the light from the one or more sample surfaces to a 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 optics via at least one of the illumination axis or the imaging axis. In another embodiment, the optical system can 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 can include one or more chambers, where the set of illumination optics, the set of imaging optics, and the detector are disposed within the one or more chambers, each configured to contain a selected purge gas, where the selected purge gas undergoes a photoreaction with at least one of the first cleaning beam or the second cleaning beam, where the photoreaction of the selected purge gas with at least one of the first cleaning beam or the second cleaning beam forms at least one of one or more ionic species or one or more free radical species, where at least one of the one or more ionic species or one or more free radical species can convert 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.

[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 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 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 optics configured to receive at least a portion of the light from one or more sample surfaces and direct at least a portion of the light from the one or more sample surfaces to a 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 optics 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, each of the one or more chambers configured to contain a selected purge gas, the selected purge gas undergoing a photoreaction with the first cleaning beam, the photoreaction of the selected purge gas with the first cleaning beam forming at least one of one or more ionic species or one or more free radical species, and the at least one of the one or more ionic species or one or more free radical species 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, a method for cleaning optical surfaces is disclosed. In one embodiment, the method includes providing a selected purge gas to one or more chambers. In another embodiment, the method includes directing one or more cleaning beams at one or more optical surfaces in the one or more chambers, wherein each of the one or more cleaning beams undergoes a photoreaction with a selected purge gas, the photoreaction of the selected purge gas with the one or more cleaning beams forming at least one of one or more ionic species or one or more free radical species, which convert contaminants from the 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.

[0009] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the invention as claimed. The accompanying drawings, which are incorporated into 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 explanation of the drawings]

[0010] Many advantages of the present disclosure may be better understood by those skilled in the art by reference to the following drawings. [Figure 1A] 1 shows a conceptual diagram of an optical system in accordance with one or more embodiments of the present disclosure. [Figure 1B] 1 shows a conceptual diagram of an optical system in accordance with one or more embodiments of the present disclosure. [Figure 1C] FIG. 1 shows a block diagram of an optical system in accordance with one or more embodiments of the present disclosure. [Figure 2] 1 illustrates a method for cleaning an optical surface according to one or more embodiments of the present disclosure. [Figure 3] 1 shows a flowchart illustrating steps in a method for cleaning optical surfaces in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present disclosure has been particularly shown and described with respect to certain embodiments and certain features thereof. The embodiments described herein are to be considered illustrative and not limiting. It will be readily apparent to those skilled in the art that various changes and modifications in form and detail may be made without departing from the spirit and scope of the present disclosure. Reference will now be made in detail to the subject matter disclosed, which is illustrated in the accompanying drawings.

[0012] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate to systems and methods for cleaning optical surfaces in overlay inspection systems. In particular, systems and methods are disclosed for optical path coupling of light for in situ photochemical cleaning in projection imaging systems.

[0013] It is recognized herein that contamination of optical surfaces in an inspection system can occur when volatile organic contaminant species adsorb to the optical surfaces, which can interact with energetic radiation (e.g., EUV or VUV light) to produce carbonaceous deposits in areas exposed to the energetic radiation. The presence of even trace amounts of deposits (e.g., deposits only a few nanometers in height) can cause significant degradation in the performance of the inspection system's optical elements.

[0014] Contaminants accumulated on optical surfaces of an inspection system can be removed by one or more photochemical reactions. For example, accumulated carbonaceous deposits can be removed through one or more reactions with ionic or free radical species (e.g., oxygen (1D) and other excited states of oxygen, as well as excited states of nitrogen, fluorine, etc.). Ionic or free radical species can be generated when a precursor gas (e.g., ozone) reacts with photons of sufficient energy (e.g., EUV, VUV, DUV, or UV photons). Thus, illumination of an optical surface with sufficient energy illumination in the presence of a precursor gas can cause removal of contaminants accumulated on the optical surface.

[0015] 1A-1C generally illustrate an embodiment of an optical system 100, in accordance with one or more embodiments of the present disclosure. Figure 1A illustrates a conceptual diagram of the optical system 100, in accordance with one or more embodiments of the present disclosure.

[0016] 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 light source). The first illumination source 102 may include a laser source configured to generate illumination having at least one of a wavelength of about 355 nanometers, about 266 nanometers, or about 193 nanometers.

[0017] In one embodiment, the illumination optics 106 may be configured to direct illumination 110 emitted from the first illumination source 102 along an illumination axis 112 (e.g., an illumination path) to one or more samples 120 disposed on a stage 118. The one or more samples 120 may include, but are not limited to, a wafer (e.g., a semiconductor wafer) or a reticle.

[0018] In another embodiment, system 100 may include a set of imagers 108 configured to receive illumination from the surfaces of one or more samples 120 and direct illumination from one or more samples 120 to detector 104 via an imaging axis 114 (e.g., an illumination collection path). For example, imaging optics 108 may include one or more projection optics suitable for collecting light scattered, reflected, diffracted, or otherwise emitted from sample 120 and directing the light to one or more detectors 104 (e.g., CCD, TDI-CCD, PMT, etc.). In another embodiment, system 100 may include a controller (as shown in FIG. 1C ) that receives and / or analyzes signals indicative of illumination collected from sample 120 via imaging optics 108 and detector 104.

[0019] It should be noted that, as shown in Figure 1A, embodiments of the present disclosure may be configured to perform one or more inspection processes and one or more cleaning processes. For example, as shown in Figure 1A, optical system 100 may be configured to perform one or more inspection processes on sample 120. As another example, as shown in Figure 1B, optical system 100 may be configured to perform one or more cleaning processes on one or more optical surfaces of optical system 100.

[0020] FIG. 1B illustrates one embodiment of an optical system 100 configured to perform one or more cleaning processes.

[0021] 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.

[0022] 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 optical elements. The second illumination source 122 (and, in some embodiments, the one or more first cleaning optical elements) can be configured to direct the first cleaning beam 124 to a point in space corresponding to the mask surface 116. For example, as shown in FIG. 1B , when configured for cleaning, the optical system 100 may not include a sample 120. However, the second illumination source 122 (and, if applicable, the one or more first cleaning optical elements) can be configured to direct the first cleaning beam 124 to a point in the system 100 to which the illumination optics 106 can be configured to direct the light 110. In this sense, the first cleaning beam 124 may be configured to propagate along the illumination axis 112 in the same manner as the light 110 propagates along (but in the opposite direction from) the illumination axis 112. Note that the first cleaning beam 124 may be configured to propagate along the illumination axis 112 in its entirety (e.g., until the first cleaning beam 124 reaches the first illumination source 102).

[0023] The second illumination source 122 may be configured to generate the first cleaning beam 124, where the first cleaning beam 124 provides uniform illumination. In another embodiment, the second illumination source 122 may be configured to generate the first cleaning beam 124 such that the first cleaning beam 124 includes one or more scanning rasters. The first cleaning beam 124 may be configured to illuminate the same field plane as the light 110 (e.g., as a result of the second illumination source 122 having a numerical aperture similar to that of the first illumination source 102).

[0024] 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 regard, second cleaning beam 128 may include, but is not limited to, an EUV, VUV, DUV, and / or UV beam.

[0025] The third illumination source 126 may be configured to direct the second cleaning beam 128 to the imaging optics 108. For example, although not shown, the third illumination source 126 may 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 optics. The third illumination source 126 (and, in some embodiments, the one or more second cleaning optics) may be configured to direct the second cleaning beam 128 to a point in space corresponding to the mask surface 116. For example, as shown in FIG. 1B , when configured for cleaning, the optical system 100 may not include a sample 120. However, the third illumination source 126 (and, if applicable, the one or more second cleaning optics) may be configured to direct the second cleaning beam 128 to a point in the system 100 from which the illumination optics 106 may be configured to receive light 110 from the sample 120. In this sense, the second cleaning beam 124 may be configured to propagate along the imaging axis 114 in the same manner as the light 110 propagates along the imaging axis 114. Note that the second cleaning beam 128 may be configured to propagate along the imaging axis 114 in its entirety (e.g., until the second cleaning beam 128 reaches the detector 104).

[0026] The third illumination source 126 may be configured to generate a second cleaning beam 128, where the second cleaning beam 128 provides uniform illumination. In another embodiment, the third illumination source 126 may be configured to generate the second cleaning beam 128 such that the second cleaning beam 128 comprises one or more scanning rasters. The second cleaning beam 128 may be configured to illuminate the same field plane as the light 110 (e.g., as a result of the third illumination source 126 having a numerical aperture similar to that of the first illumination source 102).

[0027] It should be noted that each of the second illumination source 122 and the third illumination source 126 may be configured to direct illumination (e.g., the first cleaning beam 124 and / or the second cleaning beam 128, as the case may be) onto the mask surface 116 through a common aperture (e.g., a viewport) of the system 100.

[0028] It is specifically contemplated that embodiments of the present disclosure may be configured to provide cleaning light (e.g., first cleaning beam 124 and / or second cleaning beam 128) in a manner that limits the cleaning light to only regions of the optical surface that are contaminated. For example, embodiments of the present disclosure may be configured such that first cleaning beam 124 is configured to propagate along illumination axis 112 in the same manner as light 110. In this regard, first cleaning beam 124 is, of course, configured to interact with contaminants only on regions that may be contaminated (e.g., via deposition catalyzed by light 110 in an inspection operation). Similarly, second cleaning beam 128 is configured to propagate along imaging axis 114 in a similar manner as light 110. In this regard, second cleaning beam 128 is, of course, configured to interact with contaminants only on regions that may be contaminated (e.g., via deposition catalyzed by light 110 in an inspection operation). This approach reduces and / or eliminates the need for additional steering optics, apertures, or beam dumps in optical system 100. Furthermore, the need for shielding (e.g., to protect surrounding components from the cleaning light) is reduced. In this sense, the illumination of the optical surfaces by the cleaning light is also distributed in a manner comparable to the distribution of light 110, thereby minimizing the risk of over- or under-cleaning the optical surfaces in conditions where the contamination rate of carbonaceous compounds is proportional to the irradiance of light 110.

[0029] Embodiments of the present disclosure are further configured to reduce the amount of cleaning light required to clean all optical surfaces of system 100. For example, because the cleaning light propagates entirely along each of illumination axis 112 and imaging axis 114, the cleaning light is reflected within and along each axis, allowing the cleaning light to be used to clean multiple optical surfaces (rather than being used to clean a single surface and allowed to dissipate outside of optical system 100).

[0030] 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 within one or more chambers 118. For example, 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, the imaging optics 108, the sample 120, and / or the stage 118 may be disposed within 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 within a common chamber, while other elements of the system may be disposed within separate chambers 118. As another example, in some embodiments, certain elements of the present disclosure may not be disposed within a chamber 118.

[0031] One or more chambers can be configured to contain a selected purge gas 202 (as shown in FIG. 2 ). The selected purge gas (or at least a component of the purge gas) can undergo ionization or radicalization in the presence of at least one of the first cleaning beam 128 or the second cleaning beam 124.

[0032] The selected purge gas 202 may include any purge gas known in the art to be 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 containing 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, etc.). In another embodiment, the purge gas may include a mixture of any one or more gases.

[0033] It should be noted that the selected purge gas may be configured to cause or assist in photodissociation of contaminants on the optical surfaces of system 100. For example, the selected purge gas may be configured to form one or more ionic or free radical species in a photoreaction with at least one of first cleaning beam 124 or second cleaning beam 128, where the one or more radical species are configured to convert contaminants on the one or more optical surfaces into volatile (e.g., gaseous) reaction products that can be exhausted from system 100.

[0034] 1C shows a block diagram of 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 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 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 to acquire inspection and / or measurement data from one or more components of the system 100 (e.g., the detector 104) and / or control 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, etc.).

[0035] FIG. 2 illustrates a method for cleaning an optical surface according to one or more embodiments of the present disclosure.

[0036] As previously mentioned, contaminant deposits on optical surfaces can be removed by one or more photochemical reactions. For example, accumulated carbonaceous deposits can be removed through one or more reactions with ionic or free radical species (e.g., oxygen (1D) and other excited states of oxygen, as well as excited states of nitrogen, fluorine, etc.). Ionic or free radical species can be generated when a precursor gas (e.g., ozone) reacts with photons of sufficient energy (e.g., EUV, VUV, DUV, or UV photons). Thus, irradiation of an optical surface with sufficient energy illumination in the presence of a precursor gas can cause removal of contaminants accumulated on the optical surface.

[0037] The second illumination source 122 may 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. For purposes of Figure 2, it should be noted that embodiments of the present disclosure are not limited to the conceptual diagram contained therein. For example, it is contemplated that the embodiment of the present disclosure shown in Figure 2 may include the illumination and propagation of the first cleaning beam 124 (e.g., propagation to the mask surface 116 via cleaning optics, propagation along the illumination axis, etc.) shown in and described with reference to Figure 1B.

[0038] 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 undergoes one or more photochemical reactions 208 in which the first cleaning beam 124 causes excitation of one or more components of the selected purge gas 202, resulting in the generation of one or more ionic species or free radicals 209.

[0039] One or more ionic species or free radicals 209, generated by a photochemical reaction between the first cleaning beam 124 and one or more components of the selected purge gas 202, may be capable of transforming, via one or more chemical reactions, one or more contaminants 204 present on the optical surfaces 210 of the system 100. For example, one or more components of the selected purge gas 202 may react with one or more contaminants to form volatile reaction products 206, which are present in a gaseous state in the one or more chambers 118.

[0040] 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, without limitation, 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.

[0041] The reaction products 206 may be evacuated from one or more chambers 118. For example, upon completion of a cleaning process, the system 100 may cause one or more pumps 136 to remove the reaction products 206 from one or more chambers 118.

[0042] The one or more pumps 136 may include any pump known in the art suitable for removing gaseous reaction product(s) formed from the interaction of the ionic and / or radical 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.

[0043] In another embodiment, the one or more pumps 136 may include a pumping 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 in conjunction with a dry pumping unit and with an exhaust system (not shown).

[0044] 2, 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 processes 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.

[0045] FIG. 3 shows a flowchart illustrating steps in a method for cleaning optical surfaces in accordance with one or more embodiments of the present disclosure.

[0046] In step 302, a selected purge gas is supplied to one or more chambers. For example, the selected purge gas 202 may be supplied to one or more chambers 118. The selected purge gas 202 may include any purge gas known in the art that is 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 containing 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, etc.). In another embodiment, the purge gas may include a mixture of any one or more gases.

[0047] In step 304, one or more cleaning beams are directed to one or more optical surfaces in one or more chambers, where the one or more cleaning beams optically interact with a 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 the case may be, 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.

[0048] By directing one or more cleaning beams at one or more optical surfaces of the system 100, the selected purge gas 202 may undergo one or more photochemical reactions 208, whereby the first cleaning beam 124 and / or the second cleaning beam 128 may cause excitation of one or more components of the selected purge gas 202, resulting in the generation of one or more ionic species or free radicals 209. The one or more ionic species or free radicals 209, generated by the photochemical reaction between the first cleaning beam 124 and one or more components of the selected purge gas 202, may transform one or more contaminants 204 present on the optical surfaces 210 of the system 100. For example, one or more components of the selected purge gas 202 may react with one or more contaminants to form volatile reaction products 206, which are present in a gaseous state in the one or more chambers 118.

[0049] In step 306, gaseous reaction products are evacuated from one or more chambers. For example, reaction products 206 may be evacuated from one or more chambers 118. For example, upon completion of the cleaning process, system 100 may cause one or more pumps 136 to remove reaction products 206 from one or more chambers 118 (e.g., via controller 130).

[0050] 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 other optical systems known in the art, such as characterization systems, metrology systems, and / or lithography systems.

[0051] For example, in one embodiment, optical system 100 is configured as a wafer inspection system or a reticle inspection system. In this regard, optical system 100 may include any wafer or reticle inspection optical architecture known in the art that is suitable for operation in the EUV and / or VUV spectral range. It is further recognized that optical system 100 may be configured as an EUV mask blank inspection system. EUV-based mask blank inspection is generally described in U.S. Patent No. 8,711,346 to Stokowski, issued April 29, 2014, which is incorporated herein by reference in its entirety. EUV-based mask blank inspection is generally described in U.S. Patent Application No. 13 / 417,982 to Xiong et al., filed March 12, 2012, which is incorporated herein by reference in its entirety. EUV-based reticle inspection is generally described in U.S. Patent Application No. 13 / 905,449 to Nasser-Ghodsi et al., filed May 30, 2013, which is incorporated herein by reference in its entirety.

[0052] As another example, in another embodiment, not shown, 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 illumination optics configured to direct output light from light source 100 onto an EUV-compatible lithography mask (e.g., an EUV reflective mask). In another embodiment, the lithography system may include a set of projection optics configured to receive illumination reflected from the mask and direct the reflected illumination from the mask onto one or more wafers positioned 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 March 13, 2012, which is incorporated herein by reference in its entirety.

[0053] It is contemplated herein that various embodiments of the present invention may be practiced in conjunction with or independently of one another, and for example, the embodiments shown in Figures 1A to 2 should be construed as being applicable in combination with one another.

[0054] The one or more processors 132 of the controller 130 may include any processor or processing element known in the art. For 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-attached computer, or any other computer system configured to execute programs configured to operate or operate in conjunction with the metering system 100, as described throughout this disclosure.

[0055] Furthermore, different subsystems of system 100, such as 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 this disclosure. Accordingly, the above description should not be construed as limiting the embodiments of the present disclosure, but merely as exemplary. Furthermore, the steps described throughout this disclosure may be performed by a single controller 130 or may be performed by multiple controllers. Additionally, controller 130 may include one or more controllers housed within a common housing or within multiple housings. In this manner, any controller or combination of controllers may be individually packaged as a module suitable for integration into metrology system 100. Furthermore, controller 130 may analyze data received from detector 104 and provide the data to additional components within system 100 or external to system 100.

[0056] The memory 134 may include any storage medium known in the art suitable for storing program instructions executable by the associated one or more processors 132. For example, the memory 134 may include a non-transitory memory medium. As another example, the memory 134 may include, but is not limited to, read-only memory (ROM), random access memory (RAM), magnetic or optical memory devices (e.g., disks), magnetic tape, solid-state drives, etc. It is further noted that the memory 134 may be housed along with one or more processors 132 within a common controller housing. In one embodiment, the memory 134 may be located remotely relative to the physical location of the one or more processors 132 and the controller 130. For example, one or more processors 132 of the controller 130 may access a remote memory (e.g., a server) accessible via a network (e.g., the Internet, an intranet, etc.).

[0057] In one embodiment, although not shown, a user interface 135 may be communicatively coupled to the controller 130. In one embodiment, the user interface 135 may include, but is not limited to, one or more desktops, laptops, tablets, etc. In another embodiment, the user interface 135 includes a display used to display data from the system 100 to a 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 that can be integrated with the user interface 135 is suitable for implementing the present disclosure. In another embodiment, a user may input selections and / or commands in response to data displayed to the user via a user input device of the user interface 135.

[0058] In another embodiment, controller 130 is communicatively coupled to one or more elements of system 100. In this regard, controller 130 may transmit and / or receive data from any component of system 100. Additionally, controller 130 may direct or control any component of system 100 by generating one or more control signals to the associated component. For example, controller 130 may be communicatively coupled to detector 104 to receive one or more images from detector 104.

[0059] All methods described herein may include storing results of one or more steps of a method embodiment in memory 134. The 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 the results are stored, they may be accessed in memory, used by any of the method or system embodiments described herein, formatted for display to a user, used by another software module, method, or system, etc. Furthermore, the results may be stored "permanently," "semi-permanently," "temporarily," or for a period of time. For example, the memory may be random access memory (RAM), and the results do not necessarily need to persist in memory indefinitely.

[0060] It is further contemplated that each of the method embodiments described above may include any other step(s) of any other method(s) described herein. In addition, each of the method embodiments described above may be performed by any of the systems described herein.

[0061] Those skilled in the art will recognize that the components, operations, devices, objects, and accompanying descriptions described herein are used as examples for conceptual clarity, and that various configuration modifications are contemplated. Thus, as used herein, the specific examples described and the accompanying discussion are intended to represent their more general classification. In general, the use of a specific example is intended to represent that classification and should not be considered a limitation that does not include the specific components, operations, devices, and objects.

[0062] As used herein, directional terms such as "top," "bottom," "over," "under," "upper," "upward," "lower," "down," and "downward" are intended to provide relative positions for purposes of description and are not intended to specify an absolute frame of reference. 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.

[0063] With respect to the use of plural and / or singular terms herein, those of skill in the art may translate from the plural to the singular and / or from the singular to the plural as appropriate to the context and / or application. The various singular / plural permutations are not expressly set forth herein for the sake of clarity.

[0064] The subject matter described herein may depict different components contained within or connected to other components. It should be understood that such depicted architectures are merely exemplary, and that in fact many other architectures that achieve the same functionality may be implemented. In a conceptual sense, any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Thus, any two components herein that combine to achieve a particular function may be considered to be “associated” with each other, such that the desired functionality is achieved without regard to the architecture or intermediate components. Similarly, any two components so associated may also be considered to be “connected” or “coupled” with each other to achieve the desired functionality, and any two components that may be so associated may be considered to be “couplable” with each other to achieve the desired functionality. Specific examples of what may be coupled include, but are not limited to, physically matable and / or physically interacting components, wirelessly interacting and / or wirelessly interacting components, and / or logically interacting and / or logically interacting components.

[0065] It should further be understood that the invention disclosed and described herein 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 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," etc.). Where a specific number of introduced claim recitations is intended, such intention will be explicitly set forth in the claims; it will further be understood by those skilled in the art that, absent such a recitation, no such intention exists. For example, to aid in understanding, the following appended claims may include the use of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to mean that the introduction of a claim recitation with the indefinite article "a" or "an" limits the scope of any particular claim containing the claim recitation so introduced to inventions containing only one such recitation, even if the same claim includes the introductory phrase "one or more" or "at least one" and the indefinite article "a" or "an" (e.g., "a" and / or "an" should generally be interpreted to mean "at least one" or "one or more"). The same applies to the use of definite articles used to introduce claim recitations. In addition, even when a specific number of introduced claim recitations is explicitly recited, those skilled in the art will recognize that such a recitation should generally be interpreted to mean at least the recited number (e.g., a recitation of "two recitations" alone, without any other modifier, generally means at least two recitations, or more than two recitations).Furthermore, in instances where phrases similar to "at least one of A, B, and C, etc." are used, such configurations are generally intended to mean what one of ordinary skill in the art would understand the phrase (e.g., "a system having at least one of A, B, and C" includes, but is not limited to, systems having A only, B only, C only, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). In instances where phrases similar to "at least one of A, B, or C, etc." are used, such configurations are generally intended to mean what one of ordinary skill in the art would understand the phrase (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, systems having A only, B only, C only, A and B together, A and C together, B and C together, and / or A, B, and C together, etc.). It will further be understood by those skilled in the art that virtually any disjunctive word and / or phrase expressing two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibility of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

[0066] The present disclosure and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes in form, construction, and arrangement of elements may be made without departing from the disclosed subject matter or sacrificing all of its important advantages. The forms described are illustrative only, and it is the intent of the following claims to embrace and include all such modifications. It is to be understood, further, that the invention is defined by the appended claims.

Claims

1. 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, each of the second illumination source and the third illumination source having a numerical aperture equal to a numerical aperture 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, each of the one or more chambers configured to contain a selected purge gas, wherein the selected purge gas undergoes a photoreaction with at least one of the first cleaning beam or the second cleaning beam, wherein the photoreaction of the selected purge gas with at least one of the first cleaning beam or the second cleaning beam forms at least one of one or more ionic species or one or more free radical species, wherein the at least one of the one or more ionic species or one or more free radical species can convert 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; An optical system comprising:

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 the first illumination source comprises a broadband illumination source.

4. The optical system of claim 3 , 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.

5. The optical system of claim 2 , wherein the first illumination source comprises a narrowband illumination source.

6. 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.

7. The optical system of claim 6 , wherein each of the first cleaning beam and the second cleaning beam comprises at least one of uniform illumination or one or more scanning rasters.

8. The optical system of claim 1 , wherein each of the second illumination source and the third illumination source is configured to generate at least ultraviolet light.

9. The optical system of claim 1 , wherein the first cleaning beam comprises ultraviolet light having a wavelength between about 210 nanometers and about 300 nanometers.

10. The optical system of claim 1 , wherein the second cleaning beam comprises ultraviolet light having a wavelength between about 210 nanometers and about 300 nanometers.

11. The optical system of claim 1 , wherein the selected purge gas comprises at least one of ozone, fluorine, or nitrogen.

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

13. 13. The optical system of claim 12, 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 in the one or more chambers.

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

15. The optical system of claim 11 , wherein the one or more free radical species comprises one or more free radicals of at least one of oxygen, nitrogen, or fluorine.

16. 16. The optical system of claim 15, 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.

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

18. The optical system of claim 1 , wherein the selected purge gas comprises a mixture of two or more gases.

19. 10. 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 about 355 nanometers, about 266 nanometers, or about 193 nanometers.

20. 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, each of the second illumination source and the third illumination source having a numerical aperture equal to a numerical aperture 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, each of the one or more chambers configured to contain a selected purge gas, the selected purge gas undergoing an optical reaction with the first cleaning beam, the optical reaction of the selected purge gas with the first cleaning beam forming at least one of one or more ionic species or one or more free radical species, the at least one of the one or more ionic species or one or more free radical species 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; An optical system comprising:

21. The optical system of claim 20 , wherein the optical system is configured as a mask inspection system.

22. 22. The optical system of claim 21, wherein each of the first cleaning beam and the second cleaning beam comprises at least one of uniform illumination or one or more scanning rasters.

23. 22. The optical system of claim 21, wherein the first illumination source comprises a broadband illumination source.

24. 24. The optical system of claim 23, 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.

25. 22. The optical system of claim 21, wherein the first illumination source comprises a narrowband illumination source.

26. 22. The optical system of claim 21, wherein each of the second illumination source and the third illumination source is configured to generate at least ultraviolet light.

27. 22. The optical system of claim 21, wherein the first cleaning beam comprises ultraviolet light having a wavelength between about 210 nanometers and about 300 nanometers.

28. 22. The optical system of claim 21, wherein the second cleaning beam comprises ultraviolet light having a wavelength between about 210 nanometers and about 300 nanometers.

29. 22. The optical system of claim 21, wherein the selected purge gas comprises at least one of ozone, fluorine, or nitrogen.

30. 22. The optical system of claim 21, wherein the one or more ion species include one or more ions of at least one of oxygen, nitrogen, or fluorine.

31. 31. The optical system of claim 30, 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 in the one or more chambers.

32. 32. The optical system of claim 31 , further comprising one or more pumps configured to evacuate the gaseous reaction products from the one or more chambers.

33. 22. The optical system of claim 21, wherein the one or more free radical species comprises one or more free radicals of at least one of oxygen, nitrogen, or fluorine.

34. 34. The optical system of claim 33, 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 in the one or more chambers.

35. 35. The optical system of claim 34, further comprising one or more pumps configured to evacuate the gaseous reaction products from the one or more chambers.

36. 22. The optical system of claim 21, wherein the selected purge gas comprises a mixture of two or more gases.

37. 21. The optical system of claim 20, wherein each of the first cleaning beam and the second cleaning beam is configured to illuminate the same field plane as the light.

38. 21. The optical system of claim 20, wherein the first illumination source comprises 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.

39. 1. A method for cleaning an optical surface, comprising: Generates light, directing at least a portion of the light through a set of illumination optics onto one or more sample surfaces; directing a portion of the light from the one or more sample surfaces through a set of imaging optics to a detector; providing a selected purge gas to one or more chambers; generating a first cleaning beam and directing at least a portion of the first cleaning beam toward the set of illumination optics and generating a second cleaning beam and directing at least a portion of the second cleaning beam toward the set of imaging optics, wherein the first cleaning beam or the second cleaning beam undergoes a photoreaction with the selected purge gas, the photoreaction of the selected purge gas with the first cleaning beam or the second cleaning beam forms at least one of one or more ionic species or one or more free radical species, the at least one of the one or more ionic species or one or more free radical species 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 to form gaseous reaction products, the first cleaning beam and the second cleaning beam having a numerical aperture equivalent to a numerical aperture of the light; evacuating the gaseous reaction products from the one or more chambers; A method comprising:

40. 40. The method of claim 39, wherein generating one or more laser beams comprises generating one or more laser beams having a wavelength of at least one of about 355 nanometers, about 266 nanometers, or about 193 nanometers.

Images