Patent Publication Number: US-2013235357-A1

Title: System and Method for Particle Control Near A Reticle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is related to and claims the benefit of the earliest available effective filing date(s) from the following listed application(s) (the “Related applications”) (e.g., claims earliest available priority dates for other than provisional patent applications or claims benefits under 35 USC §119(e) for provisional patent applications, for any and all parent, grandparent, great-grandparent, etc. applications of the Related application(s)). 
     RELATED APPLICATIONS 
     For purposes of the USPTO extra-statutory requirements, the present application constitutes a regular (non-provisional) patent application of United States Provisional Patent Application entitled PARTICLE CONTROL NEAR RETICLE USING UV LIGHT CURTAIN, naming Gildardo Delgado and Frank Chilese as inventors, filed Mar. 12, 2012, Application Ser. No. 61/609,640. 
    
    
     TECHNICAL FIELD 
     The present invention generally relates to the control of particles in the vicinity of a reticle mounted on a reticle stage of a lithography tool, including a reticle inspection tool or a wafer processing tool. 
     BACKGROUND 
     The continued shrinking of design geometries in integrated circuit devices generates a continual need for improved optical inspection tools. For example, light sources for photolithography systems have historically evolved to smaller and smaller wavelengths, thereby allowing the construction of smaller and smaller structures. For instance, the use of visible wavelength light (e.g., 400 nm) gave way to near ultraviolet light (e.g., 300 nm), which then gave way to deep ultraviolet (DUV) light (e.g., 200 nm). Then, more recently, DUV light based sources have given way to extreme ultraviolet (EUV) sources (e.g., 13.5 nm). 
     Generally, particles scatter less energy than larger defects and, therefore, tend to be more difficult to detect using longer wavelength radiation. As such, light sources and systems capable of utilizing smaller wavelengths and increased illumination energy are more effective at locating particles. This allows particles to be detected or identified by class, based on shape, location, device effect and the like, in an automated fashion. This also allows for detected troublesome defects to be distinguished from “nuisance defects.” 
     One disadvantage of inspection tools operating in the EUV regime is that a particle protection device, such as a pellicle, which is commonly used in tools at longer wavelengths, cannot be used in EUV settings because the protection device is opaque at EUV wavelengths. Further, the critical dimensions of the reticles intended to be inspected on a EUV tool may be so small that nearly any particle present on the reticle surface will cause unacceptable problems. Several particle protection mechanisms have been proposed, studied or used to protect the reticle from particles. By way of example, the contaminant particles may commonly emanate from nearby optics used to direct inspection light to the reticle, which is generally directed to the reticle via a central hole in a nearby plate. In addition, the reticle stage used to move the reticle during inspection may also be a source of contaminant particles, which may come into contact with the reticle around the circumference of the reticle, rather than near the center of the reticle. 
     Presently, particle control in light-based reticle inspection system is carried out with flowing air, which pushes the particles in a known direction. In vacuum systems, such as in e-beam inspect systems, particle control is done with slight amounts of positive pressure and particle reduction methods designed to reduce the number of particles in general. The prior methods have several advantages. For example, they have not shown capable of eliminating particles down to 10 nm in diameter. In addition, prior art methods have only been used in processes that allow reticle cleaning after inspection. However, the EUV reticle inspection tool must contend with smaller particles since no cleaning is allowed after inspection. Therefore, it would be desirable to provide a system and method that cures the defects of the prior art, providing for improved contaminant particle control and capture for reticle inspection tools and lithography tools operating in the EUV regime. 
     SUMMARY 
     An apparatus for particle control near a reticle of a lithography tool is disclosed. In a first aspect, the apparatus may include, but is not limited to, a curtain generation unit configured to generate a curtain of ultraviolet light about a reticle protection area surrounding a reticle by directing ultraviolet light to a selected region about the reticle protection area, the ultraviolet light having sufficient energy to induce a charge on one or more particles traversing the curtain of ultraviolet light; and an electric field generation unit configured to generate an electric field spanning a region positioned between the curtain of ultraviolet light and the reticle protection area. 
     In another aspect, the apparatus may include, but is not limited to, a curtain generation unit configured to generate a curtain of ultraviolet light about a reticle protection area surrounding a reticle by directing ultraviolet light to a selected region about the reticle protection area, the ultraviolet light having sufficient energy to induce a charge on one or more particles traversing the curtain of ultraviolet light; a thermophoretic plate arranged near a surface of the reticle and suitable for directing one or more particles away from the reticle protection area about the reticle via the thermophoretic effect; and an electric field generation unit configured to generate an electric field spanning a region positioned between the curtain of ultraviolet light and the reticle protection area, wherein the electric field generation unit is configured to charge the thermophoretic plate and charge a second charging element, wherein the thermophoretic plate and the second charging element have opposite polarity. 
     In another aspect, the apparatus may include, but is not limited to, a curtain generation unit configured to generate a curtain of ultraviolet light about a critical region of an extreme ultraviolet light optical tool by directing ultraviolet light to a selected region about the critical region, the ultraviolet light having sufficient energy to induce a charge on one or more particles traversing the curtain of ultraviolet light; and an electric field generation unit configured to generate an electric field spanning a region positioned between the curtain of ultraviolet light and the critical region. 
     A method for particle control near a reticle of a lithography tool is disclosed. In a first aspect, the method may include, but is not limited to, generating a curtain of ultraviolet light about a reticle protection area of a reticle by illuminating a region surrounding the reticle protection area with ultraviolet light having sufficient energy to induce a charge on one or more particles traversing the curtain of ultraviolet light; generating an electric field in a region positioned between the generated curtain of ultraviolet light and the reticle protection area, the electric field generated between a first charging element and a second charging element having an opposite charge to the first charging element; directing one or more charged particles to the first charging element or the second charging element using the generated electric field; and capturing the one or more charged particles on the first charging element or the second charging element. 
     In another aspect, the method may include, but is not limited to, generating a curtain of ultraviolet light about a critical region of an extreme ultraviolet optical tool by illuminating a region surrounding the critical region with ultraviolet light having sufficient energy to induce a charge on one or more particles traversing the curtain of ultraviolet light; generating an electric field in a region positioned between the generated curtain of ultraviolet light and the critical region, the electric field generated between a first charging element and a second charging element having an opposite charge to the first charging element; directing one or more charged particles to the first charging element or the second charging element using the generated electric field; and capturing the one or more charged particles on the first charging element or the second charging element. 
     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 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 
       The numerous advantages of the disclosure may be better understood by those skilled in the art by reference to the accompanying figures in which: 
         FIG. 1A  is a schematic view of system for controlling particles near a reticle, in accordance with one embodiment of the present invention. 
         FIG. 1B  is a schematic view of a voltage source of an electric field generation unit of the system for controlling particles near a reticle, in accordance with one embodiment of the present invention. 
         FIG. 1C  is a schematic view of an annular metal plate of an electric field generation unit of the system for controlling particles near a reticle, in accordance with one embodiment of the present invention. 
         FIG. 2A  is a schematic view of system for controlling particles near a reticle, in accordance with one embodiment of the present invention. 
         FIG. 2B  is a schematic view of system for controlling particles near a reticle, in accordance with one embodiment of the present invention. 
         FIG. 3  is a process flow diagram depicting a method for controlling particles near a reticle, in accordance with one embodiment of the present invention 
         FIG. 4  is a process flow diagram depicting a method for controlling particles near a critical region of an extreme ultraviolet optical tool, in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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 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. Reference will now be made in detail to the subject matter disclosed, which is illustrated in the accompanying drawings. 
     Referring generally to  FIGS. 1A through 2B , a system  100  for particle control near a reticle is described in accordance with the present disclosure. The present invention is directed to a method and system for controlling particles (e.g., contaminant particles) near a reticle of a lithography system, such as an EUV lithography system. Embodiments of the present invention are suitable for generating a curtain of ultraviolet (UV) light about the moving portion of a reticle stage of a lithography system. The curtain (e.g., annular curtain) of ultraviolet light acts to illuminate particles traveling toward the reticle protection area of the reticle with UV light. The illumination of particles with UV light acts to induce a positive charge on the particles by stripping one or more free electrons from the particles. In turn, the present invention is further suitable for directing and/or capturing the particles charged by UV light exposure from the UV curtain using an electric field generated between a pair of oppositely charged plates. The charged plates and voltage control are configured to establish an electric field “zone” (e.g., annular zone) that extends across a region positioned between the UV light curtain and the reticle protection area of the reticle. The large generated electric field (e.g., 1-100 Volts/mm) provides a large force on the charged particles, which in turn acts to direct the charged particles along the electric field to one of the charged plates, thereby stopping the captured charged particles from reaching the reticle of the lithography system. In this regard, the light curtain and electric field zone of the present invention serve as a charged particle trap, thereby isolating the reticle protection area about the reticle from particles originating external to the reticle protection area. 
       FIGS. 1A and 1B  illustrate a high level schematic view of a system  100  for particle control near a reticle, in accordance with the present invention. In one aspect of the present invention, the system  100  includes a light curtain generation unit  114  configured to generate a curtain of ultraviolet (UV) light  102  about a reticle protection area  106  surrounding a reticle  104  (e.g., reticle of lithography system) by directing ultraviolet light  102  to a selected region  105  about the reticle protection area  106 . In one embodiment, the reticle  104  of the system  100  includes a reticle of a lithography system. For example, the reticle  104  of the system  100  may include a reticle of a EUV lithography system. 
     In another aspect of the present invention, the UV light utilized to form the curtain of UV light  102  has sufficient energy to induce a charge on one or more particles (e.g., contaminant particles) traversing the curtain of UV light  102 . 
     In another aspect of the present invention, the system  100  includes an electric field generation unit  107  configured to generate an electric field  103  in a zone  105  between the curtain of UV light  102  and the reticle protection area  106  surrounding the reticle  104 . In this regard, the electric field  103  extending across zone  105  may be used to direct and capture particles charged by the UV light curtain  102 , thereby aiding in reducing the number of particles entering the reticle protection area  106  surrounding the reticle  104 . In the case of particles positively charged by the UV light curtain, the particles will be directed toward the negatively charged element (e.g., charged plate). In cases where the initial state of the particles includes a sufficient negative charge level to disallow the positive charging via the UV light curtain, the electric field may still act to direct and capture the charged particles to the positively charged element (e.g., charged plate). In one embodiment, the electric field generation unit  107  may generate an annular electric field zone  105  about a reticle protection area surrounding reticle  104 , but within the UV light curtain  102 . 
     A simplified EUVL lithography system near the reticle  104  is shown in  FIG. 1A , in accordance with an embodiment of the present invention. The EUVL system includes a vacuum chamber having a first region  122  and a second region  124  separated by barrier  112 . In one embodiment, the first region  122  generally houses the reticle stage  101  that supports the reticle chuck  126  suitable for securing the reticle  104 . In a further embodiment, the second region  124  generally contains the projection optics (not shown in  FIG. 1A ). In addition, in some instances, the second region  124  may contain a wafer stage (not shown in  FIG. 1A ). For example, in cases where the system  100  is adapted to control particles in a printing lithographic tool, the second region  124  may include a wafer stage. The barrier  112  that acts to generally separate the first region  122  and the second region  124  includes an aperture  113 , suitable for allowing EUV light to and from the reticle. 
     In one embodiment, the light curtain generation unit  114  includes one or more ultraviolet light sources  116 . In another embodiment, the light curtain generation unit  114  includes one or more optical elements  118  configured to form a curtain of ultraviolet light  102  by directing light from the one or more ultraviolet light sources  116  into a region, or “zone,” about the reticle protection area  106  surrounding the reticle  104 , as shown in  FIG. 1A . 
     In one embodiment, the UV light utilized to form the curtain of UV light  102  has an energy above the work function of at least some of the particles traversing through and illuminated by the curtain of UV light. In another embodiment, the UV light generated to form the curtain of UV light  102  has an energy below the ionization threshold of the material of the particles. For example, it may be desirable to utilize UV light below the ionization threshold of the material of the particles in order to avoid ionization within the particles, which may lead to unknown or uncontrollable charging phenomena. Further, the UV light generated to form the curtain of UV light  102  may have an energy above the work function of the particles traversing the curtain of UV light  102 , but below the ionization energy of the particles traversing the curtain of UV light  102 . 
     The UV light source  116  of the light curtain generation unit  114  may include any UV light source known in the art. In one embodiment, the light source  116  may include a narrow band source configured to generate UV light at one or more selected bands within the UV spectral region. For example, the light source  116  may include one or more excimer lamps (e.g., 172 nm excimer lamp). By way of another example, the light source  116  may include one or more laser sources suitable for emitting ultraviolet light. In another embodiment, the light source  116  may include a broadband source configured to generate UV light at one or more selected bands within the UV spectral region. For example, the light source  116  may include one or more broadband lamps suitable for emitting ultraviolet light. For instance, the broadband lamp may include, but is not limited to, a mercury lamp. It is noted herein that a mercury lamp may display multiple strong emission UV wavelengths, such as 165 nm, 185 nm, 194 nm, 253.6 nm, 365 nm and 400 nm. In another instance, the broadband UV lamp may include, but is not limited to, a Hg—Xe lamp, a Xe lamp, a Kr lamp, an Argon lamp or combinations thereof. In yet another instance, the broadband UV lamp may include a laser produced plasma (LPP) source or laser-sustained plasma source. It is further noted herein that the spectra emitted by a given broadband lamp may be tuned by the implemented gas type or pressure of the lamp. In some embodiments, the broadband lamp suitable for emitting ultraviolet light may include, but is not limited to, a DC lamp, a pulsed AC lamp, or an RF lamp. In a further embodiment, the light source  116  of the present invention may include any combination of the various light sources described herein. 
     The one or more optical elements  118  of the UV curtain generation unit  114  of the system  100  may include any optical element known in the art. In this regard, those skilled in the art will recognize that numerous optical elements and configurations may be implemented to direct UV light from the UV light source  116  onto region or zone (e.g., annular zone) surrounding the reticle protection area  106  about the reticle  104 . For example, the one or more optical elements  116  may include, but are not limited to, one or more optical fibers, one or more lenses (e.g., cylindrical lens), one or more mirrors, one or more beam splitters, one or more filters and the like. 
     In one embodiment of the present invention, one or more optical fibers (not shown) maybe used to route UV light (190-400 nm) from the UV source  116  to one or more cylindrical glass lenses (not shown) configured to form a UV light curtain  102  about the reticle protection area  106  about the reticle  104 . In this regard, the light curtain formed by the one or more cylindrical lenses may be of fixed location relative to the reticle stage  101  carrying the reticle  104 . Those skilled in the art will recognize that, due to the difficulty of optical fibers to transmit UV light below 190 nm, the UV light of the UV light curtain  102  of this embodiment will include UV wavelengths in the range of approximately 190-400 nm. 
     In another embodiment of the present invention, UV light (e.g., 165-400 nm) is generated by multiple light sources on the outside of the vacuum chamber of the lithography system at multiple locations. It is noted herein that a laser-produced or laser-sustain plasma light source is suitable for generating light in the 165-400 nm regime. The light sources  116  then flood the stage volume (i.e., volume near the vicinity of reticle stage  101  with a uniform UV light field that is substantially perpendicular to the stage  101 . In this regard, the reticle stage  101  may act to create a shadow in this flooding UV light field. In turn, the shadowing effect caused by the reticle stage  101  acts to form an annular UV light curtain  102  about the reticle protection area  106  near the reticle stage  101 , as shown in  FIG. 1A . It is noted herein that in this scenario the positioning of the UV light curtain  102  is generally defined by the geometry and size of the reticle stage  101 . 
     In another embodiment of the present invention, UV light (165-400 nm) is generated and collimated on the outside of the vacuum chamber of the lithography system. Then, the UV light passes through a cylindrical or other shaped lens and immediately passes through a vacuum window. Further, the curtain of light  102  may then be steered to track the reticle stage  104  as the reticle stage  104  moves in X- and Y-directions, thereby creating a moving curtain of UV light  102  (e.g., annular curtain of UV light) around the reticle stage  101 . 
     In one embodiment, the electric field generation unit  107  includes a first charging element  108  (e.g., charged plate) holding a first charge and a second charge element  110  holding a second charge, the first charge and second charge having opposite signs. For example, a voltage source  120  may be electrically coupled to the first charging element  108  and the second charging element  110  and suitable for biasing the first charging element  108  and the second charging element  110  such that the first charging element  108  has a negative charge, while the second charge element has a positive charge  110  (or vice-versa). In this regard, the voltage bias applied to the first charge element and the second charge element act to establish a net electric field  103  that extends (e.g., extends laterally in  FIG. 1A ) across a spatial zone  105  positioned between the UV light curtain  102  and the reticle protection volume  106  surrounding the reticle  104 . In one embodiment, one or both of the first charge element and the second charge element may include a metal charging plate, as shown in  FIG. 1A . In one embodiment, one or both of the first charging element  108  and the second charging element  110  may include a dedicated charging plate. In another embodiment, one or more of the first charging element or the second charging element may include a metal plate arranged about the reticle protection volume  106  of the reticle  104 . It is noted herein that the first charging plate  108  and the second charging plate  110  may take on a number of geometrical forms. In one embodiment, the first charging plate  108  may include an annular bias plate, as depicted in  FIG. 1C , suitable for surrounding the reticle protection area  106  about the reticle  104 . In this regard, the annular bias plate  108  may be positioned concentrically between the external edge of the reticle protection area  106  and the internal edge of the UV light curtain  102 , as shown in  FIG. 1A . In a further embodiment, the second charging plate  110  may also include an annular bias plate, with the center of the second charging plate  110  being substantially aligned with the center of the first charging plate  108 . It is noted herein that the first charging plate  108  and the second charging plate  110  may take on any geometric shape known in the art. 
     In another embodiment, one or both of the first charging element and the second charging element may include a preexisting metal component of the lithography system, such as, but not limited to, a portion of the positioning interferometer of the lithography system (see  FIG. 2B ) or a portion of the reticle stage of the lithography system. It is noted herein that the above description of the charging elements is not limiting and it is recognized that any number of metal components with a given lithography tool may be utilized as one or both of the first charging element or the second charging element of the system  100 . 
     In a further embodiment, the second charging element  110  may consist of a thermophoretic plate suitable for aiding in removing particles from the reticle protection area  106  by the process of thermophoresis. In this regard, the second charging element  110  may serve a dual purpose by providing particle control via thermophoresis and by serving as a metal charging plate in the electric field generation unit  107 , as described previously herein. In an alternative embodiment, the system  100  of the present invention may include an independent thermophoretic plate which acts to provide particle control in conjunction with the UV light curtain  102  and electric field generation unit  107 . Thermophoresis is described generally and configurations for implementing thermophoresis based control in a EUV lithography setting are described specifically in U.S. Pat. No. 7,030,959, issued on Apr. 18, 2006; and U.S. Pat. No. 7,875,864, issued on Jan. 25, 2011, which are incorporated herein by reference in their entirety. 
     While the description provided throughout the present disclosure has focused on particle control near a reticle of a EUV lithography tool or EUV reticle inspection tool, it is noted herein that the present invention should be interpreted to apply to any critical region of an EUV optical tool sensitive to the presences of particles. For example, the UV light generation unit  114  and the electric field generation unit  107  of the system  100  may be extended to produce an UV light curtain  102  and an electric field zone  105  around any EUV critical region or critical zone. In one embodiment, the system  100  may generate an UV light curtain  102  and electric field zone  105  about a particle sensitive region of a sensor of an EUV reticle inspection tool. In another embodiment, the system  100  may generate an UV light curtain  102  and electric field zone  105  about a particle sensitive region of a wafer of an EUV lithography tool. In another embodiment, the system  100  may generate an UV light curtain  102  and electric field zone  105  near one or more surfaces of one or more optical elements (e.g., mirror) of an EUV reticle inspection tool or an EUV lithography tool. 
       FIGS. 2A and 2B  illustrate schematic views of a system  200  for particle control in an actinic EUV reticle inspection tool, in accordance with embodiments of the present invention. It is noted herein that the description throughout the present disclosure with respect to the various embodiments of the present invention should be interpreted to apply to system  200  unless otherwise noted. In a general sense, the EUV reticle inspection tool includes a set of EUV capable optics  202  suitable for directing EUV light to the reticle  104 . In this regard, the set of EUV optics  202  directs EUV light through barrier  112  to reticle  104 . As shown in  FIG. 2A , the curtain of UV light  102  may be generated by system  200  in a manner described previously herein, providing a zone (e.g., annular zone) of UV light  102  that surrounds the reticle  104  mounted on the reticle stage  101  of the EUV reticle inspection tool. 
     As noted previously herein, the first or second charging elements used to generate the electric field zone of the present invention may include dedicated charging elements or metallic components of the implementing EUV optical system. For example, as shown in  FIG. 2A , the electric field generated by system  200  may be formed utilizing a first charging plate  208  and the thermophoretic plate  206  of the EUV reticle inspection tool. The electric field generated between dedicated plate  208  and the thermophoretic plate  206  using an applied voltage source (not shown in  FIG. 2A ) acts to generate an electric field extending across an electric field zone located between the reticle  104  and the generated UV light curtain  102 . 
     By way of another example, as shown in  FIG. 2B , the second charging element may include a portion of the stage interferometer mirror  214  of the EUV inspection tool. The electric field generated between dedicated plate  208  and the charged stage interferometer mirror  214  of the EUV inspection tool using an applied voltage source (not shown in  FIG. 2B ) acts to generate an electric field extending across an electric field zone located between the reticle  104  and the generated UV light curtain  102 . It is noted herein that any metal portion of the EUV inspection tool may serve one of the charging elements used to generate the electric field of the present invention and the examples provided above should not be interpreted as limiting. 
     Further, it is noted that additional particle control or capture techniques may be used in concert with the UV light curtain/Electric Field approach described throughout the present disclosure. For example, the system  200  may be equipped with gas curtain capabilities used to fluidically control particles near the reticle  104 . For instance, the system  200  may include a gas supply  210 , which acts to supply a clean selected gas to assembly  204  of the EUV system. The supplied gas acts to “move” particles in the vicinity of the reticle  104  to positions away from the reticle via the gas exhaust  210 . Particle control via a gas curtain and/or thermophoresis is described generally in U.S. Pat. No. 7,030,959, incorporated previously herein by reference in the entirety. 
       FIG. 3  illustrates a process flow diagram  300  depicting a method for controlling particles near a reticle, in accordance with an embodiment of the present invention. It is noted herein that the process  300  may be carried out in all or in part using systems  100  or  200  described previously. However, it is further noted that process  300  is not limited to the embodiments and configurations of systems  100  and  200  as other configurations and architectures may be implemented to carry out process  300 . 
     In step  302 , a curtain of ultraviolet light is generated about a reticle protection area  106  about a reticle  104 . For example, a curtain of ultraviolet light  102  may be generated by illuminating a region (e.g., annular region) surrounding the reticle protection area  106  with ultraviolet light  102  having sufficient energy to induce a charge on one or more particles traversing the curtain of ultraviolet light  102 . In step  304 , an electric field  103  may be generated in a region  105  (e.g., annular region) positioned between the generated curtain of ultraviolet light  102  and the reticle protection area  106 . For example, the electric field  103  may be generated between a first charging element  108  and a second charging element  110  having an opposite charge to the first charging element. 
     In step  306 , one or more charged particles may be directed to a first charging element or a second charging element using the generated electric field  103 . In this regard, a particle having a positive charge induced by the UV light curtain  102  will generally follow the electric field lines established between the first charging plate  108  and the second charging plate  110 . In step  308 , the one or more charged particles may be captured on the first charged element  108  or the second charged element  110 . In this regard, in the case of a positive charge, the positively charge particle will travel toward the negatively charged charging element ( 108  or  110 ) until the positively charged particle is captured by the negatively charged charging element. 
       FIG. 4  illustrates a process flow diagram  400  depicting a method for controlling particles near a critical region of an EUV optical tool, in accordance with an embodiment of the present invention. It is noted herein that the process  400  may be carried out in all or in part using systems  100  or  200  described previously. However, it is further noted that process  400  is not limited to the embodiments and configurations of systems  100  and  200  as other configurations and architectures may be implemented to carry out process  400 . 
     In step  402 , a curtain of ultraviolet light is generated about a critical region of an EUV optical tool. For example, a curtain of ultraviolet light  102  may be generated by illuminating a region (e.g., annular region) surrounding a critical region (e.g., reticle protection area, sensor area, wafer area, area near optical element and the like) of an EUV optical tool (e.g., reticle inspection tool or lithography tool) with ultraviolet light  102  having sufficient energy to induce a charge on one or more particles traversing the curtain of ultraviolet light  102 . In step  404 , an electric field  103  may be generated in a region  105  (e.g., annular region) positioned between the generated curtain of ultraviolet light  102  and the critical region. For example, the electric field  103  may be generated between a first charging element  108  and a second charging element  110  having an opposite charge to the first charging element. 
     In step  406 , one or more charged particles may be directed to a first charging element or a second charging element using the generated electric field  103 . In this regard, a particle having a positive charge induced by the UV light curtain  102  will generally follow the electric field lines established between the first charging plate  108  and the second charging plate  110 . In step  308 , the one or more charged particles may be captured on the first charging element  108  or the second charging element  110 . In this regard, in the case of a positive charge, the positively charge particle will travel toward the negatively charged charging element ( 108  or  110 ) until the positively charged particle is captured by the negatively charged charging element. 
     While particular aspects of the present subject matter described herein have been shown and described, it will be apparent to those skilled in the art that, based upon the teachings herein, changes and modifications may be made without departing from the subject matter described herein and its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as are within the true spirit and scope of the subject matter described herein. It is believed that the present disclosure and many of its attendant advantages will be understood by the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the components without departing from the disclosed subject matter or without sacrificing all of its material advantages. The form described is merely explanatory, and it is the intention of the following claims to encompass and include such changes. Furthermore, it is to be understood that the invention is defined by the appended claims.