High power broadband illumination source

Abstract

A high power broadband illumination source is disclosed. A system for generating broadband radiation includes a target material source configured to deliver one or more of a liquid or solid target material to a plasma formation region of a chamber. The system further includes a pump source configured to generate pump radiation to excite the target material in the plasma formation region of the chamber to generate broadband radiation. The system is further configured to transmit at least a portion of the broadband radiation generated in the plasma formation region of the chamber out of the chamber through a windowless aperture.

Description

[0001] Information about divisional applications

[0002] This application is a divisional application of the invention patent application with the application date of July 23, 2018, application number 201880046059.0, and invention name “High-power broadband illumination source”.

[0003] CROSS REFERENCE TO RELATED APPLICATIONS

[0004] This application claims priority to U.S. Provisional Application No. 62 / 536,914, filed on July 25, 2017 by inventors named Oleg Khodykin and Ilya Bezel, entitled “HIGH POWER HIGH BRIGHTNESS VUV AND DUVBROADBAND CW AND MODULATED SOURCE AND METHOD OF PRODUCING THEREOF,” the entire contents of which are incorporated herein by reference. Technical Field

[0005] The present invention relates generally to plasma-based radiation sources, and more particularly to laser-sustained plasma (LSP) broadband radiation sources including plasmas produced at near atmospheric pressure. Background Art

[0006] As the demand for integrated circuits with increasingly smaller device features continues to increase, the need for improved illumination sources for inspecting these ever-shrinking devices continues to grow. One such illumination source includes a laser-sustained plasma (LSP) radiation source. A laser-sustained plasma light source is capable of producing high-power, broadband light. A laser-sustained plasma light source operates by focusing laser radiation into a gas volume to excite a gas, such as argon or xenon, into a plasma state capable of emitting light. This effect is often referred to as "pumping" the plasma. In current applications, relatively high density plasmas are required and are achieved by providing a high pressure (30 atm to 200 atm) to the target gas.

[0007] The transmission elements in LSP radiation sources experience high pressure and high temperature due to the target gas in the chamber containing the plasma. The transmission window, which is usually made of materials such as calcium fluoride, magnesium fluoride or lithium fluoride, also transmits the radiation below 190 nm generated by the plasma. The combination of high pressure, high temperature and radiation below 190 nm makes the lifetime of the transmission optics used in LSP radiation sources very short.

[0008] Therefore, it is desirable to provide a system and method that compensates for one or more deficiencies of the above-mentioned methods. Summary of the invention

[0009] According to one or more embodiments of the present invention, an apparatus is disclosed. In one embodiment, the apparatus includes a chamber. In another embodiment, the chamber is configured to contain a quantity of buffer gas. In another embodiment, the apparatus includes a source of target material positioned on a first side of the chamber. In another embodiment, the apparatus includes a debris collector. In another embodiment, the apparatus includes a debris collector positioned on a second side of the chamber opposite the source of target material. In another embodiment, the source of target material is configured to deliver a stream of target material through a plasma formation region of the chamber. In another embodiment, the debris collector is configured to collect target material. In another embodiment, the apparatus includes a pump source. In another embodiment, the apparatus includes a pump source configured to deliver pump radiation to the plasma formation region of the chamber. In another embodiment, the pump radiation from the pump source is sufficient to generate broadband radiation by forming a plasma by exciting the target material within the plasma formation region of the chamber. In another embodiment, the apparatus includes one or more focusing optical elements. In another embodiment, the one or more focusing optical elements are configured to focus the pump radiation into the plasma formation region. In another embodiment, the apparatus comprises one or more reflective collection optical elements. In another embodiment, the one or more reflective collection optical elements are configured to collect a portion of the broadband radiation from the plasma and transport the portion of the broadband radiation through apertures in the wall of the chamber to one or more optical elements outside the chamber.

[0010] According to one or more embodiments of the present invention, a system is disclosed. In one embodiment, the system includes a broadband source. In another embodiment, the broadband source includes a chamber configured to contain a certain amount of inert gas. In another embodiment, the broadband source includes a target material source positioned on a first side of the chamber. In another embodiment, the broadband source includes a debris collector positioned on a second side of the chamber opposite the target material source. In another embodiment, the target material source is configured to convey a flow of target material through a plasma formation region of the chamber. In another embodiment, the debris collector is configured to collect target material. In another embodiment, the broadband source includes a pump source. In another embodiment, the pump source is configured to convey pump radiation to the plasma formation region of the chamber. In another embodiment, the pump radiation from the pump source is sufficient to generate broadband radiation by forming a plasma by exciting the target material in the plasma formation region of the chamber. In another embodiment, the broadband source includes one or more focusing optical elements. In another embodiment, the one or more focusing optical elements are configured to focus the pump radiation into the plasma formation region. In another embodiment, the broadband source includes one or more reflective collection optical elements. In another embodiment, the one or more reflective collection optical elements are configured to collect a portion of the broadband radiation from the plasma and transport the portion of the broadband radiation to one or more optical elements outside the chamber through apertures in the wall of the chamber. In another embodiment, the broadband source includes a set of illuminator optics. In another embodiment, the set of illuminator optics is configured to direct the broadband radiation from the one or more reflective collection optics to one or more samples. In another embodiment, the broadband source includes a detector. In another embodiment, the broadband source includes a set of projection optics. In another embodiment, the set of projection optics is configured to receive illumination from a surface of the one or more samples and direct the illumination from the one or more samples to the detector.

[0011] According to one or more embodiments of the present invention, a method is disclosed. In one embodiment, the method includes: conveying a stream of a target material through a plasma formation region of a gas chamber. In another embodiment, the method includes: collecting debris from the plasma formation region. In another embodiment, the method includes: generating pump radiation. In another embodiment, the method includes: focusing the pump radiation into the plasma formation region of the chamber to generate broadband radiation by forming a plasma by exciting the target material within the plasma formation region of the chamber. In another embodiment, the method includes: collecting a portion of the broadband radiation from the plasma and conveying the portion of the broadband radiation to one or more optical elements outside the chamber through a windowless aperture in a wall of the chamber. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Those skilled in the art may better understand the advantages of the present invention by referring to the accompanying drawings, in which:

[0013] Figure 1 A simplified schematic diagram illustrating a laser-sustained plasma (LSP) broadband radiation source according to one or more embodiments of the present invention;

[0014] Figure 2A Describing a pump and collection configuration including a low NA pump and a high NA collection according to one or more embodiments of the present invention;

[0015] Figure 2B Describing a pump and collection configuration including a high NA pump and a low NA collection according to one or more embodiments of the present invention;

[0016] Figure 3 A simplified schematic diagram illustrating a system for implementing an optical characterization of an LSP radiation source according to one or more embodiments of the present invention; and

[0017] Figure 4 The description depicts a flow chart of a method for generating broadband radiation in accordance with one or more embodiments of the present invention. DETAILED DESCRIPTION

[0018] The present invention has been particularly shown and described with respect to specific embodiments and specific features thereof. The embodiments described herein are considered to be intended to be illustrative rather than limiting. It should be readily apparent to those skilled in the art that various changes and modifications may be made to form and details without departing from the spirit and scope of the present invention.

[0019] The present invention generally relates to a laser sustained plasma (LSP) radiation source. The LSP includes a material source that provides one or more target materials (such as argon, xenon, neon or helium) in a non-gaseous form for laser excitation. For example, the LSP can provide a target material in the form of at least a liquid, a solid, or a combination of a liquid and a solid. For example, the target material provided by the material source can be provided by one or more of a jet, a flow, a slurry, a mist, a spray, a droplet, a bead, a granule, a particle, or another other non-gaseous form of material. The plasma generated by the LSP emits broadband radiation that is guided out of the LSP through a windowless aperture by a reflective collection optical device. It should be noted herein that an advantage of the present invention is the use of reflective optical devices that do not require a transmission window. It should be noted herein that another advantage of the present invention is that a high-pressure gas chamber is not required to transport a high-density target material in the form of a solid, a liquid, or a combination of a solid and a liquid.

[0020] Reference will now be made in detail to the disclosed subject matter illustrated in the accompanying drawings.

[0021] Generally speaking Figures 1 to 4 , describing systems and methods for producing an improved laser sustained plasma (LSP) radiation source according to one or more embodiments of the present invention. Embodiments of the present invention are directed to delivering a target material in the form of a liquid jet, droplets, frozen jets, frozen droplets, slurry, stream, or a combination of these target material forms. Additional embodiments of the present invention are directed to liquid jets having diameters of 10 microns to 2000 microns and / or droplets having velocities of about 10 m / s to about 300 m / s. Additional embodiments of the present invention are directed to delivering a target material at atmospheric or near atmospheric pressure (e.g., 0.1 atm to 2 atm). Additional embodiments of the present invention utilize reflective collection optics to transmit broadband radiation from an LSP radiation source through a windowless aperture. It should be noted herein that the enhanced rapid flow of target material within the chamber can promote the generation of a stable plasma 116. Additional embodiments of the present invention use high numerical aperture (NA) (e.g., about π srad) broadband reflective optics to collect broadband radiation such as (but not limited to) VUV and / or DUV radiation. It should be further noted herein that in order for the LSP radiation source to have significant brightness in the DUV and / or VUV, a relatively high density plasma is required. For example, the density of the LSP radiation source should be high enough to absorb the pump laser beam and also dense enough to provide sufficient emissivity in the DUV and / or VUV and other spectral regions. Embodiments of the present invention deliver a high density working gas to the plasma in the form of a liquid or solid jet.

[0022] Figure 1A simplified schematic diagram illustrating a broadband LSP radiation source 100 in accordance with one or more embodiments of the present invention. In one embodiment, the LSP radiation source 100 includes a target material source 102, a pump source 108, a pump laser focusing optics 110, and a set of collection optics 120. In another embodiment, the LSP radiation source 100 includes a debris collector 124. It should be noted that the LSP radiation source 100 may generate broadband radiation 118 of any wavelength range including, but not limited to, vacuum ultraviolet (VUV) (e.g., 100 nm to 190 nm) and / or deep ultraviolet (DUV) (e.g., 190 nm to 260 nm).

[0023] In one embodiment, the target material source 102 delivers one or more target materials 104 into the chamber 106. For example, the target material source 102 may introduce the one or more target materials 104 into the chamber 106 in the form of a liquid jet, liquid droplets, frozen jets, frozen droplets, or a combination of these target material forms. In another embodiment, flow delivery parameters of the target material 104 from the target material source 102 are adjusted so that all of the material delivered by the target material source 102 vaporizes in the plasma region or some of the material passes through the plasma and is collected by the debris collector 124. In another embodiment, the debris collector 124 is positioned on the side of the chamber opposite the target material source 102. It should be noted herein that the adjustment of the flow delivery parameters may facilitate the generation of a stable plasma 116 and the generation of broadband radiation 118 having one or more substantially constant properties.

[0024] The target material source 102 may deliver any type of target material known in the art of LSP broadband source. For example, the target material may include, but is not limited to, Ar, Xe, Ne, and He, or a mixture of Ar, Xe, Ne, and He.

[0025] In one embodiment, the pump source 108 is configured to generate a pump beam 112 (e.g., laser radiation) that is focused by the pump laser focusing optics 110. In another embodiment, the pump source 108 comprises any radiation source known in the art, including, but not limited to, one or more lasers. In another embodiment, the pump beam 112 comprises radiation of any wavelength or range of wavelengths known in the art, including, but not limited to, infrared (IR) radiation, near infrared (NIR) radiation, ultraviolet (UV) radiation, visible radiation, or other radiation suitable for forming a plasma when incident on an appropriate target material.

[0026] In one embodiment, the pump laser focusing optics 110 focuses the pump beam 112 into the chamber 106 through the pump laser window 114. In another embodiment, the pump laser focusing optics 110 focuses the pump beam 112 into one or more target materials 104 to create and / or maintain a plasma 116. In another embodiment, the target material 104 is vaporized and ionized by the pump beam 112 to provide a high local concentration of plasma in the chamber. In another embodiment, the pressure of the heated material ejected from the plasma will decrease rapidly outward from the plasma region. It should be noted herein that the pump laser focusing optics 110 may include any optical element known in the art for directing and / or focusing radiation, including but not limited to lenses, mirrors, prisms, polarizers, gratings, filters, or beam splitters.

[0027] Focusing the pump beam 112 into the target material 104 causes energy to be absorbed by one or more absorption lines of the target material and / or plasma 116 contained within the chamber 106, thereby "pumping" the one or more target materials 104 to create and / or maintain the plasma 116. For example, the pump laser focusing optics 110 may create and / or maintain the plasma 116 by focusing the pump beam 112 to one or more focal points within the one or more target materials 104 contained within the chamber 106 to create and / or maintain the plasma 116. It should be noted herein that the LSP radiation source 100 may include one or more additional ignition sources for facilitating the creation of the plasma 116 without departing from the spirit or scope of the present invention. For example, the chamber 106 may include one or more electrodes that may initiate and / or maintain the plasma 116.

[0028] In one embodiment, the broadband radiation 118 generated by the plasma 116 exits the chamber 106 through one or more apertures 122. For example, the collection optics 120 may be configured to collect the broadband radiation 118 from the plasma 116 and to direct at least a portion of the collected broadband plasma through the one or more apertures 122. In another embodiment, the one or more apertures 122 are windowless and located in a wall of the chamber 106. For example, the one or more apertures 122 may include, but are not limited to, holes, ports, outlets, vents, spaces, or any other openings that allow the broadband radiation 118 to exit the chamber 106 through a wall of the chamber 106 without being transmitted through a material other than the surrounding atmosphere.

[0029] In one embodiment, the chamber 106 is fluidly coupled to a vacuum pump 126. In another embodiment, the pressure in the chamber 106 is maintained at about 1 atm. For example, the pressure in the chamber 106 can be maintained in the range of 0.1 atm to 2 atm. For example, the vacuum pump 126 can remove gas (e.g., gas ejected from the plasma, buffer gas) from the chamber 106 to maintain the pressure in the chamber 106 in the range of 0.1 atm to 2 atm.

[0030] In one embodiment, the set of optics 120 includes one or more optical elements known in the art configured to collect radiation (e.g., broadband radiation 118), including, but not limited to, one or more mirrors, one or more prisms, one or more lenses, one or more diffractive optical elements, one or more parabolic mirrors, one or more elliptical mirrors, and the like. It is noted herein that the set of optics 120 may be configured to collect and / or focus the broadband radiation 118 generated by the plasma 116 for one or more downstream processes including, but not limited to, imaging processes, inspection processes, metrology processes, photolithography processes, and the like. In another embodiment, the set of optics 120 is protected from damage by being positioned a sufficient distance from the plasma 116. For example, the set of optics 120 may be positioned within a range from 5 cm to 100 cm of the plasma to avoid being damaged by the plasma 116.

[0031] In one embodiment, the pump laser focusing optics 110 and the collection optics 120 are physically separated. It should be noted that the physical separation of the pump laser focusing optics 110 and the collection optics 120 eliminates the need for cold mirrors and / or dual bandwidth reflecting elliptical optics.

[0032] In one embodiment, the reflective optical surfaces of the collection optics 120 in the chamber 106 are protected by a buffer gas. For example, the buffer gas (eg, an inert gas, the same material as the target material, a material different from the target material) maintains about 1 atm in the chamber 106.

[0033] In one embodiment, the specific geometries of the pump laser focusing optics 110 and the collection optics 120 are optimized depending on the laser power and collection etendue requirements. In another embodiment, the collection optics 120 direct broadband radiation to the collection location 128.

[0034] In one embodiment, the pump source 108 comprises one or more radiation sources. For example, the pump source 108 may comprise any laser system known in the art. For example, the pump source 108 may comprise any laser system known in the art capable of emitting radiation in the infrared, visible, and / or ultraviolet portions of the electromagnetic spectrum. In another embodiment, the pump source 108 comprises a laser system configured to emit continuous wave (CW) laser radiation. For example, the pump source 108 may comprise one or more CW infrared laser sources.

[0035] In another embodiment, the pump source 108 includes one or more modulated CW lasers configured to provide modulated laser light to the plasma 116. In another embodiment, the pump source 108 may include one or more pulsed lasers configured to provide pulsed laser light to the plasma 116.

[0036] In one embodiment, the pump source 108 may include one or more diode lasers. For example, the pump source 108 may include one or more diode lasers that emit radiation at a wavelength corresponding to any one or more absorption lines of a species of the target material 104 contained within the chamber 106. It should be noted that the diode lasers implementing the pump source 108 may be selected such that the wavelength of the diode laser is tuned to any absorption line of any plasma (e.g., an ion transition line) or any absorption line of a plasma-generated target material known in the art (e.g., a highly excited neutral transition line). Thus, the selection of a given diode laser (or set of diode lasers) will depend on the type of target material contained within the chamber 106 of the system 100.

[0037] In another embodiment, the pump source 108 comprises an ion laser. For example, the pump source 108 may comprise any noble gas ion laser known in the art. For example, in the case of an argon-based plasma, the pump source 108 for pumping argon ions may comprise an Ar+ laser.

[0038] In another embodiment, the pump source 108 includes one or more frequency converted laser systems. For example, the pump source 108 may include a Nd:YAG or Nd:YLF laser.

[0039] In another embodiment, the pump source 108 includes one or more non-laser sources. In general, the pump source 108 can include any non-laser light source known in the art. For example, the pump source 108 can include any non-laser system known in the art that can discretely or continuously emit radiation in the infrared, visible, and / or ultraviolet portions of the electromagnetic spectrum.

[0040] In another embodiment, the pump source 108 includes two or more radiation sources. For example, the pump source 108 may include, but is not limited to, two or more lasers. For example, the pump source 108 (or several pump sources) may include multiple diode lasers. In another example, the pump source 108 may include multiple CW lasers and / or pulsed lasers. In another embodiment, each of the two or more lasers may emit laser radiation tuned to a different absorption line of the target material or plasma within the chamber 106 of the system 100.

[0041] In one embodiment, the pump source 108 generates pump radiation having a pulse interval of 100 ns to 1000 ns. In another embodiment, the pump source 108 operates at a power in the range of 3 kW to 100 kW. In another embodiment, the pump source 108 comprises greater than 10,000 W / cm 2 For example, the pump source 108 may include a peak laser intensity greater than 10 5 W / cm 2 In another embodiment, a short pulse (e.g., <100 ns) with high peak power (>108 W / cm 2 ) laser to perform ignition of one or more target materials 104 for generating plasma 116.

[0042] Figure 2A A pump and collection configuration 200 including a low NA pump and a high NA collection according to one or more embodiments of the present invention is illustrated. In one embodiment, the pump source 108, the one or more focusing optics 110, and the reflective collection optics 120 are configured so that the broadband radiation 118 has a numerical aperture that is higher than the NA of the pump radiation 112. In another embodiment, the collection optics 120 direct the broadband radiation to a collection location 128.

[0043] Figure 2B A pump and collection configuration 200 including a high NA pump and a low NA collection according to one or more embodiments of the present invention is illustrated. In one embodiment, the pump source 108, the one or more focusing optical elements 110, and the reflective collection optical element 120 are configured so that the broadband radiation 118 has a numerical aperture lower than the NA of the pump radiation. In another embodiment, the collection optical device 120 directs the broadband radiation to the collection location 128.

[0044] Figure 3 A simplified schematic diagram illustrates an optical characterization system 300 implementing an LSP radiation source 100 in accordance with one or more embodiments of the present invention. In one embodiment, the system 300 includes the LSP radiation source 100, an illumination branch 303, a collection branch 305, a detector 314, and a controller 318 including one or more processors 320 and a memory 322.

[0045] It should be noted herein that system 300 may include any imaging, inspection, metrology, lithography, or other characterization system known in the art. In this regard, system 300 may be configured to perform inspection, optical metrology, lithography, and / or any form of imaging on sample 307. Sample 307 may include any specimen known in the art, including, but not limited to, a wafer, a reticle, a photomask, and the like. It should be noted that system 300 may incorporate one or more of the various embodiments of LSP radiation source 100 described in this disclosure.

[0046] In one embodiment, the sample 307 is placed on a stage assembly 312 to facilitate movement of the sample 307. The stage assembly 312 may include any stage assembly 312 known in the art, including but not limited to an XY stage, an R-theta stage, and the like. In another embodiment, the stage assembly 312 is capable of adjusting the height of the sample 307 to maintain focus on the sample 307 during inspection or imaging.

[0047] In one embodiment, the illumination branch 303 is configured to direct broadband radiation 118 from the LSP radiation source 100 to the sample 307. The illumination branch 303 may include any number and type of optical components known in the art. In one embodiment, the illumination branch 303 includes one or more optical elements 302, a beam splitter 304, and an objective lens 306. In this regard, the illumination branch 303 may be configured to focus the broadband radiation 118 from the LSP radiation source 100 onto the surface of the sample 307. The one or more optical elements 302 may include any optical element or combination of optical elements known in the art, including, but not limited to, one or more mirrors, one or more lenses, one or more polarizers, one or more gratings, one or more filters, one or more beam splitters, and the like. It should be noted herein that the collection location 128 may include, but is not limited to, one or more of the optical element 302, the beam splitter 304, or the objective lens 306.

[0048] In one embodiment, system 300 includes a collection branch 305 configured to collect light reflected, scattered, diffracted, and / or emitted from sample 307. In another embodiment, collection branch 305 can direct and / or focus light from sample 307 to sensor 316 of detector assembly 314. It should be noted that sensor 316 and detector assembly 314 can include any sensor and detector assembly known in the art. Sensor 316 can include, but is not limited to, a CCD sensor or a CCD-TDI sensor. In addition, sensor 316 can include, but is not limited to, a line sensor or an electron impact line sensor.

[0049] In one embodiment, the detector assembly 314 is communicatively coupled to a controller 318 including one or more processors 320 and a memory 322. For example, the one or more processors 320 may be communicatively coupled to the memory 322, wherein the one or more processors 320 are configured to execute a set of program instructions stored on the memory 322. In one embodiment, the one or more processors 320 are configured to analyze the output of the detector assembly 314. In one embodiment, the set of program instructions is configured to cause the one or more processors 320 to analyze one or more characteristics of the sample 307. In another embodiment, the set of program instructions is configured to cause the one or more processors 320 to modify one or more characteristics of the system 300 to maintain focus on the sample 307 and / or the sensor 316. For example, the one or more processors 320 may be configured to adjust the objective lens 306 or the one or more optical elements 302 to focus the broadband radiation 118 from the LSP radiation source 100 onto the surface of the sample 307. As another example, the one or more processors 320 may be configured to adjust the objective lens 306 and / or the one or more optical elements 310 to collect illumination from the surface of the sample 307 and focus the collected illumination onto the sensor 316 .

[0050] It should be noted that system 300 may be configured in any optical configuration known in the art, including, but not limited to, a dark field configuration, a bright field orientation, and the like.

[0051] It should be noted herein that one or more components of the system 100 may be communicatively coupled to various other components of the system 100 in any manner known in the art. For example, the LSP radiation source 100, the detector assembly 314, the controller 318, and the one or more processors 320 may be communicatively coupled to each other and to other components via wired (e.g., copper wire, fiber optic cable, and the like) or wireless connections (e.g., RF coupling, IR coupling, data network communications (e.g., WiFi, WiMax, Bluetooth, and the like)).

[0052] Additional details of various embodiments of the optical characterization system 300 are described in each of the following: U.S. Patent Application No. 13 / 554,954, entitled “Wafer Inspection System,” filed on July 9, 2012; U.S. Published Patent Application No. 2009 / 0180176, entitled “Split Field Inspection System Using Small Catadioptric Objectives,” published on July 16, 2009; U.S. Published Patent Application No. 2007 / 0002465, entitled “Beam Delivery System for Laser Dark-Field Illumination in a Catadioptric Optical System,” published on January 4, 2007; and U.S. Published Patent Application No. 2007 / 0002465, entitled “Ultra-broadband UV Microscope Imaging System with Wide Range Zoom Capability,” published on December 7, 1999. U.S. Patent No. 5,999,310 entitled “Surface Inspection System Using Laser Line Illumination with Two Dimensional Imaging”, issued on April 28, 2009; U.S. Patent No. 7,525,649 entitled “Surface Inspection System Using Laser Line Illumination with Two Dimensional Imaging”, published on April 28, 2009; U.S. Published Patent Application No. 2013 / 0114085 entitled “Dynamically Adjustable Semiconductor Metrology System”, published on May 9, 2013 by Wang et al.; U.S. Patent No. 5,608 entitled “Focused Beam Spectroscopic Ellipsometry Method and System”, published on March 4, 1997 by Piwonka-Corle et al.526 and U.S. Pat. No. 6,297,880, entitled “Apparatus for Analyzing Multi-Layer Thin Film Stacks on Semiconductors”, issued Oct. 2, 2001 to Rosencwaig et al., each of which is incorporated herein by reference in its entirety.

[0053] The one or more processors 320 of the present invention may include any one or more processing elements known in the art. In this sense, the one or more processors 320 may include any microprocessor-type device configured to execute software algorithms and / or instructions. In one embodiment, the one or more processors 320 may be composed of a desktop computer, a main computer system, a workstation, an image computer, a parallel processor, or other computer systems (such as network computers) configured to execute programs configured to operate the system 300 and / or the LSP radiation source 100, as described in the present invention. It should be recognized that the steps described in the present invention may be implemented by a single computer system or alternatively multiple computer systems. In general, the term "processor" may be broadly defined to encompass any device having one or more processing components that execute program instructions from a non-temporary memory medium 322. In addition, the different subsystems of the various systems disclosed may include processors or logic elements suitable for implementing at least part of the steps described in the present invention. Therefore, the above description should not be interpreted as a limitation to the present invention but should only be interpreted as an explanation.

[0054] The memory medium 322 may include any storage medium known in the art that is suitable for storing program instructions that can be executed by the associated one or more processors 320. For example, the memory medium 322 may include a non-transitory memory medium. For example, the memory medium 322 may include (but is not limited to) a read-only memory, a random access memory, a magnetic or optical storage device (e.g., a disk), a tape, a solid-state drive, etc. In another embodiment, the memory 322 is configured to store one or more results and / or outputs of the various steps described herein. It should be further noted that the memory 322 may be housed in a common controller housing with the one or more processors 320. In an alternative embodiment, the memory 322 may be remotely located relative to the physical location of the processor 320. For example, the one or more processors 320 may access a remote memory (e.g., a server), which may be accessed via a network (e.g., the Internet, an intranet, etc.). In another embodiment, the memory medium 322 stores program instructions for causing the one or more processors 320 to implement the various steps described in the present invention.

[0055] In one embodiment, the system 300 may include a user interface (not shown). In one embodiment, the user interface is communicatively coupled to the one or more processors 320. In another embodiment, a user interface device may be used to accept selections and / or instructions from a user. In some embodiments further described herein, a display may be used to display data to a user. The user may in turn input selections and / or instructions (e.g., selection of a filter box, setting size and / or position) in response to data displayed to the user via the display device.

[0056] The user interface device may include any user interface known in the art. For example, the user interface may include, but is not limited to, a keyboard, a keypad, a touch screen, a joystick, a knob, a roller, a trackball, a switch, a dial, a slide bar, a scroll bar, a slider, a handle, a touch pad, a pedal, a steering wheel, a joystick, a panel mounted input device, and the like. In the case of a touch screen interface device, one skilled in the art will recognize that a wide variety of touch screen interface devices may be suitable for implementation in the present invention. For example, a display device may be integrated with a touch screen interface such as, but not limited to, a capacitive touch screen, a resistive touch screen, a surface acoustic wave-based touch screen, an infrared-based touch screen, or the like. In general, any touch screen interface capable of being integrated with the display portion of a display device is suitable for implementation in the present invention.

[0057] The display device may include any display device known in the art. In one embodiment, the display device 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 a variety of display devices may be suitable for implementation in the present invention and that the specific selection of a display device may depend on various factors including, but not limited to, form factor, cost, and the like. In general, any display device capable of being integrated with a user interface device, such as a touch screen, a panel mounted interface, a keyboard, a mouse, a touch pad, and the like, is suitable for implementation in the present invention.

[0058] In some embodiments, the LSP radiation source 100 and system 300 described herein may be configured as a "stand-alone tool" or a tool that is not physically coupled to a processing tool. In other embodiments, this inspection or metrology system may be coupled to a tool (not shown) via a transmission medium that may include wired and / or wireless portions. The processing tool may include any processing tool known in the art, such as a lithography tool, an etching tool, a deposition tool, a polishing tool, a plating tool, a cleaning tool, or an ion implantation tool. The results of the inspection or measurement performed by the system described herein may be used to change the parameters of a process or a process tool using feedback control techniques, feedforward control techniques, and / or in-situ control techniques. The parameters of a process or a processing process may be changed manually or automatically.

[0059] Embodiments of the LSP radiation source 100 and system 300 may be further configured as described herein. Additionally, the LSP radiation source 100 and system 300 may be configured to perform any other step(s) of the method embodiment(s) described herein.

[0060] Figure 4 A flow chart depicting a method 400 for generating broadband radiation 118 according to one or more embodiments of the present invention is described. It should be noted herein that the steps of method 400 may be fully or partially implemented by LSP radiation source 100. However, it should be further appreciated that method 400 is not limited to LSP radiation source 100, as additional or alternative system-level embodiments may implement all or part of the steps of method 400.

[0061] In step 402, a stream of a target material 104 is delivered through a plasma formation region of a chamber 106. In one embodiment, a target material source 102 introduces one or more target materials 104 into the chamber 106 in the form of a liquid jet, liquid droplets, frozen jets, frozen droplets, or a combination of these target material forms. For example, the target material source 102 may deliver one or more of argon, xenon, neon, or helium into the chamber 106 in one or more of a solid or liquid state to generate and / or sustain a plasma. For example, the target material source 102 may be configured to deliver the stream of target material through the plasma formation region at a speed between 10 m / s and 300 m / s. As another example, the target material source 102 may be configured to deliver a stream of target material having a diameter between 10 μm and 2000 μm through the plasma formation region.

[0062] In step 404, debris is collected by a debris collector. For example, the plasma-formed target material 104 from step 402 that is not consumed by the plasma 116 is collected by the debris collector 124. In one embodiment, the flow delivery parameters are adjusted so that all of the material delivered by the target material source 102 is vaporized in the plasma region or some of the material passes through the plasma and is collected by the debris collector 124. It should be noted herein that the adjustment of the flow delivery parameters can facilitate the generation of a stable plasma 116 and the generation of broadband radiation 118 having one or more substantially constant properties.

[0063] In step 406, the pump source 108 generates pump radiation 112. In one embodiment, the pump source 108 generates pump radiation 112 that is focused into the chamber 106 by the pump laser focusing optics 110. For example, the pump source 108 may include one or more lasers to generate the pump radiation 112 directed into the chamber 106. As another example, one or more non-laser sources may generate the pump radiation 112 directed into the chamber 106.

[0064] In step 408, the pump radiation 112 is focused into the plasma formation region of the chamber 106 to generate broadband radiation 118 by forming a plasma 116 by exciting the target material 104 in the plasma formation region of the chamber 106. For example, the pump source 108 may direct the pump radiation 112 into the chamber 106 to generate the plasma 116. In another embodiment, the LSP radiation source 100 generates radiation including, but not limited to, broadband radiation 118. For example, the LSP radiation source 100 may generate broadband radiation 118 in the range of vacuum ultraviolet (VUV) (100 nm to 190 nm) and deep ultraviolet (DUV) (190 nm to 260 nm). It is noted herein that the chamber 106 may include one or more additional ignition sources (e.g., electrodes) configured to initiate and / or maintain the plasma 116.

[0065] In step 410, a portion of the broadband radiation 118 is collected from the plasma 116 and transported through the windowless apertures 122 in the wall of the chamber 106 to one or more optical elements outside the chamber 106 at a collection location 128. For example, the broadband radiation 118 generated by the plasma 116 in the chamber 106 may be collected by the collection optics 120 and directed through the apertures 122 to the collection location 128 where the external optical elements receive the broadband radiation 118.

[0066] Those skilled in the art will recognize that for conceptual clarity, the components (e.g., operations), devices, objects, and the accompanying discussions described herein are used as examples and that various configuration modifications are contemplated. Therefore, as used herein, the specific examples set forth and the accompanying discussions are intended to represent their more general classes. In general, the use of any specific example is intended to represent its class, and the non-inclusion of specific components (e.g., operations), devices, and objects should not be considered limiting.

[0067] Those skilled in the art will appreciate that there are various vehicles (e.g., hardware, software, and / or firmware) by which the processes and / or systems and / or other techniques described herein may be implemented, and that the preferred vehicle will vary with the context in which the processes and / or systems and / or other techniques are deployed. For example, if the implementer determines that speed and accuracy are primary, then the implementer may select a vehicle that is primarily hardware and / or firmware; or, if flexibility is primary, then the implementer may select a software-based implementation; or, the implementer may select some combination of hardware, software, and / or firmware. Thus, there are several possible vehicles by which the processes and / or devices and / or other techniques described herein may be implemented, none of which is inherently superior to the others, as utilizing any vehicle is a choice that depends on the context in which the vehicle will be deployed and the implementer's particular concerns (e.g., speed, flexibility, or predictability) (any of which may vary).

[0068] The above description is presented to enable one skilled in the art to make and use the present invention provided in the context of a particular application and its requirements. As used herein, directional terms such as "top", "bottom", "on", "below", "up", "down", "below", and "downward" are intended to provide relative positions for the purpose of description and are not intended to specify an absolute reference system. Various modifications of the described embodiments should be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments. Therefore, the present invention is not intended to be limited to the specific embodiments shown and described, but should be given the widest scope consistent with the principles and novel features disclosed herein.

[0069] With respect to substantially any plural and / or singular terms used herein, those skilled in the art may translate from the plural to the singular and / or from the singular to the plural as required by the context and / or application. For clarity, various singular / plural permutations are not explicitly set forth herein.

[0070] All methods described herein may include storing the result of one or more steps of the method embodiment in a memory. The result may include any result described herein and may be stored in any manner known in the art. The memory may include any memory described herein or any other suitable storage medium known in the art. After the result has been stored, the result may be accessed in the memory and used by anyone in the method or system embodiment described herein, formatted to be displayed to the user, used by another software module, method or system, etc. In addition, the result may be "permanent", "semi-permanent", "temporary" or stored in a certain period of time. For example, the memory may be a random access memory (RAM), and the result may not necessarily remain in the memory indefinitely.

[0071] It is further contemplated that each of the above method embodiments may include any other steps of any other method(s) described herein. In addition, each of the above method embodiments may be performed by any of the systems described herein.

[0072] Embodiments of the present invention are directed to a buoyancy-driven closed recirculating gas loop for facilitating rapid gas flow through an LSP radiation source. Advantageously, the LSP radiation source 100 of the present invention may include fewer mechanical actuation components than previous approaches. Thus, the LSP radiation source 100 of the present invention may generate less noise, require smaller gas volumes, and require lower maintenance costs and safety management.

[0073] The objectives described herein sometimes illustrate different components that are housed in or connected to other components. It should be understood that such depicted architectures are exemplary only, and in fact many other architectures that implement the same functionality can be implemented. Conceptually, any configuration of components for implementing the same functionality is effectively "associated" to achieve the desired functionality. Therefore, any two components of this article that are combined to achieve a specific functionality can be considered to be "associated" with each other to achieve the desired functionality, regardless of the architecture or intermediate components. Similarly, any two components so associated can also be considered to be "connected" or "coupled" to each other to achieve the desired functionality, and any two components that can be so associated can also be considered to be "coupleable" to each other to achieve the desired functionality. Specific examples of "coupleable" include, but are not limited to, physically matable and / or physically interactive components and / or wirelessly interactive and / or wirelessly interactive components and / or logically interactive and / or logically interactive components.

[0074] In addition, it should be understood that the present invention is defined by the appended claims. Those skilled in the art will understand that, in general, the terms used herein and particularly the terms used in the appended claims (e.g., the body of the appended claims) are intended to be "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.). Those skilled in the art will further understand that if a specific number of introduced claim statements is intended, such intention will be explicitly stated in the claims, and in the absence of such a statement, such intention does not exist. For example, to aid understanding, the following appended claims may contain the use of the introductory phrases "at least one" and "one or more" to introduce claim statements. However, even when the same claim contains the introductory phrases "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should generally be interpreted as meaning "at least one" or "one or more"), the use of such phrases should not be understood to imply that a claim recitation introduced by the indefinite article "a" or "an" limits any particular claim containing such introduced claim recitation to the invention containing only such recitation; the same is true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of introduced claim recitations is explicitly recited, those skilled in the art will recognize that such recitation should generally be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations" without other modifiers generally means at least two recitations, or two or more recitations). Furthermore, in the examples where a convention similar to “at least one of A, B, and C, etc.” is used, such construction is generally intended in the sense that a person skilled in the art understands such construction (e.g., “a system having at least one of A, B, and C” should include, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or both A, B, and C, etc.). In the examples where a convention similar to “at least one of A, B, or C, etc.” is used, such construction is generally intended in the sense that a person skilled in the art understands such construction (e.g., “a system having at least one of A, B, or C” should include, but is not limited to, systems having only A, only B, only C, both A and B, both A and C, both B and C, and / or both A, B, and C, etc.). Those skilled in the art should further understand that any disjunctive words and / or phrases that actually present two or more alternative items, whether in the description, claims or drawings, should be understood to consider the possibility of including one of the items, any one of the items, or both of the items.For example, the phrase "A or B" should be understood to include the possibilities of "A" or "B" or "A and B."

[0075] It is believed that from the foregoing description, the present invention and its many attendant advantages will be understood and it will be appreciated that various changes may be made to the form, construction and arrangement of components without departing from the disclosed subject matter or sacrificing all of its material advantages. The forms described are illustrative only, and the appended claims are intended to cover and include such changes. Furthermore, it should be understood that the present invention is defined by the appended claims.

Claims

1. A device comprising: a chamber configured to contain a quantity of buffer gas; a target material source positioned on a first side of the chamber; a debris collector positioned on a second side of the chamber opposite the source of target material, wherein the target material source is configured to deliver a flow of target material through a plasma formation region of the chamber, wherein the debris collector is configured to collect the target material; a pump source configured to deliver pump radiation to the plasma formation region of the chamber, wherein the pump radiation is sufficient to generate broadband radiation by forming a plasma by exciting the target material within the plasma formation region of the chamber; one or more focusing optical elements configured to focus the pump radiation into the plasma formation region; and one or more reflective collection optics configured to collect a portion of the broadband radiation from the plasma and transport the portion of the broadband radiation through an aperture in a wall of the chamber to one or more optical elements outside the chamber without transmission through material other than the surrounding atmosphere, wherein the aperture in the wall of the chamber is windowless, and the pump source, the one or more focusing optics, and the reflective collection optics are arranged so that the broadband radiation has a numerical aperture higher than the NA of the pump radiation; The one or more focusing optical elements are disposed outside the chamber, and the one or more reflection collecting optical elements are disposed inside the chamber.

2. The apparatus of claim 1, wherein the broadband radiation comprises: At least one of vacuum ultraviolet (VUV) or deep ultraviolet (DUV) radiation.

3. The apparatus of claim 1, wherein the target material stream comprises: At least one of a stream of liquid target material, a stream of solid target material, or a series of droplets of said target material.

4. The apparatus of claim 1, wherein the target material source is configured to deliver the target material stream at a velocity between 10 m / s and 300 m / s.

5. The apparatus of claim 1, wherein the target material stream has a diameter between 10 μm and 2000 μm.

6. The apparatus of claim 1, wherein the target material comprises: At least one of argon, xenon, neon or helium.

7. The apparatus of claim 6, wherein the target material comprises: A mixture containing at least one of argon, xenon, neon or helium.

8. The apparatus of claim 1, wherein the buffer gas comprises: Inert gas.

9. The apparatus of claim 1, wherein the buffer gas is the same as the target material.

10. The apparatus of claim 1, wherein the buffer gas is different from the target material.

11. The apparatus of claim 1, wherein the chamber is configured to contain the gas at a pressure between 0.1 atm and 2.0 atm.

12. The apparatus of claim 1, wherein the pump source comprises: At least one of a continuous wave (CW) laser, a pulsed laser or a modulated CW laser.

13. The apparatus of claim 12, wherein the pump source is configured to generate pump radiation having a pulse interval of 100 nanoseconds to 1000 nanoseconds.

14. The apparatus of claim 12, wherein the pump source is configured to generate pump radiation at a power between 3 kW and 100 kW.

15. The apparatus of claim 12, wherein the pump source is configured to generate a 5 W / cm 2 The peak laser intensity of the pump radiation.

16. An apparatus comprising: Broadband sources including: a chamber configured to contain a quantity of an inert gas; a target material source positioned on a first side of the chamber; a debris collector positioned on a second side of the chamber opposite the source of target material, wherein the target material source is configured to deliver a flow of target material through a plasma formation region of the chamber, wherein the debris collector is configured to collect the target material, a pump source configured to deliver pump radiation to the plasma formation region of the chamber, wherein the pump radiation is sufficient to generate broadband radiation by forming a plasma by exciting the target material within the plasma formation region of the chamber; one or more focusing optical elements configured to focus the pump radiation into the plasma formation region; and one or more reflective collection optical elements configured to collect a portion of the broadband radiation from the plasma and transport the portion of the broadband radiation to one or more optical elements outside the chamber through an aperture in a wall of the chamber without transmission through materials other than the surrounding atmosphere, the aperture in the wall of the chamber being windowless; and a set of illuminator optics configured to direct the broadband radiation from the one or more reflective collection optics to one or more samples; detector; and a set of projection optics configured to receive illumination from a surface of the one or more samples and direct the illumination from the one or more samples to the detector, wherein the pump source, the one or more focusing optics, and the reflective collection optics are arranged so that the broadband radiation has a numerical aperture higher than the NA of the pump radiation; The one or more focusing optical elements are disposed outside the chamber, and the one or more reflection collecting optical elements are disposed inside the chamber.

17. The apparatus of claim 16, wherein the broadband radiation comprises: At least one of vacuum ultraviolet (VUV) or deep ultraviolet (DUV) radiation.

18. A method comprising: conveying a stream of target material through a plasma formation region of a gas chamber; collecting debris from the plasma formation region; Producing pump radiation; focusing the pump radiation into the plasma formation region of the chamber via one or more focusing optical elements to produce broadband radiation by forming a plasma by exciting the target material within the plasma formation region of the chamber; and collecting a portion of the broadband radiation from the plasma via one or more reflective collection optical elements and transporting the portion of the broadband radiation through windowless apertures in a wall of the chamber to one or more optical elements outside the chamber without transmission through materials other than the surrounding atmosphere, wherein the broadband radiation has a numerical aperture higher than the NA of the pump radiation; The one or more focusing optical elements are disposed outside the chamber, and the one or more reflection collecting optical elements are disposed inside the chamber.

19. An apparatus comprising: a chamber configured to contain a quantity of buffer gas; a target material source positioned on a first side of the chamber; a debris collector positioned on a second side of the chamber opposite the source of target material, wherein the target material source is configured to deliver a flow of target material through a plasma formation region of the chamber, wherein the debris collector is configured to collect the target material; a pump source configured to deliver pump radiation to the plasma formation region of the chamber, wherein the pump radiation is sufficient to generate broadband radiation by forming a plasma by exciting the target material within the plasma formation region of the chamber; one or more focusing optical elements configured to focus the pump radiation into the plasma formation region; and one or more reflective collection optics configured to collect a portion of the broadband radiation from the plasma and transport the portion of the broadband radiation through an aperture in a wall of the chamber to one or more optical elements outside the chamber without transmission through material other than an ambient atmosphere, wherein the aperture in the wall of the chamber is windowless, and the pump source, the one or more focusing optics, and the reflective collection optics are arranged so that the broadband radiation has a lower numerical aperture than the NA of the pump radiation; The one or more focusing optical elements are disposed outside the chamber, and the one or more reflection collecting optical elements are disposed inside the chamber.

20. The apparatus of claim 19, wherein the broadband radiation comprises: At least one of vacuum ultraviolet (VUV) or deep ultraviolet (DUV) radiation.

21. The apparatus of claim 19, wherein the target material stream comprises: At least one of a stream of liquid target material, a stream of solid target material, or a series of droplets of said target material.

22. The apparatus of claim 19, wherein the target material source is configured to deliver the target material stream at a velocity between 10 m / s and 300 m / s.

23. The apparatus of claim 19, wherein the target material stream has a diameter between 10 μm and 2000 μm.

24. The apparatus of claim 19, wherein the target material comprises: At least one of argon, xenon, neon or helium.

25. The apparatus of claim 24, wherein the target material comprises: A mixture containing at least one of argon, xenon, neon or helium.

26. The apparatus of claim 19, wherein the buffer gas comprises: Inert gas.

27. The apparatus of claim 19, wherein the buffer gas is the same as the target material.

28. The apparatus of claim 19, wherein the buffer gas is different from the target material.

29. The apparatus of claim 19, wherein the chamber is configured to contain the gas at a pressure between 0.1 atm and 2.0 atm.

30. The apparatus of claim 19, wherein the pump source comprises: At least one of a continuous wave (CW) laser, a pulsed laser or a modulated CW laser.

31. The apparatus of claim 30, wherein the pump source is configured to generate pump radiation having a pulse spacing of 100 nanoseconds to 1000 nanoseconds.

32. The apparatus of claim 30, wherein the pump source is configured to generate pump radiation at a power between 3 kW and 100 kW.

33. The apparatus of claim 30, wherein the pump source is configured to generate a 5 W / cm 2 The peak laser intensity of the pump radiation.

34. An apparatus comprising: Broadband sources including: a chamber configured to contain a quantity of an inert gas; a target material source positioned on a first side of the chamber; a debris collector positioned on a second side of the chamber opposite the source of target material, wherein the target material source is configured to deliver a flow of target material through a plasma formation region of the chamber, wherein the debris collector is configured to collect the target material, a pump source configured to deliver pump radiation to the plasma formation region of the chamber, wherein the pump radiation is sufficient to generate broadband radiation by forming a plasma by exciting the target material within the plasma formation region of the chamber; one or more focusing optical elements configured to focus the pump radiation into the plasma formation region; and one or more reflective collection optical elements configured to collect a portion of the broadband radiation from the plasma and transport the portion of the broadband radiation through an aperture in a wall of the chamber to one or more optical elements outside the chamber without transmission through materials other than the surrounding atmosphere, wherein the aperture in the wall of the chamber is windowless; a set of illuminator optics configured to direct the broadband radiation from the one or more reflective collection optics to one or more samples; detector; and a set of projection optics configured to receive illumination from a surface of the one or more samples and direct the illumination from the one or more samples to the detector, wherein the pump source, the one or more focusing optics, and the reflective collection optics are arranged so that the broadband radiation has a lower numerical aperture than the NA of the pump radiation; The one or more focusing optical elements are disposed outside the chamber, and the one or more reflection collecting optical elements are disposed inside the chamber.

35. The apparatus of claim 34, wherein the broadband radiation comprises: At least one of vacuum ultraviolet (VUV) or deep ultraviolet (DUV) radiation.

36. A method comprising: conveying a stream of target material through a plasma formation region of a gas chamber; collecting debris from the plasma formation region; Producing pump radiation; focusing the pump radiation into the plasma formation region of the chamber via one or more focusing optical elements to produce broadband radiation by forming a plasma by exciting the target material within the plasma formation region of the chamber; and collecting a portion of the broadband radiation from the plasma via one or more reflective collection optical elements and transporting the portion of the broadband radiation through windowless apertures in a wall of the chamber to one or more optical elements outside the chamber without transmission through materials other than the surrounding atmosphere, wherein the broadband radiation has a numerical aperture lower than the NA of the pump radiation; The one or more focusing optical elements are disposed outside the chamber, and the one or more reflection collecting optical elements are disposed inside the chamber.

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