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`US007989786B2
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`(12)
`
`United States Patent
`Smith et al.
`
`(10) Patent No.:
`(45; Date of Patent:
`
`US 7,989,736 B2
`Aug. 2, 2011
`
`LASER-DRIVEN LIGHT SOURCE
`
`(56)
`
`References Cited
`
`US. PA'l”liN'I‘ D()C.‘UMliN'l'S
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`313-"634
`362-"208
`. 235-"4fi2.37
`372.-"S
`.............. . 250-"S04
`
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`
`JP
`
`FOREIGN PA'l‘l9IN'I' DOCUMENTS
`6l—|933S8
`S-"I986
`
`O'l‘[Il"£R PUB-I.1(.‘_/\'l'l()NS
`
`Wilbcrs ct al.. "The VLIV limissivity ofa High-Pressure Cascade
`Argon Are from 125 to 200 nm." 1 Qmiiir. Specririxc. Racliar. firms-
`_,f£>.r. vol. 45. 1991. pp. 299-303.
`Wilbers et al.. "The Continuuin [Emission of an Arc Plasma.” J.
`Qmzm‘.
`.'s})er~.'i\o.9c. Radiar. ?7'airsfer-. vol. 45. No. 1. 1991. pp. I-10.
`
`[(’nl11i11ucd)
`
`Primary E.\'a.miner — Nikita Wells
`(74) Ati‘orm:_1'. xigrmf. or Firiii -- Proskaucr Rose I.l.,l"
`
`(57)
`
`ABSTRACT
`
`An apparatus for producing light includes a cllamber and an
`ignition source that ioni'/cs a gas within the clulmbcr. The
`apparatus also includes at least one laser that provides energy
`to the ionized gas within the chamber to produce a high
`brigllmess light. The laser can provide a substantially con-
`tinuous amount of energy to the ionized gas to generate a
`substantially continuous high brightness light.
`
`39 Claims, I7 Drawing Sheets
`
`(54)
`
`(75)
`
`(73)
`
`Inventors: Donald K. Smith, Boston. MA (U S):
`Jeffrey A. Casey. Wi11cl1cs1L‘r. MA (US)
`
`Assigm-.‘c: Energetiq Technology, Inc.. Woburn.
`MA (US)
`
`(’“)
`
`Notice:
`
`Subject to any disclaimer. the term of this
`patent is extended or adjusted under 35
`U.S.(.‘.. 15403) by 551 days.
`
`(21)
`
`_1\pp1.No.: 127166318
`
`(22)
`
`Filed:
`
`Jul. 2. 2008
`
`(65)
`
`(63)
`
`Prior Publication Data
`
`US 2009fO=032740 A1
`
`Feb. 5. 2009
`
`Related U.S. Application Data
`
`(‘outinualion-in-part ul‘ application No. 117695.348.
`filed on Apr. 2. 2007. now l-‘:11. No. 7.786.455. whicl] is
`a continuation—in—part of application No. 117395.523,
`filed on Mar. 31. 2006. now Pat. No. 7.435.982.
`
`(51)
`
`Int. (11.
`
`GM] 3/’!!!
`GM} I/34
`I-HIIJ 63/08
`H05}! [/24
`U.S. (fl.
`
`(2006.01)
`(2006.01)
`(200601 )
`(2006.01)
`250.~‘503.1:250i’504 R; 2507365:
`313723131: 3157ll1.21;700e’12l: 7007166
`Field ofClassification Search
`250r’503.l.
`250504 R, 365: 313x'231.3l: 3-157111.21:
`7007121. 166
`See application file for complete Search history.
`
`(52)
`
`(58)
`
`108
`
`104
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`1
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`ASML 1115
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`ASML 1115
`
`

`
`US 7,989,786 B2
`Page 2
`
`OTHER PUBLICATIONS
`
`Beck. "Simple Pulse Generator for Pulsing Xenon Arcs with High
`Repetition Rate." Rev. Sci. Ii.I.m'mrI.. vol. 45. No. 2. Feb. 19'i4. pp.
`318-319.
`Raizcr. “Optical Discharges.“ Sov. Pt‘r_1's. Usp. 23(l1), Nov. 1980. pp.
`789-806.
`Fiedorowicz et al.. “X-Ray Emission f'om1I.aser-Irradiated Gas Puff
`Targets.”Ap;)i. Phys. Left. 62 (22). May 3 l. 1993. pp. 2778-2780.
`Keefer et al., “Experimental Study of a Stationary Laser-Sustained
`Air Plasma." Joarrmzt‘ ofidppiied Physics. vol. 46. No. 3. Mar. 1975.
`pp. 1080-1083.
`Jeng et al.. “Theoretical Investigation of I..aser-Sustained Argon Plas-
`mas.“ J'. Appi. Phys. 60 ('1'), Oct. 1. 1985. pp. 2272-22?9.
`l-'ra.nzen. “CW Gas Breakdown in Argon Using 10.6-pm Laser Radia-
`tion.“ Appi. Pirys. Le-1rt.. vol. 2|. No. 2. Jul. 15. 1972. pp. 62-64.
`Moody. “Maintenance ot'aGas Breakdown in Argon Using 10.6-pow
`Radiation." .iom'mzi cfAWiied Pi:_i-‘sin’. vol. 46. No. 6. Jun. 1925. pp.
`2475-2482.
`Generalov et al.. “E.‘v:peri1nenta1 Investigation of :1 Continuous Opti-
`cal Discharge." Soviet Pia)-‘sic: ..’i;'TP. vol. 34. No. 4. Apr. 1922. pp.
`763-769.
`
`Generalov et 51]., “Continuous Optical Discharge." Z!1ETFPi.\: Red.
`11. No. 9. May S. 1970. pp. 302-304.
`Kozlov at al. “Radiative Losses by Argon Plasma and the Emissive
`Model of :1 Continuous Optical Discharge.“ Sou Phys. JE Eff’. vol. 39.
`No. 3. Sop. 1974. pp. 463-468.
`Czlllhofli el al., "Contirlllmls Optical Discharges at Very High Pros-
`sure." Pa;.~.\-rm 103C. 1931. pp. 439-44?.
`Cremers et al.._ “Evaluation of the Continuous Optical Discha.I'ge for
`Spectrochemical Analysis,” Specrrvciriiriica Acre. vol. 4013. No. 4.
`1935. pp. 665-679.
`Kozlov er a1.. “Sustained Optical Discharges in Molecular Gases."
`Sov. Phys. Tecir. Pit)-'5. 49(l 1). Nov. 1979, pp. 1283-1281
`Keefer. “I .a_ser—Suslained Plasmas." Laser-irrduced Pia.\‘imzs' and
`Applications‘. published by Marcel Dekkcr. edited by Radzicmski ct
`al.. 1989. pp. 169-206.
`“Super-Quiet Xenon Lamp Super-Quiet Mercury-Xenon Lamp.”
`Hamairtafsu Pnoduci hifoi'ma.'i0i:. Nov. 2005. pp. 1-16.
`Hecht. “Refraction". Optics (Tirinri Editioii). I998. Chapter 4. pp.
`100-101.
`
`* cited by examiner
`
`2
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`

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`Aug. 2, 2011
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`2
`
`1
`LASER-DRIVEN LIGHT SOURCE
`
`RELATED APPLICATIONS
`
`This application is a continuation-in-part of U.S. Ser. No.
`1 li'695_.348. filed on Apr. 2, 2007. which is a continuation-im
`part of U.S. Set". No. 1 1895.523, filed on Mar. 31. 2006. the
`entire disclosures of which are incorporated by reference
`herein.
`
`FIELD OF THE INVENTION
`
`The invention relates to tnetliods and apparatus for provid-
`ing a laser-driven light source.
`
`BACKGROUND OF THE INVENTION
`
`High brightness light sources can be ttsed in a variety of
`applications. For example. a high brightness light source can
`be used for inspection, testing or measuring properties asso-
`ciated with semiconductor wafers or materials used in the
`
`fabrication of wafers (e.g.. reticles and photomasks). The
`electromagnetic energy produced by high brightness light
`sources can. alternatively. be used as a source ofilltnninatioii
`in a lithography system used in the fabrication ofwafers. a
`microscopy system. or a pliotoresist curing system. The
`parameters (e.g.. wavelength, power level and brightness) of
`the light vary depending upon the application.
`The state of the art in. for example. wafer inspection sys-
`tems involves the use of xenon or mercury arc lamps to
`produce light. The are lamps include an anode and cathode
`that are used to excite xenon or mercury gas located in a
`chamber of the lamp. An electrical discharge is generated
`between the anode and cathode to provide power to the
`excited (e.g.. ionized) gas to sustain the light emitted by the
`ionized gas during operation of the light source. During
`operation. the anode and cathode become very hot due to
`electrical discharge delivered to the ionized gas located
`between the anode and cathode. As a result. the anode andfor
`cathode are prone to wear and may emit particles that can
`contaminate the light source or result in failure of the light
`source. Also. these are lamps do not provide suflicient bright-
`ness for some applications. especially in the ultraviolet spec-
`trum. Furtlter. the position of the arc can be unstable in these
`lariips.
`E1 need therefore exists for improved high
`Accordingly.
`brightness light sources. A need also exists for improved high
`brightness light sources that do not rely on an electrical dis-
`charge to maintain a plasma that generates a high brightness
`light.
`The properties of light produced by many light sources
`(e.g.. arc l2t.t't'tpS_. microwave lamps) are affected when the light
`passes through a wall of. for example. a chamber that includes
`the location from which the light is emitted.
`Accordingly, a need therefore exists for an improved light
`source whose emitted light is not significantly affected when
`the light passes through a wall of a chamber that includes the
`location from which the light is emitted.
`
`SUMMARY OF THE INVENTION
`
`The present invention features a light source for generating
`a high brightness light.
`The invention in one aspect. features a light source having
`a chamber. The light source also includes an ignition source
`for ionizing a gas within the cliamber. The light source also
`
`5
`
`1D
`
`includes at least one laser for providing energy to the ionized
`gas within the chamber to produce a high brightness light.
`In some embodiments, the at least one laser is a plurality of
`lasers directed at a region from which the high brightness
`light originates. In some embodiments. the light source also
`includes at least one optical element for liiodi lying a property
`ofthe laser energy provided to the ionized gas. The optical
`element can be. for example. a lens (e.g.. an aplanatic lens. an
`achromatic lens_. a single element lens. and a fresnel lens) or
`mirror (e.g._. a coated mirror. a dielectric coated mirror. a
`narrow band mirror, and an ultraviolet transparent infrared
`retiecti ng mirror). In some enibodinients. the optical element
`is one or more fiber optic elements for directing the laser
`energy to the gas.
`The chamber can include an ultraviolet transparent region.
`The chamber or a window in the chamber can include a
`
`material selected from the group consisting of quartz. Supra-
`sildii quartz (I-Ieraeus Quartz America, LLC. Buford, Ga.]_.
`sapphire. MgI73. diamond, and (Talia. In some embodiments.
`the chamber is a sealed chamber. In some embodiiuents. the
`chamber is capable of being actively pumped.
`In some
`embodiments. the chamber includes a dielectric material
`(e.g., quartz). The chamber can be, for example, a glass bulb.
`In some embodiments. the chamber is an ultraviolet transpar-
`ent dielectric chamber.
`
`3n
`
`The gas can be one or more ofa noble gas, Xe. Ar, Ne. Kr.
`I-le. D3. H1. ()2, F3. at metal halide. a lialogeii. I-lg. Cd. Zn. Sn.
`Ga, Fe, Li, Na, an excimer forming gas, air. a vapor, a metal
`oxide. an aerosol. a flowing media. or a recycled media. The
`gas can be produced by a pulsed laser beam that impacts a
`target {c.g._. a solid or liquid) in the chamber. The target cart be
`a pool or film of metal. In some embodiments. the target is
`capable of moving. For example, the target may be a liquid
`that is directed to a region from which the high brightness
`light originates.
`In some embodiments, the at least one laser is multiple
`diode lasers coupled into a fiber optic element. In some
`embodinieiits, the at least one laser includes a pulse or con-
`tinuous wave laser. In some embodiments. the at least one
`laser is an IR laser. a diode laser. a fiber laser. an ytterbium
`laser. a C0; laser. a YAG laser. or a gas discharge laser. In
`some embodiments, the at least one laser emits at least one
`wavelength of electromagnetic energy that
`is strongly
`absorbed by the ionized medium.
`The ignition source can be or can include electrodes. an
`ultraviolet ignition source. a capacitive ignition source. an
`inductive ignition source. ati RI’ ignition source. a microwave
`ignition source. a liash lamp. a pulsed laser, or a pulsed lamp.
`The ignition source can be a continuous wave {CW} or pulsed
`laser impinging on a solid or liquid target in the chamber. The
`ignition source can be extenial or intenial to the chamber.
`The light source can include at least one optical element for
`modifying a property of electromagnet ic radiation emitted by
`the ionized gas. The optical element can be. for example. one
`or more mirrors or lenses. In some eiitbodiuients. the optical
`element is configtired to deliver the electromagnetic radiation
`emitted by the ionized gas to a tool (e.g._. a wafer inspection
`tool, a microscope, a metrology tool, a lithography tool. or an
`endoscopic tool).
`The invention. in another aspect. relates to a method for
`producing light. The method involves ionizing with an igni-
`tion source a gas within a chamber. The method also involves
`providing laser energy to the ionized gas in the chamber to
`produce a high brightness light.
`In some embodiments. the method also involves directing
`the laser energy tliriough at least one optical element for
`modifying a property of the laser energy provided to the
`20
`20
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`US ?,989,786 B2
`
`ionized gas. 111 some embodiments. the method also involves
`actively pumping the chamber. The ionizable medium can be
`a moving target. In some embodiments_. the method also
`involves directing the high brightness light through at least
`one optical element to modify a property of the light. In some
`embodiments, the method also involves delivering the high
`brightness light emitted by the ionized medium to a tool (e.g..
`a wafer inspection tool. a microscope. at metrology tool. a
`lithography tool, or an endoscopic tool).
`In another aspect. the invention features a light source. The
`lights source includes a chamber and an ignition source for
`ionizing an ionizable medium within the chamber. The light
`source also includes at least one laser for providing substan-
`tially continuous energy to the ionized medium within the
`chamber to produce a high brightness light.
`In some embodiments. the at least one laser is a continuous
`wave laser or a high pulse rate laser. In some embodiments.
`the at least one laser is a high pulse rate laser that provides
`pulses ofenerg to the ionized medium so the high brightness
`light is substantially continuous. In some embodiments. the
`magnitude of the high brightness light does not vary by more
`than about 90% during operation. In some embodiments. the
`at least one laser provides energy substantially continuously
`to minimize cooling of the ionized rnedium when energy is
`not provided to the ionized medium.
`In some cnibodiments. the light source can include at least
`one optical element (e.g.. a lens or mirror) for modifying a
`property of the laser energy provided to the ionized medium.
`The optical element can be. for example, an aplanatic lens. an
`achromatic lens, a single element lens, a fresne] lens, a coated
`mirror, a dielectric coated mirror, a narrow band mirror_. or an
`ultraviolet trzuisparent
`infrared reflecting mirror. In some
`embodiments. the optical element is one or more fiber optic
`elements for directing the laser energy to the ionizable
`medium.
`111 some embodiments. the chamber includes an ultraviolet
`transparent region. In some embodiments. the chamber or a
`window in the chamber includes a quartz material. suprasil
`quartz material. sapphire material. Mgl-'2 material. diamond
`material. or Cal-'2 material. In some embodiments. the cham-
`ber is a sealed chamber. The chamber can be capable ofbeing
`actively pumped.
`In some embodiments.
`the chamber
`includes a dielectric material (e.g.. quartz). In some en1bodi—
`ments. the chamber is a glass bulb. In some embodintents. the
`chamber is an ultraviolet transparent dielectric chamber.
`The ionizable medium can be a solid. liqtrid or gas. The
`ionizable medium can include one or more o fa noble gas. Xe,
`Ar. Ne. Kr, I-le. D3, [-13, ()3, F3. :1 metal halide_. a halogen, I-lg.
`Cd. Zn. Sn. Ga. Fe, Li. Na. an excimer forrning gas. air. a
`vapor. a metal oxide, an aerosol, a flowing media. a recycled
`media. or an evaporating target. In some embodiments. the
`ionizable medium is a target in the chamber and the ignition
`source is a pulsed laser that provides a pulsed laser beam that
`strikes the target. The target can be a pool or film of metal. In
`sortie embodiments. the target is capable of moving.
`In some embodiments. the at least one laser is multiple
`diode lasers coupled imo a fiber optic element. The at least
`one laser can emit at least one wavelength of electromagnetic
`energy that is strongly absorbed by the ionized medium.
`The ignition source can be or can include electrodes. an
`ultraviolet ignition source. a capacitive ignition source. an
`inductive ignition source. an RF ignition source, a microwave
`ignition source, a flash lamp. a pulsed laser. or a pulsed lamp.
`The ignition source can be external or internal to the chamber.
`In some embodiments, the light source includes at least one
`optical element (e.g.. a mirror or lens) for modifying a prop-
`erty of electromagnetic radiation emitted by the ionized
`
`1U
`
`medium. The optical element can be configured to deliver the
`electromagnetic radiation emitted by me ionized meditun to a
`tool (e.g.. a wafer inspection tool. a microscope, at metre-logy
`tool. a lithography tool. or an endoscopic tool).
`The invention. in another aspect relates to a method for
`producing light. The method involves ionizing with an igni-
`tion source an ionizable medium within a chamber. The
`
`method also involves providing substantially continuous
`laser energy to the ionized medium in the chamber to produce
`a high brightness light.
`In some embodiments. the method also involves directing
`the laser energy through at least one optical element for
`modifying a property of the laser energy provided to the
`ionizable medium. The method also can involve actively
`pumping the chamber. In some embodiments. the ionizable
`medium is a moving target. The ionizable medium can
`include a solid.
`liqtrid or gas. In some embodiments. the
`method also involves directing the high brightness light
`through at least one optical element to modify a property of
`the light. In seine einbodiments. the method also involves
`delivering the high brightness light emitted by the ionized
`medium to a tool.
`The invention. in another aspect, features a light source
`having a chamber. The light source includes a first ignition
`means for ionizing an ionizable medium within the chamber.
`The light source also includes a means lbr providing substan-
`tially continuous laser energy to the ionized medium within
`the chamber.
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`The invention. in another aspect, features a light source
`having a chamber that includes a reflective surface. The light
`source also includes an ignition source for ionizing a gas
`within the chamber. The light source also includes a reflector
`that at least substantially reflects a first set of predefined
`wavelengths of electromagnetic energy directed toward the
`reflector and at least substantially allows a second set of
`predefined wavelengths of electromagnetic energy to pass
`through the reflector. The light source also includes at least
`one laser (e.g._. a continuous-wave fiber laser) external to the
`chamber for providing electromagnetic energy to the ionized
`gas within the chamber to produce a plasma that generates a
`high brightness light. A continuous-wave laser emits radia-
`tion continuously or substantially continuously rather than in
`short bursts, as in a pulsed laser.
`In some embodiments. at least one laser directs a first set of
`wavelengths of electromagnetic energy through the reflector
`toward the reflective surface [e.g.. inner surface) ofthe cham-
`ber and the reflective surface directs at least a portion ofthe
`first set ofwavelengths ofelectromagnetic energy toward the
`plasma. I11 some embodiments. at least a portion of the high
`brightness light is directed toward the reflective surface ofthe
`chamber. is reflected toward the reflector. and is reflected by
`the reflector toward a tool. In some embodi1nents_. at least one
`laser directs a first set of wavelengths of electromagnetic
`energy toward the reflector. the reflector reflects at least a
`portion of the first wavelengths of electromagnetic energy
`towards the reflective surface ofthe chamber. and the reflec-
`tive surface directs a portion ofthe first set ofwavelengths of
`electromagnetic energy toward the plasma.
`In some embodiments. at least a portion of the high bright-
`ness light is directed toward the reflective surface of the
`chamber. is reflected toward the reflector. and passes through
`the reflector toward an output of the light source. In some
`e1nbodiments_. the light source comprises a microscope. ultra-
`violet microscope, wafer inspection system, reticle inspec-
`tion system or lithography system spaced relative to the out-
`put of the light source to receive the high brightness light. In
`some embodiments, a portion of the high brightness light is
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`is
`directed toward the reflective surfboe of the chamber.
`reflected toward the reflector. and electromagnetic energy
`comprising the second set of predefined wavelengths of elec-
`tromagnetic energy passes through the reflector.
`The chamber of the light source can include a window. In .3
`some embodiments, the chamber is a sealed chamber. In some
`embodiments, the reflective surface of the chamber com-
`prises a curved shape. parabolic shape. elliptical shape.
`spherical shape or aspherical shape. In some embodiments.
`the chamber has a reflective inner surface. 111 some embodi-
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`ments, a coating or film is located on the outside of the
`chamber to produce the reflective surface. In seine embodi-
`ments, a coating or film is located on the inside ofthe Cl1Ei.t'I'1l'JCl'
`to produce the reflective surface. In some embodinients. the
`reflective surface is a structure or optical element that is
`distinct from the inner surface of the chamber.
`
`The light source can include zm optical element disposed
`along a path the electromagnetic energy from the laser travels.
`In some embodiments. the optical element is adapted to pro-
`vide electromagnetic energy from the laser to the plasma over
`a large solid angle. In some embodiments. the reflective sur-
`face of the chamber is adapted to provide electromagnetic
`energy from the laser to the plasma over a large solid angle. In
`some embodiments. the reflective surface of the chamber is
`adapted to collect the high brightness light generated by the
`plasma over a large solid angle. In some embodiments. one or
`more of the reflective surface. reflector and the window
`include (e.g.. are coated or include} a material to filter pre-
`defined wavelengths (e.g.. infrared wavelengths of electro-
`magnetic energy] of electromagnetic energy.
`The invention. inanotheraspect. features a light sourcethat
`includes a chamber that has a reflective surface. The light
`source also includes an ignition source for ionizing a gas
`within the chamber. The light source also includes at least one
`laser external to the chamber for providing electromagnetic
`energy to the ionized gas within the chamber to produce a
`plasma that generates a high brightness light. The light source
`also includes a reflector positioned along a path that the
`electromagnetic energy travels from the at least one laser to
`the reflective surface of the chamber.
`
`In some embodiments. the reflector is adapted to at least
`substantially reflect a first set of predefined wavelengths of
`electromagnetic energy directed toward the reflector and at
`least substantially allow a second set of predefined wave-
`lengths of electromagnetic energy to pass through the reflec-
`tor.
`
`The invention, in another aspect. relates to a method for
`producing light. The method involves ionizing with an igni-
`tion source a gas within a chamber that has a reflective sur-
`face. The method also involves providing laser energy to the
`ionized gas in the chamber to produce a plasma that generates
`a high brightness light.
`In some embodiments, the method involves directing the
`laser energy comprising a first set of wavelengths of electro-
`magnetic energy through a refltxtor toward the reflective
`surface of the chamber. the reflective surface reflecting at
`least a portion of the first set of wavelengths of electromag-
`netic energy toward the plasma. In some embodiments. the
`method involves directing at least a portion ofthe high bright-
`ness light toward the reflective surface of the chamber which
`is reflected toward the reflector and is reflected by the reflec-
`tor toward a tool.
`In some embodiments, the method involves directing the
`laser energy comprising a first set of wavelengths of electro-
`magnetic energy toward the rellector. the reflector refiects at
`least a pt)t1i0t’t of the first wavelengths of electromagnetic
`energy toward the reflective surface of the chamber.
`the
`
`reflective surface directs a portion of the first set of wave-
`lengths ofelcctromagnetic energy toward the plasma. In some
`embodiments, the method involves directing a portion ofthe
`high brightness light toward the reflective surface of the
`chamber which is reflected toward the reflector and. electro-
`magnetic energy comprising the second set of predefined
`wavelengths of electromagnetic energy passes through the
`reflector.
`The method cart involve directing the laser energy through
`an optical element that modifies a property ofthe laser energy
`to direct the laser energy toward the plasma over a large solid
`angle. In some embodiments. the method involves directing
`the laser energy through an optical element that modifies a
`property of the laser energy to direct the laser energy toward
`the plasma over a solid angle of approximately 0.012 stera—
`dians. In some embodiments, the method involves directing
`the laser energy through an optical element that modifies a
`property of the laser energy to direct the laser energy toward
`the plasma over a solid angle of approximately 0.048 stera-
`dians. In some embodiments. the method involves directing
`the laser energy through an optical element that modifies a
`property of the laser energy to direct the laser energy toward
`the plasma over a solid angle of greater than about 2:’: (about
`6.28) steradians. In seine enibodiments, the reflective surface
`of the chamber is adapted to provide the laser energy to the
`plasma over a large solid angle. in some embodiments. the
`reflective surface of the chamber is adapted to collect the high
`brightness light generated by the plasma over a large solid
`angle.
`The invention. in another aspect, relates to a method for
`producing light. The method involves ionizing with an igni-
`tion source a gas within a chamber that has a reflective sur-
`face. The method also involves directing electromagnetic
`energy from a laser toward a reflector that at least substan-
`tially reflects a first set of wavelengths of electromagnetic
`energy toward the ionized gas in the chamber to produce a
`plasma that generates a high brightness light.
`In some embodiments, the electromagnetic energy from
`the laser first is reflected by the reflector toward the reflective
`surface of the chamber.
`l.n sortie embodiments, the electro-
`magnetic energy directed toward the reflective surface of the
`chamber is reflected toward the plasma. In some embodi-
`ments. a portion ofthe high brightness light is directed toward
`the reflective surface of the chamber. reflected toward the
`reflector and passes through the reflector.
`In some embodiments. the electromagnetic energy from
`the laser first passes tfuough the reflector and travels toward
`the reflective surface of the chamber. In some embodiments,
`the electromagnetic energy directed toward the reflective sur-
`face of the chamber is reflected toward the plasma. In some
`embodiments. a portion of the high brightness light is directed
`toward the reflective surface of the chamber, reflected toward
`the reflector and reflected by the reflector.
`The invention. in another aspect. features a light source that
`includes a chamber having a reflective surface. The light
`source also includes a means for ionizing a gas within the
`chamber. The light source also includes a means for at least
`substantially reflecting a first set ofpredefined wavelengths of
`electromagnetic energy directed toward the reflector and at
`least substantially allowing a second set of predefined wave-
`lengths of electromagnetic energy to pass through the reflec-
`tor. Thc light sottrcc also includes a means for providing
`electromagnetic energy to the ionized gas within the chamber
`to produce a plasma that generates a high brightness light.
`The invention. in another aspect, features a light source that
`includes a sealed chamber. The light source also includes an
`ignition source for ionizing a gas within the cliamber. The
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`In some embodiments. the light source also includes an
`ignition source for ionizing the gas within the chamber. The
`ignition sottrce can include electrodes. an ultraviolet ignition
`source, a capacitive ignition source. an inductive ignition
`source. a flash lamp, a pulsed laser. or a pulsed lamp. The
`ignition source can include electrodes located on opposite
`sides of the plasma.
`In some embodiments, the light source also includes a
`support element that
`locates the chamber relative to the
`reflector. The support element can include a fitting to allow at
`least one of pressure control or filling of the chamber.
`In sotne embodiments. the light source includes at least one
`optical element. The optical element can modify a property of
`the light emitted through the walls of the chamber and
`reflected by the reflector. The optical element can be a mirror
`or a lens. The optical element can be configured to deliver the
`light emitted through the walls of the chamber rmd reflected
`by the reflector to a tool (e.g. a wafer inspection tool, a
`microscope. an ultraviolet microscope. a reticle inspection
`system. a metrology tool. a lithography tool. or an endoscopic
`tool}.
`The invention. in another aspect. features a method for
`producing light. The method involves emitting a light through
`the walls of a chamber. The method also involves using a
`reflective surface ofa reflector to reflect the light. wherein the
`reflective surface has a shape configured to compensate for
`the refractive index of the walls of the chamber.
`In some embodiments, the method also involves flowing
`gas into the chamber. In some embodiments. the method also
`involves igniting the gas in the chamber to produce an ionized
`gas. In some embodiments. the method also involves direct-
`ing energy to the ionized gas to produce a plasma that gener-
`ates a light (e.g. a high brightness light). In some embodi-
`tttcnts. the method also involves directing laser energy into
`the chamber from at least one laser extemal to the chamber. In
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`light source also includes at least one laser external to the
`sealed chamber for providing electromagnetic energy to the
`ionized gas within the chamber to produce a plasma that
`generates a high brightness light. The light source also
`includes a curved reflective surface disposed external to the
`sealed chamber to receive at lcas a portion of the high bright-
`ness light emitted by the sealed chamber and reflect tl1c high
`brightness light toward an output ofthe light source.
`In some embodiments. the light source includes an optical
`element disposed along a path the electromagnetic energy
`from the laser travels. In some embodiments, the sealed
`chamber includes a support element that locates the sealed
`chamber relative to the curved reflective sttrface. In some
`
`embodi