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`US007786-45532
`
`U?)
`
`United States Patent
`Smith
`
`(10) Patent No.:
`(45; Date of Patent:
`
`US 7,786,455 B2
`Aug. 31. 2010
`
`355.-"2311
`315.-111.21
`355.-"2312
`. 315-111.31
`313.-53.1
`359.-‘S53
`31351534
`362.-"258
`3'i'2.'5
`250."5L|4R
`363-"240
`
`
`
`lairlcycinl.
`9:200:
`5.238.730 Bl
`7-"2502 Brooks 5: 51.
`5.417.525 B1 -=
`9.-"2504 Lange ......... ..
`5.153.404 B2
`5.955.329 132* 15.2005 1115515..-mi.
`7.552.430 131*
`122010
`tit-15.555
`2002-0021505 Al
`2.-"2502
`lshihnra
`21103.-'(}l68982 Al
`9-‘Z3003 Kim ......... ..
`2003 0231495 Al
`ll-"2003 Sate at :1].
`2Dl]4.'l'}264513 AI‘
`ll-‘"2004
`llafllove ct nl.
`200111167613 AI "
`8.-‘E0115 Hrishino at :11.
`3{l|]7"D3S592l Al‘°
`ll.-‘"2007 7.LI[i1'I‘lE1al.
`
`(54)
`
`(751
`
`(73)
`
`LASER-DRIVEN LIGIIT SOURCE
`
`l1'l\.'t;.“1]T.01'Z Donald K. Smith. I3clt11ottL MA {US}
`
`A:-tsignec: Eucrgctiq 'l"cchu0l0g_v. lnc.. Woburn.
`MA (US)
`
`[*1
`
`Notice:
`
`Su Inject to any disclaimer. the term of this
`patent is extended or adjusted under 35
`U.S.('. 154th) by 820 days.
`
`(21)
`
`Appl. N11,: 112595.343
`
`(231
`
`Filed:
`
`Apr. 2, 2110'?
`
`(551
`
`(631
`
`(51)
`
`(53)
`
`(531
`
`(56)
`
`Prior Publication Data
`
`[C‘nn1iuuedl
`
`US ?.O07t’0228300 A1
`
`Oct. 4. 2007
`
`FOREIGN PATENT DOCUMENTS
`
`Related U.2 .Application Data
`
`JP
`
`fil-193358
`
`S-"1936
`
`Ccmlinuiitiun-iii-pan 01" application No. 113395.523.
`filed on Mar. 31. 2006. now Put. N11. 1435.982.
`
`Int. (.‘1.
`H053 31'/26
`(2005.01)
`GOIJ 3/I0
`(2005.01)
`G216 -I/00
`(200501;
`(2(}U0'.t}l}
`I-MIJ 6}/28
`25tll493.1;250f50-1 R:
`U.S. (fl.
`3151111.21:3151111.71:3l51’ll|.9l:3l?-£231.31:
`313K231 .41; 313123] .71
`Field 01' Classification Search ........... ..
`250/-123 R.
`25111423 P. 424. 426. 494.1. 403.1. 504 R.
`250150-1 H: 3115!] 11.21. 111.71. 111.9]:
`313123131.231.41.231.61. 331.71. 631.
`3131632. 633
`See application lilc fur complete search liistnry.
`References Cited
`
`U .8. PATENT DOCUMENTS
`
`I-1.{J¥13.EJ66 A "‘
`4.-198.1129 A '7‘
`4.fi45.2lS A
`RF32.G26 If
`
`“
`
`5-‘ E973
`251985
`11987
`3.-"1988
`
`Samis
`Yushizawn etal.
`Levin et al.
`Ynshiznwaei al.
`
`313-131.51
`315139
`3fi2.’296
`3153*";
`
`OTI-IER PUl3l.1C'A1'l0NS
`
`Wilbcrs ct :11.. “'l'l1c VIJV lsinissivity 01' a lligh-Pressure Cascade
`ArgunArc l‘rorn 1.2510 200 n1'n.“.f. g_3mm:_ Spa'r1'm,s'£‘. Radial. i'i‘a::.1-—
`ft-r. 551. 45. 1091.55. 290-303.
`
`t'C'u:mlinued)
`
`Prtiiiury }<.‘.-.mnEmu-—-Bcrtiard E Sc-uw
`{T4} .~1.ft‘rir.nejI‘, .-fgeiit‘, or Firm Pruskaller Rust.‘ I.I_.l3'
`
`( 57 1
`
`.-\BS TR.-\(.‘T
`
`An apparatus for pmdncing light includes a cl‘l£LL]1l3t:1‘ and an
`ignition source that ionizcs a gas within the cltaunhcr. 'l‘l1c
`ztpparallts also includes at least one laser that ['1l'L‘IViClL"l~'- energy
`to 1111:
`iun.i7,i-:d gas within the cliarnbcr to produce 8 high
`brightness light. T111: laser can pl‘t‘J\u"l(.lC a sttbstuiiliaily cun-
`linuoni-; amount 0.1‘ energy to the ionized gas to generate a
`substantially coitlittucaus high brightness light.
`
`43 Claims. 8 Drawing Sheets
`
`228
`
`
`
`ASML 1119
`ASML 111%
`
`

`
`US 7,736,455 132
`Page 2
`
`US. PATENT DOCUMENTS
`
`2009.-'0(}32'.-'40 .—'\l"'
`
`Z.'2lJ(}S| Smilll et al.
`
`250.-'5I'.l3.l
`
`OTHER PUBLICATJONS
`
`Wilbers cl 31.. “The Fonrinuuin Flnission of an Air: Plasma." J.
`Qmrmi. Specrmsc. Kadiczr.
`.D'ans_,"a'. vol. 45. No. 1. 1991. pp. l-10.
`Bock. "Simple Pulse Gencralor for Pulsing Xenon Arcs with High
`Repeiilion Rate." Rev. Sci. mm-m.u.. vol. 45. No. 2. Feb. 1974. pp.
`313-319.
`R:-lizer. “Op$ic.'IJ Discl1u:gos."."Ia1: Phys. Lrfip. 23{_l J]. Nov. 1980.
`789-304.5.
`Fiedorowicz el a.l.. “X-Ray Elnission fortn Laser-Irradiated Gas Puff
`Ta.Ige‘zs."App."_ Phys. Lerr. 52 (223. May 31, 1993. pp. z'.r7s~27sn.
`Keeliar at £11.. "F.xp::riman1al Study of a Stationary I.aser—Su:nained
`Air Plasma." Jourmzl qfxtppliad Physics. vol. 46. No. 3. Mar. 1975.
`pp. [U80-1083.
`long at nl., “Theoretical Invesl'igation ut'I_:i.-aer-Siistained Angon Plas-
`mas.“ J’. Appl. PJ!_1-'.~‘. 60 (T). Uzi.
`l. 1936. pp. 227.‘.-327‘).
`Franzen. "CW fins Breakdown in Argon Using lfl.t'1-pm Laser Radia-
`tion," Appl. Phys. Le=.n‘.. vol. 21. No. 2. Jul. 15. I972, pp. 152-64.
`Moody. “Maintenance ofa Gas Breakdown in Argon Using. [(1 .6-pow
`Radiation." Jaw-no.’ qfAppIied F'.~‘:ysi'c.r. vol. --16. No. l5,.lu11. 1975. pp.
`1475-2482.
`
`Generalov el al.. "E:4:perimenJnl lnvesfigation ofa Continuous Opti-
`cnl Discha.I'gs." Sc‘-14:‘! PI.I_v5’1'r‘s.!;E’TP. vol. 34. No. -1. Apr. I973. pp.
`"H33-769.
`
`Gcnuralov cl‘ al.. "Continuous Optical Disclinrge." ZIEETF-’P:'s'. Rod.
`l 1. No. 9. May S. 1970. pp. 302-304.
`Kozlov at 3.1.. "Radiative Losses by Argon Plasma and the limissivc
`Model ofn Fonlinuotls Optical Discharge." Sm: Plays. ..-‘T5 H". vol. 3‘).
`No. 3. Sep. 1974. pp. 463-168.
`Car|hofl'cI nJ.. “|’.‘-nntinuotls Optical Discharges at Very High Pres-
`sure."PJ'r}'sir.'a 103C. l98l. pp. 439447.
`Cnamarss el al.. "F.va]ua1ion of the Continuous Opl icnl Discharge for
`Spcctrochcmical Analysis.“ Spwtmrhiniica Arm. vol. 4013. No. 4.
`1935. pp. 555-579.
`Kozlov :1 al.. “Sustained Option] Ifischzugcs in Molecular Gnscs."
`Sm; Pig-'5. Ti-r.&.PJ:_|r.\'. -19(1l).Nov. 1979. pp. 1233-1237.
`Keefer. “Laser-Sustained Plasmas." I.a.mr—Indm-ed Phzsirnas and
`.-l'ppIirn.rt'a:r.I'. published by Marcel Dekker. edited by R11c|7:ierns}u' el
`ziI.. l9S9.pp. I69-206.
`Ila.I'na.m:iisu Product Inforrnation, "Super-Quiet Xenon Lamp Super-
`Quiet Mcrctlry-Xenon L:J.mp." Nov. 20:15.
`
`* cited by exaniiiicr
`
`

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`U.S. Patent
`
`Aug. 31, 2010
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`Sheet 1 of8
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`US 7,786,455 B2
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`Aug. 31, 2010
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`narrow band minor, and an ultraviolet transparent infrared
`rieflectiiig mirror]. in some enihodiments, 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 cltamber or a window in the chamber can include a
`material selected from the group consisting ofquartz. Supra-
`sil® quartz (Heraeus Quartz America. LLC. Buford. Ga].
`sapphire. Mgliz. diamond. and C‘aF—_,. In some enibodintents.
`the cliarnber is a sealed chamber. In some ernbodiments. the
`chamber is capable of being actively pumped.
`In some
`cmborlintcnts, Lhe chamber includes a dielectric tnaterial
`(e.g._. quartz}. The chamber can be. For example. a glass bulb.
`In some embodiments. the chamber is an ultraviolet transpar-
`ent dielectric chamber.
`
`‘J!
`
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`
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`
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`LASER-DRIVEN LIGIIT SOURCE
`
`R]-El_.A'l‘|-ED AI=‘PL.lCA'l'[ONS
`
`This application is a continuation-in-part ofU.S. Ser. No.
`1 1895.523. tiled on Mar’. 31, 2006. now US. Pat. No. 7.435,
`982. tl1e entire disclosure of which is incorporated by refer-
`ence herein.
`
`I"ll;‘Ll) OI’ TI-Iii lNV'l?.N'l'ION
`
`The invention relates to methods and apparatus for provid-
`ing a laser-driven light source.
`
`BACKGROUND OF THE INVENTION
`
`lligh brightness light sources can be used in a variety of
`applications. For example, a high brightness light source cart
`be used for inspection. testing or measuring. properties asso-
`ciated with semiconductor wafers or materials used in the
`
`fabrication of waters (e.g.. reticles and photomasks). The
`electromagnetic energy produced by high brightness lights
`sources can. alternatively. be used as a source of illumination
`in a lithography system used in the tiihrication of waters. a
`microscopy systems. or a photoresist curing system. The
`parameters l_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 rnercury gas located in a
`chamber of the lamp. An electrical discharge is generated
`between the anode and cathode to provide power to the
`excited t_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
`electt'ical 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 cart
`contaminate the lig.ht source or result in failure ol‘ the light
`source. Also. these are lamps do not provide sullicient bright-
`ness for some applications, especially in the ultraviolet spec—
`trum. Further. the position of the arc can be unstable in these
`lamps.
`Accordiiigly. a need therelotc exists for improved high
`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.
`
`SUMMARY or='n-112 INV'1iN't‘l()N
`
`The present invention features a light source for generating
`a high briflttness light.
`The invention. itt one aspect. leatures a light source having
`a chamber. The light source also includes an ignition source
`for ionizing a gas within the chamber. The light source also
`includes at least one laser for providing energy to the ionized
`gas within the charnber to produce a high briglttncss light.
`In some embodinients. 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 tor modi lying a property
`of the 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
`ntirror (e.g.. a coated minor. a dielectric coated mirror. at
`
`The gas can be one or more ul'a noble gas. Xe, Ar. Ne. Kr,
`He, D3, Hz. (J._._. F2. at metal halide. a halogen. Ilg, Cd, 211, Sn.
`Ga. I"-‘e. 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 (e.g.. a solid or liquid) in the chamber. The target can be
`a pool or film of metal. In some emboditneitts, the target is
`capable of moving. For example. the target may be a liquid
`that is directed to at 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
`embodiments. Lhc at least one laser inclttdes 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. on ytlerhiunt
`laser. a C0: laser. a YAG laser. or a gas discharge laser. In
`some ernbodiniettts, the at least one laser emits at least one
`wavelength of electromagnetic energy that
`is strongly
`absorbed by the ionized mediiun.
`The ignition source can be or can include electrodes. an
`ultraviolet ignition source. a capacitive ignition source, an
`inductive ignition sottrce. an R]? ignition source. a microwave
`ignition source. a flasli lamp. a pulsed laser, or a pulsed lamp.
`The ignition source can be a continuous wave (CW l or pu lscd
`laser impinging on a solid or liquid target in the chamber. The
`ignition source can be external or internal to the chamber.
`The light source can include at least one optical element for
`rnocli lying a property ofelectromagnet ic radiation emitted by
`the ionized gas. The optical element can be, for example. one
`or more minors or lenses. 111 some embodiments. the optical
`element is couligured to del iver 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 too] ).
`The invention, in another aspect. relates to El 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.
`ln 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
`ionized gas. In some er1.tbodi_mr:rtts. the method also involves
`actively pumping the chamber. The ionizable rncdium can be
`a moving target. In some embodiments. the method also
`involves directing the high brightness light through at least
`one optical element to rnodily a property ofthe light. In some
`embodiments. the method also involves delivering the high
`' brightness light emitted by the ionized medium to a tool (eg._.
`a wafer inspection tool. a l11lC1't‘I5Ct)ptl‘. a tnetrology tool. a
`lithography tool. or an endoscopic tool).
`
`3t:
`
`40
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`
`3
`
`4
`
`US 7.'?86,455 B2
`
`In another aspect, the invention features a light source. The
`lights source includes a chamber and an igmtioii source for
`ionizing an ioiiirrable medium within the chamber. The light
`source also includes at least one laser for providing substan-
`tially contirtuous energy to the ionized medium within the
`cltantber to produce a big: brightness light.
`In some embodintents. the at least one laser is a continuous
`
`wave laser or a high pulse rate laser. In some embodiments.
`tl1e at least one laser is a high pulse rate laser that provides
`pulses ofenergy to the ionized rnediurn so the high brightness
`light is substantially continuous. In some embodiments. the
`magnitude ofthe high brightness light does not vary by more
`than about 90% during operation. In some embodiments. the
`at least one laser provides energy substantially continttottsly
`to iitiitintizc cooling of the ionized medium when energy is
`ttot provided to the ionized medium.
`In some embodiments, the ligltt 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 l'resnel lens. a coated
`mirror. a dielectric coated mirror, a narrow band mirror. or an
`ultraviolet transparent
`infrared reflecting mirror.
`In some
`embodimcnts. the optical element is one or more fiber optic
`elements for directing the laser energy to the ionizahle
`medium.
`In some emboditnents. 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. MgF2 material. diamond
`material, or Cal’; material. In some embodiments. the cham-
`ber is a sealed chamber. The chamber can be capable o fbcirtg
`actively ptunped.
`In some embodiments,
`the chamber
`includes a dielectric material (e.g., quartz). In some embodi-
`ments. the chamber is a glass bulb. In some embodiments. the
`chamber is an ultraviolet transparent dielectric chamber.
`The ionizable medium can he a solid. liquid or gas. 'Ilte
`ionizable medium can include one or more of a noble gas. Xe.
`Ar. Ne, Kr. l-Ie. D3. I-I2. 02, F1. :1 metal halide. a halogen, I-lg.
`Cd, Zn, Sn. Ga. Fe. Li. Na. an cxcimcr fnrntirtg gas. air. a
`vapor. a metal oxide. an aenvsol. :1 {lowing media. it 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 he a pool or film of metal. In
`some enibodiments. the target is capable of moving.
`In some embodiments, the at least one laser is multiple
`diode lasers coupled into a liber optic element. The at least
`one laser can emit at least one wavelength ol'elect.m1nagnetic
`energy that is strongly absorbed by the ionized medium.
`"Ihc ignition source can be or can include electrodes. an
`ultraviolet ignition source. a capacitive ignition source. an
`inductive ignition source, an RI’ ignition sottrce. a microwave
`ignition source. at 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 (eg. a minor or lens] for modifying a prop-
`erty of electromagnetic radiation emitted by the ionized
`medium. The optical element can be configured to deliver the
`electromagnetic radiation 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 1.
`The invention. in another aspect relates to a method for
`producing light. ‘the ntethod involves ionizing with an igni-
`tion sourcc an ionizable medium within a chamber. The
`
`‘Jr
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`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 tor
`ntodifying a property of the laser energy provided to the
`ionizable medium. The method also can involve actively
`pumping. the chamber. In some embodiinents. the ionizahle
`medium is a moving target. The ionizahle ntedittrn can
`include a solid. liquid or gas. In some entbodiments. the
`method also involves directing the high brighmess light
`through at least one optical element to modify a property ol’
`the light. In some embodiments. 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 chatnber. The light source includes a first ignition
`means for ionizing an ionizablc medium within the chamber.
`The light source also includes a means for providing substati-
`tially continttous laser energy to the l0l1l?"L-.‘.Cl medium within
`the cllamber.
`The invention. in another aspect. features a light source
`having a cltamber that includes a reflective surface. 'l'"hc light
`source also includes an igiition source for ionizing a gas
`within the churnbcr. The light‘ source also includes a rcllector
`that at least substantially rellects a first set of predefined
`wavelengths of electromagnetic energy directed toward the
`reflcctor and at least‘ substantially allows a second set of
`predefined wavelengths of electromagnetic energy to pass
`tltrough the retlcctor. The light source also includes at least
`one laser (c.g.. a continuous-wave fiber laser} external to the
`chamber for providing electromagnetic energy to the ionized
`gas within the chatttbcr 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 direct s a first set of
`wavelcrtgtlis of electromagnetic eiiergy through the reflector
`toward the rellective surface [e.g.. inner surface] of the cham-
`ber and the reflective surlace directs at least a portion olthe
`first set ofwavelengths olleleclromagnetie energy toward the
`plasma. In some embodiments. at least a portion of the high
`brightness light is directed toward the reflective surface of the
`chamber. is rellccted toward the reflector. and is rcflected by
`the rcflectortoward a tool. In some embodiments. at least one
`
`laser directs a first set of wavelengths of electromagnetic
`energy toward the retlcctor. the reflector reflects at least a
`portion of the first wavelengths of electrotttagttetic energy
`towards the reflective surface of the chamber, and the reflec-
`tive surface directs a portion of the I'lt'SI set of wavelengths of
`electromagnetic energy toward the plasma.
`In some embodiments. at least a portion ofthc high bright-
`ness light is directed toward the reflective surface of the
`chamber. is reflected toward the rellector. and passes througlt
`the reflector toward an output of the light source. In some
`embodiments. the light source comprises a microscope. ultra-
`violet microscope, wafer inspection system. reticie inspec-
`tion system or lithography system spaced relative to the out-
`put ofthe light source to receive the high brightness light. In
`some embodiments. a portion of the high hriglitness light is
`directed toward the reflectivc surface of the chamber.
`is
`
`reflected toward the rellector. and electromagnetic energy
`comprising the second set ofpredefined wavelengths ot'elec-
`tromagnetic energy passes through the reflector.
`The chamber of the light source can inclttdc a window. In
`some embodiments. the chamber is a sealed chamber. In some
`embodiments. the reflective surface of die chamber corn-
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`US 7.'?86,455 B2
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`prises a curved shape. parabolic shape. elliptical shape.
`splterical shape or asplterical shape. In some embodiments.
`the chamber has a reflective inner surface. in some embodi-
`
`magnetic energy comprising the second set of predefined
`wavelengtlis of electromayetic energy passes tlirough the
`reflector.
`
`ments. a coating or film is located on the outside of the
`cltatnber to produce tlte reflective surface. In some embodi-
`ments. is coatiugor film is located on the inside o fthe chnrnber
`to produce the reflective sttrfaee. In some emhodintents, the
`reflective surface is a structure or optical eletnent that is
`distinct from the inner surface of the chatnher.
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`The light source can include an optical element disposed
`along a path the electromagnetic energy Ito m the laser travels.
`In some embodiments. the optical element is adapted to pro-
`vide electromagnetic energy from the laserto the plasma over
`a large solid angle. In some embodiments. the reflective sur-
`face of the chamber is adapted to provide electromagnetic
`energy tiom the laser to the plasma crvera large solid angle. In
`smite einbodinteitts, 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 poe-
`dcflned wavelengths (e.g.. infrared wavelengths of electro-
`magnetic energy] of electromagnetic energy.
`The invention. in another aspect. features a light source that
`includes a chamber that has a reflective surface. The light
`source also includes an ignition source for ionizing :1 gas
`within the Cl}.tiJ‘lJl:tt3]'. Tht-2 light sottrce 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
`suhstaittially reflect a first set of predefined wavelengths of
`electromagtetic energy directed toward the reflector and at
`least substantially allow a second set of predefined wave-
`lengths ofelectromagnetic energy to pass through the reflec-
`tor.
`
`The invention. in another aspect. relates to a method for
`producing light. The method involves iottizittg with an igt‘Li-
`tiolt 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 plastna that generates
`a high brightness light.
`In some entbodilnents. the method involves directing the
`laser energy comprising a first set ofwavelengths of electro-
`magnetic energy through a reflector toward the reflective
`surface of the chamber. the reflective sui-Face reflecting at
`least a portion of the first set of wavelengths of electromag-
`netic energy toward the plasma. In some embodintents. the
`tnethod involves directing at least a portion ofthe high bright-
`ness light toward the reflective surface of the chatnber which
`is reflected toward the reflector and is reflected by the reflec-
`tor toward a tool.
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`In some errtbodiments. the method involves directing the
`laser energy comprising a first set olvravelengths of electro-
`magnetic energy toward the reflector. the reflector reflects at
`least a portion 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 ofelectrom agnetie energy toward the plasma. In some
`embodiments- the method involves directing a portion of the
`high briglttness light toward the reflective surface of the
`chamber which is reflected toward the reflector and. electro-
`
`till
`
`’
`
`The method can 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 sortie 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 stem-
`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 :1 solid angle of approximately 0.048 :-Itera-
`dians. In some entbodiments, the method involves directing
`the laser energy ttirougli 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) stcradiuns. In some ernbodiments. the reflective surface
`of the chambet‘ is adapted to provide the laser energy to the
`plasma over a large solid angle. In some embodiments. the
`reflective surface oftbe ch:-tniber 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 :1 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 ehznnber 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. In some embodiments. the electro-
`magnetic energy directed toward the retlective surface of the
`chatnber 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 through 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 ofthe high briglitness light is directed
`toward the reflective surface of the chamber. reflected toward
`the reflector and reflected by the reflector.
`The invention. in anotheraspect. features a light source that
`includes 11 chamber having a reflective surface. The light
`source also includes a l.‘t1B£tt1S for ionizing a gas within the
`chamber. 'lhc light source also includes at means for at least
`substantially reflecting a first set o fpredefi ned wavelengths of
`electromagnetic energy directed toward the reflector and at
`least substantially allowing a second set ofprcdefincd wave-
`lengths of electromagnetic energy to pass through the reflec-
`tor. The light source 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 anotheraspect. features a light source that
`includes a sealed chamber. The light source also includes an
`ignition source for ion.i7.ing a gas within the chamber. The
`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 it high brightness light. The light source also
`includes a curved reflective surface disposed external to the
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`US 7.'?86,455 B2
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`7
`sealed chamber to receive at leas a portion of the high bright-
`ness light emitted by the sealed cliamber and rellect the high
`brightness light toward an output of the light source.
`[[1 some entbodinttents. 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 sea led
`chamber relative to the curved rellective surface. In some
`embodiments. the sealed chamber is a quartz bulb. In some
`embodiments. the light source includes u second curved
`reflective sttrface disposed internal or external to the sealed
`chamber to receive at least a portion oftltc laser electromag-
`netic energy and Focus the electrtitttagttetje energy on the
`plasma tl1at generates the high brightness light.
`The invention. in anotlieraspect. features a light source that
`includes a sealed chambcrand an ignition source for ionizing
`a gas within the chamber. The light source also includes at
`least one laser external to the sealed chamber for providing
`electrontagnetic energy. The light source also includes a
`curved reflective surface to receive and rellect at least a por-
`tion of the electromagnetic energy toward the ionized gas
`within the chamber to produce a plasma that generates a high
`brightness light. the curved reilective surface also receives at
`least a portion of the high brightness light emitted by the
`plasma and reflects the high brightness light toward an output
`o I" the light source.
`the curved retlective surface
`In some emboditnents.
`lhcuses the electromagnetic energy on a region in the cham-
`ber where the plasma is located. in some embodiments. the
`curved reflective surface is located within the chamber. In
`some embodiments. the curved reflective surface is located
`external to the chamber. in some embodiments. the high
`brightness light is ultraviolet light. includes ultraviolet light
`or is substantially ultraviolet light.
`The foregoing and other objects. aspects. features. and
`advantages of the invention will beconte more apparent frorn
`the following description and from the claims.
`
`Bllllil-' l)L7.SCRIP'I'lON O1’ 'l‘I-lli DRAWINGS
`
`The foregoing and other objects. Feature and advantages of
`tltt’: invention. as well as the invention itself. will be more liilly
`understood from the following illustrative description. when
`read together with the accompanying drawings which are not
`necessarily to scale.
`FIG.
`I
`is a schematic block diagram of :1 light source.
`according to an illustrative embodiment of the invention.
`FIG. 2 is it schen1:.ttic block diagram ofa portion ofa light
`source. according to an illustrative L’rl'1l:l0Llll1‘lEDl.Ol‘ll1€
`inven-
`tion.
`
`FIG. 3 is a graphical representation ol'UV' brightness as a
`Function ozfthe laser power provided to a plasma. using a light"
`source according to the invention.
`FIG. 4 is a graphical representation of the transniission ol‘
`laser energy through a plasma generated front mercury. using
`a light source according to the iuvetttiott.
`FIG. 5 is a schematic block diagram of a light source.
`according to an illustrative embodiment ol‘ the invention.
`FIG. 6 is a schematic block diagram of a light source.
`according to an illustrative embodiment of the invention.
`FIG. 7 is a schematic block diagram of a light source.
`according to an illustrative embodiment of the invention.
`FIG. 8A is it. schematic block diagram o.l'a light source in
`which electromagnetic energy from a laser is provided to a
`plasma over a first solid angle. acconlirtg. to an illustrative
`embodiment of the invention.
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`8
`FIG . 8B is a schematic block diagram ofthe light source of
`FIG. 8A in which the electroniagnetic energy front the laser is
`provided to the plasma ov