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`US00?'786-5.5532
`
`{:2} Ulllted States Patent
`Smith
`
`(10; Patent No.:
`(45; Date of Patent:
`
`US 7,786,455 B2
`Aug. 31. 2010
`
`('54)
`
`I.A5ER-DRIVEN LIGHT SOURCE
`
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`.-\pp1.N0.2 113695.348
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`(22)
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`Filed:
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`Apr. 2. 2007
`
`30D?"O335*J2l Al '°
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`l.‘_.-"2007 Zulim e1 :11.
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`(65)
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`Prior Publication Data
`
`[(‘mui,u,9d;
`
`Related U.S..-Kpplicalion Data
`
`JP
`
`“.1933”
`
`3.1935
`
`[(13)
`
`(‘onlinnation-in-pain :11" {application No. 113395.523.
`filed on Mar. 31. 2006. now Pal. Nu. 7.435.982.
`
`(51)
`
`Int. (.‘1.
`(300631)
`H053 31/26
`(200601)
`G01‘J 3/I0
`130051011
`G319 WW
`(2000.01)
`H011 01x23
`25111493.]; 350504 R:
`(53) U5. ('1.
`315/111.21:315111|.7i:3l5e’l1l.9l:3|3f231.3l:
`3131231 .41: 313.12.31.71
`(53) Field 91' Classification Search ........... ..
`2501423 R.
`
`2501423 P. 434. 426. 494.1. 493.1. 504 R.
`250150-*lH: ?-152'1l1.2l.lll.71,111.91:
`313931.31. 231.41.231.61. 231.71. 631.
`3131632. 533
`See application lilc for enmplctc searcli 11islnry.
`
`(55)
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`3.'1'_JR8 Ynshizilwa et al.
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`“$.39
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`O'1'[-I1:f.R PUB1..1C'.=\'1'10NS
`Wilbcrs et :11.. "'1'l1e \r'L.\r' lnnissivity 01' a lligh-Pressun: Cascade
`.=\l‘2(.'II‘l Are l]‘0II‘I 115 lo 200 nI‘n.".F. Qu(:flJ'. Sprr.'m,\'t‘. Rrldmf.
`]'i'<m.-.-—
`r.-£001.45. I991. pp. 299-308.
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`l‘rnskaI.Iu-.‘r |{u:u-2 1.1.1’
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`{-571
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`An apparatus for producing light includes 3 chamber and an
`igmtion -sutures: that icinires a gas wit11iu the eliamber. The
`app:-m-11115 also incltldca :11 least one laser that provides ¢:11ei'gy
`lo the ior|.i'!..ed gas wlthm the L‘1'I2:.l111JL‘1' to pmduce :1 high
`briglltncss light. The laser can provide a h'llbSltIl111:l11_y eun-
`1111110115 antount all energy‘ to the 10n1zed_gas In generate a
`substantially cm111111Ious1t1g11brightness llght.
`
`315-'31}
`
`43 Claims. 8 Drawing Sheets
`
`228
`
`(cid:36)(cid:54)(cid:48)(cid:47)(cid:3)(cid:20)(cid:19)(cid:20)(cid:28)
`
`ASML 1019
`
`

`
`US 7,736,455 B2
`Page 2
`
`US. PATENT DOCUMENTS
`
`2009-‘"003 ZMU .—'\l "'
`
`I-"2009 Smith :91 al.
`
`250-'5(J3.l
`
`OTHER PUBLICATIONS
`
`Wilbers el 31.. “The ("ontinuum Flnissinn of an Art: I’I:1su1a." J.
`Qmim. Spccrmsc. Kadiczr.
`.T."arrs_,"cr'. vol. 45. No. 1. 1991. pp. l-10.
`Bock. "Simple Pulse (iencralor far Pulsing Xenon Arcs with High
`Repeiiliun R;1tc." Rev. Sci. !.I1.m'um.. vol. 45. N0. 2. Feb. 1974. pp.
`313-349.
`Riliier, “(}p!II:.'I.i Disch€!.rges."3a1£ Phy.i'. Lip. 33H I il. Nov. 1930. pp.
`T89-RM.
`1-" iedorowicz cl a.l.. “X-Ray Einission farm Laser-Irradiated Gas P“ufl'
`Tmgetsmzppr. Pm. Leh‘. 52 (221. May 31, 1993. pp. 2773-2730.
`Keelier et aI.. "Exp:-.-rimental Study of a Stationary I.:1ser—Sustained
`Ai.r Plasma." .J'm.rmm' Q)".-tppfivd Hi_1‘.v:'c'..1'. vol. 46. No. 3. Mar. 1975.
`pp. l{J8(J-I083.
`Jeng cl .11.. "The4'.>rclic:1l [n\.re3l'ig2ltion ul‘I_aser-Stistained Argon Plas-
`m:1s.“.»’. slppl. P19-'.¢. 60 ('1'). Uvzi.
`l. 1986. pp. 22’.n"3-2279.
`]3rzu1'1en."CW Gas Breakdown in Argon Using Ifl.G-pm Laser Radia-
`tion," .-‘lpp'.r'. Phys. Lc=..P1'.. vol. 2 I. No. 2. Jul. 15. I972, pp. 62-64.
`Moody. “Maintenance ofa Gas Breakdown in Argon Using. lU.fi-pew
`Radiation." .Iaw'.rm.i' q.C4ppt'ied P!:_r.\‘ir.r. val.»-16. Nu. IS. Jun. 1975. pp.
`1475-2482.
`
`Generalov el al., "]£xperimL=n1nl Investigation a|'a Continuum; Upii-
`ca] l)iscI*::u'ge." Savior PI:_i-:w'rs.J';E’TP. vol. 34. No. -1. Apr. I973. pp.
`"H33-1'69.
`
`Gcnuralov at al.. "C'ontin11ous Optical Disch.1rge.“ ZJEETI-‘Pix. Red.
`I]. No. 9. May S. 1970. pp. 302-304.
`]~?.ozlo\«' ct al.. "Radiative Losses by Argon 1-‘lasma and the limissivc
`Model ofn Conlinumls Optical Discharge." S01: Ph_1.J.\‘_ .H§ H”. \'o1.39.
`No. 3. Sop. 197-1. pp. 463-168.
`Car|ho!T-::I a].. "{.‘onlin1mu5 Optical Dischaiigcs at Very High Pres-
`sL1re."P!'r3'sr'r'a l{J3C. l98l. pp. ~=l3*}J1-4?.
`(‘mmerrc cl a1.. "F'.\«‘a]ua1i-;m of the Continuous Opl ical Dischalge liar
`Spcctrochcmical Analysis." Sgiecrmririiiiiciz Arm. vol. 4013. No. 4.
`1935. pp. 665-679.
`linzlpv at al.. “Sustained Optical Ifischargcs in Molecular Cmscs."
`SW. P.-‘.=_1-'5. 12-ca. pm. 490 1). Nov. 1979. pp. I233-I287.
`Keefer. “Laser-Suslnined Plas1:1zI.s." i'.a.s'er—Indm'm' Phzsnms and
`.-Ip,m'£rnrfo::.i-. published by Marcel Dekker. edited by Ratdxiemski el
`ai.. 1939. pp. I69-206.
`Ilaunmnmsll Product Informnlion, "Super-Quiet Xenon Lamp Super-
`Quiel Mcrcilry-Xenon L:unp.” Nov. 2005.
`
`* cited by r:xanJi11er
`
`

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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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`US 7,786,455 B2
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`US 7,786,455 B2
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`U.S. Patent
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`Aug. 31, 2010
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`US 7,786,455 B2
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`Aug. 31, 2010
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`U.S. Patent
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`Aug. 31, 2010
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`1
`LASER-DRIVEN LIGHT SOURCE
`
`REI_.A'I‘t£[) At’Pl_-lC.Nl‘[(')NS
`
`US 7,786,455 B2
`
`2
`
`This application is a continuation-in-part ofl.J.S. Scr. No.
`11/395,523. filed on Mar. 3], 2006. now US. Pat. No. 7.435.
`982. tl1e entire disclosure of which is incorporated by refer-
`ence herein.
`
`l"ll£l..l) OI’ Tl-ll: lNV'l}fN‘l'lON
`
`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 ttsed in a variety of
`applications. For example, 3 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 waters (e.g.. reticles and photomasks). The
`electromagnetic energy produced by high brightness lights
`sources can, alternatively. be used as a source ofilltimination
`in a lithography system used in the titbrication of wafers. :1
`microscopy systems. or a photoresist curing system. The
`parameters ('_e.g.. wavelengtli. power level and briglttnesst of
`the light vary depending upon the application.
`The state of the art in. tor exantple. wafer inspection sys-
`tems involves the use of xenon or mercury arc lamps to
`p1‘L'ICll.tCC‘ light. The are lamps include an anode and catltodt:
`that are used to excite xenon or mercury gas located in a
`chamber oi’ the lump. An electrical discharge is generated
`between the anode and cathode to provide power to the
`excited t_c.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
`contaminttte the light source or result in failure ol‘ the light
`source. Also. these are lamps do not provide su tlicient bright-
`ness for some applicat ions. especially in the ultraviolet spec—
`trum. Further. the position of the arc can be unstable in these
`lamps.
`fteeordingly. a ttccd therelote exists for improved high
`brightness light sources._-'\ need also exists for improved high
`briglttness light sources that do not rely on an electrical dis-
`charge to maintain a plasma that generates a high briglttness
`light.
`
`SUMMARY OF TI-Ilzi Il\lVl7.N'l‘I()N
`
`It
`
`to
`
`15
`
`3ft
`
`-'13
`
`‘Fhe present invention features a light source for generating
`a l1igl1 brightness light.
`The invention. in one aspect. leatures a light source having ..'
`a chamber. The light source also includes an ignition source
`for ionizing a gas within the chzurtber. The light source also
`includes at least one laser for providiilg energy to the ionized
`gas withitl the charuber to produce :1 high briglttncss light.
`In some embodiments. the at least one laser is a plurality of
`lasers directed at a region frotu 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
`The optical
`element can be. torexample. a lens (e.g.. an aplartatic lens, an
`achromatic lens. a single element lens. and at Fresnel lens] or
`mirror (e.g.. a coated minor. a dielectric coated mirror. a
`
`fill
`
`as
`
`narrow l3a!1tlt.11lt'l‘0l', and an ultraviolet transparent intrared
`ttefiecting mirror). tn some et:nbodin'ients_. the optical element
`is one or more fiber optic elements tor directing the laser
`energy to the gas.
`The eliarnber can include an ultraviolet transparent region.
`The chatrtber or a window iii the chamber can include a
`material selected from the group consisting of quartz. Supra-
`siliit‘ quartz (E-leraeus Quartz America. LLC. Buford. Gajj.
`sapphire. Mgliz. diamond. and Cat’, In some embodiments.
`the ctiarnhcr is a sealed chamber. In some ernbodiments. the
`chamber is capable of being actively pumped.
`In some
`etnbotlintents,
`the chamber includes a dit-.‘lectt'iL‘ material
`(e.g._. quartz). The chamber can be. l‘or example. a glass bulb.
`In some embodiments. the chamber is an ultraviolet transpar-
`ent dielectric chamber.
`
`The gas can be one or more ol'a noble gas. Xe. Ar. Ne. Kr.
`I-le, D3, ill, 0:. F2. in metal halide. a halogen. Ilg, Cd. Zn. Sn.
`Ga. lie. Li. Na. an excimer limping gas. air. a vapor. a metal
`oxide, an aerosol. a flowing media. or a recycled media. The
`gas can he produced by a pulsed laser beam that impacts a
`target e.g.. a solid or liquid) in the cltalnber. The target can be
`a pool or film of metal. In some embodiments. the target is
`capable of moving. For example. the target may be :1 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
`embodinients, Lhe at least one laser includes a pulse or cott-
`tinuous wave laser. In some embodiments. the at least one
`laser is an IR laser. a diode laser. a tiber laser. an yttcrhiunt
`laser. a C0: laser. :1 YAG laser. or a gas discharge laser. In
`some erubodiments. the at least one laser emits at least one
`
`is
`
`strongly
`
`wavelength of electromagnetic energy that
`absorbed by the ionized medium.
`The ignition source can be or can include elecuttdes. an
`Llllraviolet ignition source. a capacitive ignition source, an
`inductive ignition source. an R]? ignition source. a microwave
`ignition source. a flash latnp. a pulsed laser. or a pulsed latup.
`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 intemal to the chamber.
`The light source can include at least one optical element for
`modifying a property ofclcctrontagnet ic radiation emitted by
`the ionized gas. The optical element can be. for example. one
`or more mirrors or lenses. I11 some embodiments. the optical
`element is eontigurcd to clcl ivcr the electromagnetic radiation
`emitted by the ionized gas to a tool (e.g.. a wafer inspection
`tool, a nncroscope. a metrology tool. a lithography tool, or an
`endoscopic tool}.
`The invention. in another aspect. relates to a nlcthocl 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 ctnbodiinents. 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 embodiments. the method also involves
`actively pumping the elianiber. The ionizable medium can be
`:1 moving target. In some embodiments. the method also
`involves directing the high brightness light through at least
`one optical element to modify a property ofthe light. in some
`embodiments. the method also involves delivering the high
`briglnuess light emitted by the ionized medium to a tool (e.g. .
`it walirr inspection] tool. at nticroscopc. ti tnelrology tool. a
`lithography tool. or an endoscopic tool ).
`
`

`
`3
`
`4
`
`US 7.786,455 B2
`
`In another aspect. the invention teatures a light source. The
`lights source includes a chamber and an iguiitjon source for
`ionizing an ionimblc tncdiutn within the chamber. The light
`source also includes at least one laser for providing substan-
`tially continuous energy to the ionized tucditun within the
`cltaiubcr to produce a hifli brightness light.
`In sortie einbodintents. tl1c at least one laser is a continuous
`
`wave laser or a high pulse rate laser. in some cntboditnents,
`the at least one laser is a high pulse rate laser that provides
`pulses ofencrgy to the ionized rnediunt so the high brightness
`light is substantially continuous. In some embodiments, the
`magnitude ofthe high brightness light does not vzuy by more
`than about 90% during operation. In some embodiments. the
`at least one laser provides energy substantially continuously
`to ntin.it'ni7.e cooling of the ionized medium when energy is
`not provided to the ionized medium.
`In some etitbodiments. the light source can include at least
`one optical element [e.g.. a lens or mirror) for modifying a
`property ofthe laser energy provided to the ionized medium.
`The optical elemettt can be, for example. an aplanatic lens. an
`achromatic lens. a single element lens. a fresnel lens. It coated
`ntirror. a dielectric coated rnii-ror, a narrow band mirror. or an
`ultraviolet
`tratisparciit
`infrared retlecting mirror.
`In some
`cnibodiments. the optical element is one or more fiber optic
`elements for directing the laser energy to the ionizable
`medium.
`In some embodiments. the chamber includes an ultraviolet‘
`transparent region. In some embodiments, the chamber or a
`window in the clinrnher includes a quartz material. suprasil
`quartz ntaterial. sapphire material. Mgliz material. diamond
`material. or Cat’; material. In some embodiments. the chant-
`bcr is a scaled chatuber. The chamber can be capable o fbcirtg
`actively ptuupcd.
`In some embodiments,
`the cha.rn‘or:r
`includes a dielectric material (c.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 be a solid. liquid or gas. The
`ionizable medium can include one or more of a noble gas. Xe.
`Ar. Ne, Kr. I-le. D3. I12. 02, F2. -.1 metal halide. a ha logen, I-lg.
`Cd. Zn. Sn. Ga. Fe. Li. Na. an cxcimcr forrnirtg fills. air. a
`vapor. a metal oxide. an aerosol. a {lowing media. a recycled
`media, or an evaporating target. In some embodiments. the
`ionizoble 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 :1 pool or film of metal. In
`some embodiments. the target is capable of moving.
`In sotue eiitboditnetits. the at least one laser is multiple
`diode lasers coupled into a fiber optic element. The at least
`one laser can emit at least one vvavelengtli ol'elecu'omagnetic
`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 RI’ ignition source. a microwave
`ignition source. a [lash lamp. a pulsed laser. or a pulsed lamp.
`The ign.ition source can be external or interna.l to the chamber.
`I I1 some cnibodimcnts. the light source includes at least one
`optical elemertl. (eg. a mirror or lens] for modifyittg a prop-
`erty of electroniagnetic radiation emitted by the ionized
`med him. 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 tight. 't11en1i:tl1od involves ionizing with an igni-
`tion source an iortizahle medium within a chamber. The
`
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`
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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 ernbodiments. the method also involves directing
`the laser energy through at
`least one optical element for
`tttodifyittg a property of the laser energy provided to the
`ionizable medium. The method also can involve actively
`pumping the chamber. In some entbodiments. the ionizahle
`medium is a moving target. The ionizahle medium can
`include a solid. liquid or gas. In some entbodimcnts. the
`method also involves directing the high brightness light
`through at least one optical element to moclil'y 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.
`
`light source
`The invention. in another aspect. fcatttres
`having a cltatnher. The light sottrcc includes a first ignition
`means for ionizing an ionizable medium within the chamber.
`The light source also includes a means for providing substan-
`tially continttous laser energy to the ionized medium within
`the chamber.
`
`The invention. in another aspect. features a light source
`having a chamber that includes a rctlective surface. 'l'"hc light
`source also includes an ignition source for ionizing a gas
`within the chamber. The light source also includes :1 rctlector
`that at least substantially rellects a first set of predelined
`wavelengths of electrotrlagnctic energy directed toward the
`reflector and at least substantially allows a second set of
`predelined wavelengths of electromagnetic energy to pass
`thmugll the rellector. The light source also inclttdcs 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‘ btnsts. as in a pulsed laser.
`In some entboditnettts. at least one laser directs a first set of
`wavelengtlts of electromagnetic energy through the reflector
`toward the rellective surface [e.g.. inner surface} ofthc cham-
`ber and the rellective surface directs at least a portion ofthe
`first set ofwavelengtlis ofelectromagitetie energy toward the
`plasma. In some embocliments. at least a portion of the high
`brightness light is directed toward the reflective surface of the
`chamber. is reticcted toward the reflector. and is reflected by
`the retlectortoward a tool. In some embodiments. at least one
`
`laser directs -.1 first set of wavelengths of electromagnetic
`energy toward the rellcctor. the reflector reflccts at least a
`portion of the first wavelengths of electromagnetic energy
`towards the reflective surface of the chamber, and the reflec-
`tive surface directs a poniori of the first set of wavelengths of
`electrontagnetic energy toward the plasma.
`In some ernbodirncnts. at least a portion ofthc high bright-
`ness light is directed toward the rctlcctive surface of the
`chamber. is reflected toward the rellector. and passes througlt
`the rcflcctor toward an output of the light source. In some
`embodiments. the light source comprises a microscope. ultra-
`violet nijeroscope. 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 brightness light is
`directed toward the reflcctivc surface of the chamber.
`is
`
`reflected toward the reflector, and electromagnetic energy
`comprising the second set ofpredefined wavelengths ot'elec-
`tromagnetic energy passes through the reflector.
`The chamber of the light source can include a window. In
`some embodiments. the chamber is a sealed cliattthcr. In some
`embotlimcnts. the rellcctive surface of the chamber com-
`
`

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`US 7386.455 B2
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`6
`
`prises a curved sltape. parabolic shape. elliptical shape.
`spherical shape or nsplterical shape. In some embodiments.
`the chamber has a reflective inner surface. In some embodi-
`
`magnetic energy comprising the second set of" predefined
`wavelcngtlis of electrornayictic energy passes through the
`reflector.
`
`ltl
`
`15
`
`ments. a coating or film is located on the outside of the
`chamber to produce the reflective surface. In some embodi-
`ments. as coatingor lilut is located on the inside o fthc chamber
`to prodttcc the reflective surface. In sortie El'l.1lJCtt‘ill'l'lC1'1lS._ the
`reflective surface is a structure or optical element that is
`distinct from the ituier surface of the chamber.
`
`The light source can include an 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 laserto the plasma over
`a large solid angle. In some einbodiments. the reflective sur-
`face of thc elrantber is adapted to provide electromagnetic
`energy liunt the laser to the plasma crvera large solid angle. In
`some embodiments. the retlective surface of the charnber is
`adapted to collect the high briglttness light generated by the
`plasma over a large solid angle. In some embodiinertts. one or
`more of the reflective surface. reflector and the window
`include (e.g.. are coated or includel a material to filter pre-
`defined wavelengtlts (e.g.. infrared wavelengths of electro-
`magnetic energy] of electromagnetic energy.
`The invention. in zmother aspect. features a light source that
`includes a chamber that has a reflective surface. The light
`source also includes an ignition source for ionizing a gas
`within the cliainber. The light source also inelttdcs at least one
`laser external to the chamber tor 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 sorne emboditnenls. the reflector is adapted to at least
`substantially reflect a first set of predcftttcd wavelettgths of
`electromagtetic energy directed toward the reflector and at
`least :~?lIl‘tSl:t!lIl.:tll}' allow a second set of predefined wave-
`lengths ot'elt-.-ctrotnagnetic energy to pass through the reflec-
`tor.
`
`-'13
`
`The invention. in another aspect. relates to a method for
`producing light. The method involves iotti/.ittg with an igni-
`tiolt sotlrcc a gas within a chamber that has a reflective stir-
`litce. 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 entbodituents. the met ltod involves directing the
`laser energy comprising a first set of wavelengths o t" electro-
`magnetic energy tluough a reilector toward the reflective
`surface of the eltantber. the reflective surface reflecting at
`least a portion oftltc first set of wavcleliglhs of clt:clromag-
`netic. energy toward the plasma. In some entbodimcnts. the
`method involves directing at least a portion ofthe high bright»
`ttess light toward the retlective surface of tlte chamber which
`is reflected toward the reflector and is reflected by the reflec-
`tor toward a tool.
`
`In some etrtbodiments. the tnethod involves directing the
`laser eltcrgy comprising a first set ofwavclettgtlts of electro-
`magnetic energy toward the rctlector. the reflector retlccts at
`least a portion of the [lost wavelengths of elcct'romagnetic
`energy toward the reflective surface of the chamber,
`the
`reflective surface directs a portion of the tirst set of wave-
`lengths ofelectrom agnetic energy toward the plasma. In some
`embodintents- the method involves directing a portion of the
`high briglttttess light toward the rcllcctive surface of‘ the
`chamber which is reflected toward the reflector and. electro-
`
`Lill
`
`'
`
`The method can involve directing the laser energy through
`an optical element that modilics a property ofthc 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 stem-
`dians. In some embodiments. the method involves directing
`the laser energy through an optical element that moditics a
`property of the laser energy to direct the laser energy toward
`the plasma over :1 solid angle of approximately 0,048 st'era—
`dians. In some embodiments. the method involves directing
`the laser energy throtlgh an optical element that modifies a
`property of the laser energy to direct the laser energy toward
`tlte plasmat over a solid angle of greater than about 2.1 (about
`6.23) steradians. In some erubodituents. the relloctive surface
`o f the chamber is adapted to provide the laser energy to the
`plasma over a large solid angle. In some embodiments. the
`reflective surface o.t'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 :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 rctlects a first set of wavelengths of electromagnetic
`energy toward the ionized gas in the chzunber to produce a
`plasma that genemtes a high brightness light.
`In some embodiments. the electromagnetic energy from
`the laser first is reflected b_v the reflector toward the reflective
`surface of the chamber. In some embodiments. the electro-
`magnetic energy directed toward the reflective surface ofthe
`chamber is retlccted 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 rellcetor.
`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-
`tiice of the chamber is rcllected toward the plasma. in some
`ernbodiments. a portion ofthe high brightness 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 a chamber having a rellective surface. The light
`source also includes a l.t1e£tt1S tor ionizing a gas within the
`chamber. "the light source also includes a means for at least
`s ubstantially retlecting a first set o fpredetined wavelengths of
`electromagnetic energy directed toward the reflector and at
`least substantially allowing a second set ofprcdclined wave-
`lengths ofelectromagnctic energy to pass through the reflec-
`tor. The non source also includes a means for providing
`electromagietic 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 ionizing 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 witlun the chamber to produce a plasma that
`generates a high hrighttless light. The light source also
`includes a curved reflective surface disposed external to the
`
`

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`US 7,786,455 B2
`
`7
`sealed chamber to receive at lens a portion of the high bright-
`ness light emitted by the sealed cliamber and rt.-llect the high
`briglimcss light toward an output of the light source.
`In some einbodiincnts. the light" source includes an optical
`element disposed along a path the electromagnetic energy a
`from the laser travels. In some embodiments. the sealed
`chamber includes a suppon element that locates the sealed
`chamber relative to the curved rellective surlace.
`In some
`ernhodinlents. the sealed chamber is at qtt:'Irtz bulb. In some
`embodiments. the light source includes a second curved
`retlective surface disposed internal or external to the sealed
`clttuuber to receive at least a portion o l‘ the laser clectrotuag-
`netic energy and locus the electromagttelic energy on the
`plasma that generates the high brightness light.
`The invention. in anotlteraspect. features a light source that
`includes a sealed chamberand an ignition source for ionizing
`a gas within the chamber. The light source also includes at
`least one laser extemal to the sealed cliamber for providing
`electromagnetic energy. The light source also includes a
`curved rellectivc surface to receive and rellecl 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 cttrved rellective surface also receives at
`least a portion of the high briglnness light emitted by the
`plasma and rellects the It igh brightness light toward an output
`o l' the light source.
`the curved rellective sttrlace
`lrl some ernhoclinlents,
`focttses the electromagnetic energy on :1 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 cliamber. ln some ernbodinients. the high
`brightness light is ttltrat-‘inlet light. includes ultraviolet light
`or is substantially ultraviolet light.
`The foregoing and other objects. aspects. features. and
`advantages ofthe invention will become more apparent front
`the following description and from the claims.
`
`25
`
`ill":
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`4h
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`-'15
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`l3Rll-El-' l)l-7.SCRlP’l'[0N 01’ THE l)R_-KWINGS
`
`The foregoing and other objects. Feature and advantages o I‘
`the invention. as well as the invention itsell. will be more litlly
`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 a light source.
`according to an illustrative embodiment of the invention.
`l'*'l(i. 2 is it schentatic block diagram of a portion olia light
`source. according to an illustrative ernbodiinent ofthe inven-
`tion.
`
`FIG. 3 is a grapltical representation ol'UV brightness as a
`function olthe laser power provided to :1 plasma. using a light
`source according to the invention.
`
`FIG. 4 is a graphical representation of the transntission ol‘ ‘_ _
`laser energy through a plasma generated from mercury. using '
`a light source according to the irtvetttion.
`l"lCi. 5 is a schematic block diagram of a light source.
`according to an illustrative embodiment ol‘ the invention.
`FIG. 6 is a scltetuatic block diagram of a light source.
`according to an illustrtuive embodiment of the invention.
`FIG. 7 is a schematic block diagram of 21 light source.
`according to an illustrative embodiment of the invention.
`FIG. 8A is a schematic block diagram ol'a light source in
`which electromagnetic energy lrorn a laser is provided to a
`plasttla over El first solid angle. ttccortlirtg to an illustrative
`embodiment of the invention.
`
`at
`
`fill
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`8