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`US00?286455B2
`
`(121
`
`United States Patent
`Smith
`
`(10) Patent No.:
`(45; Date of Patent:
`
`US 7,786,455 B2
`Aug. 31, 2010
`
`(541
`
`(751
`
`(731
`
`LASER-DRIVEN LIGI-IT SOURCE
`
`Inventor: Donald K. Smith. 1?oe1n1ont, MA (US)
`
`Assignee: Energetiq Technoloy, Inc.. Woburn.
`MA (US)
`
`(*1
`
`Notice:
`
`Subject to any disclaimer, t11e term of this
`patent is extended or adjusted under 35
`U.S.(T. 154(1)) by 820 days.
`
`(211
`
`Appi. No.2 l1a"695.,3-18
`
`(32)
`
`Filed:
`
`Apr. 2, 200’?
`
`(651
`
`Prior Publication Data
`
`US 200720228300 Al
`
`Oct. 4, 2007
`
`5.233.730 Bl
`6.417.625 Bl '“
`6.788.404 B2
`6.956.329 132*
`7.652.430 131+
`200290021508 Al
`200310168982 A1
`200310231496 Al
`200100264512 A1‘
`2005.-"016'a'618 Al*
`200'.-‘#0285921 Al‘
`
`
`
`356.-"23'?.l
`9:200: Fairleyetal.
`315-"11|.3l
`752002 Brooks elal.
`356.-"2312
`932004 Lange
`315-"1i1.3l
`1052005 Brooks eta.l.
`3l3.«'633
`1.--2010 Delgado
`359»-3.-:3
`2.-nun:
`Ishihara
`.... .. 313.-“G34
`9.-‘"2003 Kim
`................. .. 362."2tS8
`I2.-‘"2003 Sate eta].
`1212004 Ilartiovcctal.
`3'22.-"5
`852005 Hoshino eta].
`250.-"S0411
`I2.-‘"2007 Zuiimetal.
`362.-"240
`
`((.‘on1iI1ued)
`FOREIGN PATENT DOCUMENTS
`
`Related U.S. Application Data
`
`JP
`
`61493358
`
`891986
`
`(631
`
`Continuation-in-pan of application No. 112395.523.
`filed on Mar. 31. 2006. now Pat. No. 7.435.982.
`
`(511
`
`(52)
`
`(561
`
`Int. Cl.
`(2006.01)
`H05B 31/26
`(2006.01)
`G01} 3/10
`(2006.01)
`GZIG 4/00
`(2006.01)
`H011 6.028
`2501493.]: 250504 R:
`U.S. (I1.
`3151']11.21:3151111.71:31S!]11.91:3l3:’231.31:
`3l3i'23l.4l:3l3f23l.71
`Field ofC1assification Search
`250K423 R,
`250K423 P. 424. 426. 494.1. 493.1. 504 R,
`250504 1-1: 315111121. 111.71. 111.91:
`313.r’231.31. 231.41, 231.61. 231.71. 631.
`3132632. 633
`See application tile for complete searcli history.
`References Cited
`
`U,S. PATENT DOCUMENTS
`
`4.088.966 A "‘
`4.498.029 A "'
`4.646.215 A
`RE32.(:26 E "
`
`313-231.51
`5.-‘I978 Samis
`315.-"39
`2e'l985 Yoshiznwaetal.
`25198? Levin et a1.
`............... .. 362-"296
`3-‘I988 Yoshirawactol.
`315.39
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`OTHER PUBLICATIONS
`
`Wilbers et 211.. “The VUV ljinissivity of a Iligh-Pressure Cascade
`Argon _—‘-\_r(: from 125 to 200 nm.” I Qmmt Sper.'rrt.u'rr_ Radial’. ?2'{J.fl'S-
`fer. vol. 46. 1991. pp. 299-308.
`
`(Continued)
`
`PrI':mIr'_t' E.\'n'miner——Ber11ard E Souw
`(74) An‘orne_1-'. /fgem‘, or Firni Proskauer Rose 1.1 P
`
`(57)
`
`ABSTRACT
`
`An app-aramts for producing light includes a clmmber and an
`ignition source that ionizes a gas within the cliamber. The
`apparatus. also includes at least one lascr that provides energy
`to the ionized gas within [he cliamhcr to produce :1 high
`briglitncss light. 'I'l1e laser can provide a subslanlialiy con-
`tinuous amount of energy to t11e ionized gas to generate a
`substantially continuous high brightness light.
`
`43 Claims, 8 Drawing Sheets
`
`228
`
`
`
`ASML 1201
`ASML 1201
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`

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`US 7,786,455 B2
`Page 2
`
`US. PATENT DOCUMENTS
`
`2DU9»"003 2740 Al "‘
`
`2."2D09 Smith et al.
`
`............ .. 25075011
`
`OTHER PUBLICATIONS
`
`Withers el 31.. "The Continuum Emission of an Arc I‘lasma.” J.
`Qmrrrr. Specmosc. Radfar. Tr'arr.y'er'. vol. 45. No. l. 1991. pp. 1-10.
`Beck. "Simple Pulse Generator for Pulsing Xenon Arcs with High
`Repetition Rate." Rev. Sm‘. 1.Im'r'mrI.. vol. 45. No. 2. Feb. 1974. pp.
`3 18-319.
`Raiser. “Optical Discharges." Sou Phys. Usp. 23(] 1). Nov. 1980. pp.
`789-806.
`
`1'-‘icdorowicz et nl.. “X-Ray Emission form Laser-Irradiated Gas Puff
`Ta.I'ge‘ts.".4pp!. P.-‘rys. Left. 62 (22). May 31. 1993. pp. 2773-2780.
`Keefer et a.l.. "Experimental Study of a Stationary I_aser—Sustained
`Air Plasma." Jortmm‘ ofApplied P.liysi'c'.r. vol. 46. No. 3. Mar. 1975.
`pp. I080-I083.
`Jeng et al.. “Theoretical Investigation of Laser-Sustained Argon Plas-
`mas.“ J’. Appf. Phys. 60 (7), Oct. 1. 1986, pp. 2272-2279.
`Franzen. "CW Gas Breakdown in Argon Using ]O.t'1—pJn Laser Radia-
`tion."Appt'. Phys. Let!..vol. 21. No. 2, Jul. 15. 1972. pp. 62-64.
`Moody. “Maintenance ofa Gas Breakdown in Argon Using 10.6-ucw
`Radiation." J6m‘mz.l gf'A'ppf:'ed P.r':_v.\'irs'. vol. 46. No. 5. Jun. 1975. pp.
`2475-2482.
`
`Generalov et al.. “Experimental Investigation of :1 Continuous Opti-
`cal Discharge." Soviet Pb)-zrirrs .7577’. vol. 34. No. 4. Apr. 1972. pp.
`763-769.
`
`Generalov et al.. “Continuous Optical Discharge.” Z)'tE7FPr's. Rod.
`1 1. No. 9. May 5. 1970. pp. 302-304.
`Kozlov et al.. “Radiative Losses by Argon Plasma and the Iiimissive
`Model of a Continuous Optical Discharge.” Sou Phys. .1}? TP. vol. 39.
`No. 3. Sep. 1974. pp. 463-468.
`Carlhoff et 31].. “Continuous Optical Discharges at Very High Pres-
`sure."PIrysfca lU'3(.‘.. 1981. pp. 439447.
`Cremers et a1.. “Evaluation of the Continuous Optical Discharge for
`Spectrochemica] Analysis,” Specrrvcfrirrlfm Acm, vol. 4013. No. 4,
`1985. pp. 665-679.
`Kozlov et al.. “Sustained Optical Discharges in Molecular Gases.“
`Sov. Phys. Tech. Phys. 49(l 1). Nov. 1979, pp. 1283-1287.
`Keefer. “Laser-Sustained Plasmas." Las'er—.'r:dm:'ed Plasmas and
`Ap_w':‘catf0n.i'. published by Mame! Dekker. edited by Radziemski et
`21].. 1989. pp. I69-206.
`1-Iamamatsu Product Information. "Super-Quiet Xenon Lamp Super-
`Quict Mercury-Xenon Lamp.” Nov. 2005.
`
`* cited by examiner
`
`

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`U.S. Patent
`
`Aug. 31, 2010
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`1
`LASER-DRIVEN LIGHT SOURCE
`
`Rl3I.ATE.D APPLICATIONS
`
`This application is a continuation-in-part of US. Ser. No.
`l li‘395.523, filed on Mar. 3] , 2006, now US. Pat. No. 7,435,
`982. the entire disclosure of which is incorporated by refer-
`ence herein.
`
`FIELD OF THE IN‘/T£N'I'lON
`
`The invention relates to methods and apparatus For provid-
`ing a laser-driven light source.
`
`BACKGROUND OF THE INVENTION
`
`liigh brightness light sources can be used 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 lights
`sources can. alternatively, be used as a source of illumination
`in a lithography system used in the fabrication of wafers. a
`microscopy systems. or a photoresist 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 sufiicient bright-
`ness for some applications. especially iii the ultraviolet spec~
`trum. Further. the position of the arc can be unstable in these
`lamps.
`Accordingly. a need therefore 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-11-:1 INVII-‘.N’I‘l()N
`
`The present invention t'eatur-es 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 chamber. The light source also
`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 modifyinga 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
`mirror (e.g.. a coated mirror. a dielectric coated mirror,
`at
`
`US ?,'?86,455 B2
`
`2
`
`narrow band mirror, and an ultraviolet transparent infrared
`reflecting mirror). In some embodiments. 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-
`sil® quartz (Heraeus Quartz America. LLC. Buford. Ga).
`sapphire. MgF3, diamond. and CaF2. In some embodiments,
`the cliamber is a sealed chamber. In some embodiments. the
`chamber is capable of being actively pumped.
`In sortie
`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.
`
`The gas can be one or r11ore ofa noble gas. Xe. Ar. Ne. Kr.
`He, D3, H3. 02, F2, a metal halide_. a halogen, Hg, Cd. Zn. Sn.
`Ga, Fe_. I.i_. 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 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
`embodiments, the at least one laser includes a pulse or con-
`tinuous wave laser. In some erlibodimertts. the at least one
`laser is an IR laser. a diode laser. a fiber laser. an ytterbium
`laser. a C03 laser. a ‘(AG laser. or a gas discharge laser. In
`some ernbodiments. 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 source. ar1 RF ignition source. a microwave
`ignition source. a flash lamp. a pulsed laser. or a pulsed lamp.
`The ignition source can be a eonti nuous wave (CW) or pulsed
`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
`modifying a property of electromagnetic radiation emitted by
`the ionized gas. The optical element can be, for example. one
`or more r11irrors or lenses. In sortie embodiments. the optical
`element is configured 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 litliography tool, oran
`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 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 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 (eg._.
`a wafer inspection tool. a microscope. at metrology tool. a
`lithography tool. or an endoscopic tool).
`
`.3
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`US ?,'?86,455 B2
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`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 enibocliments. t.he at least o11e laser is a continuous
`wave laser or a high pulse rate laser. In some embodiments.
`die at least o11e laser is a high pulse rate laser that provides
`pulses ofenergy to the ionized medium 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 embodinients, the
`at least one laser provides energy substantially continuously
`to l1‘lll‘l.ll‘l1i?2l2 cooling of the ionized medimn when energy is
`not provided to the ionized medium.
`In some embodiments. 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 le11s. an
`achromatic lens. a single element lens. a fresnel lens, a coated
`mirror. a dielectric coated mirror. a narrow band mirror. or an
`ultraviolet transparent
`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.
`In some embodiments. the chamber includes an ultraviolet
`transparent region. In some embodiments. the chamber or a
`window in the chamber includes a quartz material. snprasil
`quartz material. sapphire material, MgF3 material. diamond
`material. or Cali‘, material. In some embodiments. the cham-
`ber is a sealed chamber. The chamber can be capable of being
`actively pumped.
`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 be a solid. liquid or gas. The
`ionizable medium can include one or more ofa noble gas. Xe.
`Ar. Ne. Kr, He, D2, H2. 02. F2, :1 metal halide_. a halogen, Hg,
`Cd, Zn, Sn, Ga. Fe, Li. Na, an excimer forming gas. air. a
`vapor, is metal oxide, an aerosol. a llowing 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. '1"he target can be a pool or film of metal. In
`some embodiments, the target is capable of moving.
`In some embodiments, 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 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
`indttctive 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 elnbodilnents. 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
`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, a metrology
`tool, a lithography tool, or an endoscopic tool).
`The invention.
`ir1 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
`
`1D
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`50
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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 embodiinents. the method also involves directing
`the laser energ 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
`niedinm is a moving target. The ionirable medium can
`include a solid. liquid 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 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 ligln 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 for providing substan-
`tially continuous laser energy to the ionized medium within
`the chamber.
`
`The invention. in another aspect, features a light source
`having a chainber that includes a rcflective 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 eontint1ous—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 refleetive surface (e.g.. inner surface) ofthe cham-
`ber and the reflective surface directs at least a portion ofthe
`first set ofwavclengths of electrornagnelie 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 reflected toward the refiector. and is reflected by
`the reflector toward a tool. In some embodiments, 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 lirst wavelengths of electromagnetic energy
`towards the reflective surface of the chamber, and the reflec-
`tive surface directs a portion of the first set ofwavelengths of
`electromagnetic energy toward the plasma.
`111 some embodiments, at least a portion of the high bright-
`ness ligln 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
`embodiments. the light source comprises a microscope. 1.1llI‘2‘l-
`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
`directed toward the reflective surface of the chamber.
`is
`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
`some embodiments. the chamber is a sealed chamber. In some
`embodiments, the reflective surface of the cheunber com-
`
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`prises a curved shape, parabolic sl1ape_. elliptical shape,
`spherical shape or aspherical shape. In some embodiments.
`the chamber has a reflective inner surface. 111 some embodi-
`
`magnetic energy comprising the second set of predefined
`wavelengths of electromagnetic energy passes through the
`reflector.
`
`ments. a coating or film is located on the outside of the
`chamber to produce the reflective surface. In some embodi-
`ments, a coating or film is located on the inside ofthe charnher
`to produce the reflective surface. I11 some embodiments. the
`reflective surface is a structure or optical element that is
`distinct from the inner 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 laser to the plasma over
`a large solid angle. In sortie 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 invemion. in anotheraspect. features a light sourcethat
`includes a chaniber that has a reflective surface. The light
`source also includes an ignition source for ionizing a gas
`within tl1e chaniber. 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 cliamber.
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`In sortie ernbodintenls, l.he 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.
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`40
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`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 reflector 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.
`
`111 some embodiments. the method involves directing the
`laser energy comprising a first set ofwavelengths ofe1ectro-
`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 of electromagnetic energy toward the plasma. In some
`embodiments. the method involves directing a portion of the
`higlt brightness light toward the reflective surface of the
`chamber which is reflected toward the reflector and, electro-
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`60
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`65
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`The method can involve directing the laser energy through
`an optical element that niodi lies a property of the 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 niodifies 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 ofthe 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 niodi fies 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 soiue embodiments. 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 reflocts 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. In some 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 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. 111 some
`embodiments. 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 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 of predefined wavelengths of
`electromagnetic energy directed toward the reflector and at
`least substantially allowing a second set ofpredefined 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 another aspect. features a ligl1t 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 within the chamber to produce a plasma that
`generates a high brightness fight. The light source also
`includes a curved reflective surface disposed extemal to the
`
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`US ?,'?86,455 B2
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`sealed chamber to receive at leas a portion ofthe high bright-
`ness light emitted by the sealed chamber and reflect the high
`brightness light toward an output of the light source.
`In sortie embodiments. the light source includes an optical
`element disposed along a path the electromagnetic energy .3
`from the laser travels. In some embodiments, the sealed
`chamber includes a support element that locates the sealed
`chamber relative to the curved reflective surface.
`111 some
`embodiments, the sealed chamber is a quartz bulb. in some
`embodiments.
`the light source includes a second curved
`reflective surface disposed internal or extemal to the sealed
`chamber to receive at least a portion of the laser electromag-
`netic energy and focus the electromagnetic energy on the
`plasma that generates the high brightness light.
`Tl1e invention. in anotheraspect. features a light source that
`includes a sealed chamber and 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 reflect 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 reflective 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
`of the light source.
`the curved reflective surface
`In some embodiments.
`focuses tl1e electromagnetic energy on a region i11 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
`extemal 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 ofthe invention will become more apparent front
`the following description and from the claims.
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`BRIEF DESCRIPTION 017 'I‘HF;‘ DRAWINGS
`
`The foregoing and other objects, feature and advantages of
`the invention, as well as the invention itself, will be more hilly
`understood from the following illustrative description. when
`read together with the accompanying drawings which are not
`necessarily to scale.
`FIG.
`1
`is a schematic block diagram of a light source.
`according to an illustrative embodiment of the invention.
`FIG. 2 is a schematic block diagram ofa portion ofa light
`source. according to an illustrative embodiment ofthe inven-
`tion.
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`4::
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`45
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`50
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`FIG. 3 is a graphical representation of UV’ brightness as a
`function ofthe laser power provided to a plasma. using a light
`source according to the invention.
`FIG. 4 is a graphical representation of the transmission of “
`laser energy through a plasma generated from mercury. using ”
`‘
`a light source according to the invention.
`l"I('i. 5 is a schematic block. diagram of a light source.
`according to a11 illustrative embodiment of 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 a schematic block diagram of a light source in
`which electromagnetic energy from a laser is provided to a 55
`plasma over a first solid angle. according to an illustrative
`embodiment ofthe invention.
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`5.3
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`FIG. 8B is a schematic block diagram ofthe light source of
`FIG. 8A in which the electromagnetic energy front the laser is
`provided to the plasma over a larger solid angle. according to
`an illustrative embodiment of the invention.
`
`l)I-7.'I'AII..l'.".I) l)[ES(?RIP'I‘I()N OF II .I..UST'R.J\'l'IV'li
`EMBODIMENTS
`
`FIG. 1 is a schematic block diagram of a light source 100
`for generating light. that embodies the invention. The light
`source 100 includes a chamber 128 that contains an ionizable
`
`medium (not shown). Thelight source 100 provides energy to
`a region 130 o fthe chamber 128 having the ionizable medium
`which crea