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`US007786455B2
`
`12 Ulllted States Patent
`Smith
`
`(10) Patent No.:
`(45) Date of Patent:
`
`9
`9
`US 7 786 455 B2
`Aug. 31, 201.0
`
`Y
`.......... .. 356/237.1
`9/2001 Fairle er al.
`6,288,780 B1
`..
`.. 315/111.31
`7/2002 Brooks em.
`6,417,625 111*
`356/237.2
`9/2004 Lzuige ...... ..
`6,788-.404 B2
`.. 315/111.31
`..
`6,956,329 B2’* 10/2005 Brooksetal.
`57,652,430 131*
`1/.2010 Delgado ................... h-31:5/'63:;
`2002/0021508 A1
`2/2002 Ishihara .................... 1359/853
`2003'/“E8982 Al
`922003 Km
`311634
`2003'02.>1496 A1
`12/2003 Sztto etal.
`................. .. 362 26.8‘
`2004/0264312 'A1"‘ 12/2004 Harllove etal.
`.............. ..
`.372/5
`2005/0167618 /11*
`8/T2005 Hoshi11oet:1.l.
`250/50411
`2007/0285921 A1 ~'=
`12/2007 Zulim 21:11.
`.............. .. 362/240
`
`
`
`54
`
`LASER-DRIVEN LIGHT SOURCE
`
`(75)
`
`Inventor: Donald K- Smith, 13611110111. MA (US)
`_
`N
`_ H
`_
`(73) ASSIBWG3 1‘4“eFg°f“1 1°“h“°‘°gY+1“°-=W°b““1>
`MAW5)
`Subject to any disclaimer, the term ofthis
`Pam‘ is extended or adjusted under 35
`U_S_C_ 1540)) by 320 days.
`
`('“"_) Notice:
`
`_
`(21) Appl.No.: 11/695,348
`
`(22) Filed:
`
`Apr. 2, 2007
`
`(65)
`
`Prior Publication Data
`
`US 2007/0228300 A1
`
`001. 4. 2007
`
`(Continued)
`
`FOREIGN PATENT DOCUNIENTS.
`
`Related U.S. Application Data
`
`JP
`
`61-193358
`
`S/1986
`
`(63) Q)nti1iuation~i11~p:-111 of application No. 11/395,523,
`filed on Mar. 31, 2006, now Pat. No. 7,435,982.
`
`(51)
`
`Int. Cl.
`(2006.01)
`H05B 31/26
`(2006.01)
`G01] 3/10
`(2006.01)
`G210’ 4/00
`(2006.01)
`H01J 61/28
`(52) U.S. Cl.
`............................. ., 250/493.1‘. 250/504 R‘,
`315/111.21; 315/111.71; 315/111.91; 313/231.31;
`313/231.41; 313/231.71
`(58) Field of Classification Search ........... .. 250/423 R,
`250/423 P, 424, 426, 494.1, 493.1, 504 R,
`250/504 H: 315/111.21,111.71,111.91;
`313/231.31, 231.41. 231.61, 231.71, 631,
`313/632, 633
`See application file for complete search history.
`
`(56)
`
`References Cited
`U.S. 1’A'l‘EN'1‘DOCUMl%‘.N'1‘S
`
`4,088,966 A "‘
`4,498,029 A *
`4,646,215 A
`RF.32,626 E *
`
`313/231.51
`5/1978 Szunis
`315/39
`2/1985 Yoshi"/.awaetal.
`
`2/1987 Levin of 111.
`............... .. 362/296
`3/1988 Yosliizawaet :11.
`315/779
`
`OTHER PUBLICATIONS
`
`Wilbers et 31., “The VUV Emissivity of a High—Pressiuc Cascade.
`Argon Arc from 125 to 200 11111,”./. Qua/zt. Speclrosc. Radial. 7711:13-
`_/‘er, vol. 46, 1991, pp. 299808.
`
`(Continued)
`
`Primar_y EA-arz1i11er—~Ber11ard E Souw
`(74) Attor/2e_v, Agent, or I7irm~---Proskauer Rose LLP
`
`(57)
`
`ABS'l‘RAC'l‘
`
`An apparatus for producing light includes a chamber and an
`ignition source that ionizes 21 gas within the chamber. The
`apparatus also includes at least one laser that provides energy
`to the ionized gas within the chamber to produce 21 high
`brightness. light. The laser can provide 11 substantially con-
`tinuous amount of energy to the ionized gas to generate a
`substantially continuous high brightness light.
`
`43 Claims, 8 Drawing Sheets
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`
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`ASML ‘I401
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`US 7,786,455 B2
`Page 2
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`U .
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`PATENT DOCUMENTS
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`2009/0032740 Al*
`
`2/2009 Smith ctal.
`
`............ .. 250/503.1
`
`OTPIER PUBLICATIONS
`
`Wilbers at al., “The Continuum Emission of an Arc Plasma,” J.
`Qua/1f. Speclrosc. Rat/int. Transfer, vo1.45,No. 1, 1991, pp. 1-10.
`Beck. “Simple Pulse Generator for Pulsing Xenon Arcs with High
`Repetition Rate,” Rev. Sci. Insrrum., vol. 45, No. 2, Feb. 1974, pp.
`318-319.
`Raizer, "Optical Discharges,” Sov. P/gas‘. Usp; 23(l 1), Nov. 1980, pp.
`789-206.
`]'*'iodorowic7. et al., “X-Ray Emission form Laser-Irradiated Gas Puff
`Targets," Appl. Phys. Letl. 62 (22), May 31, 1993. pp. 2778-2780.
`Keefer et al., “Experimental Study of a Stationary Laser-Sustained
`Air Plasn1a,”Jourm1l of/Ipplied1’l:y.vicr, vol. 46, No. 3, Mar. 1975,
`pp. 1080-1083.
`Jeng et al., “’I'hoorel'ical Investigation oflsaser-Sustained Argon Plas-
`mas,” J. Appl. P/tys. 60 (7), Oct. 1, 1986. pp. 2272-2279.
`Franzen, “CW Gas Breakdown in Argon Using 10.6-pm’Laser Radia-
`t‘ion,”A1)/)I. Plays. LeII., vol. 21, No. 2, Jul. 15, 1972, pp. 62-64.
`Moody, “Maintenance ofa Gas Breakdown in Argon Using 10.6-pew
`Radiation,” Journal Q/"Applied Physics, vol. 46, No. 6, Jun. 1975, pp.
`2475-2432.
`
`Generalov eta1., “II'Ixpcrimental Investigation of a Continuous Opti-
`cal Discharge,” SovicrPlzys1‘c's JETP. vol. 34, No. 4, Apr. 1972, pp.
`763-769.
`
`Generalov et al., “Continuous Optical Discharge,” ZI1ETFPI'.r. Red.
`ll, No. 9, May 5, 1970, pp. 302-304.
`Kozlov et al., “Radiative Losses by Argon Plasma and the Emissive
`Model ofa Continuous Optical Discharge." Sov. Phys. J/HP, vol. 39.
`No.3, Sep. 1974, pp. 463-468.
`‘
`Carlhoff et al., “Continuous Optical Discharges at Very High Pres-
`sure,” P/zysica 103C, 1981. pp. 439-447.
`Cromors et al., “livaluation of the Continuous Optical Discharge for
`Spectrochemical Analysis,” Specrroclzimica Acta, vol. 40B, No. 4,
`1985, pp. 665 -679.
`Kozlov et al., “Sustained Optical Discharges in Molecular Gases,”
`Sov. Phys. Zbc/1. Phys. 49(1l), Nov. 1979, pp. 1283-1287.
`Keefer, "I_aser—Sustained Plasmas,” Lax('I'—I1Ir/(med P1a.s'ma.s' and
`Applications, published by Marcel Dekker, edited by Radziemski et
`al., 1989, pp. 169-206.
`Hamamatsu Product Information, “Super-Quiet Xenon Lzunp Super-
`Quiet Mercury-Xenon I_a.mp,” Nov. 2005.
`
`’-”‘ cited by examiner
`
`

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`US 7,786,455 B2
`
`1
`LASER—DRIVEN LIGHT SOURCE
`
`REI,.A'l'I3D APl’l.,ICATl()NS
`
`This application is a continuation-in-part o1‘U.S. Ser. No.
`I 1/395,523, filed on Mar. 31-, 2006, now U.S. Pat. No. 7,435,
`982, the entire disclosure of which is incorporated by refer-
`ence herein.
`
`FIELD OF TI~IlE INVENTION
`
`The invention relates to methods and apparatus for provid-
`ing a laser—driven light source.
`
`BACKGROUND OF TI-lP.INVl:"1,NTION
`
`High 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 waters 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 andbrightness) 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 and/or
`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 in the ultraviolet spec-
`trum. Furthcr, 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 higi brightness
`light.
`
`SUMMARY OF TI-IE INVENTION
`
`10
`
`20
`
`30
`
`40
`
`45
`
`The present invention features a light source for generating
`a high brightness light.
`The invention, in one aspect‘, features a light source having
`a chamber. The light source also includes an ignition source
`for ionizing a gas within the 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 inodilyiii g a property
`of the laser energy provided to the ioni7.ed gas. The optical
`element can be. for example. a lens (e.g.. an aplanatic lens, an
`achromatic lens, a single element lens. and a fresncl lens) or
`mirror (e.g., a coated mirror. a dielectric coated mirror. a
`
`u.'11
`
`60
`
`65
`
`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, Buhird, Ga.),
`sapphire, MgF2, diamond, and CaF3. In some embodiments,
`the chamber is a sealed chamber. In some embodiments, the
`chamber is capable of being actively pumped.
`In, some
`embodiments, the chamber includes a dielectric material
`(e.g., quartz). The chamber can be, for example, a glass bulb.
`In some embodiments, the chamber is an ultraviolet transpar-
`ent dielectric chamber.
`The gas can be one or more of a noble gas, Xe, Ar, Ne, Kr,
`He, D2, H2, 02, F2, a metal halide, a halogen, Hg, Cd, Zn, Sn,
`Ga, Fe, Li-, Na, an excimer forming gas, air, a Vapor, a metal
`oxide, an aerosol, allowing media, or a recycled media. The
`gas can be producedby a pulsed laser beam that impacts a
`target (e.g., a solid orliquid) 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 embodiments, the at least one
`laser is an IR laser, a diode laser, aflber laser, an ytterbium
`laser, a C03 laser, a YAG laser, or a gas discharge laser. In
`some embodiments, the at least one laser emits at least one
`wavelength of electromagnetic energy that
`is strongly
`absorbed by the ionized medium.
`The ignition source can. be or can include electrodes, an
`ultraviolet ignition source, a capacitive ignition source, an
`inductive ignition source, an RF ignition source, a microwave
`ignition source, a llash lamp, a pulsed laser, or a pulsed lamp.
`The ignition source can be a continuous wave (CW) or pulsed
`laser impingingon a solid or liquid target in the chamber. The
`ignition source can be external or internal to the chamber.
`The light sotu*ce can include at least one optical element for
`modi fying a property ofelectromagnetic radiation emitted by
`the ionized gas. The optical element can be. for example, one
`or more mirrors or lenses. In some embodiments, the optical
`element is configured to deliverthe electromagnetic radiation
`emitted by the ionized gas to a tool (e.g., a wafer inspection
`tool, a microscope, a mctrology tool, a lithography tool, or an
`endoscopic tool).
`The invention, in another aspect, relates to a method for
`producing light. The method involves ionizing with an igni-
`tion sourcc 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 throuv 1 at
`least one optical element for
`lnodifying a property of the laser energy provided to the
`ionized gas. In some embodiments, the method also involves
`actively pumping the Cllal1‘lbCI'.'.lill€
`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 ofthe ligit. In some
`embodiments, the method also involves delivering the high
`brightness light emitted by the ionized medium to a tool (cg.
`a wafer inspection tool, a microscope, a metrology tool, a
`lithography tool. or an endoscopic tool).
`
`

`
`US 7,786,455 B2
`
`3
`In another aspect, the invention features a light source. Tl1e
`lights source includes a chamber and an ignition source for
`ionizing an ionizable medium within the chamber. The light
`source also includes at least one laser for providing substan-
`tially continuous energy to the ionized medium within the
`chamber to produce a high brightness light.
`In some embodiments, the at least one laser is a continuous
`wave laser or a high pulse rate laser. In some embodiments,
`the at least one laser is a high pulse rate laser that provides
`pulses ofenergy to the ionized medium so the high brightness
`light is substantially continuous. In some embodiments, the
`magnitude ofthe high brightness lign does not vary by more
`than about 90% during operation. I11 some embodiments, the
`at least one laser provides energy substantially continuously
`to _minimize cooling of the ionized medium 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 lens, an
`acliromatic 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, suprasil
`quartz material, sapphire material, Mgllz, material, diamond
`material, or Cal’, material. In some embodiments, the cham-
`ber is a sealed chamber. The chamber can be capable ofbeing
`actively ‘pumped.
`In some embodiments,
`the chamber
`includes a dielectric material (e.g., quartz). In some 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, D3, H2, ()3, F2, a metal halide, a halogen, I-lg,
`Cd, 7n, Sn, Ga, Fe, l..i, Na, an excimer forming gas, air, a
`vapor, a metal oxide,,an aerosol, a flowing media, a recycled
`media, or an evaporating target. In some embodiments, the
`ionizable medium is a target in the chamber and the ignition
`source is a pulsed laser that provides a pulsed laser beam that
`strikes the target. The target can be a pool or film ofmetal. 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 ofelectromagnctic
`energy that is strongly absorbed by the ionized medium.
`The ignition source ca11 be or can include electrodes. an
`ultraviolet ignition source, a capacitive ignition source, an
`inductive ignition source, an Rf‘ ignition source, a microwave
`ignition source, a flash lamp, a pulsed laser, or a pulsed lamp.
`The ignition source can be external or internal to the chamber.
`ln some embodiments, the light source includes at least one
`optical element (eg, 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 (eg., a wafer inspection tool. a microscope, at metrology
`tool, a lithography tool. or an endoscopic tool).
`The invention, in another aspect relates to a method for
`producing light. The method involves ionizing with an igni-
`tion source an ionizable medium within a chamber. The
`
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`20
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`4
`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 throng) at least one optical element for
`modifying a property of the laser energy provided to the
`ionizable medium. The method also can involve actively
`ptunping the chamber. In some embodiments, the ioni7.able
`medium is a moving target. The ionizable 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. I11 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 alight source
`having a chamber. The light source includes a first ignition
`means for ionizing em 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 chamber that includes a reflective surface. The light
`source also includes an ignition source for ionizing a gas
`within the chamber. The light source also includes a reflector
`that at least substantially reflects a first set of predefined
`wavelengths of electromagnetic energy directed toweud 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 (cg. a continuous-wave fiber laser) external to the
`chamber for providing electromagnetic energy to the ionized
`gas within the chamber to produce a plasma that generates a
`high brightness light. A continuous—wave laser emits.radia-
`tion continuously or substantially continuously rather than in
`short bursts, as in a pulsed laser.
`In some embodiments, at least one laser directs a first set of
`wavelengths of electromagnetic energy through the reflector
`toward the reflective surface (e.g._, inner surface) of the cham-
`ber and the reflective surface directs at least a portion of the
`first set ofwavelengths ofelcctromagnetic 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 reflector, 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 refiector, the reflector reflects at least a
`portion of the flrst wavelengths of electromagnetic energy
`towards the reflective surface of the chzunber, and the reflec-
`tive surface directs a portion ofthe first set of wavelengths of
`electromagnetic energy toward the plasma.
`In some embodiments, at least a portion of tlie high bright-
`ness light
`is directed toward the reflective surface of the
`chamber, is reflected toward the reflector, and passes through
`the reflector toward an output of the light source. In some
`embodiments, the light source comprises a microscope, ultra-
`violet microscope, wafer inspection system, reticle inspec~
`tion system or lithography system spaced relative to the out-
`put of the light source to receive the high brightness light. In
`some embodiments, a portion of the high brightness light is
`directed toward the reflective surface of the chamber,
`is
`reflected toward the reflector, and electromagnetic energy
`comprising the second set ofpredefined wavelengths of elec-
`tromagnetic energy passes through the reflector.
`The chamber ofthe light source can include a Window. In
`some embodiments, the chamber is a sealed chamber. In some
`embodiments, the reflective surface of the chamber com-
`
`

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`5
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`US 7,786,455 B2
`
`prises a curved shape, parabolic shape, elliptical shape,
`spherical shape or aspherical shape. In seine embodiments‘,
`the chamber has a reflective inner surface. In some embodi-
`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 chamber
`to produce the reflective surface. In some embodiments, the
`reflective surface is a structure or optical element
`that is
`distinct from the inner surface of the chamber.
`
`The ligl1t source can include an optical element disposed
`along 21 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 seine embodiments, the refiective sur-
`face of the chamber is adapted to provide electromagnetic
`energy from the laser to the plasma over a large solid angle. In
`some embodiments, the reflective surface of the chamber is
`adapted to collect the high brightness light generated by the
`plasma over a large solid angle. In some embodiments, one or
`more of the reflective surface, reflector and the window
`include (e.g., are coated or include) a material to filter pre-
`defined wavelengths (e.g., infrared wavelengths of electro-
`magnetic energy) of electromagnetic energy.
`The invention, in anotheraspect, 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 chamber. The light source also includes at least one
`laser external to the chamber for providing electromagnetic
`energy to the ionized gas within the chamber to produce a
`plasma that generates a high brightness light. The light source
`also includes a reflector positioned along a path that the
`electromagnetic energy travels from the at least one laser to
`the reflective surface of the chamber.
`
`In some embodiments, the reflector is adapted to at least
`substantially reflect a first set of predefined wavelengths of-
`electromagnetic energy directed toward the reflector and at
`least substantially allow a second set of predefined wave-
`lengths of electromagnetic energy to pass through the reflec-
`tor.
`
`The invention, in another aspect, relates to a method for
`producing light. The method involves ionizing with an igni-
`tion source a gas within a chamber that has a reflective sur-
`face. The method also involves providing laser energy to the
`ionized gas in the chamber to produce a plasma that generates
`a high brightness light.
`.In some embodiments, the method involves directing the
`laser energy comprising a first set of wavelengths of electro-
`magnetic energy through a 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 of the high bright-
`ness light toward the reflective surface of the chamber which
`is reflected toward the reflector and is reflected by the reflec-
`tor toward a tool.
`
`In some embodiments, the method involves directing the
`laser energy comprising a first set of wavelengths ofelectro—
`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 ofclcctromagnetic energy toward the plasma. In some
`embodiments. the method involves directing a portion of the
`high brightness light toward the reflective surface of the
`chamber which is reflected toward the reflector and, electro-
`
`magnetic energy comprising the second set of predefined
`wavelengths of electromagnetic energy passes through the
`reflector.
`
`The method can involve directing the laser energy through
`an optical element that modifies a property ofthe la ser 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
`properly of the laser energy to direct the laser energy toward
`the plasma over a solid angle ofapproximately 0.012 stera-
`dians. In some embodiments, the method involves directing
`the laser energy through‘ an optical element that modifies a
`property of the laser energy to direct the laser energy toward
`the plasma over a solid angle of approximately 0.048 stera-
`dians. In some embodiments, the method involves directing
`the laser energy through an optical element that modifies a
`property of the laser energy to direct the laser energy toward
`the plasma over a solid angle of greater than about 23': (about
`6.28) steradians. In some 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
`reflective stir-
`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 rellective surface of the
`chamber is reflected toward the ‘plasma. In seine 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 andtravels toward
`the reflective surface of the chamber. In some embodiments,
`the electromagnetic energy directed toward the reflective sur-
`face of the chamber is reflected toward the plasma. In some
`embodiments, a portion of the high brightness light is directed
`- toward the reflective surface of the chamber, reflected toward
`the reflector and reflected by the reflector.
`The invention, in another aspect, features alight source that
`includes a chamber having a reflective surface. The light
`source also includes a means for ionizing a gas within the
`chamber. The light source also includes a means for at least
`substantially reflecting a first set ofpredefined wavelengths of
`electromagnetic energy directed toward the reflector and at
`least substantially allowing a second set of predefined wave-
`lengths ofelectromagietic 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 light source that
`includes a sealed chamber. The light source also includes an
`ignition source for ioni'/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 a high brightness light. The light source also
`includes a curved reflective surface disposed external to the
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`US 7,786,455 B2
`
`8
`FIG. 8B is a schematic block diagram of the light source of
`FIG. 8A in which the electromagnetic energy from the laser is
`provided to the plasma over a larger solid angle, according to
`an illustrative embodiment of the invention.
`
`DETAILI1",D DESCRIPTION OF ILLUSTRATIVE
`EMBODIMENTS
`
`7.
`
`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
`from the laser travels. In some embodiments, the sealed
`chamber includes a support element that locates the sealed
`chamber relative to the curved refiective surface. In some
`embodiments, the sealed chamber is a quartz bulb. In some
`embodiments, the light source includes a second curved
`reflective surface disposed internal or external 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.
`The invention, in another aspect, features a light source that
`includes a sealed chamber and an ignition source for ionizing
`a gas withinthe chamber. The light source also includes at
`least one laser external to the sealed chamber for providing
`electromagnetic energy. The light source also includes a
`curved rellectivc 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 rellective 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 the electromagnetic energy on a region in the cham-
`ber where the plasma is located. In some enibodintents, 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 become more apparent from
`the following description and from the claims.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The foregoing and other obj ects. feature and advantages of
`the invention, as well as the invention itself, will be more fully
`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.
`f"IG. 2 is a schematic block diagram of a portion ofa light
`source, according to an illustrative embodiment ofthe inven-
`tion.
`
`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.
`FIG. 5 is a schematic block diagram of a light source,
`according to an illustrative embodiment ofthe 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.
`l7‘lG. SA is a schematic block diagram of a light source in
`which electromagnetic energy from a laser is provided to a
`plasma over a first solid angle, according to an illustrative
`embodiment ofthe invention.
`
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`FIG. 1 is a schematic block diagram of a light source 100
`for generating light, that embodies the invention. The light
`source 1 00 includes a chamber 128 that contains an ionizable
`medium (not shown). The light source 100 provides energy to
`a regi