||||||||||||||||||||||||||||||||||||l||||||||||||||||||||||||||||||||||||||
`
`US00??86455B2
`
`(12)
`
`United States Patent
`Smith
`
`(10) Patent No.:
`(45; Date of Patent:
`
`US 7,786,455 B2
`Aug. 31, 2010
`
`(54)
`
`(75)
`
`(73)
`
`LASER-DRIVEN LIGHT SOURCE
`
`Inventor: Donald K. Smith. Bellliollt. MA (US)
`
`Assignee: Energetiq Technoloy, Inc.. Woburn.
`MA (US)
`
`Notice:
`
`Subject to any disclaimer, tl1e term of this
`patent is extended or adjusted under 35
`U.S.(T. 154(1)) by 820 days.
`
`(21)
`
`Appl. No.: 111695.348
`
`(32)
`
`Filed:
`
`Apr. 2, 2007
`
`(65)
`
`Prior Publication Data
`
`US 2007110228300 Al
`
`Oct. 4. 2007
`
`5.232.730 Bl
`5.417.525 Bl*
`6.788.404 B2
`6.956.329 132*
`7.652.430 131+
`zuuzruuzisus Al
`200310168982 Al
`2003.-"0231496 Al
`200400264512 Al‘
`2005.-'0167618 Al‘
`200'.-‘#0285921 Al"‘
`
`
`
`355.-'237.I
`9:200: Fairleyetal.
`315.-111.31
`7.’-"2902 Brookselal.
`356.-"2312
`932004
`I.a.uge
`315-"1il.3l
`1052005 Brooks eta.l.
`3:3»-633
`H2010 Delgado
`359»-253
`2.-zuuz
`Ishihara
`.... .. 313.1634
`9.-‘"2003 Kim
`................. .. 3625268
`I2.-‘"2003 Sate eta].
`l2:"2004 I-lartlovcctal.
`3'12.-"5
`852005 Hashim: eta].
`250.-"S0411
`I2.-‘"200? Zuiimet al.
`.............. .. 362.-'240
`
`((.‘on1i11ued)
`FOREIGN PATENT DOCUMENTS
`
`Related U.S. Application Data
`
`JP
`
`61493358
`
`831986
`
`(63)
`
`Continuatiun-in-pan of application No. 111395.523.
`filed on Mar. 31. 2006. now Pat. No. 7.435.982.
`
`(51)
`
`(52)
`
`(56)
`
`Int. Cl.
`(2006.01)
`H05B 31/26
`(2006.01)
`G01} 3/10
`(2005.01)
`(;21(; 4/00
`(2006.01)
`H011 61.08
`2501493.]: 250504 R:
`U.S. (I1.
`31511I1.21:315)'11l.71:3lS!]11.91:3l3x’231.31:
`3l3)'231.4l:3l3f23l.7l
`Field ofClassifieation Search
`25011423 R,
`250a‘423 P. 424. 426. 494.1. 493.1. 504 R,
`250504 1-1: 315111121. 111.71. 111.91:
`3l3.r’23l.3l. 231.41.231.61. 231.71. 631.
`313K632. 633
`See application file for complete searcli history.
`References Cited
`
`U,S. PATENT DOCUMENTS
`
`4.088.966 A “‘
`4.498.029 A "‘
`4.646.215 A
`RE32.626 E ’°
`
`313-231.51
`5.-‘I928 Samis
`315.-"39
`211985 Yosl1i?;1waetal.
`25198? Levin et al.
`............... .. 362-"296
`3-‘I988 ‘{oshi7awacl:1l.
`315.539
`
`OTHER PUBLICATIONS
`
`Wilbers et al.. “The \«'Li'V L-‘mi ssivity of a Iligh-Pressure Cascade
`Argon _—‘-\_rc from 125 to 200 nI‘rL”.I.
`t,'_)mm!_ S_:)e.r.'rn:.u'rr_ Radial’. Tl'{J'!]'S-
`fer. Vol.45, 1991. pp. 299-308.
`
`(Continued)
`
`Pr.I'mar_1' E.\'rm:iner——Ber11ard E Se-uw
`(74) /lr.=‘orm3_1-'. /1gem‘, or Fire: Pmskauer Rose 1.1 P
`
`(57)
`
`ABSTRACT
`
`An app-aramis for producing light includes a cliamber and an
`ignition source that ionizes a gas within the cliamber. The
`apparatus also includes at least one laser that provides energy
`to the ionized gas within lhe chamber to produce :1 high
`briglitncss light. The laser can provide a stlbslanlially con-
`tinuous amount of energy to the ionized gas to generate a
`substantially continuous high brightness light.
`
`43 Claims, 8 Drawing Sheets
`
`228
`
`
`
`ASML 1101
`
`ASML 1101
`
`

`
`US 7,786,455 B2
`Page 2
`
`US. PATENT DOCUMENTS
`
`20097003 2740 Al ‘°
`
`2."2D09 Smith et al.
`
`25Df503.l
`
`OTHER PUBLICATIONS
`
`Wilbers el al.. "The Continuum Emission of an Arc I‘lasn1a.” J’.
`Qrrarrr. Specmosc. Rndfar. Tr'arr.y'e7'. vol. 45. No. l. 1991. pp. 1-10.
`Beck. "Simple Pulse Generator for Pulsing Xenon Arcs with Iligh
`Repetition Rate." Rev. Sci‘. 1rm'r'rmI.. 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 al.. “X-Ray Emission form Laser-Irradiated Gas Puff
`TaJge1s.”.4pp7_ Pays. Lea. 62 (22). May 31. 1993. pp. 27732730.
`Keefer et al.. "F.~<perimenIal Study of a Stationary Laser-Sustained
`Air Plasma." Jorrrrrm‘ ofApplied PIrysr'c.r. vol. 46. No. 3. Mar. 1975.
`pp. I080-I083.
`Jeng et aI.. “Theoretical Investigation of Laser-Sustained Argon Plas-
`mas.“ J’. Appt‘. Phys. 60 (7), Oct. l. 1986. pp. 2272-2279.
`Franzen. "CW Gas Breakdown in Argon Using 10.6-tun 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." Jom"mz.l c5t}4'p_£>fr'€d Physics-. vol. 46. No. 6. Jun. 1975. pp.
`2475-2482.
`
`Generalov et al.. “Experimental Investigation ol"a Continuous Opti-
`cal Discharge." Soviet Physics .H5TP. vol. 34. No. 4. Apr. 1972. pp.
`763-769.
`
`(ieneralov et al.. “Continuous Optical Discharge.” Z)'tE]l’FPr's. Red.
`1 1. No. 9. May 5. I970. pp. 302-304.
`Kozlov et al.. “Radiative Losses by Argon Plasma and the Iiimissive
`Model of a Continuous Optical Discharge." Sou P}rys.JE1"P.vo[.39.
`No. 3. Sep. 1974. pp. 463-468.
`Carlhoff et 31].. “Continuous Optical Discharges at Very High Pres-
`sure.”PIry.vfca 103C. 1981. pp. 439-447.
`Cremers at al.. “Evaluation of the Continuous Optical Discharge for
`Spectrochemica] Analysis,” Specnvclrirrtfcn Acre, 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." La.s'er—."rrdaced Ptasrrras and
`A'ppt':‘ca.'f0n.i'. published by Marcel Dekker. edited by Radziemski et
`21].. 1989. pp. I69-206.
`I-Iatnamatsu Product I.nforrnation._ "Super-Quiet Xenon Lamp Super-
`Quict Mercury-Xenon Lamp.” Nov. 2005.
`
`* cited by examiner
`
`

`
`U.S. Patent
`
`Aug. 31, 2010
`
`Sheet] of8
`
`US 7,786,455 B2
`
`_,.O_n_
`
`2:
`
`mo_
`
`.
`
`

`
`U.S. Patent
`
`Aug. 31, 2010
`
`Sheet 2 of8
`
`US 7,786,455 B2
`
`mum
`
`

`
`U.S. Patent
`
`Aug. 31, 2010
`
`Sheet 3 0f8
`
`US 7,786,455 B2
`
`c:
`N%
`
`ca
`:2
`w-
`
`co
`
`/0
`
`c:
`00
`
`‘0
`3
`on?
`(03
`Q
`__|
`
`C3
`
`V
`
`c:
`N
`
`c:
`
`O0
`'
`(D
`U.
`
`O
`\~c':
`(0
`
`(O‘=1'IT\lDO0(.OVI'C\lO
`F TV"?
`
`(1 atuw/M) (wu 0017-002:) sseu1u5!Ja
`
`0 E
`
`L
`5
`$
`.4
`9'
`3
`‘D
`E
`..C
`
`.9
`I--
`
`00
`>
`D
`
`ON f
`
`N 2
`
`6
`
`

`
`U.S. Patent
`
`Aug. 31, 2010
`
`Sheet 4 of 8
`
`US 7,786,455 B2
`
`
`
`
`
`mEmm_n_9..smacks....mmm._.6co_mm_Emcm.._.
`
`
`
`._®>>Dn_.mmm._
`
`w.O_u_
`
`cow
`
`

`
`U.S. Patent
`
`Aug. 31, 2010
`
`Sheet 5 of8
`
`US 7,786,455 B2
`
`omm
`
`own
`
`com
`
`

`
`U.S. Patent
`
`Aug. 31, 2010
`
`Sheet 6 of8
`
`US 7,786,455 B2
`
`(0
`C0
`(0
`
`(D
`C’)
`(.0
`
`com
`
`®.0:
`
`

`
`U.S. Patent
`
`Aug. 31, 2010
`
`Sheet 7 of8
`
`US 7,786,455 B2
`
`N.O_n_
`
`won
`
`3»
`
`

`
`U.S. Patent
`
`H
`
`g
`
`0M
`
`.MS
`
`.m8
`
`8
`
`US 7,786,455 B2
`
`L,com3\
`
`Awow
`
`wow
`
`com\
`
`mom
`
`Em
`
`

`
`1
`LASER-DRIVEN LIGHT SOURCE
`
`RELATED APPLICATIONS
`
`This application is a continuation-in-part of U.S. Ser. No.
`l lt‘39S.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 INV"EN'l'l0N
`
`The invention relates to methods and apparatus For provid-
`ing a laser-driven light source.
`
`BACKGROUND OF THE INVENTION
`
`l-ligh 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
`electromayetic 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 wa fers. 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 in the ultraviolet spec-
`trum. Further. the position of the arc can be unstable in these
`lamps.
`Accordingly, a need Llierefore 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 TI 11-; INV-'IJ‘.N‘l‘l()N
`
`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 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 fresncl lens] or
`mirror (e.g.. a coated mirror. a dielectric coated inirror, a
`
`US ?,786,455 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 11] traviolet transparent region.
`The chamber or a window in the chamber can include a
`material selected from the group consisting of quartz. Supra-
`sil® quartz (I-Ieraeus 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 more ofa noble gas. Xe. Ar. Ne. Kr.
`He. D3, H3, 02, F2, :1 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 at
`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 embodiments. tl1c 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 meditun.
`The ignition source can be or can include electrodes. an
`ultraviolet ignition source, a capacitive ignition source, an
`inductive ignition source, an RF ignition source. a microwave
`ignition source. a flash lamp. a pulsed laser. or a pulsed lamp.
`The ignition source can be 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 ofelectrontagnetic radiation emitted by
`the ionized gas. The optical element czut be, for example. one
`or more 111irrors or lenses. in some embodiments. the optical
`element is configured to deliver the electromagnetic radiation
`emitted by the ionized gas to a tool (e.g.. a wafier inspection
`tool, a 1nicroscope_. a metrology tool. a lithography tool, oran
`endoscopic tool).
`The i11ve11tion_. 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 meditun can be
`a moving target. In some embodiments. the method also
`involves directing the high brightness light through at least
`one optical element to modify a property of the light. In some
`embodiments. the method also involves delivering the high
`brightness light emitted by the ionized medium to a tool (e.g._.
`a wafer inspection tool. a microscope. at metrology tool. a
`lithography tool, or an endoscopic tool).
`
`.3
`
`1U
`
`25
`
`3o
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`

`
`3
`
`4
`
`US ?,786,455 B2
`
`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 brightrtess light.
`In some embodiments. the at least one laser is a coritirtuous
`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 of energy to the ionized medium so the high brightness
`light is substantially continuous. In some embodiments. the
`magnitttde ofthe high brightness light does not vary by more
`than about 90% during operation. in some embodiments, the
`at least one laser provides energy substantially continuously
`to minimize cooling of the ionized medium when energy is
`not provided to the ionized medium.
`In sotne 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
`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 tnore 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, MgF2 material. diamond
`material. or Cali‘; material. In seine 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 (eg.. quartz). In some e1nbodi-
`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. I-I2. 02. F2, a 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. The target can be a pool or film of metal. In
`some embodiments, the target is capable of moving.
`In some enibodiments, 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 n1ediu111.
`The ignition source can be or can include electrodes. an
`ultraviolet ignition source. a capacitive ignition source. an
`inductive ignition source. an RF ignition source, a microwave
`ignition source. a flash lamp. a pulsed laser. or a pulsed lamp.
`The ignition source can be external or internal to the chamber.
`In some e111bod.i1i1cnts. 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 (e.g., a wafer inspection tool. a microscope, a metre-logy
`tool, a lithography tool, or an endoscopic tool).
`The invention.
`in another aspect relates to a method for
`producing light. "lhe method involves ionizing with an igni-
`tion source an ionizable medium within a chamber. The
`
`1U
`
`3U
`
`4U
`
`45
`
`50
`
`55
`
`60
`
`65
`
`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 encrg through at least one optical element for
`modifying a property of the laser energy provided to the
`ionizable medium. The method also can involve actively
`pumping the chamber. In some embodiments. the ionizable
`medium is a moving target. The 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 light source
`having a chamber. The light source includes a first ignition
`means for ionizing an ionizable medium within the chamber.
`The light source also includes a means 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 refleetive 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
`wavelengtlls 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 eontit1uous—wave laser emits radia-
`tion continuously or substantially continuously rather than in
`short bursts. as in a pulsed laser.
`In some embodiments. at least one laser directs a first set of
`wavelengths of electromagnetic energy through the reflector
`toward the reflective surface [e-.g.. inner surface) ofthe cham-
`ber and the reflective surface directs at least a portion ofthe
`first set ofwavelengths ofeleetrornagltetie 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 rellector. 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 rellector, the reflector reflects at least a
`portion of the lirsl 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 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. 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 retiective 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 chamber com-
`
`

`
`5
`
`6
`
`US ?,786,455 B2
`
`shape_.
`prises a curved shape, parabolic shape. elliptical
`spherical shape or asplierical 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 cllamher
`to produce the reflective surface. I11 some embodiments. the
`reflective surface is a structure or optical element that is
`distinct fi'otn the inner surface of the chamber.
`
`The light source can include an optical element disposed
`along a path the electromagnetic energy fro tn 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 invention. inanotheraspect. features a light sourcethat
`includes a chamber that has a reflective Surface. The light
`source also includes an ignition source for ionizing a gas
`within tl1e 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 cliatnber.
`
`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 sottrce 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 sortie etnbodintents. the Iuethod 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 of electro-
`magnetic energy toward the reflector, the reflector reflects at
`least a portion of the first wavelengths of electromagnetic
`energy toward the reflective surface of the chamber.
`the
`reflective surface directs a portion of the first set of wave-
`lengths of electromagnetic energy toward the plasma. In some
`e1nbodin1e11ts_. 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-
`
`1U
`
`3U
`
`4U
`
`45
`
`50
`
`55
`
`60
`
`65
`
`The method can involve directing the laser energy through
`an optical element that nrodi lies a property of the laser energy
`to direct the laser energy toward the plasma over a large solid
`angle. In some e1nbodi111ents_. the method involves directing
`the laser energy through an optical element that modifies a
`property of the laser energy to direct the laser energy toward
`the plasma over a solid angle of approximately 0.012 stera-
`dians. in sortie 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 modi fies a
`property of the laser energy to direct the laser energy toward
`the plasma over a solid angle of greater than about Zr: (about
`6.28) steradians. In sortie ernbodintcnts. 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 cltarnber that has a reflective sur-
`face. The method also involves directing electromagnetic
`energy from a laser toward a reflector that at least substan-
`tially rellects 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 sortie embodi-
`ments. a portion ofthe high brightness light is directed toward
`the reflective surface of the chamber. reflected toward the
`reflector and passes through the reflector.
`In some embodiments, the electromagnetic energy from
`the laser first passes through the reflector and travels toward
`the reflective surface of the chamber. In some embodiments,
`the electromagnetic energy directed toward the reflective sur-
`face of the chamber is reflected toward the plasma. In some
`embodiments. a portion ofthe high 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 ofpredeflned 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 light. The light source also
`includes a curved reflective surface disposed extemal to the
`
`

`
`7
`
`8
`
`US ?,786,455 B2
`
`sealed chamber to receive at leas a portion ofthe high bright-
`ness light emitted by tlte sealed cltamber and reflect the high
`brightness light toward an output of the ligltt source.
`In some embodiments. the ligltt source includes an optical
`element disposed along a path tlte electromagnetic energy
`front the laser travels. In some embodiments, the sealed
`chamber includes a support elentent that locates the sealed
`chamber relative to the curved reflective surface.
`111 some
`entbodintents. the sealed chamber is a quartz bulb. In some
`embodiments.
`the ligltt source includes a second curved
`reflective surface disposed internal or extental 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 anotheraspect. features a ligltt source that
`includes a sealed cltamber and an ignition source for ionizing.
`a gas within the chaunber. 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 ltigh brightness light emitted by the
`plasma and reflects tlte high brightness light toward an output
`of the light source.
`tlte curved reflective surface
`In some embodiments.
`focuses tltc electrolttagnetic energy on a region in the cham-
`ber where the plasma is located. In some embodintents. the
`curved reflective surface is located within the chamber. In
`sonte embodiments. tlte curved reflective surface is located
`extental to the chamber.
`In some ernbodintents. the high
`brightness ligltt is ultraviolet light. includes ultraviolet light
`or is substantially Ktltraviolet light.
`The foregoing attd other objects. aspects, features. and
`advantages ofthe invention will become more apparent front
`the following description and from the claims.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Tllll‘ 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 ernbodintent 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 tlte transmission of
`laser energy through a plasma generated front mercury. using
`a light source according to the invention.
`l"I('i. 5 is a schematic block. diagram of a light source.
`according to an illustrative cntbodimertt 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
`wltich electromagnetic energy from a laser is provided to a
`plasma over a first solid angle. according to an illustrative
`embodiment ofthe invention.
`
`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 ernbodintent of the invention.
`
`DI-7.'I1’\II..lF.I) l)I_7.S(.‘RIP'I‘I()N O1" I[.I..lIS"l‘RA'l'IV'li
`EMBODIMENTS
`
`10
`
`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 eliantber 128 that contains an ioitizable
`
`medium (not shown). Thelight source 100 provides energy to
`a region 130 o fthe chamber 128 having the ionizable rnediu