US008309943B2
`
`(12) United States Patent
`Smith et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 8,309,943 B2
`Nov. 13, 2012
`
`(54)
`
`(75)
`
`(73)
`
`(21)
`
`(22)
`
`(65)
`
`(63)
`
`(51)
`
`(52)
`
`(58)
`
`LASER-DRIVEN LIGHT SOURCE
`
`(56)
`
`References Cited
`
`Inventors: Donald K. Smith, Boston, MA (US);
`William M. Holber, Winchester, MA
`(US); Jeffrey A. Casey, Winchester, MA
`(Us)
`Assignee: Energetiq Technology, Inc., Woburn,
`MA (US)
`
`Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 41 days.
`
`Appl. N0.: 13/099,823
`
`Filed:
`
`May 3, 2011
`
`Prior Publication Data
`
`US 2011/0204265 A1
`
`Aug. 25,2011
`
`Related US. Application Data
`
`Continuation of application No. 12/ 166,918, ?led on
`Jul. 2, 2008, noW Pat. No. 7,989,786, Which is a
`continuation-in-part of application No. 11/695,348,
`?led onApr. 2, 2007, noW Pat. No. 7,786,455, Which is
`a continuation-in-part of application No. 11/395,523,
`?led on Mar. 31, 2006, noW Pat. No. 7,435,982.
`
`Int. Cl.
`(2006.01)
`H01J 63/08
`(2006.01)
`H05H 1/24
`(2006.01)
`H05B 31/00
`US. Cl. ............ .. 250/493.1; 250/504 R; 250/503.1;
`250/365; 315/149; 315/111.21; 313/231.31
`Field of Classi?cation Search ............. .. 250/503.1,
`250/504 R, 365, 493.1; 315/149, 111.21;
`3 1 3/ 23 1 .3 1
`See application ?le for complete search history.
`
`U.S. PATENT DOCUMENTS
`4,646,215 A
`2/1987 Levin et a1.
`6,184,517 B1* 2/2001 SaWada et a1. ........... .. 250/222.2
`6,288,780 B1
`9/2001 Fairley et a1.
`6,788,404 B2
`9/2004 Lange
`7,050,149 B2
`5/2006 OWa et a1.
`7,427,167 B2
`9/2008 Holder et a1.
`7,429,818 B2
`9/2008 Chang et a1.
`7,435,982 B2 * 10/2008 Smith ..................... .. 250/504 R
`7,989,786 B2 *
`8/2011 Smith et a1. .............. .. 250/503.1
`2002/0021508 A1
`2/2002 Ishihara
`2003/0168982 A1
`9/2003 Kim
`2003/0231496 A1 12/2003 Sato et a1.
`(Continued)
`
`JP
`
`FOREIGN PATENT DOCUMENTS
`61-193358
`8/1986
`
`OTHER PUBLICATIONS
`
`Beck, “Simple Pulse Generator for Pulsing Xenon Arcs with High
`Repetition Rate,” Rev. Sci. Instrum., vol. 45, No. 2, Feb. 1974, pp.
`3 18-3 19.
`
`(Continued)
`
`Primary Examiner * Nikita Wells
`(74) Attorney, Agent, or Firm * Proskauer Rose LLP
`
`ABSTRACT
`
`(57)
`An apparatus for producing light includes a chamber and an
`ignition source that ioniZes a gas Within the chamber. The
`apparatus also includes at least one laser that provides energy
`to the ionized gas Within the chamber to produce a high
`brightness light. The laser can provide a substantially con
`tinuous amount of energy to the ionized gas to generate a
`substantially continuous high brightness light.
`
`21 Claims, 17 Drawing Sheets
`
`ASML 1001
`
`

`
`US 8,309,943 B2
`Page 2
`
`US. PATENT DOCUMENTS
`2004/0026512 A1
`2/2004 Otsubo
`2004/0264512 A1 12/2004 Hartlove et al.
`2005/0167618 A1
`8/2005 Hoshino et al.
`2011/0181191 A1* 7/2011 Smith etal. ................. .. 315/149
`
`OTHER PUBLICATIONS
`
`Carlhoff et al., “Continuous Optical Discharges at Very High Pres
`sure,” Physica 103C, 1981, pp. 439-447.
`Cremers et al., “Evaluation of the Continuous Optical Discharge for
`Spectrochemical Analysis,” Spectrochimica Acta, vol. 40B, No. 4,
`1985, pp. 665-679.
`FiedoroWicZ et al., “X-Ray Emission form Laser-Irradiated Gas Puff
`Targets,”Appl. Phys. Lett. 62 (22), May 31, 1993, pp. 2778-2780.
`Franzen, “CW Gas Breakdown in Argon Using 10.6- um Laser
`Radiation,”Appl. Phys. Lett., vol. 21, No. 2, Jul. 15, 1972, pp. 62-64.
`Generalov et al., “Continuous Optical Discharge,” ZhE T F Pis. Red.
`11, No. 9, May 5, 1970, pp. 302-304.
`Generalov et al., “Experimental Investigation of a Continuous Opti
`cal Discharge,” Soviet Physics JETP, vol. 34, No. 4, Apr. 1972, pp.
`763-769.
`Hecht, “Refraction”, Optics (Third Edition), 1998, Chapter 4, pp.
`100-101.
`J eng et al., “Theoretical Investigation of Laser-Sustained Argon Plas
`mas,” J'. Appl. Phys. 60 (7), Oct. 1, 1986, pp. 2272-2279.
`
`Keefer, “Laser-Sustained Plasmas,” Laser-Induced Plasmas and
`Applications, published by Marcel Dekker, edited by Radziemski et
`al., 1989, pp. 169-206.
`Keefer et al., “Experimental Study of a Stationary Laser-Sustained
`Air Plasma,” Journal ofApplied Physics, vol. 46, No. 3, Mar. 1975,
`pp. 1080-1083.
`KoZlov et al., “Radiative Losses by Argon Plasma and the Emissive
`Model of a Continuous Optical Discharge,”Sov. Phys. JE T P, vol. 39,
`No.3, Sep. 1974, pp. 463-468.
`KoZlov et al., “Sustained Optical Discharges in Molecular Gases,”
`Soy. Phys. Tech. Phys. 49(11), Nov. 1979, pp. 1283-1287.
`Moody, “Maintenance of a Gas Breakdown in Argon Using 10 .6-u cW
`Radiation,”Journal ofApplied Physics, vol. 46, No. 6, Jun. 1975, pp.
`2475-2482.
`RaiZer, “Optical Discharges,”Sov. Phys. Usp. 23(11), Nov. 1980, pp.
`789-806.
`“Super-Quiet Xenon Lamp Super-Quiet Mercury-Xenon 1-16.
`Lamp,” Hamamatsu Product Information, Nov. 2005, pp. 1-16.
`Wilbers et al., “The Continuum Emission of an Arc Plasma,” J'.
`Quant. Spectrosc. Radiat. Transfer, vol. 45, No. 1, 1991, pp. 1-10.
`Wilbers et al., “The VUV Emissivity of a High-Pressure Cascade
`Argon Arc from 125 to 200 nm,” .1. Quant. Spectrosc. Radiat. Trans
`fer, vol. 46, 1991, pp. 299-308.
`
`* cited by examiner
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 1 0f 17
`
`US 8,309,943 B2
`
`Yum,
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 2 0f 17
`
`US 8,309,943 B2
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 3 0f 17
`
`US 8,309,943 B2
`
`wmw
`
`
`
`
`
`326mm Ewmlm .w> wwmcimzm >3
`
`gm 536g Emmi
`
`am? / mm mm 3 am
`
`
`
`
`
`£30
`
`mom
`
`13C)
`
`am
`2
`ww
`,2‘ (Jgwwmzx) (Wu (10mm?) wwu?ma
`Q
`
`N ,
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 4 0f 17
`
`US 8,309,943 B2
`
`ONF
`
`..
`
`3“, N; g S 5, mm
`
`
`
`hwgaa Emmi“
`
`mwé
`
`@QQ
`
`oms
`
`mow
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 5 0f 17
`
`US 8,309,943 B2
`
`m mm x...
`
`23:5} ...................L................,.,.,.,...,.,..............
`
`I
`
`@Ex.
`
`0cm
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 6 0f 17
`
`US 8,309,943 B2
`
`wmwk.
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 7 0f 17
`
`US 8,309,943 B2
`
`GE,
`
`.\
`
`wan
`
`

`
`U.S. Patent
`
`Nov. 13, 2012
`
`Sheet 8 of 17
`
`US 8,309,943 B2
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 9 0f 17
`
`US 8,309,943 B2
`
`Z /
`
`‘W.
`
`a f
`
`£33 ,3 .
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 10 0f 17
`
`US 8,309,943 B2
`
`m8 ,wi
`
`H“
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 11 0117
`
`US 8,309,943 B2
`
`wax
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 12 0f 17
`
`US 8,309,943 B2
`
`MJETM
`
`1242
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 13 0f 17
`
`US 8,309,943 B2
`
`
`
`M mm mm, mm, m
`
`
`
`
`
`AEEV ANN wmxm “ma?a
`
`(mus) (A) SHEDQJ
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 14 0f 17
`
`US 8,309,943 B2
`
`mmw w.)
`
`m m m m m m m m w: m m m m m m m m m m m
`
`oncwmwmmmmoccmmwmmmmmmmwm
`
`E2311;
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 15 0f 17
`
`US 8,309,943 B2
`
`mm?
`
`NW3,
`
`1%,,
`
`warm“,
`
`a
`
`A
`
`Qttlf. ,
`
`mm“, .
`
`wow“.
`
`

`
`US. Patent
`
`Nov. 13, 2012
`
`Sheet 16 0f 17
`
`US 8,309,943 B2
`
`

`
`U.S. Patent
`
`Nov. 13, 2012
`
`Sheet 17 of 17
`
`US 8,309,943 B2
`
`
`
`
`
`$339.Q3Q83cmgflQW$:.0mgfimmwiEmmx.m>mmmzflmcm
`
`0
`
`mwmwmmachmv
`
`wfiwwmiEmmx3gm_odw.QdmQQNmdwas
`
`S.®E
`
`$3
`
`$81:5ammémww$33$1
`
` :
`
`Ln
`
`W
`
`("J
`
`N
`
`(«as ZVWWIM) 333U1L§§E~58
`
`
`
`
`
`3%,.:35SwxgmwN553.9.
`
`

`
`US 8,309,943 B2
`
`1
`LASER-DRIVEN LIGHT SOURCE
`
`RELATED APPLICATIONS
`
`This application is a continuation of US. Ser. No. 12/166,
`918, ?led on Jul. 2, 2008, Which is a continuation-in-part of
`US. Ser. No. 11/695,348, ?led onApr. 2, 2007, now US. Pat.
`No. 7,786,455, Which is a continuation-in-part of US. Ser.
`No. 11/395,523, ?led on Mar. 31, 2006, now US. Pat. No.
`7,435,982, the entire disclosures of Which are hereby incor
`porated by reference herein.
`
`FIELD OF THE INVENTION
`
`The invention relates to methods and apparatus for provid
`ing a laser-driven light source.
`
`BACKGROUND OF THE INVENTION
`
`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 Wafers or materials used in the
`fabrication of Wafers (e.g., reticles and photomasks). The
`electromagnetic energy produced by high brightness light
`sources can, alternatively, be used as a source of illumination
`in a lithography system used in the fabrication of Wafers, a
`microscopy system, 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 arc 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 arc lamps do not provide su?icient 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 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.
`The properties of light produced by many light sources
`(e. g., arc lamps, microWave lamps) are affected When the light
`passes through a Wall of, for example, a chamber that includes
`the location from Which the light is emitted.
`Accordingly, a need therefore exists for an improved light
`source Whose emitted light is not signi?cantly affected When
`the light passes through a Wall of a chamber that includes the
`location from Which the light is emitted.
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`SUMMARY OF THE INVENTION
`
`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
`
`65
`
`2
`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 modifying a property
`of the laser energy provided to the ionized gas. The optical
`element can be, for example, a lens (e. g., an aplanatic lens, an
`achromatic lens, a single element lens, and a fresnel lens) or
`mirror (e.g., a coated mirror, a dielectric coated mirror, a
`narroW band mirror, and an ultraviolet transparent infrared
`re?ecting mirror). In some embodiments, the optical element
`is one or more ?ber 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, MgF2, diamond, and CaF2. 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, O2, 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, a ?oWing 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 ?lm 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 ?ber 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, a ?ber laser, an ytterbium
`laser, a CO2 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 ?ash lamp, a pulsed laser, or a pulsed lamp.
`The ignition source can be a continuous 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 mirrors or lenses. In some embodiments, the optical
`element is con?gured 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 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 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
`
`

`
`US 8,309,943 B2
`
`3
`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 ofthe 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, a metrology tool, a
`lithography tool, or an endoscopic tool).
`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 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 of energy to the ionized medium so the high brightness
`light is substantially continuous. In some embodiments, the
`magnitude of the 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 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
`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, suprasil
`quartz material, sapphire material, MgF2 material, diamond
`material, or CaF2 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 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, 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 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
`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 embodiments, the light source includes at least one
`optical element (e.g., a mirror or lens) for modifying a prop-
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`
`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, 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
`
`method also involves providing substantially continuous
`laser energy to the ionized medium in the chamber to produce
`a high brightness light.
`In some embodiments, the method also involves directing
`the laser energy through at least one optical element 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 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. 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 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 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 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) ofthe cham-
`ber and the reflective surface directs at least a portion of the
`first set of wavelengths of electromagnetic 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 reflector, the reflector reflects at least a
`portion of the first wavelengths of electromagnetic energy
`towards the reflective surface of the chamber, and the reflec-
`tive surface directs a portion of the first set of wavelengths of
`electromagnetic energy toward the plasma.
`In 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, 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
`
`

`
`US 8,309,943 B2
`
`5
`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 chamber com-
`prises a curved shape, parabolic shape, elliptical shape,
`spherical shape or aspherical shape. In some 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 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 some 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, in another aspect, features a light source that
`includes a chamber that has a reflective surface. The light
`source also includes an ignition source for ionizing 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 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.
`
`In some embodiments, the method involves directing the
`laser energy comprising a first set of wavelengths of electro-
`magnetic energy toward the reflector, the reflector reflects at
`least a portion of the first wavelengths of electromagnetic
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`energy toward the reflective surface of the chamber, the
`reflective surface directs a portion of the first set of wave-
`lengths ofelectromagnetic 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 laser energy
`to direct the laser energy toward the plasma over a large solid
`angle. In some embodiments, the method involves directing
`the laser energy through an optical element that modifies a
`property of the laser energy to direct the laser energy toward
`the plasma over a solid angle of approximately 0.012 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 275 (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 ofthe 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 reflects 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. 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 ofpredefined wavelengths of
`electromagnetic energy directed toward the reflector and at
`least substantially allowing a second set of predefined 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 light source that
`includes a sealed chamber. The light source also includes an
`
`

`
`US 8,309,943 B2
`
`7
`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 external to the
`sealed chamber to receive at leas a portion of the high bright-
`ness light emitted by the sealed chamber and reflect the high
`brightness light toward an output of the light source.
`In some 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 reflective 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 within the 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 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 the electromagnetic energy on a region in the cham-
`ber where the plasma is located. In some embodiments, the
`curved reflective surface is located within the chamber. In
`some embodiments, the curved reflective surface is located
`external to the chamber. In some embodiments, the high
`brightness light is ultraviolet light, includes ultraviolet light
`or is substantially ultraviolet light.
`The invention, in another aspect, features a light source that
`includes a chamber. The light source also includes an energy
`source for providing energy to a gas within the chamber to
`produce a plasma that generates a light emitted through the
`walls ofthe chamber. The light source also includes a reflector
`that reflects the light emitted through the walls of the cham-
`ber. The reflector includes a reflective surface with a shape
`configured to compensa