`

`US 8,969,841 B2
`Page 2
`
`Related U.S. Application Data
`
`FOREIGN PATENT DOCUMENTS
`
`application No. 12/166,918, filed on Jul. 2, 2008, now
`Pat. No. 7,989,786, which is a continuation-in-part of
`application No. 11/695,348, filed on Apr. 2, 2007, now
`Pat. No. 7,786,455, which is a continuation-in-part of
`application No. 11/395,523, filed on Mar. 31, 2006,
`now Pat. No. 7,435,982.
`
`JP
`JP
`JP
`JP
`JP
`JP
`wo
`
`04-144053
`05-82087
`08-299951
`09-288995
`2006-10675
`2006-080255
`2010/093903
`
`5/1992
`4/1993
`1111996
`1111997
`112006
`3/2006
`8/2010
`
`OTHER PUBLICATIONS
`
`(60) Provisional application No. 61/302,797, filed on Feb.
`9, 2010.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,780,608 A *
`4,789,788 A
`4,868,458 A
`5,801,495 A
`6,184,517 B1
`6,288,780 B1
`6,417,625 B1
`6,541,924 B1 *
`6,788,404 B2
`6,956,329 B2
`7,050,149 B2
`7,427,167 B2
`7,429,818 B2
`7,652,430 B1
`2002/0021508 A1
`2002/0044629 A1
`2002/0080834 A1
`2002/0172235 A1
`2003/0052609 A1 *
`2003/0068012 A1
`2003/0147499 A1 *
`2003/0168982 A1
`2003/0231496 A1
`2004/0016894 A1
`2004/0026512 A1
`2004/0129896 A1
`2004/0183038 A1
`2004/0238762 A1
`2004/0264512 A1
`2005/0167618 A1
`2005/0199829 A1
`2005/0205811 A1
`2005/0243390 A1
`2006/0039435 A1
`2006/0131515 A1
`2006/0152128 A1 *
`2006/0186356 A1
`2006/0192152 A1 *
`2006/0219957 A1 *
`2007/0228288 A1
`2007/0228300 A1
`2007/0285921 A1
`2009/0032740 A1
`
`10/1988
`12/1988
`9/1989
`9/1998
`2/2001
`9/2001
`7/2002
`4/2003
`9/2004
`10/2005
`5/2006
`9/2008
`9/2008
`112010
`212002
`4/2002
`6/2002
`1112002
`3/2003
`4/2003
`8/2003
`9/2003
`12/2003
`112004
`2/2004
`7/2004
`9/2004
`12/2004
`12/2004
`8/2005
`9/2005
`9/2005
`1112005
`2/2006
`6/2006
`7/2006
`8/2006
`8/2006
`10/2006
`10/2007
`10/2007
`12/2007
`212009
`
`315/246
`
`Cross et al .................... 250/281
`Cox
`Davenport et a!.
`Smolka eta!.
`Sawada
`Fairley et a!.
`Brooks eta!.
`Kane eta!.
`Lange
`Brooks eta!.
`Owaetal.
`Holder eta!.
`Chang et al.
`Delgado
`Ishihara
`Hertz et al.
`Kusunose
`Chang et al.
`Eastlund eta!. .............. 313/634
`Ahmadet al.
`Kondo .......................... 378/119
`Kim
`Sato eta!.
`Wester
`Otsubo
`Schmidt et al.
`Hiramoto et a!.
`Mizoguchi et a!.
`Hartlove et a!.
`Hoshino eta!.
`Partlo et al.
`Partlo et al.
`Tejnil
`Cheymol et a!.
`Partlo et al.
`Manning ....................... 313/113
`Iami et al.
`Ershov eta!. .............. 250/503.1
`Ershov eta!.
`250/504 R
`Smith
`Smith
`Zulimetal.
`Smith eta!.
`
`Bussialm, R., et. a!., "Experimental and theoretical investigations of
`a low-pressure He-Xe discharge for lighting purpose," Journal of
`Applied Physics, vol. 95, No.9, May 1, 2004, pp. 4627-4634.
`Carlhoff et al., "Continuous Optical Discharges at Very High Pres(cid:173)
`sure," Physica 103C, 1981, pp. 439-447.
`Cremers eta!., "Evaluation of the Continuous Optical Discharge for
`Spectrochemical Analys1s," Spectrochimica Acta, vol. 40B, No. 4,
`1985, pp. 665-679.
`Fiedorowicz eta!., "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 1 0.6-f!m Laser Radia(cid:173)
`tion," Appl. Phys. Lett., vol. 21, No.2, Jul. 15, 1972, pp. 62-64.
`Generalov eta!., "Continuous Optical Discharge," ZhETF Pis. Red.
`11, No. 9, May 5, 1970, pp. 302-304.
`Generalov eta!., "Experimental Investigation of a Continuous Opti(cid:173)
`cal Discharge," Soviet Physics JETP, vol. 34, No. 4, Apr. 1972 pp.
`'
`763-769.
`Hamamatsu Product Information, "Super-Quiet Xenon Lamp Super(cid:173)
`Qmet Mercury-Xenon Lamp," Nov. 2005. pp. 1-16.
`Hecht, "Refraction", Optics (Third Edition), 1998, Chapter 4 pp.
`100-101.
`'
`Jeng eta!., "Theoretical Investigation ofLaser-SustainedArgon Plas(cid:173)
`mas," J Appl. Phys. 60 (7), Oct. 1, 1986, pp. 2272-2279.
`Keefer eta!., "Experimental Study of a Laser-Sustained Air Plasma,"
`Journal of Applied Physics, vol. 46, No.3, Mar. 1975,pp. 1080-1083.
`Keefer, "Laser-Sustained Plasmas," Laser-Induced Plasmas and
`Applications, published by Marcel Dekker, edited by Radziemski et
`a!., 1989, pp. 169-206.
`Kozlov et a!., "Radiative Losses by Argon Plasma and the Emissive
`Model of a Continuous Optical Discharge," Sov. Phys. JETP, vol. 39,
`No.3, Sep. 1974, pp. 463-468.
`Kozlov et al., "Sustained Optical Discharges in Molecular Gases,"
`Sov. Phys. Tech. Phys. 49(11), Nov. 1979, pp. 1283-1287.
`Moody, "Maintenance of a Gas Breakdown in Argon Using 10 .6-f! cw
`Radiation," Journal of Applied Physics, vol. 46, No.6, Jun. 1975, pp.
`2475-2482.
`Naki, "Radiometric Characterization of Ultrahigh Radiance Xenon
`Short-acr Dichage Lamps", Applied Optics, vol. 47, No. 2, Jan. 9,
`2008, pp. 224-229.
`Ralzer, "Optical Discharges," Sov. Phys. Usp. 23(11), Nov. 1980, pp.
`789-806.
`Wilbers et al., "The Continuum Emission of an Arc Plasma" J
`Quant. Spectrosc. Radiat. Transfer, vol. 45, No.1, 1991, pp. 1-lO ..
`Wilbers eta!., "The VUV Emissivity of a High-Pressure Cascade
`Argon Arc from 125 to 200 nm," J Quant. Spectrosc. Radiat. Trans(cid:173)
`fer, vol. 46, 1991, pp. 299-308.
`* cited by examiner
`
`

`

`

`

`

`

`

`

`

`

`

`

`U.S. Patent
`U.S. Patent
`
`Mar.3,2015
`Diar.3,2015
`
`Sheet 6 of 39
`Sheet60f39
`
`US 8,969,841 B2
`US 8,969,841 B2
`
`{.t:)
`'>;'"'""
`(.p
`
`I
`:
`I
`
`I
`I
`I
`
`I
`I
`I
`
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`I
`!
`I
`
`I
`!
`
`I
`
`t
`I
`I
`I
`I
`t
`I
`I
`I
`I
`I
`I
`I
`I
`
`t
`I
`
`mGE
`
`~ !
`:
`r -, - _,_
`. :
`! :
`! :
`
`!
`I
`i I
`i
`I
`i
`I
`... ~ ........................................ ;. ... t ................................................................................ .,,., ................ ...
`!
`I
`I
`j
`I
`I
`i 1
`l
`i I
`!
`i
`1
`I
`~!I
`:
`! I
`CD
`!
`! I
`("")
`i
`l'r.
`l I
`I
`'-V
`!
`' '
`I
`I
`! :.;.
`,..r
`" '
`!
`~
`
`~
`
`... '4
`CD
`
`I
`/;
`"\--·--•
`\
`\
`\
`
`'
`
`mam
`
`.
`(!)
`LL
`
`

`

`

`

`
`
`gm.3:2::3.m.3:252wa3cm“reach“:3
`
`$32G. 8A
`F!G.8A
`
`Fig 88
`F!G. 88
`
`
`
`

`

`U.S. Patent
`US. Patent
`
`Mar.3,2015
`Mar. 3, 2015
`
`Sheet 9 of 39
`Sheet 9 of 39
`
`US 8,969,841 B2
`US 8,969,841 B2
`
`
`
`'~
`
`""
`900
`
`HQ, 9
`FIG.9
`
`928
`928
`
`942
`
`

`

`

`

`

`

`U.S. Patent
`US. Patent
`
`Mar. 3, 2015
`Mar.3,2015
`
`Sheet 12 of 39
`Sheet 12 of 39
`
`US 8,969,841 B2
`US 8,969,841 B2
`
`
`
`\wb. N 0‘) 3:».
`
`‘V!W},
`
`:1mk
`
`dm
`
`m). N G}4».
`
`/®,.wmm1m.
`a!Mun-mm“may«..Waura
`
`1236
`
`1232 -~-,
`
`
`
`1274
`
`1200
`120C?
`
`FIG. 12
`FEG. 12
`
`

`

`

`

`

`

`U.S. Patent
`U.S. Patent
`
`Mar.3,2015
`Diar.3,2015
`
`Sheet 15 of 39
`Sheet150f39
`
`US 8,969,841 B2
`US 8,969,841 B2
`
`«mw.wrw
`
`
`

`

`U.S. Patent
`U.S. Patent
`
`Mar.3,2015
`Diar.3,2015
`
`Sheet 16 of 39
`Sheet160f39
`
`US 8,969,841 B2
`US 8,969,841 B2
`
`
`
`mmwmxu
`
`

`

`

`

`

`

`

`

`

`

`U.S. Patent
`US. Patent
`
`Mar. 3, 2015
`Mar.3,2015
`
`Sheet 21 of 39
`Sheet 21 of 39
`
`US 8,969,841 B2
`US 8,969,841 B2
`
`1
`3“
`:3, wafi
`*-
`x»
`3533:} ,mwwwmwymwmwWVWNMWWMNW...»0mm ~ -.mu,1umw‘mwu“w:ww,
`
`E E E
`
`2000
`x“
`
`2'100
`.,,
`'-,
`-...... ":6.
`
`
` ________________1
`
`s
`,,
`i W‘x ‘
`S4fi0
`
`s
`
`"x.
`
`-:
`
`"
`
`“’9:
`K
`XX
`
`{3 m-“mwwwwwmw...n...«M-MA..'.-.
`a
`w
`
`“mm...".u.M..1..,......,_.,.,.,....‘._.M«9....«x.»g.r.~.r.,:....-.M_.wn...Q.‘.....,,..M.‘.,....
`:-
`3:3
`
`FIG, 20
`
`2200
`
`

`

`U.S. Patent
`US. Patent
`
`Mar. 3, 2015
`Mar.3,2015
`
`Sheet 22 of 39
`Sheet 22 of 39
`
`US 8,969,841 B2
`US 8,969,841 B2
`
`2105
`”X
`A
`2113‘
`'
`NW
`27:;5
`,\
`:“r‘g~~-f“‘- \
`2110
`f
`\
`2115
`it)
`2
`“~23?ka
`\
`I!
`\\
`210 y
`\
`SW-~EN
`\ ~~~~~T” \x
`\
`M”
`if:
`K
`“““““L
`”‘QTN \
`\Mfi‘v:”””””;;
`g‘f‘
`31‘
`\M—mrfizggfi
`1ii
`,53
`:Z; gfww
`’ N7T\~\\2
`-'
`‘
`2.~«w—H"“::'3"’
`:KQLwar-f‘;#################Sf”
`[R‘1';¢..‘~:\\~
`i‘
`1
`/
`I]
`\ ’’’’’ '\
`I‘M \
`N~~w~
`‘K
`:
`i ‘‘‘‘‘‘‘‘\H’ w“
`212C 2134”}
`f!
`:j “N-
`,
`”'7“
`”w”
`2115
`1
`\J‘Vw
`x
`2 10
`i
`2105
`2115’
`
`2110
`
`,
`
`FIG. 21
`PEG. 21
`
`

`

`U.S. Patent
`
`Mar.3,2015
`
`Sheet 23 of 39
`
`US 8,969,841 B2
`
`2200" ........
`
`20
`
`Spectral Radiance vs NJ\
`
`0
`0.3
`
`0.35
`
`0.4
`
`0.5
`
`0.55
`
`0.6
`
`0.45
`NA
`
`FIG. 22
`
`

`

`U.S. Patent
`
`Mar.3,2015
`
`Sheet 24 of 39
`
`US 8,969,841 B2
`
`2305
`
`2300
`I
`I
`
`FIG. 23A
`
`2300
`
`2310
`
`2311
`
`FIG. 238
`
`

`

`U.S. Patent
`US. Patent
`
`Mar.3,2015
`Mar. 3, 2015
`
`Sheet 25 of 39
`Sheet 25 of 39
`
`US 8,969,841 B2
`US 8,969,841 132
`
`2405
`\
`
`, ,4“
`.74"
`
`///fi\. 3
`f I
`I
`l
`f
`///,/ /
`4
`\5.
`{.x
`\1///
`z/ /////
`/’ 5::
`i
`1
`
`x” \
`
`E
`
`//\#\~
`
`,1
`
`\
`
`\ a .
`
`
`
`j
`
`/’l
`
`/’
`
`/’
`
`/.r//
`
`\.
`
`\\.
`
`\\
`/’\"3
`
`///
`
`//
`
`S
`i
`
`////
`
`//
`4/1/
`
`/./
`
`//.
`
`/
`
`FIG. 24
`FIG. 24
`
`\:
`
`flf/
`\
`
`:
`‘
`
`I
`
`/
`
`x/
`
`I
`K
`
`

`

`

`

`

`

`

`

`

`

`U.S. Patent
`US. Patent
`
`Mar. 3, 2015
`Mar.3,2015
`
`Sheet 30 of 39
`Sheet 30 of 39
`
`US 8,969,841 B2
`US 8,969,841 B2
`
`2800
`2900
`\\
`
`\'\¥.
`
`2910
`
`2920
`
`
`
`F!G. 29
`HG. 29
`
`

`

`

`

`

`

`

`

`

`

`U.S. Patent
`U.S. Patent
`
`Mar.3,2015
`Mar. 3, 2015
`
`Sheet 35 of 39
`Sheet 35 of 39
`
`US 8,969,841 B2
`US 8,969,841 B2
`
`3400
`
`3440
`
`
`
`FIG, 34
`PK}. 34
`
`

`

`

`

`

`

`U.S. Patent
`
`Mar.3,2015
`
`Sheet 38 of 39
`
`US 8,969,841 B2
`
`3760
`·····································'~
`
`'·
`
`I
`
`/
`
`011\ l ~ ~L~J
`(\ )( /'
`/
`\ /
`/
`f
`\/ /
`I
`/
`.·
`I !~\/
`/ • I
`,I \,
`\.
`I
`',
`\
`\ ~ \
`, / 3751}
`
`'
`·-·r-.mmmmi 3740
`I
`I
`.
`!
`3715 L_ _
`
`\
`\
`\
`
`\
`
`1
`
`\
`
`I
`
`\
`
`3745
`
`,
`\
`3745
`
`3700
`
`I I
`I
`
`3710
`
`n ~
`~ u\
`I I I
`jl \ i
`\\I
`I I
`.__ _ _j.
`I
`I
`./
`I ./
`
`'
`
`I
`I
`
`3730
`
`,:4
`
`I
`
`1,! 3720
`
`, /
`.·
`
`/ '
`
`\
`
`\
`
`,,
`
`//
`I
`3715/
`
`FIG. 37
`
`

`

`U.S. Patent
`
`Mar.3,2015
`
`Sheet 39 of 39
`
`US 8,969,841 B2
`
`3800
`/
`I
`I
`II
`
`3860
`
`f\
`I \
`! \
`4\\\
`! i
`/fi\
`i
`I
`\\
`....... --_----_----_----_-----~---_----_-----i--t_----_----_----_---_----_----_----_--_,_----+·-t-i·-t_---_----_----=_-=_-=_-=:~=~~~~_:_:-_-++,i-=_-=_~,H-L.+\=-_-j
`-<1----f--+-----~~ +-! ----+--+----+--+-11 _______ ___\ __ \----
`
`3815
`
`----------------------.
`:
`!
`
`I
`
`3810 I
`: ;
`!
`
`I
`
`I
`!;\\
`c.:=_(_~---~:_~- 3850
`t+
`-e:-::::::H
`I !
`3815 ":;; -r---
`l i ·"-,
`!
`j - ' ---+---+---1-+-+--------l
`
`l
`
`~mml I
`
`/
`
`' I
`3845
`
`\ I
`3830
`
`- t
`
`3840
`
`/
`I I
`\v
`\'I
`\
`3820
`
`FIG. 38
`
`

`

`US 8,969,841 B2
`
`1
`LIGHT SOURCE FOR GENERATING LIGHT
`FROM A LASER SUSTAINED PLASMA IN A
`ABOVE-ATMOSPHERIC PRESSURE
`CHAMBER
`
`2
`Accordingly, a need therefore exists for an improved light
`source whose emitted light is not significantly affected when
`the light passes through a wall of a chamber that includes the
`location from which the light is emitted.
`
`RELATED APPLICATIONS
`
`SUMMARY OF THE INVENTION
`
`This application is a continuation of U.S. Ser. No. 13/964,
`938, filed on Aug. 12,2013, which is a continuation of U.S.
`Ser. No. 13/024,027, filed on Feb. 9, 2011, now U.S. Pat. No. 10
`8,525,138, which claims the benefit of, and priority to U.S.
`Provisional Patent Application No. 61/302,797, filed on Feb.
`9, 2010, the entire disclosure of which is incorporated by
`reference herein, Ser. No. 13/024,027 is also a continuation- 15
`in-part ofU.S. Ser. No. 12/166,918, filed on Jul. 2, 2008, now
`U.S. Pat. No. 7,989,786, which is a continuation-in-part of
`U.S. Ser. No. 11/695,348, filed on Apr. 2, 2007, now U.S. Pat.
`No. 7,786,455, which is a continuation-in-part of U.S. Ser.
`No. 11/395,523, filed on Mar. 31, 2006, now U.S. Pat. No.
`7,435,982, the entire disclosures of each of which are hereby
`incorporated by reference herein.
`
`FIELD OF THE INVENTION
`
`The invention relates to methods and apparatus for provid(cid:173)
`ing a laser-driven light source.
`
`BACKGROUND 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
`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
`20 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
`reflecting mirror). In some embodiments, the optical element
`25 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-
`30 sil® quartz (Heraeus Quartz Anlerica, LLC, Buford, Ga.),
`sapphire, MgF 2 , diamond, and CaF 2 . 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
`35 (e.g., quartz). The chamber can be, for example, a glass bulb.
`In some embodiments, the chamber is an ultraviolet transpar(cid:173)
`ent dielectric chamber.
`The gas can be one or more of a noble gas, Xe, Ar, Ne, Kr,
`He, D2 , H2 , 0 2 , F 2 , 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, or a recycled media. The
`gas can be produced by a pulsed laser beam that impacts a
`target (e.g., a solid or liquid) in the chamber. The target can be
`a pool or film of metal. In some embodiments, the target is
`capable of moving. For example, the target may be a liquid
`that is directed to a region from which the high brightness
`light originates.
`In some embodiments, the at least one laser is multiple
`diode lasers coupled into a fiber optic element. In some
`embodiments, the at least one laser includes a pulse or con(cid:173)
`tinuous wave laser. In some embodiments, the at least one
`laser is an IR laser, a diode laser, a fiber laser, an ytterbium
`laser, a C02 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 flash 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
`
`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(cid:173)
`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 40
`the light vary depending upon the application.
`The state of the art in, for example, wafer inspection sys(cid:173)
`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 45
`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 50
`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 sufficient bright- 55
`ness for some applications, especially in the ultraviolet spec(cid:173)
`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 60
`brightness light sources that do not rely on an electrical dis(cid:173)
`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 65
`passes through a wall of, for example, a chamber that includes
`the location from which the light is emitted.
`
`

`

`US 8,969,841 B2
`
`3
`element is configured to deliver the electromagnetic radiation
`emitted by the ionized gas to a tool (e.g., a wafer inspection
`tool, a microscope, a metrology tool, a 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(cid:173)
`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 10
`the laser energy through at least one optical element for
`modifYing a property of the laser energy provided to the
`ionized gas. In some embodiments, the method also involves
`actively pumping the chamber. The ionizable medium can be
`a moving target. In some embodiments, the method also
`involves directing the high brightness light through at least
`one optical element to modifY a property of the light. In some
`embodiments, the method also involves delivering the high
`brightness light emitted by the ionized medium to a tool (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(cid:173)
`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 35
`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. 40
`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 45
`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 50
`quartz material, sapphire material, MgF 2 material, diamond
`material, or CaF 2 material. In some embodiments, the cham(cid:173)
`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- 55
`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, D 2 , H2 , 0 2 , F 2 , a metal halide, a halogen, Hg, 60
`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 65
`strikes the target. The target can be a pool or film of metal. In
`some embodiments, the target is capable of moving.
`
`4
`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(cid:173)
`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
`15 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(cid:173)
`tion source an ionizable medium within a chamber. The
`20 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
`25 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
`30 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(cid:173)
`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(cid:173)
`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(cid:173)
`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
`
`

`

`US 8,969,841 B2
`
`5
`6
`towards the reflective surface of the chamber, and the reflec(cid:173)
`surface of the chamber, the reflective surface reflecting at
`tive surface directs a portion of the first set of wavelengths of
`least a portion of the first set of wavelengths of electromag(cid:173)
`netic energy toward the plasma. In some embodiments, the
`electromagnetic energy toward the plasma.
`In some embodiments, at least a portion of the high bright(cid:173)
`method involves directing at least a portion of the high bright(cid:173)
`ness light is directed toward the reflective surface of the
`ness light toward the reflective surface of the chamber which
`chamber, is reflected toward the reflector, and passes through
`is reflected toward the reflector and is reflected by the reflec(cid:173)
`the reflector toward an output of the light source. In some
`tor toward a tool.
`In some embodiments, the method involves directing the
`embodiments, the light source comprises a microscope, ultra(cid:173)
`laser energy comprising a first set of wavelengths of electro(cid:173)
`violet microscope, wafer inspection system, reticle inspec(cid:173)
`tion system or lithography system spaced relative to the out- 10
`magnetic energy toward the reflector, the reflector reflects at
`put of the light source to receive the high brightness light. In
`least a portion of the first wavelengths of electromagnetic
`some embodiments, a portion of the high brightness light is
`energy toward the reflective surface of the chamber, the
`directed toward the reflective surface of the chamber, is
`reflective surface directs a portion of the first set of wave(cid:173)
`lengths of electromagnetic energy toward the plasma. In some
`reflected toward the reflector, and electromagnetic energy
`comprising the second set of predefined wavelengths of elec- 15
`embodiments, the method involves directing a portion of the
`high brightness light toward the reflective surface of the
`tromagnetic energy passes through the reflector.
`chamber which is reflected toward the reflector and, electro(cid:173)
`The chamber of the light source can include a window. In
`some embodiments, the chamber is a sealed chamber. In some
`magnetic energy comprising the second set of predefined
`embodiments, the reflective surface of the chamber com(cid:173)
`wavelengths of electromagnetic energy passes through the
`prises a curved shape, parabolic shape, elliptical shape, 20
`reflector.
`The method can involve directing the laser energy through
`spherical shape or aspherical shape. In some embodiments,
`the chamber has a reflective inner surface. In some embodi(cid:173)
`an optical element that modifies a property of the laser energy
`ments, a coating or film is located on the outside of the
`to direct the laser energy toward the plasma over a large solid
`chamber to produce the reflective surface. In some embodi(cid:173)
`angle. In some embodiments, the method involves directing
`ments, a coating or film is located on the inside of the chamber 25 the laser energy through an optical element that modifies a
`property of the laser energy to direct the laser energy toward
`to produce the reflective surface. In some embodiments, the
`the plasma over a solid angle of approximately 0.012 stera(cid:173)
`reflective surface is a structure or optical element that is
`distinct from the inner surface of the chamber.
`dians. In some embodiments, the method involves directing
`the laser energy through an optical element that modifies a
`The light source can include an optical element disposed
`30 property of the laser energy to direct the laser energy toward
`along a path the electromagnetic energy from the laser travels.
`In some embodiments, the optical element is adapted to pro(cid:173)
`the plasma over a solid angle of approximately 0.048 stera(cid:173)
`vide electromagnetic energy from the laser to the plasma over
`dians. In some embodiments, the method involves directing
`the laser energy through an optical element that modifies a
`a large solid angle. In some embodiments, the reflective sur(cid:173)
`face of the chamber is adapted to provide electromagnetic
`property of the laser energy to direct the laser energy toward
`35 the plasma over a solid angle of greater than about 2n (about
`energy from the laser to the plasma over a large solid angle. In
`6.28) steradians. In some embodiments, the reflective surface
`some embodiments, the reflective surface of the chamber is
`adapted to collect the high brightness light generated by the
`of the chamber is adapted to provide the laser energy to the
`plasma over a large solid angle. In some embodiments, one or
`plasma over a large solid angle. In some embodiments, the
`reflective surface of the chamber is adapted to collect the high
`more of the reflective surface, reflector and the window
`40 brightness light generated by the plasma over a large solid
`include (e.g., are coated or include) a material to filter pre(cid:173)
`defined wavelengths (e.g., infrared wavelengths of electro(cid:173)
`angle.
`magnetic energy) of electromagnetic energy.
`The invention, in another aspect, relates to a method for
`producing light. The method involves ionizing with an igni(cid:173)
`The invention, in another aspect, features a light source that
`tion source a gas within a chamber that has a reflective sur-
`includes a chamber that has a reflective surface. The light
`45 face. The method also involves directing electromagnetic
`source also includes an ignition source for ionizing a gas
`energy from a laser toward a reflector that at least substan(cid:173)
`within the chamber. The light source also includes at least one
`tially reflects a first set of wavelengths of electromagnetic
`laser external to the chamber for providing electromagnetic
`energy toward the ionized gas in the chamber to produce a
`energy to the ionized gas within the chamber to produce a
`plasma that generates a high brightness light.
`plasma that generates a high brightness light. The light source
`also includes a reflector positioned along a path that the so
`In some embodiments, the electromagnetic energy from
`electromagnetic energy travels from the at least one laser to
`the laser first is reflected by the reflector toward the reflective
`surface of the chamber. In some embodiments, the electro(cid:173)
`the reflective surface of the chamber.
`magnetic energy directed toward the reflective surface of the
`In some embodiments, the reflector is adapted to at least
`chamber is reflected toward the plasma. In some embodi-
`substantially reflect a first set of predefined wavelengths of
`55 ments, a portion of the high brightness light is directed toward
`electromagnetic energy directed toward the reflector and at
`least substantially allow a second set of predefined wave(cid:173)
`the reflective surface of the chamber, reflected toward the
`lengths of electromagnetic energy to pass through the reflec-
`reflector and passes through the reflector.
`In some embodiments, the electromagnetic energy from
`tor.
`the laser first passes through the reflector and travels toward
`The invention, in another aspect, relates to a method for
`producing light. The method involves ionizing with an igni(cid:173)
`60 the reflective surface of the chamber. In some embodiments,
`tion source a gas within a chamber that has a reflective sur(cid:173)
`the electromagnetic energy directed toward the reflective sur(cid:173)
`face of the chamber is reflected toward the plasma. In some
`face. The method also involves providing laser energy to the
`embodiments, a portion of the high brightness light is directed
`ionized gas in the chamber to produce a plasma that generates
`a high brightness light.
`toward the reflective surface of the chamber, reflected toward
`65 the reflector and reflected by the reflector.
`In