(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property
`Organization
`International Bureau
`
`
`
`(43) International Publication Date
`11 November 2004 (11.11.2004)
`
`(10) International Publication Number
`
`PCT
`
`WO 2004/097520 A2
`
`(51) International Patent Classification7:
`
`G03F
`
`(21) International Application Number:
`PCT/US2004/012714
`
`(22) International Filing Date:
`
`26 April 2004 (26.04.2004)
`
`14526 (US). NEES, John [US/US]; 2520 Victoria, Ann
`Arbor, MI 48104 (US). HOU, Bixue [CN/US]; 1666 Cram
`Circle #3, Ann Arbor, MI 48104 (US).
`
`(74)
`
`Agent: FORBIS, Glenn, E.; Rader, Fishman & Grauer
`PLLC, 39533 Woodward Avenue, Suite 140, Bloomfield
`Hills, MI 48304 (US).
`
`(25) Filing Language:
`
`English
`
`(31)
`
`(26) Publication Language:
`
`English
`
`(30) Priority Data:
`60/465,062
`
`24 April 2003 (24.04.2003)
`
`US
`
`(71) Applicant (for all designated States except US): THE
`REGENTS OF THE UNIVERSITY OF MICHIGAN
`[US/US]; Wolverine Tower, Room 2071, 3003 S. State
`Street, Ann Arbor, MI 48109 (US).
`
`(34)
`
`(72) Inventors; and
`(75) Inventors/Applicants (for US only): MOUROU, Gerard,
`A. [US/US]; 4151 Thornoaks Dr., Ann Arbor, MI 48104
`(US). GALVANAUSKAS, Almantas
`[LT/US]; 4963
`Ravine Ct., Ann Arbor, MI 48104 (US). THEOBALD,
`Wolfgang [DE/US]: 16, Pond Valley Circle, Penfield, NY
`
`Designated States (unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`AT, AU, AZ, BA, BB, BG, BR, BW, BY, BZ, CA, CH, CN,
`CO, CR, CU, CZ, DE, DK, DM, DZ, EC, EE, EG, ES, FI,
`GB, GD, GE, GH, GM, HR, HU, ID, IL, IN, IS, JP, KE,
`KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD,
`MG, MK, MN, MW, MX, MZ, NA, NI, NO, NZ, OM, PG,
`PH, PL, PT, RO, RU, SC, SD, SE, SG, SK, SL, SY, TJ, TM,
`TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, YU, ZA, ZM,
`ZW.
`
`Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, ZM,
`ZW), Eurasian (AM, AZ, BY, KG, K7,, MD, RU, TJ, TM),
`European (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI,
`FR, GB, GR, HU, IE, IT, LU, MC, NL, PL, PT, RO, SE, SI,
`SK, TR), OAPI (BF, BI, CF, CG, CI, CM, GA, GN, GQ,
`GW, l\/IL, MR, NE, SN, TD, TG).
`
`[Continued on next page]
`
`(54) Title: FIBER LASER—BASED EUV—LITHOGRAPHY
`
`34
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`32
`
`/74
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`20
`
`/76'
`
`78
`
`721
`
`30
`
`(57) Abstract: A method and apparatus is disclosed for performing lithography operation. A fiber laser (18) is provided that gen-
`erates laser light that is used by adaptive optics (20) to focus the laser light onto a plasma target (30) to generate plasma as a source
`of EUV radiation.
`
`ASML 1117
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`ASML 1117
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`

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`WO 2004/097520 A2
`
`Declarations under Rule 4.17:
`
`as to applicants entitlement to apply for and be granted
`a patent (Rule 4.1 7(ii)) for the following designations AE,
`AG, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BW, BY, BZ,
`CA, CH, CN, CO, CR, CU, CZ, DE, DK, DM, DZ, EC, EE,
`EG, ES, FI, GB, GD. GE, GH, GM, HR, HU, ID, IL, IN, IS,
`JP KE, KG, KP. KR, KZ, LC, LK, LR, LS, LT, LU, LV MA,
`MD, MG, MK, MN, MW, MX, MZ, NA, NI, NO, NZ, OM,
`PG, PH, PL, PT, RO, RU, SC, SD, SE, SG, SK, SL. SY TJ,
`TM, TN, TR, TT, TZ, UA, UG, UZ, VC, VN, YU, ZA, ZM,
`ZW. ARIPO patent (BW, GH, GM, KE, LS, MW, MZ, NA,
`SD, SL, SZ, TZ, UG, ZM, ZW), Eurasian patent (AM, AZ,
`BY, KG, KZ, MD, RU, TJ, TM), European patent (AT, BE,
`BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GB, GR, HU, IE,
`IT, LU, MC, NL, PL, PT, RO, SE, SI, SK, TR), 0APIpatenl
`(BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, ML, MR, NE,
`SN, 11), TG)
`as to the applicants entitlement to claim the priority of the
`earlier application (Rule 4. I 7(iii))for thefollowing desig-
`nations AE, AG, AL, AM, AZ, AU, AZ, BA, BB, BG, BR, BW,
`BY, BZ, CA, CH, CN, CO, CR, CU, CZ, DE, DK, DM, DZ,
`
`EC, EE, EG, ES, FI, GB, GD, GE, GH. GM, HR, HU, ID,
`IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU,
`LV, MA, MD, MG, MK, MN, MW, MX, MZ, NA, N1, NO, NZ,
`OM, PG, PH, PL, PT, R0, RU, SC, SD, SE, SG, SK, SL, SY,
`TJ, TM, TN, TR, TT. TZ, UA, UG, UZ, VC, VN, YU, ZA, ZM,
`ZW, ARIPO patent (BW, GH, GM, KE, LS, MW, MZ, NA,
`SD, SL, SZ, TZ, UG, ZM, ZW), Eurasian patent (AM, AZ,
`BY, KG, KZ, MD, RU, TJ, TM), European patent (AT, BE,
`BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GB, GR, HU, IE,
`IT, LU, MC, NL, PL, PT, R0, SE, SI, SK, TR), OAPI patent
`(BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GW, ML, MR, NE,
`SN, TD, TG)
`of inventorship (Rule 4.I7(iv)) for US only
`
`Published:
`
`without international search report and to be republished
`upon receipt of that report
`
`For two—letter codes and other abbreviations, refer to the ”Guid—
`ance Notes on Codes and Abbreviations" appearing at the begin-
`ning of each regular issue of the PCT Gazette‘
`
`
`
`

`
`WO 2004/097520
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`PCT/US2004/012714
`
`FIBER LASER - BASED EUV-LITHOGRAPHY
`
`BACKGROUND
`
`[0001]
`
`Lithoraphy is a process used in semiconductor fabrication. In order to
`
`continue semiconductor integrated circuit speed increase at the rate predicted by the
`
`Moore’s Law, which states that the circuit density of microchips doubles every 18 months,
`
`the limits of optical lithography must be expanded. To meet this prediction, the
`
`manufacturing of next generation electronic devices will demand lithography light sources
`
`having wavelengths with high power and hi gh-frequency, otherwise known as EUV
`
`(extreme ultraviolet). However, producing radiation at such high power and frequencies is
`
`technologically very difficult and, although some sources of EUV radiation do exist, none
`
`of these systems are currently adequate for practical use in industrial EUV lithography.
`
`[0002]
`
`One way to produce EUV radiation having such desired characteristics is by
`
`generating laser—produced plasma and then using the radiation from the plasma to perform
`
`the lithography process. In such a method, a pulsed laser beam is focused on a plasma
`
`target having the requisite material for producing plasma. The laser—matter interaction,
`
`resulting from the targeted laser pulse on the material, leads to the formation of hot plasma.
`
`The formation of such hot plasma serves as a source of EUV radiation for the lithography
`
`process.
`
`[0003]
`
`Typically, such EUV generation requires very high laser light peak
`
`intensities on the target, thus necessitating the use of large and complex laser systems
`
`capable of producing high energy pulses at high average power. This also presents a
`
`further problem that it is essential that laser sources are sufficiently compact, robust and
`
`affordable for productive industrial use. The present invention was developed in light of
`
`these and other drawbacks.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0004]
`
`Figure 1 is a schematic view of a lithography device according to an
`
`embodiment of the invention;
`
`[0005]
`
`Figure 2 is a schematic view of a lithography device according to an
`
`embodiment; and
`
`
`
`

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`W0 2004/097520
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`PCT/US2004/012714
`
`[0006]
`
`Figure 3 is a schematic view of a lithography device according to an
`
`embodiment.
`
`DETAILED DESCRIPTION OF AN EMBODINIENT
`
`[0007]
`
`A method and apparatus for EUV lithography provides a high EUV
`
`radiation source having a lower power consumption by the laser and a reduced amount of
`
`debris generated by the plasma target. As a result, this radiation source does not require a
`
`large complex laser or a high-energy supply to the laser. The method and apparatus
`
`includes an improved laser source that uses fiber lasers in combination with adaptive
`
`optics. In addition, the method and apparatus allows for minimal debris generation as the
`
`overall power and target size is reduced from that of the conventional art.
`
`[0008] Further, the present invention uses a pulsed high—power fiber laser configuration
`
`which uses optimum-duration pulses to further enhance the generation of EUV radiation.
`
`Additionally, to utilize the enhanced wave front characteristics of laser light from the fiber
`
`laser configuration to achieve the desired spot size on the plasma target, the present
`
`invention includes adaptive optics which enable the laser light to be focused into a small
`
`diffraction-lirnited spot on the plasma target with an improved energy concentration, thus
`
`reducing energy requirements by the laser, minimizing the needed volume of the plasma
`
`target and substantially reducing the amount of laser-produced debris.
`
`[0009] Referring now to Figure 1, an embodiment of the present invention is shown and
`
`described. In Figure 1, an optical lithography system 10 is shown including optics 12,
`
`plasma portion 14, and lithography target 16. The optics 12 generally includes a fiber laser
`
`18 and adaptive optics 20. As will be readily understood by one skilled in the art, fiber
`
`lasers, such as fiber laser 18, use optical fiber to culminate laser light to its diffraction limit
`
`while maintaining wave front control. As will be readily understood by one skilled in the
`
`art, fiber lasers use optical fiber to produce high quality optical beam (diffraction limited
`
`beam) which can be focused into a diffraction limited spot of minimum size, compared to
`
`the optical wavelength, by using wave front control. Wave front control ensures that all
`
`the beam distortions acquired during beam generation and transmission to the target are
`
`compensated for. More specifically, the fiber laser 18, as opposed to conventional solid
`
`state laser configurations, maximizes the organization of light at a given energy level to
`
`allow it to be focused on a relatively small area. Preferably, fiber laser 18 includes a high
`
`
`
`

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`WO 2004/097520
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`PCT/US2004/012714
`
`gain fiber amplifier, which allows for the production of laser pulses with pulse durations in
`
`the 1-ps to 1—ns duration range for reasons that will be described in greater detail. Also
`
`preferably, fiber laser 18 uses a diode—laser source, which enables enhanced control over
`
`the temporal profile of the laser pulse as will also be described in greater detail.
`
`[00010]
`
`The adaptive optics 20, as will be readily understood by one skilled in the
`
`art, is a series of optical components including lenses mirrors and other known optical
`
`devices that adapt or change to achieve the desired image sharpness or image size. The
`
`adaptive optics includes deformable mirrors and high NA (numerical aperture) optics that
`
`allows enhanced control over the focusing of laser light generated by fiber laser 18. The
`
`adaptive optics will be described in greater detail below.
`
`[00011]
`
`The plasma portion 14 generally includes a plasma target 30, plasma 32 and
`
`focusing element 34. The plasma target 30 is constructed of a material that generates
`plasma 32 upon sufficient laser energy being transmitted to the plasma target 30 by optics
`
`12. The plasma 32 emits EUV radiation that is used for conducting lithography operations
`
`on lithography target 16. The focusing element 34 focuses the resulting EUV radiation on
`
`the lithography target 16.
`
`[00012]
`
`The adaptive optics 20 serves to reduce the focused spot size on the plasma
`
`target 30 relative to that achievable with standard optics. Reduction of the focused spot
`
`size on the plasma target 30 reduces the amount of energy needed to be supplied to the
`
`fiber laser 18 to generate the desired plasma with the desired EUV radiation. Specifically,
`
`the pulse energy Epulse provided by the laser and the fluence F, or flux of photons, of a
`
`beam are related through the beam cross-section area A. Specifically, Epulse = AF. A is the
`
`cross-sectional area of a beam at any point and F is the fluence at that same point along the
`
`beam. Therefore:
`
`ALFL EATFT
`
`[00013]
`
`Where ALFL is the cross-sectional area of the laser beam at the laser
`
`multiplied by the fluence FL of the laser light at the laser and ATFT is the area of the laser
`
`beam at the plasma target 30 times the fluence FT at the plasma target 30. The energy
`
`fluence on a plasma target 30 needed for generating plasma 32 with the desired EUV
`
`output is approximately FT = 1 l<I/cm2. Therefore, the required fluence at the laser is
`
`determined by the ratio between the areas of the focused spot on the plasma target and the
`
`beam in the fiber of the fiber laser 18: FLs(Ar /AL)FT. For light at ~1—p.m wavelengths,
`
`
`
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`WO 2004/097520
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`
`the diffraction-limited spot size on a plasma target 30 attainable with compensated high-
`
`NA (numerical aperture) adaptive optics is ~ 1-,LLm in diameter. Therefore, achievable 10
`
`to 30-um diameter beams in fiber lasers use fiber fluencies of approximately 100 to 1000
`
`times lower than on the plasma target (approximately 1 — 10 J/cmf), which is significantly
`
`below the current approximate ~50 I/cmz limit in fiber lasers. As such, use of fiber
`
`technology allows greater than 10kW average power to be distributed to the target with
`
`diffraction-lirnited beam quality, which generates the needed 100 W of power on the
`
`plasma target 30 with a diameter of 13.5nm for generating plasma 32.
`
`[00014]
`
`The adaptive optics 12 focuses a spot on plasma target 30 limited by the
`
`wavelength of the light with a Strehl ratio close to 1. The Strehl ratio defines how small
`
`the spot focused on the plasma target 30 can be as a function limited by the wavelength of
`
`the projected light. As can be seen, such a condition demands a well corrected wave front,
`
`which is generally provided through use of fiber lasers. For small wave front variations,
`
`the Strehl ratio is given by the Maréchal expression, which is:
`
`275 2
`I(P) z 1 - ——
`,1
`
`2
`
`(ACID)
`
`where 7t is the wavelength of the laser light,
`
`(ACID) 2 is the root-mean-square deviation from the ideal wavefront.
`
`[00015]
`
`Therefore, to obtain 80% of the light projected by optics 12 into the desired
`
`focal spot on the plasma target 30, as described above, the wavefront must be corrected by
`
`M14. For 50% of the light to be projected into the desired focal spot, the correction must
`
`be greater than 9»/8. This type of wavefront quality is obtainable by using adaptive optics
`
`such as those including deformable mirrors.
`
`[00016]
`
`The plasma target 30 is constructed of a material type that preferably
`
`reduces the amount of solid debris that results from generation of plasma 32. Such solid
`
`debris constitutes solid particles other than the plasma 32 which may cause damage to
`
`optical components in the system. A reduced debris laser, or a “clean” source, is where
`
`plasma particle emission is below a level that would otherwise cause damage or
`
`degradation of the optics. Preferably, mass limited targets are used as plasma target 30.
`
`Such targets may include solid films, liquids and gaseous targets. A mass limited target
`
`
`
`

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`WO 2004/097520
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`PCT/US2004/012714
`
`limits the amount of produced debris, as the target contains less mass from which solid
`
`particles may be formed that interfere with the optical components of optics 12. In an
`
`embodiment, xenon or another noble element is used to realize high EUV emissions and
`
`clean operation. Plasma target 30 may by provided in the optical path of the fiber laser 18
`
`by a liquid rare gas jet or a fast spinning disc covered with a cryogenically cooled rare gas-
`
`film such as a xenon film.
`
`[00017]
`
`In another embodiment, as shown in figure 3, shielding 50 is provided over
`
`the optics 12. Shielding 50 may take the form of a film of material with high transmission,
`
`but which stops the debris from hitting the optics 12. The film is preferably constantly
`
`refreshed to avoid accumulation of ablated material on the shielding film. Shielding 50
`
`may also be an electrostatic capacitor or a magnetic field to deflect charged plasma
`
`particles away from the optics 12. Additionally, plasma portion 14 may include a chamber
`
`52 which maintains the environment with a low pressure inert gas.
`
`[00018]
`
`In one example, a spot size of 1,um is generated on plasma target 30. Here,
`
`plasma target 30 is a spinning disc. The spot is displaced at least twice the focus size
`
`(2,um) from the center of the plasma target 30. The plasma target 30 has a rotation rate of
`
`3Mhz and a target velocity of ~6m/s. With a disc radius of 10cm and a rotation of the disc
`
`with ~l00 revolutions per second, the target lasts for approximately 15 minutes. A film
`
`thickness of at least 3 times the confocal parameter of the focusing optics is therefore used
`
`to retain the overall thickness of the plasma target 30.
`
`[00019]
`
`As shown in Figure 2, scaling of power may be achieved by combining the
`
`outputs of multiple fibers. Specifically, fiber laser 18 is shown having a plurality of fibers
`
`26 that feed into a combining device 28. The combining device 28 may be any known
`
`combining device for combining a plurality of optical outputs. The output of the
`
`combining device 28 is then fed into adaptive optics 20 (see Figure 1). As mode properties
`
`of fiber lasers are fixed by the fiber core structure, it is possible to maintain strong single-
`mode operation even at very high output powers by using this multiple fiber approach.
`
`Combining device 28 may either use coherent or incoherent combining methods, which
`
`will be understood by one skilled in the art. In the case of coherent combining, nearly
`
`diffraction-limited spot sizes can be maintained for a multi—fiber structure. Conversely,
`
`incoherent combining would result in larger focused spot sizes on the target, which can be
`
`compensated by the increase in the overall output energy by combining the output from
`
`
`
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`WO 2004/097520
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`PCT/US2004/012714
`
`several fibers 26. In this case, energy requirements for each individual fiber 26 can remain
`
`low.
`
`[00020]
`
`In addition, pulse shaping can be used to further enhance EUV efficiency.
`
`By EUV efficiency, the amount of energy supplied to the fiber laser 18 is compared with
`
`the amount of energy or EUV radiation generated from the plasma 32. The use of fiber
`
`lasers enhances EUV efficiency by pulse shaping and the implementation of pre-pulses, in
`
`order to tailor the plasma conditions of the plasma 32 for the highest laser energy.
`
`Specifically, more precise control provided by Virtue of a more organized light source
`
`allows better control of the energy supplied by a given pulse. As such, the laser pulses can
`
`be specifically tailored to provide a specific amount of energy to create a specific amount
`
`of plasma. Likewise, pre-pulses may be used to assist in generating the requisite amount of
`
`plasma required for the given task.
`
`[00021]
`
`The efficiency of laser—to—EUV light conversion is a function of optical
`
`pulse duration and on the use of pre-pulses. Overall, this dependence is affected by a
`
`number of factors, such as laser wavelength, pre—pulse delay, pre—pulse energy, target
`
`material and geometry. However, the preferable pulse duration for a given material ranges
`
`from ~lps to <lns for EUV generation. Use of such preferable duration pulses leads to a
`
`significant increase in laser—to—EUV conversion efficiency compared to non—optimum
`
`duration pulses. As a result, the amount of EUV energy per unit of energy supplied to the
`
`laser is maximized when pulses in this range are used.
`
`[00022]
`
`In one example, water is used as the plasma target 30. In this example,
`
`conversion efficiencies of laser energy into 13.5nm radiation energy are obtained from
`
`water droplet targets at various pulse durations using a Tizsapphire laser at 800nm. The
`
`optimum pulse duration is ~120ps with an efficiency of 0.2% for a pulse energy of 50m.T,
`
`and the efficiency is reduced by a factor of two for a pulse duration of 6ns.
`
`[00023]
`
`In another example, xenon cluster targets are used as plasma target 30.
`
`Plasma target 30 exhibits a continuous decrease in efficiency with longer pulse duration.
`
`Starting with an efficiency of about 0.2% for lps pulse duration generated with 3.5mJ
`
`Ti:sapphire laser pulses, the EUV efficiency drops by almost three times in magnitude for a
`
`lOns pulse duration and approximately 50ml pulse energy. Applying l.7l<W Q-switched
`
`Nd:YAG lasers with pulse energies of about 11, state-of-the-art EUV sources with liquid
`
`xenon spray targets yield efficiencies of about 0.6%. With the implementation of pre-
`
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`WO 2004/097520
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`
`pulses, the EUV efficiency increases by a factor of 15. A pre—pulse is a specifically shaped
`
`part of the pulse having a lower amplitude compared to the pulse energy peak, which
`
`precedes the energy peak in time. A pre-pulse modified target material prior to the arrival
`
`of the main energy peak in such a way as to facilitate EUV light production from plasma
`
`generated at the main laser pulse energy peak.
`
`[00024]
`
`For pulses of greater than 50ps duration, the required energies can be
`
`amplified in the fiber laser 18 directly, while pulses of less than 50ps duration can be
`
`obtained through the additional use of chirped pulse amplification arrangements as will
`
`readily be understood by one skilled in the art. The high spatial quality obtainable from
`
`high-power fiber lasers allows focusing of the energy over a small focal Rayleigh volume
`
`of few X3 (cubic wavelengths). Because of how relatively small the focal Volume of the
`
`plasma target 30 is, plasma target 30 is preferably solid or liquid.
`
`
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`WO 2004/097520
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`PCT/US2004/012714
`
`CLAIMS
`
`1.
`
`A system for performing lithography operations, comprising:
`
`a fiber laser (18); and
`
`adaptive optics (20) adapted to receive light from the fiber laser (18) and
`
`focus it on a target.
`
`2.
`
`The system according to claim 1, wherein:
`
`the target (30) is a plasma target (30); and
`
`the plasma target (30) is adapted to generate plasma when light from the
`
`adaptive optics (20) having desired characteristics is directed on a spot on the plasma target
`
`(30).
`
`3.
`
`The system according to claim 2, wherein the characteristics include a fluence of
`
`about 1kJ/cm2.
`
`4.
`
`The system according to claim 3, wherein at least one fiber of the fiber laser (18)
`
`exhibits a fluence of less than 10 J/cmz.
`
`5.
`
`6.
`
`The system according to claim 4, wherein a size of the spot is about 1—um.
`
`The system according to claim 5, wherein the adaptive optics (20) includes
`
`deformable mirrors.
`
`7.
`
`The system according to claim 1, wherein the fiber laser (18) comprises a plurality
`
`of fibers.
`
`8.
`
`9.
`
`The system according to claim 7, further comprising a combining device (34).
`
`The system according to claim 8, wherein the system is adapted to combine outputs
`
`of each of the plurality of fibers to increase an output power from the adaptive optics (20).
`
`10.
`
`The system according to claim 9, wherein the combining device (34) is adapted to
`
`combine the outputs of each of the fibers by either coherent or incoherent methods.
`
`
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`WO 2004/097520
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`PCT/US2004/012714
`
`11.
`
`The system according to claim 2, wherein the plasma target (30) is xenon.
`
`12.
`
`The system according to claim 11, wherein the fiber laser (18) is adapted to
`
`generate light on the plasma target (30) at a pulse duration of lps and a pulse energy of ll.
`
`13.
`
`The system according to claim 12, wherein the plasma target (30) is liquid xenon
`
`spray.
`
`14.
`
`The system according to claim 13, wherein the laser is adapted to implement pre-
`
`pulses of light on the plasma target (30).
`
`15.
`
`The system according to claim 2, wherein the fiber laser (18) is adapted to generate
`
`light at a pulse duration of between about lps to lns.
`
`16.
`
`The system according to claim 2, further comprising:
`
`a lithography target (16); and
`
`a focusing element that focuses EUV radiation from plasma generated from
`
`the plasma target (30) onto the lithography target (16).
`
`17.
`
`A method for generating EUV radiation, comprising:
`
`providing a plasma target (30);
`
`generating laser light with a fiber laser (18); and
`
`focusing the laser light on the plasma target (30) with adaptive optics (20).
`
`18.
`
`The method according to claim 17, wherein the plasma target (30) is xenon.
`
`19.
`
`The method according to claim 17, further comprising the step of generating the
`
`laser light on the plasma target (30) and a pulse duration of lps and a pulse energy of II.
`
`20.
`
`The method according to claim 17, wherein the plasma target (30) is liquid xenon
`
`spray.
`
`21.
`
`The method according to claim 20, wherein the laser is adapted to implement pre-
`
`pulses of light on the plasma target (30).
`
`
`
`

`
`WO 2004/097520
`
`PCT/US2004/012714
`
`22.
`
`The method according to claim 17, further comprising the step of generating light at
`
`a pulse duration of between about lps to lns.
`
`10
`
`

`
`
`
`WO 2004/097520WO 2004/097520
`
`
`
`PCT/US2004/012714PCT/US2004/012714
`
`
`
`7/27/2
`
`
`
`’?’?
`
`
`
`3434
`
`
`
`3232
`
`
`
`f 74f 74
`
`
`
`2020
`
`
`
`76'76'
`
`
`
`76’76’
`
`
`
`72/‘72/‘
`
`
`
`3”3”
`
`
`
`F/G. 7F/G. 7
`
`
`
`26’26’
`
`
`
`26 '26 '
`
`
`
`26'26'
`
`
`
`2626
`
`
`
`26'26'
`
`
`
`H6. 2H6. 2
`
`

`
`
`
`WO 2004/097520WO 2004/097520
`
`
`
`PCT/US2004/012714PCT/US2004/012714
`
`
`
`2/22/2
`
`
`
`7878
`
`
`
`H6‘. 3H6‘. 3