(12) United States Patent
`Melnychuk et al.
`
`(10) Patent N0.:
`
`(45) Date of Patent:
`
`US 6,972,421 B2
`Dec. 6, 2005
`
`US006972421B2
`
`(54) EXTREME ULTRAVIOLET LIGHT SOURCE
`
`(60)
`
`(75)
`
`Inventors: Stephan T. Melnychuk, Carlsbad, CA
`(US); William N. Partlo, Poway, CA
`(US); Igor V. Fomenkov, San Diego,
`CA (US); I. Roger Oliver, San Diego,
`CA (US); Richard M. Ness, San Diego,
`CA (US); Norbert Bowering, San
`Diego, CA (US); Oleh Khodykin, San
`Diego, CA (US); Curtis L. Rettig,
`Vista, CA (US); Gerry M.
`Blumenstock, San Diego, CA (US);
`Timothy S. Dyer, Oceanside, CA (US);
`Rodney D. Simmons, San Diego, CA
`(US); Jerzy R. Hoffman, Escondido,
`CA (US); R. Mark Johnson, Ramona,
`CA (US)
`
`(73) Assignee: Cymer, Inc., San Diego, CA (US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 107 days.
`
`(21) Appl. No.: 10/409,254
`
`(22)
`
`Filed:
`
`Apr. 8, 2003
`
`(65)
`
`Prior Publication Data
`US 2004/0108473 A1 Jun. 10, 2004
`
`Related U.S. Application Data
`
`(63)
`
`Continuation—in—part of application No. 10/384,967, filed on
`Mar. 8, 2003, which is a continuation—in—part of application
`No. 10/189,824, filed on Jul. 3, 2002, now Pat. No. 6,815,
`700, which is a continuation—in—part of application No.
`10/120,655, filed on Apr. 10, 2002, now Pat. No. 6,744,060,
`which is a continuation-in-part of application No. 09/875,
`719, filed on Jun. 6, 2001, now Pat. No. 6,586,757, which is
`a continuation—in—part of application No. 09/875,721. filed
`on Jun. 6, 2001, now Pat. No. 6,566,668, which is a
`continuation—in—part of application No. 09/696,084, filed on
`Oct. 16, 2000, now Pat. No. 6,566,667, which is a continu-
`ation—in—part of application No. 09/590,962, filed on Jun. 9,
`2000, now abandoned.
`
`Provisional application No. 60/422,808, filed on Oct. 31,
`2002, and provisional application No. 60/419,805, filed on
`Oct. 18, 2002.
`
`Int. Cl.7 ............................................... .. H01J 35/20
`(51)
`(52) U.S. Cl.
`............................. .. 250/504 R; 250/493.1;
`378/119
`
`(58) Field of Search ........................ .. 250/504 R, 493.1;
`378/119; 372/5, 87
`
`(56)
`
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`Primary Examiner—Kiet T. Nguyen
`(74) Attorney, Agent, or Firm—William C. Cray; Cymar,
`Inc.
`
`(57)
`
`ABSTRACT
`
`The present invention provides a reliable, high-repetition
`rate, production line compatible high energy photon source.
`Avery hot plasma containing an active material is produced
`in vacuum chamber. The active material is an atomic ele-
`ment having an emission line within a desired extreme
`ultraviolet (EUV) range. Apulse power source comprising a
`charging capacitor and a magnetic compression circuit com-
`prising a pulse transformer, provides electrical pulses having
`sufficient energy and electrical potential sufficient to pro-
`duce the EUV light at an intermediate focus at rates in excess
`of 5 Watts. In preferred embodiments designed by Appli-
`cants in-band, EUV light energy at the intermediate focus is
`45 Watts extendable to 105.8 Watts.
`
`78 Claims, 50 Drawing Sheets
`
`
`
`(cid:34)(cid:52)(cid:46)(cid:45)(cid:1)(cid:18)(cid:17)(cid:18)(cid:20)
`
`ASML 1013
`
`

`
`US 6,972,421 B2
`Page 2
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`..
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`...... ..
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`.......... .. 378/119
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`................ .. 378/34
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`.
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`...... .. 25 /504
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`..
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`.
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`

`
`US 6,972,421 B2
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`
`* cited by examiner
`
`

`
`U.S. Patent
`
`ceD
`
`US 6,972,421 B2
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`U.S. Patent
`
`Dec. 6,2005
`
`Sheet 2 of 50
`
`US 6,972,421 B2
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`U.S. Patent
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`Dec. 6, 2005
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`Sheet 12 of 50
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`US 6,972,421 B2
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`Dec. 6,2005
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`Sheet 13 of 50
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`U.S. Patent
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`Dec. 6,2005
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`US 6,972,421 B2
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`Sheet 46 of 50
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`US 6,972,421 B2
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`PRIOR ART
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`U.S. Patent
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`Dec. 6, 2005
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`Sheet 47 of 50
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`US 6,972,421 B2
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`Sheet 50 of 50
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`US 6,972,421 B2
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`US 6,972,421 B2
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`1
`EXTREME ULTRAVIOLET LIGHT SOURCE
`
`This application is a continuation-in-part of U.S. Ser. No.
`10/384,967 filed Mar. 8, 2003, Ser. No. 10/189,824 filed Jul.
`3, 2002 now U.S. Pat. No. 6,815,700, U.S. Ser. No. 10/120,
`655 filed Apr. 10, 2002, now U.S Pat. No. 6,744,060, U.S.
`Ser. No. 09/875,719 filed Jun. 6, 2001 now U.S. Pat. No.
`6,586,757, and U.S. Ser. No. 09/875,721 filed Jun. 6, 2001
`now U.S. Pat No. 6,566,668, U.S. Ser. No. 09/690,084 filed
`Oct. 16, 2000 now U.S. Pat. No. 6,566,667 ; and claims the
`benefit of patent application Ser. No. 60/422,808 filed Oct.
`31, 2002 and patent application Ser. No. 60/419,805 filed
`Oct. 18, 2002; all of which is incorporated by reference
`herein. This invention relates to high-energy photon sources
`and in particular highly reliable x-ray and high-energy
`ultraviolet sources.
`
`BACKGROUND OF THE INVENTION
`
`The semiconductor industry continues to develop litho-
`graphic technologies, which can print ever-smaller inte-
`grated circuit dimensions. These systems must have high
`reliability, cost effective throughput, and reasonable process
`latitude. The integrated circuit fabrication industry has
`recently changed over from mercury G-line (436 nm) and
`I-line (365 nm) exposure sources to 248 nm and 193 nm
`excimer laser sources. This transition was precipitated by the
`need for higher lithographic resolution with minimum loss
`in depth-of-focus.
`The demands of the integrated circuit industry will soon
`exceed the resolution capabilities of 193 nm exposure
`sources, thus creating a need for a reliable exposure source
`at a wavelength significantly shorter than 193 nm. An
`excimer line exists at 157 nm, but optical materials with
`sufficient transmission at this wavelength and sufficiently
`high optical quality are difficult to obtain. Therefore, all-
`reflective imaging systems may be required. An all reflective
`optical system requires a smaller numerical aperture (NA)
`than the transmissive systems. The loss in resolution caused
`by the smaller NA can only be made up by reducing the
`wavelength by a large factor. Thus, a light source in the
`range of 10 to 20 nm is required if the resolution of optical
`lithography is to be improved beyond that achieved with 193
`nm or 157 nm. Optical components for light at wavelengths
`below 157 nm are very limited. However, effective incidents
`reflectors are available and good reflectors multi-layer at
`near normal angles of incidence can be made for light in the
`wavelength range of between about 10 and 14 nm. (Light in
`this wavelength range is within a spectral range known as
`extreme ultraviolet light and some would light in this range,
`soft x-rays.) For these reasons there is a need for a good
`reliable light source at wavelengths in this range such as of
`about 13.5 nm.
`
`The present state of the art in high energy ultraviolet and
`x-ray sources utilizes plasmas produced by bombarding
`various target materials with laser beams, electrons or other
`particles. Solid targets have been used, but the debris created
`by ablation of the solid target has detrimental effects on
`various components of a system intended for production line
`operation. A proposed solution to the debris problem is to
`use a frozen liquid or liquidfied or frozen gas target so that
`the debris will not plate out onto the optical equipment.
`However, none of these systems have so far proven to be
`practical for production line operation.
`It has been well known for many years that x-rays and
`high energy ultraviolet radiation could be produced in a
`plasma pinch operation. In a plasma pinch an electric current
`
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`is passed through a plasma in one of several possible
`configuration such that the magnetic field created by the
`flowing electric current accelerates the electrons and ions in
`the plasma into a tiny volume with sufficient energy to cause
`substantial stripping of outer electrons from the ions and a
`consequent production of x-rays and high energy ultraviolet
`radiation. Various prior art techniques for generation of high
`energy radiation from focusing or pinching plasmas are
`described in the background section of U.S. Pat. No. 6,452,
`199.
`
`Typical prior art plasma focus devices can generate large
`amounts of radiation suitable for proximity x-ray
`lithography, but are limited in repetition rate due to large per
`pulse electrical energy requirements, and short lived internal
`components. The stored electrical energy requirements for
`these systems range from 1 kJ to 100 kJ. The repetition rates
`typically did not exceed a few pulses per second.
`What is needed are production line reliable, systems for
`producing collecting and directing high energy ultraviolet
`x-radiation within desired wavelength ranges which can
`operate reliably at high repetition rates and avoid prior art
`problems associated with debris formation.
`SUMMARY OF THE INVENTION
`
`The present invention provides a reliable, high-repetition
`rate, production line compatible high energy photon source.
`Avery hot plasma containing an active material is produced
`in vacuum chamber. The active material is an atomic ele-
`
`ment having an emission line within a desired extreme
`ultraviolet (EUV) wavelength range. A pulse power source,
`comprising a charging capacitor and a magnetic compres-
`sion circuit comprising a pulse transformer, provides elec-
`trical pulses having sufficient energy and electrical potential
`sufficient to produce the EUV light at an intermediate focus
`at rates in excess of 5 Watts on a continuous basis and in
`
`excess of 20 Watts on a burst basis. In preferred embodi-
`ments designed by Applicants in-band, EUV light energy at
`the intermediate focus is 45 Watts extendable to 105.8 Watts.
`
`In preferred embodiments the high energy photon source
`is a dense plasma focus device with co-axial electrodes. the
`electrodes are configured co-axially. The central electrode is
`preferably hollow and an active gas is introduced out of the
`hollow electrode. This permits an optimization of the spec-
`tral line source and a separate optimization of a buffer gas.
`In preferred embodiments the central electrode is pulsed
`with a high negative electrical pulse so that the central
`electrode functions as a hollow cathode. Preferred embodi-
`
`ments present optimization of capacitance values, anode
`length and shape and preferred active gas delivery systems
`are disclosed. Special techniques are described for cooling
`the central electrode. In one example, water is circulated
`through the walls of the hollow electrode.
`In another
`example, a heat pipe cooling system is described for cooling
`the central electrode.
`An external reflection radiation collector-director collects
`
`radiation produced in the plasma pinch and directs the
`radiation in a desired direction. Good choices for the reflec-
`
`ruthenium,
`tor material are molybdenum, palladium,
`rhodium, gold or tungsten. In preferred embodiments the
`active material may be xenon, lithium vapor, tin vapor and
`the buffer gas is helium and the radiation-collector is made
`of or coated with a material possessing high grazing inci-
`dence reflectivity. Other potential active materials are
`described.
`
`In preferred embodiments the buffer gas is helium or
`argon. Lithium vapor may be produced by vaporization of
`
`

`
`US 6,972,421 B2
`
`3
`solid or liquid lithium located in a hole along the axis of the
`central electrode of a coaxial electrode configuration.
`Lithium may also be provided in solutions since alkali
`metals dissolve in amines. A lithium solution in ammonia
`
`(NH3) is a good candidate. Lithium may also be provided by
`a sputtering process in which pre-ionization discharges
`serves the double purpose of providing lithium vapor and
`also pre-ionization. In preferred embodiments, debris is
`collected on a conical nested debris collector having sur-
`faces aligned with light rays extending out from the pinch
`site and directed toward the radiation