(12)
`
`United States Patent
`Melnychuk et al.
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`US 6,972,421 B2
`Dec. 6, 2005
`
`US006972421B2
`
`(60) Provisional application No. 60/422,808, ?led on Oct. 31,
`2002, and provisional application No. 60/419,805, ?led on
`Oct- 18’ 2002
`(51) Im. c1.7 ............................................... .. H01J 35/20
`(52) U.S. c1. ............................. .. 250/504 R; 250/4931;
`378/119
`
`
`
`
`
`
`
`
`
`h f S 0 earc ........................ "378/119 37,2/5 R ’ ’
`
`
`
`F
`1e
`
`(
`
`)
`
`(56)
`
`(54) EXTREME ULTRAVIOLET LIGHT SOURCE
`
`(75) Inventors: Stephan T. Melnychuk, Carlsbad, CA
`(US); William N- Partlo, Poway, CA
`(US); Igor V- Fomenkflv, San Diego,
`CA (US); I. Roger Oliver, San Diego,
`CA
`Richard M- NESS, San Diego,
`
`CA (Us); Norbert Bowering, San Diego, CA (US); Oleh Khodykin, San
`
`Diego, CA (US); CllI‘tlS L. Rettlg,
`Vista, CA (US); Gerry M.
`Blumenstock, San Diego, CA (US);
`Tlmothy S‘ Dyer’ Oceanslde: CA (Us);
`Rodney D- slmmons, San D1eg°>_ CA
`(Us); Jerly R- Ho?mall, Escond1d°>
`CA (US); R. Mark Johnson, Ramona,
`CA (Us)
`
`(73) Assignee: Cymer, Inc., San Diego, CA (US)
`
`( * ) Notice:
`
`(21) Appl- NOJ 10/409!254
`(22) Filed:
`Apr. 8,2003
`(65)
`Prior Publication Data
`
`References Cited
`
`US PATENT DOCUMENTS
`. 250/53
`2,759,106 A
`8/1956 Wolter ............ ..
`60/355
`3,150,483 A
`9/1964 May?eld et al. ..
`3,232,046 A
`2/1966 Meyer ...................... .. 50/355
`
`.
`
`(Continued)
`
`ABSTRACT
`
`OTHER PUBLICATIONS
`ApruZese, J.P., “X—Ray Laser Research Using Z Pinches,”
`Subject to any disclaimer, the term of this Am Inst' of phys_ 399403, (1994)_
`patent is extended or adjusted under 35
`_
`U.S.C. 154(b) by 107 days.
`(Con?rmed)
`g y
`y
`Primar Examiner—Kiet T. N u en
`(74) Attorney, Agent, or Firm—William C. Cray; Cymar,
`I“
`(57)
`
`Us 2OO4/01O8473 A1 Jun 10’ 2004
`
`Related US Application Data
`
`(63) Continuation-in-part of application No. 10/384,967, ?led on
`Mar. 8, 2003, which is a continuation-in-part of application
`No. 10/189,824, ?led on Jul. 3, 2002, now Pat. No. 6,815,
`700, which is a continuation-in-part of application No.
`10/120,655, ?led on Apr. 10, 2002, now Pat. No. 6,744,060,
`which is a continuation-in-part of application No. 09/875,
`719, ?led on Jun. 6, 2001, now Pat. No. 6,586,757, which is
`a continuation-in-part of application No. 09/875,721, ?led
`on Jun. 6, 2001, now Pat. No. 6,566,668, which is a
`continuation-in-part of application No. 09/696,084, ?led on
`Oct. 16, 2000, now Pat. No. 6,566,667, which is a continu
`ation-in-part of application No. 09/590,962, ?led on Jun. 9,
`2000, now abandoned.
`
`The present 'invention provides a reliable, high-repetition
`rate, production lme 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
`suf?cient energy and electrical potential suf?cient 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
`
`RAZING INCIDENCE COLLECTOR
`r _,/
`
`//
`
`ASML 1230
`
`

`
`US 6,972,421 B2
`Page 2
`
`Us. PATENT DOCUMENTS
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`
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`
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`4,143,275 A
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`
`. . . .. 425/467
`
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`
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`
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`
`. . . .. 123/620
`
`4,504,964 A
`
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`
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`
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`
`3/1985 Asmussen et al.
`
`315/39
`
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`
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`
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`
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`
`8/1985 IWamatsu
`
`378/119
`
`4,561,406 A 12/1985 Ward . . . . . . . . . . . . . .
`
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`
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`1/1987 Okada et al.
`4,751,723 A
`6/1988 Gupta et al. .............. .. 378/119
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`6/1988 Gupta et al. .............. .. 378/119
`
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`
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`
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`
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`
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`
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`
`5/1990 Birx et al. . . . . . .
`. . . .. 307/106
`6/1991 Neff et al. ................ .. 378/122
`6/1991 Horsley et al. ........... .. 324/674
`4/1992 Hammer et al.
`430/311
`
`6/1992 Dethlefsen . . . . . .
`5,126,638 A
`8/1992 Birx .......... ..
`5,142,166 A
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`5/1994 Cook et al.
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`5/1995 Dearman et al.
`5,448,580 A
`9/1995 Birx et al. .... ..
`5,504,795 A
`4/1996 McGeoch
`5,729,562 A
`3/1998 Birx et al.
`5,763,930 A
`6/1998 Partlo .... ..
`5,866,871 A
`2/1999 Birx .......... ..
`5,936,988 A
`8/1999 Partlo et al.
`5,963,616 A 10/1999 Silfvast et al. ..
`6,031,241 A
`2/2000 Silfvast et al. ..
`6,039,850 A
`3/2000 Schulz ...... ..
`
`. . . .. 315/326
`307/419
`378/34
`372/37
`244/53
`372/38
`378/119
`372/38
`250/504
`.. 219/121
`..... .. 372/38
`378/122
`250/504
`204/192.15
`
`6,051,841 A
`
`4/2000 Partlo . . . . . . . . . .
`
`. . . .. 250/504
`
`250/504
`5/2000 Partlo et al. .
`6,064,072 A
`1/2001 Birx .................... .. 219/121.57
`6,172,324 B1
`2/2001 Pascente .................... .. 363/21
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`5/2003 Partlo et al.
`250/504
`6,566,667 B1
`5/2003 Rauch et al.
`250/504
`6,566,668 B2
`6,567,499 B2 * 5/2003 McGeoch ................. .. 378/119
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`7/2003 Melnychuk et al. ...... .. 250/504
`2001/0055364 A1 12/2001 Kandaka et al. .......... .. 378/119
`
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`
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`
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`
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`* cited by examiner
`
`

`
`U.S. Patent
`
`Dec. 6, 2005
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`U.S. Patent
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`Dec. 6,2005
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`Sheet 12 0f 50
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`US 6,972,421 B2
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`U.S. Patent
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`Dec. 6,2005
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`Sheet 13 0f 50
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`US 6,972,421 B2
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`U.S. Patent
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`Dec. 6, 2005
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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
`
`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 sufliciently
`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 suflicient 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 suflicient energy and electrical potential
`suflicient 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
`
`

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`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 collector-director. The
`reflection radiation collector-director and the conical nested
`
`debris collector could be fabricated together as one part or
`they could be separate parts aligned with each other and the
`pinch site.
`This prototype devices actually built and test by Appli-
`cants convert electrical pulses (either positive or negative) of
`about 10 J of stored electrical energy per pulse into approxi-
`mately 50 m] of in-band 13.5 nm radiation emitted into 231
`steradians. Thus, these tests have demonstrated a conversion
`efliciency of about 0.5%, Applicants estimate that they can
`collect about 20 percent of the 50 m] 13.5 nm radiation so
`that this demonstrated collected energy per pulse will be in
`about of 10 m]. Applicants have demonstrated 1000 Hz
`continuous operation and