WWWWWWWI
`
`IWWWWWWWMWW
`
`US 20050225739A1
`
`(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2005/0225739 A1
`(43) Pub. Date:
`Oct. 13, 2005
`Hiura
`
`(S4) EXPOSURE APPARATUS AND DEVICE
`FABRICATION METHOI) USING THE SAME
`
`(52) U.S. Cl.
`
`............................................... .. 355/67; 355/53
`
`(76)
`
`Inventor: Mitsuru Hiura, Tochigi (JP)
`
`(57)
`
`ABSTRACT
`
`Correspondence Address:
`MORGAN & FINNEGAN, L.L.R
`3 WORLD FINANCIAL CENTER
`NEW YORK, NY 10281-2101 (US)
`
`(21) Appl. No.:
`
`10/512,312
`
`(22
`
`PCT Filed:
`
`Apr. 11, 2003
`
`(86) PCT No.:
`
`I’C'I‘/,II’03/04644
`
`(30)
`
`Foreign Application Priority Data
`
`Apr. 26, 2002 (JP) 2002127343
`
`Publication Classification
`
`(51)
`
`Int. Cl.7
`
`G031} 27/54
`
`An exposure apparatus that irradiates excitation laser onto a
`target, and generates from generated plasma a light source
`for generating illumination light of an extreme ultraviolet
`region or an X-ray region includes an illumination optical
`system that uses the illumination light
`to illuminate a
`catoptric reticle that forms a pattern to be transferred, the
`illumination optical system including a first mirror closest to
`the light source, an ellipsoidal mirror for condensing the
`illumination light in front of the first mirror in the illumi-
`nation optical system, and a projection optical system that
`reduces and projects the pattern reflected on the reticle onto
`an object to be exposed, wherein light where an optical-axis
`direction of the excitation laser proceeds beyond a position
`that generates the plasma by the excitation laser does not
`interfere with components in the exposure apparatus includ-
`ing the illumination and projection optical systems, and the
`ellipsoidal minor.
`
`ASML 1004
`
`

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`Patent Application Publication Oct. 13, 2005 Sheet 1 of 13
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`US 2005/0225739 A1
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`«S2:
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`FIG.1
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`

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`Patent Application Publication Oct. 13,2005 Sheet 2 of 13
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`US 2005/0225739 A1
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`—N—5
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`NN—
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`MNF
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`mN_.
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`2:
`
`FIG.2
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`

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`Patent Application Publication Oct. 13, 2005 Sheet 3 of 13
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`US 2005/0225739 A1
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`190
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`

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`Patent Application Publication Oct. 13, 2005 Sheet 4 of 13
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`US 2005/0225739 A1
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`190
`
`FIG.4
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`

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`Patent Application Publication Oct. 13, 2005 Sheet 5 of 13
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`US 2005/0225739 A1
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`525
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`

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`Patent Application Publication Oct. 13, 2005 Sheet 6 of 13
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`604
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`601
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`

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`Patent Application Publication Oct. 13,2005 Sheet 7 of 13
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`US 2005/0225739 A1
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`704 %
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`.r 701
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`FIG.7A
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`@@@§@Qa
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`FIG.7C
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`

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`Patent Application Publication Oct. 13, 2005 Sheet 8 of 13
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`US 2005/0225739 A1
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`

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`Patent Application Publication Oct. 13, 2005 Sheet 9 of 13
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`US 2005/0225739 A1
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`
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`FIG.9A
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`105 /
`
`50
`
`101
`
`107
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`FlG.9B
`
`

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`Patent Application Publication Oct. 13,2005 Sheet 10 of 13
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`US 2005/0225739 A1
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`2:
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`om.
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`§/mm.
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`FIG.10
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`

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`Patent Application Publication Oct. 13,2005 Sheet 11 of 13
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`US 2005/0225739 A1
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`VNF
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`--4
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`FIG.11
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`
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`

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`Patent Application Publication Oct. 13,2005 Sheet 12 of 13
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`US 2005/0225739 A1
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`CIRCUIT
`[)Es1GN
`
`WAFER MAKING
`
`(STEP1)
`
`(STEP3)
`
`MASK
`
`FABRICATION
`
`(STEP2)
`
`WAFER PROCESS
`(PREPROCESS)
`
`(STEP4)
`
`ASSEMBLY
`IPOSTPROCESS) .
`
`(STEP5)
`
`INSPECTION
`
`(STEP6)
`
`SHIPPING
`
`(STEP?)
`
`FIG.12
`
`

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`Patent Application Publication Oct. 13, 2005 Sheet 13 of 13
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`US 2005/0225739 A1
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`
`
` OXIDIZATION
`
`
`
`ELECTRODE
`
`DEVELOPMENT
`
`(STEP17)
`
`I FORMATION I
` IMPLANTATION
`
`
`
`ION
`
`CSTEPW
`
`ETCHING
`
`(STEP18)
`
`. RESIST
`
`STRIPPING
`
`(STEP19) REPEAT
`
`FIG.13
`
`
`
`RESIST
`
`PROCESS
`
`(STEP15)
`
`EXPOSURE
`
`(STEP16)
`
`
`
`
`
`

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`US 2005/0225739 A1
`
`Oct. 13, 2005
`
`EXPOSURE APPARATUS AND DEVICE
`FABRICATION METHOD USING THE SAME
`
`[0001] This application claims the right of priority based
`on Japanese Patent Applications Nos. 2002-127343, filed on
`Apr. 26, 2002, and 2003-73637, filed on Mar. 18, 2003,
`which are hereby incorporated by reference herein in their
`entirety as if fully set forth herein.
`
`TECHNICAL FIELD
`
`[0002] The present invention relates generally to exposure
`apparatuses and device fabrication methods, and more par-
`ticularly to an extreme ultraviolet (“EUV”) exposure appa-
`ratus used for a
`lithography process for manufacturing
`devices, eg., semiconductor devices, such as K35 and I,Sls,
`liquid crystal devices, image-pickup devices, such as CCDS,
`and magnetic heads.
`
`BACKGROUND ART
`
`[0003] Along with recent demands for smaller and lower
`profile electronic devices, finer semiconductor devices to be
`mounted onto these electronic devices have been increas-
`ingly demanded. Conventionally, a lithography method for
`manufacturing a semiconductor device has used a reduction
`projection exposure using ultraviolet ("UV”) light, but the
`minimum critical dimension transferable in the reduction
`projection exposure is in proportion to a wavelength of light
`used for transfer and in reverse proportion to a numerical
`aperture (“NA”) of a projection optical system. In order to
`transfer finer circuit patterns, a wavelength of used exposure
`light has been shortened from an i-line mercury lamp (with
`a wavelength of 365 nm) to KIF excimer laser (with a
`wavelength of 248 nm) and ArF excimer laser (with a
`wavelength of approximately 193 nm).
`
`[0004] However, as the semiconductor device has rapidly
`become finer,
`the lithography using the UV light has a
`limited resolution Accordingly, in order to cfiiciently print
`a very fine circuit pattern below 0.1 /cm, a projection
`exposure apparatus has developed that uses EUV light
`having a wavelength between 10 and 15 nm, which is much
`smaller than that of the UV light.
`
`[0005] The EUV light source uses, for example, a laser
`plasma light source. It uses YAG laser, etc.
`to irradiate a
`highly intensified pulse laser beam to a target material put in
`a vacuum chamber,
`thus generating high-temperature
`plasma for use as EUV light with a wavelength of about 13.5
`rrm emitted from this. The target material may use a metallic
`thin film, inert gas, and droplets, etc, and supplied to the
`vacuum chamber by gas jetting means and other means. The
`higher repetitive frequency of the pulse laser, e.g., repetitive
`frequency of typically several kHz,
`is preferable for the
`increased average intensity of the EUV light.
`
`Japanese Patent Application Publications Nos.
`[0006]
`53217858, 8-236292, 11-40479, and US. Pat. No. 5,335,258
`teach use of solid materials as the target material, while US.
`Pat. No. 5,459,771 teaches use of droplets as the target
`material.
`
`Japanese Patent Application Publications Nos.
`[0007]
`2003-43196 (corresponding to US. Patent Application Pub-
`lication No. US, 2002/0162975 A1), 2000110709, 2002-
`8891 and 2000-346817 teach use of a paraboloid—oE—revo—
`lution mirror as a mirror for condensing the EUV light
`
`emitted from the generated plasma, while Japanese Patent
`Application Publications Nos. 2000-91209 (corresponding
`to U.S. Pat. No. 6,266,389) and 2001-332489 teach use of a
`ellipsoidal mirror.
`
`[0008] The pulse laser beam with high intensity generates,
`when irradiating the target, flying particles called debris as
`well as the EUV light. The debris when adhering to an
`optical element causes pollution, damages and lowered
`reflectance, and thus debris removal means has convention-
`ally been proposed to prevent the debris from reaching an
`optical element from the target. For example, a debris filter
`as one exemplary debris removal means is made of molyb-
`denum, beryllium, zirconium. etc., and the transmittance to
`the EUV light is set between about 50% and 70%.
`
`[0009] For easier prevention of the debris from entering
`the illumination optical system,
`it
`is preferable that
`the
`condenser mirror of the EUV light uses an ellipsoidal mirror
`that has one focal point where the plasma occurs, and
`another focal point for condensing light, as well as physi-
`cally narrowing a path between the light source and the
`illumination system.
`
`In principle, the EUV light is isotropically emitted
`[0010]
`from the plasma, and thus may be elliciently condensed
`when a cover angle of the condenser ellipsoidal mirror is
`made larger.
`
`[0011] An illumination optical system that illuminates a
`target area using the EUV light
`is arranged below the
`emission point of the EUV light, and the conventional
`exposure apparatus arranges a laser light source such that an
`optical axis of the excitation laser accords with that of the
`EUV light incident upon the first mirror in the illumination
`optical system.
`
`[0012] Due to vibrations and mechanical deformations,
`the excitation laser may go wide of the target entirely or
`partially. Due to causes other than a positional otfset
`between the excitation laser and the target,
`the excitation
`laser may entirely or partially cross the emission point.
`When the excitation laser that crosses the emission point
`goes straight ahead and reaches the illumination optical
`system, it thermally deforms the first and subsequent mirrors
`or thermally destroys the multilayer on the mirror, lowering
`the resolution and hindering high-quality exposure. A repair
`and replacement of the mirror remarkably lowers the work-
`ing efficiency of the apparatus since the illumination and
`projection optical systems are housed in a vacuum cha mber.
`It is conceivable to considerably decrease a beam diameter
`of the laser light such that the excitation laser falls within the
`target even when it offsets slightly, but
`this undesirably
`decreases the power of the EUV light and lowers the
`throughput.
`
`[0013] The above debris filter has transmittance between
`about 50% and 70% to the EUV light, but transmittance to
`a laser beam from YAG laser of about 100%. Therefore, the
`conventional debris filter has been insutlicient to shield the
`laser beam that goes straight ahead beyond the EUV emis-
`sion point.
`
`[0014] Another conventional exposure apparatus arranges
`the laser light source such that an optical axis of the EUV
`light incident upon the first mirror in the illumination optical
`system does not accord with an optical axis of the excitation
`laser. However, this exposure apparatus restricts the cover
`
`

`
`US 2005/0225739 A1
`
`Oct. 13, 2005
`
`angle of the condenser mirror so as to maintain the intro-
`duction space of the excitation laser to the target, and does
`not sufliciently high emission efficiency of the EUV light.
`
`[0015] The prior art does not teach a large cover angle of
`the condenser ellipsoidal mirror, directions of the excitation
`laser incident onto a target and exiting the target, or inter-
`ference between the excitation laser and the illumination
`system including the ellipsoidal mirror.
`
`DISCLOSURE OF INVENTION
`
`is an exemplified object of the
`it
`[0016] Accordingly,
`present
`invention to provide an exposure apparatus and
`device fabrication method using the same, which uses an
`ellipsoidal mirror as a condenser minor to condense the
`EUV light into one point, increases its cover angle or size,
`and prevents the laser beam that goes straight ahead beyond
`a target
`from damaging optical elements including the
`ellipsoidal mirror for high-quality exposure without lower-
`ing the throughput.
`
`[0017] An exposure apparatus according to one aspect of
`the present invention that irradiates excitation laser onto a
`target, and generates from generated plasma a light source
`for generating illumination light of an extreme ultraviolet
`region or an X-ray region includes illumination light
`to
`illuminate a catoptric reticle that forms a pattern to be
`transferred, the illumination optical system including a first
`mirror closest to the light source, an ellipsoidal mirror for
`condensing the illumination light in front of the first mirror
`in the illumination optical system, and a projection optical
`system that reduces and projects the pattern reflected on the
`reticle onto an object to be exposed, wherein light where an
`optical-axis direction of the excitation laser proceeds beyond
`a position that generates the plasma by the excitation laser
`does not interfere with components in the exposure appara-
`tus including the illumination and projection optical sys-
`tems, and the ellipsoidal mirror.
`
`[0018] An optical axis of the excitation laser may be ollfset
`from an optical-axis direction of the illumination light that
`enters the first mirror in the illumination optical system.
`
`[0019] The excitation laser incident upon the target and
`the excitation laser exiting the target may pass through
`passage part provided in the ellipsoidal mirror. The excita-
`tion laser incident upon the target may pass through passage
`part provided in the ellipsoidal mirror, and the excitation
`laser exiting the target may pass through an opening of the
`ellipsoidal mirror through which the illumination light
`passes. The excitation laser exiting the target may pass
`through passage part
`in the ellipsoidal mirror, and the
`excitation laser incident upon the target may pass through an
`opening ol the ellipsoidal mirror through which the illumi-
`nation light passes. The exposure apparatus may further
`include a mechanism for three-dimensionally inclining the
`optical-axis direction of the excitation laser relative to an
`optical-axis direction of the illumination light.
`
`[0020] The exposure apparatus may further include a
`light-shielding member that prevents the excitation laser
`from reaching the illumination optical system beyond the
`target. The exposure apparatus may further include a debris
`removal member that prevents debris that is generated at an
`emission point of the plasma from reaching the illumination
`optical system. The exposure apparatus may further include
`
`a light-shielding member that prevents the excitation laser
`from reaching the illumination optical system beyond the
`target, the light—shielding member having transmittance of
`about 10% or less to the excitation laser, and a debris
`removal member that prevents debris that is generated at an
`emission point of the plasma from reaching the illumination
`optical system, the debris removal member having transmit-
`tance of about 90% or higher to the excitation laser. The
`light-shielding member may include a metal member and an
`antirefiective coating on the metal member.
`
`[0021] An angle of an optical axis of the excitation laser
`relative to an optical-axis direction of the illumination light
`may be determined such that the light from the excitation
`laser that proceeds beyond the light source may not be
`irradiated onto the outermost element in the exposure appa-
`ratus when viewed from the light source from the optical-
`axis direction of the illumination um incident upon the first
`mirror to the optical-axis direction of the excitation laser.
`The exposure apparatus may further include a cooling
`mechanism for cooling the light-shielding member. The
`light-shielding member may be located outside a chamber
`that houses the illumination and projection optical systems.
`An opening of the ellipsoidal mirror through which the
`illumination light passes, may be located closer to the first
`mirror than a condensing point of the excitation laser in an
`optical-axis direction of the illumination light.
`
`[0022] An exposure apparatus of another aspect of the
`present
`invention that
`irradiates excitation laser onto a
`target, and generates from generated plasma a light source
`for generating illumination light of an extreme ultraviolet
`region or an X-ray region includes an illumination optical
`system that uses the illumination light
`to illuminate a
`catoptric reticle forming a pattern, the illumination optical
`system including a first mirror closest to the light source, a
`condenser mirror for introducing the illumination light to the
`first mirror in the illumination optical system, and a projec-
`tion optical system that reduces and projects the pattern
`reflected on the reticle onto an object to be exposed, wherein
`an opening of the condenser mirror through which the
`illumination light passes, is located closer to the first mirror
`than a condensing point of the excitation laser in an optical-
`axis direction of the illumination light, and wherein light
`where an optical-axis direction of the excitation laser pro-
`ceeds beyond a position that generates the plasma by the
`excitation laser does not interfere with components in the
`exposure apparatus including the illumination and projec-
`tion optical systems, and the condenser mirror. The con-
`denser mirror may be an ellipsoidal mirror.
`
`[0023] A device fabricating method of still another aspect
`of the present invention includes the steps of exposing an
`object using the above exposure apparatus, and performing
`a predetermined process for the exposed object. Claims for
`a device fabricating method for performing operations simi-
`lar to that of the above exposure apparatus cover devices as
`intermediate and final products. Such devices include semi-
`conductor chips like an ISI and VISI, CCDs,
`I,(‘.Ds,
`magnetic sensors, thin film magnetic beads, and the like.
`
`[0024] Other objects and further features of the present
`invention will become readily apparent from the following
`description of the preferred embodiments with reference to
`accompanying drawings.
`
`

`
`US 2005/0225739 A1
`
`Oct. 13, 2005
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`[0025] FIG. 1 is a schematic plane view of an exposure
`apparatus of a first embodiment according to the present
`invention.
`
`[0026] FIG. 2 is a schematic plane view of an exposure
`apparatus of a second embodiment according to the present
`invention.
`
`:0027] FIG. 3 is a schematic plane View of an exposure
`apparatus of a third embodiment according to the present
`invention.
`
`[0028] FIG. 4 is a schematic plane View of an exposure
`apparatus of a fourth embodiment according to the present
`invention.
`
`[0029] FIG. 5 is a View for explaining a supply of a target
`near a plasma light source.
`
`:0030] FIG. 6 is a schematic View for explaining an
`example that uses excitation laser to irradiate the target.
`
`[0031] FIG. 7 is another schematic view for explaining an
`example that uses excitation laser to irradiate the target.
`
`[0032] FIG. 8 is still another schematic View for explain-
`ing an example that uses excitation laser to irradiate the
`target.
`
`[0033] FIG. 9 is a schematic plane View of an exposure
`apparatus of a fifth embodiment according to the present
`invention.
`
`[0034] FIG. 10 is a schematic plane view of an exposure
`apparatus of a sixth embodiment according to the present
`invention.
`
`[0035] FIG. 11 is a schematic plane view of an exposure
`apparatus of a seventh embodiment according to the present
`invention.
`
`[0036] FIG. 12 is a flowchart for explaining a method for
`fabricating devices (semiconductor chips such as ICs, LSIs,
`and the like, LCDS, CCDs, etc).
`
`[0037] FIG. 13 is a detailed flowchart for Step 4 of wafer
`process shown in FIG. 12.
`
`BEST MODE FOR CARRYING OUT THE
`INVENTION
`
`First Embodiment
`
`[0038] A description will now be given of an IZUV expo-
`sure apparatus of a first embodiment according to the present
`invention, with reference to FIG. 1. FIG. 1 is a schematic
`plane view of the EUV exposurc apparatus. The inventive
`exposure apparatus is an exposure apparatus that uses EUV
`light having a wavelength between 10 and 15 rim smaller
`than that of the UV light (e.g., with a wavelength of 13.5 nm)
`as exposure light for scan-type exposure.
`
`the exposure apparatus
`[0039] Referring to FIG. 1,
`includes a laser plasma light source part, an illumination
`optical system 120, a catoptric reticle or mask (these terms
`are used interchangeably in this application) 121, a projec-
`tion optical system 122, a reticle stage 124, a wafer 123, and
`a wafer stage 125, and accommodates the illumination
`optical system 120 to the wafer stage 125 in the vacuum
`chamber 190.
`
`the instant
`[0040] The laser plasma light source of
`embodiment irradiates a highly intensified pulse laser beam
`101 from a laser light source 100 through a condenser
`optical system 102 to a target 104 supplied at a condensing
`point 103 by a target supply system 105 accommodated in
`a vacuum chamber 180, thus generating high-temperature
`plasma for use as EUV light with a wavelength of about 13.5
`nm emitted from this. More specifically, the laser plasma
`light source irradiates high intensity excitation pulse laser
`101 onto the target 104, and excites the target 104 in a
`high-temperature plasma state. The condenser mirror 108
`condenses the EUV light from among light of a wave range
`from the infrared light to UV light and EUV light so as to
`use the EUV light as exposure light.
`[0041] As described above, for easy prevention of the
`debris that is generated with the EUV light, from entering
`the illumination optical system,
`it
`is preferable that
`the
`condenser mirror of the EUV light uses an ellipsoidal mirror
`that has one focal point where the plasma occurs, and
`another focal point for condensing light, and physically
`narrows a path between the light source and the illumination
`system.
`
`In addition, for desired power of the EUV light and
`[0042]
`enhanced productivity of the exposure apparatus or through-
`put,
`the EUV light emitted from the plasma should be
`condensed efliciently. This is achieved by condensing the
`emitted EUV light with a large cover solid angle, and this
`purpose requires a large condenser mirror.
`[0043] The pulse laser beam 101 is derived, for example,
`from Nd: YAG laser, cxcimcr laser, etc. The vacuum cham-
`ber 180 maintains a vacuum atmosphere environment for the
`EUV light that has small transmittance to the air. The pulse
`laser beam 101 is condensed at the condensing position 103
`through a window 112 provided in the vacuum chamber 180.
`Preferably, the window 112 is made of quarts, etc. that have
`large transmittance to the pulse laser beam 101.
`[0044] The target 104 depends upon a wavelength of the
`generated EUV light, and may use a metallic thin film, such
`as Cu, Li, and Zn, inert gas, such as Xe, and droplets, etc.,
`and supplied by the target supply system 105, such as gas jet
`into the vacuum chamber 180. Among them, Xe is a potent
`candidate as the target 104 for reasons including the debris
`that is generated with the EUV light and would disadvan-
`tageously pollute other illumination systems, conversion
`elliciency from the excitation pulse laser 101 to the EUV
`light 106, and handling convenience of the target I04. A
`target recovery system 107 is provided to recover the target
`104 since all of supplied target 104 does not necessarily
`contribute to the plasma generation.
`[0045] Referring to FIG. 5, a description will be given of
`a supply method of Xe as the target 104 to the condensing
`position 103. In FIG. 5A, a nozzle 505 jets Xe gas 504, and
`the condensed pulse laser beam 501 generates EUV light
`506 at a condensing point 503 when the high temperature
`plasma cools. In FIG. 5B, a nozzle 515 jets Xe liquid 514
`like a rod, and the condensed pulse laser beam 501 similarly
`generates EUV light 506 at a condensing point 503 when the
`high temperature plasma cools. In FIG. 5C, a no7.7.le 525
`drops Xe droplets 524 under synchronous control such that
`when the Xe droplet 524 reaches the emission point 503, the
`pulse laser beam 501 reaches the emission point 503. As a
`result, the EUV light 506 occurs when the high temperature
`plasma cools.
`
`

`
`US 2005/0225739 A1
`
`Oct. 13, 2005
`
`In general, the Xe density should be increased for
`[0046]
`enhanced conversion efficiency from the pulse laser to the
`EUV light, and liquid forms shown in FIGS. SB and 5C are
`a more preferable supply method than a gas form shown in
`FIG. 5A. Nevertheless, even the Xe liquid produces the
`conversion efficiency from the pulse laser beam 101 to the
`EUV light 106 of a little over 1% at most. For the improved
`productivity or throughput, an EUV light source is required
`to produce the EUV light with power of 50 to 150 W.
`Therefore, the pulse laser that excites the plasma needs such
`large power as 5 to 15 kW.
`
`[0047] The target supply system 105 is housed in the
`vacuum chamber 180. The laser light source 100 is such a
`large unit that it has a large output of 5 to 15 kW class, and
`mounted on a support rack (not shown) different from the
`vacuum chamber 180. This requires high alignment accu-
`racy between the pulse laser beam 101 emitted from the laser
`light source 100 and the Xe target system 104, and precise
`synchronous control between an emission timing of the
`pulse laser 501 and a drop timing of the liquid target 524 in
`the target supply system shown in FIG. SC.
`
`[0048] The alignment may provide, for example, an inter~
`ferometer system 140 to the laser light source 100 and the
`vacuum chamber 180, and detect a positional offset between
`them. The precise alignment of positions between the pulse
`laser 100 and the target 104 may be achieved by using an
`actuator (not shown) to drive an optical element (not shown)
`for controlling a position of the laser light source or the pulse
`laser beam 101.
`
`[0049] However, the interferometer system 140 does not
`measure a position of the pulse laser beam 101 at
`the
`condensing point 103 and a position of the target 104 at the
`condensing point 103, and thus it is difficult to accurately
`align the pulse laser beam 101 with the target 101 at the
`condensing point 103. Therefore, the vibrations, mechanical
`deformations, etc. generate a positional olfset between them.
`
`[0050] FIG. 6 shows a relationship between a pulse laser
`beam 601 and a target 604 in the target supply system shown
`in FIG. 5B when viewed from an arrow direction. Without
`a positional offset, a center of the puhse laser beam 601 and
`a center of the rod—shztped target 604 accords with each other
`as shown in FIG. 6A. With a slight positional offset, the
`pulse laser beam 601 partially irradiates the target 604 as
`shown in FIG. 6B. With a significant positional ofset, the
`pulse laser beam 601 does not irradiate the target 604 as
`shown in FIG. 6C.
`
`[0051] Similarly, FIG. 7 shows a relationship between a
`pulse laser beam 701 and a target 704 in the target supply
`system shown in FIG. 5C when viewed from an arrow
`direction. Without a positional offset, a center of the pulse
`laser beam 701 and a center of the liquid target 704 accords
`with each other as shown in FIG. 7A. With a slight posi-
`tional otfset, the pulse laser beam 701 partially iiradiates the
`target 704 as shown in FIG. 7B. With a significant positional
`ofiset, the pulse laser beam 701 does not irradiate the target
`704 as shown in FIG. 7C.
`
`In FIGS. 6B and 7B, parts of the pulse laser beams
`[0052]
`601 and 701, which do not irradiate the targets 604 and 704,
`pass the condensing points. Similarly, in FIGS. 6C and 7C,
`all of pulse laser beams 601 and 701 pass the condensing
`points.
`
`configuration that
`the conventional
`in
`[0053] Thus,
`accords an optical axis of the pulse laser beam 101 with that
`of the EUV light 106 that is generated at the condensing
`point 103 and incident upon the first mirror 131, when the
`condenser ellipsoidal mirror 108 has a larger cover angle or
`size in order to elfectively condensing the EUV light, the
`condensed EUV light is emitted towards the opening of the
`condenser ellipsoidal mirror. The condensed pulse laser
`beam does not directly irradiate the condenser ellipsoidal
`mirror, but directly irradiates the first mirror 131.
`
`[0054] For example, suppose that the pulse laser beam is
`derived from Nd: YAG laser with a wavelength of 1,064 nm,
`and the mirror 131 forms a multilayer of Mo and Si to reflect
`the EUV light. Then, the reflectance of the multilayer to the
`wavelength of 1,064 nm is about 30% at most, and most of
`the light is absorbed and converted into heat. In this case, the
`pulse laser beam is not condensed at the first mirror 131, but
`the pulse laser beam has such a high output as about 5 to 15
`kW and injects an considerable amount of heat into the first
`mirror 131. Therefore, the first mirror 131 becomes at high
`temperature, and causes thermal deformations and alter-
`ations of the multilayer. The imaging performance of the
`first mirror 131 becomes consequently too deteriorated to
`provide high-quality exposure, and should be replaced.
`Since the mirror 131 is housed in the vacuum chamber 190,
`the replacement requires a release to the atmosphere pres-
`sure once, a replacement and adjustment of the first mirror
`131, and a draw of vacuum again. Since the illumination and
`projection optical systems 120 and 122 are precise optical
`systems, the adjustment is sometimes not limited to the first
`mirror 131, but
`the illumination and projection optical
`systems 120 and 122 should be readjusted, extending the
`downtime of the apparatus. The above discusses the first
`mirror 131 which the pulse laser beam directly enters, but
`the subsequent mirrors may also be subject to replacements
`clue to thermal deformations resulting from the temperature
`rise and an alteration of the multilayer, although the injected
`heat is smaller than that of the first mirror 131. In particular,
`optical elements in the exposure apparatus do not have high
`heat resistance, and are easily negatively alfected by the
`pulse laser beam.
`
`[0055] For example, the condenser mirror 108, the illu-
`mination optical system 120, the catoptric mask 121, and the
`projection optical system 122 form a several tens of pairs of
`multilayer made of Mo and Si, etc., on a substrate so as to
`efficiently reflect the EUV light 106, and its surface rough-
`ness is required to be in the angstroni order of in the standard
`deviation in order to prevent the reflectance from lowering.
`In addition, the shape precision of the mirror in the projec-
`tion optical system 122 is required to be in the angstrom
`order of in the standard deviation in addition to the surface
`roughness, and the projection optical system 122 should be
`an extremely precise optical system. Of course, it should be
`stable to disturbances, such as temperature.
`
`[0056] On the other hand, in order to mitigate the permis-
`sible alignment accuracy between the pulse laser beam 101
`and the target 104,
`it
`is conceivable to make variable a
`condensing diameter of the pulse laser beam 101. FIGS. 8A
`and 8B show a case where the pulse laser beams 801 and
`811 are larger than the targets 804 and 814. FIG. 8A shows
`that the nozzle jets rod—shaped Xe liquid shown in FIG. 5B,
`and FIG. 8B shows that the nozzle jets Xe droplets shown
`in FIG. 5C. Since the pulse laser beam is larger than the
`
`

`
`US 2005/0225739 A1
`
`Oct. 13, 2005
`
`target in both cases, the pulse laser beam may irradiate the
`target entirely even with a little positional olfset between
`them. However, part of the pulse laser beam necessarily
`proceeds without irradiating the target, and highly possibly
`damages other components in the apparatus as discussed
`above.
`
`[0057] On the other hand, FIGS. 8C and SD show a case
`where the pulse laser beams 821 and 831 are smaller than the
`targets 824 and 834. FIG. 8C shows that the nozzle jets
`rod-shaped Xe liquid shown in FIG. 5B. and FIG. 8D shows
`that the nozzle jets Xe droplets shown in FIG. 5C. Since the
`pulse laser beam is smaller than the target in both cases, all
`of pulse laser beam may irradiate the target entirely even
`with a little positional offset between them and there is no
`problem associated with FIGS. 8A and 8B. However, it is
`not easy to increase the size of the target, and a new problem
`arises in that power of the EUV light and thus the throughput
`reduce by the reduction amount of a condensing diameter of
`the pulse laser beams 821, 831.
`[0058]
`It
`is thus preferable that the pulse laser beam is
`equal in size to the target, as shown in FIG. 5.
`[0059] Of course, in the conventional configuration where
`the optical axis of the pulse laser beam 101 accords with the
`optical axis of the EUV light 106 that is generated at the
`emission point "103 and incident upon the first mirror 131, an
`unforeseen case occurs in which all or part of the pulse laser
`beam passes through the condensing point 103 for reasons
`other than a positional offset between them. For example, the
`target supply system shown in FIG. 5C might have poor
`synchronous controllablity between the liquid target 524 and
`the pulse laser 501, and a discordance may occur between
`the pulse laser emission period and the liquid drop period.
`Alternatively, the target 524 may be not supplied due to a
`failure of the target supply system 522 itself. Moreover, even
`part of the pulse laser that completely irradiates the target
`possibly maintains a component of going straight ahead as
`a result of non-interaction between the pulse laser and the
`target. Either case negatively affects the illumination and
`projection optical systems 120 and 122 significantly, as
`discussed above.
`
`[0060] The instant embodiment shown in FIG. 1 solves
`the above problems by offsetting an optical-axis direction
`AA’ of the laser beam 101 from an optical-axis direction 109
`of the EUV light 106 that is generated at the condensing
`point 103 and incident upon the first mirror 131, and by
`providing the condenser ellipsoidal mirror with passage part
`through which the pulse laser beam incident upon the target
`passes, passage part through