(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property
`Organization
`International Bureau
`
`
`
`(43) International Publication Date
`3 February 2005 (03.02.2005)
`
`(10) International Publication Number
`
`WO 2005/010611 A2
`
`(51) International Patent Classificati0n7:
`
`G03F
`
`(21) International Application Number:
`PCT/U82004/01745 2
`
`(22) International Filing Date:
`
`2 June 2004 (02.06.2004)
`
`(25) Filing Language:
`
`(26) Publication Language:
`
`(30) Priority Data:
`60/485,868
`
`English
`
`English
`
`8 July 2003 (08.07.2003)
`
`US
`
`(71) Applicant (for all designated States except US): NIKON
`CORPORATION [JP/JP];
`2—3 Marunouchi, 3—Chome,
`Chiyoda—ku, Tokyo 100—8331 (JP).
`
`(72) Inventors; and
`(75) Inventors/Applicants (for US only): HAZELTON,
`Andrew, J.
`[US/US]; 409 Phelps Road, San Carlos,
`CA 94070 (US). TAKAIWA, Hiroaki [JP/US]; Kuma—
`gaya—shi, Saitama—ken (JP).
`
`(81) 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.
`
`(84) Designated States (unless otherwise indicated. for even:
`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, KZ, MD, RU, TJ, TM),
`European (AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI,
`FR, GB, GR, IIU, IE, IT, LU, MC, NL, PL, PT, RO, SE, SI,
`SK, TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ,
`GW, ML, MR, NE, SN, TD, TG).
`
`Published:
`
`(74) Agents: SU, Peggy, A. et al.; Ritter, Lang & Kaplan LLP,
`12930 Saratoga Ave., Suite Dl, Saratoga, CA 95070 (US).
`
`without international search report and to be republished
`upon receipt of that report
`
`[Continued on next page]
`
`(54) Title: WAFER TABLE FOR IMMERSION LITI IOGRAPI IY
`
`55.?
`559 55a
`/
`
`DOSE
`SENSOR
`
`
`
`M512.
`
`
`
`/
`
`WAFER
`
`5,ng
`
`
`
`
`
`
`L507
`
`~—REF.
`
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`/ 55°?
`
`
`
`5/010611A2|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
`
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`(57) Abstract: Methods and apparatus for allowing a liquid to be substantially contained between a lens and a wafer table assembly
`G of an immersion lithography system are disclosed. According to one aspect of the present invention, an exposure apparatus includes
`c a lens and a wafer table assembly. The wafer table assembly has a top surface, and is arranged to support a wafer to be moved with
`N respect to the lens as well as at least one component. The top surface of the wafer and the top surface of the component are each at
`substantially a same height as the top surface of the wafer table assembly. An overall top surface of the wafer table assembly which
`includes the top surface of the wafer, the top surface of the wafer table assembly, and the top surface of the at least one component
`is substantially planar.
`
`Nikon
`
`Exhibit 1020 Page 1
`
`Nikon Exhibit 1020 Page 1
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`

`

`WO 2005/010611 A2
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`|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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`For two-letter codes and other abbreviations, refer to the ”Guid—
`ance Notes on Codes and Abbreviations ” appearing at the beg in—
`ning of each regular issue of the PCT Gazette.
`
`Nikon
`
`Exhibit 1020 Page 2
`
`Nikon Exhibit 1020 Page 2
`
`

`

`WO 2005/010611
`
`PCT/US2004/017452
`
`WAFER TABLE FOR IMMERSION LITHOGRAPHY
`
`CROSS-REFERENCE TO RELATED APPLICATION
`
`This application claims priority to U.S. Provisional Patent Application No.
`
`60/485,868, filed July 8, 2003, which is hereby incorporated by reference in its entirety.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of Invention
`
`The present invention relates generally to semiconductor processing equipment.
`
`More particularly, the present invention relates to a method and an apparatus for enabling
`
`liquid in an immersion lithography system to effectively be contained between a surface
`
`of a lens and a plane that is moved relative to the lens.
`
`10
`
`2.
`
`Description of the Related Art
`
`For precision instruments such as photolithography machines which are used in
`
`semiconductor processing, factors which affect the performance, e.g., accuracy, of the
`
`precision instrument generally must be dealt with and, insofar as possible, eliminated.
`
`When the performance of a precision instrument such as an immersion lithograph
`
`exposure system is adversely affected, products formed using the precision instrument
`
`may be improperly formed and, hence, function improperly.
`
`In an immersion lithography system, a liquid is provided between a lens and the
`
`surface of a wafer in order to improve the imaging performance of the lens. The use of
`
`liquid allows a numerical aperture associated with the lens, 1'. e. , an effective numerical
`
`aperture of the lens, to essentially be increased substantially without altering
`
`characteristics of the lens, since a liquid such as water generally has a refractive index
`
`that is greater than one. In general, a higher numerical aperture enables a sharper image
`
`to be formed on the wafer. As will be appreciated by those skilled in the art, a high
`
`15
`
`20
`
`refractive index liquid allows for a high numerical aperture of the lens since an effective
`
`25
`
`numerical aperture of a lens system of an immersion lithography system is generally
`
`defined to be approximately equal to the sine of an angle of diffraction of light which
`
`passes through a lens and reflects off a surface multiplied by the refractive index of the
`
`liquid. Since the refractive index of the liquid is greater than one, the use of liquid allows
`
`the effective numerical aperture of the lens to be increased, thereby enabling the
`
`30
`
`resolution associated with the lens to essentially be improved.
`
`Nikon
`
`Exhibit 1020 Page 3
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`Nikon Exhibit 1020 Page 3
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`

`

`WO 2005/010611
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`‘
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`PCT/U82004/017452
`
`Within most conventional lithography systems, air is present between a lens and a
`
`surface which passes under the lens, e.g., the surface of a wafer. In such systems, the
`
`numerical aperture associated with the lens is often in the range of approximately 0.8 to
`
`0.9. Increasing the numerical aperture of a lens to achieve an improved resolution is
`
`generally impractical, as the diameter of a lens generally must be increased, which adds
`
`significant difficulty to a lens manufacturing process. In addition, the numerical aperture
`
`of a lens in air is theoretically limited to one, and, in practice, is limited to being
`
`somewhat less than one. Hence, immersion lithography systems enable the effective
`
`numerical aperture of a lens to be increased substantially beyond what is possible with a
`
`10
`
`lens in air.
`
`Fig. 1 is a diagrammatic cross—sectional representation of a portion of an
`
`immersion lithography apparatus. An immersion lithography apparatus 100 includes a
`
`lens assembly 104 which is positioned over a wafer table 112 which supports a wafer 108.
`
`Wafer table 112 is arranged to be scanned or otherwise moved under lens assembly 104.
`
`15
`
`A liquid 116, which may be water in a typical application which uses approximately 193
`
`nanometers (nm) of radiation, is present in a gap between lens assembly 104 and wafer
`
`108. In order to effectively prevent liquid 1 16 from leaking out from under lens assembly
`
`104, i. e. , to effectively laterally contain liquid 116 between lens assembly 104 and wafer
`
`108, a retaining ring 120 may be positioned such that retaining ring 120 enables liquid
`
`20
`
`116 to remain between lens assembly 104 and wafer 108, and within an area defined by
`
`retaining ring 120.
`
`While retaining ring 120 is generally effective in containing liquid 116 when lens
`
`assembly 104 is positioned such that a small gap between retaining ring 120 and a surface
`
`of wafer 108 is maintained, for a situation in which at least a part of retaining ring 120 is
`
`25
`
`above wafer 108, liquid 116 may leak out from between lens assembly 104 and wafer
`
`108. By way of example, when an edge of wafer 108 is to be patterned, lens assembly
`
`104 may be substantially centered over the edge such that a portion of retaining ring 120
`
`fails to maintain the small gap under the bottom surface of retaining ring 120, and liquid
`
`116 is allowed to leak out from between lens assembly 104 and wafer 108. As shown in
`
`30
`
`Fig. 2, when lens assembly 104 is positioned such that at least part of a bottom surface of
`
`retaining ring 120 is not in contact with wafer 108, liquid 116 may not be contained in an
`
`area defined by retaining ring 120 between lens assembly 104 and wafer 108.
`
`In an immersion lithography apparatus, a wafer table may support sensors and
`
`other components, e.g., a reference flat that is used to calibrate automatic focusing
`
`35
`
`operations. Such sensors and other components generally may be positioned beneath a
`
`Nikon
`
`Exhibit 1020 Page 4
`
`Nikon Exhibit 1020 Page 4
`
`

`

`WO 2005/010611
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`h
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`PCT/U82004/017452
`
`lens at some point. That is, sensors and other components associated with a wafer table
`
`may be occasionally positioned beneath a lens during the course of operating the lens and
`
`the wafer table. While the use of a retaining ring may prevent liquid from leaking out of
`
`a gap between a lens assembly and the top surface of the wafer, liquid may leak out from
`
`between the lens assembly and top surfaces of sensors and other components when the
`
`lens assembly is positioned over the sensors or other components.
`
`Fig. 3 is a block diagram representation of a wafer table which supports a sensor
`
`and a wafer holder that holds a wafer. A wafer table 312 supports a wafer holder 310
`
`which is arranged to hold a wafer (not shown), a sensor 350, and an interferometer mirror
`
`352. Sensor 350 may be used through a lens (not shown) with liquid (not shown)
`
`between the lens and sensor 350. However, liquid will often flow out of the gap between
`
`a lens (not shown) and sensor 350 particularly when an edge of sensor 350 is positioned
`
`substantially beneath a center of the lens. The effectiveness of sensor 350 may be
`
`compromised when sensor 350 is designed and calibrated to operate in a liquid, and there
`
`is insufficient liquid present between a lens (not shown) and sensor 350. Further, when
`
`liquid (not shown) flows out of the gap between a lens (not shown) and sensor 350, the
`
`liquid which flowed out of the gap is effectively lost such that when the lens is
`
`subsequently positioned over a wafer (not shown) supported by wafer holder 310, the
`
`amount of liquid between the lens and the wafer may not be sufficient to enable the
`
`effective numerical aperture of the lens to be as high as desired. Hence, when liquid is
`
`not successfully contained between a lens (not shown) and sensor 350 while sensor 350 is
`
`at least partially positioned under the lens, an overall lithography process which involves
`
`the lens and sensor 350 may be compromised.
`
`Therefore, what is needed is a method and an apparatus for allowing liquid to be
`
`maintained in a relatively small gap defined between a surface of a lens and a surface of
`
`substantially any sensors or components which are supported by a wafer table. That is,
`
`what is desired is a system which is suitable for preventing liquid which is positioned
`
`between a lens and substantially any surface on a wafer table which is moved under the
`
`lens from leaking out from between the lens and the surface.
`
`SUMNIARY OF THE INVENTION
`
`The present invention relates to a wafer table arrangement which is suitable for
`
`use in an immersion lithography system. According to one aspect of the present
`
`invention, an exposure apparatus includes a lens and a wafer table assembly. The wafer
`
`table assembly has a top surface, and is arranged to support a wafer to be moved with
`
`10
`
`15
`
`20
`
`25
`
`30
`
`Nikon
`
`Exhibit 1020 Page 5
`
`Nikon Exhibit 1020 Page 5
`
`

`

`WO 2005/010611
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`PCT/U82004/017452
`
`respect to the lens as well as at least one component. The top surface of the wafer and the
`
`top surface of the component are each at substantially a same height as the top surface of
`
`the wafer table assembly. An overall top surface of the wafer table assembly which
`
`includes the top surface of the wafer, the top surface of the wafer table assembly, and the
`
`top surface of the at least one component is substantially planar.
`
`In one embodiment, the component may be at least one of a reference flat, an
`
`aerial image sensor, a dose sensor, and a dose uniformity sensor. In another embodiment,
`
`the wafer table assembly is arranged to support a wafer holder that holds the wafer such
`
`that the top surface of the wafer is at substantially the same height as the top surface of
`
`10
`
`the wafer table assembly.
`
`A wafer table arrangement which is configured to enable surfaces which are to
`
`viewed through a lens to form a relatively planar overall surface of substantially the same
`
`height facilitates an immersion lithography process. When substantially all elements
`
`carried on a wafer table have top surfaces that are substantially level with the top surface
`
`15
`
`of the wafer table, and any gaps between the sides of the components and the sides of
`
`openings in the wafer table are relatively small, the overall top surface of a wafer table
`
`arrangement may traverse under a lens while a layer or a film of liquid is effectively
`
`maintained between a surface of the lens and the overall top surface. Hence, an
`
`immersion lithography process may be performed substantially without the integrity of
`
`20
`
`the layer of liquid between the surface of the lens and the overall top surface of the wafer
`
`table arrangement being compromised by the loss of liquid from the layer of liquid
`
`between the surface of the lens and the overall top surface of the wafer table arrangement.
`
`According to another aspect of the present invention, an immersion lithography
`
`apparatus includes a lens which has a first surface and an associated effective numerical
`
`25
`
`aperture. The apparatus also includes a liquid that is suitable for enhancing the effective
`
`numerical aperture of the lens, and a table arrangement. The table arrangement has a
`
`substantially flat top surface that opposes the first surface, and the liquid is arranged
`
`substantially between the substantially flat top surface and the first surface. The
`
`substantially flat top surface includes a top surface of an object to be scanned and a top
`
`30
`
`surface of at least one sensor.
`
`These and other advantages of the present invention will become apparent upon
`
`reading the following detailed descriptions and studying the various figures of the
`
`drawings.
`
`Nikon
`
`Exhibit 1020 Page 6
`
`Nikon Exhibit 1020 Page 6
`
`

`

`WO 2005/010611
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`PCT/U82004/017452
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The invention may best be understood by reference to the following description
`
`taken in conjunction with the accompanying drawings in which:
`
`Fig. 1 is a diagrammatic cross-sectional representation of a portion of an
`
`immersion lithography apparatus in a first orientation.
`
`Fig. 2 is a diagrammatic representation cross—sectional representation of a portion
`
`of an immersion lithography apparatus, i. a, apparatus 100 of Fig. 1, in a second
`
`orientation.
`
`Fig. 3 is a block diagram representation of a wafer table which supports a sensor
`
`10
`
`and a wafer holder that holds a wafer.
`
`Fig. 4 is a block diagram representation of a top View of a wafer table assembly in
`
`accordance With an embodiment of the present invention.
`
`Fig. 5 is a block diagram representation of a top View of components which are
`
`supported by a wafer table assembly with a substantially uniform, planar overall top
`
`15
`
`surface in accordance with an embodiment of the present invention.
`
`Fig. 6a is a diagrammatic cross—sectional representation of a wafer table assembly
`
`which has a substantially uniform, planar overall top surface in accordance with an
`
`embodiment of the present invention.
`
`2O
`
`25
`
`3O
`
`Fig. 6b is a diagrammatic representation of a wafer table assembly, e. g., wafer
`
`table assembly 600 of Fig. 6a, with a lens assembly positioned over a wafer holder in
`
`accordance with an embodiment of the present invention.
`
`Fig. 6c is a diagrammatic representation of a wafer table assembly, e.g., wafer
`
`table assembly 600 of Fig. 6a, with a lens assembly positioned over a component in
`
`accordance with an embodiment of the present invention.
`
`Fig. 7 is a diagrammatic representation of a photolithography apparatus in
`
`accordance with an embodiment of the present invention.
`
`Fig. 8 is a process flow diagram which illustrates the steps associated with
`
`fabricating a semiconductor device in accordance with an embodiment of the present
`invention.
`
`Fig. 9 is a process flow diagram which illustrates the steps associated with
`
`processing a wafer, i.e., step 1304 of Fig. 4, in accordance with an embodiment of the
`
`present invention.
`
`Fig. 10a is a diagrammatic representation of a wafer table surface plate and a
`
`wafer table in accordance with an embodiment of the present invention.
`
`Nikon
`
`Exhibit 1020 Page 7
`
`Nikon Exhibit 1020 Page 7
`
`

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`WO 2005/010611
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`PCT/U82004/017452
`
`Fig. 10b is a diagrammatic cross-sectional representation of wafer table assembly
`
`Which includes a‘ wafer table and a wafer table surface plate in accordance with an
`
`embodiment of the present invention.
`
`Fig. 1 la is a diagrammatic cross-sectional representation of a wafer table and a
`
`wafer table surface plate with Windows in accordance With an embodiment of the present
`
`invention.
`
`Fig. 11b is a diagrammatic cross—sectional representation of wafer table assembly
`
`which includes a wafer table and a wafer table surface plate with Windows, i.e., wafer
`
`table 904 and wafer table surface plate 908 of Fig. 11a, in accordance with an
`
`10
`
`embodiment of the present invention.
`
`DETAILED DESCRIPTION OF THE EMBODIMENTS
`
`In immersion lithography systems, a wafer surface must generally be viewed
`
`through a lens with a layer of liquid such as a relatively thin film of liquid between the
`
`lens and the wafer surface. Some components such as sensors and/or reference members
`
`15
`
`may often be viewed through the lens with a layer of liquid between the lens and the
`
`surfaces of the components. Maintaining the layer of liquid in a gap between the lens and
`
`the surface of the wafer, even when the lens is arranged to View edge portions of the
`
`wafer, allows the immersion lithography system to operate substantially as desired.
`
`Similarly, maintaining the layer of liquid in a gap between the lens and the surface of
`
`20
`
`components such as sensors and/or reference members also facilitates the efficient
`
`operation of the immersion lithography system.
`
`By utilizing a wafer table arrangement which is configured to enable surfaces
`
`which are to viewed through a lens and a top surface of the wafer table arrangement to
`
`form a relatively planar, substantially uniform overall surface. When substantially all
`
`25
`
`components associated with the wafer table arrangement have a surface which is
`
`substantially level with the top surface of a wafer and the top surface of a wafer table, and
`
`any gaps between the sides of the components and the sides of openings in the wafer table
`
`are relatively small, the overall top surface of the wafer table arrangement may traverse
`
`under a lens While a layer or a film of liquid is effectively maintained between a surface
`
`30
`
`of the lens and the overall top surface. As a result, an immersion lithography process may
`
`be performed substantially without having the integrity of the layer of liquid, 1‘. e. , the
`
`layer of liquid between the surface of the lens and the overall top surface of the wafer
`
`table arrangement, compromised.
`
`Nikon
`
`Exhibit 1020 Page 8
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`Nikon Exhibit 1020 Page 8
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`

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`WO 2005/010611
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`PCT/US2004/017452
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`A wafer table which has a substantially raised, flat top surface of a uniform height
`
`allows a wafer and other components, eg. , sensors, to be installed such that a flat surface
`
`of the wafer and flat surfaces of the components are at substantially the same level or
`
`height as the raised, flat top surface of the wafer table. In one embodiment, an overall
`
`wafer table assembly includes openings within which a wafer, or a wafer holder on which
`
`the wafer is supported, and sensors may be positioned. Fig. 4 is a block diagram
`
`representation of a top View of a wafer table assembly in accordance with an embodiment
`
`of the present invention. A wafer table assembly 402 includes openings 409, 452 which
`
`are sized to effectively house a wafer 408 and components 450, respectively, such that top
`
`surfaces of wafer 408 and components 450 are at substantially the same level as a top
`
`surface 414 of wafer table assembly 402. Typically, openings 409, 452 are sized to
`
`accommodate wafer 408 and components 450, respectively, such that a spacing between
`
`the outer edges or wafer 408 or components 450 and their respective openings 409, 452 is
`
`relatively small, e.g. , between approximately ten and approximately 500 micrometers.
`
`In general, the spacing between wafer 408, or in some cases, a wafer holder (not
`
`shown) and opening 409, as well as the spacing between components 450 and their
`
`corresponding openings 452 does not significantly affect the overall planar quality of an
`
`overall top surface of wafer table assembly 402. That is, an overall top surface of wafer
`
`table assembly 402 which includes top surface 414, the top surface of wafer 408, and the
`
`top surfaces of components 450 is substantially planar, with the planarity of the overall
`
`top surface being substantially unaffected by the presence of the small gaps between the
`
`sides of wafer 408 and opening 409, and the sides of components 450 and openings 452.
`
`Components 450 may include, but are not limited to, various sensors and
`
`reference marks. With reference to Fig. 5, components which are supported by a wafer
`
`table assembly with a substantially uniform, planar overall top surface will be described
`
`in accordance with an embodiment of the present invention. A wafer table assembly 502
`
`includes a raised, substantially uniform top surface 514 in which openings 509, 552 are
`
`defined. Opening 509 is arranged to hold a wafer 508 which may be supported by a
`
`wafer holder (not shown). Openings 552 are arranged to support any number of
`
`components. In the described embodiment, openings 552 are arranged to support a dose
`
`sensor or a dose uniformity sensor 556, an aerial image sensor 558, a reference flat 560,
`
`and a fiducial mark 562, which each have top surfaces that are arranged to be of
`
`substantially the same height as top surface 514 such that an overall, substantially
`
`uniform, planar top surface is formed. Examples of a suitable dose sensor or dose
`
`uniformity sensor 556 are described in US. Patent No. 4,465,368, US. Patent No.
`
`10
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`15
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`20
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`25
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`3O
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`35
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`Nikon
`
`Exhibit 1020 Page 9
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`Nikon Exhibit 1020 Page 9
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`

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`WO 2005/010611
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`PCT/US2004/017452
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`6,078,380, and U.S. Patent Publication No. 2002/0061469A1, which are each
`
`incorporated herein by reference in their entireties. An example of an aerial image sensor
`
`55 8 is described in U.S. Patent Publication No. 2002/0041377Al, which is incorporated
`
`herein by reference in its entirety. An example of a reference fiat 560 is described in U.S.
`
`Patent No. 5,985,495, which is incorporated herein by reference in its entirety, while an
`
`example of a fiducial mark 562 is described in U.S. Patent No. 5,243,195, which is
`
`incorporated herein by reference in its entirety.
`
`It should be appreciated that openings 552 are sized to accommodate components
`
`such that gaps between the sides of components, as for example dose sensor or dose
`
`uniformity sensor 556, aerial image sensor 558, reference flat 560, and fiducial mark 562,
`
`and edges of openings 552 are not large enough to significantly affect the uniformity and
`
`planarity of the overall top surface. In other words, components are relatively tightly fit
`
`within openings 552.
`
`Dose sensor or a dose uniformity sensor 5 56, one or both of which may be
`
`included in openings 552, is arranged to be used to determine a strength of a light source
`
`associated with a lens assembly (not shown) by studying light energy at the level of the
`
`top surface of wafer 508. In one embodiment, only a dose uniformity sensor is typically
`
`included. A dose sensor generally measures absolute illumination intensity, while a dose
`
`uniformity sensor typically measures variations over an area. As such, dose sensor or
`
`does uniformity sensor 556 is positioned in the same plane as the top surface of wafer
`
`508. Aerial image sensor 558 is arranged to effectively measure an aerial image that is to
`
`be projected onto the surface of wafer 508 and, hence, exposed on photoresist. In order
`
`for aerial image sensor to accurately measure an aerial image, aerial image sensor 558 is
`
`essentially positioned at the same level or plane as the top surface of wafer 508.
`
`Reference fiat 560 is generally used to calibrate the automatic focus functionality
`
`of a lens assembly (not shown), while fiducial mark 562 is a pattern that is used to enable
`
`wafer 508 to be aligned with respect to the lens assembly and reticle, as will be
`
`understood by those skilled in the art. Both reference flat 560 and fiducial mark 562 are
`
`positioned in the same plane as wafer 508.
`
`Fig. 6a is a diagrammatic cross-sectional representation of a wafer table assembly
`
`which has a substantially uniform, planar overall top surface in accordance with an
`
`embodiment of the present invention. An overall wafer table assembly 600 includes a
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`wafer table 602 which is arranged to support a wafer holder 608 that holds a wafer (not
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`shown) such that a top surface of the wafer is substantially flush with an overall top
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`surface 614 of wafer table assembly 600. Wafer table 602 also supports components 650,
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`which may include sensors and reference marks, such that top surfaces of components
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`650 are also substantially flush with overall top surface 614, as discussed above. In other
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`words, top surfaces of components 650, wafer holder 608 when supporting a wafer (not
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`shown), and wafer table 602 effectively form a substantially flat overall top surface 614
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`of relatively uniform height. Wafer holder 608 and components 650 are arranged to be
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`relatively tightly fit into openings defined within wafer table 602 such that a gap between
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`the side of wafer holder 608 and the sides of an associated opening within wafer table
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`602, as well as gaps between components 650 and the sides of associated openings within
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`wafer table 602, are each relatively small, and do not have a significant effect on the
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`uniformity of overall top surface 614.
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`Wafer table 602 may supports additional components or elements in addition to
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`wafer holder 608, a wafer (not shown), and components 650. By way of example, wafer
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`table 602 may support an interferometer mirror 670. It should be appreciated that a top
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`surface of interferometer mirror 602 may also be substantially level with overall top
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`surface 614. Hence, in one embodiment, overall top surface 614 may include
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`interferometer mirror 670.
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`Overall top surface 614 enables liquid to be maintained in a gap between a lens
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`assembly and overall top surface 614 when a component 650 or wafer holder 608
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`traverses beneath the lens. Fig. 6b is a diagrammatic representation of a wafer table
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`assembly, e.g., wafer table assembly 600 of Fig. 6a, which is arranged to scan beneath a
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`lens assembly in accordance with an embodiment of the present invention. A lens
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`assembly 684, which is arranged to be positioned over overall top surface 614 is
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`effectively separated from overall top surface 614 along a z—axis 690a by a layer of liquid
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`682. The size of the immersion area covered by liquid 682 is relatively small, e.g., the
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`size of the immersion area may be smaller than that of the wafer (not shown). Local fill
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`methods which are used to provide the liquid of the immersion area are described in co—
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`pending PCT International Patent Application No. PCT/U804/10055 (filed March 29,
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`2004), co-pending PCT International Patent Application No. PCT/US04/O9994 (filed
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`April 1, 2004), and co—pending PCT International Patent Application No.
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`PCT/U304/ 10071 (filed April 1, 2004), which are each incorporated herein by reference
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`in their entireties. Layer of liquid 682 is effectively held between overall top surface 614
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`and lens assembly 684 with respect to an x—axis 69Gb and a y-axis 690C by a retaining
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`ring 680, although substantially any suitable arrangement may be used to effectively hold
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`layer of liquid 682 in place relative to x—axis 690b and y-axis 690c.' Retaining ring 680 is
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`arranged as a ring-like structure with respect to x-axis 69% and y-axis 6900 which
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`contains liquid 682 in an area defined by the edges of retaining ring 680. That is,
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`retaining ring 680 forms a ring-like shape about z—axis 690a.
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`In another embodiment, retaining ring 680 may not be necessary. If the gap
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`between lens assembly 684 and overall top surface 614 (or wafer surface) is relatively
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`small, e.g., between approximately 0.5 mm and approximately 5 mm, layer of liquid 682
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`may be effectively held between the gap with surface tension of liquid 682.
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`In general, liquid 682 may be substantially any suitable liquid which fills a gap or
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`a space between a surface of lens assembly 684 and overall top surface 614 within an area
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`defined by retaining ring 680 that allows an effective numerical aperture of a lens
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`included in lens assembly 684 to be increased for the same wavelength of light and the
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`same physical size of the lens. Liquids including various oils, e. g., FomblinTM oil, may be
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`suitable for use as liquid 682. In one embodiment, as for example within an overall
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`system which uses approximatelyl93 nanometers (nm) of radiation, liquid 682 is water.
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`However, for shorter wavelengths, liquid 682 may be an oil.
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`Since overall top surface 614 is substantially flat and uniform, when lens
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`assembly 684 is positioned over wafer holder 608, liquid 682 does not leak out from
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`between overall top surface 614 and lens assembly 684, since retaining ring 680 remains
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`in contact or in close proximity with overall top surface 614, even when lens assembly
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`684 is positioned over an edge of wafer holder 608. The uniformity and planarity of
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`overall top surface 614 also allows liquid 682 to remain between lens assembly 684 and
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`overall top surface 614 when lens assembly 684 is oriented over a component 650, as
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`shown in Fig. 6c.
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`While a wafer table arrangement may include a wafer table in which openings
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`have been defined to house a wafer or a wafer holder and any number of components, a
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`wafer table arrangement may instead include a wafer table which has no openings to
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`house a wafer or a wafer holder and any number of components and structures which may
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`cooperate with the wafer table to effectively form openings in which a wafer or a wafer
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`holder and any number of components may be placed. In other words, a substantially
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`planar wafer table arrangement may either include openings formed within a wafer table
`as discussed above, or openings defined by a structure or structures positioned atop a
`wafer table.
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`When a wafer table arrangement includes a structure that defines openings which
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`may effectively house a wafer and components and provides a substantially planar top
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`surface for the wafer table arrangement, the structure may generally be a plate-like
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`structure within which openings are formed. With reference to Fig. 10a, a wafer table
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`arrangement which includes a wafer table and a wafer table surface plate will be
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`described in accordance with an embodiment of the present invention. A wafer table
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`arrangement 700 includes a wafer table 704 and a wafer table surface plate 708, Wafer
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`table 704 supports a wafer 712 and one or more components 716 which may include
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`various sensors, a fiducial mark, or a reference flat. Wafer table surface plate 708, which
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`may be formed from any suitable material, e.g., Teflon, includes an opening 720 within
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`which wafer 712, may be positioned when wafer t