United States Patent [191
`Suenaga et al.
`
`I
`
`||||||||||||||||||||||||||||||||||I||||||||||||||||||||||||||u||||||||||||
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`l
`USOO5668673A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,668,673
`Sep. 16, 1997
`
`[54] CATADIOPTRIC REDUCTION PROJECTION
`OPTICAL SYSTEM
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`[75] Inventors: Yutaka Suenaga, Yokohama; Toshiro
`Ishiyama, Kawasaki; Yoshiyuki
`Shimizu, Miura; Kiyoshi Hayashi,
`Koganei, all of Japan
`
`[73] Assignee: Nikon Corporation, Tokyo, Japan
`
`[21] Appl. No.: 456,624
`[22] Filed:
`Jun. 1, 1995
`
`Related US. Application Data
`
`[63] Continuation-impart of Ser. No. 167,209, Dec. 16, 1993,
`abandoned, which is a continuation-in-part of Ser. No.
`95,919, Jul. 23, 1993, abandoned, which is a continuation
`in-part of Ser. No. 65,046, May 24, 1993, abandoned, which
`is a continuation of Ser. No. 918,763, Jul. 27, 1992, aban
`doned.
`Foreign Application Priority Data
`
`[30]
`
`Aug. 5, 1991
`Jul. 29, 1992
`
`[JP]
`[JP]
`
`Japan .................................. .. 3-195500
`Japan . . . . . .
`. . . . .. 4-202359
`
`Dec. 24, 1992
`
`[JP]
`
`Japan . . . . . .
`
`. . . . .. 4-343976
`
`Nov. 16, 1993
`Jul, 7, 1994
`
`[JP]
`[JP]
`
`Japan . . . . . .
`. . . . .. 5-286516
`Japan .................................. .. 6-155799
`
`[51] Int. Cl.6 .......................... .. G02B 17/00; G02B 21/00
`[52] US. Cl. ........................ .. 359/731; 359/364; 359/366;
`‘
`359/727
`[58] Field of Search ................................... .. 359/364-366,
`359/726-732, 857-863
`
`4,241,390 12/1980 Markle et al. ........................ .. 359/366
`
`4,812,028
`
`3/1989 Matsumoto . . . . . . . . . . .
`
`. . . . .. 359/731
`
`.... .. 359/727
`5/1993 Williamson et al. .
`‘5,212,593
`6/1993 Ichihara et al. ............... .. 359/727
`5,220,454
`5,251,070 10/1993 Hashimoto et al. ..
`.... .. 359/727
`5,323,263
`6/1994?Schoenmakers ...................... .. 359/365
`
`FOREIGN PATENT DOCUMENTS
`
`350955
`1/1990 European Pat. 01f. ............. .. 359/366
`Primary Examiner—Thong Nguyen
`Attorney, Agent, or Firm-Shapiro and Shapiro
`[57]
`ABSTRACT
`
`A ?rst partial optical system including a ?rst group of lenses
`having a positive refractive power, a ?rst concave re?ection
`mirror and a second group of lenses having a positive
`refractive power, for forming a primary reduced image of an
`object, a second partial optical system including a second
`concave reelection mirror and a third group of lenses having
`a positive refractive power, for further reducing the primary
`reduced image and refocusing it, and a re?ection mirror
`arranged between the ?rst partial optical system and the
`second partial optical system, for de?ecting a light path are
`arranged in a sequence as viewed from the object. A good
`image-forming ability as a projection optical system for
`fabricating a semiconductor device is attained with a simple
`construction.
`
`28 Claims, 26 Drawing Sheets
`
`M2
`
`M1
`
`L12 L11
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`0
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`

`
`' US. Patent
`
`Sep. 16, 1997
`
`Sheet 1 0f 26
`
`5,668,673
`
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`

`
`US. Patent
`
`Sep. 16, 1997
`
`Sheet 2 0f 26
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`5,668,673
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`Ex. 2009, p. 3
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`

`
`US. Patent
`
`Sep. 16, 1997
`
`Sheet 3 0f 26
`
`5,668,673
`
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`
`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2009, p. 4
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`

`
`US. Patent
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`Sep. 16, 1997
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`Sheet 4 of 26
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`U.S. Patent
`
`Sep. 16, 1997
`
`Sheet 5 of 26
`
`5,668,673
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`FIG. 5
`
`1
`
`L11 L12
`6|
`
`L13
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`M3
`
`M1
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`U.S. Patent
`
`Sep. 16, 1997
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`Sheet 6 of 26
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`5,668,673
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`FIG.6
`
`COMA
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`0.0 010
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`-0.0 O10
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`US. Patent
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`Sep. 16, 1997
`
`Sheet 7 0f 26
`
`5,668,673
`
`FIG.7
`
`L11
`
`L12 G1
`
`L13
`
`G3 L33
`L35
`
`L32 L23L22L21
`L34
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`Axs
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`CARL ZEISS V. NIKON
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`US. Patent
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`Sep. 16, 1997
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`Sheet 8 of 26
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`5,668,673
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`FIG. 8
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`COMA
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`0.0010
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`—0.001O
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`US. Patent
`
`Sep. 16, 1997
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`Sheet 9 0f 26
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`5,668,673
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`L23 L22 L21
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`US. Patent
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`Sep. 16, 1997
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`Sheet 10 of 26
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`5,668,673
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`FIG.1O
`
`COMA
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`0.0010
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`US. Patent
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`Sep. 16, 1997
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`Sheet 11 0f 26
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`US. Patent
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`Sep. 16, 1997
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`Sheet 12 of 26
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`5,668,673
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`FIGJZ
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`COMA
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`US. Patent
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`Sep. 16, 1997
`Sheet 13 0f 26
`F IG .1 3
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`US. Patent
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`Sep. 16, 1997
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`Sheet 14 of 26
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`5,668,673
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`F1614
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`COMA ‘
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`0.0010
`
`-0.0010
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`

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`US. Patent
`
`Sep. 16, 1997
`
`Sheet 15 of 26
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`5,668,673
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`F|G.15
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`L12
`L13
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`US. Patent
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`Sep. 16, 1997
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`Sheet 16 0f 26
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`5,668,673
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`IPR2013-00362
`Ex. 2009, p. 17
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`

`
`US. Patent
`
`Sep. 16, 1997
`
`Sheet 17 of 26
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`5,668,673
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`CARL ZEISS V. NIKON
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`

`
`US. Patent
`
`Sep. 16, 1997
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`Sheet 18 of 26
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`5,668,673
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`-0.001O
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`

`
`U.S. Patent
`
`Sep. 16, 1997
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`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2009, p. 20
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`

`
`U.S. Patent
`
`Sep. 16, 1997
`
`Sheet 20 of 26
`
`5,668,673
`
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`CARL ZEISS V. NIKON
`-IPRZO13-00362
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`EX. 2009, p. 21
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`CARL ZEISS V. NIKON
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`Ex. 2009, p. 21
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`

`
`U.S. Patent
`
`Sep. 16, 1997
`
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`CARL ZEISS V. NIKON
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`EX. 2009, p. 22
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`

`
`U.S. Patent
`
`Sep. 16, 1997
`
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`Ex. 2009, p. 23
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`

`
`U.S. Patent
`
`Sep. 16, 1997
`
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`CARL ZEISS V. NIKON
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`

`
`U.S. Patent
`
`Sep. 16, 1997
`
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`U.S. Patent
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`Sep. 16, 1997
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`Sheet 25 of 26
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`5,668,673
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`U.S. Patent
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`Sep. 16, 1997
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`Sheet 26 of 26
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`5,668,673
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`

`
`5,668,673
`
`1
`CATADIOPTRIC REDUCTION PROJECTION
`OPTICAL SYSTEM
`
`This application is a continuation-in-part of application
`Ser. No. 08/167,209 filed Dec. 16, 1993, (abandoned), which
`is a continuation-in-part of application Ser. No. 08/095,919
`filed Jul. 23, 1993 (abandoned). which is a continuation—in-
`part of application Ser. No. 08/065,046 filed May 24, 1993
`(abandoned). which is a continuation of application Ser. No.
`07/918,763 filed Jul. 27, 1992 (abandoned).
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`
`The present invention relates to a catadioptric optical
`system having a reflection surface and a refraction surface,
`and more particularly to an image forming optical system for
`reduction projection.
`'
`2. Related Background Art
`Various optical systems .for projecting and exposing a
`mask pattern onto a photoresist on a wafer to manufacture an
`integrated circuit such as an LSI have been proposed. It is
`known that an aberration is well corrected at a relatively
`large aperture in a Dyson type catadioptric optical system.
`However, since a focusing magnification in the Dyson type
`catadioptric optical system is unity, there is a limit in the
`transfer of a fine pattern.
`As an optical system having areduction factor suitable for
`the manufacture of a semiconductor device having a finer
`pattern, an optical system which is a modification of the
`Dyson type catadioptric optical system is disclosed U.S. Pat.
`No. 4,747,678 and U.S. Pat No. 4,953,960.
`The optical system disclosed in U.S. Pat. No. 4,747,678
`which permits the reduction projection allows the reduction
`focusing of a ring-shaped view field. Basically, it comprises
`three concave mirrors and a convex mirror and is used as a
`light exposure device for microlithography. Accordingly, it
`uses a very complex optical construction of a combination of
`a number of lenses.
`
`The reduction projection optical system disclosed in U.S.
`Pat. No. 4,953,960 comprises a combination of a concave
`mirror and a lens system. Since the reduction is attained by
`one time of focusing, the aberration is large and a combi-
`nation of a number of lenses is needed to correct the
`
`aberration. Since it is essential to provide a large scale beam
`splitter such as a half mirror in a light path, a loss of light
`intensity is more than 75% and the increase of exposure time
`due to the loss of light intensity causes a fatal shortcoming
`of the reduction of throughput in the manufacturing process
`of the semiconductor device. Further, a stray light which
`causes flare and ununiformity in illumination occurs in the
`large beam splitter in the light path, and it is diflicult to
`manufacture a large semitransparent plane.
`SUMMARY OF THE INVENTION
`
`It is an object of the present invention to provide a
`reduction projection optical system which solves problems
`encountered in the prior an optical system and which is
`simple in structure and has a good image-forming ability as
`a projection optical system for use in semiconductor fabri-
`cation.
`
`Other objects, features, and eifects of the present inven-
`tion will become apparent from the following detailed
`description taken in conjunction with the accompanying
`drawings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows a light path of a first embodiment of a
`catadioptric reduction projection optical system of the
`present invention;
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`
`FIG. 2 shows a light path of a second embodiment of the
`present invention;
`FIG. 3 shows a light path of a third embodiment of the
`present invention;
`FIG. 4 shows a light path of a fourth embodiment of the
`present invention;
`
`FIG. 5 shows a light path of a fifth embodiment according
`to the present invention;
`FIG. 6 is a graph showing the coma aberration of the fifth
`embodiment according to the present invention;
`FIG. 7 shows a light path of a sixth embodiment accord-
`ing to the present invention;
`FIG. 8 is a graph showing the coma aberration of the sixth
`embodiment according to the present invention;
`FIG. 9 shows a light path of a seventh embodiment
`according to the present invention;
`FIG. 10 is a graph showing the coma aberration of the
`seventh embodiment according to the present invention;
`FIG. 11 shows a light path of an eighth embodiment
`according to the present invention;
`FIG. 12 is a graph showing the coma aberration of the
`eighth embodiment according to the present invention;
`FIG. 13 shows a light path of a ninth embodiment
`according to the present invention;
`FIG. 14 is a graph showing the coma aberration of the
`ninth embodiment according to the present invention;
`FIG. 15 shows a light path of a 10th embodiment accord-
`ing to the present invention;
`FIG. 16 is a graph showing the coma aberration of the
`10th embodiment according to the present invention;
`FIG. 17 shows a light path of an 11th embodiment
`according to the present invention;
`FIG. 18 is a graph showing the coma aberration of the
`11th embodiment according to the present invention;
`FIG. 19 shows a light path of a 12th embodiment accord-
`ing to the present invention;
`FIG. 20 is a graph showing the coma aberration of the
`12th embodiment according to the present invention;
`FIG. 21 shows a light path of a 13th embodiment of a
`catadioptric reduction projection optical system of the
`present invention;
`FIG. 22 is a graph showing the coma aberration of the
`13th embodiment;
`
`FIG. 23 shows a light path of a 14th embodiment of a
`catadioptric reduction projection optical system of the
`present invention;
`FIG. 24 is a graph showing the coma aberration of the
`14th embodiment;
`
`FIG. 25 shows a light path of a 15th embodiment of a
`catadioptric reduction projection optical system of the
`present invention; and
`FIG. 26 is a graph showing the coma aberration of the
`15tl1 embodiment.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`A catadioptric reduction projection optical system accord-
`ing to the present invention has, in succession from the
`object side, a first partial optical system having a lens group
`G1 of positive refractive power and a first concave reflecting
`mirror M1 for forming the primary reduced image of an
`object, a second partial optical system having a second
`
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`5,668,673
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`3
`concave reflecting mirror M2 and a lens group G3 of positive
`refractive power for further reducing and re-imaging said
`primary reduced image. and a lens group G2 disposed near
`said primary reduced image. and further has a reflecting
`mirror disposed in the optical path between said first con-
`cave reflecting mirror M1 and said second concave reflecting
`mirror M2 for bending the optical path.
`In a catadioptric reduction projection optical according to
`the present invention as described above. the first and second
`partial optical systems have concave reflecting mirrors that
`provide considerable refractive power among the total posi-
`tive refractive power of the entire optical system and a lens "
`group of positive refractive power and both make reduction
`imaging possible and therefore. a predetermined reduction
`magnification can be obtained as a whole system without
`each partial optical system being made to bear a treat burden
`in aberration correction.
`
`By the lens group G2 being disposed near the primary
`reduced image I1, it becomes possible to apply a reduction
`magnification more and correct off-axis aberrations better.
`Where the lens group G2 disposed near the primary
`reduced image I1 is disposed at the first partial optical
`system side. it can be considered to be included in the first
`partial optical system. and where it is positive refractive
`power disposed immediately forwardly of the primary
`reduced image, it becomes possible to construct the whole
`optical system most simply. In this case, the catadioptric
`reduction projection optical system has. in succession from
`the object side. a first partial optical system having a first
`lens group G1 of positive refractive power. a first concave
`reflecting mirror M1 and a second lens group G2 of positive
`refractive power and for forming the primary reduced image
`of an object. and a second partial optical system having a
`second concave reflecting mirror M2 and a third lens group
`G3 of positive refractive power and for further reducing and
`re-imaging said primary reduced image. and further has a
`reflecting mirror disposed in the optical path between the
`first partial optical system and the second partial optical
`system for bending the optical path.
`In such a construction, the first and second partial optical
`systems have concave reflecting mirrors that provide con-
`siderable refractive power among the total positive refrac-
`tive power of the entire optical system. and lens groups (a
`second lens group G2 and a third lens group G3) of positive
`refractive power near the image thereof, whereby both of
`them make reduction imaging possible and therefore, with-
`out each partial optical system being made to bear a great
`burden in aberration correction. it is possible to be simple in
`construction and yet maintain an excellent imaging perfor-
`mance.
`~
`
`Further. it is effective to make the construction of the first
`
`lens group G1 into the so-called telephoto type comprising,
`in succession from the object side, a front group G11 of
`positive refractive power and a rear group G12 of negative
`refiactive power. In this case, the reduction magnification in
`the first lens group G1 can be earned and at the same time.
`the amount of aberration in the first concave reflecting
`mirror M1 can be made small and therefore, it becomes
`unnecessary to obtain a reduction magnification by the
`second lens group G2 and it becomes unnecessary to earn a
`reduction magnification by the second lens group G2, and
`the second lens group G2 can be used as a lens group
`exclusively foe aberration correction. and it becomes pos-
`sible to endow it with a greater numerical aperture (N.A.).
`Accordingly. the secondlens group G2 can be made into not
`only a construction which. as described above. earns a
`
`4
`
`reduction magnification with relatively strong refractive
`power immediately forwardly of the primary reduced image,
`but also a construction in which the second lens group G2 is
`made to function as a lens group exclusively for aberration
`correction, near the primary reduced image.
`Where each concave reflecting mirror is a spherical
`mirror,
`it is desirable that in the second partial optical
`system. a fourth lens group G4 for aberration correction be
`disposed between the second concave mirror M2 and the
`third lens group G3. It is also eifective to dispose. in the first
`partial optical system, a fifth lens group G3 for aberration
`correction between the first lens group G1 and the first
`concave reflecting mirror M1.
`In the manner described above. it is possible to be simple
`in optical construction and yet maintain an excellent imag-
`ing performance. and by having a great numerical aperture
`(N.A.). the transfer of more minute patterns is possible.
`In addition, in an optical system according to the present
`invention. a plane reflecting mirror M3 for bending the
`optical path is disposed in the optical path from-the first
`partial optical system to the second partial optical system.
`and preferably between the first concave reflecting mirror
`M1 and the second concave reflecting mirror M2, whereby
`the optical path can be completely separated. Therefore. this
`reflecting mirror can be a total reflection mirror. and a beam
`splitter such as a half mirror is not required as is in the
`aforementioned U.S. Pat. No. 4,953,960. This leads to the
`advantage that the loss of the quantity of light is much
`smaller and the possibility of creating harmful stray light
`such as flare is little.
`
`Also, in an optical system of the present invention, all of
`the optical members. except the plane reflecting mirror M3
`for bending the optical path. have centers of curvature on the
`same optical axis.
`The essential difference of the construction of the present
`invention as described above from the optical system dis-
`closed in the aforementioned U.S. Pat. No. 4,747,678 is that
`a convex reflecting mirror is not required as an optical
`element. This is because the above-described optical system
`according to the prior art has adopted a correcting technique
`whereby negative Petzval sum created by the Concave
`reflecting mirror is negated by the convex reflecting mirror
`and the refracting system eifects auxiliary aberration
`correction, whereas the present invention adopts a correcting
`technique whereby negative Petzval sum created by the
`concave reflecting mirror is negated by positive Petzval sum
`in the third lens group G3 which is a lens group of positive
`refractive power. Therefore, in the present invention, the
`positive refractive power of the third lens group G3 is made
`considerably strong and is positively used. Where the second
`lens group G2 is a lens group of positive refractive power
`disposed immediately forwardly of the primary reduced
`image I1. It is possible to cause the second lens group G2 to
`act in addition to the positive refractive power of the third
`lens group G3, thereby enhancing the eifect.
`Features of the present invention are now described in
`detail. The first and second partial optical systems are
`reduced irnage-forrning systems as described above but the
`second concave reflection mirror M2 in the second partial
`optical system preferably has a small magnification factor
`although it is close to unity magnification in order to
`facilitate the separation of the light path by the planar
`reflection mirror M3. Specifically. it is preferable that the
`following condition is met:
`
`10
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`65
`
`—1.5<t3,,,,<—1.o
`
`CARL ZEISS V. NIKON
`IPRZO13-00362
`
`EX. 2009, p. 29
`
`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2009, p. 29
`
`

`
`5,668,673
`
`5
`
`where BM2 is the magnification of the second concave
`reflection mirror M2.
`As a result, a position of an object image 11 by the first
`partial optical system is closer to the second concave reflec-
`tion mirror M2 than a position of an image I2 by the second
`partial optical system is so that the interference of the light
`path is prevented even for a light beam of a large numerical
`aperture. When BM2 exceeds the upper limit, the magnifi-
`cation of the second concave reflection mirror exceeds unity
`and the separation of the light path is diflicult to attain.
`Conversely, when the magnification exceeds the lower limit,
`it is diflicult for the second partial optical system to attain the
`desired reduction factor, and the burden of the flrst partial
`optical system increases and a complex construction is
`required to correct the aberration,
`The first concave reflection mirror M1 has a relatively
`large reduction factor and plays an important role in bal-
`ancing the compactness of the entire system and the correc-
`tion of aberration. It is preferable to meet the following
`condition:
`
`—0.7<|3M1<—0.3
`
`where BM1 is the magnification of the first concave reflection
`mirror M1.
`The balance of aberration of the groups of lenses is now
`discussed, The first group of lenses G1 is arranged in the
`Vicinity of the object surface and functions as a so-called
`view field lens and also corrects direction aberration. The
`
`second and third groups of lenses G2 and G3 have large
`positive refractive powers as described above, contribute to
`the formation of the reduced image and positively function
`to correct the Petzval sum, and the negative distortion
`aberration generated therein is corrected by the positive
`distortion aberration of the first group of lenses G1. The
`fourth group of lenses G4 provisionally arranged in the
`second partial optical system is effective to correct higher
`order spherical aberration. Where the concave reflection
`mirrors, particularly the first concave reflection mirror M1
`which shares a large portion of the reduction factor are
`non-spherical rather than spherical,
`the fourth group of
`lenses G4 may be omitted
`A catadioptric reduction projection optical system accord-
`ing to the present invention has a first partial optical system
`including, in succession from the object side, a first lens
`group G1 of positive refractive power and a first concave
`reflecting (or reflection) mirror M1 for forming a primary
`reduced image of an object, and a second partial optical
`system including, in succession from the object side, a
`second concave reflection mirror M2 and a third lens group
`G3 of positive refractive power for re-imaging the primary
`reduced image, and a second lens group G2 of positive or
`negative refractive power is arranged in the optical path (or
`light path) between the first and second concave reflection
`mirrors M1 and M2.
`In a catadioptric reduction projection optical system
`according to the present invention with the above-mentioned
`construction, the first and second partial optical systems
`have concave reflection mirrors that provide considerable
`refractive power among the total positive refractive power of
`the entire optical system and a lens group (first or third lens
`group G1 or G3) of positive refractive power, and both make
`reduction imaging possible. Therefore, a predetermined
`reduction factor can be obtained as a whole system without
`forcing a partial optical system to bear a great burden in
`aberration correction. For this reason.
`it is possible to
`simplify the optical construction and yet maintain an excel-
`lent imaging performance.
`
`6
`The balance of aberration of the lens groups in a cata-
`dioptric reduction projection optical system according to the
`present invention will now be discussed. The first lens group
`G1 is arranged in the vicinity of the object surface, has a
`function of maintaining telecentric characteristics, and cor-
`rects distortion. The second and third lens groups G2 and G3
`contribute to formation of the reduced image and to correc-
`tion of the Petzval sum. In particular, the second lens group
`G2 functions as a so-called field lens, and allows a light
`beam from a position near the optical axis of the first
`concave reflection mirror M1 to pass therethrough. ‘Thus, the
`light beam through second concave Inirror M2 at a position
`near the optical axis and generation of aberration in the
`second concave reflection Inirror M2 can be prevented. The
`negative distortion generated in the second and third lens
`groups G2 and G3 is corrected by the positive distortion of
`the first lens group G1. Lens groups (fourth and fifth lens
`groups G4 and G5) provisionally disposed in the vicinity of
`the concave reflection mirrors are eifective to correct higher
`order spherical aberration generated by the concave reflec-
`tion mirrors. When the concave reflection mirror is consti-
`tuted to be a non-spherical mirror, since aberration generated
`by the concave reflection mirror is minimized, the fourth and
`fifth lens groups G4 and G5 may be omitted.
`The characteristic features of the construction according
`to the present invention will be described in detail below.
`It is preferable that a catadioptric reduction projection
`optical system according to the present
`invention be
`arranged to satisfy the following condition:
`
`—2.5<t3,,,,<—o.7
`
`(1)
`
`where BM2 is the magnification of the second concave
`reflection mirror M2. The condition (1) defines a preferable
`magnification of the second concave reflection mirror M2.
`When BM2 exceeds the upper limit of the condition (1), the
`refractive power of the concave reflection .mirror M2
`increases, aberrations, especially spherical aberration and
`coma, generated by the concave reflection mirror M2
`increase, and it becomes difficult to satisfactorily correct the
`aberrations. Furthermore, a light beam propagating toward
`the concave reflection mirror M2 considerably overlaps a
`light beam propagating from the concave reflection mirror
`M2 toward the secondary image surface, and it becomes
`diflicult to obtain a physically constructible optical system.
`When BM2 is set below the lower limit, the refractive power
`of the concave reflection mirror M2 decreases, and the
`decrease in refractive power must be compensated for by a
`refracting optical system. thus losing the merits of a reflect-
`ing optical system At this time, the construction of the
`refracting optical system is more complicated, and aberra-
`tion correction becomes harder to attain.
`Furthermore, in order to facilitate separation of the light
`path by a planar reflection mirror (plane reflection mirror) in
`the catadioptric reduction projection optical system accord-
`ing to the present invention, it is ftnther preferable to satisfy
`the following condition:
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`—1.5<[3M2<—1.0
`
`65
`
`where BM2 is the magnification of the second concave
`reflection Inirror M2. Under this condition, when both the
`first and second optical systems are reduction imaging
`systems, since the position of an object image (primary
`image) 11 formed by the first partial optical system becomes
`closer to the second concave reflection mirror M2 than the
`
`CARL ZEISS V. NIKON
`IPRZO13-00362
`
`EX. 2009, p. 30
`
`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2009, p. 30
`
`

`
`5,668,673
`
`7
`
`position of an image 12 formed by the second partial optical
`system, the interference of the light path can be prevented
`for a light beam of a large numerical aperture. When BM;
`exceeds the upper limit of this condition, since the magni-
`fication of the second concave reflection mirror M2 exceeds
`unity. the separation of the light path may become difficult
`to attain. Conversely. when the magnification decreases
`beyond the lower limit of the condition. it is difficult for the
`second partial optical system to attain a desired reduction
`factor. and the burden of the first partial optical system
`increases.
`thus requiring a complicated construction for
`aberration correction.
`
`It is preferable that a catadioptric reduction projection
`optical system according to the present invention be
`arranged to satisfy the following condition:
`
`—2.0<|3m<—0.3
`
`(2)
`
`where BM1 is the magnification of the first concave reflection
`mirror. This condition defines a proper magnification of the
`first concave reflection mirror M1. When BM, exceeds the
`upper limit of the condition (2). the refiactive power of the
`first concave reflection mirror M1 increases, and aberrations,
`especially spherical aberration and coma, generated by the
`first concave reflection mirror M1 increase. Thus. the nega-
`tive refractive power of a refracting optical system must be
`strengthened to cancel these aberrations. and it becomes
`difficult to satisfactorily correct aberrations. When the mag-
`nification is set below the lower limit of the condition (2),
`the refractive power of the refracting optical system must be
`strengthened to compensate for the refractive power of the
`concave reflection mirror M1. At this time, the merits of a
`reflecting optical system are lost. the construction of the
`retracting optical system is more complicated, and aberra-
`tion correction becomes harder to attain.
`
`With the above-mentioned construction, a catadioptric
`reduction projection optical system according to the present
`invention preferably satisfies the following condition:
`
`o.o5<§3,,,<o.6
`
`(3)
`
`where BG3 is the magnification of the third lens group G3 of
`positive refractivepower. This condition defines a proper
`magnification of the third lens group G3, and allows for
`realization of a catadioptric reduction projection optical
`system having an excellent optical performance, and allows
`for obtaining a physically constructible catadioptric reduc-
`tion projection optical system. The physically constructible
`optical system means an optical system in which optical
`members do not interfere with each other in an arrangement
`of optical members constituting the catadioptric reduction
`projection optical system.
`When [$63 exceeds the upper limit of the above-
`mentioned condition (3). a light beam propagating between
`the concave reflection mirrors M1 and M2 considerably
`overlaps a light beam propagating from the concave reflec-
`tion mirror M2 to the secondary image surface, and the
`arrangement of optical members constituting the catadiop-
`tric reduction protection optical system cannot be realized.
`When [563 is set below the lower limit of the above-
`mentioned condition (3), the refractive power of the third
`lens group G3 increases. and coma and chromatic aberration
`are generated considerably.
`In a catadioptric reduction projection optical system
`according to the present invention. it is preferable that at
`least one of the first to third lens groups G,
`to G3 be
`
`8
`constituted by at least two different glass materials. Then,
`chromatic aberration can be satisfactorily corrected. and an
`imaging performance can be further improved. In particular,
`this construction is effective when a light source having a
`predetermined wavelength width is used.
`It is preferable that a catadioptric reduction projection
`optical system according to the present invention have at
`least two planar reflection mirrors. With