(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2002/0024741 A1
`(43) Pub. Date: Feb. 28, 2002
`
`Terasawa et al.
`
`US 20020024741A1
`
`(54) PROJECTION OPTICAL SYSTEM AND
`PROJECTION EXPOSURE APPARATUS
`
`Publication Classification
`
`(76)
`
`Inventors: Chiaki Terasawa, Utsunomiya-shi (JP);
`Hiroyuki Ishii, Utsunomiya-shi (JP);
`Takashi Kato, Utsunomiya-shi (JP)
`
`Correspondence Address:
`FITZPATRICK CELLA HARPER & SCINTO
`30 ROCKEFELLER PLAZA
`
`NEW YORK, NY 10112 (US)
`
`(21)
`
`Appl. No.:
`
`09/784,021
`
`(22)
`
`Filed:
`
`Feb. 16, 2001
`
`(30)
`
`Foreign Application Priority Data
`
`Feb. 16, 2000
`
`(JP) ....................................... 037981/2000
`
`Int. Cl.7 ........................... G02B 27/10; G02B 27/14
`(51)
`(52) U.S.Cl.
`........................... 359/627; 359/628; 359/629
`
`ABSTRACT
`(57)
`Disclosed is a projection optical system for projecting an
`image of an object onto an image plane, which includes a
`first imaging optical system for forming an image of the
`object, a second imaging optical system for re-imaging the
`image upon the image plane, wherein the first and second
`imaging optical systems are disposed in an order from the
`object side and are disposed along a common straight optical
`axis, wherein the first imaging optical system includes a first
`mirror for reflecting and collecting abaXial light from the
`object, wherein one of the first and second imaging optical
`systems includes a second mirror for reflecting light from
`the first mirror to the image plane side, and wherein, with the
`second mirror, the abaXial light is caused to pass an outside
`of an effective diameter of the first mirror.
`
`
`
` |02
`
`|03
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`--
`-- 1 --
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`ZEISS 1008
`ZEISS 1008
`
`

`

`Patent Application Publication
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`US 2002/0024741 A1
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`l02
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`|O3
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`-- 2 --
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`Patent Application Publication
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`Feb. 28, 2002 Sheet 2 0f 20
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`US 2002/0024741 A1
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`Patent Application Publication
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`Feb. 28, 2002 Sheet 3 0f 20
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`US 2002/0024741 A1
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`FIG. 4
`
`FIG. 5
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`-- 4 --
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`Patent Application Publication
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`Feb. 28, 2002 Sheet 4 0f 20
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`US 2002/0024741 A1
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`
`
`FIG. 7
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`-- 5 --
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`

`

`Patent Application Publication
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`Feb. 28, 2002 Sheet 5 0f 20
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`US 2002/0024741 A1
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`Patent Application Publication
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`Feb. 28, 2002 Sheet 6 0f 20
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`Patent Application Publication
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`Feb. 28, 2002 Sheet 7 0f 20
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`US 2002/0024741 A1
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`Patent Application Publication
`
`Feb. 28, 2002 Sheet 8 0f 20
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`US 2002/0024741 A1
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`

`

`Patent Application Publication
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`Feb. 28, 2002 Sheet 9 0f 20
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`US 2002/0024741 A1
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`__ 10 __
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`Patent Application Publication
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`Feb. 28, 2002 Sheet 13 0f 20
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`US 2002/0024741 A1
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`Patent Application Publication
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`Feb. 28, 2002 Sheet 14 0f 20
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`US 2002/0024741 A1
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`

`

`Patent Application Publication
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`Feb. 28, 2002 Sheet 15 0f 20
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`US 2002/0024741 A1
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`

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`Patent Application Publication
`
`Feb. 28, 2002 Sheet 16 0f 20
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`US 2002/0024741 A1
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`Patent Application Publication
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`Feb. 28, 2002 Sheet 17 0f 20
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`US 2002/0024741 A1
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`

`

`Patent Application Publication
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`Feb. 28, 2002 Sheet 18 0f 20
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`US 2002/0024741 A1
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`-- 19 --
`
`

`

`Patent Application Publication
`
`Feb. 28, 2002 Sheet 19 0f 20
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`US 2002/0024741 A1
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`-- 20 --
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`

`

`Patent Application Publication
`
`Feb. 28, 2002 Sheet 20 0f 20
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`US 2002/0024741 A1
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`__ 21 __
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`

`

`US 2002/0024741 A1
`
`Feb. 28, 2002
`
`PROJECTION OPTICAL SYSTEM AND
`PROJECTION EXPOSURE APPARATUS
`
`FIELD OF THE INVENTION AND RELATED
`ART
`
`[0001] This invention relates to a projection optical system
`and a projection exposure apparatus for projecting a pattern
`of a mask onto a substrate through the projection optical
`system. More particularly, the invention concerns a cata—
`dioptric projection optical system having a reflection mirror,
`for printing, by projection exposure, a reticle pattern oil a
`semiconductor wafer.
`
`[0002] The density of an integrated circuit increases more
`and more, and the specification and performance required
`for a projection (exposure) optical system become much
`strict. Generally, in order to obtain a higher resolving power,
`the exposure wavelength is shortened and/or the numerical
`aperture (NA) of a projection optical system is enlarged.
`
`[0003] However, as the exposure wavelength reaches a
`region of 193 nm (ArF excimer laser light) or 157 nm (F2
`excimer laser light), usable lens materials are limited to
`quartz and fluorite. This is mainly because of decreases of
`the light transmission factor. For example, in a projection
`optical system such as disclosed in Japanese Laid—Open
`Patent Application, Laid—Open No. 79345/1935, wherein it
`comprises all dioptric lenses of a large number and wherein
`all lenses have a largo glass material thickness, the exposure
`amount on a wafer becomes low and it causes a decrease of
`
`the throughput. Also, due to thermal absorption by lenses,
`there occur problems (thermal aberration) such as changes
`of aberration or shift of the focal point position. Where the
`exposure wavelength is 193 nm, quartz and fluorite can be
`used as a projection optical system. However, because the
`difference in dispersion between them is not large, correc—
`tion of chromatic aberration is difficult to accomplish. In
`order to correct the chromatic aberration of a projection
`optical system completely,
`it
`is necessary to use a few
`achromatic lenses having a small curvature radius at its
`achromatic surface. This leads to an increase of the total
`
`glass material thickness of the optical system, which then
`raises the above—described problems of thermal aberration
`and transmission factor. Further, currently, it is very difficult
`to produce a projection optical system by use of fluorite,
`having a sufficient property to assure its design performance.
`It is further difficult to produce one having a large diameter.
`This makes it very difficult to accomplish color correction,
`and results in an increase of the cost.
`
`[0004] As for the exposure wavelength of 157 nm, only
`fluorite is the usable lens material. The chromatic aberration
`
`can not be corrected only with a single lens material Any
`way, it is very difficult to provide a projection optical system
`only by use of dioptric systems.
`
`In consideration of these inconveniences, many
`[0005]
`proposals have been made to introduce a reflecting system,
`having a mirror, into an optical system to thereby avoid the
`problems of transmission factor and color correction. For
`example, Japanese Laid—Open Patent Applications, Laid—
`Open Nos. 211332/1997 and 90602/1998 show a catoptric
`projection optical system which is constituted only by use of
`reflecting systems. Further, US. Pat. No. 5,650,877 and
`Japanese Laid—Open Patent Applications, Laid—Open Nos.
`210415/1987, 258414/1987, 163319/1988, 66510/1990,
`
`282527/1991, 234722/1992, 188298/1993, 230287/1994,
`and 304705/1996 show a catadioptric projection optical
`system having a combination of catoptric and dioptric
`systems.
`
`[0006] Where a projection optical system which includes
`a catoptric system to meet the shortening of the exposure
`wavelength and the enlargement of NA (numerical aperture)
`is produced,
`the structure should of course be one that
`enables correction of chromatic aberration.
`In addition,
`idealistically, the structure should be simple and enough to
`enable that an imaging region of sufficient size is defined
`upon an image plane, that the number of optical elements
`such as mirrors or lenses is small, that the mirror incidence
`angle and reflection angle are not large, and that a sufficient
`image—side working distance is assured.
`
`If an imaging region width of sufficient size is
`[0007]
`attainable on the image plane, in the case of a scan type
`projection exposure apparatus, it is advantageous in respect
`to the throughput, such that the exposure variation can be
`suppressed. If the number of optical elements is small, the
`process load in the production of optical elements such as
`mirrors and lenses can be reduced. Also, since the total glass
`material thickness can be made smaller, the loss of light
`quantity can be reduced. Further, the increase of the foot—
`print of the apparatus can be suppressed, and the loss of light
`quantity due to the film can also be decreased. Particularly,
`this is very advantageous because, where the exposure
`wavelength is 157 nm (F2 excimer laser light), the loss of
`light quantity at the mirror reflection film can not be disre—
`garded. Where the mirror incidence angle and reflection
`angle are not large, the influence of a change in light quantity
`due to the angular characteristic of the reflection film can be
`suppressed. If a sufficient image—side working distance can
`be maintained, it is advantageous in respect to structuring an
`autofocusing system or a wafer stage conveyance system in
`the apparatus. If the structure is simple, complicatedness of
`a mechanical barrel, for example, can be avoided, and it
`provides an advantage to the manufacture.
`
`[0008] Here, the conventional examples are considered in
`respect to the above—described points.
`
`In the projection optical system shown in US. Pat.
`[0009]
`No 5,650,877, a Mangin mirror and a refracting member are
`disposed in an optical system to print an image of a reticle
`on a wafer. This optical system has inconveniences that, in
`every picture angle used,
`there occurs light interception
`(void) at the central portion of a pupil and that the exposure
`region can not be made large. If the exposure region is to be
`enlarged, it disadvantageously causes widening of the light
`interception at the central portion of the pupil. Further, the
`refractive surface of the Mangin mirror defines a beam
`splitting surface such that the light quantity decreases to a
`half each time the light passes this surface. The light quantity
`will be decreased to about 10% upon the image plane (wafer
`surface).
`
`In the projection optical systems shown in Japanese
`[0010]
`Laid—Open Patent Applications, Laid—Open Nos. 211332/
`1997 and 90602/1998, the basic structure comprises a reflec—
`tion system only However, in respect to aberration (Petzval
`sum) and mirror disposition, it is difficult to keep sufficient
`imaging region width on the image plane. Also, since in this
`structure a concave mirror adjacent the image plane and
`having a large power mainly has an imaging function,
`
`__ 22 __
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`

`US 2002/0024741 A1
`
`Feb. 28, 2002
`
`enlargement of NA is difficult to accomplish. Since a convex
`mirror is placed just before the concave mirror, a sufficient
`image—side working distance can not be maintained.
`
`In the projection optical systems shown in Japanese
`[0011]
`Laid—Open Patent Applications, Laid—Open Nos. 210415/
`1987 and 258414/1987, a Cassegrain type or Schwarzschild
`type mirror system is used. An opening is formed at the
`central portion of the mirror, by which a void is defined in
`the pupil such that only the peripheral portion of the pupil
`contributes to the imaging However, the presence of a void
`in the pupil will have an influence on the imaging perfor—
`mance. If the pupil void is to be made smaller, the power of
`the mirror must be large. This causes enlargement of the
`incidence and reflection angles of the mirror Further, an
`enlarged NA (numerical aperture) will cause a large increase
`of the mirror diameter.
`
`In the projection optical systems shown in Japanese
`[0012]
`Laid—Open Patent Applications, Laid—Open Nos. 163319/
`1988, 188298/1993 and 230287/1994, the structure is com—
`plicated due to deflection and bend of the optical path. Since
`most of the power of optical groups for imaging an inter—
`mediate image, as a final image, is sustained by a concave
`mirror,
`it is structurally difficult to enlarge the NA. The
`magnification of the lens system which is disposed between
`the concave mirror and the image plane is at a reduction ratio
`and also it has a positive sign. Because of it, a sufficient
`image—side working distance can not be kept. Further, in
`order that the object plane and the image plane are placed
`opposed, it is necessary to use two flat mirrors only for the
`sake of deflection of the optical path, without any contribu—
`tion to aberration correction. As the exposure wavelength is
`shorted to 157 nm, this is undesirable also in respect to the
`loss of light quantity. Further, it is structurally difficult to
`hold the imaging region width because of the necessity of
`light path division. Since the optical system has to be large,
`there is a disadvantage in respect to the footprint.
`
`In the projection optical systems shown in Japanese
`[0013]
`Laid—Open Patent Applications, Laid—Open Nos. 66510/
`1990 and 282527/1991, the optical path is divided by a beam
`splitter, and this makes the barrel structure complicated. It
`needs a beam splitter of large diameter and, if this is of a
`prism type, the loss of light quantity is large because of its
`thickness. For a larger NA, a larger diameter is necessary,
`and thus the loss of light quantity becomes larger If the beam
`splitter is of a flat plate type, there will occur astigmatism
`and comma even in regard to axial light rays. Further, there
`may occur aberrations due to a change in characteristic at the
`light dividing surface or production of asymmetric aberra—
`tion resulting from thermal absorption. It is therefore diffi—
`cult to manufacture the beam splitter very accurately.
`
`In the projection optical systems shown in Japanese
`[0014]
`Laid—Open Patent Applications, Laid—Open Nos. 234722/
`1992 and 304705/1996, many of the above—described incon—
`veniences may be removed. However, each time the optical
`path is deflected, the light path from a concave mirror is
`divided. This requires eccentric optical handling and it
`makes the structure and assembling very complicated.
`
`SUMMARY OF THE INVENTION
`
`disclosed in Japanese Laid—Open Patent Applications, Laid—
`Open Nos. 234722/1992 and 304705/1996, described above,
`is improved. It is another object of the present invention to
`provide a projection exposure apparatus and/or a device
`manufacturing method using the same.
`
`In accordance with the present invention, a projec—
`[0016]
`tion optical system, a projection exposure apparatus and a
`device manufacturing method having features as stated in
`Items (1)—(37) below are provided.
`
`(1) A projection optical system for projecting an
`[0017]
`image of an object onto an image plane, comprising: a first
`imaging optical system for forming an image of the object;
`a second imaging optical system for re—imaging the image
`upon the image plane; wherein said first and second imaging
`optical systems are disposed in an order from the object side
`and are disposed along a common straight optical axis,
`wherein said first imaging optical system includes a first
`mirror for reflecting and collecting abaxial light from the
`object, wherein one of said first and second imaging optical
`systems includes a second mirror for reflecting light from
`said first mirror to the image plane side, and wherein, with
`said second mirror, the abaxial light is caused to pass an
`outside of an effective diameter of said first mirror.
`
`(2) A projection optical system according to Item
`[0018]
`(1) wherein said first imaging optical system has a magni—
`fication [3 which satisfies a relation IBIEL
`
`(3) A projection optical system according to Item
`[0019]
`(1) or (2) wherein said first imaging optical system includes
`at least one lens.
`
`(4) A projection optical system according to Item
`[0020]
`(3) wherein said lens has a positive refracting power.
`
`(5) A projection optical system according to any
`[0021]
`one of Items (1) to (4) wherein said second imaging optical
`system includes at least one lens.
`
`(6) A projection optical system according to Item
`[0022]
`(5) wherein said lens has a positive refracting power
`
`(7) A projection optical system according to any
`[0023]
`one of Items (1) to (6), further comprising a lens group
`disposed between said first and second mirrors.
`
`(8) A projection optical system according to Item
`[0024]
`(7) wherein said lens group has a negative refracting power
`and wherein said lens group is disposed between said first
`mirror and a refractive lens of said first imaging optical
`system, having a positive refracting power.
`
`(9) A projection optical system according to Item
`[0025]
`(1), further comprising a field optical system disposed
`between said first and second imaging optical systems, for
`projecting a pupil of said first imaging optical system onto
`said second imaging optical system, wherein said first imag—
`ing optical system comprises a first mirror group of positive
`refracting power, including at least said first mirror, and a
`second mirror group including said second mirror, wherein
`light from said first mirror group as reflected by said second
`mirror group is caused to pass an outside of an effective
`diameter of said first mirror group.
`
`It is accordingly an object of the present invention
`[0015]
`to provide a projection optical system of simple structure
`and easy assembling wherein an optical system such as
`
`(10) Aprojection optical system according to Item
`[0026]
`(9) wherein said second imaging optical system is consti—
`tuted by lenses only and it has a positive refracting power
`
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`

`US 2002/0024741 A1
`
`Feb. 28, 2002
`
`(11) Aprojection optical system according to Item
`[0027]
`(9) or (10) wherein said second imaging optical system has
`a magnification BG2 which satisfies a relation —0.5<BG2<—
`0.05.
`
`(23) A projection optical system according to any
`[0039]
`one of Items (9) to (22), wherein said first imaging optical
`system has a lens group of positive refracting power, dis—
`posed closest to the object side.
`
`(12) A projection optical system according to any
`[0028]
`one of Items (9) to (11), wherein said first imaging optical
`system has a magnification BG1 which satisfies a relation
`—40.0<BG1<—0.5.
`
`(24) A projection optical system according to any
`[0040]
`one of Items (9) to (23), wherein said first mirror group
`includes a lens of negative refracting power and said first
`mirror.
`
`(13) A projection optical system according to any
`[0029]
`one of Items (9) to (12), wherein said field optical system is
`all constituted by lenses.
`
`(14) A projection optical system according to any
`[0030]
`one of Items (9) to (12), wherein said field optical system
`comprises a first field mirror and a second field mirror group
`including a second field mirror, wherein abaxial light passed
`through the outside of the effective diameter of said first
`mirror group is reflected by said first field mirror and said
`second field mirror, in this order, and after that, the light
`passes a region adjacent the optical axis of said first filed
`mirror and enters said second imaging optical system.
`
`(15) Aprojection optical system according to Item
`[0031]
`(14) wherein said first filed mirror comprises a concave
`mirror and wherein said second field mirror comprises a
`convex mirror
`
`(16) Aprojection optical system according to Item
`[0032]
`(14) wherein said first filed mirror comprises a concave
`mirror and wherein said second field mirror comprises a
`concave mirror.
`
`(17) A projection optical system according to any
`[0033]
`one of Items (9)
`to (16), wherein relations P1<0 and
`Pf+P2>0 are satisfied where P1, Pf and P2 are Petzval sums
`of said first imaging optical system, said field optical system
`and said second imaging optical system, respectively.
`
`(18) A projection optical system according to any
`[0034]
`one of Items (9) to (17), wherein a relation 0.6<e/LM1<2.5
`is satisfied where LM1 is a paraxial distance between the
`object and said first mirror, and e is a distance from the
`object
`to a pupil conjugate point defined by an optical
`element positioned at the object side of said first mirror.
`
`(19) A projection optical system according to any
`[0035]
`one of Items (9) to (18), wherein the distance LM1 satisfies
`a relation 0.5<OIL/(LM1+2><LM2)<20 where LM2 is a
`paraxial distance between said first and second mirrors, and
`OIL is a paraxial distance along the optical path, from the
`object to the image defined by said first imaging optical
`system
`
`(20) A projection optical system according to any
`[0036]
`one of Items (9) to (19), wherein the distances LM1 and
`LM2 satisfy a relation 0.2<LM2/LM1<0.95.
`
`(21) A projection optical system according to any
`[0037]
`one of Items (9) to (20), wherein the distance LM1 satisfies
`a relation 0.15<LM1/L<0.55 where L is a distance from an
`object plane to an image plane in said projection optical
`system.
`
`(22) A projection optical system according to any
`[0038]
`one of Items (9) to (21), wherein said first mirror group has
`a magnification BGM1 which satisfies a relation —2.0<1/
`BGM1<0.4.
`
`(25) A projection optical system according to any
`[0041]
`one of Items (9) to (24), wherein said second mirror group
`includes said second mirror and a lens.
`
`(26) A projection optical system according to any
`[0042]
`one of Items (9) to (25), wherein the abaxial light from the
`object passes a lens of said second mirror group before it is
`incident on said first mirror group.
`
`(27) A projection optical system according to any
`[0043]
`one of Items (9) to (26), wherein a positive lens, included by
`said field optical system, is disposed just after the image
`plane side of said first mirror group of said first imaging
`optical system.
`
`(28) A projection optical system according to any
`[0044]
`one of Items (14) to (16), wherein a relation 0.45<LFM1/
`LFM2<0.8 is satisfied where LFM1 is a distance between
`said second field mirror and said first field mirror, and LFM2
`is a distance between said second field mirror and the image
`plane.
`
`(29) A projection optical system according to any
`[0045]
`one of Items (14) to (16), wherein said second field mirror
`group includes said second field mirror and a lens.
`
`(30) A projection optical system according to any
`[0046]
`one of Items (14) to (16), (28) and (29), wherein a positive
`lens,
`included by said field optical system,
`is disposed
`between said first mirror of said first imaging optical system
`and said second field mirror of said field optical system,
`wherein light reflected by said second mirror of said first
`imaging optical system passes said positive lens and then is
`reflected by said first field mirror.
`
`(31) A projection optical system according to any
`[0047]
`one of Items (1) to (30), wherein said projection optical
`system is telecentric with respect to each of the object side
`and the image plane side.
`
`(32) A projection optical system according to any
`[0048]
`one of Items (1) to (31), wherein said projection optical
`system has a magnification of reduction ratio.
`
`(33) A projection optical system according to any
`[0049]
`one of Items (1) to (32), further comprising a field stop
`disposed at the position of the image defined by said first
`imaging optical system, for changing at least one of a size
`and a shape of an imaging region upon the image plane.
`
`(34) A projection optical system according to any
`[0050]
`one of Items (1) to (33), further comprising a stop disposed
`inside said second imaging optical system.
`
`(35) Aprojection exposure apparatus for projecting
`[0051]
`a pattern of a mask onto a substrate through a projection
`optical system as recited in any one of Items (1) to (34)
`
`(36) Aprojection exposure apparatus according to
`[0052]
`Item (35) wherein laser light from one of an ArF excimer
`laser and an F2 laser is used for the projection exposure.
`
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`

`

`US 2002/0024741 A1
`
`Feb. 28, 2002
`
`(37) A device manufacturing method, comprising
`[0053]
`the steps of: printing a device pattern on a wafer by
`exposure, using a projection exposure apparatus as recited in
`item (35) or (36); and developing the exposed wafer.
`
`[0054] These and other objects, features and advantages of
`the present invention will become more apparent upon a
`consideration of the following description of the preferred
`embodiments of the present invention taken in conjunction
`with the accompanying drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0055] FIG. 1 is a schematic view of an example of the
`structure of a projection optical system according to an
`embodiment of the present invention
`
`[0056] FIG. 2 is a schematic view of an example of the
`structure of a projection optical system according to a first
`embodiment of the present invention, wherein a refractive
`lens group R is disposed in a group L2.
`
`[0057] FIG. 3 is a schematic view of a basic structure of
`a projection optical system according to a second embodi—
`ment of the present invention.
`
`[0058] FIG. 4 is a sectional view of a lens structure in
`Example 1 of the present invention.
`
`[0059] FIG. 5 is a sectional view of a lens structure in
`Example 2 of the present invention,
`
`[0060] FIG. 6 is a sectional view of a lens structure in
`Example 3 of the present invention.
`
`[0061] FIG. 7 is a sectional view of a lens structure in
`Example 4 of the present invention.
`
`[0062] FIG. 8 illustrates aberrations in Example 1 of the
`present invention.
`
`[0063] FIG. 9 illustrates aberrations in Example 2 of the
`present invention.
`
`[0064] FIG. 10 illustrates aberrations in Example 3 of the
`present invention.
`
`[0065] FIG. 11 illustrates aberrations in Example 4 of the
`present invention.
`
`[0066] FIG. 12 is a schematic view of a light path in a
`case, in Example 5 of the present invention, wherein a field
`optical system is all constituted by lens systems.
`
`[0067] FIG. 13 is a schematic view of a light path in a
`case, in Example 6 of the present invention, wherein a field
`optical system is all constituted by lens Systems
`
`[0068] FIG. 14 is a schematic view of a light path in a
`case, in Example 7 of the present invention, wherein a field
`optical system is all constituted by lens systems.
`
`[0069] FIG. 15 is a schematic view of a light path in a
`case, in Example 8 of the present invention, wherein a field
`optical system is all constituted by lens systems.
`
`[0070] FIG. 16 is a schematic view of a light path in a
`case, in Example 9 of the present invention, wherein a field
`optical system is all constituted by lens systems.
`
`[0071] FIG. 17 is a schematic view of a light path in a
`case, in Example 10 of the present invention, wherein a field
`optical system is all constituted by lens systems.
`
`[0072] FIG. 18 is a schematic view of a light path in a
`case, in Example 11 of the present invention, wherein a field
`optical system is all constituted by lens systems.
`
`[0073] FIG. 19 is a schematic view of a light path in a
`case, in Example 12 of the present invention, wherein a field
`optical system is all constituted by lens systems.
`
`[0074] FIG. 20 is a schematic view of a light path in a
`case, in Example 13 of the present invention, wherein a field
`optical system includes two mirrors.
`
`[0075] FIG. 21 is a schematic view of a light path in a
`case, in Example 14 of the present invention, wherein a field
`optical system includes two mirrors.
`
`[0076] FIG. 22 is a schematic view of a light path in a
`case, in Example 15 of the present invention, wherein a field
`optical system includes two mirrors.
`
`[0077] FIG. 23 is a schematic view of a light path in a
`case, in Example 16 of the present invention, wherein a field
`optical system includes two mirrors.
`
`[0078] FIG. 24 is a schematic view of a light path in a
`case, in Example 17 of the present invention, wherein a field
`optical system includes two mirrors.
`
`[0079] FIG. 25 is a schematic view of a light path in a
`case, in Example 18 of the present invention, wherein a field
`optical system includes two mirrors.
`
`[0080] FIG. 26 is a schematic view of a light path in a
`case, in Example 19 of the present invention, wherein a field
`optical system includes two mirrors.
`
`[0081] FIG. 27 is a schematic view of a light path in a
`case, in Example 20 of the present invention, wherein a field
`optical system includes two mirrors.
`
`[0082] FIG. 28 is a schematic view of a light path in a
`case, in Example 21 of the present invention, wherein a field
`optical system includes two mirrors.
`
`[0083] FIG. 29 illustrates aberrations in Example 5 of the
`present invention.
`
`[0084] FIG. 30 illustrates aberrations in Example 6 of thee
`present invention.
`
`[0085] FIG. 31 illustrates aberrations in Example 7 of the
`present invention.
`
`[0086] FIG. 32 illustrates aberrations in Example 8 of the
`present invention.
`
`[0087] FIG. 33 illustrates aberrations in Example 9 of the
`present invention.
`
`[0088] FIG. 34 illustrates aberrations in Example 10 of
`the present invention.
`
`[0089] FIG. 35 illustrates aberrations in Example 11 or the
`present invention.
`
`[0090] FIG. 36 illustrates aberrations in Example 12 of
`the present invention.
`
`[0091] FIG. 37 illustrates aberrations in Example 13 of
`the present invention.
`
`[0092] FIG. 38 illustrates aberrations in Example 14 of
`the present invention.
`
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`
`

`

`US 2002/0024741 A1
`
`Feb. 28, 2002
`
`[0093] FIG. 39 illustrates aberrations in Example 15 of
`the present invention.
`
`[0094] FIG. 40 illustrates aberrations in Example 16 of
`the present invention.
`
`[0095] FIG. 41 illustrates aberrations in Example 17 of
`the present invention.
`
`[0096] FIG. 42 illustrates aberrations in Example 18 of
`the present invention.
`
`[0097] FIG. 43 illustrates aberrations in Example 19 of
`the present invention.
`
`[0098] FIG. 44 illustrates aberrations in Example 20 of
`the present invention.
`
`[0099] FIG. 45 illustrates aberrations in Example 21 of
`the present invention.
`
`[0100] FIG. 46 illustrates numerical parameters
`Examples 1—12 of the present invention.
`
`[0101] FIG. 47 illustrates numerical parameters
`Examples 13—21 of the present invention.
`
`in
`
`in
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`In accordance with an embodiment of the present
`[0102]
`invention, a catadioptric