United States Patent [191
`Matsumoto
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,812,028
`Mar. 14, 1989
`
`[54] ' REFLECTION TYPE REDUCI‘ION
`PROJ'ECI'ION OPTICAL SYSTEM
`[75] Inventor: Kohichi Matsumoto, Kita, Japan
`[73] Assignee: Nikon Corporation, Tokyo, Japan
`[21] Appl. No.: 171,169
`[22] Filed:
`Mar. 21, 1988
`
`[63]
`
`Related US. Application Data
`Continuation of Ser. No. 755,356, Jul. 16, 1985, aban
`doned.
`Foreign Application Priority Data
`[30]
`Jul. 23, 1984 [JP]
`Japan .............................. .. 59-152502
`Mar. 6, 1985 [JP]
`Japan ................................ .. 60-44123
`
`[51] Int. Cl.4 ............................................ .. G02B 17/08
`[52] US. Cl. .................................. .. 350/444; 350/442;
`350/505
`[58] Field of Search .............. .. 350/442, 443, 444, 505
`[56]
`References Cited
`U.S. PATENT DOCUMENTS
`
`3,748,015 7/1973 Offner ................................. .. 350/55
`4,293,186 10/1981 Offner ....................... .. 350/444 X
`4,331,390 5/ 1982 Shafer ........................... .. 350/444
`4,469,414 9/1984 Shafer ............................... .. 350/414
`
`OTHER PUBLICATIONS
`.1. Dyson, “Unit Magni?cation Optical System Without
`Seidel Aberrations”, Jul. 1959, pp. 713-716, Journal of
`Optical Society of America, vol. 49, No. 7.
`C. G. Wynne, “A Unit-Power Telescope for Projection
`Copying”, 1970, pp. 429-434, Optical Instruments and
`Techniques, Oriel Press Limited.
`A. P. Grammatin, “Some Properties of Concentric Op
`tical Systems”, Apr. 1971, pp. 210-211, Optical Tech
`nology, vol. 38, No. 4.
`Primary Examiner-John K. Corbin
`Assistant Examiner—Scott J. Sugarman
`Attorney, Agent, or Firm-Shapiro and Shapiro
`[57]
`ABSTRACT
`A re?ection type projection optical system suitable for
`projection of a micropattern object is capable of per
`forming reduction projection. The projection optical
`system comprises ?rst and second optical subsystems
`which are combined to set a Petzval sum to zero. A ?rst
`optical subsystem S1 forms a reduced image of an ob
`ject, and a second optical subsystem S2 forms a further
`reduced object image from the image formed by the
`?rst optical subsystem S1.
`
`15 Claims, 8 Drawing Sheets
`
`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2007, p. 1
`
`

`

`US. Patent Mar. 14,1989
`
`Sheet 1 of8
`
`4,812,028
`
`FIG. I
`
`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2007, p. 2
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`

`

`US. Patent Mar. 14, 1989
`
`Sheet 2 01's
`
`4,812,028
`
`52
`
`FIG. 3
`
`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2007, p. 3
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`

`

`US. Patent Mar. 14,1989
`
`Sheet 3 of8
`
`4,812,028
`
`A2
`
`FIG. 4
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`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2007, p. 4
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`

`

`,
`
`US. Patent Mar.14, 1989
`
`Sheet 4 of8
`
`4,812,028
`
`M4
`
`FIG. 5
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`Ex. 2007, p. 5
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`Sheet 5 of8_
`US. Patent Mar. 14,1989
`FIG. 6
`
`4,812,028
`
`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2007, p. 6
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`

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`US. Patent Mar. 14,1989
`
`Sheet 6 of8
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`4,812,028
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`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2007, p. 7
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`

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`US. Patent Mar. 14, 1989
`
`Sheet 7 of 8
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`4,812,028
`
`i
`
`FIG. 8
`
`RC2
`
`RAE
`
`LA2
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`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2007, p. 8
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`US. Patent Mar. 14, 1989
`
`Sheet 8 of8
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`4,812,028
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`CARL ZEISS V. NIKON
`|PR2013-00362
`
`EX. 2007, p. 9
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`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2007, p. 9
`
`

`

`1
`
`REFLECTION TYPE REDUCTION PROJECTION
`OPTICAL SYSTEM
`
`This is a continuation application of Ser. No. 755,356,
`?led July 16, 1985, now abandoned.
`
`5
`
`4,812,028
`2
`along the optical axis do not change their inclined an
`gles irrespective of the numerical aperture (NA). There
`fore, the spherical aberration and the sine condition are
`strictly zero. When the sine condition is satis?ed, coma
`is corrected in at least a third-order aberration region.
`Furthermore, when sagittal pencil and meridional pen
`cil image surfaces are considered, the sagittal pencil
`image surface does not have a curvature of ?eld for the
`same reason as for zero spherical aberration.
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`The present invention relates to a re?ection optical
`system for forming a projection image and, more partic
`ularly, to a re?ection optical system suitable for projec
`tion of a micropattern image such as of semiconductor
`device pattern.
`2. Description of the Prior Art
`A conventional re?ection optical system of this type
`projects a mask pattern on a wafer pattern at an equal
`size. In a re?ection type optical system disclosed in US.
`Pat. No. 3,748,015, a high-quality image is formed in an
`arcuate ?eld of view by using concave and convex
`re?ection surfaces, as in an optical system of Offner.
`Another re?ection optical system using one concave
`re?ection surface and one refracting member is pro
`posed by J. Dyson, as per “Unit Magni?cation Optical
`System without Seidel aberrations”, Journal of Optical
`Society of America, Vol. 49. P. 713, 1959.
`In an Offner optical system, high performance is
`achieved by inserting a meniscus lens member, as exem
`pli?ed in US. Pat. No. 4,331,390. In a Dyson optical
`system, various improvements including use of an ach
`romatic lens are proposed by C. G. Wynne, “A Unit
`Power Telescope for Projection Copying” in “Optical
`Instruments and Techniques” published by Oriel Press
`Limited and edited by J. H. Dickson, 1970.
`However, these conventional systems are based on a
`unit magni?cation factor. When any of these conven
`tional systems is used as an optical system in a projec
`tion exposure apparatus for semiconductor device man
`ufacture, the size of the photomask must be the same as
`that of an integrated circuit, thus resulting in dif?culty
`in the manufacture of photomasks. Another optical
`system is also proposed to project a reduction image
`using only a refracting system without a re?ecting sur
`face. This optical system comprises ten to 20 glass mem
`bers. In this case, light absorption by the glass members
`45
`is increased, resulting in inconvenience. In particular,
`when an exposure wavelength is shortened and far ul
`traviolet rays are used to satisfy the needs of further
`micropatterning of ICs, light absorption by the glass
`members becomes a critical problem. It is thus to be
`expected that patterning by the refracting system will
`be limited.
`An advantage of a conventional optical system has
`been proposed by A. P. Grammatin in “Some Proper
`ties of Concentric Optical Systems”, Optical Technol
`ogy Vol. 38, No. 4, P. 210, 1970, wherein optical planes
`are monocentrically arranged, and an object point and
`an image point are formed in a plane perpendicular to an
`optical axis and including the center of the monocentric
`optical planes. The principle of operation of this optical
`system will be brie?y described.
`Since all the optical planes are monocentric, inclined
`angles of paraxial rays emitted from the monocentric
`center, i.e., from a point on an optical axis of the object
`surface, do not change their values except for their
`signs. A magni?cation factor is equal to a ratio of a
`refractive index of the object space to that of the image
`space. Similarly, the rays emitted from the object point
`
`55
`
`25
`
`30
`
`35
`
`60
`
`65
`
`SUMMARY OF THE INVENTION
`It is an object of the present invention to resolve the
`problems of a conventional projection optical system
`and to provide a re?ection type projection optical sys
`tem capable of performing reduction projection.
`According to an aspect of the present invention, the
`re?ection type projection optical system comprises ?rst
`and second optical subsystems which are combined to
`set a Petzval sum to zero. A ?rst optical subsystem S1
`forms a reduced image of an object, and a second opti
`cal subsystem S2 forms a further reduced object image
`of the image reduced by the ?rst optical subsystem S1.
`According to an aspect of the resent invention, the
`?rst optical subsystem S1 has a concave ?rst re?ecting
`surface M1, a convex second re?ecting surface M2 and
`a concave third reflecting surface M3 which are mono
`centrically arranged. The ?rst and third reflecting sur
`faces M1 and M3 oppose the second re?ecting plane
`M2. An object plane 0 and an image plane I in the ?rst
`optical subsystem S1 are located within a plane perpen
`dicular to an optical axis A1 of the subsystem S1 and
`including a monocentric center C. The ?rst optical
`subsystem S1 has a ?rst refracting member P1 at an exit
`side of the third re?ecting surface M3. The ?rst refract
`ing member Pl has a refracting incident surface R1
`having its center substantially coinciding with the
`monocentric center C and a refractive exit surface R2
`which is located near the image plane I and which is
`substantially parallel to the image plane I. The second
`optical subsystem S2 has a concave fourth re?ecting
`surface M4 having as its center the monocentric center
`C of the ?rst optical subsystem S1 or a point optically
`equivalent to the center C. The second optical subsys
`tem S2 has as an object surface 0' the image plane I of
`the ?rst optical system. The second optical subsystem
`S2 has the object plane 0' and an image plane I’ in a
`plane which includes the curvature center of the fourth
`re?ecting surface and which is perpendicular to an
`optical axis A2 of the second optical subsystem. The
`second optical subsystem S2 also has a refracting mem
`ber P2 at the exit side of the fourth re?ecting surface
`R4. The refracting member P2 has a refracting incident
`surface R3 substantially monocentric with the center C
`of the fourth re?ecting surface R4 and a refracting exit
`surface R4 which is located near the image plane I’ and
`which is substantially parallel thereto. In the monocen
`tric optical system of the present invention, the object
`plane and the image plane are located in a plane includ
`ing the monocentric center, so that the optical axis
`passes through the center and can be de?ned as a line
`perpendicular to the plane.
`According to another aspect of the present invention,
`an aplanatic surface is used in addition to the monocen
`tric re?ecting surfaces, thereby performing projection
`at a high reduction factor (or a high magni?cation fac
`tor). In this aspect, there are provided a plurality of
`re?ecting surfaces and a plurality of refracting surfaces
`which have an identical curvature center along a given
`
`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2007, p. 10
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`

`

`4,812,028
`3
`optical axis. The plurality of refracting surfaces include
`an aplanatic refracting surface. Object point positions of
`the plurality of re?ecting surfaces along the optical axis
`are coincident substantially with the centers thereof.
`The refracting surfaces excluding the aplanatic refract
`ing surface comprise flat refracting surfaces which have
`curvature centers coincident with object points thereas
`along the optical axis or which are coincident with
`object or image points or conjugate positions therewith
`of the optical system.
`One of the features of the present invention is that a
`magni?cation factor of the re?ecting surfaces is -—l,
`i.e., that the object point of each re?ecting surface along
`the optical axis is the same as the image point along the
`optical axis thereof.
`Another feature of the present invention is to satisfy
`one of the following conditions for the refracting sur
`faces.
`First, the object position of the refracting surface
`along the optical axis is coincident with the curvature
`center thereof. In other words, a monocentric refract
`ing surface is formed.
`Second, if an object point distance of the refracting
`surface is s, an image point distance thereof is s’, a re
`fractive index of a medium located just in front of the
`refracting surface along the beam propagation direction
`is N, and a refractive index of a medium located just
`behind the refracting surface is N’, a radius R of curva
`ture of the refracting surface must satisfy the following
`equation:
`
`4
`medium having the refractive index n to air, a magni?
`cation factor of the surface is r12.
`According to this aspect, the property of such an
`aplanatic surface is utilized to obtain a combination of
`the aplanatic surface and monocentric re?ecting and
`refracting surfaces, thereby realizing a re?ection type
`projection optical system having a high reduction or
`magni?cation factor.
`In a re?ection optical system having monocentric
`optical surfaces and object and image points located in
`a plane which is perpendicular to an optical axis and
`which includes the centers of the monocentric optical
`surfaces, the optical properties of the system can be
`expressed as:
`
`10
`
`where IV is the sagittal aberration, III is the astigma
`tism and P is the Petzval sum.
`When the object point on the optical axis of the re
`?ecting or refracting surface of interest is aligned with
`the curvature center thereof, the following relation is
`established:
`
`where I is the spherical aberration and II is the coma.
`Since the sagittal pencil is incident at an angle of 90“,
`it passes through the surface without being regularly
`re?ected or refracted, so that
`
`30
`
`35
`
`A refracting surface having an in?nite radius of cur
`vature and the curvature center located at the object or
`image point or at a conjugate position therewith along
`the axis of the entire optical system satis?es the follow
`ing relation, since an incident height h of the paraxial
`marginal ray is O:
`
`In other words, an aplanatic refracting surface must be
`formed.
`Third, the refracting surface must be located at the
`object or image point or at a conjugate position there
`with along the optical axis of the entire optical system,
`and its radius of curvature is in?nite.
`As is apparent from Gauss optics, a monocentric
`re?ecting surface has a magni?cation factor of — l, and
`a monocentric refracting surface with an in?nite radius
`of curvature has a magni?cation of +1. If a refractive
`index of a medium located in front of the monocentric
`refracting surface is N and a refractive index of a me
`dium located behind the monocentric refracting surface
`is N’, a magni?cation factor Bc of this refracting surface
`is given as follows:
`
`When light is incident through air on a monocentric
`refracting surface of a medium having a refractive index
`n, a magnification of this furface is l/n. However, when
`light exits from this medium to air, a magni?cation
`factor of the monocentric refracting surface is n.
`A magni?cation factor Ba of the aplanatic refracting
`surface is given as follows:
`
`In other words, the image magni?cation factor of the
`aplanatic surface is a square of a ratio of the refractive
`index of the medium located in front of the aplanatic
`refracting surface to that therebehind. Therefore, when
`65
`light is incident through air on the aplanatic surface of
`a medium having the refractive index n, a magni?cation
`factor is (l/n)2. However, when light exits from the
`
`At the same time, since the radius of curvature is in?
`nite,
`
`Relation IV=O is derived from relation IV=III+P.
`In the re?ection optical system having monocentric
`optical surfaces and object and image points located in
`a plane which is perpendicular to an optical axis and
`which includes the centers of the monocentric optical
`surfaces, the radii of curvature of the monocentric re
`?ecting and refracting surfaces are properly selected to
`establish P=O, thereby realizing an optical system
`which satis?es the following relation:
`
`The aplanatic refracting surface satis?es the follow
`ing relation:
`
`When the radius of curvature of the aplanatic refract
`ing surface is selected to cancel the Petzval sum based
`on only the aplanatic refracting surface so as to set the
`sum to zero, i.e., when P=O is established, the sagittal
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`

`4,812,028
`5
`aberration IV caused by only the aplanatic refracting
`surface is given as follows since IV=III+P:
`
`6
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`FIG. 1 shows a re?ection type reduction projection
`optical system according to a ?rst embodiment of the
`present invention. The ?rst embodiment exempli?ed is
`the simplest con?guration of the present invention.
`Light from an object point of a ?rst optical subsystem
`S1 is converged by a concave ?rst re?ecting surface
`M1. The light is scattered by a convex second re?ecting
`surface M2 and is converged by a concave third re?ect
`ing surface M3. The light is refracted by a ?rst refract
`ing member P1 to form an image I of the ?rst optical
`subsystem on an ideal image plane on an exit plane R2.
`In this case, the focusing magni?cation B1 is given as
`follows:
`
`where n1 is the refractive index of the ?rst refracting
`member P1. The image I serves as an object O’ of a
`second optical subsystem S2. Light from the object O’ is
`converged by a concave fourth re?ecting surface M4
`and is refracted by a second refracting member P2,
`thereby forming an object image I’ on an exit surface
`R4. In this case, the focusing magni?cation factor 82 of
`the second optical subsystem S2 is given as follows:
`
`where n2 is the refractive index of the second refracting
`member P2. Therefore, a total magni?cation factor of
`the entire system is given as follows:
`
`If the refractive index of the ?rst refracting member
`P1 is the same as that of the second refracting member
`P2 and is n, the total reduction factor of the entire sys
`tem is n2.
`When the fourth re?ecting surface M4 of the second
`optical system S2 serves as the numerical aperture of
`the entire system, i.e., in order to obtain a telecentric
`system at the image side, light emitted along the optical
`axis of the fourth re?ecting surface M4 must be incident
`so as to be perpendicular to the image plane I’, i.e., to be
`parallel to the optical axis. In other words, equation (I)
`must be satis?ed:
`
`where RM4 is the radius of curvature of the fourth
`re?ecting surface M4 and the RP2 is the radius of cur
`vature of the incident surface R3 of the second refract
`ing member P2.
`A light propagation direction from the left to the
`right is de?ned as a positive direction. A radius of cur
`vature of the convex surface facing in the left direction
`is de?ned as a positive radius of curvature, while a
`radius of curvature of the concave surface facing in the
`left direction is de?ned as a negative radius of curva
`ture. A medium has a positive refractive index when
`light propagates in the positive direction. However,
`when light propagates in the negative direction, a me
`dium has a negative refractive index.
`The Petzval sum of the second optical subsystem S2
`is given as follows:
`
`When a plurality of aplanatic refracting surfaces are
`formed in the optical system of the present invention,
`the Petzval sum for only the aplanatic refracting sur
`faces must be separately corrected. Still another feature
`of the present invention is to satisfy the following condi
`tiOn:
`
`k
`.21 (Nr - NO/RiNiNi' = o
`1:
`
`where Ri is the radius of curvature of the aplanatic
`refracting surface, Ni is the refractive index of the front
`space along the beam propagation direction, Ni’ is the
`refractive index of the rear space, and K is the number
`of aplanatic refracting surfaces in the entire optical
`system.
`Furthermore, the Petzval sum of the refracting and
`re?ecting surfaces excluding the aplanatic refracting
`surfaces must also be corrected. More particularly, this
`Petzval sum must satisfy the following condition:
`
`10
`
`15
`
`20
`
`L
`_21 (Ni’ —- ND/riNiNi’ = 0
`1:
`
`where ri is the radius of curvature of the re?ecting and
`refracting surfaces excluding the aplanatic refracting
`surfaces, and L is the number of re?ecting and refract
`ing surfaces excluding the aplanatic refracting surfaces
`in the entire optical system.
`
`35
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a diagram of a re?ection type reduction
`projection optical system according to a ?rst embodi
`ment of the present invention;
`FIG. 2 is a diagram of a re?ection type reduction
`projection optical system according to a second em
`bodiment of the present invention;
`FIG. 3 is a diagram of a re?ection type reduction
`projection optical system according to a third embodi~
`45
`ment of the present invention;
`FIG. 4 is a diagram of a re?ection type reduction
`projection optical system according to a fourth embodi
`ment of the present invention;
`FIG. 5 is a diagram of a re?ection type reduction
`projection optical system according to a ?fth embodi
`ment of the present invention;
`FIG. 6 is a diagram of a re?ection type reduction
`projection optical system according to a sixth embodi
`ment of the present invention;
`FIG. 7 is a diagram of a reflection type reduction
`projection optical system according to a seventh em
`bodiment of the present invention;
`FIG. 8 is a diagram of a re?ection type reduction
`projection optical system according to an eighth em
`bodiment of the present invention;
`FIG. 9 is an enlarged view showing part of the sys
`tem shown in FIG. 8;
`FIG. 10 is a diagram of a re?ection type reduction
`projection optical system according to a ninth embodi
`ment of the present invention; and
`FIG. 11 is an enlarged view showing part of the
`system shown in FIG. 10.
`
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`

`

`PZ2= l/RM4<O
`
`(3)
`
`As long as a telecentric arrangement at the image side is
`given, the second optical subsystem S2 has essentially a
`negative Petzval sum.
`The Petzval sum of the ?rst optical system S1 is given
`as follows:
`
`10
`
`4,812,028
`7
`8
`Substitution of equation (1) into equation (2) yields the
`?rst and second optical subsystems effectively corrects
`following:
`the curvature of ?eld.
`The numerical data of the ?rst embodiment are
`shown in Table 1. In the following tables including
`Table l, the radii of curvature, surface distances and
`refractive indices of the respective curved surfaces from
`the object plane 0 to the ?nal image plane I’ are listed.
`In the tables, the radii of curvature and the refractive
`indices of the respective surfaces are positive along the
`light propagation direction from left to right. In this
`manner, the positive and negative values of the radii and
`refractive indices are determined with reference to the
`predetermined light propagation direction. A medium
`has a positive surface distance when the light propaga
`tion direction is positive. However, when the light
`propagation direction is negative, a medium has a nega
`tive surface distance.
`
`(4)
`
`For simplicity, the radius of curvature of the ?rst re
`?ecting surface is the same as that of the third reflecting
`surface, i.e., RM1=RM3 is established. At the same
`time, the radius of curvatue of the second re?ecting
`surface is the same as that of the incident surface R1 of
`the ?rst refracting member, i.e., RM2=PR1 is estab
`lished. Under these conditions,
`
`PZ1= _4/RM1+2/RM2+(n- 1)/(n-RM2)
`
`(5)
`
`If the refractive index of the ?rst refractive member is
`given as n=l.5, the Petzval sum of the ?rst optical
`subsystem S1 is
`
`as long as the following condition is satis?ed:
`
`3O
`
`35
`
`When a magni?cation difference of 1.7 times or more is
`given for the radii RMl and RM2 of the ?rst and second
`re?ecting surfaces to allow reciprocal re?ection there
`between, the ?rst optical subsystem S1 has essentially a
`positive Petzval sum.
`Since the Petzval sums of the ?rst and second optical
`40
`subsystems have different signs, the total Petzval sum of
`the entire system can be corrected by combining the
`Petzval sums of the ?rst and second optical subsystems.
`More particularly, the radii of curvatures of the ?rst
`and second optical subsystems are selected such that a
`sum PZT of the petzuel sum PZ2 of the second optical
`subsystem which is given by equation (2) and the Petz
`val sum PZl of the ?rst optical subsystem which is
`given by equation (4) is set to zero, thereby completely
`correcting the total Petzval sum of the entire system:
`
`45
`
`As is apparent from the above theory, the ?rst and
`second optical subsystems, independently, have their
`own reduction factors in principle, and these subsys
`tems are combined to cancel the Petzval sums. As a
`result, the total Petzval sum of the entire system can be
`properly corrected. This can also be understood from
`FIG. 1. According to light rays representing a conju
`gate relationship between the object point and the
`image point in FIG. 1, the focusing point of the ?rst
`optical subsystem S1 is in a plane slightly deviated from
`the ideal image plane I and not perpendicular to the
`optical axis. However, the focusing point of the second
`optical subsystem lies on the image plane I’ which is
`substantially perpendicular to the optical axis. It can
`thus be readily understood that a combination of the
`
`60
`
`65
`
`TABLE 1
`First Embodiment)
`Surface
`Distance
`
`Radius of Curvature
`
`Ob'ect Plane 0
`M‘
`100.000
`M2
`50.000
`M3
`100.000
`R1
`50.000
`R1
`in
`[Image Plane I!
`M4
`— 150.000
`R3
`—~50.000
`R4
`co
`(Image Plane I’)
`
`— 100.000
`50.000
`— 50.000
`50.000
`50.000
`0.000
`150.000
`— 100.000
`—50.000
`0.000
`
`No.
`
`1
`2
`3
`4
`5
`
`6
`7
`8
`
`PZl = 0.00667 PZ2 = —0.00667
`PZT = PZl + PZ2 = 0.000
`
`Refractive
`Index
`
`— 1.000
`1.000
`— 1.000
`1.000
`1.500
`1.000
`1.000
`—1.000
`—1.500
`— 1000
`
`51
`
`S2
`
`It is apparent that the total Petzval sum is completely
`corrected by a combination of the ?rst and second opti
`cal subsystems S1 and S2.
`FIG. 2 shows a basic con?guration of a reflection
`type reduction projection optical system according to a
`second embodiment of the present invention. The same
`reference numerals in the second embodiment denote
`the same parts as in the ?rst embodiment. According to
`the second embodiment, each of ?rst and second re
`fracting members P1 and P2 comprises a group of sepa
`rate or joined, refracting members to improve chro
`matic aberration. In the optical system of the present
`invention, since the re?ecting unit has a high power, it
`is easy to eliminate chromatic aberration when a system
`is designed with consideration for chromatic aberration.
`The refracting and re?ecting surfaces of the optical
`system are monocentrically arranged, and ?at refract
`ing surfaces are substantially coincident with an image
`plane perpendicular to the optical axis and including the
`monocentric center. Chromatic aberration on the opti
`cal axis will not substantially occur irrespective of scat
`tering by the respective refracting members. Therefore,
`it is essential to correct chromatic aberration in magni?
`cation factors. The arrangement of the second embodi
`ment of FIG. 2 aims at properly correcting chromatic
`aberration in magni?cation factors. For this purpose,
`the ?rst refracting member P1 comprises a monocentric
`meniscus lens member P11 and a positive lens member
`P12 located slightly distant from the lens member P11.
`The second refracting member P2 comprises a mono
`centric meniscus lens member P21 and a positive lens
`member P22 combined therewith. The optical system
`arrangement is not limited to that illustrated in FIG. 2,
`
`CARL ZEISS V. NIKON
`IPR2013-00362
`Ex. 2007, p. 13
`
`

`

`4,812,028
`
`9
`but can be extended to an arrangement wherein two or
`more refracting members are separated or combined to
`provide each of predetermined ?rst and second refract
`ing members. In order to correct chromatic aberration,
`the separation surfaces and contact surfaces of the re
`fracting members need not be monocentric. In the fol
`lowing embodiment, monochromatic light is exempli
`?ed for simplicity since chromatic aberration can be
`independently corrected if a proper focusing property
`for the reference light ray is guaranteed. Chromatic
`aberration is not speci?cally considered.
`In an arrangement of a third embodiment shown in
`FIG. 3, a monocentric meniscus lens member L1 is
`inserted between an object plane 0 and a ?rst re?ecting
`surface M1 of a ?rst optical subsystem. A convex sec
`ond re?ecting surface M2 constitutes the rear re?ecting
`surface of the same member as the meniscus lens mem
`ber L1. In the basic arrangement described with refer
`ence to FIG. 1, the meridional image plane is curved
`due to high-order aberration. However, by employing
`the monocentric meniscus lens member of the third
`embodiment, the curvature of the meridional image
`plane can be greatly decreased.
`In an arrangement of a fourth embodiment shown in
`FIG. 4, a monocentric meniscus lens member L2 is also
`arranged between a fourth re?ecting surface M4 of a
`second optical subsystem S2 and an object plane 0' (Le,
`an image plane I of a ?rst optical subsystem S1) of the
`second optical subsystem S2. The meniscus lens mem
`ber L2 has the same radius of curvature as that of a
`monocentric incident refracting surface R3 of a second
`refracting member P2. By adding the meniscus lens
`member L2 to obtain the arrangement of the fourth
`embodiment, the object point and the image point can
`be formed near the optical axis without causing eclipse.
`In general, a good image can be obtained in a coaxial
`optical system when the object and image points are
`formed near the optical axis. Therefore, focusing can be
`greatly improved.
`Numerical data of the fourth embodiment are shown
`in Table 2 below. The same denotation as in Table l is
`employed in Table 2. In the respective optical subsys
`tems, the contact surfaces between refracting members
`45
`P1 and P2 and meniscus lens members L1 and L2 are
`TABLE 2
`{Fourth Embodiment!
`Radius of
`Surface
`Curvature
`Distance
`{Object Plane 0!
`—66.667
`L1
`66.667
`—24.242
`L1
`90.909
`—96.591
`M1
`187.500
`96.591
`90.909
`24.242
`66.667
`--24.242
`90.909
`_ 96.591
`187.500
`96.591
`M3
`90.909
`90.909
`R1
`an
`0.000
`R;
`{Image Plane I!
`40.000
`L;
`—40.000
`10.000
`L2
`- 50.000
`100.000
`M4
`— 150.000
`—-100.000
`R3
`— 50.000
`— 50.000
`0.000
`
`20
`
`25
`
`30
`
`Refractive
`Index
`—1.000
`— 1.500
`— 1.000 '
`1.000
`1.500
`— 1.500
`—1.000
`1.000
`1.500
`1.000
`1.000
`1.500
`1.000
`—1.000
`— 1.500
`—1.000
`
`S1
`
`55
`
`S2
`
`60
`
`65
`
`10
`It is apparent that the total Petzval sum is completely
`corrected by a combination of the ?rst and second opti
`cal subsystems.
`In an arrangement of a ?fth embodiment shown in
`FIG. 5, the respective concave re?ecting surfaces of
`?rst and second optical subsystems serve as rear re?ect
`ing surfaces. With this arrangement, spherical aberra
`tion of a higher order caused by an out-of-axis pencil
`can be effectively corrected.
`In an arrangement of a sixth embodiment shown in
`FIG. 6, a third optical subsystem S3 having a magni?ca
`tion factor of 1 is added to the arrangement of FIG. 4.
`All re?ecting and refracting surfaces of the third optical
`subsystem S3 are substantially monocentrically ar
`ranged. A monocentric center C’ of these re?ecting and
`refracting surfaces is located at a position optically
`equivalent to a monocentric center of a re?ection type
`reduction system. More particularly, the third optical
`subsystem S3 has a concave ?fth re?ecting surface MS,
`a convex sixth reflecting surface M6 and a concave
`seventh re?ecting surface M7. In order to provide a
`margin for aberration correction, monocentric meniscus
`lens members L3 and L4 are arranged in the third opti
`cal subsystem S3. With this arrangement, the third opti
`cal subsystem S3 has a positive Petzval sum while the
`second optical subsystem S2 essentially has a negative
`Petzval sum. At the same time, the ?rst optical subsys
`tem S1 has a positive Petzval sum, thereby correcting
`the total Petzval sum of the entire system. A slight
`distortion occurs in the arrangement of FIG. 4 How
`ever, in the arrangement of the sixth embodiment, the
`optical surfaces along the forward path are asymmerti
`cal along the path in the third optical system S3, thereby
`decreasing the distortion.
`Numerical data of the sixth embodiment are given in
`Table 3. This table employs the same denotation as
`Table 2. The flat re?ecting mirror is not essential in
`optical design.
`
`'
`No.
`
`1
`2
`3
`4
`5
`6
`7
`8
`9
`
`10
`11
`12
`13
`14
`15
`16
`17
`18
`
`19
`20
`21
`22
`23
`
`M6
`
`TABLE 3
`{Sixth Embodiment)
`Radius of
`Surface
`Curvature
`Distance
`{Object Plane 0Q!
`74.500
`L3
`—74.500
`30.500
`L3
`- 105.000
`167.000
`M5
`—272.000
`-167.000
`—l05.000
`—15.000
`-90.000
`15.000
`-105.000
`167.000
`—272.000
`—167.000
`M7
`—105.000
`—1S.000
`L4
`— 90.000
`— 90.000
`L4
`{Image Plane IQ!
`—90.000
`L1
`90.000
`—15.000
`L1
`105.000
`—93.947
`M1
`198.947
`93.947
`105.000
`15.000
`90.000
`—15.000
`105.000
`—93.947
`198.947
`93.947
`M3
`105.000
`105.000
`R1
`00
`0.000
`R1
`{Image Plane I!
`40.000
`L2
`—40.000
`10.000
`L2
`— 50.000
`100.000
`M4
`—150.000
`—100.000
`R3
`— 50.000
`— 50.000
`R4
`m
`0.000
`(Image