High resolution reduction catadioptric relay lens

An optical system of a NX reduction catadioptric relay lens having sub-half micron resolution over the utlraviolet band width is described. A spherical mirror with a stop at the mirror is used to work at substantially the desired reduction ratio and the desired high numerical aperture sufficient to provide the desired high resolution. A beam splitting cube with appropriate coatings is used to form an accessible image of an object on an image plane. Refracting correctors in the path of the slow beam incident on the mirror and in the path of the fast beam reflected on the mirror are designed to fix the aberrations of the image formed by the mirror. The beam splitter coatings are chosen in such a way that beams reflected from and transmitted therethrough suffer no net aberration as a result of multiple reflections within the thin film beam splitter coatings and therefore are substantially free of aberration, distortion and apodization which would result from the beam splitting surface in the absence of these coatings.

CROSS REFERENCE TO A RELATED APPLICATION 
U.S. application Ser. No. 07/185,187 filed Apr. 22, 1988 now U.S. Pat. No. 
4,896,952 entitled "Thin Film Beam Splitter Optical Element For Use In An 
Image-Forming Lens System" to A. E. Rosenbluth describes a beam splitter 
optical element, including a triangular substrate, such as a prism having 
a plane face corresponding to the hypotenuse of the prims which is coated 
with a thin film structure having materials and thickness, which effect 
the division of each light beam such as into a reflected and transmitted 
portion in such a way, that the beam suffers no net aberration as a result 
of multiple reflection in the thin film structure and a second triangular 
substrate, such as a prism having a plain face, corresponding to the 
hypotenuse, optically bonded to the thin film structure deposited on the 
hypotenuse of the first prism. 
FIELD OF THE INVENTION 
This invention relates to a catadioptric relay lens, particularly to a high 
resolution reduction catadioptric relay lens containing a beam splitting 
surface and a curved reflecting surface, more particularly to a 4.times. 
and a 5.times. reduction catadioptric relay lens having a sub-micron 
resolution at ultra-violet wavelengths. 
BACKGROUND OF THE INVENTION 
In the fabrication of microelectronic components, for example, 
semiconductor chips and semiconductor chip packaging substrates, increase 
in performance is generally achieved by reducing the image size of the 
electronic devices on the chips and by reducing the width and spacing of 
the electrical conductors of the wiring planes of the semiconductor chip 
and semiconductor chip packaging substrate. Reduced image size and spacing 
is achievable by using improved optical systems to project higher 
resolution images. 
Generally, an optical system for fabricating an electronic component has a 
mask containing a pattern at the input of the optical system through which 
light of a preselected frequency is passed. The optical system contains a 
component, typically a lens to reduce the size of the patterns in the mask 
which is projected as a reduced image onto the surface of an electronic 
component. A reduction system is used to reduce the width and spacings of 
the patterns on the mask. The image is typically projected onto a resist 
material on the surface of the electronic component. The light projected 
onto the resist material causes a chemical change therein which either 
renders the exposed regions soluble or insoluble with respect to the 
un-exposed regions of the resist. The soluble regions are removed by 
exposing the resist to a solvent leaving a pattern which is either the 
positive or negative image of the mask reduced in size. 
The reducing system is used to reduce the size of the patterns on the mask 
and to demagnify imperfections in the structure. The use of an optical 
system for producing a reduced image on the mask introduces distortions 
referred to as aberrations which are inherent in the optical components of 
the system. 
Prior art reduction systems employed in tools known as steppers use a 
series of lenses to reduce the mask image and to correct the various 
commonly known aberrations of an optical system. However, the applicants 
have discovered that by using a curved mirror to provide the predominant 
fraction of the reducing power of the optical system, the inherent 
aberrations of the optical system can be corrected more effectively and 
with fewer optical components. 
The preferred curved surface is a concave spherical mirror. A problem with 
using a spherical mirror in place of a lens for reducing the mask size is 
that the projected image of the mask is reflected back from the mirror 
towards the direction of the mask. Such an image cannot be easily used 
since the substrate on which the image is to be projected must be placed 
in the path of the optical beam which is incident on the spherical 
surface. This effectively prevents a useful image from being formed using 
the full field of the mirror. Therefore, such systems typically use 
reflecting surfaces to split the mirror field of view, into a field for 
the object being focused and a field for the substrate on which the image 
of the object is focused. In such systems the size of the substrate object 
being imaged is constrained since the object and the image can only occupy 
one half the total field of the focusing mirror. The field of the focusing 
mirror is that region of an object or image field, over which the mirror, 
in conjunction with the remainder of the optical system, can properly form 
images. 
Applicants have discovered that by using an appropriate beam splitting 
surface the output beam can be directed away from the input beam so that 
the output beam can be used to project an image onto a substrate. 
The beam transmitted through and reflected from the beam splitting surface 
must be substantially free of distortion, aberration and apodization as a 
result of passing through or being reflected from the beam splitting 
surface. Beam splitting surfaces suitable for the optical systems of the 
present invention are described in U.S. patent application Ser. No. 
07/185,187 filed on Apr. 22, 1988 now U.S. Pat. No. 4,896,952 entitled 
"Thin Film Beam Splitter Optical Element For Use In An Image-Forming Lens 
System" to A. E. Rosenbluth, the teaching of which is incorporated herein 
by reference. 
U.S. Pat. No. 4,444,464 to Minott describes a catadioptric optical system 
having two symmetrically aligned off-axis Schmit optical objectives. 
Incident light is reflected from two primary spherical mirrors off the 
axis of the incident light. The light from each mirror is reflected from a 
beam splitter which separates the light into a plurality of spectral 
bands. 
U.S. Pat. No. 4,694,151 describes a mirror free auto focus system having a 
half mirror prism and a sensor capable of detecting light in conjunction 
with the half mirror prism inserted between the front lens and rear lens 
group of the lens system. 
U.S. Pat. No. 4,311,366 describes an image focusing system free of curved 
mirrors for use in a reprographic camera containing a flat mirror or prism 
or roof prism for folding an input beam. The input beam and output beam 
pass through lens combinations providing focusing and aberration 
correction. 
U.S. Pat. No. 4,265,529 describes a view finder for a camera including an 
input lens, a flat reflecting mirror, a roof type pentagonal mirror and an 
eye piece. 
U.S. Pat. No. 3,536,380 describes a 1.times. catadioprtric projection 
system for semiconductor chip photolithographic applications. Light is 
directed through a lens, through a mask, onto a half silvered mirror from 
which it is reflected through a lens onto a concave mirror from which it 
reflects onto the target substrate. 
U.S. Pat. No. 4,387,969 describes an optical system having an objective 
lens group, a beam splitting prism which deflects light at a right angle 
through a lens to focus an image on a film. 
U.S. Pat. No. 2,166,102 describes a telescope having an objective lens and 
using a prism or a plane mirror to reflect light at an angle to a concave 
mirror. 
U.S. Pat. No. 3,001,448 describes a system using a beam splitter for 
correcting astigmatism produced by a shallow dome by introducing positive 
stigmatism by using rotating prism. 
U.S. Pat. No. 4,742,376 describes a step and repeat system which uses a 
Dyson-Wynne catadioptric projection system. 
U.S. Pat. No. 4,743,103 describes a lens system for a photographic printer 
which rotates the image through 90 degrees without effecting the inversion 
needed in a printer lens. 
It is an object of this invention to provide an optical projection system 
with an extended field which will faithfully reproduce submicron 
geometries over a large substrate area. 
It is another object of this invention to provide a substantially 
telecentric reduction catadioptric relay lens with diffraction limited 
performance over the ultraviolet bandwidth, most preferably of an excimer 
laser. 
It is another object of the invention to exploit the very sensitive deep UV 
resists and highly intense excimer laser beams for the optical 
microlithography for microelectronic integrated circuits by sacrificing 
net transmittance of the optical system which is a consequence of 
employing the beam splitting technique to form an accessible and useful 
image. 
It is another object of this invention to extend the limits of optical 
microlithography to quarter micron resolution by employing a high 
numerical aperture with partially coherent illumination of the mask 
improving the recordability of the image due to the resulting enhancement 
of contrast beyond the limit of 48% for incoherent illumination in the 
case of aberration free in focus lens at a numerical aperture of 0.6. 
These and other objects, features and advantages will be apparent from the 
following more particular description of the preferred embodiments and the 
figures appended thereto.

SUMMARY FO THE INVENTION 
In its broadest aspect the present invention is a catadioptric rela lens 
system. 
In a more specific aspect of the present invention, the lens system is a 
reduction system. 
Another more specific aspect of the present invention is an optical system 
containing an optical element formed from a material capable of supporting 
propagation of image forming beams of radiation. The optical element has 
at least one substantially planar surface. A plurality of thin film 
coatings are disposed on the substantially planar surface to provide a 
beam, reflected from the surface or transmitted through the surface which 
is substantially free from aberration, distortion and apodization due to 
reflection from and transmission through the surface. The system also 
contains a concave reflective surface for receiving a beam reflected from 
or transmitted through the substantially planar surface. The system 
contains an input and output lens group to substantially correct for 
aberrations arising from reflection at the concave reflective surface. 
In another more particular aspect of the present invention, an input beam 
reflects off the substantially planar surface to a concave reflective 
surface from which it is reflected back through the substantially planar 
surface and focused at the output onto a target. 
In another more particular aspect of the present invention, the input beam 
passes through the substantially planar surface onto the concave 
reflective surface from where it is reflected back to the substantially 
planar surface from which it is reflected off the axes of the input beam 
and focused at the output onto a target. 
In another more particular aspect of the present invention, the optical 
system is NX reduction where N is greater than one. 
In another more particular aspect of the present invention, the optical 
system is a mask projection system for projecting and reducing a 
predetermined pattern in the mask onto a target substrate. 
In another more particular aspect of the present invention, the optical 
system has sub-micron resolution over the total ultraviolet bandwidth, in 
particular the ultra-violet bandwidth of an excimer laser. 
In another more particular aspect of the present invention, the plurality 
of thin film coatings are composed of materials having substantial uniform 
thickness over the substantially planar surface to produce a 
self-compensating phase distribution and a self-compensating amplitude 
distribution in the beam reflected from the substantially planar surface 
and in the beam transmitted through the substantially planar surface, the 
resulting phase and amplitude distributions of the beam reflected from and 
transmitted through are then substantially free from distortion, 
aberration and apodization. 
These and other objects, features and advantages will become apparent from 
the following more particular description of the preferred embodiments and 
the figures appended thereto. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a schematic representation of the optical system according to 
the present invention. 
The apparatus of FIG. 1 has an input axes 2 and an output axes 4 which are 
not colinear; in the preferred embodiment axes 2 and 4 are perpendicular. 
Radiation is directed along input axes 2 towards an object 6 to be imaged 
at target 8. The radiation is preferably ultraviolet light, most 
preferably the output of KrF excimer laser operating at 248 nm wavelength. 
In the preferred embodiment of the present invention object 6 to be imaged 
is a mask having regions transparent and regions opaque in a predetermined 
pattern to the radiation incident along the input axes 2. Radiation 10 
passing through object 6 is incident on substantially planar surface 12 
which transmits a fraction of the incident light and reflects a fraction 
of the incident light represented by 14 towards a concave reflective 
surface 16 which is the aperture stop of the optical system. Beam 14 
reflects off of surface 16 as radiation 18 along the output axes 4 to be 
focused upon target 8. In the preferred embodiment target 8 is an 
electronic component, for example, a semiconductor chip or a semiconductor 
chip packaging substrate having thereon a resist material. The image of 
the mask 6 is focused upon the resist material at target 8 forming an 
exposed pattern in the resist. Depending upon whether the resist is a 
positive or a negative resist, the exposed regions are either made soluble 
or insoluble with respect to the unexposed regions. In the preferred 
embodiment the exposed regions or the image of the mask has submicron 
resolution, preferably in the sub-half-micron range, most preferably in 
the 0.25 micron range. To achieve such fine resolution in the projected 
image distortions, aberrations and apodization introduced into beam 14 
reflected from surface 12 and beam 18 transmitted through surface 12 must 
be substantially eliminated. This is achieved by using thin film coatings 
20 disposed on surface 12. A surface having thin film coatings thereon 
useful to practice the present invention are described in U.S. patent 
application Ser. No. 07/185,187 to Rosenbluth, the teaching of which is 
incorporated herein by reference. Rosenbluth provides a thin film 
structure that divides an incident beam into a beam reflected from the 
thin film structure and into a beam transmitted through the thin film 
structure without introducing aberration, apodization or illumination 
nonuniformities in the image field. In the preferred embodiment, beam 
splitting surface 12 is contained within beam splitting cube 22 so that 
input axes 2 is substantially perpendicular to face 24 of cube 22 and so 
that output axes 4 is substantially perpendicular to face 26 of cube 22. 
For practical applications, there is a need for lithographic lenses that 
operate with wave lengths as short as 248 nm or below. However, at 
wavelengths below 300 nm, it becomes more difficult to design lithographic 
imaging systems whose only elements are conventional transparent lenses, 
due to material limitations. 
Beam splitter optical element 22 contains a prism 26 whose hypotenuse face 
30, is coated by conventional processes with a thin film structure having 
materials of thicknesses, determined by means disclosed in the application 
of Rosenbluth, incorporated by reference herein above, which affect the 
desired division of each light beam such as 10 into a reflected portion 14 
and a transmitted portion 18 in such a way that the beams suffer no net 
aberration as a result of multiple reflections within the thin film 
structure. A second substrate, such as prism 28 whose face 32 
corresponding to the prism hypotenuse, is bonded through conventional 
means to the thin film structure disposed on the hypotenuse of prism 26 to 
form beam splitting optical element 22. 
Most dividing films will introduce significant variations across the 
angular divergence of beams such as 10, due to the intrinsic angular 
dependence of the optical properties of thin films. This angular 
dependency is most pronounced when the films are tilted relative to the 
central axes 2 of the beam. Beam 10 is projected from object 6 to prism 
face 32. A reflected portion 14 of beam 10 is then propagated to mirror 
surface 16. The fraction of the beam that is reflected in this pass will 
be referred to as the first-pass beam splitter efficiency. 
After being focused, beam 10 is again incident for a second pass at the 
thin film coating on prism face 32. The portion of incident beam 10 that 
is transmitted during this second pass is then focused to an image 34 on 
the substrate 8. The efficiency of this pass is equal to the transmitted 
fraction. Substrate 8 may be large enough to fully occupy the field of 
view of reflecting surface 16, rather than merely half the field as with 
reflecting mirrors in the prior art apparatus. 
Thin film structure 20 forming the beam splitting surface must be tilted to 
divert incident beam 10 from the input axes 2 along the output axes 4. 
However, any tilts at entrance face 24 or exit face 26 of beam splitting 
element 22 will introduce aberrations in the imaging beams. Thus, in the 
preferred embodiments faces 24 and 26 are parallel to the object being 
imaged 6 and to the substrate on which the image is being projected 8 
respectively so that the beam splitter element 22 forms a unitary 
structure with the spape of a cube in the preferred embodiment. 
The input side of the apparatus schematically shown in FIG. 1 is from 
object plane to curved reflecting surface 16. The output side of the 
apparatus is from surface 16 to image plane 8. Rectangle 7 of FIG. 1 
represents optical elements, such as lenses, which can be anywhere on 
there input side and rectangle 9 represents optical elements which can be 
anywhere on the output side. The optical elements represented by 7 and 9 
correct for aberrations introduced by the optical elements, the curved 
surface 16 and the beam splitting element 22. 
FIG. 2 is a specific embodiment of an optical design of a 5.times. optical 
reduction catadiotric relay lens having sub-micron resolution over the 
total ultra-violet bandwidth of an excimer laser. A spherical primary 
mirror with a stop at the mirror is used to work at substantially the 
desired reduction ratio and the desired high numerical aperture sufficient 
to provide substantially the desired high resolution. A beam splitting 
cube of fused silica with appropriate coatings is provided to form an 
accessible image of an object which represents a mask used to pattern a 
wafer located at the image. Refracting correctors in the path of the slow 
incident beam on the mirror and also in the path of the fast reflected 
beam from the mirror are designed to fix the aberrations of the image 
formed by the mirror. 
The spherical concave mirror 50 is used at conjugates giving substantially 
the desired reduction ratio of 5 with field flatting provided by separate 
refractive correctors placed in the proximity of the object plane 52 and 
image planes 54. Lenses 56, 58, 60, 62 and 64, form an air space 
refracting group 66 on the long conjugate side 68 of mirror 50. Air space 
refracting group 66 is complemented by compact compound field corrector 
group 70 on the short conjugate side 72 of mirror 50. Field corrector 
group 70 is made up of lens 74 and 76. The lens combination 66 on the 
input axes and lens combination 70 on the output axes correst for field 
curvature of the mirror 50. Spherical aberration arising at reflection on 
the mirror 50 is corrected by providing separate compound correctors 78 on 
the input axes 68 and 80 on the output axes 72. Corrector 78 is made up of 
lens 82 and 84. Corrector 80 is made up of lens 86 and 88. 
The substantially symmetrical disposition of correctors 66, 78 on the input 
axes 78 and correctors 70 and 80 on the output axes about the mirror 50, 
which is also used as a stop, allows excellent coma correction of the 
optical system. The optical system is designed with beam splitting cube 90 
in its path to permit the image forming beams of light to clear the 
incident beam on the mirror thereby requiring a two pass use on the 
optical path in the glass of the beam splitting cube. Without this 
arrangement, there will always be present an obstruction in the pupil 
which is not recommended to be used in optical microlithography 
principally on account of variation in the size of obstruction with field 
leading to non-uniform exposure dose falling on the silicon wafer. 
The design of FIG. 2 has a high numerical aperture of approximately 0.6. 
This permits a high resolution reaching a quarter micron resolution. 
However, the field of the object 52 covered depends on the scale on which 
the beam splitting cube 90 and thin film coatings on beam splitting 
surface 92 may be successfully fabricated. 
Table 1 lists the preferred constructional parameters of the embodiment of 
FIG. 2 for a 5.times. reduction catadioptric relay lens having numerical 
aperture of 0.6 at the output and a circular field on the image side 52 of 
diameter 14.4 millimeters sufficient to cover a one square centimeter 
area. Table 1 lists the surfaces shown in FIG. 2, the radius of a 
curvature of the surface in millimeters. The thickness or separation from 
one surface to the next surface and the index of refraction between these 
surfaces, for example the spacing between surface 100 and 101 is 2.6936 
millimeters and the index of refraction between surfaces 101 and 102 is 
1.508807. Table 1 also lists one half the diameter of each refracting 
surface. 
TABLE 1 
__________________________________________________________________________ 
Index 
of One Half 
Radius Refraction 
Diameter of 
Curvature 
Thickness 
n = 1.5085507 
Surface 
Surface 
mm mm a = 1.0 mm 
__________________________________________________________________________ 
Mask 100 2.6936 
a 36.0 
101 416.1907 
15.6 n 36.8 
102 -352.6095 
0.1 a 37.9 
103 216.3507 
9.9996 
n 38.4 
104 -9143 100 a 38.4 
105 165.0775 
6.0 n 37.5 
106 -141.8095 
6.4339 
a 37.8 
107 -544.5087 
9.0 n 37.5 
108 276.6342 
158.9991 
a 37.5 
109 -106.1731 
5.0 n 48.2 
110 -221.0308 
95.9982 
a 50.5 
111 7177.482 
15.0 n 71.4 
112 -235.2796 
3.0 a 71.9 
113 -253.3041 
15.0 n 72.0 
114 -367.28 
18.0 a 74.0 
Cube Face 
115 75.0 n 
Cube Diagonal 
116 75.0 n 
Cube Face 
117 24.0 a 
Mirror 118 322.0703 
24.0 a 88.0 
Cube Face 
119 75.0 n 
120 -267.7909 
15.0 n 44.1 
121 -313.664 
1.0 a 41.1 
122 80.2329 
16.4981 
n 36.6 
123 328.6877 
5.8627 
a 32.7 
124 110.6656 
18.0 n 27.9 
125 56.8994 
4.8224 
a 19.3 
126 65.4243 
18.0 n 17.3 
127 -425.502 
1.5 a 10.3 
128 -212.3753 
3.0 n 9.2 
129 -756.9179 
.7043 
a 7.8 
Target 130 
__________________________________________________________________________ 
The kinds of glasses used in constructing lenses of the optical system 
according to the present invention hardly have limitations. Glasses must 
only transmit well at the wavelengths desired for the specific 
application. The design of FIG. 2 and Table 1 is for a wavelength of 248 
mm and all lenses are made of fused silica. However, the lenses may be 
achromatised in the usual manner by adding glasses of differing 
dispersions to the field correcting and spherical aberration correcting 
lens groups and in applications where such a choice of glass exists. 
The size of the field achievable by the embodiment of FIG. 2 and Table 1 
enables its use primarily in the tools of optical microlithography known 
as steppers but does not prevent it from being applied in scanners of the 
ring field type or of the slot field type and will actually be of 
significant importance in the tools that combine stepping and scanning to 
print wafers of very large size. 
For the embodiment of FIG. 2 and Table 1, FIG. 3 gives the modulation 
transfer function as a function of spatial frequency for both tangential 
and sagittal features for three regions of the optical system: one at a 
point 132 where the input axes 68 intersects the object plane 100; another 
point at 0.7 of the full field away from the point 132 with input axes 68 
intersects the object plane 100; and, a third point at the full field away 
from the point where the input axes 68 intersects the object plane 100. As 
can be seen from FIG. 3 the modulation transfer function for the 
tangential and sagittal features at these three points are almost 
identical. 
In FIG. 4 the through focus MTF for the tangential and sagittal features at 
the three field points corresponding to modulation transfer functions 
plotted in FIG. 3 are shown for a MTF frequency of 2,000 cycles/mm. FIG. 5 
provides the through focus MTF for the same conditions at frequency of 
1,000 cycles/mm. As can be seen from FIGS. 4 and 5 there is little 
difference between the through focus MTF of the tangential and sagittal 
features for the three points plotted. 
FIG. 6 and Table 2 show another embodiment of an optical design of a 
5.times. reduction catadioptric relay lens having submicron resolution 
over the total band width of a line narrowed deep UV excimer laser, for 
example, a KrF laser. The embodiment consists of a concave mirror and a 
beam splitting cube with appropriate coatings to produce accessible images 
of an object, such as a mask, with refracting correctors having certain 
preferred features of curvature relationship in both the slow incident 
beam to the mirror and the fast image forming beam reflected from the 
mirror, all of which cooperate to produce the highly corrected images with 
submicron features over an extended field. The constructional parameters 
of the embodiment of FIG. 6 and Table 2 have a numerical aperture of 0.6 
for a circular field of diameter 30.0 mm sufficient to cover a 20 mm.sup.2 
image field. FIG. 7 is a plot of the MTF as a function of frequency for 
the embodiment of FIG. 6. FIG. 8 is a plot of through focus MTF at a 
frequency of 1,500 cycles/mm for the embodiment of FIG. 6. FIG. 9 is a 
plot of through focus MTF at a frequency of 2,000 cycles/mm for the 
embodiment of FIG. 6. FIG. 7, FIG. 8, and FIG. 9 plot the MTF for the 
tangential and sagittal features for a point on 201 axis, where the input 
axis 142 intersects the object plane, for a point at 0.7 of the full half 
field away from the point 201 and for a point at on axes the full half 
field of 15 millimeters. The off-axes values are given for both tangential 
and sagittal lines resulting in five curves in each of the plots of FIG. 
7, FIG. 8 and FIG. 9. In FIG. 7 the five curves are essentially 
indistinguishable. In FIG. 8 curve 300 corresponds to the on axis 
tangential and sagittal features, curve 302 corresponds to the sagittal 
feature at 0.7 of the full field, curve 304 corresponds to the tangential 
feature at 0.7 of full field, curve 306 corresponds to the tangential 
feature at full field and curve 308 corresponds to the sagittal feature at 
full field. In FIG. 9 curve 310 corresponds to the on axis tangential and 
sagittal features, curve 312 corresponds to the sagittal feature at 0.7 of 
full field, curve 314 corresponds to the tangential features at 0.7 of 
full field, curve 316 corresponds to the tangential features at full field 
and curve 318 corresponds to the sagittal features at full field. 
TABLE 2 
__________________________________________________________________________ 
Index 
of One Half 
Radius Refraction 
Diameter of 
Curvature 
Thickness 
n = 1.5085507 
Surface 
Surface 
mm mm a = 1.0 mm 
__________________________________________________________________________ 
Mask 200 114.6494 
a 75.1 
201 1792.5223 
19.0019 
n 81.9 
202 -866.1057 
0.0050 
a 82.3 
203 322.7983 
24.9952 
n 82.1 
204 612.9103 
94.9297 
a 80.1 
205 -365.5172 
20.9984 
n 73.7 
206 272.002 
26.1477 
a 74.4 
207 180.1773 
20.9943 
n 80.8 
208 162.6329 
26.7939 
a 79.4 
209 222.2809 
35.0014 
n 84.3 
210 -382.3895 
0.0034 
a 84.3 
211 628.8815 
19.0011 
n 82.4 
212 176.4534 
97.4083 
a 78.3 
213 1180.4521 
19.0039 
n 83.0 
214 -1466.00 
0.5012 
a 83.2 
215 165.2104 
19.8943 
n 83.0 
216 144.1937 
87.6403 
a 78.9 
Cube Face 
217 85.00 n 
Cube Diagonal 
218 85.00 n 
Cube Face 
219 0.00 a 
220 20.0 n 
221 727.5375 
7.4995 
a 85.0 
Mirror 222 354.6364 
7.4995 
a 83.9 
221 727.5375 
20.0 n 85.0 
220 0.00 a 
Cube Face 
219 85.00 n 
Cube Diagonal 
218 85.00 n 
Cube Face 
223 1.00 a 37.4 
224 60.0903 
9.5832 
n 33.2 
225 112.4998 
0.1 a 31.4 
226 59.7906 
4.9017 
n 29.4 
227 47.6875 
5.6044 
a 26.5 
228 102.4535 
7.511 n 26.0 
229 -602.3941 
1.000 a 24.5 
230 -388.6705 
19.6132 
n 23.9 
231 -578.1068 
0.5 a 15.5 
Target 232 
__________________________________________________________________________ 
The kinds of glass used in constructing the embodiment of FIG. 6 hardly 
have limitations except that they must transmit well at the wavelengths 
desired for the specific application. The design is shown for a wavelength 
of 248 nm and all lenses are made of fused silica in the embodiment of 
Table 2. However, they may be achromatised in the usual manner by adding 
glasses at different dispersions to the field correcting and the spherical 
aberration correcting lenses in applications where such a choices of glass 
exists. It is expected that such use will favorably influence the 
achievable performance of designs embodying the present invention. 
FIG. 10 and Table 3 show another embodiment of the optical system of FIG. 
1. FIG. 10 and Table 3 show a 4.times. reduction catadioptric relay lens 
having sub micron resolution over the total UV bandwidth of an excimer 
laser, for example, a KrF laser. The construction and parameters of the 
embodiment of FIG. 10 and Table 2 have a numerical aperture of 0.6 for a 
circular field of diameter 30 mm sufficient to cover a 2.0 mm.sup.2 image 
field. The MTF through frequency and through focus, for the embodiment of 
FIG. 10 is similar to that shown for the embodiments of FIG. 2 and FIG. 6. 
TABLE 3 
__________________________________________________________________________ 
Index 
of One Half 
Radius Refraction 
Diameter of 
Curvature 
Thickness 
n = 1.5085507 
Surface 
Surface 
mm mm a = 1.0 mm 
__________________________________________________________________________ 
Mask 100 115.0 a 60.1 
301 370.2948 
30.0 n 67.9 
302 -196.6212 
2.0 a 67.6 
303 -195.9992 
21.0 n 67.1 
304 281.8649 
104.0 a 66.3 
305 -111.9241 
21.0 n 72.7 
306 -100.9789 
7.5 a 76.7 
307 -97.6046 
21.0 n 76.5 
308 -189.1799 
2.0 a 88.9 
309 -649.7924 
34.0 n 93.4 
310 -159.9606 
104.0 a 95.5 
311 3078.1555 
28.0 n 91.7 
312 -455.0276 
12.0 a 91.2 
313 -238.3554 
19.0 n 90.7 
314 -407.0824 
2.0 a 91.7 
315 204.3396 
18.0 n 90.1 
316 170.3065 
53.0 a 86.1 
Cube Face 
117 85.0 n 
Cube Diagonal 
318 85.0 n 
Cube Face 
319 0 a 
320 20.0 n 
321 825.0556 
7.5 a 84.5 
Mirror 322 383.2405 
7.5 a 84.7 
321 825.0556 
20.0 n 84.5 
320 0 a 
Cube Face 
319 85.0 n 
Cube Diagonal 
318 85.0 n 
Cube Face 
323 1.0 a 
324 56.5102 
12.0 n 34.5 
325 387.1705 
0.25 a 33.7 
326 -229.1068 
5.0 n 32.8 
327 44.8281 
6.2 a 26.9 
328 46.1373 
7.5 n 25.1 
329 52.1721 
2.0 a 22.6 
330 64.1946 
19.6 n 22.2 
331 526.9378 
0.5991 
a 15.3 
Target 332 
__________________________________________________________________________ 
The embodiment of FIG. 11 having constructional parameters of Table 4 and 
the embodiment of FIG. 12 having constructional parameters of Table 5 
incorporate Mangin mirrors 440 and 550 respectfully. The Mangin mirror (3) 
is used at conjugates giving substantially the desired reduction ratio of 
four. A air-spaced refracting group on the long conjugate side of the 
Magin mirror is complimented by a corrector group on short conjugate side 
of Mangin mirror. The optical system is designed with a beam splitting 
cube in its path to permit the image forming beam of light clear the beam 
incident on the Mangin mirror, thereby having a two pass use of the 
optical path in the glass of the beamsplitting cube. Without this 
arrangement, there will always be present an obstruction in the pupil 
which is not recommended to be used in optical microlithography 
principally on account of variation in the size of obscuration with field 
leading to a non-uniform exposure dose falling on the silicon wafer. A 
high resolution reaching quarter micron is achievable with the high 
numerical aperture of 0.6 of this design. 
For our present purposes, a Mangin mirror is taken to imply any meniscus 
lens concave towards the incident light with its rear surface coated with 
appropriate highly reflecting materials so that this surface acts as a 
mirror. A Mangin mirror with the stop at it mirror surface is used to work 
at substantially the desired reduction ratio and the desired high 
numerical aperture sufficient to provide substantially the desired high 
resolution. 
The embodiment of FIG. 11 and Table 4 is a 4.times. reduction catadiptric 
relay lens having submicron resolution in the UV bandwidth having a 
numerical aperture of 0.6 for a circular field of diameter 13 mm which is 
sufficient to cover a 12.times.5 mm.sup.2 image field. 
The embodiment of FIG. 12 and Table 5 is a 4.times. reduction catadioptric 
relay lens having submicron resolution in the UV bandwidth and having 
aperture of 0.6 for a circular field of diameter 13 mm which is sufficient 
to cover a 12.times.5 mm.sup.2 image field. 
The MTF, through frequency and through focus, for the embodiment of FIGS. 
11 and 12 are similar to that shown for the embodiments of FIGS. 2 and 6. 
TABLE 4 
__________________________________________________________________________ 
Index 
of One Half 
Radius Refraction 
Diameter of 
Curvature 
Thickness 
n = 1.5607691 
Surface 
Surface 
mm mm a = 1.0 mm 
__________________________________________________________________________ 
Mask 400 3.2 a 26.0 
401 90.5124 
15.0029 
n 27.1 
402 142.8582 
1.5025 
a 26.9 
403 182.2398 
25.9982 
n 26.9 
404 -299.07 
9.74 a 27.1 
405 -86.3963 
20.8177 
n 26.6 
406 -85.4725 
21.4984 
a 28.2 
407 -241.1435 
9.5051 
n 26.2 
408 -279.9286 
11.3470 
a 25.8 
409 -65.7503 
9.515 n 25.6 
410 -122.0252 
14.9563 
a 27.1 
411 -467.2583 
15.0053 
n 27.9 
412 -421.69 
3.0012 
a 28.8 
413 92.35 
15.0042 
n 29.2 
414 64.0283 
15.0038 
a 27.7 
Cube Face 
415 35 n 
Cube Diagonal 
416 35 n 
Cube Face 
417 5.0056 
a 
418 -199.4415 
10.0012 
n 34.7 
Mirror 419 -161.8844 
10.0012 
n 35.2 
Cube Face 
420 .9026 
a 
421 57.6041 
9.5017 
n 25.8 
422 920.0489 
0.4015 
a 24.7 
423 98.133 
11.2929 
n 23.4 
424 316.5883 
2.0022 
a 20.1 
425 92.5216 
5.9018 
n 18.1 
426 -502.4227 
0.5 a 16.5 
427 -274.9772 
21.9375 
n 16.2 
428 768.7248 
0.1933 
a 6.6 
Target 429 
__________________________________________________________________________ 
TABLE 5 
__________________________________________________________________________ 
Index 
of One Half 
Radius Refraction 
Diameter of 
Curvature 
Thickness 
n = 1.5085507 
Surface 
Surface 
mm mm a = 1.0 mm 
__________________________________________________________________________ 
Mask 500 3.2 a 26.0 
501 123.3741 
15.0029 
n 26.9 
502 407.9745 
0.5025 
a 27.3 
503 247.922 25.9982 
n 27.4 
504 -301.6128 
10.0065 
a -26.9 
505 -77.1852 
20.9961 
n 26.8 
506 -72.9392 
6.8449 
a 28.1 
507 114.6524 
9.5051 
n 27.3 
508 89.3922 
11.347 
a 26.4 
509 -60.3066 
9.506 n 26.5 
510 -86.8179 
41.2581 
a 28.1 
511 234.3202 
15.0019 
n 32.0 
512 194.5769 
3.0012 
a 32.0 
513 79.4623 
15.0042 
n 32.3 
514 61.2837 
15.0058 
a 30.4 
Cube Face 
515 0 n 
Cube Diagonal 
516 0 n 
Cube Face 
517 5.0056 
a 
518 -179.4187 
10.0012 
n 35.2 
Mirror 519 -158.6218 
10.0012 
518 -179.4187 
5.0056 
a 35.2 
Cube Face 
517 35 n 
Cube Diagonal 
516 35 n 
Cube Face 
520 0.9026 
a 
521 52.4412 
9.5028 
n 23.4 
522 921.1127 
0.4015 
a 22.1 
523 85.1741 
8.3991 
n 21.0 
524 357.8853 
2.0022 
a 19.6 
525 87.1228 
2.9024 
n 17.7 
526 -3505 0.5 a 17.0 
527 -483.0228 
24.2156 
n 16.7 
528 429.6715 
0.1903 
a 6.6 
Target 529 
__________________________________________________________________________ 
The very large size of the field achievable, particularly that of FIG. 6 
and Table 2 and of FIG. 10 and Table 3, enables its use primarily in tools 
of optical microlithography known as steppers but does not prevent it from 
being applied in scanners of the ring field type or of the slot field type 
to build even larger fields. The very large field of the design also 
enables sub-die scanning to implement continuous throughout the field 
monitoring for better alignment and focus as a way to accommodate the 
naturally limited depth of focus of the design and also to take care of 
the demanding wafer flatness requirements for the ultra-high resolution 
optical microlithography of integrated circuits. 
Examples of coatings, methods of fabricating the coatings and techniques 
for designing the coatings for the beam splitting surface 12 of the 
schematic diagram of FIG. 1 which are disposed on the beam splitting 
surfaces herein can be found in the patent application of Rosenbluth, in 
particular, the specific embodiments which have been incorporated herein 
by a reference herein above. The Rosenbluth coating include, but are not 
limited to, layers of hafnia, magnesium fluoride, alumina and silicone 
dioxide. Following is the teaching of Rosenbluth the following beam 
splitter coating are for the embodiment of Table 2. 
______________________________________ 
1) Alumina (Al2O3) 226 .ANG. +/- 14 A 
2) Magnesium Fluoride (MgF2) 
432 .ANG. +/- 22 A 
3) Hafnia (HfO2) 204 .ANG. +/- 10 A 
4) Magnesium Fluoride (MgF2) 
462 .ANG. +/- 24 A 
5) Alumina (Al2O3) 209 .ANG. +/- 12 A 
6) Hafnia (HfO2) 230 .ANG. +/- 10 A 
______________________________________ 
The right column is thickness in Angstroms. As the radiation propagates 
from the mask (input side) it is incident on layer #1 in the first 
(transmission) pass through the coating. After undergoing multiple 
reflections within the layers, the radiation emerges from layer #6. In the 
second (reflection) pass, the radiation is incident on layer #6. After 
reflection, it propagates towards the wafer. 
Although the specific embodiments are for UV wavelengths, the general 
design of FIG. 1 is not limited thereto. Variations on the constructional 
parameters for the specific embodiments can be preferably .+-.20%, more 
preferably, .+-.10%, most preferably .+-.5%. 
In summary, the invention herein is an optical system of a NX reduction 
catadioptric relay lens having sub-half micron resolution over the total 
uv band width, in particular that of a UV excimer laser. A spherical 
mirror with a stop at the mirror is used to work at substantially the 
desired reduction ratio and the desired high numerical aperture sufficient 
to provide the desired high resolution. A beam splitting cube with 
appropriate coatings is essential to form an accessible image of an object 
which represents a mask used to pattern the substrate located at the 
image. Refracting correctors in the path of the slow beam incident on the 
mirror and in the path of the fast beam reflected from the mirror are 
designed to fix the aberrations of the image formed by the mirror. 
It is to be understood that the above described embodiments are simply 
illustrative of the principles of the invention, various other 
modifications and changes may be devised by those of skill in the art 
which will embody the principles of the invention and fall within the 
spirit and scope thereof.