U.S. patent application number 10/233314 was filed with the patent office on 2003-04-03 for projection exposure system.
Invention is credited to Kneer, Bernhard, Richter, Gerald.
Application Number | 20030063268 10/233314 |
Document ID | / |
Family ID | 7697717 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030063268 |
Kind Code |
A1 |
Kneer, Bernhard ; et
al. |
April 3, 2003 |
Projection exposure system
Abstract
A projection exposure system, intended in particular for
microlithography, is used for generating, in an image plane, an
image of a mask arranged in an object plane. The projection
exposure system has a light source emitting projection light and
projection optics arranged between the mask and the image. Starting
from the mask, the following are arranged in the beam path of the
projection optics: a first group of optical components with an
overall positive refractive power; a second group of optical
components with an overall negative refractive power; a third group
of optical components with an overall positive refractive power; a
fourth group of optical components with an overall negative
refractive power, and, a fifth group of optical components with an
overall positive refractive power. At least three optical subgroups
having at least one optical component can be displaced along the
optical axis of the projection optics. The first optical subgroup
comprises the mask or at least one optical component from the first
group of optical components. The second optical subgroup comprises
at least one optical component from the second or the third group
of optical components. The third optical subgroup comprises at
least one optical component from the third or the fourth group of
optical components. With such subgroups, efficient imaging error
correction of the projection optics is possible.
Inventors: |
Kneer, Bernhard; (Altheim,
DE) ; Richter, Gerald; (Abtsgmund, DE) |
Correspondence
Address: |
FACTOR & PARTNERS, LLC
1327 W. WASHINGTON BLVD.
SUITE 5G/H
CHICAGO
IL
60607
US
|
Family ID: |
7697717 |
Appl. No.: |
10/233314 |
Filed: |
August 30, 2002 |
Current U.S.
Class: |
355/67 ; 355/53;
359/763; 359/766 |
Current CPC
Class: |
G03F 7/70241 20130101;
G03F 7/70258 20130101; G03F 7/70575 20130101; G02B 13/143
20130101 |
Class at
Publication: |
355/67 ; 359/763;
359/766; 355/53 |
International
Class: |
G03B 027/54 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 5, 2001 |
DE |
101 43 385.9 |
Claims
What is claimed is
1. A projection exposure system, in particular for
microlithography, for generating, in an image plane, an image of a
mask arranged in an object plane, with a light source emitting
projection light and projection optics arranged between the mask
and the image, wherein the following are arranged in a beam path of
the projection optics, starting from the mask: a) a first group of
optical components with an overall positive refractive power; b) a
second group of optical components with an overall negative
refractive power; c) a third group of optical components with an
overall positive refractive power; d) a fourth group of optical
components with an overall negative refractive power; and e) a
fifth group of optical components with an overall positive
refractive power; characterised in that f) at least a first, second
and third optical subgroup each having at least one optical
component can be displaced along an optical axis of the projection
optics, wherein g) the first optical subgroup comprises one of the
mask and at least one optical component from the first group of
optical components, h) the second optical subgroup comprises at
least one optical component from one of the second and the third
group of optical components, and i) the third optical subgroup
comprises at least one optical component from one of the third and
the fourth group of optical components.
2. The projection exposure system according to claim 1,
characterised in that the second optical subgroup is arranged next
to the first group of optical components.
3. The projection exposure system according to claim 1,
characterised in that the third optical subgroup is arranged in a
transition region between the third and the fourth groups of
optical components.
4. The projection exposure system according to claim 1,
characterised in that a pair of optical components, whose
displacements along the optical axis are expediently coupled
together, is provided as the second optical subgroup.
5. The projection exposure system according to claim 4,
characterised in that a support body is provided, which can be
displaced along the optical axis of the projection optics and which
supports said pair of optical components together.
6. The projection exposure system according to claim 1,
characterised in that an instrument for adjusting a wavelength is
provided.
7. The projection exposure system according to claim 6,
characterised in that the adjustment instrument includes means for
altering an emission wavelength of the light source.
8. The projection exposure system according to claim 6,
characterised in that the adjustment instrument includes means for
altering a projection light wavelength after exiting the light
source.
9. The projection exposure system according to claim 1,
characterised by at least a fourth optical subgroup, having at
least one optical component, which can be displaced along the
optical axis of the projection optics and which comprises at least
one optical component from the fifth group of optical
components.
10. The projection exposure system according to claim 9,
characterised by an at most fourth and a fifth optical subgroup
which can be displaced along the optical axis of projection
optics.
11. The projection exposure system according to claim 1,
characterised in that the optical components are designed as
refractive components.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to a projection exposure system, in
particular for microlithography, for generating, in an image plane,
an image of a mask arranged in an object plane, with a light source
emitting projection light and projection optics arranged between
the mask and the image, wherein the following are arranged in the
beam path of the projection optics, starting from the mask:
[0002] a) a first group of optical components with an overall
positive refractive power;
[0003] b) a second group of optical components with an overall
negative refractive power;
[0004] c) a third group of optical components with an overall
positive refractive power;
[0005] d) a fourth group of optical components with an overall
negative refractive power and
[0006] e) a fifth group of optical components with an overall
positive refractive power.
[0007] Such projection optics are known from DE 198 55 108 A and DE
199 42 281 A in the name of the Applicant. They are suitable, in
particular, for use with projection light wavelengths in the DUV
wavelength range. Instead of the fifth group of optical components
with an overall positive refractive power, these documents also
refer in places to a fifth and a sixth group of optical components,
although these may be combined as a fifth group of optical
components with an overall positive refractive power for the
purposes of describing the invention below.
[0008] Owing to the very high numerical aperture which projection
optics of this type generally have, residual imaging errors occur,
for example because of changes in the ambient parameters such as
temperature and air pressure.
[0009] It is therefore an object of the present invention to
provide projection optics for a projection exposure system of the
type mentioned in the introduction, whose residual imaging errors
are reduced.
[0010] This object is achieved according to the invention by the
fact that
[0011] f) at least three (first, second and third) optical
subgroups each having at least one optical component can be
displaced along an optical axis of the projection optics,
wherein
[0012] g) the first optical subgroup comprises one of the mask and
at least one optical component from the first group of optical
components,
[0013] h) the second optical subgroup comprises at least one
optical component from one of the second and the third group of
optical components,
[0014] i) the third optical subgroup comprises at least one optical
component from one of the third and the fourth group of optical
components.
[0015] According to the invention, it has been discovered that if
at least three optical subgroups according to the above selection
are chosen as instruments, which can be displaced along the optical
axis, for correction of imaging errors of the projection optics,
then good correction is ensured for the imaging errors which
typically occur, for example scaling, distortion and image field
curvature. In this case, the individual subgroups need not act
selectively on one imaging error in each case, but rather it is
sufficient for the combination of the actions of the three
subgroups to bring about the desired correction effect. The optimum
adjustment of the respective subgroups can be determined with the
aid of known optical design programs.
[0016] Preferably, the second optical subgroup is arranged next to
the first group of optical components. In this case, at least two
displaceable subgroups are present in spatial proximity, which
offers the possibility of simplifying the design of the projection
optics.
[0017] The third optical subgroup may be arranged in the transition
region between the third and the fourth groups of optical
components. For most designs of projection optics of the type
mentioned in the introduction, good correction of imaging errors
which typically occur is obtained in this case.
[0018] A pair of optical components, whose displacements along the
optical axis are expediently coupled together, may be provided as
the second optical subgroup. Such a component pair has been found
to be efficient in terms of optical corrective action, as has been
shown by optical calculations.
[0019] Preferably, a support body is in this case provided, which
can be displaced along the optical axis of the projection optics
and which supports the pair of optical components together. This
permits a simple mechanical structure for the optical components
which can be displaced together.
[0020] An instrument for adjusting the wavelength may additionally
be provided. According to the invention, it has been established
that an instrument for adjusting the wavelength can in many cases
fulfil the corrective function of an additional displaceable
subgroup of optical components. In most cases, the wavelength
adjustment means is easier to produce than an additional
displaceable subgroup.
[0021] Preferably, the adjustment instrument includes means for
altering the emission wavelength of the light source. Such an
adjustment instrument is energy-efficient.
[0022] As an alternative or in addition, the adjustment instrument
may include means for altering the projection light wavelength
after exiting the light source. Such an adjustment instrument is
easy to produce, for example by means of colour filters.
[0023] In a preferred refinement, at least a fourth optical
subgroup, having at least one optical component, is provided which
can be displaced along the optical axis and which comprises at
least one optical component from the fifth group of optical
components. With such an additional optical subgroup, it is
possible to reduce other imaging errors which typically occur, such
as coma and spherical aberration.
[0024] The at least a fourth optical subgroup may comprise an at
most fourth and a fifth optical subgroup. With comparatively minor
mechanical outlay, such an embodiment provides good reduction of
imaging errors which occur, as has been shown by optical
calculations.
[0025] The optical components may be designed as refractive
components. With refractive optical components, it is possible to
produce projection optics of the type mentioned in the introduction
with comparatively minor mechanical outlay. As an alternative,
however, it is likewise possible to embody the projection optics as
reflective components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Exemplary embodiments of the invention will be explained in
more detail below with the aid of the drawing, in which
[0027] FIG. 1 shows a lens section of a projection objective of a
projection exposure system;
[0028] FIG. 2 shows a similar lens section to FIG. 1 of an
alternative projection objective; and
[0029] FIG. 3 shows a similar lens section to FIG. 1 of a further
projection objective.
DETAILED DESCRIPTION OF THE DRAWINGS
[0030] While this invention is susceptible of embodiment in many
different forms, there is shown in the drawings and will be
described in detail, several specific embodiments with the
understanding that the present disclosure is to be considered as an
exemplification of the principles of the invention and is not
intended to limit the invention to the embodiments illustrated.
[0031] The projection objectives described below with the aid of
their lens designs are used in the scope of microlithography
projection exposure in order for an image of a structure located on
a mask to be formed onto a wafer, the image of the structure lying
in a corrected image field of the projection objective. The
projection objectives which are shown are refractive systems, and
all the lenses used there are made of quartz glass. The projection
objectives are designed for operation with the wavelength of a KrF
excimer laser at 248 nm. The beam paths, through the objective, of
two pencils of rays respectively starting from an object point are
represented in the following figures for illustration.
[0032] In the first exemplary embodiment of the projection
objective denoted overall by the reference number 1 in FIG. 1,
whose lens data are published in Table 3 of DE 198 55 108 A1 to
which reference is hereby made, a mask 2 is arranged in the object
plane of the projection objective.
[0033] A first lens group LG1 with an overall positive refractive
power, which has five lenses 3, 4, 5, 6 and 7 in all, is arranged
behind the mask 2 in the beam direction of the projection light
pencil.
[0034] In the projection beam direction, the first lens group LG1
with an overall positive refractive power is adjoined by a second
lens group LG2 with an overall negative refractive power, which
likewise comprises five lenses 8, 9, 10, 11, 12. The second lens
group LG2 is followed by a third lens group LG3 with an overall
positive refractive power, comprising six lenses 13, 14, 15, 16,
17, 18 in all. This is adjoined by a fourth lens group LG4 with an
overall negative refractive power and two lenses 19, 20. The
remaining optical components of the projection objective 1 can be
combined into a fifth lens group LG5 with an overall positive
refractive power. This has, in the projection beam direction,
firstly three lenses 21, 22, 23, which are followed by a
plane-parallel plate 24. Continuing in the projection beam
direction, ten lenses 25, 26, 27, 28, 29, 30, 31, 32, 33, 34
follow. The projection objective 1 is terminated, towards a wafer
36 situated in the image plane of the projection objective 1, by a
further plane-parallel plate 35.
[0035] With reference to the lens design of FIG. 1, various
embodiments of projection objectives with this lens design will be
described below, which in each case have various combinations of
instruments for correction of imaging errors. The correction
components comprise a plurality of subgroups of optical components,
in each case comprising at least one optical component, which can
be displaced in the direction of the optical axis.
[0036] All these exemplary embodiments, as well as the embodiments
of projection optics with correction instruments described in
connection with the following figures, have the following structure
in common:
[0037] The reticle holding the mask 2, or at least one lens from
the first lens group LG1, can be displaced in the direction of the
optical axis. The mask 2 and the lenses from the lens group LG1 can
therefore be regarded as belonging to a first subgroup of optical
components.
[0038] Independently of this, at least one lens from the second or
the third lens group LG2, LG3 can be displaced in the direction of
the optical axis. These lenses from the second or the third lens
group LG2, LG3 can therefore be regarded as belonging to a second
subgroup of optical components.
[0039] Lastly, at least one lens from the third or the fourth lens
group LG3, LG4 can also be displaced in the direction of the
optical axis. These lenses from the third or the fourth lens group
LG3, LG4 can therefore be regarded as belonging to a third subgroup
of optical components.
[0040] With the correction instruments common to all the exemplary
embodiments, it possible to compensate for the image errors of
scaling, distortion and image field curvature, as will be shown
more quantitatively below.
[0041] In addition to the said correction instruments, depending on
the exemplary embodiment, it is possible to provide correction
instruments which, on the one hand, are used to optimise the
compensation for the said image errors and, on the other hand, can
additionally influence the image errors of coma and spherical
aberration as well. Besides manipulation of optical components in
the direction of the optical axis, alteration of the projection
light wavelength is also in principle viable for this.
[0042] The effectiveness of the individual exemplary embodiments
will be discussed with the aid of the value of a merit function,
which is obtained from the sum of the squares of the Zernike
coefficients, summed over the image field points. These merit
functions can be evaluated with the aid of an optical design
program.
[0043] In order to assess the effectiveness, a particular
combination of image errors is specified, and the extent to which
it is possible to compensate for these, with the aid of the
correction instruments specified according to the respective
exemplary embodiment, is then quantitatively determined.
[0044] In a first exemplary embodiment, the reticle holding the
mask 2, the lenses 8 and 9 as well as the lens 17 can be displaced
in the direction of the optical axis in the projection objective 1.
The lenses 8 and 9 can in this case be displaced not independently
of one another, but rather together as a group. To that end, the
lenses 8 and 9 can be displaced together on a support body (not
shown in the drawing) which is arranged so that it can be displaced
along the optical axis.
[0045] For the correction instruments according to the first
exemplary embodiment, the following image error values were used as
starting values to determine the corrective action: 50 ppm for the
scaling, 50 nm for the distortion and 100 nm for the image field
curvature coupled in the ratio 1:1 to 100 nm of astigmatism, since
these image errors can be corrected only simultaneously by Z
manipulators. With the aid of the correction instruments according
to the first exemplary embodiment, the value of the merit function
for these starting values can be reduced to an end value whose
absolute value now amounts to only 1.9% of the starting value.
[0046] The statistical sums over the residual image errors after
compensation for the three said starting image errors by the
correction instruments of the first exemplary embodiment are
represented in the first row of Table 1, which is given at the end
of the Description. Here, the values for the distortion (Disto),
focal plane deviation (FPD), astigmatism (AST) as geometrical image
errors, as well as the most important wavefront errors as Zemike
coefficients (Z7, Z9, Z10, Z12, Z14, Z16, Z17, Z25), are indicated.
The residual image error is the maximum value of an image error,
for example distortion, in the image field. The residual image
error is determined upon each compensation for a model image-error
profile. The root of the sum of the squares of the individual
residual image errors obtained from the compensations is formed
during the statistical summation.
[0047] In the second exemplary embodiment, the projection objective
1 has, as correction instruments, lenses 6, 8, 9 and 17 which can
be displaced in the direction of the optical axis. The reticle 2 is
not displaceable here. The lenses 8 and 9 can here again be
displaced in the direction of the optical axis not independently of
one another, but rather together as a group. Similarly to the above
comments in connection with the first exemplary embodiment, the
reduction of the value of the merit function, as well as the
residual image errors after compensation has been carried out, are
here again calculated with the aid of the same starting values for
the image errors of scaling, distortion and image field curvature.
The merit function is reduced to 1.7% of the starting value.
[0048] The values for the residual image errors are entered in the
second row of Table 1. The distortion value, in particular, is
further reduced significantly in relation to the first exemplary
embodiment.
[0049] In a third exemplary embodiment, the following correction
instruments are used in the projection objective 1: A reticle which
holds the mask 2 and can be displaced in the direction of the
optical axis, lenses 8, 9, 17 and 31 which can be displaced in the
direction of the optical axis, as well as a means of adjusting the
wavelength of the projection light. Here again, the lenses 8 and 9
can be displaced not independently of one another but rather
together as a group.
[0050] In this exemplary embodiment, a lens from the fifth lens
group LG5 is hence additionally displaceable as well. These lenses
from the fifth lens group LG5 can therefore be regarded as
belonging to a further subgroup of optical components.
[0051] In order to adjust the wavelength of the projection light,
the emission wavelength of the light source may be altered. In the
case of a laser, this may be carried out, for example, using a
dispersive optical element, for example a grating, which is
internal to the resonator.
[0052] Alternatively, it is possible to alter the wavelength of the
projection light after exiting the light source. This is done, for
example, likewise using an adjustable dispersive optical element,
for example a grating or a prism, which in this case is arranged
externally with respect to the light source. The use of a colour
filter to alter the wavelength is also possible.
[0053] If error values for coma (10 nm Z7) and spherical aberration
(10 nm Z9) are also assumed here, in addition to the starting image
error values for the scaling, the distortion and the image field
curvature (cf. the first exemplary embodiment), then a reduction of
the starting value of the merit function resulting in this case,
after the compensation by the correction instruments of the second
exemplary embodiment, is now obtained to only 0.78% of the starting
value. The resulting residual image errors can be seen in the third
a row of Table 1. In comparison with the first and second exemplary
embodiments, the geometrical image errors are reduced
significantly. In the case of the higher Zernike coefficients, a
slight increase in the absolute values is obtained, which is
primarily attributable to the additionally introduced error values
for coma and spherical aberration.
[0054] In the fourth exemplary embodiment, the following are
provided as correction instruments in the projection objective 1: A
reticle which holds the mask 2 and can be displaced in the
direction of the optical axis, displaceable lenses 8, 9, 17, 23 and
31. Here again, the lenses 8 and 9 can be displaced not
independently of one another but rather together as a group. If the
same starting image errors as in the third exemplary embodiment are
assumed, a reduction of the merit function to 0.67% of the starting
value is obtained. The residual image error data are entered in the
fourth row of Table 1. Especially in the case of the higher Zernike
coefficients, reductions of the absolute values in relation to the
third exemplary embodiment are obtained here.
[0055] In a fifth exemplary embodiment, the following correction
instruments are provided in the projection objective 1: Lenses 6,
8, 9, 17, 23 and 31 which can be displaced in the direction of the
optical axis. The reticle 2 is not displaceable. Here again, the
lenses 8 and 9 can be displaced not independently of one another
but rather together as a group. A reduction of the merit function
to 0.60% of the starting value is obtained here. The residual image
error data are entered in the fifth row of Table 1. These data
correspond approximately to those of the fourth exemplary
embodiment.
[0056] A second projection objective 101, for which a series of
exemplary embodiments of correction instrument combinations will
likewise be discussed below, is represented in FIG. 2. Components
which correspond to those that have already been explained in
connection with FIG. 1 carry reference numbers increased by 100,
and they will not be explained in detail again.
[0057] The lens data for the projection objective 101 are disclosed
in DE 199 42 281 A, Table 4, to which reference is hereby made.
[0058] The first lens group LG1 comprises, in the projection
objective 101, five lenses 137, 138, 139, 140, 141. The second lens
group LG2 is made up of four lenses 142, 143, 144, 145. The third
lens group LG3 has four lenses 146, 147, 148, 149 in all. The
fourth lens group LG4 comprises the four lenses 150, 151, 152,
153.
[0059] In contrast to the projection objective 1, the lenses
following the lens group LG4 are, for their part, divided into two
lens groups: The lens group LG4 is followed, in the projection beam
direction, firstly by a lens group LG5 with an overall positive
refractive power. It has 10 lenses 154, 155, 156, 157, 158, 159,
160, 161, 162, 163 in all. Between the lenses 157, 158, an aperture
diaphragm AP is arranged in a pupil plane of the projection
objective 101.
[0060] The lens group LG5 is followed, in the projection beam
direction, by a lens group LG6, likewise with an overall positive
refractive power. It has two lenses 164, 165 in all, the lens 164
having a negative refractive power. The last two lens groups LG5,
LG6 can be considered as one lens group with an overall positive
refractive power.
[0061] The lens 165 is next to the wafer 136.
[0062] In a sixth exemplary embodiment of a combination of
correction instruments, the projection objective 101 of FIG. 2 has
the following correction instruments: A reticle which holds the
mask 102 and can be displaced in the direction of the optical axis,
lenses 141, 142, 149 which can be displaced in the direction of the
optical axis. The lenses 141, 142 are in this case displaceable not
independently of one another but rather only together as a
group.
[0063] In order to assess the effectiveness of these correction
instruments, the same starting image errors for the scaling, the
distortion and the image field curvature as previously in the first
exemplary embodiment are again assumed. In the sixth exemplary
embodiment, the merit function is reduced to 3.3% of the starting
value. The residual image error data can be seen in the sixth row
of Table 1.
[0064] In a seventh exemplary embodiment, the following correction
instruments are present in the projection objective 101: Lenses
140, 141, 142 and 149 which can be displaced in the direction of
the optical axis. The reticle 102 is not displaceable. The lenses
141, 142 are here again displaceable not independently of one
another but rather together as a group. Assuming the starting image
errors according to the first exemplary embodiment, a reduction of
the merit function to 2.7% of the starting value is obtained here.
The residual image error data are entered in the seventh row of
Table 1.
[0065] In an eighth exemplary embodiment, the following correction
instruments are present in the projection objective 101: A reticle
which holds the mask 102 and can be displaced in the direction of
the optical axis, displaceable lenses 140, 141, 142 and 149, as
well as a means of adjusting the wavelength. The lenses 141, 142
are in this case displaceable not independently of one another but
rather only together as a group.
[0066] Here again, as in exemplary embodiments 3 to 5, starting
image errors for the coma (10 nm Z7) and the spherical aberration
(10 nm Z9) are also assumed, in addition to the starting image
errors for the scaling, the distortion and the image field
curvature. In the eighth exemplary embodiment, a reduction of the
merit function calculated for these starting image errors to 1.5%
of the starting value is obtained after use of the correction
instruments. The residual image error data are given in the eighth
row of Table 1.
[0067] In a ninth exemplary embodiment, the projection objective
101 has the following correction instruments: A reticle which holds
the mask 102 and can be displaced in the direction of the optical
axis, lenses 140, 141, 142, 149 and 157 which can be displaced in
the direction of the optical axis. Here again, the lenses 141, 142
are in this case displaceable not independently of one another but
rather together as a group. Assuming the same starting image errors
as in the eighth exemplary embodiment, a reduction of the merit
function to 1.4% of the starting value is obtained here. The
residual image error data are given in the ninth row of Table
1.
[0068] In a tenth exemplary embodiment, the following correction
instruments are provided in the projection objective 101: Lenses
140, 141, 142, 149, 157, 159 which can be displaced in the
direction of the optical axis. The reticle 102 is not displaceable.
Here again, the lenses 141, 142 are displaceable not independently
of one another but rather together as a group. Assuming starting
image errors as in the eighth exemplary embodiment, a reduction of
the merit function to 1.4% of the starting value is obtained here.
The residual image error data are given in the tenth row of Table
1.
[0069] A third projection objective 201, for which further
exemplary embodiments of combinations for correction instruments
will be given below, is represented in FIG. 3. Components which
correspond to those that have already been explained with reference
to FIG. 1 or FIG. 2 carry reference numbers increased respectively
by 200 and 100, and they will not be explained in detail again.
[0070] The lens data for the projection objective 201 are disclosed
in DE 199 42 281 A, Table 1, to which reference is hereby made.
[0071] The first lens group LG1 of the projection objective 201 has
five lenses 266, 267, 268, 269, 270 in all. The second lens group
LG2 of the projection objective 201 is made up of five lenses 271,
272, 273, 274, 175 in all. The third lens group LG3 of the
projection objective 201 comprises four lenses 276, 277, 278, 279
in all. The fourth lens group LG4 of the projection objective 201
has four lenses 280, 281, 282, 283 in all.
[0072] The projection objective 201 of FIG. 3 is constructed
similarly to the projection objective 101 of FIG. 2 in respect of
the lens groups LG5, LG6. The fifth lens group of the projection
objective 201 comprises eight lenses 284, 285, 286, 287, 288, 289,
290, 291 in all. Between the lenses 286, 287, an aperture diaphragm
AP is provided in the vicinity of a pupil plane of the projection
objective 201. The sixth lens group LG6 of the projection objective
201 comprises, in the projection beam direction, firstly three
lenses 292, 293, 294 as well as a plane-parallel plate 295
terminating the projection objective 201 in the direction of the
wafer 236.
[0073] In an eleventh exemplary embodiment, the following
correction instruments are provided in the projection objective 201
of FIG. 3: A reticle which holds the mask 202 and can be displaced
in the direction of the optical axis, lenses 271, 272 and 280 which
can be displaced in the direction of the optical axis. The lenses
271, 272 are displaceable not independently of one another but
rather together as a group.
[0074] With the starting image errors for the scaling, the
distortion and the image field curvature according to the first
exemplary embodiment, a reduction of the merit function to 2.1% of
the starting value is obtained here after the correction by the
correction instruments. The residual image error data after the
compensation are entered in the eleventh row of Table 1.
[0075] In the twelfth exemplary embodiment, the projection
objective 201 has the following correction instruments: Lenses 269,
271, 272 and 280 which can be displaced in the direction of the
optical axis. The reticle 202 is not displaceable. Here again, the
lenses 271, 272 are displaceable not independently of one another
but rather together as a group. With the starting image errors
according to the first exemplary embodiment, a reduction of the
merit function to 1.9% of the starting value is obtained here. The
residual image error data are entered in the twelfth row of Table
1.
[0076] In the thirteenth exemplary embodiment, the following
correction instruments are present in the projection objective 201:
A reticle which supports the mask 202 and can be displaced in the
direction of the optical axis, lenses 269, 271, 272 and 279 which
can be displaced in the direction of the optical axis, as well as a
means of adjusting the wavelength. Here again, the lenses 271, 272
are displaceable not independently of one another but rather
together as a group. In the thirteenth exemplary embodiment,
starting image errors for the coma (10 nm Z7) and the spherical
aberration (10 nm Z9) are also assumed as starting image errors,
besides those mentioned above for the scaling, the distortion and
the image field curvature. With the correction instruments of the
thirteenth exemplary embodiment, a reduction of the merit function
to 1.02% of the starting value is obtained. The associated residual
image error data are entered in the thirteenth row of Table 1.
[0077] In the fourteenth exemplary embodiment, the projection
objective 201 has the following correction instruments: A reticle
which holds the mask 202 and can be displaced in the direction of
the optical axis, lenses 271, 280, 286 and 290 which can be
displaced independently in the direction of the optical axis.
Assuming the starting image errors according to the thirteenth
exemplary embodiment, a reduction of the merit function to 0.82% of
the starting value is obtained here. The associated residual image
error data are entered in the fourteenth row of Table 1.
[0078] In a fifteenth exemplary embodiment, the following
correction instruments are provided in the projection objective
201: Lenses 268, 271, 280, 286 and 290 which can be displaced
independently in the direction of the optical axis. The reticle 202
is not displaceable. Assuming the starting image errors as in the
thirteenth exemplary embodiment, a reduction of the merit function
to 0.68% of the starting value is obtained here. The associated
residual image error data are entered in the fifteenth row of Table
1.
[0079] In the sixteenth exemplary embodiment, the following
correction instruments are provided in the projection objective
201: A reticle which holds the mask 202 and can be displaced in the
direction of the optical axis, lenses 271, 272, 280 and 284 which
can be displaced in the direction of the optical axis. The lenses
271, 272 are displaceable not independently of one another but
rather only together as a group.
[0080] In the sixteenth exemplary embodiment, the following
starting image errors were assumed: 30 ppm scaling, 50 nm
third-order distortion and 0.25 .mu.m average image field
curvature. After carrying out the correction with the correction
instruments of the sixteenth exemplary embodiment, the following
residual image errors are obtained as geometrical longitudinal
aberrations: a coma at the field edge of 100 nm maximum, a coma in
the field zone of 61 nm maximum, a coma in the aperture zone at the
field edge of 154 nm maximum, and a variation of the spherical
aberration in the image field of 85 nm maximum.
[0081] In the seventeenth exemplary embodiment, the following
correction instruments are provided in the projection objective
201: A reticle which holds the mask 202 and can be displaced in the
direction of the optical axis, lenses 271, 278, 280 and 284 which
can be displaced independently in the direction of the optical
axis. Assuming the same starting image errors as in the sixteenth
exemplary embodiment, the following residual image errors are
obtained as geometrical longitudinal aberrations: a coma in the
field zone of 15 nm maximum, a coma in the aperture zone at the
field edge of 122 nm maximum, and a variation of the spherical
aberration in the image field of 48 nm maximum.
[0082] In the eighteenth exemplary embodiment, the following
correction instruments are provided in the projection objective
201: A reticle which holds the mask 202 and can be displaced in the
direction of the optical axis, lenses 271, 280 and 284 which can be
displaced independently in the direction of the optical axis, as
well as a means of adjusting the wavelength. Assuming starting
image errors as in the sixteenth exemplary embodiment, the
following residual image errors are obtained as geometrical
longitudinal aberrations after the correction by the correction
instruments in the eighteenth exemplary embodiment: a coma in the
field zone of 7 nm maximum, a coma in the aperture zone at the
field edge of 112 nm maximum, and a variation of the spherical
aberration in the image field of 123 nm maximum.
[0083] As a variant of the first or eleventh exemplary embodiment,
in a nineteenth exemplary embodiment the lens of the third lens
group LG3 with the maximum diameter may also be provided as a
displaceable individual lens, instead of a lens in the vicinity of
the transition between the third and fourth lens groups LG3, LG4.
This means that the lens 15 would be displaceable instead of the
lens 17 in the first exemplary embodiment, and the lens 278 would
be displaceable instead of the lens 280 in the eleventh exemplary
embodiment.
[0084] As a variant of the eighteenth exemplary embodiment, in a
twentieth exemplary embodiment a lens in the vicinity of the
transition between the second and the third lens groups LG2, LG3
(for example the lens 276 in the direction of the optical axis) may
be designed as displaceable instead of a lens in the vicinity of
the transition between the first and the second lens groups LG1,
LG2 (lens 271 in the eighteenth exemplary embodiment).
[0085] In a further variant of the eighteenth exemplary embodiment,
instead of the lenses 271, 280 and 284 which are displaceable
there, the following lenses can be displaced in the direction of
the optical axis in a twenty-first exemplary embodiment: two lenses
in the vicinity of the maximum diameter of the third lens group
LG3, for example the lenses 278 and 279, and one lens in the
vicinity of the transition between the third and the fourth lens
groups LG3, LG4, for example the lens 280.
[0086] The optimum positions of the individual correction
instruments for the image error correction were determined as
follows:
[0087] Taking the specified starting image errors into account, all
possible combinations of the adjustments of the correction
instruments were analysed with the aid of a known optical design
program, by means of image error specifications and evaluation of a
merit function according to the above comments. Combinations of
correction instruments were rejected in which a residual image
error exceeds a specified upper limit, in which a correction
instrument departs from the maximum specified adjustment range, or
in which the change of the adjustment of a correction instrument
leads to an image-error alteration which lies above a specified
limit value for the alteration. The latter case takes into account
the limited adjustment accuracy of the correction instruments.
[0088] The foregoing description merely explains and illustrates
the invention and the invention is not limited thereto except
insofar as the appended claims are so limited, as those skilled in
the art who have the disclosure before them will be able to make
modifications without departing from the scope of the
invention.
1TABLE 1 Exemplary Disto FPD AST Z7 Z9 Z10 Z12 Z14 Z16 Z17 Z25
embodiment [nm] [nm] [nm] [nm] [nm] [nm] [nm] [nm] [nm] [nm] [nm] 1
4.66 12.74 9.29 2.36 3.17 0.37 0.23 0.57 0.41 0.03 0.06 2 2.21
13.13 7.50 2.07 3.19 0.37 0.21 0.49 0.42 0.03 0.06 3 0.35 9.90 4.75
0.54 0.35 1.00 0.70 0.95 0.86 0.04 0.11 4 0.29 10.40 5.04 0.39 0.28
0.51 0.56 0.76 0.74 0.03 0.10 5 0.32 8.30 4.03 0.41 0.28 0.54 0.48
0.64 0.74 0.03 0.09 6 5.6 28.08 7.2 9.97 4.36 0.39 1.11 2.35 0.95
1.02 0.78 7 4.43 26.4 5.77 8.74 3.51 0.36 0.98 2.04 0.87 0.89 0.68
8 2.23 20.9 7.9 1.27 0.88 1.09 1.18 2.44 1.57 1.42 1.21 9 2.32 21.1
8.3 1.06 0.83 0.47 1.13 1.98 1.41 0.96 0.76 10 2.34 21.71 8 0.77
0.58 0.6 1.11 1.92 1.5 0.78 0.7 11 5.42 21.03 13.70 2.95 3.82 0.96
0.35 0.40 0.64 0.06 0.12 12 3.16 18.16 8.50 3.02 3.97 0.81 0.34
0.35 0.61 0.05 0.10 13 0.96 10.78 3.87 0.80 0.56 0.79 1.01 1.90
1.24 0.56 0.43 14 0.34 16.26 7.17 0.32 0.50 0.53 0.35 0.82 1.00
0.03 0.18 15 0.29 11.37 5.06 0.35 0.35 0.49 0.35 0.82 0.90 0.02
0.13
* * * * *