U.S. patent application number 12/467879 was filed with the patent office on 2009-09-10 for projection objective of a microlithographic projection exposure apparatus.
This patent application is currently assigned to CARL ZEISS SMT AG. Invention is credited to Juergen Fischer.
Application Number | 20090225296 12/467879 |
Document ID | / |
Family ID | 34960147 |
Filed Date | 2009-09-10 |
United States Patent
Application |
20090225296 |
Kind Code |
A1 |
Fischer; Juergen |
September 10, 2009 |
PROJECTION OBJECTIVE OF A MICROLITHOGRAPHIC PROJECTION EXPOSURE
APPARATUS
Abstract
A projection objective of a microlithographic projection
exposure apparatus has a plurality of optical elements, for example
lenses or mirrors. The objective furthermore includes an actuator
for exerting a mechanical force that deforms a selected optical
element of the projection objective. A manipulator modifies the
spatial position of one of the optical elements as a function of
the force exerted by the actuator.
Inventors: |
Fischer; Juergen;
(Heidenheim, DE) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
CARL ZEISS SMT AG
Oberkochen
DE
|
Family ID: |
34960147 |
Appl. No.: |
12/467879 |
Filed: |
May 18, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11464934 |
Aug 16, 2006 |
7545482 |
|
|
12467879 |
|
|
|
|
PCT/EP2005/000947 |
Feb 1, 2005 |
|
|
|
11464934 |
|
|
|
|
Current U.S.
Class: |
355/66 |
Current CPC
Class: |
G03F 7/70825 20130101;
G03F 7/70266 20130101 |
Class at
Publication: |
355/66 |
International
Class: |
G03B 27/54 20060101
G03B027/54 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 20, 2004 |
DE |
102004008285.5 |
Claims
1. An objective, comprising: a) a plurality of optical elements, b)
at least one actuator configured to exert a mechanical force that
deforms a first optical element of the plurality of optical
elements such that the first optical element is deformed and
changes its spatial position, wherein a change of the spatial
position of the first optical element causes an impairment of the
imaging properties of the objective, c) at least one manipulator
configured to modify the spatial position of a second optical
element of the plurality of optical elements without deforming the
second optical element when the manipulator is driven, d) a device
adapted to drive the at least one manipulator such that the second
optical element changes its spatial position in a way that reduces
the impairment of the imaging properties, wherein the objective is
designed to be used as projection objective of a microlithographic
projection exposure apparatus.
2. The objective of claim 1, wherein the device is adapted to
automatically modify the spatial position of the second optical
element.
3. The objective of claim 1, wherein the at least one manipulator
is configured to tilt the second optical element about an axis that
is substantially perpendicular to a symmetry axis of the second
optical element.
4. The objective of claim 1, wherein the at least one manipulator
is configured to displace the second optical element in a plane
that is substantially perpendicular to a symmetry axis of the
second optical element.
5. The objective of claim 1, wherein the second optical element is
the first optical element.
6. The objective of claim 1, wherein the at least one actuator is
configured to be fluidically actuated.
7. The objective of claim 1, wherein the at least one manipulator
is configured to be fluidically actuated.
8. The objective of claim 6, wherein the at least one manipulator
is configured to be fluidically actuated, and wherein the at least
one actuator and the at least one manipulator are connected to a
fluidic pressure system which is configured to fluidically actuate
the at least one actuator and the at least one manipulator
simultaneously.
9. The objective of claim 8, wherein the fluidic pressure system is
configured such that changes in the fluid pressure applied to the
at least one actuator result in changes in the fluid pressure
applied to the at least one manipulator.
10. The objective of claim 9, wherein the at least one manipulator
is connected in series with the at least one actuator in the
fluidic pressure system.
11. The objective of claim 1, wherein the device adapted to drive
the at least one manipulator comprises a regulator configured to
regulate spatial position changes of the second optical element as
a function of the changes of the spatial position of the first
optical element caused by the actuator.
12. The objective of claim 1, wherein the device adapted to drive
the at least one manipulator comprises a controller configured to
control the spatial position changes of the second optical element
as a function of the changes of the spatial position of the first
optical element caused by the actuator.
13. The objective of claim 6, further comprising a pressure line,
which leads to the at least one actuator, and a resilient
compensating element, which is integrated into the pressure line,
wherein deformations of the compensating element caused by pressure
fluctuations are transmitted via a transmission element to the at
least one manipulator.
14. The objective of claim 1, wherein the at least one manipulator
engages directly on the second optical element.
15. The objective of claim 1, wherein the at least one manipulator
engages on a mounting containing the second optical element.
16. The objective of claim 1, wherein the at least one manipulator
engages on a frame on which a mounting containing the second
optical element is supported.
17. The objective of claim 6, comprising a pressure line, which
leads to the at least one actuator, and a plurality of resilient
compensating elements, which are integrated in the pressure line
and are arranged relative to one another so that deformation forces
in the compensating elements caused by pressure changes mutually
compensate at least substantially.
18. The objective of claim 17, wherein two compensating elements
are connected together to a pressure feed line and together to a
pressure discharge line such that they are arranged diametrically
opposite each other.
19. The objective of claim 1, wherein the first and second optical
elements are mirrors.
20. An objective, comprising: a) a plurality of optical elements,
b) at least one actuator configured to exert a mechanical force
that deforms a first optical element of the plurality of optical
elements, c) at least one manipulator configured to modify the
spatial position of a second optical element of the plurality of
optical elements when the manipulator is driven, d) a controller
adapted to drive the at least one manipulator as a function of the
forces exerted by the at least one actuator if the at least one
actuator is actuated, wherein the objective is a projection
objective designed to be used in a microlithographic projection
exposure apparatus.
21. The objective of claim 20, wherein the controller is adapted to
drive the at least one manipulator synchronously with an actuation
of the at least one actuator.
22. The objective of claim 20, wherein the controller is in
configured to be in communication with a look up table comprising a
first set of data related to positions of the at least one
manipulator and a second set of data related to forces exerted by
the at least one actuator.
23. The objective of claim 20, wherein the first and second optical
elements are mirrors.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of U.S. patent application Ser. No.
11/464,934, filed Aug. 16, 2006, which is a continuation of
International Patent Application PCT/EP2005/000947, filed on Feb.
1, 2005 and claims priority of German Patent Application 10 2004
008 285.5 filed Feb. 20, 2004. The full disclosure of these earlier
applications is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a projection objective for
microlithographic projection exposure apparatus, such as those used
for the production of large-scale integrated electrical circuits
and other microstructured components. The invention relates in
particular to projection objectives in which at least one optical
element can be deformed with the aid of an actuator. The invention
furthermore relates to a method for correcting optical properties
of such a projection objective.
[0004] 2. Description of the Prior Art
[0005] The purpose of projection objectives in microlithographic
projection exposure apparatus is to project a reduced image of
structures contained in a mask onto a photosensitive layer, which
is applied on a support. Very stringent requirements are placed on
the imaging properties of the projection objectives owing to the
small size of the structures to be image.
[0006] U.S. Pat. No. 6,388,823 assigned to the Applicant discloses
a projection objective in which forces can be exerted on an optical
element with the aid of actuators, which are distributed around the
circumference of the optical element. These forces lead to bending
of the optical element which, for example, may be a lens or a
mirror. The bending does not affect the thickness profile of the
optical element, or at least does not substantially affect it. In
particular, astigmatic imaging errors can be corrected with such a
bendable optical element.
[0007] It has however been found that the bending is not only
accompanied by the desired corrective effect; rather, undesired
impairment of the imaging properties of the projection objective
can also occur. This applies in particular to optical elements
which are isostatically mounted. Isostatic mounting means that the
optical element is held merely at three mounting points offset by
120.degree. along the circumference.
[0008] Such undesired impairment of the imaging properties,
however, may also be caused by optical elements which are not bent
but otherwise deformed in order to correct imaging errors, as is
known per se in the prior art.
SUMMARY OF THE INVENTION
[0009] It is an object of the invention to provide a projection
objective of a microlithographic projection exposure apparatus, in
which such undesired impairment of the imaging due to deliberate
deformations of optical elements is substantially avoided.
[0010] It is a further object of the invention to provide an
improved method for correcting optical properties of a projection
objective.
[0011] The first object is achieved by a projection objective
comprising a plurality of optical elements and at least one
actuator, by which a selected optical element of the projection
objective can be deformed. According to the invention, the
projection objective has at least one manipulator by which the
spatial position of one of the optical elements can be modified
preferably automatically as a function of a force exerted by at
least one actuator.
[0012] With respect to the method, the object is achieved in such a
projection objective in that the spatial position of one of the
optical elements is modified as a function of a force exerted by
the at least one actuator.
[0013] The invention is based on the discovery that, particularly
when the relevant optical element is mounted only at relatively few
points as is the case for instance with isostatic mounting, the
actuators induce forces which lead not only to a deformation but
also to a change in the spatial position of the optical element.
The type of position change depends in particular on the points at
which the optical element is held and where the forces generated by
the actuators engage on the optical element. With isostatic
mounting of the optical element in which three mounting points are
provided offset by 120.degree. along the circumference, for
example, tilting of the optical element takes place about a
transverse axis of the optical element when it is bent in a saddle
fashion to correct astigmatism. With a different constellation of
mounting points of the optical element and actuators engaging
thereon, the position change may also consist in a translational
displacement of the optical element in a plane perpendicular to the
symmetry axis.
[0014] However, undesired position changes due to deformations can
take place even when the optical element is mounted at very many
points. The reasons for this are in general fabrication tolerances
and mounting-induced asymmetries.
[0015] With the aid of the at least one manipulator according to
the invention, it is possible to compensate for the aforementioned
position changes of the optical element which lead to impairment of
the imaging properties. A single manipulator is not sufficient for
this in most cases, so that a plurality of manipulators are to be
provided and their effects on the optical element should be
appropriately tuned.
[0016] The at least one manipulator preferably acts on the selected
optical element for which the undesired position change has
occurred owing to the deformation. Nevertheless, it is also
possible for an optical element other than the deformed optical
element to be tilted, displaced or otherwise have its position
changed with the aid of the at least one manipulator, so as to
compensate for the effects which have been caused by the position
change of the selected optical element owing to the
deformation.
[0017] If both the at least one actuator, which can deform the
optical element, and the at least one manipulator, which induces
the position change, can be actuated fluidically i.e. hydraulically
or pneumatically, then it is preferable for the at least one
actuator and the at least one manipulator to be connected to a
fluidic pressure system so that they can both be fluidically
actuated simultaneously. Specifically, fluidic pressure systems
provide the opportunity to make forces act simultaneously at
different positions inside the system. With an appropriate design
of the pressure system, it is then possible to induce an automatic
position change with the at least one manipulator so that, when the
at least one actuator is actuated, the at least one manipulator
without its own additional control or regulation applies the
required force which leads to the desired position change of the
optical element.
[0018] One possibility for simultaneous actuation of the at least
one actuator and the at least one manipulator consists in designing
the pressure system so that changes in the fluid pressure applied
to the actuator lead to corresponding changes in the fluid pressure
applied to the manipulator. For example, this may be done by
connecting the manipulator in parallel with the actuator in the
pressure system.
[0019] In a particularly preferred configuration of the invention a
resilient compensating element, whose deformations caused by
pressure fluctuations can be transmitted via a transmission element
to the at least one manipulator, is integrated into a pressure line
leading to the at least one actuator. The manipulator will in this
way be actuated not by changes in the fluid pressure in the
pressure line, but mechanically via the transmission element which
is coupled to the compensating element. The purpose of the
resilient compensating element, which may for example be a kind of
bellows, is to decouple the actuator from supply devices of the
pressure system and the housing of the projection objective so that
vibrations cannot be transmitted onto the selected optical element.
Since pressure changes in such a compensating element lead to
deformations and therefore to movements, a mechanical force which
can be used for the position change of the one optical element with
the aid of the at least one manipulator can be derived from the
compensating element or the pressure line connected to it.
[0020] If such transmission of forces from the compensating element
to the at least one manipulator is not provided, then it may be
expedient to improve the decoupling of the pressure line from the
optical element by integrating a plurality of resilient
compensating elements in a pressure line, which are arranged
relative to one another so that the deformation forces formed
therein in the event of a pressure change mutually compensate least
substantially. Deformation forces which act in the event of a
pressure change in a compensating element cannot therefore be
undesirably transmitted to the optical element. This force-free
connection of the optical element to a supply device of the
pressure system may also advantageously be used independently of
the manipulators according to the invention.
[0021] Such an arrangement can be produced most simply if two
compensating elements, connected together to a pressure feed line
and together to a pressure discharge line, are arranged lying
diametrically opposite each other. Merely one additional
compensating element is required in such an arrangement.
[0022] The at least one manipulator itself may engage directly on
the optical element or, alternatively, it may engage thereon via a
mounting which contains the selected optical element. If the at
least one manipulator engages on the mounting, then when the at
least one manipulator is actuated this leads to a relative movement
between the mounting and the optical element contained in it, on
the one hand, and the housing of the objective on the other
hand.
[0023] If the mounting is in turn supported in a frame, which is
fixed relative to the housing of the objective, then the at least
one manipulator may also engage on such a frame. In this way, the
mounting of the optical element in the mounting is not affected by
the at least one manipulator.
[0024] Instead of a fluidic pressure system, the at least one
actuator and/or the at least one manipulator may of course also be
actuated with the aid of other controlling elements. For example,
precisely adjustable forces may be exerted with the aid of
piezoelectric elements. In this case, it is generally necessary to
provide a control or regulating device for driving the at least one
actuator and/or the at least one manipulator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Various features and advantages of the present invention may
be more readily understood with reference to the following detailed
description taken in conjunction with the accompanying drawing in
which:
[0026] FIG. 1 shows a catadioptric projection objective of a
microlithographic exposure apparatus having a mirror unit in a
meridian section;
[0027] FIG. 2 shows a side view of the mirror unit for the
projection objective shown in FIG. 1 according to a first exemplary
embodiment in an enlarged, highly schematised representation;
[0028] FIG. 3 shows a section along the line III-III of the mirror
unit shown in FIG. 2;
[0029] FIG. 4 shows the mirror unit shown in FIG. 2, but with
tilting due to bending generated by actuators;
[0030] FIG. 5 shows the mirror unit shown in FIG. 4, in which the
tilting is rectified by manipulators;
[0031] FIG. 6 shows a side view of the mirror unit for the
projection objective shown in FIG. 1 according to a second
exemplary embodiment in an enlarged, highly schematised
representation;
[0032] FIG. 7 shows a side view of the mirror unit for the
projection objective shown in FIG. 1 according to a third exemplary
embodiment in an enlarged, highly schematised representation
[0033] FIG. 8 shows the mirror unit shown in FIGS. 1 to 5 with a
hydraulic system;
[0034] FIG. 9 shows the mirror unit shown in FIGS. 1 to 5 with
another hydraulic system;
[0035] FIG. 10 shows the mirror unit shown in FIGS. 1 to 5 with a
further hydraulic system in the undeformed state;
[0036] FIG. 11 shows the mirror unit shown in FIG. 10 in the
deformed state with tilting correction;
[0037] FIG. 12 shows a compensating unit for force-free connection
of a mirror unit to a housing via a pressure line.
DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS
[0038] FIG. 1 shows a simplified representation of a meridian
section through a projection objective, denoted overall by 10, of a
microlithographic projection exposure apparatus. The projection
objective, which is also described in PCT/EP03/04015 assigned to
the Applicant, is used to project a reduced image of structures
contained in a reticle 11 onto a photosensitive layer 12, which
consists of a photoresist and is applied on a substrate 13. The
reticle 11 is arranged in an object plane OP and the photosensitive
layer 12 is arranged in an image plane IP of the projection
objective 10.
[0039] After passing through the reticle 11, projection light 14
indicated by dashes in FIG. 1 which is generated by an illuminating
device of the projection exposure apparatus and has a wavelength of
157 nm in the exemplary embodiment represented, travels through a
plane-parallel plate 15 and a lens L1 into a beam splitter cube 16.
There, the projection light 14 is reflected by a
polarisation-selective beam splitter layer 17 contained in it and
sent through a lens L2, a quarter-wave plate 18 and two further
lenses L3 and L4 onto a mirror unit 19 having a spherical mirror 20
and a mounting, which will be explained in more detail below.
[0040] After reflection by the spherical mirror 20, the projection
light 14 passes back through the lenses L4 and L3, the quarter-wave
plate 18 and the lens L2, and strikes the polarisation-selective
beam splitter layer 17. There, however, the projection light 14 is
not reflected but transmitted since the polarisation of the
projection light 14 has been rotated through 90.degree. by the
double transit through the quarter-wave plate 18. From the beam
splitter cube 16, the projection light 14 travels via a plane
mirror 21 into a purely dioptric parts 23 of the projection
objective 10, in which refractive optical elements (not denoted in
detail) are arranged along an optical axis indicated by 25.
[0041] FIGS. 2 and 3 give a highly schematised representation of
the mirror unit 19 for the projection objective 10 according to a
first exemplary embodiment, respectively in a side view and a
horizontal section along the line III-III. The mirror 20 of the
mirror unit 19 is contained in an isostatic mounting, which is
formed by three mounting units 22a, 22b and 22c. The mounting units
22a, 22b and 22c are distributed at intervals of 120.degree. over
the circumference of the mirror 20, as can be seen in FIG. 3. Owing
to the isostatic mounting, the mirror 20 is contained stiffly but
nevertheless almost force-free in the mounting. Possible designs
for the mounting units 22a, 22b, 22c are known in the prior art,
see for example EP 1 245 982 A2, which corresponds to US Pat. Appl.
2002/0176094 A1.
[0042] The mounting units 22a, 22b, 22c are fastened on a frame 24
which, for example, may have a circularly round base shape. For the
isostatic mounting described here, it is nevertheless also
conceivable to use a triangular base shape as likewise known from
the aforementioned EP 1 245 982 A2.
[0043] The frame 24 is fixed relative to a housing 28 of the
projection objective 10 via three manipulators 26a, 26b and 26c,
which are arranged at the vertices of an imaginary equilateral
triangle. The manipulators 26a to 26c in the exemplary embodiment
represented respectively comprise two hydraulically telescopable
cylinders, so that the length of the manipulators 26a to 26c can be
mechanically varied. With appropriate driving of the manipulators
26a to 26c, the frame 24 can be tilted relative to the housing 28
about any axis perpendicular to the optical axis 25 of the
projection objective 10.
[0044] An actuator unit denoted overall by 30, by which the mirror
20 can be bent, is arranged on the lower side of the mirror 20. To
this end, the actuator unit 30 comprises a plurality of individual
actuators (not shown because they are known per se) which are
arranged around the optical axis 25. The actuator unit 30 may be
designed so that the individual actuators act on the mirror 20 from
the circumference. Possible embodiments of an actuator unit 30
having a plurality of individual actuators can be found in DE 198
59 634 A1, which corresponds to U.S. Pat. No. 6,307,688, and DE 198
27 603 A1, which corresponds to U.S. Pat. No. 6,388,823.
[0045] In the exemplary embodiment represented, it is assumed that
a second-order astigmatism can be corrected with the aid of the
actuator unit 30. To this end, the individual actuators contained
in the actuator unit 30 should engage on the mirror 20 so that the
mirror 20 is bent in a saddle fashion owing to the bending moments
thereby generated. This saddle-like bending is indicated in FIG. 3
by circled capital letters H and T. Circles containing a letter H
indicate positions on the mirror 20 which lie uppermost, in so far
as they are furthest away from the frame 24. Circles containing a
letter T indicate positions which lie lowermost and are thus at the
smallest distance from the frame 24.
[0046] In order to generate such saddle-like bending, the
individual actuators of the actuator unit 30 may be arranged and
actuated so that compressive forces in the direction of the optical
axis 25 are generated at two points lying opposite each other at an
angle of 180.degree., whereas oppositely directed forces act on the
mirror 20 at two points respectively offset by angles of 90.degree.
thereto.
[0047] As can be seen clearly from FIG. 3, such forces in the
isostatic mounting as shown lead to tilting of the mirror 20 about
a horizontal axis 34, which extends through the lower-lying points
T. The direction of the tilting is indicated by an arrow 36 in FIG.
3. The reason for the tilting is the fact that the two-fold
symmetry of the forces cannot be made to match the three-fold
symmetry of the mounting in the mounting units 22a, 22b, 22c. With
mounting at four suitably selected points, this tilting would not
occur. Mounting at four points, however, is known to be
disadvantageous in many respects compared to isostatic
mounting.
[0048] The tilting about the axis 34 is absorbed by the mounting
units 22a to 22c which, to this end, may have resilient properties
as described in EP 1 245 982 A2, which corresponds to US Pat. Appl.
2002/0176094 A1.
[0049] FIG. 4 shows the mirror 20 in a side view corresponding to
FIG. 2, although the mirror 20 is tilted about the axis 34 in the
aforementioned way owing to the saddle-like bending (which cannot
be seen in FIG. 4). The symmetry axis 32 of the mirror 20, which
normally coincides with the optical axis 25 of the projection
objective 20, is offset by the tilt angle relative to the original
setpoint position owing to the tilting. This tilt angle is
represented very exaggeratedly for the sake of clarity.
[0050] The three manipulators 26a to 26c are now driven so that the
tilted symmetry axis 32 of the mirror 20 is returned to its
setpoint position which is vertical in FIG. 4. To this end, the
manipulators 26a to 26c which are arranged outside the tilting axis
are adjusted so that the entire frame 24, including the mounting
units 22a to 22c fastened therein and the mirror 20 contained
therein, is tilted back by the required compensating angle. In
magnitude, this compensating angle coincides with the tilt angle by
which the mirror 20 is tilted relative to the frame 24 during the
bending. Owing to the compensatory tilting generated by the three
manipulators 26a to 26c, as can be seen clearly in FIG. 5, the
symmetry axis 32 of the mirror 20 even after it is bent lies in the
setpoint position pointing vertically upwards in FIG. 5. The
tilting of the mirror 20 in the mounting units 22a to 22c, as
generated by the bending, does not therefore impair the imaging
properties of the mirror 20.
[0051] FIG. 6 shows a mirror unit 119 suitable for the projection
objective 10 according to a second exemplary embodiment. Parts
which are the same as in the exemplary embodiment described above
are denoted by the same reference numerals, and parts corresponding
to one another are denoted by reference numerals increased by
100.
[0052] In the mirror unit 119, it is not the frame 24 but only the
mirror 20 which is correspondingly tilted in order to compensate
for tilting movements due to bending. To this end, a manipulator
126a or 126b which can adjust the lengths of the three mounting
units is respectively integrated into two mounting units 122a, 122b
and a third mounting unit (concealed by the mounting unit 122b in
FIG. 6). The frame, however, is firmly connected to the housing 28
via connecting elements 38a, 38b. In order to rectify the tilting
of the mirror 20, as represented in FIG. 4 for the mirror unit 19,
the manipulator 126a and the manipulator lying behind it (not
visible in FIG. 6) should be retracted and the manipulator 126b
should be deployed, so that their lengths are respectively reduced
and increased.
[0053] FIG. 7 shows a mirror unit 219 suitable for the projection
objective 10 according to a third exemplary embodiment. Parts which
are the same as in the mirror unit 19 are denoted by the same
reference numerals, and parts corresponding to one another are
denoted by reference numerals increased by 200.
[0054] The mirror unit 219 represented in FIG. 7 differs from the
mirror unit 119 represented in FIG. 6 merely in that mounting units
222a, 222b are fastened directly via manipulators 226a, 226b, i.e.
without an interposed frame 24, on the housing 28 of the projection
objective 10.
[0055] FIG. 8 shows a mirror unit 319 suitable for the projection
objective 10 according to a fourth exemplary embodiment. Parts
which are the same as in the mirror unit 19 are denoted by the same
reference numerals, and parts corresponding to one another are
denoted by reference numerals increased by 300.
[0056] The mirror unit 319 corresponds essentially to the mirror
unit 19 as represented in FIG. 2. A hydraulic device 40 for
supplying a hydraulic liquid to an actuator unit 330 and
manipulators 326a, 326b, 326c is also shown.
[0057] The hydraulic device 40 contains a controller 42 which, via
valves (in a manner not represented in detail), controls the
pressure of the hydraulic liquid which is used to actuate the
individual actuators contained in the actuator unit 30 and the
manipulators 26a, 26b, 26c. To this end, in the mirror unit 319,
the four individual actuators contained in the actuator unit 30 are
connected to the hydraulic device 40 via respectively independent
first pressure lines 44a to 44d.
[0058] The hydraulic device 40 is furthermore connected via second
pressure lines 46a, 46b and 46c to the manipulators 326a, 326b,
326c. A compensating element 48 in the form of a bellows is
integrated into each of the first and second pressure lines 44a to
44d and 46a to 46c. The purpose of the compensating element is to
decouple the hydraulic device 40 from the actuator unit 330 and the
manipulators 326a to 326c so that vibrations, which are caused in
the hydraulic device 40 by valves or pumps contained therein or by
the projection objective housing 28 connected thereto, cannot be
transmitted to the mirror 20 via the first and second pressure
lines 44a to 44d and 46a to 46c.
[0059] The controller 42 of the hydraulic device 40 is designed so
that actuation of the actuator unit 330 is accompanied by
synchronous actuation of the manipulators 326a to 326c. To this
end, the controller 42 accesses a stored table in which the
setpoint excursions of the manipulators 326a to 326c, which are
necessary so that the tilting of the mirror 20 due to the bending
caused by the actuator unit 330 can be rectified again, are stored
for a multiplicity of settings of the individual actuators
contained in the actuator unit 330.
[0060] FIG. 9 shows a mirror unit 419 suitable for the projection
objective 10 according to a fifth exemplary embodiment. Parts which
are the same as in the mirror unit 19 are denoted by the same
reference numerals, and parts corresponding to one another are
denoted by reference numerals increased by 400.
[0061] The mirror unit 419 differs from the mirror unit 319 shown
in FIG. 8 inter alia in that the controller 42 is replaced by a
regulator 42', which is connected via a line 49 (represented by
dashes) to position sensors which record the spatial position of
the mirror 20. Furthermore, only one pressure line 50 leads from
the hydraulic device 40' to the actuator unit 430. The latter is
connected via a further pressure line 52 in series with
manipulators 426a to 426c. Any pressure change in the pressure line
50 therefore leads to a corresponding pressure change in the
actuator unit 430 and in the manipulators 426a to 426c. The effect
which can be achieved via correspondingly preset valves, which are
assigned to the individual actuators of the actuator unit 430 and
to the manipulators 426a to 426c, is to set up the desired
deformation of the mirror 20 as well as simultaneously tilting of
the frame 24 relative to the housing 28 merely by changing the
pressure of the hydraulic liquid in the pressure line 50. Although
the actuator unit 430 and the manipulators 426a to 426c can
therefore no longer be controlled independently of one another, the
control of the mirror unit 419 is thereby greatly simplified.
[0062] FIGS. 10 and 11 show a mirror unit 519 suitable for the
projection objective 10 according to a sixth exemplary embodiment,
respectively with an unbent mirror and a bent mirror. Parts which
are the same as in the mirror unit 19 are denoted by the same
reference numerals, and parts corresponding to one another are
denoted by reference numerals increased by 500.
[0063] In the mirror unit 519, only the manipulator 526b is
actively configured. The other two manipulators 526a and 526c, on
the other hand, are passively configured. This means that the
manipulators 526a, 526c can in turn accomplish length changes only
passively; an active length change, for example by varying an
applied hydraulic pressure, is not possible.
[0064] The active manipulator 526b consists essentially of the
upper arm of a lever mechanism 54, the lower arm 55 of which is
coupled to a pressure line 56 which connects a pressure device (not
shown) to an actuator unit 530.
[0065] When the pressure of the hydraulic liquid in the pressure
line 56 increases in order to actuate the individual actuators
contained in the actuator unit 530, this leads to an extension of
the resilient compensating element 48 as indicated by a double
arrow 58 in FIG. 11. Via the lever mechanism 54, this extension 58
is converted into a tilting movement of the frame 24 in the
direction indicated by arrows 60. The frame 24 is thereby
automatically tilted in the desired way each time the mirror 20
bends, without additional control or regulating devices. It is
readily possible to adapt the tilt angle by appropriately
configuring the lever mechanism 54.
[0066] If the tilting movement generated by manipulators is
intended to be controllable independently of the actuator unit 30,
as is the case in the mirror unit 319 according to FIG. 8, then it
is advantageous to replace the compensating elements 48 in the
first and second pressure lines 44a to 44d and 46a to 46c
respectively by a compensating unit 48' as represented in FIG. 12.
The compensating unit 48' contains a first T-piece 64, which
divides a pressure line 44 into two parallel pressure lines 66, 68.
A compensating element 48a or 48b is respectively integrated into
each of the parallel pressure lines 66, 68, and specifically so
that the compensating elements 48a, 48b lie opposite each other.
Via a second T-piece 70, the parallel pressure lines 66, 68 are
recombined into a pressure line 44' downstream of the compensating
elements 48a, 48b.
[0067] Since the compensating elements 48a, 48b lie symmetrically
opposite each other, length changes of the compensating elements
48a, 48b as indicated by double arrows 72, 74 do not lead to a
force in the longitudinal direction of the pressure line 44'
leading off from the second T-piece 70. The take-off through the
second T-piece 70, lying between the two compensating elements 48a,
48b, thus induces a force equilibrium which prevents undesired
controlling forces from propagating via the pressure line 44' and
an actuator unit and/or a manipulator to the mirror 20.
[0068] The above description of the preferred embodiments has been
given by way of example. From the disclosure given, those skilled
in the art will not only understand the present invention and its
attendant advantages, but will also find apparent various changes
and modifications to the structures and methods disclosed. The
applicant seeks, therefore, to cover all such changes and
modifications as fall within the spirit and scope of the invention,
as defined by the appended claims, and equivalents thereof.
* * * * *