U.S. patent application number 12/337262 was filed with the patent office on 2009-05-28 for optical system for semiconductor lithography.
This patent application is currently assigned to CARL ZEISS SMT AG. Invention is credited to Damian Fiolka, Yim-Bun Patrick Kwan, Frank Melzer, Stefan Xalter.
Application Number | 20090135395 12/337262 |
Document ID | / |
Family ID | 38954819 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090135395 |
Kind Code |
A1 |
Melzer; Frank ; et
al. |
May 28, 2009 |
OPTICAL SYSTEM FOR SEMICONDUCTOR LITHOGRAPHY
Abstract
An optical system for semiconductor lithography including a
plurality of optical components, as well as related components and
methods, are disclosed. The apparatus can include an optical
component that can be moved by a distance along a straight line
within a time of between 5 ms and 500 ms. The straight line can
have a polar and azimuth angle of between 0.degree. and 90.degree.,
and a distance between the straight line and an optical axis of the
apparatus being less than a cross-sectional dimension of a
projection exposure beam bundle of the projection exposure
apparatus. The apparatus can also include a guide unit configured
to guide the optical component. The apparatus can further include a
drive unit configured to drive the optical component via drive
forces so that torques generated by inertial forces of the optical
component and of optional components concomitantly moved with the
optical component, and the torques generated by the drive forces,
which act on the guide unit, compensate for one another to less
than 10%.
Inventors: |
Melzer; Frank;
(Utzmemmingen, DE) ; Kwan; Yim-Bun Patrick;
(Aalen, DE) ; Xalter; Stefan; (Oberkochen, DE)
; Fiolka; Damian; (Oberkochen, DE) |
Correspondence
Address: |
FISH & RICHARDSON PC
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
CARL ZEISS SMT AG
Oberkochen
DE
|
Family ID: |
38954819 |
Appl. No.: |
12/337262 |
Filed: |
December 17, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/EP2007/007256 |
Aug 16, 2007 |
|
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12337262 |
|
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60822547 |
Aug 16, 2006 |
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Current U.S.
Class: |
355/67 |
Current CPC
Class: |
G02B 7/14 20130101; G03F
7/70825 20130101; G02B 7/023 20130101; G03F 7/70108 20130101; G03F
7/70116 20130101; G02B 7/102 20130101 |
Class at
Publication: |
355/67 |
International
Class: |
G03B 27/54 20060101
G03B027/54 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 16, 2006 |
DE |
10 2006 038 455.5 |
Claims
1. An apparatus, comprising: an optical component that can be moved
by a distance along a straight line within a time of between 5 ms
and 500 ms, the straight line having a polar and azimuth angle of
between 0.degree. and 90.degree., and a distance between the
straight line and an optical axis of the apparatus being less than
a cross-sectional dimension of a projection exposure beam bundle of
the projection exposure apparatus; a guide unit configured to guide
the optical component; and a drive unit configured to drive the
optical component via drive forces so that torques generated by
inertial forces of the optical component and of optional components
concomitantly moved with the optical component, and the torques
generated by the drive forces, which act on the guide unit,
compensate for one another to less than 10%, wherein the apparatus
is a lithographic projection exposure apparatus.
2. The apparatus as claimed in claim 1, wherein forces transmitted
to the guide unit by the drive unit, in a direction perpendicular
to a guide direction, are less than 10% of the drive forces in a
direction of the straight line.
3. The apparatus as claimed in claim 1, wherein the torques
generated by inertial forces of the optical component and of the
optional possible components concomitantly moved with the optical
component and the torques generated by the drive forces add up to
zero, and wherein the forces in a direction perpendicular to the
guide direction are zero.
4. The apparatus as claimed in claim 1, wherein a movable distance
of the optical component is between 20 mm and 1000 mm.
5. The apparatus as claimed in claim 1, wherein the guide direction
is parallel to the straight line to within production and alignment
tolerances.
6. The apparatus as claimed in claim 1, wherein the polar angle is
0.degree. and the straight line is vertical.
7. The apparatus as claimed in claim 1, wherein the polar angle is
90.degree. and the straight line is horizontal.
8. The apparatus as claimed in claim 1, wherein the straight line
is vertically parallel to the optical axis of the apparatus.
9. The apparatus as claimed in claim 1, wherein the straight line
is vertically perpendicular to the optical axis of the
apparatus.
10. The apparatus as claimed in claim 1, wherein the straight line
intersects the optical axis of the apparatus.
11. The apparatus as claimed in claim 1, wherein the optical
component is optically centered with respect to the straight
line.
12. The apparatus as claimed in claim 1, wherein the guide axis and
the drive axis coincide.
13. The apparatus as claimed in claim 12, wherein the guide unit
comprises a slide guided by a guide and having guide areas spaced
apart by a magnitude SL in the guide direction, the guide and the
slide have a bearing play y, and, between an oscillation amplitude
L--occurring in the direction of the straight line--of the optical
component, which is spaced apart from the guide by the magnitude b,
the relationship SL>y*b/L is complied with.
14. The apparatus as claimed in claim 13, wherein the magnitude SL
of the spaced-apart guide areas have more than three times the
distance of the centroid of the optical component with respect to
the guide.
15. The apparatus as claimed in claim 13, wherein a balancing mass
M.sub.A is arranged on a side opposite to the optical component
with respect to the guide axix such that the inertial forces
generated by the optical component, the slide and the balancing
mass M.sub.A in total no torque perpendicular to the guide
direction acts on the guide unit.
16. The apparatus as claimed in claim 13, wherein the guide
direction has a parallel offset with respect to the drive direction
apart from production and alignment tolerances.
17. The apparatus as claimed in claim 16, wherein the drive forces
act on the common centroid of optical component and optional
components concomitantly moved with the optical component.
18. The apparatus as claimed in claim 16, wherein the drive forces
act on two edge regions of the optical component, and a connecting
straight line that connects the edge regions runs through the
common centroid of optical component and optional components
concomitantly moved with the optical component.
19. The apparatus as claimed in claim 18, wherein the drive forces
acting on the edge regions are generated by separately controllable
or regulatable drive units with drive directions that are parallel
apart from production and alignment tolerances.
20. An apparatus, comprising: optical component that can be moved
by a distance along a straight line, the straight line having
having a polar and azimuth angle of between 0.degree. and
90.degree., and a distance between the straight line and an optical
axis of the apparatus being less than a cross-sectional dimension
of a projection exposure beam bundle of the projection exposure
apparatus; a guide unit configured to guide the optical component,
the guide unit having a guide axis; and a drive unit configured to
drive the optical component via drive forces so that torques
generated by inertial forces of the optical component and of
optional components concomitantly moved with the optical component,
and the torques generated by the drive forces, which act on the
guide unit, compensate for one another down to a magnitude of less
than 10%, the drive unit having a drive axis, wherein: the guide
axis and the drive axis coincide; the guide unit comprises a slide
guided by a guide and having guide areas spaced apart by a
magnitude SL in the guide direction; the guide and the slide have a
bearing play y, and, between an oscillation amplitude L--occurring
in the direction of the straight line--of the optical component,
which is spaced apart from the guide by the magnitude b; the
relationship SL>y*b/L is complied with; a balancing mass MA is
arranged on a side opposite to the optical component with respect
to the guide axis such that the inertial forces generated by the
optical component, the slide and the balancing mass MA in total no
torque perpendicular to the guide direction acts on the guide unit;
and the apparatus is a lithographic projection exposure
apparatus.
21. An optical system, comprising: a plurality of optical
components; an actuating unit configured to position at least one
of the plurality of optical components at defined positions along
an optical axis of the optical system to set different operational
configurations of the optical system, wherein the actuating unit
acts on the optical component at least one point of action, the
actuating unit is configured so that it is possible to change
between two different operational configurations within a time
period of less than 500 ms, and the optical system is configured to
be used in semiconductor lithography.
22. The optical system as claimed in claim 21, wherein the optical
component is mechanically connected to a balancing mass to reduce
parasitic forces/moments.
23. The optical system as claimed in claim 22, wherein the
balancing mass has a larger mass than a mass of the optical
component, and a distance between a centroid of the balancing mass
and a bearing point is less than a distance between the centroid of
the optical component and the bearing point.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] 1. Field
[0002] The disclosure relates to an optical system for
semiconductor lithography including a plurality of optical
components, as well as related components and methods.
[0003] 2. Background
[0004] Optical systems for semiconductor lithography can be
flexibly set to a wide variety of operational configurations.
SUMMARY
[0005] In some embodiments, the disclosure provides a device and a
method which permit the rapid changing of the operational
configuration of an optical system for semiconductor
lithography.
[0006] In one aspect, the disclosure provides an optical system
configured to be used in semiconductor microlithography. The
optical system includes a plurality of optical components and an
actuating unit. The actuating unit is configured to position at
least one of the plurality of optical components at defined
positions along an optical axis of the optical system to set
different operational configurations of the optical system. The
actuating unit acts on the optical component at least one point of
action, and the actuating unit is configured so that it is possible
to change between two different operational configurations within a
time period of less than 500 ms.
[0007] In another aspect, the disclosure provides a method that
includes changing between two different operational configurations
of an optical system for semiconductor lithography in a time period
of less than 50 ms by positioning at least one optical component of
a plurality of optical components of the optical system along an
axis of the optical system.
[0008] In a further aspect, the disclosure provides an illumination
system for a projection exposure apparatus in semiconductor
lithography. The illumination system includes an optical element
configured to set a light distribution in a pupil plane of the
system. The illumination system also includes a manipulable optical
component arranged in a light path upstream of the optical element
so that different regions of the optical element can be illuminated
by manipulating the optical component.
[0009] In an additional aspect, the disclosure provides a
lithographic projection exposure apparatus. The apparatus includes
an optical component that can be moved by a distance along a
straight line. The straight line has a polar and azimuth angle of
between 0.degree. and 90.degree.. A distance between the straight
line and an optical axis of the apparatus being less than a
cross-sectional dimension of a projection exposure beam bundle of
the projection exposure apparatus. The apparatus also includes a
guide unit configured to guide the optical component. The apparatus
further includes a drive unit configured to drive the optical
component via drive forces so that torques generated by inertial
forces of the optical component and of optional components
concomitantly moved with the optical component, and the torques
generated by the drive forces, which act on the guide unit,
compensate for one another down to a magnitude of less than
10%.
[0010] In another aspect, the disclosure provides an illumination
system for a projection exposure apparatus in semiconductor
lithography. The illumination system includes an optical component
configured to set a radiation distribution in a pupil plane of the
system, the optical component comprising at least two optical
partial elements. Each of the partial optical components is capable
of being introduced periodically at a frequency into a beam bundle
used to illuminate. The illumination system also includes a source
of pulsed electromagnetic radiation configured to generate the beam
bundle, a pulse frequency of the electromagnetic radiation
corresponding to the frequency at which the partial elements are
introduced into the beam bundle.
[0011] In some embodiments, the optical system for semiconductor
lithography includes a plurality of optical components, where, for
setting different operational configurations of the optical system,
there is at least one actuating unit for positioning at least one
optical component at defined positions along an optical axis of the
optical system. In this case, the actuating unit acts on the
optical component at least one point of action and is designed so
that it is possible to change between two different operational
configurations within a time period of less than 500 ms (e.g., 50
ms). Appropriate optical components include all optical elements
that are usually used in optical systems, such as, for example,
lenses, mirrors, diaphragms, plane-parallel plates or else
diffractive optical elements such as, for example, diffraction
gratings, in each case with mounts, if appropriate.
[0012] The optical system can be, for example, an illumination
system or else a projection objective of a lithographic projection
exposure apparatus.
[0013] In some embodiments, the points of action of the actuating
unit on the optical component are chosen in such a way that no
moments arise on the optical component. In other words, as a result
of the acceleration of the optical components during their movement
for positioning, no torques or tilting moments take effect on the
optical component. This means that only a linear acceleration is
present at the optical component as a result. As soon as the
optical component has reached the desired position, only the
inertial forces resulting from the linear acceleration have to be
compensated for in order to prevent or effectively attenuate a
subsequent oscillation of the optical component. In this case, a
linear acceleration encompasses positive accelerations, during
which the kinetic energy of the optical component increases with
respect to time, and also negative accelerations or decelerations,
in which the kinetic energy of the optical component decreases with
respect to time. By way of example, the linear acceleration of the
optical component is provided shortly before reaching a desired end
position via a retardation of the optical component. In this case,
the forces of the actuating unit act on the optical component in
such a way according to the disclosure that after vector addition
of all the forces (including the inertial forces), no resultant
torque having a component perpendicular to the acceleration takes
effect on the optical component. Optionally, the resultant torque
is zero, or less than 10% with regard to its magnitude, such as
less than 1% of the magnitude of the maximum occurring individual
torque generated by the forces (including inertial forces). In this
case, the lower limit for the resultant torque also depends, inter
alia, on the friction occurring in the actuating unit. As a result,
this has the effect that the time required overall for positioning
the optical component is significantly reduced by comparison with
certain known times. This is because avoiding the resultant torque
mentioned considerably reduces or completely prevents the
oscillation excitation of the actuating unit and/or of a guide unit
for the optical component (for the precise linear guidance
thereof), by the movement of the optical component, such that
possible oscillation amplitudes of the optical element do not
affect the desired end position of the element. This affords the
possibility of switching an optical system for semiconductor
lithography from one operational configuration to another within
extremely short time periods.
[0014] The optical component's freedom from moments during the
adjusting process as outlined above can be achieved in this case by
virtue of the fact that precisely one point of action of the
actuating unit on the optical component is present, which is chosen
in such a way that the vector of the force exerted on the optical
component by the actuating unit at the point of action runs through
the centroid of the optical component. By virtue of the fact that
the actuating unit acts on the optical component only at one
location and the vector of the force exerted on the optical
component by the actuating unit runs through the centroid of the
optical component, the required freedom from moments or the moment
equilibrium can be ensured in a simple manner. This variant need
not involve the force that is exerted on the optical component at
different points by one or a plurality of actuating units to be
apportioned in such a way that a moment equilibrium or a freedom
from moments for the optical component arises as a result--this
requirement is automatically fulfilled by the choice of the point
of action and the direction of the force.
[0015] As a result of geometrical conditions of the device it may
be appropriate to provide precisely two points of action of the
actuating unit on the optical component. In this case, the desired
mechanical behavior of the optical component can be achieved by
virtue of the fact that the points of action are chosen in such a
way that the centroid of the optical component lies on the area
which is defined by a straight line through the two points of
action and the vector of the resultant force acting on the optical
component. In this case, the optical component can be moved at the
points of action either by one actuating unit or by two actuating
units for positioning. In this case, the use of just one actuating
unit for positioning has the advantage that a coordination of the
forces acting on the optical component at the points of action is
already inherently ensured by this structural measure. Since only
one actuating unit acts on the optical component, it is ensured
that the forces acting at the two points of action are always in
the same relationship with respect to one another, which is
determined only by the geometry of the arrangement and not by the
forces exerted by different actuating units. It goes without saying
that the actuating unit can also act on the optical component via
more than two points of action; in this case, it is merely
necessary to ensure that no resultant torques or tilting moments
arise at the optical component as a result.
[0016] In this case, it has proved worthwhile to embody the
actuating unit in such a way that it has at least one Lorentz
linear actuator. In this case, a Lorentz linear actuator is
understood to be a linear motor in which a translational, linear
movement is achieved directly on account of the force interaction
between magnets that is based on the Lorentz force. In this case,
the magnets can be realized as coils through which current flows,
that is to say as electromagnets, or--in some instances--as
permanent magnets. One advantage of using Lorentz linear actuators
is that extremely rapid movements can be realized in a precise
manner using the actuators. In this case, the Lorentz linear
actuator operates practically contactlessly and hence in a manner
free of wear and maintenance; furthermore, the force exerted by the
Lorentz linear actuator is dependent only on the current flowing
through the coils and not on the present actuator position. As a
result, the use of the linear actuator permits the positioning of
an optical component over travels of a few cm, such as in the
region of 20 cm, with an accuracy in the .mu.m range within a time
period of less than 500 ms, such as less than 50 ms.
[0017] For the case where the Lorentz linear actuator has permanent
magnets, it is advantageous if the magnets are mechanically
connected to the optical component. The arrangement of the
permanent magnets on the optical component has the advantage that
the desire for a cabling of the optical component to be moved, as
would be necessary in the case of using coils through which current
flows, is effectively avoided in this way and the mobility of the
optical component is therefore not restricted by the cabling as a
result. This variant is advantageous particularly for those cases
where the optical component is intended to be positioned over a
longer path, in particular in the region of greater than 50 mm.
[0018] For cases where the optical component is positioned over a
shorter path, it can also be advantageous if the Lorentz linear
actuator has coils that are mechanically connected to the optical
component. Although this procedure has the implication that the
electrical cables required for making contact with the coils have
to be concomitantly moved, this procedure has the advantage that
the coils used usually have a smaller weight than the permanent
magnets, such that the inertial forces resulting from the
accelerations of the optical component are lower than in the case
of using permanent magnets.
[0019] The technical characteristics of the Lorentz linear actuator
as outlined above make it possible for at least one Lorentz linear
actuator to be designed to position a plurality of optical
components. Via suitable driving of the coils through which current
flows, it is possible in this case to achieve a mutually
independent movement of different optical components via the same
Lorentz linear actuator. The apparatus outlay and hence the
complexity of the overall system can be effectively limited in this
way.
[0020] For guiding the movement of the optical component during the
positioning, a linear guide has proved to be worthwhile, which
guide can be a rolling bearing guide or as an aerostatic bearing,
such as a gas bearing, air bearing or air cushion bearing. In this
case, the linear guide ensures that the optical element, during its
positioning, does not experience an offset or tilting with respect
to the optical axis of the optical system. The use of a linear
guide with rolling bearings--as ball recirculation or cross roller
guide--has the advantage that a guide of this type can be realized
in very stiff fashion.
[0021] The functioning of an aerostatic bearing is based on the
fact that two elements moved relative to one another are separated
by a thin gas film and therefore do not come into mechanical
contact with one another. In this way, the elements are enabled to
be moved relative to one another in a manner exhibiting very little
wear and friction, whereby particle abrasion that leads to
contaminations can also be avoided. In this case, the gas film can
be established dynamically by feeding in gas. The purge
gas--generally nitrogen--used anyway in optical systems for
semiconductor lithography can advantageously be employed as the
gas.
[0022] An encoder having a measuring head and a reference grating
can be used for determining the position of the optical component.
In this case, the reference grating can be realized as a line
grating structure on a plastic film adhesively bonded onto the
optical component. The measuring head registers the number of lines
passing it during a movement of the optical component and derives
the position of the optical component therefrom. It goes without
saying that it is also conceivable for the measuring head to be
arranged on the optical component; this is advantageous primarily
when the structural space is greatly restricted in an axial
direction.
[0023] A compensation device can be employed for the compensation
of the weight force acting on the optical component, the
compensation device being realized for example as a counterweight
or as a frictionless pneumatic cylinder with gap seals. This
variant has the advantage that it is possible to avoid
contamination of the interior of the optical system by escaping
gas. The compensation of the weight force has the effect that in
the rest state the optical component does not have to be held by
the actuating unit against the weight force and heating of the
actuating unit in the rest state is thus prevented.
[0024] The actuating unit can be designed so that it includes an
axial actuating mechanism for positioning the optical component in
a direction of an optical axis of the optical system and a pivoting
mechanism for pivoting the optical component out of or into the
beam path of the optical system. It goes without saying that it is
also conceivable for only the pivoting mechanism to be connected,
and for a movement of the optical component in an axial direction
not to be provided. This measure has the effect that optical
components, as long as they are situated outside the beam path of
the optical system, can be brought ready to the axial position at
which they are intended to be situated in a new operational
configuration of the optical system. In this case, the axial
positioning of the optical components can already be effected
during the operation of the optical system in the old operational
configuration; for setting the new operational configuration it
then suffices merely to pivot the relevant optical components into
the beam path of the optical system, thus reducing the time
required for changing from one operational configuration to the
next. For this purpose, it is advantageous if the pivoting
mechanism and the axial actuating mechanism are designed so that
there is a free travel of the optical component in an axial
direction if the optical component is pivoted out of the beam path
of the optical system.
[0025] Since a comparatively long time, usually between one and six
seconds, is available on account of the variant outlined above for
the axial positioning of the optical components, the requirements
made of the axial actuating mechanism are comparatively moderate.
They can be spindle drives, Lorentz linear actuators, toothed racks
or else cable pulls.
[0026] In this case, the pivoting mechanism can a rotatable
element; the centroid of the arrangement of pivoting mechanism and
optical component can advantageously be arranged in the region of
the axis of rotation of the pivoting mechanism; rotational
oscillations of the optical component can be avoided particularly
effectively in this way. If the centroid is on the axis of
rotation, then the sum of the centrifugal or centripetal forces is
advantageously zero. As a result, the axis of rotation is not
burdened by a possible unbalance. An oscillation excitation of the
axis of rotation and thus also an oscillation excitation of the
optical element or of the optical component are thus effectively
avoided, whereby a precise positioning of the optical component
within a very short time becomes possible. Furthermore, it is
advantageous to design the pivoting mechanism in stiff and
lightweight fashion for avoiding oscillations. Materials having a
large modulus of elasticity with low density, that is to say for
example titanium alloys or else carbon fiber composite materials,
are appropriate for realizing the pivoting mechanism. Because only
individual optical components are pivoted into the beam path of the
optical system, the accelerated masses and hence the resultant
inertial forces are small--also on account of the aforementioned
choice of the materials for the pivoting mechanism--, such that
fast movements can be realized without excessively severe
oscillations of the device occurring. In this case, the pivoting
operation mentioned is effected within 500 ms, such as within 50
ms, in modern lithography apparatuses within 10 ms. It should be
mentioned that it is also possible for more than one optical
component to be pivoted into the beam path, or with the pivoting of
an optical component or a group of optical components into the beam
path of a lithographic projection exposure apparatus it is possible
at the same time for at least one other optical component to be
pivoted out of the beam path. Thus, e.g. just by pivoting optical
components into and out of the beam path of a projection exposure
apparatus for example in a zoom axicon system, it is possible to
obtain two different configurations with regard to the illumination
setting respectively arising.
[0027] For rapidly pivoting the optical components into the beam
path it has proved worthwhile to embody the pivoting mechanism in
such a way that they have a prestress element and a releasable
retention element. It is thus possible to establish a prestress
relative to the retention element even before the optical component
is pivoted into the beam path; after the release of the retention
element, the full force is then immediately present at the optical
component, which can then be introduced rapidly into the beam path.
In this case, the prestress element can be realized as an
electromagnet, for example.
[0028] As a further variant of the arrangement according to the
disclosure, at least two actuating units having in each case at
least one axial actuating mechanism and in each case at least one
pivoting mechanism assigned to the axial actuating mechanism can be
present. In this case, the optical components that can be
positioned by the actuating units can be substantially identical or
else different with regard to their optical properties. The
coupling of the optical component(s) to the actuating units can be
effected in such a way that, as illustrated above, the oscillation
excitation of actuating units and/or guide units for guiding the
optical component, such as e.g. the axis of rotation, are
minimal.
[0029] In a further advantageous variant of the disclosure, at
least one of the optical components has a centering tolerance
within the range of between 30 .mu.m and 60 .mu.m. The centering
tolerance of the relevant optical component to be positioned is
thus higher than the centering tolerance of the optical components
fixedly incorporated in the optical system. The higher centering
tolerance of the optical components to be positioned can be
achieved for example by a corresponding rebudgeting in the design
of the optical system. As a result of the higher centering
tolerance of the optical components to be positioned, the
requirements made of the actuating unit and the mechanisms assigned
thereto decrease, thus reducing the outlay in the construction and
realization of the device according to the disclosure.
[0030] As a further possibility, e.g. for the case where the
optical component is mounted such that it is pivotable or rotatable
with respect to a bearing point, the optical component can be
mechanically connected to a balancing mass in order to reduce
parasitic forces/moments. In this case, the balancing mass can have
a larger mass than the mass of the optical component, which can be
compensated for by virtue of the fact that the distance between the
centroid of the balancing mass and the bearing point is less than
the distance r between the centroid of the optical component and
the bearing point. The balancing mass can itself again be formed by
an optical component.
[0031] The disclosure described above can advantageously be used in
an illumination system for a projection exposure apparatus in
semiconductor lithography. In this case, the illumination system
can include an optical element, e.g. a micromirror array, which can
serve for setting a light distribution in a pupil plane of the
illumination system. For setting or for supporting the setting of
the light distribution, a manipulable optical component is arranged
in the light path upstream of the optical element in such a way
that different regions of the optical element, such as e.g. of the
micromirror array, can be illuminated by a manipulation of the
optical component.
[0032] The manipulable optical component can be a mirror which is
movable, such as displaceable or tiltable, in the light path. It is
likewise possible to use a diffractive optical element which can be
introduced, such as inserted, into the light path, a conical lens
of an axicon or a refractive optical component.
[0033] In addition, it is advantageous if optically active elements
for polarization rotation are arranged in the light path upstream
of the optical element, which elements can be used to set different
polarizations for the different regions of the optical element; the
arrangement of at least one neutral filter in the light path
upstream of the optical element is also conceivable.
[0034] Some exemplary embodiments of the disclosure are explained
in more detail below with reference to the drawings.
[0035] In the figures:
[0036] FIG. 1 shows a device according to the disclosure;
[0037] FIG. 2 shows a first variant of the present disclosure;
[0038] FIG. 2a shows a schematic bearing device for moving an
optical element according to the prior art;
[0039] FIG. 2b shows a bearing device according to FIG. 2a with an
end position of the optical component and possible oscillations
thereof;
[0040] FIG. 2c shows a schematic illustration of a further variant
of the present disclosure, with a guide device for guiding the
optical component and an actuating unit or drive device, for
linearly displacing the optical component;
[0041] FIG. 2d shows an embodiment according to FIG. 2c taking
account of friction in the guide device;
[0042] FIG. 2e shows a schematic illustration of the forces that
occur in an embodiment according to FIG. 2c taking account of the
friction according to FIG. 2d;
[0043] FIG. 2f shows a further embodiment of the disclosure with
drive forces acting on the edge of the optical component;
[0044] FIG. 2g shows a further embodiment of the disclosure;
[0045] FIGS. 3a-3c show various possibilities for varying the
arrangement of optical component, actuating units and linear
guide;
[0046] FIG. 4 shows a variant of the disclosure in which the linear
guides are realized as air bearings;
[0047] FIGS. 5a-5b show two embodiments of the device according to
the disclosure in which the weight force of the optical component
is compensated for;
[0048] FIG. 6 shows a further embodiment of the device according to
the disclosure, in which the optical components, in addition to a
displacement in a direction of the optical axis of the optical
system, can also be pivoted out of the region of the optical axis
or into the region of the optical axis;
[0049] FIG. 7 shows an embodiment of a pivoting mechanism for
pivoting the optical component into and out of the beam path of the
optical system;
[0050] FIG. 8 shows an example of the use of a balancing mass;
[0051] FIG. 9 shows a part of an illumination system of a
projection exposure apparatus for semiconductor lithography;
[0052] FIG. 10 shows partial regions of a micromirror array and
corresponding light distributions in a pupil plane;
[0053] FIGS. 11a-11b show a first possibility for setting a light
distribution on a micromirror array;
[0054] FIG. 12 shows a further possibility for setting a light
distribution on a micromirror array;
[0055] FIG. 13 shows a possibility for selectively choosing the
polarization in different regions of the pupil plane;
[0056] FIG. 14 shows an additional possibility for setting a light
distribution on a micromirror array using a so-called axicon;
[0057] FIG. 15 shows a neutral filter for use in an optical system
according to the disclosure; and
[0058] FIG. 16 shows a further possibility for setting a light
distribution without linearly accelerated elements.
[0059] FIG. 1 shows a device according to the disclosure. In this
case, the optical component 1 is moved via the actuating units 2
along the optical axis, which in the present case runs
perpendicular to the plane of the drawing. In the present case, the
two actuating units 2 are realized as Lorentz linear actuators with
permanent magnets 4 and coils 5; in this case, the permanent
magnets 4 are mechanically connected to the optical component 1 via
a respective point of action 3. As indicated in FIG. 1, in this
case the straight line through the two points of action 3 runs
through the centroid--designated by "S"--of the optical component
1. This arrangement of the points of action has the advantage that,
assuming an at least approximately identical behavior of the
actuating units 2, the optical component 1 can be moved without
torques acting on it. What is achieved in this way is that
oscillations of the optical component 1 during or after the
positioning, which oscillations could originate from such torques,
cannot arise. As a result this provides a possibility of moving the
optical component 1 very rapidly along the optical axis to the
desired position in the optical system, since, firstly, the time
period required for the optical component 1 to come to rest after
reaching its position in the optical system is significantly
shortened and, secondly, overall higher speeds become possible for
the positioning of the optical component 1. In this case, the
movement of the optical component 1 along the optical axis is
stabilized by the linear guide 6 and measured by the displacement
measuring system 12. The displacement measuring system 12 can be a
so-called encoder whose measuring head 15 is fixedly connected to
the housing (not illustrated in FIG. 1) of the optical system and
whose reference grating 16 is concomitantly moved with the optical
component 1; it is likewise conceivable to arrange the measuring
head 15 on the optical component 1 and to fixedly connect the
reference grating 16 to the housing of the optical system. The
second variant is advantageous particularly when little structural
space is available in an axial direction. Instead of an encoder
measuring system, it is alternatively possible to use a different
position detecting system if the latter has the required accuracy.
A position detecting system is ideally used for each Lorentz linear
actuator.
[0060] FIG. 2 shows a variant which differs from FIG. 1 in terms of
the concrete configuration of the actuating unit 2. In the variant
shown in FIG. 2, in contrast to FIG. 1, the coils 5 rather than the
permanent magnets 4 are mechanically connected to the optical
component 1, that is to say that the coils 5 concomitantly move
with the optical component 1. What is advantageous about this
variant is that the coils 5 generally have a smaller mass than the
permanent magnets 4, whereby the mass moved in total is reduced.
This variant can be expedient for the realization of short
adjusting distances, where making electrical contact with the coils
5 via cable connections, for example, is unproblematic.
[0061] In order to illustrate the advantages of the present
disclosure, a technical embodiment of an adjustable optical
component 1 with an adjusting unit known in the prior art is
described schematically referring to FIG. 2a. In this case, the
optical component 1 is displaced along an optical axis 200. In
order to produce this linear displacement of the optical component
1, an actuating unit is used which moves a slide 62 by a magnitude
X along the coordinate axis X, and in this case the optical
component 1 moves by substantially the same magnitude X along the
optical axis 200. As shown in FIG. 2a, the slide 62 can be guided
via a guide 63, wherein the guide axis 60 is substantially parallel
to optical axis 200 within mechanical production and alignment
tolerances.
[0062] The optical component 1 illustrated in FIG. 2a is connected
to the slide 62 via a connection 64 (not illustrated in more
specific detail). The optical component 1 is a refractive element,
for example, which can include polyhedral and/or convex or concave
surfaces 101, 102. The guide 63 and the slide 62 usually form a
driven actuating unit such as can be realized e.g. via the linear
actuators described above. In this case, e.g. the slide 62 is moved
along the guide 63 via electromagnetic forces. A force F is
required for accelerating the slide 62 and the optical component 1,
and also for overcoming the friction force of the actuating unit.
If the friction force is initially disregarded, then an
acceleration a=F/(m+ms) results from the force F taking account of
the mass m of the optical component 1. In this case, the mass of
the slide 62 is designated by ms. This acceleration brings about an
inertial force F.sub.T, which acts on the centroid 103 of the
optical component 1 and which results as F.sub.T=m*a. If the
optical component 1 is constructed in such a way that its centroid
is displaced along the optical axis 200, then F.sub.T acts along
the optical axis 200. It should be mentioned, however, that for the
present exemplary embodiment and for the subsequent exemplary
embodiments it is not necessarily a requirement that the centroid
of the optical component or the centroid of the system of optical
components 1 and slide 62 moves along the optical axis 200. The
centroids can alternatively also move along an axis displaced
parallel to the optical axis 200.
[0063] Disregarding possible bearing play of the slide 62
perpendicular to the guide axis 60 of the actuating unit including
the guide 63 and the slide 62, and likewise disregarding the
geometrical extent of the guide 63 in this direction, e.g. since
the distance b between the optical axis 200 and the guide axis 60
is very much greater than the extent of the guide 63, the inertial
force F.sub.T generates a torque M.sub.T=b*F.sub.T oriented in a
direction perpendicular to the guide axis 60. A further torque in
this direction can be generated e.g. by the inertial force of the
slide 62 if its centroid does not lie on the guide axis 60 of the
guide 63.
[0064] The torques generated by the inertial forces dynamically
load the guide 63 and the slide 62 (and the optical component 1),
such that these elements are excited to effect constrained
oscillations as a result of the torque input, or as a result of the
forces caused by the torques. If the optical component 1 is
transferred from a position A (see FIG. 2a) into an end position B
(see FIG. 2b), the deceleration of the optical component 1 on
account of its inertial force F.sub.T brings about a torque M.sub.T
which brings about excitation to form oscillations mentioned above.
The excitation of such oscillations can result in an oscillation
202 of the optical component 1, wherein an imaginary plane 201
through the optical component 1, running perpendicular to the
optical axis 200, oscillates about an axis C. The position of this
oscillation axis C need not coincide with the position and
direction of the torque M.sub.T as shown in FIG. 2b. Rather, the
position and the direction of this axis of rotation C depend on the
constrained oscillations, wherein the position of the axis of
rotation C is substantially determined by the geometry of the guide
63 and of the slide 62 since the effect of the torque M.sub.T is
substantially taken up by this guide device 62, 63. In FIGS. 2a and
2b, tilting oscillations are also produced by the torque M.sub.T.
The tilting oscillations are not damped by the drive device, which
can be, for example, a Lorentz linear drive, rather they are
predominantly damped by the damping effect of the guide device 62,
63. This damping effect is very small, however, particularly in the
case of "frictionless" bearing, which is why, according to the
inventors' knowledge, a tilting oscillation excitation by the
torque makes a fast precision positioning very difficult or even
impossible, as is also explained in more detail below.
[0065] In order to position the optical component 1 within less
than 500 ms down to less than 50 ms, in modern lithography
apparatuses even within 5 ms, to approximately 10 .mu.m down to 1
.mu.m accuracy with respect to the end point B of its displacement,
it is necessary for the optical component 1 to reach its end
position with as little oscillation as possible with regard to
possible oscillations in a direction of the optical axis 200. This
is necessary since any oscillation excitation which has an
oscillation component 202 in a direction of the optical axis 200
and an amplitude within the range of 1 to 10 .mu.m makes it
impossible to position the optical component 1 within the time
mentioned. This is owing to the fact that the oscillations 202
usually decay very much more slowly than the time available for
positioning the optical component 1 in its end position B, the time
being less than 500 ms (e.g., less than 50 ms, less than 5 ms).
This relatively slow decay behavior of the constrained oscillations
is caused by the fact that the oscillation frequencies are in the
range from a few Hz up to a few kHz.
[0066] The precision with regard to the actuating accuracy of the
optical component 1 relative to its end position B of between 1 and
10 .mu.m within a minimal time within the range of a new ms to 500
ms can advantageously be obtained within a lithographic projection
exposure apparatus via the present disclosure, as has already been
explained above in connection with FIGS. 1 and 2.
[0067] The disclosure therefore includes a lithographic projection
exposure apparatus including an optical component that can be moved
by a distance along a straight line within a positioning time. In
this case, the optical component 1 includes one or a plurality of
optical elements 34, which, if appropriate, also have mount
elements. The straight line generally furthermore has a polar and
azimuth angle of between 0.degree. and 90.degree.. These angles
define the direction of the straight line or of the degree of
freedom of movement along which the optical component 1 can move.
Furthermore, the distance between the straight line and an optical
axis is less than a cross-sectional dimension of a projection
exposure beam bundle of the projection exposure apparatus. Since
the straight line need not necessarily intersect an optical axis
within the projection exposure apparatus, since this is dependent
on the optical components used, the straight line can also be
spaced apart from the optical axis. According to the disclosure,
the optical component 1 is guided by a guide unit or guide device
(e.g. a linear guide) having a guide direction and is driven via a
drive or adjusting unit (actuating unit) having a drive direction
via drive forces in such a way that the torques generated by
inertial forces of the optical component 1 and of possible
components concomitantly moved with the optical component 1, and
the torques generated by the drive forces, which act on the guide
unit, compensate for one another down to a magnitude of less than
10%. A complete compensation is striven for in this case. However,
this depends on the requirements with regard to positioning time
and distance to be moved, and also on the technical configuration
of the guide unit.
[0068] In order to ensure no oscillation excitation of the guide
unit as far as possible also at a constant speed of the optical
component 1, the drive unit can be configured in such a way that
the forces transmitted to the guide unit, in a direction
perpendicular to the guide direction, are less than 10% of the
drive force in a direction of the straight line or in a direction
of movement. Here, too, a best possible avoidance of such forces is
striven for, wherein ideally no forces act perpendicular to the
guide direction.
[0069] In the case of lithographic projection exposure apparatuses,
the movable distance of the optical component 1 is between 20 mm
and 1000 mm, wherein, as already mentioned, the positioning time is
between 5 ms and 500 ms.
[0070] As already becomes clear in the previous examples, the guide
direction can be arranged, apart from production and alignment
tolerances, parallel to the straight line along which the optical
component 1 is moved. This requires a stiff and rigid linking of
the optical component 1 to the guide unit. Of technical interest
are those movements of the optical component 1 which enable a
horizontal or vertical displacement. Displacements along an optical
axis of the projection exposure apparatus or perpendicular thereto
are likewise advantageous. Moreover, it can be advantageous to
permit the straight line to intersect the optical axis or to bring
it to coincidence therewith.
[0071] If the optical component 1 includes for example a
rotationally symmetrical optical element, or an optical element 34
which has a rotationally symmetrical effect on the projection
exposure beam bundle at least in sections, then the optical
component 1 can be optically centered with respect to the straight
line along which it moves. In this case, optical centering is
understood to mean that e.g. an optical element 34 having the
symmetry properties mentioned lies with its point of symmetry on
the straight line.
[0072] FIG. 2c illustrates this, wherein the essential components
are only illustrated schematically. In this case, an optical
component 1, which has e.g. a reflective surface on a substrate,
such as e.g. the concave mirror illustrated in FIG. 2c, is
displaced along the optical axis 200 in the X direction. In this
case, the optical component 1 having the reflective surface can
also be e.g. a diffractive optical element, such as e.g. a
reflection grating, but it can also be e.g. a mirror array. In this
case, the optical element 1 is guided via the slide 462 and the
guide 463, wherein the guide axis 460 of the linear guide 463 is
oriented parallel to the optical axis 200 within the scope of the
production and alignment tolerances. Furthermore, the guide 463
with its slide 462 has no drive unit serving for the linear drive
of the optical component 1. In this case, the guide 463 and the
slide 462 can be, for example, an air cushion guide, a magnetic
guide, or in the form of a sliding or rolling bearing guide. The
optical component 1 is driven via a drive unit 300, which likewise
includes a slide 362 and a guide 363. The drive unit 300 can be
designed analogously to the adjusting unit illustrated above. The
drive unit 300 usually has a drive axis 360 oriented parallel to
the guide axis 460 of the guide 463 of the optical element. In this
case, the drive unit 300 can be configured e.g. as an
electromagnetic linear drive, as has already been described above
in connection with the exemplary embodiments of FIGS. 1 to 2b. In
this case, the drive slide 362 acts on the optical element in such
a way that, via an operative connection 364, the drive forces
(accelerating or decelerating forces) pass with their force action
line through or substantially through the centroid 103 of the
optical component 1. In this case, analogously to the explanations
concerning in FIGS. 2a and 2b, the centroid 103 is not necessarily
arranged on the optical axis 200, as is illustrated merely by way
of example in FIG. 2c. For the case where the drive unit 300
likewise represents a guide for the optical component 1, the latter
would be mounted in a statically overdetermined manner, whereby
forces and moments would be input onto the optical element. In
order to avoid this, a moment decoupling element (not illustrated
in FIG. 2c) is advantageously fitted to the operative connection
364, which can include e.g. a ball-and-socket joint on which the
drive force acts and from which the drive force is transmitted to
the optical component 1.
[0073] If the mass ratio between optical component 1 and the mass
of the guide slide 462 is such that the mass of the slide 462 is no
longer negligible in comparison with the mass of the optical
component 1, then the operative connection 364 is chosen such that
the force action line of the force applied by the drive unit 300
passes through the overall centroid of optical component 1 and
guide slide 462. In this case, possible mount element for the
optical component 1, which connect the optical component 1 to the
guide slide 462 and hold it in position, are likewise taken into
account. Such a directing of the drive force onto the system
including optical component 1 and guide slide 462 has the advantage
that the drive force and the inertial force caused by the masses of
the guide slide 462 and of the optical component 1 upon
acceleration (or deceleration) add up to zero, for which reason no
torque having a component perpendicular to the optical axis 200 or
perpendicular to the guide axis 460 is transmitted to the guide 463
via the guide slide 462. An oscillation excitation of the guide 463
during the movement of the optical component 1 along the optical
axis 200 thus fails to occur, thereby enabling the optical
component 1 to be rapidly positioned into an end position with
extremely high precision.
[0074] At very high speeds or accelerations of the optical
component 1, a no longer negligible friction force occurs at the
guide 463 and at the slide 462, depending on the technical
configuration of the guide, which friction force, in the embodiment
according to FIG. 2c, can likewise excite the guide 463 to
oscillation. This is because as a result of the friction force,
which occurs e.g. also at a constant speed of the optical component
1, the drive unit 300 has to counteract this friction force via the
operative connection 364 via a force that is correspondingly
identical in magnitude but directed in the opposite direction, in
order to overcome the friction force F.sub.R. This force F applied
by the drive unit 300 and introduced via the operative connection
364 brings about a torque M.sub.R in a direction perpendicular to
the guide axis 460, as is illustrated schematically in FIG. 2d. In
this case, FIG. 2d shows an excerpt from FIG. 2c with the presence
of friction forces between guide 463 and slide 462 during constant
movement of the optical component 1 along the axis 200, that is to
say in arrow direction x. Since the friction also occurs during
acceleration, the friction force additionally has to be overcome
there as well. This makes it necessary for the drive force that
acts on the optical element from the drive unit 300 via the
operative connection 364 not only to be predetermined by the
necessary acceleration but to be increased by the magnitude of the
friction force F.sub.R with regard to its magnitude. This increased
magnitude of the drive force is not compensated for by the inertial
force F.sub.T with regard to the generation of torques. This
non-compensated force likewise generates, as illustrated above, a
torque perpendicular to the guide axis 460 or perpendicular to the
direction of movement, which takes place along the optical axis 200
in the exemplary embodiment shown. This torque can excite the guide
463 of the optical component 1 and hence the slide 462 and the
optical component 1 to effect oscillations, thereby preventing a
rapid precise positioning.
[0075] In the case where virtually speed-independent sliding
friction is present, the influence of the friction forces F.sub.R
and the influence of the torques M.sub.R associated therewith can
be reduced firstly by temporally minimizing the uniform movement of
the optical component 1 during the adjustment of the optical
component 1 or by completely dispensing with a uniform movement.
Secondly, the acceleration can be chosen in such a way that an
inertial force F.sub.T acts which is equal to the drive force F
reduced by the magnitude of the friction force F.sub.R. In
addition, the operative connection 364, at which the drive force is
introduced onto the optical component 1, between the optical
component 1 and the slide 462 is no longer introduced in such a way
that the force action line passes through the common centroid
thereof, as was mentioned in connection with FIG. 2c. The operative
connection 364 is chosen in such a way that the inertial force
acting at the common centroid 103 (which results from optical
component 1 and the slide 462) and the torque M.sub.T associated
therewith precisely compensate for the torque M.sub.F generated by
the drive force. Since the inertial force F.sub.T is given and the
drive force F is increased by the friction force F.sub.R, it is the
case that F.sub.T=F-F.sub.R holds true, where F.sub.T is <F, an
offset V of the centroid 103 in a direction of the guide axis 460
is necessary for the operative connection 364 in order to obtain
the above compensation of the torques M.sub.T=M.sub.F. The drive
force F is then introduced into the operative connection 364,
displaced by the offset V, in such a way that the force action
line, instead of passing through the centroid, is displaced by the
offset V parallel thereto in a direction of the guide axis 460.
This force situation is illustrated schematically in FIG. 2e, which
shows the forces occurring in FIG. 2d in relation to the common
centroid 103 together with the offset V. In the case of the guides
462, 463 used in projection exposure apparatuses in the course of
precise positioning, the friction force is usually very much
smaller than 0.001 times the drive force. In the case of aerostatic
or magnetic guides, the friction force tends toward zero, such that
the offset is very small and often negligible.
[0076] On account of the above explanation, the present disclosure
encompasses embodiments in which an optical component 1 is guided
linearly as precisely as possible via a guide device, and to move
the optical component 1 linearly along the device. In this case,
via a drive unit 300 or an actuating unit 2, a drive force F is
directed into the optical component 1 in such a way that neither
forces nor torques having direction components perpendicular to the
direction of movement of the optical component 1 input onto the
guide 463 by the drive force F. In this case, the direction of
movement of the optical component 1 corresponds to the guide axis
460 of the guide 463 apart from production and alignment
tolerances. Via this, according to the disclosure, an oscillation
excitation of the guide 463 of the optical component 1 (and hence
also of the optical element 1) by the drive force F of the drive
unit 300 is prevented or at least reduced to an extent such that
highly precise linear position changes of the optical component 1
within a very short time in the range of ms, such as, for example,
between 5 ms through to 500 ms, are made possible.
[0077] In order also to displace or position transparent optical
component 1 according to the embodiments described in FIGS. 2c to
2e, the drive-force-transmitting operative connection 364a of the
optical component 1 is configured in such a way that e.g. the
optical component 1 is connected to the drive unit in each case at
an edge region in such a way that a straight line through the edge
regions intersects the centroid 103, wherein the straight line can
be chosen to be perpendicular to the plane spanned by the optical
axis 200 and the guide axis 460. This is illustrated in the
exemplary embodiment according to FIG. 2f. This schematically shows
a section perpendicular to the direction of movement, which is
intended to be identical to the optical axis 200, wherein the
optical component 1 (or the optical component) is provided with
edge regions 110, 111 at which the drive forces generated by the
drive slide 362 of the drive unit 300 with the drive axis 360 is
input via a suitable operative connection 364 in the direction of
movement. In this case, as mentioned above, the operative
connection can include elements which permit a moment decoupling,
as is the case e.g. for ball-and-socket joints. The abovementioned
straight line is designated by 112 and runs through the common
centroid 103 of the optical component 1 and of the slide 462
perpendicular to the spanned plane. In the case of friction in
accordance with the embodiments according to FIG. 2d, the straight
line has a corresponding offset V according to FIG. 2e and runs in
a manner displaced parallel by the offset parallel to the straight
line 112 shown in FIG. 2f in a direction of the guide axis 460. In
order to avoid a statically overdetermined guide of the optical
component 1, a dedicated drive device that acts with its respective
drive force on the edge regions 110 and 111 can in each case be
provided instead of the drive device 300 with the drive axis 360
(also see FIG. 2c). The drive devices that act on the optical
component 1 in such a way are controlled or regulated independently
of one another. This embodiment corresponds to the embodiment of
the disclosure illustrated in FIG. 1, wherein the drive units have
parallel drive directions apart from production and alignment
tolerances.
[0078] In the context of the knowledge according to the disclosure
that in lithography apparatuses a precise and rapid positioning of
optical component 1 in accordance with the above explanations
necessitates as far as possible avoiding (or minimizing)
oscillation excitations of the guides of the optical component 1 by
the forces of the drive system, FIG. 2g shows a further embodiment,
based on the embodiment of FIGS. 2a and 2b. Guide axis and drive
axis coincide here as in the exemplary embodiment according to
FIGS. 2a and 2b. In this case, the optical component 1 connected to
the slide 62 is guided via the slide in such a way that on account
of the length SL of the slide in a direction of the guide axis 60,
the oscillation amplitude 202 of the optical component 1 in the
direction is reduced, wherein the oscillations essentially result
on account of the mechanical play between the guide slide 62 and
the guide 63. In this case, the guide slide can be dimensioned in
such a way that the oscillation amplitudes that are possible as a
result of the bearing play in the region and in the direction of
the optical axis 200 is less than L=10 .mu.m. Given a typical
bearing play of y=1 .mu.m, this means that for instance y/SL=L/b.
In this case, SL is the length of slide 62 and b is the distance
between the guide axis 60 and the optical axis 200. By way of
example, if b exhibits 50 mm, this results in a length of the slide
62 of SL=5 mm. This means that for the bearing play of 1 .mu.m and
the distance b of approximately 50 mm, the slide 62 should have at
least a length of 5 mm in order, on account of the mechanical play,
to be able to position the optical component 1 within the desired
positioning accuracy of better than 10 .mu.m in the region of the
optical axis. More generally, the above condition can be formulated
in such a way that the guide unit includes a slide guided by a
guide and having guide areas spaced apart by a magnitude SL in a
guide direction. In this case, the guide and the guide slide have a
bearing play y. Furthermore, between an oscillation amplitude
L--occurring in a direction of the straight line (along which the
optical component 1 moves)--of the optical component 1, which is
spaced apart from the guide by the magnitude b, the relationship
SL>y*b/L is intended to be complied with. In practice, SL values
in the range of 3 to 10 times the distance between the centroid of
the optical component 1 and the guide often result in this case,
wherein, if the structural space is available, even the 10-fold
value can be exceeded, as is explained in more detail below.
[0079] The abovementioned condition with regard to the bearing play
can be supplemented further by also reducing a reduction of the
effect of the torque effects that arise as a result of the inertial
force F.sub.T, and its effects with regard to constrained
oscillations. During deceleration of the optical component 1, the
inertial force F.sub.T generates a torque M.sub.T, which is
compensated for by a torque generated by the force F.sub.S, wherein
the force F.sub.S acts at least in the vicinity of a slide end. In
this case, approximately F.sub.S*S.sub.L=M.sub.T. These are only
approximations since, depending on the configuration of the slide
62 and the guide 63, given the presence of bearing play, the
possible axes of rotation about which the slide 62 is induced to
rotate on account of the torques caused on account of the inertial
forces are not precisely defined. Furthermore, the exact torque
condition also depends on the position of the optical element 1
relative to the slide 62. Overall it can be stated, however, that
the oscillation excitation of the guide 63 will turn out to be all
the smaller, the smaller the force F.sub.S acting on the guide. The
force can be reduced by suitable configuration of the length SL of
the guide slide 62 to approximately 10% of the inertial force
F.sub.T which results during acceleration or deceleration of the
optical component 1 (the optical component 1) together with the
slide 62. It is thus possible to specify a rough dimensioning rule
that can be represented on the basis of a torque equilibrium in the
form F.sub.T*b=F.sub.S*S.sub.L=0.1.times.F.sub.T*SL. This permits
the determination of SL, wherein SL is then approximately 10*b. In
this case, b, as illustrated in FIG. 2g, is the distance between
the guide axis 60 and the optical axis 200. The first condition
with regard to the bearing play is generally fulfilled via the
dimensioning rule. What is disadvantageous about this dimensioning
is that in general the slide 62 exceeds the length of 10 cm up to
50 cm, whereby an increased mass is disadvantageously to be moved,
which results in an increased drive power. Furthermore, the
necessary structural space for this demonstrated inventive solution
according to FIG. 2g is often not available.
[0080] In a further embodiment of the disclosure, the embodiment
according to FIGS. 2a, 2b is modified in such a way that a
balancing mass M.sub.A is fitted on a side opposite to the optical
component 1 with respect to the guide axis 60, as is indicated
schematically in FIG. 2g. The balancing mass M.sub.A is rigidly
connected to the slide 62 and chosen with regard to size and
distance from the guide axis 60 in such a way that the inertial
force proceeding from it during acceleration of the optical
component 1 generates a torque in such a way that the torque
M.sub.T of the optical component 1 (and possibly of the slide) is
precisely compensated for. This means that no resultant torque
arises in a direction perpendicular to the guide axis 60 during
acceleration or deceleration of the optical component 1. By virtue
of this measure, during acceleration of the optical component 1,
the guide axis 60 is likewise not excited to effect oscillations,
or is at least only excited to effect oscillations to a reduced
extent. What is disadvantageous here, too, is that an additional
mass has to be moved, which increases the drive power and which
requires an additional structural space.
[0081] FIGS. 3a, 3b and 3c show various possibilities for varying
the arrangement of optical component 1, actuating units 2 and
linear guide 6. In the variant illustrated in FIG. 3A, the two
optical components 1 are in each case guided on dedicated linear
guides 6 in a direction of the optical axis, wherein the actuating
units 2 serve for the drive, the actuating units being in the form
of Lorentz linear actuators in the example shown. In the example
shown, the permanent magnet 4 is mechanically connected to the
optical component 1 and concomitantly moves with the latter; it
goes without saying that a variant in which the coil 5 is
mechanically connected to the optical component 1 is also
conceivable. In this case, the linear guide 6 can be, for example,
a rolling bearing guide, sliding bearing guide, air or magnetic
bearing guide.
[0082] FIG. 3B shows a variant which is modified by comparison with
the arrangement in FIG. 3A and in which the arrangement of the
optical components 1 on the linear guides 6 is realized oppositely
to the embodiment shown in FIG. 3A, whereby the required structural
space can be reduced in the direction orthogonal to the optical
axis.
[0083] FIG. 3C illustrates a variant in which the two optical
components 1 are guided on a common linear guide 6, which likewise
results in a reduction of the required structural space. In this
case, a magnetic arrangement is used jointly by a plurality of
optical components, but each force action point on each optical
component 1 can be regulated or controlled completely independently
of the other force action points.
[0084] In the exemplary embodiments illustrated in FIG. 3, two
optical components 1 are moved by the same Lorentz linear actuator
as actuating unit 2. A further advantage of the use of a Lorentz
linear actuator as actuating unit 2 becomes clear as a result of
this: on account of the purely electronic driving, it is possible
for two optical components 1 to be moved independently of one
another by the same actuator merely via a suitable driving.
[0085] FIG. 4 shows, in a section orthogonal to the optical axis, a
variant of the disclosure in which the linear guides 6 are realized
as air bearings. In this case, the four air bearings 6 are arranged
opposite one another respectively in pairs between the two
actuating units 2--realized as Lorentz linear actuator--along the
inner circumference of the housing 7. The use of air bearings as
linear guides 6 has the advantage that a mechanical sliding contact
is obviated and a friction of mechanical components against one
another is thus precluded. This effectively avoids firstly the
desire for lubrication and also the risk of particle abrasion of
the mechanical components rubbing against one another. The use of
air bearings is thus advantageous particularly in the case of high
cycle numbers. As an alternative to the air bearings, it is also
possible to use rolling bearings for the linear guide; such ball
recirculation or else cross roller guides have the advantage that
they can be designed as components having a high stiffness.
[0086] FIGS. 5a and 5b show two embodiments of the device according
to the disclosure in which the weight force of the optical
component 1 is compensated for. In FIG. 5a this is achieved via the
counterweight 9, which acts on the optical component 1 in the
region of the linear guide 6 via a cable pull 11 via the deflection
rollers 10. FIG. 5b shows the variant wherein the weight force is
compensated for by the two pneumatic cylinders 17a and 17b with gap
seals. In this case, the two pneumatic cylinders 17a and 17b are
arranged on the optical component 1 in such a way that the straight
line through the points of action of the two pneumatic cylinders
17a and 17b runs through the centroid of the optical component 1
and, as a result, no additional moments arise at the optical
component 1. This variant has the effect that the total mass to be
moved during the positioning of the optical component 1 is kept
small. The compensation of the weight force of the optical
component 1 has the advantage that the actuating units can merely
be used to bring the optical component 1 to the desired position as
necessary, rather than having to hold the position of the optical
component 1 against its entire weight force during operation. The
use of the weight force compensation illustrated is appropriate
particularly for cases where the optical axis of the optical system
and thus the movement axis of the devices lie in a vertical
direction. In other words, the actuating unit can be used
exclusively for moving the optical component 1 and not for working
on it against the gravitational force, which would lead to a
considerable heating of the actuating unit 2. If the optical axis
and/or the direction of movement of the optical component 1 has a
direction deviating from the horizontal, then the weight force
resolved by resolution of forces in a direction of the direction of
movement and in a perpendicular direction thereto is compensated
for in a direction of the direction of movement. This compensation
can be effected in accordance with FIGS. 5a and 5b. This affords
the advantage that only the inertial forces and friction forces
have to be applied for moving the optical element.
[0087] FIG. 6 shows a further embodiment of the device according to
the disclosure, in which the optical components 1, in addition to a
displacement in a direction of the optical axis of the optical
system, can also be pivoted out of the region of the optical axis
or into the region of the optical axis. For this purpose, the
actuating unit 2a is provided with the two axial actuating
mechanism 13a and with the pivoting mechanism 14a, by which the
abovementioned movements of the optical components 1a can be
carried out. The optical system is additionally provided with the
actuating mechanism 2b, which, for their part, have the axial
actuating mechanism 13b and the pivoting mechanism 14b; in FIG. 6,
the optical components 1b connected to the second actuating unit 2b
have been pivoted out of the beam path of the optical system and
thus out of the optical axis indicated by a dash-dotted line. The
embodiment illustrated in FIG. 6 permits the optical properties of
the optical system and hence the operational configuration of the
optical system to be changed over in an extremely rapid manner. For
this purpose, it is merely necessary for the optical components 1a
situated in the beam path to be pivoted out of the beam path by the
pivoting mechanism 14a and, simultaneously or shortly afterward,
for the optical components 1b to be pivoted into the beam path of
the optical system using the pivoting mechanism 14b. In this case,
the optical components 1b can already be brought into their axial
position along the optical axis by the axial actuating mechanism
13b before the pivoting-in process, that is to say still during the
operation of the optical system in the first operational
configuration, such that this step does not lead to a loss of time
when changing over the optical system from one operational
configuration to the next. In the example shown, the optical
components 1a are merely replaced by the optical components 1b,
which are substantially identical to them with regard to their
optical properties, at other locations along the optical axis in
the optical system. However, the case where the optical components
1 that can be positioned by the actuating units 2a and 2b have
different optical properties is also conceivable. In this case,
further optical degrees of freedom result for the possible
operational configurations of the optical system.
[0088] FIG. 7 shows an embodiment of a pivoting mechanism 14,
corresponding to the pivoting mechanism 14a, 14b from FIG. 6, for
pivoting the optical component 1 into or out of the beam path of
the optical system, in which a prestress element 18 and a
releasable retention element 19 are provided. In this case, the
prestress element 18 is an electromagnet which, upon its
activation, has an attracting effect on the magnetizable part of
the optical component 1 that faces it. In this case, the rotation
of the optical component 1 about the axis indicated by the arrow in
the shape of an arc of a circle in FIG. 7 is initially prevented by
the releasable retention element 19. At the instant at which the
releasable retention element 19 is moved in a direction of the
arrow, the optical element 1 is rotated on account of the magnetic
attraction force between the electromagnet and the magnetizable
part of the optical element 1. A rapid pivoting of the optical
component 1 can be ensured in this way. If appropriate, an
electromagnet (not illustrated) can likewise be present on the
opposite side to the prestress element 18, via which electromagnet
the movement of the optical component 1 into its original position
can be achieved; a restoring of the of the optical component 1 via
a resilient element (likewise not illustrated) is equally
conceivable.
[0089] FIG. 8 shows a further exemplary embodiment of the
disclosure, which takes account of the requirement that,
particularly during a rapid pivoting of the optical component 1, as
illustrated in FIG. 7, for example, without corresponding
countermeasures, parasitic forces/moments such as e.g. transverse
forces or tilting moments act on the bearing about which the
optical component 1 is pivoted.
[0090] Such parasitic forces and/or moments can be effectively
minimized, as illustrated in FIG. 8, by the balancing mass 20 being
arranged on the opposite side of the optical component 1 with
respect to the bearing point 21. In this case, the position of the
centroids S' of the optical component 1 and of the centroid S'' of
the balancing mass 20 with respect to the bearing point 21 are
chosen such that the following holds true:
r R = M m . ##EQU00001##
where r: distance between the centroid S' of the optical component
1 and the bearing point 21 R: distance between the centroid S'' of
the balancing mass 20 and the bearing point 21 M: mass of the
balancing mass 20 m: mass of the optical component 1.
[0091] In this case, the bearing point (21) should be understood as
the point at which the plane in which the pivoting/rotation of the
centroid S' of the optical component (1) is effected intersects the
axis of rotation/pivoting axis. If the above condition is complied
with, then the bearing force in a radial direction of the rotation
axis upon rotation is minimized in the sense that no centrifugal or
centripetal forces occur whose vector sum is not equal to zero,
since the axis of rotation of the arrangement passes through the
common centroid. This avoids excitation of any oscillations of the
axis of rotation as a result of a possible unbalance which, after
reaching an end position of the optical component 1, have the
effect that the latter performs oscillations about the end
position, such that the position of the optical component 1 varies
relative to the optical axis or in a direction of the optical
axis.
[0092] The moment of inertia I of the overall arrangement is
calculated as a sum of the two moments of inertia with respect to
the bearing point 21 as
I=mr.sup.2+MR.sup.2+I.sub.m+I.sub.M.
Substitution leads to
I = mr 2 ( 1 + R r ) + I m + I M . ##EQU00002##
[0093] In this case, I.sub.m+I.sub.M are the moments of inertia of
the optical component 1 with the mass m and, respectively of the
balancing mass M relative to the respective axis of rotation which
passes through the respective centroid of the optical component and
of the balancing mass, and which run parallel to the abovementioned
axis of rotation/pivoting axis through the bearing point 21.
[0094] It becomes clear from the relationships illustrated that the
variant illustrated in FIG. 8 opens up the possibility, given a
suitable choice of R, that is to say of the distance between the
balancing mass 20 and the location of the bearing 21, of providing
the possibility that, via the use of the balancing weight 20, the
parasitic forces on the bearing 31 are largely minimized without
the total moment of inertia I of the entire arrangement of optical
component 1 and balancing mass 20 assuming such a high value that a
rapid pivoting of the arrangement about the bearing point 21 is
made excessively more difficult. This is achieved by making the
radius of the balancing mass M from the axis of rotation as small
as possible, which as a counterpart action means an increase in the
balancing mass M. The measure illustrated in FIG. 8 thus has the
effect that a subsequent oscillation of the overall arrangement
after the rapid pivoting of the optical component 1 into the beam
path of the optical system is shortened considerably and the
optical system reaches its operational readiness more rapidly after
the pivoting. It goes without saying that the use of the balancing
mass 20 for reducing parasitic forces in bearing points is not
restricted to the variant illustrated in FIG. 8; it is likewise
conceivable for the teaching of FIG. 8 also to be applied to the
arrangements illustrated in FIGS. 1 to 5, for example as a
supporting measure.
[0095] FIG. 9 shows an optical system in which the principles
described above can advantageously be employed.
[0096] The system described with reference to FIG. 9 is a subsystem
30 of an illumination system of a projection exposure apparatus for
semiconductor lithography as far as the first pupil plane 31, which
is indicated via the dashed line in FIG. 9. The light
distribution--usually referred to as setting--in the pupil plane 31
is set by way of the beam deflection of a previously homogenized
and collimated laser beam 33 via a micromirror array (MMA) 32 in a
field plane. The other optical elements illustrated in FIG. 9,
which are designated in combination by the reference symbol 34,
serve for beam shaping on the path of the laser beam 33 from the
micromirror array 32 as far as the pupil plane 31; they are not
discussed explicitly below.
[0097] The method of so-called double exposure, which is widespread
in semiconductor lithography, imposes on the illumination system
the requirement of changing between two settings within a few
milliseconds, such as within the range of 10 to 30 milliseconds. In
this case, the frequency of the changes themselves is of a similar
order of magnitude. This setting change means that thousands of the
micromirrors (not explicitly illustrated in FIG. 9) arranged on the
micromirror array 32 have to be adjusted per change of the setting.
The associated mechanical loading on the micromirrors leads,
particularly in the case of a high number of cycles, to the
occurrence increasingly of mechanical failures of individual
mirrors or a shortening of the recalibration intervals for the
absolute mirror position on account of drift. The objective
consists in minimizing the mechanical loading on the individual
micromirrors of the micromirror array 32 during the fast setting
changes described.
[0098] This can be achieved in accordance with the exemplary
embodiment illustrated in FIG. 9 by dividing the micromirror array
32 into at least two partial regions. In this case, each partial
region of the two regions mentioned contains approximately half of
all the micromirrors or, given a subdivision into three partial
regions, for example, a third of all the micromirrors, etc. The
first partial region is configured, with regard to the position of
the individual micromirrors, to the first setting to be chosen,
whereas the second partial region, with regard to the arrangement
of its micromirrors, is adapted for the second setting. For a
change of the setting, in accordance with the exemplary embodiment
shown in FIG. 9, the individual micromirrors of the entire
micromirror array 32 are now no longer adjusted, rather care is
merely taken to ensure that exclusively that partial region of the
micromirror array 32 which is respectively adapted to the chosen
setting is illuminated. This has the effect that, in the event of a
change of the setting, the micromirrors themselves do not have to
be moved since only a different illumination of the micromirror
array 32 is chosen.
[0099] FIG. 10 illustrates, in the upper region of the figure, the
two light distributions that are set alternately in the pupil plane
31. Setting 1 (left-hand part of FIG. 9a) in this case shows the
locations--called poles--having a high light intensity 210, 212,
213 and 214, whereas setting 2 (right-hand part of FIG. 9a) shows
the poles 215, 216, 217 and 218.
[0100] In the example illustrated in FIG. 10, setting 1 is produced
by the beam deflection of the micromirrors lying in the region 101
and 102 of the micromirror array 32, whereas setting 2 is produced
by the illumination of the micromirrors of the regions 103 and 104
(cf. lower part of FIG. 9a).
[0101] FIGS. 11a and 11b show the arrangement according to the
disclosure for setting the light distributions on the micromirror
array 32. The optical components 1' and 1'' are diffractive optical
components in the variant illustrated in subfigures a and b in FIG.
11. It goes without saying that it is likewise possible to use
refractive optical components instead of diffractive optical
components 1' and 1''; one advantage of this variant is for example
because refractive optical components are generally more efficient
and cause less scattered light.
[0102] By displacing the optical components 1' and 1'' in the beam
path of the laser beam 33 in a direction of the double-headed arrow
36 in such a way that the optical component 1' or 1'' is
alternately situated in the beam path of the laser beam 33, what
can then be achieved is that the regions 101, 102 (optical
component 1') or 103 and 104 (optical component 1'') on the
micromirror array 32 are alternately illuminated. The lens 35 in
the light path between the optical components 1' and 1'' and the
micromirror array 32 serves for beam shaping in this case.
[0103] An essential aspect of the embodiment shown in FIG. 11 is
that the micromirror array 32 is arranged in the pupil plane (not
designated in FIG. 11) of the lens 35 and the light distribution on
the micromirror array 32 is determined by the position or setting
of the optical components 1' and 1'' in the field plane upstream of
the lens 35. In the example illustrated in FIG. 11, the optical
components 1' and 1'' and also the micromirror array 32 are
arranged in a respective focal plane of the lens 35. In this case,
it is advantageous if the focal length of the lens 35 has a highest
possible value; ranges from 500 millimeters to 100 millimeters can
be advantageous here. The described arrangement of lens 35, optical
components 1' and 1'' and micromirror array 32 has the effect that
an approximately collimated illumination on the micromirror array
32 becomes possible, the illumination thus exhibiting little
divergence. In this case, the application of the possibilities
shown in FIGS. 1 to 8 for rapidly changing the optical component 1
in the beam path of the optical system enable the rapid setting
changes striven for; it goes without saying that it is likewise
conceivable to apply the teaching of FIGS. 9 and 10 without
resorting to the technical solutions illustrated in FIGS. 1 to 8.
Assuming that the laser beam 33 exhibits a diameter of
approximately 20 millimeters and a switching time of 20
milliseconds is necessary, the speed at which the optical component
1' or 1'' has to be moved in the beam path of the laser beam 33 is
approximately one meter per second, which represents a value that
can perfectly well be controlled in respect of mechanical
aspects.
[0104] One advantage of the embodiment illustrated in FIGS. 10 and
11 is that the shape of the pupil in the illumination system, in
contrast to a procedure according to the prior art, is not set via
a for example diffractive optical component without a micromirror
array 32, but rather via the micromirror array 32 itself. This has
the effect that in the extreme case the number of optical
components to be kept available can be limited to two, since the
micromirror array 32 exhibits the necessary flexibility with regard
to the settings to be set. It goes without saying that the
arrangement and the geometry of the regions 101 to 104 is not
restricted to the form illustrated in FIGS. 9 and 10. In a
simplified embodiment, a mirror can be used as the optical
component 1, which mirror is shifted to and fro or else tilted in
the beam path of the laser beam 33 in order to illuminate the
different regions, such as 101 and 102 for example, on the
micromirror array 32. This embodiment is depicted schematically in
FIG. 12. It goes without saying that the use of prisms, beam
deflectors or other optical components is also conceivable.
[0105] A subdivision of the regions 101, 102 and/or 103, 104 into
subregions having a different polarization enables a change in
polarization at the speed discussed above. For this purpose, the
polarization in each of the regions mentioned is set by 90.degree.
rotators, that is to say optically active plane plates, in the
arrangement of a so-called "Schuster plate". The "Schuster plate"
includes at least two birifrigent elements having a different
orientation of the crystal axes or thicknesses with respect to one
another. It utilizes the linear birefringence in order to convert a
first polarization distribution into a second polarization
distribution varying locally in its profile. A detailed description
of the functioning is contained in DE 195 35 392 A1. FIG. 13 shows
a possible assignment between the polarization, the partial regions
101, 102, 103, 104 of the micromirror array 32 and the poles of the
settings 210, 212, 213, 214, 215, 216, 217, 218 in the pupil plane
31 (cf. FIG. 13). The light linearly polarized in the y direction
becomes linearly polarized light in the x direction in the region
101 owing to the use of a 90.degree. rotator (not illustrated) that
covers the region 101.
[0106] Further rotators in the regions 103 and 104 correspondingly
rotate by 45.degree. and -45.degree., respectively, relative to the
orientation of the laser polarization. In this case, in a known
manner, the polarization rotation is proportional to the thickness
of the optically active substrate of the rotator, whereby different
angles of rotation can be realized.
[0107] FIG. 14 shows a further variant, which is suitable for
generating rotationally symmetrical light distributions on the
micromirror array 32. In this case, the micromirror array 32 is
divided into the two regions 101 and 102 having a different
functionality. In the example shown in FIG. 13, the optical
component 1 is realized as one of the two conical lenses of an
axicon 40. The two conical lenses hollow cone in one instance and
as cone in one instance and have an identical acute angle.
Furthermore, the distance B between the two conical lenses is
adjustable. For the case where the two conical lenses are in
contact with one another, and the distance B is equal to zero, this
results in a light distribution in the form of a circle. Where B is
greater than zero, the beam 33 is expanded to the effect that this
results in an annular light distribution with a dark field in the
center. After passing through the axicon 40, the laser beam 33
impinges on the lens arrangement including the lenses 37, 38 and
having a variable distance D, which lens arrangement acts in the
manner of a zoom lens and expands the laser beam 33. The neutral
filter 39 is arranged in the further course of the light path in a
direction of the micromirror array 32. A setting of the distance B
between the two conical lenses of the axicon 40 in conjunction with
the setting of the distance D between the two lenses 37 and 38
makes it possible to illuminate, alternatively or else jointly, the
partial regions 102 and/or 101 on the micromirror array 32. In
addition, an arrangement for beam homogenization can be disposed
(not illustrated in FIG. 13) in the light path upstream of the
axicon 40.
[0108] The beam conditioning can be implemented in such a way that
any desired light distributions on the micromirror array 32, such
as, for example, multipoles, segments or the like, are possible.
For this purpose, it is possible, if appropriate, to adapt the
geometry of the conical lenses of the axicon 40; a prismatic
embodiment of the conical lenses is conceivable, by way of
example.
[0109] An abaxial illumination of the micromirror array 32 is also
possible. For this purpose, the relative orientation between the
laser beam 33 and the axicon 40 is changed; by way of example, the
position of the laser beam 33 on the axicon 40 is displaced in the
z-y plane. This can be effected for example by two tiltable mirrors
(not illustrated) disposed upstream of the arrangement. This makes
it possible to illuminate only the upper partial region of the
micromirror array 32 by a displacement of the laser beam 33 upward
(z direction).
[0110] For intensity correction in the pupil plane 31 already on
the plane of the micromirror array 32, it is possible for example
to use the neutral filter 39 illustrated in FIG. 15. In the neutral
filter 39 shown in FIG. 15, the light is attenuated to a greater
extent in the central region 231 than in the peripheral region 232.
In this case, the region 231 corresponds to the region 101 on the
micromirror array 32, the region 232 corresponding to the partial
region 102 on the micromirror array 32. The embodiment of the
neutral filter 39 depends on the magnitude of the parameters D and
B. Consequently, it will be necessary to introduce different
neutral filters 39 into the beam path depending on the setting
chosen. In this case, for rapidly changing the neutral filters, it
is possible to have recourse to the concepts illustrated with
reference to FIGS. 1 to 8.
[0111] Correspondingly, the teaching illustrated in FIGS. 1-8 can
be employed for the manipulation of the optical components 1, 1',
1'' illustrated in FIGS. 11, 12 and 14; a realization independently
thereof is likewise possible, of course.
[0112] A further possibility for setting the desired settings,
which manages completely without linearly accelerated masses in the
system and the inertia effects associated therewith, is described
below with reference to FIG. 16: the optical component 1 is
accordingly realized as a rotating, for example circular, disk with
partial elements 1' 1'' as circle sectors. In principle, it
suffices to embody the optical component 1 in such a way that it
has at least two optical partial elements which can each be
introduced periodically at a specific frequency f into a beam
bundle used for illumination, such as into the laser beam 33, for
example. In the case of the rotating circular disk, the rotational
angular frequency 2.pi.f of the optical component 1 corresponds
here for example to the pulse frequency of a laser used for
illumination. This has the effect that the light used for
illumination is always incident on the same optical partial element
1' or 1'' of the rotating optical component 1. When using a CW
(continuous wave) laser, the necessary pulses can be generated for
example by the use of a periodically operated shutter or a chopper
wheel. The choice of the partial element 1' or 1'' to be used and
thus of the desired setting is effected in this case via the start
instant of the sequence of laser pulses used for the respective
exposure, of the so-called burst. The essential advantage of this
variant is that changing the setting does not require any
accelerated linear or rotational movements of optical elements in
the light path and thus in the system. This means that no
oscillations on account of the inertial forces are input into the
system. The setting is chosen purely electronically via the
synchronized, temporally controlled choice of the start instant of
the respective burst. In order to obtain a temporally stable
radiation distribution, it is advantageous if the radiation
distribution generated by the partial elements 1' and 1'' does not
change while the respective partial element 1' or 1'' stays in the
beam bundle 33, which can be achieved via a corresponding
geometrical configuration of the partial element 1' or 1''. In
order to minimize undesirable effects when the respective partial
element 1' or 1'' enters into or exits from the beam bundle 33, the
length and the start and end instants of the pulses can be chosen
in such a way that the entrance and the exit of the respective
partial element 1' and 1'' is effected during the dark phases
between the pulses; in other words, in this case the pulsed beam
bundle 33 only ever lies completely on one of the partial elements
1' or 1''.
* * * * *