Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B13/00—Optical objectives specially designed for the purposes specified below
  • G02B13/14—Optical objectives specially designed for the purposes specified below for use with infrared or ultraviolet radiation
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/0025—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration
  • G02B27/0068—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical correction, e.g. distorsion, aberration having means for controlling the degree of correction, e.g. using phase modulators, movable elements
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70216—Mask projection systems
  • G03F7/70258—Projection system adjustments, e.g. adjustments during exposure or alignment during assembly of projection system
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70216—Mask projection systems
  • G03F7/70258—Projection system adjustments, e.g. adjustments during exposure or alignment during assembly of projection system
  • G03F7/70266—Adaptive optics, e.g. deformable optical elements for wavefront control, e.g. for aberration adjustment or correction
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70216—Mask projection systems
  • G03F7/70308—Optical correction elements, filters or phase plates for manipulating imaging light, e.g. intensity, wavelength, polarisation, phase or image shift

Definitions

• the invention relates to a projection lens for imaging a pattern arranged in an object plane of the projection lens into an image plane of the projection lens by means of electromagnetic radiation having an operating wavelength ⁇ ⁇ 260 nm, and to a projection exposure method which can be carried out with the aid of the projection lens.
• microlithographic projection exposure methods are used for producing semiconductor components and other finely structured components, such as e.g. photolithography masks.
• the pattern is positioned in a projection exposure apparatus between an illumina- tion system and a projection lens in the region of an object plane of the projection lens and is illuminated with an illumination radiation provided by the illumination system.
• the radiation altered by the pattern passes as prediction radiation through the projection lens, which images the pattern on a reduced scale onto the substrate to be exposed.
• the surface of the substrate is arranged in the image plane of the projection lens, said image plane being optically conjugated with respect to the object plane.
• the substrate is generally coated with a radiation-sensitive layer (resist, photoresist).
• One of the aims in the development of projection exposure apparatuses is to lithographically produce structures having increasingly smaller dimensions on the substrate. Smaller structures lead to higher integration densities e.g. in semiconductor components, which generally has an advantageous effect on the performance of the microstructured components produced.
• the size of the structures that can be produced is crucially dependent on the resolution capability of the projection lens used and can be increased on the one hand by reducing the wave- length of the projection radiation used for the projection, and on the other hand by increasing the image-side numerical aperture NA of the projection lens that is used in the process.
• High-resolution projection lenses nowadays operate at wavelengths of less than 260 nm in the deep ultraviolet range (DUV) or in the extreme ultraviolet range (EUV).
• DUV deep ultraviolet range
• EUV extreme ultraviolet range
• catadioptric projection lenses are usually used, which contain both transparent refractive optical elements having refractive power (lens elements) and reflective elements having refractive power, that is to say curved mirrors.
• at least one concave mirror is contained.
• Integrated circuits are produced by a sequence of photolithographic patterning steps (exposures) and subsequent process steps, such as etching and doping, on the substrate.
• the individual exposures are usually carried out with different masks or different patterns.
• the individual photolithographic exposure steps it is necessary for the individual photolithographic exposure steps to be coordinated with one another as well as possible, with the result that the fabricated structures, for example contacts, lines and the constituents of diodes, transistors and other electrically functional units, come as close as possible to the ideal of the planned circuit layouts. Fabrication faults can arise, inter alia, if the structures produced in successive exposure steps do not lie one on top of another sufficiently accurately, that is to say if the superimposition accuracy is not sufficient.
• overlay The superimposition accuracy of structures from different fabrication steps of a photolithographic process is usually designated by the term "overlay”. This term denotes e.g. the superimposition accuracy of two successive lithographic planes. Overlay is an important parameter in the fabrication of integrated circuits since alignment errors of any type can cause fabrication faults such as short circuits or missing connections and thus restrict the functioning of the circuit.
• double-patterning method for example, a substrate, for example a semiconductor wafer, is exposed twice in succession and the photoresist is then processed further.
• a first exposure process e.g. a normal structure having a suitable structure width is projected.
• a second exposure process a second mask is used, having a different mask structure.
• periodic structures of the second mask can be displaced by half a period relative to periodic structures of the first mask.
• the differences between the layouts of the two masks can be large. Double patterning makes it possible to achieve a reduction of the period of periodic structures on the substrate. This can be accomplished only if the super- imposition accuracy of the successive exposures is good enough, that is to say if the overlay errors do not exceed a critical value.
• the invention addresses the problem of providing a projection lens and a projection exposure method for microlithography which allow different photolithographic processes to be carried out with small overlay errors.
• the projection lens has a wavefront manipulation system for dynamically influencing the wave- front of the projection radiation passing from the object plane to the image plane of the projec- tion lens.
• the effect of the components of the wavefront manipulation system which are arranged in the projection beam path can be set in a variable manner depending on control signals of a control device, as a result of which the wavefront of the projection radiation can be altered in a targeted manner.
• the optical effect of the wavefront manipulation system can be changed e.g. in the case of specific, previously defined causes or in a situation-dependent manner before an exposure or else during an exposure.
• the wavefront manipulation system has a first manipulator, which has a first manipulator surface arranged in the projection beam path.
• the first manipulator includes a first actuating device, which allows the surface shape and/or the refractive index distribution of the first manipulator surface to be altered reversibly.
• the wavefront of the projection radiation which is influenced by the first manipulator surface can be dynamically altered in a targeted manner. This alteration of the optical effect is possible without the first manipulator being exchanged for another manipulator.
• a manipulator surface is understood to mean a planar or curved surface which (i) is arranged in the projection beam path and (ii) in the case of which a change in its surface shape and/or its orientation with respect to the projection radiation leads to a change in the wavefront of the projection radiation.
• any curved surface of a lens element that is dis- placeable relative to the other optical components of a projection lens is a manipulator surface.
• Further examples are mechanically or thermally deformable surfaces of lens elements or mirrors.
• thermal manipulation of a lens element generally the refractive index of the lens will also vary locally spatially. If - e.g.
• this variation has no component in the direction of the projection radiation, that is to say that the refractive index varies only orthogonally with respect to the direction of the projection radiation then it makes sense also to regard a local variation of the refractive index of a lens element as an effect which occurs at a manipulator surface. This applies to thin plane plates, for example.
• the first manipulator according to the claimed invention is configured in such a way that over an optically used region of the first manipulator surface within an effective diameter D F P of said first manipulator surface it is possible to generate a plurality of maxima and a plurality of minima of an optical path length change of the projection radiation.
• N M AX is the number of maxima and NMIN is the number of minima of the optical path length change in the direction under considera- tion
• PCHAR DFP/((N M AX + NMIN)/2).
• the multiple alternation of the optical path length change caused by the first manipulator over the influenced cross section of the projection radiation need not be strictly periodic, with the result that, for example, the absolute values of the maxima and/or of the minima of the optical path length change and/or the lateral distances thereof can vary over the cross section of the influenced projection radiation.
• the first manipulator surface is arranged "in optical proximity" to a closest field plane of the projection lens.
• This "near-field arrangement” means, inter alia, that the first manipulator surface is arranged significantly closer to the closest field plane than to a pupil plane of the projection lens.
• each beam emerging from a field point of the field plane at the first manipulator surface illuminates a subaperture having a subaperture diameter SAD that is significantly less than the maximum diameter D F P of the optically used region of the first manipulator surface, with the result that the condition SAD / D F P ⁇ 0.2 holds true.
• the condition SAD / D FP ⁇ 0.1 it is even possible for the condition SAD / D FP ⁇ 0.1 to hold true.
• the subaperture diameter SAD should be understood to mean the diameter of the beam of projection light that emerges from an individual field point.
• the quotient SAD / D F P is generally independent of the height of the field point under consideration.
• the wavefront manipulator system is able to set or alter the distortion of the projection lens in the image field in a targeted manner in a field-dependent manner. This means, inter alia, that distortion values having different magnitudes can be set in a targeted manner for different field points.
• a wavefront manipulation system which is able to set a field-dependent distortion in a targeted manner depending on control signals allows a specific field-dependent distortion correction or distortion alteration to be introduced during each exposure process.
• the projection lens has an effective object field lying outside the optical axis (off-axis field) and having an aspect ratio of greater than 2: 1 between a longer side and a shorter side, wherein the optically used region has approximately a rectangular shape having an aspect ratio of greater than 2:1 and the first manipulator acts parallel to the longer side.
• the first manipulator should be able to generate a plurality of maxima and a plurality of minima of the optical path length change of the projection radiation.
• the longer side can be used particularly simply for varying the path length change.
• the wavefront manipulation system has only the first manipulator in optical proximity to the field plane and the finite first distance is dimensioned such that at the first manipulator surface upon activation of the first manipulator the condition
• NA M is the numerical aperture of the projection radiation at the first manipulator surface.
• the first manipulator surface should be arranged neither too close to said closest field plane nor too far away from said closest field plane.
• An advantageous first distance is provided when condition (1 ) above is fulfilled.
• the parameter SAD stands for the subaperture diameter of the projection radiation at the first manipulator surface. This parameter takes ac- count of the fact that each beam emerging from a field point of a field at the first manipulator surface illuminates a subaperture having a subaperture diameter SAD.
• the subaperture diameter can be understood as the diameter of the footprint of a single beam emerging from a field point at an optical surface.
• the subaperture diameter increases with increasing distance from the field.
• the lower limit is undershot, then although the level of undesirable aberrations, such as astigmatism, for example, can be kept low, at the same time normally the distortion can no longer be influenced in a field-dependent manner, to a sufficiently great extent, with the result that the effect of the first manipulator remains restricted to relatively low distortion values. More- over, unfavorable contributions to the defocus budget can arise if the first manipulator surface lies too close to the field plane.
• the closest field plane is the object plane of the projection lens. It is particularly advantageous if no optical surface having refractive power is arranged between the object plane and the first manipulator surface, with the result that the numerical aperture NA M of the projection radiation at the first manipulator surface is equal to the object-side numerical aperture NA 0 . Directly downstream of the mask pattern to be imaged, the effect of the manipulator cannot be disturbed by aberrations of intervening optical elements, with the result that the first manipulator can be used in a particularly targeted manner. Moreover, it can happen that there is no or no accessible intermediate image plane. The manipulation of the distortion by a single manipulator can be difficult if, for example, the relatively small first distance then required with respect to a field plane can be realized only with difficulty on account of structural prerequisites.
• some embodiments provide for the wavefront manipulation system to have in addition to the first manipulator a second manipulator, which has a second manipulator surface arranged in the projection beam path and a second actuating device for reversibly altering the surface shape and/or refractive index distribution of the second manipulator surface.
• the two manipulators can preferably be set independently of one another.
• manipulators With the use of at least two manipulators, this gives rise to larger ranges of suitable distances with respect to adjacent field planes, which can simplify the insertion of manipulators into the projection lens.
• two or more manipulators can be operated jointly such that their desired effects with regard to the field-dependent distortion mutually amplify one another, while the undesired effects on other aberrations, such as e.g. defocus and/or astigmatism, can at least partly mutually compensate for one another.
• the first manipulator surface and the second manipulator surface are arranged in such a way that the numerical aperture of the projection radiation at the first manipulator surface is equal to the numerical aperture of the projection radiation at the second manipulator surface.
• no optical element having refractive power should be situated between the manipulator surfaces. What can thereby be achieved, inter alia, is that the adjustments of the manipulators (e.g. with regard to the characteristic period) can be coordinated with one another particularly simply. It is also possible for a wavefront manipulation system to have more than two mutually independently drivable manipulators which are situated in near-field arrangement and the effects of which can be coordinated with one another, e.g. three or four manipulators.
• the projection lens is configured in such a way that between the object plane and the image plane at least one real intermediate image is generated in the region of an intermediate image plane, then the field plane closest to the first manipulator surface can also be said intermediate image plane.
• the first manipulator surface can lie upstream of the intermediate image plane or downstream of the intermediate image plane in the radiation direction.
• the numerical aperture at the location of the first manipulator surface is then dependent on the magnification scale with which the object is imaged into the corresponding intermediate image.
• the numerical aperture in the vicinity of the intermediate image is greater than the object-side numerical aperture NA 0 , with the result that the suitable first distances D1 are smaller than in the case of an arrangement in the vicinity of the object plane.
• magnifying imaging is present be- tween object plane and intermediate image plane, the distance values with respect to the intermediate image plane that are suitable for fitting the first manipulator surface are increased.
• An arrangement in the vicinity of a real intermediate image can therefore be advantageous e.g. for reasons of structural space.
• the first manipulator surface is arranged upstream of the intermediate image plane and the second manipulator sur- face is arranged downstream of the intermediate image plane.
• the opposite arrangement is also possible. What can thereby be achieved, for example, is that the effects on the odd aberrations amplify one another, while in the case of the even aberrations, in particular defocus and astigmatism, the contributions of the two manipulators partly or completely mutually compen- sate for one another.
• first distance and the second distance should then be dimensioned such that at the first manipulator surface (upon activation of the first manipulator) and also at the sec- ond manipulator surface (upon activation of the second manipulator) in each case the condition
• the second manipulator surface is arranged directly downstream of the first manipulator surface, wherein the numerical aperture of the projection radiation at the first manipulator surface is equal to the numerical ap- erture of the projection radiation at the second manipulator surface and the first distance is less than the second distance, with the result that the subaperture diameters differ at the manipulator surfaces, wherein for the first manipulator surface the condition
• the invention also relates to a projection exposure method for exposing a radiation-sensitive substrate arranged in the region of an image surface of a projection lens with at least one image of a mask pattern arranged in the region of an object surface of the projection lens, wherein a projection lens according to the invention is used.
• the invention relates to a projection exposure apparatus for exposing a radiation-sensitive substrate arranged in the region of an image plane of a projection lens with at least one image of a mask pattern arranged in the region of an object plane of the projection lens, comprising: a primary radiation source for emitting primary radiation; an illumination system for receiving the primary radiation and for generating an illumination radiation that is directed onto the mask; and a projection lens for generating at least one image of the pattern in the region of the image surface of the projection lens, wherein the projection lens is designed according to the invention.
• the projection exposure apparatus preferably has a central controller for controlling functions of the projection exposure apparatus, wherein the control device is assigned a control module for driving the wavefront manipulation system (WFM) and one manipulator or a plurality of manipulators can be driven by means of the control module e.g. by means of electrical signals in coordination with other control signals during the operation of the projection exposure apparatus.
• WFM wavefront manipulation system
• Figure 1 shows a schematic illustration of a microlithography projection exposure apparatus in accordance with one embodiment of the invention
• Figure 2 shows a schematic longitudinal section in an x-z plane in the region of the mask and of a directly succeeding first manipulator element
• Figure 3 shows a plan view of the first manipulator element in Figure 2 parallel to the optical axis
• Figures 4 to 8 illustrate effects of a first manipulator element positioned in a near-field arrangement on the correction state of the wavefront in the image field of a projection lens as a function of various influencing parameters
• Figure 9 schematically shows elements of a wavefront manipulation system which has manipulator elements upstream and downstream of an intermediate image plane
• Figure 10 shows, analogously to the illustrations in Figures 4 and 5, the dependence of different Zernike coefficients on the normalized manipulator distance on both sides of an in- termediate image plane;
• Figure 1 1 schematically shows elements of a wavefront manipulation system which has two closely adjacent manipulator elements downstream of a field plane;
• Figures 12 to 15 in each case show bar diagrams for elucidating the effects of manipulations on selected aberrations, wherein the height of the bars in each case indicates the contribu- tions to the individual aberrations indicated on the x-axis (represented by Zernike coefficients);
• Figures 16 and 17 show schematic meridional lens element sections of embodiments of cat- adioptric projection lenses which are equipped with near-field manipulator elements;
• Figures 18 to 21 schematically show exemplary embodiments of dynamically adjustable manipulators which can be used at near-field positions within a projection lens in the context of wavefront manipulation systems.
• Figure 1 shows an example of a microlithographic projection exposure apparatus WSC which can be used in the production of semiconductor components and other finely structured components and operates with light or electromagnetic radiation from the deep ultraviolet range (DUV) in order to achieve resolutions down to fractions of micrometers.
• An ArF excimer laser having an operating wavelength ⁇ of approximately 193 nm serves as primary radiation source or light source LS.
• Other UV laser light sources for example F 2 lasers having an operating wavelength of 157 nm or ArF excimer lasers having an operating wavelength of 248 nm, are likewise possible.
• An illumination system ILL disposed downstream of the light source LS generates in its exit surface ES a large, sharply delimited and substantially homogeneously illuminated illumination field adapted to the telecentricity requirements of the projection lens PO arranged downstream thereof in the light path.
• the illumination system ILL has devices for setting different illumination modes (illumination settings, and can be changed over for example between conventional on-axis illumination with a varying degree of coherence ⁇ and off-axis illumination.
• the off-axis illumination modes comprise, for example, annular illumination or dipole illumination or quadrupole illumination or some other multipolar illumination.
• suitable illumination systems is known per se and will therefore not be explained in greater detail here.
• the patent application US 2007/0165202 A1 (corresponding to WO 2005/026843 A2) discloses examples of illumination systems which can be used in the context of various embodiments.
• Those optical components which receive the light from the laser LS and form from the light illu- mination radiation which is directed onto the reticle M belong to the illumination system I LL of the projection exposure apparatus.
• a device RS for holding and manipulating the mask M is arranged downstream of the illumination system such that the pattern arranged on the reticle lies in the object plane OS of the projection lens PO, which plane coincides with the exit plane ES of the illumination system and is also designated here as reticle plane OS.
• the mask is movable in this plane for scanner operation in a scanning direction (y-direction) perpendicular to the optical axis OA (z-direction) with the aid of a scan drive.
• the projection lens PO acts as a reducing lens and images an image of the pattern arranged on the mask M on a reduced scale, for example on the scale 1 :4 (
• 0.25) or 1 :5 (
• 0.20), onto a substrate W coated with a photoresist layer, the light-sensitive substrate surface SS of said substrate lying in the region of the image plane IS of the projection lens PO.
• the substrate to be exposed which is a semiconductor wafer W in the case of the example, is held by a device WS comprising a scanner drive in order to move the wafer synchronously with the reticle M perpendicular to the optical axis OA in a scanning direction (y-direction).
• the device WS which is also designated as "wafer stage”
• the device RS which is also designated as "reticle stage” are part of a scanner device controlled by means of a scanning control device, which in the embodiment is integrated into the central control device CU of the projection exposure apparatus.
• the illumination field generated by the illumination system I LL defines the effective object field OF used during the projection exposure.
• Said object field is rectangular in the case of the example and has a height A* measured parallel to the scanning direction (y-direction), and a width B* > A* measured perpendicularly thereto (in the x-direction).
• the aspect ratio AR B7A* is generally between 2 and 10, in particular between 3 and 6.
• the effective object field lies at a distance in the y-direction alongside the optical axis (off-axis field).
• A* and B I ⁇ I B*.
• the projection lens is designed and operated as an immersion lens, then during the operation of the projection lens radiation passes through a thin layer of an immersion liquid situated be- tween the exit surface of the projection lens and the image plane IS.
• Image-side numerical apertures NA > 1 are possible during immersion operation.
• a configuration as a dry lens is also possible; here the image-side numerical aperture is restricted to values of NA ⁇ 1 .
• projection radiation having a relatively large numerical aperture e.g. having values of greater than 0.15 or greater than 0.2 or greater than 0.3, is present in the region of some or all field planes (object plane, image plane, possibly one or more intermediate image planes) of the projection lens.
• the projection lens or the projection exposure apparatus is equipped with a wavefront manipulation system WFM, which is configured for dynamically altering the wavefront of the projection radiation passing from the object plane OS to the image plane IS in the sense that the optical effect of the wavefront manipulation system can be set in a variable manner by means of control signals.
• the wavefront manipulation system in the exemplary embodiment comprises a first manipulator MAN 1 having a first manipulator element ME1 , which is arranged in direct proximity to the object plane of the projection lens in the projection beam path and has a first manipulator surface MS1 , which is arranged in the projection beam path and the surface shape and/or re- fractive index distribution of which can be reversibly altered with the aid of a first actuating device DR1 .
• Figure 2 shows a schematic longitudinal section in an x-z plane in the region of the mask M and of the directly succeeding first manipulator element ME1 .
• the first manipulator element ME1 is a plate-shaped optical element composed of a material which is transparent to the projection radiation, for example composed of synthetic fused silica.
• a light entrance side facing the object plane OS serves as first manipulator surface MS1 , and the opposite light exit surface is a planar surface.
• the first actuating device comprises a multiplicity of mutually independently drivable actuators (not illustrated) which act on the plate-shaped manipulator element ME1 in such a way that the surface shape of the first manipulator surface MS1 can be brought to a wave shape in a defined manner.
• both the "amplitude" of the waves measured parallel to the z-direction, i.e. the deflection of the manipulator surface in the z-direction, and the distance between adjacent wave peaks measured in the x-direction, i.e. the wavelength or the period of the wave pattern, can be set to different values.
• the (average) wavelength of which in the x-direction can be characterized by a characteristic period PCHAR-
• the first manipulator surface is arranged at a finite first distance D1 from the object plane OS of the projection lens, said object plane being the closest field plane to the first manipulator surface.
• the first manipulator surface MS1 from an optical standpoint, is arranged in direct proximity to the object plane OS, that is to say in a "near-field position". This can be discerned from Figure 3, inter alia.
• Figure 3 shows a plan view of the first manipulator surface MS1 or the first manipulator element ME1 parallel to the optical axis OA (in the z-direction).
• the rectangular region FP having rounded corners in this case represents that region of the first manipulator surface which is illuminated by the rays coming from the effective object field OF. This region is also designated as "footprint”.
• the footprint of the projection radiation represents in size and shape the intersection area between the projection beam and the area (here first manipulator surface MS1 ), through which the projection beam passes.
• the optical proximity to the object plane OS can be discerned from the fact that the footprint substantially has the rectangular shape of the object field OF, the corner regions being somewhat rounded.
• the footprint exactly like the object field lies outside the optical axis OA. While the optical region used by the protection radiation in optical proximity to the field substantially has the shape of the illuminated field region, a substantially circular region is illuminated in the region of the pupil plane Fourier-transformed with respect to a field plane, with the result that a footprint has an at least approximately circular shape in the region of a pupil.
• the region illuminated at the first manipulator surface MS1 has an effective diameter D F P in the x-direction.
• Figures 2 and 3 schematically show that the surface shape of the first manipulator surface in this direction has a plurality of local maxima (represented by wave peaks in Figure 2 and by "+” symbols in Figure 3) and a plurality of intervening local minima (represented by wave valleys and "-" symbols in Figure 3). Consequently, this results in a "waviness" in the x-direction or in the direction of the effective diameter.
• the object-side numerical aperture NA 0 corresponds to the sine of the aperture angle a of each of the beams.
• Each beam emerging from a field point illuminates at the first manipulator surface MS1 a circular subaperture, the diameter of which is designated as the subaperture diameter SAD. It is directly evident from Figure 2 that the subaperture diameter SAD increases as the first distance D1 increases and as the image-side numerical aperture increases.
• the first manipulator is arranged so close to the object plane that a plurality of subapertures fit into the illu- minated region FP alongside one another without mutual overlap in the x-direction.
• the condition SAD/D F p ⁇ 0.2 should be fulfilled, in particular even the condition SAD/D F P ⁇ 0.1 .
• a first beam emerges from the first field point FP1 , the chief ray (dashed line) of which beam, such chief ray running parallel to the optical axis, impinges in the region of a "wave valley", that is to say in the region of a local minimum of the plate thickness.
• the chief ray (illustrated in a dashed line) impinges in the region of a wave peak, i.e. in the region of a local maximum of the plate thick- ness.
• the beams emerging from the two field points thus experience different changes in the optical path length.
• the local distribution of the optical path length changes in the x-direction is variable by means of the driving of the actuating devices of the first manipulator such that a differently deformed surface shape having different waviness can be set, with the result that the field dependence of the wavefront correction can also be set.
• the form and intensity of the wavefront change depend on the profile of the optical path length change by the first manipulator surface MS1 within the subaperture associated with the beam.
• a linear rise or fall of the optical path length change over the subaperture diameter leads to a tilt of the wavefront, for example, and a quadratic profile leads to the influencing of focus and astigmatism.
• the Zernike coefficients Z2 and Z3 represent the tilting of a wavefront in the x-direction and y-direction, respectively, as a result of which a distortion-like aberration arises.
• the Zernike coefficient Z4 describes a curvature of the wavefront, whereby a defocus error can be described.
• the Zernike coefficient Z5 describes a saddle-shaped deformation of the wavefront and thus the astigmatism component of a wavefront deformation.
• the Zernike coefficients Z7 and Z8 represent coma
• the Zernike coefficient Z9 represents spherical aberration
• the Zernike coefficients Z10 and Z1 1 represent three leaf clover.
• FIG. 4 to 7 illustrate the sensitivities of such a manipulator as a function of the axial position, i.e. as a function of the distance from the closest field plane.
• the effect on the distortion aberration (Z2/3), is an odd function in the sense that the effect in the case of positioning upstream of the field plane and the effect in the case of positioning downstream of the field plane have opposite signs.
• the sensitivity curve of Z2/3 has a point of inflection at the field plane.
• the sensitivities for defocus (Z4) and astigmatism (Z5) are even functions in the sense that their profile is mirror-symmetrical with respect to the field plane and has a local extremum (maximum in the case of defocus, minimum in the case of astigmatism), in the field plane.
• the astigmatism term and the distortion term vanishes in the field plane
• the defocus term Z4 has a local maximum directly in the field plane and vanishes only at a certain distance outside the field plane.
• the solid lines represent higher-order aberrations, namely coma (Z7/8), spherical aberration (Z9) and three leaf clover (Z 10/1 1 ). These will initially not be taken into consideration here).
• the relations in the case of a higher numerical aperture ( Figure 5) are similar, wherein it is evident that the extent of the defo- cus term increases with increasing numerical aperture at the manipulator surface.
• the first manipulator is intended to be used to influence distortion aberrations in a field-dependent manner.
• Said distortion aberrations are also described by the values Z3, which thus represents that aberration which is intended to be influenced, i.e. the "desired aberration".
• the other aberrations in particular Z4 (defocus) and Z5 (astigmatism), are intended as far as possible not to be influenced, or to be influenced only to such a small extent that the resulting aberrations are of a regularly negligible order of magnitude.
• the readily useful distance range UR is limited by the contributions to the astigmatism. It is typically assumed in this application that astigmatism terms of less than 0.4 nm can be afforded tolerance in most cases, while the astigmatism contribution (Z5) should not be higher than this limit value.
• a corresponding plotting for a numerical aperture of double the magnitude at the first manipulator surface is plotted in Figure 7.
• the upper limit governed by the astigmatism term is independent of the numerical aperture at the manipulator surface.
• the dashed line here shows in each case the results of the simulations described in the previous figures; the solid line is given by 0.25 * NA M 2 . Consequently, if a single dynamically manipulatable manipulator surface situated in a near-field arrangement is used, then the useful distance range of the normalized manipulator distance for a well functioning manipulator results from the following inequality:
• a wavefront manipulation system can also comprise more than two manipulators which can be set independently of one another, for example three or four manipulators.
• the projection lens is configured such that an intermediate image plane IMIS lies between the object plane OS and the image plane IS, a real intermediate image I MI being generated in said intermediate image plane.
• the projection lens has between the object plane OS and the intermediate image plane IMIS a plurality of optical elements which jointly form an optical imaging system, which forms a first lens part of the projection lens.
• the intermediate image can be magnified or reduced relative to the effective object field situated in the object plane OS, or can have the same size as said object field.
• the intermediate image is imaged directly or via at least one further intermediate image into the image plane IS, typically with a greatly reduced imaging scale.
• the wavefront manipulation system has a first manipulator MAN 1 having a first manipulator element ME1 , the first manipulator surface MS1 of which is arranged at a first distance D1 downstream of the intermediate image plane, that is to say between the latter and the image plane.
• a second manipulator MAN2 has a second manipulator element ME2 having a second manipulator surface MS1 , which is arranged at a finite second distance D2 upstream of the in- termediate image plane, that is to say between the latter and the object plane.
• the plate-shaped manipulator elements are in each case situated in a near-field arrangement with respect to the intermediate image plane, with the result that the condition SAD/DFP ⁇ 0.2 holds true for the respective manipulator surfaces.
• Each of the manipulator elements can be driven such that a multiple alternation of the effect on the change in the optical path length can be generated in the x-direction.
• the patterns for setting the optical path length changes AOPL are the inverse of one another. That is symbolized by the symbols "+” and where "+” represents a local maximum and "-" represents a local minimum of the optical path length changes AOPL. What can thus be achieved is that the contributions produced by the two manipulators to the even aberrations, such as defocus and astigmatism, for example, mutually compensate for one another, with the result that the combination of the two manipulators practically produces no contributions to defocus and astigmatism.
• condition SAD/P C HAR > 0.012 results as the condition for the lower limit of the normalized manipulator distance.
• the upper limit of the useful distance range can expediently be described by the condition SAD/P C HAR ⁇ 0.85, if the intention is to avoid excessively large contributions for coma and three leaf clover. Consequently, the following preferably holds true: 0.012 ⁇ SAD/PCHAR ⁇ 0.85 (2)
• Figure 1 1 shows a schematic illustration of an exemplary embodiment in which the wavefront manipulation system has two manipulators MAN 1 , MAN2, which are arranged one directly behind the other at different distances from a field plane (here object plane OS) of the projection lens, which field plane is arranged upstream thereof in the direction of transmission of radiation.
• a field plane here object plane OS
• the first and second manipulator elements ME1 , ME2 which are of substantially plate-shaped design, are arranged one directly behind the other without the interposition of an optical element having refractive power in the diversion beam path such that the numerical aperture of the projection radiation at both manipulator surfaces (first manipulator surface MS1 , second manipulator surface MS2) is the same.
• the first manipulator element is closer to the closest field plane OS, with the result that the first distance D1 is less than the second distance D2.
• the subaperture diameters are in each case smaller at the first manipulator surface than at the second manipulator surface. This leads to different sensitivities with regard to the target variable to be altered (here distortion Z2/3) and with regard to the remaining unde- sired aberrations. What can be achieved by means of suitable driving of the two manipulators is that, with the same effect on the target variable, the undesired aberrations are reduced in comparison with the case of only one manipulator (see Figure 2).
• the first manipulator lying closer to the field plane should not lie closer to the field plane than in the case of only a single manipulator, in order to obtain for this manipulator a good compromise between sufficiently high sensi- tivity and sufficiently small contributions to the undesired aberrations.
• the normalized manipulator distance should, if possible, not be less than 0.25 * NA M 2 .
• the second manipulator surface can lie significantly further away from the closest field plane, wherein the normalized manipulator distance should preferably be less than 1 .5.
• Figures 12 to 15 in each case show bar diagrams, wherein the height of the bars in each case represents the contributions to the individual aberra- tions Zi [nm] indicated on the x-axis.
• the first example is illustrated in Figures 12 and 13.
• the bar heights in all the diagrams are normalized to a value of 1 nm of the desired aberration Z3. This means that the manipulator is driven such that it yields a contribute) tion of 1 nm to the tilt of the wavefront.
• the darker left bars in each case show the aber-
• Figure 1 6 shows a schematic meridional lens element section of an embodiment of a catadiop- trie projection lens 1600 with selected beams for clarifying the imaging beam path of the projection radiation passing through the projection lens during operation.
• the projection lens is provided, as an imaging system having a demagnifying effect, for imaging a mask pattern arranged in its object plane OS on a reduced scale, for example on a scale of 4: 1 , onto its image plane IS oriented parallel to the object plane.
• exactly two real intermediate images I Ml 1 , I MI2 are generated between object plane and image plane.
• a first lens part OP1 which is constructed explicitly with transparent optical elements and is therefore purely refractive (dioptric), is designed such that the pattern of the object plane is imaged into the first intermediate image I Ml 1 substantially without any change in size.
• a second, catadioptric lens part OP2 images the first intermediate image I Ml 1 onto the second intermediate image I MI2 substantially without any change in size.
• a third, purely refractive lens part OP3 is designed for imaging the second intermediate image I MI2 into the image plane IS with high demagnification.
• Pupil surfaces P1 , P2, P3 of the imaging system lie between the object plane and the first intermediate image, between the first and second intermediate images, and also between the second intermediate image and the image plane, in each case where the chief ray CR of the optical imaging intersects the optical axis OA.
• the aperture stop AS of the system is fitted in the region of the pupil surface P3 of the third lens part OP3.
• the pupil surface P2 within the catadioptric second lens part OP2 lies in direct proximity to a concave mirror CM. If the projection lens is designed and operated as an immersion lens, then during the operation of the projection lens radiation passes through a thin layer of an immersion liquid situated between the exit surface of the projection lens and the image plane IS.
• Immersion lenses having a comparable basic construction are disclosed e.g. in the International Patent Application WO 2004/019128 A2.
• Image-side numerical apertures NA > 1 are possible during immersion operation.
• a configuration as a dry lens is also possible; here the image-side numerical aperture is restricted to values NA ⁇ 1 .
• the exemplary embodiment shown in Figure 16 corresponds, in terms of the optical construction (without manipulator elements), to the exemplary embodiment from Figure 6 of US 2009/0046268 A1 .
• the disclosure content of said document with regard to the basic construction of the projection lens (optical specification) is incorporated by reference in the content of this description.
• the catadioptric second lens part OP2 contains the sole concave mirror CM of the projection lens.
• a negative group NG comprising two negative lens elements is situated directly upstream of the concave mirror.
• the Petzval correction i.e. the correction of the image field curvature
• the chromatic correction is achieved by the refractive power of the negative lens elements upstream of the concave mirror and the stop position with respect to the concave mirror.
• a reflective deflection device serves for separating the beam passing from the object plane OS to the concave mirror CM, or the corresponding partial beam path, from that beam or partial beam path which passes, after reflection at the concave mirror, between the latter and the image plane IS.
• the deflection device has a planar first deflection mirror FM1 for reflecting the radiation coming from the object plane to the concave mirror CM, and a second deflection mirror FM2, which is oriented at right angles with respect to the first deflection mirror FM1 and which deflects the radiation reflected by the concave mirror in the direction of the image plane IS. Since the optical axis is folded at the deflection mirrors, the deflection mirrors are also designated as folding mirrors in this application.
• the deflection mirrors are tilted, e.g. by 45°, relative to the optical axis OA of the projection lens about tilting axes running perpendicular to the optical axis and parallel to a first direction (x-direction).
• first direction (x-direction) is perpendicular to the scanning direction (y-direction) and thus perpendicular to the direction of movement of the mask (reticle) and the substrate (wafer).
• the deflection device is realized by a prism whose externally reflectively coated cathetus surfaces oriented perpendicularly to one another serve as deflection mirrors.
• the intermediate images I MM , IMI2 in each case lie in optical proximity to the folding mirrors FM1 and FM2, respectively, closest to them, but are at a minimum optical distance from said folding mirrors, with the result that possible defects on the mirror surfaces are not imaged sharply into the image plane and the planar deflection mirrors (plane mirrors) FM1 , FM2 lie in the region of moderate radiation energy density.
• the positions of the (paraxial) intermediate images define field planes of the system which are optically conjugate with respect to the object plane and with respect to the image plane.
• the deflection mirrors therefore lie in optical proximity to field planes of the system, which is also designated as "near-field" in the context of this application.
• the first deflection mirror is arranged in optical proximity to a first field plane, which is associated with the first intermediate image I MM
• the second deflection mirror is arranged in optical proximity to a second field plane, which is optically conjugate with respect to the first field plane and is associated with the second intermediate image I MI2.
• the subaperture ratio SAR can be used for quantifying the position of an optical element or an optical surface in the beam path.
• the subaperture diameter SAD is given by the maximum diameter of a partial surface of the optical element that is illuminated with rays of a beam emerging from a given field point.
• the optically free diameter DCA is the diameter of the smallest circle around a reference axis of the optical element, wherein the circle includes that region of the surface of the optical element which is illuminated by all rays coming from the object field.
• the optical proximity or the optical distance of an optical surface with respect to a reference plane is described by the so-called subaper- ture ratio SAR.
• the subaperture ratio SAR of an optical surface is defined for the purposes of this application as follows:
• SAR sign CRH (MRH/(
• )) where MRH denotes the marginal ray height, CRH denotes the chief ray height and the signum function sign x denotes the sign of x, where according to convention sign 0 1 holds true.
• Chief ray height is understood to mean the ray height of the chief ray of a field point of the object field with maximum field height in terms of absolute value. The ray height should be understood here to be signed.
• Marginal ray height is understood to mean the ray height of a ray with maximum aperture proceeding from the point of intersection of the optical axis with the object plane. This field point does not have to contribute to the transfer of the pattern arranged in the object plane - particularly in the case of off-axis image fields.
• the subaperture ratio is a signed variable that is a measure of the field or pupil proximity of a plane in the beam path.
• the subaperture ratio is normalized by definition to values of between - 1 and +1 , the subaperture ratio being zero in each field plane and the subaperture ratio jumping from -1 to +1 , or vice versa, in a pupil plane.
• a subaperture ratio of 1 in terms of absolute value thus determines a pupil plane.
• Near-field planes therefore have subaperture ratios which are close to 0, while near-pupil planes have subaperture ratios which are close to 1 in terms of absolute value.
• the sign of the subaperture ratio indicates the position of the plane upstream or downstream of a reference plane.
• a first manipulator element ME1 of a wavefront manipulation system is arranged in the projection beam path at a small finite distance directly downstream of the object plane OS.
• the manipulator element substantially has the form of a rectangular plate, the longer side of which runs in the x-direction and the shorter side of which runs in the y-direction (scanning direction).
• the plate is situated completely outside the optical axis at a distance alongside the optical axis (off-axis arrangement).
• the manipulator element is dimensioned and arranged such that the footprint (FP, illustrated in a dashed manner) - which is largely rectangular in this region - of the projection radiation lies on that region of the manipula- tor element through which radiation can be transmitted (also cf. Figure 3).
• the surface shape and/or refractive index distribution of the first manipulator surface formed by the first manipulator element can be reversibly altered in such a way that a plurality of maxima and adjacent minima of an optical path length change of the projection radiation can be generated in the x-direction across the optically used region.
• the profiles of the maxima and minima are schematically illustrated by solid lines running in the y- direction.
• the distance between the active manipulator surface and the object plane as measured parallel to the optical axis is so small that a subaperture ratio SAR of less than 0.1 is present at the location of the manipulator surface and that the condition SAD/DFP ⁇ 0.1 holds true.
• the first manipulator element ME1 is arranged between the object plane OS and the first lens element L1 of the projection lens, said lens element exhibiting refractive power, to be precise said first manipulator element being arranged closer to the object plane than to said lens element.
• a manipulator element can be arranged in the projection beam path.
• One position is situated geometrically between the prism carrying the folding mirrors FM1 , FM2 and the concave mirror CM, to be precise near the folding mirrors FM 1 , FM2.
• the illustrated position of the first manipulator element ME1 ' is situated in direct optical proximity to the first intermediate image IMI 1 directly downstream thereof, and furthermore in direct optical proximity to the second intermediate image IMI2 directly upstream of said intermediate image.
• the subaperture ratio SAR is less than 0.2 in both cases; the condition SAD/DFP ⁇ 0.2 holds true in each case.
• a first footprint FP1 arises at the location of the manipulator in the first partial beam path, while a second footprint FP2 is present in the second partial beam path.
• the footprints are situated diametrically opposite one another with respect to the optical axis OH, as shown by the detail at the bottom left.
• a manipulator element such that it acts only in one of the partial beam paths, that is to say either only in the first partial beam path (between object plane and concave mirror) or only in the second partial beam path (between con- cave mirror and image plane). It is also possible to fit at this position a manipulator element through which radiation passes in different directions and which acts in both partial beam paths. In a manner similar to that in the position directly downstream of the object plane it is possible to set a desired wavefront change which alternates multiply between maximum values and minimum values in the x-direction, with the result that a characteristic period in the x-direction can be assigned to the optical path length change.
• Figure 1 7 shows an exemplary embodiment of a projection lens 1700 which is equipped with a first manipulator element ME1 situated in a near-field arrangement in the projection beam path.
• the optical construction of the projection lens corresponds to that from Figure 13 of the Patent US 7,446,952 B2, which is incorporated by reference in the content of this description.
• the projection lens has a first, refractive lens part OP1 , which generates a first intermediate image IMI 1 proceeding from the object in the object plane OS. Said first intermediate image is imaged into a second intermediate image IMI2 with the aid of a cataoptric second lens part OP2.
• the second lens part consists of two concave mirrors CM1 , CM2, the mirror surfaces of which face one another and are in each case situated in a near-field arrangement (near an intermediate image, remote from the intervening pupil plane).
• a refractive third lens part OP3 images the second intermediate image into a third intermediate image I MI3, which is in turn imaged by a refractive fourth lens part OP4 with high demagnification to form the final image in the image plane IS.
• All the lens parts have a common, rectilinear (non-folded) optical axis OA (in-line system). Further details can be gathered from US 7,446,952 B2 and are therefore not specifically indicated here.
• a first manipulator element ME1 can be inserted into the projection beam path without risk of collision with the lens elements of the basic construction. If appropriate, provision can be made of a changing device for exchanging and replacing manipulator elements in the projection beam path.
• the first manipulator element ME1 can have the rectangular shape - illustrated in the axial schematic detail view - having the long side in the x-direction and the short side in the y-direction and can be arranged outside the optical axis OA.
• the footprint FP - depicted in a dashed manner - of the projection radiation here lies fully in the usable area of the first manipulator element.
• a suitable actuating device makes it possible to set an optical effect which varies multiply between maximum values and minimum values in the x-direction and which corresponds to a varying optical path length change of the projection radiation.
• the projection lens can also have a corresponding manipulator element at other locations as well, for example directly downstream of the object plane OS in a near-field position.
• a near-field dynamically variable manipulator element can be arranged directly downstream of the object plane between the latter and the first lens element there in a position at which the subaperture ratio SAR is less than 0.2 and/or the condition SAD/DFP ⁇ 0.2 holds true.
• Manipulator elements of wavefront manipulation systems of the type described here can oper- ate according to different principles.
• Figures 18 to 21 illustrate by way of example manipulators which can be used alternatively or in combination within a projection lens of the type illustrated here (e.g. Figures 16 and 17) or in other suitable projection lenses in the context of wavefront manipulation systems.
• the manipulator 1850 in Figure 18 has two transparent plates P1 , P2, which can be incorpo- rated with their plate surfaces in each case perpendicular to the optical axis OA of the projection lens in a near-field position where SAR ⁇ 0.2 for example directly downstream of the object plane OS.
• the plates can have a rectangular shape having an extent which can be multiply greater in the x-direction than in the y-direction - running perpendicular thereto - of the projection lens.
• the entrance side of the first plate P1 facing the object plane OS is planar. Equally, the exit side of the second plate P2 facing the image plane is planar.
• the plate surfaces facing one another each have a wavy surface shape, wherein the wave valleys and wave peaks run parallel to the y-direction and the plate thickness d varies periodically in the x-direction.
• the wave pattern at the exit side of the first plate P1 and the wave pattern of the entrance side of the second plate P2 are complementary to one another with regard to the characteristic period measured in the x-direction and with regard to the amplitude of the thickness variation.
• the plates can be displaced relative to one another in the x-direction, which is achieved in the exemplary embodiment by virtue of the fact that the first plate P1 is installed in a fixed manner and the second plate P2 is movable parallel to the x-direction with the aid of an actuating device DR1 .
• n refractive index
• a single manipulator of this type having two plates may be sufficient in some cases, in particular in those cases in which only basic deformations have to be set.
• two or more plate pairs disposed one behind another can be provided, as indicated by the second manipulator shown by dashed lines.
• a plurality of manipulators disposed one behind another can be designed such that different displacement directions perpendicular to the optical axis are possible, e.g. displacement directions perpendicular to one another. More flexible manipulator functions can thereby be realized.
• Figures 19 and 20 schematically show sections through a different embodiment of a manipulator element 1950, which is shown in a neutral position (zero position) in Figure 19 and as an excerpt in Figure 20 in a functional position in which a multiple alternation between minimum values and maximum values of the optically active thickness or of an optical path length change is set in the x-direction.
• the manipulator element uses principles described for different purposes and in a different design in the Patent US 7,830,61 1 B2 in the name of the present applicant. The disclosure content of said document is incorporated by reference in the content of the present description.
• the manipulator element 1950 has a multilayered construction. A relatively thick, flexurally stiff transparent plane plate 1955 is accommodated in a frame-type mount 1952, the thickness of which plane plate can be e.g.
• a further plane plate 1960 is accommodated at a distance from said plate, and is significantly thinner than the relatively torsionally stiff plate 1955.
• the thickness can be e.g. in the range of one to 2 mm.
• a plane-parallel interspace remains between the plates 1955, 1960, and a liquid 1970 that is transparent to the projection radiation is filled into said interspace when the manipulator is ready for operation.
• the thickness of the interspace is generally small, e.g. less than 1 mm, in particular less than 10 ⁇ .
• the liquid reservoir between the plates is connected to a pressure device 1980, by means of which the liquid pressure of the liquid in the interspace can be set e.g. to a constant value.
• the liquid and the transparent materials of the plates have a very similar refractive index, wherein a ratio between the refractive index of the plates and the refractive index of the liquid is preferably between 0.99 and 1 .01 .
• the entire arrangement is rectangular in axial plan view (parallel to the z-direction) and some- what larger than that region through which radiation is transmitted in the case of a near-field arrangement of the manipulator in the region of the "footprint".
• actuators 1990 situated opposite in pairs outside the region through which radiation can be transmitted at regular distances from one another at the longitudinal sides of the manipulator.
• piezoelectrically actuated actuators can be involved.
• the actuators are designed such that they can act on the outer side of the thin plate with a press-on force acting substantially perpendicularly to the plate surface of the thin plate (cf. Figure 20).
• Suitable driving of the actuators makes it possible to establish a wavy deformation of the thin plate 1960 with a predefinable amplitude, wherein the "wave valleys" run parallel to the y- direction and the characteristic period length PCHAR of the wavy deformation, said characteris- tic period length being measured in the x-direction, can be set to different values by selection of the actuators respectively driven.
• a wavelength change that varies periodically in the x-direction can be set in a manner similar to that explained in connection with Figures 2 and 3.
• By driving different groups of actuators it is possible to set different "wavelengths" or different characteristic periods PCHAR in x-direction.
• actuators are arranged not only at the edge outside the region through which radiation can be transmitted, but also within the region through which radiation can be transmitted (cf. Figures 10, 1 1 from US 7,830,61 1 B2).
• FIG. 21 shows a further exemplary embodiment of a manipulator 2100 which can be used in the context of a wavelength manipulator sys- tern of the type described here.
• groups of actuators 2190 are fitted alternately on opposite sides of the plane plate.
• actuators being suitably driven in groups, it is possible to deform the plane plate in a wavy manner, wherein the wave valleys and wave peaks then run parallel to the y-direction and the wave peaks and respectively valleys are at a distance from one another in the x-direction, which dis- tance corresponds to the characteristic period PCHAR of the corresponding case of application.

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