Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
  • G01B9/02002—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies
  • G01B9/02003—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies using beat frequencies
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
  • G01B9/02007—Two or more frequencies or sources used for interferometric measurement
  • G01B9/02008—Two or more frequencies or sources used for interferometric measurement by using a frequency comb
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02015—Interferometers characterised by the beam path configuration
  • G01B9/02017—Interferometers characterised by the beam path configuration with multiple interactions between the target object and light beams, e.g. beam reflections occurring from different locations
  • G01B9/02018—Multipass interferometers, e.g. double-pass
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02015—Interferometers characterised by the beam path configuration
  • G01B9/02017—Interferometers characterised by the beam path configuration with multiple interactions between the target object and light beams, e.g. beam reflections occurring from different locations
  • G01B9/02019—Interferometers characterised by the beam path configuration with multiple interactions between the target object and light beams, e.g. beam reflections occurring from different locations contacting different points on same face of object
• • 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
  • G03F7/70691—Handling of masks or workpieces
  • G03F7/70775—Position control, e.g. interferometers or encoders for determining the stage position
• • 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
  • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
  • G03F7/7085—Detection arrangement, e.g. detectors of apparatus alignment possibly mounted on wafers, exposure dose, photo-cleaning flux, stray light, thermal load

Definitions

• the invention relates to a measuring arrangement for the frequency-based position determination of a component, in particular in an optical system for microlithography.
• Microlithography is used to fabricate microstructured devices such as integrated circuits or LCDs.
• the microlithography process is carried out in a so-called projection exposure apparatus, which has an illumination device and a projection objective.
• mirrors are used as optical components for the imaging process due to the lack of availability of suitable transparent refractive materials.
• the positions of the mirrors which are in some cases movable in all six degrees of freedom, have to be adjusted to each other as well as to mask or wafer with high accuracy and maintained in order to avoid or at least reduce aberrations and the associated impairment of the imaging result.
• this position determination e.g. be required over a path length of 1 meter accuracy of the length measurement in the picometer (pm) range.
• a resonator 152 in the form of a Fabry-Perot resonator comprises two resonator mirrors 154 and 155, of which the first resonator mirror 154 is connected to a reference element 140 in FIG In the form of a measuring frame fixedly connected to the housing of the projection lens of the projection exposure apparatus, and the second resonator mirror 155 (as a "measuring target") is fastened to an EUV mirror M to be measured with respect to its position.
• the actual distance measuring device comprises a radiation source 156 that can be tuned with regard to its optical frequency generates a coupling radiation 158, which passes through a beam splitter 162 and is coupled into the optical resonator 152.
• the radiation source 156 is controlled by a coupling device 160 so that the optical frequency of the radiation source 156 is tuned to the resonance frequency of the optical resonator 152 and thus coupled to this resonance frequency.
• Coupling radiation 158 coupled out via a beam splitter 162 is analyzed by means of an optical frequency measuring device 164, which may comprise, for example, a frequency comb generator 132 for the highly accurate determination of the absolute frequency.
• the resonant frequency of the optical resonator 152 also changes with the distance between the resonator mirrors 154 and 155 and thus - due to the coupling of the frequency of the tunable radiation source 156 to the resonant frequency of the resonator 152 - and also the optical frequency of the coupling-in radiation 158, which in turn is registered directly with the frequency measuring device 164.
• the measuring beam within the optical resonator can perform as large a number of circulations as possible within the resonator (without leaving the cavity formed by the resonator), so that eigenmodes can be formed in the resonator ,
• the coupling efficiency characteristic of said coupling is defined here by the overlap integral between the coupling field and the resonator field, so that, in order to achieve a high coupling efficiency, coupling field and resonator field must match as well as possible in all relevant parameters.
• Such (parasitic) movements not taking place along the measuring direction eg intentional or unintentional tilting or lateral displacements of the measuring target, can lead to an "emigration" of the main beam on which the modes of the resonator are simultaneously “threaded” , in position and angle takes place with the result that a sufficient coupling of the resonator field is no longer given to the coupling field.
• a measuring arrangement for the frequency-based position determination of a component in particular in an optical system for microlithography, comprises: at least one optical resonator, this resonator having a stationary first resonator mirror, a movable measuring target associated with the component, and a stationary second resonator mirror,
• the second resonator is formed by a reversing mirror, which reflects back a coming from the measurement target measurement beam in itself.
• the resonator further comprises a retroreflector, which reverses the measuring beam parallel-offset identically in its direction.
• This retroreflector may be designed as a cube-corner retroreflector (hollow or vitreous retro-reflector) or as a cat-eye retro-reflector (for example with a Fourier lens with a mirror arranged in its focal plane).
• the invention is based in particular on the concept of repeatedly traversing the path to be traveled by the measuring beam in an optical resonator by placing a reversing mirror.
• the measuring arrangement according to the invention has an increased insensitivity with respect to the said parasitic movements with the result that a highly accurate position measurement can also be realized in scenarios in which a stable control of the position of said measuring target is not possible or the associated measurement Effort should be avoided.
• the measurement target is formed by a retroreflector.
• the measurement target is formed by a plane mirror.
• the measuring arrangement has a polarization-optical beam splitter.
• a vertical incidence on a measuring target designed as a plane mirror can be achieved by folding the beam path directly onto the optical axis using the polarization-optical beam splitter.
• a measuring beam coming from the polarization-optical beam splitter hits the measuring target perpendicularly.
• the measuring arrangement has an optical group with two lenses in Kepler arrangement.
• the optical group in a common focal plane of these two lenses has a mirror with an opening which reflects back the beam path returning from the measurement target.
• the retroreflector is designed to be polarization-preserving.
• the first resonator mirror has a curvature such that a light field present in the resonator is stably enclosed.
• the first resonator mirror is designed as a cat's eye mirror.
• this mirror is preferably arranged defocused relative to the focal planes of a lens in order to produce a wavefront curvature required for the field inclusion in the resonator.
• the measuring arrangement has at least one tunable laser stabilized on a resonator mode of the optical resonator.
• the measuring arrangement has a control loop which is configured to stabilize the tunable laser according to the Pound-Drever-Hall method.
• the measuring arrangement has at least one femtosecond laser for determining the frequency of the laser radiation of the at least one tunable laser.
• the measuring arrangement further has a frequency standard, in particular a gas cell.
• the measuring arrangement for realizing an absolute length measurement has two different resonator modes with known frequency spacing of the optical resonator stabilizable, tunable laser.
• each of these two tunable lasers can be assigned a beat frequency analyzer unit.
• an otherwise existing ambiguity problem can be taken into account, which is the spectrum of the beat frequencies that represents a periodic diamond pattern eg between a tunable laser stabilized on a resonator mode and a femtosecond laser with respect to the counting direction of the passages through cell boundaries in the diamond pattern.
• the laser frequencies of the two tunable lasers show at the o.g. Embodiment of the invention namely two entangled grid of beat frequencies, on the basis of which said counting direction ambiguity can be eliminated as further described below.
• the measuring arrangement has an acousto-optical modulator for realizing a frequency shift in a partial beam branched off from the laser beam generated by the tunable laser.
• the component for position determination in six degrees of freedom is assigned six optical resonators for frequency-based length measurement.
• the component is a mirror.
• the optical system is a microlithographic projection exposure apparatus.
• FIG. 12 shows a schematic illustration for explaining a conventional construction of a measuring arrangement for frequency-based position measurement
• Figure 13 is a schematic representation for explaining the possible
• FIG. 14 shows a schematic illustration for explaining a possible realization of measuring sections according to the invention on a mirror in a structure with a load-bearing supporting structure and independently provided measuring structure;
• FIG. 15 shows a schematic illustration for explaining a possible determination of the position of a mirror in six degrees of freedom.
• FIGS. 1 a - 1 b show schematic representations for explaining the structure and mode of operation of a measuring arrangement in exemplary embodiments of the invention.
• a measurement beam strikes a unit 101 (the structure and operation of which will be described in more detail with reference to FIGS. 6-11) and an optical fiber 102 through a fixed curved resonator mirror 110 after passing through a free - Space path A off-axis on a retroreflector 120 (as a measurement target) and is reflected parallel offset back.
• the measuring beam After passing through a free space path B, the measuring beam is reflected back into itself by means of a reversing mirror 130 which is perpendicular to the beam propagation direction and without beam offset.
• the measuring beam After again passing through the free space sections B and A, including the retroreflector 120, the measuring beam in turn strikes the stationary curved resonator mirror 110, so that the circulation closes.
• FIG. 1 b differs from that of FIG. 1 a only in that, instead of the fixed curved resonator mirror 110, a stationary "cat's eye optic" consisting of a Fourier lens 112 with a mirror 113 arranged in its focal plane is used. In order to generate the wavefront curvature required for inclusion in the resonator, this mirror 113 is arranged in a defocused manner with respect to the focal plane of the lens.
• the expanded formalism of the paraxial matrix optics is briefly introduced below, and with this, fundamentals of the optics of resonators are then presented.
• the extension of formalism involves the consideration of beam offsets and beam bends, which inevitably occur in measuring resonators for position determination.
• the general transfer matrix of an optical system or of a subsystem consisting of spherically curved and / or planar elements (mirrors and plates) is in this formalism
• the entries A, B, C, D describe the paraxial beam propagation parameters of a system which is rotationally symmetrical about the optical axis (propagation axis), if appropriate after corresponding unfolding of the nominal deflecting reflections.
• the attached column with the one entry at the last position makes it possible to describe the rotational symmetry-breaking effect of elements which cause a beam offset and / or a beam tilt.
• the parameters t x , t y are the translational displacements perpendicular to the optical axis, which corresponds here to the z-axis.
• the parameters f c , f n denote the angles (in radians) of the beam dips.
• Retroreflector with offset (s, s y ) to the optical axis
• n-fold pass means an n-fold successive switching of the simple resonator path accordingly
• the input beam R 0 is represented by its components R k 0 , k - 1,2, 3, 4, 5 with respect to the eigenvectors.
• a Gaussian ray in fundamental mode (TEM00) is completely described by the complex ray parameter q. This combines the two beam-large radius of curvature R and beam size w. He is defined as follows through his reciprocal:
• q out denotes the output-side beam parameter and q in denotes the input-side beam parameter.
• the stable modes of a resonator must satisfy two stationarity conditions.
• the stationarity of the main ray R c (“Chief Ray"), along which the light field propagates, firstly requires L ⁇ ⁇ KL ⁇ (25)
• FIG. 1 c shows a derived equivalent circuit diagram for the embodiments of FIGS. 1 a-1 b for the simple resonator path for the description in the expanded formalism of the paraxial matrix optics.
• the corresponding transfer matrix is exemplary for the case of a curved fixed resonator mirror 110 according to FIG. 1 a
• K KFS (L) RR (S) KFS (L 'KFSW) KRR (S) FSO K L ens (R / 2)
• L denotes the variable distance between the stationary curved resonator mirror 110 and the measurement target forming retroreflector 120
• R the radius of curvature of the curved resonator mirror 110 and (s x , s y ) the transverse displacement of the retroreflector 120 to the optical axis (which extends in the drawn coordinate system in the z-direction).
• R c (O, O, O, O, I) 7 ' applies to the jet vector of the main jet.
• the satisfaction of the stability condition requires L + V ⁇ R ⁇ oo.
• FIG. 2 shows in a further schematic representation of a diagram for explaining the inventive concept.
• a conventional optical resonator with fixed resonator mirror 10 and measuring target 20 is indicated.
• a recirculation optic 230 is provided between the stationary resonator mirror 210 and the measuring target 220.
• FIGS. 3a-3b show schematic illustrations for explaining further embodiments of a measuring arrangement according to the invention, wherein in comparison to FIGS. 1a-1b analogous or substantially functionally identical components are designated by reference numerals increased by "200".
• the embodiments of FIGS. 3a-3b differ from those of FIGS. 1a-1b in that, instead of the retroreflector 120, a plane mirror 340 serves as a movable measurement target, wherein the retroreflector 320 is arranged on the side of the stationary part of the resonator.
• the transfer matrix of the distance which is unfolded by the nominal angle is exemplary for the embodiment of the curved solid resonator mirror 310 according to FIG. 3a
• L denotes the variable distance between the stationary curved resonator mirror 310 and the movable plane mirror 340, the variable distance between the fixed retroreflector 320 and the movable plane mirror 340, L "denotes the variable distance between the stationary envelope. sweeping mirror 330 and the movable plane mirror 340 and R the curvature radius of the curved stationary resonator mirror 310th
• FIG. 3 b differs from that of FIG. 3 a again (analogously to FIGS. 1 a - 1 b) only in that, instead of the fixed curved resonator mirror 310, a fixed "cat eye optic" comprising a Fourier lens 312 in its focal plane arranged mirror 313 is used.
• Fig. 3c shows, starting from the embodiments of Figs. 3a-3b and from the direction of the measuring target forming plane mirror 340, some possible configurations differing in their geometrical arrangement.
• FIGS. 3a-3b show schematic representations for explaining further embodiments of a measuring arrangement according to the invention, again analogous or essentially functionally identical components having reference numbers increased by "100" being compared to FIGS. 3a-3b.
• a measuring beam in turn passes through a unit 401 (the structure and mode of operation of which will be described in more detail with reference to FIGS. 6-11) and an optical fiber 402 into the resonator through the curved fixed resonator mirror 410 (with mirror surface 411) and hits after passing through a free space path on a polarization optical beam splitter 450, which has a beam splitter layer 450a.
• the p-polarized component of the measuring beam is transmitted, whereas the s-component is reflected out of the resonator and thus destroyed.
• the now p-polarized beam is transformed into a circularly polarized beam by means of a lambda / 4 plate 460 and passes through a further free space path up to the plane mirror 440 forming the measurement target. There it is reflected back and again passes through the lambda / 4-plate 460, whereby it is transformed into a linearly polarized beam with 90 ° rotation in relation to the original p-polarization, ie into an s-polarized beam.
• the now s-polarized beam is completely reflected at the polarization-optical beam splitter 450 and introduced into the (eg monolithically attached) retroreflector 420. There, the beam is reflected back with a parallel offset and again deflected at the beam splitter layer 450a in the direction of the plane target 440 forming the measurement target.
• the beam is once again circularly polarized and after a free-space path arrives at the plane mirror 440 forming the measurement target, where it is again reflected back.
• the retroreflector is designed in such a way that the polarization of the beam after the passage is maintained, which can be achieved by coating with a suitably designed optical multilayer coating system on the mirror surfaces.
• FIG. 4 b differs from that of FIG. 4 a again (analogously to FIGS. 1 a - 1 b) only in that, instead of the stationary curved resonator mirror 410, a fixed "cat eye optic" comprising a Fourier lens 412 In its focal plane arranged, defined defocused mirror 413 is used.
• FIGS. 4a-4b show schematic representations for explaining further embodiments of a measuring arrangement according to the invention, again analogous or substantially functionally identical components having reference numerals increased by "100" being compared with FIGS. 4a-4b.
• an optical group 520 of two lenses 521, 523 in Kepler arrangement is used.
• the so-called spatial filter plane - there is a mirror 522 (also referred to as a retina mirror) with a central opening, which throws back the beam path returning from the plane target 540 forming the measurement target, if the plane mirror 540 has a sufficiently large angle of attack.
• the transfer matrix of the unfolded nominal system (at which the nominal angle of attack of the plane mirror 540 is folded out) is
• L denotes the variable distance between the output side lens 523 and the measurement target plane mirror 540
• F and F 2 denote the focal lengths of the two lenses 521, 523.
• q (q c , q n ) represents the inclination deviations of the measurement target planing mirror 540 over its nominal values.
• the output-side lens 523, together with the (retina) mirror 522 in its focal plane forms a functional retroreflector in the form of a cat's eye.
• the focal plane of the first lens 521 is selected as the input-side reference plane.
• the transfer matrix shows the property of retroreflection in the form of the identical disappearance of its entries M S 1 and M 5 3.
• FIG. 5a-5c The optics described above are completed according to Fig. 5a-5c to an optical resonator by input side with a curved mirror 510 (FIG. 5a) or alternatively with a "cat's eye optics" of a Fourier lens 512 with arranged in its focal plane mirror 513 (as shown in FIG. 5b) is completed.
• the transfer matrix for the simple passage passage of such a resonator for the curved mirror embodiment according to FIG. 5a is
• the fulfillment of the stability condition requires L eff - 4 (L - F 2 ) ⁇ RF 2 2 / F 2 ⁇ oo.
• the scaling factor corresponds to the depth scale of the afocal optics.
• any retroreflector present may also be configured in a "cat's eye configuration" (i.e., with a Fourier optic or lens having a mirror disposed in its focal plane). This allows for the fact that the losses in the optical resonator typically have to be limited to a maximum of 0.1% -0.5%, which is made more difficult when designing the retroreflector with a plurality of reflection surfaces due to the plurality of reflections occurring.
• the retroreflector is designed such that the polarization of the beam is maintained after the passage.
• the property of the polarization maintenance of the retroreflector can be achieved by coating by means of a suitably designed optical multilayer coating system on the mirror surfaces.
• FIG. 6 shows a diagram for explaining the principle known per se, according to which a tunable laser 601 follows a frequency of a resonator 602 via a suitable control circuit (in the illustrated example according to the Pound-Drever-Hall method), so that the ultimate to be measured Length L of the resonator 602 is coded as the frequency of the tunable laser 601.
• Fig. 6 the area surrounded by the dashed line corresponds to the unit "501" of Fig. 5 (or the units "102", “301” and “401” in Fig. 1, Fig. 3 and Fig. 4).
• the arrangement according to FIG. 6 comprises a Faraday isolator 605, an electro-optical modulator 606, a polarization-optical beam splitter 607, a lambda / 4-plate 608, a photodetector 609 and a low-pass filter 610.
• a Faraday isolator 605 For frequency measurement, part of the signal from the tunable laser 601 emitted laser light via a beam splitter 603 coupled and supplied to an analyzer 604 for frequency measurement.
• the actual frequency measurement in the analyzer 604 can be made, for example, by comparison with a frequency reference (for example, as explained below, an fs frequency comb of a femtosecond laser).
• regulation of two tunable lasers 701, 702 can be performed on two different resonator modes known to their mode index spacing respectively.
• the sought length L of the resonator can then according to
• FIG. 8 is illustrative of the principle of frequency-based length measurement based on the beat between a tunable laser 801 stabilized on a resonator mode of a resonator 802 and a femtosecond laser 803.
• the beat between the laser beams of the tunable laser 801 and the femtosecond laser 803 becomes realized by their superposition on a fast photodetector 805.
• the individual beating frequencies are extracted.
• a frequency standard 806 eg in the form of a gas cell, in particular approximately an acetylene gas cell in the S and C telecommunications frequency bands around 1500 nm
• Downstream of the frequency standard 806 are a photodetector 810 and a signal analyzer 811.
• the desired frequency of the tunable laser 801 can be reconstructed according to FIG.
• the carrier envelope frequency (comb offset frequency) of the femtosecond laser 803 is given by and can be measured with the aid of a non-linear, so-called f-2f interferometer and kept constant via a control loop or eliminated via an optically non-linear process.
• the pulse repetition frequency f rep - lie in the radio frequency range and can be measured with high precision and stabilized on atomic clocks.
• FIG. 9a An exemplary spectrum of beat frequencies between a tunable laser stabilized to a resonator mode and a femtosecond laser as a function of resonator length change is shown in FIG. 9a. It is a periodic diamond pattern along both axes, which can also be called a beat raster. A basically resulting ambiguity must be eliminated in analogy to the counting distance-measuring interferometry by gapless counting the passages through cell boundaries in the diamond pattern, starting from a fixed starting position by zeroing. The remaining uncertainty with regard to the counting direction and the elimination of this uncertainty will be discussed below with reference to FIG. 10.
• Fig. 10 shows an extension of the structure of Fig. 8, wherein to Fig. 8 analog or substantially functionally identical components are designated by reference numerals increased by "200".
• a second tunable laser 1012 with photodetector 1008 and associated beat frequency analyzer unit 1009 is integrated with the measurement system.
• FSR (L) c / 2L designates the so-called free spectral range, which corresponds to the frequency spacing between adjacent modes in the mode comb of the resonator.
• the laser frequencies of the lasers 1001 and 1012 of FIG. 10 have two restricted rasters of beat frequencies (analogous to the diamond pattern shown schematically in FIG. 9b), by which an otherwise given "directional ambiguity" with respect to the counting direction (in counting the With the aid of the laser beam generated by this further laser 1012 and coupled to the frequency comb of the optical resonator, the solution of the uniqueness problem with respect to the counting direction succeeds, since with the aid of the additional information in FIG Form of the frequencies of the second beat grid always clearly the counting direction can be determined (see Fig. 9b). It is possible in an advantageous manner, the absolute length of the optical resonator according to c
• the two o.g. Beat signals are also superimposed additively fed to a single common beat analyzer, but then the beat frequencies of both rasters coincide and the separation and assignment of the grid in the presence of measurement errors is at least difficult or in extreme cases is no longer possible.
• FIG. 11 shows an alternative embodiment to FIG. 10, wherein components analogous or substantially functionally identical to FIG. 10 are designated by reference numerals increased by "100".
• a further laser beam for generating a further shifted beat raster is realized in that a partial beam is branched off from the tunable laser 1101 that can be stabilized on the resonator comb and is shifted by an acousto-optic modulator (AOM) 1114 in its frequency by the value f aom .
• AOM acousto-optic modulator
• the beat signal obtained in this case is analyzed by means of another beat frequency analyzer unit 1113 in its frequency composition.
• FIG. 13 shows a schematic representation of an exemplary microlithographic projection exposure apparatus designed for operation in the EUV. 1300.
• the measuring arrangement according to the invention can be used in this projection exposure apparatus for the distance measurement of the individual mirrors in the projection objective or in the illumination device.
• the invention is not limited to the application in systems designed for operation in the EUV, but also in the measurement of optical systems for other operating wavelengths (eg in the VUV range or at wavelengths less than 250nm) feasible.
• the invention can also be implemented in a mask inspection system or a wafer inspection system.
• a lighting device of the projection exposure apparatus 1300 has a field facet mirror 1303 and a pupil facet mirror 1304.
• the light of a light source unit comprising a plasma light source 1301 and a collector mirror 1302 is directed.
• a first telescope mirror 1305 and a second telescope mirror 1306 are arranged.
• a deflecting mirror 1307 is arranged downstream of the light path, which deflects the radiation impinging on it onto an object field in the object plane of a projection objective comprising six mirrors 1351-1356.
• a reflective structure-carrying mask 1321 is arranged on a mask table 1320, which is imaged by means of the projection lens into an image plane in which a photosensitive layer (photoresist) -coated substrate 1361 is located on a wafer table 1360.
• both supporting structure 1403 and measuring structure 1404 are mechanically connected to a base plate or base 1430 of the optical system independently of one another via mechanical connections (eg springs) 1405 or 1406 acting as dynamic decoupling.
• the mirror 1401 in turn is attached via a mirror attachment 1402 to the support structure 1403.
• Shown schematically in FIG. 14 are two measurement sections 1411 and 1421 measured via optical resonators according to the invention, which extend from the measurement structure 1404 to the mirror 1401.
• FIG. 15 Shown are six measuring sections 1505, each with a starting point 1504 located on a measuring frame 1506 and an end point 1503 located on a mirror 1501.

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• 2018
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