WO2020244937A1 - Dispositif de mesure pour déterminer par interférométrie une forme d'une surface optique d'un objet de test - Google Patents

Dispositif de mesure pour déterminer par interférométrie une forme d'une surface optique d'un objet de test Download PDF

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Publication number
WO2020244937A1
WO2020244937A1 PCT/EP2020/064294 EP2020064294W WO2020244937A1 WO 2020244937 A1 WO2020244937 A1 WO 2020244937A1 EP 2020064294 W EP2020064294 W EP 2020064294W WO 2020244937 A1 WO2020244937 A1 WO 2020244937A1
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WIPO (PCT)
Prior art keywords
test
wave
positions
interferograms
optical surface
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PCT/EP2020/064294
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German (de)
English (en)
Inventor
Ulrich Löring
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Carl Zeiss Smt Gmbh
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Publication of WO2020244937A1 publication Critical patent/WO2020244937A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
    • G01B11/2441—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures using interferometry
    • 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
    • G01B9/02034—Interferometers characterised by particularly shaped beams or wavefronts
    • G01B9/02038—Shaping the wavefront, e.g. generating a spherical wavefront
    • G01B9/02039—Shaping the wavefront, e.g. generating a spherical wavefront by matching the wavefront with a particular object surface shape
    • 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
    • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
    • G01B9/02056—Passive reduction of errors
    • G01B9/02059—Reducing effect of parasitic reflections, e.g. cyclic errors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/005—Testing of reflective surfaces, e.g. mirrors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
    • G01B2290/30—Grating as beam-splitter

Definitions

  • Measuring device for the interferometric determination of a shape of an optical surface of a test object
  • the invention relates to a measuring device and a method for interferometric determination of a shape of an optical surface of a test object.
  • a highly precise interferometric measurement of a surface shape of a test object for example an optical element for a projection objective of a microlithographic exposure system, is often carried out by means of a measuring device comprising a diffractive optical module as so-called zero optics or compensation optics.
  • the wavefront of a measurement wave is adapted to a target shape of the surface by the diffractive optical module in such a way that it strikes the surface perpendicularly at every location and is reflected back by this when the target shape is present. Deviations from the nominal shape can be determined by superimposing the reflected test wave with a reference wave likewise generated by the diffractive optical module.
  • the diffractive optical module can comprise a diffractive element in the form of a computer-generated hologram (CGH).
  • scattered radiation that occurs in the measuring device often falsifies the measurement result.
  • This scattered radiation is often referred to as “false light” and in particular includes measurement radiation diffusely reflected in the measuring device, caused for example due to lens reflections, mirror inaccuracies, light leakage and soiling in the measuring device as well as reflection and scattering on imperfectly blackened mechanical components / surfaces.
  • the scattered radiation interferes with the useful light and causes falsifications of the measurement result due to the accompanying phase change of the useful light, which conventionally often does not differ from the measurement results of actual surface deviations. In any case, scattered radiation reduces the measurement accuracy.
  • the aforementioned object can be achieved according to the invention, for example, with the measuring device described below for interferometric determination of a shape of an optical surface of a test object.
  • This measuring device comprises a diffractive optical module for generating a test wave which is directed onto the optical surface and which has at least a wave front which is partially adapted to a nominal shape of the optical surface, as well as a reference wave.
  • the measuring device comprises a reflective reference element arranged in the beam path of the reference wave, which is mounted displaceably in the direction of the beam path of the reference wave for arrangement at different reference positions, a holding device which is mounted displaceably in the direction of the beam path of the test shaft for arranging the test object at different test positions, and a detection device for capturing interferograms generated at the different test positions of the test object, each of which is based on a superimposition of the test wave Interaction with the optical surface and the reference wave are formed after reflection on the reference element.
  • at least one of the test positions is assigned a plurality of interferograms in each case, the generation of which the reference element is arranged at different reference positions.
  • the measuring device comprises an evaluation device which is configured to determine a deviation of an actual shape of the optical surface from the nominal shape by determining a deviation result for each of the test positions by evaluating the interferograms generated at the different test positions and averaging the deviation results, for the at least one test position with a plurality of assigned interferograms, the determination of the deviation result takes place on the basis of the assigned interferograms.
  • the interferogram is generated in particular by superimposing the test wave with the reference wave in a detection plane after the test wave has interacted with the optical surface of the test object and renewed diffraction on the diffractive optical module and back reflection of the reference wave on the reference element and renewed diffraction on the diffractive optical element.
  • the shape of the optical surface is determined by calculating a deviation of the optical surface from its nominal shape.
  • the diffractive optical module can consist of a diffractive optical element; alternatively, it can additionally comprise a further optical element, in particular also a further diffractive optical element.
  • the reference element is mounted displaceably for arrangement at different reference positions.
  • the reference element is mounted in such a way that it can be displaced in the direction of the beam path of the reference wave.
  • the reference element is mounted displaceably over an area of at least 1 times, in particular at least 2 times or at least 3 times the wavelength of the test shaft.
  • the displaceability relates to an optical displacement, ie a displacement occurring in the wavefront effect. Mechanically, the reference element may only have to be shifted by half the value.
  • the evaluation device is configured to evaluate the interferograms in such a way that errors in the evaluation result generated by scattered radiation are minimized.
  • adjacent test positions are at most a fraction of a wavelength of the test shaft spaced apart from one another.
  • the adjacent test positions are spaced apart from one another by exactly a fraction of the wavelength of the test wave.
  • the evaluation device is configured to determine the deviation of the actual shape of the optical surface from the target shape by determining a deviation result for each of the test positions by evaluating the interferograms generated at the different test positions and averaging the deviation results.
  • averaging can be the formation of a simple mean value in which the deviation results are included in the mean value without weighting.
  • a weighted average can also be used.
  • a mathematical adaptation (fit) of the course of the error expected for different test positions can also take place by means of scattered radiation in order to separate it as far as possible.
  • the reference element is mounted in such a way that it can be displaced in steps of less than a fifth, in particular less than a tenth or less than a twentieth of the wavelength of the test shaft.
  • the displaceability relates to an optical displacement, that is to say which occurs in the wavefront effect.
  • the respective deviation result is determined for each of the test positions using interferograms, the generation of which the reference element is arranged at different reference positions.
  • the reference element for arrangement at different reference positions is mounted displaceably in the direction of the beam path of the reference wave and the measuring device is configured to arrange the test object one after the other at the different test positions and at the same time to change the reference position of the reference element.
  • the measuring device is configured to move the reference element simultaneously when the test object is moved between test positions in such a way that the effect of the displacement of the test object and the effect of the displacement of the reference element on the phase difference between the test wave and the reference wave in the resulting interferogram have the same sign. This means that the phase difference generated in the interferogram is generated by simultaneous phase shifting of the test object and reference element.
  • the evaluation device is configured to use the interferograms as a basis for at least one measurement point on the optical surface, which varies from interferogram to interferogram as a function of the respective interferogram to determine lying phase difference between the test wave and the reference wave and to calculate a portion to be traced back to scattered radiation from the determined intensity profile.
  • This calculated portion of the scattered radiation is, in particular, a phase difference variable scattered radiation portion.
  • calculating the portion attributable to scattered radiation is to be understood as first determining the portion and then partially or completely mathematically eliminating it from the intensity curve.
  • an intensity profile that varies from interferogram to interferogram is determined as a function of the phase difference, and one for each of the measurement points
  • Part of the scattered radiation attributable to the corresponding intensity curve is calculated.
  • the evaluation device is configured to perform a Fourier decomposition of the intensity profile determined when calculating out the portion attributable to scattered radiation.
  • the measuring device is configured to determine the shape of a surface of an EUV mirror for microlithography.
  • the measuring device described below for interferometric determination of a shape of an optical surface of a test object comprises a diffractive optical module for generating a test wave directed onto the optical surface, which test wave has at least a wavefront partially adapted to a nominal shape of the optical surface, and a reference wave directed onto a reflective reference element.
  • the measuring device comprises a holding device, mounted displaceably in the direction of the beam path of the test shaft, for arranging the test object at different test positions, as well as a detection device for detecting those generated at the different test positions of the test object Interferog rams, which are each formed by superimposing the test wave after interaction with the optical surface and the reference wave after reflection on the reference element.
  • the measuring device comprises an evaluation device which is configured to determine a deviation of an actual shape of the optical surface from the nominal shape by evaluating the interferograms generated at the different test positions.
  • the reference element is mounted displaceably in the direction of the beam path of the reference shaft for arrangement at different reference positions and the measuring device is configured to arrange the test object one after the other at the different test positions and at the same time to change the reference position of the reference element.
  • the measuring device is configured to move the reference element simultaneously when the test object is moved between test positions in such a way that the effect of the displacement of the test object and the effect of the displacement of the reference element on the phase difference between the test wave and the reference wave resulting interferogram have the same sign. This means that the phase difference generated in the interferogram is generated by simultaneous phase shifting of the test object and reference element.
  • the evaluation device is configured to determine from the interferograms with respect to at least one measurement point on the optical surface an intensity profile that varies from interferogram to interferogram depending on a phase difference between the test wave and the reference wave on which the respective interferogram is based, and from the determined intensity profile to subtract a portion attributable to scattered radiation.
  • This calculated portion of the scattered radiation is, in particular, a phase difference variable scattered radiation portion.
  • Part of the scattered radiation attributable to the corresponding intensity curve is calculated.
  • the evaluation device is configured to perform a Fourier decomposition of the intensity profile determined when calculating out the portion attributable to scattered radiation.
  • a method for the interferometric determination of a shape of an optical surface of a test object comprises the steps of: generating a test wave directed onto the optical surface, which has at least a wavefront that is partially adapted to a nominal shape of the optical surface, and a reference wave directed onto a reflective reference element by means of a diffractive optical module, arranging the reference element at different reference positions in Direction of the beam path of the reference wave, arranging the test object in the direction of the beam path of the test wave one after the other at different test positions, recording of interferograms generated at the different test positions of the test object, each of which occurs by superimposing the test wave after interaction with the optical surface and the reference wave after reflection the reference element are formed, with at least one of the test positions being assigned a plurality of interferograms, when the reference element is generated at different Refe renzpositionen is arranged, and determining a deviation of an actual shape of the optical surface from the desired shape by respective determination a deviation result for each of the
  • the test object is arranged one after the other at the different test positions and, at the same time, a reference position of the reference element is changed in the direction of the beam path of the reference wave.
  • an intensity profile varying from interferogram to interferogram is determined from the interferograms with respect to at least one measuring point on the optical surface, depending on a phase difference between the test wave and reference wave on which the respective interferogram is based, and a portion attributable to scattered radiation is calculated from the determined intensity profile.
  • a Fourier decomposition of the intensity profile determined is carried out in the case of calculating out the portion attributable to scattered radiation.
  • a method for interferometric determination of a shape of an optical surface of a test object comprises the steps of: generating a test wave directed onto the optical surface, which has at least one wavefront partially adapted to a nominal shape of the optical surface, and a reference wave directed onto a reflective reference element by means of a diffractive optical module, arranging the test object in the direction of the Beam path of the test wave one after the other at different test positions, acquisition of interferograms generated at the different test positions of the test object, each of which is achieved by superimposing the Test wave are formed after interaction with the optical surface and the reference wave after reflection on the reference element, as well as determination of a deviation of an actual shape of the optical surface from the target shape by evaluating the interferograms generated at the different test positions.
  • the test object is arranged one after the other at the different test positions and at the same time a reference position of the reference element is changed in the direction of the beam path of the reference wave.
  • an intensity profile that varies from interferogram to interferogram is determined from the interferograms with respect to at least one measuring point on the optical surface, depending on a phase difference between test wave and reference wave on which the respective interferogram is based, and from the determined intensity profile
  • a Fourier decomposition of the intensity profile determined is carried out when calculating out the portion attributable to scattered radiation.
  • FIG. 1 shows an illustration of a measuring device according to the invention for the interferometric determination of a shape of an optical surface of a test object from recorded interferograms
  • FIG. 3 shows a diagram to illustrate the vectors of the field strength of a test wave and of false light
  • FIG. 5 shows the diagram according to FIG. 3 for different test positions of the test object
  • FIG. 6 shows the intensity curves according to FIG. 4 for the nominal shape of the optical surface without false light and with false light of a further phase difference
  • 7 shows the course of a phase error Aw as a function of the phase difference between the field vectors of the false light and the test wave
  • FIG. 9 shows the profile of the phase error Aw according to FIG. 7 for the different test positions
  • FIG. 12 shows the intensity profile recorded according to a second embodiment according to the invention according to FIG. 8 for the nominal shape of the optical surface without and with false light, as well as intensity profiles determined during the evaluation according to the invention.
  • FIG. 1 an exemplary embodiment of a measuring device 10 for the interferometric determination of the shape of an optical surface 12 of a test object 14 is illustrated.
  • the optical surface 12 has an actual shape 12-1 (TF) which deviates from a nominal shape 12-2 (SF). This is illustrated by way of example in the left section of the test object 14:
  • the actual shape TF has a spherical deviation from the nominal shape SF, at the point 29 (Mj) arranged there this is a deviation in the direction of the surface normals by Ah.
  • a deviation of the actual shape 12-1 of the surface 12 from its desired shape 12-2 can be determined.
  • a test object 14 for example, a mirror of a projection lens for EUV microlithography with a non-spherical surface for reflecting EUV radiation with a wavelength of less than 100 nm, in particular a wavelength of about 13.5 nm or about 6.8 nm.
  • the non-spherical nominal shape 12-2 of the surface of the mirror can have a free-form surface with a deviation from each rotationally symmetrical asphere of more than 5 ⁇ m and a deviation from each sphere of at least 1 mm.
  • the measuring device 10 contains a holding device 15 for arranging the test object 14 at different test positions 17 as well as a measuring radiation source 16 for providing a sufficiently coherent measuring radiation 19 as an input wave 20.
  • the measuring radiation source 16 comprises an optical waveguide with an exit surface 18.
  • the optical waveguide is on a radiation generator not shown in FIG. 1, for example in the form of a Lasers, connected.
  • a helium-neon laser with a wavelength of approximately 633 nm, for example, can be provided for this purpose.
  • the measuring radiation 19 can, however, also have a different wavelength in the visible or invisible wavelength range of electromagnetic radiation.
  • the measuring radiation source 16 with the optical waveguide is only one example of a radiation source that can be used for the measuring device.
  • an optical arrangement with lens elements, mirror elements or the like to provide a suitable input shaft 20 can be provided.
  • the measuring device 10 also contains a beam splitter 22, a diffractive optical module 24 and a reference element 30. After passing through the beam splitter 22 undisturbed, the input shaft 20 meets the diffractive optical element 24 to generate a test wave 26 and a reference wave 28 from the input wave 20.
  • the diffractive optical module 24 can comprise one or more diffractive optical elements.
  • it has an optical element in the form of a complex coded CGH and contains diffractive structures which form two diffractive structure patterns that are superimposed on one another in a plane.
  • These two diffractive structure patterns can e.g. be formed by a first structure pattern in the form of a basic lattice and a second diffractive structure pattern in the form of a superlattice.
  • One of the diffractive structure patterns is configured to generate the test wave 26 with a wave front that is at least partially adapted to the nominal shape 12 - 2 of the optical surface 12.
  • the other diffractive structure pattern generates the reference wave 28 with an even wavefront.
  • a simply coded CGH with a diffractive structure or another optical grating can also be used instead of the complex coded CGH.
  • the test shaft 26 can for example in a first diffraction order and the reference wave 28 can be generated in the zeroth or any other diffraction order on the diffractive structure.
  • the reference element 30 is configured as a reflective optical element and is used to reflect back the reference wave 28. Since the reference wave 28 is a plane wave in the present case, the reference element 30 is configured here as a plane mirror.
  • the reference wave 28 can have a spherical wavefront and the reflective optical element can be designed as a spherical mirror.
  • the measuring device 10 contains a detection device 32.
  • the detection device includes a two-dimensionally resolving detector 34 and a Focussing lens 36 located in front of it for detecting an interferogram generated by superimposing test wave 26 with reference wave 28. The interferograms recorded by the detector are evaluated by an evaluation device 38, as described in more detail below.
  • test object 14 is arranged in a fixed test position, i. not displaceable between different test positions 17 (1 to Nmax) as in the measuring device 10.
  • the functional principle of such a conventional measuring device will now be explained below with reference to the measuring device 10 illustrated in FIG. 1, in which the holding device 15 for the test object 14 is arranged in a test position 1.
  • the reference element 30 is mounted to be displaceable in the direction of the beam path of the reference shaft 28 for arrangement at different reference positions 31 (1 to Mmax). During the measurement, the reference element 30 is successively arranged at the different reference positions 31 (1 to Mmax) and the Interferograms imaged on the detector 34 at the different reference positions 31 are recorded. Depending on the reference position, there is a shift w of the wavefront of the reference wave 28 (the greater the index of the reference position 1 to Mmax, the greater the wavefront shift w).
  • FIG. 2 shows an example of an evaluation of the interferograms recorded at the different reference positions 31 for the two cases illustrated in FIG. 1 in which the optical surface 12 has the actual shape 12-1 (TF) or the desired shape 12-2 (SF ) having.
  • the intensity at the point of the respective interferogram which corresponds to the measurement point 29 (Mj) on the surface 12 is plotted on the y-axis as a function of the wavefront shift w.
  • the individual beams 26i and 28i of the test wave 26 and the reference wave 28 are superimposed at the point of the corresponding interference pattern corresponding to the point 29 (Mj).
  • Fig. 2 now illustrates the intensity profile at the point of the interferograms corresponding to the measuring point Mj, on the one hand with Ig es (S) for the case in which the optical surface 12 has the nominal shape 12-2 (SF), and on the other hand with Ig it for the case in which the optical surface 12 has the actual shape 12-1, which is lowered by Ah at the measuring point Mj.
  • Ig es S
  • Ig it for the case in which the optical surface 12 has the actual shape 12-1
  • Ah the intensity profile
  • coherent scattered radiation present in the measuring device 10 can produce effects similar to the deviation Ah in the aforementioned intensity profiles, as explained below with reference to FIGS. 3 and 4. This has the consequence that the measurement results for the deviation between the actual shape 12-1 from the desired shape 12-2 of the optical surface are often falsified by such scattered radiation effects.
  • the above-mentioned scattered radiation is also referred to below as “false light” and in particular comprises measurement radiation 19 that is diffusely reflected in the measuring device 10, caused for example by lens reflections, reflections and scattering on imperfectly blackened mechanical components / surfaces, e.g. by light outside the target beam cone of the measuring radiation 19, mirror inaccuracies, light leakage and contamination in the measuring device 10, as well as other interfering light.
  • the real part (Re (E)) and imaginary part (lm (E)) of the vector of the field strength E of the test wave 26 (Ep) in connection with a field strength vector of false light (EFL) are shown by way of example.
  • the phase of the field strength vector EP of the test wave 26 is denoted by f ° r and the phase of the field strength vector EFL of the false light is denoted by cpFL.
  • the phase ⁇ PFL of the false light can assume any value between 0 and 2p, so that the vector EFL can be anywhere within of the circle drawn in with a broken line in FIG. 3, ie the tip of the vector EFL can point to any point on the circle assuming a constant vector length.
  • the phase difference Df ° between the phase ⁇ PFL of the false light and the phase f ° r of the test wave 26 can thus vary between 0 and 2p.
  • the intensity curve Ige S (SF is shifted to the left analogously to the intensity curve Ig es (TF) illustrated in FIG. 2, which results without the presence of false light for the actual shape TF which deviates from the nominal shape SF by Ah.
  • the shift represents an error in the wavefront of test wave 26 and is referred to as Aw or as deviation result 40.
  • the error Aw shown in FIG. 4 in the wavefront of the test wave 26 is calculated as follows:
  • the following table 1 shows simulation results for the resulting phase error Awmax (in pm) as a function of different false light levels I FL / IP.
  • the field strength vector of the reference wave 28 is denoted by ER
  • the amplitude of the reference wave 28 is denoted by AR
  • the intensity of the reference wave 28 is denoted by IR.
  • the intensity undisturbed interferogram which is present without the presence of false light, can be described as follows:
  • EP + FL is analogous to the above when considering the interference between
  • Iges (O) differs from Ig es ( 0) only in contrast, offset and phase shift DF.
  • the intensity profile / es (-S ' ) shown in FIG. 6 results at the point corresponding to the measuring point Mj as a function of the wavefront shift w.
  • / gS (5F) is shifted slightly upwards and has an increased amplitude.
  • Stray light can thus 26 perform a function of the phase difference ACPO between the field vector EFL of false light and the field vector Ep of the test wave to a commonly indistinguishable from the surface deviation Ah phase error Aw with a value between -AW ma x and + Aw ax.
  • N 1 to Nmax
  • the above-described recording of the interferograms imaged at the different reference positions 31 on the detector 34 and determination of the resulting intensity profile Iges as a function of the wavefront shift w takes place.
  • Phase CPFL of the false light remains unchanged.
  • this situation is shown for the sake of a simplified illustration using the analog situation in which the phase CPFL of the false light is shifted by 2p / 3 and the phase for the test wave 26 remains the same.
  • the phase difference Df between the field vector EFL of the false light and the field vector Ep of the test wave 26 shifts by 2TT / 3.
  • Fig. 11 shows this behavior for different levels of false light.
  • phase error distributions Aw (x, y) resulting from 1 to Nmax depending on the location (x, y) of the surface 12 are determined for each of the test positions 17.
  • the reference element 30 can, as described above, be arranged one after the other at the different reference positions 31.
  • This variant of the phase measurement is based on the configuration of the measuring device 10 shown in FIG. 1, which is designed as a so-called “common path interferometer”.
  • phase error distributions Aw (x, y) can also be measured without shifting the reference element 30 in an interferometer which differs from the measuring device 10 according to FIG. 1 only in that the Reference element 30 is tilted somewhat, so that the beam path of the returning reference wave 28 deviates somewhat from the beam path of the returning test shaft 26.
  • phase error distributions Aw (x, y) representing a deviation result 40 for the different test positions 17, these are averaged; this is preferably a simple mean, i.e. all phase error distributions Aw (x, y) are included in the mean without weighting .
  • the phase error distributions Aw (x, y) can also be weighted before averaging.
  • the averaged phase error distribution serves as a measurement result for the deviation of the actual shape 12-1 of the optical surface 12 from the nominal shape 12-2.
  • the phase errors induced by the false light are therefore completely and exactly averaged to zero.
  • the mean wavefront error describes in this limit case the exact wavefront error DW ° of the actual surface error (TF) h. This exact means of removing the false light interference ! FL
  • phase error due to false light according to equation (29) no longer runs exactly sinusoidally with the position of the test object and the averaging is no longer exactly zero. But the course of the phase error is still approximately sinusoidal (given a sufficiently small false light). As explained above, the averaging still supplies very small values, the closer to zero the greater Nmax is.
  • equation (35) the exact expression in equation (29) can also be used for the greatest possible accuracy to determine the three parameters Zlw °, and yri
  • the displacement of the reference element 30 and the test object 14 takes place simultaneously, in fact stepwise in opposite directions, for example by the same phase difference.
  • the test object 14 is then moved to the position Nmax-1 and the reference element 30 to the position 2 and so on.
  • Fo (cp ° p -f ° r).
  • the two effects should have at least the same sign.
  • the reference element 30 must be in each step can only be shifted by half the shift amount of the above-described operation.
  • the reference element only contributes F / 2 to the phase shift, while the remaining phase shift by F / 2 is brought about by shifting the test object 14.
  • Iges () can be written as follows:
  • IFL represents a small modification of the offset through a constant stray light intensity and can therefore be neglected.
  • Ig es f (0) thus varies with the shift frequency 1 (ie with F).
  • the first factor of / y (0) is constant with variation of F, while the second factor
  • the component I f (0) abse- w ges, 2 can be pared by means of Fourier decomposition of I qes (0) according to (38), which means the remaining intensity Ig es (0) of the undisturbed phase shift interferogram can be determined.
  • Ig es y the intensity distribution / ⁇ es (0) that would result in the absence of stray light.

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Abstract

La présente invention concerne un dispositif de mesure (10) pour déterminer par interférométrie une forme d'une surface optique (12) d'un objet de test (14). Ledit dispositif de mesure comporte un module optique diffractif (24) pour générer une onde de vérification (26), dirigée vers la surface optique, qui comprend au moins un front d'onde adapté en partie à une forme prévue (12-2) de la surface optique, ainsi qu'une onde de référence (28), un élément de référence réflectif, disposé dans la trajectoire de l'onde de référence, qui est logé mobile en direction de la trajectoire de l'onde de référence pour être placé à différentes positions de référence, un système de maintien (15) logé mobile en direction de la trajectoire de l'onde de vérification (26) pour placer l'objet de test à différentes positions de test (17), un système de détection (32) pour détecter des interférogrammes, générés aux différentes positions de test de l'objet de test, qui sont formés chacun par une superposition de l'onde de vérification après une interaction avec la surface optique et de l'onde de référence après une réflexion sur l'élément de référence. Selon la présente invention, à au moins une des positions de test sont associés respectivement plusieurs interférogrammes lors de la génération desquels l'élément de référence est associé à différentes positions de référence. Le dispositif de mesure comporte en outre un système d'évaluation (38) qui est configuré pour déterminer une divergence entre une forme réelle (12-1) de la surface optique (12) et la forme prévue (12-2) par chaque détermination d'un résultat de divergence pour chacune des positions de test au moyen d'une évaluation des interférogrammes générés aux différentes positions de test et par calcul de la moyenne des résultats de divergence, pour la ou les positions de test ayant plusieurs interférogrammes associés, la détermination du résultat de divergence étant effectuée à l'aide des interférogrammes associés.
PCT/EP2020/064294 2019-06-03 2020-05-22 Dispositif de mesure pour déterminer par interférométrie une forme d'une surface optique d'un objet de test WO2020244937A1 (fr)

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DE102019208029.4A DE102019208029A1 (de) 2019-06-03 2019-06-03 Messvorrichtung zur interferometrischen Bestimmung einer Form einer optischen Oberfläche eines Testobjekts
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WO2023051939A1 (fr) * 2021-10-01 2023-04-06 Carl Zeiss Smt Gmbh Procédé de caractérisation de la forme de surface d'un élément optique et dispositif de test interférométrique
DE102022204645B4 (de) 2022-05-12 2024-01-25 Carl Zeiss Smt Gmbh Verfahren sowie interferometrische Messanordnung zur Bestimmung der Oberflächenform eines Prüflings

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US6717680B1 (en) * 2001-05-25 2004-04-06 Zygo Corp Apparatus and method for phase-shifting interferometry
US20180106591A1 (en) * 2015-05-22 2018-04-19 Carl Zeiss Smt Gmbh Interferometric measuring arrangement

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