EP1495369A2 - Dispositif de mesure interferometrique et installation d'eclairage de projection pourvue d'un dispositif de mesure de ce type - Google Patents

Dispositif de mesure interferometrique et installation d'eclairage de projection pourvue d'un dispositif de mesure de ce type

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Publication number
EP1495369A2
EP1495369A2 EP03718735A EP03718735A EP1495369A2 EP 1495369 A2 EP1495369 A2 EP 1495369A2 EP 03718735 A EP03718735 A EP 03718735A EP 03718735 A EP03718735 A EP 03718735A EP 1495369 A2 EP1495369 A2 EP 1495369A2
Authority
EP
European Patent Office
Prior art keywords
measuring device
pupil
periodicity
mask
diffraction grating
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP03718735A
Other languages
German (de)
English (en)
Inventor
Martin Schriever
Ulrich Wegmann
Helmut Haidner
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Carl Zeiss SMT GmbH
Original Assignee
Carl Zeiss SMT GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Carl Zeiss SMT GmbH filed Critical Carl Zeiss SMT GmbH
Publication of EP1495369A2 publication Critical patent/EP1495369A2/fr
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/02—Diffusing elements; Afocal elements
    • G02B5/0205—Diffusing elements; Afocal elements characterised by the diffusing properties
    • G02B5/021—Diffusing elements; Afocal elements characterised by the diffusing properties the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures
    • G02B5/0221—Diffusing elements; Afocal elements characterised by the diffusing properties the diffusion taking place at the element's surface, e.g. by means of surface roughening or microprismatic structures the surface having an irregular structure
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/02—Diffusing elements; Afocal elements
    • G02B5/0205—Diffusing elements; Afocal elements characterised by the diffusing properties
    • G02B5/0252—Diffusing elements; Afocal elements characterised by the diffusing properties using holographic or diffractive means
    • 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
    • G03F7/70058—Mask illumination systems
    • G03F7/70075—Homogenization of illumination intensity in the mask plane by using an integrator, e.g. fly's eye lens, facet mirror or glass rod, by using a diffusing optical element or by beam deflection
    • 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
    • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
    • G03F7/70591—Testing optical components
    • G03F7/706—Aberration measurement

Definitions

  • the invention relates to a measuring device for interferometric measurement of an optical imaging system and to a microlithographic projection exposure system in which such a measuring device is integrated.
  • optical imaging systems are subject to ever increasing demands.
  • An example of this are projection objectives for the microlithographic production of semiconductor components and other finely structured components, which are supposed to produce structures in the submicrometer range largely free of aberrations. Since it is generally impossible to derive the optical properties of the lenses from theoretical calculations due to the complex optical structure, the optical properties must be measured reliably, at least when assembling and adjusting the optical imaging systems. It is also desirable to be able to measure the optical properties of the projection lenses during operation at the place of use in order to be able to counteract any deterioration in the imaging quality in a timely manner.
  • a device for wave front detection working in the manner of a shearing interferometer which enables fast, highly accurate measurement of high-resolution photolithographic projection objectives, is described in German patent application DE 101 09 929.
  • This comprises a wavefront source for generating at least one wavefront passing through the imaging system, a diffraction grating arranged downstream of the imaging system for interacting with the wavefront transformed by the imaging system and a position-resolving detector arranged downstream of the diffraction grating for detecting interferometric information.
  • the spatial structure of the wavefront source serves to form the spatial coherence of the wavefront.
  • different locations of the pupil of the imaging system are in principle interferometrically compared with one another, for example by superimposing the light of a zeroth diffraction order passing through the diffraction grating with the light of the first diffraction orders.
  • a wavefront module can be used as the wavefront source, which has a shadow mask with a two-dimensional hole structure to be arranged in the object plane, refractive, diffractive or reflective focusing optics upstream of the shadow mask for concentrating incident illuminating light on the holes of the shadow mask and a focusing screen upstream of the focusing optics for homogenizing the intensity distribution in the mask level and possibly to reduce spatial coherence.
  • the illumination system of a projection exposure system at the same time as the illumination system of the interferometric measuring device in order to check the imaging quality of the projection objective from time to time, for example at the location of the projection exposure system. For this purpose, an exchange of the reticles provided for the chip production operation with the useful patterns representing the chip structure against such a wavefront module is necessary.
  • the measuring device should be easy to integrate into a microlithographic projection exposure system and enable rapid and interference-free measurements on projection lenses in their operating state.
  • the invention proposes a measuring device with the features of claim 1. Furthermore, a projection exposure system for microlithography according to the features of claim 17 is proposed, in which such a measuring device is integrated. Advantageous further developments are specified in the dependent claims. The wording of all claims is incorporated by reference into the content of the description.
  • a measuring device for the interferometric measurement of optical imaging systems, which are provided for imaging a useful pattern provided on a mask in the image plane of the imaging system.
  • This useful pattern provided on the mask or the reticle represents, for example, the structure of a semiconductor component in a specific manufacturing step.
  • the measuring device has a wavefront source for generating at least one wavefront passing through the imaging system, a diffraction grating arranged or arranged behind the imaging system for interacting with the wavefront transformed by the imaging system, and a spatially resolving detector assigned to the diffraction grating for detecting interferometric information.
  • the wavefront source comprises at least one measurement pattern which is provided on the mask or on the reticle in addition to the useful pattern.
  • the measurement structures for the interferometer which were conventionally present in a separate measurement reticle, in the usual reticles for the chip structures.
  • the measurement pattern which due to its coherence-forming properties can also be referred to as a coherence pattern, is provided on this reticle as part of the reticle used for the production of structured components.
  • the costs for providing an interferometric measuring device can be significantly reduced.
  • interferometric measurements on built-in lenses are possible faster than before, which reduces machine downtimes and thereby increases the productivity of the projection exposure system.
  • the spatially resolving detector can be permanently integrated in the projection exposure system or can be exchanged or exchanged together with the diffraction grating.
  • the locations of the measurement structure and the diffraction grating can also be interchanged. They are to be arranged in optically conjugate levels.
  • the grid can thus be provided on the reticle in addition to the useful pattern.
  • several interferograms with different phase positions are necessary in a preferred measuring method.
  • the phase position can be varied by phase shifting, ie by shifting the diffraction grating on the image side and / or by shifting the mask on the object side.
  • the measuring device can have suitable displacement devices, one of which can be integrated into the wafer stage, for example.
  • the measurement pattern can have a one-dimensional periodic structure with a single periodicity direction. Measurement patterns with a two-dimensional structure and at least two periodicity directions running transversely to one another are preferred, in particular those with two orthogonal periodicity directions. Due to the preferably two-dimensional structure of the wavefront source, the spatial coherence of the radiation can be adapted such that the wavefronts transformed by the optical system can be measured with high precision in several directions. All structures described in DE 101 09 929 can be considered as two-dimensional structures.
  • the diffraction grating which can also be one-dimensional or two-dimensional periodic, is preferably designed as a function of the structure of the measurement pattern in such a way that only certain diffraction orders contribute to interference on the diffraction grating, for example only the zeroth and first diffraction orders.
  • Diffraction gratings are preferred which each have a diffractive, periodic structure for different directions, which makes it possible to to determine phase gradients in more than one direction from individual interferograms.
  • Diffraction gratings with orthogonal directions of periodicity for example checkerboard gratings or cross gratings, are favorable, but gratings with other symmetries, for example with angles of 45 °, 60 ° or 120 ° between periodicity directions, are also possible.
  • an illumination system of a microlithographic projection exposure system is used to illuminate the wavefront source, whereby a targeted shaping of the illumination light is possible.
  • the lighting system can also be part of a separate measuring stand, in order to measure it, for example, for adjustment purposes, in particular when assembling projection objectives.
  • the lighting systems preferably used here have a light mixing device for homogenizing the illuminating light of a light source.
  • the light mixing devices which in particular have at least one honeycomb condenser or at least one light guide rod working in the manner of a kaleidoscope, generate a two-dimensional grid of secondary light sources in a pupil plane of the lighting system
  • Honeycomb condensers are essentially circular and in the case of
  • Light guide rods are usually rectangular. Corresponding divided illumination can then also be present in a pupil plane of the imaging system conjugated to the pupil plane of the illumination system. This creates an inhomogeneous
  • Pupil illumination with intensities that change periodically in several directions of periodicity This inhomogeneity of the Pupil illumination, which is also referred to below as parceling, can impair the accuracy of the interferometric measurement.
  • several alternative or cumulative measures can be provided to avoid such impairments.
  • the mask has a scattering structure in at least one area for homogenizing the intensity distribution in the light path of the scattering structure and possibly for reducing the spatial coherence of the illuminating light.
  • the scattering structure can bring about a change in the light conductance of the radiation by adding previously non-existent angles of light rays and / or modifying the existing angular distribution.
  • the scattering structure can have a statistical distribution of scattering centers, such as in the case of a focusing screen. There may also be regularly distributed scattering centers, e.g. in the form of crossed cylindrical lenses. It can be irregular or regular structures, e.g. generated by etching or other surface-roughening treatment.
  • Computer-generated holograms are also possible as scattering structures.
  • Scattering structures on the reticle can e.g. enable an imaging system to be measured at its full numerical aperture, even if the upstream lighting system has a smaller numerical aperture. With the help of the scattering, otherwise unexposed areas of the pupil can also be illuminated. In this way, scattering structures between the lighting system and the system to be measured can act as intermediaries by introducing additional angles.
  • the scattering structure can be arranged such that the measurement pattern is independent of the degree of intensity inhomogeneity of the Illumination light is largely homogeneously illuminated, so that essentially only the measurement pattern contributes to the spatial coherence formation of the measurement light.
  • the mask has a transparent support with a light entry side facing the light source and a light exit side carrying the measurement pattern, and that the scattering structure is arranged in the area of the measurement pattern on the light entry side of the support.
  • the scattering structure acting in the manner of a focusing screen or lens is arranged in the light path in front of the measurement pattern and can, if necessary ensure that, despite parceling light, the measurement structure is illuminated essentially without parceling, ie largely incoherently.
  • the transparent support can consist, for example, of synthetic quartz glass, calcium fluoride or another fluoride crystal material.
  • the scattering structure can be formed by local matting or roughening of the light entry side.
  • At least one scattering structure on one level or surface with the measurement pattern (e.g. on the light exit side of a transparent mask).
  • Scattering structures that lie next to and / or between the structures of a useful pattern can also be advantageous, in particular, in the case of reflective masks that operate at the shortest wavelengths in the extreme ultraviolet range (EUV), e.g. at 13nm wavelength.
  • EUV extreme ultraviolet range
  • a pupil plane of the imaging system has a pupil intensity distribution that varies periodically in at least one periodicity direction with a pupil period it may be advantageous if the measurement pattern and the diffraction grating have periodic structures which are matched to one another and are matched to the pupil intensity distribution in such a way that a shear spacing in a shear direction corresponding to the periodicity direction of the pupil plane corresponds to this pupil period or to an integral multiple of the pupil period. It can thereby be achieved that only those areas of the pupil plane of the imaging system are compared with one another by means of shearing interferometry that have essentially the same illumination intensity. With a high basic intensity of the interference pattern, a large modulation range of the interference intensity is therefore available for the measurement. This measure can also be advantageous independently of the other measures of the invention, for example in the case of measuring devices of the type described in DE 101 09 929.
  • the periodic structures of the measurement pattern and diffraction grating are preferably designed such that a first shear distance in one of the first periodicity directions corresponds to the first shear direction of the first pupil period or an integer multiple thereof and a second shear distance in a second shear direction corresponding to the second periodicity corresponds to the second pupil period or an integer multiple thereof. This enables multidimensional measurements without being affected by inhomogeneous lighting.
  • the periodicity directions of the pupil plane or of the measurement pattern and of the diffraction grating can in particular be perpendicular to one another, for example in lighting systems with rod integrators as the light mixing element.
  • the first and second pupil periods can have different lengths, which is the case, for example, if a rod integrator with a rectangular cross section is used in the lighting system, in which the ratio of the side lengths has a different aspect ratio.
  • the measurement pattern and the diffraction grating can have a corresponding non-square polygonal structure, for example in the form of diamond-shaped checkerboard gratings.
  • the shear spacing is not or only incompletely adapted to the periodicity of an inhomogeneous pupil illumination, in the absence of effective measures for homogenizing the intensity or destroying the division of the illuminating light, the modulation can fluctuate via the pupil.
  • preferred further developments provide for the interferograms to be evaluated only in those selected areas which have a sufficient signal / noise ratio.
  • an evaluation device for spatially resolving evaluation of detector signals can be provided, in which the evaluation is spatially selective as a function of at least one
  • Evaluation threshold condition is possible. This way can be achieved that only signals from "good” areas are selected and processed, while signals from "bad” areas are not used for further evaluation.
  • a preferred variant of this selective evaluation provides that only signals from detector areas for which the signal intensity exceeds an intensity threshold value and at the same time signal modulation exceeds a modulation threshold value contribute to the formation of a signal provided for further processing.
  • the invention also relates to a projection exposure system for microlithography, for example a wafer stepper or wafer scanner, in which an interferometric measuring device according to the invention is integrated.
  • Projection exposure systems of this type can be monitored for their production quality, for example for compliance with tolerance limits of the respective image errors of the projection lens, without major disruptions to the production process at the production location and during a production cycle. Since the measurement structure is already integrated in the reticle used for chip production and the lighting system of the projection exposure system can be used for illumination, it is only necessary for a transition between production and measurement to bring the diffraction grating into the image plane of the projection lens and out of it during operation remove and arrange a detector so that emerging interference patterns can be detected.
  • the projection exposure system has an aberration control or regulation, which can act on the imaging properties of the projection objective as a function of measurement signals from the measurement device via active elements or manipulator elements.
  • Production monitoring and optical quality monitoring can be carried out with the operating light source at the operating wavelength of the projection exposure system.
  • FIG. 1 is a schematic illustration of a microlithography projection exposure system designed as a wafer stepper, in which an embodiment of a measuring device according to the invention is integrated;
  • 2 is a schematic representation of the division of the illumination intensity into the pupil plane of the projection objective
  • FIG. 3 is a schematic section through a preferred embodiment of a reticle, which contains a useful pattern for chip production and next to it a measurement pattern of the interferometric measuring device;
  • FIG. 4 shows a section of a diffraction grating with a diamond structure and different grating periods in (a) orthogonal grating directions and in (b) a variant with orthogonal linear grids of different periods, which are arranged side by side;
  • FIG. 5 is a schematic section through the area of the pupil and the image plane of the projection objective with diffraction grating and detector for explaining a location-selective evaluation of detector signals with the identification of areas (a) and areas (b) that are difficult to evaluate.
  • the projection exposure system comprises an excimer laser 2 as the light source, which emits light with a working wavelength of 248 nm, the working wavelength in other embodiments also being less, for example 193 nm or 157 nm or more.
  • a downstream lighting system 3 generates a large, sharply delimited and homogeneously illuminated image field which is adapted to the telecentricity requirements of the downstream projection lens 4.
  • the projection objective 4 is a preferred embodiment of an optical imaging system to be measured.
  • the lighting system has devices for selecting the lighting mode and can be switched, for example, between conventional lighting with a variable degree of coherence, ring field lighting and dipole or quadrupole lighting.
  • a light mixing element it comprises a rod integrator 5 with a rectangular cross section, which consists of transparent material and which generates a dividedled grid arrangement of secondary light sources in a pupil plane 6 of the lighting system, each of which has the rectangular shape of the Have rod cross-section and are arranged at a lateral distance from each other.
  • a device 7 for holding and manipulating a mask 8 is arranged behind the lighting system in such a way that the mask (reticle) lies in the region of the object plane 9 of the projection objective and in this plane for scanner operation in a departure direction 10 (y direction) with the aid of a scanner drive 1 1 is movable.
  • Behind the object plane or mask plane 9 follows the projection lens 4, which acts as a reduction lens and, during chip production, an image of a useful pattern 35 (FIG. 3) provided on the mask 8 on a reduced scale, for example on a scale of 1: 4 or 1: 5, images onto a wafer, not shown, which is covered with a photoresist layer and which is arranged in the image plane 16 of the reduction objective 4.
  • a useful pattern 35 FIG. 3
  • the wafer is held in the production mode by a device 17 which comprises a scanner drive 18 in order to move the wafer in parallel with the retraction direction 10 in synchronism with the reticle 8.
  • the device 17, which is also referred to as the wafer stage, also allows controlled movement of objects accommodated in the wafer stage in two directions running perpendicular to one another and perpendicular to the optical axis 12, as well as displacements parallel to the optical axis. All systems are controlled by a control unit 19.
  • the projection objective is designed, for example, as a purely refractive objective that is rotationally symmetrical with respect to the optical axis 12. It can also be a catadioptric projection lens with physical or geometric beam splitting. Purely reflective systems are also possible for lower wavelengths, for example in the area of soft X-rays.
  • the projection exposure system is designed such that in the area of the exit surface of the rod integrator 5 there is a field plane of the lighting system which is optically conjugated to the object plane 9 and to the image plane 16 of the projection objective.
  • the pupil 6 of the illumination system lies between the light guide rod 5 and the image plane 9 of the illumination system and is optically conjugated to the pupil plane 20 of the projection objective. Accordingly, an inhomogeneous, rasterized or divided intensity distribution corresponding to the intensity distribution in the pupil plane 6 of the illumination system can be present in the pupil plane 20 of the projection objective. This is shown schematically in FIG. 2.
  • An interferometric measuring device operating in the manner of a shearing interferometer for measuring the imaging quality of the projection objective 4 is integrated into the projection exposure system 1.
  • the measuring device has a wavefront source 31 with a two-dimensional periodic structure for generating a large number of wavefronts passing through the projection objective 4, a diffraction grating 32 which can be arranged in the image plane 16 of the projection objective for interaction with the wavefronts transformed by the imaging system 4, and a spatially resolving detector 33 arranged downstream of the diffraction grating for the spatially resolving acquisition of interferometric information which results from the superimposition of wave fronts which are diffracted and diffracted at the diffraction grating 32 (cf. FIG. 5).
  • the detector is connected to an evaluation device 43.
  • the detector 33 for detecting the resulting interference pattern is arranged directly behind the diffraction grating 32 without the interposition of optical elements and, as an image sensor, has a CCD chip 60, which forms a spatially resolving, light-sensitive sensor surface and fills a large number of surfaces arranged pixels (pixels) is divided (Fig. 5). It can be movable separately from the diffraction grating, but is preferably combined with the diffraction grating to form a simply constructed, compact diffraction grating detector unit 61, which as a whole can be introduced into or removed from the wafer stage 17.
  • the detector is permanently installed behind the image plane 16 and only one diffraction grating unit is designed to be exchangeable.
  • the combination of diffraction grating and detector can in particular have any design described in DE 101 09 929.
  • a preferably telecentric, optical imaging system and / or a flat or curved secondary radiator surface can be provided between the diffraction grating 32 and the sensor surface 60.
  • phase position is varied by phase shifting, ie by a relative shift between the measurement pattern and the diffraction grating perpendicular to the optical axis.
  • the displacement paths in this process are typically fractions of the grating period.
  • the diffraction grating 32 on the image side is displaced.
  • the mask with the measurement pattern can also be moved.
  • the shifts take place parallel to the periodicity directions to be evaluated.
  • the measuring device has a suitable displacement device for this purpose, which in the example is formed by the wafer stage 17.
  • an intensity signal l (t) (FIG.
  • the wavefront source 31 uses the light from the illumination system 3. As illustrated in FIG. 3, the wavefront source comprises a measurement pattern 34 illuminated with this light, which is located in a separate edge area of the reticle 8 next to the useful pattern 35 used for chip production on the flat light exit side 37 of the reticle 8 is provided and has a diamond-shaped unit cell in the example shown.
  • the reticle 8 has a transparent support made of synthetic quartz glass or calcium fluoride in the form of a plane-parallel plate 36, which is built into the reticle stage 7 in such a way that its light exit side 37 facing away from the light source lies in the object plane 9 of the projection objective.
  • a scattering structure 39 is formed on the opposite light entry side 38 in the area of the measurement pattern 34 by roughening the otherwise smoothly polished, flat surface 38. It serves to form radiation 40 which is spatially inhomogeneous due to the division of the pupil 6 from the illumination system and which is essentially spatially homogeneous, which falls on the measurement pattern 34.
  • the essential function of the scattering structure is thus the homogenization of the intensity distribution or the destruction of the parceling by means of intensity determination.
  • the spatial coherence of the radiation leaving the measurement area 42 is essentially only determined by the coherence-forming properties of the measurement pattern 34.
  • the measurement pattern can be designed in the manner of a shadow mask with transparent and opaque areas in order to form a wavefront source with high contrast.
  • the diffraction grating 32 which is introduced into the image plane 16 of the projection objective for the measurement, comprises a diffraction grating which is formed in the manner of a diamond checkerboard grating and which Interference, ie the lateral shear of the wave fronts.
  • the periodicity of the diffraction pattern is different in the two perpendicularity directions x and y which are perpendicular to one another. It can be seen from Fig. 4 (a) that the lattice constant is larger in the x direction of the diamond pattern than in the y direction.
  • the lattice constants correspond to the short or long diameter of the rhombuses or rhombuses, which are perpendicular to each other.
  • the periodicity lengths of the diffraction grating structure are matched to the different periodicity lengths of the divided objective pupil (FIG. 2) such that the respective shear distances 50, 51 generated by diffraction in orthogonal shear directions exactly correspond to the periodicity lengths of the divided pupil in the corresponding directions x and y (Fig. 2).
  • a preferred alternative to a diffraction grating with a diamond-shaped unit cell is to provide two linear gratings lying next to one another, that is to say spatially separated from one another, with different periods, the periodicity directions of which are preferably perpendicular to one another.
  • 4 (b) shows an example of a diffraction grating 32 ' .
  • the structures that are provided on a common carrier are used in succession during the measurement.
  • Corresponding structures can also be provided as a measurement pattern.
  • Different types of measurement pattern and grating structures can be combined with one another, so that, for example, a measurement pattern with linear gratings lying next to one another of different period and perpendicular periodicity directions can be used in connection with a diamond-shaped diffraction grating or an inverse combination.
  • the diffraction grating determines the shear distance.
  • the measurement pattern defines the coherence function. By choosing more suitable Measurement patterns are only able to interfere with certain rays from the pupil, undesired interference is suppressed.
  • the areas from the pupil that are separated from one another by a shear distance should preferably be capable of interference. In this way, the structure sizes of the measurement pattern and the diffraction grating are related. The two structures thus perform separate functions, but reliable measurements are only possible if the dimensions are coordinated.
  • the periodicity directions of the measurement pattern and the diffraction grating are perpendicular to one another. Angles between the periodicity directions deviating from 90 ° are also possible. It is also possible to use structures with more than two directions of periodicity.
  • the shear spacing 50 depends on the diffraction angle 52 of the diffraction grating 32 in the shear direction running parallel to the x direction, the diffraction angle of the first diffraction order preferably being considered here.
  • the first-order diffraction angle 52 is selected such that the areas of two plots 53, 54 lying directly next to one another in the pupil plane 20 are compared with one another by means of shearing interferometry. The same applies to the y direction, in which a smaller diffraction grating constant leads to larger shear distances.
  • grating spacings of the diffraction grating it is also possible to compare the areas of plots further away from one another or to set the shear spacing so small that it becomes small compared to the corresponding extension of the parcel. In any case, it can be achieved by adapting the diffraction grating periods to the geometry of the pupil parceling that the interfering wave fronts have essentially the same intensity, whereby a high measurement accuracy can be achieved.
  • a diffracted beam 67 is shown with a broken line, in which the shear distance 65 in the direction under consideration corresponds to approximately half the periodicity of the pupil parceling.
  • the associated detector area 66 accordingly detects the superposition of waves from a strongly and a weakly illuminated area of the pupil 20. This leads to the intensity curve shown schematically in FIG. 5 (b) during phase shifting, in which the intensity signal is temporally with a weak modulation amplitude by one intensity -
  • the mean value l fluctuates, which is lower than in the case of a good adaptation to the pupil parceling (FIG.
  • Intensity threshold lies and at which the signal modulation, ie the absolute difference between maximum intensity l ma ⁇ and minimum intensity l m j n during the periodic fluctuation, exceeds a modulation threshold.
  • This double evaluation threshold condition is to be preferred over a simple evaluation threshold condition, for example based on the contrast of the intensity fluctuation, because it enables reliable identification of areas that can be evaluated. If, for example, the contrast alone, defined as the ratio between the difference between maximum and minimum intensity and the sum of maximum and minimum intensity, is used as the threshold criterion, a reliable distinction between good (Fig. 5 (a)) and bad (Fig. 5 (b )) Areas not reliably possible, since according to this definition of the contrast, both areas would provide approximately the same contrast.
  • Adjustment procedures e.g. using the least squares method to reconstruct the overall interferogram. Missing data from "bad" areas can be determined by interpolation.
  • This evaluation method stabilizes the measuring system against malfunctions that occur during operation, for example caused by contamination can be. It may also make it easier to find the edges and is very useful when measuring optical systems with obscurations, for example with central shading.
  • This advantageous evaluation method can optionally be dispensed with if the negative effects of the pupil division are reduced or eliminated by other, in particular by the constructive measures described above, for example by adapting the shear spacing in all periodicity directions to the pupil division and / or by destroying the division the pupil illumination by a scattering structure, especially in front of the measurement pattern.
  • the invention enables the integration of an interferometric measuring device in a particularly simple manner
  • the measuring device preferably includes an aberration control or aberration control in order to set the imaging properties of the projection objective to specific values on the basis of the interferometric measurement.
  • the embodiment shown has the aforementioned evaluation unit 43, which determines the instantaneous wavefront topography characteristic of the imaging properties of the projection lens 4 from the interferograms recorded by the detector.
  • An actual signal 71 representing the current actual state is transferred to a comparator 72, which compares the actual signal with a desired signal 73 which the represents the desired imaging properties of the projection lens.
  • active signals 74 are transmitted to active elements 75 to 77, which act on the optical elements 78 to 80 coupled to the active elements in a manner that reduces the aberrations of the projection objective.
  • the active elements can be, for example, actuators which move or rotate the assigned lenses axially and / or transversely to the optical axis 12 or other actuators with which the assigned lenses can be deliberately deformed or subjected to mechanical stress.
  • an aberration control the steps mentioned are repeated in a closed circle until the desired imaging properties of the projection objective are established.
  • an aberration control operating without feedback is also possible.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
  • Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)
  • Instruments For Measurement Of Length By Optical Means (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
  • Testing Of Optical Devices Or Fibers (AREA)

Abstract

L'invention concerne un dispositif de mesure interférométrique d'un système d'imagerie optique qui sert à représenter un modèle utile prévu sur un masque dans le plan d'image dudit système d'imagerie. Ce dispositif de mesure comprend les éléments suivants : une source de front d'onde générant au moins un front d'onde qui traverse le système d'imagerie ; un réseau de diffraction disposé derrière le système d'imagerie pour interagir avec le front d'onde modifié par le système d'imagerie ; un détecteur à résolution locale, associé au réseau de diffraction, pour saisir l'information interférométrique. Selon l'invention, la source de front d'onde comporte au moins un modèle de mesure (34), configuré en plus du modèle utile (35) sur le masque (8).
EP03718735A 2002-04-15 2003-04-05 Dispositif de mesure interferometrique et installation d'eclairage de projection pourvue d'un dispositif de mesure de ce type Withdrawn EP1495369A2 (fr)

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DE10217242 2002-04-15
PCT/EP2003/003566 WO2003087945A2 (fr) 2002-04-15 2003-04-05 Dispositif de mesure interferometrique et installation d'eclairage de projection pourvue d'un dispositif de mesure de ce type

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US (2) US7158237B2 (fr)
EP (1) EP1495369A2 (fr)
JP (1) JP2005522871A (fr)
AU (1) AU2003222799A1 (fr)
DE (1) DE10317278A1 (fr)
WO (1) WO2003087945A2 (fr)

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JP2005522871A (ja) 2005-07-28
DE10317278A1 (de) 2003-11-06
US20050264827A1 (en) 2005-12-01
AU2003222799A1 (en) 2003-10-27
AU2003222799A8 (en) 2003-10-27
US7158237B2 (en) 2007-01-02
WO2003087945A3 (fr) 2004-09-16
WO2003087945A2 (fr) 2003-10-23
US20070046912A1 (en) 2007-03-01

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