Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
  • G02B19/0004—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed
  • G02B19/0019—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed having reflective surfaces only (e.g. louvre systems, systems with multiple planar reflectors)
  • G02B19/0023—Condensers, e.g. light collectors or similar non-imaging optics characterised by the optical means employed having reflective surfaces only (e.g. louvre systems, systems with multiple planar reflectors) at least one surface having optical power
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/08—Mirrors
  • G02B5/09—Multifaceted or polygonal mirrors, e.g. polygonal scanning mirrors; Fresnel mirrors
• • 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
  • G03F7/70008—Production of exposure light, i.e. light sources
  • G03F7/70033—Production of exposure light, i.e. light sources by plasma extreme ultraviolet [EUV] sources
• • 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
  • G03F7/7015—Details of optical elements
  • G03F7/70158—Diffractive optical elements
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70058—Mask illumination systems
  • G03F7/7015—Details of optical elements
  • G03F7/70175—Lamphouse reflector arrangements or collector mirrors, i.e. collecting light from solid angle upstream of the light source
• • 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
  • G03F7/7055—Exposure light control in all parts of the microlithographic apparatus, e.g. pulse length control or light interruption
  • G03F7/70575—Wavelength control, e.g. control of bandwidth, multiple wavelength, selection of wavelength or matching of optical components to wavelength
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21K—HANDLING OF PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
  • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
  • G21K1/06—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating using diffraction, refraction or reflection, e.g. monochromators
  • G21K1/062—Devices having a multilayer structure
• • G—PHYSICS
  • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
  • G21K—HANDLING OF PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
  • G21K2201/00—Arrangements for handling radiation or particles
  • G21K2201/06—Arrangements for handling radiation or particles using diffractive, refractive or reflecting elements
  • G21K2201/064—Arrangements for handling radiation or particles using diffractive, refractive or reflecting elements having a curved surface

Definitions

• the invention relates to a collector mirror for an EUV microlithography system having an optical grating with an optically effective mirror surface, the electromagnetic reflected radiation of an EUV spectral range emanating from a first focal point, and focused on a second focal point, wherein the The first and second focal points lie on a side of the optical grating facing the mirror surface and define an optical axis, wherein the optical grating is designed to work in combination with the optical grating.
• the optical grating comprises a Blazegitter of a plurality of mirror facets, each having a facet surface, wherein the facet surfaces Mirror surface of Blazegitters form.
• a collector mirror of the type mentioned is known from US 2009/0267003 A1.
• Such a collector mirror is used in EUV microlithography, which is a process for the production and structuring of semiconductor devices, integrated circuits and micro- and nanosystemischen components.
• EUV microlithography is a process for the production and structuring of semiconductor devices, integrated circuits and micro- and nanosystemischen components.
• predefined structures are imaged on a reticle by means of exposure processes on a substrate, for example a silicon substrate.
• the exposure light interacts with the photoresist layer, so that the chemical properties of the exposed areas of the photoresist layer change Photoresist in the exposed or unexposed areas, depending on whether a "positive” or “negative” photoresist is used
• the areas of the substrate surface not covered by the remaining photoresist are etched in an etching process such as wet chemical etching, plasma etching or plasma enhanced
• the predefined structures of the reticle on the processed substrate surface are formed at a projection scale which is characteristic of the microlithography system used, in particular a projection exposure apparatus.
• the performance of the microlithographically produced semiconductor components or integrated circuits is higher, the higher the integration density of the structures in the components. In other words, one endeavor is to image increasingly finer structures on the substrate.
• the lower limit of in The structure size achievable with optical lithography is determined inter alia by the wavelength of the exposure light used. Therefore, it is advantageous to use shortest possible exposure light. From this point of view, projection exposure systems are known which use extreme ultraviolet (EUV) light as exposure light whose wavelength is 13.5 nm.
• EUV extreme ultraviolet
• the EUV light is generated by an EUV light source, in which a plasma is generated by strong electrical discharges (Gas Discharge Produced Plasma, GDPP) or by focusing of laser radiation (laser-produced plasma, LPP) is generated.
• a plasma is generated by strong electrical discharges (Gas Discharge Produced Plasma, GDPP) or by focusing of laser radiation (laser-produced plasma, LPP) is generated.
• a tin droplet is bombarded with pumping light, with the pumping light usually being infrared (IR) light.
• the generated plasma contains a multiplicity of charged particles, for example electrons, which fall from energetically high states into energetically lower states and thereby emit the desired EUV light.
• EUV light can be emitted in the form of black body radiation.
• the generated EUV light propagates in all spatial directions. In order for the EUV light to be usable as useful radiation for the exposure process, as much of it as possible has to be directed towards the illumination and projection optics by means of
• Collector mirrors known from the prior art have an elliptical mirror surface for better light focusing. However, they have the disadvantage that with increasing density of the tin plasma, the plasma frequency can increase greatly.
• the useful rays and residual rays ie electromagnetic radiation from a different from the EUV spectral residual spectral range, which are not available for the exposure process, reflected at the mirror surface of the collector mirror and focused on the second focus.
• the residual rays can get into the illumination and imaging optics and even to the substrate.
• the residual rays typically include high intensity IR light and deep ultraviolet (DUV) light. The residual rays cause a significant heat input to the Collector mirror downstream optics and thus an unacceptable impairment of the optical properties of these optics.
• elliptical collector mirrors which are formed as a spectral purity filter (SPF) and have a binary grid.
• the binary grating serves to reflect the EUV light emitted at the first focus and to focus on a second focus, the focused EUV light passing through a second focus aperture while blocking the IR pump light there. This suppresses the IR pump light.
• collector mirror have the disadvantage that the binary lattice can suppress only residual rays of a single wavelength effectively, and this is only possible if the lattice parameters of the binary lattice, for example, the grating period, very accurately controlled in manufacturing were. This creates additional manufacturing costs.
• the residual rays of a broadband residual spectral range in the imaging beam path must be suppressed, which additionally increases the production cost.
• the binary lattice surface roughness whose dimensions are in the range medium wavelengths. Such surface roughness is due to vibrations and accuracy limitations of the devices used to make the binary grating. They cause the generated EUV light is not focused exactly on the second focus of the collector mirror, but on a widened area around the second focal point.
• the second focus for the EUV light is also referred to as the "intermediate focal point (IF)." It is undesirable for the IF to broaden and the aperture must be increased accordingly to allow the useful rays to pass through the aperture as much as possible to increased fürse the residual rays.
• the collector mirror must be formed with a very large diameter in order to simultaneously take into account the requirement for a large working distance and a small IF-side numerical aperture (NA).
• NA numerical aperture
• the magnification is defined as the ratio between the distance from the first focal point to the beam incident point on the mirror surface on the one hand and the distance from the beam incident point to the second focal point on the other. This undesirably leads to an enlargement of the envelope of the etendue, in particular in the IF and / or in the far field.
• the surface roughness mentioned above also favor the enlargement of the envelopes of Etendue.
• An increase in the envelope of the etendue causes a loss of the generated useful beams, which has a serious effect on the exposure quality and / or the image quality in extreme illumination modes of an EUV microlithography system.
• a collector mirror for collecting EUV radiation which has an optical grating having a plurality of Gitterlemente.
• the grating elements may be formed to represent sections of ellipsoids.
• this object is achieved with respect to the collector mirror mentioned above in that the facet surfaces are arranged in a comprehensive optical axis sectional plane on a plurality of imaginary, along the optical axis mutually displaced Ellipsenschalen whose common mathematical focus points with the first and the second focus coincide, wherein the mirror surface extends along the imaginary elliptical shells, and that an edge region-side mirror facet of an adjacent mirror facet pair is arranged on a first ellipse shell, wherein a vertex-side mirror facet of the mirror facet pair is arranged on a second ellipse shell adjacent to the first ellipse shell, wherein the first ellipse shell along the optical axis is shifted from the second ellipse shell to the first focal point.
• Each facet surface is arranged on the ellipse shell such that the facet surface extends along the ellipse shell or tangentially to the ellipse shell. Since the several imaginary elliptical shells have common focus points, these elliptical shells form an imaginary confocal ellipse group.
• Each elliptical shell corresponds mathematically to an imaginary ellipsoidal shell which is at least partially rotationally symmetrical with respect to the optical axis.
• each facet surface is spatially arranged on an imaginary ellipsoidal shell, with the individual imaginary ellipsoid shells forming a confocal elliptical sphere.
• the resulting mirror surface extends along a path arrangement of concentric with respect to the optical axis, spaced apart in the direction of the optical axis circular paths, or alternatively along a spiral path about the optical axis.
• the collector mirror according to the invention is thus able to block residual rays from a particularly broad residual spectral range.
• the collector mirror according to the invention advantageously achieves a broadband residual radiation suppression.
• the mirror surface of the collector mirror deviates from an elliptical mirror surface.
• elliptic collector mirrors i. Collector mirrors with an elliptical mirror surface, the magnification of the image from the first focus to the second focus of the collector mirror varies. This leads to a greatly enlarged envelope of the etendue, especially in the IF and / or in the far field. This results in a high loss of useful radiation, since the useful beams are not focused in the IF to a beam with a sufficiently small diameter to completely pass through the aperture.
• the collector mirror according to the invention reflects useful rays from the first focus to the second focus, wherein the variation of the image scale along the mirror surface due to the arrangement of the facet surfaces on the confocal ellipse crowd is at least reduced.
• the enlargement of the envelopes of the etendue is thus reduced.
• the generated EUV light is focused in the IF into a beam with a reduced diameter.
• a shutter with a smaller aperture can be used. This increases the proportion of blocked by the aperture residual rays.
• the collector mirror downstream optics are better protected from contamination by the EUV light source.
• cleaning gases for example of the H2 gas, which serve to protect the optics can be used with a reduced gas pressure, which, in addition to a cost-effectiveness, improves the transmission of the EUV light through the gas atmosphere.
• the mirror surface of the collector mirror may extend from a vertex region to an edge region of the imaginary elliptical shell. However, it is also possible that the mirror surface does not reach the vertex area. stretches, for example, the mirror surface in the apex region of the imaginary Ellipsenschalen not be present, for example, there have an opening or a hole.
• an edge region-side mirror facet of an adjacent mirror facet pair is arranged on a first ellipse shell, wherein a vertex area side mirror facet of the mirror facet pair is arranged on a second ellipse shell adjacent to the first ellipse shell, wherein the first ellipse shell along the optical axis of the second ellipse shell shifted to the first focal point.
• the edge region of the mirror surface closer Spiegelfacette on an imaginary Ellipsenschale that is closer to the first focal point than the imaginary Ellipsenschale on which the top portion closer Spiegelfacette the two mirror facets is , If this is the case for all mirror facets, for example, the mirror surface of the collector mirror in the sectional plane can be "bowed" towards the vertex as compared to an elliptical mirror surface. In other words, in relation to an imaginary ellipse shell which overlaps the mirror surface of the collector mirror in the edge region, the mirror surface of the collector mirror in the apex region is then curved in the direction away from the imaginary ellipse shell.
• the collector mirror according to the invention can be formed at a constant working distance with a smaller collector diameter and thus more compact and / or at a constant collector diameter with a larger working distance and thus radiation resistant in comparison to the previous collector mirrors.
• the above-mentioned embodiment may result in a non "pearled” mirror surface, as described later in connection with an embodiment of the constant magnification collector mirror.
• the terms "apex area” and “marginal area” are to be understood relative to the course of the mirror surface and have the meaning "comparatively closer to the apex area or farther from the edge area” or “comparatively closer to the edge area or farther from the apex area”.
• the plurality of imaginary elliptical shells are not physical shells of the collector mirror, but merely serve to illustrate the structure of Blazegitters mathematically.
• the term "focal point” is to be understood as a physical or optical feature of the present collector mirror, while the term “focal point” merely serves for the mathematical illustration of the present invention.
• the Blazegitter a Blazewinkel by which the facet surfaces are each locally inclined to a grid surface, wherein the blaze angle increases from the edge region to the apex area.
• the blaze angle can increase continuously from the edge region to the apex region, wherein this embodiment also includes the case in which the blaze angle is constant in sections from the edge region to the vertex region.
• shading effects occur in which part of the specular facet reflex, i. the reflected on the mirror surface Nutzstrahlen is blocked by an adjacent mirror facet. These shadowing effects are related to the Blazewinkelverlauf.
• this measure achieves a reduction in the shadowing effects.
• the facet surfaces are distributed on the elliptical shells such that the facet surfaces are arranged at intersections of the elliptical shells with at least a portion of an imaginary circular line, wherein for each point on the circumference the ratio of the distance of the first focal point this point and the distance of this point to the second focal point has the same value.
• This measure has the advantage that the imaging scale for the mirror facets that satisfy this AnOrdnungsvorschrift is constant or at least approximately constant. Light from the first focal point is sharply focused on the second focal point of all mirror facets satisfying this ordinance. point shown.
• the collector mirror can be designed so that all existing mirror facets meet this arrangement rule, so that the imaging scale of the mirror surface as a whole is constant.
• the collector mirror may have a spherical surface on the substrate side, which advantageously simplifies the production of the collector mirror.
• an edge region-side mirror facet of an adjacent pair of mirror facets is arranged on a first ellipse shell, wherein a vertex area-side mirror facet of the mirror facet pair is arranged on a second ellipse shell adjacent to the first ellipse shell, wherein the first Ellipse shell along the optical axis as seen from the first focal point of the second ellipse shell is shifted to the first focal point, considered as an independent invention.
• this embodiment can be used not only for a collector mirror, but also advantageously for an imaging mirror within the EUV lithography system, for example in the projection lens, because such a mirror allows a very sharp image.
• the mirror surface of such an imaging mirror can in particular be arranged completely outside the optical axis ("off-axis").
• only one facet surface is arranged on the elliptical shells.
• the design effort for the Blazegitter is reduced, so that the collector mirror according to the invention is particularly simple and, consequently, particularly inexpensive to produce.
• the elliptical shells are spaced substantially equidistant from each other along the optical axis. Due to the simplified geometric shape of the confocal ellipse crowd, the Blazegitter can be constructed without much computational effort. This advantageously leads to increased ease of manufacture and cost-effectiveness.
• At least two mirror facets have a focal sweep value of at least approximately 0 or the at least two mirror facets have a same focal length sweep value.
• a plurality of mirror facets can be formed and / or used with the same focal length.
• the collector mirror according to the invention can be produced thereby with less effort.
• the focal length sweep for all mirror facets is vanishingly small or equal to zero. This leads to an advantageously reduced pitch error of the facet surfaces and / or the facet edges.
• the facet surfaces can be formed as planar facet surfaces, which increases the manufacturing simplicity of the collector mirror.
• the Blazegitter a diffraction grating for diffracting the residual rays, wherein the reflected at the mirror surface Nutzstrahlen deflected by at least twice the Blazewinkels of the diffracted residual rays of the zeroth diffraction order and / or between the diffracted residual rays of zeroth and the first diffraction order.
• the specular facet reflex of the incident useful rays is separated from the diffracted residual rays.
• the useful beams are focused solely on the intermediate focal point (IF).
• the residual beams of different diffraction orders are effectively suppressed, so that essentially only the useful beams pass through the diaphragm.
• the residual spectral range comprises an infrared spectral range, wherein the zeroth and the first diffraction orders tion to the diffracted residual rays of a minimum wavelength of the residual spectral range are related.
• the specular facet reflectance of the incident useful rays is separated from the diffracted IR light of the zeroth and first diffraction orders and thus can pass through the aperture alone without being superimposed on the IR light of the lowest orders of diffraction.
• the undesired for the exposure process, high-intensity IR light is thereby suppressed particularly effective.
• the facet surfaces in the sectional plane each have a facet length, wherein at least two facet lengths are different and / or the facet length does not exceed a maximum facet length that is selected as a function of a minimum wavelength of the residual spectral range.
• the collector mirror can be made particularly flexible to meet a variety of practical requirements in EUV microlithography. Furthermore, the collector mirror suppressed short-wave residual rays particularly effective.
• the facet length is in the range of 10 ⁇ to 200 ⁇ .
• the facet length compared to the wavelength of the EUV light is sufficiently large, so that diffraction effects are largely suppressed with respect to the EUV light.
• the reflected EUV light runs essentially in one direction and can thus be focused particularly effectively on the second focal point.
• the facet length is sufficiently short that diffraction effects with respect to the IR and DUV light can not be neglected.
• the blazed grating has a surface roughness in the range of 0 to 0.2 nm.
• the useful beams can thus be focused with increased accuracy on the second focal point.
• the broadening of the intermediate focus is reduced, so that apertures with reduced aperture can be used to more effectively suppress the residual rays.
• the Blazegitter has a Kantenverrundung with a radius in the range of 0 to 1 ⁇ .
• the edge rounding of the collector mirror according to the invention is sufficiently reduced, so that the accuracy of Nutzstrahlfokusstechnik is increased. Apertures with additionally reduced aperture can be used, which reduces the exposure of the illumination and projection optics to the residual rays.
• the blazed grating is made from a grating workpiece in an ultra-precision turning process in which a cutting tool is driven relative to the grating workpiece along a spiral path and / or a concentric circle path arrangement.
• the Blazegitter is formed in terms of blaze angle and / or the facet length with increased precision.
• a spiral relative movement of the cutting tool for example a diamond tool
• an alternating approach and retraction of the tool is not required, so that the structuring times are advantageously particularly short.
• the influence of vibrations of the diamond tool on the lattice quality is reduced.
• the mirror facets are each made in a single chip operation in which the mirror surface of one of the Mirror surface facing the pressure side of the cutting tool is detected.
• the processing time of the mirror facets is thereby shorter than in conventional mirror facets.
• the facet surfaces can be formed as an "image" of the printed side, for example a flat printed page, so that the surface quality of the facet surfaces essentially depends only on the nature of the printed page.
• the facet surfaces are surface-treated in a smoothing process following the ultraprecision turning process using ion beams and / or at least one liquid film.
• the surface roughness of the facet surfaces is thereby additionally reduced. Furthermore, the facet surfaces processed with this surface are particularly uniform.
• the facet surfaces are coated with a layer stack of a plurality of alternating individual layers of molybdenum and silicon (MoSi), wherein a layer thickness of each individual layers is selected as a function of a local beam incidence angle with respect to the individual facet surfaces.
• MoSi molybdenum and silicon
• the reflection properties of the individual mirror facets are improved with the aid of the MoSi layers. Due to the selected layer thickness of the MoSi layers, the EUV light is advantageously focused onto the second focal point with an increased precision that is uniform for all mirror facets.
• the invention is based on the object of providing a mirror, in particular for an EUV microlithography system, or for the UV radiation Spectral range to provide, which has an optical grating with an optically effective mirror surface, and the overall over the mirror surface across an at least approximately constant magnification.
• this object is achieved by a mirror having an optical grating with an optically effective mirror surface, which reflects electromagnetic radiation emanating from a first focal point and focused on a second focal point, wherein the first and the second focal point lie on a side of the optical grating facing the mirror surface and define an optical axis, the optical grating having a plurality of mirror facets each having a facet surface, the facet surfaces forming the mirror surface of the grating.
• the facet surfaces in a sectional plane encompassing the optical axis are arranged on a plurality of imaginary ellipse shells displaced from one another along the optical axis, whose common mathematical focus points coincide with the first and second focal points, the facet surfaces being distributed on the elliptical shells so that the facet surfaces are arranged at intersections of the elliptical shells with at least a portion of an imaginary circular line, wherein for each point on the circular line the ratio of the distance of the first focal point to this point and the distance of this point to the second focal point has the same value.
• the set of all points for which the ratio of the distances to two given points has a predetermined value is also called the Apolonius circle.
• the facet surfaces are therefore arranged not only on mutually displaced elliptical coulters, but in such a way that the facet surfaces are additionally arranged on an Apolonius circle, with the first and second focal point as fixed points.
• the advantage here is that the substrate surface of the mirror can be spherical, which significantly simplifies the production of the mirror. Due to the arrangement of the facet surfaces distributed on the elliptical shells along an apolloidal circle section, all the facet surfaces form the first focal point with the same magnification on the second focal point.
• Such a mirror can not be used only as a collector mirror, but also generally as imaging mirror, because the mirror causes a very sharp image from the first focal point to the second focal point by the inventive design.
• the foot points of the mirror facets are arranged at the intersections.
• the mirror surface is arranged completely outside the optical axis.
• the mirror according to the invention is particularly suitable as an imaging mirror, for example in an EUV microlithography system, or else in a UV-optical system.
• the optical grating of the mirror according to the invention is preferably a blazed grating or a Fresnel structure.
• FIG. 1 is a schematic sectional view of a collector mirror according to a
• Fig. 2 is a schematic sectional view of a collector mirror according to the
• 3A-B is a schematic representation for explaining the effects of different mirror surface curves
• FIG. 4 shows a schematic representation for explaining the spatial separation of reflected useful beams of diffracted residual beams by means of the collector mirror in FIG. 1;
• Fig. 5 is a schematic diagram of an intensity distribution in the far field as
• FIG. 6A is a schematic diagram for explaining the course of the blaze angle
• Fig. 6B is a schematic diagram for explaining the shading effects between adjacent mirror facets
• Fig. 7A-B is an illustrative view of a method for manufacturing the collector mirror in Fig. 1;
• 8A-B is an illustrative illustration of a path of movement of a cutting
• FIG. 9 is a schematic diagram of a pitch error as a function of a
• the collector mirror 10 is used for collecting or focusing EUV light in an EUV light source of an EUV microlithography system and has an optical grating 12, which is referred to below as a blazed grating.
• the blaze grating 12 has a plurality of mirror facets 14 each having a facet surface 15. The facet surfaces 15 of the mirror facets 14 together form a sawtooth-shaped, "blazed" mirror surface 17.
• the facet surfaces 15 are arranged in a sectional plane 16 on a plurality of imaginary elliptical shells 18a-j. In FIG. 1, for reasons of clarity, only the innermost ellipse shell 18a and the outermost ellipse shell 18j are each provided with a reference numeral.
• the facet surfaces 15 are each disposed on one of the plurality of imaginary elliptical shells 18a-j, with the facet surfaces 15 extending along or tangential to the respective ellipse shell 18a-j.
• the elliptical shells 18a-j have two common focus points, which coincide with a first focus F1 and a second focus F2 of the collector mirror.
• the elliptical shells 18a-j thus form an imaginary confocal ellipse group 18.
• the mirror surface 17 of the blazed grating 12 extends in the embodiment shown in the sectional plane 16 from a vertex region 20 to an edge region 22 of the confocal ellipse group 18.
• the mirror surface 17 can be in the apex region 20 However, also not be present, and the collector mirror 10 may have an opening or a hole there.
• the facet faces 15 are shown for simplicity only on one half of the elliptical shells 18a-j.
• the blaze grating 12 is at least partially rotationally symmetrical about an optical axis OA, wherein the optical axis OA is defined by the first focus F1 and the second focus F2.
• the mirror surface 17 along a spiral path about the optical axis OA run.
• the mirror surface 17 may extend along a plurality of concentric with respect to the optical axis OA, spaced apart in the direction of the optical axis OA circular paths.
• a Cartesian coordinate system is shown for mathematical illustration of the confocal Ellipsenschar 18 whose Y-axis coincides with the optical axis OA and whose origin is the midpoint between the first and the second focus F1, F2.
• all coordinates are normalized to the focal length, that is, the distance from the origin to the focal point F1, F2.
• each of the imaginary elliptical shells 18a-j intersects the Y-axis respectively at an associated longitudinal axis intersection point 24a-j, with only the innermost and outermost longitudinal intersection points 24a, j respectively having a reference numeral for reasons of clarity are provided.
• the longitudinal axis intersection points 24a-j are assigned the coordinates (0, yn).
• Each imaginary ellipse shell 18a-j is part of an associated ellipse that intersects the x-axis at a cross-axis intercept with coordinates (xn, 0), which is not shown in FIG. 1 for the sake of simplicity.
• the points (x, y) that obey the following ellipse function can thus be assigned to the points lying on each imaginary ellipse shell 18a-j:
• the collector mirror 10 is capable of electromagnetic radiation an EUV spectral range, which emanate from the first focus F1 and reach the mirror surface 17 of the collector mirror 10, to reflect on at least one of the facet surfaces 15 and to focus on the second focus F2.
• two useful beams 23, 25 are shown by way of example, which arrive at a respective beam incident point P1, P2 on the respective facet surface 15 at an angle ⁇ 1, ⁇ 2 to the optical axis OA.
• the useful beams 23, 25 are reflected and directed in the direction of the second focal point F2.
• the useful beams 23, 25 are focused on the second focal point F2.
• the focused useful beams 23, 25 in FIG. 1 are shown as individual lines for reasons of simplification, the mirror surface 17 generally being detected with a beam of finite diameter.
• the collector mirror 10 is simultaneously capable of directing residual electromagnetic radiation of a residual spectral range other than the EUV spectral range, which also emanates from the first focal point F1, after reflecting on the blazed grating 12 in at least one direction, that of the beam exit direction the useful rays 23, 25 deviates, so that the residual rays are blocked by a second focal point F2 located aperture 38, which is shown in Fig. 2.
• Fig. 1 nine mirror facets 14 are shown, wherein on each of the elliptical shells 18a-j only one facet surface 15 is arranged. However, the number of mirror facets 14 may be less than or greater than nine. In addition, the number of facet surfaces 15 disposed on an ellipse shell 18a-j may be greater than one. In FIG. 1, furthermore, the elliptical shells 18a-j are spaced substantially equidistant from each other along the optical axis OA. Thus, the longitudinal axis intersections 24a-j of the elliptical shells 18a-j are also equidistant from each other.
• the facet surfaces 15 are further arranged such that the ellipse shell 18a-j, on which the facet surface 15 of the peripheral region-side mirror facet 14 of each adjacent mirror facet pair is disposed, from the ellipse shell 18a-j, on which the facet surface 15 of the apex-side mirror facet 14 of the same mirror facet pair is displaced along the optical axis OA to the first focus point F1.
• the mirror surface 17 resulting therefrom is curved in the sectional plane 16 towards the outermost apex 24j in comparison to the innermost ellipse shell 18a.
• mirror surface 17 is curved towards the innermost ellipse shell 18a in the edge region 22 compared to the outermost ellipse shell 18j
• mirror surface 17 is referred to as a "pearled mirror surface" to distinguish it from an elliptical or spherical mirror surface.
• FIG. 2 shows an exemplary collector mirror 10 'according to the prior art, with a binary grating 26, wherein the binary grating 26 has a plurality of mirror facets 28.
• the collector mirror 10 ' has an elliptical mirror surface 33, wherein the mirror facets 28 are arranged in the sectional plane 30 shown here on a single ellipse shell 31.
• a target located at a first focal point F1 'is bombarded.
• a target for example, a tin droplet is used.
• a plasma in particular a tin plasma is generated at the electronic transitions EUV light is generated.
• the generated EUV light impinges as a useful beam 35 on a beam incident point P 'on one of the mirror facets 28, at which the useful beam 35 is reflected and focused on a second focal point F2'.
• a diaphragm 38 is arranged through the aperture 40 of the reflected useful beam 35' passes.
• an incident residual beam 36 which is superimposed on the incident useful beam 35, is diffracted at the mirror facet 28.
• the diffracted residual beam 36 'extends in two directions outside the reflected useful beam 35' and is blocked by the aperture 38. In this way, residual rays are suppressed by the collector mirror 10 'in cooperation with the aperture 38.
• the facet faces 15 of the "pierced" collector mirror 10 in Fig. 1 are not arranged on a single ellipse shell, but on a confocal ellipse family 18.
• the collector mirror 10 an at least reduced change of the magnification along the mirror surface 17, so that the magnification of the envelope of the etendue in the IF and in the far field is reduced.
• FIG. 3A shows three schematic mirror surface curves S1 -S3.
• the first curve S1 corresponds to a spherical mirror surface
• the second curve S2 to a "polished-through” mirror surface
• the third curve S3 to an elliptical mirror surface
• a useful beam 42 emerges from the first focal point F1 at an angle ⁇ to the optical axis OA on the beam incident point P on a from the three mirror surface curves S1 -S3 and is reflected from there to the second focal point F2.
• FIG. 3A shows three schematic mirror surface curves S1 -S3.
• the first curve S1 corresponds to a spherical mirror surface
• the second curve S2 to a "polished-through” mirror surface
• the third curve S3 to an elliptical mirror surface
• a useful beam 42 emerges from the first focal point F1 at an angle ⁇ to the optical axis OA on the beam incident point P on a from the three mirror surface curves S1 -S
• the intensity of a useful beam 42 'focused by the respective mirror surface in the far field as a function of a far field radius, i. the distance between the location of the beam intensity measurement and the optical axis OA is shown in the diagram D1 by 11, 12, 13.
• the intensity distribution 12 of the "swept-away" mirror surface with variable far-field radius weakly changes, in other words the intensity distribution 12 of the "beaded-through” mirror surface is more homogeneous compared to the elliptical mirror surface. This is due to a reduced enlargement of the envelope of the etendue and finally to the reduced variation of the magnification of the "sagged" collector mirror compared to the elliptical collector mirror.
• magnification V (cp) The dependence of the magnification V (cp) on the angle ⁇ differs depending on the type of mirror surface.
• the magnification V (cp) behaves almost independently of the angle ⁇ , while in the case of elliptic mirror surfaces (S3) the magnification V (cp) varies greatly with varying angle ⁇ .
• the magnification V (cp) varies with angle ⁇ , it is less pronounced than in the case of elliptical mirror surfaces.
• the mirror surface curves S1 -S3 open at the same ends 41st This means that the collector mirrors associated with these gradients S1 -S3 have substantially the same collector mirror diameter. Further, the longitudinal axis intersection A2 of the "pearled" course S2 is farther from the first focussing point F1 than the longitudinal axis intersection A3 of the elliptical course S3. The distance between the longitudinal axis intersection A2, A3 and the first focal point F1 is known as the "working distance" of a collector mirror. The greater the working distance, the further the collector mirror is spaced from the high-energy plasma, which promises increased resistance to heat and radiation. This means that the " tellgeeulte" collector mirror is compared to an elliptical collector mirror with the same diameter less heat and radiation load.
• the longitudinal axis intersection points A coincide.
• the collector mirrors associated with these gradients S1 -S3 therefore have the same working distance.
• the "pearled" course S2 has a smaller extent between its two ends 41 than the elliptical course S3.
• the "pearled” collector mirror associated with the course S2 thus has a smaller diameter than the elliptical collector mirror associated with the course S3. The smaller the diameter, the more compact and lighter the collector mirror. This means that the "pearled” collector mirror faces an elliptical collector mirror with the same working distance compact and low-weight can be formed.
• Fig. 4 shows a schematic representation for explaining the spatial separation of reflected useful rays of residual rays by means of the collector mirror 10 in Fig. 1.
• Fig. 4 contains three areas (l) - (IN), in each of which a transition between two adjacent Mirror facets 14a, b of a blazed grating 12, wherein regions (II) and (III) show the same transition of region (I).
• an incident useful ray 43 enters the incident point P at a useful ray incidence angle 45, the useful ray incident angle 45 being related to facet normal 46 perpendicular to the facet surface 15, and the incident point P having a connection point R between the adjacent ones Mirror facets 14a, b coincide.
• the incident useful beam 43 is reflected on the facet surface 15.
• the useful beam 45 'reflected at the facet surface 15 is referred to as a "specular facet reflex".
• the course of the grating surface 48 corresponds in the sectional plane 16 shown here a connecting line of the connection points R between the adjacent mirror facets 14a, b. In the beam incident point P occur due to the much larger wavelength of the residual beam 47 diffraction effects.
• the diffracted diffraction order 0 diffracted beam 47 ' extends at a zeroth residual beam deflection angle 48' with respect to the grating surface normal 46, the zeroth residual beam angle of deflection 48 'being equal to the residual beam angle of incidence 44.
• a blaze angle 60 is shown for the mirror facet 14b, ie the angle by which the facet surface 15 of the mirror facet 14b is inclined towards the grating surface 50.
• the mirror facet 14b has a step height 62 and a facet length 64, wherein the ratio between the step height 62 and the facet length 64 corresponds to the tangent of the blaze angle 60.
• the respective residual beams 51, 52, 53 diffracted under the diffraction orders 1, -1 and -2 can be seen, which are under a first, second or third residual beam deflection angle 54, 55, 56, with respect to the grid surface normal 49 extend.
• the grating surface normal 49 and the facet normal 46 include an angle 58 equal to the blaze angle 60.
• the residual beam 47 ' is deflected by the reflected useful ray 43' by a deflection angle 66.
• the deflection angle 66 is at least twice the blaze angle 60.
• the reflected useful ray 43 ' extends between the diffracted residual rays of the diffraction order 0 on the one hand and the diffracted residual ray 51 of the diffraction order 1 on the other hand.
• the diffraction orders 0, 1, -1 and / or -2 relate to a minimum wavelength ⁇ an IR spectral range.
• FIG. 5 shows a schematic diagram of an intensity distribution of reflected useful beams and diffracted residual beams of different diffraction orders in the far field as a function of the spatial frequency q.
• a spatial direction 68 in which the spectral facet reflex runs, the intensity in the far field assumes its maximum, the intensity distribution around the spatial direction 68 being substantially mirror-symmetrical.
• the specular facets reflex extends as centrally as possible between the diffracted residual beams of the diffraction orders 0 and 1, since these two diffraction orders, as shown in FIG have highest intensity values under the diffraction orders of the residual beam.
• the intensity of the diffracted residual beam decays to at least approximately 0 within a few diffraction orders about the spatial direction 68 of the specular facet reflex.
• This can be achieved by an appropriate choice of Blazegitters 12, for example, with a Spalt colllgrad of about one.
• Column fill is a measure of the diffraction efficiency of a diffraction grating. For the diffraction efficiency l (q) of the reflected useful ray and the diffracted residual ray of different diffraction orders as a function of the spatial frequency q, the following applies in the far field:
• ⁇ is the column filling degree and ⁇ is the spatial frequency of the specular reflex.
• ⁇ usually depends on the wavelength of the useful beam.
• ⁇ is therefore a fixed quantity, ⁇ can vary between 0 and 1, with o ⁇ 1 being the intensity of the diffracted residual beam decays to at least approximately 0 within two or three orders of diffraction about the spatial direction 68 of the specular facet reflex. This advantageously promotes efficient suppression of residual rays and allows focusing of the EUV light with homogeneous far-field intensity distribution and high purity.
• the Blazewinkelverlauf ⁇ ( ⁇ ), as shown schematically in Fig. 6A, be set.
• the blaze angle 60 increases from the edge region 22 toward the apex region 20, so that the imaging scale varies only slightly along the mirror surface 17. The enlargement of the envelope of the Etendue is thereby reduced.
• the blaze angle 60 is selected from a range of 1 mrad to 100 mrad.
• the Blazewinkelverlaufs ⁇ ( ⁇ ) and the local shape deviation of the mirror surface 17 of the blazed grating 12 is determined by an elliptical mirror surface.
• the local beam incidence angle 45 or the direction of the specular facet reflex for each mirror facet 14 and thus also the basic shape of the surface of the blazed grating 12 are fixed.
• the facet length profile ⁇ ( ⁇ ) can be set, whereby the directions in which the diffracted residual beams of higher wavelength-dependent diffraction orders extend are fixed.
• the facet length 64 can be chosen to be sufficiently large, preferably in the range ⁇ ( ⁇ )> 10 ⁇ m, so that diffraction effects of the EUV light can be largely neglected.
• the step height curve h (cp) can additionally be set at least partially to additionally suppress diffraction effects of the useful ray 43.
• the facet length 64 is sufficiently small, preferably in the range ⁇ ( ⁇ ) ⁇ 200 ⁇ selected. This results in a plurality of exit directions for the diffracted residual beam, so that the probability that the diffracted residual beam is focused in the same direction as the specular reflex 43 'to the second focal point F2 is reduced.
• mirror facets 14 having a focal sweep value that is at least approximately 0, to be worked. This corresponds to a nearly planar facet surface 15, which can be produced particularly simply and with high quality with regard to minimal surface roughness and pitch errors.
• a maximum facet length Imax can be selected as a function of the minimum wavelength ⁇ the IR spectral range in order to suppress the highly intense IR light as effectively as possible.
• ⁇ min may assume one of the following values: 10 ⁇ m, 1 ⁇ m, 200 nm, the associated maximum facet length Imax being in each case 1000 ⁇ m, 100 ⁇ m or 20 ⁇ m, respectively.
• These three examples relate to a focal length of 0.5 m, a diaphragm radius of 1 mm and a deflection angle of 5 mrad between the specular facet reflex and the diffracted residual beam under the diffraction order zero.
• Fig. 6B illustratively shows the shadowing effect of two adjacent mirror facets 14a, b of the blazed grating 12.
• the incident useful beam 43 is reflected at the facet face 15 of the first mirror facet 14a, with the specular facet reflex 43 'extending in a direction through the beam incident point P and a vertex Q of the second mirror facet 14b is defined.
• the area of the facet area 15 of the first mirror facet 14a between the beam incidence point P and the connection point R is thus shaded since specular facets reflexes 43 'originating from this area are blocked by a side surface 67 of the second mirror facet 14b.
• the length of the shading area in the illustration shown here results from the length of the side surface 67 multiplied by the tangent of the useful beam incidence angle 45.
• the blaze grating 12 of the collector mirror 10 is preferably made by means of an ultra-precision (UP) turning method illustratively shown in Figs. 7A, B.
• a flush-mounted rotary unit 69 is used which has a main body 73, a rotary body 75 mounted on the main body 73 and a structuring unit 77.
• the rotary body 75 is rotatable about a spindle axis 76.
• a grating workpiece 71 is fixed to the rotary body 75.
• the grating workpiece 71 preferably has an amorphous chipable layer which, for example, nickel Phosphorus (NiP) and / or Oxygen Free High Conductivity Copper (OFHC-Cu).
• the structuring unit 77 has a cutting tool 70, for example a diamond tool, which has a pressure side 72.
• the structuring unit 77 can be moved parallel to the spindle axis 76 in both directions, as the double arrow 78 indicates.
• the tool 70 is rotatable about a machine axis 74, which is perpendicular to the plane of the paper in the illustration shown here, in a clockwise and / or counterclockwise direction.
• the pressure side 72 is formed flat and / or curved.
• the rotary body 75 is height-adjustable on the base body 73, which is indicated by the double arrow 80.
• FIG. 8A shows a schematic spiral track 82 which is formed spirally around an axis 83 which is perpendicular to the plane of the drawing.
• the spiral path 82 is shown in FIG. 8A in a view along the axis 83, the spiral path 82 spatially extending along the axis 83 with increasing path radius 85 in the direction of the plane continuously.
• FIG. 8B shows a schematic path arrangement 84 with respect to an axis 83 'of concentric circular paths 84a-j.
• the circular paths 84a-j in FIG. 8B are shown in a view along the axis 83 ', the orbits 84a-j extending spatially with increasing path radius 85' in the direction of the plane of the drawing.
• the grating workpiece 71 For structuring the grating workpiece 71, this is first attached to the rotary body 75 of the UP rotary unit 69. Thereafter, the tool 70 is brought to a desired position relative to the grating workpiece 71, which corresponds to the desired surface shape of the facet surface 15 to be formed. Thereafter, the grating workpiece 71 is moved relative to the tool 70 along the spiral path 82 (FIG. 8A) and / or the web assembly 84 (FIG. 8B) by means of the rotating body 75, with the relative displacement required for movement along the spiral path 82 and the web assembly 84 Rotary movement is accomplished by rotating the rotary body 75 about the spindle axis 76.
• the mirror surface 17 of the blazed grille 12 acquires its desired course. This means that the course of the blaze angle 60 is fixed.
• the Blazegitter 12 thus produced is at least partially rotationally symmetrical about the spindle axis 76.
• the pressure side 72 of the tool 70 has a flat surface, which is particularly advantageous in terms of reducing the edge rounding, since with a flat pressure side 72, the edge rounding even at large step heights is vanishingly small. This results in an increase of the useful beam transmission by up to 10%.
• the track distance i. the dimension of the contact surface between the pressure side 72 and the grating workpiece 71, significantly increased due to the flat pressure side 72, so that the required for structuring the entire Blazegitters 12 number of turning and clamping operations is reduced.
• the processing time and / or wear of the tool 70 is advantageously reduced.
• the influence of vibrations of the tool 70 on the surface roughness is negligible.
• a maximum surface roughness in the range of 1 nm to 2 nm can be realized with the aid of the DP turning process. Furthermore, due to the small path distances, the lateral offset of the second focal point F2 during the movement of the spiral track 82 is negligible.
• FIG. 9 shows a schematic diagram in which a maximum pitch error 86 and a mean pitch error 88 as a function of a radius coordinate of the radius 85, 85 'of the spiral track 82 and the web assembly 84 is applied.
• the radius coordinate varies between a minimum radius 90 and a minimum radius 92.
• the mirror facets 14 and / or the facet surfaces 15 are each formed by means of a single chip operation, in which the facet surface 15 is gripped by the pressure side 72 of the tool 70 facing the grating workpiece 71.
• the individual mirror facets 14 and / or the individual facet surfaces 15 result as an "image" of the printed page 72.
• the processing time can thereby advantageously be further reduced.
• the prestructured grating workpiece 71 is smoothed in a smoothing process according to an embodiment following the UP turning process.
• non-mechanical smoothing for example ion beam smoothing and / or liquid film smoothing
• Ion beam flattening is known from the publication Frost et al., "Large area smoothing of surfaces by ion bombardment: fundamental and applications, J. Phys .: Condens. Matter 21, 22, 224026", the content of which is herewith incorporated into the application.
• the liquid film smoothing is known from the patent application US2014 / 01 18830A1, the content of which is hereby incorporated into the application. A reduced rounding of the lattice structure can hereby advantageously be achieved.
• the smoothing process surface-processed side of the grating workpiece 71 is coated with a layer stack of several alternating molybdenum and silicon monolayers, wherein a layer thickness of the individual layers in dependence on a local beam angle with respect to the individual facet surfaces is selected.
• a MoSi stacking layer is advantageous, since each mirror facet 14 is individually optimized in its reflection properties to its desired local beam angle of incidence.
• the mirror surface 17 focuses that EUV light at the mirror surface 17 advantageously evenly and precisely to the second focal point F2.
• the structured side of the grating workpiece is overcoated with a material before and / or after the application of the MoSi stacking layer, the material comprising aluminum and / or a dielectric protection, for example MgF 2.
• a material before and / or after the application of the MoSi stacking layer the material comprising aluminum and / or a dielectric protection, for example MgF 2. This additionally protects the mirror surface 17 of the blade grid 12 against degradation effects.
• the blaze grating 12 preferably has a root mean square (RMS) micro-roughness in the range of 0 to 0.2 nm, with an upper limit of 0.2 nm corresponding to about 1/80 of the EUV wavelength.
• RMS root mean square
• the collector mirror 10 has at least one anti-lobe facet with a tilt angle of at least 25 °.
• the collector mirror 10 is suitable not only for EUV microlithography with a wavelength of 13.5 nm, but also for microlithographic applications in which exposure light with a different wavelength, for example up to 400 nm, preferably to 200 nm, can be used.
• FIG. 10 another embodiment of a mirror 100 will be described. Elements of the mirror 100 which are identical, similar or comparable to elements of the embodiment in FIG. 1 are provided with reference numerals increased by 100. Unless otherwise described below, the above description also applies to the mirror 100.
• the mirror 100 has an optical grating 12 which has an optically effective mirror surface 117, which focuses electromagnetic radiation 125 emanating from a first focal point F1 into a second focal point F2.
• the foci F1 and F2 define the optical axis OA.
• the optical grating 1 12 has a plurality of mirror facets 1 14, each having a Have facet surface 1 15, wherein the facet surfaces 1 15, the mirror surface 1 17 of the optical grating 1 12 form.
• the mirror 100 On its rear side, the mirror 100 has a substrate 200.
• the facet surfaces 15 are arranged on a plurality of imaginary ellipse shells 1 18a-j of an ellipse set 1 18, which are displaced from one another along the optical axis OA, as in the case of the collector mirror 10.
• the individual facet surfaces 1 15 additionally satisfy a further AnOrdnungsvorschrift, which will be described below.
• FIG. 1 an imaginary circular line 204 is shown, which is given by the set k of all points P, for which applies: where ⁇ is a constant.
• the circle or circle 204 is also referred to as Appoloniusnik.
• the ratio of the distance from the focal point F2 to the respective point P and the distance of the point P to the focal point F1 is therefore equal to the fixed value ⁇ for all points P on the circle 204.
• the facet surfaces 1 15 are now distributed to the elliptical shells 1 18a-j of the ellipse share 1 18 so that the facet surfaces 15 are arranged at intersections Pn of the elliptical shells 1 18a-j with at least a portion of the imaginary circle line 204.
• the image scales of the individual mirror facets 1 14 are at least approximately equal to each other.
• the mirror 100 thus has seen over its mirror surface 1 17 on a constant magnification, that is, the focal point F1 is focused in the present case of all mirror facets 1 14 on the focal point F2. In the focus F2 thus creates a sharp image or intermediate image.
• foot points 1 15n of the facet surfaces 1 15 arranged at the intersection points Pn of the circular line 204 with the elliptical shells 1 18a-j.
• the mirror 100 not only has a constant imaging scale, viewed over its mirror surface 11, but rather a surface 202 of the substrate 200 may be spherical in particular, which considerably simplifies the production.
• the mirror surface 17 is not dented in contrast to the mirror surface 17, but spherical.
• the mirror surface 17 of the mirror 100 is arranged completely outside the optical axis OA in the exemplary embodiment shown.
• the mirror 100 is thus operated "off-axis".
• the optical grating 112 is preferably a blazed grating, but may also be a Fresnel structure.
• the collector mirror 10 in FIG. 1 can likewise be designed so that the facet surfaces 15, as in the case of the mirror 100, are arranged at intersections of an appolonential circle with the elliptical shells 18a-j. It is thus possible to use a mirror construction as in the case of the mirror 100 also for a collector mirror. In this case, the individual mirror facets 14 are at least partially rotationally symmetrical about the optical axis OA.
• the mirror 100 in particular in the "off-axis" embodiment according to FIG. 10, can be used as an imaging mirror within an optical system, for example an EUV microlithography system, or an optical UV system.

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• 2014
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