Optical elements and associated assemblies and optical systems

Abstract

The optical element (OE) incorporated into the holding device for the purpose of forming the assembly (BG) for constructing the optical system is transparent to light from the wavelength range of use and comprises a body (K) on which a first light passage surface (LF1) and an opposite second light passage surface (LF2) are formed. Each light passage surface (LF1, LF2) has an optical use area (NB1, NB2) arranged in the use beam path of the optical system and an edge area (RB1, RB2) located outside the area and serving as an engagement area for the holding element (HE) of the holding device, and has a surface shape designed according to the use area specification specified by the function of the optical element (OE) in the use beam path. A light deflection structure (LUS1) is formed in at least one edge area (RB1) of the light passage surface (LF1) and is designed according to an edge area specification that deviates from the use area specification and deflects a portion of the light deflected by the light deflection structure into a target area (ZB) outside the use beam path.

Description

[Technical Field]

[0001] The following disclosure is based on German Patent Application No. 10 2022 205 143.2, filed May 24, 2022, which is incorporated herein by reference. [Background technology]

[0002] The present invention relates to an optical element for incorporation into a holding device in order to form an assembly for constructing an optical system of a microlithography projection exposure apparatus, an assembly comprising an optical element and a holding device for holding the optical element, and an optical system having at least one such optical element.

[0003] A preferred field of application is that of optical imaging systems for building microlithographic projection exposure apparatus, in particular optical imaging systems in the form of dioptric or catadioptric microlithographic projection lenses.

[0004] Nowadays, microlithography projection exposure methods are primarily used to manufacture semiconductor components and other microstructured components. Here, a mask (photomask, reticle) is used, which holds or forms the pattern of the structure to be imaged, e.g., a line pattern of a layer of a semiconductor component. In a projection exposure apparatus, the mask is arranged in the beam path between the illumination system and the projection lens, so that the pattern is located in the region of the object plane of the projection lens. The substrate to be exposed, e.g., a semiconductor wafer coated with a radiation-sensitive layer (resist, photoresist), is held so that its radiation-sensitive surface is located in the region of the image plane of the projection lens, which is optically conjugate to the object plane. During the exposure procedure, the pattern is illuminated by an illumination system that generates radiation from a primary radiation source, which is directed toward the pattern and is characterized by specific illumination parameters, and which forms radiation incident on the pattern within the illumination field with a defined shape and size. The radiation modified by the pattern travels as projection radiation through the projection lens, which images the pattern onto the substrate to be exposed, which is coated with a radiation-sensitive layer. For example, microlithographic projection exposure methods can also be used for the manufacture of masks (reticles).

[0005] One of the aims in the development of projection exposure apparatus is to lithographically produce structures with ever smaller dimensions on a substrate. For example, in the case of semiconductor components, smaller structures lead to higher integration densities, which generally have a beneficial effect on the performance of the microstructured components produced. The size of the structures that can be produced depends crucially on the resolution of the projection lens used, and resolution can be improved, firstly, by reducing the wavelength of the projection radiation used for projection and, secondly, by increasing the image-side numerical aperture NA of the projection lens used in the process.

[0006] Projection lenses are optical imaging systems that generally comprise a large number of optical elements, in order to partially satisfy the conflicting requirements for the correction of imaging aberrations, even when large numerical apertures are used. In the field of microlithography, both dioptric or refractive imaging systems and catadioptric imaging systems often contain ten or more transparent optical elements.

[0007] Using a holding device, an optical element is held at a defined position along the used beam path of the optical system. In the case of an imaging system, the used beam path is usually called the imaging beam path. An optical element of the imaging system that contributes to imaging has an optically used area located within the imaging beam path and an edge area located outside the optically used area. A refractive or reflective surface is prepared to an optical quality within the optically used area. The surface shape is specified according to the desired optical effect of the optical element by the design parameters of the optical design of the imaging system, and the specification is usually in the form of polynomial coefficients of a polynomial that defines the surface shape. In specification tables, the optically used area is often also called the "clear optical diameter" or "clear aperture" of the optical element. It is not necessary to achieve optical quality in the edge area. When assembling assemblies with lens elements and other transparent optical elements, the holding elements of the holding device assigned to the optical element usually engage with the edge area. A corresponding description applies to optical elements in an illumination system, and the used beam path is often called the illumination beam path.

[0008] Various options have been proposed for fixing the optical element to the holding element. US Patent Application Publication No. 2003 / 0234918 discloses an example of a clamping mount technique, in which the optical element is held by anti-vibration holding elements in the edge region (soft mount). In another holding device, the elastic holding elements of the holding device are adhesively bonded to the optical element in the region of the respectively assigned contact zone by means of an adhesive layer. Examples of adhesive bonding techniques are disclosed in US Patent No. 4,733,945 or US Patent No. 6,097,536.

[0009] In fact, in optical imaging systems with complex structures, not only does radiation reach the image plane from the object along the imaging beam path, which is desired for imaging, but also portions of radiation that do not contribute to imaging but may interfere or cause degradation in some cases. For example, what is called "superaperture light" can lead to degradation of imaging quality in projection exposure methods. In this context, "superaperture light" refers to light that is diffracted by a structure-imparting mask and emitted at an angle larger than the object-side aperture angle used for imaging, which is determined by the actual diameter of the aperture stop that bounds the imaging beam path. Since superaperture light cannot reach the image plane through the aperture stop, it does not directly contribute to imaging. However, superaperture light heats optical elements located between the mask and the aperture stop. This heating results in changes in refractive index and lens element shape, resulting in wavefront disturbances that contribute to image generation. Alternatively or additionally, scattered light can also be generated, which generally reduces the contrast of the generated image when it reaches the image plane. In this case, the term "scattered light" refers inter alia to light that may arise as a result of residual reflections, for example, on the surfaces of anti-reflection coated transparent optical elements behind mirrors and / or elsewhere in the region of the imaging beam path. This unwanted portion of light of the wavelengths designated for imaging, in particular scattered light and superaperture light, is also referred to as "stray light" within the scope of this application, regardless of its cause.

[0010] In addition to the inherent imaging aberrations that a projection lens may have due to its optical design and manufacture, imaging aberrations may also occur during use, for example, during operation of the projection exposure apparatus at the user. The cause of such imaging aberrations is often found to be changes in the optical elements used in the projection lens caused by the radiation utilized during use. For example, a portion of this radiation may be absorbed by the optical elements in the projection lens. The extent of absorption depends, among other things, on the properties of the materials used in the optical elements, such as the lens element material, the mirror material, and / or any anti-reflection or reflective coatings that may be applied. Absorption of the projection radiation may heat the optical elements, which may result in surface deformations in the optical elements and, in the case of refractive elements, directly and indirectly, through thermally induced mechanical stresses, which may cause changes in the refractive index. The changes in refractive index and surface deformations may change the imaging properties of individual optical elements and thus the entire projection lens. This problem area is often addressed under the heading of "lens heating."

[0011] Illumination systems can also suffer from reduced performance due to light propagating outside the illumination beam path.

[0012] In order to improve customer benefits of high-performance microlithography optics, throughput increases for projection exposure apparatuses are realized within the scope of the roadmap for lithography using deep ultraviolet (DUV) radiation. Due to the higher light intensities required in this case, the throughput increase is expected to increase the "lens heating" effect. However, a significant increase in lens heating effects is hardly acceptable in the case of unchanged and even more stringent lithography requirements. Summary of the Invention [Problem to be solved by the invention]

[0013] Therefore, even in the case of increased light intensity, measures are required that can contribute to avoiding, where possible, the negative effects of the "lens heating" effect or limiting it to insignificant levels.

[0014] To solve this problem, the present invention provides an optical element having the features of claim 1. Also provided is an assembly having the features of claim 9, and an optical system comprising at least one such optical element. Advantageous developments are specified in the dependent claims. The wording of all claims is incorporated into the content of the description by reference. [Means for solving the problem]

[0015] According to a first aspect, the present invention provides an optical element for incorporation into a holding device, the optical element in the incorporated state jointly forming an assembly with the holding device. The assembly serves to construct an optical system, in particular a projection lens or imaging system, for a microlithography projection exposure apparatus. Such an optical system typically comprises a number of assemblies with optical elements held thereby, which in the assembled state jointly define a used beam path, which in the case of an imaging system is also called an imaging beam path.

[0016] The optical element has a transparent body made of a material that has a high transmittance or is transparent to light in the wavelength range used. For example, the material can be synthetic fused silica or a fluoride crystalline material, such as calcium fluoride. Light-transmitting surfaces are formed on both sides of the transparent body, i.e., a first light-transmitting surface and a second light-transmitting surface on the opposite side. When light passes through the optical element, one of the light-transmitting surfaces serves as a light entrance surface and the other as a light exit surface.

[0017] For example, the optical element can be a lens element with positive or negative refractive power, or a plane-parallel plate with almost no refractive power.

[0018] Each light-passing surface has an optically used area and an edge area located outside the optically used area. In the assembled state, the optically used area is provided for placement in the used beam path of the optical system. The edge areas are provided as engagement areas for the holding elements of the holding device. In the assembled state, they can engage with the edge areas in the area of ​​the contact zone. The optically used area can be used without being impaired by the holding elements of the holding device. Each light-passing surface is prepared to optical quality in the optically used area, which means, among other things, that there is practically no surface roughness that interferes with light passage. The surface shape in the optically used area is designed according to specified use area specifications, which are determined by the desired optical effect or function of the optical element in the used beam path and are accordingly specified by what is called optical design.

[0019] As a rule, the surface shape of the optically used area continues beyond the area boundary between the optically used area and the edge area, but particularly strict requirements are no longer imposed on the surface quality. Occasionally, parts of the edge area near the used area may still have approximately optical quality as a result of overshooting of the polishing tool, but this quality decreases with increasing distance from the area boundary between the used area and the edge area.

[0020] In the case of an optical element according to this aspect of the invention, a light-deflecting structure(s) having a geometrically defined surface design designed according to an edge region specification that deviates from the use region specification is formed in at least one edge region of the light-passing surface, the light-deflecting structure or its surface design being configured to deflect a portion of light deflected or redirected by the light-deflecting structure into a target region outside the use beam path, specifiable by the edge region specification.

[0021] This aspect is based in part on the discovery that the portion of light that propagates outside the used beam path during operation of the optical system and that may impinge on a light-passing surface in the edge region does not, for the most part, occur from arbitrary or randomly occurring incident directions. Instead, the structure of the optical system makes it possible to calculate, for the majority of stray light, the incident directions and positions at which the stray light can impinge on the edge region. For example, this predictability arises for the portion of stray light that results from even highly effective anti-reflection coatings having sufficient residual reflectivity, at least for some incident directions of radiation, to reflect a portion of the incident light in a strictly predictable exit direction.

[0022] The inventors have recognized that the defined structure of the edge region can hereby provide additional benefits to the operation of the optical system: when a light-deflecting structure is provided having a geometrically defined surface design, which can be specified by an edge region specification, it is possible to deflect, completely, or at least largely, incident stray light into a specifiable target region outside the used beam path in a targeted manner by refraction and / or diffraction and / or reflection.

[0023] Thus, with appropriate edge area specifications, stray light, previously considered a source of interference and uncontrollable, can be targeted and directed and thus used to improve the performance of the optical system.

[0024] Preferably, the light deflection structure comprises a refractive and / or diffractive light deflection structure. Thus, deflection by the light deflection structure can be achieved in this case by light refraction (refraction), by light diffraction (diffraction), or by a combination of diffraction and refraction. In part, such a light deflection structure can be produced without significant expenditure during the manufacture of the optical element, for example in one piece together with the rest of the optical element. In some cases, reflective light deflection structures can also be provided, and options exist in the case of reflective light deflection structures that combine these with refractive and / or diffractive light deflection structures, or even in the case of using them exclusively as mirror-reflecting (reflective) light deflection structures.

[0025] There are various options for "using" the deflected stray light: one option consists in arranging the target area so that the stray light affected by the light deflection structure is steered into an area that is not important for the performance of the optical system, for example incident on an absorbing structure there that absorbs the stray light and thus renders it harmless with respect to the functioning of the optical system.

[0026] In the case of an assembly assembled with a holding device and a held optical element, the holding device comprises a holding element that engages in a contact zone area in the edge region. The contact zone is an area where there is direct or indirect mechanical contact between the holding element and the optical element. If stray light is incident in the contact zone area, this can cause heating of the contact zone and therefore undesirable lens heating effects. In the case of clamping holding, this can occur, for example, by the holding element being directly heated by stray light and the resulting heat being transferred into the material of the optical element through the contact area. In the case of an assembly in which the holding elements of the holding device are adhesively bonded to the optical element in the area of ​​the respective assigned contact zone, the adhesive material can be heated by the effect of stray light, thus indirectly resulting in lens heating effects. Provided that an adhesive protective layer is provided in the contact zone area to protect the curable adhesive from damage by light of the wavelength used, localized heating can occur in the contact zone area as a result of absorption effects in the adhesive protective layer, alternatively or additionally. If the light deflection structure is designed so that the deflected portion of the light is deflected into a target area outside the contact zone, such problems can be avoided or significantly reduced when the present invention is applied.

[0027] The targeted deflection of stray light to a specifiable target area also makes it possible to obtain improved performance of the imaging system by having the component of the stray light intensity deflected into the target area be used in a targeted manner to heat components located in the target area for the purpose of obtaining thermally induced manipulations within the optical system, in particular the imaging system.

[0028] The use of this approach can be understood as follows: The distribution of stray light in position and angle space, as well as the intensity distribution of the stray light within the distribution, depends, in principle, not only on the optical design of the optical system but also on the type of use during production operations. For example, the stray light distribution within the projection lens of a projection exposure apparatus depends on the mask structure of the mask (reticle) used for imaging. Alternatively or additionally, the stray light distribution also depends on the way the mask is illuminated, i.e., it depends on what is called the illumination setup. Therefore, a coherent illumination setup (on-axis illumination) with a specifiable sigma value results in a stray light distribution that is significantly different from off-axis illumination, such as a dipole illumination setup, in which the mask is primarily illuminated from two oblique, opposing directions.

[0029] Furthermore, the stray light distribution and the used light distribution are influenced by the shape and position of the (effective) image field. The image field may have a rectangular shape or an arc-curved shape ("ring field"). The image field may be centered relative to the optical axis ("on-axis field") or located outside the center of the optical axis ("off-axis field").

[0030] The spatial distribution of stray light intensity in the optical system can be calculated for a typical combination of mask structure and illumination setting, where the stray light can be deflected by the light deflection structure such that a thermally activated manipulator is created, which is designed such that its effect can counteract the adverse effects of lens heating in the region of the used beam path, thus at least partially compensating for the adverse effects.

[0031] Such thermally activatable manipulators are passive, i.e., they do not have a dedicated drive or actuator. They are "controlled" by targeted deflected stray light.

[0032] Further advantages and aspects of the present invention will be apparent from the claims and the description of exemplary embodiments thereof, which are described below with reference to the figures. [Brief explanation of the drawings]

[0033] [Figure 1] 1 illustrates an exemplary embodiment of a microlithography projection exposure apparatus; [Figure 2] FIG. 1 shows a schematic lens element cross-section of one embodiment of a catadioptric projection lens, next to a footprint to indicate the beam path used. [Figure 3A] 3A shows an enlarged portion of the projection lens of FIG. 2 from the area immediately behind the object plane OS, and 3B shows an enlarged detail in the area of ​​the contact zone between the holding element and the lens element. [Figure 3B] 3A shows an enlarged portion of the projection lens of FIG. 2 from the area immediately behind the object plane OS, and 3B shows an enlarged detail in the area of ​​the contact zone between the holding element and the lens element. [Figure 4A] 10A-10C illustrate exemplary embodiments in which superaperture light deflection is achieved by diffraction through diffractive light deflection structures in the edge regions of the lens elements. [Figure 4B] 10A-10C illustrate exemplary embodiments in which superaperture light deflection is achieved by diffraction through diffractive light deflection structures in the edge regions of the lens elements. [Figure 5A] 5A and 5B show a meridional cross section and a plan view of the upper surface of a lens element, respectively, of an exemplary embodiment having azimuthal diffractive structures in the edge region. [Figure 5B] 5A and 5B show a meridional cross section and a plan view of the upper surface of a lens element, respectively, of an exemplary embodiment having azimuthal diffractive structures in the edge region. [Figure 6A] 6A and 6B are a meridional cross section and a plan view of the upper surface of a lens element of an exemplary embodiment having radially refracting, separately manufactured prism-shaped refractive light deflection structures in the edge region. [Figure 6B] 6A and 6B are a meridional cross section and a plan view of the upper surface of a lens element of an exemplary embodiment having radially refracting, separately manufactured prism-shaped refractive light deflection structures in the edge region. [Figure 7A]7A and 7B are a meridional cross section and a plan view of the upper surface of a lens element of an exemplary embodiment having circumferentially refracting, separately manufactured prism-shaped refractive light deflection structures in the edge region. [Figure 7B] 7A and 7B are a meridional cross section and a plan view of the upper surface of a lens element of an exemplary embodiment having circumferentially refracting, separately manufactured prism-shaped refractive light deflection structures in the edge region. [Figure 8A] FIG. 1 shows an example of a thermal manipulator operating with targeted deflected stray light. [Figure 8B] FIG. 1 shows an example of a thermal manipulator operating with targeted deflected stray light. [Figure 9] 10A-10C illustrate an exemplary embodiment having reflective light-deflecting structures on the lens element surface that slope towards the edge. DETAILED DESCRIPTION OF THE INVENTION

[0034] 1 shows an example of a microlithography projection exposure apparatus WSC that can be used in the manufacture of semiconductor components and other microstructured components and operates with light or electromagnetic radiation in the deep ultraviolet (DUV) range to obtain a resolution of a fraction of a micrometer. An ArF excimer laser with an operating wavelength λ of approximately 193 nm serves as the primary radiation source or light source LS. Other UV laser sources are also possible, such as an F2 laser with an operating wavelength of 157 nm or an ArF excimer laser with an operating wavelength of 248 nm.

[0035] At its exit surface ES, an illumination system ILL arranged downstream of the light source LS generates a large, sharply defined, and approximately uniformly illuminated illumination field that is adapted to the telecentricity requirements of a projection lens PO arranged downstream of the illumination system ILL in the optical path. The illumination system ILL has a device for setting various illumination modes (illumination settings), and can switch between, for example, conventional on-axis illumination with various coherence degrees σ and off-axis illumination. By way of example, off-axis illumination modes include annular illumination, dipole illumination, quadrupole illumination, or any other multipole illumination. The design of suitable illumination systems is known per se and will not be described in further detail here. U.S. Patent Application Publication No. 2007 / 0165202 (corresponding to WO2005 / 026843A2) shows examples of illumination systems that can be used within the scope of various embodiments.

[0036] The optical components that receive light from the laser LS, form illumination radiation from the light, and direct the illumination radiation onto the reticle M are part of the illumination system ILL of the projection exposure apparatus.

[0037] A device RS for holding and manipulating the mask M (reticle) is arranged downstream of the illumination system so that the pattern arranged on the reticle coincides with the exit plane ES of the illumination system and is in the object plane OS of the projection lens PO, also called here the reticle plane OS. For scanning movements, the mask is movable in this plane in a scanning direction (y-direction) perpendicular to the optical axis OA (z-direction) by means of a scanner device.

[0038] A projection lens PO follows downstream of the reticle plane OS and acts as a reduction lens, imaging the image of the pattern arranged on the mask M at a reduced scale, for example at a scale of 1:4 (|β|=0.25) or 1:5 (|β|=0.20), onto a substrate W coated with a photoresist layer, whose photosensitive substrate surface SS is in the area of ​​the image plane IS of the projection lens PO.

[0039] The substrate to be exposed, in the exemplary case a semiconductor wafer W, is held by a device WS which comprises a scanner drive for moving the wafer in the scanning direction (y-direction) synchronously with the reticle M perpendicular to the optical axis OA. The device WS, also called "wafer stage", and the device RS, also called "reticle stage", are components of a scanner device which are controlled by a scan control device, which in this embodiment is integrated in a central control device CU of the projection exposure apparatus.

[0040] The illumination field generated by the illumination system ILL defines the effective object field OF used during projection exposure. In the exemplary case, the effective object field is rectangular and has a height A measured parallel to the scanning direction (y direction). * and a width B measured perpendicular (in the x direction) to the scanning direction (in the y direction). * >A * Generally, the aspect ratio AR=B * / A * is between 2 and 10, in particular between 3 and 8. The effective object field is located at a distance next to the optical axis in the y direction (off-axis field). The effective image field IF in the image plane IS, optically conjugate to the effective object field, has the same shape and the same aspect ratio between height B and width A as the effective object field, but the absolute field dimensions are reduced by the imaging scale β of the projection lens, i.e. A = |β|A * and B = |β|B * is.

[0041] If a projection lens is designed and operated as an immersion lens, radiation is directed through a thin layer of immersion liquid during operation of the projection lens, which thin layer is located between the exit surface of the projection lens and the image plane IS. During immersion operation, image-side numerical apertures NA>1 are possible. A dry lens configuration is also possible, in which case the image-side numerical aperture is limited to values ​​NA<1.

[0042] FIG. 2 shows a schematic meridional lens element cross-section of one embodiment of a catadioptric projection lens PO, with selected beams illustrating the imaging beam path of the projection radiation passing through the projection lens during operation. The projection lens is provided as an imaging system with a demagnification effect for imaging the pattern of a mask disposed in the object plane OS of the projection lens at a reduced scale, e.g., 4:1, onto the image plane IS of the projection lens aligned parallel to the object plane. Here, exactly two real intermediate images IMI1 and IMI2 are generated between the object and image planes. The first lens portion OP1, constructed exclusively of transparent optical elements and therefore refractive (dioptric), is designed so that the pattern in the object plane is imaged onto the first intermediate image IMI1 with almost no change in size. Second, the catadioptric lens portion OP2 images the first intermediate image IMI1 onto the second intermediate image IMI2 with almost no change in size. Third, the refractive lens portion OP3 is designed to image the second intermediate image IMI2 at the image plane IS with a large reduction.

[0043] The imaging system has pupil surfaces or pupil planes P1, P2, P3 located between the object plane and the first intermediate image, between the first intermediate image and the second intermediate image, and between the second intermediate image and the image plane, respectively, and the chief ray CR of the optical imaging intersects the optical axis OA. An aperture stop AS of the system can be mounted in the region of the pupil surface P3 of the third lens part OP3. The pupil surface P2 in the catadioptric second lens part OP2 is immediately adjacent to the concave mirror CM.

[0044] The catadioptric second lens section OP2 contains the only concave mirror CM of the projection lens. A negative group NG with two negative lens elements is located immediately upstream of the concave mirror. In this arrangement, sometimes called a Supmann achromat, Petzval correction, i.e., correction of image field curvature, is achieved as a result of the curvature of the concave mirror and its adjacent negative lens elements, and chromatic correction is achieved as a result of the refractive power of the negative lens elements upstream of and adjacent to the concave mirror.

[0045] The reflective deflection device serves to separate the beam or corresponding partial beam path passing from the object plane OS to the concave mirror CM from the beam or corresponding partial beam path passing between the concave mirror and the image plane IS after reflection at the concave mirror. For this purpose, the deflection device has a planar first deflection mirror FM1 with a first mirror surface MS1 for reflecting radiation coming from the object plane to the concave mirror CM, and a planar second deflection mirror FM2 with a second mirror surface MS2 aligned perpendicular to the first deflection mirror FM1, which deflects the radiation reflected from the concave mirror toward the image plane IS. Because the optical axis is folded by the deflection mirror, the deflection mirror is also referred to herein as a folding mirror. The deflection mirror extends perpendicular to the optical axis and is tilted, for example, by 45° with respect to the optical axis OA of the projection lens around a tilt axis parallel to the first direction (x-direction). When configuring a projection lens for scanning operation, the first direction (x-direction) is perpendicular to the scanning direction (y-direction) and thus to the direction of movement of the mask (reticle) and substrate (wafer). For this purpose, the deflection device is realized by prisms aligned at right angles to each other, with their outer reflectively coated adjacent side surfaces acting as deflection mirrors.

[0046] The intermediate images IMI1, IMI2 are optically close to their nearest folding mirrors FM1 and FM2, respectively, but at a minimum optical distance from them so that possible defects on the mirror surfaces are not clearly imaged onto the image plane, and the plane deflection mirrors (plane mirrors) FM1, FM2 are within a region of medium radiation energy density.

[0047] The positions of the (paraxial) intermediate images define field planes of the system that are optically conjugate to the object plane and the image plane, respectively. The deflection mirrors are therefore optically close to the field planes of the system, which in the context of this application are also called "near fields." In this case, the first deflection mirror is arranged optically close to a first field plane belonging to the first intermediate image IMI1, and the second deflection mirror is arranged optically close to a second field plane belonging to the second intermediate image IMI2, which is optically conjugate to the first field plane.

[0048] The optical proximity or optical distance of an optical surface relative to a reference plane (e.g., a field plane or a pupil plane) is described herein by the so-called subaperture ratio SAR. The subaperture ratio SAR of an optical surface is defined herein as follows: SAR=sign h(|r| / (|h|+|r|)) In the above equation, r represents the marginal ray height, h represents the chief ray height, and the negative function sign x represents the sign of x, with sign 0=1 by convention. Chief ray height is understood to mean the ray height of the chief ray of the field point of the object field that has the maximum field height in terms of size. It should be understood that the ray height is signed. Marginal ray height is understood to mean the ray height of the ray with the maximum aperture proceeding from the intersection point between the optical axis and the object plane. This field point does not need to contribute to transferring the pattern located in the object plane, especially in the case of an off-axis image field.

[0049] The subaperture ratio is a signed variable that is a measure of the proximity of the field or pupil to a plane in the beam path. By definition, the subaperture ratio is normalized to a value between -1 and +1, where the subaperture ratio is zero in each field plane and the subaperture ratio jumps from -1 to +1 or +1 to -1 in the pupil plane. Thus, a subaperture ratio with an absolute value of 1 determines the pupil plane.

[0050] Then, if the sub-aperture ratios of an optical surface or optical plane and an optical reference surface are comparable in terms of numerical value, these two surfaces are said to be "(optically) close."

[0051] In particular, if an optical surface or plane has a subaperture ratio close to 0, it is called "(optically) near field". If an optical surface or plane has a subaperture ratio close to 1 in absolute value, it is called "(optically) near pupil".

[0052] The working beam path of a projection lens, also called the imaging beam path or projection beam path, extends from the effective object field OF to the effective image field IF. The working beam path is defined as a volume in three-dimensional space ("R 3 ("subset of"), and a volume in three-dimensional space is defined in that each point in said space has at least one continuous ray passing through it from an object field OF in the object-side used aperture to an image field IF in the image-side used aperture. The shape and position of the imaging beam path in the process generally depend on the actual field size and the order of diffraction.

[0053] The area of ​​an optical surface illuminated by rays of the projection beam path coming from the effective object field OF is also referred to herein as the "footprint." Here, the footprint of the projection radiation on an optical surface represents the size and shape of the intersection of the projection beam with the surface illuminated by the projection beam. Next to the lens element section, FIG. 2 schematically shows the footprint FP at various positions along the projection beam path. The optical vicinity of the nearest field plane can be identified by a footprint with an approximately rectangular effective object field OF, with slightly rounded edge regions (see, for example, near lens element L1-1 or on a deflection mirror near the intermediate image). The footprint, like the object field, is outside the optical axis OA. In contrast, an approximately circular area is illuminated within the region of the pupil plane that is Fourier transformed with respect to the field plane, so that the footprint in the pupil region has at least an approximately circular shape (see P1 of the refractive first lens part OP1 or P2 in the optical vicinity of the concave mirror CM). The footprint may provide information, among other things, about the spatial distribution of radiation-induced heating.

[0054] During operation, rays exist that are not normally part of the used beam path. These include, among others, what are called "super aperture rays." In this context, these are understood to mean rays that are diffracted by the structuring mask and emitted at an angle greater than the object-side aperture angle used for imaging, the object-side aperture angle being determined by the actual diameter of the aperture stop that bounds the projection beam path. This object-side aperture angle defines the object-side used aperture. Corresponding statements apply to the image side, i.e., the side of the image that is optically conjugate to the object.

[0055] For further explanation of the problem underlying the present application and some of its solutions, Figure 3A shows an enlarged portion of the projection lens of Figure 2 from the region immediately after the object plane OS, in which a mask M having a structure PAT to be imaged is located during operation. The object plane is immediately followed by a plane-parallel plate PP (an optical element with no refractive power), and immediately following this plane-parallel plate, as part of the projection lens, is a lens element L1-1, which is the first transparent optical element with refractive power closest to the object. Generally, the reference OE shall denote an optical element.

[0056] The lens element L1-1 has a body K (e.g., made of synthetic fused silica) that is transparent to ultraviolet light and is formed as a relatively thick biconvex lens element having a first light-passing surface LF1 facing the object plane (light entrance surface LF1) and a second light-passing surface (LF2) on the opposite side (light exit surface LF2).

[0057] A lens element must realize its assigned optical function in the beam path to the best possible extent under all conditions of use. Therefore, each light-passing surface LF1, LF2 has an optically active area NB1, NB2 that encompasses the area of ​​the optical axis and extends radially outward from the optical axis to such an extent that, under all operating conditions, all rays of the projection beam path, both on the entrance and exit sides, pass through the optically active area. Ray ST1 is shown propagating at the edge of the projection beam. Each lens element surface has an edge area RB1, RB2 radially outward from the optically active area, surrounding the respective optically active area in a ring shape.

[0058] In the assembled state, the optical element or lens element L1-1 is held by a holding device or mount comprising several holding elements HE distributed over the periphery of the lens element and on which the lens element rests in the case of a vertically oriented projection lens. Together with the lens element mounted or held therein, the mount or holding device forms an assembly BG which, together with other assemblies containing other optical elements, forms the projection lens.

[0059] Contact zones KZO between the holding element and the exit-side light-passing surface LF2 are located azimuthally distributed in the edge region of the lens element and contact the lens element in the area of ​​the contact zone KZO. From the enlarged detail of the area of ​​the contact zone KZO in FIG. 3B, it is clear that the lens element is adhesively bonded to the holding element HE by its light exit side LF2. The area of ​​the adhesive connection has a multi-layer structure. An adhesive layer KL made of an adhesive material is applied to the support surface of the holding element. Before the adhesive connection is established in the area of ​​the contact zone, an adhesive protective layer KSS is applied to the edge region of the light exit side LF2, disposed between the adhesive layer and the light exit surface LF2. A UV-radiation-absorbing adhesive protective layer protects the adjacent adhesive layer KL from UV radiation that may reach the adhesive layer through the lens element in the edge region, thus improving the service life of the adhesive connection.

[0060] Each of the light-transmitting surfaces has a surface shape that is prepared to optical quality within the optical use area NB1, NB2 and designed according to the use area specification. The use area specification is specified by the function of the optical element within the use beam path. The use area specification is defined within the scope of the optical design calculation. In the exemplary case, both lens element surfaces LF1, LF2 are spherically curved in the use area.

[0061] In contrast, the intention is that the edge regions RB1, RB2 do not contribute to imaging. Although the surface shape in the edge regions still corresponds to the mathematical continuation of the surface shape in the used regions in the case of conventional lens elements, the optical surface is significantly rougher and of poor optical quality in this respect, at least in the region of the radial distance from the transition between the used regions and the edge regions (dashed lines), since these surface parts are not required for imaging.

[0062] The properties of this optical element L1-1 affect the rays that travel outside the projection beam path and reach the radially outer edge of the optically used area. Figure 3A shows what are called superaperture rays UAP, which are deflected by the structure-imparting mask M and propagate at angles greater than the object-side aperture angle used for imaging. The object-side aperture angle is specified by the diameter of the aperture stop.

[0063] 3 indicates the path of the superaperture array UAP, which penetrates through the light-passing surface LF1 into the lens element material in the entrance-side edge region RB1, passes through said lens element material, and reaches the region of the contact zone KZO on the light-exit side through the light-passing surface LF2. Radiant energy is absorbed by the adhesive protective layer KSS, which heats adjacent lens elements and adjacent retaining elements, and optionally adjacent regions of the mount. This locally generated heat can cause undesirable lens heating effects.

[0064] In the illustrated embodiment, this problem is avoided by the edge region of the entrance-side light-passing surface LF1 being given a geometrically defined surface design during manufacturing, rather than a simple extrapolation of the surface shape of the light entrance side in the use area, and the edge region is designed according to an edge region specification that deviates from the use area specification. In the exemplary case, the specified shaping of the light entrance surface in the entrance-side edge region RB1 is selected so that the entrance-side edge region RB1 has a rotationally symmetric aspherical shape. In the transition region between the use area and the edge region, the entrance-side edge region RB1 appears smooth or continuous, i.e., without edges or jumps, from the surface shape of the use area, whereas in the edge region there is a significant deviation from the mathematical continuation of the use area, as indicated by the dashed lines.

[0065] In the exemplary case, the entrance light-passing surface LF1 is convexly spherically curved within the optically used region, and as the distance from the optical axis increases, the convex curvature changes to a narrow region with concave curvature in the edge region after the inflection point before the convex curvature reappears further on. This creates a refractive light-deflecting structure LUS1 that ensures that the diffracted superaperture light UAP reaches a target region ZB outside the used beam path, which can be specified by the edge region specification. In this case, the target region is defined to be located (radially) outside the contact zone KZO. In other words, the contact zone is protected from the superaperture light by the refractive light-deflecting structure LUS1 by deflecting the superaperture light UAP beyond the outer contact zone into a non-critical region outside the contact zone, as indicated by the dashed superaperture light ray UAP′ drawn using a dashed line.

[0066] The target area ZB onto which the deflected superaperture light that has bypassed the contact zone is incident should be fairly large or have a fairly large mass so that it is only affected by a small temperature change in the case of incident radiation. Furthermore, the area should have a good thermal connection to the outside so that heat does not flow back into the lens element via the retaining element.

[0067] Since the rotationally symmetric aspheric surface (light deflection structure LUS1) can be manufactured in one work step together with a rotationally symmetric design in the optical use area, the targeted deflection of the super aperture light by the aspheric surface in the edge area of ​​the lens element on the light entrance side of the lens element can be realized relatively easily from a manufacturing point of view.

[0068] In the example of Fig. 3A, the light deflection structure LUS1 has a continuously curved surface shape over the entire edge region, said surface shape having a negative radius of curvature in at least one region, such that the center of curvature is located on the light entrance side in that region, thereby creating a diverging function or a ring-shaped circumferentially diverging lens element or diverging zone.

[0069] An alternative option for designing a refractive light deflection structure for the purpose of deflecting super-aperture light can be achieved by a light deflection structure having a Fresnel lens ring at the edge region. Thus, the aspheric surface in the edge region can be implemented as a ring-type Fresnel lens element, which can result in saving installation space compared to the larger aspheric surface of FIG. 3A.

[0070] In the exemplary embodiments described below, for clarity, the same reference numerals as in Figure 3A are used for the same or similar features. Regarding the arrangement and basic shape of the lens element L1-1, reference is made to the above example.

[0071] 4A and 4B show an exemplary embodiment in which the deflection of superaperture light is achieved by diffraction using a light deflection structure LUS2 in the form of a diffractive structure in the edge region of the lens element. In this respect, FIG. 4A shows a meridional cross section similar to FIG. 3A, and FIG. 4B shows in plan view the upper surface of the lens element facing the object plane (first light-passing surface LF1). The diffractive light deflection structure LUS2 is formed by a diffraction grating with a circular diffractive structure and rotational symmetry with respect to the optical axis, so that the diffraction of the incident radiation is in each case predominantly radially outward. In the exemplary case, the light deflection structure LUS2 has a blazed grating with a diffractive effect for light of the wavelength used. As is clearly evident from FIG. 4A, this has rings designed with a sawtooth shape in cross section. The radial spacing and the angle of the sawtooth faces are matched to each other so that the diffraction efficiency at the wavelength used is maximized for a certain diffraction order. Thus, most of the intensity components of the narrowband projection radiation are concentrated in a single desired diffraction order, leaving almost no intensity in other orders, especially the zeroth diffraction order, i.e., none remaining during linear passage through the diffraction grating. In this way, the desired deflection angle can be set very precisely, and the light intensity of the deflected superaperture light beam UAP' is concentrated only in a narrow target area ZB, which can be particularly advantageous in complex installation situations. Here, too, the light deflection structure is designed so that deflected stray light is redirected and does not reach the contact zone KZO. During the manufacture of the lens element, a rotationally symmetric blazed grating can be manufactured simultaneously with the lens element and from the same material.

[0072] Although creating a light-deflecting structure that is rotationally symmetric about the optical axis of the optical element can be advantageous for manufacturing reasons, in many cases this may be unnecessary or undesirable for functional reasons. Thus, there are exemplary embodiments in which the optically effective surface shape of the edge region is not rotationally symmetric about the optical axis. In particular, the surface shape may have n-fold rotational symmetry about the optical axis in the edge region, where n may be, for example, 2, 3, 4, 6, or 8. Some examples are described below.

[0073] 5A and 5B show a meridional cross section (5A) and a plan view (5B) of the lens element upper surface of an exemplary embodiment in which superaperture light deflection is achieved by an azimuthal structure diffraction structure in the entrance-side edge region RB1 of the lens element. As is clear from FIG. 5A, the light deflection structure LUS3 is designed as a diffraction structure, i.e., a diffraction grating, specifically in the form of a blazed grating. However, in deviation from the variants of FIGS. 4A and 4B, eight approximately rectangular grating regions GB are provided in the ring-shaped edge region RB1 in a locally restricted manner only within angular regions offset by 45° in the circumferential direction, with a contact zone or retaining element located approximately centrally below them. Again, the grating lines do not extend continuously in the circumferential direction, but only over a narrow angular range, e.g., between 10° and 30°, so as to curve in the circumferential direction with a uniform radius of curvature.

[0074] The diffractive structure with a sawtooth cross section can be formed in one piece with the material of the lens element body and manufactured jointly with the lens element body. However, in the exemplary case, a different procedure is chosen, in which the light deflection structure LUS3 is formed on a separate optical light deflection element LUE. The optical light deflection element LUE is manufactured separately from the transparent body of the optical element and, after its completion, is simply fixed to a designated area in the inlet-side edge region RB1 of the body of the optical element. Here, each light deflection element LUE has a contact surface opposite the light deflection structure, the design of which is matched to the surface shape of the lens element body in the edge region. Therefore, reliable fixing is possible, for example, directly by optical contact bonding without auxiliary means or with a thin adhesive layer or optical cement. In this way, even a relatively complex distribution of light deflection properties in the edge region can be realized within a relatively well-controllable manufacturing process. Optionally, flat surfaces can also be incorporated into the edge region at positions provided for the light deflection elements. These are particularly suitable for unassisted contact with the plane of the light deflection element by optical contact bonding.

[0075] A variant for deflecting superaperture light using refractive light deflection structures in the form of prisms PR in the edge region of a lens element is described with reference to FIGS. 6A and 6B. The representation is identical to the previous example. The plan view of the upper surface of the lens element in FIG. 6B shows that a total of eight light deflection elements LUE in the form of triangular prisms, distributed over the periphery at the same 45° angular division, are attached to the edge region RB1, with each bonding position assigned to a prism. From the meridional cross section in FIG. 6A, it can be seen that the oblique prism surfaces with the normal direction PN face radially inward, resulting in an outward deflection of the radially incident superaperture light. As in the example of FIG. 5, the refractive light deflection structures designed as prisms are manufactured in the form of separate light deflection elements LUE, which, following completion of the lens element surface, are placed at appropriate positions in the edge region and optically neutrally connected to the lens element body, for example, by optical contact bonding or using optical cement.

[0076] 7A and 7B are used to illustrate another embodiment, in which the light deflection structure LUS5 is in the form of a prism PR, which is initially manufactured as a separate prism element separately from the lens element body and then fixed in a suitable position in the entrance edge region RB1 of the lens element by optical contact bonding or optical cement. Deviating from the variants of FIGS. 6A and 6B, the prism surface PF in the beam path at the oblique angle intended for light deflection has its surface normal PN pointing not radially but circumferentially (azimuthally). As can be seen from FIG. 7A, this also makes it possible to deflect the superaperture light in the region so that it does not enter the contact zone KZO with the holding element.

[0077] Circumferential light deflection can also be achieved using a diffractive structure. For example, the light deflection element of Figures 5A and 5B can be designed so that the grating lines of the diffractive structure are approximately aligned in the radial direction. Therefore, the basic concept allows for a large number of degrees of freedom regarding the deflection angle and direction to which stray light is intended to be deflected. In other words, the target area can be located at a clearly different position within the projection lens.

[0078] In particular in the previous example, for example, wherever the retaining elements are provided and optionally wherever the absorbing layer is present in the region of the contact zone, the light deflection structure is largely designed with consideration to prevent superaperture light and other stray light from entering the light exit surface in a certain region, so that the connection points between the retaining elements and the lens elements can be protected from stray light induced heating effects.

[0079] However, it is also possible to improve the performance of the projection lens by targeted deflection of stray light into defined target areas, by deflecting a certain component of the stray light intensity or the entire stray light intensity into the target area or multiple target areas in order to target-heat component parts located in the target area and thus independently achieve desired, predictable thermally induced operations within the optical system.

[0080] An example of thermal manipulation using targeted deflection of stray light is described with reference to FIGS. 8A and 8B. In particular, a thermal manipulator is created that independently homogenizes or equalizes the temperature distribution within an operating optical element OE, e.g., a lens element. FIGS. 8A and 8B each show an axial plan view of a transparent optical element OE optically positioned near the field plane of a projection lens (off-axis system) having an off-axis object field and image field. For example, the optical element can be the plane-parallel plate PP or the first lens element L1-1 of the projection lens in FIG. 2, or a lens element positioned near one of the intermediate images. The optical element is mounted in a holding device comprising eight holding elements HE1, HE2, etc., uniformly distributed around the periphery of the optical element, with the edge region RB of the optical element positioned on the holding elements. The transparent optical element is firmly connected to the holding elements by an adhesive layer protected by an adhesive protective layer.

[0081] Due to the near-field configuration of the illustrated light entrance surface (first light passing surface LF1), light propagating along the projection beam path generates an illumination footprint FP on the lens element surface, which has the approximately rectangular shape of the effective object field, with at least slightly rounded corners due to its distance from the field plane. In this case of illumination that is asymmetric with respect to the optical axis OA, the passing projection light generates a non-rotationally symmetric, asymmetric temperature distribution within the optical element OA. If the temperature distribution within the edge region RB is considered, a relatively warm zone WZ is found wherever the corner of the illumination field is close to the edge of the optical element.

[0082] Stray light propagating outside the imaging beam path impinges on the lens element almost uniformly across the entire edge region. The contact zones of the holding elements HE1 and HE3-HE7 are not protected, so that the superaperture light can slightly heat the contact zones located there. In contrast, the contact zones of the holding elements HE2 (at 2 o'clock) and HE8 (at 10 o'clock) are protected from the incident stray light by the light deflection structure LUS6 formed on the light entrance side, so that the contact zones remain relatively cool compared to the contact zones of the other holding elements exposed to stray light. As a result of this non-uniform circumferential heat distribution due to stray light, the asymmetric heat distribution occurring in the area of ​​the footprint FP can be at least partially compensated for, and the temperature distribution within the optical element OE is therefore more uniform or better homogenized than would be the case without the light deflection structure LUS5.

[0083] In this example, a diffractive light deflection structure LUS6 is used that deflects stray light radially outward. A similar effect can also be achieved using refractive light deflection structures and / or light deflection structures that deflect light in a circumferential direction.

[0084] FIG. 8B shows a modification of the arrangement of FIG. 8A that can generate a well-homogenized temperature distribution. In contrast to the example of FIG. 8A, in the example of FIG. 8B, an adhesive protective layer KSS is attached to the light exit side in the edge region RB, which covers and surrounds all holding elements HE3-HE7 and the circumferentially inserted region. The adhesive protective layer KSS is attached between the light exit side and the holding elements located there. If superaperture light is incident on this region, the edge region is locally heated over the covered angular range (slightly greater than 180°) due to the absorption of stray light in the adhesive protective layer. In combination with the light deflection structure LUS6 in the region of holding elements HE2 and HE8 closest to the footprint, this results in an even better homogenization of the temperature distribution within the optical element.

[0085] The concept of the present invention is not limited to the use of refractive and / or diffractive light deflection structures. The preparation of light deflection structures operating on the reflection principle is also possible and, in some cases, advantageous. FIG. 9 shows an example diagrammatically. A lens element L1-1M therein has an exit-side light-passing surface LF2, the surface shape of which corresponds to the corresponding light-exit surface in FIG. 3. In the use area NB1, the entrance-side light-passing surface LF1 also has the same surface shape. A deviation in this respect is found in the light-entrance-side edge area RB1. While the edge area specifications in the exemplary embodiment of FIG. 3 are chosen so that the light-passing surface curves radially upward, i.e., toward the light entrance side, the exact opposite is true in the variant of FIG. 9. In this case, the edge area specifications are such that the edge area has a significantly larger radial curvature than would be the case for the assumed extension V of the surface shape from the use area. In other words, an entrance surface with a convex curvature exists in the use area, and the adjacent edge area RB1 also has a convex curvature, albeit with a smaller radius of curvature. The ring-shaped edge region RB1 therefore has a radially outwardly sloping design.

[0086] A single-layer or multi-layer reflective coating (mirror coating) REF is applied to the entire surface within the edge region RB1. The target region ZB is located upstream of the lens element, i.e., between the lens element and the object plane, so that when superaperture light UAP enters the reflective edge region, it is reflected radially outward, opposite the normal light propagation direction, into the target region ZB and viewed along the optical axis. An absorber or any other light-absorbing structure is provided in this target region. In this way, the contact zone in the region of the holding element can be further protected from irradiation by the superaperture light. In this variant, the specific specification of the surface shape within the edge region by the edge region specification further ensures that it is possible to precisely calculate how the surface design of the mirror must be designed to precisely deflect superaperture light from a known range of incident angles into the desired target region ZB.

[0087] Aspects of the invention have been described above using the example of an optical imaging system in the form of a microlithography projection lens. The invention can also be used in other optical systems, for example in illumination systems for building microlithography projection exposure apparatuses. Problems with superaperture light, such as damage to adhesives due to radiation loads due to a lack of adhesive protection, can also occur in illumination systems.

Claims

1. An optical element (L1-1, OE) for incorporation into a holding device in order to form an assembly (BG) for constructing an optical system (PO) of a microlithography projection exposure apparatus, comprising: the optical element comprises a body (K) that is transparent to light from a used wavelength range and on which a first light-passing surface (LF1) and an opposite second light-passing surface (LF2) are formed, each of the light passing surfaces (LF1, LF2) has an optically used area (NB1, NB2) provided for being placed in the used beam path of the optical system and an edge area (RB1, RB2) located outside the optically used area and designated as an engagement area for a holding element (HE) of the holding device, each light-passing surface is prepared to optical quality within said optical use area (NB1, NB2) and has a surface shape designed according to use area specifications dictated by the function of said optical elements (L1-1, OE) within said use beam path; a light deflection structure (LUS1, LUS2, LUS3, LUS4, LUS5, LUS6) ​​having a geometrically defined surface design is formed in the edge region (RB1) of at least one of the light passing surfaces (LF1), the surface design being designed according to an edge region specification that deviates from the use region specification and configured to deflect a portion of the light deflected by the light deflection structure into a target region (ZB) outside the use beam path; a plurality of contact zones (KZO) distributed around the periphery of the edge region are defined in the edge region of the light-passing surface opposite the light-passing surface comprising the light-deflecting structures, and the light-deflecting structures (LUS1, LUS2, LUS3, LUS4, LUS5, LUS6) ​​are configured such that a portion of light deflected by the light-deflecting structures can be deflected into a target region (ZB) outside the contact zones, The following conditions are met: (i) the edge region specification is adapted to the use region specification such that the surface shape of the use region (NB1) in a transition region located outside the use region in the edge region (RB1) smoothly transitions into the surface shape of the edge region; (ii) the light-passing surface has a continuously curved aspherical shape in the edge region in accordance with the edge region specification, and a spherical or aspherical shape in the optically used region in accordance with the used region specification; (iii) the light turning structure has a continuously curved surface profile across the edge region, with at least one region having a negative radius of curvature; (iv) an inflection point region is located in the edge region, the inflection point region having a transition from a positive radius of curvature of the light-passing surface on the side of the optically used region to a negative radius of curvature of the light-passing surface away from the optically used region; The optical element, wherein at least one of the following applies to the light deflection structure.

2. 2. The optical element according to claim 1, characterized in that the light deflection structure comprises a refractive and / or diffractive light deflection structure (LUS1, LUS2, LUS3, LUS4, LUS5).

3. 3. The optical element according to claim 2, characterized in that the light deflection structure alternatively or additionally comprises a reflective light deflection structure (LUS6).

4. 2. The optical element of claim 1, wherein the light deflection structure comprises a Fresnel lens ring, and / or the light deflection structure comprises a diffraction grating (LUS2, LUS3, LUS6) ​​having a diffraction effect for light of the wavelength used, and / or the light deflection structure comprises a blazed grating (LUS2, LUS3) having a diffraction effect for light of the wavelength used.

5. 2. The optical element of claim 1, wherein the optical element (OE) has an optical axis (OA), the surface shape of the optically used area (NB) is rotationally symmetrical about the optical axis, and the surface shape of the edge area (RB) is not rotationally symmetrical about the optical axis.

6. 6. The optical element according to claim 5, characterized in that the surface shape in the edge region has n-fold rotational symmetry about the optical axis, where n is in particular 2, 3, 4 or 6.

7. 2. The optical element according to claim 1, characterized in that the light deflection structure is formed in one piece together with the material of the optical element and / or the light deflection structure (LUS3) is formed on a separate optical light deflection element (LUE) that is manufactured separately from the transparent body (K) of the optical element and attached to the edge region (RB) in a designated area.

8. 8. The optical element according to claim 1, wherein the light deflection structure is designed based on calculations on the spatial distribution of stray light intensity in the optical system for a specified combination of mask structure and irradiation setting, so that a thermally activated manipulator is present, the thermally activated manipulator being designed in such a way that its effect can counteract and at least partially compensate for the adverse effects of lens heating in the region of the used beam path.

9. An assembly (BG) comprising an optical element (OE) and a holding device for holding said optical element, said optical element (OE) comprising a body (K) transparent to light from a working wavelength range and having a first light-passing surface (LF1) and an opposite second light-passing surface (LF2) formed thereon, Each of the light-passing surfaces has an optically used area (NB) located for placement in a used beam path and an edge area (RB) located outside the optically used area, in which the light-passing surface is prepared to optical quality according to a specified surface shape dictated by the function of the optical element in the used beam path, the holding device comprises a holding element (HE) which engages in the region of a contact zone in the edge region (RB) of the second light passing surface (LF2), In assembly, 1. An assembly, characterized in that light deflection structures (LUS1, LUS2, LUS3, LUS4, LUS5, LUS6) ​​having a geometrically defined surface design are formed in the edge region (RB) of the first light passing surface and are configured to deflect a portion of light deflected by the light deflection structures into a target region (ZB) outside the contact zone (KZ).

10. 10. The assembly of claim 9, wherein the surface shape of the light deflection structures is irregularly configured in the azimuth direction, and the greatest density of the light deflection structures is located near an optically used footprint where the used beam path intersects with the light passing surface.

11. 11. An assembly according to claim 9 or 10, characterized in that a material that is strongly absorbing at the operating wavelength is arranged in the target area (ZB) of the light deflection structure, the absorptivity of said material being greater than the absorptivity of the transparent material of the optical element.

12. Optical system comprising at least one optical element according to any one of claims 1 to 7 and / or at least one assembly (BG) according to any one of claims 9 to 11.

13. 13. The optical system according to claim 12, characterized in that it is an optical imaging system, in particular a dioptric or catadioptric microlithography projection lens (PO), for constructing a microlithography projection exposure apparatus.

Images