Field facet system and lithographic apparatus

Abstract

The present invention relates to a field facet system (300A, 300B, 300C, 300D, 300E, 300F, 300G, 300H) for a lithography apparatus (100A, 100B), comprising an optical element (302) including a base body (204) and an elastically deformable facet portion (306) connected to the base body (204) and having a light-reflective optically effective surface (308), and a facet portion (306) configured to change a radius of curvature (K1, K2) of the optically effective surface (308). and a plurality of actuating elements (332, 334, 336, 338) for deforming the facet portion (306), the actuating elements (332, 334, 336, 338) being operatively connected to the facet portion (306) in a manner that decouples thermal deflection of the actuating elements (332, 334, 336, 338) from the facet portion (306) such that the radii of curvature (K1, I2) are not affected by said thermal deflection of the actuating elements (332, 334, 336, 338).

Description

[Technical Field]

[0001] The present invention relates to a field facet system for a lithographic apparatus and to a lithographic apparatus comprising such a facet system.

[0002] The entire content of German Patent Application No. 10 2020 214 800.7, from which priority is claimed, is incorporated by reference. [Background technology]

[0003] Microlithography is used in the manufacture of finely structured components, such as integrated circuits. The microlithography process is carried out using a lithography apparatus having an illumination system and a projection system, in which an image of a mask (reticle), illuminated by the illumination system, is projected by the projection system onto a substrate, e.g., a silicon wafer, that is coated with a photosensitive layer (photoresist) and positioned in the image plane of the projection system, in order to transfer the mask structure into the photosensitive coating on the substrate.

[0004] Due to the desire for further miniaturization of structures in the manufacture of integrated circuits, EUV lithography systems (extreme ultraviolet, EUV) using light with wavelengths in the range of 0.1 nm to 30 nm, particularly 13.5 nm, are currently under development. Since most materials exhibit high absorption of light at this wavelength, in such EUV lithography systems, reflective optical units, i.e., mirrors, must be used instead of the previous refractive optical units, i.e., lens elements. The mirrors operate at near-normal incidence or at oblique incidence.

[0005] The illumination system comprises, inter alia, a field facet mirror and a pupil facet mirror. The field facet mirror and the pupil facet mirror may be in the form of so-called facet mirrors, which often have several hundred facets each. The facets of the field facet mirror are also called "field facets", and the facets of the pupil facet mirror are also called "pupil facets". Several pupil facets can be assigned to one field facet. In order to obtain good illumination in conjunction with a high numerical aperture, it is desirable to switch said one field facet between the pupil facets assigned to it.

[0006] Because the field facet is switchable, the distance between the field facet and the pupil facet assigned to it varies depending on the switching position. If the refractive power of the field facet is fixed, the image on the corresponding pupil facet may be defocused depending on the switching position. This defocusing limits the reduction of the pupil filling. In this case, "pupil filling" should be understood to mean the ratio of the illuminated surface area to the total optically effective area of ​​each pupil facet. However, to achieve a high resolution of the projection system, it is necessary to further reduce the pupil filling. Therefore, it is desirable to make the field facets variable depending on the switching position of the field facet in order to at least reduce or completely eliminate the defocusing.

[0007] US Patent No. 6,299,949 describes an EUV illumination system for an EUV lithography apparatus, a lithography apparatus, and a method for generating illumination radiation using an EUV illumination system.

[0008] US Pat. No. 5,699,499 discloses a facet mirror for a projection exposure apparatus, a corresponding projection exposure apparatus, and methods of operating the facet mirror and the projection exposure apparatus, respectively.

[0009] US Pat. No. 5,699,499 describes an optical element having an optical axis and a device for introducing a two-wave or multi-wave deformation into the optical element. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] DE 10 2017 221 420 [Patent Document 2] DE 10 2013 206 981 A1 [Patent Document 3] DE 101 51 919 A1 Summary of the Invention [Problem to be solved by the invention]

[0011] Against this background, the object of the present invention is to propose an improved field facet system. [Means for solving the problem]

[0012] Therefore, a field facet system for a lithographic apparatus is proposed, the field facet system comprising an optical element including a base body and elastically deformable facets connected to the base body and having a light-reflective optically active surface, and a plurality of actuating elements for deforming the facets to vary a radius of curvature of the optically active surface, the actuating elements being operatively connected to the facets in such a way that thermal deflections of the actuating elements are decoupled from the facets so that the radius of curvature is not affected by thermal deflections of the actuating elements.

[0013] By decoupling the thermal deflection of the actuating element from the facets, it is possible to reliably prevent undesired deformations of the optically active surface due to the thermal deflection of the actuating element, thereby improving the performance of the field facet system.

[0014] The field facet system is in particular part of a beam shaping and illumination system of a lithographic apparatus. In particular, the field facet system is part of a facet mirror, in particular a field facet mirror. Such a facet mirror preferably comprises a plurality of such field facet systems arranged in a line or in the form of a pattern. In this case, each field facet system can be tilted independently to a plurality of different tilt positions. For this purpose, each field facet system may comprise a further actuating element suitable for tilting the entire field facet system as a unit. The actuating element may be a so-called Lorentz actuator.

[0015] The optical elements are preferably or can be called facets, mirror facets or field facets. The facets are in particular rod- or beam-shaped and can have a rectangular, trapezoidal or any other geometric cross section. The facets have, for example, a width, a length and a thickness. The length-to-width ratio is preferably about 10:1. The thickness is preferably smaller than the width. A coordinate system is assigned to the field facet system with a first spatial direction or x-direction, a second spatial direction or y-direction and a third spatial direction or z-direction. The spatial directions are positioned perpendicular to each other.

[0016] The width is oriented in the x-direction. The x-direction can therefore also be referred to as the width direction. The length is oriented in the y-direction. The y-direction can therefore also be referred to as the longitudinal direction or length direction. The thickness is oriented in the z-direction. The z-direction can therefore also be referred to as the thickness direction or vertical direction. The "length direction" is to be understood to mean in particular the spatial direction along which the optical element extends geometrically the longest.

[0017] The optical element is manufactured from a mirror substrate or substrate. The substrate may in particular comprise copper, in particular a copper alloy, an iron-nickel alloy, such as Invar, or any other suitable material. The optically effective surface is provided on the front side of the facet, i.e., the side opposite the body. The optically effective surface may be a mirror surface. The optically effective surface is produced by means of a coating applied to the substrate.

[0018] The optically effective surface is suitable for reflecting light, in particular EUV radiation. However, this does not exclude that heat is introduced into the facets as a result of at least a portion of the light being absorbed by the facets. The facets or optically effective surface have a rectangular geometric shape in plan view, i.e., in a line of sight perpendicular to the optically effective surface. However, the facets or optically effective surface can also be curved in an arc or crescent shape in plan view.

[0019] Preferably, the optically effective surface is a curved surface. In the simplest case, the optically effective surface is a cylindrically curved surface. However, the shape of the optically effective surface can also be a torus or an ellipsoid. If a toroidal geometric shape is given, it has a vertex. Preferably, the optically effective surface includes a first radius of curvature that indicates the curvature of the optically effective surface in a plane extending in the y and z directions.

[0020] Furthermore, the optically effective surface comprises a second radius of curvature, which is different from the first radius of curvature and indicates the curvature of the optically effective surface in a plane extending in the x- and z-directions. The first and second radii of curvature are positioned perpendicular to each other. The radii of curvature intersect, in particular, at the vertex. The first radius of curvature is preferably larger than the second radius of curvature. In particular, the first radius of curvature is changed by means of deformation of the facet. However, depending on the arrangement of the actuating element, the second radius of curvature may also be influenced.

[0021] The actuating elements can be called actuators. Preferably, at least two actuating elements are provided. However, it is also possible to provide three, four, five, six, seven, eight, nine, ten, or eleven actuating elements. Even twelve or more actuating elements are possible. In principle, any number of actuating elements is possible. Preferably, the actuating elements are so-called displacement actuators. A "displacement actuator" is understood to mean an actuating element that, in contrast to a force actuator, predefines a displacement rather than a fixed force. In contrast, a "force actuator" is understood to mean an actuating element that, in contrast to a displacement actuator, predefines a force rather than a fixed displacement. An example of a displacement actuator is a piezo element. An example of a force actuator is a Lorentz actuator, as already mentioned above. That is, the actuating element can be or include a piezo element or a piezo stack. However, the actuating element can also be, for example, a pneumatic or hydraulic actuator.

[0022] A control unit is preferably assigned to the actuating elements, so that they are controlled, in particular energized, so that they deform the facets. By way of example, the actuating elements are brought from a non-deflected state to a deflected state by energization. Any number of intermediate states are provided between the non-deflected state and the deflected state. Preferably, the actuating elements automatically return from the deflected state to the non-deflected state as soon as they are no longer energized. Preferably, the radius of curvature, in particular the first radius of curvature or the first and second radii of curvature, can be varied in a stepless manner by means of the actuating elements.

[0023] Actuating elements based on piezoelectric ceramics such as lead zirconate titanate (PZT), i.e., the piezo elements mentioned above, have a negative coefficient of thermal expansion. This leads to a thermal deflection, e.g., a change in length, of each actuating element relative to the body in the event of uniform heating of the optical element, and thus to a concomitant change in the displacement of the actuating element. The thermal change in displacement of the actuating element, or more generally, the thermal deflection, can be compensated for by using a suitable arrangement, in particular the orientation of its effective direction relative to the intended effective direction of deformation, and the design of an operable connection between the actuating element and the facet. This means that the thermal deflection of each actuating element does not lead to undesired deformation of the facet. The "deflection" of an actuating element may be understood to mean, for example, a change in length or distortion of the actuating element.

[0024] That the facet is "elastically deformable" in this case means that the facet can be changed from an undeflected or undeformed state to a deflected or deformed state and back again. In the undeflected state, the radius of curvature, in particular the first radius of curvature, can be larger than in the deformed state. To bring the facet from the undeflected state to the deformed state, a bending moment is introduced into the facet by means of an actuating element. By way of example, two opposing bending moments are introduced into the two end regions of the facet. However, only one bending moment will be mentioned below.

[0025] As soon as the bending moment is no longer applied to the facets, the facets automatically transform from the deformed state to the undeformed state, i.e., the deformation of the facets is reversible. In particular, the facets are prestressed in the direction of the undeformed state, in particular by springs. In the undeformed state, the optically effective surface can be flat or have a cylindrical curvature.

[0026] The operable connection between the actuating element and the facet can be designed as desired. However, this operable connection is always designed in such a way that thermal deflections of the actuating element, for example when the field facet system is uniformly heated, do not or hardly cause deformation of the facet. In this case, the radius of curvature being "insensitive" to thermal deflections of the actuating element means that the radius of curvature does not change even in the event of thermal deflections, e.g. contraction or expansion, of the actuating element. That is, the radius of curvature can only be changed by deliberate control of the actuating element. No undesired changes in the radius of curvature due to thermal deflections of the actuating element occur.

[0027] According to one embodiment, at least some of the actuating elements are coupled to the facets by means of lever arms.

[0028] The field facet system preferably comprises a first actuating element and a second actuating element. In particular, the first actuating element is coupled to the facet by means of a lever arm. The second actuating element is in particular coupled to the base body. The bending moment can be applied to the facet by means of the lever arm. For this purpose, a force is applied to the lever arm by means of the actuating element. In particular, two opposite bending moments are applied to the periphery or end of the facet. The lever arm is connected to the facet by means of in particular a connection region. A gap is provided between the lever arm and the facet, which is filled by means of the connection region. The gap prevents undesired stiffening of the facet in the region of the lever arm.

[0029] According to yet another embodiment, a first lever arm of the lever arm is articulatedly connected to the body using a first joint that allows only rotational movement of the first lever arm around the first spatial direction, and a second lever arm of the lever arm is articulatedly connected to the body using a second joint that allows rotational movement of the second lever arm around the first spatial direction.

[0030] The first and second lever arms are preferably designed as so-called flexures. In this case, "flexure" is understood to mean a region of a component that allows relative movement between two rigid regions by bending. The two rigid regions are formed by the base body and the respective lever arms. The joints are elastically deformable. The second joint can be designed to only allow rotational movement of the second lever arm about the first spatial direction. Alternatively, the second joint can be designed to allow further movement in addition to the rotational movement of the second lever arm about the first spatial direction.

[0031] According to yet another embodiment, the second joint portion further allows translational movement of the second joint portion along a second spatial direction different from the first spatial direction to compensate for thermal expansion of the facet portion along the second spatial direction.

[0032] The reflected light used, in particular EUV radiation, is incident on the optically active surface and heats the facet, i.e. the facet experiences a higher heat input than the main body. As a result, the facet expands more due to heat than the main body. This thermal expansion of the facet can be compensated for by means of the second joint part. In doing so, the second joint part can be deformed into an S-shape. In this context, a "translational" movement is understood to mean a linear movement along a straight line, i.e. along the second spatial direction. The first spatial direction and the second spatial direction are in particular oriented perpendicular to each other.

[0033] According to yet another embodiment, the actuating element is a linear actuating element that is subject to equal extension and contraction control along a third spatial direction different from the first and second spatial directions.

[0034] A "linear actuating element" is therefore understood below to be an actuating element that can expand and contract along its main direction of extension, here the third spatial direction. In this case, the actuating element is arranged so that the expansion and contraction occurs perpendicular to the optically effective surface. The third spatial direction is therefore oriented perpendicular to the facet or the optically effective surface. Controlling can include energizing. For example, the deflection of the actuating element increases with increasing voltage applied to each actuating element.

[0035] According to yet another embodiment, the actuating element is a linear actuating element that is subject to equal extension and contraction control along a second spatial direction different from the first spatial direction.

[0036] That is, the actuating elements are arranged such that the extension and contraction occurs parallel to the optically active surface or parallel to the second spatial direction, which results in a reduction in the installation space, i.e. the field facet system can be designed to be more compact when viewed along the third spatial direction.

[0037] According to yet another embodiment, the actuating element is a shear actuating element that is subject to the same bending control in a plane extending in the second and third spatial directions.

[0038] That is, an actuation element designed as a shear actuation element, in contrast to an actuation element designed as a linear actuation element, bends rather than stretches, where this curvature is variable depending on the control of the actuation element, for example depending on an applied voltage.

[0039] According to yet another embodiment, the actuating element is coupled to the lever arm by means of a decoupling joint that is flexible in bending along the second spatial direction.

[0040] In this case, "flexibly flexible" means that the decoupling joint is unable or virtually unable to transmit any force along the second spatial direction. As a result, thermal decoupling of the actuating element can be achieved. Thermal deflection of the actuating element is thus compensated for by means of the decoupling joint. Each decoupling joint can comprise two leaf springs with interconnected ends, one of which is coupled to each actuating element and the other leaf spring is connected to each lever arm.

[0041] According to yet another embodiment, the actuating elements are arranged in parallel pairs as actuating element pairs, a first actuating element of each actuating element pair being coupled to the facet portion, a second actuating element of each actuating element pair being coupled to the body, and the first actuating element and second actuating element of each actuating element pair being coupled to each other.

[0042] The actuating elements are preferably designed as linear actuating elements in this case. In this case, arranging the actuating elements "parallel" to one another means that the actuating elements of an actuating element pair are placed next to one another and that the effective directions of the two actuating elements extend parallel to one another. The actuating elements of an actuating element pair are connected to one another, for example, by means of a connecting element. The connecting element may be rod-shaped. The connecting element is preferably made of the same material as the main body.

[0043] According to yet another embodiment, the first actuating element is coupled to the facet portion by means of a lever arm and the second actuating element is coupled to the body by means of an arm portion.

[0044] A gap is provided between the lever arm and the arm portion. The first operating element is connected to the lever arm. The second operating element is connected to the arm portion. The first operating element and the second operating element form a pair and are connected to each other by the connecting element.

[0045] According to yet another embodiment, the actuation element is disposed within the body.

[0046] As a result, a particularly compact installation space can be achieved, while at the same time uniform heating of the actuating element can be ensured.

[0047] According to yet another embodiment, the field facet system also includes a temperature sensor used to detect the temperature of the body, the facet portion and / or the operating element, and / or the field facet system also includes a displacement measurement sensor used to detect deformation of the facet portion.

[0048] By way of example, temperature sensors can be provided in or on the body, in or on the facets and in or on the actuating elements. The temperature sensors can be used to detect uneven heating of the field facet system. According to this temperature distribution, correction signals can be used to control the actuating elements and to correct this uneven heating of the field facet system.

[0049] According to yet another embodiment, the actuating element is a piezo actuator.

[0050] By way of example, the actuating element can be a linear piezo actuator or a shear piezo actuator. Any other type of actuating element can also be used. By way of example, shape memory alloys, pneumatic or hydraulic actuating elements, servo motors, etc. can be used as actuating elements.

[0051] According to yet another embodiment, the body and the facets are formed integrally, in particular materially integrally.

[0052] In this case, "integrally" or "integrally" means that the body and facets form a common component and are not made of different components. In this case, "materially integrally" means that the body and facets are made entirely from the same material. Alternatively, the body and facets can be two separate components that are connected to each other.

[0053] According to yet another embodiment, the facet portion is curved in an arc in plan view of the optically effective surface, and the stiffness of the facet portion as viewed along the longitudinal direction of the facet portion is variable such that, when a bending moment is introduced into the facet portion, a normal vector oriented perpendicular to the optically effective surface tilts only around one spatial direction.

[0054] As mentioned above, a plan view should be understood to refer to a line of sight perpendicular to the optically active surface. In this case, "rigidity" should be understood to specifically refer to the resistance of a facet, or the body generally, to elastic deformation due to a force or moment. In particular, "rigidity" should be understood to refer to the torsional rigidity of a facet, i.e., its ability to withstand a torsional moment that twists or torsions the facet. The rigidity of a component depends firstly on the elastic properties of the material, such as Young's modulus, and secondly on the geometric shape of the deformed component. The variable rigidity can prevent the facet from twisting, i.e., twisting around a second spatial direction, when a bending moment is applied to the facet. This prevents the normal vector from tilting around the second spatial direction. In this case, "normal vector" should be understood to refer to a vector oriented perpendicular to the optically active surface. The bending moment acts around the first spatial direction. The bending moment bends the facet but does not twist or twist it. The longitudinal direction extends substantially along the second spatial direction. In this case, the longitudinal direction can be curved like the facet itself. The facet preferably has a first end region and a second end region, to which opposing bending moments can be introduced. A plane of symmetry of the facet is provided midway between the end regions. The longitudinal direction is from each end region to the plane of symmetry.

[0055] According to yet another embodiment, the Young's modulus of the facets is variable along the longitudinal direction.

[0056] For example, the Young's modulus may decrease from the end region toward the plane of symmetry. A Young's modulus profile or gradient is thus provided. In this case, the gradient indicates the profile of the change in a numerical physical variable as a function of location. The gradient of the variable indicates the extent of the change in the variable and the direction of its maximum change, location by location. The above-mentioned change in Young's modulus can be achieved by using a monolithically manufactured base body, particularly facets, made of two or more different materials. In this case, the base body forms the facets or the facets are manufactured from the base body. The base body may also include a main body. Such a base body can be manufactured from different materials, particularly metal powders, by welding, plating, or preferably by additive manufacturing, particularly 3D printing. In particular, additive manufacturing methods can be used to manufacture hybrid components, particularly facets, that have a continuous transition between two different materials, for example, copper and steel. Thus, at least the facets may have a hybrid structure, particularly made of steel and copper. The main body may also have such a hybrid structure.

[0057] According to yet another embodiment, the polar section modulus of the cross section of the facet is variable when viewed along the longitudinal direction.

[0058] A combination of variable Young's modulus and variable polar section modulus can also be provided. Polar section modulus is a measure of the resistance by a beam to the development of internal stresses under load. Polar section modulus can be influenced by the cross-sectional geometry. For example, the polar section modulus can decrease from the end regions of the facets towards the plane of symmetry.

[0059] According to yet another embodiment, the cross section is trapezoidal.

[0060] The cross-section of the facets is not limited to a trapezoidal cross-section in particular, but may have any geometric shape with at least two variable cross-sectional parameters, such as width and height, etc. Rectangular, triangular, semi-elliptical, truncated rectangular or other more complex cross-sections are for example conceivable.

[0061] According to yet another embodiment, the cross section includes a first width facing the optically effective surface and a second width opposite the optically effective surface, the first width being greater than the second width.

[0062] That is, the cross section tapers from the optically effective surface. The facet portion has, in particular, an upper surface provided with the optically effective surface and a lower surface. The upper surface has a first width. The lower surface has a second width.

[0063] According to yet another embodiment, the first width is constant along the longitudinal direction and the second width is variable along the longitudinal direction.

[0064] That is, the first width is not particularly changed or variable, and the second width, for example, decreases from the end region towards the plane of symmetry.

[0065] According to yet another embodiment, the cross-section includes a height that is variable when viewed along the longitudinal direction.

[0066] The height is oriented in particular along the third spatial direction, for example decreasing from the end region of the facet towards the plane of symmetry.

[0067] According to yet another embodiment, the facet portion includes a first end region and a second end region, the facet portion being configured in mirror symmetry with respect to a plane of symmetry located between the first end region and the second end region.

[0068] Mirror symmetry relates to the geometric configuration, i.e. dimensions, of the facets. However, mirror symmetry also relates to the stiffness of the facets. For example, a facet has the same stiffness on both sides of its plane of symmetry at a given distance from the plane of symmetry.

[0069] According to yet another embodiment, the cross section is smallest at the plane of symmetry.

[0070] In particular, the cross-sectional area of ​​the cross section is smallest at the plane of symmetry.

[0071] According to yet another embodiment, the cross section increases in size from the plane of symmetry in the direction of the first end region and in the direction of the second end region.

[0072] That is, the cross-sectional area of ​​the cross section is greater in the end regions than at the plane of symmetry.

[0073] Furthermore, a lithographic apparatus comprising such a field facet system is provided.

[0074] A lithographic apparatus may include a plurality of such field facet systems. The lithographic apparatus may be an EUV lithographic apparatus or a DUV lithographic apparatus. EUV stands for "extreme ultraviolet" and refers to wavelengths of light used between 0.1 nm and 30 nm. DUV stands for "deep ultraviolet" and refers to wavelengths of light used between 30 nm and 250 nm.

[0075] In this context, "a" or "an" should not necessarily be construed as limiting to exactly one element. Rather, there can be a plurality of elements, e.g., two, three, or more. Any other numbers used herein should not be construed as limiting to a precise recited number of elements. Rather, unless otherwise indicated, more or less numbers are possible.

[0076] The embodiments and features described with respect to the field facet system also apply to the proposed lithographic apparatus and vice versa.

[0077] Further possible implementations of the invention also include unstated combinations of the features or embodiments described above or below with respect to the exemplary embodiments, in which case a person skilled in the art may add individual aspects as improvements or supplements to each basic form of the invention.

[0078] Further advantageous configurations and aspects of the invention are the subject of the dependent claims and also of the exemplary embodiments of the invention that will be described below. The invention will be explained in more detail below on the basis of preferred embodiments and with reference to the attached drawings. [Brief explanation of the drawings]

[0079] [Figure 1] Figure 1A shows a schematic diagram of an embodiment of an EUV lithography apparatus, and Figure 1B shows a schematic diagram of an embodiment of a DUV lithography apparatus. [Figure 2] 1C shows a schematic diagram of an embodiment of an optical device of the lithographic apparatus shown in FIG. 1A or FIG. 1B; [Figure 3] 3 shows a schematic plan view of an embodiment of a field facet mirror of the optical arrangement shown in FIG. 2; [Figure 4] 3 shows yet another schematic diagram of the optical device shown in FIG. 2. [Figure 5] 3 shows yet another schematic diagram of the optical device shown in FIG. 2. [Figure 6] 3 shows yet another schematic diagram of the optical device shown in FIG. 2. [Figure 7] 3 shows a schematic diagram of an embodiment of a pupil facet of a pupil facet mirror of the optical arrangement shown in FIG. 2; [Figure 8] 8 shows yet another schematic diagram of the pupil facet shown in FIG. 7; [Figure 9] 3 shows a schematic diagram of yet another embodiment of a pupil facet of the pupil facet mirror of the optical arrangement shown in FIG. 2; [Figure 10] 3 shows a schematic diagram of an embodiment of the optical system of the optical device shown in FIG. 2. [Figure 11] 3 shows a schematic diagram of yet another embodiment of the optical system of the optical device shown in FIG. 2. [Figure 12] 3 shows a schematic diagram of yet another embodiment of the optical system of the optical device shown in FIG. 2. [Figure 13] 3 shows a schematic diagram of yet another embodiment of the optical system of the optical device shown in FIG. 2. [Figure 14] 3 shows a schematic diagram of yet another embodiment of the optical system of the optical device shown in FIG. 2. [Figure 15] 3 shows a schematic diagram of yet another embodiment of the optical system of the optical device shown in FIG. 2. [Figure 16] 3 shows a schematic diagram of yet another embodiment of the optical system of the optical device shown in FIG. 2. [Figure 17]3 shows a schematic diagram of yet another embodiment of the optical system of the optical device shown in FIG. 2. [Figure 18] 3 shows a schematic side view of an embodiment of a facet of the optical system of the optical device shown in FIG. 2. [Figure 19] FIG. 18 shows a schematic plan view of the facet portion. [Figure 20] FIG. 19 is a schematic front view of the facet portion shown in FIG. 18. [Figure 21] 3 shows a schematic side view of yet another embodiment of a facet of the optical system of the optical device shown in FIG. 2; [Figure 22] 22 shows a schematic plan view of the facet portion shown in FIG. 21. [Figure 23] 22 shows a schematic cross-sectional view of the facet portion taken along the cross-sectional line AA in FIG. 21. [Figure 24] 22 shows yet another schematic cross-sectional view of the facet portion taken along the cross-sectional line BB in FIG. 21. [Figure 25] 3 shows a schematic plan view of yet another embodiment of a facet of the optical system of the optical device shown in FIG. 2; [Figure 26] 26 shows a schematic cross-sectional view of the facet portion taken along the cross-sectional line CC in FIG. 25. [Figure 27] 26 shows yet another schematic cross-sectional view of the facet portion taken along the cross-sectional line DD in FIG. 25. [Figure 28] 26 shows yet another schematic cross-sectional view of the facet portion taken along the section line EE of FIG. 25. [Figure 29] 22 shows a schematic graph illustrating the error profile of the normal vector over the length of the facet shown in FIG. 21; [Figure 30] 26 shows a schematic graph illustrating the error profile of the normal vector over the length of the facet shown in FIG. 25. DETAILED DESCRIPTION OF THE INVENTION

[0080] Unless otherwise indicated, identical or functionally identical elements are provided with the same reference numerals throughout the figures. It should also be noted that the illustrations are not necessarily to scale.

[0081] FIG. 1A shows a schematic diagram of an EUV lithography apparatus 100A equipped with a beam shaping and illumination system 102 and a projection system 104. In this case, EUV stands for "extreme ultraviolet" and refers to the wavelength of light used, which is between 0.1 nm and 30 nm. The beam shaping and illumination system 102 and the projection system 104 are each provided in a vacuum housing (not shown), and each vacuum housing is evacuated using an exhaust device (not shown). The vacuum housing is surrounded by a machine room (not shown) in which drive devices that mechanically move or set optical elements are provided. Furthermore, an electrical controller and the like may also be provided in the machine room.

[0082] The EUV lithography apparatus 100A includes an EUV light source 106A. The EUV light source 106A can be, for example, a plasma source (or a synchrotron) that emits radiation 108A in the EUV range (extreme ultraviolet), i.e., in a wavelength range of, for example, 5 nm to 20 nm. In the beam shaping and illumination system 102, the EUV radiation 108A is focused and a desired operating wavelength is filtered from the EUV radiation 108A. The EUV radiation 108A generated by the EUV light source 106A has a relatively low transmittance in air, and for this reason, the light-conducting spaces of the beam shaping and illumination system 102 and the projection system 104 are evacuated.

[0083] 1A includes five mirrors 110, 112, 114, 116, and 118. After passing through beam shaping and illumination system 102, EUV radiation 108A is directed to a photomask (also known as a reticle) 120. Photomask 120 is also in the form of a reflective optical element and may be located external to systems 102, 104. Furthermore, EUV radiation 108A may be directed by mirror 122 to reticle 120. Reticle 120 has a structure that is imaged by projection system 104 in a reduced size, such as onto wafer 124.

[0084] The projection system 104 (also referred to as a projection lens) has six mirrors M1-M6 for imaging the photomask 120 onto the wafer 124. In this case, the individual mirrors M1-M6 of the projection system 104 may be arranged symmetrically about the optical axis 126 of the projection system 104. It should be noted that the number of mirrors M1-M6 in the EUV lithography apparatus 100A is not limited to the number shown. More or fewer mirrors M1-M6 may be provided. Furthermore, the mirrors M1-M6 generally have curved front surfaces for beam shaping.

[0085] 1B shows a schematic diagram of a DUV lithography apparatus 100B comprising a beam shaping and illumination system 102 and a projection system 104. In this case, DUV stands for "deep ultraviolet" and refers to the wavelength of the light used, which is between 30 nm and 250 nm. As already described with reference to FIG. 1A, the beam shaping and illumination system 102 and the projection system 104 may be enclosed by a machine room with corresponding drive devices.

[0086] The DUV lithography apparatus 100B comprises a DUV light source 106B, which may be, for example, an ArF excimer laser emitting radiation 108B in the DUV range, for example at 193 nm.

[0087] 1B, beam shaping and illumination system 102 directs DUV radiation 108B to photomask 120. Photomask 120 may be formed as a transmissive optical element and may be located external to systems 102, 104. Photomask 120 has structures that are imaged by projection system 104 at a reduced size, such as onto wafer 124.

[0088] The projection system 104 has a plurality of lens elements 128 and / or mirrors 130 for imaging the reticle 120 onto the wafer 124. In this case, the individual lens elements 128 and / or mirrors 130 of the projection system 104 may be arranged symmetrically about the optical axis 126 of the projection system 104. It should be noted that the number of lens elements 128 and mirrors 130 in the DUV lithography apparatus 100B is not limited to the number shown. More or fewer lens elements 128 and / or mirrors 130 may be provided. Furthermore, the mirrors 130 generally have curved front surfaces for beam shaping.

[0089] The gap between the final lens element 128 and the wafer 124 can be replaced with a liquid medium 132 having a refractive index greater than 1. The liquid medium 132 can be, for example, high-purity water. This configuration is also referred to as immersion lithography and has high photolithographic resolution. The medium 132 can also be referred to as an immersion liquid.

[0090] 2 shows a schematic diagram of an optical apparatus 200. The optical apparatus 200 is a beam shaping and illumination system 102, particularly the beam shaping and illumination system 102 of the EUV lithography apparatus 100A. Therefore, the optical apparatus 200 can also be referred to as a beam shaping and illumination system, and the beam shaping and illumination system 102 can be referred to as an optical apparatus. The optical apparatus 200 can be located upstream of the projection system 104 as described above.

[0091] However, optical apparatus 200 can also be part of DUV lithography apparatus 100B. However, in the following, it will be assumed that optical apparatus 200 is part of EUV lithography apparatus 100A. In addition to optical apparatus 200, Figure 2 also shows an EUV light source 106A, as previously described, emitting EUV radiation 108A, and a photomask 120. EUV light source 106A can be part of optical apparatus 200.

[0092] Optical device 200 includes a plurality of mirrors 202, 204, 206, and 208. Additionally, an optional deflecting mirror 210 may be provided. Deflecting mirror 210 operates at grazing incidence and may therefore also be referred to as a grazing incidence mirror. Deflecting mirror 210 may correspond to mirror 122 shown in FIG. 1A. Mirrors 202, 204, 206, and 208 may correspond to mirrors 110, 112, 114, 116, and 118 shown in FIG. 1A. In particular, mirror 202 corresponds to mirror 110, and mirror 204 corresponds to mirror 112.

[0093] Mirror 202 is a so-called facet mirror, in particular a field facet mirror, of optical device 200. Mirror 204 is also a facet mirror, in particular a pupil facet mirror, of optical device 200. Mirror 202 reflects EUV radiation 108A to mirror 204. At least one of mirrors 206, 208 can be a condenser mirror of optical device 200. The number of mirrors 202, 204, 206, 208 can be any number. By way of example, it is possible to provide five mirrors 202, 204, 206, 208, i.e., mirrors 110, 112, 114, 116, 118, as shown in FIG. 1A, or four mirrors 202, 204, 206, 208, as shown in FIG. 2. However, preferably, at least three mirrors 202, 204, 206, 208 are provided, i.e., a field facet mirror, a pupil facet mirror, and a condenser mirror.

[0094] A facet mirror includes a plurality of thin plates or facets that may be arranged linearly. The facets may be curved in an arc or crescent shape. The facets may also be polygonal, particularly rectangular. By way of example, a facet mirror may have hundreds or even thousands of facets. Each facet may be individually tiltable.

[0095] The mirrors 202, 204, 206, 208 are disposed within a housing 212. The housing 212 can be evacuated during operation of the optical apparatus 200, particularly during exposure operations, i.e., the mirrors 202, 204, 206, 208 are disposed in a vacuum.

[0096] During operation of the optical arrangement 200, the EUV light source 106A emits EUV radiation 108A. By way of example, a tin plasma can be generated for this purpose. To generate the tin plasma, a laser pulse can be impinged on a tin body, such as a tin bead or tin droplet. The tin plasma emits EUV radiation 108, which is collected using a collector, such as an ellipsoidal mirror, of the EUV light source 106A and directed toward the optical arrangement 200. The collector focuses the EUV radiation 108A to an intermediate focus 214, which can also be referred to as an intermediate focal plane or is within the intermediate focal plane.

[0097] Upon passing through optical arrangement 200, EUV radiation 108A is reflected by each of mirrors 202, 204, 206, and 208 and by deflecting mirror 210. The beam path of EUV radiation 108A is indicated by reference numeral 216. Photomask 120 is positioned in an object plane 218 of optical arrangement 200. Object field 220 is positioned in object plane 218.

[0098] 3 shows a schematic plan view of an embodiment of a mirror 202 as previously described in the form of a facet mirror, in particular a field facet mirror. The facet mirror or field facet mirror is therefore designated here with the reference numeral 202. The field facet mirror 202 comprises a plurality of linearly arranged lamellae or facets 222. The facets 222 are in particular field facets and will also be referred to as such in the following.

[0099] The field facets 222 may be curved in the shape of an arc or a crescent. The facets 222 may also be polygonal, for example quadrangular. In particular, the field facets 222 may each have an elongated rectangular geometric shape. Only a small number of field facets 222 are shown in FIG. 3. By way of example, the field facet mirror 202 may comprise hundreds or even thousands of field facets 222. Each field facet 222 may be individually tiltable. For this purpose, an actuation element or actuator may be assigned to each field facet 222. The actuator may be a so-called Lorentz actuator.

[0100] Figure 4 shows an enlarged detail view from the optical arrangement 200 shown in Figure 2. The optical arrangement 200 includes an EUV light source 106A (not shown) emitting EUV radiation 108A, an intermediate focus 214, a field facet mirror 202, and a mirror 204 in the form of a pupil facet mirror. Mirror 204 will be referred to hereinafter as the pupil facet mirror. Mirrors 206, 208, deflection mirror 210, and housing 212 are not shown in Figure 4. Pupil facet mirror 204 is at least approximately located in an entrance pupil plane of projection system 104 or in a conjugate plane therewith.

[0101] Intermediate focus 214 is the aperture stop of EUV light source 106 A. For simplicity, the following description does not distinguish between the aperture stop for creating intermediate focus 214 and the actual intermediate focus, i.e., the opening of the aperture stop.

[0102] The field facet mirror 202 comprises a carrier or body 224 that carries a plurality of field facets 222A, 222B, 222C, 222D, 222E, 222F as described above. The field facets 222A, 222B, 222C, 222D, 222E, 222F may have the same form, but may also differ from one another, in particular the shape of their boundaries and / or the curvature of their respective optically effective surfaces 226. The optically effective surfaces 226 are mirror surfaces. The optically effective surfaces 226 serve to reflect the EUV radiation 108A towards the pupil facet mirror 204. In Figure 4, only the optically effective surface 226 of the field facet 222A is provided with a reference number. However, the field facets 222B, 222C, 222D, 222E, 222F also have such optically effective surfaces 226. The optically active surface 226 may be referred to as the field facet surface.

[0103] Only field facet 222C will be discussed below. However, all discussion regarding field facet 222C also applies to field facets 222A, 222B, 222D, 222E, and 222F. Therefore, only the portion of EUV radiation 108A that strikes field facet 222C is shown. However, the entire field facet mirror 202 is illuminated using the EUV light source 106A.

[0104] The pupil facet mirror 204 comprises a carrier or body 228 that carries a plurality of pupil facets 230A, 230B, 230C, 230D, 230E, and 230F. Each of the pupil facets 230A, 230B, 230C, 230D, 230E, and 230F has an optically effective surface 232, in particular a mirror surface. In Figure 4, only the optically effective surface 232 of pupil facet 230A is provided with a reference number. The optically effective surface 232 is suitable for reflecting EUV radiation 108A. The optically effective surface 232 can be referred to as a pupil facet surface.

[0105] To switch between different pupils, the field facet 222C can be switched between the different pupil facets 230A, 230B, 230C, 230D, 230E, 230F. In particular, for this purpose, the pupil facets 230C, 230D, 230E are assigned to the field facet 222C. This requires tilting the field facet 222C. This tilting is done mechanically by 25 mrad to 40 mrad, resulting in a deflection of the EUV radiation 108 by 50 mrad to 80 mrad, subject to the condition that the angle of incidence is equal to the angle of reflection. This angle indication relates to the half angle, i.e., is measured from the center to the edge, not from one (left) edge to the other (right) edge.

[0106] The field facet 222C is tiltable between a plurality of positions or tilt positions P1, P2, P3 using an actuator (not shown), for example a Lorentz actuator, as described above. In the first tilt position P1, the field facet 222C images the intermediate focus 214 with imaging light beam 234A (shown in dashed lines) onto pupil facet 230C. In the second tilt position P2, the field facet 222C images the intermediate focus 214 with imaging light beam 234B (shown in solid lines) onto pupil facet 230D. In the third tilt position P3, the field facet 222C images the intermediate focus 214 with imaging light beam 234C (shown in dotted lines) onto pupil facet 230E. Each pupil facet 230C, 230D, 230E images the field facet 222C onto or near the photomask 120 (not shown here).

[0107] At each of the tilt positions P1, P2, P3, the imaging light beams 234A, 234B, 234C illuminate a portion of the optically effective surface 232 of the pupil facet 230C, 230D, 230E assigned to the respective tilt position P1, P2, P3. The effect of switching between the tilt positions P1, P2, P3 to illuminate the optically effective surface 232 of the pupil facets 230C, 230D, 230E is described in more detail below with reference to Figures 5 and 6.

[0108] 5 and 6 show further diagrams of the optical device 200 shown in FIG. 4. In FIGS. 5 and 6, the EUV light source 106A, intermediate focus 214, field facets 222C, and pupil facets 230D are shown in a line for ease of illustration. However, in reality, they are arranged at a specific angle relative to one another, as shown in FIG. 2. FIG. 5 shows field facets 222C in tilted position P2, and the curvature of the optically active surface 226 is not modified and is not specifically adapted to tilt position P2. As shown in FIGS. 5 and 6, the EUV light source 106A includes a plasma source 236 that generates EUV radiation 108A and a collector 238 that focuses the EUV radiation 108A. The intermediate focus 214 and pupil facets 230D are typically circular. The pupil facets 230D can also be hexagonal.

[0109] 5 is closer to field facet 222C than to image plane 240, and the image of intermediate focus 214 is not focused on pupil facet 230D with imaging light beam 234B. There is a distance a between optically effective surface 232 of pupil facet 230D and image plane 240.

[0110] This defocusing limits the reduction in pupil filling. However, to achieve even higher resolution in the EUV lithography optical unit, the pupil filling must be further reduced. If there is a defocused image of the intermediate focus 214 at one of the pupil facets 230A, 230B, 230C, 230D, 230E, or 230F, that pupil facet must be larger than actually necessary, resulting in a larger area of ​​the pupil facet mirror 204, and therefore a larger illumination area. The ratio of the illumination area of ​​the pupil facets 230A, 230B, 230C, 230D, 230E, or 230F of the pupil facet mirror 204 to the entire optically active surface 232 (i.e., to the area that the EUV lithography apparatus 100A can maximally accommodate) is called the "pupil filling." Typically, small unfilled areas within an otherwise filled area, especially areas smaller than the area of ​​the pupil facet, are simultaneously included in the calculation of the pupil filling.

[0111] This defocused image is characterized by an area 242 illuminated by the imaging light beam 234B, which is shown hatched in Figures 7 to 9 and is relatively large. This is due to the fact that the curvature of the optically effective surface 226 of the field facet 222C is not optimized. Figure 7 shows a plan view of the optically effective surface 232 of the pupil facet 230D. The optically effective surface 232 is substantially circular or hexagonal. Therefore, the pupil facet 230D is also preferably circular or hexagonal. The area 242 of the optically effective surface 232 of the pupil facet 230D illuminated by the imaging light beam 234B corresponds in size substantially to the optically effective surface 232 itself. Therefore, the illuminated area 242 covers substantially the entire optically effective surface 232 of the pupil facet 230D.

[0112] Figure 6 shows field facet 222C in tilted position P2 after the curvature of optically effective surface 226 has been changed. In Figure 6, the curvature of optically effective surface 226 has been changed so that the distance a between optically effective surface 232 and image plane 240 is reduced. In Figure 6, distance a is zero, and optically effective surface 232 and image plane 240 overlap each other. In Figure 6, the image of intermediate focus 214 is perfectly focused on pupil facet 230D by imaging light beam 234B, and illuminated area 242 is significantly reduced in size compared to illuminated area 242 in Figure 7, as shown in Figure 8.

[0113] Figure 8 shows yet another plan view of the optically effective surface 232 of pupil facet 230D. As shown in Figure 8, the illuminated area 242 is significantly reduced compared to the illuminated area 242 shown in Figure 7 before the change in curvature of the optically effective surface 226 of field facet 222C.

[0114] As shown in yet another plan view in FIG. 9 , there is the possibility of reducing the size of pupil facets 230A, 230B, 230C, 230D, 230E, and 230F and further compacting them. As a result, the resolution of EUV lithography apparatus 100A can be increased. The reduced optically active surface 232 of pupil facets 230A, 230B, 230C, 230D, 230E, and 230F is circular or hexagonal. The hatched illumination area 242, which is the same size as in FIG. 8 , occupies a large portion of the optically active surface 232 of pupil facet 230D shown in FIG. 9 . Therefore, optimizing the curvature of the optically active surface 226 of field facet 222C allows for a reduction in the size of pupil facets 230.

[0115] It will be explained below how the curvature of the curved optically active surface 226 of the field facet 222C can be varied to always achieve focusing onto each pupil facet 230C, 230D, 230E and / or to reduce the illuminated area 242 as explained above, while at the same time achieving sufficient robustness to withstand thermal disturbances, as will be explained below.

[0116] 10 shows a schematic diagram of one embodiment of an optical system 300A. The optical system 300A is part of the optical arrangement 200 as described above. In particular, the optical arrangement 200 may include a plurality of such optical systems 300A. The optical system 300A is also part of the field facet mirror 202 as described above. The optical system 300A is the field facets 222A, 222B, 222C, 222D, 222E, 222F as described above. Therefore, the optical system 300A can also be referred to as a field facet, a field facet system, or a field facet device. Preferably, the optical system 300A is a field facet system. However, in the following, the field facet system will be referred to as the optical system 300A.

[0117] A coordinate system having a first spatial direction or x-direction x, a second spatial direction or y-direction y, and a third spatial direction or z-direction z is assigned to the optical system 300A. The spatial directions x, y, and z are positioned perpendicular to one another. The x-direction x may also be referred to as the width direction. The y-direction y may also be referred to as the length direction or longitudinal direction. The z-direction z may also be referred to as the vertical direction or thickness direction.

[0118] The optical system 300A includes an optical element 302. The optical element 302 is made from a mirror substrate or substrate. The substrate may include, in particular, copper, in particular a copper alloy, an iron-nickel alloy, such as Invar, silicon, or any other suitable material. The substrate is responsible for the mechanical properties of the optical element 302.

[0119] The optical system 302 includes a body 304 and a facet 306. The facet 306 may also be referred to as a facet or an optical facet. The facet 306 preferably has an arcuately curved or crescent-shaped geometric shape in plan view. However, the facet 306 may also have an elongated rectangular geometric shape in plan view. The body 304 and the facet 306 are embodied integrally, in particular, materially integrally. In this case, "integrally" or "integrally" means that the body and the facet 306 form a common component and are not made of different component parts. "Materially integrally" means that the body 304 and the facet 306 are manufactured entirely from the same material.

[0120] An optically effective surface 308 is provided on the front surface of the optical element 302, i.e., on the facet portion 306. The optically effective surface 308 corresponds to the optically effective surface 226 shown in FIG. 4. The optically effective surface 308 is a mirror surface. The optically effective surface 308 can be created using a coating. The optically effective surface 308 can be applied to a substrate as a coating. An abrasive layer can be provided between the substrate and the optically effective surface 308. The optically effective surface 302 is, or can be referred to as, a mirror facet.

[0121] The optically effective surface 308 or facet portion 306 has a first radius of curvature K1. The first radius of curvature K1 describes the curvature of the optically effective surface 308 in a plane extending in the y-direction y and the z-direction z. The optically effective surface 308 or facet portion 306 may further have a second radius of curvature K2. The second radius of curvature K2 is oriented perpendicular to the first radius of curvature K1. This gives the optically effective surface 308 a toroidal shape. The second radius of curvature K2 describes the curvature of the optically effective surface 308 in a plane extending in the x-direction x and the z-direction z.

[0122] During operation, the optical element 302 is exposed to EUV radiation 108A, which causes a significant energy input, particularly to the facet 306. Despite measures to achieve maximum heat dissipation, such as the use of copper as a substrate for the optical element 302, facet temperatures of up to 80°C can occur at a system temperature of 22°C. This means that the optical element 302, and in particular the facet 306, heats up by up to 60 K during operation compared to a non-operating system. The temperature increase in the optical element 302 leads to an expansion of the body 304 and the facet 306, including the photoactive layer that forms the optically active surface 308. Therefore, the actuation element or actuator that deforms the facet 306 is also subjected to temperature changes.

[0123] Actuating elements based on piezoelectric ceramics, such as lead zirconate titanate (PZT), known as piezo elements, have a negative coefficient of thermal expansion. This can lead to a change in the length of the piezo element relative to the body 304 when the optical element 302 is heated uniformly, resulting in a corresponding change in the displacement of the piezo element. To achieve a desired displacement of the optically active surface 308, a corresponding displacement of the piezo element is required along with a corresponding mechanical transmission ratio. In this case, the desired displacement of the optically active surface 308 is greater than the corresponding displacement of the piezo element due to the transmission ratio. For example, if the substrate material is copper and there is a uniform temperature change of 10 K, the resulting displacement error can be 30% to 40%, particularly 32% to 38%, particularly 33% to 37%, and especially 35% of the nominal displacement. From the above example, it is clear that maximum passive temperature compensation is highly desirable.

[0124] A gap 310 is provided between the facet 306 and the body 304. The facet 306 has two lever arms 312, 314 that are integrally, in particular materially, connected to the facet 306 via connection regions 316, 318. The gap 310 extends between the facet 306 and the lever arms 312, 314. The connection regions 316, 318 constitute cross-sectional narrowings provided between the facet 306 and the lever arms 312, 314, respectively.

[0125] The lever arms 312, 314 are furthermore integrally, in particular materially integrally, connected to the body 304 via joints 320, 322. The joints 320, 322 are embodied as so-called flexures. In this case, "flexure" is understood to mean a region of a component that allows relative movement between two rigid regions by bending. The joints 320, 322 are elastically deformable. In this case, a first joint 320 and a second joint 322 are provided.

[0126] The first joint 320 allows movement of the facet 306 only about an axis parallel to the x-direction x. The second joint 322 similarly allows movement of the facet 306 about an axis parallel to the x-direction x. Furthermore, unlike the first joint 320, the second joint 322 also allows movement parallel to or in the y-direction y. To this end, the second joint 322 is designed to be flexible. The second joint 322 can be moved from an unflexed state shown in FIG. 10 to a flexed state (not shown) in which the second joint 322 flexes in an S-shape. Deformation of the second joint 322 can be used to compensate for constraints acting on the facet 306 in the y-direction y as a result of thermal expansion of the facet 306. If not compensated for, these constraints in the y-direction y could result in bending of the facet 306 in the z-direction z and, therefore, in the direction of the intended curvature change.

[0127] The body 304 includes arm portions 324, 326. The arm portion 324 is assigned to the lever arm 312. A gap 328 is provided between the arm portion 324 and the lever arm 312. The arm portion 326 is assigned to the lever arm 314. A gap 330 is provided between the arm portion 326 and the lever arm 314.

[0128] The optical system 300A includes actuating elements 332, 334, 336, and 338. The actuating elements 332, 334, 336, and 338 can also be referred to as actuators. The actuating elements 332, 334, 336, and 338 are piezo actuating elements or piezo actuators. However, any other actuators can be used for the actuating elements 332, 334, 336, and 338. A temperature sensor 340, 342, 344, and 346 is assigned to each actuating element 332, 334, 336, and 338. The temperature sensors 340, 342, 344, and 346 can be used to detect the temperature of each actuating element 332, 334, 336, and 338.

[0129] The actuating elements 332, 334, 336, 338 are arranged in pairs. In this case, the actuating elements 332, 334 form a first actuating element pair 348 assigned to the first joint part 320, and the actuating elements 336, 338 form a second actuating element pair 350 assigned to the second joint part 322. A connecting element 352, 354 is assigned to each actuating element pair 348, 350. The first connecting element 352 connects the actuating elements 332, 334 of the first actuating element pair 348 to each other. The second connecting element 354 connects the actuating elements 336, 338 of the second actuating element pair 350 to each other. The first actuating element pair 348 and the first connecting element 352 are housed in a first cutout 356 in the main body 304. The second actuation element pair 350 and the second connecting element 354 are received in a second cutout 358 in the body 304. The cutouts 356, 358 are connected to the cavity 310 via the cavities 328, 330.

[0130] Additionally, the optical system 300A includes temperature sensors 360, 362, 364, 366 that can be positioned in corresponding cutouts in the body 304. Additionally, the optical system 300A can include displacement measurement sensors 368, 370 that can be used to detect deformation of the facet 306.

[0131] The function of optical system 300A is explained below. Facet 306 is connected to body 304 via lever arms 312, 314 located at both ends of facet 306, actuating element pairs 348, 350, and respective connecting elements 352, 354. Facet 306 is further connected to body 304 via joints 320, 322. To actuate facet 306, for example, actuating element 334 on the left side of facet 306 in the orientation of Figure 10 is controlled to be extended, i.e., along the z-direction z.

[0132] In the orientation of FIG. 10 , the actuating element 332 is pulled downward, i.e., in the direction opposite to the z-direction z, via the first connecting element 352. At the same time, the actuating element 332 is controlled to contract in the z-direction z. As a result, the lever arm 312 is also pulled downward in the orientation of FIG. 10 . As a result, a clockwise bending moment B1 acts on the facet 306. The bending moment B1 acts around an axis arranged parallel to the z-direction z. When the actuating elements 336, 338 on the right side of the facet 306 in the orientation of FIG. 10 are similarly actuated, but in the opposite direction, this leads to a cylindrical deformation of the optically active surface 308 along the entire length of the facet 306. The actuating elements 336, 338 apply a bending moment B2 to the facet 306 that is opposite to the bending moment B1.

[0133] When all of the components of the optical system 300A are uniformly heated, the two actuating elements 332, 334, 336, and 338 of each actuating element pair 348 and 350 contract due to their negative thermal expansion coefficients. However, because the actuating elements 332, 334, 336, and 338 are arranged in pairs, this contraction only displaces each connecting element 352 and 354 upward in the orientation shown in FIG. 10 , i.e., in the z-direction. Because the connecting elements 352 and 354 are not connected to the body 304, no force is generated on each lever arm 312 and 314. Therefore, despite the thermal contraction of the actuating elements 332, 334, 336, and 338, the facet 306 does not deform.

[0134] In the case of uneven heating of the body 304 and facet 306, a higher temperature of the facet 306 relative to the body 304 will result in a constraint force acting horizontally on the facet 306, i.e., in the y-direction. The facet 306 is not flat and typically has a radius of curvature machined into its upper and lower surfaces. The horizontal constraint force will result in the facet 306 bending downward in the orientation shown in FIG. 10, which can lead to changes in the radii of curvature K1, K2 relevant to optical imaging. The flexible second joint 322 can be used to prevent this bending, as it allows for compensation for longitudinal expansion of the facet 306.

[0135] Both joints 320, 322 are designed to provide minimal stiffness against rotation about an axis parallel to the x-direction. The first joint 320 is designed to have maximum stiffness against forces in the horizontal direction, i.e., the y-direction. In contrast, the second joint 322 is designed to be significantly longer in the vertical direction, i.e., the z-direction, than the first joint 320, resulting in the second joint 322 having lower horizontal stiffness than the first joint 320. When the facet 306 and the body 304 undergo different expansions, the difference in length between the facet 306 and the body 304 is compensated for by the S-shaped deformation of the second joint 322. The horizontal constraint forces, and therefore the bending of the facet 306, are significantly reduced.

[0136] Heat input to the optical system 300A is mainly via the facets 306, while heat removal is via the base of the body 304. Therefore, a non-uniform temperature distribution occurs in the optical system 300A. Depending on the temperature distribution in the optical system 300A, the above-mentioned temperature compensation may only be partially effective. For this reason, it is advantageous to detect the temperature distribution in the optical system 300A by temperature sensors 340, 342, 344, 346, 360, 362, 364, 366, and therefrom detect the deformation state of the optical system 300A by an external control unit 372, calculate corresponding correction signals, and apply them to the actuating elements 343, 334, 336, 338.

[0137] The temperature sensors 340, 342, 344, 346, 360, 362, 364, 366 preferably detect the temperature of the actuating elements 332, 334, 336, 338, respectively, and of the areas of the body 304 and lever arms 312, 314 associated with the perturbation effect. Embodiments of the temperature sensors 340, 342, 344, 346, 360, 362, 364, 366 can be NTC sensors (negative temperature coefficient, NTC), thermocouples, platinum sensors, or thermopiles. The thermopiles allow for positioning the measuring element on the body 304 with non-contact temperature measurement of the facet 306.

[0138] Alternatively or additionally, the actual deformation of the facet 306 can be detected using displacement measuring sensors 368, 370 and correction signals for the actuating elements 332, 334, 336, 338 can be calculated therefrom using an external control unit 372. This procedure has the advantage that further errors, such as for example hysteresis of the actuating elements 332, 334, 336, 338, mechanical drift and creep effects of the actuating elements 332, 334, 336, 338 and the connecting elements 352, 354, or electrical drift of the control unit 372, can be detected and compensated for.

[0139] If displacement measuring sensors 368, 370 are provided, it is advantageous to arrange at least two of them at the same distance from the outer edge of the facet 306. Furthermore, it is advantageous to choose a displacement measuring system that is as insensitive as possible to temperature changes. The displacement measurement can be performed directly by a change in the distance between the facet 306 and the body 304, or by extension of the facet 306 or the lever arms 312, 314.

[0140] Advantageous embodiments of the direct displacement measurement sensors 368, 370 can be capacitive or inductive sensors due to the severely limited construction space. For minimum temperature sensitivity, the use of confocal optical sensors is advantageous. For maximum error compensation, the use of actuating elements 332, 334, 336, 338 in a closed control loop taking into account correction signals from the displacement and temperature measurements is advantageous.

[0141] 11 shows a schematic diagram of yet another embodiment of optical system 300B. The structure and function of optical system 300B substantially corresponds to that of optical system 300A. Only the differences between optical systems 300A and 300B are described below.

[0142] In order to reduce the installation space that must be occupied in the vertical direction in optical system 300B, actuating elements 332, 334, 336, 338 are oriented horizontally rather than vertically. Furthermore, lever arms 312, 314 are provided on the sides of facet 306. Lever arms 312, 314 are connected to body 304, particularly arms 324, 326, and couplings 378, 380, by means of joints 320, 322, 374, 376. Actuating elements 332, 336 are attached to couplings 378, 380. Joints 320, 322, 374, 376 are preferably embodied as flexures.

[0143] The aforementioned length compensation feature of the horizontal facets 306 is not present or kinematically possible in this exemplary embodiment of optical system 300B. Temperature sensors 340, 342, 344, 346, 360, 362, 364, 366 and displacement measurement sensors 368, 370 are positioned similarly to optical system 300A shown in FIG.

[0144] 12 shows a schematic diagram of yet another embodiment of optical system 300C. The structure and function of optical system 300C substantially corresponds to that of optical system 300A. Only the differences between optical systems 300A and 300C are described below.

[0145] Unlike optical system 300A, optical system 300C does not include a pair of vertically arranged actuating elements 348, 350, but rather includes individual actuating elements 332, 336 that are arranged horizontally rather than vertically. Furthermore, the actuating elements 332, 336 are designed as shear actuating elements, and in particular as shear piezo actuators, which means that the actuating elements 332, 336 do not change length when energized, but are instead suitable to bend as shown by the arrows in FIG. 12 .

[0146] The facet 306 is coupled to the body 304 via lever arms 312, 314 and joints 320, 322 as previously described. In this case, the second joint 322 allows for compensation of thermal length changes of the facet 306, as described with reference to optical system 300A. That is, if the facet 306 and the body 304 undergo different expansions, the S-shaped deformation of the second joint 322 again compensates for the difference in length.

[0147] The actuating elements 332, 336 are operatively connected to the lever arms 312, 314 via decoupling joints 382, ​​384. Each decoupling joint 382, ​​384 comprises two interconnected leaf springs that are flexible in the horizontal direction, i.e., in the y-direction y, and therefore practically impossible or even impossible to transmit forces in the y-direction y. However, force transmission in the vertical direction, i.e., in the z-direction z, is possible to deform the facet 306. The decoupling joints 382, ​​384 also provide thermal isolation. Therefore, the decoupling joints 382, ​​384 can also be referred to as thermal decoupling.

[0148] The use of shear piezo actuators is advantageous for compensating for displacement errors when all components of the optical system 300C are subjected to uniform temperature changes. With this type of actuation, thermal expansion occurs perpendicular to the active surface, thus allowing for effective and incidental motion to be decoupled from each other.

[0149] To actuate facet 306, for example, actuation element 332, located on the left side in the orientation of FIG. 12, is controlled so that the end facing decoupling joint 382 in the orientation of FIG. 12 moves downward, i.e., against the z-direction z. This movement is transmitted as a downward force to lever arm 312 via decoupling joint 382. As a result, lever arm 312 is also pressed down, applying a clockwise bending moment B1 to facet 306, similar to the bending moment described above. When actuating element 336 on the right side in the orientation of FIG. 12 synchronously, this leads to a cylindrical deformation of facet 306 along its entire length.

[0150] If all the component parts are heated, either uniformly or non-uniformly, the two actuating elements 332, 336 will contract due to their negative thermal expansion coefficients. However, this occurs perpendicular to the effective direction of the corresponding actuating element 332, 336, i.e., in the y-direction. However, due to the presence of the decoupling joints 382, ​​384, no force acts on the lever arms 312, 314. Therefore, there is no deformation of the facet 306. Therefore, the optical system 300C is also not affected by temperature changes.

[0151] Also in optical system 300C, it is advantageous to use a number of temperature sensors 340, 344, 360, 362 to detect the temperature distribution in optical system 300C, and therefrom the deformation state of facet 306 is detected by the external control unit 372 described above, which calculates corresponding correction signals and applies them to actuating elements 332, 336. Displacement measuring sensors 368, 370 are arranged in the same way as in optical system 300A.

[0152] 13 shows a schematic diagram of yet another embodiment of an optical system 300D. The structure and function of the optical system 300D substantially corresponds to that of the optical system 300C. Only the differences between the optical systems 300C and 300C are described below.

[0153] Unlike optical system 300C, in optical system 300D, the actuating elements 332, 336 are arranged vertically, not horizontally. The actuating elements 332, 336 are designed as shear actuating elements, in particular as shear piezo actuators. The actuating elements 332, 336 are operatively connected to the lever arms 312, 314 by means of couplings 378, 380. The couplings 378, 380 preferably only allow force transmission in the horizontal direction, i.e., in the y-direction. The previously described length compensation function of the horizontal facet 306 is not provided or kinematically possible in this exemplary embodiment of optical system 300D. The temperature sensors 340, 344, 360, 362 and the displacement measurement sensors 368, 370 are arranged similarly to optical system 300C.

[0154] 10 to 13 show embodiments of optical systems 300A, 300B, 300C, and 300D in which the curvature of the facet 306, and therefore of the optically active surface 308, can advantageously be set to a constant radius of curvature over the length of the facet 306. In these embodiments of optical systems 300A, 300B, 300C, and 300D, the kinematic arrangement is optimized to minimize the deviation of the radii of curvature K1, K2 over the length of the facet 306 from their target values. For this purpose, respective bending moments B1, B2 of equal magnitude but opposite rotational sense are introduced at each end of the facet 306.

[0155] However, in certain applications of the optical systems 300A, 300B, 300C, and 300D, it may be advantageous to set different, independent radii of curvature for different lengths of the facets 306. This may be necessary, for example, to be able to compensate for inaccuracies or errors during the fabrication of the optically active surface 308. The facets 306 are embodied relatively thin. As a result, when polishing the optically active surface 308, the forces acting on the facets 306 during the polishing process may result in deformations of the facets 306, which may affect the accuracy of the polishing process. This may result in wavy deviations between the target cylindrical or toric contour and the actual contour that is actually fabricated.

[0156] 14 shows a schematic diagram of yet another embodiment of optical system 300E. Only the differences between optical systems 300A and 300E are described below.

[0157] Optical system 300E includes actuating elements 332, 334, 336, and 338, which, unlike optical system 300A, are embodied as shear actuating elements, specifically as shear piezo actuators. In the orientation of Figure 14, these actuating elements 332, 334, 336, and 338 can bend up and down, as indicated by the arrows. Actuating elements 332, 334, 336, and 338 are arranged side-by-side or front-to-back when viewed in the y-direction.

[0158] A lever arm 386, 388, 390, 392 is assigned to each actuating element 332, 334, 336, 338. Each lever arm 386, 388, 390, 392 is firstly connected to the body 304 and secondly connected to the facet 306 using two joints 394, 396, as shown based on lever arm 386. The joints 394, 396 are provided at the end sides of each lever arm 386, 388, 390, 392, respectively. The joints 394, 396 are flexures.

[0159] The actuating elements 332, 334, 336, 338 are operatively connected to the lever arms 386, 388, 390, 392 via decoupling joints 398, 400, 402, 404. In this case, the function of the decoupling joints 398, 400, 402, 404 corresponds to that of the previously described decoupling joints 382, ​​384. A displacement measuring sensor 406, 408, 410, 412 is assigned to each lever arm 386, 388, 390, 392.

[0160] The function of optical system 300E is explained below. The downward deflection of actuating elements 332, 334, 336, 338, for example in the orientation of FIG. 14, intensifies the downward pulling force exerted on facet 306 via respective lever arms 386, 388, 390, 392. Facet 306 is supported relative to body 304 by joints 320, 322. The force that can be exerted by each actuating element 332, 334, 336, 338 results in a change in the curvature of facet 306.

[0161] By varying the control of the actuating elements 332, 334, 336, 338, multiple curvatures of the facet 306 can be set. As in the optical system 300A, thermal effects are compensated for by the second joint 322 and the decoupling joints 398, 400, 402, 404. The temperature sensors 340, 342, 344, 346, 360, 362 are similarly arranged. Advantageously, each actuating element 332, 334, 336, 338 is assigned a displacement measuring sensor 406, 408, 410, 412 to determine the local deformation.

[0162] 15 shows a schematic diagram of yet another embodiment of optical system 300F. Only the differences between optical systems 300E and 300C are described below.

[0163] Optical system 300F includes actuating elements 332, 334, 336, 338 that are embodied as linear actuating elements rather than shear actuating elements. That is, actuating elements 332, 334, 336, 338 can extend and retract along their longitudinal axis, i.e., in the y-direction. As with optical system 300E, a lever arm 386, 388, 390, 392 is assigned to each actuating element 332, 334, 336, 338, and each is operatively connected to body 304 using joint 394 and to facet 306 using joint 396. Actuating elements 332, 334, 336, 338 can exert tensile or compressive forces on lever arms 386, 388, 390, 392.

[0164] By means of the corresponding lever arms 386, 388, 390, 392, the change in length of each actuating element 332, 334, 336, 338 is converted into a tensile or compressive force on the facet 306 in the vertical direction, i.e. in and against the z-direction z. Here too, by various control of the actuating elements 332, 334, 336, 338, multiple curvatures of the facet 306 can be set. Compensation for thermal interference effects, as in the case of optical system 300E, is not possible here. The temperature sensors 360, 362 and the displacement measuring sensors 406, 408, 410 are arranged according to the embodiment of optical element 300E shown in FIG. 14. As already explained with reference to optical element 300E, temperature sensors (not shown) can also be assigned to the actuating elements 332, 334, 336, 338.

[0165] 16 shows a schematic diagram of yet another embodiment of optical system 300G. Only the differences between optical systems 300F and 300G are described below.

[0166] Optical system 300G corresponds to optical system 300F, but differs in that in optical system 300G, joints 320, 322 are not provided on the periphery of facet 306, but are shifted inward when viewed in the y direction. Optical system 300G also has a temperature sensor and a displacement measurement sensor (not shown).

[0167] 17 shows a schematic diagram of yet another embodiment of optical system 300H. Only the differences between optical systems 300G and 300H are described below.

[0168] Unlike optical system 300G, optical system 300H has only two actuating elements 332, 334 instead of four. Furthermore, joints 320, 322 are provided at the periphery of facet 306. Optical system 300H also has temperature and displacement measurement sensors (not shown).

[0169] In all of the above embodiments of the optical systems 300A, 300B, 300C, 300D, 300E, 300F, 300G, and 300H, the body 304 and the facets 306 can be manufactured integrally or monolithically, i.e., from one raw material without additional joints. Therefore, in these embodiments of the optical systems 300A, 300B, 300C, 300D, 300E, 300F, 300G, and 300H, it is possible to use the same material for the kinematics, such as the joints 320 and 322 and the facets 306. Copper, silicon, silicon carbide (SiSiC), or cordierite are suitable materials.

[0170] Alternatively, the body 304 and the facets 306 can be manufactured in separate ways and these parts can be connected to one another by suitable joining methods, such as at the joints 320, 322. This is particularly advantageous, since the different functional requirements for both components make different manufacturing processes advantageous. By way of example, one requirement for the facets 306 is minimal inherent stresses. This can be achieved in particular by milling or erosion followed by a heat treatment. By way of example, one requirement for the body 304 is to produce as precisely as possible the microstructures required, for example, for the lever arms 312, 314 or the joints 320, 322. Advantageously, said structures can be obtained by erosion, etching or additive manufacturing followed by different heat treatments.

[0171] Therefore, in the above case, a method for connecting the body 304 and the facet 306, for example, at the joints 320, 322, is required. The facet 306 can be connected to the body 304 by, for example, welding, optical contact bonding, soldering, adhesive bonding, diffusion welding, electron beam welding, laser welding, or reactive bonding. In these embodiments of connection at the joints 320, 322, inherent stresses or deformations at the joints may remain in the optically active surface 308 and deteriorate its optical properties. Correction of surface defects of the optically active surface 308 after the connection is made is advantageous for this purpose. This can be done by mechanical, electrochemical, or electron beam optical methods.

[0172] In all of the above embodiments of the optical systems 300A, 300B, 300C, 300D, 300E, 300F, 300G, and 300H, piezo actuating elements or piezo actuators are proposed as actuating elements 332, 334, 336, and 338. However, as an alternative, the facets 306 could also be actuated by magnetic, magnetostrictive, pneumatic, or hydraulic drive. However, the use of piezo actuators is particularly advantageous because of their very good force / installation space ratio. This means that large deformations of the optically active surface 308 can be achieved within the very limited installation space available. As a further advantage, due to the small size of the piezo actuators, the width of the facets 306 can be chosen to be very narrow. As a result, a large number of optical systems 300A, 300B, 300C, 300D, 300E, 300F, 300G, 300H with actuatable facets 306, and therefore light channels, can be arranged in the beam shaping and illumination system 102. This is advantageous for the optical performance of the beam shaping and illumination system 102.

[0173] Yet another advantage is that, as mentioned above, the small size of the actuating elements 332, 334, 336, 338 in the form of piezoelectric actuators allows them to be positioned to compensate for thermal interference effects. Furthermore, unlike other actuators, piezoelectric actuators require very little power during steady-state or quasi-steady-state operation. Due to their high internal resistance, the power required for a piezoelectric actuator to maintain its position is negligible and is determined primarily by the external wiring. Piezo actuators can also maintain their position after power is removed. This is well-suited to reducing power consumption, and therefore self-heating, and reducing the thermally induced errors mentioned above.

[0174] 18-20 show highly simplified schematic diagrams of embodiments of facet 306. FIG. 18 shows a side view of facet 306. FIG. 19 shows a plan view of facet 306. FIG. 20 shows a front view of facet 306. In simplified terms, optical systems 300A, 300B, 300C, 300D, 300E, 300F, 300G, and 300H are based on the principle of motion of a curved beam forming facet 306 and supported on both sides to introduce bending moments B1 and B2 on both sides. FIG. 18 shows a curved beam in the form of facet 306 in an undeformed state, shown by solid lines, and in a deformed state, shown by dashed lines. In the deformed state, the facet is designated by reference numeral 306'.

[0175] According to a possible embodiment, a facet 306 that is straight in the y-direction y (the long axis of the facet 306) corresponds to a straight curved beam. The facet 306 has a width b and a height h that are both constant when viewed in the y-direction y. Such a facet 306 with a homogeneous cross section Q deforms only in the plane extending in the y-direction y and the z-direction z when opposite bending moments B1, B2 are introduced on both sides. As a result, the surface normal or normal vector N of the optically active surface 308 rotates only around the x-direction x (the short axis of the facet 306) depending on its position on the facet 306 in the y-direction y.

[0176] 21 to 24 show greatly simplified schematic diagrams of yet another embodiment of facet 306. FIG. 21 shows a side view of facet 306. FIG. 22 shows a plan view of facet 306. FIG. 23 shows a cross-section of facet 306 according to section line AA in FIG. 21. FIG. 24 shows a cross-section of facet 306 according to section line BB in FIG. 21. In certain applications, it may be advantageous to give facet 306 a crescent-shaped or arc-shaped configuration in plan view. In this case, facet 306 corresponds to a curved beam. Again, facet 306 has a uniform cross-section Q.

[0177] When opposing bending moments B1 and B2 as described above are applied to such a crescent-shaped facet 306, the facet 306 also deforms primarily in a plane extending in the y-direction y and z-direction z. However, the facet 306 also twists in the y-direction y. This twist is zero at both ends of the facet 306 and is greatest at the center of the facet 306.

[0178] As a result, the normal vector N of the optically effective surface 308 rotates around the x-direction (x) and around the y-direction (y). The rotation around the y-direction (y) is maximum at the center of the facet 306, as shown in Figure 24. In contrast, the rotation around the x-direction (x) is zero at the center of the facet 306 and maximum at both ends of the facet 306. Both rotations have a fixed relationship to each other that is determined geometrically.

[0179] Figures 25-28 show greatly simplified schematic diagrams of further embodiments of facet portion 306. In the plan view shown in Figure 25, facet portion 306 or optically effective surface 308 is curved in an arc or crescent shape. Figure 26 shows a cross-section of facet portion 306 taken along section line CC in Figure 25. Figure 27 shows a cross-section of facet portion 306 taken along section line DD in Figure 25. Figure 28 shows a cross-section of facet portion 306 taken along section line EE in Figure 25. In particular applications, it is advantageous to minimize the rotation of normal vector N about the y-direction y.

[0180] This can be achieved by deliberately modifying the stiffness of the facets 306. In this case, "stiffness" should be understood to mean the resistance of the facets 306, or the body in general, to elastic deformation due to forces or moments. In particular, "stiffness" should be understood to mean the torsional stiffness of the facets 306, i.e., the stiffness to withstand a torsional moment that twists or torsions the facets 306. The stiffness of a component depends firstly on the elastic properties of the material, such as Young's modulus, and secondly on the geometry of the deformed component.

[0181] The stiffness of the facet 306 can thus be varied by varying the Young's modulus of the material used for the facet 306. The aforementioned variation in Young's modulus can be achieved by using a monolithically manufactured base body made of two or more different materials. Said base body forms the facet 306 or the facet 306 is manufactured from the base body. The base body may also include the main body 304. Such a base body can be manufactured from different metal powders by welding, plating, or preferably by additive manufacturing, in particular 3D printing. Additive manufacturing, in particular, makes it possible to manufacture hybrid components with a continuous transition between two different materials, for example, between copper and steel. Thus, the facet 306 may have a hybrid construction, in particular made of steel and copper.

[0182] However, it is particularly preferred to vary the geometry of the facet 306, in particular the cross section Q. However, there is also the possibility of varying both Young's modulus and cross section Q. According to an advantageous embodiment, the facet 306 comprises a trapezoidal cross section Q, the width b1 of which of its upper surface, i.e. the optically active surface 308, is constant or variable. The width b2 of its lower surface is also variable, but is advantageously narrower at all points of the facet 306 than the upper surface. The height h of the cross section Q can likewise be selected to be variably.

[0183] For a constant cross section Q, the polar section modulus of the facet 306 in the x-direction x and y-direction y is constant along the entire length of the facet 306. The "polar section modulus" is a measure of the resistance of the facet 306, or more generally, a beam, to the development of internal stresses under load. With a variable cross section Q as described above, the polar section modulus can be influenced in a targeted manner. This method is not limited to trapezoidal cross sections Q, but can be applied to any cross section with at least two variable cross-sectional parameters, such as width and height. Rectangular, triangular, semi-elliptical, truncated rectangular, or other more complex cross sections Q are, for example, conceivable.

[0184] The facet portion 306 includes a first end region 414 and a second end region 416. Bending moments B1 and B2 are introduced into the end regions 414 and 416. A plane of symmetry E1 is provided midway between the end regions 414 and 416, with the facet portion 306 having mirror symmetry with respect to it. The cross section shown in FIG. 27 is aligned with the plane of symmetry E1. The plane of symmetry E1 extends in the x-direction x and the z-direction z, or is aligned parallel to a plane extending in the x-direction x and the z-direction z.

[0185] The facet portion 306 has longitudinal directions L1 and L2. The longitudinal directions L1 and L2 are oriented from the corresponding end regions 414 and 416 toward the plane of symmetry E1. In this case, the longitudinal directions L1 and L2 each have an arcuate curved profile. For example, the stiffness of the facet portion 306 decreases from the end regions 414 and 416 toward the plane of symmetry E1 when viewed along the longitudinal directions L1 and L2.

[0186] By way of example, this can be achieved by having cross section Q or the cross-sectional area of ​​cross section Q be smallest at the plane of symmetry E1 and increasing towards the end regions 414, 416. However, the stiffness profile or gradient, i.e., the stiffness profile along each longitudinal direction L1, L2, is symmetrical with respect to the plane of symmetry E1. That is, cross section Q along section line DD shown in FIG. 25 is smaller than cross section Q along section lines CC and EE. The same is true for the polar section modulus.

[0187] Figure 29 shows the error profile of the normal vector N over the length of the facet 306 for a particular change in cross section Q. In this case, the y-direction y in mm is plotted on the horizontal axis. The error angle θ in μrad is plotted on the vertical axis. As an example, consider a 90 mm long facet 306 (Figure 24) with an overall rectangular cross section Q of width b and height h of 4 mm.

[0188] Curve 418 represents the gradient of normal vector N on plane E2 extending in the y-direction y and z-direction z. Curve 420 represents the gradient of normal vector N on plane E2 extending in the x-direction x and z-direction z. Curve 422 represents the gradient of normal vector N obtained from curves 418 and 420. As is clear from curve 422, the error angle θ of the composite normal vector N varies from 5 μrad to 19 μrad.

[0189] Unlike Fig. 29, Fig. 30 shows the error profile of the normal vector M of an 80 mm long facet 306 with a variable height h (Fig. 26), a constant upper surface width b1 (Fig. 26) of cross section Q, and a variable lower surface width b2 (Fig. 26). For the specific variable cross section Q selected according to the above method, the resultant error of the resultant normal vector N can be completely eliminated, as shown based on curve 424. That is, deformation of facet 306 occurs only in plane E2 extending in the y-direction y and z-direction z. Plane E2 is oriented perpendicular to the plane of symmetry E1.

[0190] Returning now to Figure 4, the optical device 200 further comprises a measurement unit 244, shown in side view (left) and top view (right) in Figure 4. The function of the measurement unit 244 is explained below. Piezo actuators can exhibit various long-term creep and drift effects in a form that cannot be recorded by the measurement system described above due to their own creep behavior.

[0191] Such effects may be, for example, creep due to stress relaxation of the adhesive connection between each actuating element 332, 334, 336, 338 and the body 304, drift of the actuating elements 332, 334, 336, 338 due to charge loss, drift of the charge amplifier, and / or material creep of the facet 306 or body 304. These creep effects may lead to deviations of the actual curvature from the target curvature specified by the control, and may occur over hours, days, or weeks depending on the creep effect and creep rate.

[0192] Advantageously, a measurement unit 244 measures these effects and obtains correction signals. The EUV radiation 108A in the beam path 216 is incident on pivotable field facets 222A, 222B, 222C, 222D, 222E, 222F, which have changeable curvatures. Depending on their switching positions, these reflect the EUV radiation to different pupil facets 230A, 230B, 230C, 230D, 230E, 230F. The apparatus shown in Figure 4 includes a measurement unit 244 that is independent of the pupil facet mirror 204.

[0193] To measure the curvature of the field facets 222A, 222B, 222C, 222D, 222E, 222F, one of the field facets 222A, 222B, 222C, 222D, 222E, 222F, for example field facet 222C, is tilted so that the EUV radiation 108 reflected therefrom is incident on the measurement unit 244. The measurement unit 244 then detects the size of the light spot, preferably in multiple spatial directions, in particular in length and width. Correction signals for the actuating elements 332, 334, 336, 338 related to the facet curvature are calculated from the size of the light spot by a control unit (shown). Using a closed loop, it is now possible to adjust the light spot to a minimum size and thus set the best focus by iterative optimization. This calibration is performed sequentially on all field facets 222A, 222B, 222C, 222D, 222E, 222F and can be performed on each field facet 222A, 222B, 222C, 222D, 222E, 222F over a period of hours, days or weeks depending on creep effects and creep rates.

[0194] By way of example, the measurement unit 244 can be designed as a CCD (charge-coupled device) sensor. In one embodiment, the pupil facets 230A, 230B, 230C, 230D, 230E, 230F of the pupil facet mirror 204 are arranged in a circular area. In this case, arranging the measurement unit 244 in the center of this area is advantageous, since this minimizes the change in the switching angle of the field facets 222A, 222B, 222C, 222D, 222E, 222F that illuminate the measurement unit 244, thereby achieving the steepest possible angle of incidence of light from all field facets onto the measurement unit. Alternatively, the measurement unit 244 can be arranged independently next to the pupil facet mirror 204, as shown in FIG. 4, or at the edge of the pupil facet mirror 204 (not shown).

[0195] Although the present invention has been described with reference to exemplary embodiments, it can be varied in many ways. [Explanation of symbols]

[0196] 100A EUV lithography equipment 100B DUV lithography equipment 102 Beam shaping and illumination system 104 Projection system 106A EUV light source 106B DUV light source 108A EUV radiation 108B DUV radiation 110 Mirror 112 Mirror 114 Mirror 116 Mirror 118 Mirror 120 Photomask 122 Mirror 124 wafers 126 Optical axis 128 lens elements 130 Mirror 132 Medium 200 Optical equipment 202 Mirror / Field Facet Mirror 204 Mirror / Eye Faceted Mirror 206 Mirror 208 Mirror 210 Deflecting Mirror 212 Housing 214 intermediate focus 216 Beam Path 218 Object plane 220 Object field of view 222 facets / field of view facets 222A Field Facet 222B Field Facets 222C Field Facets 222D field facets 222E Field of View Facets 222F Field of View Facets 224 Main Unit 226 Optically Effective Surface 228 Main Unit 230A pupil facet 230B pupil facet 230C pupil facet 230D pupil facet 230E pupil facet 230F pupil facet 232 Optically Effective Surface 234A Imaging light beam 234B Imaging light beam 234C Imaging light beam 236 Plasma Source 238 Collector 240 imaging plane 242 Area 244 measurement units 300A Optics / Field Facet System 300B Optics / Field Facet System 300C Optics / Field Facet System 300D Optics / Field Facet System 300E Optics / Field Facet System 300F Optics / Field Facet System 300G Optics / Field Facet System 300H Optics / Field Facet System 302 Optical Elements 304 Main Unit 306 Facet section 306' Facet section 308 Optically Effective Surface 310 void 312 Lever arm 314 Lever Arm 316 Connection Area 318 Connection Area 320 Joint 322 Joint 324 Arm 326 Arm 328 void 330 void 332 Actuating element 334 Actuating element 336 Actuating element 338 Actuating element 340 Temperature Sensor 342 Temperature Sensor 344 Temperature Sensor 346 Temperature Sensor 348 Actuating Element Pair 350 actuation element pairs 352 Connection Elements 354 Connection Elements 356 Notch 358 Notch 360 Temperature Sensor 362 Temperature Sensor 364 Temperature Sensor 366 Temperature Sensor 368 Displacement Measurement Sensor 370 Displacement measurement sensor 372 Control Unit 374 Joint 376 Joint 378 Joint 380 Joint 382 Decoupling joint 384 Decoupling fittings 386 Lever Arm 388 Lever Arm 390 Lever Arm 392 Lever Arm 304 Joint 306 Joint 398 Decoupling Fittings 400 Decoupling Fittings 402 Decoupling joint 404 Decoupling fitting 406 Displacement measurement sensor 408 Displacement measurement sensor 410 Displacement measurement sensor 412 Displacement measurement sensor 414 End area 416 End area 418 Curve 420 curve 422 Curve 424 Curve b Width b1 width b2 width B1 bending moment B2 bending moment E1 symmetry plane E2 plane h height K1 radius of curvature K2 radius of curvature L1 Longitudinal direction L2 Longitudinal direction M1 mirror M2 mirror M3 mirror M4 mirror M5 mirror M6 mirror N normal vectors P1 tilt position P2 tilt position P3 tilt position Q cross section xx direction yy direction zz direction θ error angle

Claims

1. A field facet system (300A, 300B, 300C, 300D, 300E, 300F, 300G, 300H) for a lithographic apparatus (100A, 100B), comprising: an optical element (302) including a body (304) and an elastically deformable facet (306) connected to the body (304) and having a light-reflective, optically active surface (308); a plurality of actuation elements (332, 334, 336, 338) for deforming the facet portion (306) to change the radius of curvature (K1, K2) of the optically effective surface (308); the actuating elements (332, 334, 336, 338) are operatively connected to the facets (306) in a manner that thermal deflection of the actuating elements (332, 334, 336, 338) is decoupled from the facets (306) such that the radii of curvature (K1, K2) are not affected by thermal deflection of the actuating elements (332, 334, 336, 338); At least some of the actuating elements (332, 338) are coupled to the facets (306) using lever arms (312, 314); A field facet system, wherein a first lever arm (312) of the lever arms (312, 314) is articulatedly connected to the body (304) by means of a first joint (320) that allows only rotational movement of the first lever arm (312) around a first spatial direction (x), and a second lever arm (314) of the lever arms (312, 314) is articulatedly connected to the body (304) by means of a second joint (322) that allows rotational movement of the second lever arm (314) around the first spatial direction (x).

2. 2. The field facet system of claim 1, wherein the second joint portion (322) further allows translational movement of the second joint portion (322) along a second spatial direction (y) different from the first spatial direction (x) to compensate for thermal expansion of the facet portion (306) along the second spatial direction (y).

3. 3. The field facet system of claim 2, wherein the actuating elements (332, 334, 336, 338) are linear actuating elements that are subject to equal expansion and contraction control along a third spatial direction (z) different from the first spatial direction (x) and the second spatial direction (y).

4. 2. The field facet system of claim 1, wherein the actuating elements (332, 334, 336, 338) are linear actuating elements that are controlled to expand and contract equally along a second spatial direction (y) that is different from the first spatial direction (x).

5. 3. A field facet system according to claim 2, wherein the actuating elements (332, 336) are shear actuating elements that are subject to the same bending control in planes extending in the second spatial direction (y) and the third spatial direction (z).

6. 6. The field facet system of claim 5, wherein the actuating element (332, 336) is coupled to the lever arm (312, 314) by means of a decoupling joint (382, 384) that is flexible in bending along the second spatial direction (y).

7. 5. A field facet system according to claim 1, wherein the actuating elements (332, 334, 336, 338) are arranged in parallel pairs as actuating element pairs (348, 350), a first actuating element (332, 338) of each actuating element pair (348, 350) is coupled to the facet portion (306), a second actuating element (334, 336) of each actuating element pair (348, 350) is coupled to the body (304), and the first actuating element (332, 338) and the second actuating element (334, 336) of each actuating element pair (348, 350) are coupled to each other.

8. 8. The field facet system of claim 7, wherein the first actuating element (332, 338) is coupled to the facet portion (306) using a lever arm (312, 314) and the second actuating element (334, 336) is coupled to the body (304) using an arm portion (324, 326).

9. A field facet system according to any one of the preceding claims, wherein said actuating elements (332, 334, 336, 338) are arranged within a body (304).

10. 10. A field facet system according to any one of claims 1 to 9, further comprising temperature sensors (340, 342, 344, 346, 360, 362, 364, 366) used to detect the temperature of the body (304), the facet portion (306) and / or the actuation element (332, 334, 336, 338) and / or displacement measurement sensors (368, 370) used to detect deformation of the facet portion (306).

11. A field facet system according to any one of the preceding claims, wherein said actuating elements (332, 334, 336, 338) are piezo actuators.

12. A field facet system according to any one of the preceding claims, wherein said body (304) and said facet portion (306) are formed integrally, in particular materially integrally.

13. Lithographic apparatus (100A, 100B) comprising a field facet system (300A, 300B, 300C, 300D, 300E, 300F, 300G, 300H) according to any one of claims 1 to 12.

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