Method for producing a substrate, an optical system, and a light source arrangement for a lithography unit, and substrate for use as part of an optical element in an optical system of a lithography unit

Abstract

The invention relates to a method for producing a substrate (202) for an optical element (200) of a lithography unit (100), the method comprising the steps of: a) providing (S1) a crystal substrate (204), which has a crystal lattice (206) with at least one first, second, third and fourth crystal direction (302, 306, 308, 310) and a surface (214) which is substantially perpendicular to the first crystal direction (302), wherein a geometric projection (306', 308', 310') of the second, third and fourth crystal direction (306, 308, 310) onto the surface (214) in each case defines an azimuthal installation orientation (138) of the crystal substrate (204) in an optical system (102, 104, 136) of the lithography unit (100) with respect to a minimum stress-induced birefringence when polarised radiation (210) is irradiated, and the installation orientation (138) has an orientation with respect to a rotation of the crystal substrate (204) about a central axis (220) which extends through the surface (214) and is arranged parallel to the first crystal direction (302); and b) determining (S2) an angular position (51, 52, 53) of at least one of the geometric projections (306', 308', 310') of the second, third and fourth crystal direction (306, 308, 310) onto the surface (214).

Description

[0001] Carl Zeiss SMT GmbH 1 METHOD FOR PRODUCING A SUBSTRATE, AN OPTICAL SYSTEM AND A LIGHT SOURCE ARRANGEMENT FOR A LITHOGRAPHY SYSTEM AND SUBSTRATE FOR USE AS PART OF AN OPTICAL ELEMENT IN AN OPTICAL SYSTEM OF A LITHOGRAPHY SYSTEM The present invention relates to a method for producing a substrate for an optical element of a lithography system, a method for producing an optical system for a lithography system, a method for producing a light source arrangement for a lithography system, and a substrate for use as part of an optical element in an optical system of a lithography system. The content of the priority application DE 10 2024 103 989.2 is incorporated in its entirety by reference. Microlithography is used to manufacture microstructured components, such as integrated circuits. The microlithography process is carried out using aLithography is carried out using a lithography system that has an illumination system and a projection system. The image of a mask (reticle) illuminated by the illumination system is projected by the projection system onto a substrate coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, for example, a silicon wafer, in order to transfer the mask structure to the light-sensitive coating of the substrate. To ensure a sufficient service life, optical elements of the lithography system can be made from a crystal substrate, such as calcium fluoride (CaF2). For example, strains can occur during the crystal growth process, due to material processing, or a temperature gradient. Carl Zeiss SMT GmbH 2, and they can change and / or amplify the optical anisotropy of the crystal substrate. These strains can, for example,mechanical stress, can lead to stress-induced birefringence. This can disrupt the polarization properties of radiation transmitted through the respective optical element. This leads to a limitation of the resolution of the lithography system. It is known that radiation propagation in the

[0111] crystal direction of the crystal lattice of the crystal substrate is beneficial in reducing disruption of the polarization properties. Furthermore, it is known, for example, from US Pat. No. 6,904,073 B2 that the disruption of the polarization properties varies when the optical element is rotated about its central axis ("clocking") and, in particular, exhibits six minima of stress birefringence in the rotation angle distribution. By appropriate rotational orientation of the optical element, the influence of stress-induced birefringence on transmitted polarized radiation can thus be minimized. However,Known methods for determining the optimal rotational orientation are complex and require a complex test setup. Against this background, it is an object of the present invention to provide an improved method for producing a substrate for an optical element of a lithography system and an improved substrate for use as part of an optical element in an optical system of a lithography system. According to a first aspect, a method for producing a substrate for an optical element of a lithography system is proposed. The method comprises the steps: Carl Zeiss SMT GmbH 3 a) Providing a crystal substrate which has a crystal lattice with at least a first, second, third and fourth crystal direction and a surface which is arranged substantially perpendicular to the first crystal direction, wherein a geometric projection of the second, third and fourth crystal direction onto theSurface each characterizes an azimuthal installation orientation of the crystal substrate in an optical system of the lithography system with respect to a minimum stress-induced birefringence upon irradiation of polarized radiation, and the installation orientation has an orientation with respect to a rotation of the crystal substrate about a central axis extending through the surface, which is arranged parallel to the first crystal direction, and b) determining an angular position of at least one of the geometric projections of the second, third, and fourth crystal direction onto the surface. This makes it easier to determine a favorable (e.g., optimal) azimuthal installation orientation of the crystal substrate with respect to a stress-induced birefringence. In particular, this makes it easier to determine a favorable azimuthal installation orientation of the optical element, which has the crystal substrate as a substrate. In particular, aThe relationship between the crystal structure of the crystal substrate and the depolarization properties is exploited. Furthermore, the favorable installation orientation for the substrate or the optical element with the substrate can be determined during the substrate's manufacture. Stress-induced birefringence, in particular, leads to changes and disturbances in the polarization properties of radiation transmitted through the optical element with the substrate. For example, if radiation passing through the optical element with the substrate experiences a change in polarization direction due to stress-induced birefringence, an image generated using the radiation may exhibit a loss of contrast. The stress-induced birefringence and the resulting change in the polarization properties of transmitted radiation vary when the optical element is rotated about its central axis.("Clocking"). By appropriately selecting the rotational orientation of the optical element with the substrate, the influence of stress-induced birefringence upon transmitted polarized radiation can thus be reduced and / or minimized. The installation orientation is determined in particular based on the determined angular position of at least one of the geometric projections of the second, third, and fourth crystal directions. The installation orientation determined in this way is in particular an installation orientation with respect to the stress-induced birefringence. The installation orientation of the optical element with the substrate in the optical system determined based on the angular position of at least one of the geometric projections of the second, third, and fourth crystal directions is in particular an orientation for which stress-induced birefringence upon irradiation with polarized radiation is low and / or minimal, so that a disturbance of thePolarization properties of radiation transmitted through the optical element is small. The disturbance of the polarization properties when rotating the optical element about its central axis has, in particular, six minima (three main minima and three secondary minima) in the rotation angle distribution. The angular positions of the geometric projections of the second, third, and fourth crystal directions correspond, for example, to the angular positions of the three main minima. However, the angular positions of the geometric projections of the second, third, and fourth crystal directions can also correspond, for example, to the angular positions of the three secondary minima. Carl Zeiss SMT GmbH 5 The surface of the provided crystal substrate and the manufactured substrate of the optical element is, in particular, a surface of an end face of the substrate. The surface of the crystal substrate or the substrate is, for example, a flat surface. The angular positions of the projections of thesecond, third and fourth crystal directions on the surface of the crystal substrate have, for example, one or more values ​​of a rotation angle (azimuth angle) with respect to the rotation around the central axis. The central axis is, for example, a surface normal of the surface. The central axis is, for example, arranged perpendicular to a main extension plane of the crystal substrate. The central axis or axis of rotation is, for example, an axis that runs through the center of mass of the provided crystal substrate, the manufactured substrate and / or the optical element. The central axis or axis of rotation is, for example, an axis that runs parallel to the surface normal of the point on the surface of the crystal substrate closest to the center of mass. The aforementioned properties of the central axis or axis of rotation can relate to both the final geometry of the crystal substrate provided in step a), the finishedsubstrate, the finished optical element, as well as to a stage in the preliminary process for the final geometry of the optical element and / or the substrate. The central axis or axis of rotation is, for example, the sum, weighted according to the light intensity, of all normal vectors of the illuminated surface of the optical element in its respective position with respect to the irradiation of the polarized radiation. Carl Zeiss SMT GmbH 6 The "irradiation of polarized radiation" during operation of the optical element in the optical system comprises the irradiation of linearly polarized, s-polarized, and / or p-polarized radiation onto the optical element. Preferably, the irradiation is of s-polarized radiation. With s-polarized radiation, the polarization direction of the electromagnetic wave of the radiation is arranged perpendicular to the plane of incidence. Here, the polarization direction is the direction of the vector of the electric field of theelectromagnetic wave. In addition, the plane of incidence is the plane spanned by the propagation direction of the electromagnetic wave and a surface normal to the optical element. For p-polarized radiation, the polarization direction of the electromagnetic wave is parallel to the plane of incidence. The polarized radiation is, for example, polarized DUV radiation. The polarized radiation has, for example, a wavelength in the range of 30 nm to 250 nm, 115 nm to 250 nm, and / or 115 nm to 200 nm. For example, a wavelength of the radiation is less than 250 nm and / or less than 200 nm. The smaller the wavelength of the radiation, the greater the effect of depolarization and the more important it is to accurately determine a favorable installation orientation with respect to the stress-induced birefringence of the crystal substrate. A propagation direction and / or radiation direction of the radiation directed onto the optical element in theThe direction of the incident radiation during operation of the optical element is, for example, an angle of incidence inclined to the central axis. The angle of incidence has, for example, a value in the range of 30° to 60°, in the range of 35° to 55°, and / or is, for example, 45°. However, the angle of incidence can also have a different value. Carl Zeiss SMT GmbH 7 The optical power of the radiation incident on the optical element with the substrate, which has the crystal substrate, is, for example, greater than 1 W, greater than 10 W, and / or greater than 40 W. The greater the said optical power of the radiation, the greater the effect of the depolarization and the more important it is to accurately determine a favorable installation orientation with respect to the stress-induced birefringence of the crystal substrate. The first, second, third, and fourth crystal directions are each, in particular, vectors of the crystal lattice of the crystal substrate. The first, second, third, andThe first, second, third, and fourth crystal directions are, in particular, different from one another. The first, second, third, and fourth crystal directions point, for example, in different directions and / or are inclined to one another (i.e., not parallel to one another). The geometric projections of the second, third, and fourth crystal directions onto the surface of the crystal substrate are, for example, spaced apart in pairs by an angular difference of substantially 120°. "Substantially 120°" encompasses, for example, an angular range of 110° to 130°, 115° to 125°, 117° to 123°, 118° to 122°, and / or 119° to 121°. The geometric projections of the second, third, and fourth crystal directions onto the surface of the crystal substrate and the first crystal direction all intersect, for example, at one point (on the surface of the crystal substrate). The geometric projections of the second, third and fourth crystal directions onto the surface of theThe crystal substrate and the central axis of the crystal substrate, for example, all intersect at one point (e.g., at the surface of the crystal substrate). Carl Zeiss SMT GmbH 8 The first, second, third, and fourth crystal directions are in particular assigned a corresponding first, second, third, and fourth crystal plane, which is arranged perpendicular to the respective crystal direction. For example, the first crystal direction is arranged perpendicular to the first crystal plane. The same applies to the second, third, and fourth crystal directions. The surface of the crystal substrate, which is arranged substantially perpendicular to the first crystal direction, is thus in particular also arranged substantially parallel to the first crystal plane. The fact that the surface of the crystal substrate is arranged substantially perpendicular to the first crystal direction means, in particular, that an angle between the surface of the crystal substrate and the first crystal direction inEssentially 90°. This includes an angle between the surface of the crystal substrate and the first crystal direction being exactly 90°, being in the range between 82° and 98°, being in the range between 85° and 95°, being in the range between 87° and 93°, being in the range between 88° and 92°, and / or being in the range between 89° and 91°. The angular position of the geometric projections of the second, third, and / or fourth crystal direction onto the surface of the crystal substrate is determined in particular on the crystal substrate (e.g., the surface of the crystal substrate). The provided crystal substrate has, for example, a cylindrical shape. A cylindrical shape has, in particular, two (e.g., parallel) base surfaces and a lateral surface connecting the base surfaces. Furthermore, the surface of the crystal substrate, which is arranged substantially perpendicular to the first crystal direction, is, for example, surrounded by one of the base surfaces of thecylindrical shape. For example only, the provided Carl Zeiss SMT GmbH 9 crystal substrate has a cylindrical shape with two circular base surfaces and a lateral surface connecting the base surfaces. However, the provided crystal substrate can also have a cylindrical shape with two D-shaped base surfaces and a lateral surface connecting the D-shaped base surfaces. A D-shaped base surface is, for example, a circular base surface in which one circular secant is truncated. However, the provided crystal substrate can also have a different shape. The lithography system (projection exposure system) is, for example, a DUV lithography system. DUV stands for "deep ultraviolet" (DUV) and refers to a wavelength of the working light between 30 nm and 250 nm. The lithography system comprises a light source, an illumination system, and a projection system. In particular,The lithography system projects the image of a mask (reticle) illuminated by the illumination system onto a substrate coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, for example a silicon wafer, by means of the projection system in order to transfer the mask structure onto the light-sensitive coating of the substrate. The optical system is, for example, a light source and / or light source arrangement, a projection optics or an illumination optics of the lithography system or part of such a light source, light source arrangement, projection optics or illumination optics. In embodiments, the provided crystal substrate has a rotationally symmetrical geometric shape with respect to the central axis. An example of such a rotationally symmetrical geometric shape is a cylindrical shape with circular bases. Carl Zeiss SMT GmbH 10In embodiments, theThe provided crystal substrate has a non-rotationally symmetric geometric shape. In this case, the central axis can be a central axis of a rotationally symmetric crystal substrate from which the provided non-rotationally symmetric crystal substrate originated. In particular, the final geometry of the provided crystal substrate is non-rotationally symmetric. Furthermore, for example, a preliminary geometry of the provided crystal substrate in a preliminary process to the final geometry is rotationally symmetric with respect to the central axis. In particular, a crystal substrate with a non-rotationally symmetric geometric shape is provided in order to produce a substrate for a non-rotationally symmetric optical element of a lithography system. One can also say that in this case, it is a method for producing a substrate for a non-rotationally symmetric optical element of a lithography system and / or aMethod for manufacturing a non-rotationally symmetric optical element of a lithography system. An example of such a non-rotationally symmetric geometric shape is a cylindrical shape with D-shaped base surfaces. However, other non-rotationally symmetric geometric shapes are also possible. For a crystal substrate with a non-rotationally symmetric geometric shape, the proposed method represents a particularly significant simplification of the manufacturing process. While for rotationally symmetric optical shapes, clocking can be performed on the final optic, for non-rotationally symmetric optical shapes, clocking must take place prior to molding. With the conventional, complex clocking method, the advantageous installation orientations can only be determined at a process stage in which the crystal substrate has already been surface-treated. This means that the substrate is firstmust be surface-treated, then oriented using a complex clocking process, and only then can shaping take place. In contrast, the method proposed here can be carried out at any process stage, in particular even on an unprocessed crystal substrate before shaping and surface treatment. This degree of freedom in the process sequence makes the process significantly more efficient. For example, even in the case of a non-rotationally symmetric optical element, the manufacturer can thus deliver the finished optical element to customers (e.g., companies that manufacture devices for wafer inspection and semiconductor production monitoring) including a marking of an advantageous installation orientation (or several such advantageous installation orientations). According to one embodiment, the crystal substrate and / or the crystal lattice has a cubic symmetry, a monocrystal, a fluoride crystal,Calcium fluoride, magnesium fluoride, barium fluoride, and / or lutetium aluminum garnet. A crystal with cubic symmetry, such as calcium fluoride (CaF2), has a high crystal symmetry. A monocrystal (also called a single crystal) is a macroscopic crystal whose building blocks (atoms, ions, or molecules) form a continuous, uniform, homogeneous crystal lattice. The molecular formula of magnesium fluoride is MgF2, that of barium fluoride is BaF2, and that of lutetium aluminum garnet is LuAG. According to a further embodiment: the first crystal direction is arranged parallel to a

[0111] crystal direction of the crystal lattice of the provided crystal substrate, and / or Carl Zeiss SMT GmbH 12 the surface of the provided crystal substrate is arranged substantially parallel to a

[0111] crystal plane of the crystal lattice of the crystal substrate. When radiation propagates in the

[0111] crystal direction of the crystal lattice of the crystal substrateany disturbance of the polarization properties by the crystal substrate is particularly small. The nomenclature used herein for crystal directions, e.g.,

[0111] , [01-1], [1-10], and [-101], and for crystal planes, e.g.,

[0111] , [01-1], [1-10], and [-101], corresponds to the nomenclature commonly used in crystallography for crystal directions [abc] and crystal planes [abc] in the crystal lattice based on Miller indices a, b, and c. It should be noted that the Miller indices are placed in square brackets not only for crystal directions but also for crystal planes, as in the case of the

[0111] crystal plane. In crystallography, however, round brackets are often used for crystal planes, e.g., B. (111) crystal plane.The expression that the surface of the provided crystal substrate is substantially parallel to a

[0111] crystal plane of the crystal substrate includes that an angle between the surface of the crystal substrate and the

[0111] crystal plane is zero, lies in the range between +5° and -5°, lies in the range between +3° and -3°, lies in the range between +2° and -2° and / or lies in the range between +1° and -1°. The fact that the first crystal direction is arranged parallel to the

[0111] crystal direction of the crystal lattice of the provided crystal substrate also includes an arrangement of the first crystal direction parallel to any crystal direction equivalent to the

[0111] crystal direction Carl Zeiss SMT GmbH 13 of the crystal lattice, e.g. B. parallel to the [-1-1-1] crystal direction. The fact that the surface of the provided crystal substrate is arranged substantially parallel to the

[0111] crystal plane of the crystal lattice of the crystal substrate also includes arrangements of the surface of the provided crystal substrate substantially parallel to any crystal plane equivalent to the

[0111] crystal plane of the crystal lattice, e.g., parallel to the [-1-1-1] crystal plane. According to a further embodiment:the second crystal direction is arranged parallel to a [01-1] crystal direction of the crystal lattice of the crystal substrate, the third crystal direction is arranged parallel to a [1-10] crystal direction of the crystal lattice of the crystal substrate, and / or the fourth crystal direction is arranged parallel to a [-101] crystal direction of the crystal lattice of the crystal substrate. The applicant has determined in experiments that the geometric projections of the [01-1] crystal direction, the [1-10] crystal direction and the [-101] crystal direction of the crystal substrate onto the surface of the crystal substrate, which is arranged substantially parallel to the

[0111] crystal plane, characterize particularly advantageous azimuthal installation orientations of the optical element with the crystal substrate. In particular, the applicant has determined in experiments that the geometric projections of the [01-1] crystal direction, the [1-10] crystal direction and the[-101] crystal direction onto the surface of the crystal substrate indicate angular positions of the crystal substrate for which – in the installed state – stress-induced birefringence upon irradiation with polarized, particularly s-polarized, radiation is minimal. In other words, by determining the angular positions of the geometric projections of the [01-1] crystal direction, the [1-10] crystal direction, and the [-101] crystal direction onto the surface of the crystal substrate, an advantageous installation orientation of the substrate or the optical element with the substrate with respect to rotation about the central axis can be easily determined. The fact that the second crystal direction is arranged parallel to the [01-1] crystal direction of the crystal lattice of the provided crystal substrate also includes an arrangement of the second crystal direction parallel to each crystal direction equivalent to the [01-1] crystal direction of the crystal lattice.Crystal direction. The fact that the third crystal direction is arranged parallel to the [1-10] crystal direction of the crystal lattice of the provided crystal substrate also includes an arrangement of the third crystal direction parallel to each crystal direction equivalent to the [1-10] crystal direction of the crystal lattice. The fact that the fourth crystal direction is arranged parallel to the [-101] crystal direction of the crystal lattice of the provided crystal substrate also includes an arrangement of the fourth crystal direction parallel to each crystal direction equivalent to the [-101] crystal direction of the crystal lattice. According to a further embodiment, the angular position of at least one of the geometric projections of the second, third and fourth crystal directions onto the surface of the crystal substrate is determined in step b) using X-ray diffractometry. As a result, the angular position(s) of the geometric projections of the second, third and / or fourthCrystal direction onto the surface of the crystal substrate can be easily determined. In particular, the one or more angular positions of the geometric projections are determined based on a diffraction of X-rays at the crystal lattice of the crystal substrate. Carl Zeiss SMT GmbH 15According to a further embodiment, step b) comprises: irradiating X-ray light onto the surface of the crystal substrate for mutually different azimuthal rotation angle settings of the crystal substrate with respect to the rotation about the central axis, detecting X-ray light diffracted at the crystal substrate for the mutually different azimuthal rotation angle settings, and determining the angular position of at least one of the geometric projections of the second, third, and fourth crystal direction of the crystal substrate based on the diffracted X-ray light detected for the mutually different azimuthal rotation angle settings of the crystal substrate.X-ray light. For example, the crystal substrate is arranged on a sample table, which is rotatably attached to a stationary holder. Furthermore, the X-ray light is irradiated, for example, with a fixed irradiation direction (i.e., at a fixed angle) with respect to the stationary holder. Furthermore, the diffracted X-ray light is detected, for example, at a fixed position with respect to the holder (e.g., by an X-ray detector arranged at the fixed position). To determine the angular position(s) of the geometric projections of the second, third, and / or fourth crystal direction onto the surface of the crystal substrate, the sample table with the crystal substrate is rotated, for example, about a rotation axis of the sample table. The rotation axis of the sample table is arranged (e.g., substantially) parallel to and / or along the central axis of the crystal substrate. As a result, the crystal substrate isits central axis is rotated and can thus be brought into different rotation angle settings. The different rotation angle settings have, for example, several rotation angles with a respective angular difference of 3° or less, 1° or less, 0.1° or less, and / or 0.01° or less. In other words, the surface of the crystal substrate is scanned with the X-ray light, for example, in angular steps of 3° or less, 1° or less, 0.1° or less, and / or 0.01° or less. According to a further embodiment, the angular position of at least one of the projections of the second, third, and fourth crystal directions is determined based on: a determined angular position of at least one other of the projections of the second, third, and fourth crystal directions, and the relationship that an angular difference between any two adjacent angular positions of the projections of the second,third and fourth crystal directions is substantially 120°. For example, a first angular position of one of the three projections of the second, third, and fourth crystal directions is determined (e.g., by means of X-ray diffraction). Furthermore, for example, a second and / or third angular position of one and / or two other of the three projections of the second, third, and fourth crystal directions is determined by adding and / or subtracting an angular difference of 120° from the first angular difference. According to a further embodiment, the method comprises the step of marking the determined angular position of the at least one of the projections of the second, third, and fourth crystal directions on the crystal substrate. As a result, the one or more determined angular positions or installation orientations can be read off at a later time on the substrate itself and / or the optical element with the substrate and / or using aCarl Zeiss SMT GmbH 17 measuring device, such as a commercially available interferometer. According to a further embodiment, one or more markings are applied to the crystal substrate, a lateral surface of the crystal substrate, the surface of the crystal substrate and / or an edge region of the surface of the crystal substrate. The respective marking can be a permanent or a non-permanent marking. The marking is, for example, painted on (e.g., with a pen, touch-up pen and / or silver touch-up pen) or engraved (e.g., by means of laser engraving and / or sandblasting). According to a further embodiment, when determining the angular position of at least one of the projections, one or more angles of rotation of the crystal substrate with respect to the rotation of the crystal substrate about the central axis are determined, for which angle(s), in the installed state of the optical element with the substrate, the stress-inducedBirefringence upon irradiation of the polarized radiation is lower and / or minimal compared to other angles of rotation with respect to the rotation of the crystal substrate about the central axis. For example, several values ​​for angles of rotation of the substrate or of the optical element with the substrate with respect to the rotation of the substrate / optical element about the central axis are also determined, for which the stress-induced birefringence upon irradiation of the polarized radiation has a (e.g., local) minimum. According to a further embodiment, when determining the angular position of at least one of the projections, one or more angles of rotation Carl Zeiss SMT GmbH 18 of the crystal substrate relative to a polarization plane of the incident polarized radiation are / are determined. The (favorable and / or optimal) angle(s) of rotation of the optical element relative to the polarization plane of the incident polarized radiation have, for example, valuesbetween 0° or 90°. The polarization plane of the incident polarized radiation, which is electromagnetic radiation, is spanned, for example, by a vector of the electric field of a linearly polarized incident radiation. According to a further embodiment, the optical element comprises a transmitting optical element, a partially transmitting optical element, a beam splitter, a beam splitter of an optical pulse extender, and / or a chamber window of the lithography system. An optical pulse extender is also called an optical pulse stretcher. The optical pulse extender is configured, for example, to temporally delay at least a portion of a pulsed polarized laser radiation. The optical pulse extender is arranged, for example, downstream of a light source with respect to a beam path. A chamber window of the lithography system is, for example, a chamber window of a gas chamber of aLight source of the lithography system. According to a further aspect, a method for producing an optical element for a lithography system is proposed. The optical element has a substrate. Furthermore, the substrate is produced as described above. Carl Zeiss SMT GmbH 19According to a second aspect, a method for producing an optical system for a lithography system is proposed. The optical system has at least one optical element with a substrate. Furthermore, the substrate is produced as described above. Furthermore, the at least one optical element with the substrate is installed in the optical system according to the determined angular position of at least one of the geometric projections of the second, third, and fourth crystal directions. According to a third aspect, a method for producing a light source arrangement for a lithography system is proposed. The light source arrangement has a laser,in particular an ArF excimer laser, for emitting pulsed polarized radiation and an optical pulse extender for temporally delaying at least a portion of the emitted radiation. Furthermore, the optical pulse extender has at least one beam splitter with a substrate. The substrate is manufactured as described above. Furthermore, the at least one beam splitter is incorporated into the pulse extender with the substrate according to the determined angular position of the at least one of the geometric projections of the second, third, and fourth crystal directions. According to a fourth aspect, a substrate for use as part of an optical element in an optical system of a lithography system is proposed. The substrate is manufactured as described above. Furthermore, the substrate is incorporated into theoptical system. Furthermore, the optical element preferably has a beam splitter, and the optical system preferably has a light source arrangement. According to the fourth aspect, a substrate for use as part of a beam splitter in a light source arrangement (e.g., in an optical Carl Zeiss SMT GmbH 20 pulse extender of the light source arrangement) of a lithography system is therefore preferably proposed. "One" is not necessarily to be understood here as being limited to exactly one element. Rather, multiple elements, such as two, three, or more, can also be provided. Any other counting term used here is also not to be understood as implying a limitation to exactly the stated number of elements. Rather, numerical deviations upwards and downwards are possible, unless otherwise stated. The methods described for the method for producing the substrate according to the first aspectEmbodiments and features apply to the proposed methods according to the further aspects and the use of the substrate according to the fourth aspect accordingly, and vice versa. Further possible implementations of the invention also include combinations of features or embodiments described above or below with regard to the exemplary embodiments, not explicitly mentioned. The person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention. Further advantageous embodiments and aspects of the invention are the subject of the subclaims and the exemplary embodiments of the invention described below. The invention will be explained in more detail below using preferred embodiments with reference to the attached figures. Fig. 1 shows a schematic view of an embodiment of a DUV lithography system; Carl Zeiss SMT GmbH 21 Fig. 2 shows an optical element of theLithography system from Fig. 1 in a perspective view according to an embodiment; Fig. 3 shows the optical element from Fig. 2 in a side view; Fig. 4 shows the optical element from Fig. 2 in a plan view of an end face of the optical element; Fig. 5 illustrates a

[0111] crystal direction of a crystal lattice; Fig. 6 illustrates a [01-1] crystal direction of a crystal lattice; Fig. 7 illustrates a [1-10] crystal direction of a crystal lattice; Fig. 8 illustrates a [-101] crystal direction of a crystal lattice; Fig. 9 shows a view similar to Fig. 4, wherein geometric projections of the crystal directions from Figs. 6 to 8 onto a surface of the optical element are illustrated according to an embodiment; Fig. 10 illustrates a stress-induced birefringence as a function of an azimuthal rotation angle for the optical element from Fig. 2 according to an embodiment; Fig. 11 shows a flow diagram of a method forProducing a substrate for an optical element of a lithography system according to one embodiment; Fig. 12 shows an arrangement for determining angular positions of the geometric projections from Fig. 9 according to one embodiment; Carl Zeiss SMT GmbH 22 Fig. 13 shows a flowchart of a method for producing an optical system for a lithography system according to one embodiment; and Fig. 14 shows a flowchart of a method for producing a light source arrangement for a lithography system according to one embodiment. In the figures, identical or functionally equivalent elements have been provided with the same reference numerals unless otherwise stated. Furthermore, it should be noted that the representations in the figures are not necessarily to scale. Fig. 1 shows a schematic view of a DUV lithography system 100, which includes a beam shaping and illumination system 102 and a projection system 104(here also referred to as a "projection lens"). DUV stands for "deep ultraviolet" (DUV) and refers to a wavelength of the working light between 30 nm and 250 nm. The beam shaping and illumination system 102 and the projection system 104 are preferably each arranged in a vacuum housing (not shown). Each vacuum housing is evacuated using an evacuation device (not shown). The vacuum housings are surrounded by a machine room (not shown), in which drive devices for mechanically moving or adjusting optical elements can be provided. Furthermore, electrical controls and the like can also be arranged in the machine room. The DUV lithography system 100 has a light source 106. For example, an ArF excimer laser can be provided as the light source 106, which emits radiation 108 in the DUV range at, for example, 193 nm.In the Carl Zeiss SMT GmbH 23 beam-shaping and illumination system 102, the radiation 108 is focused. Furthermore, the desired operating wavelength (working light), for example, is extracted from the radiation 108 by filtering. The beam-shaping and illumination system 102 may also include optical elements not shown, such as mirrors or lenses. After passing through the beam-shaping and illumination system 102, the radiation 108 is directed onto a photomask (reticle) 110. The photomask 110 is designed as a transmissive optical element and may be arranged outside the systems 102, 104. The photomask 110 has a structure which is imaged in a reduced size onto a wafer 112 by means of the projection system 104. The projection system 104 has a plurality of lenses 114, 116, 118 and / or mirrors 120, 122 for imaging the photomask 110 onto the wafer 112. Individual lenses 114, 116, 118 and / or mirrors 120, 122 of theProjection system 104 can be arranged symmetrically to an optical axis 124 of the projection system 104. It should be noted that the number of lenses and mirrors shown here is purely exemplary and not limited to the number shown. More or fewer lenses 114, 116, 118 and / or mirrors 120, 122 can also be provided. An air gap between the last lens (not shown) and the wafer 112 can be replaced by a liquid medium 126 having a refractive index > 1. The liquid medium 126 can be, for example, ultrapure water. Such a setup is also referred to as immersion lithography and has an increased photolithographic resolution. The medium 126 can also be referred to as an immersion liquid. Carl Zeiss SMT GmbH 24 The ArF excimer laser used as light source 106 in a DUV lithography system 100, for example, can emit radiation in the form of short light pulses of approximately 20 ns duration. In typicalAt pulse energies of 10 mJ or more, the high power peaks of the laser represent a significant risk of degradation for downstream optical elements of the beam-shaping and illumination system 102 and the projection system 104. To avoid degradation of downstream optics, an optical pulse extender (optical pulse stretcher, OPuS) 128 can be used. The optical pulse extender 128 comprises one or more beam splitters 130 (e.g., 45° beam splitters) that decouple a portion of the radiation 108. The decoupled portion of the radiation 108 is subsequently delayed in time relative to the portion of the radiation 108 transmitted through the beam splitter 130 by means of multiple reflections from highly reflective mirrors (not shown), before following the portion of the radiation 108 after being reflected again from the beam splitter 130. The highly reflective mirrors are, for example, adjustably mounted on holders 132. The optical pulse extender 128 usedBeam splitters 130 are made, in particular, from a crystal material with cubic symmetry, such as calcium fluoride (CaF2). Lenses of the DUV lithography system 100, such as lenses 114, 116, 118, or a chamber window 134 of a gas chamber of the light source 106, can also be made from a crystal material with cubic symmetry, such as CaF2. It is known that optically isotropic crystals can cause stress-induced birefringence of an incident light beam, for example, due to strain or mechanical stress. Birefringence means that the refractive index depends on the polarization direction. Even cubic crystals such as CaF2, which are intrinsically optically isotropic, can become birefringent under mechanical stress (stress-induced birefringence). Causes of such disturbances and strains can arise fromthe crystal growth process, material processing, mechanical stress, mechanical action by a mount, temperature gradients due to inhomogeneous heating during operation, and / or as a result of material degradation (possibly in conjunction with the occurrence of slip planes). Stress-induced birefringence of the beam splitter 130, the chamber window 134, or other optical elements of the DUV lithography system 100 can disrupt the polarization properties of the transmitted radiation 108. In particular, a different refraction of the two polarization components of the radiation 108 can occur at a surface of the respective optical element 130, 134, resulting in different deflections and thus splitting of the polarization components. In addition, a phase difference between the polarization components of the transmitted radiation can occur when passing through the respective optical element 130, 134.occur. The result is blurred imaging, which limits the achievable resolution of the DUV lithography system 100. Fig. 2 shows an example of an optical element 200 of the DUV lithography system 100. The optical element 200 is, for example, a beam splitter 130 of the optical pulse extender 128 (Fig. 1). In other examples, however, it can also be a different optical element of the DUV lithography system 100. The optical element 200 has a substrate 202 with a crystal substrate 204. The crystal substrate 204 comprises, for example, a crystal lattice 206 with a cubic crystal order 208. The crystal substrate 204 has, for example, a CaF2 crystal. In the finished state, the optical element 200 also has coatings and the like, which are not shown in the figures and are not described further below. Carl Zeiss SMT GmbH 26The substrate 202 has a surface facing an incident radiation 210.End face 212 with a surface 214. It should be noted that in the state in which a coating (not shown) is applied to end face 212, surface 214 of crystal substrate 204 is not visible—contrary to the illustration in the figures (e.g., Fig. 2). Surface 214 of crystal substrate 204 can, for example, be arranged substantially perpendicular to a

[0111] crystal direction 302 (Fig. 5) of crystal lattice 206, 300 of crystal substrate 204.

[0111] crystal direction 302 is, in particular, arranged perpendicular to a

[0111] crystal plane 304 of crystal lattice 206, 300, as can be seen in Fig. 5. This means that the surface 214 of the crystal substrate 204 can, for example, be arranged substantially parallel to the

[0111] crystal plane 304 of the crystal lattice 206, 300 of the crystal substrate 204. In Figures 5 to 8, a first crystal direction 302 and further crystal directions 306, 308, 310 (second, third and fourthCrystal direction 306, 308, 310) of the crystal substrate 204 shown in Fig. 2 is illustrated. The crystal directions 302, 306, 308, 310 shown in Figures 5 to 8 are, in particular, crystal directions of a cubic crystal 300, e.g., a CaF2 monocrystal. The nomenclature of the crystal directions 302, 306, 308, 310 shown and described herein and the crystal plane 304 follows the nomenclature of crystal directions and planes in the crystal lattice, based on Miller indices a, b, c, customary in crystallography. In particular, Fig. 5 illustrates a first crystal direction 302 and a first crystal plane 304 of the crystal substrate 204 from Fig. 2. The first crystal direction 302 corresponds to a

[0111] crystal direction of the crystal lattice 206, 300. The first crystal plane 304 corresponds to a

[0111] crystal plane of the Carl Zeiss SMT GmbH 27 crystal lattice 206, 300 and is arranged perpendicular to the

[0111] crystal direction. In other words, in Fig.5, theCrystal direction 302 and the associated crystal plane 304 of the cubic crystal lattice 206, 300 are shown, for which the Miller indices [abc] are equal to

[0111] . In particular, Fig. 6 shows - for the Miller indices [abc] = [01-1] - a second crystal direction 306 of the crystal substrate 204, which corresponds to a [01-1] crystal direction of the crystal lattice 206, 300. The second crystal plane perpendicular to the second crystal direction 306 is not shown in Fig. 6 for illustrative reasons. Furthermore, Fig. 7 shows – for the Miller indices [abc] = [1-10] – a third crystal direction 308 of the crystal substrate 204, which corresponds to a [1-10] crystal direction of the crystal lattice 206, 300. The third crystal plane perpendicular to the third crystal direction 308 is not shown in Fig. 7 for illustrative reasons. Furthermore, Fig. 8 shows – for the Miller indices [abc] = [-101] – a fourth crystal direction 310 of the crystal substrate 204, which corresponds to a [-101] crystal direction.of the crystal lattice 206, 300. The fourth crystal plane perpendicular to the fourth crystal direction 310 is not shown in Fig. 8 for illustrative purposes. The radiation 210 incident on the optical element 200 shown in Fig. 2 is, for example, linearly polarized DUV radiation (similar to the radiation 108 in Fig. 1) with a propagation direction 216. A vector of the electric field of the radiation 210 is denoted by the reference symbol E. A polarization direction of the radiation 210 is a direction of the E-field vector E. A polarization plane 218 of the radiation 210 is spanned by the E-field vector E and the propagation direction 216. The radiation 210 shown in Fig. 2 is, in particular, s-polarized. The fact that the radiation 210 is s-polarized means that the polarization direction (ie the direction of the E-field vector E) is perpendicular to a plane of incidence of the radiation 210. The plane of incidence of the radiation210 through the propagation direction 216 and a surface normal to the optical element 200 or the substrate 202 (in Fig. 2, the surface normal is arranged parallel to a central axis 220 of the optical element 200). In other examples, however, the radiation 210 can also be p-polarized, for example. As described in more detail below, by suitably rotating the optical element 200 about a central axis 220, i.e., by suitably setting a rotation angle α (azimuth angle α) of the optical element 200, any disturbance in the polarization properties of the radiation 210 as it passes through the optical element 200 can be kept to a minimum. Fig. 3 shows the optical element 200 from Fig. 2 in a side view. As shown in Fig. 3, the propagation direction 216 of the incident radiation 210 is inclined relative to the surface 214 by an angle β. The angle β is, for example, 45º. However, the angle β can also have other values ​​in the rangefrom 30° to 60° and / or in the range from 35° to 55°. The radiation transmitted through the optical element 200 is designated by reference numeral 210'. If the optical element 200 is a beam splitter, there is also a reflected portion 210 of the radiation 210, as shown in Fig. 3. Fig. 4 shows the optical element 200 from Fig. 2 in a view looking at the end face 212 and the surface 214 of the substrate 202 or the crystal substrate 204 (it is also pointed out here that in the state in which one or more coatings are applied to the surface 214 of the crystal substrate 204, the surface 214 is no longer visible—contrary to the illustration in the Carl Zeiss SMT GmbH 29 figures). In Fig. 4, the rotation of the optical element 200 about its central axis 220 for adjusting the azimuth angle α is illustrated again. Adjusting the angle α is also referred to as "clocking." Furthermore,In Fig. 4, values ​​of the angle α of 0°, 90°, 180°, 270°, and 360° are marked by way of example. The applicant has determined in experiments that there are crystal directions 306, 308, 310 in the cubic crystal 206, 300, whose projections 306', 308', 310' onto the surface 214 arranged essentially parallel to the

[0111] crystal plane 304 indicate one or more advantageous installation orientations of the substrate 202 or of the optical element 200 with the substrate 202 in an optical system 102, 104, 136. In particular, the crystal directions 306, 308, 310 are the second, third and fourth crystal directions 306, 308, 310 in Figures 6 to 8. That is, the crystal directions 306, 308, 310, whose projections 306', 308', 310' characterize the one or more advantageous installation orientations, are the [01-1] crystal direction, [1-10] crystal direction and the [-101] crystal direction of the crystal lattice 206, 300. Accordingly, by determiningAngular positions δ1, δ2, δ3 (Fig. 9) of the projections 306', 308', 310' of the crystal directions 306, 308, 310 onto the surface 214, one or more favorable and / or optimal installation orientations (in particular one or more favorable and / or optimal azimuth angles α) of the substrate 202 or of the optical element 200 with the substrate 202 can be determined. Fig. 9 shows a view of the optical element 200 or of the substrate 202 similar to Fig. 4. In Fig. 9, the central axis 220 is marked, which runs essentially parallel and along the first crystal direction 302 (ie the

[0111] crystal direction). In Fig. 9, the first crystal direction 302 points, for example, into the plane of the drawing. Carl Zeiss SMT GmbH 30 Furthermore, the geometric projections 306', 308', 310' of the second, third and fourth crystal directions 306, 308, 310 onto the surface 214 are illustrated in Fig. 9. The projections 306', 308', 310' are in particularProjections 306', 308', 310' of the [O1-1], [I-10], and [-101] crystal directions 306, 308, 310 onto the surface 214 of the substrate 202 of the optical element 200. As can be seen in Fig. 9, the projections 306', 308', 310' are arranged at angular positions δ1, δ2, δ3, respectively. An angular difference Δδ between any two adjacent projections 306', 308', 310' is 120° in Fig. 9. Fig. 10 shows the experimental results of tests conducted by the applicant. Fig. 10 illustrates a stress-induced birefringence as a function of an azimuthal rotation angle (e.g., the angle α in Fig. 3) for an optical element 200 or substrate 202 as shown in Figs. 2, 3, 9. In particular, Fig. 10 shows a graph 400 which shows the extent as intensity I of the intrinsic stress birefringence as a function of the azimuthal rotation angle for the optical element 200 or substrate 202. To determine the intensity I, behind the optical element200, a Brewster plate (not shown) is placed. P-polarized components of the beam 210, which arise from stress-induced birefringence, are almost completely transmitted through the Brewster plate, and the reflection from the Brewster plate is close to zero. In addition, a power meter (not shown) is positioned behind the Brewster plate to measure the transmitted power. If the stress-induced birefringence creates p-polarized components in the beam, the signal I measured there increases. In favorable positions with low stress-induced birefringence and thus also low p-components, this signal decreases. The graph 400 has six minima 402, 404, 406, 408, 410, 412 (three main minima 402, 406, 410 and three secondary minima 404, 408, 412) at which the stress-induced birefringence exhibits a local or global minimum. Carl Zeiss SMT GmbH 31 Furthermore, Fig. 10 shows the angular positions δ1, δ2, δ3 of the projections 306', 308', 310'.of the crystal directions 306, 308, 310 are plotted. As can be seen in Fig. 10, the angular positions δ1, δ2, δ3 of the projections 306', 308', 310' correspond well with angular positions ε1, ε2, ε3 of the principal minima 402, 406, 410. Consequently, by determining the angular positions δ1, δ2, δ3 of the projections 306', 308', 310' of the crystal directions 306, 308, 310, advantageous angular positions for incorporating the substrate 202 or the optical element 200 with the substrate 202 in an optical system 102, 104, 136 can be determined. In other examples, however, the angular positions δ1, δ2, δ3 of the projections 306', 308', 310' may also reflect angular positions of the secondary minima 404, 408, 412. In the following, a method for producing a substrate 202 for an optical element 200 for a lithography system 100 according to a first aspect is described with reference to Fig. 11. For example, the optical element 200 shown in Figures 2 to 4 is used for the embodiment shown in Fig. 1The DUV lithography system 100 shown is manufactured. In particular, the method determines a favorable installation orientation of the substrate 202 or of the optical element 200 with the substrate 202 in an optical system (e.g., the beam-shaping and illumination system 102, the projection system 104, or the light source arrangement 136 in Fig. 1) with respect to stress-induced birefringence. In a first step S1 of the method, a crystal substrate 204 (Figures 2, 3) is provided. The crystal substrate 204 has a crystal lattice 206, 300 (e.g., with cubic symmetry 208) with at least a first, second, third, and fourth crystal direction 302, 306, 308, 310 (Figures 5 to 8). The crystal substrate 204 also has a surface 214 that is arranged substantially perpendicular to the first crystal direction 302, wherein the first crystal direction 302 is a

[0111] crystal direction of the crystal lattice 206, 300 (Fig. 5). One can also say thatthe surface 214 is arranged substantially parallel to the Carl Zeiss SMT GmbH 32first crystal plane 304, wherein the first crystal plane 304 is a

[0111] crystal plane of the crystal lattice 206. Furthermore, the second, third, and fourth crystal directions 306, 308, 310 are, in particular, a [O1-1], [I-10], and [I-101] crystal direction of the crystal lattice 206, 300 (Figures 5 to 8). Furthermore, as the applicant has determined in experiments (Figures 9, 10), a geometric projection 306', 308', 310' corresponding to the second, third, and fourth crystal directions 306, 308, 310 onto the surface 214 each indicates an azimuthal installation orientation 138 of the crystal substrate 204 in an optical system 102, 104, 136 of the lithography system 100 with respect to a minimum stress-induced birefringence upon irradiation with polarized radiation. 210. Herein, the installation orientation 138 is an orientation with respect to a rotation of theCrystal substrate 204 about a central axis 220 extending through the surface 214 and arranged parallel to the first crystal direction 302. In a second step S2 of the method, an angular position δ1, δ2, δ3 of at least one of the geometric projections 306', 308', 310' of the second, third, and fourth crystal directions 306, 308, 310 onto the surface 214 is determined. For example, an angular position δ1, δ2, δ3 of at least one of the geometric projections 306', 308', 310' of the second, third, and fourth crystal directions 306, 308, 310 onto the surface 214 is determined using X-ray diffraction. In this case, X-ray light 508 is diffracted at the crystal lattice 206 of the crystal substrate 204 and the diffracted X-ray light 512 is detected by a detector 510. Carl Zeiss SMT GmbH 33 Fig. 12 shows an exemplary arrangement 500 for determining the angular positions δ1, δ2, δ3 of the geometric projections 306', 308', 310' of the second, third andfourth crystal direction 306, 308, 310 onto the surface 214. The arrangement 500 comprises, for example, a sample table 502 on which the crystal substrate 204 is arranged. The crystal substrate 204 is arranged on the sample table 502 in such a way that the surface 214 of the crystal substrate is arranged on a side opposite the sample table 502. In addition, the sample table 502 is rotatably attached to a stationary holder 504 so that the crystal substrate 204 can be rotated about its central axis 220 (Figs. 2, 3). The arrangement 500 also comprises an X-ray source 506 for emitting (e.g., monochromatic) X-ray light 508. Furthermore, a detector 510 is provided for detecting an X-ray light 512 diffracted at the crystal substrate 204. The diffraction is, in particular, a Bragg diffraction at lattice planes of the crystal substrate 204. Furthermore, the detector 510 detects, in particular, an X-ray radiation 512 which isconstructive interference of radiation reflected from various lattice planes of the crystal substrate 204. The detector 510 is, for example, a scintillation counter or another type of X-ray detector. The X-ray light 508 is irradiated onto the crystal substrate 204, for example, at a fixed angle γ1 relative to the surface 214 of the crystal substrate 204. In addition, the X-ray light 512 diffracted by the crystal substrate 204 is emitted from the crystal substrate 204, for example, at the same angle γ2 relative to the surface 214 of the crystal substrate 204, and detected by the detector 510. Carl Zeiss SMT GmbH 34 To determine the one or more angular positions δ1, δ2, δ3 of the geometric projections 306', 308', 310' of the second, third and / or fourth crystal direction 306, 308, 310, the X-ray light 508 is directed onto the surface 214 of the crystal substrate 204 for mutually different azimuthalRotation angle settings α of the crystal substrate 204 with respect to a rotation about the central axis 220 (Fig. 3) are irradiated. In particular, the sample stage 502 with the crystal substrate 204 is rotated, for example, about a rotation axis 514 of the sample stage 502. The rotation axis 514 of the sample stage 502 is arranged (e.g., substantially) parallel to and along the central axis 220 of the crystal substrate 204. By rotating the sample table 502 with the crystal substrate 204 about the rotation axis 514, the crystal substrate 204 is rotated about its central axis 220 and can thus be brought into the mutually different rotation angle settings α. Furthermore, for the mutually different azimuthal rotation angle settings α, X-ray light 512, which was diffracted at the surface 214 of the crystal substrate 204, is detected by the detector 510. Then, the one or more angular positions δ1, δ2, δ3 of the geometric projections 306', 308', 310' of the second, third and fourthCrystal direction 306, 308, 310 of the crystal substrate 204 can be determined based on the diffracted X-ray light 512 detected for the different azimuthal rotation angle settings α of the crystal substrate 204. In particular, X-ray reflections are recorded for the angular positions δ1, δ2, δ3 belonging to the geometric projections 306', 308', 310' of the second, third and fourth crystal directions 306, 308, 310, which thus allow conclusions to be drawn about the angular positions δ1, δ2, δ3 of the geometric projections 306', 308', 310'. It is possible that in step S2 only the angular position δ1, δ2, δ3 of one of the geometric projections 306', 308', 310' of the second, third and fourth crystal directions 306, 308, 310 of the crystal substrate 204 is recorded by means of Carl Zeiss SMT GmbH 35 X-ray diffractometry. Then the other two angular positions δ1, δ2, δ3 can be derived from it, because an angular difference Δδ between any two adjacent angular positionsδ1, δ2, δ3 of the geometric projections 306', 308', 310' of the second, third, and fourth crystal directions 306, 308, 310 is 120° (see Fig. 9). For example, in step S2, only the angular position δ1 of the geometric projection 306' of the second crystal direction 306 of the crystal substrate 204 is determined by X-ray diffractometry. Then, the other two angular positions δ2, δ3 of the geometric projections 308', 310' of the third and fourth crystal directions 308, 310 of the crystal substrate 204 can be determined by adding 120° to δ1 and δ2, respectively. Subtraction of 120º from δ1 (e.g., δ2 = δ1 + 120º and δ3 = δ1 - 120º). Based on the relationship, an angular difference Δδ between any two adjacent angular positions δ1, δ2, δ3 of the projections 306', 308', 310' of the second, third, and fourth crystal directions 306, 308, 310 is essentially 120º. The angular position δ1, δ2, δ3 of the one or more ge-ometric projections 306', 308', 310' of the second, third and fourth crystal directions 306, 308, 310 each indicate a favorable installation orientation 138 of the substrate 202 or of the optical element 200 with the substrate 202 in an optical system 102, 104, 136. In particular, this is an installation orientation 138 of the optical element 200 for which a stress-induced birefringence upon irradiation of a polarized radiation 108, 210 (Fig. 1, 2) is minimal. The installation orientation 138 is an orientation with respect to the rotation (azimuth rotation) of the substrate 202 or of the optical element 200 with the substrate 202 about its central axis 220. Carl Zeiss SMT GmbH 36In particular, a rotation angle α (Fig. 2) of the substrate 202 or of the optical element 200 with the substrate 202 with respect to the rotation about the central axis 220, for which the stress-induced birefringence upon irradiation of the polarized radiation 210 is small and / oris minimal. For example, several values ​​of the rotation angle α can be determined for which the stress-induced birefringence exhibits a (e.g., local) minimum upon irradiation of the polarized radiation 210. Furthermore, the rotation angle α can also be determined relative to the polarization plane 212 (Fig. 2) of the incident polarized radiation 210. For example, the rotation angle α = 0° in Fig. 4 is defined as one of the angular positions δ1, δ2, δ3 of the one or more geometric projections 306', 308', 310' of the second, third and fourth crystal directions 306, 308, 310 determined in step S2. In an optional third step S3 of the method, the determined favorable installation orientation 138, for example, one of the angles δ1, δ2, δ3, is marked on the substrate 202. As a result, the determined favorable installation orientation 138 can, for example, be marked by a customer on the substrate 202 or the optical element 200 with theSubstrate 202 itself can be read and / or determined using a measuring device, such as a commercially available interferometer. In step S3, in particular, a marking 222 (Figures 2 and 3) is applied to the substrate 202 at one or more of the favorable rotation angles δ1, δ2, δ3 determined in step S2. In the example shown, the marking 222 is painted onto a lateral surface 224 of the substrate 202 (e.g., with a touch-up pen). In other examples, a marking 222 can also be engraved into the substrate 202 and / or applied in an edge region of the surface 214. Carl Zeiss SMT GmbH 37 The marking 222 is therefore applied to the substrate 202 at one or more of the favorable rotation angles δ1, δ2, δ3 determined in step S2. If α = 0º(Fig. 4) has been defined as corresponding to one of the favorable angles of rotation δ1, δ2, δ3 (e.g. δ1), then this corresponding angle of rotation (e.g. δ1) =0º and the otherboth angles of rotation (e.g. δ2 and δ3) for example 120º and 240º (e.g. δ2 = δ1 + 120º and δ3 = δ2 + 120º). One can also say that in this case, a possible favorable rotation angle δ1, δ2, δ3 is at α = 0°, and the optical element 200 is aligned with the substrate 202 such that α = 0° is arranged relative to a pointer that (i) is part of the intersection of the surface 214 of the optical element 200 / the substrate 202 and the plane of incidence 218 of the beam 210 onto the surface 214, and (ii) has an angle of 135° (at an angle of incidence of 45°) between the beam 210 and the pointer. A method for manufacturing an optical system 102, 104, 136 for a lithography system 100 according to a second aspect is described below with reference to Fig. 13. The optical system 102, 104, 136 comprises an optical element 200 with a substrate 202. In a first and second step S101, S102 of the method according to the second aspect, theSubstrate 202 is produced as in steps S1, S2 of the method according to the first aspect. In an optional third step S103 of the method according to the second aspect, the angular position δ1, δ2, δ3 determined in step S102 is marked on the crystal substrate 204. The third step S103 of the method according to the second aspect corresponds to step S3 of the method according to the first aspect. Carl Zeiss SMT GmbH 38 In a fourth step S104 of the method according to the second aspect, the optical element 200 with the substrate 202 is installed in the optical system 102, 104, 136 according to the determined angular position δ1, δ2, δ3 of at least one of the geometric projections 306', 308', 310' of the second, third and fourth crystal directions 306, 308, 310. In the following, a method for manufacturing a light source arrangement 136 for a lithography system 100 according to a third aspect is described with reference to Fig. 14. The light source arrangement 136 (Fig. 1) has aLight source 106, in particular a laser (e.g., an ArF excimer laser), for emitting pulsed polarized radiation 108. The light source arrangement 136 also has an optical pulse extender 128 for temporally delaying at least a portion of the emitted radiation 108. The optical pulse extender 128 comprises at least one beam splitter 130 (Fig. 1) as an optical element 200 (Fig. 2) with a substrate 202. In a first and second step S201, S202 of the method according to the third aspect, the substrate 202 is produced as in steps S1, S2 of the method according to the first aspect. In an optional third step S203 of the method according to the third aspect, the angular position δ1, δ2, δ3 determined in step S202 is marked on the crystal substrate 204. The third step S203 of the method according to the third aspect corresponds to step S3 of the method according to the first aspect. In a fourth step S204 of the method according toIn the third aspect, the optical element 200 is installed in the pulse extender 128 with the substrate 202 according to the determined angular position δ1, δ2, δ3 of at least one of the geometric projections 306', 308', 310' of Carl Zeiss SMT GmbH 39second, third, and fourth crystal directions 306, 308, 310. Although the present invention has been described using exemplary embodiments, it is capable of numerous modifications.

[0002] Carl Zeiss SMT GmbH 40 LIST OF REFERENCE SYMBOLS 100 DUV lithography system 102 Beam shaping and illumination system 104 Projection system 106 Light source 108 Radiation 110 Photomask 112 Wafer 114 Linse 116 Linse 118 Linse120 Mirror 122 Mirror 124 Optical axis 126 Medium 128 Optical pulse extender 130 Beam splitter 132 Mount 134 Chamber window 136 Light source arrangement 138 Orientation 200 Optical element 202 Substrate 204 Crystal substrate 206 Crystal lattice 208 Cubic crystal 210, 210', 210" Radiation 212 End face 214 Surface Carl Zeiss SMT GmbH 41216 Propagation direction 218 Polarization plane 220 Central axis 222 Marking 224 Lateral surface 300 Crystal lattice 302 Crystal direction 304 Crystal plane 306 Crystal direction 306' Projection 308 Crystal direction 308' Projection 310 Crystal direction 310' Projection 400 Graph 402 Minimum404 Minimum406 Minimum408 Minimum410 Minimum412 Minimum500 Arrangement502 Sample table504 Holder506 X-ray source508 X-ray light510 Detector512 X-ray light514 Rotation axis Carl Zeiss SMT GmbH 42 α Winkel β Winkel γ1 Winkel γ2 Winkel δ Winkel δ1 Winkel δ2 Winkel δ3 Winkel Δδ angle difference ε1 Winkel ε2 Winkel ε3 Winkela Miller indexb Miller indexc Miller index E Vektor I Intensity valueS1-S3 Process stepsS101-S104 Process stepsS201-S204 Process stepx Directiony Directionz Direction

Claims

Carl Zeiss SMT GmbH 43 PATENT CLAIMS1. Method for producing a substrate (202) for an optical element (200) of a lithography system (100), comprising the steps of: a) providing (S1) a crystal substrate (204) having a non-rotationally symmetrical geometric shape, a crystal lattice (206) with at least a first, second, third and fourth crystal direction (302, 306, 308, 310) and a surface (214) arranged substantially perpendicular to the first crystal direction (302), wherein a geometric projection (306', 308', 310') of the second, third and fourth crystal direction (306, 308, 310) onto the surface (214) each represents an azimuthal installation orientation (138) of the crystal substrate (204) in an optical system (102, 104, 136) of the lithography system (100) with respect to a minimum stress-induced birefringence upon irradiation of a polarized radiation (210),and the installation orientation (138) has an orientation with respect to a rotation of the crystal substrate (204) about a central axis (220) extending through the surface (214) and arranged parallel to the first crystal direction (302), and b) determining (S2) an angular position (δ1, δ2, δ3) of at least one of the geometric projections (306', 308', 310') of the second, third and fourth crystal directions (306, 308, 310) onto the surface (214).

2. The method according to claim 1, wherein the crystal substrate (204) and / or the crystal lattice (206) has a cubic symmetry (208), a monocrystal, a fluoride crystal, calcium fluoride, magnesium fluoride, barium fluoride, and / or lutetium aluminum garnet.

3. The method according to claim 1 or 2, wherein the first crystal direction (302) is arranged parallel to a [111] crystal direction of the crystal lattice (206) of the provided crystal substrate (204), and / or Carl Zeiss SMT GmbH 44 the surface (214) of the provided crystal substrate (204) is arranged substantially parallel to a [111] crystal plane of the crystal lattice (206) of the crystal substrate (204).

4. Method according to one of claims 1-3, wherein the second crystal direction (306) is arranged parallel to a [01-1] crystal direction of the crystal lattice (206) of the crystal substrate (204), the third crystal direction (308) is arranged parallel to a [1-10] crystal direction of the crystal lattice (206) of the crystal substrate (204), and / or the fourth crystal direction (310) is arranged parallel to a [-101] crystal direction of the crystal lattice (206) of the crystal substrate (204).5.Method according to one of claims 1-4, wherein the angular position (δ1, δ2, δ3) of at least one of the geometric projections (306', 308', 310') of the second, third and fourth crystal directions (306, 308, 310) onto the surface (214) of the crystal substrate (204) is determined in step b) using X-ray diffractometry.6.Method according to one of claims 1 - 5, wherein step b) comprises: irradiating X-ray light (508) onto the surface (214) of the crystal substrate (204) for mutually different azimuthal rotation angle settings (α) of the crystal substrate (204) with respect to the rotation about the central axis (220), detecting, for the mutually different azimuthal rotation angle settings (α), X-ray light (512) diffracted at the crystal substrate (204), and determining the angular position (δ1, δ2, δ3) of at least one of the geometric projections (306', 308', 310') of the second, third and fourth crystal directions (306, 308, 310) of the crystal substrate (204) based on the azimuthal rotation angle settings (α) of the Crystal substrate (204) detected diffracted X-ray light (512). Carl Zeiss SMT GmbH 457. Method according to one of claims 1 - 6, wherein the angular position (δ1, δ2, δ3) of at least one of the projections (306', 308', 310') of the second, third and fourth crystal directions (306, 308, 310) is determined based on: a determined angular position (δ1, δ2, δ3) of at least one other of the projections (306', 308', 310') of the second, third and fourth crystal directions (306, 308, 310), and the relationship that an angular difference (Δδ) between each two adjacent angular positions (δ1, δ2, δ3) of the projections (306', 308', 310') of the second, third and fourth crystal directions (306, 308, 310) is substantially 120°.

8. Method according to one of claims 1-7, comprising:marking (S3) the determined angular position (δ1, δ2, δ3) of the at least one of the projections (306', 308', 310') of the second, third and fourth crystal directions (306, 308, 310) on the crystal substrate (204).9.Method according to claim 8, wherein one or more markings (222) are applied to the crystal substrate (204), a lateral surface (224) of the crystal substrate (204), the surface (214) of the crystal substrate (204) and / or an edge region of the surface (214) of the crystal substrate (204).

10. Method according to one of claims 1-9, wherein, when determining the angular position (δ1, δ2, δ3) of at least one of the projections (306', 308', 310'), one or more angles of rotation (α) of the crystal substrate (204) with respect to the rotation of the crystal substrate (204) about the central axis (220) are determined, for which angle(s), in the installed state of the optical element (200) with the substrate (202), the stress-induced birefringence upon irradiation of the polarized radiation (210) is lower and / or minimal compared to other angles of rotation with respect to the rotation of the crystal substrate (204) about the central axis (220). Carl Zeiss SMT GmbH 4611. Method according to one of claims 1-10, wherein, when determining the angular position (δ1, δ2, δ3) of at least one of the projections (306', 308', 310'), one or more angles of rotation (α) of the crystal substrate (204) relative to a polarization plane (212) of the incident polarized radiation (210) are determined.

12. Method according to one of claims 1-11, wherein the optical element (200) comprises a transmitting optical element (130), a partially transmitting optical element (130), a beam splitter (130), a beam splitter (130) of an optical pulse extender (128), and / or a chamber window (134) of the lithography system (100).13.A method for producing an optical system (102, 104, 136) for a lithography system (100), wherein the optical system (102, 104, 136) comprises at least one optical element (200) with a substrate (202), the substrate (202) is produced according to one of claims 1-12, and the at least one optical element (200) is installed in the optical system (102, 104, 136) with the substrate (202) according to the determined angular position (δ1, δ2, δ3) of the at least one of the geometric projections (306', 308', 310') of the second, third and fourth crystal directions (306, 308, 310).14.Method for producing a light source arrangement (136) for a lithography system (100), wherein the light source arrangement (136) has a laser (106), in particular an ArF excimer laser, for emitting pulsed polarized radiation (108, 210) and an optical pulse extender (128) for delaying at least a portion of the emitted radiation (108, 210), the optical pulse extender (128) has at least one beam splitter (130) with a substrate (202). Carl Zeiss SMT GmbH 47 the substrate (202) of the at least one beam splitter (130) is manufactured according to one of claims 1 - 12, and the at least one beam splitter (130) with the substrate (202) is installed in the pulse extender (128) according to the determined angular position (δ1, δ2, δ3) of the at least one of the geometric projections (306', 308', 310') of the second, third and fourth crystal directions (306, 308, 310).15.Substrate (202) for use as part of an optical element (200) in an optical system (102, 104, 136) of a lithography system (100), wherein the substrate (202) is manufactured according to one of claims 1-12, the optical element (200) with the substrate (202) is installed in the optical system (102, 104, 136) according to the determined angular position (δ1, δ2, δ3) of at least one of the geometric projections (306', 308', 310') of the second, third and fourth crystal directions (306, 308, 310), the optical element (200) preferably has a beam splitter (130), and the optical system (102, 104, 136) preferably has a light source arrangement (136).

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