Multi-mirror array

Abstract

The multi-mirror array (MMA) comprises a carrier structure and a number of mirror units (MU) arranged side by side on the carrier structure in a grid arrangement. Each mirror unit comprises a base element (BE) and a mirror element (ME), which is individually movably mounted relative to the base element and has a mirror substrate (SUB), which has a reflective coating (REF) on its front surface opposite the base element (BE) to form a mirror surface (MS) reflecting EUV radiation. The reflective coating can be designed for example for EUV radiation or for DUV radiation. The mirror surfaces are arranged side by side to substantially fill the surface area. To ensure a collision-free relative movement of adjacent mirror elements, a gap (SP) defined by the side surfaces of the adjacent mirror substrates remains between directly adjacent mirror elements. In the case of each mirror unit, a functional component of the multi-mirror array is arranged between the base element and the mirror element. Each of the side surfaces (SF1, SF2) of the mirror substrates (SUB1, SUB2) is at least partially oriented obliquely at an angle other than 90° to the assigned mirror surface (MS).

Description

[Technical Field]

[0001] This application is based on German patent application serial number 102021211619.1, filed on October 14, 2021, the disclosure content of which is incorporated herein by reference.

[0002] The present invention relates to a multi-mirror array according to the preamble of claim 1 and to an illumination system of an apparatus comprising at least one such multi-mirror array. A preferred field of application is that of EUV apparatus, i.e. apparatus with operating wavelengths from the extreme ultraviolet (EUV) range. [Background technology]

[0003] Nowadays, microlithography projection exposure methods are primarily used in the production of semiconductor components and other microstructured components. A mask (reticle) or other pattern-generating device is used, which carries or forms the pattern of the structure to be imaged, e.g., the line pattern of a layer of a semiconductor component. The pattern is illuminated using an illumination system that forms illumination radiation from the radiation of a primary radiation source. The illumination radiation is directed toward the pattern and impinges on the pattern within an illumination field characterized by specific illumination parameters and having a defined shape and size. The radiation modified by the pattern passes through a projection lens, which images the pattern onto a substrate to be exposed, which is coated with a radiation-sensitive layer.

[0004] Many current microlithography projection exposure methods and apparatus utilize radiation in the relatively short wavelength portion of the ultraviolet (UV) range, particularly radiation with wavelengths below 260 nm. These include in particular systems that use operating wavelengths in the deep ultraviolet (DUV) range, for example around 248 nm or around 193 nm, which can be used to fabricate many mid-critical structures. The wavelength range below around 200 nm, up to the EUV range, is sometimes referred to as the vacuum ultraviolet (VUV) range.

[0005] In order to be able to produce finer structures, optical systems have been developed in recent years that obtain high resolution by using short wavelengths of electromagnetic radiation, essentially in the extreme ultraviolet range (EUV), especially for operating wavelengths in the range of 5 nm to 30 nm. Since short wavelengths are absorbed by known optical materials that are transparent at higher wavelengths, EUV radiation cannot be focused or guided using refractive optical elements. Therefore, mirror systems are used in EUV devices, for example for EUV lithography.

[0006] Depending on the type of structure to be imaged, different illumination modes (also called illumination settings) are usually used, which can be characterized by different local intensity distributions of the illumination radiation in the pupil plane of the illumination system. To be able to flexibly set these, the illumination system comprises a pupil shaping unit which receives radiation from a primary radiation source and produces a variably settable two-dimensional intensity distribution in the pupil region of the illumination system.

[0007] Some concepts involve the use of at least one controllable multi-mirror array (MMA) in the pupil shaping unit, which comprises a plurality of individual mirror elements carried by a joint carrier structure and which can be tilted independently of one another to targetably modify the angular distribution of radiation incident on the entire mirror element to produce a desired spatial illumination intensity distribution at the pupil plane. The mirror surfaces are arranged to substantially fill the area. Gaps remain between immediately adjacent mirror elements, defined by the mirror substrate side surfaces and serving to ensure collision-free relative movement of the mirror elements. Such multi-mirror arrays are often also referred to as faceted mirrors, with the reflective front sides of the mirror elements forming the facets.

[0008] In order to be able to set the geometrical reflection properties of the controllable multi-mirror array in a targeted manner, the multi-mirror array generally comprises, for each mirror element, an actuator system coupled to the mirror element for controllably changing the attitude of the mirror element relative to a carrier structure carrying the mirror element. The actuator movements of the actuator system are controlled by a control unit assigned to the multi-mirror array. Under the control of the control device, the orientation of the mirror surface of the mirror element can be changed in a targeted manner from a zero position.

[0009] Further reduction of the size of the individually addressable mirror surface is often the goal, so that the geometrical-optical reflection properties of the MMA can be set with high spatial resolution. For this purpose, techniques from the field of microelectromechanical systems (MEMS for short) manufacturing are often repeated for manufacturing purposes, in order to form the actuating, sensor and mechanical elements as MEMS structures in the area between the mirror surface and the carrier structure.

[0010] Patent Document 1 (corresponding to Patent Document 2) describes a displacement device for pivoting a mirror element manufactured using MEMS technology with two degrees of rotational freedom. This displacement device includes an electrode structure with actuator electrodes designed as comb electrodes, which are arranged in a single plane and form a direct drive for pivoting the mirror element. Other examples of MMS with MEMS mirror elements are disclosed in Patent Documents 3, 4, or 5.

[0011] Due to the underlying fundamental principles, the operation of an EUV device with high-energy EUV radiation can lead to degradation of the device. Patent Document 6 (corresponding to Patent Document 7) describes, for example, the generation of contaminants in an EUV light source in which tin droplets are used to generate EUV radiation. The tin droplets are transformed into a plasma state by a laser beam, which causes some of the tin droplets to evaporate, resulting in tin particles that spread throughout the EUV lithography device and deposit directly or in the form of a tin layer on, for example, optical surfaces of optical elements in the illumination or projection system, as well as on mechanical or electromechanical components of the EUV lithography device. Tin contamination can also be caused by the outgassing effect of tin-containing components in the EUV lithography device, induced by hydrogen or hydrogen plasma present in the EUV lithography device. To protect individual mirrors of an MMA manufactured using MEMS technology, a protective element is described, which includes a thin film supported by a frame with a grid-like structure and formed by multiple thin film segments, each of which protects a portion of the MMA's surface, e.g., a group of adjacent mirror elements, from contaminants. A membrane carried by a frame is spaced in front of the mirror surface.

[0012] Patent Document 8 describes an optical assembly having a multi-mirror array, in which, in order to avoid contamination of the mirror elements by tin particles and other contaminants originating from an EUV radiation source, the optical assembly includes a purge device that generates a purge gas flow passing through gaps between the mirror bodies of at least two adjacent individual mirrors, the purge gas flow being aligned in a direction from a second surface of the mirror body facing the carrier structure to a radiation incident side of the mirror body.

[0013] Patent Document 9 discloses a multi-mirror array with individually tiltable mirror elements. To allow collision-free relative movement of adjacent mirror elements, gaps defined by the side surfaces of adjacent mirror substrates are located between each directly adjacent mirror element. To protect components of the multi-mirror array located behind the mirror surface from radiation-related damage (heating, radiation degradation), various measures have been proposed to prevent incident light from passing through the gaps and reaching the area behind the mirror surface. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] US Patent Application Publication No. 2017 / 363861 [Patent Document 2] DE 10 2015 204 874 [Patent Document 3] U.S. Patent No. 10,261,424 [Patent Document 4] DE 10 2013 201 509 A1 [Patent Document 5] International Publication No. 2021 / 032483 Brochure [Patent Document 6] International Publication No. 2017 / 072195 Brochure [Patent Document 7] DE 10 2015 221 209 A1 [Patent Document 8] DE 10 2016 206 202 [Patent Document 9] US Patent Application Publication No. 2014 / 0218708 Summary of the Invention [Problem to be solved by the invention]

[0015] Against this background, the present invention is based on the problem of providing a multi-mirror array which, when used in a device operating with relatively short-wavelength radiation in the ultraviolet range, remains functional for a relatively long period of time under the influence of short-wavelength UV radiation. [Means for solving the problem]

[0016] To achieve this object, the invention provides a multi-mirror array having the features of claim 1 and an illumination system having the features of claim 21. Advantageous developments are specified in the dependent claims, the wording of all claims being incorporated into the content of this description by reference.

[0017] The multi-mirror array according to the claimed invention comprises a carrier structure and a plurality of mirror units arranged side by side in a grid array on the carrier structure. Each mirror unit includes a base element and mirror elements mounted so as to be individually movable relative to the base element. The mirror elements include a mirror substrate having a reflective coating on its front surface opposite the base element to form a mirror surface that effectively reflects the radiation used. Each mirror substrate also includes a back surface facing the base element and a peripheral side surface. The array of mirror elements is structurally designed so that the mirror elements can move relative to one another without colliding with one another throughout their designated range of movement, thereby intentionally preventing the mirror elements from contacting one another.

[0018] The mirror surfaces of a multi-mirror array are arranged side by side to substantially fill the area. Thus, the mirror surfaces form a total reflective area that is significantly larger than the individual mirror surfaces. However, the total area is not entirely reflective. Instead, gaps defined by the sides of adjacent mirror substrates are located between directly adjacent mirror elements. Functionally, it is necessary to allow collision-free relative movement between adjacent mirror elements.

[0019] In the case of each mirror unit, the functional components of the mirror unit are arranged in the intermediate space between the base element and the mirror element. For example, in the intermediate space between the base element and the mirror substrate, each mirror unit may include components of a suspension system for movably mounting the mirror element on the base element and components of an actuator system for generating movement of the mirror element relative to the base element in response to receiving a control signal. Furthermore, sensor elements, such as position sensor elements, that sense the respective orientation of the mirror surface relative to the base element may also be arranged in this intermediate space. Components of the control electronics may be arranged on the upper side of the base element opposite the mirror element.

[0020] The suspension system mechanically connects the mirror element to the base element. The suspension system may, for example, include elastic or flexible parts or components that provide the necessary mobility. The suspension system may contain joints, for example in the form of flexures, that articulate its components or parts. The actuator system may be a system configured independently from the suspension system and provides forces and torques for movement of the mirror element. It is also possible to integrate the suspension system and the actuator system, with parts of the suspension system also serving as functional parts of the actuator system. Components of the sensor system may be integrated as well.

[0021] Therefore, the actuator system, the sensor system and further mechanical elements can all be arranged below the mirror surface, i.e., in this design, between the mirror surface and the carrier structure, resulting in a very large area ratio of the reflective mirror surface of the individual mirrors to the total area of ​​the multi-mirror array.

[0022] In order to obtain higher integration densities, manufacturing processes increasingly use techniques from the field of manufacturing microelectromechanical systems (abbreviated MEMS) for the production of, for example, drive elements (elements of actuator systems), mechanical elements (e.g. elements of suspension systems) and / or sensor elements etc. Nowadays, such MEMS processes are substantially based on structuring processes in which an initial substrate, for example made of silicon or silicon compounds, is structurized to design the required components.

[0023] The inventors recognize that the advantages of applying MEMS technology to the fabrication of multi-mirror arrays are offset by disadvantages. This is particularly true for applications using EUV radiation. In these applications, ionization processes in hydrogen-containing atmospheres under the action of high-energy EUV radiation produce positively charged hydrogen ions (H + ion) and neutral H * It is particularly considered that an EUV-induced hydrogen plasma containing radicals may occur, and since hydrogen ions and radicals have a strong corrosive effect, particularly on silicon, under the action of the hydrogen plasma, components of the mirror unit may undergo corrosive ablation and therefore structural changes and other degradation processes.

[0024] Due to the gaps between the individual mirror substrates, functionally important components located in the intermediate space behind the mirror surface or the mirror substrate and the carrier structure may also be attacked. This is particularly true for MEMS structures. Many influences can contribute to this. First, a hydrogen plasma containing hydrogen ions may be generated in the area in front of the mirror surface and subsequently pass through the gap into the intermediate space, where it may attack the structure. This is particularly dangerous if EUV radiation passes through the gap into the intermediate space between the mirror substrate and the carrier structure and potentially generates hydrogen ions within the volume of the MEMS structure located there. For example, this may be the case when EUV radiation is irradiated onto an area on the MMA that has a lateral extent larger than the normal lateral extent of the individual mirror surfaces.

[0025] Ablation due to corrosion of components of the mirror unit located behind the mirror surface, especially silicon corrosion, can cause two problems in particular. First, silicon can deposit on optical surfaces, not only precisely on the surface of the multi-mirror array, but also on other optical surfaces as a result of spreading. This can result in significant transmission losses within a relatively short period of time, resulting in the practically usable service life of the EUV device being significantly shorter than the theoretically expected service life. Furthermore, internal and external photoelectric effects can be induced, which can alter the properties, especially the electrical properties, of the functional structural elements of the mirror unit, leading to unacceptable changes in properties and even complete failure in a relatively short period of time (e.g., within one year).

[0026] In addition to these defects caused by uncontrolled corrosion attack, performance degradation is already known as a result of the influx of contaminant particles, for example consisting of tin or tin compounds, into the region between the mirror substrate and the carrier structure. These can block or impede the movement of structural elements that are movable relative to one another, and can also affect the positioning of the mirror during controlled tilting by interfering with the interaction between the actuators and sensors. Furthermore, further problems can arise due to radiation-induced heating and degradation processes, especially in the regions of the surface directly exposed to the incident EUV radiation, and due to electrical disturbances caused by plasma flows and the photoelectric effect.

[0027] Even if corrosion issues are not prominent in DUV applications, functionality and service life can still be significantly limited in DUV equipment due to failures caused by radiation heating effects and induced photoelectric effects.

[0028] The present inventors have developed a solution that may contribute to significantly reducing or avoiding such problems.

[0029] According to one aspect of the invention, particularly in view of the corrosion problem, significant improvements can be achieved by orienting at least a portion of, or the entirety of, each of the side surfaces of the mirror substrate at an angle other than 90° relative to the assigned mirror surface or to the front surface of the mirror substrate. This represents a departure from known design principles in which mirror elements are each designed so that their side surfaces are substantially perpendicular to the front surface or mirror surface provided with a reflective coating. In this case, the term "substantially perpendicular" particularly means that, within respective manufacturing tolerances, the side surfaces of conventional mirror substrates are oriented perpendicular to the reflective front side in the edge region of the mirror surface. In other words, to the inventors' knowledge, no significant measures have been taken to deviate from this conventional design in typical multi-mirror arrays.

[0030] Deviating therefrom, it is proposed here to intentionally manufacture the entire side surface, or at least a functionally significant portion of each of the side surfaces, in an oblique position relative to the mirror surface that deviates significantly from the manufacturing tolerances of the respective manufacturing process. Thus, according to this aspect of the invention, the edge regions of the mirror substrates are designed as protective structures, in that the mirror substrate side surfaces of directly adjacent mirror substrates are each completely or at least partially oblique, or at an angle that on average deviates from 90°, relative to the associated mirror surface.

[0031] In this regard, different configurations of the oblique side surfaces are possible: the entire height of the side surfaces as a macroscopic plane (located between the front and back surfaces) can be obliquely oriented at the same angle relative to the mirror surface. If the back surface extends parallel to the front surface and the opposite side surfaces of the same mirror element are symmetrically oblique thereto, the mirror substrate will obtain a substantially trapezoidal cross-sectional form in a cross section passing between the opposite side surfaces.

[0032] The side surface can also be completely or at least partially convexly or concavely curved. Such curved portions can be advantageous for manufacturability reasons and / or in terms of functionality. The side surface can include at least one portion oriented substantially perpendicular to the mirror surface. However, such perpendicular portions should preferably be small in area, i.e., the oblique portions should dominate.

[0033] However, the side surface may also have smaller scale stepped features resulting in a macroscopic oblique orientation of the side surface.

[0034] There are various options for realizing this concept of angled sides.

[0035] According to one development, the mirror substrate side surfaces of directly adjacent mirror substrates are designed and oriented in such a way that the gap width (at least in the case of non-tilted mirror elements) formed between the directly adjacent mirror substrates increases continuously or on average at least in one or more sections from the front surface provided with the reflective coating in the direction towards the base element, In the neutral position of the mirror element, the gap is consequently narrower on the side of the mirror surface, i.e. the radiation entrance side, than on the side facing the base element (radiation exit side).

[0036] Preferably, the design is selected so that the front surface of the mirror element provided with the reflective coating has a larger surface area than the area enclosed by the outer edge of the back surface, the outer edge of the back surface being recessed inward by a lateral offset relative to the outer edge of the front surface at all circumferential positions. This geometry can also be described as a taper of the mirror substrate from the reflective front side towards the back side or base element. Preferably, the back surface extends substantially parallel to the front surface.

[0037] To help understand the advantages of this approach, some of the inventors' findings are briefly described below. The inventors have recognized that side surfaces can significantly contribute to the coupling of incident radiation into the intermediate spaces between adjacent mirror elements, especially when the adjacent mirror elements are tilted relative to one another. One reason for this unwanted role is that, during the manufacturing process of a multi-mirror array, a reflective coating is generally applied to the side surfaces adjacent to the front surface as well as the front surface. Although not necessary for the intended use of the multi-mirror array, this situation generally arises automatically if no measures are taken. When the relevant mirror element is in its non-tilted neutral position (tilt angle = 0°) and the angle of incidence of the radiation relative to the normal to the base surface is not too large, the side surfaces generally receive no or relatively little direct radiation. However, when the mirror element is tilted, a relatively large portion of the incident radiation may directly impinge on the side surfaces at more or less large angles of incidence (grazing incidence). This means that a significant amount of radiation can be reflected at the side surfaces with low losses or high reflectivity and then coupled into the intermediate spaces between adjacent mirror units with a significantly altered beam direction. Thus, one or more reflections of incident radiation off the sides of a tilted mirror element may allow harmful radiation to reach areas behind adjacent mirror elements that would otherwise be "dark", i.e. in the shadow of the mirror element, in the case of a non-tilted mirror element. Thus, only a small area behind the mirror element, at the same height as the base element, protected from direct radiation may remain that can be used for mounting particularly radiation-sensitive components.

[0038] On the other hand, if the side surfaces are angled "inward" behind the mirror element partially or over the entire height, this harmful effect can be attenuated and the size of the radiation-protected area behind the mirror element can be increased, which increases the radiation-protected installation space behind each mirror element and slows down or completely suppresses possible degradation processes and electrical disturbances (plasma flow, photoelectric effect) due to harmful radiation.

[0039] The range of oblique positions can be adapted to the respective installation situation in use. Particular consideration can be given to the local incidence angle range of the EUV radiation. Generally, the oblique position does not need to be particularly significant. In some embodiments, the offset can be of the order of 10% or less of the thickness or height (measured between the front and rear surface) of the mirror substrate. In particular, the offset can be 3% or more of the thickness / height, preferably 5% or more, and / or 15% or less of the thickness / height.

[0040] Alternatively or additionally, it may be advantageous if the included angle of the transition between the front face and the adjacent side face is in the range of 80° to 89°, in particular in the range of 84° to 88°.

[0041] If the angle is significantly greater than the upper limit, it is usually not possible to obtain much improvement over conventional vertical sidewalls, whereas if the angle is significantly less than the lower limit, in particular in the neutral position of the mirror element, higher intensities may reach the area to be protected in the case of obliquely incident radiation at relatively large angles of incidence and / or the protected (dark) area may be smaller than in conventional solutions with vertical sidewalls.

[0042] Yet another approach is to control the manufacturing process so that the side surfaces have a surface roughness at least one order of magnitude (i.e., 10 times or more) greater than the surface roughness of the front surface provided with the reflective coating. For example, the surface roughness of the side surfaces can be 100 nm RMS or greater, or even 1000 nm RMS or greater. By comparison, for the applications considered here, the surface roughness of polished optical surfaces ranges from less than 1 nm RMS, or even less than 0.2 nm RMS. This value relates to the so-called root-mean-square roughness (RMS). If the side surfaces are manufactured with a large surface roughness by appropriate measures, specular reflection at the side surfaces can be significantly suppressed, and the incident radiation can only be scattered over a large solid angle range. As a result, radiation incident on a rough side surface is "harmless" because its energy is dispersed in space and / or absorbed in the area of ​​the side surface.

[0043] This measure (design of side surfaces with high surface roughness) can be advantageous regardless of other characteristics of the side surfaces, especially in the case of side surfaces that are substantially perpendicular to the mirror surface.

[0044] The oblique flank solution can also be implemented in different ways.

[0045] In one development, the edge region of the mirror substrate is designed as a corrosion protection structure by having the mirror substrate side surfaces of directly adjacent mirror elements each oriented at an angle offset from 90° to the assigned mirror surface, such that the gap formed by the oriented side surfaces of adjacent mirror elements is oriented obliquely to the mirror surface and / or to the incident EUV radiation and / or to the base surface of the multi-mirror array. The gap can be designed such that direct radiation passing through the gap is blocked for normal radiation incidence (to the base surface) (normal incidence), at least whenever the mirror element is in its zero position. As a result, the intermediate space is shielded from transmitted EUV radiation by the mirror substrate, even in the gap region. The shielding can be complete or total. However, other partial shielding can also be performed.

[0046] The edge region of the mirror substrate can be designed such that the gap has a first (front) gap opening with a first gap width adjacent to the mirror surface and a second (rear) gap opening with a second gap width adjacent to the backside of the mirror substrate, the first and second gap openings having a lateral offset due to the oblique orientation of the gaps, such that the effective gap width of the oblique gap effective for (direct) radiation passage is smaller than the first and / or second gap widths. In particular, the effective gap width vanishes, i.e., a radiopaque gap is achieved. For a given absolute gap width, the effective gap width for radiation passage can be less than the absolute gap width but greater than zero. For example, for mirror substrates with edge lengths in the range of one or a few millimeters and thicknesses in the range of one or a few tenths of a millimeter, the gap width can be in the range of 10 μm to 100 μm, in particular in the range of 20 μm to 60 μm.

[0047] The lateral offset between the first and second gap openings is preferably at least as large as the maximum of the first and second gap widths. The beam direction at the installation site should be considered in the design phase so that the effective lateral offset, i.e., the lateral offset perpendicular to the beam direction, is decisive. This makes it possible to eliminate EUV radiation that can pass through the gap directly into the intermediate space behind it, regardless of whether the EUV radiation incident on the mirror surface is normal or virtually normal incidence or oblique radiation incidence.

[0048] Preferably, the mirror substrate sides are oriented such that a substantially planar parallel gap results when the mirror elements are in their neutral positions. In this sense, a gap is "substantially planar parallel" if the sides defining the gap extend parallel to one another within manufacturing tolerances or subtend an angle of 10° or less. In particular, this is facilitated by alignment.

[0049] The mirror substrate side surfaces of adjacent mirror elements can be oriented such that on one side of the gap formed between the mirror elements there is an angle of less than 90° (acute angle) between the mirror substrate side surface and the mirror surface, and on the other side there is an angle of more than 90° (obtuse angle), and the absolute values ​​of the deviations from 90° on both sides are the same or virtually the same (deviation of 5° or less).

[0050] It has been found to be advantageous in many cases if the oblique orientation of the mirror substrate side surface is selected such that its deviation from the 90° orientation relative to the mirror surface is at least 10°, and in particular can be in the range of 20° to 30°. As a result, for relatively small absolute gap widths, a good compromise can be achieved between the gap width (which should generally be as small as possible) and the available pivoting area without collisions.

[0051] A particularly preferred arrangement is one in which each mirror substrate has two oblique mirror substrate side surfaces, each of which includes an angle greater than or less than 90° with respect to the mirror surface on one side and an angle of the same absolute angle, but in the opposite direction, on the other side. As a result, the mirror substrate has a substantially trapezoidal cross-sectional shape in a cross section passing between the opposing side surfaces. In this case, the mirror elements in a continuous row alternate inverted trapezoidal cross-sectional shapes, so that the orientation of the intervening oblique gaps alternates for each gap. Preferably, this applies in all directions along the length of the continuous mirror substrate; for example, in the case of individual mirrors with square mirror surfaces, the mirror substrate may have the shape of a regular square pyramid truncated.

[0052] Therefore, the edge regions of the mirror substrates may be designed as anti-corrosion structures by orienting the mirror substrate side surfaces of directly adjacent mirror substrates at angles other than 90° to the associated mirror surface.

[0053] As a result of the oblique position of the side surfaces, the edge regions of the mirror substrate can contribute in various ways to the protection of the components behind them and can therefore also serve as components of a corrosion protection system and / or a protection system against electrical disturbances.

[0054] Thus, according to one wording of this aspect of the invention, the multi-mirror array comprises a corrosion protection system, which is particularly configured to prevent or reduce corrosive attack resulting in material removal and / or structural modification of EUV radiation-induced hydrogen plasma on components of the mirror unit arranged between the mirror surface and the carrier structure compared to a mirror unit without the corrosion protection system. In this case, the corrosion protection system comprises a corrosion protection structure. As described, the corrosion protection structure may be formed or disposed on the mirror elements. The corrosion protection structure may also be formed or disposed on the base elements and / or components of the suspension system and / or components of the actuator system and / or components of an optionally present sensor system.

[0055] A "corrosion-resistant structure" within the meaning of this application is a structural component of a multi-mirror array that is specifically designed and effective to address the above-mentioned corrosion problem. Compared to multi-mirror arrays from the prior art, a corrosion-resistant structure can be provided by being attached to the prior structure as an additional structural feature. It is also possible to create a corrosion-resistant structure by giving components present in a prior art multi-mirror array a specific design or structure that improves their protection against corrosive attack.

[0056] The corrosion protection system or structure can be used to reduce or even completely prevent the effects of such corrosion attack, such that corrosion degradation phenomena are largely avoided or in any case their occurrence is delayed over time, so that production runs are possible for a significantly longer period of use than would be possible without the corrosion protection system. Because the corrosion protection system includes corrosion protection structures on one or more components of the mirror unit, and the corrosion protection structures are formed on or attached to each component, they can be readily fabricated and / or attached as appropriate during the manufacture of the multi-mirror array, rather than having to be manufactured as separate units and, in some cases, separately installed and adjusted relative to the multi-mirror array.

[0057] Problems caused by corrosion attack can be reduced or avoided in various ways using corrosion protection structures. For example, the corrosion protection structure can be designed so that, for example, EUV radiation is emitted into the intermediate space between the mirror surface and the carrier structure, or the amount of incident radiation is reduced compared to a design without the corrosion protection structure. This can avoid the generation of corrosive plasma in the intermediate space, thereby reducing the corrosion rate in this area. Alternatively or additionally, the corrosion protection structure can be designed so that plasma generated in front of the mirror surface is prevented from penetrating the gap into the intermediate space and contributing to the corrosion attack.

[0058] Preferably, at least the base element, the suspension system, and the actuator system are formed as MEMS structures made of silicon (Si) or silicon compounds. Conventional MEMS techniques for manufacturing miniature structures can then be adapted accordingly. However, at least some of the structures, in particular the mirror substrate, can be designed from a material that cannot be attacked by corrosion or that is attacked to a lesser extent than silicon, such as aluminum oxide (Al2O3).

[0059] According to one development, directly adjacent mirror elements or their mirror surfaces can be arranged with a permanent or temporary height offset relative to one another so that a first reference point defined by one mirror surface and a second reference point defined by the immediately adjacent mirror surface are positioned one above the other at a height distance, the reference points corresponding to the geometric centers of the mirror surfaces. The height offset, which is the same or similar in size, also exists in the region of the gap formed between the mirror elements, further separating the interference contours formed by the opposing edges of the mirror elements, thereby enabling a relatively large tilt range to be achieved without collisions. The height offset can be predefined and fixed. For example, it can be in the range of 25% to 75% of the substrate thickness. As a result, a particularly effective overlap of adjacent mirror substrates can be achieved.

[0060] The multi-mirror array may comprise a controllable height adjustment device for reversibly and continuously adjusting the height of individual mirror elements relative to adjacent mirror elements in response to a control signal.

[0061] To this end, in some embodiments, the actuator system for generating the movement of the mirror elements is designed with two rotational degrees of freedom as well as one translational degree of freedom, which can be used for controllable height adjustment. The translational degree of freedom may correspond to movement of the mirror elements along a translation axis that is perpendicular or at an angle to the rotation axis of the rotational degree of freedom. The rotation axes of the rotational degrees of freedom are preferably positioned substantially orthogonal to each other in a plane, and the translation axis of the translational degree of freedom extends perpendicular to said plane.

[0062] Alternatively or additionally, the base elements can be individually height adjustable, so that the entire mirror unit can be raised and lowered again, for example using at least one thickness-variable piezoelectric layer between the carrier structure and the base element.

[0063] As mentioned, a height offset may be advantageous, in particular for collision reasons, and therefore desirable. In the overall optical system containing the EUV multi-mirror array, i.e. for example in the illumination system of an EUV device, corresponding tolerances may be provided to take into account that the heights of adjacent mirror elements of the EUV multi-mirror array are offset relative to one another, resulting in the mirror elements reflecting off planes or surfaces that are offset from one another in the direction of incident radiation.

[0064] In some embodiments, the controller of the height adjustment device is configured to allow for height adjustment of a mirror element depending on the tilt position of the neighboring mirror element, which in particular allows to avoid collisions depending on the switching position and to optimize the illumination according to the switching state.

[0065] Controllable relative height adjustment of adjacent mirror elements of an EUV multi-mirror array may also be advantageous independently of other features of the EUV multi-mirror array described herein, and may be a protectable invention in its own right, for example in an EUV multi-mirror array in which the mirror elements include side surfaces oriented perpendicular to the mirror surface, thereby eliminating diagonal gaps.

[0066] Alternatively or additionally to the measures described above, in some embodiments the corrosion protection system comprises a corrosion protection structure in the form of a radiation trapping element, comprising a radiation entrance surface each arranged in the region of the gap on the back side of the mirror substrate opposite the mirror surface. Such radiation entrance surfaces can be arranged in close proximity to the second gap opening on the carrier side of the gap and can protrude beyond the second gap opening on both sides so that even EUV light passing through the gap at an angle can be incident on the radiation entrance surface and thus its adverse effects can be mitigated. The radiation trapping element can possibly be fabricated as a MEMS structure, optionally integrally with other structures during the manufacture of the mirror unit.

[0067] In some cases, the radiation trapping element can use different functional mechanisms individually or in combination with each other. According to one embodiment, at least the region of the radiation entrance surface of the radiation trapping element consists of a functional material that is an absorbing material that has an absorbing effect on EUV radiation and / or a recombination catalyst that increases the recombination probability for the formation of H molecules when it comes into contact with hydrogen ions and hydrogen atoms. According to current knowledge, particularly suitable functional materials are materials from the group of ruthenium (Ru), platinum (Pt), rhenium (Rh), rhodium (Rh), iridium (Ir), molybdenum (Mo), nickel (Ni) and iron (Fe), which have both absorbing and recombination-promoting properties.

[0068] The radiation trapping elements may be partially height adjustable, and the height setting of each radiation trapping element may be optionally effected depending on the tilt position and / or height position of the adjacent mirror element in order to improve individual corrosion protection.

[0069] According to one development, yet another approach to reducing corrosion problems consists of a corrosion protection system including at least one protective film, which includes a gap covering that spans the gap formed between directly adjacent mirror substrates and contacts the mirror substrates defining the gap, in particular, is fixed to the mirror substrate. Thus, the protective film and / or the gap covering are directly carried by the adjacent mirror elements and can be attached and detached together with them. Therefore, instead of separate elements, the gap covering can be manufactured together with the adjacent mirror elements carrying the gap covering. In some cases, the protective film or the gap covering can be fixed to the mirror element at a later date. The gap covering can be arranged on the front side of the mirror element and cover the first gap opening, thereby already protecting the gap area. However, it is also possible for the gap covering to be attached in the area of ​​the second gap opening, i.e., to only act after the gap has been passed.

[0070] There are various options for the design of the gap coating. In some embodiments, the entire gap coating is made of an EUV-transparent material. This allows EUV radiation to pass through the gap coating area and reach the intermediate space. However, hydrogen plasma is prevented from reaching the intermediate space from the area of ​​the mirror arrangement, thereby reducing corrosion attack in this respect. This arrangement also prevents blocking of two adjacent illumination channels due to particle contamination.

[0071] In other embodiments, the protective film comprises an absorbing material in the region of the mirror coating that has an absorbing effect on EUV radiation, which absorbing material may for example be selected from the group of Ru, Pt, Re, Rh, Ir, Mo, Ni, Fe. In these variants, the gap coating not only provides protection against hydrogen plasma penetrating into the intermediate space, but also blocks EUV radiation, so that in this respect no new hydrogen plasma can be generated in the intermediate space either.

[0072] In embodiments where the protective film is attached to the entrance side of the gap, i.e., flush with the front side of the mirror, the protective film can be attached to the outer surface of the mirror, in the edge region of the mirror. In the case of EUV-transparent protective films, they can also be applied as large-area films extending across multiple adjacent mirror faces, thereby spanning intervening gaps. The film can be designed to be very flexible, allowing the mirrors to be tilted relative to each other without excessive mechanical loads on the gap coverings that cover intervening gaps.

[0073] In one development, a protective film on the front side of the mirror substrate is arranged as part of the multilayer arrangement between the mirror substrate and the reflective coating, which allows for a particularly high reflectivity since the free surface of the reflective coating is not occupied by the protective film, as the multilayer arrangement is not covered by the film.

[0074] It is also possible to arrange the protective film on the back side of the mirror substrate. In a variant with a radiation trapping element, the protective film can be arranged, for example, between the back side of the mirror substrate and the front side or back side of the radiation trapping element. In the case of a radiation trapping element mounted in a height-adjustable manner, the radiation trapping element can be moved in the height adjustment direction as a result of layer stress in the protective film between the mirror unit and the radiation trapping element, so that height adjustment can be achieved depending on the tilt position of the radiation trapping element. As a result, a separate actuator for adjusting the height of the radiation trapping element can be omitted.

[0075] Alternatively or in addition to one or more of the above measures, the corrosion protection system may comprise at least one corrosion protection structure in the form of a corrosion protection layer applied to components of the mirror unit made of a component material in areas susceptible to corrosion attack, the corrosion protection layer comprising at least one protective layer material that is more corrosion resistant to corrosive attack by hydrogen ions than the component material. In the case of components made of silicon or silicon compounds, the corrosion protection layer may for example consist of aluminium in the unoxidized or oxidized state, i.e. Al2O3.

[0076] The application of the present invention and its exemplary embodiments is not limited to mirror units whose components are manufactured using MEMS manufacturing techniques and based on silicon or silicon compounds. It is therefore possible to manufacture some or all of the components susceptible to corrosive attack, at least in the surface areas of the components likely to be exposed to the attack, from a material that is particularly resistant to the attack, for example from aluminum oxide.

[0077] The invention also relates to an illumination system for an EUV device, the illumination system being embodied to receive EUV radiation from an EUV radiation source during operation of the EUV device and to shape from at least a portion of the received EUV radiation illumination radiation directed to an illumination field at an exit surface of the illumination system, the illumination system comprising at least one EUV multi-mirror array of the type described herein.

[0078] The EUV apparatus can be, for example, a projection exposure apparatus for EUV microlithography or a mask inspection apparatus that uses EUV radiation for inspecting masks (reticles) for EUV microlithography.

[0079] Further advantages and aspects of the present invention are apparent from the claims and from the following description of exemplary embodiments of the invention which proceeds with reference to the drawings. [Brief explanation of the drawings]

[0080] [Figure 1] 1 shows a schematic illustration of optical components of an EUV microlithography projection exposure apparatus having an illumination system housing one or more EUV multi-mirror arrays according to an exemplary embodiment; [Figure 2] 1 shows a schematic cross section of a conventional EUV multi-mirror array in a plasma environment containing H+ ions. [Figure 3] 1 shows a vertical cross section of the transition region between two directly adjacent mirror units, with an oblique gap positioned between the mirror substrates that blocks EUV radiation. [Figure 4A]1 shows the shielding effect of a diagonal gap compared to a vertically extending gap from the prior art. [Figure 4B] 1 shows the shielding effect of a diagonal gap compared to a vertically extending gap from the prior art. [Figure 4C] 1 shows the shielding effect of a diagonal gap compared to a vertically extending gap from the prior art. [Figure 4D] 1 shows the shielding effect of a diagonal gap compared to a vertically extending gap from the prior art. [Figure 5A] 10 shows an example in which directly adjacent mirror elements are permanently or intermittently offset in height from one another. [Figure 5B] 10 shows an example in which directly adjacent mirror elements are permanently or intermittently offset in height from one another. [Figure 5C] 10 shows an example in which directly adjacent mirror elements are permanently or intermittently offset in height from one another. [Figure 6] 1 shows an exemplary embodiment with an anti-erosion structure in the form of a radiation trapping element behind the gap. [Figure 7A] 1 shows an exemplary embodiment having a corrosion protection structure in the form of a protective coating with gap coverage carried by the mirror element. [Figure 7B] 1 shows an exemplary embodiment having a corrosion protection structure in the form of a protective coating with gap coverage carried by the mirror element. [Figure 7C] 1 shows an exemplary embodiment having a corrosion protection structure in the form of a protective coating with gap coverage carried by the mirror element. [Figure 7D] 1 shows an exemplary embodiment having a corrosion protection structure in the form of a protective coating with gap coverage carried by the mirror element. [Figure 7E] 1 shows an exemplary embodiment having a corrosion protection structure in the form of a protective coating with gap coverage carried by the mirror element. [Figure 7F] 1 shows an exemplary embodiment having a corrosion protection structure in the form of a protective coating with gap coverage carried by the mirror element. [Figure 8A] 1 shows one option for applying a protective coating to the area of ​​the reflective coating. [Figure 8B] 1 shows one option for applying a protective coating to the area of ​​the reflective coating. [Figure 9A] 1 shows a first variant of a method for manufacturing a multi-mirror array with oblique gaps; [Figure 9B] 1 shows a first variant of a method for manufacturing a multi-mirror array with oblique gaps; [Figure 9C] 1 shows a first variant of a method for manufacturing a multi-mirror array with oblique gaps; [Figure 10A] 10 shows a second variant of the method for manufacturing a multi-mirror array with oblique gaps. [Figure 10B] 10 shows a second variant of the method for manufacturing a multi-mirror array with oblique gaps. [Figure 10C] 10 shows a second variant of the method for manufacturing a multi-mirror array with oblique gaps. [Figure 11] 10A and 10B illustrate schematically an exemplary embodiment in which the mirror substrate includes side surfaces positioned at an angle such that the gap width increases in the direction of the base element. [Figure 12A] 10 shows an alternative design option for diagonally positioned sides. [Figure 12B] 10 shows an alternative design option for diagonally positioned sides. [Figure 12C] 10 shows an alternative design option for diagonally positioned sides. [Figure 13] 1 shows a diagram illustrating an exemplary simulation calculation showing the relationship between the tilt position of a mirror element and the illumination of a base element. [Figure 14A] 1 shows a comparison of illumination conditions for a conventional mirror element with vertical sides. [Figure 14B] 10 shows a comparison of illumination conditions for an exemplary embodiment with angled sides. DETAILED DESCRIPTION OF THE INVENTION

[0081] Examples of multi-mirror array designs are described below by way of example with reference to a possible use in an EUV device from the field of microlithography: A multi-mirror array having a reflective layer that has a reflective effect on EUV radiation is referred to here as an EUV multi-mirror array.

[0082] The essential components of a microlithography projection exposure apparatus 1 are described below, first by way of example, with reference to Figure 1. The description here of the basic construction of the projection exposure apparatus 1 and its components should not be considered limiting.

[0083] In addition to the radiation source 3, the illumination system 2 of the projection exposure apparatus 1 comprises an illumination optical unit 4, which illuminates an object field 5 in an object plane 6. A reticle 7, which is arranged in the object field 5, is exposed here. The reticle 7 is held by a reticle holder 8, which is displaceable, in particular in the scanning direction, by a reticle displacement drive 9.

[0084] For purposes of illustration, Figure 1 shows a Cartesian xyz coordinate system. The x direction extends perpendicular to the plane of the figure. The y direction extends horizontally and the z direction extends vertically. In Figure 1, the scanning direction extends in the y direction. The z direction extends perpendicular to the object plane 6.

[0085] The projection exposure apparatus 1 comprises a projection optical system 10. The projection optical system 10 serves to image the object field 5 into an image field 11 in an image plane 12. The image plane 12 extends parallel to the object plane 6. Alternatively, an angle other than 0° between the object plane 6 and the image plane 12 is also possible.

[0086] The structures on the reticle 7 are imaged onto a photosensitive layer of a wafer 13 arranged in the region of the image field 11 of the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 is displaceable, in particular along the y direction, by a wafer displacement drive 15. Both the displacement of the reticle 7 by the reticle displacement drive 9 on the one hand and the displacement of the wafer 13 by the wafer displacement drive 15 on the other hand can be synchronized with each other.

[0087] The radiation source 3 is an EUV radiation source. The radiation source 3 in particular emits EUV radiation 16, hereinafter also referred to as working radiation or illumination radiation. In particular, the working radiation has a wavelength in the range of 5 nm to 30 nm. The radiation source 3 can be a plasma source, for example an LPP (Laser Produced Plasma) source or a GDPP (Gas Discharge Plasma) source. It can also be a synchrotron-based radiation source. The radiation source 3 can be a Free Electron Laser (FEL).

[0088] Illumination radiation 16 leaving the radiation source 3 is focused by a collector 17. The collector 17 may be a collector with one or more ellipsoidal and / or hyperbolic reflecting surfaces. The illumination radiation 16 may be incident on at least one reflecting surface of the collector 11 at grazing incidence (GI), i.e. at an angle of incidence greater than 45°, or at normal incidence (NI), i.e. at an angle of incidence smaller than 45°. The collector 17 may be structured and / or coated to optimize its reflectivity for the radiation used and to suppress extraneous light.

[0089] Downstream of the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 may form a separation between the radiation source module comprising the radiation source 3 and the collector 17 and the illumination optical unit 4.

[0090] The illumination optical unit 4 comprises a deflection mirror 19 and, downstream in the beam path, a first facet mirror 20. The deflection mirror 19 can be a plane deflection mirror or a mirror with a beam-influencing effect beyond a pure deflection effect. Alternatively or additionally, the deflection mirror 19 can be in the form of a spectral filter that separates the used optical wavelength of the illumination radiation 16 from extraneous light of a different wavelength. If the first facet mirror 20 is arranged in a plane of the illumination optical unit 4 that is optically conjugate with the object plane 6 as a field plane, this facet mirror is also referred to as a field facet mirror. The first facet mirror 20 comprises a plurality of individual first facets 21, also referred to as field facets in the following. FIG. 1 shows only some of these facets 21 by way of example.

[0091] The first facet 21 may be in the form of a macroscopic facet, in particular a rectangular facet, or a facet having an arcuate edge profile or an edge profile formed as a partial circle. The first facet 21 may be in the form of a planar facet, or a convexly or concavely curved facet.

[0092] The first facet 21 itself can also consist of a number of individual mirrors, in particular a number of micromirrors, as is known, for example, from DE 10 2008 009 600. The first facet mirror 20 can in particular be in the form of a microelectromechanical system (MEMS system). See DE 10 2008 009 600 for further details.

[0093] The illumination radiation 16 travels horizontally between the collector 17 and the deflection mirror 19, ie along the y-direction.

[0094] A second facet mirror 22 is arranged downstream of the first facet mirror 20 in the beam path of the illumination optical unit 4. If the second facet mirror 22 is arranged in the pupil plane of the illumination optical unit 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 can also be arranged away from the pupil plane of the illumination optical unit 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US Patent Application Publication No. 2006 / 0132747, EP 1 614 008 and US 6,573,978.

[0095] The second facet mirror 22 includes a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

[0096] The second facet 23 may likewise be a macroscopic facet which may have, for example, a circular, rectangular or hexagonal perimeter, or may be a facet made up of a micromirror. In this respect, reference is also made to DE 10 2008 009 600 A1.

[0097] The second facet 23 may have a flat reflecting surface or a convexly or concavely curved reflecting surface.

[0098] The illumination optical unit 4 therefore forms a double-faceted system, this basic principle also being called a fly's eye integrator.

[0099] It may be advantageous not to position the second facet mirror 22 exactly in a plane that is optically conjugate with the pupil plane of the projection optical unit 7 .

[0100] The individual first facets 21 are imaged into the object field 5 by means of a second facet mirror 22. The second facet mirror 22 is the last beam-shaping mirror in the beam path upstream of the object field 5 or indeed the final mirror for the illumination radiation 16.

[0101] In yet another embodiment (not shown) of the illumination optical unit 4, a transfer optical unit can be arranged in the beam path between the second facet mirror 22 and the object field 5, which in particular contributes to the imaging of the first facet 21 into the object field 5. The transfer optical unit can have exactly one mirror or two or more mirrors arranged in succession in the beam path of the illumination optical unit 4. The transfer optical unit can in particular include one or two normal incidence mirrors (NI mirrors) and / or one or two grazing incidence mirrors (GI mirrors).

[0102] In the design shown in FIG. 1, the illumination optical unit 4 comprises exactly three mirrors downstream of the collector 17 , namely a deflection mirror 19 , a field facet mirror 20 and a pupil facet mirror 22 .

[0103] In yet another embodiment of the illumination optical unit 4, the deflection mirror 19 can also be omitted, so that the illumination optical unit 4 then has exactly two mirrors downstream of the collector 17, specifically a first facet mirror 20 and a second facet mirror 22.

[0104] The imaging of the first facet 21 onto the object plane 6 by the second facet 23 or by means of the second facet 23 and the transfer optical unit is usually only an approximate imaging.

[0105] The projection optical unit 10 comprises a number of mirrors Mi, which are numbered according to their position in the beam path of the projection exposure apparatus 1 .

[0106] 1, the projection optical unit 10 includes six mirrors M1 to M6. 4, 8, 10, 12 or any other number of mirrors Mi are equally possible. The penultimate mirror M5 and the final mirror M6 each have a passage aperture for the illumination radiation 16. The projection optical unit 10 is a double-shielded optical unit. The projection optical unit 10 has an image-side numerical aperture that is greater than 0.5, may be greater than 0.6, and may be, for example, 0.7 or 0.75.

[0107] The reflective surface of the mirror Mi can be in the form of a freeform surface without an axis of rotational symmetry. Alternatively, the reflective surface of the mirror Mi can be designed as an aspheric surface, in which case the reflective surface shape has exactly one axis of rotational symmetry. Like the mirrors of the illumination optical unit 4, the mirror Mi can have a coating that is highly reflective with respect to the illumination radiation 16. These coatings can in particular be in the form of a multilayer coating with alternating layers of molybdenum and silicon.

[0108] Projection optical unit 10 has a large object-image offset in the y direction between the y coordinate of the center of object field 5 and the y coordinate of the center of image field 11. In the y direction, this object-image offset may have approximately the same magnitude as the z distance between object plane 6 and image plane 12.

[0109] The projection optical unit 10 can have an anamorphic form in particular. In particular, it has different imaging scales βx, βy in the x and y directions. The two imaging scales βx, βy of the projection optical unit 7 are preferably (βx, βy)=(+ / -0.25, + / -0.125). A positive imaging scale β means imaging without image inversion. A negative sign for the imaging scale β means imaging with image inversion.

[0110] The projection optical unit 7 results in a size reduction in the x-direction, ie perpendicular to the scanning direction, of a ratio of 4:1.

[0111] The shadow optical unit 10 provides a size reduction of 8:1 in the y-direction, ie the scanning direction.

[0112] Other imaging scales are possible as well, including imaging scales of the same sign and magnitude in the x and y directions, for example 0.125 or 0.25.

[0113] The number of intermediate image planes in the x and y directions in the beam path between the object field 5 and the image field 11 may be the same or may differ depending on the design of the projection optical unit 10. An example of a projection optical unit with a different number of such intermediate images in the x and y directions is known from US Patent Application Publication No. 2018 / 0074303.

[0114] Each pupil facet 23 is assigned to exactly one of the field facets 21 in order to form a respective illumination channel that illuminates the object field 5. In particular, this makes it possible to obtain illumination according to the Köhler principle. The far field is decomposed into a plurality of object fields 5 by means of the field facets 21. The field facets 21 generate a plurality of images of intermediate foci on the respectively assigned pupil facets 23.

[0115] The field facets 21 are imaged onto the reticle 7 in an overlapping manner by means of the respectively assigned pupil facets 23 in order to illuminate the object field 5. The illumination of the object field 5 is in particular as uniform as possible. Its uniformity error is preferably less than 2%. By overlapping the different illumination channels, field uniformity can be obtained.

[0116] The illumination of the entrance pupil of the projection optical unit 10 can be geometrically defined by the arrangement of the pupil facets. By selecting the illumination channels, and in particular the subset of pupil facets, that direct light, the intensity distribution at the entrance pupil of the projection optical unit 10 can be set. This intensity distribution is also referred to as the illumination setting.

[0117] A similarly favorable pupil uniformity in the region of a defined illuminated portion of the illumination pupil of the illumination optical unit 4 can be achieved by redistribution of the illumination channels.

[0118] Further aspects and details of the illumination of the object field 5, in particular the entrance pupil of the projection optical unit 10, are explained below.

[0119] The projection optical unit 10 may in particular have a concentric entrance pupil, which may be accessible, or which may be inaccessible.

[0120] The entrance pupil of the projection optical unit 10 generally cannot be illuminated exactly using the pupil facet mirror 22. In the case of imaging of the projection optical unit 10 telecentrically imaging the center of the pupil facet mirror 22 onto the wafer 13, the aperture rays often do not intersect at a single point. However, it is possible to find a surface at which the distance determined for the pair of aperture rays is minimal. This surface represents the entrance pupil or a surface conjugate to it in real space. In particular, this surface exhibits a finite curvature.

[0121] The projection optical unit 10 may have different entrance pupil positions for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transfer optical unit, should be provided between the second facet mirror 22 and the reticle 7. This optical element can be used to take into account the different positions of the tangential and sagittal entrance pupils.

[0122] In the arrangement of the components of the illumination optical unit 4 shown in Figure 1, the pupil facet mirror 22 is arranged in a plane conjugate with the entrance pupil of the projection optical unit 10. The field facet mirror 20 is arranged at an inclination with respect to the object plane 5. The first facet mirror 20 is arranged at an inclination with respect to the arrangement plane defined by the deflection mirror 19.

[0123] The first facet mirror 20 is disposed at an angle with respect to the arrangement plane defined by the second facet mirror 22 .

[0124] The mirror modules of the illumination system 1, which define the illumination beam path, are housed in an evacuable chamber inside a housing surrounded by a negative pressure atmosphere containing a small amount of hydrogen (H2). The chamber communicates with a vacuum pump via a fluid line containing a shut-off valve. The operating pressure in the evacuable chamber is a few Pascals. For example, the partial pressure of hydrogen (H2) can be in the range of 2 Pa to 20 Pa. All other partial pressures are typically in the ppm range.

[0125] The first facet mirror (field facet mirror) 20 and the second facet mirror (pupil facet mirror) 22 are examples of a controllable EUV multi-mirror array in the form of a multi-mirror array (MMA).

[0126] FIG. 2 is used to describe an exemplary configuration of such an EUV multi-mirror array (reference system with reference MMA-REF) from the prior art.

[0127] A dimensionally stable carrier structure TS in the form of a base plate has a number of mirror units MU arranged on it, which are arranged side by side in a matrix-type two-dimensional lattice arrangement in rows and columns.

[0128] Each mirror unit MU is fixed to a carrier structure and a mirror element ME, which is mounted by a flexible suspension system SUS so as to be individually movable relative to the base element BE. In this example, the mirror elements ME can be individually tilted with two rotational degrees of freedom relative to the associated base element BE. Each mirror element ME has a substantially plate-shaped mirror substrate SUB, which carries a reflective coating REF on its front surface opposite the base element BE, forming a mirror surface MS that is reflective to EUV radiation. The reflective coating has a multilayer structure (multilayer) with several pairs of layer materials (e.g., Mo-Si) with alternating high and low refractive indexes, possibly with intermediate layers. The front surface or the corresponding mirror surface MS can be planar or slightly concave or convex curved. The curved surface can be spherical or aspherical.

[0129] The mirror units MU are mounted so close to one another that their mirror surfaces MS are arranged side by side in a manner that substantially fills the area. This means, in particular, that the ratio of the sum of the mirror surfaces of the individual mirror elements ME to the total area of ​​the mirror array occupied by the mirror unit, the so-called integration density, is relatively high, for example, greater than 0.7, or greater than 0.8, or greater than 0.9. Complete filling of the area is not possible, since gaps SP defined by the side surfaces SF of adjacent mirror substrates SUB remain between directly adjacent mirror elements ME, through which collision-free relative movement of adjacent mirror elements relative to one another is ensured. The gap width between the side surfaces of directly adjacent mirror substrates facing each other can be, for example, on the order of several tens of micrometers, for example, in the range of 20 μm to 100 μm.

[0130] In each mirror unit MU, components of an elastic suspension system SUS are arranged between the base element BE and the mirror element ME, structurally connecting the mirror element ME and the base element BE, providing movable support of the mirror element relative to the base element in defined degrees of freedom, and providing a restoring force that automatically brings the mirror element to its zero position without tilting even without actuator forces. Furthermore, actuator system components (not shown in detail) are arranged in the intermediate space between the mirror substrate and the base element for generating movement of the mirror element relative to the base element in response to receiving control signals from a control device. These may be integrated into the structure of the suspension system, for example, in the form of parts that change length and / or bend in response to the control signals. Furthermore, components (not shown), for example, capacitive position sensors, are present, which can sense the current relative position of the mirror element with respect to the base element and output a corresponding signal to the control unit. Closed-loop control of the individual tilt angles of the mirror substrate relative to the carrier structure is thus ensured. The tiltable mirror element can be tilted around the zero position with a displacement range of, for example, ±50 mrad, in particular ±100 mrad or more, and the setting accuracy can be, for example, better than 0.2 mrad, in particular better than 0.1 mrad.

[0131] In particular, a high integration density can be achieved by manufacturing the mirror array using techniques from the field of microelectromechanical systems (MEMS) manufacturing. In the example of FIG. 2, at least the base element BE, the suspension system SUS, the actuator system, and the position sensor system are formed as MEMS structures. Nowadays, MEMS structures are usually manufactured from silicon or silicon compounds. Patent Document 2 (corresponding to Patent Document 1) describes an EUV multi-mirror array having a MEMS structure made of silicon or silicon compounds, which can be an example of a conventional EUV multi-mirror array and is hereby incorporated by reference into the content of this specification.

[0132] Figure 2 shows a schematic of some of the problems that can lead to premature degradation of the functionality of EUV multi-mirror arrays, especially those containing MEMS structures. As mentioned, multi-mirror systems are generally used in evacuated chambers, where the partial pressure of hydrogen (H2) is generally low. High-energy EUV radiation in the illumination beam path (EUV arrows) converts H2 molecules into positively charged hydrogen ions (H3 + , H + ) and electrons to a large extent. As a result, a hydrogen ion-containing plasma is generated in the area through which the radiation passes. A high concentration of hydrogen ions can occur in the irradiated area in front of the mirror surface, i.e., on the side opposite the carrier structure TS of the multi-mirror array. However, EUV radiation can also pass through the gap SP into the intermediate space ZR between the mirror substrate SUB and the carrier structure TS and generate hydrogen ions there.

[0133] The hydrogen ion-containing plasma induced by EUV radiation has a corrosive effect on the mechanical components of the EUV multi-mirror array, especially if they are made of silicon or silicon compounds. As a result, surfaces exposed to the plasma are attacked by material removal, as shown by the detail in FIG. 2. The corrosive attack may also release silicon compounds, which can be redeposited at other points within the structure. The resulting structural changes due to the corrosive material removal and resulting deposits can impair the functionality of the MEMS. The deposits formed on the mirror surfaces MS further reduce the reflectivity and therefore the transmittance of the illumination system.

[0134] In view of this problem, exemplary embodiments of the EUV multi-mirror array according to the present invention comprise anti-corrosion structures of a corrosion protection system, which are specially designed and adapted to prevent or at least reduce the corrosive attack of EUV radiation-induced hydrogen plasma on components of the mirror unit arranged between the mirror surface and the carrier structure, which leads to the described material removal and / or structural modifications, compared to a mirror unit without the corrosion protection system. In this case, the corrosion protection system comprises anti-corrosion structures located on or formed on selected components of the EUV multi-mirror array. Some preferred structural measures in the form of anti-corrosion structures for reducing or avoiding problems due to corrosive attack are exemplarily described below.

[0135] Schematic diagram FIG. 3 shows, not to scale, a vertical cross section of the transition region between two directly adjacent mirror units MU1, MU2 of the MMA in the region of the mirror substrates (first mirror substrate SUB1, second mirror substrate SUB2) of two adjacent mirror elements ME1, ME2. Between the mirror substrates, there is a gap SP defined by the first side surface SF1 on the side of the first mirror substrate SUB1 and the closest second side surface SF2 on the side of the second mirror substrate SUB2. The two mirror elements are in a neutral position, i.e., not tilted relative to each other. The mirror surface MS1, MS2 facing the incident EUV radiation EUV, together with the mirror surface of the other mirror element, defines a total mirror surface, the overall surface normal NOR of which extends obliquely with respect to the main incidence direction of the incident EUV radiation. In practice, the incident EUV radiation originates from an incidence angle range extending, for example, by ±5° or ±10° around the main incidence direction.

[0136] In terms of basic design, the multi-mirror array MMA can correspond to the example from FIG. 2, and reference is made in this respect to that description. However, in deviating from the prior art shown in FIG. 2, the side surfaces SF1, SF2 extend in the edge regions of the mirror substrates SUB1, SUB2 obliquely, rather than perpendicularly, to the respective mirror surfaces MS1, MS2, at an angle significantly different from 90°. In particular, the first side surface SF1 forms an acute angle W1 of less than 90° with the assigned mirror surface MS1, where W1 can be, for example, in the range of 50° to 80°. The opposite second side surface SF2 forms an obtuse angle W2 with the assigned mirror surface MS2, where W2 can be, for example, in the order of 100° to 130°.

[0137] In this example, the absolute value of the deviation from 90° is the same on both sides, and the sides are planar. The sides SF1, SF2 define a gap SP, which extends obliquely with respect to the adjacent mirror surfaces MS1, MS2 and therefore also obliquely with respect to the primary direction of incidence HE of EUV radiation. The gap SP has a gap width SB corresponding to the internal width between the sides measured in a plane perpendicular to the global mirror normal NOR at each location along the gap SP.

[0138] The gap SP extends in depth (parallel to the mirror normal NOR) between a first gap opening SO1 on the entrance side of the region of the reflective coating REF and a second gap opening SO2 on the opposite side, that is, the back side of the mirror substrate, facing the base element. When the mirror element is in a neutral position (as shown in FIG. 3), the gap width SB between the first gap opening SO1 and the second gap opening SO2 is substantially constant, whereas when tilted relative to one another, the gap width varies in depth.

[0139] Due to the oblique orientation of the gap SP, a lateral offset LV occurs between the first gap opening SO1 and the second gap opening SO2 in the direction in which the gap width SB is measured, which can be measured, for example, between the edges of the gap opening on the side of the first mirror substrate SUB2. The lateral offset LV can correspond to the gap width, but in this exemplary case is, for example, 10% or more, or 20% or more, or 30% or more, larger than the gap width SB. As a result, EUV radiation incident on the mirror element in the main incident direction HE is completely blocked by the mirror substrates SUB1, SUB2, so that no EUV radiation can reach the intermediate space ZR between the mirror substrate SUB and the base element BE in this incident direction. More precisely, EUV radiation incident on the gap SP only strikes the upper part of the side surface SF2 of the second substrate and can be absorbed there.

[0140] In this exemplary case, the lateral offset is dimensioned such that EUV radiation from an incident angle range of ±20° around the main incident direction HE cannot pass through the gap directly into the intermediate space ZR behind the mirror substrate. Thus, the oblique positioning of the gap makes it a radiation trap that prevents EUV radiation from being emitted directly into the intermediate space ZR behind the mirror substrate.

[0141] Since no hydrogen ions are generated in this intermediate space due to the absence of incident high energy EUV radiation, this particular shape of the edge region of the mirror substrate forms a corrosion protection structure integrated into the mirror substrate, which overall leads to a substantial reduction in the corrosion rate of components located behind the mirror substrate SUB1, SUB2, etc. A slight corrosion attack can be caused by hydrogen ions that occur in the region in front of the mirror surface MS of the mirror element and that progress through the gap SP due to diffusion.

[0142] Incidentally, the oblique position of the gap is dimensioned such that complete blocking of EUV radiation emitted directly into the rear region of the mirror substrate is provided for all tilt angles of the adjacent mirror substrates SUB1, SUB2 within their respective tilt tolerance ranges. The gap angles W1, W2 or the oblique position can be locally adapted to the incident direction there.

[0143] The schematic diagrams of Figures 4A-4D provide a clear overview of the shielding effect of a diagonal gap compared to a vertically extending gap (rather than a diagonal position) from the prior art. EUV radiation (arrow) is incident from the radiation entrance side (top of the figure) parallel to the main incidence direction HE, which extends parallel to the z-axis (height axis) of the mirror coordinate system, which is fixed relative to the carrier. Figure 4A shows a conventional mirror arrangement in which adjacent mirror elements are at the zero position. In this case, the mirror surfaces MS are aligned parallel to the xy-plane of the mirror coordinate system. The thickness of the EUV arrow indicates that a relatively large amount of EUV radiation from the front side (mirror surface MS) reaches the intermediate space ZR located behind it. Figure 4C shows a conventional arrangement in which adjacent mirror elements are uniformly tilted a few degrees from the zero position. This slightly reduces the effective gap width, but a relatively large proportion of EUV radiation still reaches the rear of the mirror substrate SUB.

[0144] 4B and 4D show a similar configuration of an exemplary embodiment in which directly adjacent mirror substrates SUB each have a trapezoidal cross section, with their short sides positioned alternately on the light-input and light-output sides, resulting in a gap SP extending obliquely relative to the mirror surface between the directly adjacent mirror substrates. The reduced thickness of the radiation arrows EUV indicates that a large portion of the EUV radiation incident in the normal direction (z direction) is blocked from passing into the intermediate space ZR behind the mirror substrates, and complete blocking can be achieved in some cases. As shown in FIG. 4D, the blocking effect is also present when the mirror elements are each uniformly tilted slightly relative to the zero position. As a result, this can result in certain gaps being undesirably large. If necessary, the resulting drawbacks can be compensated for by further measures.

[0145] Schematic Figures 5A-5C illustrate an exemplary embodiment in which directly adjacent mirror elements are permanently or intermittently offset in height from one another, thereby contributing to improved EUV radiation shielding. In this case, the height direction refers to the z-direction of the mirror coordinate system, which is aligned more or less precisely parallel to the main direction of EUV radiation incidence. Figure 5A schematically shows mirror substrates SUB1, SUB2, and SUB3 of three mirror elements ME1, ME2, and ME3 positioned directly next to one another. These mirror elements have two different widths, specifically B1 and B2, respectively, in the region of their mirror surfaces MS1, MS2, and MS3, measured in the direction of their side-by-side positioning (y-direction). For the outer mirror elements ME1 and ME3, the mutually opposing oblique side surfaces are oriented such that the substrate backside facing the carrier structure (bottom) is narrower than the mirror side. This situation is reversed for the intervening mirror element ME2. In this case, the mirror surface is narrower in the width direction than the substrate backside. Therefore, the mirror substrates are arranged with their wide and narrow sides alternately facing in different directions.

[0146] Mirror elements ME1 and ME3, whose mirror surfaces are larger in the width direction than the backside of the substrate, have a height offset toward the light incident side relative to a mirror substrate with a different orientation. The height offset Δz can be defined as the distance measured in the height direction between a reference point RP1 defined by a first mirror surface MS1 at the geometric center of the mirror surface and a corresponding reference point RP2 defined by the directly adjacent mirror surface MS2. Typically, the height offset is smaller than the thickness of the mirror substrate measured in the height direction, e.g., 20% to 80% of this thickness. The height offset is also present in the region of the gap SP between the mirror elements, with the same or similar size. It is clear from FIG. 5A that complete blocking of normally incident EUV radiation is achieved with mirror elements positioned at the zero position. The height offset positions the interference contours formed by the mirror elements farther apart than if the mirror substrates were positioned at the same level, thereby increasing the tilt angle range of the individual mirrors available without collision (FIG. 5B).

[0147] Compared to the previous embodiment, the relative height offset also allows for a more pronounced trapezoid along the cross section shown when the tilt angle is unchanged, thereby increasing the effective lateral offset.

[0148] The relative height offset of adjacent mirror elements can be fixed. In this case, the mirror elements are preferably arranged alternately at two different levels, with two mirror substrates at a common height being sandwiched between mirror substrates at the other height. Thus, two height levels are provided alternately. The relative height offset can be adapted to the expected tilt range of adjacent mirror elements (defined by the optical design) and can also include additional height levels.

[0149] FIG. 5C shows another exemplary embodiment with a height offset between adjacent mirror substrates. The multi-mirror array of the exemplary embodiment of FIG. 5C is provided with a controllable height adjustment device HVE for reversibly and continuously adjusting the height of individual mirror elements relative to adjacent mirror elements in response to a control signal. This can be used in particular to realize the concept of setting the height position depending on the actual tilt and height positions (height or z-direction) of adjacent mirror substrates. In this regard, FIG. 5C shows three mirror substrates SUB1, SUB2, and SUB3 in the same tilt position as in FIG. 5B. However, while in FIG. 5B a relatively large gap SP+ occurs between the second and third mirror substrates SUB2 and SUB3 due to the different tilt angles, in the variant of FIG. 5C the height adjustment device is used to retract the third mirror (see double arrow) so that it approaches the height level of the directly adjacent second mirror element ME2. As a result, the intervening gap SP− is so narrow that the intermediate space behind it is completely blocked by normally incident EUV radiation.

[0150] The mirror element displacement component that can be applied in addition to the displacement caused by tilt can only act in the height direction, however, it is also possible to design the actuator so that it is capable of a combination of height and perpendicular lateral (y and x) displacements.

[0151] For example, by positioning a piezoelectric layer between the carrier structure and the base element, the thickness of which can be controlled, the entire mirror unit (including the base element) can be displaced in height. Alternatively or additionally, the height adjustment can be achieved by an actuator system of parts of a MEMS structure positioned between the base element and the mirror substrate.

[0152] Schematic diagram 6 shows a further optional measure for reducing or avoiding EUV radiation being emitted into the intermediate space ZR between the mirror substrate SUB and the carrier structure TS by means of a corrosion protection structure of the individual mirror units. Two directly adjacent mirror units MU1 and MU2 are shown, whose mirror substrates SUB1, SUB2 have oblique side faces such that an obliquely positioned gap SP occurs between the mirror substrates. Furthermore, a portion of the MEMS structure serving as a radiation trapping element TRP is formed in each mirror unit. For example, the radiation trapping element can be fabricated integrally with the base element BE during structuring of the component.

[0153] Each radiation trapping element TRP, shown only diagrammatically, has a radiation entrance surface AF aligned parallel to the xy-plane in the region immediately behind the second gap opening on the carrier side of the gap SP, which is wider than the carrier-side gap opening SO2 and protrudes slightly beyond it on both sides. The radiation entrance surface extends along the gap, i.e., its length, which runs perpendicular to the plane of the drawing, is several times longer than its width. The height distance between the radiation entrance surface AF and the backside of the substrate is such that the mirror substrate can be tilted over the maximum tilt angle range without colliding with the radiation trapping element. To minimize the effective gap without collision, it is also possible to adapt the height of some of the radiation trapping elements TRP to the current tilt position of the mirror positioned above it.

[0154] The basic structure of the radiation trapping element can consist of the material of the base element (e.g., silicon), but the radiation entrance surface can have special properties as a result of an appropriate coating with a functional material FM. First, the functional material can be designed to have an absorption effect on EUV radiation, so that the radiation trapping element acts as an EUV absorber. Alternatively or additionally, the functional material can also be designed to act as a recombination catalyst for hydrogen ions and hydrogen atoms, so that hydrogen ions that may penetrate through the gap recombine there to form hydrogen atoms, which in turn recombine to form hydrogen molecules, which are harmless in terms of the risk of corrosion. Such a radiation trapping structure can also capture contaminant particles that may penetrate through the gap, and in this respect also helps to protect the structure located behind it.

[0155] The radiation trapping element may also be provided in combination with a conventional multi-mirror array (with a vertical gap) where it acts as an anti-scattering element.

[0156] The double arrow in Fig. 6 indicates an optional embodiment in which the radiation trapping elements are partially height-adjustable. The height setting of each radiation trapping element can be actuated depending on the tilt position and / or height position of the adjacent mirror element in order to set the optimum distance from the gap at each tilt position. For example, piezo-actuators or pneumatic actuators can be provided for the height adjustment. Instead of arranging the radiation trapping elements on the base elements, it is also possible to fix them to a carrier structure in the intermediate space between adjacent base elements.

[0157] 7A to 7F show different examples of parts of a corrosion protection system with a corrosion protection structure in the form of a protective film MEM comprising a gap covering part AA spanning or covering each gap for each gap to be covered. The gaps are formed between two directly adjacent mirror substrates SUB1, SUB2. The film MEM or gap covering part AA is carried by the mirror substrate SUB and for this purpose is fixed to the mirror substrate, for example on the radiation entrance side provided with a reflective coating in the case of FIGS. 7A to 7C (see FIGS. 7A to 7C) or on the back side of the mirror substrate (see FIGS. 7D to 7F), respectively.

[0158] The protective membrane MEM may be a flexible and / or slightly stretchable membrane, capable of following slight tilting movements of the mirror elements relative to one another or compensating for dimensional changes that may occur in the region of the gap (see FIG. 7B). For example, the protective membrane may comprise or be formed by a thin metal foil and / or a thin polyimide foil.

[0159] In the example of FIG. 7A, the protective film MEM1 is very thin and made of the above-mentioned material, and therefore has a high transmittance for EUV radiation. Therefore, EUV radiation can penetrate the gap even in the region of the radiation-coated portion AA, but is largely or completely blocked there due to the oblique position of the gap. However, the film completely prevents the hydrogen-ion-containing plasma from flowing through the gap into the intermediate space behind it, and therefore protects the MEMS structure behind it from corrosion degradation. The film MEM1 can have the same transmission characteristics over a large area. This allows for only a slight decrease in reflectivity even on the mirror surface covered with the film.

[0160] It is also possible to design the protective film as a laterally structured film, which in the broadest sense means that the film has regions with different properties according to a given structure for manufacturing reasons. In the example of FIG. 7C, a structured film MEM3 is attached to the reflective side of the mirror element. It extends across the entire mirror surface and spans the intervening gap with a corresponding gap covering AA. The protective film is structured so that the EUV transmittance is substantially lower in the region of the gap covering AA than in the region where the film is located in the region of the mirror surface. As a result, in the region of the gap, the gap can be at least partially shielded from the penetration of EUV radiation, which not only blocks intruding contaminants and plasma, but also reduces or prevents the possibility of new hydrogen ion generation in the intermediate region between the mirror substrate and the base element.

[0161] The benefits of the structured protective film can be enhanced by removing it from the region of the reflective coating after application to the mirror element carrying it, or by thinning it, such as by etching, to an extent that it has no or only a slight reflectivity reducing effect. In the region of the gap coverage AA, the film can remain to an extent that its opposing edge regions can be secured to the edge regions between adjacent mirror substrates next to the gap.

[0162] In the examples of Figures 7A to 7C, a protective film is fixed to the reflective side of the mirror element, i.e., to the front side of the mirror substrate. This is not necessary. Gap coverings can also be fixed to the rear side of the adjacent mirror substrates, so that the second gap opening is covered (see Figure 7D). In that case, contaminants can still penetrate into the gap area, but are prevented from penetrating into the intermediate space behind it. The radiation blocking effect can also be maintained in the case of a suitable design of the gap coverings. In that case, the reflective surface of the mirror element is free of film portions, which is advantageous in terms of obtaining a high reflectivity.

[0163] In the modified embodiment of Fig. 7E, a protective film MEM5 is disposed between the rear side of the mirror substrate and the rear side of the radiation trapping element. In this case, the protective film is first fixed to the rear sides of the adjacent mirror substrates SUB1, SUB2, and then fixed to the front side of the radiation trapping element TRP via an intervening portion. The radiation trapping element TRP is mounted so that its height can be adjusted. When adjacent mirror elements are tilted relative to each other, the layer stress of the protective film MEM5 between the mirror unit and the radiation trapping element moves the radiation trapping element TRP along the z direction, thereby achieving height adjustment according to the tilted position of the radiation trapping element.

[0164] Figure 7F shows a variation of the arrangement from Figure 7E without the radiation trapping element. In this case, a protective film MEM6 is fixed to the backside of the adjacent mirror substrates SUB1, SUSB2 and spans the gap region with a slightly slack absorbing portion AA that absorbs EUV radiation passing through the gap. Like an elastic seal, the protective film can compensate for the increase in gap size that may occur upon tilting of the mirror substrates without exerting tensile stress on the fixed position or preventing tilting.

[0165] 8A and 8B respectively show a schematic cross-section of adjacent mirror substrates SUB in the region of the intervening gap SP in the area of ​​the reflective coating REF and the protective film MEM. In this case, FIG. 8A shows an enlarged view of the protective film arrangement also selected for the example of FIGS. 7A to 7C. In this case, the layer sequence of the reflective coating REF is located on the front side of the mirror substrate SUB. Subsequently, a stable protective film MEM covering the gap SP with a gap covering part AA is applied to the free outer side of said reflective coating.

[0166] FIG. 8B shows an alternative example of an anti-corrosion structure having a protective film MEM. Adjacent mirror substrates SUB1 and SUB2 define an intervening gap SP. The protective film MEM is first applied directly (or via one or more functional layers) to the free surface of the mirror substrate. The layer sequence of the multilayer reflective coating REF is then applied to the outside of the protective film MEM, so that the mirror surface MS is formed by the free surface of the reflective coating REF. The protective film MEM still covers the gap with its gap covering portion AA, but the reflective effect of the reflective coating is not impaired by the protective film. Therefore, a particularly low EUV transmittance does not need to be considered when selecting and designing the protective film. Instead, the EUV transmittance can be relatively low so that the radiation blocking effect is large. The reflectance of the reflective coating is not impaired by such an anti-corrosion structure.

[0167] In some embodiments, the corrosion protection system comprises only one of the above types of corrosion protection structures. For example, it may be sufficient to simply provide an obliquely positioned gap. However, corrosion protection systems that combine two or more of the above corrosion protection structures are often advantageous. For example, height adjustment of the individual mirror substrates can be provided in combination with radiation trapping structures and / or in combination with protective coatings.

[0168] Further measures can be provided for the functional structures of the mirror unit to avoid degradation as a result of corrosion attack. For example, the MEMS structures in at least some or all of the surface areas preferably exposed to corrosion attack can be manufactured from a material that is substantially more resistant to corrosion attack by hydrogen ions than the silicon typically used for MEMS structures. For example, a corrosion protection layer made of aluminum oxide or aluminum can be provided, for example, on the backside or sidewall of the mirror substrate, on the plunger that may support the mirror substrate, and on parts of the base element. An example of such a corrosion protection layer SS is shown schematically on the right side of FIG. 6.

[0169] 9A-9C and 10A-10C, two options for the fabrication of a multi-mirror array with diagonally positioned gaps between adjacent mirror elements are now described. FIG. 9A shows a schematic cross-section of the finished multi-mirror array MMA along a row or column of mirror units mounted on a carrier structure TS in the form of a silicon plate. Each mirror unit has a mirror element ME and a solid stand or support STD attached to its center. The carrier structure TS, shown only diagrammatically, contains mechatronic components. These include, among other things, flexible suspensions, actuators, and optionally sensors, such as orientation sensors. The mirror surface MS is formed on the side opposite the carrier structure. In the cross-section shown, the mirror substrate has a substantially trapezoidal cross-section, with the trapezoids alternating in orientation so that the narrow and wide sides of every other mirror element are oriented in the same direction, resulting in diagonal gaps SP between the mirror elements.

[0170] An exemplary manufacturing process includes two manufacturing steps, in each of which a group of mirror units MU with the same orientation is fixed to a carrier structure together with a suspension system by bonding. Figure 9B illustrates the first manufacturing step. A separation layer SEP is provided on one side of a holding substrate HS in the form of a planar wafer. A group of trapezoidal first mirror elements MU1 with the same orientation is attached to it. In this exemplary case, each mirror element is oriented so that its front side, on which the mirror coating is to be applied, is smaller than the back side of the mirror substrate to which the support posts STD are attached. Gaps remain between the individual mirror units in the illustrated cutting direction and obliquely thereto for the second mirror substrate SUB2 with the opposite orientation. The mirror elements, still held by the holding substrate, are subsequently connected and fixed to the upper side of the carrier structure TS under the action of pressure and temperature in a bonding step (e.g., eutectic or thermal bonding), so that the central support post STD is fixed to the carrier structure. The separation layer is then heated or melted to such an extent that the holding substrate can be removed. Alternatively, the holding layer with the holding substrate can be etched away chemically or by plasma etching.

[0171] Subsequently, in a second step (FIG. 9C), a second group of second mirror units MU2 are connected to the carrier structure in the same manner. Each second group includes a second mirror substrate, whose wide side is attached to a carrier substrate HS, and whose narrow side, where the suspension is located, faces the carrier structure TS. The second joining step is possible because the first mirror units MU1 of the first group applied in the first step expand upward, allowing the second mirror units, facing in the opposite direction, to be inserted between them in one step.

[0172] 10A-10C illustrate a second variant, which is implemented in the manner of additive manufacturing. In this case, layers of different lateral extent are successively fabricated one on top of the other to form the respective mirror substrates, resulting in a stepped-sided mirror substrate. Again, FIG. 10A shows a cross-section of a finished multi-mirror array MMA with diagonally oriented gaps between the individual mirror elements. Again, the mirror elements, which are substantially trapezoidal in cross-section and have alternating orientations of wide and narrow sides, are arranged so that between directly adjacent mirror elements there are respectively diagonally positioned gaps with stepped lateral boundaries.

[0173] In a first step, the mirror elements, together with their attached suspensions, are fabricated on a carrier substrate HS (Fig. 10B). The carrier substrate is first covered with a separation layer SEP. Then, a first layer made entirely of the material intended for the mirror substrate, for example silicon, is applied. This first layer is structured in a lithographic process where gaps between adjacent mirror units are to occur, and material is removed by etching. The resulting gaps in the first layer are then filled with a sacrificial material (for example SiO2). This is followed by a planarization step to create a plane for the application of the next layer, partly made of the material of the first layer and partly made of the sacrificial material in the areas of the gaps.

[0174] A continuous second layer made of the material (e.g., silicon) selected to form the mirror substrate is then applied. This second layer is then structured in a lithographic process by etching away the material of the second layer in the gap regions. Depending on whether a left- or right-extending diagonal gap is to be formed, the areas of the second layer to be etched away are located to the left or right of the corresponding areas of the first layer. The areas free after the etching step are filled with sacrificial material, followed by a further planarization step. After an appropriate number of repetitions of this structuring process, the mirror substrate is available with alternating gaps still filled with sacrificial material. The application or creation of the suspension structure is followed by a bonding step (FIG. 10B), which connects (bonds) the individual mirror elements to the carrier structure TS under the action of force and temperature. To remove the sacrificial material, the volume filled with sacrificial material is etched after the bonding step. The material of the separation layer SEP is then also removed, exposing the front surface of the mirror substrate, which is then covered with a reflective coating. FIG. 10C shows a cross section of the completed multi-mirror array.

[0175] 11 and subsequent figures, methods for solving the above-mentioned problems will be described as examples. For clarity, the same reference numerals as in the above examples will be used for features that are equivalent or similar from a structural and / or functional standpoint. In particular, these solutions take into account the findings described below.

[0176] The position and spatial extent of the area behind the mirror surface, where radiation, for example EUV radiation, can reach directly or indirectly after reflection, depends, inter alia, on the size of the mirror element, the thickness of the mirror element, the height of the mirror element from the base plane formed by the surface BE-O of the base element, the height of the mirror surface from the position of the individual tilt axes, the maximum achievable tilt angle, the dimensions and position of the gap SP, and the angular distribution of the incident radiation. The surface area and / or volume area exposed to radiation penetrating the intermediate area can be large if the mirror elements are tilted with respect to each other.

[0177] During the coating process for producing the reflective coating REF on the front surface VF of the mirror substrate SUB, it is possible that the coating material may also penetrate into the gap, resulting in a coating on the side surface SF that reflects EUV radiation to a greater or lesser extent.

[0178] EUV light rays reflected from the side edges SF can change their direction of propagation significantly relative to the incident direction, with a range of deflection angles that depends, inter alia, on the angle of incidence and the tilt angle of the mirror element. As a result, EUV radiation can also be incident on regions of the surface BE-O of the base element that would be shadowed by the mirror element in the absence of side reflections.

[0179] As a result, the "radiation-protected" surface and volume components that are not directly exposed to radiation are actually smaller than in the ideal case without side reflections, which can exacerbate the problems mentioned at the beginning, such as heating by radiation, degradation under the influence of radiation due to corrosion, electrical failure of functional electrical components, etc., and the resulting shortened service life.

[0180] In the exemplary embodiment of the EUV multi-mirror array MMA of Figure 11, the mirror unit MU, in terms of its basic components (base element BE, mirror element ME, flexible suspension system SUS, reflective coating REF), generally corresponds to the prior art described with reference to Figure 2, so in this regard reference is made to the description therein.

[0181] In contrast, significant differences can be seen in the edge regions of the mirror elements in the region of the side surfaces SF of the mirror substrate SUB. At the edges of the mirror surface, i.e., at the transitions between the front surface VF and the side surface SF, the side surfaces are not aligned substantially perpendicular to the reflective front surface, but are systematically angled at an angle W deviating from 90° to their respective assigned mirror surface. Consequently, the front surface VF, provided with the reflective coating REF, has a larger surface area than the rear surface RF, which faces the opposite side of the mirror substrate, specifically the base element BE. This results in the mirror substrate, in an approximately plate-shaped mirror substrate overall, having the lateral or outer edge RDR of the rear surface recessed inward at all circumferential positions by a lateral offset LV relative to the outer edge RDV of the front surface VF. As a result, the mirror substrate, in the cross section shown, has a trapezoidal shape with a wider base toward the reflective front surface. Since adjacent mirror substrates in all adjacent directions have the same shape, gaps SP occur between adjacent mirror substrates, the gap width SB of which increases from the radiation entrance side, located in the plane of the front surface, to the radiation exit side facing the base element.

[0182] In the exemplary case of Figure 11, the side surfaces are macroscopically planar in both cases and therefore angled at a uniform angle W with respect to the front surface. In some exemplary embodiments, the oblique position is only partially present, resulting in portions oriented approximately perpendicular to the front surface (see Figure 12A). The side surfaces may also have at least partially convex (see Figure 12C) or concave (see Figure 12B) curvature.

[0183] The oblique angle position W can be adapted to this application. Typically, the deviation from 90° is relatively small, for example 2° to 10°, in particular 3° to 8°. Depending on the thickness or height HS of the mirror substrate, this can lead to a lateral offset LV of the order of a few micrometers, for example 2 μm to 10 μm. For example, the lateral offset can be 3% to 10% of the substrate thickness HS. Deviations from these exemplary dimensions are possible. The advantageous technical effects of this configuration are explained in more detail below.

[0184] The technical effect of the described obliquely positioned side surfaces is explained below with reference to FIGS. 13 and 14. To estimate this effect, the inventors performed ray tracing in an exemplary model system to identify the area behind the mirror substrate SUB where EUV or DUV radiation can reach, either directly or via reflection at the side surfaces, for a given distribution of incident angles. In this case, a reference example of a plate-shaped mirror substrate with vertical side surfaces and an exemplary embodiment with obliquely positioned side surfaces were considered. Without loss of generality, for the width B between the opposing side surfaces, a value of BV = 950 μm was assumed for the front surface and a value of BR = 940 μm for the rear surface, given a thickness HR of 75 μm. Therefore, the lateral offset LV was set to 5 μm on each side. A value of 250 μm was assumed as a typical size for the height of the back side of the mirror substrate relative to the base plane (surface BE-O of the base element).

[0185] FIG. 13 shows the substrate SUB in its neutral, non-tilted position as a flat rectangle in solid lines. Dashed lines are used to indicate the extremes of left and right tilt. The maximum assumed tilt angle was on the order of 100 mrad to each side. Typically, the tilt angle on each side can be in the range of, for example, 50 mrad to 150 mrad. The tilt is realized about a tilt or rotation axis ROT, which is located at a height of approximately 125 μm between the mirror element and the base plane (width coordinate 0 on the y-axis of the figure). The vertical dashed lines at x=-500 and x=500 μm correspond to the central plane MIT of the gap between adjacent mirror units and thus to the edges of the area of ​​a single mirror unit.

[0186] For incident (EUV) radiation, we assume an incidence angle spectrum ranging between normal incidence (0° incidence angle relative to the surface normal of the non-tilted mirror substrate) and a maximum incidence angle on the order of approximately 10°-20°.

[0187] Various representative rays are plotted at the edge region of the mirror substrate.

[0188] The solid line R1 represents the most unfavorable ray of the incidence direction spectrum for a non-tilted mirror substrate. This ray R1 is tangent to the lower edge of the mirror substrate formed between the side and back surfaces and enters the base plane BE-O at location R1-A0. If the mirror element is tilted to the left, the right rear edge of the mirror substrate moves inward in the direction of a smaller absolute value of the spatial coordinate x. As a result, there is a ray R1-1 with the same angle of incidence as ray R1, but it is tangent to the rear edge of the tilted mirror substrate and enters the base plane at location R1-A1. Because the mirror is tilted to the left, this location is closer to the center of the mirror element (x = 0). This indicates that tilting the mirror can reduce the size of the area or volume near the center of the mirror unit that is not illuminated by the base plate BE-O.

[0189] When the mirror substrate is tilted to the right, the ray R1-2 with the most unfavorable angle of incidence has an incidence location R1-A2 that is positioned further from the center than in the case of a non-tilted substrate, which shows that the size of the non-illuminated area behind the mirror substrate varies depending on the tilt angle and the incidence angle spectrum, among other things.

[0190] The simulation or ray tracing also considers the reflection of the ray at the side surface SF. For this purpose, in this exemplary case, we consider the reflection at the side surface SF-N of the immediately adjacent mirror substrate, which in this exemplary case is tilted to the right. Ray R2 represents the most unfavorably reflected ray, which is incident on the side surface SF-N, which is assumed to be reflective, at a relatively large angle of incidence (more or less oblique incidence) and is reflected from there toward the base plane. The point of incidence R2-A2 of this once-reflected ray is located further inside the mirror substrate, i.e., closer to the center of the mirror substrate, resulting in a smaller size of the area near the center that is not directly hit by EUV radiation. The size of this area decreases as the tilt angle and the height of the mirror element above the base plane increase. Corresponding conditions occur on the opposite and other side surfaces of the mirror substrate.

[0191] Using this geometric model as a basis, we investigated the effect of the oblique position of the side surfaces on the size of the area under the mirror substrate that is not directly illuminated, for a given range of angles of incidence. Figures 14A and 14B show a comparison. In this case, Figure 14A represents a conventional substrate with side surfaces perpendicular to the front surface, while Figure 14B shows a calculation with a substrate whose side surfaces are recessed inward by being positioned obliquely by a few degrees (approximately 5°).

[0192] For a given distribution of incident angles, in the case of a conventional substrate with vertical sidewalls (FIG. 14A), the outer edge of the region EUV-N, which is located at the center behind the mirror substrate and is not directly exposed to EUV radiation, is positioned at approximately 341 μm (corresponding to x-coordinate X1). In contrast, in the case of a diagonally recessed sidewall (FIG. 14B), this outer edge of the inner region EUV-N, which is not directly exposed to EUV radiation, is displaced outward to approximately 359 μm (corresponding to x-coordinate X2, where X2>X1). Therefore, the non-irradiated region EUV-N is significantly larger than in the case of vertical sidewalls.

[0193] This result represents a number of examples where the tilt angle of the side faces is appropriately selected and the distribution of the incident angles is typical: therefore, the "guaranteed" dark area on the base element of the mirror unit is larger with the side faces positioned obliquely inwards, and the area under the gap SP that is directly exposed to EUV or DUV radiation is smaller.

[0194] In the following, further differences from the prior art are mentioned: The front surface VF to be provided with the reflective coating REF must be prepared with high optical quality, for example by polishing, in order to obtain a surface roughness that is as low as possible. Typically, the surface roughness is in the range of less than 1 nm RMS (root mean square roughness), in particular the surface roughness can be in the range of less than 0.2 nm RMS.

[0195] Although the side surfaces SF are not conventionally etched with such precision, they do have a relatively low surface roughness, which may be, for example, in the range of a few nm RMS or tens of nm RMS.

[0196] In contrast, the side surfaces SF of the exemplary embodiment are significantly roughened by suitable surface treatment, so that the side surfaces have a surface roughness that is at least one order of magnitude, preferably two or more orders of magnitude, greater than the surface roughness of the front surface VF. For example, the surface roughness can be in the range of 100 nm RMS or greater, or even greater than 1 μm RMS. A very rough surface cannot, in principle, cause specular reflection, even if it carries a reflective coating. Such a surface primarily scatters incident EUV radiation.

[0197] The combination of side surface roughening with geometrical side surface beveling, as shown in FIG. 11, is particularly advantageous in that it prevents EUV radiation from being emitted directly behind the plane of the mirror surface. This further reduces the proportion of EUV radiation that is directed toward the area behind the mirror substrate as a result of interaction with the side surface SF. In doing so, some of the radiation energy may be absorbed by the side surface, while another portion may be dispersed over a relatively large solid angle by scattering, so that the locally effective intensity remains low. This can therefore reduce the risk of any type of EUV radiation-related problem.

[0198] Techniques known per se from the field of microelectromechanical systems (MEMS) manufacturing can be used to manufacture mirror substrates with obliquely inwardly offset sidewalls. In particular, a variant of deep reactive ion etching (DRIE, also known as the Bosch process) can be used to create trenches of appropriate depth with oblique sidewalls in the volume of substrate material (particularly silicon) intended to serve as the mirror substrate. For the DRIE method, see, for example, the following publication: R Li, Y Lamy, WFA Besling, F Roozeboom, PM Sarro, "Continuous deep reactive ion etching of tapered via holes for three-dimensional integration", J. Micromech. Microeng. 18 (2008) 125023 doi:10.1088 / 0960-1317 / 18 / 12 / 125023.

[0199] A suitable DRIE method includes cycles of passivation and etching. During passivation, the holes can be protected by the deposition of a Teflon-like passivation layer. In a potentially highly anisotropic etching step, ions are accelerated substantially vertically to remove passivation material from the bottom of the trench while simultaneously maintaining sidewall passivation. Several micrometers of substrate material (e.g., silicon) can then be etched before the next passivation step is performed. The depth profile of the etched trench can be set by various process parameters, such as gas flow, ion power, pressure, and the ratio of passivation time to etching time. Thus, it is possible to create trenches that are narrower or wider at the entrance than at the depth. Since such processes are known per se, a detailed description of the manufacturing process is omitted.

Claims

1. A multi-mirror array (20, 22, MMA), a carrier structure (TS); a plurality of mirror units (MUs) arranged side by side in a grid array on the carrier structure; each mirror unit (MU) comprises a base element (BE) and a mirror element (ME) mounted opposite the base element (BE) so as to be individually movable, the mirror element (ME) comprising a mirror substrate (SUB) having a reflective coating (REF) on a front surface opposite the base element (BE) to form a mirror surface (MS) that reflects ultraviolet light, the mirror substrate (SUB) comprising a back surface facing the base element and side surfaces around the periphery thereof; the array of mirror elements is structurally designed such that the mirror elements can move relative to one another without colliding with one another over an expected range of movement of the mirror elements; the mirror surfaces (MS) are arranged side by side to substantially fill the area, and gaps (SP) defined by the side surfaces (SF1, SF2) of adjacent mirror substrates (SUB) remain between immediately adjacent mirror elements to ensure collision-free relative movement between adjacent mirror elements; and In a multi-mirror array (20, 22, MMA), in which for each mirror unit (MU), the functional components of said mirror unit are arranged in an intermediate space (ZR) between said base element (BE) and said mirror element (ME), A multi-mirror array characterized in that at least a portion of each of the side surfaces (SF1, SF2) of the mirror substrates (SUB1, SUB2) is obliquely oriented at an angle different from 90° with respect to the assigned mirror surface (MS).

2. 2. A multi-mirror array according to claim 1, characterized in that components of a suspension system (SUS) for movably mounting the mirror elements (ME) on the base element (BE) and components of an actuator system (AKT) for generating movement of the mirror elements (ME) relative to the base element (BE) in response to receiving a control signal are arranged in the intermediate space (ZR) between the base element (BE) and the mirror substrate (SUB), and / or the reflective coating (REF) forms a mirror surface (MS) that reflects EUV radiation and / or DUV radiation.

3. A multi-mirror array as described in claim 2, characterized in that at least the base element (BE), the suspension system (SUS), and the actuator system (AKT) are designed as MEMS structures made of silicon (Si) or a silicon compound.

4. 3. A multi-mirror array according to claim 1 or 2, characterized in that the side surfaces of the mirror substrates (SUB) of directly adjacent mirror substrates (SUB1, SUB2) are each designed and oriented such that a gap width (SB) of the gap (SP) formed between directly adjacent mirror substrates increases in the direction from the front surface (VF) of the mirror element provided with the reflective coating (REF) towards the base element (BE).

5. 3. A multi-mirror array according to claim 1 or 2, characterized in that the front surface (VF) of the mirror element provided with the reflective coating (REF) has a surface area larger than the area enclosed by the outer edge of the back surface, and the outer edge of the back surface is recessed inward by a lateral offset (LV) relative to the outer edge of the front surface at all circumferential positions.

6. A multi-mirror array as described in claim 5, characterized in that the mirror substrate has a thickness measured between the front surface and the back surface, and the offset (LV) is 3% or more of the thickness and / or 10% or less of the thickness.

7. 3. A multi-mirror array according to claim 1 or 2, characterized in that the included angle (W) of the transition between the front surface (VF) and the adjacent side surface (SF) is in the range of 80° to 89°.

8. 3. A multi-mirror array according to claim 1, wherein the mirror substrates (SUB1, SUB2) have a substantially trapezoidal cross-sectional shape in a cross section passing between opposing side surfaces, the cross-section being wider at the base on the side of the front surface (VF).

9. 3. A multi-mirror array according to claim 1 or 2, characterized in that the side surfaces (SF) have a surface roughness that is at least one order of magnitude greater than the surface roughness of the front surface (VF) provided with the reflective coating (REF).

10. 3. A multi-mirror array according to claim 1 or 2, characterized in that the edge regions of the mirror substrates (SUB) of directly adjacent mirror substrates (SU1, SUB2) are each obliquely oriented at an angle deviated from 90° with respect to the assigned mirror surface (MS), such that the oblique side surfaces define a gap (SP) obliquely oriented with respect to the mirror surface (MS).

11. 11. A multi-mirror array according to claim 10, wherein the gap (SP) comprises a first gap opening (SO1) having a first gap width next to the mirror surface (MS1, MS2) and a second gap opening (SO2) having a second gap width next to the back side of the mirror substrate, the first gap opening and the second gap opening having a lateral offset (LV) due to the oblique orientation of the gap (SP), such that an effective gap width for direct radiation passage is smaller than the first gap width and / or the second gap width.

12. 3. A multi-mirror array according to claim 1, wherein the mirror substrate has a substantially trapezoidal cross section in a cross section passing between opposing side surfaces.

13. A multi-mirror array as described in claim 12, wherein the mirror elements in a continuous row have alternately inverted trapezoidal cross-sectional shapes, so that the orientation of the sandwiched diagonal gaps alternates for each gap.

14. 3. A multi-mirror array according to claim 2, characterized in that the multi-mirror array comprises a controllable height adjustment device (HVE) for reversibly and continuously adjusting the height of each individual mirror element (ME) relative to its neighboring mirror elements (ME) in response to a control signal, and / or the actuator system is designed to generate a movement of the mirror element (ME) in two rotational degrees of freedom and one translational degree of freedom, the translational degree of freedom corresponding to a movement of the mirror element (ME) along a translational axis perpendicular or at an angle to the rotational axis of the rotational degree of freedom.

15. 15. A multi-mirror array according to claim 14, characterized in that the controller of the height adjustment device (HVE) is configured to be able to adjust the height of a mirror element depending on the tilt position of an adjacent mirror element.

16. 3. The multi-mirror array according to claim 1, wherein the radiation trapping element (TRP) includes a radiation incident surface (AF) arranged on the back side of the mirror substrate (SUB) opposite to the mirror surface in the region of the gap (SP), and wherein a functional material (FM) constituting at least the region of the radiation incident surface (AF) of the radiation trapping element (TRP) has the following properties: The functional material (FM) is an absorbing material that has an absorbing effect on EUV radiation; The functional material (FM) is a recombination catalyst that increases the recombination probability of hydrogen ions when it comes into contact with hydrogen ions. The functional material (FM) is selected from the group consisting of ruthenium (Ru), platinum (Pt), rhenium (Rh), rhodium (Rh), iridium (Ir), molybdenum (Mo), nickel (Ni), and iron (Fe); A multi-mirror array characterized by a radiation trapping element (TRP) having at least one of:

17. 17. A multi-mirror array according to claim 16, wherein the radiation trapping elements (TRP) are partially height-adjustable, and the height adjustment of each radiation trapping element (TRP) is possible depending on the tilt position and / or height position of the adjacent mirror element (ME).

18. 3. A multi-mirror array according to claim 1, further comprising at least one protective film (MEM), the protective film (MEM) including a gap covering portion (AA) in contact with the mirror substrates (SUB1, SUB2) that spans a gap (SP) formed between directly adjacent mirror substrates (SUB1, SUB2) and defines the gap, and the protective film (MEM) is fixed to the mirror substrates (SUB1, SUB2).

19. 19. A multi-mirror array according to claim 18, wherein the protective film (MEM3) contains, in the region of the gap covering portion (AA), an absorbing material having an absorbing effect on EUV radiation, the absorbing material being selected from the group consisting of ruthenium (Ru), platinum (Pt), rhenium (Rh), rhodium (Rh), iridium (Ir), molybdenum (Mo), nickel (Ni), and iron (Fe).

20. 19. A multi-mirror array according to claim 18, characterized in that the protective film (MEM) is arranged in a multi-layer arrangement on the front side of the mirror substrate (SUB1, SUB2) between the mirror substrate (SUB1, SUB2) and the reflective coating (REF).

21. 20. The multi-mirror array of claim 18, further comprising: A protective film (MEM4) is disposed on the back side of the mirror substrate (SUB1, SUB2). a protective film (MEM5) is disposed between the rear side of the mirror substrate (SUB) and the rear side of the radiation trapping element (TRP); a layer stress of the protective film (MEM5) between the mirror unit (MU) and the radiation trapping element (TRP) causes height adjustment according to the tilt position of the radiation trapping element (TRP); A multi-mirror array characterized by having at least one of the following:

22. 3. A multi-mirror array according to claim 1 or 2, characterized by a corrosion protection structure in the form of a corrosion protection layer (SS) applied to components of the mirror units made of a component material in areas prone to corrosion attack, said corrosion protection layer comprising at least one protective layer material that is more corrosion resistant to corrosive attack by hydrogen ions than said component material.

23. 3. A multi-mirror array according to claim 1 or 2, characterized in that the reflective coating (REF) has a high reflectivity for EUV radiation, so that the multi-mirror array is designed as an EUV multi-mirror array.

24. 1. An illumination system (2) of a UV device (1), which is designed to receive UV radiation from a UV radiation source (3) during operation of the UV device and to shape from at least a portion of the received UV radiation an illumination radiation directed to an illumination field of an exit surface (6) of the illumination system, characterized in that the illumination system (2) comprises at least one multi-mirror array (MMA, 20, 22) according to claim 1 or 2.

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