EUV Multi-Mirror Device

Abstract

The EUV multi-mirror apparatus (MMA) comprises a plurality of mirror units (MU) arranged side by side in a grid arrangement on a carrier structure (TS), each mirror unit having a base element (BE) and an individually tiltable mirror element (ME) facing the base element (BE), the mirror element (ME) having a mirror substrate (SUB) carrying a reflective coating (REF) on a front surface opposite the base element to form a mirror surface (MS) for reflecting EUV radiation. In each mirror unit (MU), components of a suspension system (SUS) for movably mounting the mirror element (ME) on the base element (BE), actuators of an actuator system (AKS) for generating a movement of the mirror element (ME) relative to the base element (BE) in response to receiving a control signal, and sensors of a sensor system (SENS) for capturing the position of the mirror element are arranged between the base element (BE) and the mirror element (ME). The actuator system (AKS) comprises a piezoelectric actuator (AKT). The sensor system (SENS) comprises a capacitive sensor (KPS).

Description

[Technical field]

[0001] The following disclosure is based on German Patent Application No. 10 2021 211 626.4, filed on October 14, 2021, which is incorporated herein by reference.

[0002] The invention relates to an EUV multi-mirror device according to the preamble of claim 1, and to an illumination system of an EUV device comprising at least one such EUV multi-mirror device. [Background technology]

[0003] Nowadays, microlithographic projection exposure methods are mainly used for the production of semiconductor components and other finely structured components. In this case, a mask (reticle) or other pattern generating device is used, which carries or forms the pattern of the structure to be imaged, for example a line pattern of a layer of a semiconductor component. The pattern is illuminated with an illumination system which forms illumination radiation from the radiation of a primary radiation source, which is directed towards the pattern and is incident on the pattern in an illumination field characterized by certain 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 an exposed substrate covered with a radiation-sensitive layer.

[0004] 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), in particular with 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 by means of refractive optical elements. Therefore, mirror systems are used, for example in EUV devices for EUV lithography.

[0005] Depending on the type of structure to be imaged, different illumination modes (also called illumination settings) are usually used which can feature different local intensity distributions of the illumination radiation in a 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.

[0006] According to some concepts, at least one controllable EUV multi-mirror arrangement (multi-mirror array, MMA) is used in the pupil shaping unit, which comprises a number of individual mirror elements carried by a common carrier structure and which can be tilted independently of one another to targetably modify the angular distribution of radiation incident on the entire mirror elements to achieve a desired spatial illumination intensity distribution at the pupil plane. The mirror surfaces are arranged in a substantially area-filling manner. Such multi-mirror arrays are often also referred to as faceted mirrors, with the reflective front sides of the mirror elements forming the facets.

[0007] In order to be able to set the geometrical reflection properties of the controllable multi-mirror device in a targeted manner, the multi-mirror device generally comprises, for each mirror element, an actuator system coupled to the mirror element for controllably varying the orientation of the mirror element relative to a carrier structure carrying the mirror element, the actuation movements by the actuator system being controlled by a control unit assigned to the multi-mirror device.

[0008] In order to obtain maximum flexibility in setting different illumination settings, the mirror elements should have as large a tilt angle range as possible. Currently, a settable maximum tilt angle of the order of 100 mrad or more seems desirable.

[0009] To capture the current position of each of the mirror elements, there is a sensor system with sensors whose signals are processed by a controller and used for precise closed-loop control of the orientation or tilt. For simplicity, the term "position" within the meaning of this application refers to a combination of location and orientation, often referred to as "attitude". In tilting mirrors, position capture is mainly focused on capturing the orientation relative to the base element. Orientation can be quantified, for example, by the tilt angle relative to a neutral position (rest position without tilt).

[0010] In particular in the illumination system of an EUV lithography apparatus, the mirror elements must furthermore be able to dissipate a high heat load due to the EUV radiation, which arises due to the reflective coating absorbing a large part of the energy of the incident EUV radiation. A further requirement relates to a high positioning accuracy of the mirror elements and an associated low sensitivity of the tilt to disturbances such as, for example, temperature variations.

[0011] Typical lateral dimensions of the facets can be of the order of a few centimeters and, in future systems, even in the sub-millimeter range ("micromirrors"). In this way, the geometrical-optical reflectance properties of the MMA can be set with a higher local resolution. For fabrication, techniques from the field of Microelectromechanical Systems (abbreviated MEMS) manufacturing are often used to produce actuators, sensors and mechanical elements, e.g. components of suspension systems, as MEMS structures.

[0012] Patent document 1 (corresponding to patent document 2) describes a displacement device for pivoting a mirror element manufactured using MEMS technology in two pivoting degrees of freedom. The displacement device comprises an electrode structure with actuator electrodes embodied as comb electrodes, which are arranged in a single plane and form a direct drive for pivoting the mirror element. A sensor system for capturing the location and orientation comprises a sensor transducer mirror electrode and a sensor transducer stator electrode.

[0013] US Patent No. 5,399,633 discloses a multi-mirror device having tiltable mirror elements, in which the actuator system includes a piezoelectric actuator, and a piezoresistive sensor element is provided to capture the displacement of the mirror elements caused by the piezoelectric actuator.

[0014] According to the observations made by the inventors, some of the conventional multi-mirror devices require relatively complicated manufacturing processes. Moreover, performance may be impaired under high and variable thermal loads. Finally, providing a large usable tilt angle range may be complicated. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] US Patent Application Publication No. 2017 / 363861 [Patent Document 2] DE 10 2015 204 874 A1 [Patent Document 3] International Publication No. 2021 / 032483 Brochure Summary of the Invention [Problem to be solved by the invention]

[0016] Against this background, it is an object of the present invention to provide an EUV multi-mirror device in which the actuator system required for actuation of the multiple arrays can be manufactured relatively simply and with few process steps, while at the same time the sensor system is relatively insensitive to temperature variations, while at the same time it is intended to allow large mirror tilt angles combined with high heat dissipation. [Means for solving the problem]

[0017] To achieve this object, the invention provides an EUV multi-mirror device having the features of claim 1 and an illumination system for an EUV device having the features of claim 14. Advantageous developments are specified in the dependent claims. The wording of all claims is incorporated by reference into the content of the present description.

[0018] The EUV multi-mirror device according to the claimed invention comprises a plurality of mirror units arranged side by side in a two-dimensional grid arrangement in a matrix on a carrier structure. Each of the mirror units comprises a base element and a mirror element mounted so as to be individually movable with respect to the base element. Each mirror unit has its own base element which exists separately from the base elements of the adjacent mirror units. The base elements of the mirror units can be mounted on a common carrier structure which can be a separate component from the base elements. It is also possible that the base elements of adjacent mirror units form a continuous base substrate, such that the base elements of the mirror units are formed by parts of a larger base substrate. The base substrate can act as the carrier structure. Thus, the carrier structure and the base element can be embodied as the same element. The base substrate can carry many mirror elements arranged in rows and columns, for example in a matrix.

[0019] The mirror elements have a mirror substrate carrying a reflective coating on a front surface opposite the base element to form a mirror surface that reflects EUV radiation. The mirror surfaces of the EUV multi-mirror device are arranged side-by-side to substantially fill the area. The mirror surfaces thus form a total reflective area that is significantly larger than any individual mirror surface. A narrow gap remains between directly adjacent mirror elements to allow collision-free relative movement between adjacent mirror elements.

[0020] Each mirror unit has components of a suspension system for movably mounting the mirror element on an associated base element in an intermediate space between the base element and the mirror substrate.

[0021] Furthermore, actuators of the actuator system are arranged therein for generating a movement of the mirror element relative to the base element in response to receiving a control signal. In this way, different orientations of the individual mirror surfaces can be set as desired. Furthermore, sensors of the sensor system are arranged in the intermediate space for capturing the respective positions or orientations of the mirror surfaces relative to the base element.

[0022] By arranging these mechanical or electromechanical components in the intermediate space, a large proportion of the area of ​​the reflective facets in the total area of ​​the MMA can be obtained, i.e. a large fill factor. In order to obtain a high integration density, in the manufacturing process it is possible to use techniques from the field of manufacturing microelectromechanical systems (MEMS for short) for manufacturing actuator elements (elements of the actuator system), mechanical elements (e.g. elements of the suspension system) and / or sensor elements etc. The suspension system can be designed to be flexible, especially in mirror units with MEMS structures, to provide a restoring force that automatically brings the mirror element to a zero position without tilting in the absence of actuator forces. The MEMS process is nowadays substantially based on a structuring process for structuring a workpiece made of silicon or silicon compounds, in which the necessary components are designed in this way.

[0023] The inventors are aware that known solutions, in particular solutions based on capacitive actuator systems (such as those in US Pat. No. 5,399,313), require a relatively large installation space for the actuator system, which may lead to a correspondingly small installation space for the sensor system and therefore to a tendency to lower sensitivity. Furthermore, capacitive actuator systems that may be capable of providing the actuator torque required to obtain large tilt angles appear to require relatively complex configurations, which are made up of many layers as a result of the presence of multiple levels with electrode combs and require a corresponding number of process steps. Concepts requiring capacitive actuator systems also place high demands on process technology, for example when structures with high aspect ratios have to be manufactured to meet the usual requirements for use in EUV lithography devices.

[0024] For these reasons in particular, an actuator system is used according to the claimed invention, which comprises a piezoelectric actuator system, also referred to herein as piezo actuator for short. Piezo actuator systems can be manufactured with small overall dimensions and can generate relatively large forces and moments in relation to the assembled size. It is therefore possible to set relatively large tilt angles, even if the suspension system is designed to generate a restoring force to move the mirror element to the zero position in the absence of actuator forces. After all, in an elastic suspension system, the greater the tilt angle, the greater the restoring force, so that the actuator must work against an increasing reaction force to set a larger tilt angle.

[0025] Piezo actuators have at least one piezo element, i.e. a controllable functional element that utilizes the piezo effect to effect mechanical movement by application of a voltage. Piezo actuators here utilize the so-called inverse piezo effect. Piezo elements can be certain crystals (piezo crystals) or piezoelectric ceramics, i.e. polycrystalline materials.

[0026] In contrast, it has been found that capacitive sensor systems are advantageous for sensor systems, for example in terms of productivity and performance. The sensor system can have, for example, a capacitive sensor element with at least one comb electrode. The sensor element can include a comb electrode with interdigitated electrode plates. The electrode combs of the capacitive sensor system can be realized, for example, on the underside of the mirror element and on the upper side of the base element. Thus, a relatively large installation space is available for the sensor system (due to the small spatial requirements of the piezoelectric actuator system) and, moreover, a relatively high sensitivity can be obtained, since it can be located in the outer area of ​​the mirror, where the mirror movement during tilting is greatest. Furthermore, capacitive sensors only have a low temperature sensitivity (unlike, for example, piezoresistive sensors).

[0027] Therefore, according to the claimed invention, a capacitive sensor system, i.e. a sensor system with capacitive sensors, is used in combination with a piezoelectric actuator system. Capacitive sensors are sensors which operate on the basis of the change in the capacitance of individual capacitors or capacitor systems. Preferably, all actuators of the actuator system are piezo actuators and / or all sensors of the sensor system are capacitive sensors.

[0028] The suspension system mechanically connects the mirror substrate to the base element. The suspension system may, for example, have elastic or flexible parts or components that provide the required mobility. The suspension system may contain joints, for example in the form of flexures, that articulately interconnect its components or parts.

[0029] The actuator system may be a system configured independently of the suspension system, providing forces and torques for movement of the mirror element, or the suspension system may be designed without actuators as a passive system.

[0030] In a preferred embodiment, the suspension system and the actuator system are integrated. This is achieved by having a part of the suspension system act as a functional part of the actuator system, i.e. as an actuator, and thus have a dual function. Components of a sensor system can be integrated as well. For example, a piezoresistive sensor, whose electrical resistance changes depending on the deformation of the spring element, may be integrated into the spring element. However, piezoresistive sensors are highly temperature sensitive.

[0031] To realize the driving, sensor and mechanical elements with techniques from the field of manufacturing microelectromechanical systems (MEMS), a layered structure of these elements is usually selected. To achieve a lift sufficient for changing the location of the mirror element, the piezoelectric actuator can be designed as a multi-layer piezoelectric actuator in the form of a piezostack, where electrode layers are between the individual piezoelectric layers, an arrangement configured such that when a voltage is applied, the thickness of the piezoelectric layers and thus the spacing between the electrodes changes. If many stacked arrangements of piezoelectric layers are selected, a larger lift can be achieved.

[0032] In a preferred embodiment, the piezoelectric actuator is embodied in the form of a multi-layer bending piezo actuator, also referred to simply as bending piezo actuator. The bending piezo actuator is preferably configured to assume a neutral shape without a control voltage, e.g. all layers arranged in a stack are substantially planar so that the piezo actuator forms an overall planar structure. The longitudinal direction of the actuator extends between the connection sites at the ends of the actuator. Between the upper and lower sides of the actuator is located a (virtual) neutral layer, i.e. a layer whose longitudinal extent does not change when the bending piezo actuator is bent. A bending line, whose profile in the unactuated neutral state is preferably linear, extends in the longitudinal direction of the neutral layer.

[0033] When a voltage is applied between the upper and lower sides of the piezo layer, the bending piezo actuator forms a bend between the coupling sites such that the bending line is curved. In this case, the cross section of the actuator positioned perpendicular to the bending line preferably does not change. Thus, application of a voltage results in a planar bend in which the profiles of the bending lines of different curvatures always lie in the same plane (the bending plane). As a result, the elements coupled to the coupling sites pivot relative to each other, specifically around a virtual rotational actuation axis that extends mainly perpendicular to the bending plane in which the bending line is positioned.

[0034] In the case of pure tilt motion, the actuation axis is fixed in space, independent of the tilt state. However, in the case of tilting enabled by bending piezo actuators, there is generally no "perfect" rotation of the mirror element about a fixed axis of rotation. There is usually additionally some small parasitic side to side and up / down movement of the mirror element. However, for the purposes of this application, it is sufficient to describe the tilt motion as a rotation about the actuation axis.

[0035] A multi-layer bending piezo actuator within the meaning of the present application has a multi-layer structure with at least one piezoelectric layer and one additional layer, where on both sides of the piezoelectric layer there is arranged one electrode layer respectively which generates an electric field penetrating the thickness direction of the piezoelectric layer, and the piezoelectric layer is designed such that when a voltage is applied to the electrode layers, the piezoelectric layer contracts in the layer extension direction, resulting in bending of the multi-layer structure.

[0036] The piezoelectric layer preferably consists of a piezoelectric ceramic material, in particular selected from the group comprising lead zirconate titanate (PZT), lithium niobate, potassium niobate, sodium niobate, PMN-PT, barium titanate, lead titanate, quartz (=silicon oxide), zinc oxide, aluminium nitride. Generally preferred is lead zirconate titanate, i.e. PZT ceramic.

[0037] The additional layer is intended to be elastically deformable or bendable to a limited extent. This can be a carrier layer made of a non-piezoelectric material. The carrier layer preferably consists of silicon or a silicon compound, which is particularly easy to achieve in terms of manufacturing, especially in the case of Si-based MEMS structures. Multilayer bending actuators that combine a single piezoelectric active layer with an inactive layer, for example a carrier layer made of a non-piezoelectric material, are also referred to here as unimorph or monomorph, since active bending occurs only in one direction.

[0038] The additional layer may be an additional piezoelectric layer, preferably with a common electrode layer disposed between the piezoelectric layers. The piezoelectric layers may then be controlled independently of one another so that two opposing bendings can be actively generated. Such a structure is referred to herein as a bimorph.

[0039] The two piezoelectric layers may be separated only by an intervening common electrode layer. However, the multi-layer structure may also be such that a carrier layer made of a non-piezoelectric material, such as silicon, is provided, in which case the piezoelectric layers are arranged on either side of the carrier layer. Bidirectional bending is also possible here.

[0040] If particularly large forces and moments are required for the displacement of the mirror element, it is also possible for the piezoelectric actuator to have more than two piezoelectric layers, in particular four, five or six piezoelectric layers, which can be controlled independently of one another. In this way, larger actuator forces can be realized.

[0041] The piezoelectric actuator can be designed with a ratio such that its longitudinal dimension (measured in the lengthwise direction or along the bending line) is greater than its transverse, i.e. width and height dimensions. In this way, even if the curvature of the piezoelectric actuator is small, a relatively large travel distance can be realized between the connected fixed end and the movable end of the actuator. However, in preferred embodiments, a different ratio is selected. In particular, the piezoelectric actuator has a preferably rectangular cross section perpendicular to the bending line with an aspect ratio of width to height greater than 1, and the width may also be greater than the effective length along the bending line.

[0042] This short and wide shape makes it possible to address the problem of increased thermal loads, especially for EUV multi-mirror devices. To accommodate high thermal loads, it appears advantageous to design the actuator and connecting elements to have a minimal overall thermal resistance, so that sufficient heat dissipation through the MEMS structure to the carrier element can be ensured, thereby avoiding overheating of the elements of the mirror unit. Contributing to achieving a low thermal resistance is the selection of the cross-sectional area of ​​the connecting and actuator elements as large as possible. Furthermore, a relatively wide actuator element is advantageous in that it reduces the thermal resistance while at the same time not adversely affecting the maximum tilt angle.

[0043] As already mentioned, the suspension system and the actuator system are preferably integrated such that a part of the suspension system is embodied as a piezoelectric actuator of the actuator system. According to one embodiment, this is implemented in that the suspension system comprises at least one connecting element group for mechanically connecting the base element to the mirror substrate, the connecting element group comprising two piezoelectric actuators that are independently controllable and have mutually orthogonal rotational actuation axes. The piezoelectric actuators can preferably be designed as multi-layer bending actuators of the type mentioned above.

[0044] Preferably, the suspension system has two connection element groups each including two integrated piezoelectric actuators that are independently controllable and have mutually orthogonal rotational actuation axes for mechanically connecting the base element to the mirror substrate, and each of the connection groups includes (i) a base connection element fixedly connected to the base element, (ii) a first piezoelectric actuator having one end attached to the base connection element and an opposite end attached to a bending-rigid connection element, (iii) the above-mentioned bending-rigid connection element, and (iv) a second piezoelectric actuator having one end attached to the bending-rigid connection element and an opposite end attached to a mirror connection element which is (v) connected and fixed to the mirror element.

[0045] In one advantageous variant of the connection element group, two piezoelectric actuators arranged at a distance and connected to each other via a rigid connection element form a flexure between the intervening connection element and the coupled components (base element and mirror element), respectively. However, whereas a typical flexure is passive and changes shape depending on the relative orientation of the coupled components, in this arrangement the opposite is true: the relative positioning of the respective coupled components is actively specified or forced by controlling the piezoelectric actuators.

[0046] The bending-rigid connecting element provides a geometrically defined connection between two coupled piezoelectric actuators that is rigid in the sense that it does not change shape even under the action of a force, the piezoelectric actuators being attached at their ends opposite the connecting element to the base element on the one hand and to the mirror element on the other hand. One advantageous property of such an arrangement is that the tilt angle at the end of the actuator element is directly converted into a tilt angle of the mirror element. This effectively converts the bending of the piezoelectric actuator element into a tilt of the mirror. The magnitude of the tilt can be precisely specified by controlling the piezoelectric actuator and varies only depending on the control voltage. The effect on the tilt position of the mirror element is here direct and not via a lever.

[0047] In a suspension system having two multi-articulated element groups with integrated piezoelectric actuators, the first piezoelectric actuator preferably defines a first rotational actuation axis, embodied and arranged such that the first rotational actuation axis is substantially coaxially aligned with respect to one another, and the second piezoelectric actuator defines a second rotational actuation axis, embodied and arranged such that the second rotational actuation axis is substantially coaxially aligned with respect to one another and orthogonally aligned with the first rotational actuation axis. Such an arrangement of actuation elements allows the linked mirror elements to tilt in positive and negative directions about two axes, respectively. By simultaneously operating multiple actuators, combinations of mirror tilts about multiple orthogonal axes can be realized such that an entire two-dimensional tilt field can be set up.

[0048] Flexible suspension systems that allow rotation about two mutually perpendicular axes, similar to a gimbal, are sometimes referred to in the art as "cardan" or cardan suspension systems.

[0049] For the sake of simplicity, one can also designate this type of suspension system with two multi-articulated connection elements as "Cardan", ignoring that in addition to the rotations about two mutually orthogonal actuation axes, this suspension system also allows parasitic relative movements between the mirror element and the base element. However, in contrast to (passive) Cardan suspensions, this suspension system is actively controllable by integrated piezo actuators, since the shape of the actuatable part and therefore the spatial arrangement of its components can be modified in a targeted manner.

[0050] In some embodiments, the piezoelectric actuator, designed as a multi-layer bending piezo actuator, has a mirror end that is connected to the mounting surface of the mirror element, either directly or via a mirror linking element that is rigidly connected to the mirror end using a rigid link. A rigid link means a non-articulated connection that provides a fixed angular relationship between the end and the mirror element. Unlike a lever connection or another type of articulated connection, the angular relationship does not change depending on the tilt angle. The rigid link is preferably designed so that at each bending position of the piezoelectric actuator, the mirror surface is aligned tangentially or parallel or nearly parallel to the mirror end. This allows a flat structure in a narrow intermediate space while at the same time allowing a large maximum tilt angle to be achieved.

[0051] According to the improvement, the capacitive sensor of the sensor system comprises at least one sensor element in the form of an interdigitated electrode, i.e. an electrode having a number of electrode plates or plate-like electrode fingers arranged side by side and spaced apart from one another similar to the teeth of a comb.

[0052] In some embodiments, mutually assigned comb electrode pairs are provided with alternating interdigitated electrode plates. The pairs of comb electrodes are preferably formed or arranged on the underside of the mirror element and on the top side of the base element. The interdigitated comb electrodes form an electric capacitor whose capacitance changes when the tilt position of the mirror element changes. Possible examples of positions and arrangements of comb electrodes for mirror units with capacitive actuators and capacitive sensors are given in US Pat. No. 5,399,433 (corresponding to US Pat. No. 5,399,433). The disclosure content of the above application regarding sensors is incorporated by reference into the content of the present application.

[0053] In a capacitive sensor with two mutually assigned comb electrodes with alternating interdigitated electrode plates, both comb electrodes of a pair are electrically connected to a voltage source and are at different potentials. Alternatively, at least one capacitive sensor can be provided with a comb electrode connected to a voltage source and with electrode plates arranged in a comb shape and electrically insulated from one another. The electrical interconnections are designed such that adjacent electrode plates are at different potentials, so that an electric field can be generated between adjacent electrode plates. Such a comb electrode thus has a number of mutually adjacent capacitors or capacitances during operation. Electric comb elements with plates arranged spaced apart from one another are provided as counterparts, which respectively engage in intermediate spaces between adjacent electrode plates of the assigned comb electrodes. The capacitance of the comb electrode capacitor formed by the adjacent electrode plate pairs varies depending on the penetration depth of the (electrically passive) plates. The comb elements can be electrically passive, so that a connection to a voltage source can be omitted. However, the comb teeth that act as a shield are typically kept at a defined potential to prevent charging by the EUV-generated plasma.

[0054] All capacitive sensors of the sensor system can be constructed and operated according to one of these two possibilities. A combination of both types is also possible.

[0055] The sensor elements of the capacitive sensor are preferably arranged in a radially outer region of the mirror unit. The electrode plates of the comb electrodes and / or the plates of the comb elements can extend to the outer periphery of the mirror substrate and / or base element.

[0056] The comb electrodes and / or plates can be arranged in rectangular, in particular square, corner regions of the base element and the mirror element. They can be kept free by rigid connecting elements with an angled shape with thin legs. The spatial arrangement of the interlocking plates or fingers can vary depending on the embodiment. In some embodiments, the plates or fingers are aligned radially with respect to the center of the mirror element. In other embodiments, arc-shaped curved plates are arranged concentrically with respect to the center. The interacting plates can also extend linearly or planarly at equal lateral distances from each other. The orientation can be parallel to the radial direction or perpendicular to the radial direction. The plates or teeth of each diagonal comb can extend parallel to each other, while in another diagonal the orientation is perpendicular thereto. It is also possible to design the electrode plates in a square shape.

[0057] The invention also relates to an illumination system of an EUV device, the illumination system being embodied, during operation of the EUV device, to receive EUV radiation from an EUV radiation source and to shape from at least a portion of the received EUV radiation an 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 device of the type described herein.

[0058] The EUV apparatus can for example be a projection exposure apparatus for EUV microlithography or a mask inspection apparatus that uses EUV radiation for inspecting masks (reticles) for EUV microlithography.

[0059] The individual mirror units comprising the base element, the mirror element and the intervening components of the suspension system, the actuators and the sensors can also be used independently of the use in the MMA, for example as an electrically controllable switching element in an optical circuit. In this respect, individual mirror units having the relevant features from at least one of the claims directed to the MMA are also disclosed.

[0060] Further advantages and aspects of the present invention are apparent from the appended claims and from the following description of exemplary embodiments of the invention taken in conjunction with the drawings. [Brief description of the drawings]

[0061] [Figure 1] 1 illustrates diagrammatically optical components of an EUV microlithography projection exposure apparatus having an illumination system housing one or more EUV multi-mirror devices according to an exemplary embodiment. [Diagram 2] 2A and 2B show schematic details of a controllable EUV multi-mirror device in the form of a multi-mirror array or facet mirror according to an exemplary embodiment; [Diagram 3] 3 shows a schematic cross-section of an exemplary piezoelectric bending actuator layer structure from region III of FIG. 2. [Figure 4] 1 illustrates a variation of a bending piezo actuator having multiple layers of different functionality arranged in a stack, where at least one layer is a piezoelectric layer, such that the bending piezo actuator can bend in response to the application of a voltage. [Diagram 5] 1 illustrates a variation of a bending piezo actuator having multiple layers of different functionality arranged in a stack, where at least one layer is a piezoelectric layer, such that the bending piezo actuator can bend in response to the application of a voltage. [Figure 6] 1 illustrates a variation of a bending piezo actuator having multiple layers of different functionality arranged in a stack, where at least one layer is a piezoelectric layer, such that the bending piezo actuator can bend in response to the application of a voltage. [Figure 7] 1 shows a schematic top view of a mirror unit having a piezoelectric actuator system, in which the piezoelectric actuator is integrated into a suspension system arranged between a base element and a mirror element; [Figure 8]

[0033] In a view similar to FIG. 7, an embodiment of a suspension system incorporating bending piezo actuators is shown. [Figure 9] FIG. 2 shows a schematic side view of an actuator element bending in the opposite direction. [Figure 10]

[0033] In a view similar to FIG. 7, an embodiment of a suspension system incorporating bending piezo actuators is shown. [Figure 11]

[0033] In a view similar to FIG. 7, an embodiment of a suspension system incorporating bending piezo actuators is shown. [Figure 12] 4 shows the difference between the tilt of a mirror element due to tangential lift and the tilt of a mirror element due to z-lift. [Figure 13A] 1 shows a variant of a mirror unit with a certain design of suspension and actuator system. [Figure 13B] 1 shows a variant of a mirror unit with a certain design of suspension and actuator system. [Figure 14] 1 shows a variant of a mirror unit with a certain design of suspension and actuator system. [Figure 15] 1 shows a variant of a mirror unit with a certain design of suspension and actuator system. [Figure 16A] 1 illustrates a schematic example of a capacitive sensor having interdigitated electrodes. [Figure 16B] 1 illustrates a schematic example of a capacitive sensor having interdigitated electrodes. [Figure 17A] 1 shows one possible spatial arrangement of interdigitated electrodes in a capacitive sensor system. [Figure 17B] 1 shows one possible spatial arrangement of interdigitated electrodes in a capacitive sensor system. [Figure 17C] 1 shows one possible spatial arrangement of interdigitated electrodes in a capacitive sensor system. [Figure 17D] 1 shows one possible spatial arrangement of interdigitated electrodes in a capacitive sensor system. [Figure 17E] 1 shows one possible spatial arrangement of interdigitated electrodes in a capacitive sensor system. [Figure 17F] 1 shows one possible spatial arrangement of interdigitated electrodes in a capacitive sensor system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0062] An example of a configuration of a multi-mirror device is explained below by way of example with reference to a possible use in an EUV device from the field of microlithography.

[0063] The essential components of a microlithographic 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 as limiting.

[0064] 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. The reticle holder 8 is displaceable, in particular in the scanning direction, by means of a reticle displacement drive 9.

[0065] For illustrative purposes, a Cartesian xyz coordinate system is shown in Fig. 1. The x direction extends perpendicular to the plane of the drawing. The y direction extends horizontally and the z direction extends vertically. In Fig. 1, the scanning direction extends along the y direction. The z direction extends perpendicular to the object plane 6.

[0066] The projection exposure apparatus 1 comprises a projection optical system 10. The projection optical system 10 serves to image an 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, angles other than 0° between the object plane 6 and the image plane 12 are also possible.

[0067] The structures on the reticle 7 are imaged onto a photosensitive layer of a wafer 13 that is 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. 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 effected in a mutually synchronous manner.

[0068] The radiation source 3 is an EUV radiation source. The radiation source 3 in particular emits EUV radiation 16, also referred to in the following 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 may be a plasma source, for example an LPP (Laser Produced Plasma) source or a GDPP (Gas Discharge Plasma) source. It may also be a synchrotron-based radiation source. The radiation source 3 may be a Free Electron Laser (FEL).

[0069] Illumination radiation 16 coming from 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 17 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 the reflectivity for the radiation used and to suppress extraneous light.

[0070] 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 represent a separation between the source module comprising the radiation source 3 and the collector 17 and the illumination optical unit 4.

[0071] 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 embodied as a spectral filter, which separates the used light 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.

[0072] The first facet 21 may be in the form of a macroscopic facet, in particular in the form of a rectangular facet or in the form of a facet having an arcuate peripheral contour or a peripheral contour formed as a partial circle. The first facet 21 may be in the form of a planar facet or in the form of a convexly or concavely curved facet.

[0073] 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.

[0074] Illumination radiation 16 travels horizontally between collector 17 and deflection mirror 19, ie along the y direction.

[0075] In the beam path of the illumination optical unit 4, a second facet mirror 22 is arranged downstream of the first facet mirror 20. If the second facet mirror 22 is arranged in a 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 2006 / 0132747, EP 1 614 008 and US 6,573,978.

[0076] 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.

[0077] The second facet 23 may likewise be a macroscopic facet, which may for example have a circular, rectangular or hexagonal perimeter, or may be a facet made up of a micromirror. In this respect, reference is likewise made to DE 10 2008 009 600 A1.

[0078] The second facet 23 may have a planar reflective surface or a convexly or concavely curved reflective surface.

[0079] The illumination optical unit 4 therefore forms a double-faceted system. This basic principle is also called fly's eye condenser (fly's eye integrator).

[0080] 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 .

[0081] 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.

[0082] In yet another embodiment (not shown) of the illumination optical unit 4, a transfer optical unit, which in particular contributes to the imaging of the first facet 21 into the object field 5, can be arranged in the beam path between the second facet mirror 22 and the object field 5. The transfer optical unit can have exactly one mirror or two or more mirrors arranged one after the other in the beam path of the illumination optical unit 4. The transfer optical unit can in particular comprise one or two normal incidence mirrors (NI mirrors) and / or one or two grazing incidence mirrors (GI mirrors).

[0083] In the design shown in FIG. 1, the illumination optical unit 4 comprises exactly three mirrors downstream of the collector 17 , in particular a deflection mirror 19 , a field facet mirror 20 and a pupil facet mirror 22 .

[0084] 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, in particular a first facet mirror 20 and a second facet mirror 22.

[0085] 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 generally only an approximate imaging.

[0086] 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 .

[0087] In the example shown in Fig. 1, the projection optical unit 10 comprises six mirrors M1-M6. A substitution of 4, 8, 10, 12 or any other number of mirrors Mi is likewise possible. The penultimate mirror M5 and the last mirror M6 each have a passing 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 which is greater than 0.5, may be greater than 0.6, and may for example be 0.7 or 0.75.

[0088] 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 with exactly one axis of rotational symmetry of the reflective surface shape. 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 designed as multilayer coatings with alternating layers of molybdenum and silicon.

[0089] The projection optical unit 10 has a large object-image offset in the y direction between the y coordinate of the center of the object field 5 and the y coordinate of the center of the image field 11. In the y direction, this object-image offset may have approximately the same magnitude as the z distance between the object plane 6 and the image plane 12.

[0090] In particular, the projection optical unit 10 can have an anamorphic form. In particular, it has different imaging scales βx, βy in the x-direction and the y-direction. 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 of the imaging scale β means imaging with image inversion.

[0091] The projection optical unit 7 results in a size reduction in the x-direction, ie perpendicular to the scanning direction, with a ratio of 4:1.

[0092] The shadow optical unit 10 provides a size reduction of 8:1 in the y-direction, ie the scanning direction.

[0093] Other imaging scales are possible as well. Imaging scales of the same sign and the same absolute value in the x and y directions, for example 0.125 or 0.25, are also possible.

[0094] 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 2018 / 0074303.

[0095] Each of the pupil facets 23 is assigned to exactly one of the field facets 21 in order to respectively form an illumination channel which illuminates the object field 5. In particular, this makes it possible to obtain an illumination according to the Köhler principle. The far field is decomposed into a number of object fields 5 by means of the field facets 21. The field facets 21 generate a number of images of intermediate foci on the respectively assigned pupil facets 23.

[0096] By means of the respectively assigned pupil facets 23, the field facets 21 are imaged onto the reticle 7 in an overlapping manner 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.

[0097] 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, which guide the light, the intensity distribution in the entrance pupil of the projection optical unit 10 can be set. This intensity distribution is also called the illumination setting.

[0098] An equally favorable pupil uniformity in the region of a defined illumination portion of the illumination pupil of the illumination optical unit 4 can be achieved by redistribution of the illumination channels.

[0099] 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.

[0100] In particular, the projection optical unit 10 may have a concentric entrance pupil. It may be accessible. It may be inaccessible.

[0101] The entrance pupil of the projection optical unit 10 generally cannot be illuminated exactly by means of the pupil facet mirror 22. In the case of imaging of the projection optical unit 10 telecentrically imaging the centre 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 for which the distance determined for the pair of aperture rays is minimal. This surface represents the entrance pupil or a surface conjugate thereto in real space. In particular, this surface exhibits a finite curvature.

[0102] 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.

[0103] In the arrangement of the components of the illumination optical unit 4 shown in Fig. 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.

[0104] The first facet mirror 20 is disposed at an angle with respect to a placement plane defined by the second facet mirror 22 .

[0105] EUV radiation is incident on both facet mirrors 20, 22 at a defined angle of incidence. The two facet mirrors are operated here at "normal incidence" or near "normal incidence", in particular at angles of incidence from a range of angles of incidence of, for example, ±25° around a main direction of incidence HE that extends perpendicularly to the global mirror normal NOR.

[0106] The field facet mirror 20 and the pupil facet mirror 22 are examples of a controllable EUV multi-mirror device in the form of a multi-mirror array (MMA). An example of the configuration of such an EUV multi-mirror device (here a field facet mirror) according to an exemplary embodiment is described in more detail with reference to FIG.

[0107] The EUV multi-mirror apparatus MMA comprises a number of mirror units MU arranged side by side in a matrix-type two-dimensional lattice arrangement on a carrier structure TS. In the illustrated variant, the individual mirror units MU are arranged on a dimensionally stable carrier structure TS in the form of a base plate. Each of the mirror units MU comprises a base element BE mounted on the carrier structure and a mirror element ME mounted by a flexible suspension system SUS so as to be individually movable relative to the base element BE.

[0108] Deviating from the figures, the carrier structure and the base elements can be embodied integrally from the same initial substrate in the form of a common structure, where the carrier structure is formed by a structural continuation of the base elements, each of which corresponds to a portion of the initial substrate, and a carrier structure separate from the base elements is therefore not necessarily required.

[0109] 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 on its front side opposite the base element BE has a reflective coating REF forming a mirror surface MS reflective to EUV radiation. The reflective coating has a multilayer structure with several pairs of layer materials (e.g. Mo-Si) of alternating high and relatively low refractive index, possibly together 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.

[0110] 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 units, the so-called integration density, is relatively high, for example more than 0.7 or more than 0.8 or more than 0.9. Complete filling of the area is not possible, since gaps SP defined by the side surfaces SF of the adjacent mirror substrates SUB remain between directly adjacent mirror elements ME, through which a collision-free relative movement of adjacent mirror elements relative to one another is ensured. The gap width can, for example, be of the order of several tens of micrometers, for example in the range from 20 μm to 100 μm.

[0111] In each mirror unit MU, components of a flexible suspension system SUS are arranged between the mirror element ME and the base element BE (see central mirror element), which structurally connects the mirror element ME and the base element BE, provides movable support of the mirror element relative to the base element with defined degrees of freedom, and provides restoring forces that automatically bring the mirror element to its zero position in the absence of actuator forces.

[0112] Furthermore, components of a piezoelectric actuator system AKS for generating a movement of the mirror element relative to the base element in response to receiving a control signal from a control device are arranged in the intermediate space between the mirror substrate and the base element. In this example, these are integrated into the structure of the suspension system SUS, for example in the form of a bending piezo actuator BPZ in which several layers with different functions are arranged in a stack and which bend in response to a control signal (see the exemplary embodiment of Figures 3 to 6). The piezo actuator (with the overall reference AKT) is also referred to below simply as "actuator".

[0113] Furthermore, in the peripheral area of ​​the mirror unit there is a component (comb-shaped electrode KE) of a capacitive position sensor KPS of the capacitive sensor system SENS, which is able to sense the current relative position of the mirror element ME with respect to the base element BE and to output a corresponding signal to the control unit, thus ensuring a closed-loop control of the individual tilt angles of the mirror substrate with respect to the carrier structure.

[0114] The tiltable mirror element may for example be tilted about a zero position with a displacement range of ±50 mrad, in particular ±100 mrad or more, and the setting accuracy may for example be less than 0.2 mrad, in particular less than 0.1 mrad.

[0115] The multi-mirror device can be manufactured to some extent using techniques from the field of manufacturing microelectromechanical systems (MEMS). In the example of Fig. 2, at least the base element BE, the suspension system SUS, the actuator system AKS and the position sensor system SENS are formed as MEMS structures.

[0116] Various aspects of the suspension system SUS and the actuator system AKS are described below.

[0117] For illustrative purposes, Fig. 3 shows by way of example a schematic cross-section of the layer structure of an exemplary piezoelectric actuator AKT from region III of Fig. 2. This actuator has a multilayer structure with at least one piezoelectric layer PZS and an additional layer WS made of an elastic material. In each case, one electrode layer E1, E2 is arranged on either side of the piezoelectric layer PZS in order to generate an electric field that penetrates the piezoelectric layer in the thickness direction (perpendicular to the extent of the layer). The piezoelectric layer PZS, made of a piezoelectrically active crystalline material, is coupled to a voltage U AKT When a current is applied to the electrode layers E1 and E2, the piezoelectric layer is designed to contract in the direction of the layer expansion (see arrows). This contraction leads to bending of the multilayer (see dashed line).

[0118] The additional layer WS may be formed by a single layer or may have a multi-layer configuration, in other words it may be subdivided into two or more layers. Variations are described in relation to figures 4 to 6.

[0119] The piezoelectric layer PZS can be, for example, a polycrystalline ceramic layer made, for example, of lead zirconate titanate (PZT). Lead-free ceramic materials are also conceivable. For thin-film MEMS, for example, (K,Na)NbO3 (potassium / sodium niobate) or AlN (aluminum nitride) can be used.

[0120] The piezo actuator itself has one or more piezoelectric layers and possibly a piezoelectrically inactive carrier layer. In the unimorph piezo actuator AKT of FIG. 4, the individual piezoelectric layers PZS are positioned on an additional layer in the form of a carrier layer TSC, which may consist of, for example, monocrystalline or polycrystalline silicon. On the upper and lower sides of the piezoelectric layer PZS, respectively, one electrode layer E1, E2, or layer electrode, is positioned. The voltage U AKT is applied between the two electrode layers, the entire actuator (carrier layer TSC and piezoelectric layer PZS as well as the electrode layers) bends in one plane (the plane of the drawing), as described above with respect to FIG.

[0121] Some bimorph piezo actuators consist of a (passive) carrier layer TSC and two piezoelectric layers located above and below the carrier layer (see FIG. 5). One electrode layer is located above and below both piezoelectric layers, respectively. By applying a voltage between the two electrodes of the piezoelectric layers, the piezoelectric layers contract in a direction parallel to the layer plane, which in turn leads to bending of the entire actuator (carrier layer, both piezoelectric layers, and also the electrode layers). If a voltage is applied between the two electrodes E1-1, E1-2 of the upper piezo layer PZS1, the entire actuator BPZ deflects upwards. If a voltage is applied to the two electrodes E2-1, E2-2 of the lower piezo layer PZS2, the entire actuator AKT deflects downwards.

[0122] It is possible to realize an actuator without a carrier layer and to directly stack two piezoelectric layers (see FIG. 6). The lower electrode of the upper piezo layer PZS1 and the upper electrode of the lower piezo layer PZS2 are realized here by a common electrode EG between the two piezo layers. It is further possible to provide several piezo layers (e.g. 4 or 6 layers) one on top of the other in order to increase the actuator force.

[0123] With reference to FIG. 7, an actuator system AKS, in which actuatable components (actuators) are integrated into a suspension system SUS, is described below. FIG. 7 shows a plan view of the mirror unit MU in the z direction. Only the base element BE and the mirror element ME (dashed lines) arranged spaced apart thereon in the z direction are shown. The suspension system SUS and the actuator system AKS or components of the drive system are arranged between them in the z direction. The actuator system AKS comprises exactly four individual piezo actuators AKT1, AKT2, AKT3, AKT4, which (in the unactuated state) are all located in the same plane. Here, two piezo actuators in each case are assigned to the mirror tilt around a specific axis. For example, the actuators AKT1 and AKT3 bring about the rotation of the mirror around the y axis, and the actuators AKT2 and AKT4 bring about the rotation of the mirror around the x axis.

[0124] In the exemplary embodiment of Fig. 7, four actuators AKT1, AKT2, AKT3, AKT4, a base element BE fixed to a carrier, and a mirror element ME are interconnected via rigid connection elements VE1, VE2 as follows: actuator AKT1 is connected on one side to the fixed base element BE (via a base connection element BA1) and on the other side to actuator AKT2 (via a first connection element VE1). Actuator AKT2 is connected on one side to actuator AKT1 (via VE1) and on the other side to the tilting mirror element ME via a mirror connection element SA1.

[0125] The connected elements BA1, AKT1, VE1, AKT2 and SA1 form a first doubly articulated element group VEG1. The actuators AKT1, AKT2 are here actively bendable flexures, the other components are rigid or bending stiff.

[0126] The actuator AKT3 is connected on one side to the fixed base element BE (via a base connecting element BA2) and on the other side to an actuator AKT4 via a second connecting element VE2. The actuator AKT4 is connected on one side to the actuator AKT3 (via VE2) and on the other side to the tilting mirror element ME (via a mirror connecting element SA2).

[0127] The connected elements BA2, AKT3, VE2, AKT4 and SA2 form a corresponding second doubly articulated element group VEG2. The actuators AKT3, AKT4 are here actively bendable flexures, the other components are rigid.

[0128] The positional relationship of the actuator elements is selected such that the actuating axes AA1, AA3 of the actuators AKT1 and AKT3 are parallel to one another, in particular coaxial, and the actuating axes AA2, AA4 of the actuators AKT2 and AKT4 are parallel to one another, in particular coaxial, and furthermore the actuating axes AA1, AA3 of the actuators AKT1 and AKT3 are perpendicular to the actuating axes AA2, AA4 of the actuators AKT2 and AKT4.

[0129] Thus, in an exemplary embodiment, a suspension system SUS with two multi-articulated connection element groups VEG1, VEG2 each including two integrated independently controllable piezoelectric actuators with mutually orthogonal rotation actuation axes is provided for mechanically connecting the base element BE to the mirror substrate or mirror element ME. Each of the connection groups includes a base connecting element BA1, BA2 fixedly connected to the base element BE, a first piezoelectric actuator, in particular a multi-layer bending piezo actuator AKT1, AKT3, with one end attached or connected to the base connecting element BA1, BA2 and the opposite end attached or connected to the bending-rigid connecting element VE1, VE2, said bending-rigid connecting element and a second piezoelectric actuator (in particular a multi-layer bending piezo actuator) AKT2, AKT4, with one end attached or connected to the bending-rigid connecting element and the opposite end attached or connected to the mirror connecting element SA1, SA2, the mirror connecting element SA1, SA2 being fixedly connected to the mirror element ME.

[0130] Tilting caused by bending piezo actuators generally does not result in a "perfect" rotation of the mirror element about a fixed axis of rotation or a spatially fixed actuation axis. In many cases, small parasitic side-to-side and up / down movements of the mirror element also occur. Therefore, the terms "orthogonal", "coaxial", etc. should be understood as approximate information to explain the principle.

[0131] Using this principle, other arrangements of the connections between the elements are possible and are shown in Fig. 8, Fig. 10 and Fig. 11. The arrangement of Fig. 8 requires more complex connection elements VE1, VE2 (three times bent) than the arrangement of Fig. 7. Both arrangements have in common that two base connection elements BA1, BA2 are connected to actuator elements AKT1 and AKT3 on different sides, respectively. This also applies to the mirror connection elements SA1, SA2 and the actuator elements AKT2 and AKT4. As a result, the actuator elements bend differently when the mirror is tilted around an axis (see Fig. 9). This property is suitable for unimorph actuators. In that case, the actuator AKT1 is only active in a positive rotation direction, for example when the mirror is tilted around the y axis, and the actuator AKT3 is only active in a negative rotation direction, for example when the mirror element is tilted around the y axis. This also applies to the actuators AKT2 and AKT4 for the mirror tilt around the x axis.

[0132] For the use of bimorph actuators, it is particularly advantageous from the point of view of control if the actuator elements assigned to the tilting axis each bend in the same direction when the mirror is tilted. For this purpose, the connection elements must each be connected to the substrate on the same side of the actuator elements AKT1 and AKT3. The same also applies to the connection elements to the mirror and to the actuator elements AKT2 and AKT4. The arrangements of figures 10 and 11 fulfill this requirement.

[0133] Figure 9 shows a side view of two actuator elements. When the mirror tilts at a certain angle, the actuator of that tilt axis (e.g. AKT1) bends upwards while the other (e.g. AKT3) bends downwards. This is shown diagrammatically in Figure 9 and relates to the coupling configurations of Figures 7 and 8. In contrast, in the coupling configurations of Figures 10 and 11, both actuators of an axis (i.e. AKT1 and AKT3 for example) bend in the same direction as the particular mirror tilt.

[0134] In the described arrangement of actuator elements, a multi-joint with two rotational degrees of freedom is formed, which allows tilting of the mirror element ME about two axes in positive and negative directions, respectively. By simultaneously operating several actuators, combinations of mirror tilts about the x- and y-axes can be realised, such that an entire two-dimensional tilt field can be set up.

[0135] One advantageous property of the described arrangement is that the tilt angle at the end of the actuator element is directly translated into a tilt angle of the mirror (tilt due to tangential lift). As shown in FIG. 12, this allows effectively translating bending of the piezoelectric actuator elements AKT into a tilt of the mirror element. This is made possible by the rigid connection of the mirror elements to the actuator elements and between the actuator elements themselves. The links and connection elements between the mirror elements and the actuator elements and between the actuator elements should be appropriately designed to be as rigid as possible in the described arrangement.

[0136] As can be easily seen in FIG. 12, the piezoelectrically active actuator element AKT is rigidly attached at its end SEA to the mirror element ME1 such that the mirror end SEA is aligned substantially parallel to the mirror surface (dashed line ME1). The bending line then runs practically parallel to the mirror surface. If there is still a curvature at this end, the link is also generally called a tangential link. In this respect, a tangential link within the meaning of the present application is a link whose mirror end is aligned parallel to the mirror surface or at a very acute angle (for example about 1° or less). Since the link is in any case rigid, the orientation of the mirror end SEA directly determines the orientation of the mirror surface. This direct transformation is also called tangential lift.

[0137] FIG. 12 shows the advantage of tilting the mirror element ME1 with a tangential lift compared to tilting the mirror element ME2 with a z-lift. The actuator elements are assumed to be planar in the unactuated state and have a central longitudinal axis BL running parallel to the axis AX. When the bending actuators AKT are actuated, bending occurs, with the bending line BL curving and at the same time remaining in a plane (here the drawing plane). In the case of tilting with a z-lift, the z-deflection Δz at the end of the actuator element AKT is used to tilt the mirror ME2 by the z-lift tilt angle WZH relative to the axis AX. However, the existing bending of the actuator elements is not used here. Tilting with a tangential lift (see mirror M1) achieves a tangential lift tilt angle WTH relative to the axis AX by using this bending, WTH>WZH. To achieve a tilt angle as large with a z-lift as with a tangential lift, a very short lever arm would be required, which is technically difficult to implement.

[0138] In order to cope with high thermal loads, it is advantageous to design the actuator elements and the connection elements so that they have a minimum overall thermal resistance. For this purpose, the cross-sectional area of ​​the connection elements should be selected as large as possible. Furthermore, wide actuator elements are advantageous because they reduce the thermal resistance while at the same time not adversely affecting the maximum tilt angle.

[0139] Figures 7 and 8 to 11 already show that the effective bending length L measured in the longitudinal direction of the actuator between the connected ends is smaller than the width B measured in the width direction aligned perpendicular thereto, which is in each case parallel to the direction of the associated actuation axis. The aspect ratio L / B of length to width can be, for example, 0.5 or less, or 0.4 or less, or 0.3 or less, or 0.2 or less, or 0.1 or less, often the aspect ratio is in the range of 1:3 to 1:10. In this way, a low thermal resistance can be achieved and furthermore installation space for the sensor element is created.

[0140] Three exemplary embodiments of the described actuator system, which correspond to one possible implementation with regard to the ratio of the individual component elements to one another, are described below (FIGS. 13A, 13B, 14 and 15). The exemplary embodiments relate here to the arrangement of the connection elements described with reference to FIG. 7, and therefore corresponding reference numbers are used. Similarly, the further described arrangements (FIGS. 8, 10 and 11) can also be realized with different arrangements of the connection elements.

[0141] Electrical contact with the actuator element AKT can be established by means of a current supply line passing through the connection element. The current supply lines for establishing contact with the actuator elements AKT2 and AKT4 remote from the base element are here in particular led through the actuator elements AKT1 and AKT3 close to the base element. The actuator elements AKT1 and AKT3 can be shortened for this purpose (in the direction of the actuation axis) so that a spring element running parallel to the actuator elements can respectively be introduced, through which the respective current supply line passes. In a similar way, the current supply lines of the capacitive sensor system can be integrated.

[0142] To detect the current tilt angle, a capacitive sensor is integrated into the structure. Figures 16A and 16B show two variants using different measurement principles.

[0143] In the exemplary embodiment of FIG. 16A, interlocking electrode comb teeth EK1, EK2 are attached both to the upper side of the base element BE and to the lower side of the mirror element ME such that an electric capacitor is formed. SENS is applied between the electrode combs. If the tilt of the mirror changes (curved arrow), the position of the electrodes relative to one another changes, and therefore the capacitance of the capacitor, which can be detected by an outflow or inflow of charge with the voltage held constant, or by a change in voltage with the current held constant.

[0144] In the exemplary embodiment of Fig. 16B, the capacitive sensor comprises a comb electrode EK3 attached or formed on the base element BE. The comb electrode cooperates with a comb electrode KE attached or formed on the underside of the mirror element ME and having a number of plates PL arranged at a distance from one another and each engaging in an intermediate space between adjacent electrode plates EPL1, EPL2 of EK3. The electrode plates EPL1, EPL2 etc. of the comb electrode EK3 are electrically insulated from one another such that adjacent electrode plates are respectively at different potentials (potential difference U SENS ) and thus form a capacitor. The comb teeth of the shield (comb electrode KE) attached to the mirror element ME are kept at a defined potential to prevent deposition from the plasma of the surrounding atmosphere (negative pressure with low hydrogen partial pressure) generated by EUV radiation. When the mirror is tilted, the plates PL of the mirror element ME penetrate into the intermediate space between the electrode plates and there act more or less strongly than the shield depending on the penetration depth, thereby changing the capacitance of the capacitor formed from the respective adjacent plates of the comb electrode on the base element BE depending on the tilt angle. The electrodes on the base element can also be called fixed comb teeth. Similarly, the comb teeth of the mirror element can also be called movable comb teeth. The comb teeth of the shield attached to the mirror element are kept at a defined potential to prevent deposition from the plasma of the surrounding atmosphere (negative pressure with low hydrogen partial pressure) generated by EUV radiation.

[0145] The different variants have certain advantages: in the arrangement of Fig. 16A the sensitivity of the capacitive sensor is higher than in the variant of Fig. 16B, on the other hand the variant of Fig. 16B is advantageous in terms of circuit technology, since here the signals for determining the position of the mirror element do not pass through lines passing through the deformable element of the suspension system.

[0146] There are different possibilities for the location and positioning of the electrodes, some of which are shown in the following exemplary embodiments (see Figs. 17A-17F). Different arrangements of the electrode combs are transferable to other exemplary embodiments of the actuator. The free areas between or outside the actuator structures are suitable for mounting the electrodes. From a process technology point of view, it is generally advantageous to mount the electrodes in the same z-plane as the actuator connection elements. In order to achieve the largest possible measurement signal, it is advantageous if the electrodes are mounted as far out as possible, since this results in a maximum translation of the electrode combs on the lower side of the mirror in the z-direction during the rotation of the mirror about the x- or y-axis. It may be useful to place a shield around the electrodes to minimize interference of neighboring mirror elements (see US Pat. No. 10,514,276).

[0147] 17A-17F respectively show plan views of the components of the mirror unit shown in FIG. 13A. Here, the connection elements VE1, VE2 of the connection group are each designed as an isosceles angle with an angle of 90° between the relatively thin legs, so that substantially square areas remain free at the four corners of the square mirror element ME of the square base element BE. Plates or plate-like fingers of the comb-shaped electrodes are arranged there. In the figures, the plates assigned to the base element BE are drawn in black, while the plates attached to the underside of the mirror element ME are drawn in light colors. In the example of FIG. 17A, the plates are arranged in two concentric segments in the corner regions, each oriented radially with respect to the center ZM of the mirror unit. In the examples of FIGS. 17B, 17C and 17D, the plates arranged in the respective diagonal corner regions are oriented parallel to each other and perpendicular to the radial direction leading to the corner region, while in the other diagonal the orientation is perpendicular thereto. In the arrangement of FIG. 17E, the individual electrode plates are each formed as right angles with equal leg lengths. The arrangement of Figure 17F provides arcuately curved plates arranged concentrically about the center of the mirror unit. All electrode arrangements have four-fold rotational symmetry about their respective centers ZM. Other arrangements are possible.

[0148] Yet another possibility is to mount the electrodes in the free area around the center ZM of the mirror, which would reduce sensitivity to tilting movements of the mirror, but the sensor would thus also be better shielded against interference from outside, especially from adjacent mirrors.

[0149] In the illustrated exemplary embodiment, a piezo actuator is used in combination with a capacitive sensor element. The piezo actuator is realized here by a piezoelectric actuator and at the same time serves here as a spring coupling, so that the micromirror, i.e. the mirror element, can be tilted about two axes. The comb teeth of the capacitive sensor are realized on the underside of the mirror substrate and on the upper side of the substrate. Thus, a relatively high sensitivity can be obtained, since the installation space of the sensor system is relatively large and, moreover, is located outside the mirror, where the mirror movement during tilting is greatest. Furthermore, capacitive sensors have only a low temperature sensitivity (for example, in contrast to piezoresistive sensors).

[0150] Some advantages of the exemplary embodiment can be summarized, for example, as follows: The actuator allows the realization of large tilt angles due to the use of piezo elements with high force density and the direct conversion of the bending of the piezo elements into mirror tilt. The actuator elements do not require much space, thus leaving a large space for integrating a sensor system, which can increase the sensitivity. The design is simple to manufacture, since it contains only a few elements, simple elements, and all elements are located in only a few planes. The system has a relatively low sensitivity to temperature variations.

Claims

1. 1. An EUV multi-mirror apparatus (MMA), comprising: a plurality of mirror units (MU) arranged side by side in a grid arrangement on a carrier structure (TS), each mirror unit having a base element (BE) and an individually tiltable mirror element (ME) facing the base element (BE), the mirror element (ME) having a mirror substrate (SUB) carrying a reflective coating (REF) on its front surface opposite the base element to form a mirror surface (MS) that reflects EUV radiation; and In an EUV multi-mirror apparatus (MMA), in each mirror unit, components of a suspension system (SUS) for movably mounting the mirror element (ME) on the base element (BE), actuators of an actuator system (AKS) for generating movement of the mirror element (ME) relative to the base element (BE) in response to receiving control signals, and sensors of a sensor system (SENS) for capturing the position of the mirror element are arranged between the base element (BE) and the mirror element (ME), An EUV multi-mirror apparatus, characterized in that the actuator system (AKS) has a piezoelectric actuator (AKT), and the sensor system (SENS) has a capacitance sensor (KPS).

2. 2. The EUV multi-mirror apparatus (MMA) according to claim 1, characterized in that the actuators of the actuator systems of the mirror units, the components of the suspension systems and / or the sensor elements of the sensors of the sensor systems are embodied in the form of MEMS structures, preferably the suspension systems being designed to be flexible so as to provide a restoring force that automatically brings the mirror elements to a zero position without tilting in the absence of actuator forces.

3. In the EUV multi-mirror apparatus (MMA) according to claim 1, the piezoelectric actuator (AKT) is realized in the form of a multilayer bending piezoelectric actuator (AKT) having a multilayer structure with at least one piezoelectric layer (PZS) and one additional layer (WS), and one electrode layer (E1, E2) is arranged on both sides of the piezoelectric layer, respectively, for generating an electric field penetrating the piezoelectric layer (PZS) in the thickness direction, and the piezoelectric layer (PZS) is connected to a voltage (U ＡＫＴ ) is applied to the electrode layers (E1, E2), the piezoelectric layer (PZS) contracts in the layer expansion direction, resulting in bending of the multilayer structure.

4. 4. The EUV multi-mirror apparatus (MMA) according to claim 3, characterized in that the additional layer (WS) is a carrier layer (TSC) made of a non-piezoelectric material, in particular silicon or a silicon compound, or that the additional layer (WS) is an additional piezoelectric layer (PZS), preferably with a common electrode layer arranged between the piezoelectric layers, or that the multilayer structure has a carrier layer (TSC) made of a non-piezoelectric material, with piezoelectric layers (PZS) arranged on each side of the carrier layer (TSC).

5. 10. The EUV multi-mirror apparatus (MMA) according to claim 1, characterized in that the piezoelectric actuator has two, three or more, in particular four, five or six independently controllable piezoelectric layers.

6. 4. The EUV multi-mirror apparatus (MMA) according to claim 3, wherein the piezoelectric actuator (AKT) has a preferably rectangular cross section perpendicular to the bending line with an aspect ratio of width (B) to height (H) greater than 1, and wherein the width (W) is greater than the effective length (L) along the bending line.

7. 2. The EUV multi-mirror apparatus (MMA) according to claim 1, wherein the suspension system (SUS) has at least one connecting element group (VEG1, VEG2) for mechanically connecting the base element (BE) to the mirror element (ME), and the connecting element group has two independently controllable piezoelectric actuators (AKT1, AKT2; AKT3, AKT4) having mutually orthogonal rotational actuation axes (AA1, AA2; AA3, AA4).

8. 2. The EUV multi-mirror apparatus (MMA) according to claim 1, wherein the suspension system (SUS) has two connection element groups (VEG1, VEG2) each including two integrated, independently controllable piezoelectric actuators (AKT1, AKT2; AKT3, AKT4) having mutually orthogonal rotation actuation axes (AA1, AA2; AA3, AA4), and each of the connection element groups includes a base connection element (BA1, BA2) fixedly connected to the base element (BE), An EUV multi-mirror device comprising: a first piezoelectric actuator (AKT) having one end attached to the base connecting element (BA1, BA2) and an opposite end attached to a flexurally rigid connecting element (VE1, VE2); the flexurally rigid connecting element (VE1, VE2); and a second piezoelectric actuator (AKT) having one end attached to the flexurally rigid connecting element (VE1, VE2) and an opposite end attached to a mirror connecting element (SA1, SA2) connected and fixed to the mirror element (ME).

9. 9. The EUV multi-mirror apparatus (MMA) according to claim 8, wherein the piezoelectric actuators (AKT) have a first rotational actuation axis (AA) and are embodied and arranged so that the first rotational actuation axes are aligned coaxially with each other, and the second piezoelectric actuators (AKT) have a second rotational actuation axis (AA) and are embodied and arranged so that the second rotational actuation axes are aligned coaxially with each other and perpendicular to the first rotational actuation axis.

10. 4. The EUV multi-mirror apparatus (MMA) according to claim 3, characterized in that the piezoelectric actuators (AKT) designed as multi-layer bending piezo actuators (AKT) have mirror-side ends connected to the mirror elements (ME) by rigid links, the rigid links being preferably designed in such a way that the mirror surfaces (MS) are aligned tangentially to the mirror-side ends in all bending positions of the piezoelectric actuators.

11. 2. The EUV multi-mirror apparatus (MMA) according to claim 1, characterized in that the capacitance sensor system (SENS) has at least one sensor element (KPS) in the form of a comb-shaped electrode (KE) including a plurality of electrode plates arranged side by side and spaced apart from each other.

12. 12. The EUV multi-mirror apparatus (MMA) according to claim 11, characterized in that the capacitance sensor has two mutually assigned comb electrodes with interdigitated electrode plates, the pair of comb electrodes being electrically connected to a voltage source during operation and at different potentials, preferably one of the comb electrodes being arranged on the base element and the other on the mirror element.

13. 12. The EUV multi-mirror apparatus (MMA) according to claim 11, wherein the capacitance sensor comprises a comb-shaped electrode connected to a voltage source and having electrode plates, the comb-shaped electrodes being arranged in a comb shape and being in electrical contact with each other so that adjacent electrode plates can be set to different potentials, and comb-tooth elements are provided as counterparts, the comb-shaped electrodes being arranged spaced apart from each other and having plates that respectively engage in intermediate spaces between adjacent electrode plates of the assigned comb-shaped electrode, and preferably the comb-shaped electrodes are arranged on the base element and the comb-tooth elements are arranged on the mirror element.

14. 14. An illumination system (2) of an EUV apparatus, in particular of a projection exposure apparatus (1) for EUV microlithography, which illumination system (2) is configured to receive EUV radiation from an EUV radiation source (3) during operation of the EUV apparatus and to shape from at least a portion of the received EUV radiation into illumination radiation directed to an illumination field at an exit surface (6) of the illumination system, characterized in that the illumination system (2) comprises at least one EUV multi-mirror apparatus (MMA) according to any one of claims 1 to 13.

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