Micromirror element, and micro-electromechanical system comprising a micromirror element

Abstract

The invention relates to a micromirror element (200), as can be used in micro-electromechanical systems (100), in particular for use in installations (1) used in semiconductor technology, and to a corresponding micro-electromechanical system (100) comprising at least one micromirror element (200). The micromirror element (200) comprises a mirror substrate (210) and a reflective coating (220) applied to a mirror surface (215) of the mirror substrate (210) that is intended to be reflective, wherein at least one intermediate layer (230) is provided between the mirror substrate (210) and the reflective coating (220), wherein the at least one intermediate layer (230) at least partially consists of an oxide of the material of the mirror substrate (210) and is designed such that the at least one intermediate layer (230), together with the reflective coating (220), can be regarded as a combined layer (240) relative to the mirror substrate (210), and the combined coefficient of thermal expansion of the reflective coating (220) and the at least one intermediate layer (230) substantially corresponds, at least for a predetermined temperature, to the coefficient of thermal expansion of the mirror substrate (210).

Description

[0001] Micromirror element and micro-electro-mechanical system with micromirror element

[0002]

[0001] The present application claims priority from German patent application 10 2024 210 151. 6, filed on 21 October 2024. The content of this German patent application is incorporated into the present application text by reference.

[0003]

[0002] The invention relates to a micromirror element, such as can be used in micro-electro-mechanical systems, in particular for use in semiconductor technology equipment, and to a corresponding micro-electro-mechanical system with at least one micromirror element.

[0004]

[0003] In the prior art, semiconductor technology equipment refers to equipment used for the production or testing of microstructured devices or the components required for their production. An example of such equipment is a projection exposure system for photolithography.

[0005]

[0004] Photolithography is used to manufacture microstructured components, such as integrated circuits. The projection exposure system used comprises an illumination system and a projection system. The image of a mask (also called a reticulum) illuminated by the illumination system is projected in a reduced size by means of the projection system onto a substrate, for example a silicon wafer, coated with a photosensitive layer and arranged in the image plane of the projection system, in order to transfer the mask structure onto the photosensitive coating of the substrate.

[0005] In illumination systems, in particular projection exposure systems designed for the EUV range, i.e., at exposure wavelengths from 5 nm (or possibly 2 nm) to 30 nm, but also for the DUV range with exposure wavelengths of, for example,At 193 nm, two faceted mirrors are typically positioned in the beam path between the actual illumination radiation source and the mask to be illuminated. The faceted mirror closer to the illumination radiation source in the beam path is often a so-called field faceted mirror, while the other is a so-called pupil faceted mirror.

[0006]

[0006] In order to produce different intensity and / or angle of incidence distributions when illuminating the mask, it is known to form the facets of at least one of the two faceted mirrors – in particular those of the field faceted mirror – from one or more individually electromechanically pivotable micromirrors. A corresponding method is disclosed, for example, in WO 2012 / 130768 A2.

[0007]

[0007] In order to achieve a small size of the individual micromirrors, it is known to form groups of micromirrors in the form of a so-called MEMS mirror array, namely a mirror array made of micro-electro-mechanical systems (MEMS).

[0008]

[0008] Micro-electro-mechanical systems (MEMS) are small components that combine micromechanical structures and electronic elements in a single chip. MEMS can be manufactured using integrated circuits, similar to microchips. A MEMS essentially comprises a basic structure on which movable elements are arranged that can be controlled relative to the basic structure.

[0009]

[0009] In a MEMS mirror array, a plurality of small mirror elements are each individually movable relative to a common base structure. At least one actuator is provided for each mirror element, allowing it to be adjusted along a predetermined degree of freedom. Frequently, the mirror elements are pivotable about two axes perpendicular to each other and parallel to the base, and sufficient actuators are provided to allow the mirror element to pivot independently about these axes. Sensors can also be provided for the individual mirror elements to determine their position relative to the base, thus enabling monitoring of the mirror alignment. A particularly advantageous embodiment for the mirrors of a MEMS mirror array is described in DE 10 2015 204 874 A1.

[0010]

[0010] A method for producing a micromirror or a MEMS mirror array comprising a plurality of such micromirrors is disclosed - together with further details of a possible embodiment of the micromirror - in DE 10 2015 220 018 Al .

[0011]

[0011] In particular, if the reflective surfaces of the individual mirror elements cannot be flat to achieve desired optical properties, but are to have a special shape, often a curvature, it is known to suitably curve the respective actual reflective surface, which is formed by a mirror plate provided with a suitable reflective coating, by introducing layer stresses into the mirror plate.

[0012]

[0012] Due to different coefficients of thermal expansion of the mirror plate and the reflective coating, the shape or curvature of a mirror element can change depending on the temperature, which then also changes the optical properties of the mirror element.

[0013] To avoid or at least reduce the temperature-dependent deformation of a mirror element, it is known to apply a counter-coating to the surface of the mirror plate facing away from the reflective coating. This counter-coating has a coefficient of thermal expansion comparable to that of the coating. This results in a symmetrical structure in which the different expansion rates of the reflective coating and the counter-coating relative to the mirror plate essentially cancel each other out.

[0013]

[0014] A disadvantage of this state of the art is the complex application of a counter-coating to the side facing away from the reflective coating. Furthermore, the mirror plate is no longer exposed on the side in question, which can complicate the integration of the mirror plate into the structure of a micro-electro-mechanical system.

[0014]

[0015] The object of the present invention is to create a micromirror element and a micro-electro-mechanical system comprising a corresponding micromirror element in which the disadvantages known from the prior art no longer occur or only occur to a reduced extent.

[0015]

[0016] This problem is solved by a micromirror element according to claim 1 and a micro-electro-mechanical system according to claim 9. Advantageous further developments are the subject of the dependent claims.

[0016]

[0017] Accordingly, the invention relates to a micromirror element for use in micro-electro-mechanical systems, in particular for semiconductor technology equipment, comprising a mirror substrate and a reflective coating applied to the mirror surface of the mirror substrate intended to reflect, wherein at least one intermediate layer is provided between the mirror substrate and the reflective coating, wherein the at least one intermediate layer is at least partially composed of an oxide of the material of the mirror substrate and is configured such that the at least one intermediate layer together with the reflective coating can be regarded as a combined layer in relation to the mirror substrate and the combined coefficient of thermal expansion of the reflective coating and the at least one intermediate layer corresponds essentially to the coefficient of thermal expansion of the mirror substrate, at least for a predetermined temperature.

[0017]

[0018] The invention further relates to a micro-electro-mechanical system, in particular for semiconductor technology equipment, comprising a micro-electro-mechanically movable element at least relative to a basic structure in at least one degree of freedom by at least one actuator, wherein the micro-electro-mechanically movable element comprises a micro-mirror element according to the invention.

[0018]

[0019] First, some terms used in connection with the invention will be explained.

[0019]

[0020] In a micro-electro-mechanical system, a "micromirror element" is the single element of a micro-electro-mechanically adjustable micromirror that forms the actual reflecting mirror surface. The micromirror element comprises at least the structural element forming the surface in question. However, particularly on the side facing away from the reflecting mirror surface, other elements, such as connecting elements or elements required for the formation of actuators and / or sensors in the final application within a micro-electro-mechanical system, may be molded onto the micromirror element.

[0021] A "reflective coating" is a coating that reflects radiation at the wavelength of the radiation incident upon the micromirror element during its subsequent proper use. Since radiation at wavelengths for which structural elements made of known materials are typically not reflective or only insufficiently reflective is used, particularly in semiconductor technology systems, it is known to achieve or ensure sufficient reflection through a suitable coating. The reflective coating can be adapted to the wavelength expected for the intended application and, for example, reflect radiation in the EUV range with a wavelength of 13.5 nm. A multilayer coating of silicon and molybdenum is generally used for this purpose.

[0020]

[0022] A micromirror element is considered "deformed" in particular when the shape of the mirror surface, and thus the optical properties of the micromirror element, fundamentally change. An enlargement or reduction of the mirror element as a whole, where the shape of the mirror surface of the micromirror element, and thus its optical properties, remain unchanged, is not considered a deformation, but merely a "change in size".

[0021]

[0023] The invention recognizes that by providing at least one suitably designed intermediate layer between the mirror substrate and the reflective coating, it is possible to consider any potential deformation of the micromirror element due to thermal expansion of the mirror substrate and a combined coating comprising the reflective coating and the at least one intermediate layer. By appropriately selecting the at least one intermediate layer, particularly with regard to its coefficient of thermal expansion, the resulting coefficient of thermal expansion of the combined coating can be adapted to the coefficient of thermal expansion of the mirror substrate, so that, at least for a given temperature, which is, for example, the expected operating temperature, an essentially identical coefficient of thermal expansion is obtained for the mirror substrate and the combined coating.This ensures that the micromirror element, at least within a narrow range around the specified temperature, does not deform or only deforms minimally, particularly within the range permitted by the design, compared to its shape at the specified temperature. The micromirror element only undergoes a change in size, namely an increase, while fundamentally maintaining its shape, especially in the area of ​​the mirror surface. A similar process occurs when the temperature is reduced from the specified temperature, except that the change in size is a decrease.

[0022]

[0024] This also applies to coefficients of thermal expansion that are at least partially temperature-dependent, since such coefficients generally change only slowly with temperature. When the temperature is increased from the given temperature, both the mirror substrate and the combined coating of reflective layer and intermediate layer(s) initially expand comparably, so that at least no change in the mirror's curvature or similar shape of the reflective surface occurs. Depending on the magnitude of the temperature deviation and any resulting changes in the coefficients of thermal expansion, larger temperature deviations can lead to fundamentally different thermal expansions of the mirror substrate and the combined coating, which can then result in an undesirable change in the shape of the mirror surface.

[0025] It is therefore preferred if the at least one intermediate layer is designed such that the combined coefficient of thermal expansion of the reflective coating and the at least one intermediate layer corresponds essentially to the coefficient of thermal expansion of the mirror substrate not only for a given temperature, but for a given temperature range. This largely prevents changes in the shape of the micromirror element over the given temperature range, which preferably includes all temperatures expected during the use of the micromirror element.

[0023]

[0026] Preferably, at least two intermediate layers are provided, wherein the intermediate layer adjacent to the reflective coating is preferably on the material of the mirror substrate. Since the intermediate layer in question is made of the same material as the mirror substrate, any coating known from the prior art to be suitable for application to the mirror substrate material can be used in the micromirror element according to the invention. It is also possible to carry out the preparatory surface processing steps that may be necessary for applying the reflective coating, e.g., adjusting the roughness, as is also known for direct application of the reflective layer directly onto the mirror substrate.

[0024]

[0027] The combined coating need not be limited to exhibiting a combined coefficient of thermal expansion essentially equal to that of the mirror substrate. Rather, the combination of the reflective coating and the at least one intermediate layer can also introduce a layer stress into the micromirror element, which causes a desired curvature of the mirror substrate and thus of the micromirror element. In this case, the combined coating, and in particular the intermediate layer it comprises, fulfills the function of a stress layer, as is generally known as a layer within a mirror substrate for achieving mirror curvature.

[0025]

[0028] In particular, to achieve a targeted shaping of the micromirror element by means of layer tension in the combined coating, or to adapt the thermal expansion of the combined coating anisotropically and / or spatially resolved, it is preferred if at least one intermediate layer is spatially resolved and consists of at least two different materials with different coefficients of thermal expansion. Furthermore, this makes it possible to protect one material of the intermediate layer from environmental influences by encapsulating it in another material that is more stable with regard to environmental influences.

[0026]

[0029] It is preferred that the thickness of the mirror substrate is several times, preferably at least four times, the thickness of the combined coating, i.e., the sum of the thicknesses of the reflective coating and the at least one intermediate layer. If the thickness of the mirror substrate is correspondingly greater than the thickness of the combined coating, which comprises at least two layers, namely the reflective coating and at least one intermediate layer, it is easily possible to consider the aforementioned layers together as a combined coating.

[0027]

[0030] Even if the combined coating is already designed as a tension layer, an alternative or additional tension layer can be provided within the mirror substrate itself. Such a tension layer allows for the controlled introduction of stresses into the mirror substrate, resulting in deformation, particularly curvature. Corresponding tension layers and their application to a mirror substrate are well-known and require no further explanation here.

[0028]

[0031] The mirror substrate can be made of silicon.

[0029]

[0032] At least one intermediate layer is at least partially composed of an oxide of the mirror substrate material, in the case of a silicon substrate, specifically silicon oxide. The use of silicon as a mirror substrate has proven successful. Silicon oxide is also a well-known material for microelectromechanical systems and their manufacturing processes, allowing for the use of established manufacturing methods, such as those for the spatially resolved deposition or incorporation of silicon oxide into a silicon substrate. The intermediate layer can also be partially composed of a nitride of the mirror substrate material, specifically silicon nitride.

[0030]

[0033] The micro-electro-mechanical system according to the invention is characterized in that at least one electro-mechanically movable element comprises a micro-mirror element according to the invention. In particular, the micro-electro-mechanical system can be a MEMS mirror array in which the individual micro-mirror elements are configured according to the invention.

[0031]

[0034] The invention will now be described by way of example with reference to advantageous embodiments and the accompanying drawings. These show:

[0032] Figure 1: a schematic representation of a projection exposure system for photolithography comprising a micro-electro-mechanical system according to the invention;Figure 2: a schematic representation of the micro-electro-mechanical system according to the invention from Figure 1 comprising a micromirror element according to the invention;

[0033] Figure 3: schematic representation of a first embodiment of a micromirror according to the invention e 1 emen ts; and

[0034] Figure 4 : schematic representation of a second embodiment of a micromirror element according to the invention .

[0035]

[0035] Figure 1 shows a schematic meridional section of a projection exposure system 1 for photolithography as an example of a system for semiconductor technology. The projection exposure system 1 comprises an illumination system 10 and a projection system 20.

[0036]

[0036] An object field 11 in an object plane or reticulum plane 12 is illuminated by means of the illumination system 10. The illumination system 10 comprises an exposure radiation source 13, which, in the illustrated embodiment, emits illumination radiation comprising at least useful light in the EUV range, i.e., in particular with a wavelength between 5 nm and 30 nm. The exposure radiation source 13 can be a plasma source, for example, an LPP source (laser-produced plasma) or a DPP source (gas-discharge-produced plasma). It can also be a synchrotron-based radiation source. The exposure radiation source 13 can also be a free-electron laser (FEL).

[0037] The illumination radiation emanating from the light source 13 is first focused in a collector 14. The collector 14 can be a collector with one or more ellipsoidal and / or hyperboloid reflective surfaces. The at least one reflective surface of the collector 14 can be illuminated at grazing incidence (Gl ), i.e., with angles of incidence greater than 45°, or at normal incidence (NI ), i.e., with angles of incidence less than 45°. The collector 14 can be structured and / or coated, on the one hand to optimize its reflectivity for the useful radiation and on the other hand to suppress stray light.

[0037]

[0038] After the collector 14, the illumination radiation propagates through an intermediate focus in an intermediate focal plane 15. If the illumination system 10 is to be constructed in a modular manner, the intermediate focal plane 15 can, in principle, be used for the separation – including structural separation – of the illumination system 10 into a radiation source module, comprising the exposure radiation source 13 and the collector 14, and the illumination optics 16 described below. With such a separation, the radiation source module and the illumination optics 16 then together form a modularly constructed illumination system 10.

[0038]

[0039] The illumination optics 16 include a deflecting mirror 17. The deflecting mirror 17 can be a flat deflecting mirror or, alternatively, a mirror with a beam-shaping effect in addition to the mere deflection effect. Alternatively or additionally, the deflecting mirror 17 can be designed as a spectral filter that separates a useful wavelength of the illumination radiation from stray light of a different wavelength.

[0040] The deflecting mirror 17 deflects the radiation from the illumination radiation source 13 onto a first faceted mirror 18. If the first faceted mirror 18 is arranged – as in the present case – in a plane of the illumination optics 16 that is optically conjugate to the reticular plane 12 as a field plane, it is also referred to as a field faceted mirror.

[0039]

[0041] The first faceted mirror 18 comprises a plurality of micromirrors 18', each individually pivotable about two mutually perpendicular axes, for the controllable formation of facets, each preferably equipped with an orientation sensor (not shown) for determining the orientation of the micromirror 18'. The first faceted mirror 18 is thus a microelectromechanical system (MEMS system), as described, for example, in DE 10 2008 009 600 A1.

[0040]

[0042] In the beam path of the illumination optics 16, a second faceted mirror 19 is arranged downstream of the first faceted mirror 18, resulting in a double-faceted system, the basic principle of which is also known as a honeycomb condenser (Fly's Eye Integrator). If the second faceted mirror 19 is arranged in a pupil plane of the illumination optics 16 – as in the illustrated embodiment – ​​it is also referred to as a pupil faceted mirror. However, the second faceted mirror 19 can also be arranged at a distance from a pupil plane of the illumination optics 16, in which case the combination of the first and second faceted mirrors 18, 19 forms a specular reflector, as used, for example, in the

[0041] US 2006 / 0132747 Al, which is described in EP 1 614 008 Bl and US 6, 573, 978 .

[0042]

[0043] The second faceted mirror 19 need not be constructed from pivotable micromirrors, but can instead comprise individual facets formed from one or a manageable number of mirrors that are significantly larger than micromirrors, and which are either fixed or tiltable only between two defined end positions. However, as shown, it is also possible to provide the second faceted mirror 19 with a microelectromechanical system comprising a plurality of micromirrors 19' that are individually pivotable about two axes perpendicular to each other, each preferably comprising an orientation sensor.

[0043]

[0044] With the aid of the second faceted mirror 19, the individual facets of the first faceted mirror 18 are projected onto the object field 11, although this is regularly only an approximate projection. The second faceted mirror 19 can be the last beam-shaping or even the last mirror for the illumination radiation in the beam path before the object field 11.

[0044]

[0045] Each of the facets of the second faceted mirror 19 is assigned to exactly one of the facets of the first faceted mirror 18 to form an illumination channel for illuminating the object field 11. This can result in illumination according to Köhler's principle.

[0045]

[0046] The facets of the first faceted mirror 18 are each imaged superimposed on a corresponding facet of the second faceted mirror 19 to illuminate the object field 11. The illumination of the object field 11 is as homogeneous as possible. It preferably exhibits a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

[0047] By selecting the illumination channels ultimately used, which is easily achieved by appropriately adjusting the micromirrors 18' of the first faceted mirror 18, the intensity distribution in the entrance pupil of the projection system 20 described below can also be adjusted. This intensity distribution is also referred to as the illumination setting. Furthermore, it can be advantageous not to arrange the second faceted mirror 19 exactly in a plane that is optically conjugate to a pupil plane of the projection system 20. In particular, the pupil faceted mirror 19 can be tilted relative to a pupil plane of the projection system 20, as described, for example, in DE 10 2017 220 586 A1.

[0046]

[0048] In the arrangement of the components of the illumination optics 16 shown in Figure 1, the second faceted mirror 19 is arranged in a surface conjugate to the entrance pupil of the projection system 20. Deflection mirror 17 and the two faceted mirrors 18, 19 are each tilted relative to both the object plane 12 and to each other.

[0047]

[0049] In an alternative embodiment of the illumination optics 16, not shown, a transmission optic comprising one or more mirrors can be provided in the beam path between the second faceted mirror 19 and the object field 11. The transmission optic can, in particular, comprise one or two mirrors for normal incidence (NI mirrors) and / or one or two mirrors for grazing incidence (Gl mirrors). With an additional transmission optic, different positions of the entrance pupil for the tangential and sagittal beam paths of the projection system 20 described below can be taken into account.

[0050] Alternatively, it is possible to dispense with the deflecting mirror 17 shown in Figure 1, in which case the faceted mirrors 18, 19 must be arranged appropriately opposite the radiation source 13 and the collector 14.

[0048]

[0051] Using the projection system 20, the object field 11 in the reticulum plane 12 is transferred to the image field 21 in the image plane 22.

[0049]

[0052] The projection system 20 comprises a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure unit 1. The mirrors Mi are optical elements 25.

[0050]

[0053] In the example shown in Figure 1, the projection system 20 comprises six mirrors Mx to M6 as optical elements 25. Alternatives with four, eight, ten, twelve, or any other number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage for the illumination radiation, making the projection system 20 a double-obscured optical system. The projection system 20 has an image-side numerical aperture that is greater than 0.3 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0051]

[0054] The reflective surfaces of the mirrors Mi can be designed as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflective surfaces of the mirrors Mi can also be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflective surface shape. The mirrors Mi, like the mirrors of the illumination optics 16, can have highly reflective coatings for the illumination radiation. These reflective coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0052]

[0055] The projection system 20 has a large object-image offset in the y-direction between a y-coordinate of a center of the object field 11 and a y-coordinate of the center of the image field 21. This object-image offset in the y-direction can be approximately as large as a z-distance between the object plane 12 and the image plane 22.

[0053]

[0056] The projection system 20 can in particular be anamorphic, i.e. it has in particular different image scales β x , ß y in the x and y directions. The two image scales ß x , ß y of the projection system 20 are preferably located at ( ß x , ß y ) = ( + / - 0.25, / + - 0.125) . A magnification β of 0.25 corresponds to a reduction in the ratio 4:1, while a magnification β of 0.125 results in a reduction in the ratio 8:1. A positive sign for the magnification β indicates a magnification without image inversion, a negative sign indicates a magnification with image inversion.

[0054]

[0057] Other magnification ratios are also possible. Magnification ratios with the same sign and those with the same absolute value are also possible. x , ß y In the x and y directions, adjustments are possible.

[0055]

[0058] The number of intermediate image planes in the x- and y-directions in the beam path between the object field 11 and the image field 21 can be the same or different, depending on the design of the projection system 20. Examples of projection systems 20 with different numbers of such intermediate images in the x- and y-directions are known from the

[0056] US 2018 / 0074303 Al .

[0059] Projection system 20 may, in particular, have a homocentric entrance pupil. This may be accessible. However, it may also be inaccessible.

[0057]

[0060] A reticle 30 (also called a mask) arranged in the object field 11 is exposed by the illumination system 10 and transferred to the image plane 21 by the projection system 20. The reticle 30 is held by a reticle holder 31. The reticle holder 31 can be moved, in particular in a scanning direction, by means of a reticle displacement drive 32. In the illustrated embodiment, the scanning direction is in the y-direction.

[0058]

[0061] The reticule 30 can have an aspect ratio between 1:1 and 1:3, preferably between 1:1 and 1:2, and particularly preferably 1:1 or 1:2. The reticule 30 can be substantially rectangular and is preferably 5 to 7 inches (12.70 to 17.78 cm) long and wide, more preferably 6 inches (15.24 cm) long and wide. Alternatively, the reticule 30 can be 5 to 7 inches (12.70 to 17.78 cm) long and 10 to 14 inches (25.40 to 35.56 cm) wide, and is preferably 6 inches (15.24 cm) long and 12 inches (30.48 cm) wide.

[0059]

[0062] A structure on the reticulum 30 is imaged onto a photosensitive layer of a wafer 35 located in the image plane 22 within the image field 21. The wafer 35 is held by a wafer holder 36. The wafer holder 36 can be displaced, particularly along the y-direction, via a wafer transfer drive 37. The displacement of the reticulum 30 via the reticulum transfer drive 32 and the displacement of the wafer 35 via the wafer transfer drive 37 can be synchronized.

[0060]

[0063] The projection exposure system 1 shown in Figure 1, or its projection system 20, the preceding description of which essentially reflects known prior art, is characterized in that the first and second faceted mirrors 18, 19 are MEMS mirror arrays comprising a micro-electro-mechanical system 100 according to the invention, one such micro-electro-mechanical system 100 of which is shown schematically in Figure 2. It is also possible that only one of the two faceted mirrors 18, 19 comprises a MEMS mirror array.

[0061]

[0064] Figure 2 shows a sectional view through a part of a micro-electro-mechanical system 100. The micro-electro-mechanical system 100 comprises a basic structure 101 on which a plurality of elements 103 are arranged to be movable, namely pivotable about two degrees of freedom. Actuators 102 are provided for the individual movement of each of the elements 103, namely for pivoting about the two degrees of freedom, so that each of the elements 103 is a movable micro-electro-mechanical element 103.

[0062]

[0065] Element 103 comprises a flat base plate 104, via which it is connected to the base structure 101 and on which parts of the actuators 102 are also arranged. A micromirror element 200 according to the invention is arranged on the upper side of the base plate 104 of each of the micro-electro-mechanically movable elements 103.

[0063]

[0066] Figure 3 shows a first embodiment of a micromirror element 200 according to the invention.

[0064]

[0067] The micromirror 200 comprises a planar mirror substrate 210, preferably made of silicon, one side of which is provided as a mirror surface 215. In order to give the mirror surface 215 a curved shape, as shown, a suitable tension layer (not shown) is provided in the mirror substrate 210 in this embodiment.

[0068] In order for the mirror surface 215 to be reflective for the intended radiation, the micromirror 200 includes a reflective coating 220 on this surface, which in the present example has alternating layers of molybdenum and silicon in order to be reflective for EUV radiation.

[0065]

[0069] An intermediate layer 230 is provided between the reflective coating 220 and the mirror substrate 210. The intermediate layer 230 is primarily composed of silicon oxide, specifically in the entire area 231. The area 231 is preferably surrounded on all sides by the silicon area 232, which ultimately forms a border. The area 232 completely encapsulates the silicon oxide in the area 231, together with the reflective coating 220 and the mirror substrate 210, which are adjacent to the intermediate layer 230, thus protecting it from environmental influences.

[0066]

[0070] The reflective coating 220 and the intermediate layer 230 together form the combined coating 240, whose combined thickness d is less than a quarter of the thickness d Substrat of the mirror substrate 210 corresponds. Since the thickness d SubstratSince the combined thickness of the mirror substrate 210 is thus several times greater than the combined thickness d, the reflective coating 220 and the intermediate layer 230 can be considered together as a singular combined coating 240 for the mirror substrate 210, at least with regard to thermal expansion.

[0067]

[0071] The coefficient of thermal expansion of the mirror substrate 210 is approximately 2.5 / °C due to the silicon material. -1 , which can be considered constant in the temperature range of 20 °C to 200 °C relevant for the micromirror element 200.

[0068]

[0072] Similarly, the coefficient of thermal expansion of the silicon oxide in area 231 of the intermediate layer 230 is approximately 0.5 K. -1 over the temperature range from 20 °C to 200 °C. The coefficient of thermal expansion of the reflective coating 220, consisting of silicon and molybdenum, is significantly above 2.5 °C. -1 , but is essentially constant within the temperature range in question.

[0069]

[0073] According to the invention, the reflective coating 220 and the intermediate layer 230 are matched to each other such that the resulting coefficient of thermal expansion for the combined coating 240 in the temperature range of 20 °C to 200 °C is essentially the same as the coefficient of thermal expansion of the mirror substrate 210, i.e., approximately 2.5 °C. -1 , corresponds to . The corresponding adjustment can be made in particular by appropriately selecting the thickness of the intermediate layer 230.

[0070]

[0074] As a result, the micromirror element 200 may undergo a change in size when the temperature changes, but the basic shape of the micromirror element 200 remains unchanged and no deformations occur, in particular the mirror surface 215, which is curved as can be seen in Figure 3.

[0071]

[0075] Figure 4 shows a second embodiment of a micromirror element 200 according to the invention.

[0072]

[0076] The micromirror element 200 in Figure 4 also comprises a planar silicon mirror substrate 210, one side of which is designed as a mirror surface 215. The mirror substrate 210 is planar in its initial state. However, the coating described below, in particular the intermediate layer 230.1, induces a stress in the mirror substrate 210, resulting in the curved shape of the micromirror element 200 shown in Figure 4.

[0077] To enable reflection of EUV radiation, a multilayer coating of silicon and molybdenum is provided as a reflective coating 220.

[0073]

[0078] In this embodiment, two intermediate layers 230, namely the intermediate layers 230.1 and 230.2, are provided between the reflective coating 220 and the mirror substrate 210.

[0074]

[0079] The intermediate layer 230.2 adjacent to the reflective coating 220 is made of the same material as the mirror substrate 210, namely silicon. Consequently, the surface of the intermediate layer 230.2 facing the reflective coating 220 can be prepared before the reflective coating 220 in the same way as a substrate to be coated according to the prior art. In particular, the surface roughness can be suitably adapted to the requirements of the reflective coating 220.

[0075]

[0080] The intermediate layer 230.1 adjacent to the mirror substrate 210 comprises both regions 231 made of silicon oxide and / or silicon dioxide, and regions 232 made of silicon, the latter regions 232 being—unlike in the embodiment shown in Figure 3—not limited to the edge of the intermediate layer 230.1. Nevertheless, the regions 231 are each completely encapsulated by the regions 232, the adjacent intermediate layer 230.2, and the mirror substrate 210, all of which are silicon, and thus protected from environmental influences.

[0076]

[0081] The intermediate layer 230.1 is designed to introduce a layer tension into the micromirror element 200, so that the desired curvature of the mirror substrate 210 and thus of the micromirror element 200 is achieved.

[0082] Furthermore, the intermediate layer 230.1 and its regions 231 made of silicon oxide and / or silicon dioxide are designed with regard to their thickness and the arrangement and configuration of the regions 231 such that, together with the intermediate layer 230 and the reflective coating 220, a combined coefficient of thermal expansion results which essentially corresponds to that of the mirror substrate 210. Since in this case the thickness d Substrat Since the thickness of the mirror substrate 210 is four times the sum of the thicknesses of the reflective coating 220 and the two intermediate layers 230.1, 230.2, the latter layers can easily be considered as a combined layer 240 with thickness d in relation to the mirror substrate 210.

[0077]

[0083] The combined layer 240 therefore exhibits a coefficient of thermal expansion that essentially matches the coefficient of thermal expansion of the mirror substrate 210. Consequently, the shape of the micromirror element 200, encompassing the curvature introduced by the combined layer 240 and the intermediate layer 230.1 contained therein, will not change with a temperature change, at least within a temperature range of 20 °C to 200 °C, which is ultimately determined by the materials used. Only a change in size is to be expected with a temperature change.

Claims

Patent claims 1. Micromirror element (200) for use in micro-electromechanical systems (100), in particular for semiconductor technology equipment (1), comprising a mirror substrate (210) and a reflective coating (220) applied to the reflective mirror surface (215) of the mirror substrate (210), characterized by the fact that at least one intermediate layer (230) is provided between the mirror substrate (210) and the reflective coating (220), wherein the at least one intermediate layer (230) is at least partially made of an oxide of the material of the mirror substrate (210) and is designed such that the at least one intermediate layer (230) together with the reflective coating (220) can be regarded as a combined layer (240) in relation to the mirror substrate (210) and the combined coefficient of thermal expansion of the reflective coating (220) and the at least one intermediate layer (230) corresponds essentially to the coefficient of thermal expansion of the mirror substrate (210) at least for a given temperature.

2. Micromirror element according to claim 1, characterized by the fact that the at least one intermediate layer (230) is designed such that the combined coefficient of thermal expansion of reflective coating (220) and the at least one intermediate layer (230) corresponds essentially to the coefficient of thermal expansion of the mirror substrate (210) at least for a specified temperature range.

3. Micromirror element according to one of the preceding claims, characterized by the fact that at least two intermediate layers (230.1, 230.2 ) are provided, wherein the intermediate layer (230.2 ) adjacent to the reflective coating (220) is preferably made of the material of the mirror substrate (210).

4. Micromirror element according to one of the preceding claims, characterized by the fact that the combination of reflective coating (220) and at least one intermediate layer (230) introduces a layer tension into the micromirror element (200) which causes a curvature of the mirror substrate (210) and thus of the micromirror element (200).

5. Micromirror element according to one of the preceding claims, characterized by the fact that at least one intermediate layer (230) spatially resolved from at least two different materials with different coefficients of thermal expansion is .

6. Micromirror element according to claim 5, characterized by the fact that one material of the intermediate layer (230) is encapsulated by a material that is more stable with regard to environmental influences.

7. Micromirror element according to one of the preceding claims, characterized by the fact that the thickness d Substrat} of the mirror substrate (210) is a multiple, preferably at least a fourfold, of the sum of the thicknesses of the reflective coating (220) and the at least one intermediate layer (230).

8. Micromirror element according to one of the preceding claims, characterized by the fact that the mirror substrate (210) comprises a tension layer .

9. Micromirror element according to one of the preceding claims, characterized by the fact that the mirror substrate (210) is made of silicon.

10. Micro-electro-mechanical system (100), in particular for semiconductor technology equipment, comprising an element (103) that is micro-electro-mechanically movable relative to at least one basic structure (101) in at least one degree of freedom by at least one actuator (102), characterized in that the micro-electro-mechanically movable element (103) comprises a micro-mirror element (200) according to any one of claims 1 to 9.

11. Micro-electro-mechanical system according to claim 10, characterized in that the micro-electro-mechanical system (100) is a MEMS mirror array with a plurality relative to the basic structure (101) by at least one, preferably two, preferably rotational, degrees of freedom movable micromirror elements (200) according to one of claims 1 to 9.

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