Method for securing a MEMS micromirror unit and MEMS micromirror unit

Abstract

The invention relates to a method for securing a MEMS micromirror unit (100) in an overarching assembly (200) having at least one receptacle (210) for a MEMS micromirror unit (110), as is used for example in projection exposure apparatuses (1) for photolithography. The invention also relates to a MEMS micromirror unit (100) with an advantageous configuration to this end. The invention is characterized by the steps of: a) introducing the MEMS micromirror unit (100) in the receptacle (210); b) aligning the MEMS micromirror unit (100) vis-à-vis the receptacle (210); c) applying an axial tensile force, which is greater than the subsequent preloading force, to an interface element (120) of the MEMS micromirror unit, whereby this gives rise to a longitudinal extension of the interface element (120); d) securing the preloading element (300) to a predetermined longitudinal position on the interface element (120); and e) reducing and removing the axial tensile force. The preloading element (300) comes into contact with the receptacle (210) no later than during the reduction in the axial tensile force and prevents complete undoing of the longitudinal extension of the interface element (120), as a result of which a preloading force remains on the interface element (120), said preloading force being able to be used to secure the MEMS micromirror unit (100) in the receptacle (210).

Description

Method for attaching a MEMS micromirror unit and MEMS micromirror unit

[0001] The invention relates to a method for attaching a MEMS micromirror unit in a higher-level assembly having at least one receptacle for a MEMS micromirror unit, such as is used, for example, in semiconductor technology systems. The invention further relates to a MEMS micromirror unit advantageously configured for carrying out the method.

[0002] In the state of the art, semiconductor technology systems refer to systems used to manufacture or test microstructured devices or the components required for them. An example of such a system is a projection exposure system for photolithography.

[0003] Photolithography is used to manufacture microstructured components, such as integrated circuits. The projection exposure system used for this purpose comprises an illumination system and a projection system. The image of a mask (also called a reticle) illuminated by the illumination system is projected in a reduced size onto a substrate coated with a light-sensitive layer and arranged in the image plane of the projection system, for example, a silicon wafer, by means of the projection system in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0004] In illumination systems, especially projection exposure systems designed for the EUV range, ie for exposure wavelengths from 5 nm to 30 nm, two facet mirrors are usually placed in the beam path between the actual exposure radiation source and the illuminating mask, which, in principle, enable homogenization of the radiation in a manner comparable to the principle of a honeycomb condenser. The facet mirror closest to the exposure radiation source in the beam path is often a so-called field facet mirror, the other a so-called pupil facet mirror.

[0005] In order to be able 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 facet mirrors—in particular those of the field facet mirror—from one or more electromechanically individually pivotable micromirrors. A corresponding method is disclosed, for example, in WO 2012 / 130768 A2.

[0006] 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 microelectromechanical systems (MEMS).

[0007] In a MEMS mirror array, a large number of small mirror elements are mounted on a common base, each individually movable. At least one actuator is provided for each mirror element, with which the mirror element can be adjusted along a predetermined degree of freedom. Frequently, the mirror elements can be pivoted about two axes running perpendicular to each other and parallel to the base, with sufficient actuators being provided to pivot the mirror element independently about these axes. Sensors can also be provided for the individual mirror elements, with which the position of the mirror element relative to the base can be determined in order to monitor the alignment of the mirrors. A particularly advantageous embodiment for the Mirrors of a MEMS mirror array are described in DE 10 2015 204 874 Al .

[0008] A method for producing a micromirror or a MEMS mirror array comprising a plurality of such micromirrors is disclosed - together with further details on a possible design of the micromirror - in DE 10 2015 220 018 A1.

[0009] To form a facet mirror for a projection exposure system, several MEMS mirror arrays are mounted in a dense, planar grid arrangement on a higher-level assembly. For this purpose, the MEMS mirror arrays are designed as MEMS micromirror units, which, in addition to the actual MEMS mirror arrays, also feature an interface element with which the units can be mounted to the higher-level assembly.

[0010] In order for the MEMS mirror arrays to be arranged with a small distance from one another for the intended purpose and to have the required precise position and alignment when inserted and fastened in the assembly, it is necessary that the individual mirror elements of a MEMS micromirror unit are positioned and aligned with high precision relative to its interface element.

[0011] At the same time, the insertion, alignment, and fixation of a MEMS micromirror unit in a higher-level assembly must be carried out in such a way that its sensitive microelectromechanical systems are not damaged. This typically means that the microelectromechanical systems must not be touched during assembly. Furthermore, alignment, once achieved, must be precisely maintained during subsequent fixation.

[0012] The object of the present invention is to provide a method for assembling MEMS micromirror units in a higher-level assembly which is improved compared to the prior art, as well as a MEMS micromirror unit which is advantageously designed for this purpose and in which the aforementioned aspects are taken into account.

[0013] This object is achieved by a method according to claim 1 and an advantageously designed MEMS micromirror unit according to claim 11. Advantageous further developments are the subject of the dependent claims.

[0014] Accordingly, the invention relates to a method for fastening a MEMS micromirror unit in a higher-level assembly with at least one receptacle for a MEMS micromirror unit, wherein the MEMS micromirror unit comprises a MEMS mirror array structure and an interface element which is elongated in an axial direction and which has a smaller transverse extent than the MEMS mirror array structure, so that the MEMS mirror array structure protrudes laterally beyond the interface element, wherein a prestressing element can be fastened to the interface element in a predetermined longitudinal position such that the interface element, when inserted into the receptacle, is axially prestressed between the MEMS mirror array structure and the prestressing element by means of the prestressing element fastened at the predetermined longitudinal position such that the MEMS micromirror unit is fixed in the receptacle,characterized by the steps: a) inserting the MEMS micromirror unit into the receptacle; b) aligning the MEMS micromirror unit with respect to the receptacle;, c) applying an axial tensile force to the interface element greater than the subsequent preload force; d) fastening the preload element at the specified longitudinal position on the interface element; and e) removing the axial tensile force.

[0015] The invention further relates to a MEMS micromirror unit for fastening in a higher-level assembly with at least one receptacle for a MEMS micromirror unit, wherein the MEMS micromirror unit comprises a MEMS mirror array structure projecting laterally beyond an elongated interface element, an axial spring element with a predetermined spring stiffness is integrated into the interface element between the MEMS mirror array structure and a predetermined longitudinal position, and the interface element is designed to fasten a prestressing element in a predetermined longitudinal position thereon, so that the interface element, when inserted into the receptacle and a prestressing element fastened at the predetermined longitudinal position, is axially prestressed between the MEMS mirror array structure and the prestressing element in such a way that the MEMS micromirror unit is fixed in the receptacle.

[0016] In the context of the present invention, "system for semiconductor technology" refers to any system that can be used to manufacture or test microstructured devices or the components required therefor. In addition to photolithography projection systems, this particularly includes inspection systems and metrology systems. In the case of inspection systems for masks or wafers, the variability of the illumination can be increased using one or more MEMS micromirror units, for example, which enables higher-contrast or completely New visual representations of the surface of a mask or wafer can be obtained, which can be advantageous for the inspection of the mask or wafer. A similar situation also applies to metrology systems with which masks, wafers, or other optical elements, such as mirrors, can be measured, where increased variability in illumination can improve the measurement results.

[0017] The invention is based on the finding that a positive fixing of a MEMS micromirror unit in a holder while maintaining a previously carried out alignment can be achieved if the element required for the positive fixing is first attached to the MEMS micromirror unit in a stress-free manner and only then is subjected to the load required for the prestressing of the positive fixing.

[0018] The method according to the invention is based on a MEMS micromirror unit in which, in addition to the actual MEMS mirror array structure - which, in addition to the microelectromechanical systems which form the individual mirrors of the mirror array, also includes the necessary support structures and elements for electrically connecting the microelectromechanical systems - an elongated interface element is provided. The interface module generally extends perpendicular to the plane of the MEMS mirror array structure in which the mirrors are arranged and has a smaller radial extent than the MEMS mirror array structure. In longitudinal section, this results in a T-shaped configuration for the MEMS micromirror unit, in which the underside of the MEMS mirror array structure serves as a contact surface or stop for the MEMS micromirror unit on the holder.Regardless of whether and, if so, which means are provided for aligning the MEMS micromirror unit with respect to the holder, the final fixation takes place - also already in the. State of the art - usually by clamping the MEMS micromirror unit in the holder using a clamping element, such as a screw nut, arranged at the end of the interface module remote from the MEMS micromirror unit. However, it has been shown that during the attachment of a clamping element in the state of the art, moments acting around the longitudinal axis of the interface module or forces acting perpendicular to this longitudinal axis are regularly introduced into the MEMS micromirror unit, which can lead to deviations from the previously established alignment.

[0019] The method according to the invention reduces this risk or even avoids it completely. After the MEMS micromirror unit has been inserted and aligned in the holder, an axial tensile force is initially applied to the interface element which is greater than the preload force later provided for the final fixing. As a result of this axial tensile force, which causes the interface element to expand longitudinally, the preload element can be attached to the interface element at the intended longitudinal position without the axial forces which later act on the preload element due to the preload required to fix the MEMS micromirror unit in the holder acting on the preload element. Rather, the preload element can generally be arranged on the interface element without any load, so that any forces and moments which might change the alignment of the MEMS micromirror unit can be reduced to a minimum.Only when the preload element is fully assembled is the axial tensile force removed—usually gradually—so that the preload force builds up between the MEMS mirror array structure and the preload element, again without disturbing forces perpendicular to the longitudinal axis of the interface element or moments about this axis. The MEMS micromirror unit remains in position during fixation. the inventive method the initially produced alignment at .

[0020] To carry out the method, it is generally sufficient and also preferred if the MEMS micromirror unit is attacked exclusively at the interface element, preferably in the region of the end remote from the MEMS mirror array structure. In particular, holding or manipulating the MEMS micromirror unit in the region of the MEMS mirror array structure, where the microelectromechanical systems could be touched and damaged, can be completely dispensed with in the method according to the invention.

[0021] It is preferred if, when an axial tensile force is applied and to maintain the preload, an axial spring element integrated into the interface element between the MEMS mirror array structure and a predetermined longitudinal position is tensioned with a predetermined spring stiffness. By providing the interface element with a corresponding axial spring element, a suitable choice of the spring constant can ensure that longitudinal expansion when the axial tensile force is applied is essentially concentrated in the area of ​​the spring element. The area of ​​the interface element away from the axial spring element - in particular between the MEMS mirror array structure and the axial spring element - does not deform or only deforms insignificantly, so that further components can be attached to the interface element there without any problem, without special consideration having to be given to deformation of the interface element.The final preload force can also be determined by selecting the spring constant and specifying the position of the preload element. The spring element can be created by suitable recesses in the interface element, with the design of the recesses and the remaining material bridges being influenced by the design. Taking the properties of the material used into account, a desired spring stiffness can be achieved in a targeted manner. The interface element can be designed as a single piece, whereby the spring element is formed from the material of the remaining interface element. However, it is also possible for the interface element, particularly in the area of ​​the spring element, to be made of a different material than, for example, adjacent to the MEMS mirror array structure. The spring element can then continue to be designed as described, i.e. comprise recesses; however, the spring stiffness can be further influenced by choosing the material in the area of ​​the spring element.

[0022] If an axial spring element is provided in the interface element, it is preferred if the interface element is engaged adjacent to the spring element to apply the axial tensile force. The prestressing element can also preferably be fastened adjacent to the spring element, for which purpose the predetermined longitudinal position is correspondingly predetermined. The region of the interface element starting from the MEMS mirror array structure beyond the axial spring element can consequently have a short longitudinal extent. Alternatively, the region in question - even if it may move in the axial direction relative to the MEMS mirror array structure due to the axial spring element when the axial tensile force or prestressing force is applied - is essentially free from axial loads due to the axial tensile force or prestressing force and thus from any deformations caused by these forces.

[0023] It is preferred if there is no contact between the pre-tensioning element and the receptacle when fastening the pre-tensioning element. If there is no such contact, it is ensured that any possible rotational movement of the pre-tensioning element around the longitudinal axis of the interface element is not Due to friction between the preload element and the mount, this leads to a moment around the longitudinal axis of the interface element that may negatively influence the alignment of the MEMS micromirror unit. The contact-free state in question can be ensured by a suitable selection of the spring constant of the interface element or its axial spring element and / or the axial tensile force.

[0024] Furthermore, it is preferred if a bayonet closure is used to fasten the prestressing element at the predetermined longitudinal position on the interface element. If the connection between the prestressing element and the interface element is designed as a bayonet closure, the introduction of moments about or forces in the direction of and transverse to the longitudinal axis of the interface element when fastening the prestressing element at the intended longitudinal position on the interface element can be reduced to a minimum. In particular, there is no flank friction as when turning a screw nut. While possibly accepting this disadvantage, a screw connection can nevertheless be provided to fasten the prestressing element at the predetermined longitudinal position on the interface element. The screw connection is preferably designed and constructed for low flank friction.

[0025] It is preferred if, in order to determine the angular position around the longitudinal axis of the interface element, the MEMS micromirror unit is brought into engagement with a suitable toothing, preferably a Hirth toothing, on the holder. Depending on the selected toothing, e.g. in the case of a Hirth toothing, in addition to the angular position, the position of the MEMS micromirror unit relative to the holder can also be determined. The toothing is provided in particular on the MEMS mirror array structure and the front side of the holder. A desired positioning and / or angular orientation of the MEMS micromirror unit in the inserted state with respect to the longitudinal axis of the interface element can be achieved in particular by adapting the toothing on the front side of the holder, which for this purpose can be designed as an element that can be positioned and aligned separately on the holder.

[0026] In order to be able to adjust the axial position of the MEMS mirror array structure relative to the holder and / or the preload force, shims can be provided between the MEMS mirror array structure and the holder and / or between the holder and the preload element. By placing a shim between the MEMS mirror array structure and the holder, the position of the MEMS mirror array structure is changed in the axial direction and the preload force is increased by extending the distance between the MEMS mirror array structure and the preload element in the fixed state. By placing a shim between the holder and the preload element, the axial position of the MEMS mirror array structure remains unchanged; however, the preload force is still increased.It is also possible that the MEMS mirror array structure is fundamentally designed for the use of shims, so that by systematically removing shims the position of the MEMS mirror array structure relative to the mount can also be changed in the other direction and the preload force can be reduced if necessary.

[0027] It is preferred to arrange an annular seal between the MEMS micromirror unit and the receptacle in such a way that it is pressed together by the preload between the MEMS micromirror unit and the receptacle. By means of a corresponding seal, the two sides of the receptacle can be sealed against each other. If all MEMS micromirror units and receptacles of an assembly are designed accordingly, the two sides of the assembly can be completely sealed against each other - provided that, in addition to the The receptacles themselves do not contain any other potential fluid channels between the two sides, or these are also suitably sealed. If a toothing is also provided, it is preferred that the annular seal is arranged radially inward of the toothing. The toothing can then serve as an optical labyrinth to protect the seal from harmful radiation.

[0028] It is particularly preferred if the MEMS micromirror unit is inserted into the receptacle using a tool that can be guided through the receptacle in its initial state and form-fitted with the end remote from the MEMS mirror array structure. Consequently, after the connection has been established, the MEMS micromirror unit can be securely inserted into the receptacle and aligned without having to touch the MEMS mirror array structure.

[0029] For an explanation of the MEMS micromirror unit according to the invention, reference is made to the above explanations.

[0030] The invention will now be described by way of example using an advantageous embodiment with reference to the accompanying drawings. They show: Figure 1: a schematic representation of a projection exposure system for photolithography comprising MEMS micromirror units according to the invention; Figures 2-9: schematic representations of the method according to the invention for attaching a MEMS micromirror unit according to the invention; Figure 10: a schematic representation of an embodiment variant for fastening a MEMS micromirror unit according to the invention.

[0031] 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.

[0032] With the help of the illumination system 10, an object field 11 in an object plane or reticle plane 12 is illuminated. The illumination system 10 comprises an exposure radiation source 13 which, in the illustrated embodiment, emits illumination radiation at least comprising 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, plasma generated with the aid of a laser) or a DPP source (gas discharge produced plasma, plasma generated by means of gas discharge). It can also be a synchrotron-based radiation source. The exposure radiation source 13 can also be a free-electron laser (FEL).

[0033] The illumination radiation emanating from the exposure radiation source 13 is first bundled in a collector 14. The collector 14 can be a collector with one or more ellipsoidal and / or hyperboloidal reflection surfaces. The at least one reflection surface of the collector 14 can be exposed to the illumination radiation at grazing incidence (Gl), i.e., at angles of incidence greater than 45°, or at normal incidence (NI), i.e., at 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.

[0034] After the collector 14, the illumination radiation propagates through an intermediate focus in an intermediate focal plane 15. If the illumination system 10 is constructed in a modular design, the intermediate focal plane 15 can in principle be used for the - also 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 illumination optics 16 then together form a modular illumination system 10.

[0035] The illumination optics 16 comprises a deflecting mirror 17. The deflecting mirror 17 can be a flat deflecting mirror or, alternatively, a mirror with a beam-influencing effect beyond the pure deflection effect. Alternatively or additionally, the deflecting mirror 17 can be designed as a spectral filter that separates a useful light wavelength of the illumination radiation from stray light of a different wavelength.

[0036] The deflecting mirror 17 deflects the radiation originating from the exposure radiation source 13 onto a first facet mirror 18. If the first facet mirror 18 is arranged—as in the present case—in a plane of the illumination optics 16 that is optically conjugated to the reticle plane 12 as a field plane, it is also referred to as a field facet mirror.

[0037] The first facet mirror 18 comprises a plurality of micromirrors 18' which can be individually pivoted about two mutually perpendicular axes for the controllable formation of facets, which are each preferably equipped with an orientation sensor (not shown) for determining the orientation of the micromirror 18'. The first facet mirror 18 is therefore a microelectromechanical system (MEMS system), as is also described, for example, in DE 10 2008 009 600 A1.

[0038] In the beam path of the illumination optics 16, a second facet mirror 19 is arranged downstream of the first facet mirror 18, resulting in a double-faceted system, the basic principle of which is also referred to as a honeycomb condenser (fly's eye integrator). If the second facet mirror 19 - as in the illustrated embodiment - is arranged in a pupil plane of the illumination optics 16, it is also referred to as a pupil facet mirror. The second facet mirror 19 can, however, also be arranged at a distance from a pupil plane of the illumination optics 16, whereby the combination of the first and the second facet mirror 18, 19 results in a specular reflector, as is the case, for example. in US 2006 / 0132747 A1, EP 1 614 008 B1 and US 6,573,978.

[0039] The second facet mirror 19 does not necessarily have to 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, which are either fixed or can only be tilted between two defined end positions. However, as shown, it is also possible to provide the second facet mirror 19 with a microelectromechanical system having a plurality of micromirrors 19' that can each be individually pivoted about two mutually perpendicular axes, each preferably comprising an orientation sensor.

[0040] By means of the second facet mirror 19, the individual facets of the first facet mirror 18 are imaged into the object field 11, whereby this is usually only a approximate imaging. The second facet mirror 19 can be the last beam-forming mirror or actually the last mirror for the illuminating radiation in the beam path in front of the object field 11.

[0041] Each facet of the second facet mirror 19 is assigned to exactly one of the facets of the first facet mirror 18 to form an illumination channel for illuminating the object field 11. This can, in particular, result in illumination according to the Köhler principle.

[0042] The facets of the first facet mirror 18 are each imaged by an associated facet of the second facet mirror 19, superimposed on one another, to illuminate the object field 11. The illumination of the object field 11 is as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

[0043] By selecting the illumination channels ultimately used, which is easily possible by suitable adjustment of the micromirrors 18' of the first facet 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. In this case, it can also be advantageous not to arrange the second facet mirror 19 exactly in a plane which is optically conjugate to a pupil plane of the projection system 20. In particular, the pupil facet mirror 19 can be arranged tilted relative to a pupil plane of the projection system 20, as is described, for example, in DE 10 2017 220 586 A1.

[0044] In the arrangement of the components of the illumination optics 16 shown in Figure 1, the second facet mirror 19 is arranged on a surface conjugated to the entrance pupil of the projection system 20. Deflecting mirror 17 and the two facet mirrors 18, 19 are tilted both relative to the object plane 12 and relative to each other.

[0045] In an alternative, not-shown embodiment of the illumination optics 16, a transmission optics comprising one or more mirrors can be provided in the beam path between the second facet mirror 19 and the object field 11. The transmission optics can, in particular, comprise one or two mirrors for normal incidence (NI mirrors, normal incidence mirrors) and / or one or two mirrors for grazing incidence (GL mirrors, gracing incidence mirrors). With an additional transmission optics, different positions of the entrance pupil for the tangential and sagittal beam path of the projection system 20 described below can be taken into account.

[0046] Alternatively, it is possible to dispense with the deflection mirror 17 shown in Figure 1, for which purpose the facet mirrors 18, 19 are then to be suitably arranged opposite the radiation source 13 and the collector 14.

[0047] With the help of the projection system 20, the object field 11 in the reticle plane 12 is transferred to the image field 21 in the image plane 22.

[0048] For this purpose, 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 system 1.

[0049] In the example shown in Figure 1, the projection system 20 comprises six mirrors Mx to M6. Alternatives with four, eight, ten, twelve, or a different number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation, thus making the projection system 20 shown a doubly obscured optics. 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.

[0050] The reflection surfaces of the mirrors M ± can be designed as freeform surfaces without a rotational symmetry axis. Alternatively, the reflection surfaces of the mirrors M ± but can also be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection 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.

[0051] 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.

[0052] The projection system 20 can in particular be anamorphic, ie it has in particular different image scales ß x , ß y in the x- and y-direction. The two magnifications ß x , ß y of the projection system 20 are preferably (ß x , ß y ) = ( + / - 0.25, / + - 0. 125) . A magnification ß of 0.25 corresponds to a A reduction in the ratio 4:1, while a magnification ratio ß of 0.125 results in a reduction in the ratio 8:1. A positive sign for the magnification ratio ß means an image without image inversion, a negative sign means an image with image inversion.

[0053] Other magnifications are also possible, including identical and absolutely identical magnifications ß x , ß y in x and y directions are possible.

[0054] 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 US 2018 / 0074303 A1.

[0055] The projection system 20 can, in particular, have a homocentric entrance pupil. This can be accessible. But it can also be inaccessible.

[0056] A reticle 30 (also called a mask) arranged in the object field 11 is illuminated 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 displaced, in particular in a scanning direction, via a reticle displacement drive 32. In the illustrated embodiment, the scanning direction runs in the y-direction.

[0057] A structure on the reticle 30 is imaged onto a light-sensitive layer of a wafer 35 arranged in the region of the image field 21 in the image plane 22. The wafer 35 is held by a wafer holder 36. The wafer holder 36 is can be displaced, in particular along the y-direction, via a wafer displacement drive 37. The displacement of the reticle 30, on the one hand, via the reticle displacement drive 32, and the wafer 35, on the other hand, via the wafer displacement drive 37, can be synchronized with each other.

[0058] The projection exposure system 1 shown in Figure 1, or its illumination system 10, the above description of which essentially reflects known prior art, is characterized in that the first and / or second facet mirrors 18, 19 are each composed of a plurality of MEMS micromirror units 100, wherein the MEMS micromirror units 100 each comprise a plurality of micromirrors 18', 19'. The individual MEMS micromirror units 100 are mounted on a higher-level assembly 200 to jointly form the facet mirrors 18, 19 sketched in Figure 1. If the MEMS micromirror units 100 are mounted in the higher-level assembly 200, the connection of the individual MEMS micromirror units 100, for example, to control electronics and / or cooling circuits, can also be provided.

[0059] Figure 2 shows an exemplary MEMS micromirror unit 100 and an assembly 200 into which the MEMS micromirror unit 100 is to be inserted.

[0060] The MEMS micromirror unit 100 comprises a MEMS mirror array structure 110, which, in addition to the actual micromirror elements 18', 19' and the microelectromechanics 111 required for their adjustment, also has a support element 112, which provides the MEMS mirror array structure 110 with the required structural integrity and strength. Application-specific integrated circuits and rewiring can be provided in the support element 110. With such rewiring, the electrical contacts of the MEMS mirror array provided for operation are Structure 111 and the application-specific integrated circuits are converted into electrical contacts to which, for example, electrical control and supply lines can be connected.

[0061] On the side facing away from the micromirror elements 18', 19', the MEMS mirror array structure 110 or the support element 112 has a first part 113 of a Hirth toothing 313 (see Figures 4 ff.). This first part 113 of a Hirth toothing 313 is formed integrally with the support element 112 or at least firmly connected thereto.

[0062] An elongated interface element 120 is firmly connected to the MEMS mirror array structure 110 and, for example, formed integrally with the support element 112 or parts thereof. The substantially rotationally symmetrical interface element 120 with an annular cross-section has a smaller transverse dimension than the MEMS mirror array structure 110, so that the MEMS mirror array structure 110 protrudes laterally beyond the interface element 120.

[0063] At the end remote from the MEMS mirror array structure 110, the interface element 120 has guide rails for two bayonet locks or connections 121, 122, namely two longitudinal slots 123 arranged on opposite sides of the interface element 120, each with adjoining transverse slots 124. The guide rail for one bayonet connection 121 serves for the subsequent attachment of a preload element 300 thereto. The design of the guide rail clearly predetermines the longitudinal position 125 for the attachment of the preload element 300.

[0064] A tool 500 for applying a axial tensile force as required, which will be explained in more detail later in connection with Figures 5 to 8.

[0065] Immediately adjacent to the slotted guides for two bayonet connections 121, 122 or the predetermined longitudinal position 125, an axial spring element 130 is integrated into the interface element 120. In the illustrated embodiment, the spring element 130 is created by recesses 131 in the interface element 120. The design of the recesses 131 and the remaining material bridges 132 allows a desired spring stiffness to be achieved in a targeted manner, taking into account the properties of the material used for the interface element 120.

[0066] A connecting element 140 is arranged inside the interface element 120 and protrudes from the MEMS mirror array structure 120. As in the present exemplary embodiment, the connecting element 140 can be connected to the interface element 120 in the region between the spring element 130 and the MEMS mirror array structure 120, the shape of which remains virtually unchanged even in the method described below. However, it is also possible for the connecting element 140 to be attached solely to the MEMS mirror array structure 120.

[0067] At the free end of the connecting element 140, an engagement recess 141 is provided, into which a hook element 401 can engage if necessary during the process (cf. Figures 3 and 4). In the part of the connecting element 140 protruding from the interface element 120, for example, electrical connections (not shown) can be arranged, via which the MEMS mirror array element 100 can be connected to a controller. Liquid connections, for example for a cooling medium, can also be arranged in the relevant area of ​​the connecting element. 140 may be provided. Alternatively, suitable lines may be routed through the space between the connecting element 140 and the interface element 120, which is present at least in the illustrated embodiment.

[0068] The higher-level assembly 200 comprises a plurality of receptacles 210, each of which can and should be inserted into a MEMS mirror array element 100. For reasons of clarity, only one receptacle 210 is discussed and illustrated below. However, the higher-level assembly 200 generally comprises more than one receptacle 210.

[0069] The receptacle 210 is elongated, the length of the receptacle 210 being fundamentally matched to the interface element 120 and in particular to the predetermined longitudinal position 125 for the prestressing element 300, as will become apparent below. The receptacle 210 further comprises a rotationally symmetrical through-opening 211 in which the interface element 120 of a MEMS mirror array element 100 can be received. The diameter of the through-opening 211 is larger than the outer diameter of the interface element 120.

[0070] In order to nevertheless be able to specify the desired position and orientation for a MEMS mirror array element 100 to be inserted into the receptacle 210, the receptacle 210 has on one side the second part 213 of a Hirth toothing 313 (cf. Figure 4 ff.). This second part 213 can be finely adjusted in the degrees of freedom indicated by the arrows 90 by suitable connection to the receptacle 201 (not shown), wherein the adjustment in the direction of the longitudinal axis of the feedthrough opening 211 can be achieved by providing compensating pieces (not shown) between the receptacle 210 and the second part 213 of a Hirth toothing 313.

[0071] An embodiment of the method according to the invention will now be explained with reference to Figures 3 to 9, in which the MEMS micromirror unit 100 according to Figure 2 is inserted and fastened in the receptacle 210 of the higher-level assembly 200.

[0072] The insertion of the MEMS micromirror unit 100 into the receptacle 210, as shown in Figures 3 and 4, is carried out with the aid of a tool 400 guided through the through-opening 211 of the receptacle 210, which tool 400 abuts the interface element 120 of the MEMS micromirror unit 100 and, with its inner side, at least partially positively engages the part of the connecting element 140 protruding from the interface element 120. The MEMS micromirror unit 100 is firmly connected to the tool 400 by means of the hook 401, which engages in the recess 414 provided for this purpose on the connecting element 140.

[0073] To attach the MEMS micromirror unit 100 to the tool 400, it is sufficient to grip the MEMS micromirror unit 100 only in the area of ​​the interface element 120. The tool 400 also grips only the interface element 120. The MEMS mirror array structure 110, however, does not need to be touched, which significantly reduces the risk of damage, particularly to the microelectromechanics 111. The MEMS mirror array structure 110 also does not need to be touched in the following steps.

[0074] If the MEMS micromirror unit 100 is firmly connected to the tool 400, it can be inserted into the receptacle 210 by appropriately moving the tool 400 (see Figure 4). It must be ensured that the two parts 113, 213 are brought into engagement with each other in the desired position in order to actually form the Hirth toothing 313 for which the two parts 113, 213 are intended. The MEMS mirror array structure 110 is then located with high precision in the desired position and orientation relative to the holder 210, as specified by the adjustable part 213 of the Hirth gearing 313. Even if the MEMS micromirror unit 100 or its part 113 of the Hirth gearing 313 is held in engagement with the other part 213 of the Hirth gearing 313 by the tool 400, the MEMS mirror array element 100 and in particular the interface element 120 and the connection element 140 are fundamentally stress-free.

[0075] Even if tool 400 remains connected to the MEMS micromirror unit 100 until the mutual engagement of the two parts 113, 213 of the Hirth toothing 313 is ensured by the tool 500 in the following steps explained with reference to Figure 5, Figure 4 already outlines how the tool 400 can be detached from the MEMS mirror array element 100: If the hook 401 is released from the recess 141 on the connection element 140, the tool 400 can be easily removed in the longitudinal direction.

[0076] Before the tool 400 is removed, another tool 500, which is sleeve-shaped and can thus be pushed over the tool 400, is connected to the interface element 120. For this purpose, the tool 500 engages with projections 501 provided for this purpose in the slotted guide provided for the bayonet connection 122 in such a way that a bayonet connection 122 is created.

[0077] Subsequently, an axial tensile force is exerted on the tool 500 in the direction of arrow 91, which is transferred to the interface element 120 due to the bayonet connection 122. Since this axial tensile force is greater than the subsequent preload force, the interface element 120 is lengthened by elastic yielding of the axial spring element 130. In In the present illustration, for example, a portion of the recesses 131 of the axial spring element 130 becomes visible (see Figure 5), which, in the still unloaded state, were located entirely within the interior of the receptacle 210 (see Figure 4). It should be noted that the tensile load alone results in a longitudinal extension of the axial spring element 130, but not of the connecting element 140.

[0078] Since the engagement of the two parts 113, 213 of the Hirth toothing 313 is ensured after the application of the axial tensile force 91, the tool 400 can then be completely removed.

[0079] The pre-tensioning element 300 has already been pushed over the tool 550. The pre-tensioning element 300 is ring-shaped and has projections 301 on its inner side which are designed to engage with the slotted guide of the bayonet connection 121.

[0080] Due to the axial tensile force 91 applied by the tool 500, the clamping element 120 or its axial spring element is stretched to such an extent that the preload element 300 can be inserted into the longitudinal slots 123 of the slotted guide of the bayonet connection 122 without the preload element 300 coming into contact with the receptacle 210 (see Figure 6, where the dashed line indicates the axial projection of the preload element 300 onto the receptacle 210). If such contact cannot be avoided, at least no preload force acts on the preload element 300, so that it can be easily fastened without significant mechanical interactions with the receptacle 210.

[0081] The subsequent turning of the pre-tensioning element 300, so that the projections 301 slide into the transverse slots 124 of the guide rail of the bayonet connection 122, also takes place in Ideally without contact between prestressing element 300 and the receptacle 210, but at least without significant mechanical interactions between the receptacle 210 and prestressing element 300 (cf. Figure 7).

[0082] During the sliding and rotating of the preload element 300, the axial tensile force 91 in interaction with the Hirth toothing 313 also ensures that the position and orientation of the MEMS mirror array structure 110 does not change.

[0083] If the prestressing element 300 is in the position shown in Figure 7, the axial tensile force 91 can be slowly reduced to zero. The longitudinal expansion of the interface element 120 or its axial spring element 130 decreases until the prestressing element 300 comes into contact with the receptacle 210, thereby preventing any further reduction in the longitudinal expansion. However, when the prestressing element 300 bears against the receptacle 210, there continues to be a longitudinal expansion of the interface element 120 or its axial spring element 130 compared to a completely stress-free state (see Figures 1 to 4).

[0084] Thus, a permanent preload remains, the magnitude of which depends significantly on the remaining longitudinal strain and the spring constant of the axial spring element 130. By appropriately selecting these parameters in particular, the preload force resulting at the end of the process can be specified.

[0085] To optionally increase the preload force - e.g. because the specifications are not fully achieved due to manufacturing tolerances - a compensating piece (not shown) can also be provided between the preload element 300 and the holder 210, whereby the permanently remaining Longitudinal expansion of the interface element 120 or its axial spring element 130 is increased.

[0086] If the axial tensile force 91 is reduced to zero, the tool 500 can be easily removed by loosening the bayonet lock 122 (see Figure 9). The position and orientation of the MEMS mirror array structure 110 remain predetermined by the Hirth toothing 313, whereby the preload force produced according to the invention ensures that the two parts 113, 213 of the Hirth toothing 313 remain permanently engaged with one another.

[0087] Figure 10 shows an embodiment for fastening the MEMS micromirror unit 100, as shown in Figures 2 to 9. Figure 10 is a schematic sectional view through the MEMS micromirror unit 100 and the receptacle 210 in the region of the Hirth toothing 313, as is also shown in the embodiment according to Figures 2 and 9. Since the MEMS micromirror unit 100 and the receptacle 210 are otherwise essentially identical to those in Figures 2 and 9, reference is made to the above explanations and only the differences in the embodiment are discussed below.

[0088] In the embodiment according to Figure 10, an annular seal 330 is arranged between the MEMS micromirror unit 100 and the receptacle 210 in such a way that it is pressed together in a sealing manner by the prestress remaining between the MEMS micromirror unit 100 and the receptacle 210 (cf. Figures 2 to 9) after the prestressing element has been applied, such that any gap that may remain between the MEMS micromirror unit 100 and the receptacle 210 is completely sealed. The seal 330 is arranged inside the Hirth toothing 313 and is protected by it from damage.

Claims

Patent claims 1. Method for mounting a MEMS micromirror unit (100) in a higher-level assembly (200) with at least one receptacle (210) for a MEMS micromirror unit (100), wherein the MEMS micromirror unit (100) comprises a MEMS mirror array structure (110) and an interface element (120) which is elongated in an axial direction and has a smaller transverse extent than the MEMS mirror array structure (110), so that the MEMS mirror array structure (110) can be laterally arranged over the interface element (120), wherein a prestressing element (300) can be fastened to the interface element (120) in a predetermined longitudinal position such that the interface element (120) in the state inserted into the receptacle (210) is axially prestressed between the MEMS mirror array structure (110) and the prestressing element (300) by means of the prestressing element (300) fastened at the predetermined longitudinal position in such a way that the MEMS micromirror unit (100) is fixed in the receptacle (210), characterized by the steps: a) inserting the MEMS micromirror unit (100) into the receptacle (210); b) aligning the MEMS micromirror unit (100) with respect to the receptacle (210); c) applying an axial tensile force to the interface element (120) that is greater than the later prestressing force; d) fastening the prestressing element (300) at the predetermined longitudinal position on the interface element (120); and e) reducing and removing the axial tensile force.

2. Method according to claim 1, characterized in that, in order to carry out the method, the MEMS micromirror unit (100) is attacked exclusively at the interface element (120), preferably in the region of the end remote from the MEMS mirror array structure (110).

3. Method according to one of the preceding claims, characterized in that when applying an axial tensile force (91) and to maintain the preload, an axial spring element (130) integrated into the interface element (120) between the MEMS mirror array structure (110) and a predetermined longitudinal position (125) is tensioned with a predetermined spring stiffness.

4. Method according to claim 3, characterized in that for applying the axial tensile force (91) adjacent to the spring element (130) is applied and / or the prestressing element (300) is fastened at the predetermined longitudinal position (125) adjacent to the spring element (130).

5. Method according to one of the preceding claims, characterized in that when the prestressing element (300) is fastened there is no contact between the prestressing element (300) and the receptacle (210).

6. Method according to one of the preceding claims, characterized in that a bayonet lock (121) or a screw connection is actuated to fasten the pretensioning element (300) at the predetermined longitudinal position (125) on the interface element (120).

7. Method according to one of the preceding claims, characterized in that in order to determine the angular position about the longitudinal axis of the interface element (120) and / or the position relative to this longitudinal axis, the MEMS micromirror unit (110) is brought into engagement with a suitable toothing (213), preferably a Hirth toothing (313), on the receptacle (310).

8. Method according to one of the preceding claims, characterized in that compensating pieces are provided for determining the axial position of the MEMS mirror array structure (110) relative to the receptacle (210) and / or for adjusting the prestressing force between the MEMS mirror array structure (110) and the receptacle (210) and / or between the receptacle (210) and the prestressing element (300).

9. Method according to one of the preceding claims, characterized in that an annular seal (330) is arranged between the MEMS micromirror unit (100) and the receptacle (210) in such a way that it is pressed by the prestress between the MEMS micromirror unit (100) and the receptacle (210).

10. Method according to one of the preceding claims, characterized in that the introduction of the MEMS micromirror unit (100) into the receptacle (210) is carried out by a tool (400) which, in the initial state, is guided through the receptacle (210) and can be positively connected to the MEMS micromirror unit (100) by the end of the interface element (120) remote from the MEMS mirror array structure (110).

11. MEMS micromirror unit (100) for fastening in a higher-level assembly (200) with at least one receptacle (210) for a MEMS micromirror unit (100), wherein the MEMS micromirror unit (100) comprises a MEMS mirror array structure (110) projecting laterally beyond an elongated interface element (120), characterized in that an axial spring element (130) with a predetermined spring stiffness is integrated into the interface element (120) between the MEMS mirror array structure (110) and a predetermined longitudinal position (125), and the interface element (120) is designed to fasten a prestressing element (300) thereto in a predetermined longitudinal position, so that the interface element (120), when inserted into the receptacle (210) and a prestressing element (300) fastened at the predetermined longitudinal position, is axially arranged between the MEMS mirror array structure (110) and prestressing element (300) is prestressed,that the MEMS micromirror unit (100) is fixed in the receptacle (210)., 12. MEMS micromirror unit according to claim 11, characterized in that a bayonet lock (121) or a screw connection is provided for fastening the prestressing element (300) at the predetermined longitudinal position (125) on the interface element (120).

13. MEMS micromirror unit according to one of claims 11 to 12, characterized in that the MEMS micromirror unit (100) has a toothing (213), preferably a Hirth toothing (313), for determining the angular position and / or the position in the receptacle (210).

14. MEMS micromirror unit according to one of claims 11 to 13, characterized in that an annular seal is arranged between the MEMS micromirror unit (100) and the receptacle (210) in such a way that it is pressed by the prestress between the MEMS micromirror unit (100) and the receptacle (210).

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