Arrangement and method for calibrating a MEMS with micromirrors

Abstract

The invention relates to an arrangement (100) for calibrating a microelectromechanical system (200) with a plurality of individually pivotable concave micromirrors (210) with a respective orientation sensor for determining the orientation of the micromirror (210), comprising at least one radiation source (110) for emitting radiation that can be reflected by the micromirrors (210) and at least one radiation detector (120) for detecting radiation emitted by the at least one radiation source (110), wherein the at least one radiation source (110) and the at least one radiation detector (120) are each arranged at the distance (210) of the effective radius of curvature of the concave micromirrors (210) in such a way that radiation from a radiation source (110) reflected by a micromirror (210) at a predefined orientation can be detected by a radiation detector (120), in that the radiation source (110) is mapped on the radiation detector (120). The invention also relates to a method for calibrating a microelectromechanical system (200) with a plurality of individually pivotable concave micromirrors (210), each comprising an orientation sensor with an arrangement (100) according to the invention and according to one of the preceding claims.

Description

Arrangement and method for calibrating a MEMS with micromirrors

[0001] The invention relates to an arrangement and a method for calibrating a micro-electro-mechanical system (MEMS) with a plurality of individually pivotable concave micromirrors, such as those used in semiconductor technology equipment.

[0002] In the prior art, semiconductor technology equipment refers to equipment used for the production or testing of microstructured components or the components required for their production. An example of such equipment is a projection exposure system for photolithography used to manufacture microstructured components, such as integrated circuits.

[0003] The exposure system used in photolithography 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 the projection system onto a substrate, for example a silicon wafer, coated with a photosensitive layer and positioned in the image plane of the projection system, in order to transfer the mask structure onto the photosensitive coating of the substrate.

[0004] In lighting systems, especially projection exposure systems designed for the EUV range, i.e., for exposure wavelengths from 5 nm (or possibly 2 nm) to 30 nm, but also for the DUV range with exposure wavelengths of, for example, 193 nm, two faceted mirrors are usually arranged in the beam path between the actual exposure radiation source and the mask to be illuminated. The faceted mirror that is closer to the source of the light source in the beam path is often a so-called field faceted mirror, the other a so-called pupil faceted mirror.

[0005] 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 design is disclosed, for example, in WO 2012 / 130768 A2. In the field faceted mirror, the individual micromirrors are regularly concave.

[0006] In order to achieve a small size for 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).

[0007] Micro-electro-mechanical systems (MEMS) are small components that combine micromechanical structures and electronic elements on a single chip. MEMS can be manufactured using integrated circuits, similar to microchips. A MEMS essentially comprises a basic structure on which movable elements, controllable relative to the basic structure, are arranged.

[0008] In a MEMS mirror array, a multitude of small mirror elements are mounted relative to a common base structure, each individually movable. Each mirror element has at least one actuator that allows it to be adjusted along a predefined degree of freedom. The mirror elements are often arranged around two axes perpendicular to each other and parallel to the base. The mirror element is pivotable, and sufficient actuators are provided to allow it to pivot independently around these axes. Sensors can also be provided for each individual mirror element to determine its position relative to the base, thus enabling monitoring of the mirror's alignment. A particularly advantageous embodiment for the mirrors of a MEMS mirror array is described in DE 10 2015 204 874 A1.

[0009] A method for manufacturing a micromirror or a MEMS mirror array comprising a plurality of such micromirrors is disclosed in DE 10 2015 220 018 Al, together with further details on a possible embodiment of the micromirror.

[0010] To achieve the necessary precision in setting a desired intensity and angle of incidence distribution, it is essential to be able to precisely adjust the orientation of each individual micromirror. In addition to the microelectromechanical drive required for swiveling the mirror, the micromirrors also include a tilt sensor that allows the orientation of the micromirror to be read and verified in two spatial directions.

[0011] The relationship between the actual orientation of the micromirror and the value determined by the tilt sensor is typically non-linear and requires calibration, resulting in a sensor characteristic curve. This calibration makes the values ​​determined by the tilt sensor usable for controlling the micromirrors. For microlithography applications, depending on the specific application, an accuracy in the range of 1 prad to 100 prad is required across the entire tilt angle range of ±10 mrad to ±1000 mrad. For a micromirror that can be tilted about two axes, To achieve such accuracy over a given tilt angle range, 10 to 1000 support points for the sensor characteristic curve in two-dimensional angular space are required. These support points must, of course, be appropriately distributed over the angular space.

[0012] The invention is based on the objective of creating an arrangement and a method with which the calibration of a microelectromechanical system with a large number of individually pivotable concave micromirrors is possible quickly and with sufficiently high accuracy.

[0013] This problem is solved by an arrangement according to claim 1 and a method according to claim 11. Advantageous further developments are the subject of the dependent claims.

[0014] Accordingly, the invention relates to an arrangement for calibrating a microelectromechanical system with a plurality of individually pivotable concave micromirrors, each with an orientation sensor for determining the orientation of the micromirror, comprising at least one radiation source for emitting radiation that can be reflected by the micromirrors and at least one radiation detector for detecting radiation emitted by the at least one radiation source, wherein the at least one radiation source and the at least one radiation detector are each arranged at a distance equal to the effective radius of curvature of the concave micromirrors such that radiation from a radiation source reflected by a micromirror at a given orientation can be detected by a radiation detector, since the radiation source is imaged onto the radiation detector by the micromirror.

[0015] The invention further relates to a method for calibrating a micro-electro-mechanical system with a A large number of individually pivotable concave micromirrors, each comprising an orientation sensor with an arrangement according to the invention, comprising the steps: - Determining multiple support points for a sensor characteristic curve for the orientation sensor of each of the micromirrors, each with the following steps: - Adjusting the orientation of at least one micromirror so that at least one radiation source is imaged by the micromirror onto a radiation detector; - Determining the actual orientation of the micromirror from the beam path from radiation source to radiation detector; - Determination of the orientation of the micromirror as detected by the orientation sensor; and - Determining the reference point for the sensor characteristic curve from the actual orientation and the orientation determined by the orientation sensor; - Determining sensor characteristics for each orientation sensor of each micromirror of the micro-electro-mechanical system from the determined support points.

[0016] First, some terms used in connection with the invention will be explained.

[0017] A "concave micromirror" is a micromirror whose reflective surface deviates from a planar shape in such a way that, according to the invention, the micromirror reflects the radiation emanating from the radiation source without significant, i.e., with regard to calibration, and whose accuracy, with sufficiently small aberrations, is projected onto the radiation detector. The surface of the micromirror can be spherically or aspherically shaped. It can also be a freeform surface. If the surface of a micromirror is concave-spherically shaped, it is a concave mirror with a concave reflective surface in the form of a spherical surface with a constant radius of curvature in all directions.

[0018] The "effective radius of curvature" refers to the radius of curvature of a micromirror that a concave-spherical mirror with comparable imaging properties would have. If a micromirror is concave-spherical, the effective radius of curvature corresponds to the actual radius of curvature. If the micromirror has a different concave shape, the effective radius of curvature corresponds to the radius of curvature that a concave-spherical micromirror would need to have to achieve comparable imaging properties.

[0019] A "non-electrical image sensor" is a device, often semiconductor-based, for capturing two-dimensional images from radiation. Such image sensors typically rely on two-dimensional arrays of regularly spaced point-like sensors, where each sensor can provide information about a single pixel, from which a two-dimensional image can then be generated. Particularly for radiation in the visible spectrum, an image sensor can be a camera sensor, such as those used in digital cameras.

[0020] The invention has recognized that in microelectromechanical systems with a large number of individually pivotable concave micromirrors, the imaging properties of the individual micromirrors can be advantageously used for calibration.

[0021] If a radiation source and a radiation detector are each arranged at a distance equal to the effective radius of curvature of a concave micromirror, and the micromirror is aligned so that the radiation emanating from the radiation source is imaged onto the radiation detector without significant aberration, a direct image is produced without intermediate imaging and without interposed optics.

[0022] If the relative positions of the radiation source, a micromirror, and a radiation detector are known with sufficient accuracy, the instantaneous orientation of the micromirror can be determined from the geometric relationships when radiation emitted by the source and reflected by the micromirror strikes the detector. This orientation can then be compared with the signal provided by the orientation sensor. If such a comparison is performed for a sufficient number of micromirror orientations, the results can be used as reference points for determining a sensor characteristic curve for the orientation sensor.

[0023] Due to the distances required for direct imaging between the radiation source(s), radiation detector(s), and micromirror(s), even small swivel ranges, e.g., a maximum of ±1000 mrad around two perpendicular axes, result in a considerable spatial extent of the region in which radiation emitted by a radiation source can be imaged depending on the orientation of the micromirror. While this spatial extent is helpful for the accuracy of determining the actual orientation of a micromirror, since even small changes in the orientation of the micromirror result in readily measurable shifts in the image of a radiation source, covering the entire region in which the radiation reflected by the micromirror is reflected presents a challenge. The fact that a radiation source can fundamentally be imaged presents a particular challenge for radiation detection.

[0024] To meet this challenge, it is particularly preferred if the arrangement comprises several radiation sources that are spatially distributed such that radiation from each radiation source strikes a radiation detector of the arrangement from a micromirror at a predetermined orientation or within a predetermined orientation range. In particular, it is possible for radiation from different radiation sources to strike a specific, shared radiation detector depending on the orientation of a micromirror. For example, with n > l radiation sources and a single radiation detector, n > l orientations can be achieved with a suitable spatial arrangement.The orientation ranges of a micromirror can be detected using a single radiation detector, whereby the spatial extent of the radiation detector can be limited to the area required to detect a specific orientation or a limited orientation range. The entire angular space of the orientation of a micromirror can thus be subdivided into angular space sections by a plurality of spatially distributed radiation sources, thereby enabling different angles of incidence of the radiation onto the micromirror. Each of these sections results in a significantly smaller region for the angle of reflection of the radiation compared to the entire angular space of the micromirror's orientation. Only within this region are one or more radiation detectors then required.

[0025] It is of course also possible, following the same principle, to arrange several radiation detectors in a spatially distributed manner, so that the radiation from a specific radiation source is reflected onto different surfaces depending on the orientation of a micromirror. The radiation is reflected by the detectors. The principle also allows for an arrangement of multiple radiation sources and multiple radiation detectors.

[0026] Regardless of whether multiple radiation sources and / or multiple radiation detectors are provided, it is in any case preferred that the number of radiation sources and radiation detectors differ, preferably by at least a factor of five, and further preferably by at least a factor of ten.

[0027] Particularly when multiple radiation sources and / or radiation detectors are provided, it is preferred to arrange one or more scatter radiation apertures between the radiation source(s) and / or radiation detector(s) and the micromechanical system. Since the beam paths from a radiation source to the micromechanical system and from the micromechanical system to a radiation detector are clearly defined by the geometric arrangement of the components relative to each other, the potentially negative influence of scatter radiation can be avoided by the appropriate arrangement of apertures. This is especially true when multiple micromirrors of a microelectromechanical system are calibrated in parallel, i.e., simultaneously.

[0028] At least one radiation detector can be a lensless image sensor for the spatially resolved detection of radiation incident on the image sensor. By using an image sensor as a radiation detector, the position of the incident radiation can be spatially resolved, whereby the resolution of conventional image sensors is regularly sufficient, due to the distance between the micromirror from which the incident radiation originates and the radiation detector, to derive the orientation of the micromirror very accurately. If the image sensor has a Given a sufficiently large area, it is also possible for radiation from several different micromirrors to be detected simultaneously. Based solely on the positions on the image sensor where the individual rays strike, it is often possible to assign the rays to specific micromirrors. This only requires a certain basic calibration of the micromirrors; that is, when a desired orientation of a micromirror is set, this orientation is actually maintained within a known tolerance. As described later, it is also possible that the radiation reflected by different micromirrors—possibly even with time resolution—each exhibits a different intensity and / or wavelength.If the image sensor has sufficient intensity and / or color resolution, the spatially resolved detection of radiation can be assigned to beam paths via specific micromirrors, from which the orientation of the individual micromirrors can in turn be determined. It is preferred if the size of a pixel detectable by the image sensor is at most 5 pm, preferably at most 3 pm. Image sensors with corresponding pixel sizes are available and sufficient for the present invention.

[0029] It is also possible that at least one radiation detector, a screen or fluorescent display for spatially resolved imaging of incident radiation, and an image capture unit for capturing the image projected onto the screen or fluorescent display. With a suitably designed radiation detector, spatially resolved detection of incident radiation over a larger area is possible than, for example, with an image sensor.

[0030] It is preferred if at least one radiation source is a point source, preferably with radiation focusing for directed radiation emission. The radiation source can be, for example, an LED radiation source, preferably with a glass rod to homogenize the emitted radiation, or a fiber-coupled radiation source.

[0031] It is also possible that at least one radiation source is a planar radiation source, wherein the emitted radiation is preferably adjustable with spatial resolution in at least one property of the emitted radiation. The property of the emitted radiation can be, for example, the intensity or the wavelength (in the visible range: the color of the light). If the radiation is adjustable with spatial resolution, a planar radiation source can also be considered an arrangement of correspondingly individually adjustable point radiation sources.

[0032] Regardless of whether multiple radiation sources, in particular point radiation sources, and / or at least one spatially adjustable planar radiation source are provided, it is preferred if at least one radiation source is adjustable with respect to the intensity and / or wavelength of the emitted radiation, preferably with temporal and / or spatial resolution. If the at least one radiation source can be adjusted accordingly, the orientation of several micromirrors can be determined in parallel or at least in rapid succession. As already explained above, the parallel determination can, for example, be based on different wavelengths or intensities, provided that the respective radiation detector is suitable for distinguishing between wavelength and / or intensity.The short time sequence is achieved particularly in comparison to a procedure in which the micromirrors of a microelectromechanical system are adjusted one after the other to determine their orientation, since radiation sources are usually significantly different. It can be switched on and off faster than the adjustment of even a single micromirror requires.

[0033] At least some of the micromirrors are preferably pivotable about two non-parallel, preferably perpendicular, axes. In particular, all micromirrors of a micro-electro-mechanical system can also be pivotable about two perpendicular axes, wherein the two pivot axes of any two micromirrors of the system are parallel to each other.

[0034] For an explanation of the method according to the invention, reference is made to the preceding statements.

[0035] The invention will now be described by way of example with reference to advantageous embodiments and the accompanying drawings. These show: Figure 1: a schematic representation of a projection exposure system for photolithography comprising a micro-electro-mechanical system calibrated according to the invention; Figure 2a-c : a schematic representation of a first embodiment of an arrangement according to the invention for calibrating an electro-mechanical system from the system according to Figure 1 ; Figure 3: a schematic representation of a second embodiment of an arrangement according to the invention for calibrating an electro-mechanical system from the system according to Figure 1; Figure 4: a schematic representation of a third embodiment of a device according to the invention Arrangement for calibrating an electro-mechanical system from the plant according to Figure 1.

[0036] Figure 1 shows a projection exposure system 1 for photolithography as an example of a system for semiconductor technology in a schematic meridional section. The projection exposure system 1 comprises an illumination system 10 and a projection system 20.

[0037] The illumination system 10 illuminates an object field 11 in an object plane or reticulum plane 12. The illumination system 10 comprises an illumination 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 illumination 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 illumination radiation source 13 can also be a free-electron laser (FEL).

[0038] 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 used, on the one hand, to optimize its reflectivity for the useful radiation and On the other hand, it may be structured and / or coated to suppress stray light.

[0039] 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.

[0040] The illumination optics 16 include a deflecting mirror 17. The deflecting mirror 17 can be a planar deflecting mirror or, alternatively, a mirror with an effect that influences the beam shape beyond 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.

[0041] 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 the field plane, it is also referred to as a field faceted mirror.

[0042] The first faceted mirror 18 comprises a plurality of concave micromirrors 18 ' that can be individually pivoted about two axes perpendicular to each other. Controllable formation of facets, each 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.

[0043] 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 results in a specular reflector, as is the case, for example, with... described in US 2006 / 0132747 Al, EP 1 614 008 Bl and US 6,573,978.

[0044] 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.

[0045] 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-forming or even the last mirror for the illumination radiation in the beam path before the object field 11.

[0046] 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.

[0047] 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.

[0048] 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 be further adjusted. This intensity distribution is also referred to as the illumination setting. Furthermore, it can be advantageous not to position 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 positioned relative to a pupil plane of the projection system 20 be arranged at an angle, as described for example in DE 10 2017 220 586 Al .

[0049] 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 conjugated 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.

[0050] 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 perpendicular incidence (NI mirrors, normal incidence mirrors) and / or one or two mirrors for grazing incidence (Gl mirrors, grazing incidence 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.

[0051] Alternatively, it is possible to dispense with the deflecting mirror 17 shown in Figure 1, for which the faceted mirrors 18 , 19 must then be arranged appropriately opposite the radiation source 13 and the collector 14.

[0052] With the help of the projection system 20, the object field is 11 in the reticulum plane 12 is transferred to the image field 21 in the image plane 22.

[0053] 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. The mirrors Mi are optical elements 25.

[0054] 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 doubly 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.

[0055] 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.

[0056] 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.

[0057] 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 pro-ection 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 of 4:1, while a magnification β of 0.125 results in a reduction in the ratio of 8:1. A positive sign for the magnification β indicates a magnification without image inversion, a negative sign indicates a magnification with image inversion.

[0058] 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.

[0059] 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 Al.

[0060] Projection system 20 can, in particular, have a homocentric entrance pupil. This may be accessible. However, it may also be inaccessible.

[0061] A reticle 30 (also called a mask) arranged in the object field 11 is exposed by the lighting 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, particularly in one scanning direction, by means of a reticle displacement drive 32. In the illustrated embodiment, the scan direction runs in the y-direction.

[0062] 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 It should be 10 to 14 inches (25.40 to 35.56 cm) wide, and preferably 6 inches (15.24 cm) long and 12 inches (30.48 cm) wide.

[0063] 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 of the wafer 35 via the wafer transfer drive 37 can be synchronized.

[0064] The projection exposure system 1 shown in Figure 1, or its projection system 20, the above description of which essentially reflects known prior art, is characterized in that at least the first faceted mirror 18 comprises a micro-electro-mechanical system 200 calibrated according to the invention.

[0065] Figure 2 shows a schematic side view (Figure 2a) and a schematic sectional view (Figure 2b) of a first arrangement 100 according to the invention, with which the calibration according to the invention of a micro-electro-mechanical system 200 with a plurality of each by two The process can be carried out using individually pivotable concave micromirrors 210 on axes perpendicular to each other. The micro-electro-mechanical system 200 can comprise 10x10 to 100x100 micromirrors 210 with an edge length of approximately 0.1 mm to 2 mm. Each of the micromirrors 210 is designed as a spherical concave mirror with an identical effective radius of curvature.

[0066] Radiation sources 110 and radiation detectors 120 of the arrangement 100 are arranged at a distance d, which corresponds to the effective radius of curvature of the individual micromirrors 210.

[0067] The radiation detectors 120 are four lensless image sensors for spatially resolved detection of radiation incident on the image sensor. Each radiation detector 120 has an optically effective area of ​​30 x 30 mm and a pixel size of 3 pm. This results in each radiation detector 120 having a resolution of 10,000 x 10,000 pixels. The four radiation detectors 120 are arranged closely together in a 2 x 2 configuration, centrally located opposite the electromechanical system 200.

[0068] Fifty-two radiation sources 110 are arranged in a grid around the radiation detectors 120, covering an almost circular area (see Figure 2b). The radiation sources 110 are individually controllable LEDs, each equipped with a glass rod to homogenize the emitted radiation. Control can be limited to simple on / off switching. However, it is also possible to adjust the intensity of each individual radiation source 110. Optionally, the individual Radiation sources 110 or at least groups of radiation sources 110 each emit radiation of different wavelengths .

[0069] As shown in Figure 2a by the dashed lines, each of the radiation sources 110 is designed to irradiate all micromirrors 210 of the micro-electro-mechanical system 200. Depending on the orientation of the individual micromirrors 210, the radiation coming from each of the individual micromirrors 210 can be deflected by each micromirror 210 to a specific point on one of the four radiation detectors 120 and detected there with spatial resolution.

[0070] Figure 2a shows, by way of example, two beam paths 130 originating from two different radiation sources 110, which can be imaged at different times by one and the same micromirror 210 with each suitable orientation onto the same point on one of the radiation detectors 120.

[0071] Figure 2c shows, from the perspective of a micromirror 210, the angular coverage at which the orientation of one of the emitted radiation sources 110 can be imaged onto one of the radiation detectors 120, indicated by the dashed lines. The angular coverage essentially corresponds to that required in the later use of the micro-electro-mechanical system 200 in a projection exposure system 1 (see Figure 1), with a substantially circular coverage. The angular coverage, which is achieved by each pair of a radiation source 110 and a radiation detector 120, can, as shown, partially overlap, so that the orientation of a micromirror 210 can be determined by more than one pair of radiation source 110 and radiation detector if appropriately oriented. 120 can be determined. Through corresponding multiple determinations, systematic errors, e.g. due to deviations in the relative position of radiation sources 110, radiation detectors 120 and micro-electro-mechanical system 200, can be detected and, if necessary, corrected computationally.

[0072] The arrangement shown in Figure 2 can be used to calibrate the micro-electro-mechanical system 200, namely to determine a sensor characteristic curve for the orientation sensor of each micromirror 210. For this purpose, predetermined pivot positions are reached for each individual micromirror 210 over the entire range in which the micromirror 210 can be pivoted by the micromirror's actuator. At each pivot position, the radiation from at least one of the radiation sources 110, which are activated for this purpose, is deflected onto one of the radiation detectors 120, so that the point of impact of the radiation on the respective radiation detector 120 can be determined.From the known relative positions of radiation sources 110, radiation detectors 120, and micro-electro-mechanical system 200, the actual orientation of the micromirror 210 can be determined based on the position of the micromirror 210 on the micro-electro-mechanical system 200 and the point of impact of the radiation reflected by this micromirror 210. Together with orientation values ​​from the orientation sensor of the micromirror 210, this yields a pair of values ​​that can be considered a reference point for the sensor characteristic curve. By repeating this procedure sufficiently often for different orientations, a multitude of corresponding reference points are obtained over the entire angular range of the micromirror 210's swivel range, on the basis of which the sensor characteristic curve can be determined with high accuracy. In the illustrated embodiment, approximately...300 support points are required, which are provided despite small gaps in the angle cover, as indicated in Figure 2, below. They can be easily achieved, while also distributing them sufficiently across the entire angular space to ensure the desired accuracy across the entire angular space.

[0073] Due to the size of the radiation detector 120, the orientations of several micromirrors 210 can be determined simultaneously, namely when the radiation deflected by the micromirrors 210 strikes different areas of a radiation detector 120. However, this may require sufficient basic calibration of the micromirrors 210 to ensure that the radiation deflected by a specific micromirror 210 onto a radiation detector 120 strikes an exclusive area designated there for that micromirror 210, so that the incident radiation can be unambiguously assigned to a specific micromirror 210.

[0074] Alternatively or additionally, it is possible that the radiation sources 110 emit radiation of different wavelengths and / or intensities at least in groups, which can be used with radiation detectors 120 with suitable resolution to assign the radiation incident on the radiation detectors 120 to individual radiation sources 110, which in turn can enable the assignment to a micromirror 210 that has deflected this radiation onto a radiation detector 120.

[0075] Finally, it is also possible to determine the orientations of different micromirrors 210 in quick succession by appropriately switching the radiation sources 110 on and off: if the radiation from a first switched-on radiation source 110 is imaged by a first micromirror 210 onto a radiation detector 120, in a next pass, in which the first radiation source 110 is switched off and a second radiation source 110 is switched on When the second radiation source 110 is switched on, the radiation from the second radiation source 110 is imaged onto the radiation detector 120 by a second micromirror 210, without requiring any fundamental adjustment of the micromirrors 210 of the micro-electro-mechanical system 200. Since adjusting the micromirrors 210 is comparatively time-consuming compared to changing the irradiation of the micro-electro-mechanical system 200 in the arrangement 100 according to the invention as shown in Figure 2, more orientations of different micromirrors 210 can be detected within a given period of time.

[0076] If the above measures for the (quasi-)parallelization of orientations of the micromirrors 210 of the micro-electro-mechanical system 200 are appropriately implemented, even assuming that a simultaneous adjustment of the orientation of the micromirrors 210 of the micro-electro-mechanical system 200 takes approximately 1 second, a complete calibration of the micro-electro-mechanical system 200 – i.e., the determination of a sensor characteristic curve for each micromirror 210 of the system 200 based on 300 support points each – is possible in 15 minutes or less.

[0077] Since the beam paths from the radiation sources 110 to the micromirrors 210, as well as from the micromirrors 210 to the radiation detectors 120, are known and clearly definable in the arrangement 100 according to Figure 2 (see dashed lines in Figure 2, top), a scatter radiation aperture 140 is provided with which all radiation paths other than those mentioned are captured. This improves the measurement result at the radiation detectors 120.

[0078] From the foregoing explanations regarding the order according to Figure 2 directly illustrates the method according to the invention.

[0079] Figure 3 shows an alternative embodiment of an arrangement 100 according to the invention for calibrating an electro-mechanical system 200 from the system according to Figure 1, which, however, is based on the same principle as the one from Figure 2, which is why, in addition to what follows, reference is made to the preceding explanations.

[0080] The arrangement 100 according to Figure 3 comprises, in addition to the micro-electro-mechanical system 200 already known from Figure 2, with a plurality of micromirrors 210 and a single radiation source 110, a single radiation detector 120, which includes an image screen 125 and an image acquisition unit 126. The image screen 125, like the radiation source 110, is arranged at a distance d of 2 m, which thus corresponds to the effective radius of curvature of the individual micromirrors 210. The image acquisition unit 126 is arranged such that it fully captures the image screen 125.

[0081] The radiation from the radiation source 110 is focused by the micromirrors 210 onto specific points on the image screen 125, depending on their individual orientation. The resulting "illuminated points" can then be imaged by the image acquisition unit 126. By evaluating the captured image, the orientations of at least some of the micromirrors 210 at the time of image acquisition can be determined and, together with the data from the orientation sensors available at that time, used to determine a suitable sensor characteristic curve. For further explanations and the possibilities of parallelization, please refer to the description of Figure 2.

[0082] Figure 4 shows an alternative embodiment of an arrangement 100 according to the invention for calibrating an electromechanical system 200 from the system according to Figure 1, which, however, is based on the same principle as the one shown in Figure 1. Figures 2 and 3 are based on the above, which is why, in addition to what follows, reference is made to the preceding statements.

[0083] The arrangement 100 comprises, in addition to the micro-electro-mechanical system 200 already known from Figure 2 with a plurality of micromirrors 210, a planar radiation source 110 and a single planar radiation detector 120, both of which are arranged at a distance corresponding to the effective radius of curvature of the micromirrors 210.

[0084] The planar radiation source 110 allows for time- and spatially resolved adjustment of the intensity of the emitted radiation. Alternatively or additionally, the wavelength of the emitted radiation can also be adjusted with spatial resolution. The planar radiation source 110 can then be considered a close arrangement of individual point radiation sources 110, as shown in Figure 2. Apart from the number and closer arrangement of the individual point radiation sources 110, the methodology for calibrating a micro-electro-mechanical system 200 does not differ from the procedure described in connection with Figure 2, so reference is made to the explanations there. For this purpose, for example, specific small areas of comparable, spatially distributed individual point radiation sources 110 can be activated on the planar radiation source 110 with time resolution.The radiation wavelength of the areas can also be changed, analogous to what is described above.

Claims

Patent claims 1. Arrangement (100) for calibrating a micro-electro-mechanical system with a plurality of individually pivotable concave micromirrors (18', 19') each with an orientation sensor for determining the orientation of the micromirror, comprising at least one radiation source for emitting radiation reflectable by the micromirrors and at least one radiation detector for detecting radiation emitted by the at least one radiation source, characterized in that the at least one radiation source and the at least one radiation detector are each arranged at a distance equal to the effective radius of curvature of the concave micromirrors such that radiation from a radiation source reflected by a micromirror at a given orientation can be detected by a radiation detector by imaging the radiation source onto the radiation detector.

2. Arrangement according to claim 1, characterized in that the arrangement comprises several radiation sources and / or several radiation detectors, wherein at least the radiation sources or the radiation detectors are arranged in such a spatially distributed manner that each pair of radiation source and radiation detector is suitable for detection by a micromirror at a predetermined orientation or in a predetermined swivel range of reflected radiation.

3. Arrangement according to one of the preceding claims, characterized in that the number of radiation sources and radiation detectors preferably differs by at least a factor of five, and further preferably by at least a factor of ten.

4. Arrangement according to one of the preceding claims, characterized in that one or more scatter radiation apertures (n) are arranged between radiation source (n) and / or radiation detector (en) and the micromechanical system.

5. Arrangement according to one of the preceding claims, characterized in that at least one radiation detector is an objective-less image sensor for spatially resolved detection of incident radiation on the image sensor.

6. Arrangement according to one of the preceding claims, characterized in that at least one radiation detector comprises a screen or a fluorescent screen for spatially resolved imaging of radiation incident thereon and an image capture unit for capturing the image projected onto the screen or fluorescent screen.

7. Arrangement according to one of the preceding claims, characterized in that at least one radiation source is a point source of radiation, preferably with radiation bundling for directed radiation emission.

8. Arrangement according to one of the preceding claims, characterized in that at least one radiation source is a planar radiation source, wherein the emitted radiation is preferably spatially resolved and adjustable in at least one radiation property.

9. Arrangement according to one of the preceding claims, characterized in that at least one radiation source is preferably adjustable with respect to the intensity and / or wavelength of the emitted radiation with temporal and / or spatial resolution.

10. Arrangement according to one of the preceding claims, characterized in that at least a part of the micromirrors is pivotable about two non-parallel, preferably perpendicular to each other, axes.

11. Method for calibrating a micro-electro-mechanical system (200) with a plurality of individually pivotable concave micromirrors (210), each comprising an orientation sensor with an arrangement (100) according to one of the preceding claims, comprising the steps: Determine multiple support points for a sensor characteristic curve for the orientation sensor of each of the micromirrors (210), each using the following steps: - Adjusting the orientation of at least one micromirror (210) such that at least one radiation source (110) is imaged by the micromirror (210) onto a radiation detector (120); - Determination of the actual orientation of the micromirror (210) from the beam path from radiation source (110) to radiation detector (120) ; - Determination of the orientation of the micromirror (210) detected by the orientation sensor; and - Determining the reference point for the sensor characteristic curve from the actual orientation and the orientation determined by the orientation sensor; - Determining sensor characteristics for each orientation sensor of each micromirror (210) of the micro-electro-mechanical system (200) from the determined support points.

12. Method according to claim 11, characterized in that the determination of a support point for at least two micromirrors (210) is carried out in parallel.

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