MEMS micromirror unit and semiconductor equipment
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- CARL ZEISS SMT GMBH
- Filing Date
- 2026-01-19
- Publication Date
- 2026-07-30
Smart Images
Figure EP2026051103_30072026_PF_FP_ABST
Abstract
Description
[0001] 19.01.2026 / BR
[0002] MEMS micromirror unit and
[0003] Semiconductor technology facility
[0004]
[0001] The present application claims priority from German patent application 10 2025 102 069.8, filed on January 21, 2025. The content of that German patent application is incorporated into the present application text by reference.
[0005]
[0002] The invention relates to a micromirror unit designed as a micro-electro-mechanical system (MEMS) for use in semiconductor technology equipment, and to a semiconductor technology equipment.
[0006]
[0003] In the prior art, semiconductor technology equipment refers to equipment used for the production or testing of microstructured devices or the components required for their production. An example of such equipment is a projection exposure system for photolithography for the production of microstructured devices, such as integrated circuits.
[0007]
[0004] The projection 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 means of the projection system onto a substrate, for example a silicon wafer, coated with a photosensitive layer and arranged in the image plane of the projection system, in order to transfer the mask structure onto the photosensitive coating of the substrate.
[0005] In illumination systems, in particular in projection exposure systems designed for the EUV range, i.e., at exposure wavelengths from 5 nm (or possibly 2 nm) to 30 nm, but also for the DUV range with exposure wavelengths of, for example, 193 nm, two faceted mirrors are generally 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.
[0008]
[0006] In order to produce different intensity and / or angle of incidence distributions when illuminating the mask, it is known to form the facets of at least one of the two faceted mirrors – in particular those of the field faceted mirror – from one or more individually electromechanically pivotable micromirrors. A corresponding method is disclosed, for example, in WO 2012 / 130768 A2.
[0009]
[0007] In order to achieve a small size of the individual micromirrors, it is known to form groups of micromirrors in the form of a so-called MEMS mirror array, namely a mirror array made of micro-electro-mechanical systems (MEMS).
[0010]
[0008] Micro-electro-mechanical systems (MEMS) are small components that combine micromechanical structures and electronic elements in a single chip. MEMS can be manufactured using integrated circuits, similar to microchips. A MEMS generally comprises a base structure on which movable elements are arranged that can be controlled relative to the base structure.
[0009] In a MEMS mirror array, a plurality of small mirror elements are mounted so that they can be moved individually relative to a common base structure. At least one actuator is provided for each mirror element, allowing it to be adjusted along a predetermined degree of freedom. Often, the mirror elements can be pivoted about two axes that are perpendicular to each other and parallel to the base, and sufficient actuators are provided to allow the mirror element to be pivoted independently about these axes.Sensors can also be provided for the individual mirror elements to determine their position relative to the base, thus enabling monitoring of the mirror alignment. A particularly advantageous embodiment for the mirrors of a MEMS mirror array is described in DE 10 2015 204 874 A1.
[0011]
[0010] A method for producing a micromirror or a MEMS mirror array comprising a plurality of such micromirrors is disclosed - together with further details of a possible embodiment of the micromirror - in DE 10 2015 220 018 Al .
[0012]
[0011] To achieve the required precision in setting a desired intensity and angle of incidence distribution, it is necessary to be able to precisely adjust the orientation of the individual micromirrors. In addition to the microelectromechanical drive required for pivoting the mirror, the micromirrors also include a tilt sensor with which the orientation of the micromirror in two spatial directions can be read and checked. The angular position of a micromirror is then achieved by a control system in which the orientation achieved by the microelectromechanical drive is monitored by the tilt angle sensor, and the drive is readjusted as needed to achieve the desired orientation.
[0013]
[0012] Both the microelectromechanical drives and the tilt angle sensors can utilize the effects of an electric field to adjust a micromirror or to detect the instantaneous tilt angle of a micromirror. Thus, the adjustment of a micromirror can be achieved by utilizing electrostatic attraction between electrodes supplied with a suitable voltage, while the tilt angle can be determined from the change in capacitance between electrodes moving relative to each other.
[0014]
[0013] However, it has been found that in MEMS mirror arrays, which can be precisely controlled with regard to their angular position without irradiating the micromirrors with a working radiation, the alignment accuracy can decrease when the MEMS mirror array is exposed to working radiation - i.e. the radiation which is to be reflected by the micromirrors in a respective predetermined direction.
[0015]
[0014] The object of the present invention is to provide a MEMS micromirror unit for use in semiconductor technology systems and a semiconductor technology system comprising such a micromirror unit in which the disadvantages known from the prior art no longer occur or only occur to a reduced extent.
[0016]
[0015] This problem is solved by a MEMS micromirror unit according to claim 1 and by a system for semiconductor technology according to claim 15. Advantageous further developments are the subject of the dependent claims.
[0016] Accordingly, the invention relates to a MEMS micromirror unit for use in semiconductor technology systems comprising a plurality of micromirrors which are pivotable relative to a base structure by means of microelectromechanical actuators, each with at least one tilt sensor for determining the orientation of the micromirror, wherein the micromirrors are designed to reflect a working radiation directed towards the MEMS micromirror unit, and wherein the MEMS micromirror unit comprises a protective device to keep or compensate for electrons released in the vicinity of the actuators and / or tilt sensors due to the working radiation on photoelectrically electron-releasing surfaces away from the actuators and / or tilt sensors.
[0017]
[0017] The invention also relates to a system for semiconductor technology comprising a MEMS micro-mirror unit according to the invention for deflecting working radiation used by the system.
[0018]
[0018] First, some terms used in connection with the invention are explained.
[0019]
[0019] The “working radiation” is radiation of a specific wavelength or wavelength range used in the semiconductor technology system to perform the task associated with the beam path that passes over the MEMS micromirror unit. If the semiconductor technology system is a photolithography exposure system or even just its illumination system, the working radiation corresponds to the exposure radiation, the wavelength of which can be, for example, 13.5 nm for EUV or 193 nm for DUV systems. The micromirrors are generally designed for the highest possible reflectivity for the working radiation and are, for example, appropriately coated for this purpose.
[0020]
[0020] The “basic structure” of the MEMS micromirror unit is the structure on which the individual micromirrors are each mounted so that they can be moved independently. Components or parts thereof can be arranged and attached to the basic structure. In addition to at least parts of the actuators and / or tilt sensors, parts of the control and monitoring electronics as well as various connecting cables can also be arranged.
[0021]
[0021] The invention is based, among other things, on the finding that the working radiation used in semiconductor technology systems can, upon striking both surfaces that reflect the working radiation and, in particular, non-reflective surfaces, release electrons which—if they enter the actuators and / or tilt sensors directly or indirectly—can immediately lead to an undesired misalignment of the micromirrors or to an error in determining the orientation of the micromirror. Assuming an actual orientation that deviates from the target orientation, this can then result in incorrect tracking of the micromirror. The latter can occur particularly with capacitive tilt sensors that detect the orientation, which can deliver an erroneous measurement result even due to a small leakage current in one electrode.
[0022]
[0022] The surfaces not designed for reflection, which consequently release electrons upon contact with operating radiation, are primarily surfaces on the MEMS micromirror unit itself, namely surfaces and surface areas away from the micromirrors themselves. Due to the geometric characteristics of the MEMS micromirror unit, these surfaces are generally, or depending on the position of individual micromirrors, exposed to the operating radiation intended for reflection by the micromirrors. Thus, a gap is generally provided between each individual micromirror to ensure the individual freedom of movement of the micromirrors relative to one another. However, operating radiation can also pass through this gap to the base structure of the MEMS micromirror unit or to another component arranged on the base structure in this area.The width and / or position of the surface area exposed to working radiation passing through such a slit can change depending on the orientation of the micromirrors forming the slit in question.
[0023]
[0023] In principle, electrons can also be photoelectrically released from surfaces not directly belonging to the MEMS micromirror unit in the vicinity of the actuators and / or tilt sensors due to incident operating radiation. These electrons can impair the actuators and / or sensors as described. For the sake of clarity, such surfaces are logically assigned to the MEMS micromirror unit in connection with the invention and, in particular, with regard to the proposed solution, even if they structurally belong to a separate unit. If such a surface is actively included by the protective device in an embodiment, this means that the MEMS micromirror unit according to the invention has a suitable interface for this purpose.
[0024]
[0024] The invention recognizes that the emission of electrons from surfaces near the actuators and / or tilt sensors due to exposure to operating radiation cannot be prevented, or at least not completely prevented, by structural measures or similar means. The invention therefore proposes to minimize the net currents acting on the actuators and / or tilt sensors of a MEMS micromirror unit due to electrons emitted in their vicinity by means of a protective device. To achieve this, the protective device is designed to keep the emitted electrons in question away from the actuators and / or tilt sensors, so that a current into the actuators and / or tilt sensors is prevented as completely as possible, or, if the electrons do reach the actuators and / or tilt sensors and thus cause a current, to compensate for such a current due to photoelectrically emitted electrons as far as possible.The protective device can at least reduce disruptive effects caused by photoelectrically triggered electrons in MEMS mirror units.
[0025]
[0025] The protective device can also reduce disruptive effects from electrons generated elsewhere. For example, it can reduce the effects of electrons from the plasma, which arises from the interaction of the working radiation with an existing gas, or from other incident particles, such as electron-, ion-, or neutral particle-induced secondary electron emission.
[0026]
[0026] The protective device can include a potential or voltage source designed to generate an electric field that keeps electrons released by the operating radiation on photoelectrically emitting surfaces away from the actuators and / or tilt sensors. In other words, an electric field is created in the area between the actuators and / or tilt sensors to be protected from photoelectrically released electrons and the surfaces that release these electrons when exposed to operating radiation. This electric field accelerates the electrons released from the surface with a certain kinetic energy so that they do not strike the actuators and / or tilt sensors. The specific components or surfaces between which the electric field is created are irrelevant, as long as the orientation and field strength are sufficient to achieve the desired effect.In principle, it is sufficient to redirect the electrons so that they strike less sensitive components. However, it is also possible to orient the electric field appropriately so that the released electrons are accelerated in the opposite direction to their initial kinetic energy, ultimately decelerating them and returning them to the surface from which they originated. This effect is similar to that of an electron energy filter. The applied voltage determines the maximum kinetic energy at which electrons can be retained.
[0027]
[0027] The protective device can in particular comprise a voltage source configured to generate a sufficiently high voltage between at least parts of the tilt sensors and / or actuators and at least one photoelectrically electron-emitting surface in order to repel at least some of the electrons released due to operating radiation back into the releasing surfaces by the electric field thus created. It is also possible that some of the released electrons are deflected in such a way that the electrons are absorbed by less sensitive components of the MEMS micromirror unit.
[0028]
[0028] Depending on the design and / or arrangement of actuators and tilt sensors in the individual micromirrors of the MEMS micromirror unit, it may be sufficient if only one actuator or tilt sensor, or parts thereof, are subjected to a voltage relative to the photoelectrically electron-releasing surface. The components subjected to a voltage, or the resulting electric field, can then serve as a kind of protective shield for the other components.
[0029]
[0029] If actuators and / or tilt sensors, as is generally known from the prior art, are designed as interlocking electrode combs, at least a part of the electrodes of the actuators and / or tilt sensors can be subjected to a voltage as described above.
[0030]
[0030] Alternatively or additionally, it is also possible that the protective device comprises at least one protective element arranged between at least one photoelectrically emitting electron surface and one or more tilt sensors and / or actuators, and a voltage source, wherein the voltage source is configured to generate a sufficiently high voltage between the protective element and at least one photoelectrically emitting electron surface to repel at least some of the electrons released due to operating radiation back into the emitting surfaces by the electric field thus created. Here, too, it is possible that some of the released electrons are deflected in such a way that the electrons are not repelled back into the surface, but are absorbed by less sensitive components of the MEMS micromirror unit. The protective element can, for example, be configured such that itThe actuators and / or tilt sensors are each enclosed by a micromirror. In other words, the protective element can be placed in the form of a ring around the actuators and / or tilt sensors, whereby the ring does not have to be round, but can also be square or rectangular, for example.
[0031] A similar principle applies if the protective device includes a potential source designed to generate a sufficiently strong electric field between at least one photoelectrically emitting electron surface and the surroundings to retract at least some of the electrons emitted due to operating radiation back into the emitting surfaces. The electric field thus generated does not directly align with the direction between the surface in question and the at least one actuator and / or tilt sensor, but can nevertheless be strong enough to capture emitted electrons moving in precisely this direction and return them to the surface. Alternatively, some of the emitted electrons may simply be deflected by the electric field in such a way that they are captured by less sensitive components of the MEMS micromirror unit.
[0031]
[0032] It is also possible that the protective device includes a voltage source designed to apply a sufficiently high voltage between at least one photoelectrically electron-emitting and irradiated surface and at least one photoelectrically electron-emitting but not irradiated surface, in order to retract at least some of the electrons released due to operational radiation into the emitting surfaces via the electric field thus created. In other words, a voltage is applied between two surfaces that both fundamentally emit photoelectric electrons, but one of which is not currently exposed to operational radiation, so that no electrons are actually emitted there.An electric field can then be established between the surfaces, which directs the electrons released from the surface actually exposed to working radiation back to that surface or at least deflects them so that they are absorbed by less sensitive components of the MEMS micromirror unit.
[0032]
[0033] Alternatively or additionally, it is possible to counteract an electron current acting on the actuators and / or tilt sensors with a suitable countercurrent. For this purpose, the protective device can include at least one photon source configured to irradiate the actuators and / or tilt sensors with high-energy photons in order to compensate for a current arising from at least one surface photoelectrically releasing electrons due to the operating radiation by means of a countercurrent of emitted electrons. The at least one photon source can be arranged directly on the MEMS micromirror unit. In particular, the radiation source can be arranged as part of the base structure or between the base structure and the micromirrors of the MEMS micromirror unit. However, it is also possible for the at least one radiation source to be arranged remotely from the MEMS micromirror unit.In this case, the radiation can be introduced through the previously described gap between the individual micromirrors. For this purpose, one or more radiation sources can be arranged so that the irradiation occurs at a shallow angle to the base structure: At certain pivoting positions of the micromirrors, a particularly large amount of radiation can thus reach the actuators and / or tilt sensors.
[0033]
[0034] The invention further recognizes that electrons can also be released from the reflective surfaces of the micromirrors due to photoelectric effects, resulting in a potential difference between the micromirror and its actuators and / or tilt sensors. This potential difference can cause electrons to migrate from the actuators and / or tilt sensors towards the micromirror, which in turn can lead to an undesired misalignment of the micromirrors or an error in determining the orientation of the micromirror. Assuming an actual orientation that deviates from the intended orientation, this can result in incorrect tracking of the micromirror.
[0034]
[0035] To compensate for this problem, the protective device can include an electron beam source designed to bombard at least one of the micromirrors of the MEMS micromirror unit with electrons. This serves to replace any electrons emitted there due to photoelectric effects and to prevent an electric current from the actuators and / or tilt sensors of the micromirror to the micromirror itself. The electron beam source is generally separate from the actual MEMS mirror unit to reliably ensure that the reflective surface from which electrons are emitted due to the operating radiation is directly bombarded with these loss-compensating electrons.
[0035]
[0036] Similarly, the protective device can also include an ion beam source designed to bombard at least one of the micromirrors of the MEMS micromirror unit with ions. Such an ion beam source can be useful if the micromirror or an electrically connected element of the actuator and / or tilt sensor becomes negatively charged. This negative charge can then be neutralized by introducing ions.
[0036]
[0037] It is preferred if the photon source, electron source, and / or ion source can be controlled with such spatial resolution that individual or at least group irradiation of the actuators, tilt sensors, and / or micromirrors is possible. This makes it possible to irradiate only those micromirrors or groups of micromirrors, or their actuators and / or tilt sensors, with photons, electrons, and / or ions where the resulting effect is actually required or desired.
[0037]
[0038] Alternatively or additionally, the protective device may include a magnet designed to create a sufficiently strong magnetic field, at least around the tilt sensors and / or actuators of a micromirror, to keep electrons and / or ions away from them. In particular, Helmholtz coils may be arranged around the actual MEMS micromirror unit. Similar to designs based on an electric field, electrons and / or ions can also be kept away from sensitive components, such as actuators and / or tilt sensors, by such a magnetic field.
[0038]
[0039] It is preferred if the actuators and / or tilt sensors of the MEMS micromirror unit are configured as interlocking combs on spaced-apart electrodes. Corresponding configurations are known in the prior art and are described, inter alia, in documents DE 10 2015 204 874 A1 and DE 10 2015 220 018 A1, so no further explanation is necessary here. Such configurations of actuators and / or tilt sensors are advantageous for MEMS micromirror units, particularly for semiconductor technology systems, but are also susceptible to currents caused by electrons striking the electrodes. The solution according to the invention is particularly effective with precisely such actuators and / or tilt sensors.
[0040] The system according to the invention for the semiconductor industry can, in particular, be a projection exposure system for photolithography. The at least one MEMS micromirror unit is generally arranged in the area of the illumination system. With the operating radiations regularly used in such systems, e.g., with a wavelength of 13.5 nm (EUV range) or 193 nm (DUV range), the effects addressed by the invention regularly occur and can negatively affect the exposure and thus the image quality beyond an acceptable level.
[0039]
[0041] The invention will now be described by way of example with reference to an advantageous embodiment and the accompanying drawings. These show:
[0040] Figure 1 : a schematic representation of a projection exposure system for photolithography;
[0041] Figure 2 : a schematic representation of a first embodiment of a MEMS micromirror unit according to the invention in a partial section;
[0042] Figure 3: a schematic representation of a second embodiment of a MEMS micromirror unit according to the invention in a partial section;
[0043] Figure 4: a schematic representation of a third embodiment of a MEMS micromirror unit according to the invention in a partial section;
[0044] Figure 5: a schematic representation of a fourth embodiment of a MEMS micromirror unit according to the invention in a partial section; Figure 6: a schematic representation of a fifth embodiment of a MEMS micromirror unit according to the invention in a partial section;
[0045] Figure 7: a schematic representation of a sixth embodiment of a MEMS micromirror unit according to the invention in a partial section; and
[0046] Figure 8: a schematic representation of a seventh embodiment of a MEMS micromirror unit according to the invention in a partial section.
[0047]
[0042] 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.
[0048]
[0043] An object field 11 in an object plane or reticulum plane 12 is illuminated by means of the illumination system 10. The illumination system 10 comprises an exposure radiation source 13, which, in the illustrated embodiment, emits illumination radiation comprising at least useful light in the EUV range, i.e., in particular with a wavelength between 5 nm and 30 nm. The exposure radiation source 13 can be a plasma source, for example, an LPP source (laser-produced plasma) or a DPP source (gas-discharge-produced plasma). It can also be a synchrotron-based radiation source. The exposure radiation source 13 can also be a free-electron laser (FEL).
[0049]
[0044] The illumination radiation emanating from the light source 13 is first focused in a collector 14. The collector 14 can be a collector with one or more ellipsoidal and / or hyperboloid reflective surfaces. The at least one reflective surface of the collector 14 can be illuminated at grazing incidence (Gl), i.e., with angles of incidence greater than 45°, or at normal incidence (NI), i.e., with angles of incidence less than 45°. The collector 14 can be structured and / or coated, on the one hand, to optimize its reflectivity for the useful radiation and, on the other hand, to suppress stray light.
[0050]
[0045] 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 design, 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.
[0051]
[0046] The illumination optics 16 comprise a deflecting mirror 17. The deflecting mirror 17 can be a planar deflecting mirror or, alternatively, a mirror with a beam-shaping effect in addition to the mere deflection effect. Alternatively or additionally, the deflecting mirror 17 can be designed as a spectral filter that separates a useful wavelength of the illumination radiation from stray light of a different wavelength.
[0047] The deflecting mirror 17 deflects the radiation originating 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.
[0052]
[0048] The first faceted mirror 18 comprises a plurality of micromirrors 18' that can be individually pivoted about two axes perpendicular to each other for the controllable formation of facets, each of which is 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), such as is also used, for example, in the
[0053] DE 10 2008 009 600 Al is described.
[0054]
[0049] 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 referred to 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 the second faceted mirrors 18, 19 results in a specular reflector, as is used, for example, in the
[0055] US 2006 / 0132747 Al, EP 1 614 008 Bl and US 6,573,978.
[0050] 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, 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.
[0056]
[0051] With the aid of the second faceted mirror 19, the individual facets of the first faceted mirror 18 are imaged into the object field 11, whereby this is regularly only an approximate image. The second faceted mirror 19 can be the last beam-shaping or even actually the last mirror for the illumination radiation in the beam path before the object field 11.
[0057]
[0052] 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.
[0058]
[0053] The facets of the first faceted mirror 18 are each superimposed on an associated 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 has a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.
[0059]
[0054] By selecting the illumination channels ultimately used, which is easily achieved by appropriately adjusting the micromirrors 18' of the first faceted mirror 18, the intensity distribution in the entrance pupil of the projection system 20 described below can also be adjusted. This intensity distribution is also referred to as the illumination setting. Furthermore, it can be advantageous not to arrange the second faceted mirror 19 exactly in a plane that is optically conjugate to a pupil plane of the projection system 20. In particular, the pupil faceted mirror 19 can be arranged tilted relative to a pupil plane of the projection system 20, as described, for example, in DE 10 2017 220 586 A1.
[0060]
[0055] In the arrangement of the components of the illumination optics 16 shown in Figure 1, the second faceted mirror 19 is arranged in a surface conjugate to the entrance pupil of the projection system 20. Deflection mirror 17 and the two faceted mirrors 18, 19 are each tilted relative to the object plane 12 and relative to each other.
[0061]
[0056] In an alternative embodiment of the illumination optics 16, not shown, a transmission optic comprising one or more mirrors can be provided in the beam path between the second faceted mirror 19 and the object field 11. The transmission optic can, in particular, comprise one or two mirrors for normal incidence (NI mirrors) and / or one or two mirrors for grazing incidence (Gl mirrors). With an additional transmission optic, different positions of the entrance pupil for the tangential and sagittal beam paths of the projection system 20 described below can be taken into account.
[0062]
[0057] Alternatively, it is possible to do without the deflecting mirror 17 shown in Figure 1, for which the faceted mirrors 18 , 19 are to be arranged appropriately opposite the radiation source 13 and the collector 14.
[0063]
[0058] Using the projection system 20, the object field 11 in the reticulum plane 12 is transferred to the image field 21 in the image plane 22.
[0064]
[0059] The projection system 20 comprises a plurality of mirrors M for this purpose. ± , which are numbered according to their arrangement in the beam path of the projection exposure system 1. Regarding the mirrors M ± These are optical elements 25.
[0065]
[0060] In the example shown in Figure 1, the projection system 20 comprises six mirrors M x up to M6 as optical elements 25. Alternatives with four, eight, ten, twelve or another number of mirrors M ±are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage for the illumination radiation, making the depicted projection system 20 a doubly obscured optic. 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.
[0066]
[0061] The reflective surfaces of the mirrors M ± can be designed as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflective surfaces of the mirrors M can be ± but can also be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflecting surface shape. The mirrors M ±Like the mirrors of the lighting optics 16, they 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.
[0067]
[0062] 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.
[0068]
[0063] The projection system 20 can in particular be anamorphic, i.e. it has in particular different image scales β x , ß y in the x and y directions. The two image scales ß x , ß y of the projection system 20 are preferably located at ( ßx , ß y ) = ( + / - 0.25, / + - 0.125) . A magnification β of 0.25 corresponds to a reduction in the ratio 4:1, while a magnification β of 0.125 results in a reduction in the ratio 8:1. A positive sign for the magnification β indicates a magnification without image inversion, a negative sign indicates a magnification with image inversion.
[0069]
[0064] Other magnification scales are also possible. Magnification scales 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.
[0070]
[0065] The number of intermediate image planes in the x- and y-directions in the beam path between the object field 11 and the image field 21 can be the same or different, depending on the design of the projection system 20. Examples of projection systems 20 with different numbers of such intermediate images in the x- and y-directions are known from the
[0071] US 2018 / 0074303 Al .
[0072]
[0066] The projection system 20 can in particular have a homocentric entrance pupil. This can be accessible. However, it can also be inaccessible.
[0073]
[0067] A reticle 30 (also called a mask) arranged in the object field 11 is exposed by the illumination system 10 and transferred to the image plane 21 by the projection system 20. The reticle 30 is held by a reticle holder 31. The reticle holder 31 can be moved, in particular in a scanning direction, by means of a reticle displacement drive 32. In the illustrated embodiment, the scanning direction is in the y-direction.
[0074]
[0068] 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 reticulum 30 can be 5 to 7 inches long (12.70 to 17.78 cm) and 10 to 14 inches wide (25.40 to 35.56 cm), and is preferably 6 inches long (15.24 cm) and 12 inches wide (30.48 cm).
[0075]
[0069] A structure on the reticulum 30 is imaged onto a light-sensitive layer of a wafer 35 arranged 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, in particular along the y-direction, via a wafer displacement drive 37. The displacement of the reticulum 30 via the reticulum displacement drive 32 and of the wafer 35 via the wafer displacement drive 37 can be synchronized with each other.
[0076]
[0070] 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 micromirrors 18', 19' of the faceted mirrors 18, 19 are each part of a MEMS micromirror unit 100. A portion of the micromirrors 18', 19' of the faceted mirrors 18, 19 are each assigned to a MEMS micromirror unit 100, wherein the totality of the micromirrors 18', 19' of the respective faceted mirrors 18, 19 is obtained by several MEMS micromirror units 100 arranged side by side.
[0077]
[0071] Figures 2 to 8 show MEMS micromirror units 100 in a schematic partial section.
[0078]
[0072] The MEMS micromirror unit 100 comprises a base structure 110 on which a plurality of micromirrors 120 are arranged to be movable, namely pivotable about two degrees of freedom. The micromirrors 120 are provided with a reflective coating 122 on the side 121 facing away from the base structure 110.
[0079]
[0073] Actuators 130 are provided for the individual movement of each of the micromirrors 120, namely for pivoting about the two degrees of freedom. The actuators 130 are designed as two rotating interlocking electrode combs 131, one of which is fixedly connected to the respective micromirror 120, the other fixedly connected to the base structure 110. By selectively applying a voltage to a portion of the electrodes of the electrode combs 131, the respective micromirror 120 can be pivoted, thus making each of the micromirrors 120 a micro-electro-mechanical movable element.
[0080]
[0074] Similar to the actuators 130, tilt sensors 140 are provided, which are also designed as interlocking electrode combs 141, one of which is fixedly connected to the respective micromirror 120, the other fixedly connected to the base structure 110. When a micromirror 120 is tilted, the capacitance changes at least between some of the electrodes of the electrode combs 141. The capacitance or its change can be detected and the orientation of the respective micromirror 120 can be determined from this.
[0081]
[0075] For the sake of clarity, the leads to the individual elements of the actuators 130 and tilt sensors 140 are not shown, nor is the control device for controlling the actuators 130 taking into account the measurement data of the tilt sensors 140.
[0082]
[0076] For the first embodiment of a MEMS micromirror unit 100 shown in Figure 2, it is illustrated by way of example how a working radiation 90 from the projection exposure system 1 (see Figure 1) falls on the MEMS micromirror unit 100, which is part of one of the two faceted mirrors 18, 19. The working radiation 90 primarily strikes the side 121 of the micromirrors 120 provided with a reflective coating 122 and is reflected by it.
[0083]
[0077] Through the gap 125 between the micromirrors 120, which is essential for the individual movement of the micromirrors 120, the operating radiation 90 passes past the micromirrors 120 but also reaches a surface 111 of the base structure 110. At these surfaces 111, which are certainly located near the actuators 130 and tilt sensors 140, electrons are emitted due to photoelectric effects. These electrons could potentially reach the electrodes of the actuators 130 and tilt sensors 140. Electrons striking the electrodes of the actuators 130 can directly lead to an unintended adjustment of the micromirrors 120; electrons striking the electrodes of the tilt sensors 140 can lead to an incorrect determination of the orientation of the micromirrors 120, which can then lead to an unintended adjustment of the micromirrors 120 by the control device.Since an incorrect determination of the orientation by the tilt sensors 140 can occur even with a comparatively small number of electrons striking their electrodes, while a considerably higher electron flow is required for an immediate adjustment of an actuator 130, the tilt sensors 140 in particular must be protected from photoelectrically triggered electrons in the environment.
[0084]
[0078] In the embodiment shown in Figure 2, it is provided to create an electric field between at least part of the electrodes and the surface 111 of the basic structure 110, where electrons are released due to the working radiation or could at least be released in principle, with which at least part of the released electrons are returned to the surface 111.
[0085]
[0079] In the embodiment shown on the left side of Figure 2, the electrodes of the actuators 130 are connected to a voltage source 150, while the other potential of the voltage source 150 is brought close to the photoelectrically electron-releasing surfaces 110 such that the voltage of the voltage source 150 is present between the electrodes of the actuators 130 and the surface 110. This results in an electric field which, if it has the correct polarity and strength (which result directly from the voltage), repels electrons released from the surface 111 back into this surface 111. Due to the tilt sensors 120 being arranged internally to the actuators 130, the tilt sensors 140 are also protected from being struck by electrons released at the surface 111 by the operating radiation 90, thus reducing the risk of an incorrectly determined orientation.
[0086]
[0080] On the right side of Figure 2, the voltage source 150 is connected to the electrodes of the tilt sensors 140, which means that the electric field generated by the applied voltage may be configured differently than the electric field in the embodiment on the left side of Figure 2. Nevertheless, at least the electrodes of the tilt sensors 140 are protected from electrons emitted from the surface 111 by the operating radiation 90 according to the same principle. If the electric field is strong enough, the electrodes of the actuators 130 can also be protected from such electrons in this embodiment; however, this may not be absolutely necessary, since an impact of the emitted electrons on the actuators 130 has no effect or an effect that can be readily compensated for by the control device based on the measurement results of the tilt sensors 140.
[0087]
[0081] It should be noted that the lines shown in Figure 2 between the voltage source 150 and the electrodes of the actuators 130 or tilt sensors 140 are only shown schematically and are to be considered exemplary. In particular, various switching elements can be provided on the lines with which the individual electrodes or surface areas 111 can be connected to the voltage source 150. The line connection points shown in Figure 2 represent a momentary state of a possible switching state of such switching elements, whereby lines that are inactive due to a switching state are not shown. This type of representation is also found in the following Figures 3 to 5.
[0088]
[0082] Figure 3 shows a second embodiment of the MEMS micromirror unit 100, which is largely similar to the one shown in Figure 2. However, in the embodiment according to Figure 3, protective elements 160 are provided, which are generally ring-shaped (square in the illustrated embodiment) and are arranged around the actuators 130 and tilt sensors 140 of each micromirror 120.
[0089] These protective elements 160 are each electrically connected to the voltage source 150, so that a voltage and thus an electric field is established between the protective elements 160 and the surface 111 of the basic structure 110, with which electrons possibly triggered by the working radiation 90 from the surface 111 are kept away from the electrodes of the actuators 130 and the tilt sensors 140.
[0090]
[0083] Figure 4 shows another embodiment of a MEMS micromirror unit 100. The MEMS micromirror unit 100 is not illuminated over its entire surface, but only in the area of one of the illustrated micromirrors 120 with working radiation 90. The working radiation 90 nevertheless penetrates the gap 125 surrounding the micromirror 120 in question and can then, as previously described, trigger electrons at the surface 111 of the base structure 110.
[0091]
[0084] The relevant areas of the surface 111 can be selectively connected to one of the poles of the voltage source 150 by suitable switching elements (not shown), with a specific circuit state being represented by the lines shown in Figure 4. The connection of the various areas of the surface 111 to the voltage source 150 results in electric fields which—at a sufficiently high voltage—are sufficient to keep any electrodes potentially triggered on the surfaces 111 by the operating radiation 90 away from the tilt sensors 140, so that their measuring accuracy is not impaired.
[0092]
[0085] The embodiment of the MEMS micromirror unit 100 according to Figure 5 is similar to that shown in Figure 4. However, in this embodiment, the areas of the surface 111 on the base body 110, where electrons can potentially be released by working radiation 90, are not selectively connected to the poles of the voltage source 150, but are instead permanently raised to a potential relative to the environment. This creates an electric field around the surfaces 111 in question, which "captures" at least some of the electrons potentially released from the surfaces 111 and returns them to the respective surface 111 before they can enter the electrodes of the actuators 130 and / or tilt sensors 140.
[0093]
[0086] In the embodiment of the MEMS micromirror unit 100 shown in Figure 6, the micromirrors 120 are pivoted, regardless of whether they are exposed to working radiation 90 or not. This results in a change in the gap 125 between the individual micromirrors 120.
[0094]
[0087] The MEMS micromirror unit 100 comprises a radiation source 170, which is arranged remotely from the MEMS micromirror unit 100 such that the irradiation from this radiation source 170 occurs at a shallow angle to the base structure 110 of the MEMS micromirror unit 100. Consequently, when the micromirrors 120 are in the pivot position shown in Figure 6, the irradiation from this radiation source 170 can pass through the gap 125 and reach at least some of the electrodes of the actuators 130 and / or tilt sensors 140. The irradiation from the radiation source 170 is spatially resolved by means of a suitable control system and is limited exclusively to those gaps 125 between the micromirrors 120 through which the operating radiation 90 also reaches the surfaces 111.
[0095]
[0088] The radiation 171 generated by the radiation source 170 comprises high-energy photons that eject electrons from the electrodes of the actuators 130 and / or tilt sensors 140 upon which the radiation strikes. The intensity of the radiation 171 from the radiation source 170 is adjusted such that the number of electrons ejected from the electrodes by the radiation 171 essentially corresponds to the number of electrons ejected from the surfaces 111 by the operating radiation 90 and striking the electrodes, resulting in a net current of approximately zero.
[0096]
[0089] The MEMS micromirror unit 100 according to Figure 7 comprises an electrically operable magnet 180 in the form of a coil, with which a magnetic field can be created, by which electrons triggered on the surfaces 111 of the basic structure 110 but also at other locations of the MEMS micromirror unit 100 are deflected in such a way that they do not at least hit the electrodes of the actuators 130 and / or tilt sensors 140.
[0097]
[0090] In the embodiment of the MEMS micromirror unit 100 shown in Figure 8, the focus is less on the emission of electrons from the surface 111 of the base structure 110 (see Figures 2 to 7). Rather, this embodiment is based on the finding that electrons are also emitted from the reflective coating 122 on the side 121 of the micromirrors 120 facing away from the base structure 110. These electrons can lead to electrical currents within the micromirrors 120 and the electrodes of actuators 130 and / or tilt sensors 140 arranged thereon, which can impair the functioning of the actuators 130 and / or tilt sensors 140. In this embodiment, a spatially resolved controllable electron beam source 190 is provided, with which those micromirrors 120 that are exposed to working radiation 90 can also be exposed to an electron beam 191.With the aid of the electron beam 191, the electrons emitted from the micromirror 120 can be immediately balanced by electrons originating from the electron beam source 190, so that no currents arise within the micromirror 120 and its associated components that could influence the actuators 130 and / or tilt sensors 140. Alternatively, the electron beam source 190 can also be directed at micromirrors 120 adjacent to those illuminated by the operating radiation 90. This also reduces the electric current on the surface 121 of the micromirrors 120 illuminated by the operating radiation 90.
[0098]
[0091] In addition to the electron beam source 190, an ion beam source can be provided alternatively or additionally, with which areas with excess electrons can be neutralized.
[0099]
[0092] Of course, it is possible to combine several of the above embodiments. In particular, the embodiment shown in Figure 8 can be easily combined with one of the embodiments shown in Figures 2 to 7.
Claims
32 Patent claims 1. MEMS micromirror unit (100) for use in semiconductor technology equipment comprising a plurality of micromirrors (120) pivotable relative to a base structure (110) by microelectromechanical actuators (130), each with at least one tilt sensor (140) for determining the orientation of the micromirror (120), wherein the micromirrors (120) are designed to reflect a working radiation (90) directed towards the MEMS micromirror unit (100), characterized by the fact that The MEMS micromirror unit (100) includes a protective device to keep away from and / or compensate for electrons released from photoelectrically electron-releasing surfaces (111, 121) in the vicinity of the actuators (130) and / or tilt sensors (140) due to the operating radiation (90) on surfaces (111, 121).
2. MEMS micromirror unit according to claim 1, characterized by the fact that the protective device comprises a potential or voltage source ( 150) designed to generate an electric field to keep electrons released due to the working radiation ( 90) on photoelectrically electron-releasing surfaces ( 111) away from the actuators ( 130) and / or tilt sensors ( 140).
3. MEMS micromirror unit according to claim 2, characterized by the fact that the protective device comprises a voltage source ( 150) designed to provide a voltage between at least parts of the tilt sensors ( 140) and / or actuators ( 130) and at least 33 to create a sufficiently high voltage on a photoelectrically electron-releasing surface ( 111 ) to force at least some of the electrons released due to work radiation ( 90 ) back into the releasing surfaces ( 111 ) by the electric field thus created .
4. MEMS micromirror unit according to one of claims 2 or 3, characterized in that the protective device comprises at least one protective element (160) arranged between at least one photoelectrically electron-releasing surface (111) and one or more tilt sensors (140) and / or actuators (130) and a voltage source (150), wherein the voltage source (150) is configured to generate a sufficiently high voltage between the protective element (160) and at least one photoelectrically electron-releasing surface (111) to repel at least some of the electrons released due to operating radiation (90) into the releasing surfaces (111) by means of the electric field thus created.
5. MEMS micromirror unit according to claim 4, characterized by the fact that at least one protective element ( 160) is arranged enclosing the actuators ( 130) and / or tilt sensors ( 140) of at least one micromirror ( 120).
6. MEMS micromirror unit according to one of claims 2 to 5, characterized in that the protective device comprises a potential source ( 150) designed to generate a sufficiently strong electric field between at least one photoelectrically electron-releasing surface ( 111 ) and the surroundings in order to withdraw at least some of the electrons released due to work radiation ( 90) into the releasing surfaces ( 111 ).
7. MEMS micromirror unit according to one of claims 2 to 6, characterized in that the protective device comprises a voltage source ( 150) designed to generate a sufficiently high voltage between at least one photoelectrically electron-releasing and irradiated surface ( 111 ) and at least one photoelectrically electron-releasing and non-irradiated surface in order to retract at least some of the electrons released due to work radiation ( 90) into the releasing surfaces ( 111) by means of the electric field thus created.
8. MEMS micromirror unit according to one of the preceding claims, characterized by the fact that the protective device comprises at least one radiation source ( 170) designed to irradiate the actuators ( 130) and / or tilt sensors ( 140) with high-energy photons in order to compensate for a current arising from at least one surface ( 111) that photoelectrically releases electrons due to the operating radiation ( 90) by means of a countercurrent of released electrons.
9. MEMS micromirror unit according to claim 8, characterized by the fact that at least one radiation source (170) is arranged at a distance from the MEMS micromirror unit (110) such that the irradiation from this radiation source (170) occurs at a shallow angle to the basic structure (110) of the MEMS micromirror unit (100).
10. MEMS micromirror unit according to one of the preceding claims, characterized by the fact that the protective device comprises an electron beam source ( 190) which is designed to bombard at least one of the micromirrors ( 120) of the MEMS micromirror unit ( 100) with electrons in order to replace electrons released there due to photoelectric effects and to prevent an electric current from the actuators ( 130) and / or tilt sensors ( 140) of the micromirror ( 120) to the micromirror ( 120) itself.
11. MEMS micromirror unit according to one of the preceding claims, characterized by the fact that the protective device comprises an ion beam source designed to bombard at least one of the micromirrors ( 120) of the MEMS micromirror unit ( 100) with ions.
12. MEMS micromirror unit according to one of claims 8 to 11, characterized in that the photon source ( 170 ), electron source ( 190 ) and / or ion source can be controlled with such spatial resolution that individual or at least group irradiation of the actuators ( 130 ), tilt sensors ( 140 ) and / or micromirrors ( 120 ) is possible .
13. MEMS micromirror unit according to one of the preceding claims, characterized by the fact that the protective device comprises a magnet ( 180) designed to generate a sufficiently strong magnetic field at least around the tilt sensors ( 140) and / or actuators36 ( 130) of a micromirror ( 120) to keep electrons and / or ions away from the tilt sensors ( 140) and / or actuators ( 130).
14. MEMS micromirror unit according to one of the preceding claims, characterized by the fact that the actuators ( 130) and / or tilt sensors ( 140) of the MEMS micromirror unit ( 120) are designed as interlocking electrode combs ( 131, 141) with electrodes spaced apart from each other.
15. Semiconductor technology system comprising a MEMS micromirror unit ( 100) according to one of the preceding claims for deflecting working radiation ( 90) used by the system.
16. System according to claim 15, characterized by the fact that the system for semiconductor technology is a projection exposure system ( 1 ) for photolithography, wherein the at least one MEMS micromirror unit ( 100 ) is preferably arranged in the illumination system ( 10 ).