Method for producing an EUV radiation-reflecting surface coating

Abstract

The invention relates to a method for producing an EUV radiation-reflecting surface coating (200) on a substrate (300), wherein the surface coating (200) comprises a multilayer coating system (210). The method comprises the steps: a) producing the surface coating (200) in inverse order of the layers of the multilayer coating system (210) on a carrier (100); b) bonding the produced surface coating (200) to the substrate (300) on the side remote from the carrier (100); and c) Detaching and removing the carrier (100) from the surface coating (300).

Description

[0001] The invention relates to a method for producing a surface coating reflecting EUV radiation, in particular for EUV photolithography.

[0002] Photolithography is used to manufacture microstructured components, such as integrated circuits. The projection exposure system used in this process comprises an illumination system and a projection system. The image of a mask (also called a reticle) illuminated by the illumination system is projected in a reduced size onto a substrate coated with a light-sensitive layer and arranged in the image plane of the projection system, for example, a silicon wafer, by means of the projection system in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0003] In projection exposure systems that operate with exposure radiation in the EUV range, the various optical elements in the exposure and projection system are designed as mirrors with a reflective surface. Due to the wavelengths of EUV exposure radiation ranging from 5 nm to 30 nm, the optically effective surface of the individual elements must be coated with a multilayer coating system to achieve the desired reflectivity.

[0004] Furthermore, in illumination systems, especially projection exposure systems designed for the EUV range, two facet mirrors are typically arranged in the beam path between the actual exposure radiation source and the mask to be illuminated. The facet mirror closest to the exposure radiation source in the beam path is often a so-called field facet mirror, while the other is a so-called pupil facet mirror.

[0005] In order to be able to produce different intensity and / or angle of incidence distributions when illuminating the mask, it is known to form the facets of at least one of the two facet mirrors – in particular those of the field facet mirror – from one or more electromechanically individually pivotable micromirrors. A corresponding approach is disclosed, for example, in WO 2012 / 130768 A2. These micromirrors are also each provided with a reflective coating.

[0006] The multilayer coating system required for the desired reflectivity is inherently sensitive and, after its fabrication on the designated surfaces of an optical element, can be damaged during subsequent manufacturing steps required to complete the optical element. This renders the optical element unusable or requires extensive rework. The risk of damage is particularly high with micromirror arrays, as micromirrors are typically designed as microelectromechanical systems (MEMS), which combine micromechanical structures and electronic elements in a single chip.

[0007] In the final state, the micromirrors of a corresponding system can be pivoted about two axes relative to a base, with sufficient actuators and sensors provided to pivot the mirror element independently about these axes and to monitor this pivoting. To apply the multilayer coating with the required precision, the base structure of the individual micromirrors should still be rigid and non-pivotable; the steps required to detach or pivot the micromirrors can damage the multilayer coating already applied to the base structure.

[0008] The object of the present invention is to provide a method for producing a surface coating reflecting EUV radiation which is improved compared to the prior art.

[0009] This object is achieved by the method according to claim 1. Advantageous further developments are the subject of the dependent claims.

[0010] Accordingly, the invention relates to a method for producing an EUV radiation-reflecting surface coating on a substrate, wherein the surface coating comprises a multilayer coating system, comprising the steps: a) Production of the surface coating in inverse order of the layers of the multilayer coating system on a carrier; b) bonding the produced surface coating to the substrate on the side remote from the carrier; and c) Loosening and removing the carrier from the surface coating.

[0011] The invention is based on the finding that, in the production of a large number of optical elements for EUV applications, the application of a multilayer coating system required for reflecting EUV radiation must, according to the prior art, already be carried out during the production process in such a way that subsequent required production steps of the optical element can damage the multilayer coating system. In addition to mechanical processing of the optical elements during production, which also directly affects an already applied multilayer coating system, such as the separation of an already coated substrate, this also includes processes in which the required process gas, such as for etching, may possibly come into contact with the multilayer coating system even unintentionally and damage it.According to the invention, the subsequent surface coating of a substrate comprising a corresponding multilayer coating system is first produced separately on a carrier and then applied as a whole to the substrate before the carrier is subsequently removed, leaving a substrate provided with the surface coating, resulting in new possibilities for the production of optical elements with a corresponding surface coating which are not feasible in the prior art.Thus, thanks to the method according to the invention for producing a surface coating reflecting EUV radiation on a substrate, it is generally possible to apply the surface coating at a later point in time in the manufacturing process of an optical element than in the case of direct production of the multilayer coating system on the substrate according to the prior art, whereby the risk of damage by subsequent manufacturing steps can be reduced or possibly even completely avoided.

[0012] To ensure that the multilayer coating system actually forms the desired surface coating of the substrate at the end of the process, the individual layers of the multilayer coating system must be applied to the carrier in an inverse or reverse order. The layer that is closest to the carrier when attached to the carrier forms the outermost layer of the substrate's surface coating in the final state. Conversely, the layer of the multilayer coating system that is exposed when arranged on the carrier serves to bond it to the substrate and is therefore closest to the substrate in the final state.

[0013] If the surface coating is arranged on the carrier in the inverse order of the layers of the multilayer coating system, the next step is to bond the exposed side of the surface coating away from the carrier to the substrate which is ultimately to be provided with the surface coating.

[0014] Finally, the carrier is removed to expose the surface coating applied to the substrate and thus actually achieve the desired reflectivity of the substrate in the area of ​​the surface coating.

[0015] It is possible for the surface coating to first be built up on an initial carrier or initial substrate using the "usual" sequence of layers of the multilayer coating system. The surface coating thus built up is then attached "upside down" to the carrier according to the invention before the initial carrier or initial substrate is suitably removed. The advantage of this type of production of the surface coating in the inverse sequence of the multilayer coating system on a carrier is that it is possible to use known and proven manufacturing processes for corresponding multilayer coating systems. This also applies in particular to the layer which, when attached to the carrier, is arranged adjacent to the carrier and lies on the outside of the substrate after removal of the carrier; the surface quality of this layer can be ensured using the known manufacturing processes.

[0016] However, it is preferred if the surface coating on the carrier is produced layer by layer, i.e., the individual layers of the multilayer coating system are applied to the carrier one after the other in reverse order. This eliminates the need for an initial carrier or substrate, thus eliminating any steps for removing these elements that are only required initially. Here, too, methods known from the prior art for producing multilayer coating systems can generally be applied.

[0017] In order to achieve a sufficiently high surface quality of the outermost layer of the multilayer coating system in the final state, it is preferable to ensure a high surface quality of the substrate on which the layer in question is initially applied during the production of the surface coating by suitable processing. Particularly when the surface coating is carried out by applying the individual layers of the multilayer coating system layer by layer to the substrate itself, a high surface quality of the substrate is desirable, since the surfaces of the substrate can be imprinted, similar to a negative, at least in layers of the multilayer coating system arranged adjacent to the substrate. It is therefore preferable to process the surface of the substrate by applying a smoothing layer, polishing, and / or cleaning. The processing methods for polishing and cleaning the surface require no further explanation.Rather, the skilled person is easily able to determine suitable polishing and cleaning processes for the carrier or its material and, if necessary, to verify the results of these processes. If the carrier or its material is not suitable for being processed to a desired high surface quality, it can be advantageous to apply a smoothing layer to the carrier. This smoothing layer is a layer that either provides the desired surface quality immediately after its application or - possibly differently than the carrier or its material itself - can be processed to the desired surface quality using suitable processes such as polishing and / or cleaning. Regardless of whether a smoothing layer is provided and which surface processing process is used,is used, it is preferred if the surface of the carrier in the area intended for the surface coating has a root mean square roughness of 0.2 nm RMS or less and / or is free of foreign particles with a size of more than 5 µm, preferably more than 1 µm. Suitable methods and devices are known for verifying compliance with the corresponding specifications.

[0018] To facilitate the detachment and removal of the carrier from the surface coating after the latter has been bonded to the substrate, a release layer can be provided between the carrier and the surface coating, allowing the carrier to be easily and damage-free detached from the surface coating. If the surface coating is applied directly to the surface of the carrier or a possible smoothing layer, the surface coating may be difficult to remove depending on the materials of the coating and the carrier or smoothing layer, which then poses a risk of damage to the surface coating when removing the carrier. In such a case, a release layer can reduce or completely prevent the risk of damage to the surface coating.The release layer can be designed in such a way that it can be easily detached from the carrier or from the surface coating, at least in the latter case without causing any damage to the surface coating. Alternatively, the release layer can also be designed in such a way that it enables the carrier and surface coating to be separated by destroying its own structure. In this case, the residues of the release layer remaining on the surface coating or the complete release layer in the case of a separation between the release layer and the carrier can then be removed from the surface coating immediately or at a later time. The release layer can be applied to the carrier as a separate layer made of a suitable material; however, it is also possible for the release layer to be formed by a chemical reaction on the surface of the carrier itself. If the carrier is, for example,made of silicon, the release layer can be made of silicon oxide, which forms on the surface of the carrier immediately upon contact with air.

[0019] It is preferred if a protective layer is provided between the carrier and the surface coating, which remains on the surface coating after the carrier has been detached and removed from the surface coating and is only removed from the surface coating at a later time. A corresponding protective layer can protect the surface coating in process steps subsequent to the method according to the invention in the production of an optical element or its installation, for example in a projection exposure system. The protective layer should be designed such that it can be easily removed from the surface coating at a later time in order to expose the actual surface coating with the reflective properties. The removal of the protective layer should be damage-free to the surface coating.

[0020] If the substrate to be provided with a surface coating has a structure, in particular if it is not continuous, it can be advantageous if the surface coating on the carrier is already divided into regions that match the structure of the substrate. For example, if the adjacent micromirrors of a micromirror unit are to be provided with a surface coating, the surface coatings for the individual micromirrors can be provided as separate sections of the surface coating on a common carrier and transferred together to the substrate or the individual micromirrors.

[0021] To achieve this, the surface of the carrier can have a structure adapted to the surface of the substrate prior to application of the surface coating such that the surface coating to be applied thereto forms only in predetermined areas in a manner suitable for bonding to a substrate. In other words, the surface of the carrier can, for example, have depressions where either no surface coating is produced, or any surface coating produced can be arranged set back in such a way that, when the surface coating provided in the non-set back areas is bonded to the substrate, it is not bonded to the substrate and, in particular, is removed together with the carrier in a subsequent step.

[0022] Particularly when producing the surface coating on the carrier in layers, it is preferred if the structural edges are designed to overhang during the structuring of the surface of the carrier. By creating an angle of more than 90°, preferably more than 120°, between the surface areas of the carrier to be provided with a surface coating and the side walls delimiting them, whereby the respective edges are designed to overhang, a sharp and clear delimitation of individual areas with surface coating can be ensured even when producing the surface coating on the carrier in layers, since the risk of enclosing an edge is minimized.

[0023] As an alternative to creating a directly structured surface coating by appropriately structuring the carrier before the surface coating is applied, it is also possible to structure the surface coating and / or the upper side of the carrier after the surface coating has been applied to match the surface of the substrate. For example, an originally continuous surface coating can be divided into suitable areas and thus structured using sawing or milling processes.

[0024] To bond the surface coating to the substrate, it can be provided that the surface coating is bonded to the substrate by means of a material bond. A suitable bonding material can be used for this purpose if necessary. It is also possible for the surface coating to be bonded to the substrate by additively applying the substrate to the surface coating produced on the carrier, whereby functional layers can be applied to the side of the substrate facing away from the surface coating.

[0025] The substrate can be curved after the inventive production of a surface coating reflecting EUV radiation. For this purpose, it can be prestressed, for example, such that the substrate changes shape after removal of the carrier, with the shape of the substrate surface provided with the surface coating also changing, in particular. Alternatively, the substrate can be curved after the surface coating has been produced thereon using other known methods.

[0026] A spacer can be provided on the side of the substrate facing away from the surface coating, reducing the contact area between the substrate and a superordinate component. Reducing the contact area also reduces the risk of the superordinate component introducing stresses into the substrate and / or its surface coating.

[0027] The multilayer coating system is preferably designed to reflect radiation with a wavelength of 1 to 20 nm, preferably 13.5 nm. Corresponding multilayer coating systems are known from the prior art and typically comprise alternating layers of molybdenum and silicon.

[0028] The substrate may have a micro-electromechanical system on the side to be provided with the surface coating. The micro-electromechanical system may in particular comprise micromirrors such as those used in semiconductor technology systems.

[0029] In this context, a "system for semiconductor technology" refers to any system that can be used to manufacture or inspect microstructured devices or the components required for them. In addition to projection exposure systems for photolithography, this also includes, in particular, inspection systems and metrology systems. In inspection systems for masks or wafers, one or more MEMS micromirror units can, for example, increase the variability of the illumination, which can result in higher-contrast or entirely new images of the surface of a mask or wafer, which can be advantageous for the inspection of the mask or wafer. The same applies to metrology systems with which masks, wafers, or other optical elements, such as mirrors, can be measured; increased variability in the illumination can improve the measurement results.

[0030] The invention will now be described by way of example using advantageous embodiments with reference to the accompanying drawings. In the drawings: Fig. 1: a schematic representation of a projection exposure system for photolithography comprising optical elements with reflective surface coatings produced according to the invention; Fig. 2: a schematic representation of a first embodiment of the method step of producing the surface coating on a carrier; Fig. 3: a schematic representation of a second embodiment of the method step of producing the surface coating on a carrier; Fig. 4: a schematic representation of a first embodiment of the method steps of bonding the surface coating to a substrate and removing the carrier; Fig. 5: a schematic representation of a second embodiment of the method steps of bonding the surface coating to a substrate and removing the carrier; Fig. 6: schematic representations of embodiments of the method according to the invention for structured substrates; and Fig. 7: a schematic representation of a design variant with a curved substrate surface in the final state.

[0031] In Fig. 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.

[0032] With the aid of the illumination system 10, an object field 11 is illuminated in an object plane or reticle plane 12. The illumination system 10 comprises an exposure radiation source 13, which, in the illustrated embodiment, emits illumination radiation at least comprising useful light in the EUV range, i.e., in particular, with a wavelength between 5 nm and 30 nm. The exposure radiation source 13 can be a plasma source, for example an LPP source (Laser Produced Plasma) 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).

[0033] The illumination radiation emanating from the exposure radiation source 13 is first focused in a collector 14. The collector 14 can be a collector with one or more ellipsoidal and / or hyperboloidal reflection surfaces. The at least one reflection surface of the collector 14 can be exposed to the illumination radiation at grazing incidence (GI), i.e., at angles of incidence greater than 45°, or at normal incidence (NI), i.e., at angles of incidence less than 45°. The collector 14 can be structured and / or coated, on the one hand, to optimize its reflectivity for the useful radiation and, on the other hand, to suppress stray light.

[0034] After the collector 14, the illumination radiation propagates through an intermediate focus in an intermediate focal plane 15. If the illumination system 10 is constructed in a modular design, the intermediate focal plane 15 can generally be used for the - also structural - separation of the illumination system 10 into a radiation source module, comprising the exposure radiation source 13 and the collector 14, and the illumination optics 16 described below. With such a separation, the radiation source module and illumination optics 16 then together form a modular illumination system 10.

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

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

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

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

[0039] The second facet mirror 19 does not necessarily have to be constructed from pivotable micromirrors, but can instead comprise individual facets formed from one or a manageable number of mirrors that are significantly larger than micromirrors, which are either fixed or can only be tilted between two defined end positions. However, as shown, it is also possible to provide the second facet mirror 19 with a microelectromechanical system comprising a plurality of micromirrors 19' that can each be individually pivoted about two mutually perpendicular axes, each preferably comprising an orientation sensor.

[0040] With the help of the second facet mirror 19, the individual facets of the first facet mirror 18 are imaged into the object field 11, which is usually only an approximate image. The second facet mirror 19 can be the last beam-forming mirror or actually the last mirror for the illumination radiation in the beam path before the object field 11.

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

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

[0043] By selecting the illumination channels ultimately used, which is easily possible by appropriately adjusting the micromirrors 18' of the first facet mirror 18, the intensity distribution in the entrance pupil of the projection system 20 described below can also be adjusted. This intensity distribution is also referred to as the illumination setting. It may also be advantageous not to arrange the second facet mirror 19 exactly in a plane that is optically conjugated to a pupil plane of the projection system 20. In particular, the pupil facet mirror 19 can be arranged tilted relative to a pupil plane of the projection system 20, as described, for example, in DE 10 2017 220 586 A1.

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

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

[0046] Alternatively, it is possible that the Fig. 1 is dispensed with, for which purpose the facet mirrors 18, 19 are then to be suitably arranged opposite the radiation source 13 and the collector 14.

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

[0048] The projection system 20 comprises a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0049] In the Fig. In the example shown in Figure 1, the projection system 20 comprises six mirrors M 1 to M 6 . Alternatives with four, eight, ten, twelve or any other number of mirrors M i are also possible. The penultimate mirror M 5 and the last mirror M 6Each has a passage opening for the illumination radiation, which means that the projection system 20 shown is a double-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.

[0050] The reflection surfaces of the mirrors M i can be designed as free-form surfaces without a rotational symmetry axis. Alternatively, the reflection surfaces of the mirrors M i but can also be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. The mirrors M i Just like the mirrors of the illumination optics 16, they may also have reflective coatings for the illumination radiation. These reflective coatings may be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0051] The projection system 20 has a large object-image offset in the y-direction between a y-coordinate of a center of the object field 11 and a y-coordinate of the center of the image field 21. This object-image offset in the y-direction can be approximately as large as a z-distance between the object plane 12 and the image plane 22.

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

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

[0054] The number of intermediate image planes in the x- and y-directions in the beam path between the object field 11 and the image field 21 can be the same or different, depending on the design of the projection system 20. Examples of projection systems 20 with different numbers of such intermediate images in the x- and y-directions are known from US 2018 / 0074303 A1.

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

[0056] A reticle 30 (also called a mask) arranged in the object field 11 is illuminated by the illumination system 10 and transferred to the image plane 21 by the projection system 20. The reticle 30 is held by a reticle holder 31. The reticle holder 31 can be displaced, in particular in a scanning direction, via a reticle displacement drive 32. In the illustrated embodiment, the scanning direction runs in the y-direction.

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

[0058] At the Fig. 1 and its illumination system 10, the above description of which essentially reflects known prior art, are the various optical elements reflecting the EUV exposure radiation, i.e. the mirrors or micromirrors 17, 18', 19' of the exposure system 10 and the mirrors M 1 to M 6of the projection system 20, with a surface coating 200 that reflects radiation with a wavelength of 1 to 20 nm and is applied to a substrate 300 that at least partially forms the structure of the respective optical element. The surface coating 200 comprises a multilayer coating system 210 of alternating layers of silicon and molybdenum.

[0059] At least a part of the surface coatings 200 of the optical elements 17, 18', 19', M 1 to M 6 has been applied to the respective substrates 300 using a method according to the invention. The method according to the invention is described below in various forms using the Fig. 2 to 7 are explained in more detail.

[0060] The method according to the invention is characterized in that the surface coating 200 intended for a substrate 300 is first produced completely on a carrier 100 before it is subsequently transferred to the substrate 300.

[0061] In Fig. 2a-e shows an example of a first embodiment of the first part of the method according to the invention, namely the production of the surface coating 200 on a carrier 100.

[0062] Starting from a carrier 100 ( Fig. 2a), whose surface is sufficiently cleaned, a smoothing layer 110 can optionally be applied ( Fig. 2b), which, on the side facing away from the carrier 100, has a surface with a square roughness of less than 0.2 µm. The smoothing layer 110 prevents the surface structure of the carrier 100, even if only microscopic, from being transferred directly or through other intermediate layers (such as the release layer 120 and protective layer 130 explained later), to the surface coating 200, and the subsequent outer surface of the surface coating 200 from having a negative of the surface structure of the carrier 100. The smoothing layer 110 can have the desired low roughness immediately after application, for example, after curing from a fluid state, or through subsequent processing, such as polishing.

[0063] If the carrier 100 already has a correspondingly low roughness or if a correspondingly low roughness can be achieved through surface treatment, such as polishing, the smoothing layer 110 can be omitted. For reasons of clarity, the only optional smoothing layer 110 is nevertheless presented in principle below.

[0064] A release layer 120 ( Fig. 2c) and then a protective layer 130 ( Fig. 2d). The release layer 120 is designed to be adapted to the protective layer 130 in such a way that these two layers 120, 130 can be easily separated from one another. The separation of the layers 120, 130 at a later point in time should in principle be able to take place in such a way that neither the protective layer 130 nor other surrounding layers, such as in particular the surface coating 200, are affected by the separation. If the separation takes place solely by applying a suitable tensile force, the force required to break the connection between the release layer 120 and the protective layer 130 should be significantly lower than that required to separate other layers from one another - in particular the layers of the multi-layer system 210 of the surface coating 200. If the separation of the release layer 120 from the protective layer 130 is made possible by the use of chemicals and / or special environmental conditions, such as, for example,certain temperatures, it must be ensured that the surrounding layers and in particular the surface coating 200 are not damaged by these chemicals and / or environmental conditions.

[0065] The protective layer 130 is designed so that it can be removed without residue at a later time (especially after completion of the method according to the invention). If the protective layer 130 is removed chemically, it must be designed so that the chemicals required for removal do not attack the surrounding layers and structures—in particular, the surface coating 200.

[0066] Both the release layer 120 and the protective layer 130 are optional. For example, a release layer 120 is not required if the detachment and removal of the carrier 100 from the surface coating 200, as described later, can be carried out without damaging the surface coating 200 even without a corresponding layer, for example because the protective layer 130 applied directly to the smoothing layer 110 can be easily removed from it. The protective layer 130 can be omitted in particular in processes in which a corresponding protective layer 130 would have to be removed practically immediately after the detachment and removal of the carrier 100 from the surface coating 200, as described later. In such a case, by omitting the protective layer 130, the additional process step for removing it can be avoided without the risk of damaging the surface coating 200 possibly increasing noticeably.

[0067] The surface coating 200 is then applied to the protective layer 130. For this purpose, the individual layers of the multilayer coating system 210 are applied one after the other, as indicated by the arrow 90. The sequence of the layers of the multilayer coating system 210 is inverse to the sequence desired for the subsequent surface coating 200 of the substrate 300. The layer of the multilayer coating system 210 directly adjacent to the protective layer 130 is later, in the state transferred to the substrate 300, the outer layer forming the free surface of the surface coating 200.

[0068] In Fig. 3 is one for Fig. 2, an alternative procedure is shown for the process step of producing the surface coating 200 on a carrier 100.

[0069] Starting from a carrier 100 ( Fig. 3a) a release layer 120 is formed directly on the carrier 100 by contact with air or a chemical ( Fig. 3b). The formation of the release layer 120 is optional. The surface coating 200 is then applied as a whole to the carrier 100 or the release layer 120 and thus produced. For this purpose, the multilayer coating system 210 of the surface coating 200 is prepared on an initial substrate 215 using known manufacturing methods and in a "normal" layer sequence and is bonded to the carrier 100 or the release layer 120 ( Fig. 3c). Finally, the initial substrate 220 is removed ( Fig. 3d).

[0070] The release layer 120 can be applied for reasons related to Fig. 2, the considerations explained above may also be omitted. On the other hand, it is also possible, for example, to provide an additional protective layer 130.

[0071] Regardless of how the surface coating 200 or its multilayer coating system 210 is produced on the carrier 100, the production is followed by the bonding of the surface coating 200 and the detachment and removal of the carrier 100, which is described below with reference to the Fig. 4 and Fig. 5, each showing alternative procedures. For the sake of simplicity, the Fig. 2 produced surface coating 200, although the Fig. 4 and Fig. 5 also directly apply to the process steps shown in Fig. 3 manufactured surface coating are applicable.

[0072] In order to connect the produced surface coating 200 to the substrate 300 in the area to be provided with a surface coating, the surface coating 200 still located on the carrier 100 is suitably brought to the substrate 300 with its side remote from the carrier 100 ( Fig. 4a) and firmly bonded to the substrate 300 ( Fig. 4b).

[0073] Subsequently, the carrier 100 is separated from the surface coating 200, whereby in the illustrated embodiment a separation takes place between the release layer 120 and the protective layer 130 ( Fig. 4c). The protective layer 130 initially remains on the surface coating 200 and is only removed at a later time, in particular only after completion of the method according to the invention ( Fig. 4d). The protective layer 130 can protect the surface coating 200 from damage, whereby the removal of the protective layer 130 must then also be carried out without causing damage to the surface coating 200.

[0074] In Fig. 4, the arrow 90 indicates the order in which the layers of the multilayer coating system 210 were produced on the carrier 100 (cf. Fig. 2 and Fig. 3). It is immediately apparent from this that the sequence on the carrier 100 is inverse to the sequence on the substrate 200. Consequently, the layers on the carrier 100 are to be produced in an inverse sequence to the ultimately desired layer sequence on the substrate 300.

[0075] In Fig. 5 is an alternative approach to that of Fig. 4 shown.

[0076] Starting from the surface coating 200 produced on the carrier 100, the substrate 300 is then applied directly onto the surface coating 200 ( Fig. 5a), for which, in particular, comparable methods such as those for the layer-by-layer application of the individual layers of the multilayer coating system 210 of the surface coating 200 can be used. In particular, the substrate 300 can also be applied layer by layer. Fig. 5 furthermore makes it possible to provide functional layers 310 on the side of the substrate 300 facing away from the surface coating 200. The Fig. The functional layer 310 shown as an example in Figure 5a can, for example, be formed directly on the substrate 300 for temperature measurement. However, any other and additional layers, such as the functional layer 310 shown, can be provided.

[0077] After complete production of the substrate 300 and possibly further layers, such as the functional layer 310, a state comparable to the approach described above exists (cf. Fig. 4b and Fig. 5b). For explanation of the Fig. 5c and Fig. 5d, reference is therefore made to the above statements, in particular to Fig. 4c and Fig. 4d.

[0078] In Fig. 6 is an embodiment of the method according to the invention for structured substrates 300, ie substrates 300 whose surface to be provided with a surface coating 200 is not continuous. Based on a projection exposure apparatus 1 as shown in Fig. 1, the facet mirrors 18, 19, whose surface is formed from a plurality of discrete micromirrors 18', 19', can be regarded as such a structured substrate 300, in which the individual mirror surfaces of the micromirrors 18', 19' are each to be provided with a surface coating 200.

[0079] In Fig. 6 shows two possibilities for producing the surface coating 200 (cf. Fig. 6a, b, left / right), while the subsequent process steps of bonding the surface coating 200 to the substrate 300 and removing the carrier 100 can be considered together (cf. Fig. 6c-e).

[0080] At the one on the left side in Fig. 6a and Fig. 6b, the carrier 100 already has the initial state (cf. Fig. 6a) has a structuring 105 with overhanging structural edges adapted to the surface of the substrate 300 - in this case the shape and arrangement of the micromirrors 18', 19'. In the production of the surface coating analogous to the Fig. 2, i.e., a layer-by-layer construction of the multilayer coating system 210, the surface coating 200 is created only in the areas of the structuring 105. The overhanging structural edges help to avoid unwanted edge effects during the layer-by-layer production of the surface coating 200. The adapted structuring 105 has a height that is greater than the thickness of the coating to be applied. This effectively prevents any material of the multilayer coating system 210 applied outside the areas actually to be coated from merging with the actually desired surface coating 200.

[0081] In the one on the right side of the Fig. 6a and Fig. 6b, a continuous surface coating 200 is first applied, for example according to Fig. 2 or Fig. 3, on the carrier 100 produced ( Fig. 6a, right) and then structured as desired. For structuring, the surface coating 200 can, for example, be suitably sawn or etched, whereby structuring down into the carrier 100 for the secure separation of the individual areas of the surface coating 200 is unproblematic as long as the structural integrity of the carrier 100 is fundamentally ensured.

[0082] Regardless of how the surface coating 200 was structured on the carrier 100, after its production, it is connected to the substrate 300 and the carrier is released and removed (cf. Fig. 6c-d). Due to the structuring of the surface coating 200, it is ensured that each individual micromirror 18', 19' is provided with a surface coating with a precise fit.

[0083] Apart from the fact that not a continuous structure but individual micromirrors 18', 19' are provided with the surface coating 200, the procedure corresponds to that of Fig. 4c-e, which is why reference is made to the explanations therein for further explanation.

[0084] In Fig. 6 are no smoothing, release or protective layers 110, 120, 130 (cf. Fig. 2-5). However, appropriate layers can, of course, be provided if necessary. For a more detailed explanation of the layers in question, please refer to the above explanations.

[0085] In Fig. 7 shows a variant embodiment with a substrate 300 curved in the final state.

[0086] Even if the substrate 300 in the final state (cf. Fig. 7b), the surface coating 200 is applied, which is produced in any way on the flat support 100 (see in particular Fig. 2 and Fig. 3) in a flat state of the substrate 300 (cf. Fig. 7a). Whether this flat state of the substrate 300 is achieved solely through contact with the surface coating 200 still present on the carrier 100, e.g., through elastic deformation of the substrate 200, or is ensured by other measures, is irrelevant.

[0087] After the carrier 100 has been released and removed, the substrate 300 assumes a curved shape, which is also followed by the surface coating 200.

[0088] The substrate 300 can be connected to a superordinate component 400. In order to minimize or avoid influencing the curvature of the substrate 300, the substrate 300 is provided with a spacer 320 on the side facing away from the surface coating 200, with which the substrate 300 is locally connected to the component 400. The spacer 320 can be formed integrally with the substrate 300 or connected to it as a separate component. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2012 / 130768 A2

[0005] DE 10 2008 009 600 A1

[0037] US 2006 / 0132747 A1

[0038] EP 1 614 008 B1

[0038] US 6,573,978

[0038] DE 10 2017 220 586 A1

[0043] US 2018 / 0074303 A1

[0054]

Claims

[1] Method for producing an EUV radiation-reflecting surface coating (200) on a substrate (300), wherein the surface coating (200) comprises a multilayer coating system (210), characterized by the steps: a) producing the surface coating (200) in inverse order of the layers of the multilayer coating system (210) on a carrier (100); b) bonding the produced surface coating (200) to the substrate (300) on the side remote from the carrier (100); and c) Detaching and removing the carrier (100) from the surface coating (200). [2] Method according to claim 1, characterized by that the surface coating (200) on the carrier (100) is produced layer by layer. [3] Method according to one of the preceding claims, characterized bythat the surface of the carrier (100) is to be processed by applying a smoothing layer (110), polishing and / or cleaning, preferably ensuring a roughness of 0.2 nm RMS or less and / or freedom from foreign particles with a size of more than 5 µm, preferably more than 1 µm. [4] Method according to one of the preceding claims, characterized by that a release layer (120) is provided between the carrier (100) and the surface coating (200), at which layer the carrier (100) can be easily and damage-free detached from the surface coating (200). [5] Method according to one of the preceding claims, characterized by that a protective layer (130) is provided between the carrier (100) and the surface coating (200), which protective layer remains on the surface coating (200) after the carrier (100) has been detached and removed from the surface coating (200) and is only removed at a later time. [6] Method according to one of the preceding claims, characterized by that the surface of the carrier (100) has a structuring (105) adapted to the surface of the substrate (300) before application of the surface coating (200), that the surface coating (200) to be applied thereon is formed only in predetermined areas in a manner suitable for connection to a substrate (300). [7] Method according to claim 6, characterized by that when structuring (105) the carrier (100) the structural edges are designed to be overhanging. [8] Method according to one of claims 1 to 5, characterized by that the surface coating (200) and / or the upper side of the carrier (100) is structured in a suitable manner to match the surface of the substrate (300) after the surface coating (200) has been produced. [9] Method according to one of the preceding claims, characterized bythat the connection of the surface coating (200) to the substrate (300) is effected by material bonding. [10] Method according to one of the preceding claims, characterized by that the connection of the surface coating (200) to the substrate (300) is effected by additive application of the substrate (200) to the surface coating (200) produced on the carrier (100), wherein functional layers (310) are preferably applied to the side of the substrate (300) facing away from the surface coating (200). [11] Method according to one of the preceding claims, characterized by that the substrate (300) is or becomes curved after the carrier (100) has been released and removed from the surface coating (200). [12] Method according to one of the preceding claims, characterized by that a spacer (320) is provided on the side of the substrate (300) facing away from the surface coating (200). [13] Method according to one of the preceding claims, characterized by that the multilayer coating system (210) is designed to reflect radiation with a wavelength of 1 to 20 nm, preferably 13.5 nm. [14] Method according to one of the preceding claims, characterized by that the substrate (300) has a micro-electromechanical system, preferably comprising micromirrors (18', 19'), on the side to be provided with the surface coating (200).

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